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Development of an Electronic size and colour grader for tomatoes Von Beckmann, Joerg Walter 1976

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DEVELOPMENT OF AN ELECTRONIC SIZE AND COLOUR GRADER FOR TOMATOES BY JOERG WALTER jvon BECKMANN B.Sc. Mount A l l i s o n U n i v e r s i t y , 1971 M.Sc. U n i v e r s i t y of B r i t i s h Columbia, 1972 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE Department of P l a n t S c i e n c e (Bio-Resource Engineering) We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1976. (c) Joerg Walter von Beckmann In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I f u r t h e r agree t h a t permiss ion for e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of Bio-Resource Engineering The U n i v e r s i t y of B r i t i s h Columbia 20 75 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date Ayvil 29, 1976. i ABSTRACT The greenhouse tomato i n d u s t r y i n B r i t i s h Columbia r e q u i r e s t h a t tomatoes be c o l o u r graded i n t o f o u r c a t e g o r i e s , and s i z e graded, based on diameter, i n t o f o u r c a t e g o r i e s . Automatic c o l o u r graders f o r o n l y two c a t e g o r y c l a s s i f i c a -t i o n s have been developed, w h i l e a s i z e grader based on weight i s commercially a v a i l a b l e . To meet i n d u s t r y demands, automatic s i z e and c o l o u r g r a d i n g of greenhouse tomatoes f o r the f r e s h market i s n e c e s s a r y . The development o f an auto-matic s i z e and c o l o u r grader, which f u l f i l l s i n d u s t r y g r a d i n g requirements i s needed to reduce p r o d u c t i o n c o s t s and to a c c e l e r a t e the implementation of complete mechanization i n tomato h a n d l i n g . T h i s t h e s i s o u t l i n e s the d e s i g n , f a b r i c a t i o n and t e s t i n g of a g r a d i n g machine capable of s i m u l t a n e o u s l y s i z e and c o l o u r g r a d i n g tomatoes i n t o f o u r t e e n d i f f e r e n t s i z e and c o l o u r c a t e g o r i e s a t a r a t e of f i v e tomatoes per second. The number o f c a t e g o r i e s may"be inc r e a s e d o r decreased t o meet i n d i v i d u a l needs. Tomatoes are randomly f e d onto a conveyor w i t h one i n c h (2.5 cm) minimum sp a c i n g and passed s i n g l e f i l e under a f i b r e o p t i c i l l u m i n a t i n g and s e n s i n g head. S i z e and c o l o u r of i n d i v i d u a l tomatoes are measured e l e c t r o n i c a l l y and the i n f o r m a t i o n s t o r e d i n a memory u n t i l each tomato reaches an a p p r o p r i a t e e j e c t l o c a t i o n , where the tomato i s p n e u m a t i c a l l y e j e c t e d i n t o a s t o r a g e b i n . The memory and e j e c t mechanisms are s y n c h r o n i z e d w i t h the conveyor b e l t so i i t h a t changes i n b e l t speed do not a f f e c t g r a d i n g . The g r a d i n g r a t e i s s t r i c t l y a f u n c t i o n of mechanical h a n d l i n g o p e r a t i o n s , and i s l i m i t e d by the a b i l i t y of the pneumatic e j e c t system to supply enough a i r to remove tomatoes from the conveyor i n the a l l o t t e d time. C o l o u r g r a d i n g i s based on the r a t i o of l i g h t r e -f l e c t e d from the tomato s u r f a c e i n two narrow bands of the v i s i b l e spectrum. S i z e g r a d i n g i s based on a diameter measurement of the tomato, as i t passes under the s e n s i n g head, w i t h a g r a d i n g r e s o l u t i o n of approximately 3/64 i n c h (0.12 cm)- M i s c l a s s i f i c a t i o n o f o v e r s i z e d o r u n d e r s i z e d tomatoes i n a g i v e n s i z e c a t e g o r y was l e s s than 10%. i i i TABLE OF CONTENTS PAGE ABSTRACT i TABLE OF CONTENTS i i i LIST OF TABLES v i i LIST OF FIGURES X ACKNOWLEDGEMENTS x i i i INTRODUCTION 1 LITERATURE REVIEW 4 SECTION I . COLOUR GRADER 12 CHAPTER 1 P h y s i c a l P r o p e r t i e s o f Tomatoes as R e l a t e d t o C o l o u r Grading 13 I n t r o d u c t i o n 14 M a t e r i a l s and Methods 15 R e s u l t s a n d , D i s c u s s i o n 18 CHAPTER 2 Theory R e l a t e d t o the Development o f a Co l o u r Grader 24 I n i t i a l C o n s i d e r a t i o n s 25 A n a l y s i s o f L i g h t Source, Sample, D e t e c t o r 30 Approximations f o r the I n t e g r a l s 3 3 R e s u l t s o f A n a l y s i s 36 E f f e c t s o f Peak T r a n s m i s s i o n 36 E f f e c t s o f F i l t e r H a l f Band Width 36 L i g h t Source E f f e c t s 39 D i s c u s s i o n 42 CHAPTER 3 Design Approach 45 I n t r o d u c t i o n 46 I n i t i a l Component S e l e c t i o n 48 L i g h t Source 48 P h o t o d e t e c t o r s 48 O p t i c F i l t e r s 48 Analog and D i g i t a l F a m i l i e s 49 E l e c t r o n i c C o l o u r Grading System: Overview 53 Analog S i g n a l P r o c e s s o r 56 D i v i d e r C i r c u i t 56 P h o t o t r a n s i s t o r and P r e a m p l i f i e r C i r c u i t s 60 Notch F i l t e r and Low Pass F i l t e r 66 i v CHAPTER 3 Design Approach (continued) PAGE Peak D e t e c t o r 1 71 Comparator 1, 2 and 3 75 Summing A m p l i f i e r 1 79 B e l t Background Monitor 82 Schmitt T r i g g e r C i r c u i t 85 D i g i t a l S i g n a l P r o c e s s o r 90 Timing C i r c u i t 90 Decoding Gates 93 L i g h t Chopper and P h o t o d e t e c t o r 96 Divide-by-3 C i r c u i t 99 Data L a t c h e s , Timers and Memory C i r c u i t s 102 O p t o - I s o l a t o r s and T r i a c s 110 D i s p l a y Timers 114 Power S u p p l i e s 118 Mecha n i c a l H a n d l i n g System 120 The Conveyor System 121 E j e c t System 123 CHAPTER 4 System T e s t i n g 126 M a t e r i a l s and Methods 127 E l e c t r o n i c System 127 E j e c t System 127 R e s u l t s and D i s c u s s i o n 128 SECTION I I . SIZE AND COLOUR GRADER 132 CHAPTER 5 P h y s i c a l P r o p e r t i e s o f Tomatoes as R e l a t e d t o S i z e Grading 133 I n t r o d u c t i o n 134 M a t e r i a l s and Methods 136 R e s u l t s 138 D i s c u s s i o n 142 CHAPTER 6 S i z e D e t e r m i n a t i o n Using the C o l o u r Grader Schmitt T r i g g e r P u l s e 146 I n t r o d u c t i o n 147 M a t e r i a l s and Methods 14 8 S i z e Standards 148 P u l s e Width Measurement Technique 150 Measurement o f B e l t Speed 150 E f f e c t o f S t y r o b a l l S i z e on Schmitt T r i g g e r P u l s e Width a t Four Conveyor B e l t Speeds 150 E f f e c t o f O f f - C e n t e r Viewing o f a S t y r o b a l l on the Measured Diameter 152 V CHAPTER 6 S i z e D e t e r m i n a t i o n (continued) R e s u l t s and D i s c u s s i o n 153 E f f e c t o f S t y r o b a l l S i z e on Schmitt T r i g g e r P u l s e Width a t Four Conveyor B e l t Speeds 153 R e s o l u t i o n 153 Schmitt T r i g g e r P u l s e Width versus Conveyor B e l t Speed f o r Three S t y r o b a l l S i z e s 157 E f f e c t o f O f f - C e n t e r Viewing o f a S t y r o b a l l on the Measured diameter 157 Summary 160 CHAPTER 7 Design Approach 162 I n t r o d u c t i o n 163 Theory 165 E l e c t r o n i c S i z e and C o l o u r Grader: Overview 169 P u l s e Generator and Timer C i r c u i t s 173 I n t e g r a t o r and Storage C i r c u i t 177 Ramp Generator and Storage C i r c u i t 182 Comparator 4, 5, 6 and 7 185 Decoding Gates 190 L a t c h i n g C i r c u i t 192 S i z e / C o l o u r Decoder 194 Memory C i r c u i t 196 O p t o - I s o l a t o r and T r i a c C i r c u i t 202 Mec h a n i c a l Handling System 203 CHAPTER 8 System T e s t i n g 204 I n t r o d u c t i o n 205 M a t e r i a l s and Methods 206 R e s u l t s and D i s c u s s i o n 210 T h e o r e t i c a l S i z e Category L i m i t s versus E x p e r i m e n t a l L i m i t s 210 E f f e c t o f Tomato C o l o u r on S i z e Measurement 212 S i z e Grading A b i l i t y o f the S i z e / C o l o u r Grader 214 Summary 224 FINAL SUMMARY 225 RECOMMENDATIONS 229 CITED REFERENCES 231 GLOSSARY OF TERMS 235 APPENDIX A F e d e r a l and In d u s t r y Grading Standards f o r Greenhouse Tomatoes APPENDIX B Grading Rate a t Peak o f . Growing Season f o r B.C. Lower Mainland Based on 1975 Y i e l d P r e d i c t i o n s , Mean Weight i n each S i z e Category, and Approximate D i s t r i b u t i o n o f S i z e C a t e g o r i e s v i i LIST OF TABLES TABLE PAGE 1 . 1 "Top 50" Wavelength R a t i o s Based on Maximum T o t a l D i f f e r e n c e s Between Means of the R e f l e c t a n c e R a t i o s f o r Four C o l o u r C a t e g o r i e s 19 1.2 "Top 5" Wavelength R a t i o s f o r Each o f Three C o l o u r Comparisons A c c o r d i n g t o P r i o r i t y o f Maximum D i f f e r e n c e Between Ad j a c e n t C o l o u r C a t e g o r i e s 20 1 . 3 "Top 5" Wavelength R a t i o s f o r Each o f Three C o l o u r Comparisons A c c o r d i n g t o P r i o r i t y o f Maximum S t u d e n t s t Values f o r Adjacent C o l o u r C a t e g o r i e s 22 2 . 1 Normalized R e f l e c t a n c e R a t i o s o f 600 nm/ 660 nm, f o r Combinations o f Equal H a l f Band Width F i l t e r s and V a r i o u s % Trans-m i s s i o n s : Values Obtained by I n t e g r a t i n g Over the Band Widths 37 2 .2 Students t V a l u e s f o r Comparison o f Mean R e f l e c t a n c e R a t i o s o f Four C o l o u r C a t e g o r i e s Based on Data i n Table 2 . 1 38 2 . 3 Normalized R e f l e c t a n c e R a t i o s o f 600 nm/ 660 nm, f o r Combinations o f V a r i o u s H a l f Band Widths and Two % T r a n s m i s s i o n s : Values Obtained by I n t e g r a t i n g Over the Band Widths 40 2 . 4 Students t V a l u e s f o r Comparison o f Mean R e f l e c t a n c e R a t i o s o f Four C o l o u r C a t e g o r i e s Based on Data i n T a b l e 2 . 3 41 3 . 1 Normalized R e f l e c t a n c e R a t i o Means, Standard D e v i a t i o n s , and S t u d e n t s t Values f o r Four Colo u r C a t e g o r i e s U s i n g a 550 nm/660 nm Wavelength R a t i o : Values Obtained by I n t e g r a t i n g Over the Band Widths 50 3 . 2 P r e d i c t e d Mean Output V o l t a g e s f o r Four C o l o u r C a t e g o r i e s Based on Equation [3-1] and the Twenty Tomatoes (Chapter 1) 59 3 . 3 Output S t a t e s o f Comparators 1 , 2 and 3 , f o r Four C o l o u r C a t e g o r i e s 78 v i i i TABLE PAGE 5.1 Diameter-Weight C o r r e l a t i o n s and L i n e a r R e g r e s s i o n Equations 139 5.2 Mean D i f f e r e n c e Between D I A . l and DIA.2 and 95% Confidence I n t e r v a l s f o r Four S i z e C a t e g o r i e s 140 6.1 D I A . l , DIA.2 and DIA.3 o f Three S t y r o b a l l S i z e Standards 149 6.2 The Co l o u r Grader CLOCK A Frequency Versus Approximate Conveyor B e l t Speed 151 6.3 Mean, Standard D e v i a t i o n , and Standard E r r o r o f Schmitt T r i g g e r P u l s e Width f o r Three S t y r o b a l l s a t Four Conveyor B e l t Speeds 154 6.4 Approximate Diameter Measurement E r r o r a t V a r i o u s O f f - C e n t e r D i s t a n c e s f o r Three S t y r o b a l l s R e l a t i v e t o the On-Center Measurement 159 7.1 T h e o r e t i c a l and Measured I n t e g r a t o r Output V o l t a g e s a t V a r i o u s Conveyor B e l t Speeds 181 7.2 Output S t a t e s o f COMP. 4, COMP. 5, COMP. 6 and COMP. 7 f o r F i v e S i z e C a t e g o r i e s 187 7.3 Output S t a t e s o f Comparators 2, 3, 5, 6, 7 f o r Twelve S i z e / C o l o u r C a t e g o r i e s 189 7.4 S h i f t R e g i s t e r Length and Input C o n d i t i o n s a t the S i x Programmable Inputs 199 8.1 T h e o r e t i c a l and E x p e r i m e n t a l Values o f D, f o r V a r i o u s Diameters 211 8.2 Values o f F R e s u l t i n g from a Comparison o f Mean Diameters o f Three C o l o u r C a t e g o r i e s i n a Given S i z e Category 213 8.3 Means, Standard D e v i a t i o n s and 95% Confidence I n t e r v a l s f o r M i s c l a s s i f i e d Tomatoes Around the 2.250 Inch (5.715 cm) and 3.000 Inch (7.620 cm) C u t - o f f s 220 Percentage o f O v e r s i z e and U n d e r s i z e Tomatoes f o r Each S i z e Category as Graded by the S i z e / C o l o u r Grader X LIST OF FIGURES FIGURE PAGE 2.1 T r i f u r c a t e d F i b r e O p t i c Assembly 26 2.2 R e l a t i v e Response o f a T y p i c a l P h o t o t r a n s i s t o r 28 2.3 S p e c t r a l D i s t r i b u t i o n of a Tungsten F i l a m e n t Lamp (3500°K C o l o u r Temperature) 28 2.4 Schematic o f Source-Sample-Detector System 31 2.5 Spectrogram o f a T y p i c a l F i r m Ripe and Green Tomato 34 3.1 Standard NPN P h o t o t r a n s i s t o r A m p l i f i e r U s i n g an FPT120A 51 3.2 C o l o u r Grader Block Diagram 54 3.3 Analog D i v i d e r C i r c u i t 57 3.4 Red and Green P h o t o t r a n s i s t o r A m p l i f i e r s 61 3.5 Notch and Low Pass F i l t e r s 68 3.6 Peak D e t e c t o r 1 72 3.7 Output V o l t a g e s f o r T y p i c a l F i r m Ripe, and Semi-Ripe Tomatoes (a) D i v i d e r Output f o r U n i f o r m l y Ripe Tomato (b) D i v i d e r Output f o r Non-Uniformly Ripe Tomato (c) Peak D e t e c t o r Output f o r (a) and (b) 73 3.8 Comparator C i r c u i t 76 3.9 Summing A m p l i f i e r 1 80 3.10 B e l t Background Monitor 83 3.11 Schmitt T r i g g e r C i r c u i t 86 3.12 Timing C i r c u i t 91 3.13 Decoding Gates 94 x i FIGURES PAGE 3.14 L i g h t Chopper P h o t o d e t e c t o r 97 3.15 Divide-by-3 C i r c u i t 100 3.16 L a t c h i n g C i r c u i t 103 3.17 Data L a t c h Timers 105 3.18 Data L a t c h Waveforms 106 3.19 Memory C i r c u i t 109 3.20 O p t o - I s o l a t o r s and T r i a c s 112 3.21 D i s p l a y Timer C i r c u i t 115 3.22 Power Supply C i r c u i t f o r T r i a c s 119 3.23 (a) Sensing Head and (b) L i g h t Chopper Assembly 122 3.24 Pneumatic E j e c t Mechanism 125 4.1 C o l o u r Groupings a t V a r i o u s Comparator V o l t a g e S e t t i n g s 129 6.1 Mean Schmitt T r i g g e r P u l s e Width v s . S t y r o b a l l Diameter a t Four Conveyor B e l t Speeds 155 7.1 S i z e Grader, and S i z e / C o l o u r Grader D i g i t a l P r o c e s s o r Block Diagram 170 7.2 P u l s e Generator and Timer C i r c u i t 174 7.3 I n t e g r a t o r and Storage C i r c u i t 178 7.4 Ramp Generator and Storage C i r c u i t 183 7.5 Comparator C i r c u i t 186 7.6 Decoding Gates 191 7.7 L a t c h i n g C i r c u i t 193 7.8 S i z e / C o l o u r Decoder C i r c u i t 195 7.9 One o f 13 S h i f t R e g i s t e r C i r c u i t s Used i n the S i z e / C o l o u r Memory C i r c u i t 198 x i i FIGURE PAGE 7.10 S i z e / C o l o u r Memory C i r c u i t 201 8.1 Machine Graded F i r m Ripe Tomatoes 215 8.2 Machine Graded Semi-Ripe Tomatoes 216 8.3 Machine Graded T u r n i n g Tomatoes 217 9 ACKNOWLEDGEMENTS The author. wtthei to t>tncen,ely thank Vn,. N. R. Bulley [Vepan.tment oh Bto-RzAoufic.il Engtne.nn.tng, Untven.&tty oh Bn,tttih Columbta), the. VtK.eo.toK. oh thti> n,ei>ean.ch pK.oje.ct, hon, ht& gutdance and cK.tttcti>m oven, the pa-t>t h0Vifl yeaK.&. Hti> zncoLLK.age.me.nt when thtngA wen,e not gotng a& ex.pe.cted and ht& enthu&ta&m when they wen.e, an.e greatly appreciated. The ehhofl^& °i mfJ Commtttee Chatn,man, Vn,. (/. C . Runeckleb tn co-oK-dtnattng tht.6 n,ei>ean.ch wtth the Ve.pan.tme.nt oh Bto-Re.AouK.ce. Engtneen.tng, and the. ttme bpent by the. memben,i> oh the. commtttee, Vn.. P . A . Jollthh<^> V*-- C . A . Hon,nby, Vn,. G . W . Eaton and especially Vn,. E.O. Nybon,g, tn fLe.vte.wtng the, thesis, an.e acknowledged. Special thanks to Mn.s. E. Stewan,t hoH- the many typings oh the manuscript, and hofl hen, pattence. Sincen,est gratitude is extended to Western Greenhouse Co-operative, Burnaby, B.C. who supplied a l l the tomatoes hoh-the research at no cost. Without t h e i r co-operation the research would have been dihh^^lt to carry out. The research was h^nanc-Z(^ by the Nattonal Research Counctl oh Canada. 1 INTRODUCTION Approximately 4.2 m i l l i o n pounds (1.9 m i l l i o n k g)* of greenhouse tomatoes were produced i n the B r i t i s h Columbia Lower Mainland i n 19 75. About 87% o f the annual p r o d u c t i o n occurs from A p r i l to l a t e August, w i t h a peak p r o d u c t i o n o f 280,000 l b (126,000 kg) per week. Most Lower Mainland tomatoes are marketed by the Western Greenhouse C o - o p e r a t i v e i n Burnaby, B.C. Tomatoes are graded a c c o r d i n g to both s i z e and c o l o u r as w e l l as f o r g e n e r a l q u a l i t y a c c o r d i n g to F e d e r a l and C o - o p e r a t i v e Standards**. A t p r e s e n t , the major g r a d i n g o p e r a t i o n i s the r e s p o n s i b i l i t y of the i n d i v i d u a l grower. The graded produce i s packed i n 20 l b (9 kg) boxes and d e l i v e r e d to the co-op warehouse where a s m a l l percentage of the boxes i s i n s p e c t e d and graded. The i n s p e c t i o n o f a few boxes which are below standar d can down-grade an e n t i r e shipment which i n many cases i s i n e q u i t a b l e to the grower. S i m i l a r l y , many boxes can c o n t a i n below average produce but be graded as prime q u a l i t y r e s u l t i n g from random sampling i n s p e c t i o n . S i n c e f e d e r a l standards l a c k t o l e r a n c e s f o r a s i n g l e s i z e measure-ment, and c o l o u r g r a d i n g i s s u b j e c t i v e , i t i s probable t h a t each grower g r a d i n g tomatoes based on the p r e s e n t s t a n d a r d s , * Data c o u r t e s y o f Western Greenhouse C o - o p e r a t i v e , Burnaby, B.C. ** The Standards f o r tomato g r a d i n g are found i n Appendix A. 2 w i l l d e l i v e r v a r y i n g grades of tomatoes a c c o r d i n g to i n d i v i d u a l i n t e r p r e t a t i o n . The need f o r one s e t of s i z e and c o l o u r standards f o r a l l growers and the g r a d i n g of every tomato a c c o r d i n g to these standards i s e v i d e n t . I f o n l y those tomatoes which do not meet the standards are down-graded, then every grower w i l l be p a i d f a i r l y f o r h i s product d e l i v e r e d . I d e a l l y , to minimize h a n d l i n g and to a v o i d unneces-sary expense to each grower i n h i r i n g a s e a s o n a l g r a d i n g s t a f f , produce should be d e l i v e r e d to the warehouse ungraded, and graded t h e r e a c c o r d i n g to a uniform s t a n d a r d . L a r g e r growers c o u l d s i z e and c o l o u r grade t h e i r own produce i f i t was b e n e f i c i a l to them. The maintenance of standards can be accomplished by use of an automatic s i z e and c o l o u r grader, which has been c a l i b r a t e d and v e r i f i e d by f e d e r a l g r a d e r s . T h i s r e p o r t d e a l s w i t h the development of an auto-matic e l e c t r o n i c s i z e and c o l o u r grader f o r tomatoes. The automatic grader, i n o r d e r to be a c c e p t a b l e must be a b l e to c a t e g o r i z e tomatoes i n t o f o u r c o l o u r c a t e g o r i e s and f o u r s i z e c a t e g o r i e s . The process of a u t o m a t i c a l l y g r a d i n g tomatoes by s i z e and c o l o u r i n v o l v e s the f o l l o w i n g s t e p s : a) Load tomatoes onto a conveyor. b) Arrange tomatoes i n s i n g l e f i l e ( s i n g u l a t e ) . c) T r a n s p o r t to a s e n s i n g and g r a d i n g a r e a . 3 d) C a t e g o r i z e i n d i v i d u a l tomatoes i n t o s p e c i f i c s i z e and c o l o u r c a t e g o r i e s . e) S t o r e c a t e g o r y i n f o r m a t i o n u n t i l tomato reaches i t s s i z e and c o l o u r c a t e g o r y e j e c t s t a t i o n . f) T r a n s p o r t tomato to a p p r o p r i a t e e j e c t s t a t i o n downstream from s e n s i n g a r e a . g) E j e c t the tomato from the conveyor i n t o a p p r o p r i a t e s t o r a g e b i n or onto a c r o s s - c o n v e y o r . The r e s e a r c h r e p o r t e d here i n v o l v e s the d e s i g n of an e l e c t r o n i c and mechanical system to i n c l u d e steps c) through g) as d e s c r i b e d above. Many l o a d i n g and conveying systems which s i n g u l a t e f r u i t are a v a i l a b l e , and i t was not the o b j e c t i v e of t h i s r e s e a r c h to develop a new conveying system f o r tomatoes. The aim of the r e s e a r c h was the development of a h i g h speed e l e c t r o n i c g r a d i n g system which would s i m u l t a n e o u s l y s i z e and c o l o u r grade tomatoes i n one o p e r a t i o n , thus i n v o l v -i n g o n l y a s i n g l e h a n d l i n g p r o c e s s . The development o f an e j e c t system was not of major importance i n t h i s study although p r e l i m i n a r y t e s t s of a pneumatic system are d e s c r i b e d . 4 LITERATURE REVIEW The e v a l u a t i o n o f f r u i t r i p e n e s s has i n c l u d e d methods such as the measure o f r e f l e c t e d l i g h t i n t e n s i t y from the f r u i t s u r f a c e (1,4,5,8,9,10,11,13,14,15,16,17,24,25,28, 29,33,35)*, the measure of t r a n s m i t t e d l i g h t i n t e n s i t y through the f r u i t , o r o p t i c a l d e n s i t y (2,3,5,10,11,18,21,22,23,25,26, 27,30,31,36,37), firmness t e s t i n g u s i n g instruments such as the Magness-Taylor F r u i t P r e s s u r e T e s t e r and an I n s t r o n U n i v e r s a l T e s t e r (11,15,24,25) and v i b r a t i o n a l t e c h n i q u e s (25,32). The most p o p u l a r methods f o r " o n - l i n e " g r a d i n g o f f r u i t are those i n v o l v i n g c o l o u r e v a l u a t i o n e i t h e r by r e f l e c -tance o r t r a n s m i t t a n c e . One reason f o r the use o f c o l o u r as a g r a d i n g c r i t e r i o n i s b e s t summarized by B i t t n e r e t a l . (4), "The o v e r a l l q u a l i t y o f f r u i t i s a f u n c t i o n o f many f a c t o r s , but appearance i s the main f a c t o r on which the consumer makes the d e c i s i o n " . Firmness t e s t i n g o r v i b r a t i o n a l techniques r e q u i r e t h a t the f r u i t be s t a t i o n a r y and p h y s i c a l l y handled which u s u a l l y r e q u i r e s more time than a c o l o u r measurement. The c o l o u r measurement may be o b t a i n e d w h i l e the f r u i t i s i n motion. Firmness t e s t s on tomatoes have shown good c o r r e l a -t i o n s w i t h v i s u a l c o l o u r e v a l u a t i o n and r e f l e c t e d l i g h t measurements a t s p e c i f i c wavelengths i n the v i s i b l e spectrum, as d e s c r i b e d by Hood e t a l . (15). C o l o u r alone t h e r e f o r e , i s Numbers i n parentheses r e f e r t o appended r e f e r e n c e s . 5 a reasonable measure o f f r u i t f irmness i n tomatoes. There appears to be no u n i v e r s a l agreement as t o which of the two l i g h t measuring t e c h n i q u e s , t r a n s m i t t a n c e or r e f l e c t a n c e i s most s u i t a b l e f o r f r u i t g r a d i n g . The t r a n s m i t t a n c e technique i n v o l v e s the i l l u m i n a -t i o n df one s i d e of the f r u i t and the s e n s i n g o f l i g h t t r a n s -m i t t e d through the f r u i t , u s u a l l y on the o t h e r s i d e . The s u r f a c e c o l o u r o f the f r u i t , such as the c o l o u r o f an apple p e e l , c o n t r i b u t e s l i t t l e t o the o p t i c a l d e n s i t y o f the f r u i t . T r a n s mittance, t h e r e f o r e , i s a measure o f i n t e r n a l f r u i t c o l o u r and not e x t e r n a l c o l o u r . T h i s t e c h n i q u e i s g e n e r a l l y used i n g r a d i n g f r u i t f o r p r o c e s s i n g . The disadvantage o f a t r a n s m i t t a n c e measurement i s t h a t the f r u i t must be p l a c e d i n t o a cup or onto an a p e r a t u r e , and a good l i g h t s e a l i s r e q u i r e d around the i l l u m i n a t e d a r e a . M o d e l l i n g c l a y has been used as a l i g h t s e a l a n t (3). F o r f r u i t such as b l u e -b e r r i e s , which are r e l a t i v e l y u n i f o r m i n s i z e , the s e a l a n t i s not necessary (21,22,23); however, the s u p p o r t i n g cup must conform w e l l t o the f r u i t shape. I n t e g r a t i n g spheres have been p l a c e d around the f r u i t (3), o r a l i g h t r e c e p t o r i s p l a c e d i n d i r e c t c o n t a c t w i t h the f r u i t (36), which f u r t h e r c o m p l i c a t e s h a n d l i n g o f the f r u i t a t h i g h s o r t i n g r a t e s . For fresh-market f r u i t , r e f l e c t a n c e would appear t o be most s u i t a b l e as a r i p e n e s s measurement, s i n c e the e x t e r n a l appearance, or r e f l e c t e d c o l o u r , i s what the consumer sees. R e f l e c t a n c e lends i t s e l f b e t t e r t o h i g h speed g r a d i n g systems 6 than t r a n s m i t t a n c e . F r u i t does not have t o be p l a c e d i n s p e c i a l cups, o n l y s e p a r a t e d by some d i s t a n c e from the next f r u i t . A l i g h t s e a l i s not r e q u i r e d , s i n c e the f r u i t i s i l l u m i n a t e d and the r e f l e c t e d l i g h t r e c e i v e d from the same s i d e . The d i s t a n c e t h a t the f r u i t i s l o c a t e d from the l i g h t source o r sensor i s not as c r i t i c a l s i n c e n e i t h e r i s p l a c e d i n d i r e c t c o n t a c t w i t h the f r u i t . The f r u i t can flow con-t i n u o u s l y p a s t the s e n s i n g element on a simple conveyor system. F r u i t s i z e u n i f o r m i t y i s not a n e c e s s i t y s i n c e s p e c i a l cups are not r e q u i r e d t o c a r r y the f r u i t . The s i z e v a r i a t i o n i s an important c o n s i d e r a t i o n when d e a l i n g w i t h tomatoes. S i z e s range from under two in c h e s (5 cm) t o 3 1/2 inches (9 cm) i n diameter. The r e f l e c t e d l i g h t i n t e n s i t y from a f r u i t s u r f a c e over the v i s i b l e spectrum alone does not c o r r e l a t e w i t h the c o l o u r o f the f r u i t . However, the i n t e n s i t i e s a t s p e c i f i c wavelengths, o r narrow wavelength bands does c o r r e l a t e w i t h the s u r f a c e c o l o u r (4,5,8,11,15,28). The q u e s t i o n a r i s e s as to which wavelength or combination o f wavelengths o f r e f l e c -t e d l i g h t produces the b e s t c o r r e l a t i o n w i t h f r u i t c o l o u r . Furthermore, how s h o u l d the measured l i g h t i n t e n s i t y , o r i n t e n s i t i e s , be handled i n o r d e r t o produce a c o l o u r index? Should a s i n g l e measurement be used, or sho u l d two or more e l e c t r o n i c s i g n a l s be added, s u b t r a c t e d , d i v i d e d , e t c . ? As e a r l y as 1953, Powers e t a l . (29) d i s c u s s e d t h r e e c r i t e r i a which c o u l d be used f o r s o r t i n g lemons based 7 on the i n t e n s i t y o f l i g h t r e f l e c t e d from t h e i r s u r f a c e s . The f i r s t i s a measure of a s i n g l e i n t e n s i t y o f a narrow wavelength band i n the v i s i b l e spectrum. The s i n g l e r e f l e c -tance measurement i s s u b j e c t t o s e n s i t i v i t y v a r i a t i o n s i n the measuring instrument as w e l l as changes i n o b j e c t d i s t a n c e from the sensor and s i z e o f f r u i t . The second c r i t e r i o n i s the measure of the r a t i o o f two r e f l e c t e d l i g h t i n t e n s i t i e s a t d i f f e r e n t narrow wavelength bands i n the v i s i b l e spectrum. The e f f e c t s of instrument s e n s i t i v i t y , d i s t a n c e and s i z e are c a n c e l l e d out u s i n g t h i s t e c h n i q u e . G r e a t e r s e n s i t i v i t y t o s m a l l v a r i a t i o n s i n c o l o u r may be o b t a i n e d u s i n g a percen-tage change i n r e f l e c t a n c e a t two narrow bands i n the v i s i b l e spectrum. T h i s i s the t h i r d c r i t e r i o n d i s c u s s e d . The method i n v o l v e s the measure o f the d i f f e r e n c e between the r e f l e c t e d l i g h t a t two wavelengths d i v i d e d by the i n t e n s i t y a t one of the wavelengths. The l a t t e r c r i t e r i o n was the one used f o r the lemon g r a d e r . I t i s c l e a r from the work o f Powers e t a l . (29) t h a t a t l e a s t two r e f l e c t e d l i g h t i n t e n s i t i e s are r e q u i r e d , combined a r i t h m e t i c a l l y by e i t h e r d i v i s i o n , or s u b t r a c t i o n and d i v i s i o n t o produce a s i g n a l p r o p o r t i o n a l to c o l o u r and independent o f extraneous i n t e r f e r e n c e s . The f i n d i n g s have been i g n o r e d by many r e s e a r c h e r s , and "new" c o l o u r graders have been developed as l a t e as 1969 and 1974 (1,9,33) which use o n l y a s i n g l e i n t e n s i t y measurement. I t i s o f no s u r -p r i s e t h a t Burkhardt e t a l . (9) encountered s o r t i n g problems 8 when the f r u i t v a r i e d i n s i z e . The c o r r e l a t i o n o f t h r e e i n t e n s i t i e s t o f r u i t m a t u r i t y by B i t t n e r e t a l . (5) by the d i v i s i o n o f one by the product o f the o t h e r two showed no s i g n i f i c a n t advantage over the simple r a t i o o f two i n t e n s i -t i e s . As t o the c h o i c e o f two wavelengths t o be combined i n a r a t i o , no two wavelengths are i d e a l f o r a l l f r u i t . The wavelength r a t i o s o f 670 nm/730 nm (5), 540 nm/630 nm (11), 520 nm/670 nm (14), and 525 nm/670 nm (15) have a l l been used t o s o r t tomatoes. The above wavelength r a t i o s have been used p r i m a r i l y t o separate tomatoes i n t o two c o l o u r c a t e g o r i e s , r e d and green, except f o r the f i r s t , which was c o r r e l a t e d over f o u r c o l o u r c a t e g o r i e s . A p p a r e n t l y , the i d e a l wavelength r a t i o t o be used i n a grader depends on the number o f c o l o u r c a t e g o r i e s t o be sepa r a t e d . Two c o l o u r c a t e g o r y s e p a r a t i o n s would r e q u i r e a d i f f e r e n t wavelength r a t i o than f o u r c o l o u r c a t e g o r y separa-t i o n s . S i n c e the development o f the lemon g r a d e r by Powers e t a l . (29) i n 1953, l i t t l e p r o g r e s s has been made i n the f i e l d o f e l e c t r o n i c c o l o u r g r a d i n g o f f r u i t s and v e g e t a b l e s u s i n g r e f l e c t a n c e as the g r a d i n g c r i t e r i o n . They d e s c r i b e d a machine c o n s i s t i n g o f a conveyor which o r i e n t e d lemons w i t h t h e i r major a x i s p e r p e n d i c u l a r t o the d i r e c t i o n o f t r a v e l . A t the end of the conveyor, the lemons were dropped through an i l l u m i n a t e d compartment, where the r e f l e c t e d l i g h t was 9 r e c e i v e d by p h o t o d e t e c t o r s . The p h o t o d e t e c t o r s i g n a l s were used to a c t i v a t e d e f l e c t i n g vanes which c a t e g o r i z e d the lemons i n t o one of f i v e c o l o u r grades. The few improvements which have been made s i n c e then are the r e s u l t of the advance-ment of e l e c t r o n i c technology s i n c e the e a r l y 1950's. In s t e a d of p h o t o - m u l t i p l i e r tubes, semiconductors are now i n use. S w i t c h i n g c i r c u i t s are no l o n g e r comprised of vacuum tubes but o f t r a n s i s t o r s and i n t e g r a t e d c i r c u i t s . Some of the s u b t l e d e t a i l s o f c o l o u r g r a d i n g systems have been i g n o r e d i n the l i t e r a t u r e , such as proper t i m i n g sequences, d a t a p r o c e s s i n g when more than two c o l o u r c a t e g o r i e s are i n v o l v e d , and s i m p l i f i c a t i o n o f t r i g g e r i n g and memory components t h a t . i s r e q u i r e d . S i n g u l a t i n g and conveying o f f r u i t i s of importance i n any g r a d i n g system. Both o p e r a t i o n s are s p e c i f i c f o r the f r u i t b e i n g handled. The o r i e n t a t i o n system used by Powers et a l . (29) would be u n s u i t a b l e f o r a n y t h i n g but lemons, and the e j e c t mechanism, or d e f l e c t i n g vanes c o u l d not be used f o r tomatoes. The s i n g l e f i l e r d e s c r i b e d by B r a n t l e y e t a l . (6), which was designed f o r sweet po t a t o e s and cucumbers, may have some p o t e n t i a l a p p l i c a t i o n f o r tomatoes. The o r i e n t a t i o n d e v i c e d e s c r i b e d by Burkhardt e t a l . (9) f o r d r i e d prunes would pro b a b l y not work f o r tomatoes. The s i n g l e f i l e r and a t r a n s p o r t conveyor d e s c r i b e d by Greenwood e t a l . (13) c o n s i s t e d o f two p a r a l l e l vee b e l t s , s i m i l a r t o t h a t o f B r a n t l e y e t a l . (6), but was designed f o r 10 tomatoes. Tomatoes were e j e c t e d u s i n g mechanical plungers and pneumatic a s s i s t a n c e t o l i f t the tomatoes from the two b e l t s . Heron e t a l . (14) suggested the use of a f l a t con-veyor b e l t f o r tomatoes w i t h no s i n g u l a t i o n of f r u i t , which i s an e x c e l l e n t i d e a l , however, the p r o p o r t i o n of s p e c u l a t i o n to t e s t r e s u l t s i s not c l e a r i n the p u b l i s h e d work. Mason e t a l . (20) d e s c r i b e a v i b r a t i o n a l technique f o r o r i e n t i n g f r u i t i n a packing t r a y which c o u l d p o s s i b l y a s s i s t i n the o r i e n t a t i o n of tomatoes on a conveyor b e l t . E l e c t r o n i c s i z e g r a d i n g of f r u i t s and v e g e t a b l e s i s v i r t u a l l y unknown. Mechanical methods of s i z e g r a d i n g i n v o l v i n g the r o l l i n g of f r u i t over h o l e s of v a r i o u s s i z e s does not appear p r o m i s i n g f o r tomatoes. The m u l t i p l e b e l t , a d j u s t a b l e vee s i z e grader f o r sweet potatoes and cucumbers d e s c r i b e d by B r a n t l y e t a l . (6) and Goodman e t a l . (12) c o u l d be used f o r tomatoes. The disadvantage of such a g r a d i n g system i s t h a t the s i z e g r a d i n g i s s t r o n g l y weighted i n favour of o v e r - s i z e g r a d i n g , i . e . the minimum diameter f o r the f r u i t becomes the measurement c r i t e r i o n r a t h e r than the maximum diameter. Maximum diameter i s used as the tomato s i z e standard (Appendix A ) . A weight grader has been developed by FMC C o r p o r a t i o n , U.S.A., and has been commercial a v a i l a b l e f o r some time. The weight grader r e q u i r e s t h a t f r u i t be s i n g u l a t e d i n t o i n d i v i d u a l weighing cups, which are then m e c h a n i c a l l y compared to p r e s e t s p r i n g - l o a d e d mechanisms, and the f r u i t dropped onto a c r o s s - c o n v e y o r when the weight of the f r u i t exceeds t h a t of the 11 s p r i n g f o r c e . Grading by weight i s not the s t a n d a r d f o r tomatoes. The use of an image s e n s i n g a r r a y , s i m i l a r t o a t e l e v i s i o n camera, has been r e c e n t l y suggested as a d e v i c e f o r measuring l e n g t h s and areas o f a g r i c u l t u r a l p r o d u c t s (7). The d e v i c e may be more s u i t e d t o a r e s e a r c h instrument than a commercial g r a d e r . A combined s i z e and c o l o u r grader f o r tomatoes has not y e t been developed. The combination o f a s i z e g r a der and a c o l o u r grader i n v o l v e s more than j u s t the o p e r a t i o n o f a s i z e grader and/or c o l o u r grader i n tandem. A c o l o u r grader, f o r f o u r c o l o u r s of tomatoes, i n c o n j u n c t i o n w i t h the B r a n t l e y e t a l . (6) s i z e grader f o r f i v e s i z e s , f o r example, would r e q u i r e e i t h e r one c o l o u r grader and f o u r s i z e g r a d e r s , o r one s i z e grader and f i v e c o l o u r graders t o perform the complete g r a d i n g o p e r a t i o n . C l e a r l y , t h e r e i s a need f o r a s i z e / c o l o u r grader which u s i n g a s i n g l e conveyor system s i m u l t a n e o u s l y s i z e and c o l o u r c a t e g o r i z e s and e j e c t s the f r u i t from the conveyor i n t o the a p p r o p r i a t e packing b i n or onto a c r o s s - c o n v e y o r . N The need f o r automatic g r a d i n g o f f r u i t s and vege-t a b l e s i s w e l l documented (19,32). The i n c r e a s i n g c o s t and shortage of l a b o u r alone has n e c e s s i t a t e d the development o f automatic h a r v e s t i n g , g r a d i n g and p a c k i n g equipment f o r a g r i c u l t u r a l produce (34), The f u t u r e f o r automatic g r a d i n g equipment l i e s i n the i n c r e a s e d s o p h i s t i c a t i o n towards m u l t i p l e o p e r a t i o n s and s i m p l i f i c a t i o n t o minimize product h a n d l i n g and damage. E C T I O N COLOUR GRADER C H A P T E R 1 PHYSICAL PROPERTIES OF TOMATES AS RELATED TO COLOUR GRADING. 