JP4029639B2 - Light amount setting method for optical scanning device - Google Patents

Description

まず、各ビームの光量分布の中心値を求めると、表２のようになる。中心値とは、走査領域内の任意の点における光量のうち最大値と最小値の平均値である。任意の点は、本実施形態では、上記中央部及び＋側、−側端部である。
【００６３】
各光ビームの光量分布の中心値より、基準となる光ビーム（ここではシアンを基準とする）に対する、差を求める。
【００６４】
【表２】

上記基準ビームとの中心値の差を、各ビームの補正量として、補正すると、表３及び図４（Ｂ）のようになる。
【００６５】
【表３】

以上の手順により、補正前は各ビーム間の光量差が走査領域において両端部で最大６％あったが、補正後は最大３％となり、半減する。
【００６６】
この結果、画像形成装置１０において用紙２４に形成された画像の各色の濃度差も抑制され、良好な画像が形成されることになる。
【００６７】
なお、本実施形態では、基準ビーム（本実施形態ではシアン）を設け、基準ビームに対する補正を行なったが、例えば、表２で求められた中心値から、さらに各色の中心値の平均値を求め、その平均値にたいして補正を行なう方法もある。
【００６８】
以上のように、各ビームの光量設定（光量の一致）を各走査領域中央部の光量で行なうのではなく、走査領域において光量差を平均的に分散させることで、画像における濃度差を小さくできる。
【００６９】
次に、半導体レーザの広がり角と光量分布の関係について図５、図６を用いて説明する。
【００７０】
図５と図６は、オーバーフィルド光学系の概略図を示している。図５は、回転多面鏡４４の反射面４２によって感光体１６における走査領域中央部に光ビームＬが導かれる状態を示し、図６は感光体１６の走査領域端部に光ビームＬが導かれる状態を示し、各図の（Ｂ）〜（Ｄ）がそれぞれ半導体レーザ出射光（各図（Ａ）における位置Ｂ）、スリット後の光束（各図（Ａ）における位置Ｃ）、ポリゴンミラー反射後の光束（各図（Ａ）における位置Ｄ）のプロファイルを示している。
【００７１】
オーバーフィルド光学系では、前述したように、回転多面鏡４４へ入射する光束を切り取るように反射して走査している。まず、半導体レーザ２６から出射された光ビームＬはある広がりを持って出射されている。出射された光ビームＬは、コリメータレンズ２８で平行光となり開口板３２の開口部３０によって光束幅を規制され、回転多面鏡４４の反射面４２へ入射される。走査中央部では、図５（Ａ）に示すように、入射光束の中央部を使用することになる。また、走査端部では、図６（Ａ）に示すように、入射光束の約半分の片側のみを使用することになる。このように、走査中央部と走査端部での入射光束の切り取り量がことなるため、端部での光量分布の減衰といった減少が生じることになる。
【００７２】
また、図５及び図６では、半導体レーザ２６の広がり角が異なるプロファイルを示している。半導体レーザ２６の広がり角はα、β、γ（度）であり、α＜β＜γの関係となっている。この広がり角の違いによって、回転多面鏡４４で切り取られる量に差が生ずる。すなわち、図５（Ｄ）に示すように走査中央部においては、広がり角α、β、γの差は小さいが、図６（Ｄ）に示すように走査端部では回転多面鏡４４で切り取られる量がα、β、γで異なり、その結果、光量分布のバラツキといった現象となる。
【００７３】
以上のように、半導体レーザ２６の広がり角の製造バラツキが、光走査装置の光量分布にバラツキの一要因となっている。
【００７４】
そこで、本実施形態では、画像形成装置１０において、全ての光走査装置２０で使用される半導体レーザ２６を、広がり角が一致したものしている。すなわち、半導体レーザ２６の広がり角を予め検査し、広がり角が一致した半導体レーザ２６を同一の画像形成装置１０の光走査装置２０に使用することによって、複数の光走査装置（光ビーム）間で広がり角の違いに起因する複数の光ビーム間の光量分布のバラツキを防止することができ、各色の濃度差を抑制することができる。
【００７５】
次に、開口板３２の開口３０の形状と光量分布の関係を図７（Ａ）、（Ｂ）を用いて説明する。図７（Ａ）は、開口の正面図、図７（Ｂ）は開口の寸法Ｘを変化させたときの光量分布をグラフで示した図である。
【００７６】
図３（Ａ）〜（Ｃ）で示したように、開口板３２の開口部３０の形状を走査方向両端部で副走査方向の幅を中央部と比較して大きくすることによって、走査領域端部における光量低下を抑制して、光量分布を均一化させることができる。しかし、それだけでは、各色の光ビーム間の光量差を抑制することができない。そこで、開口部３０の形状の変化による走査領域端部の光量変化を関数化することによって、これに対処しようというものである。
【００７７】
開口部３０の形状は、図７（Ａ）に示すように、光軸Ｃが通過する位置の副走査幅Ｗ１の中央部３０Ａに対して副走査幅がＷ１よりも広いＷ２である走査方向端部３０Ｂが両端に形成されたものである。
【００７８】
ここで、開口部３０の中央部の走査方向長さＸを変化させることにより、図７（Ｂ）に示すように、走査領域端部の光量の走査領域中央部に対する光量比が変化することが確認された。すなわち、走査方向長さＸと光量比には、関数で表すことができる相関関係があるため、所望の光量分布（光量比）を得るために寸法Ｘを前記関数より求めることができる。また、異なる光学系でも同様の関係を導くと、図７（Ｂ）の光学系▲２▼のようになる。この場合でも、走査方向長さＸと光量分布は関数で表され、所望の光量分布を得ることは容易である。
【００７９】
また、上記走査方向長さＸに限らず開口部３０形状を異ならせることで、所望の光量分布を得ることが可能である。
【００８０】
本実施形態では、前記開口板３２は、容易に着脱可能に構成され、着脱により半導体レーザ２６、凹レンズ３４、シリンドリカルレンズ３６との光軸がずれないような取付け構造となっている。前記開口板３２は開口３０の形状が異なるものが少なくとも２種類以上用意されており、光量分布形状により前記開口板３２を交換することになる。
【００８１】
このように構成することによって、光ビームＬの光量分布を均一化することができると共に、他の光ビームＬの光量分布との光量差を低減させるために調整することが可能となる。
【００８２】
このように、本実施形態では、画像形成装置１０に搭載される複数の光走査装置２０から出射される光ビームの光量分布を略一致させることができるため、形成される画像の色の濃度差を抑制することができる。
【００８３】
また、ここでは、光量分布の設定方法、開口形状の異なる開口板３２を配設することによって端部と中央部の光量比を調整する方法、広がり角の一致した半導体レーザ２６を使用すること、を説明したが、これらのいずれか１つだけ採用しても効果があると共に、これらの複数を組み合せても同様に効果がある。
〔第２実施形態〕
本発明の第２実施形態に係る光走査装置について説明する。本発明では、第１実施形態と異なるのが、光走査装置の構成のみなので該当部分のみを説明する。第１実施形態と同様の構成要素には同一の参照符号を付し、その詳細な説明を省略する。
【００８４】
第１実施形態と異なるのは、本発明の実施の形態に係る光走査装置５０が、多色（カラー）画像形成装置に搭載されるタイプであり、各色（Ｙ，Ｍ，Ｃ，Ｋ）用の感光体ドラムを走査するための複数の光学系、及び複数の光源が一つの光走査装置５０内に装備されている。
【００８５】
図８および図９に示すように、光走査装置５０の光学箱５２内部に４色に相当する４本の光学系が構成されている。光学箱５２の内部には、それぞれ２色に相当する光ビームが出射される光源装置部５４、５６から出射された２本ずつの光ビームがそれぞれ回転多面鏡５８の対向する反射面６０に入射して、各色に対応した感光体ドラム６２Ｙ、６２Ｍ、６２Ｃ、６２Ｋに入射する構成である。
【００８６】
したがって、光走査装置５０の光学系は回転多面鏡５８の両側で対称となる光学系となっている。ここでは、図９における右側の光学系について説明する。便宜的に、光源装置部５４Ａからの光ビームを“光ビームＬＡ”、光源装置部５４Ｂからの光ビームを“光ビームＬＢ”と称する。
