This paper describes the design, simulation and testing of a piezoelectrically-actuated two stage spool valve. The first stage is a small spool controlled by a piezoelectric ring bender and the second stage is a closed loop position controlled main spool. A dynamic mathematical model of the valve has been derived. Step response tests for both the first stage and second stage are presented, and experimental second stage frequency response results are shown. The mathematical models for the amplifier, first stage and second stage spool behaviour are validated against experimental data. The second stage spool behaviour is found to be very sensitive to the first stage flow characteristics. In addition, the displacement of the hydraulic fluid by the piezoelectric ring bender, from one side of the piezoelectric ring bender to the other, had a significant impact on the valve characteristics.

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