JP3576891B2

JP3576891B2 - Multi-beam optical scanning device

Info

Publication number: JP3576891B2
Application number: JP28846799A
Authority: JP
Inventors: 芳浩石部; 博樹吉田
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1999-01-26
Filing date: 1999-10-08
Publication date: 2004-10-13
Anticipated expiration: 2019-10-08
Also published as: JP2000284194A

Description

【０００１】
【発明の属する技術分野】
本発明は、レーザービームプリンタやデジタル複写機等に使用されるマルチビーム光走査装置に関するものである。
【０００２】
【従来の技術】
図１６は従来例のマルチビーム光走査装置の平面図を示す。複数の発光点を有する半導体レーザー光源１ａ、１ｂから射出した光束Ａ、Ｂは、それぞれコリメータレンズ２で略平行光又は収束光とされ、その光束が開口絞り３で整形され、シリンドリカルレンズ４によって副走査方向にのみ収束して、光偏向器であるポリゴンミラー５の偏向反射面５ａの近傍において、主走査方向に長く伸びた焦線状に結像する。矢印Ｒ方向に一定角速度で回転しているポリゴンミラー５によって反射され偏向走査された光束は、それぞれｆθレンズ６によって感光ドラム等から成る被走査面７上にスポット状に集光し、矢印Ｄ方向に一定速度で走査される。このとき、同期検知用のスリット８ａ、レンズ８ｂ、センサ８ｃから成る書出し位置検知手段によって、走査光の一部が検出されて書出し位置が検知される。
【０００３】
このようなマルチビーム光走査装置においては、図１７（ａ）に示すように複数の光源１ａ、１ｂを副走査方向に縦に並べて配置すると、被走査面７上で副走査方向のそれぞれの線の間隔が記録密度よりも大幅に開いてしまう。このために、通常は図１７（ｂ）に示すように複数の光源１ａ、１ｂを斜めに配置し、その傾斜角度αを調整することによって、被走査面７上の副走査方向の各線の間隔を記録密度に合わせて、正確な調整を行っている。
【０００４】
【発明が解決しようとする課題】
しかしながら、上述の従来例のマルチビーム光走査装置においては、複数の光源１ａ、１ｂを斜めに配置することによって、これらの光源１ａ、１ｂから出射した光束が、図１８に示すようにポリゴンミラー５の反射面５ａ上において、主走査方向に離れた位置に到達し、かつポリゴンミラー５から反射される光束の角度もそれぞれ異なるために、被走査面７上において光束Ａ、Ｂのように、互いに主走査方向に離れた位置にスポット光が結像することになる。
【０００５】
このために、基準とする一方の光源１ａが被走査面７上に結像する位置に、他方の光源１ｂからの光束の結像位置を合わせるように、所定時間δＴだけタイミングをずらして画像データを送っている。この所定時間δＴだけずれたときのポリゴンミラー５の反射面５ａは角度βだけ回転しており、このとき反射される光束Ｂは光束Ａと同じ方向の光束Ｂ’の方向に反射されて、スポット光の結像位置が一致する。
【０００６】
各ビームそれぞれの被走査面７上での書出し開始点は次のように決定する。即ち、被走査面７の走査方向の上流に設けられた書出し位置検知手段８のセンサ８ｃに走査光束が到達したタイミングを同期検知として、この同期検知を各ビームそれぞれについて独立に行い、その同期検知結果から所定の遅延時間後を書出し開始としている。ここで、走査光束がセンサ８ｃに到達するときのタイミングをより正確に検知するために、スリット８ａはセンサ８ｃの前面の走査光束の集光点位置に配置されており、走査光束がこのスリット８ａを通過するときの光量の立上がりを検知して同期検知を行っている。
【０００７】
スリット８ａは複数光源１ａ、１ｂからの光束が走査することによって形成する面に対して斜めに配置されていると、各光束の結像位置が主走査方向にずれを生ずる。このために、通常スリット８ａは図１９に示すように、走査光束が走査することによって形成する面に対して垂直に配置されている。しかしながら、スリット８ａが走査光束の走査面に対して垂直に配置されていても、各光束の光量の差や、各光束のスポット形状の差や、各光源光束の立ち上がり特性や、各光束内部の光強度分布の差等の要因によって、各光束の同期検知のタイミングにずれが発生し、その結果として複数光束の結像位置にずれが生じ、印字精度の低下や画質の劣化を招くという問題点が存在する。
【０００８】
本発明の目的は、上述の問題点を解消し、走査開始タイミングを検出する検知手段のスリット部材を配置する角度及び位置を最適に設定して、高速かつ高画質なマルチビーム光走査装置を提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するための本発明に係るマルチビーム光走査装置は、複数の光束を発する光源と、偏向器と、該偏向器によって偏向走査された光束を被走査面上に集光する結像光学系と、該走査された複数の光束に対して走査開始タイミングを検知する検知手段とを備えたマルチビーム光走査装置において、前記検知手段の光束入射側に、前記検知手段に入射する光束が走査する平面と直交する面に対し、下記の（１）〜（５）の何れかの手段により決定した角度だけ傾斜させてスリット部材を配置し、該スリット部材を横切る光束の光量の立ち上がりを検出することによって、前記走査開始タイミングの検知を行うことを特徴とする。
（１）前記角度は前記複数の光束の光量の差を基に決定する。
（２）前記角度は前記スリット部材上での前記複数の光束のスポット形状の差を基に決定する。
（３）前記角度は前記複数の光源自身の光量の立ち上がり特性を基に決定する。
（４）前記角度は前記複数の光束の内部光強度分布の差を基に決定する。
（５）前記角度は前記複数の光束の光量の差と、前記スリット部材上での前記複数の光束のスポット形状の差と、前記複数の光源自身の光量の立ち上がり特性と、前記複数の光束の内部光強度分布の差の内の２つ以上の要因の組み合わせを基に決定する。
また、本発明に係るマルチビーム光走査装置は、複数の光束を発する光源と、偏向器と、該偏向器によって偏向走査された光束を被走査面上に集光する結像光学系と、該走査された複数の光束に対して走査開始タイミングを検知する検知手段と、前記複数の光束を少なくとも副走査方向に反射して前記検知手段に導く反射手段とを備えたマルチビーム光走査装置において、前記検知手段の光束入射側に、前記検知手段に入射する光束が走査する平面と直交する面に対し、下記の（１）〜（５）の何れかの手段により決定した角度だけ傾斜させてスリット部材を配置し、該スリット部材を横切る光束の光量の立ち上がりを検出することによって、前記走査開始タイミングの検知を行うことを特徴とする。
