| Precise air hydrostatic guideway owns many advantages,such as high-precision,non-polluting etc,so it was widely used in IC fabrication,coordinate measure machines,precise machine tools and other equipment.The traditional study on aerostatic guideway is based on the static characteristics of aerostatic guideway,such as bearing capacity,static stiffness and so on.Then the structural parameters and working conditions are obtained.With the continuous improvement of precision requirements,the research methods based on steady flow and laminar flow are challenged,when the air gap of the aerostatic guideway is reduced to 10 microns.The self-excited vibration of the air hydrostatic guideway becomes the bottleneck of the further development of the hydrostatic guideway.The impinging jet method is used as the research method in this paper.Single degree of freedom vibration model is established,then the vibration differential equation of the system is obtained.The flow pattern in the lubricating film is analyzed by using large eddy simulation(LES)method and experimental research method.Though further study on the formation mechanism of air bearing micro vibration,the theory and experience on design and analysis of aerostatic guideway are enriched.The main contents of this paper are as follows:1.Based on the theory of impinging jet,the partition model of flow field in high pressure region of aerostatic guideway is established.According to the characteristics of velocity vector and pressure distribution in the flow field,the high-pressure turbulent region near the inlet is divided into four part:free jet region,stagnation region,transition region and wall jet region.Flow characteristics and energy transfer characteristics of each region are expounded,then the corresponding control equations are given.The internal gas of the throttle is divided into four parts:free jet region,stagnation zone,transition zone and exit wall jet region.The cause of the fluctuation of the gas film is divided into three parts:the main rotation,the secondary rotation and the outlet vorticity.The governing equations of each part are given.The relationship between the cause of the fluctuation of the gas film and the main rotation,the secondary rotation,the outlet vorticity is put forward.2.The finite element analysis software is used to analyze the micro vibration of gas film.Firstly,the steady state solution of the flow field is obtained by using the Reynolds averaged numerical simulation(RANS)method,which is the initial value in order to ensure iterative stability convergence.Secondly,the characteristics of flow field at different time are analyzed by means of three-dimensional large eddy simulation(3DLES).The fluctuation of gas film is related to transient process of cyclone formation and vortex shedding.The origin of micro vibration is revealed from the dynamic point of view.Cyclone intensity,moving speed and stable position have different effects on micro vibration intensity.Finally,the effects of different operating parameters and structural parameters on the micro vibration intensity of the gas film are obtained3.Test platform for micro vibration of air bearing support is established.The reliability and validity of the theoretical analysis and the numerical results are verified,The experimental error is analyzed.The natural frequency,time average amplitude of nonlinear self-excited vibration of bearings under different working parameters and structural parameters are observed.The relationship between the phenomenon of cyclone in the film and the nonlinear self-excited vibration of the bearing is verified. |
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