A Semi-Automated Harvesting Prototype for Shaking Fruit Tree Limbs

Abstract

Mechanizing the fruit removal operation during fresh-market apple harvesting is essential for labor and cost savings for fruit growers. This study introduces a semi-automated mechanical fruit harvesting system that uses a fruit removal technique based a unique limb shaking mechanism called a dual motor actuator (DMA). The harvesting system was tested on ‘Gala‘ apples grown in a formally trained fruiting wall orchard. A manipulator arm, positioned by a human, held a fruit catchframe and an end-effector. The system was mounted on a mobile orchard platform. The DMA was developed as an infinitely variable pattern end-effector that applies rhythmic motions to a fruiting limb to remove fruit. The novelty of the DMA design is the use of two eccentrics mounted to electric motors that are pinned together to form a triangle with an adjustable base. Pattern, rhythm, and actuation time were varied to characterize the removal efficiency and fruit damage percentages. Removal efficiency averaged only 35% across the fruiting limb but increased to 88% within the actuation zone of the fruiting section, showing the potential of a semi-selective harvesting technique for localized fruit removal on branches trained to trellis wires. A circular pattern using a 200 cycles min-1 rhythm achieved the lowest overall damage (10%) of all combinations of the patterns and rhythms tested. Bruise percentage was also lowest (4%) using the same pattern and rhythm. Rhythm and actuation time were significant factors that influenced the fruit removal condition. No fruit was removed outside of the targeted actuation zone when using a single limb grasper. This localized limb actuation method shows great potential for removing apples from a limb while maintaining fresh-market quality fruit.