JP2000241727A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a division optical scanner capable of eliminating the deviation of a joint caused by guiding two independent beams to a surface to be scanned and preventing double writing by light from an adjacent surface by making a rotary polyhedron have non-reflecting characteristic within a range under a specified incident angle. SOLUTION: The rotary polyhedron has the non-reflecting characteristic within the range under the specified incident angle. Owing to the reflecting and non-reflecting characteristic of a polygon mirror 104, for example, in accordance with the incident angles of the laser beams A and B, the laser beam is not reflected when the incident angle on the mirror 104 is <5 deg., and the laser beam is reflected when it is >=6.5 deg.. Therefore, the laser beam A made incident on the adjacent surface in a state where the incident angle on the mirror 104 is <5 deg. is not reflected, whereby unnecessary light is not caused at a scanning center part. Meanwhile, the laser beam A made incident on a present reflection surface at the incident angle >=6.5 deg. is reflected to scan the surface (1) to the surface (2) of a photoreceptor drum 106. The same processing is performed in the case of the laser beam B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in an image recording apparatus for recording an image by scanning and exposing a laser beam on a photosensitive member according to image information.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning apparatus using a rotary polygon mirror, two beams are incident at angles of + α and −α with respect to a line connecting the center of the rotary polygon mirror and the center of the surface to be scanned. An optical device that divides one line on a photoconductor at a scanning angle of 2α and scans each line has been proposed (for example, Japanese Patent Application Laid-Open No. H10-177147, hereinafter referred to as Prior Art 1).

Further, in the above prior art 1, two beams are made to enter the rotary polygonal mirror at mutually different angles in the sub-scanning direction and reflect the beams deflected by the rotary polygonal mirror independently. A technique of disposing a mirror and cutting unnecessary light has been proposed (for example, Japanese Patent Application Laid-Open No. H10-206761, hereinafter referred to as Prior Art 2).

[0004] Further, in prior art 2, there is proposed one in which the conditions of the incident / exit angle and the position of the reflecting mirror for preventing double writing and ensuring an overlap area for main scanning are set (as an example). , Japanese Patent Application Hei 9-321
680, hereinafter referred to as Prior Art 3).

[0005]

The objects of the prior arts 1 to 3 are to achieve high speed / high resolution.
This is an overfilled type in which the width of the beam incident on the polygon mirror is larger than the width of the reflection surface of the polygon mirror.

Therefore, in the prior art 1, there is a problem of double writing by adjacent surface light (reflected light from an adjacent mirror surface which becomes a reflection surface next due to rotation of the rotating polygon mirror).

Further, in Prior Art 2 and Prior Art 3,
Double writing is prevented by arranging three reflecting mirrors to make two beams independent.
The polygon system is divided in the sub-scanning direction, and causes independent fluctuation. The deviation occurs at the joint of the divided main scanning lines, and an image is dubbed or blank. In order to compensate for this, it is necessary to perform a means for detecting the amount of displacement and electrically correcting (delay of image recording timing, etc.) It is difficult to maintain the accuracy because it can occur due to environmental changes and the like.

In view of the above-mentioned facts, the present invention can eliminate a seam shift caused by guiding at least two independent beams to a surface to be scanned in a divided scanning device, and can reduce the number of beams caused by adjacent surface light. An object is to obtain an optical scanning device capable of preventing double writing.

[0009]

According to a first aspect of the present invention, there is provided a rotating polygonal mirror for deflecting an incident beam in a main scanning direction by rotationally driving, a rotation center of the rotating polygonal mirror, and a surface to be scanned. At a uniform angle (+ α, −α, α is a positive number) in the main scanning direction with respect to a center line connecting the main scanning center positions of the main scanning center positions. Two beams in the main scanning direction are -2α and + 2α with respect to the center line so as to perform １ ／ of the main scanning.
An optical scanning device comprising: two light source units arranged so as to be deflected in an angle range of: wherein the rotary polygon mirror has a non-reflection characteristic in a range not exceeding an incident angle α / 2. It is characterized by that.

According to a second aspect of the present invention, there is provided a rotating polygon mirror for deflecting an incident beam in a main scanning direction by rotationally driving, and a rotation center of the rotating polygon mirror and a main scanning center position of a surface to be scanned. With respect to the center line to be connected, the light is made incident at an equal angle (+ α, −α, α is a positive number) in the main scanning direction, and while the rotating polygon mirror is rotated by an α angle, each one of the main scanning is rotated.
An optical scanning device comprising: two light source units arranged and arranged so that two beams are deflected in the main scanning direction in the main scanning direction within an angle range of −2α and + 2α so as to carry each of the light beams. Wherein the rotating polygon mirror has an incident angle α
/ 2, the two beams are set so that the electric field vectors are orthogonal to each other, and at least the scanning end is provided in the optical path from the rotary polygon mirror to the surface to be scanned. And has a filter function having polarization characteristics.

