JP3608327B2 - Magnetic bearing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic bearing device, and more particularly to a magnetic bearing device for a drive motor that drives an optical deflector used in an electrophotographic apparatus such as a laser beam printer or an electrophotographic copying machine.
[0002]
[Prior art]
In general, an optical scanning device that scans a recording medium as a member to be scanned with a light beam deflects a light beam containing information in a predetermined direction and scans it. An optical deflector in which a mirror is rotated by a drive motor such as a coreless motor is used.
[0003]
That is, it is modulated by an image reading device that scans an image carrier as a member to be scanned with a light beam emitted from a light source such as a laser, or an image signal or a character signal (hereinafter referred to as an image signal). In an image recording apparatus for recording an image by scanning a recording medium with a light beam, an optical deflector in which a polygon mirror is fixed to a drive motor is used as means for scanning the light beam.
[0004]
A conventional example of a magnetic bearing device that attempts to hold a polygon mirror (rotating body) in the axial direction is disclosed in Japanese Patent Application Laid-Open No. 61-32812. As a conventional example of means for detecting the rotational speed of a rotating body, It is disclosed in Kaihei 1-204211, etc. Japanese Patent Laid-Open No. 61-32812 discloses that a permanent magnet is opposed to the rotating side and the fixed side with a gap in the radial direction to obtain an attractive force. An apparatus is disclosed in which a detection signal is obtained by a permanent magnet for detection and a search coil for detecting the number of rotations.
[0005]
Furthermore, another magnetic bearing device (optical deflector) is shown in FIG. Hereinafter, a structure and an effect | action are demonstrated based on FIG. FIG. 9 is a cross-sectional view of a conventional optical deflector.
[0006]
The optical deflector is a coreless coil on a coil substrate 18 disposed on the base member 12 by supporting a rotor 16 provided with a polygon mirror on a fixed shaft 14 erected on the base member 12 on the stator 10 side by a dynamic pressure bearing. A certain drive coil 20 is controlled to be excited and switched, and the rotor 16 is rotated by a magnetic force acting between the main magnet 22 on the rotor 16 side.
[0007]
That is, a fixed shaft 14 is erected at the center portion of the base member 12, and a herringbone groove 24 for forming a dynamic pressure bearing is formed on the outer peripheral surface portion of the fixed shaft 14.
[0008]
A coil substrate 18 is disposed on a plane portion of the base member 12 on the side where the fixed shaft 14 is erected, and a plurality of drive coils 20 are disposed at predetermined positions on the coil substrate 18. A control circuit (not shown) for the drive coil 20 is configured. A hall element 21 as a position detection element of the rotor 16 is fixed on the coil substrate 18 at the center of the drive coil 20, and a plurality of magnetic poles of a main magnet 22, which will be described later, are detected by the hall element 21. The position of is detected.
[0009]
Further, a back yoke 28 for directing magnetic lines of force generated by the drive coil 20 toward the base member 12 toward the rotor 16 side at a corresponding position on the coil substrate 18 opposite to the drive coil 20 (below the drive coil 20). Is placed in a shallow groove 30 drilled on the base member 12.
[0010]
Further, a search coil 26 for detecting the rotational speed as shown in FIG. 10 is formed on the coil substrate 18, and this search coil 26 is disposed so as to face an FG magnet 57 for generating a rotational speed detection pulse, which will be described later. ing.
[0011]
As shown in FIG. 9, a thrust magnet holder 32 is attached on the base member 12. The holder 32 is positioned and arranged 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 adhesion.
[0012]
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 is fixed by rotating the rotating shaft 40 at a high speed. A radial bearing which is a dynamic pressure bearing is configured between the shaft 14 and the rotating shaft 40.
[0013]
A ring-shaped aluminum-made flange 42 is fixed at a predetermined position on the outer periphery of the rotary shaft 40 by a method such as shrink fitting and press-fitting. A mounting surface 46 is formed on the upper surface of the flange 42, and a polygon mirror 48 is fixed on the mounting surface 46 by a fixing spring 50. The mounting surface 46 is machined so as to be perpendicular to the axis of the rotary shaft 40 with high accuracy. The polygon mirror 48 is formed in a polygonal column shape, and its side surface is processed into a mirror surface.