（１）前記角度は前記反射手段の反射角度と前記複数の光束の光量の差とを基に決定する。
（２）前記角度は前記反射手段の反射角度と前記スリット部材上での前記複数の光束のスポット形状の差とを基に決定する。
（３）前記角度は前記反射手段の反射角度と前記複数の光源自身の光量の立ち上がり特性とを基に決定する。
（４）前記角度は前記反射手段の反射角度と前記複数の光束の内部光強度分布の差とを基に決定する。
（５）前記角度は前記複数の光束の光量の差と、前記スリット部材上での前記複数の光束のスポット形状の差と、前記複数の光源自身の光量の立ち上がり特性と、前記複数の光束の内部光強度分布の差の内の２つ以上の要因の組み合わせと、前記反射手段の反射角度とを基に決定する。
【００１０】
更に、本発明に係るマルチビーム光走査装置は、複数の光束を発する光源と、偏向器と、該偏向器によって偏向走査された光束を被走査面上に集光する結像光学系と、該走査された複数の光束に対して走査開始タイミングを検知する検知手段とを備えたマルチビーム光走査装置において、前記検知手段の光束入射側に、前記検知手段に入射する光束の集光点から、下記の（１）〜（５）の何れかの手段により決定した距離だけずらした位置にスリット部材を配置して、該スリット部材を横切る光束の光量の立ち上がりを検出することによって、前記走査開始タイミングの検知を行うことを特徴とする。
（１）前記距離は前記複数の光束の光量の差を基に決定する。
（２）前記距離は前記スリット部材上での前記複数の光束のスポット形状の差を基に決定する。
（３）前記距離は前記複数の光源自身の光量の立ち上がり特性を基に決定する。
（４）前記距離は前記複数の光束の内部光強度分布の差を基に決定する。
（５）前記距離は前記複数の光束の光量の差と、前記スリット部材上での前記複数の光束のスポット形状の差と、前記複数の光源自身の光量の立ち上がり特性と、前記複数の光束の内部光強度分布の差の内の２つ以上の要因の組み合わせを基に決定する。
本発明に係るマルチビーム光走査装置は、複数の光束を発する光源と、偏向器と、該偏向器によって偏向走査された光束を被走査面上に集光する結像光学系と、該走査された複数の光束に対して走査開始タイミングを検知する検知手段と、前記複数の光束を少なくとも副走査方向に反射して前記検知手段へ導く反射手段とを備えたマルチビーム光走査装置において、前記検知手段の光束入射側に、前記検知手段に入射する光束の集光点から、下記の（１）〜（５）の何れかの手段により決定した距離だけずらした位置にスリット部材を配置して、該スリット部材を横切る光束の光量の立ち上がりを検出することによって、前記走査開始タイミングの検知を行うことを特徴とする。
（１）前記距離は前記反射手段の反射角度と前記複数の光束の光量の差とを基に決定する。
（２）前記距離は前記反射手段の反射角度と前記スリット部材上の前記複数の光束のスポット形状の差とを基に決定する。
（３）前記距離は前記反射手段の反射角度と前記複数の光源自身の光量の立ち上がり特性とを基に決定する。
（４）前記距離は前記反射手段の反射角度と前記複数の光束の内部光強度分布の差とを基に決定する。
（５）前記距離は前記複数の光束の光量の差と、前記スリット部材上での前記複数の光束のスポット形状の差と、前記複数の光源自身の光量の立ち上がり特性と、前記複数の光束の内部光強度分布の差の内の２つ以上の要因の組み合わせと、前記反射手段の反射角度とを基に決定する。
【００１１】
【発明の実施の形態】
本発明を図１〜図１５に図示の実施例に基づいて詳細に説明する。
図１は第１の実施例のマルチビーム光走査装置の平面図を示し、２つの半導体光源１１ａ、１１ｂから成る半導体レーザー光源１１の前方の光路上には、第１の光学系であるコリメータレンズ１２、第２の光学系であるシリンドリカルレンズ１３、開口絞り１４、矢印Ｒ方向に一定角速度で回転している光偏向器であるポリゴンミラー１５が順次に配列されている。ポリゴンミラー１５の反射方向には、第３の光学系であるｆθレンズ１６、感光ドラム等の被走査面１７が配置されている。
【００１２】
また、各ビームそれぞれの被走査面１７上での書出し開始点を決定するために、スリット１８ａ、レンズ１８ｂ、センサ１８ｃから成る書出し位置検知手段１８が、被走査面１７の走査方向上流位置に設けられている。ここで、スリット１８ａは走査光束がセンサ１８ｃに到達するタイミングをより正確に検知するために、センサ１８ｃ前方の走査光束の集光点位置に配置されている。
【００１３】
このような構成により、半導体レーザー光源１１から射出した光束は、コリメータレンズ１２で略平行光又は収束光とされ、シリンドリカルレンズ１３によって副走査方向にのみ収束し、開口絞り１４を通って光束幅が制限されて、ポリゴンミラー１５の偏向反射面１５ａ上において、主走査方向に長く伸びる焦線状に結像する。そして、ポリゴンミラー１５によって反射され偏向走査された光束は、ｆθレンズ１６によって感光ドラムの被走査面１７上にスポット状に集光して、矢印Ｄ方向に一定速度で走査される。
【００１４】
このとき、書出し位置検知手段１８のセンサ１８ｃに走査光束が到達するタイミングを同期検知とし、この同期検知を各ビームそれぞれについて独立に行い、その同期検知から所定の遅延時間後を書出し開始とする。即ち、図２に示すように、走査光束がスリット１８ａを通過するときのセンサ１８ｃの出力が、或る一定のスライスレベルＳ以上になったときに同期検知信号が出力され、この時点から一定時間ｔ１後に画像信号が送られる。この動作をそれぞれの光束に対して行うことによって、各光束の書出し位置を一致させることができる。
【００１５】
従来例の場合では、スリット１８ａは光束が走査する面に対して垂直に配置されているが、各光束においてその光量、スリット１８ａ上でのスポット形状、各光束に対応する光源の光量や立ち上がり特性、光束内部の光強度分布などが完全に同じではないために、これらの要因による相対的な差異があり、このためにそれぞれの光束の書出し位置に誤差が発生する。例えば、印字品質の向上を目的としてスポット径を小さくしたり、或いは印字領域を広げた場合などでは、ポリゴンミラー１５の偏向反射面１５ａに余裕がなくなるので、例えば書出し位置検知に使用する同期検知光束を意識的に外して使用する必要が生ずる。
【００１６】
その場合には、それぞれの光源１１ａ、１１ｂから出射した光束は、ポリゴンミラー１５の偏向反射面１５ａ上で主走査方向に位置がずれているために、光束のけられ量が同一とはならず、その結果として光量に差が生ずる。例えば図１においては、光源１１ａに対応する光束Ａのけられ量の方が、光源１１ｂに対応する光束Ｂのけられ量よりも大きくなり、前者の同期検知光の方が光量が小さくなる。
【００１７】
このように、光源１１ａ、１１ｂに対応するそれぞれの同期検知光Ａ、Ｂに光量差がある場合には、図３に示すように光源１１ａに対応する同期検知信号の出力と、光源１１ｂに対応する同期検知信号の出力のタイミングにδｔ２だけのずれが発生し、この結果として両者の書出し位置がδｔ２に相当する量だけずれることになる。即ち、スリット１８ａ上での各光束の主走査方向の走査速度をＶｍｍ／秒とすると、δｔ２秒だけ同期検知信号の出力タイミングにずれが生じた場合には、δＹ（ｍｍ）＝Ｖ・δｔ２だけ光源１１ｂに対応する光束の書出し位置が遅れることになる。
