Impedance Control for Underwater Gripper Compliant Grasping in Unstructured Environment

Liang Lu, Qi Liu, Chengyuan Liang, Xiaofan Tang, Denan Xu, Xin Yang, Bin Han

Abstract: Impedance control, which is a classical compliant control method, does not possess a good force tracking ability in the underwater environment as in the air environment, due to the underwater factors such as water resistance, random disturbance of water flow and buoyancy. In this paper, two controllers are presented to solve the force tracking problem of underwater compliant grasping, the impedance controller based on parameter identification and the adaptive impedance controller. The former one updates the environment information in real time through RLS method that introduces a forgetting factor. The latter one adjusts the target stiffness and desired position of the impedance model and introduces an adaptive compensation term. Further, simulations to compare the performance with the two controllers, are conducted. It is strongly proved that the impedance controller based on parameter identification is less sensitive to the response speed of the position inner loop, and has better robustness. Finally, it is proved by experiments that the controller has a good performance in the real underwater compliant grasping task.