JPH0540237A - Rotating mirror and method of manufacturing the rotating mirror - Google Patents

Abstract

(57) [Summary] [Object] It is an object of the present invention to propose a rotating mirror capable of reducing the adverse effects of the tilt of the reflecting mirror surface and reducing the scanning unevenness, and a manufacturing method thereof. A rotating mirror according to the present invention is characterized in that only two surfaces are provided as reflecting mirror surfaces at positions facing each other about a rotation axis, and the cylindrical outer peripheral surface of a base material having a cylindrical outer peripheral surface. It is characterized in that two opposing positions around the upper rotation axis are cut into planes by a fly-cutting method to form only two reflecting mirror surfaces. With respect to the surface tilt of the rotary mirror cut by the fly cutting method, the relative error between the reflecting mirror surfaces facing each other with the phase difference of 180 ° about the rotation axis has a minimum relative error, and uneven scanning due to the surface tilt can be reduced. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary mirror and a method for manufacturing the rotary mirror, and more particularly to a rotary mirror suitable for use in an optical scanning device for use in a laser beam printer, an image reading device, a display device or the like. And its manufacturing method.

[0002]

2. Description of the Related Art An optical scanning device used in a laser beam printer, an image reading device, a display device, or the like, repeatedly deflects a light beam by a large number of reflecting mirror surfaces (FACET) of rotating mirrors and irradiates the surface with the light beam. The spot to be formed on is repeatedly scanned. The scanning device must be capable of repeatedly moving (scanning) the spot across a predetermined area in a clear parallel line separation relationship (holding the variation in the direction perpendicular to the scanning direction to a minimum value). Is.

However, if each reflecting mirror surface of the rotating mirror is inclined with respect to the axis of rotation, that is, if there is so-called surface tilt, unevenness occurs between the scanning lines due to the deflection of each reflecting mirror surface,
This hinders high-resolution scanning. Such a phenomenon similarly occurs even when the rotation axis of the rotating mirror oscillates. The main causes of these are processing errors and assembly errors of the components, but the above-mentioned phenomenon is unbalanced in the shape of the rotating mirror or wind pressure or air in the high-definition / high-speed optical scanning device that rotates the rotating mirror at high speed. It tends to be increased by turbulence. For this reason, the surface tilt accuracy of the rotary mirror is usually required to be extremely high within 3 to 5 seconds, which is difficult to manufacture, and even if it is obtained, there is a problem that it becomes expensive.

Further, the imbalance of the shape of the rotating mirror and the turbulent flow of air also cause vibration and noise.

In order to reduce the influence of the tilt of the rotating mirror, many methods of optically correcting have been proposed. Figure 2
The optical scanning device of the laser beam printer shown in FIG. 4 is an example, and the optical beam emitted from the light source device 1 is modulated by the modulator 3
Intensity modulation according to the image signal through the beam expander 4, and after that, the beam expander 4 shapes it to an appropriate size, and the light beam is formed on the deflection surface (reflecting mirror surface) of the rotating mirror 6 fixed to the end of the rotating shaft 9 by a cylindrical lens. The light beam reflected by the rotary mirror 6 is substantially collimated in the sub-scanning direction by the cylindrical lens 7 and is projected through the Fθ lens 8 on the scanning surface of the photosensitive drum 10 (irradiation). It is configured to focus on a surface) to form a minute spot and scan the spot.

The laser beam printer further comprises a charger for uniformly charging the surface of the photosensitive drum 10 in advance, and scans and exposes the uniformly charged surface of the photosensitive drum 10 with the spot. A developing device that forms an electrostatic latent image and causes a developer to act on the surface of the photosensitive drum is provided to convert the electrostatic latent image into a toner image. Further, the toner image on the surface of the photosensitive drum is transferred onto a recording sheet and fixed on the recording sheet to obtain a printed matter.

In the above-described optical scanning device, since the two cylindrical lenses 5 and 7 in front of and behind the rotating mirror 6 on the light beam path have a common relationship with respect to the reflecting mirror surface of the rotating mirror 6 (see FIG. 3), reflection is performed. Tilting of the mirror surface with respect to the axis of rotation 2 and the axis of rotation 9
Even if there is a runout, the scanning is always performed at the same position on the scanning surface, and if the photosensitive drum 10 rotates at a constant speed, the scanning line pitch unevenness on the scanning surface does not occur (see FIG. 4). ).

However, since this optical scanning device requires the two cylindrical lenses 5 and 7, it has the drawback that the optical system is complicated, large and expensive, and that the shape of the rotating mirror is unbalanced, the wind pressure or the air pressure is increased. It is not a measure to prevent the generation of vibration and noise due to turbulent flow.

Such an optical scanning device is disclosed in Japanese Patent Publication No. 52-
It is disclosed in Japanese Patent No. 28666.

