JP2004009465A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to normally form the image even if the light spot is failed, in an image forming apparatus for defining an image writing position by generating a signal for starting a scan by receiving the light from a light spot of a multi-beam light source. <P>SOLUTION: An image is formed by scanning a photoreceptor drum 31 using a VCSEL light source group 380 in which the light spots are two-dimensionally arranged. Pairs, in which positions of beam spots formed on a surface to be scanned in the main scanning direction are almost equal, are grouped within a SOS detection group. A photosensor in a scan-start-signal generating section 27 scans the surface in the state that a plurality of light spots are lighted for each group. A scan-start-signal SOS is generated according to the output from the photosensor according to this scanning. When failure of the light spot for detecting the scan-start-signal SOS is detected by a light amount detecting sensor 16 and a SOS detecting group lighting control circuit 229, the SOS detecting group is switched to other group having normal light spots only. <P>COPYRIGHT: (C)2004,JPO

Description

【００６３】
図４は、上記構成のＶＣＳＥＬ光源群３８０を備えた画像形成装置１にて画像を形成するための処理回路（画像記録制御部）の概要を示す図である。走査開始信号生成部２７は、マルチビーム光源の一例であるＶＣＳＥＬ光源群３８０の個々のＶＣＳＥＬ３８０ａのうちの走査方向の位置ごとに分けられたグループ単位で点灯された光を受光することで走査開始信号を生成する。このとき、この画像記録制御部においては、走査開始信号の検出に関わる発光点の発光状態を検出し、この検出結果に基づいて、発光点の発光状態が異常であるか否かを判定する。
【００６４】
そして、異常発光点を補完し、つまり走査開始信号が正常に検出できるように、かつ、グループ単位で点灯するように、異常発光点を残りの正常な発光点に切り替える。たとえば、異常発光点を含むグループを、正常な発光点のみを有する他のグループに切り替えたり、あるいは異常発光点を含むグループ内において、異常発光点を他の発光点に切り替える。あるいは、異常状態の判定結果に基づいて走査開始信号生成部２７が使用する基準信号（検知閾値）を、走査開始信号が正常に検出できる方向に制御する。
【００６５】
なお、「グループ単位で点灯することで走査開始信号ＳＯＳを生成する」とはとは、マルチビーム光源の各発光点を主走査方向の位置ごとにグループ分けして点灯しそのグループの発光点の光を受光して走査開始信号ＳＯＳを生成するものであればよい。その限りにおいて、グループ数は１グループであるのか複数ブループの組合せであるのかは問わない。また、グループ内の全部の発光点を点灯し受光するものに限らず、グループ内の一部の発光点を点灯し受光するものであってもよい。以下具体的に説明する。
【００６６】
図４に示すように、画像記録制御部は、スキャナなどの画像取得部５、あるいはネットワークを介してパーソナルコンピュータなどのクライアント端末から画像データを取得する画像データ生成部７と、画像データ生成部７からの画像データに基づいて個々のＶＣＳＥＬ３８０ａ用のレーザ変調信号を生成する書込信号生成部２２０とを備える。
【００６７】
画像データ生成部７は、画像取得部５などから入力されたＲＧＢ表色系の画像データをＹＣｒＣｂ表色系の画像データに変換し、さらにＹＣｒＣｂ表色系からＣＭＹＫ表色系へのマッピングをしプリント出力用に色分解された解像度が６００ｄｐｉ／多階調（たとえば８ビット）の中間調画像や文字画像を表すラスタデータ（中間調データ）を生成し、書込信号生成部２２０に渡す。
【００６８】
またこの際には、カラー画像のＣＭＹ成分を減色するアンダーカラー除去（ＵＣＲ）、減色されたＣＭＹ成分を部分的にＫ成分と交換するグレー成分交換（ＧＣＲ）をする。また、出力データ（ＣＭＹＫなど）に応答して作成される出力画像のトナー像を調整するために、色分解の直線化などの処理をする。
【００６９】
書込信号生成部２２０は、画像データ生成部７とのインターフェース機能をなすＩ／Ｆ（インターフェース）部２２２と、レーザ変調信号（光ビーム変調信号）を生成する変調信号生成部２２４と、複数のラインバッファメモリ（ビデオメモリ）２２６ａを有し、変調信号生成部２２４からのレーザ変調信号に対して、書込タイミングを粗調整するラインバッファメモリ群２２６とを備える。このラインバッファメモリ群２２６が、データ遅延部として機能する。
【００７０】
また書込信号生成部２２０は、Ｉ／Ｆ部２２２、変調信号生成部２２４、およびラインバッファメモリ群２２６を制御するメモリコントローラ２２８と、Ｉ／Ｆ部２２２、変調信号生成部２２４、ラインバッファメモリ群２２６、およびメモリコントローラ２２８を制御するタイミング信号発生部２３０とを備える。
【００７１】
さらに画像記録制御部は、画像形成装置１の走査開始信号生成部２７から得られた走査開始信号ＳＯＳに基づいて書込タイミングを制御する基準信号などを生成する同期信号発生器２６０と、カラー複写装置１の全体を制御するための機能部分であるマシンコントローラ２７０とを備える。
【００７２】
タイミング信号発生部２３０は、走査ビームが感光体ドラム３２に入射する直前の位置に到達したことを示す走査開始信号ＳＯＳとマシンコントローラ２７０が出力する画像記録開始を指示するプリントリクエスト信号ＰＲＱより各種の制御信号を生成し、各部に供給する。たとえば、書出基準信号ＲＯＳ＿ＰＳ、ライン選択信号ＲＯＳ＿ＬＳ、ページ同期信号Ｐａｇｅ、あるいは画素クロックＰＣＫなどである。
【００７３】
またタイミング信号発生部２３０は、副走査方向の画像記録開始を指示するページ同期信号Ｐａｇｅと走査開始信号ＳＯＳとの位相差を判定し、メモリコントローラ２２８を制御する。メモリコントローラ２２８は、この位相差に応じて各ラインバッファメモリ２２６ａへの書き込みに余白データを付与し、感光体ドラム３２上への副走査方向の画像記録位置を調整する。
【００７４】
また画像形成装置１は、レーザ変調信号に基づいて、ＶＣＳＥＬ光源群３８０の個々のＶＣＳＥＬ３８０ａを駆動する駆動するレーザ駆動回路（マルチＬＤＤ）３００と、個々のＶＣＳＥＬ３８０ａの駆動電流を制御するための種々の制御信号や感光体ドラム３２の回転量（副走査方向への回転量）を制御する駆動制御部３１０とを備える。
【００７５】
駆動制御部３１０は、図示しない温度センサ、ポリゴンミラー１９の使用ミラー枚数（使用枚数カウンタ；本例では６枚）、たとえばスクリーン種別などを示すプリントモード、あるいは外部入力などに基づいて、個々のＶＣＳＥＬ３８０ａの光量を設定するための光量制御レベル変更信号を生成する光量設定条件選択部３０４を含む。また駆動制御部３１０は、光量検出用センサ１６にて取得された各ＶＣＳＥＬ３８０ａの光量を示す光量検出信号、光量設定条件選択部３０４にて生成された光量制御レベル変更信号、およびマシンコントローラ２７０からの光量設定信号に基づいて、光量レベルを変更するレベル変更部３０６と、このレベル変更部３０６の制御の元に、個々のＶＣＳＥＬ３８０ａの駆動電流を制御するための駆動量設定信号（それぞれに対応する１〜３２）および光量制御用駆動信号を生成する駆動量制御部３０８とを含む。さらに駆動制御部３１０は、タイミング信号発生部２３０からのタイミング信号に基づいて、感光体ドラム３２の副走査方向への回転量などを制御する回転制御部３０９を含む。
【００７６】
感光体ドラム３２に照射されるビームの光量が一定でないと、感光体ドラム３２上に形成される潜像の濃度が一定にならずに、画質が安定しない。また複数のビーム光で画像を形成する場合、各ビーム光の光量も一定にしないと形成された画像に濃度むらが発生し、画質を低下させる。光量検出用センサ１６にて各ＶＣＳＥＬ３８０ａの光量を検知し、一定の光量となるようにレーザ駆動量を制御（ＡＰＣ；Ａｕｔｏ　Ｐｏｗｅｒ　Ｃｏｎｔｒｏｌ）する機構を設けているのはこのためである。
【００７７】
ラインバッファメモリ２２６ａは、メモリコントローラ２２８による制御を受けて、ＶＣＳＥＬ３８０ａの主走査方向の遅延量（図３に示したＯＤに相当）を補正するよう所定タイミングで変調信号を同時に出力する。つまり、ＶＣＳＥＬ光源群３８０にて使用される３２本レーザ光用の変調信号が同時に出力され、光源（ＶＣＳＥＬ３８０ａ）への画像データの出力タイミングは同時になる。そして、縦（プロセス方向）に８個の光源（ＶＣＳＥＬ３８０ａ）を持ち且つ８×４のマトリックス構造を持つＶＣＳＥＬ光源群３８０を、３２ラインビーム同時走査の光源として機能させることができる。
【００７８】
また、本実施形態の画像記録制御部における書込信号生成部２２０内には、ＳＯＳ検知グループ点灯制御回路２２９が設けられている。また、駆動制御部３１０内には光量検出用センサ１６が設けられている。ＳＯＳ検知グループ点灯制御回路２２９は、光量検出用センサ１６によるビーム光量の検知結果に基づいて、ＶＣＳＥＬ光源群３８０の個々のＶＣＳＥＬ３８０ａが異常か否かを判断する。たとえば、ビーム光量（光強度）が予め定められた下限閾値以下あるいは上限閾値以上であるとき、ＶＣＳＥＬが故障もしくは異常であると判定する。
【００７９】
そして、ＳＯＳ検知グループ点灯制御回路２２９は、ＶＣＳＥＬ３８０ａが異常であると判断した場合に、異常と検知したＶＣＳＥＬ３８０ａの数や２次元アレイにおける何処のＶＣＳＥＬ３８０ａが異常なのか（つまり故障位置）を特定する。そして、この判定結果に基づいて、異常である発光点を使用せずに走査開始信号ＳＯＳを生成するためのＳＯＳ検知群のグループを選択し、選択したＳＯＳ検知グループ示すＳＯＳ切替信号を書込信号生成部２２０（特にメモリコントローラ２２８）やＶＣＳＥＬ光源群３８０に入力する。
【００８０】
上記構成において、画像形成装置１に入力された印字画像データは変調信号生成部２２４に入力される。変調信号生成部２２４は印字画像データを３２本のレーザそれぞれに対する画像データに分解し、３２本の変調信号としてラインバッファメモリ群２２６に入力する。ラインバッファメモリ群２２６は所定タイミングで画像データをレーザ駆動回路（マルチＬＤＤ）３００に出力する。レーザ駆動回路３００は入力された変調信号に応じてレーザをオン／オフさせる駆動電流をＶＣＳＥＬ光源群（ＶＣＳＥＬアレイ）３８０の各発光部に出力する。ＶＣＳＥＬ光源群３８０から出力されたレーザ光の一部はハーフミラー１４によって反射され、光量検出用センサ１６に導かれる。ハーフミラー１４を透過したレーザ光は感光体ドラム３２の露光に用いられる。
【００８１】
駆動量制御部３０８は、レーザ光の光量が所定の量となるようにレーザ駆動回路３００が出力する駆動電流量を制御するもので、感光体ドラム３２を露光しない期間にレーザ光を１，２，…，３２と順次切り替えて点灯させる駆動量設定信号および光量制御用駆動信号をレーザ駆動回路３００に出力することによって、１つの光量検出用センサ１６で全レーザ光の光量を検出する。
【００８２】
なお、本実施形態では、本願出願人が提案した特開平８−２６４８７３号に記載の技術を利用して、制御対象とする全てのＶＣＳＥＬ３８０ａを同時点灯させた状態で全体光量（総光量）を光量検出用センサ１６によって検出し、この検出によって得られた全体光量が所定量となるようにフィードバック制御することによって、制御対象とする全てのＶＣＳＥＬ３８０ａの射出光量が一定光量となるように一括して制御する。なお、この技術では、光源を構成する各ＶＣＳＥＬ３８０ａの発光特性に応じて予め各ＶＣＳＥＬ３８０ａの発光強度をバランスさせる光強度バランス調整手段が備えられており、該光強度バランス調整手段によって予め各ＶＣＳＥＬ３８０ａの発光強度のばらつきがなくなるように調整する。
【００８３】
また本実施形態においては、光量検出用センサ１６を、発光点の故障検知にも使用する。たとえば、光量検出用センサ１６が検知した光量検出信号は、ＳＯＳ検知グループ点灯制御回路２２９に入力されている。ＳＯＳ検知グループ点灯制御回路２２９は、駆動量制御部３０８で光量を最大にしても、所定の光量を検知できない場合は、そのＶＣＳＥＬ３８０ａは故障であると判断する。
【００８４】
また、走査開始信号ＳＯＳを生成するためには、レーザ光が走査開始信号生成部２７内のフォトダイオードＰＤに入射するタイミングの前後に強制的に走査開始信号ＳＯＳの検出に使用するグループの発光点を点灯する必要がある。このため、先にも述べたように、ＳＯＳ検出に使用するグループを切り替えるためのＳＯＳ切替信号がＳＯＳ検知グループ点灯制御回路２２９からレーザ駆動回路３００に入力される。
【００８５】
以上から分かるように、光量検出用センサ１６とＳＯＳ検知グループ点灯制御回路２２９とにより、本発明に係る光源状態判定部が構成される。またＳＯＳ検知グループ点灯制御回路２２９は、本発明に係る発光点切替制御部としても機能する。
【００８６】
図５は、画像形成装置１における露光制御（ＶＣＳＥＬ３８０ａを駆動する制御部）に関わる部分を示す機能ブロック図である。本実施形態の画像形成装置１は、本願出願人が提案した特開２００２−１３１６６２号記載の方法を利用して、マルチビーム光源の各発光点を主走査方向の位置ごとにグループ分けし、１グループのみもしくは複数グループを点灯して走査開始信号ＳＯＳを生成する。
【００８７】
ここでは、ＶＣＳＥＬ光源群３８０におけるＶＣＳＥＬ３８０ａが、図３に示すビームスポットに対応する構成、すなわち、主走査方向に直交する副走査方向に沿った直線上に略等間隔で８つのＶＣＳＥＬが配置されて構成された４つのＶＣＳＥＬ群が、主走査方向に沿って、各ＶＣＳＥＬの副走査方向位置が互いにずれるように配置された構成とされ、さらに各ＶＣＳＥＬ群をＧ１グループ、Ｇ２グループ、Ｇ３グループ、およびＧ４グループとし、正常時には最も早いタイミングで光検知器を走査するＧ１グループをＳＯＳ検知グループとし、Ｇ１グループのみの８個のＶＣＳＥＬ３８０ａからのレーザビームによって走査開始信号ＳＯＳを生成する場合について説明する。
【００８８】
図５に示すように、露光制御機能部分は、走査開始信号生成部２７、ラインバッファメモリ群２２６、メモリコントローラ２２８、ＳＯＳ検知グループ点灯制御回路２２９、およびレーザ駆動３００を含んで構成されている。
【００８９】
