DIGITAL-CONTROL OF ELECTROHYDRAULIC SERVO SYSTEM OPERATED BY DIFFERENTIAL-PULSE WIDTH MODULATION

In the preceding papers, the authors proposed a new method of differen tial PWM for a hydraulic actuator operated by two 3-way solenoid valve s. An arbitrary pulse width of the pressure difference across both sid es of the actuator piston was realized by adjusting the switching time of each valve. The actuator operated by differential PWM shows good l inearity as a control element, achieving accurate positioning. This st udy, as an application, deals with a hydraulic servo system composed o f a 4-way spool valve and a load cylinder, where the spool valve is dr iven directly by the differential PWM actuator. The servo system is de signed based on the optimal regulator method of the state variable mod el. The system performance is investigated through simulations and exp eriments. Consequently, it is shown that the actuator, operated by dif ferential PWM, plays the role of a linear control element, and that th e servo system is well designed by the optimal regulator.