Disturbance-observer-based motion control of redundant manipulators using inertially decoupled dynamics

In this paper, a robust motion control method for kinematically redundant manipulators is addressed to control the motion of the end-effector, as well as the null-space motion. To reduce the disturbance effects on the system performance, a new disturbance observer is proposed to improve the performance of the conventional structure. A minimal parametrization of the null space is performed to visualize the null-space motion explicitly using the weighted decomposition of joint space. Augmenting this null motion with conventional velocity relations, an extended task space formulation is obtained. The proposed disturbance observer is adopted in the extended task space formulation and a motion control method is devised based on the passivity concept. The performance of the proposed controller is verified through experiments with a three-link planar direct-drive manipulator.