14 INTRODUCTION Based on the work of Powers e t a l . (29) and o t h e r s , i t was de c i d e d t h a t a r a t i o o f r e f l e c t a n c e s a t two narrow wavelength bands of the v i s i b l e spectrum would be a s u i t a b l e c r i t e r i o n f o r c o l o u r e v a l u a t i o n . A study was conducted t o determine the wavelength r a t i o which would p r o v i d e the b e s t s e p a r a t i o n among the f o u r c o l o u r c a t e g o r i e s — f i r m r i p e , s e m i - r i p e , t u r n i n g and green — based on the r e f l e c t e d i n t e n s i t i e s a t each wavelength band. MATERIALS AND METHODS Twenty tomatoes* ( v a r i e t y Vendor) were chosen f o r the study, and grouped i n t o f o u r c o l o u r c a t e g o r i e s o f f i v e tomatoes each: f i r m r i p e , s e m i - r i p e , t u r n i n g and green, as d e s c r i b e d by the Canada Department o f A g r i c u l t u r e Standards (Appendix A ) . No attempt was made t o sepa r a t e mature green from immature green tomatoes. The green tomato group probably i n c l u d e d a mixture o f mature and immature tomatoes. A spectrophotometer (Unicam U l t r a v i o l e t S p e c t r o -photometer, Model SP800B) was c a l i b r a t e d t o 100% r e f l e c t a n c e (zero absorbance) f o r the range 350 nm to 800 nm u s i n g a magnesium oxide s t a n d a r d . S i n c e p l e x i g l a s s p e t r i d i s h e s were t o be used t o h o l d the tomatoes d u r i n g the r e f l e c t a n c e t e s t s , the magnesium oxide s t a n d a r d was then p l a c e d behind a p l e x i -g l a s s p e t r i d i s h . The r e f l e c t a n c e dropped t o approximately 85% a c r o s s the 350 nm to 80.0. nm range. The spectrophotometer was r e c a l i b r a t e d t o 100% r e f l e c t a n c e w i t h the p l e x i g l a s s d i s h i n f r o n t o f the st a n d a r d . A tomato s e c t i o n was c u t from each tomato t o f i l l the p e t r i d i s h (60 mm d i a X 20 mm deep) and the tomato s k i n was f l a t t e n e d a g a i n s t the viewed s i d e o f the p e t r i d i s h . The d i s h was covered and p l a c e d i n the sample h o l d e r . S e v e r a l samples were scanned a t a f a s t ( a p p r o x i -mately 2 minutes f o r t o t a l spectrum) and then a t a slow _ A l l tomatoes used i n t h i s r e s e a r c h were o b t a i n e d from Western Greenhouse Growers C o - o p e r a t i v e , Burnaby, B.C. 16 (approximately 8 minutes for the t o t a l spectrum) rate, and no difference was noted between the two traces. Consequently, a l l subsequent scans were ca r r i e d out at the f a s t speed. The absorbance (A) was measured at 10 nm i n t e r v a l s from 380 nm to 800 nm for each of the twenty spectrograms and converted to percent reflectance using the r e l a t i o n s h i p : R(%) = 10 _ A X 100% * [1-1] Reflectance r a t i o s were calculated by d i v i d i n g the percent reflectances of 903 d i f f e r e n t wavelength pairs beginning with 380 nm/390 nm, 380 nm/400 nm to 790 nm/800 nm for each tomato. The mean reflectance r a t i o of the f i v e tomatoes i n each colour category was calaculated for each permutation. The differences of mean reflectance r a t i o s between adjacent colour categories, i . e . firm ripe-semi-ripe; semi-ripe-turning; and turning-green were calculated for each permutation. The three differences of mean reflectance r a t i o s between adjacent colour categories were summed to produce a maximum reflectance r a t i o difference for each wavelength r a t i o , as suggested by Goddard et a l . (11). To i l l u s t r a t e , i f the difference between mean reflectance r a t i o s of the firm r i p e and semi-ripe tomatoes at the 60 0 nm/66 0 nm wavelength r a t i o was 0.34, and the difference between semi-ripe and turning was 0.63, and the difference between turning and green was 0.5, then the maximum difference between the means at the 600 nm/660 nm wavelength r a t i o would be 1.51. * See Unicam Spectrophotomer Model SP800B Manual. 17 The l a r g e r the d i f f e r e n c e between the means o f ad j a c e n t c o l o u r c a t e g o r i e s , the l a r g e r w i l l be the sum o f the t h r e e means, and the g r e a t e r the s e p a r a t i o n between c o l o u r c a t e g o r i e s , a c c o r d i n g t o Goddard e t a l . (11). 18 RESULTS AND DISCUSSION The "top 50" maximum t o t a l d i f f e r e n c e s between means o f a d j a c e n t c o l o u r c a t e g o r i e s and t h e i r a s s o c i a t e d wavelength r a t i o s are l i s t e d i n Table 1.1 i n descending o r d e r b e g i n n i n g w i t h the g r e a t e s t d i f f e r e n c e . The r e s u l t s agree.with those of Goddard e t a l . (11), who found t h a t the 550 nm/680 nm and 540 nm/680 nm wavelength r a t i o s y i e l d e d "a reas o n a b l y a c c u r a t e s e p a r a t i o n f o r the good tomatoes (red) and green tomatoes c a t e g o r i e s from the o t h e r grade c a t e g o r i e s " . C a r e f u l examination o f each o f the a d j a c e n t c o l o u r c a t e g o r y mean r e f l e c t a n c e r a t i o d i f f e r e n c e s i n d i c a t e s t h a t the 55 0 nm/680 nm wavelength r a t i o does not i n c l u d e the g r e a t e s t d i f f e r e n c e between f i r m r i p e and s e m i - r i p e , nor between s e m i - r i p e and t u r n i n g . The l a r g e d i f f e r e n c e between t u r n i n g and green a t t h i s r a t i o i s the predominant f a c t o r i n the t o t a l (maximum) d i f f e r e n c e . The 550 nm/680 nm r a t i o i s probably a c c e p t a b l e f o r the s e p a r a t i o n o f green from t u r n i n g tomatoes, but i t i s not the b e s t r a t i o f o r s e p a r a t i n g the se m i - r i p e from f i r m r i p e o r s e m i - r i p e from t u r n i n g . The wavelength r a t i o which b e s t s e p a r a t e s a l l f o u r c o l o u r c a t e g o r i e s e q u a l l y would show approximately the same d i f f e r e n c e s between the means o f each c a t e g o r y , assuming the standard d e v i a t i o n s about the mean to be s m a l l , and e q u a l . The "top 5" wavelength r a t i o s f o r each o f the thr e e c o l o u r comparisons are l i s t e d i n Table 1.2, i n descending order a c c o r d i n g t o the p r i o r i t y o f maximum d i f f e r e n c e between 19 TABLE 1.1 "TOP 50" WAVELENGTH RATIOS BASED ON MAXIMUM TOTAL DIFFERENCES BETWEEN MEANS OF THE REFLECTANCE RATIOS FOR FOUR COLOUR CATEGORIES. T o t a l Semi Turning Green No. Rat i o D i f f e r e n c e - Firm -Semi -Turning 1 550/680 3.776 0.212 1.426 2.139 2 540/680 3. 690 0.196 1. 340 2.154 3 560/680 3.686 0.206 1.448 2. 033 4 530/680 3.501 0.160 1.128 2 . 213 5 570/680 3.458 0.220 1.421 1.817 6 550/670 3.422 0. 207 1.301 1. 914 7 540/670 3.343 0.191 1.221 1.931 8 560/670 3.340 0. 201 1. 322 1.817 9 530/670 3.173 0.156 1.031 1. 986 10 570/670 3.129 0.215 1. 294 1.620 11 580/680 3.078 0.286 1. 306 1.486 12 520/680 2. 974 0.133 0. 908 1.928 13 590/680 2. 798 0. 352 1.154 1. 292 14 580/670 2.778 0.278 1.180 1. 320 15 520/670 2.697 0.134 0.831 1.732 16 600/680 2. 588 0.390 0. 980 1. 218 17 590/670 2.512 0.341 1.028 1.144 18 550/660 2.388 0.190 1. 061 1.137 19 540/660 2.333 0.176 0.995 1.163 20 560/660 2.329 0.184 1. 078 1.067 21 600/670 2.301 0. 373 0.853 1.075 22 530/660 2.218 0.143 0. 841 1.234 23 570/660 2.175 0.197 1.052 0. 927 24 610/680 2.157 0. 350 0. 778 1. 030 25 510/680 2.139 0.127 0. 682 1.330 26 510/670 1. 939 0.124 0.622 1.1-92 27 580/660 1.913 0.256 0.944 0. 713 28 520/660 1.885 0.124 0. 676 1. 086 29 610/670 1.885 0. 326 0.656 0. 904 30 550/690 1.863 0.173 0. 941 0.749 31 620/680 1.841 0. 295 0.647 0.899 32 540/690 1.820 0.160 0. 882 0.778 33 560/690 1.816 0.168 0.956 0.692 34 550/650 1.750 0.178 0.881 0.692 35 530/690 1.7 33 0.130 0.744 0.858 36 540/650 1.710 0.164 0.825 0.721 37 560/650 1.706 0.172 0.897 0.638 38 590/660 1.701 0. 313 0.799 0.589 39 570/690 1.691 0.178 0.931 0. 581 40 530/650 1.628 0.134 0.699 0. 796 41 630/680 1.594 0.196 0. 568 0.830 42 570/650 1.585 0.183 0.870 0.531 43 620/670 1. 582 0.266 0.529 0.786 44 550/640 1. 568 0.172 0.809 0.587 45 500/680 1.560 0.118 0.540 0.902 46 540/640 1.532 0.158 0. 757 0.616 47 560/640 1.528 0.166 0.823 0. 539 48 600/660 1.508 0.341 0.631 0.536 49 580/690 1.475 0. 233 0.832 0.410 50 520/690 1.472 0.113 0. 597 0. 762 20 TABLE 1.2 "TOP 5 " WAVELENGTH RATIOS FOR EACH OF THREE COLOUR COMPARISONS ACCORDING TO PRIORITY OF MAXIMUM DIFFERENCE BETWEEN ADJACENT COLOUR CATEGORIES. A /A, a b Semi-Firm Turning-Semi Green-Turning PRIORITY: Semi-Ripe -- Firm Ripe 600/680 . 3 9 0 i . 9 8 0 1 . 218 600/670 . 3 7 3 . 8 5 3 1 . 0 7 5 590/680 . 3 5 2 1 . 1 5 4 1 . 2 9 2 610/680 . 350 . 7 7 8 1 . 0 3 0 590/670 . 3 4 1 1 . 0 2 8 1 . 1 4 4 PRIORITY: Turning - - Semi-Ripe 560/680 . 206 1 . 4 4 3 2 . 033 550/680 . 2 1 2 1 . 4 2 6 2 . 1 3 9 570/680 . 2 2 0 1 . 4 2 1 1 . 8 1 7 540/680 . 1 9 6 1 . 3 4 0 2 . 1 5 4 560/670 . 2 0 1 1 . 322 1 . 8 1 7 PRIORITY: Green -- Turning 530/680 . 1 6 0 1 . 1 2 8 2 . 2 1 3 540/680 . 1 9 6 1 . 3 4 0 2 . 1 5 4 550/680 . 2 1 2 1 . 4 2 6 2 . 1 3 9 560/680 . 206 1 . 4 4 8 2 . 0 3 3 530/670 . 1 5 6 1 . 031 1 . 9 8 6 21 the means of f i r m r i p e - s e m i - r i p e ; s e m i - r i p e - t u r n i n g ; and t u r n i n g - g r e e n The data i n d i c a t e s t h a t the maximum s e p a r a t i o n o f f i r m r i p e and s e m i - r i p e i s o b t a i n e d w i t h the 600 nm/680 nm r a t i o ; f o r s e m i - r i p e t o t u r n i n g , 560 nm/680nm and f o r t u r n i n g t o green, 530 nm/680 nm. Although the l a r g e d i f f e r e n c e s between the means of two c o l o u r c a t e g o r i e s imply good s e p a r a t i o n , the st a n d a r d d e v i a t i o n i n each group may be so l a r g e t h a t no s i g n i f i c a n t d i f f e r e n c e between the means e x i s t s . The Students' t - t e s t was used t o compare the means, of a d j a c e n t c o l o u r c a t e g o r i e s f o r the 50 wavelength r a t i o s l i s t e d i n Table 1.1. The "top 5" wavelength r a t i o s f o r each o f the t h r e e c o l o u r comparisions are l i s t e d i n Table 1.3, i n descending o r d e r a c c o r d i n g t o the p r i o r i t y o f maximum t v a l u e s f o r f i r m r i p e v s . s e m i - r i p e ; s e m i - r i p e vs. t u r n i n g , and t u r n i n g v s . green. Comparisons o f the sequence of wavelength r a t i o s i n Table 1.2 t o those i n Tabl e 1.3 shows t h a t s e l e c t i o n o f an optimum wavelength r a t i o based on the d i f f e r e n c e s between means w i l l be d i f f e r e n t from the s e l e c t i o n based on Students' t - t e s t . The d i f f e r e n c e p o i n t s i n the d i r e c t i o n o f the i d e a l wavelength r a t i o f o r the s e p a r a t i o n o f the groups, but Students' t - t e s t i s pro b a b l y a more r e l i a b l e i n d i c a t o r . The q u e s t i o n s t i l l remains, "Which s i n g l e wave-l e n g t h r a t i o w i l l e q u a l l y s e p a r a t e a l l f o u r c o l o u r c a t e g o r i e s ? " Based on the va l u e s o f t i n Tabl e 1.3 and t h e i r a s s o c i a t e d c o n f i d e n c e l e v e l s , i t appears t h a t any wavelength r a t i o from 22 TABLE 1.3 "TOP 5" WAVELENGTH RATIOS FOR EACH OF THREE COLOUR COMPARISONS ACCORDING TO PRIORITY OF MAXIMUM STUDENTS t VALUES FOR ADJACENT COLOUR CATEGORIES. a b Firm-Semi Semi-Turning Turning-Green PRIORITY: Firm-Ripe -- Semi-Ripe 600/660 4.648** 6.751*** 610/680 4.366** 5.797*** 620/680 4.234** 5.407*** 600/680 4.094** 6.313*** 610/670 3.971** 5.896*** 8 . 542*** 7 .084*** 7.246*** 7.314*** 9.074*** PRIORITY: 560/640 550/640 540/640 570/690 560/690 Semi-Ripe 2.932* 3.088* 3.262* 2.905* 2.895* -- Turning 9.147*** 9.146*** 9.027*** 9.009*** 8.786*** 7.123*** 7.867*** 8. 320*** 5.627*** 6.189*** PRIORITY: 520/670 510/670 530/670 520/660 510/680 Turn i n g 2.876* 3.198* 2.790* 3.187* 3.295* - Green 6.973*** 6.599*** 7.346*** 7 .068*** 6.815*** 13.938*** 13.514*** 12.844*** 12.143*** 11.964*** S i g n i f i c a n t at 0.1% l e v e l S i g n i f i c a n t at 1% l e v e l S i g n i f i c a n t at 5% l e v e l 23 one of the thr e e p r i o r i t y groups would se p a r a t e s e r a i - r i p e from t u r n i n g , and t u r n i n g from green. However, o n l y the wavelength r a t i o s i n the f i r m r i p e v s . s e m i - r i p e p r i o r i t y group separate f i r m r i p e from s e m i - r i p e a t the 99% c o n f i d e n c e l e v e l — the wavelength r a t i o s i n the oth e r two groups separate a t o n l y the 95% c o n f i d e n c e l e v e l . A c h o i c e of any one wavelength r a t i o i n the 600 nm/660 nm to 610nm/670 nm group should r e s u l t i n good s e p a r a t i o n among the f o u r c o l o u r c a t e g o r i e s , but the b e s t wavelength r a t i o would be 600 nm/660 nm, s i n c e i t shows the g r e a t e s t v a l u e s of t f o r both f i r m r i p e v s . s e m i - r i p e and s e m i - r i p e v s . t u r n i n g , and the second l a r g e s t v a l u e o f t f o r t u r n i n g v s . green. 24 C H A P T E R 2. THEORY R E L A T E D TO T H E D E V E L O P M E N T OF A COLOUR GRADER. 25 INITIAL CONSIDERATIONS I d e a l l y , t o maximize the use of the r e f l e c t a n c e r a t i o t e c h n i q u e , the same ar e a on the tomato s u r f a c e s h o u l d be viewed by both s e n s i n g elements. T h i s minimizes v a r i a -t i o n s due t o c o l o u r d i f f e r e n c e s over the tomato s u r f a c e . A measure o f the r a t i o o f the r e f l e c t e d l i g h t a t two wavelengths c a n c e l s any e f f e c t o f r e f l e c t e d l i g h t i n t e n s i t y v a r i a t i o n (as a r e s u l t o f v a r y i n g tomato s i z e s ) i f the same area i s viewed by the two s e n s o r s . I n i t i a l t e s t s were conducted w i t h a com-b i n a t i o n o f in c a n d e s c e n t and f l u o r e s c e n t l i g h t sources and two s e n s i n g elements a l l mounted i n a metal housing. Both g e o m e t r i c a l and thermal problems were encountered. The measured r e f l e c t a n c e r a t i o was found t o vary w i t h tomato s i z e u s i n g t h i s housing, i n d i c a t i n g t h a t d i f f e r e n t areas o f the tomato were b e i n g sensed. A t r i f u r c a t e d f i b r e o p t i c assembly, F i g u r e 2.1, was c o n s i d e r e d . One f u r c a t i o n would be used t o d i r e c t the l i g h t source onto the tomato s u r f a c e , and the o t h e r two to d i r e c t e q u a l p o r t i o n s o f the r e f l e c t e d l i g h t t o each o f the photo-d e t e c t o r s . The l i g h t e m i t t i n g and r e c e i v i n g end o f the f i b r e o p t i c bundle was chosen so t h a t i t would emit l i g h t through a rectangle 1 i n (2.5 cm) X 0.063 i n (0.16 cm) with i t s lengths being per-p e n d i c u l a r t o the movement of the tomato under the f i b r e bundle. A random f i b r e arrangement was chosen t o ensure uniform l i g h t i n g o f the tomato s u r f a c e as w e l l as uniform F I G U R E 2.1 T R I F U R C A T E D F IBRE O P T I C A S S E M B L Y 26 FIBRE MOLD NO. X-7Z3 M F D . B Y D O L f c N -JENN£.X MASSACHUSETTS 27 l i g h t r e c e p t i o n . The minimum tomato s u r f a c e a r e a i l l u m i n a -te d and viewed would be an i n c h (2.5 cm) wide s t r i p over the l e n g t h o f the tomato as i t passed under the f i b r e bundle. A p h o t o t r a n s i s t o r was chosen as the p h o t o d e t e c t o r over o t h e r d e v i c e s such as photo d i o d e s , photo m u l t i p l i e r tubes, and photo c e l l s , s i n c e i t i s designed p r i m a r i l y f o r analog a p p l i c a t i o n s (as opposed to d i g i t a l f o r the photo d i o d e ) , has a h i g h l i g h t s e n s i t i v i t y , a wide o p e r a t i n g v o l -tage range and would be s u i t a b l e f o r use i n c o n j u n c t i o n w i t h i n t e g r a t e d c i r c u i t s . A t y p i c a l s p e c t r a l response curve f o r a photo-t r a n s i s t o r i s shown i n F i g u r e 2.2. Most s i l i c o n p h o t o t r a n -s i s t o r s and photo diodes e x h i b i t the same response. A h i g h i n t e n s i t y tungsten lamp (350 0°K c o l o u r temperature) was c o n s i d e r e d f o r use as a l i g h t s ource, s i n c e i t p r o v i d e s a s p e c t r a l o u t p u t r a t e o f change t h a t i s r e l a t i v e l y u n i form over the v i s i b l e range. The s p e c t r a l energy d i s t r i b u -t i o n o f a tungsten lamp a t 3500°K f i l a m e n t temperature i s shown i n F i g u r e 2.3. Lower o p e r a t i n g temperatures (e.g. 3300°K) have l i t t l e e f f e c t on the shape of the s p e c t r a l energy d i s t r i b u t i o n . A f l u o r e s c e n t lamp was deemed u n d e s i r -a b l e due t o the sharp s p i k e s i n i t s s p e c t r a l d i s t r i b u t i o n a t s p e c i f i c wavelengths. Based on the f i n d i n g s i n Chapter 1, the i d e a l o p t i c f i l t e r s would r e q u i r e peak wavelengths o f 600 nm and 660 nm r e s p e c t i v e l y . O p t i c f i l t e r s vary i n t h e i r r e l a t i v e peak F I G U R E 2 . 2 R E L A T I V E R E S P O N S E O F A T Y P I C A L P H O T O T R A N S I S T O R 28 4oo soo goo 700 300 WAVELE/VGrH ( N M ) F I G U R E 2 . 3 T U N G S T E N F I L A M E N T L A M P j S P E C T R A L D I S T R I B U T I O N j + 0 0 SOO SOO 700 QOO WAVELENGTH ( N M ) 29 t r a n s m i s s i o n s and have f i n i t e band widths encompassing more than a d i s c r e t e wavelength. The range of t r a n s m i t t e d wave-le n g t h s f o r a p a r t i c u l a r f i l t e r i s u s u a l l y expressed i n terms o f a h a l f bandwidth. The c h o i c e o f h a l f bandwidths f o r the• above f i l t e r s i s governed p r i m a r i l y by the data i n Tab l e 1.3. The data shows t h a t d e v i a t i o n from e i t h e r the 600 nm o r 660 nm peak wavelength by 10 nm g e n e r a l l y decreases the s e p a r a t i o n between c o l o u r c a t e g o r i e s . I f p o s s i b l e , t h e r e f o r e , the f i l t e r s s h o u l d have narrow bandwidths. I n t e g r a t i o n o f the energy b e i n g t r a n s m i t t e d over the band width o f the o p t i c f i l t e r must be taken i n t o account when d e s i g n i n g the o p t i c system. What i s the e f f e c t on the f i n a l r e f l e c t a n c e r a t i o i f the band width of one or both f i l t e r s o r t h e i r r e l a t i v e peak t r a n s m s i s s i o n s are changed? What e f f e c t w i l l the use o f a l i g h t source o t h e r than a standard tungsten lamp have on the f i n a l r a t i o obtained? An a n a l y s i s o f t h e e n t i r e l i g h t s o u r c e , sample, l i g h t d e t e c t o r system w i l l p r o v i d e answers t o these and o t h e r q u e s t i o n s . 30 ANALYSIS OF LIGHT SOURCE, SAMPLE, DETECTOR An a n a l y s i s was c a r r i e d out t o study the e f f e c t s o f l i g h t s o u r ce-sample-detector geometry on the measurement o f r e f l e c t a n c e . The e f f e c t s o f u s i n g v a r i o u s o p t i c f i l t e r s , and l i g h t sources were a l s o i n v e s t i g a t e d . A schematic of the source-sample-detector system i s shown i n F i g u r e 2.4. Each o p t i c f i l t e r was c o n v e n i e n t l y l o c a t e d between the output of the f i b r e o p t i c bundle and the p h o t o d e t e c t o r . S i n c e the f i n a l r a t i o t o be o b t a i n e d from the photo-t r a n s i s t o r s w i l l be the r a t i o o f e i t h e r two v o l t a g e s o r c u r r e n t s , the r a t i o w i l l be a d i m e n s i o n l e s s q u a n t i t y , which w i l l s i m p l i f y the system a n a l y s i s through the use of r e l a t i v e r a t h e r than a b s o l u t e q u a n t i t i e s . The components o f the a n a l y s i s are as f o l l o w s : Xi = peak wavelength o f the s h o r t wavelength o p t i c f i l t e r . A 2 = peak wavelength o f the l o n g wavelength o p t i c f i l t e r . Xx - a = s h o r t wavelength f i l t e r t r a n s m i s s i o n lower l i m i t (at a p proximately 0.1% peak t r a n s m i s s i o n ) . Xi + a = s h o r t wavelength f i l t e r t r a n s m i s s i o n upper l i m i t (at a pproximately 0.1% peak t r a n s m i s s i o n s ) . A 2 - b = l o n g wavelength f i l t e r t r a n s m i s s i o n lower l i m i t (at a pproximately 0.1% peak t r a n s m i s s i o n ) . A 2 + b = l o n g wavelength f i l t e r t r a n s m i s s i o n upper l i m i t (at a p proximately 0.1% peak t r a n s m i s s i o n ) . A = r e l a t i v e energy o f the l i g h t source, a t a g i v e n A between 380 and 800 nm. B = r e l a t i v e r e f l e c t a n c e o f a tomato, a t a g i v e n A between 380 and 800 nm. F I G U R E 2.4 S C H E M A T I C . O F S O U R C E - S A M P L E - D E T E C T O R S Y S T E M 31 TRIFURCATED FIBRE OPTIC ASSEMBLY COhfVBYOR BS.LT 32 D E. E. r e l a t i v e t r a n s m i s s i o n of the s h o r t wavelength o p t i c f i l t e r , a t a g i v e n X between 380 and 800 nm. r e l a t i v e t r a n s m i s s i o n of the long wavelength o p t i c f i l t e r , a t a g i v e n X between 380 and 800 nm. r e l a t i v e response of the p h o t o d e t e c t o r , a t A between 3 80 and 800 nm. output of the p h o t o d e t e c t o r r e c e i v i n g the s h o r t wavelengths of l i g h t i n t e g r a t e d between (A x - a) and (Ai + a ) . output of the p h o t o d e t e c t o r r e c e i v i n g the l o n g wavelengths of l i g h t i n t e g r a t e d between (A 2 - b) and (A 2 + b ) . In t h i s a n a l y s i s , the r e f l e c t a n c e r a t i o E^/E2 i s the r a t i o o f output c u r r e n t s o f the p h o t o d e t e c t o r s , each c u r r e n t b e i n g p r o p o r t i o n a l to the energy impinging on the semi-conductor s u r f a c e s . T h i s energy i s a f u n c t i o n of f a c t o r s such as the output of the l i g h t source, the r e f l e c -tance of the tomato, and the t r a n s m i s s i o n s of the f i l t e r s . T a k i n g these f a c t o r s i n to account y i e l d s the f o l l o w i n g r e l a t i o n s h i p : E n (Ai + a) [A (A) . B ( A) C 1(A) D ( A) ] dA (X; a) [2-1] (A 2 + b) [A ( A) . B ( A) C 2(A) D ( A) ] dA (X; b) 33 Approximations f o r the I n t e g r a l s A ( A ) , B ( A ) , C ( A ) and D ( A ) are complex f u n c t i o n s whose d e f i n i t i o n as equations i s not necessary f o r the pur-pose of t h i s a n a l y s i s . Approximations f o r the i n t e g r a l s may be o b t a i n e d by summation o f i n c r e m e n t a l areas under the r e p r e s e n t a t i v e curves of the f u n c t i o n s from { X \ - a) t o ( A i + a) and from ( A 2 - b) to ( A 2 + b ) . The i n c r e m e n t a l d i s t a n c e , AA = 10 nm was chosen f o r each area measurement. Data f o r the s p e c t r a l energy d i s t r i b u t i o n of the l i g h t source and f o r the response o f the p h o t o d e t e c t o r was c o l l e c t e d from 380 nm to 800 nm i n 10 nm s t e p s , from the curves i n F i g u r e s 2.2 and 2.3. The data from the 20 spectrograms was a l s o c o l l e c t e d over the same range i n 10 nm s t e p s . The spectrograms f o r a t y p i c a l f i r m r i p e and green tomato are shown i n F i g u r e 2.5. For the a n a l y s i s , the curve r e p r e s e n t i n g the o p t i c band pass f i l t e r was to be f l e x i b l e i n peak t r a n s -m i s s i o n and band width, and due to the complexity o f the Gaussian f u n c t i o n which n o r m a l l y r e p r e s e n t s the t r a n s -m i s s i o n c h a r a c t e r i s t i c s o f t h i s type of f i l t e r , i t was decided t h a t an i s o s c e l e s t r i a n g l e would serve as a reasonable approximation f o r the t r a n s m i s s i o n c u r v e s . The r e l a t i v e t r a n s m i s s i o n over the band width (where band width = 2 h a l f band width f o r the t r i a n g l e ) was c a l c u l a t e d from the equal s i d e s of the t r i a n g l e , a f t e r peak t r a n s m i s s i o n , peak wavelength, and h a l f band width were chosen f o r a n a l y s i s . So FIRM RIPE. 400 SOO 600 700 BOO WME.LEN6TH • ( N M ) j F I G U R E 2 . 5 S P E C T R O G R A M O F A T Y P I C A L F I R M R I P E A N D G R E E N T O M A T O 35 U s i n g t h e summation o f a r e a s , the i n t e g r a l s c o u l d be a p p r o x i m a t e d and t h e r a t i o E ^ / ^ c a l c u l a t e d u s i n g the r e l a t i o n s h i p : m E A A A B A A C, A A D A A P P i p P i = 0,10,20 f l -E 2 [2-2] E A A A B A A C_ A A D A A q q 2 q q j = 0,10,20 where p = A x - a + i q = A 2 - b + j m = 2 X h a l f band w i d t h o f t h e s h o r t w a v e l e n g t h f i l t e r n = 2 X h a l f band w i d t h o f t h e l o n g w a v e l e n g t h f i l t e r . V a r i o u s o p t i c f i l t e r s , h a l f band w i d t h s , i l l u m i n a -t i n g lamp s p e c t r a l c u r v e s , e t c . were t e s t e d i n e q u a t i o n [2-2] and t h e r a t i o E^/E^ c a l c u l a t e d f o r each o f t h e 20 tomatoes (Chapter 1 ) . F o r any s e t o f i n p u t c o n d i t i o n s , t h e l a r g e s t o f t h e 20 r a t i o s G = E^/lE^ ( c o r r e s p o n d i n g t o t h e g r e e n e s t tomato) was a d j u s t e d t o a v a l u e o f 10, and s u b s e q u e n t l y t h e r e m a i n i n g 19 r a t i o s were n o r m a l i z e d by m u l t i p l y i n g each by t h e n o r m a l i -z i n g f a c t o r : F = 10/G. [2-3] 36 RESULTS OF ANALYSIS The e f f e c t s of v a r y i n g peak t r a n s m i s s i o n and h a l f band width o f the o p t i c f i l t e r s on the measured r e f l e c t a n c e r a t i o were s t u d i e d to enable a f i l t e r s e l e c t i o n t o be made which s u i t e d the requirements f o r maximum s t a t i s t i c a l separa-t i o n among c o l o u r c a t e g o r i e s . The wavelength r a t i o of prime concern was 600 nm/660 nm — p r e v i o u s l y suggested as the optimum r a t i o . The e f f e c t o f u s i n g d i f f e r e n t l i g h t sources was s t u d i e d by r e v e r s i n g the s p e c t r a l output curve of the 3500K 0 tungsten lamp t o produce a h y p o t h e t i c a l lamp whose i r r a d i a n c e a t 350 nm was t h a t of the normal tungsten a t 80 0 nm; the i r r a d i a n c e a t 360 nm was t h a t o f the normal tungsten lamp a t 790 nm e t c . E f f e c t s of Peak T r a n s m i s s i o n The 600 nm/660 nm mean r e f l e c t a n c e r a t i o s , o b t a i n e d when f i l t e r s o f e q u a l h a l f band widths o f 20 nm and 40 nm and v a r i o u s combinations o f peak t r a n s m i s s i o n s from 20% to 60% were used i n the a n a l y s i s , are shown i n T a b l e 2.1. Values o f t r e s u l t i n g from a t - t e s t on the means o f a d j a c e n t c o l o u r c a t e g o r i e s are l i s t e d i n Table 2.2. E f f e c t s o f F i l t e r H a l f Band Width The 600 nm/660 nm mean r e f l e c t a n c e r a t i o s , o b t a i n e d when combinations o f 20 nm/20 nm to 40 nm/40 nm h a l f band widths, and 20% and 40% peak t r a n s m i s s i o n s were used f o r the 600 nm and 660 nm f i l t e r s r e s p e c t i v e l y , are 37 TABLE 2.1 NORMALIZED REFLECTANCE RATIOS OF 600nm/660nm, FOR COMBINATIONS OF EQUAL HALF BAND WIDTH FILTERS AND VARIOUS % TRANSMISSIONS: VALUES OBTAINED BY INTEGRATING OVER THE BAND WIDTHS. H a l f Band Width of 600 nm F i l t e r = 20 nm H a l f Band Width of 660 nm F i l t e r 20 nm T r a n s m i s s i o n o f 600 nm F i l t e r 20% to 60% T r a n s m i s s i o n of 660 nm F i l t e r 20% to 60% F i r m Ripe Semi-Ripe T u r n i n g Green Mean* 2.35 3.95 7.14 9.65 S.D.** 0.13 0.80 0.67 0 .27 H a l f Band Width f o r 600 nm F i l t e r = 40 nm H a l f Band Width f o r 660 nm F i l t e r = 40 nm T r a n s m i s s i o n of 600 nm F i l t e r 20% to 60% T r a n s m i s s i o n o f 660 nm F i l t e r 20% t o 60% F i r m Ripe Semi-Ripe T u r n i n g Green Mean* 1.83 2.97 6.11 9 .61 S.D.** 0.10 0.67 0 .80 0 .51 * Mean = Average of 5 tomatoes. ** S.D. = Standard D e v i a t i o n . 38 TABLE 2.2 STUDENTS t VALUES FOR COMPARISON OF MEAN REFLECTANCE RATIOS OF FOUR COLOUR CATEGORIES BASED ON DATA IN TABLE 2.1 H a l f Band Width of 600 nm F i l t e r = 20 nm H a l f Band Width o f 660 nm F i l t e r 20 nm T r a n s m i s s i o n o f 600 nm F i l t e r 20% t o 60% T r a n s m i s s i o n o f 660 nm F i l t e r 20% t o 60% F i r m Ripe Semi-Ripe T u r n i n g v s . v s . vs. Semi-Ripe T u r n i n g Green 4.387** 6.806*** 7.730*** H a l f Band Width f o r 600 nm F i l t e r = 40 nm H a l f Band Width f o r 660 nm F i l t e r = 40 nm T r a n s m i s s i o n o f 600 nm F i l t e r 20% t o 60% T r a n s m i s s i o n of 660 nm F i l t e r 20% t o 60% F i r m Ripe Semi-Ripe T u r n i n g v s . v s . vs. Semi-Ripe T u r n i n g Green 3.807** 6.711*** 8.216*** *** S i g n i f i c a n t a t 0.1% l e v e l ** S i g n i f i c a n t a t 1% l e v e l 39 shown i n Table 2.3. Tab l e 2.4 l i s t s the v a l u e s o f t r e s u l t i n g from the comparison of means of a d j a c e n t c o l o u r c a t e g o r i e s shown i n Table 2.3. L i g h t Source E f f e c t s R e v e r s i n g the s p e c t r a l output curve of the tung-s t e n lamp, and t e s t i n g t h i s new h y p o t h e t i c a l lamp i n the a n a l y s i s showed no s i g n i f i c a n t change i n the s t a t i s t i c a l s e p a r a t i o n between a d j a c e n t c o l o u r c a t e g o r i e s . 40 TABLE 2.3 NORMALIZED REFLECTANCE RATIOS OF 600 nm/660 nm, FOR COMBINATIONS OF VARIOUS HALF BAND WIDTHS AND TWO % TRANSMISSIONS: VALUES OBTAINED BY INTE-GRATING OVER THE BAND WIDTHS. H a l f Band Percent Firm Semi- Turning Green Width (nm) Tra n s m i s s i o n Ripe Ripe f o r f o r Mean* Mean Mean Mean 600nm 660nm 600nm 660nm S.D.** S.D. S.D. S.D. 20 20 20 40 2. 35 3.95 7.14 9.65 0.13 0.80 0.67 0. 27 30 20 20 40 2.42 3.94 7.13 9.66 0.13 0.78 0.68 0.27 40 20 20 40 2.52 3.94 7.11 9.66 0.12 0.75 0.69 0.26 20 30 20 40 2.42 4. 05 7.27 9.69 0.14 0.81 0.67 0.27 30 30 20 40 2.46 3.99 7.19 9.67 0.13 0. 78 0. 68 0.27 40 30 20 40 1.77 2.89 5.98 9.56 0.10 0.66 0.80 0. 54 20 40 20 40 2. 52 4. 20 7.44 9.75 0.14 0.82 0.65 0. 25 30 40 20 40 2.30 3.79 7.12 9. 58 0.12 0.73 0. 76 0.39 40 40 20 40 1.85 2. 97 6.11 9.61 0.10 0.67 0.80 0. 51 * Mean = Average o f 5 tomatoes S.D. = Standard D e v i a t i o n . 41 TABLE 2.4 STUDENTS t VALUES FOR COMPARISON OF MEAN REFLECTANCE RATIOS OF FOUR COLOUR CATE-GORIES BASED ON DATA IN TABLE 2.3. Half Width for Band (nm) Percent Transmission for Firm-Ripe vs. Semi-Ripe Semi-Ripe vs. Turning Turning vs. Green 600nm 660nm 600nm 660nm 20 20 20 40 4.387** 6.806*** 7 . 