JP4227404B2 - Scanning optical device and image forming apparatus using the same - Google Patents

Description

【００２３】
（但し、Rは曲率半径、K、B₄、B₆、B₈、B₁₀は非球面係数）
副走査方向（光軸を含み主走査方向に対して直交する方向）と対応する子線方向が、
【００２４】
【数２】

【００２５】
ここで ｒ'＝ｒ₀（１＋Ｄ₂Y²＋Ｄ₄Y⁴＋Ｄ₆Y⁶＋Ｄ₈Y⁸＋Ｄ₁₀Y¹⁰）
（但し、ｒ₀は光軸上の子線曲率半径、Ｄ₂、Ｄ₄、Ｄ₆、Ｄ₈、Ｄ₁₀は係数）
Ｓは母線方向の各々の位置における母線の法線を含み主走査断面と垂直な面内に定義される子線形状である。
【００２６】
さらに子線方向の非球面成分として、
Ｘ＝E₂₁YZ²＋（E₄₀＋E₄₁Y＋E₄₂Y²＋E₄₄Y⁴＋E₄₆Y⁶）Z⁴
なる値を付加した面である。
【００２７】
尚、本表現式では面形状表現式における次数を制限して記してあるが、本発明の権利の範囲はこれを制限するものではなく、次数を上げるほど設計自由度が増し、収差が少なくなることは言うまでも無い。また面形状表現式自体も同等の面表現自由度を有した表現式であれば、問題無く本発明の効果を得ることが可能である。
【００２８】
ここで偏向素子であるポリゴンミラーの面偏心による副走査方向の照射位置変動を考察する。
【００２９】
まず簡単のため光束がポリゴンミラーの回転軸を含み偏向走査面に直交する面に対して角度を有さず入射する場合について説明する。
【００３０】
図３はポリゴンミラーから被走査面までの副走査断面図である。同図において偏向面５ａ上の点Ａと被走査面８上の点Ａ’は光学的に完全共役であり、シリンドリカルレンズ(不図示)による線像は点Ａ上に結像するとともに、走査光学系６により点Ａ’に再結像している。もし偏向面が点線で示したように偏心量Ｈだけ偏心したとき、点Ａ上にある線像は点Ｂに虚像として移る。この虚像Ｂの光学的な共役点は点Ｂ’であり、偏心時の光束は点Ｂを通り被走査面８上に到達し、副走査方向の照射位置変動を生じる。ここで照射位置ずれ量（照射位置変動量）ｄＺはポリゴンミラー５の偏向面５ａに入射する光束の斜入射角をα、走査光学系６の副走査方向の倍率（副走査倍率）をβsとするとき、
ｄＺ＝２Ｈ｜βs｜α …(1)
で表される。
【００３１】
次に光束がポリゴンミラーの回転軸を含み偏向走査面に直交する面に対して角度を有して入射する場合の説明を行う。
【００３２】
図４（Ａ），（Ｂ）は各々ポリゴンミラーの偏向面近傍の主走査断面図であり、同図（Ａ）が光源手段側（第２光学系から出射した光束は主走査断面内において該走査光学系の光軸に対し角度を有して該ポリゴンミラーの偏光面に入射する側）の像高への偏向、同図（Ｂ）が反光源手段側の像高への偏向を示している。この場合、面偏心により生じる線像と虚像間の距離が上記(1)式の２Ｈではなく、以下のようにポリゴンミラー５への入射角θi、ポリゴンミラー５からの偏向角θe（共に走査光学系の光軸方向を０度とした座標系）の関数で表されることになる。
【００３３】

従って、走査光学系６の副走査倍率βs、斜入射角αが一定の場合、照射位置変動量ｄＺは偏向角依存性を有する。この偏向角依存性は図４における線像と虚像間の距離、及び上記(2)式から明らかなように光源手段側の軸外に向け偏向される場合、つまりポリゴンミラー５への入射角θi、ポリゴンミラー５からの偏向角θeが同符号のときに大きくなり、光源手段側の最軸外に向け偏向されるときに最大となる。
【００３４】
図１６は比較例におけるポリゴンミラーの面偏心、面倒れによる照射位置変動を示す図である。図１６において点線は比較例としてβs＝-2.28、α＝1.8度、Ｈ＝30μｍの条件下におけるポリゴンミラーの面偏心による照射位置変動量ｄＺの偏向角依存性を示す。同図より照射位置変動量ｄＺは入射角θiによらず光源手段側の最軸外(Y=105mm)において最大値をとることが分かる。
【００３５】
次にポリゴンミラーの面倒れによる副走査方向の照射位置変動を考察する。面倒れにおいても面偏心の場合と同様、その照射位置変動量ｄＺに偏向角依存性を有する。
【００３６】
一般的に副走査断面内の像面湾曲はほぼ補正されているため、シリンドリカルレンズによる線像と被走査面上の各ポイントは偏向角によらず副走査断面内において光学的に共役関係となっている。従って線像位置において光束が偏向されれば偏向面と被走査面とが共役関係となり、面倒れが生じても照射位置変動は発生しない（以下このような像高を「副走査完全共役像高」と呼ぶ。）。
【００３７】
しかしながらほとんどの偏向角においてはポリゴンミラーの回転による偏向面の出入りにより、偏向面と線像の位置にずれを生じるため、偏向面と被走査面との共役関係にずれが生じ、照射位置変動を生じる。
【００３８】
尚、面倒れによる照射位置変動は設計時にシリンドリカルレンズの線像をどの位置に置くか、つまり被走査面との共役点をどの位置におき走査光学系の副走査方向のパワーを決定するのかで決まるため、面偏心の場合と異なり、その照射位置変動量の偏向角依存性や面倒れを発生しても照射位置変動を生じない副走査完全共役像高を自由に設定することが可能である。
【００３９】
また副走査断面内の像面湾曲がほぼ補正されている場合、ポリゴンミラーの配置により画像有効域の１点もしくは２点が副走査断面内において完全共役点となり得る。
【００４０】
図１６において一点鎖線は比較例におけるポリゴンミラーの面倒れによる照射位置変動量ｄＺの偏向角依存性を示す。偏向面の出入りは軸上近傍と最軸外近傍で最も大きくなるため、同位置付近で照射位置変動量は最も大きくなり、通常はそれらが振り分けとなるよう副走査完全共役像高を設定し、走査光学系の副走査方向のパワーが決定される。比較例では副走査完全共役像高を最大像高の６割付近に設定することにより、軸上と最軸外の像高付近の照射位置変動のバランスを取っている。
【００４１】
図１６において実線は比較例におけるポリゴンミラーの面偏心と面倒れによる照射位置変動量のそれぞれの絶対値の総和である（面倒れ方向、面偏心方向とも＋−両方向あるため、照射位置変動量の総和はそれぞれの値の絶対値をとった後、加算している。）。このように面偏心による照射位置変動量は必ず光源手段側の最軸外(Y=105mm)で最大値をとるため、従来の手法で面倒れ設計を行った場合、面偏心、面倒れトータルの照射位置変動量も同位置において最大となることが分かる。
【００４２】
以上の考察から画像有効全域において面偏心および面倒れによる照射位置変動を最も低減するには、ポリゴンミラーの偏向面に面倒れが発生したときに被走査面上において照射位置変動を生じない像高のうち最も光源手段側の像高（副走査完全共役像高）をＹ_m∞、該被走査面上における最大像高をＬ（符号正）としたとき、
０．７Ｌ＜Ｙ_m∞≦１．０Ｌ …(3)（像高の符号は光源手段側が正）
より望ましくは、
０．７５Ｌ＜Ｙ_m∞≦０．９５Ｌ …(3a)（像高の符号は光源側が正）
となるよう走査光学系の副走査方向のパワーを設定している。これにより面偏心による照射位置変動の大きい光源手段側の最軸外近傍における倒れ補正効果を向上させることができる。
【００４３】
本実施形態では副走査完全共役像高Ｙ_m∞を光源手段１側の最大像高Ｌの８割の像高位置（Ｙ_m∞＝84mm＝0.8Ｌ）になるよう、シリンドリカルレンズ４による線像位置を同像高に向かう光束の偏向点近傍に配置し、光源手段１側の８割の像高Ｙ_m∞に向かう光束の偏向面５ａと被走査面８とが副走査断面内において共役関係となるよう走査光学系６の副走査方向のパワーを設定している。
【００４４】
表−１は本実施形態における走査光学装置の設計値であり、図５は同走査光学装置におけるポリゴンミラーの面偏心、面倒れによる照射位置変動を示す図である。尚、図５はポリゴンミラーの公差を面偏心３０μｍ、面倒れ２’と仮定し計算されている。
【００４５】
図５より面偏心による照射位置変動の大きい光源手段側の最軸外近傍における倒れ補正効果を向上させることにより、ポリゴンミラーの偏向面の面倒れによる照射位置変動量の絶対値と、該ポリゴンミラーの偏向面の面偏心による照射位置変動量の絶対値との総和が、被走査面上の軸上像高(Y=0mm)での値と、光源手段側の最軸外像高(Y=105mm)での値と略等しくしており、比較例と比べ最も照射位置変動の大きい像高における変動量が低減していることが読み取れる。
【００４６】
【表１】

