JP4642182B2 - Optical scanning optical device and image forming apparatus using the same - Google Patents

Description

【００６２】
次に各光学要素の光学的作用について説明する。
【００６３】
レーザユニット１は半導体レーザ２とコリメーターレンズ部３との間隔および画角が調整されたものであり、コリメーターレンズ部３の光軸と平行に平行光束を出射し、所定の精度で取り付けられている。コリメーターレンズ部３は球面収差および色収差を低減するために半導体レーザ２側から凹、凸で硝材が異なる２つの球面レンズを貼り合わせて一体化した貼り合わせレンズより成っている。OFS光学系ではレーザユニット１から出射した平行光束の一部が主走査方向にポリゴンミラー１０の偏向面１０ａで切り取られて偏向光束となるため、上記平行光束の走査に寄与する有効光束は走査角に比例して軸外に移動し、光束に含まれる球面収差の量が増大するためである。このため従来のUFS光学系であれば単レンズで十分なほど暗いＦ値（Ｆナンバー）であってもOFS光学系では球面収差を低減する貼り合わせレンズが必要になる。色収差は半導体レーザ２の波長が環境温度で変化するため、ピント変動を抑える目的で行われる。
【００６４】
レーザユニット１から出射した平行光束は凹レンズ４で弱発散光束に変換され第２、第１のｆθレンズ９、８を透過して再び拡大された平行光束に変換される。このような光学構成にするとレーザユニット１の半導体レーザ２とコリメーターレンズ部３とを一体として主走査方向に平行シフトするだけで半導体レーザ素子のチップの傾きによる平行光束中のレーザ強度分布の横ずれを補正することができる。図３（Ｃ）はこのときの補正状態を示した要部概略図である。尚、図３（Ａ）は半導体レーザ素子のチップが傾いていない場合，図３（Ｂ）は半導体レーザ素子のチップが傾いている場合を示している。
【００６５】
シフト調整手段はレーザユニット１内の構成に含まれ、入射光学系４１への取付け部材に対し半導体レーザ２とコリメーターレンズ部３との位置関係を保持したまま主走査方向にシフト可能な機構を備えている。単独の治具上で行なわれるレーザーユニット１の光学特性の調整はピント及び画角調整を行なった後、光源２とコリメーターレンズ部３とを一体として主走査方向へシフトさせ、基準軸上に設けられた所定の開口を透過する光束について主走査方向に２分割された光束の強度の比が所定の値以下に成るようにシフト量が調整される。調整済みのレーザユニット１はレーザ強度のピークがほぼ入射光学系４１の光軸に一致し、該光軸と平行な平行光束を出射するので単品としての互換性が保証できる。
すなわち、レーザユニット１の調整は、単独の（専用の）治具にて、
１)ピントは平行光束を出射するように光源とコリメータレンズの間隔が調整され、
２)画角調整はコリメータレンズの光軸と垂直な断面上にて光源が光軸に一致するよう調整され、
３)シフト調整は基準軸（光軸）上に設けられた開口中心にレーザ光束の強度分布が一致するように
レーザユニットのシフト調整される。
このように調整されたレーザユニットはレーザユニットの光学性能が一定なので交換可能であり、互換性が保証される性能を有する。
【００６６】
また凹レンズ４を光軸方向に移動させて主走査方向のピント変動を補正する。主走査方向のピントを補正する目的は以下に示す３つの理由による。
【００６７】
（１）OFS光学系はUFS光学系に対してポリゴンミラーの偏向面の主走査方向の幅が狭く、等価な主走査方向の面精度を確保するのが困難である。
【００６８】
（２）光束は第１、第２のｆθレンズ８，９を往復で透過するためｆθレンズの面精度の影響が２倍になる。さらにOFS光学系ではポリゴン面数が増えるのでｆθレンズの焦点距離が長くなり、面精度の敏感度が増大してピント変動が無視できなくなる。
【００６９】
（３）高解像度で微小スポットの要求に対し、狭い焦点深度範囲内にピント
を補正する機構が必要である。
【００７０】
一方、副走査方向のピント補正は凹レンズ４を調整した後に従来どおりシリンドリカルレンズ６を光軸方向に移動させて行なえば良い。
【００７１】
折り返しミラー７は入射光束をポリゴンミラーの走査中心（偏向角の略中央）から入射させるための折り曲げミラーであり、入射光学系４１を折り畳んでコンパクトにしている。また折り返しミラー７はレーザユニット１からシリンドリカルレンズ６までの入射光学系４１の部品公差で生じる斜入射角の誤差を補正し、ポリゴンミラー１０の偏向面１０ａに所定の角度で入射させるために、図４（Ａ），（Ｂ）に示すように主走査断面内で該折り返しミラー７と平行な回転軸廻りに調整可能な初期調整の機構を備えている。
【００７２】
図４（Ａ），（Ｂ）において回転軸は入射光線の高さと略一致し、ミラーの裏面にはこの高さに配置された支持部材（７ａ，７ｂ）が支点となり、矢印で示したセットビスを回すことによりミラーを回転調整する。折り返しミラー７は反射された光束を観測系（不図示）で観察することにより所定の角度に調整され固定される。
【００７３】
ポリゴンミラー１０の偏向面１０ａに入射する光束の主走査方向の幅は開口絞り５で制限され、ポリゴンミラー１０の走査角、入射光学系４１の公差による光束のずれやポリゴンミラー１０の位置精度を考慮して、該偏向面１０ａの主走査方向の幅の約２〜３倍に設定される。本実施形態では外接円径２９ｍｍ、１２面のポリゴンミラーであり、偏向面の幅７．５ｍｍに対して１８ｍｍ程度の入射光束である。副走査方向の絞りの幅は感光ドラム面１２上のスポット径に関わっている。
【００７４】
［遮光板の作用の説明］
次に遮光部材としての遮光板１３の作用について説明する。
【００７５】
本実施形態においては上述の如く半導体レーザ２は光束が有効走査領域外（非有効走査部）を走査するときにおいても消灯せず、常時点灯するように設定している。そこで本実施形態ではポリゴンミラー１０で偏向反射された光束のうち走査開始側および走査終端側の不要な光束を遮光板１３により遮断することにより、第１、第２のｆθレンズ８、９や長尺シリンドリカルレンズ１１の有効部外を照射してフレアー光が発生しないようにしている。
【００７６】
尚、本実施形態では遮光板１３を象徴的にポリゴンミラー１０と第１のｆθレンズ８との間に配置しているが、これに限らず遮光板１３をさらに他の光学部材の前後に追加して複数配置しても良い。これによりフレアーの遮光効果はより完全なものとなる。
【００７７】
［偏向面の境界部の形状の説明］
次にポリゴンミラーの隣接面（隣接する偏向面）の境界部（エッジ部）の形状について図５（Ａ），（Ｂ）を用いて説明する。
【００７８】
本実施形態においてポリゴンミラー１０は１２面の正多角形である。ポリゴンミラー１０の隣接面の境界部（エッジ部）１０ｂは稜線状のエッジ形状より成り、図５（Ｂ）に示すようにある程度の幅を有している。本実施形態ではこの境界部１０ｂの幅（ポリゴンミラーが回転する方向の幅）がポリゴンミラー１０の偏向面１０ａで偏向反射される光束の主走査方向の光束幅Ｗ、即ち偏向面１０ａに対して１％以下（好ましくは０．０２％〜１％）と成るように設定している。本実施形態においては上述の如く光源が常時点灯しているので、隣接面の境界部１０ｂが被走査面１２と正対する瞬間が発生する。このとき境界部１０ｂに正面から入射した光束の一部は図５（Ａ）に示すように、該境界部１０ｂの幅に比例した強度で正反射し、通常の走査光と同一の光路をたどって被走査面１２上の中央を照射し、フレアー光となる。
【００７９】
しかしながら本実施形態では上述の如く境界部１０ｂの幅をポリゴンミラー１０の偏向面１０ａで反射される光束の主走査方向の走査幅Ｗ（即ち偏向面１０ａの幅）に対して１％以下になるように設定しているので、フレアー光の強度比は同様に１％程度となり、これは実質的に画像に悪影響を与えることはない。また本実施形態では半導体レーザの放射面の広い方向を主走査方向に一致させ、図３に示す調整を行うことにより、光束の主走査方向の強度ピークの９０％以上となる領域がポリゴンミラーの隣接面の境界部１０ｂに入射するように設定している。
【００８０】
このように本実施形態においては上述の如く走査有効領域外においても光源が常に点灯する光走査光学装置において、ポリゴンミラー１０の隣接面の境界部１０ｂの幅をポリゴンミラー１０の偏向面１０ａで反射される光束の主走査方向の走査幅Ｗに対して１％以下になるように設定することにより、該ポリゴンミラー１０の境界部１０ｂからの反射光がフレアー光として被走査面１２に到達しても実質的に画像劣化が生じないようにしている。
【００８１】
［長尺シリンドリカルレンズの支持方法の説明］
次に本発明に関わる長尺シリンドリカルレンズ１１の支持方法について図７を用いて説明する。
【００８２】
長尺シリンドリカルレンズ１１は被走査面１２近傍に配置されるので長尺の形状となる。そのため熱収縮や振動等を防止するには長尺シリンドリカルレンズ１１を図６（Ａ），（Ｂ），（Ｃ）に示すように取り付ける。
【００８３】
即ち、同図（Ａ）は長尺シリンドリカルレンズ１１を入射面側から見た側面図、同図（Ｂ）は長尺シリンドリカルレンズ１１を上方から見た上面図、同図（Ｃ）は出射面側から長尺シリンドリカルレンズ１１が取り付けられている様子を示した説明図である。Ｌｉは光入射面、Ｌｏは光射出面である。
【００８４】
同図（Ａ）において１４，１４’は各々レンズ中央基準部である位置決め部であり、凹形状より成り、長尺シリンドリカルレンズ１１の長手方向（主走査方向）の中央の上下に設けられている。本実施形態では位置決め部１４と、ハウジング２５から突出した嵌合部材２２とを嵌合させることにより、該長尺シリンドリカルレンズ１１の長手方向の位置を決めている。尚、嵌合部材２２はハウジング２５における長尺シリンドリカル１１の長手方向の中央部に相当する所に設けられている。
【００８５】
