Investigations on robust motion control designs for mobile manipulators

Abstract

Keywords: Mobile manipulator; kinematic redundancy; nonlinear proportional-integral-derivative control; adaptive control; backstepping control design; operational-space motion control; disturbance observer; resolved motion control; computed velocity control; omni-directional mobile robot; mecanum wheel-drive; differential-drive; fault-tolerant control; line-of-sight; kinematic control; double-loop control; robust control; This thesis proposes various robust and adaptive motion control schemes such as a simplified operational-space control, an adaptive motion control, an improved backstepping control design, a double-loop motion control or dual loop control and an actuator fault tolerant control schemes for mobile manipulators. Mobile manipulator comprises of a manipulator arm mounted on a mobile platform. A mobile manipulation system offers a dual advantage of mobility offered by a mobile platform and dexterity offered by the manipulator. The thesis work is folded in three parts, the dynamic model formulation of a generalized mobile manipulator based on the recursive Newton-Euler method is discussed and the dynamic model developed for a real-time mobile manipulator namely JR2 consists of a four mecanum wheeled mobile base and a six degrees of freedom serial chain manipulator arm. Further, a robust nonlinear control method with an uncertainty estimator is proposed and applied to the mobile manipulator for its position tracking in its operational-space (Cartesian space). The proposed robust motion control method incorporates a feed-forward control term to reinforce the control action with extravagance from the desired acceleration vector; an uncertainty estimator to reimburse for the unknown effects such as parametric uncertainties, unknown external disturbances, unmodeled dynamics and a decentralized PID (proportional-integral-derivative) controller as a feedback loop to strengthen the stability of the system. It is observed that the main strengths of the proposed scheme are its high robustness against parameter uncertainties and external disturbances, simplicity in design and ease of implementation. The effectiveness, feasibility, and robustness of the proposed method are illustrated using the computer-based simulations based on the derived dynamic model of the JR2 with and without uncertainty estimator.