JP2004070109A - Optical scanner and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner capable of reducing a scanning line deflection, and to obtain an image forming apparatus using the optical scanner. <P>SOLUTION: The optical scanner is provided with a light source means 1, a deflection means 5 which deflects a light flux emitted from the light source means, and a scanning optical system 6 which images the deflected light flux deflected by the deflection means on a surface to be scanned 8. The scanning optical system includes a scanning optical element arranged so that the principal ray of the deflected light flux passes through out of an optical axis in the sub-scanning direction. The scanning optical element includes the extent change of the aspherical surface of line in which the extent of the aspherical surface of the line changes along in the main scanning direction of the scanning optical element, and aligns the position in the sub-scanning direction where the deflected light flux arrives over the whole surface to be scanned. <P>COPYRIGHT: (C)2004,JPO

Description

【００３２】
なる条件を満足することを特徴としている。
【００３３】
請求項１２の発明の画像形成装置は、
請求項１乃至１１の何れか１項に記載の光走査装置と、前記被走査面に配置された感光体と、前記光走査装置で走査された光束によって前記感光体上に形成された静電潜像をトナー像として現像する現像器と、前記現像されたトナー像を被転写材に転写する転写器と、転写されたトナー像を被転写材に定着させる定着器とを有することを特徴としている。
【００３４】
請求項１３の発明の画像形成装置は、
請求項１乃至１１の何れか１項に記載の光走査装置と、外部機器から入力したコードデータを画像信号に変換して前記光走査装置に入力せしめるプリンタコントローラとを有することを特徴としている。
【００３５】
請求項１４の発明のカラー画像形成装置は、
請求項１乃至１１の何れか１項に記載の光走査装置を１以上と、夫々異なった色の画像を形成する複数の像担持体とを有することを特徴としている。
【００３６】
請求項１５の発明は請求項１４の発明において、
外部機器から入力した色信号を異なった色の画像データに変換して各々の光走査装置に入力せしめるプリンタコントローラを備えたことを特徴としている。
【００３７】
【発明の実施の形態】
［実施形態１］
図１Ａは本発明の実施形態１における光走査装置の主走査方向の要部断面図（主走査断面図）、図１Ｂは本発明の実施形態１における光走査装置の副走査方向の要部断面図（副走査断面図）である。
【００３８】
ここで、主走査方向とは偏向手段の回転軸及び走査光学素子の光軸に垂直な方向（偏向手段で光束が反射偏向（偏向走査）される方向）を示し、副走査方向とは偏向手段の回転軸と平行な方向を示す。また主走査断面とは主走査方向に平行で走査光学系の光軸を含む平面を示す。また副走査断面とは主走査断面と垂直な断面を示す。
【００３９】
図１Ａ、図１Ｂにおいて１は光源手段である半導体レーザーである。半導体レーザー１からの１以上の発散光をコリメーターレンズ２により平行光束又は略平行光束（収斂又は発散光束であっても良い。）に変換した後、絞り３により所望のスポット径が得られるように光束幅が制限される。４は副走査方向のみに所定の屈折力を有したシリンドリカルレンズであって後述する偏向手段５の偏向面５ａ近傍に主走査断面と平行方向に長手の線像として結像させている。５は例えば４面（４面以上いくつであっても良い。）構成のポリゴンミラー（回転多面鏡）から成る偏向手段であり、モーターの駆動手段（不図示）により図中矢印Ａ方向に一定速度で回転している。
【００４０】
６はｆθ特性を有する１枚の走査光学素子（ｆθレンズ）によって構成される走査光学系であって、偏向手段５によって反射偏向された偏向光束を被走査面としての感光体ドラム面（感光体）８上に結像させ、且つ該偏向手段５の偏向面５ａの面倒れを補正している。以下、走査光学系６を走査光学素子６とも言う。このとき、偏向手段５の偏向面５ａで反射偏向された偏向光束は走査光学系６を介して感光体ドラム面８上に導光され、ポリゴンミラー５を矢印Ａ方向に回転させることによって該感光体ドラム面８上を矢印Ｂ方向に光走査している。これにより感光体ドラム面上に走査線を形成し、画像記録を行っている。
【００４１】
図１Ｂに示した通り、実施形態１では光源手段１から発せられた光束を偏向面５ａに斜め下方から副走査方向に角度γを有して入射させており、走査光学系を構成する１枚の合成樹脂製又はガラス製の走査光学素子６に入射している。走査光学素子６は偏向光束を被走査面８上にスポットとして結像させている。
【００４２】
ここで、実施形態１における各光学部材の光学配置を表１に示す。
【００４３】
【表１】

【００４４】
また実施形態１における走査光学素子６の入射面ならびに出射面の形状を表２に示した。
【００４５】
【表２】

【００４６】
図２は本発明の実施形態１における光走査装置の光学系の光路を展開したときの副走査断面図である。
【００４７】
図１Ｂや図２に示した通り、実施形態１では光源手段１から発せられた光束を斜め下から偏向面５ａへ副走査方向に角度γを有して入射させており、走査光学系６を構成する１枚の合成樹脂製又はガラス製の走査光学素子に入射している。走査光学素子６はアナモフィックな面を含み偏向光束を被走査面８上にスポット又は略スポットとして結像させている。
【００４８】
図６に実施形態１で用いている走査光学素子６の面の概念図を示す。
【００４９】
走査光学素子６の入射面６ａならびに出射面６ｂの母線形状は、１０次までの関数として表せる非球面形状により構成している。例えば図６に示すように走査光学素子６と光軸Ｌａとの交点を原点Ｏ１とし、光軸方向ＬａをＸ軸、主走査断面内（ＸＹ面内）において光軸Ｌａと直交する軸をＹ軸、ＸＹ面内に直交する方向をＺ軸とする。このとき主走査方向（Ｙ方向）と対応する母線方向の母線形状Ｘａが、
【００５０】
【数３】

【００５１】
（但し、Ｒは母線曲率半径，Ｋ，Ｂ４，Ｂ６，Ｂ８，Ｂ１０，Ｂ１２，Ｂ１４，Ｂ１６は非球面係数）なる式で表されるものである。
【００５２】
また副走査方向と対応する子線方向の子線形状Ｓが、
【００５３】
【数４】

【００５４】
なる式で表されるものである。Ｓは母線方向の各々の位置Ｙにおける母線の法線を含み主走査断面（ＸＹ面）と垂直な面内に定義される子線形状である。
【００５５】
ここで主走査方向に光軸Ｌａから距離Ｙだけ離れた位置Ｙにおける副走査方向の曲率半径（子線曲率半径）Ｒｓ＊が、
【００５６】
【数５】

【００５７】
（但し、Ｒｓは光軸Ｌａ上の子線曲率半径，Ｄ２，Ｄ４，Ｄ６，Ｄ８，Ｄ１０は子線変化係数）なる式で表されるものであり、更に子線方向の非球面成分として
【００５８】
【数６】

