JP3740972B2 - Image forming apparatus and image forming method - Google Patents

Description

【００５８】
＜シーケンスフラグＦ1：第２印字シーケンス＞
第２印字シーケンスは、図９に示したように２枚目以降のカラー印字を連続して行う場合のものである。このように２枚目以降では、図４を用いて詳述したようにイエロートナー像の転写開始位置が副走査方向にずれ、また一次転写中においてもクリーナブレード４９１などの中間転写ベルト４１への離当接によってレジストズレ量が変化する。シアントナー像の一次転写中にも、図５を用いて説明したように、転写開始位置が副走査方向にずれる。しかも、ブラックトナー像についても、１枚目と同様に、一次転写している最中にクリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１に当接してレジストズレが発生する。
【００５９】
そこで、第２印字シーケンスでは、フラグＦ1が設定され、表１に示すように、このシーケンスフラグＦ1に対応してイエロートナー像Ｙ２のレジスト制御量として制御量Ｒbが設定され、シアントナー像Ｃ２のレジスト制御量として制御量Ｒcが設定され、マゼンタトナー像Ｍ２のレジスト制御量として「０」が設定されるとともに、ブラックトナー像（Ｋ２）のレジスト制御量として制御量Ｒaが設定される。
【００６０】
＜シーケンスフラグＦ2：第３印字シーケンス＞
第３印字シーケンスは、図９に示したように２枚目以降のカラー印字であるが、その直前に空転処理が行われた場合のものである。このように空転処理が存在する場合、次のｎ枚目（ｎ≧２）の画像形成を開始すると、すでに説明したように、イエロートナー像を一次転写する前に、クリーナブレード４９１が中間転写ベルト４１から離間し、転写開始位置が副走査方向にずれる（図６）。そして、続くシアンおよびマゼンタトナー像の一次転写は常時クリーナブレード４９１が中間転写ベルト４１から離間した状態で実行されるため、レジストズレは発生しないが、最後のブラックトナー像については、第１および第２印字シーケンスの場合と同様に一次転写している最中にクリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１に当接してレジストズレが発生する。
【００６１】
そこで、この印字シーケンスでは、フラグＦ2が設定され、表１に示すように、このシーケンスフラグＦ2に対応してイエロートナー像のレジスト制御量として制御量Ｒcが設定され、シアントナー像およびマゼンタトナー像のレジスト制御量として「０」が設定されるとともに、ブラックトナー像のレジスト制御量として制御量Ｒaが設定される。
【００６２】
上記のようにして印字シーケンスに対応したシーケンスフラグの更新が完了すると、そのシーケンスフラグに応じたレジスト制御量を設定した（レジスト制御量設定工程：ステップＳ５）後、各トナー像を一次転写するにあたって、感光体２１を所定の加減速可能期間の間に加減速制御して潜像形成位置を基準潜像形成位置に対して副走査方向にレジスト制御量だけシフト移動させる。これによって一次転写される中間転写ベルト４１上でのトナー像の転写位置も副走査方向にレジスト制御量だけ移動する。例えば、１枚目のカラー画像を印字する場合には、ステップＳ４で第１印字シーケンスに対応するシーケンスフラグＦ0が設定されるため、ステップＳ５でイエロートナー像Ｙ１、シアントナー像Ｃ１、マゼンタトナー像Ｍ１のレジスト制御量として「０」が設定される一方、ブラックトナー像Ｋ１のレジスト制御量として制御量Ｒaが設定される。したがって、イエロートナー像Ｙ１、シアントナー像Ｃ１、マゼンタトナー像Ｍ１は、従来例と同様に、すべて感光体２１上の所定位置、つまり基準潜像形成位置に形成されることとなり、感光体２１と同期して回転する中間転写ベルト４１に対しても同一位置で一次転写される。その結果、図１０に示すように、これら３つのトナー像Ｙ１，Ｃ１，Ｍ１の転写開始位置はすべて基準転写開始位置に一致し、しかもそれらの転写後端位置も基準転写後端位置にすべて一致している。
【００６３】
一方、ブラックトナー像Ｋ１については、レジスト制御量として制御量Ｒaが設定されていることから、図１１に示すように、タイミングＶＴ4で出力された垂直同期信号ＶSYNCを基準として加減速可能期間Ｔ11のタイミングｔ11で、感光体２１を加減速制御してブラックトナー像の潜像形成位置を基準潜像形成位置に対し副走査方向の（＋）側に制御量Ｒa（＝Ａ32／２）だけシフト移動させる。ここで、「加減速可能期間」とは、ＶＩＤＥＯ信号がＨレベルにあり、露光処理が停止している間の期間をいう。また、この加減速可能期間Ｔ11においては、１つ前のトナー像（マゼンタトナー像Ｍ１）の一次転写処理を継続中であるが、この実施形態では中間転写ベルト４１は感光体２１と同期して駆動制御されるため、感光体２１および中間転写ベルト４１の加減速制御と並行して一次転写されるトナー像に乱れは生じない。
【００６４】
上記のようにして感光体２１の上に形成された潜像を現像器２３Ｋで顕在化し、そのブラックトナー像Ｋ１を中間転写ベルト４１上に一次転写する。その結果、図１０に示すように、ブラックトナー像Ｋ１の転写開始位置は基準転写開始位置に対して（＋）方向にレジスト制御量Ｒaだけずれる。
【００６５】
そして、図１１に示すように、この一次転写処理が進行し、その後半部分に差し掛ったタイミングｔ1で、クリーナブレード４９１の動作を制御するＣＢ信号がＬレベルからＨレベルに立ち上がり、クリーナブレード４９１が中間転写ベルト４１に当接してブラックトナー像Ｋ１がその他のトナー像Ｙ１，Ｃ１，Ｍ１に対して副走査方向にずれる。さらに当該当接状態がタイミングｔ2まで継続され、その結果、レジストズレはさらに大きくなるが、最終的なブラックトナー像Ｋ１の副走査方向におけるレジストズレ量は、（−）方向にズレ量（Ａ32／２）となる。つまり、ブラックトナー像Ｋ１の転写開始位置を基準転写開始位置に対して（＋）方向にレジスト制御量Ｒaだけ移動させることで、ブラック色についての振れ幅中心ＡＣ1を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させており、こうすることで、すべてのトナー色について一次転写処理中における各トナー色ごとの副走査方向におけるレジストズレの振れ幅中心が相互に一致している。
【００６６】
この結果、この実施形態では、図１０に示すように、ブラックトナー像Ｋ１は他のトナー像Ｙ１，Ｃ１，Ｍ１に対して転写開始側で（＋）方向に（Ａ32／２）だけずれるとともに、転写後端側で（−）方向に（Ａ32／２）だけずれており、最大ズレ量はレジスト制御を行わない場合（図２および図３）の半分になる。
【００６７】
このようにしてレジスト制御量に基づきレジストズレを抑制しながら、１枚目のカラー画像の形成が完了すると、ステップＳ７で印字を終了したか否かを判断し、印字終了と判断した場合には、ステップＳ２に戻り、次の印字要求を待つ。一方、印字が終了していないと判断した場合には、ステップＳ３に戻り、上記と同様の処理を繰り返す。したがって、上記したように１枚目のカラー画像形成に続いて２枚目のカラー画像を形成する場合（第２印字シーケンス）には、ステップＳ３からさらにステップＳ４に進み、シーケンスフラグとしてフラグＦ1が設定された後、以下のようにして、レジストズレを抑えて高品質な画像形成が可能となる。
【００６８】
すなわち、ステップＳ５でそのシーケンスフラグＦ1に対応するレジスト制御量が設定される。つまり、イエロートナー像Ｙ２のレジスト制御量として制御量Ｒbが設定され、シアントナー像Ｃ２のレジスト制御量として制御量Ｒcが設定され、マゼンタトナー像Ｍ２のレジスト制御量として「０」が設定されるとともに、ブラックトナー像Ｋ２のレジスト制御量として制御量Ｒaが設定される。そして、各トナー像についてレジスト制御が実行される。
【００６９】
まず、イエロートナー像Ｙ２については、レジスト制御量として制御量Ｒbが設定されていることから、図１２に示すように、タイミングＶＴ5で出力された垂直同期信号ＶSYNCを基準として加減速可能期間Ｔ11のタイミングｔ11で、感光体２１を加減速制御してイエロートナー像の潜像形成位置を基準潜像形成位置に対して副走査方向の（＋）側に制御量Ｒbだけシフト移動させる。そして、この潜像を現像器２３Ｙで顕在化する。
【００７０】
そして、タイミングｔ1でＣＢ信号がＬレベルからＨレベルに立ち上がり、離間していたクリーナブレード４９１が中間転写ベルト４１に当接する。その後、同図の太実線で示すプロファイルでレジストズレ量が変化しながら、イエロートナー像Ｙ２の転写処理が行われて転写後端側で（＋）方向に（Ａ26／２）だけずれるが、基準トナー像（マゼンタトナー像Ｍ２）に対する最大ズレ量はレジスト制御を行わない場合（図４）に比べて大幅に縮小される。
【００７１】
このように、この実施形態では、感光体２１上での潜像形成位置をレジスト制御量Ｒbだけ基準潜像形成位置に対して副走査方向にシフト移動させることで２枚目のイエロートナー像Ｙ２の転写開始位置を調整している。これにより、イエロー色についての振れ幅中心ＡＣ2を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させている。このため、基準トナー像（マゼンタトナー像Ｍ２）に対するズレ量を振れ幅（Ａ26／２）の範囲内に抑制することができる。
【００７２】
イエロートナー像Ｙ２に続いて、シアントナー像Ｃ２の一次転写処理が行われるが、このシアントナー像Ｃ２のレジスト制御量として制御量Ｒcが設定されている。そのため、図１３に示すように、タイミングＶＴ6で出力された垂直同期信号ＶSYNCを基準として加減速可能期間Ｔ11のタイミングｔ11で、感光体２１の回転速度および中間転写ベルト４１の搬送速度Ｖを一時的に遅くすることで、一定速度で回転搬送する場合（基準トナー像、つまりマゼンタトナー像の場合）に比べて感光体２１の回転量および中間転写ベルト４１の搬送量をレジスト制御量Ｒcだけ少なくする。その結果、感光体２１上での潜像形成位置が基準潜像形成位置に対して副走査方向にレジスト制御量Ｒcだけシフト移動する。
【００７３】
そして、上記のようにして感光体２１の上に形成された潜像を現像器２３Ｃで顕在化し、そのシアントナー像Ｃ２を中間転写ベルト４１上に一次転写する。したがって、クリーナブレード４９１の離当接によるレジストズレ量（Ａ26）と、感光体２１上でのトナー像Ｃ２のシフト量Ｒcとが一致してシアントナー像Ｃ２の転写開始位置は基準転写開始位置と一致する。
【００７４】
また、シアントナー像Ｃ２の中間転写ベルト４１への一次転写処理が開始される前のタイミングｔ4でＣＢ信号がＬレベルからＨレベルに立ち上がり、当接していたクリーナブレード４９１が中間転写ベルト４１から離間しているため、一次転写処理中でのレジストズレは生じない。このため、シアントナー像Ｃ２の転写後端位置は転写後端位置と一致する。
【００７５】
このように、この実施形態では、レジスト制御量Ｒcに基づき感光体２１および中間転写ベルト４１を加減速制御することで、シアン色についての振れ幅中心ＡＣ3を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させている。このため、基準トナー像（マゼンタトナー像Ｍ２）に対するズレ量をゼロに抑制することができる。
【００７６】
シアントナー像Ｃ２に続いてマゼンタトナー像Ｍ２の一次転写処理が実行されるが、この転写処理においては、クリーナブレード４９１および二次転写ローラ４８の離当接は一切なく、マゼンタトナー像Ｍ２の転写開始位置および転写後端位置はそれぞれ基準転写開始位置および転写後端位置と一致する。
【００７７】
こうして、３色のトナー像Ｙ２，Ｃ２，Ｍ２が完了すると、次に最終トナー色、つまりブラックトナー像Ｋ２の一次転写処理が実行される。この一次転写処理では、１枚目のブラックトナー像Ｋ１の場合と同様に、感光体２１上での潜像形成位置をレジスト制御量Ｒbだけ副走査方向にシフト移動させることで、ブラック色についての振れ幅中心ＡＣ1を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させている。
【００７８】
したがって、基準トナー像に対して転写開始側で（＋）方向に（Ａ32／２）だけずれるとともに、転写後端側で（−）方向に（Ａ32／２）だけずれており、最大ズレ量はレジスト制御を行わない場合（図２および図３）の半分になる。
【００７９】
このように、２枚目についても、すべてのトナー色について、転写処理中における各トナー色ごとの副走査方向におけるレジストズレの振れ幅中心が相互に一致するように、各トナー色ごとに対応するレジスト制御量に基づき感光体２１の回転速度および中間転写ベルト４１の搬送速度を同期して加減速制御することでトナー像の転写開始位置を補正している。つまり、ここでは４色のトナー色のうちイエロー（Ｙ）、シアン（Ｃ）およびブラック（Ｋ）の３色について各トナー像の転写開始位置をレジスト制御量に基づき補正している。その結果、シアントナー像Ｃ２を基準トナー像であるマゼンタトナー像Ｍ２に完全にレジストさせることができるとともに、イエロートナー像Ｙ２およびブラックトナー像Ｋ２については基準トナー像に完全にレジストすることができないまでも、レジストズレ量を最小限に抑えることができ、高品質な画像形成が可能となる。
【００８０】
また、シーケンスフラグＦ2が設定されている場合には、イエロートナー像Ｙnのレジスト制御量として制御量Ｒcが設定され、シアントナー像Ｃnおよびマゼンタトナー像Ｍnのレジスト制御量として「０」が設定されるとともに、ブラックトナー像Ｋnのレジスト制御量として制御量Ｒaが設定される。そして、各トナー像についてレジスト制御が実行される。
【００８１】
まず、イエロートナー像Ｙnについては、レジスト制御量として制御量Ｒcが設定されていることから、図１４に示すように、タイミングＶＴ01で出力された垂直同期信号ＶSYNCを基準として加減速可能期間Ｔ11のタイミングｔ11で、感光体２１の回転速度および中間転写ベルト４１の搬送速度Ｖを一時的に遅くすることで、一定速度で回転搬送する場合（基準トナー像、つまりマゼンタトナー像の場合）に比べて感光体２１の回転量および中間転写ベルト４１の搬送量をレジスト制御量Ｒcだけ少なくする。その結果、感光体２１上での潜像形成位置が基準潜像形成位置に対して副走査方向にレジスト制御量Ｒcだけシフト移動する。
【００８２】
そして、上記のようにして感光体２１の上に形成された潜像を現像器２３Ｙで顕在化し、そのイエロートナー像Ｙnを中間転写ベルト４１上に一次転写する。したがって、クリーナブレード４９１の離当接によるレジストズレ量（Ａ26）と、感光体２１上でのトナー像Ｙnのシフト量Ｒcとが一致してイエロートナー像Ｙnの転写開始位置は基準転写開始位置と一致する。
【００８３】
また、イエロートナー像Ｙnの中間転写ベルト４１への一次転写処理が開始される前のタイミングｔ4でＣＢ信号がＬレベルからＨレベルに立ち上がり、当接していたクリーナブレード４９１が中間転写ベルト４１から離間しているため、一次転写処理中でのレジストズレは生じない。このため、イエロートナー像Ｙnの転写後端位置は転写後端位置と一致する。
【００８４】
このように、この実施形態では、レジスト制御量Ｒcに基づき感光体２１および中間転写ベルト４１を加減速制御することで、イエロー色についての振れ幅中心ＡＣ4を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させている。このため、基準トナー像（マゼンタトナー像Ｍn）に対するズレ量をゼロに抑制することができる。
【００８５】
イエロートナー像Ｙnに続いて、シアントナー像Ｃnおよびマゼンタトナー像Ｍnの一次転写処理が順次行われるが、これらの転写処理においては、クリーナブレード４９１および二次転写ローラ４８の離当接は一切なく、両トナー色についての振れ幅中心は相互に一致しており、両トナー像ＣnおよびＭnの転写開始位置および転写後端位置はそれぞれ基準転写開始位置および転写後端位置と一致する。
【００８６】
こうして、３色のトナー像Ｙn，Ｃn，Ｍnが完了すると、次に最終トナー色、つまりブラックトナー像Ｋnの一次転写処理が実行される。この一次転写処理では、第１および第２印字シーケンスの場合と同様に、レジスト制御量Ｒcに基づき感光体２１および中間転写ベルト４１を加減速制御することで、ブラック色についての振れ幅中心ＡＣ1を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0と一致させている。したがって、基準トナー像に対して転写開始側で（＋）方向に（Ａ32／２）だけずれるとともに、転写後端側で（−）方向に（Ａ32／２）だけずれており、最大ズレ量はレジスト制御を行わない場合（図２および図３）の半分になる。
【００８７】
このように、空転処理後のカラー印字についても、４色のトナー色のうちイエロー（Ｙ）およびブラック（Ｋ）の２色について各トナー像の転写開始位置をレジスト制御量に基づき補正している。つまり、すべてのトナー色について、転写処理中における各トナー色ごとの副走査方向におけるレジストズレの振れ幅中心が相互に一致するように、各トナー色ごとにレジスト制御量Ｒcに基づき感光体２１および中間転写ベルト４１を加減速制御することで、トナー像の転写開始位置を補正している。その結果、イエロートナー像Ｙn、シアントナー像Ｃnおよびマゼンタトナー像（基準トナー像）Ｍnを完全にレジストさせることができるとともに、ブラックトナー像Ｋnについては基準トナー像に完全にレジストすることができないまでも、レジストズレ量を最小限に抑えることができ、高品質な画像形成が可能となる。
【００８８】
Ｂ−３．作用効果について
以上のように、この第１実施形態によれば、転写処理の繰返し中に、転写媒体である中間転写ベルト４１への当接手段（二次転写ローラ４８やクリーナブレード４９１）の離当接を実行しているため、当接手段が中間転写ベルト４１に当接することでレジストズレが発生するが、印字シーケンス状態に応じてレジストズレを補正するために必要なレジスト制御量を求め、このレジスト制御量に基づき４色のトナー色のうち少なくとも１色以上のトナー色についてトナー像の転写開始位置を補正することでレジストズレを最小限に抑えることができる。より具体的には、この実施形態では、ブラック、イエローおよびシアン色について、一次転写処理中における各トナー色ごとの副走査方向におけるレジストズレの振れ幅中心ＡＣ1，ＡＣ2（またはＡＣ4）およびＡＣ3を基準トナー色であるマゼンタ色についての振れ幅中心ＡＣ0に一致させることで、すべてのトナー色の間でのレジストズレを最小限に抑制して高品質なカラー画像が得られる。
