JPH0720396A - Rotary polygonal mirror - Google Patents

Abstract

PURPOSE:To reduce the wind whisle of a rotary polygonal mirror and to prevent the stain of a reflection area on a reflection surface. CONSTITUTION:The rotary polygonal mirror 1 consisting of a square polelike main body 11 having a center hole 12 has four mirror surfaces 1a and four dihedral angles 1b on its side surface, and only the center part of the dihedral angle 1b is chamfered by a cylindrical curved surface 13. The stain O caused on the back side of the dihedral angle 1b in a rotating direction shown by an arrow R is concentrated on the back sides of both end parts of the dihedral angle 1b which are not chamfered, so that there is no possibility of the stain of the reflection area reflecting a laser beam scanning the center part of the mirror surface 1a in a direction shown by an arrow B.

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 of a scanning optical device used in laser printers, laser facsimiles and the like.

[0002]

2. Description of the Related Art In a scanning optical device used for a laser printer, a laser facsimile, etc., as shown in FIG. 8, a laser beam generated from a semiconductor laser S ₀ is collimated by a collimator lens C ₁ and then a cylindrical lens is used. The rotary polygon mirror 101 collects linearly with C ₂ .
The reflective surface 101A composed of the respective mirror surfaces 101a is irradiated.
The laser light deflected and scanned by the rotation of the rotary polygon mirror 101 passes through an imaging lens system F _{0 including} a spherical lens f ₁ and a toric lens f ₂ and a folding mirror M ₀ (shown in FIG. 9) to a rotating drum D ₀ ( An image is formed on the photoconductor on the surface (shown in FIG. 9), and an electrostatic latent image is formed by main scanning by rotation of the rotary polygon mirror 101 and sub-scanning by rotation of the rotating drum D ₀ . Further, a part of the laser light is reflected by the detection mirror (not shown) to the light receiving end of the optical fiber,
The write start signal is input to the semiconductor laser S ₀ .

The drive system for rotating the rotary polygon mirror 101 is
As shown in FIG. 9, it has a shaft 109 supported by a bearing 108 held in a housing 107, and the shaft 109 is integrally coupled to a driving magnet 102 via a flange 100 and a yoke 102a. The magnet 102 constitutes a motor M together with the driving coil 103 fixed to the housing 107. Rotating polygon mirror 101
Is a flange 1 with a spring 104 and a clasp 105.
00, which is integrally connected to the shaft 109 and is rotated by the motor M described above.

The rotating polygon mirror 101 is not limited to one having six mirror surfaces 101a in which all the sides of the regular hexagonal prism 6 are mirror-finished as shown in FIGS.
A rotating polygon mirror 111 having four mirror surfaces 111a in which all the side surfaces of a regular square prism as shown in FIG. 11 are used, or a polygonal prism other than the above, which has a reflecting surface on all the side surfaces, A part of the side surface may be used as a mirror surface.

In recent years, it has become necessary to rotate a rotary polygon mirror at a high speed of 10,000 rpm or more and 20,000 rpm or more as the scanning optical device becomes faster and more accurate.

[0006]

However, according to the above-mentioned prior art, as described above, the rotary polygon mirror has a size of 10,0.
When rotating at a high speed of 00 rpm to 20,000 rpm or more, the air resistance at the ridge angle between the mirror surfaces of the rotating polygon mirror increases significantly, generating a large wind noise and at the front end of each mirror surface in the rotation direction. The foreign matters X and Y as shown in FIGS. 10 and 11 are attached to locally reduce the reflectance. When the reflectance of each mirror surface is locally reduced in this way, the amount of laser light used as a writing start signal becomes insufficient and detection becomes impossible, or a part of the electrostatic latent image formed on the photosensitive drum is partially detected. Problems such as blurring occur.

Further, as shown by broken lines in FIGS. 10 and 11, a technique for preventing the above-described wind noise by chamfering each ridge angle of the rotary polygon mirror has been developed. Even if chamfered, as shown in FIG.
It is unavoidable that the foreign matter Z adheres to the downstream side of the chamfered portion 121c of the rotary polygon mirror 121, and the trouble due to this has not been solved.