【００５９】
なる値を（ａ）式に付加した面である。
【００６０】
なお実施形態１では面形状を上記数式にて定義したが、子線方向の非球面成分を表現できる数式であれば良く、上記数式に制限されるものではない。
【００６１】
また実施形態１の走査光学素子６の各面は副走査方向にシフトやチルトを与えておらず、被走査面８の端部へ向う偏向光束がポリゴンミラー５の偏向面５ａで反射偏向される位置５ａ１を走査光学素子６の光軸Ｌａと同じ高さに構成している。
【００６２】
表２に示した通り、走査光学素子６の入射面６ａは母線形状が非球面形状（非円弧形状）であり、子線形状が平面（直線）である主走査方向のみにパワー（屈折力）を有するシリンドリカル面である。走査光学素子６の出射面６ｂは母線形状が円弧であり、子線形状は母線方向に沿って光軸から離れるに従い曲率半径が連続的に変化する子線曲率半径変化面であり、更に光軸上は円弧形状であり光軸以外の場所では非球面形状（非円弧形状）であって母線方向に沿って光軸から離れるに従い非球面量が変化する子線非球面量変化面でもある面で形成されている。
【００６３】
また走査光学素子６の主走査断面内における非球面の非球面形状は曲率変化に変曲点を持たない形状で形成されている。
【００６４】
次に図２に示す実施形態１における光走査装置の副走査方向の概要図について説明する。
【００６５】
実施形態１では光源手段１から発せられた入射光束Ｌｉが主走査断面に対して副走査方向に角度γ＝３（ｄｅｇ）を有して偏向手段５の偏向面５ａに入射している。また偏向面５ａで反射した偏向光束Ｌｄも主走査断面に対して副走査方向に角度γ＝３（ｄｅｇ）を有して走査光学素子６へ入射している。その為、偏向光束Ｌｄの主光線（一点鎖線）が走査光学素子６の入射面６ａならびに出射面６ｂ上に到達する位置は子線光軸（もしくは母線）Ｌａから大きく離れた位置を通過する。レンズ面の通過位置Ｚａ，Ｚｂ、光軸Ｌａからの距離Ｚｌｅｎｓは母線位置（Ｚｌｅｎｓ＝０）よりも上方であり、Ｚｌｅｎｓ＞＞０　となる。
【００６６】
実施形態１では偏向光束Ｌｄが走査光学素子６の入射面６ａに到達する副走査方向の位置Ｚａの距離Ｚｌｅｎｓ＝２．７３ｍｍであり、出射面６ｂに到達する副走査方向の位置Ｚｂの距離Ｚｌｅｎｓ＝３．３４ｍｍである。
【００６７】
走査光学素子６を通過した偏向光束Ｌｄは走査光学素子６の集光作用により被走査面８上にスポットとして結像される。
【００６８】
このように母線（もしくは子線光軸）Ｌａから離れた位置を偏向光束Ｌｄの主光線が通過する場合、走査光学素子６を通過した光束はレンズのパワー（屈折力）により下方へと向きを変えられる。
【００６９】
このとき走査光学素子６の構成を適切に設定しないと、被走査面８上の手前で光軸Ｌａと交差して被走査面８上では主走査断面よりも下方の位置に到達する。ここで偏向光束Ｌｄが被走査面８上に到達する副走査方向の位置のことを照射位置Ｚｏといい、光軸Ｌａからの距離をＺｉｍａｇｅと呼ぶこととする。
【００７０】
このとき走査光学素子６の入射面６ａ及び出射面６ｂに到達する偏向光束Ｌｄの副走査方向の位置ならびに走査光学素子６を通過した偏向光束Ｌｄを下方へと向きを変えるパワー（屈折力）が像高によって異なることにより、照射位置Ｚｏの距離Ｚｉｍａｇｅが同一に揃わず、所謂走査線曲がりの問題点が発生する。
【００７１】
この問題点を解決するために実施形態１における光走査装置では走査光学系を構成する１枚の走査光学素子６の出射面６ｂを前述の式（ｂ）の子線形状Ｓ及び図６の数値で示す子線非球面量変化面としている。ここで子線非球面量変化面とはレンズ面の母線方向に沿ってレンズ面の光軸Ｌａから離れるに従って子線の非球面量ΔＸｚを変化させた面である。
【００７２】
ここで子線非球面量ΔＸｚとは図６に示すように母線上以外（子線光軸上以外）の副走査方向のある位置Ｚｌｅｎｓ（Ｚｌｅｎｓ≠０ｍｍ）において、レンズ面がベースの子線曲率半径Ｒｓ＊から光軸方向に変位する量ΔＸｚのことをいい、子線非球面量ΔＸｚが変化するとは副走査方向の同一位置Ｚｌｅｎｓ（Ｚｌｅｎｓ≠０ｍｍ）における子線非球面量ΔＸｚが母線方向の位置Ｙによって変化することを言う。つまり、ｄΔＸｚ／ｄＹ≠０であることを指す。
【００７３】
図３に実施形態１における走査光学素子６の出射面６ｂの子線非球面量ΔＸｚが変化する様子を示す。また図４にある子線光軸からの距離Ｚにおける子線非球面量ΔＸｚが母線方向（Ｙの値）に沿って変化する様子（図７の位置ＺＲａの子線非球面量ΔＸｚ）を示し、図５にある出射面６ｂの光軸Ｌａから母線方向に沿った距離Ｙにおける子線非球面量ΔＸｚが副走査方向（Ｚ方向）に沿って変化する様子（図８の位置ＹＲａの子線非球面量ΔＸｚ）を示す。
【００７４】
実施形態１では出射面６ｂの光軸Ｌａ上の子線形状を円弧とし、光軸Ｌａから母線方向に離れた場所では子線形状を非円弧（非球面）とし、更に図４に示したように母線方向に沿って出射面６ｂは光軸Ｌａから離れるに従って子線の非球面量ΔＸｚがゼロから徐々に増加し、途中で極値を有して今度は徐々に減少するように変化させた子線非球面量変化面としている。
【００７５】
また図５に示した通り、出射面６ｂ光軸Ｌａ上以外の場所において、子線光軸Ｌａから副走査方向に沿って離れるに従い徐々に増加する様に子線非球面量を付加している。ここで、符号のプラスとはベースの円弧形状から被走査面側に変位することを示している。
【００７６】
母線方向に沿って出射面６ｂ光軸Ｌａから離れるに従って子線非球面パワーがゼロから徐々に減少する様に変化さており、出射面６ｂ光軸Ｌａ上以外の場所において、子線光軸Ｌａから副走査方向に沿って離れるに従い子線非球面パワーが徐々に減少する様に変化させた子線非球面量変化面としている。
【００７７】
また付加した子線非球面パワーはベース円弧形状の約１／１００と微少のパワーであって、子線非球面は副走査方向の像面湾曲に殆ど寄与することなく、走査線曲がり補正のみに効力を有している。
【００７８】
図９に実施形態１における収差図を示した。
【００７９】
主走査方向の像面湾曲は±０．６ｍｍ以内であり、副走査方向の像面湾曲は±０．３ｍｍ以内であって共に良好に補正されている。また歪曲収差（ｆθ特性）は±０．３％以内であり、像高ずれは±０．０８ｍｍ以内であって良好に補正されている。
【００８０】
これによりベース円弧形状が及ぼす集光作用によって副走査方向の像面湾曲を補正することとは別に、子線の非球面効果によって被走査面上の照射位置を制御することが可能となる。その非球面効果によって各像高へ向う偏向光束の照射位置Ｚｏａを中心像高の照射位置Ｚｏに揃えることができる。つまり、副走査方向の像面湾曲と走査線曲がりとを独立に補正可能となる。具体的には副走査方向の位置ずれ量が１０μｍ以下、好ましくは５μｍ以下の揃えている。
【００８１】
図１０には実施形態１と比較例とにおける光走査装置の照射位置及び走査線曲がりを示した。比較例として挙げた光走査装置は実施形態１の非球面効果を除外した走査光学系を用いた。また走査線曲がりとは各像高と中心像高とにおける照射位置のずれを取ったものである。
【００８２】
図１０に示した通り、走査光学系６の光軸上にあたる中心像高の照射位置は実施形態１、比較例共にＺｉｍａｇｅ＝０．１８１９ｍｍであり、子線光軸よりも上方に位置している。各像高においても照射位置は子線光軸より上方に位置している。
【００８３】
比較例では中心像高に対して端部像高の照射位置が下方に変位しており、走査線曲がりが１１μｍ発生している。これに対して、実施形態１では各像高において照射位置を揃えており、走査線曲がりが５．０μｍと十分に小さく補正している。
【００８４】
以上により、母線方向に沿って光軸Ｌａから離れるに従い子線非球面量ΔＸｚを変化させたことにより、各像高における照射位置を揃えて走査線曲がりの問題を飛躍的に改善させることが可能となることが分かる。
【００８５】
また実施形態１の光走査装置において、偏向光束Ｌｄが走査光学素子６の入射面６ａならびに出射面６ｂに到達する副走査方向の位置Ｚａ，Ｚｂより被走査面８上の照射位置Ｚｏを子線光軸Ｌａに近づけたので、走査線曲がりをより良好に補正することができる。
【００８６】
次に実施形態１の走査光学系を構成する１枚の走査光学素子６について説明する。入射面６ａは主走査方向のみにパワーを有するシリンドリカルレンズ面である。出射面６ｂは母線が円弧形状であり、子線が凸形状で母線方向に沿って光軸から離れるに従って徐々に曲率半径の絶対値が大きくなる子線曲率半径変化面である。また走査光学系６の光軸を挟んだ主走査方向の左右で非対称に子線曲率半径が変化している。このように走査光学系６の副走査方向の全パワー（屈折力）を出射面６ｂに集中させている。
【００８７】
具体的には全パワーの９０％以上を集中させている。即ち、走査光学系６の副走査方向のパワーをφｓｏ、子線非球面量変化面の副走査方向のパワーをφｓｉとするとき、
０．９×φｓｏ≦φｓｉ≦１．１×φｓｏ
なる条件を満足するようにしている。
【００８８】
図１１には実施形態１の主走査方向の要部概要図を示す。
【００８９】
図１１に示した様に出射面６ｂの母線形状は、主走査方向において走査光学系６の光軸上における偏向光束が偏向面５ａにより反射される位置から偏向光束が出射面６ｂに到達する位置までの距離Ｐ１と偏向光束が出射面６ｂに到達する位置から被走査面８上に到達する位置までの距離Ｐ２との比　Ｐ２／Ｐ１が、被走査面８上の全ての像高へ向う偏向光束の光路について略一定（Ｐ２／Ｐ１＝Ｃｏｎｓｔ）もしくは一定値より±１０％以内である形状を成した円弧形状としている。例えば、像高の端部Ｉｐへ向う偏向光束Ｌｄの光路を例に取った場合、偏向光束Ｌｄが偏向面５ａにより反射される位置から偏向光束Ｌｄが出射面６ｂに到達する位置までの距離Ｍ１と偏向光束Ｌｄが出射面６ｂに到達する位置から被走査面８上に到達する位置までの距離Ｍ２との比　Ｍ２／Ｍ１が、Ｐ２／Ｐ１と略等しくなる（Ｍ２／Ｍ１≒Ｐ２／Ｐ１　具体的には±１０％以内の範囲内と成ること。）ように母線形状を決定している。
【００９０】
即ち、
【００９１】
【数７】

【００９２】
と成るようにしている。
【００９３】
実施形態１では走査光学系６の副走査方向の全パワー（屈折力）を出射面６ｂに集中させているが、前述した母線形状により副走査方向の像面湾曲を揃えることと副走査方向の横倍率（副走査倍率）βｓを略一定の値に揃えることを両立できる。実施形態の走査光学系６の副走査倍率βｓ＝−２．３１（倍）である。
【００９４】
これにより製造誤差や組立誤差などによって走査光学素子６が副走査方向に変位したり傾いたりした場合等、所謂副走査方向の偏心が生じた場合においても設計上（初期）の走査線曲がりの性能を維持することができる。
【００９５】
つまり実施形態１における光走査装置では、被走査面８上の全像高に渡って走査線曲がりを良好に補正することができると共に、走査光学素子６が副走査方向に偏心した場合においても良好な走査線曲がり性能を維持することができる。
【００９６】
そのため常に走査線曲がりが良好に補正され、常に良好なる画像が得られる光走査装置を提供することができる。
【００９７】
実施形態１では光源手段１から発せられた光束を主走査断面に対して斜入射角γで偏向手段に入射させ、被走査面８の端部へ向う偏向光束がポリゴンミラー５の偏向面５ａで反射偏向される位置を走査光学系６の光軸と同じ高さに構成した例を挙げたが、これに限ったものではなく、例えば全像高へ向う偏向光束が偏向面５ａで反射偏向される位置を走査光学系６の光軸よりも上方に配置しても、本発明の効果を十分に得ることができる。
【００９８】
また実施形態１では１本の光束を光走査する光走査装置を例に挙げたが、これに限ったものではなく、例えば２本、３本、４本…と複数の光束を同時に光走査するマルチビーム型の光走査装置においても同等の効果を得ることができる。
【００９９】
また実施形態１では１枚の走査光学素子により構成した走査光学系を例に挙げたが、これに限ったものではなく、例えば走査光学素子や結像ミラーなどの光学部材を複数枚用いて構成された走査光学系であっても良く、該走査光学素子のうち少なくとも１面を子線非球面量変化面とすることで、走査線曲がりを良好に補正することができる。
【０１００】
尚、実施形態１において走査光学素子の入射面又は／及び出射面に回折部を設けて、前述と同様の非球面作用を有するように構成しても良い。
【０１０１】
［実施形態２］
図１２は本発明の実施形態２における光走査装置の副走査断面の要部概要図である。
【０１０２】
実施形態２と実施形態１との相違点は、走査光学素子６の出射面６ｂの子線非球面量を変更した点である。
【０１０３】
表３に実施形態３における走査光学素子６の入射面６ａならびに出射面６ｂの形状を示した。
【０１０４】
【表３】

