Observer-Based Robust Control of 6-DOF Parallel Electrical Manipulator With Fast Friction Estimation

This paper presents an observer-based robust controller equipped with a fast friction estimator for a 6-DOF parallel electrical manipulator (PEM) in the joint-task space. First, the joint-task space framework for a 6-DOF PEM is constructed, which not only avoids time-consuming forward kinematics, but also contains the dynamic model. Second, a nonlinear disturbance observer is designed to estimate the deviation uncertainties which are modeled as disturbances in the proposed joint-task space. In addition, a fast friction estimator based on Lyapunov design method is proposed to estimate the uncertain friction caused by the spiral drive way of the electrical cylinder fast and effectively. The sufficient condition for the convergence of the estimation errors is given. The robust control scheme by employing the disturbance observer and the fast friction estimator is proposed based on the Lyapunov design method to guarantee a practical stability under uncertainties. Finally, the friction property identification method and comparative experimental results are presented to show the effectiveness of the proposed scheme.