JP4409823B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

ここで、梁の長さＬと振れ角θは比例関係にあるため、
θ＝Ａ／Ｉｆ＾２、 （Ａは定数）
で表され、振れ角θは慣性モーメントＩに反比例し、共振振動数ｆを高めるには慣性モーメントを低減しないと振れ角θが小さくなってしまう。そこで、実施例では可動ミラー裏側２１９の基板厚ｄを格子状に残し、それ以外をｄ／１０以下の厚さまでエッチングにより肉抜きすることで、慣性モーメントを約１／５に低減している。
【００１３】
一方、空気の誘電率をε、電極長さをＨ、印加電圧をＶ、電極間距離をδとすると、
電極間の静電力ｆ＝εＨＶ＾２／２δ
となり、振れ角θ＝Ｂ・Ｆ／Ｉ、 （Ｂは定数）
とも表すことができ、電極長さＨが長いほど振れ角θが大きくなり、櫛歯状とすることで櫛歯数ｎに対して２ｎ倍の駆動トルクが得られる。
反面、可動ミラーの速度υ、面積Ｅに対して、空気の密度ηとすると、
空気の粘性抵抗Ｐ＝Ｃ・ηυ＾２・Ｅ＾３、 （Ｃは定数）
が可動ミラー２０２の回転に対向して働くため、カバー２０５で密封し減圧状態に保持するのが好ましい。実施例では非蒸発型ゲッタを同梱し、外部からの加熱で活性化させ１ｔｏｒｒ以下としている。
【００１４】
第２の基板２０７は厚さ２８０μｍのＳｉ基板からなり、中央部を貫通して第１のＳｉ基板２０６の支持部に絶縁層を挟んで接合され、可動ミラー２０２の揺動空間を形成している。第２の基板２０７の上面には２枚のＳｉ基板により構成した対向ミラーチップ２１６、２１５が架橋された状態で接着されている。第2のミラーチップ２１６は結晶面方位＜１１１＞から、第１のミラーチップ２１５は結晶面方位＜１１０＞からそれぞれ約９°スライス角度を傾けたウエハを用い、エッチングにより＜１１１＞面を露出させ、基板面より各々９°、２６．３°傾けた傾斜面を形成して切り出されている。この切り出し面を接合面となし、この面と連続した基板面に金属被膜が蒸着されて反射面となっている。２枚の対向ミラーチップ２１６、２１５は、相互間に配された開口部を挟み、屋根状に１４４．７°の角度をなす反射面２１７と２１８とを対で配備された構成となっている。
【００１５】
図４は上記振動ミラーモジュール２００の副走査断面のレイアウトを示す。半導体レーザ４０１から射出した光ビームは後述するようにカップリングレンズ４０２、シリンダミラー４０３を介して、可動ミラー２０２に対しねじり梁を含む副走査断面内で法線に対して副走査方向に約２０°傾けて開口部２１４より光ビームが入射され、可動ミラー２０２の面で反射された光ビームは第１の反射面２１７に入射され可動ミラー２０２に戻され、さらに可動ミラー２０２で反射した光ビームは開口部２１４を超えて第２の反射面２１８に入射され、可動ミラー２０２との間で３往復しながら反射位置を副走査方向に移動させ、合計５回の可動ミラー２０２での反射により再度、開口部２１４から射出される。図示の実施例では、このように複数回反射を繰り返すことで、可動ミラー２０２の小さい振れ角で大きな走査角が得られるように工夫し、光路長を短縮している。
いま、可動ミラー２０２での総反射回数をＮ、振れ角をαとすると、走査角θは２Ｎαで表すことができる。実施例では、Ｎ＝５、α＝５°であるから、最大走査角は５０°となり、そのうち３５°を画像記録領域としている。
【００１６】
前述の共振を利用することで印加電圧は微小で済み発熱も少ないが、上式から明らかなように記録速度が速くなるに従って、つまり共振周波数が高くなるに従って、トーションバーのばね定数を高める必要があり、振れ角がとれなくなってしまう。そこで、上記したように対向ミラーを設けることで走査角を拡大し、記録速度によらず必要十分な走査角が得られるようにしている。
また、二つの反射面２１７、２１８を屋根状に配置し、これらの反射面で反射される毎に、可動ミラー２０２への副走査方向での入射角度が繰り返し正負方向に振り分けられるように、言いかえれば、反射に伴う進行方向が右向き、左向き、に振り分けられるようにすることで、斜入射に伴う被走査面での走査線の曲がりを抑え、直線性を維持するとともに、光軸と直交する面内での光束の回転が、射出時にはもとの姿勢に戻るようにして、結像性能の劣化が起きないように配慮している。
【００１７】
上記基板２０６は絶縁基板２１３上に積み重ねて接合され、支持基板２０１に固定されている。絶縁基板２１３は中央部が貫通され、窓枠状に形成されることで可動ミラー２０２の揺動空間が形成され、第１の基板２０６に配備された固定電極と導通するパッド部２１３を備える。リード端子２１２は絶縁材を介して支持基板２０１を貫通して挿入され、上側に突出したリード端子２１２の端部と上記パッド部２１３とがワイヤーボンディングによって結線され、封止された内外の電気配線がなされている。
カバー２０５は、支持基板２０１の外周に設けられた段差部にはめ込まれ、光ビームの射出開口にはガラス窓２０４がカバー内部から接合されている。図中、符号２２０は上記ゲッタを入れる窪みであり、絶縁基板２１３が接合されて目隠しされる。
なお、上記実施例においては振動ミラーを静電力によって駆動する方式としたが、圧電素子を用いて励振する方式、可動ミラー２０２に薄膜コイルを形成し電磁力を発生して駆動する方式であってもよい。
【００１８】
図１、図２は、本発明にかかる光走査装置の実施例を示す斜視図である。光源である半導体レーザ１０１は、ホルダ部材１０２の光走査装置ハウジング１０６への当接面に対し反対側から貫通孔１０３に圧入されている。ホルダ部材１０２の上記当接面側に設けられた突起部１０５には、カップリングレンズ１１０が固定されている。カップリングレンズ１１０は、その光軸を半導体レーザ１０１からの射出光軸と合わせ、カップリングレンズ１１０の射出光束が平行光束となるように、半導体レーザ１０１の発光点との光軸方向の位置決めをして、上記突起部１０５の先端の半円筒部に接着、固定されている。こうして光源ユニット１００が構成されている。実施例の場合、３つの光源ユニットを用いるが、これらは全て同一構成である。
【００１９】
光源ユニット１００は貫通孔と同軸に設けられた円筒部１０４を備え、ハウジング１０６の嵌合孔１０７に各々係合して取り付け面１０８に当接され、ネジ固定されている。
光源ユニット１００より射出した光ビームは取り付け面１０８と対向する斜面１０９に接合配備され、副走査方向に凹面の曲率を有するシリンダミラー１３６に入射され、副走査方向において前記可動ミラー面で集束する集束光束として振動ミラーモジュール２００にガラス窓１３０から入射される。
【００２０】
シリンダミラー１３６は斜面１０９の開口１３１からミラー面を覗かせるように外側から当接され、斜面１０９に沿って、同面内での回転方向と副走査方向とを、光束の主走査方向が後述する走査レンズの焦線方向と合うように、また、走査位置が揃うように位置決めされ接着固定される。
振動ミラーモジュール２００は前記ねじり梁の方向が各々平行となるように均等間隔で、実施例の場合３つの振動ミラーモジュール２００が、同一のプリント基板１１２上に実装され、ハウジング１０６の下側開口をふさぐように基板上面を当接させてネジ固定されている。
【００２１】
被走査面において各振動ミラーモジュール２００の走査線は、被走査面(感光体)の移動方向と直交する方向から所定角度（β）、実施例では走査終端側が走査開始側に対して記録密度ｐ分進む方向に傾けて配置され、隣接する光走査手段との走査線が平行になるように実装されている。
プリント基板１１２には半導体レーザの駆動回路、前記可動ミラー２０２の駆動回路を構成する電子部品、および同期検知センサ１１３が実装されており、振動ミラーモジュール２００はその支持基板の底面をプリント基板面に突き当て、下側に突出したリード端子をスルーホールに通して半田付けすることで回路接続がなされ、コネクタ１１４を介して外部回路との配線がなされている。一端をプリント基板に結線されたケーブル１１５は半導体レーザのリード端子と接続されている。
【００２２】
ハウジング１０６はある程度剛性が確保できるガラス繊維強化樹脂やアルミダイキャスト等からなり、ハウジング１０６内部には、結像手段を構成する第１の走査レンズ１１６、第２の走査レンズ１１７を主走査方向に配列して接合する接合面１１８が形成され、各レンズの副走査方向基準面をハウジング１０６に当接させた際に、振動ミラーモジュール２００から射出した光ビームと副走査方向の光軸高さが合うように配備されている。
第１の走査レンズ１１６には副走査各面の中央に突出され主走査方向の位置決めを行う突起１２０、第１面側両端に光軸方向の突き当てを行う平押面１１９を備え、各接合面１１８に一体形成された切欠１２２に突起１２０を係合させ、突起対１２１に平押面１１９を突き当ててそれぞれ相対的な配置を合わせて支持されている。
一方、第２の走査レンズ１１７は主走査に連結し枠体１２２に収められ樹脂にて一体的に形成されており、枠体第２面側中央部の突起１２３を接合面に一体形成された切欠１２５に係合し、枠体第１面側両端部１２４を突起対１２６に突き当てて支持されている。
【００２３】
ピンフォトダイオードなどからなる同期検知センサ１１３は、隣接する振動ミラーモジュール２００で共用する中間位置と両端位置に配置され、各光走査モジュール２００の走査開始側と走査終端側とでビームが検出できるように計４箇所に実装されている。第２の走査レンズ１１７の第２面側には各レンズの走査領域間にＶ字状のミラー部１２８を、走査領域に開口部１２９を形成した高輝アルミ板１２７が配備され、上記ミラー部１２８によって反射した光ビームが各々の同期検知センサ１１３へ導かれるよう隣接する走査開始側と走査終端側に対応した反射面が向かい合って配置されている。
【００２４】
図２において、カバー１３８は光ビームが通過する開口１３９を形成し、ハウジング１０６上面を密閉するようにしてネジ止めされている。高輝アルミ板１２７は第２の走査レンズとカバーとの間に挟み込まれて支持され、反射した光ビームは再度、走査レンズ１１７を通過してハウジング１０６内に戻されるように構成されている。
上記のように構成された光走査装置は、ハウジング１０６の主走査端に形成された鍔部１５９に設けられた基準ピン１３２により装置本体のフレームと位置決めを行い、上面を基準にして取り付けられ、ネジ固定されている。
なお、実施例では、３つの光走査装置が配列された例を示したが、光走査装置の数はいくつであっても同様である。
【００２５】
図１１は、隣接する振動ミラーモジュール間の走査線の、継ぎ目部の様子を示す。図示の如く各走査線は各々走査レンズの配置誤差、走査レンズ自体の反り等に伴う走査線の曲がりと、振動ミラー回転軸の平行度ずれ等に伴う傾きとが合成された状態で、個別に発生しているため、図示のように、主走査方向、副走査方向のレジストずれ以外に、継ぎ目近傍での接線方向の傾きが異なる。
後述するように、主走査方向のレジストずれＬは倍率調整により、副走査方向のレジストずれＤは振動ミラーの位相調整と書出しのタイミング調整により補正がなされ、継ぎ目位置が合わせられる。
一方、走査線継ぎ目近傍での接線方向の傾きは、図１４のように、横軸に各接線方向の主走査軸とのなす角度差、縦軸に識別のし易さをとって示すとおり、角度差が同じであっても、図に示すように副走査方向で正負に反転している方が識別しにくい。そこで、実施例では走査線全体の曲がり、傾きを抑えるのではなく、継ぎ目近傍のみに着目し、各走査線の継ぎ目を原点とし、主走査方向、副走査方向を各々ｘ軸、ｙ軸としたときに、接線方向が第１象限と第３象限の関係、あるいは第２象限と第４象限の関係となるように曲がり、傾きを合わせるようにしている。
【００２６】
具体的には、第１の走査レンズ１１６における副走査方向の両基準面を母線に対して非対称とし、隣接したモジュールの走査レンズの設置方向を反転する、つまり、接合面１１８から母線までの高さを隣接する走査レンズで互い違いにすることで、図１３に示すように曲がりの方向が交互に反転するようにしている。当然、両基準面を母線に対して対称とし、接合面１１８の高さを各々変えてもよい。図１３において、上段（ａ）は走査レンズを正面から見た図、下段（ｂ）は走査線の軌跡を示す。
【００２７】
