JPH10220474A - Magnetic bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing device small as well as inexpensive by reducing the number of parts. SOLUTION: This magnetic bearing device has a floating magnet 84 mounted on a control circuit board 68 of magnetic substance so as to be faced to the periphery of the board 68 at a radial gap, and a search coil for detecting the number of revolutions of a rotor 64 is laid at such a position as corresponding to the magnet 84 of the board 68. Also, a sleeve 70 (rotor 64) is axially held in a non-contact state, due to magnetic attraction acting across the circuit board 68 and the magnet 84. Furthermore, induced voltage is generated in the search coil 72, due to the leakage flux of the magnet 84 during the rotation of the rotor 64. The number of revolutions of the rotor 64 is detected via the induced voltage, and controlled at a constant value. According to this construction, the single magnet 84 functions as a magnet in common as a means for detecting the number of revolutions, and the number of magnets as components of a motor can be reduced. At the same time, the magnetic bearing device becomes small as well as inexpensive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing device, and more particularly to a magnetic bearing device of a drive motor for driving an optical deflector used in an electrophotographic apparatus such as a laser beam printer, an electrophotographic copying machine or the like. .

[0002]

2. Description of the Related Art In general, an optical scanning device that scans a light beam on a recording medium as a member to be scanned is provided with, for example, a large number of reflecting surfaces in order to deflect and scan the light beam containing information in a predetermined direction. An optical deflector is used in which a polygon mirror formed on the outer periphery is rotated by a drive motor such as a coreless motor.

That is, an image reading device that scans an image carrier as a scanned member with a light beam emitted from a light source such as a laser to read the image, or an image signal or a character signal (hereinafter, referred to as an image signal). In an image recording apparatus that records an image by scanning a recording medium with a modulated light beam,
As a means for scanning the light beam, an optical deflector having a polygon mirror fixed to a drive motor is used.

A conventional example of a magnetic bearing device for holding a polygon mirror (rotating body) in the axial direction is disclosed in Japanese Patent Application Laid-Open No. 61-328.
12 and the like, and a conventional example of a means for detecting the number of revolutions of a rotating body is disclosed in Japanese Patent Application Laid-Open No. 1-2042112. Japanese Patent Application Laid-Open No. 61-32812 discloses an apparatus in which a permanent magnet is opposed to a rotating side and a fixed side with a radial gap therebetween to obtain an attractive force.
Japanese Patent Application Publication No. 2042041 discloses a method in which a detection signal is obtained by a permanent magnet for detecting the rotation speed and a search coil for detecting the rotation speed.

FIG. 9 shows another magnetic bearing device (optical deflector). Hereinafter, the configuration and operation will be described with reference to FIG. FIG. 9 is a sectional view of a conventional optical deflector.

The optical deflector comprises a rotor 16 having a polygonal mirror provided on a fixed shaft 14 erected on a base member 12 on the side of the stator 10.
Is supported by a dynamic pressure bearing, and a drive coil 2 which is a coreless coil on a coil substrate 18 disposed on the base member 12.
The excitation switching control is performed on 0, and the rotor 16 is rotated by a magnetic force acting between the main magnet 22 and the rotor 16.

That is, a fixed shaft 14 is provided upright at the center of the base member 12, and a herringbone groove 24 for forming a dynamic pressure bearing is formed on the outer peripheral surface of the fixed shaft 14.

A coil substrate 18 is disposed on a plane portion of the base member 12 on which the fixed shaft 14 is erected, and a plurality of drive coils 20 are disposed on the coil substrate 18 at predetermined positions. In addition, a control circuit (not shown) for the drive coil 20 is configured. A Hall element 21 as a position detecting element of the rotor 16 is fixed on the center of the drive coil 20 on the coil substrate 18, and the Hall element 21 detects a plurality of magnetic poles of a main magnet 22, which will be described later. Is detected.

At a corresponding position on the opposite side of the coil substrate 18 from the drive coil 20 (below the drive coil 20), a magnetic field line generated by the drive coil 20 and directed toward the base member 12 is directed toward the rotor 16. The back yoke 28 is placed and arranged in a shallow groove 30 formed on the base member 12.

Further, a search coil 26 for detecting the number of revolutions is formed on the coil substrate 18 as shown in FIG.
The search coil 26 is disposed so as to face an FG magnet 57 for generating a rotation number detection pulse, which will be described later.