【００８７】
光源装置部５４Ａ、５４Ｂにおいて、半導体レーザ２６から出射された光ビームＬＡ、ＬＢはコリメータレンズ２８によって光ビーム整形され、開口絞り３２で光束幅を規制された後、シリンドリカルレンズ３４によって所定形状（副走査方向に集束し主走査方向には長い）の線状光束とされる。
【００８８】
シリンドリカルレンズ３４を透過後、光ビームＬＡは平面ミラー６４に直接入射し、光ビームＬＢは平面ミラー６６での反射によって光ビームＬＡとほぼ同じ向きとされて平面ミラー６４に入射する。
【００８９】
ここでの光ビームＬＡ、ＬＢは副走査方向で所定の角度差を有して平面ミラー６４に入射し、回転多面鏡５８側に反射される。
【００９０】
また、光ビームＬＡ、ＬＢは回転多面鏡５８へ入射する時と回転多面鏡５８で反射偏向された後に主走査方向においてｆθレンズ４０を透過すると共に、回転多面鏡５８の反射面へ正面から入射する、いわゆる正面入射ダブルパス光学系とされている。
【００９１】
なお、光ビームＬＡ、ＬＢの回転多面鏡５８の反射面６０上での高さ方向の入射位置は、副走査方向での入射角を大きく設定された光ビームＬＢが、入射角を小さく設定された光ビームＬＡより下側に入射するように設定されている。
これにより回転多面鏡５８の反射面上における両光ビームの副走査方向での間隔が確保される。さらに、回転多面鏡５８の反射面６０で反射された光ビームＬＡ、ＬＢの副走査方向での間隔は光路が進に従い徐々に広がる。よって、ｆθレンズ４０を透過した後に確保される両光ビームの間隔が広くされることで、その後の各光学部品の配置を可能な限り容易にしている。
【００９２】
なお、回転多面鏡５８で偏向され、ｆθレンズ４０を透過した光ビームＬＡ、ＬＢは各光ビームに対応して設けられた平面ミラー６８Ａ、６８Ｂによって所定の光路になるよう角度調整される。この後、光ビームＬＡ、ＬＢは回転多面鏡５８の上方を通過して各シリンドリカルミラー４６に至る。
【００９３】
シリンドリカルミラー４６により下方へ反射された光ビームＬＡ、ＬＢはｆθレンズ４０の間を通過し、すなわち光走査装置５０の内部を再度通過して、感光体ドラム６２Ｃ、６２Ｋに至る。
【００９４】
以上が片側の光学系及び、光ビームの光路であり、他方も同ような光学系、光路によって各感光体ドラム６２Ｍ、６２Ｙに至る。
【００９５】
このように、本実施形態の光走査装置５０における光学系では回転多面鏡５８の片側で２本の光ビームを、両側で計４本の光ビームを同時に偏向走査し、各光源から出射される光ビームにより、ブラック（Ｋ）、イエロー（Ｙ）、マゼンタ（Ｍ）、シアン（Ｃ）の各色に対応して配置された感光体ドラム上を走査する構成である。
【００９６】
このように、光走査装置５０では、同一の装置上で各色に対応する複数の光ビームの光量ビームの調整及び計測をできるため、複数の光ビームの光量分布の計測を同時に行なうことができる。すなわち、光量分布の差を瞬時に把握することができる。光量分布の差が求められれば、本発明の光量分布の中心値を合わせる手段、及びスリット交換による光量分布調整を容易に行なうことができる。
【０１００】
【発明の効果】
以上説明したように、請求項１の発明によれば、複数の光ビームの初期設定光量は、走査領域内の光量分布の中心値が、すべての光ビームで一致するようにしたことで、走査領域内のあるポイントで一致させるよりも、走査領域全域で平均的に差を小さくすることができる。この結果、複数の光ビームを重ねあわせたときに走査領域内のどこのポイントでも光ビーム間に光量差が小さく、各光ビームで形成された画像の濃度差が抑制される。
【０１０１】
請求項２の発明によれば、任意の光ビームの光量分布の中心値を基準とし、他の光ビームの中心値を一致させることで請求項１の発明と同様の効果を得ることができる。
【図面の簡単な説明】
【図１】 本発明の第１実施形態に係る画像形成装置の側面図である。
【図２】 本発明の第１実施形態に係る光走査装置の斜視図である。
【図３】 （Ａ）〜（Ｃ）は、本発明の第１実施形態に係るスリットの開口形状の例を示す図である。
【図４】 本発明の第１実施形態に係る複数の光走査装置における光量分布のバラツキの説明図である。
【図５】本発明の第１実施形態に係る走査中央部の半導体レーザの広がり角と光量分布の関係を示すである。
【図６】本発明の第１実施形態に係る走査端部の半導体レーザの広がり角と光量分布の関係を示すである。
【図７】本発明の第１実施形態に係る（Ａ）開口板の正面図、（Ｂ）開口部形状と光量分布の関係を示すグラフである。
【図８】 本発明の第２実施形態に係る光走査装置の斜視図である。
【図９】 本発明の第２実施形態に係る光走査装置の側面図である。
【図１０】 従来のフルカラー画像形成装置の構成を示す摸式図である。
【図１１】 従来例に係る光走査装置の概略斜視図である
【図１２】 従来例に係るアンダーフィルド光学系による光走査装置の概略構成を示す図であり、（Ａ）は平面図、（Ｂ）は側面図である。
【図１３】 従来例に係る開口板の開口の形状、及び開口と光ビームとの位置関係を示す概略図である。
【図１４】 従来例に係るオーバーフィルド光学系による光走査装置の概略構成を示す図であり、（Ａ）は平面図、（Ｂ）は側面図である。
【図１５】 特開平９−９６７６９号公報に開示された光走査装置の光軸調整装置を説明する図である。
【図１６】 特開平９−１６４７１８号公報に開示された感光体面上のレーザパワーと走査角度の関係を示す図である。
【図１７】 特開２０００−８３４４５号公報に開示された光学部品の反射面に薄膜層を形成した場合の入射角に対する反射率の増加比率をグラフとして示した図である。
【図１８】特開平１１−２１８７０２号公報に開示された光量分布の補正を効果を示すグラフである。
【符号の説明】
２０、５０…光走査装置
２６…光源
３２…開口板（開口部材）
４４、５８…回転多面鏡（偏向手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning apparatus that scans a light beam and writes an image, and is suitable for a copying machine or a laser printer that forms an image with a plurality of light beams. More specifically, the present invention relates to an optical scanning device provided with means for correcting so that the difference in the light amount distribution in the scanning direction of a plurality of light beams on a scanned object is minimized or substantially matched, and a light amount setting method for the optical scanning device.
[0002]
[Prior art]
