JP2004325608A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of solving troubles that any correction is not performed at all by correcting color slippage as much as possible even when abnormality occurs in a resist mark. <P>SOLUTION: The image forming apparatus is provided with an image forming part 22 for transferring toner images of different colors so as to be superposed to each other, a pattern generator 42 for forming resist marks 61, 62 for detecting color slippage quantity of toner images on a transfer belt 243, reflection type photosensors 245 for detecting the positions of the formed resist marks 61, 62, a color slippage correction quantity calculation means for calculating color slippage correction quantity on the basis of detection signals outputted from these photosensors 245, and a sensor abnormality determination parts 523, 524 for determining the abnormality of respective resist marks 61, 62. The color slippage correction quantity calculation means corrects color slippage on the basis of the detection signal of the remaining resist mark without adopting the detection signal of the resist mark whose abnormality is determined by the resist mark abnormality determination parts 523, 524. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００７０】
なお、Ｓ波出力では上に凸となる波形となるため、所定時間毎（例えば、１ｍｓ毎）に得た出力値Ｓ［ｎ］のうちの予め設定した閾値Ｓｔｈ以上のもの（Ｓ［ｎ］≧Ｓｔｈ）について（すなわち、カウント値ｍ〜ｐ（ｍｓ）の範囲内のもの）、カウント値とそのカウント値に対応する出力値との積を各カウント値毎に合算し、この合算値を各カウント値の出力値を合算した値で除したものとして求めることができる。すなわち、Ｓ波出力の重心ＧＳは、下記の数２で示す式により求めることができる。これらの求めた重心ＧＰ，ＧＳは、算出する毎に制御部５０を構成するＲＡＭ等の記憶部に記憶される。このため、出力値Ｐ［ｎ］，Ｓ［ｎ］のすべてを記憶部に記憶させ、その後に重心ＧＰ，ＧＳを算出する場合に比べて記憶部は記憶容量の小さなものでよいことになる。
【００７１】
【数２】

【００７２】
そして、各線状パターンの色ずれ（位置ずれ）に対する補正量は、前記補正演算部５３０において算出される。すなわち、各線状パターンの色ずれについては、対向する左右両側の各横線Ｌ２，Ｌ２′の各線状パターンＫ２，Ｙ２，Ｃ２，Ｍ２の位置を検出することで斜め方向（傾き方向）の色ずれ量を検出することができ（すなわち、斜めになっていると一方の横線Ｌ２の検出時間と、他方の横線Ｌ２′の検出時間との間に差がでるため）、また、対向する左右両側の各横線Ｌ２，Ｌ２′の各線状パターンＫ２，Ｙ２，Ｃ２，Ｍ２の副走査方向の間隔を検出することで副走査方向の色ずれ量を検出することができ、対向する左右両側の少なくともいずれか一方の一組の斜め線Ｌ１（又はＬ１´）の各線状パターンＫ１，Ｙ１，Ｃ１，Ｍ１および横線Ｌ２（又はＬ２´）の各線状パターンＫ２，Ｙ２，Ｃ２，Ｍ２の同色どうしの間隔を検出することで主走査方向の色ずれ量を検出することができ（レジストパターンが幅方向にずれていると斜め線Ｌ１と横線Ｌ２との間の距離が変わってくるため）、これら検出された色ずれ量（ライン数乃至は画素数）から色ずれ補正量（ライン数乃至は画素数）が求められる。
【００７３】
なお、本実施形態では、斜め方向の色ずれ補正をする場合および副走査方向の色ずれ補正をする場合については、色ずれ補正により生じる画像の不具合を抑制するため、第４画像形成ユニット２２４により形成されるブラックトナー画像は補正せず、第１〜第３の画像形成ユニット２２１〜２２３により形成されるカラートナー画像をブラックトナー画像の位置に合わせるような色ずれ補正を行うようにしている。
【００７４】
ついで、傾きずれ補正部５３２が行う斜め方向の色ずれ補正（傾きずれ色ずれ補正）について詳細に説明する。斜め方向の色ずれ量（ライン数乃至は画素数）は、対向する左右両側の各横線Ｌ２，Ｌ２′のブラックトナー画像である第２の線状パターンＫ２の色ずれ量の総和ＫＡと、カラートナー画像である第２の線状パターンＹ２，Ｃ２，Ｍ２の色ずれ量の総和ＹＡ，ＣＡ，ＭＡとをそれぞれ求め、この求めたブラックトナー画像の色ずれ量の総和ＫＡに対する各カラートナー画像の色ずれ量の総和ＹＡ，ＣＡ，ＭＡの差を求め、これら各差を各カラートナー画像の色ずれ補正量（ライン数乃至は画素数）としている。
【００７５】
すなわち、ＬＥＤプリントヘッドからなる露光部２２７の主走査方向（ライン方向）の画素数をＮ（例えば、Ｎ＝７１６８）、一対の第１および第２フォトセンサ２４５１，２４５２間の距離（画素数）をＤ（例えば、Ｄ＝５１８４画素）、転写ベルト２４３の周速をＳ（ｍｍ／ｓ）（例えば、Ｓ＝１１６ｍｍ／ｓ）、１画素の幅をＧ（ｍｍ）（例えば、Ｇ＝０．０４２３ｍｍ）とする一方、一方端部側のブラックトナー画像である４本の第２の線状パターンＫ２の位置を下流側から上流側に向けて順にＫ２１Ｆ，Ｋ２２Ｆ，Ｋ２３Ｆ，Ｋ２４Ｆとするとともに、他方端部側のブラックトナー画像である４本の第２の線状パターンＫ２の位置を下流側から上流側に向けて順にＫ２１Ｒ，Ｋ２２Ｒ，Ｋ２３Ｒ，Ｋ２４Ｒとすると、ブラックトナー画像である第２の線状パターンＫ２の色ずれ量の総和ＫＡは、下記の数３で示す式により求めることができる。
【００７６】
【数３】

