Study On Modeling And Simulation Of Two-stage Nozzle-flapper Servovalve With Force Feedback

Two-stage nozzle-flapper servovalves with force feedback are widely used inthe electrohydraulic servo systems, duo to their advantages of fast response, highpower magnification, good linearity, and small dead zone. Unfortunately, lacking forperfectly mathematical model, it is very difficult to offer a sc ientific theory to guidethe designer of servo valve torque motors, hence, it is often based on theexperiential method. Besides, there is a big difference among the results acquired byusing the existing mathematical model of the two-stage nozzle-flapper servovalve,the simulation results, and the experiment results. Therefore, it is very significant tostudy the mathematical model of the two-stage nozzle-flapper servovalve, in orderto guide the designer of the two-stage nozzle-flapper servovalve and consummate itsmathematical model.The mathematical model of the servovalve torque motor and the mathematicalmodel of the two-stage nozzle-flapper servovalve are studied by means oftheoretical deduction, simulation and experiments. Considering the reluctances ofmagnetic elements and the leakage flux of permanent magnet, the magnetic circuitof the servovalve torque motor is analysed by applying the kirchhoff theorem, andthe output linear torque of servovalve torque motor is obtained. The expressions ofelectromagnetic torque constant and magnetic spring stiffness are modified, and theinfluence of magnetic reluctance of magnetic elements on servovalve torque motoris analyzed. In order to verify the magnetic circuit of the servovalve torque motor,the simulation model based on the physical mechanis m in software AMESim and theexperiment of the SFL218servovalve torque motor are studied.Combing the mathematical model of the servovalve torque motor, andconsidering the cantilever flexure tube with two degrees of freedom, the spool valveresonance and pressure feedback on the flapper, the mathematical model of thetwo-stage nozzle-flapper servovalve is studied by modern control theory, hence, thestate-space model of the two-stage nozzle-flapper servovalve is obtained. In order toverify this mathematical model, the software Matlab is used to simulated thismathematical model, and the simulation results are compared with the results fromthe simulation model based on physical mechanism in software AMESim.