According to a third aspect of the present invention, in the second aspect of the present invention, the filter function is a reflection type,
When the scanning angle of unnecessary light θ and the tilt angle of the reflecting mirror are φ,
The arrangement is characterized by tan45 ^o = sin θ / tan φ.

According to a fourth aspect of the present invention, in the second aspect of the invention, the filter function is of a transmission type.
When the scanning angle of unnecessary light θ and the tilt angle of the reflecting mirror are φ,
The arrangement is characterized by tan45 ^o = sin θ / tan φ.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the effective scanning range is -α-β and α + β (α>
β (both positive numbers).

According to a sixth aspect of the present invention, in the first aspect of the present invention, the rotating polygonal mirror having the non-reflection characteristic is provided on a transmission type substrate with an incident angle dependent. It has a characteristic reflective characteristic.

According to a seventh aspect of the present invention, in the first to fifth aspects of the present invention, the rotary polygon mirror having the non-reflection characteristic has an incident angle-dependent absorption characteristic on a reflection surface. It is characterized by having.

According to the first aspect of the present invention, at least unnecessary light at the center of the main scanning can be removed by providing the rotating polygon mirror with non-reflection characteristics. In other words, the unnecessary light is reflected light from the adjacent reflection surface (adjacent surface light), and it is noted that the angle of incidence of this beam is smaller than the angle of incidence on the reflection surface that is actually performing main scanning. This can be achieved by not reflecting a beam whose incident angle is smaller than a predetermined value.

As a result, it is possible to eliminate the division of the Post Polygon system in the sub-scanning direction and significantly improve the maintainability of the joint. In addition, double writing by adjacent surface light can be prevented, and high speed / high image quality can be obtained. Also, since the division of the Post Polygon system in the sub-scanning direction is eliminated, it is possible to easily assemble the optical scanning device.

According to the second aspect of the invention, unnecessary light at the main scanning end is removed by the non-reflection characteristic of the rotary polygon mirror and the filter function (polarization characteristic) described in the invention of the second aspect. ing. Thereby, the main scanning width can be enlarged.

According to the third aspect of the present invention, the condition of the effective scanning range according to the second aspect is shown. In order to determine the effective scanning range, -α-β and α + β are set with respect to the center line.
May be configured to be deflected in the angle range described above, and α> β may be satisfied.

According to the fourth aspect of the present invention, the filter is a reflection type, and the scanning angle θ of the unnecessary light and the tilt angle φ of the reflecting mirror are tan 45 ° = sin θ / tan φ. This reflection-type filter function can be incorporated in an imaging optical system such as a folding mirror or a cylindrical mirror.

According to the fifth aspect of the present invention, the filter is of a transmission type, and a scanning angle θ of unnecessary light and a tilt angle φ of a reflecting mirror are provided.
And tan45 ^° = sinθ / tanφ.
As this transmission type filter function, in addition to an imaging optical system such as a cylindrical lens, a casing provided for housing an optical scanning device is provided to prevent dust from entering a through hole for guiding only the beam to the surface to be scanned. It can be incorporated in the provided glass or plastic transparent plate. Also,
It is also possible to separately provide a transparent plate material in the optical path.

According to the sixth and seventh aspects of the invention, the rotating polygonal mirror having non-reflection characteristics forms a film having reflection characteristics or absorption characteristics depending on the incident angle on the transmission type substrate. I do. That is, the reflection surface has a double structure, and unnecessary light can be removed by reflecting or non-reflecting according to the incident angle.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. "Configuration of Optical Scanning Device" FIG. 1 is a schematic diagram of an optical system of the optical scanning device according to the first embodiment. In addition,
The optical scanning device (FIG. 1) according to the first embodiment is used for a laser printer, a digital copying machine, and the like.

As shown in FIG. 1, the optical scanning apparatus according to the present invention receives two units of light source units 100 and 102, receives laser beams emitted from these light sources 100 and 102, and deflects them in the main scanning direction. Polygon mirror for scanning
(Rotating polygon mirror) 104 and an imaging optical system 108 for guiding and imaging the laser beam deflected and scanned on the surface of the photosensitive drum 106. "Light source unit" The light source units 100 and 102 are arranged symmetrically with respect to the polygon mirror 104 in plan view. More specifically, the polygon mirror 104
Is symmetrical with respect to a center line CL connecting the rotation center of the photoconductor drum 106 and the scanning center position to the photoconductor drum 106.