長尺シリンドリカルレンズ１１の入出射面方向の姿勢は同図（Ａ），（Ｂ）に示す各支持部材１６、１７により擬似的な３点受けと成り、これにより該当位置の長尺シリンドリカルレンズ１１側は所定の平面度を確保している。支持部材１６は長尺シリンドリカルレンズ１１の高さ中央まで突出した線状の受け面より成り、支持部材１７は長尺シリンドリカルレンズ１１の高さに渡って突出した線状の受け面より成る。
【００８６】
また長尺シリンドリカルレンズ１１の上下方向（副走査方向）Ｔは同図（Ａ）、（Ｃ）に示す該長尺シリンドリカルレンズ１１の長手方向の端部に設けられた２つの突起１５がハウジング２５の座面に突き当たることによって位置決めされる。長尺シリンドリカルレンズ１１は各位置決め部１５と１６，１７に対向する位置を矢印２０，２１で示した方向からバネ部材（不図示）で押すことにより固定される。本実施形態では合計４点の支持点を持つ。尚、同図（Ｂ）に示す１９は取付け方向の識別用面取り部である。外形形状を非対称にすることで取付け方向を間違えた場合は設置できないようにするためである。
【００８７】
長尺シリンドリカルレンズ１１は、その長手方向の両端で支持されるので中央部は空間に浮いており、外部からの振動の影響を受けやすい。
本実施形態ではこの対策として同図（Ａ），（Ｂ），（Ｃ）に示すように接着台座２６を嵌合部材２２とは独立に、かつ長尺シリンドリカルレンズ１１と接触しないようにハウジング２５上に設け、該長尺シリンドリカルレンズ１１の外枠と該接着台座２６との間隔を約０．４ｍｍ以下（好ましくは０．０３ｍｍ〜０．４ｍｍ）に狭め、その位置に接着剤２３を塗布して軽微な接着を行っている。このようにすれば接着強度は振動を抑える程度に軽微なものに管理することができ、前述の長尺シリンドリカルレンズ１１の中央基準による嵌合及び４点支持による位置決め基準と矛盾することはない。尚、上記軽微とは位置決めの作用を乱さない程度に管理された接着力を意味する。接着剤２３は紫外線硬化である。
【００８８】
また本実施形態では同図（Ｄ）に示すように接着台座２６と嵌合部材２２との間（中央基準の間）に溝部２７が形成されてあるので接着剤２３が中央基準の間まで広がる心配はない。接着台座２６を長尺シリンドリカルレンズ１１側に設けないのは、該長尺シリンドリカルレンズ１１の外形形状が複雑になって成形安定性を損なうことを避けるためである。
【００８９】
このように本実施形態では上述の如く第２の光学系４３を構成する長尺シリンドリカルレンズ１１の長手方向の中央部に位置決め部１４，１４’を設け、ハウジング２５上に該長尺シリンドリカルレンズ１１とは接触しない接着台座２６を備え、該接着台座２６と該長尺シリンドリカルレンズ１１との隙間に接着剤２３を充てんし、該長尺シリンドリカルレンズ１１を該ハウジング２５に固定することにより、外部からの振動の影響を防止し、該レンズの振動を抑えている。
【００９０】
尚、長尺シリンドリカルレンズ側に突出した嵌合部材を設け、接着台座に凹形状の位置決め部を設けても良い。また後述するブランク露光があるＢＡＥプロセスを用いた画像形成装置では、有効走査領域が長くなるので長尺シリンドリカルレンズの主走査方向の形状も同様に長くする必要があり、振動を拾いやすくなる。このことから上記に示した長尺レンズの支持方法は、特に有効といえる。また本実施形態では長尺シリンドリカルレンズを例にとり、その支持方法について説明してきたが、もちろん他の長尺レンズであっても良いことは言うまでもない。
【００９１】
［コンパクトに構成した走査光学装置の説明］
図７は図１に示した走査光学装置をコンパクトに構成したときの副走査断面図である。同図において図１に示した要素と同一要素には同符番を付している。
【００９２】
同図において入射光学系及びポリゴンミラー１０からｆθレンズ系４４までの光学部材は光学箱２５の上面に配置され、ハの字ミラー５２としての第１、第２の折り曲げミラー２７、２８を直角（ハの字）に配置することにより、光路を光学箱２５の下面に取り回している。同図に示す１点鎖線は前記図１（Ｂ）のＢＢ′で示した直線を第１、第２、第３の折り曲げミラー２７，２８，２９によって折り曲げられた様子を示している。第１、第２の折り曲げミラー２７，２８はそれぞれ別個に光学箱２５に取り付けられるが、互いの直角度の誤差を所定の範囲内に収めるために一方の折り曲げミラーには調整機構が設けられており、光学箱２５の基準、例えばポリゴンミラーユニットの取付け座面に対して平行な光束がハの字ミラー５２の透過後も平行で所定の高さを通るように該光学箱２５との関係があらかじめ調整されている。
【００９３】
第３の折り曲げミラー２９は光学箱２５から出射する光束を感光ドラム面１２側に折り曲げるためのミラーである。第３の折り曲げミラー２９は該ミラー２９の裏面側を３点のセットビスで支持され、該３点のセットビスを調整することにより、感光ドラム面１２への照射位置高さ（感光ドラム周方向の位置）、走査線傾き（感光ドラム回転軸と走査線の平行度）、全体倍率（第３の折り曲げミラーから感光ドラムまでの距離）が所定の性能に合わせられる。
【００９４】
防塵ガラス３０は感光ドラム面１２近傍からの塵埃、飛散トナー等から光学部材の汚れを防止している。また防塵ガラス３０は着脱可能で、適時清掃することによって汚れを取り除くことができる。ゴースト遮光板４１はｆθレンズ系４４からの正反射光を遮光するための部材であり、光学箱２５の底面を補強しているリブと遮光板とを兼用しており、ハの字ミラー５２以降へ正反射光が抜けないように所定の高さに決められている。３２，３３は各々光学箱２５を密閉するための蓋である。
【００９５】
［実施形態２］
図８は本発明の実施形態２のポリゴンミラーの主要部分の要部概略図である。同図において図５に示した要素と同一要素には同符番を付している。
【００９６】
本実施形態においてはポリゴンミラー１０の隣接面の境界部において、一方の偏向面が他方の偏向面に延在しており、該延在する領域１０ｃの長さが該ポリゴンミラー１０の偏向面１０ａで偏向反射される光束の主走査方向の光束幅Ｗに対して５％以下（好ましくは１％〜５％）となるように設定している。即ち，ポリゴンミラー１０の偏向面１０ａは、一方の境界部が隣接面から延在され、他方の境界部が隣接面に延在するように設定されている。
【００９７】
このように本実施形態では上述の如く境界部の形状を形成することにより、前記図５（Ａ）に示すような入射光が偏向面を照射してもフレアとはならず、延在する偏向面の光束幅γ分，該偏向面１０ａの幅が長くなっただけである。
【００９８】
OFS光学系の場合は偏向面の主走査方向の幅が光束幅、すなわち主走査方向のスポット径を決めているので、これらの変化量を抑えるように許容値を決めればよい。ここで、「これらの変化量」とは、光束幅やスポット径の変化量のことを意味する。また「許容値」とは延在する領域１０ｃの幅γのことである。通常５％程度のスポット径は許容されるので加工方法を工夫することにより、このような延在する形状を形成するとフレアは生じなくなる。また常に隣接面の一方向に延在するように加工すれば、延在量を含んだ偏向面の幅を略均一に管理でき、これにより主走査方向のスポット径の変動も抑えることができる。尚、本実施形態において、その他の構成及び光学的作用は前述の実施形態１と略同様である。
【００９９】
［参考例１］
図９（Ａ）は本発明の走査光学装置の参考例１の主走査断面図、図９（Ｂ）は図９（Ａ）のＣＣ′断面図（ＣＣ′副走査断面図）である。同図（Ａ），（Ｂ）において図１に示した要素と同一要素には同符番を付している。尚、同図（Ａ）においては前記図１（Ａ）に示した走査開始位置のタイミングを制御する書き出し位置検出光学系３５等は省略している。
【０１００】
本参考例において前述の実施形態１、２と特に異なる点は入射光学系４１をＵＦＳ光学系より構成し、ポリゴンミラー１０の偏向面１０ａの大きさを実施形態１、２のポリゴンミラーに比して大きくした点、第２の光学系４３を単一のレンズ（ｆθレンズ）４５より構成した点である。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。
【０１０１】
即ち、本参考例におけるポリゴンミラー１０の偏向面１０ａの主走査方向の幅は、該ポリゴンミラー１０で偏向反射されてｆθレンズ４５に向かう光束の光束径はOFS光学系と同じ幅であるが、OFS光学系のポリゴンミラーの偏向面より３倍以上大きい。従って走査角が大きくなると入射光束径が偏向面でケラレてしまうので、例えば解像度６００ｄｐｉ、５０枚機相当の装置では走査効率（duty）はせいぜい７０％程度である。しかしながら、更なる高速化を目指すと１ラインの点灯時間そのものが短くなり、光源を消灯することが困難になってくる。UFS光学系の場合もOFS光学系ほどではないが、光源の常時点灯は必須となる。
【０１０２】
同図（Ｂ）においてレーザユニット１から出射した光束はシリンドリカルレンズ６の光軸を外れた位置を通過し、ポリゴンミラー１０の偏向面１０ａに対して斜め方向から入射している。このようにポリゴンミラー１０の偏向面１０ａに対し副走査断面内において斜め方向から光束を入射させることにより、該偏向面１０ａが主走査断面内において入射光学系の光軸と垂直な関係にあっても、該偏向面１０ａからの正反射光は光源に戻らないので、該光源の動作の安定性を確保することができる。
【０１０３】
尚、本参考例においても前述の実施形態と同様にポリゴンミラー１０の隣接面の境界部（エッジ部）の幅を該ポリゴンミラー１０で偏向反射される光束の主走査方向の走査幅に対して１％以下に成るように設定しており、もしくは隣接面の境界部を偏向面の延在部として加工処理している。これによりポリゴンミラー１０の境界部からの反射光がフレアー光として被走査面に到達しても実質的に画像劣化に成らないようにし、もしくはフレアー光が発生しないように防止している。また本実施形態では走査効率が７０％以上と成るように各要素を設定している。
【０１０４】
［画像形成装置］
図１０は本発明の光走査光学装置を用いた画像形成装置である電子写真プリンタの構成例を示す副走査方向の要部断面図である。
【０１０５】
