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Mechanical strawberry harvesting Shikaze, George 1973

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MECHANICAL STRAWBERRY HARVESTING by GEORGE SHIKAZE B.A.Sc, University of B r i t i s h Columbia, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of AGRICULTURAL ENGINEERING We accept th i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 19 7 3 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C olumbia, I agree t h a t 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 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 agree 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 p urposes 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 n o t 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 The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada ABSTRACT Total strawberry production i n both Canada and the United States has been s t e a d i l y declining for the past decade. This trend can, to a large extent, be att r i b u t e d to the increasing cost and d i f f i c u l t y of getting t h i s crop manually harvested. This research, therefore, i s directed toward development of a mechanical harvesting system f o r strawberries. During i n i t i a l development of any new concept, a system analysis should be undertaken to ensure that excessively complicated problems w i l l not arise unexpectedly and to ensure that redundant research i s not undertaken. Such an analysis indicated that the development of a once-over harvesting system i s more f e a s i b l e than the development of a s e l e c t i v e harvesting system. The analysis also indicated that system development w i l l require input from engineers, f r u i t growers, f r u i t processors and h o r t i c u l t u r a l i s t s . Ah attempt i s made to allocat e appropriate areas of i n v e s t i g a t i o n and research to each of these groups. Group interactions are also investigated. To successfully develop the proposed system, one e s s e n t i a l step i s development of a mechanical picking machine. A design, based on the physical and mechanical properties of the strawberry f r u i t and plant, was used to b u i l d a picking -machine model. This model was f i e l d tested and evaluated. Limited f i e l d t e s t s indicated that some f i e l d preparation for mechanical harvesting i s e s s e n t i a l and that a vacuum f r u i t pick up device should be considered to a s s i s t machine feeding. Tests indicated, however, that the proposed concept can be used to remove berries from the plant with very l i t t l e f r u i t damage. - i -TABLE OF CONTENTS PAGE LIST OF FIGURES i i ± LIST OF TABLES v TERMINOLOGY v i NOMENCLATURE v i i i ACKNOWLEDGEMENTS x i 1. INTRODUCTION 1 1.1 Purpose of t h i s Research 1 1.2 Scope of t h i s Research 1" 1.3 Survey of Previous Work ' 2 2. DEVELOPMENT OF A HARVESTING SYSTEM 4 2.1 I n i t i a l and F i n a l Conditions 4 2.2 System Components 4 2.3 The Processor Component 6 2.4 The Engineering Component 8 2.5 The Grower Component - 11 2.6 The H o r t i c u l t u r a l Component 11 2.7 Summary 14 3. THE MECHANICAL STRAWBERRY HARVESTER 16 3.1 Operational Requirements 16 3.2 The Process 16 3.3 Tool Configuration 18 3.4 F a c t o r i a l Analysis of Picking Machine Function 20 - i i -3. Continued PAGE 3.4.1 The feeding function 20 3.4.2 The picking function 22 3.4.3 The conveying function 2 5 3.4.4 Summary 2 5 3.5 Analysis of Plant C h a r a c t e r i s t i c s 26 3.5.1 Fr u i t weight and size 27 3.5.2 Fru i t retention force and t e n s i l e strength of main stems 29 .3.5.3 Y i e l d c h a r a c t e r i s t i c s of the strawberry f r u i t 30 3.6 Mathematical Analysis for some Machine Parameters \ 36 3.6.1 Picking finger spacing 36 3.6.2 Picking finger length 36 3.6.3 The picking belt 38 3.6.4 The f r u i t conveying t o o l 40 3.7 The Test Model 42 3.8 Model Evaluation . 47 CONCLUSIONS 5 3 LITERATURE CITED 5 5 - I l l -LIST OF FIGURES FIGURE PAGE 1 System Boundaries 5 2 System Components 5 3 The Processor Component 7 4 The Engineering Component 9 5 Comparison Between Mechanically Harvesting 12 Surface and Upright Setting Strawberry F r u i t 6 Mechanical Harvesting Alternatives 12 7 The Grower Component 13 8 The Horticulture Component , 15 9 A Flow Chart I l l u s t r a t i n g those Functions 17 which must be Performed by the Proposed Mechanical Strawberry Harvester 10 A Flow Chart f o r the Proposed Picking 19 Machine 11 A Schematic of the Proposed Picking Machine 21 12 The Feeding Function 21 13 The Picking Function 23 14 Vector Action of a Picking Belt 23 15 Strength Comparison between the Main Stem and the F r u i t Retention Force 31 16 T y p i c a l Force-Deformation Curve for Whole 3l Strawberries subjected to Uniaxial Compression between Two F l a t Plates at .5 cm/min. 17 The Maxwell and Hooke Models i l l u s t r a t i n g 33 Ty p i c a l Stress-Strain Response 18 Assumed Response of Whole Berries to Rapid 33 Deformation - i v -FIGURE PAGE 19 Comparison between the B i o y i e l d Force for 34 the Hertz and Boussinesq Conditions on Northwest Strawberries 20 Loading Configuration during the Picking 37 Operation 21 Zone of Influence f o r Blowers 41 22 The Test Model 43 23 Close-Up of the Test Model 43 24 Top View of Picking Fingers 44 25 View I l l u s t r a t i n g F l o a t a b i l i t y of 44 | Individual Picking Fingers 26 I l l u s t r a t i o n of the Engine Drive Mechanism 45 27 I l l u s t r a t i o n of the Ground Drive Mechanism 45 2 8 Side View of the Picking Machine i n Operation 46 29 Top View of the Picking Machine i n 46 Operation 30 Typical Picking Machine Output 49 31 Machine Output Separated into Three 49 Categories 32 Close-Up of Prototype D a f f o d i l Header During 52 F i e l d Tests 3 3 A P a r t i a l l y Mechanically Headed D a f f o d i l 52 F i e l d v -LIST OF TABLES TABLE PAGE I Some Properties of the Strawberry Fr u i t and Attachment System 2 8 II Test Results 50 - v i -TERMINOLOGY Bi o y i e l d Point: The f i r s t point on the force-deformation curve at which there occurs no increase i n force with increased f r u i t deformation. For v i s c o - e l a s t i c materials, the corresponding force (the b i o y i e l d force) w i l l increase with increased deformation rate. Bruising: Damage to plant t i s s u e by external forces causing change in texture and/or eventual chemical a l t e r a t i o n of color, f l a v o r and texture ( 9 ) 1 . In t h i s study, bruising was assumed to occur when the b i o y i e l d stress was exceeded. Fr u i t Retention Force: The t e n s i l e force required to detach a strawberry from i t s plant. In t h i s study, detachment occurred at e i t h e r the f r u i t - p e t i o l e i n t e r f a c e or at a secondary stem l o c a t i o n . Growth Regulator: An organic compound which, when introduced into a plant i n a r e l a t i v e l y small quantity, induces e f f e c t s i n the growth pattern of the f r u i t ( 9 ) . I n i t i a l Tangent Modulus: The slope, at the o r i g i n , of the force-deformation curve for strawberries under compressive loading. Linear Limit: The force at which the force-deformation curve fo r a compressed berry deviates from l i n e a r i t y . 1 Numbers i n parentheses r e f e r to references l i s t e d i n the l i t e r a t u r e c i t e d . Normal Population: A population whose frequency function i s f( Y ) = [ — i — • ] e T T Q Y - y ; /TiT a 2 a where: y = any random variable a = population standard deviation u = population mean A l l b i o l o g i c a l populations which were investigated i n t h i s study were assumed to be normally d i s t r i b u -ted. Furthermore, the sample mean and deviation were assumed to equal the mean and deviation for the population. Runners: Vine-like structures, grown by strawberry plants, which subsequently root and form new plants. Solid-bed Plantings: Cultures where plants are not confined to rows but are permitted to cover the entire f i e l d area. Terminal Velocity: The v e l o c i t y at which the drag forces on a p a r t i c l e equal i t s g r a v i t a t i o n a l force. Upright V a r i e t i e s : Strawberry v a r i e t i e s that produce f r u i t which mature above the ground surface. NOMENCLATURE a constant, used i n the Hertz contact stress problem dependent upon the e l a s t i c and deformation pro-perties of strawberries and picking b e l t s . a constant, used i n the Hertz contact stress problem dependent upon the e l a s t i c and deformation pro-perties of strawberries and s t e e l . b i o y i e l d force of whole strawberry f r u i t under u n i a x i a l compression at a loading rate of .5 cm/min. sphere diameter used i n the Hertz equation, p a r t i c l e diameter. base