JP3925997B2 - Beam light scanning apparatus and image forming apparatus - Google Patents

Description

【０２６３】
【表２】

【０２６４】
図２６は、図２３のビーム光検知装置３８を用いたときのビーム光の通過位置制御を説明するための図であり、図８との相違点は、ビーム光検知装置出力処理回路４０の構成において、センサパターンＳＢ１〜ＳＦ１，ＳＢ２〜ＳＦ２に対応して差動増幅器が設けられている点、および、センサ選択信号に解像度切換信号が追加された点にあり、その他の構成は基本的に図８と同様であるので、説明は省略する。
【０２６５】
すなわち、差動増幅器６３１は、センサパターンＳＢ１，ＳＣ１の各出力信号 の差を増幅し、差動増幅器６４１は、センサパターンＳＣ１，ＳＤ１の各出力信号の差を増幅し、差動増幅器６５１は、センサパターンＳＤ１，ＳＥ１の各出力信号の差を増幅し、差動増幅器６６１は、センサパターンＳＥ１，ＳＦ１の各出力信号の差を増幅する。また、差動増幅器６３２は、センサパターンＳＢ２，Ｓ Ｃ２の各出力信号の差を増幅し、差動増幅器６４２は、センサパターンＳＣ２，ＳＤ２の各出力信号の差を増幅し、差動増幅器６５２は、センサパターンＳＤ２，ＳＥ２の各出力信号の差を増幅し、差動増幅器６６２は、センサパターンＳＥ２，ＳＦ２の各出力信号の差を増幅する。
【０２６６】
増幅器６３１〜６６１，６３２〜６６２の各出力信号は、それぞれ選択回路（アナログスイッチ）４１に入力される。選択回路４１は、主制御部（ＣＰＵ）５１からのセンサ選択信号により、積分器４２へ入力する信号を選択する。
【０２６７】
すなわち、第１の解像度（６００ｄｐｉ）でビーム光の通過位置制御を行なう場合は、選択回路４１によって下記の差動増幅器を選択し、それに対応するビーム光の通過位置制御を行なう。
【０２６８】
・差動増幅器６３１：ビーム光ａ
・差動増幅器６４１：ビーム光ｂ
・差動増幅器６５１：ビーム光ｃ
・差動増幅器６６１：ビーム光ｄ
同様に、第２の解像度（４００ｄｐｉ）でビーム光の通過位置制御を行なう場合は、選択回路４１によって下記の差動増幅器を選択し、それに対応するビーム光の通過位置制御を行なう。
【０２６９】
・差動増幅器６３２：ビーム光ａ
・差動増幅器６４２：ビーム光ｂ
・差動増幅器６５２：ビーム光ｃ
・差動増幅器６６２：ビーム光ｄ
図２７は、図２３のビーム光検知装置３８を用いたときのプリンタ部２の電源投入時における概略的な動作を説明したフローチャートである。図１４との相違点は、ステップＳ２とＳ３との間に解像度選択ルーチンとしてのステップＳ１７の処理が追加された点にあり、その他は図１４と同様であるので、説明は省略する。解像度選択ルーチン（Ｓ１７）では、選択された解像度に応じたポリゴンモータ３６の回転数、画像形成時のビーム光のパワー、選択回路４１の設定などが実行される。すなわち、

となる。
【０２７０】
このように、既に説明済み（図５（ａ）（ｂ））であるが、ビーム光通過位置検知センサパターンをビーム光の走査方向と直交する方向に平行に配設することによって、従来方式（図５（ｂ））に比較して、取付け傾きに充分余裕のあるビーム光検知装置３８を構築することができる。さらに、本実施の形態は、この構成で複数の解像度に対応したものであり、本実施の形態によれば、複数の解像度を有した取付け傾きに充分余裕のあるビーム光検知装置３８を構築できる。
【０２７１】
次に、主走査方向の画像形成位置制御（レーザ発振器の発光タイミング制御）について詳細に説明する。
【０２７２】
図２８は、本制御に用いるビーム光検知装置３８の構成を模式的に示している。このビーム光検知装置３８は、前述した図２３のビーム光検知装置３８において、ビーム光の通過タイミングを検知する第５の光検知部としての縦に長い４つのセンサパターンＳ３，Ｓ４，Ｓ５，Ｓ６を追加したもので、その他の構成は基本的に図２３と同様であるので、説明は省略する。
【０２７３】
すなわち、センサパターンＳ３は、センサパターンＳ１とＳＨとの間にそれらと平行に設けられ、センサパターンＳ４，Ｓ５，Ｓ６は、センサパターンＳＡ〜ＳＧの右隣り（図面に対して）に、Ｓ４，Ｓ５，Ｓ６の順序でそれらと平行に設けられている。なお、センサパターンＳ６は、前記センサパターンＳ２の機能をも兼ねている。
【０２７４】
ここに、センサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５は、第１の解像度（６００ｄｐｉ）と第２の解像度（４００ｄｐｉ）のそれぞれの画像クロック（同期回路５５から出力される同期クロックパルス）の１周期（１パルス時間）に、ビーム光が走査方向に移動する距離の最小公倍数の整数倍（ｎ）となっており、以下、それについて説明する。
【０２７５】
本実施の形態では、２種類の解像度を有している場合を例にとるとすると、
・センサパターンＳ３とＳ４との間隔：Ｐ３
・センサパターンＳ４とＳ５との間隔：Ｐ４
・センサパターンＳ５とＳ６との間隔：Ｐ５
・第１の解像度時のビーム光の走査速度：ＶＳ
・第１の解像度時の同期クロックパルスの１パルスの時間：ＴＣ
・第２の解像度時のビーム光の走査速度：ＶＳ′
・第２の解像度時の同期クロックパルスの１パルスの時間：ＴＣＣ
とした場合、
・Ｐ３＝Ｌ．Ｃ．Ｍ．（ＶＳ×ＴＣ、ＶＳ′×ＴＣＣ）×ｎ1（ｎ1は整数、Ｌ．Ｃ．Ｍ．は最小公倍数）
・Ｐ４＝Ｌ．Ｃ．Ｍ．（ＶＳ×ＴＣ、ＶＳ′×ＴＣＣ）×ｎ2（ｎ2は整数、Ｌ．Ｃ．Ｍ．は最小公倍数）
・Ｐ５＝Ｌ．Ｃ．Ｍ．（ＶＳ×ＴＣ、ＶＳ′×ＴＣＣ）×ｎ3（ｎ3は整数、Ｌ．Ｃ．Ｍ．は最小公倍数）
である。
【０２７６】
本実施の形態に用いるビーム光検知装置３８の特徴は、ビーム光通過位置検知用のセンサパターンＳＢ１〜ＳＦ１，ＳＢ２〜ＳＦ２（ビーム光位置検知手段）、ビーム光通過タイミング検知用のセンサパターンＳ３，Ｓ４，Ｓ５，Ｓ６（ビーム光通過タイミング検知手段）、および、ビーム光パワー検知用のセンサパターンＳＨ（ビーム光パワー検知手段）を１つの保持基板３８ａ内に一体的に保持した点にある。これによれば、センサパターンが同一の検知装置内にあるので、各センサパターンごとのメカニカルな位置合せといった取付け調整行程が不要となる。
【０２７７】
図２９は、図２８のビーム光検知装置３８を用いた主走査方向の画像形成位置制御を説明するためのブロック図であり、これは、図６のブロック図の中から主走査方向の画像形成位置制御に関連する部分を抜き出して示したものである。なお、レーザ発振器３１、レーザドライバ３２、ビーム光検知装置３８のセンサパターンなどを複数具備しているが、図２９では説明を簡単にするために、それぞれ１系統のみを示している。
【０２７８】
まず、図２９ないし図３１を用いて、１本のビーム光（シングルビーム）の発光タイミング制御（主走査方向の画像形成位置制御）について説明する。
【０２７９】
主制御部５１は、ポリゴンモータ３６の回転数を指定し、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は所定の回転数で回転する。
【０２８０】
続いて、主制御部５１は、強制発光信号をレーザドライバ３２に入力し、レーザ発振器３１を強制発光させる。この強制発光によるビーム光は、ポリゴンミラー３５によって走査されて、ビーム光検知装置３８上を通過し、ビーム光検知装置３８はビーム光の通過タイミングに同期した通過タイミング検知信号を出力する。
【０２８１】
この通過タイミング検知信号は、ビーム光検知装置出力処理回路４０の主走査側回路４０ａによって、増幅された後に２値化され、ビーム光検知出力として、主制御部５１および同期回路５５に入力される。主制御部５１は、ビーム光検知出力が入力されると、強制発光信号の出力を停止して、レーザ発振器３１を消灯する。
【０２８２】
一方、同期回路５５は、ビーム光検知出力に同期して基準クロックパルスを同期クロックパルスとして出力する。すなわち、同期回路５５は、ビーム光の通過タイミングに同期した同期クロックパルスを発生する。この同期クロックパルスが画像データの基準となるクロックパルスで、カウンタ９８に送られる。カウンタ９８は、このクロックパルスをカウントし、所定値をカウントすると主制御部５１にカウント終了信号を出力する。
【０２８３】
主制御部５１は、このカウント終了信号に基づいて画像形成領域を決定し、画像クロックパルスとして、画像データとともにレーザドライバ３２に出力する。レーザドライバ３２は、画像クロックパルスと画像データとに基づいて、レーザ発振器３１を発光動作させることにより、画像を形成する。
【０２８４】
ところが、ビーム光が複数の場合、ポリゴンミラー３５の面精度などが原因で、各ビーム光に位相差が生じる。すなわち、ビーム光検知装置３８上を通過するタイミングがビーム光によって異なる（到来順が異なる）。そのうえ、ビーム光の到来順は、走査するポリゴンミラー３５の面によっても異なる。このため、シングルビームと同様の方法では、ビーム光の到来順が判断できず、主走査方向の画像形成位置制御を行なうことができない。
【０２８５】
そこで、本実施の形態では、画像を形成する前に、あらかじめ複数のビーム光の到来順を判定し、その判定結果に基づいて、ビーム光とそのビーム光の通過タイミングを検知するビーム光検知装置３８のセンサパターンＳ３〜Ｓ６との組合わせを決定し、主走査方向の画像形成位置制御を行なうとともに、上記組合わせをビーム光の到来順に走査方向に近いセンサパターンを割り当てるものであり、以下、それについて説明する。なお、以下の説明ではビーム光が４つの場合を例に説明する。
【０２８６】
前述したように、主走査方向の画像形成位置制御には、４つのセンサパターンＳ３，Ｓ４，Ｓ５，Ｓ６を使用する。これらのセンサパターンＳ３〜Ｓ６は、相互にビーム光の走査方向に対して異なった位置に配置された光検知部（フオトダイオード）で、センサパターンの表面に照射されるビーム光の光量に対応した電流値を出力する。したがって、センサパターンＳ３〜Ｓ６は、ビーム光の通過タイミングに伴った通過タイミング検知信号を出力する。
【０２８７】
図３２は、ビーム光検知装置出力処理回路４０における主走査側回路４０ａの構成例を示すものである。センサパターン（フォトダイオード）Ｓ３を流れる電流Ｉ３は、抵抗ＲＰ，ＲＬによって電流・電圧変換され、電圧Ｖ１３（通過タイミング検知出力）となる。この電圧Ｖ１３は、非反転増幅器Ａ１１によって増幅された後、２値化回路Ａ１２によって２値化される。この２値化された信号Ｓ３ＯＵＴは、ビーム光検知出力として主制御部５１、同期回路５５およびカウンタ９８に送られる。センサパターンＳ４，Ｓ５，Ｓ６についても同様である。
【０２８８】
主制御部５１は、このビーム光検知出力Ｓ３ＯＵＴ〜Ｓ６ＯＵＴを使用して、ビーム光の到来順を判定するものであり、以下、その判定方法について説明する。
【０２８９】
まず、４本のビーム光がどのような状態で走査されているのかを判定する、ビーム光到来状態の判定について説明する。すなわち、以下の５つの状態の判定を行なう（図３３、図３４参照）。
【０２９０】
(1) ４本のビーム光がそれぞれ重なっていない（全て位相が異なる）
(2) ４本のビーム光の２本だけが重なっている（２本だけが同位相、他の２本は異なる）
(3) ４本のビーム光の２本ずつが重なっている（２本ペアが同位相）
(4) ４本のビーム光の３本だけが重なっている（３本だけが同位相、残り１本は異なる）
(5) ４本のビーム光の全てが重なっている（４本全てが同位相）
以下、図３５に示すフローチャートを参照してビーム光到来状態の判定の手順を説明する。主制御部５１は、ポリゴンモータ３６の回転数を指定し、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は所定の回転数で回転する。
【０２９１】
続いて、主制御部５１は、強制発光信号をレーザドライバ３２ａ〜３２ｄに入力し、４つのレーザ発振器３１ａ〜３１ｄを強制発光させる。レーザ発振器３１ａ〜３１ｄから発光された４本のビーム光ａ〜ｄは、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。これにより、センサパターンＳ３は、４本のビーム光ａ〜ｄの通過タイミングに同期した通過タイミング検知信号を出力する。
【０２９２】
通過タイミング検知信号は、先に説明したビーム光検知装置出力処理回路４０の主走査側回路４０ａによって増幅された後、２値化され、ビーム光検知出力Ｓ３ＯＵＴａ，Ｓ３ＯＵＴｂ，Ｓ３ＯＵＴｃ，Ｓ３ＯＵＴｄとして、主制御部５１、同期回路５５およびカウンタ９８に入力される。
【０２９３】
ビーム光検知出力Ｓ３ＯＵＴは、カウンタ９８に入力されており、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。カウント値は、前述のビーム光到来状態によって、以下のケース１〜ケース４に分類される（図３３、図３４参照）。
【０２９４】

主制御部５１は、カウンタ９８のカウント値に基づいて、ビーム光の到来状態を判定する。たとえば、カウント値が「１」、すなわち、ケース１の場合は、４本のビーム光ａ〜ｄが全て同位相であることから、１本のビーム光と同様に取り扱える。
【０２９５】
すなわち、センサパターンＳ３〜Ｓ６とビーム光ａ〜ｄの割付けは自由で、ビーム光検知出力Ｓ３ＯＵＴ，Ｓ４ＯＵＴ，Ｓ５ＯＵＴ，Ｓ６ＯＵＴをビーム光ａ〜ｄに適当に設定すればよい。図３５の例では、ビーム光ａをセンサパターンＳ３に、ビーム光ｂをセンサパターンＳ４に、ビーム光ｃをセンサパターンＳ５に、ビーム光ｄをセンサパターンＳ６に割付けた場合を示している。
【０２９６】
ケース２、ケース３、ケース４の場合は、少なくとも１本のビーム光の位相が異なっており、先頭ビーム光、２番目、３番目といったビーム光到来順の判定がさらに必要である。
【０２９７】
図３６に示すフローチャートを参照して、ケース４の場合のセンサ割付手順を説明する。まず、先頭ビーム光を判定し、続いて２番目、３番目、４番目のビーム光到来順判定を行なった後に、先頭ビーム光をセンサパターンＳ３に、２番目ビーム光をセンサパターンＳ４に、３番目ビーム光をセンサパターンＳ５に、４番目ビーム光をセンサパターンＳ５に割付ける。以下にビーム光の判定手順を詳細に説明する。
【０２９８】
まず、先頭ビーム光の判定手順について、図３７および図３８に示すフローチャートを参照して説明する。主制御部５１は、ポリゴンモータ３６の回転数を指定し、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は所定の回転数で回転する。
【０２９９】
続いて、主制御部５１は、強制発光信号をレーザドライバ３２ａ〜３２ｄに入力し、４つのレーザ発振器３１ａ〜３１ｄを強制発光させる。さらに、主制御部５１は、先頭のビーム光がセンサパターンＳ３を通過して、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器３１ａを消灯（オフ）するように設定を行なう。
【０３００】
レーザ発振器３１ａ〜３１ｄから発光された４本のビーム光ａ〜ｄは、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。このとき、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過し、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器３１ａを消灯する。
【０３０１】
ビーム光検知出力Ｓ３ＯＵＴはカウンタ９８に入力され、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。主制御部５１は、このカウント値を読込み、カウント値が「４」であれば、ビーム光ａが先頭であり、カウント値が 「４」以外であれば、ビーム光ａ以外のビーム光が先頭であると判定して、再度判定を行なう。
【０３０２】
すなわち、ビーム光ａが先頭の場合は、まず、ビーム光ａの通過に伴うビーム光検知出力Ｓ３ＯＵＴａが出力されると、カウント値は「１」となり、同時にレーザ発振器３１ａを消灯する。さらに、カウンタ９８はビーム光ｂ，ｃ，ｄの通過に伴い、ビーム光検知出力Ｓ３ＯＵＴｂ，Ｓ３ＯＵＴｃ，Ｓ３ＯＵＴｄをカウントするため、カウント値が「４」となる。ビーム光ａが先頭でない場合は、ビーム光ａ以外のビーム光（たとえば、ビーム光ｂ）の通過に伴うビーム光検知出力Ｓ３ＯＵＴｂが出力されると、カウント値は「１」となり、同時にレーザ発振器３１ａを消灯する。さらに、カウンタ９８は、ビーム光ｃ，ｄの通過に伴いビーム光検知出力Ｓ３ＯＵＴｃ，Ｓ３ＯＵＴｄをカウントするため、カウント値が「３」となる。
【０３０３】
ビーム光ａが先頭でない場合、主制御部５１は再度、先頭ビーム光の判定を行なう。今度は、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過すると、レーザ発振器３１ｂを消灯するように設定して、同様の判定を行なう。
【０３０４】
主制御部５１は、強制発光信号をレーザドライバ３２ａ〜３２ｄに入力し、４つのレーザ発振器３１ａ〜３１ｄを強制発光させる。さらに、主制御部５１は、先頭のビーム光がセンサパターンＳ３を通過して、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器３１ｂを消灯するように設定を行なう。
【０３０５】
レーザ発振器３１ａ〜３１ｄから発光された４本のビーム光ａ〜ｄは、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。このとき、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過し、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器３１ｂを消灯する。
【０３０６】
ビーム光検知出力Ｓ３ＯＵＴはカウンタ９８に入力され、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。主制御部５１は、カウント値を読込み、カウント値が「４」であれば、ビーム光ｂが先頭であり、カウント値が「４」以外であれば、ビーム光ｂ以外のビーム光が先頭であると判定して、再度判定を行なう。
【０３０７】
ビーム光ｂが先頭でない場合、主制御部５１は再度、先頭ビーム光の判定を行なう。今度は、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過すると、レーザ発振器３１ｃを消灯するように設定して同様の判定を行なう。カウンタ９８のカウント値が「４」であれば、ビーム光ｃが先頭であり、カウント値が「４」以外であれば、ビーム光ｃ以外のビーム光が先頭であると判定して、再度判定を行なう。
【０３０８】
ビーム光ｃが先頭でない場合、主制御部５１は再度、先頭ビーム光の判定を行なう。今度は、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過すると、レーザ発振器３１ｄを消灯するように設定して同様の判定を行なう。カウンタ６０のカウント値が「４」であれば、ビーム光ｄが先頭であり、カウント値が「４」以外であれば、エラー信号を出力する。
【０３０９】
上記の手順によって先頭ビーム光の判定を行なった後は、先頭ビーム光以外で２番目のビーム光の判定を行なう。２番目のビーム光の判定手順は、先頭ビーム光以外の３つのビーム光の中で先頭を判定するもので、先頭ビーム光の判定と同様の手法で行なう。
【０３１０】
以下、図３９および図４０に示すフローチャートを参照して２番目のビーム光の判定手順を説明する。主制御部５１は、ポリゴンモータ３６の回転数を指定し、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は所定の回転数で回転する。
【０３１１】
続いて、主制御部５１は、強制発光信号を先頭ビーム光以外の３本のビーム光に対応する３つのレーザドライバに入力し、先頭ビーム光以外の３本のビーム光に対応する３つのレーザ発振器を強制発光させる。また、主制御部５１は、３つのレーザ発振器から発光させた３本のビーム光の中で、先頭のビーム光がセンサパターンＳ３を通過して、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器＊１を消灯するように設定を行なう。
【０３１２】
・ビーム光＊１：先頭ビーム光以外のビーム光その１（レーザ発振器＊１に対応）
・ビーム光＊２：先頭ビーム光以外のビーム光その２（レーザ発振器＊２に対応）
・ビーム光＊３：先頭ビーム光以外のビーム光その３（レーザ発振器＊３に対応）
３つのレーザ発振器から発光された３本のビーム光＊１，＊２，＊３は、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。このとき、主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過し、ビーム光検知出力Ｓ３ＯＵＴが出力されると、レーザ発振器＊１を消灯する。
【０３１３】
ビーム光検知出力Ｓ３ＯＵＴはカウンタ９８に入力され、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。主制御部５１は、カウント値を読込み、カウント値が「３」であれば、ビーム光＊１が２番目のビーム光であると判定する。カウント値が「３」以外であれば、ビーム光＊１以外のビーム光が２番目であると判定して、再度判定を行なう。
【０３１４】
主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過すると、レーザ発振器＊２を消灯するように設定して同様の判定を行なう。カウンタ９８のカウント値が「３」であれば、ビーム光＊２が２番目であり、カウント値が「３」以外であれば、ビーム光＊２以外のビーム光が２番目であると判定して、再度判定を行なう。
【０３１５】
主制御部５１は、先頭ビーム光がセンサパターンＳ３を通過すると、レーザ発振器＊３を消灯するように設定して同様の判定を行なう。カウンタ９８のカウント値が「３」であれば、ビーム光＊３が２番目であり、カウント値が「３」以外であれば、エラー信号を出力する。
【０３１６】
上記の手順によって先頭ビーム光と２番目ビーム光の判定を行なった後は、同様の手順で３番目、４番目の判定を行なう。なお、図４１は、３番目ビーム光の判定手順を示したフローチャートであるが、２番目ビーム光の判定手順と同様であるので、その説明は省略する。
【０３１７】
このように、先頭、２番目、３番目、４番目のビーム光到来順判定を行なった後に、先頭ビーム光をセンサパターンＳ３に、２番目ビーム光をセンサパターンＳ４に、３番目ビーム光をセンサパターンＳ５に、４番目ビーム光をセンサパターンＳ５に、それぞれ割付けて、ケース４の場合のセンサ割付けを終了する。
【０３１８】
次に、図４２に示すフローチャートを参照して、ケース３の場合のセンサ割付手順を説明する。ケース３は、４本のビーム光ａ〜ｄのうちで、２本（１組）のビーム光が重なっている状態であるので、まず、重なっている２本のビーム光を判定し、重なっている２本と、残りの重なっていない（独立している）２本の３つのグループに分類する。グループ分けが終了した後に、３つのグループの中で、先頭、２番目、３番目のグループの到来順を判定する。先頭グループのビーム光が重なっていれば、以下のように割付ける。
【０３１９】
・先頭の２つのビーム光：Ｓ３，Ｓ４
・２番目のビーム光 ：Ｓ５
・３番目のビーム光 ：Ｓ６
先頭グループが重なっていない場合は、２番目のグループのビーム光が重なっているか否かを判定し、重なっている場合は、以下のように割付ける。
【０３２０】
・先頭のビーム光 ：Ｓ３
・２番目の２つのビーム光：Ｓ４，Ｓ５
・３番目のビーム光 ：Ｓ６
先頭グループも、２番目のグループも重なっていない場合は、以下のように割付ける。
【０３２１】
・先頭のビーム光 ：Ｓ３
・２番目のビーム光 ：Ｓ４
・３番目の２つのビーム光：Ｓ５，Ｓ６
以下、各判定方法について詳細に説明する。
【０３２２】
まず、重なっているビーム光の判定とグループ分けの手順について、図４３および図４４に示すフローチャートを参照して説明する。
【０３２３】
主制御部５１は、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は回転する。続いて、主制御部５１は、強制発光信号をレーザドライバ３２ａ以外の３つのレーザドライバ３２ｂ〜３２ｄに入力し、レーザ発振器３１ａ以外の３つのレーザ発振器３１ｂ〜３１ｄを強制発光させる。
【０３２４】
３つのレーザ発振器３１ｂ〜３１ｄから発光された３本のビーム光ｂ，ｃ，ｄは、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。このビーム光の通過に伴って、センサパターンＳ３は、ビーム光検知出力Ｓ３ＯＵＴをカウンタ９８に出力し、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。
【０３２５】
主制御部５１は、カウンタ９８のカウント値を読込み、カウント値が「３」であれば、ビーム光ａが重なっていると判断し、カウント値が「３」以外であれば、ビーム光ａは重なっていない（独立している）と判断する。ケース３の場合は、４本のビーム光ａ〜ｄのうちで２本のビーム光だけが重なっているため、ビーム光ａが重なっている場合、残りの３本のビーム光ｂ〜ｄは重なっていない（独立している）ため、センサパターンＳ３は、３本のビーム光ｂ〜ｄの通過に伴って、ビーム光検知出力Ｓ３ＯＵＴｂ，Ｓ３ＯＵＴｃ，Ｓ３ＯＵＴｄをカウンタ９８に出力する。カウンタ９８は、ビーム光検知出力Ｓ３ＯＵＴｂ，Ｓ３ＯＵＴｃ，Ｓ３ＯＵＴｄをカウントするため、カウント値は「３」となる。
【０３２６】
ビーム光ａが重なっていない場合は、残りの３本のビーム光ｂ〜ｄのうちの２本が重なっているため、カウント値は「２」となる。たとえば、ビーム光ｂとビーム光ｃとが重なっていると仮定すると、ビーム光検知出力Ｓ３ＯＵＴｂとＳ３ＯＵＴｃは同時に１個だけ出力される（Ｓ３ＯＵＴｂｃ）ため、Ｓ３ＯＵＴｄの２つがビーム光検知出力として出力される。すなわち、カウント値は「２」となる。
【０３２７】
続いて、ビーム光ｂ、ビーム光ｃ、ビーム光ｄについても同様の判定を行ない、重なっているビーム光と、重なっていない（独立している）ビーム光にグループ分けを行なう。
【０３２８】
グループ分けが終了すると、次に、各グループの到来順を判定する。重なっているグループからは、２本のビーム光のうちの１本を代表として選択する（２本のうちどちらでもよい）。これによって、３本のビーム光の到来順を判定することになるため、前述の図３９〜図４１と全く同様の手順でビーム光の到来順を判定する。
【０３２９】
この後に、前述の割付けを行ない、ケース３の場合のセンサ割付けを終了する。
【０３３０】
次に、図４５に示すフローチャートを参照して、ケース２の場合のセンサ割付手順を説明する。ケース２は、４本のビーム光ａ〜ｄのうちで、２本のビーム光が２組（２ペア）重なっている組合わせと、１本のビーム光と３本のビーム光の組合わせの場合があるので、まず、これらの組合わせを判定する。そして、２ビーム光と２ビーム光の組合わせの場合は、２グループの到来順を判定し、以下のように割付ける。
【０３３１】
・先頭グループ（先頭の２本ビーム光） ：Ｓ３，Ｓ４
・２番目グループ（２番目の２本ビーム光）：Ｓ５，Ｓ６
一方、１本のビーム光と３本のビーム光の組合わせの場合は、やはり、２グループの到来順を判定し、先頭グループが１本ビーム光の場合は、以下のように割付ける。
【０３３２】
・先頭グループ（１本ビーム光） ：Ｓ３
・２番目グループ（３本ビーム光）：Ｓ４，Ｓ５，Ｓ６
また、先頭グループが３本ビーム光の場合は、以下のように割付ける。
【０３３３】
・先頭グループ（３本ビーム光） ：Ｓ３，Ｓ４，Ｓ５
・２番目グループ（１本ビーム光）：Ｓ６
以下、各判定方法について詳細に説明する。
【０３３４】
まず、１本ビーム光と３本ビーム光との組合わせか、２本ビーム光と２本ビーム光との組合わせであるかを判定する手順について、図４６に示すフローチャートを参照して説明する。
【０３３５】
主制御部５１は、回転オン信号をポリゴンモータドライバ３７に入力する。これによって、ポリゴンモータ３６は回転する。続いて、主制御部５１は、強制発光信号をレーザドライバ３２ａ，３２ｂ以外のレーザドライバ３２ｃ，３２ｄに入力し、レーザ発振器３１ａ，３１ｂ以外の２つのレーザ発振器３１ｃ，３１ｄを強制発光させる。
【０３３６】
２つのレーザ発振器３１ｃ，３１ｄから発光された２本のビーム光ｃ，ｄは、ポリゴンミラー３５によって走査されて、センサパターンＳ３上を通過する。このビーム光の通過に伴って、センサパターンＳ３は、ビーム光検知出力Ｓ３ＯＵＴをカウンタ９８に出力し、カウンタ９８はビーム光検知出力Ｓ３ＯＵＴをカウントする。主制御部５１は、カウンタ９８のカウント値を読込み、カウント値によって以下の組合わせが考えられる。（ステップ１）
・カウント値＝２：（ａｃ，ｂｄ）（ａｄ，ｂｃ）（ａｂｄ，ｃ）（ａｂｃ，ｄ）
・カウント値＝１：（ａｂ，ｃｄ）（ａｃｄ，ｂ）（ａ，ｂｃｄ）
続いて、カウント値が「２」の場合、レーザ発振器３１ａ，３１ｃ以外の２つのレーザ発振器３１ｂ，３１ｄを強制発光させ、ビーム光検知出力をカウントし、カウント値によって以下の組合わせが考えられる。（ステップ２）
・カウント値＝２：（ａｄ，ｂｃ）（ａｂｃ，ｄ）
・カウント値＝１：（ａｃ，ｂｄ）（ａｂｄ，ｃ）
さらに、カウント値が「２」の場合、レーザ発振器３１ｄ以外の３つのレーザ発振器３１ａ，３１ｂ，３１ｃを強制発光させ、ビーム光検知出力をカウントし、カウント値を読込む。カウント値によって以下の組合わせであることが判定できる。（ステップ３）
・カウント値＝２：（ａｄ，ｂｃ）
・カウント値＝１：（ａｂｃ，ｄ）
一方、ステップ１のカウント値が「１」の場合は、レーザ発振器３１ｃ，３１ｄ以外の２つのレーザ発振器３１ａ，３１ｂを強制発光させ、ビーム光検知出力をカウントし、カウント値を読込む。カウント値によって以下の組合わせが考えられる。（ステップ４）
・カウント値＝２：（ａｃｄ，ｂ）（ａ，ｂｃｄ）
・カウント値＝１：（ａｂ，ｃｄ）
さらに、ステップ４において、カウント値が「２」の場合、レーザ発振器３１ｂ以外の３つのレーザ発振器３１ａ，３１ｃ，３１ｄを強制発光させ、ビーム光検知出力をカウントし、カウント値を読込む。カウント値によって以下の組合わせであることが判定できる。（ステップ５）
・カウント値＝２：（ａ，ｂｃｄ）
・カウント値＝１：（ａｃｄ，ｂ）
上記の手順によって２グループの組合わせが判定される。
【０３３７】
組合わせの判定が終了すると、次にグループの到来順を判定する。重なっているグループからは、２本（あるいは３本）のビーム光のうちの１本を代表として選択する（２本あるいは３本のうちのどれでもよい）。これによって、２本のビーム光の到来順を判定することになるため、前述の図４１と全く同様の手順で判定することができる。したがって、ここでは説明は省略する。
【０３３８】
この後に前述の割付けを行ない、ケース２の場合のセンサ割付けを終了する。
【０３３９】
上記の手順によってケース１〜４の場合のセンサ割付けを終了する。
【０３４０】
各ビーム光のセンサ割付けが決まれば、各ビーム光に対する水平同期信号が決まるため、シングルビーム光の場合と同様に主走査方向の画像形成位置制御を行なうことが可能になる（図３０、図３１参照）。たとえば、以下のような割付けを行なった場合を仮定する。
【０３４１】
・ビーム光到来順：ビーム光ａ、ビーム光ｂ、ビーム光ｃ、ビーム光ｄ
・ビーム光ａ：センサパターンＳ３
・ビーム光ｂ：センサパターンＳ４
・ビーム光ｃ：センサパターンＳ５
・ビーム光ｄ：センサパターンＳ６
