JP3596970B2

JP3596970B2 - Light beam scanning device

Info

Publication number: JP3596970B2
Application number: JP03564296A
Authority: JP
Inventors: 雄久前田
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1996-01-30
Filing date: 1996-01-30
Publication date: 2004-12-02
Anticipated expiration: 2016-01-30
Also published as: JPH09211927A

Description

【０００１】
【発明の属する技術分野】
本発明は、複写機、ファクシミリ、プリンター、印刷機等の画像形成装置（カラー画像形成装置を含む）に用いる光ビーム走査装置に係り、詳しくは複数の回転多面鏡を備えた光ビーム走査装置における各回転多面鏡間の回転位相の制御に関するものである。
【０００２】
【従来の技術】
従来、複写機、ファクシミリ、プリンター、印刷機等の画像形成装置に用いる光ビーム走査装置として、光ビーム発生手段と、前記光ビーム発生手段で発生した光ビームを像担持体に偏向走査する回転多面鏡と、前記回転多面鏡を回転駆動する駆動手段と、前記回転多面鏡の回転位置を検出する回転位置検出手段と、回転基準信号及び前記回転位置検出手段の出力信号に基づいて前記回転多面鏡が等速回転するように前記駆動手段を制御する回転駆動制御手段とを複数組備え、且つ、前記各回転多面鏡に対応させて前記回転基準信号を発生する回転基準信号発生手段を備えたものが知られている。
【０００３】
上記構成の光ビーム走査装置においては、回転基準信号発生手段で発生した各回転基準信号及び各回転位置検出手段の出力信号に基づいて、各回転多面鏡が等速回転するように各駆動手段を制御する。そして、この光ビーム走査装置を備えた画像形成装置においては、各回転多面鏡で偏向走査された光ビームによってそれぞれ対応する像担持体上に独立した潜像を形成し、この潜像を現像した各画像を記録媒体上に重ね合わせて転写する。ここで、各画像を記録媒体上の正確な位置に重ね合わせるためには、像担持体上の各画像の主走査方向（光ビームの走査方向）及び副走査方向（像担持体表面の移動方向）における画像形成開始位置が正確に調整されていなければならない。
【０００４】
上記主走査方向については、例えば、光ビームを走査経路上の所定位置で検出し、その検出結果に基づいて画像の各走査ラインの書き込みタイミングを調整することにより、各光ビーム走査装置における回転多面鏡の像担持体に対する初期取付角度、すなわち各回転多面鏡の面位相が互いに完全に一致していなくても、主走査方向の画像ずれの発生を防止することができる。
【０００５】
一方、上記副走査方向については、例えば複数の回転多面鏡に対応させて複数の像担持体が設けられている場合、像担持体の間隔（ピッチ）を走査ピッチの整数倍に設定し、画像の書き込み開始のタイミングを一回の光ビーム走査に要する時間単位で調整するとともに、同一周波数の回転基準信号に基づいて回転多面鏡を回転駆動して画像書き込みを行うことにより、画像全体にわたって１走査ピッチよりも大きな副走査方向の画像ずれの発生を防止できる。
【０００６】
ところが、前記一回の光ビーム走査に要する時間単位での画像の書き込み開始タイミングの調整を行った場合でも、各回転多面鏡間の面位相が互いに完全に一致していないと、１走査ピッチ以下（画像分解能３００ｄｐｉの場合で８４．６７μｍ以下）の副走査方向の画像ずれが発生してしまうという不具合があった。この画像ずれは、カラー画像を形成する場合に色ずれという不具合となる。
【０００７】
そこで、従来、上記１走査ピッチ以下の副走査方向の画像ずれを防止するために、次のように各回転多面鏡間の回転位相を制御するものが知られている。
【０００８】
例えば、特開昭６４−７３３６９号公報では、前記回転駆動制御手段としてのＰＬＬ制御手段のそれぞれに対して、前記回転基準信号としての基準周波数信号を発生する前記回転基準信号発生手段としての基準周波数信号発生手段と、前記光ビーム検出手段としての一つの同期センサから出力される前記出力信号としての水平同期信号の出力に同期して残る各同期センサから出力される水平同期信号出力タイミング差を前記基準周波数信号に基づいて計測するタイミング計測手段と、このタイミング計測手段により計測された各水平同期信号出力タイミング差に基づいて、前記ＰＬＬ制御手段に供給する基準周波数信号の位相を調整する位相調整手段とを備えた装置が開示されている。
【０００９】
この装置によれば、基準周波数信号発生手段から発生された基準周波数信号に基づいて、１つのＰＬＬ制御手段が回転多面体（回転多面鏡）の回転速度制御を開始する。一定速度で回転する回転多面体により偏向されるレーザビームを受光して、同期センサが水平同期信号を発生すると、タイミング計測手段が１つの同期センサから出力される水平同期信号の出力に同期して残る各同期センサから出力される水平同期信号出力タイミング差を基準周波数信号に基づいて計測する。そして、この計測された各水平同期信号出力タイミング差に基づいて、位相調整手段がＰＬＬ制御手段に供給する基準周波数信号の位相を調整する。これにより、位相ずれを画素単位距離間内で微細に調整でき、レーザビームの各感光ドラム（像担持体）上のトップ走査ラインずれを最小に設定することができる。
【００１０】
また例えば、特開平２−１７０１１０号公報では、各回転多面鏡に偏向される各光ビームをそれぞれ受光して各ビームの位相差を検知する検知手段と、この検知手段により検知される位相差に基づいて、少なくとも１つの回転多面鏡と残る各回転多面鏡との位相角差を相殺するように、各回転多面鏡を等速回転させる駆動手段の回転位相角を前記１つの回転多面鏡に従属して個別に制御する位相制御手段とを備えた光ビーム走査装置が開示されている。
【００１１】
この装置によれば、各駆動手段により各回転多面鏡が始動されて定速回転に到達したら、検知手段が各回転多面鏡により偏向される各光ビームをそれぞれ受光して各光ビームの位相差を検知し、この位相差情報が位相制御手段に送出される。この位相制御手段は検知された位相差に基づいて少なくとも１つの回転多面鏡と残る各回転多面鏡との位相差が相殺されるように各駆動手段の回転位相角を個別、かつ１つの回転多面鏡に従属させて制御し、各回転多面鏡から像担持体に偏向走査される各光ビームの書き出し位置を一致させることができる。
【００１２】
また、上記特開平２−１７０１１０号公報には、次のような２ビーム方式の実施例が開示されている。前記検出手段及び前記位相制御手段を兼ねた回転位相同期制御装置は、前記光ビーム検出手段としての第１レーザピーム検知器からの出力信号である第１のビームデイテクトパルス信号と、同じく光ビーム検出手段としての第２レーザビーム検知器からの出力信号である第２のビームデイテクトパルス信号とが位相差をもって送出されてくると、その位相差を内部カウンタ回路などの計時手段により測定し、回転基準信号発生手段としての基準信号発生器から出力されている複数の基準信号のうち、前記測定された位相差に近い位相を発生させる基準信号を選択スイッチで選択して第２の回転多面鏡の回転駆動を制御する回転駆動制御手段としての第２位相同期制御部に送出する。これにより、前記駆動手段としての第１及び第２モータは、前記測定された位相差を発生させる基準信号を用いて前記第２位相同期制御部及び第１の回転多面鏡の回転駆動を制御する第１位相同期制御部で位相同期制御が行われ、以後の第１及び第２のビームディテクトパルス信号の位相はほぼ同位相となり、第１及び第２の回転多面鏡のビーム反射面が同位相となる。従って、第１及び第２の回転多面鏡から像担持体としての感光体ドラムに偏向走査される各光ビームによる画像書き出し位置が一致するようになる。
【００１３】
また例えば、特開平５−２２７３８３号公報では、基準となる回転多面鏡の駆動手段であるスキャナーモータからの基準書き出し位置検知信号及び残りの回転多面鏡のスキャナーモータからの書き出し位置検知信号を、判断手段としてのマイクロプロセッサに取り込み、前記基準書き出し位置検知信号に対する他の書き出し位置検知信号の時間ずれを判断し、その判断結果に基づいて前記残りの回転多面鏡のスキャナーモータに対して、そのモータの回転速度を増減させる位相制御信号を供給するものが開示されている。この構成により、前記基準となる回転多面鏡による書き出し位置に対して前記残りの回転多面鏡による書き出し位置を一致させ、副走査方向の位置ずれを補正している。
【００１４】
【発明が解決しようとする課題】
ところが、上記各回転多面鏡の回転位相を制御する位相制御を行う従来の装置で用いられる回転多面鏡は、その駆動手段の駆動ムラによって微小ながら回転ムラが発生している。この回転ムラは、前記駆動手段及びそれを制御する回転駆動制御手段等における温度上昇、経時劣化によって大きくなっていく傾向にある。また、前記回転多面鏡に形成されている光反射面の回転方向の長さも、微小ながらばらついている。このような回転多面鏡の回転ムラや光反射面の長さのばらつきがあると、基準回転多面鏡に対応する光ビーム検出手段の出力信号と残りの回転多面鏡に対応する光ビーム検出手段の出力信号との時間差もばらついてしまうと考えられる。
【００１５】
また、上記従来の装置の位相制御では、複数の回転多面鏡のうち基準回転多面鏡に対応した光ビーム検出信号に基づいて、残りの各回転多面鏡による画像書込位置を制御するように光ビーム発生手段を制御することにより、前記基準となる回転多面鏡による画像書込位置に対して前記残りの各回転多面鏡による画像書込位置を一致させるように位相制御している。例えば、基準回転多面鏡に対応した光ビーム検出信号からの出力信号をそれぞれ所定回数検知したところで、前記残りの回転多面鏡による画像書き込みを開始するように光ビーム発生手段を制御する。従って、画像書込動作期間等の位相制御を行っていない期間に、前述のように光ビーム検出手段の出力信号の時間差がばらつくと、基準回転多面鏡に対応する光ビーム検出手段の出力信号を受けた後、残りの回転多面鏡に対応する光ビーム検出手段の出力信号を受けるまでの時間が、この出力信号の周期に近い時間分だけ突然変化し、１走査ピッチに近い副走査方向の画像ずれが突然発生するおそれがある。
【００１６】
この副走査方向の画像ずれを、図１７（ａ）及び（ｂ）に示した位相制御前及び位相制御後における光ビーム検出手段の出力信号のタイムチャートの具体例で説明する。この具体例では、光ビーム発生手段としてのレーザや回転多面鏡等からなるレーザ走査ユニットを２組備えており、レーザが点灯し、回転多面鏡が等速回転することにより、図１７（ａ）のように各回転多面鏡に対応した光ビーム検出手段から出力信号（前述の従来例では、書き出し位置検知信号、水平同期信号又はディテクタパルス信号と呼ばれている。）ＤＰ１，ＤＰ２が出力される。ここで、出力信号ＤＰ１を基準とし、それに対する他の出力信号ＤＰ２の時間差（タイミング差）を計測するわけであるが、基準の出力信号ＤＰ１に対して他の出力信号ＤＰ２が図中の一点鎖線で示すようにＴ４の２倍だけ時間差が変動するとし、計測した時間差を図２のようにＴ１とする。このような条件下で時間差Ｔ１に基づいた従来の位相制御を行うと、各出力信号のタイムチャートは図１７（ｂ）のようになる。この位相制御後において、基準の出力信号ＤＰ１に対して他の出力信号ＤＰ２がＴ４の２倍だけ時間差が変動するので、例えば、出力信号ＤＰ２がｂの位置にあるとすると、２組のレーザ走査ユニットの回転多面鏡の光反射面の向き（面位相）が合っていて、画像ずれのない画像が得られる。また、出力信号ＤＰ２がｃの位置に変動したときは、基準の出力信号ＤＰ１に対する他の出力信号ＤＰ２の時間差がＴ４分だけずれ、その分だけ画像ずれが生じる。そして、出力信号ＤＰ２がａの位置に変動すると、回転多面鏡の光反射面の向き（面位相）は上記ｃの位置にずれた場合と同様にＴ４分だけずれているだけであるが、出力信号の周期に近い時間分だけ変化し、１走査ピッチに近い画像ずれ（カラー画像を形成する場合は色ずれ）が突然生じることになる。より正確にいうと、（１ライン書込時間−Ｔ４）だけ画像ずれ（色ずれ）が生じることになる。
【００１７】
本発明は以上の問題点に鑑みなされたものであり、その目的は、各回転多面鏡間の回転位相をほぼ一致させるように調整する位相制御を所定のタイミングで行う光ビーム走査装置であって、各回転多面鏡の回転位相差による画像ずれ量をできる限り少なくするとともに、前記位相制御を行っていない期間に回転多面鏡の回転ムラ等による副走査方向の画像ずれが突然発生するのを防止することができる光ビーム走査装置を提供することである。
【００１８】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明は、光ビーム発生手段と、前記光ビーム発生手段で発生した光ビームを像担持体に偏向走査する回転多面鏡と、前記回転多面鏡を回転駆動する駆動手段と、前記回転多面鏡の回転位置を検出する回転位置検出手段と、回転基準信号及び前記回転位置検出手段の出力信号に基づいて前記駆動手段を制御する回転駆動制御手段と、前記回転多面鏡により偏向走査された光ビームを走査経路上の所定位置で検出する光ビーム検出手段とを複数組備え、前記各回転多面鏡に対応させて前記回転基準信号を発生する回転基準信号発生手段と、前記複数の回転多面鏡のうち基準回転多面鏡に対応する光ビーム検出手段の出力信号と、残りの各回転多面鏡に対応する光ビーム検出手段の出力信号との間の時間差を算出し、その時間差に基づいて、前記基準回転多面鏡に対して前記残りの各回転多面鏡の回転位相がほぼ一致するように前記回転基準信号発生手段を制御する位相制御手段と、前記各光ビーム検出手段の出力信号に基づいて各主走査方向における光ビーム走査を開始するとともに、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に基づいて、前記残りの各回転多面鏡で偏向走査される光ビームによる副走査方向の画像書き込みを開始するように、前記光ビーム発生手段を制御する光ビーム発生制御手段とを備えた光ビーム走査装置において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を複数回算出するとともに、その複数の時間差の最小値である最小時間差に基づいて、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御することを特徴とするものである。
【００２０】
請求項２の発明は、請求項１の光ビーム走査装置において、画像書込待機時に、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差をある周期で算出し、その時間差が予め規定した時間差よりも大きくなったときに、そのときの時間差に基づく位相制御を行うことを特徴とするものである。
