JP2004020787A

JP2004020787A - Optical scanner and laser printer

Info

Publication number: JP2004020787A
Application number: JP2002174035A
Authority: JP
Inventors: Kenji Mochizuki; 望月　健至; Susumu Tateyama; 立山　晋; Kazutaka Setoma; 瀬戸間　和隆
Original assignee: Hitachi Printing Solutions Inc
Current assignee: Ricoh Printing Systems Ltd
Priority date: 2002-06-14
Filing date: 2002-06-14
Publication date: 2004-01-22
Anticipated expiration: 2022-06-14
Also published as: JP4106537B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner by which the image formation luminous flux of an isotropic shape is obtained on a surface to be scanned by making NA in a main scanning direction nearly equal to NA in a subscanning direction without using a rotationally asymmetrical slit or the like. <P>SOLUTION: When the focal distance of a second optical system is set as f<SB>2</SB>, that of a third optical system is set as f<SB>3</SB>, that of a fourth optical system in a plane where a luminous flux is deflected and scanning is performed is set as f<SB>4</SB>and the lateral magnification of the fourth optical system in a plane perpendicular to the plane where the luminous flux is deflected and the scanning is performed is set as M, the relation of M = f<SB>2</SB>f<SB>4</SB>/f<SB>3</SB><SP>2</SP>is nearly satisfied. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はレーザプリンタ等に用いられる光走査装置およびレーザプリンタ装置に係る。
【０００２】
【従来の技術】
レーザプリンタの印刷速度の高速化、および高ドット密度化に伴い、複数光束による光走査装置が広く用いられている。これら光走査装置にはアレイ状に配列された半導体レーザ光源を用いる例がある（特許第２７４１１９５号明細書）。
【０００３】
光偏向手段として、反射面を有する回転多面鏡が一般に用いられているが、この反射面の倒れ誤差補正のために、光束が偏向走査される方向（以下主走査方向と称す）とそれに垂直な方向（以下副走査方向と称す）で異なる光学素子の配置をとっている。
【０００４】
このような光走査装置において、スリットなどの光束径を制限する開口部材を用い、その開口を主走査方向と副走査方向で夫々適切な幅として、感光ドラム面上で等方的な形状の結像光束が得られるようにした例がある（特開平６−２０８０６８号公報）。この場合、一般に開口幅は主走査方向と副走査方向で異なる、すなわち回転非対称な形状である。