以下、図４７を参照して説明すると、まず、主制御部５１は、ポリゴンモータ３６をオンし、ポリゴンモータ３６を回転させ、全てのレーザ発振器３１ａ〜３１ｄを発光させる。ポリゴンミラー３５で走査されたビーム光ａ〜ｄは、到来順の判定通り、ビーム光ａが先頭ビーム光となってセンサパターンＳ３を通過し、ビーム光検知出力Ｓ３ＯＵＴが出力される。ビーム光検知出力Ｓ３ＯＵＴがビーム光ａの水平同期信号となる。
【０３４２】
ビーム光検知出力Ｓ３ＯＵＴが出力されると、主制御部５１はレーザ発振器３１ａを消灯する。また、同期回路５５は、ビーム光検知出力Ｓ３ＯＵＴの出力に同期して、遅延時間ｔ3 後に同期クロックパルスを出力する。カウンタ９８は、この同期クロックパルスをカウントし、所定のカウント値（左マージン）になると、主制御部５１へカウント終了信号を出力する。
【０３４３】
主制御部５１は、このカウント終了信号を受取ると、画像形成を開始し、レーザドライバ３２ａ〜３２ｄに画像クロックパルスを出力して、主走査方向の画像形成を開始する。また、所定のカウント値（右マージン）になると、画像クロックパルスの出力を停止し、主走査方向の画像形成を終了する。
【０３４４】
一方、ビーム光ｂがセンサパターンＳ４を通過すると、ビーム光検知出力Ｓ４ＯＵＴが出力され、主制御部５１は、レーザ発振器３１ｂを消灯する。同期回路５５は、ビーム光検知出力Ｓ４ＯＵＴの出力に同期して、遅延時間ｔ4 後に同期クロックパルスを出力する（ビーム光検知出力Ｓ４ＯＵＴがビーム光ｂの水平同期信号）。カウンタ６０は、この同期クロックパルスをカウントし、上記同様、主走査方向の画像形成が行なわれる。
【０３４５】
上記の動作は、ビーム光ｃ、ビーム光ｄについても同様に行なわれ、画像形成を行なう。すなわち、ビーム光検知出力Ｓ５ＯＵＴがビーム光ｃの水平同期信号となり、ビーム光検知出力Ｓ６ＯＵＴがビーム光ｄの水平同期信号となる。
【０３４６】
次に、ビーム光検知装置３８における、ビーム光の通過タイミングを検知するためのセンサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５を、同期回路５５から出力される同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の整数倍とする点について説明する。
【０３４７】
前述したように、本実施の形態では、センサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５は、解像度の整数倍となっている。そして、本実施の形態の場合、第１の解像度（Ｐ１）と第２の解像度（Ｐ２＝３／２×Ｐ１）で画像形成が可能なように構成されており、センサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５は、双方の解像度の最小公倍数（Ｌ．Ｃ．Ｍ．（Ｐ１，Ｐ２））の整数倍のＬ．Ｃ．Ｍ．（Ｐ１，Ｐ２）×２となっている。これは、第１の解像度で画像形成した場合の６ドットの距離に相当し、また、第２の解像度で画像形成した場合の４ドットに相当する距離である。
【０３４８】
まず、ビーム光の通過タイミングを検知するセンサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５が、同期回路５５から出力される同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の最小公倍数の整数倍ではない場合の問題点を以下に説明する。ここでは、第１の解像度および第２の解像度の２種類の解像度を有する場合を例に説明する。
【０３４９】
図４８は、たとえば、センサパターンＳ３とＳ４との間隔Ｐ３が、同期回路５５から出力される複数の同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の最小公倍数の整数倍ではない場合に、主走査方向の画像形成位置制御を行なう様子を示したものである。センサパターンＳ３とＳ４との間隔Ｐ３はＤ１×５で、第１の解像度で画像形成した場合の５ドットの距離に相当し、第２の解像度で画像形成した場合の約３．３ドットの距離に相当する。
【０３５０】
図４８では、ビーム光ａはセンサパターンＳ３で、また、ビーム光ｂはセンサパターンＳ４で、主走査方向の画像形成位置制御のタイミング（すなわち、水平同期信号）をとるものとしている。また、第１の解像度と第２の解像度に対応した基準クロックパルス（同期クロックパルスの基準となるクロックパルス）の１パルス時間（すなわち、１周期）をそれぞれＴＣ，ＴＣＣとした。
【０３５１】
第１の解像度の場合の主走査方向の画像形成位置制御の方法は、前述したように既に説明済みであるので、ここでは説明を省略する。
【０３５２】
第２の解像度を選択し、第２の解像度で画像形成する場合の主走査方向の画像形成位置制御について以下に説明する。
【０３５３】
ビーム光ａの通過に伴い、２値化されたセンサパターンＳ３の出力であるビーム光検知出力Ｓ３ＯＵＴが出力される。同期回路５５は、このビーム光検知出力Ｓ３ＯＵＴの出力（信号がロウレベルからハイレベルへ変化する立ち上がりのエッジ）に同期して、回路遅延時間ｔ13経過後に同期クロックパルスＣＬＫ１３を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ１３をカウントし、所定のカウント値（図ではカウント値：８）に達すると、主制御部５１へカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３５４】
一方、ビーム光ｂについても同様に、ビーム光ｂの通過に伴い、ビーム光検知出力Ｓ４ＯＵＴが出力され、同期回路５５は、このビーム光検知出力Ｓ４ＯＵＴの立ち上がりエッジに同期して、回路遅延時間ｔ14経過後に同期クロックパルスＣＬＫ１４を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ１４をカウントし、所定のカウント値（図ではカウント値：５）に達すると、主制御部５１へカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３５５】
ここでも、前述同様に画像の先端に注目すると、第１の解像度の場合は当然、画像形成位置のずれは生じないが、第２の解像度の場合には、同期クロックパルスＣＬＫ１３と同期クロックパルスＣＬＫ１４とに位相差が生じており、ビーム光ａによる画像先端よりも、ビーム光ｂによる画像先端がビーム光の走査方向にずれていることが分かる（ずれ量：−ＶＳ×ｔｂｂ、約０．３ドット）。
【０３５６】
すなわち、ビーム光ａの画像形成領域ＨＡＡと、ビーム光ｂの画像形成領域ＨＢＢにずれが生じており、出力画像上では縦線の揺れとして認識される。このずれを補正するために、ビーム光ｂの同期クロックパルスＣＬＫ１４をカウントする際に、所定の値よりも少なくカウントし（図では４）、ビーム光ｂによって形成される画像形成領域をビーム光の走査方向と反対方向にずらすことが考えられる。
【０３５７】
しかし、カウント値は１パルス単位（言い換えると１ドット単位）でしか変更することができないため、図４８の場合はかえってずれ量が大きくなる（ずれ量：＋ＶＳ×ｔａａ）。したがって、ずれの補正ができず、定常的にレンジで１ドット未満のずれが生じていることになる。
【０３５８】
ビーム光ａとビーム光ｂの主走査方向の画像形成位置制御の基準は、水平同期信号（Ｓ３ＯＵＴとＳ４ＯＵＴ）であるが、この基準信号の間隔が第２の解像度の同期クロックパルスと無関係であることから、上記のずれが生じる。
【０３５９】
そこで、本実施の形態では、水平同期信号を出力するセンサパターンＳ３〜Ｓ６の間隔Ｐ３，Ｐ４，Ｐ５を、同期回路５５から出力される同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の最小公倍数の整数倍としている。これによって、主走査方向の画像形成位置のずれを小さくすることができる。
【０３６０】
以下、図４９を参照して本実施の形態について説明する。同図において、センサパターンＳ３とＳ４との間隔（距離）Ｐ３は、第１の解像度の場合の同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離と、第２の解像度の場合の同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離との最小公倍数の整数倍としている（Ｐ３＝Ｌ．Ｃ．Ｍ．（ＶＳ×ＴＣ＝Ｐ１、ＶＳ′×ＴＣＣ＝Ｐ２）×ｎ）。
【０３６１】
すなわち、Ｐ３は第１の解像度で画像形成した場合の６ドットの距離に相当し、第２の解像度で画像形成した場合の４ドットの距離に相当する。また、図４８と同様に、ビーム光ａはセンサパターンＳ３で、また、ビーム光ｂはセンサパターンＳ４で主走査方向の画像形成位置制御（水平同期）のタイミングをとるものとしている。
【０３６２】
まず、第１の解像度の場合について説明する。
【０３６３】
ビーム光ａの通過に伴い、ビーム光検知出力Ｓ３ＯＵＴ（ビーム光ａの水平同期信号）が出力され、同期回路５５は、このビーム光検知出力Ｓ３ＯＵＴの出力（立ち上がりエッジ）に同期して、回路遅延時間ｔ3 経過後に同期クロックパルスＣＬＫ３を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ３をカウントし、所定のカウント値（図ではカウント値：１０）に達すると、主制御部５１にカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３６４】
一方、ビーム光ｂについても同様に、ビーム光ｂの通過に伴い、ビーム光検知出力Ｓ４ＯＵＴが出力され、同期回路５１は、このビーム光検知出力Ｓ４ＯＵＴの立ち上がりエッジに同期して、回路遅延時間ｔ4 経過後に同期クロックパルスＣＬＫ４を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ４をカウントし、所定のカウント値（図では４）に達すると、主制御部５１にカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３６５】
この場合、センサパターンＳ３とＳ４との間隔Ｐ３は、第１の解像度で画像形成した場合の６ドットの距離に相当するために、同期クロックパルスＣＬＫ３と同期クロックパルスＣＬＫ４との位相差が生じることがなく、画像先端のずれは生じない。すなわち、ビーム光ａによる主走査画像形成領域ＨＡと、ビーム光ｂによる主走査画像形成領域ＨＢとのずれは起こらない。
【０３６６】
次に、第２の解像度の場合について説明する。
【０３６７】
ビーム光ａの通過に伴い、ビーム光検知出力Ｓ３ＯＵＴ（ビーム光ａの水平同期信号）が出力され、同期回路５５は、このビーム光検知出力Ｓ３ＯＵＴの出力（立ち上がりエッジ）に同期して、回路遅延時間ｔ13経過後に同期クロックパルスＣＬＫ１３を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ１３をカウントして、所定のカウント値（図ではカウント値：７）に達すると、主制御部５１にカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３６８】
一方、ビーム光ｂについても同様に、ビーム光ｂの通過に伴い、ビーム光検知出力Ｓ４ＯＵＴが出力され、同期回路５１は、このビーム光検知出力Ｓ４ＯＵＴの立ち上がりエッジに同期して、回路遅延時間ｔ14経過後に同期クロックパルスＣＬＫ１４を出力する。カウンタ９８は、この同期クロックパルスＣＬＫ１４をカウントして、所定のカウント値（図では３）に達すると、主制御部５１にカウント終了信号を出力する。主制御部５１は、このカウント終了信号を受取ると、画像クロックパルスをレーザドライバに出力する（画像形成を開始する）。
【０３６９】
この場合、センサパターンＳ３とＳ４との間隔Ｐ３は、第２の解像度で画像形成した場合の４ドットの距離に相当するために、同期クロックパルスＣＬＫ１３と同期クロックパルスＣＬＫ１４との位相差が生じることがなく、画像先端のずれは生じない。すなわち、ビーム光ａによる主走査画像形成領域ＨＡＡと、ビーム光ｂによる主走査画像形成領域ＨＢＢとのずれは起こらない。
【０３７０】
なお、副走査方向のビーム光通過位置制御については、前述した図３のビーム光検知装置３８を用いた場合と同様であるので、説明は省略する。
【０３７１】
このように、上記実施の形態によれば、複数の解像度を有した画像形成装置においても、主走査画像形成領域のずれが生ずることのない高画質の画像を形成することができる。
【０３７２】
次に、ビーム光の走査方向とビーム光検知装置との相対的な傾きを検知する点について説明する。
【０３７３】
図５０は、ビーム光の走査方向とビーム光検知装置との相対的な傾きを検知する傾き検知機能を有したビーム光検知装置３８の構成例を示している。このビーム光検知装置３８は、前述した図２８の構成に対して、センサパターンＳ１，Ｓ６の外側近傍に、それぞれ傾きを検知するための第6の光検知部としてのセンサ パターンＳ７ａ，Ｓ７ｂおよびＳ８ａ，Ｓ８ｂを設けたもので、その他の構成は基本的に図２８と同様であるので、説明は省略する。
【０３７４】
センサパターンＳ７ａとＳ７ｂおよびＳ８ａとＳ８ｂは、それぞれ上下に配設されてペアを組んでおり、他のセンサパターンと基本的に同一の構成である。ただし、センサパターンＳ７ａとＳ７ｂ、Ｓ８ａとＳ８ｂの中心位置は、同一直線上である。
【０３７５】
また、センサパターンＳ７ａ，Ｓ７ｂ、Ｓ８ａ，Ｓ８ｂの各出力は、たとえば、図５１に示すビーム光検知装置出力処理回路４０における傾き検知側回路によって処理され、ビーム光位置情報として出力される。図５１の傾き検知側回路は、図９に示した回路から積分器４２を削除したもので、その他の構成は基本的に図９と同様であるので、説明は省略する。
【０３７６】
図５１の傾き検知側回路によれば、センサパターンＳ７ａとＳ７ｂ、Ｓ８ａとＳ８ｂの中心位置は同一直線上にあるため、センサパターンＳ７ａ，Ｓ７ｂ、Ｓ８ａ，Ｓ８ｂから得られるビーム光位置情報によって傾きが検出できる。すなわち、センサパターンＳ７ａ，Ｓ７ｂからのビーム光位置情報とセンサパターンＳ８ａ，Ｓ８ｂからのビーム光位置情報とが等しければ傾きはなく、両ビーム光位置情報が異なれば傾きがあるものとみなせる。
【０３７７】
図５２は、傾きの状態を説明するための図で、図５０からセンサパターンＳ７ａ，Ｓ７ｂ、Ｓ８ａ，Ｓ８ｂを抜き出したものであり、他のセンサパターンは省略してある。図５２において、状態Ａは傾きあり、状態Ｂは傾きあり（Ａとは反対方向に傾いている）、状態Ｃは傾きなし、状態Ｃ′は傾きなし、をそれぞれ示している。なお、図５２において、ＢＭはビーム光を示している。
【０３７８】
本実施の形態では、ビーム光がセンサパターンＳ７ａ，Ｓ７ｂとＳ８ａ，Ｓ１８ｂを通過するときのビーム光通過位置情報によって傾きを判定するようになっている。
【０３７９】
図５３は、図５２における状態Ａのときのビーム光位置情報（図５１の回路の出力ＶＯ７，ＶＯ８）の一例を示すもので、（ａ）図はセンサパターンＳ７ａ，Ｓ７ｂによるビーム光位置情報（ＶＯ７）、（ｂ）図はセンサパターンＳ８ａ，Ｓ８ｂによるビーム光位置情報（ＶＯ８）、（ｃ）図はＶＯ７とＶＯ８とを比較した図である。この場合、両ビーム光位置情報が異なるため傾きありとなる。なお、ＶＯ７＜ＶＯ８のときは状態Ａの傾きとなる。
【０３８０】
図５４は、図５２における状態Ｂのときのビーム光位置情報（図５１の回路の出力ＶＯ７，ＶＯ８）の一例を示すもので、（ａ）図はセンサパターンＳ７ａ，Ｓ７ｂによるビーム光位置情報（ＶＯ７）、（ｂ）図はセンサパターンＳ８ａ，Ｓ８ｂによるビーム光位置情報（ＶＯ８）、（ｃ）図はＶＯ７とＶＯ８とを比較した図である。この場合、両ビーム光位置情報が異なるため傾きありとなる。なお、ＶＯ７＞ＶＯ８のときは状態Ｂの傾きとなる。
【０３８１】
図５５は、図５２における状態Ｃ′のときのビーム光位置情報（図５１の回路の出力ＶＯ７，ＶＯ８）の一例を示すもので、（ａ）図はセンサパターンＳ７ａ，Ｓ７ｂによるビーム光位置情報（ＶＯ７）、（ｂ）図はセンサパターンＳ８ａ，Ｓ８ｂによるビーム光位置情報（ＶＯ８）、（ｃ）図はＶＯ７とＶＯ８とを比較した図である。この場合、両ビーム光位置情報が等しいため傾きなしとなる。
【０３８２】
図５６は、ビーム光検知装置３８の傾きを調整する調整機構の具体例を示している。すなわち、ビーム光検知装置３８は基板９１上に固定されている。また、基板９１上には、前述したビーム光検知装置出力処理回路４０（図示しない）が、たとえば、集積回路（ＩＣ）化されて構成されている。基板９１は、θステージ９２に固定されており、このθステージ９２を回転させることで、ビーム光検知装置３８の傾きを調整できるようになっている。θステージ９２には、いずれも図示しないギアヘッドを介してパルスモータが装着されており、このパルスモータを、上記したＶＯ７とＶＯ８との比較結果に応じて回転制御することで、高精度に傾きを調整できる。
【０３８３】
以上説明したように、上記実施の形態によれば、マルチビーム光学系を用いたデジタル複写機において、感光体ドラムの表面を走査する複数のビーム光の位置を検知するビーム光位置検知装置における複数のセンサパターンを、複数のビーム光の走査方向に対してほぼ直交する方向に複数の解像度に対応した間隔で平行に並列配設することによって、取付け傾きに充分余裕のあるビーム光位置検知装置を構築することができる。
【０３８４】
したがって、正確にビーム光の走査位置を検知することができるので、複数の解像度で、感光体ドラムの表面における数のビーム光の位置を常に理想的な位置に高精度に制御できる。これにより、常に高画質を維持することができる。
【０３８５】
また、感光体ドラムの表面を走査するビーム光のパワーを検知して、その値が所定の範囲内に収まるようにパワー制御した上で、感光体ドラムの表面におけるビーム光の通過位置制御、および、主走査方向の同期を取る制御を行なうことによって、制御精度を落とすことなく、感光体ドラムの表面における各ビーム光のパワーを均一に制御できるとともに、感光体ドラムの表面における複数のビーム光の位置を常に理想的な位置に高精度に制御でき、よって、常に高画質を維持することができる。
【０３８６】
また、画像を形成する前に、あらかじめ、複数のビーム光のビーム光検知装置内の複数のビーム光通過タイミング検知用のセンサパターンに対する到来順を判定し、その判定結果に基づいて、ビーム光とそのビーム光の通過タイミングを検知するセンサパターンとの組合わせを決定し、主走査方向の位置制御を行なうことにより、特に複数のビーム光を用いる場合、光学系の組立てに特別な精度や調整を必要とせず、しかも、環境変化や経時変化などによって光学系に変化が生じても、感光体ドラムの表面における各ビーム光相互の位置関係を常に理想的な位置に制御できる。したがって、主走査方向のドットずれのない高画質の画像を常に得ることができる。
【０３８７】
さらに、ビーム光の走査方向とビーム光検知装置との相対的な傾きを検知する傾き検知手段を有するので、その傾きを容易に調整することが可能になる。
【０３８８】
なお、前記実施の形態では、マルチビーム光学系を用いたデジタル複写機に適用した場合について説明したが、本発明はこれに限定されるものでなく、シングルビーム光学系を用いたものでも同様に適用でき、さらに、デジタル複写機以外の画像形成装置にも同様に適用できる。
【０３８９】
【発明の効果】
以上詳述したように本発明によれば、複数の解像度で、被走査面におけるビーム光の位置を常に適正位置に高精度に制御でき、また、被走査面におけるビーム光のパワーを均一に制御でき、よって、常に高画質を維持することができるビーム光走査装置および画像形成装置を提供できる。
【０３９０】
また、本発明によれば、複数のビーム光を用いる場合、複数の解像度で、被走査面における複数のビーム光相互の位置関係を常に理想的な位置に高精度に制御でき、また、被走査面における各ビーム光のパワーを均一に制御でき、よって、常に高画質を維持することができるビーム光走査装置および画像形成装置を提供できる。
【図面の簡単な説明】
【図１】本発明の実施の形態に係るデジタル複写機の構成を概略的に示す構成図。
【図２】光学系ユニットの構成と感光体ドラムの位置関係を示す図。
【図３】ビーム光検知装置の構成を概略的に示す構成図。
【図４】図３のビーム光検知装置の要部構成を概略的に示す構成図。
【図５】ビーム光検知装置とビーム光の走査方向との傾きを説明するための図。
【図６】光学系の制御を主体にした制御系を示すブロック図。
【図７】主走査方向の画像形成精度がビーム光のパワーに依存することを説明するための図。
【図８】図３のビーム光検知装置を用いたビーム光の通過位置制御を説明するためのブロック図。
【図９】ビーム光検知装置出力処理回路の具体的な回路例を示す構成図。
【図１０】ビーム光の通過位置とビーム光検知装置の受光パターンの出力、差動増幅器の出力、積分器の出力との関係を示す図。
【図１１】ビーム光の通過位置とＡ／Ｄ変換器の出力との関係を示すグラフ。
【図１２】ガルバノミラーの動作分解能を説明するグラフ。
【図１３】ガルバノミラーの動作分解能を説明するグラフ。
【図１４】図３のビーム光検知装置を用いた場合のプリンタ部の電源投入時における概略的な動作を説明するフローチャート。
【図１５】ビーム光通過位置制御ルーチンを説明するフローチャート。
【図１６】１つのビーム光通過位置制御ルーチンを説明するフローチャート。
【図１７】１つのビーム光通過位置制御ルーチンを説明するフローチャート。
【図１８】ビーム光通過位置制御における各ビーム光のパワーのばらつきが与える影響について説明するための図。
【図１９】ビーム光パワー制御ルーチンの第１の例を説明するフローチャート。
【図２０】ビーム光パワー制御ルーチンの第１の例を説明するフローチャート。
【図２１】ビーム光パワー制御ルーチンの第２の例を説明するフローチャート。
【図２２】ビーム光パワー制御ルーチンの第２の例を説明するフローチャート。
【図２３】２種類の解像度に対応したビーム光検知装置の構成を模式的に示す概略構成図。
【図２４】図２３のビーム光検知装置の要部構成を概略的に示す構成図。
【図２５】図２３のビーム光検知装置とビーム光の走査方向との傾きを説明するための図。
【図２６】図２３のビーム光検知装置を用いたビーム光の通過位置制御を説明するためのブロック図。
【図２７】図２３のビーム光検知装置を用いた場合のプリンタ部の電源投入時における概略的な動作を説明するフローチャート。
【図２８】ビーム光通過タイミング検知機能を備えたビーム光検知装置の構成を模式的に示す概略構成図。
【図２９】主走査方向の画像形成位置制御を説明するためのブロック図。
【図３０】１本ビーム光時の主走査方向の画像形成位置制御を説明するタイミングチャート。
【図３１】１本ビーム光時の主走査方向の画像形成位置制御を説明するフローチャート。
【図３２】ビーム光検知装置出力処理回路における主走査側回路の構成図。
【図３３】ビーム光の到来状態を説明する図。
【図３４】ビーム光の到来状態を説明する図。
【図３５】ビーム光到来状態の判定手順を説明するフローチャート。
【図３６】ケース４の場合のセンサ割付手順を説明するフローチャート。
【図３７】先頭ビーム光の判定手順を説明するフローチャート。
【図３８】先頭ビーム光の判定手順を説明するフローチャート。
【図３９】２番目のビーム光の判定手順を説明するフローチャート。
【図４０】２番目のビーム光の判定手順を説明するフローチャート。
【図４１】３番目のビーム光の判定手順を説明するフローチャート。
【図４２】ケース３の場合のセンサ割付手順を説明するフローチャート。
【図４３】重なっているビーム光の判定とグループ分けの手順を説明するフローチャート。
【図４４】重なっているビーム光の判定とグループ分けの手順を説明するフローチャート。
【図４５】ケース２の場合のセンサ割付手順を説明するフローチャート。
【図４６】ビーム光の判定手順を説明するフローチャート。
【図４７】４本ビーム光時の主走査方向の画像形成位置制御を説明するタイミングチャート。
【図４８】ビーム光の通過タイミング検知用センサパターンの間隔が同期回路から出力される同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の最小公倍数の整数倍ではない場合の主走査方向の画像形成位置制御を説明するタイミングチャート。
【図４９】ビーム光の通過タイミング検知用センサパターンの間隔を同期回路から出力される同期クロックパルスの１パルス時間にビーム光が走査方向に移動する距離の最小公倍数の整数倍とした場合の主走査方向の画像形成位置制御を説明するタイミングチャート。
【図５０】傾き検知機能を備えたビーム光検知装置の構成を模式的に示す概略構成図。
【図５１】ビーム光検知装置出力処理回路における傾き検知回路の構成図。
【図５２】傾きの状態を説明するための図。
【図５３】図５２における状態Ａのときのビーム光位置情報の一例を示す図。
【図５４】図５２における状態Ｂのときのビーム光位置情報の一例を示す図。
【図５５】図５２における状態Ｃ′のときのビーム光位置情報の一例を示す図。
【図５６】ビーム光検知装置の傾きを調整する調整機構の具体例を概略的に示す斜視図。
【図５７】位置ずれしたビーム光を用いて画像形成した場合に起こり得る画像不良を説明するための図。
【図５８】位置ずれしたビーム光を用いて画像形成した場合に起こり得る画像不良を説明するための図。
【符号の説明】
１……スキャナ部、２……プリンタ部、６……光電変換素子、９……光源、１３……光学系ユニット、１４……画像形成部、１５……感光体ドラム（像担持体）、３１ａ〜３１ｄ……半導体レーザ発振器（ビーム光発生手段）、３３ａ〜３３ｄ……ガルバノミラー、３５……ポリゴンミラー、３８……ビーム光検知装置（ビーム光通過タイミング検知手段、ビーム光位置検知手段、ビーム光パワー検知手段）、３８ａ……保持基板（保持手段）、３９ａ〜３９ｄ……ガルバノミラー駆動回路、４０……ビーム光検知装置出力処理回路、４１……選択回路、４２……積分器、４３……Ａ／Ｄ変換器、Ｓ１〜Ｓ６，ＳＨ，ＳＡ〜ＳＧ，ＳＢ１〜ＳＦ１，ＳＢ２〜ＳＦ２……センサパターン（光検知部）、５１……主制御部、５２……メモリ、６１，６２，９９……増幅器、６４〜６６……差動増幅器。[0001]
BACKGROUND OF THE INVENTION
The present invention includes, for example, a beam light scanning device for simultaneously scanning and exposing a single photosensitive drum with a plurality of laser beam lights to form a single electrostatic latent image on the photosensitive drum, and The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer using the same.
[0002]
[Prior art]
In recent years, for example, various digital copying machines have been developed that perform image formation by scanning exposure using a laser beam and an electrophotographic process.
[0003]
Recently, in order to further increase the image forming speed, a multi-beam method, that is, a plurality of laser beam lights is generated, and a plurality of lines are simultaneously scanned by the plurality of laser beam lights. A digital copier has been developed.
[0004]
In such a multi-beam type digital copying machine, a plurality of semiconductor laser oscillators that generate laser beam light, each laser beam light output from the plurality of laser oscillators is reflected toward a photosensitive drum, and each laser beam is reflected. It has an optical system unit as a beam light scanning device mainly composed of a multi-surface rotating mirror such as a polygon mirror that scans the photosensitive drum with the beam light, and a collimator lens and an f-θ lens.
[0005]
[Problems to be solved by the invention]
However, in the configuration of the conventional optical system unit, it is very difficult to make the positional relationship between a plurality of light beams ideal on the photosensitive drum (scanned surface). However, very high component accuracy and assembly accuracy were required, which was a factor in increasing the cost of the apparatus.
[0006]
In addition, even if assembled in an ideal positional relationship, the lens shape changes slightly due to environmental changes such as temperature changes and humidity changes, or changes over time, or the positional relationship between components changes slightly. The positional relationship between the light beams is distorted and a high-quality image cannot be formed. Therefore, in order to realize such an optical system, it is necessary to use structures and parts that are resistant to these changes.
[0007]
Here, image defects that may occur when an image is formed using misaligned light beams in a multi-beam will be described with reference to FIGS. 57 and 58. FIG.