図中、１００は先に説明した本発明の実施形態１、２のいずれかの光走査光学装置を示す。１０１は静電潜像担持体たる感光ドラム（感光体）であり、該感光ドラム１０１の上方には該感光ドラム１０１の表面を一様に帯電せしめる帯電ローラ１０２が該表面に当接している。該帯電ローラ１０２の当接位置よりも上方の上記感光ドラム１０１の回転方向Ａ下流側の帯電された表面には、光走査光学装置１００によって走査される光ビーム（光束）１０３が照射されるようになっている。
【０１０６】
光ビーム１０３は、画像データ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上記感光ドラム１０１の表面に静電潜像を形成せしめる。該静電潜像は、上記光ビーム１０３の照射位置よりもさらに上記感光ドラム１０１の回転方向Ａ下流側で該感光ドラム１０１に当接するように配設された現像手段としての現像装置１０７によってトナー像として現像される。該トナー像は、上記感光ドラム１０１の下方で該感光ドラム１０１に対向するように配設された転写手段としての転写ローラ１０８によって転写材たる用紙１１２上に転写される。該用紙１１２は上記感光ドラム１０１の前方（図１０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。該用紙カセット１０９端部には、給紙ローラ１１０が配設されており、該用紙カセット１０９内の用紙１１２を搬送路へ送り込む。
【０１０７】
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１０において左側）の定着手段としての定着器へと搬送される。該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と該定着ローラ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を上記定着ローラ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をプリンタの外に排出する。
【０１０８】
［ＢＡＥプロセスを用いた画像形成装置］
また上記の画像形成装置はＢＡＥプロセス（バックグランド露光方式）の画像形成装置に用いても好適である。
【０１０９】
ここでＢＡＥプロセスとはBackground area exposureの略でネガトナーを用いた露光プロセスのことである。被走査面である感光ドラム面上に光束を照射していない部分が画像を形成する。ＢＡＥプロセスはアナログ複写機の露光プロセスの為、通常走査光学系に適用されるＩＡＥ（image area exposure）プロセスとはネガとポジとの関係にある。
【０１１０】
感光ドラムの露光面は走査方向の幅が画像形成領域よりも幅広いため、画像形成領域外の感光ドラムの領域を露光して現像されないようにする必要がある。この領域の露光をブランク露光と呼ぶ。アナログ機では一般に補助光源によって露光されていたが、走査光学系では走査ビームの走査幅を延長し、画像形成領域にブランク露光の幅を加えた領域を光学的に有効な走査領域とする。BAEプロセスでは露光する走査幅が長くなるので、露光走査終端から次の書き出し位置までのライン間の時間は一層短くなる。光源を常時点灯させることにより、光源の安定性を確保でき、これにより画像の書き出し位置の検出精度や光源の出力安定性が向上し、良好なる画像を得ることができる。
【０１１１】
図１１にBAEプロセスに適用した場合の１ラインの走査（１ライン走査幅）における有効走査領域、画像形成領域、ブランク露光領域の関係を示す。
【０１１２】
同図に示すようにBAEプロセスを用いた画像形成装置では被走査面を露光する有効走査部（有効走査領域）は画像形成領域の両側にブランク露光領域を備えるので走査幅が長くなり、走査効率が増大する。画像の書き出し位置を検出するＢＤセンサーはブランク露光よりも上流側に位置するので走査終了から書き出し位置までの時間はますます短くなる。この為、光源の安定には常時レーザーが点灯している必要がある。フレア対策としても遮光部材は必要である。これはUFS光学系およびOFS光学系に共通であるが、特にOFS光学系とBAEプロセスとを組み合わせた場合は走査効率（duty）が大きいので非有効走査部の時間は短く、光源の常時点灯は必須である。
【０１１３】
【発明の効果】
本発明によれば前述の如く１ライン中の有効走査領域外においても常に光源が点灯する光走査光学装置において、ポリゴンミラーの隣接面の境界部（エッジ部）の幅を該ポリゴンミラーで偏向反射される光束の主走査方向の走査幅に対して１％以下に成るように設定することにより、該ポリゴンミラーの境界部からの反射光がフレアー光として被走査面に到達しても実質的に画像劣化に成らないようにすることができる光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。
【０１１５】
本発明は通常のUFS光学系はもちろんのこと、OFS光学系を用いた光走査光学装置やBAEプロセスを用いた画像形成装置においても特に有効である。
【図面の簡単な説明】
【図１】 本発明の実施形態１の要部断面図 （Ａ）主走査断面図、（Ｂ）副走査断面図、（Ｃ）入射系ＡＡ′断面図
【図２】 長尺シリンドリカルレンズの偏心構造図
【図３】 レーザユニットのシフト調整の原理説明図
【図４】 ミラーの調整機構を示した説明図
【図５】 ポリゴンミラーのエッジによるフレアー光の説明図
【図６】 長尺シリンドリカルレンズの支持方法の説明図
【図７】 本発明の実施形態１の他の要部概略図
【図８】 本発明の実施形態２のポリゴンミラーのエッジによるフレアー光の説明図
【図９】 本発明の参考例１の要部概略図
【図１０】 本発明の画像形成装置の副走査断面図
【図１１】 BAEプロセスの走査光学系の１ラインの有効走査領域の説明図
【符号の説明】
１…レーザユニット
２…光源（半導体レーザ）
３…コリメータ−レンズ部
４…凹レンズ
５…開口絞り
６…シリンドリカルレンズ
７…折り返しミラー
８…球面凹レンズ
９…シリンドリカルレンズ
１０…偏向手段（ポリゴンミラー）
１１…長尺シリンドリカルレンズ
１２…被走査面
１３…遮光部材
４１…入射光学系
４２…第１の光学系
４３…第２の光学系
４４…ｆθレンズ系
４５…ｆθレンズ
３４…反射ミラー
３５…書き出し位置検出光学系
３６…スリット
３７…集光レンズ
３８…同期検出素子
１４，１４′…中央基準
１５…基準
１６，１７…基準受け面
１８…ゲート
１９…面取り部
２０…基準押さえバネ
２１…基準押さえバネ
２２…中央基準カンゴウ部材
２３…UV接着剤
２５…ハウジング
２６…接着台座
２７…ミラー
２８…ミラー
２９…ミラー
３０…防塵ガラス
３１…感光ドラム
３２…上蓋
３３…下蓋
１００ 走査光学装置
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
１１２ 転写材（用紙）
１１３ 定着ローラ
１１４ 加圧ローラ
１１６ 排紙ローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning optical apparatus and an image forming apparatus using the optical scanning optical apparatus, and in particular, a light source is always turned on without turning off, and optical scanning is performed at a high speed. It is suitable for a device such as a printer.
[0002]
[Prior art]
Conventionally, an optical scanning optical apparatus has been widely applied as a writing optical system such as a laser beam printer (LBP) or a digital copying machine. In recent years, with the widespread use of these devices, demands for higher image quality and higher speed are increasing. For example, in order to improve the image quality with a resolution of 600 dpi or more, it is necessary to form a minute spot of about 60 μm on the surface to be scanned. However, since the diameter of the light beam to be scanned increases, the size of the optical deflector (polygon mirror) is required. Thus, it is difficult to achieve high speed.
[0003]
However, various approaches for speeding up have been proposed. For example, a polygon mirror is used to counter the multi-beam scanning system that performs parallel line scanning by increasing the number of beams and the conventional UFS (Under Filled Scanner) system (UFS optical system). OFS (Over Filled Scanner) method (OFS optical system) has been proposed.
