JP4384372B2 - Scanning optical apparatus and image forming apparatus - Google Patents

Description

なお、表１において、＊が付された面は共軸非球面であり、数１で表される。
【００２３】
【数１】

数１において、面番号１の面は、
Ｋ＝２．６６７，Ａ＝１．７９Ｅ−０７，Ｂ＝−１．０８Ｅ−１２，
Ｃ＝−３．１８Ｅ−１４，そしてＤ＝３．７４Ｅ−１８である。
また、面番号２の面は、
Ｋ＝０．０２，Ａ＝２．５０Ｅ−０７，Ｂ＝９．６１Ｅ−１２，
Ｃ＝４．５４Ｅ−１５，そしてＤ＝−３．０３Ｅ−１８である。
【００２４】
また、＊＊が付された面は、主走査方向の形状が非円弧形状であり、副走査方向の曲率半径は、レンズ高さによって連続的に変化する。面番号３の主走査形状は、数１において、Ｋ＝−７１．７３，Ａ＝４．３３Ｅ−０８，Ｂ＝−５．９７Ｅ−１３，Ｃ＝−１．２８Ｅ−１６，そしてＤ＝５．７３Ｅ−２１である。この面番号３の面は、主走査対応方向における光軸からの距離：Ｙを変数とする偏向直交面内の曲率半径をＲｓ（Ｙ）とした時、該Ｒｓ（Ｙ）を特定するのに、多項式：
Ｒｓ（Ｙ）＝Ｒｓ（０）＋Σｂｊ・Ｙ^ｊ （ｊ＝１，２，３，…）
で表すことにする。面番号３の面は、主走査対応方向において光軸対称で、Ｒｓ（０）＝−４７．７，ｂ２＝１．６０Ｅ−０３，ｂ４＝−２．３２Ｅ−０７，ｂ６＝１．６０Ｅ−１１，ｂ８＝−５．６１Ｅ−１６，ｂ１０＝２．１８Ｅ−２０，およびｂ１２＝−１．２５Ｅ−２４として示すことができる。
なお、本光学系においては、厚さ１．９ｍｍの防音ガラス１１（屈折率１．５１１）および厚さ１．９ｍｍの防塵ガラス１０（屈折率１．５１１）を挿入して、計算している。
また、各光学要素の反射防止膜のコーティングの条件は、表２の通りである。
【００２５】
【表２】

【００２６】
なお像高は、図４において、ポリゴンミラー４の回転軸から像面に下ろした足を像高０ｍｍとし、上をプラス像高、下をマイナス像高としている。
この場合、シェーディングを改善するには、偏向反射面と被走査面の間に、入射角が４５°以下で、反射防止膜は単層である反射部材を少なくとも１つ有することが望ましい。図５に、光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を４５°として、反射防止膜を４層とした場合Ａと単層とした場合Ｂのシェーディング特性の比較を示す。図５によれば、４層は７．４％なのに対して、単層は７．３％となり、シェーディング特性が改善している。ここで、４層の各層の厚みは１／４λ、単層の厚みは１／２λとしている。
また、光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を２０°とした場合（図６）でも、４層は７．０％なのに対して、単層は６．４％となり、シェーディング特性が改善している。さらに、光源からの光束の偏光方向の副走査方向に対する角度を３５°、折り返しミラーへの入射角を４５°とした場合（図７）でも、４層は５．３％なのに対して、単層は３．４％となり、シェーディング特性が改善している。
【００２７】
また、複数の折り返しミラーがある場合、副走査断面から見た光線入射角が４５°以上であれば像高の中央付近の反射率が高くなり、周辺の反射率が低くなるように逆の効果を持ち、これを相殺するためにも副走査断面から見た光線入射角が４５°以下である折り返しミラーが必要である。上記反射率は、反射防止膜の厚みｄと光源波長λに応じて変化する。
さらに望ましくは単層の反射防止膜の光学的厚みｄは、光源波長をλとして、
（１／２）λ＜ｄ≦（３／４）λ
とすると、シェーディングがさらに改善される。
また、単層の厚みを０．７λにすると、光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を４５°とした場合は、図５のＣのように５．２％となりシェーディング特性は改善する。光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を２０°とした場合でも図６のＣのように５．２％となりシェーディングは改善する。さらに、光源からの光束の偏光方向の副走査方向に対する角度を３５°、折り返しミラーへの入射角を４５°とした場合でも図７のＣのように、２．７％となり、シェーディングが改善する。
【００２８】
次に、像面の絶対光量が不足する為に単層のミラーが使えず、多層膜を使わざるをえない場合でも、各層の厚みを（１／４）λ＜ｄ＜（１／２）λとすれば、それ以外の場合よりもシェーディング特性が改善する。
ここではｄ＝０．４５λの場合を示す。光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの副走査断面から見た光線入射角を４５°とすると図５のＤのように４．４％、光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を２０°とすると図６のＤのように４．７％、光源からの光束の偏光方向の副走査方向に対する角度を３５°、折り返しミラーへの副走査断面から見た光線入射角を４５°とすると図７のＤのように０．６％となり、いずれもシェーディングが低減されることがわかる。
また、複数の折り返しミラーがある場合、副走査断面から見た光線入射角が４５°以上であれば像高の中央付近の反射率が高くなり、周辺の反射率が低くなるように逆の効果を持ち、これを相殺するためにさらに副走査断面から見た光線入射角が４５°以下である折り返しミラーが必要となり、同数以上必要となる。
【００２９】
次に、図８および図９に４色対応のカラー画像形成装置の具体的な構成図を示す。図８は、転写ベルト１１５上に記録媒体１４を乗せ、記録媒体１４に直接トナー像を転写するタイプ、図９は一旦トナー像を転写ベルト１１５上に転写し、さらに記録媒体１４に転写するタイプを示している。さらに記録媒体１４に画像形成されるまでのプロセスは通常の多色画像形成装置と同様である。これらの各色の光走査装置に上述したシェーディング低減技術を適用することにより、色むらを低減し、画像品質を向上させることができる。なお、図８および図９に示した構成については特開平１１−３２６８０４号公報等に詳細に示されているので、ここでは簡単な説明にとどめる。