[0008]
For example, when forming the letter “T” as shown in FIG. 57 (a), if the beam light passing position deviates from a predetermined position, an image as shown in FIG. 57 (b) is obtained. End up. The example of this figure is the case where four beam lights a to d are used, the passing position of the beam light b deviates from a predetermined position, the distance between the beam lights a and b is narrow, and the distance between the beam lights b and c is wide. This is an example.
[0009]
FIG. 58A is an example of an image when the light emission timings of the respective light beams are not controlled correctly. As is apparent from the figure, if the light emission timing between the light beams is not correctly controlled, the image forming position in the main scanning direction is incorrect, and the vertical lines are not formed straight.
[0010]
FIG. 58B shows an image in a case where both the light beam passage position and the light emission timing are not controlled correctly. An image defect in the sub-scanning direction and an image defect in the main scanning direction occur simultaneously. .
[0011]
As described above, when forming an image with multiple beams, a beam light detection device for detecting the passage positions of a plurality of light beams is attached with high accuracy so that the beam light passage positions in the sub-scanning direction are always set at predetermined intervals. It is necessary to control the light emission timing of each light beam with high accuracy in order to perform control so that the image forming positions in the main scanning direction are aligned.
[0012]
In addition, as a condition for obtaining a high-quality image using a multi-beam optical system,
(1) The light power on the photosensitive drum of each light beam is equal,
(2) The positional relationship between the light beams (passing position in the sub-scanning direction) is a predetermined relationship,
(3) The exposure timing for image formation in the main scanning direction is correctly controlled according to the positional relationship between the light beams,
It is possible to satisfy.
[0013]
The point here is that the control in (2) and (3) is operating correctly if (1) is established and the optical power on the photosensitive drum in (1) is not equal. Even so, something that is virtually incorrect can happen. That is, the control accuracy of (2) and (3) depends on the power of the light beam.
[0014]
Therefore, it is necessary to control each beam light scanned on the photosensitive drum, that is, each beam light output from a plurality of laser oscillators, to have the same power after being synthesized by optical means such as a half mirror. is there.
[0016]
In the present invention, when a plurality of light beams are used, the power of each light beam on the surface to be scanned is easily and uniformly controlled, and the positional relationship between the plurality of light beams on the surface to be scanned is always ideal at a plurality of resolutions. It is an object of the present invention to provide a beam light scanning device and an image forming apparatus that can be accurately controlled at various positions, and thus can always maintain high image quality.
[0017]
[Means for Solving the Problems]
The beam light scanning device of the present invention optically combines a plurality of beam light generating means for generating beam light and the plurality of beam lights generated from the plurality of beam light generating means, and then toward the surface to be scanned. Scanning means for reflecting and scanning the surface to be scanned in the main scanning direction with the plurality of light beams, and light power for detecting each power of the plurality of light beams for scanning the surface to be scanned by the scanning means. Based on the detection results of each of the detection means and the light beam power detection means, the plurality of light beam generation means are controlled so that the difference in power between the plurality of light beams that scan the surface to be scanned is less than a predetermined value. And a plurality of light receiving elements linearly arranged at intervals corresponding to the first resolution in the sub-scanning direction orthogonal to the main scanning direction. First beam light position detecting means for detecting the sub-scanning direction passing positions of a plurality of light beams that scan the surface to be scanned by the scanning unit using an optical element, and a first resolution different from the first resolution. A plurality of light-receiving elements that are linearly arranged in the sub-scanning direction at intervals corresponding to a resolution of 2, and that use the plurality of light-receiving elements to scan the surface to be scanned by the scanning unit. A plurality of beams scanned by the scanning unit based on detection results of the second beam light position detecting unit for detecting the passage position of the light in the sub-scanning direction and the first and second beam light position detecting units; Beam light passing position control means for controlling the light passing position on the surface to be scanned to be an appropriate position corresponding to the first or second resolution, and the beam light power detecting means is a first light receiving unit. And children, and the second and third light receiving elements arranged on opposite sides of the first light receiving element, an integrator for integrating the output of the first light receiving element, the integration result of the integrator A / D Convert A / D converter The integrator is reset when the beam light passes over the second light receiving element, and simultaneously starts integration, A / D converter Performs conversion when the light beam passes over the third light receiving element.
[0019]
In the light beam scanning apparatus of the present invention, the power control by the light beam power control means and the position control by the beam passage position control means are performed immediately after the power is turned on and every predetermined time.
[0020]
The beam light passage position control means is configured such that the power of each beam light is the beam light. power After being controlled by the control means, the passing position of each light beam on the scanned surface is controlled.
[0021]
Further, the beam light scanning device of the present invention includes first to third light receiving elements of the beam light power detecting means, the plurality of light receiving elements included in the first beam light position detecting means, and the second beam. A holding unit that integrally holds the plurality of light receiving elements included in the optical position detection unit;
[0022]
Further, an image forming apparatus according to the present invention includes the beam light scanning device described above and an image carrier that is scanned and exposed on the surface thereof by the beam light from the beam light scanning device.
[0023]
According to the present invention, when a plurality of light beams are used, the power of each light beam on the scanned surface is easily and uniformly controlled, and the positional relationship between the plurality of light beams on the scanned surface is always maintained at a plurality of resolutions. Provided are a beam light scanning apparatus and an image forming apparatus that can be controlled to an ideal position with high accuracy, and can therefore always maintain high image quality.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0035]
FIG. 1 shows the configuration of a digital copying machine as an image forming apparatus to which the light beam scanning apparatus according to this embodiment is applied. In other words, this digital copying machine includes, for example, a scanner unit 1 as an image reading unit and a printer unit 2 as an image forming unit. The scanner unit 1 includes a first carriage 3 and a second carriage 4 that can move in the direction of the arrow, an imaging lens 5, a photoelectric conversion element 6, and the like.
[0036]
In FIG. 1, a document O is placed downward on a document table 7 made of transparent glass, and the document O is placed on the center right on the front right side of the document table 7 in the short direction. The document O is pressed onto the document table 7 by a document fixing cover 8 provided so as to be freely opened and closed.
[0037]
The document O is illuminated by a light source 9, and the reflected light is condensed on the light receiving surface of the photoelectric conversion element 6 via the mirrors 10, 11, 12 and the imaging lens 5. Here, the first carriage 3 on which the light source 9 and the mirror 10 are mounted and the second carriage 4 on which the mirrors 11 and 12 are mounted move at a relative speed of 2: 1 so as to make the optical path length constant. It has become. The first carriage 3 and the second carriage 4 are moved from right to left by a carriage driving motor (not shown) in synchronization with the reading timing signal.
[0038]
As described above, the image of the document O placed on the document table 7 is sequentially read line by line by the scanner unit 1, and the read output is 8 indicating the density of the image in the image processing unit (not shown). It is converted into a bit digital image signal.
[0039]
The printer unit 2 includes an optical system unit 13 and an image forming unit 14 that combines an electrophotographic system capable of forming an image on a sheet P that is an image forming medium. That is, an image signal read from the document O by the scanner unit 1 is processed by an image processing unit (not shown) and then converted into a laser beam light (hereinafter simply referred to as a beam light) from a semiconductor laser oscillator. . In this embodiment, a multi-beam optical system using a plurality (two or more) of semiconductor laser oscillators is employed.
[0040]
The configuration of the optical system unit 13 will be described in detail later. The plurality of semiconductor laser oscillators provided in the unit emit light in accordance with a laser modulation signal output from an image processing unit (not shown) and output from these. The plurality of light beams are reflected by a polygon mirror to become scanning light and output to the outside of the unit.
[0041]
A plurality of light beams output from the optical system unit 13 are imaged as spot scanning light having a necessary resolution at the exposure position X on the photosensitive drum 15 as an image carrier, and are subjected to scanning exposure. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 15.
[0042]
Around the photosensitive drum 15, a charging charger 16, a developing unit 17, a transfer charger 18, a peeling charger 19, a cleaner 20, and the like are disposed. The photosensitive drum 17 is rotationally driven at a predetermined outer peripheral speed by a drive motor (not shown), and is charged by a charging charger 16 provided facing the surface thereof. A plurality of light beams (scanning light) are spot-imaged at the position of the exposure position X on the charged photosensitive drum 15.
[0043]
The electrostatic latent image formed on the photosensitive drum 15 is developed with toner (developer) from the developing unit 17. The photosensitive drum 15 on which the toner image is formed by development is transferred by the transfer charger 18 onto the paper P supplied at a timing of the transfer position by the paper feed system.
[0044]
The paper feed system separates and feeds the paper P in the paper feed cassette 21 provided at the bottom by the paper feed roller 22 and the separation roller 23 one by one. Then, it is sent to the registration roller 24 and supplied to the transfer position at a predetermined timing. On the downstream side of the transfer charger 18, a paper transport mechanism 25, a fixing device 26, and a paper discharge roller 27 for discharging the paper P on which an image has been formed are disposed. As a result, the toner image is transferred onto the paper P on which the toner image has been transferred, and is then discharged onto the external paper discharge tray 28 via the paper discharge roller 27.
[0045]
In addition, the photosensitive drum 15 whose transfer to the paper P has been completed, the residual toner on the surface thereof is removed by the cleaner 20, the initial state is restored, and a standby state for the next image formation is entered.
[0046]
By repeating the above process operation, the image forming operation is continuously performed.
[0047]
As described above, the document O placed on the document table 7 is read by the scanner unit 1, and the read information is processed as a toner image on the paper P after being subjected to a series of processing by the printer unit 2. It will be recorded.
[0048]
Next, the optical system unit 13 will be described.
[0049]
FIG. 2 shows the configuration of the optical system unit 13 and the positional relationship between the photosensitive drum 15. The optical system unit 13 includes, for example, four semiconductor laser oscillators 31a, 31b, 31c, and 31d as beam light generating means, and each laser oscillator 31a to 31d simultaneously forms an image for each scanning line. By doing so, high-speed image formation is possible without extremely increasing the rotational speed of the polygon mirror.
[0050]
That is, the laser oscillator 31a is driven by the laser driver 32a, and the output light beam passes through a collimator lens (not shown) and then enters a galvanometer mirror 33a serving as an optical path changing unit. The beam light reflected by the galvanometer mirror 33a passes through the half mirror 34a and the half mirror 34b, and is incident on the polygon mirror 35 as a polyhedral rotating mirror.