In a conventional image forming apparatus, a light beam output from a single laser is incident on a polygon mirror as a light deflecting unit via an optical system such as a cylindrical lens, and the reflected light is subjected to main scanning (deflection) by rotation of the polygon mirror. Scanning). The light beam reflected by the polygon mirror passes through an fθ lens as an optical means, and forms an image on a photoconductor as an image carrier. By repeating this while sub-scanning the photoconductor, an image can be formed on the photoconductor. Since the image formed on the photoconductor is an electrostatic image, a desired image can be obtained on a sheet by supplying toner or the like to reveal (develop) it and transfer it to a predetermined sheet.
[0003]
In recent years, as the colorization of documents has progressed, full-color images are formed by forming developers for each color of black (K), yellow (Y), magenta (M), and cyan (C), and transferring them sequentially. Image forming apparatuses have been developed.
[0004]
Among them, a plurality of independent image forming apparatuses are provided for applications that require a particularly high image forming speed, and the developed images formed here are continuously transferred onto a single transfer medium. Tandem-type full-color image forming apparatuses that form a full-color image in one cycle have been developed.
[0005]
Here, an example of a conventional full-color image forming apparatus will be described with reference to FIGS.
[0006]
As shown in FIGS. 10A and 10B, in the image forming apparatus 100, black (K), yellow (Y), magenta (M), cyan (C) from the upstream side of the sheet conveying belt 102 in the sheet conveying direction. ) In the order of the image forming apparatus 104K, the image forming apparatus 104Y, the image forming apparatus 104M, and the image forming apparatus 104C. In each of the image forming apparatuses, an electrophotographic process is performed around the photosensitive member 106 as an image carrier. The constituent subunits are arranged.
[0007]
In this apparatus, after the photosensitive member 106 is charged by the charging device 108, a light beam according to image information is exposed and scanned by the optical scanning device 110 to form a latent image. Next, after the latent image is developed by the developing device 112, the image is transferred to the paper 114 conveyed at a constant speed.
[0008]
This process is performed in the order of K, Y, M, and C, and the transfer image is fixed on the paper 114 by a fixing device (not shown) and discharged.
[0009]
The optical scanning device 110 deflects a light beam emitted from a laser light source (not shown) that is turned on according to image information at an equal angular velocity by a rotating polygonal mirror 116, and two photoreceptors 106 by two fθ lenses 118. An image is formed on a spot that is scanned at a constant speed.
[0010]
Further, in the tandem full-color image forming apparatus, there is one in which a plurality of lasers (scanning optical systems) are provided in one optical scanning apparatus. As shown in FIG. 11, in such an optical scanning device 120, the optical system disposed inside the optical box 122 includes a plurality of light source device units 124, and beams from the light source device units 124 pass through the plane reflection mirror 126 and the like. Through the fθ lens 130, the reflection mirror 132, and the cylindrical mirror 134, and the photosensitive drums 136Y and 136M corresponding to the respective colors disposed below the optical scanning device 120. 136C, 136K is scanned.
[0011]
Further, as an optical system that meets the demand for high speed and high resolution, an overfilled optical system that irradiates a light beam to the entire scanning direction of each reflecting surface of a rotary polygon mirror and a part of the adjacent reflecting surface is used.