【００２１】
請求項３の発明は、光ビーム発生手段と、前記光ビーム発生手段で発生した光ビームを像担持体に偏向走査する回転多面鏡と、前記回転多面鏡を回転駆動する駆動手段と、前記回転多面鏡の回転位置を検出する回転位置検出手段と、回転基準信号及び前記回転位置検出手段の出力信号に基づいて前記駆動手段を制御する回転駆動制御手段と、前記回転多面鏡により偏向走査された光ビームを走査経路上の所定位置で検出する光ビーム検出手段とを複数組備え、前記各回転多面鏡に対応させて前記回転基準信号を発生する回転基準信号発生手段と、前記複数の回転多面鏡のうち基準回転多面鏡に対応する光ビーム検出手段の出力信号と、残りの各回転多面鏡に対応する光ビーム検出手段の出力信号との間の時間差を算出し、その時間差に基づいて、前記基準回転多面鏡に対して前記残りの各回転多面鏡の回転位相がほぼ一致するように前記回転基準信号発生手段を制御する位相制御手段と、前記各光ビーム検出手段の出力信号に基づいて各主走査方向における光ビーム走査を開始するとともに、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に基づいて、前記残りの各回転多面鏡で偏向走査される光ビームによる副走査方向の画像書き込みを開始するように、前記光ビーム発生手段を制御する光ビーム発生制御手段とを備えた光ビーム走査装置において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を複数回算出し、その複数の時間差から変動幅を求め、前記複数の時間差のいずれか一つから前記変動幅を引いた減算値に基づいて、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御することを特徴とするものである。
【００２２】
請求項４の発明は、光ビーム発生手段と、前記光ビーム発生手段で発生した光ビームを像担持体に偏向走査する回転多面鏡と、前記回転多面鏡を回転駆動する駆動手段と、前記回転多面鏡の回転位置を検出する回転位置検出手段と、回転基準信号及び前記回転位置検出手段の出力信号に基づいて前記駆動手段を制御する回転駆動制御手段と、前記回転多面鏡により偏向走査された光ビームを走査経路上の所定位置で検出する光ビーム検出手段とを複数組備え、前記各回転多面鏡に対応させて前記回転基準信号を発生する回転基準信号発生手段と、前記複数の回転多面鏡のうち基準回転多面鏡に対応する光ビーム検出手段の出力信号と、残りの各回転多面鏡に対応する光ビーム検出手段の出力信号との間の時間差を算出し、その時間差に基づいて、前記基準回転多面鏡に対して前記残りの各回転多面鏡の回転位相がほぼ一致するように前記回転基準信号発生手段を制御する位相制御手段と、前記各光ビーム検出手段の出力信号に基づいて各主走査方向における光ビーム走査を開始するとともに、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に基づいて、前記残りの各回転多面鏡で偏向走査される光ビームによる副走査方向の画像書き込みを開始するように、前記光ビーム発生手段を制御する光ビーム発生制御手段とを備えた光ビーム走査装置において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を算出し、その時間差から予め測定して記憶している前記時間差の変動幅を引いた減算値に基づいて、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御することを特徴とするものである。
【００２３】
請求項５の発明は、請求項３又は４の光ビーム走査装置において、電源ＯＮ時に前記減算値に基づく前記回転基準信号発生手段の制御を行った後、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差をある周期で複数回算出し、その複数の時間差のいずれか一つが予め規定した時間差よりも大きくなったとき又はその複数の時間差から求めた変動幅が前回の位相制御に用いた変動幅よりも大きくなったとき、画像書込中でなければ、そのときの時間差から変動幅を引いた減算値に基づいて、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御する位相制御を行うことを特徴とするものである。
【００２４】
請求項６の発明は、請求項３の光ビーム走査装置において、前記位相制御に用いる時間差として、前記複数の時間差の最大値を用いることを特徴とするものである。
【００２５】
請求項７の発明は、光ビーム発生手段と、前記光ビーム発生手段で発生した光ビームを像担持体に偏向走査する回転多面鏡と、前記回転多面鏡を回転駆動する駆動手段と、前記回転多面鏡の回転位置を検出する回転位置検出手段と、回転基準信号及び前記回転位置検出手段の出力信号に基づいて前記駆動手段を制御する回転駆動制御手段と、前記回転多面鏡により偏向走査された光ビームを走査経路上の所定位置で検出する光ビーム検出手段とを複数組備え、前記各回転多面鏡に対応させて前記回転基準信号を発生する回転基準信号発生手段と、前記複数の回転多面鏡のうち基準回転多面鏡に対応する光ビーム検出手段の出力信号と、残りの各回転多面鏡に対応する光ビーム検出手段の出力信号との間の時間差を算出し、その時間差に基づいて、前記基準回転多面鏡に対して前記残りの各回転多面鏡の回転位相がほぼ一致するように前記回転基準信号発生手段を制御する位相制御手段と、前記各光ビーム検出手段の出力信号に基づいて各主走査方向における光ビーム走査を開始するとともに、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に基づいて、前記残りの各回転多面鏡で偏向走査される光ビームによる副走査方向の画像書き込みを開始するように、前記光ビーム発生手段を制御する光ビーム発生制御手段とを備えた光ビーム走査装置において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御し、前記時間差に基づく位相制御を前記画像書込動作中に行わないようにし、且つ前記時間差に基づく位相制御を行っている間は画像書込動作を禁止した画像書込待機状態にすることを特徴とするものである。
【００２６】
請求項１乃至７の発明においては、各駆動手段で回転駆動された各回転多面鏡により、各光ビーム発生手段で発生した光ビームをそれぞれ対応する像担持体に偏向走査する。
また、各回転位置検出手段により、前記各回転多面鏡の回転位置を検出し、回転駆動制御手段により、回転基準信号発生手段で発生した回転基準信号及び前記各回転位置検出手段の出力信号に基づいて、前記出力信号の周波数及び位相が前記回転基準信号の周波数及び位相に一致して前記各回転多面鏡が等速回転するように前記各駆動手段を制御する。
更に、各光ビーム検出手段により、前記各回転多面鏡により走査偏向された光ビームを各走査経路上の所定位置で検出し、光ビーム発生制御手段で光ビーム発生手段を制御し、前記各光ビーム検出手段の出力信号に基づいて各主走査方向における光ビーム走査を開始するとともに、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に基づいて、前記残りの各回転多面鏡で偏向走査される光ビームによる副走査方向の画像書き込みを開始することにより、主走査方向の画像の書き込み開始位置を所定位置に合わせるとともに、副走査方向の画像の書き込み開始位置を１走査ピッチの精度で所定位置に合わせる。
また更に、位相制御手段で前記回転基準信号発生手段を制御して、前記複数の回転多面鏡のうち基準回転多面鏡に対応する光ビーム検出手段の出力信号と、残りの各回転多面鏡に対応する光ビーム検出手段の出力信号との間の時間差を算出し、その時間差に基づいて、前記基準回転多面鏡に対して前記残りの各回転多面鏡の回転位相をほぼ一致させることにより、副走査方向の画像の書き込み開始位置を１走査ピッチ以下の精度で所定位置に合わせる。
【００２７】
そして、前記回転基準信号発生手段を制御して、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるようにすることにより、次の位相制御までの期間内において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差すなわち画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００２８】
特に、請求項１の発明では、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を複数回算出し、その複数の時間差の最小値である最小時間差に基づいて、その最小値をゼロにする方向に前記回転基準信号発生手段を制御することにより、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００２９】
また特に、請求項２の発明では、請求項１の光ビーム走査装置において、画像書込待機時に、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差をある周期で算出し、その時間差が予め規定した時間差よりも大きくなったときに、そのときの時間差の最小値に基づく位相制御を行うことにより、前記時間差が通常の変動だけでなく経時的に変化しようとする場合でも、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００３０】
また特に、請求項３の発明では、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を複数回算出し、その複数の時間差から変動幅を求め、前記複数の時間差のいずれか一つから前記変動幅を引いた減算値に基づいて、その減算値をゼロにする方向に前記回転基準信号発生手段を制御することにより、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００３１】
また特に、請求項４の発明では、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差を算出し、その時間差から予め測定して記憶している前記時間差の変動幅を引いた減算値に基づいて、その減算値をゼロにする方向に前記回転基準信号発生手段を制御することにより、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００３２】
また特に、請求項５の発明では、請求項３又は４の光ビーム走査装置において、前記減算値に基づく位相制御を電源ＯＮ時に行った後、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの時間差をある周期で複数回算出し、その複数の時間差のいずれか一つが予め規定した時間差よりも大きくなったとき又はその複数の時間差から求めた変動幅が前回の位相制御に用いた変動幅よりも大きくなったとき、画像書込中でなければ、次のような位相制御を行う。すなわち、そのときに画像書込中でなければ、そのときの時間差から変動幅を引いた減算値に基づいて、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対して、前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が同時又は常に遅れて出力されるように、前記回転基準信号発生手段を制御する。この制御により、前記時間差が通常の変動だけでなく経時的に変化しようとする場合でも、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにする。
【００３３】
また特に、請求項６の発明では、請求項３の光ビーム走査装置において、前記複数の時間差の最大値から前記変動幅を引いた減算値に基づいて、その減算値をゼロにする方向に前記回転基準信号発生手段を制御することにより、前記画像ずれ量に対応した時間差がより短くなるようにする。
【００３４】
また特に、請求項７の発明では、前記時間差に基づく位相制御を前記画像書込動作中に行わないようにし、且つ前記時間差に基づく位相制御を行っている間は画像書込動作を禁止した画像書込待機状態にすることにより、画像書込動作中に前記画像ずれ量に対応した時間差が突然変化しないようにする。
【００３５】
【発明の実施の形態】
以下、本発明を画像形成装置としての４ドラム方式のカラーレーザビームプリンタ（以下「カラープリンタ」という）に用いる光ビーム走査装置に適用した実施形態について説明する。
〔実施形態１〕
図１は本実施形態に係るカラープリンタの概略構成を示す斜視図である。このカラープリンタは４色（イエロー、マゼンタ、シアン、ブラック）の画像を重ね合わせたカラー画像を形成するために４組の画像形成部等を備えている。各画像形成部は、像担持体としての感光体ドラム１、帯電チャージャ２、光ビーム走査ユニット３、現像ユニット４、転写チャージャ５とを備え、通常の電子写真プロセスである帯電、露光、現像、転写プロセスを行い、転写ベルト６で矢印Ａ方向に搬送されている記録紙７に１色目の画像を転写し、次に２色目、３色目、４色目の順に画像を転写することにより、４色の画像が重ね合わさったカラー画像を記録紙７上に形成することができる。
【００３６】
図２は上記レーザビーム走査ユニット３の光学系の説明図であり、図３は上記レーザビーム走査ユニット３を４組備えた光ビーム走査装置の制御系のブロック図である。ここで、図３中の符号のかっこ内の数値は、その構成要素が属するレーザー走査ユニットの組数を示している。
本カラープリンタの光ビーム走査装置の各レーザ走査ユニット３は、光ビーム発生手段としてのレーザ光源（ＬＤ）８と、レーザ光源８からのレーザビームを感光体ドラム１に偏向走査する回転多面鏡としてのポリゴンミラー９と、ポリゴンミラー９を矢印Ｂ方向に回転駆動する駆動手段としてのポリゴンモータ１０と、ポリゴンミラー９の回転位置を検出する回転位置検出手段としてのホール素子１１と、後述の回転基準信号発生手段で発生した回転基準信号及びホール素子１１の出力信号に基づいてポリゴンミラー９が等速回転するようにポリゴンモータ１０を制御する回転駆動制御手段としてのモータドライバ（ＰＬＬ制御部）１２と、ポリゴンミラー９で走査偏向されたレーザビームを走査開始位置で検出する光ビーム検出手段としてのレーザビーム検知器１３と、レーザビーム検知器１３の出力信号に基づいてレーザ光源８を制御する光ビーム発生制御手段としてのコントローラ１４等を備えている。
【００３７】
