Design and Experimental Evaluation of a Segmented Pneu-Net Soft Gripper for Agaricus bisporus Harvesting

Conventional pneumatic bending actuators cannot perform the in-grasp twisting required to detach mature Agaricus bisporus from the cultivation substrate. Manual harvesting was characterized by measuring fingertip contact forces, fruiting-body rotation, and motion timing using flexible-film force sensors and an inertial measurement unit. The resulting grasp–twist–lift characteristics informed the design of a three-finger segmented variable-angle symmetric oblique-chamber (SVA-SOC) pneu-net soft gripper. Each SVA-SOC actuator integrates upper parallel chambers and lower symmetric oblique chambers that are synchronously pressurized to generate inward bending for grasping; after grasp establishment, differential pressure between the lower oblique chamber groups induces torsional deformation while the grasping pressure is maintained. A reduced-order model based on the Yeoh constitutive model and segmented constant-curvature assumption was validated against finite-element simulations and experiments, yielding root mean square error (RMSE) values of 12.82° and 3.36° for bending and twisting angles, respectively. At 85 kPa, a single actuator generated bending and tangential contact forces of 1.41 and 1.31 N, respectively. The three-finger gripper achieved a maximum target rotation of 44.59°, an initial grasping force of 5.38 N, and a pull-off force of 18.59 N. In 50 harvesting trials, grasping, harvesting, and undamaged harvesting rates were 100%, 94% and 86%, respectively, indicating feasibility for low-damage harvesting of mature Agaricus bisporus.