走査開始信号生成部２７は、前述のように、図１１に示した走査開始信号生成部３９２と同様の構成のものである。
【００９０】
ＳＯＳ検知グループ点灯制御回路２２９は、ピックアップミラー２６（図２参照）にレーザビームが入射できる時間帯に亘って、レーザ駆動回路３００に対してＳＯＳ検知グループ（本実施形態ではＧ１グループ）に属する全てのＶＣＳＥＬ３８０ａを点灯させることができる信号を出力する。これによって、走査開始信号生成部２７内のフォトダイオードＰＤにＳＯＳ検知グループとしてのＧ１グループに属する複数（本例では８個）のＶＣＳＥＬ３８０ａから射出された複数（本例では８個）のレーザビームが入射され、この複数（本例では８個）のレーザビームの光量レベルに応じた走査開始信号ＳＯＳが走査開始信号生成部２７によって生成される。
【００９１】
タイミング信号発生部２３０は、発振器２３３およびクロック位相同期回路２３４を含んで構成されている。このタイミング信号発生部２３０では、走査開始信号生成部２７によって生成された走査開始信号ＳＯＳと、発振器２３３によって生成されたクロック信号とがクロック位相同期回路２３４に入力され、走査開始信号ＳＯＳの立ち上りタイミングに同期したビデオクロック信号ＰＣＫが出力される。
【００９２】
メモリコントローラ２２８は、オフセットレジタ部２５５およびカウンタ回路部２５６を含んで構成されている。オフセットレジタ部２５５は、ＶＣＳＥＬ３８０ａの各グループに対応するレジスタＧ１〜Ｇ４を有している。またカウンタ回路部２５６は、各グループに対応するカウンタ回路Ｇ１〜Ｇ４を有している。オフセットレジタ部２５５内の各レジスタＧ１〜Ｇ４は、走査開始信号ＳＯＳが検知されてから各グループ用のライン同期信号ＬＳをアクティブにするタイミングを規定するＬＳオフセットＯＦ１〜ＯＦ４をカウンタ回路部２５６内の対応するカウンタ回路Ｇ１〜Ｇ４にセットする。
【００９３】
カウンタ回路部２５６の各カウンタ回路Ｇ１〜Ｇ４には走査開始信号ＳＯＳとビデオクロック信号ＰＣＫが入力されている。カウント回路Ｇ１〜Ｇ４はビデオクロックＰＣＫと走査開始信号ＳＯＳとに基づいてライン同期信号ＬＳ１〜ＬＳ４を生成する。このとき、ライン同期信号ＬＳ１〜ＬＳ４の走査開始信号ＳＯＳからのオフセット量は、レジスタＧ１〜Ｇ４のレジスタ値であるＬＳオフセットＯＦ１〜ＯＦ４を変更することにより、各々調整可能である。
【００９４】
ラインバッファメモリ群２２６は、複数のビデオメモリＭＧ１−１〜ＭＧ４−８を含んで構成されている。ビデオメモリＭＧ１−１〜ＭＧ１−８がＧ１グループに属する各ＶＣＳＥＬ３８０ａに対応するものであり、ビデオメモリＭＧ２−１〜ＭＧ２−８がＧ２グループに属する各ＶＣＳＥＬ３８０ａに対応するものであり、ビデオメモリＭＧ３−１〜ＭＧ３−８がＧ３グループに属する各ＶＣＳＥＬ３８０ａに対応するものであり、ビデオメモリＭＧ４−１〜ＭＧ４−８がＧ４グループに属する各ＶＣＳＥＬ３８０ａに対応するものである。
【００９５】
ビデオメモリＭＧ１−１〜ＭＧ４−８は各々ＦＩＦＯ（Ｆｉｒｓｔ−Ｉｎ　Ｆｉｒｓｔ−Ｏｕｔ）メモリで構成されており、変調信号生成部２２４によって変換された各ビーム点灯用のビデオ信号を記憶しておく。そして、格納してあるビデオ信号をビデオクロックＰＣＫとライン同期信号ＬＳ１〜ＬＳ４に同期して出力することにより、ビデオ信号ＳＧ１−１〜ＳＧ４−８を生成する。
【００９６】
たとえば、カウンタ回路部２５６内のカウンタ回路Ｇ１から出力されるＬＳ１信号がハイレベルになると、図３に示されるＧ１グループのＶＣＳＥＬ３８０ａに対応するＭＧ１−１〜ＭＧ１−８に読出許可信号として入力され、ＭＧ１−１〜ＭＧ１−８からビデオクロック信号ＰＣＫに同期してＧ１グループに属するＶＣＳＥＬ３８０ａに対するビデオ信号ＳＧ１−１〜ＳＧ１−８が出力され、各ビデオ信号がオンのときは、レーザ駆動回路３００が対応するＶＣＳＥＬ３８０ａを点灯させる。
【００９７】
図６は、図５に示す露光制御機能部分の要部信号を示すタイミングチャートである。ここで、図６（Ａ）は正常モードにおけるタイミングチャートの一例、図６（Ｂ）はＳＯＳ検知グループ内の発光点が故障した場合の異常モードにおけるタイミングチャートの一例である。
【００９８】
通常モードでは、走査開始信号生成部２７はＧ１グループの発光点を使用してＳＯＳ検出を行ない、メモリコントローラ２２８はライン同期信号ＬＳ１〜ＬＳ４を生成する。点線のラインは、Ｇ２〜Ｇ４の発光点をＳＯＳ検出として使用した場合の、走査開始信号ＳＯＳのタイミングである。主走査方向の位置のずれに応じて、出力タイミングが異なっていることが分かる。
【００９９】
ここで、図３におけるＧ１グループに属するＶＣＳＥＬ３８０ａの点灯タイミングは、走査開始信号ＳＯＳに対し、オフセットＯＦ１の分だけ遅延させる必要がある。また、Ｇ２グループ、Ｇ３グループ、およびＧ４グループに属するＶＣＳＥＬ３８０ａの点灯タイミングは、Ｇ１グループに属するＶＣＳＥＬ３８０ａの点灯タイミングに対し、各々図３に示されるオフセットＯＦ２、オフセットＯＦ３、およびオフセットＯＦ４の分だけ遅延させる必要がある。各々の遅延時間は、図６（Ａ）に示すように、次の式（２）〜（５）で求めることができる。
【数２】

【０１００】
また、Ｇ１グループをＳＯＳ検知グループとして得た走査開始信号ＳＯＳに対する、各グループに属するＶＣＳＥＬ３８０ａの点灯タイミングは、式（６）〜（９）で求めることができる。
【数３】

【０１０１】
図５に示す回路構成においては、上記式（６）〜（９）に従って、Ｇ１グループをＳＯＳ検知グループとして得た走査開始信号ＳＯＳに対して遅延時間を表すオフセット成分ＬＳオフセット１〜４を設定する。たとえば、所定の位置にＧ１グループ、Ｇ２グループ、Ｇ３グループ、およびＧ４グループの各グループに属するＶＣＳＥＬ３８０ａのビームによって露光を行なうために、走査開始信号ＳＯＳをＬＳオフセット１の遅延時間だけ遅延させたＬＳ１信号をカウンタ回路Ｇ１から、走査開始信号ＳＯＳをＬＳオフセット２の遅延時間だけ遅延させたＬＳ２信号をカウンタ回路Ｇ２から、走査開始信号ＳＯＳをＬＳオフセット３の遅延時間だけ遅延させたＬＳ３信号をカウンタ回路Ｇ３から、走査開始信号ＳＯＳをＬＳオフセット４の遅延時間だけ遅延させたＬＳ４信号をカウンタ回路Ｇ４から出力し、各信号を“Ｇ１グループのビデオメモリ読出許可信号”、“Ｇ２グループのビデオメモリ読出許可信号”、“Ｇ３グループのビデオメモリ読出許可信号”、“Ｇ４グループのビデオメモリ読出許可信号”として適用する。
【０１０２】
たとえばカウンタ回路Ｇ１では、走査開始信号ＳＯＳの立ち上りからの経過時間としてビデオクロックの数をカウントし、レジスタＧ１にて設定されたＬＳオフセット１に対応する遅延時間Ｔ１が経過した時点でハイレベルとなり、予め定められたビデオ信号読出許可時間の経過後にローレベルとなるＧ１グループ用のライン同期信号ＬＳ１を生成して出力する。カウンタ回路Ｇ２〜Ｇ４についても同様である。
【０１０３】
一方、Ｇ１グループの発光点の何れかに故障が発生したことをＳＯＳ検知グループ点灯制御回路２２９が検知した場合には、ＳＯＳ検知グループ点灯制御回路２２９は、ＳＯＳ検知グループをＧ１グループ以外のグループに切り替える。
【０１０４】
たとえば、Ｇ１グループの発光点の何れかが故障した場合にＳＯＳ検知グループをＧ１グループとしたままでは、図１２（Ｃ）にて説明したようにＰＤ出力を反映したＯＰ出力が低下する。また、ＰＤ出力は、電源電圧変動、フォトダイオードＰＤの経時劣化、あるいはノイズなどの要因により変動するので、ＰＤ出力を反映したＯＰ出力が閾値電圧を下回った場合には、走査開始信号ＳＯＳが出力されない場合がある。そこで、Ｇ１グループの発光点に故障が発生した場合は、その他のグループの発光点を使用して走査開始信号ＳＯＳを生成する。
【０１０５】
Ｇ１グループの代わりに、グループＧ２〜Ｇ４のいずれのグループの発光点を使用してＳＯＳ検出を行なってもよい。たとえば、図６（Ｂ）は、グループＧ２をＳＯＳ検知グループとして使用した場合を例示している。グループＧ２の発光点の光量の合計は、故障前のＧ１グループの光量の合計とほぼ等しくなるので、ＰＤ出力やＰＤ出力を反映したＯＰ出力もほぼ同じになる。したがって、図１１（Ｂ）や図１２（Ａ）に示すように正常に走査開始信号ＳＯＳを生成することができる。
【０１０６】
ただし、この場合、ＳＯＳ検知グループをＧ１グループとする場合と、他のグループとする場合とでは、検出タイミングがオフセットＯＦ２〜ＯＦ４の分だけずれることになる。そこで、ＳＯＳ検知グループのグループＧ２への切り替えに連動して、Ｇ２グループをＳＯＳ検知グループとして得た走査開始信号ＳＯＳに対して遅延時間を表すオフセット成分ＬＳオフセット１−２〜４−２を対応するレジスタＧ１〜Ｇ４に設定する。すなわち、走査開始信号ＳＯＳの出力タイミングの変動量に応じてＬＳオフセット１〜４レジスタの値を変更する。Ｇ２グループをＳＯＳ検知グループとして得た走査開始信号ＳＯＳに対する、各グループに属するＶＣＳＥＬ３８０ａの点灯タイミングは、式（１０）〜（１３）で求めることができる。
【数４】

【０１０７】
これにより、図６（Ｂ）に示すように、Ｇ２グループをＳＯＳ検知グループとした場合にも、Ｇ１グループをＳＯＳ検知グループとした場合とほぼ同様のタイミングで、各グループ用のライン同期信号ＬＳ１〜ＬＳ４を生成することができる。よって、走査開始信号ＳＯＳの検出に使用したＧ１グループの発光点に異常が発生しても、正常に走査開始信号ＳＯＳの検出とライン同期信号ＬＳ１〜ＬＳ４の作成を行なうことができる。
【０１０８】
なお、実質的に上記の時間関係を維持できる限り、ＬＳ１〜ＬＳ４の生成手順は上記例に限るものではない。たとえば、上記式（２）〜（５）に従って、各グループ用のライン同期信号ＬＳを生成してもよい。すなわち、先ず、走査開始信号ＳＯＳをＬＳオフセット１の遅延時間だけ遅延させたＬＳ１信号をカウンタ回路Ｇ１から“Ｇ１グループのビデオメモリ読出許可信号”として出力する。次に所定の位置にＧ２グループ、Ｇ３グループ、およびＧ４グループの各グループに属するＶＣＳＥＬ３８０ａのビームによって露光を行なうために、ＬＳ１信号を遅延時間Ｔ２だけ遅延させたＬＳ２信号をカウンタ回路Ｇ２から、ＬＳ１信号を遅延時間Ｔ３だけ遅延させたＬＳ３信号をカウンタ回路Ｇ３から、ＬＳ１信号を遅延時間Ｔ４だけ遅延させたＬＳ４信号をカウンタ回路Ｇ４から出力し、各信号を“Ｇ２グループのビデオメモリ読出許可信号”、“Ｇ３グループのビデオメモリ読出許可信号”、“Ｇ４グループのビデオメモリ読出許可信号”として適用する。故障が発生した場合に、ＳＯＳ検知グループを他のグループに変更する場合についても同様である。
【０１０９】
図７は、ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第２実施形態を説明する図である。上記実施形態（以下他の実施形態との差別のため第１実施形態という）では、感光体ドラム３２上の走査方向位置が略等しいレーザビームを射出するＶＣＳＥＬの全てによってＳＯＳ検知グループを構成した場合について説明したが、これに限らず、各々に対応する「被走査面上の光走査方向位置が略等しい」という条件を満たしていればよく、一例として、感光体ドラム３２上の光走査方向位置が略等しいレーザビームを射出するＶＣＳＥＬの一部のみでＳＯＳ検知グループを構成してもよい。
【０１１０】
そしてこの場合に、ＳＯＳ検知グループを構成する発光点の一部に故障が発生した場合には、その故障した発光点である異常発光点を「被走査面上の光走査方向位置が略等しい」他の発光点のうちの何れかと置き換えるとよい。こうすることで、上記実施形態と同様の効果を奏することができる。加えて、この場合には、元の検出タイミングとのオフセットは生じないので、レジスタＧ１〜Ｇ４の設定値の変更処理は不要である。
【０１１１】
たとえば図７（Ａ１）に示すように、Ｇ１グループの発光点Ｐ２５〜Ｐ３２の全てでＳＯＳ検知グループを構成するのではなく、そのうちの発光点Ｐ２９〜Ｐ３２の４つでＳＯＳ検知グループを構成してもよい。そしてこの場合に、図７（Ａ２）に示すように、ＳＯＳ検知グループを構成する発光点Ｐ２９〜Ｐ３２の一部に故障が発生した場合には、その異常発光点を「被走査面上の光走査方向位置が略等しい」すなわち同一グループ内の他の発光点Ｐ２５〜Ｐ２８のうちの何れかと置き換えるとよい。図７（Ａ３）では異常発光点Ｐ３１に対して発光点Ｐ２８に置き換えた例を示している。
【０１１２】
また、この場合、故障した発光点だけでなく正常な発光点の全部もしくは一部についても組合せを切り替えてもかまわない。たとえば図７（Ａ４）では異常発光点Ｐ３１だけでなく、全体の組合せを変えて、発光点Ｐ２５〜Ｐ２８の４つでＳＯＳ検知グループを構成し直した例を示している。
【０１１３】
また、ＳＯＳ検知グループとして選択する発光点は連続したものである必要はなく、たとえば図７（Ｂ１）に示すように、Ｇ１グループの発光点Ｐ２７、Ｐ２８とＰ３１，Ｐ３２の４点を選択してもよい。この場合においても、そのうちの何れかに故障が生じた場合には同一グループ内の他の発光点Ｐ２５，Ｐ２６，Ｐ２９、Ｐ３０のうちの何れかと置き換えるとよい。この場合にも、図７（Ｂ２）に示すように、故障した発光点だけでなく正常な発光点の全部もしくは一部についても組合せを切り替えてもかまわない。
【０１１４】
図８は、ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第３実施形態を説明する図である。上記第１あるいは第２実施形態では、１つのグループに属するＶＣＳＥＬ群のみのレーザビームに基づいて走査開始信号ＳＯＳを生成し、各グループ間の位置ずれを設計または測定タイミング値に応じて補正する場合の一形態について説明したが、さらに高精度にビームスポット位置を制御するためには、各グループで独立して走査開始信号ＳＯＳを生成し、ビデオ信号の同期を取る必要がある。この第３実施形態では、この場合の一形態について説明する。なお、第３実施形態の画像形成装置１の全体構成は、第１実施形態の画像形成装置１と同様であるので、ここでの説明は割愛する。
【０１１５】
第３実施形態の画像形成装置１では、図８に示すように、感光体ドラム３２上に形成されるビームスポットの配置位置に基づき複数のＶＣＳＥＬによって構成されるＳＯＳ検知グループを、次の条件を満足するように決定することによって、各ＳＯＳ検知グループに独立して走査開始信号ＳＯＳを生成する。
【０１１６】
すなわち、先ず前提として、第１実施形態と同様に、ＳＯＳ検知用光センサ（前例のフォトダイオードＰＤ）の受光エネルギ量が検知閾値に相当するエネルギレベル以上の期間と該エネルギレベル未満の期間とで信号レベルが相違する信号を生成する。
【０１１７】
また、複数のＳＯＳ検知グループのなかの任意の１グループを構成する全てのＶＣＳＥＬを点灯した場合に、図１１に示す状態と同様に、光走査方向（主走査方向）に対する走査開始信号生成部２７内のフォトダイオードＰＤ（光センサ）上での合計露光エネルギプロファイルと、走査開始信号生成部２７の検知閾値に相当するエネルギレベルとが２点のみで交差する。つまり、任意の１つのＳＯＳ検知グループに属する全てのＶＣＳＥＬを点灯させたときのＳＯＳ検知用光センサの受光面上での各レーザビームの合成エネルギ分布が、走査方向に沿った個々のレーザビームのビーム中心の間に相当する箇所に検知閾値に相当するエネルギレベル未満となる部分を生じない分布となるようにする。
【０１１８】
さらに図８に示すように、複数のＳＯＳ検知グループのなかの任意の２グループ（同図ではＧ１グループおよびＧ２グループ）を構成する全てのＶＣＳＥＬを点灯した場合に、上記合計露光エネルギプロファイルと走査開始信号生成部２７の検知閾値に相当するエネルギレベルとが４点のみで交差し、かつ一方のグループの光走査方向中心と、他方のグループの光走査方向中心との間で、合計露光エネルギプロファイルと上記検知閾値に相当するエネルギレベルとが２点のみで交差する。