The present invention has been made in view of the above problems of the prior art, and reduces air resistance at the ridge angle of the rotary polygon mirror and reflects the contamination of the mirror surface generated near the ridge angle on the mirror surface. It is an object of the present invention to provide a rotating polygon mirror that can be concentrated in areas other than the area to prevent a decrease in reflectance due to the contamination.

[0009]

In order to achieve the above object, a rotary polygon mirror of the present invention has a plurality of side surfaces adjacent to each other with a ridge angle parallel to the axis of rotation interposed therebetween, and at least one of them is provided.
One of the ridge angles is a rotary polygon mirror, and at least the rest of the ridge angles except for a predetermined end of the ridge angle at the front end in the rotation direction is chamfered.

The ridge angle is chamfered by an inclined surface inclined at a predetermined inclination angle with respect to the rotation axis.

[0011]

According to the above-mentioned device, since the predetermined end portion of the ridge angle of the front end in the rotation direction of the reflecting surface is left without being chamfered, the pollution is concentrated behind this portion, and the rear portion of the chamfered portion is contaminated. Contamination of the reflective area can be prevented. Since the ridge angle is partially chamfered, wind noise can be reduced accordingly.

Further, if the ridge angle is chamfered by an inclined surface inclined at a predetermined angle with respect to the rotation axis, it is possible to prevent noise and the like due to reflected light at the chamfered portion.

[0013]

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

FIG. 1 shows a first embodiment, (a) is a perspective view, and (b) is a sectional view taken along the line AA of (a). The rotary polygon mirror 1 of the present embodiment comprises a main body 11 having a quadrangular prism-shaped outer shape, the main body 11 has a central hole 12 that penetrates the main body 11 in the axial direction, and each side surface of the main body 11 is mirror-finished to form a reflecting surface. It constitutes a certain mirror surface 1a. That is,
The rotary polygon mirror 1 has four mirror surfaces 1a parallel to the central axis and four ridge angles 1b formed between the respective mirror surfaces 1a.

The size of the rotary polygonal mirror 1 in the direction of the rotation axis, that is, the size of the mirror surface 1a in the direction parallel to the rotation axis (hereinafter referred to as "thickness") is generally 20,000 rpm or more at high speed. At this time, about 1/10 of the diameter of the circumscribed circle of the main body 11 is required so that the rigidity does not become insufficient. In the present embodiment, the circumscribed circle of the rotary polygon mirror 1 has a diameter of 40 m.
m and its thickness H is 4 mm.

Each ridge angle 1b of the rotary polygon mirror 1 is partially chamfered by a curved surface 13 by a predetermined dimension (hereinafter referred to as "chamfered dimension") h in the central portion of the thickness H of the rotary polygon mirror 1. Each curved surface 13 is a part of a cylindrical surface parallel to the rotation axis direction of the rotary polygon mirror 1. In this way, by locally chamfering the central portion of each ridge angle 1b, the length of each ridge angle 1b is reduced and the air resistance at each ridge angle 1b when the rotary polygon mirror 1 rotates at high speed is reduced. At the same time, the contamination due to the foreign matter O adhering to the rear side of each ridge angle 1b in the rotation direction is concentrated on both end portions in the thickness direction of each mirror surface 1a to prevent the contamination of the central portion of each mirror surface 1a.

A shaft (not shown) is fitted in the center hole 12 of the rotary polygon mirror 1, and the shaft is connected to a drive unit of a known motor. When the rotary polygon mirror 1 is rotated at a high speed by driving the motor, the laser light emitted from the light source (not shown) to the rotary polygon mirror 1 is deflected and scanned by each mirror surface 1a, passes through the image forming lens system (not shown), and is rotated on the rotary drum. Form an image on the photoconductor.