As shown in FIG. 9, a thrust magnet holder 32 is mounted on the base member 12. The holder 32 is positioned at a predetermined position on the base member 12 by a fastening member (not shown). A stator-side thrust magnet 38 formed in a ring shape having a rectangular cross section is attached to the upper portion of the holder 32 by a method such as press fitting or bonding.

The rotating shaft 40 of the rotor 16 mounted on the stator 10 configured as described above is formed in a hollow cylindrical shape, is inserted through the fixed shaft 14 of the stator 10, and
0 is rotated at a high speed, so that the fixed shaft 14 and the rotating shaft 4 are rotated.
0 to form a radial bearing as a dynamic pressure bearing.

A ring-shaped flange 42 made of aluminum is shrink-fitted at a predetermined position on the outer peripheral portion of the rotating shaft 40.
It is fixed by a method such as press fitting. This flange 42
Has a mounting surface 46 formed on its upper surface, and a polygon mirror 48 is fixed on the mounting surface 46 by a fixing spring 50. The mounting surface 46 is machined to be perpendicular to the axis of the rotating shaft 40 with high precision. The polygon mirror 48 is formed in a polygonal column shape, and the side surface portion is machined into a mirror surface.

A cut-out portion 42A is formed in a portion of the flange 42 corresponding to the drive coil 20 on the stator 10 side, and the main drive magnet 22 is attached to this cut-out portion 42A by press-fitting, bonding, or the like. Have been. The main magnet 22 has a ring shape as a whole, and a step opening peripheral portion 52 having an opening whose inner diameter is increased by one step is formed in a portion near the stator 10 in the center hole. The main magnet 22 is magnetized with N poles and S poles in each of the sections divided into eight equal parts each having a central angle of 45 degrees such that adjacent sections have different polarities.

The stator 10 in the flange 42
The lower surface of the side is cut out in an annular shape having a rectangular cross section to form a stepped portion 56, and a cylindrical FG magnet 57 is
It is attached by a method such as press-fitting or bonding so that one end surface thereof is attached to the flat surface of the flange 42. The FG magnet 57 is divided into 12 sections each having a central angle of 30 degrees.
The N pole and the S pole are magnetized so that adjacent sections have different poles.

The stator 10 on the flange 42
The upper surface on the opposite side is cut out in an annular shape with a rectangular cross section to form a groove portion 54, and a balancing weight (not shown) for balance adjustment is attached to the groove portion 54.

A rotor-side thrust magnet 58 formed in a ring shape is attached to the upper portion of the outer peripheral surface of the flange 42 by a method such as press fitting or bonding.

This rotor-side thrust magnet 58 is
It is concentric with the stator-side thrust magnet 38 and is disposed adjacent to the thrust magnet 38 at a predetermined interval. The outer peripheral surface of the rotor-side thrust magnet 58 and the inner peripheral surface of the stator-side thrust magnet 38 are mutually magnetized to have different polarities so that an attractive force is exerted, thereby forming a thrust magnetic bearing. In this thrust magnetic bearing, the attraction force exerted by the two magnets 38 and 58 overcomes the load in the thrust direction (axial direction) on the rotating shaft 40 of the rotor 16 and acts so that the entire rotor 16 floats.

For this reason, the rotor 16 is supported in the thrust direction by the thrust magnetic bearing and in the radial direction (radiation direction) by the dynamic pressure bearing.
As a result, the drive circuit of the coil substrate 18 controls the application of the alternating voltage to the plurality of drive coils 20, thereby enabling the rotor 16 to rotate at high speed while floating in the air.

The rotation of the rotor 16 is controlled by the rotor 1
Search coil 2 by FG magnet 57 rotating 6 times
6 is performed by using a fluctuation component of the frequency of the voltage induced in 6 as a detection signal. That is, the rotor 16 is controlled to be constant based on the detection signal.

[0021]

By the way, in the above-mentioned prior art, a thrust magnetic bearing means is provided on the rotor side and the stator side for obtaining an attractive force by opposing a permanent magnet for thrust with a gap therebetween. Further, there is provided a rotor rotation speed detecting means for obtaining a detection signal by a permanent magnet for detecting the rotation speed of the rotor and a search coil corresponding thereto.