diameter of strawberry f r u i t . calculated f r u i t diameter-,; spacing between adjacent picking fingers. sample mean of berry base diameters. Young's modulus for picking b e l t s . Young's modulus for s t e e l . Young's modulus for strawberries. .f f u n c t i o n a l r e l a t i o n s h i D S . n drag c o e f f i c i e n t . f a c t o r dependent upon picking finger length and nozzle shape. difference between the t e n s i l e strength of the main stem and the FRF ( f r u i t retention f o r c e ) . compressive force between a sphe r i c a l body and a f l a t plate. - i x -F ] n a x the estimated maximum compressive force that picking belts can exert on berries without causing br u i s i n g . F compressive force exerted on berries by the picking r b e l t during the f r u i t removal operation. FRF force required to remove berries from the plant ( f r u i t retention f o r c e ) . g g r a v i t a t i o n a l constant. G t e r r a i n s u i t a b i l i t y for shoe f l o a t a t i o n . t stem length ( t h i s i s also the maximum height that a berry can be l i f t e d without removing i t from the plant. I ' sample mean of stem lengths. L picking f i n g e r length. Poisson's r a t i o f o r picking b e l t s . u Poisson's r a t i o f o r s t e e l . P u Poisson's r a t i o f o r strawberries, s M strawberry volume. P c f r u i t conveying e f f i c i e n c y . P^ f r u i t feeding e f f i c i e n c y . P f r u i t removal e f f i c i e n c y , r P a i r density. a. Pp p a r t i c l e density. R berry b r u i s i n g resistance to impact force. estimated f r u i t b r u i sing s t r e s s . S nozzle shape factor, n S g shoe shape f a c t o r . S.D. sample standard deviation. - x -S maximum contact stress as estimated by the Hertz max .. J equation. 9 the angle between the upper bel t surface and the s o i l surface (also c a l l e d the t o o l i n c l i n a t i o n ) . T type of picking b e l t . V, v e l o c i t y of the upper bel t surface with respect to the picking machine. V 2 ground speed of the picking machine. v e l o c i t y of the upper belt surface with respect to ground - » • - * • - » -cv 3 = w1 + v 2) blower face v e l o c i t y . V estimated f r u i t conveying v e l o c i t y at;' maximum t o o l i n c l i n a t i o n . Vxr terminal or f l o a t i n g v e l o c i t y f o r a spherical p a r t i c l e . terminal v e l o c i t y for strawberries. - x i -ACKNOWLEDGEMENTS The author wishes to thank Dr. E.O. Nyborg for d i r e c t i n g t h i s research, Mr. W. Gleave (deceased May 29, 1972) for his many helpful model design suggestions and Mrs. E. Stewart for typing and arranging this thesis. For t h e i r many ideas and suggestions during 1970-1971, Dr. B. Evans, H o r t i c u l t u r a l Sciences Department, University of Guelph, Dr. L. Ricketson, H.R.I.0., Vineland Station and Dr. W. B i l a n s k i , School of Engineering, University of Guelph are also g r a t e f u l l y acknowledged. This research was financed by the Canada Department of A g r i c u l t u r e . 1. INTRODUCTION 1.1 The Purpose of t h i s Research In spite of the introduction of high y i e l d , disease r e s i s t a n t strawberry v a r i e t i e s and the widespread use of cost saving chemicals, strawberry production i n both Canada and the United States has been s t e a d i l y d e c l i n i n g for the past decade. This trend can be at t r i b u t e d to the increasing d i f f i c u l t y of r e c r u i t i n g pickers to manually harvest the strawberry crop. People are becoming increasingly reluctant to accept the wage rates which growers are presently o f f e r i n g to harvest t h e i r crop. Growers, on the other hand, f i n d i t economically impossible to o f f e r more a t t r a c t i v e rates. I f commercial strawberry production i s not to become obsolete within the next several decades, a system for mechanically harvesting t h i s crop must be developed. 1.2 The Scope of t h i s Research A l l harvesting systems, whether manual or mechanical are of two types. F r u i t can be s e l e c t i v e l y harvested as the crop matures or the entire crop can be harvested at an optimum harvesting time (once-over system). Once-over harvesters are simpler to construct and easier to design than s e l e c t i v e harvesters. Most e x i s t i n g mechanical harvesters f o r a l l types of crops are the once-over type. Preliminary i n v e s t i g a t i o n shows that, for strawberries, the once-over concept i s more suitable than the s e l e c t i v e harvesting concept. Many problems associated with s e l e c t i v e harvesting do not have p r a c t i c a l 2. solutions at present. P r a c t i c a l and economically sound solu-tions to problems associated with once-over harvesting are easier to f i n d . This t h e s i s , therefore, outlines the phases for development of a once-over harvesting system for strawberries. 1.3 Survey of Previous Work Due to the increasing cost and decreasing a v a i l a -b i l i t y of appropriate labor, much research has recently been directed towards the mechanization of f r u i t and vegetable crops. Labor d i f f i c u l t i e s have prompted several researchers to search for means of mechanically harvesting strawberries. Buchele and Denisen (2) were among the f i r s t to attempt to develop a mechanical strawberry harvesting system. As well as suggesting several c u l t u r a l modifications, they suggested that the "stone fork" p r i n c i p l e could be used to mechanically harvest strawberries. Only moderate success i s indicated by t h e i r reported r e s u l t s ; however, suggested c u l t u r a l modifications such as the use of c e r t a i n types of mulches, removing leaves before mechanical harvesting, and the use of bed l e v e l i n g and raking operations have been used by most subsequent researchers and w i l l l i k e l y form necessary'" operations f o r commercial mechanical harvesting. To feed berries i n t o the picking t o o l more e f f i c -i e n t l y than multi-forked "scoop" and " r e e l " type pick e r s , Quick (13) suggested the use of v i b r a t i n g picker-teeth. Picking teeth, v i b r a t i n g i n the hor i z o n t a l plane, could be maintained close to the s o i l surface at a l l times — a condition I 3. that cannot be attained by using "scoop" or " r e e l " mechanisms. It i s reported that the use of a machine embodying t h i s p r i n c i p l e , on wide f l a t strawberry beds, could p o t e n t i a l l y harvest 9 5 percent or more of available b e r r i e s . Nelson and Kattan (10) appear to be the f i r s t to use a vacuum pick-up to a s s i s t machine feeding. I f s o i l contamina-t i o n of the harvested f r u i t can be held within acceptable l i m i t s , t h i s concept w i l l l i k e l y be used on commercial harves-t i n g machines. Hanson (5) indicates that a harvester using the vacuum pick-up p r i n c i p l e has been used i n Michigan with s a t i s f a c t o r y r e s u l t s . 4. DEVELOPMENT OF A HARVESTING SYSTEM 2.1 I n i t i a l and F i n a l Conditions Logical i n v e s t i g a t i o n of any system requires a c l e a r understanding of system boundaries (16). The purpose of t h i s research i s to develop a mechanical harvesting system for strawberries. The i n i t i a l (inputO condition for the proposed harvesting system i s defined as " e x i s t i n g commercially grown strawberry cultures" (Figure 1). The f i n a l (output) condition i s defined as "mechanically harvested f r u i t suitable for pro-cessing by e x i s t i n g methods". System components convert the i n i t i a l condition into the f i n a l condition. 2.2 System Components Investigation shows that the mechanical harvester w i l l form only a small part of a new harvesting system. It seems u n l i k e l y that a mechanical harvester can be designed to acceptably harvest e x i s t i n g v a r i e t i e s grown under present c u l t u r a l methods; nor does i t seem l i k e l y that harvester output w i l l be acceptable to processors u n t i l subsequent operations are performed on the harvested b e r r i e s . Obviously, the proposed harvesting system cannot be developed by researchers of a single d i s c i p l i n e . A coopera-t i v e e f f o r t by h o r t i c u l t u r a l i s t s , f r u i t growers, engineers and f r u i t processors i s required. B a s i c a l l y , therefore, the proposed system w i l l have four components i n t e r r e l a t e d by appropriate feedback loops (Figure 2). 5 . SYSTEM INPUT EXISTING COMMERCIAL VARIETIES (E.C.V.) HARVESTING SYSTEM SYSTEM OUTPUT FRUIT SUITABLE FOR PROCESSING BY EXISTING METHODS (F.S.P.) FIGURE 1 System Boundaries INPUT (E.C.V. ) THE HARVESTING SYSTEM HORTICULTURE FUNCTIONS ENGINEERINGS FUNCTIONS FEEDBACK GROWER FUNCTIONS FEEDBACK PROCESSOR FUNCTIONS FEEDBACK FEEDBACK OUTPUT (F.S.P.) FIGURE 2 System Components 6. 