[0012]
Conventionally, in an optical scanning device that scans a light beam using a rotating polygon mirror having a plurality of reflecting surfaces on the outer peripheral surface, the rotating polygon is used as an optical system upstream of the rotating polygon mirror (on the light source side that emits the light beam). In general, an underfilled optical system that irradiates only a part of one reflecting surface of a rotating polygonal mirror with a light beam emitted toward the mirror is adopted.
[0013]
The underfilled optical system will be described with reference to the schematic diagram of FIG. In FIG. 12, the optical axis C of the laser beam L as a light beam is shown as a straight line, (A) is a plan view, and (B) is a side view.
[0014]
As shown in FIG. 12, in the underfilled optical system, the laser beam L emitted from the semiconductor laser 140 and made into a parallel beam by the collimator lens 142 is shaped by the aperture plate 144 and collected by the cylindrical lens 146 in the sub-scanning direction. The light is incident on a part of one reflecting surface 148A of the rotating polygon mirror 148. The beam reflected by the reflecting surface 148A forms an image on the photosensitive drum 154 via the fθ lens 150 and the cylindrical mirror 152.
[0015]
The aperture plate 144 is configured by a plate-like member having a rectangular opening at a substantially central portion, and the center of the aperture 156 of the aperture plate 144 is emitted from the semiconductor laser 140 as shown in FIG. The laser beam L is arranged so as to substantially coincide with the center (optical axis) C of the laser beam L.
In contrast to such an underfilled optical system, an overfilled optical system that irradiates a light beam to the entire surface in the scanning direction of each reflecting surface of the rotary polygon mirror and a part of the adjacent reflecting surface as shown in FIG. Was not included. In the overfilled optical system, as shown in FIG. 14A, the laser beam L is magnified by the beam expander 158 or the like with respect to the reflecting surface 148A of the rotary polygon mirror 148, and is incident with a width in the main scanning direction wider than the entire width. Then, only the laser beam L incident on the reflecting surface 148A is deflected and scanned with respect to the photosensitive drum 154. Therefore, in the overfilled optical system, compared to the underfilled optical system, the size of the reflecting surface required to generate a beam spot of a certain size on the photosensitive drum 154 can be made very small. It is possible to provide more reflecting surfaces on the rotating polygon mirror. This means that the rotating polygon mirror can be operated at a relatively low rotation speed, and a motor and a driving device with lower power can be used as a driving system for rotating the rotating polygon mirror.
[0016]
However, in the overfilled optical system having such an effect, since there is a negative factor that the light amount distribution on the recording medium is not uniform, it is not generally adopted. The problem of non-uniform light quantity distribution will be described more specifically as follows.
[0017]
That is, a laser beam emitted from a light source such as a semiconductor laser has a Gaussian beam shape, and is expanded by a beam expander or the like so as to irradiate one or more reflecting surfaces of a rotary polygon mirror in an overfilled optical system. The In this state, when the rotary polygon mirror is rotated so that the laser beam spot scans the surface of the recording medium, the amount of laser beam reflected toward the recording medium changes as the rotation proceeds, and the light quantity distribution Is non-uniform. This is due to the fact that the reflecting surface of the rotating polygonal mirror cuts out different portions of the Gaussian beam profile as it rotates, and that the effective reflection width of the reflecting surface changes as the rotating polygonal mirror rotates.
[0018]
The non-uniformity of the light amount distribution, which is a negative factor of the above-described overfilled optical system, is a big problem because it causes problems such as non-uniform image density and non-uniform thin line width. Further, when employed in the above-described tandem-type full-color image forming apparatus, the difference in the light amount distribution of a plurality of light beams becomes a problem such as a difference in density of each color.
[0019]
Therefore, if this non-uniform light quantity distribution problem is improved, the overfilled optical system can reduce the load on the motor that rotates the rotary polygon mirror, and can achieve high speed and high resolution while reducing power consumption and noise. It can be widely used as a device that can constitute an optical scanning device.
[0020]
Therefore, various proposals have been made conventionally. For example, a method for adjusting the optical axis in an overfilled optical system is disclosed in Japanese Patent Laid-Open No. 9-96769 (hereinafter referred to as Conventional Example 1). That is, as shown in FIG. 15, by driving the optical scanning device 164 in a state where the optical scanning device 164 is disposed with respect to an assembly jig 162 provided with a plurality of sensors 160 for detecting the power of the light beam, The sensor 160 detects the amount of light at the center and both ends of the scanning area at a position corresponding to the surface to be scanned, and adjusts the optical axis so that the amounts of light at both ends are substantially equal.
[0021]
Japanese Patent Laid-Open No. 9-164718 (hereinafter referred to as Conventional Example 2) discloses a technique for performing electrical correction in order to solve the problem of unevenness of the light amount distribution. This conventional example will be described with reference to FIG. 16 showing the relationship between the laser power on the photosensitive member surface and the scanning angle. That is, when scanning is performed with a constant light amount, the laser power on the surface of the photoconductor is attenuated as the scanning angle is increased as shown by curve 2 in FIG. This is due to the transmittance / reflectance characteristics of lenses, mirrors and the like in the optical scanning device. Therefore, electrical correction is performed to compensate for this attenuation (becomes curve 1).
[0022]
Further, a technique for performing correction using a reflective coating system for optical members is disclosed in Japanese Patent Laid-Open No. 2000-83445 (hereinafter referred to as Conventional Example 3). In Conventional Example 3, as shown in FIG. 17, the reflectance that attenuates as the incident angle increases usually increases as the incident angle increases by forming a thin film layer. As a result, the amount of light at the end of the scanning region is increased to make the light amount distribution uniform.
[0023]
Further, a technique for correcting by changing the slit shape is disclosed in Japanese Patent Laid-Open No. 11-218702 (hereinafter referred to as Conventional Example 4). That is, the shape of the slit 170, which has been a rectangular opening for shaping the beam L as shown in FIG. By increasing the amount, the amount of light beam passing through the scanning end can be increased to correct from the uncorrected state 172 to the corrected state 174 as shown in FIG. That is, the light quantity distribution can be made uniform.