【００１８】
従って、本実施例においては、ずれ量δＹを補正するために、スリット１８ａが同期検知光が走査する平面と直交する面に対して所定角度傾けて配置されている。具体的には、副走査の解像度が６００ＤＰＩの場合には、スリット１８ａ上での２本の走査線の副走査方向の離間距離は０．０４２３３ｍｍであるから、スリット１８ａは図４に示す方向にθ＝ｔａｎ^−１（δＹ／０．０４２３３）度だけ傾ければよい。
【００１９】
図５は第２の実施例のセンサ１８ｃの出力グラフ図を示し、第１の実施例において光束Ａ、Ｂのけられ量に差がある場合には、光量に差が発生するだけでなく、スリット１８ａ上での主走査方向のスポット形状にも差が生ずる。具体的には、光束Ｂの光束幅よりも光束Ａの光束幅の方が狭くなるために、射出時の光束ＡのＦナンバが光束Ｂに比べて暗くなり、スリット１８ａ上でのスポット形状は、光束Ａの主走査方向のスポット径が光束Ｂのスポット径に比べて大きくなる。
【００２０】
このように、主走査方向のスポット径が大きくなると、スリット１８ａを通過する時間が長くなるために、光量及び主走査方向スポット径に差がある２つのスポット光束がスリット１８ａ上を走査するときに、センサ１８ｃの出力が図５に示すようにδｔ３だけずれる。その結果、δＹ（ｍｍ）＝Ｖ・δｔ３だけ光源１１ｂに対応する光束Ｂの書出し位置にずれが生ずることになる。
【００２１】
このために、本実施例においても、光源１１ａ、１１ｂに対応する光束Ａ、Ｂのスリット１８ａ上でのスポット形状及び光量の差により生ずる書出し位置ずれδＹを補正するために、同期検知光が走査する平面と直交する面に対して、スリット１８ａが所定角度傾けて配置されている。
【００２２】
図６は第３の実施例の発光光量制御のタイミングの説明図を示す。レーザービームプリンタやデジタル複写機等に使用される光走査装置においては、通常では印字品質を高品位にするために、光源１１ａ、１１ｂの発光光量を制御している。例えばレーザー光源には、通常自己の発光光量をモニタするために、パッケージ内部にフォトダイオードが設けられており、このフォトダイオードからの出力電流つまりモニタ電流の値をモニタすることによって、所定の発光光量になるようにレーザー駆動電流を調節して発光光量を制御することが可能である。
【００２３】
この発光光量の制御は、画像範囲内において実時間で行うことが理想ではあるが、マルチビームレーザー光を使用した光走査装置においては、複数の光源１１ａ、１１ｂが同時に発光する場合があるので、実時間で発光光量を制御することは不可能である。従って、１走査毎に同期検知の直前にそれぞれの光源１１ａ、１１ｂを時間的に独立に発光し、そのときのモニタ電流からレーザー駆動電流を決定している。
【００２４】
図６（ａ）は光源１１ａ、１１ｂそれぞれに対応するスポット光Ａ、Ｂが、共にスリット１８ａまで到達していないときの位置関係を表している。このときには、先ず光源１１ａだけを発光して、モニタ電流から光源１１ａの駆動電流を決定する。また、図６（ｂ）は光源１１ａに対応するスポット光Ａだけがスリット１８ａを通過して、光源１１ｂに対応するスポット光Ｂはスリット１８ａの手前にある状態を表している。このときには、スポット光Ａはスリット１８ａを通過しているので、光源１１ａに対しては同期検知は完了している。従って、同期検知完了直後に光源１１ａを消灯し、直ちに光源１１ｂを発光する。その後に、光源１１ｂもスリット１８ａを通過した図６（ｃ）に示すような状態になったときに、光源１１ｂに対しての同期検知を完了する。
【００２５】
モニタ電流の立ち上がりを、受光光量の立ち上がりと完全に一致させることは不可能であり、モニタ電流の立ち上がりの方が受光光量の立ち上がりよりも遅れる場合が普通である。その場合には、レーザー駆動電流はモニタ電流を基にフィードバックをかけているので、モニタ電流の立ち上がり特性が悪いと発光光量が低いと見做して、図７に示すように光量のオーバシュートが発生する。
【００２６】
ここで、図６（ｂ）に示した状態から光源１１ｂのスポット光Ｂがスリット１８ａを通過する時間が短い場合には、光源１１ｂの光量がオーバシュートしている状態で同期検知を行ってしまうことがある。その場合には、光源１１ａと１１ｂの間に光量差のある状態でセンサ１８ｃの出力による同期検知を行うことになり、図８に示すように書出位置のずれδｔ４が発生し、その結果δＹ（ｍｍ）＝Ｖ・δｔ４だけ光源１１ｂに対応する光束Ｂの書出し位置が遅れることになる。
【００２７】
本実施例においては、このような光源自身の立ち上がり特性によって生ずるずれδｔ４に起因する書出し位置ずれを補正するために、同期検知光が走査する平面と直交する面に対して、スリット１８ａが所定角度傾けて配置されている。
【００２８】
図９は第４の実施例を示し、（ａ）に示すようにマルチビームレーザー光源１１ａ、１１ｂから出射された光束が、コリメータレンズ１２によって略平行光或いは収束光に変換される場合に、（ｂ）、（ｃ）に示すようにそれぞれの光束の主走査方向の内部光強度分布に違いが生ずる。このように、光束内部の光強度分布に違いのある光束がスポット状に結像する場合には、図１０に示すように光源１１ａのスポット光Ａと光源１１ｂのスポット光Ｂとで、そのスポット断面の主走査方向の強度分布に違いが発生する。
【００２９】
このように強度分布が異なるスポット光Ａ、Ｂがスリット１８ａを横切ると、図１１に示すように光源１１ａに対応する同期検知信号と光源１１ｂに対応する同期検知信号との出力のタイミングに、δｔ５だけのずれが発生する。その結果、δＹ（ｍｍ）＝Ｖ・δｔ５だけ光源１１ｂに対応する光束Ａの書出し位置がずれる。
【００３０】
本実施例においては、このようなそれぞれの光束の主走査方向の内部光強度分布の相違によって生ずるδｔ５に起因する書出し位置ずれを補正するために、同期検知光が走査する平面と直交する面に対して、所定角度傾けてスリット１８ａが配置されている。
【００３１】
以上の第１〜第４の実施例においては、書出し位置にずれが生ずる要因がそれぞれ単独に存在するとは限らないので、その場合にはその主たる要因の複数の組み合わせを考慮して所定角度を決定すればよい。更に、全ての要因を考慮して所定角度を決定すれば、より一層書出し位置ずれを正確に補正することが可能となる。
【００３２】
図１２は第５の実施例の主走査断面の平面図、図１３は被走査面側から見た同期検知光の副走査断面の側面図を示す。同期検知光のみを反射する折返しミラー１９が設けられ、折返しミラー１９の反射方向にスリット１８ａ、レンズ１８ｂ、センサ１８ｃが配置されている。このように、同期検知光を偏向主走査面内では所定角度で折り曲げ、更に副走査方向にも所定角度で反射することによって、光学ハウジングをできるだけ小さくしてスキャナユニットとしての小型化を達成している。
【００３３】
