JPH08114226A - Bearing device - Google Patents

Abstract

PURPOSE: To provide a bearing device with less vibration and noise and long life at a low cost, which can support both a radial load and a thrust load. CONSTITUTION: A bearing device is provided with a fluid bearing 13 formed by a permanent magnet magnetized in a radial direction and a shaft 4 consisting of a magnetic substance whose large diameter shaft part 4a is formed on a part facing to the fluid bearing 13, which is provided so that the fluid bearing 13 may be penetrated. A thrust load is supported by a magnetic attraction force acting between the fluid bearing 13 and the large diameter shaft part 4a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing device, and more particularly to a bearing device which can support a radial load and a thrust load by a fluid bearing formed of a permanent magnet.

[0002]

2. Description of the Related Art Conventionally, a bearing for supporting a shaft that rotates at a high speed, such as a shaft of a polygon mirror motor used in a laser printer or a copying machine, is generally disclosed in Japanese Patent Laid-Open No. 4-15615. Rolling bearings such as ball bearings are used, and fluid bearings that perform fluid lubrication by filling a fluid such as lubricating oil between the shaft and the bearing are also widely used. FIG. 3 shows an example in which the ball bearing 2 is used as a bearing that supports the rotating portion of the polygon mirror motor. In the figure, the housing 1 of the polygon mirror motor is mounted inside the main body of a device such as a laser printer or a copying machine. A shaft 4 is rotatably provided by ball bearings 2 and 2 arranged above and below the housing 1. Further, between the upper and lower ball bearings 2 and 2, there is arranged a preload spring 3 for applying a preload in the axial direction in order to suppress rattling of the ball bearings 2 and 2. The preload spring 3 applies a constant pressure between the grooves of the inner and outer races of the ball bearings 2 and the steel balls to suppress the looseness between the inner and outer races and the steel balls. The ball bearings 2 and 2 support both a radial load and a thrust load applied to the shaft.

A polygon mirror (not shown) is attached to the upper end of the shaft 4. The polygon mirror reflects a light beam, such as a laser beam, which transmits image information emitted from a light source, on a large number of reflecting mirror surfaces in the shape of a polygonal column, and scans the surface of a photosensitive drum or the like with the rotation of the reflecting mirror surface. It is used to form a latent image. The shaft 4 has
The magnet 6 is fixed, and a magnet magnetized portion 6a having a large number of magnetic poles is provided on the peripheral portion thereof. On the other hand, a circuit board 9 on which a drive control circuit necessary for rotationally driving a polygon motor is mounted is arranged on the housing 1, and a position detecting element 10 composed of a Hall element or the like is provided on the circuit board 9. ing. The position detection element 10 is provided to detect the rotational position of the rotating body composed of the shaft 4 and the magnet 6. A core 7 made of a laminated steel plate or the like is arranged on the housing 1, and a plurality of coils 8 are wound around the core 7. Core 7
Has a general teeth structure. In the above structure, the magnet 6 fixed to the shaft 4 and rotating and the core 7 fixed to the housing 1 constitute a magnetic circuit. A closed magnetic circuit is formed in the radial gap between the magnetized portion 6 a and the core 7. When a plurality of coils 8 are energized through a drive control circuit provided on the circuit board 9, a drive torque is generated according to the theory of electromagnetism, and the rotating body constituted by the shaft 4 and the magnet 6 is a ball bearing 2.
It is supported by 2 and rotates. The rotational movement of the shaft 4 is obtained by detecting the rotational position of the magnetic poles of the magnetized portion 6a, which is magnetized into a plurality of magnets, by the position detecting element 10 and providing the rotational position detecting signal generated from the position detecting element 10 on the circuit board 9. Input to a drive control element (not shown) composed of a drive circuit such as a plurality of transistors, and the current is supplied only to the coils required for rotational driving among the plurality of coils 8. It

[0004]

In the above-described example, the shaft is supported by the housing by a pair of upper and lower ball bearings. Generally, a ball bearing or the like is mounted on a bearing portion such as a polygon mirror motor which rotates at high speed. When a rolling bearing is used, there is a problem that vibration and noise increase at high speed rotation and the life of the ball bearing is shortened. This is because, due to the number of balls in the ball bearing, vibration of an asynchronous frequency occurs with respect to the rotation of the shaft, and this vibration also causes noise. The vibrations and noises become particularly remarkable at high speed rotation and also affect the life of the ball bearings, so that the wear of the ball bearings progresses over time, and the vibrations and noises tend to increase.