[0014]
Further, a notch portion 42A is formed in a portion of the flange 42 corresponding to the drive coil 20 on the stator 10 side, and the driving main magnet 22 is attached to the notch portion 42A by a method such as press fitting or adhesion. . 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 expanded by one step is formed in a portion near the stator 10 in the central hole portion. Further, the main magnet 22 is magnetized with N poles and S poles so that adjacent sections have different polarities in each of the sections divided into eight equal parts with a central angle of 45 degrees.
[0015]
Further, a lower surface of the flange 42 on the stator 10 side is cut out in an annular shape having a rectangular cross section to form a stepped portion 56, a cylindrical FG magnet 57 is formed in the stepped portion 56, and one end surface thereof is a flat surface of the flange 42. It is attached by a method such as press-fitting or adhesion. In this FG magnet 57, the N pole and the S pole are magnetized so that the adjacent sections have different polarities in each of the sections divided into 12 equal parts with a central angle of 30 degrees.
[0016]
Note that the upper surface of the flange 42 opposite to the stator 10 is cut out in an annular shape having a rectangular cross section to form a groove portion 54, and a balance weight (not shown) for balance adjustment is attached to the groove portion 54.
[0017]
A rotor-side thrust magnet 58 formed in a ring shape is attached to the upper part of the outer peripheral surface of the flange 42 by a method such as press fitting or adhesion.
[0018]
The rotor-side thrust magnet 58 is concentric with the stator-side thrust magnet 38 and is arranged adjacent to each other with a predetermined interval. The outer peripheral surface portion of the rotor-side thrust magnet 58 and the inner peripheral surface portion of the stator-side thrust magnet 38 are magnetized to have different polarities so that an attractive force is exerted, thereby forming a thrust magnetic bearing. This thrust magnetic bearing acts so that the attractive force of 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 causes the entire rotor 16 to float.
[0019]
For this reason, the rotor 16 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. As a result, the drive circuit of the coil substrate 18 is controlled to apply an alternating voltage to the plurality of drive coils 20, and the rotor 16 can be rotated at high speed while being suspended in the air.
[0020]
The rotation control of the rotor 16 is performed by using a fluctuation component of the frequency of the voltage induced in the search coil 26 by the FG magnet 57 during the rotation of the rotor 16 as a detection signal. That is, the rotor 16 is controlled to be constant based on this detection signal.
[0021]
[Problems to be solved by the invention]
By the way, in the above-described conventional example, thrust magnetic bearing means for obtaining an attractive force is provided by making a thrust permanent magnet face the rotor side and the stator side with a gap therebetween. In addition, there is provided a rotor speed detecting means for obtaining a detection signal by a permanent magnet for detecting the rotor speed and a search coil corresponding to the permanent magnet.
[0022]
That is, the thrust magnetic bearing means and the rotor rotation speed detecting means are indispensable means for exerting the function of the optical deflector, but the number of parts is increased due to the necessity of individual permanent magnets. This is not desirable because the vessel becomes large and expensive.
[0023]
An object of the present invention is to provide a magnetic bearing device that is small and inexpensive in consideration of the above-described facts.
[0024]
[Means for Solving the Problems]
The magnetic bearing device according to claim 1 is a magnetic bearing device in which one of a shaft and a sleeve arranged in a housing rotates with respect to the other, and a groove for generating dynamic pressure is formed in at least one of the shaft and the sleeve. A radial air bearing that forms and supports the shaft or the sleeve in the radial direction by dynamic pressure, and a permanent magnet for levitation for levitation of the shaft or the sleeve that is arranged in an annular shape and is magnetized in a plurality of poles. A yoke made of a magnetic material disposed so as to face the outer periphery of the levitation permanent magnet with a gap in the radial direction, and the shaft or sleeve disposed on the yoke corresponding to the levitation permanent magnet A search coil for detecting the number of rotations, and the shaft or the sleeve is not contacted in the axial direction by a magnetic attractive force acting between the levitation permanent magnet and the yoke. Causes supported by the state, 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.
[0025]
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 a magnetic attractive force acting between the yoke of the levitation permanent magnet. Further, during the rotation of the shaft or sleeve, an induced voltage is generated in the search coil due to the leakage magnetic flux of the levitation permanent magnet. The rotational speed of the shaft or sleeve is detected by this induced voltage, and this rotational speed is controlled to be constant.
[0026]
Therefore, in the magnetic bearing device according to claim 1, since one permanent magnet, that is, the permanent magnet for levitation of the rotating body is also used as the magnet of the rotation speed detecting means, the number of magnets constituting the motor can be reduced, The magnetic bearing device is small and inexpensive.
