JPH06294937A - Rotary polygon mirror driving device - Google Patents

Abstract

PURPOSE:To suppress a nonrepetitive deflection error at the time of rotation by providing a partial gap difference between the rotary member of a rotor and an external wall, and generating a pressure difference based upon the gap difference by using wind pressure generated at the time of the rotation of the rotor and applying lateral pressure to the rotor. CONSTITUTION:An eccentricity quantity epsilon is given between the center axis of the inner peripheral surface of a bracket 6 which faces a rotary polygon mirror 3 and the center axis of rotation of the rotary polygon mirror 3 to leave gaps delta1 and delta2 between the outer periphery of the rotary polygon mirror 3 and the inner peripheral surface of the bracket 6. Here, a flow of air is generated along the outer periphery of the rotary polygon mirror 3 to generate pressure in the gaps delta1 and delta2. At this time, the gap delta2 is narrower than the gap delta1, so the pressure generated in the gap delta2 becomes larger than the pressure generated in the gap delta1 to apply the lateral pressure by pressing the rotor as shown by an arrow C. Namely, the center axis of rotation of the rotary polygon mirror 3 and the center axis of the inner peripheral surface of the bracket 6 are made eccentric to provide the partial gaps and then the lateral pressure based upon the pressure difference at the time of the rotation can be applied to the rotor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary polygon mirror driving device used in the field of office automation and the like.

[0002]

2. Description of the Related Art In recent years, copying machines and laser beam printers have been digitized and increased in speed, and a laser scanner unit (hereinafter abbreviated as LSU) used therein is required to have high accuracy. However, on the other hand, the demand for cost reduction is becoming severe, and in particular, the rotary polygon mirror driving device for driving the rotary polygon mirror is heavily weighted for cost reduction.

Usually, the rotary polygon mirror mounting portion of the rotor is cut or polished by self-driving or external driving to improve the accuracy of the dynamic plane tilt and the L.L. S. A surface tilt correction lens is often provided inside the U, and as the processing accuracy of the dynamic surface tilt improves, the surface tilt correction lens can be omitted.

However, in reality, the rotor does not always pass the same locus of rotation due to the clearance of the bearing of the rotor, etc., and the so-called non-repetitive run-out error causes an error in the face-correction lens to be omitted even if the machining precision of the dynamic face-error is improved. In many cases.

In order to suppress such non-repetitive run-out error, a method such as applying lateral pressure to the bearing portion has been adopted.

A conventional rotary polygon mirror driving device will be described below. FIG. 3 shows an example of a conventional rotary polygon mirror driving device. In FIG. 3, a shaft 1 is fitted and fixed to a rotor boss 2, and a rotary polygon mirror 3 is fixed to the rotor boss 2 with screws (not shown) using a pressing plate 4. Also,
A magnet 5 is attached to the rotor boss 2, and a stator 7 is attached to the bracket 6 at a position facing the magnet 5. Further, a ball bearing 9 and a ball bearing 10 are mounted on the bracket 6 and the bracket cover 8, respectively, and rotatably supports the jaft 1. Further, the spring 11 applies a preload to the ball bearing 9 and the ball bearing 10, and the rubber 12 applies a lateral pressure.

The operation of the rotary polygon mirror driving device configured as described above will be described below. First, an electric current flows through the drive winding of the stator 7, a driving force is generated between the stator 5 and the magnet 5, and the rotary polygon mirror 3 starts rotating together with the shaft 1 to perform scanning. At this time, the non-repetitive shake error is suppressed by the lateral pressure of the rubber 12, and the optical axis shift when the rotary polygon mirror 3 is rotated is suppressed.

[0008]

However, in the above-mentioned conventional structure, since the upper and lower bearings must be assembled in a twisted state, the assembly is complicated and difficult, and the bearing life is shortened.
In particular, it deteriorates the acoustic life of the bearing and increases process defects. Further, if a method of applying a lateral pressure after assembling is adopted, there is a problem that enormous cost is required to adjust the lateral pressure.

The present invention solves the above-mentioned problems of the prior art, and is excellent in that it is easy to assemble, the process defects are reduced, the bearing life is extended, the cost is low and the non-repetitive runout error during rotation is suppressed, and the rotation accuracy is high. An object of the present invention is to provide a rotary polygon mirror driving device.

[0010]

In order to achieve this object, a rotary polygon mirror driving device of the present invention has an outer wall at a position opposed to a rotating member of a rotor assembly in the radial direction, and further, an inner wall of the outer wall in the radial direction. The central axis of the peripheral surface is eccentric with respect to the central axis of rotation of the rotor assembly, or the inner peripheral surface of the outer wall is provided with at least one concave portion or convex portion.

[0011]

According to this structure, by providing a partial gap difference between the rotating member of the rotor and the outer wall, the wind pressure generated during the rotation of the rotor is used to generate a pressure difference due to the gap difference, thereby applying a lateral pressure to the rotor. Non-repetitive shake error during rotation can be suppressed.

[0012]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. The description of the same structure and structure as the conventional rotary polygon mirror driving device will be omitted.

In FIG. 1, an eccentricity ε is given to the central axis of the inner peripheral surface of the bracket 6 facing the rotary polygonal mirror 3 and the central axis of rotation of the rotary polygonal mirror 3, and the outer circumference of the rotary polygonal mirror 3 and the bracket 6 are given. Gaps δ1 and δ2 (δ1> δ
2) is given.

