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UBC Theses and Dissertations

Mechanical raspberry harvesting Nyborg, Erling Orvald


Raspberry growers in the lower mainland of British Columbia are contending with increasing production costs and are facing problems in obtaining seasonal labour for fruit picking. Since cost of hand harvesting represents a large proportion of the total production cost, the purpose of this research was to investigate the feasibility of mechanical raspberry harvesting and to design a mechanical harvesting system suitable for the lower mainland of British Columbia. A systematic design procedure, oriented toward design and testing of a bio-machine system, was employed and the selected design was based upon the physical and mechanical properties of the raspberry plant and its fruit. An economic analysis, comparing the mechanical harvesting system to present hand harvesting methods was used to determine the necessary relationships among machine cost, machine capacity and machine efficiency. The selected design for a mechanical raspberry harvesting system included tools for feeding, cane orientation, selective harvesting, fruit collection, fruit conveying and fruit storage. Mathematical models for these tools were constructed, based on a series of tests determining pertinent physical and mechanical properties of the raspberry plant and fruit. In addition, tests to define fruit quality were undertaken and the relationships among fruit quality and selective harvesting parameters were investigated. The use of chemical growth, regulator's to alter fruit retention force was also investigated. Force-deformation moduli, resulting from flat plate compression tests of raspberry fruit, were found to be good indicators of fruit quality. Correlations among force-deformation moduli and fruit properties indicated that either fruit retention force or F/W ratio could be used as control variables for a selective harvesting tool. Prototype units for feeding, cane orientation and selective harvesting tools were designed and fabricated. The selective harvesting tool was a fixed displacement shaker designed to apply equal maximum acceleration to all fruiting portions of the plant, independent of plant properties. F/W ratio was used as the control variable for selective harvesting. Limited field testing indicated that the tools for feeding, cane orientation and selective harvesting could satisfactorily be used in a mechanical raspberry harvesting system. Results also indicated that mechanical harvesting could be substantially more profitable than hand harvesting. The Willamette variety of raspberries as commonly grown in British Columbia was found not especially suitable for mechanical harvesting. Due to the high ratio of fruit retention force to fruit stem strength in the Willamette variety, the quality of machine harvested fruit must be lower than the quality of hand harvested fruit. Since fruit retention force is dependent upon fruit variety, investigation of physical properties of other suitable raspberry varieties should be undertaken in order to find a variety having properties more compatible with mechanical harvesting methods.

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