That is, the above-mentioned thrust magnetic bearing means and rotor rotation speed detecting means are indispensable means for exerting the function of the optical deflector, but the number of parts is increased because individual permanent magnets are required. This increases the size of the optical deflector and increases the cost, which is not desirable.

An object of the present invention is to provide a small and inexpensive magnetic bearing device in which the number of parts is reduced in consideration of the above fact.

[0024]

According to a first aspect of the present invention, there is provided a magnetic bearing device in which one of a shaft and a sleeve disposed in a housing rotates with respect to the other. A groove for dynamic pressure generation is formed on one side, and a radial air bearing that supports the shaft or the sleeve in the radial direction by dynamic pressure, and the shaft or the sleeve that is arranged in a ring shape and is magnetized to a plurality of poles. A floating permanent magnet for floating, a yoke made of a magnetic material disposed so as to face the outer periphery of the floating permanent magnet with a radial gap therebetween, and the yoke corresponds to the floating permanent magnet. A search coil for detecting the number of revolutions of the shaft or the sleeve, which is disposed at a predetermined position, and the shaft or the shaft is actuated by a magnetic attraction force acting between the floating magnet and the yoke. Causes supported in a state of non-contact the sleeve in the axial direction, and detects the rotational speed of the shaft or the sleeve with the induced voltage generated in the search coil by the leakage flux of the floating permanent magnet.

In the magnetic bearing device according to the first aspect, the shaft or the sleeve is supported in a non-contact state in the axial direction by magnetic attraction acting between the yoke of the floating permanent magnet and the yoke. Further, during rotation of the shaft or the sleeve, an induced voltage is generated in the search coil by the leakage magnetic flux of the floating permanent magnet. The rotation speed of the shaft or the sleeve is detected based on the induced voltage, and the rotation speed is controlled to be constant.

Therefore, in the magnetic bearing device according to the first aspect, since one permanent magnet, that is, the floating permanent magnet of the rotating body also serves as the magnet of the rotation speed detecting means, the magnet as a component constituting the motor is used. The magnetic bearing device can be reduced in size and inexpensive.

According to a second aspect of the present invention, there is provided the magnetic bearing device according to the first aspect, wherein a polygon mirror having a plurality of reflection surfaces on an outer periphery is attached to the shaft or the sleeve.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 8, an optical deflector shown in FIG. 1 will be described as an embodiment using a magnetic bearing device of the present invention. FIG. 1 is a sectional view of an optical deflector according to an embodiment of the present invention.

As shown in FIG. 1, the optical deflector is mounted so that a rotor 64 is driven to rotate on a fixed shaft 62 which is shrink-fitted into a housing 61 on the stator 60 side and fixed by a method such as press fitting. ing.

(Structure of Stator) A cylindrical fixed shaft 6 erected at the center of the housing 61 of the stator 60.
2 has a groove 6 on its outer peripheral surface for forming a dynamic pressure bearing.
6 are formed. The groove 66 may be formed in a sleeve 76 described later, or in both the fixed shaft 62 and the sleeve 76. The housing 61 has a circular recess 67 centered on the fixed shaft 62.
The lower portion of the rotor 64 (specifically, the lower half of the floating permanent magnet 84 described later) is inserted into the portion 7.

A control circuit board 68 as a yoke made of a magnetic material on which electronic components for controlling the rotation of the rotor 64 are mounted is fixed on a plane of the housing 61 on which the fixed shaft 62 is erected. . The control circuit board 6
Numeral 8 has such a size or magnetic characteristics that the magnetic flux density passing therethrough is not saturated.

As shown in FIG. 2, a plurality of (six in this embodiment) stator coils 70 are arranged at predetermined positions around the rotor 64 on the control circuit board 68.
A control circuit (not shown) for the stator coil 70 as a drive coil is formed on the control circuit board 68.

As shown in FIG. 1, the control circuit board 6
8, a Hall element 71 as a position detecting element of the rotor 64 is fixed to the center of the stator coil 70. The Hall element 71 detects a plurality of magnetic poles of a main magnet 82 described later, and detects the position of the rotor 64. Is done.
Further, the control circuit board 68 includes a recess 6 of the housing 61.
A hole 68A having substantially the same diameter is formed in correspondence with.