折返しミラー１９により同期検知光を副走査方向に所定角度で折り返す配置の場合には、同期検知光が走査する面は走査光が走査する偏向主走査面に対して傾いてしまうために、同期検知光はスリット１８ａ上を図１４（ａ）に示すように斜めに走査することになる。このように、同期検知光がスリット１８ａ上を斜めに走査すると、ｔａｎ（θｂｄ）だけ光源１１ａの光束Ａの書出しタイミングが進んでしまうために、従来例では図１４（ｂ）に示すようにスリット１８ａをθｂｄだけ傾けて同期検知光の走査する面と垂直になるように設定している。
【００３４】
しかし、このように同期検知光の走査する面と垂直になるようにスリット１８ａを配置しただけでは、光量の差、スポット形状の差、光源自身の光量の立ち上がり特性、光束の内部光強度分布の差等が存在する場合には、書出し位置にずれが発生する。例えば光量の差がある場合には、δＹ（ｍｍ）＝Ｖ・δｔ２だけ光源１１ｂに対応する光束Ｂの書出し位置が遅れることになる。
【００３５】
このために、本実施例では図１４（ｃ）に示すように、同期検知ミラー１９に同期検知光を副走査方向に所定角度で反射させた場合の、スリット１８ａ上における光束の走査する角度θｂｄと、例えば６００ＤＰＩの場合のずれ量δＹを補正する角度θ＝ｔａｎ^−１（δＹ／０．０４２３３）とを合計した量だけ、スリット１８ａを傾けて配置することによって、より正確に書出し位置のずれを補正している。
【００３６】
このとき、書出し位置ずれが生ずる要因は光源１ａ、１ｂにそれぞれに単独に存在するとは限らないために、その場合には折返しミラー１９によって同期検知光を副走査方向に所定角度で反射させた場合の、スリット１８ａ上における光束の走査する角度θｂｄと、その主たる要因の複数の組み合わせとを考慮して所定角度を決定する。更に、全ての要因を考慮して所定角度を決定すれば、より一層正確に書出し位置ずれを補正することができる。
【００３７】
図１５は第６の実施例を示し、第１〜第５の実施例では、書出し位置ずれを補正するためにスリット１８ａを傾けて配置したが、スリット１８ａの角度は垂直のままで、その位置をずらすことによって書出し位置ずれを補正することもできる。図１５（ａ）は矢印Ｃ方向に走査されている光束Ａ、Ｂがスリット１８ａに到達する様子を示している。光束Ａがスリット１８ａの端面に到達してからδＴ後に、光束Ｂがスリット１８ａの端面に到達する。
【００３８】
この状態で書出し位置ずれを発生させる誤差要因が全くなければ、スリット１８ａの位置はこのままでよいが、実際には各光束Ａ、Ｂにおいて、その光量、スリット１８ａ上でのスポット形状、各光束に対応する光源の光量立ち上がり特性、光束内部の光強度分布などが完全に同じではないために、書出し位置にずれが発生する。例えば、光量差があるとδＹ（ｍｍ）＝Ｖ・δｔ２だけ光源１１ｂに対応する光束Ｂの書出し位置が遅れることになる。
【００３９】
従って、本実施例においては、図１５（ｂ）に示すようにずれδＹを補正するために、スリット１８ａをＬ＝２・ｔａｎ（δＹ／２）だけ集光点の後方に配置している。このように配置することによって、同期検知光Ａは規定の時間よりも遅くスリット１８ａの端面に到達し、一方で同期検知光Ｂは規定の時間よりも早くスリット１８ａの端面に到達する。この結果、光源１１ｂに対応する光束Ｂの書出し位置を光束Ａと同じ位置まで進めることができる。
【００４０】
このとき、書出し位置にずれが生ずる要因が光源１ａ、１ｂそれぞれに単独に存在するとは限らないので、その主たる要因の複数の組み合わせを考慮して所定のずらし量Ｌを決定する。更に、全部の要因を考慮して所定角度を決定すれば、より一層正確に書出し位置ずれを補正することができる。
【００４１】
また、第５の実施例で述べたように、折返しミラー１９によって同期検知光を副走査方向に所定角度で反射させた場合の、スリット１８ａ上における光束の走査する角度θｂｄによって、発生する書出し位置ずれを補正するようにずらし量Ｌを決定してもよい。更に、光量の差、スポット形状の差、光源自身の光量の立ち上がり特性、光束の内部光強度分布の差等の影響を考慮してずらし量Ｌを決定すれば、より効果的である。
【００４２】
以上の実施例において、スリット１８ａの傾き角度・ずらし量Ｌを予め決定しておいてもよいが、光量の差、スポット形状の差、光源自身の光量の立ち上がり特性、光束の内部光強度分布の差等の誤差要因にばらつきがある場合には、傾き角度・ずらし量を調整可能とする構成としてもよい。
【００４３】
【発明の効果】
以上説明したように本発明に係るマルチビーム光走査装置は、各同期検知光が通過するスリット部材を、検知手段への入射光束の走査平面と直交する面に対して所定角度傾けて配置することにより、スリット部材を横切る光束の光量の立ち上がりから走査開始タイミングの検知を正確に行って、高速かつ高画質の画像を形成する。
【００４４】
また、本発明に係るマルチビーム光走査装置は、各同期検知光が通過するスリット部材を、検知手段への入射光束の集光点から所定距離ずらした位置に配置することによって、スリット部材を横切る光束の光量の立ち上がりから走査開始タイミングの検知を正確に行って、高速かつ高画質の画像を形成する。
【図面の簡単な説明】
【図１】第１の実施例のマルチビーム光走査装置の平面図である。
【図２】同期検知信号と画像信号のグラフ図である。
【図３】光量差による同期検知信号のずれの説明図である。
【図４】ずれ補正のためのスリットの傾け方の説明図である。
【図５】第２の実施例の同期検知信号のずれのグラフ図である。
【図６】第３の実施例の同期検知における発光光量制御の説明図である。
【図７】光量のオーバシュートのグラフ図である。
【図８】光源の立ち上がり特性による同期検知信号のずれのグラフ図である。
【図９】第４の実施例の複数光束の内部光強度分布の説明図である。
【図１０】光強度分布に差がある場合のスポット光の強度分布のグラフ図である。
【図１１】光強度分布に差がある場合の同期検知信号のずれのグラフ図である。
【図１２】第５の実施例のマルチビーム光走査光学装置の平面図である。
【図１３】側面図である。
【図１４】光量差がある場合のスリットの傾け方の説明図である。
【図１５】第６の実施例のずれ補正のためのスリットのずらし方の説明図である。
【図１６】従来例のマルチビーム光走査装置の平面図である。
【図１７】複数光源の配置の説明図である。
【図１８】画像書込みタイミングの平面図である。
【図１９】スリットの配置の説明図である。
【符号の説明】
１１半導体レーザー光源
１３シリンドリカルレンズ
１４絞り
１５ポリゴンミラー
１６ｆθレンズ
１７被走査面
１８位置検知手段
１８ａスリット
１８ｃセンサ
１９折返しミラー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-beam optical scanning device used for a laser beam printer, a digital copier, and the like.