[0051]
The polygon mirror 35 is rotated at a constant speed by a polygon motor 36 driven by a polygon motor driver 37. Thereby, the reflected light from the polygon mirror 35 is scanned in a fixed direction at an angular velocity determined by the number of rotations of the polygon motor 36. The light beam scanned by the polygon mirror 35 passes through the f-θ characteristic of an unillustrated f-θ lens, thereby passing the light beam at a constant speed, thereby detecting the light beam position detecting means, the light beam passage timing detecting means, and the light beam. Scanning is performed on the light receiving surface of the light beam detector 38 as the power detector and on the photosensitive drum 15.
[0052]
The laser oscillator 31b is driven by the laser driver 32b, and the output beam light passes through a collimator lens (not shown), is reflected by the galvano mirror 33b, and is further reflected by the half mirror 34a. The reflected light from the half mirror 34 a passes through the half mirror 34 b and enters the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillator 31a described above, passes through an f-θ lens (not shown), and scans the light receiving surface of the beam light detector 38 and the photosensitive drum 15 at a constant speed.
[0053]
The laser oscillator 31c is driven by the laser driver 32c, and the output beam light passes through a collimator lens (not shown), is reflected by the galvanometer mirror 33c, further passes through the half mirror 34c, and is reflected by the half mirror 34b. Incident on the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillators 31a and 31b described above, passes through an f-θ lens (not shown), and scans the light receiving surface of the beam light detector 38 and the photosensitive drum 15 at a constant speed. To do.
[0054]
The laser oscillator 31d is driven by a laser driver 32d, and the output beam light passes through a collimator lens (not shown), is reflected by a galvano mirror 33d, is further reflected by a half mirror 34c, and is reflected by a half mirror 34b. Incident on the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillators 31a, 31b, 31c described above, passes through an f-θ lens (not shown), and on the light receiving surface of the light beam detector 38 and the photosensitive drum 15 at a constant speed. Scan.
[0055]
Each of the laser drivers 32a to 32d incorporates an auto power control (APC) circuit, and always emits the laser oscillators 31a to 31d at a light emission power level set by a main control unit (CPU) 51 described later. It is supposed to work.
[0056]
In this way, the light beams output from the separate laser oscillators 31a, 31b, 31c, and 31d are combined by the half mirrors 34a, 34b, and 34c, and the four light beams travel in the direction of the polygon mirror 35. Become.
[0057]
Therefore, the four light beams can simultaneously scan the photosensitive drum 15, and when the rotation speed of the polygon mirror 35 is the same as that of the conventional single beam, an image is recorded at a speed four times higher. It becomes possible to do.
[0058]
The galvanometer mirrors 33a, 33b, 33c, and 33d are for adjusting (controlling) the positional relationship between the light beams in the sub-scanning direction. The galvanometer mirror drive circuits 39a, 39b, 39c, and 39d that drive the galvanometer mirrors 33a, 33b, 33c, and 33d It is connected.
[0059]
The beam light detection device 38 is for detecting the passage position, passage timing and power of the four light beams, and the photosensitive drum 15 has a light receiving surface equal to the surface of the photosensitive drum 15. It is arrange | positioned in the edge part vicinity. Based on the detection signal from the light beam detector 38, control of the galvanometer mirrors 33a, 33b, 33c, 33d corresponding to each light beam (image forming position control in the sub-scanning direction), laser oscillators 31a, 31b, 31c. , 31d and the light emission timing (image forming position control in the main scanning direction) are controlled (details will be described later). In order to generate a signal for performing these controls, the light beam detector 38 is connected to a light beam detector output processing circuit 40.
[0060]
Next, the light beam detector 38 will be described.
[0061]
FIG. 3 schematically shows the relationship between the configuration of the beam light detector 38 and the scanning direction of the beam light. The beam lights a to d from the four semiconductor laser oscillators 31a, 31b, 31c, and 31d are scanned from the left to the right by the rotation of the polygon mirror 35, and cross the beam light detector 38.
[0062]
The beam light detector 38 includes two vertically long sensor patterns S1 and S2 serving as a first light detector, and second and third lights disposed so as to be sandwiched between the two sensor patterns S1 and S2. Seven sensors patterns SA, SB, SC, SD, SE, SF, SG as detectors, and one sensor as a fourth light detector provided at a site adjacent to sensor pattern S1 (right adjacent to the drawing) The pattern SH and the sensor substrate S1, S2, SA, SB, SC, SD, SE, SF, SG, and SH are configured by a holding substrate 38a as a holding unit that holds the patterns integrally. In addition, sensor pattern S1, S2, SA-SG, SH is comprised by the photodiode, for example.
[0063]
Here, the sensor pattern S1 detects the passage of the beam light and generates a reset signal (integration operation start signal) of an integrator described later, and the sensor pattern S2 similarly detects the passage of the beam light, This is a pattern for generating a conversion start signal of an A / D converter to be described later. The sensor patterns SA to SG are patterns for detecting the passage position of the beam light. The sensor pattern SH is a pattern for detecting the power of the beam light.
[0064]
As shown in FIG. 3, the sensor patterns S <b> 1 and S <b> 2 are arranged with respect to the scanning direction of the light beam so that the light beams a to d scanned by the polygon mirror 35 always cross regardless of the positions of the galvanometer mirrors 33 a to 33 d. It is long in the perpendicular direction. For example, in this example, the widths W1 and W3 in the scanning direction of the light beam are 200 μm, while the length L1 in the direction perpendicular to the scanning direction of the light beam is 2000 μm.
[0065]
As shown in FIG. 3, the sensor patterns SA to SG are arranged so as to be stacked between the sensor patterns S1 and S2 in a direction perpendicular to the scanning direction of the beam light. It is the same as the length L1 of S1 and S2. The width W2 in the scanning direction of the beam light of the sensor patterns SA to SG is, for example, 600 μm.
[0066]
As is apparent from the figure, the sensor pattern SH has a sufficiently large size in the sub-scanning direction (the size in the direction perpendicular to the scanning direction of the light beam) as well as the length L1 of the sensor patterns S1 and S2. When the light beam passes through the light beam detector 38, the light beam always passes through the sensor pattern SH.
[0067]
FIG. 4 is an enlarged view of the pattern shapes of the sensor patterns SA to SG of the beam light detector 38.
[0068]
The pattern shape of the sensor patterns SB to SF is, for example, a rectangle of 32.3 μm × 600 μm, and a minute gap G of about 10 μm is formed in a direction perpendicular to the beam light scanning direction. Therefore, the arrangement pitch between the gaps is 42.3 μm. Further, the sensor patterns SA and SB and the gaps between the sensor patterns SF and SG are also arranged to be about 10 μm. Note that the width of the sensor patterns SA and SG in the direction perpendicular to the scanning direction of the beam light is larger than the width of the sensor patterns SB to SF.
[0069]
The details of the control using the output of the light beam detector 38 configured as described above will be described later. A gap formed at a pitch of 42.3 μm determines the passage position of the light beams a, b, c, and d. This is a target for controlling the pitch (42.3 μm in this example). That is, the beam light a has a gap G (BC) formed by the sensor patterns SB and SC, the beam light b has a gap G (CD) formed by the sensor patterns SC and SD, and the beam light c has The gap G (DE) formed by the sensor patterns SD and SE, and the gap G (EF) formed by the sensor patterns SE and SF for the beam light d are targets of the passing positions.
[0070]
Next, the features of the beam light detection device 38 having such a sensor pattern will be described with reference to FIG.
[0071]
As described above, the present beam light detection device 38 is arranged near the end of the photosensitive drum 15 or from the polygon mirror 35 so that the light receiving surface thereof is at the same position as the photosensitive drum 15. It is arrange | positioned in the position which can obtain the optical path length equivalent to the distance to. In order to accurately capture the passage position of the light beam with the light beam detection device 38 arranged in this way, the sensor pattern described above is arranged in a direction perpendicular to the light beam passage direction. Ideal. However, in practice, there is a slight inclination in the mounting of the beam light detector 38.
[0072]
In contrast to such an attachment position being inclined with respect to an ideal position, in the light beam detection device 38 of this example, the point for detecting the passing position for each light beam is the position of the sensor pattern. By arranging it so as not to deviate with respect to the light passing direction, even if the beam light detector 38 is mounted with a slight inclination, the detection pitch can be minimized.
[0073]
Further, as will be described in detail later, an integrator is provided in the output processing circuit for processing the output of the light beam detector 38, so that the light beam can be transmitted regardless of the inclination of the light beam detector 38. The influence on the position detection result can be minimized.
[0074]
FIG. 5A shows the relationship between the sensor patterns SA to SG and the scanning positions of the light beams a to d when the light beam detection device 38 of the present example is mounted inclined with respect to the scanning direction of the light beam. Is. However, in the figure, the scanning direction of the light beams a to d is expressed as being inclined with respect to the light beam detector 38. The scanning lines of the beam lights a to d in the figure are those when controlled at an ideal interval (42.3 μm pitch).
[0075]
Further, between the sensor patterns SA to SG, control target points (white circles) in the present sensor pattern are shown. As will be described later in detail, this point is in the middle (intermediate) between patterns even when the beam lights a to d are incident obliquely due to the effect of the integrator.
[0076]
As is apparent from the figure, the trajectory of the scanning line controlled at an ideal interval (42.3 μm pitch) passes through the approximate center of the control target on the sensor patterns SA to SG. That is, even if the light beam detection device 38 of this example is mounted with a slight inclination, the influence on the detection accuracy is extremely small.
[0077]
For example, when the light beam detection device 38 is mounted with an inclination of 5 degrees with respect to the scanning line of the light beam, the scanning position pitch of each light beam to be controlled with a 42.3 μm pitch as a target is originally inclined. Due to the detection error of the light beam detector 38 caused by the above, the pitch is controlled to a target of 42.14 μm. The error at this time is about 0.16 μm (0.03%), and if controlled in this way, the influence on the image quality is very small. This value can be easily obtained using a trigonometric function, but will not be described in detail here.
[0078]
As described above, by using the sensor patterns SA to SG of the light beam detection device 38 of this example, it is possible to accurately detect the scanning position of the light beam even if the mounting accuracy with respect to the inclination of the light beam detection device 38 is somewhat poor. It becomes.
[0079]
On the other hand, the light beam detection device 80 shown in FIG. 5B is an example of a sensor pattern for realizing the same function as the light beam detection device 38 of the present invention that has been conventionally used.
[0080]
When such a sensor pattern is adopted, the light beam passage position cannot be accurately detected if the sensor pattern is attached with a slight inclination with respect to the scanning direction of the light beams a to d. The cause is that a sensor pattern (in this example, S3 *, S4 *, S5 *, S6 *: * indicates a and b) that detects the passing positions of the light beams a to d in the scanning direction of the light beams. It is located at a distance from it. In other words, the longer the distance is in the scanning direction of the light beam, the larger the detection error is even for a slight inclination.
[0081]
In FIG. 5 (b), similarly to FIG. 5 (a), it is assumed that the light beam detector 80 is mounted at an inclination, and the scanning line controlled to an ideal interval (42.3 μm pitch) is used. The trajectory is shown. As is apparent from FIG. 5B, it can be seen that the conventional light beam detection device 80 requires much higher mounting accuracy than the light beam detection device 38 of this example shown in FIG.
[0082]
For example, similar to the beam light detection device 38 in FIG. 5A, the beam light detection device 80 in FIG. 5B is attached with an inclination of 5 degrees, and the distance between the sensor patterns S3a, S3b and S6a, S6b. Is 900 μm, the control target of the beam light d is shifted by 78.34 μm from the ideal position. This value is an error far exceeding the target control pitch of 42.3 μm in this example, and gives a serious defect to the image quality. Therefore, when such a beam light detector 80 is used, a very high mounting accuracy is required at least with respect to the inclination of the beam light with respect to the scanning direction.
[0083]
Conventionally, in order to make up for such a problem, the sensor pattern width W in the scanning direction of the beam light is reduced as much as possible without sacrificing some sensitivity, and the passage position of the beam light with respect to the scanning direction of the beam light. It is necessary to consider that detection points are not separated. In addition, in order to compensate for the lack of sensitivity, it is essential to increase the power of the laser oscillator and decrease the rotation speed of the polygon motor when detecting the passage position of the beam light.
[0084]
Next, the control system will be described.
[0085]
FIG. 6 shows a control system mainly for controlling the multi-beam optical system. That is, 51 is a main control unit that controls the entire control, and is composed of, for example, a CPU, which includes a memory 52, a control panel 53, an external communication interface (I / F) 54, and laser drivers 32a, 32b, and 32c. , 32d, polygon mirror motor driver 37, galvanometer mirror drive circuits 39a, 39b, 39c, 39d, beam light detector output processing circuit 40 as signal processing means, synchronization circuit 55, and image data interface (I / F) 56 is connected.
[0086]
An image data I / F 56 is connected to the synchronization circuit 55, and an image processing unit 57 and a page memory 58 are connected to the image data I / F 56. The scanner unit 1 is connected to the image processing unit 57, and an external interface (I / F) 59 is connected to the page memory 58.
[0087]
Here, the flow of image data when forming an image will be briefly described as follows.
[0088]
First, in the case of the copying operation, as described above, the image of the document O set on the document table 7 is read by the scanner unit 1 and sent to the image processing unit 57. The image processing unit 57 performs, for example, known shading correction, various filtering processes, gradation processing, gamma correction and the like on the image signal from the scanner unit 1.
[0089]
Image data from the image processing unit 57 is sent to the image data I / F 56. The image data I / F 56 plays a role of distributing the image data to the four laser drivers 32a, 32b, 32c, and 32d.
[0090]
The synchronization circuit 55 generates a clock synchronized with the timing of each light beam passing through the light beam detector 38, and in synchronization with this clock, the laser driver 32a, 32b, 32c, 32d from the image data I / F 56. The image data is transmitted as a laser modulation signal.
[0091]
In this way, image data is transferred while being synchronized with the scanning of each light beam, so that image formation synchronized with the main scanning direction (to the correct position) is performed.
[0092]
Further, the synchronization circuit 55 forcibly causes each laser oscillator 31a, 31b, 31c, 31d to emit light in the non-image region and controls the power of each beam light, and image formation of each beam light. In order to take timing, a logic circuit for causing each laser oscillator 31a, 31b, 31c, 31d to emit light on the light beam detector 38 in the order of the light beams is included.
[0093]
Here, the influence on the image forming accuracy in the main scanning direction when the power of the light beam varies will be described.
[0094]
In this example, the light emission timing of each laser oscillator is controlled based on the timing at which each light beam passes through the sensor pattern S1 or S2. That is, in FIG. 6, the output of the sensor pattern S1 or S2 of the light beam detection device 38 is shaped by the light beam detection device output processing circuit 40 and input to the synchronization circuit 55 as a synchronization signal in the main scanning direction. Based on this synchronization signal, the image data is sent from the image data I / F 56 to each laser driver 32a to 32d in accordance with the passage timing of each light beam, and a correct image is formed.
[0095]
Now, with reference to FIG. 7, a description will be given of the synchronization accuracy when the power is different between the light beams in the multi-beam optical system. FIG. 7 is a diagram for explaining that the image forming accuracy in the main scanning direction depends on the power of the light beam.
[0096]
FIG. 7 shows the sensor pattern output when the power of the light beam is different in three stages (A, B, C), and the synchronization signal generated by waveform shaping based on the output. The sensor pattern output (analog signal) A shows a case where the power of the light beam is small, and has the smallest mountain shape among the three. When this sensor pattern output A is binarized (waveform shaping) at the threshold level TH shown in the figure, it becomes a small pulse signal (synchronization signal of A).
[0097]
On the other hand, the sensor pattern output C shows a case where the power of the beam light is large, and has the largest mountain shape among the three. Similarly, when the sensor pattern output C is binarized at the threshold level TH shown in the figure, the largest pulse signal (synchronization signal of C) is obtained.
[0098]
The sensor pattern output B and its synchronization signal indicate the case of the power of the light beam between the sensor pattern outputs A and C.
[0099]
When the laser emission timing for image formation is controlled on the basis of the edges (rising or falling) of three kinds of synchronizing signals A, B, and C, for example, as shown in FIG. The image is shifted in the main scanning direction between lines having different light powers. This is because, as shown in FIG. 7, the edge of the synchronization signal does not match the phase of the center.
[0100]
As described above, in order to form an image with no misalignment in the main scanning direction using the multi-beam optical system, each light beam is placed on the sensor pattern (photosensitive drum) for generating a synchronization signal. It is necessary to scan with the same power.
[0101]
Returning to the description of FIG. 6, the control panel 53 is a man-machine interface for starting a copying operation, setting the number of sheets, and the like.
[0102]
This digital copying machine is configured not only to perform a copying operation but also to form and output image data input from the outside via an external I / F 59 connected to the page memory 58. The image data input from the external I / F 59 is once stored in the page memory 58 and then sent to the synchronization circuit 55 via the image data I / F 56.
[0103]
Further, when the digital copying machine is controlled from the outside via a network or the like, for example, the external communication I / F 54 serves as the control panel 53.
[0104]
The galvanometer mirror drive circuits 39a, 39b, 39c, and 39d are circuits that drive the galvanometer mirrors 33a, 33b, 33c, and 33d in accordance with the instruction value from the main control unit 51. Therefore, the main controller 51 can freely control the angles of the galvanometer mirrors 33a, 33b, 33c, and 33d via the galvanometer mirror drive circuits 39a, 39b, 39c, and 39d.
[0105]
The polygon motor driver 37 is a driver that drives the polygon motor 36 for rotating the polygon mirror 35 that scans the four light beams described above. The main control unit 51 can start and stop the rotation of the polygon motor driver 37 and change the number of rotations. The switching of the rotational speed is used when the rotational speed is decreased below a predetermined rotational speed as necessary when the beam light detecting device 38 confirms the passage position of the light beam.
[0106]
The laser drivers 32a, 32b, 32c, and 32d emit a laser beam in accordance with a laser modulation signal synchronized with the scanning of the beam light from the synchronization circuit 55 described above, and a forced emission signal from the main control unit 51. The laser oscillators 31a, 31b, 31c, and 31d are forced to emit light regardless of the image data.
[0107]
Further, the main control unit 51 sets the power at which each laser oscillator 31a, 31b, 31c, 31d emits light for each laser driver 32a, 32b, 32c, 32d. The setting of the light emission power is changed in accordance with a change in process conditions, detection of a light beam passage position, and the like.
[0108]
The memory 52 is for storing information necessary for control. For example, by storing the control amount of each galvanometer mirror 33a, 33b, 33c, 33d, circuit characteristics (amplifier offset value) for detecting the passage position of the beam light, the order of arrival of the beam light, etc. The optical system unit 13 can be brought into a state in which image formation is possible immediately after the power is turned on.
[0109]
Next, beam light passage (scanning) position control will be described in detail.
[0110]
FIG. 8 is a diagram for explaining beam light passage position control when the beam light detector 38 of FIG. 3 is used. Focusing on the beam light control in the block diagram of FIG. The relevant parts are extracted and shown in detail.
[0111]
As described above, a pulse signal indicating that the light beam has passed is output from the sensor patterns S1 and S2 of the light beam detector 38. Further, independent signals are output from the plurality of sensor patterns SA to SG, SH according to the passage position of the beam light.
[0112]
Among the plurality of sensor patterns SA to SG, SH, output signals of the sensor patterns SA, SG, SH are respectively input to amplifiers 61, 62, 99 (hereinafter also referred to as amplifiers A, G, H). Is done. Note that the amplification factors of the amplifiers 61, 62, and 99 are set by a main control unit 51 including a CPU.
[0113]
In addition, among the plurality of sensor patterns SA to SG, the output signals of the sensor patterns SB to SF are differential amplifiers 63 to 66 (hereinafter referred to as differential) that amplify the difference between adjacent output signals of the sensor patterns SB to SF. Amplifiers BC, CD, DE, and EF). The differential amplifier 63 amplifies the difference between the output signals of the sensor patterns SB and SC, the differential amplifier 64 amplifies the difference between the output signals of the sensor patterns SC and SD, and the differential amplifier 65 The difference between the output signals of the sensor patterns SD and SE is amplified, and the differential amplifier 66 amplifies the difference between the output signals of the sensor patterns SE and SF.
[0114]
The output signals of the amplifiers 61 to 66, 99 are input to the selection circuit (analog switch) 41, respectively. The selection circuit 41 selects a signal to be input to the integrator 42 based on a sensor selection signal from the main control unit (CPU) 51. The output signal of the amplifier selected by the selection circuit 41 is input to the integrator 42 and integrated.
[0115]
On the other hand, a pulsed signal output from the sensor pattern S1 is also input to the integrator 42. The pulse signal from the sensor pattern S1 is used as a reset signal (integration operation start signal) for resetting the integrator 42 and starting a new integration operation at the same time. The role of the integrator 42 is to remove noise and remove the influence of the mounting inclination of the beam light detector 38, which will be described in detail later.
[0116]
The output of the integrator 42 is input to the A / D converter 43. A pulse signal output from the sensor pattern S 2 is also input to the A / D converter 43. The A / D conversion operation of the A / D converter 43 is started by applying a signal from the sensor pattern S2 as a conversion start signal. That is, A / D conversion is started at the timing when the light beam passes through the sensor pattern S2.
[0117]
In this way, the pulse signal from the sensor pattern S1 resets the integrator 42 immediately before the beam light passes through the sensor patterns SA to SG, and simultaneously starts the integration operation, so that the beam light passes over the sensor patterns SA to SG. During this time, the integrator 42 integrates a signal indicating the passage position of the beam light.
[0118]
Immediately after the beam light has passed through the sensor patterns SA to SG, the A / D converter 43 performs A / D conversion on the result of integration by the integrator 42 using the pulse signal from the sensor pattern S2 as a trigger. As a result, for the detection of the light beam passage position, the detection signal from which the influence of the inclination of the light beam detection device 38 is removed can be converted into a digital signal.
[0119]
Further, the laser oscillator of the light beam whose power is to be measured is forced to emit light, the light beam detector 38 is scanned at a predetermined speed by the polygon mirror 35, and the electric signal output from the sensor pattern SH is supplied to the amplifier 99 ( H) is amplified and integrated by the integrator 42 based on the timing of the pulse signals output from the sensor patterns S1 and S2, A / D converted by the A / D converter 43, and taken into the main controller 51. As a result, the power of the beam light on the photosensitive drum 15 can be detected.
[0120]
The A / D converter 43 that has completed the A / D conversion outputs an interrupt signal INT indicating that the processing has been completed to the main control unit 51.
[0121]
Here, the amplifiers 61 to 66, 99, the selection circuit 41, the integrator 42, and the A / D converter 43 constitute a beam light detector output processing circuit 40.
[0122]
In this way, the light beam power detection signal and the light beam position detection signal from the light beam detection device 38 converted into a digital signal are used as relative light beam power information or beam light position information on the photosensitive drum 15. To the main control unit 51, and the light power of each light beam on the photosensitive drum 15 and the passage position of the light beam are determined.
[0123]
Based on the relative light beam power detection signal and the light beam position detection signal obtained on the photosensitive drum 15 thus obtained, the main control unit 51 determines the light emission power for each of the laser oscillators 31a to 31d. Settings and control amounts of the galvanometer mirrors 33a to 33d are calculated. The calculation results are stored in the memory 52 as necessary. The main control unit 51 sends out the calculation results to the laser drivers 32a to 32d and the galvanometer mirror drive circuits 39a to 39d.
[0124]
As shown in FIG. 8, the galvanometer mirror drive circuits 39a to 39d are provided with latches 44a to 44d for holding data of the calculation results. Once the main control unit 51 writes the data, This value is held until the next data update.