また、調整によっても上記関係とすることができる。図１２はその各種の例を示す。（ａ）は第２の走査レンズ１２１の両端部、および各走査レンズの境界部を副走査方向に突き当てる当接ネジ１４２を上記ハウジングに備えている。また、（ｂ）は、各走査レンズの中央部を突き当てる当接ネジ１４３をハウジングに備えている。いずれの例も、当接部位を可変することでレンズ全体をこれに沿わせ、波状にうねらせることで、各々傾き、曲がりを上記関係に合致するように調節することができる。
図１２中（ａ）は左側の走査線傾きを調整した例、（ｂ）は曲がりを調整した例を示す。板バネ１４１は、上記カバーとの間に挟み込まれ、各当接部位に確実に突き当たるようになっている。
なお、後述する転写ベルト上での接線方向の検出結果に基づいて、上記当接ネジをステッピングモータで送るようにすれば、経時的なずれを補正することもできる。
また、傾きや曲がりの調節は、上記のような構成に限らず、第１の走査レンズを副走査方向にシフトする、あるいはチルトする等の構成によっても実現可能である。
【００２８】
図５は、本発明にかかる上記光走査装置を、単一の光走査装置５００によって１色ずつ画像形成され、転写ベルト５０１を４回転させて回転毎に色重ねがなされる画像形成装置としてのカラーレーザプリンタに適用した例を示す。図５において、転写ベルト５０１は駆動ローラと２本の従動ローラとで三角形をなすように支持されている。各色に対応したトナーを補給する現像ローラ５０２およびトナーホッパ５０３は、回転支持体５０９上に一体的に配備され、リボルバー式に１／４ずつ回転しながら感光体ドラム５０４に対向するように構成されている。
【００２９】
画像は、転写ベルト５０１端に形成されたレジストマークを検出するセンサ５０５の信号をトリガとして、副走査方向の書出しタイミングをはかって、光走査装置５００によって感光体ドラム５０４に静電潜像として記録される。この静電潜像は現像部にてトナーをのせることによって現像され、このトナー像は転写ベルト５０１に転写される。転写された後の残トナーは、混色しないように、クリーニング部５０８で掻き取られ備蓄される。これらの動作を各色毎に行うことで、順次画像を重ねていく。用紙は給紙トレイ５０７から給紙コロ５０６により供給され、４色目の画像形成にタイミングを合わせてレジストローラ５０により送り出されて、転写部５１１にて転写ベルト５０１から４色同時に転写される。転写されたトナー像は定着ローラ５１２により定着され、排紙トレイ５１４に排出される。
【００３０】
光走査装置５００は上記したように複数の光走査手段の走査線をつなぎ合わせて１ラインを形成する。１ラインの総ドット数Ｌを３分割し、画像始端から各々１〜Ｌ１、Ｌ１＋１〜Ｌ２、Ｌ２＋１〜Ｌドットを割り当てて印字するが、実施例では各走査領域が感光体上で数ｍｍ重なるようにオーバーラップ領域を設け、割り当てる画素数Ｌ１、Ｌ２を固定せず、各色で異なるようにすることで、同一ラインを構成する各色の走査線の継ぎ目が重ならないようにして走査領域の境界をより目立ち難くしている。
【００３１】
画像データは、上記したように主走査方向に３分割され、各光走査手段毎にビットマップメモリに保存され、振動ミラーモジュール毎にラスター展開がなされ、ラインデータとしてバッファに保存される。
保存されたラインデータは各同期検知信号をトリガとして読み出され、個別に画像記録が行われるが、後述するように書出しタイミングを各々設定することで、書出し始端のレジストが合わせられる。
【００３２】
なお、実施例では、各振動ミラーの共振ピークは異なっても、共振帯域が重複する領域において共通の駆動周波数を与えるようにしている。環境温度変化等でバネ定数が変化し共振帯域が一様にシフトすることに伴って、それに応じて駆動周波数もシフトする必要があるが、この場合も共通の駆動周波数が与えられる。従って、走査周波数が各振動ミラーモジュールで異なることはなく、各領域の終端まで各ラインのレジストは一致する。
各画像領域の境界近傍を監視するＣＣＤエリアセンサ５１５が転写ベルト５０１に対向させて設けられている。ＣＣＤエリアセンサ５１５は、転写ベルト５０１に形成される検出パターンのトナー像を、対物レンズ５１６を介して２次元的に読み取り、画像処理によって記録位置の相対的なレジストずれｄ、および継ぎ目における相対的な接線傾き（微分値）を検出するようになっている。
【００３３】
図６は、半導体レーザ、可動ミラーの駆動制御回路の例を示すブロック図である。図６において、駆動パルス生成部６０１は、基準クロックをプログラマブル分周器で分周し、図７に示すように、可動ミラーの１／２周期に１回、かつ最大振幅時から水平となるまでの期間のみに電圧パルスが印加されるように、共振周波数ｆ０（＝１／Ｔ０）の２倍の周波数でデューティが５０％以下のパルス列（Ｔ＜Ｔ０／４）を生成し、ＰＬＬ回路により所定の位相遅れδを生じさせて駆動周波数ｆｄとしてこれを可動ミラー駆動部６０２に与える。
ここで、振動ミラー間の相対的な位相遅れδを、１走査ラインピッチｐを用いて
δ＝（１／ｆｄ）・｛（ｄ／ｐ）−ｎ｝
ここで、ｎは、(ｄ／ｐ)−ｎ＜１
を満足する自然数となるように与えれば、振動ミラーの１周期おきの書出しタイミング補正を行うことができる。つまり、ｎライン周期分ずらして書き出すことによりレジストずれｄを無効化することができ、このチェックを起動時に、または定期的にかけることで、経時的にも継ぎ目の位置ずれのない高品位な画像が得られる。
【００３４】
可動ミラーは走査角θ０を起点として−θ０に達するまでの往期間のうち、θｓ〜−θｓの期間（０＜θｓ＜θ）、同一方向の走査時のみ画像記録を行い、走査角−θ０から＋θ０の復期間には画像記録を行わない。言い換えれば、駆動周波数ｆｄの1周期毎に画像記録を行う。ちなみにθｓ／θ０＝０．７である。
【００３５】
電源投入時、および待機状態から起動する際には、プログラマブル分周器で連続的に分周比を変えることで駆動周波数ｆｄを高周波側から可変して励振し、同期検知センサ６０４で光ビームが検出されるまで走査角が拡大したことをもって共振帯域であることを判断する。この際、印可する駆動電圧のゲインを可変して、振れ角を微調節してもよい。
また、実施例では、走査角−θ０となる近傍にもセンサ６０５を配備して走査終端のビームを検出し、この終端検知信号と走査開始端の同期検知信号との時間差を計測して可動ミラーの走査速度変動や走査レンズの形状誤差に伴う画像記録幅の変化を検出している。後述するように、この画像記録幅の変化は画素クロックを変更することで補正する。
【００３６】
図８に、実施例における上記センサ６０４、６０５の詳細を示す。センサ６０４、６０５は、主走査方向に垂直なフォトダイオード８０１と非平行なフォトダイオード８０２を有し、フォトダイオード８０１のエッジを光ビームが通過した際に同期検知信号、または終端検知信号を発生し、走査光がフォトダイオード８０１からフォトダイオード８０２に至る時間差Δｔを計測して、上記レジストずれの主要因である副走査方向の走査位置ずれΔｙを検出する。
なお、Δｙはセンサ部８０２の傾斜角γ、光ビームの走査速度Ｖを用いて
Δｙ＝（Ｖ／ｔａｎγ）・Δｔ
で表され、Δｔが一定であれば、走査位置ずれが生じていないことになる。
【００３７】
図６に示す回路例では、上記時間差を走査位置ずれ演算部６１０で監視することで走査位置ずれを検出し、Δｔ基準値に合うよう振動ミラー間の位相を可変して補正を行う。この補正は振動ミラーモジュールの各々で行われ、実施例では３つの光走査手段から構成されるので、全ての補正が終了した後に印字動作を可能としている。
【００３８】
ところで、可動ミラーは共振振動されるため、図９に示すようにｓｉｎ波状に走査角θが変化する。
θ=θ０・ｓｉｎ２πｆｄ・ｔ、 −１／４ｆｄ＜ｔ＜１／４ｆｄ
一方、被走査面である感光体ドラム面では均一間隔で主走査ドットを印字する必要があり、上記した走査レンズの結像特性は、単位走査角あたりの走査距離ｄＨ／ｄθがｓｉｎ^−１／θ０に比例するように、つまり、画像中央で遅く、周辺に行くに従って加速度的に速くなるように光線の向きを補正しなければならない。しかし、走査レンズ中央部から周辺部にかけて結像点を遠ざけるようにパワー配分を行う必要があり、最大振幅θ０に対して有効走査領域θｓを広げるには限界がある。
【００３９】
走査レンズのみでスポット径を均一に保つには、走査効率θｓ／θ０＜０．５としなければならない。実施例では図１０に示すように、振幅による走査速度の変化に対抗して各画素に対応する位相が記録開始から記録終端にかけて進んだ状態から、段階的に遅れるようにすると同時に、各画素のパルス幅が記録開始位置から画像中央に至るまで領域では長い状態から段階的に短くなるような、画像中央から記録終端に至る領域では長くなるような画素クロックｆｍを半導体レーザ（ＬＤ）駆動部６０６に与えている。これにより、θｓ／θ０＝０．７まで向上している。
【００４０】
以下、画素クロックｆｍの可変方法について説明する。図６に示すクロックパルス生成部６０７は、可変データに基づいて基準クロックｆ０をプログラマブル分周器で分周した分周クロックをカウントして、ｋクロック分の長さのパルスを有するＰＬＬ基準信号ｆａが形成され、ＰＬＬ回路において、可変データに基づいて基準クロックｆ０との位相を選択し画素クロックｆｋが発生される。これを数十画素毎に繰り返し行うことで、主走査に沿って任意な位置にドットが印字できる。
【００４１】
基準クロックｆ０は位相同期部６０８において、基準クロックｆ０の１周期を１／ｎ毎に遅延したクロックの中から同期検知センサ６０４より発生される同期検知信号と位相が合ったクロックを選択し、新たに基準クロックｆ０とする位相同期を走査毎に行う。実施例では、この際に位相が異なったクロックを選択できるようにしており、クロック可変を開始するタイミングを、可動ミラーの水平な状態（θ＝０）が画像記録の中央位置と確実に一致するように補正する。ちなみに、このタイミングがずれると画像が主走査方向のドット間隔が一方側で縮み、もう一方側で延びた、歪んだ画像になってしまう。
また、基準クロックｆ０の分周比を可変することで、主走査方向の画像幅を合わせることができ、上記したように終端検知信号と同期検知信号との時間差を倍率演算部６０９で計測し、時間差が所定値より短い場合は周波数を高める方向に、長い場合は低める方向に補正する。
【００４２】
【発明の効果】
請求項１記載の発明は、発光源と、一定の駆動周波数で往復振動し、発光源からの光ビームを走査する振動ミラーと、走査された光ビームを被走査面に結像する結像光学系とを具備する光走査手段を複数備え、画像領域を主走査に分割して、それぞれ画像記録を行う光走査装置であって、相隣接する光走査手段による各走査線の走査線曲がりの極値の位置が、上記相隣接する光走査手段による走査線の継ぎ目に対して副走査方向で反対であり、この相隣接する光走査手段による走査線の曲がりが互いに相反する方向となるようにした。これにより、各光走査手段の曲がりや傾きを精度良く合わせなくても、各画像領域間の継ぎ目を目立たなくすることができ、面倒であった調整作業を簡略化でき、生産効率が向上する利点がある。
また、走査線の曲がりがあっても、特別な調整を行うことなく容易に各画像領域間の継ぎ目を目立たなくすることができ、高品位な画像記録を行うことができる。
【００４４】
請求項２記載の発明によれば、上記隣接する光走査手段の少なくとも一方には、走査線の曲がり量を可変する曲がり調節手段を備え、上記接線方向を補正することにより、組み立てのばらつきや加工誤差等があっても、走査線の継ぎ目を目立ちにくくすることができ、生産効率が向上するうえ、高品位な画像記録を行うことができる。
【００４５】
請求項３記載の発明によれば、上記隣接する光走査手段の少なくとも一方には、走査線の傾き量を可変する傾き調節手段を備え、上記接線方向を補正することにより、組み立てのばらつきや加工誤差等があっても、継ぎ目を目立ちにくくすることができ、生産効率が向上するうえ、高品位な画像記録を行うことができる。
【００４６】
請求項４記載の発明によれば、上記結像光学系を構成する少なくとも１つの光学素子を複数の光走査手段で連続して形成するとともに、主走査方向における複数箇所に副走査方向に突き当てる当接部位を備え、上記各当接部位の高さを可変することで、上記曲がり、または傾きを調節することにより、個別に調整手段を有するのに比べ、構成が簡単で設置環境の変化等があってもずれが少なく、年月が経過しても走査線の継ぎ目が目立ちにくい高品位な画像記録を行うことができる。
