JP2005037629A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the accuracy of a relative arrangement of recording lines is kept stable over time and consequently such environment protection measures as power saving and resource saving are taken into consideration. <P>SOLUTION: In the image forming apparatus, a plurality of optical scanners which are each provided with a plurality of optical scanning means having a light source means and a movable mirror which scans by reflecting a light beam emitted from the light source means and forms an electrostatic latent image on a image carrier drum by combining individual scanning regions along a main scanning direction in main scanning, and a plurality of image development means which visualize the electrostatic latent image with toner, are arranged in parallel along the moving direction of a transfer body, and a color image is formed by successively transferring and superimposing the toner images visualized with the toner onto the transfer body. The image forming apparatus is provided with a pair of side plates facing to each other which are orthogonal to the main scanning direction and interposing the the scanning regions, and supports the plurality of optical scanners as a unit by bridging the side plates. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ここで、ねじり梁２０８の長さＬと振れ角θとは比例関係にあるため、
θ＝Ａ／Ｉ・ｆ^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Ｉを低減しないと振れ角θが小さくなってしまう。
【００２７】
そこで、実施例では可動ミラー２０２の反射面の裏側２１９の基板厚さをｄとし、反射面以外の部分の厚さをｄ／１以下となるように格子状にエッチングして肉抜きすることで、慣性モーメントＩが約１／５に低減するようにしている。
これらの慣性モーメントＩに利くパラメータ、ねじり梁２０８の寸法誤差等が共振周波数のばらつきを発生させる要因となる。
【００２８】
一方、空気の誘電率をεとし、電極長さをＨとし、印加電圧をＶとし、電極間距離をδとすると電極間の静電力Ｆは
Ｆ＝εＨＶ^２ ／２δとなり、振れ角θ＝Ｂ・Ｆ／Ｉ（Ｂは定数）
とも表され、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倍の駆動トルクを得ている。
【００２９】
このように外周長をできるだけ長くして電極長を長くすることで、低電圧でより大きい静電トルクが得られるように配慮している。
ところで、可動ミラー２０２の速度υ、面積Ｅに対して、空気の密度を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（回動）に対向して働く。
従って、可動ミラー２０２を密封し減圧状態に保持するのが望ましい。
【００３０】
実施例では、第１、第２の基板２０６、２０７が接合されてなる振動ミラー基板を、中央部に凹状に可動ミラー２０２の揺動空間を形成した基体２１２上に、反射面を上側に向け、基体の外縁に形成された一対のＶ溝を結ぶ直線上にねじり梁２０８を合わせて、第１の基板下面を基準にして装着し、また、第２の基板２０７上面にキャップ状に一体成形された透明樹脂製のカバー２０５を接合して可動ミラー２０２の揺動空間が密封されるようにし、揺動空間には非蒸発型ゲッタを同梱し、外部からの加熱で活性化することにより１Ｔｏｒｒ以下の圧力となるようにしている。
【００３１】
カバー２０５は透気性を下げるため、比較的吸湿性の低いポリ・オレフィン系の樹脂を用い、その表面にはＳｉＯ等のコートを施している。
光ビームは、カバー２０５に形成されたスリット窓２１３を通じて入出射される。
【００３２】
上記したように、接合面に配線を介在すると気密性が損なわれるため、実施例では、接合面に垂直となるように、セラミック等絶縁部材で形成した基体２１２にリード端子２１６が基体２１２を貫通して一体化されている。振動ミラー（可動ミラー２０２）が基体２１２に接合された際に、上記分離された島部２２１、２２２、２２３、２２４、２２５に端子径よりわずかに小さく形成された各係合穴２２６、２２７、２２８、２２９、２３０に、上側に突出した端部が圧入され、接続される。
【００３３】
尚、上側に配置される第２のＳｉ基板２０７の係合穴２２９、２３０に圧入されるリード端子は、第１のＳｉ基板２０６の厚さ分だけ突出量が長く設定されており、第１のＳｉ基板２０６に端子径よりも大きく形成された貫通穴２３１、２３２を通って挿入される。
カバー２０５の内側には、可動ミラー２０２と対向して対向ミラー２１５が、ねじり梁２０８と直交する方向に一体的に形成される。２枚の対向ミラー２１５はスリット窓２１３を挟んで屋根状に１４４．７°の角度をなすよう基板面より各々９°、および２６．３°傾けた傾斜面に、金属被膜を蒸着して反射面２１７と２１８とを対で配備した構成とする。
【００３４】
カバー２０５の底面は可動ミラー面と平行に形成され、第２のＳｉ基板２１２の枠部上面に当接して接合されるが、この接合の際、第２のＳｉ基板２１２には対向ミラー２１５を位置決めするための指標２１６が両サイドにエッチングによって描かれ、この指標２１８に対向ミラー２１５のエッジを合わせるように第２のＳｉ基板２１２上でアライメントしており、主走査方向に対向ミラー２１５の方向を正確に合わせることができる。
【００３５】
図４は光走査装置の副走査断面を示す。
半導体レーザ１０１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１１０、シリンダミラー１３６を介して、可動ミラー４０１（２０２）に対しねじり梁２０８を含む副走査断面内で法線に対して副走査方向に約２０°傾けてスリット窓４０４より光ビームが入射される。可動ミラー４０１で反射した光ビームは第１の反射面４０２に入射され可動ミラー４０１に戻され、さらに反射した光ビームはスリット窓４０４を超えて第２の反射面４０３に入射される。すなわち、半導体レーザ１０１から出射した光ビームは可動ミラー４０１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４０１での反射により再度、スリット窓４０４から射出される。
【００３６】
実施例ではこのように半導体レーザ１０１から出射した光ビームが複数回反射を繰り返すことで、可動ミラー４０１の振れ角が小さくても大きな走査角が得られるようにし、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とし、振れ角をαとすると、走査角θは２Ｎαで表せる。実施例では、Ｎ＝５、α＝５°であるため、最大走査角は５０°となり、その内３５°を画像記録領域としている。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、つまり共振周波数が高くなるに従ってねじり梁２０８のばね定数Ｋを高める必要があり振れ角がとれなくなってしまう。
【００３７】
そこで、上記したように対向ミラー２１５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、屋根状（切り妻屋根状）に対向して反射面を構成し、可動ミラー２０２への副走査方向での入射角度が繰り返し反射毎に正負、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における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こらないよう配慮している。
【００３８】
図１は本発明の画像形成装置に係る一実施例における光走査装置の分解斜視図を示し、図２は光学素子の配置を示す。
図１において、光源である半導体レーザ１０１は、副走査方向に約５０μｍのピッチで２つの発光源がモノリシックに形成され、フレーム部材１０２に立設された壁に配備された段付きの貫通穴１０３に反対側からステム外周を基準に係合され、段差部に鍔面を突き当てて光軸方向の位置決めがなされ、押え板１４１０により背面から押圧固定される。
【００３９】
図２０に図１に示した光学装置への半導体レーザの取り付けについての詳細を示すが、押え板の突起１４２をステム外周に形成された切欠に係合し、貫通穴１０３の中心軸の周りに回転することで、外周部を切り起こして形成した一対の板ばね１４３をフレーム部材１０２に形成した庇状の突起１４４に係合して半導体レーザ１０１を押圧するとともに、発光源の配列方向が所定量だけ主走査方向から傾くように調整され、ネジ１４５０により回転止めがなされる。
【００４０】
また、図１に示すＵ字状の凹部１０５にはＵＶ接着剤を介してカップリングレンズ１１０の光軸が半導体レーザ１０１から射出する光ビームの光軸と一致するようにし、また、射出光束が平行光束となるように発光点の光軸方向の位置決めを行い、凹部１０５とカップリングレンズ１１０との隙間のＵＶ接着剤を硬化させて固定する。
尚、カップリングレンズ１１０の光軸調整は後述する振動ミラーモジュール１３０および、シリンダミラー１３６を取付けた状態でも行うことができ、可動ミラー２０２（図３参照）の面精度やシリンダミラー１３６の焦線位置ずれを無効化できるので、それらの精度を緩和できる。
【００４１】
実施例の場合、３つの光源部を有するが、全て同一構成である。
カップリングレンズ１１０から射出した２本の光ビームは、一対の取り付け斜面１０９に接合配備され副走査方向に負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１３０のスリット窓２１３（図３参照）から入射される。
【００４２】
図１７には、被走査面におけるビームスポットの配列を示すが、上記したように半導体レーザ１０１を傾けて装着することにより副走査方向のビームスポット間隔Ｐを設定する。
ビームスポット間隔Ｐは、後述する第１、第２の走査レンズ１１６、１１７を含め光源から被走査面に至る全系の副走査倍率β、２つの光源間のピッチＰを用いて、
Ｐ＝β・Ｐ・ｓｉｎφ
で表され、後述するように、転写ベルト５０１（図５参照）上に形成されたラインの傾き補正量に応じてピッチＰを調整している。
【００４３】
振動ミラーモジュール１３０は、ねじり梁２０８（図３参照）の方向が光軸方向に合うように、フレーム底面側に設けられた段付きの角穴１０４の裏側より基体２１２（図３参照）の外縁を基準に位置決めされ、段差部に鍔面を突き当てて可動ミラー面の位置を合わせされる。実施例の場合、均等間隔に３つの振動ミラーモジュール１３０が単一のフレーム部材１０２により位置決めされる。
各振動ミラーモジュール１３０は、プリント基板１１２に、基体底面から突出したリード端子を各々スルーホールに挿入して半田付けし、フレーム部材１０２の下側開口を塞ぐように基板上面を当接して固定すると同時に、回路接続がなされる。
プリント基板１１２には半導体レーザの駆動回路、可動ミラー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、外部回路との配線が一括してなされる。
【００４４】
一端がプリント基板１１２に結線されたケーブル１１５の他端は半導体レーザ１０１のリード端子と接続される。
フレーム部材１０２の上面は角穴１０４の裏側に設けられた各振動ミラーモジュール１３０のミラー法線方向の突き当て面と平行な面となし、走査レンズを収納するハウジング１０６の底面より突出した２本の突起１３５をフレーム部材の係合穴に挿入して同面上での位置決めを行い、４隅をネジ止めして配備される。実施例では、ネジ１３７はフレーム部材の貫通穴を介してプリント基板１１２に螺合され、フレーム部材を挟むように（三位一体で）結合され、この後に上記半田付けがなされる。
【００４５】
ハウジング１０６には結像手段を構成する第１の走査レンズ１１６及び第２の走査レンズ１１７が主走査方向に配列され、各々の走査領域がわずかに重なるように位置決めされて一体的に保持される。
第１の走査レンズ１１６は、副走査方向の基準面の中央に突出し主走査方向の位置決めを行うための突起１２０、および両端を係合して光軸方向の位置決めを行うための平押面１１９を入射面側、出射面側各々に備えている。ハウジング１０６には溝１２２、一対の切欠１２１および一対の突起１４２が一体形成されている。
第１の走査レンズ１１６の突起１２０を溝１２２に係合させ、切欠１２１の各々に各端の平押面１１９を挿入し、波板バネ１４３を用いて入射面側に押し付け同面内での姿勢を保持することで、第１の走査レンズ１１６の光軸と直交する同一面に各第１の走査レンズ１１６同士の相対的な配置を合わせることができる。第１の走査レンズ１１６の副走査方向の基準面をハウジング１０６の突起１４２の先端に突き当てることで、第１の走査レンズ１１６の光軸と直交する面内での位置決めがなされ、副走査方向の設置高さが決定され、カバー１３８と一体形成された板バネ１４１で押圧支持される。
