Hiromasa Fukuyama

An Improvement of the Static and Dynamic Characteristics of Superconducting Magnetic Bearings Using MPMG-YBaCuO

The effects on the static and dynamic characteristics of the superconducting magnetic bearings owing to the difference in the constitution of the radial and axial permanent magnets have been studied in this paper. By improved design of the axial bearing magnet ring and the radial bearing magnet sleeve, the magnetic flux density became increased at superconductor ring position. As the results show, the static and dynamic characteristics were improved remarkably, and the 2.4kg shaft could rotate with amplitudes within 15 µ m peak to peak at 12000 rpm.

Superconducting Magnetic Bearing Using MPMG YBaCuO

A large superconducting magnetic bearing with MPMG YBaCuO material was built in this study. The bearing was driven with a high frequency motor. A pair of the MPMG YBaCuO rings(ϕ4OXϕ65X t20) were fixed in the cooling spaces which were partitioned with thin seal plate. The spaces were cooled with liquid nitrogen.

High Precision Superconducting Magnetic Bearings Using Advanced MPMG-YBaCuO

The realization of high rotational accuracy is of prime concern when designers wish to design superconducting magnetic bearings. This paper describes excellent results obtained in rotational accuracy of superconducting magnetic bearings which use advanced MPMG YBaCuO and incorporate several bearing design improvements. Advanced MPMG YBaCuO displays a remarkably enhanced pinning force, and this leads to showing large levitation or suspension force when used in superconducting magnetic bearings. In this paper,in order to display the pinning force of the advanced MPMG YBaCuO effectively, the bearing gaps between the permanent magnets and the superconductors were decreased in the axial direction. And an AC servo motor was used as the driving device to minimize driving disturbances. In the bottom centering and lifting device a ball bush guide was used to increase radial stiffness of the centering portion. As the result of these improvements, the amplitude of the rotating 2.1 kg shaft decrease its vibration to a few micrometers at 12000 rpm.

Stiffness and Damping Coefficients for Superconducting Magnetic Bearings Using MPMG2-YBaCuO

Dynamic performance of bearings is mainly determined by stiffness and damping. In applying superconducting magnetic bearings to high speed rotational machines, it is an essential matter to know quantitatively the stiffness and damping coefficients of superconducting magnetic bearings. This paper reports experimental results of the stiffness and damping coefficients of a ring shaped superconducting magnetic axial bearing using MPMG2-YBaCuO which was used in a high precision rotational test at 12000 rpm with an amplitude of 1.8 µ m p-p. Experimental results show that the measured stiffness coefficient is mainly determined by acting gap, and there is a small difference between attractive type and repulsive type. On the other hand, the damping coefficients is mainly determined by the setting gap under field cooling, and the attractive type shows a higher value than the repulsive type at the same acting gap. The stiffness and damping coefficients in radial direction are about 2/3 of those in the axial direction. The larger the setting gap, the smaller the value of the stiffness and damping coefficients become.

The Improvement of Levitation Force of the Advanced MPMG YBaCuO for Superconducting Magnetic Bearings

In the superconducting magnetic bearings, it is important to reduce the vibration amplitude of the rotor. For the reduction of vibration amplitude, it is required to improve the levitation force between the superconductor and the magnet. We report an advanced MPMG process for the improvement of the levitation force. During the melt processing, different from a simple slow cooling in the usual MPMG process, seeding and large temperature gradient were employed in the advanced process. With the advanced process, we could successfully produce large oriented grains and thus enhance the levitation force about twice larger than the previously reported value. Consequently, a drastic reduction in the vibration amplitude was expected and actually confirmed by others with our sample.