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Some physical properties of strawberries related to design of a selective harvester Mehra, Harsh Kumar 1971

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SOME PHYSICAL PROPERTIES OF STRAWBERRIES RELATED TO DESIGN OF " : ~ " A SELECTIVE HARVESTER BY HARSH KUMAR MEHRA B.E.(Agric.) Hons. University of Udaipur, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of Ag r i c u l t u r a l Engineering . We accept t h i s thesis as conforming to the required standard ..THE UNIVERSITY OF BRITISH COLUMBIA September, 1 9 7 1 . 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 r e q u i r e m e n t s f o r an advanced deg ree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r ee t h a t t he 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 f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r ee t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rpo se s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f AGRICULTURAL ENGINEERING The U n i v e r s i t y o f B r i t i s h Co l umb i a Vancouve r 8, Canada Date September 30, 1971. ABSTRACT A f r u i t s e l e c t i o n t o o l , which c o u l d be used as a component o f a s e l e c t i v e strawberry h a r v e s t i n g system, was designed and t e s t e d . Design was based upon p h y s i c a l and T h e o l o g i c a l p r o p e r t i e s o f the Northwest v a r i e t y of s t r a w b e r r i e s which i s commonly grown i n B r i t i s h Columbia. F r u i t r e t e n t i o n f o r c e was measured as a f u n c t i o n o f time over the h a r v e s t season. Three r h e o l o g i c a l parameters, l i n e a r l i m i t , b i o y i e l d p o i n t and tangent modulus, were c a l c u l a t e d from f o r c e - d e f o r m a t i o n curves o b t a i n e d from f l a t p l a t e l o a d i n g t e s t s . These parameters were used to e v a l u a t e f r u i t q u a l i t y and i t s v a r i a t i o n over the h a r v e s t season. C o r r e l a t i o n s among q u a l i t y parameters, f r u i t r e t e n t i o n force, and f r u i t s u r f a c e c o l o u r i n d i c a t e d t h a t c o l o u r c o u l d be used as an a c c u r a t e i n d i c a t o r o f f r u i t q u a l i t y and f r u i t m a t u r i t y . F r u i t s u r f a c e c o l o u r was, t h e r e f o r e , used as the s e l e c t i o n parameter c o n t r o l l i n g the f r u i t s e l e c t i o n t o o l . S u b j e c t i v e and o b j e c t i v e c o l o u r measurements were made. R e l a t i v e r e f l e c t a n c e curves f o r strawberry s u r f a c e were ob t a i n e d from a Unicam automatic r e c o r d i n g spectrophotometer by scanning a 2.54 cm. diameter s u r f a c e o f the f r u i t at f a s t speed. Spectrum v a r i a b l e s o b t a i n e d from the r e f l e c t a n c e curves were used f o r o b j e c t i v e c o l o u r e v a l u a t i o n and m a t u r i t y assessment. The r e l a t i v e r e f l e c t a n c e s at v a r i o u s wavelengths had good c o r r e l a t i o n w i t h s u r f a c e c o l o u r , the h i g h e s t being t h a t between r e f l e c t a n c e at 52 5 nanometers and percent s u r f a c e r e d c o l o u r . M a t u r i t y r a t i o f o r s t r a w b e r r i e s was c a l c u l a t e d from r e f l e c t a n c e curves and was e s t a b l i s h e d as the r a t i o o f r e f l e c t a n c e s at 650 nm t o 525 nm. M a t u r i t y r a t i o best r e p r e s e n t e d the s u r f a c e c o l o u r and was used to d e f i n e f r u i t r i p e n e s s . An e l e c t r o n i c system was designed and used to measure m a t u r i t y r a t i o and to i d e n t i f y f r u i t m a t u r i t y . T e s t s conducted on t h i s system i n the l a b o r a t o r y i n d i c a t e d a minimum response time o f 0.16 6 seconds per f r u i t . The i n f l u e n c e o f i l l u m i n a t i o n and i t s geometry were a l s o i n v e s t i - gated. - I l l - ACKNOWLEDGEMENTS The author wishes to thank Professor L.M. Staley for d i r e c t i n g this research. Thanks are also due to Dr. N.H. Bulley for his valuable suggestions and Mr. W. Gleave and Mr. J. Pehlke for t h e i r assistance in constructing the equipment j a l l in the Department of A g r i c u l t u r a l Engineeringt University of B r i t i s h Columbia. Thanks are also extended to Canada Department of Agriculture j Agassis for providing the strawberries. This research was financed by the National Research Council of Canada. - i v - TABLE OF CONTENTS ABSTRACT ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES TERMINOLOGY 1. INTRODUCTION 1.1 Purpose o f t h e r e s e a r c h 2. REVIEW OF LITERATURE 2.1 P r e s e n t h a r v e s t i n g systems 2.2 A p p l i c a t i o n o f c o l o r i m e t r i c methods 2.3 Study o f p r e s e n t s t r a w b e r r y h a r v e s t e r s 2.4 C o l o r i m e t r y 3. ANALYSIS OF PHYSICAL PROPERTIES AND COLOUR MEASUREMENT 3 . 1 The s t r a w b e r r y p l a n t and f r u i t 3. 2 F r u i t and p l a n t d i s t r i b u t i o n 3. 3 F r u i t s i z e and we i gh t 3. 4 F r u i t r e t e n t i o n f o r c e 3. 5 F/W r a t i o 3. 6 R h e o l o g i c a l p r o p e r t i e s 3. 7 F r u i t q u a l i t y e v a l u a t i o n 3. 8 C o l o u r e v a l u a t i o n and m a t u r i t y o f f r u i t 3. 9. S u b j e c t i v e c o l o u r e v a l u a t i o n V - PAGE 3.10 S p e c t r a l c h a r a c t e r i s t i c s 27 3.11 Colour c r i t e r i a 34 3.12 M a t u r i t y r a t i o 35 ,4. DESIGN OF COLOUR MEASURING SYSTEM 40 4.1 Theory of design 4 0 4.2 Colour d i s c r i m i n a t o r 41 4.3 O p t i c a l requirements 44 4.3.1 The i l l u m i n a n t 44 4.3.2 The o b j e c t 45 4.3.3 The d e t e c t o r 4 5 4.4 Design of o p t i c a l apparatus 46 4.5 The e l e c t r o n i c apparatus 4 7 4.5.1 The probe 4 9 4.5.2 A m p l i f i e r 49 4.5.3 Voltage comparator 5 2 4.5.4 The s o l e n o i d 52 4.6 Test r e s u l t s 54 4.6.1 Speed o f response 54 4.6.2 Surface and i l l u m i n a t i o n c o n d i t i o n s 57 4.6.3 The angle of i l l u m i n a t i o n and d e t e c t i o n 58 4.6.4 The instrument s t a b i l i t y 58 CONCLUSIONS 59 • SUGGESTIONS FOR FUTURE WORK 6 0 LITERATURE CITED 61 APPENDIX '66 - v i - L IST OF FIGURES FIGURE PAGE l a A t y p i c a l s t r a w b e r r y f i e l d . 8 l b A t y p i c a l s t r a w b e r r y p l a n t . 8 2 S t r a w b e r r y p l a n t showing b e r r i e s h i d d e n under 10 dense f o l i a g e . 3 C r o s s - s e c t i o n v i ew o f a s t r a w b e r r y . 10 4 C u m u l a t i v e f r e q u e n c y f r u i t d i s t r i b u t i o n . 12 cui^ve p e r f o o t (30 cm.) o f s t r a w b e r r y c r o p measured about t he c e n t e r o f t h e row. 5 A t y p i c a l . s t r a w b e r r y f r u i t . 15 6 Hand dynamometer mounted on s u r v e y o r ' s 15 t r i p o d and s t r a w b e r r y h e l d i n h o l d e r . 7 L e a s t s qua re s i m p l e r e g r e s s i o n o f FRF and 17 F/W r a t i o on day o f h a r v e s t . 8 I n s t r o n l o a d i n g mach i ne . 19 9 O r i e n t a t i o n o f s t r a w b e r r y compressed between 19 two f l a t p l a t e s . 10 T y p i c a l f o r c e - d e f o r m a t i o n c u r v e f o r s t r a w b e r r y 20 - s u b j e c t e d t o f l a t p l a t e l o a d i n g a t r a t e o f 2 cm. p e r m i n u t e . 11 Lea s t squa re s i m p l e r e g r e s s i o n o f FRF on 2 3 b i o y i e l d p o i n t . 12 L e a s t squa re s i m p l e r e g r e s s i o n o f FRF on 25 t a n g e n t modu lus . - v i i - FJGURE PAGE 13 T y p i c a l s t r a w b e r r y sample o f v a r y i n g s u r f a c e 2 8 r e d n e s s . 14 Unicam a u t o m a t i c r e c o r d i n g s p e c t r o p h o t o m e t e r . 28 15 S t r a w b e r r y s u r f a c e h e l d i n sample h o l d e r . 29 16 "' A t y p i c a l r e l a t i v e r e f l e c t a n c e c u r v e f o r a 30 s t r a w b e r r y s u r f a c e r e c o r d e d on t he l o g a r i t h m i c s c a l e . 17 T y p i c a l s p e c t r a l r e f l e c t a n c e c u r v e s f o r 31 t o t a l l y g r e e n , ready t o p i c k (100% r e d ) and o v e r - r i p e s t r a w b e r r i e s p l o t t e d on an a r i t h m e t i c s c a l e . 18 L e a s t square s i m p l e r e g r e s s i o n o f m a t u r i t y 36 r a t i o on p e r c e n t s u r f a c e r e d . 19 T h e o r e t i c a l Toss d i s t r i b u t i o n by s e l e c t i n g 42 d i f f e r e n t v a l u e s o f m a t u r i t y c o e f f i c i e n t . 20 O p t i c a l a p p a r a t u s f o r c o l o u r mea su r i n g 48 s y s tem. 21 C ro s s s e c t i o n a l v i ew o f t h e f i l t e r - p r o b e 48 a s sembly (no t t o s c a l e ) . 22 C i r c u i t d i a g ram f o r probe a s semb l y . 50 23 C i r c u i t d i a g r am f o r s i g n a l a m p l i f i e r . 51 24 S chemat i c d i a g ram f o r v o l t a g e c ompa ra t o r and 53 s o l e n o i d . 25 S chemat i c d i a g r am o f e x p e r i m e n t a l a r rangement 55 f o r t e s t i n g c o l o u r d i s c r i m i n a t o r equ ipment . - V l l l - FIGURE • PAGE 2 6 General view of the experimental equipment 5 6 f o r t e s t i n g c o l o u r d i s c r i m i n a t o r equipment. LIST OF TABLES C o r r e l a t i o n matrix f o r p h y s i c a l dimensions of s t r a w b e r r i e s C o r r e l a t i o n matrix f o r r h e o l o g i c a l p r o p e r t i e s C o r r e l a t i o n matrix f o r s p e c t r a l and r h e o l o g i c a l p r o p e r t i e s C o r r e l a t i o n matrix f o r C I E - c o l o u r v a r i a b l e s of strawberry s u r f a c e R e s u l t s of the t e s t s conducted on the e l e c t r o n i c c o l o u r - d e t e c t i o n system f o r performance e f f i c i e n c y u s i n g Northwest v a r i e t y of s t r a w b e r r i e s . TERMINOLOGY Commission I n t e r n a t i o n a l e de L ' E c l a i r a g e Day of the h a r v e s t F r u i t r e t e n t i o n f o r c e R a t i o o f f r u i t r e t e n t i o n f o r c e to weight o f strawberry Current i n amperes Index o f v a r i a n c e i n r e f l e c t a n c e L i n e a r l i m i t M a t u r i t y r a t i o Sample s i z e Nanometer P r o b a b i l i t y l e v e l ; (1 - a ) , where a i s the l e v e l o f s i g n i f i c a n c e Simple c o r r e l a t i o n c o e f f i c i e n t R e f l e c t a n c e f a c t o r Percent red c o l o u r o f the be r r y s u r f a c e S e n s i t i v i t y o f the e l e c t r o n i c instrument Standard e r r o r o f estimate o f y B i o y i e l d p o i n t Angle between the i n i t i a l l i n e a r p o r t i o n o f the fo r c e - d e f o r m a t i o n curve and the deformation a x i s 1. INTRODUCTION St r a w b e r r i e s are about a 1 1/2 m i l l i o n d o l l a r annual crop i n the lower mainland o f B r i t i s h Columbia. About 80 perc e n t o f the crop goes to the p r o c e s s i n g p l a n t s and the remaining 2 0 percent i s s o l d to the f r e s h f r u i t market, (7)"*". In r e c e n t years farmers have been handicapped by adverse economic c o n d i t i o n s and repeated l a b o u r shortages d u r i n g the h a r v e s t i n g p e r i o d . High l a b o u r and p r o d u c t i o n c o s t s do not p r o v i d e f o r p r o f i t a b l e r e t u r n s . Most o f t h i s i n c r e a s e d cost i s i n c u r r e d d u r i n g the h a r v e s t i n g p e r i o d . T h i s p o p u l a r f r u i t c o u l d soon be p r i c e d out o f the market i f some mechanical means o f cheaply h a r v e s t i n g the strawberry are not ev o l v e d . 