JP2000154822A - Dynamic pressure bearing device and deflecting scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a gall at the time of decrease of rigidity of a bearing due to decrease of viscosity of oil by forming herringbone shaped dynamic pressure generating grooves which consist of a pair of the inclining groove parts on either one of a spindle and a sleeve engaged freely to rotate with each other, and by providing a circumferential groove communicating to inclining groove parts on a central part of the dynamic pressure generating grooves. SOLUTION: A spindle 2 for integratedly rotating with a rotating polygon mirror is rotatively fitted into a sleeve 3, and the sleeve 3 is fitted into a boss part of an outer cylinder. A space of 3 to 10 μm of a bearing is formed between the sleeve 3 and the spindle 2, and oil in the space flows by rotation of the spindle 2 to journal the spindle 2 in a non-contact state in a radial direction by the dynamic pressure. Two herringbone shaped dynamic pressure generating grooves 22b are formed on an outer circumferential surface (an outer diameter part) of the spindle 2. A circumferential groove 31 is formed on a central part of the dynamic pressure generating grooves 22b, and a pair of inclining groove parts arranged above and below which are composed of the herringbone shaped dynamic pressure generating grooves 22b is formed by communicating to the central part intersected with the grooves in a V-shape, and thereby producing a stably annular groove. When the spindle 2 is sopped or rotated at a low speed, and an exothermic action of bearing is generated, the spindle 2 inclines, and then abrasive powders generated by contact with the sleeve 3 are collected in the central part by pumping actions of the grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing device and a deflection scanning device used for an image forming apparatus such as a laser beam printer and a laser facsimile.

[0002]

2. Description of the Related Art A deflection scanning device used in an image forming apparatus such as a laser beam printer or a laser facsimile reflects a light beam such as a laser beam (laser beam) by a rotating polygon mirror rotating at a high speed, and deflects and scans the beam. Then, the obtained scanning light is imaged on a photoreceptor on a rotating drum to form an electrostatic latent image. Next, the electrostatic latent image on the photoreceptor is visualized into a toner image by a developing device, transferred to a recording medium such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording medium ( Print) is performed.

[0003] In recent years, further miniaturization and cost reduction have been demanded for deflection scanning devices such as laser beam printers. In addition, bearings for rotatably supporting a rotating polygon mirror have little rotation fluctuation and low noise. And high rotational accuracy. In order to meet these demands, attention has been paid to a dynamic pressure bearing device that supports a rotating body by dynamic pressure of a fluid.

[0004] In the dynamic bearing device, a dynamic pressure generating groove is formed in at least one of a sleeve and a shaft rotatably fitted to each other, and a fluid in a minute gap between the sleeve and the shaft is pumped by relative motion of the sleeve and the shaft. It is constituted to flow by action and to support an axial load. A motor using such a hydrodynamic bearing device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-180311 using a gas as a working fluid, and disclosed in Japanese Patent Application Laid-Open No. Hei 2-180311 using a liquid such as oil. 1
No. 54808, for example.

FIG. 5 shows a main part of a conventional deflection scanning apparatus, which comprises a shaft 102 which rotates integrally with a rotary polygon mirror 101, and a sleeve 103 in which the shaft 102 is rotatably fitted. The sleeve 103 is fitted to the boss of the outer cylinder 104, and the outer cylinder 104 is supported upright on the fixed plate 105. The fixed plate 105 includes a thrust plate 106 that supports the lower end of the shaft 102 in the thrust direction.
A flange 107 is fixed to an upper end portion of the reference numeral 02. The rotary polygon mirror 101 is supported on the upper surface of the flange 107 and is configured to rotate with the shaft 102.

A yoke 109 for holding a rotor magnet 108 is fixed to a lower surface of an outer peripheral portion of the flange 107, and the rotor magnet 108 faces a stator coil 110 fixed to an outer peripheral surface of a boss portion of the outer cylinder 104. It is arranged to be. When the stator coil 110 is excited by a drive current supplied from a drive circuit (not shown), the rotor magnet 108 rotates at high speed together with the shaft 102 and the rotating polygon mirror 101.

