Experimental Study on Control Method for Robot Arms with Redundant Joints Based upon Virtual Spring-Damper Hypothesis

Abstract

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 ill-posedness of inverse kinematics 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 movements without incurring any annoying selfmotion. It is shown further that virtual damper effects in task space enable endpoint trajectories of the robot arm to be rectilinear and the effects can be enhanced by compensating the viscosity inherent in the robot.