図８および図９に示す画像形成装置は、光走査装置１１７、帯電器１１２Ｍ，１１２Ｃ，１１２Ｙ，１１２Ｋ、現像器１１３Ｍ，１１３Ｃ，１１３Ｙ，１１３Ｋ、転写器１１４Ｍ，１１４Ｃ，１１４Ｙ，１１４Ｋ、転写ベルト１１５および定着装置１１６を備えている。図８と図９は、主として定着装置１１６の位置および記録媒体１４を挿入する個所が相違する。
【００３０】
【発明の効果】
以上述べたように、本発明によれば、光源から射出される光束を光偏向器によって偏向し、結像光学系を介して被走査面上に走査線を形成する走査光学系と、この走査光学系に対応して配置した感光体とを複数組備え、１枚のシートへの多重印刷に用いるタンデム方式の走査光学系において、シェーディングを有効に軽減して、形成される画像の品質を向上させ、画像の濃度むらおよび色味のむらを抑制し、高品位のカラー画像等を形成することを可能とする走査光学装置および画像形成装置を提供することができる。
また、本発明の請求項１の走査光学装置によれば、光源から射出される光束を光偏向器によって偏向し、結像光学系を介して被走査面上に走査線を形成する走査光学系と、この走査光学系に対応して配置した感光体とを複数組備え、１枚のシートへの多重印刷に用いるタンデム方式の走査光学装置において、
前記光源からの前記光束の偏光方向の副走査方向に対する角度を４０°未満とし、且つ前記光偏向器の偏向反射面と被走査面との間に、副走査断面から見た光線入射角が４５°以下で、反射防止膜は単層である反射部材を少なくとも１つ配設しており、前記反射防止膜の光学的厚みｄは、光源波長をλとして、
（１／２）λ＜ｄ≦（３／４）λ
であることにより、シェーディングを有効に軽減し、形成画像の品質を向上させることができる。
【００３２】
さらに、本発明の請求項２の画像形成装置によれば、上述した請求項１に記載の走査光学装置を含んで画像形成装置を構成することにより、画像の濃度むら、色味のむらを抑え、高品位のカラー画像等を形成することが可能となる。
【図面の簡単な説明】
【図１】本発明の一つの実施の形態に係る走査光学装置における主として光偏向器である回転多面鏡以降の副走査系を含む要部を示す断面図である。
【図２】図１の走査光学装置の偏向走査面を含む平面に走査光学系を展開して示す模式図である。
【図３】図１の走査光学装置における単一色の走査光学系の主として光偏向器である回転多面鏡以降の副走査系を含む要部を示す断面図である。
【図４】図１の走査光学装置における単一色の偏向走査面を含む平面に走査光学系を展開して示す模式図である。
【図５】光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を４５°とした場合のシェーディング特性を示す図である。
【図６】光源からの光束の偏光方向の副走査方向に対する角度を０°、折り返しミラーへの入射角を２０°とした場合のシェーディング特性を示す図である。
【図７】光源からの光束の偏光方向の副走査方向に対する角度を３５°、折り返しミラーへの入射角を４５°とした場合のシェーディング特性を示す図である。
【図８】転写ベルト上に記録媒体を乗せ、記録媒体に直接トナー像を転写するタイプの４色対応のカラー画像形成装置の具体的な構成図である
【図９】一旦トナー像を転写ベルト上に転写し、さらに記録媒体に転写するタイプの４色対応のカラー画像形成装置の具体的な構成図である
【符号の説明】
１，１Ａ，１Ｂ，１Ｃ 半導体レーザ
２，２Ａ，２Ｂ，２Ｃ カップリングレンズ
３，３Ａ，３Ｂ，３Ｃ シリンドリカルレンズ
４ ポリゴンミラー
５，５Ａ，５Ｂ，５Ｃ 第１の走査結像レンズ
６，６Ａ，６Ｂ，６Ｃ 第１の折返しミラー
７，７Ａ，７Ｂ，７Ｃ 第２の折返しミラー
８Ａ，８Ｂ，８Ｃ 第３の折返しミラー
９，９Ａ，９Ｂ，９Ｃ 感光体
１０，１０Ａ，１０Ｂ，１０Ｃ 防塵ガラス
１１，１１Ａ 防音ガラス
１２，１２Ａ，１２Ｂ，１２Ｃ 第２の走査結像レンズ
１４ 記録媒体
１１２Ｍ，１１２Ｃ，１１２Ｙ，１１２Ｋ 帯電器
１１３Ｍ，１１３Ｃ，１１３Ｙ，１１３Ｋ 現像器
１１４Ｍ，１１４Ｃ，１１４Ｙ，１１４Ｋ 転写器
１１５ 転写ベルト
１１６ 定着装置
１１７ 光走査装置
ＡＰ アパーチャ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning optical apparatus that scans a light beam used for an image forming apparatus such as a laser printer, a facsimile, and a digital PPC (Plain Paper Copier) copying machine to write and form an image. The present invention relates to a scanning optical apparatus and an image forming apparatus suitable for a color image forming apparatus such as a color laser printer and a digital color copying machine.
[0002]
[Prior art]
Conventionally, image forming apparatuses such as laser printers and digital PPC copying machines have been mainly monochromatic ones, but in recent years, color image forming apparatuses such as color laser printers and digital color copying machines have been developed. Higher performance and lower prices are being promoted. The color image forming apparatus achieves this by superimposing a plurality of single color images such as three primary colors and performing multiple printing.