[0125]
The data held in the latches 44a to 44d are converted into analog signals (voltages) by the D / A converters 45a to 45d and input to the drivers 46a to 46d for driving the galvanometer mirrors 33a to 33d. The drivers 46a to 46d drive and control the galvanometer mirrors 33a to 33d according to the analog signals (voltages) input from the D / A converters 45a to 45d.
[0126]
In this example, since the amplified output signals of the sensor patterns SA to SG are selected and integrated by the selection circuit 41 and integrated and A / D converted, the sensor patterns SA to SG at a time are selected. Cannot be input to the main control unit 51.
[0127]
Therefore, in a state where it is unknown where the light beam is passing, the selection circuit 41 is sequentially switched, and output signals from all the sensor patterns SA to SG are input to the main control unit 51, and the light beam is transmitted. It is necessary to determine the passing position.
[0128]
However, once it can be recognized where the light beam passes, unless the galvano mirrors 33a to 33d are moved extremely, the position where the light beam passes can be almost predicted, and the output signals of all sensor patterns are always obtained. Is not required to be input to the main control unit 51. Detailed processing will be described later.
[0129]
FIG. 9 shows a detailed configuration example up to the integrator 42 for the sensor patterns SB and SC in the beam light detector output processing circuit 40. In FIG. 9, currents flowing through the sensor patterns (photodiodes) SB and SC are converted into currents and voltages by resistors PR1, RL1, RP2 and RL2, respectively, and then amplified by operational amplifiers A1 and A2 as voltage follower circuits, respectively. It is sent to the differential amplifier 63. The differential amplifier 63 includes resistors R1 to R4 and an operational amplifier A3.
[0130]
The output of the differential amplifier 63 is sent to the integrator 42 via the analog switch SW1 constituting the selection circuit 41. The integrator 42 includes an operational amplifier A4, an integration resistor R5, an integration capacitor C, an integrator reset analog switch SW7, and a protection resistor R6. The output of the integrator 42 is sent to the A / D converter 43 and converted from an analog value to a digital value. When the A / D conversion is completed, the A / D converter 43 transmits a conversion end signal to the main control unit 51. When receiving the conversion end signal, the main control unit 51 reads the light beam position information converted into a digital value.
[0131]
Note that the configuration example up to the integrator 42 for the sensor patterns SD, SE, SF is basically the same as the configuration example up to the integrator 42 for the sensor patterns SB, SC, and thus the description thereof is omitted. To do.
[0132]
Hereinafter, the relationship between the light beam passage position and the output of the light beam detector 38, the outputs of the differential amplifiers 63 to 66, and the output of the integrator 42 in the circuit operation of FIG. 8 will be described with reference to FIG.
[0133]
FIG. 10A shows a case where the light beam passes through the middle of the sensor patterns SB and SC, and FIG. 10B shows the sensor light beam as compared to the case of FIG. 10A. The case where the pattern SB side is passed is shown. FIG. 10C shows a case where the light beam detection device 38 is attached to be inclined with respect to the light beam passing direction.
[0134]
Hereinafter, the output of the beam light detector 38, the output of the differential amplifier 63, and the output of the integrator 42 in each case will be described.
[0135]
Circuit operation in the case of FIG.
First, the light beam crosses the sensor pattern S1, and a pulse signal is output from the sensor pattern S1. This pulse-like signal resets the integrator 42 and makes its output “0” as shown in the figure. Therefore, when the light beam crosses the sensor pattern S1, the previous detection result is reset and the new detection result is integrated.
[0136]
When the beam light passes through the middle between the sensor patterns SB and SC, the output magnitudes of the sensor patterns SB and SC are equal as shown in FIG. However, since the output of the sensor pattern is very small, some noise components may be superimposed as shown in FIG.
[0137]
Such a signal is input to the differential amplifier 63, and the difference is amplified. The outputs of the sensor patterns SB and SC are substantially equal. In this case, the output of the differential amplifier 63 is substantially “0” as shown in FIG. 10A, but some noise components may be superimposed. . The differential amplification result thus obtained is input to the integrator 42 through the selection circuit 41.
[0138]
Here, it is the offset of the differential amplifier 63 that requires attention. Here, the offset is a phenomenon in which the output is shifted to either plus or minus even when an equal value is input to the differential amplifier 63, for example. Such a phenomenon is present in any differential amplifier more or less. In the case of this example, this offset appears as a beam light passing position detection error, which hinders correct beam light passing position control. Therefore, it is necessary to remove this offset by some method. Hereinafter, this offset will be ignored and described.
[0139]
The integrator 42 integrates the output of the differential amplifier 63 and outputs the result to the next A / D converter 43. The output of the integrator 42 is a noise as shown in FIG. The signal is the component removed. This is because the high frequency component noise superimposed on the differential amplification result is removed by integration. In this way, simultaneously with the passage of the beam light, the output difference between the sensor patterns SB and SC is amplified, further integrated, and input to the A / D converter 43.
[0140]
On the other hand, the output of the sensor pattern S2 is input to the A / D converter 43, and at the timing when the light beam has passed through the sensor patterns SB and SC, a pulse shape as shown in FIG. Is output from the sensor pattern S2 to the A / D converter 43. The A / D converter 43 starts A / D conversion of the output of the integrator 42 with this pulse signal as a trigger. Therefore, the A / D converter 43 can convert analog beam passage position information with a good S / N ratio from which noise components are removed into a digital signal in a timely manner.
[0141]
Circuit operation in the case of FIG.
The basic operation is the same as that of FIG. 10A, but the output of the sensor pattern SB is increased and the output of the sensor pattern SC is decreased by the amount that the light beam passing position is shifted to the sensor pattern SB side. Therefore, the output of the differential amplifier 63 becomes positive by the difference.
[0142]
As in the case of FIG. 10A, the integrator 42 is reset at the timing when the light beam passes through the sensor pattern S1, and then such differential amplification result is input to the integrator 42. Is done. The integrator 42 gradually increases its output to the plus side while the input (output of the differential amplifier 63) is on the plus side. When the input returns to “0”, the value is maintained. Therefore, the output of the integrator 42 shows the degree of deviation of the light beam passage position.
[0143]
As in the case of FIG. 10A, this integration result is A / D converted by the A / D converter 43 at the timing when the sensor pattern S2 of the light beam passes, so that the accurate beam passing position is time-resolved. Is converted into digital information.
[0144]
Circuit operation in the case of FIG.
The basic operation is the same as in FIGS. 10A and 10B. However, the output of the sensor patterns SB and SC and the differential amplifier are equivalent to the amount that the light beam passes through the light beam detector 38 obliquely. The output of 63 and the output of the integrator 42 are characteristic.
[0145]
As shown in FIG. 10 (c), after the light beam has passed through the sensor pattern S1, the sensor patterns SB and SC are incident obliquely from the sensor pattern SC side, and pass through almost the center between the sensor patterns SB and SC. After that, the sensor pattern SB side is obliquely passed. When the light beam passes in this way, the output of the sensor pattern SB is small immediately after the light beam is incident and becomes larger as the light beam passes as shown in FIG. On the other hand, the output of the sensor pattern SC is large immediately after the light beam is incident, and gradually decreases as the light beam passes.
[0146]
The output of the differential amplifier 63 to which the outputs of the sensor patterns SB and SC are input is large on the minus side immediately after the incidence of the beam light as shown in FIG. Thus, when the light beam passes between the sensor patterns SB and SC, it becomes almost “0”. After that, it gradually increases to the plus side, and reaches the maximum value on the plus side immediately before the beam light finishes passing.
[0147]
The output of the integrator 42 to which the output of the differential amplifier 63 is input increases toward the minus side immediately after the incident light beam. The negative value increases until the output of the differential amplifier 63 becomes almost “0”. Thereafter, when the output of the differential amplifier 63 turns to the plus side, the minus value gradually decreases, and becomes almost “0” at the point where the beam light finishes passing.
[0148]
This is because although the light beam crosses the light beam detector 38 obliquely, on the average, it passes through the middle of the sensor patterns SB and SC. Therefore, the A / D conversion operation of the A / D converter 43 is started when the light beam passes through the sensor pattern S2. In this case, the integrated value is “0”, and the beam passing position is The digital information shown is also processed as “0”, that is, the beam light passes through the middle of the sensor patterns SB and SC.
[0149]
The beam light passing position, the output of the sensor patterns S1, S2, SB, and SC, the output of the differential amplifier 63, the output of the integrator 42, and the operation of the A / D converter 43 have been described above. Since the operations of the sensor patterns SC, SD, SE, SF and the differential amplifiers 64, 65, 66 are basically the same as the operations of the sensor patterns SB, SC and the differential amplifier 63, the description of each operation is omitted. .
[0150]
Next, the relationship between the light beam passage position and the output of the A / D converter 43 will be described with reference to FIG.
[0151]
The vertical axis of the graph of FIG. 11 indicates the magnitude of the output of the A / D converter (12 bits) 43 corresponding to FIG. 8, and the horizontal axis indicates the light beam passage position. The beam light passing position on the horizontal axis indicates that the beam light passes the sensor pattern SG side as it goes to the left, and that the beam light passes the sensor pattern SA side as it goes to the right. .
[0152]
There is a possibility that the output of the differential amplifier (63, 64, 65, 66) is output in both positive and negative directions, and the output of the A / D converter 43 at that time is as follows. That is, when the output of the differential amplifier (63, 64, 65, 66) is on the plus side, the output (A / D conversion value) of the A / D converter 43 is 000H (as the output of the differential amplifier increases). The value of 7FFH (maximum value) is output from the minimum value.
[0153]
On the other hand, when the output of the differential amplifier (63, 64, 65, 66) is negative, the output (A / D conversion value) of the A / D converter 43 is from 800H (minimum value) to FFFH (maximum value). The value of is output. In this case, the one where the absolute value of the output of the differential amplifier is larger corresponds to the 800H (minimum value) side, and the one where the output of the differential amplifier is closer to “0” corresponds to the FFFH (maximum value) side.
[0154]
Here, the case where the outputs of the differential amplifiers 63 of the sensor patterns SB and SC are A / D converted by the A / D converter 43 will be specifically described.
[0155]
The output of the sensor pattern SB is connected to the plus terminal of the differential amplifier 63, and the output of the sensor pattern SC is connected to the minus terminal of the differential amplifier 63. Therefore, as shown in FIG. 11, the output of the differential amplifier 63 becomes the largest when the light beam passes near the center of the sensor pattern SB, and the A / D conversion value in the A / D converter 43 is 7FFH. It becomes. This is because the output of the sensor pattern SB is the largest in this vicinity.
[0156]
Further, even if the light beam is shifted from this position to the sensor pattern SA side or to the sensor pattern SC side, the A / D conversion value (the output of the differential amplifier 63) becomes small.
[0157]
Further, considering the case where the light beam passage position is shifted to the sensor pattern SA side, neither the sensor pattern SB nor SC can detect the passage of the light beam, and the A / D conversion value (the output of the differential amplifier 63) is almost equal. It becomes “0”.
[0158]
On the other hand, when the passage position of the beam light is shifted to the sensor pattern SC side, the A / D conversion value (output of the differential amplifier 63) is gradually decreased, and the beam light is reduced to the sensor patterns SB and SC. The value becomes “0” when passing just between. This is because the outputs of the sensor patterns SB and SC are equal. In this example, this point becomes the passage target point of the beam light a.
[0159]
When the light beam passing point is shifted to the sensor pattern SC side, the output of the differential amplifier 63 becomes a negative output, the A / D conversion value changes from 000H to FFFH, and then the A / D conversion value gradually increases. To decrease. Further, when the light beam passage position is near the center of the sensor pattern SC, the output of the differential amplifier 63 becomes a negative maximum, and the A / D conversion value at this time is 800H.
[0160]
Further, when the light beam passage position is shifted to the sensor pattern SD side, the negative value of the output of the differential amplifier 63 decreases this time, and the A / D conversion value increases from 800H. It changes from FFFH to 000H. This is because the passage position of the beam light is too shifted to the sensor pattern SD (SE) side, and neither of the sensor patterns SB and SC can detect the passage of the beam light, and both outputs become “0”. This is because the difference disappears.
[0161]
Next, control characteristics of the galvanometer mirror 33 will be described.
[0162]
FIGS. 12 and 13 show the relationship between the data given to the galvano mirror drive circuits 39a to 39d and the beam light passage position on the beam light detector 38 (that is, on the photosensitive drum 15). As shown in FIG. 8, the inputs of the D / A converters 45a to 45d of the galvano mirror drive circuits 39a to 39d are 16 bits.
[0163]
FIG. 12 shows how the beam light passing position changes with respect to the input of the upper 8 bits of the 16-bit data. As shown in the figure, the passing position of the beam light moves 2000 μm (2 mm) with respect to the data 00H to FFH. In addition, for the input near 00H and near FFH, the response range of the galvanometer mirror is exceeded, and the passage position of the beam light does not change.
[0164]
However, when the input is in the range of approximately 18H to E8H, the light beam passage position changes substantially linearly with respect to the input, and the ratio corresponds to a distance of approximately 10 μm per LSB.
[0165]
FIG. 13 shows how the beam light passing position changes with respect to the lower 8 bits input of the D / A converters 45a to 45d of the galvanometer mirror drive circuits 39a to 39d. However, FIG. 13 shows the change in the passage position of the light beam with respect to the input of the lower 8 bits when the above-described range value in which the passage position of the light beam changes linearly is inputted as the upper 8 bits. Represents. As is apparent from the figure, for the lower 8 bits, the beam light passage position changes from 00H to FFH, and changes by 0.04 μm per 1LSB.
[0166]
In this way, the main control unit 51 gives 16-bit data to the galvanometer mirror drive circuits 39a to 39d, so that the beam light passing position on the beam light detector 38, that is, on the photosensitive drum 15. Can be moved within a range of about 2000 μm (2 mm) with a resolution of about 0.04 μm.
[0167]
Next, a schematic operation when the printer unit 2 is turned on will be described with reference to a flowchart shown in FIG. The operation of the scanner unit 1 is omitted.
[0168]
When the power of the copying machine is turned on, the main controller 51 rotates the fixing roller in the fixing device 26 and starts heating control of the fixing device 26 (S1, S2). Next, a light beam power control routine is executed to control the power of each light beam on the photosensitive drum 15 to be the same (S3).
[0169]
When the power of the light beams on the photosensitive drum 15 is controlled to be the same, an offset correction routine is executed to detect the offset value of the beam light detector output processing circuit 40 and perform the correction process. (S4). Next, a beam light passing position control routine is executed (S5).
[0170]
Next, synchronous pull-in in the main scanning direction is executed (S6). Next, process-related initialization such as rotating the photosensitive drum 15 to make conditions such as the surface of the photosensitive drum 15 constant is executed (S7).
[0171]
Thus, after executing a series of initializations, the fixing roller continues to rotate until the temperature of the fixing device 26 rises to a predetermined temperature, and enters a standby state (S8). When the temperature of the fixing device 26 rises to a predetermined temperature, the rotation of the fixing roller is stopped (S9), and a copy command waiting state is entered (S10).
[0172]
When a copy command is not received from the control panel 53 while waiting for a copy command (S10), for example, 30 minutes elapses after the beam light passage position control routine is executed (S11), and the beam light is automatically transmitted. A power control routine is executed (S12), and an offset correction routine similar to that in step S4 is automatically executed (S13). Thereafter, a beam light passing position control routine is executed again (S14). When this is finished, the process returns to step S10 and again enters the copy command wait state.
[0173]
When a copy command is received from the control panel 53 while waiting for a copy command (S10), a beam light passing position control routine is executed (S15), and a copy operation is executed (S16). When the copying operation is completed, the process returns to step S10 and the above operation is repeated.
[0174]
Next, a schematic operation of the light beam passage position control routine in steps S5, S14, and S15 of FIG. 14 will be described using the flowchart shown in FIG.
[0175]
First, the main controller 51 turns on the polygon motor 36 and rotates the polygon mirror 35 at a predetermined rotational speed (S20). Next, the main control unit 51 reads the latest drive values of the galvanometer mirrors 33a to 33d from the memory 52, and drives the galvanometer mirrors 33a to 33d based on the values (S21).
[0176]
Next, the main control unit 51 controls the passing position of the beam light a (S22). The control content here is to detect the passing position of the beam light a, check whether the passing position is within the specified value, and if not, change the angle of the galvano mirror 33a. If it is within the specified value, the flag is set to indicate that the passing position of the beam light a is within the specified value.
[0177]
Subsequently, the main control unit 51 also detects the passing positions of the light beams b, c, and d for the light beams b, c, and d as in the case of the light beam a. It is checked whether the position is within the specified value. If the position is not within the specified value, the angle of each of the galvanometer mirrors 33b to 33d is changed. A flag indicating that the passing position is within the specified value is set (S23, S24, S25).
[0178]
In this way, after performing the passing position control of each of the light beams a, b, c, d, the main control unit 51 checks each flag and determines whether or not to end the light beam passing position control. Determine (S26). That is, if all the flags are set, the light beam passing position control is terminated, and if any one of the flags is not set, the process returns to step S22 to control the passing position of each light beam.
[0179]
Here, the behavior of the galvanometer mirrors 33a to 33d in such a control flow will be briefly described.
[0180]
As described above, the galvanometer mirrors 33a to 33d change the angle according to the control value from the main control unit 51 and change the passing position of the scanned light beam. It is not always possible to respond immediately to an instruction. That is, control data is output from the main control unit 51, the data is latched by the latches 44a to 44d, D / A converted by the D / A converters 45a to 45d, and a drive signal proportional to the magnitude thereof. Is output on the order of “ns” or “μs”, whereas, for example, the response time of the galvanometer mirrors 33a to 33d used in this example is 4 to There is a problem that the order is 5 ms.
[0181]
The response time here refers to the time when the angle change of the galvano mirrors 33a to 33d starts with respect to a new drive signal, moves (vibrates) for a certain period of time, and then the movement (vibration) stops and settles to a new angle. Of time. Therefore, the main control unit 51 sends the new control data to the galvanometer mirrors 33a to 33d and then checks the control result. It is necessary to confirm.
[0182]
As is clear from FIG. 15, in this example, the effect of controlling a certain galvanometer mirror is confirmed after performing another beam position detection operation or galvanometer mirror operation. The effect is confirmed after the time required for the response of the galvanometer mirror has elapsed.
[0183]
For example, in steps S21, S22, S23, and S24, the time required to acquire the output of at least one amplifier or differential amplifier by the number of faces of the polygon mirror 35 (for example, eight faces) is required for one scan. When the time is 330 μs, it becomes 2.64 ms.
[0184]
Therefore, after controlling a certain galvanometer mirror, after detecting the passing position of the other three light beams, to confirm the effect, there is a time interval of at least 7.92 ms, and the movement (vibration) of the galvanometer mirror is Thus, it is possible to confirm the beam light passing position in a state where it has already been accommodated.
[0185]
The reason why the output of the amplifier or differential amplifier is obtained by the number of faces of the polygon mirror 35 is to remove the surface tilt component of the polygon mirror 35.
[0186]
FIGS. 16 and 17 are flowcharts for explaining in detail the operation of the beam light a passing position control in step S22 of FIG. As described above, the relationship between the passage position of the light beam and the output of the A / D converter 43 is as shown in FIG. 11, and will be described with reference to FIG.
[0187]
First, the main control unit 51 causes the laser oscillator 31a to emit light forcibly (S31). As a result, the beam light a periodically scans the beam light detector 38 as the polygon mirror 35 rotates.
[0188]
Next, in accordance with the interrupt signal INT output from the A / D converter 43, the main control unit 51 reads values obtained by A / D converting the outputs of the amplifiers and the differential amplifier. Normally, the scanning position of the beam light is often slightly different for each surface due to the surface tilt component of the polygon mirror 35, and in order to remove the influence, the number of times equal to the number of surfaces of the polygon mirror 35, or It is desirable to read a value that has been A / D converted continuously in an integral number of times. In that case, the main control unit 51 averages the output values of the A / D converters 43 corresponding to the respective amplifiers and differential amplifiers, and uses the result as the outputs of the respective amplifiers and differential amplifiers (S32).
[0189]
Therefore, for the amplifiers 61 and 62 (amplifiers A and G) and the differential amplifiers 63 to 66 (amplifiers BC, CD, DE, and EF), the number of faces of the polygon mirror 35 (eight), respectively. If the value of the A / D converter 43 is read the same number of times, it is necessary to scan the light beam 48 times.
[0190]
First, the main control unit 51 compares the output (A / D conversion value) of the amplifier 61 (A) obtained in this way with the determination reference value 100H stored in advance in the memory 52 to thereby obtain the amplifier 61. Is determined to be greater than the determination reference value 100H (S33).
[0191]
If the result of this determination is that the output of the amplifier 61 is greater than 100H, it indicates that the passing position of the beam light a is on the sensor pattern SA or in the vicinity of the sensor pattern SA. Yes. That is, the light beam a passes through the area A in FIG. Since the target passage position of the beam light a is between the sensor patterns SB and SC, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SG side (S34).
[0192]
At this time, the control amount (the amount of movement of the light beam) is about 120 μm. The reason why the control amount is 120 μm is that the sensor patterns SA and SG have large patterns on both sides from the area of the control target point, as described in the sensor pattern of FIGS. This is because it is necessary to change the passage position of the beam light relatively large in order to quickly bring the passage position of the beam light closer to the target point.
[0193]
However, even when the output of the amplifier 61 is greater than 100H, if the beam light a passes through a range close to the sensor pattern SB, the beam light passing position may be excessively changed. There is also. However, considering the total efficiency, this amount of movement is necessary.
[0194]
If it is determined in step S33 that the output of the amplifier 61 is not greater than 100H, the output (A / D conversion value) of the amplifier 62 (G) is set to the determination reference value 100H stored in the memory 52 in advance. By comparing, it is determined whether the output of the amplifier 62 is larger than the determination reference value 100H (S35).
[0195]
As a result of this determination, if the output of the amplifier 62 is greater than 100H, it indicates that the passing position of the beam light a is on the sensor pattern SG or in the vicinity of the sensor pattern SG. Yes. That is, the light beam a passes through the area G in FIG.
[0196]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S36). ). Note that the control amount at this time requires a control amount (movement amount) of about 120 μm, as in step S34.
[0197]
If it is determined in step S35 that the output of the amplifier 62 is not greater than 100H, the output (A / D conversion value) of the differential amplifier 66 (EF) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 66 is equal to or higher than the determination reference value 800H (S37).
[0198]
As a result of this determination, when the output of the differential amplifier 66 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SF. That is, the light beam a passes through the area F in FIG.
[0199]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S38). ). The control amount at this time needs a control amount (movement amount) of about 120 μm in consideration of the distance between the target point and the area F.
[0200]
If it is determined in step S37 that the output of the differential amplifier 66 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 65 (DE) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 65 is equal to or higher than the determination reference value 800H (S39).
[0201]
As a result of this determination, if the output of the differential amplifier 65 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SE. That is, the light beam a passes through the area E in FIG.
[0202]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S40). ). Note that the control amount at this time needs a control amount (movement amount) of about 80 μm in consideration of the distance between the target point and the area E.
[0203]
If it is determined in step S39 that the output of the differential amplifier 65 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 64 (CD) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 64 is equal to or higher than the determination reference value 800H (S41).
[0204]
As a result of this determination, when the output of the differential amplifier 64 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SD. That is, the light beam a passes through the area D in FIG.
[0205]
Accordingly, in such a case, the galvano mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle of the sensor patterns SB and SC, which are target points for the beam light a (S42). . The control amount at this time needs a control amount (movement amount) of about 40 μm in consideration of the distance between the target point and the area D.
