Magnetic bearing device
By incorporating a dual-disk configuration with strategically positioned coils, the magnetic bearing device enhances the facing area and supporting force density, addressing the limitations of conventional designs.
Patent Information
- Application Number
- JP2023197192
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-11-21
- Publication Date
- 2025-06-02
AI Technical Summary
Conventional magnetic bearing devices have a small facing area between the rotor and the stator core, resulting in a low supporting force density.
The magnetic bearing device includes a first disk and a second disk facing the stator core, with axial coils and radial coils strategically positioned to increase the facing area and supporting force density.
This configuration significantly increases the facing area between the rotor and the stator core, achieving a high supporting force density compared to conventional magnetic bearing devices.
Smart Images
Figure 2025083677000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a magnetic bearing device capable of supporting a rotor in a non-contact manner.
Background Art
[0002] A magnetic bearing is a bearing capable of supporting a rotor in a non-contact manner by electromagnetic force, having no frictional loss, and enabling the rotor to rotate at an ultra-high speed. Further, since a magnetic bearing does not require lubricating oil, there is an advantage that the system environment is not contaminated, and it can be operated in a long-life and vacuum / ultra-low temperature / high-temperature environment.
[0003] FIG. 14 is a schematic diagram showing the structure of a conventional magnetic bearing. As shown in FIG. 14, the stator 500 of the magnetic bearing is composed of an axial stator portion 501 and a radial stator portion 502. The axial stator portion 501 has two axial coils 512 wound around the rotor shaft 510 in the winding direction. The radial stator portion 502 has a 4-slot structure and has four radial coils 513 (only two radial coils 513 are drawn in FIG. 14) for generating a radial force. The radial stator portion 502 forms a magnetic circuit in a plane perpendicular to the axial direction of the rotor 520. The rotor 520 has a disk 525. This magnetic bearing supports the rotor 520 by generating a magnetic attractive force between the disk 525 of the rotor 520 and the stator core 526.
Prior Art Documents
Patent Documents
[0004]
Non-Patent Document 1
[0005] However, the magnetic bearing has a problem in that the facing area between the disk 525 and the stator core 526 (the area of the region surrounded by the dotted line) is small, and the supporting force of the rotor 520 per unit volume (also referred to as the supporting force density) is small.
[0006] Therefore, the present invention provides an improved magnetic bearing device capable of increasing the supporting force (supporting force density). Means for Solving the Problems
[0007] In one aspect, there is provided a magnetic bearing device including a rotor shaft, a first disk protruding radially outward from an outer peripheral surface of the rotor shaft, a second disk protruding radially outward from an outer peripheral surface of the first disk, axial coils disposed on both sides of the second disk, a plurality of radial coils disposed radially outside the axial coils, and a stator core that houses the axial coils and the plurality of radial coils. The stator core includes a pair of first axial stator cores positioned on both sides of the first disk, a plurality of pairs of second axial stator cores positioned on both sides of the second disk and between the second disk and the axial coils, and a plurality of radial stator cores around which the plurality of radial coils are wound respectively.
[0008] In one aspect, the axial coils surround the periphery of the first disk. In one aspect, the thickness of the first disk is greater than the thickness of the second disk. In one aspect, the plurality of radial coils surround the periphery of the axial coils. In one aspect, the magnetic bearing device further includes a pair of side disks protruding radially outward from an outer peripheral surface of the first disk. The second disk is positioned between the pair of side disks, and the stator core further includes a pair of side stator cores disposed outside the pair of side disks in the axial direction of the rotor shaft.
[0009] In one aspect, the magnetic bearing device further includes a current controller that controls currents supplied to the axial coils and the plurality of radial coils. In one aspect, the current controller is configured to supply a current to one of the axial coils disposed on both sides of the second disk while supplying currents to the plurality of radial coils. In one aspect, the current controller is configured to supply currents of the same magnitude and the same direction to the plurality of radial coils. In one aspect, while supplying current to the axial coil, the current controller is configured to supply current to two radial coils located on opposite sides of each other among the plurality of radial coils. In one aspect, the current controller is configured to supply current to the two radial coils such that the two radial coils generate magnetic fluxes in the same direction within the second disk. In one aspect, the current controller is configured to supply current in opposite directions to the axial coil.
