Theoretical Analysis And Experimental Research On Nonlinear Friction In Water Hydraulic Servo Valve

Water hydraulics is a rising technology to make use of raw fresh water or seawater as pressure medium in hydraulic systems instead of mineral oil, which has become more and more attractive owing to the great advantages such as environmentally friendly, nonflammable, inexpensive, clean and easily disposable. However, it is a great challenge for research on water hydraulics components as the different characteristics between water and oil. As the high-level control precision element of water hydraulic servo system, water hydraulic servo valve plays an important role in the developing of water hydraulic transmission.Nonlinear friction characteristics in water hydraulic servo valve have great effects on the control precision of water hydraulic servo system. Most parameters and methods for oil hydraulic can't be directly used in the design for water hydraulic components. Therefore, in order to design a high-level precision water hydraulic servo system, it is necessary to make more research on nonlinear friction characteristics about water hydraulic servo valve. First, this paper focuses on a research of nonlinear friction in water servo control components. Based on analyzing and comparing the researches and developing pattern of friction compensation control at home and abroad, nonlinear friction characteristics in servo system and the differences of the friction models are detailedly analyzed. LuGre friction model is built, which has such properties as rising static friction and friction memory. The model captures most friction phenomena that are of interest for feedback control, and can describe arbitrary steady-state friction characteristics. On the basis of analyzing the friction in water servo valve, the LuGre model is regarded as the key technology of the performance control system.While the experimental system is technologically reconstructed, designed friction measurement and control experiment device for water servo valve, developed the hardware interface circuit of the experiment device, compiled Multifunction data acquisition and control software. A series of coupled elements, are designed and manufactured. Under the conditions of various clearances, contact length and inlet and outlet pressure levels, experimental test are conducted to obtain the friction characteristics of these typical coupled elements. The experimental results exhibit that: pressure can lead to the change of friction and the offset of valve core, clearance has great influence to the increase of friction, and contact length is nearly direct proportion to friction. The configuration of groovy valve core can be beneficial to cause the movement close to the center. Finally, on the basis of analyzing the experiment data curve, friction compensation control methods have been posed and compared, such as PID control, and model reference control. The best efficient control method has been choose and validated by simulation with MATLAB.