[0002]
[Prior art]
FIG. 16 is a plan view of a conventional multi-beam optical scanning device. Light beams A and B emitted from the semiconductor laser light sources 1a and 1b having a plurality of light-emitting points are converted into substantially parallel light or convergent light by a collimator lens 2, respectively, and the light beams are shaped by an aperture stop 3 and are subordinate by a cylindrical lens 4. It converges only in the scanning direction, and forms an image in the form of a focal line elongated in the main scanning direction in the vicinity of the deflecting reflection surface 5a of the polygon mirror 5, which is an optical deflector. Light beams reflected and deflected by the polygon mirror 5 rotating at a constant angular velocity in the direction of the arrow R are condensed in a spot shape on the surface to be scanned 7 made of a photosensitive drum or the like by the fθ lens 6, and are directed in the direction of the arrow D. At a constant speed. At this time, a part of the scanning light is detected by the writing position detecting means including the slit 8a for synchronization detection, the lens 8b, and the sensor 8c to detect the writing position.
[0003]
In such a multi-beam optical scanning device, when a plurality of light sources 1a and 1b are arranged vertically in the sub-scanning direction as shown in FIG. Are significantly larger than the recording density. For this purpose, a plurality of light sources 1a and 1b are usually arranged obliquely as shown in FIG. 17 (b), and the inclination angle α is adjusted so that the distance between the respective lines in the sub-scanning direction on the surface 7 to be scanned. Is precisely adjusted according to the recording density.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional multi-beam optical scanning device, by arranging the plurality of light sources 1a and 1b obliquely, the light beams emitted from these light sources 1a and 1b are reflected by the polygon mirror 5 as shown in FIG. On the reflection surface 5a, the light beams reaching the positions separated in the main scanning direction and the angles of the light beams reflected from the polygon mirror 5 are also different from each other. The spot light forms an image at a position separated in the main scanning direction.
[0005]
For this purpose, the image data is shifted by a predetermined time δT so that the image forming position of the light beam from the other light source 1b is adjusted to the position where one of the light sources 1a as the reference forms an image on the surface 7 to be scanned. Has been sent. The reflection surface 5a of the polygon mirror 5 at the time when the predetermined time δT is shifted is rotated by the angle β, and the light beam B reflected at this time is reflected in the light beam B ' The light imaging positions coincide.
[0006]
The writing start point of each beam on the scanned surface 7 is determined as follows. That is, the timing at which the scanning light beam arrives at the sensor 8c of the writing position detection means 8 provided upstream in the scanning direction of the surface to be scanned 7 is used as synchronization detection, and this synchronization detection is performed independently for each beam. The writing is started after a predetermined delay time from the result. Here, in order to more accurately detect the timing when the scanning light beam reaches the sensor 8c, the slit 8a is disposed at the focal point of the scanning light beam on the front surface of the sensor 8c. The synchronous detection is performed by detecting the rise of the amount of light when passing through.
[0007]
If the slits 8a are arranged obliquely with respect to the surface formed by scanning the light beams from the plurality of light sources 1a and 1b, the image forming position of each light beam is shifted in the main scanning direction. For this purpose, as shown in FIG. 19, the slit 8a is normally arranged perpendicularly to a surface formed by scanning with a scanning light beam. However, even if the slit 8a is arranged perpendicular to the scanning surface of the scanning light beam, the difference in the light amount of each light beam, the difference in the spot shape of each light beam, the rising characteristic of each light source light beam, the inside of each light beam, Due to factors such as differences in light intensity distribution, a shift occurs in the timing of synchronization detection of each light beam, and as a result, a shift occurs in an imaging position of a plurality of light beams, resulting in a decrease in printing accuracy and image quality. Exists.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-speed and high-quality multi-beam optical scanning device which solves the above-described problems and optimally sets an angle and a position at which a slit member of a detection unit for detecting a scanning start timing is arranged. Is to do.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a multi-beam optical scanning device according to the present invention includes a light source that emits a plurality of light beams, a deflector, and an imaging device that condenses a light beam deflected and scanned by the deflector on a surface to be scanned. In a multi-beam optical scanning device including an optical system and a detection unit that detects a scanning start timing for the plurality of scanned light beams, a light beam incident on the detection unit is incident on a light beam incident side of the detection unit. A slit member is arranged at an angle determined by any of the following means (1) to (5) with respect to a plane orthogonal to the plane to be scanned, and a rising of the light amount of the light beam crossing the slit member is detected. Thus, the scanning start timing is detected.
(1) The angle is determined based on a difference between the light amounts of the plurality of light beams.
(2) The angle is determined based on a difference between spot shapes of the plurality of light beams on the slit member.
(3) The angle is determined based on the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The angle is determined based on a difference between internal light intensity distributions of the plurality of light beams.
(5) The angle is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution.
Further, the multi-beam optical scanning device according to the present invention includes a light source that emits a plurality of light beams, a deflector, and an imaging optical system that condenses a light beam deflected and scanned by the deflector on a surface to be scanned. In a multi-beam optical scanning device including a detection unit that detects a scanning start timing for a plurality of scanned light beams, and a reflection unit that reflects the plurality of light beams at least in a sub-scanning direction and guides the plurality of light beams to the detection unit, On the light beam incident side of the detecting means, a slit is formed by inclining by an angle determined by any of the following means (1) to (5) with respect to a plane orthogonal to a plane scanned by the light beam incident on the detecting means. The scanning start timing is detected by arranging a member and detecting the rising of the light amount of the light beam crossing the slit member.
(1) The angle is determined based on a reflection angle of the reflection unit and a difference between light amounts of the plurality of light fluxes.
(2) The angle is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member.
(3) The angle is determined based on the reflection angles of the reflection means and the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The angle is determined based on a reflection angle of the reflection means and a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The angle is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution and the reflection angle of the reflection means.
[0010]
Further, the multi-beam optical scanning device according to the present invention includes a light source that emits a plurality of light beams, a deflector, and an imaging optical system that condenses a light beam deflected and scanned by the deflector on a surface to be scanned. In a multi-beam optical scanning device comprising: a detection unit that detects a scanning start timing for a plurality of scanned light beams, a light beam incident side of the detection device, from a condensing point of a light beam incident on the detection device, The scanning start timing is obtained by disposing a slit member at a position shifted by a distance determined by any of the following means (1) to (5), and detecting a rise in the amount of light flux crossing the slit member. Is detected.
(1) The distance is determined based on a difference between the light amounts of the plurality of light beams.
(2) The distance is determined based on a difference between spot shapes of the plurality of light beams on the slit member.
(3) The distance is determined based on the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The distance is determined based on a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The distance is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and a difference between the plurality of light beams. The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution.
A multi-beam optical scanning device according to the present invention includes a light source that emits a plurality of light beams, a deflector, an imaging optical system that focuses a light beam deflected and scanned by the deflector on a surface to be scanned, A multi-beam optical scanning device comprising: a detecting unit that detects a scanning start timing for the plurality of light beams; and a reflecting unit that reflects the plurality of light beams at least in the sub-scanning direction and guides the plurality of light beams to the detecting device. A slit member is arranged on the light beam incident side of the means at a position shifted from the focal point of the light beam incident on the detection means by a distance determined by any of the following (1) to (5), The scanning start timing is detected by detecting the rising of the light amount of the light beam crossing the slit member.
(1) The distance is determined based on a reflection angle of the reflection means and a difference between light amounts of the plurality of light fluxes.
(2) The distance is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member.