【００８９】
また、この実施形態では次のような作用効果が得られる。すなわち、上記のようにクリーナブレード４９１が当接してレジストズレを発生させるが、ズレ量を抑制するために例えば中間転写ベルト４１のヤング率を高くし当接時の弾性伸びを抑制することも考えられるが、これでは使用可能なベルト材質が限定されてしまい、コスト増大を招いていしまう。また、既に設計・製造されている装置に対しては、そのまま適用できず、装置改良が必要となってしまう。これに対して、上記実施形態によれば、装置構成の依存せずにレジストズレを抑制し、画像品質を向上させることができ、より汎用性の高い技術といえる。
【００９０】
さらに、この種の画像形成装置は終日通電されているのではなく、１日の業務を開始する際に電源を投入し、また１日の業務が完了すると電源を落とすのが一般的な使用態様であり、装置電源の投入のたびに、レジスト制御量の制定処理（ステップＳ１）を実行してレジスト制御量Ｒa，Ｒb，Ｒcを自動的に求めており、画像形成装置を長期間使用したとしても、常に毎日最新かつ最適なレジスト制御量Ｒa，Ｒb，Ｒcでレジストズレを補正することができ、長期間に亘って安定した高品質のカラー画像が得られる。以下、このレジスト制御量の制定処理について詳述する。
【００９１】
Ｂ−４．レジスト制御量の制定処理について
図１５は、レジスト制御量を自動的に制定する処理内容を示すフローチャートである。まず、第１実施形態にかかる画像形成装置の装置構成および動作シーケンスに基づき以下の初期設定条件を予め設定し、ＲＯＭ１２６に記憶させておく。そして、図１６に示すように、ＶSYNC信号を基準として、(1)クリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１に当接する周期Ｔ1、(2)クリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１に当接し続ける周期Ｔ2、(3)クリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１から離間する周期Ｔ3、および、(4)クリーナブレード４９１および二次転写ローラ４８が中間転写ベルト４１から離間し続ける周期Ｔ4を１ジョブとするレジスト制御量制定ジョブ（ステップＳ１１）を、所定回数、例えば２０回繰り返す（ステップＳ１２）。
【００９２】
なお、初期条件は、
Ａ2：プロセス速度（中間転写ベルト４１の周速）、
Ａ7：クリーナブレード４９１の当接からブラックトナー像の一次転写終了までの時間（図３および図１１参照）、
Ａ8：中間転写ベルト４１が一周するのに要する時間
Ａ10：クリーナブレード当接からイエロートナー像の一次転写開始までの時間（図４および図１２参照）、
Ａ12：イエロートナー像の転写開始位置からクリーナブレード離間までの時間（図４および図１２参照）、
Ａ14：ＶSYNC信号からクリーナブレード離間までの時間（図５および図１３参照）、
Ａ17：周期Ｔ1におけるＶSYNC信号からクリーナブレード当接までの時間間隔（図１６参照）、
Ａ18：周期Ｔ3におけるＶSYNC信号からクリーナブレード離間までの時間間隔（図１６参照）、
となっている。
【００９３】
また、この実施形態では、レジスト制御量制定ジョブ（ステップＳ１１）を繰り返して実行している間、帯電バイアスおよび一次転写バイアスについては常時ＯＮ状態に設定されている。また、図２４への図示を省略しているが、一次転写領域Ｒ1と感光体用クリーナブレード２４との間に除電ランプが設けられているが、この除電ランプも常時ＯＮ状態に設定されている。さらに、二次転写ローラ４８が中間転写ベルト４１に当接している間、二次転写バイアスを与えて実印字に近い状態でレジスト制御量を求めている。
【００９４】
こうして、各周期Ｔ1〜Ｔ4について、それぞれ２０個の実測値が得られると、これらの平均値Ｔ1(av)〜Ｔ4(av)をそれぞれ演算する（ステップＳ１３）。さらに、レジスト制御量Ｒa，Ｒb，Ｒcをそれぞれ以下の数式に基づき演算によって求める（ステップＳ１４）。なお、その理由について、それぞれ分けて説明する。
【００９５】
＜レジスト制御量Ｒaについて＞
図３に示すように、ブラックトナー像Ｋ１を中間転写ベルト４１に一次転写している最中に、クリーナブレード４９１の当接が開始され、例えばＡ３サイズのブラックトナー像Ｋ１の一次転写が完了する時点においてもクリーナブレード４９１の当接が継続されているため、副走査方向におけるレジストズレ量Ａ32が発生する。そのレジストズレ量Ａ32は２つの伸びＡ6，Ａ27の総和となる。つまり、
Ａ32＝Ａ6＋Ａ27
となる。
【００９６】
ここで、当接伸びＡ6は、クリーナブレード４９１が当接した状態で中間転写ベルト４１が回転搬送されることで発生する当接伸びであり、伸びＡ27は、クリーナブレード４９１が中間転写ベルト４１に当接した時の瞬間伸び（弾性分＋滑り分）と、中間転写ベルト４１に動力を伝達する駆動系（例えばギア、ベルト）の弾性変形分をあわせたものである。
【００９７】
まず、伸びＡ6について検討する。クリーナブレード４９１が当接していることで、周期差Ａ1が発生するが、この周期差Ａ1については次式、
Ａ1＝（Ｔ2(av)−Ｔ4(av)）×Ａ2×１０００
で求めることができる。そして、ブラックトナー像Ｋ１の一次転写中においてクリーナブレード４９１は所定時間Ａ7だけしか当接していないので、当接伸びＡ6は、
Ａ6＝Ａ1×Ａ7／Ａ8
となる。
【００９８】
一方、瞬間伸びＡ27は、周期Ｔ1，Ｔ4を比較することで求めることができる。すなわち、瞬間伸びＡ27は、次式
Ａ27＝（Ｔ1(av)−Ｔ4(av)）×Ａ2×１０００−Ａ15
で求めることができる。ただし、伸びＡ15は、図１６に示すように、周期Ｔ1中においてクリーナブレード４９１が所定時間Ａ17だけ当接していることによる伸びであり、この伸びＡ15は、
Ａ15＝Ａ1×（Ａ8−Ａ17）／Ａ8
で求めることができる。
【００９９】
したがって、レジストズレ量Ａ32を、
Ａ32＝Ａ6＋Ａ27
によって求めることができ、この半分の値だけ予め転写開始位置を基準転写開始位置に対して副走査方向にずらしておくことでブラックトナー像Ｋ１のレジストズレを最小限に抑えることができる。そこで、この実施形態では、レジスト制御量Ｒaを、
Ｒa＝Ａ32／２
に設定している。
【０１００】
＜レジスト制御量Ｒbについて＞
図４に示すように、ブラックトナー像Ｋ１の一次転写に続いてイエロートナー像Ｙ２を中間転写ベルト４１に一次転写する場合、クリーナブレード当接からイエロートナー像の一次転写開始までの時間Ａ10の間に副走査方向に伸びＡ30（＝Ａ27＋Ａ9）が発生している。また、一次転写が開始された後もクリーナブレード４９１が中間転写ベルト４１に当接しているために伸びＡ11が生じる反面、一次転写が完了する直前にクリーナブレード４９１が中間転写ベルト４１から離間し、縮みＡ26が発生する。したがって、同図に示すように、縮みＡ26が伸びＡ11よりも大きな場合には、レジスト制御量Ｒbを、
Ｒb＝Ａ35−Ａ26／２
ただし、Ａ35＝Ａ30＋Ａ11
に設定する一方、逆の場合（Ａ26＜Ａ11）には、レジスト制御量Ｒbを、
Ｒb＝Ａ35−Ａ11／２
に設定することで、イエロートナー像のレジストズレを最小限に抑えることができる。
【０１０１】
ここで、一次転写開始時点での伸びＡ30は、上記したように、
Ａ30＝Ａ27＋Ａ9
となるが、伸びＡ9はクリーナブレード４９１が当接した状態で中間転写ベルト４１が時間Ａ10の間だけ回転搬送されることにより生じた伸びであり、次式
Ａ9＝Ａ1×Ａ10／Ａ8
で求めることができる。
【０１０２】
また、伸びＡ11は一次転写が開始された後もクリーナブレード４９１が中間転写ベルト４１に当接しているために生じた伸びであり、次式
Ａ11＝Ａ1×Ａ12／Ａ8
で求めることができる。
【０１０３】
さらに、縮みＡ26は、クリーナブレード４９１が中間転写ベルト４１から離間したことによるものであり、周期Ｔ3，Ｔ4を比較することで求めることができる。すなわち、次式
Ａ26＝Ａ25−（Ｔ3(av)−Ｔ4(av)）×Ａ2×１０００
に基づき求めることができる。なお、同式中のＡ25は、図１６に示すように、周期Ｔ3における伸びであり、次式
Ａ25＝Ａ1×Ａ18／Ａ8
で求めることができる。
【０１０４】
＜レジスト制御量Ｒcについて＞
図５に示すように、イエロートナー像の一次転写に続いてシアントナー像を中間転写ベルト４１に一次転写する場合、当該一次転写の基準となるＶSYNC信号ＶＴ6が出力された時点でクリーナブレード４９１が中間転写ベルト４１に当接されており、その後、シアントナー像の一次転写が開始されるまでに、時間Ａ14の間だけ当接状態のまま中間転写ベルト４１が回転搬送されるため、伸びＡ13が発生する。つまり、その伸びＡ13は、
Ａ13＝Ａ1×Ａ14／Ａ8
となる。
【０１０５】
また、クリーナブレード４９１が中間転写ベルト４１から離間すると、上記＜レジスト制御量Ｒbについて＞の項で説明したように、縮みＡ26が発生する。したがって、シアントナー像の一次転写開始時点では、レジストズレ量Ａ34（＝Ａ13−Ａ26）が生じているが、一次転写をしている間では、副走査方向におけるズレは発生しない。そこで、この実施形態では、この値（レジストズレ量Ａ34）だけ予め転写開始位置を副走査方向にずらしておくことでシアントナー像のレジストズレをゼロに抑えることができるため、レジスト制御量Ｒcを、
Ｒc＝Ａ34
に設定している。
【０１０６】
以上のように、このレジスト制御量制定処理においては、カラー画像を形成するための印字シーケンス（図１）と異なる専用シーケンス（図１６）で行っているので、高精度なレジスト制御を行う上で欠くことのできないレジスト制御量Ｒa，Ｒb，Ｒcを正確に求めることができる。
【０１０７】
なお、この実施形態では、中間転写ベルト４１が１周するたびに基準信号たる垂直同期信号ＶSYNCが１回出力されるように構成されているが、例えば中間転写ベルト４１に複数の基準位置が設けられており、中間転写ベルト４１が１周する間に基準信号が複数回出力される場合にも本発明を適用することができることはいうまでもない。特に、この場合、上記各周期を短く設定することができる。
【０１０８】
また、このレジスト制御量の制定処理においては、二次転写ローラ４８を中間転写ベルト４１に当接している間、二次転写バイアスを与えているが、これはレジスト制御量を制定する上で必須の要件ではなく、二次転写バイアスを与えない、あるいは二次転写バイアスと逆極性のバイアスを与えるようにしてもよく、それぞれの場合で以下のような効果が得られる。すなわち、二次転写バイアスを与えない場合には、レジスト制御量の制定処理を簡素化することができる。また、二次転写バイアスを与えた場合には、二次転写ローラ４８によって中間転写ベルト４１や感光体／ベルト駆動部４１ａに対して与える負荷が実印字状態に近づき、レジスト制御量を正確に求めることができる。さらに、逆極性のバイアスを与える場合には、二次転写ローラ４８に付着したトナーを中間転写ベルト４１側に戻して二次転写ローラ４８をクリーニングして二次転写ローラ４８によるシート部材の裏汚れを防いで、良好な印字結果を得ることができる。
【０１０９】
また、上記したレジスト制御量の制定処理では、一次転写バイアスを中間転写ベルト４１に与えて実印字に近い状態でレジスト制御量を求めているため、レジスト制御量を正確に求めることができる。
【０１１０】
さらに、上記したレジスト制御量の制定処理では、駆動開始からレジスト制御量制定ジョブ（ステップＳ１１）を２０回繰り返し（ステップＳ１２）、周期Ｔ1〜Ｔ4の実測値をそれぞれ２０個ずつ測定し、これらの実測値に基づきレジスト制御量を求めている。しかしながら、駆動開始直後において、中間転写ベルト４１の回転搬送が安定していないことがあり、このような状態で実測した周期Ｔ1〜Ｔ4に基づきレジスト制御量を求めたのでは、レジスト制御量の精度が低下してしまうおそれがある。そこで、このような問題を解消するためには、駆動開始から所定回数だけ中間転写ベルト４１が回転搬送され、その動作が安定した後で、各周期Ｔ1〜Ｔ4を実測し、それらの実測値に基づきレジスト制御量を求めるようにすればよく、こうすることで、レジスト制御量を精度良く求めることができる。
【０１１１】
Ｃ．第２実施形態
ところで、上記第１実施形態では、レジスト制御量に応じて転写開始位置を調整するために、感光体２１と中間転写ベルト４１とを同期して可変速制御することで、感光体２１上での潜像形成位置をレジスト制御量に応じて副走査方向にシフト移動させている。ここで、感光体２１上での潜像形成位置をシフト移動させる方法としては、上記感光体／ベルト駆動制御以外に、露光タイミングを制御することでも可能である。また、感光体／ベルト駆動制御と露光タイミング制御とを組み合わせてもよく、この実施形態について図１７ないし図２０を参照しつつ説明する。
【０１１２】
図１７は、この発明にかかる画像形成装置の第２実施形態の動作を示すフローチャートである。この第２実施形態では、第１実施形態と同様にして各シーケンスフラグに応じたレジスト制御量が設定される（ステップＳ４）と、そのレジスト制御量に基づき感光体２１および中間転写ベルト４１を可変速可能期間Ｔ11で可変速制御する（ステップＳ６）とともに、露光開始タイミングを早めたり、遅くすることで、感光体２１上での潜像形成位置を副走査方向にシフト移動させる（ステップＳ８）。
【０１１３】
このように感光体／ベルト駆動制御（ステップＳ６）と露光タイミング制御（ステップＳ８）とを組み合わせることは、レジスト制御量が比較的大きい場合に効果的である。というのも、例えば第２印字シーケンスにおけるイエロートナー像Ｙ２やシアントナー像Ｃ２を転写する場合、また第３印字シーケンスにおけるイエロートナー像Ｙnを転写する場合、レジスト制御量は比較的大きく、感光体／ベルト駆動制御のみによってレジストズレを補正しようとすれば、その分、感光体２１の回転速度およびベルト搬送速度Ｖの変化率を大きく設定する必要があり、感光体／ベルト駆動制御の精度低下やモータ負荷が増大してしまう。
【０１１４】
これに対して、第２印字シーケンスのイエロートナー像Ｙ２を転写する際、図１８に示すように、露光タイミング制御によって副走査方向に１ドットライン分、つまり副走査方向のライン間隔Ｒeだけ（＋）方向にずれるように設定しておくことで、感光体／ベルト駆動制御による潜像形成位置のシフト移動量をΔＲb（＜Ｒb）に抑えることができる。
【０１１５】
また、第２印字シーケンスのシアントナー像Ｃ２を転写する際、図１９に示すように、露光タイミング制御によって予め副走査方向に１ドットライン分、つまり副走査方向のライン間隔Ｒeだけ（−）方向にずれるように設定しておくことで、感光体／ベルト駆動制御による潜像形成位置のシフト移動量をΔＲc（＜Ｒc）に抑えることができる。
【０１１６】
さらに、第３印字シーケンスのイエロートナー像Ｙnを転写する際、図２０に示すように、露光タイミング制御によって予め副走査方向に１ドットライン分、つまり副走査方向のライン間隔Ｒeだけ（−）方向にずれるように設定しておくことで、感光体／ベルト駆動制御による潜像形成位置のシフト移動量をΔＲc（＜Ｒc）に抑えることができる。したがって、中間転写ベルト４１を回転駆動するモータに対して過剰な負荷がかかるのを防止し、また感光体／ベルト駆動制御を高精度に行うことができる。
【０１１７】
なお、この第２実施形態では、露光タイミング制御によって１ドットラインＲeだけ感光体２１上での潜像形成位置を副走査方向にずらしている（ステップＳ８）が、レジスト制御量が大きい場合には複数ドットライン分ずらすように露光タイミング制御してもよい。
【０１１８】
また、上記第２実施形態では、レジスト制御を行うために露光タイミング制御と感光体／ベルト駆動制御とを組み合わせているが、露光タイミング制御のみで感光体２１上での潜像形成位置をレジスト制御量に応じてシフト移動するようにしてもよい。
【０１１９】
Ｄ．第３実施形態
上記実施形態では、装置電源の投入後にレジスト制御量制定工程（ステップＳ１）を実行して３種類のレジスト制御量Ｒa，Ｒb，Ｒcを自動的に制定し、記憶部たるＲＡＭ１２５に記憶し、シーケンスフラグの更新処理（ステップＳ４）によって印字シーケンスに対応するシーケンスフラグを更新・設定することで印字シーケンスに対応するレジスト制御量を設定しているが、レジスト制御量制定工程（ステップＳ１）によって求められた３種類のレジスト制御量Ｒa，Ｒb，Ｒcを印字シーケンスと対応したテーブル形式で記憶するようにしてもよい。
【０１２０】
すなわち、３つの印字シーケンスに１対１で対応してシーケンスフラグＦ0，Ｆ1，Ｆ2が設けられているが、表１に示すようにシーケンスフラグと、各シーケンスフラグに対応する印字シーケンスに応じたレジスト制御量とを相互に関連付けた状態でＲＡＭ１２５に記憶してもよい。この場合、シーケンスフラグの更新処理（ステップＳ４）によって印字シーケンスに対応するシーケンスフラグが設定されると、そのシーケンスフラグに対応するレジスト制御量をＲＡＭ１２５中のテーブルから一括して読み出し、当該レジスト制御量に基づき４色のトナー色のうち少なくとも１色以上のトナー色についてトナー像の転写開始位置を補正することで、上記実施形態と同様の効果が得られる。
【０１２１】
Ｄ．第４実施形態
図２１は、この発明にかかる画像形成装置の第４実施形態の動作を示すフローチャートである。この第４実施形態にかかる画像形成装置が第１実施形態と大きく相違する点は、この第４実施形態ではレジスト制御量の制定処理の開始条件が追加されている点である。すなわち、第１実施形態では装置電源が投入されると直ちにレジスト制御量制定ジョブが実行されているが、この第４実施形態ではステップＳ１０で温度センサ５１からの出力（定着ローラ温度）をＣＰＵ１２１が受け、定着ローラ温度が所定の制定開始温度ＴＰ0を超えたか否かを判断し、定着ローラ温度が制定開始温度を超えることを条件としてレジスト制御量制定ジョブを開始している。その理由は以下のとおりである。
【０１２２】
この種の画像形成装置では、図２２に示すように、電源投入前における定着ユニットの定着ローラ温度は低温となっており、タイミングｔ11で装置電源が投入されると、ウォーミングアップ処理が開始される。このウォーミングアップ処理の一動作として定着ローラが加熱され、所定の定着温度になった時点でウォーミングアップ処理が完了し、画像形成を開始することが可能となる。したがって、このウォーミングアップ処理中にレジスト制御量の制定処理を完了することができれば、ウォーミングアップ処理完了後、直ちに画像形成処理に移ることができる。それ故、ウォーミングアップ処理中にレジスト制御量の制定処理（ステップＳ１）を完了するのが望ましい。
