DEVELOPMENT OF ULTRA HIGH SPEED SPINDLE USING A POROUS FLOATING BUSH FOR DRILLING MACHINES

近年来，信息相关设备的尺寸迅速缩小。因此，安装在这些设备中的印刷电路板上的孔的直径变得越来越小，并且对于钻孔主轴的超过200，000 rpm的更高旋转速度的需求也在增加以制造小孔。考虑到这些设备的小型化的未来趋势，高速主轴的转速超过30万转/分。在这项研究中，我们提出了一种带有多孔浮动衬套的空气静压轴颈轴承，以提高由空气静压轴承支撑的转子在高速下的稳定性。在所提出的轴承中，加压空气仅供给到浮动衬套的两端，但由于多孔材料的作用，浮动衬套的外壁和内壁都可以起到空气静压轴承的作用。此外，浮动衬套两端的间隙非常小，可以避免加压供给空气的压力降低，这使得该多孔轴承保持与普通多孔轴承相当的刚度和承载能力。对该轴承的承载能力、刚度和高速不稳定性等性能进行了理论研究，并在此基础上研制了浮动瓦径向滑动轴承，将实验结果与理论计算结果进行了比较，得出了以下结论。（1）.实验证实，所提出的具有多孔浮动衬套的空气静压径向轴承在高速下具有优异的稳定性。（2）通过与实验结果的比较，验证了理论计算的正确性。（3）.发现使用所提出的轴承制造的高速主轴作为用于非常小的孔的钻孔机具有优异的性能。

Recently, the size of devices associated with information has been rapidly reduced.Accordingly the diameter of holes in printed circuit boards installed in these devices is getting smaller and the demand of higher rotational speed of more than 200,000 rpm is also increasing for drilling spindles to manufacture small holes.Considering the future trend for miniaturization in these devices, high speed spindles with rotational speed of more than 300,000 rpm has to be developed.In this research, we proposed aerostatic journal bearings with a porous floating bush to improve the stability of a rotor supported by aerostatic bearings at high speeds.In the proposed bearing, pressurized air is fed only to both floating bush ends, but both the outer and the inner walls of a floating bush can function as an aero static bearing due to the effect of porous material.In addition, a very small gap at both ends of a floating bush can avoid the pressure reduction of pressurized supply air, which makes this porous bearing maintain stiffness and load capacity comparable to an ordinary porous bearing. We theoretically investigated various performances of the proposed bearing such as load capacity, stiffness and instability at high speeds.Then we manufactured the proposed floating bush journal bearings based on, the theoretical calculations and compared experimental results with theoretical calculations.As a result, the following conclusions were obtained.(1).It was experimentally confirmed that the proposed aerostatic journal bearing with a porous floating bush has an excellent stability at high speeds.(2).The validity of theoretical calculations was confirmed by comparing them with experimental results.(3).It was found that the manufactured high speed spindle using the proposed bearings has excellent performances as a drilling machine for very small holes.