[0010]

As described above, in the conventional optical scanning device, the influence of the tilt of the reflecting mirror surface of the rotating mirror is optically corrected, so that the structure is complicated, large in size, and expensive. Was becoming. An object of the present invention is to propose a rotary mirror and a manufacturing method thereof that can reduce the adverse effects caused by the surface tilt of the reflecting mirror surface and the uneven scanning.

[0011]

According to the present invention, there is provided a rotating mirror having a reflecting mirror surface which is fixed to a rotating shaft and rotates and which reflects a light beam on an outer periphery thereof, wherein the reflecting mirror surface is centered on a rotating shaft center. In a method of manufacturing a rotating mirror having a reflecting mirror surface which is fixed to a rotating shaft and rotates and which reflects a light beam on an outer periphery thereof, the mother having a cylindrical outer peripheral surface is characterized in that only two surfaces are provided at opposing positions. It is characterized in that two opposing positions about the rotation axis on the cylindrical outer peripheral surface of the material are cut into flat surfaces by a fly cutting method to form only two reflecting mirror surfaces.

[0012]

The plane tilt distribution of the rotary polygon mirror cut by the fly-cutting method has a sinusoidal shape within one rotation cycle, and the reflecting mirror surfaces which are opposed to each other about the rotation axis and have a phase difference of 180 ° (for example, 6 In the case of a face body, the relative error between the first surface and the fourth surface) is minimal. Therefore, the relative error between the two reflecting mirror surfaces facing each other of the rotating mirror is extremely small. If the rotating mirror is formed with only these two reflecting mirror surfaces, it is possible to reduce scanning unevenness due to surface tilt, and the correction optical system. Is unnecessary.

[0013]

EXAMPLES First, in order to help the technical understanding of Examples,
The tilting of the rotating mirror will be described in detail. FIG. 5 is a diagram showing an example of a manufacturing process of a rotating boundary used in the optical scanning device, a surface tilt distribution, and an image printed by a laser beam printer using the optical scanning device.

As shown in FIG. 5A, for example, a case of processing a hexahedral rotating polygon mirror will be described. When the aluminum material is used as the base material and the mirror cutting method known as the fly cutting method is used for cutting, the workpiece is θm after cutting the first surface (60 ° for a hexahedron).
Just rotate and cut the next face. Hereinafter, this procedure is repeated until the sixth surface is cut.

The surface tilt accuracy of the rotary polygon mirror thus obtained is affected by the mechanical accuracy such as an error of the index device, and its relative with respect to the first surface as shown in FIG. 5 (b). When the target surface tilt angles are plotted in the order of the mirror surface numbers, there is a strong tendency to show a sinusoidal periodic distribution. Therefore,
An optical scanning device using a rotating polygon mirror with such a tendency,
For example, when used in a laser beam printer, as shown in FIG.
As shown in (c), image printing unevenness is generated at a regular cycle corresponding to one rotation cycle of the rotary polygon mirror. FIG. 5C is an example in which a repetitive image in which black and white are reversed is printed on each surface of the rotary polygon mirror, and reference numerals 1 to 6 attached to the right side of the line drawing are the first numbers of the rotary polygon mirror. It corresponds to the surface to the sixth surface.

Next, the reason why the surface tilt of the rotary polygon mirror exhibits a sinusoidal distribution within one rotation cycle will be described in detail with reference to FIG.

FIG. 6 is a diagram schematically showing the cutting state of the rotary polygon mirror, and FIG. 6 (a) schematically shows a state in which the rotary polygon mirror is mirror-cut by a fly-cut machine. The processing jig 51 to which the rotary polygon mirror 50 is fixed has a center 52 on one side.
Is rotatably supported and the other side is fixed to the air chuck 53, and the index of θm described above is possible. At this time, when the center of rotation of the index device eccentrically swings as shown in the figure, the rotary polygon mirror 5
The cut surface of 0 has an inclination of an angle θ peculiar to each surface, and as a result, the reflecting mirror surface is tilted.

FIG. 6 (b) shows the above-mentioned eccentric form of the shaft, which takes various forms depending on the state of the fly-cut machine. Depending on this eccentric form, the surface tilt distribution shown in FIG. 5 (b) takes various forms other than the sinusoidal form (generally, since the eccentric form is often close to a perfect circle, FIG. ) Will be the form). In any case, the troubles show a periodic distribution, and the main cause is the eccentricity of the index device.

Embodiments in which the present invention is applied to a laser beam printer will be described in detail below with reference to the drawings. Detailed description of the technical contents common to the above-mentioned technical contents will be omitted.

Most of the structure of the laser beam printer is the same as the structure of the laser beam printer described above, and the characteristic point thereof is that only two reflecting mirror surfaces that face each other about the rotation axis as an optical scanning device are rotated. The use of a deflection device with a mirror.

Therefore, the rotating mirror will be described in detail below.

FIG. 1 (a) is a plan view showing an embodiment of a rotary mirror in an optical scanning device according to the present invention, and FIG. 1 (b) is an image printed by a laser beam printer using the rotary mirror in FIG. It is the figure shown corresponding to (c).