【０１２３】
ここで、第１実施形態のようにウォーミングアップ処理の開始、つまり装置電源の投入直後にレジスト制御量の制定処理（ステップＳ１）を実行すれば、ウォーミングアップ処理の完了前にレジスト制御量の制定処理（ステップＳ１）を確実に完了することができる。しかしながら、定着ローラ温度が十分に上昇せず、実印字時の装置環境から離れた状態でレジスト制御量の制定処理（ステップＳ１）が実行されることとなり、正確なレジスト制御量を得ることができない場合がある。
【０１２４】
そこで、第４実施形態の如く、定着ローラ温度が所定の制定開始温度ＴＰ0まで上昇し、実印字時の装置環境に近づいた後でレジスト制御量の制定処理を開始すれば、レジスト制御量をより正確に求めることができる。また、この制定開始温度ＴＰ0を設定するにあたっては、この設定温度に達した時点でレジスト制御量の制定処理を開始したとしても、ウォーミングアップ処理完了前に当該制定処理が完了するのが望ましい。このような制定開始温度ＴＰ0を選択設定することで、装置パフォーマンスを落とすことなく、しかも実印字時に近い状態でレジスト制御量を正確に求めることができる。
【０１２５】
Ｅ．第５実施形態
上記第１実施形態では、装置電源の投入後のレジスト制御量制定工程（ステップＳ１）によってレジスト制御量Ｒa，Ｒb，Ｒcを自動的に制定し、ＲＡＭ１２５に記憶させているが、装置電源の投入毎のレジスト制御量制定工程の実行が必須というわけではなく、レジスト制御量制定工程の実行条件については任意に設定することができ、次のように連続する印字処理中に行うようにしてもよい。
【０１２６】
この種の画像形成装置では、メインコントローラ１１に対して外部装置から画像形成指令が与えられると、メインコントローラ１１はこの画像形成指令を１または複数のジョブデータに変換してエンジンコントローラ１２に順次与える。例えば、外部装置からＡ４サイズの文書を５頁印字する旨の画像形成指令がメインコントローラ１１に送信されると、本実施形態にかかる画像形成装置では、メインコントローラ１１は画像形成指令をエンジン部Ｅの動作指示に適した形式とすべく、次の３つのジョブデータに変換する。
【０１２７】
(1)Ａ４サイズの文書を２頁分印字するジョブ；
(2)Ａ４サイズの文書を２頁分印字するジョブ；
(3)Ａ４サイズの文書を１頁分印字するジョブ；
そこで、ジョブとジョブの間でレジスト制御量制定工程を実行するようにしてもよい。このように、一のカラー画像を形成した後で、しかも次のカラー画像を形成する前にレジスト制御量制定工程を実行するようにしてもよい。
【０１２８】
また、レジスト制御量制定工程を、装置電源の投入から所定時間だけ経過した時点、装置電源の投入から所定枚数だけ印字処理を実行した時点、または上記ジョブを所定回数だけ繰り返した時点などに行うようにしてもよく、このように装置の稼動状況に基づきレジスト制御量制定工程の実行タイミングを決定してもよい。
【０１２９】
Ｆ．第６実施形態
上記実施形態では、装置の稼動中にレジスト制御量制定工程を実行することでレジスト制御量を求めているが、レジスト制御量制定工程の代わりに予めレジスト制御量を求めておき、ＲＯＭ１２６に記憶させるように構成してもよい。例えば、転写ユニット４に対して記憶手段を組み込んでおき、転写ユニット４の組立段階で当該転写ユニット４のみを単独で駆動させてレジスト制御量を求め、転写ユニット４の記憶手段に記憶させるようにしてもよい。この場合、転写ユニット４の製造組立時点でレジスト制御量を求めることができ、他のユニット、例えば像担持体ユニット２や露光ユニット３などの完成を待つことなく、レジスト制御量を求めることができるため、装置全体の組立作業効率を向上させることができる。
【０１３０】
また、画像形成装置全体が組み上がった段階でレジスト制御量を求め、ＲＯＭ１２６に記憶するようにしてもよい。こうすることで、転写ユニット４以外のユニットがレジスト制御量に与える影響を反映した結果が得られ、転写ユニット４単独でレジスト制御量を求める場合に比べて精度の高いレジスト制御量が得られる。
【０１３１】
Ｇ．第７実施形態
中間転写ベルト４１や周辺各部は温度・湿度などの装置内部環境の影響を受けやすい。そこで、装置内部の温度・湿度を計測し、その計測値に基づきレジスト制御量を補正することで、より高精度なレジスト補正を行い、高品質な画像を得ることができる。
【０１３２】
また、消耗品の交換や装置メンテナンスなどのために装置カバーを開いて作業を行う場合があるが、このカバー開動作に伴って装置内部の温度・湿度は大きく変化する場合がある。ここで、上記のように温・湿度センサなどで直接装置内部の温度・湿度を計測し、レジスト制御量を補正するようにしてもよいが、カバーが開いているという情報に基づきレジスト制御量の補正が必要であると判断してレジスト制御量制定工程を実行するようにしてもよい。
【０１３３】
さらに、装置内部の温度・湿度に影響を与える因子として、エナジーセーブモード（スリープモード）の設定がある。というのも、このモードでは印字処理以外では定着ユニットを停止もしくは低温制御している。したがって、エナジーセーブモードからの復帰時には温度低下が認められる可能性が高いため、エナジーセーブモードから復帰したという情報に基づき、復帰直後あるいは所定時間経過後にレジスト制御量制定工程を実行してもよい。このような情報については、一般的に「装置のステータス」として称されるものであり、ステータスに基づきレジスト制御量制定工程の実行タイミングを決定することで装置内部の環境に適合したレジスト制御量を適宜求めることができ、高品質なカラー画像が得られる。
【０１３４】
Ｈ．第８実施形態
図２３は、この発明にかかる画像形成装置の第８実施形態の動作シーケンスを示すタイミングチャートである。この第８実施形態では、レジスト制御量の制定処理（ステップＳ１）を実行するのに先立って、感光体用クリーナブレード２４にブラックトナーを供給することで、次のような問題が発生するのを未然に防止している。すなわち、感光体用クリーナブレード２４にトナーが存在しない状態のままレジスト制御量制定ジョブを繰り返すと、その間にクリーナブレード２４のメクレが発生してしまう。また、感光体用クリーナブレード２４と感光体２１との間で非常に大きな摩擦力が作用して感光体２１を回転駆動するモータに大きな負荷を与えて実印字状態から外れ、モータ制御性も低下してしまう。しかしながら、以下に説明するように構成された第８実施形態では、これらの問題発生を未然に防止することができる。
【０１３５】
この第８実施形態では、装置電源が投入されると、感光体２１および中間転写ベルト４１を回転駆動する駆動モータの駆動を開始する。ここでは、帯電ローラ２２への帯電バイアスおよび一次転写バイアスは常時ＯＦＦ状態に設定されている。
【０１３６】
それに続いて、ブラック用現像器２３Ｋの離当接制御信号がＬレベルからＨレベルに立ち上がり、ΔＴ40のタイムラグを経てブラック用現像器２３Ｋが当接する。このようにタイムラグΔＴ40が生じるのは、図２４の画像形成装置では、カム機構を利用して各現像器を感光体２１に対して離当接駆動しているからである。そして、再度、ブラック用現像器２３Ｋの離当接制御信号がＬレベルからＨレベルに立ち上がると、ブラック用現像器２３Ｋは感光体２１から離間する。こうして、ブラック用現像器２３Ｋが感光体２１に当接している間、感光体２１に対してブラックトナーが付着されてブラック印字処理が実行される。
【０１３７】
こうして、感光体２１に付着されたブラックトナーは感光体用クリーナブレード２４によって感光体２１から除去され、感光体用クリーナブレード２４へのブラックトナー供給が完了する。なお、この実施形態では、ブラックトナーを感光体用クリーナブレード２４に供給しているが、ブラックトナーの代わりに他のトナーを供給するようにしてもよい。
【０１３８】
また、上記のようにしてブラック印字を行うとともに、その印字後にクリーナブレード４９１を所定タイミングで一定時間だけ当接させているが、これは次の理由に基づくものである。この実施形態では、一次転写バイアスをＯＦＦ状態としているが、感光体２１上のブラックトナーの一部、例えば１０％程度が中間転写ベルト４１に付着する。そこで、この付着トナーを中間転写ベルト４１から取り除くために、上記のように適用なタイミングでクリーナブレード４９１を中間転写ベルト４１に当接させている。
【０１３９】
以上のように、この第８実施形態によれば、常時感光体２１に当接している感光体用クリーナブレード２４にトナーを供給した後、レジスト制御量の制定処理（ステップＳ１）を実行しているので、レジスト制御量制定ジョブを繰り返している間、感光体用クリーナブレード２４が捲れるのを防止し、また感光体用クリーナブレード２４と感光体２１との間の摩擦力を低減し、実印字に近い状態でレジスト制御量の制定処理（ステップＳ１）を実行することができ、レジスト制御量をより正確に求めることができる。
【０１４０】
Ｉ．その他
なお、本発明は上記した実施形態に限定されるものではなく、その趣旨を逸脱しない限りにおいて上述したもの以外に種々の変更を行うことが可能である。例えば、上記実施形態では、マゼンタ色を基準トナー色とし、その他のトナー色（イエロー、シアンおよびブラック色）の振れ幅中心がマゼンタ色について振れ幅中心に一致させているが、マゼンタ色以外のトナー色を基準トナー色としてもよい。ただし、この実施形態では、４つのトナー色をイエロー（Ｙ）、シアン（Ｃ）、マゼンタ（Ｍ）およびブラック（Ｋ）の順番で行い、マゼンタのトナー像が第３番目に一次転写されるため、上記したように当接手段（二次転写ローラ４８やクリーナブレード４９１）の離当接による影響を最も受けないため、マゼンタ色は基準トナー色とする上で好適であるといえる。また、基準トナー色を設けずに、すべてのトナー色についての振れ幅中心を適当な位置、例えば図５に示すように直線ＡＣ00（「副走査方向におけるレジストズレ量＝ｋ」）で相互に一致させるようにしてもよい。この場合、すべてのトナー色についてトナー像の転写開始位置を補正することになる。
【０１４１】
また、上記実施形態では、すべてのトナー色について各振れ幅中心を相互に一致させているが、４種類のトナー色のうち少なくとも２色について各振れ幅中心を相互に一致させることによって画像品質を向上させることが可能である。
【０１４２】
また、上記実施形態では、感光体２１と中間転写ベルト４１とを同一の感光体／ベルト駆動部（駆動手段）４１ａで駆動制御することで両者を同期して駆動しているが、感光体２１を駆動制御する感光体駆動部と、中間転写ベルト４１を駆動制御するベルト駆動部とを設け、これらの感光体駆動部とベルト駆動部とで本発明にかかる「駆動手段」が構成され、この駆動手段によって感光体２１と中間転写ベルト４１とを同期駆動するようにしてもよい。
【０１４３】
また、上記のように感光体駆動部とベルト駆動部とを別個に設けた場合には、感光体２１を一定速度で回転駆動する一方、中間転写ベルト４１のうちトナー像の形成されない領域が一次転写領域Ｒ1に位置している期間（一次転写を行わない期間）において、レジスト制御量に基づき中間転写ベルト４１のみを可変速制御して転写開始位置を調整するようにしてもよい。
【０１４４】
また、上記実施形態では、３種類の印字シーケンスに１対１で対応して識別変数としてシーケンスフラグＦ0，Ｆ1，Ｆ2を設定しているが、これ以外に特定の文字や数字などの識別変数を用いてもよい。
【０１４５】
また、上記実施形態では、３種類の印字シーケンスに区分けし、各印字シーケンスに対応する識別変数をそれぞれ設定しているが、印字シーケンスの区分け数はこれに限定されるものではなく、区分け数が２以上であれば、上記実施形態と同様の作用効果、つまりシーケンスが変化するごとにレジスト制御量を新たに求め直す必要がなくなり、優れた制御性が得られる。
【０１４６】
また、上記実施形態では、中間転写ベルト４１を回転駆動する駆動源としてＤＣモータを採用し、レジスト制御量に基づきＤＣモータを加減速制御することでレジスト制御しているが、ＤＣモータの代わりにステッピングモータなどのパルスモータを用い、レジスト制御量に基づきパルス駆動制御することでレジスト制御するようにしてもよい。
【０１４７】
また、上記実施形態にかかる画像形成装置は、ホストコンピュータなどの外部装置よりインターフェース１１２を介して与えられた画像を複写紙、転写紙、用紙およびＯＨＰ用透明シートなどのシート部材に印字するプリンタであるが、本発明は複写機やファクシミリ装置などの電子写真方式のカラー画像形成装置、つまり複数色のトナーを重ね合わせてカラー画像を形成する画像形成装置全般に適用することができる。
【０１４８】
さらに、上記実施形態では、感光体２１上に形成されたトナー像を中間転写ベルト４１上に転写する転写工程を、各トナー色について実行して中間転写ベルト４１上にカラー画像を形成しているが、中間転写ベルト以外の転写媒体（転写ドラム、転写ベルト、転写シート、中間転写ドラム、中間転写シート、反射型記録シートあるいは透過性記憶シートなど）にトナー像を転写してカラー画像を形成する画像形成装置にも本発明を適用することができる。
【０１４９】
【発明の効果】
以上のように、この発明によれば、転写処理の繰返し中に、転写媒体への当接手段の離当接を実行しているので、当接手段が転写媒体に当接することでレジストズレが発生するが、レジストズレを補正するために必要なレジスト制御量を求め、このレジスト制御量に基づき複数のトナー色のうち少なくとも１色以上のトナー色についてトナー像の転写開始位置を補正しているので、レジストズレを抑制して高品質なカラー画像を得ることができる。
【０１５０】
また、この発明では、装置電源の投入のたびにレジスト制御量を求めるように構成しているので、画像形成装置を長期間使用したとしても、常に毎日最新かつ最適なレジスト制御量でレジストズレを補正することができ、長期間に亘って安定した高品質のカラー画像を得ることができる。
【図面の簡単な説明】
【図１】この発明に適用対象である画像形成装置における動作タイミングの一例を示すタイミングチャートである。
【図２】レジスト制御を行うことなしに図１の動作タイミングで一次転写処理を行った場合の各トナー像のレジスト状況を模式的に示す図である。
【図３】レジスト制御を行うことなしにブラックトナー像を転写した際のレジストズレ状況を示す図である。
【図４】レジスト制御を行うことなしにイエロートナー像を転写した際のレジストズレ状況を示す図である。
【図５】レジスト制御を行うことなしにシアントナー像を転写した際のレジストズレ状況を示す図である。
【図６】レジスト制御を行うことなしにイエロートナー像を転写した際のレジストズレ状況を示す図である。
【図７】この発明にかかる画像形成装置の実施形態を示す電気的構成図である。
【図８】第１実施形態にかかる画像形成装置の動作を示すフローチャートである。
【図９】図８のシーケンスフラグの更新内容を示すフローチャートである。
【図１０】レジスト制御しながら、図１の動作タイミングで一次転写処理を行った場合の各トナー像のレジスト状況を模式的に示す図である。
【図１１】図８に示す画像形成装置においてブラックトナー像を転写する際のレジスト制御内容を示す図である。
【図１２】図８に示す画像形成装置においてイエロートナー像を転写する際のレジスト制御内容を示す図である。
【図１３】図８に示す画像形成装置においてシアントナー像を転写する際のレジスト制御内容を示す図である。
【図１４】図８に示す画像形成装置においてイエロートナー像を転写する際のレジスト制御内容を示す図である。
【図１５】レジスト制御量を自動的に制定する処理内容を示すフローチャートである。
【図１６】レジスト制御量制定ジョブの内容を示すタイミングチャートである。
【図１７】この発明にかかる画像形成装置の第２実施形態の動作を示すフローチャートである。
【図１８】図１７に示す画像形成装置においてイエロートナー像を転写する際のレジスト制御内容を示す図である。
【図１９】図１７に示す画像形成装置においてシアントナー像を転写する際のレジスト制御内容を示す図である。
【図２０】図１７に示す画像形成装置においてイエロートナー像を転写する際のレジスト制御内容を示す図である。
【図２１】この発明にかかる画像形成装置の第４実施形態の動作を示すフローチャートである。
【図２２】図２４に示す画像形成装置におけるレジスト制御量の制定開始条件を示すグラフである。
【図２３】この発明にかかる画像形成装置の第８実施形態の動作シーケンスを示すタイミングチャートである。
【図２４】この発明の背景技術となる画像形成装置の構成を示す図である。
【符号の説明】
１…制御ユニット（制御手段）
３…露光ユニット（露光手段）
４…転写ユニット
５…定着ユニット（定着手段）
１１…メインコントローラ
１２…エンジンコントローラ（制御手段）
２１…感光体
２３…現像部
２３Ｙ，２３Ｃ，２３Ｍ，２３Ｋ…現像器
２４…感光体用クリーナブレード
４０…垂直同期用読取センサ
４１…中間転写ベルト（転写媒体）
４１ａ…感光体／ベルト駆動部（駆動手段）
４８…二次転写ローラ（当接手段）
５１…温度センサ
１２１…ＣＰＵ（制御手段）
１２２…感光体／ベルト駆動制御回路（駆動手段）
１２３…転写ローラ離当接制御回路
１２４…ベルトクリーナ離当接制御回路
４９１…クリーナブレード（当接手段）
Ｃ１，Ｃ２…シアントナー像
Ｅ…エンジン部
Ｋ１…ブラックトナー像
Ｍ１，Ｍ２…マゼンタトナー像
Ｒa，Ｒb，Ｒc…レジスト制御量
Ｔ1〜Ｔ4…周期
ＴＰ0…制定開始温度
ＶSYNC…垂直同期信号
Ｖ…ベルト搬送速度
Ｙ１，Ｙ２…イエロートナー像[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method for forming a color image by superimposing a plurality of color toners, and in particular, a toner image formed on a photoreceptor is transferred to an intermediate transfer belt, an intermediate transfer drum, A transfer process of transferring onto a transfer medium such as a transfer sheet is performed for each toner color to form a color image on the transfer medium.
