Design and experimental evaluation of a nonlinear position controller for a pneumatic actuator with friction

This paper documents the development and experimental evaluation of a practical nonlinear position controller for a typical industrial pneumatic actuator that gives good performance for both regulating and reference tracking tasks. The system is comprised of a low-cost 5-port proportional valve with flow deadband and a double-rod actuator exhibiting significant friction. Quantitative feedback theory is employed to design a simple fixed-gain PI control law that minimizes the effects of the nonlinear control valve flows, uncertainty in the physical system parameters and variations in the plant operating point. Easy to implement nonlinear modifications to the designed PI control law are then tuned experimentally in a step-by-step fashion to reduce overshoot and to negate the effects of the control valve deadband and actuator friction. Experimental results clearly illustrating the efficacy of the approach are presented.