Optimization Design and Experiment of a Pulling–Cutting–Clamping End-Effector for Hang Pepper Harvesting

Abstract

Existing studies on selective pepper harvesting commonly use the pedicel as the picking target. However, for Hang pepper, dense branches and leaves cause severe fruit stem occlusion, resulting in a low harvesting success rate. To address this limitation, an end-effector that uses the fruit body as the picking target was designed in this study. Physical property tests of Hang pepper were first conducted. In radial compression tests, a post-release deformation of less than 5% was used as the criterion for low-damage clamping. The maximum allowable clamping force was determined to be 3.5 N, under which the maximum fruit compression ratio was 10%. The maximum cutting force required to shear the pedicel was 15.03 N. Based on these results, a harvesting strategy consisting of fruit clamping, fruit pull-down, and pedicel cutting was proposed. A five-bar linkage was adopted as the main mechanism of the end-effector, and its kinematic and mechanical models were established. Taking the minimum driving torque as the optimization objective, a genetic algorithm was used to optimize the linkage dimensions. The optimized driving torque was 0.801 N m, and a calculation method relating the target fruit diameter to the servo rotation angle was established. Harvesting experiments under prescribed target diameters showed a harvesting success rate of 95%, and the single-fruit harvesting time was 5.1 s, demonstrating the excellent harvesting capability of the proposed end-effector.