A recently developed vacuum-based harvesting robot has shown promise in picking fruit from clusters, providing better access to tree canopies and minimizing fruit bruising. One of the main technical issues for this harvesting robot is the design of an end effector that can effectively grip the fruit for detachment. Field fruit picking studies using manual straight pull and twisting picking methods were first conducted for three varieties of apple. The critical pulling force and torque needed to detach 95% of apples were determined to be 28.3 N and 0.257 N-m (equivalent suction force of 21.0 N for the current robot's vacuum tube). Three new conformable silicone end effectors with different configurations (i.e., "Straight", "Bellow", and "Curved") were designed and fabricated to provide more effective air sealing, and thus lower vacuum pressure for increased gripping force to effectively detach fruit compared to the robot's original end effector. Laboratory and field picking performance studies with the harvesting robot showed that all three new end effectors performed significantly better than the original, non-conformable end effector. The straight end effector achieved 87% picking success rate; performing consistently better than the other two new end effectors based on multiple performance metrics, and hence should be used in further development of the robotic harvesting system. To enhance robotic harvest research, an indoor simulated orchard environment was constructed, which allows to mimic real fruit picking processes by using artificial trees embedded with specially designed tree branches and magnetic artificial stems for use with real fruit and a unique light system that can simulate different natural lighting conditions for different times of day.
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