Design of nonlinear controller for bi-axial inverted pendulum system

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°(X-axis)/±12° (Y-axis); the steady-state error of the pendulum angle is ±0.2° (X-axis)/±0.3°(Y-axis), and the cart position is within±4mm. Experimental results are illustrated and films are provided at the website http://midistudio.myweb.hinet.net to show the effectiveness and robustness of the proposed control schema.