(3) The distance is determined based on the reflection angles of the reflection means and the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The distance is determined based on a reflection angle of the reflection means and a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The distance is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and a difference between the plurality of light beams. The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution and the reflection angle of the reflection means.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 1 is a plan view of a multi-beam optical scanning device according to a first embodiment, and a collimator lens as a first optical system is provided on an optical path in front of a semiconductor laser light source 11 including two semiconductor light sources 11a and 11b. 12, a cylindrical lens 13 as a second optical system, an aperture stop 14, and a polygon mirror 15 as an optical deflector rotating at a constant angular velocity in the direction of arrow R are sequentially arranged. In the reflection direction of the polygon mirror 15, an fθ lens 16, which is a third optical system, and a scanned surface 17 such as a photosensitive drum are arranged.
[0012]
In order to determine the writing start point of each beam on the surface 17 to be scanned, a writing position detecting means 18 comprising a slit 18a, a lens 18b, and a sensor 18c is provided upstream of the surface 17 to be scanned in the scanning direction. Has been. Here, the slit 18a is disposed at the focal point of the scanning light beam in front of the sensor 18c in order to more accurately detect the timing at which the scanning light beam reaches the sensor 18c.
[0013]
With such a configuration, the light beam emitted from the semiconductor laser light source 11 is converted into substantially parallel light or convergent light by the collimator lens 12, converged only in the sub-scanning direction by the cylindrical lens 13, and passes through the aperture stop 14 so that the light beam width is reduced. As a result, an image is formed on the deflecting / reflecting surface 15a of the polygon mirror 15 in a focal line shape extending in the main scanning direction. The light beam reflected and deflected by the polygon mirror 15 is condensed in the form of a spot on the surface 17 to be scanned of the photosensitive drum by the fθ lens 16 and scanned at a constant speed in the direction of arrow D.
[0014]
At this time, the timing at which the scanning light beam reaches the sensor 18c of the writing position detection means 18 is defined as synchronization detection, and the synchronization detection is performed independently for each beam, and writing is started after a predetermined delay time from the synchronization detection. That is, as shown in FIG. 2, when the output of the sensor 18c when the scanning light beam passes through the slit 18a becomes higher than a certain slice level S, a synchronization detection signal is output. An image signal is sent after t1. By performing this operation for each light beam, the writing position of each light beam can be matched.
[0015]
In the case of the conventional example, the slit 18a is arranged perpendicularly to the surface on which the light beam scans, but the light amount of each light beam, the spot shape on the slit 18a, the light amount of the light source corresponding to each light beam and the rising characteristics Since the light intensity distribution inside the light beam is not completely the same, there is a relative difference due to these factors, and an error occurs in the writing position of each light beam. For example, when the spot diameter is reduced or the printing area is enlarged for the purpose of improving the printing quality, the deflection reflecting surface 15a of the polygon mirror 15 has no margin. Need to be intentionally removed and used.
[0016]
In this case, the light beams emitted from the respective light sources 11a and 11b are displaced in the main scanning direction on the deflecting / reflecting surface 15a of the polygon mirror 15, so that the amount of light beam displacement is not the same. As a result, a difference occurs in the amount of light. For example, in FIG. 1, the amount of the light beam A corresponding to the light source 11a is larger than the amount of the light beam B corresponding to the light source 11b, and the light amount of the former synchronization detection light is smaller.
[0017]
As described above, when there is a light amount difference between the respective synchronization detection lights A and B corresponding to the light sources 11a and 11b, the output of the synchronization detection signal corresponding to the light source 11a and the The timing of the output of the synchronization detection signal is shifted by δt2, and as a result, the writing positions of the two are shifted by an amount corresponding to δt2. That is, assuming that the scanning speed of each light beam in the main scanning direction on the slit 18a is Vmm / sec, if there is a shift in the output timing of the synchronization detection signal by δt2 seconds, δY (mm) = V · δt2 The writing position of the light beam corresponding to the light source 11b is delayed.
[0018]
Therefore, in this embodiment, in order to correct the shift amount δY, the slit 18a is arranged at a predetermined angle with respect to a plane perpendicular to the plane scanned by the synchronization detection light. Specifically, when the sub-scanning resolution is 600 DPI, the distance between the two scanning lines on the slit 18a in the sub-scanning direction is 0.04233 mm, so that the slit 18a moves in the direction shown in FIG. θ = tan ^-1 What is necessary is just to incline by (δY / 0.04233) degrees.
[0019]
FIG. 5 is a graph showing the output of the sensor 18c according to the second embodiment. In the first embodiment, when there is a difference between the amounts of light beams A and B, not only a difference occurs in the light amount but also a difference. A difference also occurs in the spot shape in the main scanning direction on the slit 18a. Specifically, since the light beam width of the light beam A is smaller than the light beam width of the light beam B, the F number of the light beam A at the time of emission becomes darker than the light beam B, and the spot shape on the slit 18a is The spot diameter of the light beam A in the main scanning direction becomes larger than the spot diameter of the light beam B.
[0020]
As described above, when the spot diameter in the main scanning direction increases, the time required to pass through the slit 18a increases, so that two spot light beams having a difference in the light amount and the spot diameter in the main scanning direction scan the slit 18a. , The output of the sensor 18c is shifted by δt3 as shown in FIG. As a result, the writing position of the light beam B corresponding to the light source 11b is shifted by δY (mm) = V · δt3.
[0021]
For this reason, in this embodiment as well, the synchronization detection light is scanned by the synchronization detection light in order to correct the writing position deviation δY caused by the difference between the spot shape and the light amount of the light beams A and B corresponding to the light sources 11a and 11b on the slit 18a. The slit 18a is arranged to be inclined at a predetermined angle with respect to a plane orthogonal to the plane to be formed.
[0022]
FIG. 6 is an explanatory diagram of the light emission light amount control timing of the third embodiment. In an optical scanning device used for a laser beam printer, a digital copying machine, or the like, the amount of light emitted from the light sources 11a and 11b is usually controlled in order to improve the printing quality. For example, a laser light source is usually provided with a photodiode inside the package in order to monitor its own light emission amount, and by monitoring the output current from this photodiode, that is, the value of the monitor current, a predetermined light emission amount is obtained. It is possible to control the amount of emitted light by adjusting the laser drive current so that
[0023]
Ideally, the control of the amount of emitted light is performed in real time within the image range. However, in an optical scanning device using multi-beam laser light, a plurality of light sources 11a and 11b may emit light at the same time. It is impossible to control the amount of emitted light in real time. Therefore, the light sources 11a and 11b emit light independently in time immediately before the synchronization detection for each scan, and the laser drive current is determined from the monitor current at that time.
[0024]
FIG. 6A shows a positional relationship when the spot lights A and B corresponding to the light sources 11a and 11b do not reach the slit 18a. At this time, first, only the light source 11a emits light, and the drive current of the light source 11a is determined from the monitor current. FIG. 6B shows a state where only the spot light A corresponding to the light source 11a passes through the slit 18a, and the spot light B corresponding to the light source 11b is in front of the slit 18a. At this time, since the spot light A has passed through the slit 18a, the synchronization detection has been completed for the light source 11a. Therefore, the light source 11a is turned off immediately after the completion of the synchronization detection, and the light source 11b emits light immediately. Thereafter, when the light source 11b also enters the state shown in FIG. 6C after passing through the slit 18a, the synchronization detection for the light source 11b is completed.
