Research On Control Technology For On/Off Valve Based Digital Valve

The digital revolution has achieved great success in the fields such as electronics, communications, control and information, and its impact on the development of hydraulic control technology is also great. Digital hydraulic technology has become a new research direction in the field of fluid power transmission and control. On/off valve based digital valve technology is a new method to achive hydraulic servo control, high price-perfor mance ratio and reliability make it particularly suitable for hydraulic control system used in poor working conditions where control accuracy is less considered.In this paper, on/off valve based digital valve is studied systematically. First of all, to follow the principle of going from part to whole, the characteristics of the on/off valve, the digital flow control unit and the digital valve are analyzed. Researches on on/off valve include structure analysis, modeling, simulation and static and dynamic characteristics. Take HSV high speed valve as an example, the mathematical model of on/off valve is established by theoretical modeling. And on this basis, the switch characteristics of on/off valve are studied. Researches on digital flow control unit launch from combination method, encoding, static and dynamic characteristics etc. The cause of the flow rate pulse and the method for reducing are emphatically analyzed. Researches on digital valve include comparison of different structure, static and dynamic characteristics. Studies on static state characteristics include unloaded flow characteristic. AMEsim simulation is used to analyze the dynamic characteristics of the digital valve. Influences of on/off valve frequency for the frequency response of the digital valve are analyzed.Next three control methods for digital valve vased hydraulic system are studied considering the characteristics of the digital valve. They are cost function based open-loop control, PID control, feedforward control. AMSim and Matlab co-simulations are used to compare these three diffirent control methods. The independent control of the velocity and pressure are almost achieved by cost function based open-loop control. However, the flow rate pulse makes the error of the open-loop controller unacceptable. The PID control has the advantages of simple structure. Besides, the position tracking performance of PID controller is also great. The idea of the feedforward control is to use the cost function based open-loop control strategy as a feed-forward term of the closed-loop controller. Compared to closed-loop controller, feedforward controller can improve the control accuracy of the system significantly. Finally, the feasibility of the research is verified through the LABVIEW-based experimental system.