1.1 Purpose o f the Research In view of the above problem i t was proposed to design a s e l e c t i v e h a r v e s t i n g t o o l . A c r i t e r i a based on the p h y s i c a l p r o p e r t i e s o r s u r f a c e c o l o u r c h a r a c t e r i s t i c s was to be e v o l v e d to decide the q u a l i t y o f f r u i t which would then be used i n the design o f a h a r v e s t i n g system. Since the Northwest v a r i e t y o f s t r a w b e r r i e s are the most popu l a r v a r i e t y grown i n B r i t i s h Columbia, the r e s u l t s d i s c u s s e d i n t h i s study are l i m i t e d t o t h i s v a r i e t y . Number i n parentheses r e f e r to r e f e r e n c e s l i s t e d i n the l i t e r a t u r e c i t e d . 2. 2. REVIEW OF LITERATURE U n t i l r e c e n t l y mechanical h a r v e s t i n g o f f r u i t and vegetable crops was l i m i t e d to a very few types. Because o f i n c r e a s i n g l a b o u r shortage and i n c r e a s e d p r o d u c t i o n c o s t s the emphasis has been to har v e s t every crop m e c h a n i c a l l y i n a sh o r t span of time. A number o f r e s e a r c h o r g a n i z a t i o n s have been engaged i n v a r i o u s aspects o f f r u i t h a r v e s t i n g mechanization (3, 8, 22, 27, 37). 2.1 Present H a r v e s t i n g Systems Present h a r v e s t i n g systems can be c l a s s i f i e d i n t o t h r e e main c l a s s e s : 1. Once-over h a r v e s t i n g systems ( r e g e n e r a t i v e p l a n t s ) . The crop under t h i s c l a s s mature a l l at the same time. The complete p l a n t may be removed from the s o i l to f a c i l i t a t e p r o c e s s i n g under c o n t r o l l e d c o n d i t i o n s . The p l a n t regenerates i t s e l f every year. Under t h i s c l a s s f r u i t and p l a n t damage can be t o l e r a t e d t o a l a r g e e x t e n t . T h i s method i s wide l y used f o r h a r v e s t i n g sugar cane and tomatoes. 2. Once-over h a r v e s t i n g (non-regenerative p l a n t s ) T h i s system i s e s s e n t i a l l y the same as the pre v i o u s one except t h a t p l a n t s do not regenerate every y e a r and hence e x c e s s i v e p l a n t damage can not be t o l e r a t e d to aboid a d v e r s e l y a f f e c t i n g the y i e l d the f o l l o w i n g year. The p l a n t , i n t h i s case, i s not h a r v e s t e d along with the f r u i t : f o r p r o c e s s i n g . T h i s method i s wi d e l y used f o r h a r v e s t i n g g r a i n crops. 3. S e l e c t i v e h a r v e s t i n g system. T h i s system i s used where the f r u i t do not r i p e n a l l at the same time. Ripe f r u i t s are h a r v e s t e d over an extended p e r i o d o f time d u r i n g the h a r v e s t - i n g season. The machine, h a r v e s t i n g such cro p s , must be able t o d i s t i n g u i s h between r i p e and unr i p e f r u i t . The p l a n t s may o r may not be r e g e n e r a t i v e and hence the machines are designed to s u i t the p a r t i c u l a r requirement. Damage to the p l a n t and unri p e f r u i t can not be t o l e r a t e d . These machines have been used f o r c o t t o n , mushrooms (32) and tomatoes (37) f o r example. Various mechanical means are employed to sever the f r u i t from the p l a n t system. In any case f r u i t s e p a r a t i o n may be achieved by a p p l y i n g a f o r c e g r e a t e r than the f r u i t r e t e n t i o n f o r c e . F r u i t s e p a r a t i o n may be achieved by apply- i n g t e n s i o n , shear, i n e r t i a o r impact f o r c e or t o r s i o n a l f o r c e . Strawberry h a r v e s t i n g machines have been designed without any c o n s i d e r a t i o n to f r u i t o r p l a n t p r o p e r t i e s (3,8). For s e l e c t i v e h a r v e s t i n g o f f r u i t s , some c r i t e r i a , based on the p r o p e r t i e s o f the f r u i t , are u s u a l l y decided upon as the b a s i s by which the r i p e and unri p e f r u i t s can be d i s c r i m i n a t e d . T h i s c r i t e r i a c o u l d be based upon r h e o l o g i c a l p r o p e r t i e s , p h y s i c a l p r o p e r t i e s o r c o l o u r o f the f r u i t . 2 • 2 A p p l i c a t i o n o f C o l o u r i m e t r i c Methods Although, the use o f c o l o u r i m e t r i c techniques i n design o f h a r v e s t i n g machines has been very l i m i t e d , these techniques have long been used f o r p r o c e s s i n g and grading purposes. Stephenson (37) used the c o l o u r o f tomatoes as the d e c i d i n g c r i t e r i a , f o r s e l e c t i v e h a r v e s t i n g o f tomatoes. The' tomatoes were i l l u m i n a t e d by an i l l u m i n a n t and the r e f l e c t a n c e o f the tomato s u r f a c e was measured at two wavelengths by photo- c e l l s . The p h o t o c e l l s were arranged i n p a r a l l e l t o get uniform response from an i r r e g u l a r l y shaped tomato. The amount o f c u r r e n t f l o w i n g out o f the c i r c u i t was used as a measure o f the m a t u r i t y o f the f r u i t . S urface c o l o u r has a l s o been used as a c r i t e r i o n f o r g r a d i n g lemons (35), tomatoes (20), and prunes (9) a c c o r d i n g to t h e i r m a t u r i t y . Heron et a l . (20) used r e f l e c t a n c e at t h r e e wave- leng t h s 528 nm, 671 nm and 730 nm to c l a s s i f y tomatoes. While working on the method to make s e p a r a t i o n by measuring r e f l e c t a n c e at one p o i n t on the s u r f a c e , they found t h a t v a r i a t i o n i n the r e f l e c t a n c e i n t e n s i t y about the s u r f a c e o f a tomato i s not s i g n i f i c a n t l y l a r g e . They ob t a i n e d 92.98% c o r r e c t c l a s s i f i c a - t i o n by making r e f l e c t a n c e measurements at one p o i n t . But the sample s i z e was too s m a l l to j u s t i f y r e s u l t s f o r l a r g e r samples. Hoover and Dennison (23) used a Hunter c o l o u r - d i f f e r e n c e meter with "Rd" c i r c u i t t o e v a l u a t e c o l o u r o f s t r a w b e r r i e s . They found out t h a t there was no d i f f e r e n c e i n the "b" value but the "a" value i n c r e a s e d s t e a d i l y w i t h i n c r e a s e i n s u r f a c e redness. T h i s method o f c o l o u r e v a l u a - t i o n i s , however, l i m i t e d i n scope unless i t can be r e l a t e d to some known r e p r o d u c i b l e standards to be u t i l i z e d i n the design o f a h a r v e s t i n g system. Gaffney and Jahn (19) d e v i s e d a c o l o u r measuring system f o r g r a d i n g tomatoes using r e f l e c t a n c e at two wave- l e n g t h s . R e f l e c t a n c e measurements made at two wavelengths, at 540 nm as measuring wavelength and 590 nm as r e f e r e n c e ' wavelength gave good c l a s s i f i c a t i o n . Since the measurements weremade by a s t a t i o n a r y machine, the system was cumbersome f o r f i e l d o p e r a t i o n s and a l s o uneconomical. Powers et_ a l . (35) while working on the develop- ment of a lemon grader used "Index of v a r i a n c e i n r e f l e c t a n c e IVR as the c r i t e r i a f o r c o l o u r measurement of lemons: where, IVR = R - R ? [1 R^ = R e f l e c t a n c e at 6780A (678 nm) R 2 = R e f l e c t a n c e at 7200A (720 nm). T h i s index enables one to c l a s s i f y lemons i n t o f i v e d i s t i n c t c o l o u r c a t a g o r i e s . 2.3 Study of Present Strawberry Harvesters A number of o r g a n i z a t i o n s have been engaged i n the development o f strawberry h a r v e s t e r s . Oregon State U n i v e r s i t y (3) developed a s e l f pro- p e l l e d , once over strawberry h a r v e s t i n g machine. The machine c o n s i s t e d of two hollow p i c k i n g r e e l s with s p r i n g - s t e e l f i n g e r s . These f i n g e r s s t r i p p e d a l l the b e r r i e s as i t moved through the crop row. A U n i v e r s i t y o f Arkansas group (3) developed a commercial h a r v e s t i n g u n i t . The machine used " a i r s u c t i o n " to r a i s e the b e r r i e s from the ground so t h a t aluminum f i n g e r s c o u l d s t r i p them from the p l a n t . Hughes and Rickson (3) designed a t r a c t o r mounted strawberry h a r v e s t e r u s i n g the p r i n c i p l e of f o r c e d a i r to l i f t the b e r r i e s . The h a r v e s t i n g was accomplished by s t r i p p i n g the b e r r i e s with p i c k i n g f i n g e r s . Strawberry h a r v e s t e r s have a l s o been developed by the U n i v e r s i t y of Iowa, U n i v e r s i t y of Tennessee and U n i v e r s i t y of I l l i n o i s . A l l these machines have been experimental u n i t s o n l y and improvement i n the designs are s t i l l underway. 2• 4 C o l o r i m e t r y C o l o r i m e t r y has been widely used i n p a i n t , dye and the t e x t i l e i n d u s t r y and l a t e l y i n petroleum and the p e t r o - chemical i n d u s t r y . The a p p l i c a t i o n of c o l o r i m e t r y to f r u i t and vegetables i s comparatively a r e c e n t i n n o v a t i o n . More- over, the a p p l i c a t i o n to the f r u i t i n d u s t r y i s not very e f f i c i e n t . T h i s i s because the nature o f the problem i s d i f f e r e n t . In the p a i n t and dye i n d u s t r y one s e t o f measure- ments i s o f t e n enough to e s t a b l i s h c o l o u r o f the e n t i r e batch and even on a continuous process the change i n c o l o u r i s g r a d u a l . Hence, apparatus t h a t should q u i c k l y a d j u s t to l a r g e changes i s not r e q u i r e d . In the f r u i t and vegetable i n d u s t r y , however, the c o l o u r o f each f r u i t must be s e p a r a t e l y determined, u s u a l l y i n a f r a c t i o n of a second. S u c c e s s i v e measurements may l i e at the extremes o f the measuring range. 3. ANALYSIS OF PHYSICAL PROPERTIES AND COLOUR MEASUREMENT. Thi s chapter presents the p h y s i c a l p r o p e r t i e s and the r h e o l o g i c a l c h a r a c t e r i s t i c s o f the strawberry f r u i t . The methods employed to measure i n d i v i d u a l c h a r a c t e r i s t i c s are a l s o d i s c u s s e d . These p r o p e r t i e s are e s s e n t i a l f o r determin- i n g the behaviour o f the f r u i t to the a p p l i e d machine f o r c e s . Various components of the machine employed i n h a n d l i n g and storage are designed on the b a s i s o f these c h a r a c t e r i s t i c s . 