Real-time zero moment point compensation method using null motion for mobile manipulators

This paper presents a method to deal with the dynamic stability for a mobile manipulator. Although the system has static stability, manipulation on the moving base or mobile locomotion with a manipulator may cause the system to turn over due to dynamics, so the controller of a mobile manipulator is carefully designed. In this paper, to define the dynamic stability for a mobile manipulator, the zero moment point (ZMP) is used. ZMP is a very useful measure of the dynamic stability. However, if the degrees of freedom of the system are large, the calculation algorithm is very complicated. So, to simplify the calculation algorithm, we define ZMP using the iterative NewtonEuler formulation. Next, a unified approach for the two subsystems, i.e., mobile and manipulator, is formulated using a redundant scheme. To conserve the dynamic stability of the system in real-time, we define the performance index for the redundant system using ZMP. Then, the redundancy resolution problem for optimizing the proposed performance index is solved using the null motion optimization. Finally, the performance of the proposed method is demonstrated by simulation.