上記各レーザ光源８からのレーザビームは、色分解された画像情報に基づいて作動するレーザドライバ（不図示）によりＯＮ／ＯＦＦ制御されながら、ポリゴンモータ１０で回転駆動されたポリゴンミラー９で偏向走査され、レンズを通って感光体ドラム１表面に照射される。また、レーザ光源８からのレーザビームの走査範囲（図２中のＬＤ走査範囲）の端（走査開始位置）にはビーム検知用ミラー１３ａが設けてあり、そのミラー１３ａで反射されたレーザービームが上記レーザビーム検知器１３で検知され、ビームディテクトパルス信号としてコントローラ１４に出力される。また、上記ホール素子１１からはポリゴンミラー９の回転に応じた周波数でＯＮ／ＯＦＦする繰り返しパルス信号が上記モータドライバ（ＰＬＬ制御部）１２に出力される。
【００３８】
また、上記光ビーム走査装置は各ポリゴンミラー９（１）〜９（４）に対応した複数の回転基準信号を発生する回転基準信号発生手段及びその制御手段を備えている。この回転基準信号発生手段は、図３に示すように基準信号発生器１５と４組の回転基準信号発生部１６（１）〜１６（４）と、３組のセレクタ１７（２）〜１７（３）とにより構成され、また、その位相制御手段としては上記コントローラ１４を用いている。このコントローラ１４はレーザ光源８及び上記セレクタ１７の制御の他、上記ポリゴンモータ１０の等速回転のチェックや後述のディテクタパルス信号の時間差の測定等にも用いている。
【００３９】
ところで、上記構成の光ビーム走査装置を備えたカラープリンタでカラー画像を形成する際、イエロー、マゼンタ、シアン、ブラックの各色毎に独立に作成した画像を記録紙上の正確な位置に重ね合わせる必要がある。各色の画像を記録紙上の正確な位置に重ね合わせるためには、感光体ドラム１上の各色に対応したレーザビームによる主走査方向及び副走査方向の書き込み開始位置が正確に調整されていなければならない。主走査方向の調整については、レーザビームの走査開始位置を常に上記レーザビーム検知器１３で検出して、記録画像データの書き込みタイミングを各色で調整することにより、プリンタ内の光ビーム走査装置と感光体ドラム１との相対的な位置関係が各色で完全に一致していなくても、各色の画像を重ね合わせた場合に色ずれを起こさないようにしている。一方、上記副走査方向の調整については、感光体ピッチ（図１のＬ）を走査ピッチの整数倍に保ち、レーザ走査開始位置を常にレーザビーム検知器１３で検出して、記録画像データの書き込みタイミングを上記コントローラ１４で制御することにより、各ポリゴンミラーを同一の走査周波数の回転基準信号に基づいて駆動して各色の画像形成を行い、各色の画像を重ね合わせた場合に色ずれを起こさないようにしている。
【００４０】
しかし、上記レーザビーム走査の制御を行う場合に同一位相を有する回転基準信号を各ポリゴンミラー９の回転駆動に用いると、副走査方向の１走査ピッチ以下（画像分解能３００ｄｐｉの場合で８４．６７μｍ以下）の色ずれが発生するおそれがあるので、本実施形態の光ビーム走査装置では、各ポリゴンミラー９を回転駆動するポリゴンモータ１０の回転位相を制御して、各ポリゴンミラー９の面位相を一致させて、上記色ずれを補正している。
【００４１】
図４は上記ポリゴンモータの回転位相制御のフローチャートであり、図５（ａ）及び（ｂ）はそれぞれ位相制御前の各回転基準信号及び各レーザビーム検知器１３の出力信号のタイムチャートであり、図６（ａ）及び（ｂ）はそれぞれ位相制御後の各回転基準信号及び各レーザビーム検知器１３の出力信号のタイムチャートである。
カラープリンタの電源スイッチをＯＮすると、ポリゴンモータ１０に電力が供給され、回転基準信号発生部１６（１）から出力された所定周波数の回転基準信号／ＰＣＬＫ１（図５（ａ）参照）がモータドライバ（ＰＬＬ制御部）１２（１）に供給されるとともに、回転基準信号発生部１６（１）からの回転基準信号／ＰＣＬＫ１を選択するようにセレクタ１７（２）〜１７（４）がコントローラ１４で制御され、この回転基準信号／ＰＣＬＫ１が回転基準信号／ＰＣＬＫ２〜／ＰＣＬＫ４（図５（ａ）参照。／ＰＣＬＫ３，／ＰＣＬＫ４は図示していないが／ＰＣＬＫ２と同様である。）として残りの各モータドライバ（ＰＬＬ制御部）１２（２）〜１２（４）に供給される（ステップ１）。そして、コントローラ１４から各モータドライバ（ＰＬＬ制御部）１２（１）〜１２（４）にＯＮ信号が送出されると、各ポリゴンモータ１０（１）〜１０（４）が回転し、ポリゴンモータ１０が等速回転すると、各モータドライバ（ＰＬＬ制御部）１２（１）〜１２（４）からコントローラ１４にモータロック信号が送出される（ステップ２〜４）。
【００４２】
次に、上記各ポリゴンモータ１０が等速回転すると、各レーザ光源８が点灯する（ステップ５）。この場合、図２のビーム検知用ミラー１３ａの部分をレーザビームが通過するときだけ各レーザ光源８を点灯させれば良い。このレーザ光源８の点灯により、各レーザビーム検知器１３（１）〜１３（４）からコントローラ１４にビームディテクトパルス信号ＤＰ１〜ＤＰ４が送出される（ステップ６）。例えば、図５（ｂ）に示すように、レーザビーム検知器１３（１）から信号ＤＰ１、レーザビーム検知器１３（２）から信号ＤＰ２が出力される。以下、残りのビームディテクトパルス信号ＤＰ３，ＤＰ４については、ＤＰ２と同様に考えることができるので省略する。また、ビームディテクトパルス信号ＤＰ１に対するＤＰ２の時間差がＴ５の幅で変動している場合を想定する。
【００４３】
本実施形態では、ポリゴンミラー９（１）及びポリゴンモータ１０（１）を基準にして上記位相制御を行うので、コントローラ１４において、各ビームディテクトパルス信号ＤＰ１，ＤＰ２のパルスの立ち上がりを検出し、上記信号ＤＰ１のパルス立ち上がりから残りの信号ＤＰ２のパルス立ち上がりまでの時間差Ｔ１を算出し、その算出した時間差を記憶する（ステップ７，８）。このようなビームディテクトパルス信号の検出、時間差の算出及び記憶をある決められた回数（ｎ回）だけ繰り返して行う（ステップ６〜９）。そして、上記記憶した複数の時間差の最小値を選択する（ステップ１０）。図５（ｂ）の例では時間差Ｔ２を選択する。そして、選択した時間差Ｔ２を回転基準信号発生部１６（２）に入力するためのデータに変換して（ステップ１１）、時間差Ｔ２から変換したデータを回転基準信号発生部１６（２）に入力する（ステップ１２）。
【００４４】
回転基準信号発生部１６（２）では、上記コントローラ１４から送出されてきたデータ及び上記基準信号発生器１５から送出されてきた基準信号に基づいて、図６（ａ）に示すように上記時間差Ｔ２だけ位相がずれた新たな回転基準信号／ＰＣＬＫ２が出力される（ステップ１３）。この回転基準信号／ＰＣＬＫ２はセレクタ１７（２）に送出され、コントローラ１４からの切替信号により、セレクタ１７（２）では信号／ＰＣＬＫ１から信号／ＰＣＬＫ２へ回転基準信号が切り替わり、モータドライバ（ＰＬＬ制御部）１２（２）に送出される（ステップ１４，１５）。
【００４５】
そして、モータドライバ（ＰＬＬ制御部）１２（１）では、回転位置検出用のホール素子１１から出力された回転位置検知信号と回転基準信号発生部１６（２）から出力された回転基準信号／ＰＣＬＫ２とに基づいてＰＬＬ制御が行われ、ポリゴンモータの位相制御が行われて再度各ポリゴンモータ１０（２）が等速回転するようになる。ポリゴンモータ１０（２）が等速回転するとモータロック信号が検出される（ステップ１６）。
【００４６】
図６（ｂ）は上記位相制御後のディテクトパルス信号ＤＰ１，ＤＰ２を示している。図５（ｂ）に示す位相制御前では最大（Ｔ２＋Ｔ５）分だけずれていたものが、最大Ｔ５分だけのずれになることが分かる。なお、上記位相制御では、ディテクトパルス信号ＤＰ１に対するＤＰ２の時間差に基づいてポリゴンミラー９（２）の回転位相を制御する場合について説明したが、残りのポリゴンミラー９（３），９（４）の回転位相についても、ディテクトパルス信号ＤＰ１に対するＤＰ３，４の時間差に基づいて同様に制御することができる。また、上記ディテクトパルス信号の検出及びその時間差の算出の回数は、できるだけ多い方が良い。
【００４７】
図７は、上記光ビーム走査装置を用いた画像書込制御のフローチャートである。この画像書込制御は、上記図４の位相制御が終了してから行われることになる。本実施形態では、上記基準のポリゴンミラー９（１）に対応したビームディテクトパルス信号ＤＰ１を、各レーザ走査ユニット３による画像書込開始信号に用いている。
図７において、カラープリンタの操作部又は外部コントロール部（ホスト）から画像書込開始の指令信号が送られてくると、コントローラ１４は基準のビームディテクトパルス信号ＤＰ１のカウントを開始する（ステップ１）。そして、この信号ＤＰ１の入力開始により、１色目の画像の書込を開始し、信号ＤＰ１をライン同期信号として１ラインずつ感光体ドラム１上に書き込んでいく（ステップ２，３）。上記信号ＤＰ１が規定ライン数（書込ライン数）カウントされたら、そのラインで１色目の画像の書込を終了する（ステップ４，５）。
【００４８】
ここで、１色目のレーザ走査ユニットと２色目のレーザ走査ユニットとの間の感光体ピッチＬは走査ピッチのｍ倍（ｍは整数）、１色目のレーザ走査ユニットと３色目のレーザ走査ユニットとの間の感光体ピッチＬは走査ピッチの２ｍ倍、１色目のレーザ走査ユニットと４色目のレーザ走査ユニットとの間の感光体ピッチＬは走査ピッチの３ｍ倍であるとする。
【００４９】
上記基準のビームディテクトパルス信号ＤＰ１のカウント数が（ｍ＋１）となったとき、２色目のビームディテクトパルス信号ＤＰ２のカウントを開始する（ステップ６，７）。そして、この信号ＤＰ２の入力開始により、２色目の画像の書込を開始し、信号ＤＰ２をライン同期信号として１ラインずつ感光体ドラム１上に書き込んでいく（ステップ８，９）。そして、上記信号ＤＰ２が規定ライン数（書込ライン数）カウントされたら、信号ＤＰ２のカウントを終了し、そのラインで２色目の画像の書込を終了する（ステップ１０〜１２）。
【００５０】
また、上記基準のビームディテクトパルス信号ＤＰ１のカウント数が（２ｍ＋１）となったとき、３色目のビームディテクトパルス信号ＤＰ３のカウントを開始する（ステップ１３，１４）。そして、この信号ＤＰ３の入力開始により、３色目の画像の書込を開始し、信号ＤＰ３をライン同期信号として１ラインずつ感光体ドラム１上に書き込んでいく（ステップ１５，１６）。そして、上記信号ＤＰ３が規定ライン数（書込ライン数）カウントされたら、信号ＤＰ３のカウントを終了し、そのラインで３色目の画像の書込を終了する（ステップ１７〜１９）。
【００５１】
また、上記基準のビームディテクトパルス信号ＤＰ１のカウント数が（３ｍ＋１）となったとき、４色目のビームディテクトパルス信号ＤＰ４のカウントを開始する（ステップ２０，２１）。そして、この信号ＤＰ４の入力開始により、４色目の画像の書込を開始し、信号ＤＰ４をライン同期信号として１ラインずつ感光体ドラム１上に書き込んでいく（ステップ２２，２３）。そして、上記信号ＤＰ４が規定ライン数（書込ライン数）カウントされたら、信号ＤＰ４のカウントを終了し、そのラインで４色目の画像の書込を終了する（ステップ２４〜２６）。
【００５２】
以上、本実施形態では、基準となる１色目の画像に対応したビームディテクトパルス信号ＤＰ１がそれぞれ所定回（ｍ＋１，２ｍ＋１，３ｍ＋１）検出された直後に検出されるビームディテクトパルス信号ＤＰ２，ＤＰ３，ＤＰ４により、２色目〜４色目の画像書込を開始することにより、副走査方向において各画像をの１走査ピッチ単位で重ね合わせ、各画像の色ずれが発生しないようにしている。
【００５３】
また、上記画像書込の開始の制御を行っているため、常にビームディテクトパルス信号ＤＰ１の直後に残りの信号ＤＰ２，ＤＰ３，ＤＰ４が検出されることにより、画像全体にわたって１走査ピッチ単位での画像の重ね合わせが行われるようになっているが、本実施形態では、前述の位相制御により、各ポリゴンミラー９の回転ムラ等によって上記信号ＤＰ１に対する残りの信号ＤＰ２，ＤＰ３，ＤＰ４の時間差が変動しても、常に上記ＤＰ１対して信号ＤＰ２，ＤＰ３，ＤＰ４が同時又は遅れて出力されるようになるので、画像書込動作中に１走査ピッチに近い色ずれが突然発生するのを防止できる。
【００５４】
また、前述の位相制御により、１走査ピッチ以下の色ずれは、上記ビームディテクトパルス信号ＤＰ１に対する信号ＤＰ２，ＤＰ３，ＤＰ４の時間ずれの変動幅Ｔ５に相当する分だけしか発生しない。
【００５５】
〔実施形態２〕
次に、本発明の他の実施形態について説明する。本実施形態に係る光ビーム走査装置の光学系、制御系は、上記図２及び図３の構成と同様とする。
図８は本実施形態に係るポリゴンモータの回転位相制御のフローチャートである。上記実施形態１における位相制御と異なるのは、電源ＯＮ後の１回目の位相制御が終了してモータロック信号を検出した後も、上記ディテクトパルス信号から時間差を算出してその値と予め規定した時間差と比較し、その結果に基づいて位相制御を行なっている点である。
【００５６】
以下、１回目の位相制御後のモータロック信号を検出してからの制御フローについて説明する。１回目の位相制御でモータロック信号を検出したら（ステップ１６）、画像書込可能（ＲＥＡＤＹ）状態となるが、その後もディテクトパルス信号ＤＰ１〜４の検出及び時間差（図５（ｂ）のＴ１，Ｔ２，Ｔ３等）の算出をｎ回続け、その複数の時間差の最小値Ｔ２を選出する（ステップ１７〜２１）。そして、その時間差データ（最小値）が、予め規定した時間差データよりも大きくなった場合、画像書込中でなければ、上記実施形態１で説明したデータの変換以降の動作を行い、同様の位相制御を行う（ステップ２２〜２９）。そして、以上の動作を繰り返し行う。ここで、新たに算出された時間差データ（最小値）が予め規定した時間差データ以下の場合や、画像書込動作中の場合は、上記ディテクトパルス信号ＤＰ１〜４の検出及び時間差の算出を繰り返し行うことになる。
【００５７】
なお、図８のフローチャートでは、ディテクトパルス信号ＤＰ１に対するＤＰ２，ＤＰ３，ＤＰ４の時間差に基づいてポリゴンミラー９（２）〜９（４）の位相制御が同時に行われるように示されているが、すべてパラレルで処理されている。よって、ディテクトパルス信号ＤＰ１と残りの信号ＤＰ２，ＤＰ３，ＤＰ４との時間差の最小値のひとつだけ、予め規定した時間差データよりも大きくなった場合は、その他は時間差の算出を続けることになり、その大きくなったところだけ位相制御することになる。上記時間差データの規定値は、許容できる色ずれ量から決まり、予め記憶しておき、さらに外部から変更可能としても良い。
【００５８】
本実施形態に係る位相制御によれば、電源ＯＮ時だけでなく、その後継続して上記時間差を算出し、必要に応じて位相制御を実行しているので、経時変化による色ずれの増大を防止できる。
【００５９】
〔実施形態３〕
次に、本発明の更に他の実施形態について説明する。本実施形態に係る光ビーム走査装置の光学系、制御系は、上記図２、図３の構成と同様とする。
