Grasping mode analysis and adaptive impedance control for apple harvesting robotic grippers

Abstract In order to reduce the mechanical damage caused by apple harvesting robot to apples and realize the non-destructive grasping during the grasping process, an adaptive impedance control strategy for apple harvesting robot compliant grasping is proposed based on the analysis of grasping modes in this paper. Firstly, burgers viscoelastic model is established to describe the rheological characteristics of apples. Then taking the plastic deformation of apples as the damage standard, three types of grasping modes of the gripper for picking apples are compared and analyzed. Finally, in view of the fact that the traditional impedance controller cannot satisfy the grasping force control under the condition of uncertain environmental stiffness and uncertain environmental position, an adaptive controller is designed to adjust the desired position online based on the error between desired force and actual grasping force so that it can track the desired force. Simulation and experiment results show that the adaptive impedance control strategy is more compliant with the actual grasping force, the overshoot and the adjustment time has been significantly improved, which provides a reference for actual apple picking.