Each of the light source units 100 and 102 includes a semiconductor laser 108 that emits a laser beam having a substantially Gaussian distribution. Hereinafter, a laser beam emitted from the light source unit 100 is referred to as a beam A (see a solid line in FIG.
Is distinguished as a beam B (see a broken line in FIG. 1).

The laser beam A emitted from the light source unit 100 is a beam having a different divergence angle in a direction parallel to and perpendicular to the plane of polarization, and
Is considered to be a loose divergent light. On the downstream side of the collimator lens 110, a beam shaping slit 112 is arranged. Immediately after passing through the collimator lens 110, only the central part of the divergent light passes through the slit 112 for beam shaping and enters the cylindrical lens 114. It is supposed to. This light becomes light converging in the sub-scanning direction near the reflection surface of the polygon mirror 104.

The laser beam A that has passed through the cylindrical lens 114 is reflected by a reflecting mirror 116,
The light is deflected in the direction of the polygon mirror 104. The angle of incidence of the laser beam A on the polygon mirror 104 is determined by the angle of incidence of the laser beam A on the reflection mirror 116 and the arrangement angle of the reflection mirror 116 itself. In the first embodiment, the laser beam A is
-Α in the main scanning direction with respect to the center line CL (0 ^° ).
The light is incident on the reflection surface of the polygon mirror at an incident angle of (-12.8 ^° ).

Next, regarding the configuration of the light source unit 102, since the configuration of the light source unit 100 and the center line CL are all symmetrical, the same reference numerals are given to the same components. The description of the configuration is omitted. The laser beam B of the light source unit 102 has an incident angle of + α (+ 12.8 °) with respect to the center line CL of the polygon mirror 104,
The laser beam A is incident on the same reflecting surface as the incident surface.

Each of the laser beams A and B is substantially parallel light wider than the reflection surface of the polygon mirror 104, and has a so-called overfilled configuration. The “imaging optical system” is provided between the reflection mirrors 116 and 116 and the polygon mirror 104, and has a power only in the main scanning.
A set of fθ lenses 118 is provided. The fθ lens 118 includes the reflection mirrors 116, 116
On the optical path reaching the polygon mirror 104.

The laser beams A and B deflected by the polygon mirror 104 pass through the fθ lens 118 again.
The light is bent (reflected) at a predetermined angle by the bending mirror 120, is reflected by the cylindrical mirror 114, and forms an image on the photosensitive drum 106. A through-hole on a slit provided in a casing (not shown) that houses the optical scanning system is provided between the cylindrical mirror 122 and the photosensitive drum 106, and a window 124 made of glass or plastic is fitted therein. I have.

By the action of the fθ lens 118, the beam spot on the photosensitive drum 106 to be imaged is
The laser beam A divides and scans one main scanning line at substantially the same speed in the main scanning direction toward the surface of the photosensitive drum 106 and the laser beam B in the main scanning direction toward the surface of the photosensitive drum 106. I do.

When one line is scanned in this way, the laser beams A and B are deflected by the next reflection surface of the polygon mirror, and the next line is scanned.

From the light source unit 100 to the polygon mirror 10
The laser beam A reaching the bending mirror 116 via the scanning mirror 4 at the start of one main scan of the polygon mirror 104
The guide is guided to a reflection mirror 126 disposed at a position different from the cylindrical mirror 122.
The laser beam A reflected by the reflection mirror 126 is
An SOS (S) for setting a write start position at which an image is recorded on the main scanning line via the focusing lens 128
(Start of Scan) signal is input to the SOS sensor 130 that detects the signal. The SOS sensor 130 is connected to a control unit (not shown), and the control unit starts modulating the image signal after a predetermined time has elapsed from the time when the output signal from the SOS sensor is detected.

The laser beam B is the laser beam A
In synchronization with the output signal from the SOS sensor 130, the modulation of the image signal is started when a predetermined time has elapsed, and the laser beam A scans from the surface of the photosensitive drum 106 and Is divided and scanned from the surface. Thus, while the polygon mirror 104 rotates by the angle α, the scanning angles θ (−2α) corresponding to the image area are generated by the laser beams A and B.
To + 2α) is scanned and an image is recorded. "Reflection / Non-reflection Characteristics of Polygon Mirror" In the optical scanning device having the above configuration, when the polygon mirror 104 scans the laser beam A from the surface of the photoconductor drum 106, the reflection surface adjacent to the polygon mirror 104 causes the photoconductor to be scanned. Part of the surface of the drum 106 is irradiated. Conversely, in the laser beam B,
When scanning from the surface of the photosensitive drum 106, a part of the surface of the photosensitive drum 106 is irradiated by the reflection surface adjacent to the polygon mirror 104.

