Development of an externally pressurized bearing-rotor system for a five-axis ultraprecision machine tool used for optical manufacture and the static performance analysis of the externally pressurized bearing

Abstract

A new design is proposed according to the requirement of a 5-axis ultra-precision machine tool for optical manufacture. This investigation was performed to see how the different configure styles influence the static performance characteristics of externally-pressurized air bearings with orifice, such as load capacity and stiffness. Based on the static performance characteristic analysis, the optimum design is done for the externally-bearing system. Finite difference method was used to obtain the numerical solution of Reynolds Equation. Load capacity was the integration of Pressure over the solution area, while the stiffness is the derivative of load capacity to gas film thickness. The load capacity of the externally-pressurized bearing grows with the increase of supply pressure and goes up with the increase of eccentricity of shaft relative to the bearing; the stiffness turns out to be tough with high supply pressure. The stiffness gets a maximum at zero eccentricity of the spindle, and gradually reduces with the increase of the eccentricity. It has proven that there exists an optimum gas-film clearance where maximum value of stiffness is obtained. There is also an optimum gas-film clearance for maximum load capacity. It should be noted that these two values is different. The restrictor throat diameter has an important influence on the stiffness and load capacity, both of which go down while larger diameter is in use. It can be concluded that there exists an optimum gas-film clearance for aerostatic bearing-rotor system. More attentions should be paid on supply pressure, gas-film thickness and orifice diameter to obtain a spindle of good performance.