In this type of image forming apparatus, for example, a digital color image forming apparatus such as a digital color copying machine, a plurality of, for example, a plurality of, for example, cylindrical photosensitive members, which are rotationally driven by a drive mechanism, A plurality of different color information is written by scanning means by scanning means to form an electrostatic latent image, and these electrostatic latent images are visualized to different colors by a plurality of visualization means. The color image is obtained by superimposing and transferring on the transfer material. The writing means in such an image forming apparatus scans the photosensitive member with a condensing spot obtained by condensing a scanning beam consisting of a writing beam from a light source such as a semiconductor laser through an optical component such as a writing lens. Information is written on the photosensitive member by the formed scanning lines to form an electrostatic latent image.
[0003]
In such an optical scanning optical system, further improvement in quality of an image to be written is required. That is, there is a problem of “density unevenness” caused by shading as a point to be improved in the quality of an image written by the optical scanning optical system. In the optical scanning optical system, the light beam is deflected by the deflecting / reflecting surface, and the incident angle at which the deflected light beam enters the scanning imaging optical system continuously changes during one deflection. Between the deflection reflection surface and the surface to be scanned, a reflection optical system such as a folding mirror for bending the optical path of the deflected light beam is provided according to the layout of the optical system. The light reflectivity changes according to the incident angle. For this reason, the reflectivity of the deflected light beam by the deflecting reflection surface or the folding mirror also varies with the deflection of the deflected light beam. As a result, the light intensity of the deflected light beam reaching the surface to be scanned fluctuates within one deflection period. Such a fluctuation in the light intensity of the light spot that occurs within one deflection period, that is, within one line of optical scanning, is called “shading”.
[0004]
If there is shading in the optical scanning by the optical scanning optical system, “density unevenness” appears in the recorded image in which the written image is visualized. Furthermore, when multiple images are printed, such as a color image, the number and angle of the folding mirrors differ for each color due to restrictions on the arrangement of the photoreceptors that form the electrostatic latent image. , The generated shading is different, and uneven coloring occurs.
