Design And Mechanical Process Research Of Piezoelectric Pre-stage Driving Mechanism Of Electro-hydraulic Servo Valve

With the vigorous development of modern science and technology,it is difficult to improve the performance of traditional servo valves driven by electromagnetic torque motor,such as frequency width,response speed and control accuracy.Piezoelectric actuators are characterized by high power density,high resolution,large output force,high working frequency and fast response.In this paper,piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve is designed.It drives the spool as a prestage driving mechanism in the piezoelectric direct drive electro-hydraulic servo valve.Instead of the torque motor of electrohydrolic servo valve,the piezoelectric actuator is used for transferring electrical signal into mechanical siganal.The performance of electro-hydraulic servo valve,such as response speed,frequency width and control precision,can be further improved.The concrete research content is as follows:First of all,the types and materials of flexure hinge are determined and the calculation formula of rotation stiffness of single axis flexible hinge flexure is deduced.Under the condition that the minimum section thickness,arc notch radius,width and other structural parameters are different,MATLAB software is used to calculate the the value of flexure hinge rotation stiffness.The value range of structural parameters is determined by the relationship between flexure hinge rotation stiffness and its structural parameters.The theoretical magnification,input-output stiffness factor of lever-type micro displacement magnifying mechanism and reasonable structural parameters of lever section were also studied.Secondly,static and dynamic analysis of the piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve was performed.The static analysis and modal analysis of the flexure hinge lever amplification mechanism with different structural parameters were carried out by ANSYS software.The displacement amplification factor was verified and the relationship between the structural parameters and their maximum stress and first-order resonance frequency was obtained.The simulation analysis of different mode shapes of vibration of optimized mode is performed.The dynamic equation of piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve is deduced.The dynamic model is established and the step response is simulated by MATLAB software.The relation curves of the step response with the stiffness of the piezoelectric actuator,the equivalent mass and the damping coefficient of the system are obtained.Then the adjustment mechanism with wedge blocks,flexure-hinge type levermechanisms and the integral structure of the piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve are designed.Finally,prototype was manufactured and experimental platform for piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve is built to study its performance.In the static characteristic test: the hysteresis of the piezoelectric actuator causes hysteresis loop of the output displacement of the piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve,but its amplification factor of output displacement is relatively stable,and the output displacement can meet the requirements of the valve spool stroke.To some extent,the output displacement of piezoelectric pre-stage driving mechanism of electro-hydraulic servo valve is influenced by the creep characteristic of piezoelectric actuator.The output displacement resolution of the piezoelectric pre-stage driver mechanism of electro-hydraulic servo valve is up to 0.1%.In the dynamic characteristic test: when iuput high frequence voltage signal,the capacitance characteristic of the piezoelectric actuator attenuates the output voltage amplitude of the power amplifier,which affects the output displacement and the frequency width of the piezoelectric actuator.The piezoelectric actuators of the piezoelectric pre-stage driving mechanism of the electro-hydraulic servo valve is applied with larger preload and smaller preload respectively,the frequency of voltage is different when the piezoelectric pre-stage driving mechanism of the electro-hydraulic servo valve resonates,which demonstrates the resonance-frequency offset.The positive step voltage signal and negative step voltage signal are input to the piezoelectric prestage driving mechanism of the electro-hydraulic servo valve,the step establishment time was 0.42 ms and 0.84 ms respectively.The restoring spring affects the response time of the piezoelectric front drive mechanism of the electro-hydraulic servo valve.