【００４６】
一方、第２の走査レンズ１１７は同様に副走査方向基準面の中央に突出され主走査方向の位置決めを行う突起１２３、両端に光軸方向の位置決めを行うための平押面１４４を備えている。溝１２２に突起１２３を係合し、切欠１２１に平押面１４４を挿入し、波板バネ１４３で出射面側に押し付け姿勢を保持するとともに、副走査方向基準面をハウジング１０６から突出した突起１４５および１４６の先端に突き当てて設置高さを位置決めし、カバー１３８と一体形成された板バネ１４１で押圧支持される。１４７はカバー１３８を固定するネジである。
【００４７】
同期検知センサ１１３（ピンフォトダイオード）は隣接する振動ミラーモジュール１３０（図１参照）で共用する中間位置と両端位置とに配置され、各光走査モジュール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箇所に実装される。第２の走査レンズ１１７の射出面側には各レンズの走査領域間にＶ字状の高輝アルミ薄板１２７を貼り付けるミラー受部１２８がハウジング１０６に形成され、高輝アルミ薄板１２７によって反射した光ビームが走査領域間に形成された開口部１２９、およびフレーム部材の矩形穴を通って各々の同期検知センサ１１３へ導かれるよう隣接する光走査手段の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。
【００４８】
カバー１３８には光ビームが通過する開口１３９が形成されている。ハウジング１０６上面を密閉するようネジ止めし、前記したように板バネ１４１により走査レンズ１１６、１１７を各当接部位に確実に突き当たるように押圧する。
図１１は、像担持体としての感光体ドラムの位置決め方法を表す図である。
上記したフレーム部材１０２、ハウジング１０６はある程度剛性が確保されるガラス繊維強化樹脂やアルミダイキャスト等で成形され、ハウジング１０６の両側面には、一対の位置決めピン１３１とネジ穴１３３とが形成されている。
【００４９】
側板６３２、６３３は板金で成形され、主走査方向に対向して配置される。各々の測板６３２、６３３には感光体ドラム５０４の軸受６３６を位置決めするための切欠６３５が形成され、係合して感光体ドラム５０４同士の配置精度を保って支持できる。
実施例では、この軸中心の間隔が感光体ドラム５０４の周長の整数倍、ドラム径をｒとすると、ｋ・πｒとなるよう均等間隔で配置される。
【００５０】
光走査装置６４０、６４１、６４２、６４３は、各々、上記位置決めピン１３１を嵌合穴６３７に挿入し、ハウジング１０６の側面を側板６３２、６３３の内側になるように当接して、側板６３２、６３３間を架橋するように位置決めし、ネジ６３７を外側から通して固定する。
この位置決め固定の際、図１５（ａ）、（ｂ）に示すように側板６３２、６３３に形成する嵌合穴６３７を感光体ドラム５０４の配列方向と平行な長穴とし、偏心カム６３８の外周を側板６３２、６３３に形成した係合穴６３９に係合してネジ固定するようにすれば、偏心カム６３８がネジ穴１３３を中心に回転することで、光走査装置６４０〜６４３が長穴（嵌合穴６３７）に沿って微動することができ、各走査ラインの位置を調節することができる。
【００５１】
尚、図１５（ａ）は走査ラインの位置調節の説明図であり、図１５（ｂ）は図１５（ａ）の矢印Ａ方向の矢視図である。
【００５２】
図１９（ａ）、（ｂ）は隣接する光走査手段におけるライン像の継ぎ目補正方法を表す説明図である。図１９（ａ）は補正前の状態を示し、図１９（ｂ）は補正後の状態を示す。
実施例では、各々の書出し位置の差が０となるように合わせている。
いま、隣接する光走査手段の記録位置がＤだけずれている場合を想定する（図１９（ａ））。Ｄ＝０となるように補正すればよいが、その補正手段としては、まず、走査ラインの書出タイミングを、ラインピッチｐ単位で補正する。
【００５３】
具体的には、画像データを読み出す同期検知信号の選択により、タイミングを１周期Ｔのｋ倍（ｋ・Ｔ）毎にずらす。ここで、ｋは自然数であり、Ｌ−ｋ・ｐが最も０に近いｋを選択する。
次に、残りの分Ｄ’を振動ミラー（可動ミラー２０２、図３参照）の振幅位相を１周期Ｔの１／ｎ倍（Ｔ／ｎ）毎にずらして、ｐ／ｎ単位で補正する。ここで、ｎは自然数で、Ｌ−（ｋ＋１／ｎ）・ｐが最も０に近いｎを選択すればよい。
このようにして転写ベルト５０１（図５参照）上において隣接する領域に記録されるライン像を繋ぎ合わせることができる。
【００５４】
図９に、副走査方向における各ビームスポットの強度分布と、ビームスポットにより形成される静電潜像の電位分布を示す。図９中、左右方向が副走査方向であり、１画素分のドットに相当する平面図（図の下側）及び断面図（図の中程）を示す。図９の左側が第１の発光源からのビーム、右側が第２の発光源からのビームによる電位分布である。
このように、各ビームスポットが近接された状態においては、それによって形成される電位分布は各ビームスポットの光量（露光エネルギー）が合成された形で一様な分布として再現され、各ビームスポットの光量が同一であれば、ちょうど中間位置を重心とした分布となる。・・・（１）
また、各ビームスポットの光量が異なる場合、静電潜像径が異なる２つの分布が複合されることで、中間位置から光量が高いほうに重心が片寄った分布となる。・・・（２）
こうして形成された電位分布の現像バイアス電位よりも高い部分に帯電したトナーが吸引され付着されてドットが形成され、各々の光量をバランスさせることにより、任意の重心位置に対して均一のドット径ｄ０とすることができる。
【００５５】
従って、各ビームスポットの光量の比を変えることにより各ライン間をまたがって静電潜像の重心位置を移動すれば、走査方向からピッチＰ分だけ傾けて１ビームで走査したときと同一幅のラインが形成できることになる。このような光量比の変化により、走査ラインが傾いていてもメカ的な機構を用いずに傾きを補正することができる。
図１８には、一例として、記録されるラインの傾きを走査ラインに対して右下がりに補正する例を示す。
【００５６】
ラインの傾き補正量Δθは、各色に対応した光走査装置６４０〜６４３（図１１参照）により転写ベルト６３８０（図１１参照）上に形成された検出パターン（トナー像）から、図１１に示すように発光ダイオード６３０から投射したビームの反射光をピンフォトダイオード６３１で受光するレジストずれ検出手段６２９を転写ベルト６３８０の両端に配置することにより、基準色に対する相対的な偏差として検出される。
この検出結果に基づき、第１、第２のビームピッチＰを、ラインの傾き補正量Δθに応じて走査幅Ｌを用い、
Ｐ＝Ｌ・ｔａｎΔθ
となるよう上記した方法により設定し、走査開始端では第２のビームの光量を最大、第１のビームを０とし、また、走査終端では、第１のビームを最大、第２のビームを０とし、第２のビームの光量が単調に増加するように、さらに、第２のビームの光量が単調に減少するように可変するとともに、走査方向の各位置で各々の和が一定となるようにすることで、図１８中太線で示すように走査方向（主走査方向）に対して、静電潜像の重心（中心）の軌跡が走査ラインに対して右上がりに斜めに形成されるようにしている。
【００５７】
隣接する領域についても同様に補正することにより、各々記録されるラインは平行に揃えられ、転写ベルト６３８０（図１１参照）上では斜めに繋ぎ合わされて、傾いたラインが形成できる。
ところで、光量はビーム強度と点灯時間との積で表され、上記の如く静電潜像を形成するには、以下のいずれかの方法を用いてもよい。
１．ビーム強度を可変する
２．ビームのパルス幅を可変する
詳細については、後述する半導体レーザの駆動制御にて説明するが、実施例では、階段状に近似して光量を可変している。
【００５８】
尚、レジストずれ検出手段６２９では、各色間の傾きずれの検出と同時にレジストずれ（平行シフト分）も検出できるが、これは、上記した隣接する光走査手段におけるライン像の継ぎ目補正方法を、光走査装置６４０〜６４３間に適用すればよく、同様に補正することができる。
【００５９】
図５は４つの光走査装置５００（６４０〜６４３）によって各々に対応した感光体ドラム５０４に１色ずつ画像形成され、転写ベルト５０１（図１１の６３８０）の回転につれて色重ねがなされるタンデム方式のカラーレーザプリンタに適用した例であり、実施例では光走査装置を光ビームの射出方向が下向きとなるよう配備される。
【００６０】
転写ベルト５０１は駆動ローラと２本の従動ローラとで支持され、移動方向に沿って均等間隔で各感光体ドラム５０４が配列される。感光体ドラム５０４の周囲にはイエロー、マゼンタ、シアン、ブラックも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部５０３、そして、転写された後の残トナーをブレードで掻き取り備蓄するクリーニング部５０８が一体的に配備される。
【００６１】
各色画像は、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ずらして各光走査装置５００によって静電潜像が形成される。静電潜像は、現像部にてトナーが載せられて転写ベルト５０１上で順次画像が重ねられていく。
転写体としての用紙は給紙トレイ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５１０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、トナー像を載せたまま搬送ベルト５１５にて定着器に送られる。
【００６２】
転写されたトナー像は定着器の定着ローラ５１２により定着され、排紙トレイ５１４に排出される。
各光走査装置５００は上記したように複数の光走査手段の走査線を繋ぎ合わせて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（印刷）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。
【００６３】
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５１１に保存され、各振動ミラーモジュール１３０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５１２に保存される。バッファ５１２に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。
また、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。
【００６４】
尚、実施例では、各振動ミラー（可動ミラー２０２、図３参照）の共振ピークは異なっても、印加電圧のゲインを変化させることによって所定の帯域において振れ角を一致させ共通の駆動周波数で走査するようにしている。
環境温度の変化でねじり梁２０８（図３参照）のバネ定数が変化し共振帯域が一様にシフトするが、それに対応して駆動周波数を選択し直す場合にも、共通の駆動周波数を与え、走査周波数を各振動ミラーモジュール１３０（図１参照）で共通とすることで、各領域の終端まで各ラインのレジストを一致させることができる。
【００６５】
図６は半導体レーザ、可動ミラーの駆動制御を表すブロック図を示す。
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、上記したように可動ミラー２０２（図３参照）の振幅に合わせたタイミングで電圧パルスが印加されるようパルス列を生成する。ＰＬＬ回路によって各振動ミラーモジュール１３０（図１参照）間で所定の位相遅れδを持たせて各可動ミラー２０２（図３参照）の駆動部６０２に与えられ電極の各々に電圧が印加される。
【００６６】
ここで、振動ミラー（可動ミラー２０２）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）・｛（Δｙ／ｐ）−ｎ｝
ここで、ｎは（Δｙ／ｐ）−ｎ＜１
を満足する自然数となるように与えれば、継ぎ目における位置ずれは１走査ラインピッチの整数倍となり、振動ミラー１３０（図１参照）の１周期おきの書出しタイミング補正、つまりｎライン周期分ずらして書き出すことにより副走査方向のレジストずれΔｙを無効化することができ、継ぎ目の位置ずれのない高品位な画像が得られる。
【００６７】
実施例において同期検知センサ６０４、終端検知センサ６０５はプリント基板上に配備されるが、検出面は被走査面に到達する光路長と等しい位置に配置されている。図８にその検出部の詳細を示すが、主走査方向に垂直に配置したフォトダイオード８０１と主走査方向に非垂直に配置したフォトダイオード８０２とを有し、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、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を計測することで、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を被走査面である感光体ドラム５０４（図５参照）上に相当する計測値として検出することができる。
【００６８】
尚、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。
【００６９】
実施例では、この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１３０（図１参照）間の位相を常時可変して補正を行うことができる。
主走査方向においては、後述するように、各画像領域における走査速度のずれを
１）各振動ミラー１３０へ印加する電圧パルスのゲイン調整により振れ角（振幅）を所定値に合わせることにより補正することができる。
【００７０】
２）また、隣接する画像領域の継ぎ目位置ずれを可動ミラー２０２（図３参照）の駆動周波数に対応して画素クロックをシフトすることで画像幅の倍率を可変し走査終端と、隣接する光走査装置の走査開始端との継ぎ目を合わせることにより補正することができる。
【００７１】
