Motion and Internal Force Control for Omnidirectional Wheeled Mobile Robots

This paper presents an integrated scheme for motion control and internal force control for a redundantly actuated omnidirectional wheeled mobile robot. The interactive forces between a robot body and its wheels can be reduced into two orthogonal parts: motion-induced forces and internal forces. First, it is shown that the internal forces reside in the null space of the coefficient matrix of the interactive forces and do not affect robotic motion. However, these forces caused by motor torques should be minimized as much as possible to increase the energy efficiency and life span of joint components. With different goals, the control for motion and the control for internal forces can be designed separately. Here, both kinematic and dynamic models of the forces are proposed. A proportional differential plus controller regulates the motion and an inverse dynamic controller tracks it. Then, to minimize the internal forces, an integral feedback internal force controller is used. The motion controller guarantees the robotic motion while the internal force controller minimizes the internal force occurring during robot motion. Simulation results verify the effectiveness of the proposed schemes.