Development of a nonlinear dynamic model for a servo pneumatic positioning system

A parametric dynamic model of a pneumatic servo system is useful for its computer simulation, mechatronic design and control algorithm design. Pneumatic servo positioning systems have advantages that include: inexpensive, clean, safe and high ratio of power to weight. However, they are difficult to accurately model. In this paper a methodology for deriving a nonlinear dynamic model for a pneumatic servo system is presented. The model includes cylinder dynamics, payload motion, friction and valve characteristics. Methods for estimating the model parameters from simple experiments are also described. It is shown that the standard mass flow rate valve model is not well suited to an open-center proportional valve. A new valve model is developed that more accurately fits the measured data. The proposed modeling methodology does not require special measurement equipment or disassembly of the system hardware. This is an advantage for a pneumatic servo system that is in continuous use. Experimental results demonstrating the ability of the model to predict the measured piston position and cylinder chamber pressures are included.