On the other hand, as in the example shown in FIG. 3, a ball bearing is not used for the bearing portion to support the radial load and the thrust load, but the radial load and the thrust load applied to the shaft by using the fluid bearing. Support is also being made. FIG. 4 shows an example thereof, which is disclosed in Japanese Utility Model Laid-Open No. 6-10623. In the figure, the shaft 21 is rotatably supported by a cylindrical bearing body 24 that is magnetized in the axial direction, and the gap between the shaft 21 and the cylindrical bearing body 24 is filled with magnetic fluid. There is. The magnetic fluid is used as a lubricant, and has the property of having magnetism and being attracted to the magnetic poles. Further, two annular members 22 facing each other with the cylindrical bearing body 24 sandwiched from both sides are fixed to the shaft 21. The annular member 22 is magnetized in the axial direction similarly to the cylindrical bearing body 24, and the facing surfaces of the annular member 22 and the cylindrical bearing body 24 are magnetized to have mutually different polarities and are mutually magnetic. It is assembled with a gap 23 in a state where a large repulsive force acts. When the shaft 21 rotates with respect to the cylindrical bearing body 24, its radial load is supported by the cylindrical bearing body 24 via the magnetic fluid filled in the gap 25, and the thrust load is fixed to the shaft 21. The annular member 22 and the cylindrical bearing body 24 are supported in a non-contact manner by the magnetic repulsive force on the opposing surfaces.

In the hydrodynamic bearing having the structure shown in FIG. 4, the shaft 2
In order to receive the thrust load applied to 1, the ring-shaped member 22 is fixed to the shaft 21 with the cylindrical bearing body 24 sandwiched therebetween. Therefore, when replenishing the magnetic fluid used as a lubricant or cleaning the inner peripheral surface of the cylindrical bearing body 24 or the shaft 21, the shaft 21 and the annular member 22 must be disassembled. However, there is a problem that the annular member 22 cannot be disassembled when it is fixed to the shaft 21 by means such as adhesion. Further, in the above bearing structure, the magnetic fluid is used in the cylindrical bearing body 24 and the annular member 22.
2 between the shaft 21 and the cylindrical bearing body 24 due to the magnetic force of
5, a gap 23 between the annular member 22 and the cylindrical bearing body 24
It is designed to be held at. However, the annular member 22 and the cylindrical bearing body 24 are magnetized in the axial direction, and the polarities of the magnetic poles of the annular member 22 and the cylindrical bearing body 24 are the same in the gap 23. Therefore, the attraction force for the magnetic fluid is small, and the gap 2
Since 3 is opened to the outside in the radial direction, there is a problem that when the shaft 21 rotates at a high speed, the magnetic fluid is scattered and lost by the centrifugal force, and the fluid lubrication state cannot be maintained.

[0007]

SUMMARY OF THE INVENTION The present invention solves various problems of the conventional bearing device as described above. A shaft made of a magnetic material and a permanent magnet which is radially magnetized to support a radial load of the shaft. The main object of the present invention is to provide a bearing device that can support both radial load and thrust load, has less vibration and noise, and has low cost and long life by including a hydrodynamic bearing formed of a magnet.