振動ミラー１３０には基本的に画像記録およびその準備期間以外は駆動電圧が印加されない。
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、振幅検出部６１０からの出力、実施例では同期検知センサ６０４、走査角が−θ０となる近傍に配置された終端検知センサ６０５とでビームを検出し、この同期検知信号と終端検知信号との時間差Ｔを振幅演算部６０９で計測することで、可動ミラー２０２の振れ角（振幅θ０）を検出する。
【００７２】
いま、同期検知センサ６０４で検出される光ビームの走査角をθｄとし、画像中央からの走査時間をｔとし、可動ミラー２０２の駆動周波数をｆｄとすると
θｄ／θ０＝ｓｉｎ２π・ｆｄ・ｔ、ｔ＝Ｔ／２
で与えられる。
この時間差Ｔがあらかじめ定められた基準値Ｔ０に達するまで印加する電圧パルスのゲインを可変することによって振れ角を補正する。この補正は、各環境下で定期的、例えばジョブ間で行われる。
【００７３】
画像記録中にこの補正を行うと画像の主走査端がゆらいでしまうため、画像記録中は同一値を保持するようにしている。
また、実施例では複数の振動ミラーを有するが、共通の駆動周波数を選択し、かつゲインの基準値を揃えるとで、各振動ミラー間の振れ角が一致するようにしている。
上記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。
【００７４】
次に半導体レーザの駆動制御について説明する。
上記したように、往復走査で潜像のラインピッチを均一にするには、ビーム強度を可変するか、ビームのパルス幅を可変する必要がある。
そこで、第１の実施例では、ビーム強度の可変方法について説明する。
【００７５】
図２１は、半導体レーザへの印加電流に対するビーム強度を示す。同図において、横軸は駆動電流を示し、縦軸はビーム強度を示す。
同図に示すように、ビーム強度はしきい値電流を超えると印加電流に比例して増加することが分かる。従って、このしきい値電流Ｉｔｈから所定のビーム強度を得る最大電流Ｉｍまでの差Ｉｍ−Ｉｔｈをｎ分割（実施例では２５５分割）し、可変データ基づいて段階的に駆動電流を可変すればよい。
【００７６】
上記したように、一方の発光源には、同期検知信号をトリガとして、主走査方向の書込開始から書込終端にかけてＩｔｈまでＩｍを徐々に減少させ、もう一方の発光源には、書込開始から書込終端にかけてＩｍをＩｔｈから徐々に増加させる。
ところで、一般的に、ＬＤ駆動部６０６では、半導体レーザからのモニタ信号によりビーム強度が一定となるよう駆動電流を加減するフィードバック制御がなされる。
これは、ケース温度の変化に伴いＩｔｈや同一のビーム強度を射出するＩｍが変化するためで、この制御を行なわないと低温状態と高温状態とで、ビーム強度が変化し画像濃度が異なるという不具合が生じる。
【００７７】
そこで、実施例では、あらかじめ定められたモニタ信号の出力値が得られる駆動電流Ｉｍ’の変化分をしきい値電流のバイアス分ΔＩｈとして一律に駆動電流に加算することで対処している。
次に第２の実施例におけるビームのパルス幅（画素クロックｆｍ）の可変方法について説明する。
【００７８】
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幅を有するＰＬＬ基準信号ｆａが形成され、ＰＬＬ回路において基準クロックｆ０との位相を選択して画素クロックｆｋが発生される。
当然、パルス幅が長ければ感光体ドラム５０４上に形成される静電潜像の径は大きくなり、パルス幅が短ければ小さくなる。
【００７９】
従って、パルス幅を主走査に沿って段階的に切り換えることで可変データに基づいた任意な径の静電潜像が形成できる。
上記と同様に一方の発光源を、同期検知信号をトリガとして、主走査方向の書込開始から書込終端にかけて１画素に相当する潜像径から減少させ、もう一方の発光源を、書込開始から書込終端にかけて１画素に相当する静電潜像径まで増加させる。
【００８０】
ところで、可動ミラー２０２は共振振動されるため、ｓｉｎ波状に走査角θが変化する。
一方、被走査面である感光体ドラム５０４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^−１θ／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ず、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された走査レンズが用いられるが、それに伴ってビームスポット径も太ってしまう。このため、均一なビームスポットを得る上で、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。
【００８１】
そこで、実施例では、図１０（ａ）、（ｂ）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書込開始から書込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書込開始から画像中央に至る領域では長い状態から段階的に短くなるように、画像中央から書込終端に至る領域では長くなるような画素クロックｆｍをＬＤ駆動部６０６に与え、電気的な補正を付加することで、走査レンズの負担を軽減し、走査効率を向上させている。
こうした制御は、各画素に対応したドット径が均一になるようにパルス幅とその位相を設定するものであるから、ここで設定された１画素に相当するパルス幅を比例配分したパルスを生成することにより、上記した静電潜像径の可変があっても、新たに制御回路を付加することもなく容易に対応できる。
【００８２】
ここで、図１０（ａ）はパルス幅と時間との関係を示す図であり、図１０（ｂ）は位相差と時間との関係を示す図である。図１０（ａ）において縦軸はパルス幅を示し、図１０（ｂ）において縦軸は位相差を示す。図１０（ａ）、（ｂ）において、横軸は時間を示す。
【００８３】
尚、実施例では、半導体レーザを２つの発光源を有する半導体レーザアレイとしたが、本発明はこの限りではなく、単一発光源の半導体レーザからのビームを合成しても、また、２以上の発光源を用いてもよい。
１）請求項１に対応する作用・効果
光源手段と、該光源手段からの光ビームを反射することにより走査する可動ミラーとを有する光走査手段を複数備え、主走査時に主走査方向に沿って各々の走査領域を繋ぎ合わせて、像担持体ドラム上に静電潜像を形成する光走査装置と、該静電潜像をトナーにより顕像化する現像手段とを複数、転写体の移動方向に沿って並列配置し、上記トナーにより顕像化されたトナー像を上記転写体に順次転写して、重ね合わせカラー画像を形成する画像形成装置において、上記主走査方向と直交すると共に上記走査領域を挟むように互いに対向する一対の側板を備え、該側板間を架橋して上記複数の光走査装置を一体的に支持することにより、光走査装置同士の相対位置を安定的に保つことができ、各ステーションで形成した画像の重ね合わせ精度を維持することができるので、上記したような転写ベルト上に検出パターンを作成してレジストずれを検出するといった補正の頻度を最小限とすることができ、ダウンタイムがほとんどない環境に配慮した画像形成装置が提供できる。
【００８４】
２）請求項２に対応する作用・効果
上記側板に、上記複数の像担持体ドラムを軸支する支持部材を上記光走査装置に対して位置決めする位置決め部を形成してなることにより、光走査装置と像担持体ドラムとの相対位置を安定的に保つことができ、像担持体ドラム上での光走査装置により照射される位置から転写位置に至るタイミングを各ステーション間で一定とすることができ、環境変化があっても偏差を最小限に抑えられるので、経時まで色ずれや色変わりのない高品位なカラー画像記録が行える。
【００８５】
３）請求項３に対応する作用・効果
上記光走査装置は、各々の走査位置が転写体の移動方向に、上記像担持体ドラムの周長の整数倍の間隔で並列するように支持することにより、各ステーション間で像担持体ドラムの回転軸の偏心に伴う周速の変動があっても、像担持体ドラム間の位相を合わせて組み込むだけで、各色転写位置における周速変動の振幅位相を揃えることができるので、色ずれや色変わりのない高品位なカラー画像記録が行える。
【００８６】
４）請求項４に対応する作用・効果
上記転写体の移動方向に対する上記光走査装置の配置を調節する調整手段を備えることにより、各光走査装置の像担持体ドラム上の照射位置を確実に合わせることができ、転写位置に至るタイミングを各ステーション間で揃えることができるので、色ずれや色変わりのない高品位なカラー画像記録が行える。
【００８７】
５）請求項５に対応する作用・効果
上記光源手段は、各々複数の発光源を有し、上記像担持体ドラム上で副走査方向に隣接する少なくとも２ビームを用いて１ラインを記録することにより、光走査装置を固定した状態で、複雑なメカ機構によらず、ライン像の位置を可変できるので、光走査装置の配置精度を安定的に保つことができ、レジストずれを検出するといった補正の頻度を最小限とし、経時まで色ずれや色変わりのない高品位なカラー画像記録が行える。
【００８８】
６）請求項６に対応する作用・効果
上記隣接する２ビーム間の光量比を、上記主走査位置に対応して可変する光量可変手段を備えることにより、転写ベルト上に形成されるライン像の傾き（スキュー）を容易、かつ確実に補正することができるので、経時まで色ずれや色変わりのない高品位なカラー画像記録が行える。
【００８９】
【発明の効果】
本発明の画像形成装置によれば、記録ライン同士の配置精度を経時的に安定に保ち、省電力、省資源等の環境に配慮した画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の画像形成装置に係る光走査装置の分解斜視図である。
【図２】図１に示した光走査装置の光学素子の配置図である。
【図３】本発明の画像形成装置に係る光走査装置に用いる振動ミラーモジュールの詳細図である。
【図４】本発明の画像形成装置に係る光走査装置の副走査断面である。
【図５】本発明の画像形成装置に係る光走査装置をタンデム方式のカラーレーザプリンタに適用した場合の断面図である。
【図６】本発明の画像形成装置に係る光走査装置に用いられる半導体レーザ、可動ミラーの駆動制御を表すブロック図である。
【図７】本発明の画像形成装置に係る光走査装置に温度に対する共振周波数の変動を示す説明図である。
【図８】図６に示したブロック図における同期検知センサおよび終端検知センサを有する検出部の詳細図である。
【図９】本発明の画像形成装置に係る副走査方向における各ビームスポットの強度分布と、ビームスポットにより形成される静電潜像の電位分布を示す説明図である。
【図１０】（ａ）は本発明の画像形成装置に係るパルス幅と時間との関係を示す図であり、（ｂ）は本発明の画像形成装置に係る位相差と時間との関係を示す図である。
【図１１】本発明の画像形成装置に係る像担持体としての感光体ドラムの位置決め方法の説明図である。
【図１２】本発明の画像形成装置に係る可動ミラーの振れ角に対応して各電極間に発生する静電トルクの様子を示す説明図である。
【図１３】（ａ）〜（ｄ）は本発明の画像形成装置に係る光走査装置の可動ミラーの振幅（回動角度）と各固定電極への印加パルスとの関係を示す説明図であり、（ａ）は可動ミラーの振幅（回動角度）を示し、（ｂ）は第１、第２の固定電極の印加パルスを示し、（ｃ）は第３の固定電極の印加パルスを示し、（ｄ）は第４の固定電極の印加パルスをそれぞれ示す。
【図１４】本発明の画像形成装置に係る光走査装置の駆動周波数に対する振れ角の特性を示す説明図である。
【図１５】（ａ）は本発明の画像形成装置に係る走査ラインの位置調節の説明図であり、（ｂ）は（ａ）の矢印Ａ方向の矢視図である。
【図１６】本発明の画像形成装置に係る可動ミラーの電極近傍の断面図である。
【図１７】本発明の画像形成装置に係る光走査装置の被走査面におけるビームスポットの配列を示す説明図である。
【図１８】本発明の画像形成装置に係る光走査装置の一例として、記録されるラインの傾きを走査ラインに対して右下がりに補正する例を示す説明図である。
【図１９】（ａ）、（ｂ）は隣接する光走査手段におけるライン像の継ぎ目補正方法を表す説明図であり、（ａ）は補正前の状態を示し、（ｂ）は補正後の状態を示す。
【図２０】図１に示した光学装置への半導体レーザの取り付けについての詳細を示す説明図である。
【図２１】本発明の画像形成装置に係る光走査装置の半導体レーザへの印加電流に対するビーム強度を示す説明図である。
【符号の説明】
１０１ 半導体レーザ
１０２ フレーム部材
１０３ 貫通穴
１０４ 角穴
１０５ 凹部
１０６ ハウジング
１０９ 取り付け斜面
１１０ カップリングレンズ
１１２ プリント基板
１１３ 同期検知センサ
１１５ ケーブル
１１６ 第１の走査レンズ
１１７ 第２の走査レンズ
１１９ 平押面
１２０、１２３、１３５、１４２、１４５、１４６ 突起
１２１ 切欠
１２２ 溝
１２７ 高輝アルミ薄板
１２８ ミラー受部
１２９ 開口部
１３０ 振動ミラーモジュール
１３１ 位置決めピン
１３３ ネジ穴
１３６ シリンダミラー
１３７、１４７ ネジ
１３８ カバー
１３９ 開口
１４１ 板バネ
１４３ 波板バネ
１４４ 庇状の突起
６３０ 発光ダイオード
６３１ ピンフォトダイオード
６３２、６３３ 側板
６３５ 切欠
６３６ 軸受
６３７ 嵌合穴
６４０、６４１、６４２、６４３ 光走査装置
６３８０ 転写ベルト[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an optical scanning apparatus used in an image forming apparatus such as a digital copying machine and a laser printer, and also applied to an optical scanning bar code reading apparatus and an on-vehicle laser radar and apparatus. The present invention relates to an image forming apparatus capable of performing the above.
