Pneumatic Positioner with Fuzzy Control

Abstract A pneumatic positioner with closed loop fuzzy logic control is described. The system consists of a pneumatic cylinder, two proportional valves, a position and speed sensor, a fuzzy controller and an A/D-D/A conversion board. No braking devices for maintaining position are provided on the cylinder rod. The control considers position error and actuator speed as antecedents, and valve control voltages as consequents. Membership functions, the set of rules and the weights of each were obtained by considering the component characteristics and the relationships between the antecedents and the flow rates to the cylinder chambers with varying control voltages. The latter were calculated using the min-max-center of gravity criteria. Experimental tests were carried out on the positioning system with different reference signal shapes and with different applied loads. Results show good positioning accuracy and repeatability, absence of overshoot and system stability under varying operating conditions.