| Because of the advantages of large output force,low time constant,quick reaction,high precision and easy control,electro-hydraulic servo load system is widely employed in laboratory environment to provide a variety of required high-power load.Such as,it is used to simulate the load force generated by the air flow in the control of the aircraft rudder.In the loaded objects of force loading system,there exists negative spring stiffness,such as large valve flow control and high-speed aircraft control and other applications.At present,the research of force loading system mainly focuses on the positive spring stiffness.Therefore,it is important significance to study the stability and the influence of working characteristics of electro-hydraulic loading system under negative spring stiffness.This paper takes the passive electro-hydraulic loading system with negative spring stiffness as the research object.Aiming at the superfluous force caused by the position disturbance of the loaded object,and stability of system under negative spring stiffness,some compensation and correction measures are adopted to reduce the superfluous force and improve the stability and loading performance of the system.After studying a great deal of literature,this paper introduces the research results of the force control system and the compensation of the superfluous force at home and abroad.On the basis of summarizing the previous experience,the work of the passive load system is as follows.Firstly,the working principle of the passive loading system was expounded and the precise physical model was established.The operating condition of the force loading system was investigated,and the reasons why the superfluous force of the passive force loading device is produced were found.Based on the basic equations of motion,the mathematical model of the passive force loading system is established.Secondly,through the superfluous force expression extracted in frequency domain,the superfluous force is analyzed,and the variation rule is obtained.The disturbance velocity is the main factor affecting the superfluous force.Based on the analysis of the reasons,the negative feedback compensator was used to compensate the superfluous force.Then the pressure parameters acquired by pressure transducers was used to correct the flow gain of the compensator.The control block diagram of the passive force loading system was established.According to the principle of load matching,the main components of the system were selected,and the basic parameters of the component were calculated.Finally,by adding double inertia link and compensator correction,the loading system can be stable when the load spring stiffness changes and it is negative.The simulation model of passive loading system is established with the help of Simulink.The simulation results show that the passive force loading device designed in this paper has good stability,and it can accurately follow the command force and also has a good performance in compensating the superfluous force after correction and compensation.The compensator with the load pressure correction can reduce the superfluous force,and the reduction is 96%.The steady-state tracking error is less than 4%,and the system tracking response time lag is not more than 0.03 s. |
PDF Full Text Request