Advantages of the Invention
[0010] The magnetic bearing device includes a first disk and a second disk facing the stator core. Therefore, compared with the conventional magnetic bearing, the facing area between the stator core and the rotor increases, and as a result, a high supporting force (high supporting force density) can be achieved.
Brief Description of the Drawings
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Embodiments for Carrying Out the Invention
[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional perspective view showing an embodiment of a magnetic bearing device, FIG. 2 is a longitudinal sectional view of the magnetic bearing device shown in FIG. 1, and FIG. 3 is a sectional view taken along line A-A of FIG. 2. The magnetic bearing device includes a rotor 1, a magnetic bearing 2 that supports the rotor 1 in a non-contact manner by magnetic attraction force, and a current controller 3 that controls the operation of the magnetic bearing 2.
[0013] The rotor 1 is a rotatable structure. Application examples of the rotor 1 rotatably supported by the magnetic bearing 2 are not particularly limited. For example, the rotor 1 is part or all of a rotor included in a rotating machine such as a liquid pump or a vacuum pump. In particular, since the magnetic bearing device can support the rotor 1 without mechanically contacting the rotor 1, it does not cause wear or frictional heat of the rotor 1. Therefore, the magnetic bearing device is suitable for applications that support rotors that rotate at high speeds, such as the turbine of a turbo molecular pump and the impeller rotor of a liquid hydrogen pump that transfers low-specific gravity liquid hydrogen.
[0014] The rotor 1 has a rotor shaft 5, a first disk 7 that projects radially outward from the outer peripheral surface of the rotor shaft 5, and a second disk 8 that projects radially outward from the outer peripheral surface of the first disk 7. The rotor shaft 5, the first disk 7, and the second disk 8 are concentric. The rotor shaft 5, the first disk 7, and the second disk 8 are an integral structure and rotate integrally. The first disk 7 has a diameter larger than that of the rotor shaft 5, and the second disk 8 has a diameter larger than that of the first disk 7. The second disk 8 is positioned at the center of the first disk 7 in the axial direction of the rotor 1. The thickness (axial width) of the first disk 7 is larger than the thickness (axial width) of the second disk 8. The rotor 1 of the present embodiment is a dual-disk rotor having the first disk 7 and the second disk 8.
[0015] The magnetic bearing 2 includes a pair of axial coils 10A, 10B disposed on both sides of the second disk 8, a plurality of radial coils 12A, 12B, 12C, 12D disposed radially outside the axial coils 10A, 10B, and a stator core 15 that houses the axial coils 10A, 10B and the plurality of radial coils 12A, 12B, 12C, 12D. The pair of axial coils 10A, 10B are arranged so as to surround the first disk 7. More specifically, these axial coils 10A, 10B are disposed radially outside the first disk 7 and on both sides of the second disk 8 in the axial direction of the rotor 1. The central axis of the axial coils 10A, 10B coincides with the axis of the rotor 1.
[0016] The plurality of radial coils 12A to 12D surround the pair of axial coils 10A and 10B and are arranged along the outer peripheral surfaces of the axial coils 10A and 10B. As shown in FIG. 3, in the present embodiment, the four radial coils 12A, 12B, 12C, and 12D are arranged at equal intervals along the circumferential direction of the rotor 1. In one embodiment, five or more radial coils may be provided. The central axis of each of the radial coils 12A, 12B, 12C, and 12D is perpendicular to the axis of the rotor 1. Therefore, each of the radial coils 12A, 12B, 12C, and 12D forms a magnetic circuit in a plane perpendicular to the axial direction of the rotor 1.
[0017] The stator core 15 is composed of a magnetic material such as silicon steel. The stator core 15 covers the axial coils 10A and 10B, the plurality of radial coils 12A to 12D, the first disk 7, and the second disk 8. As shown in FIG. 2, the stator core 15 has a pair of first axial stator cores 19A and 19B, a plurality of pairs of second axial stator cores 17A and 17B, and a plurality of radial stator cores 18.
[0018] The pair of first axial stator cores 19A and 19B are located on both sides of the first disk 7 in the axial direction of the rotor 1. More specifically, the first axial stator cores 19A and 19B have first opposing surfaces 19c and 19d that face the both side surfaces 7a and 7b of the first disk 7. The first axial stator cores 19A and 19B extend radially inward from the outer wall portion 21 of the stator core 15.