[0004]
The OFS method is promising as a method for overcoming the problems of the UFS method, which is described below.
[0005]
The UFS method is a method of performing deflection scanning by causing a light beam having a predetermined width for forming a minute spot, which is narrower than the width of the deflection surface in the main scanning direction, to enter one deflection surface (reflection surface) of a polygon mirror. This UFS method changes the position of the incident light beam on the deflection surface as the deflection surface rotates, so that the width of the deflection surface in the main scanning direction is reduced in order to prevent the incident light beam from vignetting in a predetermined scanning angle range. There is a problem in that the polygon mirror must be larger than a certain size. Increasing the number of deflection surfaces of the polygon mirror further increases the size and rotational load, making it difficult to rotate at high speed. Therefore, the UFS method generally employs a high-speed method using multi-beams, and requires a complicated configuration for multi-beams.
[0006]
The ratio of the theoretical scanning angle that can be scanned on one deflection surface and the scanning angle that scans the effective scanning area is called scanning efficiency. In the UFS method, the incident beam has a predetermined beam width. The constraint is that the light beam does not vignett on the deflection surface. The scanning efficiency is at most about 70% in the UFS method with high resolution and a high resolution specification. The remaining 30% is distributed before and after the image forming area, and is used for electrical processing such as stabilizing the light source at a predetermined output or detecting the timing of the image writing position.
[0007]
The light source is once turned off immediately after the scanning of the image forming area of one line. This is because an unnecessary light beam that does not contribute to scanning hits the end of the optical member or a structure that supports the optical member, and reflected light or scattered light reaches the surface to be scanned as a flare, which degrades the image. It is preventing.
[0008]
In addition, since it is necessary to turn on the light source before the effective scanning area in order to detect the image writing position on the scanning start side, the occurrence of the same flare is unavoidable, and the shape of the light shielding plate, the optical member, and the support member In order to prevent the flare light from being generated, it is prevented from reaching the surface to be scanned.
[0009]
On the other hand, in the OFS system, the light beam emitted from the light source is incident on the deflecting surface of the polygon mirror in a state wider than the width of the deflecting surface in the main scanning direction (the light beam is incident across the deflecting surfaces of the polygon mirror), In this method, one deflecting surface rotates and scans in an incident light beam. Since the incident light beam width is set to be sufficiently large, there is no fear that the light beam will be vignetted due to the scanning angle of the polygon mirror. The width of the deflecting surface can be matched with the incident beam width in the UFS method, so even if the number of deflecting surfaces is increased, the polygon mirror diameter does not become as large as the UFS method, and it is possible to scan at a higher speed by increasing the number of surfaces. .
[0010]
The OFS method is capable of scanning with 100% scanning efficiency in principle, but in reality, it takes time to stabilize the output of the light source and to detect the timing of the image writing position until the start of scanning. Therefore, the scanning efficiency is suppressed to about 90%, for example.
[0011]
Thus, in the OFS method, the scanning optical device can be speeded up by increasing the number of surfaces without increasing the polygon mirror and increasing the scanning efficiency. Furthermore, it goes without saying that even higher speeds can be expected if the OFS system is made into a multi-beam.
[0012]
[Problems to be solved by the invention]
As the speed of the apparatus increases, the scanning time for one line is shortened, and considerable high-speed processing is required within a slight lighting preparation period before the start of scanning. These processing speeds have limits that are determined by the performance of the circuit control device and the rise stability of the light source.
[0013]
Furthermore, the OFS method is more severe because the scanning efficiency is higher than that of the UFS method, and there is almost no time margin for temporarily turning off the light source immediately after the end of the effective scanning area of one line. That is, if the light source is turned off once because the next line scan starts immediately, the rise time until reaching the predetermined light amount after lighting cannot be secured. There is a problem that the accuracy of detecting the output of the light source is reduced, leading to deterioration of the image.
[0014]
  In the optical scanning optical apparatus in which the light source is always turned on even outside the effective scanning area in one line, the width of the boundary portion (edge portion) of the adjacent surface of the polygon mirror is set to the main part of the light beam deflected and reflected by the polygon mirror. By setting it to be 1% or less with respect to the scanning width in the scanning direction, even if the reflected light from the boundary portion of the polygon mirror reaches the surface to be scanned as flare light, the image does not substantially deteriorate. It is an object to provide an optical scanning optical device that can be configured and an image forming apparatus using the same.
[0015]
[Means and Actions for Solving the Problems]
  An optical scanning optical device according to a first aspect of the present invention comprises light source means,There are 12 deflection surfacesA polygon mirror, a first optical system that causes the light beam emitted from the light source means to enter the polygon mirror, and a light beam deflected by the deflection surface of the polygon mirror is imaged in an effective scanning area on the surface to be scanned. An optical scanning optical device having a second optical system,
  The first optical system causes the light beam emitted from the light source means to enter the deflection surface of the polygon mirror in a state wider than the width of the deflection surface in the main scanning direction within the main scanning section,
  When the light beam emitted from the light source means scans outside the effective scanning area on the surface to be scanned, it is set so that the light beam emitted from the light source means always lights up,
  The polygon mirror has a ridge-line edge portion formed at the boundary between adjacent deflection surfaces of the plurality of deflection surfaces constituting the polygon mirror,
  In the main scanning section, the width of the edge portion of the ridgeline is relative to the width of the deflection surface of the polygon mirror in the main scanning direction.0.02% to 1%It is characterized by being set as follows.
[0016]
  According to a second aspect of the present invention, there is provided an image forming apparatus according to the first aspect, wherein the optical scanning optical device according to the first aspect, a photosensitive drum disposed on a scanned surface of the optical scanning optical device, and a light beam scan on the photosensitive drum. Developing means for developing the electrostatic latent image formed by toner as a toner image, transfer means for transferring the developed toner image to a sheet, and fixing means for fixing the transferred toner image to the sheet. It is characterized by that.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
1A is a main scanning sectional view of Embodiment 1 of the scanning optical apparatus of the present invention, FIG. 1B is a sub-scanning sectional view of FIG. 1A, and FIG. It is principal part sectional drawing (AA 'sectional drawing) cut with the plane orthogonal to a scanning cross section.
[0036]
In this specification, the main scanning section is a section of the scanning optical system projected onto a plane perpendicular to the rotation axis of the polygon mirror, and the sub-scanning section is a plane that passes through the rotation axis of the polygon mirror and is orthogonal to the main scanning section. Refers to the cross section cut out at.
[0037]
In the figure, reference numeral 1 denotes a laser unit (optical unit), which is formed by integrating a semiconductor laser (laser light source) 2 as a light source and a collimator lens unit 3 formed by bonding two spherical lenses. By performing predetermined optical adjustment, a parallel light beam parallel to the optical axis of the collimator lens unit 3 is emitted. The laser unit 1 also includes shift adjusting means (not shown) that can be fixed in parallel with a predetermined amount in the direction of arrow E perpendicular to the optical axis of the collimator lens unit 3 in the main scanning section.
[0038]
The semiconductor laser 2 in the present embodiment is set so that the light beam is always turned on and not turned off even when the light beam scans outside the effective scanning region (ineffective scanning portion). That is, the semiconductor laser 2 continues to be turned off even after the image formation is completed, and is not turned off until the next line scan starts.
[0039]
Reference numeral 4 denotes a concave lens having negative refractive power, and a parallel light beam emitted from the laser unit 1 is a weakly divergent light beam. Reference numeral 5 denotes an aperture stop, which regulates a passing light beam and shapes a beam shape. A cylindrical lens 6 has a predetermined refractive power only in the sub-scanning direction. Reference numeral 7 denotes a folding mirror that bends the optical path of the light beam that has passed through the cylindrical lens 6 toward the optical deflector 10.
[0040]
  Each element of the laser unit 1, the concave lens 4, the aperture stop 5, the cylindrical lens 6 and the folding mirror 7 constitutes one element of the incident optical system 41. The incident optical system 41 and first, Each element of the second fθ lenses 8 and 9 isfθ lens system 42It constitutes one element.
[0041]
Reference numeral 10 denotes a polygon mirror (optical deflector) as a deflecting means, which is rotated at a constant speed in the direction of arrow P in the figure by a driving means (not shown) such as a motor.
[0042]
Reference numeral 43 denotes a second optical system, which has an fθ lens system 44 having first and second fθ lenses and a long cylindrical lens (long cylindrical lens) 11. The fθ lens system 44 in this embodiment has a spherical concave lens 8 as a first fθ lens and a cylindrical lens 9 as a second fθ lens, and has refractive power mainly in the main scanning direction, and fθ. The characteristics and the curvature of field in the main scanning direction are corrected well over the effective scanning area. The long cylindrical lens 11 has refracting power mainly in the sub-scanning direction, and the deflection surface of the polygon mirror 10 and the surface to be scanned are in a substantially conjugate relationship in the sub-scanning cross section. The irradiation position on the photosensitive drum surface 12 as the surface to be scanned is prevented from shifting and image pitch unevenness. The long cylindrical lens 11 suppresses field curvature in the sub-scanning direction on the photosensitive drum surface 12, and keeps the magnification substantially constant to suppress variation in spot diameter.
