Tracking Control and Vibration Reduction of Flexible Cable-Suspended Parallel Robots using a Robust Input Shaper

The control of flexible cable-driven parallel robots usually requires not only the feedback from the joints, but the feedback from the end-effector pose or cable tension. This paper presents a new approach for reducing the vibration of flexible cable-suspended robots, using only the feedback from the joints. First, the dynamic equations of a 6DOF cable-suspended parallel robot with elastic cables were derived by Gibbs-Appel formulation. Subsequently, three different control approaches were investigated based on the computation load and required sensors. As a result, a feedback linearization method based on the rigid model of the system was selected. In order to reduce the vibration, a robust input shaping method was employed to prevent excitation of natural modes. Simulation results revealed that the proposed approach leads to a noticeable vibration and settling time reduction in cases of low and high cable stiffness, respectively. Moreover, another simulation compares the presented approach with a composite controller, which uses the feedbacks from the end-effector and actuators. Thereafter, the performance of the approach in vibration reduction is quantitatively shown. Finally, experimental validation of the approach was accomplished by frequency analysis of the vibration obtained from the IMU sensor, attached to the end-effector.