DIGITAL-CONTROL OF HYDRAULIC ACTUATOR SYSTEM OPERATED BY DIFFERENTIAL PULSE WIDTH MODULATION

This study deals with an electrohydraulic servo system which is operated by two 3-way high-speed soleniod values in the PWM digital mode. It has often been pointed out that there are practical problems to be solved in the conventional PWM systems, such as serious nonlinearities in the value characteristics. In order to overcome such problems, a new concept of PWM control, that is, a differential PWM method, is proposed in this study. The strategy of this method is to eliminate/minimize significant nonlinearities, such as the dead zone, which regularly appear with conventional methods. In the new method, the pressure difference for driving the actuator is given by pulse trains, their widths modulated by duty input to the valves The dynamic characteristics of the system driven by the proposed method are investigated by experiment and digital simulation. Consequently, the availability of the proposed method is confirmed well.