図９は本実施形態に係るポリゴンミラーの回転位相制御のフローチャートである。上記実施形態１における位相制御と異なるのは、最小時間差ではなく、ｎ回取り込んだ分の変動幅を算出し、その中の任意の時間差から変動幅を引いたものに基づいて位相制御を行なっている点（図中のステップ１０及び１１）である。
【００６０】
図１０〜図１２はそれぞれ本実施形態３における位相制御後のボリゴンミラー９（１），９（２）の回転基準信号と位相制御後のディテクトパルス信号ＤＰ１、２を示している。位相制御前のＤＰ１とＤＰ２との関係は、図５（ｂ）に示したものとし、そのＤＰ１に対するＤＰ２の時間差の変動幅はＴ５とする。ここで、仮に上記時間差がＴ２だったとすると、回転基準信号／ＰＣＬＫ２は図１０（ａ）に示したように基準の／ＰＣＬＫ１よりＴ２‐Ｔ５だけ位相が進んだものとなり、その結果、図１０（ｂ）のように、最小Ｔ５、最大Ｔ５×２の時間差となり、その分だけ色ずれが生じる（その１）。また、仮に上記時間差がＴ１だったとすると、回転基準信号／ＰＣＬＫ２は図１１（ａ）に示したように基準の／ＰＣＬＫ１よりＴ１−Ｔ５だけ位相が進んだものとなり、その結果、図１１（ｂ）のように、最小Ｔ４、最大Ｔ４＋Ｔ５の時間差となり、その分だけ色ずれが生じる（その２）。また、仮に上記時間差がＴ３だったとすると、回転基準信号／ＰＣＬＫ２は図１２（ａ）に示したように基準の／ＰＣＬＫ１よりＴ３−Ｔ５だけ位相が進んだものとなり、その結果、図１２（ｂ）のように、最小０、最大Ｔ５の時間差となり、その分だけ色ずれが生じる（その３）。
以上、３通りの例を挙げたが、それぞれ色ずれ量に差はあるものの、いずれの場合も、１ライン近い色ずれは生じないことが分かる。
【００６１】
〔実施形態４〕
図１３は、更に他の実施形態に係る位相制御のフローチャートである。この位相制御は、基本的には上記実施形態３の図９に示す制御フローと同じであるが、ディテクトパルス信号ＤＰ１に対する信号ＤＰ２、ＤＰ３、ＤＰ４の時間差の変動幅をあらかじめ測定して記憶し、その記憶値を制御に用いている点が異なる。この場合は、図１３の制御フローのステップ７，８に示すように、上記時間差のみ算出し、その値からあらかじめ記憶してある変動幅のデータを引いて、その減算値を用いて位相制御することになる。
本実施形態に係る位相制御によれば、変動幅を算出するための機能が不要となるため、コントローラ１４の構成を簡素化することができる。
【００６２】
〔実施形態５〕
次に、本発明の更に他の実施形態について説明する。本実施形態に係る光ビーム走査装置の光学系、制御系は、上記図２、図３の構成と同様とする。
図１４は本実施形態に係るポリゴンミラーの回転位相制御のフローチャートである。本実施形態の位相制御は、基本的には上記実施形態３の制御と同じであるが、上記ディテクトパルス信号から算出した時間差の変動幅を記憶している点（図中のステップ１１）と、電源ＯＮ後の１回目の位相制御が終了してモータロック信号を検出した後も、複数のディテクトパルス信号から算出した時間差の変動幅と前回の値とを比較し、更に複数のディテクトパルス信号から選出した任意の時間差の値と予め規定した時間差とを比較し、その比較結果に基づいて位相制御を行なっている点が、上記実施形態３と異なっている。
【００６３】
図１４において、電源をＯＮした後、１回目の位相制御を行ってモータロック信号が検出されたら、画像書込可能（ＲＥＡＤＹ）状態となる（ステップ１〜１７）。このＲＥＡＤＹ状態になった後も、ディテクトパルス信号ＤＰ１〜４の検出を行い、ｎ回取り込んだ分の変動幅を算出し、複数の時間差の中から任意の時間差を選出する（ステップ１８〜２２）。そして、上記変動幅もしくは上記選出した時間差が前の位相制御で用いて記憶している変動幅、予め規定した時間差よりも大きくなった場合、画像書込中でなければ、その新しい変動幅を記憶し、時間差から変動幅を引いた減算値に基づいて位相制御を行う（ステップ２３〜３１）。変動幅が記憶されている値以下、時間差が規定値以下であった場合や、画像書込動作中の場合は、上記ディテクトパルス信号ＤＰ１〜４の検出からデータの比較までの処理を行う。また、位相制御が終了すれば、再度、上記ディテクトパルス信号ＤＰ１〜４の検出からデータの比較までの処理を行う。
【００６４】
なお、図１４のフローチャートでは、ディテクトパルス信号ＤＰ１に対するＤＰ２，ＤＰ３，ＤＰ４の時間差に基づいてポリゴンミラー９（２）〜９（４）の位相制御が同時に行われるように示されているが、すべてパラレルで処理されている。よって、ディテクトパルス信号ＤＰ１と残りの信号ＤＰ２，ＤＰ３，ＤＰ４との時間差若しくは変動幅のひとつだけ、予め規定した時間差、記憶されている変動幅と異なった場合は、その他は時間差若しくは変動幅の算出を続けることになり、異なったところだけ位相制御することになる。上記時間差データの規定値は、許容できる色ずれ量から決まり、予め記憶しておき、さらに外部から変更可能としても良い。
【００６５】
本実施形態に係る位相制御によれば、電源ＯＮ時だけでなく、その後継続して上記時間差を算出し、必要に応じて位相制御を実行しているので、経時変化による色ずれの増大を防止できる。
【００６６】
〔実施形態６〕
図１５は、更に他の実施形態に係る位相制御のフローチャートである。この位相制御は、基本的には上記実施形態５の図１４に示す制御フローと同じであるが、検出した複数の時間差から最大の時間差を選出して制御に用いている点が異なる。図５（ｂ）のディテクトパルス信号の例では、Ｔ３が最大時間差となる。
本実施形態に係る位相制御によれば、上記実施形態５の場合に比して、更に色ずれ量を少なくすることができる。
【００６７】
〔実施形態７〕
図１６は、更に他の実施形態に係る位相制御のフローチャートである。この位相制御は、基本的には上記実施形態２の図８の制御フローと同じであるが、位相制御を画像書込動作中に行わないようにし、且つ位相制御中は画像書込を禁止した画像書込待機状態にしている点が異なる。
図１６において、電源をＯＮした後、１回目の位相制御を行ってモータロック信号が検出されたら、画像書込可能（ＲＥＡＤＹ）状態となる（ステップ１〜１６）。このＲＥＡＤＹ状態になった後、画像書込可状態であることを画像書込コントロール部に知らせる（ステップ１７）。さらに最小値Ｔ２を選出して位相制御を行う際に、画像書込不可状態を同じく画像書込コントロール部に知らせ、画像書込待機状態とし、書込開始信号がきても待機していてもらう（ステップ１８〜２５）。そして、位相制御後、モータロック信号が検出されたら、画像書込を開始する（ステップ２６〜３２）。
本実施形態に係る位相制御によれば、位相制御中に画像書込を行うことによる画像の乱れを防止できる。
【００６８】
なお、上記各実施形態においては、本発明に係る光ビーム走査装置をレーザ走査ユニット及び感光体ドラムを４組備えた４ドラム方式のカラープリンターに適用した例について示したが、本発明は、４ドラム方式に限定されることなく、２ドラム、３ドラム、若しくは５ドラム方式にも適用できるものである。更に、感光体ドラム１に対して複数のレーザ走査ユニットを備えたものにも適用できるものである。
【００６９】
また、上記各実施形態においては、本発明に係る光ビーム走査装置をカラープリンターに適用した例について示したが、本発明は、複写機、ファクシミリ等の他の画像形成装置に用いる光ビーム走査装置にも適用できるものである。
【００７０】
【発明の効果】
請求項１乃至７の発明によれば、次の位相制御までの期間内において、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号が出力されてから、その直後の前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号が出力されるまでの画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにしている。従って、各回転多面鏡の回転位相差による画像ずれ量をできる限り少なくするとともに、回転多面鏡の回転ムラ等による副走査方向の画像ずれが突然発生するのを防止することができるという効果がある。
【００７１】
特に、請求項２又は５の発明によれば、前記画像ずれ量に対応した時間差が通常の変動だけでなく経時的に変化しようとする場合でも、前記画像ずれ量に対応した時間差をできるだけ短くするとともに、前記画像ずれ量に対応した時間差が前記出力信号の１周期に近い時間分だけ突然長くならないようにしているので、経時的な変化による画像ずれも防止できるという効果がある。
【００７２】
また特に、請求項４の発明によれば、前記基準回転多面鏡に対応する光ビーム検出手段の出力信号に対する前記残りの各回転多面鏡に対応する光ビーム検出手段の出力信号の時間差から、予め測定して記憶している前記時間差の変動幅を引いた減算値に基づいて、前記回転基準信号発生手段を制御しているので、前記時間差を複数回算出し、その複数の時間差から変動幅を更に算出するものに比して、前記変動幅を算出する機能の分だけ位相制御手段の構成を簡素化することができるという効果がある。
【００７３】
また特に、請求項６の発明によれば、前記複数の時間差の最大値から前記変動幅を引いた減算値に基づいて、その減算値をゼロにする方向に前記回転基準信号発生手段を制御することにより、前記画像ずれ量に対応した時間差がより短くなるので、更に画像ずれ量を少なくすることができるという効果がある。
【００７４】
また特に、請求項７の発明によれば、前記時間差に基づく位相制御を前記画像書込動作中に行わないようにし、且つ前記時間差に基づく位相制御を行っている間は画像書込動作を禁止した画像書込待機状態にすることにより、画像書込動作中に前記画像ずれ量に対応した時間差が突然変化しないようにしているので、位相制御中に画像書込を行うことによる画像の乱れを防ぐことができるという効果がある。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るカラープリンタの概略構成を示す斜視図。
【図２】同カラープリンタのレーザビーム走査ユニットの光学系の説明図。
【図３】同カラープリンタの光ビーム走査装置の制御系のブロック図。
【図４】同光ビーム走査装置における回転位相制御のフローチャート。
【図５】（ａ）及び（ｂ）はそれぞれ位相制御前の回転基準信号及び各レーザビーム検知器の出力信号のタイムチャート。
【図６】（ａ）及び（ｂ）はそれぞれ位相制御後の回転基準信号及び各レーザビーム検知器の出力信号のタイムチャート。
【図７】同光ビーム走査装置による画像書込制御のフローチャート。
【図８】他の実施形態に係る回転位相制御のフローチャート。
【図９】更に他の実施形態に係る回転位相制御のフローチャート。
【図１０】（ａ）及び（ｂ）は、同回転位相制御における位相制御後の回転基準信号及びレーザビーム検知器の出力信号の一例を示すタイムチャート。
【図１１】（ａ）及び（ｂ）は、同回転位相制御における位相制御後の回転基準信号及びレーザビーム検知器の出力信号の他の一例を示すタイムチャート。
【図１２】（ａ）及び（ｂ）はそれぞれ同回転位相制御における位相制御後の回転基準信号及びレーザビーム検知器の出力信号の更に他の一例を示すタイムチャート。
【図１３】更に他の実施形態に係る回転位相制御のフローチャート。
【図１４】更に他の実施形態に係る回転位相制御のフローチャート。
【図１５】更に他の実施形態に係る回転位相制御のフローチャート。
【図１６】更に他の実施形態に係る回転位相制御のフローチャート。
【図１７】（ａ）及び（ｂ）はそれぞれ従来例に係る回転位相制御の前及び後におけるレーザビーム検知器の出力信号のタイムチャート。
【符号の説明】
１感光体ドラム
３光ビーム走査ユニット
８レーザ光源
９ポリゴンミラー
１０ポリゴンモータ
１１ホール素子
１２モータドライバ
１３レーザビーム検知器
１４コントローラ
１５基準信号発生器
１６回転基準信号発生部
１７セレクタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light beam scanning device used for an image forming device (including a color image forming device) such as a copying machine, a facsimile, a printer, a printing machine, and more particularly to a light beam scanning device having a plurality of rotating polygon mirrors. It relates to the control of the rotation phase between the respective rotating polygon mirrors.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a light beam scanning device used in an image forming apparatus such as a copying machine, a facsimile, a printer, a printing machine, etc., a light beam generating means, and a rotating polygonal surface which deflects and scans an image carrier with a light beam generated by the light beam generating means. A mirror, driving means for rotating the rotating polygon mirror, rotating position detecting means for detecting a rotating position of the rotating polygon mirror, and the rotating polygon mirror based on a rotation reference signal and an output signal of the rotating position detecting means. A plurality of sets of rotation drive control means for controlling the drive means so as to rotate at a constant speed, and a rotation reference signal generating means for generating the rotation reference signal corresponding to each of the rotary polygon mirrors It has been known.