【０１１９】
つまり、任意の２つのＳＯＳ検知グループに属する全てのＶＣＳＥＬを点灯させたときのＳＯＳ検知用光センサの受光面上での各レーザビームの合成エネルギ分布が、一方のＳＯＳ検知グループに属するレーザビーム群の走査方向に沿った中心と、他方のＳＯＳ検知グループに属するレーザビーム群の走査方向に沿った中心と、の間に相当する箇所に上記検知閾値に相当するエネルギレベル未満となる部分が生じる分布となるように、ＶＣＳＥＬ光源群３８０のＶＣＳＥＬが複数のＳＯＳ検知グループにグループ分けする。
【０１２０】
そして、走査開始信号ＳＯＳの生成に用いるＶＣＳＥＬとして個々のＳＯＳ検知グループごとに予め選択された複数のＶＣＳＥＬを、この複数のＶＣＳＥＬから射出された光ビームがＳＯＳ検知用光センサの受光面を横切る期間に各々点灯させる。
【０１２１】
これによって、任意の１つのＳＯＳ検知グループに属する全てのＶＣＳＥＬを点灯させたときの受光面上での各レーザビームの合成エネルギ分布を、走査方向に沿った個々のレーザビームのビーム中心の間に相当する箇所に上記検知閾値に相当するエネルギレベル未満となる部分を生じない分布とすることができ、かつ、任意の２つのＳＯＳ検知グループに属する全てのＶＣＳＥＬを点灯させたときのフォトダイオードＰＤの受光面上での各レーザビームの合成エネルギ分布を、一方のＳＯＳ検知グループに属するレーザビーム群の走査方向に沿った中心と、他方のＳＯＳ検知グループに属するレーザビーム群の走査方向に沿った中心と、の間に相当する箇所に上記検知閾値に相当するエネルギレベル未満となる部分が生じる分布とすることができる。
【０１２２】
このようにして複数グループにより走査開始信号ＳＯＳの検知を行なう場合には、全ＶＣＳＥＬを同時、または時系列に点灯させて走査開始信号ＳＯＳの検知を行なうために、走査開始信号生成部２７からは、グループ数と同数だけの走査開始信号ＳＯＳを表す信号が出力される。しかしながら、たとえば特開２００２−１３１６６２号に記載の方法を利用するなどして、これらの複数の走査開始信号ＳＯＳを表す信号を各グループに対応する走査開始信号ＳＯＳに分離し、分離した走査開始信号ＳＯＳを用いて各別にライン同期信号をすることで、ＳＯＳ検知グループごとに安定した走査開始信号ＳＯＳを得ることができる。これにより、高精度にビームスポット位置を制御することができる。
【０１２３】
そして、このように複数のＳＯＳ検知グループを組み合わせる構成においても、発光点に故障が生じた場合には、第１実施形態のように、その異常発光点を含むＳＯＳ検知グループを正常な発光点のみを含む他のグループに切り替えることで、走査開始信号ＳＯＳを正常に検知することができる。また、グループ内の一部のみでＳＯＳ検知グループを構成する場合において、それらの複数のグループを組み合わせて構成する場合、第２実施形態のように、グループ内の他の正常な発光点に切り替える対処方法を採用してもかまわない。
【０１２４】
図９は、ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第４実施形態を説明する図である。上記第１〜第３実施形態では、ＳＯＳ検知グループ内の発光点が故障した際、この異常発光点を含まない他のグループに置き換える、あるいは同一グループ内の他の正常な発光点に置き換えることで、走査開始信号ＳＯＳ信号を正常に検出するようにしていたが、この第４実施形態では、故障を検知したら比較の基準である検知閾値を変更することで故障に対処する点に特徴を有する。
【０１２５】
たとえば図９（Ａ）に示すように、走査開始信号生成部２７内の閾値電源ＳＰを出力電圧可変型の構成とする。そして、ＳＯＳ検知グループ点灯制御回路２２９が発光点の故障を検知すると、閾値電圧変更信号を閾値電源ＳＰの制御入力端子に入力する。この閾値電圧変更信号は、故障した発光点の数に応じた信号とすることが好ましい。閾値電源ＳＰは、閾値電圧変更信号に基づいて、元のＳＯＳ検知グループ内の発光点の数と故障数とに応じて検知閾値電圧を変更し比較器ＣＰに設定する。このことから分かるように、ＳＯＳ検知グループ点灯制御回路２２９と出力電圧可変型の閾値電源ＳＰとで、本発明に係る基準信号制御部が構成される。
【０１２６】
このような構成とすることで、たとえば図９（Ｂ）に示すように、発光点に故障が生じると、検知閾値電圧を変更しなければＰＤ出力を反映したＯＰ出力が低下し走査開始信号ＳＯＳが出力されない場合が生じるが、故障数に応じて検知閾値電圧を変更することで走査開始信号ＳＯＳを確実に出力させることができる。元々複数の発光点を利用して走査開始信号ＳＯＳを生成しているので、１つの発光点のみ点灯させて光検出器を走査する場合に比べて、閾値電圧を変更させてもノイズの影響が少なく、誤作動発生の虞れは少ない。
【０１２７】
なお、この場合、図９（Ｂ）に示すように、閾値電圧の変更に連動してΔ１やΔ２のように走査開始信号ＳＯＳの出力タイミングが若干ずれることがある。しかしながら、上記第１実施形態のようなグループ切替えとは異なり、同一グループ内での微小な変動であり殆ど問題とならない。Δ１やΔ２の変動が問題となる場合は、上記第１実施形態のように、その変動分を補正すればよい。
【０１２８】
以上説明したように、上記の各実施形態の画像形成装置１によれば、走査開始信号ＳＯＳの生成に用いる発光点（前例ではＶＣＳＥＬ３８０ａ）に故障が生じた場合であっても、異常発光点を補間するようにＳＯＳ検知グループを他のグループに切り替えたり、同一グループ内で他の正常な発光点に切り替えたり、あるいは検知閾値を変更するようにしたので、発光点の故障に伴う受光エネルギ量の減少の影響を受けることを防止することができ、この結果として走査開始信号ＳＯＳを確実に取得することができる。
【０１２９】
また、上記実施形態の画像形成装置１は、本願出願人が提案した特開２００２−１３１６６２号記載の方法を利用して、マルチビーム光源の各発光点を主走査方向の位置ごとにグループ分けし、グループ単位で点灯して、すなわち１グループのみもしくは複数グループを点灯して走査開始信号ＳＯＳを生成するようにしている。つまり、ＳＯＳ検出グループとして予め選択された、射出した光ビームによって被走査面上に形成されるビームスポットの走査方向に沿った位置が互いに略等しい複数の発光点を、この複数の発光点から射出された光ビームがＳＯＳ検知用光センサの受光面を横切る期間に各々点灯させている。これにより、ＳＯＳ検知用光センサの受光エネルギ量を大きくすることができ、この結果として安定した走査開始信号ＳＯＳを得ることができるなど、特開２００２−１３１６６２号記載の方法による効果を同様に享受することができる（詳細は特開２００２−１３１６６２号を参照）。
【０１３０】
以上、本発明を実施形態を用いて説明したが、本発明の技術的範囲は上記実施形態に記載の範囲には限定されない。発明の要旨を逸脱しない範囲で上記実施形態に多様な変更または改良を加えることができ、そのような変更または改良を加えた形態も本発明の技術的範囲に含まれる。
【０１３１】
また、上記の実施形態は、クレーム（請求項）にかかる発明を限定するものではなく、また実施形態の中で説明されている特徴の組合せの全てが発明の解決手段に必須であるとは限らない。前述した実施形態には種々の段階の発明が含まれており、開示される複数の構成要件における適宜の組み合わせにより種々の発明を抽出できる。実施形態に示される全構成要件から幾つかの構成要件が削除されても、効果が得られる限りにおいて、この幾つかの構成要件が削除された構成が発明として抽出され得る。
【０１３２】
たとえば、上記の各実施形態は、走査開始信号生成部２７として、本願出願人が特開２００２−１３１６６２号にて提案した構成のものを利用していたが、必ずしもこれに限定されるものではなく、マルチビーム光源の複数の発光点からの光であって、走査方向の位置ごとに分けられたグループ単位で点灯された光を受光することで、走査開始信号を生成する構成のものであれば、どのようなものであってもよい。たとえば特開２００２−１３１６６２号にて提案した構成は、２次元状に複数の発光点が配列されたマルチビーム光源を前提としたものであるが、上記第２実施形態や第４実施形態の手法を採用する場合には、複数の発光点がライン状に配列されたラインセンサであってもよい。
【０１３３】
また、上記の各実施形態は、走査開始信号ＳＯＳ検出用の専用の光検出器（前例ではフォトダイオードＰＤ）を含む走査開始信号生成部２７を使用したが、これに限らず、たとえば、ＳＯＳ検知用光センサに代えて、走査開始信号ＳＯＳ生成のためのレーザ光検知と、ＡＰＣのためのレーザ光の光量検知の双方を行なう役割を光量検出用センサ１６に担当させてもよい。この場合、光量検知用の光センサとＳＯＳ検知用の光センサとを光量検出用センサ１６で兼用するので、装置の構成を簡略化でき、低コスト化および小型化ができる。
【０１３４】
また、専用のＳＯＳ検知用光センサを用いる場合であっても、たとえば特開平５−３２３２２０号に記載の技術のように、ＳＯＳ検知用光センサを複数のフォトダイオードで構成してもよい。
【０１３５】
また、上記実施形態では、正常時のＳＯＳ検知グループを最も早いタイミングで光検知器を走査するグループとした場合について説明したが、これに限定されるものではなく、他のグループを正常時のＳＯＳ検知グループとしてもよく、この場合、メモリコントローラ２２８の設定を適正化すれば問題はない。これは、正常時にＧ１グループをＳＯＳ検知グループする場合において、異常時に他のグループをＳＯＳ検知グループする場合の変更態様と同じである。
【０１３６】
また、上記実施形態では、メモリコントローラ２２８によるビデオメモリ読出許可信号の遅延をビデオクロック信号単位で行なう場合について説明したが、これに限定されるものではなく、アナログ素子やロジックゲートによる遅延を利用した微調整機構を備えることによって、より高精度にＧ２〜Ｇ４グループに属する発光点のビームスポット位置を制御することができる。
【０１３７】
また、上記実施形態では、ＳＯＳ検知グループ（正常時はＧ１グループ）とそれ以外のグループ（正常時はＧ２〜Ｇ４グループ）とのビーム位置オフセットの補正を設計値に応じて行なう場合について説明したが、これに限定されるものではなく、測定値に応じて行なう形態とすることもできる。
【０１３８】
また、図１１（Ｂ）に示したように、Ｇ１グループ、Ｇ２グループ、Ｇ３グループ、およびＧ４グループと各々を構成する複数のＶＣＳＥＬの間でもオフセットがある場合、各ビーム単位でタイミング調整を行なう構成とすることによって、上記の各実施形態と同様の対処が可能である。
【０１３９】
また上記実施形態では、発光点にＶＣＳＥＬを配していたが、ＶＣＳＥＬに限らず、端面発光型のレーザアレイ、あるいはＬＥＤなどを並べても上記実施形態の効果に変わりない。なお、ＶＣＳＥＬを配した２次元アレイの光源群の場合、１つの半導体チップ上に２次元状に発光部が配列されたモノリシック構造とできる。また、ＶＣＳＥＬでは、レーザ光の出射部の断面積が、従来の端面発光型の半導体レーザに比べて大きくとれるため、レーザ光の拡がり角は小さくなる。よって、コンパクトな光源とすることができる。
【０１４０】
また上記実施形態では、偏向装置としてポリゴンミラー（回転多面鏡）を用いていたが、このほか、ガルバノミラーやホログラムディスクなど光の方向を周期的に偏向できるものであれば、上記例と同等の効果を有する。また、光学系の構成においてコリメータレンズ、走査レンズ、倒れ補正光学系は必須のものではなく、その有無は上記の効果に影響を与えない。
【０１４１】
【発明の効果】
以上のように、走査開始信号ＳＯＳの生成に用いる発光点に故障が生じた場合に、この異常発光点を補間するように、走査開始信号ＳＯＳ信号を検出するためのＳＯＳ検知グループを他のグループに切り替えたり、同一グループ内で他の正常な発光点に切り替えたりする第１の構成とすれば、発光点の故障に伴う受光エネルギ量の減少の影響を受けることを防止することができ、この結果として走査開始信号ＳＯＳやライン同期信号ＬＳを確実に取得することができる。
【０１４２】
また、ＳＯＳ検知グループの発光点から発せられた光のエネルギを表す信号と基準信号とを比較することで走査開始信号ＳＯＳを生成する場合において、走査開始信号ＳＯＳの生成に用いる発光点に故障が生じた場合に、比較対象の基準信号を、走査開始信号が正常に検出できる方向に制御する第２の構成としても、第１の構成と同様に、発光点の故障に伴う受光エネルギ量の減少の影響を受けることを防止することができ、この結果として走査開始信号ＳＯＳやライン同期信号ＬＳを確実に取得することができる。
【０１４３】
そしてこれにより、第１あるいは第２の構成の何れにおいても、走査開始信号の検知に関わる発光点が故障した場合であっても、正しい書出位置から露光を行なうことができ、画像を正常に形成することができる。
【図面の簡単な説明】
【図１】ＶＣＳＥＬ光源群を用いてカラー画像を記録する画像形成装置の一例の機構図である。
【図２】上記の画像形成装置に使用される光走査装置の構成例を示す図である。
【図３】ＶＣＳＥＬ光源群から発せられるレーザビームによる被走査面における走査線と結像スポットの関係を示す図である。
【図４】ＶＣＳＥＬ光源群を備えた画像形成装置にて画像を形成するための処理回路（画像記録制御部）の概要を示す図である。
【図５】画像形成装置における露光制御に関わる部分を示す機能ブロック図である。
【図６】図５に示す露光制御機能部分の要部信号を示すタイミングチャートである。
【図７】ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第２実施形態を説明する図である。
【図８】ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第３実施形態を説明する図である。
【図９】ＳＯＳ検知グループの設定方法と発光点異常時の対処方法の第４実施形態を説明する図である。
【図１０】マルチビーム光源を用いた光走査装置の一例を示す図である。
【図１１】光検出器の一例を説明する図である。
【図１２】特開２００２−１３１６６２号に記載のＳＯＳ検知の手法を説明する図である。
【符号の説明】
１…画像形成装置、５…画像取得部、７…画像データ生成部、１０…光走査装置、１１…レンズ群、１２…マルチビーム光源、１４…ハーフミラー、１６…光量検出用センサ、１９…回転多面鏡（ポリゴンミラー）、２７…走査開始信号生成部、３０…潜像記録部、３２…感光体ドラム、５０…搬送部、２２０…書込信号生成部、２２２…Ｉ／Ｆ部、２２４…変調信号生成部、２２６…ラインバッファメモリ群、２２８…メモリコントローラ、２２９…ＳＯＳ検知グループ点灯制御回路、２３０…タイミング信号発生部、２３３…発振器、２３４…クロック位相同期回路、２５５…オフセットレジタ部、２５６…カウンタ回路部、２７０…マシンコントローラ、３００…レーザ駆動回路、３０４…光量設定条件選択部、３０６…レベル変更部、３０８…駆動量制御部、３１０…駆動制御部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus using a multi-beam light source having a plurality of light emitting points. More specifically, the present invention relates to a countermeasure against a failure of a light emitting point when a scanning start signal is generated by receiving a light beam from the light emitting point.