3 • 1 The Strawberry P l a n t and F r u i t Before the h a r v e s t i n g system o r machine can be designed i t i s necessary to have a knowledge o f p h y s i c a l and mor p h o l o g i c a l c h a r a c t e r i s t i c s . A knowledge o f these c h a r a c t e r i s t i c s are necessary to achieve a r a t i o n a l d e s i g n . The strawberry i s a p e r e n n i a l herb o f the genus Fvagavia and f a m i l y Rosaceae. S t r a w b e r r i e s are propagated by removing runners, which form n a t u r a l l y , and s e t t i n g them i n t o new f i e l d s . In many cases a new p l a n t i n g i s made every y e a r , produces f r u i t the f o l l o w i n g y e a r and i s then plowed under. However, two annual crops may be produced from one p l a n t i n g . The strawberry i s grown i n s o l i d beds o r matted rows. When grown i n rows, the crop rows are spaced 1.2 M a p a r t . F u l l y mature, the crop row i s about 0.6 6 M wide and about 0.33 M h i g h , ( F i g u r e s l a , l b ) . As the b e r r i e s mature they get h e a v i e r and sag down and are hidden under the dense f o l i a g e ( F i g u r e 2 ) . F i g u r e i a . A t y p i c a l s t r a w b e r r y f i e l d F i g u r e l b . A t y p i c a l s t r a w b e r r y p l a n t 9. The strawberry i s a j u i c y , e d i b l e and aggregate f r u i t . Strawberry f r u i t can best be d e s c r i b e d as. c o n i c a l but the shape changes with v a r i e t y . The strawberry changes i t s c o l o u r from green to red as i t r i p e n s . The r i p e straw- b e r r y i s b r i g h t red i n c o l o u r on the s u r f a c e and y e l l o w achenes (seed) are a t t a c h e d . The f r u i t i s a t t a c h e d to the p l a n t system at the p i t h ( F i g u r e 3). The p i t h area becomes s o f t , f l u f f y and hollow when the b e r r y r i p e n s and the f r u i t attachment f o r c e decreases. Almost a l l the h a r v e s t i n g i s achieved by hand p i c k i n g . Since the crop matures over an extended p e r i o d o f time the p i c k i n g i s scheduled every two o r three days. When p i c k e d w i t h machine, the complete p l a n t i s s t r i p p e d . T h i s causes e x t e n s i v e damage to the p l a n t and hence new p l a n t i n g s are done every year. 3.2 F r u i t and P l a n t D i s t r i b u t i o n The number o f p l a n t s were counted per f o o t (0.3 M) at s i x d i f f e r e n t p l a c e s on each o f s i x rows (18 months o l d ) s e l e c t e d f o r the study. A metal wire frame 1' x 2' x 1' (0.33 x 0.66 x 0.33 M) was used to count the d i s t r i b u t i o n o f f r u i t a c r o s s the row. The f r u i t d i s t r i b u t i o n was a l s o counted at 36 f e e t (12 M) o f row at 36 p l a c e s . The number o f b e r r i e s were counted between the f o u r s u c c e s s i v e 3 i n c h (7.6 cm) s e c t i o n s about the row c e n t e r l i n e . A l l the f r u i t s were c o n t a i n e d w i t h i n the 1 f o o t (0.33 M) o f the p l a n t h e i g h t and hence no attempt was made to f i n d the f r u i t d i s t r i b u t i o n along the h e i g h t of the p l a n t . 10. Figure 3. C r o s s - s e c t i o n view of a strawberry 11 . R e s u l t s o b t a i n e d f rom 36 o b s e r v a t i o n s showed t h a t p l a n t d i s t r i b u t i o n (number o f p l a n t s ) p e r f o o t (30 cm) o f t h e row was 2 1 + 5 . F i g u r e 4 shows t he c u m u l a t i v e f r e q u e n c y f r u i t d i s t r i b u t i o n c u r v e a c r o s s t h e row w i d t h . T h i s f i g u r e i n d i c a t e s t h a t 60 p e r c e n t o f t he b e r r i e s a re l o c a t e d w i t h i n 15 cm o f t h e row cente3 ? l i n e and t o p i c k ' 85 p e r c e n t o f t h e b e r r i e s , row s l i c e s 22.5 cm t h i c k about t h e row c e n t e r l i n e s h o u l d be ha r ve s ted . , and t o h a r v e s t 10 0 p e r c e n t o f t h e c rop the e n t i r e row w i d t h o f 6 0 cm s h o u l d be h a r v e s t e d . 3. 3 F r u i t S i z e J*nj3_J^/eJ^g_ht S t r a w b e r r y w e i g h t and s i z e a r e i m p o r t a n t f rom t h e p o i n t o f v i ew o f a p i c k i n g r e e l d e s i g n , f i n g e r s p a c i n g s and c o n v e y o r c a p a c i t i e s . The we i gh t o f t h e i n d i v i d u a l s t r a w b e r r y was measured on a M e t t l e r H-16 t y p e c h e m i c a l b a l a n c e . A sample o f 172 b e r r i e s was used t o f i n d ave rage w e i g h t o f s t r a w b e r r y f r u i t . I n t h e 1970 h a r v e s t season t he mean we i gh t o f s t r a w b e r r y was 11.08 + 4.15 gms. J a n i c k (24) f ound t h e ave rage we i gh t o f s t r a w b e r r y t o be 14.2 gms. I t was found t h a t ave rage we i gh t o f r i p e b e r r i e s d i d . no t change s i g n i f i c a n t l y o v e r t h e h a r v e s t s e a s on . Fo r t he 1970 sea son t h e s i m p l e r e g r e s s i o n o f Z on X gave t h e f o l l o w i n g e q u a t i o n : Z = 12.34 - 0.22 X [ 2 ] n = 112 , r = 0.258 , Sy = 3.914 12. DISTANCE FROM CENTER (cms.) FIGURE 4. C u m u l a t i v e f r e q u e n c y f r u i t d i s t r i b u t i o n c u r v e p e r f o o t (30 cm.) o f s t r a w b e r r y c r o p measured about t he . c e n t e r o f t he row. where Z = Mean we i gh t p e r b e r r y i n gms, X = Day o f h a r v e s t 1 < X < 10 The above r e l a t i o n i n d i c a t e s t h a t r i p e n i n g t i m e i s i n d e p e n - dent o f b e r r y w e i g h t and e q u a l number o f heavy and l i g h t b e r r i e s can be e x p e c t e d on t h e f i r s t day o f h a r v e s t . The shape o f t h e s t r a w b e r r y i s no t c o n s i s t e n t and can not be d e s c r i b e d . But most o f t h e No r thwes t v a r i e t y o f s t r a w b e r r i e s can b e s t be d e s c r i b e d as c o n i c a l ( F i g u r e 5 ) . From t h e d e s i g n p o i n t o f v i ew t he h e i g h t and maximum and minimum d i a m e t e r o f s t r a w b e r r y a re most i m p o r t a n t v a r i a b l e s . The measurement s , d i a m e t e r and h e i g h t , were made w i t h hand c a l i p e r s . F i g u r e 5 shows t he t y p i c a l shape o f a s t r a w b e r r y f r u i t and t h e s t a t i s t i c a l c o r r e l a t i o n o f t he p h y s i c a l d i m e n s i o n s i s g i v e n i n T a b l e I. TABLE I CORRELATION MATRIX FOR PHYSICAL DIMENSIONS OF STRAWBERRIES FRF Weight. H e i g h t Mean D i a . Mean 6 6 7.8 gms. 12.3 gms. 2.260 cms. 2.015 cms. S t d . D e v i a t i o n +236.7 FRF 1.0 Weight 0.286 H e i g h t 0.282 Mean D i a . 0.38 3 From t h e t a b l e the mean d i a m e t e r i s 2.02 + 0.56 cm and mean h e i g h t o f s t r a w b e r r y i s 2.2 6 + 0.40 cm. Te s t c o n d u c t e d by + 4 . 8 +0.404 +0.565 1.0 0.054 1.0 0.445 0.746 1.0 J a n i c k (24) on 144 s t r a w b e r r i e s o f mi s c e l l a n e o u s v a r i e t i e s i n d i c a t e d a v a r i a t i o n i n average strawberry diameter from a minimum o f 1.90 cm. to a maximum o f 4.06 cm. 3• 4 F r u i t R e t e n t i o n Force F r u i t r e t e n t i o n f o r c e (FRF) was d e f i n e d as the f o r c e r e q u i r e d to remove the f r u i t from the p e t i o l e . The FRF was measured by a C h a t t i l o n type DPP1 hand dynamometer ( F i g u r e 6) ( c a p a c i t y 1140 gms). Measurements were made with the dynamometer mounted on a surveyor's t r i p o d as shown. The f r u i t stem was h e l d i n a s p r i n g loaded clamp and the jaws o f the clamp were coated w i t h s i l i c o n c a r b i d e paper t o a v o i d s l i p p i n g . A strawberry was h e l d i n a 1 cm s l o t t e d b r a s s r i n g o f 5 cm diameter. The d i a l was s e t to zero and t e n s i o n f o r c e was a p p l i e d by t i g h t e n i n g the screw. As the stem broke o r the f r u i t detached, the f r u i t detachment f o r c e was read on the d i a l . Since the f r u i t was h e l d v e r t i c a l l y the weight o f f r u i t was added to the f r u i t detachment f o r c e t o get f r u i t r e t e n t i o n f o r c e (FRF). The d i a l was then r e s e t to zero to t e s t the next sample. For the 1970 h a r v e s t season, the mean FRF f o r 112 r i p e b e r r i e s was 667.8 + 236.7 grams. Hoag and Hunt (22) i n t e s t s conducted d u r i n g 1963 and 1964 on s i x d i f f e r e n t v a r i e t i e s ( S t e l e m a s t e r , V e r m i l l i o n , Red Glow, S p a r k l e , Sure crop and Midway) found t h a t the mean p i c k i n g f o r c e o f d i f f e r e n t v a r i e t i e s o f s t r a w b e r r i e s was s i g n i f i c a n t l y d i f f e r e n t at the 5% l e v e l o f s i g n i f i c a n c e . For 1953 the range of p i c k i n g f o r c e was a maximum o f 1155 grams f o r Figure 6. Hand dynamometer mounted on surveyor's tripod and straw- berry held in the holder V e r m i l l i o n to a minimum o f 2 6 6 . 5 grams f o r the Sure crop v a r i e t y o f s t r a w b e r r i e s . F i g u r e 7 shows the v a r i a t i o n o f mean f r u i t r e t e n t i o n f o r c e f o r r i p e o r ready to p i c k b e r r i e s o v e r the h a r v e s t p e r i o d . Ready to p i c k b e r r i e s are those having 8 0 % o r more s u r f a c e redness. • The f i g u r e i n d i c a t e s t h a t mean FRF f o r the r i p e b e r r i e s decreases as the h a r v e s t season p r o g r e s s e s . The eq u a t i o n o f the l i n e o f simple r e g r e s s i o n i n d i c a t i n g the r e l a t i o n between the two v a r i a b l e s i s : FRF = 8 6 7 . 3 - 3 2 . 7 D [ 3 ] n = 1 1 2 Sy = 2 1 5 . 7 r 2 r 0 . 1 2 2 where FRF = F r u i t r e t e n t i o n f o r c e i n gms, D - Day of h a r v e s t f o r 1 < D < 1 0 . C o e f f i c i e n t o f c o r r e l a t i o n between the f r u i t r e t e n t i o n f o r c e and day of ha r v e s t gave a value o f - 0 . 3 4 9 . 3 . 5 F/W Ratio The F/W r a t i o i s the r a t i o o f f r u i t r e t e n t i o n f o r c e to the weight of an i n d i v i d u a l b e r r y . T h i s r a t i o was measured f o r a sample o f 1 7 2 b e r r i e s . The m a t u r i t y of the s t r a w b e r r i e s ranged from t o t a l l y green b e r r i e s to o v e r - r i p e b e r r i e s . Mean F/W r a t i o over the e n t i r e h a r v e s t p e r i o d was found to be 7 1 . 3 6 + 2 4 . 2 6 . The a n a l y s i s o f data gave the f o l l o w i n g equation f o r simple r e g r e s s i o n o f F/W on day of h a r v e s t : 17. 1200r 1000 F * 800 LU g 600| IJU 400 z o z UJ I— UJ at 5 200 a. 0 ! F RF = 867-3 -32 -7 D n = 112 Sy = 215-7 r 2 = 0-122 jr/W" 64-6 + 1-731 D n :: \\2 Sy :, 23-99 r2 r. 0-03 llGO 80' 60 40 20 0 4 IB 10 DAY OF HARVEST FIGURE 7. L e a s t s qua re s i m p l e r e g r e s s i o n o f f r u r t f o r c e and F/W r a t i o on day o f h a r v e s t . 18. F/W = 64.6 + 1.73 D [4] n = 112 Sy = 23.99 r 2 = 0.030 Equations [3] and [4] have been i l l u s t r a t e d i n F i g u r e 7. 