[0008]

In order to achieve the above object, a bearing device of the present invention is provided with a fluid bearing formed by a permanent magnet magnetized in a radial direction and penetrating the fluid bearing. A shaft made of a magnetic material in which a large-diameter shaft portion is formed in a portion corresponding to the fluid bearing, and a thrust load is supported by a magnetic attraction force acting between the fluid bearing and the large-diameter shaft portion. It is the one. in this case,
A plurality of the fluid bearings are arranged in the axial direction, and the shaft has a large-diameter shaft portion formed at a position corresponding to two on both sides of the plurality of fluid bearings, and corresponds to a fluid bearing arranged in the middle. A medium-diameter shaft portion having a diameter smaller than that of the large-diameter shaft portion may be formed at the position. Further, the fluid bearing may have a plurality of magnetized portions formed in the axial direction, and the magnetized directions of adjacent magnetized portions may have opposite polarities. Further, the axial length of the fluid bearing can be configured to be longer than the length of the large diameter shaft portion facing the fluid bearing.
Further, it is preferable to interpose a magnetic lubricating fluid between the shaft and the fluid bearing.

[0009]

The radial load acting on the shaft is supported by the fluid bearing formed by the permanent magnet. On the other hand, when the magnetic attraction force of the hydrodynamic bearing magnetized in the radial direction acts on the large-diameter shaft part formed on the magnetic shaft, when the shaft position is displaced by the thrust load, a restoring force acts on the shaft. Thrust load is supported. Further, by providing a medium-diameter shaft portion having a smaller diameter than the large-diameter shaft portion, a magnetic attraction force from the fluid bearing acts on the medium-diameter shaft portion, and a larger thrust load can be supported. Furthermore, by making the magnetizing directions of the adjacent magnetizing parts of the fluid bearing opposite to each other, a closed magnetic circuit is formed between the corresponding large-diameter shaft part and the medium-diameter shaft part. The suction power increases. Further, by making the axial length of the fluid bearing longer than the length of the corresponding large-diameter shaft portion to increase the magnetic flux concentration, the thrust supporting force can be generated with a small displacement of the shaft in the axial direction. Further, by interposing the magnetic lubricating fluid between the shaft and the fluid bearing, the magnetic attraction force of the fluid bearing prevents the magnetic lubricating fluid from scattering and flowing out.

[0010]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 shows the structure of a motor in which the hydrodynamic bearing device of the present invention is used, which is used for rotationally driving a polygon mirror of a laser printer or the like. A polygon mirror (not shown) is attached to the upper end of the shaft 4 so as to rotate together with the shaft 4 rotatably supported by bearings 13, 13. A magnet 6 is fixed to the shaft 4, and a plurality of magnet magnetizing portions 6 are provided on the outer periphery thereof.
a is formed. On the other hand, the housing is provided with a core 7 made of laminated steel plates or the like, and a plurality of coils 8 are wound around the core 7. The core 7 is arranged such that its peripheral portion faces the magnet magnetized portion 6a. A circuit board 9 on which a drive control circuit necessary for rotationally driving a polygon motor is mounted is arranged on the housing 1, and a rotational position of a rotating body composed of a shaft 4 and a magnet 6 is arranged on the circuit board 9. A position detection element 10 including a Hall element or the like is provided for detection.

The bearings 13, 13 are formed of permanent magnets and are fixed to the housing 1. Bearing 13,
13 are arranged at two positions in the vertical direction, and are arranged so as to surround the circumference of the shaft 4 in an annular shape. The upper and lower bearings 13, 13 are each magnetized in the radial direction, and are also adjacent in the axial direction and magnetized in opposite polarities. That is, in the upper bearing 13, the outer peripheral portion of the upper portion of the bearing 13 is magnetized to the N pole, and the inner peripheral portion facing the shaft 4 is magnetized to the S pole. The outer peripheral portion of the lower portion is magnetized to the S pole, and the inner peripheral portion facing the shaft 4 is magnetized to the N pole. Therefore, in the upper bearing 13, in the inner peripheral portion facing the shaft 4, the upper portion is the S pole and the lower portion is the N pole. Further, in the lower bearing 13, the upper bearing 1
It is magnetized in the same direction as 3. The bearings 13, 13 are fixed by being fitted in the upper and lower expanded portions 1b, 1b formed in the shaft hole 1a provided in the housing 1 with proper shape accuracy and upper and lower assembly accuracy. The shaft 4 is inserted into the upper and lower bearings 13, 13, and the shaft 4 and the bearings 13, 13 are inserted.
The magnetic lubricating fluid 12 is enclosed in the gap between the and.