[0007] The sleeve 103 forms a fluid film between the shaft 102 and the shaft 102 by rotation of the shaft 102, and constitutes a dynamic pressure bearing device that rotatably supports the shaft 102 in a non-contact manner by the dynamic pressure of the fluid film. On the outer peripheral surface of the shaft 102, the first dynamic pressure generating grooves 1 are sequentially spaced upward from the lower end of the shaft 102.
02a, a second dynamic pressure generating groove 102b, and a spiral lubricating groove 102c for guiding a working fluid (oil) are formed. Further, a groove (not shown) constituting a dynamic pressure thrust bearing is provided on a portion of the upper surface of the thrust plate 106 facing the lower end of the shaft 102.

[0008] With the rotation of the shaft 102, oil is sucked into the center of the dynamic pressure generating grooves 102a and 102b to generate a high pressure region. The shaft 102 and the sleeve 103 are supported in a radially non-contact state by the high pressure region.
Because of this non-contact rotation, rolling bearings can be obtained in addition to excellent bearing characteristics such as low noise and high rotational accuracy compared to, for example, sliding bearings with metal contact. There is an advantage that size and cost can be reduced as compared with the above.

While the shaft 102 rotates, the sleeve 103 is maintained in a non-contact state by the dynamic pressure of the fluid film as described above. However, when the motor is started or stopped, sufficient dynamic pressure is not generated. The sleeve 103 and the shaft 102 come into contact and wear. In order to reduce such wear, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 0858, there has been developed a device in which the shape of the herringbone-shaped dynamic pressure generating groove is devised so that the working fluid is held at the central portion as much as possible.

[0010]

However, according to the above-mentioned prior art, when the working fluid is oil, not only during the low-speed rotation such as when the dynamic pressure bearing is stopped or started, but also when the working fluid is oil, the heat generated by the bearing at the high-speed rotation is generated. A decrease in oil viscosity causes a decrease in bearing rigidity, and the shaft is inclined and comes into contact with the sleeve. Particularly, in a motor for rotating a rotary polygon mirror such as a laser beam printer, the starting and stopping are repeated frequently, so that the wear of the bearing progresses each time, and the abrasion powder generated by the abrasion is reduced to a herringbone-shaped dynamic pressure generating groove. Gather at the central portion of the surface of the substrate, where an agglomerate of wear powder is formed.

If the size of the agglomerates of the abrasion powder is larger than the minute gap between the shaft and the sleeve, the galling of the bearing is caused. Further, in the configuration described in JP-A-6-280858, when the working fluid is air, a wear reduction effect cannot be expected, and once wear powder is formed, a herringbone-shaped dynamic force is generated as in a conventional bearing. There is a problem that an adhesive is formed at the center of the pressure generating groove and eventually causes a bearing galling.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is intended for use in low-speed rotation such as when the motor is stopped or started, or in high-speed rotation when the working fluid is oil. When bearing rigidity decreases due to oil viscosity decrease due to bearing heat generation, even if the shaft tilts and comes into contact with the sleeve to generate abrasion powder, inexpensive to effectively prevent bearing galling etc. and maintain bearing performance It is an object of the present invention to provide a dynamic pressure bearing device and a deflection scanning device excellent in long-term stability.

[0013]

In order to achieve the above object, a dynamic pressure bearing device according to the present invention has a shaft and a sleeve rotatably fitted to each other, and at least one of the shaft and the sleeve. Is provided with a herringbone-shaped dynamic pressure generating groove composed of a pair of inclined grooves, and a circumferential groove communicating with each inclined groove is provided at a central portion of the herringbone-shaped dynamic pressure generating groove. Features.

An annular land is provided between a pair of inclined grooves of the herringbone-shaped dynamic pressure generating groove, and a pair of circumferential grooves communicating with each inclined groove are provided at both ends of the annular land. May be.

Preferably, the depth of the circumferential groove is substantially equal to the depth of each inclined groove.

[0016]

[Function] Even when the motor is rotating at a low speed, such as when the motor is stopped or started, or during a high-speed rotation, the bearing rigidity is reduced due to a decrease in the viscosity of oil or the like that has been heated due to heat generation of the bearing, causing the shaft to tilt, Contact with sleeve. When the sleeve and the shaft come into contact with each other and rotate as described above, abrasion powder is generated, and if these become large-diameter cohesive bodies, they cause galling of the bearing. Therefore, a circumferential groove is provided in a central portion of the dynamic pressure generating groove where the wear powder gathers, and the bearing gap in this portion is locally enlarged to prevent the adhesion of the wear powder.