In the rotating mirror 100 shown in FIG. 1A, two opposing positions centering around the rotation axis of the aluminum base material having a cylindrical outer peripheral surface are cut out in a plane.
Only one reflecting mirror surface 101, 102 is formed. The reason why the base material having the cylindrical outer peripheral surface is the basic shape is to minimize the unbalance of the shape and the generation of wind pressure and turbulence of air at high speed rotation, but it has a surface other than the cylindrical outer peripheral surface. Needless to say, it does not matter if it is a thing. In the case of an optical scanning device in which the influence of wind pressure and air turbulence due to unbalanced shapes and high-speed rotation does not pose a problem, it is necessary to use a shape in which only two opposing surfaces are used as effective reflecting mirror surfaces. Good.

Two reflecting mirror surfaces 1 as shown in FIG.
As a cutting method for forming 01 and 102, the fly cutting method by the above-mentioned fly cutting machine is suitable, and the position of the phase difference of 180 ° facing each other about the rotation axis is cut into a mirror surface to be relatively processed. It is possible to obtain the two reflecting mirror surfaces 101 and 102 with a small error. The machining accuracy can be further improved by arranging the spindle on which the rotating blade is placed without using the index device at two opposing positions and simultaneously performing machining on the two surfaces.

When the rotating mirror 100 manufactured as described above is used, as shown in FIG.
Even if the first and second surfaces of No. 1 and 102 have a surface misalignment error, black and black and white and white are all printed by being deflected by the same surface. It is constant, and image unevenness that can be visually identified does not occur. That is, the two reflecting mirror surfaces 10
It is possible to substantially avoid the influence of the trouble of 1,102.

Since the surface connecting the two reflecting mirror surfaces 101 and 102 of the rotating mirror 100 is an arcuate surface,
It is possible to reduce the shape imbalance, the influence of wind pressure, and the occurrence of air turbulence, and it is possible to reduce the adverse effects that occur during high-speed rotation.

[0027]

As described above, since the rotating mirror of the present invention is provided with only two reflecting mirror surfaces, the influence of surface tilt due to manufacturing error can be reduced and scanning unevenness can be eliminated. it can. Since the optical system for correcting the surface tilt is simple, it is effective in constructing a small and inexpensive optical scanning device.

Moreover, there is an effect that the mirror surface cutting method known as the fly cutting method can be used for easy cutting.

[Brief description of drawings]

FIG. 1A is a plan view of a rotary mirror in an optical scanning device according to the present invention, and FIG. 1B is a diagram showing an image printed by a laser beam printer using the optical scanning device.

FIG. 2 is a schematic configuration diagram of a laser beam printer.

3 is a diagram showing an expanded optical path of the laser beam printer of FIG.

FIG. 4 is a diagram for explaining the operation of the surface tilt correction optical system.

FIG. 5A is an explanatory view of a manufacturing process of a rotating mirror used in the optical scanning device according to the present invention, and FIG.
(C) is a diagram showing an example of an image printed by a laser beam printer using the optical scanning device.

6A is a diagram schematically showing a cutting situation of a rotary mirror, and FIG. 6B is an eccentricity characteristic diagram.

[Explanation of symbols]

51 ... Processing jig, 52 ... Center, 53 ... Air chuck, 100 ... Rotating mirror, 101, 102 ... Reflecting mirror surface.

Claims (7)

[Claims] 1. A rotating mirror fixed to a rotating shaft and having a reflecting mirror surface for reflecting a light beam on an outer periphery thereof, wherein the reflecting mirror surfaces are only two surfaces facing each other around a rotating shaft center. A rotating mirror that is equipped with. 2. The rotating mirror according to claim 1, wherein the two reflecting mirror surfaces are arranged at positions facing each other on a circumference centered on a rotation axis. 3. The rotating mirror according to claim 1, wherein the two reflecting mirror surfaces of the rotating mirror are formed by notching flat surfaces at opposing positions on a circumference around the rotation axis. .. 4. A rotary mirror according to claim 1, wherein an arc surface is interposed between the two reflecting mirror surfaces. 5. A method of manufacturing a rotating mirror, which is fixed to a rotating shaft and rotates and which has a reflecting mirror surface for reflecting a light beam on its outer periphery, comprising: a base material having a cylindrical outer peripheral surface on the cylindrical outer peripheral surface. A method of manufacturing a rotating mirror, characterized in that two opposing positions about the rotation axis are cut into planes by a fly cutting method to form only two reflecting mirror surfaces. 6. The method of manufacturing a rotating mirror according to claim 5, wherein the two reflecting mirror surfaces are cut at the same time. 7. A method of manufacturing a rotating mirror according to claim 5, wherein a part of the cylindrical outer peripheral surface is cut out between the two reflecting mirror surfaces while leaving an arc shape.