Experimental Study on Reaching Movements of Robot Arms with Redundant DOFs Based upon Virtual Spring-Damper Hypothesis

A simple control method for redundant multi-joint arm was proposed recently by gaining a physical insight into human multi-joint reaching movements in redundancy of DOFs. Differently from the traditional approaches, the method need neither introduce any artificial performance index to resolve kinematics ill-posedness nor calculate the pseudo-inverse of the Jacobian matrix of task coordinates with respect to joint coordinates. This novel approach is based upon an idea of "virtual spring-damper hypothesis," and the control signal is composed of linear superposition of three terms 1) joint-damping, and 2) virtual damper effects in parallel to 3) virtual spring effects in task space. This paper shows through experiments by using an industrial robot arm (PA-10) with redundant multi-joints that the control signal can generate smooth reaching motions without incurring any annoying self-motion even in the case of industrial robots. It is shown further that virtual damping effects in task space play an important rule in making endpoint trajectories of the robot arm quasi-straight. Consequently, the control signal can easily generate human-like multi-joint movements of robot arms without spending a huge amount of computational cost for motion plannings of not only the endpoint trajectory but also each joint trajectory