【０１０５】
走査光学素子６の出射面６ｂの子線形状は、有効面内全ての位置において非球面（非円弧）形状であり、更に走査光学素子６の母線方向に沿って光軸から離れるに従って子線非球面量が変化する子線非球面量変化面である。
【０１０６】
図１３に実施形態２における走査光学素子６の出射面６ｂの子線非球面量が変化する様子（図７）を示した。また図１４にある子線光軸からの距離（Ｚ）における子線非球面量が母線方向に沿って変化する様子（図８）を示し、図１５に出射面６ｂの光軸から母線方向に沿った距離（　Ｙ　）における子線非球面量が副走査方向に沿って変化する様子を示した。
【０１０７】
実施形態２では出射面６ｂの子線形状を全て非円弧（非球面）とし、更に図１４に示した様に母線方向に沿って出射面６ｂを光軸から離れるに従って子線の非球面量が徐々に減少する様に変化させた子線非球面量変化面としている。また図１５に示した通り、子線光軸から副走査方向に沿って離れるに従い徐々に増加する様に子線非球面量を付加している。
【０１０８】
母線方向に沿って出射面６ｂは光軸から離れるに従って子線非球面パワーが徐々に増加する様に変化さており、子線光軸から副走査方向に沿って離れるに従い子線非球面パワーが徐々に減少する様に変化させた子線非球面量変化面としている。
【０１０９】
図１６には実施形態２と子線非球面効果を除外した比較例における光走査装置の照射位置ならびに走査線曲がりを示した。
【０１１０】
実施形態２の走査光学素子６は出射面６ｂの光軸上における子線形状を非球面（非円弧）形状とし、被走査面８の光軸上（中心像高）へ向う偏向光束が子線光軸上に照射されるように構成している。つまり、被走査面８上の照射位置Ｚｏの距離Ｚｉｍａｇｅ＝０．００ｍｍとしている。
【０１１１】
また被走査面８上の有効走査範囲内の全ての像高において、照射位置Ｚｏが中心像高と同じ子線光軸上となるように走査光学素子６の出射面６ｂの子線非球面量を母線方向に沿って変化させている。
【０１１２】
比較例では走査線曲がりが１１μｍであったのに対して実施形態２では走査線曲りが４．７μｍと非常に小さく補正されていることが分かる。
【０１１３】
よって子線非球面変化面により全像高における照射位置を主走査断面上に揃え、走査線曲がりが非常に小さく抑えられた光走査装置を提供することができる。
【０１１４】
また走査光学素子６の出射面のベース円弧形状の曲率半径の絶対値が光軸から離れるに従って徐々に大きくなることにより、副走査方向の像面湾曲も十分に補正することができる。
【０１１５】
更に実施形態２では偏向手段の偏向面５ａと被走査面８とをほぼ完全な共役関係を結ぶことができるので、偏向面が製造誤差等によって傾いた場合であってもピッチムラを小さく抑えることができる。
【０１１６】
これにより走査線曲がりを良好に補正し、更に副走査方向の像面湾曲ならびにピッチムラを良好に補正した高品位な画像が得られる光走査装置を提供することができる。
【０１１７】
実施形態２では走査光学素子６の出射面６ｂのみを子線非球面量変化面とした子線非球面量変化面が１面だけの光走査装置の例を挙げたが、これに限ったものではなく、走査光学素子６の入射面６ａも子線非球面量変化面として非球面量を両面に分担させた子線非球面量変化面を複数面とした光走査装置であっても同等の効果を得ることができる。
【０１１８】
また実施形態２の走査光学系は出射面の母線形状を円弧としたがこれに限ったものではなく、非円弧（非球面形状）とすれば、主走査方向の各収差をより良好に補正することができ、実施形態２と同等以上の効果を得ることができる。
【０１１９】
更に実施形態２では子線の非球面項の係数をＺ^４　，Ｚ^４Ｙ^２，Ｚ^４Ｙ^４の３つとしたが、これに限ったものではなく、Ｚ^４Ｙ^６，Ｚ^４Ｙ^８，…，と「Ｚ^４」に掛かる「Ｙ」の次数を増加させた多項式や、また、Ｚ^６，Ｚ^６Ｙ^２，Ｚ^６Ｙ^４，Ｚ^６Ｙ^６，Ｚ^６Ｙ^８，…，Ｚ^８，Ｚ^８Ｙ^２，Ｚ^８Ｙ^４，Ｚ^８Ｙ^６，Ｚ^８Ｙ^８，…，と上記に加えて「Ｙ」の各次数項に掛かる「Ｚ」の次数を増加した多項式を子線非球面の表現式に用いることにより、本発明の効果をより向上させることができるようになる。
【０１２０】
［実施形態３］
図１７Ａは本発明の実施形態３における光走査装置の主走査断面図であり、図１７Ｂは副走査断面図である。
【０１２１】
実施形態３は実施形態１又は２における光走査装置を２つ備え（但し、偏向手段は共有している。）、更に夫々の走査光学系６へ２本の光束を入射させて、更に１つの偏向手段５に同時に４本の光束を入射させ、１つの偏向手段５で４つの光束を偏向し、夫々に対応した感光体ドラム８ａ〜８ｄ上を光走査させたカラー画像形成用の光走査装置である。
【０１２２】
図１７中、１は光源手段（マルチビームレーザ）であり、夫々１本の光束を出射する４つの半導体レーザー１ａ，１ｂ，１ｃ，１ｄから成っている。４つの半導体レーザー１ａ，１ｂ，１ｃ，１ｄから発せられた４本の発散光束は夫々に対応したコリメーターレンズ（第１の光学素子）２ａ，２ｂ，２ｃ，２ｄにより略平行光束（収斂光束又は発散光束であっても良い。）に変換され、夫々に対応した開口絞り３ａ，３ｂ，３ｃ，３ｄによって光束幅を制限される。このうち開口絞り３ａ，３ｂを通過した２つの略平行光束は副走査方向のみにパワーを有する第１のシリンドリカルレンズ（第２の光学素子）４ａにより、後述する偏向手段５の偏向面５ａ近傍に主走査断面内に長手の線像として結像される。また開口絞り３ｃ，３ｄを通過した２つの略平行光束は副走査方向のみにパワーを有する第２のシリンドリカルレンズ４ｂにより、後述する偏向手段５の偏向面５ｂ近傍に主走査断面内に長手の線像として結像される。
【０１２３】
５は例えば４面構成のポリゴンミラー（回転多面鏡）から成る偏向手段であり、モーター等の駆動手段（不図示）により図中矢印Ａ方向に一定の角速度で回転している。
【０１２４】
６１はプラスチック成型により作製されたｆθ特性を有する１枚の走査光学素子（ｆθレンズ）によって構成される第１の走査光学系であり、６２はプラスチック成型により作製されたｆθ特性を有する１枚の走査光学素子（走査光学素子）によって構成される第２の走査光学系であって、偏向手段５によって反射偏向された夫々２本の偏向光束ＢＭａ，ＢＭｂ（ＢＭｃ，ＢＭｄ）を被走査面としての感光ドラム面８ａ，８ｂ（８ｃ，８ｄ）上に結像させ、且つ該偏向手段５の偏向面５ａ（５ｂ）の面倒れを補正している。このとき偏向手段５の偏向面５ａ，５ｂで反射偏向された４本の偏向光束ＢＭａ，ＢＭｂ，ＢＭｃ，ＢＭｄは第１の走査光学系６１及び第２の走査光学系６２を介して４本の光束夫々に対応した夫々４つの感光ドラム面（シアン、マゼンタ、イエロー、ブラック）８ａ，８ｂ，８ｃ，８ｄ上に導光され、偏向手段５を矢印Ａ方向に回転させることによって、該感光ドラム面８ａ，８ｂ，８ｃ，８ｄ上を矢印Ｂ方向に光走査している。これにより４つの感光ドラム面８ａ，８ｂ，８ｃ，８ｄ上に夫々１本ずつの走査線を形成し、画像記録を行っている。
【０１２５】
走査光学系６１（６２）では２本の光束ＢＭａ，ＢＭｂ（ＢＭｃ，ＢＭｄ）に対して走査光学素子を共用して使用している。これにより４つの感光体ドラム面８ａ，８ｂ，８ｃ，８ｄ上に夫々１本ずつの走査線を形成し、画像記録を行っている。
【０１２６】
以下簡単の為、走査光学系６１，６２を走査光学系６と、コリメーターレンズ２ａ，２ｂ，２ｃ，２ｄをコリメーターレンズ２と、開口絞り３ａ，３ｂ，３ｃ，３ｄを開口絞り３と、シリンドリカルレンズ４ａ，４ｂをシリンドリカルレンズ４と、被走査面８ａ，８ｂ，８ｃ，８ｄを被走査面８と称する。
【０１２７】
実施形態３ではシアン、マゼンタ、イエロー、ブラックの各色に対応した４つの感光ドラムを有するカラー画像形成装置に適用した場合を示している。カラー画像は上述の４色を重ね合わせて形成されており、各色に対応した走査線の印字位置がずれると色ずれが発生し、画質劣化を招く。そこで、各色に対応した走査線の印字位置を合わせる必要がある。
【０１２８】
実施形態３では図１７Ｂに示すように１つのポリゴンミラー５に対して２つの走査光学系６１，６２を用いて４本の光束を同時に光走査する光走査装置であって、各走査光学素子６１，６２の子線光軸より上方に入射した偏向光束ＢＭａ，ＢＭｃを各走査光学素子６１，６２に近接した位置で第１もしくは第２の折り返しミラー７ａ，７ｄにより下方へ折り返し、更に第３もしくは第４の折り返しミラー７ｃ，７ｆにより感光体ドラム面８ａ，８ｃへ向けて反射させている。また各走査光学素子６１，６２の子線光軸より下方に入射した偏向光束ＢＭｂ，ＢＭｄを各走査光学素子６１，６２から離れた位置で第５もしくは第６の折り返しミラー７ｂ，７ｅによって感光体ドラム面８ｂ，８ｄへ向けて反射させている。
【０１２９】
このように折り返しミラーの配置はポリゴンミラーの回転軸に対して略線対称な配置としており、簡単な構成でコンパクトな光走査装置を提供している。
【０１３０】
一般に実施形態３のようにポリゴンミラー５の回転軸に対して線対称な折り返しミラーの配置とした場合、各感光体ドラム面上に光走査される走査線の曲がりの方向が逆転し、走査線曲がりの大きな光走査装置を用いると色ずれの問題が顕著に表れる虞があった。また折り返しミラーの配置を本実施形態とは逆転させて第２の走査光学素子６２の子線光軸より下方に入射した偏向光束を偶数枚の折り返しミラーを用いて感光ドラム面８上に導光させ、子線光軸より上方に入射した光束を奇数枚の折り返しミラーを用いて感光ドラム面８上に導光させた場合、走査線曲がりの方向を揃えることができるが、光路の取り回しが複雑となり、光走査装置の大型化や折り返しミラーの枚数が増加して構成が複雑になる虞があった。
【０１３１】
そこで実施形態３では第１の走査光学系６１ならびに第２の走査光学系６２の出射面６ｂの子線形状を非円弧（非球面）とし、更に母線方向に沿って出射面６ｂの光軸Ｌａから離れるにしたがって子線非球面量が変化する子線非球面量変化面を採用し、走査線曲がりを非常に小さく抑えている。これにより走査線曲がりの方向が逆転する光路の取り回し方法（もしくは折り返しミラーの配置）を用いても色ずれの問題が発生することが無い常に高品位なカラー画像が得られる光走査装置を提供することができる。
【０１３２】
尚、実施形態３では走査光学系を構成する走査光学素子の枚数を１枚としたがこれに限ったものではなく、複数枚としても本発明の効果を十分に得ることができる。もしろん、副走査方向のみにパワーを有する走査光学素子に子線非球面量変化面を採用しても良い。
【０１３３】
また実施形態３では各色に対応して感光体ドラム面上に光走査される光束を１本としたがこれに限ったものではなく、例えば８本の光束をポリゴンミラーによって同時に反射偏向し２つの走査光学系の夫々に４本ずつの光束を入射させ、各感光体ドラムへ２本ずつの光束を導光して光走査する光走査装置としても本発明と同等の効果を得ることができる。
【０１３４】
［画像形成装置］
図１８は、本発明の画像形成装置の実施形態を示す副走査方向の要部断面図である。図１８において、符号１０４は画像形成装置を示す。この画像形成装置１０４には、パーソナルコンピュータ等の外部機器１１７からコードデータＤｃが入力する。このコードデータＤｃは、装置内のプリンタコントローラ１１１によって、画像データ（ドットデータ）Ｄｉに変換される。この画像データＤｉは、実施形態１，２に示した構成を有する光走査ユニット１００に入力される。そして、この光走査ユニット１００からは、画像データＤｉに応じて変調された光ビーム１０３が出射され、この光ビーム１０３によって感光ドラム１０１の感光面が主走査方向に走査される。
【０１３５】
静電潜像担持体（感光体）たる感光ドラム１０１は、モータ１１５によって時計廻りに回転させられる。そして、この回転に伴って、感光ドラム１０１の感光面が光ビーム１０３に対して、主走査方向と直交する副走査方向に移動する。感光ドラム１０１の上方には、感光ドラム１０１の表面を一様に帯電せしめる帯電ローラ１０２が表面に当接するように設けられている。そして、帯電ローラ１０２によって帯電された感光ドラム１０１の表面に、前記光走査ユニット１００によって走査される光ビーム１０３が照射されるようになっている。
【０１３６】
先に説明したように、光ビーム１０３は、画像データＤｉに基づいて変調されており、この光ビーム１０３を照射することによって感光ドラム１０１の表面に静電潜像を形成せしめる。この静電潜像は、上記光ビーム１０３の照射位置よりもさらに感光ドラム１０１の回転方向の下流側で感光ドラム１０１に当接するように配設された現像器１０７によってトナー像として現像される。
【０１３７】
現像器１０７によって現像されたトナー像は、感光ドラム１０１の下方で、感光ドラム１０１に対向するように配設された転写ローラ１０８によって被転写材たる用紙１１２上に転写される。用紙１１２は感光ドラム１０１の前方（図１８において右側）の用紙カセット１０９内に収納されているが、手差しでも給紙が可能である。用紙カセット１０９端部には、給紙ローラ１１０が配設されており、用紙カセット１０９内の用紙１１２を搬送路へ送り込む。
【０１３８】
以上のようにして、未定着トナー像を転写された用紙１１２はさらに感光ドラム１０１後方（図１８において左側）の定着器へと搬送される。定着器は内部に定着ヒータ（図示せず）を有する定着ローラ１１３とこの定着ローラ１１３に圧接するように配設された加圧ローラ１１４とで構成されており、転写部から搬送されてきた用紙１１２を定着ローラ１１３と加圧ローラ１１４の圧接部にて加圧しながら加熱することにより用紙１１２上の未定着トナー像を定着せしめる。更に定着ローラ１１３の後方には排紙ローラ１１６が配設されており、定着された用紙１１２を画像形成装置の外に排出せしめる。
【０１３９】
図１８においては図示していないが、プリントコントローラ１１１は、先に説明したデータの変換だけでなく、モータ１１５を始め画像形成装置内の各部や、後述する光走査ユニット内のポリゴンモータなどの制御を行う。
【０１４０】
［カラー画像形成装置］
図１９は本発明の実施態様のカラー画像形成装置の要部概略図である。本実施形態は、光走査装置を４個並べ各々並行して像担持体である感光ドラム面上に画像情報を記録するタンデムタイプのカラー画像形成装置である。図１９において、６０はカラー画像形成装置、１１，１２，１３，１４は各々実施形態１、２に示したいずれかの構成を有する光走査装置、２１，２２，２３，２４は各々像担持体としての感光ドラム、３１，３２，３３，３４は各々現像器、５１は搬送ベルトである。
【０１４１】
図１９において、カラー画像形成装置６０には、パーソナルコンピュータ等の外部機器５２からＲ（レッド）、Ｇ（グリーン）、Ｂ（ブルー）の各色信号が入力する。これらの色信号は、装置内のプリンタコントローラ５３によって、Ｃ（シアン），Ｍ（マゼンタ），Ｙ（イエロー）、Ｂ（ブラック）の各画像データ（ドットデータ）に変換される。これらの画像データは、それぞれ光走査装置１１，１２，１３，１４に入力される。そして、これらの光走査装置からは、各画像データに応じて変調された光ビーム４１，４２，４３，４４が出射され、これらの光ビームによって感光ドラム２１，２２，２３，２４の感光面が主走査方向に走査される。
【０１４２】
本実施態様におけるカラー画像形成装置は光走査装置（１１，１２，１３，１４）を４個並べ、各々がＣ（シアン），Ｍ（マゼンタ），Ｙ（イエロー）、Ｂ（ブラック）の各色に対応し、各々平行して感光ドラム２１，２２，２３，２４面上に画像信号（画像情報）を記録し、カラー画像を高速に印字するものである。
【０１４３】
本実施態様におけるカラー画像形成装置は上述の如く４つの光走査装置１１，１２，１３，１４により各々の画像データに基づいた光ビームを用いて各色の潜像を各々対応する感光ドラム２１，２２，２３，２４面上に形成している。その後、記録材に多重転写して１枚のフルカラー画像を形成している。
【０１４４】
前記外部機器５２としては、例えばＣＣＤセンサを備えたカラー画像読取装置が用いられても良い。この場合には、このカラー画像読取装置と、カラー画像形成装置６０とで、カラーデジタル複写機が構成される。
【０１４５】
【発明の効果】
本発明によれば前述の如く走査光学系を構成する走査光学素子の少なくとも１面に子線の非球面量が母線方向に沿って変化する子線非球面量変化面を用いることにより、走査線曲がりを低減することができる光走査装置及びそれを用いた画像形成装置を達成することができる。
【０１４６】
またこの光走査装置を複数用いたカラー画像形成装置に搭載した場合においては、光路の取り回しや折り返しミラーの配置の自由度を向上させることにより、折り返しミラーの枚数を削減し、簡易な構成で且つコンパクトで色ずれの少ないカラー画像形成装置を達成することができる。
【図面の簡単な説明】
【図１Ａ】本発明の実施形態１における主走査断面図
【図１Ｂ】本発明の実施形態１における副走査断面図
【図２】本発明の実施形態１における副走査方向の要部概要図
【図３】本発明の実施形態１における子線非球面量
【図４】本発明の実施形態１における子線非球面量
【図５】本発明の実施形態１における子線非球面量
【図６】本発明の実施形態１における面の概念図
【図７】本発明の実施形態１における面の子線非球面量の変化を示した図
【図８】本発明の実施形態１における面の子線非球面量の変化を示した図
【図９】本発明の実施形態１における収差図
【図１０】本発明の実施形態１における照射位置と走査線曲がり
【図１１】本発明の実施形態１における母線形状を説明する図
【図１２】本発明の実施形態２における副走査方向の要部概要図
【図１３】本発明の実施形態２における子線非球面量
【図１４】本発明の実施形態２における子線非球面量
【図１５】本発明の実施形態２における子線非球面量
【図１６】本発明の実施形態２における照射位置と走査線曲がり
【図１７Ａ】本発明の実施形態３における主走査断面図
【図１７Ｂ】本発明の実施形態３における副走査断面図
【図１８】本発明の画像形成装置の要部概要図。
【図１９】本発明のカラー画像形成装置の要部概要図
【図２０】従来の光走査装置における斜視図
【符号の説明】
１　光源手段
２　コリメーターレンズ
３　開口絞り
４　シリンドリカルレンズ
５　偏向手段（ポリゴンミラー）
６　走査光学系（走査光学素子）
８　被走査面（感光ドラム面）
１ａ，１ｂ，１ｃ，１ｄ　光源手段
２ａ，２ｂ，２ｃ，２ｄ　コリメーターレンズ
３ａ，３ｂ，３ｃ，３ｄ　開口絞り
４ａ，４ｂ　シリンドリカルレンズ
６１，６２　走査光学系（走査光学素子）
８ａ，８ｂ，８ｃ，８ｄ　被走査面（感光ドラム面）
１１，１２，１３，１４　光走査装置
２１、２２、２３、２４　像担持体（感光ドラム）
３１、３２、３３、３４　現像器
５１　搬送ベルト
５２　外部機器
５３　プリンタコントローラ
６０　カラー画像形成装置
１００　光走査装置
１０１　感光ドラム
１０２　帯電ローラ
１０３　光ビーム
１０７　現像装置
１０８　転写ローラ
１０９　用紙カセット
１１０　給紙ローラ
１１１　プリンタコントローラ
１１２　転写材（用紙）
１１３　定着ローラ
１１４　加圧ローラ
１１５　モータ
１１６　排紙ローラ
１１７　外部機器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device and an image forming apparatus using the same, and for example, reflects and deflects a light beam or a plurality of light beams emitted from a light source means through a scanning optical system. The present invention is suitable for apparatuses such as a laser beam printer having an electrophotographic process, a digital copying machine, a multifunction printer (multifunction printer), and the like, in which image information is recorded by optically scanning a scanning surface.
[0002]
In addition, the present invention always corrects a light beam incident on a plane perpendicular to the rotation axis of the deflecting means from an oblique direction (oblique incidence), and corrects a scan line curve on a scanned surface caused by oblique incidence. The present invention relates to an optical scanning device capable of obtaining a good image and an image forming apparatus using the same. Further, the present invention is suitable for a color image forming apparatus including a plurality of image carriers corresponding to each color using one or more optical scanning devices.
[0003]
[Prior art]
2. Description of the Related Art Conventionally, in an optical scanning device such as a laser beam printer (LBP), a light beam that is light-modulated from a light source means in accordance with an image signal and emitted is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror (polygon mirror). The light is focused in the form of a spot on a photosensitive recording medium (photosensitive drum) surface by a scanning optical system having fθ characteristics, and the surface is optically scanned to record an image.
[0004]
FIG. 20 is a schematic view of a main part of a conventional optical scanning device.
[0005]
In the figure, a divergent light beam emitted from a light source means 91 is converted into a substantially parallel light beam by a collimator lens 92, and the light beam is restricted by a stop 93 and is incident on a cylindrical lens 94 having a predetermined refractive power only in the sub-scanning direction. ing. Of the substantially parallel light beam incident on the cylindrical lens 94, it is emitted as it is in the main scanning section. In the sub-scanning section, the light is converged and formed as a substantially linear image on a deflecting surface (reflection surface) 95a of a deflecting means (optical deflector) 95 composed of a polygon mirror.
[0006]
Then, the light beam deflected by the deflecting surface 95a of the deflecting means 95 is guided onto a photosensitive drum surface 98 as a surface to be scanned through a scanning optical system 96 having fθ characteristics, and the deflecting means 95 is rotated in the direction of arrow A. Thus, the photosensitive drum surface 98 is optically scanned in the direction of arrow B to record image information.
[0007]
[Problems to be solved by the invention]
In such an optical scanning device, in order to record image information with high accuracy, it is necessary that the curvature of field is well corrected over the entire surface to be scanned, that the angle of view (scan angle) θ and the image height are high. (Distance from scanning center) Y and distortion characteristics (fθ characteristics) with uniform velocity, and spot diameter on the image plane (scanned surface) is uniform at each image height. Is necessary. Various optical scanning devices or scanning optical systems satisfying such optical characteristics have been conventionally proposed.
[0008]
On the other hand, when a plurality of light beams are scanned by using one light deflector, the incident light beams are separated in the sub-scanning direction in order to separate the light beams in the sub-scanning direction from the necessity of guiding the scanned light beams onto a photoconductor corresponding to each color. It becomes necessary to make light obliquely enter the plane perpendicular to the rotation axis of the deflecting means (oblique incidence). When the light beam is obliquely incident on the deflecting means, a so-called "scanning line bending" in which the scanning line is curved on the surface to be scanned occurs.
[0009]
Particularly, a laser beam is guided from an optical scanning device to four photoconductors (photosensitive drums) to form latent images, and images of originals of respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black) are formed. Are formed on the corresponding photoreceptor surfaces, respectively, in order to superimpose the four color images of Y, M, C, and Bk formed on the respective photoreceptor surfaces on a transfer body such as paper. If the scanning line of the optical scanning device corresponding to the photoreceptor is curved, an error occurs in the shape of the scanning line among the four colors, and color misregistration occurs in the image on the transfer body, so that the image performance is significantly deteriorated. The problem of inviting the problem arises.
[0010]
Some optical scanning devices have been proposed as means for solving the problem of the scanning line bending.
[0011]
Japanese Patent Application Laid-Open No. Hei 7-191272 discloses an optical scanning device in which a light beam is incident from an oblique direction with respect to a plane perpendicular to the rotation axis of a deflecting means. One of the scanning optical elements constituting a scanning optical system is anamorphic. A main scanning cross-sectional shape of the anamorphic lens is aspherical; a radius of curvature of the sub-scanning cross section is set independently of the main scanning cross-sectional shape; There is disclosed an example in which the scanning line bending is corrected by eccentric arrangement in the scanning direction.
[0012]
Japanese Patent Application Laid-Open No. Hei 9-184991 discloses an example in which a scanning flat plate is corrected by tilting a parallel flat plate used as dust-proof glass.
[0013]
These techniques involve displacing a scanning optical element (imaging optical element) such as an anamorphic lens included in the scanning optical system in the sub-scanning direction, or tilting an optical element that does not exert an imaging action such as dust-proof glass, The scanning line bending is corrected by decentering the optical element.
[0014]
However, when these optical elements are decentered in the optical path, the scanning line bending is corrected, but other optical characteristics change. Further, the eccentricity of the optical element has the effect of correcting the scanning line bending only for a specific light beam, and it becomes difficult to correct the scanning line bending for a plurality of light beams at the same time. In this case, it is necessary to prepare one optical element for one light beam. When a plurality of light beams are used, a plurality of optical elements are required for each light beam, and the number of components increases.
[0015]
Japanese Patent Application Laid-Open No. 9-90254 discloses an example in which the sagittal line of a cylindrical lens is made to be a non-cylindrical surface, so that the wavefront of a light beam transmitted through the cylindrical lens is delayed with respect to a reference spherical surface around the sub-scanning direction. I have.
[0016]
In this example, when the beam diameter in the sub-scanning direction is small, the beam waist separates from the Gaussian image plane, the beam diameter changes due to defocusing, and the drawing performance is prevented from deteriorating. It was not about turning.
[0017]
The present invention eliminates the possibility that a light beam is incident obliquely to a plane perpendicular to the rotation axis of the deflecting means (oblique incidence), and that the scanning optical system is decentered in the sub-scanning direction to prevent the scanning line from being bent. It is an object of the present invention to provide an optical scanning device which can be improved well and an image forming apparatus using the same.
[0018]
In addition, the present invention provides an optical scanning device having a simple configuration capable of always minimizing the scan line bending without being restricted by the arrangement of the optical elements such as the folding mirror, and an image forming apparatus using the optical scanning device. Aim.
[0019]
In addition, another object of the present invention is to provide a color image forming apparatus that can always obtain a good image without color shift by using one or more optical scanning devices that can always suppress scanning line bending to a minute level.
[0020]
[Means for Solving the Problems]
The optical scanning device of the invention according to claim 1 is
A light source unit, a deflecting unit that deflects a light beam emitted from the light source unit, and a scanning optical system that forms an image of a deflected light beam deflected by the deflecting unit on a surface to be scanned.
The scanning optical system includes a scanning optical element arranged such that a principal ray of the deflected light beam passes through a portion other than the optical axis in the sub-scanning direction, and the scanning optical element has an aspherical amount of a sagittal line of the scanning optical element. It includes a sagittal aspherical amount changing surface that changes along the main scanning direction, and is characterized in that the positions in the sub-scanning direction where the deflected light beam reaches are uniform over the entire surface to be scanned.
[0021]
The invention of claim 2 is the invention according to claim 1,
The scanning optical system is characterized in that, within an effective scanning range on the surface to be scanned, a deviation amount of a position in the sub-scanning direction where the deflection light beam reaches is suppressed to 10 μm or less.
[0022]
The invention of claim 3 is the invention according to claim 1 or 2,
The light beam emitted from the light source means is incident on the plane perpendicular to the rotation axis of the deflecting means at an angle.
[0023]
The invention of claim 4 is the invention according to claim 1, 2 or 3,
In the sub-scanning direction, the position at which the principal ray of the deflected light beam reaches the surface to be scanned is smaller than the position at which the principal ray passes through the surface of the scanning optical element having the largest power. It is characterized by being close to the optical axis of the element.
[0024]
The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The scanning optical system is characterized by having at least one sagittal curvature radius changing surface whose sagittal curvature radius changes along the main scanning direction of the scanning optical system.
[0025]
The invention according to claim 6 is the invention according to any one of claims 1 to 5,
The scanning optical system is characterized by comprising one scanning optical element.
[0026]
The invention according to claim 7 is the invention according to any one of claims 1 to 6,
The power of the scanning optical system in the sub-scanning direction is equal to or substantially equal to the power of the sagittal aspherical surface variation surface.
[0027]
The invention of claim 8 is the invention of claim 7,
When the power of the scanning optical system in the sub-scanning direction is φso and the power of the sagittal aspherical surface variation surface in the sub-scanning direction is φsi,
0.9 × φso ≦ φsi ≦ 1.1 × φso
It is characterized by satisfying certain conditions.
[0028]
The invention according to claim 9 is the invention according to any one of claims 1 to 8,
The light source unit emits two or more light beams, and a main ray of at least one light beam passes above the optical axis of the scanning optical system in the sub-scanning cross section, and another at least one light beam is emitted. The principal ray passes below the optical axis of the scanning optical system.
[0029]
The invention according to claim 10 is the invention according to any one of claims 1 to 9,
The deflecting unit deflects a plurality of light beams, and the scanning optical system forms a plurality of scanning optical elements that form an image of the plurality of light beams deflected by the deflecting unit on a plurality of scanned surfaces corresponding to each light beam. And the deflection means is shared by a plurality of scanning optical systems.
[0030]
The invention according to claim 11 is the invention according to any one of claims 1 to 10,
In the main scanning section, the air-equivalent distance from the deflecting means to the light emitting surface of the scanning optical element on the optical axis is P1, the distance from the light emitting surface of the scanning optical element to the surface to be scanned is P2, and off-axis. Where M1 is the air-equivalent distance from the deflecting means to the light emission surface of the scanning optical element, and M2 is the distance from the light emission surface of the scanning optical element to the surface to be scanned.
[0031]
(Equation 2)