[0002]
[Prior art]
An example of this type of image forming apparatus is shown in FIG. This image forming apparatus is an apparatus that forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), and is supplied from an external device such as a host computer. When an image signal is given to a control unit (not shown), each part of the engine unit E is controlled in accordance with a command from the control unit to correspond to the image signal on the sheet member S such as transfer paper, copy paper, or OHP sheet. The image to be formed is formed.
[0003]
In the engine unit E, a toner image can be formed on the photoconductor 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photosensitive member 21 that can rotate in the direction of the arrow in FIG. 24, and further, a charging roller 22 as a charging unit and a developing unit around the photosensitive member 21 along the rotating direction. Developing units 23Y, 23C, 23M, and 23K, and a photoreceptor cleaner blade 24 are disposed.
[0004]
In this apparatus, the charging roller 22 contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface, and then the laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21. As shown in the figure, the exposure unit 3 includes a light emitting element 31 such as a semiconductor laser that is modulated and driven in accordance with an image signal. The laser light L from the light emitting element 31 is rotationally driven by a high speed motor 32. Is incident on the polygon mirror 33. The laser beam L reflected by the polygon mirror 33 scans the photoconductor 21 via the lens 34 and the mirror 35 in the main scanning direction (direction perpendicular to the paper surface of the figure) and corresponds to the image signal. An electrostatic latent image is formed. Reference numeral 36 denotes a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal HSYNC.
[0005]
The electrostatic latent image thus formed is developed with toner by the developing unit 23. That is, in this embodiment, as the developing unit 23, a yellow developing unit 23Y, a cyan developing unit 23C, a magenta developing unit 23M, and a black developing unit 23K are arranged along the photoconductor 21 in this order. Has been. These developing units 23Y, 23C, 23M, and 23K are configured so as to be freely contacted and separated from the photosensitive member 21, and according to instructions from the control unit, the above four developing units 23Y, 23C, 23M, and 23K. One of the developing devices selectively contacts the photoconductor 21 and a high voltage is applied to apply toner of the selected color to the surface of the photoconductor 21 so that an electrostatic latent image on the photoconductor 21 is applied. To manifest.
[0006]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in the primary transfer region R1 positioned between the black developing device 23K and the photoreceptor cleaner blade 24. Further, a photoreceptor cleaner blade 24 is disposed at a position advanced in the circumferential direction (arrow direction in FIG. 24) from the primary transfer region R1, and remains attached to the outer peripheral surface of the photoreceptor 21 after the primary transfer. Scrape off the toner.
[0007]
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes rollers 42 to 47, an intermediate transfer belt 41 stretched between the rollers 42 to 47, and an intermediate toner image transferred to the intermediate transfer belt 41 on the sheet member S. A secondary transfer roller 48 for secondary transfer, and a photoconductor / belt drive unit (not shown) that drives the photoconductor 21 and the intermediate transfer belt 41 to rotate synchronously are provided. When a color image is transferred to the sheet member S, each color toner image formed on the photoreceptor 21 is superimposed on the intermediate transfer belt 41 to form a color image, and A sheet member S is taken out from the cassette 61, the manual feed tray 62, or an additional cassette (not shown) by the paper supply unit 63 and conveyed to the secondary transfer region R2. Further, a full color image is obtained by secondary transfer of the color image to the sheet member S.
[0008]
Note that toner remaining on the outer peripheral surface of the intermediate transfer belt 41 after the secondary transfer is removed by a cleaner blade 491 provided in the belt cleaner 49. In other words, the belt cleaner 49 is disposed so as to face the roller 46 with the intermediate transfer belt 41 interposed therebetween, and the cleaner blade 491 comes into contact with the intermediate transfer belt 41 at an appropriate timing and remains on the outer peripheral surface thereof. Scrape off the toner.
[0009]
A sensor 40 for detecting the reference position of the intermediate transfer belt 41 is disposed in the vicinity of the roller 43, and obtains a synchronization signal in the sub-scanning direction substantially perpendicular to the main scanning direction, that is, a vertical synchronization signal VSYNC. Functions as a vertical synchronization reading sensor.
[0010]
The sheet member S on which the toner image is transferred by the transfer unit 4 as described above is transferred to the secondary transfer region R2 along a predetermined paper feed path (two-dot chain line) by the paper feed unit 63 of the paper feed / discharge unit 6. The toner image on the sheet member S conveyed to the fixing unit 5 disposed on the downstream side is fixed to the sheet member S. Then, the sheet member S is further transported to the paper discharge unit 64 along the paper feed path, and then discharged to the standard paper discharge tray.
[0011]
[Problems to be solved by the invention]
By the way, the image forming apparatus configured as described above uses the vertical synchronization signal VSYNC output from the vertical synchronization reading sensor 40 in order to superimpose a plurality of color toner images while registering each other. That is, each time the vertical synchronization signal VSYNC is output, a toner image is formed on the photoconductor 21 at a predetermined timing, and then the toner image is formed on the intermediate transfer belt 41 that rotates at a constant conveyance speed in synchronization with the photoconductor 21. The toner images of a plurality of colors are accurately superimposed by controlling the resist in this way. Therefore, it is necessary to rotate and convey the intermediate transfer belt 41 at a constant speed in synchronization with the photosensitive member 21 until the primary transfer is completed after the vertical synchronization signal VSYNC is output.
[0012]
However, as described above, the secondary transfer roller 48 and the cleaner blade 491 are temporarily in contact with the intermediate transfer belt 41 at an appropriate timing. Therefore, the contact prevents the intermediate transfer belt 41 from being rotated and conveyed, the intermediate transfer belt 41 elastically stretches, and the drive system (for example, a gear or belt) that transmits power to the intermediate transfer belt 41 is also elastic. In addition, a load is applied to a belt driving unit (not shown) that rotationally drives the intermediate transfer belt 41, and the intermediate transfer belt 41 is not rotated and conveyed at a constant speed due to the separation and contact. As a result, the secondary transfer roller 48 or the cleaner blade 491 separates and comes into contact with the intermediate transfer belt 41, so that the toner images are deviated from each other, that is, registration deviation occurs. In some cases, it caused a drop.
[0013]
The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus and an image forming method capable of forming a high-quality image.
[0014]
[Means for Solving the Problems]
In the present invention, a transfer process for transferring a toner image formed on a photoconductor to a transfer medium that is rotationally driven in the sub-scanning direction is repeated for a plurality of different toner colors, and the toner images of the respective toner colors are superimposed. The present invention relates to an image forming apparatus and an image forming method for forming a color image, and has the following configuration in order to achieve the above object.
[0015]
The image forming apparatus according to the present invention includes a contact unit that temporarily contacts the transfer medium when the transfer process is repeated, and the contact unit that comes into contact with the transfer medium. Based on the registration control amount necessary for correcting the relative registration shift of the toner image on the transfer medium, the transfer start position of the toner image is corrected for at least one of the plurality of toner colors. Control means and reference signal detection means for outputting a reference signal in relation to the rotation operation of the transfer medium are provided.
[0016]
The image forming method according to the present invention also provides a relative registration shift of the toner image on the transfer medium caused by the contact means temporarily contacting the transfer medium when the transfer process is repeated. A registration control amount establishment step for obtaining a registration control amount required to correct the toner, and a correction for correcting a transfer start position of a toner image for at least one of the plurality of toner colors based on the registration control amount And a reference signal detection step of outputting a reference signal in relation to the rotation operation of the transfer medium.
[0017]
In the invention configured as described above, the abutting means comes into contact with the transfer medium while the transfer process is repeated. In this case, as described above, the registration deviation occurs when the contact means abuts against the transfer medium. In the present invention, the registration deviation is corrected as follows. That is, based on the reference signal, (1) a period when the abutting means that is separated from the transfer medium abuts on the transfer medium, and (2) when the abutting means continues to abut on the transfer medium. And (3) a cycle when the abutting means that has been in contact with the transfer medium is separated from the transfer medium, and (4) a period when the abutment means continues to be separated from the transfer medium. Then, a registration control amount necessary for correcting the registration deviation is obtained from the difference between the periods, and based on the registration control amount, the toner image transfer start position for at least one toner color among the plurality of toner colors is obtained. Is corrected. Therefore, a high-quality color image can be obtained while suppressing registration error.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present invention utilizes the basic principle first discovered by the inventor of the present invention. Hereinafter, after describing the basic principle of the present invention, the present embodiment using the basic principle will be described in detail.
[0019]
A. Basic principles of the invention
Conventionally, when the primary transfer process is repeated, if a contact means such as a secondary transfer roller or a cleaner blade is brought into contact with the intermediate transfer belt, registration deviation occurs and the image quality is degraded. Was known. However, it has not been analyzed in detail about what kind of technical matter it occurs and the relationship between the separation contact of the contact means and the resist misregistration amount. In particular, no consideration was given to elastic expansion and contraction of the transfer medium and elastic deformation of a drive system (for example, a gear or a belt) that transmits power to the transfer medium. Therefore, in order to improve the image quality by correcting the registration deviation based on the examination result in detail when the image forming apparatus of FIG. 24 is operated in the operation sequence shown in FIG. The required resist control amount was obtained. Hereinafter, this will be described in detail with reference to FIGS.
[0020]
FIG. 1 is a timing chart showing an example of an operation sequence in the image forming apparatus of FIG. As shown in the figure, after the apparatus power is turned on or when the sleep mode of the image forming apparatus is released, the intermediate transfer belt 41 is rotated and conveyed, and the vertical synchronization signal VSYNC is intermittently transmitted from the vertical synchronization reading sensor 40. Is output. Each time the vertical synchronization signal VSYNC is output at timings VT1 to VT7,..., A yellow electrostatic latent image, a cyan electrostatic latent image, a magenta electrostatic latent image, and a black electrostatic latent image are displayed at a predetermined time. It is repeatedly formed in order on the photoconductor 21. After the electrostatic latent image is formed, one of the developing units 23Y, 23C, 23M, and 23K selectively abuts on the photosensitive member 21 to reveal the electrostatic latent image on the photosensitive member 21, The toner image is primarily transferred onto the intermediate transfer belt 41. Accordingly, the toner images of the respective colors are all formed at a predetermined position on the photoconductor 21, that is, at the reference latent image forming position, and the intermediate transfer belt 41 that rotates in synchronization with the photoconductor 21 is also primary at the same position. Transferred (primary transfer process for each toner color).
[0021]
When the primary transfer process is repeated for four colors, four color toner images are superimposed on the intermediate transfer belt 41 to form a color image. When a color image is obtained in this manner, the secondary transfer roller 48 contacts the intermediate transfer belt 41 with the sheet member S interposed therebetween, and the color image is secondarily transferred to the sheet member S, and the cleaner blade 491 is activated in response to the CB signal. The toner remaining on the belt surface in contact with the intermediate transfer belt 41 is removed. The sheet member S on which the color image is formed by repeating such an operation is sequentially discharged to the standard discharge tray.
[0022]
This is an outline of the operation of the image forming apparatus according to the operation sequence of FIG. 1. When the relationship between such operation and the amount of registration deviation in the sub-scanning direction is examined, the results differ between the first sheet and the second and subsequent sheets. was gotten. Such a difference is caused by a difference in operation sequence. Hereinafter, an operation sequence for forming an image on the first sheet (hereinafter referred to as “first print sequence”) and an image formation on the second and subsequent sheets are performed. The operation sequence will be described separately (hereinafter referred to as “second print sequence”). In addition, in this type of apparatus, there is a third print sequence that accompanies the idling process, and this will also be described.
[0023]
A-1. First printing sequence
First, when the apparatus power is turned on (or the sleep mode of the image forming apparatus is canceled), the intermediate transfer belt 41 is rotated and conveyed, and the vertical synchronization signal VSYNC is sequentially transmitted from the vertical synchronization reading sensor 40 at timings VT1 to VT3. The yellow toner image Y1 is primarily transferred onto the intermediate transfer belt 41 as described above corresponding to the first timing VT1, and the cyan toner image C1 is converted to the yellow toner image Y1 corresponding to the timing VT2. The magenta toner image M1 is primarily transferred onto the intermediate transfer belt 41 so as to overlap the yellow toner image Y1 and the cyan toner image C1 corresponding to the timing VT3. During this time, the cleaning process and the secondary transfer process of the intermediate transfer belt 41 are not performed, and the contact means (the secondary transfer roller 48 and the cleaner blade 491) are separated from the intermediate transfer belt 41.
[0024]
Therefore, these three toner images Y1, C1, and M1 are all superimposed at the same position on the intermediate transfer belt 41, and are accurately registered in the sub-scanning direction. That is, as shown in FIG. 2, the transfer start positions of these three toner images Y1, C1, and M1 all coincide with the reference transfer start position, and the transfer rear end position also coincides with the reference transfer rear end position. ing. Note that the alternate long and short dash line in FIG. 10 (and FIG. 10 described later) indicates the primary transfer position to which each toner image is transferred. Although superposed one after another, for convenience of explanation, the toner images are illustrated separately in the vertical direction.
[0025]
Next, when the vertical synchronization signal VSYNC is output at timing VT4, as shown in FIG. 3, a VIDEO signal is given to the exposure unit 3 after a predetermined time T10, and the electrostatic latent image corresponding to the black toner image K1 is displayed. The toner is developed by the black developing device 23K while being formed at a predetermined reference latent image forming position in the same manner as the toner color of. Then, the primary transfer process is started when a certain time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT4). At this time, as in the case of the yellow toner image Y1, the cyan toner image C1, and the magenta toner image M1, the cleaner blade 491 is separated from the intermediate transfer belt 41. As a result, as shown in FIG. Similarly to the other toner images Y1, C1, and M1, the transfer start position of the image K1 also coincides with the reference transfer start position. During the separation, the conveying speed V of the intermediate transfer belt 41 is constant, and the black toner image K1 is superimposed while being accurately registered with the other toner images Y1, C1, and M1 that have already been primarily transferred. Go.
[0026]
However, the CB signal for controlling the operation of the cleaner blade 491 rises from the L level to the H level at a certain point in time during the first half of the primary transfer of the black toner image K1, that is, at timing t1, and the cleaner blade 491 moves to the intermediate transfer belt 41. The black toner image K1 is in contact with the other toner images Y1, C1, and M1 in the sub-scanning direction. That is, at timing t1, the cleaner blade 491 contacts the intermediate transfer belt 41, acts as a transport load for the intermediate transfer belt 41, and the intermediate transfer belt 41 instantaneously expands in the sub-scanning direction. In addition, a drive system (for example, a gear and a belt) that transmits power to the intermediate transfer belt 41 is similarly elastically deformed. As a result, a resist misalignment occurs in the (−) direction by a resist misalignment amount A27.
[0027]
Further, after the timing t1, the cleaner blade 491 is maintained in contact with the intermediate transfer belt 41 until the CB signal rises again from the L level to the H level, and the intermediate transfer belt 41 is cleaned. The primary transfer process of the black toner image K1 is continued in the contact state until the timing t2. As a result, the registration deviation is further increased, and the registration deviation amount in the sub-scanning direction of the final black toner image K1 is
A32 = A27 + A6
As shown in FIG. 2, the transfer rear end position of the black toner image K1 is deviated from the reference transfer rear end position by the amount of deviation A32 in the (−) direction. However, symbol A6 corresponds to belt elongation caused by the cleaner blade 491 being kept in contact with the intermediate transfer belt 41 from timing t1 to timing t2 (that is, time A7). Further, in the figure (and a diagram showing a registration error state described later), a thick solid line indicates a registration error for a toner image of a corresponding toner color, while a thick broken line indicates an assist for helping understanding of the registration error occurrence state. Is a line.
[0028]
Thus, as shown in FIG. 2, in the first color image, only the black toner image K1 is shifted from the other toner images Y1, C1, and M1 in the latter half portion. It will shift by the amount of deviation A32. More specifically, as shown in FIG. 3, with respect to the first black toner image, the registration shift in the sub-scanning direction during the primary transfer is (+) and ( This occurs in the range of the amount of deviation (A32 / 2) in the-) direction, leading to a decrease in image quality. The secondary transfer roller 48 also comes into contact with the intermediate transfer belt 41 before the cleaner blade 491 comes into contact, and the same registration shift occurs. However, the corresponding registration shift amount is smaller than that of the cleaner blade 491. In order to facilitate understanding of the basic principle of the invention, here, the description will be made ignoring the registration shift caused by the separation and contact of the secondary transfer roller 48 with respect to the intermediate transfer belt 41.
