JP2005049535A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner of multibeam scanning system, a scanner that enables a spot diameter to be reduced using a coupling lens of a short focal distance and that has the ability to effectively diminish image fluctuation due to ambient temperature change. <P>SOLUTION: The optical scanner performs optical writing of a multibeam scanning system by converting a plurality of luminous fluxes from a light source 1 with multiple light emitting sources to essentially parallel luminous fluxes by a first optical system 2, linearly converging in the main scanning corresponding direction by a second optical system 100, deflecting by an optical deflector 5, and converging on a surface 7 to be scanned as an optical spot by a third optical system 600. The third optical system 600 has at least a single resin-made image forming element; the second optical system 100 has at least a single resin-made image forming element 11 and at least single glass-made image forming elements 10, 12; and the second optical system 100 is provided with a beam expanding function for expanding a luminous flux diameter by maintaining the parallel luminous flux shape in the main scanning direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

奇数次の係数：Ａ１、Ａ３、Ａ５・・の１以上が０でないとき、非円弧形状は主走査方向に非対称形状となるが、実施例では、偶数次の係数のみを用いており、主走査方向に対称形である。
副走査断面内の曲率の主走査方向における変化
「副走査断面」は、主走査方向に直交する仮想的な平断面である。
光軸を含む副走査断面における副走査方向の曲率半径：Ｒｓ（０）、主走査方向における光軸からの距離：Ｙ、係数：Ｂ１、Ｂ２、Ｂ３、・・を用い、上記Ｙの位置における曲率：Ｃｓ（Ｙ）を次式で表す。
【００５８】
Ｃｓ（Ｙ）＝１／Ｒｓ（０）＋Ｂ１・Ｙ＋Ｂ２・Ｙ^２＋Ｂ３・Ｙ^３＋Ｂ４・Ｙ^４＋Ｂ５・Ｙ^５＋・・（２）
「副非円弧面（主・副走査断面内の形状が何れも非円弧である形状）」
光軸から主走査方向の距離：Ｙ、主走査断面からの副走査方向の距離：Ｚを用い、光軸方向のデプス：Ｘ（Ｙ，Ｚ）を以下の式で表す。
【００５９】

式（３）右辺の第２項の和は、サフィックス：ｎについてとる。右辺第１項及び第２項は、式（１）の右辺と同一である。
【００６０】
式（３）右辺の第４項を、
ｆ_ＳＡＧ（Ｙ，Ｚ）＝Σ（Σｄ_ｊ，ｈＹ^ｈ）Ｚ^ｊ
とすると、これは、以下のように書くことができる。
【００６１】

【００６２】
ここに、
Ｃｍ（＝１／Ｒｍ）：光軸を含む主走査断面内の近軸曲率
Ｃｓ（０）（＝１／Ｒｓ（０））：光軸を含む副走査断面内の近軸曲率
Ｃｓ（Ｙ）：主走査方向の位置：Ｙにおける副走査断面内の近軸曲率
Ｋｚ（Ｙ）：主走査方向の位置：Ｙにおける副走査断面内の２次曲線を表す円錐定数
Ｆ_ＳＡＧ（Ｙ，Ｚ）：非球面高次補正量
Ｃｓ（Ｙ）＝｛１／Ｒｓ（０）｝＋Ｂ１・Ｙ＋Ｂ２・Ｙ^２＋Ｂ３・Ｙ^３＋Ｂ４・Ｙ^４＋Ｂ５・Ｙ^５＋・・
Ｋｚ（Ｙ）＝Ｃ０＋Ｃ１・Ｙ＋Ｃ２・Ｙ^２＋Ｃ３・Ｙ^３＋Ｃ４・Ｙ^４＋Ｃ５・Ｙ^５＋・・
Ｃｓ（Ｙ）の右辺における「Ｙの奇数次係数：Ｂ１、Ｂ３、Ｂ５、・・」の１以上が０でないとき、副走査方向の曲率半径が主走査方向に非対称となる。
同様に、Ｃ１、Ｃ３、Ｃ５、・・Ｆ１、Ｆ３、Ｆ５・・Ｇ１、Ｇ３、Ｇ５・・等の非円弧量を表すＹの奇数次係数が０でないとき、副走査方向の非円弧量が主走査方向に非対称となる。
実施例
図２は、図１の光走査装置の光学配置を、光源１から被走査面７まで直線的に展開した状態を、上下方向を副走査方向として描いている。面間隔を図２に示す如く、ｄ１〜ｄ１１とする。また、図１に示すように、レンズ６１、６２の主走査方向におけるシフト量（図の上方へのシフトを正とする。）を図の如く、ｄ１２、ｄ１３とする。
【００６３】
光源１：半導体レーザアレイ
発光源ピッチ：８０μｍ、発光源数：４チャンネル、発光波長：６５５ｎｍ
発光源配列方向の副走査方向に対する傾け角：θ＝８３．３度 。
【００６４】
走査線ピッチ：
「第１光学系（カップリングレンズ２）」
非球面を持つガラスレンズで収差を良好に補正されている。
焦点距離：２７ｍｍ、カップリング作用：コリメート作用 。
【００６５】
開口絞り２０
「開口幅」 主走査方向：４．５２ｍｍ 副走査方向：１．４７ｍｍ
設置位置：カップリングレンズ２の光偏向器側の焦点面位置 。
【００６６】
「光偏向器（ポリゴンミラー５）」
偏向反射面数：５、内接円半径：１８ｍｍ
光源側からの光束入射角と第３光学系の光軸とがなす角：６０度
光書込み幅：±１５０ｍｍ
画角：±３８度
書込密度：１２００ｄｐｉ
走査線ピッチ：２１．２μｍ 。
【００６７】
Ａｍ＝４．５２ｍｍ、Ａｐ＝７．８１ｍｍ、Ａｐ／Ａｍ＝１．７３
ｄ１＝３ｍｍ、ｄ２＝４０ｍｍ、ｄ３＝４ｍｍ、ｄ４＝１２．５ｍｍ、
ｄ５＝６ｍｍ、ｄ６＝１３５．１ｍｍ
ガラス製レンズ１０のレンズ面１０ａの曲率半径
主走査方向：−８０．００１ｍｍ 副走査方向：∞
ガラス製レンズ１０のレンズ面１０ｂの曲率半径
主走査方向：∞ 副走査方向：∞ 。
【００６８】
樹脂製レンズ１１のレンズ面１１ａの曲率半径
主走査方向：−７９．３ｍｍ 副走査方向：−１６ｍｍ（副非円弧面）
樹脂製レンズ１１のレンズ面１１ａの曲率半径
主走査方向：∞ 副走査方向：１６ｍｍ 。
【００６９】
ガラス製レンズ１２のレンズ面１２ａの曲率半径
主走査方向：∞ 副走査方向：２３ｍｍ
ガラス製レンズ１２のレンズ面１２ａの曲率半径
主走査方向：−６９．２０５ｍｍ 副走査方向：−６９．２０５ｍｍ（球面）
副非円弧面（レンズ面１１ａ）の形状のデータ
Ｒｍ＝−７９．３ Ｒｓ＝−１６
Ａ０＝ ３．８３０６２６Ｅ−０
Ｃ０＝−４．５７５４３５Ｅ−０
Ｃ２＝−４．１１５９１０Ｅ−０
Ｃ４＝ １．４４４１０９Ｅ−１
Ｉ０＝−４．２９６５９３Ｅ−４
Ｉ２＝−１．７４４０６０Ｅ−４
Ｉ４＝ ４．５８０５９４Ｅ−６
Ｋ０＝−１．４３４８１８Ｅ−４
Ｋ２＝ ３．３４２２７９Ｅ−５
Ｋ４＝−２．２７５３８７Ｅ−７
上の表記において、例えば、「３．３４２２７９Ｅ−５」は、「３．３４２２７９×１０^−５」を意味する。以下においても同様である。
