Modelling and robust control of an inverted pendulum driven by a pneumatic cylinder

In this paper a practical method for robust control of an inverted pendulum driven by a linear pneumatic actuator is presented. The whole system mathematical model is derived, verified and utilized in the paper to guide the initial design of the robust control strategy. The control strategy consists of an inner loop controlling the force acting on the piston by means of a PI controller; and the position and angle of the pendulum are controlled via a full state feedback outer loop controller. A friction estimator compensates for the variable nonlinear friction distribution. The merits and strength of the controllers are highlighted by comparison of the control strategy with a more complex model-based nonlinear feedback linearization controller for the inner loop. The proposed control strategy can achieve the desired control performance under disturbances and uncertainties caused by unknown external forces, frictions, initial positions and sudden changes in desired position.