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Dual Closed-loop Impedance Control for Wheeled Mobile Manipulator in Trajectory Tracking

This paper presents a dual closed-loop 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 n-links manipulator are established based on the Euler-Lagrangian 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.