[0032]
It is characterized by satisfying certain conditions.
[0033]
The image forming apparatus according to claim 12 is:
An optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and an electrostatic member formed on the photosensitive member by a light beam scanned by the optical scanning device. A developing device for developing the latent image as a toner image, a transfer device for transferring the developed toner image to a transfer material, and a fixing device for fixing the transferred toner image to the transfer material. I have.
[0034]
The image forming apparatus according to claim 13 is:
An optical scanning device according to any one of claims 1 to 11, further comprising a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device.
[0035]
According to a fourteenth aspect of the present invention, there is provided a color image forming apparatus.
The optical scanning device according to any one of claims 1 to 11, further comprising at least one optical scanning device and a plurality of image carriers that form images of different colors.
[0036]
The invention of claim 15 is the invention of claim 14,
A printer controller is provided which converts a color signal input from an external device into image data of a different color and inputs the image data to each optical scanning device.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
1A is a cross-sectional view (main scanning cross-sectional view) of a main scanning direction of the optical scanning device according to the first embodiment of the present invention, and FIG. 1B is a main cross-sectional view of the optical scanning device according to the first embodiment of the present invention in the sub-scanning direction. It is a figure (sub-scan sectional drawing).
[0038]
Here, the main scanning direction indicates a direction perpendicular to the rotation axis of the deflecting means and the optical axis of the scanning optical element (the direction in which the light beam is reflected and deflected (deflection scanning) by the deflecting means). 3 shows a direction parallel to the rotation axis. The main scanning section indicates a plane parallel to the main scanning direction and including the optical axis of the scanning optical system. The sub-scanning section indicates a section perpendicular to the main scanning section.
[0039]
1A and 1B, reference numeral 1 denotes a semiconductor laser as light source means. After converting at least one divergent light from the semiconductor laser 1 into a parallel light beam or a substantially parallel light beam (which may be a convergent light beam or a divergent light beam) by the collimator lens 2, the stop 3 can obtain a desired spot diameter. The light beam width is limited. Reference numeral 4 denotes a cylindrical lens having a predetermined refractive power only in the sub-scanning direction, and forms a linear image in the direction parallel to the main scanning section in the vicinity of a deflecting surface 5a of a deflecting means 5 described later. Numeral 5 denotes a deflecting means comprising a polygon mirror (rotating polygon mirror) having a construction of, for example, four surfaces (the number may be any number of four or more), and a constant speed in the direction of arrow A in the figure by a motor driving means (not shown). Is spinning.
[0040]
Reference numeral 6 denotes a scanning optical system constituted by a single scanning optical element (fθ lens) having fθ characteristics. The scanning optical system includes a photosensitive drum surface (photosensitive member) which uses the deflected light beam reflected and deflected by the deflecting means 5 as a surface to be scanned. 8), and corrects the surface inclination of the deflecting surface 5a of the deflecting means 5. Hereinafter, the scanning optical system 6 is also referred to as a scanning optical element 6. At this time, the deflecting light beam reflected and deflected by the deflecting surface 5a of the deflecting means 5 is guided onto the photosensitive drum surface 8 via the scanning optical system 6, and the polygon mirror 5 is rotated in the direction of arrow A so as to rotate the deflecting light beam. Optical scanning is performed on the body drum surface 8 in the direction of arrow B. As a result, scanning lines are formed on the surface of the photosensitive drum, and image recording is performed.
[0041]
As shown in FIG. 1B, in the first embodiment, the light beam emitted from the light source means 1 is incident on the deflecting surface 5a at an angle γ in the sub-scanning direction from obliquely below, and one sheet constituting the scanning optical system Is incident on the scanning optical element 6 made of synthetic resin or glass. The scanning optical element 6 forms an image of the deflected light beam as a spot on the surface 8 to be scanned.
[0042]
Here, Table 1 shows the optical arrangement of each optical member in the first embodiment.
[0043]
[Table 1]