[0002]
[Prior art]
In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector for scanning a light beam. To achieve a higher resolution image and high-speed printing, the polygon mirror or the galvanometer mirror can be rotated. Therefore, the durability of the bearing, heat generation due to windage loss, and noise become problems, and there is a limit to high-speed scanning.
[0003]
In contrast, in recent years, research on optical deflectors using silicon micromachining has been underway, and a method has been proposed in which a vibrating mirror and a torsion beam that pivotally supports it are integrally formed on a Si substrate (for example, patent documents). 1 and 2).
According to this method, since reciprocal vibration is performed using resonance, there is an advantage that noise is low although high speed operation is possible. Furthermore, since the driving force for rotating the oscillating mirror is small, the power consumption can be kept low.
However, in the image forming apparatus using these vibrating mirrors, since the mirror surface size is small and the deflection angle is small, it is not possible to scan a wide area like a conventional polygon mirror, and the main scanning of a plurality of optical scanning devices A method is employed in which images are recorded by arranging the images in the same direction and dividing the image area into main scans (see, for example, Patent Document 3).
On the other hand, techniques for forming latent image dots by overlapping two lines of beam spots have also been proposed (see, for example, Patent Documents 4 and 5).
As described above, in the method of recording an image by dividing an image area into main scans, the optical scanning device can be downsized by reducing the scanning width and the optical path length, and using a minute vibrating mirror or the like. In addition, since light scanning can be performed with a low load, an image forming apparatus with low noise and power saving can be provided.
[0004]
According to such a method of recording an image by dividing an image region into main scans, there is an advantage that the optical path length can be shortened in inverse proportion to the number of divisions, and the scan position is not easily displaced. When forming a color image by aligning the scanning device in the direction of movement of the transfer body and overlaying each image, the image quality such as color shift and color change is degraded unless the relative position between the optical scanning devices is accurately controlled. This is the same as the conventional factor.
[0005]
In general, it is necessary to suppress the deviation between the scanning lines to several tens of μm or less, and even if adjustment is made during manufacturing, the deviation will occur with time due to environmental changes, etc., so conventional (method in which the image area is not divided into main scanning) As in the image forming apparatus, it is necessary to periodically detect the sub-scanning position between jobs or the like by the registration deviation detection pattern recorded on the transfer body, and to match the timing of writing (for example, Patent Document 6 and 7).
[0006]
[Patent Document 1]
Japanese Patent No. 2924200
[Patent Document 2]
Japanese Patent No. 30111144
[Patent Document 3]
JP 2001-18472 A
[Patent Document 4]
Japanese Patent No. 2898785
[Patent Document 5]
JP 2002-347271 A
[Patent Document 6]
Japanese Patent Publication No.7-19084
[Patent Document 7]
Japanese Patent Publication No.7-19085
[0007]
[Problems to be solved by the invention]
However, since it is necessary to record the detection pattern on the transfer body in order to detect the registration error, the apparatus becomes unrecordable during that time, and the printing waiting time becomes longer, resulting in an obstruction of work efficiency. In addition, there is a problem that wasteful toner consumption increases if correction is frequent, so that the arrangement accuracy between recording lines is kept stable over time so that the correction interval can be extended as much as possible, for example, only when the power is turned on. Is desired.
[0008]
In the present invention, in the tandem type image forming apparatus using a plurality of optical scanning devices that record an image by dividing the image region into main scanning, the arrangement accuracy between the recording lines is kept stable over time, power saving, An object of the present invention is to provide an environment-friendly image forming apparatus that saves resources. Claims 1 and 2 maintain the placement accuracy of each optical scanning device and photosensitive drum, and provide stable image quality over time. In the third to sixth aspects of the present invention, it is an object to perform high-quality image formation by reliably matching the arrangement of the recording lines of each optical scanning device without complicated adjustment. To do.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, an image forming apparatus according to the present invention includes a plurality of optical scanning units having a light source unit and a movable mirror that scans by reflecting a light beam from the light source unit, and performs main scanning. A plurality of optical scanning devices for forming an electrostatic latent image on the image carrier drum by joining the scanning regions along the main scanning direction, and developing means for developing the electrostatic latent image with toner. In the image forming apparatus which forms a superimposed color image by sequentially transferring the toner images visualized by the toner to the transfer body by arranging in parallel along the moving direction of the transfer body, A pair of side plates that are orthogonal to each other and sandwich the scanning region are provided, and the plurality of optical scanning devices are integrally supported by bridging the side plates. Therefore, it is possible to maintain the placement accuracy of the recording lines with time and to perform image formation in consideration of the environment such as power saving and resource saving.
[0010]
In addition, the side plate is formed with a positioning portion for positioning the support member that pivotally supports the plurality of image carrier drums with respect to the optical scanning device, thereby arranging each optical scanning device and the photosensitive drum. It is possible to maintain accuracy and obtain stable image quality over time.
Further, the optical scanning device supports each scanning position so that the scanning positions are arranged in parallel in the moving direction of the transfer body at an interval that is an integral multiple of the circumference of the image carrier drum. Therefore, high-quality image formation can be performed by surely matching the arrangement of the first and second arrangements without complicated adjustment.
[0011]
In addition, by providing an adjusting means for adjusting the arrangement of the optical scanning device with respect to the moving direction of the transfer body, it is possible to ensure high quality by matching the arrangement of the recording lines of each optical scanning device without complicated adjustment. Image formation can be performed.
[0012]
Further, each of the light source means has a plurality of light emitting sources, and records one line using at least two beams adjacent in the sub-scanning direction on the image carrier drum, so that the recording line of each optical scanning device is recorded. High-quality image formation can be performed by reliably matching the arrangement of the two without complicated adjustment.
[0013]
Further, by providing a light amount variable means for changing the light amount ratio between the two adjacent beams in accordance with the main scanning position, the arrangement of the recording lines of each optical scanning device can be adjusted without complicated adjustment. High-quality image formation can be performed by surely matching.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The image forming apparatus of the present invention includes a plurality of optical scanning units each having a light source unit and a movable mirror that scans by reflecting a light beam from the light source unit, and performs each scanning along the main scanning direction during main scanning. A plurality of optical scanning devices that connect the regions to form an electrostatic latent image on the image carrier drum and a developing unit that visualizes the electrostatic latent image with toner along the moving direction of the transfer body. In an image forming apparatus that is arranged in parallel and sequentially transfers toner images visualized by the toner to the transfer body to form a superimposed color image, so as to be orthogonal to the main scanning direction and sandwich the scanning area. A pair of side plates facing each other is provided, and the side plates are bridged to support the plurality of optical scanning devices integrally.
[0015]
【Example】
FIG. 3 is a detailed view of a vibrating mirror module used in the optical scanning device according to an embodiment of the present invention.
The vibration mirror substrate (also referred to as a movable mirror substrate) is configured by joining two Si substrates 206 and 207 via an insulating film such as an oxide film.
The first Si substrate 206 is made of a Si substrate having a thickness of 60 μm, and the movable mirror 202 and the torsion beam 208 pivotally supported on the same straight line are formed by etching and are separated from the fixed frame 210 by etching.
[0016]
The movable mirror 202 is formed symmetrically with respect to the torsion beam 208, and has comb-like irregularities formed on the edges of both ends and the inner side of the fixed frame 210 facing each other with a gap of several μm so as to alternately engage with each other. Yes.
A metal film such as Au is deposited on the surface of the movable mirror 202 to form a reflection surface, and the periphery of each electrode is etched from the fixed frame 210 in a state where each substrate is bonded via an insulating layer as shown in the figure. Thus, the substrate itself is formed as an electrode by penetrating to an insulating layer (oxide film) as an etch stop layer and individually separating.
[0017]
In the embodiment, the concavo-convex portions at both ends of the movable mirror 202 are the first and second movable electrodes (separated for convenience, but the same potential), and the concavo-convex portions of the opposing fixed frame are the first and second fixed electrodes 203. 204, the movable mirror 202, the torsion beam 208, and the island portion 221 having the root portion of the torsion beam 208 and the island portions 222 and 223 having the respective fixed electrodes are separated from the fixed frame 210 with a separation groove gap of about 5 μm. It is configured.
[0018]
Further, the second substrate 207 is made of a 140 μm Si substrate, penetrates the central portion by etching, and has concave and convex shapes like comb teeth so that the inner side overlaps with the concave and convex portions formed on the fixed frame 210. Similarly, the third and fourth fixed electrodes 211 and 212 are formed, and the islands 224 and 225 are separated from the fixed frame 210. At this time, the separation groove is formed so as not to overlap with the separation groove in the first substrate, so that the joined state can be maintained even if the periphery is penetrated in an island shape.
[0019]
The third and fourth fixed electrodes 211 and 212 pass so that the first and second movable electrodes mesh with each other along the swinging direction of the movable mirror 202.
In the embodiment, voltage pulses having the same phase are applied to the first and second fixed electrodes 203 and 204, and voltage pulses applied to the first and second fixed electrodes 203 and 204 are applied to the third fixed electrode 211. A voltage pulse having a phase more advanced than that is applied, and a voltage pulse having a phase delayed from the voltage pulse applied to the first and second fixed electrodes 203 and 204 is applied to the fourth fixed electrode 212.
[0020]
FIG. 12 shows the state of electrostatic torque generated between the electrodes corresponding to the deflection angle of the movable mirror 202. In FIG. 12, the horizontal axis indicates the angle, and the vertical axis indicates the electrostatic torque.
