Vibration Characteristics Of Aerostatic Bearing In Ultra-precision Motion Stage

Ultra-precision motion stages, the core part of a wide range of precision manufacturing equipments, differentiate themselves from traditional motion mechanisms characterized of contacted motion pairs and rigid structures. It is well recognized that the limit precision of traditional motion stages can only achieve micron-level, far beyond the needs of nanometer level of motion precision required in some nano-manufacturing devices such as semiconductor lithography, due to serious issues such as friction, heat generation and vibration transmission phenomena. Therefore, in modern ultra-precision motion stages, aerostatic bearings are widely applied in place of traditional contact moving pairs, as a result, significantly improving dynamic performance of ultra-precision motion stages, in comparison with that of traditional motion stages. Nevertheless, vibrations induced by gas flowing in aerostatic bearing can still not be ignored, and it has become one of the major factors, which limit further improvement of motion precision of the stages. In this dissertation, aiming at this problem, the combinational methods of simulations and experiments are conducted to further investigate the vibration characteristics of aerostatic bearing. The content and achievement of this dissertation are as follows.1) A 3D mechanical model is built by applying the gas lubrication theory. The simulation and experimental results indicate that the accuracy of the proposed model has greatly been improved, comparing to that of the existing 2D model.2) The patterns of influence of the structure factors, such as shape and dimension of chambers, and the process parameters, such as gas supply pressure and gas film clearance, on the gas vortex in aerostatic bearing are analyzed by applying numerical simulation methods. The micro-vibration characteristics under different conditions are studied through a serial physical experiment. It is clarified that the gas vortex existing in aerostatic bearing is the major factor of the phenomenon of system micro-vibration.3) The intrinsic relationship between pressure chamber shapes of aerostatic bearings and pneumatic hammer phenomena has been studied based on physical experiments. The patterns of the influence of chamber shapes on the pneumatic hammer phenomena are revealed, and the design rules of chamber shapes in aerostatic bearings are established, which provide a theoretical guidance for the design of aerostatic bearings.4) Based on a combination of numerical analyses and physical experiments, the patterns of the influence of chamber shapes, orifice dimensions and condition parameters on the vibration transmission characteristics of aerostatic bearings are studied, and a method for real-time regulation of dynamical performance of aerostatic bearings is proposed.In general, in this dissertation, the vibration mechanisms of aerostatic bearings are revealed, and the patterns of the influences of bearing structures and operating conditions on the phenomena of the gas vortex and the pneumatic hammer are clarified, and the dynamics analysis methods of aerostatic bearings are proposed. The research results are believed to provide a theoretical basis for the design and manufacturing of ultra-precision motion stages.