The lower end of the expanded diameter portion 1b below the shaft hole 1a formed in the housing 1 is closed by a collar 11. Further, the shaft 4 is formed on the large-diameter shaft portion 4a at a position corresponding to the upper and lower bearings 13, 13,
The radial load is supported on the large-diameter shaft portion 4a by the inner circumference of the.

The shaft 4 is formed of a magnetic material such as an iron-based material, and a magnetic attraction force is exerted by a bearing 13 formed of a permanent magnet. Since the bearing 13 is magnetized with its opposite polarities adjacent to each other in the axial direction, a closed magnetic circuit is formed between the bearing 13 and the magnetic attraction force of the bearing 13 acting on the shaft 4, The inner peripheral surface of the bearing 13 acts more strongly than in the case where the inner peripheral surface of the bearing 13 is magnetized to a single pole of N pole or S pole. Further, since the magnetic flux of the bearing 13 is concentrated on the large-diameter shaft portion 4a, the shaft 4 is axially displaced by the thrust load applied from the outside, and the bearing 13 and the large-diameter shaft portion 4 are displaced.
If the position facing "a" shifts to either the upper or lower position, a restoring force to return to the original position is generated. This restoring force serves as a force for supporting the thrust load applied to the shaft 4. In this case, as shown in the embodiment of FIG. 1, the axial length of the bearing 13 is made longer than the axial length of the large diameter shaft portion 4a, so that the magnetic flux of the bearing 13 is large. It is easy to concentrate on the radial shaft portion 4a, and the magnetic attraction force can be increased. this is,
Due to the difference in the axial length between the bearing 13 and the large-diameter shaft portion 4a, the magnetic flux from the bearing 13 to the large-diameter shaft portion 4a is not parallel but oblique, so that the large-diameter shaft portion 4a moves in the axial direction of the bearing 13. When the shaft 4 is displaced in the vertical direction by an external thrust load, a slight displacement balances the magnetic attraction force in the vertical direction. It collapses and a great restoring force acts.
Further, a separator 14 is attached around the expanded diameter portion 1b above the housing 1. The separating plate 14 separates the air flow generated above the bearing 13 by the rotation of the shaft 4 from the bearing 13, and the magnetic lubricating fluid 12 held by the magnetic attraction force in the bearing 13 portion is not scattered to the outside by the air flow. Is provided.

The motor constructed as described above has a plurality of coils 8 through a drive control circuit formed on the circuit board 9.
When a current is applied to the shaft 4, a driving torque is generated in the rotating body constituted by the shaft 4 and the magnet 6, and the shaft 4 is rotationally driven. With respect to the rotational movement of the shaft 4, the rotational position of the magnetic poles of the magnetized portions, which are magnetized into a plurality of magnets, is detected by the position detection element 10, and a rotational position detection signal generated from the position detection element 10 is provided on the circuit board 9. This is performed by inputting the current to a drive control element (not shown) that is provided and supplying current only to the coil necessary for rotational driving among the plurality of coils 8. The magnetic lubricating fluid 12 trapped by the magnetic attraction between the bearing 13 and the large-diameter shaft portion 4a as the shaft 4 rotates is moved by the relative rotational motion between the bearing 13 and the large-diameter shaft portion 4a. A dynamic pressure is generated, and the dynamic load supports the radial load of the shaft 4. Therefore, the shaft 4 has the bearings 13 at the positions corresponding to the upper and lower large-diameter shaft portions 4a.
It is supported by the fluid lubrication state and rotates in a stable state. Further, the thrust load applied to the shaft 4 is the upper and lower bearings 1.
Since it is supported by a magnetic attraction force by 3, the rotation is performed with a gap between the lower end of the shaft 4 and the collar 11 provided on the bottom of the housing 1. That is, the thrust load of the shaft 4 is magnetically supported by the bearing 13 in a non-contact state.