[0029]
A-2. Second printing sequence
Such a registration error does not occur only in the first sheet but also appears in the second color image. That is, in order to form the second yellow toner image Y2, as shown in FIG. 4, to form the yellow toner image Y2 after a predetermined time T10 has elapsed since the vertical synchronization signal VSYNC was output at the timing VT5. The VIDEO signal is supplied to the exposure unit 3. Then, while developing an electrostatic latent image corresponding to the yellow toner image Y2 on the photosensitive member 21, the toner is developed by the yellow developing unit 23Y. Further, the primary transfer process is started when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT5), that is, at timing t3.
[0030]
However, after a while from the output timing VT5 of the vertical synchronization signal VSYNC, the cleaner blade 491 contacts the intermediate transfer belt 41 as described above, and the instantaneous extension of the intermediate transfer belt 41 in the sub-scanning direction and the drive system (for example, gears and belts). A resist misregistration amount A27 is generated due to elastic deformation. Moreover, since the contact state continues until the CB signal rises to the H level next time as will be described later, the extension in the sub-scanning direction increases with time. At the primary transfer start timing t3, the registration deviation amount A30 in the sub-scanning direction is
A30 = A27 + A9
It becomes. However, reference symbol A9 corresponds to belt elongation caused by the cleaner blade 491 being kept in contact with the intermediate transfer belt 41 from timing t1 to timing t3 (that is, time A10).
[0031]
When the intermediate transfer belt 41 passes the belt cleaner 49 for about one turn, the entire belt is cleaned and the cleaning process is completed. Therefore, the CB signal rises from the L level to the H level again at the timing t4, and the cleaner blade 491 is returned. Is separated from the intermediate transfer belt 41. During the period from the start of primary transfer (timing t3) to the separation of the cleaner blade 491 (timing t4), the cleaner blade 491 continues to contact the intermediate transfer belt 41, and during this time, the intermediate transfer belt 41 is at A12 (= t4−t3). The registration shift is further increased by extending by the extension amount A11 in the sub-scanning direction, and the registration shift amount immediately before the timing t4 becomes the shift amount A35 in the (-) direction.
[0032]
On the other hand, at this timing t 4, the cleaner blade 491 is separated from the intermediate transfer belt 41. Therefore, contrary to the contact, the load applied to the intermediate transfer belt 41 is released, so that the intermediate transfer belt 41 contracts and the drive system (for example, gears and belts) that is elastically deformed is the original. At the same time, the registration shift amount in the sub-scanning direction is reduced by A26. As described above, for the second color image, the transfer start position of the yellow toner image Y2 is greatly shifted from the reference transfer start position. In addition, as the primary transfer progresses, the amount of deviation increases, and if the cleaner blade 491 is separated at the timing t4 during the primary transfer, the amount of registration deviation is reduced. That is, as shown in FIG. 4, with respect to the second yellow toner image Y2, the registration shift in the sub-scanning direction during primary transfer is (+) and (− ) Occurs in the range of the amount of deviation (A26 / 2) in each of the directions), causing a reduction in image quality.
[0033]
Further, the cyan toner image C2 that is primarily transferred following the yellow toner image Y2 is also affected by the separation and contact of the cleaner blade 491, so that the transfer start position deviates from the reference transfer start position. This phenomenon will be described with reference to FIG.
[0034]
In order to form the second cyan toner image C2, a VIDEO signal for forming the cyan toner image C2 is given to the exposure unit 3 after a predetermined time T10 has elapsed since the vertical synchronization signal VSYNC was output at the timing VT6. It is done. The toner is developed by the cyan developer 23C while an electrostatic latent image corresponding to the cyan toner image C2 is formed on the photosensitive member 21. Further, the primary transfer process is started when a predetermined time T20 has elapsed from the output of the vertical synchronization signal VSYNC (timing VT6), that is, at timing t5.
[0035]
Here, at the output timing VT6 of the vertical synchronization signal VSYNC, the cleaner blade 491 is in contact with the intermediate transfer belt 41 as described above, and until timing t4 (the CB signal rises again from the L level to the H level), that is, This contact state is maintained only for time A14. Therefore, the intermediate transfer belt 41 extends by A13 between timing VT6 and timing t4. On the other hand, when the cleaner blade 491 is separated from the intermediate transfer belt 41 at timing t4, the load applied to the intermediate transfer belt 41 and the drive system (for example, gears, etc.) are reversed, as described above. Both the load applied to the belt) is released and the intermediate transfer belt 41 contracts by A26. Thereafter, the CB signal is kept in the separated state until the CB signal rises again from the L level to the H level. As a result, at the primary transfer start time (timing t5) of the cyan toner image C2, the registration deviation amount A34 in the sub-scanning direction is
A34 = A26-A13
It becomes.
[0036]
As described above, for the second cyan toner image C2, the registration deviation in the sub-scanning direction during the primary transfer has an amplitude amount of 0 centering on the fluctuation center AC3, and the registration deviation during the primary transfer process. Although the amount does not change, the fluctuation center AC3 itself is shifted in parallel in the sub-scanning direction (+) by the amount of deviation A34, which causes a reduction in image quality. That is, for the second toner color among the four toner colors, the contact means (secondary transfer roller 48 and cleaner blade 491) are in contact with and separate from the intermediate transfer belt 41 during the primary transfer process. Regardless of the fact, there is a misregistration. Accordingly, in order to suppress the registration error and form a high-quality color image, it is important how to suppress the registration error occurring in the second toner color.
[0037]
When the primary transfer of the cyan toner image C2 is completed as described above, the toner image formation and the primary transfer process of the magenta toner image M2 are performed next. During this process, the cleaner blade 491 is removed from the intermediate transfer belt 41. Since the separated state remains, no registration deviation occurs in the sub-scanning direction as in the first sheet, and the deviation amount becomes zero. Accordingly, with respect to the magenta toner image M2, the registration deviation in the sub-scanning direction during the primary transfer is centered on the axis where the registration deviation amount is zero (the one-dot chain line AC0 in FIGS. 3 and 4) and the amplitude thereof. The amount is also zero. Therefore, in the image forming apparatus that forms an image in the operation sequence shown in FIG. 1, the magenta toner image is set as the reference toner image, and the transfer start position and the transfer rear end position are set as “reference transfer start position” and “reference transfer position”, respectively. It can be referred to as “transfer rear end position”.
[0038]
When the primary transfer of the magenta toner image M2 is completed, the image formation and the primary transfer process of the third black toner image are performed. In this case, the cleaner blade 491 is in the middle of the primary transfer in the same manner as the second sheet. The intermediate transfer belt 41 is brought into contact with the intermediate transfer belt 41 to extend by A32, and registration shift occurs in the (−) direction in the sub-scanning direction. Note that a profile (hereinafter, simply referred to as “profile”) indicating a change in the registration shift amount with respect to the operation sequence is the same as that in FIG. 3, and the registration shift in the sub-scanning direction during the primary transfer is the fluctuation width center AC1. Centering on the center, and in the (+) and (−) directions in the sub-scanning direction within the range of the amount of deviation (A32 / 2), respectively, leading to a decrease in image quality.
[0039]
Further, when the fourth and subsequent color images are successively formed following the third color image, the same registration shift as that of the second image described above occurs.
[0040]
A-3. Third printing sequence
Further, in this type of image forming apparatus, the intermediate transfer belt 41 may be idled. For example, if the interval of image data from an external device such as a host computer is more than a certain distance, the intermediate transfer belt 41 is idled. If it is necessary to idle twice or more, the device is temporarily stopped. At this time, the cleaner blade 491 is in contact with the intermediate transfer belt 41. When a new image formation is started, the intermediate transfer belt 41 is rotationally driven to start the image formation. However, when the first yellow toner image is primarily transferred, the second and subsequent sheets shown in FIG. The same registration deviation as in the case of a cyan toner image occurs.
[0041]
That is, as shown in FIG. 6, when image formation is resumed and the intermediate transfer belt 41 is rotationally driven, a vertical synchronization signal VSYNC is output from the vertical synchronization reading sensor 40 at timing VT01, and from the timing VT01 for a certain period of time. After A14, after the cleaner blade 491 is separated from the intermediate transfer belt 41, the primary transfer of the yellow toner image is started. Therefore, for the same reason as in the case of the cyan toner image C2 in the “A-2. Second printing sequence”, the transfer start position is shifted by the shift amount A34 in the (+) direction. In other words, the registration deviation in the sub-scanning direction during the primary transfer has an amplitude amount of 0 centering on the fluctuation center AC3, and the registration deviation amount does not change during the primary transfer process, but the fluctuation width center AC4 itself is the secondary deviation. The amount of shift A34 is shifted in parallel in the scanning direction (+), which causes a reduction in image quality.
[0042]
Since the primary transfer of the subsequent cyan and magenta toner images is always performed in a state where the cleaner blade 491 is separated from the intermediate transfer belt 41, no registration deviation occurs, but the first black toner image and the first black toner image are not generated. As in the case of the two-printing sequence, during the primary transfer, the cleaner blade 491 and the secondary transfer roller 48 come into contact with the intermediate transfer belt 41, and a registration shift of a shift amount A32 occurs in the (−) direction.
[0043]
As described above, when the contact means such as the cleaner blade 491 separates from the intermediate transfer belt 41 while the primary transfer process is repeated, a predetermined registration shift amount is generated according to the separation contact timing. The profile itself is unique depending on the device configuration and operating conditions. The profile itself does not change unless the device configuration or operation sequence is changed, but the toner image for at least one or more toner colors based on the amount of registration deviation. By shifting the transfer start position in the sub-scanning direction, the registration deviation with respect to the reference toner image can be zero or suppressed. For example, for the cyan toner image C2, as shown in FIG. 5, the transfer start position of the cyan toner image C2 is a shift amount A34 in the (+) direction with respect to the reference transfer start position. Therefore, the amount of registration deviation can be reduced to zero by controlling the transfer start position of the cyan toner image C2 to be shifted in the (−) direction by the registration deviation amount A34 from the reference transfer start position. .
[0044]
Therefore, prior to actual image formation processing, the same analysis as described above is performed in advance from the apparatus configuration and operation sequence, etc., to derive the registration deviation amount, and the registration control necessary for zeroing or suppressing the registration deviation amount. The amount (for example, equivalent to A34 in the case of cyan) is obtained, and in actual image forming processing, the toner image transfer start position is corrected in the sub-scanning direction for at least one toner color based on the resist control amount. By doing so, registration shift can be suppressed and a high quality image can be formed. For example, by aligning the fluctuation width centers AC1 to AC4 of toner colors (Y, C, K) other than the reference toner color (magenta) with the fluctuation width center AC0 of the reference toner color, it is possible to suppress registration deviation and achieve high quality. An image can be formed.
[0045]
B. First embodiment
The image forming apparatus according to the first embodiment, including the first embodiment, utilizes the “basic principle of the invention” described above, and its mechanical configuration is the same as that of FIG. The electrical configuration and image forming method have distinctive features not found in the prior art. Therefore, in the following, description of the mechanical configuration is omitted, and the electrical configuration and the image forming method will be described in detail.
[0046]
B-1. Electrical configuration
FIG. 7 is an electrical configuration diagram showing an embodiment of the image forming apparatus according to the present invention, and has a configuration common to all the embodiments. In this image forming apparatus, when an image signal is given to the main controller 11 of the control unit 1 from an external device such as a host computer, the engine controller 12 responds to a command from the CPU 111 of the main controller 11 as shown in FIG. An image corresponding to the image signal is formed on the sheet member S by controlling each part of the configured engine part E.
[0047]
The engine controller 12 has a CPU 121, and as an input signal from the engine unit E, a horizontal synchronization signal HSYNC from the horizontal synchronization read sensor 36, a vertical synchronization signal VSYNC from the vertical synchronization read sensor 40, and a fixing unit. The temperature signal indicating the fixing temperature is received from the temperature sensor 51 provided in the circuit 5. Further, based on these input signals and various information, the CPU 121 sends a photoconductor / belt drive unit 41a for rotationally driving the photoconductor 21 and the intermediate transfer belt 41 in synchronization with each other, and a drive command signal for driving control. To the belt drive control circuit 122, and the photoreceptor / belt drive control circuit 122 controls the photoreceptor / belt drive unit 41 a using the DC motor as a drive source to control the rotational speed of the photoreceptor 21 and the conveyance of the intermediate transfer belt 41. Acceleration / deceleration control of speed V is performed. Further, the CPU 121 executes registration control amount establishment / storage processing, sequence flag update processing, registration control amount establishment processing, and the like, which will be described later.
[0048]
In addition to the photoconductor / belt drive control circuit 122, the engine controller 12 further includes a transfer roller separation / contact control circuit 123 and a belt cleaner separation / contact control circuit 124 as dedicated control circuits for controlling the transfer unit 4. I have. The transfer roller separation / contact control circuit 123 controls the secondary transfer roller drive unit 48a based on a command signal from the CPU 121 to bring the secondary transfer roller 48 into contact with the intermediate transfer belt 41 at an appropriate timing. On the other hand, the belt cleaner separation / contact control circuit 124 gives a CB signal to the belt cleaner drive unit 49a based on a command signal from the CPU 121 to control the belt cleaner drive unit 49a, and intermediately transfers the cleaner blade 491 at an appropriate timing. The belt 41 is separated and abutted.
[0049]
Reference numeral 113 in the figure denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 125 controls the engine unit E. Is a RAM for temporarily storing control data for the CPU 121 and calculation results in the CPU 121, and a reference numeral 126 is a ROM for storing calculation programs executed by the CPU 121.
[0050]
B-2. About operation
Next, the operation of the image forming apparatus according to this embodiment will be described. FIG. 8 is a flowchart showing the operation of the image forming apparatus. In this image forming apparatus, when the apparatus power is turned on, prior to the actual image forming process, a registration control amount establishing step (step S1) is executed to automatically establish and store three types of resist control amounts. It is stored in the RAM 125 as a part. In this embodiment, the following resist control amounts Ra, Rb, Rc as three types of resist control amounts, that is,
Ra: For example, as shown in FIG. 2 and FIG. 3, registration control for correcting a registration shift that occurs when the cleaner blade 491 comes into contact during the primary transfer process and the primary transfer process is completed in the contact state. amount,
Rb: For example, as shown in FIG. 4, the cleaner blade 491 abuts before the start of the primary transfer, the primary transfer process is continued in the abutted state, and the registration deviation that occurs when the cleaner blade 491 separates during the process. Resist control amount to correct
Rc: For example, as shown in FIGS. 5 and 6, the cleaner blade 491 that has been in contact before the start of the primary transfer is separated, and then the registration shift that occurs when the primary transfer process is performed in the separated state is corrected. Resist control amount,
Is enacted. Details of these three types of registration control amount automatic establishment operations (step S1) will be described later.
[0051]
When the establishment of the three types of registration control amounts Ra, Rb, and Rc (step S1) is completed in this way, a print request from an external device such as a host computer is awaited (step S2). When there is a print request, it is determined whether the print mode is monochrome print or color print (step S3). If it is determined that the print mode is monochrome print, normal image forming processing is performed without performing registration control. Execute and return to step S2. On the other hand, when it is determined in step S3 that color printing is performed, a sequence flag corresponding to the print sequence state is selectively set from the three sequence flags F0, F1, and F2 (identification variable setting step: step S4). ). Here, three sequence flags F0, F1, and F2 are prepared. These are identification variables corresponding to the first to third print sequences, respectively. This is because they can be associated with the control amounts Ra, Rb, and Rc.
[0052]
FIG. 9 is a flowchart showing the update contents of the sequence flag of FIG. In this sequence flag update process, it is determined whether or not the print content is the first color print (step S41). If it is determined that it is the first sheet, that is, if it is detected that the first print sequence is executed, the sequence flag F0 is set (step S42). On the other hand, if it is determined in step S41 that it is the second or subsequent sheet, the process proceeds to step S43 to determine whether or not the idling process is being performed.
[0053]
When the idling process is not performed, that is, when continuous printing is performed, the second printing sequence is executed, and therefore the sequence flag F1 is set (step S44). On the other hand, if the idling process is being performed, the third printing sequence is executed, so the sequence flag F2 is set (step S45).
[0054]
As described above, the print sequence is detected by the sequence flag update process (step S4), and the corresponding sequence flag is set / updated. The sequence flags F0, F1, F2 Such an association is made.
[0055]
<Sequence flag F0: First printing sequence>
As shown in FIG. 9, the first print sequence is for the first color print, that is, the first color image formed after the power is turned on or the sleep mode is canceled. When the power is turned on or the sleep mode is released in this way, no toner remains on the intermediate transfer belt 41 and the primary transfer process can be executed as it is. During the primary transfer of cyan and magenta toner images, the cleaner blade 491 and the secondary transfer roller 48 are separated from the intermediate transfer belt 41, and no registration deviation occurs during the primary transfer. . On the other hand, during the primary transfer of the black toner image, the cleaner blade 491 and the secondary transfer roller 48 come into contact with the intermediate transfer belt 41 to cause registration deviation.
[0056]
Therefore, in the first printing sequence, the flag F0 is set, and as shown in Table 1, “0” is set as the registration control amount of the yellow toner image Y1, the cyan toner image C1, and the magenta toner image M1 corresponding to the sequence flag F0. ”Is set, the control amount Ra is set as the registration control amount of the black toner image K1.
[0057]
[Table 1]

[0058]
<Sequence flag F1: Second printing sequence>
The second printing sequence is a case where color printing for the second and subsequent sheets is continuously performed as shown in FIG. In this way, for the second and subsequent sheets, as described in detail with reference to FIG. 4, the transfer start position of the yellow toner image is shifted in the sub-scanning direction, and the primary transfer to the intermediate transfer belt 41 such as the cleaner blade 491 is also performed during the primary transfer. The amount of misregistration changes due to separation and contact. During the primary transfer of the cyan toner image, the transfer start position is shifted in the sub-scanning direction as described with reference to FIG. In addition, as with the first sheet of the black toner image, the cleaner blade 491 and the secondary transfer roller 48 come into contact with the intermediate transfer belt 41 during the primary transfer, and registration shift occurs.