2.3 The Processor Component Within the system, the processor must perform three basic functions on the mechanically harvested aggregate ( f o l i a g e , mature f r u i t and greens). These are to ensure that the harvested f r u i t w i l l have good processing c h a r a c t e r i s t i c s , to sort out usable f r u i t from the mechanically harvested aggregate and, i f required, to h u l l the usable f r u i t (Figure 3). The mechanical harvesting strawberry culture must y i e l d f r u i t which has suitable processing c h a r a c t e r i s t i c s . Mechanically harvesting strawberries which are unacceptable to consumers i s a f r u i t l e s s task. Feedback information to the h o r t i c u l t u r a l i s t w i l l specify the e s s e n t i a l processing c h a r a c t e r i s t i c s . The mechanically harvested aggregate w i l l , i n a l l l i k e l i h o o d , contain some plant f o l i a g e , as well as green, moldy and mechanically damaged f r u i t . These are undesirable f o r most processed products and therefore must be sorted from the usable f r u i t . Feedback information w i l l t e l l the engineers whether the l e v e l of mechanical f r u i t damage and the amount of plant f o l i a g e i s within acceptable l i m i t s . I f these are unacceptable, engineers must f i n d a method of reducing the unwanted debris to acceptable l e v e l s . This w i l l involve redesigning the harvesting machine and/or mechanically harvesting more suitable strawberry cultures. Other feedback information w i l l t e l l h o r t i c u l t u r a l i s t s whether the amount of 7. - INPUT -MECHANICALLY HARVESTED AGGREGATE (cont a i n s moldy, green, mechanically damaged and usable f r u i t s as w e l l as some leaves and stems) PROCESSOR FUNCTIONS DETERMINE PROCESSING QUALITY r-JRIPEN GREENS SORTING FUNCTION HULLING FUNCTION - OUTPUT -FRUIT ACCEP-TABLE FOR SUCH PROCESSED PRO-DUCTS AS CANNING, JAM, WINE AND FLAVORINGS. FEEDBACK TO ENGINEERS - MECHANICAL DAMAGE - DEBRIS FEEDBACK TO HORTICULTURE - FRUIT-FLAVOR, TEXTURE ETC. - PROCESSABILITY - HULLING CHARACTERISTICS - EXCESSIVE GREEN AND MOLDY BERRIES FIGURE 3 The Processor Component 8. green and moldy berries contained i n the harvester output aggregate i s within acceptable l e v e l s . I f i t i s not, h o r t i -c u l t u r a l i s t s w i l l have to consider the use of growth regulating chemicals, fungicides and genetic s e l e c t i o n . F r u i t stems and h u l l s are undesirable f o r processing. The harvested f r u i t must eith e r s e l f - h u l l when mechanically picked ( f r u i t retention force < stem strength) or else have h u l l s which can e a s i l y be mechanically detached. Feedback information to h o r t i c u l t u r a l i s t s w i l l indicate whether the mechanical harvesting culture has the necessary h u l l i n g c h a r a c t e r i s t i c s . 2.4 The Engineering Component The engineer's primary function i s to design a mechanical strawberry harvesting machine. The type of machine w i l l depend pr i m a r i l y upon the culture developed by the h o r t i c u l t u r a l i s t s (the input to engineering functions). Feed-back information to the h o r t i c u l t u r a l i s t w i l l indicate those c u l t u r a l c h a r a c t e r i s t i c s which are desirable for mechanical harvesting (Figure 4). A l l mechanical harvesters can be c l a s s i f i e d into two groups, s e l e c t i v e harvesters and once-over harvesters. Because once-over harvesters are simpler i n construction and much easi e r to design than s e l e c t i v e harvesters, most mechanical harvesters used i n agr i c u l t u r e (grain combines, tomato harves-t e r s , grape harvesters etc.) are of the once-over type (11). Preliminary i n v e s t i g a t i o n indicated that, f o r 9. - INPUT - ENGINEERING FUNCTION - OUTPUT -MECHANICAL HARVESTING STRAWBERRY CULTURE - DESIGN AN APPROPRIATE HARVESTER MECHANICALLY HARVESTED AGGREGATE FEEDBACK TO HORTICULTURE FEEDBACK FROM PROCESSORS (see FIG.3) - UPRIGHT MATURING FRUIT PREFERABLY - FIRM FRUIT - BED FORMING - BED RAKING - SOLID BED PLANTING ETC. FIGURE 4 The E n g i n e e r i n g Component 10. strawberries, the once-over concept i s more suitable than the se l e c t i v e harvesting concept. Some reasons for s e l e c t i n g a once-over harvesting system are: 1) Selective picking mechanisms which would be capable of s e l e c t i v e l y picking only q u a l i t y berries at high rates without causing excessive mechanical damage to the f r u i t would make a harvester excessively complicated. 2) Mechanical damage to both the plant and f r u i t r e s u l t i n g from' multiple passes over the crop would be more d i f f i c u l t to resolve than f o r a single pass. 3) Genetic s e l e c t i o n of uniformly maturing plants, judicious use of fungicides such as Captan, and sound maturity monitoring techniques w i l l l i k e l y make s e l e c t i v e harvesting unnecessary. Present commercially grown strawberry v a r i e t i e s y i e l d f r u i t which mature primarily on the ground surface. These are referred to as "surface maturing" v a r i e t i e s . The development of mechanical harvesters to date has been primarily directed towards harvesting these v a r i e t i e s . Plant breeders i n Ontario and C a l i f o r n i a have recently begun development of strawberry v a r i e t i e s which y i e l d f r u i t that matures above the s o i l surface. These are referred to as "upright" v a r i e t i e s . The development of a machine f o r mechanically harvesting these v a r i e t i e s can be expected to be much easier than development of a harvester for surface maturing v a r i e t i e s . Since the f r u i t i s located 11. above the s o i l surface, ground contour and surface debris w i l l not hinder operation. Greater forward speeds should be possible since picking head height control need not be as c r i t i c a l and better f r u i t q u a l i t y can be expected since s o i l contamination i s l e s s l i k e l y to occur. For these v a r i e t i e s , the designer need only consider machine-plant i n t e r a c t i o n s , whereas fo r surface maturing v a r i e t i e s , he must consider not only machine-plant interactions but also machine-soil and s o i l - p l a n t i n t e r -actions (Figure 5). Test r e s u l t s with a prototype mechanical d a f f o d i l header (15) indicated that a once-over harvester for upright strawberry v a r i e t i e s (Machine A, Figure 6) would be r e l a t i v e l y easy to design. Less r a d i c a l c u l t u r a l modifications would be required to once-over mechanically harvest surface maturing v a r i e t i e s (Machine B, Figure 6). Most of the published r e s u l t s on mechanical strawberry harvesting have had t h i s objective i n mind. Cultural modifications would include solid-bed plantings and preharvest bed preparation (bed raking, forming and compacting). 2.5 The Grower Component The mechanical harvesting culture developed by the h o r t i c u l t u r a l i s t w i l l not form part of a commercially valuable system unless i t i s acceptable to commercial growers. The new culture must be easy to grow and give more economic returns than e x i s t i n g strawberry cultures (Figure 7). 2 . 6 The H o r t i c u l t u r a l Component The h o r t i c u l t u r a l input i s probably the most important 12. HARVESTING MACHINE FRUIT AND PLANT A. INTERACTIONS FOR MECHANICALLY HARVESTING SURFACE MATURING FRUIT HARVESTING MACHINE FRUIT AND PLANT B. INTERACTIONS FOR MECHANICALLY HARVESTING UPRIGHT MATURING FRUIT FIGURE 5 Comparison Between Mechanically Harvesting Surface and Upright Setting Strawberry F r u i t . SELECTIVE HARVESTING• SURFACE MATURING VARIETIES UPRIGHT VARIETIES ONCE-OVER HARVESTING SURFACE MATURING VARIETIES Machine B UPRIGHT VARIETIES Machine A FIGURE 6 Mechanical Harvesting Alternatives INPUT MECHANICAL-H A R V E S T I N G STRAWBERRY CULTURE GROWER FUNCTION •ECONOMICAL PRODUCTION OF STRAWBERRIES FEEDBACK TO HORTICULTURE -ECONOMICS OF GROWING MECHANICAL HARVESTING CULTURE FIGURE 7 The Grower Component 14. and most d i f f i c u l t to resolve part of the proposed harvesting system. Research to date indicates that e x i s t i n g strawberry cultures are not well suited f o r mechanical harvesting. Commercial v a r i e t i e s and commonly employed c u l t u r a l practices have been developed to optimize manual harvesting. E x i s t i n g v a r i e t i e s and c u l t u r a l methods must be modified i f mechanical harvesting i s to become a r e a l i t y . Using feedback informa-t i o n from growers, engineers and processors, the h o r t i c u l t u r a -l i s t s ' task i s to produce a commercially valuable, strawberry culture suitable f o r mechanical harvesting (Figure 8). 