【００４７】
尚、ポリゴンミラーの面偏心、面倒れによるトータルの照射位置変動量ｄＺは被走査面上の画像有効全域において５μｍを越えると視覚的にピッチむらとして認識され易くなるため、５μｍ以下に抑えることが望ましい。特に面偏心による照射位置変動量ｄＺは上記(2)式より一義的に決定されるため、同数式内に含まれるパラメータである走査光学系の副走査方向の結像倍率（副走査倍率）βsを、
｜βs｜＜２．５
を満足するよう光学配置を決定する必要がある。本実施形態における走査光学系の副走査倍率は
βs＝−２．２８
であり、図５に示すように画像有効全域において照射位置変動量ｄＺを５μｍ以下に抑えている。
【００４８】
［画像形成装置］
図１２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。
【００４９】
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。
【００５０】
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。
【００５１】
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１２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。
【００５２】
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１２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。
【００５３】
図１２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。
【００５４】
このように本実施形態では上記の如く走査光学系６の副走査方向のパワー及び共役関係を適切な値に設定することにより、光源手段１側の最軸外位置近傍におけるポリゴンミラー５の面倒れによる照射位置変動量を低減し、ポリゴンミラー５の面偏心と面倒れによる照射位置変動量の総和を低減している。これにより画像有効全域においてピッチむらの少ない一様性の高い高品位な画像を得ることができる走査光学装置及びそれを用いた画像形成装置を実現している。
【００５５】
［実施形態２］
図６は本発明の走査光学装置の実施形態２の主走査断面図、図７は図６の副走査断面図である。図６、図７において前記図１、図２に示した要素と同一要素には同符番を付している。
【００５６】
本実施形態において前述の実施形態１と異なる点は、副走査完全共役像高Ｙ_m∞を実施形態１と比較し、さらに最軸外寄りに設定した点、走査光学装置を複数の光束を複数の異なる被走査面に同時に走査するタンデム型の走査光学装置にした点、それをカラー画像形成装置に搭載した点であり、その他の構成及び光学的作用は実施形態１と略同様であり、これにより同様な効果を得ている。
【００５７】
即ち、本実施形態はポリゴンミラー５を挟み走査光学素子を２つを備え、更に夫々の走査光学素子１４，１５へ２本の光束を入射させて１つのポリゴンミラー５により同時に４本の光束を反射偏向し、夫々に対応した感光ドラム面8a,8b,8c,8d上を光走査させたタンデム型の走査光学装置である。
【００５８】
図中、Ｓ１，Ｓ２は各々第１、第２のステーション（走査ユニット）であり、ポリゴンミラー５を挟み対向配置されている。１２は光源手段であり、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から成る。４つの半導体レーザー1a,1b,1c,1dから出射した４本の発散光束は夫々に対応したコリメーターレンズ2a,2b,2c,2dにより略平行光束に変換され、夫々に対応した開口絞り3a,3b,3c,3dによって光束幅が制限される。開口絞り3a,3bを通過した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４ａにより、ポリゴンミラー５の偏向面５ａ近傍に主走査方向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、ポリゴンミラー５の偏向面５ｂ近傍に主走査方向に長手の線像として結像される。
【００５９】
５は偏向素子としての光偏向器であり、例えば４面構成のポリゴンミラー（回転多面鏡）から成り、モータ等の駆動手段(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。
【００６０】
１４，１５は各々集光機能とｆθ特性とを有する第１、第２の走査光学系（ｆθレンズ系）であり、主走査方向と副走査方向とに異なる屈折力を有するプラスチック樹脂製の単一のトーリックレンズ（走査光学素子）より成り、ポリゴンミラー５によって反射偏向された画像情報に基づく２本の光束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、かつ副走査断面内においてポリゴンミラー５の偏向面５ａ、５ｂと感光ドラム面8a,8b,8c,8dとの間を共役関係にすることにより、倒れ補正機能を有している。
【００６１】
ポリゴンミラー５の偏向面５ａ、５ｂで反射偏向された４本の光束は第１の走査光学系１４もしくは第２の走査光学系１５を介して夫々の光束に対応した感光体ドラム面8a,8b,8c,8d上に導光され、該ポリゴンミラー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。
【００６２】
表−２は本実施形態における走査光学装置の設計値である。本実施形態では副走査完全共役像高Ｙ_m∞を光源手段１２側の最大像高の9.5割の像高位置（Ｙ_m∞＝100mm＝0.95Ｌ）になるよう、シリンドリカルレンズ４による線像位置を同像高に向かう光束の偏向点近傍に配置し、光源手段１２側の9.5割の像高Ｙ_m∞に向かう光束の偏向面５ａ，５ｂと感光ドラム面8a,8b,8c,8dとが副走査断面内において共役関係となるよう第１、第２の走査光学系１４，１５の副走査方向のパワーを設定している。
【００６３】
【表２】

