JPH10111469A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the ununiformity of dynamic pressure of an air bearing for supporting a rotating polygon mirror. SOLUTION: A rotary sleeve 3 integrated with a rotating polygon mirror 1 rotates in a non-contact state by the dynamic pressure of an air film formed between the sleeve and a fixed shaft 2. Nine linear grooves 21-29 extending in the axial direction are formed on the outer peripheral surface of the fixed shaft, since the peak of dynamic pressure dispersively appears in the vicinities of the respective linear grooves 21-29, there is no fear of generation of the ununiformity of dynamic pressure even when the roundness of the fixed shaft is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 7 illustrates a general scanning optical device used in an image forming apparatus such as a laser beam printer or a laser facsimile.
The light beam L ₀ generated from ₀ is condensed linearly on the reflecting surface of the rotating polygon mirror 101 by the cylindrical lens 51, and the light beam L ₀ is deflected and scanned by the rotation of the rotating polygon mirror 101, and is rotated via the imaging lens system 52. An image is formed on the photosensitive member on the drum. The imaging lens system 52 includes a spherical lens 52a, a toric lens 52b, and the like, and has a function of correcting distortion of a point image formed on the photoconductor. A part of the light beam that has been deflected and scanned is introduced into the light receiving end of the optical fiber 54 by the reflection mirror 53, converted into a scanning start signal, and transmitted to the light source unit 50.

As shown in FIG. 6, a driving section of the rotary polygon mirror 101 integrates a flange member 103a with a rotary sleeve 103 fitted on a fixed shaft 102, and fixes a rotor magnet 104 to the flange member 103a. Pressing spring 10
5, the motor substrate 107 is supported by a motor housing 106 to which the fixed shaft 102 is fixed while being pressed against the flange member 103a and integrally connected to the flange member 103a.
, The rotor magnet 104 and the rotary polygon mirror 101 are integrally rotated.

The rotating sleeve 103 forms an air film between itself and the fixed shaft 102 by its rotation, and forms an air bearing which rotates without contact with the fixed shaft 102. Rotating sleeve 10
The first permanent magnet 109a is fixed to the lower end of the third permanent magnet 109a. The permanent magnet 109a faces the second permanent magnet 109b integrated with the motor housing 106.
A thrust bearing for supporting the lower end of the rotary sleeve 103 in a non-contact manner with respect to the motor housing 106 is formed by the magnetic repulsion acting between 9a and 109b.

The rotating polygon mirror 101 is connected to a flange member 103a.
The pressing spring 105 is a dish-shaped spring assembled to the side surface of the rotating sleeve 103, the inner peripheral edge of which is locked in the annular groove of the rotating sleeve 103, and the outer peripheral edge thereof is pressed against the upper surface of the rotating polygon mirror 101. Is done.

The opening end of the rotating sleeve 103 is closed by a lid member 103b, and an air reservoir 110 is formed at the upper end of the fixed shaft 102. When the position of the rotating sleeve 103 in the axial direction with respect to the fixed shaft 102 changes, the air in the air pool 110 is pressurized or decompressed, and a force acts to return the rotating sleeve 103 to the original position. By the function of such an air damper, displacement of the rotating sleeve 103 in the axial direction can be prevented, and the rotating polygon mirror 101 can be stably rotated.

[0007]

However, according to the above-mentioned prior art, the above-mentioned air bearing keeps both members out of contact by the dynamic pressure of an air film formed between the rotating sleeve and the fixed shaft. However, there is an unsolved problem that the dynamic pressure of the air film is not stable, and the rotating sleeve comes into contact with the fixed shaft to easily cause galling and wear.

In order to stabilize the dynamic pressure of the air bearing, a dynamic pressure generating groove such as a herringbone groove is provided on the inner surface of the rotating sleeve or the outer peripheral surface of the fixed shaft to promote the flow of air in the bearing gap. Is effective, but the process of forming the herringbone groove or the like into a fixed shaft or a rotating sleeve is complicated and the processing cost is high.

Further, instead of a herringbone groove having a complicated shape or the like, the outer peripheral surface of the fixed shaft is provided at equal intervals in the circumferential direction.
A device provided with individual straight grooves and a band-shaped flat portion has been developed. Since it is only necessary to machine three straight grooves or band-shaped flat portions in the axial direction of the fixed shaft by a known machining method such as cutting, there is no possibility that machining costs are increased as in the case of a herringbone groove. Each straight groove is formed by cutting a predetermined portion of the cylindrical surface of the fixed shaft in a band shape in the axial direction, and if the amount of cutting is reduced, it is substantially composed of one or a plurality of single planes. It becomes a band-shaped plane portion.