[0044]
Table 2 shows the shapes of the entrance surface and the exit surface of the scanning optical element 6 in the first embodiment.
[0045]
[Table 2]

[0046]
FIG. 2 is a sub-scan sectional view when the optical path of the optical system of the optical scanning device according to the first embodiment of the present invention is developed.
[0047]
As shown in FIG. 1B and FIG. 2, in the first embodiment, the light beam emitted from the light source means 1 is incident on the deflection surface 5 a at an angle γ in the sub-scanning direction from obliquely below. The light is incident on one of the constituent scanning optical elements made of synthetic resin or glass. The scanning optical element 6 includes an anamorphic surface and forms an image of the deflected light beam as a spot or a substantially spot on the surface 8 to be scanned.
[0048]
FIG. 6 shows a conceptual diagram of the surface of the scanning optical element 6 used in the first embodiment.
[0049]
The generatrix shapes of the entrance surface 6a and the exit surface 6b of the scanning optical element 6 are constituted by aspherical shapes that can be expressed as a function up to the tenth order. For example, as shown in FIG. 6, an intersection point between the scanning optical element 6 and the optical axis La is defined as an origin O1, an optical axis direction La is an X axis, and an axis orthogonal to the optical axis La in a main scanning section (in the XY plane) is Y. The direction orthogonal to the axis and the XY plane is defined as the Z axis. At this time, a generatrix shape Xa in the generatrix direction corresponding to the main scanning direction (Y direction) is
[0050]
[Equation 3]

[0051]
(Where R is the radius of curvature of the generatrix, and K, B4, B6, B8, B10, B12, B14, and B16 are aspherical coefficients).
[0052]
Also, the sagittal shape S in the sagittal direction corresponding to the sub-scanning direction is
[0053]
(Equation 4)

[0054]
It is represented by the following formula. S is a sagittal shape defined in a plane perpendicular to the main scanning section (XY plane), including the normal line of the generatrix at each position Y in the generatrix direction.
[0055]
Here, the radius of curvature (sagittal radius of curvature) Rs * in the sub-scanning direction at a position Y separated from the optical axis La by the distance Y in the main scanning direction is:
[0056]
(Equation 5)

[0057]
(However, Rs is a sagittal radius of curvature on the optical axis La, and D2, D4, D6, D8, and D10 are sagittal change coefficients.) Further, as an aspherical component in the sagittal direction, 0058
(Equation 6)