For example, in Japanese Patent Laid-Open No. 11-326807, a light beam from a light source is deflected at an equiangular velocity by an optical deflector having a deflecting reflection surface, and the deflected light beam is formed as a light spot on a surface to be scanned by a scanning imaging optical system. In an optical scanning optical system that condenses and optically scans the surface to be scanned at a constant speed, a semiconductor laser that emits a linearly polarized light beam is used as a light source, and the direction of linear polarization of the light beam emitted from this semiconductor laser However, a technique for reducing shading by adjusting the deployed state of the semiconductor laser so as to be inclined around the optical axis with respect to the sub-scanning corresponding direction is shown.
[0005]
[Problems to be solved by the invention]
However, even using the technique disclosed in Japanese Patent Application Laid-Open No. 11-326807, it has not been possible to effectively reduce shading and sufficiently improve the quality of the formed image in the optical scanning optical system. Therefore, the shading is more effectively reduced in the optical scanning optical system, the density unevenness and the color unevenness of the formed image are effectively suppressed, the image quality is improved, and a high-quality color image is formed. It is requested.
The present invention has been made in view of the above-described circumstances, and includes a scanning optical system that deflects a light beam emitted from a light source by an optical deflector and forms a scanning line on a surface to be scanned via an imaging optical system. In a tandem scanning optical system comprising a plurality of photoconductors arranged corresponding to the scanning optical system and used for multiple printing on a single sheet, shading is effectively reduced and an image formed An object of the present invention is to provide a scanning optical device and an image forming apparatus that can improve quality, suppress unevenness in density and color of an image, and form a high-quality color image or the like.
An object of claim 1 of the present invention is to provide a scanning optical device that can effectively reduce shading and improve the quality of a formed image, particularly in an optical scanning optical system.
The object of claim 2 of the present invention is to effectively reduce shading in an optical scanning optical system, to suppress unevenness in image density and color, and to obtain a high-quality color image or the like. An object is to provide an image forming apparatus.
[0006]
[Means for Solving the Problems]
In order to achieve the above-described object, a scanning optical device according to the present invention described in claim 1 is provided.
A light beam emitted from a light source is deflected by an optical deflector, a scanning optical system that forms a scanning line on a surface to be scanned via an imaging optical system, and a photoconductor disposed corresponding to the scanning optical system. In a tandem scanning optical device that is used for multiple printing on a single sheet with multiple sets,
The angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is less than 40 °, and the light incident angle as seen from the sub-scanning section is 45 between the deflection reflection surface and the surface to be scanned of the optical deflector. Or less, the antireflection film is provided with at least one reflecting member that is a single layer, and the optical thickness d of the antireflection film is such that the light source wavelength is λ,
(1/2) λ <d ≦ (3/4) λ
It is characterized by being.
[0008]
The image forming apparatus according to the present invention described in 請 Motomeko 2, in order to achieve the above object,
The scanning optical device according to claim 1 is included.
[0009]
[Action]
That is, a scanning optical device according to claim 1 of the present invention includes a scanning optical system that deflects a light beam emitted from a light source by an optical deflector and forms a scanning line on a surface to be scanned via an imaging optical system; In a tandem scanning optical apparatus comprising a plurality of sets of photoreceptors arranged corresponding to the scanning optical system and used for multiple printing on one sheet,
The angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is less than 40 °, and the light incident angle as seen from the sub-scanning section is 45 between the deflection reflection surface and the surface to be scanned of the optical deflector. Or less, the antireflection film is provided with at least one reflecting member that is a single layer, and the optical thickness d of the antireflection film is such that the light source wavelength is λ,
(1/2) λ <d ≦ (3/4) λ
It is .
With this structure, effectively reduce sheet Edingu, it is possible to improve the quality of the formed image.
[0014]
Et al of the image forming apparatus according to claim 2 of the present invention, including the scanning optical apparatus according to claim 1 described above.
With such a configuration, the image forming apparatus is configured to include the scanning optical device according to claim 1, so that it is possible to suppress unevenness in image density and unevenness in color and form a high-quality color image or the like. Become.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, based on an embodiment of the present invention, a scanning optical device according to the present invention will be described in detail with reference to the drawings.
1 and 2 show the configuration of the main part of a scanning optical device according to one embodiment of the present invention. FIG. 1 is a sub-scanning cross-sectional view after the rotary polygon mirror, which is mainly an optical deflector in the scanning optical device, and FIG. 2 is a diagram in which the scanning optical system is developed on a plane including the deflection scanning surface of the scanning optical device. .