[0027]
A magnetic bearing device according to a second aspect is characterized in that, in the invention according to the first aspect, a polygon mirror having a plurality of reflecting surfaces on the outer periphery is attached to the shaft or the sleeve.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Based on FIGS. 1-8, the optical deflector shown in FIG. 1 is demonstrated as one Embodiment using the magnetic bearing apparatus of this invention. FIG. 1 is a cross-sectional view of an optical deflector according to an embodiment of the present invention.
[0029]
As shown in FIG. 1, the optical deflector is mounted so that a rotor 64 is rotationally driven with respect to a fixed shaft 62 that is shrink-fitted into a housing 61 on the stator 60 side and fixed by a method such as press fitting.
[0030]
(Structure of stator)
A cylindrical fixed shaft 62 erected at the center of the housing 61 in the stator 60 is formed with a groove 66 for forming a dynamic pressure bearing on its outer peripheral surface. The groove 66 may be formed in a sleeve 76, which will be described later, or both the fixed shaft 62 and the sleeve 76. The housing 61 is formed with a circular recess 67 centered on the fixed shaft 62, and the lower portion of the rotor 64 (specifically, the lower half of a levitation permanent magnet 84 described later) is inserted into the recess 67. The
[0031]
On the plane of the housing 61 on the side where the fixed shaft 62 is erected, a control circuit board 68 is fixed as a yoke made of a magnetic body on which electronic components for controlling the rotation of the rotor 64 are mounted. The control circuit board 68 has such a size or magnetic characteristics that the magnetic flux density passing through the control circuit board 68 is not saturated.
[0032]
A plurality (six in this embodiment) of stator coils 70 are arranged at predetermined positions around the rotor 64 on the control circuit board 68 as shown in FIG. On the control circuit board 68, a control circuit (not shown) for the stator coil 70 as a drive coil is configured.
[0033]
As shown in FIG. 1, a hall element 71 as a position detection element of the rotor 64 is fixed on the center of the stator coil 70 on the control circuit board 68, and a plurality of main magnets 82 to be described later are formed by the hall element 71. Are detected, and the position of the rotor 64 is detected. The control circuit board 68 has a hole 68 </ b> A having substantially the same diameter corresponding to the recess 67 of the housing 61.
[0034]
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 the 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 protrudes toward the stator coil 70 in a substantially U shape. In addition, a pair of lead-out portions 72 </ b> A for leading the electromotive force generated in the stator coil 70 is formed at the end of the search coil 72.
[0035]
[Configuration of rotor]
As shown in FIG. 1, a sleeve 76 is provided on the rotor 64 mounted on the stator 60 configured as described above.
[0036]
The sleeve 76 formed in a cylindrical shape is inserted into the fixed shaft 62 with a gap, and when the sleeve 76 is rotated at a high speed, ambient air is taken in between the fixed shaft 62 and the sleeve 76 to generate pressure. A radial bearing, which is a hydrodynamic bearing that is configured to be configured, is configured.
[0037]
A ring-shaped flange 78 is fixed by shrink fitting at a predetermined position on the outer peripheral portion of the sleeve 76. A mirror mounting surface 79 is formed on the upper surface of the flange 78, and a polygon mirror 80 having a reflection surface 80 A on the outer periphery formed on the mirror mounting surface 79 is fixed by a fixing spring 86. Has been. 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.
[0038]
A notch 78C is formed in a portion corresponding to the stator coil 70 on the stator 60 side of the flange 78, and an inner diameter 78C of a main magnet 82 which is a permanent magnet as a rotational drive magnet is formed in the notch 78C. It is fixed with etc. The main magnet 82 has a ring shape as a whole. As shown in FIG. 1, a step opening peripheral portion 82 </ b> A having a diameter larger than the inner diameter portion 78 </ b> C is formed in the central hole portion near the stator 60. Further, the main magnet 82 has N poles and S poles magnetized so that adjacent sections have different polarities in each section divided into eight equal parts at 45 degrees of the central angle.
[0039]
The upper surface of the flange 78 opposite to the stator 60 is cut out in an annular shape having a rectangular cross section to form a groove 78A, and a balance weight (not shown) for balancing is attached to the groove 78A. Further, a stepped portion 78B notched in an annular shape having a rectangular cross section is formed on the lower surface of the flange 78 on the stator 60 side.