Therefore, the polygon mirror 104 according to the first embodiment has reflection and non-reflection characteristics according to the incident angles of the laser beams A and B. Due to this characteristic, when the incident angle γ to the polygon mirror 104 is less than 5 °, the light is not reflected, and when the incident angle γ is 6.5 ° or more, the light can be reflected.

As a result, it is possible to suppress the reflection on the adjacent reflecting surface and to eliminate unnecessary light generated at least in the central portion of the scanning. “Embodiment of Polygon Mirror 104 (Part 1)” The polygon mirror 104 is formed of a transmission base material such as glass or plastic, and a filter film having an incident angle dependence is formed thereon, as shown in FIG. As shown in the figure, the beam is transmitted at a low incident angle (0 ° to 6.5 °) and is reflected at a high incident angle (8.5 ° or more).

The structure of a transmission type film having the characteristics shown in FIG.
Is shown in equation (3). Note that the wavelength λ ₀Against
λ₀Layers having an optical thin film of / 4 are represented by H, M, L and A.
You.

Air | H · 1.01M ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ ¹² · a ｛(9/8) L ・ (5/4) H ・(9/8) L｝ b ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ c ｛(9/8) L ・ (5/4) H ・ (9 / 8) L｝ · 0. 58A · 1.56H · 0.58A · {(9/8) L · (5/4) H · (9/8) L} ¹² · a ｛(9/8) L · (5/4) H · (9/8) L｝ · b ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ · c ｛(9/8) L ・ (5/4) H ・ (9 / 8) L｝ | Glass Equation (3) The settings for obtaining the characteristics of FIG. 8 are shown below.

Λ ₀ = 797 nm, coefficient a = 1.00
5, b = 1.007, and c = 1.035, the refractive index of the optical thin _{film, n H = 2.3, n L} = 1.56, n M = 1.6
8, n _A = 1.37, the film thickness as the optical thin film of lambda _{0/4, respectively, d H = λ 0 / n} H / 4, d L = λ 0 / n L /
4, d _M = λ ₀ / n _M / 4 and d _A = λ ₀ / n _A / 4.

The refractive index of air is 1.0, the refractive index of glass as a base material is 1.52, and the wavelength used is 780 nm.
And "Example (part 2) of polygon mirror 104" The polygon mirror 104 is formed of a reflective substrate such as aluminum.
By forming a filter film having an incident angle dependency thereon, as shown in FIG. 8, a low incident angle (0 ° to
At 6.5 °), the beam is absorbed, and at a high incident angle (8.5 ° or more), the beam is reflected.

Equation (4) shows the structure of an absorption type film having the characteristics shown in FIG. In addition, each with respect to the wavelength λ ₀ λ ₀
Layers having an optical thin film of / 4 are represented by H, M, L and A.

Next, the structure of the absorption type film is shown in (Equation 4).

Air | H · 1.01M · {(9/8) L · (5/4) H · (9/8) L} ¹² · a ｛(9/8) L · (5/4) H・ (9/8) L｝ b ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ c９ (9/8) L ・ (5/4) H ・ ( 9/8) L｝ 0.58A ・ 1.56H ・ 0.58A ｛{(9/8) L ・ (5/4) H ・ (9/8) L｝ ¹²・ a ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ b ｛(9/8) L ・ (5/4) H ・ (9/8) L｝ c ｛(9/8) L ・(5/4) H · (9/8) L｝ · Al · 1.19H | Aluminum Formula (4) The settings for obtaining the characteristics of FIG. 8 are shown below.

Λ ₀ = 797 nm, coefficient a = 1.00
5, b = 1.007, and c = 1.035, the refractive index of the optical thin _{film, n H = 2.3, n L} = 1.56, n M = 1.6
8, n _A = 1.37, the film thickness as the optical thin film of lambda _{0/4, respectively, d H = λ 0 / n} H / 4, d L = λ 0 / n L /
4, d _M = λ ₀ / n _M / 4 and d _A = λ ₀ / n _A / 4.

Air has a refractive index of 1.0, and Al has a thickness of 4.5 nm and a refractive index of 2 + i7. The refractive index of aluminum as the base material was also set to 2 + i7, and the used wavelength λ was set to 780 nm. "Polarization Characteristics of Filter" Next, in the first embodiment,
As shown in FIG. 1, a cylindrical mirror 122 provided between the polygon mirror 104 and the photosensitive drum 106 is used as a filter. The cylindrical mirror 122 having this filter function is generated so as to have a polarization characteristic in the vicinity of the scanning end, and makes the electric field vectors of the laser beam A and the laser beam B orthogonal to each other to thereby make the scanning end. The unnecessary light in the vicinity can be removed.

