Design of Robust Controller for Enhanced Performance of 2-DOF Torsion System

Abstract

This paper presents the design of a robust control law for stabilization of the 2-DOF torsion system, which is an underactuated system, characterized by a higher number of degrees of freedom than the number of actuators. The output of the given servo dynamical system with two flexible torsional couplings should be positioned properly with minimum vibrations and response time. Control design focuses on application of nonlinear control technique, hierarchical sliding mode control, for desired and robust performance. HSMC is a robust controller which is capable of rejecting matched uncertainties like its conventional counterpart, sliding mode control. It has the added benefit of having a simpler subsystem-wise sliding mode design, which makes it more convenient to apply on underactuated system. The HSMC technique is applied by choosing the angular position error as the sliding surface. The accuracy and robustness of the controller are presented and compared with conventional linear quadratic regulator (LQR) and proportional, integral, derivative (PID) controller. The study of performance of the proposed scheme is based on bounded matched disturbance, randomly varying viscous damping coefficient, parameter uncertainties, and varying frictional force. MATLAB simulations have been carried out to verify the above proposition. The results show the superiority of HSMC over conventional LQR and PID controller in robustness.