1 and 2 includes a semiconductor laser 1, 1A, 1B, 1C, coupling lenses 2, 2A, 2B, 2C, cylindrical lenses 3, 3A, 3B, 3C, a polygon mirror 4 and a first mirror. Scanning imaging lenses 5, 5A, 5B, 5C, first folding mirrors 6, 6A, 6B, 6C, second folding mirrors 7, 7A, 7B, 7C, third folding mirrors 8, 8A, 8B, 8C , Photoconductors 9, 9A, 9B, 9C, dustproof glass 10, 10A, 10B, 10C, soundproof glass 11, 11A, and second scanning imaging lenses 12, 12A, 12B, 12C.
[0016]
The semiconductor lasers 1, 1A, 1B and 1C are light sources and generate laser beams as light beams. Coupling lenses 2, 2A, 2B, and 2C respectively adjust the divergent light beams emitted from semiconductor lasers 1, 1A, 1B, and 1C to form appropriate laser beams into cylindrical lenses 3, 3A, 3B, and 3C. Make it incident. In this case, the cylindrical lenses 3, 3A, 3B, and 3C have power, that is, refractive power only in the sub-scanning direction, and collect laser beams from the semiconductor lasers 1, 1A, 1B, and 1C in only one predetermined direction, respectively. Light is emitted to form a line image in the vicinity of the polygon mirror 4. The polygon mirror 4 is a rotary polygon mirror that is commonly used for the laser beams of the semiconductor lasers 1, 1A, 1B, and 1C. Each scanning imaging lens is scanned while rotating and deflecting each laser beam. 5,5A, 5B, 5C, etc. First scanning imaging lenses 5, 5A, 5B and 5C, first folding mirrors 6, 6A, 6B and 6C, second folding mirrors 7, 7A, 7B and 7C, third folding mirrors 8, 8A, 8B and 8C and the second scanning imaging lenses 12, 12A, 12B and 12C appropriately guide and condense the deflection-scanned laser beam, and the photoreceptors 9, 9A, 9B, which are the scanned surfaces, and An image is formed on the surface of 9C. In this case, the photoconductors 9, 9A, 9B and 9C form a surface to be scanned on a cylindrical surface, and form a latent image by exposure. The dustproof glasses 10, 10A, 10B and 10C are glasses for protecting dust between the periphery of the photoreceptors 9, 9A, 9B and 9C and the outside.
[0017]
The soundproof glass 11 and 11A include a polygon mirror 4, semiconductor lasers 1 and 1A, coupling lenses 2 and 2A, cylindrical lenses 3 and 3A, first scanning imaging lenses 5 and 5A, a first folding mirror 6, and the like. 6A, second folding mirrors 7, 7A, third folding mirrors 8, 8A, photoconductors 9, 9A, dust-proof glass 10, 10A, and second scanning imaging lenses 12, 12A, and a polygon mirror 4, semiconductor lasers 1B and 1C, coupling lenses 2B and 2C, cylindrical lenses 3B and 3C, first scanning imaging lenses 5B and 5C, first folding mirrors 6B and 6C, and second folding mirrors 7B and 7C. , The third folding mirrors 8B and 8C, the photoreceptors 9B and 9C, the dust-proof glasses 10B and 10C, and the second scanning imaging lenses 12B and 12C, respectively. Interpolated, to shield the rotation noise of the polygon mirror 4 which is rotated at a high speed.
[0018]
As described above, the semiconductor laser 1, the coupling lens 2, the cylindrical lens 3, the first scanning imaging lens 5, the first folding mirror 6, the second folding mirror 7, the third folding mirror 8, the photoconductor 9, The dust-proof glass 10 and the second scanning imaging lens 12 constitute a first set of a scanning optical system and a photoconductor, and include a semiconductor laser 1A, a coupling lens 2A, a cylindrical lens 3A, and a first scanning imaging lens. 5A, the first folding mirror 6A, the second folding mirror 7A, the third folding mirror 8A, the photoconductor 9A, the dustproof glass 10A, and the second scanning imaging lens 12A are composed of a scanning optical system and a photoconductor. 2 sets, a semiconductor laser 1B, a coupling lens 2B, a cylindrical lens 3B, a first scanning imaging lens 5B, a first folding mirror 6B, and a second folding mirror B, the third folding mirror 8B, the photoconductor 9B, the dust-proof glass 10B, and the second scanning imaging lens 12B constitute a third set of the scanning optical system and the photoconductor, and the semiconductor laser 1C, the coupling lens 2C, cylindrical lens 3C, first scanning imaging lens 5C, first folding mirror 6C, second folding mirror 7C, third folding mirror 8C, photoconductor 9C, dust-proof glass 10C, and second scanning connection The image lens 12C constitutes a fourth set of a scanning optical system and a photosensitive member.