The laser beams A and B are applied to the semiconductor laser 10
By making 8 a structure that can rotate around the optical axis,
(See arrows AA and BB in FIG. 1), it is easy to make the electric field vectors orthogonal to each other.

Here, as shown in FIG. 2, the electric field vectors of the laser beams A and B reflected from the polygon mirror 104 are set to 0 ° in a direction perpendicular to the scanning plane, and the electric field vector of the laser beam A is set to-. The electric field vector of the laser beam B is adjusted to + 45 ° (clockwise in the traveling direction of the laser beam A as +, and counterclockwise as − in the traveling direction of the laser beam A). This makes it possible to obtain a condition that the electric field vectors are orthogonal to each other.

Based on the above conditions, the filter function will be described with respect to the set angle of the cylindrical mirror 122 in accordance with FIG. 4, but for convenience of description, only the filter function will be described as a single filter FT. As shown in FIG.
The angle between the scanning plane formed by the laser beams A and B reflected and deflected by the polygon mirror 104 and the vertical line of the filter FT is defined as a tilt angle φ, the scanning angle is defined as θ (described above),
The angle between the laser beams A and B incident on the filter FT and the surface of the filter FT is an incident angle θ1, the rotation axis is the optical axis, and the direction perpendicular to the scanning plane is 0 ° (clockwise toward the traveling direction of the laser beam A). The direction is +, and the counterclockwise direction is-)
Then, the angle δ of the incident surface can be expressed by the following equations (1) and (2).

Tan δ = sin θ / tan φ (1) Further, the incident angle θ 1 to the filter FT is: cos θ 1 = cos θ · cos φ (2) Next, this filter FT is connected to the cylindrical mirror 122.
And the reflection characteristics when used as a reflection type filter will be described.

As shown in FIG. 2, the remaining unnecessary light near the scanning edge is −26 ° <θ <−22 ° and + 22 °.
<Θ <+ 26 °.

Therefore, the cylindrical mirror may be raised so that the incident angles near the scanning end are orthogonal to each other.

From the above equation (1), when θ = −25 °, δ
= 45 °, θ = 25 °, the tilt angle φ at which δ = −45 ° is −22.9 °, and as a result, the cylindrical mirror is arranged at the tilt angle (φt = −22.9 °). You. At this time, in a scanning range of −26 ° <θ <−22 ° (hereinafter, referred to as a minus scanning range), the laser beam A
Is S-polarized light, laser beam B is P-polarized light, and +2
In an operation range of 2 ° <θ <+ 26 ° (hereinafter, referred to as a plus-side scanning range), the laser beam A is P-polarized light and the laser beam B is an S-polarized light. Only the unnecessary light is transmitted, and only the unnecessary light of the laser beam A is transmitted in the plus side scanning range.

From equation (2), the incident angle θ1 to the filter FT where unnecessary light is generated is 31.5 ° <θ1 <37.
°, the above characteristics (transmission of unnecessary light) can be obtained in this range. “Example of filter (cylindrical mirror 122)”
Equation (5) shows an embodiment of the film configuration of the reflection type filter having the reflectance characteristics shown in FIG.

Air | (0.5H'L'0.5H ') ^3. (0.5H "L" 0.5H ") ^8. (0.5H'L'0.5H') ³ | Glass formula ( 5) Note that λ ₀ = 610 nm, H ′ = 1.01H, L ′ =
1.146L, H "= 1.076H, L" = 1.220
_{L, n ll = 2.25, n} L = 1.45, n G = 1.52,
d _H = λ ₀ / n _H / 4, dL = λ ₀ / n _L / 4, wavelength used λ
Was set to 780 nm.

The operation of the first embodiment will be described below with reference to FIG.

The laser beam A output from the semiconductor laser 108 and the laser beam B output from the semiconductor laser 108 are converted into a mild divergent light by the collimator lens 110 and then by the beam shaping slit 112.
Light at the center of the divergent light is extracted (passed) and enters the cylindrical lens 114.

The laser beams A and B passing through the cylindrical lens 114 become light converging in the sub-scanning direction, and the scanning angles θ = −α and θ with respect to the center line CL.
= Α enters the polygon mirror.

At this time, the polygon mirror 104 is rotating at a high speed. As shown in FIG. 1, the laser beam A scans from the surface of the photosensitive drum 106 while rotating by the angle α, B scans from the surface of the photosensitive drum 106. Therefore, the exposure from -2α to + 2α within the range of the scanning angle θ is exposed.