[0019] A plurality of pairs of second axial stator cores 17A, 17B are provided corresponding to the plurality of radial coils 12A to 12D. In the present embodiment, since four radial coils 12A to 12D are provided, four pairs of second axial stator cores 17A, 17B are provided. In FIG. 2, only two pairs of second axial stator cores 17A, 17B are depicted. Each pair of second axial stator cores 17A, 17B is located on both sides of the second disk 8 and between a pair of axial coils 10A, 10B. More specifically, the second axial stator core 17A is located between the second disk 8 and the axial coil 10A, and the second axial stator core 17B is located between the second disk 8 and the axial coil 10B. The plurality of pairs of second axial stator cores 17A, 17B have second opposing surfaces 17c, 17d facing the both side surfaces 8a, 8b of the second disk 8.
[0020] A plurality of radial stator cores 18 are provided corresponding to the plurality of radial coils 12A to 12D. In the present embodiment, since four radial coils 12A to 12D are provided, four radial stator cores 18 are provided. In FIG. 2, only two radial stator cores 18 are depicted. The plurality of radial stator cores 18 are located radially outside the second disk 8 and the plurality of pairs of second axial stator cores 17A, 17B.
[0021] As shown in FIG. 3, the plurality of radial stator cores 18 surround the second disk 8. Each radial stator core 18 has an inner peripheral surface 18a facing the outer peripheral surface 8c of the second disk 8. The plurality of radial coils 12A to 12D are respectively wound around the plurality of radial stator cores 18. In the present embodiment, the four radial coils 12A to 12D are respectively wound around the four radial stator cores 18.
[0022] As shown in FIG. 2, a plurality of pairs of second axial stator cores 17A and 17B are respectively connected to a plurality of radial stator cores 18, and the plurality of radial stator cores 18 extend radially inward from the outer wall portion 21 of the stator core 15.
[0023] According to the embodiment described with reference to FIGS. 1 to 3, the thickness of the first disk 7 is larger than the thickness of the second disk 8, and the second disk 8 is located at the center of the outer peripheral surface of the first disk 7. With such a configuration, magnetic flux leakage from the radial stator core 18 to the first axial stator cores 19A and 19B can be reduced.
[0024] The embodiment described with reference to FIGS. 1 to 3 has the first opposing surfaces 19c and 19d and the second opposing surfaces 17c and 17d, so the opposing area between the rotor 1 and the stator core 15 increases. Specifically, the magnetic bearing 2 shown in FIGS. 1 to 3 has an opposing area that is more than three times that of the conventional magnetic bearing shown in FIG. 14. Therefore, the magnetic bearing device according to the embodiment described with reference to FIGS. 1 to 3 can achieve a high supporting force (supporting force density).
[0025] The magnetic bearing device includes a plurality of displacement sensors (not shown) for measuring the axial displacement and the radial displacement of the rotor 1. The measured values of the axial displacement and the radial displacement of the rotor 1 are sent to the current controller 3. The current controller 3 controls the currents to be supplied to the axial coils 10A and 10B and the plurality of radial coils 12A to 12D based on the measured values of the axial displacement and the radial displacement of the rotor 1. The rotor 1 is supported non - contact by the magnetic attraction forces generated by the axial coils 10A and 10B and the plurality of radial coils 12A to 12D.
[0026] The current controller 3 includes a storage device 3a storing a program for controlling the position of the rotor 1, an arithmetic unit 3b that executes arithmetic operations according to instructions included in the program, and a power supply 3c that supplies current to a pair of axial coils 10A, 10B and a plurality of radial coils 12A to 12D. The current controller 3 includes at least one computer. The storage device 3a includes a main storage device such as a random access memory (RAM) and auxiliary storage devices such as a hard disk drive (HDD) and a solid state drive (SSD). Examples of the arithmetic unit 3b include a CPU (central processing unit) and a GPU (graphics processing unit). However, as long as the current controller 3 can control the current to be supplied to the pair of axial coils 10A, 10B and the plurality of radial coils 12A to 12D based on the measured values of the axial displacement and the radial displacement of the rotor 1, the specific configuration of the current controller 3 is not limited to these examples.
