| Electro-hydraulic loading simulator is used to reproduce the force of the rudder surface of the aircraft in the air under experimental conditions and its core component is the electro-hydraulic force loading system,which applies the required loading force to the loaded position system timely.Because the displacement is an active action,and the force of the force loading system is a passive action,therefore,displacement disturbance of the position system will cause superfluous force in the force loading system,which will affect the output accuracy and response speed of the force loading system.Reducing superfluous force and increasing system bandwidth have become the first tasks to improve system performance.Therefore,this paper has carried out in-depth theoretical study and technical discussion on the electro-hydraulic force loading system with perturbation of displacement,and two strategies are proposed from the means of structural compensation and control compensation to provide certain theoretical support and technical means for electro-hydraulic servo loading control.The research work of this paper as follow:(1)The working principle of the electro-hydraulic force loading system with perturbation of displacement is described.The causes of forced flow and superfluous force are analyzed.The overall mathematical model of the system and the expression of superfluous force in literature [2] are sorted out.The effects of velocity of perturbation of displacement,piston rod area,and system dynamics on superfluous force are discussed.(2)From the means of structural compensation,the scheme of the compensation valve is improved from the original compensation method of literature [2] that only used the output force as the compensation valve signal to the forced flow caused by the perturbation of displacement itself as the new compensation signal.The control signal of the compensation valve is derived from the equation,and the control signal is applied to the electro-hydraulic loading model to improve the simulation model and simulate under different working conditions.The simulation results of Matlab software show that after adopting the new flow compensation method,the electro-hydraulic force loading system with perturbation of displacement can apply the corresponding force to the load more accurately and quickly according to the displacement of the loaded object.The superfluous force can be reduced by up to 98.3%.When the perturbation of displacement signal is a simple harmonic signal,the tracking performance of the force loading system after the improved compensation signal is better,the tracking speed is increased by 25%,and the magnitude error is reduced by 51.4%.(3)In order to improve the structural reliability and make the system economical and make the adjustment of the parameters easier,another control compensation scheme that uses only one electro-hydraulic servo valve in combination with the method of backstepping control to reduce superfluous force is proposed,and a backstepping controller is designed by backstepping idea and Lyapunov stability condition inversion.The simulation model was established in the Simulink simulation software and the simulation was performed under different working conditions.The simulation results show that when the force loading system added with the backstepping controller is disturbed,the valve port of the electro-hydraulic servo valve of the force loading system moves in the reverse direction,so as to discharge the forced flow and reduce the superfluous force;the different backstepping coefficients in the backstepping controller have different effects on the system output.The larger the value of k,the faster the response,and the smaller the tracking error after the initial stage,but the magnitude of overshoot will also increase.The simulation and comparison of the force loading system with backstepping controller and PID controller separately under various working conditions.The simulation results show that in the presence of perturbation of displacement,compared to PID control,the step force output by the designed backstepping controller can accurately track the step force loading command after a maximum of 0.0984 s,and the response speed is faster;the maximum error of the output step force does not exceed 2.5N,and the steady state error is smaller.When the sinusoidal force is output,the loading curve can be accurately tracked after the initial stage of 0.06 s at most,and the good tracking performance has been maintained for the following time,with the maximum error not exceeding 1.93%. |
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