However, when the three linear grooves and the like are formed on the outer peripheral surface of the fixed shaft as described above, when the accuracy of the shape such as the roundness of the fixed shaft is low, remarkable movement is caused by the arrangement position of the linear grooves. A pressure distribution occurs. As a result, there is an inconvenience that the required number of revolutions for obtaining stable bearing performance is not constant.

In general, it is known that the lower the number of rotations required for obtaining a predetermined bearing performance, the more stable the bearing performance and the longer the life of the air bearing.

The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and an air bearing for rotatably supporting a rotary polygon mirror has stable bearing performance, excellent durability, and is inexpensive. It is an object of the present invention to provide a scanning optical device.

[0013]

In order to achieve the above object, a scanning optical device according to the present invention comprises: an air bearing comprising a shaft member and a sleeve member which are fitted to each other and are relatively rotatable; A rotating polygon mirror integrally connected to the shaft member or the sleeve member; and driving means for rotating the rotating polygon mirror, wherein the shaft member has at least nine linear movements at equal intervals in a circumferential direction. It is characterized by having a pressure generating groove.

[0014]

[Function] Because the linear dynamic pressure generating groove only needs to cut off the outer peripheral surface of the shaft member linearly in the axial direction to form a linear groove or a band-shaped flat portion composed of at least one single plane. ,
The processing is simple, and there is no possibility that the processing cost will rise as in the case of a herringbone groove. When nine or more such linear dynamic pressure generating grooves are provided at equal intervals in the circumferential direction of the shaft member, the roundness of the shaft member is low, and for example, even if the cross section is elliptical, the shaft member has A substantially uniform dynamic pressure can be generated in the circumferential direction.

As a result, the bearing performance of the air bearing is stabilized,
The number of rotations required to keep the shaft member and the sleeve member out of contact is also reduced, and the life of the air bearing is extended.

Thus, the rotation performance of the rotary polygon mirror of the scanning optical device can be improved, and the life of the scanning optical device can be greatly extended.

[0017]

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

FIG. 1 shows a main part of a scanning optical device according to an embodiment, which is a reflecting surface 1 for reflecting a light beam.
a rotary polygon mirror 1 provided with a rotating shaft 3 as a sleeve member is fitted to a fixed shaft 2 as a shaft member, and a rotor is fitted to a flange member 4 provided integrally therewith. The rotary polygon mirror 1 is pressed against the flange member 4 by the holding spring 6 with the magnet 5 fixed thereto, and the fixed shaft 2 is fixed.
A motor substrate 7a is supported on a motor housing 7 on which is fixed, and a stator 8 is erected on the motor substrate 7a. The rotor magnet 5 and the stator 8 constitute a motor which is a driving means for rotating the rotary polygon mirror 1, and a stator When the magnet 8 is excited, the rotor magnet 5 and the rotary polygon mirror 1 are integrally rotated.

The rotary sleeve 3 forms an air film between itself and the fixed shaft 2 by its rotation, and constitutes a radial air bearing which rotates without contact with the fixed shaft 2. A first permanent magnet 9a is fixed to a lower end of the rotating sleeve 3, and a lower surface of the permanent magnet 9a faces an upper surface of a second permanent magnet 9b fixed to the motor housing 7.

The outer peripheral surface of the first permanent magnet 9a faces the inner peripheral surface of the third permanent magnet 9c fixed to the motor housing 7. First and second permanent magnets 9a, 9b
The thrust bearing is magnetized so that the magnetic poles are opposite to each other in the axial direction of the rotating sleeve 3, and the lower end of the rotating sleeve 3 is supported in a non-contact manner with respect to the motor housing 7 by the magnetic repulsion of the two. Is configured. Third permanent magnet 9
c is magnetized in the same direction as the first permanent magnet 9a, and serves to apply a preload to the thrust bearing to stabilize the position of the rotary sleeve 3 in the axial direction.

In other words, the rotary polygon mirror 1 is provided with a magnetic repulsive force acting between the first and second permanent magnets 9a, 9b and the first,
The third permanent magnets 9a and 9c are stably supported at a predetermined height in a non-contact manner by an axial urging force acting between the third permanent magnets 9a and 9c.