[0019]
In the thus configured scanning optical apparatus, divergent light beams of laser light emitted from the semiconductor lasers 1, 1A, 1B, and 1C are coupled by the coupling lenses 2, 2A, 2B, and 2C, and only in the sub-scanning direction. The light is condensed by cylindrical lenses 3, 3 A, 3 B, and 3 C having power, and is formed as a line image near the reflection point of the polygon mirror 4. Here, the line image is in the vicinity of the reflection point, but may be slightly away from the reflection point. The light beam reflected and deflected by the polygon mirror 4 passes through the soundproof glass 11, 11A, and is scanned by the first scanning lenses 5, 5A, 5B, 5C and the second scanning lenses 12, 12A, 12B, 12C. Are imaged on the surfaces of the photoconductors 9, 9A, 9B, 9C. Here, the first scanning lenses 5, 5A, 5B, and 5C as scanning optical elements are used one by one for each light beam. However, a plurality of scanning lenses may be used, or scanning vertically stacked. The lenses 5 and 5A or 5B and 5C may be integrated into one lens.
[0020]
Thereafter, each luminous flux passes through the dust-proof glass 10, 10A, 10B, 10C, and enters the photoreceptor 9, 9A, 9B, 9C to form a latent image, and a toner image is formed by a developing device (not shown). Then, the image is transferred to a transfer medium or a recording medium such as a recording sheet placed on the transfer belt.
In this case, two light beams are distributed on both sides of the polygon mirror 4, but the total number of light beams may be further increased or the number of light beams to be distributed may be changed as appropriate.
Since the scanning optical system for each color in the case of multicolor printing or the like has basically the same configuration, only the optical system for one color will be described below.
[0021]
FIG. 3 is a sub-scanning sectional view mainly after the rotary polygon mirror which is an optical deflector in the scanning optical device, and FIG. 4 is a diagram in which the scanning optical system is developed on a plane including the deflection scanning surface of the scanning optical device. . In FIG. 4, an aperture AP is shown between the coupling lens 2 and the cylindrical lens 3.
Here, the optical system data after the polygon mirror 4 which is an optical deflector will be considered.
Light source wavelength: 650 nm
Rm: radius of curvature in the meridional direction [mm]
Rs: Sagittal radius of curvature [mm]
N: Refractive index at the wavelength used [mm]
X: Distance in the optical axis direction [mm]
Y: Distance in the direction perpendicular to the optical axis [mm]
Table 1 is obtained for each surface number shown in FIG.
[0022]
[Table 1]

In Table 1, the surface marked with * is a coaxial aspheric surface, and is expressed by the following equation (1).
[0023]
[Expression 1]

In equation 1, the surface with surface number 1 is
K = 2.667, A = 1.79E-07, B = −1.08E-12
C = -3.18E-14, and D = 3.74E-18.
The surface with surface number 2 is
K = 0.02, A = 2.50E-07, B = 9.61E-12
C = 4.54E-15, and D = −3.03E-18.
[0024]
In addition, the surface marked with ** has a non-arc shape in the main scanning direction, and the radius of curvature in the sub-scanning direction continuously changes depending on the lens height. The main scanning shape of surface number 3 is K = −71.73, A = 4.33E−08, B = −5.97E−13, C = −1.28E−16, and D = 5 in Equation 1. 73E-21. This surface of surface number 3 is used to specify Rs (Y), where Rs (Y) is the radius of curvature in the deflection orthogonal plane with the variable Y from the optical axis in the main scanning direction. , Polynomial:
Rs (Y) = Rs (0) + Σbj · Y ^j (j = 1, 2, 3,...)
It will be expressed as The surface of surface number 3 is symmetric about the optical axis in the main scanning direction, and Rs (0) = − 47.7, b2 = 1.60E-03, b4 = −2.32E-07, b6 = 1.60E−. 11, b8 = −5.61E−16, b10 = 2.18E−20, and b12 = −1.25E−24.
In this optical system, calculation is performed by inserting soundproof glass 11 (refractive index 1.511) having a thickness of 1.9 mm and dustproof glass 10 having a thickness of 1.9 mm (refractive index 1.511). .
The conditions for coating the antireflection film of each optical element are as shown in Table 2.