2.7 Summary . A new system of strawberry production must be developed before commercial mechanical harvesting can become a r e a l i t y . System development w i l l be a j o i n t task among h o r t i c u l t u r a l i s t s , growers, engineers and processors. The mechanical harvesting machine i s only one component of t h i s system. Equally important i s the development of a strawberry culture suitable f o r mechanical harvesting. In a l l l i k e l i h o o d , mechanically harvested f r u i t w i l l be i n f e r i o r i n q u a l i t y to hand picked f r u i t and therefore must be used f o r processing. One p o s s i -b i l i t y i s to manually harvest the primary (king) berries for premium fresh market prices and to mechanically harvest the remainder for the processing market. INPUT EXISTING STRAW-BERRY VARIETIES SELECT AND/OR BREED VARIETY - HULLING CHARACTERISTICS - FRUIT SETTING CHARACTERISTICS - UNIFORM RIPENING - ETC. HORTICULTURE FUNCTIONS (Aim i s to develop a mechanical harvesting strawberry culture ) MODIFY CULTURAL PRACTICES - SOLID-BED PLANTINGS - BED FORMING - BED RAKING - ETC. MANAGEMENT CONTROL - FUNGICIDES - HERBICIDES - GROWTH REGULATORS - MATURITY MONITOR-ING - ETC. OUTPUT MECHANICAL HARVESTING STRAWBERRY CULTURE FEEDBACK FROM GROWERS SEE FIGURE 7 FEEDBACK FROM ENGINEERS SEE FIGURE 4 FEEDBACK FROM PROCESSORS SEE FIGURE 3 FIGURE 8 The Horticulture Component 16. THE MECHANICAL STRAWBERRY HARVESTER 3.1 Operational Requirements As previously indicated, h o r t i c u l t u r a l i s t s , growers, processors and engineers w i l l a l l be required to develop the proposed mechanical strawberry harvesting system. The engineers' primary function i s to b u i l d the mechanical harves-t e r . Many problems associated with s e l e c t i v e l y harvesting strawberries do not have p r a c t i c a l solutions. P r a c t i c a l and economically sound solutions to problems associated with once-over harvesting appear to be easier to f i n d . Machine design was, therefore, directed toward development of a once-over harvester. A machine suitable f o r harvesting upright v a r i e t i e s w i l l be r e l a t i v e l y simple and can be expected to possess high f r u i t removal e f f i c i e n c y . At present, however, most commer-c i a l l y grown strawberries are of the surface maturing type. I f a mechanical harvester i s to be suitable f o r present commercial v a r i e t i e s , i t must be capable of harvesting surface maturing v a r i e t i e s . Harvester design, discussed i n the following pages, i s therefore directed toward development of a once-over machine fo r surface maturing strawberries. 3.2 The Process A flow chart, o u t l i n i n g the basic operations which must be performed by a once-over mechanical strawberry harvester i s shown i n Figure 9. Each block i n the flow chart represents a basic process function. Functions 2 to 4 MACHINE INPUT - MECHANICAL HARVESTING STRAWBERRY CULTURE • w I z M H H W E CO M O W X, < > EH 2: M CC o >4 C J M a, 2 O X M Q 2 < H W < H W Di CD GO E-> I 1. EXPOSE BERRIES TO PICKING TOOL BY MOWING OF PLANT CANOPY 2. LIFT BERRIES OFF THE SOIL SURFACE AND FEED THEM INTO THE PICKING TOOL 3. ALLOW FOLIAGE TO SLIP THROUGH THE PICKING FINGERS AND REMOVE ALL BERRIES 4. CONVEY HARVESTED BERRIES UP THE TOOL INCLINE 5. BLOW AWAY EXCESS DEBRIS 6. STORE HARVESTED MATERIAL ON THE HARVESTER MACHINE OUTPUT - MECHANICALLY HARVESTED AGGREGATE READY FOR TRANSPORT TO THE PROCESSING PLANT FIGURE 9 A flow chart i l l u s t r a t i n g those functions which must be performed by the proposed once-over mechanical strawberry harvester. 18. l o g i c a l l y f i t into one machine. The following sections outline the design and f a b r i c a t i o n of a machine to perform these three functions. This machine w i l l subsequently be ref e r r e d to as the picking machine i n order to d i f f e r e n t i a t e i t from the mechanical harvester which must perform a l l the functions out-l i n e d i n Figure 9. The flow chart for the proposed picking machine i s shown i n Figure 10. 3.3 Tool Configuration The proposed picking machine i s schematically -==^ i l l u s t r a t e d in- Figure 11. It i s comprised of two basic tools — a picking t o o l and a f r u i t conveying t o o l . .The picking t o o l feeds berries between adjacent picking fingers and removes berries from the plant. The conveying t o o l transports harves-ted berries to the rear of the picking t o o l . The picking t o o l consists of a series of fingers mounted on a common drive shaft. This shaft drives endless b e l t s mounted on each picking finger. Fingers, spaced at less than minimum f r u i t diameter, are pivoted about the drive shaft, thus permitting them to follow s o i l surface i r r e g u l a r i t i e s . The front pulley on each finge r i s small enough to go beneath i n d i v i d u a l f r u i t . A pointed shoe positioned around each front pulley aids both i n f l o a t a t i o n and i n feeding. The conveying t o o l consists e s s e n t i a l l y of an a i r blower. As well as conveying harvested berries to the rear of the picking t o o l , the blower aids i n cleaning the harvested aggregate of leaves and other debris. INITIAL CONDITION: EXPOSED BERRIES READY FOR MECHANICAL HARVESTING 1. LIFT BERRIES OFF THE SOIL SURFACE 'AND FEED THEM INTO THE PICKING TOOL 2. ALLOW PLANT MATERIAL TO SLIP THROUGH THE PICKING FINGERS AND REMOVE ALL BERRIES 3. CONVEY HARVESTED BERRIES UP THE PICKING TOOL INCLINE FINAL CONDITIONS: MECHANICALLY HARVESTED BERRIES IN TEMPORARY STORAGE FIGURE 10 A Flow Chart f o r the Proposed Pi c k i n Machine. 20. 3.4 Factoral Analysis of Picking Machine Functions The o v e r a l l performance of the proposed picking machine w i l l depend upon the e f f i c i e n c y with which t h i s machine performs each of i t s intended functions. Functional e f f i c i e n c y w i l l be determined by a number of machine design parameters. These parameters w i l l i n turn be governed by relevant physical properties of the strawberry plant and f r u i t . 3.4.1 The feeding function For f r u i t l y i n g at random on the s o i l surface, the feeding operation occurs i n two steps. The f r u i t i s f i r s t picked o f f the s o i l surface and placed on the moving be l t of the picking finger. The f r u i t then positions i t s e l f between two picking fingers so that the picking operation can occur. Obviously, f o r upright growing v a r i e t i e s , the picking t o o l w i l l not have to perform the f i r s t operation. Figure 12 i l l u s t r a t e s the expected i n t e r a c t i o n between the front end of a f l o a t i n g picking finger and a strawberry. As contact i s made between the shoe and the f r u i t , the f r u i t , due to i t s mass, momentarily remains stationary. The r e l a t i v e motion of the f r u i t with respect to the shoe at t h i s instant causes the f r u i t to s l i d e up the shoe and onto the b e l t . I f the width of the b e l t i s narrow compared to the space between adjacent f i n g e r s , no p o s i t i o n i n g device i s required. The only requirement i s that the strawberry stem i s situated between two fingers. The t o o l parameters which can be expected to a f f e c t FIGURE 11 A Schematic of the Proposed P i c k i n g Machine Berry Motion FIGURE 12 The Feeding Function the feeding e f f i c i e n c y of the proposed design can be summarized by the following functional r e l a t i o n s h i p . P f = f x <Df, S s, V 2) . Cl] where: = feeding e f f i c i e n c y Df = spacing between adjacent picking fingers S g = shoe shape factor V 2 = ground speed of the picking machine ( f r u i t impact v e l o c i t y ) Optimum values f o r the parameters on the r i g h t side of the equation [1] w i l l be determined by relevant properties of the f r u i t and plant. v (D f, S , V 2) = f 2 (G, R) [2] where: R = berry resistance to impact forces. G = t e r r a i n s u i t a b i l i t y for shoe f l o a t a t i o n . 3.4.2 The picking function I f picking b e l t v e l o c i t y (Figure 13) i s appropriately synchronized with the forward v e l o c i t y of the prime mover ( t r a c t o r ) , the f r u i t , a f t e r being placed on the picking b e l t s , w i l l be l i f t e d v e r t i c a l l y upward u n t i l stem f a i l u r e occurs. When stem f a i l u r e occurs, the berry i s picked. For proper synchronization of belt to t r a c t o r v e l o c i t y | T2 | = | T± | cos 9 [ 3 3 . where: = v e l o c i t y of the top surface of picking belts with respect to the machine 9 = the angle between the top belt surface and the s o i l surface. The vector v e l o c i t y diagram for a point on the top C o l l e c t i n g T r a y Travel — Dir e c t i o n FIGURE 13 The Picking Function Travel D i r e c t i o n 3 V 3 v e l o c i t y of the b e l t with respect to prime move prime move v e l o c i t y b e l t v e l o c i t y with respect to ground " \ + ? 