[0024]
[Problems to be solved by the invention]
However, Conventional Example 1 has a disadvantage in that the final light amount distribution varies due to variations in detection output and adjustment tolerances.
[0025]
In addition, the conventional examples 2 and 3 for making the light quantity distribution uniform have a problem that the component configuration becomes complicated, and the manufacturing cost of the optical scanning device is increased by using a special technique.
[0026]
On the other hand, Conventional Example 4 is advantageous in terms of cost because it uses conventional parts, but has the disadvantage of causing problems such as variations in light intensity distribution due to dimensional variations in parts.
[0027]
Furthermore, in the overfilled optical system, there is a problem in that the tendency of the light amount distribution on the image plane differs depending on the manufacturing variation in the spread angle of the light beam emitted from the laser diode as the light source. In addition, in the overfilled optical system, a part of the light beam incident on the deflector is cut off and reflected, so that the amount of reflected light guided to the scanning end differs depending on the spread angle, resulting in a difference in light amount distribution. There was a problem that it would appear.
[0028]
Further, even if the light quantity distribution can be made uniform by the above-described conventional example, when a plurality of optical scanning devices (scanning optical systems) are compared, it is not possible to improve the variation between the scanning optical systems and the difference in the light quantity distribution. .
[0029]
That is, the light amount distribution in the plurality of scanning optical systems varies depending on the transmittance / reflectance characteristics of the optical components in the optical scanning device, and thus the light amount distribution in each scanning optical system can be made uniform. Variations in the light quantity distribution of the scanning optical system cannot be suppressed.
[0030]
Further, by tightening adjustment and manufacturing tolerances, it is possible to reduce the difference in the light amount distribution, but as a result, the cost of components and the number of adjustment steps increase, resulting in an expensive product.
[0031]
In order to solve the above problems, the present invention provides an inexpensive and easily achieved optical scanning device that can improve the difference in the light amount distribution of a plurality of light beams on a scanned object. The purpose is that.
[0043]
[Means for Solving the Problems]
  In order to achieve the above object, the light quantity setting method for an optical scanning device according to claim 1 is a multicolor image obtained by superimposing a plurality of images formed on a photosensitive member by a plurality of light beams to form a multicolor image. Used in image forming devices,An optical scanning device that includes a light source that emits a light beam, and a deflecting unit that deflects the light beam in a scanning direction, and a light beam having a width that exceeds a deflection surface width in the scanning direction of the deflecting unit is incident on the deflecting unitThe light amount distribution method of each light beam is set so that the central value ((maximum value + minimum value) / 2) of the light amount distribution of each light beam in the scanning region of the plurality of light beams coincides. It has been adjusted.
[0044]
  Claim1The operation of the light amount setting method of the optical scanning device described in the above will be described.
[0045]
  The optical scanning apparatus of the present invention is configured with an overfilled optical system in which a light beam having a width exceeding the deflection surface width of the deflecting means is incident on the deflecting means. AndIf there is a difference in the light amount distribution of each light beam, the light amount distribution of each light beam is adjusted, and the center value ((maximum value + minimum value) / 2 of each light amount distribution in the scanning region of all the light beams. ) Can be averaged to make the difference between the light quantity distributions in the entire scanning region smaller than the matching at a specific point (position) in the scanning region. As a result, when a plurality of light beams are superimposed, the light amount difference between the light beams is small at any point in the scanning region, and the density difference between the images formed by the light beams is suppressed.
[0046]
  Claim2The light amount setting method for the optical scanning device described in claim1In the light amount setting method for the optical scanning device described above, the center value of another light beam is set to coincide with the center value of an arbitrary light beam.
[0047]
  Claim2The operation of the light amount setting method of the optical scanning device described in the above will be described.
[0048]
Adjustment can be simplified by matching the center values of the other light beams with the center value of the light quantity distribution of an arbitrary light beam as a reference.
[0049]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the first embodiment, the optical scanning device includes one scanning optical system, and images are formed by irradiating a plurality of light beams from the plurality of optical scanning devices onto the photosensitive member, for example, a tandem type image. It is used for a forming apparatus.
[First Embodiment]
An optical scanning device according to a first embodiment of the present invention will be described. First, an example of an image forming apparatus in which the optical scanning device according to this embodiment is mounted will be briefly described, and the configuration of the optical scanning device will be described.
[0050]
As shown in FIG. 1, the image forming apparatus 10 is arranged in the order of black (K), yellow (Y), magenta (M), and cyan (C) from the upstream side of the sheet conveying belt 12 in the sheet conveying direction. 14K, the image forming apparatus 14Y, the image forming apparatus 14M, and the image forming apparatus 14C are provided in this order. In each of the image forming apparatuses 14K to 14C, a charging device 18 and optical scanning are provided around each photosensitive member 16 as an image carrier. Sub-units constituting the electrophotographic process such as the apparatus 20 and the developing apparatus 22 are arranged.
[0051]
Therefore, in the image forming apparatus 10, after the photosensitive member 16 is charged by the charging device 18, a light beam according to the image information is exposed and scanned by the optical scanning device 20 to form a latent image. Next, after the latent image is developed by the developing device 22, it is transferred to a sheet 24 conveyed at a constant speed to form an image.
[0052]
This process is performed in the order of K, Y, M, and C, and the transfer image is fixed on the paper 24 by a fixing device (not shown) and then discharged.
[0053]
The configuration of the optical scanning device 20 used in this way will be described.
[0054]
As shown in FIG. 2, the optical scanning device 20 includes a semiconductor laser 26 that generates a light beam L. In the emission direction of the light beam L from the semiconductor laser 26, the incident light beam L is converted into a parallel beam. A concave lens that expands an incident light beam in the scanning direction by combining a collimator lens 28 for converting to an aperture plate 32, an aperture plate 32 constituted by a plate-like member having an aperture 30 in the substantially central portion, and an fθ lens 40 described later. 34, a cylindrical lens 36, and a bending mirror 38 are arranged in this order.