[0206]
If it is determined in step S41 that the output of the differential amplifier 64 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 63 (BC) is stored in the memory 52 in advance. By comparing with the reference values 400H and 7FFH, it is determined whether the output of the differential amplifier 63 is greater than the determination reference value 400H and less than or equal to 7FFH (S43).
[0207]
As a result of this determination, if the output of the differential amplifier 63 is greater than 400H and less than or equal to 7FFH, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are passage target points. Although it is present, it indicates that it is slightly closer to the sensor pattern SB. That is, the light beam a passes through the area BA of the area B in FIG.
[0208]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SG side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S44). ). The control amount at this time needs a control amount (movement amount) of about 10 μm in consideration of the distance between the target point and the area D.
[0209]
If it is determined in step S43 that the output of the differential amplifier 63 is greater than 400H and not less than 7FFH, the output of the differential amplifier 63 is stored as determination reference values 60H and 400H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is greater than the determination reference value 60H and equal to or less than 400H (S45).
[0210]
If the result of this determination is that the output of the differential amplifier 63 is greater than 60H and less than or equal to 400H, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC which are passage target points. Although it is present, it indicates that it is slightly closer to the sensor pattern SB. That is, the light beam a passes through the area BC of the area B in FIG.
[0211]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SG side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S46). ). The control amount at this time needs a control amount (movement amount) of about 0.5 μm in consideration of the distance between the target point and the area D.
[0212]
If it is determined in step S45 that the output of the differential amplifier 63 is greater than 60H and not less than 400H, the output of the differential amplifier 63 is determined as the determination reference values 800H and A00H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is equal to or higher than the determination reference value 800H and smaller than A00H (S47).
[0213]
As a result of this determination, when the output of the differential amplifier 63 is 800H or more and smaller than A00H, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are passage target points. Although it exists, it represents that it is slightly close to the sensor pattern SC. That is, the light beam a passes through the area CD of the area C in FIG.
[0214]
Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the passage target points of the beam light a (S48). ). The control amount at this time requires a control amount (movement amount) of about 10 μm in consideration of the distance between the target point and the area CD.
[0215]
If it is determined in step S47 that the output of the differential amplifier 63 is equal to or higher than 800H and not smaller than A00H, the output of the differential amplifier 63 is determined as determination reference values A00H and FA0H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is equal to or greater than the determination reference value A00H and smaller than FA0H (S49).
[0216]
If the output of the differential amplifier 63 is equal to or greater than A00H and smaller than FA0H as a result of this determination, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are the passage target points. Although it exists, it represents that it is slightly close to the sensor pattern SC. That is, the light beam a passes through the area CB of the area C in FIG.
[0217]
Accordingly, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S50). ). Note that the control amount at this time needs a control amount (movement amount) of about 0.5 μm in consideration of the distance between the target point and the area CB.
[0218]
If it is determined in step S49 that the output of the differential amplifier 63 is not less than A00H and not less than FA0H, the passing position of the beam light a is within a predetermined range (a range of ± 1 μm of the target point). Therefore, the control end flag A of the galvanometer mirror 33a is set (S51).
[0219]
In this way, when the light beam a does not pass within the range of ± 1 μm from the ideal passing point (S34, S36, S38, S40, S42, S44, S46, S48, S50), the galvano The mirror 33a is controlled by a predetermined amount, and the value at that time is written in the memory 52 (S52).
[0220]
As described above, the main control unit 51 sets the control end flag A of the galvanometer mirror 33a when the light beam a passes through the range of ± 1 μm from the ideal passing point, and passes outside this range. If it is, the galvano mirror control amount is adjusted according to the passing position (area), and the value is written in the memory 52.
[0221]
Finally, the main control unit 51 cancels the forced light emission of the laser oscillator 31a, and finishes the series of passage position control of the light beam a (S53).
[0222]
As already described with reference to FIG. 15, when the control end flag A of the galvano mirror 33a is not set, the beam light a passing position control routine is executed again. That is, this routine is repeatedly executed until the beam light a passes within the range of ± 1 μm with respect to the ideal passing point.
[0223]
The above explanation is the control for the beam light a, but the control for the beam lights b, c, d is basically the same as the case of the beam light a, and the respective laser oscillators 31b to 31d. Are forcibly emitted, and the outputs of the amplifiers 61 and 62 and the differential amplifiers 63 to 66 are determined. If the outputs pass within the range of ± 1 μm from the ideal control point, the respective galvanometer mirrors The control end flags B to D of 33b to 33d are set. In addition, when it does not pass through this range, after determining which area each of the light beams b to d passes, the control corresponding to the passing area is performed on the galvanometer mirrors 33b to 33d. The control value is written in the memory 52.
[0224]
Here, the influence given by the power variation of each light beam in the light beam passage position control described above will be described.
[0225]
FIG. 18 shows the light beam passage position when the light beam power changes on the photosensitive drum 15 (beam light detector 38), and the output of the differential amplifier (integrated and A / D converted value). This shows the relationship.
[0226]
In the graph of FIG. 18, the curve B shows the same output characteristics as the amplifiers 63, 64, 65, and 66 shown in FIG. 11, and the light beam moves away from the target passing point, and 000H to 7FFH, Alternatively, it gradually changes from FFFH to 800H, and further changes gradually from 7FFH to 000H or from 800H to FFFH when moving away from the target point. This characteristic is convenient in terms of control because the correspondence between the light beam passage position and the output of the differential amplifier can be easily obtained.
[0227]
On the other hand, for example, in the case of the characteristic of curve C when the power of the light beam is large, the output of the differential amplifier changes greatly only when the light beam passage position slightly deviates from the target point. Therefore, if the beam passage position deviates more than a certain value, the output of the differential amplifier is fixed to 7FFH or 800H. Further, the output value of the differential amplifier does not change unless the beam light passing position changes significantly.
[0228]
On the contrary, when the power of the light beam is small, the characteristic of the curve A is obtained, the change in the output of the differential amplifier is small with respect to the change in the passage position of the light beam, and the S / N ratio is poor.
[0229]
As described above, when the power of the beam light passing on the photosensitive drum 15 changes, the relationship between the beam light passing position and the output of the differential amplifier changes.
[0230]
Therefore, when the light beam passage position is controlled in such a state that the power of each light beam varies, the light beam passage position is controlled within a certain standard when the light beam power is small. Even if it is intended, if the accuracy is insufficient and the power of the light beam is large, the change in the output of the differential amplifier relative to the change in the light beam passing position may be too large or not change. The control operation may become unstable.
[0231]
Therefore, when performing the light beam passing position control, it is necessary that the power of each light beam is at least equal. Further, ideally, the power of the light beam having the characteristics as shown by the curve B in FIG. 18 is desirable, but for the graph shown in FIG. 18, for example, the amplification factor of the differential amplifier is set to an appropriate value. Thus, the characteristic of the curve A can be changed to the characteristic of the curve B, or the characteristic of the curve C can be changed to the characteristic of the curve B.
[0232]
Next, a first example of the light beam power control routine in steps S3 and S12 of FIG. 14 will be described using the flowcharts shown in FIGS.
[0233]
First, the main control unit 51 sets the amplification factor of the amplifier 99 (H) to a predetermined value (S231). The predetermined value here means that the output of the amplifier 99 (H) is integrated by the integrator 42 and A / D converted by the A / D converter 43 when each light beam passes on the sensor pattern SH. In this case, the gain value is a value that does not saturate and changes in proportion to the power of the light beam.
[0234]
Next, the main control unit 51 turns on the polygon motor 36 and rotates the polygon mirror 35 at a predetermined rotational speed (S232). Next, the main controller 51 forcibly causes the laser oscillator 31a to emit light at a predetermined value stored in the memory 52 (S233). By this operation, the beam light a starts to be scanned by the polygon mirror 35. Here, the predetermined value is a value suitable for image formation at that time.
[0235]
In general, in an image forming apparatus using an electrophotographic process, it is necessary to change the power of beam light depending on the environment in which the image forming apparatus is placed and the usage situation (change over time). The memory 52 stores power information of appropriate beam light under such conditions.
[0236]
Next, the main control unit 51 controls the galvanometer mirror 33a so that the beam light a passes over the sensor pattern SH (S234). Here, the beam light a needs to pass through the substantially central portion of the sensor pattern SH sufficiently so as not to protrude from the sensor pattern SH. If the sensor pattern SH protrudes, the detected power value becomes small. However, as described above (in FIG. 3), the sensor pattern SH used for power control of the light beam has a sufficient size, and such a problem cannot usually occur.
[0237]
Note that, for example, when the light beam a is set so as to pass almost the center of the sensor pattern SH as an initial setting when the power is turned on, the process of step S234 can be omitted.
[0238]
When the beam light a passes over the sensor pattern SH, a value proportional to the power of the beam light a is input from the A / D converter 43 to the main control unit 51. The main control unit 51 stores this value (ideally, an average value of integral multiples of the number of faces of the polygon mirror 35) in the memory 52 as the optical power Pa of the beam light a on the photosensitive drum 15 ( In step S235, the laser oscillator 31a is turned off (S236).
[0239]
Next, the main control unit 51 forcibly causes the laser oscillator 31b to emit light (S237), and controls the galvano mirror 33b to control the beam light b in the same manner as in the case of the beam light a. Is passed (S238). Also in this case, when the beam light b is initially set so as to pass through the substantially central portion of the sensor pattern SH, the process of step S238 can be omitted.
[0240]
As a result, a value proportional to the light power of the light beam b on the photosensitive drum 15 is input from the A / D converter 43 to the main control unit 51, and this value is set as the light power Pb first. The light beam a stored in the memory 52 is compared with the optical power Pa on the photosensitive drum 15 (S239). In the case of this light beam b, ideally, it is desirable that the output value of the A / D converter 43 is taken as an integral multiple of the number of faces of the polygon mirror 35, and the averaged value is Pb. .
[0241]
As a result of comparing the light powers Pa and Pb of the light beam a and the light beam b on the photosensitive drum 15 in this way, the difference is equal to or less than a certain value (ΔP) (ideally “0”). If so, there is no problem in image quality. However, if there is a difference greater than that, it becomes a problem in image quality, and correction is necessary.
[0242]
For example, as a result of comparing the optical powers Pb and Pa, when Pb is larger than Pa and the difference is larger than ΔP (S240, S241), the beam power is reduced by lowering the light emission power setting value to the laser driver 32b. It is possible to reduce the optical power of the light b on the photosensitive drum 15 (S242).
[0243]
Conversely, as a result of comparing the optical powers Pb and Pa, if Pa is larger than Pb and the difference is larger than ΔP (S240, S241), by increasing the emission power setting value to the laser driver 32b, It is possible to increase the optical power of the beam b on the photosensitive drum 15 (S243).
[0244]
When the light power of the light beam b on the photosensitive drum 15 is corrected in this way, the light emission power setting value at this time is stored in the memory 52 as the value of the laser oscillator 31b (S244), and the process returns to step S239. Returning again, the optical power of the light beam b on the photosensitive drum 15 is detected, compared with Pa, and correction is repeated until the difference becomes ΔP or less.
[0245]
In this way, the difference between the power of the beam light a and the power of the beam light b can be made equal to or less than a predetermined value (ΔP).
[0246]
Thereafter, the same operation is performed for the beam light c and the beam light d in steps S245 to S264, so that the optical power difference between the beam light a, the beam light b, the beam light c, and the beam light d on the photosensitive drum 15 is determined. Can be set to a predetermined value (ΔP) or less.
[0247]
In the above example, the light beam a is used as a reference, but it is also possible to control the light beam b, the light beam c, or the light beam d as a reference. Further, the predetermined value (ΔP) here is desirably 1% or less of the reference (value of Pa).
[0248]
Next, a second example of the light beam power control routine in steps S3 and S12 of FIG. 14 will be described using the flowcharts shown in FIGS.
[0249]
The difference of the second example of the light beam power control routine from the first example described above is the difference in the method of taking a reference when controlling the power of the light beam, and the other points are the same as in the first example. . In the first example, the light beam power control reference is the beam light a. Therefore, as a result, the relative optical powers between the light beams are made to coincide. On the other hand, in the second example, power control of each light beam is performed based on a predetermined reference value Pref. Therefore, if the sensitivity of the sensor pattern SH is corrected in advance, the power of each light beam can be controlled based on an absolute reference.
[0250]
For example, when a beam light having an optical power equivalent to 100 μW at a predetermined scanning speed passes over the sensor pattern SH, a value output from the amplifier 99 (H) is 100H and a beam light having an optical power equivalent to 200 μW. On the other hand, the sensor pattern SH is used as a kind of measuring device if it has been adjusted (calibrated) in advance so as to give a value such as 300H for a beam light having an optical power equivalent to 200H and 300 μW. be able to. With such a configuration, it is possible to control the light beam power on the image plane without variations between the airframes.
[0251]
As described above, according to the above-described embodiment, the difference in power between the light beams on the photosensitive drum 15 is controlled to a predetermined value or less using the light beam detector 38 having the sensor pattern as described above. It is possible to control the absolute value, and even if the mounting accuracy with respect to the tilt of the light beam detector 38 is not so high, the scanning position of the light beam can be detected accurately without degrading the control accuracy. It becomes possible.
[0252]
Further, in a digital copying machine using a multi-beam optical system, a beam light detection device 38 disposed at a position equivalent to the surface of the photoconductor drum 15 is used on the photoconductor drum 15 (beam light detection device 38). The power of the light beam, its difference, and the passing position of each light beam are detected. Based on the detection result, the power of each light beam on the surface of the photosensitive drum 15 is set, and the relative position of each light beam is appropriate. By calculating a control amount for controlling to be a position and controlling a galvanometer mirror for changing the relative position of each light beam on the surface of the photosensitive drum 15 according to the calculated control amount, an optical system is obtained. No special accuracy or adjustment is required for the assembly of the photosensitive drum 15, and even if changes occur in the optical system due to environmental changes or changes over time, the control accuracy of the photosensitive drum 15 is not reduced. Always controlled in an ideal position to positional relationship between the light beams cross in. Therefore, high image quality can always be maintained.
[0253]
Furthermore, since the sensor pattern SH for detecting the beam light power in the beam light detector 38 has a sufficiently long size in the sub-scanning direction, it is necessary to bother the beam light controlled to an appropriate position each time. Absent. For this reason, it is possible to sufficiently cope with an increase in copying speed.
[0254]
Next, the beam light detection device 38 corresponding to a plurality of (for example, two types) resolutions will be described.
[0255]
FIG. 23 schematically shows the relationship between the configuration of the beam light detection device 38 corresponding to two types of resolutions and the scanning direction of the beam light. The difference from the beam light detection device 38 in FIG. Sensor patterns SB to SF for detecting the passage position of the light beam are provided corresponding to two kinds of resolutions, respectively, and the rest is the same as the beam light detection device 38 of FIG. .
[0256]
That is, the sensor patterns SB1 to SF1 are beam light passing position detection sensor patterns for the first resolution (for example, 600 dpi), and as shown in FIG. 24, they have the same shape (the same area), and approximately 42 By controlling the passing position so that the beam lights a to d pass through the middle (gap G) between the adjacent sensor patterns, which are arranged at intervals of .3 μm (25.4 mm ÷ 600), 42.3 μm. Are scanned at intervals of.
[0257]
That is,
Beam light a: controlled to be between the sensor patterns SB1 and SC1
Beam light b: Control is performed between the sensor patterns SC1 and SD1.
Beam light c: Control is performed between the sensor patterns SD1 and SE1
Beam light d: Control is performed between the sensor patterns SE1 and SF1.
Since the light beam passage position control has already been described, it is omitted here.
[0258]
Further, the sensor patterns SB2 to SF2 are beam light passing position detecting sensor patterns for the second resolution (for example, 400 dpi), and as shown in FIG. 24, they have the same shape (the same area), and approximately 63 By controlling the passing position so that the beam lights a to d pass through the middle (gap G) of the adjacent sensor patterns, which are arranged at intervals of .5 μm (25.4 mm ÷ 400), 63.5 μm Scanning is performed at intervals.
[0259]
That is,
Beam light a: Control is performed between the sensor patterns SB2 and SC2.
Beam light b: Control is performed between the sensor patterns SC2 and SD2.
Beam light c: Control is performed between the sensor patterns SD2 and SE2.
Beam light d: Control is performed between the sensor patterns SE2 and SF2.
The basic operation of the beam light passing position control is the same as that in the case of 600 dpi, and the description thereof is omitted here.
[0260]
FIG. 25 shows the relationship between the sensor patterns SB1 to SF1 and SB2 to SF2 and the scanning positions of the beam lights a to d when the beam light detection device 38 of this example is mounted inclined with respect to the beam light scanning direction. FIG. 25A shows the case of the first resolution (600 dpi), and FIG. 25B shows the case of the second resolution (400 dpi). In the drawing, the scanning direction of the light beams a to d is expressed with respect to the light beam detector 38.
[0261]
For example, assuming that the relative inclination between the sensor pattern and the beam light is 5 degrees, the interval between the beam light a and the beam light d is as shown in Table 1 below in the case of the first resolution, and is about The 0.5 μm interval is only narrowed. In the case of the second resolution, as shown in Table 2 below, the interval of about 0.7 μm is only narrowed.
[0262]
[Table 1]

[0263]
[Table 2]

[0264]
FIG. 26 is a diagram for explaining beam light passage position control when the light beam detector 38 of FIG. 23 is used. The difference from FIG. 8 is the configuration of the light beam detector output processing circuit 40. In FIG. 4, a differential amplifier is provided corresponding to the sensor patterns SB1 to SF1 and SB2 to SF2, and a resolution switching signal is added to the sensor selection signal. Since this is the same as FIG.
[0265]
That is, the differential amplifier 631 amplifies the difference between the output signals of the sensor patterns SB1 and SC1, the differential amplifier 641 amplifies the difference between the output signals of the sensor patterns SC1 and SD1, and the differential amplifier 651 The difference between the output signals of the sensor patterns SD1 and SE1 is amplified, and the differential amplifier 661 amplifies the difference between the output signals of the sensor patterns SE1 and SF1. The differential amplifier 632 amplifies the difference between the output signals of the sensor patterns SB2 and SC2, the differential amplifier 642 amplifies the difference between the output signals of the sensor patterns SC2 and SD2, and the differential amplifier 652 The difference between the output signals of the sensor patterns SD2 and SE2 is amplified, and the differential amplifier 662 amplifies the difference between the output signals of the sensor patterns SE2 and SF2.
[0266]
The output signals of the amplifiers 631 to 661 and 632 to 662 are input to the selection circuit (analog switch) 41, respectively. The selection circuit 41 selects a signal to be input to the integrator 42 based on a sensor selection signal from the main control unit (CPU) 51.
[0267]
That is, when the light beam passage position control is performed at the first resolution (600 dpi), the selection circuit 41 selects the following differential amplifier and performs the corresponding beam light passage position control.
[0268]
Differential amplifier 631: Beam light a
Differential amplifier 641: Beam light b
Differential amplifier 651: beam light c
Differential amplifier 661: beam light d
Similarly, when the light beam passage position control is performed at the second resolution (400 dpi), the following differential amplifier is selected by the selection circuit 41, and the corresponding light beam passage position control is performed.
[0269]
Differential amplifier 632: beam light a
Differential amplifier 642: beam light b
Differential amplifier 652: beam light c
Differential amplifier 662: beam light d
FIG. 27 is a flowchart illustrating a schematic operation when the printer unit 2 is turned on when the beam light detection device 38 of FIG. 23 is used. The difference from FIG. 14 is that the process of step S17 as a resolution selection routine is added between steps S2 and S3, and the other processes are the same as those of FIG. In the resolution selection routine (S17), the rotation speed of the polygon motor 36 corresponding to the selected resolution, the power of the beam light at the time of image formation, the setting of the selection circuit 41, and the like are executed. That is,

It becomes.
[0270]
As described above (FIGS. 5 (a) and 5 (b)), the conventional method (see FIG. 5A and FIG. 5B) is provided by arranging the light beam passage position detection sensor pattern in parallel to the direction perpendicular to the scanning direction of the light beam. Compared to FIG. 5B, it is possible to construct the beam light detector 38 having a sufficient margin for the mounting inclination. Furthermore, this embodiment corresponds to a plurality of resolutions with this configuration, and according to this embodiment, it is possible to construct a beam light detection device 38 having a plurality of resolutions and having a sufficient margin for mounting inclination. .
[0271]
Next, image formation position control in the main scanning direction (light emission timing control of the laser oscillator) will be described in detail.
[0272]
FIG. 28 schematically shows the configuration of the beam light detector 38 used for this control. This beam light detection device 38 has four vertically long sensor patterns S3, S4, S5, S6 as a fifth light detection unit for detecting the passage timing of the beam light in the beam light detection device 38 of FIG. Since other configurations are basically the same as those in FIG. 23, the description thereof is omitted.
[0273]
That is, the sensor pattern S3 is provided in parallel between the sensor patterns S1 and SH, and the sensor patterns S4, S5, and S6 are located on the right side of the sensor patterns SA to SG (with respect to the drawing), S4 and S4. They are provided in parallel with them in the order of S5 and S6. The sensor pattern S6 also has the function of the sensor pattern S2.
[0274]
Here, the intervals P3, P4, and P5 between the sensor patterns S3 to S6 are image clocks (synchronous clock pulses output from the synchronization circuit 55) of the first resolution (600 dpi) and the second resolution (400 dpi). This is an integral multiple (n) of the least common multiple of the distance that the light beam moves in the scanning direction in one cycle (one pulse time), which will be described below.
[0275]
In the present embodiment, taking the case of having two types of resolutions as an example,
-Interval between sensor patterns S3 and S4: P3
-Interval between sensor patterns S4 and S5: P4
-Interval between sensor patterns S5 and S6: P5
-Scanning speed of beam light at the first resolution: VS
-Time of one pulse of the synchronous clock pulse at the first resolution: TC
Scanning speed of light beam at the second resolution: VS ′
-Time of one synchronous clock pulse at the second resolution: TCC
If
-P3 = L. C. M.M. (VS × TC, VS ′ × TCC) × n1 (n1 is an integer, LCM is the least common multiple)
-P4 = L. C. M.M. (VS × TC, VS ′ × TCC) × n 2 (n 2 is an integer, LCM is the least common multiple)
-P5 = L. C. M.M. (VS × TC, VS ′ × TCC) × n3 (n3 is an integer, LCM is the least common multiple)
It is.
[0276]
The features of the beam light detection device 38 used in the present embodiment are sensor patterns SB1 to SF1, SB2 to SF2 (beam light position detecting means) for detecting the light beam passage position, and a sensor pattern S3 for detecting the light beam passage timing. S4, S5, S6 (beam light passage timing detecting means) and sensor pattern SH (beam light power detecting means) for detecting the light beam power are integrally held in one holding substrate 38a. According to this, since the sensor pattern is in the same detection device, an attachment adjustment process such as mechanical alignment for each sensor pattern becomes unnecessary.
[0277]
FIG. 29 is a block diagram for explaining image forming position control in the main scanning direction using the beam light detector 38 of FIG. 28. This is the image forming in the main scanning direction from the block diagram of FIG. The part related to position control is extracted and shown. Note that a plurality of sensor patterns of the laser oscillator 31, the laser driver 32, and the beam light detection device 38 are provided. In FIG. 29, only one system is shown for the sake of simplicity.
[0278]
First, light emission timing control (image formation position control in the main scanning direction) of one light beam (single beam) will be described with reference to FIGS.
[0279]
The main control unit 51 designates the number of rotations of the polygon motor 36 and inputs a rotation-on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates at a predetermined rotational speed.