Next, FIG. 2 shows another embodiment of the present invention. In this embodiment, only the structure of the bearing device is different from the embodiment of FIG. Is the same as that of the embodiment shown in FIG. In FIG. 2, the bearings 15, 15, 15 are formed of permanent magnets, and are fitted and fixed in the shaft hole 1 a of the housing 1. Also, the lower end of the housing 1 has a collar 11
Is blocked by. The bearings 15, 15, 15 are arranged adjacent to each other in the vertical direction, and are arranged so as to surround the shaft 4 in an annular shape. Furthermore, the bearings 15, 15,
Each of the magnets 15 is magnetized in the radial direction and adjacent to the axial direction and magnetized in the opposite direction. For example,
The outer peripheral portion of the upper portion of the bearing 15 is magnetized to the N pole, and the inner peripheral portion facing the shaft 4 is magnetized to the S pole. The outer peripheral portion of the lower portion is magnetized to the S pole, and the inner peripheral portion facing the shaft 4 is magnetized to the N pole. Therefore, axis 4
In the inner peripheral portion facing to, the upper part is the S pole and the lower part is the N pole. Since the bearings 15, 15, 15 arranged in the vertical direction of the housing 1 are all magnetized in the same manner,
The two bearings 15 are arranged so that the magnetizing directions alternate in the axial direction, that is, in the vertical direction.

In the case of this embodiment, the bearing 15 of the same type is used.
3 are arranged adjacent to each other vertically, but the three may be integrally formed and magnetized so that the poles alternate with each other as described above.

On the other hand, the shaft 4 is made of a magnetic material such as iron, and two large-diameter shaft portions 4a are formed corresponding to the upper and lower bearings 15 provided in the housing 1.
A medium-diameter shaft portion 4b is formed at an intermediate position between the two large-diameter shaft portions 4a, corresponding to the intermediate bearing 15. The medium-diameter shaft portion 4b has a smaller diameter than the large-diameter shaft portion 4a, and the diameter between the large-diameter shaft portion 4a and the medium-diameter shaft portion 4b is smaller than that of the medium-diameter shaft portion 4b. They are connected by the reduced diameter portion 4c. The axial length of each bearing 15 is set longer than the axial length of the corresponding large diameter shaft portion 4a and medium diameter shaft portion 4b. Each bearing 15, 1
A magnetic lubricating fluid 12 is enclosed in a gap between the shafts 5 and 15 and the shaft 4, and the magnetic lubricating fluid 12 forms a large-diameter shaft portion 4a and a medium-diameter shaft portion 4b formed on the shaft 4, and a bearing corresponding to each of them. Since a closed magnetic circuit is formed between 15 and
It is confined inside the bearing 15 by the magnetic flux concentrated in the gaps between the large-diameter shaft portion 4a and the medium-diameter shaft portion 4b and the corresponding bearings 15.

In the above structure, when the shaft 4 is driven to rotate, the gaps between the upper and lower large-diameter shaft portions 4a formed on the shaft 4 and the corresponding bearings 15 are narrowed. , The magnetic lubricating fluid 12 interposed between the two
A dynamic pressure is generated on the shaft 4, and the radial load acting on the shaft 4 is supported. In this case, since the magnetic lubricating fluid 12 is trapped and trapped in the closed magnetic circuit formed between the bearing 15 and the large-diameter shaft portion 4a, the magnetic lubricating fluid 12 does not scatter to the outside and disappear. The shaft 4 is always rotationally driven in a fluid lubricated state. Since the gap between the intermediate diameter shaft portion 4b and the corresponding intermediate bearing 15 is large, almost no dynamic pressure is generated even when the shaft 4 rotates, and the intermediate bearing 15 does not support the radial load. Therefore, the shaft 4 is separated by 2
Since it is supported at various places, it is supported stably. The axial magnetic attraction acting on the shaft 4 is balanced at the positions where the bearings 15 correspond to the upper and lower large-diameter shaft portions 4a and 4b, respectively, but the thrust load acts from the outside. Then, as soon as it is displaced in the axial direction, the suction force from each bearing 15 acts immediately. As a result, the thrust load that acts on the shaft 4 from the outside is supported by the magnetic attraction forces from the bearings 15 at the three upper and lower locations, and a large thrust load is magnetically supported.