【０００５】
しかしながら、回転非対称な形状のスリットは配置時の回転誤差を抑える必要があるため、配置上の制約が多い。例えば、コリメート光学系など回転対称な光学素子の鏡筒などとの一体化は困難である。また、回転誤差が大きいと結像光束に影響を及ぼす。
【０００６】
【発明が解決しようとする課題】
本発明の課題は、回転非対称な形状のスリット等を用いる事なく、被走査面上で等方的な形状の結像光束が得られる光走査装置を提供することにある。
【０００７】
【課題を解決するための手段】
前記の課題は、回転対称な開口に対して主走査方向および副走査方向において開口数（ＮＡ）が略同一となるように、光学素子の焦点距離等を最適化することによって達成される。
【０００８】
【発明の実施の形態】
本発明の作用を模式的に示す。図２に光走査装置の主走査方向の配置を示す。
１１は光源、１２は光束、１０はコリメート光学系、１３は第２光学系、１４は第３光学系、１５は回転多面鏡反射面、１６は第４光学系、１７は被走査面である。第２光学系の焦点距離をｆ_２、第３光学系の焦点距離をｆ_３、第４光学系の光束が偏向走査される平面内における焦点距離をｆ_４とする。コリメート光学系１０を透過した光束１２の径をδ_１とする。被走査面１７における光束１２の開口数ＮＡ_１は（２）式で与えられる。
【０００９】
ＮＡ_１＝δ_１ｆ_３／（ｆ_２ｆ_４）　　…（２）
図３に副走査方向の配置を示す。コリメート光学系１０を透過した光束１２の径をδ_２とする。第４光学系の副走査方向横倍率をＭとする。被走査面１７における光束１２の開口数ＮＡ_２は（３）式で与えられる。
【００１０】
ＮＡ_２＝δ_２／（ｆ_３Ｍ）　　…（３）
（２）式、および（３）式から、ＮＡ_１＝ＮＡ_２、δ_１＝δ_２となる条件を求めると、（１）式となる。
【００１１】
Ｍ＝ｆ_２ｆ_４／ｆ_３ ^２　　　　…（１）
図１に本発明の実施例を示す。図において１はレーザ光源、２はコリメータレンズ、３はスリット、４は主走査方向に屈折作用を有するシリンドリカルレンズ、５は球面レンズ、６は回転多面鏡、７は走査レンズ、８は感光ドラム、９は光軸、１０１および１０２は光束である。走査レンズ７は３個のレンズ７１乃至７３で構成されている。レーザ光源１は概略主走査方向に配列された２個の発光点１１および１２を有している。発光点１１、１２から出射された光束１０１、１０２は、コリメート光学系であるコリメータレンズ２、光束径を制限する開口部材であるスリット３、第２光学系であるシリンドリカルレンズ４、第３光学系である球面レンズ５、光偏向手段である回転多面鏡６、第４光学系である走査レンズ７を介して、被走査面である感光ドラム８に結像される。
【００１２】
本発明の実施例の諸元を表１乃至表３に示す。表中の（１）はスリット３の面、（２）、（３）はシリンドリカルレンズ４の面、（４）、（５）は球面レンズ５の面、（６）は回転多面鏡６の反射面、（７）、（８）は走査レンズ７１の面、（９）、（１０）は走査レンズ７２の面、（１１）、（１２）は走査レンズ７３の面、（１３）は感光ドラム８の面である。Ｒは主走査方向の光軸９上の曲率半径、ｒは副走査方向の光軸９上の曲率半径、ｔｈは面間距離、ｎは屈折率である。（１０）は、主走査方向をＸ、副走査方向をＹ、光軸方向をＺとして、（４）式で与えられる。
【００１３】
Ｚ＝ｆ_０（Ｘ、Ｙ）＋ｆ_２（Ｘ、Ｙ）　…（４）
ここでｆ_０（Ｘ、Ｙ）は基本的なトーリック形状を表し、ｆ_２（Ｘ、Ｙ）は回転非対称な追加関数を表す。光軸との交点を原点としたローカル座標系のＸＺ平面における断面が（５）式で表され、ＸＺ平面にあり、Ｘ軸に平行で、Ｚ軸に沿って原点からｒの距離にある軸について回転対称である。
【００１４】
ｆ_０（Ｘ、Ｙ）＝（Ｘ^２／Ｒ）／（１＋ＳＱＲＴ（１−（Ｘ／Ｒ）^２））　…（５）
従って、ＹＺ平面における断面は曲率半径ｒの円となる。ｆ_２（Ｘ、Ｙ）は（６）式で表される。
【００１５】
ｆ_２（Ｘ、Ｙ）＝ａ_０９ＸＹ^２＋ａ_１３Ｘ^２Ｙ^２　　…（６）
ここでａ_ｌｍは定数である。
【００１６】
【表１】

