Abstract
The aerostatic spindle in the ultra-precision machine tool shows the complex multi-field coupling dynamics behavior under working condition. The numerical investigation helps to better understand the dynamic characteristics of the aerostatic spindle and improve its structure and performance with low cost. A multi-field coupling 5-DOF dynamics model for the aerostatic spindle is proposed in this paper, which considers the interaction between the air film, spindle shaft and the motor. The restoring force method is employed to deal with the times varying air film force, the transient Reynolds equation of the aerostatic journal bearing and the aerostatic thrust bearing is solved using ADI method and Thomas method. The transient air film pressure of aerostatic bearings is obtained which clearly presents the influence induced by the tilt motion of the spindle shaft. The motion trajectory of the spindle shaft is obtained which shows different stability of the shaft under different external forces. The dynamics model shows good performance on simulating the multi-field coupling behavior of the aerostatic spindle under external force. which is quite meaningful and useful for the further research on the dynamic characteristics of the aerostatic spindle.
Highlights
The aerostatic spindle plays a key role in an ultra-precision machine tool in the nanoprecision machining, which directly affects the machining quality [1,2]
The simulation for the motion trajectory of the spindle shaft is realized under the coupling of the restoring force of the aerostatic bearing, the unbalanced magnetic force (UMF) of permanent magnet synchronous motor (PMSM) and the external force on the shaft, where the shaft is regarded as a rigid rotor
The typical structure diagram of the aerostatic spindle is shown in Figure 1, the spindle shaft is directly driven by the motor, and the shaft is supported by an aerostatic journal bearing and two aerostatic thrust bearing
Summary
The aerostatic spindle plays a key role in an ultra-precision machine tool in the nanoprecision machining, which directly affects the machining quality [1,2]. Xu and Jiang [22,23] analyzed the 5-DOF rotor dynamics model of an aerostatic spindle, in which the stability, the unbalance response, and the forced response of the rotor-bearing system were investigated Both Li and Xu adopted the dynamic coefficient method in their model, it may lose the numerical accuracy when taking this method which largely improved the efficiency. The restoring force commonly used in 2-DOF models aims to obtain force directly by solving the transient Reynold equation [24,25], and it can obtain the torque in a 5-DOF model It can be optimized of the dynamic coefficient method, but if this measure is taken, massive extra work needs to be done. The simulation for the motion trajectory of the spindle shaft is realized under the coupling of the restoring force of the aerostatic bearing, the UMF of PMSM and the external force on the shaft, where the shaft is regarded as a rigid rotor
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