Null Space Based Robot Compliant Control with Prescribed Motion Performance

In this paper, a null space controller is proposed to achieve a compliant motion behaviour of a redundant manipulator for a safety human-robot interaction. The robot end-effector is controlled using a prescribed performance controller, such that the transient tracking performance of the main task is guaranteed. The compliant behaviour of the robot motion is ensured by using a null space control law, by which the external torque acting on the main task can be projected to a null space and the effects of the external force can be reduced. The external torque is estimated and canceled by using an adaptive disturbance observer. Lyapunov synthesis illustrates the asymptotic stability of the robot system while simulation studies based on a 3-DOF planner robot show the effectiveness of the proposed control algorithm.