Characteristics Analysis And Experimental Research On The Micro Self-excited Vibration Of Aerostatic Thrust Bearing

Profiting from its low friction, high speed, high precision, less pollutionand low heat generation, aerostatic bearing is widely used in fields of ultra-precisionmachining, measurement or micro machining. With the development of themanufacturing and measurement, higher accuracy of position motion is needed tomeet the requirements of corresponding equipments. However, the unstable flow inbearing clearance makes aerostatic bearing to be micro self-excited vibration inmagnitude from several nanometers to decades nanometers and frequency fromdecades hertz to thousands hertz. It severely affects the accuracy of the systemsupported by aerostatic bearing. In this thesis, the mechanism of the microself-vibration is researched by simulation and experiments. And the main work is asfollowing:(1) Large Eddy Simulation (LES) is used to analyze the flow field of the bearingwith pocketed orifice-type restrictor. The results show that there are complicatedvortexes near orifice outlet. Gas pressure and velocity change gradually from thecentre to the edge of the vortexes. It is the repetition of the generation and crack ofvortexes causes gas pressure to fluctuate with gas flow inside the bearing and inducesthe bearing to be micro self-excited vibration. Moreover, the mechanism of vortexesinduce the micro self-excited vibration of aerostatic thrust bearing is validated bycomparing to the flow field of aerostatic thrust bearing with inherently orifice-typerestrictor.(2) The influence of bearing diameter, orifice diameter and air chamber depth onthe vibration is obtained by analyzing the pressure fluctuation characteristics of thebearing with different structural parameters. The calculation results indicate thatthere exists a maximum value of the magnitude of pressure fluctuation with theincreases of film thickness. Therefore, the film thickness of the maximum pressurefluctuation should not be close to that of the maximum stiffness in order to make thebearings with better stiffness and less self-vibration simultaneously. A new aerostatic bearing with spoiler desk is designed, the spoiler desk effectively reduces thepressure fluctuation of the gas film and restrain the micro self-excited vibration ofbearing.(3) The performance testing apparatus of aerostatic bearing is designed andmanufactured. In the apparatus, lever mechanism is adopted for loading and polarcoordinate platform is used to achieve gas pressure sensors positioning. Unlikeweight loading, air cylinder or spring, lever mechanism loading can generatecontinuous forces and can not influence the dynamic performance of the bearing.Moreover, polar coordinate positioning platform avoids the biaxial position error.The data acquisition and controlling system is designed based ATmega16. Thesystem can drive motors and gas pressure automatic testing.(4) The experiments show that the testing apparatus can meet the measuringrequirements of load carrying capacity and gas pressure distribution. Furthermore,the vibration characteristics of aerostatic bearing with different structural parametersare tested using signal analyzer instrument Coco-80. The experiments arecoincidence to calculation results very well. Therefore, the mechanism of vortexesinduce the micro self-excited vibration of aerostatic bearing is validated.In this thesis, the mechanism of the micro self-excited vibration of aerostaticbearing is obtained. Moreover, the mechanism is validated by exiting experimentsand the experimental results of the designed testing apparatus. The influence ofstructural parameters on the bearing performance is researched and the new typebearing structure is designed to restrain the micro self-vibration. The conclusions ofthis thesis can be helpful to the designing of ultra-precision aerostatic bearing.