FIG. 16 shows a cross section near the electrode of the movable mirror. In the figure, the counterclockwise electrostatic torque is positive.
The movable mirror 202 is horizontal in the initial state, but when a voltage is applied to the third fixed electrode 211, an electrostatic force is generated in a negative direction between the movable electrode 202 and the movable mirror 202, and the movable mirror 202 is rotated by twisting the torsion beam 208. Then, it tilts to a swing angle that balances with the return force of the torsion beam 208. When the voltage is released, the movable mirror 202 returns to the horizontal by the return force of the torsion beam 208, but in the positive direction by applying a voltage to the first and second fixed electrodes 203 and 204 immediately before returning to the horizontal. The movable mirror 202 can be moved at both ends by repeatedly switching the electrodes such that the electrostatic torque in the positive direction is increased and the electrostatic torque in the positive direction is further increased by applying a voltage to the fourth fixed electrode 212. The electrodes reciprocally vibrate at a deflection angle passing through the first and second fixed electrodes 203 and 204 facing each other, in the embodiment, about 2 °.
[0021]
Here, the moment of inertia of the movable mirror 202 and the width and length of the torsion beam 208 are matched with the desired drive frequency to be scanned, and the first resonance mode band with the torsion beam 208 as the rotation axis is applied. When excited, the amplitude is remarkably enlarged, and the movable electrodes at both ends of the movable mirror 202 can be expanded to a deflection angle that passes through the third and fourth fixed electrodes 211 and 212 facing each other.
As a result, an electrostatic force is generated in the direction in which the movable mirror 202 that has escaped from the third and fourth fixed electrodes 211 and 212 returns to the horizontal direction even when the swing angle of the movable mirror 202, and in the third fixed electrode 211, the electrostatic force is generated in the positive direction in the movable mirror 202. In addition, the deflection angle range in which the electrostatic torque acts can be expanded, and a large deflection angle can be maintained even at a driving frequency that deviates from the resonance frequency.
[0022]
On the other hand, FIGS. 13A to 13D show the relationship between the amplitude (rotation angle) of the movable mirror and the pulse applied to each fixed electrode. 13 (a) shows the amplitude (rotation angle) of the movable mirror, FIG. 13 (b) shows the applied pulses of the first and second fixed electrodes, and FIG. 13 (c) shows the third fixed. The applied pulse of the electrode is shown, and FIG. 13D shows the applied pulse of the fourth fixed electrode. In FIG. 13A, the vertical axis indicates the amplitude (rotation angle), in FIG. 13B, the vertical axis indicates the voltage of the first and second fixed electrodes, and in FIG. 13C, the vertical axis Indicates the voltage of the third fixed electrode. In FIG. 13D, the vertical axis indicates the voltage of the fourth fixed electrode, and in FIGS. 13B to 13D, the horizontal axis indicates time.
[0023]
In the embodiment, writing is performed only in one of the reciprocating scans, and the voltage pulse is applied at an optimal timing with respect to the amplitude of the movable mirror 202 so that the electrostatic torque works efficiently, that is, The phase of the amplitude and the applied pulse is set so that torque against the moving direction of the end of the movable mirror 202 is not generated.
The conditions are shown below. Now, the thickness of the third and fourth fixed electrodes 211 and 212, in other words, the thickness of the second Si substrate 207 is t, the deflection angle of the movable mirror 202 is θ (= 5 °), and the width is 2L. (= 4 mm) and the thickness of the first Si substrate 206 is
When t0 (= 60 μm),
t0 <t <L · sin θ
Set the relationship to be
θ0 = arcsin (t0 / L)
The second fixed electrodes 203 and 204 include
0 <α1 <θ0
The third and fourth fixed electrodes 211 and 212 include
θ0 <α2 <θ0
A voltage pulse is applied within the range of the swing angle of the movable mirror 202.
[0024]
FIG. 14 shows the characteristic of the deflection angle with respect to the driving frequency. If the driving frequency is made to coincide with the resonance frequency, the deflection angle can be maximized, but the deflection angle changes steeply in the vicinity of the resonance frequency.
In FIG. 14, the horizontal axis represents the scanning frequency, and the vertical axis represents the deflection angle.
Therefore, initially, the drive frequency applied to the fixed electrode can be set to match the resonance frequency in the drive control unit of the movable mirror 202. However, when the resonance frequency fluctuates due to a temperature change or the like, the deflection angle is changed. There is a drawback that the stability over time is poor due to the drastic decrease.
[0025]
FIG. 7 shows the variation of the resonance frequency with respect to temperature.
In FIG. 7, the horizontal axis indicates the temperature, and the vertical axis indicates the resonance frequency.
Further, in the case where a plurality of movable mirrors 202 are provided as in an embodiment described later, there is a problem in that they cannot be driven at a common drive frequency because the resonance frequencies unique to each of them vary.
Therefore, in the embodiment, the drive frequency is set to a frequency band that is relatively high in the vicinity of the resonance frequency of the vibration part composed of the movable mirror 202 and the torsion beam 208 and that has a relatively small change in the deflection angle and is far from the resonance frequency. The drive frequency is 2.5 kHz with respect to the resonance frequency of 2 kHz, and the swing angle is adjusted to ± 5 ° by adjusting the gain of the applied voltage.
[0026]
At this time, even if there is a variation in the resonance frequency due to a processing error of the vibrating mirror (movable mirror), in the embodiment, 300 Hz, a fluctuation in the resonance frequency due to temperature, in the embodiment, 3 Hz, the drive frequency does not affect any resonance frequency. In such a frequency band and a resonance frequency of 2 kHz, it is desirable to set the frequency to 2,303 Hz or more, or 1,697 Hz or less.
Now, assuming that the dimensions of the movable mirror 202 are the length 2a, the width 2b, the thickness d, the length of the torsion beam 208 is L, and the width c is
Using the density ρ of Si and the material constant G,
Moment of inertia I = (4abρd / 3) · a²
Spring constant K = (G / 2L) · {cd (c²+ D²) / 12]
And the resonant frequency f is

Here, since the length L of the torsion beam 208 and the deflection angle θ are in a proportional relationship,
θ = A / I · f²(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 I is reduced in order to increase the resonance frequency f.
[0027]
Therefore, in this embodiment, the thickness of the substrate on the back side 219 of the reflecting surface of the movable mirror 202 is d, and the thickness of the portion other than the reflecting surface is etched in a lattice shape so as to be equal to or less than d / 1. The moment of inertia I is reduced to about 1/5.
These parameters that are useful for the moment of inertia I, the dimensional error of the torsion beam 208, and the like cause variations in the resonance frequency.
[0028]
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, the electrostatic force F between the electrodes is
F = εHV²/ 2δ, and the deflection angle θ = B · F / I (B is a constant)
The deflection angle θ increases as the electrode length H is longer, and a driving torque of 2n times the number of comb teeth n is obtained by using a comb-teeth shape.
[0029]
In this way, consideration is given to obtaining a larger electrostatic torque at a low voltage by making the outer peripheral length as long as possible to increase the electrode length.
By the way, with respect to the speed υ and the area E of the movable mirror 202, if the air density is η, the air viscous resistance P = C · ηυ²・ E³(C is a constant) works against the rotation (rotation) of the movable mirror 202.
Therefore, it is desirable to seal the movable mirror 202 and keep it in a reduced pressure state.
[0030]
In the embodiment, the vibrating mirror substrate formed by bonding the first and second substrates 206 and 207 is placed on the base body 212 in which the oscillating space of the movable mirror 202 is formed in a concave shape at the center, and the reflecting surface is directed upward. The torsion beam 208 is aligned with a straight line connecting a pair of V-grooves formed on the outer edge of the base, and is mounted with reference to the lower surface of the first substrate, and is integrally formed in a cap shape on the upper surface of the second substrate 207. A transparent resin cover 205 is joined so that the oscillating space of the movable mirror 202 is sealed, and a non-evaporable getter is enclosed in the oscillating space and activated by heating from the outside. The pressure is 1 Torr or less.
[0031]
In order to lower the air permeability, the cover 205 uses a poly-olefin resin having a relatively low hygroscopic property, and the surface thereof is coated with SiO or the like.
The light beam enters and exits through a slit window 213 formed in the cover 205.
[0032]
As described above, since airtightness is impaired when wiring is interposed on the joint surface, in the embodiment, the lead terminal 216 penetrates the base body 212 through the base body 212 formed of an insulating member such as ceramic so as to be perpendicular to the joint surface. And integrated. When the vibrating mirror (movable mirror 202) is joined to the base body 212, the engagement holes 226, 227, which are formed in the separated island portions 221, 222, 223, 224, 225 slightly smaller than the terminal diameter, End portions protruding upward are pressed into and connected to 228, 229, and 230.
[0033]
The lead terminal press-fitted into the engagement holes 229 and 230 of the second Si substrate 207 disposed on the upper side is set to have a long projection amount corresponding to the thickness of the first Si substrate 206. The Si substrate 206 is inserted through through holes 231 and 232 formed larger than the terminal diameter.
On the inner side of the cover 205, a counter mirror 215 is formed integrally with the movable mirror 202 in a direction orthogonal to the torsion beam 208. The two opposing mirrors 215 are reflective by depositing a metal film on inclined surfaces inclined by 9 ° and 26.3 ° respectively from the substrate surface so as to form a roof-like angle of 144.7 ° across the slit window 213. The planes 217 and 218 are arranged in pairs.
[0034]
The bottom surface of the cover 205 is formed in parallel with the movable mirror surface, and is in contact with and joined to the upper surface of the frame part of the second Si substrate 212. At the time of this joining, the opposing mirror 215 is attached to the second Si substrate 212. Indexes 216 for positioning are drawn by etching on both sides, and aligned on the second Si substrate 212 so that the edges of the counter mirror 215 are aligned with the indexes 218, and the direction of the counter mirror 215 in the main scanning direction Can be adjusted accurately.
[0035]
FIG. 4 shows a sub-scan section of the optical scanning device.
The light beam emitted from the semiconductor laser 101 is sub-scanned with respect to the normal line in the sub-scan section including the torsion beam 208 with respect to the movable mirror 401 (202) via the coupling lens 110 and the cylinder mirror 136 as will be described later. The light beam is incident from the slit window 404 at an angle of about 20 °. The light beam reflected by the movable mirror 401 is incident on the first reflection surface 402 and returned to the movable mirror 401, and the reflected light beam is incident on the second reflection surface 403 through the slit window 404. That is, the light beam emitted from the semiconductor laser 101 moves in the sub-scanning direction while reciprocating three times with the movable mirror 401, and is again emitted from the slit window 404 by the reflection by the movable mirror 401 a total of five times. Is done.
[0036]
In this embodiment, the light beam emitted from the semiconductor laser 101 is repeatedly reflected a plurality of times in this manner, so that a large scanning angle can be obtained even when the deflection angle of the movable mirror 401 is small, and the optical path length is shortened.
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. By using resonance, the applied voltage is very small and little heat is generated. However, as apparent from the above equation, the spring constant K of the torsion beam 208 needs to be increased as the recording speed, that is, the resonance frequency increases, and the deflection angle can be increased. It will disappear.
[0037]
Therefore, by providing the counter mirror 215 as described above, the scanning angle is enlarged so that a necessary and sufficient scanning angle can be obtained regardless of the recording speed.
Further, a reflecting surface is formed facing the roof shape (gable roof shape), and the incident angle in the sub-scanning direction to the movable mirror 202 is positive or negative for each reflection repeatedly. In other words, the traveling direction accompanying the reflection is rightward. By allocating to the left side, the bending of the scanning line on the scanned surface due to the oblique incidence is suppressed, the linearity is maintained, and the rotation of the light beam in the plane orthogonal to the optical axis is originally caused at the time of emission. Consideration is made so that the imaging performance is not deteriorated by returning to the posture.
