Position control of a pneumatic actuator under varying external force

In this paper a high accuracy position control strategy for a pneumatic actuation system subjected to a varying external force is proposed. A novel approach for the mathematical modeling of the pneumatic actuator, based on energy methods, is presented. The Lagrangian is derived from combining the kinetic and potential energies, leading to formulation of the Euler-Lagrange equation of motion. The nonlinear backstepping method is applied to derive the control law, and the derivative of the potential energy is used as the controlled parameter. Experimental results show that tracking a sine wave of 0.1m magnitude produces a maximum error of ±0.008m while the actuator is subjected to a time varying external force with a magnitude ranging from 570N to 1150N.