【００７０】
樹脂製レンズ１１の材料の屈折率：１．５２７２３８（λ＝６５５ｎｍ、２５℃時）
樹脂製レンズ１１の線膨張係数：７Ｅ−５
ガラス製レンズ１０、１２の材料の屈折率：１．７３８７５５（λ＝６５５ｎｍ、２５℃時）
ガラス製レンズ１０、１２の線膨張係数：５．４Ｅ−６
レンズ取り付け部（ベース部材）の線膨張係数：２．３１Ｅ−５ 。
【００７１】
ｄ７＝７１．２ｍｍ、ｄ８＝３０ｍｍ、ｄ９＝６６．５ｍｍ、
ｄ１０＝８．５ｍｍ、ｄ１１＝１５７．８ｍｍ、ｄ１２＝０．２ｍｍ、
ｄ１３＝０．２ｍｍ 。
【００７２】
樹脂製走査レンズ６１、６２の材料の屈折率：１．５２７２３８（λ＝６５５ｎｍ、２５℃時）
樹脂製走査レンズ６１、６２の線膨張係数：７Ｅ−５ 。
【００７３】
樹脂製レンズ６１のレンズ面６１ａの形状のデータ
Ｒｍ＝−１０３０．２３３３４６ Ｒｓ＝ −８９．５１８９２７
Ａ０＝−４．０４１６１９Ｅ＋２
Ａ４＝ ６．００５０１７Ｅ−８
Ａ６＝−７．５３８１５５Ｅ−１３
Ａ８＝−４．０３６８２４Ｅ−１６
Ａ１０＝ ４．５９２１６４Ｅ−２０
Ａ１２＝−２．３９６５２４Ｅ−２４
Ｂ１＝−９．３１７８５１Ｅ−６
Ｂ２＝ ３．２６９９０５Ｅ−６
Ｂ３＝ ４．１３２４９７Ｅ−９
Ｂ４＝−４．２０７７１６Ｅ−１０
Ｂ５＝−１．１７０１１４Ｅ−１２
Ｂ６＝ ４．３７０６４０Ｅ−１４
Ｂ７＝ ２．３４７９６５Ｅ−１６
Ｂ８＝−６．２１２７９５Ｅ−１８
Ｂ９＝−３．９６７９９４Ｅ−２０
Ｂ１０＝−３．８７３８６９Ｅ−２１
Ｂ１１＝ ３．８１６８２３Ｅ−２４
Ｂ１２＝ ４．５３５８４３Ｅ−２５ 。
【００７４】
樹脂製レンズ６１のレンズ面６１ｂの形状のデータ
Ｒｍ＝−１０９．０８２４７４ Ｒｓ＝ −１１０．８８１３３２
Ａ０＝−５．４２７６４２Ｅ−１
Ａ４＝ ９．５３９０２４Ｅ−８
Ａ６＝ ４．８８２１９４Ｅ−１３
Ａ８＝−１．１９８９９３Ｅ−１６
Ａ１０＝ ５．０２９９８９Ｅ−２０
Ａ１２＝−５．６５４２６９Ｅ−２４
Ｂ２＝−３．６５２５７５Ｅ−７
Ｂ４＝ ２．３３６７６２Ｅ−１１
Ｂ６＝ ８．４２６２２４Ｅ−１４
Ｂ８＝−１．０２６１２７Ｅ−１７
Ｂ１０＝−２．２０２３４４Ｅ−２１
Ｂ１２＝ １．２２４５５５Ｅ−２６ 。
【００７５】
樹脂製レンズ６２のレンズ面６２ａの形状のデータ
Ｒｍ＝１４９３．６５４５８７ Ｒｓ＝ −７０．０７２４３２
Ａ０＝ ５．４７９３８９Ｅ＋１
Ａ４＝−７．６０６７５７Ｅ−９
Ａ６＝−６．３１１２０３Ｅ−１３
Ａ８＝ ６．１３３８１３Ｅ−１７
Ａ１０＝−１．４８２１４４Ｅ−２１
Ａ１２＝ ２．４２９２７５Ｅ−２６
Ａ１４＝−１．６８８７７１Ｅ−３０
Ｂ２＝−８．７０１５７３Ｅ−８
Ｂ４＝ ２．８２９３１５Ｅ−１１
Ｂ６＝−１．９３００８０Ｅ−１５
Ｂ８＝ ２．７６６８６２Ｅ−２０
Ｂ１０＝ ２．１７６９９５Ｅ−２４
Ｂ１２＝−６．１０７７９９Ｅ−２９ 。
【００７６】
樹脂製レンズ６２のレンズ面６２ｂの形状のデータ
Ｒｍ＝１７４８．５８３９００ Ｒｓ＝ −２８．０３４６１２
Ａ０＝−５．４８８７４０Ｅ＋２
Ａ４＝−４．９７８３４８Ｅ−８
Ａ６＝ ２．３２５１０４Ｅ−１２
Ａ８＝−７．６１９４６５Ｅ−１７
Ａ１０＝ ３．３２２７３０Ｅ−２１
Ａ１２＝−３．５７１３２８Ｅ−２６
Ａ１４＝−２．１９８７８２Ｅ−３０
Ｂ１＝−１．４４０１８８Ｅ−６
Ｂ２＝ ４．６９６１４２Ｅ−７
Ｂ３＝ １．８５３９９９Ｅ−１１
Ｂ４＝−４．１５３０９２Ｅ−１１
Ｂ５＝−８．４９４２７８Ｅ−１６
Ｂ６＝ ２．１９３１７２Ｅ−１５
Ｂ７＝ ９．００３６３１Ｅ−１９
Ｂ８＝−９．２７１６３７Ｅ−２１
Ｂ９＝−１．３２８１１１Ｅ−２２
Ｂ１０＝−１．４０９６４７Ｅ−２４
Ｂ１１＝ ５．５２０１８３Ｅ−２７
Ｂ１２＝ ４．５１３１０４Ｅ−３０
Ｃ０＝−９．９９９９９９Ｅ−１
Ｉ０＝−１．３２０８４９Ｅ−７
Ｉ２＝−１．０８７６７４Ｅ−１１
Ｉ４＝−９．０２２５７７Ｅ−１６
Ｉ６＝−７．３４４１３４Ｅ−２０
Ｋ０＝ ９．３９６６２２Ｅ−９
Ｋ２＝ １．１４８８４０Ｅ−１２
Ｋ４＝ ８．０６３５１８Ｅ−１７
Ｋ６＝−１．４７３８４４Ｅ−２０ 。
【００７７】
なお、実施例の光学系において、図１、図２に図示されていないが、第２光学系１００とポリゴンミラー５の間と、ポリゴンミラー５と第３光学系６００との間に、共通の防音ガラス（厚さ：１．９ｍｍ、屈折率：１．５１４３７）が設けられ、第３光学系６００と被走査面７との間には、防塵ガラス（厚さ：１．９ｍｍ、屈折率：１．５１４３７）が設けられている。
【００７８】
防音ガラスは、第３光学系６００の光軸に対して傾き角：８度をもって傾けて配置され、防塵ガラスは、副走査方向に対して２０度傾けて配置されている。
半導体レーザアレイ１の各発光源から放射される発散性の光束の発散角は、半値全角で、接合面直交方向が３０度、接合面平行方向が８度である。
図５に上記実施例のスポット径を示す。（ａ）は主走査方向、（ｂ）は副走査方向のもので、像高：±１５０ｍｍ、±８０ｍｍ、および０ｍｍにつき示す。横軸のデフォーカス（ｍｍ）は、主・副走査方向のビームウエスト位置（主走査方向の像面）の「被走査面からのずれ量」を示し、縦軸が「スポット径」を示す。
【００７９】
設計上、主走査方向のスポット径は３０μｍ、副走査方向のスポット径は４０μｍをねらいとしている。主・副走査方向とも良好な焦点深度を有している。
【００８０】
即ち、実施例の光走査装置では、半導体レーザアレイ１における発光源間隔が８０μｍであり、開口絞り２０を通過して第２光学系１００に入射する各光束の主走査方向の光束径：Ａｍ＝４．５２ｍｍ、第２光学系１００を射出した各光束の主走査方向の光束径：Ａｐ＝７．８１ｍｍが、条件：
（１） Ａｐ／Ａｍ＝１．７３＞１．２
を満足する（請求項１０）。
【００８１】
上記実施例において、環境温度変動に伴なう像面変動は、標準温度：２５℃、温度範囲：０〜４５℃の範囲において、主走査方向において±０．１ｍｍ程度、副走査方向において±０．３ｍｍ程度であり、図５のスポット径の特性図から明らかなように、像面変動が上記範囲であれば、像面変動に伴うデフォーカスによるスポット径変動は、上記狙いとする主走査方向のスポット径：３０μｍ、副走査方向のスポット径：４０μｍを外れることがない。
【００８２】
【発明の実施の形態】
図６に画像形成装置の実施の１形態として光プリンタ（レーザプリンタ）を示す。
レーザプリンタ２００は潜像担持体１１１として「円筒状に形成された光導電性の感光体」を有している。潜像担持体１１１の周囲には、帯電手段としての帯電ローラ１１２、現像装置１１３、転写ローラ１１４、クリーニング装置１１５が配備されている。帯電手段としては「コロナチャージャ」を用いることもできる。更に、レーザビームＬＢによりマルチビーム走査方式の光走査を行う光走査装置１１７が設けられ、帯電ローラ１１２と現像装置１１３との間で「光書込による露光」を行うようになっている。
【００８３】
図６において、符号１１６は定着装置、符号１１８はカセット、符号１１９はレジストローラ対、符号１２０は給紙コロ、符号１２１は搬送路、符号１２２は排紙ローラ対、符号１２３はトレイ、符号Ｐは記録媒体としての転写紙を示している。
【００８４】
画像形成を行うときは、光導電性の感光体である像担持体１１１が時計回りに等速回転され、その表面が帯電ローラ１１２により均一帯電され、光走査装置１１７のレーザビームＬＢによるマルチビーム走査方式の光書込による露光を受けて静電潜像が形成される。形成された静電潜像は所謂「ネガ潜像」であって画像部が露光されている。
【００８５】
この静電潜像は現像装置１１３により反転現像され、像担持体１１１上にトナー画像が形成される。
【００８６】
