| Because of its advantages of low friction,high precision,clean and pollution-free,aerostatic bearings are widely used in IC manufacturing,high precision inspection equipment,ultra-precision machining machine tools and other equipment.The traditional research on aerostatic bearing mainly focuses on the static characteristics(such as loading capacity,static stiffness,etc.)of the aerostatic bearing,for example,by solving the N-S equation of the gas film flow.Obtain the structure parameters and working conditions that meet the requirements for use.However,with the decrease of gas film thickness and the improvement of the precision,the flow pattern of the gas film at the micro-scale will present a tendency of transition from layer to slip flow,and the pressure distribution in the gas film is obviously sensitive to temperature.The loading capacity and stiffness of bearing system will be seriously affected.The research methods based on steady flow and traditional laminar flow hypothesis are challenged.The selfexcited vibration inside the aerostatic bearing becomes the key problem that restricts the further development of the bearing.The main contents of this paper are as follows:(1)Based on gas lubrication theory and rarefied gas dynamics,combined with boundary slip and thermal-temperature coupled analysis technology,a bidirectional fluid-solid coupling model of aerostatic bearing is established.With the help of finite element analysis software,the gas flow characteristics and pressure distribution in the gas film of aerostatic bearing under ideal conditions are studied and analyzed,the gas flow characteristics and energy transfer characteristics in the gas film are clarified,and the corresponding governing equations are summarized and put forward.The relationship between the cause of the gas film fluctuation and the gas-vortex phenomenon and vorticity is put forward.(2)The loading characteristics and self-excited micro-vibration of aerostatic bearing under the condition of temperature and thermal coupling are studied and analyzed.The Fluent module and the Static Structural module in Ansys Workbench are used to initialize the fluid domain and the solid domain respectively.The transient processes of gas-vortex formation and development and vortex detachment are obtained,and the causes of self-excited micro-vibration are revealed from the dynamic point of view.Then the ambient temperature is changed in the Static Structural module to obtain the small deformation of the aerostatic bearing at different temperatures.In the case of gas film deformation,the change of gas-vortex strength,moving speed and stable position and its influence on loading characteristics and gas film self-excited microvibration are analyzed.Finally,the effect of different working temperature and working environment on the micro vibration intensity of gas film is obtained.(3)Design and build the test platform of micro-vibration of aerostatic bearing,verify the reliability and validity of the theoretical analysis and numerical calculation results,and analyze the experimental error.The natural frequency and time-averaged amplitude of the nonlinear self-excited micro-vibration in the bearing under different operating temperature,working parameters and gas environment are observed.The relationship between the phenomenon of the gas-vortex in the gas film and the nonlinear self-excited vibration of the bearing is verified.Enriching the theoretical methods and research experiences in the design and analysis of aerostatic bearings plays a guiding role in improving the machining accuracy of high precision instruments. |
