Modeling and characteristics of pneumatic servo system

The static and dynamic characteristics of the pneumatic proportional flow-rate control valve were studied. It was found that the variation of the critical pressure ratio versus the valve opening is non-linear, it increases at first and then decreases, and the ratio ranges from 0.17 to 0.38. The discharge coefficient was calculated with the help of Sanville flow formula by measuring the flow-rate through the valve at different openings, and the coefficient ranges from 0.55 to 0.77. The relationship between the discharge coefficient and the valve opening was found non-linear also. The frequency response of the valve was acquired by the sine sweep excitation and the spool position measurement. The results show that the bandwidth of the valve decreases with the increase of the input signal amplitude, and the supply gas pressure has no effect on its bandwidth. The heat transfer processes between gas in the cylinder and the cylinder wall, as well as between the cylinder wall and the environment were described using a lumped parameter mathematical model. A differential equation of the gas temperature was deduced and a thermodynamic model of in-cylinder gas was established. The simulation and experiment of the pneumatic servo system were performed and the simulation results agree well with the experiment ones.