PWM flow rate control of ER valve and its application to ER actuator control

The PWM (Pulse Width Modulation) control of ER valve consisting of two para llel electrodes has been investigated to continuously control the flow rate of an electrorheological (ER) suspension containing sulfonated polymer par ticles in silicone oil. PWM wave voltages are applied to the electrodes of the ER valve. It is possible to control continuously the flow rate by chang ing the duty ratio of the PWM wave from I to 0, where the duty ratio of 1 c orresponds to the state to stop the flow. A miniature bellows actuator driven by a pair of PWM controlled ER valves h as been developed, and the control characteristics of the actuator have bee n investigated. The duty ratios of both ER valves have been proposed to be changed alternately in proportion to the control voltage V to control the f low rate into and out of the bellows chamber, and also an overlap duty rati o D-ov at V=0 V has been introduced. The introduction of the overlap duty r atio D-ov was found to be very important to smoothly control the actuator a nd to improve the control performance.