[0002]
[Prior art]
2. Description of the Related Art Recent advances in network technology and higher performance of computers have demanded higher resolution of an image recording device as an output device. For example, in a printer, in order to output a high-quality image, high resolution is pursued, and accordingly, the resolution has been increased to 400 dpi (dot per inch; the number of print dots per inch), 600 dpi, and 1200 dpi. Was. For example, in a laser printer, an improvement in the scanning density of a laser beam is required in order to cope with higher image quality.
[0003]
In the image recording apparatus, high productivity such as improvement in output speed (print speed) has been pursued. In order to respond to the demand for writing speed which increases with this, for example, a rotating polygon mirror (scanning with a laser beam) is used. The speed of polygon mirrors has been increased. Further, a multi-beam scanning device for simultaneously scanning a plurality of laser beams to form a single color image has been put to practical use, and high-speed and high-quality images have been improved. For example, there are cases where a dual beam laser scanning optical system using two laser beams is used.
[0004]
On the other hand, as a writing technique for obtaining higher definition of writing resolution and higher productivity, a case in which ten or more multi-beams are used, a VCSEL in which a plurality of light emitting points are two-dimensionally arranged. (Vertical Cavity Surface Emitting Laser) is a technology that uses a light source as a light source.
[0005]
In this technique, a plurality of laser beams output from a VCSEL are deflected by a rotating polygon mirror (polygon mirror) to increase the number of beams simultaneously scanned on the photoconductor, thereby improving a substantial scanning rate. Higher speed and higher resolution have been achieved.
[0006]
FIG. 10 is a diagram showing a conventional example of an optical scanning device using a multi-beam light source. The multi-beam light source is configured as a VCSEL light source group 380 by arranging VCSELs 380 a in a two-dimensional array on a semiconductor substrate 381. The plurality of laser beams L emitted from the individual light emitting points of the VCSEL light source group 380, that is, the VCSEL 380a, are collimated (parallelized) into laser beams having a predetermined beam diameter by the collimator lens 382. This laser light is incident on the polygon mirror 339 via the cylindrical lens 387, and is reflected by its reflection surface (there are six surfaces in the figure) and deflected as the polygon mirror 339 rotates.
[0007]
The laser light L reflected and deflected by the polygon mirror 339 passes through a toroidal lens 388 having a tilt correction function and a scanning lens group 384 having an fθ function, and is a photosensitive drum 332 as an image carrier placed on the surface to be scanned. Is formed on the spot 386 on the surface to be scanned.
[0008]
By the way, in an optical scanning device, in general, a laser beam output from a light source is reflected and scanned by a rotating polygon mirror to perform exposure on a photosensitive member. It is necessary to adjust the writing position.
[0009]
For this reason, in the optical scanning device having the above-described configuration, the reflection mirror 391 and the photodetector (scanning start signal detection unit) 392 are placed in a position within the deflection range of the laser beam and not involved in scanning the surface to be scanned. The laser light L1 reflected at 391 is arranged so as to enter the photodiode PD in the photodetector 392. Since the laser beam L1 turned back by the reflection mirror 391 is detected by the photodetector 392, the laser is turned on immediately before the laser beam L1 is deflected by the photodiode PD during the scanning period, and the laser beam is necessary for the original scanning. Control for turning off the light in the middle of the scanning range is performed.
[0010]
Then, the spectral component (laser light L1) of the scanning beam is detected by a photodetector 392 arranged so that the laser beam at the start of the main scanning is incident, and the scanning start signal SOS (SOS ( Start of Scan), and controls the main scanning and the start of laser beam modulation according to image data based on the generated scanning start signal SOS.
[0011]
For example, a line synchronization signal LS (Line Sync) is created based on the scanning start signal SOS, and is used as a timing signal at the time of exposure. At this time, the offset amount (hereinafter referred to as LS offset) between the scanning start signal SOS and the line synchronization signal LS depends on the positional relationship between the photodetector 392 as the SOS sensor and the image writing start position P1 on the photosensitive drum 332, and the laser light. It is determined by the light scanning speed of L and the like.
[0012]
11A and 11B are diagrams illustrating an example of the photodetector 392, in which FIG. 11A is a circuit block diagram, FIG. 11B is a diagram illustrating an example of an output waveform in a normal state, and FIG. (C) is a diagram showing an example of an output waveform when a light source having a plurality of light emitting points is used.
[0013]
As shown in FIG. 11A, a photodetector 392 is a photodiode PD, which is an example of a light receiving unit that flows a current corresponding to the amount of incident light, amplifies an input current, and obtains I (current) / V (voltage). ) It comprises an amplifier OP for conversion, a threshold power supply SP for generating a voltage indicating a threshold, and a comparator CP for comparing each output voltage of the amplifier OP and the threshold power SP. In the photodetector 392, as shown in FIG. 11B, when the OP output, which is the output voltage of the amplifier OP, becomes higher than the threshold voltage, the scanning start signal SOS becomes high level. The photodiode PD is used as an SOS detection optical sensor.
[0014]
In addition to applying such a photodetector 392 as a means for generating the scanning start signal SOS, an optical scanning device using a multi-beam light source in which a plurality of VCSELs (light emitting points) are two-dimensionally arranged is used. When the photodetector 392 is scanned while all the laser beams are turned on when the two-dimensional arrangement is close to each other, as shown in FIG. 11C, the output voltage of the amplifier OP between the beams cannot be reduced completely. When the voltage becomes close to the threshold voltage, the scanning start signal SOS becomes a single rectangular wave like the scanning start signal SOS1 in the figure or a rectangular falling like a scanning start signal SOS2 for each laser beam. There is a problem that a stable scanning start signal SOS cannot be obtained due to a wave shape.
[0015]
As one method of solving this problem, the present applicant divides each light emitting point of the multi-beam light source into groups in the main scanning direction, and turns on only one group or a plurality of groups to generate the scanning start signal SOS. A method has been proposed (see JP-A-2002-131662).
[0016]
FIG. 12 is a diagram illustrating a method of generating a scanning start signal SOS (hereinafter, also referred to as SOS detection) proposed by the present applicant in Japanese Patent Application Laid-Open No. 2002-131662. Here, FIG. 12A shows an example in which the positions of the beams in the light scanning direction are completely aligned, and FIG. 12B shows an offset between a plurality of groups and a plurality of VCSELs constituting each. FIG. 12C shows an example of an output waveform at the time of an abnormality.
[0017]
As shown in FIGS. 12A and 12B, a VCSEL group (hereinafter referred to as an SOS detection group) that emits a laser beam in which a beam spot formed on a photoconductor has substantially the same position in the light scanning direction (main scanning direction). Is turned on, the photodiode PD for scanning SOS in the photodetector 392 is scanned, and a scanning start signal SOS is generated according to the output from the photodiode PD according to this scanning. Thereby, a stable scanning start signal SOS can be obtained. When the line synchronization signal LS is created from the scanning start signal SOS, the line synchronization signal LS is created for each group and an image is output.
[0018]
The offset OF (OF2, OF3 in the figure) between the scanning start signal SOS and each line synchronizing signal LS is the distance between the photodiode in the photodetector 392 for SOS detection and the image writing start position on the photosensitive drum, the laser , And the beam spot offset distance between the groups when exposed on the photosensitive drum.
[0019]
[Problems to be solved by the invention]
However, when the light emitting point of the group used for detecting the scanning start signal SOS is in an abnormal state, the fluctuation component of the amplifier output (OP output) is a voltage near the threshold voltage as shown in FIG. , The scanning start signal SOS becomes unstable due to insufficient light amount, or the scanning start signal SOS cannot be detected (no detection). If the scan start signal SOS cannot be normally detected, the line synchronization signal LS and the like to be generated based on the scan start signal SOS cannot be normally generated, and as a result, normal image formation cannot be performed.
[0020]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above-described circumstances. In the configuration in which the SOS detection photodetector is scanned in the lit state and the scan start signal SOS is generated in accordance with the output from the photodetector corresponding to the scan, any of the light emission in the SOS detection group is generated. It is an object of the present invention to provide an image forming apparatus capable of stably obtaining a synchronization signal such as a scanning start signal even when an abnormality occurs in a point.
[0021]
[Means for Solving the Problems]
That is, the first image forming apparatus according to the present invention forms a light beam emitted from each of the light-emitting points of a multi-beam light source having a plurality of light-emitting points that can be independently modulated on a surface to be scanned. Scanning start to generate a scanning start signal by receiving light emitted from a plurality of light emitting points of the multi-beam light source, the lights being turned on in units of groups divided for each position in the scanning direction. A signal generation unit, generates image data for recording corresponding to a plurality of light-emitting points based on the image data, drives the light-emitting points based on the generated image data for recording, and generates a scan start signal. An image writing signal generation unit that controls image writing timing based on the generated scanning start signal.
[0022]
Further, the first image forming apparatus according to the present invention further detects a light emitting state of a light emitting point related to detection of a scanning start signal among a plurality of light emitting points of the multi-beam light source, and based on the detection result, A light source state determining unit that determines whether the light emitting state of the light emitting point is abnormal, and an abnormal light emitting point that is determined to be abnormal as indicated by the determination result of the light source state determining unit complements the light emitting point, and in group units. A light-emitting point switching unit that switches the abnormal light-emitting point to the remaining light-emitting point among the plurality of light-emitting points so that the light-emitting point is turned on.
[0023]
The light emitting point switching unit switches, for example, a group including the abnormal light emitting point to one of the groups excluding the group including the abnormal light emitting point, or an abnormal light emitting point within the group including the abnormal light emitting point. Can be switched to another light emitting point.
[0024]
When the light emitting point switching unit performs group switching, the image writing signal generation unit writes an image in accordance with the difference in the scanning direction between the group including the abnormal light emitting point and the group switched by the light emitting point switching unit. It is desirable to adjust the timing.
[0025]
Further, the second image forming apparatus according to the present invention forms an image on a surface to be scanned with light beams emitted from individual light emitting points of a multi-beam light source having a plurality of light emitting points that can be independently modulated. The optical system receives light emitted from a plurality of light-emitting points of the multi-beam light source, the light being turned on in a group unit divided for each position in the scanning direction, and a signal representing the energy of the received light and a signal. A scan start signal generation unit that generates a scan start signal by comparing the scan start signal with a predetermined reference signal.
[0026]
In addition, the second image forming apparatus according to the present invention further generates recording image data corresponding to a plurality of light emitting points based on the image data, and generates light emitting points based on the generated recording image data. And an image writing signal generator for controlling image writing timing based on the scanning start signal generated by the scanning start signal generator, and detecting a scanning start signal among a plurality of light emitting points of the multi-beam light source. The light emitting state of the light emitting point related to is detected, it is determined whether the light emitting state of the light emitting point is abnormal based on the detection result, and a reference signal used by the scanning start signal generation unit is determined based on the determination result. And a reference signal control unit for controlling.