転写紙Ｐを収納したカセット１１８は、画像形成装置１００本体に脱着可能であり、図のごとく装着された状態において、収納された転写紙Ｐの最上位の１枚が給紙コロ１２０により給紙され、給紙された転写紙Ｐは、その先端部をレジストローラ対１１９に捉えられる。レジストローラ対１１９は、像担持体１１１上のトナー画像が転写位置へ移動するのにタイミングを合わせて、転写紙Ｐを転写部へ送り込む。送り込まれた転写紙Ｐは、転写部においてトナー画像と重ね合わせられ転写ローラ１１４の作用によりトナー画像を静電転写される。
【００８７】
トナー画像を転写された転写紙Ｐは定着装置１１６へ送られ、定着装置１１６においてトナー画像を定着され、搬送路１２１を通り、排紙ローラ対１２２によりトレイ１２３上に排出される。トナー画像が転写された後の像担持体１１１の表面は、クリーニング装置１１５によりクリーニングされ、残留トナーや紙粉等が除去される。
【００８８】
光走査装置として、上に説明した実施の形態や実施例のものを用いて、高密度の良好な画像形成を実現できる。
【００８９】
【発明の効果】
以上に説明したように、この発明によればマルチビーム走査方式の新規な光走査装置および画像形成装置を実現できる。この発明の光走査装置は、光源からの複数の光束をカップリングする第１光学系として、焦点距離の短いカップリングレンズを用いても、第２光学系のビームエキスパンダ機能により「小径の光スポットを実現するに必要な光束径」を確保でき、また、樹脂製結像素子そのものに結像位置のずれを補正する作用を持たせることで、機械的に結像位置のずれを調整する従来技術にくらべて、コストを削減し、消費電力を抑えることができる。
【００９０】
この発明の光走査装置を用いることにより、この発明の画像形成装置は小径の光スポットにより高密度の精細な画像を形成することができる。
【図面の簡単な説明】
【図１】光走査装置の実施の１形態を説明するための図である。
【図２】図１の光学配置を、光源から被走査面にいたる光路を直線的に展開して描いた図である。
【図３】複数の発光源を有する光源の１例である半導体レーザアレイを説明するための図である。
【図４】第２光学系の光学作用を説明するための図である。
【図５】実施例におけるスポット径の特性を説明するための図である。
【図６】画像形成装置の実施の１形態を説明するための図である。
【図７】カップリングレンズのＮＡとレンズ外径の関係を説明するための図である。
【符号の説明】
１ 光源（半導体レーザアレイ）
２ 第１光学系（カップリングレンズ）
５ 光偏向器（ポリゴンミラー）
５Ａ 偏向反射面
２０ 開口絞り
１００ 第２光学系
６００ 第３光学系[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device and an image forming apparatus. The optical scanning device of the present invention is a “multi-beam scanning optical scanning device”, and the image forming apparatus of the present invention uses the optical scanning device of the present invention, such as a digital copying machine, an optical printer, an optical plotter, and a laser facsimile. It can be implemented as an image forming apparatus.
[0002]
[Prior art]
In an optical scanning device used in the optical writing system of an image forming apparatus such as a digital copying apparatus, an optical printer, an optical plotter, or a laser facsimile, as a measure for improving the optical writing speed, a plurality of lines on a scanned surface are simultaneously irradiated with a plurality of light beams. A “multi-beam scanning method” for scanning has been proposed.
[0003]
In recent years, in the image forming apparatus described above, the density of image writing by optical scanning is increasing, and it is desired that the diameter of the light spot on the surface to be scanned be further reduced.
In order to reduce the diameter of the light spot, it is necessary to increase the diameter of the light beam after coupling. As a measure for this, as shown in FIG. 7, coupling has been conventionally performed in order to ensure NA (numerical aperture). Although the focal length of the lens CPL is increased (f ′> f), as the focal length increases, the “outer diameter of the coupling lens CPL” increases as shown in FIG. is doing.
[0004]
In addition, in an optical system used for an optical scanning device, a resin lens has become indispensable in order to realize cost reduction and a special surface shape.
[0005]
However, a resin lens has a larger “radius of curvature and refractive index due to environmental temperature fluctuations” than a glass lens, and if the image plane fluctuates due to environmental temperature fluctuations, A so-called “spot diameter thickening” in which the diameter of the light spot increases causes image deterioration. Image plane fluctuations due to environmental temperature fluctuations are also caused by thermal expansion of the holder that holds the lens.
