An intelligent microactuator robust against disturbance using electro-rheological fluid

Abstract The paper presents a novel intelligent ER microactuator with inherent position feedback mechanism. The actuator consists of a variable ER valve and an upstream restrictor. The variable ER valve is composed of a pair of movable and fixed parallel plate electrodes with variable gap length and is supplied with an ERF (electro-rheological fluid) whose apparent viscosity changes according to the applied electric field. The movement of the movable electrode is used as the output displacement. By applying voltage to the variable ER valve, its pressure drop increases due to the ERF's apparent viscosity increase, so that the electrode gap length, i.e., the output displacement increases. Also, the actuator can suppress the displacement due to disturbance force with the inherent position feedback mechanism without additional sensors and controllers. The mechanism utilizes the pressure drop change of the variable ER valve with the changes of the electrode gap length and the ERF's apparent viscosity due to the disturbance force. The feature of the proposed actuator is robustness against disturbance with simple and compact structure. In this study, the structure and working principle were revealed and the mathematical model was derived. An actuator prototype having effective working part with 14 mm diameter was fabricated and the static and dynamic characteristics were experimentally clarified. The actuator stiffness was proved to be 4.5 times higher than the actuator without the inherent position feedback mechanism. Furthermore, a mechanism to magnify the output displacement using the control pressure was proposed and the validity was confirmed through experiments.