【００１７】
【表２】

【００１８】
【表３】

【００１９】
δ_１、δ_２＝２．０ｍｍである事を基に、（２）式、（３）式を用いてＮＡ_１、ＮＡ_２を求めると、次のようになる。
【００２０】
ＮＡ_１＝ＮＡ_２＝０．０２
このように主走査方向と副走査方向のＮＡが等しくなるので、ドラム面上で概略等方的な形状の結像光束を得る事ができる。
【００２１】
図４にコリメータレンズとスリットの配置例を示す。図において、２１は鏡筒であり、鏡筒を介してコリメータレンズとスリットが一体化されている。また、スリットはコリメータレンズの後側焦点近傍に配置されている。
【００２２】
光源から出射された光束の拡がり角が非等方的である場合には、本実施例のように主走査方向と副走査方向で開口幅の等しいスリットを用いた場合であっても光束内の光量分布は必ずしも等方的とはならない。結像光束の形状はＮＡのみで決定されるものではないため、このような場合厳密な意味で等方的な形状とはなり得ないが、実用上問題無い程度であれば差し支えない。
【００２３】
光源から出射された光束の拡がり角度が等方的である場合には必ずしもスリットを設ける必要は無い。
【００２４】
スリットをコリメータレンズの後側焦点近傍に配置する事は、スリット透過後の複数の光束径を等しくするのに適当である。
【００２５】
スリットをコリメータレンズの鏡筒と一体化する事により、調整等によりコリメータレンズの位置が変わっても上記スリットとの相対的位置関係を維持する事ができ、また部品点数を削減するのに効果がある。
【００２６】
スリットの開口が回転対称であれば、コリメータレンズとスリットが一体化されている場合でも、コリメータレンズを回転させて位置調整する事が可能である。この光走査装置はレーザプリンタ装置の印刷速度の高速化、および高ドット密度化に適している。
【００２７】
【発明の効果】
以上説明したように、本発明によれば回転非対称なスリット等を用いることなく、主走査方向、副走査方向のＮＡを概略等しくする事ができるため、被走査面上で等方的な形状の結像光束が得られる。
【図面の簡単な説明】
【図１】本発明の実施例を示す図。
【図２】本発明の主走査方向の作用を示す図。
【図３】本発明の副走査方向の作用を示す図。
【図４】本発明のコリメータレンズとスリットの配置例を示す図。
【符号の説明】
１…光源
２…コリメート光学系
３…開口部材
４…第２光学系
５…第３光学系
６…光偏向手段
７…第４光学系
８…被走査面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device and a laser printer used for a laser printer or the like.
[0002]
[Prior art]
With the increase in printing speed and the increase in dot density of laser printers, optical scanning devices using a plurality of light beams have been widely used. Some of these optical scanning devices use semiconductor laser light sources arranged in an array (Japanese Patent No. 2741195).
[0003]
A rotating polygon mirror having a reflecting surface is generally used as the light deflecting means. To correct the tilt error of the reflecting surface, a direction in which the light beam is deflected and scanned (hereinafter referred to as a main scanning direction) and a direction perpendicular to the direction. Different optical elements are arranged in different directions (hereinafter referred to as sub-scanning directions).
[0004]
In such an optical scanning device, an opening member such as a slit for limiting the light beam diameter is used, and the opening is formed to have an appropriate width in the main scanning direction and the sub-scanning direction, respectively, and isotropically formed on the photosensitive drum surface. There is an example in which an image light beam is obtained (Japanese Patent Laid-Open No. 6-208068). In this case, the opening width generally differs in the main scanning direction and the sub-scanning direction, that is, has a rotationally asymmetric shape.
[0005]
However, since a rotationally asymmetric slit needs to suppress a rotation error during arrangement, there are many restrictions on arrangement. For example, it is difficult to integrate a rotationally symmetric optical element such as a collimating optical system with a lens barrel. Also, a large rotation error affects the imaged light beam.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical scanning device capable of obtaining an imaging light flux having an isotropic shape on a surface to be scanned without using a rotationally asymmetric slit or the like.
[0007]
[Means for Solving the Problems]
The above object is achieved by optimizing the focal length and the like of the optical element so that the numerical aperture (NA) is substantially the same in the main scanning direction and the sub-scanning direction with respect to the rotationally symmetric aperture.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The operation of the present invention is schematically shown. FIG. 2 shows the arrangement of the optical scanning device in the main scanning direction.
11 is a light source, 12 is a light beam, 10 is a collimating optical system, 13 is a second optical system, 14 is a third optical system, 15 is a reflecting surface of a rotating polygon mirror, 16 is a fourth optical system, and 17 is a surface to be scanned. . The focal length of the second optical system is f ₂ , the focal length of the third optical system is f ₃ , and the focal length of the fourth optical system in the plane where the light beam is deflected and scanned is f ₄ . The diameter of the light beam 12 transmitted through the collimating optical system 10 and [delta] _1. Numerical aperture NA ₁ of the light beam 12 on the scanned surface 17 is given by equation (2).
[0009]
NA ₁ = δ ₁ f ₃ / (f ₂ f ₄ ) (2)
FIG. 3 shows the arrangement in the sub-scanning direction. The diameter of the light beam 12 transmitted through the collimating optical system 10 and [delta] _2. Let M be the lateral magnification in the sub-scanning direction of the fourth optical system. Numerical aperture NA ₂ of the light beam 12 on the scanned surface 17 is given by equation (3).
[0010]
NA ₂ = δ ₂ / (f ₃ M) (3)
When the conditions that satisfy NA ₁ = NA ₂ and δ ₁ = δ ₂ are obtained from Expressions (2) and (3), Expression (1) is obtained.
[0011]
M = f ₂ f ₄ / f ₃ ² (1)
FIG. 1 shows an embodiment of the present invention. In the figure, 1 is a laser light source, 2 is a collimator lens, 3 is a slit, 4 is a cylindrical lens having a refracting action in the main scanning direction, 5 is a spherical lens, 6 is a rotating polygon mirror, 7 is a scanning lens, 8 is a photosensitive drum, 9 is an optical axis, 101 and 102 are light beams. The scanning lens 7 is composed of three lenses 71 to 73. The laser light source 1 has two light emitting points 11 and 12 arranged substantially in the main scanning direction.