[0006]
Patent Documents 1 to 4 are known as proposals for reducing or eliminating such “image surface fluctuations due to environmental temperature fluctuations”, but none of them are perfect.
[0007]
[Patent Document 1]
JP-A-8-292388
[Patent Document 2]
JP-A-8-292388
[Patent Document 3]
JP 10-20225 A
[Patent Document 4]
Patent Publication 2671723
[0008]
[Problems to be solved by the invention]
In view of the above, the present invention can reduce the spot diameter by using a coupling lens with a short focal length, and can reduce the spot diameter. It is an object of the present invention to realize a novel optical scanning apparatus of a multi-beam scanning system that can effectively reduce surface fluctuations, and to realize an image forming apparatus using the optical scanning apparatus.
[0009]
[Means for Solving the Problems]
The optical scanning device of the present invention is a “multi-beam scanning optical scanning device” and includes a light source, first to third optical systems, an optical deflector, and an aperture stop.
[0010]
The “light source” has a plurality of light sources and emits a plurality of light fluxes.
The “first optical system” receives a plurality of light beams from a light source, converts each light beam into a desired light beam, and couples it to a subsequent optical system. The “desired light beam” is appropriately set according to the subsequent optical system. For example, the “desired light beam” may be a “substantially parallel light beam”, a “weakly divergent light beam”, or a “weakly convergent light beam”. it can.
[0011]
The “second optical system” is an optical system that collects each light beam from the first optical system in a substantially linear shape that is long in the main scanning corresponding direction.
The “optical deflector” has a deflecting / reflecting surface in the vicinity of the substantially linear condensing unit by the second optical system, and deflects a plurality of light beams by the deflecting / reflecting surface. As the optical deflector, a rotary type such as a polygon mirror, a rotary single mirror, a rotary dihedral mirror, or a swing type such as a galvano mirror can be used.
[0012]
The “aperture stop” is disposed between the first optical system and the optical deflector, and performs beam shaping for each light beam. That is, the aperture stop may be disposed between the first optical system and the second optical system, and each light beam after beam shaping may be incident on the second optical system. May be arranged between the optical deflector and the optical deflector to perform beam shaping on “each light beam that forms an image in a substantially linear shape in the main scanning direction by the action of the second optical system”.
[0013]
The “third optical system” is an optical system that condenses a plurality of light beams deflected by the optical deflector as a plurality of light spots separated in the sub-scanning direction on the surface to be scanned. If the optical deflector is a rotary type, the third optical system is an fθ lens. Further, when the optical deflector is of a swinging type, it becomes an f · sin θ lens.
[0014]
The third optical system has at least one resinous imaging element.
The second optical system includes at least one resin imaging element and at least one glass imaging element.
[0015]
The second optical system has a “beam expanding function for expanding the beam diameter in the main scanning direction”.
[0016]
The second optical system in the optical scanning device according to claim 1 can “at least one imaging element has a negative power in the main scanning direction” (claim 2). That is, the beam expanding function can be realized as a configuration in which the focal positions of a pair of convex lenses are matched, but the length of the lens system tends to be large. According to the optical scanning device of claim 2, by including at least one "imaging element having negative power in the main scanning direction" in the second optical system, the length of the lens system is not increased. The beam expanding function in the main scanning direction can be realized.
[0017]
3. The optical scanning device according to claim 1, wherein the resin imaging element included in the second optical system has “two or more surfaces having negative power in the sub-scanning direction, and holds the first optical system. The surface shape is determined so as to effectively correct the field curvature variation caused by deformation due to temperature change of the holding member and / or the image surface variation caused by temperature change of the resin imaging element in the third optical system. (Claim 3).
[0018]
Here, “image plane fluctuation” means that the image plane in the image formation of the light spot by the third optical system fluctuates by a minute distance in the optical axis direction of the third optical system. As the image plane moves, the shape of the field curvature also changes slightly.
[0019]
4. The optical scanning device according to claim 1, wherein the second optical system includes at least one “imaging element having power in the sub-scanning direction”. The “beam waist position in the sub-scanning direction by the first to third optical systems” can be positioned so as to substantially match the surface to be scanned.
[0020]
Further, in the optical scanning device according to any one of claims 1 to 4, the second optical system includes at least one "imaging element having power in the main scanning direction", and the imaging element includes: Positioning can be performed so that the “beam waist position in the main scanning direction by the first to third optical systems” of each light beam substantially coincides with the surface to be scanned.
[0021]
6. The optical scanning device according to claim 1, wherein at least one of the imaging elements constituting the second optical system preferably has power in “main scanning direction or only in the sub-scanning direction” ( Claim 6).
[0022]
A second optical system in an optical scanning device according to any one of claims 1 to 6, wherein a glass lens having a negative power only in the main scanning direction sequentially from the light source side to the optical deflector side, main scanning A resin lens having negative power different in the direction and the sub-scanning direction and a glass lens having different positive power in the main scanning direction and the sub-scanning direction can be provided.
[0023]
The light source used in the optical scanning device of the present invention is “having a plurality of light emitting sources”, and various types can be used, but “semiconductor laser array having a plurality of light emitting sources” is suitable as a light source ( Claim 8).
Although it is possible to shorten the interval between the light emitting sources in the semiconductor laser array, in order to eliminate the influence of “thermal crosstalk” between adjacent light emitting sources, it is better that the light source interval is somewhat large. Larger is more advantageous in terms of cost.
[0024]
However, on the surface to be scanned, it is necessary to set the interval in the sub-scanning direction of the light spots formed by the light flux from each light source to a value corresponding to the pixel density in the sub-scanning direction. PLs is the light emitting point interval in the scanning direction, Ps is the scanning line interval on the surface to be scanned, and β is the lateral magnification in the sub-scanning direction by the optical system (first to third optical systems) between the light source and the surface to be scanned. Then, the scanning line interval: Ps is
Ps = PLs × β
Set by. Therefore, in order to make “the scanning line interval a value that can correspond to high density (21.2 μm in the case of 1200 dpi)”, the horizontal magnification in the sub-scanning direction: β is reduced or the light source interval in the sub-scanning direction: PLs is set. It needs to be small.
[0025]
When the magnification β is reduced, the aperture width of the aperture stop in the sub-scanning direction is reduced, the light use efficiency is reduced, and it becomes difficult to obtain a sufficient amount of light on the surface to be scanned.
If the light source spacing: PLs is reduced, the problem of “thermal crosstalk and the like” occurs. Light emitting source interval: In order to reduce the scanning line interval without reducing PLs, it is preferable to arrange the semiconductor laser array “inclined the light emitting source arrangement direction with respect to the sub-scanning direction”.
[0026]
For example, when the interval between the light emitting sources in the semiconductor laser array is 80 μm and the arrangement direction of the light emitting sources is inclined by 83.3 degrees with respect to the sub-scanning direction, the first surface of the second optical system (most light source side) The light beam diameter in the main scanning direction of each light beam incident on the surface) is Am, and the light beam diameter in the main scanning direction of each light beam emitted from the last surface of the second optical system is Ap.
(1) Ap / Am> 1.2
Is preferably satisfied (claim 10).
[0027]
As the light source spacing increases, it is necessary to increase the tilt angle in order to obtain a desired pitch on the surface to be scanned. When the light emitting source array direction is tilted by about 30 degrees or more with respect to the sub-scanning direction, It is preferable to satisfy the conditional expression.
The “Ap / Am” is the “beam expansion ratio in the main scanning direction” by the second optical system.
[0028]
The image forming apparatus of the present invention is “an image forming apparatus that performs optical writing by a multi-beam scanning method using the optical scanning device according to any one of claims 1 to 10” (claim 11).
