A Motion Control Scheme in Task Oriented Coordinates and its Robustness for Parallel Wire Driven Systems.

Abstract

Parallel wire driven robots have some advantages such as high speed, heavy load and so on. In the previous works in the parallel wire driven robots, the object or the end-effector is controlled through each wire length. However, each actuator position in the base coordinates and each measured length of wires include errors. Therefore, even if fine positioning in wire length coordinates is realized, the end-effector position may deviate from a desired position in task oriented coordinates. To overcome such difficulty, we propose a new motion control scheme for the parallel wire driven robots in this paper. In the proposed scheme, a pseudo inverse matrix which shows the relation between a wire tensions vector and a force vector of the end-effector is utilized to operate the object in the task oriented coodinates. When the proposed control scheme based on the force relation is used, it is easy to attain more precise positioning by using external sensors such as cameras, and to apply it to force control. In this paper, we prove the motion convergence to desired points and discuss its robustness based on Lyapunov stability analysis. Finally the usefulness of the proposed control scheme is demonstrated through some experimental results.