【００６４】
本実施形態において副走査完全共役像高Ｙ_m∞を実施形態１と比較してより最軸外寄りに設定したのは、走査光学素子の製造公差による副走査断面内の共役関係のずれが光軸上より最軸外近傍が大きいことに留意し、最軸外近傍における面倒れ補正効果をあらかじめ向上させておくことにより、同位置における許容公差を緩める狙いがあるからである。
【００６５】
図８は同走査光学装置におけるポリゴンミラーの面偏心、面倒れによる照射位置変動を示す図である。尚、図８はポリゴンミラーの公差を面偏心３０μｍ、面倒れ２’と仮定し計算されている。
【００６６】
図８より面偏心による照射位置変動の大きい光源手段側の最軸外近傍における倒れ補正効果を向上させることにより、面偏心、面倒れトータルの照射位置変動量が画像全域において低減していることが読み取れる。
【００６７】
［カラー画像形成装置］
図１３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、走査光学装置により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１３において、６０はカラー画像形成装置、１１は実施形態２に示した走査光学装置、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。
【００６８】
同図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、それぞれ走査光学装置１１に入力される。そして走査光学装置１１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。
【００６９】
本実施態様におけるカラー画像形成装置は１つの走査光学装置１１からＣ（シアン），Ｍ（マゼンタ），Ｙ（イエロー）、Ｂ（ブラック）の各色に対応した光束を射出し、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。
【００７０】
本実施態様におけるカラー画像形成装置は上述の如く１つの走査光学装置１１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。
【００７１】
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。
【００７２】
このように本実施形態では上記の如くタンデム型の走査光学装置においても実施形態１と同様に第１、第２の走査光学系１４、１５の副走査方向のパワー及び共役関係を適切な値に設定することにより、光源手段１２側の最軸外位置近傍におけるポリゴンミラー５の面倒れによる照射位置変動量を低減し、該ポリゴンミラー５の面偏心と面倒れによる照射位置変動量の総和を低減している。これにより画像有効全域においてピッチむらの少ない一様性の高い高品位な画像を得ることができるタンデム型の走査光学装置及びそれを用いたカラー画像形成装置を実現している。
【００７３】
尚、カラー画像形成装置としては上記の構成に限らず、例えば図１４に示すカラー画像形成装置においても本発明は適用することができる。
【００７４】
［カラー画像形成装置］
即ち、図１４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、実施形態１に示した走査光学装置を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１４において、２６０はカラー画像形成装置、２１１，２１２，２１３，２１４は各々実施形態１に示した走査光学装置、２２１，２２２，２２３，２２４は各々像担持体としての感光ドラム、２３１，２３２，２３３，２３４は各々現像器、２５１は搬送ベルトである。
【００７５】
図１４において、カラー画像形成装置２６０には、パーソナルコンピュータ等の外部機器２５２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２５３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、それぞれ走査光学装置２１１，２１２，２１３，２１４に入力される。そして、これらの走査光学装置からは、各画像データに応じて変調された光ビーム２４１，２４２，２４３，２４４が出射され、これらの光ビームによって感光ドラム２２１，２２２，２２３，２２４の感光面が主走査方向に走査される。
【００７６】
本実施態様におけるカラー画像形成装置は走査光学装置（２１１，２１２，２１３，２１４）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２２１，２２２，２２３，２２４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。
【００７７】
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つの走査光学装置２１１，２１２，２１３，２１４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２２１，２２２，２２３，２２４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。
【００７８】
前記外部機器２５２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２６０とで、カラーデジタル複写機が構成される。
【００７９】
［実施形態３］
図９は本発明の走査光学装置の実施形態３の主走査断面図、図１０は図９の副走査断面図である。図９、図１０において前記図１、図２に示した要素と同一要素には同符番を付している。
【００８０】
本実施形態において前述の実施形態１と異なる点は、副走査完全共役像高Ｙ_m∞を変更した点、走査光学系１６を第１、第２の２枚の光学素子６１，６２から構成した点、光源手段１３にマルチビーム半導体レーザーを用いた点であり、その他の構成及び光学的作用は実施形態１と略同様であり、これにより同様な効果を得ている。
【００８１】
即ち、同図において１３は光源手段であり、独立に変調可能な複数の発光点を有するマルチビーム半導体レーザーより成っている。１６は集光機能とｆθ特性とを有する走査光学系としての走査レンズ系であり、主走査方向と副走査方向とに異なる屈折力を有するプラスチック樹脂製の第１、第２の２枚のトーリックレンズ６１，６２より成り、ポリゴンミラー５によって反射偏向された画像情報に基づく複数の光束を被走査面としての感光ドラム面８上に結像させ、かつ副走査断面内においてポリゴンミラー５の偏向面５ａと感光ドラム面８との間を共役関係にすることにより、倒れ補正機能を有している。
【００８２】
表−３は本実施形態における走査光学装置の設計値である。本実施形態では副走査完全共役像高Ｙ_m∞を光源手段１３側の最大像高の９割の像高位置（Ｙ_m∞＝95mm＝0.9Ｌ）になるよう、シリンドリカルレンズ４による線像位置を同像高に向かう光束の偏向点近傍に配置し、光源手段１３側の９割の像高Ｙ_m∞に向かう光束の偏向面５ａと被走査面８とが副走査断面内において共役関係となるよう走査光学系１６の副走査方向のパワーを設定している。
【００８３】
【表３】