[0055]
The opening 30 provided in the opening plate 32 of the present embodiment uses the technique disclosed in Japanese Patent Application Laid-Open No. 11-218702. That is, the opening 30 has a shape in which the opening width in the vertical direction (direction perpendicular to the scanning direction) is larger at both ends in the left-right direction (scanning direction) than the central portion in the left-right direction. The shape can be any one of A) to (C). 3A to 3C, the aperture plate 32 is configured such that the center of the aperture 30 substantially coincides with the center (optical axis) C of a later-described light beam L emitted from the semiconductor laser 26. It is arranged.
[0056]
On the other hand, in the reflection direction of the light beam of the bending mirror 38, an fθ lens 40 and a rotating polygon mirror 44 having a plurality (12 in this embodiment) of reflecting surfaces 42 on the outer peripheral surface are arranged in order. In the reflection direction of the light beam by the reflection surface 42 of the polygonal mirror 44, the fθ lens 40 and the cylindrical mirror 46 for correcting the surface tilt of the rotary polygonal mirror 44 are disposed in order, and the reflection direction of the light beam of the cylindrical mirror 46 is arranged. A drum-type photoconductor 16 is disposed in the case.
[0057]
As described above, in the optical scanning device 20, both the light beam reflected by the bending mirror 38 and the light beam reflected by the reflecting surface 42 of the rotary polygon mirror 44 pass through the same fθ lens 40. In addition, the light beam that has passed through the fθ lens 40 is incident on the reflecting surface 42 of the rotating polygonal mirror 44 obliquely from above, and the incident light beam is reflected obliquely downward by the reflecting surface 42 of the rotating polygonal mirror 44 and again fθ. Each part is disposed so as to be incident on the lens 40.
[0058]
However, in the optical scanning device 20 configured as described above, the light amount distribution in the scanning direction on the photosensitive member 16 varies depending on the reflection / transmittance characteristics of the optical components and the spread angle of the semiconductor laser 26.
[0059]
As a result, as shown in FIG. 4A, the intensity distribution of the latent image exposed on the photoconductor and the fixing on the paper are different because the light amount distribution of the light beams scanned by the plurality of optical scanning devices 20 is different. The resulting toner image has a different density distribution for each color.
[0060]
First, the difference in the light amount distribution of each light beam will be described with reference to FIG. FIG. 4A shows an example in which the light amount distribution of the light beam varies. The horizontal axis shows the scanning width, and the vertical axis shows the light quantity distribution with the central portion (horizontal axis 0) being 100%. In the comparative example shown in FIG. 4A, the light amount distribution of each color light beam varies up to 6% at the scanning end in order to adjust the light amount in the central portion so as to match between the light beams. Yes.
[0061]
Further, as described above, this variation is caused by the manufacturing variation of the semiconductor laser, the optical component, etc., and therefore it is impossible to make the variation zero at the design stage. In this state, means for minimizing the variation between the light beams will be described. The graph shown in FIG. 4A is a light amount distribution as shown in Table 1 below.
[0062]
[Table 1]

First, the center value of the light quantity distribution of each beam is obtained as shown in Table 2. The center value is an average value of the maximum value and the minimum value among the light amounts at arbitrary points in the scanning region. In the present embodiment, the arbitrary points are the central portion, the + side, and the − side end portion.
[0063]
A difference with respect to the reference light beam (here, cyan is used as a reference) is obtained from the center value of the light amount distribution of each light beam.
[0064]
[Table 2]

When the difference in the center value from the reference beam is corrected as the correction amount of each beam, the result is as shown in Table 3 and FIG.
[0065]
[Table 3]

According to the above procedure, the light amount difference between the beams before the correction was 6% at the maximum in the scanning region, but after the correction, the difference was 3% at the maximum and halved.
[0066]
As a result, the density difference of each color of the image formed on the paper 24 in the image forming apparatus 10 is also suppressed, and a good image is formed.
[0067]
In this embodiment, a reference beam (cyan in this embodiment) is provided and correction for the reference beam is performed. For example, an average value of the center values of the respective colors is obtained from the center values obtained in Table 2. There is also a method of correcting the average value.
[0068]
As described above, instead of setting the light amount of each beam (matching the light amount) with the light amount at the center of each scanning region, the density difference in the image can be reduced by dispersing the light amount difference in the scanning region on average. .
[0069]
Next, the relationship between the spread angle of the semiconductor laser and the light amount distribution will be described with reference to FIGS.
[0070]
5 and 6 show schematic views of the overfilled optical system. FIG. 5 shows a state in which the light beam L is guided to the center of the scanning region of the photosensitive member 16 by the reflecting surface 42 of the rotating polygon mirror 44, and FIG. 6 shows the light beam L being guided to the end of the scanning region of the photosensitive member 16. (B) to (D) in each figure indicate the light emitted from the semiconductor laser (position B in each figure (A)), the luminous flux after slit (position C in each figure (A)), and after reflection of the polygon mirror The profile of the light flux (position D in each figure (A)) is shown.
[0071]
In the overfilled optical system, as described above, the light beam incident on the rotary polygon mirror 44 is reflected and scanned so as to be cut off. First, the light beam L emitted from the semiconductor laser 26 is emitted with a certain spread. The emitted light beam L becomes parallel light by the collimator lens 28, the light beam width is regulated by the opening 30 of the aperture plate 32, and is incident on the reflecting surface 42 of the rotary polygon mirror 44. In the scanning center portion, as shown in FIG. 5A, the center portion of the incident light beam is used. At the scanning end, as shown in FIG. 6A, only about one half of the incident light beam is used. As described above, since the amount of incident light beam cut off at the scanning center and the scanning end is different, a decrease such as attenuation of the light amount distribution at the end occurs.
[0072]
5 and 6 show profiles in which the spread angle of the semiconductor laser 26 is different. The spread angles of the semiconductor laser 26 are α, β, and γ (degrees), and α <β <γ. Due to this difference in divergence angle, a difference occurs in the amount cut by the rotary polygon mirror 44. That is, as shown in FIG. 5D, the difference between the spread angles α, β, and γ is small in the center of the scan, but is cut off by the rotary polygon mirror 44 at the scan end as shown in FIG. The amount differs depending on α, β, and γ, and as a result, a phenomenon such as variation in light amount distribution occurs.