[0027]
[Action]
In the above-described first image forming apparatus, the scanning start signal generation unit generates a scanning start signal by receiving light that is turned on in units of groups of the multi-beam light source that are divided for each position in the scanning direction. . At this time, the light source state determination unit detects the light emitting state of the light emitting point related to the detection of the scanning start signal, and determines whether the light emitting state of the light emitting point is abnormal based on the detection result. The light emitting point switching unit switches the abnormal light emitting point to the remaining normal light emitting points so as to complement the abnormal light emitting point, that is, so that the scanning start signal can be normally detected and the lighting is performed in group units. For example, the group including the abnormal light emitting point is switched to another group having only the normal light emitting point, or the abnormal light emitting point is switched to another light emitting point in the group including the abnormal light emitting point.
[0028]
In the above-described second image forming apparatus, the scan start signal generation unit generates a scan start signal by comparing a signal representing the energy of light that is turned on in group units with a predetermined reference signal. . At this time, the reference signal control unit detects the light emitting state of the light emitting point related to the detection of the scanning start signal, and determines whether the light emitting state of the light emitting point is abnormal based on the detection result. Based on the determination result, the reference signal used by the scanning start signal generator is controlled in a direction in which the scanning start signal can be normally detected.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0030]
FIG. 1 is a mechanism diagram of an example of an image forming apparatus that records a color image using a VCSEL light source group in which surface emitting semiconductor lasers (VCSELs), which are examples of a multi-beam light source, are two-dimensionally arranged.
[0031]
The image forming apparatus 1 records an image on a predetermined recording medium using an electrophotographic process (xerography), and includes an optical scanning device 10, a latent image recording unit 30, and a transport unit 50. . The image forming apparatus 1 is used as a printing function part of, for example, a printer or a copier.
[0032]
In the optical scanning device 10, laser light (laser beam) emitted from a semiconductor laser (not shown) comprising a VCSEL light source group is directed by a polygon mirror (rotating polygon mirror) 19 to a photosensitive drum 32 which is an example of a photosensitive member. The laser beam modulated by the image information is reflected and deflected to form an image on the surface to be scanned on the photosensitive drum 32 by the lens group 11.
[0033]
Although not shown in the figure, the lens group 11 includes various lenses constituting an optical system such as a collimator lens and a scanning lens, or a half-beam for causing laser light emitted from the VCSEL to enter a light amount detection sensor. In this configuration, a mirror and the like are arranged on the optical axis of the laser light.
[0034]
In the latent image recording section 30, first, the surface of the photosensitive drum 32 rotating in the direction of the arrow is charged by the charger 33. The laser beam reflected and deflected by the polygon mirror 19 of the optical scanning device 10 further scans the photosensitive drum 32 charged by the primary charger 33 via the lens group 11 so that an image portion or a background portion is formed. The photosensitive drum 32 is selectively exposed to light to form an electrostatic latent image on the photosensitive drum 32. This electrostatic latent image is formed into a visible image as a toner image by a developing device 34 to which toners of respective colors of Y (yellow), M (magenta), C (cyan), and K (black) (hereinafter collectively referred to as YMCK) are supplied. The toner image is transferred to the intermediate transfer belt 43 by the primary transfer device 35. The toner remaining on the photosensitive drum 32 after the primary transfer is collected from the surface of the photosensitive drum 32 by the cleaner 36.
[0035]
In the transport unit 50, first, the toner image on the intermediate transfer belt 43 is transferred by the secondary transfer unit 52 onto the sheet transported from the sheet tray 56 by the sheet transport roll 54 or the like, and the toner image is fixed by the fixing unit 58. Is fused and fixed on the paper.
[0036]
The image forming apparatus 1 is a color image forming apparatus, and develops in each cycle so that charging, exposure, development, and primary transfer are repeated for each color of YMCK (four times) to form a full-color image. The toner to be developed is switched by rotating the container 34 by 90 degrees. That is, in the image forming apparatus 1, the electrostatic latent images of the respective colors of YMCK are sequentially formed on one photosensitive drum by one laser beam scanner, and the electrostatic latent images are provided around the photosensitive drum. Further, toner images of respective colors of Y, M, C, and K are sequentially formed into toner images by a developing device, and the toner images are adsorbed on an intermediate transfer belt and sequentially transferred in a multiplex manner.
[0037]
Since the four-color toner images are superimposed on the intermediate transfer belt 43, the sheet is not conveyed to the secondary transfer unit 52 until the formation of the four-color image is completed. When the sheet is in contact with the transfer belt 43, the secondary transfer section 52 is retracted so as not to touch the intermediate transfer belt 43 until the sheet is conveyed.
[0038]
Note that the image forming apparatus 1 may have a so-called tandem configuration in which printing units (image forming units) on which an image forming process is performed are prepared by the number of color materials and arranged in a line in the sheet conveying direction. .
[0039]
FIG. 2 is a diagram illustrating a configuration example of the optical scanning device 10 used in the image forming apparatus 1 described above. The optical scanning device 10 uses a VCSEL light source group 380 that is an example of a multi-beam light source that emits a plurality of laser beams.
[0040]
As shown in the drawing, the optical scanning device 10 includes a VCSEL light source group 380 in which a plurality of VCSELs 380a are two-dimensionally arranged. On the light emission side of the VCSEL light source group 380, a collimating lens 13, a half mirror 14, An aperture 17, a cylindrical lens 18, and a polygon mirror 19 are sequentially arranged.
[0041]
Further, the optical scanning device 10 includes a lens 15 for condensing a part of the oscillator light separated by the half mirror 14, and a light amount detection sensor 16 for detecting the laser light condensed by the lens 15. Further, fθ lenses 21 and 22, cylindrical mirrors 24 and 25, and a photosensitive drum 32 are arranged in this order on the light deflection side of the polygon mirror 19 of the optical scanning device 10. The cylindrical mirrors 24 and 25 have a tilt correction function of making the scanned surface of the polygon mirror 19 and the photosensitive drum 32 conjugate in the sub-scanning direction.
[0042]
In addition, the optical scanning device 10 detects the laser beam reflected by the pickup mirror 26 and the pickup mirror 26 that reflects the laser beam before the scanning, and generates the scanning start signal SOS as a mechanism for generating the scanning start signal SOS. A scanning start signal generation unit (SOS sensor) 27 for generating is provided.
[0043]
The laser light emitted from each VCSEL 380 a of the VCSEL light source group 380 is converted into substantially parallel light by the collimator lens 13, passes through the half mirror 14, and is shaped by the aperture 17. The aperture 17 is desirably arranged near the focal position of the collimator lens 13 to evenly shape the plurality of beams. The laser beam shaped by the aperture 17 passes through the cylindrical lens 18 and is turned back by the turning mirror 20, and then is imaged on the reflecting surface (having six surfaces in this example) of the polygon mirror 19. At this time, the laser light is condensed by the cylindrical lens 18 having power only in the sub-scanning direction, in the vicinity of the reflection surface of the polygon mirror 19, in a long line in the main scanning direction.
[0044]
In this process, a part of the laser light L is separated by the half mirror 14, and the separated laser light L2 is guided to the light quantity detection sensor 16 via the lens 15. Since the surface emitting laser cannot emit a beam from the rear side of the resonator unlike the edge emitting laser, the light amount control is realized by separating a part of the laser light and detecting the light amount. .
[0045]
The polygon mirror 19 is rotated by a drive motor (not shown), and deflects and reflects the laser light in the main scanning direction. The laser light deflected and reflected by the polygon mirror 19 is moved at substantially the same speed in the main scanning direction by the Fθ lenses 21 and 22 having power only in the main scanning direction, and further, has a cylindrical shape having power only in the sub-scanning direction. An image is formed on the photosensitive drum 32 by the mirrors 24 and 25.
[0046]
As described above, the optical scanning device 10 reflects and deflects the laser light emitted from the VCSEL light source group 380 by the polygon mirror 19 and forms an image on the photosensitive drum 32 via the fθ lenses 21 and 22. The main scan is performed by the rotation of the polygon mirror 19 in the direction of arrow A, and the sub-scan is performed by the rotation of the photosensitive drum 32 in the direction of arrow B.
[0047]
A pickup mirror 26 is provided in the vicinity of the photosensitive drum 32 and at a main scanning start position by the laser beam, and a scanning start signal constituted by a photodiode, an amplifier, a comparator, and the like is provided in a reflection direction of the pickup mirror 26. A generation unit 27 is provided so that the laser beam L1 at the start of main scanning is incident on the photodiode PD.
[0048]
The scanning start signal generator 27 has the same configuration as the photodetector 392 described in the related art. Since the photodiode PD outputs a weak voltage corresponding to the intensity of the incident laser light L1, it is amplified by the amplifier OP and compared with the threshold voltage by the comparator CP to extract the scanning start signal SOS. I do. That is, the scanning start signal SOS is generated by the scanning start signal generation unit 27 in accordance with the incidence of the laser light on the photodiode PD.
[0049]
In order for the scanning start signal generation unit 27 to detect the laser beam L1, the laser is turned on immediately before the laser beam L1 is deflected by the photodiode PD during the scanning period, and the laser is turned on just before the scanning range necessary for the original scanning. Control for turning off the light is performed. The image writing start position Q1 is defined by the scanning start signal SOS output from the scanning start signal generation unit 27, and the modulation start of the laser beam according to the image data is controlled.
[0050]
FIG. 3 is a diagram showing a relationship between a scanning line on a surface to be scanned and an imaging spot by a laser beam emitted from the VCSEL light source group 380. The illustrated VCSEL light source group 380 is obtained by arranging VCSELs 380a two-dimensionally on the surface of a semiconductor substrate so as to be 8 × 4 and generates 8 × 4 = 32 laser beams. In addition, it is not limited to 8 × 4, but 4 × 8, 8 × 2, 8 × 4, 4 × 4, 4 × 2, or 3 × 3, etc. Is also possible.
[0051]
In the optical scanning device 10 of the present embodiment, the vertical arrangement (eight in this example) of the VCSEL light source group 380 is arranged in the vertical direction with respect to the polygon mirror 19, that is, the photosensitive member which is the surface to be scanned. It is arranged so as to be optically parallel to the sub-scanning direction on the drum 32. This arrangement form is called vertical arrangement. It should be noted that the VCSEL light source group 380 is arranged so that the vertical arrangement is horizontal to the polygon mirror 19, that is, it is optically parallel to the sub-scanning direction on the photosensitive drum 32 which is the surface to be scanned. The arrangement form is called horizontal arrangement.
[0052]
As shown in the figure, the VCSEL light source group 380 has a base line (one point in the drawing) having an angle φ with respect to the main scanning direction and an arbitrary line (main scanning line) in the main scanning direction and passing over the VCSEL 380a on the main scanning line. An array pattern is defined by a dashed line (inclination line). Each VCSEL 380a is formed on a single semiconductor substrate, and eight at equal intervals along an arbitrary line (sub-scanning line) in the sub-scanning direction and four at equal intervals along the main scanning line, for a total of eight. × 4 VCSELs 380a are arranged in a two-dimensional matrix. Reference numerals L1 to L32 indicate sub-scanning lines.
[0053]
In the VCSEL light source group 380, each VCSEL 380a (that is, a light-emitting point) is located at each vertex of a parallelogram, and a scanning line of a predetermined resolution (for example, 2400 dpi) is formed on the photosensitive drum 32 by being inclined at an appropriate angle. To make up. For example, when the interval in the main scanning direction of the VCSEL 380a, that is, the beam spot offset distance on the photosensitive drum 32 is OD (Offset Distance), the interval Δ between the sub-scanning lines is set to OD × tanφ.
[0054]
In other words, the spot formed by the laser beam periodically moves at a substantially constant speed in the main scanning direction (from the left to the right in the figure), and the scanning lines are scanned at equal intervals at a pitch Δ. The scanning surface moves by a predetermined interval in the sub-scanning direction in the figure. Regardless of the positional relationship of the positions of the spots to be scanned, the movement of the scanned surface in the sub-scanning direction is equivalent to 32 scanning lines per main scanning cycle. Note that the figure shows two main scans, and the positions of the first and second VCSEL light source groups 380 are shown shifted from each other in the main scanning direction, but this is convenient for illustration. Thus, the scanning actually starts from the same position.
[0055]
During scanning, the laser is turned on / off or the intensity is modulated according to the image density according to the image data. The start of the modulation or the lighting control is performed based on the scan start signal SOS output from the scan start signal generation unit 27. At this time, a total of 32 8 × 4 laser beams operate simultaneously. By repeating this operation, the entire surface to be scanned is completely and completely filled with equally spaced scanning lines, and two-dimensional scanning is realized. Such a scanning form is called adjacent exposure. Of course, the present invention can be used not only in adjacent exposure but also in a multiple exposure mode in which exposure is performed with a part of the exposure being overlapped.
[0056]
It should be noted that if the distance measured in the sub-scanning direction from one spot to another spot in the sub-scanning direction is divided by the scanning line pitch Δ, and the remainder divided by the number of scanning lines scanned simultaneously is a natural number different from each other, they always overlap. The surface to be scanned can be filled with equally spaced scanning lines without the need. The interval OD of the spot in the main scanning direction can be set arbitrarily as long as the interval Δ = OD × tanφ of the sub-scanning lines is satisfied.
[0057]
Here, since the VCSEL 380a is arranged such that the image forming position in the main scanning direction is shifted by OD, each light beam corresponding to one line on the image data emitted from the VCSEL 380a as a light emitting point is emitted in the sub-scanning direction. By performing delay control on the modulated signal of each VCSEL 380a by a data delay unit (for example, a 4-bit FIFO or an 8-bit FIFO) so as to form an image substantially on one line, the signal has 32 lines (4 × 8 lines). Are simultaneously scanned adjacently.
[0058]
In the optical scanning device 10 according to the present embodiment, as shown in FIG. 11 of the related art, a laser beam is emitted from the beam spot formed on the photosensitive drum 32 at a position substantially equal in the optical scanning direction (main scanning direction). With the VCSEL group (SOS detection group) to be turned on, the photodiode PD in the scan start signal generation unit 27 is scanned, and the scan start signal SOS is generated according to the output from the photodiode PD according to this scan. I do.
[0059]
The definition of the “SOS detection group that emits laser beams having substantially the same position in the optical scanning direction” in the present embodiment is as follows. That is, when all VCSELs 380a constituting the SOS detection group are turned on, the total exposure energy profile on the photodiode PD in the light scanning direction and the detection threshold of the scanning start signal generation unit 27 (the voltage of the threshold power supply SP in FIG. (Threshold indicated by) intersects at only two points.
