Modeling of a pneumatic system for high-accuracy position control

In this paper, a detailed model was developed for a rodless pneumatic cylinder controlled by a proportional directional control valve. The dynamic of the valve spool was firstly investigated and an equation was introduced to describe the mass flow through the valve´s variable orifice. The thermodynamics in cylinder chambers was carefully considered and the heat transfer coefficient between the air in the chamber and the inside of the barrel was identified experimentally. In addition, the friction force of the pneumatic cylinder seals was described using the LuGre model, and several experiments were conducted to estimate the friction parameters. The proposed system model was validated by comparing experimental and simulated open loop step input responses, and can be used to develop a controller for high accuracy positioning.