[0059]
This is a surface obtained by adding the following values to the expression (a).
[0060]
In the first embodiment, the surface shape is defined by the above formula, but the formula may be any formula that can express the aspherical component in the sagittal direction, and is not limited to the above formula.
[0061]
Further, each surface of the scanning optical element 6 of the first embodiment does not shift or tilt in the sub-scanning direction, and the deflecting light beam directed to the end of the scanned surface 8 is reflected and deflected by the deflecting surface 5 a of the polygon mirror 5. The position 5a1 is formed at the same height as the optical axis La of the scanning optical element 6.
[0062]
As shown in Table 2, the incident surface 6a of the scanning optical element 6 has a power (refractive power) only in the main scanning direction in which the generatrix shape is an aspherical shape (non-arc shape) and the sagittal shape is a plane (straight line). Is a cylindrical surface having The exit surface 6b of the scanning optical element 6 has a generatrix shape of a circular arc, and a sagittal shape is a sagittal curvature radius changing surface in which the radius of curvature changes continuously as the distance from the optical axis increases in the generatrix direction. Above is a surface that is an arc shape, is an aspherical shape (aspherical shape) at places other than the optical axis, and is also a sagittal aspherical amount changing surface in which the amount of aspherical surface changes as the distance from the optical axis along the generatrix direction increases. Is formed.
[0063]
The aspherical shape of the aspherical surface in the main scanning section of the scanning optical element 6 is formed so as to have no inflection point in the curvature change.
[0064]
Next, a schematic diagram in the sub-scanning direction of the optical scanning device according to the first embodiment shown in FIG. 2 will be described.
[0065]
In the first embodiment, the incident light beam Li emitted from the light source means 1 is incident on the deflecting surface 5a of the deflecting means 5 at an angle γ = 3 (deg) in the sub-scanning direction with respect to the main scanning section. The deflection light beam Ld reflected by the deflection surface 5a is also incident on the scanning optical element 6 at an angle γ = 3 (deg) in the sub-scanning direction with respect to the main scanning section. Therefore, the position where the principal ray (dashed line) of the deflected light beam Ld reaches the entrance surface 6a and the exit surface 6b of the scanning optical element 6 passes through a position far away from the sagittal optical axis (or the generating line) La. The passing positions Za and Zb of the lens surface and the distance Zlens from the optical axis La are higher than the generatrix position (Zlens = 0), and Zlens >> 0.
[0066]
In the first embodiment, the distance Zlens of the position Za in the sub-scanning direction at which the deflected light beam Ld reaches the incident surface 6a of the scanning optical element 6 is 2.73 mm, and the distance Zlens of the position Zb in the sub-scanning direction reaching the emission surface 6b. = 3.34 mm.
[0067]
The deflected light beam Ld that has passed through the scanning optical element 6 is imaged as a spot on the surface 8 to be scanned by the condensing action of the scanning optical element 6.
[0068]
When the principal ray of the deflected light beam Ld passes through a position distant from the generatrix (or sagittal optical axis) La as described above, the light beam that has passed through the scanning optical element 6 turns downward due to the power (refractive power) of the lens. be changed.
[0069]
At this time, if the configuration of the scanning optical element 6 is not properly set, the scanning optical element 6 crosses the optical axis La before the surface 8 to be scanned, and reaches a position below the main scanning section on the surface 8 to be scanned. Here, the position in the sub-scanning direction at which the deflected light beam Ld reaches the surface 8 to be scanned is referred to as an irradiation position Zo, and the distance from the optical axis La is referred to as Zimage.
[0070]
At this time, the position in the sub-scanning direction of the deflected light beam Ld reaching the incident surface 6a and the outgoing surface 6b of the scanning optical element 6 and the power (refractive power) for changing the direction of the deflected light beam Ld passing through the scanning optical element 6 downward. Since the distance differs depending on the image height, the distance Zimage of the irradiation position Zo is not uniform, and a problem of so-called scanning line bending occurs.
[0071]
In order to solve this problem, in the optical scanning device according to the first embodiment, the exit surface 6b of one scanning optical element 6 constituting the scanning optical system is set to the sagittal line shape S of the above-described equation (b) and the numerical value of FIG. A sagittal aspherical surface variation surface indicated by. Here, the sagittal aspherical surface variation surface is a surface in which the sagittal aspherical surface amount ΔXz is changed as the distance from the optical axis La of the lens surface increases along the generatrix direction of the lens surface.
[0072]
Here, the sagittal aspherical amount ΔXz refers to the sagittal curvature of the base of the lens surface at a position Zlens (Zlens ≠ 0 mm) in the sub-scanning direction other than on the generatrix (other than on the sagittal optical axis) as shown in FIG. The amount ΔXz displaced in the optical axis direction from the radius Rs * means that the sagittal aspherical amount ΔXz changes when the sagittal aspherical amount ΔXz at the same position Zlens (Zlens ≠ 0 mm) in the sub-scanning direction This means that it changes depending on the position Y. That is, it indicates that dΔXz / dY ≠ 0.
[0073]
FIG. 3 shows how the sagittal aspherical amount ΔXz of the exit surface 6b of the scanning optical element 6 in the first embodiment changes. 7 shows how the sagittal aspherical amount ΔXz at the distance Z from the sagittal optical axis shown in FIG. 4 changes along the generatrix direction (the value of Y) (the sagittal aspherical amount ΔXz at the position ZRa in FIG. 7). A state in which the sagittal aspherical amount ΔXz at a distance Y along the generatrix direction from the optical axis La of the exit surface 6b in FIG. 5 changes along the sub-scanning direction (Z direction) (sagittal at the position YRa in FIG. 8). Aspherical amount ΔXz).
[0074]
In the first embodiment, the sagittal shape on the optical axis La of the emission surface 6b is a circular arc, and the sagittal shape is a non-circular arc (aspherical surface) at a location away from the optical axis La in the generatrix direction, as shown in FIG. In the exit surface 6b along the generatrix direction, the aspherical amount ΔXz of the sagittal line gradually increases from zero as the distance from the optical axis La increases, and has an extreme value on the way, and then gradually decreases. The sagittal aspherical surface is changed.
[0075]
Further, as shown in FIG. 5, the sagittal aspherical amount is added so as to gradually increase as the distance from the sagittal optical axis La in the sub-scanning direction is increased at a place other than the optical axis La of the exit surface 6b. . Here, the plus sign indicates that the base is displaced from the arc shape of the base toward the surface to be scanned.
[0076]
The sagittal aspherical power changes gradually from zero as the distance from the exit surface 6b optical axis La increases along the generatrix direction, and at positions other than the exit surface 6b optical axis La, the sagittal optical axis La The sagittal aspherical surface power is changed so that the sagittal aspherical surface power gradually decreases as the distance from the sub-scanning direction increases.
[0077]
Also, the added sagittal aspherical power is a very small power of about 1/100 of the base arc shape, and the sagittal aspherical surface hardly contributes to the field curvature in the sub-scanning direction, and is used only for scanning line curvature correction. Has efficacy.
[0078]
FIG. 9 shows an aberration diagram in the first embodiment.
[0079]
The curvature of field in the main scanning direction is within ± 0.6 mm, and the curvature of field in the sub-scanning direction is within ± 0.3 mm, and both are well corrected. The distortion (fθ characteristic) is within ± 0.3%, and the image height deviation is within ± 0.08 mm, which is well corrected.
[0080]
This makes it possible to control the irradiation position on the surface to be scanned by the aspherical effect of the sagittal line, separately from correcting the field curvature in the sub-scanning direction by the light condensing action exerted by the base arc shape. By the aspherical surface effect, the irradiation position Zoa of the deflected light beam toward each image height can be aligned with the irradiation position Zo of the center image height. That is, it is possible to independently correct the field curvature in the sub-scanning direction and the scanning line curvature. Specifically, the misalignment in the sub-scanning direction is equal to or less than 10 μm, preferably equal to or less than 5 μm.
[0081]
FIG. 10 shows the irradiation position and the scanning line bending of the optical scanning device in the first embodiment and the comparative example. The optical scanning device described as a comparative example uses the scanning optical system of Embodiment 1 from which the aspherical surface effect is excluded. In addition, the scanning line bending is obtained by removing the deviation of the irradiation position between each image height and the center image height.
[0082]
As shown in FIG. 10, the irradiation position of the center image height corresponding to the optical axis of the scanning optical system 6 is Zimage = 0.1819 mm in both the first embodiment and the comparative example, and is located above the sagittal optical axis. . At each image height, the irradiation position is located above the sagittal optical axis.
[0083]
In the comparative example, the irradiation position of the end image height is displaced downward with respect to the center image height, and a scanning line curve of 11 μm occurs. On the other hand, in the first embodiment, the irradiation positions are aligned at each image height, and the scanning line curvature is corrected to a sufficiently small value of 5.0 μm.
[0084]
As described above, by changing the sagittal aspherical amount ΔXz as the distance from the optical axis La increases along the generatrix direction, the irradiation position at each image height can be aligned and the problem of scanning line bending can be dramatically improved. It turns out that it becomes.
[0085]
In the optical scanning device according to the first embodiment, the irradiation position Zo on the surface 8 to be scanned is changed from the position Za, Zb in the sub-scanning direction where the deflected light beam Ld reaches the entrance surface 6a and the exit surface 6b of the scanning optical element 6 to the sub-line. Since it is closer to the optical axis La, it is possible to better correct the scanning line bending.
[0086]
Next, one scanning optical element 6 constituting the scanning optical system according to the first embodiment will be described. The incident surface 6a is a cylindrical lens surface having power only in the main scanning direction. The exit surface 6b is a sagittal curvature changing surface in which the generatrix has an arc shape, the sagittal shape is convex, and the absolute value of the radius of curvature gradually increases as the distance from the optical axis increases along the generatrix direction. Further, the sagittal radius of curvature changes asymmetrically on the left and right sides in the main scanning direction with the optical axis of the scanning optical system 6 interposed therebetween. Thus, the entire power (refractive power) of the scanning optical system 6 in the sub-scanning direction is concentrated on the emission surface 6b.
[0087]
Specifically, 90% or more of the total power is concentrated. That is, when the power of the scanning optical system 6 in the sub-scanning direction is φso and the power of the sagittal aspherical surface variation surface in the sub-scanning direction is φsi,
0.9 × φso ≦ φsi ≦ 1.1 × φso
To satisfy certain conditions.
[0088]
FIG. 11 is a schematic diagram of a main portion in the main scanning direction according to the first embodiment.
[0089]
As shown in FIG. 11, the generatrix shape of the exit surface 6b is determined by the position at which the deflected light beam reaches the output surface 6b from the position on the optical axis of the scanning optical system 6 where the deflected light beam is reflected by the deflection surface 5a in the main scanning direction. The ratio P2 / P1 of the distance P1 to the position P2 from the position at which the deflected light beam reaches the emission surface 6b to the position at which the deflection light flux reaches the surface to be scanned 8 is deflected toward all image heights on the surface 8 to be scanned. The optical path of the light beam is substantially constant (P2 / P1 = Const) or an arc shape having a shape within ± 10% of the constant value. For example, in the case of taking the optical path of the deflecting light beam Ld toward the image height end Ip as an example, the distance M1 from the position where the deflecting light beam Ld is reflected by the deflecting surface 5a to the position where the deflecting light beam Ld reaches the emission surface 6b. The ratio M2 / M1 of the distance from the position where the deflected light beam Ld reaches the emission surface 6b to the position where the deflection light beam Ld reaches the surface to be scanned 8 becomes substantially equal to P2 / P1 (M2 / M1 ≒ P2 / P1 The shape of the generatrix is determined as follows.
[0090]
That is,
[0091]
(Equation 7)

