Design of nonlinear controller for bi-axial inverted pendulum system

Abstract

This study presents the use of Tustin's friction model and a disturbance observer to improve the steady-state error of a bi-axial inverted pendulum system. Then, a three-phase controller, including a swing-up control, a sliding-mode with feedback linearisation to control the angle of the pendulum, and a sliding-mode plus PID control for the pendulum-cart system is employed to eliminate the system's nonlinear and unstable characteristics. Experimental results reveal that the pendulum maximum angle of operation is +/- 14 degrees(X-axis)/ +/- 12 degrees (Y-axis); the steady-state error of the pendulum angle is +/- 0.2 degrees (X-axis)/ +/- 0.3 degrees(Y-axis), and the cart position is within +/- 4 mm. Experimental results are illustrated and films are provided at the website http://midi studio. myweb.hinet.net to show the effectiveness and robustness of the proposed control schema.