[0003]
In the light beam scanning device having the above configuration, based on each rotation reference signal generated by the rotation reference signal generation unit and the output signal of each rotation position detection unit, each driving unit is controlled so that each rotating polygon mirror rotates at a constant speed. Control. In the image forming apparatus equipped with the light beam scanning device, an independent latent image is formed on the corresponding image carrier by the light beam deflected and scanned by each rotating polygon mirror, and the latent image is developed. Each image is superimposed and transferred on a recording medium. Here, in order to superimpose each image on an accurate position on a recording medium, the main scanning direction (light beam scanning direction) and the sub-scanning direction (moving direction of the image carrier surface) of each image on the image carrier are required. ) Must be accurately adjusted.
[0004]
For the main scanning direction, for example, a light beam is detected at a predetermined position on a scanning path, and the writing timing of each scanning line of an image is adjusted based on the detection result. Even if the initial mounting angle of the mirror to the image carrier, that is, the surface phase of each rotary polygon mirror does not completely coincide with each other, it is possible to prevent the occurrence of image shift in the main scanning direction.
[0005]
On the other hand, in the sub-scanning direction, for example, when a plurality of image carriers are provided corresponding to a plurality of rotating polygon mirrors, the interval (pitch) between the image carriers is set to an integral multiple of the scanning pitch, and The writing start timing is adjusted in units of time required for one light beam scanning, and the image is written by rotating the polygon mirror based on the rotation reference signal of the same frequency, thereby performing one scanning over the entire image. It is possible to prevent the occurrence of an image shift in the sub-scanning direction larger than the pitch.
[0006]
However, even when the image writing start timing is adjusted in the unit of time required for the one light beam scanning, if the surface phases between the rotating polygon mirrors do not completely match each other, the scanning pitch is equal to or less than one scanning pitch. There is a problem that an image shift in the sub-scanning direction occurs (84.67 μm or less at an image resolution of 300 dpi). This image shift causes a problem of color shift when a color image is formed.
[0007]
Therefore, conventionally, in order to prevent the image shift in the sub-scanning direction of one scanning pitch or less, a method of controlling the rotation phase between the rotating polygon mirrors as follows is known.
[0008]
For example, in Japanese Patent Application Laid-Open No. 64-73369, a reference frequency as the rotation reference signal generating means for generating a reference frequency signal as the rotation reference signal is provided to each of the PLL control means as the rotation drive control means. The signal generation means and the horizontal synchronization signal output timing difference output from each of the synchronization sensors remaining in synchronization with the output of the horizontal synchronization signal as the output signal output from one synchronization sensor as the light beam detection means, Timing measuring means for measuring based on the reference frequency signal, and phase adjusting means for adjusting the phase of the reference frequency signal to be supplied to the PLL control means based on the difference between each horizontal synchronization signal output timing measured by the timing measuring means An apparatus comprising:
[0009]
According to this device, one PLL control unit starts the rotation speed control of the rotating polyhedron (rotating polygon mirror) based on the reference frequency signal generated by the reference frequency signal generating unit. When the synchronous sensor generates a horizontal synchronizing signal after receiving the laser beam deflected by the rotating polyhedron rotating at a constant speed, the timing measuring means remains in synchronization with the output of the horizontal synchronizing signal output from one synchronous sensor. A horizontal synchronization signal output timing difference output from each synchronization sensor is measured based on the reference frequency signal. Then, based on the measured horizontal synchronization signal output timing differences, the phase adjustment unit adjusts the phase of the reference frequency signal supplied to the PLL control unit. Thus, the phase shift can be finely adjusted within the pixel unit distance, and the top scan line shift of each laser beam on each photosensitive drum (image carrier) can be set to the minimum.
[0010]
In addition, for example, in Japanese Patent Application Laid-Open No. 2-170110, detecting means for receiving each light beam deflected by each rotating polygon mirror and detecting a phase difference between the beams, and detecting the phase difference detected by the detecting means The rotation phase angle of the driving means for rotating each rotating polygon mirror at a constant speed depends on the one rotating polygon mirror so as to cancel a phase angle difference between at least one rotating polygon mirror and each of the remaining rotating polygon mirrors. A light beam scanning device having phase control means for individually controlling the light beam is disclosed.
[0011]
According to this device, when each rotating polygon mirror is started by each driving means and reaches a constant speed rotation, the detecting means receives each light beam deflected by each rotating polygon mirror and detects a phase difference of each light beam. And the phase difference information is sent to the phase control means. The phase control means individually sets the rotation phase angle of each drive means and one rotation polygon so that the phase difference between at least one rotation polygon mirror and each of the remaining rotation polygon mirrors is canceled based on the detected phase difference. By controlling the mirrors to be dependent on each other, it is possible to match the write start positions of the respective light beams which are deflected and scanned from each rotary polygon mirror to the image carrier.
[0012]
Also, the above-mentioned Japanese Patent Application Laid-Open No. 2-170110 discloses an embodiment of the following two-beam system. The rotation phase synchronization control device, which also serves as the detection means and the phase control means, comprises: a first beam detect pulse signal which is an output signal from a first laser beam detector as the light beam detection means; When a second beam detect pulse signal, which is an output signal from the second laser beam detector as a means, is transmitted with a phase difference, the phase difference is measured by a time measuring means such as an internal counter circuit, and the rotation is measured. Of the plurality of reference signals output from the reference signal generator as the reference signal generating means, a reference signal for generating a phase close to the measured phase difference is selected by a selection switch and the second rotary polygon mirror is selected. The signal is sent to a second phase synchronization control unit as a rotation drive control unit for controlling the rotation drive. Accordingly, the first and second motors as the driving unit control the rotation drive of the second phase synchronization control unit and the first rotary polygon mirror using the reference signal for generating the measured phase difference. The phase synchronization control is performed by the first phase synchronization control unit. The phases of the subsequent first and second beam detection pulse signals are substantially the same, and the beam reflection surfaces of the first and second rotary polygon mirrors are in the same phase. It becomes. Therefore, the image writing positions by the respective light beams that are deflected and scanned from the first and second rotary polygon mirrors to the photosensitive drum as the image carrier become coincident.
[0013]
For example, in Japanese Patent Application Laid-Open No. Hei 5-227383, a reference write start position detection signal from a scanner motor serving as a driving means of a rotary polygon mirror serving as a reference and a write start position detection signal from a scanner motor of the remaining rotary polygon mirror are determined. It takes in the microprocessor as means, judges the time lag of the other writing position detection signal with respect to the reference writing position detection signal, and based on the judgment result, the scanner motor of the remaining rotary polygon mirror, the motor of the motor is used. One that supplies a phase control signal that increases or decreases the rotation speed is disclosed. With this configuration, the write start position by the remaining rotary polygon mirror is made coincident with the write start position by the reference rotary polygon mirror to correct the positional deviation in the sub-scanning direction.
[0014]
[Problems to be solved by the invention]
However, in the rotary polygon mirror used in the conventional apparatus that performs the phase control for controlling the rotation phase of each of the rotary polygon mirrors, the rotation unevenness is slightly generated due to the drive unevenness of the driving unit. This uneven rotation tends to increase due to a rise in temperature and deterioration over time in the driving means and the rotation driving control means for controlling the driving means. Further, the length in the rotation direction of the light reflecting surface formed on the rotary polygon mirror also varies slightly. If there is such a rotation unevenness of the rotating polygon mirror or a variation in the length of the light reflecting surface, the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror and the output signal of the light beam detecting means corresponding to the remaining rotating polygon mirror will be reduced. It is considered that the time difference from the output signal also varies.
[0015]
Further, in the phase control of the above-described conventional apparatus, based on a light beam detection signal corresponding to a reference rotary polygon among a plurality of rotary polygons, an optical writing position is controlled so as to control an image writing position of each of the remaining rotary polygons. By controlling the beam generating means, phase control is performed so that the image writing position of each of the remaining rotary polygon mirrors coincides with the image writing position of the reference rotary polygon mirror. For example, when an output signal from the light beam detection signal corresponding to the reference rotary polygon mirror is detected a predetermined number of times, the light beam generating means is controlled so as to start image writing by the remaining rotary polygon mirror. Therefore, if the time difference between the output signals of the light beam detecting means varies as described above during the period in which the phase control is not performed, such as the image writing operation period, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is changed. After receiving, the time until receiving the output signal of the light beam detecting means corresponding to the remaining rotary polygon mirror suddenly changes by a time close to the cycle of this output signal, and the image in the sub-scanning direction close to one scanning pitch The displacement may occur suddenly.
[0016]
The image shift in the sub-scanning direction will be described with reference to a specific example of a time chart of the output signal of the light beam detecting means before and after the phase control shown in FIGS. 17A and 17B. In this specific example, two sets of laser scanning units including a laser as a light beam generating means and a rotating polygon mirror are provided, and the laser is turned on and the rotating polygon mirror is rotated at a constant speed. As described above, output signals (referred to as a write start position detection signal, a horizontal synchronization signal, or a detector pulse signal in the above-described conventional example) are output from the light beam detection means corresponding to each rotary polygon mirror. . Here, the time difference (timing difference) of another output signal DP2 with respect to the output signal DP1 is measured with reference to the output signal DP1. Assuming that the time difference fluctuates by twice the value of T4 as shown by, the measured time difference is defined as T1 as shown in FIG. When the conventional phase control based on the time difference T1 is performed under such a condition, a time chart of each output signal is as shown in FIG. After this phase control, the time difference between the other output signal DP2 and the reference output signal DP1 is twice as long as T4. For example, if the output signal DP2 is located at the position b, two sets of laser scanning are performed. The direction (surface phase) of the light reflecting surface of the rotary polygon mirror of the unit is matched, and an image without image shift can be obtained. Further, when the output signal DP2 changes to the position c, the time difference between the reference output signal DP1 and the other output signal DP2 is shifted by T4, and an image shift occurs by that amount. When the output signal DP2 changes to the position a, the direction (surface phase) of the light reflecting surface of the rotary polygon mirror is shifted only by T4 as in the case of shifting to the position c above. It changes by the amount of time close to the signal period, and an image shift close to one scanning pitch (color shift when a color image is formed) suddenly occurs. More precisely, an image shift (color shift) occurs by (one line writing time-T4).
[0017]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a light beam scanning device that performs phase control at a predetermined timing to adjust the rotational phases of respective rotary polygon mirrors so as to substantially match each other. In addition, while minimizing the amount of image shift due to the rotational phase difference between the rotary polygon mirrors, it is possible to prevent sudden occurrence of image shift in the sub-scanning direction due to uneven rotation of the rotary polygon mirror during the period when the phase control is not performed. It is to provide a light beam scanning device that can perform the scanning.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on an image carrier, and rotating the rotating polygon mirror. A driving unit for driving, a rotation position detection unit for detecting a rotation position of the rotary polygon mirror, a rotation drive control unit for controlling the driving unit based on a rotation reference signal and an output signal of the rotation position detection unit, A plurality of sets of light beam detecting means for detecting a light beam deflected and scanned by the rotating polygon mirror at a predetermined position on a scanning path, and generating a rotation reference signal for generating the rotation reference signal corresponding to each of the rotating polygon mirrors Means, and a time difference between an output signal of the light beam detecting means corresponding to the reference rotating polygon mirror among the plurality of rotating polygon mirrors and an output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors. Phase control means for controlling the rotation reference signal generating means so that the rotation phases of the remaining rotary polygon mirrors substantially match the reference rotary polygon mirror based on the time difference, and each of the light beams The light beam scanning in each main scanning direction is started based on the output signal of the detecting means, and the deflection scanning is performed by each of the remaining rotating polygon mirrors based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror. Light beam generating control means for controlling the light beam generating means, so as to start image writing in the sub-scanning direction by the light beam to be performed,A plurality of time differences from when the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors immediately after the output signal are output are plural. Times, and based on the minimum time difference that is the minimum value of the plurality of time differences,With respect to the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, the rotation signal is output such that the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors is output simultaneously or always with a delay. It is characterized by controlling the reference signal generating means.
[0020]
Claim2The invention of claim1In the light beam scanning device, when an output signal of the light beam detecting means corresponding to the reference rotating polygon is output during standby for image writing, light beam detection corresponding to each of the remaining rotating polygons immediately after the output signal is performed. A time difference until an output signal of the means is output is calculated in a certain cycle, and when the time difference becomes larger than a predetermined time difference, phase control based on the time difference at that time is performed. is there.
[0021]
Claim3The invention ofA light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position, a rotation reference signal generating means for generating the rotation reference signal corresponding to each of the rotary polygon mirrors, and a reference rotation polygon mirror among the plurality of rotation polygon mirrors The time difference between the output signal of the light beam detecting means corresponding to the above and the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is calculated, and based on the time difference, the reference rotation time is calculated. Phase control means for controlling the rotation reference signal generation means so that the rotation phases of the remaining rotary polygon mirrors substantially coincide with the mirror; and each main scanning direction based on the output signal of each light beam detection means. At the same time, and based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, write the image in the sub-scanning direction with the light beam deflected and scanned by each of the remaining rotating polygon mirrors. Light beam generation control means for controlling the light beam generation means to startIn the light beam scanning device, after the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output, the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors immediately thereafter is output. Calculate the time difference until a plurality of times, obtain a variation range from the plurality of time differences, based on a subtraction value obtained by subtracting the variation range from any one of the plurality of time differences,For the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, so that the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors is output simultaneously or always with a delay,The rotation reference signal generating means is controlled.