【００８４】
図１１は走査光学装置におけるポリゴンミラーの面偏心、面倒れによる照射位置変動を示す図である。尚、図１１はポリゴンミラーの公差を面偏心３０μｍ、面倒れ２’と仮定し計算されている。
【００８５】
図１１より面偏心による照射位置変動の大きい光源手段側の最軸外近傍における倒れ補正効果を向上させることにより、面偏心、面倒れトータルの照射位置変動量が軸上近傍と最軸外とで略等しくしており、光源手段側の最軸外像高における照射位置変動量が低減していることが読み取れる。
【００８６】
このように本実施形態においても前述の実施形態１と同様、走査光学系１６の副走査方向のパワー及び共役関係を適切な値に設定することにより、光源手段１３側の最軸外位置近傍におけるポリゴンミラー５の面倒れによる照射位置変動量を低減し、ポリゴンミラー５の面偏心と面倒れによる照射位置変動量の総和を低減している。これにより画像有効全域においてピッチむらの少ない一様性の高い高品位な画像を得ることができる走査光学装置及びそれを用いた画像形成装置を実現している。
【００８７】
［本発明の実施態様］
本発明の様々な例と実施形態が示され説明されたが、当業者であれば、本発明の趣旨と範囲は本明細書内の特定の説明と図に限定されるのではなく、本願特許請求の範囲に全て述べられた様々の修正と変更に及ぶことが理解されるであろう。
【０１０７】
【発明の効果】
本発明によれば前述の如く光源手段から出射した光束を偏向走査面および偏向素子の回転軸を含み偏向走査面に直交する面に対しそれぞれ角度を有して偏向素子に入射させ、さらに偏向素子に面倒れが発生したときに被走査面上において照射位置変動を生じない像高のうち最も光源手段側の像高Ｙ_m∞を適当な範囲内に入れるよう走査光学系の副走査方向のパワーを設定することにより、光源手段側の最軸外位置近傍における偏向素子の面倒れによる照射位置変動量を低減し、偏向素子の面偏心と面倒れによる照射位置変動量の絶対値の総和を低減し、これにより画像有効全域においてピッチむらの少ない一様性の高い高品位な画像を得ることができる走査光学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。
【図面の簡単な説明】
【図１】 本発明の実施形態１の主走査断面図
【図２】 本発明の実施形態１の副走査断面図
【図３】 本発明の実施形態１の偏向素子から被走査面までの副走査断面図
【図４】 偏向面近傍の主走査断面図であり、（Ａ）が光源側像高への偏向、（Ｂ）が反光源側像高への偏向を示す図
【図５】 本発明の実施形態１における偏向素子の面偏心、面倒れによる照射位置変動を示す図
【図６】 本発明の実施形態２の主走査断面図
【図７】 本発明の実施形態２の副走査断面図
【図８】 本発明の実施形態２における偏向素子の面偏心、面倒れによる照射位置変動を示す図。
【図９】 本発明の実施形態３の主走査断面図
【図１０】 本発明の実施形態３の副走査断面図
【図１１】 本発明の実施形態３における偏向素子の面偏心、面倒れによる照射位置変動を示す図
【図１２】 本発明の画像形成装置の実施形態を示す副走査断面図
【図１３】 本発明の実施態様のカラー画像形成装置の要部概略図
【図１４】 本発明の実施態様のカラー画像形成装置の要部概略図
【図１５】 従来の走査光学装置の要部概略図
【図１６】 比較例における偏向素子の面偏心、面倒れによる照射位置変動を示す図
【符号の説明】
１ 光源手段
２ 第１光学系（コリメーターレンズ）
３ 絞り
４ 第２光学系（シリンドリカルレンズ）
５ 偏向素子（ポリゴンミラー）
６ 走査光学系
８ 被走査面
１１ 走査光学装置
２１、２２、２３、２４ 像担持体（感光ドラム）
３１、３２、３３、３４ 現像器
６０ カラー画像形成装置
５１ 搬送ベルト
５２ 外部機器
５３ プリンタコントローラ
４１，４２，４３，４４ レーザー光束
１００ 走査光学装置
１０１ 感光ドラム
１０２ 帯電ローラ
１０３ 光ビーム
１０４ 画像形成装置
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]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning optical apparatus and an image forming apparatus using the same, and in particular, a light beam emitted from a light source means is reflected and deflected by a polygon mirror as a deflecting element, and is scanned on a surface to be scanned via a scanning optical system having fθ characteristics. For example, it is suitable for an image forming apparatus such as a laser beam printer having an electrophotographic process, a digital copying machine, or a multi-function printer (multi-function printer), which records image information by optical scanning.
[0002]
[Prior art]
Conventionally, in a scanning optical device such as a laser beam printer, a light beam modulated and emitted from a light source unit according to an image signal is periodically deflected by an optical deflector composed of, for example, a polygon mirror (rotating polygon mirror), and fθ characteristics are obtained. Is converged in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by a scanning optical system, and image recording is performed by optically scanning the surface of the recording medium.
[0003]
FIG. 15 is a schematic view of the main part of a conventional scanning optical apparatus. In the same figure, the divergent light beam emitted from the light source means 91 is made into a substantially parallel light beam (or convergent light beam) by the collimator lens 92, and the light beam (light amount) is shaped by the aperture stop 93 and has refractive power only in the sub-scanning direction. It is incident on the cylindrical lens 94. Out of the light beam incident on the cylindrical lens 94, it exits as it is in the main scanning section, converges in the sub-scanning section, and converges in the vicinity of the deflecting surface 95a of the optical deflector 95 composed of a polygon mirror. I image.
[0004]
Then, the light beam reflected and deflected by the deflecting surface 95a of the optical deflector 95 is guided to a photosensitive drum surface 98 as a surface to be scanned through a scanning optical system (fθ lens system) 96 having fθ characteristics, and the light deflection is performed. By rotating the device 95 in the arrow A direction, the photosensitive drum surface 98 is optically scanned in the arrow B direction (main scanning direction) to record image information.
[0005]
A tandem scanning optical apparatus used in a color image forming apparatus has a plurality of light source means and makes a light beam incident on one or a plurality of optical deflectors (deflection elements). The plurality of light beams incident at this time have an angle with respect to the deflection scanning plane (main scanning section) and the plane (sub-scanning section) perpendicular to the deflection scanning plane including the optical axis of the optical deflector. After passing through a plurality of scanning optical elements, light beams are separated by a mirror or the like, and a plurality of different scanned surfaces are scanned with a plurality of light spots. There is also a method of arranging a plurality of scanning optical devices shown in FIG. 15 and scanning a plurality of scanned surfaces.
[0006]
[Problems to be solved by the invention]
Conventionally, in a scanning optical device, surface tilt correction is performed to reduce irradiation position deviation (pitch unevenness) in the sub-scanning direction on the surface to be scanned due to surface tilt of each deflecting surface (reflection surface) of the optical deflector. Yes. This is because the light beam emitted from the light source means in the sub-scan section is temporarily imaged in the vicinity of the deflecting surface of the optical deflector by the cylindrical lens and re-imaged on the surface to be scanned by the scanning optical system. In this, the vicinity of the deflecting surface of the optical deflector and the surface to be scanned are optically conjugate.
[0007]
However, when a polygon mirror is used as the optical deflector, the rotation axis and the deflection surface are separated from each other, so that the deflection point differs depending on the deflection direction, and it is difficult to make an optically complete conjugate relationship at all image heights. It is. Therefore, even if surface tilt occurs at a certain image height, the irradiation position does not change on the scanned surface.However, if surface tilt occurs at a certain image height, the irradiation position on the scanned surface may be lost due to the loss of conjugate relation. There was a problem that the image fluctuated and the uniformity of the image deteriorated.
[0008]
On the other hand, in the so-called oblique incidence scanning optical device in which the light beam from the light source means is incident on the optical deflector at an angle with respect to the deflection scanning surface, the surface eccentricity (each center of rotation from the center of rotation) The irradiation position shift in the sub-scanning direction also occurs due to the difference in the distance to the deflection surface. In particular, a scanning optical device is arranged on each of four photoconductors, and a latent image is formed by laser light. Documents of respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black) are used. In the case of a tandem type scanning optical device used in a color image forming apparatus that forms images of the respective images on the corresponding photoreceptor surface, the four beams are spatially separated. There is a problem that the irradiation position variation on the surface to be scanned due to the surface eccentricity of the optical deflector becomes remarkable, and the uniformity of the image is deteriorated.
[0009]
The present invention reduces the total amount of variation in irradiation position due to surface eccentricity and surface tilt of the deflecting element, and provides a scanning optical device capable of obtaining a high-quality image with high uniformity and little pitch unevenness over the entire effective image area. An object is to provide an image forming apparatus used.
[0010]
[Means for Solving the Problems]
  A scanning optical device according to a first aspect of the present invention includes a light source means, a first optical system that converts a light beam emitted from the light source means into a light beam in another state, and a light beam emitted from the first optical system in a main scanning direction. A second optical system for converting the light beam into a longitudinal light beam, a polygon mirror having a plurality of deflection surfaces for deflecting and scanning the light beam emitted from the second optical system, and a light beam deflected and scanned by the deflection surface of the polygon mirror. A scanning optical system that forms an image on the scanning surface,
  In the scanning optical device in which the deflection surface of the polygon mirror and the scanned surface satisfy a conjugate relationship in the sub-scanning section,
  The light beam emitted from the second optical system is obliquely incident on the deflection surface of the polygon mirror within the sub-scanning section, and the light beam emitted from the second optical system is within the main scanning section. And obliquely incident on the deflecting surface of the polygon mirror with an angle with respect to the optical axis of the scanning optical system,
  The image height satisfying the complete conjugate relationship between the deflection surface of the polygon mirror and the scanned surface in the sub-scan section is one point or two points,
  The maximum image height on the scanned surface is L, and the light of the scanning optical system in the main scanning section of the image height that satisfies the complete conjugate relationship between the deflection surface of the polygon mirror and the scanned surface in the sub-scanning section. The image height closest to the maximum image height on the light beam side obliquely incident on the deflection surface of the polygon mirror with an angle to the axis is defined as Y_mWhen ∞,
    0.7L <Y_m∞ ≦ 1.0L
The power of the scanning optical system in the sub-scanning direction is set so as to satisfy the above condition.
  However, the sign of the image height on the light beam side incident on the deflection surface of the polygon mirror having an angle with respect to the optical axis of the scanning optical system in the main scanning section is positive.
  The invention of claim 2 is the invention of claim 1, wherein the imaging magnification βs in the sub-scanning direction of the scanning optical system is
    | Βs | <2.5
It is characterized by being.
  According to a third aspect of the present invention, in the first or second aspect of the present invention, the light source means is a multi-beam light source having a plurality of light emitting points that can be independently modulated.
  The invention according to claim 4 is the invention according to any one of claims 1 to 3, further comprising the following conditional expression:
    0.75L <Y_m∞ ≦ 0.95L
The power of the scanning optical system in the sub-scanning direction is set so as to satisfy the above condition.
  An image forming apparatus according to a fifth aspect of the present invention is a scanning optical device according to any one of the first to fourth aspects, a photoconductor disposed on the surface to be scanned, and light scanned by the scanning optical device. A developing unit that develops an electrostatic latent image formed on the photosensitive member by a beam as a toner image; a transfer unit that transfers the developed toner image to a transfer material; and the transferred toner image that is a transfer material And a fixing device for fixing to the head.
  An image forming apparatus according to a sixth aspect of the invention converts the code data input from the scanning optical apparatus according to any one of the first to fourth aspects and an external device into an image signal and inputs the image signal to the scanning optical apparatus. And a printer controller.
  According to a seventh aspect of the present invention, there is provided a color image forming apparatus comprising a plurality of the scanning optical devices according to any one of the first to fourth aspects, and an image carrier on each scanned surface of the plurality of scanning optical devices. Are arranged, and the plurality of image carriers form images of different colors.
  The invention of claim 8 is characterized in that in the invention of claim 7, there is provided a printer controller for converting color signals inputted from an external device into image data of different colors and inputting them into respective scanning optical devices. Yes.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 is a sectional view (main scanning sectional view) of the main scanning direction of the first embodiment of the scanning optical apparatus of the present invention, and FIG. 2 is a sectional view of the main section of the first embodiment of the scanning optical apparatus of the present invention in the sub scanning direction. It is a figure (sub-scanning sectional view).
[0012]
Here, the main scanning section corresponds to a deflection scanning plane, and the sub-scanning section refers to a plane that includes the deflection scanning plane and the rotation axis of the deflection element and is perpendicular to the deflection scanning plane.
[0013]
In the figure, reference numeral 1 denotes light source means, which is composed of, for example, a semiconductor laser. Reference numeral 2 denotes a condensing lens (collimator lens) as a first optical system, which converts a light beam emitted from the light source means 1 into a light beam in another state (for example, a substantially parallel light beam). Reference numeral 3 denotes an aperture stop which shapes the beam shape by limiting the passing light flux. Reference numeral 4 denotes a lens system (cylindrical lens) as a second optical system, which has a predetermined power only in the sub-scan section, and an optical deflector to be described later in the sub-scan section with the light beam that has passed through the aperture stop 3. 5 is formed as a substantially linear image on the deflection surface (reflection surface) 5a. Each element such as the collimator lens 2, the aperture stop 3, and the cylindrical lens 4 constitutes an element of the incident optical system.
[0014]
An optical deflector 5 as a deflecting element is composed of, for example, a four-sided polygon mirror (rotating polygon mirror), and is rotated at a constant speed in the direction of arrow A in the figure by driving means (not shown) such as a motor. ing.
[0015]
Reference numeral 6 denotes a scanning optical system (fθ lens system) having a condensing function and an fθ characteristic, which is composed of a single toric lens made of a plastic resin having different refractive powers in the main scanning direction and the sub-scanning direction. A light beam based on the image information reflected and deflected by 5 is imaged on the photosensitive drum surface 8 as the surface to be scanned, and conjugate between the deflection surface 5a of the polygon mirror 5 and the photosensitive drum surface 8 in the sub-scan section. By having a relationship, it has a tilt correction function.
[0016]
Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.
[0017]
In this embodiment, the divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2, the light beam (light quantity) is limited by the aperture stop 3, and is incident on the cylindrical lens 4. Of the substantially parallel light beam incident on the cylindrical lens 4, it is emitted as it is in the main scanning section. In the sub-scan section, the light beam converges and forms an almost linear image (a linear image longitudinal in the main scanning direction) on the deflection surface 5a of the polygon mirror 5.
[0018]
The light beams incident on the polygon mirror 5 are incident on the deflection scanning plane (main scanning section) and the plane (sub scanning section) that includes the rotation axis of the optical deflector 5 and is orthogonal to the deflection scanning plane. (Oblique incidence optical system).
[0019]
Then, the light beam reflected and deflected by the deflecting surface 5a of the polygon mirror 5 is imaged in a spot shape on the photosensitive drum surface 8 through the toric lens 6, and the polygon mirror 5 is rotated in the direction of the arrow A to rotate the photosensitive mirror. Optical scanning is performed on the drum surface 8 in the direction of arrow B (main scanning direction) at a constant speed. Thereby, an image is recorded on the photosensitive drum surface 8 as a recording medium.
[0020]
The surface shape of the refractive surface of the scanning optical system 6 in the present invention is expressed by the following shape expression.
[0021]
When the intersection point with the optical axis is the origin, the optical axis direction is the x axis, the axis orthogonal to the optical axis in the main scanning section is the y axis, and the axis orthogonal to the optical axis in the sub scanning section is the z axis, The bus direction corresponding to the scanning direction is
[0022]
[Expression 1]