[0073]
As described above, the manufacturing variation in the divergence angle of the semiconductor laser 26 is a factor in the variation in the light amount distribution of the optical scanning device.
[0074]
Therefore, in the present embodiment, in the image forming apparatus 10, the semiconductor lasers 26 used in all the optical scanning devices 20 have the same spread angle. That is, the divergence angle of the semiconductor laser 26 is inspected in advance, and the semiconductor lasers 26 having the same divergence angle are used in the optical scanning device 20 of the same image forming apparatus 10, so that a plurality of optical scanning devices (light beams) are used. Variations in the light amount distribution among the plurality of light beams due to the difference in divergence angle can be prevented, and density differences between the colors can be suppressed.
[0075]
Next, the relationship between the shape of the opening 30 of the opening plate 32 and the light amount distribution will be described with reference to FIGS. 7A is a front view of the opening, and FIG. 7B is a graph showing the light amount distribution when the dimension X of the opening is changed.
[0076]
As shown in FIGS. 3A to 3C, the shape of the opening 30 of the opening plate 32 is increased at both ends in the scanning direction and the width in the sub-scanning direction is larger than that at the center, thereby allowing the end of the scanning region to be It is possible to make the light amount distribution uniform by suppressing the light amount decrease in the portion. However, the light amount difference between the light beams of the respective colors cannot be suppressed by that alone. Therefore, this is to be dealt with by functionalizing the change in the amount of light at the end of the scanning region due to the change in the shape of the opening 30.
[0077]
As shown in FIG. 7A, the shape of the opening 30 is an end in the scanning direction where the sub-scanning width is W2 wider than W1 with respect to the central portion 30A of the sub-scanning width W1 at the position where the optical axis C passes. The part 30B is formed at both ends.
[0078]
Here, by changing the length X in the center of the opening 30 in the scanning direction, as shown in FIG. 7B, the light amount ratio of the light amount at the end of the scanning region to the center of the scanning region may change. confirmed. That is, since the scanning direction length X and the light amount ratio have a correlation that can be expressed by a function, the dimension X can be obtained from the function in order to obtain a desired light amount distribution (light amount ratio). Further, when a similar relationship is derived even in different optical systems, an optical system {circle around (2)} in FIG. 7B is obtained. Even in this case, the scanning direction length X and the light quantity distribution are expressed as functions, and it is easy to obtain a desired light quantity distribution.
[0079]
Further, not only the length X in the scanning direction but also the shape of the opening 30 is made different, so that a desired light amount distribution can be obtained.
[0080]
In the present embodiment, the aperture plate 32 is configured to be easily detachable, and has an attachment structure so that the optical axes of the semiconductor laser 26, the concave lens 34, and the cylindrical lens 36 are not shifted by detachment. At least two types of aperture plates 32 having different shapes of the apertures 30 are prepared, and the aperture plate 32 is exchanged depending on the light amount distribution shape.
[0081]
With this configuration, the light amount distribution of the light beam L can be made uniform, and adjustment can be made to reduce the light amount difference from the light amount distributions of the other light beams L.
[0082]
As described above, in the present embodiment, the light amount distributions of the light beams emitted from the plurality of optical scanning devices 20 mounted on the image forming apparatus 10 can be substantially matched. Can be suppressed.
[0083]
Also, here, a method for setting the light amount distribution, a method for adjusting the light amount ratio between the end portion and the central portion by disposing the aperture plates 32 having different opening shapes, the use of the semiconductor laser 26 having the same spread angle, However, even if only one of these is adopted, there is an effect, and the combination of a plurality of these is also effective.
[Second Embodiment]
An optical scanning device according to a second embodiment of the present invention will be described. Since the present invention is different from the first embodiment only in the configuration of the optical scanning device, only the relevant part will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0084]
The difference from the first embodiment is that the optical scanning device 50 according to the embodiment of the present invention is mounted on a multicolor (color) image forming apparatus, for each color (Y, M, C, K). A plurality of optical systems and a plurality of light sources for scanning the photosensitive drum are provided in one optical scanning device 50.
[0085]
As shown in FIGS. 8 and 9, four optical systems corresponding to four colors are formed inside the optical box 52 of the optical scanning device 50. Inside the optical box 52, two light beams emitted from the light source device portions 54 and 56 from which light beams corresponding to two colors are emitted are respectively incident on the opposing reflecting surfaces 60 of the rotary polygon mirror 58. Thus, the light enters the photosensitive drums 62Y, 62M, 62C, and 62K corresponding to the respective colors.
[0086]
Therefore, the optical system of the optical scanning device 50 is an optical system that is symmetrical on both sides of the rotary polygon mirror 58. Here, the optical system on the right side in FIG. 9 will be described. For convenience, the light beam from the light source device unit 54A is referred to as “light beam LA”, and the light beam from the light source device unit 54B is referred to as “light beam LB”.
[0087]
In the light source device portions 54A and 54B, the light beams LA and LB emitted from the semiconductor laser 26 are shaped by the collimator lens 28, the light beam width is regulated by the aperture stop 32, and then the predetermined shape (sub-secondary) by the cylindrical lens 34. A linear light beam that is focused in the scanning direction and long in the main scanning direction).
[0088]
After passing through the cylindrical lens 34, the light beam LA is directly incident on the plane mirror 64, and the light beam LB is incident on the plane mirror 64 in the same direction as the light beam LA due to reflection by the plane mirror 66.
[0089]
The light beams LA and LB here are incident on the plane mirror 64 with a predetermined angle difference in the sub-scanning direction, and are reflected to the rotating polygon mirror 58 side.
[0090]
Further, the light beams LA and LB are transmitted through the fθ lens 40 in the main scanning direction when incident on the rotating polygon mirror 58 and after being reflected and deflected by the rotating polygon mirror 58, and are incident on the reflecting surface of the rotating polygon mirror 58 from the front. The so-called front-incidence double-pass optical system.