[0022]
Claim4The invention ofA light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position, a rotation reference signal generating means for generating the rotation reference signal corresponding to each of the rotary polygon mirrors, and a reference rotation polygon mirror among the plurality of rotation polygon mirrors The time difference between the output signal of the light beam detecting means corresponding to the above and the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is calculated, and based on the time difference, the reference rotation time is calculated. Phase control means for controlling the rotation reference signal generation means so that the rotation phases of the remaining rotary polygon mirrors substantially coincide with the mirror; and each main scanning direction based on the output signal of each light beam detection means. At the same time, and based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, write the image in the sub-scanning direction with the light beam deflected and scanned by each of the remaining rotating polygon mirrors. Light beam generation control means for controlling the light beam generation means to startIn the light beam scanning device, after the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output, the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors immediately thereafter is output. Is calculated based on a subtraction value obtained by subtracting a fluctuation range of the time difference measured and stored in advance from the time difference,For the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, so that the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors is output simultaneously or always with a delay,The rotation reference signal generating means is controlled.
[0023]
Claim5The invention of claim3Or4Light beam scanning deviceAfter the power is turned on, the control of the rotation reference signal generating means based on the subtraction value is performed.There is a time difference from when the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors immediately after the output signal is output. Calculated multiple times in a cycle, and one of the multiple time differencesWhen the time difference becomes larger than a predetermined time difference or when the fluctuation width obtained from the plurality of time differences becomes larger than the fluctuation width used for the previous phase control, unless the image is being written, the time difference at that time is used. Based on the subtraction value obtained by subtracting the fluctuation range, the output signal of the light beam detecting means corresponding to each of the remaining rotating polygons is simultaneously or simultaneously output with respect to the output signal of the light beam detecting means corresponding to the reference rotating polygon. The rotation reference signal generating means is controlled so that the output is always delayed.It is characterized by performing phase control.
[0024]
Claim6The invention of claim3Wherein the maximum value of the plurality of time differences is used as the time difference used for the phase control.
[0025]
Claim7The invention ofA light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position, a rotation reference signal generating means for generating the rotation reference signal corresponding to each of the rotary polygon mirrors, and a reference rotation polygon mirror among the plurality of rotation polygon mirrors The time difference between the output signal of the light beam detecting means corresponding to the above and the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is calculated, and based on the time difference, the reference rotation time is calculated. Phase control means for controlling the rotation reference signal generation means so that the rotation phases of the remaining rotary polygon mirrors substantially coincide with the mirror; and each main scanning direction based on the output signal of each light beam detection means. At the same time, and based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, write the image in the sub-scanning direction with the light beam deflected and scanned by each of the remaining rotating polygon mirrors. Light beam generation control means for controlling the light beam generation means to startIn a light beam scanning device,With respect to the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, the rotation signal is output such that the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors is output simultaneously or always with a delay. Controlling the reference signal generating means,The phase control based on the time difference is not performed during the image writing operation, and the image writing operation is prohibited while the phase control based on the time difference is performed. To do.
[0026]
Claims 1 through7According to the invention, the light beams generated by the light beam generating means are deflected and scanned by the respective rotating polygon mirrors driven by the respective driving means onto the corresponding image carriers.
In addition, each rotation position detection means detects the rotation position of each of the rotary polygon mirrors, and the rotation drive control means based on the rotation reference signal generated by the rotation reference signal generation means and the output signal of each rotation position detection means. The driving means is controlled such that the frequency and the phase of the output signal coincide with the frequency and the phase of the rotation reference signal, and the respective rotating polygon mirrors rotate at a constant speed.
Further, each light beam detecting means detects a light beam scanned and deflected by each of the rotating polygonal mirrors at a predetermined position on each scanning path, and the light beam generation control means controls the light beam generating means, and The light beam scanning in each main scanning direction is started based on the output signal of the beam detecting means, and is deflected by each of the remaining rotating polygon mirrors based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror. By starting image writing in the sub-scanning direction by the scanned light beam, the writing start position of the image in the main scanning direction is adjusted to a predetermined position, and the writing start position of the image in the sub-scanning direction is adjusted with an accuracy of one scanning pitch. Adjust to the predetermined position.
Still further, the rotation control signal generation means is controlled by the phase control means, and the output signal of the light beam detection means corresponding to the reference rotation polygon mirror among the plurality of rotation polygon mirrors, and the output signal corresponding to each of the remaining rotation polygon mirrors A sub-scan is performed by calculating a time difference between the output signal of the light beam detecting means and the rotation phase of each of the remaining rotary polygon mirrors with respect to the reference rotary polygon mirror based on the time difference. The writing start position of the image in the direction is adjusted to a predetermined position with an accuracy of one scanning pitch or less.
[0027]
Then, by controlling the rotation reference signal generation means, the output signal of the light beam detection means corresponding to each of the remaining rotation polygon mirrors is changed with respect to the output signal of the light beam detection means corresponding to the reference rotation polygon mirror. By simultaneously or always delaying the output, during the period until the next phase control, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, and then the remaining The time difference until the output signal of the light beam detecting means corresponding to each rotary polygon mirror is output, that is, the time difference corresponding to the image shift amount is made as short as possible, and the time difference corresponding to the image shift amount is one of the output signals. Make sure that it does not suddenly become longer by the time close to the cycle.
[0028]
In particular,Claim1In the invention of,PreviousA plurality of time differences from when the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors immediately after the output signal is output are plural. Times, and based on the minimum time difference that is the minimum value of the plurality of time differences, controlling the rotation reference signal generating means in a direction to reduce the minimum value to zero, so that the time difference corresponding to the image shift amount can be reduced as much as possible. In addition to shortening, the time difference corresponding to the image shift amount is prevented from being suddenly increased by a time close to one cycle of the output signal.
[0029]
In particular,Claim2In the invention of the claim,1In the light beam scanning device, when an output signal of the light beam detecting means corresponding to the reference rotating polygon is output during standby for image writing, light beam detection corresponding to each of the remaining rotating polygons immediately after the output signal is performed. By calculating the time difference until the output signal of the means is output in a certain cycle, and when the time difference becomes larger than a predetermined time difference, by performing phase control based on the minimum value of the time difference at that time, Even when the time difference is going to change over time as well as the normal fluctuation, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is close to one cycle of the output signal. Don't suddenly lengthen by minutes.
[0030]
In particular,Claim3In the invention of,PreviousA plurality of time differences from when the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors immediately after the output signal is output are plural. The rotation reference signal is generated in a direction to make the subtraction value zero based on a subtraction value obtained by subtracting the variation width from any one of the plurality of time differences. By controlling the means, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is prevented from suddenly increasing by a time close to one cycle of the output signal.
[0031]
In particular,Claim4In the invention of,PreviousThe time difference from when the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors immediately after that is output is calculated. Then, based on a subtraction value obtained by subtracting a variation width of the time difference measured and stored in advance from the time difference, the rotation reference signal generating unit is controlled in a direction to make the subtraction value zero, thereby obtaining the image. The time difference corresponding to the shift amount is made as short as possible, and the time difference corresponding to the image shift amount is prevented from suddenly increasing by a time close to one cycle of the output signal.
[0032]
In particular,Claim5In the invention of the claim,3Or4Light beam scanning device, After performing the phase control based on the subtraction value when the power is turned on,There is a time difference from when the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors immediately after the output signal is output. Calculated multiple times in a cycle, and one of the multiple time differencesWhen the time difference becomes larger than a predetermined time difference or when the fluctuation width obtained from the plurality of time differences becomes larger than the fluctuation width used in the previous phase control, if the image writing is not being performed, the following phase is used. Perform control. That is, if the image writing is not being performed at that time, the output signal of the light beam detecting means corresponding to the reference rotary polygon is based on the subtraction value obtained by subtracting the fluctuation range from the time difference at that time, and The rotation reference signal generating means is controlled so that the output signals of the light beam detecting means corresponding to each of the rotary polygon mirrors are output simultaneously or always with a delay. This controlTherefore, even when the time difference is not only a normal change but also changes with time, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is one cycle of the output signal. Avoid suddenly increasing the time close to.
[0033]
In particular,Claim6In the invention of,Request3In the light beam scanning device, based on a subtraction value obtained by subtracting the fluctuation range from a maximum value of the plurality of time differences, the rotation reference signal generating unit is controlled in a direction to make the subtraction value zero, thereby obtaining the image. The time difference corresponding to the shift amount is made shorter.
[0034]
In particular,Claim7In the invention of,PreviousThe phase control based on the time difference is prevented from being performed during the image writing operation, and the image writing operation is prohibited while the phase control based on the time difference is being performed. The time difference corresponding to the image shift amount does not suddenly change during the writing operation.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a light beam scanning device used in a four-drum type color laser beam printer (hereinafter, referred to as a “color printer”) as an image forming apparatus will be described.
[Embodiment 1]
FIG. 1 is a perspective view illustrating a schematic configuration of the color printer according to the present embodiment. This color printer includes four sets of image forming units and the like for forming a color image in which images of four colors (yellow, magenta, cyan, and black) are superimposed. Each image forming unit includes a photosensitive drum 1 as an image carrier, a charging charger 2, a light beam scanning unit 3, a developing unit 4, and a transfer charger 5, and performs charging, exposure, development, and normal electrophotographic processes. By performing a transfer process, the first color image is transferred onto the recording paper 7 conveyed by the transfer belt 6 in the direction of arrow A, and then the second color image, the third color image, and the fourth color image are transferred in this order. Can be formed on the recording paper 7.
[0036]
FIG. 2 is an explanatory diagram of an optical system of the laser beam scanning unit 3, and FIG. 3 is a block diagram of a control system of a light beam scanning device including four sets of the laser beam scanning unit 3. Here, the numerical values in parentheses of the reference numerals in FIG. 3 indicate the number of sets of laser scanning units to which the constituent elements belong.
Each laser scanning unit 3 of the light beam scanning device of the present color printer includes a laser light source (LD) 8 as a light beam generating means and a rotary polygon mirror for deflecting and scanning the laser beam from the laser light source 8 onto the photosensitive drum 1. A polygon mirror 9, a polygon motor 10 as driving means for driving the polygon mirror 9 to rotate in the direction of arrow B, a Hall element 11 as rotation position detecting means for detecting the rotation position of the polygon mirror 9, and a rotation reference A motor driver (PLL control unit) 12 as rotation drive control means for controlling the polygon motor 10 so that the polygon mirror 9 rotates at a constant speed based on the rotation reference signal generated by the signal generation means and the output signal of the Hall element 11; A light beam detecting means for detecting a laser beam scanned and deflected by the polygon mirror 9 at a scanning start position. A laser beam sensor 13, a controller 14 such as a light beam generation control unit for controlling the laser light source 8 based on the output signal of the laser beam sensor 13.
[0037]
The laser beam from each of the laser light sources 8 is turned on / off by a laser driver (not shown) operating based on the color-separated image information, and is deflected and scanned by a polygon mirror 9 rotationally driven by a polygon motor 10. Then, the light is irradiated on the surface of the photosensitive drum 1 through the lens. Further, a beam detecting mirror 13a is provided at an end (scanning start position) of a scanning range (LD scanning range in FIG. 2) of the laser beam from the laser light source 8, and the laser beam reflected by the mirror 13a is used for the mirror 13a. The laser beam is detected by the laser beam detector 13 and output to the controller 14 as a beam detect pulse signal. Further, a repetitive pulse signal that is turned on / off at a frequency corresponding to the rotation of the polygon mirror 9 is output from the Hall element 11 to the motor driver (PLL control unit) 12.
[0038]
Further, the light beam scanning device includes a rotation reference signal generating means for generating a plurality of rotation reference signals corresponding to each of the polygon mirrors 9 (1) to 9 (4), and a control means therefor. As shown in FIG. 3, the rotation reference signal generating means includes a reference signal generator 15, four sets of rotation reference signal generators 16 (1) to 16 (4), and three sets of selectors 17 (2) to 17 ( 3), and the controller 14 is used as the phase control means. In addition to controlling the laser light source 8 and the selector 17, the controller 14 is also used for checking the rotation of the polygon motor 10 at a constant speed, measuring the time difference between detector pulse signals described later, and the like.
[0039]
By the way, when forming a color image with a color printer equipped with the light beam scanning device having the above configuration, it is necessary to superimpose independently created images for each color of yellow, magenta, cyan, and black at an accurate position on recording paper. is there. In order to superimpose the image of each color on the accurate position on the recording paper, the writing start position in the main scanning direction and the sub-scanning direction by the laser beam corresponding to each color on the photosensitive drum 1 must be accurately adjusted. . The main scanning direction is adjusted by always detecting the scanning start position of the laser beam with the laser beam detector 13 and adjusting the writing timing of the recording image data for each color, thereby making the light beam scanning device in the printer compatible with the light beam scanning device. Even if the relative positional relationship with the body drum 1 does not completely match for each color, color misregistration does not occur when images of each color are superimposed. On the other hand, for the adjustment in the sub-scanning direction, the photoconductor pitch (L in FIG. 1) is maintained at an integral multiple of the scanning pitch, and the laser scanning start position is always detected by the laser beam detector 13 to write the recording image data. By controlling the timing by the controller 14, each polygon mirror is driven based on the rotation reference signal of the same scanning frequency to form an image of each color, and no color shift occurs when the images of each color are superimposed. Like that.
[0040]
However, if the rotation reference signals having the same phase are used for the rotation drive of each polygon mirror 9 in controlling the laser beam scanning, one rotation pitch or less in the sub-scanning direction (84.67 μm or less in the case of 300 dpi image resolution) In the light beam scanning device according to the present embodiment, the rotational phase of the polygon motor 10 for driving the polygon mirrors 9 is controlled so that the surface phases of the polygon mirrors 9 match. Thus, the color shift is corrected.
[0041]
FIG. 4 is a flowchart of the rotation phase control of the polygon motor, and FIGS. 5A and 5B are time charts of each rotation reference signal and the output signal of each laser beam detector 13 before the phase control, respectively. FIGS. 6A and 6B are time charts of the respective rotation reference signals and the output signals of the respective laser beam detectors 13 after the phase control.