Here, as shown in FIG. 2, in each of the laser beam A and the laser beam B, except for writing an image on the photosensitive drum 106 by scanning light,
Light reflected on a reflection surface (adjacent surface) adjacent to the current scanning surface of the polygon mirror 104 may be guided to the surface of the photosensitive drum 106. In other words, as shown in step 0 in FIG.
The reflected light from the adjacent surface of the photosensitive drum 106 is regarded as unnecessary light.
Irradiates a part from above. Laser beam B
At the same time as scanning the object, reflected light from the adjacent surface of the polygon mirror 104 irradiates a part of the photosensitive drum 106 as unnecessary light.

This unnecessary light traces the image recording surface. It is light that must be eliminated. (Removal of Unwanted Light Near the Scanning Center) In the first embodiment, the angle of incidence γ to the polygon mirror 104 is 5 due to the reflection and non-reflection characteristics of the polygon mirror 104 according to the angle of incidence of the laser beams A and B. If it is less than °, it will not be reflected,
The light is reflected when the angle is 6.5 ° or more.

Therefore, as shown in step 1 in FIG. 2, the laser beam A incident on the adjacent surface when the incident angle γ to the polygon mirror 104 is less than 5 ° is not reflected, and unnecessary light in the central portion of the scanning is not generated. . On the other hand, the laser beam A incident on the current reflection surface at an incident angle γ to the polygon mirror 104 of 6.5 ° or more is reflected and scans from the surface of the photosensitive drum 106. Similarly, the laser beam B incident on the adjacent surface is not reflected, and the incident laser beam B is reflected on the current reflection surface.
In addition, scanning can be performed from the surface of the photosensitive drum 106.

As described above, the polygon mirror 104 is provided with a non-reflection characteristic at a low incident angle, so that unnecessary light at the center of scanning can be removed. (Removal of unnecessary light at the scanning end) Next, in the exposure area from -2α to + 2α within the range of the scanning angle θ, removal of unnecessary light by the reflection / non-reflection characteristics of the polygon mirror 104 is performed at the scanning center. Since there is only the vicinity, unnecessary light may remain at the scanning end.

Therefore, in the first embodiment, the cylindrical mirror 122 is provided with a filter function so as to have a polarization characteristic in accordance with the incident angle (including the tilt angle) of the incident laser beams A and B, and to perform the scanning. Removal of unnecessary light at the end is realized. In the first embodiment, the tilt angle φ is set to φ = 22.9 °, and the incident angle θ ₁ is set to 31.5 ° <θ ₁ <37 ° from the expressions (1) and (2). Have been. In this case, a precondition is that the electric field spectra of the laser beam A and the laser beam B are orthogonal to each other.

For this reason, in the first embodiment, the semiconductor laser 108 is rotated around the axis by arrows AA and BB in FIG.
It can be rotated in any direction and can be adjusted. Less than,
The description will be given on the assumption that the semiconductor laser 108 maintains the above condition (the electric field spectra are orthogonal to each other between the laser beam A and the laser beam B).

That is, as shown in step 2 in FIG. 2, when the direction perpendicular to the scanning plane formed by the laser beams A and B reflected from the polygon mirror 104 is 0 °, the electric field vector of the laser beam A becomes −45. ° (+ in the clockwise direction in the beam traveling direction,-in the counterclockwise direction,
And the electric field vector of the laser beam B is + 45 °.

Therefore, the scanning range -26 ° <θ <−22
In °, beam A is S-polarized and beam B is P-polarized.
In the scanning range 22 ° <θ <26 °, the beam A is P-polarized,
The beam B becomes S-polarized light, and the scanning range is −26 ° <θ <.
At −22 °, only the unnecessary light of the beam B is transmitted, and when the scanning range is 22 ° <θ <26 °, only the unnecessary light of the beam A is transmitted.

The incident angle θ ₁ to the filter where unnecessary light is generated
Is 31.5 ° <θ ₁ <37 °, and the filter function of the cylindrical mirror 122 can exhibit transmission characteristics for P-polarized light and reflection characteristics for S-polarized light in this range.

As described above, in the first embodiment, the two light source units 100 and 102 can be guided and scanned on the photosensitive drum 106 by the common (single unit) optical system, and Unnecessary light on the scanning surface (image recording surface) generated by scanning by the optical system is reflected by the reflection / non-reflection characteristics of the polygon mirror 104 and the filter FT (actually, the cylindrical mirror 12).
Since the elimination is performed by the polarization characteristic of 2), the number of components of the optical scanning device can be reduced, and appropriate image quality can be maintained. Further, since the optical system is a common optical system, it is possible to almost eliminate the displacement of the joint between the two scanning lines (particularly the displacement in the sub-scanning direction). (Second Embodiment) Hereinafter, a second embodiment of the present invention will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and the description of the components will be omitted.

