Abstract
The air bearing motorized spindle (ABMS) is the key component of the ultra-precision machine tool, which plays an important role in the ultra-precision machining process and directly influences machining accuracy. The influence of unbalanced magnetic force (UMF) on the nonlinear dynamic behavior of the ABMS is not understood clearly. To reveal the potential influence of the UMF, a mathematical model of the ABMS considering multiphysics fields is established. The variation trend of the UMF is simulated, and the nonlinear dynamic behavior of the ABMS is analyzed which emphasizes on the stability of the rotating shaft. It is shown that the UMF varies linearly at large rotor eccentricity which meets well with previous research, but it is noteworthy the UMF varies nearly to a quadratic function at small rotor eccentricity. The result of rotor dynamics shows that the UMF can change the converge position of the rotor center and the converge speed. Moreover, when at certain rotor mass and external load, the UMF can enlarge the stability boundary of the rotor. This research provides an example of analyzing the nonlinear dynamic behavior of the ABMS considering multiphysics fields which may help to the further investigation.
Highlights
The air bearing motorized spindle is commonly equipped in the ultra-precision machine, in which the rotor shaft is directly driven by usually a permanent magnet synchronous motor (PMSM) and supported by the air journal bearing [1,2,3,4]
Due to its compact structure, high efficiency, pollution free, high precision and other advantages, extensive studies of the air bearing motorized spindle (ABMS) have been conducted in the past few decades, which mainly focus on the dynamic characteristic of air journal bearing [5,6,7,8]
The exact critical value which result in unconditional stable and unstable consequence can only be approached but not obtained exactly. Both the external force and the rotor mass have influence on the stability boundary, and the result shows that the stability boundary with considering the unbalanced magnetic force (UMF) exceeds the stability without considering the UMF, the possible explanation for it is that the UMF is potentially equivalent to the increase of the external force, it needs to be further explored
Summary
The air bearing motorized spindle is commonly equipped in the ultra-precision machine, in which the rotor shaft is directly driven by usually a permanent magnet synchronous motor (PMSM) and supported by the air journal bearing [1,2,3,4]. Dynamic coefficients method and restoring force method are two mainly analytical methods investigating the nonlinear dynamic behavior of bearing-rotor system [9,10]. The transient Reynolds equation can be solved using finite element method (FEM) or finite difference method (FDM), due to less complex meshing and iterative, the FDM gets more preference which is easy to obtain the transient restoring force, especially when considering multiphysics fields [20,21,22]. To the ABMS, the influence of Electromagnetic factors on the dynamic behavior of the ABMS system is not understood clearly It had been pointed out the existence of stability boundary of air journal bearing, and the stability boundary varying with rotating speed is investigated [27,28]. The restoring force and the UMF are coupled within the dynamic model in which the rotor is treated as a rigid rotor
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