[0027] FIG. 4 is a perspective view showing another embodiment of the magnetic bearing device, and FIG. 5 is a longitudinal sectional view of the magnetic bearing device shown in FIG. 4. The configuration and operation of this embodiment not particularly described are the same as those of the embodiment described with reference to FIGS. 1 to 3, and thus the overlapping descriptions thereof are omitted. The sectional view shown in FIG. 3 is also applicable to this embodiment shown in FIGS. 4 and 5.
[0028] In addition to the first disk 7 and the second disk 8 described above, the magnetic bearing device further includes a pair of side disks 24A, 24B. The rotor shaft 5, the first disk 7, the second disk 8, and the pair of side disks 24A, 24B are concentric. The rotor shaft 5, the first disk 7, the second disk 8, and the pair of side disks 24A, 24B are integrally configured and rotate integrally.
[0029] The side disks 24A and 24B protrude radially outward from the outer peripheral surface of the first disk 7. The second disk 8 is positioned between the pair of side disks 24A and 24B. In the present embodiment, the side disks 24A and 24B are positioned at both ends of the first disk 7. The rotor 1 of the present embodiment is a multi-disk rotor having the first disk 7, the second disk 8, and the side disks 24A and 24B.
[0030] In one embodiment, each of the side disks 24A and 24B has a diameter larger than that of the second disk 8. Further, in one embodiment, the thickness of each of the side disks 24A and 24B is smaller than the thickness of the second disk 8. The pair of axial coils 10A and 10B and the plurality of radial coils 12A to 12D are positioned between the pair of side disks 24A and 24B. That is, the pair of side disks 24A and 24B are arranged outside the pair of axial coils 10A and 10B and the plurality of radial coils 12A to 12D in the axial direction of the rotor 1.
[0031] The stator core 15 includes a pair of side stator cores 26A and 26B arranged outside the pair of side disks 24A and 24B in the axial direction of the rotor shaft 5. The side stator cores 26A and 26B extend radially inward from the outer wall portion 21 of the stator core 15, and the first axial stator cores 19A and 19B extend radially inward from the side stator cores 26A and 26B. The side stator cores 26A and 26B have third opposing surfaces 26c and 26d that face the outer surfaces 24c and 24d of the side disks 24A and 24B.
[0032] The embodiments described with reference to FIGS. 4 and 5 have the first opposing surfaces 19c and 19d, the second opposing surfaces 17c and 17d, and the third opposing surfaces 26c and 26d, so that the opposing area between the rotor 1 and the stator core 15 is further increased. Specifically, the magnetic bearing 2 shown in FIGS. 4 and 5 has an opposing area that is about seven times that of the conventional magnetic bearing shown in FIG. 14. Therefore, the magnetic bearing device according to the embodiments described with reference to FIGS. 4 and 5 can achieve a higher supporting force (supporting force density).
[0033] FIG. 6 is a graph showing an example of the axial force generated by the magnetic bearing device (hereinafter referred to as Model A) described with reference to FIGS. 1 to 3, the axial force generated by the magnetic bearing device (hereinafter referred to as Model B) described with reference to FIGS. 4 and 5, and the axial force generated by the conventional magnetic bearing (hereinafter referred to as Model C) described with reference to FIG. 14.
[0034] Models A, B, and C were designed so that their outer diameters were the same. Models A, B, and C generated an axial force by passing an electric current through only one of the two axial coils. The current value was a low current of 0 to 0.1 A. As can be seen from FIG. 6, Models A and B can generate a larger axial force with a relatively small current compared to Model C. In addition, Model B can generate a larger axial force than Model A.
[0035] FIG. 7 is a graph showing an example of the radial force generated by Model A, the radial force generated by Model B, and the radial force generated by Model C.
[0036] Models A, B, and C were designed so that their outer diameters were the same. Models A, B, and C generated a radial force by passing an electric current through only one of the four axial coils. The current value was a high current of 0 to 1 A. As can be seen from FIG. 7, Models A and B can generate a larger radial force compared to Model C. In addition, Model B can generate a larger radial force than Model A.
[0037] Next, an embodiment of a novel method of supplying current to the axial coils 10A and 10B and the radial coils 12A to 12D will be described. The following description applies to each of the embodiments described with reference to FIGS. 1 to 5. The supply of current to the axial coils 10A and 10B and the radial coils 12A to 12D is controlled by the current controller 3.