[0060]
Thus, when all VCSELs 380a belonging to the SOS detection group are turned on, the combined energy distribution of each light beam on the light receiving surface of the photodiode PD is set between the beam centers of the individual light beams along the light scanning direction. The distribution can be such that a portion having an energy level lower than the detection threshold does not occur in a corresponding portion. At this time, as shown in FIG. 3 (see also FIG. 12A), even if the positions of the beams in the light scanning direction are not completely aligned, as shown in FIG. Any group that satisfies the condition may be set as the SOS detection group.
[0061]
Here, as a factor of the positional deviation of the beam spot on the photosensitive drum 32, a light emitting point interval error on the VCSEL 380a, a characteristic error of the optical member of the optical scanning device 10, and a mounting position error can be considered. However, since the VCSEL light source group 380 is formed by a semiconductor process, the light emitting point interval error on the VCSEL light source group 380 becomes sub-μm or less, which is not a problem. In addition, regarding the characteristic error and the mounting position error of the optical member of the optical scanning device 10, a certain mechanism for adjusting the mounting position after appropriately designing and manufacturing each optical member is provided. Although there is a displacement, a beam spot position almost as calculated can be obtained.
[0062]
Therefore, when the scanning start signal SOS is generated using only one group (G1 group) as the SOS detection group as shown in FIG. 12A of the related art, the SOS detection group is different from the SOS detection group in the main scanning direction. The lighting timings of the laser beams of the other groups that are offset (here, the G2 group and the G3 group) are corrected so that the designed beam position offset is corrected with respect to the timing derived based on the generated scanning start signal SOS. By adding or subtracting the timing correction time HT obtained by the following equation (1), a sufficient quality image can be obtained when the optical scanning device 10 is applied to the image forming apparatus 1. it can. However, OD (Offset Distance) is a beam spot offset distance on the photosensitive drum 32, and SS (Scan Speed) is a beam spot scanning speed on the photosensitive drum 32.
(Equation 1)

[0063]
FIG. 4 is a diagram illustrating an outline of a processing circuit (image recording control unit) for forming an image in the image forming apparatus 1 including the VCSEL light source group 380 having the above configuration. The scanning start signal generation unit 27 receives the light that is turned on in a unit of each VCSEL 380a of the VCSEL light source group 380, which is an example of a multi-beam light source, divided for each position in the scanning direction, and thereby receives a scanning start signal. Generate At this time, the image recording control unit detects the light emitting state of the light emitting point related to the detection of the scanning start signal, and determines whether the light emitting state of the light emitting point is abnormal based on the detection result.
[0064]
Then, the abnormal light emitting points are switched to the remaining normal light emitting points so that the abnormal light emitting points are complemented, that is, so that the scanning start signal can be normally detected and the lighting is performed in group units. For example, the group including the abnormal light emitting point is switched to another group having only the normal light emitting point, or the abnormal light emitting point is switched to another light emitting point in the group including the abnormal light emitting point. Alternatively, the reference signal (detection threshold) used by the scan start signal generation unit 27 is controlled based on the determination result of the abnormal state so that the scan start signal can be normally detected.
[0065]
Here, “to generate the scanning start signal SOS by lighting in groups” means that the light emitting points of the multi-beam light source are grouped for each position in the main scanning direction and lighted, and the light emitting points of the group are turned on. Any device that receives light and generates the scan start signal SOS may be used. It does not matter whether the number of groups is one group or a combination of a plurality of groups. Further, the present invention is not limited to the one in which all the light emitting points in the group are turned on and receives light, but may be the one in which some light emitting points in the group are turned on and received. This will be specifically described below.
[0066]
As shown in FIG. 4, the image recording control unit includes an image acquisition unit 5 such as a scanner, or an image data generation unit 7 that acquires image data from a client terminal such as a personal computer via a network, and an image data generation unit 7. And a write signal generation unit 220 that generates a laser modulation signal for each VCSEL 380a based on the image data from.
[0067]
The image data generation unit 7 converts the RGB color system image data input from the image acquisition unit 5 and the like into YCrCb color system image data, and further performs mapping from the YCrCb color system to the CMYK color system. Raster data (halftone data) representing a halftone image or a character image with a resolution of 600 dpi / multi-gradation (for example, 8 bits), which is color-separated for print output, is passed to the write signal generation unit 220.
[0068]
At this time, under color removal (UCR) for reducing the CMY components of the color image and gray component replacement (GCR) for partially replacing the CMY components with the reduced colors with the K component are performed. Further, in order to adjust a toner image of an output image created in response to output data (CMYK or the like), processing such as linearization of color separation is performed.
[0069]
The write signal generation unit 220 includes an I / F (interface) unit 222 that functions as an interface with the image data generation unit 7, a modulation signal generation unit 224 that generates a laser modulation signal (light beam modulation signal), and a plurality of write signal generation units. It has a line buffer memory (video memory) 226a and a line buffer memory group 226 for roughly adjusting the write timing for the laser modulation signal from the modulation signal generation unit 224. This line buffer memory group 226 functions as a data delay unit.
[0070]
The write signal generation unit 220 includes a memory controller 228 that controls the I / F unit 222, the modulation signal generation unit 224, and the line buffer memory group 226, and the I / F unit 222, the modulation signal generation unit 224, and the line buffer memory. A group 226 and a timing signal generator 230 for controlling the memory controller 228.
[0071]
Further, the image recording control unit includes a synchronization signal generator 260 for generating a reference signal for controlling a writing timing based on the scanning start signal SOS obtained from the scanning start signal generation unit 27 of the image forming apparatus 1, and a color copying machine. A machine controller 270 which is a functional part for controlling the entire apparatus 1 is provided.
[0072]
The timing signal generator 230 receives various signals from the scan start signal SOS indicating that the scanning beam has reached the position immediately before the photosensitive drum 32 is incident on the photosensitive drum 32 and the print request signal PRQ output from the machine controller 270 to start image recording. A control signal is generated and supplied to each unit. For example, the writing reference signal ROS_PS, the line selection signal ROS_LS, the page synchronization signal Page, or the pixel clock PCK.
[0073]
The timing signal generator 230 determines the phase difference between the page synchronization signal Page for instructing the start of image recording in the sub-scanning direction and the scanning start signal SOS, and controls the memory controller 228. The memory controller 228 gives margin data to the writing to each line buffer memory 226a according to the phase difference, and adjusts the image recording position on the photosensitive drum 32 in the sub-scanning direction.
[0074]
In addition, the image forming apparatus 1 controls the laser drive circuit (multi-LDD) 300 that drives the individual VCSELs 380a of the VCSEL light source group 380 based on the laser modulation signal and various types of drive currents for controlling the individual VCSELs 380a. A drive control unit 310 that controls a control signal and a rotation amount of the photosensitive drum 32 (a rotation amount in the sub-scanning direction).
[0075]
The drive control unit 310 controls the individual VCSELs 380a based on a temperature sensor (not shown), the number of used mirrors of the polygon mirror 19 (used number counter; six in this example), for example, a print mode indicating a screen type, an external input, or the like. A light amount setting condition selection unit 304 that generates a light amount control level change signal for setting the light amount of the light. The drive control unit 310 also includes a light amount detection signal indicating the light amount of each VCSEL 380 a acquired by the light amount detection sensor 16, a light amount control level change signal generated by the light amount setting condition selection unit 304, and a signal from the machine controller 270. A level changing unit 306 that changes the light amount level based on the light amount setting signal, and a driving amount setting signal (one corresponding to each one) that controls the driving current of each VCSEL 380a under the control of the level changing unit 306. 32) and a drive amount control unit 308 that generates a light amount control drive signal. Further, the drive control unit 310 includes a rotation control unit 309 that controls the amount of rotation of the photosensitive drum 32 in the sub-scanning direction based on a timing signal from the timing signal generation unit 230.
[0076]
If the light amount of the beam applied to the photosensitive drum 32 is not constant, the density of the latent image formed on the photosensitive drum 32 will not be constant, and the image quality will not be stable. Further, when an image is formed by a plurality of light beams, if the light amounts of the respective light beams are not constant, unevenness in density occurs in the formed image and the image quality is degraded. This is why a mechanism for detecting the light amount of each VCSEL 380a by the light amount detection sensor 16 and controlling the laser drive amount (APC; Auto Power Control) so that the light amount becomes constant is provided.
[0077]
Under control of the memory controller 228, the line buffer memory 226a simultaneously outputs a modulation signal at a predetermined timing so as to correct the delay amount (corresponding to the OD shown in FIG. 3) of the VCSEL 380a in the main scanning direction. That is, the modulation signals for the 32 laser beams used in the VCSEL light source group 380 are simultaneously output, and the output timing of the image data to the light source (VCSEL 380a) is simultaneous. Then, the VCSEL light source group 380 having eight light sources (VCSEL 380a) in the vertical direction (process direction) and having an 8 × 4 matrix structure can function as a light source for 32 line beam simultaneous scanning.
[0078]
Further, an SOS detection group lighting control circuit 229 is provided in the write signal generation unit 220 in the image recording control unit of the present embodiment. The drive control unit 310 includes a light amount detection sensor 16. The SOS detection group lighting control circuit 229 determines whether or not each VCSEL 380a of the VCSEL light source group 380 is abnormal based on the detection result of the beam light amount by the light amount detection sensor 16. For example, when the beam light amount (light intensity) is equal to or smaller than a predetermined lower threshold or equal to or larger than an upper threshold, it is determined that the VCSEL is out of order or abnormal.
[0079]
When the SOS detection group lighting control circuit 229 determines that the VCSEL 380a is abnormal, the SOS detection group lighting control circuit 229 specifies the number of VCSELs 380a detected as abnormal and where the VCSEL 380a in the two-dimensional array is abnormal (that is, a failure position). Then, based on the determination result, a group of the SOS detection groups for generating the scanning start signal SOS without using the abnormal light emitting point is selected, and the SOS switching signal indicating the selected SOS detection group is written into the write signal. The data is input to the generation unit 220 (particularly, the memory controller 228) and the VCSEL light source group 380.
[0080]
In the above configuration, the print image data input to the image forming apparatus 1 is input to the modulation signal generation unit 224. The modulation signal generation unit 224 decomposes the print image data into image data for each of the 32 lasers, and inputs the image data to the line buffer memory group 226 as 32 modulation signals. The line buffer memory group 226 outputs image data to the laser drive circuit (multi-LDD) 300 at a predetermined timing. The laser drive circuit 300 outputs a drive current for turning on / off the laser according to the input modulation signal to each light emitting unit of the VCSEL light source group (VCSEL array) 380. A part of the laser light output from the VCSEL light source group 380 is reflected by the half mirror 14 and guided to the light quantity detection sensor 16. The laser beam transmitted through the half mirror 14 is used for exposing the photosensitive drum 32.
[0081]
The drive amount control unit 308 controls the amount of drive current output from the laser drive circuit 300 so that the amount of laser light becomes a predetermined amount. ,..., 32 are sequentially switched to output a drive amount setting signal and a light amount control drive signal to the laser drive circuit 300, so that one light amount detection sensor 16 detects the light amount of all laser beams.
[0082]
In the present embodiment, the total amount of light (total amount of light) is calculated in a state where all VCSELs 380a to be controlled are simultaneously turned on by utilizing the technology described in Japanese Patent Application Laid-Open No. 8-264873 proposed by the present applicant. The detection is performed by the detection sensor 16 and feedback control is performed so that the total light amount obtained by the detection becomes a predetermined amount, so that the emission light amounts of all the VCSELs 380a to be controlled are collectively controlled so as to be a constant light amount. I do. In this technique, light intensity balance adjusting means for previously balancing the light emission intensity of each VCSEL 380a in accordance with the light emission characteristics of each VCSEL 380a constituting the light source is provided, and the light intensity balance adjustment means previously emits light of each VCSEL 380a. Adjust so that there is no variation in strength.
[0083]
In the present embodiment, the light amount detection sensor 16 is also used for detecting a failure of a light emitting point. For example, a light amount detection signal detected by the light amount detection sensor 16 is input to the SOS detection group lighting control circuit 229. The SOS detection group lighting control circuit 229 determines that the VCSEL 380a is faulty if the predetermined light amount cannot be detected even when the light amount is maximized by the drive amount control unit 308.
[0084]
Further, in order to generate the scanning start signal SOS, the emission points of the group used for detecting the scanning start signal SOS are forcibly before and after the timing when the laser light is incident on the photodiode PD in the scanning start signal generation unit 27. Need to be lit. Therefore, as described above, the SOS switching signal for switching the group used for SOS detection is input from the SOS detection group lighting control circuit 229 to the laser driving circuit 300.
[0085]
As can be understood from the above, the light amount detection sensor 16 and the SOS detection group lighting control circuit 229 constitute a light source state determination unit according to the present invention. The SOS detection group lighting control circuit 229 also functions as a light emitting point switching control unit according to the present invention.
[0086]
FIG. 5 is a functional block diagram illustrating a part related to exposure control (a control unit that drives the VCSEL 380a) in the image forming apparatus 1. The image forming apparatus 1 according to the present embodiment uses the method described in Japanese Patent Application Laid-Open No. 2002-131662 proposed by the present applicant to divide the light emitting points of the multi-beam light source into groups by position in the main scanning direction. The scanning start signal SOS is generated by lighting only the group or a plurality of groups.
[0087]
Here, the VCSEL 380a in the VCSEL light source group 380 has a configuration corresponding to the beam spot shown in FIG. 3, that is, eight VCSELs are arranged at substantially equal intervals on a straight line along the sub-scanning direction orthogonal to the main scanning direction. The four VCSEL groups thus configured are arranged so that the positions of the respective VCSELs in the sub-scanning direction are shifted from each other along the main scanning direction, and the respective VCSEL groups are further divided into G1, G2, G3, and G3 groups. A case will be described in which the G4 group is used, the G1 group that scans the photodetector at the earliest timing in a normal state is the SOS detection group, and the scanning start signal SOS is generated by laser beams from eight VCSELs 380a of only the G1 group.
[0088]
As shown in FIG. 5, the exposure control function part includes a scan start signal generation unit 27, a line buffer memory group 226, a memory controller 228, an SOS detection group lighting control circuit 229, and a laser drive 300.
[0089]
As described above, the scan start signal generator 27 has the same configuration as the scan start signal generator 392 shown in FIG.
[0090]
The SOS detection group lighting control circuit 229 controls the laser drive circuit 300 to belong to the SOS detection group (G1 group in the present embodiment) for a time period during which the laser beam can be incident on the pickup mirror 26 (see FIG. 2). Of the VCSEL 380a is output. As a result, a plurality of (eight in this example) laser beams emitted from a plurality (eight in this example) of VCSELs 380a belonging to the G1 group as the SOS detection group are applied to the photodiode PD in the scanning start signal generation unit 27. The scanning start signal SOS is generated by the scanning start signal generator 27 in accordance with the light intensity levels of the plurality of (eight in this example) laser beams.