When the power switch of the color printer is turned on, power is supplied to the polygon motor 10, and the rotation reference signal / PCLK1 (see FIG. 5A) of a predetermined frequency output from the rotation reference signal generator 16 (1) is output to the motor driver. (PLL control unit) The selectors 17 (2) to 17 (4) are supplied to the controller 14 so as to select the rotation reference signal / PCLK1 from the rotation reference signal generation unit 16 (1). The remaining motors are controlled and this rotation reference signal / PCLK1 is used as rotation reference signals / PCLK2 to / PCLK4 (see FIG. 5A. / PCLK3 and / PCLK4 are not shown but are the same as / PCLK2). The signals are supplied to drivers (PLL control units) 12 (2) to 12 (4) (step 1). When an ON signal is sent from the controller 14 to each of the motor drivers (PLL control units) 12 (1) to 12 (4), the polygon motors 10 (1) to 10 (4) rotate, and the polygon motors 10 (1) to 10 (4) rotate. Is rotated at a constant speed, a motor lock signal is sent from the motor drivers (PLL control units) 12 (1) to 12 (4) to the controller 14 (steps 2 to 4).
[0042]
Next, when each polygon motor 10 rotates at a constant speed, each laser light source 8 is turned on (step 5). In this case, each laser light source 8 may be turned on only when the laser beam passes through the beam detecting mirror 13a in FIG. When the laser light source 8 is turned on, beam detection pulse signals DP1 to DP4 are transmitted from the laser beam detectors 13 (1) to 13 (4) to the controller 14 (step 6). For example, as shown in FIG. 5B, a signal DP1 is output from the laser beam detector 13 (1), and a signal DP2 is output from the laser beam detector 13 (2). Hereinafter, the remaining beam detect pulse signals DP3 and DP4 will not be described because they can be considered in the same manner as DP2. It is also assumed that the time difference between DP2 and the beam detect pulse signal DP1 fluctuates within the width of T5.
[0043]
In the present embodiment, since the phase control is performed with reference to the polygon mirror 9 (1) and the polygon motor 10 (1), the controller 14 detects the rise of the pulse of each of the beam detect pulse signals DP1 and DP2, and The time difference T1 from the pulse rise of the signal DP1 to the pulse rise of the remaining signal DP2 is calculated, and the calculated time difference is stored (steps 7, 8). Such detection of the beam detect pulse signal, calculation and storage of the time difference are repeated a predetermined number of times (n times) (steps 6 to 9). Then, the minimum value of the plurality of stored time differences is selected (step 10). In the example of FIG. 5B, the time difference T2 is selected. Then, the selected time difference T2 is converted into data for input to the rotation reference signal generator 16 (2) (step 11), and the data converted from the time difference T2 is input to the rotation reference signal generator 16 (2). (Step 12).
[0044]
In the rotation reference signal generator 16 (2), based on the data sent from the controller 14 and the reference signal sent from the reference signal generator 15, as shown in FIG. A new rotation reference signal / PCLK2 whose phase is shifted by only this is output (step 13). The rotation reference signal / PCLK2 is sent to the selector 17 (2), and the switching signal from the controller 14 causes the selector 17 (2) to switch the rotation reference signal from the signal / PCLK1 to the signal / PCLK2, and the motor driver (PLL control unit) ) 12 (2) (steps 14 and 15).
[0045]
Then, the motor driver (PLL control unit) 12 (1) receives the rotation position detection signal output from the rotation position detection hall element 11 and the rotation reference signal / PCLK2 output from the rotation reference signal generation unit 16 (2). And the phase control of the polygon motors is performed, so that each polygon motor 10 (2) rotates at a constant speed again. When the polygon motor 10 (2) rotates at a constant speed, a motor lock signal is detected (step 16).
[0046]
FIG. 6B shows detect pulse signals DP1 and DP2 after the phase control. Before the phase control shown in FIG. 5 (b), it can be seen that the phase is shifted by the maximum (T2 + T5), but is shifted by the maximum T5. In the above-described phase control, the case has been described where the rotation phase of the polygon mirror 9 (2) is controlled based on the time difference between DP2 and the detect pulse signal DP1, but the remaining polygon mirrors 9 (3) and 9 (4) are controlled. The rotation phase can be similarly controlled based on the time difference between DP3 and DP4 with respect to detect pulse signal DP1. It is preferable that the number of times of detection of the detect pulse signal and the calculation of the time difference be as large as possible.
[0047]
FIG. 7 is a flowchart of image writing control using the light beam scanning device. This image writing control is performed after the phase control of FIG. 4 is completed. In this embodiment, the beam detection pulse signal DP1 corresponding to the reference polygon mirror 9 (1) is used as an image writing start signal by each laser scanning unit 3.
In FIG. 7, when an image writing start command signal is sent from the operation unit or the external control unit (host) of the color printer, the controller 14 starts counting the reference beam detect pulse signal DP1 (step 1). . Then, when the input of the signal DP1 is started, the writing of the image of the first color is started, and the signal DP1 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 2, 3). When the signal DP1 has been counted for the specified number of lines (the number of writing lines), the writing of the image of the first color is completed on that line (steps 4 and 5).
[0048]
Here, the photoconductor pitch L between the first color laser scanning unit and the second color laser scanning unit is m times the scanning pitch (m is an integer), and the first color laser scanning unit and the third color laser scanning unit are different. Is 2 m times the scanning pitch, and the photoconductor pitch L between the first color laser scanning unit and the fourth color laser scanning unit is 3 m times the scanning pitch.
[0049]
When the count number of the reference beam detect pulse signal DP1 becomes (m + 1), the counting of the beam detect pulse signal DP2 of the second color is started (steps 6, 7). Then, when the input of the signal DP2 is started, the writing of the image of the second color is started, and the signal DP2 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 8 and 9). When the specified number of lines (number of writing lines) of the signal DP2 has been counted, the counting of the signal DP2 is terminated, and the writing of the image of the second color is terminated on that line (steps 10 to 12).
[0050]
When the count number of the reference beam detect pulse signal DP1 becomes (2m + 1), the counting of the beam detect pulse signal DP3 for the third color is started (steps 13 and 14). Then, when the input of the signal DP3 is started, the writing of the image of the third color is started, and the signal DP3 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 15 and 16). When the signal DP3 has been counted the specified number of lines (the number of writing lines), the counting of the signal DP3 is terminated, and the writing of the image of the third color is terminated on that line (steps 17 to 19).
[0051]
When the count number of the reference beam detect pulse signal DP1 becomes (3m + 1), the counting of the fourth color beam detect pulse signal DP4 is started (steps 20 and 21). Then, when the input of the signal DP4 is started, the writing of the image of the fourth color is started, and the signal DP4 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 22 and 23). When the signal DP4 has been counted the specified number of lines (the number of writing lines), the counting of the signal DP4 is terminated, and the writing of the image of the fourth color is terminated on that line (steps 24 to 26).
[0052]
As described above, in the present embodiment, the beam detect pulse signals DP2, DP3, DP4 detected immediately after the beam detect pulse signals DP1 corresponding to the reference first color image are detected a predetermined number of times (m + 1, 2m + 1, 3m + 1), respectively. By starting image writing for the second to fourth colors, the images are superimposed in units of one scanning pitch in the sub-scanning direction, so that color shift of each image does not occur.
[0053]
In addition, since the start of the image writing is controlled, the remaining signals DP2, DP3, and DP4 are always detected immediately after the beam detect pulse signal DP1, so that the entire image is scanned in units of one scanning pitch. In the present embodiment, the time difference between the remaining signals DP2, DP3, and DP4 with respect to the signal DP1 fluctuates due to uneven rotation of each polygon mirror 9 due to the above-described phase control. However, since the signals DP2, DP3, and DP4 are always output simultaneously or with a delay with respect to the DP1, it is possible to prevent sudden occurrence of a color shift close to one scanning pitch during the image writing operation.
[0054]
Further, due to the above-described phase control, the color shift of one scanning pitch or less is generated only by an amount corresponding to the variation width T5 of the time shift of the signals DP2, DP3, and DP4 with respect to the beam detect pulse signal DP1..
[0055]
[Embodiment 2]
Next, another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to the present embodiment are the same as those in the configurations shown in FIGS.
FIG. 8 is a flowchart of the rotation phase control of the polygon motor according to the present embodiment. The difference from the phase control in the first embodiment is that, even after the first phase control after the power is turned on and the motor lock signal is detected, the time difference is calculated from the detect pulse signal and the value is defined in advance as the value. The point is that phase control is performed based on the result of comparison with the time difference.
[0056]
Hereinafter, a control flow after detecting the motor lock signal after the first phase control will be described. When the motor lock signal is detected in the first phase control (step 16), the image writing is enabled (READY). However, the detection of the detect pulse signals DP1 to DP4 and the time difference (T1, T1 in FIG. The calculation of T2, T3, etc.) is continued n times, and the minimum value T2 of the plurality of time differences is selected (steps 17 to 21). When the time difference data (minimum value) becomes larger than the predetermined time difference data, unless the image writing is being performed, the operation after the data conversion described in the first embodiment is performed, and the same phase is obtained. Control is performed (steps 22 to 29). Then, the above operation is repeated. Here, when the newly calculated time difference data (minimum value) is equal to or less than the predetermined time difference data or during the image writing operation, the detection of the detect pulse signals DP1 to DP4 and the calculation of the time difference are repeatedly performed. Will be.
[0057]
In the flowchart of FIG. 8, the phase control of the polygon mirrors 9 (2) to 9 (4) is performed at the same time based on the time difference between DP2, DP3, and DP4 with respect to the detect pulse signal DP1. It is processed in parallel. Therefore, when only one of the minimum values of the time difference between the detect pulse signal DP1 and the remaining signals DP2, DP3, DP4 becomes larger than the predetermined time difference data, the other time difference calculation is continued. Phase control is performed only at the position where the size becomes large. The specified value of the time difference data is determined from an allowable color shift amount, may be stored in advance, and may be externally changeable.
[0058]
According to the phase control according to the present embodiment, the time difference is calculated not only when the power is turned on, but also continuously thereafter, and the phase control is executed as necessary. it can.
[0059]
[Embodiment 3]
Next, still another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to the present embodiment are the same as those in the configurations shown in FIGS.
FIG. 9 is a flowchart of the rotation phase control of the polygon mirror according to the present embodiment. The difference from the phase control in the first embodiment is not the minimum time difference, but the variation width calculated for n times, and the phase control is performed based on the difference obtained by subtracting the variation width from an arbitrary time difference. (Steps 10 and 11 in the figure).
[0060]
FIGS. 10 to 12 show the rotation reference signals of the polygon mirrors 9 (1) and 9 (2) after the phase control and the detect pulse signals DP1 and DP2 after the phase control, respectively, in the third embodiment. The relationship between DP1 and DP2 before the phase control is as shown in FIG. 5B, and the variation width of the time difference between DP1 and DP2 is T5. Assuming that the time difference is T2, the rotation reference signal / PCLK2 has a phase advanced by T2-T5 from the reference / PCLK1 as shown in FIG. 10A, and as a result, as shown in FIG. As shown in b), there is a time difference between the minimum T5 and the maximum T5 × 2, and a color shift occurs correspondingly (part 1). Assuming that the time difference is T1, the rotation reference signal / PCLK2 has a phase advanced by T1-T5 from the reference / PCLK1 as shown in FIG. 11A, and as a result, FIG. ), The time difference between the minimum T4 and the maximum T4 + T5, and a color shift occurs by that amount (part 2). Assuming that the time difference is T3, the rotation reference signal / PCLK2 has a phase advanced by T3-T5 from the reference / PCLK1 as shown in FIG. 12A, and as a result, FIG. ), There is a time difference between the minimum 0 and the maximum T5, and a color shift occurs correspondingly (part 3).
Although three examples have been described above, it can be seen that although there is a difference in the amount of color misregistration, color misregistration close to one line does not occur in any case.
[0061]
[Embodiment 4]
FIG. 13 is a flowchart of the phase control according to still another embodiment. This phase control is basically the same as the control flow shown in FIG. 9 of the third embodiment, except that the variation width of the time difference between the signals DP2, DP3, and DP4 with respect to the detect pulse signal DP1 is measured and stored in advance. The difference is that the stored value is used for control. In this case, as shown in steps 7 and 8 of the control flow of FIG. 13, only the time difference is calculated, the data of the fluctuation width stored in advance is subtracted from the time difference, and phase control is performed using the subtraction value. Will be.
According to the phase control according to the present embodiment, the function for calculating the fluctuation width is not required, and thus the configuration of the controller 14 can be simplified.
[0062]
[Embodiment 5]
Next, still another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to the present embodiment are the same as those in the configurations shown in FIGS.
FIG. 14 is a flowchart of the rotation phase control of the polygon mirror according to the present embodiment. The phase control according to the present embodiment is basically the same as the control according to the third embodiment, except that the variation width of the time difference calculated from the detect pulse signal is stored (step 11 in the figure). Even after the first phase control after power-on is completed and the motor lock signal is detected, the fluctuation width of the time difference calculated from the plurality of detect pulse signals is compared with the previous value, and further the plurality of detect pulse signals are detected. The third embodiment differs from the third embodiment in that a selected arbitrary time difference value is compared with a predetermined time difference, and phase control is performed based on the comparison result.