[0038] Referring to FIGS. 8 and 9, an embodiment of a method of energizing to generate an axial magnetic attraction force will be described. The current controller 3 is configured to supply current to one of the axial coils 10A and 10B while supplying current to all of the plurality of radial coils 12A to 12D. In the example shown in FIG. 8, current is passed only through the right axial coil 10A and not through the left axial coil 10B.
[0039] The current controller 3 is configured to supply current of the same magnitude and in the same direction to all of the plurality of radial coils 12A to 12D. In the example shown in FIG. 9, the plurality of radial coils 12A to 12D generate a radially outward force as indicated by the white arrows. Since these radially outward forces have the same magnitude, they cancel each other out.
[0040] When current is supplied to one axial coil 10A while supplying current to the radial coils 12A to 12D, as shown in FIG. 8, magnetization and demagnetization occur on the first opposing surfaces 19c and 19d of the first axial stator cores 19A and 19B and on the side surfaces 7a and 7b of the first disk 7 (see the circles drawn by dotted lines). In the example shown in FIG. 8, the magnetic flux increases between the first opposing surface 19c of the right first axial stator core 19A and the right side surface 7a of the first disk 7, while the magnetic flux decreases between the first opposing surface 19d of the left first axial stator core 19B and the left side surface 7b of the first disk 7. Therefore, a magnetic flux density difference occurs between the left and right of the rotor 1. As a result, in the example shown in FIG. 8, a magnetic attraction force directed to the right is generated as indicated by the white arrow, and the rotor 1 is displaced to the right.
[0041] Although not shown, when generating a magnetic attractive force toward the left side, similarly, the current controller 3 supplies current to only the axial coil 10B on the left side while supplying current to all of the plurality of radial coils 12A to 12D. FIG. 8 shows the magnetic bearing device described with reference to FIGS. 1 to 3, but the magnetic bearing devices described with reference to FIGS. 4 and 5 operate in the same manner.
[0042] FIG. 10 is a graph showing the analysis result of the axial force of the embodiment described with reference to FIGS. 8 and 9. Current was passed through only one axial coil 10A while changing the current from 0 to 0.2 A, and the four radial coils 12A to 12D were energized in four patterns of 0 A, 0.1 A, 0.2 A, and 0.3 A. As can be seen from FIG. 10, the axial force increased as the current flowing through the four radial coils 12A to 12D increased. This is because a larger magnetic flux density difference was generated on the left and right sides of the rotor 1 due to the increase in the current flowing through the four radial coils 12A to 12D.
[0043] Next, with reference to FIGS. 11 and 12, an embodiment of a current application method for generating a radial magnetic attractive force will be described. The current controller 3 is configured to supply current to two radial coils located on opposite sides of the plurality of radial coils 12A to 12D while supplying current to both axial coils 10A and 10B. As shown in FIG. 11, the current controller 3 supplies currents in opposite directions to the axial coils 10A and 10B.
[0044] In the example shown in FIG. 12, the current controller 3 supplies current to two radial coils 12A and 12C located on opposite sides of each other, and does not supply current to the other two radial coils 12B and 12D. The two radial coils 12A and 12C to which current is supplied generate magnetic fluxes in the same direction within the second disk 8. In the example shown in FIG. 11, the two radial coils 12A and 12C generate upward magnetic fluxes within the second disk 8. In addition to energizing one radial coil 12A, by energizing the radial coil 12C on the opposite side so as to generate magnetic fluxes in the same direction, the radial magnetic fluxes are strengthened. At the same time, the two axial coils 10A and 10B are energized so as to form a magnetic circuit symmetric with respect to the second disk 8.
[0045] When current is supplied to two radial coils 12A and 12C located on opposite sides of each other while supplying current to both axial coils 10A and 10B, as shown in FIG. 11, magnetization and demagnetization occur on the opposing surfaces of the two radial stator cores 18 and the second disk 8 (see the circle drawn with a dotted line). In the example shown in FIG. 11, between the upper radial stator core 18 and the second disk 8, the magnetic flux increases, while between the lower radial stator core 18 and the second disk 8, the magnetic flux decreases. Therefore, a magnetic flux density difference occurs above and below the rotor 1. As a result, in the example shown in FIG. 11, an upward magnetic attraction force is generated, and the rotor 1 is displaced upward.