[0023]
(However, R is the radius of curvature, K, B_Four, B₆, B₈, B_TenIs aspheric coefficient)
The sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) and the sub-line direction are
[0024]
[Expression 2]

[0025]
Where r '= r₀(1 + D₂Y²+ D_FourY^Four+ D₆Y⁶+ D₈Y⁸+ D_TenY^Ten)
(However, r₀Is the radius of curvature on the optical axis, D₂, D_Four, D₆, D₈, D_TenIs a coefficient)
S is a child line shape defined in a plane perpendicular to the main scanning section including the normal line of the bus bar at each position in the bus bar direction.
[0026]
Furthermore, as an aspherical component in the direction of the child line,
X = E_{twenty one}YZ²+ (E₄₀+ E₄₁Y + E₄₂Y²+ E₄₄Y^Four+ E₄₆Y⁶) Z^Four
It is the surface which added the value which becomes.
[0027]
In this expression, the order in the surface shape expression is limited. However, the scope of the right of the present invention does not limit this, and as the order is increased, the degree of design freedom increases and aberrations decrease. Needless to say. If the surface shape expression itself is an expression having the same degree of freedom of surface expression, the effect of the present invention can be obtained without any problem.
[0028]
Here, the irradiation position fluctuation in the sub-scanning direction due to the surface eccentricity of the polygon mirror which is a deflection element will be considered.
[0029]
First, for the sake of simplicity, a description will be given of a case where a light beam is incident on the surface including the rotation axis of the polygon mirror and orthogonal to the deflection scanning surface without an angle.
[0030]
FIG. 3 is a sub-scan sectional view from the polygon mirror to the surface to be scanned. In the figure, a point A on the deflection surface 5a and a point A 'on the surface to be scanned 8 are optically conjugate, and a line image formed by a cylindrical lens (not shown) is formed on the point A, and scanning optics. The image is re-imaged at the point A ′ by the system 6. If the deflection surface is decentered by the amount of eccentricity H as shown by the dotted line, the line image on point A moves to point B as a virtual image. The optical conjugate point of the virtual image B is a point B ′, and the light beam at the time of decentration passes through the point B and reaches the surface to be scanned 8, causing an irradiation position variation in the sub-scanning direction. Here, the irradiation position deviation amount (irradiation position fluctuation amount) dZ is α, which is the oblique incident angle of the light beam incident on the deflecting surface 5a of the polygon mirror 5, and βs is the magnification in the sub-scanning direction of the scanning optical system 6 (sub-scan magnification). and when,
dZ = 2H | βs | α (1)
It is represented by
[0031]
Next, a description will be given of a case where the light beam is incident at an angle with respect to a plane that includes the rotation axis of the polygon mirror and is orthogonal to the deflection scanning plane.
[0032]
  4 (A) and 4 (B) are main scanning sectional views in the vicinity of the deflection surface of the polygon mirror. FIG. 4 (A) shows the light source means side.(The light beam emitted from the second optical system has an angle with respect to the optical axis of the scanning optical system in the main scanning section and is incident on the polarization plane of the polygon mirror)The deflection to the image height of FIG. 4B shows the deflection to the image height on the side opposite to the light source means. In this case, the distance between the line image and the virtual image caused by the surface decentering is not 2H in the above equation (1), but the incident angle θi to the polygon mirror 5 and the deflection angle θe from the polygon mirror 5 (both scanning optics) as follows. It is expressed by a function of a coordinate system in which the optical axis direction of the system is 0 degree.
[0033]

