Physical Effects of Pulse Width Modulation on Valves and Loads

The rapid advances in computer technology over the past decade have provided the Fluid Power industry with a means of integrating modern control concepts with high performance hydraulic devices such as servo valves. One such concept, pulse width modulation (PWM), has been around for several decades, but it has been only recently that the full potential of the technique has been realized from an application's point of view.

This paper shall consider the use of pulse width modulation techniques as a means of driving a two-stage flapper type servovalve and load. This work presents both analytical and experimental open loop responses of the valve and load under conditions in which variations from an operating point are substantial. The effects of signal filtration of the modulated input are traced through the valve and load by placing the modulation signal at various locations in the valve. Through dynamic simulation techniques, the effects of pulse width modulation on the response of the load are examined when slip-stick friction effects are included. A method of utilizing pulse width modulation in a “burst” mode is considered as a means of reducing the nonlinear effects associated with slip-stick forces.