2 FIGURE 14 Vector Action of a Picking Belt b e l t surface, i l l u s t r a t i n g proper synchronization i s shown i n Figure 14. Tool parameters a f f e c t i n g picking performance can be summarized by the following functional r e l a t i o n s h i p : P p = f 3 ( D f , L , 0, T, V 3 ) [4] where: P p = picking e f f i c i e n c y L = picking f i n g e r length T = type of picking b e l t V o = v e l o c i t y of the upper b e l t surface with respect to ground (V 3 = V^ + V 2 ) , and other symbols are as previously defined. The machine parameters on the r i g h t side of equation [4] w i l l be determined by appropriate physical properties of the strawberry f r u i t . Fingers must be spaced so that no f r u i t w i l l pass between adjacent picking f i n g e r s , fingers must be capable of l i f t i n g berries higher than the longest f r u i t stem, berries must not be harvested i n c l u s t e r s and b r u i s i n g damage occurring during the picking operation must be held to acceptable l e v e l s . The following functional r e l a t i o n s h i p can be used to summarize the r e l a t i o n s h i p between machine and plant parameters. ( D f , L , ©, T, V 3 ) = f 4 (BYF, D b , F f l, FRF, I) [5] where: BYF = b i o y i e l d force of the compressed f r u i t at a loading rate equal to V j . = base diameter of strawberry f r u i t F, = difference between the t e n s i l e strength of the f r u i t stem and the f r u i t retention force FRF = f r u i t retention force I = stem length, and other symbols are as previously defined. 3.4.3 The conveying function After berries have been fed into the picking t o o l , they are conveyed up the picking t o o l i n c l i n e to the point where the picking operation occurs. Experience has shown (17) that harvested berries tend to r o l l down the picking t o o l regardless of t o o l i n c l i n a t i o n , 9. An a i r blower can be used to convey the harvested berries to the rear of the pick-ing t o o l as well as to clean the harvested aggregate of excess debris. The success of the conveying function appears to be primarily a function of the length and i n c l i n a t i o n of picking f i n g e r s , the shape of the blower nozzle, and the blower face v e l o c i t y . P c = f 5 (L, S n, 9, V b) [6] where: P c = conveying e f f i c i e n c y S = nozzle shape factor n ^ = blower face v e l o c i t y and other parameters are as previously defined. Optimum values f o r these machine parameters w i l l be determined by the terminal v e l o c i t y of the f r u i t . (L, S n, 9, V b) = f 6 (V t) [7] where: V = terminal v e l o c i t y f o r strawberries, and other parameters are as previously defined. 3.4.4 Summary The design parameters which w i l l determine the o v e r a l l performance of the proposed picking machine can be summarized as i n e q u a t i o n [ 8 ] , P = f ? ( P f , P p, P c) = f 8 ( D f , L, S n , S s , 9, T, V 2, V 3, V b ) [8] where: P = o v e r a l l e f f i c i e n c y of the proposed p i c k i n g machine and a l l o t h e r parameters are as p r e v i o u s l y d e f i n e d . To e x p e r i m e n t a l l y determine the machine d e s i g n parameters f o r optimum p i c k i n g e f f i c i e n c y , a model wi t h which each of the f a c t o r s on the r i g h t s i d e of e q u a t i o n [8] can be i n d e p e n d e n t l y i n v e s t i g a t e d , must be b u i l t and r i g o r o u s l y t e s t e d under f i e l d c o n d i t i o n s . E s t i m a t e s f o r many o f the d e s i r e d machine parameters can be o b t a i n e d by a n a l y s i n g a p p r o p r i a t e p h y s i c a l p r o p e r t i e s of the strawberry p l a n t and f r u i t . The r e l a t i o n s h i p among design parameters and p h y s i c a l p r o p e r t i e s may be summarized as i n e q u a t i o n [ 9 ] . ( D f , L, S n , S s , 0, T, V 2, V 3, Vb> = f g (BYF, D b, F d , FRF, G, A, R, V t> t9] 3.5 A n a l y s i s of P l a n t C h a r a c t e r i s t i c s Some knowledge o f those p l a n t p h y s i c a l p r o p e r t i e s which are r e l e v a n t t o the proposed p i c k i n g machine d e s i g n must be o b t a i n e d b e f o r e r a t i o n a l model d e s i g n can proceed.,-As w i t h most h o r t i c u l t u r a l c r o p s , the p h y s 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 are dependent upon a l a r g e number o f f a c t o r s . I n c l u ded among these are p l a n t v a r i e t y , c l i m a t e and s o i l f e r t i l i t y . O b v i o u s l y , p r e c i s e f i g u r e s d e f i n i n g s p e c i f i c strawberry p h y s i c a l p r o p e r t i e s cannot be o b t a i n e d on the b a s i s of a small sample taken from a given experimental plot over a single season. Information of t h i s type; however, can give useful figures which can be used as a guide for r a t i o n a l bio-machine design. 3.5.1 F r u i t weight and size Some properties of the strawberry f r u i t and stem which are necessary to design the proposed picking machine are included i n Table I. The figures i n t h i s table represent t y p i c a l values f o r the Northwest variety of f r u i t grown i n the P a c i f i c Northwest. The f r u i t weight, berry base diameter and stem length were obtained from available l i t e r a t u r e ( 1 2 ) . The f r u i t base diameter i s defined as the average base diameter of the f r u i t and the stem length i s defined as the maximum v e r t i c a l height above the strawberry bed which a f r u i t can be l i f t e d without removing the f r u i t from the plant. It i s convenient to have a representative f r u i t diameter when attempting to estimate some design factors such as terminal v e l o c i t i e s and contact stresses. For t h i s purpose, the berry was assumed to have the same density as water and to be s p h e r i c a l l y shaped. Using the measured f r u i t weight and the geometric formula for the volume of a sphere, the e f f e c t i v e f r u i t diameter was calculated. D = (Hi) [10] C TT where: D = e f f e c t i v e f r u i t diameter (cm) c 3 M = strawberry volume (cm ) 28. TABLE I. SOME PROPERTIES OF THE STRAWBERRY FRUIT AND ATTACHMENT SYSTEM1 BIOLOGICAL PARAMETER Y*2 S.D. F r u i t Weight (gm) 12. 3 4. 8 F r u i t Base Diameter (cm) 2. 0 • 57 Calculated F r u i t Diameter (cm) 2. 8 • 4 Stem Length (cm) 14. 2. 8 F r u i t Retention Force (gm) 1 Tensile Strength of Main Stem (KG) 414. 92. 5. 75 1. 13 Bi o y i e l d Point (gm) 390. 80. Tangent Modulus (gm/cm) 980. 308. 2 Calculated Bruising Stress (gm/cm ) 3. 4A" 2 / 3 NA3. 1. A l l populations were assumed to be normally d i s t r i b u t e d 2. Y i s the calculated sample mean and S.D. i s the sample standard deviation 3. Bruising stress was calculated using the Hertz contact stress theory f o r u n i a x i a l compression between two f l a t p lates. See page 35. 4. Samples of mature f r u i t were used to obtain a l l b i o l o g i c a l parameters. 2 9 . 3.5.2 F r u i t retention force and t e n s i l e strength of main stems F r u i t retention force i s define as the t e n s i l e force required to remove the f r u i t from the plant. F r u i t detachment can occur e i t h e r at some point along the stem or at the p e t i o l e -f r u i t i n t e r f a c e . For a sample of mature Northwest f r u i t taken during the 1968 harvest season (12), the mean and standard deviation were 414 + 92 grams. This value i s close to that found f o r a sample of mature Redcoat f r u i t taken i n Ontario during 1971 where the sample mean and standard deviation were 500 + 100* grams (17). Hoag and Hunt (6) i n 1963 found a retention force range from a minimum of 26 6 grams f o r Sure Crop to a maximum of 1155 grams f o r Vermillion. The extent of f r u i t b r u i sing during the picking operation, using the proposed design, w i l l be related to the f r u i t retention force. The higher t h i s force, the greater the expected f r u i t damage. The proposed picking t o o l i s designed to apply s u f f i c i e n t t e n s i l e force to i n d i v i d u a l f r u i t to cause f a i l u r e at some point along the stem. Failur e w i l l , of course, occur at the weakest point. I d e a l l y , the f a i l u r e l o c a t i o n w i l l be at the p e t i o l e - f r u i t i n t e r f a c e . Processors w i l l then not be required to perform a h u l l i n g operation on the harvested f r u i t . For s e l f - h u l l i n g to occur consis t e n t l y , the f r u i t r e tention force must be much less than the t e n s i l e strength of e i t h e r secondary or main stems. Experimentation with the Northwest var i e t y has shown that consistent s e l f - h u l l i n g cannot be expected. Machines to h u l l strawberries with c e r t a i n types of h u l l structures w i l l soon be commercially available (3, 5, 7). These machines w i l l not h u l l berries joined together i n cl u s t e r s . I f the proposed picking t o o l cannot harvest berries i n d i v i d u a l l y , accessory equipment w i l l have to be designed to break up c l u s t e r s . No data were available for the Northwest va r i e t y ; however, data c o l l e c t e d on the Red Coat variety (Figure 15) i n 1971 (17) indicated that the proposed picking t o o l w i l l be capable of harvesting the berries of some v a r i e t i e s i n d i v i d u a l l y . Subsequent information obtained i n 1972 showed that Northwest berries are among these. 