[0059]
Therefore, in the second print sequence, the flag F1 is set. As shown in Table 1, the control amount Rb is set as the registration control amount of the yellow toner image Y2 corresponding to the sequence flag F1, and the cyan toner image C2 is set. The control amount Rc is set as the registration control amount, “0” is set as the registration control amount of the magenta toner image M2, and the control amount Ra is set as the registration control amount of the black toner image (K2).
[0060]
<Sequence flag F2: Third print sequence>
As shown in FIG. 9, the third printing sequence is the second and subsequent color printing, and is the case where the idling process is performed immediately before that. In this way, when the idling process is present, when the next n-th (n ≧ 2) image formation is started, as described above, the cleaner blade 491 moves the intermediate transfer belt before primary transfer of the yellow toner image. The transfer start position deviates from the position 41 in the sub-scanning direction (FIG. 6). Since the primary transfer of the subsequent cyan and magenta toner images is always performed in a state where the cleaner blade 491 is separated from the intermediate transfer belt 41, no registration deviation occurs, but the first black toner image and the first black toner image are not generated. As in the case of the two-printing sequence, during the primary transfer, the cleaner blade 491 and the secondary transfer roller 48 come into contact with the intermediate transfer belt 41 to cause registration deviation.
[0061]
Therefore, in this printing sequence, the flag F2 is set, and as shown in Table 1, the control amount Rc is set as the registration control amount of the yellow toner image corresponding to the sequence flag F2, and the cyan toner image and the magenta toner image are set. “0” is set as the registration control amount of the black toner image, and the control amount Ra is set as the registration control amount of the black toner image.
[0062]
When the update of the sequence flag corresponding to the print sequence is completed as described above, a registration control amount corresponding to the sequence flag is set (registration control amount setting step: step S5), and then each toner image is primarily transferred. Then, the photosensitive member 21 is subjected to acceleration / deceleration control during a predetermined acceleration / deceleration period to shift the latent image formation position by a registration control amount in the sub-scanning direction with respect to the reference latent image formation position. As a result, the transfer position of the toner image on the intermediate transfer belt 41 to which the primary transfer is performed is also moved by the registration control amount in the sub-scanning direction. For example, when printing the first color image, since the sequence flag F0 corresponding to the first print sequence is set in step S4, the yellow toner image Y1, cyan toner image C1, magenta toner image is set in step S5. While “0” is set as the registration control amount for M1, the control amount Ra is set as the registration control amount for the black toner image K1. Accordingly, the yellow toner image Y1, the cyan toner image C1, and the magenta toner image M1 are all formed at a predetermined position on the photoconductor 21, that is, the reference latent image forming position, as in the conventional example. The intermediate transfer belt 41 that rotates synchronously is also primarily transferred at the same position. As a result, as shown in FIG. 10, the transfer start positions of these three toner images Y1, C1, and M1 all coincide with the reference transfer start position, and the transfer rear end position is also identical to the reference transfer rear end position. I'm doing it.
[0063]
On the other hand, since the control amount Ra is set as the registration control amount for the black toner image K1, as shown in FIG. 11, the acceleration / deceleration possible period T11 is based on the vertical synchronization signal VSYNC output at the timing VT4. At timing t11, acceleration / deceleration control of the photosensitive member 21 is performed to shift the latent image formation position of the black toner image by a control amount Ra (= A32 / 2) to the (+) side in the sub scanning direction with respect to the reference latent image formation position. Let Here, the “acceleration / deceleration possible period” refers to a period during which the VIDEO signal is at the H level and the exposure process is stopped. In the acceleration / deceleration possible period T11, the primary transfer process of the previous toner image (magenta toner image M1) is continued. In this embodiment, the intermediate transfer belt 41 is synchronized with the photosensitive member 21. Since the drive is controlled, the toner image that is primarily transferred in parallel with the acceleration / deceleration control of the photosensitive member 21 and the intermediate transfer belt 41 is not disturbed.
[0064]
The latent image formed on the photoconductor 21 as described above is visualized by the developing unit 23K, and the black toner image K1 is primarily transferred onto the intermediate transfer belt 41. As a result, as shown in FIG. 10, the transfer start position of the black toner image K1 is shifted by the registration control amount Ra in the (+) direction with respect to the reference transfer start position.
[0065]
As shown in FIG. 11, the CB signal for controlling the operation of the cleaner blade 491 rises from the L level to the H level at the timing t1 at which the primary transfer process proceeds and the latter half of the process proceeds. Comes into contact with the intermediate transfer belt 41, and the black toner image K1 shifts in the sub-scanning direction with respect to the other toner images Y1, C1, and M1. Further, the contact state is continued until timing t2, and as a result, the registration deviation is further increased. However, the registration deviation amount of the final black toner image K1 in the sub-scanning direction is a deviation amount (A32 / 2). That is, by moving the transfer start position of the black toner image K1 by the registration control amount Ra in the (+) direction with respect to the reference transfer start position, the fluctuation width center AC1 for the black color is set for the magenta color that is the reference toner color. In this way, the center of the deviation width of the registration shift in the sub-scanning direction for each toner color during the primary transfer process coincides with each other.
[0066]
As a result, in this embodiment, as shown in FIG. 10, the black toner image K1 is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the other toner images Y1, C1, and M1. It is shifted by (A32 / 2) in the (-) direction on the rear end side of the transfer, and the maximum shift amount is half that when the resist control is not performed (FIGS. 2 and 3).
[0067]
In this way, when the formation of the first color image is completed while suppressing the registration deviation based on the registration control amount, it is determined whether or not the printing is finished in step S7. Returning to step S2, the next print request is awaited. On the other hand, if it is determined that printing has not ended, the process returns to step S3 and the same processing as described above is repeated. Therefore, when the second color image is formed following the first color image formation as described above (second print sequence), the process further proceeds from step S3 to step S4, and the flag F1 is set as a sequence flag. After the setting, a high-quality image can be formed while suppressing registration shift as follows.
[0068]
That is, in step S5, the registration control amount corresponding to the sequence flag F1 is set. That is, the control amount Rb is set as the registration control amount for the yellow toner image Y2, the control amount Rc is set as the registration control amount for the cyan toner image C2, and “0” is set as the registration control amount for the magenta toner image M2. At the same time, a control amount Ra is set as the registration control amount of the black toner image K2. Then, registration control is executed for each toner image.
[0069]
First, since the control amount Rb is set as the registration control amount for the yellow toner image Y2, as shown in FIG. 12, the acceleration / deceleration possible period T11 is based on the vertical synchronization signal VSYNC output at the timing VT5. At timing t11, the photosensitive member 21 is accelerated / decelerated to shift the yellow toner image latent image forming position to the (+) side in the sub-scanning direction by the control amount Rb with respect to the reference latent image forming position. Then, this latent image is made visible by the developing unit 23Y.
[0070]
At time t1, the CB signal rises from the L level to the H level, and the cleaner blade 491 that has been separated comes into contact with the intermediate transfer belt 41. Thereafter, while the amount of registration deviation changes with the profile indicated by the thick solid line in the figure, the transfer process of the yellow toner image Y2 is performed and the transfer rear end side shifts by (A26 / 2) in the (+) direction. The maximum shift amount with respect to the toner image (magenta toner image M2) is significantly reduced as compared with the case where the resist control is not performed (FIG. 4).
[0071]
As described above, in this embodiment, the second yellow toner image Y2 is obtained by shifting the latent image forming position on the photosensitive member 21 in the sub-scanning direction with respect to the reference latent image forming position by the registration control amount Rb. The transfer start position is adjusted. Thus, the shake width center AC2 for the yellow color is matched with the shake width center AC0 for the magenta color that is the reference toner color. Therefore, the amount of deviation with respect to the reference toner image (magenta toner image M2) can be suppressed within the range of the shake width (A26 / 2).
[0072]
Subsequent to the yellow toner image Y2, primary transfer processing of the cyan toner image C2 is performed, and a control amount Rc is set as a registration control amount of the cyan toner image C2. Therefore, as shown in FIG. 13, the rotational speed of the photosensitive member 21 and the transport speed V of the intermediate transfer belt 41 are temporarily set at the timing t11 in the acceleration / deceleration period T11 with reference to the vertical synchronization signal VSYNC output at the timing VT6. Therefore, the rotation amount of the photosensitive member 21 and the conveyance amount of the intermediate transfer belt 41 are reduced by the registration control amount Rc as compared with the case of rotating and conveying at a constant speed (in the case of a reference toner image, that is, a magenta toner image). . As a result, the latent image forming position on the photosensitive member 21 is shifted by the registration control amount Rc in the sub scanning direction with respect to the reference latent image forming position.
[0073]
Then, the latent image formed on the photoconductor 21 as described above is visualized by the developing unit 23C, and the cyan toner image C2 is primarily transferred onto the intermediate transfer belt 41. Accordingly, the registration deviation amount (A26) due to the separation and contact of the cleaner blade 491 and the shift amount Rc of the toner image C2 on the photosensitive member 21 coincide with each other, and the transfer start position of the cyan toner image C2 is the reference transfer start position. Match.
[0074]
In addition, the CB signal rises from the L level to the H level at a timing t4 before the primary transfer processing of the cyan toner image C2 to the intermediate transfer belt 41 is started, and the cleaner blade 491 that is in contact with the intermediate transfer belt 41 is separated. Therefore, there is no registration shift during the primary transfer process. For this reason, the transfer rear end position of the cyan toner image C2 coincides with the transfer rear end position.
[0075]
As described above, in this embodiment, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the shake center AC3 for cyan is the shake for the magenta color that is the reference toner color. It is made to coincide with the width center AC0. For this reason, the amount of deviation with respect to the reference toner image (magenta toner image M2) can be suppressed to zero.
[0076]
The primary transfer process of the magenta toner image M2 is executed following the cyan toner image C2. In this transfer process, the cleaner blade 491 and the secondary transfer roller 48 are not separated and contacted at all, and the magenta toner image M2 is transferred. The start position and the transfer rear end position coincide with the reference transfer start position and the transfer rear end position, respectively.
[0077]
When the three-color toner images Y2, C2, and M2 are completed in this manner, the final transfer process for the final toner color, that is, the black toner image K2, is executed. In this primary transfer process, as in the case of the first black toner image K1, the latent image formation position on the photoconductor 21 is shifted in the sub-scanning direction by the registration control amount Rb, so that the black color is changed. The shake width center AC1 is made to coincide with the shake width center AC0 for the magenta color that is the reference toner color.
[0078]
Therefore, it is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the reference toner image, and is shifted by (A32 / 2) in the (−) direction on the transfer rear end side. This is half that when the resist control is not performed (FIGS. 2 and 3).
[0079]
As described above, the second sheet also corresponds to each toner color so that the center of the width of the registration shift in the sub-scanning direction for each toner color during the transfer process coincides with each other. The toner image transfer start position is corrected by performing acceleration / deceleration control in synchronism with the rotation speed of the photosensitive member 21 and the conveyance speed of the intermediate transfer belt 41 based on the registration control amount. That is, here, the transfer start position of each toner image is corrected based on the resist control amount for three colors of yellow (Y), cyan (C), and black (K) among the four toner colors. As a result, the cyan toner image C2 can be completely registered with the magenta toner image M2 that is the reference toner image, and the yellow toner image Y2 and the black toner image K2 cannot be completely registered with the reference toner image. However, the amount of resist misregistration can be minimized, and high-quality image formation is possible.
[0080]
When the sequence flag F2 is set, the control amount Rc is set as the registration control amount for the yellow toner image Yn, and “0” is set as the registration control amount for the cyan toner image Cn and the magenta toner image Mn. At the same time, the control amount Ra is set as the registration control amount of the black toner image Kn. Then, registration control is executed for each toner image.
[0081]
First, since the control amount Rc is set as the registration control amount for the yellow toner image Yn, as shown in FIG. 14, the acceleration / deceleration possible period T11 is based on the vertical synchronization signal VSYNC output at the timing VT01. At a timing t11, the rotational speed of the photosensitive member 21 and the transport speed V of the intermediate transfer belt 41 are temporarily reduced to compare with the case of rotational transport at a constant speed (in the case of a reference toner image, that is, a magenta toner image). The rotation amount of the photosensitive member 21 and the conveyance amount of the intermediate transfer belt 41 are reduced by the registration control amount Rc. As a result, the latent image forming position on the photosensitive member 21 is shifted by the registration control amount Rc in the sub scanning direction with respect to the reference latent image forming position.
[0082]
Then, the latent image formed on the photoreceptor 21 as described above is manifested by the developing unit 23Y, and the yellow toner image Yn is primarily transferred onto the intermediate transfer belt 41. Therefore, the registration deviation amount (A26) due to the separation and contact of the cleaner blade 491 and the shift amount Rc of the toner image Yn on the photosensitive member 21 coincide with each other, and the transfer start position of the yellow toner image Yn is the reference transfer start position. Match.
[0083]
The CB signal rises from the L level to the H level at the timing t4 before the primary transfer process of the yellow toner image Yn to the intermediate transfer belt 41 is started, and the cleaner blade 491 that has been in contact with the intermediate transfer belt 41 is separated. Therefore, there is no registration shift during the primary transfer process. Therefore, the transfer rear end position of the yellow toner image Yn coincides with the transfer rear end position.
[0084]
As described above, in this embodiment, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the shake center AC4 for yellow is the shake for the magenta color that is the reference toner color. It is made to coincide with the width center AC0. For this reason, the deviation amount with respect to the reference toner image (magenta toner image Mn) can be suppressed to zero.
[0085]
Subsequent to the yellow toner image Yn, the primary transfer process of the cyan toner image Cn and the magenta toner image Mn is sequentially performed. In these transfer processes, there is no separation contact between the cleaner blade 491 and the secondary transfer roller 48. The center of shake width for both toner colors coincides with each other, and the transfer start position and the transfer rear end position of both toner images Cn and Mn match the reference transfer start position and the transfer rear end position, respectively.
[0086]
When the three color toner images Yn, Cn, and Mn are completed in this manner, the final transfer process of the final toner color, that is, the black toner image Kn is performed. In this primary transfer process, as in the case of the first and second printing sequences, the photosensitive member 21 and the intermediate transfer belt 41 are subjected to acceleration / deceleration control based on the registration control amount Rc, so that the fluctuation width center AC1 for the black color is obtained. It is made to coincide with the shake width center AC0 for the magenta color which is the reference toner color. Therefore, it is shifted by (A32 / 2) in the (+) direction on the transfer start side with respect to the reference toner image, and is shifted by (A32 / 2) in the (−) direction on the transfer rear end side. This is half that when the resist control is not performed (FIGS. 2 and 3).
[0087]
As described above, in the color printing after the idling process, the transfer start position of each toner image is corrected based on the resist control amount for two colors of yellow (Y) and black (K) among the four toner colors. . That is, for all toner colors, the photosensitive member 21 and the photosensitive member 21 and the toner 21 are controlled based on the resist control amount Rc for each toner color so that the centers of the deviation widths in the sub-scanning direction for each toner color during the transfer process coincide with each other. By controlling the acceleration / deceleration of the intermediate transfer belt 41, the transfer start position of the toner image is corrected. As a result, the yellow toner image Yn, the cyan toner image Cn, and the magenta toner image (reference toner image) Mn can be completely registered, and the black toner image Kn cannot be completely registered with the reference toner image. However, the amount of resist misregistration can be minimized, and high-quality image formation is possible.
[0088]
B-3. About effect
As described above, according to the first embodiment, the contact means (secondary transfer roller 48 and cleaner blade 491) is brought into and out of contact with the intermediate transfer belt 41 as a transfer medium during the repetition of the transfer process. Therefore, registration deviation occurs when the abutting means comes into contact with the intermediate transfer belt 41. The registration control amount necessary for correcting the registration deviation according to the print sequence state is obtained, and this registration control is performed. The registration shift can be minimized by correcting the transfer start position of the toner image for at least one of the four toner colors based on the amount. More specifically, in this embodiment, for black, yellow, and cyan colors, the registration displacement center AC1, AC2 (or AC4) and AC3 in the sub-scanning direction for each toner color during the primary transfer process is used as a reference. By matching the deviation width center AC0 for the magenta color, which is the toner color, registration deviation among all the toner colors is minimized, and a high-quality color image can be obtained.
[0089]
In this embodiment, the following operational effects can be obtained. That is, as described above, the cleaner blade 491 abuts to generate registration misalignment. However, in order to suppress the misalignment amount, for example, the Young's modulus of the intermediate transfer belt 41 may be increased to suppress elastic elongation at the time of abutment. However, this limits the belt material that can be used, which leads to an increase in cost. Moreover, it cannot be applied as it is to an apparatus that has already been designed and manufactured, and the apparatus needs to be improved. On the other hand, according to the above-described embodiment, it is possible to suppress the registration error without depending on the apparatus configuration and improve the image quality, and it can be said that the technique is more versatile.
[0090]
Further, this type of image forming apparatus is not energized all day, but is generally turned on when starting a day's work, and is turned off when the day's work is completed. Each time the apparatus power is turned on, the registration control amount establishment process (step S1) is executed to automatically obtain the registration control amounts Ra, Rb, Rc, and the image forming apparatus has been used for a long time. However, it is possible to always correct the registration shift with the latest and optimum registration control amounts Ra, Rb, and Rc every day, and a stable and high-quality color image can be obtained over a long period of time. The registration control amount establishment process will be described in detail below.
[0091]
B-4. Registration control amount registration process
FIG. 15 is a flowchart showing the processing contents for automatically establishing the registration control amount. First, the following initial setting conditions are set in advance based on the apparatus configuration and operation sequence of the image forming apparatus according to the first embodiment, and are stored in the ROM 126. As shown in FIG. 16, with reference to the VSYNC signal, (1) a period T1 in which the cleaner blade 491 and the secondary transfer roller 48 contact the intermediate transfer belt 41, and (2) a cleaner blade 491 and the secondary transfer roller 48. Is continuously in contact with the intermediate transfer belt 41, (3) the period T3 in which the cleaner blade 491 and the secondary transfer roller 48 are separated from the intermediate transfer belt 41, and (4) the cleaner blade 491 and the secondary transfer roller 48 are The registration control amount establishment job (step S11) in which the period T4 that continues to be separated from the intermediate transfer belt 41 is one job is repeated a predetermined number of times, for example, 20 times (step S12).
