Hybrid position/force control using an admittance control scheme in Cartesian space for a 3-DOF planar cable-driven parallel robot

This paper proposes a hybrid position/force control algorithm for a 3-degree-of-freedom (DOF) planar cable-driven parallel robot (CDPR). The control algorithm is implemented using an admittance control scheme so that an external wrench error is used for modification of the pose of an end-effector in Cartesian space. Since the CDPR system is different from that of conventional serial or mobile robots, the control algorithm is constructed so as to convert the desired position of the end-effector into the desired cable lengths, to convert the measured tension of cables into the estimated wrench, and to modify the desired Cartesian position of the end-effector using the wrench difference and the admittance control scheme. Instead using two selection matrices at both the position-control loop and the force-control loop, one selection matrix is used to modify the desired position using the wrench difference. To evaluate the proposed algorithm, an experimental setup using the 3-DOF planar CDPR is constructed. A series of experiments shows that the external wrench is well-calculated using the cable tensions, and that the force control alone and the hybrid position/force control for CDPR are implemented with sufficient control performance.