Further, even if the abrasion powder adheres, no bearing galling occurs if the outer diameter of the adhered body is smaller than the bearing gap in the circumferential groove.

An inexpensive hydrodynamic bearing device that effectively avoids galling of the bearing and maintains stable bearing performance for a long period of time by simply forming a simple groove in the center of the herringbone-shaped hydrodynamic groove. realizable.

By using such a dynamic pressure bearing device for the bearing of a rotary polygon mirror, it is possible to contribute to lowering the cost and improving long-term stability of the deflection scanning device.

[0020]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a main part of a deflection scanning apparatus according to one embodiment. This comprises a rotating polygon mirror 1 having a reflecting surface 1a, a shaft 2 rotating integrally with the rotating polygon mirror 1, and a bearing unit (dynamic fluid bearing) provided with a sleeve 3 for rotatably fitting the shaft. The sleeve 3 is fitted to the boss of the outer cylinder 4, and the fixed plate 5 has a thrust plate 6 that supports the lower end 2 a of the shaft 2 in the thrust direction. A flange 7 is fitted to the upper end of the shaft 2, the rotary polygon mirror 1 is mounted on the upper surface of the flange 7, and is integrated with the flange 7 by an elastic pressing mechanism 8 including an elastic ring 8a, a holding ring 8b, and a C ring 8c. And are configured to rotate with the shaft 2.

A yoke 9a for holding a rotor magnet 9 is fixed to a lower surface of an outer peripheral portion of the flange 7, and the rotor magnet 9 faces a stator coil 10 fixed to an outer peripheral surface of a boss portion of the outer cylinder 4. Thus, a motor as a driving unit is configured. When the stator coil 10 is excited by a drive current supplied from a drive circuit (not shown), the rotor magnet 9 rotates at high speed together with the shaft 2 and the rotary polygon mirror 1.

The gap size between the sleeve 3 and the shaft 2 is 3 to
A bearing gap A of 10 μm is formed, and is filled with oil as a working fluid. The rotation of the shaft 2 causes the oil in the bearing gap A to flow, and the dynamic pressure supports the shaft 2 in the radial direction in a non-contact manner. On the outer peripheral surface (outer diameter portion) of the shaft 2,
Two herringbone-shaped dynamic pressure generating grooves 2b are formed. The lower end 2a of the shaft 2 facing the upper surface of the thrust plate 6 is spherical, and forms a pivot bearing together with the thrust plate 6.

The gap size of the bearing gap A between the shaft 2 and the sleeve 3 is about 3 to 10 μm as described above, and the depth of the dynamic pressure generating groove 2b is equal to or smaller than the gap size of the bearing gap. Generally, it is generally slightly larger (see FIG. 2).

A circumferential groove 11 is provided at the center of each herringbone-shaped dynamic pressure generating groove 2b. The circumferential groove 11 is
As shown in FIG. 1B in an enlarged manner, an annular groove is formed at a central portion where a pair of upper and lower inclined grooves constituting each herringbone-shaped dynamic pressure generating groove 2b intersect with each other. is there.

When the shaft 2 is stopped or rotating at a low speed, or when the working fluid is oil, when the bearing stiffness is reduced due to a decrease in oil viscosity due to heat generation of the bearing at a high rotation speed, the shaft 2 is tilted, and the abrasion powder is generated due to contact with the sleeve 3. Occurs. Abrasion powder generated by such bearing contact is collected at the center by the pumping action of the herringbone-shaped dynamic pressure generating groove 2b.

When a durability test in which the rotation and stop of the bearing were repeated was performed, the particle size of the initially generated wear powder was 0.1%.
If the particle size does not grow large due to adhesion, there is no problem in bearing characteristics except for a slight increase in bearing loss. However, for example, when the working fluid is air or the like, especially in a high-humidity environment, adhesion of wear powder occurs due to dew condensation due to pressure increase in the herringbone-shaped dynamic pressure generating groove, and the working fluid is oil. In such a case, the oil itself becomes a medium, and gradually forms a large agglomerate of wear powder.

Here, if there is no circumferential groove as in the conventional example, and if the cross section also has the shape shown in FIG. 2 at the center of the dynamic pressure generating groove, there is undulation of the pressure distribution in the circumferential direction. The abrasion powder is frequently mixed, and the adhesion proceeds particularly in the vicinity of the boundary between the land portion and the groove of the dynamic pressure generating groove 2b, and if the size of the adhered body becomes larger than the bearing gap, the galling of the bearing is caused.