【００７７】
また、一方端部側のイエロートナー画像である４本の第２の線状パターンＹ２の位置を下流側から上流側に向けて順にＹ２１Ｆ，Ｙ２２Ｆ，Ｙ２３Ｆ，Ｙ２４Ｆとするとともに、他方端部側のイエロートナー画像である４本の第２の線状パターンＹ２の位置を下流側から上流側に向けて順にＹ２１Ｒ，Ｙ２２Ｒ，Ｙ２３Ｒ，Ｙ２４Ｒとすると、イエロートナー画像である第２の線状パターンＹ２の色ずれ量の総和ＹＡは、下記の数４で示す式により求めることができる。
【００７８】
【数４】

【００７９】
また、一方端部側のシアントナー画像である４本の第２の線状パターンＣ２の位置を下流側から上流側に向けて順にＣ２１Ｆ，Ｃ２２Ｆ，Ｃ２３Ｆ，Ｃ２４Ｆとするとともに、他方端部側のシアントナー画像である４本の第２の線状パターンＣ２の位置を下流側から上流側に向けて順にＣ２１Ｒ，Ｃ２２Ｒ，Ｃ２３Ｒ，Ｃ２４Ｒとすると、シアントナー画像である第２の線状パターンＣ２の色ずれ量の総和ＣＡは、下記の数５で示す式により求めることができる。
【００８０】
【数５】

【００８１】
さらに、一方端部側のマゼンタトナー画像である４本の第２の線状パターンＭ２の位置を下流側から上流側に向けて順にＭ２１Ｆ，Ｍ２２Ｆ，Ｍ２３Ｆ，Ｍ２４Ｆとするとともに、他方端部側のマゼンタトナー画像である４本の第２の線状パターンＭ２の位置を下流側から上流側に向けて順にＭ２１Ｒ，Ｍ２２Ｒ，Ｍ２３Ｒ，Ｍ２４Ｒとすると、シアントナー画像である第２の線状パターンＭ２の色ずれ量の総和ＭＡは、下記の数６で示す式により求めることができる。
【００８２】
【数６】

【００８３】
従って、ブラックトナー画像に対するイエロートナー画像の色ずれ量ＹＡ′、シアントナー画像の色ずれ量ＣＡ′、および、マゼンタトナー画像の色ずれ量ＭＡ′は、それぞれ下記の数７で示す式により求めることができる。この数７で示す式により求めたＹＡ′、ＣＡ′およびＭＡ′が各カラートナー画像の色ずれ補正量となる。なお、今までにすでに色ずれ補正を行っている場合は、今回の色ずれ補正量と前回の色ずれ補正量とから実際に補正を行うべき色ずれ補正量を再算出するようにすればよい。
【００８４】
【数７】

