Robust Impedance Control of Uncertain Mobile Manipulators Using Time-Delay Compensation

A stable robust impedance controller is proposed here for mobile manipulators with time-delay compensation, for handling uncertainties and disturbances in the presence of nonholonomic constraints, nonlinear dynamics, and the coupling of mobile manipulator that includes motor dynamics. A novel state-space model of the electrically driven nonholonomic mobile manipulator is also presented. In contrast to the usual current-based (torque mode) control laws, the use of motor dynamics in this model leads to a computationally faster and more realistic voltage-based controller. The most important advantage of the proposed control strategy is that the nonlinear dynamics of the mobile manipulator are handled as an external load, hence the control law is free from the robot dynamics and the impedance controller becomes computationally simpler, faster, and more robust with negligible tracking error. The control approach is verified by the bounded-input bounded-output stability analysis. Simulation and experimental laboratory results demonstrate the effectiveness of the proposed controller on a nonholonomic mobile manipulator driven by permanent magnet dc motors.