Micro-Vibration Characteristics of Aerostatic Bearing with Multiple Inclined Orifice Restrictor

Aerostatic bearings are widely used in ultra-precision manufacturing equipment due to their noncontact, near-zero friction, high accuracy, and pollution-free characteristics. Loading capacity, stiffness and stability are the important parameters of aerostatic bearings. Traditionally, the load capacity and stiffness of aerostatic bearings are improved by adding the pocket. However, turbulent vortices in the pocket can cause the pressure fluctuation of the aerostatic bearing flow field and induce the micro-vibration of aerostatic bearings, which seriously affects the stability and positioning accuracy. In order to improve the stability of the aerostatic bearing and its positioning accuracy, the transient flow characteristics of a classical orifice restriction aerostatic bearing are analyzed, and the formation mechanism of the vortex inside the pocket is described. According to the formation mechanism of the turbulent vortices inside the pocket, a novel aerostatic bearing with an inclined orifice restrictor (IOR) is designed. The IOR structure can suppress the generation of turbulent vortices by changing the direction of airflows in the pocket, which can reduce the micro-vibration of aerostatic bearings. In the simulation calculation, the airflow calculational field is divided into 4 parts due to the symmetry of the aerostatic bearing structure, and a quarter structure is utilized as the airflow computational field to improve the computational efficiency. To improve the mesh quality and ensure calculation accuracy, structured grids are used in the CFD model. In order to capture the turbulent flow structures inside the pocket the grid is refined in the orifice and the pocket. The large eddy simulation method is utilized to analyze the flow field inside the aerostatic bearing with the IOR. In order to verify the proposed numerical model, the simulation results of the aerostatic bearing are compared with the existing experimental data. Furthermore, the influence of the working condition and structure parameters of the aerostatic bearing with IOR on its performance is analyzed, such as the angle of the inclined orifice, the height of the inclined orifice, the diameter of the inclined orifice and the supply pressure of the aerostatic bearing with IOR. The simulation results show that the micro-vibration of the aerostatic bearing with IOR decreases first and then increases as the angle of the inclined orifice increases, while the loading capacity remains basically unchanged. When the inclined orifice angle is 110°, the aerostatic bearing with IOR has the weakest amplitude of micro-vibration and the best stability. The micro-vibration of the aerostatic bearing with IOR increases as the inclined orifice height decreases, and the loading capacity remains basically unchanged. When the orifice height is increased to 0.4 mm, further increase of the inclined orifice height has little effect on the micro-vibration of the aerostatic bearing with IOR. The micro-vibration of the aerostatic bearing with IOR decreases as the diameter of the inclined orifice increases, and the loading capacity increases as the diameter of the orifice increases. The micro-vibration and the loading capacity of the aerostatic bearing with IOR both increase as the increasing of supply pressure. The formation of turbulence can be inhibited by changing the structural parameters of the aerostatic bearings, thus improving the stability of the aerostatic bearings. The research results can provide a theoretical reference for the design of high-stability aerostatic bearings.