[0025]
It is impossible to completely match the rise of the monitor current with the rise of the amount of received light, and it is common that the rise of the monitor current is later than the rise of the amount of received light. In this case, since the laser drive current is fed back based on the monitor current, if the rising characteristic of the monitor current is poor, it is considered that the amount of emitted light is low, and as shown in FIG. appear.
[0026]
Here, if the time when the spot light B of the light source 11b passes through the slit 18a is short from the state shown in FIG. 6B, the synchronization detection is performed in a state where the light amount of the light source 11b is overshooting. Sometimes. In this case, synchronization detection based on the output of the sensor 18c is performed in a state where there is a light amount difference between the light sources 11a and 11b, and a writing position shift δt4 occurs as shown in FIG. The writing position of the light flux B corresponding to the light source 11b is delayed by (mm) = V · δt4.
[0027]
In this embodiment, in order to correct the writing position shift caused by the shift δt4 caused by the rising characteristic of the light source itself, the slit 18a is set at a predetermined angle with respect to a plane orthogonal to the plane scanned by the synchronization detection light. It is arranged at an angle.
[0028]
FIG. 9 shows a fourth embodiment, in which the light beams emitted from the multi-beam laser light sources 11a and 11b are converted by the collimator lens 12 into substantially parallel light or convergent light as shown in FIG. As shown in (b) and (c), a difference occurs in the internal light intensity distribution of each light beam in the main scanning direction. As described above, when a light beam having a difference in light intensity distribution inside the light beam forms an image in the form of a spot, the spot light A of the light source 11a and the spot light B of the light source 11b form the spot as shown in FIG. A difference occurs in the intensity distribution of the cross section in the main scanning direction.
[0029]
When the spot lights A and B having different intensity distributions traverse the slit 18a, the output timing of the synchronization detection signal corresponding to the light source 11a and the synchronization detection signal corresponding to the light source 11b becomes δt5 as shown in FIG. Only shift occurs. As a result, the writing position of the light flux A corresponding to the light source 11b is shifted by δY (mm) = V · δt5.
[0030]
In the present embodiment, in order to correct the writing position deviation caused by δt5 caused by the difference in the internal light intensity distribution of the respective light beams in the main scanning direction, a plane perpendicular to the plane scanned by the synchronization detection light is used. On the other hand, the slit 18a is arranged at a predetermined angle.
[0031]
In the above-described first to fourth embodiments, factors that cause a shift in the writing start position do not always exist independently. In that case, the predetermined angle is determined in consideration of a plurality of combinations of the main factors. do it. Further, if the predetermined angle is determined in consideration of all the factors, it becomes possible to correct the writing start position deviation more accurately.
[0032]
FIG. 12 is a plan view of a main scanning section of the fifth embodiment, and FIG. 13 is a side view of a sub-scanning section of the synchronization detection light viewed from the surface to be scanned. A folding mirror 19 that reflects only the synchronization detection light is provided, and a slit 18a, a lens 18b, and a sensor 18c are arranged in the reflection direction of the folding mirror 19. As described above, the synchronization detection light is bent at a predetermined angle in the deflection main scanning plane, and further reflected at a predetermined angle in the sub-scanning direction, so that the optical housing is made as small as possible and the scanner unit is downsized. I have.
[0033]
In a case where the synchronization detection light is folded back at a predetermined angle in the sub-scanning direction by the folding mirror 19, the surface scanned by the synchronization detection light is inclined with respect to the deflection main scanning surface scanned by the scanning light. The light scans obliquely on the slit 18a as shown in FIG. As described above, when the synchronization detection light scans obliquely on the slit 18a, the writing timing of the light flux A of the light source 11a advances by tan (θbd). Therefore, in the conventional example, as shown in FIG. 18a is tilted by θbd so as to be perpendicular to the surface on which the synchronization detection light scans.
[0034]
However, by merely arranging the slit 18a so as to be perpendicular to the surface on which the synchronization detection light scans, the difference in light amount, the difference in spot shape, the rising characteristic of the light amount of the light source itself, and the distribution of the internal light intensity distribution of the light beam. If there is a difference or the like, a shift occurs in the writing start position. For example, when there is a difference in light amount, the writing position of the light flux B corresponding to the light source 11b is delayed by δY (mm) = V · δt2.
[0035]
Therefore, in the present embodiment, as shown in FIG. 14C, the angle θbd at which the light beam scans on the slit 18a when the synchronization detection light is reflected by the synchronization detection mirror 19 at a predetermined angle in the sub-scanning direction. And the angle θ = tan for correcting the shift amount δY in the case of 600 DPI, for example. ^-1 (ΔY / 0.04233) and by disposing the slit 18a at an angle so as to correct the deviation of the writing position more accurately.
[0036]
At this time, the cause of the writing start position deviation is not always present in each of the light sources 1a and 1b, and in that case, the synchronization detection light is reflected by the folding mirror 19 at a predetermined angle in the sub-scanning direction. The predetermined angle is determined in consideration of the scanning angle θbd of the light beam on the slit 18a and a plurality of combinations of the main factors. Furthermore, if the predetermined angle is determined in consideration of all the factors, the writing position deviation can be more accurately corrected.
[0037]
FIG. 15 shows the sixth embodiment. In the first to fifth embodiments, the slit 18a is arranged to be inclined in order to correct the writing start position deviation. , The writing position shift can be corrected. FIG. 15A shows how the light beams A and B scanned in the direction of arrow C reach the slit 18a. The light beam B reaches the end surface of the slit 18a δT after the light beam A reaches the end surface of the slit 18a.
[0038]
In this state, if there is no error factor that causes a writing position shift, the position of the slit 18a may be left as it is. Since the light intensity rising characteristics of the corresponding light sources, the light intensity distribution inside the light beam, and the like are not completely the same, a shift occurs in the writing start position. For example, if there is a light amount difference, the writing position of the light flux B corresponding to the light source 11b is delayed by δY (mm) = V · δt2.
[0039]
Therefore, in this embodiment, as shown in FIG. 15B, in order to correct the shift δY, the slit 18a is disposed behind the converging point by L = 2 · tan (δY / 2). With such an arrangement, the synchronization detection light A reaches the end face of the slit 18a later than the prescribed time, while the synchronization detection light B reaches the end face of the slit 18a earlier than the prescribed time. As a result, the writing position of the light beam B corresponding to the light source 11b can be advanced to the same position as the light beam A.
[0040]
At this time, the cause of the shift in the writing position does not always exist solely in each of the light sources 1a and 1b. Therefore, the predetermined shift amount L is determined in consideration of a plurality of combinations of the main factors. Furthermore, if the predetermined angle is determined in consideration of all the factors, the writing start position deviation can be more accurately corrected.
[0041]
Further, as described in the fifth embodiment, when the synchronization detection light is reflected at a predetermined angle in the sub-scanning direction by the folding mirror 19, the writing position generated by the scanning angle θbd of the light beam on the slit 18a is generated. The shift amount L may be determined so as to correct the shift. Further, it is more effective to determine the shift amount L in consideration of the influence of the difference in the light amount, the difference in the spot shape, the rising characteristic of the light amount of the light source itself, the difference in the internal light intensity distribution of the light beam, and the like.