[0046] Although not shown, when generating a downward, rightward, or leftward magnetic attraction force, similarly, the current controller 3 supplies current to two radial coils located on opposite sides of each other while supplying current to both axial coils 10A and 10B. FIG. 11 shows the magnetic bearing device described with reference to FIGS. 1 to 3, but the magnetic bearing device described with reference to FIGS. 4 and 5 operates in the same manner.
[0047] Figure 13 is a graph showing the analysis results of the radial force of the embodiment described with reference to FIGS. 11 and 12. Currents were passed through the two radial coils 12A and 12C while changing the current from 0 to 1 A, and currents were passed through the two axial coils 10A and 10B in three patterns of 0 A, 0.2 A, and 0.4 A. As can be seen from FIG. 13, the radial force increased as the current flowing through the two axial coils 10A and 10B increased. This is because a larger magnetic flux density difference was generated above and below the rotor 1 due to the increase in the current flowing through the two axial coils 10A and 10B.
[0048] The magnetic bearing device of each of the above-described embodiments is a three-degree-of-freedom magnetic bearing device. The energization method described with reference to FIGS. 8 to 13 is suitable for a three-degree-of-freedom magnetic bearing device and can improve the support force density.
[0049] The above-described embodiments are described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention pertains to practice the present invention. Various modifications of the above embodiments can be naturally made by those skilled in the art, and the technical idea of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be construed in the broadest scope in accordance with the technical idea defined by the claims.
Description of Reference Numerals
[0050] 1 Rotor 2 Magnetic bearing 3 Current controller 3a Storage device 3b Arithmetic device 3c Power supply 5 Rotor shaft 7 First disk 7a, 7b Side surfaces of the first disk 8 Second disk 8a, 8b Side surfaces of the second disk 10A, 10B Axial coils 12A, 12B, 12C, 12D Radial coils 15 Stator Core 17A, 17B Second Axial Stator Core 17c, 17d Second Opposite Surface 18 Radial Stator Core 18a Inner Peripheral Surface of Radial Stator Core 19A, 19B First Axial Stator Core 19c, 19d First Opposite Surface 21 Outer Wall Portion 24A, 24B Side Disk 24c, 24d Outer Surface of Side Disk 26A, 26B Side Stator Core 26c, 26d Third Opposite Surface
Claims
1. A rotor shaft, a first disk protruding radially outward from the outer peripheral surface of the rotor shaft, a second disk protruding radially outward from the outer peripheral surface of the first disk, axial coils disposed on both sides of the second disk, a plurality of radial coils disposed radially outside the axial coils, and a stator core that houses the axial coils and the plurality of radial coils, wherein the stator core includes a pair of first axial stator cores located on both sides of the first disk, a plurality of pairs of second axial stator cores located on both sides of the second disk and between the second disk and the axial coils, and a plurality of radial stator cores around which the plurality of radial coils are respectively wound, a magnetic bearing device.
2. The magnetic bearing device according to claim 1, wherein the axial coils surround the periphery of the first disk.
3. The magnetic bearing device according to claim 1, wherein the thickness of the first disk is greater than the thickness of the second disk.
4. The magnetic bearing device according to claim 1, wherein the plurality of radial coils surround the periphery of the axial coils.
5. The magnetic bearing device further includes a pair of side disks protruding radially outward from the outer peripheral surface of the first disk, the second disk is located between the pair of side disks, and the stator core further includes a pair of side stator cores disposed outside the pair of side disks in the axial direction of the rotor shaft, the magnetic bearing device according to claim 1.
6. The magnetic bearing device according to claim 1, further comprising a current controller that controls currents supplied to the axial coils and the plurality of radial coils.
7. The magnetic bearing device according to claim 6, wherein the current controller is configured to supply a current to one of the axial coils disposed on both sides of the second disk while supplying a current to the plurality of radial coils.
8. The magnetic bearing device according to claim 7, wherein the current controller is configured to supply currents of the same magnitude and the same direction to the plurality of radial coils.
9. The magnetic bearing device according to claim 6, wherein the current controller is configured to supply current to two radial coils located on opposite sides of the plurality of radial coils while supplying current to the axial coil.
10. The magnetic bearing device according to claim 9, wherein the current controller is configured to supply current to the two radial coils such that the two radial coils generate magnetic fluxes in the same direction within the second disk.
11. The magnetic bearing device according to claim 9, wherein the current controller is configured to supply currents in opposite directions to the axial coil.