Semi-active damping for industrial robots

The dynamic accuracy of industrial robots is significantly influenced by the elastic drive trains of the axes. Their behavior is composed of the coupled dynamics of drive control and gear mechanics. As an undesirable consequence, increasing elasticity leads to growing tracking errors. One approach to reduce tracking errors is semi-active damping. The functional principle is based on damping the gear mechanics by selective braking of an additional actuator. From a drive control perspective, this results in a more favorable system behavior, which, in turn, allows the selection of more performant control parameter values. This leads to better tracking and disturbance behavior. The aim of this paper is to transfer the semi-active damping with a low-cost additional actuator to cascade-controlled industrial robots. For this purpose, a novel semi-active control law is proposed for actuator control. A damping actuator for the first robot axis is designed, design rules are derived, and an integration concept is proposed. Finally, a H infinity synthesis methodology for simultaneous parameterization of the drive and actuator control is introduced. An experimental validation proves the effectiveness of the solution at axis level resulting in an average 17.3 % reduction in tracking errors, and in a milling experiment, reducing the average Euclidean tracking error by 42.7 %.