| In the reverse-pressure test of the wheel,the constant reverse pressure plays a crucial role in the assembly quality of the wheel assembly.Maintaining reverse pressure stability is controlled by a proportional relief valve.However,proportional relief valves are characterized by hysteresis,non-linearity,time-varying characteristics,and are easily influenced by external disturbances,resulting in frequent and severe pressure fluctuations in the actual reverse-pressure process.Therefore,this paper aims to study a high-precision,high-stability control strategy to suppress various interference to ensure the reliability of the reverse-pressure test.The main research contents of this article are as follows:(1)Summarize the research status of friction compensation methods and electrohydraulic system control strategies at home and abroad.The pros and cons of each friction model are analyzed and the LuGre model is used.Explain the basic principles of fuzzy control,and establish mathematical models such as pilot valve,main valve and oil cylinder,then derive the open-loop transfer function of reverse-pressure test.(2)Based on the hysteresis characteristics caused by the friction factor of the proportional electromagnet,the LuGre model friction compensation method is proposed.The significance of each parameter of the model is analyzed,and a parameter identification method is proposed.Then a friction model is established in Simulink.The AMESim model of the proportional relief valve is formed and the friction compensation effect of the LuGre model is verified by AMESim/Simulink cosimulation.After friction compensation,the valve core responds faster,the tracking effect is good,and the hysteresis rate is reduced to 0.8%.(3)Proposed frictional feedforward compensation variable domain fuzzy PID control strategy.Combining the simple of PID and fuzzy control structure can dynamically adjust the advantage of parameters to design fuzzy PID.However,the accuracy of the algorithm is not satisfactory when the error is near zero.Therefore,the idea of changing the universe of thoughts is introduced,and the variable domain is changed according to the size of the error to make up for the short board with low control accuracy.The simulation results show that variable universe fuzzy PID can effectively reduce overshoot and ease oscillation,but the response time is not significantly improved.A feedforward and feedback compound control strategy is proposed.First,the friction feedforward compensation is used to reduce the hysteresis loop,so that the characteristics of control voltage—pressure is constant and the number of adjustments is small.Then combine with variable domain fuzzy PID,external interference is suppressed.By verifying the effectiveness of the algorithm by simulation,the response time is shortened by 22.2%,and the system can be adaptively adjusted and have good robustness when the disturbance,damping and frequency are changed.(4)Based on the hardware of the wheel inspection press,and the original control program,the control strategy program is written.Firstly,the friction compensation effect is verified through experiments,and the hysteresis rate is greatly reduced.Compared with the without compensation,the maximum pressure difference is reduced from 0.52 MPa to 0.14 MPa at same control voltage.Secondly,the control strategy is applied to the wheel reverse-pressure test.This strategy can effectively deal with external disturbances and the pressure remains basically constant,which verifies the effectiveness and reliability of the algorithm. |
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