【００４７】
請求項５記載の発明によれば、上記隣接する光走査手段の少なくとも一方には、振動ミラーの位相を可変するミラー駆動手段を備え、副走査方向におけるレジストずれを補正することにより、光軸方向を可変するような複雑な補正手段を用いなくとも、確実に書出し位置が可変できるので、生産効率が向上するうえ、高品位な画像記録を行うことができる。
【００４８】
請求項６記載の発明によれば、上記ミラー駆動手段は、上記隣接する光走査手段のレジストずれｄのうち、
ｄ₂＝ｄ−ｎ・ｐ、 （ｎは自然数、ｐは副走査方向の記録ピッチ）
なる分を補正することにより、確実に書出し位置が可変できるので、走査線の継ぎ目が目立ちにくい高品位な画像記録を行うことができる。
【００４９】
請求項７記載の発明によれば、上記発光源を変調するタイミングを補正する光源駆動手段を備え、上記隣接する光走査手段のレジストずれｄのうち、
ｄ₁＝ｎ・ｐ＝ｄ−ｄ₂ 但し、ｄ₂＜ｐ
なる分を補正することにより、レジストずれが大きくても上記ミラー駆動手段での位相の可変量を１周期以内とすることができ、確実に書出し位置が可変できるので、走査線の継ぎ目が目立ちにくい高品位な画像記録を行うことができる。
【００５０】
請求項８記載の発明によれば、上記隣接する光走査手段の走査領域に重なり部を設けるとともに、上記重なり部において、各走査位置ずれを検出する走査位置ずれ検出手段を備え、上記検出結果に基づいて上記位相を可変することにより、設置環境の変化等によって走査位置ずれが生じても、状況に応じてフィードバック補正することができ、年月が経過しても走査線の継ぎ目が目立ちにくい高品位な画像記録を維持することができる。
【００５１】
請求項１０記載の発明は、発光源と、一定の駆動周波数で往復振動し、発光源からの光ビームを走査する振動ミラーと、走査された光ビームを被走査面に結像する結像光学系とを有する光走査手段を複数備える光走査装置と、上記光走査手段により画像領域を主走査に分割して、静電画像が形成される感光体と、上記静電画像をトナーで顕像化する現像手段と、顕像化されたトナー像を記録紙に転写する転写手段とを有する画像形成装置であって、上記顕像化されたトナー像により上記光走査手段の継ぎ目近傍における隣接ラインの接線方向を検出する接線方向検出手段を備えている。そのため、出荷後においても画像品質を監視することができるので、設置環境の変化等によって出荷時の品質が維持されなくても、状況に応じてフィードバック補正することができ、年月が経過しても走査線の継ぎ目が目立ちにくい高品位な画像記録を維持することができる。
【００５２】
請求項１１記載の発明は、発光源と、一定の駆動周波数で往復振動し、発光源からの光ビームを走査する振動ミラーと、走査された光ビームを被走査面に結像する結像光学系と、を有する光走査手段を複数備える光走査装置と、上記光走査手段により画像領域を主走査に分割して、静電画像が形成される感光体と、上記静電画像をトナーで顕像化する現像手段と、顕像化されたトナー像を記録紙に転写する転写手段とを有する画像形成装置であって、上記顕像化されたトナー像により上記光走査手段の継ぎ目近傍におけるレジストずれを検出するレジストずれ検出手段を備える。そのため、出荷後においても画像品質を監視することができるので設置環境の変化等によって出荷時の品質が維持されなくても、状況に応じてフィードバック補正することができ、年月が経過しても走査線の継ぎ目が目立ちにくい高品位な画像記録を維持することができる。
【図面の簡単な説明】
【図１】本発明にかかる光走査装置の実施の形態を示す分解斜視図である。
【図２】同上実施の形態を反対側から見た分解斜視図である。
【図３】本発明にかかる光走査装置に用いることができる振動ミラーモジュールの例を示す分解斜視図である。
【図４】同上振動ミラーモジュールの正面断面図である。
【図５】本発明かかる光走査装置を有する画像形成装置の実施形態を模式的に示す正面図である。
【図６】上記振動ミラーモジュールにおける可動ミラーの駆動制御回路の例を示すブロック図である。
【図７】振動ミラーモジュールの可動ミラーに印加する電圧パルスの例を示す波形図である。
【図８】本発明に用いることができる同期検知センサの例を示す光学配置図である。
【図９】上記振動ミラーモジュールの可動ミラーによる走査角の変化の例を示す線図である。
【図１０】上記可動ミラーの振幅による走査速度の変化に対抗して各画素に対応する位相を変化させる様子を示す線図である。
【図１１】隣接する振動ミラーモジュール間の走査線の、継ぎ目部の様子を示す線図である。
【図１２】本発明に適用可能な走査レンズ調整手段の例を示すもので、（ａ）は走査線傾きを調整する手段の例、（ｂ）は走査線曲がりを調整する手段の例を示す、それぞれ平面図と走査線に軌跡を示す線図である。
【図１３】隣接した振動ミラーモジュールの走査レンズの設置方向とそれに対する走査線の軌跡に例を示すもので、（ａ）は走査レンズを正面から見た図、（ｂ）は走査線の軌跡を示す線図である。
【図１４】走査線継ぎ目近傍での接線方向の傾きの例を示すグラフである。
【符号の説明】
１０１ 発光源
２００ 振動ミラーモジュール
２０１ 支持基板
２０２ 可動ミラー
２０８ ねじり梁
２０９ ねじり梁[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical scanning device used in an image forming apparatus such as a digital copying machine or a laser printer.PlaceIn addition, the present invention relates to an image forming apparatus using the optical scanning device, and can be applied to an optical scanning bar code reading device, a three-dimensional shape measuring device, and the like.
[0002]
[Prior art]
In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector that scans a light beam. However, in order to achieve higher resolution images and high-speed printing, these mirrors must be driven at high speeds to scan at high speeds, and there are problems with bearing durability, heat generation due to windage damage, and noise. Unless this problem is solved, there is a limit to high-speed scanning.
In recent years, research on optical deflectors using silicon micromachining has been promoted. The oscillating mirror and the torsion beam supporting the oscillating mirror are integrally formed of an Si substrate, a voltage is applied between the electrode on the oscillating mirror side and the electrode on the fixed side, and the torsion beam is generated by electrostatic attraction generated between the two. One method is to vibrate the vibrating mirror while twisting (see, for example, Patent Document 1 and Patent Document 2).
According to this method, since the oscillating mirror is reciprocally oscillated using resonance, there is an advantage that noise is low although high speed operation is possible. Further, since the driving force for rotating the vibrating mirror is small, there is an advantage that the power consumption can be kept low.
[0003]
On the other hand, a method has been proposed in which a plurality of optical scanning devices are arranged in accordance with the main scanning direction, and image recording is performed by dividing the image area into the number corresponding to the optical scanning device in the main scanning direction (for example, Patent Documents). 3, see Patent Document 4). In such a system, a contrivance is made so that the scanning lines are smoothly connected to each other so that the joints between the scanning lines are not conspicuous. For example, by tilting the entire optical scanning device, the tilt direction of each scanning line is corrected so that the joints are not noticeable (see, for example, Patent Document 5). In addition, there is a technique in which the seam is not noticeable by correcting the recorded image information (see, for example, Patent Document 6).
[0004]
[Problems to be solved by the invention]
As described above, by utilizing the torsion beam type vibrating mirror made of the Si substrate as the light deflecting means, it is possible to provide an optical scanning device that is smaller and consumes less power than the conventionally used polygon mirror method. .
