A novel, low-cost pneumatic positioning system

Applications requiring accurate position control are in increasing use in industry. Pneumatic servo systems can provide a clean, accurate, robust positioning system; however, the proportional valves used in such systems are relatively expensive. The use of solenoid valves to replace a proportional flow control valve can significantly lower the price of a positioning system. This substitution is possible if the solenoid valves are operated using a pulse-width-modulated (PWM) control scheme. This work presents a design in which position control is realized on a single-rod, double-acting cylinder. Two solenoid valves operate conventionally to fill either chamber of the cylinder, while a third valve uses pulse-width modulation in metering the exhaust flow.The experimental apparatus is capable of positioning a load along a horizontal axis to within ±0. 10 mm.