The open end of the rotating sleeve 3 is closed by a lid member 10 to form an air reservoir 10a at the upper end of the fixed shaft 2. When the position of the rotating sleeve 3 in the axial direction with respect to the fixed shaft 2 changes, the air in the air pool 10a is pressurized or decompressed, and a force acts to return the rotating sleeve 3 to the original position. The function of the air damper prevents the axial displacement of the rotary sleeve 3 and allows the rotary polygon mirror 1 to rotate stably.

On the outer peripheral surface of the fixed shaft 2, there are nine linear grooves 21 to 29, which are nine linear dynamic pressure generating grooves for stabilizing the dynamic pressure of the air film formed between the fixed shaft 2 and the rotating sleeve 3. Is formed. These are arranged at equal intervals in the circumferential direction of the fixed shaft 2 as shown in FIG.
As shown in FIG. 2, is constituted by three single planes 30a to 30c obtained by cutting the cylindrical surface of the fixed shaft 2 in a band shape in the axial direction with a predetermined width.

In general, the fixed shaft 2 and the rotary sleeve 3 are made of a ceramic material such as high-strength silicon nitride (Si ₃ N ₄ ) in order to reduce galling due to friction between the two and intrusion of dust and the like. The flange member 4 is made of a metal such as aluminum or brass, and the rotating sleeve 3 is formed by shrink fitting.
The end face of the rotor magnet 5 is abutted against the lower surface of the flange portion of the flange member 4, and an adhesive is interposed between the outer peripheral surface of the cylindrical portion of the flange member 4 and the inner peripheral surface of the rotor magnet 5. It is adhered to the flange member 4.

The lid member 10 is made of a metal such as aluminum or stainless steel or resin, and is fixed to the upper end of the rotary sleeve 3 by a known method such as bonding.

The fixed shaft 2 is made of a ceramic material as described above. Therefore, the workability is low and it is difficult to machine a complicated dynamic pressure generating groove such as a herringbone groove on the outer peripheral surface thereof. Since the grooves 21 to 29 are obtained by simply cutting the cylindrical surface of the fixed shaft 2 in a band shape in the axial direction, there is no possibility that the processing cost is significantly increased unlike a herringbone groove or the like.

In this embodiment, straight grooves 21 to 2 which are easy to process are used.
9 are arranged on the outer peripheral surface of the fixed shaft 2 so that the fixed shaft 2
Even if there is some variation in the shape accuracy (roundness, etc.) of the bearing, the dynamic pressure distribution of the air film is prevented from becoming extremely uneven, and stable bearing performance is obtained at a low rotation speed. It was done. As a result, the rotating performance of the rotating polygon mirror is improved, the life of the bearing portion is extended, and the scanning optical device can greatly contribute to lower cost and higher performance.

The number of linear grooves is not limited to nine, but may be any number as long as it is nine or more.

The substantial depth of each straight groove is 0.02.
0 mm or less, and the width thereof is desirably an outer peripheral dimension corresponding to a range of the central angle of the fixed shaft of 3 to 20 °.

The reason why at least nine straight grooves are required is as follows.

When the roundness of the fixed shaft 2 is high and the dimension of the bearing gap forming the air film between the fixed shaft 2 and the rotary sleeve 3 is uniform in the circumferential direction, as shown in FIG. dynamic pressure distribution has a peak P ₁ to P ₉ of the same height in the vicinity of the straight grooves 21 and 22. With such a uniform dynamic pressure distribution, the number of rotations required to support the fixed shaft 2 and the rotary sleeve 3 in a non-contact manner can be small, and the bearing performance is extremely stable.

However, as shown in FIG. 4, the fixed shaft 2 has a low roundness and its cross section is shifted from the first straight groove 21 by a central angle of 30 °, and has an ellipse having a long axis 0-0. In the case of the shape, the size of the bearing gap on the major axis 0-0 is small and the dimension of the bearing gap on the axis orthogonal to the major axis 0-0 is large, so that the rotating sleeve 3, that is, the rotating polygon mirror 1 is time-consuming. When rotating in the direction, the dynamic pressure peaks P _{7 to} P ₉ gradually increase from the clockwise upstream toward the first linear groove 21, and the dynamic pressure peaks toward the sixth linear groove 26. P _{3 to} P ₅ gradually increase. Thus, each straight groove 21
Although the dynamic pressure peaks P _{1 to} P _{9 in} the vicinity of 29 to ２９29 tend to gradually increase and decrease, since the nine linear grooves 21 to 29 are uniformly distributed in the circumferential direction of the fixed shaft 2, the dynamic pressure The non-uniform distribution is distributed in the vicinity of each of the straight grooves 21 to 29, and is substantially balanced on the same diameter. As a result, the bearing performance is stable as compared with the case where the number of linear grooves is small, for example, three, and the number of rotations required to keep the fixed shaft 2 and the rotating sleeve 3 in non-contact can be reduced.