3.6 v R h e o l o g i c a l P r o p e r t i e s I n c r e a s i n g demand f o r a b e t t e r end product t o g e t h e r with the d e l i c a t e and s o f t s k i n s t r u c t u r e o f s t r a w b e r r i e s demand a b e t t e r knowledge of t h e i r s i g n i f i c a n t p h y s i c a l p r o p e r t i e s f o r b e t t e r h a n d l i n g . S t r a w b e r r i e s must undergo v a r i o u s k i n d s o f mechanical, o p t i c a l and e l e c t r i c a l t r e a t - ment before the product reaches the consumer or p r o c e s s i n g u n i t from the farm. I t i s e s s e n t i a l , t h e r e f o r e , to under- stand the behaviour and response of s t r a w b e r r i e s when su b j e c t e d to such treatments so t h a t a machine h a n d l i n g and p r o c e s s i n g o p e r a t i o n can be designed f o r maximum e f f i c i e n c y and b e t t e r q u a l i t y of end product. Moreover, r h e o l o g i c a l c h a r a c t e r i s t i c s can a l s o be u t i l i z e d as apparent m a t u r i t y i n d i c a t o r s and q u a l i t y e v a l u a t i o n s . A t a b l e model I n s t r o n t e s t e r ( F i g u r e 8) was used to _ o b t a i n f o r c e - d e f o r m a t i o n curves f o r s t r a w b e r r i e s , r a n g i n g i n m a t u r i t y from t o t a l l y green to over r i p e s t r a w b e r r i e s . To o b t a i n the c r i t i c a l values of r h e o l o g i c a l parameters, b e r r i e s were p l a c e d i n an u p r i g h t p o s i t i o n , as shown i n F i g u r e 9, and compressed between two f l a t p l a t e s at a l o a d i n g r a t e of 2 centimeters per minute. A t y p i c a l f o r c e - d e f o r m a t i o n curve o b t a i n e d from these t e s t s i s shown i n F i g u r e 10. F i g u r e 9. O r i e n t a t i o n of strawberry compressed between two f l a t p l a t e s . 20. 250 £ 200 O tu 150 u . cm. O 100 50 .0 0-*arT1(e) .Bioyield poinf(y) 10 15 DEFORMATION IN M M . 20 FIGURE 10. T y p i c a l f o r c e - d e f o r m a t i o n curve f o r strawberry s u b j e c t e d t o l o a d i n g between two f l a t p l a t e s at a r a t e o f 2 cm. per minute. From these curves the values o f l i n e a r l i m i t (LL) o r the minimum l o a d when load-deformation curve becomes n o n - l i n e a r , b i o y i e l d p o i n t (Y) o r maximum l o a d beyond which f o r c e decreases o r remains constant with i n c r e a s e i n deformation, and tangent modulus ( 0 ) , or the slope o f the force-deforma- t i o n curve, were measured. C o r r e l a t i o n c o e f f i c i e n t s o f l i n e a r c o r r e l a t i o n between r h e o l o g i c a l parameters and FRF and F/W were c a l c u l a t e d to f i n d s i g n i f i c a n c e o f r h e o l o g i c a l c h a r a c t e r i s t i c s on f r u i t r e t e n t i o n f o r c e and F/W r a t i o . The c o r r e l a t i o n c o e f f i c i e n t s among these v a r i a b l e s are shown i n Table I I . TABLE I I CORRELATION MATRIX FOR RHEOLOGICAL PROPERTIES FRF F/W Lin.Lmt BYP. Tan,Mod Mean 667.8 71. 36 49 .97 116. 6 1. 622 S t d . D e v i a t i o n +236.70 +24.26 +26.10 + 47.70 0.65 FRF 1.0 0 - — F/W 0.41 1.00 Lin.Lmt. 0.26 0. 00 1.00 BYP. 0.42 0.25 0.47 1.00 Tan.Mod. 0. 41 0.26 0.28 0.75 1.00 The FRF had the h i g h e s t c o e f f i c i e n t o f c o r r e l a t i o n o f 0.42 3 w i t h b i o y i e l d po i n t ( Y ) , ( s i g n i f i c a n t at P < 0.05). Least square simple r e g r e s s i o n o f FRF on b i o y i e l d r e s u l t i n g from a.sample o f 118 s t r a w b e r r i e s i s : 2.2. FRF = 504.8 + 2.0 Y [5] n = 118 Sy = 208.6 r 2 =• 0.178 where FRF = F r u i t r e t e n t i o n f o r c e i n gms Y = B i o y i e l d p o i n t i n gms. The above r e s u l t i s i l l u s t r a t e d i n Fi g u r e 11. I t can be d e r i v e d from the above r e s u l t s that an i n c r e a s e i n b i o y i e l d p o i n t i s c o n s i s t a n t with the i n c r e a s e i n f r u i t r e t e n t i o n f o r c e . The mean value of b i o y i e l d p o i n t f o r 30 r i p e straw- b e r r i e s on the f i r s t day of h a r v e s t was 12 6.1 gms, whereas on the l a s t day (tenth) of h a r v e s t season, the value was 78.1 gms. I t shows t h a t there i s a marked decrease i n the value of b i o y i e l d p o i n t of r i p e s t r a w b e r r i e s as the harvest season p r o g r e s s e s . Hence the f r u i t h a r v ested on the l a s t day of the harvest season i s more s u s c e p t i b l e to mechanical damage and b r u i s i n g than those h a r v e s t e d on previous days. I t may a l s o be de r i v e d . f r o m the r e s u l t s i n the pr e v i o u s t a b l e t h a t the r a t i o o f f r u i t r e t e n t i o n f o r c e to . weight of the ber r y (^) i s not b e t t e r than FRF i n i n d i c a t i n g r h e o l o g i c a l parameters as might have f i r s t been expected. 3•7 F r u i t Q u a l i t y E v a l u a t i o n The q u a l i t y o f s t r a w b e r r i e s can be e v a l u a t e d by s u r f a c e c o l o u r , s i z e o r f i r m n e s s . In the p r o c e s s i n g u n i t s q u a l i t y , i s e v a l u a t e d manually by f e e l i n g the b e r r i e s i n between the f i n g e r s . . In o r d e r t o commercialize the process 900 E cn U J 800 V ca. O u- Z 700 O (— z LU * - £ 600 u. 500 0 20 40 60 80 FRF - 504-8+ 2-03 Y n - 118 Syr 208 6 r 2 = 0178 100 l i o * BIOYIELD POINT (gms.) FIGURE 11. Least square simple r e g r e s s i o n o f f r u i t r e t e n t i o n f o r c e on b i o y i e l d p o i n t . the 'mechanical o r e l e c t r o n i c s o r t e r has to make the d e c i s i o n s ; and the rheology o f the f r u i t p r o v i d e s the obvious s o l u t i o n to r e p l a c e the manual o p e r a t i o n . Since the b i o y i e l d p o i n t , which i s the p o i n t when the s k i n s t a r t s r u p t u r i n g , i s a d e s t r u c t i v e t e s t , i t i s not d e s i r a b l e f o r q u a l i t y e v a l u a t i o n . T h e r e f o r e , to d e f i n e q u a l i t y o f s t r a w b e r r i e s , tangent modulus seems to be a b e t t e r parameter. Tangent modulus, which i s a measure of f r u i t behaviour i n response to a p p l i e d mechanical f o r c e u n t i l the i n i t i a l c e l l r u pture occurs i n the f r u i t , i s a l s o a n o n - d e s t r u c t i v e t e s t . Moreover, t h i s i s probably the c r i t e r i a measured by manually compressing the strawberry between the f i n g e r s . Hence, the tangent modulus can be used as an i n d i c a t o r o f f r u i t q u a l i t y . The simple r e g r e s s i o n o f FRF on tangent modulus i s : FRF = 644.7 + 59.6 9 n = 118 Sy = 2 26.8 r 2 = 0.410 where FRF = F r u i t r e t e n t i o n f o r c e gms, 0 = Tangent modulus. Although complete design o f h a r v e s t i n g and h a n d l i n g equipment r e q u i r e s knowledge o f the behaviour o f s t r a w b e r r i e s to shock l o a d i n g , v i b r a t i o n , heat and many o t h e r types o f treatments, the f o r c e - d e f o r m a t i o n c h a r a c t e r i s t i c s p rovide most o f the essen- t i a l data. The a n a l y s i s o f f o r c e - d e f o r m a t i o n c h a r a c t e r i s t i c s , 900 -800 E CD 700 u D i o FRF - 644 59-64© 6001 Z o I— z £500] LU D i n =H8 S y= 226-8 r2=-. 0-168 z> 400| D i 300 h 200 ! J L 0 0 0-5 TANGENT 1-0 M O D U L U S 1-5 2-0 FIGURE 12. Least square simple r e g r e s s i o n of FRF on Tangent Modulus, apart from the above t h r e e measured parameters, p r o v i d e knowledge of parameters which can be used i n the design o f strawberry s t r i p p i n g mechanisms, conveying systems, hopper storage and even f u r t h e r treatments i n the p r o c e s s i n g o p e r a t i o n s . ^• 8 Colour Eva1uation and M a t u r i t y of F r u i t Normally f r u i t r i p e n e s s i s judged on the b a s i s of s u r f a c e redness, and p i c k i n g and s o r t i n g i s c a r r i e d out by t v i s u a l c o l o u r judgement. I f b e r r i e s are to be p i c k e d m e c h a n i c a l l y , or processed on a continuous p r o c e s s i n g opera t i o n , some s u i t a b l e c o l o u r c r i t e r i a i s needed f o r quick and a c c u r a t e c o l o u r e v a l u a t i o n which i n d i c a t e s the r i p e n e s s of the b e r r y . T h e r e f o r e , t o f i n d the c o l o u r c r i t e r i a f o r the design of a s u i t a b l e s e l e c t i v e h a r v e s t i n g system, the r e f l e c t a n c e spectrum o f the b e r r y s u r f a c e was a n a l y z e d . 3 . 9 S u b j e c t i v e Colour Evaluations S u b j e c t i v e c o l o u r d e t e r m i n a t i o n s were made on a sample of 118 s t r a w b e r r i e s over a 10 day h a r v e s t p e r i o d . A value o f zero percent red was given to a t o t a l l y green strawberry, 100 percent to a completely red and ready to p i c k strawberry and 120 percent to t h a t which was o v e r - r i p e and becoming deep red i n s u r f a c e c o l o u r ( F i g u r e 13). A p p r o p r i a t e values o f percent s u r f a c e red c o l o u r were gi v e n to p a r t i a l l y r e d c o l o u r e d s t r a w b e r r i e s . A t y p i c a l sample o s t r a w b e r r i e s o f Northwest v a r i e t y are shown i n F i g u r e 13. 3.10 S p e c t r a l C h a r a c t e r i s t i c s The v i s u a l o r s u b j e c t i v e c o l o u r measurements were compared with the s p e c t r a l c h a r a c t e r i s t i c s of the strawberry s u r f a c e . These r e s u l t s were then used i n the design o f an e l e c t r o n i c c o l o u r d e t e c t o r . A Unicam automatic spectrum r e c o r d e r ( F i g u r e 14) was used t o o b t a i n the r e l a t i v e r e f l e c t a n c e curves of the strawberry s u r f a c e . A 2.54 cm diameter s u r f a c e from the lower p o r t i o n o f each strawberry was h e l d i n a metal h o l d e r ( F i g u r e 15), covered with saran wrap, and scanned over the v i s i b l e spectrum (400 nm* t o 700 nm) on the f a s t speed o f the Unicam. The spectrophotometer was c a l i b r a t e d f o r 100 percent r e f l e c t a n c e on a magnesium oxide s u r f a c e ( r e f l e c t a n c e factor 5'" 1 0.97). S p e c t r a l analyses were c a r r i e d out on 118 samples over the 1970 har v e s t season. The r e l a t i v e r e f l e c - tance curves p l o t t e d by the instrument were recorded on a l o g a r i t h m i c s c a l e ( F i g u r e 16). These curves were converted i n t o normal curves and p l o t t e d on an a r i t h m e t i c s c a l e . F i g u r e 17 shows t y p i c a l r e l a t i v e r e f l e c t a n c e curves f o r t o t a l l y green, ready t o p i c k and o v e r - r i p e s t r a w b e r r i e s . The s i m p l e s t way t o d i s c r i m i n a t e s t r a w b e r r i e s as .to c o l o u r i s to c h a r a c t e r i z e i t s r e f l e c t a n c e curve by a s i n g l e measurement of r e f l e c t a n c e . I t may be assumed t h a t any one p e c u l i a r i t y i n the r e f l e c t a n c e p r o p e r t i e s o f straw- _c * 1 nanometer (nm) = 1 x 10 meters. Is the r a t i o o f r e f l e c t e d l i g h t t o i n c i d e n t l i g h t . Figure 14. Unicam a u t o m a t i c r e c o r d i n g spectrophotomet e r 29. Figure 15. Strawberry s u r f a c e h e l d i n sample holder ;.».:f'.':.»:i:.' :"T.i i L'-I:M.'