[0040]
A magnet 84 as a levitation permanent magnet for levitation of 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 thickness of the magnet 84 in the radial direction is substantially the same as the thickness of the sleeve 76 in the radial direction. The magnet 84 corresponds to the search coil 72 and has an integer multiple or an integer multiple of 1, that is, each segment divided into 12 equal parts at a central angle of 30 degrees so that the adjacent segments in the circumferential direction have different polarities. And the S pole are magnetized, and the N pole and the S pole are magnetized so that the sections adjacent to each other in the radial direction (the outer peripheral surface side and the inner peripheral surface side) are different from each other (FIG. 2). reference).
[0041]
As another example, as shown in FIG. 4, the N pole and the S pole are magnetized so that the adjacent sections in the axial direction (vertical direction) of the magnet 84 have different polarities, and the phases are circumferentially aligned. The N and S poles are magnetized so that adjacent sections have different polarities (see FIG. 2). 4B is a front view of the magnet 84 (viewed from the right side of FIG. 4A).
[0042]
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) (ie, the axis of the magnet 84 and The control circuit board 68 is opposed to the parallel plane of the control circuit board 68 at a right angle. The magnetic flux becomes perpendicular to the surface of the search coil 72 due to the bending phenomenon of leakage magnetic flux from the magnet 84. Therefore, when the magnet 84 rotates, an induced voltage is generated in the search coil 72.
[0043]
In the present embodiment, since the magnetic circuit (magnetic path) L1 (see FIG. 3) is formed by the magnet 84, as shown in FIG. 1, the peripheral edge of the hole 68A of the control circuit board 68 is separated from the gap in the radial direction. A thrust bearing that supports the entire weight of the rotor 64 in the thrust direction is formed by a magnetic attractive force acting between the outer peripheral surfaces of the opposing magnets 84. In addition, the same effect is produced also in the example of FIG.
[0044]
The magnetic flux density increases toward the peripheral edge of the hole 68A of the control circuit board 68. However, the control circuit board 68 has a high saturation magnetic flux density, and the distance between the main magnet 82 and the peripheral edge of the hole 68A is set to an appropriate length. A magnetic circuit sufficient to pass the magnetic flux emitted from the main magnet 82 is formed. Therefore, magnetic circuits for driving the rotor and thrust bearing are formed without affecting the rotation of the rotor 64.
[0045]
In the optical deflector configured as described above, the rotor 64 is supported in the radial direction by a dynamic pressure bearing between the fixed shaft 62 and the sleeve 76, and the magnet 84 and the search coil 72 (formed of a magnetic material). The control circuit board 68) is supported by a thrust bearing.
[0046]
That is, when the rotor 64 is in a suspended state, and the control circuit (not shown) of the control circuit board 68 performs excitation switching to the six stator coils 70 to control application of alternating voltage, the stator coil It rotates at high speed by the rotational torque acting between the main magnet 82 and the main magnet 82.
[0047]
The lines of magnetic force generated in the stator coil 70 toward the housing 61 are directed toward the rotor 16 by the control circuit board 68 formed of a magnetic material. That is, in the present embodiment, the control circuit board 68 functions as a yoke that forms a magnetic circuit for driving the rotor that generates rotational torque in the rotor 64, and is a thrust bearing that forms the magnetic path L1.
[0048]
In the present embodiment, the control circuit board 68 has a relative magnetic permeability (for example, 1000) or a saturation magnetic flux density (for example, 1) as compared with a permanent magnet (relative magnetic permeability 1, saturation magnetic flux density of 0.3 to 0.9 T). .5T) is a high magnetic material, the magnet 84 can be made thicker than the control circuit board 68. 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 this embodiment, since magnetic efficiency is improved, magnetic attractive force is increased.
[0049]
The optical deflector configured as described above is used by being assembled in an optical scanning device as shown in FIG. 7, for example. This optical scanning device is configured so that an optical deflector is attached to the optical box 94 and the polygon mirror 80 faces the space sealed by the dust-proof cover of the optical box 94. A light beam 98A emitted from a light source 96 such as a semiconductor laser or a gas laser is modulated with an image signal or the like by a modulation means (not shown). After this modulation, the light beam 98A passes through the collimator lens 99, enters 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 pass through a lens 100, pass through dustproof glass (not shown), and form an appropriate image on a scanned member 102 such as a reading member or a recording member. Make or sensitize film.
