Unified Contact Force Control Approach for Cable-driven Parallel Robots using an Impedance/Admittance Control Strategy

Abstract

In this paper a unified contact force control approach for cable-driven parallel robots (CDPR) is proposed. The contact force controller is governed by two control loops: 1) An inner impedance control loop enforcing a dynamical relationship between the internal forces and the end-effector velocities to maintain a desired tension level in the cable system. 2) An outer admittance control loop considering the contact wrench by altering the desired end-effector trajectory. For the parametrization of the admittance controller the desired stiffness of the virtual manipulator system is defined by the mechanical stiffness of the end-effector. Further, the influences of changing the stiffness of the virtual system are discussed. To reconstruct the contact wrench a disturbance observer based on the generalized momentum approach is incorporated into both control loops. Experiments with a 6-DOF CDPR with industrial electric synchronous machines are presented validating the proposed contact force control approach.