Modeling, Simulation and Experimental Validation of a Servo-Pneumatic Control System With Off-the-Shelf Components

Industrial applications of servo-pneumatics have seen rapid growth in the past few decades due to the recent availability of sophisticated high-speed proportional valves, particularly in the five-ported, “four-way”, center-closed, bidirectional configuration. This paper offers a simple and effective dynamic model and simulation of a complete servo-pneumatic system using off-the-shelf valves and standard PID control, which remains the industry standard. The model combines piston dynamics, thermodynamics of the working fluid (air), mass-flow inlet and exhaust dynamics through the valve, valve dynamics, and a control system. The simulation results are experimentally validated through various closed-loop position control arrangements. The simulation model parameters are for the most part easily measurable, except for the damping coefficient of the moving mass and the discharge coefficient of the valve. A simple approach to effectively estimating each of these is shown. An experimental setup was built using off-the-shelf components: Bimba standard round-line air cylinders, Enfield Technologies high-speed proportional valves, Balluff non-contact magnetostrictive displacement transducer, and pressure sensors from Omegadyne. It is intended that this work can be easily recreated by industrial and academic designers who are considering servo-pneumatic systems.