Formation Mechanism Research Of Self-excited Vibration Of Ultra-precision Aerostatic Bearing

Gas lubrication technology has important applications in the field of ultra-precision manufacturing.The research of the aerostatic bearing with various throttling forms is basically mature,such as bearing capacity,stiffness and other static characteristics.The optimization of aerostatic bearing inevitably encountered limitations in the process of improving static characteristics with high level of accuracy.However,aerostatic bearing has phenomenon of self-excited vibration or "pneumatic hammer" vibration under certain conditions that is different from the nano-vibration.It is a kind of non-stationary destructive vibration and will lead to the damage of the shaft and the bearing in serious condition.And the pneumatic hammer has characteristics of larger amplitude with continuous howling.Domestic and foreign scholars have carried out relevant research on the generation and inhibition of pneumatic hammer vibration simulation and experiment,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)The micro flow field of gas film is simulated and analyzed based on the large eddy simulation equation.The governing equations of fluid mechanics is obtained through the scale filtration method of turbulence fluctuation which is based on the three conservation laws of gas lubrication.Then the relevant scale modeling is carried out to realize the large eddy simulation.The influence rules of bearing parameters are analyzed on the gas film flow filed,such as the diameter,depth of the bearing pressure equalizing chamber and air supply pressure.Based on the simulation results,the factors causing the self-excited vibration at the micro level are analyzed,which provides a micro level explanation for the coupling of the micro flow field and the macro vibration.(2)The bearing self-excited vibration is simulated and analyzed based on the fluidsolid coupling equation.Based on the coupling principle of rigid body motion and microscopic flow field,the fluid-structure coupling model of the gas film and the spindle is established.The vibration shapes of bearings with different structures are observed combined with modal analysis when the bearing pneumatic hammer occurs.And the vibration nature of the bearing pneumatic hammer will be obtained.The influence rules of bearing parameters are analyzed on the macro-vibration of the spindle,such as the diameter,depth of the bearing pressure equalizing chamber,air supply pressure and bearing load quality.Combined with the change rule of the microscopic flow field in the previous chapter,the mechanism of the bearing pneumatic hammer will be revealed comprehensively.(3)Pneumatic hammer vibration experiments of the orifice restrictor thrust aerostatic bearing are studied and new pressure equalizing cavity structures are proposed to suppress the vibration.The pneumatic hammer vibration experimental platform is built based on the working principle of the aerostatic support.The vibration curves of different structures under different air supply pressures are measured and the actual influence rules are analyzed.Then the results are compared with the simulation results to verify the correctness of the numerical simulation results.Based on the mechanism of the bearing pneumatic hammer vibration,some new types of pressure equalizing chamber structure are proposed to ensure the static performance of the bearing and to suppress the bearing pneumatic hammer vibration.