[0043]
The long cylindrical lens 11 is mainly provided with a refractive power in the sub-scanning direction and disposed in the vicinity of the photosensitive drum surface 12. The imaging magnification in the sub-scanning direction from the polygon mirror 10 to the photosensitive drum surface 12 is 1 or less. This is because a reduction system is used to alleviate the occurrence of pitch unevenness with respect to the eccentricity around the rotation axis of the polygon mirror 10.
[0044]
Reference numeral 12 denotes a photosensitive drum surface as a surface to be scanned.
A light shielding member 13 is disposed between the polygon mirror 10 and the fθ lens system 44. Unnecessary light beams on the scanning start side and the scanning end side deflected and reflected by the polygon mirror 10 (deflected and reflected by the polygon mirror 10). (Of at least a part of the light beam scanned outside the effective scanning area) is shielded.
[0045]
Reference numeral 34 denotes a reflection mirror (hereinafter also referred to as “BD mirror”), which is arranged on a scanning line in the main scanning direction, and is a light beam for synchronization detection for adjusting the timing of the scanning start position on the photosensitive drum surface 12. (BD light flux) is reflected toward the synchronization detecting element 38 described later. Reference numeral 36 denotes a synchronization detection slit (hereinafter also referred to as a “BD slit”), which is arranged at a position equivalent to the photosensitive drum surface 12 and determines an image writing position. Reference numeral 37 denotes a condensing lens (hereinafter also referred to as “BD lens”) for making a conjugated relationship between the BD mirror 34 and the synchronization detecting element 38, and correcting the surface tilt of the BD mirror 34. . Reference numeral 38 denotes an optical sensor (hereinafter also referred to as a “BD sensor”) as a synchronization detection element. In this embodiment, a synchronization signal (BD signal) obtained by detecting an output signal from the BD sensor 38 is used. The timing of the scanning start position for image recording on the photosensitive drum surface 12 is adjusted. Each element of the BD slit 36, the BD lens 37, and the BD sensor 38 constitutes one element of the writing position detection optical system 35.
[0046]
In the present embodiment, as described above, the light source is not turned off even outside the effective scanning area in one line, and is always turned on, thereby improving the detection accuracy of the image writing position and the output stability of the light source, and always A good image is obtained. In addition, each element is set so that the scanning efficiency of the optical scanning optical apparatus of this embodiment is 80% or more.
[0047]
Here, the optical action of the present embodiment will be described with reference to FIG.
[0048]
In FIG. 1A, the parallel light beam emitted from the laser unit 1 is converted into a weak divergent light beam by the concave lens 4, the light beam diameter is shaped by the aperture stop 5, transmitted through the cylindrical lens 6, and bent by the folding mirror 7. This light beam passes through the second and first fθ lenses 9 and 8 constituting the fθ lens system 44, and becomes a parallel light beam again and enters the deflection surface from approximately the center of the deflection angle of the polygon mirror 10 (front surface). incident). The beam width of the parallel beam at this time is set to be sufficiently wider than the facet width of the deflection surface of the polygon mirror 10 in the main scanning direction. That is, a plurality of deflection surfaces of the polygon mirror 10 are irradiated (overfilled scanning system).
[0049]
The light beam deflected and reflected by the polygon mirror 10 is blocked by the light shielding plate 13 from unnecessary light beams on the scanning start side and the scanning end side, passes through the first and second fθ lenses 8 and 9 again, and passes through the photosensitive drum surface 12. The light is guided upward, and the polygon mirror 10 is rotated in the direction of arrow P to scan the photosensitive drum surface 12 in the direction of arrow S with a constant linear motion. Thereby, an image is recorded on the photosensitive drum surface 12 as a recording medium.
[0050]
  At this time, a part of the light beam deflected and reflected by the polygon mirror 10 has its optical path bent by the BD mirror 34 on the upstream side outside the effective scanning region, and enters the writing position detection optical system 35, and the writing position detection optical system 35. The time when the luminous flux has passed is detected. That is, the light beam crossing the BD slit 36 is detected as a signal waveform by the BD sensor 38, and the rise time of the waveform is detected. This detection timePlaceBy starting to write an image after a certain delay time, it is possible to align the writing start positions between lines.
[0051]
Next, the optical action of this embodiment will be described with reference to FIG.
[0052]
In FIG. 1C, the optical elements from the laser unit 1 to the cylindrical lens 6 are arranged on the same optical axis (AA ′), and this optical axis AA ′ is a plane (straight line) perpendicular to the rotation axis of the polygon mirror 10. It is inclined at an angle of θ / 2 with respect to BB ′. In the present embodiment, θ / 2 = 0.8 degrees. The oblique incident angle θ / 2 is indispensable for separating from the scanning light beam deflected and reflected by the polygon mirror 10 in the case where the oblique incidence angle θ / 2 is incident on the polygon mirror 10 from within the scanning range. The oblique incident angle θ / 2 is preferably as large as possible for separation, but is preferably about 1 ° or less in order to suppress the imaging performance and the scanning line curvature without using a special lens.
[0053]
The parallel light beam emitted from the laser unit 1 becomes a weak divergent light beam by the concave lens 4, is shaped into a predetermined light beam diameter by the aperture stop 5, is transmitted through the second and first fθ lenses 9 and 8 by the cylindrical lens 6, and is a polygon. An image is formed on the deflection surface 10 a of the mirror 10. The folding mirror 7 is arranged in parallel with the rotation axis of the polygon mirror 10, so that the convergent light incident obliquely from the cylindrical lens 6 is not twisted, and the focal line incident on the deflecting surface 10a is perpendicular to the optical axis. The orientation is maintained without rotating in the plane.
[0054]
In the optical system in which the light beam emitted from the light source is incident on the deflecting surface of the optical deflector in the main scanning section, the position of the deflecting surface of the optical deflector is the rotation of the optical deflector when the light source is always turned on. May be perpendicular to the incident light flux. In this case, the specularly reflected light from the deflecting surface returns to the light source, resulting in a phenomenon that the output stability of the light source is significantly impaired. Even if the light source continues to be turned on, it is meaningless if such a phenomenon occurs.
[0055]
Accordingly, in the present embodiment, as described above, the light beam that has passed through the first optical system 42 is incident on the deflection surface 10a of the polygon mirror 10 in an oblique direction within the sub-scanning section, thereby causing regular reflection from the deflection surface 10a. The light does not return to the light source, and further stability of the light source is obtained.
[0056]
Next, the optical action of this embodiment will be described with reference to FIG.
[0057]
In FIG. 1B, the light beam incident on the deflection surface 10a of the polygon mirror 10 from an oblique direction is deflected and reflected while drawing the conical surface while the deflection surface 10a rotates. The optical axes of the first and second fθ lenses 8 and 9 are set in a direction substantially parallel to the straight line BB ′ shown in FIG. Yes. However, in practice, the first and second fθ lenses 8 and 9 are inclined and slightly inclined in the sub-scanning section by a little less than 1 degree with reference to this arrangement. Even if the light beam reflected by the folding mirror 7 is specularly reflected by the surfaces of the first and second fθ lenses 8 and 9 by being arranged in this manner, the specularly reflected light is prevented from traveling toward the surface to be scanned. be able to.
[0058]
Between the second fθ lens 9 and the photosensitive drum surface 12, as described above, the long cylindrical lens 11 having a refractive power mainly in the sub-scanning direction is disposed, whereby the sub-scanning is performed on the photosensitive drum surface 12. Imaging in the direction is performed, and the tilting of the polygon mirror is corrected with the deflecting surface 10a of the polygon mirror 10 and the photosensitive drum surface 12 in a substantially conjugate relationship. Further, the long cylindrical lens 11 suppresses the curvature of field in the sub-scanning direction on the photosensitive drum surface 12, and the curvature radius in the sub-scan cross section of the lens is reduced on both sides in order to keep the magnification substantially constant and suppress the variation of the spot diameter. It is changed in the longitudinal direction. Further, since the scanning trajectory of the light beam incident on the long cylindrical lens 11 is curved, the optical axis of the long cylindrical lens 11 is reduced in order to suppress the scanning line curvature on the photosensitive drum surface 12 and improve the imaging performance. It is decentered in the sub-scanning direction, so that the incident light beam passes through a position off the optical axis.
[0059]
FIG. 2 shows the lens shape of the decentered long cylindrical lens 11. As shown in the figure, the center of the light beam is positioned above the lens optical axis. In order to realize such a lens shape, the long cylindrical lens 11 is formed by molding plastic. In addition, since the long cylindrical lens 11 does not need to have refractive power in the main scanning direction, both surfaces have the same curvature, a shape with a constant thickness and a stable moldability.
[0060]
Table 1 shows the configuration of the optical system from the polygon mirror 10 to the photosensitive drum surface 12.
[0061]
[Table 1]

[0062]
Next, the optical action of each optical element will be described.
[0063]
The laser unit 1 has an adjusted interval and angle of view between the semiconductor laser 2 and the collimator lens unit 3, emits a parallel light beam parallel to the optical axis of the collimator lens unit 3, and is attached with a predetermined accuracy. ing. The collimator lens unit 3 is composed of a cemented lens in which two spherical lenses, which are concave and convex from the semiconductor laser 2 side and are made of different glass materials, are bonded together to reduce spherical aberration and chromatic aberration. In the OFS optical system, a part of the parallel light beam emitted from the laser unit 1 is cut off by the deflecting surface 10a of the polygon mirror 10 in the main scanning direction to become a deflected light beam. Therefore, the effective light beam contributing to the scanning of the parallel light beam has a scanning angle. This is because the amount of spherical aberration contained in the light flux increases in proportion to the off-axis movement. For this reason, in the case of the conventional UFS optical system, even if the F value (F number) is sufficiently dark with a single lens, the OFS optical system requires a cemented lens that reduces spherical aberration. Chromatic aberration is performed for the purpose of suppressing focus fluctuation because the wavelength of the semiconductor laser 2 changes with the ambient temperature.
