Solving the pulley inclusion problem for a cable-driven parallel robotic system: Extended kinematics and twin-pulley mechanism

For a cable-driven parallel robot system, the robot kinematic models usually assume that the cable connection in the system comprises ideal fixed points on the base and an end-effector. However, the cables are usually guided around pulleys, so the pulley geometry can induce movable connection points when operating the robot system. Some previous studies have addressed the influence of the geometry of the guiding pulleys on the parallel cable robot’s kinematics, and extended pulley kinematics have been proposed by considering the pulley radius. However, the inverse kinematics of the extended pulley kinematics may hinder the implementation of an actual system, especially owing to the real-time computation capacity. Hence, in this study, to solve the pulley kinematic inclusion problem for a cabledriven robotic system and to improve the position control performance, we investigated the actual pulley kinematic effect and we proposed two methods for a fully constrained planar cable robot. Comparison and evaluations based on simulations and experiments using the proposed methods in terms of the end-effector posture demonstrated their validity for solving pulley inclusion problems for a cabledriven parallel robot.