730*** 30 20 20 40 4.293** 6.885*** 7 .706*** 40 20 20 40 4.177** 6.951*** 7.727*** 20 30 20 40 4.444** 6.866*** 7.551*** 30 30 20 40 4.326** 6.915*** 7.563*** 40 30 20 40 3.767** 6.674*** 8.302*** 20 40 20 40 4.511** 6.926*** 7.386*** 30 40 20 40 4.465** 7.075*** 6.457*** 40 40 20 40 3.807** 6.711*** 8 .261*** S i g n i f i c a n t at 0.1% l e v e l S i g n i f i c a n t at 1% l e v e l 42 DISCUSSION The mean r e f l e c t a n c e r a t i o s l i s t e d i n Table 2.1 i n d i c a t e t h a t t h e r e i s no e f f e c t on the 600 nm/660 nm r e f l e c t a n c e r a t i o i f the h a l f band widths o f the f i l t e r s are h e l d c o n s t a n t and the peak t r a n s m i s s i o n s a l t e r e d . I f the h a l f band widths o f the 600 nm and 660 nm f i l t e r s are i n c r e a s e d from 20 nm to 40 nm each, the means f o r each c o l o u r c a t e g o r y are decreased. The decrease i s not s i g n i f i c a n t f o r any c o l o u r c a t e g o r y a t the 1% c o n f i d e n c e l e v e l . Widening the band width o f the f i l t e r s r e s u l t s i n i n t e g r a t i o n remote from 600 nm and 660 nm where s e p a r a t i o n o f f i r m r i p e and s e m i - r i p e tomatoes i s g r e a t e s t . The decreased s e p a r a t i o n between these two c a t e g o r i e s i s r e f l e c t e d by the lower v a l u e of t as shown i n T a b l e 2.2. T y p i c a l peak t r a n s m i s s i o n s o f 20% f o r the 600 nm f i l t e r and 40% f o r the 660 nm f i l t e r were chosen f o r the r e s t of the 600 nm/660 nm r a t i o a n a l y s i s . T a b l e 2.3.shows t h a t combinations o f h a l f band widths from 20 nm/20 nm t o 40 nm/40 nm produces a g r a d u a l decrease i n the mean r e f l e c -tance r a t i o s of each c o l o u r c a t e g o r y . The c o r r e s p o n d i n g v a l u e s o f t f o r the comparison of the means o f a d j a c e n t c o l o u r c a t e g o r i e s o f T a b l e 2.3 are l i s t e d i n Table 2.4. The v a l u e o f t f o r the f i r m r i p e v s . s e m i - r i p e decreases c o n s i s t e n t l y w i t h the i n c r e a s i n g band-width of the 600 nm f i l t e r . Widening the 66 0 nm h a l f band-width shows a s l i g h t i n c r e a s e i n t v a l u e s except when i n 4 3 combination w i t h the 6 0 0 nm - 4 0 nm f i l t e r . The 6 0 0 nm -2 0 nm f i l t e r combined w i t h the 6 6 0 nm - 4 0 nm f i l t e r i n d i c a t e s the b e s t s e p a r a t i o n between f i r m r i p e and s e m i - r i p e . The v a l u e s of t f o r s e m i - r i p e vs. t u r n i n g and t u r n i n g v s . green do not seem to change w i t h h a l f band width v a r i a t i o n s , but remain r e l a t i v e l y c o n s t a n t . The changes i n h a l f band width from 2 0 nm t o 4 0 nm f o r e i t h e r f i l t e r do not s i g n i f i c a n t l y a f f e c t the separa-t i o n o f f i r m r i p e v s. s e m i - r i p e , s e m i - r i p e vs. t u r n i n g , and t u r n i n g v s . green. Examination o f e f f e c t s beyond 4 0 nm h a l f band widths was unnecessary s i n c e a 4 0 nm h a l f band width d e s c r i b e s an i n e x p e n s i v e band pass (as opposed to narrow band pass or very narrow band pass) f i l t e r . In summary, the h a l f band width of the i n t e r f e r e n c e f i l t e r chosen f o r the c o l o u r s e p a r a t i o n i s l e s s c r i t i c a l than the c h o i c e o f peak wavelength. The peak t r a n s m i s s i o n of the f i l t e r does not a f f e c t the s e p a r a t i o n between c o l o u r c a t e -g o r i e s . The type o f l i g h t source used i s not c r i t i c a l , p r o v i d e d t h a t the peak wavelengths of the f i l t e r s a l s o e x i s t i n the l i g h t source to a d e t e c t a b l e degree. Inexpensive narrow band pass i n t e r f e r e n c e f i l t e r s h a v i ng h a l f band widths of 2 0 nm are common, and the c h o i c e of one a t 6 0 0 nm and one a t 6 6 0 nm should be a c c e p t a b l e . The comparison o f t v a l u e s i n Table 2 . 2 and T a b l e 1 . 3 i n d i c a t e s t h a t a n a l y s i s u s i n g e q u a t i o n [ 2 - 2 ] does not a l t e r the s t a t i s t i c a l s e p a r a t i o n of the mean r e f l e c t a n c e 44 r a t i o s examined. T h e r e f o r e the complete a n a l y s i s i s not necessary to e s t a b l i s h t h i s s e p a r a t i o n and the r e f l e c t a n c e r a t i o a t two wavelengths may be used as d e s c r i b e d i n Chapter 1. The a n a l y s i s o f the system i s n e c e s s a r y , however, to o b t a i n the f o l l o w i n g i n f o r m a t i o n . The n o r m a l i z i n g f a c t o r F [2-3] i s the g a i n r a t i o o f the two p h o t o d e t e c t o r a m p l i f i e r s . A s c a l e o f 10 was used f o r the a n a l y s i s , but any convenient s c a l e , N, w i l l produce s i m i l a r r e s u l t s . Now, F = N/G [2-4] where G = maximum v a l u e o f E ^ / E 2 , c a l c u l a t e d from [2-2] f o r the greenest tomato. The two p h o t o d e t e c t o r a m p l i f i e r s must be a d j u s t e d so t h a t t h e i r g a i n r a t i o ( s h o r t wavelength p h o t o d e t e c t o r g a i n / l o n g wavelength p h o t o d e t e c t o r gain) i s equal t o F. R e f l e c t a n c e r a t i o s f o r a l l tomatoes w i l l then be maintained w i t h i n the l i m i t s 0 < E../E., _< N. C H A P T E R 3 D E S I G N A P P R O A C H 46 INTRODUCTION I t has been e s t a b l i s h e d t h a t the r a t i o o f r e f l e c -t e d l i g h t a t two narrow wavelength bands i n the v i s i b l e spectrum w i l l be the c r i t e r i o n f o r c o l o u r g r a d i n g i n the pr e s e n t d e s i g n . S p e c i f i c components such as p h o t o d e t e c t o r s and o p t i c f i l t e r s must now be s e l e c t e d . Having made the s e l e c t i o n , a s i g n a l p r o c e s s i n g u n i t must be designed to c a r r y out the ta s k o f d i v i d i n g the two p h o t o d e t e c t o r s i g n a l s t o produce the r e f l e c t a n c e r a t i o , t o c a t e g o r i z e the tomato based on the r e f l e c t a n c e r a t i o , and to t r a n s f e r the s i g n a l t o an a p p r o p r i a t e e j e c t mechanism. The mechanism i s a c t i v a -t e d when the tomato and e j e c t mechanism are i n j u x t a p o s i t i o n . The s i g n a l p r o c e s s o r w i l l be d i v i d e d i n t o two s e c t i o n s — the analog p r o c e s s o r , and the d i g i t a l p r o c e s s o r . The analog p r o -c e s s o r handles the i n f o r m a t i o n up t o the p o i n t where c a t e g o r i -z a t i o n o c c u r s . S i g n a l h a n d l i n g then proceeds through the d i g i t a l p r o c e s s o r . F r u i t and v e g e t a b l e conveying systems a r e a v a i l a b l e commercially and i t was not the aim of t h i s r e -sea r c h t o i n v e n t a new conveying system f o r tomatoes. Since many conveyors are f l a t b e l t s , i t was d e c i d e d t h a t a l l e f f o r t s should be c o n c e n t r a t e d towards d e s i g n i n g a tomato grader which would be compatible w i t h e x i s t i n g conveying systems. T h i s would a l l o w the purchase o f " o f f the s h e l f " conveyors, as w e l l as easy a d a p t a t i o n o f the grader f o r o r g a n i z a t i o n s which a l r e a d y had such conveyors i n use. 47 The f r u i t e j e c t i o n mechanism was not a stock item, and i t s d e s i g n w i l l be d e s c r i b e d . Many p o s s i b i l i t i e s were c o n s i d e r e d f o r moving the tomatoes o f f the b e l t , but a h i g h p r e s s u r e pneumatic system was found the most s u i t a b l e . A t e s t conveyor, 6 f e e t i n l e n g t h , was b u i l t u s i n g a f l a t , matte b l a c k b e l t , 6 i n c h e s wide. A b l a c k b e l t was chosen, s i n c e i t p r o v i d e d a low r e f l e c t a n c e a t the two c r i t i c a l wavelengths r e l a t i v e t o the tomatoes t r a n s p o r t e d on i t . T h i s p r o v i d e d a c o n s t a n t low r e f l e c t a n c e background. The b e l t was c h a i n d r i v e n by a v a r i a b l e speed motor, a l l o w i n g t e s t i n g a t v a r i o u s conveyor speeds. In many cas e s , the " i d e a l " components r e q u i r e d f o r the system d e s i g n were not commercially o r r e a d i l y a v a i l a b l e . Consequently, r e a s o n a b l e s u b s t i t u t i o n s have been i n c o r p o r a t e d where ne c e s s a r y . 48 INITIAL COMPONENT SELECTION L i g h t Source \ A Dolan-Jenner Model No. 150, v a r i a b l e i n t e n s i t y l i g h t source comprising a st a n d a r d DNE p r o j e c t i o n lamp (3350°K c o l o u r temperature) w i t h d i c h r o i c r e f l e c t o r was used. P h o t o d e t e c t o r s Two FPT 120A* p h o t o t r a n s i s t o r s were chosen p r i m a r i l y f o r t h e i r h i g h s e n s i t i v i t y . The s p e c t r a l response curve o f the FPT 120A was p r e v i o u s l y shown i n F i g u r e 2.2. O p t i c F i l t e r s A t the b e g i n n i n g o f the r e s e a r c h , both the 600 nm and 660 nm i n t e r f e r e n c e f i l t e r s were not a v a i l a b l e . I t was dec i d e d t h a t the 600 nm f i l t e r might be s u b s t i t u t e d by a 550 nm f i l t e r which was a v a i l a b l e . The s p e c i f i c a t i o n s f o r the two f i l t e r s are l i s t e d below: Peak wavelength 550 nm 660 nm H a l f bandwidth 20 nm 20 nm Peak T r a n s m i s s i o n 20% 40% R e f e r r i n g t o Table 1.1, the 550 nm/660 nm wave-l e n g t h r a t i o ranks e i g h t e e n t h i n the l i s t , based on the maximum t o t a l d i f f e r e n c e between means o f a d j a c e n t c o l o u r c a t e g o r i e s . The s t a t i s t i c a l s e p a r a t i o n between a d j a c e n t c o l o u r c a t e g o r i e s u s i n g the 550 nm/660 nm wavelength r a t i o * Manufactured by F a i r c h i l d Semiconductor Corp., Mountain View, C a l i f o r n i a . 4 9 was s t u d i e d u s i n g the a n a l y s i s d e s c r i b e d i n Chapter 2, to ensure t h a t t h i s r a t i o c o u l d be used as a reaso n a b l e sub-s t i t u t e f o r the i d e a l 600 nm/660 nm r a t i o . The s p e c t r a l d i s t r i b u t i o n o f the DNE b u l b , the o p t i c f i l t e r d ata, the FPT 120A response curve, and the s p e c t r o g r a p h i c d a t a o f the p r e v i o u s l y t e s t e d 20 tomatoes was programmed i n t o e q u a t i o n [2-2] to generate p r e d i c t e d v a l u e s o f E^/E 2- The r e s u l t i n g means and standard d e v i a t i o n s f o r the f o u r c o l o u r c a t e g o r i e s , and the t - v a l u e s o f a d j a c e n t c o l o u r c a t e g o r i e s are l i s t e d i n Table 3.1. The data i n Table 3.1 suggests t h a t good separa-t i o n between s e m i - r i p e and t u r n i n g , and t u r n i n g and green may be expected. The s e p a r a t i o n between f i r m r i p e and semi-r i p e w i l l be r e l a t i v e l y poor, u s i n g the 550 nm/660 nm f i l t e r combination; however, the r e s t of the system d e s i g n s h o u l d not be a d v e r s e l y a f f e c t e d . The 550 nm f i l t e r was t h e r e f o r e used as a s u b s t i t u t e f o r the 600 nm f i l t e r . A nalog and D i g i t a l F a m i l i e s F i g u r e 3.1 shows a sta n d a r d p h o t o t r a n s i s t o r a m p l i f y i n g c i r c u i t where the output v o l t a g e , V , i s a f u n c t i o n of i n c i d e n t r a d i a n t energy on the p h o t o - s e n s i t i v e semi-conductor a r e a . Two a m p l i f i e r s measuring the energy t r a n s -m i t t e d through the o p t i c f i l t e r s produce two v o l t a g e s which are f u n c t i o n s o f the l i g h t r e f l e c t e d from the tomato s u r f a c e . D i v i s i o n o f the two v o l t a g e s t o produce the d e s i r e d r e f l e c -tance r a t i o i s r e a d i l y accomplished through the use o f a standard O p e r a t i o n a l A m p l i f i e r (Op Amp) c i r c u i t . S i n c e the 50 TABLE 3.1 NORMALIZED REFLECTANCE RATIO MEANS, STANDARD DEVIATIONS, AND STUDENTS t VALUES FOR FOUR COLOUR CATEGORIES USING A 5 50 nm/660 nm WAVELENGTH RATIO: VALUES OBTAINED BY INTE-GRATING OVER THE BAND WIDTHS. Half Band Width Peak Transmission F i l t e r 550 nm 660 nm 20 nm 20 nm 20 % 401 Firm-Ripe Semi-Ripe Turning Green Mean 0.458 1.193 5.329 9.646 S.D. 0.051 0.583 0.961 0.388 t - Values Firm-Ripe vs. Semi-Ripe 2.805* Semi-Ripe vs. Turning 8.227*** Turning vs. Green 9.313*** *** S i g n i f i c a n t at 0.11 l e v e l * S i g n i f i c a n t at 5% l e v e l FIGURE 3.1 STANDARD NPN PHOTOTRANSISTOR AMPLIFIER USING AN FPT120A v 51 V+ O LIGHT 52 d i v i d i n g c i r c u i t i s an i n t e g r a l p a r t o f the system, i t was dec i d e d t h a t analog s i g n a l p r o c e s s i n g s h o u l d be done u s i n g the Op Amps. Modern Op Amps are a v a i l a b l e as i n t e g r a t e d c i r c u i t s , which g e n e r a l l y operate on a s p l i t + 15 v o l t power supply. The c h o i c e o f d i g i t a l f a m i l i e s t h a t c o u l d be used was broad. The hig h speed s w i t c h i n g c a p a b i l i t y o f the popular TTL ( T r a n s i s t o r - T r a n s i s t o r L o g i c ) c i r c u i t s was b e l i e v e d to be more o f a hindrance than an a s s e t f o r t h i s type o f instrument. The d e v i c e s are very s u s c e p t i b l e t o noise, r e q u i r i n g much e l e c t r i c a l s h i e l d i n g . The low +5 v o l t supply v o l t a g e o f the TTL c i r c u i t s rendered i t even l e s s compatible w i t h the Op Amps. The newly developed and r a p i d l y expanding f a m i l y of CMOS (Complementary Symmetry-Metal Oxide Semiconductor) was found t o be very s u i t a b l e f o r t h i s d e s i g n . The CMOS f a m i l y has many advantages over TTL c i r c u i t s . The CMOS de v i c e s w i l l operate on a +15 v o l t power supply making them h i g h l y compatible w i t h the Op Amps. T h e i r q u i e s c e n t power d i s s i p a t i o n i s t y p i c a l l y 10 ^ t h a t o f TTL c i r c u i t s , and s w i t c h i n g o f s m a l l a n a l o g s i g n a l s i s ac h i e v e d w i t h b i l a t e r a l switches unknown t o the TTL f a m i l y . The n o i s e immunity o f the CMOS d e v i c e s i s much h i g h e r than TTL l o g i c d e v i c e s . The lower s w i t c h i n g speed o f 5 megahertz (MHz) as opposed t o 30 MHz f o r TTLs was not a hi n d r a n c e , s i n c e s o r t i n g o p e r a t i o n s w i l l t y p i c a l l y be below 10H . For these reasons, the CMOS f a m i l y was chosen f o r the d i g i t a l p r o c e s s i n g s e c t i o n o f the c o l o u r g r a d e r . ELECTRONIC COLOUR GRADING SYSTEM: OVERVIEW A b l o c k diagram o f the e l e c t r o n i c s i g n a l p r o c e s s o r o f the c o l o u r grader i s shown i n F i g u r e 3.2. There are two s e c t i o n s t o the s i g n a l p r o c e s s o r — the analog p r o c e s s o r and the d i g i t a l p r o c e s s o r . The analog p r o c e s s o r senses the presence o f the tomato through the summation o f the photo-d e t e c t o r output s i g n a l s and c o n t i n u o u s l y c a l c u l a t e s the r e f l e c -tance r a t i o as the tomato passes under the s e n s i n g head. The peak r e f l e c t a n c e r a t i o i s used t o c a t e g o r i z e the tomato i n t o one o f f o u r c o l o u r c a t e g o r i e s . The c a t e g o r y i n f o r m a t i o n i s en t e r e d i n t o the d i g i t a l p r o c e s s o r a t the time the tomato l e a v e s the s e n s i n g a r e a , and the d a t a moves through a memory as the tomato t r a v e l s downstream from the s e n s i n g head. When the c a t e g o r i z e d tomato i s i n l i n e w i t h i t s e j e c t s t a t i o n , a s i g n a l appears a t the output o f the memory which i s used to operate an e l e c t r o m e c h a n i c a l e j e c t mechanism. A l i g h t beam chopper d i s k and p h o t o d e t e c t o r are a t t a c h e d t o the a x l e o f one o f the conveyor p u l l e y s , and the chopped e l e c t r i c a l s i g n a l i s used t o s y n c h r o n i z e the movement o f the data i n the memory w i t h the movement o f the conveyor b e l t . The memory i s comprised o f t h r e e s h i f t r e g i s t e r s , one f o r each o f the th r e e c o l o u r c a t e g o r i e s : f i r m r i p e , semi-r i p e and t u r n i n g . The green tomatoes were a l l o w e d t o f a l l o f f the end o f the conveyor. Each s h i f t r e g i s t e r has a d i f f e r e n t s t o r a g e c a p a c i t y , depending on the l i n e a l d i s t a n c e RED FlLTERl GREEN} FILTER] A PHOTO-TUMSISTOR B PRE-AMR e NOTCH 6, 10W PASS FILTER A PHOTO-TRANSISW, B PKE-AMP. C NOTCH & tOW PASS FILTER (LE^ L^ fp) " I DISPLAY TIMER TURNING SEMI-RIPE. FIRM RIPE RESET IN 1 D E ANAtOS PEAK DIVIDER DETECTOR 1 O COMPARATOR I OUT O COMPARATOR Z OUT-O COMPARATOR 3 Ot/r G |Sl/MM/W6 AMP. / H LOW PASS FILTER I [INVERTER J P E A K DETECTOR Z K St/MMWfi AMP. 2 SCHM/TT T/?/<5SER ANALOG PROCESSOR N IDECODJNG S A f f S -O wi?ire w — — O COMP. I IN O COMP. 2 W O CTO/WP.3 W DIGITAL PROCESSOR M TIMERS TiM£RS> LATCHES <$• MEMORIES OPTO-ISOLATORS & TF.lhCS SOLENOID' I SOLENOID 2 m WRITE /?EI5£7 SKMPLE OUT OUT OUT F I G U R E 3 . 2 C O L O U R G R A D E R B L O C K D I A G R A M 55 downstream from the s e n s i n g head t h a t a p a r t i c u l a r e j e c t s t a t i o n i s l o c a t e d . A c a t e g o r i z e d tomato and i t s e j e c t s t a t i o n w i l l always c o i n c i d e a t e j e c t i o n time r e g a r d l e s s of conveyor b e l t speed, due to the memory-conveyor b e l t s y n c h r o n i z a t i o n . The s o l e n o i d s i n c o r p o r a t e d i n the pneumatic e j e c t system were st a n d a r d l l O v AC t y p e s , and i t was necessary to i s o l a t e these d e v i c e s from the low v o l t a g e s i g n a l p r o c e s s i n g c i r c u i t by means o f an o p t o - i s o l a t o r i n t e r f a c e . Each o f the b l o c k s i n F i g u r e 3.2 w i l l be d i s c u s s e d i n more d e t a i l , w i t h r e s p e c t t o f u n c t i o n , d e s i g n and n e c e s s i t y . Where p o s s i b l e , the analog and d i g i t a l p r o c e s s o r s w i l l be d e a l t w i t h s e p a r a t e l y . 56 ANALOG SIGNAL PROCESSOR D i v i d e r C i r c u i t (Box D, F i g u r e 3.2) The c i r c u i t chosen t o d i v i d e the two p h o t o d e t e c t o r v o l t a g e s i s shown i n F i g u r e 3.3. I t c o n s i s t s o f an MC1495* and two type 741** Op Amps. The second 741 Op Amp i s used as a summing a m p l i f i e r , whereas the MC1495 and f i r s t 741 are used f o r the d i v i s i o n o p e r a t i o n . The c h a r a c t e r i s t i c s o f the c i r c u i t are as f o l l o w s : (a) 0 < V < + 10 v o l t s . x — (b) -10 v o l t s < V < + 10 v o l t s . — z — (c) V , = -10 V /V o l z' X where = output v o l t a g e from the "green" photo-z t r a n s i s t o r V = output v o l t a g e from the "red " photo-t r a n s i s t o r I n i t i a l t e s t i n g o f t h i s c i r c u i t showed t h a t the s a t u r a t i o n v o l t a g e (V , = c o n s t a n t , f o r any V , V ) was -12.5 o l J x z v o l t s . The output v o l t a g e range o f the d i v i d e r i s t h e r e f o r e zero t o -12.5 v o l t s i f V and V are p o s i t i v e . S i n c e the x z c CMOS d e v i c e s operate from zero t o +15 v o l t s , i t was found advantageous t o add +12.5 v o l t s t o the d i v i d e r output u s i n g a summing a m p l i f i e r t o change the output range o f +12.5 t o zero v o l t s . The new e q u a t i o n f o r the c i r c u i t i s : * MC p r e f i x i n d i c a t e s component manufactured by M o t o r o l a Semi-conductor, Inc., Phoenix, A r i z o n a . ** Type 741 Op Amps are manufactured by Mot o r o l a Semi-conductor, Inc. (MC1741); F a i r c h i l d Semi-conductor Corp. (UA741), Mountain View, C a l i f o r n i a ; RCA Corp. (CA3741) S o m e r v i l l e , New J e r s e y ; and o t h e r s . F I G U R E 3.3 A N A L O G D I V I D E R C I R C U I T 5 8 V Q 2 = 1 2 . 5 - 1 0 V Z / V X [ 3 - 1 ] From [ 3 - 1 ] i t may be shown t h a t f o r the range 0 £ £ 1 2 . 5 , the i n p u t range to the d i v i d e r must be 0 £ V / V < 1 . 2 5 . T h e r e f o r e , i n e q u a t i o n [2-4], N = 1 . 2 5 . I t may be shown u s i n g the a n a l y s i s i n Chapter 2 , t h a t a g i v e n r a t i o F = 1 . 6 0 w i l l m a i n t a i n V / V w i t h i n the above l i m i t s . z' x Consequently the g a i n o f the "green" a m p l i f i e r s h o u l d be 1 . 6 0 X g a i n of the "red" a m p l i f i e r . Using e q u a t i o n [ 3 - 1 ] , the p r e d i c t e d mean output v o l t a g e s f o r the f o u r c o l o u r c a t e -g o r i e s based on the twenty tomatoes (Chapter 1 ) were c a l c u -l a t e d , and are l i s t e d i n T a b l e 3 . 2 . The p o t e n t i o m e t e r s , P^ through P^, i n F i g u r e 3 . 3 , are a d j u s t e d i n i t i a l l y so t h a t the c i r c u i t o p e rates w i t h i n the s p e c i f i e d l i m i t s and i s b a l a n c e d * . Potentiometer P,. i s a d j u s t e d t o approximately - 1 2 . 5 v o l t s so t h a t V 2 i s zero when V > 1 . 2 5 V . z x * See M o t o r o l a L i n e a r I n t e g r a t e d C i r c u i t s Data Book, 1 9 7 2 , (second e d i t i o n ) p. 7 - 3 8 7 f o r c a l i b r a t i o n procedure. 59 TABLE 3.2 PREDICTED MEAN OUTPUT VOLTAGES FOR FOUR COLOUR CATEGORIES BASED ON EQUATION [3-1] AND THE TWENTY TOMATOES (Chapter 1). Colour V q 2 (volts) Firm Ripe 11.93 Semi-Ripe 11.00 Turning 5.82 Green 0.41 60 P h o t o t r a n s i s t o r and P r e a m p l i f i e r C i r c u i t s (Box A,B,Figure 3.2) The. h i g h impedance output o f the p h o t o t r a n s i s t o r a m p l i f i e r shown i n F i g u r e 3.1 was f o l l o w e d by a low-gain, n o n - i n v e r t i n g type 741 Op Amp which p r o v i d e d a low impedance output. The 741 Op Amp a l s o p r o v i d e s a f i n e o f f s e t adjustment to e s t a b l i s h the b l a c k conveyor b e l t as a zero v o l t a g e r e f e r e n c e . The schematics f o r the " r e d " and "green" ampli-f i e r s are shown i n F i g u r e 3.4. (a) The output v o l t a g e o f the r e d a m p l i f i e r may not exceed + 10 v o l t s ( i n p u t r e s t r i c t i o n on V o f the d i v i d e r ) . A l a r g e , f i r m r i p e tomato was p l a c e d under the l i g h t s e n s i n g head, 1/2 i n (1.3 cm) from the fibre optic bundle*, and 2 a quantum measurement o f 0.25 uE/m sec (micro E i n s t e i n s / 2 meter sec) was o b t a i n e d through the 660 nm f i l t e r a t 75% o f the l i g h t i n t e n s i t y s c a l e o f the i l l u m i n a t o r . -3 T h i s r e f l e c t e d quantum l e v e l i s e q u i v a l e n t t o 1.5 X 10 2 2 mw/cm ( m i l l i w a t t s / c m ). S p e c i f i c a t i o n sheets f o r the -3 FPT 120A do not y i e l d i n f o r m a t i o n below 5 X 10 2 mw/cm ; consequently the p h o t o t r a n s i s t o r c o l l e c t o r c u r r e n t a t +15 v o l t s s u p p l y was measured a t v a r i o u s quantum l e v e l s , and a l i n e a r r e g r e s s i o n performed on the data. The r e s u l t i n g e q u a t i o n was: I C E = 54.2 Q 1 , 3 9 2 [3-2] * T h i s w i l l produce the maximum v o l t a g e expected f o r the red a m p l i f i e r . F I G U R E 3.4 R E D A N D G R E E N P H O T O T R A N S I S T O R A M P L I F I E R S R E D A M P L I F I E R t/Sv G R E E N A M P L I F I E R 62 where I_„ = c o l l e c t o r c u r r e n t i n uA (micro amps) 2 Q = quanta, i n uE/m s e c . Equ a t i o n [3-2] y i e l d s I,„ = 7.9 uA f o r the f i r m r i p e tomato. The b l a c k conveyor b e l t r e f l e c t a n c e was a l s o measured through the 660 nm f i l t e r , and found to be 2 0.06 uE/m sec. The c u r r e n t generated due to the back-ground u s i n g e q u a t i o n [3-2] y i e l d s I' „ = 1.1 yA. e h N e g l e c t i n g the f i n e o f f s e t adjustment, the e q u a t i o n governing the output o f each o f the n o n - i n v e r t i n g a m p l i f i e r c i r c u i t s i s : R 2 V = + 1) V. [3-3] o R 1 i n L J where V = output v o l t a g e ( r e f e r e n c e d t o ground) V\ = i n p u t v o l t a g e ( r e f e r e n c e d t o ground) R 2 (— + 1 ) = A v = c l o s e d loop g a i n . I f R, = R„ = 10K3:, then A = 2 , and i f the maximum 1 2 v va l u e o f V = 1 0 v o l t s , then V. = 5 v o l t s f o r the o i n l a r g e f i r m r i p e tomato. I f Rg i s s u f f i c i e n t l y s m a l l so as not to c o n t r i b u t e s i g n i f i c a n t l y t o R^, then the c u r r e n t through the photo-t r a n s i s t o r .and the r e s i s t o r , R^, i s the same. When the photo i n p u t r e s u l t s from the b l a c k b e l t o n l y , 63 V. - V i n c- = 1.1 uA [3-4] R 3 where V\ = 0 (zero v o l t s f o r background) V c = course o f f s e t adjustment v o l t a g e t h e r e f o r e , V = -1.1 R [3-5] When the photo i n p u t i s from the f i r m r i p e tomato, again the c u r r e n t through the p h o t o t r a n s i s t o r and R^ i s the same. S u b s t i t u t i n g [3-5], and the f i r m r i p e tomato photo c u r r e n t y i e l d s : V. - (-1.1 R,) i n 2. = 7.9 uA R 3 s i n c e , V. = 5 v o l t s , i n t h e r e f o r e , R^ = 735 KX2 , o r a s u i t a b l e v a l u e would be R 3 = 750 YSl [3-6] S u b s t i t u t i n g [3-6] i n [3-5] y i e l d s V = -0.825 v o l t s , c A value o f Rg = 10 KQ would be s u i t a b l e f o r the course o f f s e t adjustment. The f i n e o f f s e t adjustment range i s governed by the e q u a t i o n : 64 V « 4. = ± V , (Rc/RJ [3-7] o f f s e t s u pply 5' 4 1 J I f , R 4 .= 4.7 Kfl, and R c = 470 a V « . = ± 1 . 5 v o l t s o f f s e t S i nce the g a i n r a t i o F i s equal t o 1.60 as d e s c r i b e d i n the d i v i d e r c i r c u i t , the g a i n o f the green a m p l i f i e r must be 1.60 times the g a i n o f the r e d a m p l i f i e r , o r A =3.20, i . e . v R2 Rf + 1 = 3 ' 2 or R 2 = 2.2 R-L [3-8] L e t R^ and R^ f o r the green a m p l i f i e r e q u a l R^ and R^ f o r the r e d a m p l i f i e r , i . e . R± = 10 Kft, and R 3 = 750 Ytt then from [3- 8] , R 2 = 22 K0-. The background r e f l e c t a n c e was measured through the 2 550 nm f i l t e r and found t o be 0.05 uE/m sec. From eq u a t i o n [3-2], the c u r r e n t generated i n the green p h o t o t r a n s i s t o r i s : I " C E = 0.84 uA. 65 As i n [3-4] , V. - V - = 0.84 uA. [3-9] 3 S u b s t i t u t i n g V, = 0 i n R 3 = 750 KQ t h e n , V = -0.63 v o l t s c The f i n e o f f s e t a d j u s t m e n t range was s e l e c t e d e q u a l t o t h a t o f t h e r e d a m p l i f i e r . 66 Notch F i l t e r and Low Pass F i l t e r (Box C, F i g u r e 3.2) The p h o t o t r a n s i s t o r a m p l i f i e r s are very s e n s i t i v e to l i g h t i n t e n s i t y v a r i a t i o n s , such as those c r e a t e d by the 60 Hz s i n e wave d r i v i n g the l i g h t s o urce. The two v o l t a g e peaks, one p o s i t i v e and one nega-t i v e per c y c l e i n the 60 Hz s i n e wave produce an u n d e s i r a b l e 120 Hz n o i s e s i g n a l a t each p h o t o t r a n s i s t o r output. A twin-T notch f i l t e r u s i n g LM302* v o l t a g e f o l l o w e r s was chosen t o s h a r p l y c u t the s i g n a l a t 120 Hz. A low pass a c t i v e f i l t e r w i t h a 24 Hz c u t - o f f frequency, u s i n g a 741 Op Amp was p l a c e d behind the notch f i l t e r to minimize o t h e r low frequency n o i s e , such as 60 Hz. The notch f i l t e r passes a l l f r e q u e n c i e s except a very narrow band of f r e q u e n c i e s around a c e n t e r frequency f Q , which i n t h i s case i s 120 Hz. The low pass f i l t e r passes a l l low f r e q u e n c i e s up t o the c u t - o f f frequency, f , where the c s i g n a l amplitude i s c u t by 3dB and a t t e n u a t i o n c o n t i n u e s through the h i g h e r f r e q u e n c i e s , a t a r a t e o f 9dB/octave. The need f o r both f i l t e r s may be i l l u s t r a t e d as f o l l o w s . Since most o f the n o i s e was 12 0 Hz, the most e f f e c t i v e f i l t e r i n g was d e s i r e d f o r t h a t frequency. The "notch depth" o r maximum a t t e n u a t i o n o f the 120 Hz notch f i l t e r was measured and found t o be -45dB. A low pass f i l t e r h a v i ng a 9dB/octave s l o p e , i n o r d e r t o be as e f f e c t i v e * LM p r e f i x r e f e r s t o components manufactured by N a t i o n a l Semi-conductor Corp., Santa C l a r a , C a l i f o r n i a . 67 as the notch f i l t e r a t 120 Hz, would r e q u i r e a c u t - o f f frequency o f 4 Hz. T h i s l i m i t a t i o n would i n t e r f e r e w i t h s o r t i n g o p e r a t i o n s which were expected t o be above 4 tomatoes/second. S o r t i n g r a t e s above approximately 20 tomatoes/second were not expected, t h e r e f o r e a low pass f i l t e r w i t h a c u t - o f f o f 24 Hz was chosen (standard compon-ents may be used) t o be p l a c e d i n s e r i e s w i t h the notch f i l t e r . F i g u r e 3.5 i s a schematic o f one o f two i d e n t i c a l f i l t e r c i r c u i t s used i n the c o l o u r grader, one c i r c u i t f o l l o w i n g the r e d p h o t o t r a n s i s t o r a m p l i f i e r , and the o t h e r f o l l o w i n g the green p h o t o t r a n s i s t o r a m p l i f i e r (Figure 3.4). The equations governing the component s e l e c t i o n f o r the notch f i l t e r are as f o l l o w s : f o = 2* l± c 2 r3-10] R 2 = Rx/2 [3-11] C1 = 2C 2 [3-12] For maximum e f f i c i e n c y , component matching i s c r i t i c a l — r e s i s t o r s s h o u l d be 0.1% t o l e r a n c e ; c a p a c i t o r s 1% t o l e r a n c e . Components w i t h these t o l e r a n c e s were not r e a d i l y a v a i l a b l e so 1% r e s i s t o r s and 2% c a p a c i t o r s were used, r e q u i r i n g a v a r i a b l e band width adjustment through the use o f the 100 Kft po t e n t i o m e t e r and the LM302 v o l t a g e f o l l o w e r i n the f e e d back loop t o the j u n c t i o n o f C, and R 0. — I f " f F I G U R E 3.5 N O T C H A N D L O W P A S S F I L T E R S ' 0 0 69 S e l e c t i o n o f components was made u s i n g e quations [3-10] through [3-12] as follows': L e t C 2 = 0.01 yF, now R 1 2u f C, O 2 R± = 133 Kfi R_ = 66.5 Kfi (two 133 Ktt r e s i s t o r s i n p a r a l l e l ) C. = 0.02 yF (two 0.01 yF c a p a c i t o r s i n p a r a l l e l ) . The equations governing component s e l e c t i o n f o r the low pass f i l t e r a r e : R_ + R. C- = - - [3-13] J 2 /2 ir f R_ R. c 3 4 C = [3-14] /2 TT f (R_ + R.) c 3 4 I f R^ = , then [3-13] becomes C, = - [3-15] J /2 TT f R, c 3 L e t R = 100 KQ , and f = 24 Hz, then 3 c C 3 = 0.094 yF, and C 4 = 2C^ = ° ' 0 4 7 y F * To l e r a n c e s f o r R^, R^, and are not c r i t i c a l , s i n c e a c u t - o f f frequency s l i g h t l y above or below 24 Hz r e s u l t i n g from component mismatch i s i n c o n s e q u e n t i a l . The u n i t y g a i n s o f the a c t i v e f i l t e r s do not 70 alter signal amplitude/ except at frequencies above 24 Hz, where attenuation occurs at a rate of 9dB/octave, as desired. 71 Peak D e t e c t o r 1 (Box E, F i g u r e 3.2) PEAK DETECTOR 1 i s an analog s t o r a g e c i r c u i t , which s t o r e s the most p o s i t i v e s i g n a l a ppearing a t the i n p u t . The s t o r e d v o l t a g e appears a t the output of the c i r c u i t . A schematic o f the peak d e t e c t o r c i r c u i t i s shown i n F i g u r e 3.6. The f u n c t i o n o f the 741 Op Amp and diodes i s to a l l o w c a p i c a t o r C^ to charge to the i n p u t v o l t a g e , but not 12 to d i s c h a r g e . The h i g h i n p u t impedance (10 ft) o f the LM302 v o l t a g e f o l l o w e r , d r a i n s v e r y l i t t l e c u r r e n t from the c a p a c i -t o r C^ r e s u l t i n g i n a c o n s t a n t v o l t a g e appearing a t the out-put a f t e r the peak i s s t o r e d ; w i t h minimal d r i f t o f the s t o r e d v o l t a g e over time. R e s e t t i n g the peak d e t e c t o r to zero i s accomplished by a p o s i t i v e (HIGH) p u l s e a t the c o n t r o l i n p u t o f the CD4066 b i l a t e r a l s w i t c h . The b i l a t e r a l s w i t c h i s i d e n t i c a l t o a s m a l l s i g n a l r e l a y , but s i n c e i t i s a semi-conductor, i t has no moving c o n t a c t s and cannot wear out. The r e s e t p u l s e a t the c o n t r o l i n p u t causes the b i l a t e r a l s w i t c h t o c l o s e , a l l o w i n g C^ t o d i s c h a r g e to a zero p o t e n t i a l through R^. The output v o l t a g e V o w i l l remain a t zero v o l t s u n t i l the r e s e t p u l s e goes LOW and a new s i g n a l appears a t the peak d e t e c t o r i n p u t . F i g u r e 3.7a shows t y p i c a l d i v i d e r output (PEAK DETECTOR 1 input) s i g n a l s f o r u n i f o r m l y c o l o u r e d f i r m r i p e and s e m i - r i p e tomatoes o f e q u a l s i z e , as the tomato passes under the s e n s i n g head. Due t o edge e f f e c t s o f the s p h e r i c a l tomato, the d i v i d e r o u t p u t s i g n a l i s b e l l shaped. I f the F I G U R E 3.6 P E A K D E T E C T O R 1 to F I G U R E 3.7 O U T P U T V O L T A G E S F O R T Y P I C A L F I R M R I P E . A N D S E M I - R I P E T O M A T O E S (o) D I V I D E R O U T P U T F O R U N I F O R M L Y R I P E -T O M A T O (b) D I V I D E R O U T P U T F O R N O N - U N I F O R M L Y R I P E T O M A T O (c) P E A K D E T E C T O R O U T P U T F O R (a) A N D (b) 74 v o l t a g e was measured midway between the l e a d i n g and t r a i l i n g edges o f the s i g n a l , the v o l t a g e read would be the peak v o l t a g e — the maximum redness — without the need f o r a peak d e t e c t o r c i r c u i t . U n f o r t u n a t e l y , tomatoes are not always u n i f o r m i n r i p e n e s s , i . e . one a r e a may be redder than another. T y p i c a l d i v i d e r output s i g n a l s f o r non-uniform f i r m r i p e and s e m i - r i p e tomatoes are shown i n F i g u r e 3.7b. Now the mid-point between l e a d i n g and t r a i l i n g edges does not i n d i c a t e maximum redness. F i g u r e 3.7c shows the peak d e t e c -t o r output s i g n a l f o r e i t h e r u n i f o r m l y r i p e o r non-uniformly r i p e tomatoes. For both types o f tomatoes, the maximum redness, V r ) T :, A i r, w i l l be measured and s t o r e d . 75 Comparators 1, 2 and 3 (Box F, F i g u r e 3.2) The schematic of the comparator c i r c u i t used i s shown i n F i g u r e 3.8. The output o f PEAK DETECTOR 1 i s con-t i n u o u s l y and s i m u l t a n e o u s l y p r e s e n t a t the i n p u t o f the thr e e comparators, COMPARATOR 1, 2 and 3. R e f e r r i n g t o F i g u r e 3.8 when the i n p u t v o l t a g e , V" I N, i . e . PEAK DETECTOR 1 output v o l t a g e , exceeds the s e t v o l t a g e V~„m o f a comparator, the v o l t a g e output, V , of t h a t comparator drops from +14 t o zero v o l t s , due t o the h i g h open loop g a i n o f the 741 ampli-f i e r ( t y p i c a l l y 200,000). The comparator e s s e n t i a l l y goes from the p o s i t i v e s a t u r a t e d s t a t e t o the n e g a t i v e s a t u r a t e d s t a t e . The IN914 diode a t the output o f each comparator clamps V between zero and +14 v o l t s , o t herwise V would o o range from +14 v o l t s to -14 v o l t s . The two IN914's a c r o s s the i n p u t o f each comparator are i n p u t p r o t e c t i o n d i o d e s . V 0 „ m i s a t h r e s h o l d v o l t a g e f o r a comparator. S i n c e f o u r c o l o u r c a t e g o r i e s are t o be sep a r a t e d , t h r e e d i f f e r e n t comparators and V S E T adjustments are r e q u i r e d . Two a d j u s t -ments, V-,™ „ and V _ „ m 0 are a v a i l a b l e on the f r o n t p a n e l o f the c o l o u r s o r t e r c a b i n e t , f o r s e t t i n g the c u t o f f v o l t a g e s s e p a r a t i n g t u r n i n g from s e m i - r i p e , and s e m i - r i p e from f i r m r i p e . The green c u t o f f v o l t a g e , V~T?m -i , i s a d j u s t e d i n t e r -n a l l y on the c i r c u i t board, s i n c e t h i s v o l t a g e r e q u i r e s o n l y an i n i t i a l s e t up. The output o f each comparator i s e i t h e r HIGH ( s t a t e 1) or LOW ( s t a t e 0 ) . F I G U R E 3 .8 C O M P A R A T O R C I R C U I T 76 O 77 The output s t a t e s o f the t h r e e comparators and the c o l o u r c a t e g o r i e s they r e p r e s e n t are shown i n Table 3.3. The outputs of the comparators are d i g i t a l wave-forms compatible w i t h CMOS d e v i c e s , and these outputs are connected to the d i g i t a l p r o c e s s o r , as shown i n F i g u r e 3.2. 