[0064]
The parallel light beam emitted from the laser unit 1 is converted into a weakly divergent light beam by the concave lens 4 and transmitted through the second and first fθ lenses 9 and 8 to be converted into a parallel light beam that has been enlarged again. With such an optical configuration, the semiconductor laser 2 of the laser unit 1 and the collimator lens unit 3 are integrated and shifted in parallel in the main scanning direction, and the lateral shift of the laser intensity distribution in the parallel light flux due to the tilt of the chip of the semiconductor laser element. Can be corrected. FIG. 3C is a main part schematic diagram showing the correction state at this time. 3A shows a case where the chip of the semiconductor laser element is not tilted, and FIG. 3B shows a case where the chip of the semiconductor laser element is tilted.
[0065]
  The shift adjustment means is included in the configuration in the laser unit 1 and has a mechanism that can shift in the main scanning direction while maintaining the positional relationship between the semiconductor laser 2 and the collimator lens unit 3 with respect to the attachment member to the incident optical system 41. I have. Adjustment of the optical characteristics of the laser unit 1 performed on a single jig is performed by adjusting the focus and angle of view, and then shifting the light source 2 and the collimator lens unit 3 together in the main scanning direction so as to be on the reference axis. The shift amount is adjusted so that the ratio of the intensity of the light beam divided into two in the main scanning direction is less than or equal to a predetermined value for the light beam that passes through the predetermined opening provided. Since the adjusted laser unit 1 has a laser intensity peak substantially coincident with the optical axis of the incident optical system 41 and emits a parallel light beam parallel to the optical axis, compatibility as a single product can be guaranteed.
That is, the adjustment of the laser unit 1 is performed with a single (dedicated) jig.
1) The distance between the light source and the collimator lens is adjusted so that the parallel light beam is emitted.
2) The angle of view is adjusted so that the light source matches the optical axis on the cross section perpendicular to the optical axis of the collimator lens.
3) Shift adjustment is performed so that the intensity distribution of the laser beam coincides with the center of the aperture provided on the reference axis (optical axis).
The shift of the laser unit is adjusted.
The laser unit adjusted in this way is replaceable because the optical performance of the laser unit is constant, and has a performance that ensures compatibility.
[0066]
Further, the concave lens 4 is moved in the optical axis direction to correct the focus variation in the main scanning direction. The purpose of correcting the focus in the main scanning direction is for the following three reasons.
[0067]
(1) In the OFS optical system, the width of the deflection surface of the polygon mirror in the main scanning direction is narrower than that of the UFS optical system, and it is difficult to ensure equivalent surface accuracy in the main scanning direction.
[0068]
(2) Since the light beam passes through the first and second fθ lenses 8 and 9 in a reciprocating manner, the influence of the surface accuracy of the fθ lens is doubled. Furthermore, since the number of polygon surfaces increases in the OFS optical system, the focal length of the fθ lens increases, the sensitivity of surface accuracy increases, and focus fluctuations cannot be ignored.
[0069]
(3) Focuses on a narrow focal depth range for high resolution and small spot requirements
A mechanism for correcting the above is required.
[0070]
On the other hand, the focus correction in the sub-scanning direction may be performed by adjusting the concave lens 4 and moving the cylindrical lens 6 in the optical axis direction as before.
[0071]
  The folding mirror 7 is a folding mirror for causing the incident light beam to enter from the scanning center of the polygon mirror (approximately the center of the deflection angle).incidentThe optical system 41 is folded to be compact. In addition, the folding mirror 7 corrects an error of the oblique incident angle caused by the component tolerance of the incident optical system 41 from the laser unit 1 to the cylindrical lens 6 and makes it incident on the deflecting surface 10a of the polygon mirror 10 at a predetermined angle. 4 (A) and 4 (B), an initial adjustment mechanism that can be adjusted around a rotation axis parallel to the folding mirror 7 in the main scanning section is provided.
[0072]
4A and 4B, the rotation axis substantially coincides with the height of the incident light beam, and the support members (7a, 7b) disposed at this height serve as fulcrums on the back surface of the mirror, and are indicated by arrows. Adjust the rotation of the mirror by turning the screw. The folding mirror 7 is adjusted and fixed at a predetermined angle by observing the reflected light beam with an observation system (not shown).
[0073]
The width of the light beam incident on the deflection surface 10a of the polygon mirror 10 in the main scanning direction is limited by the aperture stop 5, and the deviation of the light beam due to the scanning angle of the polygon mirror 10, the tolerance of the incident optical system 41, and the positional accuracy of the polygon mirror 10 are controlled. Considering this, the width is set to about 2 to 3 times the width of the deflecting surface 10a in the main scanning direction. In this embodiment, it is a 12-sided polygon mirror with a circumscribed circle diameter of 29 mm, and an incident light flux of about 18 mm with respect to a deflection surface width of 7.5 mm. The aperture width in the sub-scanning direction is related to the spot diameter on the photosensitive drum surface 12.
[0074]
[Explanation of the action of the shading plate]
Next, the operation of the light shielding plate 13 as a light shielding member will be described.
[0075]
In the present embodiment, as described above, the semiconductor laser 2 is set not to be turned off but always turned on even when the light beam scans outside the effective scanning region (ineffective scanning portion). Therefore, in this embodiment, unnecessary light beams on the scanning start side and the scanning end side among the light beams deflected and reflected by the polygon mirror 10 are blocked by the light shielding plate 13, so that the first and second fθ lenses 8, 9 and The flare light is not generated by irradiating the outside of the effective portion of the long cylindrical lens 11.
[0076]
In the present embodiment, the light shielding plate 13 is symbolically disposed between the polygon mirror 10 and the first fθ lens 8, but the present invention is not limited to this, and the light shielding plate 13 is further added before and after another optical member. A plurality of them may be arranged. This makes the flare shading effect more complete.
[0077]
[Description of the shape of the boundary of the deflection surface]
Next, the shape of the boundary portion (edge portion) of the adjacent surface (adjacent deflection surface) of the polygon mirror will be described with reference to FIGS.
[0078]
In the present embodiment, the polygon mirror 10 is a 12-sided regular polygon. The boundary portion (edge portion) 10b of the adjacent surface of the polygon mirror 10 has a ridgeline edge shape, and has a certain width as shown in FIG. In this embodiment, the width of the boundary portion 10b (the width in the direction in which the polygon mirror rotates) is the light beam width W in the main scanning direction of the light beam deflected and reflected by the deflection surface 10a of the polygon mirror 10, that is, the deflection surface 10a. It is set to be 1% or less (preferably 0.02% to 1%). In the present embodiment, since the light source is always turned on as described above, a moment occurs when the boundary portion 10b of the adjacent surface faces the scanned surface 12 directly. At this time, as shown in FIG. 5A, a part of the light beam incident on the boundary portion 10b from the front is specularly reflected with an intensity proportional to the width of the boundary portion 10b, and follows the same optical path as the normal scanning light. The center of the surface to be scanned 12 is irradiated and becomes flare light.
[0079]
However, in the present embodiment, as described above, the width of the boundary portion 10b is 1% or less with respect to the scanning width W in the main scanning direction of the light beam reflected by the deflection surface 10a of the polygon mirror 10 (that is, the width of the deflection surface 10a). Thus, the flare light intensity ratio is similarly about 1%, which does not substantially adversely affect the image. Further, in this embodiment, by making the wide direction of the emission surface of the semiconductor laser coincide with the main scanning direction and performing the adjustment shown in FIG. 3, the region that becomes 90% or more of the intensity peak of the light beam in the main scanning direction is It is set to enter the boundary portion 10b of the adjacent surface.
[0080]
Thus, in the present embodiment, as described above, in the optical scanning optical device in which the light source is always lit even outside the effective scanning region, the width of the boundary portion 10b of the adjacent surface of the polygon mirror 10 is reflected by the deflection surface 10a of the polygon mirror 10. By setting the light flux to be 1% or less with respect to the scanning width W in the main scanning direction, the reflected light from the boundary portion 10b of the polygon mirror 10 reaches the scanned surface 12 as flare light. However, image degradation is substantially prevented.
[0081]
[Description of support method for long cylindrical lens]
Next, a method for supporting the long cylindrical lens 11 according to the present invention will be described with reference to FIG.
[0082]
  Since the long cylindrical lens 11 is disposed in the vicinity of the scanned surface 12, the long cylindrical lens 11 has a long shape. Therefore, in order to prevent thermal contraction, vibration, etc., the long cylindrical lens 11 is illustrated.6Install as shown in (A), (B), (C).
[0083]
1A is a side view of the long cylindrical lens 11 viewed from the incident surface side, FIG. 1B is a top view of the long cylindrical lens 11 viewed from above, and FIG. It is explanatory drawing which showed a mode that the elongate cylindrical lens 11 was attached from the side. Li is a light incident surface, and Lo is a light exit surface.