3.5.3 Y i e l d c h a r a c t e r i s t i c s of the strawberry f r u i t The following analysis was undertaken to gain some insi g h t i n t o factors that cause f r u i t b r u i s i n g . Such informa-t i o n can be used to q u a l i t a t i v e l y design picking b e l t types and belt loading configurations which could be expected to minimize bruising damage. For purposes of t h i s study, some assumptions which would not be j u s t i f i e d f o r more precise work, were made. Rather than using a s t a t i s t i c a l approach to define pertinent populations and using these to calculate pertinent parameters and expected d i s t r i b u t i o n s , only the sample means were used f o r c a l c u l a t i o n s . A t y p i c a l force-deformation curve obtained when strawberries are loaded under u n i a x i a l compression at .5 cm/min between two f l a t plates i s i l l u s t r a t e d i n Figure 16. The curve shape indicates that t h i s f r u i t i s a v i s c o e l a s t i c 31 • o 2 k 6 8 . 10 T E N S I L E STRENGTH (KG) FIGURE 15 S t r e n g t h C o m p a r i s o n B e t w e e n t h e M a i n S t e m and t h e F r u i t R e t e n t i o n F o r c e ( F R F ) . BERRY DEFORMATION (MM) FIGURE 16 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 i e s Subjected t o U n i a x i a l C o m p r e s s i o n B e t w e e n Two F l a t P l a t e s a t .5 cm/rnin. material and can be studied with the aid of a Maxwell rheo-l o g i c a l model (Figure 17). No information was avail a b l e f o r f r u i t loaded at speeds comparable to those produced by the proposed picking t o o l during the picking operation; however, Maxwell's model predicts that under t h i s condition both the l i n e a r l i m i t and the b i o y i e l d point f o r the stressed f r u i t w i l l be greater than those obtained at .5 cm/min. A f a i r l y safe assumption i s that under t y p i c a l f i e l d loading speeds, the l i n e a r l i m i t f or stressed berries w i l l be greater than the b i o y i e l d force obtained when berries are stressed at .5 cm/min and that no br u i s i n g w i l l occur when the b i o y i e l d force at .5 cm/min i s applied at the higher loading speed (Figure 18). For purposes of thi s study, i t was therefore assumed that, at f i e l d loading speed, bruise inception occurs at the b i o y i e l d force f o r berries loaded at .5 cm/min and that berries behave e l a s t i c a l l y up to that point (point A, Figure 18). The b i o y i e l d force f o r strawberries i s a measure of the compressive force required to cause c e l l rupture i n the loaded specimen;- however, the b i o y i e l d force for d i f f e r e n t loading configurations w i l l d i f f e r (Figure 19) due to the contact stress phenomenon. In order to r e l a t e the b i o y i e l d force f o r berries loaded under u n i a x i a l compression between two f l a t plates to the b i o y i e l d force for berries compressed on picking belts during the picking operation, the contact stress problem must be investigated. 33. STRAIN STRAIN (1) ei,and E 2 are two d i f f e r e n t s t r a i n rates. Note that f o r b i o l o g i c a l materials e x h i b i t i n g a Maxwell type response, the b i o y i e l d point w i l l increase with increased s t r a i n rates and that the i n i t i a l portion of the Maxwell response for high s t r a i n rates resembles Hookean response. FIGURE 17 The Maxwell and Kooke Models I l l u s t r a t i n g T y p i c a l Stress-Strain Response DEFORMATION (CM) FIGURE 18 Assumed Response of Whole Berries to Rapid Deformation. JULY, 19 6 8 LOAD RATE = . 5 cm/min SAMPLE SIZE = 5 5 BOUSSINESQ DIE DIAMETER FOR BOUSSINESQ CONDITION CONDITION = .63 5 cm ( . 2 5 in) —I 1 1 1 1 100 200 300 400 500 600 BIOYIELD POINT (GMS) FIGURE 19 Comparison of BYF for Kertz and Boussinesq Conditions on Northwest Strawberries. The Hertz contact stress theory can be applied to both the f l a t plate and picking b e l t conditions. The maximum contact stress between a spherical body and a f l a t plate can be calculated using equation [11] (4,9). where max = 0.918 ( 1/3 2 2 A zd l - y : max y 1 , E 1 = maximum contact stress as estimated by the Hertz equation = compression force between a spherical body and a f l a t p late. = sphere diameter = Poisson's r a t i o and Young's modulus respectively for sphere. [11] [12] ^2'^2 = P 0^- s s o n' s r a t i o and Young's modulus respectively for the plate By su b s t i t u t i n g the b i o y i e l d force and f r u i t diameter D c, into equation [11], the f r u i t b r u i sing stress can be estimated as = 3.4 A -2/3 i - y p 2 where A [13] [14] = estimated f r u i t b r u i sing stress = Young's modulus f o r strawberries = Poisson's r a t i o f o r strawberries 3.6 Mathematical Analysis for Some Machine Parameters The proposed picking machine must perform, i n sequence, each of the three functions outlined i n Figure 10. Overall performance w i l l depend upon a number of machine parameters as shown i n equation [8]. In the following section, an attempt i s made to estimate values for many of these i n a l o g i c a l way. 3.6.1 Picking finger spacing When the plant canopy has been mowed o f f , the optimum finger spacing i s a function of berry base diameter only. D~ = f , n (D. ) [15 3 f 10 b where: D^ = spacing between adjacent picking fingers D^ = base diameter of strawberry f r u i t (Figure 20) Assuming that a machine loss of 10 percent (by number)is acceptable, fingers should be spaced at: D r = D - 1.28 S.D. [16] f m where: D = mean berry base diameter m J S.D. = standard deviation A sample of mature Northwest berries taken i n 1971 (8) had base diameters of 2.0 + .57 cm. Substituting these values in t o equation [16], fing e r spacing can be estimated as 1.27 cm (0.5 i n ) . 3.6.2 Picking fing e r length In order to remove a berry from the plant by use of the proposed picking machine, picking fingers must be capable of l i f t i n g the berry to a height greater than i t s stem length. Belt Force Stem Force THEORETICAL NO BRUISING CONFIGURATION - use f l a t belts (e.g. Dixylon D-0 type)at an angle to reduce contact stresses. Round Polyura-thane Picking Belt Compressive Force Applied to F r u i t During the Picking Operation FRUIT LOADING CONFIGURATION FOR 19 72 TEST MODEL C O FIGURE 2 0 Loading Configuration During the Picking Operation 38. For t h i s to be true, SL < L s i n 9 [17] where: £ = stem length L = picking f i n g e r length 9 = t o o l i n c l i n a t i o n A sample of Redcoat berries taken i n 1971 (17) had stem lengths of 14.0 + 2.8 cm. Assuming a normal population, approximately 9 8 percent of these berries had stem lengths less than or equal to 19.6 cm (7.7 i n ) . Substituting t h i s value for the l i f t i n g height, I, into equation [17] and se l e c t i n g a minimum t o o l i n c l i n a t i o n of 30 degrees, picking fingers must be at lea s t 39.2 cm (15.4 in) long i n order to pick 9 8 percent of be r r i e s . To ensure that finger length would not l i m i t picking e f f i c i e n c y , picking fingers f o r the Northwest variety were made 19 inches long. 3.6.3 The picking b e l t To simplify the design and construction of.the 1972 f i e l d model, the picking belts were made from .53 cm (.21 in) diameter round polyurethane b e l t i n g . The picking belts exert a compressive force on the f r u i t during the picking operation as shown i n Figure 20. Using the Hertz contact stress theory (9) for a belt diameter of .53 cm and a f r u i t diameter of 2.8 cm, and assuming that E^ >> E the maximum contact stress can be estimated as s S = .94 A ~ 2 / 3 F 1 / 3 [18] max b r 2 where: = A P S max Maximum contact stress as estimated by the Hertz equation = Young's modulus for a polyurethane picking b e l t F r Compressive force exerted on a berry by a picking belt during f r u i t removal and other parameters are as previously defined. Substituting the maximum allowable stress from equation [13] into equation [18], the maximum force that a picking b e l t can exert on berries without causing bruises , was estimated as 47 grams. Since each berry i s held by two picking b e l t s , the maximum force which the belts can exert on a berry during the picking operation, without b r u i s i n g , i s approximately 100 grams. This estimated force i s approximately two standard deviations less than the mean f r u i t retention force measured for the Northwest variety i n 1968. Although i n i t i a l c a l c u l a -tions indicated the p o s s i b i l i t y of bruise damage, the previousl; described belts were used i n model f a b r i c a t i o n to aid i n design s i m p l i c i t y . I f the f r u i t b r u i sing l e v e l i s unacceptable, d i f f e r e n t picking belts and loading configurations must be , considered. A loading configuration which can be expected to eliminate b r u i s i n g during the picking operation i s i l l u s t r a t e d i n Figure 20. To b u i l d a prototype with t h i s loading configura t i o n would, however, be quite d i f f i c u l t . 