Tracking controller design of omnidirectional mobile manipulator system

This paper proposed a tracking controller for an omnidirectional mobile manipulator system, a three-linked manipulator mounted on a three-wheeled omnidirectional mobile platform, to track a desired trajectory with constant desired velocity. An end-effector mounted at the end of a manipulator of the omnidirectional mobile manipulator system is controlled to track a desired trajectory with constant desired velocity. A distributed control method is applied to control the omnidirectional mobile manipulator system that includes two subsystems such as an omnidirectional mobile platform and a manipulator. Two controllers are designed to control two subsystems, respectively. Firstly, based on a tracking error vector between a point of the end-effector and a reference point, a kinematic controller is designed for the end-effector of the manipulator to track a reference point. Secondly, based on a tracking error vector between a target point and a real point of the end-effector, a sliding mode controller based on its dynamic model is designed for the omnidirectional mobile platform to move so that the manipulator tracks the desired posture without its singulariry. The control laws are obtained based on backstepping technique and make the tracking error vectors go to zero asymtotically. The system stability is proved using the Lyapunov stability theory. The simulation results are presented to illustrate the usefulness of the proposed control scheme in the presence uncertainties and external disturbances.