(V I I C 8 +-> 10 4H 7 0 0 •10 6 0 2 0 0 0 WAVELENGTH MILLIMICRONS A L I G N W I T H INDEX C N T H E RECORDER SAMPLE A N D F O R M U L A READY TQ PICK STRAWBERRY C O N C E N T R A T I O N ( S C A N SPEC!) FAS I . SI Ov/ : : :ENCE MgO. R. F. 0. 97AIE June 19, 1970 I'ATII L E N G T H M M | O P E R A T O R FIGURE 16. A t y p i c a l r e l a t i v e r e f l e c t a n c e curve f o r a strawberry s u r f a c e recorded on the l o g a r i t h m i c s c a l e . PERCENT RELATIVE R E F L E C T A N C E © f— O 1 o T " O CO o ,'v O O O O 3 b e r r i e s i s c h a r a c t e r i s t i c o f a l l the s t r a w b e r r i e s . Hence, c o l o u r measurements o f f r u i t can be c o n f i n e d only to one o r more narrow r e g i o n s o f the spectrum where such anamolies are known to oc c u r . I t i s e v i d e n t t h a t t h i s measurement should be made i n the r e g i o n o f the spectrum where change i n r e f l e c t a n c e between c o n s e c u t i v e c o l o u r c l a s s e s i s g r e a t e s t . In t h i s r e s p e c t the r e s u l t s shown i n Figure 17 are o f p a r t i c u l a r s i g n i f i c a n c e s i n c e the r e l a t i v e r e f l e c t a n c e up to 520 nm does not change s i g n i f i c a n t l y over the range o f b e r r y r i p e n e s s ; and from the 650 nm wavelength and above, the d i f f e r e n c e i n r e l a t i v e r e f l e c t a n c e i s once again i n s i g n i f i c a n t over the b e r r y r i p e n e s s . However, there i s a sharp d i f f e r e n c e between the r e l a t i v e r e f l e c t a n c e s over the 520 nm to 650 nm range and b e r r y r i p e n e s s . The wavelength which best r e p r e s e n t s the s u r f a c e c o l o u r c o u l d be found by c o r r e l a t i n g the r e f l e c t a n c e s a t d i f f e r e n t wavelengths wi t h t h e , v i s u a l c o l o u r judgements. E i g h t wavelengths were s e l e c t e d and r e f l e c t a n c e s at these wavelengths were c o r r e l a t e d with the v i s u a l c o l o u r e v a l u a - t i o n s . The a n a l y s i s i n d i c a t e s t h a t the h i g h 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 was -0.740 at 525 nm wavelength. The n e g a t i v e value o f c o r r e l a t i o n c o e f f i c i e n t i n d i c a t e s t h a t r e f l e c t a n c e at 525 nm (green r e g i o n o f the spectrum) decreases as the s u r f a c e red c o l o u r i n c r e a s e s o r the b e r r y matures. The simple r e g r e s s i o n of r e f l e c t a n c e at 525 nm on v i s u a l e v a l u a t i o n of percent s u r f a c e redness f o r 118 samples gave the f o l l o w i n g e q u a t i o n : R c o c = 17.16 - 0.17 R [7] 525 : : 17.16 - n = = 118 Sy : : 27.33 2 r = = 0.551 525 : = Percent R : = Percent where R I P The h i g h e s t c o r r e l a t i o n o f v i s u a l c o l o u r e v a l u a t i o n with' t h a t o f r e f l e c t a n c e i n the red r e g i o n o f the spectrum was 0.562 at 630 nm wavelength. To measure the r e f l e c t a n c e at 525 nm f o r the c o l o u r measuring system, the f r u i t can be i l l u m i n a t e d with l i g h t r e s t r i c t e d t o a narrow band o f wavelengths i n the v i c i n i t y o f 525 nm. A p o r t i o n of l i g h t r e f l e c t e d i s i n t e r c e p t e d by a p h o t o c e l l . The r e s u l t i n g p h o t o e l e c t r i c c u r r e n t i s propor- t i o n a l to the r e f l e c t a n c e o f the b e r r y . The c u r r e n t magnitude i s a l s o i n f l u e n c e d by f a c t o r s o t h e r than strawberry r e f l e c t a n c e . These f u n c t i o n a l r e l a t i o n s h i p s can be expressed by: I = SR [8] where I i s the p h o t o e l e c t r i c c u r r e n t , R i s the p e r c e n t strawberry r e f l e c t a n c e , S i s the s e n s i t i v i t y of the system. The component S comprises such q u a n t i t i e s as p h o t o c e l l s e n s i t i v i t y , i n t e n s i t y of i l l u m i n a t i o n , b e r r y shape and s i z e , l o c a t i o n and o r i e n t a t i o n of b e r r y w i t h r e s p e c t to i l l u m i n a n t 34. and p h o t o c e l l , s u r f a c e roughness, g l o s s , and wetness. Although the e l e c t r o n i c measurement of s u r f a c e r e f l e c t a n c e o f b e r r i e s at t h i s wavelength would g i v e a reasonably good e v a l u a t i o n o f b e r r y r i p e n e s s , i t would, however, i n c o r p o r a t e many e r r o r s caused by v a r i a b l e s r e p r e s e n - t e d by S, and v a r i a t i o n i n instrument response at d i f f e r e n t r e f l e c t a n c e s . T h e r e f o r e , i f measurements o f s u r f a c e r e f l e c - tances are made at one wavelength, i n a c c u r a c i e s caused by measurements would be i n c o n s i s t e n t f o r d i f f e r e n t l e v e l s o f r e f l e c t a n c e s . T h i s method might, n e v e r t h e l e s s , be u s e f u l i f the v a r i a t i o n i n R between c o n s e c u t i v e r e f l e c t a n c e s o f v a r i o u s b e r r i e s were very great i n comparison to the v a r i a t i o n i n the f a c t o r s r e p r e s e n t e d by S. And, ag a i n , because of hetrogeneous mixture of green and red c o l o u r f o r d i f f e r e n t b e r r i e s even of the same l e v e l of m a t u r i t y , t h i s method i s i m p r a c t i c a l f o r d i s c r i m i n a t i n g b e r r i e s a c c o r d i n g to t h e i r c o l o u r . 3.11 Colour C r i t e r i a Another q u a n t i t y proposed as a c r i t e r i o n of colour 1 i s the r a t i o o f r e f l e c t a n c e at two s e l e c t e d wavelengths. T h i s c o l o u r c r i t e r i o n whose measured value i s independent o f instrument s e n s i t i v i t y has long been used i n c o l o r i m e t r y . The r a t i o o f r e f l e c t a n c e s at two wavelengths, c a l l e d the r e f l e c t a n c e r a t i o , was computed f o r each b e r r y f o r a number - ., . . , . 600 640 650 . of p o s s i b l e combinations, e.g. gTjrjs j f ^ o ' "530" e t c . Out o f a l l the r e f l e c t a n c e . r a t i o s f o r each b e r r y , one r e f l e c t a n c e r a t i o was r e q u i r e d to r e p r e s e n t the s u r f a c e c o l o u r . T h i s was determined by s t a t i s t i c a l l y comparing a l l r e f l e c t a n c e r a t i o s f o r each b e r r y w i t h each b e r r y ' s s u r f a c e c o l o u r . The r e f l e c t a n c e r a t i o f o r a l l the b e r r i e s which gave the h i g h 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 was c o n s i d e r e d to b e s t r e p r e s e n t the s u r f a c e c o l o u r and was c a l l e d the m a t u r i t y r a t i o . 3.12 M a t u r i t y R a t i o The m a t u r i t y r a t i o has been e s t a b l i s h e d as the r a t i o o f r e f l e c t a n c e s at 650 nm and 525 nm. I t i s a good i n d i c a t o r o f strawberry r i p e n e s s and can be used e f f e c t i v e l y to d e f i n e m a t u r i t y o f the f r u i t . In the p r e s e n t study i t would be used t o d e f i n e q u a l i t y f o r h a r v e s t i n g purposes. A n a l y s i s i n d i c a t e d that the m a t u r i t y r a t i o i n c r e a s e s w i t h the i n c r e a s e i n s u r f a c e redness. F i g u r e 18 shows the r e l a t i o n between m a t u r i t y r a t i o and percent s u r f a c e redness o f s t r a w b e r r i e s . The simple r e g r e s s i o n i n d i c a t i n g the r e l a t i o n between the two values i s : . Mr = -1.7 6 + 0.11 Rp [9] n = 118 Sy = 29.05 r 2 = 0.493 where Mr = M a t u r i t y r a t i o , Rp = Percent s u r f a c e redness. F I G U R E 1 8 . Least square simple r e g r e s s i o n of m a t u r i t y r a t i o on percent s u r f a c e r e d . 37. I t can be d e r i v e d from the above r e l a t i o n t h a t as the f r u i t r i p e n s the value o f m a t u r i t y r a t i o i n c r e a s e s , Almost a l l the s t r a w b e r r i e s from green to o v e r - r i p e have m a t u r i t y r a t i o s ranging between 0 to 10. Negative c o r r e l a - t i o n between m a t u r i t y r a t i o and r e f l e c t a n c e at 52 5 nm wave- l e n g t h i n d i c a t e s the percent green c o l o u r on the s u r f a c e decreases as the ma t u r i t y r a t i o i n c r e a s e s . Simple c o r r e l a - t i o n among m a t u r i t y r a t i o , FRF, F/W, percent s u r f a c e redness and BYP are given i n Table I I I . TABLE I I I ' CORRELATION MATRIX FOR SPECTRAL AND RHEOLOGICAL PROPERTIES Lin.Lmt. BYP. 5 2 5 nm r r. n Matu-650 nm .. r i t y R a t i o Tan. Percent Day Mod. Red Lin.Lmt. 1.0 BYP. 0.47 1.0 nm-5 25 0.14 0. 54 1.0 nm-6 5 0 0. 20 0.00 -0,06 1.0 M a t u r i t y R a t i o -0.18 -0.47 -0.76 0.24 1.0 Tan.Mod. 0.28 0.76 0.57 -0.06 -0.44 1.0 Percent Red -0.19 -0 . 57 -0.74 -0.05 0.70 -0.51 1.0 Day -0.27 -0.27 0..14 -0.44 -0.21 -0.05 -0.01 1.0 The b i o y i e l d p o i n t and tangent modulus have poor c o r r e l a t i o n with rnaturi t y r a t i o . The value of tangent modulus decreases as the ma t u r i t y r a t i o i n c r e a s e s f u r t h e r c o n f i r m i n g t h e f a c t t h a t t he b e r r y becomes s o f t e r as i t r i p e n s . The d e c r e a s e d v a l u e o f b i o y i e l d p o i n t w i t h i n c r e a s i n g r i p e n e s s ( i n c r e a s e d v a l u e o f m a t u r i t y r a t i o ) shows t h a t t he b e r r y becomes i n c r e a s i n g l y s u s c e p t i b l e t o m e c h a n i c a l damage. I n q u a l i t y c o n t r o l o p e r a t i o n s t h e c o l o u r o f p r oduc t s i s u s u a l l y e v a l u a t e d i n CIE (Commiss ion I n t e r n a t i o n a l e de L ' E c l a i r a g e ) v a r i a b l e s . Because o f h i g h p r i c e s o f s o p h i s t i - c a t e d s p e c t r o p h o t o m e t e r s t h e measurements i n c o l o u r v a r i a b l e s a r e made on l e s s e x p e n s i v e equ ipment such as a Hun te r C o l o u r D i f f e r e n c e Me te r o r H i t a c h i P e r k i n - E l m e r S p e c t r o p h o t o m e t e r . These v a r i a b l e s c a n , however , be c o n v e r t e d i n t o CIE s t a n d a r d s f o r c o m p a r i s o n . A s t u d y c a r r i e d out on a l i m i t e d number o f samples show ( T a b l e IV) t h a t CIE '>", y and ss v a l u e s have good c o r r e l a t i o n w i t h t h e s u r f a c e r edne s s v a l u e o f a s t r a w b e r r y . TABLE IV CORRELATION MATRIX FOR CIE COLOUR VARIA3LES OF STRAWBERRY SURFACE P e r c e n t S u r f a c e Red Y - v a l u e C I E - x C IE -y Percent- S u r f a c e . Red 1.00 0. 893 0. 8 74 0. 