A search coil 72 for detecting the number of revolutions as shown in FIG. 2 is formed on the control circuit board 68 by etching, and this search coil 72 is disposed along the periphery of the hole 68A. That is, the search coil 72 has a loop shape as a whole, and a portion corresponding to the stator coil 70 projects in a substantially U-shape toward the stator coil 70. Further, a pair of deriving portions 72A for deriving an electromotive force generated in the stator coil 70 is provided at an end of the search coil 72.
Are formed.

[Structure of rotor] As shown in FIG. 1, a rotor 64 mounted on the stator 60 constructed as described above is used.
Is provided with a sleeve 76.

The cylindrical sleeve 76 is inserted through the fixed shaft 62 with a gap provided therebetween. When the sleeve 76 is rotated at a high speed, ambient air is taken in between the fixed shaft 62 and the sleeve 76. A radial bearing, which is a dynamic pressure bearing for generating pressure, is configured.

A ring-shaped flange 78 is fixed at a predetermined position on the outer peripheral portion of the sleeve 76 by shrink fitting. A mirror mounting surface 79 is formed on the upper surface of the flange 78, and the reflecting surface 8 on the outer periphery is formed on the mirror mounting surface 79.
A polygon mirror (polygon mirror) 80 on which 0A is formed is fixed by a fixing spring 86. The mirror mounting surface 79 is machined so as to be perpendicular to the axis of the sleeve 76 with high accuracy. The polygon mirror 80 is formed in a polygonal column shape, and its reflection surface 80A is processed into a mirror surface.

A notch 78C is formed in a portion of the flange 78 corresponding to the stator coil 70 on the stator 60 side. The notch 78C has an inner diameter 78C of a main magnet 82 which is a permanent magnet as a rotation driving magnet. Are fixed with an adhesive or the like. The main magnet 82 has a ring shape as a whole. As shown in FIG. 1, a step opening peripheral portion 82A having a diameter larger than the inner diameter portion 78C is formed in a central hole near the stator 60 as shown in FIG. In the main magnet 82, N poles and S poles are magnetized so that adjacent sections have different polarities in each section divided into eight equal parts each having a central angle of 45 degrees.

The stator 60 at the flange 78
The upper surface on the opposite side to the groove 78A is cut out in an annular shape having a rectangular cross section.
A balance weight (not shown) for balance adjustment is attached to the groove 78A. On the lower surface of the flange 78 on the side of the stator 60, there is formed a stepped portion 78B which is cut out in a ring shape with a rectangular cross section.

A magnet 84 as a floating permanent magnet for floating the cylindrical rotor 64 is fixed with an adhesive or the like so that its upper surface is attached to the lower surface of the sleeve 76. The radial thickness of the magnet 84 is substantially the same as the radial thickness of the sleeve 76. The magnet 84 has an N pole corresponding to the search coil 72 such that the circumferentially adjacent section has a different polarity from each section obtained by dividing the number into integer multiples or integer multiples of 1, that is, 12 equal parts at a central angle of 30 degrees. And S
The poles are magnetized, and the N pole and the S pole are magnetized so that the radially adjacent sections (outer peripheral side and inner peripheral side) have different poles (see FIG. 2). .

As another example, as shown in FIG. 4, the N pole and the S pole are magnetized so that sections adjacent to each other in the axial direction (vertical direction) of the magnet 84 have different polarities.
The N pole and the S pole are magnetized so that sections adjacent in the circumferential direction have different poles (see FIG. 2). FIG. 4B is a front view of the magnet 84 (view from the right side of FIG. 4A).

The outer peripheral surface of the magnet 84 and the inner peripheral edge of the hole 68A of the control circuit board 68 are parallel to each other with a gap in the radial direction (for example, 0.25 mm to 1.0 mm) (that is, the magnet 84 is not closed). The shaft core and the parallel surface of the control circuit board 68 are perpendicular to each other). And
Due to the bending phenomenon of the magnetic flux leakage from the magnet 84,
This magnetic flux is orthogonal to the plane of the search coil 72.
Therefore, when the magnet 84 rotates, the search coil 7
2, an induced voltage is generated.

In this embodiment, since the magnetic circuit (magnetic path) L1 (see FIG. 3) is formed by the magnet 84, as shown in FIG. 1, the periphery of the hole 68A of the control circuit board 68 and the gap are formed in the radial direction. Magnet 8 opposed to each other
The magnetic attraction force acting between the outer peripheral surface of the rotor 6 and the rotor 6
A thrust bearing for supporting the total weight in the thrust direction of No. 4 is formed. Note that the same operation and effect are also obtained in the example of FIG.

