Control of mobile manipulators for power assist systems

We present a control algorithm for mobile power assist systems. Most mobile power assist systems have a heavy mobile base to prevent easy tumbling. So continual movement of the base during operations causes high energy consumption and gives the high risk of human injury. Furthermore, the slow dynamics of the base limits the frequency bandwidth of the whole system. Thus we propose a cooperation control method of the mobile base and manipulator to remove the unnecessary movement of the base. In our scheme, the mobile base does not move until the center of gravity (C.G.) of the system goes outside the safety region. When C.G. reaches the boundary of the safety region, the base starts to move to recover the manipulator's initial configuration. By varying the parameters of a human impedance controller, the operator is warned by a force feedback that C.G. is on the marginal safety region. Assigning a nonlinear mass-damper-spring impedance to the tip of the manipulator, our scheme is implemented. The experimental results are presented to demonstrate the efficacy of the control algorithm.