Dual Closedloop Impedance Control for Wheeled Mobile Manipulator in Trajectory Tracking This paper presents a dual closedloop impedance control scheme for a nonholonomic wheeled mobile manipulator in trajectory tracking with nonlinear contact disturbance. The kinematics and dynamics models of the mobile platform and nlinks manipulator are established based on the EulerLagrangian approach. In order to control and eliminate the influences caused by system uncertainties and nonlinear contact disturbance, a control scheme which consists of double closed loops is proposed. The impedance control is applied to realize force tracking control in the outer loop. The inner loop is then designed to deal with chattering of measured parameters by using extended Kalman filter. The proposed controller ensures the tracking error in workspace converges to zero and the input torques are smooth. Utilizing the Lyapunov method, the stability of the system is proved. Simulation compared with conventional control methods on two driving wheeled mobile manipulator shows the effectiveness and robustness of the proposed control scheme.

Impedance Control Strategy and Experimental Analysis of Collaborative Robots Based on Torque Feedback In this paper, through the modeling and analysis of flexible joints, an impedance controller based on torque feedback is proposed, which is used to realize the active compliance of collaborative robots. The controller includes two parts: torque controller and impedance controller. The torque controller is used to compensate the robot dynamics, and the impedance controller is used to adjust the joint stiffness and damping. The theoretical analysis of the control strategy shows that the significance of torque feedback is that it can reshape the inertia of the motor, reduce friction torque and suppress unknown disturbances. In order to ensure tracking accuracy, a task errorbased disturbance observer is designed. Experiments with a 7DOF collaborative robot show that the proposed controller in this paper can realize the body compliance and obtain better compliance performance than the traditional compliance control method.