Compliant Robotic Gripper with Integrated Ripeness Sensing for Blackberry Harvesting

摘要

Global blackberry demand has been surging due to their antioxidant and nutritional value in a traditional diet. However, blackberries have extreme fragility (resulting in up to 85% of harvest batches sustaining damage) and near-ripe and ripe blackberries are difficult to distinguish in normal lighting conditions. These challenges in maintaining the blackberry supply motivate the development of an autonomous robotic solution to harvest fully ripe blackberries with minimal damage. The present paper details the mechanical design, methodology, analysis, and experimental results of a compliant robotic gripper created for this purpose. The gripper has a compact form factor and retractable fingers with specialized TPU finger pads for gentle picks, a near-infrared (NIR) reflectance-based probe for detecting full ripeness and a standardized harvesting sequence for effectively picking berries. In an outdoor harvesting experiment, the gripper attempted picking 26 berries without ripeness sensing, with 65.4% (17) being successfully picked and 38.5% (10) sustaining damage. The movements of the robot arm in the harvesting sequence were accordingly adjusted and finalized for following in-lab experiments, in which the gripper was also outfitted with ripeness sensing. Out of 40 berries, 62.5% (25) were successfully picked, with 0% of them sustaining damage. The ripeness probe classified 56 ripe and 11 near-ripe berries, with 89% (50) of the ripe and 64% (7) of the near-ripe berries being correctly classified. In a second in-lab experiment, 16 of 20 berries were successfully picked, with 2 sustaining damage.