| Proportional valve achieves the continuous control of the pressure and flow through electrical signal, and the control accuracy of proportional valve is improved through the introduction of electric closed-loop control. Valvistor valve using proportional valve as the pilot valve has the advantages of simple structure, low cost, large capacity and so on, its output flow is linear amplification of the pilot valve flow, and is very widely applied in the industrial field. However, in practical application, the bad electromagnetic force output linearity of the proportional electromagnet, the low detection accuracy of displacement feedback, the machining asymmetry of shoulder in the valve port, the large dead zone of the proportional valve, the variety of load pressure difference and so on, which will cause the output flow of proportional flow valve large nonlinear and influence the performance of the proportional valve seriously. Focused on the nonlinear problems, the multi-level nonlinear adjustment is studied from the aspects of control circuit, signal processing, control strategy and so on. This research provides advanced theory and method to improve the control accuracy of proportional flow valve, and has actual theoretical significance and economic merit to promote our country electro-hydraulic technical progress and enhance the competitiveness of products.Electro-hydraulic proportional control valve is a complicated hydromechatronics element whose drive control and adjustment is susceptible to the coupling of external disturbances and internal characteristics. Especially, the electro-hydraulic proportional systems combined with new digital control technology have greater flexibility and also increase the development complexity of the systems. So in this paper, the research on improving the control precision of proportional flow valve is carried out from the following aspects: the sensor feedback detection circuit, power driving circuit, digital nonlinear adjustment, signal processing and pressure difference compensation.The performance of digital proportional controller influences the output performance of proportional valve directly. Currently the detection accuracy and sensitivity of detection circuit of conductive displacement sensor is not high, its flexibility is low and commonality is poor. In this paper,an improved modulation and demodulation measurement amplifier circuit is proposed, the experiment platform of measurement circuit is established, and the three-coordinates measuring machine is used to detect micro-displacement. The static and dynamic characteristics of circuit for phase sensitive detection and the improved modulation and demodulation measurement amplifier circuit are compared by experiment. The experiment results show that the improved circuit has the advantages of high sensitive, small hysteresis, good linearity, fast dynamic response and so on. And it can be used for the detection of three wire differential inductance sensor with three wire and two wire system at the same time. In order to eliminate or reduce the hysteresis caused by the incomplete discharge of coil, an improved H bridge anti-unloading power amplifying circuit is used to realize the coil current attenuation rapidly, and the ultrafast recovery diode RC buffer circuit is set in the circuit to improve the stability of the circuit. The Multisim is used for simulation analysis of the power amplifier circuit. The simulation results show that the current ripple of the designed power amplifier circuit is small and the response speed is fast, the anti-unloading circuit improves the speed of current attenuation greatly.Aimed at the problems that shock overshoot, small interfering fluctuation, zero position dead zone and friction-hysteretic exists in proportional valve, and non-constant force output and magnetic hysteresis exists in proportional electromagnet, and so on, a method of digital adjustment is proposed to make the nonlinear adjustment; a variety of software signal processing module is set up in the digital controller to solve the above problems; mainly include: ramp generator, threshold voltage, zero compensation, flutter signal, gain adjustment, linearity adjustment and so on. The experiment platform of the digital nonlinear adjustment of proportional valve is established, the ECON AVANT digital sampling and signal analyzer is used to detect the displacement of the valve spool, a upper monitor is used to set the parameters. The output characteristics of valve spool displacement under different parameters setting is detected. The experiment results show that digital control nonlinear adjustment can change the output characteristics of valve spool displacement. So in the practical application, the parameters can be adjusted according to loading conditions to achieve the purpose of nonlinear adjustment. The digital nonlinear adjustment can improve the control accuracy, reduce the manufacturing cost, and it has the advantages of debugging convenience and strong commonality.In industrial application, the control application and anti-interference ability has been restricting the development of the Valvistor cartridge flow valve. In order to improve the control precision and realize flexible control, a control algorithm based on deviation discrimination is put forward. When the system is in large deviation and large disturbances condition, the fuzzy PID control algorithm is used to improve the control precision and stability; when the valve opening is small, the incomplete differential PID control is used to avoid the system oscillation. The static and dynamic mathematics model and the simulation model of the DN 16 Valvistor cartridge flow valve are established, the simulation analysis of the static, dynamic and load characteristics of the proportional valve are carried out under the closed-loop PID control, the adjusted experience value of control parameters is gotten, and the relation between the displacement and output flow of main valve and the pilot valve is analyzed. The Simulink is used to establish the transfer function simulation model of the pilot valve, the dynamic response characteristics of the PID control and the deviation discrimination control is compared, and the frequency-response characteristic of the pilot valve is detected. The simulation results show that the control precision of deviation discrimination control is higher, its stability is better, and it has good frequency-response characteristic.In order to improve the anti-load-disturbance capacity of the output flow of the cartridge flow control valve, a method of flow compensation adjustment based on pilot pressure difference-displacement is proposed. The relational expression between the variety of pressure difference and the input signal of control voltage is gotten through theoretical analysis. The simulation model of the Valvistor cartridge proportional flow control valve with displacement-pressure difference compensation of pilot valve is established in SimulationX, the semi physical simulation experiment platform combined with dSPACE is set up. The experiment platform is used to research the static and dynamic characteristics of Valvistor cartridge flow valve to validate the accuracy of the model. The results of simulation and experiment show that through the pilot pressure difference-electro-displacement compensation, the nonlinearity adjustment of the output flow of the flow control valve can be realized, the flow control precision can be improved, and the overshoot of load step change can be restrained effectively. |
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