Therefore, when the sub-scanning magnification βs and the oblique incident angle α of the scanning optical system 6 are constant, the irradiation position variation dZ has a deflection angle dependency. This deflection angle dependency is the case where the deflection is made toward the distance between the line image and the virtual image in FIG. 4 and the axis on the light source means side as is apparent from the above equation (2), that is, the incident angle θi to the polygon mirror 5. When the deflection angle θe from the polygon mirror 5 has the same sign, it becomes large, and when the deflection angle θe is deflected toward the outermost axis on the light source means side, it becomes the maximum.
[0034]
FIG. 16 is a diagram showing irradiation position fluctuations due to surface eccentricity and surface tilt of a polygon mirror in a comparative example. In FIG. 16, the dotted line shows the deflection angle dependence of the irradiation position variation dZ due to the surface eccentricity of the polygon mirror under the conditions of βs = −2.28, α = 1.8 degrees, and H = 30 μm as a comparative example. From the figure, it can be seen that the irradiation position fluctuation amount dZ takes the maximum value outside the outermost axis (Y = 105 mm) on the light source means side regardless of the incident angle θi.
[0035]
Next, the irradiation position fluctuation in the sub-scanning direction due to the surface tilt of the polygon mirror will be considered. Even in the case of surface tilt, the irradiation position variation dZ has a deflection angle dependency as in the case of surface eccentricity.
[0036]
In general, since the field curvature in the sub-scanning section is almost corrected, the line image by the cylindrical lens and each point on the surface to be scanned are optically conjugate in the sub-scanning section regardless of the deflection angle. ing. Therefore, if the light beam is deflected at the line image position, the deflection surface and the surface to be scanned have a conjugate relationship, and even if the surface tilts, the irradiation position does not change (hereinafter, such an image height is referred to as “sub-scanning complete conjugate image height”). ").
[0037]
However, at most deflection angles, the position of the deflection surface and the line image shifts due to the entrance and exit of the deflection surface due to the rotation of the polygon mirror. Arise.
[0038]
Note that the irradiation position variation due to surface tilt depends on which position the cylindrical lens line image is placed at the time of design, that is, where the conjugate point with the surface to be scanned is located and the power in the sub-scanning direction of the scanning optical system is determined. Therefore, unlike the case of surface decentering, it is possible to freely set a sub-scanning complete conjugate image height that does not cause irradiation position fluctuation even if the irradiation position fluctuation amount depends on the deflection angle or surface tilt occurs. .
[0039]
When the field curvature in the sub-scanning section is substantially corrected, one or two points in the effective image area can be a complete conjugate point in the sub-scanning section due to the arrangement of the polygon mirror.
[0040]
In FIG. 16, the alternate long and short dash line indicates the deflection angle dependence of the irradiation position variation dZ due to the surface tilt of the polygon mirror in the comparative example. Since the entrance / exit of the deflection surface is greatest near the on-axis and near the most off-axis, the irradiation position fluctuation amount is the largest near the same position, and normally the sub-scanning complete conjugate image height is set so that they are distributed, The power in the sub-scanning direction of the scanning optical system is determined. In the comparative example, the sub-scanning complete conjugate image height is set to around 60% of the maximum image height, thereby balancing the irradiation position fluctuations near the image height on the axis and off the most axis.
[0041]
In FIG. 16, the solid line is the sum of the absolute values of the irradiation position fluctuation amount due to the surface eccentricity and the surface inclination of the polygon mirror in the comparative example (because both the surface inclination direction and the surface eccentricity direction are both in the + −direction, The sum is taken after taking the absolute value of each value.) In this way, the irradiation position fluctuation amount due to surface eccentricity always takes the maximum value on the most off-axis (Y = 105mm) side of the light source means, so when surface tilt design is performed by the conventional method, surface eccentricity and surface tilt total It can be seen that the irradiation position fluctuation amount becomes maximum at the same position.
[0042]
From the above considerations, in order to minimize the irradiation position fluctuation due to surface eccentricity and surface tilt over the entire effective image area, the image height that does not cause irradiation position fluctuation on the scanned surface when the surface tilt of the polygon mirror deflection surface occurs. Y is the image height closest to the light source means (sub-scanning complete conjugate image height)._m∞, when the maximum image height on the scanned surface is L (sign positive),
0.7L <Y_m∞ ≦ 1.0L (3) (The sign of the image height is positive on the light source means side)
More preferably,
0.75L <Y_m∞ ≦ 0.95L (3a) (The sign of the image height is positive on the light source side)
The power in the sub-scanning direction of the scanning optical system is set so that As a result, it is possible to improve the tilt correction effect in the vicinity of the outermost axis on the light source means side where the irradiation position variation due to surface eccentricity is large.
[0043]
In this embodiment, the sub-scanning complete conjugate image height Y_m∞ is 80% of the maximum image height L on the light source means 1 side (Y_m∞ = 84 mm = 0.8 L), the line image position by the cylindrical lens 4 is arranged in the vicinity of the deflection point of the light beam toward the same image height, and the image height Y of 80% on the light source means 1 side._mThe power in the sub-scanning direction of the scanning optical system 6 is set so that the deflection surface 5a of the light beam directed to ∞ and the scanned surface 8 have a conjugate relationship in the sub-scan section.
[0044]
Table 1 shows design values of the scanning optical device according to the present embodiment, and FIG. 5 is a diagram showing irradiation position fluctuations due to surface eccentricity and surface tilt of the polygon mirror in the scanning optical device. FIG. 5 is calculated assuming that the tolerance of the polygon mirror is a surface eccentricity of 30 μm and a surface tilt of 2 ′.
[0045]
As shown in FIG. 5, by improving the tilt correction effect near the most off-axis on the light source means side where the irradiation position variation is large due to surface eccentricity, the absolute value of the irradiation position variation due to the surface tilt of the deflection surface of the polygon mirror and the polygon mirror are improved. The sum of the absolute value of the irradiation position variation due to the surface eccentricity of the deflection surface of the light source means the value at the on-axis image height (Y = 0 mm) and the most off-axis image height (Y = 105 mm), which is substantially equal to the value at 105 mm), and it can be seen that the fluctuation amount at the image height where the irradiation position fluctuation is the largest is reduced as compared with the comparative example.
[0046]
[Table 1]

[0047]
Note that the total irradiation position fluctuation amount dZ due to the surface eccentricity and surface tilt of the polygon mirror exceeds 5 μm in the entire effective image area on the surface to be scanned and is easily recognized as pitch unevenness, so it is suppressed to 5 μm or less. desirable. In particular, since the irradiation position fluctuation amount dZ due to surface eccentricity is uniquely determined from the above equation (2), the imaging magnification (sub-scan magnification) βs in the sub-scanning direction of the scanning optical system, which is a parameter included in the equation. The
| Βs | <2.5
It is necessary to determine the optical arrangement so as to satisfy The sub-scan magnification of the scanning optical system in this embodiment is
βs = -2.28
As shown in FIG. 5, the irradiation position variation dZ is suppressed to 5 μm or less over the entire effective image area.
[0048]
[Image forming apparatus]
FIG. 12 is a cross-sectional view of the main part in the sub-scanning direction showing the embodiment of the image forming apparatus of the present invention. In the figure, 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 a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in the first embodiment. The light scanning unit 100 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.
[0049]
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 the light beam 103 scanned by the optical scanning unit 100.
[0050]
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. The electrostatic latent image is developed as a toner image by a developing unit 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.
[0051]
The toner image developed by the developing unit 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 the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 12), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.
[0052]
As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to a fixing device behind the photosensitive drum 101 (left side in FIG. 12). 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 sheet conveyed from the transfer unit. The unfixed toner image on the paper 112 is fixed by heating 112 while applying pressure at the 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 the fixed paper 112 is discharged out of the image forming apparatus.
[0053]
Although not shown in FIG. 12, the print controller 111 controls not only the data conversion described above, but also controls each part in the image forming apparatus including the motor 115 and a polygon motor in the optical scanning unit described later. I do.
[0054]
As described above, in this embodiment, the surface tilt of the polygon mirror 5 in the vicinity of the most off-axis position on the light source means 1 side is set by setting the power and conjugate relationship of the scanning optical system 6 in the sub-scanning direction to appropriate values. The amount of irradiation position fluctuation due to the above is reduced, and the total amount of irradiation position fluctuation due to surface eccentricity and surface tilt of the polygon mirror 5 is reduced. As a result, a scanning optical device capable of obtaining a high-quality image with high uniformity and little pitch unevenness over the entire effective image area and an image forming apparatus using the same are realized.
[0055]
[Embodiment 2]
FIG. 6 is a main scanning sectional view of Embodiment 2 of the scanning optical apparatus of the present invention, and FIG. 7 is a sub-scanning sectional view of FIG. 6 and 7, the same elements as those shown in FIGS. 1 and 2 are given the same reference numerals.
[0056]
This embodiment is different from the first embodiment described above in that the sub-scanning complete conjugate image height Y_mCompared with the first embodiment, ∞ is set further to the outermost axis, and the scanning optical device is a tandem scanning optical device that simultaneously scans a plurality of light beams onto a plurality of different scanning surfaces. In other respects, the configuration and optical action of the image forming apparatus are substantially the same as those of the first embodiment, thereby obtaining the same effects.
[0057]
In other words, the present embodiment includes two scanning optical elements sandwiching the polygon mirror 5, and further causes two light beams to enter the respective scanning optical elements 14 and 15, and simultaneously four light beams are generated by one polygon mirror 5. This is a tandem type scanning optical apparatus that performs reflection scanning and optical scanning on the corresponding photosensitive drum surfaces 8a, 8b, 8c, and 8d.
[0058]
In the figure, S1 and S2 are first and second stations (scanning units), respectively, which are arranged opposite to each other with the polygon mirror 5 interposed therebetween. A light source means 12 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, and 1d are converted into substantially parallel light beams by the corresponding collimator lenses 2a, 2b, 2c, and 2d, and the corresponding aperture stops 3a, The beam width is limited by 3b, 3c, and 3d. The substantially parallel light flux that has passed through the aperture stops 3a and 3b is imaged as a longitudinal line image in the main scanning direction in the vicinity of the deflection surface 5a of the polygon mirror 5 by the first cylindrical lens 4a having power only in the sub-scanning direction. . The substantially parallel light beam that has passed through the aperture stops 3c and 3d is formed as a long line image in the main scanning direction near the deflection surface 5b of the polygon mirror 5 by the second cylindrical lens 4b having power only in the sub-scanning direction. The
[0059]
An optical deflector 5 as a deflecting element is composed of, for example, a four-sided polygon mirror (rotating polygon mirror), and is rotated at a constant angular velocity in the direction of arrow A in the figure by a driving means (not shown) such as a motor. Yes.
[0060]
Reference numerals 14 and 15 denote first and second scanning optical systems (fθ lens systems) each having a condensing function and an fθ characteristic, and are made of a single plastic resin having different refractive powers in the main scanning direction and the sub-scanning direction. One toric lens (scanning optical element), and two light beams based on image information reflected and deflected by the polygon mirror 5 are imaged on the photosensitive drum surfaces 8a, 8b, 8c, and 8d as scanned surfaces; In addition, a tilt correction function is provided by providing a conjugate relationship between the deflection surfaces 5a and 5b of the polygon mirror 5 and the photosensitive drum surfaces 8a, 8b, 8c and 8d in the sub-scan section.
[0061]
The four light beams reflected and deflected by the deflecting surfaces 5a and 5b of the polygon mirror 5 pass through the first scanning optical system 14 or the second scanning optical system 15 and correspond to the respective light beam drum surfaces 8a and 8b. , 8c, 8d and the polygon mirror 5 is rotated in the direction of arrow A, thereby optically scanning the photosensitive drum surfaces 8a, 8b, 8c, 8d in the direction of arrow B. As a result, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, and 8d to perform image recording.
[0062]
Table 2 shows design values of the scanning optical apparatus in the present embodiment. In this embodiment, the sub-scanning complete conjugate image height Y_m∞ is the image height position (Y of 9.5% of the maximum image height on the light source means 12 side._m∞ = 100 mm = 0.95 L), the line image position by the cylindrical lens 4 is arranged in the vicinity of the deflection point of the light beam toward the same image height, and the image height Y of 9.5% on the light source means 12 side._mIn the sub-scanning direction of the first and second scanning optical systems 14 and 15, the deflecting surfaces 5a and 5b of the light beam directed to ∞ and the photosensitive drum surfaces 8a, 8b, 8c and 8d have a conjugate relationship in the sub-scanning section. The power is set.
[0063]
[Table 2]