[0084]
In FIG. 4A, reference numerals 14 and 14 ′ denote positioning portions which are lens center reference portions, each having a concave shape, and provided above and below the center in the longitudinal direction (main scanning direction) of the long cylindrical lens 11. . In the present embodiment, the position of the long cylindrical lens 11 in the longitudinal direction is determined by fitting the positioning portion 14 and the fitting member 22 protruding from the housing 25. The fitting member 22 is provided at a location corresponding to the central portion of the long cylindrical 11 in the housing 25 in the longitudinal direction.
[0085]
The posture of the long cylindrical lens 11 in the direction of the light incident / exiting surface becomes a pseudo three-point reception by the support members 16 and 17 shown in FIGS. 6A and 6B, whereby the long cylindrical lens 11 at the corresponding position. The side has a predetermined flatness. The support member 16 is composed of a linear receiving surface protruding to the center of the height of the long cylindrical lens 11, and the support member 17 is composed of a linear receiving surface protruding over the height of the long cylindrical lens 11.
[0086]
In the vertical direction (sub-scanning direction) T of the long cylindrical lens 11, two protrusions 15 provided at the end in the longitudinal direction of the long cylindrical lens 11 shown in FIGS. It is positioned by abutting against the seating surface. The long cylindrical lens 11 is fixed by pushing the positions facing the positioning portions 15, 16, and 17 with spring members (not shown) from the directions indicated by the arrows 20 and 21. In this embodiment, there are a total of four support points. Note that reference numeral 19 shown in FIG. 4B denotes a chamfering portion for identifying the mounting direction. This is to prevent installation when the mounting direction is wrong by making the outer shape asymmetric.
[0087]
Since the long cylindrical lens 11 is supported at both ends in the longitudinal direction, the central portion is floating in the space and is easily affected by vibration from the outside.
In this embodiment, as a countermeasure against this, as shown in FIGS. 6A, 6B, and 6C, the housing 25 is provided so that the adhesive base 26 does not come into contact with the long cylindrical lens 11 independently of the fitting member 22. The gap between the outer frame of the long cylindrical lens 11 and the adhesive pedestal 26 is narrowed to about 0.4 mm or less (preferably 0.03 mm to 0.4 mm), and an adhesive 23 is applied to the position. And light adhesion. In this way, the adhesive strength can be managed so as to be small enough to suppress vibrations, and there is no contradiction with the above-described positioning reference by the center reference of the long cylindrical lens 11 and the four-point support. Incidentally, the above-mentioned “minor” means an adhesive force controlled to such an extent that the positioning operation is not disturbed. The adhesive 23 is UV curable.
[0088]
Further, in this embodiment, as shown in FIG. 4D, since the groove portion 27 is formed between the adhesive pedestal 26 and the fitting member 22 (between the center reference), the adhesive 23 spreads between the center reference. Don't worry. The reason why the adhesive base 26 is not provided on the side of the long cylindrical lens 11 is to prevent the outer shape of the long cylindrical lens 11 from becoming complicated and impairing molding stability.
[0089]
Thus, in the present embodiment, as described above, the positioning portions 14 and 14 ′ are provided in the center portion in the longitudinal direction of the long cylindrical lens 11 constituting the second optical system 43, and the long cylindrical lens 11 is provided on the housing 25. The adhesive pedestal 26 that does not come into contact with the adhesive pedestal 26 is filled with an adhesive 23 in the gap between the adhesive pedestal 26 and the long cylindrical lens 11, and the long cylindrical lens 11 is fixed to the housing 25 from the outside. The vibration of the lens is prevented and the vibration of the lens is suppressed.
[0090]
A fitting member protruding toward the long cylindrical lens may be provided, and a concave positioning portion may be provided on the adhesive pedestal. Further, in an image forming apparatus using a BAE process with blank exposure, which will be described later, the effective scanning area becomes long, so that the shape of the long cylindrical lens in the main scanning direction needs to be lengthened in the same manner, and vibrations can be easily picked up. From this, it can be said that the method for supporting the long lens described above is particularly effective. In the present embodiment, a long cylindrical lens is taken as an example and the supporting method thereof has been described, but it goes without saying that other long lenses may be used.
[0091]
[Description of Compact Scanning Optical Device]
FIG. 7 is a sub-scanning sectional view of the scanning optical device shown in FIG. In the figure, the same elements as those shown in FIG.
[0092]
In the figure, the incident optical system and the optical members from the polygon mirror 10 to the fθ lens system 44 are arranged on the upper surface of the optical box 25, and the first and second folding mirrors 27 and 28 as the C-shaped mirror 52 are arranged at right angles ( The optical path is routed to the lower surface of the optical box 25. A one-dot chain line shown in the figure shows a state where the straight line indicated by BB ′ in FIG. 1B is bent by the first, second and third bending mirrors 27, 28 and 29. The first and second folding mirrors 27 and 28 are separately attached to the optical box 25, but an adjustment mechanism is provided on one of the folding mirrors in order to keep the perpendicularity error within a predetermined range. The relationship with the optical box 25 is such that the light beam parallel to the reference of the optical box 25, for example, the mounting seating surface of the polygon mirror unit, is parallel to the predetermined height after passing through the C-shaped mirror 52. It has been adjusted in advance.
[0093]
The third folding mirror 29 is a mirror for bending the light beam emitted from the optical box 25 to the photosensitive drum surface 12 side. The third bending mirror 29 is supported on the back side of the mirror 29 by three set screws, and the height of the irradiation position on the photosensitive drum surface 12 (the circumferential direction of the photosensitive drum) is adjusted by adjusting the three set screws. ), The scanning line inclination (parallelism between the photosensitive drum rotating shaft and the scanning line), and the overall magnification (distance from the third folding mirror to the photosensitive drum) are adjusted to predetermined performance.
[0094]
The dustproof glass 30 prevents the optical member from being contaminated by dust, scattered toner, etc. from the vicinity of the photosensitive drum surface 12. Further, the dust-proof glass 30 is detachable, and dirt can be removed by timely cleaning. The ghost light-shielding plate 41 is a member for shielding regular reflection light from the fθ lens system 44, and also serves as a rib that reinforces the bottom surface of the optical box 25 and the light-shielding plate. The predetermined height is determined so that the regular reflection light does not escape. Reference numerals 32 and 33 denote lids for sealing the optical box 25, respectively.
[0095]
[Embodiment 2]
FIG. 8 is a schematic view of the main part of the main part of the polygon mirror according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG.
[0096]
In the present embodiment, at the boundary portion between adjacent surfaces of the polygon mirror 10, one deflection surface extends to the other deflection surface, and the length of the extending region 10c is the deflection surface 10a of the polygon mirror 10. Is set to be 5% or less (preferably 1% to 5%) with respect to the light beam width W in the main scanning direction. That is, the deflection surface 10a of the polygon mirror 10 is set so that one boundary extends from the adjacent surface and the other boundary extends to the adjacent surface.
[0097]
Thus, in this embodiment, by forming the shape of the boundary portion as described above, even if incident light as shown in FIG. 5A irradiates the deflection surface, it does not flare, but extends deflection. Only the width of the deflection surface 10a is increased by the luminous flux width γ of the surface.
[0098]
  In the case of the OFS optical system, the width of the deflecting surface in the main scanning direction determines the light beam width, that is, the spot diameter in the main scanning direction. Therefore, an allowable value may be determined so as to suppress these variations.Here, “the amount of these changes” means the amount of change in the light beam width and the spot diameter. The “allowable value” is the width γ of the extending region 10c.Normally, a spot diameter of about 5% is allowed, and flare does not occur when such an extended shape is formed by devising a processing method. Further, if processing is performed so as to always extend in one direction of the adjacent surface, the width of the deflecting surface including the extending amount can be managed substantially uniformly, thereby suppressing the fluctuation of the spot diameter in the main scanning direction. In the present embodiment, other configurations and optical actions are substantially the same as those in the first embodiment.
[0099]
  [Reference example 1]
  FIG. 9A shows a scanning optical device according to the present invention.Reference example 1FIG. 9B is a CC ′ sectional view (CC ′ sub-scan sectional view) of FIG. 9A. In FIGS. 2A and 2B, the same elements as those shown in FIG. In FIG. 1A, the writing position detection optical system 35 for controlling the timing of the scanning start position shown in FIG. 1A is omitted.
[0100]
  BookReference exampleHowever, the difference from the first and second embodiments is that the incident optical system 41 is composed of a UFS optical system, and the size of the deflecting surface 10a of the polygon mirror 10 is larger than that of the polygon mirror of the first and second embodiments. The point is that the second optical system 43 is constituted by a single lens (fθ lens) 45. Other configurations and optical actions are substantially the same as those of the first embodiment, and the same effects are obtained.
[0101]
  That is, bookReference exampleThe width of the deflecting surface 10a of the polygon mirror 10 in the main scanning direction is the diameter of the light beam that is deflected and reflected by the polygon mirror 10 toward the fθ lens 45.Is the OFS optical systemIs the same width as, but is more than three times larger than the deflection surface of the polygon mirror of the OFS optical system. Therefore, when the scanning angle is increased, the incident light beam diameter is vignetted on the deflection surface. For example, in a device having a resolution of 600 dpi and a 50-sheet machine, the scanning efficiency (duty) is about 70% at most. However, if further speeding up is aimed at, the lighting time of one line itself becomes short, and it becomes difficult to turn off the light source. In the case of the UFS optical system, although not as much as the OFS optical system, it is essential to always turn on the light source.
