JP2020084977A - Electromagnetic damper of uniaxial control magnetic bearing - Google Patents

Abstract

To provide a magnetic bearing system capable of appropriately supporting change in parameters of a supported body for different supported bodies without needing design of a magnetic bearing individually, to rotate a large-sized supported body stably.SOLUTION: A magnetic bearing system is configured such that a certain basic magnetic bearing unit is set as a reference, and a radial passive magnetic bearing is set and added thereto according to change in parameters of a supported body. A radial electromagnetic damper is added to increase the damping capacity of the radial passive magnetic bearing.SELECTED DRAWING: Figure 3

Description

The present invention relates to an electromagnetic damper of a uniaxial control type magnetic bearing.

A turbo molecular pump is the most successful mass-produced product that uses magnetic bearings. It is a relatively simple application for magnetic bearings, but its features are clean (no lubrication oil required), ultra-low vibration (no contact between rotor and stator) and high reliability compared to conventional ball bearings. This is because it is an application that can make the most of the selling point of high resistance (strong against corrosive gas). In fact, large magnetic bearing type turbo molecular pumps (2,000 L/S or more) are used in almost all etching apparatuses for manufacturing semiconductors, flat panels and the like. However, since magnetic bearings are more expensive than ball bearings, the current situation is that they have not been adopted for small turbo molecular pumps (500 L/S or less) in the low price range. A magnetic bearing type turbo molecular pump is used in some high-performance electron microscopes, but a small turbo molecular pump that uses a ceramic ball bearing is standardly used in popular electron microscopes and mass spectrometers. ing. Also, unlike the etching equipment, not only small turbo molecular pumps but also medium-sized turbo molecular pumps (500L/S to 2000L/S) are used for PVD equipment that does not flow corrosive gas. Type turbo molecular pump is adopted.

Prior art for realizing a low-priced magnetic bearing includes the following.

Japanese Patent Publication No. 6-46036 The present invention relates to an axial flow molecular pump characterized in that a part of a radial magnetic bearing is of a passive type using a permanent magnet without using a control electromagnet.
JP, 2010-230161, A The present invention relates to an axial flow molecular pump characterized by a magnetic bearing system capable of supporting a variety of supported objects, by changing the design of only one radial passive magnetic bearing according to changes in the parameters of the supported object. It is a thing.

This report shows that even if two radial magnetic bearings other than the axial active magnetic bearing are passive type, a magnetic bearing system that is stable up to high speed rotation can be obtained by adding an appropriate passive damper. It is explained by the experimental data.

Aiming to reduce the price of fully active control type magnetic bearings (generally called 5-axis control type magnetic bearings) that are used in large turbo molecular pumps, compressors, and various other industrial products. Although there is a prior art in which a passive magnetic bearing in which a permanent magnet is applied to a part of the magnetic bearing is adopted, the applicable range is limited to a specific small turbo molecular pump. There are two causes,
1) Unlike the fully active control type magnetic bearing, it is free to change the parameters (weight, center of gravity position, moment of inertia, moment of inertia ratio, steady speed, resonance frequency of structure, etc.) of the supported object (rotor). It is not possible to cope with this, and it is necessary to design the magnetic bearing individually for different supported bodies. 2) It is difficult to increase the damping capacity for whirling phenomenon of the rotor with a passive damper, so it is difficult That is, it is not easy to stably rotate the supported body.
Eliminating these causes 1) and 2) is an issue for expanding the products that use passive magnetic bearings.

In order to solve the above-mentioned problem 1), as shown in the prior patent document 2, a certain basic magnetic bearing unit is used as a reference, and a radial passive magnetic bearing is used for changing the parameter of the supported body. This will be handled by using a magnetic bearing system with additional settings depending on the situation.
In order to solve the problem of 2) above, an electromagnetic damper is added to the radial passive magnetic bearing in order to increase the damping capacity of the radial passive magnetic bearing, and in order to avoid cost increase, the radial electromagnetic The damper can be used as a radial position sensor or as an axial electromagnet of an axial active magnetic bearing.

The magnetic bearing unit can be standardized, and the price of the magnetic bearing can be reduced due to mass production effects (close to conventional ball bearings), so the magnetic bearing features clean (no lubrication oil required) and ultra-low vibration. Application products that require high reliability (strong resistance to corrosive gases), etc. (no contact between rotor and stator, effective low rigidity), but difficult to adopt at high prices, such as large and small turbo It can be used as a bearing for a turbo molecular pump in the middle zone of the molecular pump or a small-sized, high-gas load split-flow turbo molecular pump for a mass spectrometer.

An explanatory view of a radial position sensor and a radial electromagnetic damper according to an embodiment of the present invention Explanatory drawing of an axial active magnetic bearing/radial electromagnetic damper according to an embodiment of the present invention Vertical cross-sectional view of a turbo molecular pump to which an embodiment of the present invention is applied Explanatory drawing of a bearing structure example of a ball bearing turbo molecular pump