Although the magnetic flux density becomes higher toward the periphery of the hole 68A of the control circuit board 68, the control circuit board 68 has a high saturation magnetic flux density and the main magnet 82 and the hole 68A
By setting the distance from the peripheral edge to an appropriate length, a magnetic circuit sufficient to pass the magnetic flux from the main magnet 82 is formed. Therefore, magnetic circuits for driving the rotor and for the thrust bearing are formed without affecting the rotation of the rotor 64.

In the optical deflector configured as described above, the rotor 64 is radially supported by a dynamic pressure bearing between the fixed shaft 62 and the sleeve 76, and the magnet 84
And a search coil 72 (control circuit board 68 formed of a magnetic material).

That is, when the rotor 64 is suspended in the air and the excitation is switched to the six stator coils 70 by the control circuit (not shown) of the control circuit board 68 so that the alternating voltage is applied. , Stator coil 70
It rotates at a high speed due to the rotational torque acting between it and the main magnet 82.

The lines of magnetic force generated by the stator coil 70 toward the housing 61 are directed toward the rotor 16 by a control circuit board 68 formed of a magnetic material. That is, in the present embodiment, the control circuit board 68 functions as a yoke forming a magnetic circuit for driving the rotor that generates a rotational torque on the rotor 64, and serves as a thrust bearing that forms the magnetic path L1.

In this embodiment, the control circuit board 68 is made of a permanent magnet (relative magnetic permeability 1, saturated magnetic flux density 0.3 to 0.9).
Since the magnetic material has a higher relative magnetic permeability (for example, 1000) and a higher saturation magnetic flux density (for example, 1.5 T) than that of T), the thickness of the magnet 84 is made larger than the thickness of the control circuit board 68. be able to. That is, the axial length of the magnet 84 magnetized in the radial direction for holding the sleeve 76 in the axial direction is longer than the axial length of the control circuit board 68 forming the magnetic path L1 (see FIG. 3). it can. Therefore, in the present embodiment, the magnetic efficiency is enhanced, and the magnetic attraction force is enhanced.

The optical deflector configured as described above is used, for example, by being assembled into an optical scanning device as shown in FIG. This optical scanning device is configured such that an optical deflector is attached to an optical box 94, and a polygon mirror 80 faces a space enclosed by a dustproof cover of the optical box 94. Then, a light source 96 such as a semiconductor laser or a gas laser is used.
The light beam 98A emitted from is modulated by an image signal or the like by modulation means (not shown). After this modulation, the light beam 98A passes through the collimator lens 99 and is incident on the polygon mirror 80 rotated in the direction of arrow A by the drive motor, and the light beam 98B scanned (scanned) by the polygon mirror 80 forms an image. An electrostatic latent image formed by a commonly used xerographic technique is configured to transmit through a lens 100, transmit through a dustproof glass (not shown), and form an appropriate image on a scanned member 102 such as a reading member or a recording member. Make
Alternatively, the film is exposed.

That is, as shown in FIG. 8, the light beam 98B reflected by the reflecting surface 80A of the reflecting mirror 80 is
The scanning member 102 is deflected in the direction of arrow B along with the rotation in the direction of arrow A to perform main scanning of the scanning member 102, and performs sub-scanning of the scanning member 102 to rotate in the direction of arrow C. As a result, a two-dimensional image is written on the scanned member 102.

Hereinafter, the operation of the present embodiment will be described. As shown in FIG. 1, the magnetic attraction force acting between the outer peripheral surface of the magnet 84 and the peripheral edge of the hole 68 </ b> A of the control circuit board 68 overcomes its own weight in the thrust direction (axial direction) of the sleeve 76 of the rotor 64, and Acts to lift the whole.

Therefore, the rotor 64 is supported in the thrust direction by the thrust magnetic bearing, and is supported in the radial direction (radiation direction) by the dynamic pressure bearing.
Thereby, the driving circuit (not shown) of the control circuit board 68
Control to apply an alternating voltage to the stator coil 70, and the rotor 64 is rotated at a high speed while floating in the air.

