Enhanced trajectory tracking control with active lower bounded stiffness control for cable robot

Cable robots have seen considerable recent interest ensuing from their ability to combine a large workspace with significant payload capacity. However, the cables can apply forces to the end-effector only when they are in tension, and thus form a subclass of control problems requiring unilateral control inputs. Furthermore, actuation redundancy occurs when surplus cables are introduced within the system. On one hand, such redundancy needs to be carefully resolved for accurate tracking of the task. On the other hand, it allows the redistribution of the actuation forces to satisfy some secondary criteria. In this paper, we apply such redundancy for enhanced trajectory tracking by actively controlling the task stiffness of the end-effector. The scheme allow us to specify a lower bound of the task stiffness, which is intended to provide improved trajectory tracking and disturbance rejection performance. Finally, we illustrate the improved control performance within a virtual prototype cosimulation framework.