When the rotary polygon mirror 1 rotates in the direction indicated by the arrow R, the reflection point of the laser light is along the respective mirror surfaces 1a and is perpendicular to the rotation axis of the rotary polygon mirror 1 in the direction indicated by the arrow B (hereinafter referred to as "scanning direction"). "."). Of the total width W ₀ scanning direction of the mirror surfaces 1a, the laser reflected by the width W ₃ of the central portion excluding the width W ₂ of the portion that reflects chamfer width W ₁ and the known write start signal dihedral angle 1b at both ends The light is used as a known writing signal for forming an image on the photosensitive member on the rotating drum. The beam size of the laser beam scanned in this manner in the direction perpendicular to the scanning direction is generally about 0.1 to 0.3 mm, and the thickness of each mirror surface 1a of the rotary polygon mirror 1 of this embodiment. Since H is 4 mm as described above, the reflection area of each mirror surface 1a is limited to a strip-shaped portion of about 0.5 mm in the thickness direction even if an error during scanning is taken into consideration. The ratio of 1a to the thickness H is extremely small. Therefore, by locally chamfering the central portion of each ridge angle 1b as described above to concentrate the above-mentioned contamination on both end portions in the thickness direction of each mirror surface 1a, the reflection area of the write signal or the adjacent area thereof is obtained. There is no possibility that the reflection area of the writing start signal is contaminated and its reflectance is lowered.

In order to concentrate the contamination of each mirror surface 1a on both end portions in the thickness direction and prevent the central portion from being contaminated as described above, the chamfered dimension h of each ridge angle 1b is the thickness H of each mirror surface 1a.
Is preferably 3/5 or less. If the chamfered dimension h is larger than this, there is a risk that the thickness of both end portions for concentrating the contamination of each mirror surface 1a is insufficient and the reflection region is contaminated.

FIG. 2 shows a first modified example of this embodiment. In the rotary polygon mirror 2 of this modified example, the central portion of each ridge angle 2b is a flat surface 23 parallel to the rotational axis direction of the rotary polygon mirror 2. Is chamfered by. This modification has an advantage that the work is simple when chamfering is performed by cutting or the like.

FIG. 3 shows a second modification of the present embodiment. In the rotary polygon mirror 3 of this modification, the central portion of each ridge angle 3b is projected as it approaches the center of the rotary polygon mirror 3 in the rotation axis direction. It is chamfered by the convex surface 33. Since each convex surface 33 reflects the laser light applied to this portion as scattered light that diffuses in a random direction, noise due to the reflected light at the end of each mirror surface can be reduced.

FIG. 4 shows a third modification of this embodiment. In the rotary polygon mirror 4 of this modification, the central portion of each ridge angle 4b is depressed as it approaches the center of the rotary polygon mirror 4 in the rotation axis direction. It is chamfered by the concave surface 43. Similar to the second modification, each concave surface 43 reflects the laser light applied to this portion in a random direction, so that noise due to the reflected light at the end of each mirror surface can be reduced.

The present embodiment has a quadrangular prism-shaped outer shape,
Although it is a rotary polygon mirror composed of four mirror surfaces, it is also applied to the case of the rotary polygon mirror 5 having a hexagonal columnar outer shape and having six mirror surfaces 5a and six ridge angles 5b as shown in FIG. it can.
It goes without saying that the present invention can also be applied to a rotary polygon mirror having another polygonal columnar outer shape.

FIG. 6 shows the second embodiment. As shown in FIG. 6A, the rotary polygon mirror 6 of this embodiment has a rectangular prism shape as in the rotary polygon mirror 1 of the first embodiment. With the outer shape of 4
It has one mirror surface 6a and four ridge angles 6b. As shown in FIG. 6B, the central portion of each ridge angle 6b is chamfered by an inclined surface 63 that is inclined at an inclination angle θ with respect to the thickness direction of each mirror surface 6a.

In the rotary polygon mirror 6 of this embodiment, as in the rotary polygon mirror 1 of the first embodiment, the length of each ridge angle 6b is an inclined surface 63.
Since it is reduced by chamfering with
The wind noise during high-speed rotation can be significantly reduced, and the contamination generated behind each ridge angle 6b can be concentrated on both sides of the inclined surface 63 to prevent the central portion of each mirror surface 6a from being contaminated. In addition, the reflected light of the inclined surface 63 is prevented from reaching the rotating drum and generating noise because the reflected light deviates by an angle 2θ with respect to the scanning direction of the laser light.

The inclination angle θ of the inclined surface 63 is set from the reflection point of the rotary polygon mirror 6 so that the light reflected by the inclined surface 63 does not reach the surface of the rotating drum D, as shown in FIG. It is desirable that the following relationship be satisfied with respect to the distance S to the center of the rotary drum De through the imaging lens system Fe and the radius T of the rotary drum De.