[0064]
In this embodiment, the sub-scanning complete conjugate image height Y_mNote that ∞ is set to be more off-axis than that of Embodiment 1 because the deviation of the conjugate relationship in the sub-scan section due to the manufacturing tolerance of the scanning optical element is larger in the vicinity of the off-axis than on the optical axis. This is because, by improving the surface tilt correction effect in the vicinity of the outermost axis in advance, there is an aim to loosen the allowable tolerance at the same position.
[0065]
FIG. 8 is a diagram showing the irradiation position variation due to the surface eccentricity and surface tilt of the polygon mirror in the scanning optical apparatus. FIG. 8 is calculated assuming that the tolerance of the polygon mirror is a surface eccentricity of 30 μm and a surface tilt of 2 ′.
[0066]
As shown in FIG. 8, by improving the tilt correction effect in the vicinity of the most off-axis on the light source means side where the irradiation position variation is large due to surface eccentricity, the total irradiation position variation amount of surface eccentricity and surface tilt is reduced in the entire image. I can read.
[0067]
[Color image forming apparatus]
FIG. 13 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. The present embodiment is a tandem type color image forming apparatus that records image information on a photosensitive drum surface, which is an image carrier, by a scanning optical device. In FIG. 13, 60 is a color image forming apparatus, 11 is a scanning optical apparatus shown in the second embodiment, 21, 22, 23 and 24 are photosensitive drums as image carriers, and 31, 32, 33 and 34 are developing. A container 51 is a conveyor belt.
[0068]
In the figure, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are respectively input to the scanning optical device 11. The scanning optical device 11 emits light beams 41, 42, 43, and 44 that are modulated in accordance with each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are subjected to main scanning by these light beams. Scanned in the direction.
[0069]
In this embodiment, the color image forming apparatus emits light beams corresponding to C (cyan), M (magenta), Y (yellow), and B (black) from one scanning optical device 11, and the photosensitive drums 21 and 22. , 23 and 24, image signals (image information) are recorded, and color images are printed at high speed.
[0070]
In the color image forming apparatus according to the present embodiment, as described above, one scanning optical device 11 uses the light beam based on each image data to convert the latent images of the respective colors onto the corresponding photosensitive drums 21, 22, 23, and 24. Is formed. Thereafter, a single full color image is formed by multiple transfer onto a recording material.
[0071]
As the external device 52, for example, a color image reading device including 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.
[0072]
As described above, in this embodiment, the power and conjugate relationship in the sub-scanning direction of the first and second scanning optical systems 14 and 15 are set to appropriate values in the tandem scanning optical apparatus as described above as in the first embodiment. By setting, the irradiation position fluctuation amount due to the surface tilt of the polygon mirror 5 near the most off-axis position on the light source means 12 side is reduced, and the total of the irradiation position fluctuation amount due to the surface eccentricity and surface tilt of the polygon mirror 5 is reduced. is doing. As a result, a tandem scanning optical device capable of obtaining a high-quality image with high uniformity and little pitch unevenness over the entire effective image area and a color image forming apparatus using the same are realized.
[0073]
The color image forming apparatus is not limited to the above configuration, and the present invention can be applied to, for example, a color image forming apparatus shown in FIG.
[0074]
[Color image forming apparatus]
That is, FIG. 14 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 scanning optical devices shown in the first embodiment are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 14, 260 is a color image forming apparatus, 211, 212, 213, and 214 are scanning optical apparatuses shown in the first embodiment, 221, 222, 223, and 224 are photosensitive drums as image carriers, and 231 and 232, respectively. , 233 and 234 are developing units, and 251 is a conveying belt.
[0075]
In FIG. 14, the color image forming apparatus 260 receives R (red), G (green), and B (blue) color signals from an external device 252 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 253 in the apparatus. These image data are input to the scanning optical devices 211, 212, 213, and 214, respectively. These scanning optical devices emit light beams 241, 242, 243, and 244 modulated in accordance with each image data, and the photosensitive surfaces of the photosensitive drums 221, 222, 223, and 224 are caused by these light beams. Scanned in the main scanning direction.
[0076]
The color image forming apparatus according to the present embodiment includes four scanning optical devices (211, 212, 213, 214) arranged in each of C (cyan), M (magenta), Y (yellow), and B (black) colors. Correspondingly, image signals (image information) are recorded on the surfaces of the photosensitive drums 221, 222, 223, and 224 in parallel, and a color image is printed at high speed.
[0077]
In the color image forming apparatus according to the present embodiment, as described above, the four scanning optical devices 211, 212, 213, and 214 use the light beams based on the respective image data, and the corresponding photosensitive drums 221 and 222 respectively correspond to the latent images of the respective colors. , 223, 224 surfaces. Thereafter, a single full color image is formed by multiple transfer onto a recording material.
[0078]
As the external device 252, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 260 constitute a color digital copying machine.
[0079]
[Embodiment 3]
FIG. 9 is a main scanning sectional view of Embodiment 3 of the scanning optical apparatus of the present invention, and FIG. 10 is a sub-scanning sectional view of FIG. 9 and 10, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.
[0080]
This embodiment is different from the first embodiment described above in that the sub-scanning complete conjugate image height Y_m∞ is changed, the scanning optical system 16 is composed of the first and second optical elements 61 and 62, a multi-beam semiconductor laser is used for the light source means 13, and other configurations and optics The operation is substantially the same as in the first embodiment, thereby obtaining the same effect.
[0081]
That is, in the figure, reference numeral 13 denotes a light source means, which comprises a multi-beam semiconductor laser having a plurality of light emitting points that can be modulated independently. Reference numeral 16 denotes a scanning lens system as a scanning optical system having a condensing function and an fθ characteristic, and first and second toric sheets made of plastic resin having different refractive powers in the main scanning direction and the sub-scanning direction. A plurality of light beams based on image information reflected and deflected by the polygon mirror 5 are formed on the photosensitive drum surface 8 as a surface to be scanned, and the deflection surface of the polygon mirror 5 in the sub-scanning section. By having a conjugate relationship between 5a and the photosensitive drum surface 8, a tilt correction function is provided.
[0082]
Table 3 shows design values of the scanning optical apparatus in the present embodiment. In this embodiment, the sub-scanning complete conjugate image height Y_m∞ represents 90% of the maximum image height on the light source means 13 side (Y_m∞ = 95 mm = 0.9 L) so that the line image position by the cylindrical lens 4 is arranged in the vicinity of the deflection point of the light beam toward the same image height, and 90% of the image height Y on the light source means 13 side._mThe power in the sub-scanning direction of the scanning optical system 16 is set so that the deflection surface 5a of the light beam directed to ∞ and the scanned surface 8 are in a conjugate relationship in the sub-scan section.
[0083]
[Table 3]

