Development and experimental evaluation of a fixed-gain nonlinear control for a low-cost pneumatic actuator

A practical, easy-to-implement and accurate fixed-gain nonlinear position controller for a typical low-cost industrial pneumatic actuator is developed and evaluated experimentally. The positioning system comprises an inexpensive 5-port three-way proportional control valve with flow deadband, and a double-rod actuator exhibiting significant dry friction. Quantitative feedback theory is used first to systematically design a robust proportional-integral (PI) control law that minimises variations in the dynamic response of the actuator over a wide range of operating conditions and in the presence of uncertainty in the system parameters. Nonlinear modifications, which condition the integral part of the designed PI control law, are then implemented in a step-by-step fashion to further improve closed-loop performance by reducing overshoot and negating the effects of the control valve deadband and actuator friction. Experimental results clearly illustrating the effectiveness of the positioning system for a number of tracking and regulating tasks are presented