[0063]
In FIG. 14, after the power is turned on, the first phase control is performed, and when the motor lock signal is detected, the image writing is enabled (READY) (steps 1 to 17). Even after the READY state, the detection of the detect pulse signals DP1 to DP4 is performed, the fluctuation width obtained by n times is calculated, and an arbitrary time difference is selected from a plurality of time differences (steps 18 to 22). . Then, when the fluctuation width or the selected time difference becomes larger than the fluctuation width stored and used in the previous phase control and the predetermined time difference, if the image is not being written, the new fluctuation width is stored. Then, phase control is performed based on a subtraction value obtained by subtracting the fluctuation range from the time difference (steps 23 to 31). When the fluctuation width is equal to or less than the stored value, the time difference is equal to or less than the specified value, or when the image writing operation is being performed, processing from detection of the detect pulse signals DP1 to DP4 to comparison of data is performed. When the phase control is completed, the processes from the detection of the detect pulse signals DP1 to DP4 to the comparison of data are performed again.
[0064]
In the flowchart of FIG. 14, the phase control of the polygon mirrors 9 (2) to 9 (4) is performed simultaneously based on the time difference between DP2, DP3, and DP4 with respect to the detect pulse signal DP1, but all are described. It is processed in parallel. Therefore, when only one of the time difference or the fluctuation width between the detect pulse signal DP1 and the remaining signals DP2, DP3, and DP4 is different from the predetermined time difference or the stored fluctuation width, the other time difference or the fluctuation width is calculated. And phase control is performed only at different points. The specified value of the time difference data is determined from an allowable color shift amount, may be stored in advance, and may be externally changeable.
[0065]
According to the phase control according to the present embodiment, the time difference is calculated not only when the power is turned on, but also continuously thereafter, and the phase control is executed as necessary. it can.
[0066]
[Embodiment 6]
FIG. 15 is a flowchart of the phase control according to still another embodiment. This phase control is basically the same as the control flow shown in FIG. 14 of the fifth embodiment, except that the maximum time difference is selected from a plurality of detected time differences and used for control. In the example of the detect pulse signal shown in FIG. 5B, T3 is the maximum time difference.
According to the phase control according to the present embodiment, the amount of color misregistration can be further reduced as compared with the case of the fifth embodiment.
[0067]
[Embodiment 7]
FIG. 16 is a flowchart of the phase control according to still another embodiment. This phase control is basically the same as the control flow of FIG. 8 of the second embodiment, except that the phase control is not performed during the image writing operation, and the image writing is prohibited during the phase control. The difference is that the image writing standby state is set.
In FIG. 16, after the power is turned on, the first phase control is performed, and when the motor lock signal is detected, the image writing is enabled (READY) (steps 1 to 16). After entering the READY state, the image writing control unit is notified that the image writing is possible (step 17). Further, when the minimum value T2 is selected and the phase control is performed, the image writing disabled state is similarly notified to the image writing control unit, and the image writing standby state is set. Steps 18-25). Then, when the motor lock signal is detected after the phase control, the image writing is started (steps 26 to 32).
According to the phase control according to the present embodiment, it is possible to prevent the image from being disturbed by performing the image writing during the phase control.
[0068]
In each of the above embodiments, an example in which the light beam scanning device according to the present invention is applied to a four-drum type color printer including a laser scanning unit and four sets of photosensitive drums has been described. The present invention is not limited to the drum system, but can be applied to a two-drum, three-drum, or five-drum system. Further, the present invention can be applied to a photosensitive drum 1 provided with a plurality of laser scanning units.
[0069]
In each of the above embodiments, an example in which the light beam scanning device according to the present invention is applied to a color printer has been described. However, the present invention relates to a light beam scanning device used in another image forming apparatus such as a copying machine and a facsimile. It can also be applied to
[0070]
【The invention's effect】
Claims 1 through7According to the invention, during the period until the next phase control, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, and then the output signal corresponding to each of the remaining rotary polygon mirrors immediately thereafter is output. The time difference corresponding to the image shift amount until the output signal of the light beam detecting means is output is made as short as possible, and the time difference corresponding to the image shift amount is not suddenly increased by a time close to one cycle of the output signal. I have to. Therefore, the amount of image shift due to the rotational phase difference between the rotary polygon mirrors can be reduced as much as possible, and the image shift in the sub-scanning direction due to uneven rotation of the rotary polygon mirror can be prevented from occurring suddenly. .
[0071]
In particular, the claims2Or5According to the invention, even when the time difference corresponding to the image shift amount is not only a normal change but also changes over time, the time difference corresponding to the image shift amount is shortened as much as possible, and the image shift amount is reduced. Since the corresponding time difference is prevented from suddenly increasing by a time close to one cycle of the output signal, there is an effect that an image shift due to a temporal change can be prevented.
[0072]
In particular, the claims4According to the invention, the time difference between the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror and the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is measured and stored in advance. Since the rotation reference signal generating means is controlled based on a subtraction value obtained by subtracting the fluctuation width of the time difference, the time difference is calculated a plurality of times, and the fluctuation width is further calculated from the plurality of time differences. Thus, there is an effect that the configuration of the phase control means can be simplified by the function of calculating the fluctuation width.
[0073]
In particular, the claims6According to the invention of,PreviousBased on a subtraction value obtained by subtracting the fluctuation range from the maximum value of the plurality of time differences, the time difference corresponding to the image shift amount is controlled by controlling the rotation reference signal generation unit in a direction to make the subtraction value zero. Since the length is shorter, there is an effect that the image shift amount can be further reduced.
[0074]
In particular, the claims7According to the invention, the phase control based on the time difference is not performed during the image writing operation, and the image writing operation is prohibited while the phase control based on the time difference is performed. By doing so, the time difference corresponding to the image shift amount does not suddenly change during the image writing operation, so that it is possible to prevent the image from being disturbed by performing the image writing during the phase control. There is.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a schematic configuration of a color printer according to an embodiment of the invention.
FIG. 2 is an explanatory diagram of an optical system of a laser beam scanning unit of the color printer.
FIG. 3 is a block diagram of a control system of the light beam scanning device of the color printer.
FIG. 4 is a flowchart of rotation phase control in the light beam scanning device.
5A and 5B are time charts of a rotation reference signal before phase control and an output signal of each laser beam detector, respectively.
6A and 6B are time charts of a rotation reference signal after phase control and an output signal of each laser beam detector, respectively.
FIG. 7 is a flowchart of image writing control by the light beam scanning device.
FIG. 8 is a flowchart of rotation phase control according to another embodiment.
FIG. 9 is a flowchart of rotational phase control according to still another embodiment.
10A and 10B are time charts showing an example of a rotation reference signal and an output signal of a laser beam detector after phase control in the same rotation phase control.
11A and 11B are time charts showing another example of the rotation reference signal and the output signal of the laser beam detector after the phase control in the rotation phase control.
12A and 12B are time charts showing still another example of the rotation reference signal and the output signal of the laser beam detector after the phase control in the same rotation phase control, respectively.
FIG. 13 is a flowchart of rotational phase control according to still another embodiment.
FIG. 14 is a flowchart of rotational phase control according to still another embodiment.
FIG. 15 is a flowchart of rotational phase control according to still another embodiment.
FIG. 16 is a flowchart of rotational phase control according to still another embodiment.
FIGS. 17A and 17B are time charts of output signals of a laser beam detector before and after rotation phase control according to a conventional example, respectively.
[Explanation of symbols]
1 Photoconductor drum
3 Light beam scanning unit
8 Laser light source
9 Polygon mirror
10 Polygon motor
11 Hall element
12 Motor driver
13 Laser beam detector
14 Controller
15 Reference signal generator
16 rotation reference signal generator
17 Selector

Claims

A light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position,
A rotation reference signal generating unit that generates the rotation reference signal in correspondence with each of the rotating polygon mirrors; an output signal of a light beam detection unit corresponding to the reference rotation polygon mirror among the plurality of rotation polygon mirrors; A time difference between the output signal of the light beam detecting means corresponding to the rotating polygon mirror is calculated, and the rotation phase of each of the remaining rotating polygon mirrors substantially matches the reference rotating polygon mirror based on the time difference. Phase control means for controlling the rotation reference signal generating means, light beam scanning in each main scanning direction is started based on an output signal of each light beam detection means, and light corresponding to the reference rotation polygon mirror is provided. The light beam generating means is controlled based on the output signal of the beam detecting means so as to start image writing in the sub-scanning direction by the light beam deflected and scanned by the remaining rotary polygon mirrors. In the light beam scanning apparatus and an optical beam generation control unit that,
A plurality of time differences from when the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors immediately after the output signal are output are plural. Times, and based on the minimum time difference that is the minimum value of the plurality of time differences, the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is used as the light signal corresponding to each of the remaining rotary polygon mirrors. A light beam scanning device , wherein the rotation reference signal generating means is controlled so that output signals of the beam detecting means are output simultaneously or always with a delay .

2. The light beam scanning device according to claim 1 , wherein an output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output during standby for image writing, and the output signal corresponds to each of the remaining rotary polygon mirrors immediately thereafter. A time difference until an output signal of the light beam detecting means is output is calculated at a certain cycle, and when the time difference becomes larger than a predetermined time difference, phase control based on the time difference at that time is performed. Light beam scanning device.

A light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position,
A rotation reference signal generating unit that generates the rotation reference signal in correspondence with each of the rotating polygon mirrors; an output signal of a light beam detection unit corresponding to the reference rotation polygon mirror among the plurality of rotation polygon mirrors; A time difference between the output signal of the light beam detecting means corresponding to the rotating polygon mirror is calculated, and the rotation phase of each of the remaining rotating polygon mirrors substantially matches the reference rotating polygon mirror based on the time difference. Phase control means for controlling the rotation reference signal generating means, light beam scanning in each main scanning direction is started based on an output signal of each light beam detection means, and light corresponding to the reference rotation polygon mirror is provided. The light beam generating means is controlled based on the output signal of the beam detecting means so as to start image writing in the sub-scanning direction by the light beam deflected and scanned by the remaining rotary polygon mirrors. In the light beam scanning apparatus and an optical beam generation control unit that,
A plurality of time differences from when the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors immediately after the output signal are output are plural. Times, the variation width is obtained from the plurality of time differences, and the output of the light beam detection means corresponding to the reference rotating polygon is based on a subtraction value obtained by subtracting the variation width from any one of the plurality of time differences. Controlling the rotation reference signal generating means so that an output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is output simultaneously or always with respect to the signal. Scanning device.

A light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position,
A rotation reference signal generating unit that generates the rotation reference signal in correspondence with each of the rotating polygon mirrors; an output signal of a light beam detection unit corresponding to the reference rotation polygon mirror among the plurality of rotation polygon mirrors; A time difference between the output signal of the light beam detecting means corresponding to the rotating polygon mirror is calculated, and the rotation phase of each of the remaining rotating polygon mirrors substantially matches the reference rotating polygon mirror based on the time difference. Phase control means for controlling the rotation reference signal generating means, light beam scanning in each main scanning direction is started based on an output signal of each light beam detection means, and light corresponding to the reference rotation polygon mirror is provided. The light beam generating means is controlled based on the output signal of the beam detecting means so as to start image writing in the sub-scanning direction by the light beam deflected and scanned by the remaining rotary polygon mirrors. In the light beam scanning apparatus and an optical beam generation control unit that,
Calculate the time difference from when the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output to when the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors immediately after is output. Then, based on a subtraction value obtained by subtracting the fluctuation width of the time difference measured and stored in advance from the time difference, an output signal of the light beam detection means corresponding to the reference rotary polygon mirror is used to output the remaining signals. A light beam scanning device , wherein the rotation reference signal generating means is controlled such that output signals of the light beam detecting means corresponding to the rotary polygon mirror are output simultaneously or always with a delay .

The light beam scanning device according to claim 3 or 4 ,
After controlling the rotation reference signal generating means based on the subtraction value at power ON,
From the output of the output signal of the light beam detecting means corresponding to the previous SL reference rotary polygon mirror, the difference in time output signal of the light beam detecting means corresponding to said each remaining rotary polygonal mirror immediately is output Calculated multiple times in a certain cycle, and when any one of the plurality of time differences is larger than the predetermined time difference or the fluctuation width obtained from the plurality of time differences is larger than the fluctuation width used for the previous phase control When the image writing is not being performed, based on the subtraction value obtained by subtracting the fluctuation range from the time difference at that time, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output to the remaining signal. so that the output signal of the light beam detecting means corresponding to each of the rotary polygon mirror is output simultaneously or constantly delayed, the light beam scanning apparatus characterized by performing phase control for controlling the rotation reference signal generating means

The light beam scanning device according to claim 3 ,
A light beam scanning device, wherein a maximum value of the plurality of time differences is used as the time difference used for the phase control.

A light beam generating means, a rotating polygon mirror for deflecting and scanning the light beam generated by the light beam generating means on the image carrier, a driving means for rotating the rotating polygon mirror, and detecting a rotational position of the rotating polygon mirror Rotation position detection means, rotation drive control means for controlling the drive means based on a rotation reference signal and an output signal of the rotation position detection means, and a light beam deflected and scanned by the rotary polygon mirror on a scanning path. A plurality of sets of light beam detecting means for detecting at a predetermined position,
A rotation reference signal generating unit that generates the rotation reference signal in correspondence with each of the rotating polygon mirrors; an output signal of a light beam detection unit corresponding to the reference rotation polygon mirror among the plurality of rotation polygon mirrors; calculating a time difference between the output signal of the light beam detecting means corresponding to the rotary polygon mirror, on the basis of the time difference between its said remaining rotational phases of the rotary polygon mirror with respect to the reference rotary polygon mirror substantially coincide Phase control means for controlling the rotation reference signal generating means, and light beam scanning in each main scanning direction based on an output signal of each light beam detection means, and corresponding to the reference rotating polygon mirror. The light beam generating means is controlled based on an output signal of the light beam detecting means so as to start image writing in a sub-scanning direction by a light beam deflected and scanned by each of the remaining rotary polygon mirrors. In the light beam scanning apparatus and an optical beam generation control unit that,
With respect to the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, the rotation signal is output such that the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors is output simultaneously or always with a delay. Controlling the reference signal generating means,
The phase control based on the time difference is not performed during the image writing operation, and the image writing operation is prohibited while the phase control based on the time difference is performed. Light beam scanning device.