Load identification and compensation for a Cable-Driven parallel robot

In Cable-Driven parallel robots, elastic cables are used to control the movement of a platform in the workspace. The accuracy of a robot system is one of the most important comparison criteria for various applications. In this paper, we present a new approach to increase the relative accuracy of a cable robot under changing payload, by compensating the error induced by elasticity. In the first step, the load is identified based on cable force sensors and the acceleration of the platform. Second, for the actual pose the stiffness matrix is computed and the expected displacement of the platform in Cartesian space is determined. Lastly, the displacement is compensated by adapting the cable lengths. Furthermore, the influence of the calibration of cable force sensors and their parameters´ inaccuracies are discussed. The algorithms are implemented and evaluated on a 6-DOF cable robot. We could experimentally prove an improvement of over 50% in the relative accuracy under changing load.