微型高速主軸之氣磁浮軸承研究與開發

在追求微型以及高速化趨勢之下，近年來微型氣高速氣動轉子已廣泛應用在高速牙醫手機及其他精密工業領域當中，在微型氣渦輪的組成元件當中，軸承是最重要並且顯著影響其效率的元件。摩擦、腐蝕以及磨耗是影響高速氣渦輪無法達到高效率運轉的主要原因。雖然透過氣靜壓軸承可實現非常小的滑動摩擦，但其低負載的特性卻限制了發展。本研究結合了磁浮以及氣浮的原理發展一套應用於微型高速氣動轉子的氣磁浮混合軸承。氣靜壓軸承主要提供了軸向以及徑向的支撐功能。然而氣體軸承也具備了因為氣體可壓縮性所造成的氣槌現象的缺點。為了消弭氣槌不穩定現象，被動磁性軸承被整合到氣靜壓軸承當中。不僅軸向的負載能力提升，氣槌現象也得到顯著改善。透過有限元素分析以及理論分析的整合，本論文探討氣磁浮軸承的軸向氣槌不穩定現象以及徑向晃轉不穩定現象。最後藉由實驗方式，測試氣磁浮軸承的性能。根據實驗結果，氣磁浮軸承高於氣靜壓軸承50%的軸向承載能力，並且能夠抑制65%的軸向氣槌振動，最高轉速可達100 krpm。

關鍵字

氣槌效應；流體自激振動；氣渦輪；氣磁浮軸承

並列摘要

Under the circumstance of pursuing high speed and miniaturization, mini-type air turbines have been widely applied to high-speed dental handpieces in recent years. Among all the components of a mini-type air turbine, bearing is the most important part which significantly affects its efficiency. Friction, collision, and wear are the main causes to make the ball bearing unable to reach higher efficiency. Though very small sliding friction can be realized by the aerostatic bearing, its poor bearing capacity limits the application. This research combines the magnetic and aerostatic levitation principle to develop a magneto-aerostatic hybrid bearing for miniature air turbine. The aerostatic bearing undertakes the main function of the radial and the axial bearings. However, the air bearing also possesses a drawback, which is pneumatic hammer effect induced by the air compressibility. In order to eliminate the pneumatic instability, an axial passive magnetic bearing is integrated into the aerostatic bearing. With the magnetic bearing, not only the bearing capacity can be improved, but also the pneumatic hammer effect can be significantly damped. Both theoretical calculation and finite element method (FEM) are used to study the cause and elimination solution of axial pneumatic hammer instability and radial whirl instability. Through experimental testing, the performance of our developed magneto-aerostatic bearing is also verified. The magneto-aerostatic bearing suppresses the axial vibration over 65%, enhances its axial bearing capacity by 50%, and it has maximum rotational speed of 100 krpm.

並列關鍵字

Pneumatic hammer effect ； Flow induced vibration ； Air turbine ； Magneto-Aerostatic bearing

參考文獻

[1] Yoshimoto, S., “Theory and Operating Principle of Aerostatic Bearings ”, Design Engineering, Vol. 37, 2002, pp. 51-56.

[4] Mizumoto, H. and Matsubara, T., “An Aerostatically-Controlled Restrictor for Obtaining an Infinite Stiffness Aerostatic Thrust Bearing”, Journal of the Japan Society for Precision Engineering, Vol. 55, 1989, pp. 135-140.

[5] Holmes, R. and Sykes, J.E.H., “The Vibration of an Aero-engine Rotor Incorporating Two Squeeze-film Dampers”, Journal of Aerospace Engineering, Vol. 210, 1996, pp. 39-51.

[7] Matta, P., Rudloff, L., and Arghir, M., “Experimental Investigation of Air Bearings Dynamic coefficients ”, Mechanics &Industry, Vol. 11, 2010, pp. 477-488.

[8] Nishikawa, F., Yoshimoto, S., and Somaya, K., “Ultrahigh-Speed Micro-Milling End Mill with Shank Directly Supported by Aerostatic Bearings”, Journal of Advanced Mechanical Design, Systems, and Manufacturing, Vol. 6, 2012, pp. 979-988.

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微型高速主軸之氣磁浮軸承研究與開發

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