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the invention will be described below.
FIG. 1 is a diagram for explaining one embodiment of an “optical scanning device”.
A light source 1 having a plurality of light emitting sources emits a plurality of light beams. However, in order to avoid complication of the drawing, a chief ray of a single light beam is shown. The light beam emitted from the light source 1 is made into a substantially parallel light beam by the coupling lens 2 which is a “first optical system” and coupled to the following optical system. The coupling lens 2 has a coaxial aspheric surface, and is formed so that the wavefront aberration of the coupled light beam is corrected well.
[0030]
The light beam emitted from the coupling lens 2 passes through an aperture stop 20 for obtaining a “light spot having a desired spot diameter” on the surface to be scanned and is “beam-shaped”, and then enters the glass lens 10. .
[0031]
The entrance surface 10a of the glass lens 10 is a “cylindrical surface having a negative power only in the main scanning direction”, and the exit surface 10b is a “plane”. The main scanning direction is in the plane of the drawing, and the sub-scanning direction is a direction orthogonal to the drawing.
[0032]
The light beam that has passed through the glass lens 10 enters the resin lens 11. The incident surface 11a of the resin lens 11 is an “anamorphic surface having different negative powers in the main and sub scanning directions”. The exit surface 11b of the resin lens 11 is a cylindrical surface having a negative power only in the sub-scanning direction.
[0033]
The light beam then enters the glass lens 12. The incident surface 12a of the glass lens 12 is a cylindrical surface having a positive power in the sub-scanning direction, and the exit surface 12b is a spherical surface having a positive power. The glass lens 12 can also be composed of a toroidal surface.
[0034]
The glass lens 10, the resin lens 11, and the glass lens 12 constitute the second optical system 100. The second optical system 100 emits the light beam as “a parallel light beam in the main scanning direction and a convergent light beam in the sub-scanning direction”, but in the main scanning direction, the emitted parallel light is larger than the incident parallel light beam diameter. Increase the beam diameter.
That is, the second optical system has a beam expanding function in the main scanning direction.
[0035]
The light beam emitted from the second optical system 100 forms an image “in the main scanning direction long and substantially linear” in the vicinity of the deflection reflection surface 5A of the polygon mirror 5 which is an “optical deflector”. The light beam reflected by the deflecting / reflecting surface 5A of the polygon mirror 5 becomes a deflected light beam deflected at a constant angular velocity as the polygon mirror 5 rotates at a constant speed, and the action of the lenses 61 and 62 constituting the third optical system 600 allows The light is condensed as a light spot on the surface to be scanned 7, and the surface to be scanned 7 is optically scanned in the main scanning direction (the vertical direction in the figure).
[0036]
The third optical system 600 is an “fθ lens”, and has a function of speeding up the optical scanning of the surface to be scanned by the light spot. Since a plurality of light beams are emitted from the light source 1, a plurality of light spots are formed on the scanned surface 7. The plurality of light spots are separated from each other in the sub-scanning direction, and the plurality of lines on the scanned surface 7 are simultaneously optically scanned.
[0037]
At least one of the lenses 61 and 62 constituting the third optical system 600 is a “resin lens”.
[0038]
Although not shown in FIG. 1, prior to optical scanning of the effective writing width, synchronous light is detected, and writing by optical scanning is started after a predetermined time from detection of the synchronous light. At this time, since it is necessary to match the writing start positions of the light spots of the plurality of light beams, it is desirable that the light beams are condensed at least in the main scanning direction on the synchronization detection element.
[0039]
That is, the optical scanning device of FIG. 1 receives a light source 1 having a plurality of light sources and a plurality of light beams from the light source 1, and each light beam is a desired light beam (in this example, “substantially parallel light beam”). And the second optical system 100 for condensing each light beam from the first optical system 2 in a substantially linear shape in the main scanning corresponding direction. And an optical deflector 5 that has a deflecting / reflecting surface 5A in the vicinity of the substantially linear condensing portion and deflects a plurality of light beams by the deflecting / reflecting surface, and between the first optical system 2 and the optical deflector 5 In the example, the aperture stop 20 disposed between the first optical system 2 and the second optical system 100) and a plurality of light beams deflected by the optical deflector 5 are separated on the surface to be scanned in the sub-scanning direction. The optical system includes a third optical system 600 that focuses light as a plurality of light spots, and the third optical system 600 includes at least one resin imaging element. The second optical system 100 has at least one resin imaging element 11 and at least one glass imaging element 10, 12, and the second optical system 100 is It has a beam expanding function for expanding the beam diameter while maintaining the parallel beam form.
[0040]
At least one imaging element 10 in the second optical system 100 has “negative power in the main scanning direction”.
The resin lens 11 which is a “resin imaging element” included in the second optical system 100 has two surfaces having negative power in the sub-scanning direction (different negative powers in the main and sub-scanning directions). The anamorphic surface 11a and the cylindrical surface 11b having a negative power only in the sub-scanning direction), and the image plane variation and / or the second variation caused by the deformation due to the temperature change of the holding member holding the first optical system 2. The surface shape is determined so as to effectively correct the image plane variation caused by the temperature change of the resin imaging element in the three optical system 600 (Claim 3).
[0041]
That is, in the embodiment of FIG. 1, it is caused by an image plane variation caused by deformation due to a temperature change of the holding member that holds the first optical system 2 and a temperature change of the resin imaging element in the third optical system 600. Among image plane variations, image plane variations in the main scanning direction are caused by power fluctuations in the main scanning direction on the incident surface 11a of the resin lens 11 (negative power fluctuations in the main scanning direction due to temperature fluctuations of the resin lens 11). The image plane variation in the sub-scanning direction is corrected by the power variation in the sub-scanning direction of the incident surface 11a and the exit surface 11b.
[0042]
The resin lens 11 distributes the negative power in the sub-scanning direction separately to the entrance surface 11a and the exit surface 11b. The curvature of the surface in the sub-scanning direction can be reduced, and the lens surface can be easily formed.
[0043]
FIG. 3A shows a coupling state when a light source 1 is a semiconductor laser array having four channels, that is, four light emitting sources.
CH1 to CH4 represent four “light emitting sources”, and reference numeral 2 represents a coupling lens as the first optical system. The four light emission sources CH1 to CH4 are arranged at equal intervals in the same straight line, and the light flux emitted from these light emission sources is a divergent light flux, and its far field pattern is as shown in the figure. It is an ellipse whose major axis is the direction orthogonal to the arrangement direction of the light emission sources CH1 to CH4.
[0044]
As described above, it is possible to reduce the distance between the light emission sources CH1 to CH4 in the semiconductor laser array. However, in order to eliminate the influence of thermal crosstalk or the like, it is preferable that the distance between the light emission sources is wide. In the embodiment being described, the interval between the light sources CH1 to CH4 is increased, and the separation amount (scanning line pitch) in the sub-scanning direction between the light spots on the surface to be scanned is set to a desired size. As shown in (b), the light emitting sources CH1 to CH4 are used with the arrangement direction inclined at an inclination angle θ with respect to the sub-scanning direction (vertical direction in the figure).
[0045]
In this way, with respect to the adjacent light source spacing: D, the light source spacing in the sub-scanning direction: P₀(P₀= D · cos θ) can be made smaller than the actual light source interval: D.
[0046]
When the semiconductor laser array 1 is tilted, as shown in FIG. 3C, the long axis direction of the far field pattern of the radiated light beam is also tilted, and the cross-sectional shape of the parallel light beam coupled by the coupling lens 2 also has a long axis. It becomes an elliptical shape inclined in the sub-scanning direction, and the aperture width Am in the main scanning direction of the aperture stop 20 must be narrowed.
