Permanent magnet array for a rotor of a magnetic bearing and method of assembling the array

Abstract

Stray magnetic fields produced by the asymmetric magnetization of the permanent magnets in the rotating magnet array of the magnetic bearing assembly can cause significant problems for devices such as scanning electron microscopes when used in turbomolecular pumps. To minimize stray fields, first measure at least the dipole and quadrupole moments of the individual magnets in the array. The magnets in the array are then arranged relative to each other such that both dipole and quadrupole moments are minimized, thereby minimizing stray magnetic fields as the magnet array in the turbomolecular pump rotates.

Description

technical field [0001] The invention relates to the field of magnetic bearings. In particular, it relates to an apparatus and method for reducing transverse stray magnetic fields caused by permanent magnetic bearing arrangements in high speed rotating machines such as turbomolecular pumps. Background technique [0002] Turbomolecular pumps are used as part of vacuum systems used to generate the high vacuum environments required for devices such as scanning electron microscopes (SEM) and lithography devices. [0003] Turbomolecular pumps commonly include an oil-free passive permanent magnetic bearing arrangement in the high vacuum end of the pump. [0004] figure 1 A section of a passive permanent magnetic bearing arrangement 10 of a turbomolecular pump (not shown) is shown in . In this example, the bearing arrangement 10 includes an array 12 of four outer rotating permanent magnet rings 12a, 12b, 12c and 12d and an array 14 of four inner non-rotating permanent magnet ring...

AI Technical Summary

Problems solved by technology

[0013] Although ferromagnetic shielding is commonly used to reduce such magnetic field emissions, such shielding is expensive and has only limited effectiveness

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