The feature of the second embodiment is that the filter function for removing unnecessary light at the scanning end is replaced by the cylindrical mirror 122 in the first embodiment. In the meantime, the filter function is applied to another optical member based on the general concept of "a filter having a polarization characteristic at least at the scanning end."

The selected optical member is that window 124 fitted in the slit-shaped through hole of the casing.

The polarization characteristics of the electric field vectors of the laser beams A and B and the window 124 as a transmission filter will be described with reference to FIG.

From equation (1), when θ = −25 °, δ = 4
5 °, θ = 25 °, δ = −45 °, tilt angle φ
Is −22.9 °, and the window 124 is disposed at this angle.

The electric field vector of the laser beam A is + 45 °
The semiconductor laser 108 is adjusted so that the clockwise direction is + and the counterclockwise direction is-in the beam traveling direction, and the semiconductor laser 108 is adjusted so that the electric field vector of the laser beam B becomes -45 °. Are arranged.

Therefore, in the scanning range -26 ° <θ <-22 ° where one unnecessary light is generated, the laser beam A becomes P-polarized light and the laser beam B becomes S-polarized light. In the scanning range of 22 ° <θ <26 ° where the other unnecessary light is generated, the laser beam A becomes S-polarized light and the laser beam B becomes P-polarized light.

Thus, the window 124 reflects only the unnecessary light of the beam B in the scanning range of −26 ° <θ <−22 °, and the beam A in the scanning range of 22 ° <θ <26 °.
This serves as a polarization low-pass filter that reflects only unnecessary light.

From equation (2), the incident angle θ ₁ to the filter where unnecessary light is generated is 31.5 ° <θ ₁ <37 °, and the window 124 transmits P-polarized light in this range. , S-polarized light.

As described above, the optical member having the filter function may be selected from the imaging optical system 108,
As described above, a member that does not contribute optically at all may be used. Further, a member having a filter function as a separate member may be arranged in a predetermined optical path.

In the second embodiment, the window 124 has the tilt angle φ (φ = 22.9 °). However, there are cases where the tilt angle cannot be set due to design. Also,
In consideration of the refractive index and the like of the window 124, it may be preferable to set the tilt angle φ to 0 °. Thus, FIG. 7 illustrates a case where the tilt angle φ of the window 124 is set to 0 °.

As shown in FIG. 7, the window 124 is disposed at a tilt angle φ = 0 ° so as to be orthogonal to the scanning plane. From equation (1), if the tilt angle φ is 0 °,
The angle δ of the incident surface is 0 °.

Scanning range -26 ° where one unnecessary light is generated
When <θ <−22 °, the polarization direction is set to 0 °,
The scanning range where the other unnecessary light is generated 22 ° <θ <26
In °, the polarization direction is set to 90 °.

Therefore, the position around the optical axis of the semiconductor laser 108 is adjusted so that the electric field vector of the laser beam A becomes 90 °, and the position around the optical axis of the semiconductor laser 108 is adjusted so that the electric field vector of the laser beam B becomes 0 °. May be adjusted.

Thus, the scanning range −26 ° <θ <−2
At 2 °, only the unnecessary light of the beam B is reflected, and the scanning range 2
When 2 ° <θ <26 °, only unnecessary light of the beam A is reflected. (Third Embodiment) Hereinafter, a third embodiment of the present invention will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and description of the configuration will be omitted.

The feature of the third embodiment is that unnecessary light removal at the scanning end as described in the first and second embodiments is unnecessary, and only unnecessary light at the center of the scan is removed.

In order to realize this, as shown in FIG. 3, the length in the main scanning direction may be simply shortened with the image area as a reference of the image center.

As shown in FIG. 3, the image area indicated by the scanning angle θ is changed from -α-β to + α + β, and α> β.
(α and β are both positive numbers). The laser beam A output from the semiconductor laser 108 and the laser beam B output from the semiconductor laser 108 form a polygon mirror 104 at a scanning angle θ = −α and θ = + α with respect to a center line CL passing through the scanning center position. Incident on. Accordingly, while the polygon mirror 104 rotates by an angle (α−10β) / 2, the laser beam A is irradiated from the surface of the photosensitive drum 106
The laser beam B is scanned from the surface of the photoreceptor drum 106 to expose the scanning area θ corresponding to the image area from −α−β to + α + β.

As shown in step 0 in FIG. 3, in the ordinary polygon mirror 104, the laser beam A scans the beam, and at the same time, the reflected light from the adjacent surface of the polygon mirror 104 is converted to unnecessary light from the surface of the photosensitive drum 106 as unnecessary light. Irradiates the part. At the same time as scanning with the laser beam B, reflected light from the adjacent surface of the polygon mirror 104 irradiates a part of the surface of the photosensitive drum 106 as unnecessary light.