870 Y - v a l u e C I E - x C IE -y 1.00 1.00 1.0 0 S t u d i e s c a r r i e d ou t by Hoover and Denn i son (23) cn a H u n t e r C o l o u r D i f f e r e n c e Me te r w i t h an ' 1 R d ' c i r c u i t t o measure t h e c o l o u r o f s t r a w b e r r i e s , showed t h a t c o r r e l a t i o n between s u r f a c e r edne s s and ' a ' v a l u e was s i g n i f i c a n t l y h i g They s u g g e s t e d t h a t ' a ' v a l u e w h i c h i s i n d i c a t i v e o f r e d p igment i n t he s t r a w b e r r i e s c o u l d be used e f f e c t i v e l y f o r q u a l i t y c o n t r o l . But any e v a l u a t i o n o f c o l o u r o f s t r a w - b e r r i e s by a method such as above i s l i m i t e d i n scope u n l e s i t can be r e l a t e d t o some known r e p r o d u c i b l e s t a n d a r d s . M o r e o v e r , t h e CIE v a l u e s and t h e Hun te r C o l o u r D i f f e r e n c e Me te r v a r i a b l e s a r e no t j u s t i f i e d f o r c o l o u r e v a l u a t i o n o f p a r t i a l l y r i p e o r even r i p e b e r r i e s because t h e c o l o u r o f t he s t r a w b e r r y i s no t u n i f o r m o v e r t he e n t i r e b e r r y s u r f a c e no. 4. DESIGN OF COLOUR MEASURING SYSTEM T h i s chapter d i s c u s s e s the design o f a c o l o u r d e t e c t i o n system. The o p t i c a l and o p e r a t i o n a l d e s i g n con- s i d e r a t i o n s which a f f e c t the performance o f the system, the e l e c t r o n i c c i r c u i t r y and i n s t r u m e n t a t i o n of the system have a l s o been d i s c u s s e d . 4 • .Theory o f Design I t has been e s t a b l i s h e d t h a t m a t u r i t y r a t i o i s a measure o f f r u i t r i p e n e s s and any d i s c r i m i n a t i o n between the r i p e and unri p e s t r a w b e r r i e s can be made based on the value o f m a t u r i t y r a t i o . .In or d e r to d i v i d e the s t r a w b e r r i e s between two c a t e g o r i e s , mature (ready t o p i c k ) and immature (not ready t o p i c k ) , one value o f m a t u r i t y r a t i o has to be s e l e c t e d . T h i s value which marks the d i v i d i n g l i n e between mature and Immature b e r r i e s was c a l l e d m a t u r i t y c o e f f i c i e n t . The s e p a r a t i o n was achieved by comparing the s u b j e c t i v e c o l o u r d e t e r m i n a t i o n s made on the strawberry c o l o u r and value o f ma t u r i t y r a t i o o b t a i n e d from r e l a t i v e r e f l e c t a n c e curves. The mature b e r r i e s were e s t a b l i s h e d as those b e r r i e s having 80 percent o r more s u r f a c e redness. The b e r r i e s were separated a l l o w i n g d i f f e r e n t , values o f the ma t u r i t y r a t i o t o be the ma t u r i t y c o e f f i c i e n t and s e p a r a t i n g the mature and immature b e r r i e s . The b e r r i e s with a m a t u r i t y r a t i o h i g h e r than the m a t u r i t y c o e f f i c i e n t are to be p i c k e d and b e r r i e s w i t h the ma t u r i t y r a t i o lower than the m a t u r i t y c o e f f i c i e n t are to be r e j e c t e d . These r e s u l t s were then compared to the v i s u a l c o l o u r judgement and the mat u r i t y 41. c o e f f i c i e n t t h a t wou ld g i v e t h e minimum l o s s o f b e r r i e s was f o u n d . The l o s t b e r r i e s i n c l u d e d t he immature b e r r i e s h a v i n g a v a l u e o f m a t u r i t y r a t i o more t h a n t h e m a t u r i t y c o e f f i c i e n t , and t h e mature b e r r i e s h a v i n g a v a l u e o f m a t u r i t y r a t i o l e s s t h a n t h e m a t u r i t y c o e f f i c i e n t . F i g u r e 19 shows t he percent- b e r r i e s l o s t by c o n s i d e r i n g d i f f e r e n t v a l u e s o f m a t u r i t y c o e f f i c i e n t s . The p e r c e n t l o s t b e r r i e s d e c r e a s e s w i t h s e l e c t i o n o f i n c r e a s i n g v a l u e o f m a t u r i t y c o e f f i c i e n t u n t i l t he v a l u e r e a c h e s 4 . 5 . H i g h e r v a l u e s g i v e i n c r e a s i n g l o s s o f b e r r i e s . A sample o f 118 b e r r i e s gave a minimum l o s s o f 10 p e r c e n t a t a m a t u r i t y c o e f f i c i e n t o f 4 . 5 . The s e l e c t i v e s e p a r a t i o n o f s t r a w b e r r i e s wou ld thu s be a c h i e v e d i n t h i s s y s tem by mak ing r e f l e c t a n c e measurements a t 650 nm and 525 nm w a v e l e n g t h s and where t h e r e f l e c t a n c e r a t i o i s e q u a l t o , o r g r e a t e r t han 4 . 5 , t he b e r r y i s r i p e and r eady t o p i c k . The pu rpo se o f t he sy s tem i s t o measure a va lu© o f r e f l e c t a n c e c o e f f i c i e n t and t o o b t a i n a c o r r e s p o n d i n g m e c h a n i c a l r e s p o n s e . 4.2 C o l o u r D i s c r i m i n a t o r The a c c u r a c y o f manual p i c k i n g i s adequate enough for c o m m e r c i a l p u r p o s e s . I t i s q u e s t i o n a b l e , t h e n , whe the r even a s m a l l i n v e s t m e n t wou ld be j u s t i f i e d s o l e l y f o r i n c r e a s e d p r e c i s i o n . The p r o b l e m , t h e r e f o r e , i s one o f r e d u c i n g c o s t s w h i l e m a i n t a i n i n g a c c u r a c y o f p i c k i n g a p p r o x i m a t e l y a t t he same l e v e l as t h a t o f hand p i c k i n g . FIGURE 19. Showing the t h e o r e t i c a l l o s s d i s t r i b u t i o n by s e l e c t i n g d i f f e r e n t values of m a t u r i t y c o e f f i c i e n t . I n a h a r v e s t i n g m a c h i n e , d e t e c t i o n o f c o l o u r i s one o f t h e many o p e r a t i o n s i n a sequence w h i c h i n c l u d e s , p i c k i n g , o r i e n t a t i o n , d e t e c t i n g , h a r v e s t i n g , c o n v e y i n g , s t o r i n g and h a u l i n g . I f any o p e r a t i o n s h o u l d i n t e r r u p t f o r a s h o r t p e r i o d o f t i m e , a l l o f them must s t o p . The c o n t i n u i t y o f o p e r a t i o n i s thus o f g r e a t i m p o r t a n c e . The d i s t r i b u t i o n o f s t r a w b e r r i e s o v e r t h e row i n d i c a t e s a t o t a l o f 144 b e r r i e s p e r f o o t (0.33 M). Even though i t m igh t be p o s s i b l e t o d e s i g n a c o l o u r s e n s o r t o h a n d l e f u l l f l o w o f b e r r i e s , i t wou ld be q u e s t i o n a b l e w h e t h e r such a machine i s a d v i s a b l e . I t wou ld be b e t t e r t o d i v i d e t h e f l o w among two o r more s en s o r s mounted on t he same machine so t h a t t empo ra r y f a i l u r e o f one s e n s o r does no t i n t e r r u p t the whole o p e r a t i o n . The c o l o u r o f s t r a w b e r r i e s i s f a r f r om u n i f o r m . Even t h e r i p e r f r u i t s a re b l o t c h y and might have p a t c h e s o f g r een c o l o u r . A l t h o u g h , t o v i ew t h e e n t i r e b e r r y s u r f a c e c o l o u r wou ld be u n e c o n o m i c a l , t h e e s s e n t i a l c r i t e r i o n f o r an e f f i c i e n t c o l o u r d e t e c t i n g s y s tem wou ld be t o v i ew as much s u r f a c e a r e a as i s e c o n o m i c a l l y p o s s i b l e . The geometry o f a l i g n m e n t o f p h o t o d i o d e s , a n g l e o f v i e w i n g and d i s t a n c e o f • p h o t o d i o d e f r om the b e r r y s u r f a c e wou ld be i m p o r t a n t i n t h i s c o n t e x t . I n c o m m e r c i a l o p e r a t i o n s t h e s t r a w b e r r i e s may be w e t , c o v e r e d w i t h mud, t o o l i t t l e o r t o o much i l l u m i n a t i o n o r s u n s h i n e . I t i s d e s i r a b l e t h e r e f o r e , t h a t t h e s y s tem i s •capable o f adjustment f o r o p e r a t i o n under these c o n d i t i o n s . A l l kinds of adverse f i e l d c o n d i t i o n s can be expected d u r i n g the machine o p e r a t i o n . The requirements c a l l not only that the machine be rugged and compact but a l s o t h a t i t perform e f f i c i e n t l y and a c c u r a t e l y d u r i n g a c t u a l o p e r a t i o n . ^•3 The O p t i c a l Requirements To simulate manual s o r t i n g by an e l e c t r o n i c system some o f the b a s i c o p t i c a l c r i t e r i a have to be c o n s i d e r e d while measuring r e f l e c t a n c e . The components, namely i l l u m i - nant, o b j e c t and d e t e c t o r are e s s e n t i a l c o n s i d e r a t i o n s i n any c o l o u r measuring o p e r a t i o n . 4.3.1 The I l l u m i n a n t The r e f l e c t a n c e of a s u r f a c e i s the percentage o f i n c i d e n t l i g h t r e f l e c t e d by i t . The e f f i c i e n c y o f a system r e q u i r e s t h a t there i s enough r e f l e c t e d l i g h t so that s m a l l changes i n i l l u m i n a t i o n do not a d v e r s e l y a f f e c t the performance. Although, too i n t e n s e an i l l u m i n a t i o n might cause a s h i f t i n hue. The i l l u m i n a n t should p r o v i d e i l l u m i n a t i o n o f the same c o l o u r temperature over an extended p e r i o d o f o p e r a t i o n . The i l l u m i n a n t whose s p e c t r a l d i s t r i b u t i o n changes due to l o n g o p e r a t i o n time are not s u i t a b l e f o r c o l o u r measurement. I l l u m i n a n t s l i k e f l u o r e s c e n t l i g h t o r mercury lamps are a l s o not s u i t a b l e f o r such o p e r a t i o n s . The i l l u m i n a t i o n p r o v i d e d must be uniform. T h i s becomes a l l the more important i n the case, o f s t r a w b e r r i e s because o f t h e i r n on-uniformity i n s u r f a c e c o l o u r . The i l l u m i n a n t should i l l u m i n a t e the e n t i r e s u r f a c e of the straw- b e r r i e s . I t i s p r e f e r a b l e , but not e s s e n t i a l t h a t the i n c i d e n t l i g h t should be s t r a i g h t and p a r a l l e l . With present day devices t h i s i s not d i f f i c u l t . An i l l u m i n a n t equipped with f o c u s s i n g l e n s would be reasonably s u f f i c i e n t f o r the purpose. The o r i e n t a t i o n o f the i l l u m i n a n t w i t h r e s p e c t to the o b j e c t has c o n s i d e r a b l e e f f e c t on the measured r e f l e c - tance. While measuring d i f f u s e r e f l e c t a n c e the o b j e c t i s i l l u m i n a t e d from an angle o f 4 5° to the s u r f a c e o f the o b j e c t . 