[0025]
[Table 2]

[0026]
In FIG. 4, the image height is 0 mm for the foot lowered from the rotation axis of the polygon mirror 4 to the image plane, the plus image height is above, and the minus image height is below.
In this case, in order to improve the shading, between the deflection reflecting surface and the surface to be scanned, at an incident angle of 45 ° or less, the antireflection film is not to want to have at least one reflecting member is a single layer. FIG. 5 shows that the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 °, the incident angle to the folding mirror is 45 °, and the antireflection film has four layers A and a single layer B. A comparison of shading characteristics is shown. According to FIG. 5, the four layers are 7.4%, while the single layer is 7.3%, which improves the shading characteristics. Here, the thickness of each of the four layers is 1 / 4λ, and the thickness of the single layer is 1 / 2λ.
Even when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 ° and the incident angle to the folding mirror is 20 ° (FIG. 6), the four layers are 7.0%, but the single layer Is 6.4%, and the shading characteristics are improved. Furthermore, even when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 35 ° and the incident angle to the folding mirror is 45 ° (FIG. 7), the four layers are 5.3%, whereas the single layer is Is 3.4%, and the shading characteristics are improved.
[0027]
In addition, when there are a plurality of folding mirrors, if the incident angle of light viewed from the sub-scanning section is 45 ° or more, the reflectivity is high near the center of the image height, and the reverse effect is such that the reflectivity at the periphery is low. In order to cancel this, a folding mirror having a light incident angle of 45 ° or less as viewed from the sub-scan section is required. The reflectance varies depending on the thickness d of the antireflection film and the light source wavelength λ.
More preferably, the optical thickness d of the single-layer antireflection film is such that the wavelength of the light source is λ,
(1/2) λ <d ≦ (3/4) λ
When, shading Ru be further improved.
When the thickness of the single layer is 0.7λ, the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 °, and the incident angle to the folding mirror is 45 °, as shown in FIG. Therefore, the shading characteristics are improved by 5.2%. Even when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 ° and the incident angle to the folding mirror is 20 °, the shading is improved as shown in FIG. Furthermore, even when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 35 ° and the incident angle to the folding mirror is 45 °, the shading is improved as shown in FIG. .
[0028]
Next, even if a single-layer mirror cannot be used because the absolute amount of light on the image plane is insufficient, and a multilayer film must be used, the thickness of each layer is set to (1/4) λ <d <(1/2) if λ, improve the shading characteristics than otherwise.
Here, a case where d = 0.45λ is shown. Assuming that the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 ° and the light incident angle as viewed from the sub-scanning cross section to the folding mirror is 45 °, 4.4% as shown in FIG. If the angle of the polarization direction of the light beam with respect to the sub-scanning direction is 0 ° and the incident angle to the folding mirror is 20 °, the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 4.7% as shown in FIG. Is 35 °, and the incident angle of the light beam viewed from the sub-scanning cross section to the folding mirror is 45 °, it becomes 0.6% as shown in D of FIG.
In addition, when there are a plurality of folding mirrors, if the incident angle of light viewed from the sub-scanning section is 45 ° or more, the reflectivity is high near the center of the image height, and the reverse effect is such that the reflectivity at the periphery is low. the have, which requires a further folding mirrors the light incident angle is 45 ° or less as viewed from the sub-scanning section in order to offset, that Do require more equal.
[0029]
Next, FIG. 8 and FIG. 9 show specific configuration diagrams of a color image forming apparatus corresponding to four colors. 8 shows a type in which the recording medium 14 is placed on the transfer belt 115 and the toner image is directly transferred to the recording medium 14. FIG. 9 shows a type in which the toner image is once transferred onto the transfer belt 115 and then transferred to the recording medium 14. Is shown. Further, the process until the image is formed on the recording medium 14 is the same as that of a normal multicolor image forming apparatus. By applying the above-described shading reduction technology to each color optical scanning device, color unevenness can be reduced and image quality can be improved. The configuration shown in FIGS. 8 and 9 is described in detail in Japanese Patent Application Laid-Open No. 11-326804 and the like, so only a brief description will be given here.
8 and 9 includes an optical scanning device 117, chargers 112M, 112C, 112Y, and 112K, developing devices 113M, 113C, 113Y, and 113K, transfer devices 114M, 114C, 114Y, and 114K, and a transfer belt 115. And a fixing device 116. 8 and 9 are mainly different in the position of the fixing device 116 and the portion where the recording medium 14 is inserted.