[0038]
FIG. 1 is an exploded perspective view of an optical scanning device according to an embodiment of the image forming apparatus of the present invention, and FIG. 2 shows an arrangement of optical elements.
In FIG. 1, a semiconductor laser 101 as a light source has a stepped through hole 103 provided on a wall standing on a frame member 102 in which two light emitting sources are monolithically formed at a pitch of about 50 μm in the sub-scanning direction. From the opposite side, the stem outer periphery is engaged as a reference, the flange surface is abutted against the stepped portion, positioning in the optical axis direction is performed, and the pressing plate 1410 is pressed and fixed from the back side.
[0039]
FIG. 20 shows details of the mounting of the semiconductor laser to the optical device shown in FIG. 1, and the protrusion 142 of the presser plate is engaged with a notch formed on the outer periphery of the stem and around the central axis of the through hole 103. By rotating, a pair of leaf springs 143 formed by cutting and raising the outer peripheral portion are engaged with hook-shaped protrusions 144 formed on the frame member 102 to press the semiconductor laser 101, and the arrangement direction of the light emitting sources is determined. A fixed amount is adjusted to be inclined from the main scanning direction, and rotation is stopped by a screw 1450.
[0040]
Further, in the U-shaped recess 105 shown in FIG. 1, the optical axis of the coupling lens 110 is made to coincide with the optical axis of the light beam emitted from the semiconductor laser 101 via the UV adhesive, and the emitted light flux The light emitting point is positioned in the optical axis direction so as to obtain a parallel light beam, and the UV adhesive in the gap between the recess 105 and the coupling lens 110 is cured and fixed.
The optical axis of the coupling lens 110 can be adjusted even when a vibration mirror module 130 and a cylinder mirror 136 (described later) are attached. The surface accuracy of the movable mirror 202 (see FIG. 3) and the focal line of the cylinder mirror 136 can be adjusted. Since the misalignment can be invalidated, the accuracy can be relaxed.
[0041]
In the case of the embodiment, there are three light source units, but all have the same configuration.
The two light beams emitted from the coupling lens 110 are joined to a pair of mounting inclined surfaces 109 and incident on a cylinder mirror 136 having a negative curvature in the sub-scanning direction, and converged on the movable mirror surface in the sub-scanning direction. A light beam is incident from a slit window 213 (see FIG. 3) of the vibrating mirror module 130.
[0042]
FIG. 17 shows the arrangement of the beam spots on the surface to be scanned. As described above, the beam spot interval P in the sub-scanning direction is set by mounting the semiconductor laser 101 at an angle.
The beam spot interval P is obtained by using the sub-scan magnification β of the entire system from the light source to the scanned surface including the first and second scanning lenses 116 and 117 described later, and the pitch P between the two light sources.
P = β ・ P ・ sinφ
As will be described later, the pitch P is adjusted in accordance with the inclination correction amount of the line formed on the transfer belt 501 (see FIG. 5).
[0043]
The vibrating mirror module 130 has an outer edge of the base body 212 (see FIG. 3) from the back side of the stepped square hole 104 provided on the bottom surface side of the frame so that the direction of the torsion beam 208 (see FIG. 3) matches the optical axis direction. The position of the movable mirror surface is adjusted by abutting the flange surface against the stepped portion. In the embodiment, the three oscillating mirror modules 130 are positioned by the single frame member 102 at equal intervals.
When each vibrating mirror module 130 is fixed to the printed circuit board 112 by inserting the lead terminals protruding from the bottom surface of the base body into the through-holes and soldering the printed circuit board 112, the upper surface of the circuit board 102 abuts and fixes the lower opening of the frame member 102. At the same time, circuit connections are made.
The printed circuit board 112 is mounted with a semiconductor laser drive circuit, an electronic component constituting a movable mirror drive circuit, and a synchronization detection sensor 113, and wiring with an external circuit is performed in a lump.
[0044]
The other end of the cable 115 whose one end is connected to the printed circuit board 112 is connected to the lead terminal of the semiconductor laser 101.
The upper surface of the frame member 102 is a surface parallel to the abutting surface in the mirror normal direction of each vibrating mirror module 130 provided on the back side of the square hole 104, and two protruding from the bottom surface of the housing 106 that houses the scanning lens. The projection 135 is inserted into the engagement hole of the frame member, positioning on the same surface is performed, and the four corners are screwed. In the embodiment, the screw 137 is screwed to the printed circuit board 112 through the through hole of the frame member, and is joined so as to sandwich the frame member (trinically integrated), and then the soldering is performed.
[0045]
In the housing 106, a first scanning lens 116 and a second scanning lens 117 constituting an image forming unit are arranged in the main scanning direction, and are positioned and integrally held so that the respective scanning regions slightly overlap each other. .
The first scanning lens 116 protrudes to the center of the reference surface in the sub-scanning direction, and a projection 120 for positioning in the main scanning direction, and a flat pressing surface 119 for engaging both ends to perform positioning in the optical axis direction. Are provided on each of the incident surface side and the output surface side. The housing 106 is integrally formed with a groove 122, a pair of notches 121 and a pair of protrusions 142.
The projection 120 of the first scanning lens 116 is engaged with the groove 122, the flat pressing surface 119 at each end is inserted into each of the notches 121, and pressed against the incident surface side using the corrugated spring 143. By maintaining the posture, the relative arrangement of the first scanning lenses 116 can be matched with the same plane orthogonal to the optical axis of the first scanning lens 116. The reference plane in the sub-scanning direction of the first scanning lens 116 is abutted against the tip of the protrusion 142 of the housing 106, thereby positioning the first scanning lens 116 in a plane orthogonal to the optical axis, and in the sub-scanning direction. Is installed and is pressed and supported by a leaf spring 141 formed integrally with the cover 138.
[0046]
On the other hand, the second scanning lens 117 is similarly provided with a protrusion 123 that projects in the center of the reference surface in the sub-scanning direction and performs positioning in the main scanning direction, and a flat pressing surface 144 that performs positioning in the optical axis direction at both ends. . The protrusion 123 is engaged with the groove 122, the flat pressing surface 144 is inserted into the notch 121, the pressing posture is held on the emitting surface side by the corrugated spring 143, and the protrusion 145 that protrudes the sub-scanning direction reference surface from the housing 106. The installation height is positioned by abutting against the tips of 146 and 146, and is pressed and supported by a leaf spring 141 integrally formed with the cover 138. Reference numeral 147 denotes a screw for fixing the cover 138.
[0047]
The synchronization detection sensor 113 (pin photodiode) is arranged at an intermediate position and both end positions shared by the adjacent vibrating mirror module 130 (see FIG. 1), and the beam is transmitted between the scanning start side and the scanning end side of each optical scanning module. It is mounted at a total of four locations so that it can be detected. On the exit surface side of the second scanning lens 117, a mirror receiving portion 128 for attaching a V-shaped high-brightness aluminum thin plate 127 between the scanning regions of each lens is formed in the housing 106, and the light beam reflected by the high-brightness aluminum thin plate 127 is formed. Are reflected on the scanning start side and the scanning end side of the adjacent optical scanning means so as to be guided to the respective synchronization detection sensors 113 through the openings 129 formed between the scanning regions and the rectangular holes of the frame member. They are placed facing each other.
[0048]
The cover 138 has an opening 139 through which the light beam passes. The upper surface of the housing 106 is screwed so as to be sealed, and the scanning lenses 116 and 117 are pressed by the leaf spring 141 so as to surely abut each contact portion as described above.
FIG. 11 is a diagram illustrating a method for positioning a photosensitive drum as an image carrier.
The frame member 102 and the housing 106 are formed of glass fiber reinforced resin, aluminum die cast, or the like that ensures a certain degree of rigidity, and a pair of positioning pins 131 and screw holes 133 are formed on both side surfaces of the housing 106. Yes.
[0049]
The side plates 632 and 633 are formed of sheet metal and are arranged to face each other in the main scanning direction. Each of the measuring plates 632 and 633 is formed with a notch 635 for positioning the bearing 636 of the photosensitive drum 504, and can be engaged and supported while maintaining the arrangement accuracy of the photosensitive drums 504.
In this embodiment, if the distance between the centers of the axes is an integral multiple of the circumferential length of the photosensitive drum 504 and the drum diameter is r, they are arranged at equal intervals so as to be k · πr.
[0050]
In each of the optical scanning devices 640, 641, 642, 643, the positioning pins 131 are inserted into the fitting holes 637, and the side surfaces of the housing 106 are brought into contact with the inner sides of the side plates 632, 633. It positions so that it may bridge | crosslink, and the screw 637 is passed from the outer side and fixed.
At the time of positioning and fixing, fitting holes 637 formed in the side plates 632 and 633 are elongated holes parallel to the arrangement direction of the photosensitive drums 504 as shown in FIGS. Is engaged with the engagement holes 639 formed in the side plates 632 and 633 and fixed with screws, the eccentric cam 638 rotates around the screw holes 133, so that the optical scanning devices 640 to 643 are oblong holes ( It can be finely moved along the fitting hole 637), and the position of each scanning line can be adjusted.
[0051]
FIG. 15A is an explanatory diagram of the position adjustment of the scanning line, and FIG. 15B is an arrow view in the direction of arrow A in FIG.
[0052]
FIGS. 19A and 19B are explanatory diagrams showing a method of correcting a seam of line images in adjacent optical scanning units. FIG. 19A shows a state before correction, and FIG. 19B shows a state after correction.
In the embodiment, they are adjusted so that the difference between the respective writing positions becomes zero.
Assume that the recording position of the adjacent optical scanning means is shifted by D (FIG. 19A). The correction may be performed so that D = 0, but the correction unit first corrects the writing timing of the scanning line in units of line pitch p.
[0053]
Specifically, the timing is shifted every k times (k · T) of one cycle T by selecting a synchronization detection signal for reading image data. Here, k is a natural number, and k with Lk · p closest to 0 is selected.
Next, the remaining portion D 'is corrected in units of p / n by shifting the amplitude phase of the vibrating mirror (movable mirror 202, see FIG. 3) every 1 / n times (T / n) of one period T. Here, n is a natural number and L- (k + 1 / n) · p may be selected as n closest to 0.
In this way, line images recorded in adjacent areas on the transfer belt 501 (see FIG. 5) can be joined together.
[0054]
FIG. 9 shows the intensity distribution of each beam spot in the sub-scanning direction and the potential distribution of the electrostatic latent image formed by the beam spot. In FIG. 9, the left-right direction is the sub-scanning direction, and a plan view (lower side of the figure) and a cross-sectional view (middle of the figure) corresponding to a dot for one pixel are shown. The left side of FIG. 9 is the potential distribution by the beam from the first light source, and the right side is the potential distribution by the beam from the second light source.
In this way, in the state where the beam spots are close to each other, the potential distribution formed thereby is reproduced as a uniform distribution by combining the light amount (exposure energy) of each beam spot, If the amount of light is the same, the distribution is centered on the middle position. ... (1)
In addition, when the light amounts of the respective beam spots are different, two distributions having different electrostatic latent image diameters are combined to obtain a distribution in which the center of gravity is shifted toward the higher light amount from the intermediate position. ... (2)
The charged toner is attracted and adhered to a portion of the potential distribution formed in this way that is higher than the developing bias potential to form dots, and by balancing each light quantity, a uniform dot diameter d0 with respect to an arbitrary center of gravity position. It can be.