[0050]
That is, as shown in FIG. 8, the light beam 98B reflected by the reflecting surface 80A of the reflecting mirror 80 is deflected in the direction of arrow B as the polygon mirror 80 rotates in the direction of arrow A, and the scanned member 102 is mainly used. While scanning, the sub-scan of the member to be scanned 102 rotated in the direction of arrow C is performed. As a result, a two-dimensional image is written on the scanned member 102.
[0051]
Hereinafter, the operation of the present embodiment will be described.
As shown in FIG. 1, the magnetic attractive 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 the weight in the thrust direction (axial direction) of the sleeve 76 of the rotor 64. It works to lift the whole thing.
[0052]
For this reason, 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. Thus, the drive circuit (not shown) of the control circuit board 68 is controlled to apply an alternating voltage to the stator coil 70, and the rotor 64 is rotated at a high speed in a suspended state.
[0053]
When the magnet 84 is rotated by the rotation of the rotor 64, 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 number of rotations of the rotor 64 is controlled based on this induced voltage signal.
[0054]
Accordingly, the rotation control of the rotor 64 is performed by using a fluctuation component of the frequency of the voltage induced in the search coil 72 by the magnet 84 rotating the rotor 64 as a detection signal.
[0055]
According to the present embodiment, as shown in FIG. 5 and FIG. 6, an induced voltage can be generated in the search coil 72 also by the magnetic path L2 due to the different polarity adjacent to the outer peripheral surface of the magnet 84. The rotation of the rotor 64 can be reliably controlled.
[0056]
In the magnetic bearing device of the present embodiment, since one magnet 84 also serves as a magnet for the rotational speed detection means, the number of magnets as components constituting the motor can be reduced, and the magnetic bearing device becomes small and inexpensive.
[0057]
In this embodiment, an example in which the magnetic bearing is applied to a drive motor that rotates the polygon mirror at a high speed has been described. However, the present invention can also be applied to mechanisms other than rotating the polygon mirror. In the present invention, the method for driving the rotor 64 is not limited to the above-described embodiment.
[0058]
Further, in the present invention, contrary to the present embodiment, the sleeve 76 may be fixed to the housing 61 and the shaft (fixed shaft 62) may be rotated. Further, in the present invention, contrary to the present embodiment, the levitating magnet 84 may be disposed on the control circuit board 68 and the yoke (member made of a magnetic material) may be disposed on the rotor 64.
[0059]
【The invention's effect】
Since the present invention has the above configuration, 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 in the present embodiment.
FIG. 2 is a perspective view showing a relationship between a magnet and a search coil in FIG.
3 is a cross-sectional view showing a relationship between a magnet and a search coil in FIG.
FIGS. 4A and 4B are diagrams showing a relationship between a magnet and a search coil of another example, FIG. 4A is a cross-sectional view thereof, and FIG. 4B is a front view of the magnet.
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.
FIG. 7 is a plan view showing a use state in which the optical deflector of the present embodiment is mounted on an optical scanning device.
8 is a perspective view showing a main part of FIG. 7. FIG.
FIG. 9 is a longitudinal sectional view showing an example of a conventional optical deflector.
10 is a perspective view showing a relationship between an FG magnet and a search coil in FIG. 9. FIG.
[Explanation of symbols]
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 Polyhedral mirror 80A Reflecting surface 82 Main magnet (rotary drive permanent magnet)
84 Magnet (Floating permanent magnet)

Claims (2)

A magnetic bearing device in which one of a shaft or a sleeve arranged in the housing rotates with respect to the other,
A radial air bearing that forms a dynamic pressure generating groove in at least one of the shaft and the sleeve, and supports the shaft or the sleeve in a radial direction by the dynamic pressure;
A permanent magnet for levitation for levitation of the shaft or the sleeve, which is arranged in a ring and is magnetized in a plurality of poles;
A yoke made of a magnetic material arranged to face the outer periphery of the levitation permanent magnet with a gap in the radial direction;
A search coil for detecting the number of rotations of the shaft or the sleeve arranged corresponding to the levitation permanent magnet in the yoke;
The shaft or the sleeve is supported in a non-contact state in the axial direction by a magnetic attractive force acting between the levitation permanent magnet and the yoke, and is generated in the search coil by a leakage magnetic flux of the levitation permanent magnet. A magnetic bearing device that detects the number of rotations of the shaft or the sleeve by an induced voltage. The magnetic bearing device according to claim 1, wherein a polygon mirror having a plurality of reflecting surfaces on an outer periphery thereof is attached to the shaft or the sleeve.

Images