[0030]
【The invention's effect】
As described above, according to the present invention, the scanning optical system that deflects the light beam emitted from the light source by the optical deflector and forms the scanning line on the scanning surface via the imaging optical system, and the scanning In the tandem scanning optical system used for multiple printing on a single sheet, with multiple sets of photoconductors arranged corresponding to the optical system, shading is effectively reduced and the quality of the image formed is improved Therefore, it is possible to provide a scanning optical apparatus and an image forming apparatus that can suppress uneven density and uneven color of an image and form a high-quality color image or the like.
According to the scanning optical apparatus of the first aspect of the present invention, the scanning optical system that deflects the light beam emitted from the light source by the optical deflector and forms the scanning line on the surface to be scanned through the imaging optical system. A plurality of photoconductors arranged corresponding to the scanning optical system, and a tandem scanning optical apparatus used for multiple printing on one sheet,
The angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is less than 40 °, and the light incident angle as seen from the sub-scanning section is 45 between the deflection reflection surface and the surface to be scanned of the optical deflector. Or less, the antireflection film is provided with at least one reflecting member that is a single layer, and the optical thickness d of the antireflection film is expressed as follows:
(1/2) λ <d ≦ (3/4) λ
Therefore , shading can be effectively reduced and the quality of the formed image can be improved .
[0032]
Et al is, according to the image forming apparatus according to claim 2 of the present invention, by constituting the image forming apparatus including a scanning optical apparatus according to claim 1 described above, the image density unevenness, the unevenness of color Therefore, it is possible to form a high-quality color image or the like.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a main part including a sub-scanning system after a rotary polygon mirror which is mainly an optical deflector in a scanning optical apparatus according to an embodiment of the present invention.
2 is a schematic diagram showing a scanning optical system developed on a plane including a deflection scanning surface of the scanning optical apparatus of FIG. 1; FIG.
3 is a cross-sectional view showing a main part including a sub-scanning system after a rotary polygon mirror which is mainly an optical deflector of a single color scanning optical system in the scanning optical apparatus of FIG. 1;
4 is a schematic diagram showing a scanning optical system developed on a plane including a single color deflection scanning surface in the scanning optical apparatus of FIG. 1; FIG.
FIG. 5 is a diagram showing shading characteristics when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 ° and the incident angle to the folding mirror is 45 °.
FIG. 6 is a diagram showing shading characteristics when the angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is 0 ° and the incident angle to the folding mirror is 20 °.
FIG. 7 is a diagram showing shading characteristics when the angle of the polarization direction of a light beam from a light source with respect to the sub-scanning direction is 35 ° and the incident angle to the folding mirror is 45 °.
FIG. 8 is a specific configuration diagram of a color image forming apparatus corresponding to four colors in which a recording medium is placed on a transfer belt and a toner image is directly transferred to the recording medium. FIG. FIG. 4 is a specific configuration diagram of a color image forming apparatus corresponding to four colors that is transferred onto a recording medium and transferred onto a recording medium.
1, 1A, 1B, 1C Semiconductor lasers 2, 2A, 2B, 2C Coupling lenses 3, 3A, 3B, 3C Cylindrical lenses 4 Polygon mirrors 5, 5A, 5B, 5C First scanning imaging lenses 6, 6A, 6B , 6C First folding mirror 7, 7A, 7B, 7C Second folding mirror 8A, 8B, 8C Third folding mirror 9, 9A, 9B, 9C Photosensitive member 10, 10A, 10B, 10C Dust-proof glass 11, 11A Soundproof glass 12, 12A, 12B, 12C Second scanning imaging lens 14 Recording medium 112M, 112C, 112Y, 112K Charger 113M, 113C, 113Y, 113K Developer 114M, 114C, 114Y, 114K Transfer device 115 Transfer belt 116 Fixing device 117 Optical scanning device AP Aperture

Claims (2)

A light beam emitted from a light source is deflected by an optical deflector, a scanning optical system that forms a scanning line on a surface to be scanned via an imaging optical system, and a photoconductor disposed corresponding to the scanning optical system. In a tandem scanning optical device that is used for multiple printing on a single sheet with multiple sets,
The angle of the polarization direction of the light beam from the light source with respect to the sub-scanning direction is less than 40 °, and the light incident angle as viewed from the sub-scanning section is 45 between the deflection reflection surface and the surface to be scanned of the optical deflector. Or less, the antireflection film is provided with at least one reflection member that is a single layer, and the optical thickness d of the antireflection film is expressed as follows:
(1/2) λ <d ≦ (3/4) λ
Scanning optical apparatus, characterized in that it. An image forming apparatus comprising the scanning optical device according to claim 1 .

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