[0280]
Subsequently, the main control unit 51 inputs a forced light emission signal to the laser driver 32 and causes the laser oscillator 31 to emit light forcibly. The beam light by the forced light emission is scanned by the polygon mirror 35 and passes on the beam light detection device 38, and the beam light detection device 38 outputs a passage timing detection signal synchronized with the passage timing of the beam light.
[0281]
The passage timing detection signal is amplified by the main scanning circuit 40a of the beam light detector output processing circuit 40 and then binarized, and is input to the main controller 51 and the synchronization circuit 55 as a beam light detection output. . When the beam light detection output is input, the main control unit 51 stops outputting the forced light emission signal and turns off the laser oscillator 31.
[0282]
On the other hand, the synchronization circuit 55 outputs the reference clock pulse as a synchronization clock pulse in synchronization with the beam light detection output. That is, the synchronization circuit 55 generates a synchronization clock pulse synchronized with the light beam passage timing. This synchronous clock pulse is a clock pulse serving as a reference for image data, and is sent to the counter 98. The counter 98 counts the clock pulses, and outputs a count end signal to the main control unit 51 when the predetermined value is counted.
[0283]
The main control unit 51 determines an image forming area based on the count end signal, and outputs it to the laser driver 32 together with the image data as an image clock pulse. The laser driver 32 forms an image by causing the laser oscillator 31 to emit light based on the image clock pulse and the image data.
[0284]
However, when there are a plurality of light beams, a phase difference occurs between the light beams due to the surface accuracy of the polygon mirror 35 and the like. That is, the timing of passing over the light beam detector 38 differs depending on the light beam (the order of arrival is different). In addition, the order of arrival of the light beams varies depending on the surface of the polygon mirror 35 to be scanned. For this reason, in the same method as the single beam, it is impossible to determine the order of arrival of the light beams, and image formation position control in the main scanning direction cannot be performed.
[0285]
Therefore, in the present embodiment, before forming an image, a beam light detection device that determines the arrival order of a plurality of light beams in advance and detects the light beam and the passage timing of the light beams based on the determination result. 38 combinations of sensor patterns S3 to S6 are determined, image formation position control in the main scanning direction is performed, and sensor patterns close to the scanning direction are assigned to the combinations in the order of arrival of the light beams. This will be described. In the following description, a case where there are four light beams will be described as an example.
[0286]
As described above, four sensor patterns S3, S4, S5, and S6 are used for image forming position control in the main scanning direction. These sensor patterns S3 to S6 correspond to the light amount of the light beam irradiated on the surface of the sensor pattern by the light detection portions (photodiodes) arranged at different positions with respect to the scanning direction of the light beam. Outputs the current value. Therefore, the sensor patterns S3 to S6 output a passage timing detection signal according to the passage timing of the light beam.
[0287]
FIG. 32 shows a configuration example of the main scanning side circuit 40 a in the beam light detector output processing circuit 40. The current I3 flowing through the sensor pattern (photodiode) S3 is subjected to current / voltage conversion by the resistors RP and RL, and becomes a voltage V13 (passing timing detection output). The voltage V13 is amplified by the non-inverting amplifier A11 and then binarized by the binarization circuit A12. This binarized signal S3OUT is sent to the main controller 51, the synchronizing circuit 55 and the counter 98 as a beam light detection output. The same applies to the sensor patterns S4, S5 and S6.
[0288]
The main control unit 51 uses these beam light detection outputs S3OUT to S6OUT to determine the order of arrival of the light beams, and the determination method will be described below.
[0289]
First, the determination of the arrival state of the beam light, which determines in what state the four light beams are being scanned, will be described. That is, the following five states are determined (see FIGS. 33 and 34).
[0290]
(1) The four beams do not overlap each other (all have different phases)
(2) Only two of the four light beams overlap (only two are in phase, the other two are different)
(3) Two of the four light beams overlap each other (two pairs are in phase)
(4) Only three of the four light beams overlap (only three have the same phase, the other one is different)
(5) All four beams overlap (all four are in phase)
The procedure for determining the arrival state of the light beam will be described below with reference to the flowchart shown in FIG. The main control unit 51 designates the number of rotations of the polygon motor 36 and inputs a rotation-on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates at a predetermined rotational speed.
[0291]
Subsequently, the main control unit 51 inputs a forced light emission signal to the laser drivers 32a to 32d and causes the four laser oscillators 31a to 31d to emit light forcibly. The four beam lights a to d emitted from the laser oscillators 31a to 31d are scanned by the polygon mirror 35 and pass on the sensor pattern S3. Thereby, the sensor pattern S3 outputs a passage timing detection signal synchronized with the passage timings of the four light beams a to d.
[0292]
The passage timing detection signal is amplified by the main scanning side circuit 40a of the beam light detector output processing circuit 40 described above, and then binarized, and is subjected to main control as beam light detection outputs S3OUTa, S3OUTb, S3OUTc, S3OUTd. Input to the unit 51, the synchronization circuit 55, and the counter 98.
[0293]
The light beam detection output S3OUT is input to the counter 98, and the counter 98 counts the light beam detection output S3OUT. The count values are classified into the following cases 1 to 4 according to the above-described beam light arrival state (see FIGS. 33 and 34).
[0294]

The main control unit 51 determines the arrival state of the light beam based on the count value of the counter 98. For example, when the count value is “1”, that is, in case 1, all the four light beams a to d have the same phase, and thus can be handled in the same manner as one light beam.
[0295]
That is, the sensor patterns S3 to S6 and the light beams a to d can be assigned freely, and the light beam detection outputs S3OUT, S4OUT, S5OUT, and S6OUT may be appropriately set to the light beams a to d. In the example of FIG. 35, the light beam a is assigned to the sensor pattern S3, the light beam b is assigned to the sensor pattern S4, the light beam c is assigned to the sensor pattern S5, and the light beam d is assigned to the sensor pattern S6.
[0296]
In the case 2, the case 3, and the case 4, the phase of at least one light beam is different, and it is further necessary to determine the order of arrival of the light beams such as the head beam light, the second light beam, and the third light beam.
[0297]
With reference to the flowchart shown in FIG. 36, the sensor allocation procedure in case 4 will be described. First, after determining the leading beam light, and subsequently determining the second, third, and fourth beam light arrival orders, the leading beam light is set to the sensor pattern S3, the second beam light is set to the sensor pattern S4, and 3 The 4th beam light is assigned to the sensor pattern S5. Hereinafter, the procedure for determining the light beam will be described in detail.
[0298]
First, the procedure for determining the head beam light will be described with reference to the flowcharts shown in FIGS. The main control unit 51 designates the number of rotations of the polygon motor 36 and inputs a rotation-on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates at a predetermined rotational speed.
[0299]
Subsequently, the main control unit 51 inputs a forced light emission signal to the laser drivers 32a to 32d and causes the four laser oscillators 31a to 31d to emit light forcibly. Further, the main control unit 51 performs setting so that the laser oscillator 31a is turned off (off) when the head light beam passes through the sensor pattern S3 and the light beam detection output S3OUT is output.
[0300]
The four beam lights a to d emitted from the laser oscillators 31a to 31d are scanned by the polygon mirror 35 and pass on the sensor pattern S3. At this time, the main controller 51 turns off the laser oscillator 31a when the head beam passes through the sensor pattern S3 and the beam detection output S3OUT is output.
[0301]
The beam light detection output S3OUT is input to the counter 98, and the counter 98 counts the beam light detection output S3OUT. The main control unit 51 reads the count value. If the count value is “4”, the beam light a is the head. If the count value is other than “4”, the beam light other than the beam light a is the head. It is determined that it is, and the determination is performed again.
[0302]
That is, when the beam light a is the head, first, when the beam light detection output S3OUTa accompanying the passage of the beam light a is output, the count value becomes “1” and the laser oscillator 31a is turned off at the same time. Further, since the counter 98 counts the beam light detection outputs S3OUTb, S3OUTc, and S3OUTd as the light beams b, c, and d pass, the count value becomes “4”. When the beam light a is not the head, when the beam light detection output S3OUTb accompanying the passage of beam light other than the beam light a (for example, the beam light b) is output, the count value becomes “1” and at the same time, the laser oscillator 31a. Turn off the light. Furthermore, since the counter 98 counts the beam light detection outputs S3OUTc and S3OUTd as the beam lights c and d pass, the count value becomes “3”.
[0303]
When the beam light a is not the head, the main control unit 51 determines the head beam again. This time, the main control unit 51 performs the same determination by setting the laser oscillator 31b to be turned off when the head beam passes through the sensor pattern S3.
[0304]
The main control unit 51 inputs forced emission signals to the laser drivers 32a to 32d and causes the four laser oscillators 31a to 31d to emit light forcibly. Further, the main control unit 51 performs setting so that the laser oscillator 31b is turned off when the head beam light passes through the sensor pattern S3 and the beam light detection output S3OUT is output.
[0305]
The four beam lights a to d emitted from the laser oscillators 31a to 31d are scanned by the polygon mirror 35 and pass on the sensor pattern S3. At this time, the main controller 51 turns off the laser oscillator 31b when the head beam passes through the sensor pattern S3 and the beam detection output S3OUT is output.
[0306]
The beam light detection output S3OUT is input to the counter 98, and the counter 98 counts the beam light detection output S3OUT. The main control unit 51 reads the count value. If the count value is “4”, the light beam b is at the head. If the count value is other than “4”, the light beams other than the light beam b are at the head. It is determined that there is, and the determination is performed again.
[0307]
If the light beam b is not the head, the main control unit 51 determines the head light again. This time, the main control unit 51 performs the same determination by setting the laser oscillator 31c to be extinguished when the head beam passes through the sensor pattern S3. If the count value of the counter 98 is “4”, the light beam c is the head, and if the count value is other than “4”, it is determined that the light beams other than the light beam c are the head, and the determination is made again. To do.
[0308]
If the light beam c is not the head, the main control unit 51 determines the head light again. This time, the main control unit 51 performs the same determination by setting the laser oscillator 31d to be turned off when the head beam passes through the sensor pattern S3. If the count value of the counter 60 is “4”, the light beam d is the head, and if the count value is other than “4”, an error signal is output.
[0309]
After the head beam light is determined by the above procedure, the second beam light is determined other than the head beam light. The second light beam determination procedure is to determine the head among the three light beams other than the head light beam, and is performed by the same method as the determination of the head light beam.
[0310]
The second light beam determination procedure will be described below with reference to the flowcharts shown in FIGS. 39 and 40. The main control unit 51 designates the number of rotations of the polygon motor 36 and inputs a rotation-on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates at a predetermined rotational speed.
[0311]
Subsequently, the main control unit 51 inputs the forced emission signal to the three laser drivers corresponding to the three beam lights other than the head beam light, and the three lasers corresponding to the three beam lights other than the head beam light. Force the oscillator to emit light. Further, the main control unit 51, when the leading beam light passes through the sensor pattern S3 among the three beam lights emitted from the three laser oscillators, and the beam light detection output S3OUT is output, Set to turn off the oscillator * 1.
[0312]
・ Beam light * 1: Beam light other than the head beam 1 (corresponding to laser oscillator * 1)
・ Beam light * 2: Beam light other than the leading beam 2 (corresponding to laser oscillator * 2)
・ Beam light * 3: Beam light other than the leading beam 3 (corresponding to laser oscillator * 3)
The three beam lights * 1, * 2, * 3 emitted from the three laser oscillators are scanned by the polygon mirror 35 and pass on the sensor pattern S3. At this time, the main controller 51 turns off the laser oscillator * 1 when the head beam passes through the sensor pattern S3 and the beam detection output S3OUT is output.
[0313]
The beam light detection output S3OUT is input to the counter 98, and the counter 98 counts the beam light detection output S3OUT. The main control unit 51 reads the count value. If the count value is “3”, the main control unit 51 determines that the light beam * 1 is the second light beam. If the count value is other than “3”, it is determined that the beam light other than the beam light * 1 is second, and the determination is performed again.
[0314]
When the head beam passes through the sensor pattern S3, the main control unit 51 sets the laser oscillator * 2 to be turned off and performs the same determination. If the count value of the counter 98 is “3”, it is determined that the beam light * 2 is the second, and if the count value is other than “3”, it is determined that the beam light other than the beam light * 2 is the second. The determination is performed again.
[0315]
The main control unit 51 performs the same determination by setting the laser oscillator * 3 to be turned off when the head beam passes through the sensor pattern S3. If the count value of the counter 98 is “3”, the beam light * 3 is second, and if the count value is other than “3”, an error signal is output.
[0316]
After the determination of the head beam light and the second beam light by the above procedure, the third and fourth determinations are performed by the same procedure. FIG. 41 is a flowchart showing the determination procedure for the third light beam, but the description is omitted because it is the same as the determination procedure for the second light beam.
[0317]
In this way, after determining the arrival order of the first, second, third, and fourth light beams, the first light beam is sensor pattern S3, the second light beam is sensor pattern S4, and the third light beam is sensor. The fourth light beam is assigned to the pattern S5 and the sensor pattern S5, and the sensor assignment in case 4 is completed.
[0318]
Next, a sensor allocation procedure in case 3 will be described with reference to the flowchart shown in FIG. Case 3 is a state in which two (one set) of the four light beams a to d are overlapped. First, the two overlapping light beams are determined and overlapped. It is classified into three groups: two existing and two remaining (non-overlapping). After grouping is completed, the arrival order of the first, second, and third groups among the three groups is determined. If the light beams of the first group overlap, they are assigned as follows.
[0319]
・ First two beams: S3, S4
-Second beam light: S5
-Third light beam: S6
If the head group does not overlap, it is determined whether or not the light beams of the second group overlap. If they overlap, they are assigned as follows.
[0320]
-Leading beam light: S3
・ Second two light beams: S4, S5
-Third light beam: S6
If the first group and the second group do not overlap, they are assigned as follows.
[0321]
-Leading beam light: S3
-Second beam light: S4
Third third beam light: S5, S6
Hereinafter, each determination method will be described in detail.
[0322]
First, the procedure for determining and grouping overlapping light beams will be described with reference to the flowcharts shown in FIGS.
[0323]
The main control unit 51 inputs a rotation on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates. Subsequently, the main control unit 51 inputs a forced light emission signal to the three laser drivers 32b to 32d other than the laser driver 32a, and causes the three laser oscillators 31b to 31d other than the laser oscillator 31a to emit light forcibly.
[0324]
The three light beams b, c and d emitted from the three laser oscillators 31b to 31d are scanned by the polygon mirror 35 and pass on the sensor pattern S3. As the light beam passes, the sensor pattern S3 outputs a light beam detection output S3OUT to the counter 98, and the counter 98 counts the light beam detection output S3OUT.
[0325]
The main control unit 51 reads the count value of the counter 98, and if the count value is “3”, the main control unit 51 determines that the beam light a is overlapped. If the count value is other than “3”, the beam light a is Judge that they do not overlap (independent). In case 3, only two of the four light beams a to d are overlapped. Therefore, when the beam light a is overlapped, the remaining three light beams b to d are overlapped. Since it is not (independent), the sensor pattern S3 outputs beam light detection outputs S3OUTb, S3OUTc, and S3OUTd to the counter 98 as the three light beams b to d pass. Since the counter 98 counts the light beam detection outputs S3OUTb, S3OUTc, and S3OUTd, the count value is “3”.
[0326]
When the beam light a does not overlap, the count value is “2” because two of the remaining three beam lights b to d overlap. For example, assuming that the light beam b and the light beam c are overlapped, only one light beam detection output S3OUTb and S3OUTc is output at the same time (S3OUTbc), so two of S3OUTd are output as the beam light detection outputs. . That is, the count value is “2”.
[0327]
Subsequently, the same determination is performed for the beam light b, the beam light c, and the beam light d, and grouping is performed on the overlapping beam light and the non-overlapping (independent) beam light.
[0328]
When the grouping is completed, the arrival order of each group is next determined. From the overlapping group, one of the two light beams is selected as a representative (any of the two beams may be selected). As a result, the arrival order of the three light beams is determined. Therefore, the arrival order of the light beams is determined in the same procedure as in FIGS. 39 to 41 described above.
[0329]
Thereafter, the above-described allocation is performed, and the sensor allocation in case 3 is terminated.
[0330]
Next, a sensor allocation procedure in case 2 will be described with reference to the flowchart shown in FIG. Case 2 includes a combination of two light beams (a pair) of two light beams (a to d), and a combination of one light beam and three light beams. Since there is a case, the combination of these is first determined. In the case of a combination of two-beam light and two-beam light, the arrival order of the two groups is determined and assigned as follows.
[0331]
・ First group (first two beams): S3, S4
-Second group (second two-beam light): S5, S6
On the other hand, in the case of a combination of one light beam and three light beams, the arrival order of the two groups is also determined, and when the leading group is one light beam, they are assigned as follows.
[0332]
-Leading group (single beam): S3
-Second group (three beams): S4, S5, S6
When the first group is a three-beam light, it is assigned as follows.
[0333]
-Leading group (3-beam light): S3, S4, S5
-Second group (single beam light): S6
Hereinafter, each determination method will be described in detail.
[0334]
First, a procedure for determining whether a combination of one beam light and three beam light or a combination of two beam light and two beam light will be described with reference to the flowchart shown in FIG. .
[0335]
The main control unit 51 inputs a rotation on signal to the polygon motor driver 37. As a result, the polygon motor 36 rotates. Subsequently, the main control unit 51 inputs a forced light emission signal to the laser drivers 32c and 32d other than the laser drivers 32a and 32b, and causes the two laser oscillators 31c and 31d other than the laser oscillators 31a and 31b to emit light forcibly.
[0336]
The two light beams c and d emitted from the two laser oscillators 31c and 31d are scanned by the polygon mirror 35 and pass on the sensor pattern S3. As the light beam passes, the sensor pattern S3 outputs a light beam detection output S3OUT to the counter 98, and the counter 98 counts the light beam detection output S3OUT. The main control unit 51 reads the count value of the counter 98, and the following combinations are conceivable depending on the count value. (Step 1)
Count value = 2: (ac, bd) (ad, bc) (abd, c) (abc, d)
Count value = 1: (ab, cd) (acd, b) (a, bcd)
Subsequently, when the count value is “2”, the two laser oscillators 31b and 31d other than the laser oscillators 31a and 31c are forced to emit light, the beam light detection output is counted, and the following combinations are considered depending on the count value. (Step 2)
Count value = 2: (ad, bc) (abc, d)
Count value = 1: (ac, bd) (abd, c)
Further, when the count value is “2”, the three laser oscillators 31a, 31b, 31c other than the laser oscillator 31d are forced to emit light, the beam light detection output is counted, and the count value is read. It can be determined from the count value that the combination is as follows. (Step 3)
Count value = 2: (ad, bc)
Count value = 1: (abc, d)
On the other hand, if the count value in step 1 is “1”, the two laser oscillators 31a and 31b other than the laser oscillators 31c and 31d are forced to emit light, the beam light detection output is counted, and the count value is read. The following combinations are possible depending on the count value. (Step 4)
Count value = 2: (acd, b) (a, bcd)
Count value = 1: (ab, cd)
Further, in step 4, when the count value is “2”, the three laser oscillators 31a, 31c, and 31d other than the laser oscillator 31b are forced to emit light, the beam light detection output is counted, and the count value is read. It can be determined from the count value that the combination is as follows. (Step 5)
Count value = 2: (a, bcd)
Count value = 1: (acd, b)
The combination of the two groups is determined by the above procedure.
[0337]
When the combination determination is completed, the arrival order of the groups is determined next. From the overlapping group, one of two (or three) light beams is selected as a representative (any of two or three) may be selected. As a result, the order of arrival of the two light beams is determined, so that the determination can be made in exactly the same procedure as in FIG. Therefore, the description is omitted here.
[0338]
Thereafter, the above-described allocation is performed, and the sensor allocation in case 2 is terminated.
[0339]
The sensor allocation for cases 1 to 4 is completed by the above procedure.
[0340]
If the sensor assignment of each light beam is determined, the horizontal synchronization signal for each light beam is determined, so that image formation position control in the main scanning direction can be performed as in the case of single beam light (FIGS. 30 and 31). reference). For example, assume that the following allocation is performed.
[0341]
Beam light arrival order: beam light a, beam light b, beam light c, beam light d
Beam light a: sensor pattern S3
Beam light b: sensor pattern S4
Beam light c: sensor pattern S5
Beam light d: sensor pattern S6
Hereinafter, a description will be given with reference to FIG. 47. First, the main control unit 51 turns on the polygon motor 36, rotates the polygon motor 36, and causes all the laser oscillators 31a to 31d to emit light. The beam lights a to d scanned by the polygon mirror 35 pass through the sensor pattern S3 with the beam light a being the leading beam light as determined in the order of arrival, and the beam light detection output S3OUT is output. The light beam detection output S3OUT becomes a horizontal synchronizing signal of the light beam a.
[0342]
When the beam light detection output S3OUT is output, the main controller 51 turns off the laser oscillator 31a. The synchronizing circuit 55 outputs a synchronous clock pulse after a delay time t3 in synchronization with the output of the light beam detection output S3OUT. The counter 98 counts the synchronous clock pulses, and outputs a count end signal to the main control unit 51 when a predetermined count value (left margin) is reached.
[0343]
When receiving the count end signal, the main control unit 51 starts image formation, outputs image clock pulses to the laser drivers 32a to 32d, and starts image formation in the main scanning direction. When a predetermined count value (right margin) is reached, output of the image clock pulse is stopped and image formation in the main scanning direction is terminated.
[0344]
On the other hand, when the light beam b passes through the sensor pattern S4, a light beam detection output S4OUT is output, and the main control unit 51 turns off the laser oscillator 31b. The synchronization circuit 55 outputs a synchronization clock pulse after a delay time t4 in synchronization with the output of the light beam detection output S4OUT (the light beam detection output S4OUT is a horizontal synchronization signal of the light beam b). The counter 60 counts the synchronous clock pulses, and image formation in the main scanning direction is performed as described above.
[0345]
The above operation is similarly performed for the beam light c and the beam light d, and image formation is performed. That is, the light beam detection output S5OUT becomes a horizontal synchronization signal of the light beam c, and the light beam detection output S6OUT becomes a horizontal synchronization signal of the light beam d.
[0346]
Next, the intervals P3, P4, and P5 of the sensor patterns S3 to S6 for detecting the passage timing of the light beam in the light beam detection device 38 are set to the beam time for one pulse time of the synchronous clock pulse output from the synchronization circuit 55. A point that is an integral multiple of the distance that the light moves in the scanning direction will be described.
[0347]
As described above, in the present embodiment, the intervals P3, P4, and P5 between the sensor patterns S3 to S6 are an integral multiple of the resolution. In the case of the present embodiment, it is configured so that an image can be formed with the first resolution (P1) and the second resolution (P2 = 3/2 × P1), and the interval between the sensor patterns S3 to S6. P3, P4, and P5 are L.P.s that are integral multiples of the least common multiple (LCM (P1, P2)) of both resolutions. C. M.M. (P1, P2) × 2. This corresponds to a distance of 6 dots when an image is formed at the first resolution, and is a distance corresponding to 4 dots when an image is formed at the second resolution.
[0348]
First, the intervals P3, P4, and P5 between the sensor patterns S3 to S6 for detecting the passage timing of the light beam are the minimum distance by which the light beam moves in the scanning direction during one pulse time of the synchronous clock pulse output from the synchronization circuit 55. Problems that are not integer multiples of the common multiple will be described below. Here, a case where there are two types of resolutions of the first resolution and the second resolution will be described as an example.