However, according to the oscillating mirror method, since the deflection angle is small and the size of the reflecting surface is limited, a plurality of optical scanning devices having a short optical path length are arranged in parallel and the image area is divided in the main scanning direction. Thus, it is desirable to make the recording widths smaller and join them together (see, for example, Patent Document 7). However, even in this case, if the positions of the respective seams do not match, the images overlap each other at the boundary portion or a gap is formed, so that the seams become conspicuous, which causes deterioration in image quality.
[0005]
By changing the scanning positions of a plurality of optical scanning devices relatively or by changing the timing of image writing, the scanning lines can be adjusted to be continuous, but even if the scanning lines are continuous. If the bend at the boundary is large, the seam becomes conspicuous, causing deterioration in image quality. The bending of the boundary portion is caused by a difference in the bending or inclination of the scanning line of each optical scanning device, but fine adjustment of these is troublesome and is not preferable from the viewpoint of production efficiency.
Further, since the above-described scanning position easily shifts due to a change in environmental temperature or the like, it has been a problem to ensure stable image quality over time.
[0006]
[Patent Document 1]
Japanese Patent No. 2924200
[Patent Document 2]
No. 3011144
[Patent Document 3]
JP-A-3-161778
[Patent Document 4]
JP 2001-18472 A
[Patent Document 5]
JP-A-3-161778
[Patent Document 6]
JP 2001-18472 A
[Patent Document 7]
JP 2001-228428 A
[0007]
  The present invention provides a vibrating mirror type optical scanning device and an image forming apparatus using the optical scanning device, which improves the above-described problems and makes the seam inconspicuous, thereby reducing the size and power consumption. An object of the present invention is to provide an optical scanning device and an image forming apparatus capable of obtaining a high-quality image.
  Claims 1 to4SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical scanning device that can perform high-quality image recording without deteriorating production efficiency by making inflections in the boundary portions of adjacent scanning lines inconspicuous. To do.
  Claim5-8The described invention provides an optical scanning device that can detect and correct a scanning position shift between adjacent scanning lines, thereby correcting a scanning position shift over time and ensuring stable image quality. With the goal.
[0008]
  According to the ninth aspect of the present invention, the image forming apparatus is configured using the optical scanning device according to any one of the first to eighth aspects, so that the scan position deviation with time can be corrected without decreasing the production efficiency. An object of the present invention is to provide an image forming apparatus capable of performing high-quality image recording.
  According to a tenth aspect of the present invention, there is provided an image forming apparatus capable of performing high-quality image recording without deteriorating production efficiency by making inflections in the boundary portions of adjacent scanning lines inconspicuous. With the goal.
  According to an eleventh aspect of the present invention, there is provided an image forming apparatus capable of correcting a scanning position deviation over time by detecting and correcting a scanning position deviation between adjacent scanning lines and ensuring stable image quality. The purpose is to provide.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.
FIG. 3 shows in detail an example of a vibrating mirror module used in the embodiment of the optical scanning device according to the present invention. In FIG. 3, the vibrating mirror module 200 has a movable mirror 202 mounted on a support substrate 201 formed of sintered metal or the like, covered and sealed with a cover 205 formed in a cap shape, and closes the opening of the cover 205. The light beam is configured to enter and exit through the glass window 204 arranged in the above. The movable mirror 202 has a plurality of vibration modes, in the embodiment, two vibration modes.
[0010]
The movable mirror 202 is configured by joining two Si substrates 206 and 207 via an insulating film. The first Si substrate 206 is made of a substrate having a thickness of 60 μm, and an approximately rectangular movable mirror 202 and a first torsion beam 208 and a second torsion beam 209 that pivotally support the movable mirror 202 are etched by the movable mirror 202. Are formed separately from the fixed frame 210. The first torsion beam 208 and the second torsion beam 209 are arranged on one straight line parallel to each other in the main scanning direction. The movable mirror 202 is formed across the torsion beams 208 and 209, and both end edges of the movable mirror 202 in a direction orthogonal to the line connecting the torsion beams 208 and 209, in other words, both end edges in the longitudinal direction of the movable mirror 202 The portion is formed with irregularities in a comb-like shape. Comb-like irregularities are also formed at both edge portions of the fixed frame 210 facing the irregularities of the movable mirror 202 so that the irregularities of the movable mirror 202 mesh with the irregularities on the fixed frame 210 side. They are intricate with a slight gap between them.