[0047]
As is well known, when a laser beam is condensed, the beam waist diameter is inversely proportional to the beam diameter before the beam is condensed. The spot diameter in the main scanning direction cannot be reduced.
[0048]
One measure for solving this problem is to increase the focal length of the coupling lens and increase the number of turns: NA as described above. However, the outer diameter of the coupling lens increases and the cost increases. .
[0049]
In the present invention, by providing the second optical system 100 with a beam expanding function in the main scanning direction, a coupling lens 2 having a short focal length is used. By expanding the beam diameter in the scanning direction by the second optical system 100, the beam diameter necessary to obtain a desired small-diameter light spot is ensured.
[0050]
FIG. 4 shows the optical action of the second optical system 100. FIG. 4A shows an optical action in the main scanning direction, which is a “beam expanding action”. The parallel light beam emitted from the aperture stop 20 has a light beam diameter: Am in the main scanning direction, but is given a tendency to diverge by the “negative power in the main scanning direction” of the glass lens 10 and the resin lens 11 and is made of glass. By the “positive power in the main scanning direction” of the lens 12, the lens 12 is returned to a parallel light beam having a light beam diameter of Ap and is incident on the deflecting / reflecting surface 5 </ b> A.
[0051]
FIG. 4B shows the optical action of the second optical system 100 in the sub-scanning direction. The parallel light beam from the aperture stop passes through the glass lens 10 as it is in the sub-scanning direction, is converted to a divergent light beam by the resin lens 11, and is converted into a convergent light beam by the glass lens 12, and the position of the deflecting / reflecting surface 5A. Focus on. At this time, the necessary NA is ensured by diverging in the sub-scanning direction by the resin lens 11 so that the focusing width on the deflecting / reflecting surface 5A becomes sufficiently small.
[0052]
The ratio of the light beam diameter Am in the main scanning direction of the parallel light beam emitted from the aperture stop 20 and the light beam diameter Ap in the main scanning direction of the light beam emitted from the second optical system 100: Ap / Am, that is, the beam expansion ratio is When the interval between the light emission sources CH1 to CH4 in the semiconductor laser array 1 is about 80 μm, it is preferable that Ap / Am> 1.2 as described above, and the spot diameter on the scanned surface 7 is reduced to about 30 μm. In this case, Ap / Am> 1.5 is preferable.
[0053]
In the embodiment described above, the glass lens 10 in the second optical system 100 has “negative power only in the main scanning direction”. Therefore, if the glass lens 10 is displaced in the optical axis direction, the sub-scanning is performed. The optical action in the direction does not change, and the optical action only in the main scanning direction changes. By utilizing this fact, the position of the glass lens 10 in the optical axis direction is finely adjusted to correct the “beam waist position shift in the main scanning direction” caused by a processing error of the third optical system 600 and the like. The beam waist position in the scanning direction can be fixed at an adjustment position that substantially coincides with the surface to be scanned.
[0054]
On the other hand, since the resin lens 11 has power in the sub-scanning direction, displacing the resin lens 11 in the optical axis direction causes the “sub-scanning direction” caused by a processing error of the third optical system 600 and the like. In this case, the beam waist position in the sub-scanning direction can be corrected and fixed at the adjustment position so that the beam waist position substantially coincides with the surface to be scanned.
[0055]
Since the resin lens 11 in the second optical system 100 has different negative powers in the main scanning direction and the sub-scanning direction, the resin lens 11 is displaced in the optical axis direction so that the beam waist position in the sub-scanning direction is substantially on the surface to be scanned. However, even if the beam waist position in the main scanning direction is deviated from the surface to be scanned, the glass lens 10 has power only in the main scanning direction. Therefore, the “deviation of the beam waist position in the main scanning direction” due to the above adjustment can be corrected by the displacement of the glass lens 10 in the optical axis direction.
[0056]
The second optical system in the above-described embodiment includes, in order from the light source side to the optical deflector side, a glass lens 10 having a negative power only in the main scanning direction, and a negative power different in the main scanning direction and the sub-scanning direction. And a glass lens 12 having different positive power in the main scanning direction and the sub-scanning direction (Claim 7), and the light source 1 is a semiconductor laser array having a plurality of light emitting sources. (Claim 8), the arrangement direction of the light sources CH1 to CH4 is inclined with respect to the sub-scanning direction (Claim 9).
[0057]
【Example】
Hereinafter, specific numerical examples related to the optical scanning device described above will be given.
The lens surface shape conforms to the following definition.
Specific arc shape in the main scanning section
The “main scanning section” is a virtual plane section including the lens optical axis and parallel to the main scanning direction. The non-arc shape in this plane has a paraxial radius of curvature in the main scanning direction on the optical axis: Rm, a distance from the optical axis in the main scanning direction: Y, a cone constant: K, and higher order coefficients: A1, A2, A3, A4, A5, A6,... Depth in optical axis direction: X is used to express the following polynomial.

When one or more of odd-order coefficients A1, A3, A5,... Is not 0, the non-circular arc shape is asymmetric in the main scanning direction, but in the embodiment, only even-order coefficients are used. Symmetric in direction.
Change in curvature in the sub-scan section in the main scan direction
The “sub-scanning cross section” is a virtual flat cross section orthogonal to the main scanning direction.
Using the radius of curvature in the sub-scanning direction in the sub-scanning section including the optical axis: Rs (0), the distance from the optical axis in the main scanning direction: Y, the coefficients: B1, B2, B3,. Curvature: Cs (Y) is expressed by the following equation.
[0058]
Cs (Y) = 1 / Rs (0) + B1 · Y + B2 · Y²+ B3 · Y³+ B4 · Y⁴+ B5 · Y⁵+ (2)
"Sub non-arc surface (shapes in the main and sub scanning sections are both non-arc)"
The distance in the main scanning direction from the optical axis: Y, the distance in the sub-scanning direction from the main scanning section: Z, and the depth in the optical axis direction: X (Y, Z) are expressed by the following equations.
[0059]

The sum of the second term on the right side of Equation (3) is taken for the suffix: n. The first term and the second term on the right side are the same as the right side of Equation (1).
[0060]
The fourth term on the right side of Equation (3) is
f_SAG(Y, Z) = Σ (Σd_{j, h}Y^hZ^j
Then this can be written as:
[0061]

[0062]
here,
Cm (= 1 / Rm): Paraxial curvature in the main scanning section including the optical axis
Cs (0) (= 1 / Rs (0)): Paraxial curvature in the sub-scan section including the optical axis
Cs (Y): position in the main scanning direction: paraxial curvature in the sub-scan section at Y
Kz (Y): position in the main scanning direction: conic constant representing a quadratic curve in the sub-scanning section at Y
F_SAG(Y, Z): Aspheric high-order correction amount
Cs (Y) = {1 / Rs (0)} + B1 · Y + B2 · Y²+ B3 · Y³+ B4 · Y⁴+ B5 · Y⁵+ ...
Kz (Y) = C0 + C1 · Y + C2 · Y²+ C3 · Y³+ C4 · Y⁴+ C5 ・ Y⁵+ ...
When one or more of “odd order coefficients of Y: B1, B3, B5,...” On the right side of Cs (Y) is not 0, the radius of curvature in the sub-scanning direction becomes asymmetric in the main scanning direction.
Similarly, when the odd-order coefficient of Y representing non-arc amounts such as C1, C3, C5,... F1, F3, F5, G1, G3, G5,. Asymmetric in the main scanning direction.
