Discussion On Stability Of Electro-hydraulic Load Simulator System With Variable Stiffness In Loads

In the field of national defense technology and precision industry,electro-hydraulic servo system is widely used,and its servo performance requirements are getting higher and higher,mainly reflected in good operational stability,ultra-low speed performance,tracking accuracy and dynamic bandwidth..As an important development and application direction of electro-hydraulic servo system,electro-hydraulic load simulator is a highly nonlinear and time-varying complex system,which is not only interfered by the disturbance factor from the electro-hydraulic position control system,but also in actual working conditions.The influence of parameter uncertainty,such as the elastic stiffness of the load and the variability of the stiffness of the hydraulic spring,makes the system not have good quality characteristics.In addition,in the case where the position disturbance factor is neglected,there is a second-order differential link with a lower oscillation frequency in the molecule of the transfer function of the electro-hydraulic control system,so that the system characteristics tend to oscillate or even be unstable.Through the research and summary of a large number of domestic and foreign literature materials,on the basis of summarizing the scientific research results of the predecessors,the following work was carried out on the electro-hydraulic load simulator.Through the research and summary of a large number of domestic and foreign literature materials,on the basis of summarizing the scientific research results of the predecessors,the following work was carried out on the electro-hydraulic load simulator.(1)Study the working mechanism of electro-hydraulic load simulator under the condition of variable load stiffness and variable hydraulic stiffness,establish its precise physical model and carry out comprehensive analysis,and the electro-hydraulic position system is the bearing object and electro-hydraulic control system.The model is simplified to explore factors that affect system stability,accuracy,and responsiveness.(2)The control block diagram and mathematical model of the position disturbance type electro-hydraulic control system are established by using the flow continuity equation and the system dynamics motion equation,and the excess force equation is separated,and a feasible scheme for suppressing the excess force is designed.(3)From the point of view of energy dissipation,this paper sorts out the third-order linear differential equations of hydraulic cylinder output force by the closed-loop transfer function of electro-hydraulic control system,and uses Lyapunov direct method to solve the system stability related conditions.,transform it into a second-order hydraulic compensator,in order to offset or weaken the influence of unstable factors on the system and improve system quality.At the same time,the specific derivation process and construction scheme are given,and the stability of the second-order hydraulic compensator is proved by the Rolls criterion.(4)The simulation software is used to build the system simulation model.Under the working condition of the hydraulic cylinder piston approaching the end position of the stroke,the effectiveness of the method of suppressing excess force and improving the stability is verified by simulation.At the same time,the traditional dual inertia controller is designed for comparative analysis and discussion.The stability and dynamic characteristics of the second-order hydraulic compensator and the traditional double inertia link correction system verify the rapid response of the system and the accuracy of tracking.The simulation results show that the electro-hydraulic load simulator designed in this paper has better stability after calibration,can reproduce the command force more accurately,and has good performance in suppressing the excess force.The introduction of the pre-speed compensator can reduce the excess force by at least 96%;the second-order hydraulic compensator can effectively improve the stability of the system and suppress the resonance peak.Under the condition that the piston of the hydraulic cylinder is close to the end position of the stroke By comparing with the double inertia link of the stability of the traditional calibration system,the system response time is shortened by more than 50%,the steady-state error is reduced by0.1%,the system reaches the steady state within 0.12 s,and the maximum steady-state error is within 3.7%.