[0011]
  Surface of movable mirror 202 and fixed frame210A metal film such as Au is vapor-deposited on the concavo-convex portions formed on each to form electrode portions. If the concave and convex portions at both ends of the movable mirror 202 are the first and second movable electrodes, and the concave and convex portions on the side of the fixed frame 210 facing the first and second fixed electrodes are the first and second fixed electrodes. When a voltage is applied, an electrostatic force is generated between the opposing movable electrodes, and the movable mirror 202 is rotated by a small angle while twisting the torsion beams 208 and 209. If the voltage applied between the electrodes is a periodic pulse voltage, the movable mirror 202 reciprocates.
  Further, if the width and length of the portion where the torsion beams 208 and 209 are vibrated are designed in accordance with the specific resonance frequency, the movable mirror 202 is excited and the amplitude can be increased., ElectricThe flow is minute and power consumption can be reduced. However, since the amplitude is reduced only by slightly deviating from the resonance frequency, it is preferable to variably control the frequency of the drive voltage applied to the fixed electrode so as to follow the change in the resonance frequency.
  The reason why the electrodes are comb-shaped is that the outer peripheral length is made as long as possible to increase the electrode length, so that a larger electrostatic torque can be obtained at a low voltage.
[0012]
Now, if the dimensions of the movable mirror 202 are the length 2a, the width 2b, the thickness d, the length of the torsion beam is L, and the width c, the density ρ of Si, which is the material of the movable mirror 202, and the material constant G are used. ,
Moment of inertia I = (4abρd / 3) · a ^ 2
Spring constant K = (G / 2L) · {cd (c ^ 2 + d ^ 2) / 12}
And the resonant frequency f is

Here, since the beam length L and the deflection angle θ are in a proportional relationship,
θ = A / If ^ 2, where A is a constant
The deflection angle θ is inversely proportional to the moment of inertia I, and the deflection angle θ is reduced unless the moment of inertia is reduced in order to increase the resonance frequency f. Therefore, in the embodiment, the moment of inertia is reduced to about 1/5 by leaving the substrate thickness d of the movable mirror back side 219 in a lattice shape and removing the other thickness by etching to a thickness of d / 10 or less.
[0013]
On the other hand, when the dielectric constant of air is ε, the electrode length is H, the applied voltage is V, and the distance between the electrodes is δ,
Electrostatic force between electrodes f = εHV ^ 2 / 2δ
And the deflection angle θ = B · F / I, where B is a constant
The deflection angle θ increases as the electrode length H increases, and a driving torque that is 2n times the number of comb teeth n can be obtained by using a comb-teeth shape.
On the other hand, if the air density is η with respect to the speed ν and area E of the movable mirror,
Viscous resistance of air P = C ・ ηυ ^ 2 ・ E ^ 3 (C is a constant)
Since it works in opposition to the rotation of the movable mirror 202, it is preferably sealed with the cover 205 and kept in a reduced pressure state. In the embodiment, a non-evaporable getter is bundled and activated by heating from the outside to be 1 torr or less.
[0014]
The second substrate 207 is made of a Si substrate having a thickness of 280 μm, penetrates through the central portion and is joined to the support portion of the first Si substrate 206 with an insulating layer interposed therebetween to form a swinging space for the movable mirror 202. Yes. On the upper surface of the second substrate 207, opposed mirror chips 216 and 215 constituted by two Si substrates are bonded in a crosslinked state. The second mirror chip 216 uses a wafer inclined at a slice angle of about 9 ° from the crystal plane orientation <111>, and the first mirror chip 215 exposes the <111> plane by etching. The substrate is cut out by forming inclined surfaces inclined by 9 ° and 26.3 °, respectively, from the substrate surface. This cut-out surface is used as a bonding surface, and a metal film is deposited on the substrate surface continuous with this surface to form a reflecting surface. The two opposing mirror chips 216 and 215 have a configuration in which reflecting surfaces 217 and 218 forming an angle of 144.7 ° in a roof shape are arranged in a pair with an opening disposed between the two opposing mirror chips 216 and 215 interposed therebetween. .
[0015]
FIG. 4 shows the layout of the sub-scan section of the vibrating mirror module 200. The light beam emitted from the semiconductor laser 401 is about 20 in the sub-scanning direction with respect to the normal line in the sub-scanning section including the torsion beam with respect to the movable mirror 202 via the coupling lens 402 and the cylinder mirror 403 as will be described later. The light beam that is tilted and incident from the opening 214 and reflected by the surface of the movable mirror 202 is incident on the first reflecting surface 217, returned to the movable mirror 202, and further reflected by the movable mirror 202. Is incident on the second reflecting surface 218 through the opening 214, and moves the reflection position in the sub-scanning direction while reciprocating three times with the movable mirror 202, and again by a total of five reflections on the movable mirror 202. Injected from the opening 214. In the embodiment shown in the figure, the optical path length is shortened by devising such that a large scanning angle can be obtained with a small swing angle of the movable mirror 202 by repeating the reflection multiple times in this way.
Now, assuming that the total number of reflections at the movable mirror 202 is N and the deflection angle is α, the scanning angle θ can be expressed by 2Nα. In the embodiment, since N = 5 and α = 5 °, the maximum scanning angle is 50 °, of which 35 ° is an image recording area.
[0016]
By using the above-mentioned resonance, the applied voltage is small and little heat is generated. However, as is clear from the above equation, it is necessary to increase the spring constant of the torsion bar as the recording speed increases, that is, as the resonance frequency increases. There will be no swing angle. Therefore, as described above, the scanning angle is enlarged by providing the counter mirror so that a necessary and sufficient scanning angle can be obtained regardless of the recording speed.
In addition, the two reflecting surfaces 217 and 218 are arranged in a roof shape, and every time they are reflected by these reflecting surfaces, the incident angle in the sub-scanning direction to the movable mirror 202 is repeatedly distributed in the positive and negative directions. In other words, the traveling direction accompanying reflection is distributed to the right and left, thereby suppressing the bending of the scanning line on the scanning surface due to the oblique incidence, maintaining the linearity and orthogonal to the optical axis. Consideration is made so that the rotation of the light beam in the plane returns to the original posture at the time of emission so that the imaging performance does not deteriorate.
[0017]
The substrate 206 is stacked and bonded on the insulating substrate 213 and fixed to the support substrate 201. The insulating substrate 213 penetrates the center portion and is formed in a window frame shape to form a swinging space for the movable mirror 202, and includes a pad portion 213 that is electrically connected to the fixed electrode provided on the first substrate 206. The lead terminal 212 is inserted through the support substrate 201 through an insulating material, and the end portion of the lead terminal 212 protruding upward and the pad portion 213 are connected by wire bonding, and sealed inside and outside electric wiring Has been made.
The cover 205 is fitted into a step portion provided on the outer periphery of the support substrate 201, and a glass window 204 is joined from the inside of the cover to the light beam emission opening. In the figure, reference numeral 220 denotes a recess for receiving the getter, and the insulating substrate 213 is bonded and hidden.
In the above embodiment, the vibration mirror is driven by an electrostatic force. However, the vibration mirror is driven by a piezoelectric element, and a thin film coil is formed on the movable mirror 202 to generate electromagnetic force and drive. Also good.
[0018]
1 and 2 are perspective views showing an embodiment of an optical scanning device according to the present invention. The semiconductor laser 101 as a light source is press-fitted into the through hole 103 from the opposite side to the contact surface of the holder member 102 with the optical scanning device housing 106. A coupling lens 110 is fixed to the protrusion 105 provided on the contact surface side of the holder member 102. The coupling lens 110 is aligned with the light emitting point of the semiconductor laser 101 so that its optical axis is aligned with the optical axis emitted from the semiconductor laser 101 and the emitted light beam of the coupling lens 110 becomes a parallel light beam. Then, it is bonded and fixed to the semi-cylindrical portion at the tip of the protruding portion 105. Thus, the light source unit 100 is configured. In the embodiment, three light source units are used, all of which have the same configuration.
[0019]
The light source unit 100 includes a cylindrical portion 104 provided coaxially with the through hole. The light source unit 100 is engaged with the fitting holes 107 of the housing 106 and is brought into contact with the mounting surface 108 and fixed with screws.
A light beam emitted from the light source unit 100 is joined and disposed on a slope 109 facing the mounting surface 108, is incident on a cylinder mirror 136 having a concave curvature in the sub-scanning direction, and is focused on the movable mirror surface in the sub-scanning direction. The light enters the vibrating mirror module 200 from the glass window 130 as a light beam.
[0020]
The cylinder mirror 136 is abutted from the outside so that the mirror surface can be seen through the opening 131 of the inclined surface 109, and along the inclined surface 109, the rotation direction in the same surface and the sub-scanning direction are described. It is positioned and bonded and fixed so that the scanning lens is aligned with the focal line direction of the scanning lens.