[0055]
Therefore, if the center of gravity position of the electrostatic latent image is moved across the lines by changing the ratio of the light amount of each beam spot, the same width as that when scanning with one beam is inclined by the pitch P from the scanning direction. A line can be formed. By such a change in the light amount ratio, even if the scanning line is inclined, the inclination can be corrected without using a mechanical mechanism.
FIG. 18 shows an example in which the inclination of the recorded line is corrected to the lower right with respect to the scanning line.
[0056]
The line inclination correction amount Δθ is as shown in FIG. 11 from the detection pattern (toner image) formed on the transfer belt 6380 (see FIG. 11) by the optical scanning devices 640 to 643 (see FIG. 11) corresponding to each color. The registration deviation detecting means 629 that receives the reflected light of the beam projected from the light emitting diode 630 at the pin photodiode 631 is disposed at both ends of the transfer belt 6380, so that it is detected as a relative deviation with respect to the reference color.
Based on the detection result, the first and second beam pitches P are determined using the scanning width L according to the line inclination correction amount Δθ,
P = L · tanΔθ
The amount of light of the second beam is set to the maximum at the scanning start end, the first beam is set to 0, and the first beam is set to maximum and the second beam is set to 0 at the scanning end. And so that the amount of light of the second beam increases monotonously and further, the amount of light of the second beam decreases monotonously, and the sum of each becomes constant at each position in the scanning direction. Thus, as shown by the thick line in FIG. 18, the locus of the center of gravity (center) of the electrostatic latent image is formed obliquely upward to the right with respect to the scanning line with respect to the scanning direction (main scanning direction). ing.
[0057]
By correcting the adjacent areas in the same manner, the lines to be recorded are aligned in parallel and are obliquely connected on the transfer belt 6380 (see FIG. 11) to form inclined lines.
By the way, the light quantity is represented by the product of the beam intensity and the lighting time, and in order to form the electrostatic latent image as described above, any of the following methods may be used.
1. Variable beam intensity
2. Varying the pulse width of the beam
Details will be described in drive control of a semiconductor laser, which will be described later, but in the embodiment, the amount of light is varied to approximate a step shape.
[0058]
The registration deviation detection means 629 can detect registration deviation (a parallel shift) simultaneously with the detection of the inclination deviation between the colors. What is necessary is just to apply between the scanning devices 640-643, and it can correct | amend similarly.
[0059]
FIG. 5 shows a tandem method in which images are formed one by one on the corresponding photosensitive drums 504 by the four optical scanning devices 500 (640 to 643), and colors are superimposed as the transfer belt 501 (6380 in FIG. 11) rotates. In this embodiment, the optical scanning device is arranged so that the light beam emission direction is downward.
[0060]
The transfer belt 501 is supported by a driving roller and two driven rollers, and the photosensitive drums 504 are arranged at equal intervals along the moving direction. Around the photosensitive drum 504, a developing roller 502 and a toner hopper 503 for supplying toner corresponding to each color of yellow, magenta, cyan, and black, and a cleaning unit for scraping and storing the transferred residual toner with a blade 508 is integrally deployed.
[0061]
For each color image, an electrostatic latent image is formed by each optical scanning device 500 by shifting the writing timing in the sub-scanning direction using a signal of a sensor 505 for detecting a registration mark formed at the end of the transfer belt 501 as a trigger. The electrostatic latent image is sequentially superimposed on the transfer belt 501 with toner on the developing unit.
A sheet as a transfer body is supplied from a paper supply tray 507 by a paper supply roller 506, sent out by a registration roller 510 in synchronization with the formation of an image of the fourth color, and simultaneously transferred from a transfer belt 501 to four colors by a transfer unit 511. Then, the toner image is sent to the fixing device by the conveying belt 515 with the toner image placed thereon.
[0062]
The transferred toner image is fixed by the fixing roller 512 of the fixing device and is discharged to the paper discharge tray 514.
As described above, each optical scanning device 500 connects one scanning line of a plurality of optical scanning units to form one line. The total number of dots L in one line is divided into three, and 1 to L1, L1 + 1 to L2, and L2 + 1 to L dots are assigned and printed (printed) from the beginning of the image. In this embodiment, each scanning area is several mm on the photosensitive member. Overlapping areas are provided so that they overlap, and the number of allocated pixels L1 and L2 is not fixed, but is different for each color, so that the seams of the scanning lines of the respective colors constituting the same line do not overlap, and the boundaries of the scanning areas are defined. It is less noticeable.
[0063]
As described above, the image data is divided into three in the main scanning direction, stored in the bitmap memory 511 for each optical scanning unit, raster-developed for each vibrating mirror module 130, and stored in the buffer 512 as line data. . The line data stored in the buffer 512 is read using each synchronization detection signal as a trigger, and image recording is performed individually.
Further, as will be described later, by setting each writing start timing, registration of the writing start end is adjusted.
[0064]
In this embodiment, even if the resonance peaks of the vibrating mirrors (movable mirror 202, see FIG. 3) are different, the deflection angles are matched in a predetermined band by changing the gain of the applied voltage, and scanning is performed at a common driving frequency. Like to do.
The spring constant of the torsion beam 208 (see FIG. 3) changes due to a change in the environmental temperature, and the resonance band shifts uniformly. However, when the drive frequency is reselected correspondingly, a common drive frequency is given, By making the scanning frequency common to each oscillating mirror module 130 (see FIG. 1), it is possible to match the resist of each line up to the end of each region.
[0065]
FIG. 6 is a block diagram showing drive control of the semiconductor laser and the movable mirror.
The drive pulse generator 601 divides the reference clock with a programmable frequency divider and generates a pulse train so that a voltage pulse is applied at a timing that matches the amplitude of the movable mirror 202 (see FIG. 3) as described above. The PLL circuit gives a predetermined phase lag δ between the vibrating mirror modules 130 (see FIG. 1) to the drive unit 602 of each movable mirror 202 (see FIG. 3), and a voltage is applied to each of the electrodes.
[0066]
Here, the relative phase lag δ between the oscillating mirrors (movable mirror 202) is calculated using one scanning line pitch p.
δ = (1 / fd) · {(Δy / p) −n}
Here, n is (Δy / p) −n <1.
If a natural number satisfying the above is given, the misalignment at the joint is an integral multiple of one scanning line pitch, and writing is corrected every other cycle of the oscillating mirror 130 (see FIG. 1), that is, shifted by n line cycles. As a result, the registration deviation Δy in the sub-scanning direction can be invalidated, and a high-quality image with no seam position deviation can be obtained.
[0067]
In the embodiment, the synchronization detection sensor 604 and the end detection sensor 605 are arranged on a printed circuit board, but the detection surface is arranged at a position equal to the optical path length reaching the scanned surface. FIG. 8 shows the details of the detection unit, which includes a photodiode 801 arranged perpendicular to the main scanning direction and a photodiode 802 arranged non-perpendicular to the main scanning direction. A synchronization detection signal or a termination detection signal is generated when the signal passes, and a time difference Δt from the photodiode 801 to the photodiode 802 is measured, whereby a scanning position deviation Δy in the sub-scanning direction, which is a main cause of the registration deviation, is obtained. It can be detected as a corresponding measurement value on the photosensitive drum 504 (see FIG. 5) which is the surface to be scanned.
[0068]
Δy is obtained by using 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 scan position deviation.
[0069]
In this embodiment, this time difference is monitored by the scanning position deviation calculation unit 610 to detect the scanning position deviation, and the phase between the oscillating mirrors 130 (see FIG. 1) is constantly varied and corrected so as to meet the Δt reference value. be able to.
In the main scanning direction, as will be described later, the deviation in scanning speed in each image area is detected.
1) Correction can be made by adjusting the deflection angle (amplitude) to a predetermined value by adjusting the gain of the voltage pulse applied to each oscillating mirror 130.
[0070]
2) Further, by shifting the pixel clock in accordance with the drive frequency of the movable mirror 202 (see FIG. 3) for the seam position shift between adjacent image areas, the magnification of the image width can be changed, and the scanning end and the adjacent optical scanning. Correction can be made by matching the seam with the scanning start end of the apparatus.
[0071]
Basically, no drive voltage is applied to the oscillating mirror 130 except for image recording and its preparation period.
When the power is turned on and when starting from the standby state, the drive frequency fd is varied from the high frequency side by continuously changing the frequency division ratio with a programmable frequency divider, and the output from the amplitude detector 610 is executed. In the example, the beam is detected by the synchronization detection sensor 604 and the termination detection sensor 605 disposed in the vicinity where the scanning angle is −θ0, and the time difference T between the synchronization detection signal and the termination detection signal is measured by the amplitude calculation unit 609. Thus, the deflection angle (amplitude θ0) of the movable mirror 202 is detected.
[0072]
Now, if the scanning angle of the light beam detected by the synchronization detection sensor 604 is θd, the scanning time from the center of the image is t, and the driving frequency of the movable mirror 202 is fd.
θd / θ0 = sin2π · fd · t, t = T / 2
Given in.
The deflection angle is corrected by varying the gain of the voltage pulse to be applied until the time difference T reaches a predetermined reference value T0. This correction is performed periodically under each environment, for example, between jobs.
[0073]
If this correction is performed during image recording, the main scanning end of the image fluctuates, so that the same value is maintained during image recording.
In the embodiment, a plurality of oscillating mirrors are provided, but by selecting a common drive frequency and aligning the reference values of gains, the deflection angles between the oscillating mirrors are made to coincide.
The above correction is performed in each of the vibrating mirror modules, and in the embodiment, it is composed of three optical scanning means, so that the printing operation can be performed after all the corrections are completed.
[0074]
Next, drive control of the semiconductor laser will be described.
As described above, in order to make the line pitch of the latent image uniform by reciprocating scanning, it is necessary to change the beam intensity or the pulse width of the beam.
Therefore, in the first embodiment, a method for changing the beam intensity will be described.
[0075]
FIG. 21 shows the beam intensity with respect to the current applied to the semiconductor laser. In the figure, the horizontal axis indicates the drive current, and the vertical axis indicates the beam intensity.
As shown in the figure, it can be seen that the beam intensity increases in proportion to the applied current when the threshold current is exceeded. Accordingly, the difference Im-Ith from the threshold current Ith to the maximum current Im for obtaining a predetermined beam intensity is divided into n (255 in the embodiment), and the drive current can be varied stepwise based on the variable data. .
[0076]
As described above, in one light source, Im is gradually decreased from the start of writing in the main scanning direction to the end of writing by using a synchronization detection signal as a trigger, and in the other light source, writing is performed. Im is gradually increased from Ith from the start to the end of writing.
By the way, in general, the LD drive unit 606 performs feedback control to increase or decrease the drive current so that the beam intensity becomes constant by the monitor signal from the semiconductor laser.
This is because Ith and Im that emits the same beam intensity change as the case temperature changes. If this control is not performed, the beam intensity changes and the image density differs between the low temperature state and the high temperature state. Occurs.
[0077]
Therefore, in the embodiment, a change in the drive current Im ′ that provides a predetermined monitor signal output value is uniformly added to the drive current as a bias current ΔIh of the threshold current.
Next, a method for changing the pulse width (pixel clock fm) of the beam in the second embodiment will be described.
[0078]
The clock pulse generator 607 counts the frequency-divided clock obtained by dividing the reference clock f0 by the programmable frequency divider based on the variable data, and the PLL reference signal fa having a pulse width as long as k clocks is formed. The phase of the reference clock f0 is selected in the PLL circuit, and the pixel clock fk is generated.
Naturally, if the pulse width is long, the diameter of the electrostatic latent image formed on the photosensitive drum 504 is large, and if the pulse width is short, the diameter is small.