[0019]

As described above, according to the bearing device of the present invention, the thrust load is supported by the magnetic attraction force acting between the fluid bearing and the large-diameter shaft portion of the shaft formed of the magnetic material. Therefore, the vibration and noise are small, the structure of the bearing device can be simplified, and the manufacturing cost can be reduced. In addition, since it is not necessary to arrange a protruding member such as a permanent magnet around the shaft to support the thrust load, the shaft can be easily pulled out from the fluid bearing, and maintenance such as cleaning and lubrication is easy. is there.

Further, a large-diameter shaft portion and a medium-diameter shaft portion having a diameter smaller than that of the large-diameter shaft portion are formed on the shaft, and the magnetic attraction force of the fluid bearing is applied to the large-diameter shaft portion and the medium-diameter shaft portion. It becomes possible to support a larger thrust load. Further, the fluid bearing has a plurality of magnetized portions formed in the axial direction, and the magnetized directions of the adjacent magnetized portions are configured to have opposite polarities, thereby increasing the magnetic attraction force and supporting the thrust load. Can be improved.

Further, by making the axial length of the fluid bearing longer than the length of the large-diameter shaft portion facing the fluid bearing, the magnetic flux is concentrated and a slight axial displacement of the shaft thrusts to obtain a magnetic force. To be Further, by interposing the magnetic lubricating fluid between the shaft and the fluid bearing, the magnetic lubricating fluid holds the magnetic lubricating fluid by the magnetic attraction force of the fluid bearing, and scattering and outflow due to the rotation of the shaft are prevented. The fluid bearing can support the radial load of the shaft in a fluid lubricated state, and a long-life bearing device can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a hydrodynamic bearing device of the present invention.

FIG. 2 is a diagram showing another embodiment of the hydrodynamic bearing device of the present invention.

FIG. 3 is a diagram showing an example of a conventional bearing device.

FIG. 4 is a diagram showing another example of a conventional bearing device.

[Explanation of symbols]

1 housing, 1a shaft hole, 1b expanded diameter part, 4 axis, 4a large diameter shaft part, 4b medium diameter shaft part, 11 collar, 12 magnetic lubricating fluid, 13
・ 15 bearings, 14c reduced diameter part.

Claims (5)

[Claims] 1. A fluid bearing formed by a permanent magnet magnetized in a radial direction, and a magnetic body provided through the fluid bearing and having a large-diameter shaft portion formed in a portion corresponding to the fluid bearing. And a thrust load is supported by a magnetic attraction force acting between the fluid bearing and the large-diameter shaft portion. 2. A plurality of the hydrodynamic bearings are arranged in the axial direction,
The shaft has a large-diameter shaft portion formed at a position corresponding to two on both sides of the plurality of fluid bearings, and has a smaller diameter than the large-diameter shaft portion at a position corresponding to the fluid bearing arranged in the middle. A medium-diameter shaft portion is formed.
Bearing device. 3. The fluid bearing according to claim 1, wherein a plurality of magnetized portions are formed in the axial direction, and the magnetized directions of the adjacent magnetized portions are opposite in polarity to each other. Bearing device. 4. The bearing device according to claim 1, wherein the axial length of the fluid bearing is longer than the length of the large diameter shaft portion facing the fluid bearing. 5. The bearing device according to claim 1 or 2, wherein a magnetic lubricating fluid is interposed between the shaft and the fluid bearing.