Stable PD and Internal Force Control of Omnidirectional Wheeled Mobile Manipulators

Omnidirectional mobile manipulator, which is composed by a three DOF omnidirectional mobile platform and a mounted manipulator, can move in any direction at any time. By reason of the redundantly actuated mechanism, the omnidirectional motion property of the mobile platform is similar to the parallel manipulator cooperatively manipulating objects, which admits internal force doing none contribution to the motion of the platform. Thus, the internal force should be controlled to reduce energy waste. Therefore, a stable PD controller is developed first for motion control of the integrated mobile manipulator system. Then, by treating the motion induced force as disturbance, a feed forward plus PI type force controller is addressed to regulate the internal force to zero. Finally, simulation results demonstrate the validity of the proposed approach.