Practical adaptive position feedback regulator for parallel robots with bounded inputs

This paper addresses the regulation problem of parallel robots by a proportional derivative plus desired gravity compensator (PD-DGC) controller. Due to inaccurate measurements, unmodeled dynamics, and vibrations specially in cable-driven robots and external disturbance in practice, the model of the robot is often plagued with kinematic and dynamic uncertainties. In this paper, two new generations of PD-DGC controller, namely adaptive with respect to the parameters in gravity term, and time-varying PD-DGC in the presence of bounded disturbance, are proposed. Toward not requiring accurate velocity measurement, PD-DGC with merely position feedback in complement to the time-varying controller is designed in the presence of bounded control efforts. Incorporating both methods to establish a simple but strong robust adaptive controller is also investigated by adding an extra assumption on adapted parameters. The asymptotic stability of the closed-loop system is analyzed by the Lyapunov direct method. Experimental results on 2-DOF eye surgery and 3-DOF flexible link ARAS cable-driven robot demonstrate the effectiveness of the proposed approaches in practice.