7 8 TABLE 3.3 OUTPUT STATES OF COMPARATORS 1, 2, and 3, FOR FOUR COLOUR CATEGORIES Colour OUTPUT STATE Category ' COMP. 1 COMP. 2 COMP. 3 Green 1 0 0 Turning 0 0 0 Semi-Ripe 0 1 0 Firm Ripe 0 1 1 79 Summing A m p l i f i e r 1 (Box G, F i g u r e 3.2) Rather than use a s e p a r a t e l i g h t a c t i v a t e d , or m e c h a n i c a l l y a c t i v a t e d t r i g g e r , which senses the presence o f a tomato under the s e n s i n g head, i t was d e c i d e d t h a t the two s i g n a l s a t the d i v i d e r i n p u t c o u l d be summed to produce a uniform output s i g n a l , r e g a r d l e s s o f the c o l o u r of the tomato. The d i v i d e r output cannot be used e f f e c t i v e l y as a t r i g g e r , s i n c e the s i g n a l amplitude v a r i e s w i t h c o l o u r . The sum o f the red and green s i g n a l s , however, i s r e l a t i v e l y c o n s t a n t f o r r e d and green tomatoes, s i n c e a r e d tomato produces a l a r g e r e d s i g n a l and a s m a l l green s i g n a l , and a green tomato produces a l a r g e green s i g n a l and a s m a l l r e d s i g n a l . The major drawback i n a summing a m p l i f i e r such as t h i s i s t h a t s m a l l d r i f t s a t the i n p u t are a d d i t i v e , r e s u l t i n g i n l a r g e d r i f t s a t the output. The d r i f t a t the i n p u t s may be due to s m a l l l i g h t i n t e n s i t y v a r i a t i o n s o r changes i n ambient temperature. The t r i g g e r v o l t a g e s h o u l d i d e a l l y be zero when no tomato i s p r e s e n t , i . e . when the s e n s i n g head sees o n l y the l i g h t r e f l e c t e d from the b l a c k conveyor b e l t . To o f f s e t the s m a l l amount o f r e f l e c t e d l i g h t from the b e l t , a background zero v o l t a g e adjustment was i n c l u d e d i n the c i r c u i t . A schematic diagram o f the n o n - i n v e r t i n g 7 4 1 SUMMING AMPLIFIER 1 i s shown i n F i g u r e 3 . 9 . The output v o l t a g e V Q i n the sum of V T . 7 , and V T „ p r o v i d e d t h a t the o f f s e t i s IN 1 IN 2 R a d j u s t e d t o z e r o . The o f f s e t adjustment i s a d j u s t e d f o r F I G U R E 3 . 9 S U M M I N G A M P L I F I E R 1 I0OK W v — i SOK ZERO BACK&NO.' APJ; -. -ISv 81 zero output a t a g i v e n l i g h t i n t e n s i t y w i t h the s e n s i n g head viewing the b l a c k conveyor b e l t . The o f f s e t range i s a p p r o x i -mately ± 4.8 v o l t s as d e s c r i b e d i n e q u a t i o n [ 3 - 7 ] . D r i f t i n the zero adjustment due to slow i n p u t v a r i a t i o n s w i l l a d v e r s e l y a f f e c t the t r i g g e r s i g n a l . 82 B e l t Background Monitor (Box H,I,J,K, F i g u r e 3.2) The f u n c t i o n o f the b e l t background monitor i s t o monitor minor d r i f t i n the i n i t i a l zero adjustment o f SUMMING AMPLIFIER 1 (Box G, F i g u r e 3.2) and t o c o n t i n u o u s l y compen-sa t e f o r any d r i f t . The c i r c u i t i s comprised o f a low pass a c t i v e f i l t e r , a n analog i n v e r t e r , PEAK DETECTOR 2, and SUMMING AMPLIFIER 2, u s i n g 741 Op Amps. The schematic o f the b e l t background monitor c i r c u i t i s shown i n F i g u r e 3.10. The low pass f i l t e r , w i t h a 10 Hz c u t o f f frequency, was r e q u i r e d t o suppress any h i g h frequency n o i s e p r e s e n t a t the SUMMING AMPLIFIER 1 output. Noise a t the i n p u t o f the peak d e t e c t o r can r e s u l t i n an erroneous background c o r r e c -t i o n . Component s e l e c t i o n was made u s i n g equations [3-13] and [3-14]. The output o f the low pass f i l t e r i s o f the same p o l a r i t y as the output o f SUMMING AMPLIFIER 1. The i n v e r t i n g a m p l i f i e r , h a v i n g u n i t g a i n , changes the p o l a r i t y o f the SUMMING AMPLIFIER 1 s i g n a l . T h i s s i g n a l i s f e d i n t o PEAK DETECTOR 2 which s t o r e s the most p o s i t i v e s i g n a l a t i t s i n p u t , i . e . the most n e g a t i v e output v o l t a g e o f SUMMING AMPLIFIER 1. SUMMING AMPLIFIER 2 sums the output o f PEAK DETECTOR 2 and the output o f SUMMING AMPLIFIER 1 to produce an output v o l t a g e , V . V q i s the same as V I N w i t h background d r i f t compensation. : S U M M I N G A M P L I F I E R 2 IOOK V v V • 7 7 F I G U R E 3 . 1 0 B E L T B A C K G R O U N D M O N I T O R j 84 To i l l u s t r a t e , suppose t h a t the output o f SUMMING AMPLIFIER 1 has d r i f t e d t o 0.5 v o l t s , w h i l e the s e n s i n g head i s v i e w i n g the b l a c k conveyor b e l t . The output o f PEAK DETECTOR 2 w i l l be -0.5 v o l t s , and the sum of the two v o l t a g e s V , w i l l be zero v o l t s . When a tomato passes under the o ^ se n s i n g head, the output o f SUMMING AMPLIFIER 1 r i s e s r a p i d l y from 0.5 t o 5 v o l t s , f o r example, and a t the same time the i n v e r t i n g a m p l i f i e r output drops from -0.5 to -5 v o l t s . But the output o f PEAK DETECTOR 2 remains a t -0.5 v o l t s , the most p o s i t i v e i n p u t v o l t a g e ; consequently V o f SUMMING AMPLIFIER 2 changes from (-0.5 + 0.5) = 0 v o l t s t o (-0.5 + 5.0) = 4.5 v o l t s . The output o f SUMMING AMPLIFIER 2 i s thus always r e f e r e n c e d t o zero v o l t s , and does not change w i t h s l i g h t v a r i a t i o n s i n b e l t background r e f l e c t a n c e . The d i v i d e r output s i g n a l as mentioned p r e v i o u s l y v a r i e s i n amplitude a c c o r d i n g t o the c o l o u r o f the tomato,, and was t h e r e f o r e not used as a t r i g g e r s i n c e many green tomatoes would not produce a s i g n a l g r e a t enough t o be de t e c -t e d above background. SUMMING AMPLIFIER 1 and 2 overcome the problem o f s i g n a l amplitude v a r i a t i o n w i t h c o l o u r , but the summing a m p l i f i e r outputs are f u n c t i o n s o f l i g h t i n t e n s i t y , i . e . tomato s i z e . Very s m a l l tomatoes may not be as r e a d i l y d e t e c t e d as l a r g e ones. 85 Schmitt T r i g g e r C i r c u i t (Box L, F i g u r e 3.2) The f u n c t i o n of the Schmitt t r i g g e r c i r c u i t , shown i n F i g u r e 3.11 i s to change the b e l l - s h a p e d s i g n a l a t the output o f SUMMING AMPLIFIER 2 i n t o a square p u l s e where the l e a d i n g edge i s used as an "on" t r i g g e r f o r the analog s i g n a l p r o c e s s o r and the t r a i l i n g edge i s used as an " o f f " t r i g g e r . When'no tomato i s p r e s e n t , PEAK DETECTOR 1 i s i n a r e s e t p o s i t i o n , w i t h the output o f the Schmitt t r i g g e r HIGH, s i n c e i t s i n v e r t i n g i n p u t i s norm a l l y a t zero v o l t s o r LOW. The two t h r e s h o l d v o l t a g e s o f the Schmitt t r i g g e r were chosen as low as p r a c t i c a l such t h a t = 1 v o l t , and V' tk = 0*5 v o l t s . The output o f the Schmitt t r i g g e r w i l l go LOW when V T „ > 1 v o l t , and w i l l r e t u r n HIGH when V T „ < 0.5 IN IN v o l t s . T h i s w i l l a l l o w up t o 0.5 v o l t s o f n o i s e t o appear a t the Schmitt t r i g g e r i n p u t as a r e s u l t o f r a p i d background f l u c t u a t i o n s , due to d i r t on the conveyor or unevenness i n i t s r e f l e c t a n c e , b e f o r e the s o r t i n g o p e r a t i o n i s a f f e c t e d . The HIGH l e v e l o f the Schmitt t r i g g e r i s about +14 v o l t s , which i s compatible w i t h the CMOS l o g i c c i r c u i t s . The LOW l e v e l o f the Schmitt t r i g g e r i s u s u a l l y -14 v o l t s , which i s 13.5 v o l t s below the lowest a c c e p t a b l e i n p u t v o l t a g e t o the CMOS d e v i c e s . The output o f the Schmitt t r i g g e r i s clamped w i t h a IN914 diode t o ground, r e s u l t i n g i n an output swing from -0.7 v o l t s t o +14 v o l t s . T h i s clamping technique was found more f a v o u r a b l e than p l a c i n g a diode i n the f e e d -back loope o f the Op Amp, which i s another clamping proced-ure . F I G U R E 3 . 1 1 S C H M I T T T R I G G E R C I R C U I T 87 R e f e r r i n g t o F i g u r e 3.11, the t h r e s h o l d v o l t a g e s are d e f i n e d as f o l l o w s : R 0 (V - V J V t h " R°+ R / + V r e f I 3 " 1 6 ! R 0 ( V - V ^) v = — - r + v r 3 -171 v t h R + R 2 v r e f L ° / J where = f i r s t t h r e s h o l d v o l t a g e V . ^ = second t h r e s h o l d v o l t a g e V o = output v o l t a g e when s o l v i n g f o r V = output v o l t a g e when s o l v i n g f o r V ^ R l ' R2 = r e s i s t a n c e v a l u e s i n the c i r c u i t . S i n c e V\. = 1 v o l t , and V' , = 0.5 v o l t s , V _, R, and R 0 t h t h r e f 1 2 t. be determined. In g e n e r a l , e q u a t i o n [3-16] y i e l d s : mus V . . ( R , + R0) - R 0  V r e f = — — t 3 " 1 8 ^ s u b s t i t u t i n g V t h = 1 and V Q = +14 i n [3-18] and s o l v i n g f o r R ^ , g i v e s : 13 R , R i = " [3-19] r e f s u b s t i t u t i n g V ' t h = 0.5 and V = -0.7 i n [3-17] and s o l v i n g f o r R 2 g i v e s : R l { 2 V r e f * 1 } R 2 = -± d p [3-20] s u b s t i t u t i n g [3-20] i n [3-19] y i e l d s : V r e f = 0 , 5 4 v o l t s [3-21] 88 s u b s t i t u t i n g [3-21] i n [3-20] y i e l d s : R 2 = 0.035 R1 ' [3-22] Now, l e t R± = 330 Kfi then R 2 = 12 Kft R^ = R^//R^* = 12 Kft f o r minimum o f f s e t e r r o r i n p u t b i a s c u r r e n t . V R E £ i s o b t a i n e d by the use o f the v o l t a g e d i v i d e r , R. and R_. 1 4 5 I f R^ i s connected t o the +15 v o l t supply and R,. to ground, then f o r V - = 0.54 v o l t s , r e f R 4 = 26.8 R5- [3-23] Choosing s u i t a b l e v a l u e s o f and R,. g i v e s : R 4 = 27 Kfi R 5 = 1 KR. I t i s e v i d e n t t h a t s i g n a l d r i f t a t the i n p u t t o the Schmitt t r i g g e r must be c o r r e c t e d by a c i r c u i t such as the b e l t background monitor s i n c e a c o n s t a n t i n p u t above 0.5 v o l t s due to d r i f t would not a l l o w the Schmitt t r i g g e r t o t u r n o f f . The output of the Schmitt t r i g g e r c i r c u i t i s a d i g i t a l waveform compatible w i t h the CMOS l o g i c d e v i c e s , and t h i s s i g n a l w i l l be t r a n s f e r r e d t o the d i g i t a l p r o c e s s o r . Although V q drops t o -0.7 v o l t s and CMOS d e v i c e s are r a t e d to -0.5 v o l t s , the " o v e r d r i v e " may be reduced by adding a _ Net p a r a l l e l r e s i s t a n c e 89 c u r r e n t l i m i t i n g r e s i s t o r between the Schmitt t r i g g e r and the CMOS d e v i c e i n p u t . Any r e s i s t o r between 1.5 KQ and 10 Kfi i s s u i t a b l e . 90 DIGITAL SIGNAL PROCESSOR Timing C i r c u i t (Box M, F i g u r e 3.2) The f u n c t i o n o f the t i m i n g c i r c u i t , F i g u r e 3.12, which i s a c t i v a t e d by the Schmitt t r i g g e r p u l s e , i s t o unlock PEAK DETECTOR 1 from i t s r e s e t s t a t e and to t r a n s f e r c o l o u r c a t e g o r y i n f o r m a t i o n t o the d i g i t a l p r o c e s s o r . When a tomato e n t e r s the view i n g area o f the s e n s i n g head, the l e a d i n g edge o f the Schmitt t r i g g e r p u l s e unlocks PEAK DETECTOR 1, and c o l o u r c a t e g o r i z a t i o n b e g i n s . When the tomato l e a v e s the viewi n g a r e a o f the s e n s i n g head, the t r a i l i n g edge o f the Schmitt t r i g g e r p u l s e t r i g g e r s the t i m i n g c i r c u i t t o produce a 210 us WRITE p u l s e , which a l l o w s the i n f o r m a t i o n a t the comparator outputs to be decoded and s t o r e d i n the memory. The t r a i l i n g edge of the WRITE p u l s e r e s e t s PEAK DETECTOR 1. The t i m i n g c i r c u i t i s comprised of f o u r NOR gates (1-CD4001)* two o f which op e r a t e as a monostable m u l t i v i b r a t o r . The 1.5 Kfl r e s i s t o r a t the i n p u t t o the f i r s t NOR gate i s a c u r r e n t p r o t e c t i o n r e s i s t o r , l i m i t i n g the i n p u t gate c u r r e n t to 10 ma, maximum. The p r o t e c t i o n was added t o prevent damage t o the gate i n the event t h a t the Schmitt t r i g g e r v o l t a g e dropped t o -15 v o l t s , due t o diode f a i l u r e i n the Sch m i t t t r i g g e r c i r c u i t . The 10 Kft d e l a y r e s i s t o r ( F i g u r e 3.12) a t i n p u t * CD p r e f i x r e f e r s t o CMOS d e v i c e s manufactured by RCA Corp., S o m e r v i l l e , New J e r s e y . i _ r I.SK o — v w SCHMITT TRI66ER IHPilT to 0 . 0 / ILF —\{ IO K AA/V DELAY O-OlpF O WRITE. OUT IS PEkK DETECTOR I RESE.T OUT Lo SAMPLE. OUT F I G U R E 3 . 1 2 T I M I N G C I R C U I T 92 #2* of the f i n a l NOR gate i s used t o compensate f o r the s i g n a l d e l a y which occurs a t i n p u t #1 due to the e x t r a gate i n t h a t i n p u t l i n e . Without d e l a y compensation, two p u l s e s w i l l appear a t the RESET output, one o f which i s i n e r r o r . The RESET output p u l s e width i s equal to the sum of the Schmitt t r i g g e r p u l s e and the WRITE s i g n a l p u l s e w i d t h s . The RESET output i s connected t o the c o n t r o l i n p u t o f the CD4066 b i l a t e r a l s w i t c h , F i g u r e 3.6. The SAMPLE output i s the complement o f the Schmitt t r i g g e r p u l s e and w i l l be d i s c u s s e d l a t e r i n S e c t i o n I I . * # r e f e r s t o c i r c l e d p o i n t s i n f i g u r e . 93 Decoding Gates (Box N, F i g u r e 3.2) The outputs o f the t h r e e comparators (COMP. 1, COMP. 2 and COMP. 3) change c o n t i n u o u s l y as the output o f PEAK DETECTOR 1 r i s e s t o i t s maximum val u e f o r a p a r t i c u l a r tomato. Once the peak v o l t a g e has been reached and i s s t o r e d , the t h r e e comparator outputs remain r e l a t i v e l y c o n s t a n t , and the c o l o u r c a t e g o r y i n f o r m a t i o n i s ready t o be t r a n s f e r r e d to the s h i f t r e g i s t e r memories, which are s y n c h r o n i z e d t o the movement o f the b e l t . S i n c e i t was d e c i d e d t h a t the green tomatoes were to t r a v e l t o the end o f the conveyor b e l t , o n l y t h r e e s h i f t r e g i s t e r memories were r e q u i r e d — one f o r f i r m r i p e , one f o r se m i - r i p e and one f o r t u r n i n g tomatoes. The memory i n p u t i n f o r m a t i o n i s decoded from the output s t a t e s o f COMP. 2 and COMP. 3, v i a the t h r e e NOR gate s , NOR 1, NOR 2, and NOR 3, F i g u r e 3.13. T u r n i n g tomatoes are c a t e g o r i z e d when the i n p u t v o l t a g e o f the comparators i s l e s s than V - ™ 0 f o r COMP. 2, F i g u r e 3.8. Note t h a t green tomatoes a l s o produce v o l t a g e s l e s s than V g E T 2 - S e p a r a t i o n o f these two c o l o u r c a t e g o r i e s i s c o n t r o l l e d by the output o f COMP. 1, which i s LOW f o r a l l except green tomatoes, p e r m i t t i n g i n f o r m a t i o n t o be w r i t t e n i n t o the memories through NOR 4, F i g u r e 3.13. For example, i f a green tomato i s b e i n g sensed, the output o f COMP. 1 i s HIGH, r e s u l t i n g i n a LOW output a t NOR 4 even when the WRITE s i g n a l appears a t the o t h e r i n p u t to NOR 4. No i n f o r m a t i o n i s t r a n s f e r r e d t o the memory through NAND gate s , NAND 1, F I G U R E 3 . 1 3 D E C O D I N G G A T E S 94 JL 95 NAND 2, and NAND 3, and the green tomato t r a v e l s t o the end of the conveyor as though i t was never sensed. For a l l o t h e r tomato c a t e g o r i e s , the output o f COMP. 1 i s LOW, thus a l l o w -i n g the WRITE p u l s e t o appear a t the output o f NOR 4, and the i n f o r m a t i o n from the NOR 1, NOR 2, and NOR 3 outputs to be t r a n s f e r r e d t o the outputs o f NAND 1, NAND 2, and NAND 3, f o r the d u r a t i o n o f the WRITE p u l s e . In theory, a l l t h r e e NAND gates w i l l n o r m a l l y be HIGH, and o n l y one w i l l go LOW f o r the WRITE p u l s e d u r a t i o n . In p r a c t i c e i t i s p o s s i b l e f o r more than one output t o be low f o r a f r a c t i o n o f the WRITE p u l s e width due t o minute d r i f t i n PEAK DETECTOR 1 which w i l l r e s u l t i n double c a t e g o r i z a t i o n o f one tomato. A c i r c u i t , the d a t a l a t c h e s , w i l l be d e s c r i b e d l a t e r which accepts o n l y the f i r s t c ategory s i g n a l r e c e i v e d . The 1.5 Kft r e s i s t o r s a t the i n p u t s to the NOR gates are c u r r e n t p r o t e c t i o n r e s i s t o r s . 96 L i g h t Chopper and P h o t o d e t e c t o r (_Box P, F i g u r e 3,2) The l i g h t chopper disk, i s a t h i n , m etal, c i r c u l a r d i s k w i t h s m a l l h o l e s , r e g u l a r l y spaced, near the circum-f e r e n c e . For the s i z e of conveyor b e l t p u l l e y used, the h o l e s p a c i n g and d i s k diameter was chosen so t h a t the c e n t e r -t o - c e n t e r d i s t a n c e between the s m a l l h o l e s was equal to approximately 1/2 i n c h (1.3 cm) o f conveyor b e l t . The d i s k was mounted on the a x l e o f one o f the conveyor p u l l e y s , and a l i g h t source p l a c e d on one s i d e o f the d i s k and a p h o t o d e t e c t o r on the o t h e r s i d e , so t h a t the l i g h t and d e t e c t o r were a l i g n e d w i t h the h o l e c e n t e r s o f the d i s k . As the d i s k r o t a t e s , the l i g h t beam i s t r a n s m i t t e d through the d i s k t o the p h o t o d e t e c t o r as the h o l e s pass, and the l i g h t i s b l o c k e d by the area between the h o l e s . The p h o t o d e t e c t o r output, as the b e l t moves, i s a d i g i t a l s i g n a l w i t h one c y c l e f o r each 1/2 i n c h (1.3 cm) o f b e l t movement. The frequency of t h i s d i g i t a l s i g n a l w i l l be determined by the conveyor b e l t speed, but each c l o c k c y c l e w i l l remain c o n s t a n t w i t h r e s p e c t t o the l e n g t h o f conveyor b e l t moving p a s t a f i x e d p o i n t . The p h o t o d e t e c t o r chosen was a CA30 62 l i g h t s e n s i -t i v e o p e r a t i o n a l a m p l i f i e r , and the schematic of the c i r c u i t used i n shown i n F i g u r e 3.14. Other p h o t o d e t e c t o r s , such as a photo diode o r p h o t o t r a n s i s t o r c o u l d have been used, but the CA3062 can be w i r e d e a s i l y as a Schmitt t r i g g e r , which, due to i t s h y s t e r e s i s c h a r a c t e r i s t i c makes the p h o t o d e t e c t o r F I G U R E 3 . 1 4 L I G H T C H O P P E R P H O T O D E T E C T O R A OUT 98 c i r c u i t v ery s t a b l e . The d i g i t a l output s i g n a l o f the CA3062 w i l l be r e f e r r e d t o as CLOCK A. 99 Divide-by-3 C i r c u i t (Box Q, F i g u r e 3.2) The f u n c t i o n o f the d i v i d e - b y - 3 c i r c u i t i s t o d i v i d e the CLOCK A frequency by 3, so t h a t each c y c l e a t the output now r e p r e s e n t s 1 1/2 i n (3.8 cm) o f conveyor b e l t . I t was i n i t i a l l y planned t h a t the CLOCK A s i g n a l be used t o s h i f t the.memory i n f o r m a t i o n one s h i f t l o c a t i o n ( b i t ) every c l o c k c y c l e . T h i s would r e q u i r e a b i t to be a v a i l a b l e i n a memory (e.g. a f i r m r i p e memory) f o r every 1/2 i n (1.3 cm) downstream t h a t . t h e e j e c t s t a t i o n i s l o c a t e d . The l a s t e j e c t s t a t i o n was l o c a t e d 24 i n (61 cm) downstream from the s e n s i n g head, thus r e q u i r i n g a 48 b i t s h i f t c a p a b i l i t y . A t the time o f the c i r c u i t d e s i g n , common s h i f t r e g i s t e r s had 4 or 8 b i t stor a g e c a p a b i l i t y , and f o r the t h r e e memories needed, about 14 i n t e g r a t e d c i r c u i t s would have been r e q u i r e d . I t was b e l i e v e d t h a t fewer b i t s c o u l d be used i f memory i n f o r m a t i o n was spaced 1 1/2 i n (3.8 cm) a p a r t r a t h e r than 1/2 i n (1.3 cm). T h i s means t h a t any two tomatoes must be a minimum o f 1 1/2 i n (3.8 cm) a p a r t on the b e l t from c e n t e r t o c e n t e r , i . e . g r e a t e r than 3/4 i n (1.9 cm) i n diameter. T h i s f a c t o r i s not l i m i t i n g , s i n c e s m a l l tomatoes are g e n e r a l l y double t h a t s i z e . The number o f s h i f t r e g i s t e r b i t s can thus be reduced by a t h i r d . The d i v i d e - b y - 3 c i r c u i t schematic i s shown i n F i g u r e 3.15. The c i r c u i t i s comprised o f CD4011 NAND gates and a CD4018 p r e - s e t t a b l e d i v i d e - b y - " N " c o u n t e r . Two NAND F I G U R E 3 . 1 5 D I V I D E - B Y - 3 CIRCUIT 100 CLOCK A INPUT o CLOCK A OUTPUT CLOCK 3 OUTPUT 101 gates are employed as p u l s e shapers a t the i n p u t t o the counter, s i n c e the CLOCK A r i s e and f a l l time i s around 10 us, which i s c l o s e t o the maximum a l l o w a b l e r i s e and f a l l time o f the CD4018 c l o c k i n p u t . The two NAND gates "speed up" the c l o c k p u l s e t r a n s i s t i o n from HIGH t o LOW, and LOW to HIGH. Two o f the outputs o f the CD4018 are connected t o the i n p u t s o f a CD4011 NAND gate, the output o f which i s i n v e r t e d and f e d back t o the "data" i n p u t o f the CD4018. T h i s i s a standard c i r c u i t c o n f i g u r a t i o n f o r a d i v i d e - b y - 3 f u n c t i o n u s i n g the CD4018. The CLOCK A frequency divided-by-3 w i l l be r e f e r r e d to as CLOCK B. The CLOCK A output w i l l be used l a t e r i n S e c t i o n I I . 102 Data L a t c h e s , Timers and Memory C i r c u i t s (Box R, F i g u r e 3.2) Data cannot be e n t e r e d i n t o the s h i f t r e g i s t e r memories a t anytime, nor can the data be r e t r i e v e d a t anytime. C e r t a i n c o n d i t i o n s must be met b e f o r e data can s u c c e s s f u l l y and c o n s i s t e n t l y be s t o r e d . (a) The data (a HIGH or LOW s t a t e ) must be p r e s e n t a t the i n p u t t o the s h i f t r e g i s t e r a t l e a s t 700 ns (nanoseconds) b e f o r e the c l o c k i n p u t goes h i g h . (b) The sto r a g e o f the data occurs as the c l o c k s i g n a l changes s t a t e from e i t h e r a HIGH t o LOW, or LOW to HIGH deperiding on the s h i f t r e g i s t e r used, so the i n p u t data must not change s t a t e d u r i n g c l o c k t r a n s i t i o n . (c) Once the c l o c k i n p u t has reached e i t h e r a HIGH or LOW l e v e l , no more data can be ent e r e d i n t o the s h i f t r e g i s t e r u n t i l the next c y c l e o f the c l o c k s t a r t s . The f u n c t i o n o f the da t a l a t c h e s , F i g u r e 3.16, (one l a t c h f o r each s h i f t r e g i s t e r memory) i s t o a c t as a temporary s t o r a g e l o c a t i o n f o r the c o l o u r c a t e g o r y d a t a u n t i l the data can be t r a n s f e r r e d i n t o the s h i f t r e g i s t e r . Maximum stor a g e time i n the l a t c h w i l l be one c y c l e o f CLOCK B. As soon as a p u l s e o c c u r s a t the output o f one of the decoding gates ( F i g u r e 3.13), i t s c o r r e s p o n d i n g l a t c h changes from a normally HIGH to a LOW output. F I G U R E 3 . 1 6 L A T C H I N G C I R C U I T IT ~r r O TURNING OUTPUT ~ i _ r O SEMI-RIPE OUTPUT i _ _ r O FIRM RIPE OUTPUT 104 The change i n s t a t e o f one l a t c h i n s t a n t l y b l o c k s , o r gates out s i g n a l s a r r i v i n g a t the o t h e r two l a t c h e s , because o f the CD4023 3-input NAND gat e s . Only a f t e r the s e t l a t c h i s r e s e t t o i t s n o r m a l l y HIGH output s t a t e can any more i n f o r m a t i o n be accepted and t r a n s f e r r e d . A l l t h r e e l a t c h e s are s i m u l t a n e o u s l y r e s e t . The two timers ( F i g u r e 3.17) a s s o c i a t e d w i t h the dat a l a t c h e s are used t o produce a " s e t up" time and a r e s e t p u l s e . The set-up time was chosen as a modest 14 us, and the r e s e t p u l s e width as 6us. At every n e g a t i v e going (from HIGH to LOW) CLOCK B p u l s e t h a t o c c u r s a t the i n p u t o f the set-up t i m e r , a 14 us p o s i t i v e p u l s e i s produced. As the t r a i l i n g edge of the 14 us p u l s e changes from HIGH t o LOW, the RESET tim e r i s t r i g g e r e d t o produce a 6 us p o s i t i v e RESET p u l s e . Since the SET UP t i m e r i s t r i g g e r e d on the n e g a t i v e going edge o f CLOCK B, and the t r a n s f e r o f da t a i n t o the s h i f t r e g i s t e r (CD4015) occurs on the p o s i t i v e edge o f the c l o c k p u l s e , i t was necessary t o i n v e r t CLOCK B (CLOCK B) f o r the s h i f t r e g i s t e r s u s i n g two CD4011 g a t e s . S i m i l a r l y , r e s e t t i n g o f the data l a t c h e s r e q u i r e s a n e g a t i v e going p u l s e , so the RESET p u l s e was a l s o i n v e r t e d (RESET) u s i n g two CD4011 ga t e s . The two gates used f o r each i n v e r s i o n were wi r e d i n p a r a l l e l i n o r d e r to i n c r e a s e t h e i r c u r r e n t d r i v e c a p a b i l i t i e s . Both the da t a i n p u t (DATA IN) and l a t c h output (LATCH OUT) are norm a l l y HIGH, as shown i n F i g u r e 3.18. The F I G U R E 3 . 1 7 D A T A L A T C H T I M E R S 105 _n_n_ CLOCK B INPUT R E S E T T IMER ~i_n_r F I G U R E 3 . 1 8 D A T A L A T C H W A V E F O R M S 106 C L O C K B J / 72 IN. CONVEYZR BELT TRAVEL R E S E T \ < D A T A IN L A T C H O U T D A T A IN to < L A T C H O U T .1 f I 107 s h i f t r e g i s t e r memory, t h e r e f o r e , sees a co n s t a n t HIGH i n p u t , and s t o r e s a "1" every time CLOCK B changes from a LOW to a HIGH s t a t e . When the data i n p u t goes LOW ( i n d i c a t i n g t h a t a tomato has been c a t e g o r i z e d ) a "0" must be t r a n s f e r r e d i n t o the s h i f t r e g i s t e r as soon as the next CLOCK B LOW to HIGH t r a n s i t i o n o c c u r s . The most d i f f i c u l t s i t u a t i o n , i . e . worst case which must be c o n s i d e r e d , o c c u r s d u r i n g the SET UP time: Case 1: WRITE p u l s e width l e s s than the sum o f SET UP and RESET times. Suppose t h a t CLOCK B has a l r e a d y changed from a LOW to a HIGH s t a t e , and the da t a l a t c h output i s s t i l l HIGH, as shown i n F i g u r e 3.18. The data l a t c h i n p u t i s s e t LOW b e f o r e the l a t c h RESET p u l s e a r r i v e s . The d u r a t i o n o f the l a t c h i n p u t LOW p u l s e i s always e q u a l t o the l e n g t h o f the WRITE p u l s e . I f the WRITE p u l s e i s v e r y s h o r t , the l a t c h output w i l l be s e t LOW u n t i l the RESET p u l s e o c c u r s , a t which time the l a t c h output r e t u r n s HIGH. At the next p o s i t i v e CLOCK B t r a n s i t i o n , the l a t c h output i s HIGH, as normal, and the data has been l o s t . Case 2: WRITE p u l s e width g r e a t e r than the sum o f SET UP and RESET times. The d i f f e r e n c e between Case 2 and Case 1 i s t h a t i n Case 2 the WRITE p u l s e width (the data l a t c h i n p u t ) i s g r e a t e r than the sum of the SET UP and RESET times ( F i g u r e 3.18). Now, when the RESET p u l s e appears, the data l a t c h output changes from LOW to HIGH f o r the d u r a t i o n o f the RESET p u l s e , and 108 r e t u r n s t o a LOW s t a t e s i n c e the data l a t c h i n p u t i s s t i l l LOW. The l a t c h output w i l l remain LOW u n t i l the next RESET p u l s e . The LOW s i g n a l w i l l be t r a n s f e r r e d i n t o the s h i f t r e g i s t e r on the next p o s i t i v e t r a n s i t i o n o f CLOCK B, a f t e r which the RESET p u l s e r e s e t s the l a t c h . The t h r e e memory c i r c u i t s used f o r t u r n i n g , semi-r i p e and f i r m r i p e c l a s s i f i c a t i o n s are shown i n F i g u r e 3.19. The f i r m r i p e memory i s comprised of one CD4015 d u a l 4 b i t s h i f t r e g i s t e r , w i t h the two 4 b i t s h i f t r e g i s t e r s w i r e d i n s e r i e s t o f o l l o w an8 b i t s h i f t . The s e m i - r i p e memory i s com-p r i s e d o f one and a h a l f CD4015's (12 b i t s ) and the t u r n i n g memory of two CD4015's (16 b i t s ) . A s h i f t o f one b i t "down the memory" i s e q u i v a l e n t t o one c l o c k c y c l e , o r l 1/2 i n (3.8 cm) o f conveyor b e l t movement. The f i r m r i p e memory i s t h e r e f o r e capable o f s h i f t i n g i n f o r m a t i o n 12 i n (30 cm) downstream from the s e n s i n g head, where the i n f o r m a t i o n was f i r s t s t o r e d i n the memory. S i m i l a r l y , the s e m i - r i p e memory s t o r e s informa-t i o n f o r 18 i n (46 cm) downstream from the s e n s i n g head, and the t u r n i n g memory f o r 24 i n (61 cm). E j e c t s t a t i o n s w i l l h a v e t o be l o c a t e d 12 i n (30 cm), 18 i n (46 cm) and 24 i n (61 cm) downstream from the s e n s i n g head, otherwise the s h i f t r e g i s t e r s w i l l have to be lengthened o r shortened. When the i n f o r m a t i o n e n t e r e d i n a memory has been s h i f t e d the maximum number o f s h i f t s , the output o f the s h i f t r e g i s t e r changes s t a t e ( i n t h i s case from HIGH to LOW) f o r the d u r a t i o n o f the one c l o c k c y c l e , i . e . the output goes LOW f o r 1 1/2 i n (3.8 cm) o f the conveyor b e l t movement. F I G U R E 3 . 1 9 M E M O R Y C I R C U I T 109 TURN INS I N P U T IS VzCDtOlS I —r— SEMI-RIPE INPUT IS- '/zCD+0/5 I FIRM RIPE INPUT JUL o — — CLOCK B INPUT IS '/ZCD40/3\ 1 c 7 IO Vz CD40/S 9 1 c 7 IO VZ.CD4-0IS 9 =3= '/2CD+0/S I0\ 9 X IS 2 '/ZCD40I5 I 1 5 '/ZCD40/S 2 / =1= 7 '/2.CD-&IS lo\ TURNING, OUTPUT ~L_r — o SEMI-RIPE OUTPUT FIRM RIPE OUTPUT 110 O p t o - I s o l a t o r s and T r i a c s (Box S, F i g u r e 3.2) I f the LOW output s i g n a l from a memory i s coup l e d t o an e l e c t r o m e c h a n i c a l d e v i c e , such as a pneumatic o r h y d r a u l i c s o l e n o i d v a l v e , the d e v i c e w i l l be a c t i v a t e d f o r 1 1/2 i n (3.8 cm) o f b e l t movement. There i s no advantage t o c o u p l i n g a s h i f t r e g i s t e r output t o a timer which operates the e l e c t r o m e c h a n i c a l d e v i c e , u n l e s s the d e v i c e must be operated f o r l e s s than 1 1/2 i n (3.8 cm) o f b e l t movement. A tim e r having a d u r a t i o n g r e a t e r than the time r e q u i r e d f o r 1 1/2 i n (3.8 cm) o f b e l t w i l l i n t e r f e r e w i t h normal o p e r a t i o n s . Two tomatoes o f d i f f e r e n t c o l o u r can be spaced by as l i t t l e as 1 1/2 i n (3.8 cm), and i f the f i r s t i s e j e c t e d by a d e v i c e o p e r a t i n g over 2 i n (5.1 cm) o f b e l t , f o r example, the second tomato w i l l p robably a l s o be e j e c t e d . For these reasons, no time r s were used t o operate the e l e c t r o m e c h a n i c a l e j e c t d e v i c e s . Relays have been used i n the p a s t t o a c t as an i n t e r f a c e between low power d e v i c e s such as t r a n s i s t o r s , and hig h power d e v i c e s such as s o l e n o i d s . However, r e l a y s have moving p a r t s and have been r e p l a c e d i n many cases by semi-conductor d e v i c e s l i k e o p t o - i s o l a t o r s and t r i a c s . The l a t t e r were used i n the c o l o u r grader t o a c t as the c o u p l e r s between the CMOS memories and the s o l e n o i d s . The o p t i c c o u p l e r s can be connected t o CMOS d e v i c e s through the use of a t r a n s i s t o r , and the o p t i c c o u p l e r can a l s o d r i v e a 110 v o l t AC t r i a c . Common s o l e n o i d s are o p e r a t e d by 110 v o l t AC s o u r c e s . The o p t i c c o u p l e r s p r o v i d e complete i s o l a t i o n o f I l l the CMOS de v i c e s from the 110 vAC l i n e v o l t a g e p r e s e n t a t the t r i a c s . T h i s i s most d e s i r a b l e s i n c e n o i s e common on the 110 vAC l i n e must not feed back i n t o the l o g i c c i r c u i t r y and d i s r u p t normal o p e r a t i o n . A schematic o f the o p t o - i s o l a t o r and t r i a c c i r c u i t i s shown i n F i g u r e 3.20. A 2N3638 PNP t r a n s i s t o r i s used t o d r i v e the l i g h t e m i t t i n g diode (LED) o f the MOC1003 opto-i s o l a t o r . When the LOW s i g n a l i n a memory reaches the end o f the s h i f t r e g i s t e r , the LED's are a c t i v a t e d and the photo-t r a n s i s t o r s o f the MOC1003's conduct c u r r e n t f o r the d u r a t i o n o f the LOW s i g n a l . The p h o t o t r a n s i s t o r s are coup l e d t o the gates o f the t r i a c s . The t r i a c s w i l l conduct the 110 vAC l i n e c u r r e n t as l o n g as the gate i s c o n d u c t i n g . The 110 vAC l o a d (the e l e c t r o m e c h a n i c a l e j e c t mechanism) i s i n s e r i e s w i t h the t r i a c s , and thus the l o a d i s a c t i v e f o r the d u r a t i o n o f the memory output LOW s i g n a l , e q u i v a l e n t t o 1 1/2 i n (3.8 cm) o f conveyor b e l t t r a v e l . Note t h a t the p h o t o t r a n s i s t o r s which d r i v e the gates of the t r i a c s o perate on a se p a r a t e power supply — not the ± 15 v o l t IC sup p l y . T h i s ensures maximum n o i s e i s o l a t i o n between the 110 vAC c i r c u i t and the low power IC c i r c u i t r y . The o n l y c o u p l i n g t h a t e x i s t s i s between the LED and photo-t r a n s i s t o r o f the MOC1003, and the i s o l a t i o n r e s i s t a n c e between the two i s t y p i c a l l y 1 0 ^ ohms. The maximum c u r r e n t h a n d l i n g c a p a b i l i t y o f the L2001L5 t r i a c s i s 1 ampere, and loads w i l l have t o be F I G U R E 3 . 