Simulation And Experimental Research On The Pneumatic Hammer Of Aerostatic Bearings

Aerostatic support technology has important applications in the field of ultra precision manufacturing,such as advanced military weapons,precision optical components and aerospace field.At present,the static characteristics of aerostatic bearing,such as bearing capacity and stiffness has been well investigated.However,the experimental results show that aerostatic bearing has phenomenon of self-excited vibration or "pneumatic hammer" vibration under certain conditions.And under the influence of different parameters,its vibration amplitude and frequency are not fixed.Compared with the nano-vibration of aerostatic bearing,the pneumatic hammer has characteristics of larger amplitude with continuous howling.,which is a kind of non-stationary destructive vibration and will lead to the damage of the shaft and the bearing in serious condition.Domestic and foreign scholars have carried out relevant research on the film flow field simulation,static characteristics,pneumatic hammer vibration simulation and experiment of aerostatic bearing,but consensus on the phenomenon of hammer vibration is not achieved.Therefore,further investigation and exploration are needed to solve these problems.The main contents of this paper are shown as the following parts:(1)Modeling and analysis of flim flow field of bearings by using MATLAB.According to Navier Stokes equation,mass conservation equation,gas state equation and simplification assumptions,a two-dimensional Reynolds equation is derived which is suitable for the study of the gas film of the orifice restrictor bearing.By using the finite difference method,the computational domain of the gas film flow field is discretized and the numerical solution program of the pressure distribution of the orifice thrust bearing is compiled in MATLAB.The simulation results are compared with the existing literature results,and the influence rules of the parameters such as the diameter,number of the orifice restrictor and air supply pressure on the static characteristics of the bearing are analyzed,which lays the foundation for the transient flow field and vibration simulation.(2)Simulation analysis of bearings' pneumatic hammer by using MATLAB.The dynamics model of bearing-flim-spindle system is established.The steady pressure of air film is separated by small disturbance method,and the transient pressure fluctuation distribution equation is obtained.The coupling mathematical model of flow field and force field is established by combining the transient pressure distribution equation of air film flow field with the dynamic equation of bearing.A matlab program of numerical simulation for the vibration of the pneumatic hammer is developed,and the pressure fluctuation of the air film flow field and the dynamic parameters of the spindle are solved iteratively.The influence rules of the bearing parameters and the air source attributing on the vibration of the pneumatic hammer are analyzed.Finally,the stability regions of the bearing under the influence of different parameters are obtained.(3)The bearing capacity experiment and pneumatic hammer vibration experiment of the orifice restrictor thrust aerostatic bearing are studied.The curves of bearing capacity changing with the eccentricity of gas film under different air supply pressure of different bearings are tested,and the correctness of the theoretical model of bearing static characteristics is verified by comparing the simulation results.Based on the experimental platform of aerostatic bearing pneumatic hammer,the acceleration time-domain data of spindle in the process of pneumatic hammer vibration are measured,and the actual influence rules of different bearing parameters and air source parameters(pressure and fluctuation)on the vibration are summarized.The results of measurement and simulation are compared to verify correctness of the flow field-force field coupling model and the numerical simulation results of pneumatic hammer vibration.