[0091]
The timing signal generator 230 includes an oscillator 233 and a clock phase synchronization circuit 234. In the timing signal generator 230, the scan start signal SOS generated by the scan start signal generator 27 and the clock signal generated by the oscillator 233 are input to the clock phase synchronization circuit 234, and the rising timing of the scan start signal SOS Is output in synchronization with the video clock signal PCK.
[0092]
The memory controller 228 includes an offset register 255 and a counter circuit 256. The offset register unit 255 has registers G1 to G4 corresponding to each group of the VCSEL 380a. The counter circuit section 256 has counter circuits G1 to G4 corresponding to each group. Each of the registers G1 to G4 in the offset register unit 255 stores in the counter circuit unit 256 an LS offset OF1 to OF4 that defines the timing at which the line synchronization signal LS for each group is activated after the scanning start signal SOS is detected. Are set in the corresponding counter circuits G1 to G4.
[0093]
The scanning start signal SOS and the video clock signal PCK are input to each of the counter circuits G1 to G4 of the counter circuit unit 256. The count circuits G1 to G4 generate line synchronization signals LS1 to LS4 based on the video clock PCK and the scan start signal SOS. At this time, the offset amount of the line synchronization signals LS1 to LS4 from the scanning start signal SOS can be adjusted by changing the LS offsets OF1 to OF4 which are the register values of the registers G1 to G4.
[0094]
The line buffer memory group 226 includes a plurality of video memories MG1-1 to MG4-8. The video memories MG1-1 to MG1-8 correspond to the respective VCSELs 380a belonging to the G1 group. The video memories MG2-1 to MG2-8 correspond to the respective VCSELs 380a belonging to the G2 group. 1 to MG3-8 correspond to the respective VCSELs 380a belonging to the G3 group, and the video memories MG4-1 to MG4-8 correspond to the respective VCSELs 380a belonging to the G4 group.
[0095]
Each of the video memories MG1-1 to MG4-8 is constituted by a FIFO (First-In First-Out) memory, and stores the video signal for lighting each beam converted by the modulation signal generation unit 224. The video signals SG1-1 to SG4-8 are generated by outputting the stored video signals in synchronization with the video clock PCK and the line synchronization signals LS1 to LS4.
[0096]
For example, when the LS1 signal output from the counter circuit G1 in the counter circuit unit 256 goes high, it is input as a read enable signal to MG1-1 to MG1-8 corresponding to the VCSEL 380a in the G1 group shown in FIG. MG1-1 to MG1-8 output video signals SG1-1 to SG1-8 for VCSEL 380a belonging to group G1 in synchronization with video clock signal PCK. When each video signal is on, laser drive circuit 300 responds. The VCSEL 380a is turned on.
[0097]
FIG. 6 is a timing chart showing a main signal of the exposure control function part shown in FIG. Here, FIG. 6A is an example of a timing chart in the normal mode, and FIG. 6B is an example of a timing chart in the abnormal mode when a light emitting point in the SOS detection group has failed.
[0098]
In the normal mode, the scanning start signal generator 27 performs SOS detection using the light emitting points of the G1 group, and the memory controller 228 generates the line synchronization signals LS1 to LS4. The dotted line is the timing of the scanning start signal SOS when the light emitting points G2 to G4 are used for SOS detection. It can be seen that the output timing is different depending on the position shift in the main scanning direction.
[0099]
Here, the lighting timing of the VCSEL 380a belonging to the G1 group in FIG. 3 needs to be delayed from the scanning start signal SOS by the offset OF1. Further, the lighting timing of the VCSELs 380a belonging to the G2 group, the G3 group, and the G4 group is delayed from the lighting timing of the VCSEL 380a belonging to the G1 group by the offset OF2, the offset OF3, and the offset OF4 shown in FIG. There is a need. As shown in FIG. 6A, each delay time can be obtained by the following equations (2) to (5).
(Equation 2)

[0100]
Further, the lighting timing of the VCSEL 380a belonging to each group with respect to the scanning start signal SOS obtained from the G1 group as the SOS detection group can be obtained by the equations (6) to (9).
[Equation 3]

[0101]
In the circuit configuration shown in FIG. 5, offset components LS offsets 1 to 4 representing a delay time are set for the scanning start signal SOS obtained by using the G1 group as the SOS detection group according to the equations (6) to (9). . For example, the LS1 signal obtained by delaying the scanning start signal SOS by the delay time of the LS offset 1 in order to perform exposure at a predetermined position using beams of the VCSEL 380a belonging to each of the G1, G2, G3, and G4 groups. LS2 signal obtained by delaying the scanning start signal SOS by the delay time of LS offset 2 from the counter circuit G1, and LS3 signal obtained by delaying the scanning start signal SOS by the delay time of LS offset 3 from the counter circuit G3. Outputs the LS4 signal obtained by delaying the scanning start signal SOS by the delay time of the LS offset 4 from the counter circuit G4, and outputs each signal as a "G1 group video memory read permission signal" and a "G2 group video memory read permission signal.""," G3 group video memory read Yes signal "," applied as a G4 group of video memory read enable signal ".
[0102]
For example, the counter circuit G1 counts the number of video clocks as an elapsed time from the rise of the scanning start signal SOS, and when the delay time T1 corresponding to the LS offset 1 set in the register G1 has elapsed, the counter circuit G1 goes high, A line synchronization signal LS1 for the G1 group, which becomes low level after a predetermined video signal read permission time has elapsed, is generated and output. The same applies to the counter circuits G2 to G4.
[0103]
On the other hand, when the SOS detection group lighting control circuit 229 detects that a failure has occurred in any of the light emitting points of the G1 group, the SOS detection group lighting control circuit 229 changes the SOS detection group to a group other than the G1 group. Switch.
[0104]
For example, if any of the light emitting points of the G1 group fails, the OP output reflecting the PD output decreases as described with reference to FIG. 12C if the SOS detection group remains the G1 group. Further, the PD output fluctuates due to power supply voltage fluctuation, deterioration of the photodiode PD over time, noise, or the like. Therefore, when the OP output reflecting the PD output falls below the threshold voltage, the scanning start signal SOS is output. May not be. Therefore, when a failure occurs in the light emitting point of the G1 group, the scanning start signal SOS is generated using the light emitting points of the other groups.
[0105]
Instead of the G1 group, the SOS detection may be performed using the light emitting points of any of the groups G2 to G4. For example, FIG. 6B illustrates a case where the group G2 is used as an SOS detection group. Since the total light amount of the light emitting points of the group G2 is substantially equal to the total light amount of the G1 group before the failure, the PD output and the OP output reflecting the PD output are also substantially the same. Therefore, as shown in FIGS. 11B and 12A, the scanning start signal SOS can be normally generated.
[0106]
However, in this case, the detection timing is shifted by the offset OF2 to OF4 between the case where the SOS detection group is the G1 group and the case where the SOS detection group is another group. Therefore, in conjunction with the switching of the SOS detection group to the group G2, the offset components LS offsets 1-2 to 4-2 representing the delay time correspond to the scanning start signal SOS obtained by setting the G2 group as the SOS detection group. Set in the registers G1 to G4. That is, the values of the LS offset 1 to 4 registers are changed according to the amount of change in the output timing of the scanning start signal SOS. The lighting timing of the VCSEL 380a belonging to each group with respect to the scanning start signal SOS obtained by using the G2 group as the SOS detection group can be obtained by Expressions (10) to (13).
(Equation 4)

[0107]
As a result, as shown in FIG. 6B, even when the G2 group is set as the SOS detection group, the line synchronization signals LS1 to LS1 for each group are set at almost the same timing as when the G1 group is set as the SOS detection group. LS4 can be generated. Therefore, even if an abnormality occurs in the light emitting point of the G1 group used for detecting the scan start signal SOS, it is possible to normally detect the scan start signal SOS and create the line synchronization signals LS1 to LS4.
[0108]
Note that the generation procedure of LS1 to LS4 is not limited to the above example as long as the above-described time relationship can be substantially maintained. For example, the line synchronization signal LS for each group may be generated according to the above equations (2) to (5). That is, first, the LS1 signal obtained by delaying the scanning start signal SOS by the delay time of the LS offset 1 is output from the counter circuit G1 as a "G1 group video memory read enable signal". Next, in order to perform exposure at a predetermined position using beams of the VCSEL 380a belonging to each of the groups G2, G3, and G4, the LS2 signal obtained by delaying the LS1 signal by the delay time T2 is output from the counter circuit G2 to the LS1 signal. Are output from the counter circuit G3, the LS3 signal obtained by delaying the LS1 signal by the delay time T4, and the LS4 signal obtained by delaying the LS1 signal by the delay time T4 are output from the counter circuit G4. This is applied as a “G3 group video memory read permission signal” and a “G4 group video memory read permission signal”. The same applies to the case where the SOS detection group is changed to another group when a failure occurs.
[0109]
FIG. 7 is a diagram illustrating a second embodiment of the method of setting the SOS detection group and the method of coping with the abnormal light emitting point. In the above embodiment (hereinafter referred to as the first embodiment for discrimination from other embodiments), the case where the SOS detection group is constituted by all VCSELs that emit laser beams having substantially the same scanning position on the photosensitive drum 32 However, the present invention is not limited to this, and it suffices to satisfy the condition that “the positions in the light scanning direction on the surface to be scanned are substantially equal”. The SOS detection group may be composed of only a part of the VCSEL which emits a laser beam having substantially the same value as the above.
[0110]
In this case, when a failure occurs in a part of the light emitting points constituting the SOS detection group, the abnormal light emitting point which is the failed light emitting point is set to “the light scanning direction positions on the surface to be scanned are substantially equal”. It may be replaced with any one of the other light emitting points. By doing so, the same effect as in the above embodiment can be obtained. In addition, in this case, since there is no offset from the original detection timing, it is unnecessary to change the set values of the registers G1 to G4.
[0111]
For example, as shown in FIG. 7 (A1), not all of the light emitting points P25 to P32 of the G1 group form an SOS detection group, but four of the light emitting points P29 to P32 form an SOS detection group. Is also good. In this case, as shown in FIG. 7A2, when a failure occurs in a part of the light emitting points P29 to P32 forming the SOS detection group, the abnormal light emitting point is referred to as “light on the surface to be scanned”. The positions in the scanning direction are substantially the same ”, that is, it may be replaced with any one of the other light emitting points P25 to P28 in the same group. FIG. 7A3 shows an example in which the abnormal light emitting point P31 is replaced with a light emitting point P28.
[0112]
In this case, the combination may be switched not only for the failed light emitting point but also for all or a part of the normal light emitting points. For example, FIG. 7 (A4) shows an example in which not only the abnormal light emitting point P31 but also the whole combination is changed to reconfigure the SOS detection group with four light emitting points P25 to P28.
[0113]
Further, the light emitting points to be selected as the SOS detection groups do not need to be continuous, and for example, as shown in FIG. 7 (B1), four light emitting points P27, P28 and P31, P32 of the G1 group are selected. Is also good. Also in this case, if a failure occurs in any of them, it may be replaced with any of the other light emitting points P25, P26, P29, and P30 in the same group. Also in this case, as shown in FIG. 7B2, the combination may be switched not only for the failed light emitting point but also for all or a part of the normal light emitting points.
[0114]
FIG. 8 is a diagram illustrating a third embodiment of a method of setting an SOS detection group and a method of coping with an abnormal light emitting point. In the first or second embodiment, the case where the scanning start signal SOS is generated based on the laser beam of only the VCSEL group belonging to one group, and the positional deviation between the groups is corrected according to the design or measurement timing value However, in order to control the beam spot position with higher accuracy, it is necessary to independently generate the scanning start signal SOS in each group and synchronize the video signals. In the third embodiment, one mode in this case will be described. Note that the overall configuration of the image forming apparatus 1 according to the third embodiment is the same as that of the image forming apparatus 1 according to the first embodiment, and a description thereof will not be repeated.
[0115]
In the image forming apparatus 1 according to the third embodiment, as shown in FIG. 8, an SOS detection group including a plurality of VCSELs is determined based on the arrangement position of a beam spot formed on the photosensitive drum 32 under the following conditions. By making the determination so as to satisfy, the scan start signal SOS is generated independently for each SOS detection group.
[0116]
That is, first, as in the first embodiment, as in the first embodiment, a period in which the amount of received light energy of the SOS detection optical sensor (the photodiode PD in the previous example) is equal to or higher than the energy level corresponding to the detection threshold and a period in which the amount of light is lower than the energy level. A signal having a different signal level is generated.
[0117]
When all VCSELs forming an arbitrary one of the plurality of SOS detection groups are turned on, the scanning start signal generation unit 27 in the optical scanning direction (main scanning direction) is turned on, as in the state shown in FIG. , The total exposure energy profile on the photodiode PD (optical sensor) and the energy level corresponding to the detection threshold of the scanning start signal generation unit 27 intersect at only two points. That is, when all VCSELs belonging to any one SOS detection group are turned on, the combined energy distribution of each laser beam on the light receiving surface of the SOS detection optical sensor is determined by the intensity of each laser beam along the scanning direction. The distribution is such that there is no portion below the energy level corresponding to the detection threshold value in the portion corresponding to between the beam centers.
[0118]
Further, as shown in FIG. 8, when all the VCSELs constituting two arbitrary groups (G1 group and G2 group in FIG. 8) among the plurality of SOS detection groups are turned on, the total exposure energy profile and the scanning start The energy level corresponding to the detection threshold of the signal generation unit 27 intersects at only four points, and the total exposure energy profile between the center of one group in the light scanning direction and the center of the other group in the light scanning direction. The energy level corresponding to the detection threshold crosses at only two points.
[0119]
That is, when all VCSELs belonging to any two SOS detection groups are turned on, the combined energy distribution of each laser beam on the light receiving surface of the SOS detection optical sensor corresponds to the laser beam group belonging to one SOS detection group. And a distribution in which a portion having an energy level lower than the detection threshold value is generated at a location corresponding to a position between the center in the scanning direction of the laser beam group and the center of the laser beam group belonging to the other SOS detection group in the scanning direction. The VCSELs of the VCSEL light source group 380 are grouped into a plurality of SOS detection groups such that
[0120]
Then, a plurality of VCSELs selected in advance for each individual SOS detection group as VCSELs used for generating the scanning start signal SOS are set in a period in which the light beams emitted from the plurality of VCSELs cross the light receiving surface of the SOS detection optical sensor. To light each.
[0121]
Thus, when all VCSELs belonging to any one SOS detection group are turned on, the combined energy distribution of each laser beam on the light receiving surface is set between the beam centers of the individual laser beams along the scanning direction. A distribution that does not cause a portion having an energy level less than the detection threshold value in a corresponding portion can be obtained, and the photodiode PD when all VCSELs belonging to any two SOS detection groups are turned on is turned on. The combined energy distribution of each laser beam on the light receiving surface is represented by the center along the scanning direction of the laser beam group belonging to one SOS detection group and the center along the scanning direction of the laser beam group belonging to the other SOS detection group. And a distribution in which a portion corresponding to the energy level corresponding to the detection threshold is lower than the energy level corresponding to the detection threshold value. It can be.
