Application of Fuzzy Logic Adaptor to the Position Control of a Pneumatic System Using On-Off Valves

The position control of a pneumatic cylinder using low cost on-off valves is studied. The modified PWM technique is applied to drive on-off valves and a three-state feedback control algorithm is adopted to control the position. A voltage/current converter is used to obtain fast valve opening. For slowly varying system parameters such as variation of valve effective area due to wear, a fuzzy logic adaptor is proposed to determine optimum gains of the state feedback controller through learning procedures. The friction behavior of a pneumatic cylinder is measured and the effective areas of on-off valves are determined by the discharge method. A partial polytropic model is applied to calculate the pressure build-up in cylinder chambers. It is shown that simulation results agree well with experimental data. It is also shown that the fuzzy adaptor presented in this paper gives satisfactory system performance.