If the number of the linear grooves is nine or less, for example, three, as shown in FIG. 5, the vicinity of the first linear groove 121 disposed near the major axis 0-0 of the fixed shaft 120 will be described. large dynamic pressure peak P ₁₁ is generated, the downstream side in the rotational direction of the second linear groove 122 from the third linear peak P ₁₂ of these near the dynamic pressure over the groove 123, P ₁₃ changes greatly. If there is such a significant non-uniformity of the dynamic pressure, the bearing performance is not easily stabilized, and the number of rotations required to keep the fixed shaft 120 and the rotating sleeve 130 out of contact is greatly increased.

According to the experiment, when the cross section of the fixed shaft is elliptical and the roundness is 0.8 μm, if the nine straight grooves are provided, the fixed shaft and the rotating sleeve are completely kept in non-contact. The required rotation speed is 1,000 rpm, but if the number of linear grooves is three, the rotation sleeve cannot be rotated stably without contact unless the rotation speed is 10,000 rpm. It is known.

The air bearing according to the present embodiment is obtained by integrally connecting a rotary polygon mirror to a rotary sleeve that rotates around a fixed shaft. The rotary polygon mirror is connected to the rotary shaft, and a motor housing and the like are provided. An air bearing in which a rotating shaft is fitted to a sleeve fixed to the sleeve may be used.

[0036]

Since the present invention is configured as described above, it has the following effects.

The processing cost of the air bearing that rotatably supports the rotary polygon mirror of the scanning optical device can be reduced, and the bearing performance and durability can be greatly improved. By using such a scanning optical device, it is possible to greatly promote higher performance and lower cost of the image forming apparatus.

[Brief description of the drawings]

FIGS. 1A and 1B show a main part of a scanning optical device according to an embodiment, wherein FIG. 1A is a schematic cross-sectional view thereof, and FIG. 1B is a cross-sectional view showing only a fixed shaft in another cross section.

FIGS. 2A and 2B are explanatory views of a straight groove of a fixed shaft of the apparatus shown in FIG. 1, wherein FIG. 2A is an elevation view thereof, and FIG. 2B is an enlarged partial cross-sectional view showing a part of FIG.

FIG. 3 is a diagram illustrating a dynamic pressure distribution of an air film between a fixed shaft and a rotating sleeve when the roundness of the fixed shaft of the apparatus of FIG. 1 is high.

FIG. 4 is a view for explaining a dynamic pressure distribution of an air film between the fixed shaft and the rotating sleeve when the cross section of the fixed shaft of the apparatus of FIG. 1 is elliptical.

FIG. 5 is a diagram illustrating a dynamic pressure distribution of an air film between the fixed shaft and the rotating sleeve when the fixed shaft has three linear grooves.

FIG. 6 is a schematic sectional view showing a main part of a scanning optical device according to a conventional example.

FIG. 7 is a diagram illustrating the entire scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotating polygon mirror 2 Fixed axis 3 Rotating sleeve 5 Rotor magnet 8 Stator 21-29 Straight groove

Claims (3)

[Claims] An air bearing comprising a shaft member and a sleeve member which are fitted to each other and are relatively rotatable; a rotary polygon mirror integrally connected to the shaft member or the sleeve member;
A scanning optical apparatus, comprising: driving means for rotating the rotary polygon mirror; wherein the shaft member has at least nine linear dynamic pressure generating grooves at equal intervals in a circumferential direction. 2. The scanning optical device according to claim 1, wherein each dynamic pressure generating groove is constituted by at least one single plane extending in the axial direction of the shaft member. 3. The difference between the outer diameter of the shaft member and the inner diameter of the sleeve member is 0.010 mm or less, and each dynamic pressure generating groove
A depth of 20 mm or less and a central angle of the shaft member of 3 to 30 °
3. The scanning optical device according to claim 1, wherein the scanning optical device has the following width.