Example
FIG. 2 depicts a state in which the optical arrangement of the optical scanning device of FIG. 1 is linearly developed from the light source 1 to the scanned surface 7, with the vertical direction as the sub-scanning direction. The surface intervals are d1 to d11 as shown in FIG. Further, as shown in FIG. 1, the shift amounts of the lenses 61 and 62 in the main scanning direction (the upward shift in the figure is positive) are d12 and d13 as shown.
[0063]
Light source 1: Semiconductor laser array
Emission source pitch: 80 μm, Emission source number: 4 channels, Emission wavelength: 655 nm
Tilt angle with respect to the sub-scanning direction of the light source array direction: θ = 83.3 degrees
[0064]
Scan line pitch:
"First optical system (coupling lens 2)"
Aberration is corrected well with a glass lens having an aspherical surface.
Focal length: 27 mm, coupling action: collimating action.
[0065]
Aperture stop 20
“Aperture width” Main scanning direction: 4.52 mm Sub-scanning direction: 1.47 mm
Installation position: focal plane position of the coupling lens 2 on the optical deflector side.
[0066]
"Optical deflector (polygon mirror 5)"
Number of deflection reflecting surfaces: 5, inscribed circle radius: 18 mm
Angle formed by the light beam incident angle from the light source side and the optical axis of the third optical system: 60 degrees
Optical writing width: ± 150mm
Angle of view: ± 38 degrees
Writing density: 1200 dpi
Scan line pitch: 21.2 μm.
[0067]
Am = 4.52 mm, Ap = 7.81 mm, Ap / Am = 1.73
d1 = 3 mm, d2 = 40 mm, d3 = 4 mm, d4 = 12.5 mm,
d5 = 6 mm, d6 = 135.1 mm
The radius of curvature of the lens surface 10a of the glass lens 10
Main scanning direction: −80.001 mm Sub scanning direction: ∞
The radius of curvature of the lens surface 10b of the glass lens 10
Main scanning direction: ∞ Sub scanning direction: ∞.
[0068]
The radius of curvature of the lens surface 11a of the resin lens 11
Main scanning direction: -79.3 mm Sub scanning direction: -16 mm (sub non-arc surface)
The radius of curvature of the lens surface 11a of the resin lens 11
Main scanning direction: ∞ Sub scanning direction: 16 mm.
[0069]
The radius of curvature of the lens surface 12a of the glass lens 12
Main scanning direction: ∞ Sub scanning direction: 23 mm
The radius of curvature of the lens surface 12a of the glass lens 12
Main scanning direction: −69.205 mm Sub scanning direction: −69.205 mm (spherical surface)
Data on the shape of the secondary non-arc surface (lens surface 11a)
Rm = -79.3 Rs = -16
A0 = 3.830626E-0
C0 = −4.575435E−0
C2 = -4.115910E-0
C4 = 1.444109E-1
I0 = -4.293593E-4
I2 = −1.744060E-4
I4 = 4.580594E-6
K0 = -1.434818E-4
K2 = 3.334279E-5
K4 = −2.275387E-7
In the above notation, for example, “3.334279E-5” is “3.334279 × 10”.^-5"Means. The same applies to the following.
[0070]
Refractive index of the material of the resin lens 11: 1.527238 (λ = 655 nm, at 25 ° C.)
Linear expansion coefficient of resin lens 11: 7E-5
Refractive index of the material of the glass lenses 10 and 12: 1.378755 (λ = 655 nm, at 25 ° C.)
Linear expansion coefficient of the glass lenses 10 and 12: 5.4E-6
The coefficient of linear expansion of the lens mounting portion (base member): 2.31E-5.
[0071]
d7 = 71.2 mm, d8 = 30 mm, d9 = 66.5 mm,
d10 = 8.5 mm, d11 = 157.8 mm, d12 = 0.2 mm,
d13 = 0.2 mm.
[0072]
Refractive index of the material of the resin scanning lenses 61 and 62: 1.527238 (λ = 655 nm, at 25 ° C.)
Linear expansion coefficient of the resin scanning lenses 61 and 62: 7E-5.
[0073]
Data of the shape of the lens surface 61a of the resin lens 61
Rm = −1030.233346 Rs = −89.518927
A0 = −4.041619E + 2
A4 = 6.005017E-8
A6 = −7.538155E-13
A8 = −4.036824E-16
A10 = 4.592164E-20
A12 = -2.396524E-24
B1 = −9.317851E-6
B2 = 3.269905E-6
B3 = 4.133297E-9
B4 = -4.207716E-10
B5 = -1.170114E-12
B6 = 4.370640E-14
B7 = 2.347965E-16
B8 = −6.212795E−18
B9 = −3.996794E-20
B10 = −3.8873869E-21
B11 = 3.881623E-24
B12 = 4.535843E-25.
[0074]
Data of the shape of the lens surface 61b of the resin lens 61
Rm = −109.082474 Rs = −110.813322
A0 = −5.427642E−1
A4 = 9.539024E-8
A6 = 4.882194E-13
A8 = -1.198993E-16
A10 = 5.029989E-20
A12 = -5.654269E-24
B2 = -3.662575E-7
B4 = 2.336762E-11
B6 = 8.426224E-14
B8 = −1.026127E-17
B10 = -2.202344E-21
B12 = 1.224555E-26.
[0075]
Data of the shape of the lens surface 62a of the resin lens 62
Rm = 1493.654545 Rs = −70.072432
A0 = 5.479389E + 1
A4 = −7.6606757E-9
A6 = −6.3311203E-13
A8 = 6.133813E-17
A10 = −1.482144E-21
A12 = 2.429275E-26
A14 = −1.6888771E-30
B2 = −8.701573E−8
B4 = 2.829315E-11
B6 = -1.930080E-15
B8 = 2.766862E-20
B10 = 2.176769E-24
B12 = -6.107799E-29.
[0076]
Data of the shape of the lens surface 62b of the resin lens 62
Rm = 17488.583900 Rs = −28.034612
A0 = −5.488740E + 2
A4 = -4.978348E-8
A6 = 2.325104E-12
A8 = −7.619465E−17
A10 = 3.332230E-21
A12 = −3.571328E−26
A14 = −2.9878782E-30
B1 = −1.440188E-6
B2 = 4.6696142E-7
B3 = 1.853999E-11
B4 = −4.153092E-11
B5 = −8.494278E-16
B6 = 2.193172E-15
B7 = 9.003631E-19
B8 = −9.271637E-21
B9 = -1.328111E-22
B10 = -1.409647E-24
B11 = 5.520183E-27
B12 = 4.513104E-30
C0 = -9.99999999E-1
I0 = -1.320849E-7
I2 = −1.08774E-11
I4 = −9.022577E-16
I6 = −7.3344134E−20
K0 = 9.396622E-9
K2 = 1.148840E-12
K4 = 8.063518E-17
K6 = -1.473844E-20.
[0077]
Although not shown in FIGS. 1 and 2 in the optical system of the embodiment, it is common between the second optical system 100 and the polygon mirror 5 and between the polygon mirror 5 and the third optical system 600. Soundproof glass (thickness: 1.9 mm, refractive index: 1.51437) is provided, and dustproof glass (thickness: 1.9 mm, refractive index: between the third optical system 600 and the scanned surface 7). 1.51437).
[0078]
The soundproof glass is disposed with an inclination angle of 8 degrees with respect to the optical axis of the third optical system 600, and the dustproof glass is disposed with an inclination of 20 degrees with respect to the sub-scanning direction.