The circumferential groove 11 provided at the center of the dynamic pressure generating groove 2b is for increasing the gap size of a portion where the wear powder gathers to prevent the adhesion of the wear powder. More specifically, at the central portion of the dynamic pressure generating groove 2b, the substantial gap size is the sum of the bearing gap and the depth of the circumferential groove 11, and the pressure distribution in the circumferential direction is also eliminated. Not only is it difficult to occur, but even if an agglomerate of abrasion powder larger than the bearing gap is generated, if the size is smaller than the sum of the bearing gap and the depth of the circumferential groove 11, the galling of the bearing may occur. Absent.

According to the present embodiment, the bearing can be effectively prevented from galling, etc., and stable bearing performance can be maintained for a long period of time by simply performing simple groove machining at the center of the herringbone-shaped dynamic pressure generating groove. An inexpensive hydrodynamic bearing device to be maintained can be realized.

By using such a dynamic pressure bearing device,
This can contribute to lowering the cost of the deflection scanning device and improving long-term stability.

The method of forming a herringbone-shaped dynamic pressure generating groove is as follows: when forming the groove on the outer diameter side of the shaft as in this embodiment, by etching or printing, and when forming the groove on the inner diameter side of the sleeve. Is generally performed by plastic working using the method disclosed in, for example, JP-A-54-84155. If the circumferential groove has a depth substantially equal to that of the herringbone-shaped dynamic pressure generating groove, the circumferential groove can be processed in the same step as the dynamic pressure generating groove by using the above method, and there is almost no increase in cost.

FIG. 3 shows a modification. As for the shape of the herringbone-shaped dynamic pressure generating groove, the shape of the "L" shape in which the inclined grooves intersect at the center as in the apparatus of FIG. 1 does not intersect with the inclined groove at the center as shown in FIG. There is a "C" shape.

In the case of the "C" shape, respective circumferential grooves 31 are provided at both ends of the center annular land portion 22c of each dynamic pressure generating groove 22b, and the circumferential grooves 31 are provided with respect to each dynamic pressure generating groove 22b. A pair of grooves 31 is provided. When the working fluid is air or the like, the viscosity is small and it is difficult to secure the bearing rigidity. Therefore, a “C” -shaped groove having higher bearing rigidity than the “C” shape is often used.

However, since the "C" shape is generally superior in terms of stability, care must be taken when using a "C" shaped dynamic pressure generating groove. For example,
If the circumferential groove 31 is not divided into two but one as shown in FIG. 3, a large air pocket is formed at the center of the bearing, which causes unstable vibration.

Therefore, if a pair of circumferential grooves are provided at both ends of the center annular land portion of each herringbone-shaped dynamic pressure generating groove as in this modification, a large bearing rigidity can be obtained without impairing the stability of the bearing. Can be secured.

In the description so far, a herringbone-shaped dynamic pressure generating groove is formed on the outer diameter side of the shaft, and the dynamic pressure bearing is of a type in which the shaft rotates. A herringbone-shaped dynamic pressure generating groove formed on the inner diameter side of the sleeve to rotate the shaft or the sleeve is also applicable.

FIG. 4 shows the entire deflection scanning device, which is a light source 5 for generating a light beam (light flux) such as a laser beam.
1 and a cylindrical lens 51a for linearly condensing the light beam on the reflection surface 1a of the rotary polygon mirror 1, and deflects and scans the light beam by the rotation of the rotary polygon mirror 1.
An image is formed on a photoreceptor 53 on a rotating drum via an image forming lens system 52 as image forming means. The imaging lens system 52 has a spherical lens 52a, a toric lens 52b, and the like.
So-called fθ for correcting the scanning speed of the point image formed on the image No. 3
Has functions.

When the rotary polygon mirror 1 is rotated by the motor, its reflection surface 1a rotates at a constant speed around the axis of the rotary polygon mirror 1. Generated from the light source 51 as described above,
The angle between the optical path of the light beam condensed by the cylindrical lens 51a and the normal to the reflecting surface 1a of the rotating polygon mirror 1, that is, the angle of incidence of the light beam on the reflecting surface 1a, changes with time as the rotating polygon mirror 1 rotates. And the reflection angle also changes, so that the point image formed by condensing the light beam on the photoconductor 53 moves (scans) in the axial direction (main scanning direction) of the rotating drum.

