Research On Vortex Suppression And Vibration Reduction Control Of Pneumatic Hammer Of Aerostatic Bearing

Gas lubrication technology has extensive applications in high-end manufacturing fields such as ultra-precision machining and medical equipment.Aerostatic bearing is a representative application of gas lubrication technology,and it has been widely used in many production fields.However,in practical applications,it is found that the small-hole throttling aerostatic bearing has phenomenon of low amplitude micro vibration when the air supply pressure gradually increases,and it has "pneumatic hammer" vibration under certain conditions.The prominent features is that the main shaft will be accompanied with noticeable noise and a large amplitude.Domestic and foreign scholars have studied the generation mechanism of pneumatic hammer vibration.The current consensus on the generation mechanism of vibration is that "the micro-vibration caused by gas vortex develops to pneumatic hammer vibration under certain excitation","pneumatic hammer vibration is a self-excited vibration caused by the phase difference between bearing rotor and air film".However,there is a lack of corresponding methods for these two mechanisms to inhibit the vibration.Therefore,this thesis carries out further research on the suppression of air hammer vibration.The main contents of this thesis are shown as the following parts:(1)The micro flow field of different aerostatic bearings is simulated and analyzed based on large Eddy simulation.The micro flow field is modeled and simulated to solve which is based on the theories of gas lubrication.Then the characteristic of flow field of small-hole throttling bearing with cavity structure and not are analyzed from steady state and transient state.The generation and crushing process of gas vortex with cavity structure is obtained,and the influence law of pressure equalizing cavity structure parameters on gas vortex is explored,which can lay a foundation for further study of the structure for suppressing gas vortex.(2)A new aerostatic bearing structure for suppressing gas vortex was designed meanwhile the related experiments are carried out.Based on micro-vibration caused by gas vortex develops to pneumatic hammer vibration under certain excitation,three kinds of aerostatic bearings with different cavity structures are designed with the relevant theory about suppression of gas vortex.The simulation analysis and structural parameters optimization of different structures are carried out,and a new structure with good bearing capacity and stability is obtained.The micro vibration experiments of aerostatic bearing with traditional cavity type or trapezoidal groove are carried out which verify the relevant simulation experiment in the second chapter.(3)A shock absorber model for suppressing pneumatic hammer vibration is established and the pneumatic hammer vibration experiment is carried out.The coupling model of pneumatic hammer vibration and vibration absorber is established based on the air hammer vibration model of small hole throttle hydrostatic thrust bearing.Then the vibration characteristics are solved,and the optimal damping ratio and mass block parameters of the shock absorber are analyzed,which provides theoretical support for design of absorber.The vibration of aerostatic spindle system with different cavity structures under different working conditions is tested,and the vibration characteristics are analyzed to reveal the vibration characteristics of pneumatic hammer vibration.