Magnetic-fluid-solid coupling dynamic analysis of aerostatic spindle considering bearing waviness

The multi-physics coupling effect of aerostatic spindle in operation has always been a problem that is difficult to be studied clearly. In practice, the spindle motor produces unbalanced magnetic pull due to rotor eccentricity, which excites the spindle in the form of multi-frequency external force, thus causing changes in the vibration characteristics of the spindle. In addition, the translation displacement and inclination angle of the spindle rotor will affect the time-varying stiffness and damping coefficient of the air bearing, which will cause the bearing performance to change. This paper first focuses on the surface roughness problem in the actual manufacturing process of air bearings, and simplifies it into a surface waviness shape that conforms to the milling marks of the tool. A 4-degree-of-freedom rotor-bearing mathematical model with bearing surface waviness is established, and the fluid-solid coupling is completed by solving the Reynolds equation. Then, the calculation formula of the unbalanced magnetic pull force of the motor is derived and incorporated into the spindle model. Finally, the Magnetic-Fluid-Solid coupling of the aerostatic spindle is completed, and the frequency response function of the spindle end is output. More important conclusions are: when UMP exists, the first-order co-amplitude value of the spindle is reduced by 12.58 %, and the second-order co-amplitude value is reduced by 19.38 %.