Cascaded ESO based multi-task priority tracking and null-space compliance control for redundant robots

Abstract

This paper investigates multi-task priority trajectory tracking and null-space compliance control of redundant robots without joint velocity and joint torque sensors. A novel multi-task priority controller is proposed to improve the dynamic performance and robustness of all level tasks. First, a cascaded extended state observer (ESO) is put forward to estimate joint velocity, lumped disturbances and the interference from high-priority tasks to low-priority tasks simultaneously. Then, a tracking controller for higher priority tasks and a null space compliance controller for the lowest priority task are designed. The stability of the closed loop system under the proposed cascaded ESO and task trajectory tracking controller is analyzed, as well as the passivity of the lowest priority task. The parameter tunning procedure of the cascaded ESO is given. Comparative simulation and experiment results verify the effectiveness of the proposed method.