Development and Field Validation of a Bivalve-Inspired Nonprehensile End-Effector for Citrus Harvesting

Fruit-body grasping can expose citrus peel to concentrated loads during robotic harvesting. This study develops a bivalve-inspired end-effector that combines opposing C-ring closure, pedicel cutting, and passive fruit reception without deliberately clamping the fruit body. Paired shell closure informed the mechanism, while the ring dimensions were selected to accommodate the target fruit sizes and provide access to the pedicel region. An idealized normal-contact analysis provided supporting mechanical interpretation of the concave inner surface. The end-effector was integrated with a four-degree-of-freedom positioning platform and a vision-assisted, operator-supervised teleoperation system. The operator aligned the closure plane, commanded reduced-output engagement and primary cutting, and applied wrist rotation only when the fruit remained attached. In a commercial Wogan mandarin orchard, 85 engaged harvesting outcomes were recovered and inspected after the cutting and reception sequence. Seventy fruits were intact and three had superficial grazes, giving an acceptable-outcome proportion of 85.9% under the study's visual inspection criteria. The remaining outcomes comprised six ring-tip punctures and six fruit-body mis-cuts. A subset of 14 harvested fruits had a median residual pedicel length of 11.0 mm and a range of 6.0-40.8 mm. These results establish the feasibility of the integrated mechanism under teleoperation and identify closure-plane placement, ring-tip contact, and cutting consistency as priorities for further development.