Next, as shown in step 1 in FIG. 3, the beam A incident on the polygon mirror 104 at an incident angle γ of less than 6.5 ° is not reflected, so that no unnecessary light is generated in the image area. 7. The angle of incidence γ on the polygon mirror 104 is 8.
The laser beam A incident at an angle of 5 ° or more is scanned from the surface of the photosensitive drum 106 because it is reflected. The laser beam B scans from the surface of the photosensitive drum 106 similarly.

That is, by making the polygon mirror 104 have a non-reflection characteristic at a low incident angle, unnecessary light in the image area can be removed.

[0089]

As described above, the optical scanning device according to the present invention has the following features.

[Brief description of the drawings]

FIG. 1 shows components of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a reflection characteristic according to the first embodiment of the present invention;

FIG. 3 is an illustration of a reflection characteristic according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a setting angle of a filter.

FIG. 5 is an explanatory diagram of an electric field vector of a beam and a reflection characteristic by a reflection filter.

FIG. 6 is an explanatory diagram of an electric field vector of a beam and reflection characteristics of a transmission filter.

FIG. 7 is an explanatory diagram of a beam electric field vector and a reflection characteristic by a transmission filter when a tilt angle = 0.

FIG. 8 is an explanatory diagram of a reflectance characteristic of a polygon mirror;

FIG. 9 is an explanatory diagram of a reflectance characteristic of a reflection type filter.

[Explanation of symbols]

100, 102 Light source unit 104 Polygon mirror (rotating polygon mirror) 106 Photoconductor drum 108 Semiconductor laser (light source unit) 110 Collimator lens (light source unit) 112 Slit (light source unit) 114 Cylindrical lens (imaging optical system) 116 Reflection mirror ( Light source unit) 118 fθ lens (imaging optical system) 120 Folding mirror (imaging optical system) 122 Cylindrical mirror (imaging optical system, filter function of first embodiment) 124 Window (of the second embodiment) Filter function) 126 Reflecting mirror 128 Focusing lens 130 SOS sensor

Claims (7)

[Claims] 1. A rotary polygonal mirror for deflecting an incident beam in a main scanning direction by rotationally driving; and a center line connecting a rotation center of the rotary polygonal mirror and a main scanning center position of a surface to be scanned. Even angle (+
α, −α, α are positive numbers), and the two beams in the main scanning direction are moved in the main scanning direction so that each half of the main scanning is performed while the rotary polygon mirror rotates by an α angle. An optical scanning device comprising: two light source units arranged and deflected with respect to a line in an angle range of −2α and + 2α, wherein the rotating polygon mirror has an incident angle of more than α / 2. An optical scanning device comprising a non-reflection characteristic in a non-existent range. 2. A rotary polygon mirror that deflects an incident beam in a main scanning direction by rotating the mirror, and a center line connecting a rotation center of the rotary polygon mirror and a main scanning center position of a surface to be scanned. Even angle (+
α, −α, α are positive numbers), and the two beams in the main scanning direction are moved in the main scanning direction so that each half of the main scanning is performed while the rotary polygon mirror rotates by an α angle. An optical scanning device comprising: two light source units arranged and deflected with respect to a line in an angle range of −2α and + 2α, wherein the rotating polygon mirror has an incident angle of more than α / 2. The two beams are set so that the electric field vectors are orthogonal to each other, and the polarization characteristics are at least at the scanning end in the optical path from the rotating polygon mirror to the surface to be scanned. An optical scanning device having a filter function. 3. The filter function is a reflection type, and when a scanning angle θ of unnecessary light and a tilt angle φ of a reflecting mirror are tan,
45 ^o = optical scanning apparatus according to claim 2, characterized in that arranged in the sin [theta / tan [phi. 4. The filter function is of a transmission type, and when a scanning angle θ of unnecessary light and a tilt angle φ of a reflecting mirror are set to tan,
45 ^o = optical scanning apparatus according to claim 2, characterized in that arranged in the sin [theta / tan [phi. 5. The method according to claim 2, wherein
4. The optical scanning device according to claim 1, wherein the effective scanning range is deflected in an angle range of -α-β and α + β (α> β, both being positive numbers) with respect to the center line. apparatus. 6. The rotating polygon mirror having a non-reflection characteristic has a reflection characteristic having an incident angle dependence on a transmission base material. An optical scanning device according to claim 1. 7. The mirror according to claim 1, wherein the rotating polygon mirror having the non-reflection characteristic has an absorption characteristic having an incident angle dependence on a reflection surface. Optical scanning device.