Active vibration canceling of a cable-driven parallel robot in modal space

Compared to other parallel robots, cable-driven parallel robots can achieve bigger workspace, higher dynamics with lighter parts and fewer energy while being economically competitive. However, such robots with big workspaces are affected either by cable sagging or by a very low end-effector stiffness, both causing positioning errors. With lightweight cables, the very low stiffness yields disturbing vibrations. In this paper, we address the problem of decoupled active canceling of those vibrations in the modal space. In modal space, vibrations are decomposed in orthogonal signals which allows to use simple SISO control methods to build an active vibration canceling algorithm for the end-effector. As the modal space depends on the end-effector position, better performances are achieved if the controller is tuned for the current robot position. The proposed method is tested both on a realistic simulation and on a 8-cables and 6-degrees of freedom robot.