An embodiment of the present invention will be described below with reference to FIG.
This embodiment is characterized in that there are two radial passive magnetic bearings in the upper and lower portions, and the radial passive magnetic bearings in the upper portion are designed according to each supported body (rotor). The permanent magnet 9 and the upper rotation-side permanent magnet 10 have magnetic poles arranged to repel each other to form an upper radial passive magnetic bearing. Due to the upper radial passive magnetic bearing, the axial fixed positions of the upper permanent magnet 9 and the upper permanent magnet 9 are arranged so that the shaft 1a is pulled downward in the axial direction. Controls the force for attracting the armature disk 5 axially upward by the axial position of the shaft 1a detected by the axial position sensor 12 to form an axial active magnetic bearing. The feature of this embodiment is that the lower radial passive magnetic bearing and the axial active magnetic bearing are integrated into one unit by the magnetic bearing holder 13, and the magnetic bearing circuit 14 is also integrated with the magnetic bearing holder 13, so that, for example, The ball bearing unit 14 of the bearing structure of the ball bearing type turbo-molecular pump shown in FIG. 4 can be designed to be freely replaceable. Further, in the radial passive magnetic bearing in the magnetic bearing holder 13 according to the present embodiment, the lower holder 16 of the lower fixed permanent magnet 15 is supported by the magnetic bearing holder 13 by the viscoelastic body 17 and by the support balls 18. The axial position is fixed and it is free to move in the radial direction. Here, the weight of the lower holder 16, the spring constant of the viscoelastic body 17, the repulsive force between the lower fixed permanent magnet 15 and the lower rotating permanent magnet 19 and the spring constant are optimal according to the lower weight of the rotor 20. By this, the optimum damping force in the lower radial direction can be obtained. However, although the support spring constant can be changed by changing the design of the upper radial passive magnetic bearings in response to changes in the parameters of the supported body (rotor), the upper and lower radial passive dampers alone are especially large In the case of the supported body (rotor), the damping ability at the resonance frequency cannot be set sufficiently. Therefore, in the embodiment of the present invention shown in FIG. 3, the radial electromagnetic damper 2 having a structure in which the radial position sensor and the radial electromagnet capable of setting the damping capacity are integrated is added.

An example of the radial electromagnetic damper structure will be described with reference to FIG. Generally, a radial active magnetic bearing is composed of a radial position sensor and a radial electromagnet, and this radial electromagnetic damper makes the magnetic circuit of the radial position sensor double as the magnetic circuit of the radial electromagnet. However, there is a feature. This is because the radial support force is already supported by the radial passive magnetic bearing, and the phase characteristic of the electromagnetic damper is more important than the generated force, so that the magnetic pole surface 21 that generates the force is positioned in the radial position. This is possible because the magnetic pole area of the sensor is sufficient. 1 is a shaft, 2a is a magnetic circuit stator which also serves as a radial position sensor and a radial electromagnetic damper, 3 is a radial sensor coil, and 4 is a radial electromagnet coil. The example of FIG. 2 is an invention in which the axial active magnetic bearing has a radial electromagnetic damper function in order to reduce the cost increase due to the addition of the radial electromagnetic damper. The magnetic pole surface of the radial electromagnetic damper/axial electromagnet 6 and the cone-shaped armature disk 5a that receives the force is made cone-shaped so that a radial force component can also be produced. As a matter of course, the position sensor also receives signals in both the axial direction and the radial direction, so that the radial direction X signal, the radial direction Y signal, and the axial direction can be calculated by calculation from the signals of the four position sensor coils 7 of ±X and ±Y. The Z signal is obtained. Further, 8 is a radial electromagnetic damper/axial electromagnet coil, and since a magnetic flux change also occurs in the radial electromagnetic damper/axial electromagnet 6 and the cone-type armature disk 5a, the generation of eddy current is reduced, so that the soft magnetic metal A material obtained by solidifying a soft magnetic powder coated with a non-magnetic material is better than a bulk material.

Magnetic bearings can be used not only for large turbo molecular pumps, but also for medium-sized turbo molecular pumps and small turbo molecular pumps that can handle high-load gas flow rates, instead of the unreliable conventional ball bearing type. become. Further, the present invention can be applied to products such as turbo molecular pumps, which have specifications that the position accuracy of the rotating shaft is not severe under a light load, such as products such as a rotating fan or a high-speed rotating beam chopper.

1,1a Shaft 2 Radial electromagnetic damper with integrated structure of radial position sensor and radial electromagnet 2a Magnetic circuit for both radial position sensor and radial electromagnetic damper Stator 3 Radial sensor coil 4 Radial electromagnetic coil 5 Armature disc 5a Cone type armature disk 6 Radial electromagnetic damper and axial electromagnet 7 Position sensor coil 8 Radial electromagnetic damper and axial electromagnet coil 9 Upper fixed permanent magnet 10 Upper rotating permanent magnet 11 Axial electromagnet 12 Axial position sensor 13 magnetic bearing holder 14 magnetic bearing circuit 15 lower fixed permanent magnet 16 lower holder 17 viscoelastic body 18 support ball 19 lower rotating permanent magnet 20 rotor 21 magnetic pole surface 22 ball bearing unit

Claims (4)

Axial flow molecular pump utilizing a magnetic bearing system consisting of two radial passive magnetic bearings, one axial active magnetic bearing and one radial electromagnetic damper. The axial flow molecular pump according to claim 1, wherein a set of radial electromagnetic dampers has a structure in which a radial position sensor and a radial electromagnet are integrated. The axial flow molecular pump according to claim 1, wherein a set of radial electromagnetic dampers is integrated with an axial active magnetic bearing. The axial flow molecular pump according to claim 1, wherein the stator yoke and the armature disk of the electromagnetic damper are made of a material obtained by solidifying soft magnetic powder, and the radial electromagnetic damper according to claim 2 or 3 is used as a component.