2 0 O P T O - I S O L A T O R S A N D T R I A C S r^/ ns v O •tlS UNREGULATED O O a A/363 3 IC GND. 113 maintained below t h a t l e v e l . The 470ft r e s i s t o r and O.luF c a p a c i t o r a c r o s s the t r i a c d i s s i p a t e s s t o r e d energy i n an i n d u c t i v e l o a d when the t r i a c i s suddenly t u r n e d o f f . 114 D i s p l a y Timers (Box T, F i g u r e 3.2) The d i s p l a y t i m e r c i r c u i t does not c o n t r i b u t e d i r e c t l y t o the s o r t i n g f u n c t i o n o f the grader. I t s f u n c t i o n i s to l i g h t one of thr e e LED's on the f r o n t p a n e l o f the grader c a b i n e t , thus i d e n t i f y i n g the c o l o u r category i n t o which a tomato has been p l a c e d by the machine. A r e d LED was used to i d e n t i f y f i r m r i p e tomatoes, an orange LED f o r semi-r i p e and a green f o r t u r n i n g tomatoes. The green tomatoes r e q u i r e d no d i s p l a y , by e l i m i n a t i o n . The d i s p l a y s were used p r i m a r i l y i n s e t t i n g up the comparator (Box F, F i g u r e 3.:2) v o l t a g e s e t t i n g s (V-,_m) . For example, a tomato would be b i l l v i s u a l l y s e l e c t e d as a s e m i - r i p e such t h a t a n y t h i n g redder would be c l a s s i f i e d as f i r m r i p e . The tomato was passed under the s e n s i n g head and the comparator v o l t a g e a d j u s t e d on the f r o n t p a n e l u n t i l the orange LED stopped f l a s h i n g a f t e r the tomato passed and the r e d LED s t a r t e d t o f l a s h i n s t e a d . The comparator v o l t a g e was then r e t u r n e d t o a p o i n t where the orange LED would f l a s h . T h i s method enabled r a p i d s e t up o f the machine wi t h o u t w a i t i n g f o r the e j e c t mechanism t o be a c t i v a t e d . The"same method was used i n s e t t i n g the ot h e r c o l o u r c a t e g o r y comparator v o l t a g e s . A schematic o f the d i s p l a y timer c i r c u i t i s shown i n F i g u r e 3.21. The c i r c u i t i s b a s i c a l l y the same as the data l a t c h c i r c u i t d e s c r i b e d p r e v i o u s l y , and shown i n F i g u r e 3.16. The i n p u t s t o NAND ga t e s , NAND 1, NAND 2 and NAND 3 are connected d i r e c t l y t o the outputs o f the decoding gates 115 F I G U R E 3 . 2 1 D I S P L A Y T I M E R C I R C U I T : 116 (Figure 3.13). The l a t c h outputs are connected t o t r a n s i s t o r b u f f e r s t o d r i v e the LED's. The CA3081 NPN t r a n s i s t o r a r r a y p r o v i d e s up t o 7 such t r a n s i s t o r s . The 33 Kft and 390 ft r e s i s t o r s are c u r r e n t l i m i t i n g r e s i s t o r s . The output Q (F i g u r e 3.21) o f a l a t c h i s normally LOW, and Q i s norma l l y h i g h . When one of the i n p u t s goes LOW, a LOW appears a t the S ( s e t ) i n p u t t o the l a t c h and Q becomes l a t c h e d i n a HIGH s t a t e , and Q i n a LOW s t a t e . As long as Q i s HIGH, the LED a t the l a t c h output w i l l l i g h t . The Q out-put o f a l a t c h i s f e d back t o the i n p u t s o f the ot h e r two l a t c h e s v i a the CD4023 t h r e e i n p u t NAND gates. As soon as one Q output goes LOW, the ot h e r two l a t c h e s are gated out. The t h r e e Q outputs are connected t o the i n p u t s o f one 3 i n p u t NAND gate, NAND 4. When one o f the Q outputs goes LOW, the normally LOW output o f NAND 4 goes HIGH. T h i s HIGH i s i n v e r t e d through the t h r e e i n p u t NAND gate, NAND 5, which has a l l t h r e e i n p u t s t i e d t o g e t h e r . As the output o f NAND 5 goes LOW, the monostable m u l t i v i b r a t o r comprised o f NAND 6 and NAND 7 produces a HIGH s t a t e a t the output o f NAND 6 f o r about 20 ms. As the outpu t o f NAND 6 r e t u r n s LOW, the mono-s t a b l e m u l t i v i b r a t o r c o n s i s t i n g of NAND 10 and NAND 11 i s t r i g g e r e d t o produce a HIGH RESET p u l s e o f about 20 us. The pu l s e i s i n v e r t e d through NAND 12, which r e s e t s a l l o f the l a t c h o u t p u t s . The two NAND gate i n v e r t e r s , NAND 8 and NAND 9 are used as p u l s e shapers, t o speed up the t r a n s i t i o n from HIGH t o LOW of the output p u l s e at NAND 6, which i s q u i t e slow 117 due t o c a p a c i t o r C^. One of the t h r e e LED's w i l l l i g h t f o r approximately 20 ms depending on which one o f the t h r e e i n p u t s f i r s t goes LOW. 118 POWER SUPPLIES The d e s i g n of a ± 15 v o l t r e g u l a t e d power supply based on the t h e o r e t i c a l , c u r r e n t consumption o f the c i r c u i t s d e s c r i b e d so f a r would r e q u i r e many long and unnecessary c a l c u l a t i o n s . I n s t e a d , the system was t e s t e d u s i n g a t e s t c i r c u i t board and ex p e r i m e n t a l power supply and the c u r r e n t consumption was measured. Maximum c u r r e n t f o r the i n t e g r a t e d c i r c u i t s was around 100 ma. A ± 15 v o l t r e g u l a t e d power supply k i t (RAE 1510 KIT) was a v a i l a b l e which was capable o f d e l i v e r i n g ± 500 ma. The power supply was more than adequate t o d r i v e the IC's. V o l t a g e r e g u l a t i o n was d e s i r a b l e i n or d e r to m a i n t a i n s t a b l e o p e r a t i o n o f the l i n e a r i n t e g r a t e d c i r c u i t s . A separate + 15 v o l t u n r e g u l a t e d power supply, shown i n F i g u r e 3.22, was designed t o d r i v e the p h o t o t r a n s i s t o r s i n the o p t o - i s o l a t o r s ( F i g u r e 3.20). Maximum c u r r e n t per opto-i s o l a t o r t r a n s i s t o r i s governed by the 1.5 Kft r e s i s t o r a t the c o l l e c t o r , and i s 10 ma. A t r a n s f o r m e r , and r e c t i f i e r diodes capable o f h a n d l i n g 1 ampere were chosen thus a l l o w i n g f u r t h e r expansion o f the system. No v o l t a g e r e g u l a t i o n was r e q u i r e d f o r t h i s power su p p l y . The supply GROUND i s connected t o the 115 vAC COMMON l e a d . The sepa r a t e power supply f o r the opto-i s o l a t o r s and t r i a c s assures maximum i s o l a t i o n between the s e n s i t i v e i n t e g r a t e d c i r c u i t s and the e l e c t r i c a l l y n o i s y 115 v o l t AC l i n e s . F I G U R E 3 . 2 2 P O W E R S U P P L Y C I R C U I T F O R T R I A C S 120 MECHANICAL HANDLING SYSTEM As mentioned i n the i n t r o d u c t i o n , i t was not the o b j e c t i v e of the p r e s e n t r e s e a r c h t o d e s i g n a new type of tomato h a n d l i n g system, b u t r a t h e r t o use a t y p i c a l f l a t con-veyor b e l t to t r a n s f e r the tomatoes to the s e n s i n g head and e j e c t s t a t i o n s . The problem of s i n g u l a t i n g and c e n t e r i n g of f r u i t on conveyor b e l t s has been s t u d i e d and developed t o a reasonable degree by l a r g e manufacturing companies such as FMC C o r p o r a t i o n i n the U n i t e d S t a t e s . The p e r f e c t i o n o f an e j e c t i o n system f o r the tomatoes from the conveyor b e l t a f t e r c l a s s i f i c a t i o n was not of prime concern e i t h e r . Of importance was the d e s i g n o f a reasonable conveyor and e j e c t system which c o u l d be used to t e s t the e l e c t r o n i c d e s i g n , f e a t u r e s of which c o u l d be employed i n a l a r g e s c a l e p r o t o t y p e . 121 The Conveyor System The conveyor system c o n s i s t e d of a f l a t , matte-b l a c k 6 i n c h (15 cm) wide b e l t h a v i n g a working l e n g t h of about 6 f e e t (2.44 cm). The b e l t was s t r e t c h e d between two r o l l e r s , one o f which was c h a i n d r i v e n by a Zero Max E2M2 motor and v a r i a b l e speed gearbox (Zero-Max I n d u s t r i e s , I n c . ) . Conveyor b e l t speed c o u l d be a d j u s t e d c o n t i n u o u s l y from zero to more than 60 i n c h e s / s e c (152 cm/sec). The b e l t system and motor was mounted on a metal frame w i t h a plywood top. The s e n s i n g head was mounted about 1/3 o f the way from the feed end of the conveyor, ac r o s s the b e l t , as shown i n F i g u r e 3.2 3a. The l i g h t copper d i s k and p h o t o d e t e c t o r assembly mounted on the i d l e r p u l l e y a t the fe e d end i s shown i n F i g u r e 3.23b. A f t e r p a s s i n g underneath the s e n s i n g head, the b e l t was t i l t e d s l i g h t l y , t o a s s i s t i n the removal of tomatoes from the b e l t a t the e j e c t s t a t i o n s . F I G U R E 3 . 2 3 (a) S E N S I N G H E A D , A N D (b) L I G H T C H O P P E R A S S E M B L Y 122 123 E j e c t System Of the many p o s s i b l e ways o f e j e c t i n g tomatoes the method chosen t o t e s t the e l e c t r o n i c system was pneumatic e j e c t i o n . The d e s i r e d o p e r a t i n g speed of the system was i n the neighbourhood o f 5 tomatoes per second. Any mechanical e j e c t system o p e r a t i n g a t t h a t speed would s u b j e c t the tomato to l a r g e u n d e s i r a b l e impact s t r e s s e s . The compressed a i r f o r the pneumatic e j e c t system was o b t a i n e d from a 1 1/2 H.P. J a c c u z z i Compressor ( J a c c u z z i Canada 3 3 Ltd.) having a 1 f t (0.028 m ) surge tank. T h i s main surge tank s u p p l i e d a secondary surge tank on which the e j e c t s o l e n o i d s were mounted. The secondary surge 3 3 tank, having a volume of 0.018ft (510 cm ) was c o n s t r u c t e d of 1 1/2 i n (3.8 cm) g a l v a n i z e d p i p e . S i n c e the s o l e n o i d s are operated f o r o n l y 1 1/2 i n (3.8 cm) o f conveyor b e l t , then a t a 2 f t / s e c (61 cm/sec) b e l t speed a s o l e n o i d would be a c t i v e f o r 62.5 ms. Using D e v i l b i s s DGD101 ( D e v i l b i s s (Canada) Ltd.) 5 2 a i r b o o s t e r n o z z l e s a 15 p s i g (10 newtons/m g) drop was measured ac r o s s the ASCO ( A s c o e l e c t r i c L i m i t e d ) 8262C90 s o l e n o i d 5 2 v a l v e a t 100 p s i g ( 6 . 9 X 10 newtons/m g) i n l e t p r e s s u r e . For 3 3 a 62.5 ms d u r a t i o n , t h i s r e p r e s e n t s a 0.005 f t (142 cm ) d e p l e t i o n o f the primary surge tank. The secondary surge tank volume was more than t h r e e times t h i s volume, hence t h r e e s o l e n o i d s c o u l d be o p e r a t e d s i m u l t a n e o u s l y f o r 62.5 ms a t a r a t e determined by the time r e q u i r e d t o recharge the secondary surge tank. The D e v i l b i s s DGD101 n o z z l e s are r a t e d a t a d e l i v e r y o f 124 11 f t 3 (0.31 m3) o f a i r / m i n a t 80 p s i g (5.5 X 10 5 newtons/m 2 g ) . 3 3 A rough measurement confirmed about 12 f t /min (0.34 m /min) a t 5 2 85 p s i g (5.9 X 10 newtons/m g ) . S i n c e f o u r c o l o u r c a t e g o r i e s were t o be s o r t e d , t h r e e s o l e n o i d v a l v e s were used t o e j e c t t h r e e of the tomato c a t e -g o r i e s t r a n s v e r s e l y to the movement o f the conveyor b e l t , and the f o u r t h c a t e g o r y was allowed to d r o p - o f f the end of the con-veyor. The s o l e n o i d v a l v e s were spaced 6 i n (15 cm) a p a r t (4 CLOCK B c y c l e s or 4 memory b i t s ) and the f i r s t was l o c a t e d 12 i n (30 cm) from the s e n s i n g head. G a l v a n i z e d 1/4 i n (0.6 cm) pipe was used to connect the s o l e n o i d v a l v e s , secondary surge tank and n o z z l e s t o g e t h e r . A photograph o f the e j e c t mechanism i s shown i n F i g u r e 3.24. A r e c e i v i n g b i n , c o n s i s t i n g o f t h r e e compartments, was c o n s t r u c t e d to c a t c h the tomatoes as they were e j e c t e d from the b e l t by the pneumatic system. The tomatoes were f o r c e d t o drop about 8 i n (20 cm) i n t o the b i n due to the t e s t conveyor d e s i g n and compartments were h e a v i l y padded w i t h p o l y u r e t h a n e to minimize mechanical damage t o the tomatoes. [In a p r o t o t y p e , the tomatoes would not need to drop t o the r e c e i v i n g u n i t more than a f r a c t i o n o f an i n c h ] . A c l o t h pouch was a l s o c o n s t r u c t e d to both guide the tomatoes i n t o the b i n compartment and break t h e i r f a l l . (Refer t o F i g u r e 3.24). The tomatoes which r o l l e d o f f the end of the conveyor were allowed to drop i n t o a p a c k i n g box j u s t below the l e v e l o f the b e l t . F I G U R E 3 . 2 4 P N E U M A T I C E J E C T M E C H A N I S M 125 C H A P T E R SYSTEM TESTING 127 MATERIALS AND METHODS (I) E l e c t r o n i c System The a b i l i t y o f the e l e c t r o n i c c o l o u r g r a d i n g system to separate tomatoes i n t o d i f f e r e n t c o l o u r c a t e g o r i e s was t e s t e d by g r a d i n g and r e g r a d i n g the same group of tomatoes, ran g i n g i n c o l o u r from green t o f i r m r i p e , a t v a r i o u s comparator s e t t i n g s and o b s e r v i n g the r e s u l t s . V^,., , bb 1 I (Figure 3 . 8 ) was s e t so t h a t the green tomatoes would always drop o f f the end o f the conveyor. V g E T 2 a n ^ v s E T 3 w e r e a d j u s t e d on the f r o n t p a n e l o f the instrument. v g E T 2 a n c ^ V O T 7, m determine the borders o r c u t - o f f s between t u r n i n g and s e m i - r i p e , and s e m i - r i p e and f i r m r i p e , r e s p e c t i v e l y . F i e l d t e s t i n g a t the Western Greenhouse C o - o p e r a t i v e Warehouse was a l s o conducted, and the a u t o m a t i c a l l y graded produce was judged by f e d e r a l government gra d e r s and members of the c o - o p e r a t i v e . (II) E j e c t System The pneumatic e j e c t system was a d j u s t e d so t h a t the tomatoes would be e j e c t e d t r a n s v e r s e l y from the conveyor b e l t i n t o t h e i r a p p r o p r i a t e s t o r a g e b i n s . The adjustment i n v o l v e d s e t t i n g the a i r p r e s s u r e r e g u l a t o r and a d j u s t i n g the a i r n o z z l e s t o optimum angles w i t h r e s p e c t t o the b e l t so t h a t a t a g i v e n conveyor speed the tomatoes would be e j e c t e d as d e s i r e d . The maximum o p e r a t i n g speed o f the e j e c t mechanism was a l s o e s t a b l i s h e d . 128 RESULTS AND DISCUSSION (I) A v o l t a g e V _ „ m , = 0.77 v o l t s , was found s u f f i c i e n t t o & £ J 1 I s e p a r a t e the green tomatoes from the t u r n i n g group. T h i s c u t - o f f v o l t a g e compares f a v o u r a b l y w i t h the p r e d i c t e d mean v o l t a g e f o r the green tomatoes, 0.41 v o l t , as suggested i n T a b l e 3.2. The e f f e c t s o f changing the comparator v o l t a g e s , V S E T 2 a n < ^ ^SET 3 a r e s n o w n ^ n t n e photographs i n F i g u r e 4.1. I f both V g E T 2 and V" S E T 3 are r e l a t i -v e l y h i g h ( F i g u r e 4.1a) then a l l tomatoes can be c a t e g o r i z e d i n t o the t u r n i n g and s e m i - r i p e groups. I f both V_,„ m „ and V„„m 0 are lowered ( F i g u r e 4.1b), then most o f the tomatoes can be c a t e g o r i z e d as f i r m r i p e . A r e a s o n a b l e c o l o u r s p l i t was o b t a i n e d w i t h V S E T 2 = 5 - 2 5 v o l t s ' a n d V S E T 3 = 8 , 2 5 v o l t s ' a s shown i n F i g u r e 4.1c. Voi:irT, 0 f a l l s between the p r e d i c t e d t u r n i n g and green v o l t a g e s p r e v i o u s l y shown i n Table 3.2, but V-,™ 0 i s much lower than the p r e d i c t e d mean of 11 v o l t s f o r the s e m i - r i p e . [ V g E T 3 would be expected t o be g r e a t e r than 11 v o l t s , but l e s s than 11.93 v o l t s ] . The d i f f e r e n c e may be e x p l a i n e d by the d a r k e r red tomatoes used f o r the p h y s i c a l p r o p e r t i e s s t u d i e s than those used f o r the p r e s e n t t e s t s . The tomatoes used i n the p h y s i c a l p r o p e r t i e s s t u d i e s were p u r p o s e l y chosen to i n c l u d e extremes i n both the green and f i r m r i p e 1 2 9 130 c a t e g o r i e s . The f i e l d t e s t r e s u l t s a t the c o - o p e r a t i v e were very p r o m i s i n g . The graded tomatoes were judged a c c e p t a b l e by both the f e d e r a l graders and the c o - o p e r a t i v e members. (II) P r e l i m i n a r y t e s t s i n v o l v i n g the e j e c t mechanism showed t h a t a l a t e r a l angle o f about 10° on the conveyor b e l t as i t passed the e j e c t n o z z l e s , g r e a t l y improved the e f f i c i e n c y o f the e j e c t system. With the i n c l i n e , the pneumatic system was o n l y r e q u i r e d to s t a r t the tomato r o l l i n g , a f t e r which g r a v i t y p u l l e d the tomato o f f the b e l t . 5 2 The 100 p s i g ( 6 . 9 X 10 newtons/m g) pneumatic system was found adequate a t conveyor speeds up to 2.5 f t / s e c (76 cm/sec). E j e c t i o n of the l a r g e tomatoes became d i f f i c u l t a t h i g h e r speeds. Allow-i n g 5 i n (13 cm) of conveyor b e l t per tomato, i . e . a maximum o f 3.5 i n (8.9 cm) f o r the tomato p l u s 1.5 i n (3.8 cm) s e p a r a t i o n between tomatoes, the c o r r e s p o n d i n g g r a d i n g r a t e i s approximately 5 tomatoes/sec. T h i s r a t e would be s u f f i c i e n t f o r an o r g a n i z a t i o n such as Western Greenhouse C o - o p e r a t i v e a t the peak h a r v e s t p e r i o d , based on 1975 y i e l d p r e d i c t i o n s (see Appendix B ) . The s o l e n o i d v a l v e s were found to f a i l a t o p e r a t i n g f r e q u e n c i e s above 10 c y c l e s / s e c . The 131 maximum g r a d i n g r a t e a t t a i n a b l e w i t h t h i s system w i l l be 10 tomatoes/sec, p r o v i d e d t h a t the a i r flow i s s u f f i c i e n t t o e j e c t the tomatoes from the b e l t . Grading r a t e i s p r e s e n t l y l i m i t e d by the a i r flow o b t a i n a b l e d u r i n g the s h o r t p e r i o d t h a t the s o l e n o i d s are a c t i v e . 132 S E C T I O N II SIZE AND COLOUR GRADER C H A P T E R 5 PHYSICAL PROPERTIES OF TOMATOES RELATED TO SIZE GRADING 134 INTRODUCTION The most common c r i t e r i a f o r s i z e c l a s s i f i c a t i o n o f f r u i t s and v e g e t a b l e s are dimension and weight. The industry s t a n d a r d i n B.C. f o r tomato s i z e c l a s s i f i c a t i o n i s based on the measure of the maximum diameter o f the f r u i t (Appendix A ) . U s u a l l y , t h i s maximum diameter i s i n a plane p e r p e n d i c u l a r t o the p o l a r a x i s formed by the blossom and c a l y x ends o f the tomato. The shape o f the f r u i t i s of utmost importance when d e s i g n i n g a machine to s i z e grade a c c o r d i n g to a s i n g l e diameter measurement. V a r i a t i o n s i n shape w i l l determine any p o s s i b l e need f o r o r i e n t a t i o n o f the f r u i t b e f o r e measurement. Dimensionless q u a n t i t i e s , such as s p h e r i c i t y have been used i n p h y s i c a l p r o p e r t i e s a n a l y s e s (25) to d e s c r i b e f r u i t shape. S p h e r i c i t y , a r e l a t i v e measure of s p h e r i c a l u n i -f o r m i t y based on t h r e e d i a m e t e r s , was of l e s s importance i n the d e s i g n of the s i z e grader than the a b s o l u t e d i f f e r e n c e s between the d i a m e t e r s . In the p r e s e n t i n v e s t i g a t i o n o f p h y s i c a l p r o p e r t i e s r e l a t e d t o s i z e g r a d i n g , the d i f f e r e n c e between diameters was s t u d i e d t o e s t a b l i s h the need, i f any, f o r f r u i t o r i e n t a t i o n b e f o r e the diameter i s measured. The c a l c u l a t i o n o f area based on two diameter measurements, and the c a l c u l a t i o n o f volume based on t h r e e diameters w i l l be d i s c u s s e d w i t h r e g a r d to the use of composite v a l u e s as c r i t e r i a f o r s i z e e v a l u a -t i o n . S i n c e the o n l y known commercially a v a i l a b l e s i z e 135 graders f o r tomatoes use weight as the s i z e c r i t e r i o n , i t was a l s o of i n t e r e s t t o i n v e s t i g a t e the r e l a t i o n s h i p between the maximum diameter and the weight of the f r u i t . 136 MATERIALS AND METHODS The e l l i p s o i d was chosen as the approximation f o r the shape of a tomato, as suggested by Mohsenin (25), having a p o l a r a x i s formed by the c a l y x and blossom ends o f the tomato. The t h r e e d i a m e t e r s , D I A . l , DIA.2, and DIA.3 are the maximum (major) diameter measured a t the e q u a t o r i a l plane; the minor diameter, p e r p e n d i c u l a r t o D I A . l , measured a t the e q u a t o r i a l plane; and the maximum p o l a r diameter measured a t a plane p e r p e n d i c u l a r to the e q u a t o r i a l p l a n e . When DIA. l i s e q u a l t o DIA.2 and DIA.3 i s l e s s than D I A . l , the shape o f the tomato approximates an o b l a t e s p h e r o i d . When DIA.2 and DIA.3 are equal and DIA.l i s g r e a t e r than DIA.2, the shape approximates a p r o l a t e s p h e r o i d . The t h r e e d i a m e t e r s , D I A . l , DIA.2, and DIA.3, and the weight o f each o f 153 tomatoes were measured and rec o r d e d . The samples ranged i n s i z e from DIA.l = 1.43 i n (3.63 cm) t o 3.85 i n (9.78 cm) (which covers the f e d e r a l s i z e c a t e g o r y s t a n d a r d from s m a l l t o e x t r a l a r g e ) and weights ranged from 0.92 oz (26.4 g) t o 10.82 oz (309.1 g ) . The are a o f the e q u a t o r i a l plane was e s t i m a t e d u s i n g the approximation o f an e l l i p s e : AREA = J (DIA.l X DIA.2). The volume of the tomato was es t i m a t e d u s i n g the approximation o f an e l l i p s o i d : VOLUME = J (DIA.l X DIA.2 X DIA.3). 137 C o r r e l a t i o n s among the measured diameters and weights, and c a l c u l a t e d areas and volumes were o b t a i n e d as w e l l as l i n e a r r e g r e s s i o n s f o r the measured weight versus each of the t h r e e diameters, c a l c u l a t e d area and volume. The c o r r e l a t i o n s and l i n e a r r e g r e s s i o n s were used t o j u s t i f y the use o f a s i n g l e diameter, D I A . l , as a measure o f the f r u i t s i z e . The data f o r the 153 tomatoes was grouped i n t o the s i z e c a t e g o r i e s , s m a l l , medium, l a r g e and e x t r a l a r g e . The d i f f e r e n c e [DIA.l - DIA.2] was c a l c u l a t e d f o r each tomato i n each o f the f o u r s i z e c a t e g o r i e s as a measure o f the c i r c u l a r u n i f o r m i t y a t the e q u a t o r i a l p l a n e . A d i f f e r e n c e o f zero would imply t h a t i n the e q u a t o r i a l plane the tomato shape c o u l d be approximated by a c i r c l e ; a d i f f e r e n c e g r e a t e r than zero would suggest an e l l i p s e as the approximation. The d i f f e r e n c e between DIA.l and DIA.2 was used to e v a l u a t e the e f f e c t o f tomato o r i e n t a t i o n on s i z e measurement a t the e q u a t o r i a l p l a n e . Each s i z e c a t e g o r y was t r e a t e d s e p a r a t e l y , r a t h e r than p o o l i n g the data, s i n c e the shape o f the f r u i t seemed to vary w i t h s i z e . The mean d i f f e r e n c e s o f [DIA.l - DIA.2] between s i z e c a t e g o r i e s were compared and 9 5 1 c o n f i d e n c e i n t e r v a l s were determined f o r the d i f f e r e n c e s w i t h i n each c a t e g o r y . 138 RESULTS The c o r r e l a t i o n m a t r i x o f D I A . l , DIA.2, DIA.3, weight, c a l c u l a t e d a r e a i n the e q u a t o r i a l p l a n e , and c a l c u -l a t e d volume i s shown i n Table 5.1, based on the 15 3 samples. F i v e l i n e a r r e g r e s s i o n equations o f weight versus each o f the t h r e e diameters, as w e l l as area and volume are l i s t e d i n descending o r d e r a c c o r d i n g t o t h e i r c o r r e l a t i o n c o e f f i c -2 i e n t s (r ) i n Table 5.1. The d i f f e r e n c e s o f [DIA.l - DIA.2] w i t h i n a s i z e c a t e g o r y were found to f o l l o w a skewed d i s t r i b u t i o n f o r a l l s i z e c a t e g o r i e s . The d i s t r i b u t i o n o f /DIA.l - DIA.2 was found to be more normal, hence the means and 95% c o n f i d e n c e i n t e r v a l s were c a l c u l a t e d on the square r o o t b a s i s , and the r e s u l t s transformed by s q u a r i n g them. The means, and 95% co n f i d e n c e i n t e r v a l s f o r the d i f f e r e n c e o f [DIA.l - DIA.2] are l i s t e d i n Table 5.2 f o r a l l f o u r s i z e c a t e g o r i e s . There was no c o r r e l a t i o n between the d i f f e r e n c e [DIA.l - DIA.2] and DIA.l i t s e l f , f o r the s m a l l , medium and l a r g e c a t e g o r i e s . As the tomatoes increased i n s i z e , the d i f f e r e n c e between DIA.l and DIA.2 remained r e l a t i v e l y con-s t a n t . The standar d d e v i a t i o n s o f [DIA.l - DIA.2] f o r the s m a l l , medium and l a r g e c a t e g o r i e s were s m a l l . A c o r r e l a t i o n d i d e x i s t between [DIA.l - DIA.2] and D I A . l f o r the e x t r a l a r g e tomatoes, r e p r e s e n t e d by a c o r r e l a t i o n c o e f f i c i e n t of 0.7393. In t h i s s i z e category the l a r g e r the tomato, the more e l l i p t i c a l i t i s i n the 139 TABLE 5.1 DIMETER-WEIGHT CORRELATIONS AND LINEAR REGRESSION EQUATIONS DIA. 1 DIA. 2 DIA. 3 WEIGHT , AREA VOLUME DIA. 1 1.0000 DIA. 2 0.9762 1.0000 DIA. 3 0.8544 0.8928 1.0000 WEIGHT 0.9836 0.9798 0.8895 1.0000 AREA 0.9940 0.9863 0.8575 0.9926 1.0000 VOLUME 0.9822 0.9820 0.8992 0.9985 0.9920 1.0000 WEIGHT it 0.150)oz = (0.599 + 0.003) VOLUME -(0.015 + 0.024) [5-1] 2 r = 0.9971 WEIGHT it 0.337)oz = (1.32 + 0.012) AREA -(1.10 + 0.063) [5-2] 2 r = 0.9852 WEIGHT it 0.499)oz = (4.15 + 0.062) DIA. 1 -(5.70 + 0.159) [5-3] 2 r 0.9675 WEIGHT it 0.553)oz = (4.89 + 0.081) DIA. 2 -(6.82 + 0.195) [5-4] 2 r = 0.9600 WEIGHT it 1.26 )oz = (6.56 + 0.274) DIA. 3 -(10.11 + 0.622) [5-5] 2 r = 0.7913 where AREA = J- (DIA. 1 X DIA. 2) inch 2 and VOLUME = J (DIA. 1 X DIA. 2 X DIA. 3) inch' 140 TABLE 5.2 MEAN DIFFERENCES BETWEEN DIA.l AND DIA.2, AND 95% CONFIDENCE INTERVALS FOR FOUR SIZE CATEGORIES. Size Category Mean IDIA.1-DIA.2], inch, (cm) 95% Confidence Interval [DIA.1-DIA.2], inch (cm) Small 0.Q45 0.000 to 0.165 (0.114) (0.111) (0.419) Medium 0.073 0.015 to 0.175 (0.185) (0.038) (0.445) Large 0.096 0.011 to 0.263 (0.244) (0.028) (0.668) Extra large 0.271 0.016 to 0.834 (0.688) (0.041) (2.118) 141 e q u a t o r i a l p l a n e . As a r e s u l t , the st a n d a r d d e v i a t i o n o f [DIA.l - DIA.2] f o r the e x t r a l a r g e category i s g r e a t e r than t h a t o f the o t h e r t h r e e c a t e g o r i e s . Because of the c o r r e -l a t i o n t h i s s t a n d a r d d e v i a t i o n does not r e p r e s e n t the range of d i f f e r e n c e between DIA.l and DIA.2 t h a t one would expect f o r a s i n g l e tomato i n the e x t r a l a r g e c a t e g o r y . A l i n e a r r e g r e s s i o n performed on [DIA.l - DIA.2] versus DIA.l f o r the e x t r a l a r g e tomatoes, produced the e q u a t i o n : [DIA.l - DIA.2] ± 0.149 = (0.659 ± 0.299) DIA.l (1.86 ± 0.091) [5-6] where DIA.l and DIA.2 are i n i n c h e s , and r 2 = 0.5466. The 95% c o n f i d e n c e i n t e r v a l f o r a tomato w i t h a DIA.l equal to 3.00 i n (7.62 cm) would be: 0.00 i n < [DIA.l - DIA.2] < 0.411 i n or 0.00 cm < [DIA.l - DIA.2] < 1.044 cm whereas a tomato w i t h a DIA.l equal t o 3.50 i n (8.89 cm) would have a 95% c o n f i d e n c e i n t e r v a l : 0.157 i n < [DIA.l - DIA.2] < 0.741 i n or 0.399 cm < [DIA.l - DIA.2] < 1.882 cm 142 DISCUSSION The c o r r e l a t i o n m a t r i x shown i n Table 5.1 i n d i c a t e s t h a t the maximum diameter a t the e q u a t o r i a l p l a n e , D I A . l , may be used as an i n d i c a t i o n of the weight of the tomato. The minor diameter, p e r p e n d i c u l a r to DIA.l a t the e q u a t o r i a l plane i s c l o s e l y c o r r e l a t e d t o D I A . l , whereas DIA.3 , the p o l a r diameter i s more independent o f D I A . l . The b e s t c o r r e -l a t i o n between a s i n g l e diameter measurement and weight i s t h a t o f D I A . l versus weight. The second l a r g e s t c o r r e l a t i o n c o e f f i c i e n t a s s o c i a t e d w i t h weight i s t h a t o f DIA.2, and the t h i r d l a r g e s t i s t h a t o f DIA. 3.. The c a l c u l a t i o n of volume based on the assumption t h a t the tomato i s an e l l i p s o i d , r e s u l t s i n the l a r g e s t c o r r e l a t i o n c o e f f i c i e n t f o r weight. The c a l c u l a t i o n o f area a t the e q u a t o r i a l plane based on an e l l i p s e r e s u l t s i n the second l a r g e s t c o r r e l a t i o n c o e f f i c i e n t f o r weight. A system of measurement which i n c l u d e s the d e t e r -m i n a t i o n o f a l l t h r e e diameters, and the c a l c u l a t i o n o f volume based on the t h r e e diameters would be i d e a l i f the b e s t c o r r e l a t i o n w i t h weight was d e s i r e d . A system o f measurement which i n c l u d e s the determination of DIA.l and DIA.2 o n l y , and the c a l c u l a t i o n o f area based on the two diameters, would be second b e s t . A system which measures o n l y the l a r g e s t diameter, D I A . l , a t the e q u a t o r i a l plane, would be t h i r d b e s t as an e s t i m a t e o f the tomato's weight. 2 The r e g r e s s i o n e q u a t i o n s and t h e i r a s s o c i a t e d r 143 v a l u e s shown i n Table 5.1 i n d i c a t e t h a t D I A . l , DIA.2, DIA.3, are a , and volume are l i n e a r l y r e l a t e d t o the tomato's weight. The t h i r d l a r g e s t c o r r e l a t i o n c o e f f i c i e n t , 0.9675, was o b t a i n e d f o r the weight versus DIA.l r e g r e s s i o n e q u a t i o n . A system which measures o n l y DIA.l c o u l d t h e r e f o r e r e a s o n a b l y estimate the weight of a tomato. As shown i n T a b l e 5.2, the mean d i f f e r e n c e s of [DIA.l - DIA.2] i n c r e a s e w i t h i n c r e a s i n g s i z e c a t e g o r i e s , from s m a l l t o e x t r a l a r g e . The e q u a t o r i a l plane becomes l e s s c i r c u l a r as the tomato s i z e i n c r e a s e s . There was no c o r r e l a -t i o n between [DIA.l - DIA.2] and DIA.l w i t h i n the s m a l l , medium and l a r g e s i z e c a t e g o r i e s . The 95% c o n f i d e n c e i n t e r -v a l s f o r [DIA.l - DIA.2] apply f o r the s m a l l e s t tomato i n a s i z e c a t e g o r y as w e l l as f o r the l a r g e s t . For example, the s m a l l e s t l a r g e tomato has DIA.l = 2.25 i n (5.72 cm) and the l a r g e s t l a r g e tomato has DIA.l = 3.00 i n (7.62 cm), and the 95% c o n f i d e n c e i n t e r v a l , 0.011 to 0.263 f o r [DIA.l - DIA.2], a p p l i e s f o r both tomatoes. The 95% c o n f i d e n c e i n t e r v a l f o r the e x t r a l a r g e tomatoes shown i n T a b l e 5.2 does not apply s i n c e [DIA.l - DIA.2] i n c r e a s e s w i t h DIA.l i n t h i s s i z e c a t e g o r y . For any g i v e n DIA.l i n the e x t r a l a r g e c a t e g o r y , the 95% c o n f i d e n c e i n t e r v a l may be c a l c u l a t e d u s i n g e q u a t i o n [5-6]. The shape o f the tomato, e s p e c i a l l y i n the equator-i a l plane w i l l determine the need f o r o r i e n t a t i o n of the 144 tomato, b e f o r e DIA.l can be measured. I f the tomato i s s p h e r i c a l , no o r i e n t a t i o n i s r e q u i r e d , s i n c e DIA.l = DIA.2 = DIA.3. I f the tomato i s an o b l a t e s p h e r o i d , the tomato tends to r e s t w i t h the p o l a r a x i s p e r p e n d i c u l a r t o the plane on which i t r e s t s , and no f u r t h e r o r i e n t a t i o n i s r e q u i r e d , s i n c e DIA.l = DIA.2. I f the tomato i s a p r o l a t e s p h e r o i d , no o r i e n t a t i o n i n the p o l a r plane w i l l be r e q u i r e d , s i n c e DIA.2 = DIA.3, however, o r i e n t a t i o n o f the DIA.l a x i s w i l l be r e q u i r e d . I f the tomato i s an e l l i p s o i d , o r i e n t a t i o n o f the p o l a r a x i s and e q u a t o r i a l plane w i l l be r e q u i r e d . The e l l i p s o i d tomatoes are g e n e r a l l y the e x t r a l a r g e tomatoes, and DIA.3 i s u s u a l l y the s m a l l e s t , making the tomato most s t a b l e i f r e s t i n g on one of i t s p o l e s . O r i e n t a t i o n i n the e q u a t o r i a l plane w i l l t h e r e f o r e be r e q u i r e d . The mean d i f f e r e n c e s and 95% c o n f i d e n c e i n t e r v a l s o f [DIA.l - DIA.2] shown i n T a b l e 5.2 i n d i c a t e the worst measurement e r r o r t h a t would be expected i f the tomatoes were not o r i e n t e d i n the e q u a t o r i a l p l a n e, i . e . o f DIA.2 was measured i n s t e a d o f D I A . l , the e r r o r i n the measure o f DIA. l would be [DIA.l - DIA.2J. Only one o r i e n t a t i o n o f the tomato i n the e q u a t o r i a l plane produces no e r r o r i n the measure of D I A . l , and o n l y one o r i e n t a t i o n produces a maximum e r r o r e q u a l t o [DIA.l - DIA.2]. A l l o t h e r o r i e n t a t i o n s i n the e q u a t o r i a l plane produce diameter measurements having e r r o r s g r e a t e r than zero but l e s s than [DIA.l - DIA.2]. I t i s concluded t h a t o r i e n t a t i o n o f the tomato f o r 145 the a c c u r a t e d e t e r m i n a t i o n o f DIA.l w i l l be more important f o r the l a r g e r tomatoes than the s m a l l ones, s i n c e the measurement e r r o r due t o l a c k o f o r i e n t a t i o n i n c r e a s e s w i t h tomato s i z e . 