[0042]
In the above embodiment, the inclination angle / shift amount L of the slit 18a may be determined in advance, but the difference in the light amount, the difference in the spot shape, the rising characteristic of the light amount of the light source itself, and the distribution of the internal light intensity distribution of the light beam. If there is a variation in error factors such as a difference, the configuration may be such that the tilt angle and the shift amount can be adjusted.
[0043]
【The invention's effect】
As described above, in the multi-beam optical scanning device according to the present invention, the slit member through which each synchronization detection light passes is disposed at a predetermined angle with respect to a plane orthogonal to the scanning plane of the light beam incident on the detection unit. Thus, the scanning start timing is accurately detected from the rising of the light amount of the light beam crossing the slit member, and a high-speed and high-quality image is formed.
[0044]
Further, in the multi-beam optical scanning device according to the present invention, the slit member through which each synchronization detection light passes is arranged at a position shifted by a predetermined distance from the focal point of the light beam incident on the detection means, so that the slit member crosses the slit member. A high-speed and high-quality image is formed by accurately detecting the scanning start timing from the rising of the light amount of the light beam.
[Brief description of the drawings]
FIG. 1 is a plan view of a multi-beam optical scanning device according to a first embodiment.
FIG. 2 is a graph showing a synchronization detection signal and an image signal.
FIG. 3 is an explanatory diagram of a shift of a synchronization detection signal due to a light amount difference.
FIG. 4 is an explanatory diagram of how a slit is tilted for deviation correction.
FIG. 5 is a graph showing a deviation of a synchronization detection signal according to the second embodiment.
FIG. 6 is an explanatory diagram of light emission amount control in synchronization detection according to the third embodiment.
FIG. 7 is a graph showing an overshoot of light quantity.
FIG. 8 is a graph showing a shift of a synchronization detection signal due to a rising characteristic of a light source.
FIG. 9 is an explanatory diagram of an internal light intensity distribution of a plurality of light beams according to the fourth embodiment.
FIG. 10 is a graph of a spot light intensity distribution when there is a difference in light intensity distribution.
FIG. 11 is a graph showing a shift of a synchronization detection signal when there is a difference in light intensity distribution.
FIG. 12 is a plan view of a multi-beam optical scanning optical device according to a fifth embodiment.
FIG. 13 is a side view.
FIG. 14 is an explanatory diagram of how to tilt a slit when there is a light amount difference.
FIG. 15 is an explanatory diagram of how to shift a slit for correcting a shift according to the sixth embodiment.
FIG. 16 is a plan view of a conventional multi-beam optical scanning device.
FIG. 17 is an explanatory diagram of an arrangement of a plurality of light sources.
FIG. 18 is a plan view of an image writing timing.
FIG. 19 is an explanatory diagram of an arrangement of slits.
[Explanation of symbols]
11 Semiconductor laser light source
13 Cylindrical lens
14 Aperture
15 Polygon mirror
16 fθ lens
17 Scanned surface
18 Position detection means
18a slit
18c sensor
19 Folded mirror

Claims

A light source that emits a plurality of light beams, a deflector, an imaging optical system that focuses the light beam deflected and scanned by the deflector on a surface to be scanned, and a scan start timing for the plurality of scanned light beams. in a multi-beam optical scanning device provided with a detecting means for detecting that said on the light incident side of the detection means, with respect to a plane of a light beam incident on said detecting means is orthogonal to the plane to be scanned, the following (1) to (5 The scanning start timing is detected by arranging the slit member at an angle determined by any one of the means and detecting the rising of the light amount of the light beam crossing the slit member. Beam light scanning device.
(1) The angle is determined based on a difference between the light amounts of the plurality of light beams.
(2) The angle is determined based on a difference between spot shapes of the plurality of light beams on the slit member.
(3) The angle is determined based on the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The angle is determined based on a difference between internal light intensity distributions of the plurality of light beams.
(5) The angle is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution.

A light source that emits a plurality of light beams, a deflector, an imaging optical system that focuses the light beam deflected and scanned by the deflector on a surface to be scanned, and a scan start timing for the plurality of scanned light beams. In a multi-beam optical scanning device comprising: a detecting unit for detecting, and a reflecting unit that reflects the plurality of light beams at least in the sub-scanning direction and guides the light to the detecting unit, the light beam incident side of the detecting unit includes the detecting unit. A slit member is arranged at an angle determined by any of the following means (1) to (5) with respect to a plane orthogonal to the plane on which the incident light beam scans, and the light amount of the light beam crossing the slit member A multi-beam optical scanning device, wherein the scanning start timing is detected by detecting a rising edge of the light beam.
(1) The angle is determined based on a reflection angle of the reflection unit and a difference between light amounts of the plurality of light fluxes.
(2) The angle is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member.
(3) The angle is determined based on the reflection angles of the reflection means and the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The angle is determined based on a reflection angle of the reflection means and a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The angle is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution and the reflection angle of the reflection means.

Multi-beam optical scanning device according to claim 1 or 2 angles and allows adjustment of the slit member.

A light source that emits a plurality of light beams, a deflector, an imaging optical system that focuses the light beam deflected and scanned by the deflector on a surface to be scanned, and a scan start timing for the plurality of scanned light beams. In the multi-beam optical scanning device provided with a detecting means for detecting , any one of the following (1) to (5) is provided on a light beam incident side of the detecting means from a focal point of a light beam incident on the detecting means . Multi-beam optical scanning, wherein the scanning start timing is detected by arranging a slit member at a position shifted by a distance determined by the means , and detecting a rise in the amount of light flux crossing the slit member. apparatus.
(1) The distance is determined based on a difference between the light amounts of the plurality of light beams.
(2) The distance is determined based on a difference between spot shapes of the plurality of light beams on the slit member.
(3) The distance is determined based on the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The distance is determined based on a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The distance is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and a difference between the plurality of light beams. The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution.

A light source that emits a plurality of light beams, a deflector, an imaging optical system that focuses the light beam deflected and scanned by the deflector on a surface to be scanned, and a scan start timing for the plurality of scanned light beams. In a multi-beam optical scanning device comprising a detecting means for detecting, and a reflecting means for reflecting the plurality of light beams at least in the sub-scanning direction and guiding the light to the detecting means, the light beam incident side of the detecting means, the detecting means A slit member is arranged at a position shifted by a distance determined by any of the following means (1) to (5) from the converging point of the incident light beam, and the rising of the light amount of the light beam crossing the slit member is measured. A multi-beam optical scanning device, wherein the detection is performed to detect the scanning start timing.
(1) The distance is determined based on a reflection angle of the reflection means and a difference between light amounts of the plurality of light fluxes.
(2) The distance is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member.
(3) The distance is determined based on the reflection angles of the reflection means and the rising characteristics of the light amounts of the plurality of light sources themselves.
(4) The distance is determined based on a reflection angle of the reflection means and a difference between internal light intensity distributions of the plurality of light fluxes.
(5) The distance is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, a rising characteristic of light amounts of the plurality of light sources themselves, and a difference between the plurality of light beams. The determination is made based on a combination of two or more factors among the differences in the internal light intensity distribution and the reflection angle of the reflection means.

The multi-beam optical scanning device according to claim 4, wherein a distance by which the slit member is shifted is adjustable.

Image forming apparatus equipped with the multi-beam optical scanning device according to at least any one of claims 1 to claim 6.