4.3 .2 The Object The s u r f a c e of the o b j e c t should be l e v e l and smooth w h i l e measuring d i f f u s e r e f l e c t a n c e . Although such a c o n d i t i o n i s i d e a l , the q u a l i t y o f s t r a w b e r r i e s cannot be s a c r i f i c e d . Moreover, the purpose here i s not c o l o u r s p e c i f i c a t i o n but e v a l u a t i o n o f b e r r y q u a l i t y . T h e r e f o r e , a l l the c o l o u r e v a l u a t i o n s would be comparative and not a b s o l u t e . Since c o n t i n u i t y o f o p e r a t i o n i s important, each b e r r y must move past the f i e l d o f i l l u m i n a n t and the viewing f i e l d o f the d e t e c t o r , and must be w i t h i n the viewing range o f d e t e c t o r f o r the time d u r i n g which measurements are made. 4 ' 3 • 3 The D e t e c t o r Of a l l the t h r e e components i n c o l o u r d e t e c t i o n , t h e c o l o u r d e t e c t o r i s most i m p o r t a n t . The u n i f o r m i t y o f o p e r a t i o n r e q u i r e s t h a t d e t e c t o r r e spon se be c o n s i s t e n t , a t l e a s t , o v e r t he range o f s pec t r um i n w h i c h t h e measu re - ments a re made. The economy o f o p e r a t i o n r e q u i r e s t h a t t h e d e t e c t o r 1 s h o u l d have t he l e a s t p o s s i b l e r e s p o n s e t i m e . A s l ow r e spon se d e t e c t o r c o u l d s l ow down t h e o p e r a t i o n o f t h e e n t i r e equ ipment t h e r e b y s e r i o u s l y r e d u c i n g t he c a p a c i t y and i n c r e a s i n g t h e c o s t . The d e t e c t o r , i n t h i s c a s e , s h o u l d p r e f e r a b l y be s m a l l and r u gged . Too b i g a d e t e c t o r wou ld cause c o n g e s t i o n a t t h e d e t e c t i o n head o f t h e mach i ne . Because t h e machine has t o o p e r a t e i n a d v e r s e f i e l d c o n d i t i o n s i t i s e s s e n t i a l t o have a d e t e c t o r wh i ch wou ld no t be a f f e c t e d by shocks and o t h e r m e c h a n i c a l h i n d r a n c e s . The d e t e c t o r s h o u l d have a w ide a n g l e o f v i ew so t h a t t h e e n t i r e o b j e c t can be v i e w e d . To measure d i f f u s e r e f l e c t a n c e t he d e t e c t o r must be a l i g n e d a t 90° t o t h e s u r f a c e o f t he o b j e c t . The d e t e c t o r must a l s o be a c c u r a t e s i n c e even a s m a l l v a r i a t i o n i n pe r f o rmance c o u l d cause s i g n i f i c a n t l o s s i n pe r f o rmance e f f i c i e n c y . 4.4 The De s i gn o f O p t i c a l Appa r a t u s A n a l y s i s has i n d i c a t e d t h a t t h e m a t u r i t y r a t i o i s a f u n c t i o n o f r e f l e c t a n c e a t 65 0 nm and 5 25 nm. I t i s e v i d e n t t h e r e f o r e t h a t t he r e f l e c t a n c e s a t t h e s e w a v e l e n g t h s s h o u l d be measured s i m u l t a n e o u s l y and w i t h equ ipment o f t h e same s e n s i t i v i t y . T h i s was done by i l l u m i n a t i n g t h e s t r a w - 47. berries with one illuminant and measuring the reflectances with two photodiodes of the same s e n s i t i v i t y . The d e t a i l s of photodiodes are discussed l a t e r i n the chapter. The o p t i c a l apparatus used for the purpose i s shown in Figure 20. The il l u m i n a t i o n was provided by a 12 V tungsten lamp, (colour temperature 2 8 5 4 ° K ) . The lamp was of fix e d i n t e n s i t y and could be operated on AC or DC voltages. A focussing lens was mounted i n front to focus the l i g h t on the object. The refl e c t e d l i g h t was f i l t e r e d through two narrow band interference f i l t e r s . Since f i l t e r s of exact s p e c i f i c a t i o n were not av a i l a b l e , f i l t e r s with a close approximation were used. In the prototype, two available Balzer interference f i l t e r s with peak transmission at 640 nm and 540 nm and with 9 nm ha l f band width were used to make measurements at these wavelengths. The f i l t e r e d reflectances were intercepted by two Hewlett-Packard #HP 5082-4205 pin photodiodes. The photodiodes were preferred over the t r a d i t i o n a l photo tubes because of t h e i r compactness-, p o r t a b i l i t y and e f f i c i e n c y . The photodiodes had a response time of less than one nanosecond. Other spe c i f i c a t i o n s f o r the photodiodes are given in Appendix A. Because of highly d i r e c t i o n a l s e n s i t i v i t y of the photodiodes, t h e i r axis has to be within + 10 degrees of the dire c t i o n of refl e c t e d l i g h t . 14 • 5 The.__E_1_< .̂CĴ £<?nAc_ A PParatus To evaluate the s u i t a b i l i t y of the system an 48 . inteference filter FIGURE 20. O p t i c a l apparatus f o r c o l o u r measuring system. FIGURE 21. Cross s e c t i o n a l view of the f i l t e r - probe assembly. (Not to s c a l e ) . 49. e x p e r i m e n t a l apparatus was t e s t e d i n the l a b o r a t o r y . The t e s t s were l i m i t e d to the o p e r a t i o n a l e f f i c i e n c y , the speed o f performance, and the e f f e c t o f d i f f e r e n t parameters on performance o f the system. The e l e c t r o n i c apparatus c o n s i s t e d o f f o u r primary components namely, the c o l o u r sensor o r probe, a m p l i f i e r , v o l t a g e comparator, and the e l e c t r o n i c switch o r s o l e n o i d . 4.5.1 The Probe The probe assembly c o n s i s t e d o f i n t e r f e r e n c e f i l t e r , the p i n photodiode and the probe c i r c u i t r y . The c o n s t r u c t i o n of f i l t e r assembly and probe c i r c u i t r y i s shown i n Fi g u r e 21 and 22. The probe c a s i n g was formed from 1/16 i n c h (1.5 mm) copper tube of 25 mm diameter. The f i l t e r was h e l d i n a rubber h o l d e r at one end o f the probe. The photodiode was h e l d behind the f i l t e r on a p l e x i g l a s s mount. Foam padding was used to cushion the photodiodes. The probe c i r c u i t was o b t a i n e d from Hewlett-Packard a p p l i c a t i o n notes 915 (21). 4.5.2 A m p l i f i e r The a m p l i f i e r ( F i g u r e 23) was m o d i f i e d from a c i r c u i t suggested by Hewlett-Packard (1967) f o r use with p i n photodiodes. The photodiodes, f i e l d e f f e c t t r a n s i s t o r , and 10 Meg fl r e s i s t o r were mounted w i i t h the probe c i r c u i t . The t h r e e l e a d s which are separated from ground by h i g h impedence were kept s h o r t t o minimize pickup. The a m p l i f i e r was mounted on a p e r f o r a t e d c i r c u i t board and e n c l o s e d i n a 5082-4205 PIN DIODE 10 M E G Q AA/WVV < FEEDBACK D 2N3457- FET < + 9 V < SIGNAL < - 9 V C i r c u i t diagram for Probe assembly 8-4 V 8-4 v FIGURE'23.. C i r c u i t diagram f o r s i g n a l a m p l i f i e r m e t a l c a s i n g . 4 .5 .3 V o l t a g e Comparato r The pu rpose o f t h e c ompa ra t o r was t o ge t a mechan i c s r e s p o n s e a t t h e s o l e n o i d c o r r e s p o n d i n g t o t h e m a t u r i t y r a t i o measurements made by t h e p r o b e s . The c i r c u i t d i a g r a m f o r t h e v o l t a g e c ompa ra t o r i s shown i n F i g u r e 24. The c u r r e n t f l o w i n g t h r o u g h t h e i n d i v i d u a l p robe i s p r o p o r t i o n a l t o t h e r e f l e c - t a n c e a t ' w h i c h t he measurements a re b e i n g made by t h a t p r o b e . The s i g n a l v o l t a g e E R o b t a i n e d f r om t h e 64 0 nm m e a s u r i n g p robe ( r ed c o l o u r r e g i o n o f t h e s pec t rum) was r e a d on a d i g i t a l v o l t m e t e r . T h i s v o l t a g e was r educed t o o n e - f i f t h , ^R/5 ' °~ ^ e o r i g i n a l v a - l u s t>y a 1 0 - t u r n p o t e n i o m e t e r . The s i g n a l s f rom the probe mea su r i n g r e f l e c t a n c e a t 540 nm ( g reen c o l o u r r e g i o n o f s p e c t r u m ) , E g , was compared w i t h t h e ou tpu t s i g n a l o f a p o t e n t i o m e t e r by o p p o s i n g c u r r e n t s f r om each p r o b e . The r e s u l t i n g s i g n a l was f e d i n t o a z eno r d i o d e wh i ch i n t u r n c o n t r o l l e d t h e s i g n a l a t t h e s o l e n o i d . 4 .5 .4 The_ SoJLenoid The s o l e n o i d was t he component used t o o b t a i n t he m e c h a n i c a l r e s p o n s e c o r r e s p o n d i n g t o t he measured v a l u e o f m a t u r i t y r a t i o . The c u r r e n t f l o w i n t h e s o l e n o i d was c o n t r o l l e d by a zeno r d i o d e i n t he c o m p a r a t o r . I f t h e measured v a l u e o f m a t u r i t y r a t i o i s more t h a n 5 ( m a t u r i t y c o e f f i c i e n t ) , t he s o l e n o i d wou ld come t o ' c l o s e ' p o s i t i o n , but i f t h e measured v a l u e o f m a t u r i t y r a t i o i s l e s s t han 5 t he s o l e n o i d wou ld r ema i n i n ' o p e n ' p o s i t i o n . SOLENOID T O A M P . R E D S I G . 10K 10 T U R N " P O T T O A M P . G R E E N S ! G 10k AAAAA FIGURE 24. Schematic diagram f o r v o l t a g e comparator and s o l e n o i d cn co 4.6 The T e s t R e s u l t s An e x p e r i m e n t a l s e t - u p shown i n F i g u r e s 2 5 and 2 6 was used t o t e s t the e l e c t r o n i c s y s t em. A c i r c u l a r d i s c , p a i n t e d w i t h b l a c k mat te p a i n t on i t s p e r i p h e r y , was r o t a t e d by a v a r i a b l e speed moto r . S t r a w b e r r i e s were p l a c e d i n 12 e q u i s p a c e d h o l e s a l o n g t h e p e r i p h e r y o f t he d i s c . Each b e r r y i n t h e h o l e was i l l u m i n a t e d f rom t h e t o p by a 12V t u n g s t e n l amp, as i t pa s sed under t h e v i e w i n g f i e l d o f two p h o t o d i o d e s . The e l e c t r o n i c s y s tem was z e r oed f o r r e f l e c t a n c e f rom a b l a c k s u r f a c e . As t h e b e r r i e s pa s sed under ' t he p h o t o d i o d e s , t he r e f l e c t a n c e was measured by p h o t o d i o d e s a t an a n g l e between 4 0° - 4 5° t o the b e r r y s u r f a c e , a r r a n g e d i n t h r e e d i m e n s i o n a l symmetry about t h e s t r a w b e r r y . 4.6.1 Speed o f Response The maximum speed o f r e spon se was measured a t the s o l e n o i d by i n c r e a s i n g t he speed o f r o t a t i o n o f t he d i s c u n t i l t he s o l e n o i d wou ld no l o n g e r r e spond t o t h e s i g n a l change. The maximum re spon se t i m e o b t a i n a b l e f rom t h e components used was 0.166 seconds p e r s t r a w b e r r y . T h i s t i m e was l i m i t e d by t he s o l e n o i d r e spon se t o t h e m a t u r i t y r a t i o s i g n a l ( e l e c t r i c a l ) . A l t h o u g h such a r e spon se i s low f o r t h e e c o n o m i c a l per formance ' o f a h a r v e s t i n g s y s t e m , t he speed can be i n c r e a s e d by u s i n g a f a s t e r r e spon se s o l e n o i d o r d i f f e r e n t t r a n s d u c e r . > o DIGITAL VOLTMETER F I G U R E 2 5 . Schematic diagram of experimental arrangement f o r t e s t i n g c o l o u r d i s c r i m i n a t o r equipment. 56. F i g u r e 26. General view of the experimental equipment f o r t e s t i n g c o l o u r d i s c r i m i n a t o r equipment. 57. 4 , 6 , 2 S u r f a c e and I l l u m i n a t i o n C o n d i t i o n s . A number o f s t r a w b e r r i e s f r e s h l y p i c k e d f rom t h e f i e l d were t e s t e d under t h e s y s t em. The shape and s u r f a c e and s u r f a c e c o n d i t i o n s have no e f f e c t on t h e p e r f o r m a n c e o f t he s y s t em. The s y s tem p e r f o r m e d s a t i s f a c t o r i l y under l a b o r a t o r y c o n d i t i o n s and a l l t h e samples c o u l d be i d e n t i f i e d by t h e e l e c t r i c a l s i g n a l , g i v i n g a 10 0 p e r c e n t p e r f o r m a n c e . The f l u o r e s c e n t and s t r a y l i g h t had no e f f e c t on t h e pe r f o rmance bu t d i r e c t s u n l i g h t causes a s h i f t i n t h e v a l u e o f measured m a t u r i t y r a t i o . The s i g n a l p r oduced by each f r u i t was f ound I ndependent o f t h e s u r f a c e c o n d i t i o n s w i t h i n the l i m i t s o f t h e a c c u r a c y o f measurements . A l t h o u g h i t seems p r o b a b l e t h a t s u r f a c e c o n d i t i o n s do t o some e x t e n t a f f e c t t h e s i g n a l , any change i n o u t p u t i s masked by t h e n o i s e l e v e l . An e f f e c t o f t h i s magn i tude i s u n i m p o r t a n t i n c o m m e r c i a l o p e r a t i o n s o f t h i s k i n d . The r e s u l t s o f t e s t s c onduc ted i n t h e 19 71 season a re g i v e n i n T a b l e V. TABLE V. R e s u l t s o f t h e t e s t s c o n d u c t e d on t h e e l e c t r o n i c c o l o u r d e t e c t i o n s y s tem f o r pe r f o rmance e f f i c i e n c y u s i n g No r thwes t v a r i e t y o f s t r a w b e r r i e s . " N o . " o f T o t a l l o s t b e r r i e s b e r r i e s u n r i p e a c c e p t e d o r r i p e r e j e c t e d P e r c e n t l o s s Not r eady t o p i c k 207 52 25 Ready t o p i c k 177 25 14.4 T o t a l 384 77 20 58 4 . 