[0079]
Therefore, an electrostatic latent image having an arbitrary diameter based on variable data can be formed by switching the pulse width stepwise along the main scan.
As described above, one light source is decreased from the latent image diameter corresponding to one pixel from the start of writing in the main scanning direction to the end of writing using the synchronization detection signal as a trigger, and the other light source is written. The electrostatic latent image diameter corresponding to one pixel is increased from the start to the writing end.
[0080]
Incidentally, since the movable mirror 202 is resonantly oscillated, the scanning angle θ changes in a sin wave shape.
On the other hand, on the surface of the photosensitive drum 504 that is the surface to be scanned, it is necessary to print main scanning dots at uniform intervals, and the imaging characteristics of the scanning lens described above are such that the scanning distance dH / dθ per unit scanning angle is sin.^-1The direction of the light beam must be corrected so that it is proportional to θ / θ0, that is, it is accelerated at a slower rate in the center of the image and is accelerated toward the periphery, and the imaging point is moved away from the center to the periphery. A power-distributed scanning lens is used, but the beam spot diameter increases accordingly. For this reason, in obtaining a uniform beam spot, there is a limit in expanding the effective scanning region θs with respect to the maximum amplitude θ0.
[0081]
Therefore, in the embodiment, as shown in FIGS. 10A and 10B, the phase corresponding to each pixel is shifted from the start of writing to the end of writing against the change in scanning speed due to the amplitude. Pixels whose pulse width is increased in the region from the center of the image to the end of writing so that the pulse width of each pixel is gradually decreased from a long state in the region from the start of writing to the center of the image. By applying the clock fm to the LD driving unit 606 and adding electrical correction, the burden on the scanning lens is reduced and the scanning efficiency is improved.
In such control, the pulse width and the phase thereof are set so that the dot diameter corresponding to each pixel is uniform. Therefore, a pulse in which the pulse width corresponding to one pixel set here is proportionally distributed is generated. Thus, even if the electrostatic latent image diameter is variable as described above, it can be easily handled without adding a new control circuit.
[0082]
Here, FIG. 10A is a diagram showing the relationship between the pulse width and time, and FIG. 10B is a diagram showing the relationship between the phase difference and time. 10A, the vertical axis indicates the pulse width, and in FIG. 10B, the vertical axis indicates the phase difference. 10A and 10B, the horizontal axis indicates time.
[0083]
In the embodiment, the semiconductor laser is a semiconductor laser array having two light emitting sources. However, the present invention is not limited to this, and two or more beams may be combined even if the beams from the semiconductor lasers of a single light emitting source are combined. The light emission source may be used.
1) Action and effect corresponding to claim 1
A plurality of optical scanning means having a light source means and a movable mirror that scans by reflecting a light beam from the light source means, and connecting each scanning area along the main scanning direction during main scanning to carry an image A plurality of optical scanning devices that form an electrostatic latent image on a body drum and a developing unit that visualizes the electrostatic latent image with toner are arranged in parallel along the moving direction of the transfer body, and are developed with the toner. In the image forming apparatus that sequentially transfers the imaged toner image to the transfer body to form a superimposed color image, a pair of side plates that are orthogonal to the main scanning direction and that face each other so as to sandwich the scanning region are provided. And by supporting the plurality of optical scanning devices integrally by bridging the side plates, the relative positions of the optical scanning devices can be stably maintained, and the overlay accuracy of images formed at each station Therefore, it is possible to minimize the frequency of correction, such as creating a detection pattern on the transfer belt as described above to detect registration deviation, and forming an image in consideration of the environment with almost no downtime. A device can be provided.
[0084]
2) Action and effect corresponding to claim 2
The side plate is formed with a positioning portion for positioning the support member that pivotally supports the plurality of image carrier drums with respect to the optical scanning device, so that the relative position between the optical scanning device and the image carrier drum can be determined. It can be kept stable, the timing from the position irradiated by the optical scanning device on the image carrier drum to the transfer position can be made constant between stations, and the deviation is minimized even if the environment changes Therefore, high-quality color image recording can be performed without color shift or color change over time.
[0085]
3) Action and effect corresponding to claim 3
The optical scanning device supports the scanning positions of the image carrier drum between the stations by supporting each scanning position in parallel with the moving direction of the transfer body at an interval that is an integral multiple of the circumference of the image carrier drum. Even if there is a change in the peripheral speed due to the eccentricity of the rotating shaft, it is possible to align the amplitude phase of the peripheral speed fluctuation at each color transfer position simply by matching the phases between the image carrier drums. High-quality color image recording can be performed.
[0086]
4) Action and effect corresponding to claim 4
By providing an adjusting means for adjusting the arrangement of the optical scanning device with respect to the moving direction of the transfer body, the irradiation position on the image carrier drum of each optical scanning device can be reliably matched, and the timing to reach the transfer position can be adjusted. Since each station can be aligned, high-quality color image recording without color shift or color change can be performed.
[0087]
5) Action and effect corresponding to claim 5
Each of the light source means includes a plurality of light sources, and records one line using at least two beams adjacent in the sub-scanning direction on the image carrier drum, thereby fixing the optical scanning device, The position of the line image can be changed regardless of a complicated mechanical mechanism, so that the placement accuracy of the optical scanning device can be kept stable, and the frequency of correction such as detection of registration deviation is minimized, and color deviation is maintained over time. And high-quality color image recording without color change.
[0088]
6) Action and effect corresponding to claim 6
Equipped with a light amount varying means that varies the light amount ratio between the two adjacent beams in accordance with the main scanning position, thereby easily and reliably correcting the inclination (skew) of the line image formed on the transfer belt. Therefore, high-quality color image recording can be performed without color shift or color change over time.
[0089]
【The invention's effect】
According to the image forming apparatus of the present invention, it is possible to provide an image forming apparatus that keeps the arrangement accuracy of the recording lines stable with time and considers the environment such as power saving and resource saving.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an optical scanning device according to an image forming apparatus of the present invention.
2 is a layout diagram of optical elements of the optical scanning device shown in FIG. 1. FIG.
FIG. 3 is a detailed view of a vibrating mirror module used in the optical scanning device according to the image forming apparatus of the present invention.
FIG. 4 is a sub-scan section of the optical scanning device according to the image forming apparatus of the present invention.
FIG. 5 is a cross-sectional view when the optical scanning device according to the image forming apparatus of the present invention is applied to a tandem color laser printer.
FIG. 6 is a block diagram showing drive control of a semiconductor laser and a movable mirror used in the optical scanning device according to the image forming apparatus of the present invention.
FIG. 7 is an explanatory diagram showing fluctuations in resonance frequency with respect to temperature in the optical scanning device according to the image forming apparatus of the present invention.
8 is a detailed diagram of a detection unit having a synchronization detection sensor and a termination detection sensor in the block diagram shown in FIG. 6. FIG.
FIG. 9 is an explanatory diagram showing the intensity distribution of each beam spot in the sub-scanning direction and the potential distribution of an electrostatic latent image formed by the beam spot according to the image forming apparatus of the present invention.
10A is a diagram showing a relationship between pulse width and time according to the image forming apparatus of the present invention, and FIG. 10B is a diagram showing a relationship between phase difference and time according to the image forming apparatus of the present invention. FIG.
FIG. 11 is an explanatory diagram of a method for positioning a photosensitive drum as an image carrier according to the image forming apparatus of the present invention.
FIG. 12 is an explanatory diagram showing a state of electrostatic torque generated between electrodes corresponding to the deflection angle of the movable mirror according to the image forming apparatus of the present invention.
FIGS. 13A to 13D are explanatory diagrams showing the relationship between the amplitude (rotation angle) of the movable mirror of the optical scanning device according to the image forming apparatus of the present invention and the pulse applied to each fixed electrode. (A) shows the amplitude (rotation angle) of the movable mirror, (b) shows the applied pulses of the first and second fixed electrodes, (c) shows the applied pulses of the third fixed electrode, (D) shows the application pulse of a 4th fixed electrode, respectively.
FIG. 14 is an explanatory diagram showing a characteristic of a deflection angle with respect to a driving frequency of the optical scanning device according to the image forming apparatus of the present invention.
FIG. 15A is an explanatory diagram of position adjustment of a scanning line according to the image forming apparatus of the present invention, and FIG. 15B is a view as viewed in the direction of arrow A in FIG.
FIG. 16 is a cross-sectional view of the vicinity of an electrode of a movable mirror according to the image forming apparatus of the present invention.
FIG. 17 is an explanatory diagram showing an array of beam spots on the surface to be scanned of the optical scanning apparatus according to the image forming apparatus of the present invention.
FIG. 18 is an explanatory diagram illustrating an example in which the inclination of a recorded line is corrected to lower right with respect to a scanning line as an example of an optical scanning device according to an image forming apparatus of the present invention.
FIGS. 19A and 19B are explanatory diagrams showing a line image seam correction method in adjacent optical scanning units, FIG. 19A shows a state before correction, and FIG. 19B shows a state after correction; Indicates.
FIG. 20 is an explanatory diagram showing details of attachment of the semiconductor laser to the optical device shown in FIG. 1;
FIG. 21 is an explanatory diagram showing the beam intensity with respect to the current applied to the semiconductor laser of the optical scanning device according to the image forming apparatus of the present invention.
[Explanation of symbols]
101 Semiconductor laser
102 Frame member
103 Through hole
104 square hole
105 recess
106 Housing
109 Mounting slope
110 Coupling lens
112 Printed circuit board
113 Synchronization detection sensor
115 cable
116 first scanning lens
117 Second scanning lens
119 Flat pressed surface
120, 123, 135, 142, 145, 146 Protrusion
121 Notch
122 groove
127 high brightness aluminum sheet
128 Mirror receiver
129 opening
130 Vibrating mirror module
131 Positioning pin
133 Screw hole
136 Cylinder mirror
137, 147 screw
138 cover
139 opening
141 leaf spring
143 Corrugated spring
144 Sponge-shaped protrusion
630 Light emitting diode
631 pin photodiode
632, 633 Side plate
635 cutout
636 Bearing
637 Mating hole
640, 641, 642, 643 Optical scanning device
6380 transfer belt

Claims (6)

A plurality of light scanning means having a light source means and a movable mirror that scans by reflecting a light beam from the light source means, and connecting each scanning region along the main scanning direction during main scanning to carry an image A plurality of optical scanning devices for forming an electrostatic latent image on the body drum and developing means for visualizing the electrostatic latent image with toner are arranged in parallel along the moving direction of the transfer body, and the toner is developed with the toner. In the image forming apparatus that sequentially transfers the imaged toner image to the transfer body to form a superimposed color image, a pair of side plates that are orthogonal to the main scanning direction and that face each other so as to sandwich the scanning region are provided. An image forming apparatus comprising: a plurality of optical scanning devices integrally supported by bridging the side plates. 2. The image forming apparatus according to claim 1, wherein a positioning portion for positioning a support member that pivotally supports the plurality of image carrier drums with respect to the optical scanning device is formed on the side plate. 2. The image forming apparatus according to claim 1, wherein the optical scanning device supports each scanning position so as to be arranged in parallel in the moving direction of the transfer body at intervals of an integral multiple of the circumferential length of the image carrier drum. apparatus. The image forming apparatus according to claim 3, further comprising an adjusting unit that adjusts an arrangement of the optical scanning device with respect to a moving direction of the transfer body. 2. The image forming apparatus according to claim 1, wherein each of the light source means has a plurality of light emitting sources, and records one line using at least two beams adjacent in the sub-scanning direction on the image carrier drum. apparatus. 6. The image forming apparatus according to claim 5, further comprising a light amount varying unit that varies a light amount ratio between the two adjacent beams in accordance with the main scanning position.

Images