Stable joint torque optimization for multiple cooperating redundant manipulator system

Abstract

In this paper, joint torque optimization for multiple cooperating redundant manipulators rigidly handling a common object is considered. This work focuses on finding the optimal and stable distribution of the operational forces of a multiple redundant manipulator system to the individual manipulators. Two joint torque optimization schemes (local joint torque minimization and natural joint motion) are formulated and compared. When a redundant manipulator with its joints free is driven by its tip, a naturally inducing joint motion can be called ‘natural joint motion’. From the simulation results of a system of three cooperating redundant manipulators, the natural joint motion scheme is shown to be better than the local joint torque minimization scheme with regard to global torque minimization capability and the resulting stability of motion. However, in order to guarantee the stability, the null space damping method is required for the both schemes. The effectiveness of the null space damping method is demonstrated by simulation. Additionally, the condition for the distribution of the operational forces required to drive the given system along a natural joint motion trajectory is addressed.