[0084]
FIG. 11 is a diagram showing the irradiation position variation due to the surface eccentricity and surface tilt of the polygon mirror in the scanning optical device. Note that FIG. 11 is calculated assuming that the tolerance of the polygon mirror is a surface eccentricity of 30 μm and a surface tilt of 2 ′.
[0085]
As shown in FIG. 11, by improving the tilt correction effect in the vicinity of the most off-axis on the light source means side where the irradiation position fluctuation is large due to surface eccentricity, the total irradiation position fluctuation amount of the surface eccentricity and surface inclination is different between the on-axis and the most off-axis. It can be read that the irradiation position fluctuation amount at the most off-axis image height on the light source means side is reduced.
[0086]
As described above, in this embodiment as well, in the same manner as in the first embodiment, the power and conjugate relationship in the sub-scanning direction of the scanning optical system 16 are set to appropriate values, so that the light source means 13 near the most off-axis position. The irradiation position fluctuation amount due to the surface tilt of the polygon mirror 5 is reduced, and the total of the irradiation position fluctuation amount due to the surface eccentricity and the surface tilt of the polygon mirror 5 is reduced. As a result, a scanning optical device capable of obtaining a high-quality image with high uniformity and little pitch unevenness over the entire effective image area and an image forming apparatus using the same are realized.
[0087]
Embodiment of the present invention
While various examples and embodiments of the present invention have been shown and described, those skilled in the art will recognize that the spirit and scope of the present invention is not limited to the specific descriptions and figures within this specification, It will be understood that various modifications and changes are fully set forth in the appended claims.
[0107]
【The invention's effect】
According to the present invention, the light beam emitted from the light source means as described above is incident on the deflection element at an angle with respect to the deflection scanning plane and the plane orthogonal to the deflection scanning plane including the rotation axes of the deflection scanning plane. The image height Y closest to the light source means among the image heights that do not cause irradiation position fluctuations on the surface to be scanned when surface tilt occurs._mBy setting the power in the sub-scanning direction of the scanning optical system so that ∞ falls within an appropriate range, the amount of variation in irradiation position due to the surface tilt of the deflection element near the most off-axis position on the light source means side is reduced, and the deflection element A scanning optical device capable of reducing the sum of absolute values of irradiation position fluctuations due to surface eccentricity and surface tilt of the image, and thereby obtaining a high-quality image with high uniformity and little pitch unevenness over the entire effective image area. The used image forming apparatus can be achieved.
[Brief description of the drawings]
FIG. 1 is a main scanning sectional view of Embodiment 1 of the present invention.
FIG. 2 is a sub-scan sectional view of Embodiment 1 of the present invention.
FIG. 3 is a sub-scan sectional view from the deflection element to the surface to be scanned according to the first embodiment of the present invention.
FIGS. 4A and 4B are main scanning sectional views in the vicinity of a deflection surface, in which FIG. 4A shows deflection to the light source side image height, and FIG. 4B shows deflection to the anti-light source side image height.
FIG. 5 is a diagram showing irradiation position variation due to surface eccentricity and surface tilt of the deflecting element according to the first embodiment of the present invention.
FIG. 6 is a main scanning sectional view of Embodiment 2 of the present invention.
FIG. 7 is a sub-scan sectional view of Embodiment 2 of the present invention.
FIG. 8 is a diagram showing irradiation position fluctuations due to surface eccentricity and surface tilt of a deflection element according to Embodiment 2 of the present invention.
FIG. 9 is a main scanning sectional view of Embodiment 3 of the present invention.
FIG. 10 is a sub-scan sectional view of Embodiment 3 of the present invention.
FIG. 11 is a diagram showing irradiation position variation due to surface eccentricity and surface tilt of the deflecting element according to the third embodiment of the present invention.
FIG. 12 is a sub-scan sectional view showing an embodiment of an image forming apparatus of the present invention.
FIG. 13 is a schematic diagram of a main part of a color image forming apparatus according to an embodiment of the present invention.
FIG. 14 is a schematic diagram of a main part of a color image forming apparatus according to an embodiment of the present invention.
FIG. 15 is a schematic diagram of a main part of a conventional scanning optical device.
FIG. 16 is a diagram showing irradiation position variation due to surface eccentricity and surface tilt of a deflection element in a comparative example.
[Explanation of symbols]
1 Light source means
2 First optical system (collimator lens)
3 Aperture
4 Second optical system (cylindrical lens)
5 Deflection element (polygon mirror)
6 Scanning optical system
8 Scanned surface
11 Scanning optical device
21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer
60 color image forming apparatus
51 Conveyor belt
52 External equipment
53 Printer Controller
41, 42, 43, 44 Laser beam
100 Scanning optical device
101 Photosensitive drum
102 Charging roller
103 Light beam
104 Image forming apparatus
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 Paper discharge roller
117 External equipment

Claims (8)

A light source means, a first optical system for converting the light beam emitted from the light source means into a light beam in another state, and a second optical system for converting the light beam emitted from the first optical system into a light beam elongated in the main scanning direction. A polygon mirror having a plurality of deflection surfaces that deflect and scan the light beam emitted from the second optical system, and a scanning optical system that forms an image on the surface to be scanned that is deflected and scanned by the deflection surface of the polygon mirror; , And
In the scanning optical device in which the deflection surface of the polygon mirror and the scanned surface satisfy a conjugate relationship in the sub-scanning section,
The light beam emitted from the second optical system is incident obliquely at an angle with respect to the deflection surface of the polygon mirror in the sub-scanning section, and the light beam emitted from the second optical system is within the main scanning section. And obliquely incident on the deflecting surface of the polygon mirror at an angle with respect to the optical axis of the scanning optical system,
The image height satisfying the complete conjugate relationship between the deflection surface of the polygon mirror and the scanned surface in the sub-scan section is one point or two points,
The maximum image height on the scanned surface is L, and the light of the scanning optical system in the main scanning section of the image height that satisfies the complete conjugate relationship between the deflection surface of the polygon mirror and the scanned surface in the sub-scanning section. When the image height closest to the maximum image height on the light beam side having an angle with respect to the axis and obliquely incident on the deflection surface of the polygon mirror is Y _m ∞,
0.7L <Y _m ∞ ≦ 1.0L
A scanning optical apparatus, wherein power in the sub-scanning direction of the scanning optical system is set so as to satisfy the above.
However, the sign of the image height on the light beam side incident on the deflection surface of the polygon mirror having an angle with respect to the optical axis of the scanning optical system in the main scanning section is positive. The imaging magnification βs in the sub-scanning direction of the scanning optical system is
| Βs | <2.5
The scanning optical apparatus according to claim 1, wherein:   3. The scanning optical apparatus according to claim 1, wherein the light source means is a multi-beam light source having a plurality of light emitting points that can be independently modulated. Furthermore, the following conditional expression: 0.75L <Y _m ∞ ≦ 0.95L
4. The scanning optical apparatus according to claim 1, wherein power in the sub-scanning direction of the scanning optical system is set so as to satisfy the above.   5. The scanning optical device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a light beam scanned by the scanning optical device. A developing unit that develops an electrostatic latent image as a toner image, a transfer unit that transfers the developed toner image onto a transfer material, and a fixing unit that fixes the transferred toner image onto the transfer material. An image forming apparatus.   5. The scanning optical 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 scanning optical device. An image forming apparatus.   A plurality of the scanning optical devices according to any one of claims 1 to 4, wherein an image carrier is arranged on each scanned surface of the plurality of scanning optical devices, and the plurality of image carriers are A color image forming apparatus for forming images of different colors.   8. The color image forming apparatus according to claim 7, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the image data to each scanning optical device.

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