The oscillating mirror module 200 is equally spaced so that the directions of the torsion beams are parallel to each other. In the embodiment, three oscillating mirror modules 200 are mounted on the same printed circuit board 112, and the lower opening of the housing 106 is opened. The top surface of the substrate is brought into contact so as to block it and is fixed with screws.
[0021]
The scanning line of each oscillating mirror module 200 on the surface to be scanned is a predetermined angle (β) from the direction orthogonal to the moving direction of the surface to be scanned (photosensitive member). In the embodiment, the scanning end side has a recording density p relative to the scanning start side. It is arranged so as to be inclined in the forward direction, and mounted so that the scanning lines with the adjacent optical scanning means are parallel.
The printed circuit board 112 is mounted with a semiconductor laser drive circuit, electronic components constituting the drive circuit of the movable mirror 202, and a synchronization detection sensor 113. The vibrating mirror module 200 has the bottom surface of the support substrate on the printed circuit board surface. Circuit connection is made by abutting and soldering the lead terminal protruding downward through the through hole, and wiring with an external circuit is made through the connector 114. A cable 115 having one end connected to a printed circuit board is connected to a lead terminal of the semiconductor laser.
[0022]
The housing 106 is made of glass fiber reinforced resin, aluminum die-casting, or the like that can ensure rigidity to some extent. Inside the housing 106, a first scanning lens 116 and a second scanning lens 117 that form an imaging unit are arranged in the main scanning direction. A joining surface 118 that is arranged and joined is formed, and when the sub-scanning direction reference surface of each lens is brought into contact with the housing 106, the light beam emitted from the vibration mirror module 200 and the optical axis height in the sub-scanning direction are It is deployed to fit.
The first scanning lens 116 is provided with a protrusion 120 that projects in the center of each sub-scanning surface and performs positioning in the main scanning direction, and a flat pressing surface 119 that performs abutment in the optical axis direction at both ends of the first surface. The protrusion 120 is engaged with the notch 122 formed integrally with the surface 118, and the flat pressing surface 119 is abutted against the pair of protrusions 121 so as to be supported in a relative arrangement.
On the other hand, the second scanning lens 117 is connected to the main scanning, is housed in the frame body 122 and is integrally formed of resin, and the protrusion 123 at the center of the frame body second surface side is integrally formed on the joint surface. The frame is engaged with the notch 125 and supported by abutting the both ends 124 on the first surface side of the frame against the projection pair 126.
[0023]
Synchronous detection sensors 113 such as pin photodiodes are arranged at intermediate positions and both end positions shared by adjacent vibrating mirror modules 200 so that beams can be detected at the scanning start side and the scanning end side of each optical scanning module 200. It is mounted in a total of four places. On the second surface side of the second scanning lens 117, a high-luminance aluminum plate 127 having a V-shaped mirror portion 128 between the scanning regions of each lens and an opening 129 in the scanning region is provided. The reflecting surfaces corresponding to the adjacent scanning start side and the scanning end side are arranged so as to face each other so that the light beam reflected by is guided to each synchronization detection sensor 113.
[0024]
In FIG. 2, the cover 138 forms an opening 139 through which the light beam passes, and is screwed so as to seal the upper surface of the housing 106. The high-luminance aluminum plate 127 is sandwiched and supported between the second scanning lens and the cover, and the reflected light beam passes through the scanning lens 117 again and is returned to the housing 106.
The optical scanning apparatus configured as described above is positioned with respect to the frame of the apparatus main body by the reference pin 132 provided on the flange part 159 formed at the main scanning end of the housing 106, and is attached with reference to the upper surface. Screws are fixed.
In the embodiment, an example in which three optical scanning devices are arranged is shown, but the same applies regardless of the number of optical scanning devices.
[0025]
FIG. 11 shows a state of a joint portion of a scanning line between adjacent vibrating mirror modules. As shown in the figure, each scanning line is individually composed of a combination of a scanning lens bending error caused by scanning lens placement error, scanning lens warpage, and the like, and an inclination caused by a parallelism deviation of the vibrating mirror rotation axis. Therefore, as shown in the drawing, the inclination in the tangential direction in the vicinity of the joint is different from the registration deviation in the main scanning direction and the sub-scanning direction.
As will be described later, the registration deviation L in the main scanning direction is corrected by adjusting the magnification, and the registration deviation D in the sub-scanning direction is corrected by adjusting the phase of the oscillating mirror and the timing of writing.
On the other hand, as shown in FIG. 14, the inclination in the tangential direction in the vicinity of the scanning line seam is shown by taking the angle difference between the horizontal scanning axis and the main scanning axis in each tangential direction, and the vertical axis as the ease of identification. Even if the angle difference is the same, it is more difficult to discriminate when it is reversed positively and negatively in the sub-scanning direction as shown in the figure. Therefore, in the embodiment, rather than suppressing the bending and inclination of the entire scanning line, attention is paid only to the vicinity of the seam, the seam of each scanning line is set as the origin, and the main scanning direction and the sub-scanning direction are set as the x axis and the y axis, respectively. Sometimes, the tangent direction is bent and the inclination is adjusted so that the tangential direction has a relationship between the first quadrant and the third quadrant, or a relationship between the second quadrant and the fourth quadrant.
[0026]
Specifically, both reference planes in the sub-scanning direction of the first scanning lens 116 are asymmetric with respect to the bus line, and the installation direction of the scanning lens of the adjacent module is reversed, that is, the height from the joint surface 118 to the bus line is high. By alternately changing the length between adjacent scanning lenses, the direction of bending is alternately reversed as shown in FIG. Naturally, both reference planes may be symmetric with respect to the generatrix, and the height of the joining surface 118 may be changed. In FIG. 13, the upper part (a) is a view of the scanning lens as viewed from the front, and the lower part (b) shows the trajectory of the scanning line.
[0027]
  The above relationship can also be obtained by adjustment. FIG. 12 shows various examples. (A) is provided with the contact screw 142 which abuts the both ends of the 2nd scanning lens 121, and the boundary part of each scanning lens to a subscanning direction in the said housing. In FIG. 5B, the housing is provided with a contact screw 143 that abuts the central portion of each scanning lens. In both cases, the abutment part can be varied to make the entire lens follow this, making it wavySwellThus, the inclination and the bending can be adjusted so as to match the above-described relationship.
  12A shows an example in which the left scanning line inclination is adjusted, and FIG. 12B shows an example in which the bending is adjusted. The leaf spring 141 is sandwiched between the cover and reliably contacts each contact portion.
  Incidentally, if the contact screw is sent by a stepping motor based on a detection result in a tangential direction on the transfer belt, which will be described later, it is possible to correct the deviation with time.
  Further, the adjustment of the tilt and the bending is not limited to the above-described configuration, but can be realized by a configuration such as shifting or tilting the first scanning lens in the sub-scanning direction.
[0028]
FIG. 5 shows an example of an image forming apparatus in which the above-described optical scanning apparatus according to the present invention forms an image one color at a time by a single optical scanning apparatus 500, and rotates the transfer belt 501 four times to superimpose colors every rotation. An example applied to a color laser printer is shown. In FIG. 5, the transfer belt 501 is supported by a driving roller and two driven rollers so as to form a triangle. A developing roller 502 and a toner hopper 503 for replenishing toner corresponding to each color are provided integrally on a rotating support 509 and are configured to face the photosensitive drum 504 while rotating by 1/4 in a revolver manner. Yes.
[0029]
The image is recorded as an electrostatic latent image on the photosensitive drum 504 by the optical scanning device 500 by using the signal of the sensor 505 that detects the registration mark formed at the end of the transfer belt 501 as a trigger to measure the writing timing in the sub-scanning direction. Is done. The electrostatic latent image is developed by applying toner in the developing unit, and the toner image is transferred to the transfer belt 501. The residual toner after the transfer is scraped and stored by the cleaning unit 508 so as not to mix colors. By performing these operations for each color, images are sequentially superimposed. The paper is supplied from the paper supply tray 507 by the paper supply roller 506, sent out by the registration roller 50 in synchronization with the image formation of the fourth color, and transferred by the transfer unit 511 from the transfer belt 501 at the same time. The transferred toner image is fixed by a fixing roller 512 and discharged to a paper discharge tray 514.
[0030]
As described above, the optical scanning device 500 connects the scanning lines of a plurality of optical scanning units to form one line. The total number of dots L per line is divided into three, and 1 to L1, L1 + 1 to L2, and L2 + 1 to L dots are assigned and printed from the beginning of the image. In this embodiment, the scanning areas overlap several mm on the photosensitive member. An overlap area is provided in the pixel, and the number of assigned pixels L1 and L2 is not fixed, but is made different for each color, so that the seams of the scan lines of the respective colors constituting the same line are not overlapped so that the boundary of the scan area is further increased. It is hard to stand out.
[0031]
As described above, the image data is divided into three in the main scanning direction, stored in the bitmap memory for each optical scanning means, raster-developed for each oscillating mirror module, and stored in the buffer as line data.
The stored line data is read using each synchronization detection signal as a trigger, and image recording is performed individually. However, by setting each writing timing as described later, registration at the start of writing is adjusted.
[0032]
In the embodiment, even if the resonance peaks of the oscillating mirrors are different, a common drive frequency is given in a region where the resonance bands overlap. As the spring constant changes due to environmental temperature changes and the resonance band shifts uniformly, it is necessary to shift the drive frequency accordingly. In this case as well, a common drive frequency is given. Therefore, the scanning frequency does not differ between the vibrating mirror modules, and the resists of the lines match up to the end of each area.
