Fast and Accurate Pressure Control using On-Off Valves

Abstract

Pneumatic cylinders and pneumatic muscles are lightweight, clean and multifunctional actuators, requiring pressure-regulating valves for positioning. To use them in mobile applications commercial pressure-regulating valves are quite heavy and rather slow. Therefore an intelligent controlled array of fast switching on-off valves is presented as an alternative. The speed of the on-off valves determines the performance of the pressure-regulating valve. To reduce the opening time of the valves, a higher voltage is applied on the coil for a short time. The influence of this method on the heating of the valve will be discussed. A diode, which drains away the electromagnetic power from the coil, reduces the closing time. When working with pneumatic muscles, it is in some cases justified to remove the internal spring to enhance the opening time. A modified bang-bang controller, with more than one level and a dead zone is presented. Experimental results on a fixed volume are discussed. A special designed collector combines 6 on-off valves into a lightweight pressure control valve island, which is perfectly suited for walking robots such as the pneumatic actuated biped Lucy.