[0092]
It is made to become.
[0093]
In the first embodiment, the total power (refractive power) of the scanning optical system 6 in the sub-scanning direction is concentrated on the emission surface 6b. The lateral magnification (sub-scanning magnification) βs can be made to be substantially constant. The sub-scanning magnification βs of the scanning optical system 6 of the embodiment is −2.31 (times).
[0094]
Accordingly, even when the scanning optical element 6 is displaced or tilted in the sub-scanning direction due to a manufacturing error, an assembly error, or the like, so-called eccentricity in the sub-scanning direction occurs, the scanning line bending performance in design (initial) is obtained. Can be maintained.
[0095]
That is, in the optical scanning device according to the first embodiment, it is possible to satisfactorily correct the scanning line bending over the entire image height on the surface 8 to be scanned, and it is possible to perform the scanning even when the scanning optical element 6 is decentered in the sub-scanning direction. Scanning line bending performance can be maintained.
[0096]
For this reason, it is possible to provide an optical scanning device in which the scanning line curvature is always satisfactorily corrected and a good image is always obtained.
[0097]
In the first embodiment, the light beam emitted from the light source means 1 is made incident on the deflecting means at an oblique incident angle γ with respect to the main scanning section, and the deflecting light beam directed toward the end of the surface 8 to be scanned is reflected by the deflecting surface 5 a of the polygon mirror 5. Although an example in which the position where the light is reflected and deflected is formed at the same height as the optical axis of the scanning optical system 6 is not limited to this, for example, a deflected light beam heading toward the entire image height is reflected and deflected by the deflection surface 5a. The effect of the present invention can be sufficiently obtained even if the position is located above the optical axis of the scanning optical system 6.
[0098]
In the first embodiment, an optical scanning device that optically scans one light beam is described as an example. However, the present invention is not limited to this. For example, two, three, four,... The same effect can be obtained in a multi-beam optical scanning device.
[0099]
In the first embodiment, a scanning optical system configured by one scanning optical element has been described as an example. However, the present invention is not limited to this. For example, the scanning optical system includes a plurality of optical members such as a scanning optical element and an imaging mirror. The scanning optical system may be configured such that at least one surface of the scanning optical element is a sagittal aspherical surface variation surface, whereby the scanning line bending can be favorably corrected.
[0100]
In the first embodiment, a diffractive portion may be provided on the entrance surface and / or the exit surface of the scanning optical element so as to have the same aspherical function as described above.
[0101]
[Embodiment 2]
FIG. 12 is a schematic diagram of a main part of a sub-scanning cross section of the optical scanning device according to the second embodiment of the present invention.
[0102]
The difference between the second embodiment and the first embodiment is that the amount of the sagittal aspherical surface of the emission surface 6b of the scanning optical element 6 is changed.
[0103]
Table 3 shows the shapes of the entrance surface 6a and the exit surface 6b of the scanning optical element 6 according to the third embodiment.
[0104]
[Table 3]

[0105]
The sagittal shape of the exit surface 6b of the scanning optical element 6 is an aspherical surface (a non-circular arc) at all positions in the effective plane, and the sagittal shape increases as the distance from the optical axis increases along the generatrix direction of the scanning optical element 6. This is a sagittal aspherical surface variation surface in which the spherical surface amount changes.
[0106]
FIG. 13 shows how the amount of sagittal aspherical surface on the exit surface 6b of the scanning optical element 6 in the second embodiment changes (FIG. 7). FIG. 14 shows how the amount of the sagittal aspherical surface at a distance (Z) from the sagittal optical axis changes along the generatrix direction (FIG. 8). FIG. The manner in which the sagittal aspherical amount changes along the sub-scanning direction at a distance along the distance (Y) is shown.
[0107]
In the second embodiment, all the sagittal shapes of the exit surface 6b are non-circular arcs (aspheric surfaces), and the amount of the aspheric surface of the sagittal line increases as the exit surface 6b moves away from the optical axis along the generatrix direction as shown in FIG. The sagittal aspherical surface is changed so as to gradually decrease. Further, as shown in FIG. 15, the sagittal aspherical amount is added so as to gradually increase as the distance from the sagittal optical axis in the sub-scanning direction increases.
[0108]
The exit surface 6b along the generatrix direction changes so that the sagittal aspherical power gradually increases as the distance from the optical axis increases, and the sagittal aspherical power gradually increases as the distance from the sagittal optical axis increases along the sub-scanning direction. The surface is a sagittal aspherical surface amount changing surface which is changed so as to be reduced to the following.
[0109]
FIG. 16 shows the irradiation position and the scanning line bending of the optical scanning device in the second embodiment and a comparative example excluding the sagittal aspherical surface effect.
[0110]
The scanning optical element 6 according to the second embodiment is configured such that the sagittal shape on the optical axis of the exit surface 6b is an aspherical surface (a non-circular arc), and the deflection light beam directed to the optical axis of the surface 8 to be scanned (center image height) is a sagittal. It is configured to be irradiated on the optical axis. That is, the distance Zimage of the irradiation position Zo on the surface 8 to be scanned is set to 0.00 mm.
[0111]
Also, at all image heights within the effective scanning range on the surface 8 to be scanned, the sagittal aspherical amount of the exit surface 6b of the scanning optical element 6 is such that the irradiation position Zo is on the same sagittal optical axis as the center image height. Is changed along the generatrix direction.
[0112]
In the comparative example, the scanning line curvature was 11 μm, whereas in the second embodiment, the scanning line curvature was corrected to be very small at 4.7 μm.
[0113]
Therefore, it is possible to provide an optical scanning device in which the irradiation position at the entire image height is aligned on the main scanning cross section by the sagittal aspherical change surface, and the scanning line bending is suppressed to be extremely small.
[0114]
In addition, since the absolute value of the radius of curvature of the base arc shape of the emission surface of the scanning optical element 6 gradually increases as the distance from the optical axis increases, the field curvature in the sub-scanning direction can be sufficiently corrected.
[0115]
Further, in the second embodiment, the deflection surface 5a of the deflection unit and the surface 8 to be scanned can be almost completely conjugated, so that even if the deflection surface is inclined due to a manufacturing error or the like, the pitch unevenness can be suppressed to be small. it can.
[0116]
As a result, it is possible to provide an optical scanning device that can satisfactorily correct the scanning line curvature, and further obtains a high-quality image in which the curvature of field and pitch unevenness in the sub-scanning direction are well corrected.
[0117]
In the second embodiment, an example of the optical scanning device in which only the exit surface 6b of the scanning optical element 6 is the sagittal aspheric surface amount change surface and the sagittal aspheric surface amount change surface is only one is described. Instead, the same is true even for an optical scanning device in which the entrance surface 6a of the scanning optical element 6 is also a sagittal aspherical amount changing surface and the sagittal aspherical amount changing surface in which the aspherical amount is shared on both surfaces is a plurality of surfaces. The effect can be obtained.
[0118]
In the scanning optical system according to the second embodiment, the generatrix of the exit surface is an arc. However, the present invention is not limited to this. If an aspherical shape (aspherical shape) is used, each aberration in the main scanning direction can be corrected more favorably. Therefore, an effect equal to or higher than that of the second embodiment can be obtained.
[0119]
Furthermore, in the second embodiment, the coefficients of the aspherical term of the sagittal are set to three of Z ⁴ , Z ⁴ Y ² , and Z ⁴ Y ^4. However, the present invention is not limited to this, and Z ⁴ Y ⁶ , Z ⁴ Y ⁸ , ..., and ^{"Z 4"} degree polynomial and increased the "Y" as applied to, ^{also, Z 6, Z 6 Y 2} , Z 6 Y 4, Z 6 Y 6, Z 6 Y 8, ..., Z 8 , Z ⁸ Y ² , Z ⁸ Y ⁴ , Z ⁸ Y ⁶ , Z ⁸ Y ⁸ ,..., And in addition to the above, a polynomial in which the order of “Z” applied to each order of “Y” is increased, By using the expression for the spherical surface, the effect of the present invention can be further improved.
[0120]
[Embodiment 3]
FIG. 17A is a main scanning cross-sectional view of the optical scanning device according to the third embodiment of the present invention, and FIG. 17B is a sub-scanning cross-sectional view.
[0121]
The third embodiment includes the two optical scanning devices according to the first and second embodiments (however, the deflecting means is shared). Further, two light beams are made incident on the respective scanning optical systems 6 to further form one more. An optical scanning device for forming a color image, in which four light beams are incident on the deflecting means 5 at the same time, the four light beams are deflected by one deflecting means 5, and the corresponding photosensitive drums 8a to 8d are optically scanned. It is.
[0122]
In FIG. 17, reference numeral 1 denotes light source means (multi-beam laser), which comprises four semiconductor lasers 1a, 1b, 1c, and 1d each emitting one light beam. The four divergent light beams emitted from the four semiconductor lasers 1a, 1b, 1c, 1d are substantially parallel light beams (convergent light beams or convergent light beams) by the corresponding collimator lenses (first optical elements) 2a, 2b, 2c, 2d. (A divergent light beam may be used), and the light beam width is limited by the corresponding aperture stops 3a, 3b, 3c, and 3d. Of these, two substantially parallel light beams that have passed through the aperture stops 3a and 3b are brought into the vicinity of a deflecting surface 5a of a deflecting means 5 to be described later by a first cylindrical lens (second optical element) 4a having power only in the sub-scanning direction. The image is formed as a long line image in the main scanning section. The two substantially parallel light beams that have passed through the aperture stops 3c and 3d are elongated by a second cylindrical lens 4b having power only in the sub-scanning direction near the deflecting surface 5b of the deflecting means 5 in the main scanning section. It is imaged as an image.
[0123]
Reference numeral 5 denotes a deflecting unit formed of, for example, a polygon mirror (rotating polygon mirror) having a four-sided configuration, and is rotated at a constant angular velocity in the direction of arrow A in the figure by a driving unit (not shown) such as a motor.
[0124]
Reference numeral 61 denotes a first scanning optical system constituted by one scanning optical element (fθ lens) having fθ characteristics manufactured by plastic molding, and 62 denotes one scanning optical element having fθ characteristics manufactured by plastic molding. A second scanning optical system constituted by a scanning optical element (scanning optical element), wherein two deflection light beams BMa and BMb (BMc, BMd) reflected and deflected by the deflecting means 5 are used as a surface to be scanned. An image is formed on the photosensitive drum surfaces 8a and 8b (8c and 8d), and the tilt of the deflecting surface 5a (5b) of the deflecting means 5 is corrected. At this time, the four deflecting light beams BMa, BMb, BMc, and BMd reflected and deflected by the deflecting surfaces 5a and 5b of the deflecting means 5 pass through the first and second scanning optical systems 61 and 62, respectively. The light is guided onto four photosensitive drum surfaces (cyan, magenta, yellow, and black) 8a, 8b, 8c, and 8d corresponding to the respective light beams, and by rotating the deflecting means 5 in the direction of arrow A, the photosensitive drum surfaces are rotated. Optical scanning is performed in the direction of arrow B on 8a, 8b, 8c and 8d. Thus, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, and 8d, and image recording is performed.
[0125]
In the scanning optical system 61 (62), the scanning optical element is used in common for the two light beams BMa and BMb (BMc and BMd). Thus, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, 8d, and image recording is performed.
[0126]
For the sake of simplicity, the scanning optical systems 61 and 62 are the scanning optical system 6, the collimator lenses 2a, 2b, 2c and 2d are the collimator lens 2, and the aperture stops 3a, 3b, 3c and 3d are the aperture stop 3. The cylindrical lenses 4a and 4b are called the cylindrical lens 4, and the scanned surfaces 8a, 8b, 8c and 8d are called the scanned surface 8.
[0127]
The third embodiment shows a case where the present invention is applied to a color image forming apparatus having four photosensitive drums corresponding to the colors of cyan, magenta, yellow, and black. The color image is formed by superimposing the above four colors, and if the printing position of the scanning line corresponding to each color is shifted, a color shift occurs, thereby deteriorating the image quality. Therefore, it is necessary to match the printing position of the scanning line corresponding to each color.
[0128]
In the third embodiment, as shown in FIG. 17B, an optical scanning device that simultaneously optically scans four light beams with respect to one polygon mirror 5 using two scanning optical systems 61 and 62 is provided. , 62 B are reflected downward by the first or second return mirrors 7 a, 7 d at positions close to the scanning optical elements 61, 62, and are further returned to the third or third position. The light is reflected toward the photosensitive drum surfaces 8a and 8c by the fourth folding mirrors 7c and 7f. Further, the deflected light beams BMb and BMd incident below the sagittal optical axes of the scanning optical elements 61 and 62 are separated from the scanning optical elements 61 and 62 by the fifth or sixth return mirrors 7b and 7e at the photoconductor. The light is reflected toward the drum surfaces 8b and 8d.
[0129]
As described above, the folding mirror is arranged substantially symmetrically with respect to the rotation axis of the polygon mirror, thereby providing a compact optical scanning device with a simple configuration.
[0130]
In general, when the folding mirrors are arranged symmetrically with respect to the rotation axis of the polygon mirror 5 as in the third embodiment, the direction of the bending of the scanning line optically scanned on each photosensitive drum surface is reversed, and the scanning line is changed. If an optical scanning device having a large bend is used, the problem of color misregistration may be noticeable. Further, the arrangement of the folding mirror is reversed from that of the present embodiment, and the deflected light beam incident below the sagittal optical axis of the second scanning optical element 62 is guided to the photosensitive drum surface 8 by using an even number of folding mirrors. When the light flux incident above the sagittal optical axis is guided on the photosensitive drum surface 8 by using an odd number of folding mirrors, the direction of the scanning line bending can be aligned, but the routing of the optical path is complicated. Therefore, there is a possibility that the configuration becomes complicated due to an increase in the size of the optical scanning device and the number of folding mirrors.
[0131]
Therefore, in the third embodiment, the sagittal shape of the exit surface 6b of the first scanning optical system 61 and the second scanning optical system 62 is a non-circular arc (aspheric surface), and the optical axis La of the exit surface 6b is further along the generatrix direction. The amount of the sagittal aspherical surface, which changes as the distance from the surface increases, is employed to minimize the scan line bending. Thus, there is provided an optical scanning device which can always obtain a high-quality color image without causing a color shift problem even if a method of arranging an optical path in which the direction of the scanning line bending is reversed (or the arrangement of the folding mirror) is used. be able to.
[0132]
In the third embodiment, the number of the scanning optical elements constituting the scanning optical system is one. However, the number is not limited to one, and the effect of the present invention can be sufficiently obtained even with a plurality of scanning optical elements. Of course, the sagittal aspherical surface variation surface may be employed for the scanning optical element having power only in the sub-scanning direction.
[0133]
In the third embodiment, one light beam is optically scanned on the photosensitive drum surface for each color. However, the light beam is not limited to one light beam. For example, eight light beams are simultaneously reflected and deflected by a polygon mirror, and two light beams are reflected. The same effects as those of the present invention can also be obtained in an optical scanning device in which four light beams are incident on each of the scanning optical systems, and two light beams are guided to each photosensitive drum to perform optical scanning.
[0134]
[Image forming apparatus]
FIG. 18 is a cross-sectional view of a main part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In FIG. 18, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by the printer controller 111 in the apparatus. This image data Di is input to the optical scanning unit 100 having the configuration shown in the first and second embodiments. The optical scanning unit 100 emits a light beam 103 modulated according to the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.
[0135]
The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning unit 100.
[0136]
As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is developed as a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 on the downstream side in the rotation direction of the photosensitive drum 101 from the irradiation position of the light beam 103.
[0137]
The toner image developed by the developing device 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (right side in FIG. 18), but can be fed manually. A paper feed roller 110 is provided at an end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 to a transport path.
[0138]
As described above, the sheet 112 onto which the unfixed toner image has been transferred is further conveyed to the fixing device behind the photosensitive drum 101 (left side in FIG. 18). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113, and the paper conveyed from the transfer unit. The unfixed toner image on the sheet 112 is fixed by heating the sheet 112 while pressing it at a pressure contact portion between the fixing roller 113 and the pressure roller 114. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and discharges the fixed paper 112 to the outside of the image forming apparatus.
[0139]
Although not shown in FIG. 18, the print controller 111 controls not only the above-described data conversion but also controls the motor 115 and other components in the image forming apparatus, a polygon motor in an optical scanning unit described later, and the like. I do.
[0140]
[Color image forming apparatus]
FIG. 19 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which four optical scanning devices are arranged and image information is recorded in parallel on the surface of a photosensitive drum as an image carrier. In FIG. 19, reference numeral 60 denotes a color image forming apparatus; 11, 12, 13, and 14 denote optical scanning apparatuses each having any of the configurations shown in the first and second embodiments; , Photosensitive drums 31, 32, 33, and 34 are developing devices, and 51 is a transport belt.
[0141]
In FIG. 19, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from an external device 52 such as a personal computer. These color signals are converted into respective image data (dot data) of C (cyan), M (magenta), Y (yellow), and B (black) by a printer controller 53 in the apparatus. These image data are input to the optical scanning devices 11, 12, 13, and 14, respectively. From these optical scanning devices, light beams 41, 42, 43, and 44 modulated in accordance with the respective image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are irradiated with these light beams. Scanning is performed in the main scanning direction.
[0142]
The color image forming apparatus according to the present embodiment includes four optical scanning devices (11, 12, 13, 14), each of which has a color of C (cyan), M (magenta), Y (yellow), and B (black). Correspondingly, an image signal (image information) is recorded on the photosensitive drums 21, 22, 23, and 24 in parallel, and a color image is printed at a high speed.
[0143]
As described above, the color image forming apparatus in this embodiment converts the latent images of each color into the corresponding photosensitive drums 21 and 22 by using the light beams based on the respective image data by the four optical scanning devices 11, 12, 13 and 14. , 23 and 24. Thereafter, multiple transfer to a recording material is performed to form one full color image.
[0144]
As the external device 52, for example, a color image reading device having a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.
[0145]
【The invention's effect】
According to the present invention, as described above, at least one surface of the scanning optical element constituting the scanning optical system uses the sagittal aspherical amount changing surface in which the sagittal amount of the sagittal changes along the generatrix direction. An optical scanning device capable of reducing bending and an image forming apparatus using the same can be achieved.
[0146]
When the optical scanning device is mounted on a color image forming apparatus using a plurality of optical scanning devices, the number of folding mirrors can be reduced by improving the degree of freedom of the arrangement of the folding mirrors and the arrangement of the optical path, and a simple configuration and A compact color image forming apparatus with less color shift can be achieved.
[Brief description of the drawings]
1A is a main scanning cross-sectional view according to the first embodiment of the present invention. FIG. 1B is a sub-scanning cross-sectional view according to the first embodiment of the present invention. FIG. 3 shows the amount of sagittal aspherical surface in Embodiment 1 of the present invention. FIG. 4 shows the amount of sagittal aspherical surface in Embodiment 1 of the present invention. FIG. 5 shows the amount of sagittal aspherical surface in Embodiment 1 of the present invention. FIG. 7 is a conceptual diagram of a surface according to the first embodiment of the present invention. FIG. 7 is a diagram showing a change in the amount of sagittal aspherical surface of the surface according to the first embodiment of the present invention. FIG. 9 is a diagram showing a change in the amount of line aspherical surface. FIG. 9 is an aberration diagram in the first embodiment of the present invention. FIG. 10 is an irradiation position and a scanning line curve in the first embodiment of the present invention. FIG. 12 is a view for explaining a bus shape in FIG. 12; FIG. 13 is a sagittal aspherical amount according to the second embodiment of the present invention. FIG. 14 is a sagittal aspherical amount according to the second embodiment of the present invention. FIG. 15 is a sagittal non-spherical amount according to the second embodiment of the present invention. Spherical quantity [FIG. 16] Irradiation position and scanning line bending in Embodiment 2 of the present invention [FIG. 17A] Main scanning cross-sectional view in Embodiment 3 of the present invention [FIG. 17B] Sub-scanning cross-sectional view in Embodiment 3 of the present invention FIG. 18 is a schematic diagram of a main part of the image forming apparatus of the present invention.
FIG. 19 is a schematic view of a main part of a color image forming apparatus of the present invention. FIG. 20 is a perspective view of a conventional optical scanning device.
DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Aperture stop 4 Cylindrical lens 5 Deflection means (polygon mirror)
6. Scanning optical system (scanning optical element)
8 Scanned surface (photosensitive drum surface)
1a, 1b, 1c, 1d Light source means 2a, 2b, 2c, 2d Collimator lens 3a, 3b, 3c, 3d Aperture stop 4a, 4b Cylindrical lens 61, 62 Scanning optical system (scanning optical element)
8a, 8b, 8c, 8d Scanned surface (photosensitive drum surface)
11, 12, 13, 14 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developing device 51 Conveyor belt 52 External device 53 Printer controller 60 Color image forming device 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 107 Developing device 108 Transfer roller 109 Paper cassette 110 Paper feed roller 111 Printer controller 112 Transfer material (paper)
113 Fixing roller 114 Pressure roller 115 Motor 116 Discharge roller 117 External device