A CCD area sensor 515 that monitors the vicinity of the boundary of each image area is provided to face the transfer belt 501. The CCD area sensor 515 reads the toner image of the detection pattern formed on the transfer belt 501 two-dimensionally through the objective lens 516, and performs relative registration shift d at the recording position by image processing, and relative at the joint. A simple tangential slope (differential value) is detected.
[0033]
FIG. 6 is a block diagram illustrating an example of a drive control circuit for a semiconductor laser and a movable mirror. In FIG. 6, the drive pulse generator 601 divides the reference clock by a programmable frequency divider, and as shown in FIG. 7, once every half cycle of the movable mirror and until it becomes horizontal from the maximum amplitude. A pulse train (T <T0 / 4) having a duty of 50% or less is generated at a frequency twice the resonance frequency f0 (= 1 / T0) so that a voltage pulse is applied only during the period of Is generated as a drive frequency fd, which is given to the movable mirror drive unit 602.
Here, the relative phase delay δ between the oscillating mirrors is calculated using one scanning line pitch p.
δ = (1 / fd) · {(d / p) −n}
Here, n is (d / p) -n <1
If the natural number satisfies the above, it is possible to correct the writing timing every other period of the oscillating mirror. In other words, the registration deviation d can be invalidated by writing the data shifted by n line cycles, and this check is performed at the time of start-up or periodically, so that a high-quality image having no seam position deviation over time can be obtained. Is obtained.
[0034]
The movable mirror records an image only during scanning in the same direction during the period from θs to −θs (0 <θs <θ) from the scanning angle θ0 as a starting point until reaching −θ0, and from the scanning angle −θ0. Image recording is not performed during the return period of + θ0. In other words, image recording is performed for each cycle of the drive frequency fd. Incidentally, θs / θ0 = 0.7.
[0035]
When the power is turned on and when the system is started from the standby state, the drive frequency fd is varied from the high frequency side by continuously changing the frequency division ratio with the programmable frequency divider, and the light beam is generated by the synchronization detection sensor 604. The resonance band is determined by the fact that the scanning angle is expanded until it is detected. At this time, the swing angle may be finely adjusted by changing the gain of the drive voltage to be applied.
In the embodiment, a sensor 605 is also provided in the vicinity of the scanning angle −θ0 to detect the scanning end beam, and the time difference between the end detection signal and the scanning start end synchronization detection signal is measured to measure the movable mirror. Changes in the image recording width due to scanning speed fluctuations and scanning lens shape errors are detected. As will be described later, this change in the image recording width is corrected by changing the pixel clock.
[0036]
FIG. 8 shows details of the sensors 604 and 605 in the embodiment. The sensors 604 and 605 have a photodiode 801 perpendicular to the main scanning direction and a non-parallel photodiode 802, and generate a synchronization detection signal or a termination detection signal when the light beam passes through the edge of the photodiode 801. The time difference Δt from when the scanning light reaches the photodiode 801 to the photodiode 802 is measured, and the scanning position deviation Δy in the sub-scanning direction, which is the main cause of the registration deviation, is detected.
Δy is the inclination angle γ of the sensor unit 802 and the scanning speed V of the light beam.
Δy = (V / tanγ) · Δt
If Δt is constant, there is no scanning position deviation.
[0037]
In the circuit example shown in FIG. 6, the above-described time difference is monitored by the scanning position deviation calculation unit 610 to detect the scanning position deviation, and the phase between the vibrating mirrors is varied and corrected so as to meet the Δt reference value. This correction is performed in each of the oscillating mirror modules. Since the embodiment includes three optical scanning units, the printing operation can be performed after all the corrections are completed.
[0038]
By the way, since the movable mirror is resonantly oscillated, the scanning angle θ changes in a sin wave shape as shown in FIG.
θ = θ0 · sin2πfd · t, −1 / 4fd <t <1 / 4fd
On the other hand, it is necessary to print the main scanning dots at a uniform interval on the surface of the photosensitive drum that is the surface to be scanned, and the imaging characteristic of the scanning lens described above is that the scanning distance dH / dθ per unit scanning angle is sin.^-1It is necessary to correct the direction of the light beam so that it is proportional to / θ0, that is, it is slow at the center of the image and is accelerated faster toward the periphery. However, it is necessary to distribute power so that the image forming point is kept away from the center to the periphery of the scanning lens, and there is a limit in expanding the effective scanning area θs with respect to the maximum amplitude θ0.
[0039]
In order to keep the spot diameter uniform with only the scanning lens, the scanning efficiency θs / θ0 <0.5 must be satisfied. In the embodiment, as shown in FIG. 10, the phase corresponding to each pixel is delayed stepwise from the state in which the phase corresponding to each pixel advances from the recording start to the recording end against the change in the scanning speed due to the amplitude. The semiconductor laser (LD) driving unit 606 generates a pixel clock fm that has a pulse width that gradually decreases from a long state in the region from the recording start position to the center of the image, and that increases in a region from the image center to the recording end. Is given to. Thereby, it has improved to (theta) s / (theta) 0 = 0.7.
[0040]
Hereinafter, a method for changing the pixel clock fm will be described. The clock pulse generation unit 607 shown in FIG. 6 counts a frequency-divided clock obtained by dividing the reference clock f0 by a programmable frequency divider based on the variable data, and a PLL reference signal fa having a pulse length of k clocks. In the PLL circuit, the phase with the reference clock f0 is selected based on the variable data, and the pixel clock fk is generated. By repeating this every tens of pixels, dots can be printed at arbitrary positions along the main scan.
[0041]
For the reference clock f0, the phase synchronization unit 608 selects a clock that is in phase with the synchronization detection signal generated by the synchronization detection sensor 604 from among the clocks delayed by 1 / n of one cycle of the reference clock f0. Phase synchronization with the reference clock f0 is performed for each scan. In this embodiment, clocks having different phases can be selected at this time, and the horizontal state (θ = 0) of the movable mirror surely matches the center position of the image recording at the timing of starting the clock variable. Correct as follows. Incidentally, if this timing is shifted, the image becomes a distorted image in which the dot interval in the main scanning direction is reduced on one side and extended on the other side.
Further, by changing the frequency division ratio of the reference clock f0, the image width in the main scanning direction can be adjusted, and the time difference between the end detection signal and the synchronization detection signal is measured by the magnification calculator 609 as described above. When the time difference is shorter than the predetermined value, the frequency is corrected to increase, and when the time difference is longer, the correction is performed to decrease.
[0042]
【The invention's effect】
  According to a first aspect of the present invention, a light source, a vibrating mirror that reciprocally vibrates at a constant driving frequency, and scans a light beam from the light source, and an imaging optical that forms an image of the scanned light beam on a surface to be scanned. A plurality of optical scanning means comprising a system, dividing an image area into main scans, and recording each image by an optical scanning means adjacent to each other.eachScan lineScanning line extreme positionBut,The scanning line by the adjacent optical scanning meansSeamVs.Therefore, the scanning lines are opposite in the sub-scanning direction, and the bending of the scanning lines by the adjacent optical scanning units is in a direction opposite to each other. As a result, the bending and inclination of each optical scanning means can be adjusted accurately.TheHowever, there is an advantage that the joint between the image areas can be made inconspicuous, the troublesome adjustment work can be simplified, and the production efficiency can be improved.
  Even if the scanning line is bent, the seam between the image areas can be easily made inconspicuous without special adjustment, and high-quality image recording can be performed.
[0044]
  Claim2According to the described invention, at least one of the adjacent optical scanning means is provided with a bending adjusting means for changing the amount of bending of the scanning line, and correction of the tangential direction causes variations in assembly, processing errors, and the like. Even in such a case, the seam of the scanning lines can be made inconspicuous, the production efficiency can be improved, and high-quality image recording can be performed.
[0045]
  Claim3According to the described invention, at least one of the adjacent optical scanning units includes the tilt adjusting unit that varies the tilt amount of the scanning line, and correction of the tangential direction causes variations in assembly, processing errors, and the like. Even in this case, the seam can be made inconspicuous, the production efficiency can be improved, and high-quality image recording can be performed.
[0046]
  Claim4According to the described invention, at least one optical element constituting the imaging optical system is continuously formed by a plurality of optical scanning means, and a contact portion that abuts in the sub-scanning direction at a plurality of locations in the main scanning direction. By adjusting the height of each contact portion, the bend or the inclination is adjusted, so that the configuration is simple and there is a change in the installation environment, etc., compared with individually adjusting means. There is little misalignment, and high-quality image recording can be performed in which the seam of the scanning lines is not noticeable even after the lapse of time.
[0047]
  Claim5According to the described invention, at least one of the adjacent optical scanning units includes the mirror driving unit that varies the phase of the oscillating mirror, and the optical axis direction is varied by correcting the registration deviation in the sub-scanning direction. Even without using such complicated correction means, the writing position can be reliably changed, so that the production efficiency is improved and high-quality image recording can be performed.
[0048]
  Claim6According to the described invention, the mirror driving means includes a registration deviation d of the adjacent optical scanning means.
  d₂= D−n · p, (n is a natural number, p is a recording pitch in the sub-scanning direction)
By correcting this, the writing position can be changed reliably, so that high-quality image recording in which the seam of the scanning lines is not noticeable can be performed.
