Development of a two-stage high speed electrohydraulic servovalve systems using stack-type piezoelectric elements

This paper presents two systems of two-stage electrohydraulic servo valve with a nozzle-flapper pilot stage, which is controlled by stack-type piezoelectric elements. Two flapper moving mechanisms proposed in this research can compensate for the hysteresis problem and thermal expansion of the piezoelectric elements. The experimental results show that the first flapper moving mechanism has the frequency response of over 500 Hz and the second one has the response of over 600 Hz. And the first simplified servovalve system using the first flapper moving mechanism has the frequency response of about 150 Hz, and the second system has the response of about 300 Hz at the supply pressure of 210 bar.