146 C H A P T E R 6 S I Z E D E T E R M I N A T I O N U S I N G T H E COLOUR GRADER S C H M I T T T R I G G E R P U L S E 1 4 7 INTRODUCTION The Schmitt t r i g g e r p u l s e width o f the c o l o u r grader i s p r o p o r t i o n a l t o the l e n g t h o f time t h a t the tomato spends under the f i b r e o p t i c s e n s i n g head. I f the tomato i s ce n t e r e d on the conveyor b e l t w i t h r e s p e c t t o the s e n s i n g head, and the conveyor b e l t i s moving a t a c o n s t a n t speed, the Schmitt t r i g g e r p u l s e width w i l l be a f u n c t i o n o f a diameter o f the tomato. I f the tomato i s not c e n t e r e d o r the conveyor b e l t i s t r a v e l l i n g a t a v a r y i n g speed, an e r r o r i n the diameter measurement w i l l r e s u l t . In t h i s c h a p t e r , the r e l a t i o n s h i p between the Schmitt t r i g g e r p u l s e width and v a r i o u s tomato s i z e s w i l l be s t u d i e d a t a f i x e d conveyor b e l t speed. F a c t o r s which a f f e c t the Schmitt t r i g g e r p u l s e , such as b e l t speed, and m i s a l i g n -ment o f the tomato w i t h r e s p e c t t o the f i b r e o p t i c s e n s i n g head w i l l a l s o be examined. The " l i m i t o f d e t e c t i o n " o f the p r e s e n t s e n s i n g head d e s i g n w i l l be d i s c u s s e d . The l i m i t o f d e t e c t i o n i s the diameter o f a tomato which i s too s m a l l t o be d e t e c t e d , and thus does not produce a Schmitt t r i g g e r p u l s e . The r e s o l u -t i o n o f the instrument i s the s m a l l e s t d i f f e r e n c e between two diameters which can be d i s c r i m i n a t e d . 148 MATERIALS AND METHODS S i z e Standards I t was e v i d e n t from the b e g i n n i n g of the study o f tomato s i z e versus Schmitt t r i g g e r p u l s e width t h a t some t a n g i b l e s i z e s t a n d a r d s , o t h e r than tomatoes, were r e q u i r e d . Tomatoes have a f i n i t e s h e l f l i f e which makes them u n d e s i r a b l e f o r l o n g term t e s t i n g . The green tomatoes, w i t h the l o n g e s t s h e l f l i f e a t room temperature change c o l o u r as they r i p e n , making them u n s u i t a b l e as s t a n d a r d s . Three white t e x t u r e d styrofoam spheres were chosen as s i z e s t a n d a r d s , one s m a l l , one medium, and one l a r g e . T h e i r diameters were 2.0 i n (5.1 cm), 2.5 i n (6.4 cm) and 2.9 i n (7.4 cm) r e s p e c t i v e l y . A segment was c u t from each sphere, so t h a t the spheres c o u l d be p l a c e d on the conveyor b e l t w i t h the f l a t s i d e down, as w e l l as approximating more r e a l i s t i c a l l y the shape o f a tomato, where the f l a t s i d e r e p r e s e n t e d the c a l y x end. The t h r e e diameters, D I A . l , DIA.2 and DIA.3 o f each s t y r o b a l l are l i s t e d i n T a b l e 6.1. The d i v i d e r output o f the c o l o u r grader was measured f o r the t h r e e s t y r o b a l l s , and s i n c e t h e i r c o l o u r s were a l l the same, the d i v i d e r output v o l t a g e f o r each of the t h r e e was approximately 2 v o l t s . T h i s v o l t a g e rendered the s t y r o -b a l l s as " t u r n i n g " i n c o l o u r , i . e . the s t y r o b a l l s r e f l e c t e d s l i g h t l y more l i g h t i n the red r e g i o n than i n the green r e g i o n . The s t y r o b a l l s were t h e r e f o r e s u i t a b l e as s t a n d a r d s . 149 TABLE 6.1 DIA.l, DIA.2, and DIA.3 of THREE STYROBALL SIZE STANDARDS Styro b a l l DIAMETERS, inch (cm) n " _ _ —— •  - 1 1 » Size D I A . l D I A . 2 DIA.3 Small 2.00 2.00 1.63 (5.08) (5.08) (4.14) Medium 2.48 2.48 2.01 (6.30) (6.30) (5.11) Large 2.85 2.85 2.35 (7.24) (7.24) (5.97) 150 P u l s e Width Measurement Technique The f l a t s i d e o f each s t y r o b a l l was a t t a c h e d t o the b l a c k conveyor b e l t f o r a l l t e s t s , u s i n g double s i d e d adhesive tape, and the Schmitt t r i g g e r p u l s e o f the c o l o u r grader was measured u s i n g a T e k t r o n i c s Frequency Counter, Model DC 503. Measurement o f B e l t Speed S i n c e the frequency of CLOCK A (F i g u r e 3.15) i s d i r e c t l y p r o p o r t i o n a l t o the r a t e o f b e l t movement, the measure of the CLOCK A frequency w i l l g i v e an a c c u r a t e measure o f b e l t speed. An approximate c o n v e r s i o n s c a l e o f the CLOCK A frequency versus b e l t speed i s shown i n Table 6.2. A T e k t r o n i c s Frequency Counter, Model DC 503 was used to measure the CLOCK A frequency. The CLOCK A frequency w i l l be quoted as the measure o f b e l t speed i n subsequent t e s t s . E f f e c t o f S t y r o b a l l S i z e on Schmitt T r i g g e r P u l s e Width  a t Four Conveyor B e l t Speeds A. The l a r g e s t y r o b a l l was c e n t e r e d and taped to the con-veyor b e l t s u r f a c e - The b e l t was s e t i n motion, and the b e l t speed determined by measuring the CLOCK A frequency. The s t y r o b a l l remained a t t a c h e d to the conveyor a l l o w i n g a Schmitt t r i g g e r p u l s e width measurement t o be o b t a i n e d every time the s t y r o b a l l passed under the s e n s i n g head, thus e l i m i n a t i n g r e c e n t e r i n g o f the s t y r o b a l l f o r each measurement. 151 TABLE 6 . 2 THE COLOUR GRADER CLOCK A FREQUENCY VERSUS APPROXI-MATE CONVEYOR BELT SPEED. CLOCK A Conveyor B e l t Frequency (Hz) Speed, i n c h / s e c (cm/sec) 20 10 (25) 40 20 (51) 60 30 (76) 80 40 0 ' (102) 100 50 (127) 120 6 (15 0 2) 152 B. T h i r t y . S c h m i t t t r i g g e r p u l s e width measurements were o b t a i n e d f o r each o f f o u r b e l t speeds -- 30, 40, 50, and 60 Hz. C. The procedure d e s c r i b e d i n A and B was repeated f o r the medium and s m a l l s t y r o b a l l s . E f f e c t o f O f f - C e n t e r Viewing o f a S t y r o b a l l on the  Measured Diameter Each of the th r e e s t y r o b a l l s was c e n t e r e d and taped to the conveyor b e l t , one a t a time, t o e s t a b l i s h the e f f e c t s of o f f - c e n t e r v i e w i n g o f the s t y r o b a l l by the f i b r e o p t i c s e n s i n g head. The measurement e r r o r produced by such o f f -c e n t e r v i e w i n g w i l l i n d i c a t e the need ( i f any) f o r c e n t e r i n g tomatoes on the conveyor b e l t . A b e l t speed of 40 Hz was chosen f o r the t e s t s . The f i b r e o p t i c s e n s i n g head was d e l i b e r a t e l y o f f - s e t from the c e n t e r o f the b e l t by about 5/8 i n c h (1.6 cm). The s e n s i n g head was moved t r a n s v e r s e l y t o the movement of the b e l t , i n f i v e 1/4 i n c h (0.64 cm) i n t e r v a l s . Ten Schmitt t r i g g e r p u l s e w i d t h measurements were o b t a i n e d as the s t y r o b a l l passed under the s e n s i n g head, f o r each 1/4 i n c h (0.64 cm) i n t e r v a l . 153 RESULTS AND DISCUSSION E f f e c t of S t y r o b a l l S i z e on Schmitt T r i g g e r Pulse.  Width at Four Conveyor B e l t Speeds The means, standar d d e v i a t i o n s , and s t a n d a r d e r r o r s o f the Schmitt t r i g g e r p u l s e widths and t h e i r a s s o c i a t e d s t y r o b a l l diameters, f o r f o u r b e l t speeds are l i s t e d i n T a b l e 6.3. The means of the Schmitt t r i g g e r p u l s e widths versus s t y r o b a l l diameter are p l o t t e d f o r f o u r b e l t speeds i n F i g u r e 6.1. I d e a l l y , the r e l a t i o n s h i p between p u l s e width and diameter shown i n F i g u r e 6.1, i s l i n e a r w i t h a l l l i n e s p a s s i n g through the o r i g i n . P r a c t i c a l l y , a r e f l e c t a n c e t h r e s h o l d must be exceeded b e f o r e the Schmitt t r i g g e r c i r c u i t responds. T h i s t h r e s h o l d i s a f u n c t i o n o f the f i e l d o f view at the s e n s i n g head and the r e f l e c t a n c e d i f f e r e n c e between a tomato and the conveyor b e l t . The t h r e s h o l d w i l l be indepen-dent of conveyor b e l t speed. A tomato, or s t y r o b a l l , must be l a r g e enough t o occupy s u f f i c i e n t area i n the f i b r e o p t i c f i e l d o f view b e f o r e i t i s d e t e c t a b l e above background. Based on exp e r i e n c e w i t h the c o l o u r grader, the t h r e s h o l d r e l a t e s t o a tomato diameter o f about 1.5 inches (3.8 cm). The d o t t e d p o r t i o n s o f the curves i n F i g u r e 6.1 are e x t r a p o l a t e d t o a probable asymtote around 1.5 i n c h e s (3.8 cm). Above 2.5 inches (6.4 cm) the curves appear q u i t e l i n e a r . R e s o l u t i o n The s t a n d a r d d e v i a t i o n s of the Schmitt t r i g g e r p u l s e widths f o r the three s t y r o b a l l s a t f o u r b e l t speeds 154 TABLE 6.3 MEANS, STANDARD DEVIATION, AND STANDARD ERRORS OF SCHMITT TRIGGER PULSE WIDTHS FOR THREE STYROBALLS AT FOUR CONVEYOR BELT SPEEDS. Styro b a l l PULSE WIDTH (ms)  Dia.,inch (cm) Mean S.D. S.E. Belt Speed: 30 Hz 2.00 (5.08) 153.7 2.935 0.545 2.48 (6.30) 199.4 1.634 0.298 2.85 (7.24) 224.3 1.509 0.276 Belt Speed: 40 Hz 2.00 (5.08) 117.1 0.888 0.165 2.48 (6.30) 150.4 1.180 0.215 2.85 (7.24) 169.9 1.093 0.200 Belt Speed: 50 Hz 2.00 (5.08) 93.3 1.241 0.230 2.48 (6.30) 120.6 0.828 0.151 2.85 (7.24) 137.8 1.300 0.237 Belt Speed: 60 Hz 2.00 (5.08) 79.0 0.883 0.164 2.48 (6.30) 102.7 1.037 0.189 2.85 (7.24) 118.2 1.210 0.221 155 F I G U R E 6 . 1 M E A N S C H M I T T T R I G G E R P U L S E W I D T H V S . S T Y R O B A L L D I A M E T E R A T F O U R C O N V E Y E R B E L T S P E E D S 40-| 1 1 1 1 1 1 1 f-O / 2 . 3 - * D i A M E T E f ? ^/NCH) 156 as l i s t e d i n Table 6.3 g i v e some i n d i c a t i o n of the r e s o l u -t i o n o f the instrument i f the Schmitt t r i g g e r p u l s e width i s used as a measure of diameter. The magnitudes o f the standard d e v i a t i o n s are pro b a b l y due to n o n - u n i f o r m i t y o f the conveyor b e l t speed, and l a t e r a l "squirming" o f the conveyor b e l t . The l a r g e s t s t a n d a r d d e v i a t i o n l i s t e d i n Table 6.3 i s 2.935 ms f o r the 2.00 i n c h (5.08 cm) s t y r o b a l l a t the 30 Hz b e l t speed. As a percentage o f the mean, and con v e r t e d t o i n c h e s , the st a n d a r d d e v i a t i o n i s 0.038 i n c h (0.10 cm) and the 95% c o n f i d e n c e i n t e r v a l f o r a g i v e n diameter w i l l be: the diameter ± 0.075 (0.19 cm). T h i s v a r i a t i o n i n s i z e i s p r o b a b l y n e g l i g i b l e . The worst case r e s o l u t i o n i s t h e r e f o r e s l i g h t l y g r e a t e r than 1/16 i n c h (0.16 cm). T y p i c a l l y , however, the sta n d a r d d e v i a t i o n w i l l be 0.023 i n c h (0.058 cm) (the mean of the standar d d e v i a t i o n s expressed as a p e r c e n t o f the diameters, i n Tab l e 6.3) and the 95% c o n f i d e n c e i n t e r v a l w i l l be: the diameter ± 0.045 i n c h (0.11 cm). T h e r e f o r e 95% o f the diameters w i l l be w i t h i n 3/64 i n c h (0.12 cm) o f t h e i r t r u e s i z e . The worst b e l t speed v a r i a t i o n f o r the p r e s e n t d e s i g n would be approximately 4%. B e t t e r r e g u l a t i o n would i n c r e a s e the r e s o l u t i o n . 157 Schmitt T r i g g e r Pulse Width versus Conveyor B e l t  Speed f o r Three S t y r o b a l l S i z e s For a g i v e n s t y r o b a l l diameter, the product o f p u l s e width and conveyor b e l t speed (measured as the CLOCK A frequency) i s c o n s t a n t . T h i s i s the r e s u l t t h a t one would expect, s i n c e a g i v e n s t y r o b a l l o c c u p i e s a c e r t a i n l e n g t h o f b e l t , and the number of CLOCK A c y c l e s are the same measure o f b e l t l e n g t h . The p r o d u c t s were approximately 4.7, 6.0 and 6.9 c y c l e s , f o r the s m a l l , medium and l a r g e s t y r o b a l l s , r e s p e c t i v e l y , c a l c u l a t e d from the data i n Table 6.3. E f f e c t o f O f f - C e n t e r Viewing o f a S t y r o b a l l on the  Measured Diameter The mean o f the ten p u l s e widths o b t a i n e d f o r each o f the 1/4 i n c h (0.64 cm) i n t e r v a l s as the s e n s i n g head was moved a c r o s s the conveyor b e l t was p l o t t e d a g a i n s t t h e - d i s -tance the head was moved. The r e s u l t i n g curve was o f p a r a -b o l i c shape, i t s maximum c o r r e s p o n d i n g to the on-center view o f the s t y r o b a l l . D e v i a t i o n s to the r i g h t o r l e f t o f c e n t e r caused a decrease i n the measured p u l s e width. Using the maximum p u l s e width o b t a i n e d from the curve as the " t r u e " measure o f the s t y r o b a l l s i z e , the e r r o r due to o f f - c e n t e r i n g c o u l d be p r e d i c t e d . For example, the maximum p u l s e width f o r the s m a l l s t y r o b a l l was 126.5 ms, and a t 1/4 i n c h (0.64 cm) from the maximum the p u l s e width was 122.5 ms. The measurement e r r o r i n the diameter due to the 1/4 i n c h (0.64 cm) o f f - c e n t e r v i e w i n g i s thus: 158 E r r o r = 2 ; ? Q c i n C h X (126.5 - 122.5) ms 12 6.5 ms = 0.063 i n c h (0.16 cm). S i m i l a r l y , e r r o r s were c a l c u l a t e d i n 1/8 i n c h (0.32 cm) i n t e r v a l s from zero t o 5/8 i n c h (1.6 cm) o f f -c e n t e r . The e r r o r v a l u e s are l i s t e d i n Table 6.4. The o f f s e t o f the s t y r o b a l l from the c e n t e r o f the conveyor b e l t (or the c e n t e r o f the s e n s i n g head) does not seem t o be too c r i t i c a l . A 1/4 i n c h (0.64 cm) o f f s e t r e s u l t s i n a measurement e r r o r o f about 0.025 i n c h (0.064 cm) f o r the 2.85 i n c h (7.24 cm) diameter s t y r o b a l l o r a 0.9% measurement e r r o r , and a 0.063 i n c h (0.16 cm) e r r o r f o r the 2.00 i n c h (5.08 cm) diameter s t y r o b a l l , or a 3.2% e r r o r . A c e n t e r i n g d e v i c e on the fe e d end o f the conveyor b e l t s h o u l d be a b l e to c e n t e r tomatoes ( e s p e c i a l l y s m a l l e r ones) w i t h i n 1/4 i n c h (0.64 cm) of the b e l t c e n t e r w i t h o u t much d i f f i c u l t y . 159 TABLE 6.4 APPROXIMATE DIAMETER MEASUREMENT ERROR AT VARIOUS OFF-CENTER DISTANCES FOR THREE STYROBALLS, RELATIVE TO THE ON-CENTER MEASUREMENT. Off-Center Distance inch (cm) Small Styroball ERROR (inch) Medium Styroball Large Styr o b a l l 0 (0) 0.000 (0.000) 0.000 (0.000) 0.000 (0.000) 1/8 (0.32) 0.016 (0.041) 0.016 (0.041) 0.008 (0.020) 1/4 (0.64) 0.063 (0.160) 0. 039 (0.099) 0.025 (0.064) 3/8 (0.95) 0.103 (0.262) 0. 078 (0.198) 0.059 (0.150) 1/2 (1.27) 0.174 (0.442) 0.132 (0.335) 0.110 (0.279) 5/8 (1.59) 0.245 (0.622) 0. 202 (0.513) 0.170 (0.432) 160 SUMMARY The c o l o u r grader Schmitt t r i g g e r p u l s e width f o r the t e s t s conducted u s i n g the s t y r o b a l l s i z e s t a n d a r d s , i s a f u n c t i o n o f the diameter o f the s t y r o b a l l and the speed o f the conveyor b e l t . The product o f the Schmitt t r i g g e r p u l s e width and the b e l t speed (when measured as the frequency o f CLOCK A) f o r a g i v e n diameter i s c o n s t a n t . The r e l a t i o n s h i p between the width of the Schmitt t r i g g e r p u l s e and the s t y r o -b a l l diameter i s q u i t e l i n e a r ( f o r a c o n s t a n t b e l t speed) down to about a 2 i n c h (5 cm) diameter, where the s t r a i g h t l i n e r o l l s o f f t o a l i m i t o f about 1.5 i n c h (3.8 cm). S t y r o -b a l l s h a v i n g diameters below t h i s l i m i t cannot be d e t e c t e d . The measurement e r r o r r e s u l t i n g from a g i v e n o f f -c e n t e r placement of the s t y r o b a l l on the conveyor b e l t i n c r e a s e s as the s t y r o b a l l s i z e d e c r e a s e s . The e r r o r i n -cr e a s e s as the o f f - c e n t e r d i s t a n c e i n c r e a s e s f o r a g i v e n s t y r o b a l l s i z e . A 1/4 i n c h (0.64 cm) o f f s e t from the c e n t e r of the b e l t r e s u l t s i n a measurement e r r o r o f about 0.063 i n c h (0.16 cm) f o r the 2.00 i n c h (5.08 cm) diameter s t y r o -b a l l and as l i t t l e as 0.025 i n c h (0.064 cm) f o r the 2.85 i n c h (7.24 cm) diameter s t y r o b a l l . With a system capable o f reas o n a b l e alignment o f tomatoes on the conveyor b e l t , i t appears f e a s i b l e t o use the Schmitt t r i g g e r p u l s e width as a measure of the tomato's diameter, p r o v i d e d t h a t the b e l t speed i s r e l a t i v e l y c o n s t a n t . The r e s o l u t i o n o b t a i n a b l e w i t h the instrument w i l l be 161 p r i m a r i l y a f u n c t i o n of the r e g u l a t i o n of conveyor b e l t speed. For the p r e s e n t d e s i g n , the r e s o l u t i o n was found to be about 3/64 i n c h (0.12 cm). C H A P T E R 7 D E S I G N AP P R OACH 163 INTRODUCTION A combined s i z e and c o l o u r grader was d e s i g n e d by i n c o r p o r a t i n g the Schmitt t r i g g e r p u l s e w i t h the c o l o u r grader d e s c r i b e d i n S e c t i o n 1. A v o l t a g e p r o p o r t i o n a l t o the Schmitt t r i g g e r p u l s e width was generated and p r o c e s s e d i n a manner s i m i l a r t o the d i v i d e r output v o l t a g e o f the c o l o u r grader. A number o f comparators p r e s e t t o the s i z e c a t e g o r y l i m i t s were used to generate a d i g i t a l s i g n a l which was s t o r e d i n a memory alo n g w i t h the c o l o u r c a t e g o r y i n f o r m a -t i o n . S i n c e f o u r c o l o u r c a t e g o r i e s and f i v e s i z e c a t e -g o r i e s e x i s t , twenty combinations of s i z e and c o l o u r a r i s e . T h i s would r e q u i r e a minimum o f n i n e t e e n s h i f t r e g i s t e r memories. I t was d e c i d e d t h a t due t o the low percentage o f green tomatoes and below s m a l l tomatoes g e n e r a l l y encountered* a l l s i z e s o f green tomatoes (4 s i z e s ) would be i n one c a t e -gory, and a l l c o l o u r s o f below s m a l l tomatoes (3 c o l o u r s ) would be i n another. T h i s reduced the number of memories r e q u i r e d t o t h i r t e e n , w i t h the f o u r t e e n t h category comprised o f those tomatoes which r o l l e d o f f the end o f the b e l t - a l l tomatoes which were below s m a l l . Not o n l y can the Schmitt t r i g g e r p u l s e o f the c o l o u r grader be used i n the s i z e / c o l o u r grader, but o t h e r t i m i n g p u l s e s common to both graders can be drawn from the * P e r s o n a l communication w i t h Western Greenhouse Co-op. members 164 c o l o u r grader. The components to be used w i l l match those of the c o l o u r grader, i . e . l i n e a r IC's w i l l be used f o r analog s i g n a l p r o c e s s i n g , and CMOS IC's w i l l be used f o r d i g i t a l s i g n a l p r o c e s s i n g . 165 THEORY I t was d e c i d e d t h a t a l i n e a r r e l a t i o n s h i p between diameter and Schmitt t r i g g e r p u l s e width would s u f f i c e as an approximation f o r the curves shown i n F i g u r e 6.1. T h e o r e t i -c a l l y , n e g l e c t i n g the t h r e s h o l d e f f e c t , the s t r a i g h t l i n e s would a l l pass through the o r i g i n , and the s l o p e s o f the l i n e s would be a f u n c t i o n of conveyor b e l t speed. Any one l i n e may be r e p r e s e n t e d by: D = Kt [7-1] where D = diameter ( v o l t s ) K = c o n s t a n t t = p u l s e width (sec) or D = Kdt [7-2] An i n t e g r a t o r c i r c u i t , which i n t e g r a t e s a c o n s t a n t v o l t a g e (K) and i s t r i g g e r e d to b e g i n i n t e g r a t i n g a t the s t a r t o f the Schmitt t r i g g e r p u l s e , a t t = 0, and to s t o p i n t e g r a t i n g a t the end o f the p u l s e would produce a f i n a l o u tput v o l t a g e which c o u l d be used as a measure o f , t h e tomato's diameter. F o r a f i x e d b e l t speed, a c o n s t a n t i n t e g r a t i n g v o l t a g e may be chosen. For the p r e s e n t t e s t model i t was d e c i d e d t h a t a range o f o p e r a t i n g b e l t speeds was d e s i r a b l e , and t h a t the v o l t a g e t o be i n t e g r a t e d , E, would be d i r e c t l y 166 p r o p o r t i o n a l t o conveyor b e l t speed. A frequency to v o l t a g e c o n v e r s i o n was t h e r e f o r e n e c e s s a r y . Frequency to v o l t a g e c o n v e r s i o n may be ach i e v e d by g e n e r a t i n g a s h o r t p u l s e o f con s t a n t h e i g h t and width and then i n t e g r a t i n g the p u l s e s over a f i x e d sampling time. T h e r e f o r e , n E = E - e. A t [7-3] i = l 1 where e^ = p u l s e h e i g h t ( v o l t s ) At = p u l s e width (sec) n = number of p u l s e s = f T = frequency X sampling time. S i n c e h e i g h t e^, and the width At, o f the p u l s e are con-s t a n t then, E = n e. At [7-4] l o r E = f e. At T [7-5] Due t o power supply l i m i t a t i o n s , the maximum d e s i r e d value o f E i s 10 v - s e c . I f the p u l s e h e i g h t , e^ = 15v, then, f At T = 2/3 [7-6] The conveyor b e l t speed was assumed not to exceed 5 f t / s e c (152 cm/sec) o r 120 Hz CLOCK A frequency, t h e r e f o r e the maximum val u e o f At i s A tmax = ISFT [ 7 ' 7 ] 167 The sampling time, T, s h o u l d be as long as p o s s i b l e so t h a t many p u l s e s are i n t e g r a t e d . I f T = 1 sec, then e q u a t i o n [7-7] becomes, At = 5.56 ms [7-8] At a slow conveyor b e l t speed, o f 10 i n c h / s e c (25 cm/sec) o r 20.Hz CLOCK A frequency, e q u a t i o n [7-5] becomes, E = 20 X 15 X 5.56 X 10~ 3 X 1 E = 1.67 v - s e c . Note t h a t the 120 Hz and T = 1 sec, 120 p u l s e s are i n t e g r a t e d and a t 20 Hz o n l y 20 p u l s e s are i n t e g r a t e d . The sampling time may be i n c r e a s e d up t o a p o i n t , p r o v i d e d t h a t E can be s t o r e d f o r the sampling p e r i o d w i t h n e g l i g i b l e l o s s . For a g i v e n b e l t speed, E remains- c o n s t a n t . The i n t e g r a t i o n o f the c o n s t a n t produces a l i n e a r ramp v o l t a g e w i t h r e s p e c t to time. S u b s t i t u t i n g E f o r K i n e q u a t i o n [7-2] and i n t e g r a t i n g from zero f o r the l e n g t h o f the Schmitt t r i g g e r p u l s e , produces: rP Edt [7-9] 0 or D = A E p [7-10] D = A where D = v o l t a g e r e p r e s e n t i n g the diameter o f the tomato E = i n t e g r a t i n g v o l t a g e 168 p = Schmitt t r i g g e r p u l s e width produced by the tomato A = c o n s t a n t . I f the l a r g e s t tomato t o be encountered has a diameter o f 4 inches (10 cm), then a t 20 Hz b e l t speed, the pu l s e width i s about p = 400 ms. The maximum va l u e of D was chosen as 12.5v, t h e r e f o r e , s o l v i n g f o r A i n e q u a t i o n [7-10], we g e t , A = 19. [7-11] Note t h a t f o r the same diameter, i f the b e l t speed = 60 Hz, or 30 i n c h e s / s e c (76 cm/sec), E = 5.00 p = 133 ms A = 19. By c o n v e r t i n g the b e l t speed, i . e . CLOCK A f r e -quency, t o a v o l t a g e , and i n t e g r a t i n g the v o l t a g e f o r the l e n g t h o f the Schmitt t r i g g e r p u l s e , a v o l t a g e D p r o p o r t i o n t o the Schmitt t r i g g e r p u l s e i s generated. The Schmitt t r i g g e r p u l s e i s a f u n c t i o n o f tomato diameter, as shown i n Chapter 6, t h e r e f o r e D i s p r o p o r t i o n a l t o diameter. 169 ELECTRONIC SIZE AND COLOUR GRADER: OVERVIEW A s i z e grader was designed u s i n g some of the s i g n a l s from the c o l o u r grader ( S e c t i o n 1) to produce d i g i t a l s i z e c a t e g o r y s i g n a l s . The s i z e c a t e g o r y d i g i t a l s i g n a l s were combined w i t h the c o l o u r c a t e g o r y s i g n a l s t o produce one s i g n a l f o r each o f the d i f f e r e n t s i z e / c o l o u r c a t e g o r y combinations. A b l o c k diagram o f the s i z e grader and s i z e / c o l o u r grader d i g i t a l p r o c e s s o r i s shown i n F i g u r e 7.1. [The c i r c l e d i n p u t s i n the diagram are s i g n a l s o b t a i n e d d i r e c t l y from the c o l o u r grader d e s c r i b e d i n S e c t i o n 1 ] . The p u l s e g e n e r a t o r and timer c i r c u i t (A i n F i g u r e 7.1) produces a p u l s e of uniform h e i g h t and width every c y c l e o f the CLOCK A s i g n a l , which i s the measure of conveyor b e l t speed. The c i r c u i t a l s o produces an INTEGRATE and an UPDATE s i g n a l , which a l l o w s the generated p u l s e s t o be i n t e g r a t e d and the r e s u l t o f the i n t e g r a t i o n t o be s t o r e d by the i n t e r -g r a t o r and storage c i r c u i t (B). The i n t e g r a t i o n takes p l a c e over a f i x e d time p e r i o d , about 1 sec, a f t e r which the s t o r e d s i g n a l i s updated and the i n t e g r a t i o n begins anew. Thus the b e l t speed i s monitored and a v o l t a g e , E, which i s a f u n c t i o n o f b e l t speed i s o b t a i n e d a t the output o f (B). The SAMPLE i n p u t from the c o l o u r grader i s the com-plement o f the Schmitt t r i g g e r p u l s e (see F i g u r e 3.12) and i s the measure o f the tomato diameter. The v o l t a g e , E, i s /PEAK ( DETECTOR I) MS ESf T INJ (SAMPLE IN) (CLOCK A ) O— A PULSE GENERATOR ANO TIMER I N P U T S COM PA O-C O M P . ^ O C O M A 61 C O M P . 7 < DECODING S A T E S INTEGRATOR AND STORAGE. C RAMP GENERATOR AND STORAGE COMP. 4 OOT COMP.S OUT ANALOG PROCESSOR D / S / T A L P R O C E S S O R (COLOUR INPUTS) (COMP. l) O , SEMI-KlPe. (LATCH RESET) SJZE INPUTS LATCHING CIRCUIT SIZE/COLOUR DECODER i. Arts.a / S E M I K . I P E C K T R K LAUGr./sCMl- R l P E . S M A L L / F I R M R I P E . ISICCHU^/FIP'I PIPE. LA&GC/FIRM mrB. e x r * A l A W t / f l R M RIPE . A i t SIXES/G&EEH SHIFT REGISTER MEMORIES OPTO-ISOUAJORS AMD TRIACS SOLENOICH IS F I G U R E 7. 1 S I Z E G R A D E R A N D S I Z E / C O L O U R G R A D E R D I G I T A L P R O C E S S O R B L O C K D I A G R A M , O 171 i n t e g r a t e d f o r the d u r a t i o n o f the SAMPLE p u l s e , and the f i n a l v o l t a g e D i s o b t a i n e d which i s a f u n c t i o n of the tomato diameter. T h i s i n t e g r a t i o n takes p l a c e i n the ramp genera t o r and storage c i r c u i t (C). The v o l t a g e , D, i s then p r o c e s s e d i n the same way as the d i v i d e r output s i g n a l o f the c o l o u r grader. D i s compared t o f o u r p r e s e t v o l t a g e s c o r r e s p o n d i n g to s i z e c a t e g o r y l i m i t s by the comparator c i r c u i t s (D), and the out-puts of the f o u r comparators form a 4 - b i t d i g i t a l s i g n a l r a n g i n g from 0000 t o 1111 depending on the s i z e c a t e g o r y . The d i g i t a l s i g n a l i s decoded (E) and s t o r e d t e m p o r a r i l y i n a l a t c h i n g c i r c u i t ( F ) . The c o l o u r c a t e g o r y i n f o r m a t i o n i s then combined w i t h the s i z e c a t e g o r y data (G) and a s i n g l e s i z e / c o l o u r s i g n a l i s s t o r e d i n a s h i f t r e g i s t e r memory (H). T h i r t e e n s h i f t r e g i s t e r memories are used and one " d r o p - o f f " a t the end o f the conveyor b e l t , t o s t o r e the i n f o r m a t i o n u n t i l the tomato gets t o i t s e j e c t s t a t i o n . When a s i g n a l s t o r e d i n a s h i f t r e g i s t e r appears at the s h i f t r e g i s t e r output, i t i s used t o c o n t r o l a pneumatic s o l e n o i d t o e j e c t the tomato. As was the case f o r the c o l o u r grader, o p t o - i s o l a t o r s and t r i a c s (I) were used t o i n t e r f a c e the low power d i g i t a l IC's to the 115 v o l t AC s o l e n o i d s . Rather than b u i l d a long conveyor and purchase ten more s o l e n o i d s and o t h e r hardware, i t was d e c i d e d t h a t the a b i l i t y o f the system t o both s i z e and c o l o u r grade tomatoes 172 c o u l d be t e s t e d u s i n g the t h i r t e e n memory c i r c u i t s t o g e t h e r w i t h the th r e e o p t o - i s o l a t o r and t r i a c c i r c u i t s and the th r e e s o l e n o i d s o f the c o l o u r grader. The same conveyor system c o u l d be used as w e l l . Tomatoes c o u l d then be graded f o r s i z e and c o l o u r i n groups of t h r e e , and the " d r o p - o f f " group would c o n t a i n a l l o t h e r s i z e / c o l o u r c a t e g o r i e s . T h i s remaining group c o u l d be regraded, but the s o l e n o i d s w i r e d to t h r e e o t h e r s h i f t r e g i s t e r memories. A l l permutations of s i z e and c o l o u r c o u l d be t e s t e d t h i s way through the use o f o n l y t h r e e s o l e n o i d s . A f i n a l p r o t o t y p e s i z e and c o l o u r grader would c o n t a i n t h i r t e e n o p t o - i s o l a t o r s and t r i a c s , and t h i r t e e n s o l e n o i d s mounted on a long conveyor system. I t was b e l i e v e d t h a t c o n s t r u c t i o n o f the f i n a l p r o t o t y p e was not nec e s s a r y t o f u l f i l l p r e s e n t o b j e c t i v e s . 173 P u l s e Generator and Timer C i r c u i t s (Box A, F i g u r e 7.1) A schematic o f the p u l s e g e n e r a t o r and ti m e r c i r -c u i t s i s shown i n F i g u r e 7.2. A p e r i o d sampling o f about one second was chosen over which the b e l t speed would be monitored. The i n p u t t o the p u l s e g e n e r a t o r i s CLOCK A, which v a r i e s from about 24 to 120 Hz. A sampling p e r i o d o f l e s s than one second c o u l d r e s u l t i n an i n t e g r a t i o n o f l e s s than 24 p u l s e s , i n c u r r i n g l a r g e e r r o r s , s i n c e the i n t e g r a t i o n e r r o r i n c r e a s e s w i t h d e c r e a s i n g number o f p u l s e s . (A b e l t speed o f l e s s than 1 f t / s e c (30 cm/sec) would produce the same e r r o r s ) . I n t e g r a t i o n over s e v e r a l seconds would r e s u l t i n too much d r i f t i n the p r e v i o u s l y s t o r e d i n t e g r a t i o n r e s u l t . A c l o c k s i g n a l o f 0.1 sec p e r i o d w a s generated u s i n g NAND 1 and NAND 2 and t i m i n g components and C^. The p e r i o d o f the c l o c k s i g n a l i s d e f i n e d as: T = 1.4 R-j^  C1 [7-12] l e t t i n g = 0.1 yF and T = 0.1 sec then R x = 714 KQ [7-13] R^ was chosen as a 1 Meg potentiometer t o a l l o w adjustment o f the p e r i o d . R i s an i n p u t p r o t e c t i o n r e s i s -t o r , which maintains s t a b i l i t y , and i s g e n e r a l l y t wice R^. The sampling c l o c k i s gated v i a one o f the NAND 1 i n p u t s , #1* i n F i g u r e 7.2. The sampling c l o c k must be * # r e f e r s t o c i r c l e d p o i n t s i n the f i g u r e . 174 FIGURE 7.2 PULSE GENERATOR AND TIMER CIRCUITS N0R6)O—<J INTEGRATE lo) SWITCH TO O UPPATE. SWITCH TO AWAiOS INVERTER PRECEDING, WTEGRATOR Rz<> IOOK 175 s y n c h r o n i z e d w i t h the CLOCK A frequency so t h a t the same number o f p u l s e s are always b e i n g i n t e g r a t e d . The s y n c h r o n i -z a t i o n i s ensured through the use o f the R/S l a t c h comprised of NOR 1 and NOR 2. The sampling c l o c k operates o n l y when #1 i s HIGH. The sampling c l o c k output, #2, i s f e d i n t o a CD4017 decade counter having t e n decoded o u t p u t s . The r e s e t i n p u t o f the CD4017 i s norma l l y low, mai n t a i n e d by the presence o f CLOCK A a t i n p u t #3 o f the l a t c h . The "8" decoded output, #4, goes HIGH f o r 100 ms a f t e r 8 sampling c l o c k p u l s e s , o r T = 800 ms. The "9" decoded output, #5, goes HIGH f o r 100 ms a f t e r 9 sampling c l o c k p u l s e s , o r T = 900 ms. As soon as #5 goes HIGH, the l a t c h output #1 goes low, thus s t o p p i n g the sampling c l o c k . A t the same time, the CD4017 r e s e t i n p u t goes HIGH, thus r e s e t t i n g the count e r t o ze r o . The sampling c l o c k does not s t a r t a g a i n u n t i l the next p o s i t i v e g o ing CLOCK A p u l s e appears a t i n p u t #3. T h i s assures s y n c h r o n i z a -t i o n o f the two c l o c k s i g n a l s . The p u l s e g e n e r a t o r i s a monostable m u l t i v i b r a t o r c i r c u i t * comprised o f NAND 3 and NAND 4. Every time the CLOCK A s i g n a l goes LOW, a s h o r t p o s i t i v e going p u l s e o f about At = 658 us i s produced a t #6. T h i s p u l s e i s i n v e r t e d through NOR 3 and appears a t the i n p u t to NOR 4, #7. The output o f NOR 4, #8, i s the complement o f #7 o n l y when #4 i s LOW. I f #4 i s HIGH, then #8 i s always LOW. As p r e v i o u s l y * The component s e l e c t i o n o f t h i s c i r c u i t i s d e s c r i b e d l a t e r . 