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 plusmn 14deg(X-axis)/ plusmn12deg (Y-axis); the steady-state error of the pendulum angle is plusmn0.2deg (X-axis)/plusmn 0.3deg(Y-axis), and the cart position is within +4 mm. Experimental results are illustrated and Alms are provided at the website http://midistudio. myweb.hinet.net to show the effectiveness and robustness of the proposed control schema.