[0102]
In FIG. 2B, the light beam emitted from the laser unit 1 passes through a position off the optical axis of the cylindrical lens 6 and is incident on the deflection surface 10a of the polygon mirror 10 from an oblique direction. In this way, the light beam is incident on the deflecting surface 10a of the polygon mirror 10 from an oblique direction in the sub-scanning section so that the deflecting surface 10a is in a vertical relationship with the optical axis of the incident optical system in the main scanning section. However, since the regular reflection light from the deflection surface 10a does not return to the light source, the stability of the operation of the light source can be ensured.
[0103]
  BookReference exampleAs in the above-described embodiment, the width of the boundary portion (edge portion) of the adjacent surface of the polygon mirror 10 is 1% or less with respect to the scanning width in the main scanning direction of the light beam deflected and reflected by the polygon mirror 10. In other words, the boundary portion between adjacent surfaces is processed as an extension portion of the deflection surface. As a result, even if the reflected light from the boundary portion of the polygon mirror 10 reaches the surface to be scanned as flare light, the image is not substantially deteriorated, or flare light is prevented from being generated. In this embodiment, each element is set so that the scanning efficiency is 70% or more.
[0104]
[Image forming apparatus]
FIG. 10 is a cross-sectional view of the main part in the sub-scanning direction showing a configuration example of an electrophotographic printer which is an image forming apparatus using the optical scanning optical device of the present invention.
[0105]
  In the figure, reference numeral 100 denotes the optical scanning optical apparatus according to any one of the first and second embodiments of the present invention described above. Reference numeral 101 denotes a photosensitive drum (photosensitive member) serving as an electrostatic latent image carrier, and a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is in contact with the surface above the photosensitive drum 101. Than the contact position of the charging roller 102UpwardThe charged surface on the downstream side in the rotation direction A of the photosensitive drum 101 is irradiated with a light beam (light beam) 103 scanned by the optical scanning optical device 100.
[0106]
The light beam 103 is modulated based on the image data. 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 converted into toner by a developing device 107 as a developing unit disposed so as to abut on the photosensitive drum 101 further downstream in the rotation direction A of the photosensitive drum 101 than the irradiation position of the light beam 103. Developed as an image. The toner image is transferred onto a sheet 112 as a transfer material by a transfer roller 108 serving as transfer means 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 (on the right side in FIG. 10), but can be fed manually. A paper feed roller 110 is disposed at the end of the paper cassette 109 and feeds the paper 112 in the paper cassette 109 to the transport path.
[0107]
As described above, the sheet 112 onto which the unfixed toner image has been transferred is further conveyed to a fixing device as a fixing unit behind the photosensitive drum 101 (left side in FIG. 10). 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 has been conveyed from a transfer unit. The sheet 112 is heated while being pressed by the pressure roller 114 and the pressure roller 114 to fix the unfixed toner image on the sheet 112. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the printer.
[0108]
[Image forming apparatus using BAE process]
The above image forming apparatus is also suitable for use in an image forming apparatus of a BAE process (background exposure method).
[0109]
Here, the BAE process is an abbreviation for Background area exposure, which is an exposure process using negative toner. A portion where the light beam is not irradiated forms an image on the surface of the photosensitive drum that is the surface to be scanned. Since the BAE process is an exposure process of an analog copying machine, it has a relationship between negative and positive with an IAE (image area exposure) process that is usually applied to a scanning optical system.
[0110]
Since the exposure surface of the photosensitive drum has a wider width in the scanning direction than the image forming area, it is necessary to expose the photosensitive drum area outside the image forming area to prevent development. This area exposure is called blank exposure. In an analog machine, exposure is generally performed by an auxiliary light source. However, in a scanning optical system, the scanning width of a scanning beam is extended, and an area obtained by adding a blank exposure width to an image forming area is used as an optically effective scanning area. In the BAE process, since the scanning width to be exposed becomes long, the time between lines from the end of exposure scanning to the next writing position is further shortened. By always turning on the light source, the stability of the light source can be ensured, whereby the detection accuracy of the image writing position and the output stability of the light source are improved, and a good image can be obtained.
[0111]
FIG. 11 shows the relationship between the effective scanning area, the image forming area, and the blank exposure area in one line scanning (one line scanning width) when applied to the BAE process.
[0112]
As shown in the figure, in the image forming apparatus using the BAE process, the effective scanning portion (effective scanning area) for exposing the surface to be scanned is provided with blank exposure areas on both sides of the image forming area. Will increase. Since the BD sensor for detecting the image writing position is located upstream of the blank exposure, the time from the end of scanning to the writing position becomes shorter. For this reason, in order to stabilize the light source, it is necessary that the laser is always on. As a countermeasure against flare, a light shielding member is necessary. This is common to UFS and OFS optical systems, but especially when the OFS optical system and the BAE process are combined, the scanning efficiency (duty) is large, so the time of the ineffective scanning section is short, and the light source is always on. It is essential.
[0113]
【The invention's effect】
According to the present invention, as described above, in the optical scanning optical device in which the light source is always turned on even outside the effective scanning area in one line, the width of the boundary portion (edge portion) of the adjacent surface of the polygon mirror is deflected and reflected by the polygon mirror. By setting the light flux to be 1% or less with respect to the scanning width in the main scanning direction, even if the reflected light from the boundary of the polygon mirror reaches the surface to be scanned as flare light It is possible to achieve an optical scanning optical device that can prevent image deterioration and an image forming apparatus using the same.
[0115]
The present invention is particularly effective not only in a normal UFS optical system but also in an optical scanning optical apparatus using an OFS optical system and an image forming apparatus using a BAE process.
[Brief description of the drawings]
1A and 1B are cross-sectional views of main parts of Embodiment 1 of the present invention. FIG. 1A is a main-scan cross-sectional view, FIG. 1B is a sub-scan cross-sectional view, and FIG.
Fig. 2 Eccentric structure of a long cylindrical lens
FIG. 3 is a diagram for explaining the principle of laser unit shift adjustment.
FIG. 4 is an explanatory diagram showing a mirror adjustment mechanism.
FIG. 5 is an explanatory diagram of flare light by the edge of a polygon mirror.
FIG. 6 is an explanatory diagram of a method for supporting a long cylindrical lens.
FIG. 7 is a schematic diagram of another main part of the first embodiment of the present invention.
FIG. 8 is an explanatory diagram of flare light caused by an edge of a polygon mirror according to the second embodiment of the present invention.
FIG. 9 shows the present invention.Reference example 1Main part schematic diagram
FIG. 10 is a sub-scan sectional view of the image forming apparatus of the present invention.
FIG. 11 is an explanatory diagram of an effective scanning area of one line of the scanning optical system of the BAE process.
[Explanation of symbols]
1 ... Laser unit
2. Light source (semiconductor laser)
3 ... Collimator-Lens
4. Concave lens
5 ... Aperture stop
6 ... Cylindrical lens
7 ... Folding mirror
8 ... Spherical concave lens
9 ... Cylindrical lens
10. Deflection means (polygon mirror)
11 ... Long cylindrical lens
12 ... surface to be scanned
13: Shading member
41. Incident optical system
42. First optical system
43 ... Second optical system
44 ... fθ lens system
45 ... fθ lens
34 ... Reflecting mirror
35. Writing position detection optical system
36 ... Slit
37 ... Condensing lens
38. Synchronization detecting element
14, 14 '... Central reference
15 ... Standard
16, 17 ... Standard receiving surface
18 ... Gate
19 ... chamfer
20 ... Reference presser spring
21 ... Standard holding spring
22 ... Central reference candy member
23 ... UV adhesive
25 ... Housing
26 ... Adhesive base
27 ... Mirror
28 ... Mirror
29 ... Mirror
30 ... Dust-proof glass
31 ... Photosensitive drum
32 ... Upper lid
33 ... Lower lid
100 Scanning optical device
101 Photosensitive drum
102 Charging roller
103 Light beam
107 Developing device
108 Transfer roller
109 Paper cassette
110 Paper feed roller
112 Transfer material (paper)
113 Fixing roller
114 Pressure roller
116 Paper discharge roller

Claims (2)

A light source means , a polygon mirror having 12 deflection surfaces, a first optical system for causing the light beam emitted from the light source means to enter the polygon mirror, and a light beam deflected by the deflection surface of the polygon mirror. A second optical system that forms an image in an effective scanning area on the surface to be scanned, and an optical scanning optical device comprising:
The first optical system causes the light beam emitted from the light source means to enter the deflection surface of the polygon mirror in a state wider than the width of the deflection surface in the main scanning direction within the main scanning section,
When the light beam emitted from the light source means scans outside the effective scanning area on the surface to be scanned, it is set so that the light beam emitted from the light source means always lights up,
The polygon mirror has a ridge-line edge portion formed at the boundary between adjacent deflection surfaces of the plurality of deflection surfaces constituting the polygon mirror,
In the main scanning section, the width of the edge portion of the ridgeline is set to be 0.02% to 1% with respect to the width of the deflecting surface of the polygon mirror in the main scanning direction. Optical device.   A toner image obtained by scanning the optical scanning optical device according to claim 1, a photosensitive drum disposed on a surface to be scanned of the optical scanning optical device, and an electrostatic latent image formed by scanning a light beam on the photosensitive drum. An image forming apparatus comprising: a developing unit that develops the toner image; a transfer unit that transfers the developed toner image onto a sheet; and a fixing unit that fixes the transferred toner image onto the sheet.

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