The imaging lens system 52 focuses the light beam reflected by the rotary polygon mirror 1 on the photosensitive member 53 into a point image having a predetermined spot shape, and scans the point image in the main scanning direction. Is designed to keep the speed constant.

The point image formed on the photoreceptor 53 is formed by the main scanning by the rotation of the rotary polygon mirror 1 and the sub-scanning by the rotation of the rotating drum having the photoreceptor 53 around its axis. Form a latent image.

Around the photosensitive member 53, a charging device for uniformly charging the surface of the photosensitive member 53, and a charging device for visualizing an electrostatic latent image formed on the surface of the photosensitive member 53 into a toner image. A developing device, a transfer device (not shown) for transferring the toner image to recording paper, and the like are arranged, and recording information by a light beam generated from the light source 51 is printed on recording paper or the like.

The detection mirror 54 reflects the light beam on the upstream side in the main scanning direction from the optical path of the light beam incident on the recording information write start position on the surface of the photoreceptor 53, and receives a light receiving element 55 having a photodiode or the like. To the light receiving surface of The light receiving element 55 outputs a scanning start signal for detecting a scanning start position (write start position) when the light receiving surface is irradiated with the light beam.

The light source 51 generates a light beam corresponding to a signal given from a processing circuit for processing information from a host computer. The signal given to the light source 51 corresponds to information to be written on the photoconductor 53, and the processing circuit represents information corresponding to one scanning line which is a locus formed by a point image formed on the surface of the photoconductor 53. The signal is given to the light source 51 as one unit. This information signal is transmitted in synchronization with a scanning start signal given from the light receiving element 55.

The rotary polygon mirror 1, the imaging lens system 52 and the like are housed in an optical box 50, and the light source 51 and the like are mounted on the side wall of the optical box 50. After assembling the rotary polygon mirror 1 and the imaging lens system 52 into the optical box 50, a lid (not shown) is attached to the upper opening of the optical box 50.

[0046]

Since the present invention is configured as described above, the following effects can be obtained.

Even when the shaft and the sleeve come into contact with each other and rotate during stop, low-speed rotation, or high-speed rotation, it is possible to effectively prevent occurrence of bearing galling and the like. As a result, a high-performance hydrodynamic bearing device having an extremely wide application range from low-speed driving to high-speed driving, and being inexpensive and having excellent long-term stability can be realized.

By using such a dynamic pressure bearing device for the bearing of a rotary polygon mirror, it is possible to greatly contribute to higher performance and lower cost of the deflection scanning device.

[Brief description of the drawings]

1A and 1B show a deflection scanning device according to an embodiment, wherein FIG. 1A is a schematic cross-sectional view thereof, and FIG. 1B is an enlarged view showing a shaft and a part of a sleeve.

FIG. 2 is a sectional view showing a fitted state of a shaft and a sleeve.

FIG. 3 is an enlarged view showing a part of a modification in an enlarged manner.

FIG. 4 is a diagram illustrating the entire deflection scanning device.

FIG. 5 is a schematic sectional view showing one conventional example.

[Explanation of symbols]

 Reference Signs List 1 rotating polygon mirror 2 shaft 2b, 22b herringbone-shaped dynamic pressure generating groove 3 sleeve 4 outer cylinder 5 fixing plate 6 thrust plate 9 rotor magnet 10 stator coil 11, 31 circumferential groove

Claims (4)

[Claims] A shaft and a sleeve which are rotatably fitted to each other, and at least one of the shaft and the sleeve has a herringbone-shaped dynamic pressure generating groove comprising a pair of inclined grooves; A hydrodynamic bearing device, wherein a circumferential groove communicating with each inclined groove portion is provided at a central portion of the herringbone-shaped dynamic pressure generating groove. 2. An annular land is provided between a pair of inclined grooves of a herringbone-shaped dynamic pressure generating groove, and a pair of circumferential grooves communicating with each inclined groove are provided at both ends of the annular land. The dynamic pressure bearing device according to claim 1, wherein the dynamic pressure bearing device is provided. 3. The hydrodynamic bearing device according to claim 1, wherein the depth of the circumferential groove is substantially equal to the depth of each inclined groove portion. 4. A deflection scanning device comprising a rotary polygon mirror rotatably supported by the dynamic pressure bearing device according to claim 1, and an image forming means for forming an image of the scanning light on a photosensitive member. .