[0049]
  Claim7According to the described invention, the light source driving means for correcting the timing for modulating the light emitting source is provided, and among the registration deviation d of the adjacent optical scanning means,
  d₁= N · p = d−d₂    Where d₂<P
By correcting this, even if the registration deviation is large, the amount of phase change in the mirror driving means can be made within one cycle, and the writing position can be surely changed, so that the seam of the scanning lines is hardly noticeable. High-quality image recording can be performed.
[0050]
  Claim8According to the described invention, an overlap portion is provided in the scanning region of the adjacent optical scanning means, and the scan position deviation detecting means for detecting each scan position deviation is provided in the overlap portion, and the above-described detection is based on the detection result. By changing the phase, it is possible to perform feedback correction according to the situation even if the scanning position shifts due to changes in the installation environment, etc. Records can be maintained.
[0051]
According to a tenth aspect of the present invention, there is provided a light source, a vibrating mirror that reciprocally vibrates at a constant driving frequency, and scans a light beam from the light source, and an imaging optical that forms an image of the scanned light beam on a surface to be scanned. An optical scanning device including a plurality of optical scanning units having a system, a photoconductor on which an image area is divided into main scans by the optical scanning unit, and an electrostatic image formed with toner. An image forming apparatus having a developing means for converting and a transfer means for transferring a visualized toner image onto a recording paper, wherein the adjacent line in the vicinity of the joint of the optical scanning means by the visualized toner image Tangential direction detecting means for detecting the tangential direction of the Therefore, since the image quality can be monitored even after shipment, even if the quality at the time of shipment is not maintained due to changes in the installation environment, feedback correction can be made according to the situation, and the years have passed. In addition, it is possible to maintain high-quality image recording in which the seam of the scanning line is not noticeable.
[0052]
According to an eleventh aspect of the present invention, a light source, a vibrating mirror that reciprocally vibrates at a constant driving frequency, and scans a light beam from the light source, and imaging optics that forms an image of the scanned light beam on a surface to be scanned. An optical scanning device comprising a plurality of optical scanning means, a photosensitive member on which an image area is divided into main scans by the optical scanning means, and an electrostatic image is formed, and the electrostatic image is developed with toner. An image forming apparatus having a developing means for imaging and a transfer means for transferring a visualized toner image onto a recording paper, wherein the resist in the vicinity of a joint of the optical scanning means is formed by the visualized toner image. A registration deviation detecting means for detecting deviation is provided. Therefore, since the image quality can be monitored even after shipment, even if the quality at the time of shipment is not maintained due to changes in the installation environment etc., feedback correction can be made according to the situation, even if the years have passed It is possible to maintain high-quality image recording in which the seam of the scanning line is not noticeable.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing an embodiment of an optical scanning device according to the present invention.
FIG. 2 is an exploded perspective view of the same embodiment as viewed from the opposite side.
FIG. 3 is an exploded perspective view showing an example of a vibrating mirror module that can be used in the optical scanning device according to the present invention.
FIG. 4 is a front sectional view of the vibrating mirror module.
FIG. 5 is a front view schematically showing an embodiment of an image forming apparatus having the optical scanning device according to the present invention.
FIG. 6 is a block diagram showing an example of a movable mirror drive control circuit in the vibrating mirror module.
FIG. 7 is a waveform diagram showing an example of voltage pulses applied to the movable mirror of the vibrating mirror module.
FIG. 8 is an optical layout diagram showing an example of a synchronization detection sensor that can be used in the present invention.
FIG. 9 is a diagram showing an example of a change in scanning angle by a movable mirror of the vibrating mirror module.
FIG. 10 is a diagram showing how the phase corresponding to each pixel is changed against the change in scanning speed due to the amplitude of the movable mirror.
FIG. 11 is a diagram showing a state of a joint portion of a scanning line between adjacent vibrating mirror modules.
FIGS. 12A and 12B show examples of scanning lens adjustment means applicable to the present invention, in which FIG. 12A shows an example of means for adjusting scanning line inclination, and FIG. 12B shows an example of means for adjusting scanning line bending; FIG. 4 is a diagram showing a locus on a plan view and a scanning line, respectively.
FIGS. 13A and 13B show examples of the installation direction of the scanning lens of the adjacent oscillating mirror module and the scanning line trajectory corresponding thereto, where FIG. 13A shows the scanning lens viewed from the front, and FIG. 13B shows the scanning line trajectory; FIG.
FIG. 14 is a graph showing an example of a tangential inclination in the vicinity of a scanning line joint.
[Explanation of symbols]
101 Light source
200 Vibration mirror module
201 Support substrate
202 Movable mirror
208 Torsion beam
209 Torsion beam

Claims (11)

A light emitting source, a vibrating mirror that reciprocally vibrates at a constant driving frequency and scans a light beam from the light emitting source, and an imaging optical system that forms an image of the light beam scanned by the vibrating mirror on a surface to be scanned An optical scanning device comprising a plurality of optical scanning means, wherein an image area is divided in the main scanning direction corresponding to the number of optical scanning means, and each image area is optically scanned by the optical scanning means corresponding thereto to record an image Because
Position phases adjacent extreme values of the bending of the scanning line of each scanning line by the optical scanning means, is opposite in the sub-scanning direction against the seam of the scan line by the phase adjacent scanning means, light this phase adjacent An optical scanning device characterized in that the bending of the scanning line by the scanning means is in a direction opposite to each other.   2. The optical scanning device according to claim 1, wherein at least one of the adjacent optical scanning units includes a bending adjusting unit that varies a bending amount of the scanning line, and includes the tangential direction correcting unit.   2. The optical scanning device according to claim 1, wherein at least one of the adjacent optical scanning units includes an inclination adjusting unit that varies an amount of inclination of the scanning line, and includes the correcting unit in the tangential direction.   At least one optical element constituting the imaging optical system is constituted by a plurality of optical scanning means formed continuously, and the at least one optical element is abutted in the sub-scanning direction at a plurality of positions in the main scanning direction. 4. The optical scanning device according to claim 2, further comprising a contact portion, wherein the bending or inclination of the scanning line is adjusted by changing a height of the contact portion. At least one is provided with a mirror driving means for varying the phase of the oscillating mirror, an optical scanning apparatus according to claim 1, wherein a registration deviation correcting unit in the sub-scanning direction of the phase adjacent optical scanning means. The mirror driving means includes a resist deviation d between adjacent optical scanning means,
d ₂ = d−n · p
(N is a natural number, p is a recording pitch in the sub-scanning direction)
The optical scanning device according to claim 5, wherein a certain amount is corrected. A light source driving unit that corrects the timing of modulating the light source;
d ₁ = n · p = d−d ₂ where d ₂ <p
The optical scanning device according to claim 6, wherein a certain amount is corrected.   An overlapping portion is provided in the scanning region of the adjacent optical scanning means, and a scanning position deviation detecting means for detecting each scanning position deviation is provided in the overlapping portion, and the phase is varied based on the detection result by the detecting means. The optical scanning device according to claim 5. A light emitting source, a vibrating mirror that reciprocally vibrates at a constant driving frequency and scans a light beam from the light emitting source, and an imaging optical system that forms an image of the light beam scanned by the vibrating mirror on a surface to be scanned An optical scanning device comprising a plurality of optical scanning means;
An image carrier in which image areas are divided in the main scanning direction corresponding to the number of optical scanning means, and each image area is optically scanned by the corresponding optical scanning means to form an electrostatic image;
Developing means for visualizing the electrostatic image with toner;
A transfer unit that transfers a visualized toner image onto a recording paper,
The image forming apparatus according to claim 1, wherein the optical scanning apparatus is the optical scanning apparatus according to claim 1. A light emitting source, a vibrating mirror that reciprocally vibrates at a constant driving frequency and scans a light beam from the light emitting source, and an imaging optical system that forms an image of the light beam scanned by the vibrating mirror on a surface to be scanned An optical scanning device comprising a plurality of optical scanning means;
An image carrier in which image areas are divided in the main scanning direction corresponding to the number of optical scanning means, and each image area is optically scanned by the corresponding optical scanning means to form an electrostatic image;
Developing means for visualizing the electrostatic image with toner;
A transfer unit that transfers a visualized toner image onto a recording paper,
The optical scanning device is the optical scanning device according to any one of claims 1 to 8,
An image forming apparatus comprising: a tangential direction detection unit configured to detect a tangential direction of an adjacent line in the vicinity of a joint of the optical scanning unit based on the visualized toner image. An optical scanning means comprising: a vibrating mirror that reciprocally vibrates at a fixed driving frequency and scans a light beam from a light source; and an imaging optical system that forms an image of the light beam scanned by the vibrating mirror on a surface to be scanned. A plurality of optical scanning devices,
An image carrier in which image areas are divided in the main scanning direction corresponding to the number of optical scanning means, and each image area is optically scanned by the corresponding optical scanning means to form an electrostatic image;
Developing means for visualizing the electrostatic image with toner;
A transfer unit that transfers a visualized toner image onto a recording paper,
The optical scanning device is the optical scanning device according to any one of claims 1 to 8,
An image forming apparatus comprising: a registration deviation detection unit configured to detect registration deviation in the vicinity of a joint of the optical scanning unit based on the visualized toner image.

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