The rotation of the rotor 64 causes the magnet 84 to rotate.
Rotates, the magnetic flux (leakage magnetic flux) forming the magnetic path L1 crosses the search coil 72, and the magnetic poles of the magnetic flux alternate. Therefore, an induced voltage corresponding to the number of magnetizations of the magnet 84 is generated in the search coil 72, and the rotation speed of the rotor 64 is controlled based on the signal of the induced voltage.

Accordingly, the rotation of the rotor 64 is controlled by the search coil 72 by the magnet 84 while the rotor 64 is rotating.
This is performed by using, as a detection signal, a fluctuation component of the frequency of the voltage induced in the device.

According to the present embodiment, FIGS.
As shown in (5), the induced voltage can be generated in the search coil 72 also by the magnetic path L2 formed by the different poles adjacent to each other on the outer peripheral surface of the magnet 84, and the rotation of the rotor 64 can be more reliably controlled.

In the magnetic bearing device of the present embodiment, one magnet 84 also serves as the magnet of the rotation speed detecting means.
The number of magnets as components constituting the motor can be reduced, and the magnetic bearing device can be reduced in size and cost.

In this embodiment, an example is shown in which the magnetic bearing is applied to a drive motor for rotating the polygon mirror at high speed. However, the present invention can be applied to a mechanism other than rotating the polygon mirror. Further, in the present invention, the driving method of the rotor 64 is not limited to the above embodiment.

Further, in the present invention, the sleeve 76 may be fixed to the housing 61 and the shaft (fixed shaft 62) may be rotated, contrary to the present embodiment. In the present invention, contrary to the present embodiment, the floating magnet 84 may be arranged on the control circuit board 68, and the yoke (a member made of a magnetic material) may be arranged on the rotor 64.

[0059]

Since the present invention has the above-described structure, the number of parts can be reduced, and a small and inexpensive magnetic bearing device can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an optical deflector according to an embodiment.

FIG. 2 is a perspective view showing a relationship between a magnet and a search coil in FIG. 1;

FIG. 3 is a sectional view showing a relationship between a magnet and a search coil in FIG. 1;

FIG. 4 is a diagram showing a relationship between a magnet and a search coil in another example, FIG. 4A is a cross-sectional view thereof, and FIG. 4B is a front view of the magnet.

FIG. 5 is a perspective view showing a relationship between a magnet and a search coil in FIG. 1;

FIG. 6 is a perspective view showing a relationship between a magnet and a search coil in FIG. 1;

FIG. 7 is a plan view showing a use state in which the optical deflector of the embodiment is mounted on an optical scanning device.

FIG. 8 is a perspective view showing a main part of FIG. 7;

FIG. 9 is a longitudinal sectional view showing an example of a conventional optical deflector.

FIG. 10 is a perspective view illustrating a relationship between the FG magnet and a search coil in FIG. 9;

[Explanation of symbols]

 Reference Signs List 60 Stator 61 Housing 62 Fixed shaft 64 Rotor 66 Groove 68 Control circuit board (yoke) 70 Stator coil (Drive coil) 72 Search coil 76 Sleeve 80 Polygon mirror 80A Reflection surface 82 Main magnet (Rotary drive permanent magnet) 84 Magnet (Floating) Permanent magnet)

Claims (2)

[Claims] 1. A magnetic bearing device in which one of a shaft and a sleeve disposed in a housing rotates with respect to the other, wherein a groove for generating a dynamic pressure is formed in at least one of the shaft and the sleeve. A radial air bearing for supporting the shaft or the sleeve in a radial direction by means of: a floating permanent magnet for floating the shaft or the sleeve which is annularly arranged and magnetized to a plurality of poles; and a floating permanent magnet. A yoke made of a magnetic material disposed so as to be opposed to the outer periphery of the magnet with a radial gap therebetween, and for detecting the rotation speed of the shaft or the sleeve disposed on the yoke corresponding to the floating permanent magnet. And supporting the shaft or the sleeve in a non-contact state in the axial direction by a magnetic attraction force acting between the floating magnet and the yoke of the permanent magnet for floating. It causes a magnetic bearing device characterized by detecting the rotational speed of the shaft or the sleeve with the induced voltage generated in the search coil by the leakage flux of the floating permanent magnet. 2. The magnetic bearing device according to claim 1, wherein a polygon mirror having a plurality of reflection surfaces on an outer periphery is attached to the shaft or the sleeve.