[0092]
The initial condition is
A2: Process speed (peripheral speed of the intermediate transfer belt 41),
A7: Time from the contact of the cleaner blade 491 to the end of the primary transfer of the black toner image (see FIGS. 3 and 11),
A8: Time required for the intermediate transfer belt 41 to make a round
A10: Time from the contact of the cleaner blade to the start of the primary transfer of the yellow toner image (see FIGS. 4 and 12),
A12: Time from the transfer start position of the yellow toner image to the cleaner blade separation (see FIGS. 4 and 12),
A14: Time from VSYNC signal to cleaner blade separation (see FIGS. 5 and 13),
A17: Time interval from VSYNC signal to cleaner blade contact in period T1 (see FIG. 16),
A18: Time interval from VSYNC signal to cleaner blade separation in period T3 (see FIG. 16),
It has become.
[0093]
In this embodiment, while the registration control amount establishment job (step S11) is repeatedly executed, the charging bias and the primary transfer bias are always set to the ON state. Although not shown in FIG. 24, a static elimination lamp is provided between the primary transfer region R1 and the photoconductor cleaner blade 24. This static elimination lamp is also always set to an ON state. . Further, while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41, a secondary transfer bias is applied to obtain the registration control amount in a state close to actual printing.
[0094]
Thus, when 20 actually measured values are obtained for each of the periods T1 to T4, the average values T1 (av) to T4 (av) are calculated (step S13). Further, registration control amounts Ra, Rb, and Rc are obtained by calculation based on the following formulas (step S14). The reason will be described separately.
[0095]
<Registration control amount Ra>
As shown in FIG. 3, the contact of the cleaner blade 491 is started during the primary transfer of the black toner image K1 to the intermediate transfer belt 41, and the primary transfer of, for example, the A3 size black toner image K1 is completed. Since the contact of the cleaner blade 491 is continued even at the time point, a registration deviation amount A32 in the sub-scanning direction is generated. The resist misregistration amount A32 is the sum of the two elongations A6 and A27. That means
A32 = A6 + A27
It becomes.
[0096]
Here, the contact elongation A6 is a contact elongation generated when the intermediate transfer belt 41 is rotated and conveyed in a state where the cleaner blade 491 is in contact, and the elongation A27 is the extension of the cleaner blade 491 to the intermediate transfer belt 41. This is a combination of the instantaneous elongation (elastic component + slip component) at the time of contact and the elastic deformation of a drive system (for example, a gear or belt) that transmits power to the intermediate transfer belt 41.
[0097]
First, consider the elongation A6. When the cleaner blade 491 is in contact, a period difference A1 occurs. The period difference A1 is expressed by the following equation:
A1 = (T2 (av) −T4 (av)) × A2 × 1000
Can be obtained. During the primary transfer of the black toner image K1, the cleaner blade 491 is in contact only for a predetermined time A7.
A6 = A1 × A7 / A8
It becomes.
[0098]
On the other hand, the instantaneous elongation A27 can be obtained by comparing the periods T1 and T4. That is, the instantaneous elongation A27 is given by
A27 = (T1 (av) −T4 (av)) × A2 × 1000−A15
Can be obtained. However, as shown in FIG. 16, the elongation A15 is an elongation due to the cleaner blade 491 being in contact for a predetermined time A17 during the period T1, and this elongation A15 is:
A15 = A1 × (A8-A17) / A8
Can be obtained.
[0099]
Therefore, the resist misregistration amount A32 is
A32 = A6 + A27
The registration shift of the black toner image K1 can be minimized by shifting the transfer start position in advance in the sub-scanning direction with respect to the reference transfer start position by a half value. Therefore, in this embodiment, the resist control amount Ra is set to
Ra = A32 / 2
Is set.
[0100]
<Registration control amount Rb>
As shown in FIG. 4, when the yellow toner image Y2 is primarily transferred to the intermediate transfer belt 41 following the primary transfer of the black toner image K1, it is during the time A10 from the contact of the cleaner blade to the start of the primary transfer of the yellow toner image. A30 (= A27 + A9) is generated in the sub-scanning direction. Further, since the cleaner blade 491 is in contact with the intermediate transfer belt 41 even after the primary transfer is started, elongation A11 occurs, but the cleaner blade 491 is separated from the intermediate transfer belt 41 immediately before the completion of the primary transfer. Shrinkage A26 occurs. Therefore, as shown in the figure, when the shrinkage A26 is larger than the elongation A11, the resist control amount Rb is
Rb = A35-A26 / 2
However, A35 = A30 + A11
In the opposite case (A26 <A11), the registration control amount Rb is set to
Rb = A35-A11 / 2
By setting to, the registration error of the yellow toner image can be minimized.
[0101]
Here, the elongation A30 at the start of the primary transfer is as described above.
A30 = A27 + A9
However, the elongation A9 is an elongation generated by the intermediate transfer belt 41 being rotated and conveyed for a time A10 in a state where the cleaner blade 491 is in contact with the following equation.
A9 = A1 × A10 / A8
Can be obtained.
[0102]
Further, the elongation A11 is an elongation generated because the cleaner blade 491 is in contact with the intermediate transfer belt 41 even after the primary transfer is started.
A11 = A1 × A12 / A8
Can be obtained.
[0103]
Further, the shrinkage A26 is caused by the cleaner blade 491 being separated from the intermediate transfer belt 41, and can be obtained by comparing the periods T3 and T4. That is, the following formula
A26 = A25− (T3 (av) −T4 (av)) × A2 × 1000
Can be determined based on In addition, A25 in the equation is the elongation in the period T3 as shown in FIG.
A25 = A1 × A18 / A8
Can be obtained.
[0104]
<Registration control amount Rc>
As shown in FIG. 5, when the cyan toner image is primarily transferred to the intermediate transfer belt 41 following the primary transfer of the yellow toner image, the cleaner blade 491 is moved when the VSYNC signal VT6 serving as a reference for the primary transfer is output. The intermediate transfer belt 41 is in contact with the intermediate transfer belt 41, and after that, until the primary transfer of the cyan toner image is started, the intermediate transfer belt 41 is rotated and conveyed in the contact state for a time A14. appear. In other words, the elongation A13 is
A13 = A1 × A14 / A8
It becomes.
[0105]
Further, when the cleaner blade 491 is separated from the intermediate transfer belt 41, the shrinkage A26 occurs as described in the section <Register control amount Rb>. Therefore, a registration deviation amount A34 (= A13-A26) occurs at the time of the primary transfer start of the cyan toner image, but no deviation in the sub-scanning direction occurs during the primary transfer. Therefore, in this embodiment, the registration start amount of the cyan toner image can be suppressed to zero by shifting the transfer start position in the sub-scanning direction in advance by this value (registration shift amount A34). ,
Rc = A34
Is set.
[0106]
As described above, the registration control amount establishment process is performed in a dedicated sequence (FIG. 16) different from the print sequence (FIG. 1) for forming a color image. Indispensable resist control amounts Ra, Rb, and Rc can be accurately obtained.
[0107]
In this embodiment, the vertical synchronization signal VSYNC, which is a reference signal, is output once every time the intermediate transfer belt 41 makes one revolution. For example, the intermediate transfer belt 41 is provided with a plurality of reference positions. Needless to say, the present invention can also be applied to the case where the reference signal is output a plurality of times while the intermediate transfer belt 41 makes one round. In particular, in this case, each period can be set short.
[0108]
In the registration control amount establishment process, a secondary transfer bias is applied while the secondary transfer roller 48 is in contact with the intermediate transfer belt 41. This is essential for establishing the registration control amount. The secondary transfer bias may not be applied, or a bias having a polarity opposite to that of the secondary transfer bias may be applied. In each case, the following effects can be obtained. That is, when the secondary transfer bias is not applied, the registration control amount establishment process can be simplified. When the secondary transfer bias is applied, the load applied to the intermediate transfer belt 41 and the photoconductor / belt drive unit 41a by the secondary transfer roller 48 approaches the actual printing state, and the registration control amount is accurately obtained. be able to. Further, when a reverse polarity bias is applied, the toner adhering to the secondary transfer roller 48 is returned to the intermediate transfer belt 41 side, the secondary transfer roller 48 is cleaned, and the back surface of the sheet member is soiled by the secondary transfer roller 48. Can be prevented and good printing results can be obtained.
[0109]
Further, in the registration control amount establishment process described above, the primary control bias is applied to the intermediate transfer belt 41 and the registration control amount is obtained in a state close to actual printing. Therefore, the registration control amount can be accurately obtained.
[0110]
Further, in the registration control amount establishment process described above, the registration control amount establishment job (step S11) is repeated 20 times from the start of driving (step S12), and 20 actually measured values of the periods T1 to T4 are measured. The resist control amount is obtained based on the actually measured value. However, the rotational transfer of the intermediate transfer belt 41 may not be stable immediately after the start of driving. If the registration control amount is obtained based on the periods T1 to T4 measured in such a state, the accuracy of the registration control amount is determined. May decrease. In order to solve such problems, the intermediate transfer belt 41 is rotated and conveyed a predetermined number of times from the start of driving, and after its operation is stabilized, the periods T1 to T4 are measured, and the measured values are obtained. The registration control amount may be obtained based on this, and in this way, the registration control amount can be obtained with high accuracy.
[0111]
C. Second embodiment
By the way, in the first embodiment, in order to adjust the transfer start position according to the registration control amount, the photosensitive member 21 and the intermediate transfer belt 41 are synchronously controlled at variable speed, so The latent image forming position is shifted in the sub-scanning direction according to the registration control amount. Here, as a method of shifting the latent image forming position on the photoconductor 21, it is possible to control the exposure timing in addition to the photoconductor / belt drive control. Further, the photoconductor / belt drive control and the exposure timing control may be combined, and this embodiment will be described with reference to FIGS.
[0112]
FIG. 17 is a flowchart showing the operation of the second embodiment of the image forming apparatus according to the present invention. In the second embodiment, similarly to the first embodiment, when the registration control amount corresponding to each sequence flag is set (step S4), the photosensitive member 21 and the intermediate transfer belt 41 are enabled based on the registration control amount. The variable speed control is performed during the variable speed period T11 (step S6), and the exposure start timing is advanced or delayed to shift the latent image forming position on the photoconductor 21 in the sub-scanning direction (step S8).
[0113]
Combining the photoreceptor / belt drive control (step S6) and the exposure timing control (step S8) in this way is effective when the registration control amount is relatively large. This is because, for example, when transferring the yellow toner image Y2 or cyan toner image C2 in the second print sequence, or when transferring the yellow toner image Yn in the third print sequence, the resist control amount is relatively large, and the photoconductor / If the registration deviation is to be corrected only by the belt drive control, it is necessary to set the rotation rate of the photosensitive member 21 and the rate of change of the belt conveyance speed V correspondingly, thereby reducing the accuracy of the photosensitive member / belt drive control and the motor. The load will increase.
[0114]
On the other hand, when transferring the yellow toner image Y2 in the second printing sequence, as shown in FIG. 18, the exposure timing control is equivalent to one dot line in the sub-scanning direction, that is, the line interval Re in the sub-scanning direction (+ ), The shift movement amount of the latent image forming position by the photoreceptor / belt drive control can be suppressed to ΔRb (<Rb).
[0115]
Further, when transferring the cyan toner image C2 of the second printing sequence, as shown in FIG. 19, by the exposure timing control, one dot line in advance in the sub-scanning direction, that is, the line interval Re in the sub-scanning direction (−) direction. By setting so as to deviate, the shift movement amount of the latent image forming position by the photoreceptor / belt drive control can be suppressed to ΔRc (<Rc).
[0116]
Further, when transferring the yellow toner image Yn in the third printing sequence, as shown in FIG. 20, the exposure timing control is performed in advance by one dot line in the sub-scanning direction, that is, the line interval Re in the sub-scanning direction (−) direction. By setting so as to deviate, the shift movement amount of the latent image forming position by the photoreceptor / belt drive control can be suppressed to ΔRc (<Rc). Therefore, it is possible to prevent an excessive load from being applied to the motor that rotationally drives the intermediate transfer belt 41, and to perform photoconductor / belt drive control with high accuracy.
[0117]
In the second embodiment, the latent image forming position on the photosensitive member 21 is shifted in the sub-scanning direction by one dot line Re by exposure timing control (step S8). However, when the registration control amount is large. The exposure timing may be controlled so as to be shifted by a plurality of dot lines.
[0118]
In the second embodiment, the exposure timing control and the photoconductor / belt drive control are combined to perform the resist control. However, the latent image forming position on the photoconductor 21 is controlled by the resist only by the exposure timing control. You may make it shift-shift according to quantity.
[0119]
D. Third embodiment
In the above embodiment, after the apparatus power is turned on, the registration control amount establishment step (step S1) is executed to automatically establish the three types of registration control amounts Ra, Rb, and Rc, and store them in the RAM 125 as a storage unit. The registration control amount corresponding to the print sequence is set by updating and setting the sequence flag corresponding to the print sequence by the flag update processing (step S4). The registration control amount is determined by the registration control amount establishment step (step S1). Alternatively, the three types of registration control amounts Ra, Rb, and Rc may be stored in a table format corresponding to the print sequence.
[0120]
That is, the sequence flags F0, F1, and F2 are provided in one-to-one correspondence with the three print sequences, but as shown in Table 1, the sequence flags and the resists corresponding to the print sequences corresponding to the respective sequence flags are provided. You may memorize | store in RAM125 in the state linked | related with the controlled variable. In this case, when the sequence flag corresponding to the print sequence is set by the sequence flag update process (step S4), the registration control amount corresponding to the sequence flag is read from the table in the RAM 125 at a time, and the registration control amount Based on the above, by correcting the transfer start position of the toner image for at least one of the four toner colors, the same effect as in the above embodiment can be obtained.
[0121]
D. Fourth embodiment
FIG. 21 is a flowchart showing the operation of the fourth embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to the fourth embodiment is greatly different from that of the first embodiment in that a starting condition for the registration control amount establishment process is added in the fourth embodiment. That is, in the first embodiment, the registration control amount establishment job is executed immediately after the apparatus power is turned on. In this fourth embodiment, the CPU 121 outputs the output (fixing roller temperature) from the temperature sensor 51 in step S10. In response, it is determined whether or not the fixing roller temperature exceeds a predetermined establishment start temperature TP0, and the registration control amount establishment job is started on the condition that the fixing roller temperature exceeds the establishment start temperature. The reason is as follows.
[0122]
In this type of image forming apparatus, as shown in FIG. 22, the fixing roller temperature of the fixing unit before power-on is low, and when the apparatus power is turned on at timing t11, warm-up processing is started. As an operation of the warm-up process, the fixing roller is heated and when the predetermined fixing temperature is reached, the warm-up process is completed and image formation can be started. Therefore, if the registration control amount establishment process can be completed during the warm-up process, the image forming process can be started immediately after the warm-up process is completed. Therefore, it is desirable to complete the registration control amount establishment process (step S1) during the warm-up process.
[0123]
Here, if the registration control amount establishment process (step S1) is executed immediately after the start of the warm-up process, that is, immediately after the apparatus power is turned on as in the first embodiment, the registration control amount establishment process ( Step S1) can be completed reliably. However, the fixing roller temperature does not rise sufficiently, and the registration control amount establishment process (step S1) is executed in a state away from the apparatus environment during actual printing, so that an accurate registration control amount cannot be obtained. There is a case.
[0124]
Therefore, as in the fourth embodiment, when the fixing roller temperature rises to a predetermined establishment start temperature TP0 and the registration control amount establishment process is started after approaching the apparatus environment at the time of actual printing, the registration control amount is further increased. It can be determined accurately. In setting the establishment start temperature TP0, it is desirable that the establishment process is completed before the warm-up process is completed, even if the registration control amount establishment process is started when the set temperature is reached. By selecting and setting the establishment start temperature TP0, the registration control amount can be accurately obtained in a state close to the actual printing without degrading the apparatus performance.
[0125]
E. Fifth embodiment
In the first embodiment, the registration control amounts Ra, Rb, and Rc are automatically established and stored in the RAM 125 by the registration control amount establishment step (step S1) after the device power is turned on. Execution of each registration control amount establishment process is not essential, and the execution conditions of the registration control amount establishment process can be arbitrarily set, and may be performed during continuous printing processing as follows. .
[0126]
In this type of image forming apparatus, when an image forming command is given to the main controller 11 from an external device, the main controller 11 converts the image forming command into one or a plurality of job data and sequentially gives it to the engine controller 12. . For example, when an image formation command for printing 5 pages of an A4 size document is transmitted from the external device to the main controller 11, in the image forming apparatus according to the present embodiment, the main controller 11 sends the image formation command to the engine unit E. Are converted into the following three job data.
[0127]
(1) A job to print two pages of A4 size document;
(2) A job that prints two pages of an A4 size document;
(3) A job for printing one page of an A4 size document;
Therefore, a registration control amount establishment process may be executed between jobs. As described above, the registration control amount establishment step may be executed after forming one color image and before forming the next color image.
[0128]
Also, the registration control amount establishment step is performed when a predetermined time has elapsed since the apparatus power was turned on, when a predetermined number of sheets have been printed since the apparatus was turned on, or when the above-mentioned job is repeated a predetermined number of times. Alternatively, the execution timing of the registration control amount establishment process may be determined based on the operation status of the apparatus.
[0129]
F. Sixth embodiment
In the above-described embodiment, the registration control amount is obtained by executing the registration control amount establishment process while the apparatus is operating. However, instead of the registration control amount establishment process, the registration control amount is obtained in advance and stored in the ROM 126. You may comprise as follows. For example, a storage unit is incorporated in the transfer unit 4, and at the assembly stage of the transfer unit 4, only the transfer unit 4 is driven alone to obtain a resist control amount and stored in the storage unit of the transfer unit 4. May be. In this case, the registration control amount can be obtained at the time of manufacture and assembly of the transfer unit 4, and the registration control amount can be obtained without waiting for completion of other units such as the image carrier unit 2 and the exposure unit 3. Therefore, the assembly work efficiency of the entire apparatus can be improved.