Claims (15)

A light source unit, a deflecting unit that deflects the light beam emitted from the light source unit, and a scanning optical system that forms an image of the deflected light beam deflected by the deflecting unit on a surface to be scanned.
The scanning optical system includes a scanning optical element arranged so that a principal ray of the deflected light beam passes other than the optical axis in the sub-scanning direction, and the scanning optical element has an aspherical amount of a sagittal line of the scanning optical element. An optical scanning device including a sagittal aspherical surface amount changing surface that changes along the main scanning direction, wherein the positions in the sub-scanning direction where the deflecting light beams reach over the entire surface to be scanned are aligned. . 2. The scanning optical system according to claim 1, wherein a deviation amount of a position in the sub-scanning direction where the deflected light beam reaches within an effective scanning range on the surface to be scanned is suppressed to 10 μm or less. An optical scanning device according to claim 1. The optical scanning device according to claim 1, wherein the light beam emitted from the light source unit is incident at a certain angle with respect to a plane perpendicular to a rotation axis of the deflecting unit. In the sub-scanning direction, the position at which the principal ray of the deflected light beam reaches the surface to be scanned is smaller than the position at which the principal ray passes through the surface of the scanning optical element having the highest power. 4. The optical scanning device according to claim 1, wherein the optical scanning device is close to the optical axis. 5. The scanning optical system according to claim 1, wherein the scanning optical system has at least one sagittal curvature radius changing surface in which the sagittal curvature changes along the main scanning direction of the scanning optical system. Item 2. The optical scanning device according to item 1. The optical scanning device according to any one of claims 1 to 5, wherein the scanning optical system includes one scanning optical element. The optical scanning device according to claim 1, wherein a power of the scanning optical system in a sub-scanning direction is equal to or approximately equal to a power of the sagittal aspherical surface variation surface. When the power of the scanning optical system in the sub-scanning direction is φso and the power of the sagittal aspherical surface variation surface in the sub-scanning direction is φsi,
0.9 × φso ≦ φsi ≦ 1.1 × φso
The optical scanning device according to claim 7, wherein the following condition is satisfied. The light source unit emits two or more light beams, and a main ray of at least one light beam passes above the optical axis of the scanning optical system in the sub-scanning cross section, and another at least one light beam is emitted. The optical scanning device according to claim 1, wherein the principal ray passes below the optical axis of the scanning optical system. The deflecting unit deflects a plurality of light beams, and the scanning optical system forms a plurality of scanning optical elements that form an image of the plurality of light beams deflected by the deflecting unit on a plurality of scan surfaces corresponding to each of the light beams. The optical scanning device according to claim 1, wherein the deflection unit is shared by a plurality of scanning optical systems. In the main scanning section, the air-equivalent distance from the deflecting means to the light emitting surface of the scanning optical element on the optical axis is P1, the distance from the light emitting surface of the scanning optical element to the surface to be scanned is P2, and off-axis. Where M1 is the air-equivalent distance from the deflecting means to the light emission surface of the scanning optical element, and M2 is the distance from the light emission surface of the scanning optical element to the surface to be scanned.

The optical scanning device according to any one of claims 1 to 10, wherein the following condition is satisfied. An optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and an electrostatic member formed on the photosensitive member by a light beam scanned by the optical scanning device. A developing device for developing the latent image as a toner image, a transfer device for transferring the developed toner image to a transfer material, and a fixing device for fixing the transferred toner image to the transfer material. Image forming apparatus. 12. An image, comprising: the optical scanning device according to claim 1; and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. Forming equipment. A color image forming apparatus comprising: at least one optical scanning device according to any one of claims 1 to 11; and a plurality of image carriers each forming an image of a different color. 15. The color image forming apparatus according to claim 14, further comprising a printer controller for converting a color signal input from an external device into image data of a different color and inputting the data to each optical scanning device.

Images