Tan2θ> T / S The rotary polygon mirror of each modification of the first and second embodiments is made of metal such as Al or synthetic resin. In the case of a metal rotary polygon mirror, it is desirable to chamfer each ridge angle by cutting or the like, and in the case of a synthetic resin rotary polygon mirror, it is desirable to form it at the time of integral molding of the main body. In particular,
In the case of the second and third modified examples of the first embodiment, it is preferable to integrally form the synthetic resin because forming the convex surface or the concave surface by cutting becomes complicated.

[0028]

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

The air resistance at the ridge angle of the rotary polygon mirror is reduced to reduce wind noise and load current of the motor, and the contamination of the mirror surface is concentrated in areas other than the reflection area to prevent the reduction of the reflectance due to the contamination. You can As a result, the noise and driving force of the scanning optical device can be reduced and the accuracy can be improved.

[Brief description of drawings]

1A and 1B show a first embodiment, FIG. 1A is a perspective view thereof, and FIG. 1B is a sectional view taken along line AA of FIG.

FIG. 2 shows a first modification of the first embodiment, (a)
Is a perspective view thereof, and (b) is a sectional view taken along line BB of (a).

FIG. 3 shows a second modification of the first embodiment, (a)
Is a perspective view thereof, and (b) is a sectional view taken along line C-C of (a).

FIG. 4 shows a third modified example of the first embodiment, (a)
Is a perspective view thereof, and (b) is a sectional view taken along the line D-D of (a).

FIG. 5 is a perspective view showing a case where the first embodiment is applied to a regular polygonal rotating polygon mirror.

6A and 6B show a second embodiment, in which FIG. 6A is a perspective view thereof, and FIG. 6B is a sectional view taken along line EE of FIG.

FIG. 7 is a diagram illustrating a relationship between an inclination angle of an inclined surface and reflected light according to the second embodiment.

FIG. 8 is an explanatory diagram illustrating a general scanning optical device.

FIG. 9 is an explanatory diagram illustrating a drive system of a rotary polygon mirror.

FIG. 10 is a perspective view showing a conventional polygonal rotary polygon mirror.

FIG. 11 is a perspective view showing a conventional polygonal rotating polygonal mirror.

FIG. 12 is a perspective view showing a conventional chamfered quadrangular prism-shaped rotating polygon mirror.

[Explanation of symbols]

 1, 2, 3, 4, 5, 6 Rotating polygon mirror 1a, 5a, 6a Mirror surface 1b, 2b, 3b, 4b, 5b, 6b Ridge angle 13 Curved surface 23 Flat surface 33 Convex surface 43 Concave surface 63 Inclined surface

Claims (6)

[Claims] 1. A rotary polygon mirror having a plurality of side surfaces adjacent to each other with an edge angle parallel to the axis of rotation interposed therebetween, at least one of which serves as a reflecting surface, wherein at least one of the edge angles is included. A rotary polygon mirror characterized in that the remainder of the reflecting surface except for a predetermined end portion of the ridge angle at the front end in the rotation direction is chamfered. 2. The rotating polygon mirror according to claim 1, wherein the ridge angle is chamfered by a cylindrical surface or a plane parallel to the rotation axis. 3. The rotary polygon mirror according to claim 1, wherein the ridge angle is chamfered by a curved surface protruding or recessed in a direction perpendicular to the rotation axis. 4. The rotary polygon mirror according to claim 1, wherein the ridge angle is chamfered by an inclined surface inclined at a predetermined inclination angle with respect to the rotation axis. 5. The rotary polygon mirror according to claim 4, wherein the tilt angle is in the following range. tan2θ> T / S where θ: inclination angle S: distance between the center of the rotary drum on which the reflecting surface of the rotary polygon mirror and the laser beam deflected and scanned by the mirror are imaged T: diameter of the rotary drum 6. The rotary polygon mirror according to claim 1, wherein the chamfered portion of the ridge angle has a length in the following range. 0.5 ≦ L ≦ 3 / 5H where L: length of chamfered ridge angle H: thickness of reflective surface