[0091]
Incidentally, the incident position of the light beams LA and LB in the height direction on the reflecting surface 60 of the rotary polygon mirror 58 is set so that the incident angle of the light beam LB having a large incident angle in the sub-scanning direction is set to be small. It is set so as to be incident below the light beam LA.
Thereby, the space | interval in the subscanning direction of both light beams on the reflective surface of the rotary polygon mirror 58 is ensured. Further, the intervals in the sub-scanning direction of the light beams LA and LB reflected by the reflecting surface 60 of the rotary polygon mirror 58 gradually increase as the optical path advances. Therefore, the interval between the two light beams secured after passing through the fθ lens 40 is widened, thereby making the subsequent arrangement of the optical components as easy as possible.
[0092]
Note that the light beams LA and LB deflected by the rotary polygon mirror 58 and transmitted through the fθ lens 40 are angle-adjusted so as to have a predetermined optical path by the plane mirrors 68A and 68B provided corresponding to the respective light beams. Thereafter, the light beams LA and LB pass above the rotary polygonal mirror 58 and reach the cylindrical mirrors 46.
[0093]
The light beams LA and LB reflected downward by the cylindrical mirror 46 pass between the fθ lenses 40, that is, pass through the inside of the optical scanning device 50 again and reach the photosensitive drums 62C and 62K.
[0094]
The above is the optical system on one side and the optical path of the light beam. The other optical system and optical path also reach the photosensitive drums 62M and 62Y.
[0095]
As described above, in the optical system of the optical scanning device 50 of the present embodiment, two light beams are simultaneously deflected and scanned on one side of the rotary polygon mirror 58 and a total of four light beams are emitted on both sides, and emitted from each light source. In this configuration, the photosensitive drum arranged corresponding to each color of black (K), yellow (Y), magenta (M), and cyan (C) is scanned by the light beam.
[0096]
As described above, the optical scanning device 50 can adjust and measure the light amount beams of a plurality of light beams corresponding to each color on the same device, so that the light amount distributions of the plurality of light beams can be simultaneously measured. That is, the difference in light quantity distribution can be grasped instantaneously. If the difference in the light quantity distribution is obtained, the means for adjusting the central value of the light quantity distribution of the present invention and the light quantity distribution adjustment by slit replacement can be easily performed.
[0100]
【The invention's effect】
  As explained above,Claim1According to the invention, the initial set light amounts of the plurality of light beams are made to coincide with each other at a certain point in the scanning region by making the central value of the light amount distribution in the scanning region coincide with all the light beams. Also, the difference can be reduced on the average over the entire scanning region.As a result, when a plurality of light beams are superimposed, the light amount difference between the light beams is small at any point in the scanning region, and the density difference between the images formed by the light beams is suppressed.
[0101]
  Claim2According to the invention, the center value of the light quantity distribution of an arbitrary light beam is used as a reference, and the center values of the other light beams are matched to each other.1The same effect as that of the present invention can be obtained.
[Brief description of the drawings]
FIG. 1 is a side view of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a perspective view of the optical scanning device according to the first embodiment of the present invention.
FIGS. 3A to 3C are diagrams showing examples of the opening shape of the slit according to the first embodiment of the present invention. FIGS.
FIG. 4 is an explanatory diagram of variations in light amount distribution in a plurality of optical scanning devices according to the first embodiment of the present invention.
FIG. 5 is a graph showing the relationship between the divergence angle and the light amount distribution of the semiconductor laser at the center of scanning according to the first embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the divergence angle of the semiconductor laser at the scanning end and the light amount distribution according to the first embodiment of the present invention.
7A is a front view of an aperture plate according to the first embodiment of the present invention, and FIG. 7B is a graph showing the relationship between the aperture shape and the light amount distribution.
FIG. 8 is a perspective view of an optical scanning device according to a second embodiment of the present invention.
FIG. 9 is a side view of an optical scanning device according to a second embodiment of the present invention.
FIG. 10 is a schematic diagram showing a configuration of a conventional full-color image forming apparatus.
FIG. 11 is a schematic perspective view of an optical scanning device according to a conventional example.
12A and 12B are diagrams showing a schematic configuration of an optical scanning device using an underfilled optical system according to a conventional example, where FIG. 12A is a plan view and FIG. 12B is a side view.
FIG. 13 is a schematic view showing the shape of the aperture of the aperture plate according to the conventional example and the positional relationship between the aperture and the light beam.
14A and 14B are diagrams showing a schematic configuration of an optical scanning device using an overfilled optical system according to a conventional example, in which FIG. 14A is a plan view and FIG. 14B is a side view.
FIG. 15 is a diagram for explaining an optical axis adjusting device of an optical scanning device disclosed in Japanese Patent Application Laid-Open No. 9-96769.
FIG. 16 is a diagram showing the relationship between the laser power on the photoreceptor surface and the scanning angle disclosed in Japanese Patent Laid-Open No. 9-164718.
FIG. 17 is a graph showing the increase ratio of the reflectance with respect to the incident angle when a thin film layer is formed on the reflection surface of the optical component disclosed in Japanese Unexamined Patent Publication No. 2000-83445.
FIG. 18 is a graph showing the effect of correcting the light amount distribution disclosed in Japanese Patent Laid-Open No. 11-218702.
[Explanation of symbols]
20, 50 ... Optical scanning device
26 ... Light source
32 ... Opening plate (opening member)
44, 58 ... rotating polygon mirror (deflection means)

Claims (2)

Used in one multicolor image forming apparatus that superimposes a plurality of images formed on a photosensitive member by a plurality of light beams to form a multicolor image, and a light source that emits a light beam, and deflects the light beam in a scanning direction. And a light quantity setting method in an optical scanning device in which a light beam having a width exceeding a deflection surface width in the scanning direction of the deflection means is incident on the deflection means, the scanning region of the plurality of light beams A light amount setting method for an optical scanning device, characterized in that the light amount distribution of each light beam is adjusted so that the center value ((maximum value + minimum value) / 2) of the light amount distribution of each of the light beams matches.   2. The light amount setting method for an optical scanning device according to claim 1, wherein the center value of another light beam is adjusted to coincide with the center value of an arbitrary light beam.

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