[0122]
When the scanning start signal SOS is detected by a plurality of groups in this manner, all the VCSELs are turned on simultaneously or in time series to detect the scanning start signal SOS. , The same number of groups as the number of scanning start signals SOS are output. However, the signals representing the plurality of scan start signals SOS are separated into scan start signals SOS corresponding to each group, for example, by utilizing the method described in JP-A-2002-131662, and the separated scan start signals SOS are separated. By separately generating a line synchronization signal using the SOS, a stable scanning start signal SOS can be obtained for each SOS detection group. Thereby, the beam spot position can be controlled with high accuracy.
[0123]
In the configuration in which a plurality of SOS detection groups are combined as described above, if a failure occurs in a light emitting point, as in the first embodiment, the SOS detection group including the abnormal light emitting point is replaced with only the normal light emitting point. By switching to another group including, the scanning start signal SOS can be normally detected. In the case where the SOS detection group is configured by only a part of the group and the plurality of groups are combined, as in the second embodiment, the switching to another normal light emitting point in the group is performed. The method may be adopted.
[0124]
FIG. 9 is a diagram illustrating a fourth embodiment of a method for setting an SOS detection group and a method for coping with an abnormal light emitting point. In the first to third embodiments, when a light emitting point in the SOS detection group fails, the light emitting point is replaced with another group not including the abnormal light emitting point, or replaced with another normal light emitting point in the same group. Although the scanning start signal SOS signal is normally detected, the fourth embodiment is characterized in that when a failure is detected, the failure is dealt with by changing a detection threshold which is a reference for comparison.
[0125]
For example, as shown in FIG. 9A, the threshold power supply SP in the scan start signal generation unit 27 is configured to have a variable output voltage type. Then, when the SOS detection group lighting control circuit 229 detects the failure of the light emitting point, it inputs a threshold voltage change signal to the control input terminal of the threshold power supply SP. This threshold voltage change signal is preferably a signal corresponding to the number of failed light emitting points. The threshold power supply SP changes the detection threshold voltage according to the number of light emitting points in the original SOS detection group and the number of failures based on the threshold voltage change signal, and sets the threshold voltage in the comparator CP. As can be seen from this, the SOS detection group lighting control circuit 229 and the variable output voltage threshold power supply SP constitute a reference signal control unit according to the present invention.
[0126]
With this configuration, for example, as shown in FIG. 9B, when a failure occurs in the light emitting point, the OP output reflecting the PD output decreases unless the detection threshold voltage is changed, and the scanning start signal SOS May not be output, but by changing the detection threshold voltage according to the number of failures, the scanning start signal SOS can be reliably output. Since the scanning start signal SOS is originally generated using a plurality of light emitting points, the influence of noise can be reduced even if the threshold voltage is changed as compared with the case where only one light emitting point is turned on and the photodetector is scanned. There is little possibility of malfunction occurring.
[0127]
In this case, as shown in FIG. 9 (B), the output timing of the scanning start signal SOS may be slightly shifted like Δ1 or Δ2 in conjunction with the change of the threshold voltage. However, unlike the group switching as in the first embodiment, it is a small change within the same group and causes almost no problem. If a change in Δ1 or Δ2 poses a problem, the change may be corrected as in the first embodiment.
[0128]
As described above, according to the image forming apparatus 1 of each of the above-described embodiments, even when a failure occurs in the light emitting point (the VCSEL 380a in the previous example) used for generating the scanning start signal SOS, the abnormal light emitting point is determined. Since the SOS detection group is switched to another group so as to interpolate, or is switched to another normal light emitting point in the same group, or the detection threshold is changed, the amount of received light energy due to the failure of the light emitting point is changed. The influence of the decrease can be prevented, and as a result, the scanning start signal SOS can be reliably obtained.
[0129]
Further, the image forming apparatus 1 of the above embodiment divides each light emitting point of the multi-beam light source into groups in the main scanning direction using the method described in Japanese Patent Application Laid-Open No. 2002-131662 proposed by the present applicant. , The scanning start signal SOS is generated by lighting one group or one group or a plurality of groups. In other words, a plurality of light emitting points, which are preselected as an SOS detection group and have substantially the same position along the scanning direction of the beam spot formed on the surface to be scanned by the emitted light beam, are emitted from the plurality of light emitting points. Each light is turned on during a period in which the emitted light beam crosses the light receiving surface of the SOS detection optical sensor. As a result, the amount of light reception energy of the SOS detection optical sensor can be increased, and as a result, a stable scanning start signal SOS can be obtained. Thus, the effects of the method described in JP-A-2002-131662 can be similarly enjoyed. (For details, see JP-A-2002-131662).
[0130]
As described above, the present invention has been described using the embodiment. However, the technical scope of the present invention is not limited to the scope described in the embodiment. Various changes or improvements can be made to the above-described embodiment without departing from the spirit of the invention, and embodiments with such changes or improvements are also included in the technical scope of the present invention.
[0131]
Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of the features described in the embodiments are not necessarily essential to the means for solving the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some components are deleted from all the components shown in the embodiment, as long as the effect is obtained, a configuration from which some components are deleted can be extracted as an invention.
[0132]
For example, in each of the above-described embodiments, the scan start signal generation unit 27 uses the configuration proposed by the present applicant in Japanese Patent Application Laid-Open No. 2002-131662, but is not necessarily limited to this. If the light is emitted from a plurality of light emitting points of the multi-beam light source and is illuminated in a group unit divided for each position in the scanning direction, a scanning start signal is generated, , May be any. For example, the configuration proposed in Japanese Patent Application Laid-Open No. 2002-131662 is based on a multi-beam light source in which a plurality of light emitting points are arranged two-dimensionally. Is adopted, a line sensor in which a plurality of light emitting points are arranged in a line may be used.
[0133]
In each of the above embodiments, the scan start signal generation unit 27 including the dedicated photodetector (photodiode PD in the previous example) for detecting the scan start signal SOS is used. However, the present invention is not limited to this. Instead of the light sensor, the light amount detection sensor 16 may be responsible for both the detection of the laser light for generating the scanning start signal SOS and the detection of the light amount of the laser light for APC. In this case, since the light amount detecting sensor 16 is also used as the light amount detecting optical sensor and the SOS detecting optical sensor, the configuration of the apparatus can be simplified, and the cost and size can be reduced.
[0134]
Further, even when a dedicated SOS detection optical sensor is used, the SOS detection optical sensor may be composed of a plurality of photodiodes, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 5-323220.
[0135]
Further, in the above embodiment, the case where the normal SOS detection group is the group that scans the photodetector at the earliest timing has been described. However, the present invention is not limited to this. The detection group may be used. In this case, there is no problem if the setting of the memory controller 228 is optimized. This is the same as the change mode in the case where the G1 group is set as the SOS detection group in the normal state and the other group is set as the SOS detection group in the abnormal state.
[0136]
Further, in the above embodiment, the case where the delay of the video memory read enable signal by the memory controller 228 is performed in video clock signal units has been described. However, the present invention is not limited to this, and the delay by analog elements or logic gates is used. By providing the fine adjustment mechanism, the beam spot positions of the light emitting points belonging to the G2 to G4 groups can be controlled with higher accuracy.
[0137]
Further, in the above-described embodiment, a case has been described in which the beam position offset of the SOS detection group (the G1 group when normal) and the other group (the G2 to G4 group when normal) are corrected in accordance with the design value. However, the present invention is not limited to this, and a mode in which the measurement is performed in accordance with a measured value may be adopted.
[0138]
Further, as shown in FIG. 11B, when there is an offset between the G1, G2, G3, and G4 groups and a plurality of VCSELs constituting each of them, the timing is adjusted for each beam. By doing so, the same measures as in each of the above embodiments can be made.
[0139]
In the above embodiment, the VCSEL is arranged at the light emitting point. However, the present invention is not limited to the VCSEL, and the effect of the above embodiment does not change even if an edge emitting type laser array or an LED is arranged. In the case of a two-dimensional array light source group provided with VCSELs, a monolithic structure in which light emitting units are two-dimensionally arranged on one semiconductor chip can be used. Further, in the VCSEL, the cross-sectional area of the laser light emitting portion can be made larger than that of a conventional edge-emitting semiconductor laser, so that the divergence angle of the laser light becomes smaller. Therefore, a compact light source can be obtained.
[0140]
In the above-described embodiment, a polygon mirror (rotating polygon mirror) is used as a deflecting device. However, other than the above, if the direction of light can be periodically deflected, such as a galvanometer mirror or a hologram disk, the same as the above example can be used. Has an effect. Further, in the configuration of the optical system, the collimator lens, the scanning lens, and the tilt correction optical system are not essential, and the presence or absence thereof does not affect the above-described effects.
[0141]
【The invention's effect】
As described above, when a failure occurs in the light emitting point used for generating the scanning start signal SOS, the SOS detection group for detecting the scanning start signal SOS is changed to another group so as to interpolate the abnormal light emitting point. Or the first configuration of switching to another normal light emitting point in the same group, it is possible to prevent the light receiving point from being affected by a decrease in the amount of received light energy due to the failure of the light emitting point. As a result, the scanning start signal SOS and the line synchronization signal LS can be reliably obtained.
[0142]
Further, in the case where the scan start signal SOS is generated by comparing a signal representing the energy of light emitted from the light emitting point of the SOS detection group with the reference signal, a failure occurs in the light emitting point used for generating the scan start signal SOS. When this occurs, the second configuration for controlling the reference signal to be compared in a direction in which the scanning start signal can be detected normally can also be reduced in the amount of received light energy due to the failure of the light emitting point as in the first configuration. Can be prevented, and as a result, the scanning start signal SOS and the line synchronization signal LS can be reliably obtained.
[0143]
Thus, in either of the first and second configurations, even if the light emitting point related to the detection of the scanning start signal fails, the exposure can be performed from the correct writing position, and the image can be normally read. Can be formed.
[Brief description of the drawings]
FIG. 1 is a mechanism diagram of an example of an image forming apparatus that records a color image using a VCSEL light source group.
FIG. 2 is a diagram illustrating a configuration example of an optical scanning device used in the image forming apparatus.
FIG. 3 is a diagram showing a relationship between a scanning line on a surface to be scanned by a laser beam emitted from a VCSEL light source group and an imaging spot.
FIG. 4 is a diagram illustrating an outline of a processing circuit (image recording control unit) for forming an image in an image forming apparatus including a VCSEL light source group.
FIG. 5 is a functional block diagram illustrating a portion related to exposure control in the image forming apparatus.
FIG. 6 is a timing chart showing a main signal of the exposure control function part shown in FIG. 5;
FIG. 7 is a diagram illustrating a second embodiment of a method of setting an SOS detection group and a method of coping with an abnormal light emitting point.
FIG. 8 is a diagram illustrating a third embodiment of a method of setting an SOS detection group and a method of coping with an abnormal light emitting point.
FIG. 9 is a diagram for explaining a fourth embodiment of a method for setting an SOS detection group and a method for coping with an abnormal light emitting point.
FIG. 10 is a diagram illustrating an example of an optical scanning device using a multi-beam light source.
FIG. 11 illustrates an example of a photodetector.
FIG. 12 is a diagram for explaining an SOS detection method described in JP-A-2002-131662.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 5 ... Image acquisition part, 7 ... Image data generation part, 10 ... Optical scanning device, 11 ... Lens group, 12 ... Multi-beam light source, 14 ... Half mirror, 16 ... Light quantity detection sensor, 19 ... Rotating polygon mirror (polygon mirror), 27: scanning start signal generation unit, 30: latent image recording unit, 32: photosensitive drum, 50: transport unit, 220: write signal generation unit, 222: I / F unit, 224 ... A modulation signal generator, 226 a line buffer memory group, 228 a memory controller, 229 a SOS detection group lighting control circuit, 230 a timing signal generator, 233 an oscillator, 234 a clock phase synchronization circuit, 255 an offset register Section, 256: counter circuit section, 270: machine controller, 300: laser drive circuit, 304: light quantity setting condition selection section, 306: level change section 308 ... drive amount control unit, 310 ... drive controller

Claims (5)

An optical system for imaging a light beam emitted from each of the light emitting points of a multi-beam light source having a plurality of light emitting points each of which can be independently modulated, on a surface to be scanned;
A scanning start signal generation unit that generates a scanning start signal by receiving light emitted from the plurality of light emitting points of the multi-beam light source and illuminated in a group unit divided for each position in a scanning direction; When,
Image data for recording corresponding to the plurality of light emitting points is generated based on the image data, and the light emitting points are driven based on the generated image data for recording, and generated by the scan start signal generating unit. An image writing signal generation unit that controls image writing timing based on the scanning start signal,
Detecting a light emitting state of the light emitting point related to the detection of the scanning start signal among a plurality of light emitting points of the multi-beam light source; based on the detection result, determining whether the light emitting state of the light emitting point is abnormal; A light source state determination unit for determining
The abnormal light emitting point, which is the light emitting point determined to be abnormal indicated by the determination result of the light source state determining unit, is complemented, and the abnormal light emitting point is a remaining light emitting point of the plurality of light emitting points so as to light up in groups. And a light emitting point switching unit for switching to the light emitting point. The image forming apparatus according to claim 1, wherein the light emitting point switching unit switches a group including the abnormal light emitting point to any one of groups excluding a group including the abnormal light emitting point. The image writing signal generation unit adjusts an image writing timing according to a difference in a position in the scanning direction between a group including the abnormal light emitting point and a group switched by the light emitting point switching unit. The image forming apparatus according to claim 2. The image according to any one of claims 1 to 3, wherein the light emitting point switching unit switches the abnormal light emitting point to another light emitting point within a group including the abnormal light emitting point. Forming equipment. An optical system for imaging a light beam emitted from each of the light emitting points of a multi-beam light source having a plurality of light emitting points each of which can be independently modulated, on a surface to be scanned;
Light from the plurality of light-emitting points of the multi-beam light source, which is light that is lit in a group unit divided for each position in the scanning direction, is received, and a signal representing the energy of the received light is predetermined. A scan start signal generation unit that generates a scan start signal by comparing the reference signal with
Image data for recording corresponding to the plurality of light emitting points is generated based on the image data, and the light emitting points are driven based on the generated image data for recording, and generated by the scan start signal generating unit. An image writing signal generation unit that controls image writing timing based on the scanning start signal,
Detecting a light emitting state of the light emitting point related to the detection of the scanning start signal among a plurality of light emitting points of the multi-beam light source; based on the detection result, determining whether the light emitting state of the light emitting point is abnormal; And a reference signal control unit that controls the reference signal based on a result of the determination.

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