The divergence angle of the divergent light beam emitted from each light source of the semiconductor laser array 1 is a full width at half maximum, 30 degrees in the orthogonal direction of the bonding surface, and 8 degrees in the parallel direction of the bonding surface.
FIG. 5 shows the spot diameter of the above example. (A) is in the main scanning direction, (b) is in the sub-scanning direction, and image heights are shown for ± 150 mm, ± 80 mm, and 0 mm. The defocus (mm) on the horizontal axis indicates the “deviation amount from the scanned surface” of the beam waist position (image plane in the main scanning direction) in the main / sub-scanning direction, and the vertical axis indicates the “spot diameter”.
[0079]
In design, the spot diameter in the main scanning direction is 30 μm, and the spot diameter in the sub-scanning direction is 40 μm. It has a good depth of focus in both the main and sub scanning directions.
[0080]
That is, in the optical scanning device of the embodiment, the light source interval in the semiconductor laser array 1 is 80 μm, and the light beam diameter in the main scanning direction of each light beam that passes through the aperture stop 20 and enters the second optical system 100: Am = 4.52 mm, the diameter of each light beam emitted from the second optical system 100 in the main scanning direction: Ap = 7.81 mm, the condition:
(1) Ap / Am = 1.73> 1.2
(Claim 10).
[0081]
In the above embodiment, the image plane variation due to the environmental temperature variation is about ± 0.1 mm in the main scanning direction and ± 0 in the sub scanning direction in the standard temperature: 25 ° C. and temperature range: 0 to 45 ° C. As is clear from the spot diameter characteristic diagram of FIG. 5, if the image plane variation is in the above range, the spot diameter variation due to defocus accompanying the image plane variation is the target main scanning direction. The spot diameter is 30 μm and the spot diameter in the sub-scanning direction is not deviated from 40 μm.
[0082]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 6 shows an optical printer (laser printer) as one embodiment of the image forming apparatus.
The laser printer 200 has a “cylindrical photoconductive photosensitive member” as the latent image carrier 111. Around the latent image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided. A “corona charger” can also be used as the charging means. Further, an optical scanning device 117 that performs multi-beam scanning optical scanning with the laser beam LB is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113.
[0083]
In FIG. 6, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a discharge roller pair, reference numeral 123 denotes a tray, reference numeral P Indicates transfer paper as a recording medium.
[0084]
When performing image formation, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 112, and a multi-beam is generated by the laser beam LB of the optical scanning device 117. An electrostatic latent image is formed upon exposure by scanning optical writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.
[0085]
This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111.
[0086]
The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper supply roller 120. The leading edge of the fed transfer paper P is caught by the registration roller pair 119. The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.
[0087]
The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122. The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like.
[0088]
As the optical scanning device, the above-described embodiment or example can be used to realize good image formation with high density.
[0089]
【The invention's effect】
As described above, according to the present invention, a novel optical scanning apparatus and image forming apparatus of a multi-beam scanning system can be realized. In the optical scanning device of the present invention, even if a coupling lens with a short focal length is used as the first optical system for coupling a plurality of light beams from the light source, the “small-diameter light” is obtained by the beam expander function of the second optical system. The beam diameter necessary to realize a spot ”can be secured, and the resin imaging element itself has a function of correcting the deviation of the imaging position to mechanically adjust the deviation of the imaging position. Compared to technology, cost can be reduced and power consumption can be reduced.
[0090]
By using the optical scanning apparatus of the present invention, the image forming apparatus of the present invention can form a high-definition and fine image with a small-diameter light spot.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an embodiment of an optical scanning device.
2 is a diagram in which the optical arrangement of FIG. 1 is drawn by linearly developing an optical path from a light source to a scanned surface.
FIG. 3 is a diagram for explaining a semiconductor laser array which is an example of a light source having a plurality of light emitting sources.
FIG. 4 is a diagram for explaining an optical action of a second optical system.
FIG. 5 is a diagram for explaining the characteristics of the spot diameter in the embodiment.
FIG. 6 is a diagram for explaining one embodiment of an image forming apparatus.
FIG. 7 is a diagram for explaining the relationship between the NA of a coupling lens and the lens outer diameter.
[Explanation of symbols]
1 Light source (semiconductor laser array)
2 First optical system (coupling lens)
5 Optical deflector (polygon mirror)
5A deflection reflective surface
20 Aperture stop
100 Second optical system
600 Third optical system

Claims (11)

A light source having a plurality of light emitting sources;
A first optical system that converts a plurality of light beams from the light source into a desired light beam and couples it to a subsequent optical system;
A second optical system for condensing each light beam from the first optical system in a substantially linear shape that is long in the main scanning correspondence direction;
An optical deflector having a deflection reflection surface in the vicinity of the substantially linear condensing unit, and deflecting the plurality of light beams by the deflection reflection surface;
An aperture stop disposed between the first optical system and the optical deflector;
A third optical system for condensing a plurality of light beams deflected by the optical deflector as a plurality of light spots separated in the sub-scanning direction on the surface to be scanned;
The third optical system has at least one resin imaging element,
The second optical system has at least one resin imaging element and at least one glass imaging element,
The multi-beam scanning type optical scanning device, wherein the second optical system has a beam expanding function for expanding a beam diameter in the main scanning direction. The optical scanning device according to claim 1,
An optical scanning device, wherein at least one imaging element in the second optical system has a negative power in the main scanning direction. The optical scanning device according to claim 1 or 2,
The resinous imaging element included in the second optical system has two or more surfaces having negative power in the sub-scanning direction, and an image surface caused by deformation due to a temperature change of the holding member that holds the first optical system. An optical scanning device characterized in that a surface shape is determined so as to effectively correct fluctuations and / or image plane fluctuations caused by temperature changes of a resin imaging element in the third optical system. The optical scanning device according to any one of claims 1 to 3,
The second optical system has at least one imaging element having power in the sub-scanning direction, and the imaging element substantially determines the beam waist position of each light beam in the sub-scanning direction by the first to third optical systems. An optical scanning device characterized by being positioned so as to coincide with a surface to be scanned. The optical scanning device according to any one of claims 1 to 4,
The second optical system has at least one imaging element having power in the main scanning direction, and this imaging element covers the beam waist position of each light beam in the main scanning direction by the first to third optical systems. An adjustment method characterized by being positioned so as to substantially coincide with a scanning plane. In the optical scanning device according to any one of claims 1 to 5,
At least one of the imaging elements constituting the second optical system has power only in the main scanning direction or the sub-scanning direction. The optical scanning device according to any one of claims 1 to 6,
A glass lens having a negative power only in the main scanning direction, a resin lens having a negative power different in the main scanning direction and the sub-scanning direction, sequentially from the light source side toward the optical deflector side, An optical scanning device comprising glass lenses having different positive powers in a main scanning direction and a sub-scanning direction. The optical scanning device according to any one of claims 1 to 7,
An optical scanning device, wherein the light source is a semiconductor laser array having a plurality of light emitting sources. The optical scanning device according to claim 8.
The semiconductor laser array is arranged with the arrangement direction of the light emitting sources inclined with respect to the sub-scanning direction. The optical scanning device according to claim 9.
Condition: The light beam diameter in the main scanning direction of each light beam incident on the first surface of the second optical system is Am, and the light beam diameter in the main scanning direction of each light beam emitted from the last surface of the second optical system is as follows:
(1) Ap / Am> 1.2
An optical scanning device characterized by satisfying An image forming apparatus that performs optical writing by a multi-beam scanning method using the optical scanning device according to claim 1.

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