6 . 3 The Angle o f I l l u m i n a t i o n and D e t e c t i o n The angle o f viewing had no e f f e c t when the measure- ments were c o n f i n e d between 10° to 60° from the i n c i d e n t i l l u m i n a t i o n on the strawberry s u r f a c e . But the maximum output s i g n a l was ob t a i n e d when the r e f l e c t a n c e was measured at an angle between 4 0° t o 45° from the i n c i d e n t i l l u m i n a t i o n 4.6.4 The Instrument S t a b i l i t y The system was t e s t e d f o r i t s s t a b i l i t y by comparing the r e s u l t s performed on the same samples at two d i f f e r e n t times. A sample o f 24 s t r a w b e r r i e s were t e s t e d j u s t a f t e r s w i t c h i n g on the. system and the same samples were t e s t e d a f t e r s e v e r a l hours. There was no a p p r e c i a b l e s h i f t i n the s i g n a l s to j u s t i f y the e f f e c t o f "warm up" p e r i o d . The system i s t h e r e f o r e capable o f performing a c c u r a t e l y without having t o wait f o r long warm up p e r i o d s . CONCLUSIONS T e s t s pe r f o rmed on t h e No r thwes t v a r i e t y o f s t r a w - b e r r i e s i n d i c a t e t h a t t h e f o l l o w i n g c o n c l u s i o n s can be drawn: 1. The mean f r u i t - r e t e n t i o n f o r c e o f r i p e s t r a w b e r r i e s d e c r e a s e s as t he h a r v e s t season p r o g r e s s e s . 2. The f r u i t - r e t e n t i o n force, d e c r e a s e s and t he s u r f a c e r edne s s i n c r e a s e s as t h e b e r r y r i p e n s . Bo th o f t h e s e c h a r a c t e r i s t i c s a r e a good measure o f b e r r y r i p e n e s s . 3. The r h e o l o g i c a l p r o p e r t i e s o f t he s t r a w b e r r i e s o b t a i n e d f rom t h e f o r c e - d e f o r m a t i o n c u r v e s a re good i n d i c a t o r s o f f r u i t q u a l i t y . The b i o y i e l d p o i n t had t h e h i g h e s t c o r r e l a t i o n w i t h FRF. These pa r amete r s can be e f f e c t i v e l y u sed i n t h e d e s i g n o f f r u i t h a n d l i n g components i n t h e h a r v e s t i n g mach ine . 4. The r e l a t i v e r e f l e c t a n c e at 525 nm ( g reen c o l o u r e d r e g i o n o f s pec t rum) d e c r e a s e d and r e l a t i v e r e f l e c - t a n c e a t 640 nm ( r e d c o l o u r e d r e g i o n o f s pec t rum) i n c r e a s e d as the b e r r y r i p e n s . 5. M a t u r i t y r a t i o i s an e x c e l l e n t i n d i c a t o r o f b e r r y r i p e - ness and c o u l d be used i n p l a c e o f v i s u a l c o l o u r e v a l u a t i o n s . I t can e f f e c t i v e l y be used as a d e c i d i n g pa r amete r f o r a s e l e c t i v e s t r a w b e r r y h a r v e s t e r . T h i s c r i t e r i a can a l s o be u sed f o r s e p a r a t i n g r i p e and u n r i p e b e r r i e s o r f o r g r a d i n g t he b e r r i e s i n a p r o c e s s i n g p l a n t . SUGGESTIONS FOR FUTURE WORK A l t h o u g h t h e r e s u l t s o f t he t e s t s c o n d u c t e d on t h e s t r a w b e r r i e s g i v e a f a i r l y good knowledge o f t he f r u i t b e h a v i o u r t o a p p l i e d mach ine f o r c e s , f u r t h e r s t u d y s h o u l d be c a r r i e d out on the s t r a w b e r r i e s t o i n v e s t i g a t e t h e e f f e c t s o f such o p e r a t i o n s as impac t l o a d i n g , b r u i s i n g due t o f r i c t i o n w i t h t he conveyo r s and v a r i a t i o n i n t he p h y s i c a l p a r a m e t e r s o f v a r i o u s v a r i e t i e s o f s t r a w b e r r i e s . The pe r f o rmance o f t h e e l e c t r o n i c s y s tem t o d i f f e r e n t i a t e between t h e r i p e and u n r i p e s t r a w b e r r i e s s h o u l d be i n v e s t i g a t e d w i t h a p r o t o t y p e o f t h e h a r v e s t e r i n a c t u a l f i e l d c o n d i t i o n s . S i n c e t h e speed o f r e spon se o f t h e s o l e n o i d may be l o w e r f o r e c o n o m i c a l o p e r a t i o n o f t he h a r v e s t i n g m a c h i n e , d i f f e r e n t t r a n s d u c e r s s h o u l d be t r i e d t o get optimum re spon se s peed . 61. LITERATURE CITED 1. A b r i d g e d C o l o r a t i o m e t e r y f o r P r o d u c t i o n Q u a l i t y C o n t r o l , A g r i c u l t u r a l C o n t r o l Systems I n c . , C a l i f o r n i a . 2. A g r i c u l t u r a l S t a t i s t i c s R e p o r t ; Department o f A g r i c u l - t u r e , P r o v i n c e o f B r i t i s h C o l u m b i a , V i c t o r i a , 19 68. 3. Where We S tand on M e c h a n i c a l H a r v e s t i n g o f S t r a w b e r r i e s , Amer i c an F r u i t G rower , May 19 69. 4. A u s t i n , M .E . , V .G . Shutak and E.P. C h r i s t o p h e r ; C o l o r Changes i n H a r v e s t Strawberry F r u i t , P r o c . Amer*, Soc. H o r t . S c i 75 : 382-386 , 1955. 5. B i r t h , G .S . ; A F i b e r O p t i c s R e f l e c t a n c e A t t a c h m e n t , A g r i c u l t u r a l E n g i n e e r i n g ,448-449 ( 8 ) , August 1967. . 6 . B i t t n e r , D.R. and K.O. S t e p h e n s o n ; R e f l e c t a n c e and T r a n s m i t t a n c e P r o p e r t i e s o f Tomatoes Ve r su s M a t u r i t y , ASAE Paper No. 6 8 -329 , June 1968. 7. B r i t i s h Co l umb i a Department o f A g r i c u l t u r e , H o r t i c u l t u r e B ranch .j P r o d u c t i o n o f B e r r y C r o p s , Grapes and F i l b e r t s t o g e t h e r w i t h an E s t i m a t e o f Farm V a l u e s , 1969. 8. B u c h e l e , W.F. and E.L. D e n i s e n ; M e c h a n i c a l H a r v e s t i n g o f S t r a w b e r r i e s , ASAE Paper No. 67 -620 , December 1967. 9. B u r k h a r d t , T .H . and R.F. M rozek ; L i g h t R e f l e c t a n c e as a C r i t e r i o n f o r S o r t i n g D r i e d P r u n e s , ASAE Pape r • No. 71 - 313 , June 19 71. 62. 10. Burr, A.H. and M.J. Duncan; P o r t a b l e S p e c t r o r a d i o m e t e r f o r Underwater Environments, Department o f B i o l o g i c a l S c i e n c e s , Simon F r a s e r U n i v e r s i t y , B.C. 11. Carne, I.C; Strawberry E n t e r p r i s e Data Sheet 1967 C o s t s , B r i t i s h Columbia Department o f A g r i c u l t u r e , A b b o t s f o r d , B.C. 12. Chen, P., M.O. B r i e n , F, Winter and S.J. Leonard; Mechanical means o f h a r v e s t i n g b e r r i e s , ASAE Paper No. 69-648, December 1969. 13. C l y d e s d a l e , F.M; The Measurement of C o l o r , Food Technology, V o l . 23, 16-22, January 1969. 14. CMT-200 and 200B C o l o r R a t i o Meters, Data Sheet; A g r i c u l t u r a l C o n t r o l Systems Inc., C a l i f o r n i a . 15. F i s c h e r , R.R., J.H. Von E l b e , R.T. S c h u l a r , H.D. Bruhn and J.D. Moore; Some P h y s i c a l P r o p e r t i e s of Sour C h e r r i e s , Trans. ASAE, V o l . 12, No. 2, 175-179, 1969. 16. F r a n c i s , F.J. and F.M. C l y d e s d a l e ; C o l o r Measurement o f Foods, Part IX; Food Product Development, February-March, 19 69, 17. ; C o l o r Measurement o f Foods, P a r t X I I I ; Food Product Development, April-May 19 69. 18. F r i d l e y , R.B., H. G o e h l i c h , L.L. C l a y p o o l and P.A. A d r i a n ; F a c t o r s A f f e c t i n g Impact I n j u r y to M e c h a n i c a l l y Harvested F r u i t , Trans. ASAE V o l . 2, No. 9; 409-411, 1964. 63. 19. Gaffney, J . J . and O.L. Jahn; P h o t o e l e c t r i c c o l o r S o r t i n g o f Vine Ripened Tomatoes, Marketing Research Report No. 868, USDA, Washington, D.C. 1970. 20. Heron, J.R., K.H. Kromer and G.L. Z a c h a r i a h ; V a r i a t i o n of Tomato R e f l e c t a n c e P r o p e r t i e s i n M a t u r i t y E v a l u a t i o n , ASAE Paper No. 71-329, J u l y 1971. 21. Hewlett Packard; T e c h n i c a l Data, P i n Photodiodes HP 5082-4200 S e r i e s , October 1968. 22. Hoag, Dean L. and D.R. Hunt; Mechanical S t r i p p i n g f o r H a r v e s t i n g S t r a w b e r r i e s , ASAE Paper No. 65-620, December 1965. 23. Hoover, M.W. and R.A. Dennison; A Rapid O b j e c t i v e Method f o r the E v a l u a t i o n of C o l o r i n S t r a w b e r r i e s , Proc. Amer. Soc. Hort. S c i . , 70: 195-198, 1955. 24. J a n i c k , J ; The Measurement o f F r u i t S i z e i n Strawberry. Proc. Amer. Soc. Hort. S c i . 76: 343-348, 1961. 25. L u r i a , S.M; C o l o r V i s i o n , P h y s i c s Today, 34-41, March 1966. 26. Mohsenin, N.N; 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 Animal M a t e r i a l . P a r t 1 of V o l . 1, Department o f A g r i c u l t u r a l E n g i n e e r i n g , The P e n n s y l v a n i a S t a t e U n i v e r s i t y , March 19 68. 27. Nelson, G.S. and A.A. K a f t a n ; Development of Mechanical H a r v e s t i n g and Grading Equipment f o r S t r a w b e r r i e s , Trans. ASAE-, V o l . 13, No. 5 , 743-745 , 1970. 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S c i . , 93: 317-325, 1969. Parker, B.E. and D.E. Waint; E f f i c i e n c y o f V i s u a l Manual Cherry S o r t i n g , A g r i c u l t u r a l E n g i n e e r i n g , V o l . 36, No. 1, 100-105, February 1955. Powers, J.B., J.T. Gunn and F.C. Jacob; E l e c t r o n i c C o l o r S o r t i n g of F r u i t s and Vegetables, A g r i c u l t u r a l E n g i n e e r i n g , V o l . 34, No. 3, 149-154, March 1953. 65. 36. Roth, L.O. and J.G. P o r t e r f i e l d ; Mechanical A i d s to Strawberry H a r v e s t i n g , ASAE Paper No. 6 0-644, December 1960. 37. Stephenson, K.Q; S e l e c t i v e F r u i t S e p a r a t i o n for Mechanical Tomato H a r v e s t e r , A g r i c u l t u r a l E n g i n e e r i n g , V o l . 45, No. 5, 250-253, May 1964. 66 APPENDIX A PIN PHOTODIODE (SERIES HP 5082-4200) SPECIFICATIONS Dimension i n i n c h e s O \o ZO 5 0 J X , \ • V, \ 40 R e l a t i v e d i r e c t i o n a l s e n s i t i v i t y o f D i n p h o t o d i o d e O p t i c a l and e l e c t r i c a l c h a r a c t e r i s t i c s a t 2 5°C S e n s i t i v e a r e a ... a v - m - 3 —,2 Diameter Speed o f response S e r i e s r e s i s t a n c e 3 X I O - 3 cm 2, 0.2 54 mm. <1 nanosecond. ' 50 fi.

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