[0130]
Alternatively, the registration control amount may be obtained at the stage when the entire image forming apparatus is assembled and stored in the ROM 126. By doing this, a result reflecting the influence of units other than the transfer unit 4 on the resist control amount is obtained, and a resist control amount with higher accuracy can be obtained as compared with a case where the resist control amount is obtained by the transfer unit 4 alone.
[0131]
G. Seventh embodiment
The intermediate transfer belt 41 and surrounding parts are easily affected by the internal environment of the apparatus such as temperature and humidity. Therefore, by measuring the temperature and humidity inside the apparatus and correcting the resist control amount based on the measured values, it is possible to perform more accurate resist correction and obtain a high-quality image.
[0132]
In some cases, the work is performed with the apparatus cover opened for exchanging consumables, apparatus maintenance, or the like. However, the temperature and humidity inside the apparatus may change greatly as the cover is opened. Here, as described above, the temperature and humidity inside the apparatus may be directly measured with a temperature / humidity sensor and the resist control amount may be corrected. However, based on the information that the cover is open, the resist control amount The registration control amount establishment process may be executed by determining that correction is necessary.
[0133]
Furthermore, as a factor affecting the temperature and humidity inside the apparatus, there is an energy save mode (sleep mode) setting. This is because in this mode, the fixing unit is stopped or controlled at a low temperature except for the printing process. Therefore, since there is a high possibility that a temperature drop will be recognized when returning from the energy save mode, the registration control amount establishment step may be executed immediately after the return or after a predetermined time has elapsed based on the information indicating that the return from the energy save mode has occurred. Such information is generally referred to as “apparatus status”, and by determining the execution timing of the resist control quantity establishment process based on the status, a resist control quantity suitable for the environment inside the apparatus is obtained. It can be determined as appropriate, and a high-quality color image can be obtained.
[0134]
H. Eighth embodiment
FIG. 23 is a timing chart showing an operation sequence of the eighth embodiment of the image forming apparatus according to the present invention. In the eighth embodiment, the black toner is supplied to the photoconductor cleaner blade 24 before the registration control amount establishment process (step S1) is executed. Prevents it in advance. That is, if the registration control amount establishment job is repeated in a state where no toner is present on the photoconductor cleaner blade 24, the clearance of the cleaner blade 24 occurs during that time. Also, a very large frictional force acts between the photoconductor cleaner blade 24 and the photoconductor 21 to apply a large load to the motor that rotationally drives the photoconductor 21 to deviate from the actual printing state, and the motor controllability is also reduced. Resulting in. However, in the eighth embodiment configured as described below, these problems can be prevented from occurring.
[0135]
In the eighth embodiment, when the apparatus power is turned on, driving of a driving motor that rotationally drives the photosensitive member 21 and the intermediate transfer belt 41 is started. Here, the charging bias and the primary transfer bias to the charging roller 22 are always set to the OFF state.
[0136]
Subsequently, the separation contact control signal of the black developing device 23K rises from the L level to the H level, and the black developing device 23K contacts after a time lag of ΔT40. The reason why the time lag ΔT40 occurs in this manner is that, in the image forming apparatus of FIG. 24, each developing device is driven to come into contact with the photosensitive member 21 by utilizing the cam mechanism. When the separation contact control signal for the black developing device 23K rises again from the L level to the H level, the black developing device 23K is separated from the photosensitive member 21. Thus, while the black developing device 23K is in contact with the photosensitive member 21, the black toner is attached to the photosensitive member 21, and the black printing process is executed.
[0137]
In this way, the black toner attached to the photoconductor 21 is removed from the photoconductor 21 by the photoconductor cleaner blade 24, and supply of the black toner to the photoconductor cleaner blade 24 is completed. In this embodiment, the black toner is supplied to the photoconductor cleaner blade 24, but other toner may be supplied instead of the black toner.
[0138]
In addition, black printing is performed as described above, and after the printing, the cleaner blade 491 is kept in contact for a predetermined time at a predetermined timing. This is based on the following reason. In this embodiment, the primary transfer bias is in the OFF state, but a part of the black toner on the photoreceptor 21, for example, about 10% adheres to the intermediate transfer belt 41. Therefore, in order to remove the adhered toner from the intermediate transfer belt 41, the cleaner blade 491 is brought into contact with the intermediate transfer belt 41 at an appropriate timing as described above.
[0139]
As described above, according to the eighth embodiment, after the toner is supplied to the photoconductor cleaner blade 24 always in contact with the photoconductor 21, the registration control amount establishment process (step S1) is executed. Therefore, while the registration control amount establishment job is repeated, the photoconductor cleaner blade 24 is prevented from rolling, and the frictional force between the photoconductor cleaner blade 24 and the photoconductor 21 is reduced. The registration control amount establishment process (step S1) can be executed in a state close to a character, and the registration control amount can be obtained more accurately.
[0140]
I. Other
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the magenta color is set as the reference toner color, and the center of the shake width of the other toner colors (yellow, cyan, and black) is made to coincide with the center of the shake width of the magenta color. The color may be a reference toner color. However, in this embodiment, the four toner colors are performed in the order of yellow (Y), cyan (C), magenta (M), and black (K), and the magenta toner image is thirdarily transferred. As described above, it is least affected by the contact of the contact means (secondary transfer roller 48 and cleaner blade 491). Further, without providing the reference toner color, the center of fluctuation width for all the toner colors coincides with each other at an appropriate position, for example, a straight line AC00 (“registration amount in the sub-scanning direction = k”) as shown in FIG. You may make it make it. In this case, the transfer start position of the toner image is corrected for all toner colors.
[0141]
In the above embodiment, the center of each shake width is made to coincide with each other for all the toner colors, but the image quality is improved by making each shake center match with respect to at least two of the four toner colors. It is possible to improve.
[0142]
In the above-described embodiment, the photosensitive member 21 and the intermediate transfer belt 41 are driven and controlled by the same photosensitive member / belt driving unit (driving unit) 41a, so that both are driven synchronously. And a belt driving unit for driving and controlling the intermediate transfer belt 41. The photosensitive member driving unit and the belt driving unit constitute a "driving unit" according to the present invention. The photosensitive member 21 and the intermediate transfer belt 41 may be driven synchronously by a driving unit.
[0143]
Further, when the photosensitive member driving unit and the belt driving unit are provided separately as described above, the photosensitive member 21 is driven to rotate at a constant speed, while the region where no toner image is formed in the intermediate transfer belt 41 is primary. In the period (the period in which primary transfer is not performed) positioned in the transfer region R1, only the intermediate transfer belt 41 may be controlled at a variable speed based on the registration control amount to adjust the transfer start position.
[0144]
In the above embodiment, the sequence flags F0, F1, and F2 are set as identification variables corresponding to the three types of print sequences on a one-to-one basis. However, other identification variables such as specific characters and numbers are used. It may be used.
[0145]
In the above-described embodiment, the print variable is divided into three types of print sequences, and the identification variable corresponding to each print sequence is set. However, the number of print sequence divisions is not limited to this, and the number of divisions is not limited. If it is 2 or more, the same effect as in the above embodiment, that is, there is no need to newly obtain a resist control amount every time the sequence changes, and excellent controllability can be obtained.
[0146]
In the above embodiment, a DC motor is employed as a drive source for rotationally driving the intermediate transfer belt 41, and registration control is performed by accelerating / decelerating the DC motor based on the registration control amount. Registration control may be performed by using a pulse motor such as a stepping motor and performing pulse drive control based on the registration control amount.
[0147]
The image forming apparatus according to the above embodiment is a printer that prints an image provided from an external device such as a host computer via the interface 112 on a sheet member such as copy paper, transfer paper, paper, and an OHP transparent sheet. However, the present invention can be applied to electrophotographic color image forming apparatuses such as copying machines and facsimile machines, that is, image forming apparatuses that form a color image by superposing a plurality of color toners.
[0148]
Further, in the above embodiment, a color image is formed on the intermediate transfer belt 41 by performing a transfer process for transferring the toner image formed on the photosensitive member 21 onto the intermediate transfer belt 41 for each toner color. However, the toner image is transferred to a transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet, or transmissive storage sheet) to form a color image. The present invention can also be applied to an image forming apparatus.
[0149]
【The invention's effect】
As described above, according to the present invention, the separation of the contact means to the transfer medium is executed during the repetition of the transfer process, so that the registration error is caused by the contact of the contact means with the transfer medium. However, the registration control amount necessary for correcting the registration deviation is obtained, and the transfer start position of the toner image is corrected for at least one of the plurality of toner colors based on the registration control amount. Therefore, it is possible to obtain a high-quality color image while suppressing registration deviation.
[0150]
Further, according to the present invention, since the registration control amount is obtained every time the apparatus power is turned on, even if the image forming apparatus is used for a long period of time, the registration deviation is always maintained at the latest and optimum registration control amount every day. Correction can be performed, and a stable and high-quality color image can be obtained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a timing chart showing an example of operation timing in an image forming apparatus to which the present invention is applied.
FIG. 2 is a diagram schematically illustrating a registration state of each toner image when primary transfer processing is performed at the operation timing of FIG. 1 without performing registration control.
FIG. 3 is a diagram illustrating a registration shift state when a black toner image is transferred without performing registration control.
FIG. 4 is a diagram illustrating a registration shift state when a yellow toner image is transferred without performing registration control.
FIG. 5 is a diagram illustrating a registration shift state when a cyan toner image is transferred without performing registration control.
FIG. 6 is a diagram illustrating a registration shift state when a yellow toner image is transferred without performing registration control.
FIG. 7 is an electrical configuration diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 8 is a flowchart showing an operation of the image forming apparatus according to the first embodiment.
9 is a flowchart showing the update contents of the sequence flag of FIG. 8. FIG.
FIG. 10 is a diagram schematically showing the registration status of each toner image when primary transfer processing is performed at the operation timing of FIG. 1 while performing registration control.
11 is a diagram showing registration control contents when a black toner image is transferred in the image forming apparatus shown in FIG. 8; FIG.
12 is a diagram showing registration control contents when a yellow toner image is transferred in the image forming apparatus shown in FIG. 8. FIG.
13 is a diagram showing registration control contents when a cyan toner image is transferred in the image forming apparatus shown in FIG. 8. FIG.
14 is a diagram showing registration control contents when a yellow toner image is transferred in the image forming apparatus shown in FIG. 8. FIG.
FIG. 15 is a flowchart showing a processing content for automatically establishing a registration control amount.
FIG. 16 is a timing chart showing the contents of a registration control amount establishment job.
FIG. 17 is a flowchart showing the operation of the second embodiment of the image forming apparatus according to the present invention;
18 is a diagram illustrating registration control contents when a yellow toner image is transferred in the image forming apparatus illustrated in FIG. 17;
FIG. 19 is a diagram showing registration control contents when a cyan toner image is transferred in the image forming apparatus shown in FIG. 17;
20 is a diagram showing registration control contents when a yellow toner image is transferred in the image forming apparatus shown in FIG.
FIG. 21 is a flowchart showing the operation of the fourth embodiment of the image forming apparatus according to the present invention;
22 is a graph showing conditions for starting establishment of registration control amounts in the image forming apparatus shown in FIG.
FIG. 23 is a timing chart showing an operation sequence of the eighth embodiment of the image forming apparatus according to the present invention;
FIG. 24 is a diagram showing a configuration of an image forming apparatus as a background art of the present invention.
[Explanation of symbols]
1 ... Control unit (control means)
3. Exposure unit (exposure means)
4 ... Transcription unit
5. Fixing unit (fixing means)
11 ... Main controller
12 ... Engine controller (control means)
21 ... Photoconductor
23. Development section
23Y, 23C, 23M, 23K ... Developer
24 ... Cleaner blade for photoconductor
40. Reading sensor for vertical synchronization
41. Intermediate transfer belt (transfer medium)
41a ... Photoconductor / belt drive section (drive means)
48. Secondary transfer roller (contact means)
51. Temperature sensor
121 ... CPU (control means)
122. Photoconductor / belt drive control circuit (drive means)
123. Transfer roller separation contact control circuit
124 ... Belt cleaner separation contact control circuit
491 ... Cleaner blade (contact means)
C1, C2 ... Cyan toner image
E ... Engine part
K1 ... Black toner image
M1, M2 ... Magenta toner image
Ra, Rb, Rc ... Registration control amount
T1 ~ T4 ... cycle
TP0 ... Establishment start temperature
VSYNC: Vertical synchronization signal
V ... Belt transport speed
Y1, Y2 ... Yellow toner image

Claims (19)

The transfer process of transferring the toner image formed on the photosensitive member to a transfer medium that is rotationally driven in the sub-scanning direction is repeated for a plurality of different toner colors to form a color image by superimposing the toner images of the respective toner colors. In the image forming apparatus to
A contact means for temporarily contacting the transfer medium when the transfer process is repeated;
Based on a registration control amount required to correct a relative registration shift of the toner image on the transfer medium caused by the contact means separating and contacting the transfer medium, at least of the plurality of toner colors. Control means for correcting the transfer start position of the toner image for one or more toner colors;
A reference signal detecting means for outputting a reference signal in relation to the rotation operation of the transfer medium,
The control means is based on the reference signal before forming a color image,
(1) a period when the contact means that has been separated from the transfer medium contacts the transfer medium;
(2) a period when the contact means continues to contact the transfer medium;
(3) a period when the contact means that is in contact with the transfer medium is separated from the transfer medium;
(4) and the period when the abutment means keeps away from the transfer medium
An image forming apparatus characterized in that the registration control amount is determined by executing a registration control amount establishment process whose processing content is to determine the registration control amount from the difference between these periods. It is configured to form a color image by superimposing toner images for three or more toner colors,
The image forming apparatus according to claim 1, wherein the control unit corrects a transfer start position of a toner image for at least a second toner color based on the registration control amount. It said control means, after the device power supply is turned on, and the first image forming apparatus registration control amount establish processing by executing obtaining the registration control amount according to claim 1 or 2, wherein before forming the color image. It said control means, the image forming apparatus according to any one of claims 1 to 3 executes the registration control amount establish processing during the warm-up process of the apparatus to be executed immediately after on of the apparatus power supply. Wherein, after the formation of the one color image, yet the registration control amount establish executes processing according to claim 1 or 2, the image forming apparatus according to prior to forming the next color image. A fixing unit for fixing the toner image;
Said control means, said fixing means image forming apparatus according to any one to five claims 1 executes the registration control amount establish processing Once at the prescribed temperature. It further comprises detection means for detecting at least one of temperature and humidity inside the apparatus,
Said control means, said detecting means detecting based on the result the registration control amount establish processing for determining the execution timing of claim 1 or 2, the image forming apparatus according. It said control means, said registration control amount establish processing image forming apparatus according to claim 1 or 2, wherein determining the execution timing in response to the status of the device. It said control means, the image forming apparatus according to claim 1 or 2, wherein determining the execution timing of the registration control amount establish processing based on the operating condition of the apparatus. 10. The registration control amount establishment process includes determining the registration control amount based on the plurality of periods measured after the transfer medium has rotated a predetermined number of times from the start of rotation . The image forming apparatus according to any one of the above. Further comprising a photoreceptor cleaner blade that is in constant contact with the photoreceptor;
11. The image forming apparatus according to claim 1, wherein the control unit supplies toner to the photoreceptor cleaner blade prior to executing the registration control amount establishment process. The image forming apparatus according to claim 1, wherein the contact unit includes at least a secondary transfer roller that transfers the toner image transferred onto the transfer medium onto a sheet member. The image forming apparatus according to claim 12 , wherein the control unit applies a secondary transfer bias to the secondary transfer roller when executing the registration control amount establishment process. The image forming apparatus according to claim 12 , wherein the control unit applies a bias having a polarity opposite to a secondary transfer bias to the secondary transfer roller when the registration control amount establishment process is executed. The image forming apparatus according to claim 1, wherein the control unit applies a primary transfer bias to the transfer medium when the registration control amount establishment process is executed. Drive means for driving the photoconductor and the transfer medium synchronously;
The controller controls acceleration / deceleration of the photosensitive member and the transfer medium by the driving unit and shifts a toner image formation position on the photosensitive member in the sub-scanning direction, thereby moving the toner image on the transfer medium. the image forming apparatus according to the transcription start position to any one of claims 1 to 15 to correct in the sub-scanning direction. Photoconductor drive means for rotationally driving the photoconductor;
A transfer medium driving means for driving the transfer medium;
16. The toner image transfer start position on the transfer medium is corrected in the sub-scanning direction by relatively accelerating / decelerating the transfer medium with respect to the photoconductor. Image forming apparatus. Exposure means for exposing an electrostatic latent image corresponding to the toner image on the photoreceptor;
The control means controls the exposure timing by the exposure means and shifts the toner image formation position on the photoconductor in the sub-scanning direction, thereby setting the transfer start position of the toner image on the transfer medium. the image forming apparatus according to any one of claims 1 to 17 to correct the scanning direction. The transfer process of transferring the toner image formed on the photoconductor to a transfer medium that is rotationally driven in the sub-scanning direction is repeated for a plurality of different toner colors to form a color image by superimposing the toner images of the respective toner colors. In the image forming method to
A registration control amount necessary for correcting a relative registration shift of the toner image on the transfer medium caused by the contact means temporarily contacting the transfer medium when the transfer process is repeated. The required resist control amount establishment process,
A correction step of correcting a transfer start position of a toner image for at least one of the plurality of toner colors based on the registration control amount;
A reference signal detection step of outputting a reference signal in relation to the rotation operation of the transfer medium,
The registration control amount establishment step is based on the reference signal before forming a color image,
(1) a period when the contact means that has been separated from the transfer medium contacts the transfer medium;
(2) a period when the contact means continues to contact the transfer medium;
(3) a period when the contact means that is in contact with the transfer medium is separated from the transfer medium;
(4) and the period when the abutment means keeps away from the transfer medium
And the registration control amount is obtained from the difference between the periods.

Images