Light beams

101 and 102 emitted from the light emitting points 11 and 12 are collimator lens 2 as a collimating optical system, slit 3 as an opening member for limiting the light beam diameter, cylindrical lens 4 as a second optical system, and third optical system. An image is formed on a photosensitive drum 8 as a surface to be scanned through a spherical lens 5 as a light source, a rotating polygon mirror 6 as a light deflecting means, and a scanning lens 7 as a fourth optical system.
[0012]
Tables 1 to 3 show the specifications of the embodiment of the present invention. In the table, (1) is the surface of the slit 3, (2) and (3) are the surfaces of the cylindrical lens 4, (4) and (5) are the surfaces of the spherical lens 5, and (6) is the reflection of the rotary polygon mirror 6. (7) and (8) are the surfaces of the scanning lens 71, (9) and (10) are the surfaces of the scanning lens 72, (11) and (12) are the surfaces of the scanning lens 73, and (13) is the photosensitive drum. This is the 8th aspect. R is the radius of curvature on the optical axis 9 in the main scanning direction, r is the radius of curvature on the optical axis 9 in the sub-scanning direction, th is the distance between surfaces, and n is the refractive index. (10) is given by equation (4), where X is the main scanning direction, Y is the sub-scanning direction, and Z is the optical axis direction.
[0013]
Z = f ₀ (X, Y) + f ₂ (X, Y) (4)
Here, f ₀ (X, Y) represents a basic toric shape, and f ₂ (X, Y) represents a rotationally asymmetric additional function. A cross section in the XZ plane of the local coordinate system with the intersection point with the optical axis as the origin is represented by Expression (5), and is an axis that is in the XZ plane, parallel to the X axis, and located at a distance r from the origin along the Z axis. Is rotationally symmetric.
[0014]
f ₀ (X, Y) = (X ² / R) / (1 + SQRT (1- (X / R) ² )) (5)
Therefore, the cross section in the YZ plane is a circle having a radius of curvature r. f ₂ (X, Y) is represented by equation (6).
[0015]
f ₂ (X, Y) = a ₀₉ XY ² + a ₁₃ X ² Y ² (6)
Here, _alm is a constant.
[0016]
[Table 1]

[0017]
[Table 2]

[0018]
[Table 3]

