Magnetorheological Valve for Hybrid Electrohydrostatic Actuation

There is an increasing demand for compact actuators capable of producing large deflections, large forces, and broad frequency bandwidths. Due to their solid state nature, smart materials can enable novel actuator solutions that compete favorably with established technologies based on electric, hydraulic, or pneumatic motors. However, in all existing active materials, large force and broadband responses are obtained at small displacements and methods for transmitting very short transducer element motion to large deformations need to be developed. We present a new hybrid actuator which operates on the principle of rectification of magnetostrictive vibrations by means of magnetorheological (MR) flow control. Experiments and theoretical calculations are aimed at substantiating the feasibility of the hybrid actuator and establishing design criteria for the development of an effective MR valve. The experiments presented here demonstrate the ability of the valve to completely block the flow due to the combined action of a pressure differential and MR fluid activation. For characterization purposes, two variations of the main valve concept are considered, one with moving coils and the other with fixed coils. Actuation measurements conducted on the complete actuator show deflections of 6.5 in. in response to fluid inputs produced with a hydraulic piston in combination with an applied quasistatic voltage of amplitude 5 V. A system-level model is presented which is developed by treating the system as an RLC equivalent electrical circuit with operation across electrical, mechanical, and fluid domains. Attributes and shortcomings of the model are discussed through comparison of model results with experimental data.