176 mentioned, #4 i s LOW f o r 800 ms thus a l l o w i n g the p u l s e s o f the p u l s e g e n e r a t o r t o appear a t #8 f o r 800 ms. The p u l s e s at #8 are the p u l s e s t o be i n t e g r a t e d . O p e r a t i o n of the i n t e g r a t o r and sto r a g e c i r c u i t (Box B, F i g u r e 7.1) i s c o n t r o l l e d by output #4 and which t r i g g e r s the UPDATE tim e r comprised o f NAND 5 and NAND 6. The UPDATE t i m e r o u t p u t , #9, i s norma l l y LOW, t h e r e f o r e the #4 s i g n a l appears f i r s t i n v e r t e d through NOR 5 and ag a i n through NOR 6 a t #10. As soon as #4 goes HIGH, the i n v e r t e d s i g n a l a t #11 goes LOW, t r i g g e r i n g the UPDATE time t o produce a 66 ms p u l s e a t #9. The 66 ms time p e r i o d was a r b i t r a r i l y chosen, and i s not c r i t i c a l . The p u l s e a l l o w s the output o f the i n t e g r a t o r to be t r a n s f e r r e d t o the sto r a g e c i r c u i t , thus u p d a t i n g the sto r a g e i n f o r m a t i o n . The output o f NOR 6, #10, has not changed d u r i n g the 66 ms p e r i o d , s i n c e the f o r -mer "1", "0" c o n d i t i o n s a t i n p u t s #11 and #9 have r e v e r s e d t o "O", "1", r e s u l t i n g i n the i n t e g r a t o r p u l s e a t #10 s t i l l b e i n g LOW. Only a f t e r the st o r a g e c i r c u i t has been updated, i . e . a f t e r the 66 ms has e l a p s e d , does #10 go HIGH, thus r e s e t t i n g the i n t e g r a t o r t o z e r o . The i n t e g r a t o r remains r e s e t f o r 34 ms. The sampling c l o c k i s then stopped by a HIGH appearing a t #5, and i s then r e s t a r t e d by the CLOCK A s i g n a l appearing a t #3. I n t e g r a t i o n o f the 658 ys p u l s e s s t a r t s again f o r a p e r i o d o f 800 ms. 177 I n t e g r a t o r and Storage C i r c u i t (Box B, F i g u r e 7.1) The i n t e g r a t o r and st o r a g e c i r c u i t i s shown i n F i g u r e 7.3. The e q u a t i o n governing the output of the i n t e -g r a t o r , comprised o f the 741 Op. Amp. and , C^, i s : E = - R 3 C 3 e ± d t [7-14] where e^ = i n p u t v o l t a g e E = output v o l t a g e or r e f e r r i n g t o e q u a t i o n [7-5]j E = - [f e. At T ] . [7-15] In o r d e r t o m a i n t a i n s m a l l r e s i s t a n c e and c a p a c i -tance v a l u e s , R 3 was chosen as 1W, and C 3 as 0.1 yF. Now eq u a t i o n [7-15] becomes: E = - 10 [f e. At T] . [7-16] In o r d e r t o s t a y w i t h i n the o p e r a t i n g v o l t a g e range, f , e^, At, or T must now be d i v i d e d by 10. I t was found advantageous to d i v i d e At by 10. T h e r e f o r e e q u a t i o n [7-7] becomes: A tmax = IMOT t 7 " 1 7 ] and s i n c e T = 800 ms ( i n t e g r a t i o n t i m e ) , [7-17] becomes At = 694 ys. [7-18] max J For t h i s reason, a n d C2 w e r e chosen i n the p u l s e g e n e r a t o r c i r c u i t t o produce a p u l s e c l o s e t o 694 ys, which turned out F I G U R E 7.3 I N T E G R A T O R A N D S T O R A G E C I R C U I T 178 179 to be At = 658 ys, when st a n d a r d c a p a c i t o r s and r e s i s t o r s were used. (Refer t o F i g u r e 7.2). R e s e t t i n g o f the i n t e g r a t o r t o zero i s accomplished through the use of a CD4066 b i l a t e r a l s w i t c h a c r o s s C^. Si n c e the b i l a t e r a l s w i t c h operates on a +15 v o l t supply, i t was u n d e s i r a b l e f o r the i n t e g r a t o r output t o go n e g a t i v e , as suggested by eq u a t i o n [7-16] . The p o s i t i v e i n p u t p u l s e s to the i n t e g r a t o r were f i r s t i n v e r t e d u s i n g a u n i t y g a i n 741 a m p l i f i e r , thus making e^ n e g a t i v e , and E p o s i t i v e . A standard o f f s e t c i r c u i t was used t o a d j u s t the i n t e g r a t o r f o r zero d r i f t . The IN914 a t the i n t e g r a t o r out-I put was used t o ensure t h a t no n e g a t i v e v o l t a g e would appear a c r o s s e i t h e r o f the two b i l a t e r a l s w i t c h e s . R . i s a c u r r e n t 4 p r o t e c t i o n r e s i s t o r . The second b i l a t e r a l s w i t c h c o n t r o l s the UPDATE i n f o r m a t i o n t o the h i g h impedence i n p u t o f the LM302 v o l t a g e f o l l o w e r . The i n t e g r a t o r output i s connected t o the i n p u t of the LM302 f o r the l a s t 66 ms o f i n t e g r a t i o n time, thus a l l o w i n g t o charge t o the new i n t e g r a t o r output v o l t a g e . When the b i l a t e r a l s w i t c h i s reopened a f t e r the 66 ms dura-12 t i o n , the c a p a c i t o r d i s c h a r g e s through the 10 ft i n p u t o f the LM302 and the 1 0 1 2 ft " o f f " r e s i s t a n c e o f the CD4066. Very l i t t l e charge i s l o s t over the 800 ms i n t e g r a t i o n p e r i o d which f o l l o w s i n i t i a l s t o r a g e . The LM302 output remains r e l a t i v e l y c o n s t a n t f o r a g i v e n conveyor b e l t speed. The output o f the LM302 was measured f o r s e v e r a l 180 conveyor b e l t speeds, and the t h e o r e t i c a l v a l u e s were c a l c u l a t e d u s i n g e q u a t i o n [7-16] by l e t t i n g e. = 15 v o l t s l At = 658 ys and T = 800 ms. The t h e o r e t i c a l and e x p e r i m e n t a l v a l u e s are l i s t e d i n Table 7.1. 181 TABLE 7.1 THEORETICAL AND MEASURED INTEGRATOR OUTPUT VOLTAGES AT VARIOUS CONVEYOR BELT SPEEDS. CLOCK A Theoretical Measured Freq. (Hz) E (volts) E (volts) 30 2.4 2.3 40 3.2 3.1 50 3.9 4.0 60 4.7 4.8 70 5.5 5.5 120 9.5. x 9.2 182 Ramp Generator and Storage C i r c u i t (Box C, F i g u r e 7.1) A schematic of the ramp ge n e r a t o r and s t o r a g e c i r c u i t i s shown i n F i g u r e 7.4. The ramp gener a t o r i s an i n t e g r a t o r as suggested by e q u a t i o n [7-9]: •P D = A Edt [7-9] . 0 The e q u a t i o n f o r the i n t e g r a t o r i s : D = - R 5 C 5 e ± d t [7-19] T h e r e f o r e i n [7-9], A = R 5 C 5 and E = - e.. x From [7-11] A = 19 / T h e r e f o r e R 5 C 5 = 0.05 [7-20] L e t t i n g R<- = 1 Mft then C r = 0.05 uF o A s u i t a b l e v a l u e f o r C 5 = 0.047 yF. As i n the case f o r the i n t e g r a t o r ( F i g u r e 7.3), the i n p u t was f i r s t i n v e r t e d w i t h a u n i t g a i n 741 Op Amp, i n o r d e r t o m a i n t a i n a p o s i t i v e ramp ge n e r a t o r output, and to prevent a n e g a t i v e v o l t a g e from appearing a c r o s s the CD4066 b i l a t e r a l s w i t c h . The IN914 a l s o a c t s as a p r o t e c t i o n a g a i n s t n e g a t i v e v o l t a g e s a t the ramp gener a t o r output. F I G U R E 7.4 R A M P G E N E R A T O R A N D S T O R A G E C I R C U I T 183 SAMPLE +SSv INPUT INPUT , ' 184 The SAMPLE s i g n a l from the c o l o u r s o r t e r ( F i g u r e 3.12) i s the measure o f the tomato diameter. I t c o n t r o l s the two b i l a t e r a l s w i t c h e s , SW1 and SW2. While a tomato i s under the s e n s i n g head, the SAMPLE i s HIGH, and t h e r e f o r e SW1 i s open (due t o the NAND gate i n v e r t e r ) and SW2 i s c l o s e d . The ramp ge n e r a t o r i n t e g r a t e s the incoming v o l t a g e , E, f o r the d u r a t i o n o f the SAMPLE p u l s e , and a t the same time charges t o the ramp ge n e r a t o r output v o l t a g e . When the SAMPLE s i g n a l goes LOW, SW1 d i s c h a r g e s c a p a c i t o r Cg, thus r e s e t t i n g the ramp g e n e r a t o r . At the same time the ramp gener a t o r i s s e p a r a t e d from Cc as SW2 i s opened, D l e a v i n g Cg charged. The b i l a t e r a l s w i t c h , SW3, i s c o n t r o l l e d by the PEAK DETECTOR 1 RESET p u l s e from the c o l o u r grader, and i s t h e r e f o r e LOW f o r the d u r a t i o n o f the SAMPLE s i g n a l p l u s the 210 ys WRITE s i g n a l from the c o l o u r grader. The 210 ys allows the s t o r e d v o l t a g e t o be compared i n the comparator c i r c u i t s a f t e r which C^ i s d i s c h a r g e d to ground u n t i l the next tomato a r r i v e s under the s e n s i n g head. 185 Comparator 4, 5, 6, and 7 (Box D, F i g u r e 7.1) The s i z e grader comparator c i r c u i t i s s i m i l a r t o the c o l o u r grader comparator c i r c u i t , except t h a t an e x t r a comparator has been added to i n c l u d e f i v e c a t e g o r i e s i n s t e a d o f o n l y f o u r . The schematic diagram o f the comparator c i r -c u i t i s shown i n F i g u r e 7.5. The comparators have been numbered from 4 t o 7 to d i s t i n g u i s h them from the t h r e e comparator c i r c u i t s o f the c o l o u r grader. The f u n c t i o n o f COMP. 4 i s analagous t o COMP. 1 of the c o l o u r grader, i n t h a t COMP. 4 has V g E T ^ i n t e r n a l l y a d j u s t e d f o r the s m a l l e s t tomato s i z e t o be c o n s i d e r e d , i n this c a s e . 1.5 inches (3.8 cm). When a tomato l e s s than 1.5 inches (3.8 cm) diameter passes under the s e n s i n g head, the output o f COMP. 4 remains HIGH, as normal, thus i n h i b i t i n g i n f o r m a t i o n from e n t e r i n g any o f the memories. Tomatoes o f g r e a t e r s i z e produce a LOW output a t COMP. 4, and data may be e n t e r e d i n t o the memories a c c o r d i n g t o the c o n d i t i o n s a t the outputs o f COMP. 5, COMP. 6, and COMP. 7. The s i z e c a t e g o r i e s and the output s t a t e s o f the f o u r comparators are l i s t e d i n Table 7.2. The pot e n t i o m e t e r s f o r V 0 „ m _, V_,_m and V 0_, m are mounted on the f r o n t p a n e l o f the s i z e and c o l o u r grader t o a l l o w ready access and adjustment. As i n the c o l o u r s o r t e r , i n p u t p r o t e c t i o n diodes and an output clamping diode a re used t o keep the compara-t o r ' s output compatible w i t h the CMOS d e v i c e s . 186 F I G U R E 7 .5 C O M P A R A T O R C I R C U I T . , 187 TABLE 7.2 OUTPUT STATES OF COMP. 4, COMP. 5, COMP. 6, and COMP. 7 FOR FIVE SIZE CATEGORIES. Size Category COMP. 4 COMP. 5 COMP., 6 COMP CULL 1 0 0 0 SMALL 0 0 0 0 MEDIUM 0 1 0 0 LARGE 0 1 1 0 EXTRA LARGE 0 1 1 1 188 S i n c e a l l green tomatoes were t o be e j e c t e d a t one l o c a t i o n , the output o f COMP. 1 o f the c o l o u r grader alone i n combination w i t h the WRITE p u l s e a c t e d as the i n p u t i n f o r m a t i o n f o r the GREEN s h i f t r e g i s t e r memory. I t was dec i d e d t h a t a l l tomatoes l e s s than 1.5 inches (3.8 cm) diameter, r e p r e s e n t e d by no change i n the output o f COMP. 4 would r o l l o f f the end o f the conveyor b e l t i n the s i z e / c o l o u r grader d e s i g n . T h i s l e a v e s COMP. 2, COMP. 3, COMP. 5, COMP. 6, and COMP. 7 t o produce output s t a t e s f o r the twelve remaining c o l o u r c a t e g o r i e s , as shown i n Table 7.3. 189 TABLE 7.3 OUTPUT STATES OF COMPARATORS 2,3,5,6,7 FOR TWELVE SIZE/COLOUR CATEGORIES. CATEGORY OUTPUT STATES Colour S i z e COMP.2 COMP.3 COMP.5 COMP.6 COMP.7 Turning Small 0 0 0 0 0 Turning Medium 0 0 1 0 0 Turning Large 0 0 1 1 0 T u r n i n g E x t r a Large 0 0 1 1 1 Semi Ripe Small 1 0 0 0 0 Semi Ripe Medium 1 0 1 0 0 Semi Ripe Large 1 0 1 1 0 Semi Ripe E x t r a Large 1 0 1 1 1 Firm Ripe Small 1 1 0 0 0 Firm Ripe Medium 1 1 1 0 0 Firm Ripe -Large 1 1 1 1 0 Firm Ripe E x t r a Large 1 1 1 1 1 190 Decoding Gates (Box E, F i g u r e 7.1) A schematic o f the decoding gates i s shown i n F i g u r e 7.6. The f u n c t i o n and d e s i g n o f the decoding gates i s s i m i l a r t o t h a t o f the c o l o u r grader decoding gates i n t h a t a s i n g l e output i s LOW f o r the d u r a t i o n o f the WRITE p u l s e f o r a s p e c i f i c combination of comparator outputs. The main d i f f e r e n c e between the c o l o u r grader and s i z e grader decoding gates i s t h a t the l a t t e r uses 3-input NOR gate s , NOR 1, NOR 2, NOR 3, and NOR 4, i n s t e a d o f the two i n p u t g a t e s . The 3-input NOR gate IC, a CD4025, c o n t a i n s 3 gates and i n o r d e r t o minimize package count, the i n v e r t e r NOR 5 i s a 3-input gate, and NOR 6 a c t s as a 2-input gate, w i t h two o f the i n p u t s t i e d t o g e t h e r . The WRITE i n p u t p u l s e i s o b t a i n e d from the c o l o u r grader, i n v e r t e d through NOR 5 and gated through NOR 6 whenever the output o f COMP. 4 i s LOW. T h i s enables the outputs o f NOR 1, NOR 2, NOR 3 and NOR 4 to be t r a n s f e r r e d t o the outputs o f NAND 1, NAND 2, NAND 3, and NAND 4. FIGURE 7.6 DECODING GATES 191 IMPUTS IL WKITE 1— l.SK o - V v V O-AA/V-COMP.S l.SK COMP- 6 l.SK C M / v V COMP. 7 NOR l N0R6) NORZ N0R.3 LARGE. 192 L a t c h i n g C i r c u i t (Box F, F i g u r e 7.1) A schematic o f the l a t c h i n g c i r c u i t i s shown i n F i g u r e 7.7. The des i g n and f u n c t i o n o f t h i s l a t c h i n g c i r c u i t i s s i m i l a r t o the c o l o u r grader l a t c h i n g c i r c u i t . The main d i f f e r e n c e s are t h a t the new c i r c u i t uses 4-input NAND gates i n s t e a d o f 3-input NAND gate s , and the l a t c h e s which were comprised o f 2-input NAND gates have been r e p l a c e d by a s i n g l e IC, a CD4044 which c o n t a i n s 4 such l a t c h e s . The output of COMP. 1 and the WRITE i n p u t , both from the c o l o u r grader are f e d i n t o NAND 1. I f the output of COMP. 1 i s HIGH and a WRITE s i g n a l appears, the output o f NAND 1 goes LOW ( i n d i c a t i n g a green tomato). The LOW s i g n a l s e t s the output o f the l a t c h comprised o f 2-input NAND gate s , NAND 2, and NAND 3, to a HIGH s t a t e . The l a t c h output i s fed d i r e c t l y i n t o the green c a t e g o r y s h i f t r e g i s t e r memory. The l a t c h i s r e s e t , as are the CD40 44 l a t c h e s by the LATCH RESET p u l s e o b t a i n e d from the c o l o u r grader. F I G U R E 7.7 L A T C H I N G C I R C U I T 193 INPUTS IS SMALL TT MEDIUM TT LAR&E. to SXTRA LAK<S£ IT. LATCH RESET V2JZD40IZ. '/ZCD+OIZ VZCD4-0/Z OUTPUTS TO DECODER V4CD4044 IS —o SMALL IS — o M E O / U M LARGE. '/4C04044 IS EXTRA LARGE. COMP. I IN o SL WRITE IN SRCLS.AI OUTPUT TO MEMORY 194 S i z e / C o l o u r Decoder (Box G, F i g u r e 7.1) The s i z e / c o l o u r decoder c i r c u i t i s a s e r i e s o f gates used t o decode the c o l o u r g r ader and s i z e grader comparator outputs i n t o a s i n g l e output c o r r e s p o n d i n g t o a p a r t i c u l a r s i z e / c o l o u r c a t e g o r y , as d e s c r i b e d i n Table 7.3. The schematic o f the s i z e / c o l o u r decoder i s shown i n F i g u r e 7.8. Both s i z e and c o l o u r c a t e g o r y i n p u t s i g n a l s are LOW s i g n a l s . F o r any s i n g l e tomato, o n l y one s i z e and one c o l o u r s i g n a l w i l l be p r e s e n t a t the decoder i n p u t s . Consequently, o n l y one o f the outputs o f the twelve NOR gates w i l l go HIGH. ^ The i n p u t s t o the 2-input NOR gates are connected t o the outputs o f the s i z e g r a d e r l a t c h i n g c i r c u i t s , F i g u r e 7.7, and the c o l o u r grader l a t c h i n g c i r c u i t , F i g u r e 3.16. The twelve outputs are connected d i r e c t l y t o the i n p u t s o f the s h i f t r e g i s t e r memories. F I G U R E 7.8 S I Z E / C O L O U R D E C O D E R C I R C U I T 195 INPUTS  SIZE COLOUR SMALL Q_ TURNING MEDIUM LARGE EXTRA LARGE SEA4I-RlPZ F I R M RIPE = 3 > ; = L > OUTPUTS SIZE/COLOUR. SMALL/TURNING MEDIUM/TURNING LARGE./* TURN/MS X L / TURNING -O SMALL/ SEMI-RIPE -O MEDIUM/SEMI-RIPE. -O L A R G C / S E M I -K / P E -O XL/S£Af/-RIPE -O SMfiLL/FIRM RIPE -O MEDIUM/FIRM R I P E -O LARGE/FIRM RIPE. -O X L / F I R M « I P £ 196 Memory C i r c u i t (Box H, F i g u r e 7.1) The d e s i g n o f the s i z e / c o l o u r memory c i r c u i t i s s i m i l a r t o t h a t o f the c o l o u r g r ader memory c i r c u i t i n t h a t each s i z e / c o l o u r c a t e g o r y s h i f t r e g i s t e r i s of a l e n g t h (no. o f b i t s ) c o r r e s p o n d i n g t o a l i n e a l d i s t a n c e downstream from the se n s i n g head where the e j e c t s t a t i o n f o r t h a t s i z e / c o l o u r c a t e g o r y i s l o c a t e d . The f u n c t i o n of each s h i f t r e g i s t e r i s the same as f o r the c o l o u r grader — t o s t o r e c a t e g o r y i n f o r m a t i o n f o r a tomato as the tomato t r a v e l s downstream from the s e n s i n g head, u n t i l i t reaches i t s e j e c t s t a t i o n , a t which time the s t o r e d s i g n a l t r i g g e r s an e l e c t r o m e c h a n i c a l d e v i c e t o e j e c t the tomato from the con-veyor b e l t . The main d i f f e r e n c e between the c o l o u r grader memory and the s i z e / c o l o u r memory i s i n the type o f s h i f t r e g i s t e r used. The s h i f t r e g i s t e r s used i n the c o l o u r grader were o f the d u a l 4 - b i t type (CD4015) ha v i n g a maximum 8 b i t s t o r a g e c a p a b i l i t y per IC. When the c o l o u r grader was b e i n g designed, pro-grammable s h i f t r e g i s t e r s were not a v a i l a b l e . However, d u r i n g the de s i g n o f the s i z e / c o l o u r grader the MC14557 became commercially a v a i l a b l e . The MC14557 can be programmed f o r a l e n g t h from 1 t o 64 b i t s , depending on the c o n d i t i o n s a t the s i x programmable i n p u t s . These new s h i f t r e g i s t e r s were i n c o r p o r a t e d i n t o the s i z e / c o l o u r grader because of t h e i r v e r s a t i l i t y . 197 The s i x programmable i n p u t s which c o n t r o l the s h i f t r e g i s t e r l e n g t h , were connected t o s i x m i n i a t u r e SPST r o c k e r s w i t c h e s . The ro c k e r s w i t c h assembly c o n s i s t e d of a bank of seven switches which c o u l d be plugged i n t o a sta n d a r d 14 p i n IC soc k e t , making . i t i d e a l f o r the p r e s e n t d e s i g n . The schematic f o r one o f the t h i r t e e n s h i f t r e g i s t e r c i r c u i t s used i n the s i z e / c o l o u r memory c i r c u i t i s shown i n F i g u r e 7.9. S i x 1 Mft " p u l l up" r e s i s t o r s are used a t the programmable i n p u t s , L I , L2, L4, L8, L16, and L32, to keep these i n p u t s n o r m a l l y HIGH u n l e s s a r o c k e r s w i t c h i s c l o s e d , making the i n p u t LOW. The r e l a t i o n s h i p between the l e n g t h o f the s h i f t r e g i s t e r and the c o n d i t i o n o f the programmable i n p u t s i s shown i n Tabl e 7.4. Note t h a t the DATA i n p u t i s a p o s i t i v e going p u l s e i n s t e a d o f the n e g a t i v e going p u l s e used i n the. CD4015 o f the c o l o u r grader. The outputs o f the s h i f t r e g i s t e r s must be LOW i n or d e r t o a c t i v a t e the o p t o - i s o l a t o r s . The CD4015 has o n l y a Q output, thus the i n p u t t o the memory must be of the same s t a t e as the d e s i r e d output — LOW. The MC14557 has two o u t p u t s , a Q and a Q. T h i s a l l o w s a c h o i c e o f e i t h e r a n o r m a l l y HIGH or norm a l l y LOW output. S i n c e the s i z e / c o l o u r decoder outputs go HIGH when a tomato i s c a t e -g o r i z e d , the HIGH may be s t o r e d i n the MC14557 and the Q output used t o fe e d a LOW s i g n a l t o the o p t o - i s o l a t o r c i r c u i t . F I G U R E 7 . 9 O N E O F 1 3 S H I F T R E G I S T E R C I R C U I T S U S E D IN T H E S I Z E / C O L O U R M E M O R Y C I R C U I T 198 +/5V CLOCK 0 IN 199 TABLE 7.4 SHIFT REGISTER LENGTH AND INPUT CONDITIONS AT THE SIX PROGRAMMABLE INPUTS. INPUT SHIFT REGISTER L32 L16 L8 L4 L2 LI LENGTH 0 0 0 0 0 0 1 Bi t 0 0 0 0 0 1 2 Bits 0 0 0 0 1 0 3 Bits 0 0 0 0 1 1 4 Bits 0 0 0 1 0 0 5 Bits 1 0 0 0 0 • 0 33 Bits 1 0 • 0 0 0 • 1 • 34 Bits • 1 • 1 1 1 1 • • 0 63 Bits 1 1 1 1 1 1 64 Bits 200 The CLOCK B s i g n a l i s used t o advance the s h i f t r e g i s t e r s , as was the case i n the c o l o u r grader. The CLOCK B s i g n a l i s o b t a i n e d from the c o l o u r grader data l a t c h t i m e r c i r c u i t , F i g u r e 3.17. The schematic o f the complete memory c i r c u i t i s shown i n F i g u r e 7.10. For s i m p l i c i t y o n l y the CLOCK, DATA and Q outputs are shown f o r each s h i f t r e g i s t e r . A l l o t h e r p i n s of each MC14557 are connected as shown i n F i g u r e 7.9. With a 64 b i t storage c a p a c i t y and 1.5 inches (3.8 cm) o f conveyor b e l t movement per CLOCK B c y c l e , the maximum d i s t a n c e downstream from the s e n s i n g head t h a t a e j e c t s t a t i o n can be l o c a t e d i s 8 f e e t (244 cm). With 6 inches (15 cm) between e j e c t s t a t i o n s , i t i s p o s s i b l e t o accommo-date the 13 s t a t i o n s r e q u i r e d . I f g r e a t e r s p a c i n g between e j e c t l o c a t i o n s i s d e s i r e d , any number of MC14557 s h i f t r e g i s t e r s may be cascaded t o o b t a i n the s h i f t l e n g t h r e q u i r e d , where the output o f the f i r s t i s connected t o the DATA i n p u t o f the second and so on. Two s h i f t r e g i s t e r s i n s e r i e s can s t o r e data up t o 16 f e e t (488 cm) downstream from the s e n s i n g head. The DATA i n p u t s o f the f i r s t 12 s h i f t r e g i s t e r s are connected t o the outputs o f the s i z e / c o l o u r decoder c i r c u i t . The t h i r t e e n t h s h i f t r e g i s t e r s t o r e s the data f o r a l l s i z e s o f green tomatoes, and i t s DATA i n p u t i s connected d i r e c t l y t o output o f the l a t c h comprised o f NAND 2 and NAND 3, F i g u r e 7.7. A l l Q to the output of the r e g i s t e r s are connected t o the o p t o - i s o l a t o r c i r c u i t . F I G U R E 7 . 1 0 S I Z E / C O L O U R M E M O R Y C I R C U I T ' ; INPUTS SIZE J COLOUR SMALL/TURNING MEDIUM/TURNING LARGE]'TURNING XL j TURNING) MCI45S7 -I DATA CLOCK MCI4S57 - 2 DATA Q" CLOCK MC/4SS7 -3 DATA <? CLOCK MCI+SS7 - 4 D A T A Q C/.OCK OUTPUTS TO OPTO-ISOLATOR S LARGE/FIRM RIPE X L / FIRM RIPE ALL SIZES/'GREEN (FROM LATCHING CIRCUIT) MCI4S57 - // DATA Q CLOCK 1  MC14-557- IZ DATA Q CLOCK MC 14-557- 13 DATA Q CLOCK z z n — o  CLOCK B IN 202 O p t o - I s o l a t o r and T r i a c C i r c u i t (Box 1, F i g u r e 7.1) The o p t o - i s o l a t o r and t r i a c c i r c u i t used to t e s t the s i z e / c o l o u r grader was the same one used i n the c o l o u r g r a d er. The s i z e / c o l o u r c a t e g o r i e s were t h e r e f o r e t e s t e d t h r e e a t a time. The proposed o p t o - i s o l a t o r and t r i a c c i r c u i t f o r the f i n a l s i z e / c o l o u r p r o t o t y p e would c o n s i s t of 13 r a t h e r than the 3 u n i t s comprised of the opto-i s o l a t o r and t r i a c shown i n F i g u r e 3.20. Of prime concern i n the d e s i g n o f the 13 u n i t c i r c u i t i s the c u r r e n t d r a i n i n each u n i t from each of the two power s u p p l i e s — the +15 v o l t IC supply, and the +15 v o l t u n r e g u l a t e d s u p p l y . The maximum c u r r e n t d r a i n per u n i t (Figure 3.20) i s 32 ma through a 470ft r e s i s t o r . The IC supply must be ab l e t o supply 416 ma f o r the 13 u n i t s , p l u s the c u r r e n t demanded by the o t h e r c i r c u i t r y . In each u n i t , the maximum c u r r e n t requirement from the +15v u n r e g u l a t e d supply i s 10 ma, due t o the 1.5 Kft r e s i s t o r i n the p h o t o t r a n s i s t o r c i r c u i t . The u n r e g u l a t e d supply must be capable o f s u p p l y i n g a minimum of 130 ma. The t r i a c power supply shown i n F i g u r e 3.22, would be adequate. The s o l e n o i d s used i n the c o l o u r grader consumed 16.7 watts each, and i f the same s o l e n o i d s were employed, the 115v AC power consumption f o r the e n t i r e s i z e / c o l o u r g r a d er u n i t would be about 2 30 watts maximum. 203 MECHANICAL HANDLING SYSTEM The s i z e / c o l o u r grader mechanical h a n d l i n g system was i d e n t i c a l to t h a t used i n the c o l o u r g r a der. The same s o l e n o i d s , pneumatic supply and conveyor were used. Recommended improvements w i l l be d i s c u s s e d i n a l a t e r s e c t i o n . H A P T E R 8 S Y S T E M T E S T I N G 205 INTRODUCTION T e s t i n g of the s i z e / c o l o u r grader was c o n c e n t r a t e d around the s i z e c a t e g o r y s e c t i o n of the grader, s i n c e c o l o u r g r a d i n g t e s t s had been conducted e a r l i e r , as o u t l i n e d i n Chapter 4. L i m i t s were s e t f o r s i z e and c o l o u r c a t e g o r i e s by a d j u s t i n g the V c o n t r o l s of the comparators. The a b i l i t y o f the grader to c l a s s i f y tomatoes a c c u r a t e l y was e v a l u a t e d by examining the number of tomatoes which were m i s c l a s s i f i e d i n a g i v e n s i z e c a t e g o r y . Both o v e r s i z e and u n d e r s i z e tomatoes were i n c l u d e d i n the m i s c l a s s i f i e d category i n a l l except the e x t r a l a r g e group, where no over-s i z e c l a s s i f i c a t i o n e x i s t s . M i s c l a s s i f i c a t i o n s due t o mechanical problems a s s o c i a t e d w i t h the e j e c t mechanisms were not i n c l u d e d . T e s t i n g of s m a l l tomatoes was v i r t u a l l y i m p o s s i b l e , s i n c e w i t h the p r e s e n t conveyor b e l t system, the r e l a t i v e l y s p h e r i c a l s m a l l tomatoes would not s t a y on the f l a t b e l t . Consequently, t e s t s were conducted on o n l y the e x t r a l a r g e , l a r g e , and medium s i z e c a t e g o r i e s . The e f f e c t of tomato c o l o u r on the s i z e measured by the grader was i n v e s t i g a t e d to e s t a b l i s h whether tomatoes of d i f f e r e n t c o l o u r but equal s i z e would be s i z e graded d i f f e r e n t l y . The c o l o u r c a t e g o r i e s t e s t e d were f i r m r i p e , semi-r i p e and t u r n i n g . The number of green tomatoes a v a i l a b l e a t the time o f t e s t i n g was too s m a l l to be i n c l u d e d i n any o f the t e s t s . 206 MATERIALS AND METHODS The tomatoes used i n t e s t i n g the s i z e / c o l o u r grader v a r i e d i n s i z e from medium t o e x t r a l a r g e , and i n c o l o u r from t u r n i n g to f i r m r i p e . S i n g u l a t i o n and f e e d i n g o f tomatoes onto the conveyor b e l t was c a r r i e d out manually. The tomatoes were u s u a l l y p l a c e d c a l y x end down, s i n c e t h i s o r i e n t a t i o n was g e n e r a l l y the most s t a b l e . No p a r t i c u l a r e f f o r t was made to p l a c e tomatoes e x a c t l y i n l i n e with the c e n t e r o f the s e n s i n g head, however, the tomatoes were not d e l i b e r a t l y o f f s e t e i t h e r . O r i e n t a t i o n i n the e q u a t o r i a l planewas g e n e r a l l y n e g l e c t e d , except where the d i f f e r e n c e s between DIA. 1 and DIA. 2 were c o n s i d e r e d u n u s u a l l y l a r g e , i n which case the tomatoes were o r i e n t e d w i t h DIA. 1 roughly p a r a l l e l t o the conveyor b e l t c e n t e r l i n e . T e s t s were conducted a t 20 i n c h e s / s e c (51 cm/sec) b e l t speed, o r 40 Hz CLOCK A frequency. The c o l o u r compara-t o r s e t t i n g s , V S E T 1 # V g E T 2 , and V S E T 3 were chosen so t h a t a r e l a t i v e l y u n i f o r m n u m e r i c a l s p l i t o f the samples i n the t h r e e c o l o u r c a t e g o r i e s , f i r m r i p e , s e m i - r i p e and t u r n i n g would r e s u l t . The g r e e n / t u r n i n g s p l i t was a t V 0 „ m , = 1 v o l t ; bhi 1 JL the t u r n i n g / s e m i - r i p e s p l i t was a t V" S E T 2 = 4.8 v o l t s ; the s e m i - r i p e / f i r m r i p e s p l i t was a t V g E T 3 = 9.3 v o l t s . 207 S i z e c l a s s i f i c a t i o n as o u t l i n e d i n Appendix A, was based on the f o l l o w i n g DIA. 1 ranges; 3.000 i n (7.62 cm) < e x t r a l a r g e 2.250 i n (5.72 cm) < l a r g e < 3.000 i n (7.62 cm) 1.875 i n (4.76 cm) < medium _< 2.250 i n (5.72 cm) The s i z e comparator s e t t i n g s were made u s i n g V S E T 4' V S E T 5' VSET 6' a n d V S E T V. T h e P r o c e d u r e f o r adjustment was as f o l l o w s : a) A tomato wi t h DIA. 1 = 3.00 i n (7.62 cm) was chosen as a s i z e s t a n d a r d . b) _ was a d j u s t e d so t h a t the st a n d a r d tomato was c o n s i s t e n t l y c l a s s i f i e d i n the l a r g e c a t e g o r y . c) V 0__ was decreased u n t i l the sta n d a r d tomato was con-far, l / s i s t e n t l y c l a s s i f i e d i n the e x t r a l a r g e c a t e g o r y . d) V 0 „ m _ was i n c r e a s e d j u s t enough so t h a t the standard SET / tomato was again c o n s i s t e n t l y c l a s s i f i e d as l a r g e . Steps a) through d) were repeated u s i n g d i f f e r e n t s t a n d a r d tomatoes f o r each o f the V c „ _ adjustments remaining. A 2.250 i n c h (5.72 cm) tomato was used t o a d j u s t V„„_ ,, and faJiJ. b a 1.875 i n c h (4.76 cm) tomato was used t o a d j u s t V o c, m c . Since s m a l l tomatoes were not i n c l u d e d i n the t e s t s , V S E T ^ was a d j u s t e d a r b i t r a r i l y , below V g E T ,.. Once the comparator v o l t a g e s were s e t , the tomatoes, 193 i n a l l , were graded by the s i z e / c o l o u r g r a der th r e e s i z e / c o l o u r c a t e g o r i e s a t a time. The o p t o - i s o l a t o r c i r c u i t i n p u t s , F i g u r e 3.20, were connected to thr e e outputs 208 of the s i z e / c o l o u r memory, F i g u r e 7.10, and a l l tomatoes p l a c e d s e q u e n t i a l l y on the conveyor b e l t . Only those tomatoes which belonged to the t h r e e s i z e / c o l o u r c a t e g o r i e s under t e s t were e j e c t e d by the pneumatic system; a l l o t h e r s i z e / c o l o u r c a t e g o r i e s were c o l l e c t e d a t the end of the conveyor. The s o r t e d tomatoes were se p a r a t e d from the r e -mainder. The three o p t o - i s o l a t o r i n p u t s were then connected to t h r e e o t h e r s i z e / c o l o u r c a t e g o r y outputs o f the memory, and the above t e s t i n g procedure c o n t i n u e d by r e g r a d i n g those tomatoes which were c o l l e c t e d at the end of the conveyor u n t i l a l l of the s i z e / c o l o u r c a t e g o r i e s had been t e s t e d (except, o f course, the s m a l l and green c a t e g o r i e s ) . An attempt was made to e s t a b l i s h whether the c o l o u r of a tomato a f f e c t s the measurement of i t s s i z e . An a n a l y s i s of v a r i a n c e on t h r e e c o l o u r c a t e g o r i e s which had been machine graded i n t o the same s i z e c a t e g o r y was c a r r i e d out. The t h r e e c o l o u r c a t e g o r y means i n each s i z e c a t e g o r y were com-pared u s i n g an F - t e s t . The nine machine graded s i z e / c o l o u r c a t e g o r i e s were grouped i n t o t h r e e t h r e e s i z e c a t e g o r i e s — e x t r a l a r g e , l a r g e , and medium. Each s i z e c a t e g o r y now c o n t a i n e d a mixture of f i r m r i p e , s e m i - r i p e , and t u r n i n g tomatoes. In each o f the s i z e c a t e g o r i e s , the number (or percentage) o f m i s c l a s s i f i e d tomatoes was r e c o r d e d . M i s c l a s s i f i e d tomatoes were a l l tomatoes which f e l l o u t s i d e the s i z e c a t e g o r y boundaries 209 s t a t e d p r e v i o u s l y . For example, a m i s c l a s s i f i e d tomato i n the l a r g e category would be any tomato having' a DIA. 1 g r e a t e r than 3.000 inches (7.62 cm) o r having a DIA. 1 l e s s than o r equal t o 2.250 inches (5.72 cm). The e x t r a l a r g e c a t e g o r y has no upper l i m i t , and thus no tomatoes can be c l a s s i f i e d as o v e r s i z e i n t h i s group. The standard d e v i a t i o n of the m i s c l a s s i f i e d tomatoes around a g i v e n s i z e c a t e g o r y c u t - o f f l i m i t was used as the measure o f the machine's a b i l i t y t o a c c u r a t e l y s i z e grade tomatoes. 210 RESULTS AND DISCUSSION A. T h e o r e t i c a l S i z e Category L i m i t s versus  Experimental L i m i t s The v o l t a g e generated by the i n t e g r a t o r c i r c u i t ( F i g ure 7.3) f o r a b e l t speed of 40 Hz or 20 i n / s e c (51 cm/sec), i s E = 3.1 v o l t s (Table 7.1). I n t e g r a t i o n of E f o r the Schmitt t r i g g e r p u l s e width produces the v o l t a g e D which i s the measure of tomato diameter. The p u l s e width may be p r e d i c t e d f o r any diameter a t a g i v e n b e l t speed, and a t h e o r e t i c a l v a l u e o f D c a l c u l a t e d . R e c a l l t h a t , D = A E p [7-10] where A = 1 ( F i g u r e 7.4) R 5 C 5 p = Schmitt t r i g g e r p u l s e width f o r a g i v e n diameter, i n seconds. S u b s t i t u t i n g R 5 = 1 Mft, C 5 = 0.047, and E = 3.1 a t 20 i n / s e c (51 cm/sec) b e l t speed, i n t o [7-10] y i e l d s D = 3.30 d [8-1] where d = 20p = diameter i n i n c h e s . Using [8-1], the t h e o r e t i c a l v o l t a g e s f o r v a r i o u s diameters, i n c l u d i n g the c r i t i c a l c u t - o f f s s e p a r a t i n g s i z e c a t e g o r i e s were c a l c u l a t e d and are l i s t e d i n Table 8.1. The exp e r i m e n t a l v a l u e s o f D, i . e . V S E T 5 , V g E T g , and V g E T ? are l i s t e d i n Table 8.1. The e x p e r i m e n t a l v a l u e s o f D were c o n s i s t e n t l y l e s s than the t h e o r e t i c a l v a l u e s , s u g g e s t i n g t h a t the 211 TABLE 8.1 THEORETICAL AND EXPERIMENTAL VALUES OF D, FOR VARIOUS DIAMETERS. D ( v o l t s ) Diameter, i n c h (cm) T h e o r e t i c a l Experimental 1.500 4.95 (3.810) 1.875 6.18 (4.763) 2.250 7.42 (5.715) 3.000 9.89 (7.620) 3.500 11.54 (8.890) 4 ' 6 5 ( VSET 5> 6.30 ( V S E T ,) 9.30 ( V S E T y) 212 tomatoes appeared s m a l l e r to the grader than t h e i r a c t u a l s i z e . The d i f f e r e n c e between the t h e o r e t i c a l and e x p e r i -mental valu e s appears to be i n v e r s e l y p r o p o r t i o n a l to s i z e , s u g g e s t i n g t h a t the l a r g e r the tomato, the more c l o s e l y the machine-measured diameter approaches the t r u e diameter. R e c a l l i n g t h a t the t h e o r e t i c a l curve o f D versus diameter i s a s t r a i g h t l i n e p a s s i n g through the o r i g i n [8-1], the i n c r e a s i n g d i f f e r e n c e between the t h e o r e t i c a l and e x p e r i -mental valu e s o f D as the diameter de c r e a s e s , as shown i n Table 8.1, suggests t h a t the a c t u a l r e l a t i o n s h i p i s c u r v i l i n e a r . The r e l a t i o n s h i p o f D versus diameter i s p r o b a b l y the same as the r e l a t i o n s h i p between Schmitt t r i g g e r p u l s e width and s t y r o b a l l diameter, shown i n F i g u r e 6.1. The v o l t a g e adjustments o f V S E T 4 , V S E T 5 , V S E T g and V g E T ? should be c a r r i e d out as o u t l i n e d p r e v i o u s l y , as opposed t o s e t t i n g the c u t - o f f v o l t a g e s to the t h e o r e t i c a l v a l u e s . B. E f f e c t of Tomato C o l o u r on S i z e Measurement The mean diameters (DIA. 1) of tomatoes i n each of the t h r e e c o l o u r c a t e g o r i e s were compared f o r each o f the three s i z e c a t e g o r i e s , u s i n g the a n a l y s i s of v a r i a n c e . The v a l u e s of F i n each s i z e c a t e g o r y are l i s t e d i n Table 8.2. The F v a l u e s i n d i c a t e t h a t , i n the l a r g e and medium s i z e c a t e g o r i e s , the mean diameters o f the t h r e e c o l o u r c a t e g o r i e s are not e q u a l . In the l a r g e and medium c a t e g o r i e s , the mean diameters o f the t h r e e c o l o u r c a t e g o r i e s c o n s i s t e n t l y i n c r e a s e d as the redness o f the tomato i n c r e a s e d . The TABLE 8.2 VALUES OF F RESULTING FROM A COMPARISON OF MEAN DIAMETERS OF THREE COLOUR CATEGORIES IN A GIVEN SIZE CATEGORY. S i z e F C a t e g o r y E x t r a l a r g e 1.6t Large 2.9* Medium 5.8** * t S i g n i f i c a n t a t 1% l e v e l S i g n i f i c a n t a t 5% l e v e l Not s i g n i f i c a n t a t 5% l e v e l . 