3.6.4 The f r u i t conveying t o o l The f l o a t i n g (terminal) v e l o c i t y of a s p h e r i c a l l y shaped p a r t i c l e i n a i r (1) i s : 4gP d d a 1/2 [19] where g f = f l o a t i n g or terminal v e l o c i t y = g r a v i t a t i o n a l constant = drag c o e f f i c i e n t d = p a r t i c l e diameter I P P = p a r t i c l e density P P = a i r density c l Assuming that the calculated f r u i t diameter (D ) can be used ° c to estimate the terminal v e l o c i t y , s u b s t i t u t i o n of the appropriate values into equation [19] indicates that 9 8 per-cent of berries w i l l have terminal v e l o c i t i e s less than 5600 ft/min. The required conveying v e l o c i t y i s a function of both the picking t o o l i n c l i n a t i o n and the terminal v e l o c i t y of the berry. V t s i n 9 [20] where: 9 = conveying v e l o c i t y = terminal v e l o c i t y = t o o l i n c l i n a t i o n Assuming that the maximum t o o l angle under f i e l d conditions w i l l be 45 degrees and using equation [20], the required conveying v e l o c i t y can be estimated at 4000 ft/min. As shown i n Figure 21, blower a i r v e l o c i t i e s decrease with distance 4000 fpm VLTX-4000 fpm •400 fpm E x h a u s t i n g 400 fDm 30 d 10% o f f a c e v e l o c i t y a t 30 d i a m e t e r s from j e t n o z z l e 10% o f f a c e v e l o c i t y a t one d i a m e t e r from e x h a u s t o p e n i n g FIGURE 21 Zone o f I n f l u e n c e f o r Blowers from t h e n o z z l e e x i s t ( 1 ) . A f a c t o r must t h e r e f o r e be i n c l u d e d i n t h e d e s i g n n o z z l e e x i t v e l o c i t y t o compensate f o r energy d i s s i p a t i o n . The v a l u e o f t h e compensation f a c t o r w i l l depend upon the shape o f t h e n o z z l e and t h e d i s t a n c e t h a t t h e b l o w e r w i l l be r e q u i r e d t o r e a c h . V. = <fT C X V ) [21] b L ,S c where: = r e q u i r e d b l o w e r f a c e v e l o c i t y fk g = a f a c t o r dependent upon t h e p i c k i n g f i n g e r ' l e n g t h and n o z z l e shape. 3.7 The T e s t Model The p r oposed d e s i g n was f i r s t t e s t e d by use o f a v e r y s i m p l e model d u r i n g t h e 1971 h a r v e s t season a t t h e H.R.I.O. r e s e a r c h s t a t i o n a t V i n e l a n d , O n t a r i o . A l t h o u g h m e c h a n i c a l d i f f i c u l t i e s p r e v e n t e d e x t e n s i v e f a c t o r i a l s t u d i e s w i t h t h i s machine, l i m i t e d f i e l d t e s t r e s u l t s were e n c o u r a g i n g . On the b a s i s o f t h e 1971 t e s t s a second t e s t model was con-s t r u c t e d a t t h e U n i v e r s i t y o f B r i t i s h Columbia i n 1972. T h i s machine c o r r e c t e d a p p a r e n t d e f i c i e n c i e s i n t h e o r i g i n a l model. The model ( F i g u r e s 22 t o 29) was mounted on a Case 444 h y d r o s t a t i c a l l y d r i v e n garden t r a c t o r t o g i v e c o n t i n u o u s model speed v a r i a b i l i t y , a t f u l l t o r q u e , i n t h e 0-2 mph r a n g e . P i c k i n g t o o l i n c l i n a t i o n c o u l d be c o n t i n u o u s l y v a r i e d i n t h e 20-45 degree range by a l t e r i n g model h e i g h t . P i c k i n g b e l t speeds c o u l d e i t h e r be s y n c h r o n i z e d w i t h t h e model ground speed ( F i g u r e 27) o r be v a r i e d by use o f t h e i n d e p e n d e n t engine d r i v e ( F i g u r e 2 6 ) . Each f i n g e r was d e s i g n e d t o " f l o a t " on FIGURE 23 Close-Up of Test Model FIGURE 2Jf Top View o f P i c k i n g F i n g e r s FIGURE 25 View I l l u s t r a t i n g F l o a t a b i l i t y o f I n d i v i d u a l P i c k i n g F i n g e r s . FIGURE 27 I l l u s t r a t i o n o f Ground D r i v e Mechanism FIGURE 28 S i d e View o f the P i c k i n g Machine i n O p e r a t i o n on t h e s o i l s u r f a c e ( F i g u r e 25) and a v a r i a b l e o u t p u t b l o w e r was used t o a s s i s t f r u i t movement up t h e p i c k i n g t o o l i n c l i n e and t o remove some d e b r i s . I n a d d i t i o n , a d j u s t a b l e shoes were used on t h e p i c k i n g f i n g e r t i p s t o a s s i s t f r u i t f e e d i n g and f i n g e r f l o a t a t i o n . 3.8 Model E v a l u a t i o n The model was t e s t e d under f i e l d c o n d i t i o n s on a com m e r c i a l p l a n t i n g i n t h e F r a s e r V a l l e y o f B r i t i s h C olumbia d u r i n g t h e 1972 h a r v e s t s e a s o n . T h i s p l a n t i n g had c o n s i d e r a b l e f r o s t damage and beds were not p r e p a r e d i n any way f o r m e c h a n i c a l h a r v e s t i n g . A l t h o u g h t h e p i c k i n g f i n g e r s f l o a t e d w e l l when t e s t e d up t o speeds o f about 2 mph on a l a w n , t h e y were not e f f e c t i v e under t h e f i e l d c o n d i t i o n s where t e s t i n g was done. F i n g e r s t e n d e d t o d i g i n t o r i d g e s formed by h o e i n g and c u l t i v a t i n g o p e r a t i o n s . These f i n g e r s w i l l not f l o a t under c o n d i t i o n s where t h e r e a r e a b r u p t s u r f a c e i r r e g u l a r i t i e s . Dead r u n n e r s and l e a v e s a l s o t e n d e d t o p r e v e n t p r o p e r f l o a t a -t i o n . T e s t i n g was s u b s e q u e n t l y done w i t h f i n g e r s s e t a t about 1 i n c h above t h e r i d g e s . The t h e o r e t i c a l c a l c u l a t i o n s i n d i c a t e d t h a t t h e p i c k i n g b e l t s used on t h e model would b r u i s e good q u a l i t y f r u i t d u r i n g t h e p i c k i n g o p e r a t i o n ; however, f i e l d t e s t s showed t h a t t h e s e f r u i t s were not n o t i c e a b l y damaged i n most c a s e s . M e c h a n i c a l damage was p r i m a r i l y c o n f i n e d t o o v e r r i p e f r u i t w h i c h were u n s u i t a b l e f o r p r o c e s s i n g p r i o r t o m e c h a n i c a l 48. harvesting. Green f r u i t was not damaged and could l i k e l y be a r t i f i c i a l l y ripened at the processing plant. Figures 30 and 31 i l l u s t r a t e samples of b e r r i e s picked by the test model. Picking machine output for two runs i s shown i n Table I I . For the optimum pick, approximately 6 0 percent of berries were considered to be of good processing q u a l i t y . Use of genetic s e l e c t i o n , growth regulators and fungicides to obtain a more uniformly mature crop would increase the percen-tage of q u a l i t y berries harvested by t h i s machine. The y i e l d o!f usable berries can be s i g n i f i c a n t l y increased by use of solid-bed rather than matted row plantings. Ricketson (14) reports that about 10 to 15 tons of usable berries per acre can be obtained with a once-over pick of Vibrant and Redcoat strawberries i n a solid-bed planting. Mechanical f r u i t damage was found to be r e l a t i v e l y independent of picking belt speed; however, i t was noted that f a s t b e l t speeds tended to c l e a r material through the picking t o o l better than slow speeds. Ground synchronization was not e s s e n t i a l and i n f a c t may not even be desirable. Except f o r some mechanical d e f i c i e n c i e s which can be r e a d i l y solved, t h i s concept appears to have only one inherent drawback. The feeding function did not work e f f e c -t i v e l y i n unprepared f i e l d s . As indicated previously, upright s e t t i n g f r u i t would overcome t h i s problem. Le v e l l i n g and smoothing of the strawberry beds i n the spring i s e s s e n t i a l f o r proper feeding i n the Northwest vari e t y . 