[0349]
FIG. 48 shows that, for example, the interval P3 between the sensor patterns S3 and S4 is an integral multiple of the least common multiple of the distance that the light beam moves in the scanning direction during one pulse time of the plurality of synchronous clock pulses output from the synchronous circuit 55. FIG. 9 shows how image formation position control in the main scanning direction is performed when there is no image. An interval P3 between the sensor patterns S3 and S4 is D1 × 5, which corresponds to a distance of 5 dots when an image is formed at the first resolution, and a distance of about 3.3 dots when an image is formed at the second resolution. It corresponds to.
[0350]
In FIG. 48, the light beam a is the sensor pattern S3, and the light beam b is the sensor pattern S4, and the image forming position control timing in the main scanning direction (that is, the horizontal synchronization signal) is taken. In addition, one pulse time (that is, one cycle) of a reference clock pulse (a clock pulse serving as a reference for the synchronous clock pulse) corresponding to the first resolution and the second resolution is set as TC and TCC, respectively.
[0351]
Since the method of controlling the image forming position in the main scanning direction in the case of the first resolution has already been described as described above, the description thereof is omitted here.
[0352]
The image forming position control in the main scanning direction when the second resolution is selected and an image is formed at the second resolution will be described below.
[0353]
Along with the passage of the beam light a, a beam light detection output S3OUT which is an output of the binarized sensor pattern S3 is output. The synchronization circuit 55 outputs the synchronization clock pulse CLK13 after the circuit delay time t13 has elapsed in synchronization with the output of the light beam detection output S3OUT (the rising edge at which the signal changes from the low level to the high level). The counter 98 counts the synchronous clock pulse CLK13, and outputs a count end signal to the main control unit 51 when it reaches a predetermined count value (count value: 8 in the figure). When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0354]
On the other hand, for the light beam b as well, the light beam detection output S4OUT is output as the light beam b passes, and the synchronization circuit 55 synchronizes with the rising edge of the light beam detection output S4OUT to delay the circuit delay time t14. After the elapse of time, the synchronous clock pulse CLK14 is output. The counter 98 counts the synchronous clock pulse CLK14, and outputs a count end signal to the main control unit 51 when it reaches a predetermined count value (count value: 5 in the figure). When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0355]
In this case as well, when attention is paid to the leading edge of the image as described above, the image forming position is not shifted in the case of the first resolution, but in the case of the second resolution, the synchronous clock pulse CLK13 and the synchronous clock pulse CLK14 are used. It can be seen that the leading edge of the image by the beam light b is shifted in the scanning direction of the beam light than the leading edge of the image by the beam light a (shift amount: −VS × tbb, about 0.3). Dot).
[0356]
That is, there is a deviation between the image forming area HAA of the beam light a and the image forming area HBB of the beam light b, which is recognized as a vertical line fluctuation on the output image. In order to correct this deviation, when the synchronous clock pulse CLK14 of the beam b is counted, the count is smaller than a predetermined value (4 in the figure), and the image forming area formed by the beam b is set in the beam light b. It is conceivable to shift in the direction opposite to the scanning direction.
[0357]
However, since the count value can be changed only in units of one pulse (in other words, in units of one dot), in the case of FIG. 48, the amount of deviation becomes rather large (deviation amount: + VS × taa). Accordingly, the shift cannot be corrected, and a shift of less than 1 dot is constantly generated in the range.
[0358]
The reference for the image forming position control in the main scanning direction of the beam light a and the beam light b is the horizontal synchronization signal (S3OUT and S4OUT), but the interval between the reference signals is unrelated to the synchronization clock pulse of the second resolution. For this reason, the above-described deviation occurs.
[0359]
Therefore, in the present embodiment, the light beam moves in the scanning direction at intervals P3, P4, and P5 of the sensor patterns S3 to S6 that output the horizontal synchronizing signal during one pulse time of the synchronizing clock pulse output from the synchronizing circuit 55. It is an integer multiple of the least common multiple of the distance. Thereby, the shift of the image forming position in the main scanning direction can be reduced.
[0360]
Hereinafter, the present embodiment will be described with reference to FIG. In the figure, the interval (distance) P3 between the sensor patterns S3 and S4 is the distance that the light beam moves in the scanning direction during one pulse time of the synchronous clock pulse in the case of the first resolution, and the case of the second resolution. The integral multiple of the least common multiple of the distance that the light beam moves in the scanning direction during one pulse time of the synchronous clock pulse (P3 = LCM (VS × TC = P1, VS ′ × TCC = P2) Xn).
[0361]
That is, P3 corresponds to a distance of 6 dots when an image is formed at the first resolution, and corresponds to a distance of 4 dots when an image is formed at the second resolution. Similarly to FIG. 48, the light beam a is the sensor pattern S3, and the light beam b is the sensor pattern S4 and takes the timing of image formation position control (horizontal synchronization) in the main scanning direction.
[0362]
First, the case of the first resolution will be described.
[0363]
Along with the passage of the beam light a, a beam light detection output S3OUT (horizontal synchronization signal of the beam light a) is output, and the synchronization circuit 55 synchronizes with the output (rising edge) of the beam light detection output S3OUT to delay the circuit. After the elapse of time t3, the synchronous clock pulse CLK3 is output. The counter 98 counts the synchronous clock pulse CLK3, and outputs a count end signal to the main control unit 51 when it reaches a predetermined count value (count value: 10 in the figure). When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0364]
On the other hand, for the light beam b as well, the light beam detection output S4OUT is output as the light beam b passes, and the synchronization circuit 51 synchronizes with the rising edge of the light beam detection output S4OUT to delay the circuit delay time t4. After the elapse of time, the synchronous clock pulse CLK4 is output. The counter 98 counts the synchronous clock pulse CLK4, and outputs a count end signal to the main control unit 51 when it reaches a predetermined count value (4 in the figure). When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0365]
In this case, since the interval P3 between the sensor patterns S3 and S4 corresponds to a distance of 6 dots when an image is formed at the first resolution, a phase difference occurs between the synchronous clock pulse CLK3 and the synchronous clock pulse CLK4. There is no misalignment of the leading edge of the image. That is, there is no deviation between the main scanning image forming area HA due to the beam light a and the main scanning image forming area HB due to the beam light b.
[0366]
Next, the case of the second resolution will be described.
[0367]
Along with the passage of the beam light a, a beam light detection output S3OUT (horizontal synchronization signal of the beam light a) is output, and the synchronization circuit 55 synchronizes with the output (rising edge) of the beam light detection output S3OUT to delay the circuit. After the time t13 has elapsed, the synchronous clock pulse CLK13 is output. The counter 98 counts the synchronous clock pulse CLK13 and outputs a count end signal to the main control unit 51 when a predetermined count value (count value: 7 in the figure) is reached. When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0368]
On the other hand, with respect to the beam light b, similarly, the beam light detection output S4OUT is output along with the passage of the beam light b, and the synchronization circuit 51 synchronizes with the rising edge of the beam light detection output S4OUT to delay the circuit delay time t14. After the elapse of time, the synchronous clock pulse CLK14 is output. The counter 98 counts the synchronous clock pulse CLK14 and outputs a count end signal to the main control unit 51 when it reaches a predetermined count value (3 in the figure). When receiving the count end signal, the main control unit 51 outputs an image clock pulse to the laser driver (starts image formation).
[0369]
In this case, since the interval P3 between the sensor patterns S3 and S4 corresponds to a distance of 4 dots when an image is formed with the second resolution, a phase difference between the synchronous clock pulse CLK13 and the synchronous clock pulse CLK14 occurs. There is no misalignment of the leading edge of the image. That is, there is no deviation between the main scanning image forming area HAA due to the beam light a and the main scanning image forming area HBB due to the beam light b.
[0370]
The light beam passage position control in the sub-scanning direction is the same as that in the case of using the light beam detection device 38 of FIG.
[0371]
As described above, according to the above-described embodiment, even in an image forming apparatus having a plurality of resolutions, it is possible to form a high-quality image without causing a shift in the main scanning image forming area.
[0372]
Next, the point of detecting the relative inclination between the scanning direction of the light beam and the light beam detection device will be described.
[0373]
FIG. 50 shows a configuration example of the beam light detection device 38 having an inclination detection function for detecting the relative inclination between the beam light scanning direction and the beam light detection device. This beam light detector 38 has sensor patterns S7a, S7b and S8a as sixth light detectors for detecting the inclination in the vicinity of the outside of the sensor patterns S1 and S6, respectively, in the configuration of FIG. , S8b are provided, and other configurations are basically the same as those in FIG.
[0374]
The sensor patterns S7a and S7b, and S8a and S8b are arranged vertically and are paired, and have basically the same configuration as the other sensor patterns. However, the center positions of the sensor patterns S7a and S7b and S8a and S8b are on the same straight line.
[0375]
Each output of the sensor patterns S7a, S7b, S8a, and S8b is processed by, for example, an inclination detection side circuit in the beam light detector output processing circuit 40 shown in FIG. 51, and is output as beam light position information. The inclination detection side circuit of FIG. 51 is obtained by deleting the integrator 42 from the circuit shown in FIG. 9, and the other configuration is basically the same as that of FIG.
[0376]
51, since the center positions of the sensor patterns S7a and S7b and S8a and S8b are on the same straight line, the inclination is determined by the light beam position information obtained from the sensor patterns S7a, S7b, S8a, and S8b. It can be detected. That is, if the light beam position information from the sensor patterns S7a and S7b is equal to the light beam position information from the sensor patterns S8a and S8b, there is no inclination, and if both the light beam position information is different, it can be considered that there is an inclination.
[0377]
FIG. 52 is a diagram for explaining the state of inclination. Sensor patterns S7a, S7b, S8a, and S8b are extracted from FIG. 50, and other sensor patterns are omitted. In FIG. 52, the state A has an inclination, the state B has an inclination (inclined in the direction opposite to A), the state C shows no inclination, and the state C ′ shows no inclination. In FIG. 52, BM indicates beam light.
[0378]
In the present embodiment, the inclination is determined based on the light beam passage position information when the light beam passes through the sensor patterns S7a, S7b and S8a, S18b.
[0379]
53 shows an example of light beam position information (outputs VO7 and VO8 of the circuit of FIG. 51) in the state A in FIG. 52. FIG. 53 (a) shows the light beam position information (by the sensor patterns S7a and S7b). VO7) and (b) are beam light position information (VO8) based on sensor patterns S8a and S8b, and (c) is a diagram comparing VO7 and VO8. In this case, since both the light beam position information is different, there is an inclination. When VO7 <VO8, the slope of state A is obtained.
[0380]
FIG. 54 shows an example of the light beam position information (outputs VO7 and VO8 of the circuit of FIG. 51) in the state B in FIG. 52. FIG. 54 (a) shows the light beam position information (by the sensor patterns S7a and S7b). VO7) and (b) are beam light position information (VO8) based on sensor patterns S8a and S8b, and (c) is a diagram comparing VO7 and VO8. In this case, since both the light beam position information is different, there is an inclination. When VO7> VO8, the slope of state B is obtained.
[0381]
FIG. 55 shows an example of beam light position information (outputs VO7 and VO8 of the circuit of FIG. 51) in the state C ′ in FIG. 52. FIG. 55 (a) shows the beam light position information by the sensor patterns S7a and S7b. (VO7) and (b) are diagrams showing the light beam position information (VO8) based on the sensor patterns S8a and S8b, and (c) is a diagram comparing VO7 and VO8. In this case, since both beam light position information is equal, there is no inclination.
[0382]
FIG. 56 shows a specific example of an adjustment mechanism that adjusts the inclination of the light beam detection device 38. That is, the beam light detection device 38 is fixed on the substrate 91. On the substrate 91, the above-described light beam detector output processing circuit 40 (not shown) is configured as an integrated circuit (IC), for example. The substrate 91 is fixed to a θ stage 92, and the inclination of the beam light detector 38 can be adjusted by rotating the θ stage 92. Each of the θ stages 92 is equipped with a pulse motor via a gear head (not shown). By controlling the rotation of the pulse motor in accordance with the comparison result between VO7 and VO8, the inclination is tilted with high accuracy. Can be adjusted.
[0383]
As described above, according to the above-described embodiment, in the digital copying machine using the multi-beam optical system, the plurality of beam light position detection devices that detect the positions of the plurality of beam lights that scan the surface of the photosensitive drum. Are arranged in parallel at intervals corresponding to a plurality of resolutions in a direction substantially perpendicular to the scanning direction of the plurality of light beams, thereby providing a light beam position detecting device having a sufficient margin for mounting inclination. Can be built.
[0384]
Therefore, since the scanning position of the light beam can be accurately detected, the position of the number of light beams on the surface of the photosensitive drum can be always controlled with high accuracy with a plurality of resolutions. As a result, high image quality can always be maintained.
[0385]
In addition, the power of the beam light that scans the surface of the photosensitive drum is detected, the power is controlled so that the value falls within a predetermined range, the beam light passing position control on the surface of the photosensitive drum, and By controlling the synchronization in the main scanning direction, the power of each light beam on the surface of the photosensitive drum can be controlled uniformly without degrading the control accuracy, and a plurality of light beams on the surface of the photosensitive drum can be controlled. The position can always be controlled to an ideal position with high accuracy, and thus high image quality can always be maintained.
[0386]
In addition, before forming an image, the arrival order of a plurality of light beams in the light beam detection device for detecting a plurality of light beam passage timings is determined in advance, and based on the determination result, By determining the combination with the sensor pattern that detects the passage timing of the light beam and performing position control in the main scanning direction, especially when using multiple light beams, special accuracy and adjustment are performed for assembling the optical system. In addition, even if the optical system changes due to environmental changes or changes over time, the positional relationship between the light beams on the surface of the photosensitive drum can always be controlled to an ideal position. Therefore, it is possible to always obtain a high-quality image with no dot shift in the main scanning direction.
[0387]
Further, since the tilt detecting means for detecting the relative tilt between the beam light scanning direction and the beam light detecting device is provided, the tilt can be easily adjusted.
[0388]
In the above-described embodiment, the case where the present invention is applied to a digital copying machine using a multi-beam optical system has been described. However, the present invention is not limited to this, and a single-beam optical system is similarly used. Further, the present invention can be applied to an image forming apparatus other than a digital copying machine.
[0389]
【The invention's effect】
As described above in detail, according to the present invention, the position of the light beam on the surface to be scanned can be controlled to a proper position with high accuracy at a plurality of resolutions, and the power of the light beam on the surface to be scanned can be uniformly controlled. Therefore, it is possible to provide a beam light scanning apparatus and an image forming apparatus that can always maintain high image quality.
[0390]
Further, according to the present invention, when a plurality of light beams are used, the positional relationship between the plurality of light beams on the surface to be scanned can be always controlled to an ideal position with a plurality of resolutions with high accuracy. It is possible to provide a beam light scanning device and an image forming apparatus that can uniformly control the power of each light beam on the surface, and can always maintain high image quality.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing a configuration of a digital copying machine according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of an optical system unit and a positional relationship between photosensitive drums.
FIG. 3 is a configuration diagram schematically showing a configuration of a beam light detection apparatus.
4 is a configuration diagram schematically showing a main configuration of the beam light detection apparatus of FIG. 3;
FIG. 5 is a diagram for explaining an inclination between the light beam detection device and the scanning direction of the light beam.
FIG. 6 is a block diagram showing a control system that mainly controls the optical system.
FIG. 7 is a diagram for explaining that the image forming accuracy in the main scanning direction depends on the power of the light beam.
8 is a block diagram for explaining beam light passage position control using the beam light detection apparatus of FIG. 3; FIG.
FIG. 9 is a configuration diagram showing a specific circuit example of a beam light detector output processing circuit;
FIG. 10 is a diagram showing the relationship between the passage position of the beam light and the output of the light receiving pattern of the beam light detector, the output of the differential amplifier, and the output of the integrator.
FIG. 11 is a graph showing the relationship between the passage position of the light beam and the output of the A / D converter.
FIG. 12 is a graph illustrating the operation resolution of a galvanometer mirror.
FIG. 13 is a graph illustrating the operation resolution of a galvanometer mirror.
14 is a flowchart for explaining a schematic operation when the printer unit is turned on when the beam light detection apparatus of FIG. 3 is used.
FIG. 15 is a flowchart illustrating a beam light passage position control routine.
FIG. 16 is a flowchart for explaining a single light beam passage position control routine;
FIG. 17 is a flowchart for explaining one beam light passing position control routine;
FIG. 18 is a diagram for explaining an influence exerted by variations in power of each light beam in beam light passage position control;
FIG. 19 is a flowchart for explaining a first example of a beam light power control routine;
FIG. 20 is a flowchart for explaining a first example of a beam light power control routine;
FIG. 21 is a flowchart for explaining a second example of a beam light power control routine.
FIG. 22 is a flowchart for explaining a second example of a beam light power control routine.
FIG. 23 is a schematic configuration diagram schematically showing a configuration of a beam light detection apparatus corresponding to two types of resolutions.
24 is a configuration diagram schematically showing a main configuration of the beam light detection device of FIG. 23. FIG.
25 is a view for explaining the inclination of the beam light detection device of FIG. 23 and the scanning direction of the beam light. FIG.
26 is a block diagram for explaining beam light passage position control using the beam light detection apparatus of FIG. 23;
FIG. 27 is a flowchart illustrating a schematic operation when the printer unit is turned on when the beam light detection apparatus of FIG. 23 is used.
FIG. 28 is a schematic configuration diagram schematically showing a configuration of a beam light detection apparatus having a beam light passage timing detection function.
FIG. 29 is a block diagram for explaining image formation position control in the main scanning direction;
FIG. 30 is a timing chart illustrating image formation position control in the main scanning direction when one beam is used.
FIG. 31 is a flowchart illustrating image formation position control in the main scanning direction when one beam is used.
FIG. 32 is a configuration diagram of a main scanning side circuit in the beam light detector output processing circuit;
FIG. 33 is a diagram for explaining the arrival state of beam light;
FIG. 34 is a diagram for explaining the arrival state of beam light;
FIG. 35 is a flowchart for explaining a procedure for determining a light beam arrival state;
FIG. 36 is a flowchart for explaining a sensor assignment procedure in case 4;
FIG. 37 is a flowchart for explaining the procedure for determining the head beam light;
FIG. 38 is a flowchart for explaining the procedure for determining the head beam light;
FIG. 39 is a flowchart for explaining a second light beam determination procedure;
FIG. 40 is a flowchart for describing a second light beam determination procedure;
FIG. 41 is a flowchart for explaining a third light beam determination procedure;
42 is a flowchart for explaining a sensor allocation procedure in case 3. FIG.
FIG. 43 is a flowchart for explaining the procedure for determining and grouping overlapping light beams.
FIG. 44 is a flowchart for explaining the procedure for determining and grouping overlapping light beams.
FIG. 45 is a flowchart for explaining a sensor assignment procedure in case 2;
FIG. 46 is a flowchart for explaining a procedure for determining a light beam.
FIG. 47 is a timing chart illustrating image formation position control in the main scanning direction when four beams are used.
FIG. 48 is a diagram in the case where the interval between the sensor patterns for detecting the passage timing of the light beam is not an integral multiple of the least common multiple of the distance that the light beam travels in the scanning direction during one pulse time of the synchronous clock pulse output from the synchronous circuit. 6 is a timing chart illustrating image formation position control in the scanning direction.
FIG. 49 is a diagram in the case where the interval between the sensor patterns for detecting the passage timing of the light beam is set to an integral multiple of the least common multiple of the distance that the light beam travels in the scanning direction during one pulse time of the synchronous clock pulse output from the synchronization circuit. 6 is a timing chart illustrating image formation position control in the scanning direction.
FIG. 50 is a schematic configuration diagram schematically showing a configuration of a beam light detection apparatus having an inclination detection function.
FIG. 51 is a configuration diagram of an inclination detection circuit in the beam light detection device output processing circuit.
FIG. 52 is a diagram for explaining a state of inclination.
53 is a diagram showing an example of light beam position information in the state A in FIG. 52. FIG.
54 is a diagram showing an example of beam light position information in the state B in FIG. 52. FIG.
55 is a diagram showing an example of light beam position information in the state C ′ in FIG. 52. FIG.
FIG. 56 is a perspective view schematically showing a specific example of an adjustment mechanism for adjusting the tilt of the light beam detection apparatus.
FIG. 57 is a diagram for explaining an image defect that may occur when an image is formed using a misaligned beam.
FIG. 58 is a diagram for explaining image defects that may occur when an image is formed using misaligned light beams.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Scanner part, 2 ... Printer part, 6 ... Photoelectric conversion element, 9 ... Light source, 13 ... Optical system unit, 14 ... Image formation part, 15 ... Photosensitive drum (image carrier), 31a to 31d... Semiconductor laser oscillator (beam light generating means), 33a to 33d... Galvano mirror, 35... Polygon mirror, 38. Beam light power detection means), 38a... Holding substrate (holding means), 39a to 39d... Galvano mirror drive circuit, 40... Light beam detector output processing circuit, 41. 43... A / D converter, S1 to S6, SH, SA to SG, SB1 to SF1, SB2 to SF2... Sensor pattern (light detection unit), 51. 62,99 ...... amplifier, 64 to 66 ...... differential amplifier.

Claims (5)

A plurality of beam light generating means for generating beam light;
Scanning in which the plurality of light beams generated from the plurality of light beam generating means are optically combined and then reflected toward the surface to be scanned, and the surface to be scanned is scanned in the main scanning direction by the plurality of light beams. Means,
Beam light power detection means for detecting each power of a plurality of light beams that scan the surface to be scanned by the scanning means;
Based on the detection results of the light beam power detection means, the light beam powers for controlling the plurality of light beam generation means respectively so that the difference between the powers of the plurality of light beams scanning the surface to be scanned is less than a predetermined value. Control means;
A plurality of light receiving elements linearly arranged at intervals corresponding to a first resolution in a sub-scanning direction orthogonal to the main scanning direction, and the scanning unit uses the plurality of light receiving elements to First beam light position detecting means for detecting a passage position in the sub-scanning direction of a plurality of light beams that scan a surface to be scanned;
A plurality of light receiving elements linearly arranged in the sub-scanning direction at intervals corresponding to a second resolution different from the first resolution, and the scanning unit uses the plurality of light receiving elements to Second beam light position detecting means for detecting the passage position of the plurality of light beams that scan the surface to be scanned in the sub-scanning direction;
Based on the detection results of the first and second beam light position detection means, the passage positions of the plurality of light beams scanned by the scanning means on the surface to be scanned correspond to the first or second resolution. A light beam passage position control means for controlling the light beam to be in an appropriate position,
The beam light power detecting means includes a first light receiving element, second and third light receiving elements disposed on both sides of the first light receiving element, an integrator for integrating the output of the first light receiving element, and the integrator An A / D converter that performs A / D conversion on the integration result, and the integrator is reset when the beam light passes through the second light receiving element, and at the same time, the integration is started and the A / D conversion is started. The light beam scanning device is characterized in that the light beam is converted when the light beam passes over the third light receiving element. 2. The beam light scanning apparatus according to claim 1 , wherein the power control by the beam light power control means and the position control by the beam passage position control means are performed immediately after turning on the power of the apparatus and every predetermined time . The light beam passage position control means controls the passage position of each light beam on the surface to be scanned after the power of each light beam is controlled by the light beam power control means . Beam light scanning device. The first to third light receiving elements of the light beam power detecting means, the plurality of light receiving elements included in the first light beam position detecting means, and the plurality of light receiving elements included in the second light beam position detecting means. 2. The light beam scanning apparatus according to claim 1 , further comprising holding means for holding the element integrally . A beam light scanning device according to any one of claims 1 to 5, and an image carrier that scans and exposes the surface of the light beam from the beam light scanning device. Image forming apparatus.

Images