214 d i f f e r e n c e between the mean of the medium/turning c a t e g o r y and the medium/firm r i p e c a t e g o r y was 0.14 i n c h (0.36 cm). Although s t a t i s t i c a l l y s i g n i f i c a n t , the d i f f e r e n c e i s o n l y 7% o f the mean diameter i n the medium ca t e g o r y , which i s probably i n s i g n i f i c a n t , p r a c t i c a l l y . The i n c r e a s i n g mean s i z e w i t h i n c r e a s i n g redness of the tomato may be e x p l a i n e d by the f a c t t h a t the p h o t o t r a n s i s t o r p r e - a m p l i f i e r c i r c u i t s are most s e n s i t i v e t o the r e d wavelengths. The "green" a m p l i f i e r output v o l t a g e i s i n most cases l e s s than the "red" a m p l i f i e r v o l t a g e , so the more r e d i n a tomato o f a g i v e n s i z e , the sooner w i l l i t be d e t e c t e d by the grader, and the lon g e r w i l l i t be seen by the s e n s i n g head. The assumption which must be made i n the use o f a n a l y s i s o f v a r i a n c e i s t h a t the p o p u l a t i o n s whose means are bei n g compared are normally d i s t r i b u t e d . At a g i v e n h a r v e s t date, the s i z e d i s t r i b u t i o n o f a l l tomatoes c o l l e c t e d from a grower are pr o b a b l y n o r m a l l y d i s t r i b u t e d about some mean s i z e . When tomatoes are s u b - d i v i d e d i n t o s i z e c a t e g o r i e s , each categ o r y i s no l o n g e r n o r m a l l y d i s t r i b u t e d . For t h i s reason, the F va l u e s l i s t e d i n Tab l e 8.2 should be c o n s i d e r e d with t h i s f a c t i n mind. C. S i z e Grading A b i l i t y of the S i z e / C o l o u r Grader The a b i l i t y o f the s i z e / c o l o u r g r ader t o s i z e and c o l o u r grade tomatoes i s p i c t o r i a l l y r e p r e s e n t e d by the photographs i n F i g u r e s 8.1, 8.2 and 8.3. F i g u r e 8.1 a, b, and c, shows machine graded e x t r a l a r g e / f i r m r i p e , 215 FIGURE 8. 1 MACHINE GRADED FIRM RIPE TOMATOES (o) EXTRA LARGE / (b) LARGE (c) MEDIUM 216 F I G U R E 8.2 M A C H I N E G R A D E D SEMI -RIPE T O M A T O E S (a) E X T R A L A R G E (b) L A R G E Ic) M E D I U M 218 l a r g e / f i r m r i p e , and medium/firm r i p e tomatoes, r e s p e c t i v e l y . F i g u r e 8.2 a, b, and c shows machine graded e x t r a l a r g e / s e m i - r i p e , l a r g e / s e m i - r i p e , and medium/semi-ripe tomatoes, r e s p e c t i v e l y . F i g u r e 8.3 a, b, and c shows machine graded e x t r a l a r g e / t u r n i n g , l a r g e / t u r n i n g and medium/turning tomatoes, r e s p e c t i v e l y . Each s i z e / c o l o u r c a t e g o r y c o n t a i n s tomatoes which f a l l w i t h i n the s p e c i f i e d boundaries f o r s i z e , and some tomatoes which f a l l o u t s i d e these l i m i t s — the m i s c l a s s i f i e d tomatoes. The percentage o f m i s c l a s s i f i e d tomatoes i n a g i v e n s i z e c a t e g o r y , alone, does not r e a l i s t i c a l l y r e p r e s e n t the s i z e g r a d i n g accuracy of the s i z e / c o l o u r grader. The d e v i a t i o n o f the m i s c l a s s i f i e d tomatoes from t h e i r c u t - o f f l i m i t s , however, does show the degree of o v e r l a p between s i z e c a t e g o r i e s . S i n c e o n l y one s i z e c u t - o f f i s used f o r a l l c o l o u r s o f tomatoes, i t i s reas o n a b l e t o p o o l a l l o f the m i s c l a s s i f i e d tomatoes around a s i z e c u t - o f f , r e g a r d l e s s o f c o l o u r . A t each c u t - o f f , i . e . a t 1.875 i n (4.76 cm), 2.250 i n (5.72 cm), and 3.000 i n (7.62 cm), i t may be assumed t h a t a normal d i s t r i b u t i o n o f m i s c l a s s i f i e d tomatoes e x i s t s . To i l l u s t r a t e , a t the 3.00 i n (7.62 cm) c u t - o f f , t h e r e w i l l be some tomatoes which are m i s c l a s s i f i e d , b e i n g o v e r s i z e f o r the l a r g e c a t e g o r y , and some tomatoes which are m i s c l a s s i f i e d , b e i n g u n d e r s i z e f o r the e x t r a l a r g e c a t e g o r y . The assumption made here, i s t h a t the o v e r s i z e 219 and u n d e r s i z e tomatoes when grouped w i l l be norm a l l y d i s -t r i b u t e d about a mean which i s c l o s e to the 3.000 i n (7.62 cm) c u t - o f f . A s i m i l a r d i s t r i b u t i o n i s expected a t each of the o t h e r two c u t - o f f l i m i t s . Confidence i n t e r v a l s may be c a l c u l a t e d f o r each of the d i s t r i b u t i o n s , and a statement made on the magnitude of the s i z e measurement e r r o r . The means and s t a n d a r d d e v i a t i o n s of the m i s c l a s s i -f i e d tomatoes around the 2.250 i n (4.76 cm) c u t - o f f and 3.000 i n (7.62 cm) c u t - o f f are l i s t e d i n Tab l e 8.3. The data f o r the 1.875 i n (4.76 cm) c u t - o f f i s not i n c l u d e d , s i n c e o n l y h a l f o f the normal d i s t r i b u t i o n (the u n d e r s i z e h a l f f o r the medium category) was a v a i l a b l e . The 95% c o n f i d e n c e i n t e r v a l f o r each m i s c l a s s i f i e d group was c a l c u l a t e d and the r e s u l t s are a l s o l i s t e d i n Tabl e 8.3. Assuming a st a n d a r d d e v i a t i o n o f 0.082 i n (0.208 cm) at 1.875 i n (4.76 cm) c u t - o f f , the 95% c o n f i d e n c e i n t e r v a l has a lower l i m i t o f 1.714 i n (4.35 cm). A l l o f the medium u n d e r s i z e tomatoes were g r e a t e r than 1.714 i n (4.35 cm) i n diameter. T h i s may suggest a s m a l l e r s t a n d a r d d e v i a t i o n a t t h a t c u t - o f f or a mean l e s s than 1.875 i n (4.76 cm) f o r t h a t group. An F - t e s t a t the 95% c o n f i d e n c e l e v e l y i e l d e d a value o f F = 1.295 ( f o r 8 and 6 degrees o f freedom i n the numerator and denominator, r e s p e c t i v e l y ) f o r the two normal d i s t r i b u t i o n s o f Tab l e 8.3. The v a r i a n c e s were t h e r e f o r e 220 TABLE 8.3 MEANS, STANDARD DEVIATIONS AND 95% CONFIDENCE INTERVALS FOR MISCLASSIFIED TOMATOES AROUND THE 2.250 INCH (5.715 CM) AND 3.000 INCH (7.620 CM) CUT-OFFS. Cut-off, Mean Standard 95% Confidence inch inch Deviation,inch Interval, inch (cm) (cm) (cm) (cm) 2.250 2.204 0.092 mean + 0.180 (5.715) (5.598) (0.234) (0.457) 3.000 (7 .620) 3.021 (7.673) 0.082 (0.208) mean + 0.161 (0.409) 221 assumed e q u a l . I t i s proposed t h a t the v a r i a n c e a t the th r e e c u t - o f f l i m i t s are e q u a l . Consequently, i t i s p o s s i b l e to apply one standar d d e v i a t i o n to each c u t - o f f . The s t a n d a r d d e v i a t i o n s e l e c t e d f o r t h i s purpose was the mean of the st a n d a r d d e v i a t i o n s l i s t e d i n Tab l e 8.3, namely, s = 0.087 i n (0.22 cm). The percentages o f o v e r s i z e and u n d e r s i z e tomatoes i n each s i z e c a t e g o r y , as graded by the machine, were re c o r d e d and are l i s t e d i n Table 8.4. Combining the data i n T a b l e 8.4 and s y i e l d s the f o l l o w i n g p r e d i c t i o n : I f tomatoes are graded w i t h V,,^ adjustment s e t as o u t l i n e d , then, a) 6.5% of the medium tomatoes w i l l be o v e r s i z e ; 68% of these w i l l be w i t h i n 0.087 i n (0.22 cm) o f 2.250 i n (5.72 cm) o r < 2.337 i n (5.936 cm) i n diameter. b) 9.7% o f the medium tomatoes w i l l be u n d e r s i z e ; 68% o f these w i l l be w i t h i n 0.087 i n (0.22 cm) o f 1.875 i n (4.76 cm) o r > 1.788 i n (4.54 cm), i n diameter. c) 5.9% of the l a r g e tomatoes w i l l be o v e r s i z e ; 68% o f these w i l l be w i t h i n 0.087 i n (0.22 cm) o f 3.000 i n (7.62 cm) o r < 3.087 i n (7.84 cm) i n diameter, d) and so on. I t i s d i f f i c u l t to assess the a c c e p t a b i l i t y o f 222 TABLE 8.4 PERCENTAGE OF OVERSIZE AND UNDERSIZE TOMATOES FOR EACH SIZE CATEGORY AS GRADED BY THE SIZE/COLOUR GRADER. Size Category Percent Percent Total No. of Tomatoes Oversize Undersize i n each size category Medium 6.5 9.7 62 Large 5.9 7.4 68 Extra Large - 4.8 63 223 the s i z e graded c a t e g o r i e s above s i n c e t o l e r a n c e s f o r s i z e ranges are not g i v e n i n the s t a n d a r d s . From a p r a c t i c a l s t a n d p o i n t , the few machine graded tomatoes which are o v e r s i z e and u n d e r s i z e are b e l i e v e d t o d e v i a t e i n s i g n i f i -c a n t l y from t h e i r s i z e c a t e g o r y b o u n d a r i e s . I t i s not n e c e s s a r y t h a t equal percentages of tomatoes are graded o v e r s i z e and u n d e r s i z e around a g i v e n s i z e c a t e g o r y c u t - o f f l i m i t . The l i m i t may be a d j u s t e d to r e q u i r e d s p e c i f i c a t i o n s , such t h a t o n l y a g i v e n percentage o f tomatoes w i l l f a l l e i t h e r t o the h i g h o r low s i d e of the boundary. The 9.7% o f u n d e r s i z e tomatoes i n the medium category can be decreased i f the 1.875 i n (4.76 cm) l i m i t i s i n c r e a s e d s l i g h t l y . The decrease i n the u n d e r s i z e percentage w i l l be a t the expense o f a g r e a t e r p r o p o r t i o n o f s m a l l tomatoes b e i n g o v e r s i z e . The l i m i t s s h o u l d be a d j u s t e d f o r an optimum o v e r s i z e / u n d e r s i z e r a t i o . SUMMARY E x p e r i m e n t a l l y o b t a i n e d v a l u e s f o r the s i z e c a t e g o r y c u t - o f f l i m i t s , V S E T 5 , V S E T g , and V S E T ? , d e v i a t e d somewhat from the t h e o r e t i c a l v a l u e s o b t a i n e d from a l i n e a r r e l a t i o n s h i p p a s s i n g through the o r i g i n . The d e v i a t i o n from the s t r a i g h t l i n e i s due t o the f a c t t h a t the Schmitt t r i g g e r p u l s e width versus diameter r e l a t i o n s h i p i s not l i n e a r . S e t t i n g o f the c u t - o f f l i m i t s s h o u l d be c a r r i e d out u s i n g tomatoes as s t a n d a r d s , r a t h e r than a d j u s t i n g the V S E T c o n t r o l s to t h e i r t h e o r e t i c a l v o l t a g e v a l u e s . The e f f e c t o f tomato c o l o u r on the measurement o f diameter has not c l e a r l y been e s t a b l i s h e d . I t appears t h a t the redder the tomato, the l a r g e r w i l l i t s machine-measured diameter be. The c o r r e l a t i o n , i f any, between c o l o u r and s i z e measurement i s p r o b a b l y i n s i g n i f i c a n t s i n c e the o v e r a l l percentage o f m i s c l a s s i f i e d tomatoes, and t h e i r d e v i a t i o n s from t h e i r s i z e c a t e g o r y boundaries are s m a l l . The g r e a t e s t percentage of m i s c l a s s i f i e d tomatoes was i n the medium ca t e g o r y , where 9.7% were graded u n d e r s i z e The s m a l l e s t percentage o f m i s c l a s s i f i e d tomatoes was i n the e x t r a l a r g e c a t e g o r y , where 4.8% were graded u n d e r s i z e . A s t a n d a r d d e v i a t i o n of 0.087 i n (0.22 cm) was a p p l i e d to a l l m i s c l a s s i f i e d tomatoes, and thus 68% of these w i l l be w i t h i n 0.087 i n (0.22 cm) o f the s i z e c a t e g o r y c u t - o f f l i m i t . The d e v i a t i o n of' the m i s c l a s s i f i e d tomatoes from the s i z e c a t e g o r y boundaries was c o n s i d e r e d p r a c t i c a l l y i n s i g n i f i c a n t 225 FINAL SUMMARY A summary o f the major f i n d i n g s o f the i n v e s t i g a -t i o n s r e p o r t e d here are l i s t e d i n p o i n t form below. 1. P h y s i c a l P r o p e r t i e s of Tomatoes as R e l a t e d to Colo u r Grading. - The wavelength r a t i o which i s a s s o c i a t e d w i t h a maximum r e f l e c t a n c e r a t i o d i f f e r e n c e between the greenest and re d d e s t tomatoes, i s not n e c e s s a r i l y the i d e a l wavelength r a t i o f o r the b e s t s t a t i s t i c a l s e p a r a t i o n o f tomatoes i n t o more than two c o l o u r c a t e g o r i e s . - The wavelength r a t i o , 600 nm/660 nm maximizes Students' t between f i r m r i p e , s e m i - r i p e , t u r n i n g and green c o l o u r c a t e g o r i e s . - R a t i o s o t h e r than 600 nm/660 nm may be used, but a t the expense of optimum s e p a r a t i o n between c a t e g o r i e s . 2. P h y s i c a l P r o p e r t i e s o f Tomatoes as R e l a t e d t o S i z e Grading. - The maximum diameter o f a tomato, i n the e q u a t o r i a l p l a n e , c o r r e l a t e s w e l l w i t h the weight o f the tomato. - The s m a l l e r the tomato, the s m a l l e r the d i f f e r e n c e between the major and minor diameters, i n the e q u a t o r i a l p l a ne . 226 - O r i e n t a t i o n of tomatoes on a conveyor b e l t before making a diameter measurement i s more c r i t i c a l f o r l a r g e r than s m a l l e r tomatoes. - The d i f f e r e n c e between the major and minor diameters i n the e q u a t o r i a l plane i s c o r r e l a t e d w i t h the major diameter i n only the e x t r a l a r g e s i z e category. 3. Colour Grader Design. - Photodetector a m p l i f i e r design can only be c a r r i e d out i f the c h a r a c t e r i s t i c s of the l i g h t source, o p t i c f i l t e r s and photodetectors are known. - Detection of the presence of a tomato can be c a r r i e d out using the a l g e b r a i c sum of the two photo-d e t e c t o r s i g n a l s as the t r i g g e r . - Reasonable c o l o u r s e p a r a t i o n i s accomplished by c o n t i n u o u s l y c a l c u l a t i n g the r a t i o of voltages from two p h o t o t r a n s i s t o r s sensing r e f l e c t e d l i g h t and ^comparing the peak vol t a g e to preset values. - Combination of the s t o r e d peak vol t a g e and the use of the sum of the two photodetector voltages as the sensing t r i g g e r , overcomes d i f f i c u l t i e s a s s o c i a t e d w i t h s y n c h r o n i z a t i o n of separate sensing and t r i g g e r i n g systems. - Without background m o n i t o r i n g , s m a l l degress of d r i f t i n the r e f l e c t a n c e of the conveyor b e l t can d e t r i m e n t a l l y a f f e c t both s e n s i n g o f the tomato and t r i g g e r i n g o f the s i g n a l p r o c e s s o r s . Conveyor b e l t background m o n i t o r i n g may be accom-p l i s h e d through the use o f a c i r c u i t which f o l l o w s t h low frequency d r i f t o f the background, but not the h i g h frequency o f the s o r t i n g o p e r a t i o n . Storage o f category i n f o r m a t i o n i n a dynamic memory sy n c h r o n i z e d w i t h the movement of the conveyor, guarantees t h a t at the e j e c t i o n time, the e j e c t mechanism and tomato are i n j u x t a p o s i t i o n , r e g a r d l e s s of conveyor b e l t speed, i z e Grader Design. Diameter measurement o f a tomato can be accomplished through the c o n v e r s i o n o f the c o l o u r grader Schmitt t r i g g e r p u l s e i n t o a v o l t a g e , and com-p a r i n g the v o l t a g e t o p r e s e t v a l u e s . Since the Schmitt t r i g g e r p u l s e width i s a f u n c t i o n o f conveyor b e l t speed, a compensating c i r c u i t must be p r o v i d e d which m a i n t a i n s a constant v o l t a g e f o r a g i v e n tomato diameter, r e g a r d l e s s o f b e l t speed. Category i n f o r m a t i o n can be processed i n the same manner as i n the c o l o u r grader. 228 5. T e s t R e s u l t s . - C o l o u r g r a d i n g can be s a t i s f a c t o r i l y accomplished w i t h the p r e s e n t d e s i g n f o r a l l tomatoes except those l e s s than o r equal to about 1 1/2 i n (4 cm) i n diameter, s i n c e d e t e c t i o n becomes d i f f i c u l t . - The g r a d i n g r a t e o f 5 tomatoes/sec, f o r both c o l o u r and s i z e / c o l o u r are l i m i t e d by the c a p a c i t y o f the pneumatic e j e c t mechanism employed i n the t e s t s . - The e l e c t r o n i c s o r t i n g o p e r a t i o n s u s i n g the p r e s e n t d e s i g n should be capable of g r a d i n g a t speeds up to 20 tomatoes/second. - The r e s o l u t i o n o f the s i z e grader, based on s t y r o b a l l measurements, appears t o be 0.045 i n (0.11 cm) a t the 95% c o n f i d e n c e l e v e l . - The e f f e c t s o f o f f - c e n t e r s e n s i n g of the tomato on the diameter measurement, based on s t y r o b a l l s t u d i e s , are p r a c t i c a l l y i n s i g n i f i c a n t a t o f f - s e t d i s t a n c e s up to 1/4 i n (0.64 cm) f o r diameters above 2 i n (5 cm). - S i z e / c o l o u r g r a d i n g , based on t e s t s conducted on 9 c a t e g o r i e s of tomatoes, w i t h the p r e s e n t d e s i g n , should y i e l d no more than 10% o v e r s i z e d and 10% u n d e r s i z e d tomatoes i n any c a t e g o r y . - Of the 10% u n d e r s i z e or o v e r s i z e tomatoes, 68% w i l l be w i t h i n 0.087 i n (0.22 cm) of the category boundary, f o r a l l c a t e g o r i e s . 229 RECOMMENDATIONS Recommendations w i t h r e s p e c t to the f u t u r e a p p l i c a -t i o n o f the pr e s e n t d e s i g n i n the manufacture of a complete s i z e / c o l o u r grader f o r tomatoes, as w e l l as f u r t h e r t e s t i n g procedures t o be c a r r i e d out on a m o d i f i e d v e r s i o n o f the pr e s e n t d e s i g n , are l i s t e d i n p o i n t form below. 1. E l e c t r o n i c and O p t i c a l System Design. - In the p r e s e n t d e s i g n , t h e r e may be a few redundancies which are nece s s a r y due to the modular d e s i g n o f the system which was c a r r i e d out over a long p e r i o d . These redundancies s h o u l d be e l i m i n a t e d i n the f i n a l d e s i g n . - The p h o t o t r a n s i s t o r a m p l i f i e r s should be rede s i g n e d f o r use w i t h 600 nm and 660 nm o p t i c f i l t e r s , and t e s t i n g conducted u s i n g the optimum 600 nm/660 nm wavelength r a t i o . - The width o f the f i b r e o p t i c s e n s i n g head c o u l d be i n c r e a s e d , to i n c r e a s e the amount of i n c i d e n t l i g h t and r e f l e c t e d l i g h t , thus i n c r e a s i n g the s i g n a l t o n o i s e r a t i o o f the p h o t o t r a n s i s t o r a m p l i f i e r s . - Background b e l t r e f l e c t a n c e s h o u l d be maintained a t a minimum wit h r e s p e c t t o a l l tomatoes so t h a t tomatoes s m a l l e r than 1 1/2 i n (4 cm) may be sensed. 230 - I f a tomato i s l a r g e enough (> 2.5 i n (6.4 cm) diameter) to occupy two b i t s o f storage area i n the s h i f t r e g i s t e r , i t may be p o s s i b l e to ent e r two c o n s e c u t i v e " e j e c t " s i g n a l s i n t o the memory. Consequently the e j e c t s o l e n o i d would be a c t i v a t e d f o r 3 i n (7.6 cm) o f conveyor b e l t , as opposed t o o n l y 1.5 i n (3.8 cm). T h i s would probably i n c r e a s e s o r t i n g speed c o n s i d e r -a b l y . 2. Mechanical H a n d l i n g System. - The e l e c t r o n i c system d e s c r i b e d should be t e s t e d with a d i f f e r e n t conveying system, p r e f e r a b l y a u n i t which a u t o m a t i c a l l y f e e d s , c e n t e r s and o r i e n t s the tomato, i n o r d e r to minimize m i s c l a s s i f i c a t i o n . A s i n g l e Vee b e l t may s u f f i c e and should be t e s t e d b e f o r e more co m p l i c a t e d systems are c o n s i d e r e d . - I t may be necessary t o i n c r e a s e the r e l a t i v e s torage c a p a c i t y o f the secondary surge tank or the o r i f i c e s i z e o f the s o l e n o i d s t o i n c r e a s e the flow o f a i r a c r o s s the tomato a t e j e c t i o n time, o r , i f necessary, operate two s o l e n o i d s i n p a r a l l e l . The l a t t e r p r o p o s a l would be con-s i d e r a b l y more expensive. - The drop from the conveyor b e l t t o the storage b i n s or cr o s s conveyors s h o u l d be maintained at a minimum, i n o r d e r t o minimize mechanical damage to the tomato. 231 CITED REFERENCES 1. A l l s h o u s e , G.W. and K.Q. Stephenson. 1969. Development o f a h a n d l i n g and s o r t i n g system f o r c e r t a i n f r u i t s and v e g e t a b l e s . T r a n s . ASAE 12(3) 290-291, 294. 2. B i r t h , G.S., K.H. 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W i l l i a m s . 1975. Development o f c r i t e r i a f o r m e c h a n i z a t i o n o f g r a d i n g p r o c e s s i n g tomatoes. T r a n s . ASAE 1 8 ( 1 ) : 190-193. 232 12. Goodman, H.C. and D.D. Hamann, 1971. A machine t o f i e l d s i z e sweet p o t a t o e s . T r a n s . ASAE 1 4 ( 1 ) : 3-6. 13. Greenwood, C.S. and D.W. C h a m b e r l i n . 1973. A p p a r a t u s f o r s o r t i n g f r u i t a c c o r d i n g to c o l o u r . U.S. P a t e n t No. 3,770,111, p a t e n t e d November 6, 1973. 14. Heron, J.R. and G.L. Z a c h a r i a h . 1974. A u t o m a t i c s o r t i n g o f p r o c e s s i n g tomatoes. Trans. ASAE 1 7 ( 5 ) : 987-992. 15. Hood, C.E., B.K. Webb and L.O. Drew. 1968. C o r r e l a t i o n s o f c e r t a i n p h y s i c a l p r o p e r t i e s o f tomatoes. ASAE Paper No. 68-120. 16. I r v i n g , D.W. and C.S. Greenwood. 1973. C i r c u i t r y f o r s o r t i n g f r u i t a c c o r d i n g t o c o l o u r . U.S. P a t e n t No. 3,750,883, p a t e n t e d August 7, 1973. 17. K e i t e l , D., H. Weinhold and R. S c h a r l e m e r . 1973. Method o f and d e v i c e f o r p h o t o m e t r i c a l l y s o r t i n g lumpy m i n e r a l s . U.S. P a t e n t No. 3,762,546, p a t e n t e d October 2, 1973. 18. K r i v o s h i e v , G.P., D.C. K o l e v , C.Y. Tanev, D . K . E r i n k o v , G.S. P e t r o v , A.T. V a s s i l e v and P.S. V a t e v . 1973. Method and a p p a r a t u s f o r s o r t i n g tomatoes by c o l o u r . U.S. P a t e n t No. 3,781,554, p a t e n t e d December 25, 1973. 19. Manfre, B.L. 1968. The m e c h a n i c a l h a r v e s t i n g o f tomatoes -- f o r p r o f i t . T r a n s . ASAE 1 1 ( 3 ) : 356-359. 20. Matson, G.D. and N.N. Mohsenin. 1973. M e c h a n i c a l o r i e n t a t i o n and p a c k i n g o f a p p l e f r u i t . T r a n s . ASAE 1 6 ( 6 ) : 1190-1193. 21. M c C l u r e , W.F., R.P. Rohrbach, L . J . Kushman and W.E. B a l l i n g e r . 1973. The B e r r y m a t i c : An a u t o m a t i c f r u i t s o r t i n g machine. ASAE Paper No. 73-6525. 22. M c C l u r e , W.F. and P. Rohrbach. 1973. B l u e b e r r y s o r t e r . U.S. P a t e n t No. 3,773,172, p a t e n t e d November 20, 1973. 23. M c C l u r e , W.F., R.P. Rohrbach, L . J . Kushman and W.E. B a l l i n g e r . 1975. D e s i g n o f a h i g h speed f i b e r o p t i c b l u e b e r r y s o r t e r . Trans ASAE 1 8 ( 3 ) : 487-490. 233 24. Mehra, H.K., N.R. B u l l e y and L.M. S t a l e y . . 1972. Some p h y s i c a l and r h e o l o g i c a l p r o p e r t i e s o f s t r a w b e r r i e s . Can. A g r i c . Eng. 1 4 ( 2 ) : 85-88. 25. Mohsenin, N.N. (ed.) 1970. P h y s i c a l P r o p e r t i e s o f P l a n t and A n i m a l M a t e r i a l s . Volume I . P u b l i s h e d by Gordon § B r e a c h , S c i e n c e P u b l i s h e r s I n c . , 150 F i f t h Avenue, New Y o r k , N.Y. 10011. 26. O ' B r i e n , M. and S.C. S a r k a r . 1973. Compu t e r i z e d g r a d i n g o f tomatoes by o p t i c a l t r a n s m i s s i o n c h a r a c t e r i s t i c s . ASAE Paper No. PC-73-09. 27. O ' B r i e n , M. and S.C. S a r k a r . 1974. System f o r o p t i c a l t r a n s m i s s i o n c h a r a c t e r i s t i c s f o r c o m p u t e r i z e d g r a d i n g tomatoes. T r a n s . ASAE 1 7 ( 2 ) : 193-194. 28. P a l m e r , J . 1961. E l e c t r o n i c s o r t i n g o f p o t a t o e s and c l o d s by t h e i r r e f l e c t a n c e . J . A g r i c . Eng. Res. 6: 104-111. 29. Powers, J.B., J.T. Gunn and F.C. J a c o b . 1953. E l e c t r o n i c c o l o u r s o r t i n g o f f r u i t s and v e g e t a b l e s . A g r i c . Eng. 34: 149-154, 158. 30. Rohrbach, R.P., W.F. M c C l u r e , L . J . Kushman and W.E. B a l l i n g e r . 1973. Developments i n a u t o m a t i c l i g h t t r a n s m i s s i o n d i f f e r e n c e s o r i n g o f b l u e b e r r i e s . ASAE Paper No. 73-6528. 31. S a r k a r , S.C. and M. O ' B r i e n . 1975. Measurement o f power s p e c t r a f o r o p t o e l e c t r o n i c sorting o f tomatoes. T r a n s . ASAE 1 8 ( 1 ) : 177-180, 184. 32. Stephenson. K.Q., R.K. B r y l e r and M.A. Wittman. 1973. V i b r a t i o n a l r e s p o n s e p r o p e r t i e s as s o r t i n g c r i t e r i a f o r tomatoes. T r a n s . ASAE 1 6 ( 2 ) : 258-260. 33. Stephenson, K.Q. 1974. C o l o u r s o r t i n g system f o r tomatoes. Trans ASAE 1 7 ( 6 ) : 1185-1186. 34. Traub, L.G., P.L. W r i g h t and H.L. S t e e l e . 1971. Machine h a r v e s t i n g tomatoes. Amer. Veg. Grower., Sept. 18-20, 47, 49. 35. Wood, R.A. 1973. App a r a t u s f o r s o r t i n g p r o d u c t s . U.S. P a t e n t No. 3,776,381, p a t e n t e d December 4, 1973. 234 36. W o r t h i n g t o n , J.T., D.R. M a s s i e and K.H. N o r r i s . 1973. L i g h t t r a n s m i s s i o n t e c h n i q u e f o r p r e d i c t i n g r i p e n i n g time f o r i n t a c t green tomatoes. ASAE Paper No.73-6526. 37. Yeatman, J.N. and K.H. N o r r i s . 1965. E v a l u a t i n g i n t e r n a l q u a l i t y o f a p p l e s w i t h new a u t o m a t i c f r u i t s o r t e r . Food T e c h n o l . 1 9 ( 3 ) : 123-125. 235 GLOSSARY band pass f i l t e r c a t e g o r y i n f o r m a t i o n c e n t r a l wavelength CMOS dB, d e c i b e l d i v i s i o n g a i n g a i n r a t i o h a l f bandwidth OF TERMS - wi t h r e f e r e n c e to o p t i c a l f i l t e r s , an i n t e r f e r e n c e f i l t e r having a h a l f band-width g r e a t e r than 5% of the c e n t r a l wavelength. - a d i g i t a l s i g n a l , e i t h e r HIGH or LOW, or combination o f s i g n a l s , generated when a tomato i s c a t e g o r i z e d e l e c -t r o n i c a l l y , which r e f e r s s p e c i f i c a l l y to a c o l o u r o r s i z e / c o l o u r c a tegory. - w i t h r e f e r e n c e t o o p t i c a l f i l t e r s , the wavelength a t the midpoint of the h a l f bandwidth. - Complementary Symmetry Metal Oxide Semiconductor. - may be expressed as 20 l o g V /V.. where ^ o 1 V = output v o l t a g e V? = i n p u t v o l t a g e . - w i t h r e f e r e n c e to analog s i g n a l s , the a l g e b r a i c opera-t i o n conducted on two v o l t a g e s . - w i t h r e s p e c t t o d i g i t a l s i g n a l s , the i n t e g r a l d i v i s i o n of a frequency. - r a t i o of output v o l t a g e to i n p u t v o l t a g e . - r a t i o of the g a i n o f one a m p l i f i e r to the g a i n o f another a m p l i f i e r . - w i t h r e f e r e n c e to o p t i c a l f i l t e r s , the width of a band measured a t h a l f peak t r a n s -m i s s i o n . 236 i n v e r t e r memory NAND gate narrow band pass f i l t e r NOR gate o c t a v e Op Amp, o p e r a t i o n a l a m p l i f i e r open l o o p g a i n o p t i c f i l t e r peak w a v e l e n g t h p e r c e n t (%) bandwidth - w i t h r e f e r e n c e to a n a l o g s i g n a l s , a d e v i c e whose i n p u t and output v o l t a g e s a r e d i f f e r e n t by a l g e b r a i c s i g n o n l y . - w i t h r e f e r e n c e t o d i g i t a l s i g n a l s , a d e v i c e whose o u t p u t i s the complement o f i t s i n p u t i . e . i f the i n p u t i s LOW, the ou t p u t i s HIGH, and v i c e v e r s a . - a d i g i t a l s t o r a g e a r e a c o m p r i s e d o f one o r more s h i f t r e g i s t e r s . - a d i g i t a l d e v i c e whose output i s LOW o n l y when a l l o f i t s i n p u t s a re HIGH. - w i t h r e f e r e n c e t o o p t i c a l f i l t e r s , an i n t e r f e r e n c e f i l t e r h a v i n g a h a l f bandwidth between 1% and 5% o f c e n t r a l w a v e l e n g t h . - a d i g i t a l d e v i c e whose o u t p u t i s HIGH o n l y when a l l o f i t s i n p u t s a r e LOW. - d o u b l i n g o f a f r e q u e n c y . - a h i g h - g a i n dc a m p l i f i e r t h a t has a d i f f e r e n t i a l i n p u t and a s i n g l e ended o u t p u t . - t h e g a i n o f an Op Amp when no n e g a t i v e feedback i s used. - an i n t e r f e r e n c e f i l t e r c a p a b l e o f t r a n s m i t t i n g a w a v e l e n g t h band o f the v i s i b l e s pectrum, and b l o c k i n g o t h e r s . - w i t h r e f e r e n c e to o p t i c a l f i l t e r s , w a v e l e n g t h at maximum t r a n s m i s s i o n . - the h a l f bandwidth e x p r e s s e d as a p e r c e n t i l e o f c e n t r a l w a v e l e n g t h ; i . e . 0.1% f i l t e r a t 440 nm has a h a l f bandwidth o f 0.4 4 nm. 237 p h o t o t r a n s i s t o r r e f l e c t a n c e r a t i o s i n g u l a t e TTL very narrow band pass f i l t e r wavelength r a t i o - s o l i d s t a t e d e v i c e s i m i l a r to an o r d i n a r y t r a n s i s t o r except t h a t l i g h t i n c i d e n t on the pn j u n c t i o n c o n t r o l s the response of t h i s d e v i c e ; o f f e r s b u i l t -i n g a i n and g r e a t e r s e n s i t i v i t y than photodiodes. - r a t i o of r e f l e c t e d e n e r g i e s a t two wavelengths when the i n c i d e n t e n e r g i e s a t the two wavelengths are e q u a l . - to arrange i n s i n g l e f i l e . - T r a n s i s t o r - T r a n s i s t o r L o g i c i n t e g r a t e d c i r c u i t . - w i t h r e f e r e n c e to o p t i c a l f i l t e r s , an i n t e r f e r e n c e f i l t e r having a h a l f bandwidth between 0.1% and 1% of c e n t r a l wavelength. - r a t i o of two wavelengths; r e f l e c t e d energy a t one of these wavelengths d i v i d e d by the r e f l e c t e d energy a t the ot h e r wavelength produces the r e f l e c t a n c e r a t i o . 238 APPENDIX A F e d e r a l * and I n d u s t r y * * G r a d i n g S t a n d a r d s f o r Greenhouse Tomatoes I . F e d e r a l and I n d u s t r y C o l o u r Grades and S t a n d a r d s * * * Canada N o . l Grade 7 1 . ( l ) ( d ) a r e , i n any i n d i v i d u a l package, one o f the f o l l o w i n g s t a t e s o f development: "mature", " t u r n i n g " , "semi-r i p e " o r " f i r m r i p e " . 7 3 . ( 1 ) ( a ) "mature" means, ( i ) e x c e p t f o r f i e l d tomatoes grown i n B r i t i s h Columbia and M a n i t o b a , t h a t the tomato shows a d e f i n i t e t i n g e o f p i n k a t the blossom end, and i n the c a s e o f f i e l d tomatoes grown i n B r i t i s h Columbia and M a n i t o b a , t h a t the tomato i s f u l l y d e v e l o p e d , w e l l f i l l e d o u t , g i v e s a f e e l i n g o f s p r i n g i n e s s when p r e s s u r e i s a p p l i e d , i s b r i g h t waxy i n a p p e a r a n c e , has seeds t h a t a r e w e l l d e v e l o p e d and seed c a v i t i e s o f a j e l l y - l i k e c o n s i s t e n c y , and ( i i ) not more t h a n 25% o f the f i e l d tomatoes by * Canada A g r i c u l t u r a l P r o d u c t s S t a n d a r d s A c t , F r u i t and V e g e t a b l e R e g u l a t i o n s , Queen's P r i n t e r , Ottawa 1968, C a t a l o g u e No. YX79-1955-27-1968. ** C o u r t e s y Western Greenhouse C o - o p e r a t i v e , Burnaby, B.C. *** Greenhouse tomato grades and s t a n d a r d s are the same as f i e l d tomato grades and s t a n d a r d s . 239 ( i i ) CONTINUED count are t u r n i n g i n the case o f tomatoes grown i n B r i t i s h Columbia and M a n i t o b a , and not more t h a n 101 o f the f i e l d tomatoes by count are t u r n i n g i n t h e case o f tomatoes grown o t h e r t h a n i n B r i t i s h Columbia and M a n i t o b a ; " t u r n i n g " means ( i ) t h a t the f i e l d tomato shows from a t i n g e t o 25 p e r c e n t p i n k or r e d c o l o u r , and ( i i ) not more t h a n 10% o f the f i e l d tomatoes by count a r e mature o r s e m i - r i p e ; " s e m i - r i p e " means ( i ) t h a t the f i e l d tomato shows from 25 p e r c e n t t o 75 p e r c e n t p i n k o r r e d c o l o u r , and ( i i ) not more th a n 10 p e r c e n t o f the f i e l d tomatoes by count a r e t u r n i n g or f i r m r i p e ; and " f i r m r i p e " means ( i ) t h a t t h e f i e l d tomato shows from 75 p e r c e n t t o 100 p e r c e n t p i n k o r r e d c o l o u r , and ( i i ) not more t h a n 10 p e r c e n t o f the f i e l d tomatoes by count a r e s e m i - r i p e . 240 I I . F e d e r a l S i z e S t a n d a r d s Canada No.1 Grade 7 6 . ( l ) ( g ) have a minimum d i a m e t e r o f 1 1/2 i n c h e s ; (h) have, when i n a package, w i t h the e x c e p t i o n o f one specimen, a maximum v a r i a t i o n i n d i a m e t e r o f 1 i n c h i n the case o f tomatoes w i t h a minimum d i a m e t e r o f 2 i n c h e s , and a maximum v a r i a t i o n i n d i a m e t e r o f 1/2 i n c h i n a l l o t h e r c a s e s ; 78. N o t w i t h s t a n d i n g a n y t h i n g i n t h e s e R e g u l a t i o n s , i n t h e g r a d i n g o f greenhouse tomatoes not more t h a n (a) 5 p e r c e n t o f the greenhouse tomatoes by count may be below t h e minimum s i z e ; (b) 10 p e r c e n t o f the p a c k a g e s , when the greenhouse tomatoes a r e i n p a c k a g e s , may c o n t a i n greenhouse tomatoes t h a t exceed the p e r m i t t e d s i z e v a r i a t i o n ; I I I . I n d u s t r y S i z e Grades i n B r i t i s h Columbia (1) Greenhouse tomatoes a r e grouped i n t o f i v e s i z e c a t e g o r i e s : (a) " c u l l " , a l l tomatoes h a v i n g a minimum d i a m e t e r l e s s t h a n 1 1/2 i n c h e s , (b) " s m a l l " , a l l tomatoes h a v i n g maximum d i a m e t e r s between 1 1/2 i n c h e s and 1 7/8 i n c h e s , 241 I I I . CONTINUED (c) "medium", a l l tomatoes h a v i n g maximum d i a m e t e r s between 1 7/8 i n c h e s and 2 1/4 i n c h e s , (d) " l a r g e " , a l l tomatoes h a v i n g maximum d i a m e t e r s between 2 1/4 i n c h e s and 3 i n c h e s , (e) " e x t r a l a r g e " , a l l tomatoes h a v i n g maximum d i a m e t e r s g r e a t e r t h a n 3 i n c h e s . (2) F e d e r a l S t a n d a r d s a p p l y t o g e n e r a l t o l e r a n c e s . 242 APPENDIX B GRADING RATE AT PEAK OF GROWING SEASON FOR B.C. LOWER MAINLAND BASED ON 1975 YIELD PREDICTIONS, MEAN WEIGHT OF TOMATOES IN EACH SIZE CATEGORY, AND APPROXIMATE DISTRIBUTION OF SIZE CATEGORIES* Size Category Small Medium Large Extra large Mean Tomato Weight (lbs) 0.107 0.163 0.346 0.495 No. of Tomatoes per 20 lb box 187 123 58 40 Maximum B.C. 1975 yield i n one week = 20,000 boxes at 20 lbs ea. Maximum Lower Mainland 1975 y i e l d i n one week = 70% X 20,000 = 14,000 boxes Size Distribution Small Medium Large Extra large . No.2 Grade % of Total 4 23 54 11 8 No. of Boxes/week 560 3220 7560 1540 1120 (hand sorted) Total without No.2's = 1,000,860 tomatoes/week Based on a 6 day work week, at 8 hours/day Grading rate = 5.8 tomatoes/sec Based on a 7 day work week, at 8 hours/day Grading rate =5.0 tomatoes/sec * Courtesy of Western Greenhouse Co-operative, Bumaby, B.C. 

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