The operation of the rotary polygon mirror driving device configured as described above will be described. First, when the rotor starts rotating, a flow of air is generated along the outer circumference of the rotary polygon mirror 3, and pressure is generated in the gaps δ1 and δ2. At this time,
Since the gap δ2 is narrower than the gap δ1, the pressure generated in the gap δ2 becomes larger than the pressure generated in the gap δ1, and the lateral pressure is applied by pushing the rotor in a certain direction (direction of arrow C).
It is generally known that such pressure is inversely proportional to the cube of the size of the void, and the smaller the void, the greater the amount of pressure generated. Also, since the pressure is proportional to the rotation speed, the faster the rotation speed, the larger the pressure.

As described above, according to this embodiment, the rotation center axis of the rotary polygon mirror 3 and the center axis of the inner peripheral surface of the bracket 6 are eccentric, and a partial gap difference is provided, so that the pressure during rotation is reduced. Lateral pressure on the rotor due to the difference can be applied.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, the difference from the configuration of FIG. 1 is that the rotation center axis of the rotary polygon mirror 3 and the center axis of the inner peripheral surface of the bracket 6 are eccentric to provide a partial gap difference. That is, the convex portion 6a and the concave portion 6b are provided on the inner peripheral surface of, and a similar gap difference is realized. It goes without saying that the same function as in the first embodiment is fulfilled.

In the first and second embodiments, the gap difference is provided between the rotary polygon mirror 3 and the bracket 6, but it is provided between the rotor boss 2 and the bracket 6 and between the holding plate 4 and the bracket cover 8. Alternatively, if the outer circumferences of the rotor boss 2 and the pressing plate 4 are formed into a prismatic shape or a gear shape similar to that of the rotary polygon mirror, the air volume is increased and a larger wind pressure can be obtained. Even if the outer circumferences of the rotor boss 2 and the holding plate 4 are columnar, they can be made to function sufficiently if the gap is made sufficiently small or the rotation speed is increased.

Although the example of the ball bearing is shown, a hydrodynamic bearing including a sintered oil-impregnated bearing, a herringbone groove, a spiral groove or the like may be used.

Further, an example is shown in which the optical scanning window of the bracket is also used in a wide space between the rotary polygon mirror and the bracket, but it is necessary to adjust the air gap in order to make it function sufficiently even if it is not used in particular. This is possible.

Further, the structure example of the both-end support type in which the bearings are provided at both ends of the rotor has been shown, but the one-end support type in which the rotary polygon mirror or the magnet is located outside the bearing may be used. Further, although an example of the inner rotor type structure has been shown, it goes without saying that the same effect can be obtained with an outer rotor type or a plane facing type.

In the second embodiment, one convex portion and one concave portion are provided, but two or more convex portions and concave portions may be provided for vector synthesis. It can be made to function sufficiently when it is made very small or the rotation speed is fast.

[0023]

As described above, according to the present invention, the outer wall is provided at a position facing the radial outer periphery of the rotating member of the rotor assembly, and the inner peripheral surface of the outer wall and the central axis of the rotor assembly are eccentric. Alternatively, by providing at least one concave portion or convex portion on a part of the inner peripheral surface of the outer wall to provide a partial gap difference between the rotating member and the inner peripheral surface of the outer wall, the wind pressure generated when the rotor rotates Causing a pressure difference due to the gap difference,
By applying lateral pressure to the rotor, non-repetitive run-out error during rotation can be suppressed.

In addition, L. S. In the case of U, it is possible to omit the internal tilt correction lens provided inside, and S. Cost reduction of U can be realized. Furthermore, compared to the conventional structure that applies lateral pressure,
It is possible to realize a rotary polygon mirror drive device having a simple structure, which does not twist the bearing and is excellent in reliability.

[Brief description of drawings]

FIG. 1A is a vertical sectional view of a rotary polygon mirror driving device according to a first embodiment of the present invention. FIG. 1B is a sectional view taken along the line AB in FIG. 1A.

2A is a vertical sectional view of a rotary polygon mirror driving device according to a second embodiment of the present invention. FIG. 2B is a sectional view taken along line AB in FIG. 2A.

FIG. 3 is a vertical sectional view of a conventional rotary polygon mirror driving device.

[Explanation of symbols]

 1 Shaft 2 Rotor Boss 3 Rotating Polygonal Mirror 4 Holding Plate 5 Magnet 6 Bracket 6a Convex 6b Recess 7 Stator 8 Bracket Cover 9, 10 Ball Bearing 11 Spring 12 Rubber

Claims (5)

[Claims] 1. An outer wall is provided at a position facing a radially outer periphery of a rotor assembly and a rotating member of the rotor assembly, and a central axis forming an inner peripheral surface of the outer wall is eccentric with respect to a central axis of rotation of the rotor assembly. A rotary polygon mirror driving device, wherein a partial gap difference is provided between the rotary member and the inner circumference of the outer wall. 2. The rotary polygon mirror driving device according to claim 1, wherein the gap difference is formed by at least one concave portion or convex portion on a part of the inner peripheral surface of the outer wall. 3. The rotary polygon mirror driving device according to claim 1, further comprising at least one gear-shaped or prism-shaped concavo-convex portion on the outer circumference in the radial direction on the rotary member. 4. The rotary polygon mirror driving device according to claim 3, wherein the concavo-convex portion is a rotary polygon mirror. 5. The rotary polygon mirror driving device according to claim 4, wherein the optical scanning window portion facing the mirror surface of the rotary polygon mirror is also used as a portion having a large gap.