[0019]
Based on the fact that δ ₁ , δ ₂ = 2.0 mm, when NA ₁ and NA ₂ are obtained using the equations (2) and (3), the following results are obtained.
[0020]
NA ₁ = NA ₂ = 0.02
Since the NAs in the main scanning direction and the sub-scanning direction are equal in this manner, it is possible to obtain an imaging light flux having a substantially isotropic shape on the drum surface.
[0021]
FIG. 4 shows an arrangement example of the collimator lens and the slit. In the figure, reference numeral 21 denotes a lens barrel, and a collimator lens and a slit are integrated via the lens barrel. Further, the slit is arranged near the rear focal point of the collimator lens.
[0022]
When the divergent angle of the light beam emitted from the light source is anisotropic, even if a slit having the same opening width in the main scanning direction and the sub-scanning direction is used as in this embodiment, the light beam is The light quantity distribution is not always isotropic. Since the shape of the image forming light beam is not determined only by the NA, in such a case, it cannot be an isotropic shape in a strict sense, but it is acceptable as long as there is no practical problem.
[0023]
When the spread angle of the light beam emitted from the light source is isotropic, it is not always necessary to provide a slit.
[0024]
Arranging the slit near the rear focal point of the collimator lens is suitable for equalizing the diameters of a plurality of light fluxes after passing through the slit.
[0025]
By integrating the slit with the lens barrel of the collimator lens, it is possible to maintain the relative positional relationship with the slit even if the position of the collimator lens changes due to adjustment or the like, and it is effective in reducing the number of parts. is there.
[0026]
If the opening of the slit is rotationally symmetric, the position can be adjusted by rotating the collimator lens even when the collimator lens and the slit are integrated. This optical scanning device is suitable for increasing the printing speed of a laser printer and increasing the dot density.
[0027]
【The invention's effect】
As described above, according to the present invention, the NA in the main scanning direction and the sub-scanning direction can be made substantially equal without using a rotationally asymmetric slit or the like. An imaging light beam is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing the operation of the present invention in the main scanning direction.
FIG. 3 is a diagram showing the operation of the present invention in the sub-scanning direction.
FIG. 4 is a diagram showing an example of the arrangement of a collimator lens and a slit according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Collimating optical system 3 ... Opening member 4 ... Second optical system 5 ... Third optical system 6 ... Light deflection means 7 ... Fourth optical system 8 ... Scanning surface

Claims

In an optical scanning device that deflects and scans a light beam emitted from a light source having a plurality of light emitting points onto a surface to be scanned by a light deflecting device, the light deflecting device has a reflecting surface for reflecting the light beam, A collimating optical system for making the light beam from the light source substantially parallel, a second optical system having a refraction function in a plane where the light beam is deflected and scanned, in order from the one closer to the light source, Forming a confocal system with the second optical system in the plane where the light beam is deflected and scanned, and forming an image of the light beam from the collimating optical system in the vicinity of the reflection surface in a plane perpendicular to the plane where the light beam is deflected and scanned A rotationally symmetric third optical system having an effect of causing the light beam to deflect and scan is disposed between the reflection surface and the scanned surface in a plane perpendicular to a plane where the light beam is deflected and scanned. And are approximately conjugated relations And the light beam deflected by the light deflecting means and the fourth optical system is arranged to have a function of forming an image on the scanned surface vicinity, the focal length of the second optical system f _2, a focal length of the third optical system f ₃ , the focal length in a plane where the light beam of the fourth optical system is deflected and scanned is f ₄ , and the lateral magnification in a plane perpendicular to the plane where the light beam of the fourth optical system is deflected and scanned is M, is an outline. optical scanning apparatus characterized by satisfying the relation of _{_{_{M = f 2 f 4 / f}}} 3 2.

Between the collimating optical system and the reflecting surface, an aperture member for limiting the beam diameter is arranged, and the aperture member is located in a plane where the beam is deflected and scanned and in a plane perpendicular to the plane where the beam is deflected and scanned. The optical scanning device according to claim 1, wherein the aperture widths are equal.

3. The optical scanning device according to claim 2, wherein the aperture member is integrated with a lens barrel of the collimating optical system.

The optical scanning device according to claim 3, wherein the aperture member is disposed near a rear focal point of the collimating optical system.

2. The optical scanning device according to claim 1, wherein a spread angle of the light beam emitted from the light source is isotropic.

A laser printer comprising the optical scanning device according to claim 1, 2, 3, 4, or 5.