49. FIGURE 31 Machine Output S e p a r a t e d i n t o Three C a t e g o r i e s 50. TABLE I I TEST RESULTS Date Green U s a b l e O v e r r i p e and/or B e r r i e s B e r r i e s M e c h a n i c a l l y Damaged B e r r i e s " ^ J u l y 1 30% 55% 1 5 % 2 J u l y 8 20% 60% 20% 1. The number o f m e c h a n i c a l l y damaged b e r r i e s w h i c h were o f good p r o c e s s i n g q u a l i t y p r i o r t o m e c h a n i c a l h a r v e s -t i n g was not s i g n i f i c a n t . M e c h a n i c a l damage was p r i m a r i l y c o n f i n e d t o o v e r r i p e f r u i t . 2. D i f f e r e n c e s between t h e t e s t r e s u l t s f o r J u l y 1 and J u l y 8 can be a t t r i b u t e d t o g r a d u a l r i p e n i n g o f the m e c h a n i c a l h a r v e s t i n g c u l t u r e as t h e season p r o g r e s s e s . To improve o v e r a l l m e c h a n i c a l h a r v e s t i n g e f f i c i e n c y , u n i f o r m l y r i p e n i n g c u l t u r e s a r e e s s e n t i a l . M e c h a n i c a l l y p i c k i n g d a f f o d i l seed pods w i l l be s i m i l a r t o h a r v e s t i n g u p r i g h t s e t t i n g f r u i t . A machine d e s i g n e d and t e s t e d t o p e r f o r m t h i s o p e r a t i o n (15) i n d i c a t e d t h a t o v e r 90 p e r c e n t o f seed pods can be m e c h a n i c a l l y d e t a c h e d a t speeds i n exc e s s o f 2 mph w i t h o u t c a u s i n g n o t i c e a b l e p l a n t damage ( F i g u r e s 32 and 3 3 ) . I t i s b e l i e v e d t h a t a s i m i l a r machine c o u l d h a r v e s t u p r i g h t s e t t i n g f r u i t e q u a l l y w e l l . F o r h a r v e s t i n g s u r f a c e m a t u r i n g v a r i e t i e s , a vacuum ty p e p i c k - u p s h o u l d be c o n s i d e r e d t o a s s i s t t h e f e e d i n g f u n c t i o n . To i n v e s t i g a t e t h e f e a s i b i l i t y o f a vacuum p i c k - u p , a p r e l i m i n a r y t h e o r e t i c a l s t u d y and l a b o r a t o r y e x p e r i m e n t a t i o n were u n d e r t a k e n . R e s u l t s , however, were i n c o n c l u s i v e . FIGURE 33 A P a r t i a l l y M e c h a n i c a l l y Headed D a f f o d i l F i e l d CONCLUSIONS P o t e n t i a l l y , a l l b e r r i e s f e d i n t o a machine u s i n g t h e pr o p o s e d concept can be p i c k e d w i t h v e r y l i t t l e damage t o f r u i t however, t h e f e e d i n g mechanism w i l l have t o be improved t o r e a l i z e good o v e r a l l machine e f f i c i e n c y . The " f l o a t i n g " f i n g e r s worked w e l l on lawn t y p e c o n d i t i o n s ; however, problems a r o s e when t h e s e f i n g e r s were used on u n p r e p a r e d s t r a w b e r r y beds. P r e h a r v e s t f i e l d p r e p a r a -t i o n such as bed r a k i n g , l e v e l l i n g and comp a c t i n g s h o u l d t h e r e f o r e be c o n s i d e r e d . To e l i m i n a t e r i d g e s w h i c h a r e u n d e s i r a b l e f o r t h e pr o p o s e d machine and t o i n c r e a s e p o t e n t i a l y i e l d s , s o l i d - b e d p l a n t i n g s s h o u l d a l s o be c o n s i d e r e d . M e c h a n i c a l l y h a r v e s t e d Northwest b e r r i e s g e n e r a l l y had h u l l s a t t a c h e d t o the f r u i t . M e c h a n i c a l h u l l i n g methods and/or s e l e c t i o n o f v a r i e t i e s w i t h b e t t e r h u l l i n g c h a r a c t e r i s -t i c s s h o u l d be c o n s i d e r e d . F i e l d t e s t i n g o f t h e model i n d i c a t e d t h a t f a s t p i c k i n g b e l t speeds t e n d t o c l e a r m a t e r i a l t h r o u g h the machine b e t t e r t h a n ground s y n c h r o n i z e d b e l t speeds. No n o t i c e a b l e d i f f e r e n c e i n f r u i t m e c h a n i c a l damage was o b s e r v e d . F u t u r e models s h o u l d t h e r e f o r e use an indepe n d e n t motor d r i v e t o o p e r a t e t h e p i c k i n g b e l t s . F o r s u r f a c e m a t u r i n g s t r a w b e r r i e s , a vacuum p i c k - u p d e v i c e s h o u l d be c o n s i d e r e d t o a s s i s t t h e f e e d i n g o p e r a t i o n . T h e o r e t i c a l i n v e s t i g a t i o n l e d t o i n c o n c l u s i v e r e s u l t s , t h e r e f o r e , f i e l d e x p e r i m e n t s must be u n d e r t a k e n t o d e t e r m i n e t h e f e a s i b i l i t y o f vacuum p i c k - u p d e v i c e s . Work w i t h the m e c h a n i c a l d a f f o d i l h e a d e r , i n d i c a t e d t h a t a s i m p l e , e f f i c i e n t machine c o u l d l i k e l y be d e s i g n e d f o r u p r i g h t s e t t i n g s t r a w b e r r i e s . H o r t i c u l t u r a l i s t s s h o u l d t h e r e f o r e d i r e c t some e f f o r t t o ward development o f such v a r i e t i e s . LITERATURE CITED A l d e n , J . L . , Kane, J.M. D e s i g n o f I n d u s t r i a l E xhaust Systems, 4 t h ed. Hew Y o r k , I n d u s t r i a l P r e s s ( 1 9 7 0 ) . B u c h e l e , W.F., D e n i s e n , E.L., 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 , Paper No. 67-620 p r e s e n t e d a t t h e 1967 w i n t e r m e e t i n g , The American S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s , D e t r o i t , M i c h i g a n (December, 1967) . D o o l e y , J.H. , F r i d l e y , R.B., M e h l s c h a u , J . J . , O r i e n t a t i o n  and Capping o f S t r a w b e r r i e s f o r P r o c e s s i n g , Paper No. 72-833 p r e s e n t e d a t t h e 1972 w i n t e r m e e t i n g , The American S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s , C h i c a g o , I l l i n o i s (December, 1972). F r i d l e y , R.B., B r a d l e y , R.A., Rumsey, J.W., A d r i e n , P.A., Some A s p e c t s o f E l a s t i c B e h a v i o r o f S e l e c t e d F r u i t , T r a n s a c t i o n o f t h e A.S.A.E., V o l . 11, No. 1 ( 1 9 6 8 ) . Hansen, CM., S t r a w b e r r y M e c h a n i z a t i o n - The P i e c e s B e g i n t o F i t , The American F r u i t Grower, p.17 ( J u n e , 1972). Hoag, D.L., Hunt, D.R., M e c h a n i c a l 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 , A.S.A.E. Paper No. 65-620 (December, 1965). K i r k , D.E., M e c h a n i c a l Capping and Stemming o f Straw-b e r r i e s , Paper No. 72-834 p r e s e n t e d a t t h e 1972 w i n t e r m e e t i n g , The American S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s , C h i c a g o , I l l i n o i s (December, 1972). 56. B. Mehra, H.K., Some P h y s 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  R e l a t e d t o D e s i g n o f a S e l e c t i v e H a r v e s t e r , u n p u b l i s h e d M.A.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h C o lumbia (1971). 9. 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 A n i m a l  M a t e r i a l s , Volume 1, Gordon and Breach S c i e n c e P u b l i s h e r s ( 1 970). v10. N e l s o n , G.S., K a t t e n , A.A. , Development o f M e c h a n i c a l H a r v e s t i n g and G r a d i n g Equipment f o r S t r a w b e r r i e s , T r a n s a c t i o n o f t h e A.S.A.E., p. 743 (1970). 11. N y b o r g , E.O., M e c h a n i c a l R a s p b e r r y H a r v e s t i n g , u n p u b l i s h e d Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h C olumbia (1970). i/l2 . N y b org, E.O., U n p u b l i s h e d d a t a on some p r o p e r t i e s o f N o r t h w e s t s t r a w b e r r i e s ( 1 9 6 8 ) . ^13. Q u i c k , G.R., New Approach t o S t r a w b e r r y H a r v e s t i n g U s i n g  V i b r a t i o n and A i r , T r a n s a c t i o n s o f t h e A.S.A.E., p. 1180 ( 1 9 7 1 ) . ^14. R i c k e t s o n , C.L., P l a n t S p a c i n g i n S o l i d - B e d S t r a w b e r r y  P l a n t i n g s , H o r t i c u l t u r a l R esearch I n s t i t u t e o f O n t a r i o , V i n e l a n d S t a t i o n , O n t a r i o . S h i k a z e , G., Nyborg, E.O., D e s i g n o f a M e c h a n i c a l D a f f o d i l  Header, Paper No. 72-315 p r e s e n t e d a t the a n n u a l m e e t i n g , Canadian S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s , C h a r l o t t e t o w n , P.E.I. ( J u n e , 1972). 57. 16. S h i k a z e , G., Nyborg, E.O., D e s i g n o f a M e c h a n i c a l Straw-b e r r y H a r v e s t e r , Paper No. 72-320 p r e s e n t e d a t t h e a n n u a l m e e t i n g , Canadian S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s , C h a r l o t t e t o w n , P.E.I. ( J u n e , 1972). 17. S h i k a z e , G., M e c h a n i c a l S t r a w b e r r y H a r v e s t i n g Program, u n p u b l i s h e d r e p o r t , U n i v e r s i t y o f Guelph ( A u g u s t , 1971). 

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