【００８５】
つぎに、副走査ずれ補正部５３３が行う副走査方向の色ずれ補正について詳細に説明する。副走査方向の色ずれ量（ライン数乃至は画素数）は、上述したように、対向する左右両側の各横線Ｌ２，Ｌ２′の各線状パターンＫ２，Ｙ２，Ｃ２，Ｍ２の副走査方向の間隔を検出することにより求めることができるが、本実施形態ではカラートナー画像の各線状パターンＹ２，Ｃ２，Ｍ２のブラックトナー画像の線状パターンＫ２に対する間隔により各線状パターンＹ２，Ｃ２，Ｍ２の色ずれ量を検出するようにしている。すなわち、カラートナー画像の線状パターンＹ２についていえば、その線状パターンＹ２の位置とブラックトナー画像の線状パターンＫ２の位置とから求めた間隔の基準値（初期設定値）との差により色ずれ量を求めるようにしている。
【００８６】
他のカラートナー画像の線状パターンＣ２，Ｍ２についても、その線状パターンＣ２，Ｍ２の位置とブラックトナー画像の線状パターンＫ２の位置とから求めた間隔の各基準値（初期設定値）との差により色ずれ量を求めることができる。但し、この求めた色ずれ量は斜め方向の色ずれ量を含んだものであるため、斜め方向の色ずれ量を補正したものが副走査方向の色ずれ補正量となる。このため、予めカラートナー画像の線状パターンＹ２，Ｃ２，Ｍ２につき、上記の「数７」に示す数式により斜め方向の色ずれ補正量を求めておく必要がある。
【００８７】
最後に、主走査ずれ補正部５３４が行う主走査方向の色ずれ補正について説明する。主走査方向の色ずれ量（画素数）は、本実施形態では一方端部側の各組の同色の斜め線Ｌ１および横線Ｌ２の各線状パターン（ブラックトナー画像については同じ組のＫ１とＫ２、イエロートナー画像については同じ組のＹ１とＹ２、シアントナー画像については同じ組のＣ１とＣ２、マゼンタトナー画像については同じ組のＭ１とＭ２）の間隔の基準値（初期設定値）との差により求めるようにしている。
【００８８】
すなわち、転写ベルト２４３の周速をＳ（ｍｍ／ｓ）（例えば、Ｓ＝１１６ｍｍ／ｓ）、１画素の幅をＧ（ｍｍ）（例えば、Ｇ＝０．０４２３ｍｍ）、各組の同色の斜め線Ｌ１の線状パターンと横線Ｌ２の線状パターンの間隔の基準値（ライン数）をＱ（例えば、Ｑ＝８６４ライン）とする一方、一方端部側のブラックトナー画像である各４本の第１線状パターンＫ１および第２の線状パターンＫ２の位置をそれぞれ下流側から上流側に向けて順にＫ１１Ｆ，Ｋ１２Ｆ，Ｋ１３Ｆ，Ｋ１４ＦおよびＫ２１Ｆ，Ｋ２２Ｆ，Ｋ２３Ｆ，Ｋ２４Ｆとすると、ブラックトナー画像の各組の色ずれ補正量ＫＨ［０］，ＫＨ［１］，ＫＨ［２］，ＫＨ［３］は、下記の数８で示す式により求めることができる。この数８で示す式により求めた各組の色ずれ補正量ＫＨ［０］，ＫＨ［１］，ＫＨ［２］，ＫＨ［３］の平均値がブラックトナー画像の色ずれ補正量（画素数）となる。
【００８９】
【数８】

【００９０】
また、一方端部側のイエロートナー画像である各４本の第１の線状パターンＹ１および第２の線状パターンＹ２の位置をそれぞれ下流側から上流側に向けて順にＹ１１Ｆ，Ｙ１２Ｆ，Ｙ１３Ｆ，Ｙ１４ＦおよびＹ２１Ｆ，Ｙ２２Ｆ，Ｙ２３Ｆ，Ｙ２４Ｆとすると、イエロートナー画像の各組の色ずれ補正量ＹＨ［０］，ＹＨ［１］，ＹＨ［２］，ＹＨ［３］は、下記の数９で示す式により求めることができる。この数９で示す式により求めた各組の色ずれ補正量ＹＨ［０］，ＹＨ［１］，ＹＨ［２］，ＹＨ［３］の平均値がイエロートナー画像の色ずれ補正量（画素数）となる。
【００９１】
【数９】

【００９２】
また、一方端部側のシアントナー画像である各４本の第１の線状パターンＣ１および第２の線状パターンＣ２の位置をそれぞれ下流側から上流側に向けて順にＣ１１Ｆ，Ｃ１２Ｆ，Ｃ１３Ｆ，Ｃ１４ＦおよびＣ２１Ｆ，Ｃ２２Ｆ，Ｃ２３Ｆ，Ｃ２４Ｆとすると、シアントナー画像の各組の色ずれ補正量ＣＨ［０］，ＣＨ［１］，ＣＨ［２］，ＣＨ［３］は、下記の数１０で示す式により求めることができる。この数１０で示す式により求めた各組の色ずれ補正量ＣＨ［０］，ＣＨ［１］，ＣＨ［２］，ＣＨ［３］の平均値がシアントナー画像の色ずれ補正量（画素数）となる。
【００９３】
【数１０】

【００９４】
さらに、一方端部側のマゼンタトナー画像である各４本の第１の線状パターンＭ１および第２の線状パターンＭ２の位置をそれぞれ下流側から上流側に向けて順にＭ１１Ｆ，Ｍ１２Ｆ，Ｍ１３Ｆ，Ｍ１４ＦおよびＭ２１Ｆ，Ｍ２２Ｆ，Ｍ２３Ｆ，Ｍ２４Ｆとすると、マゼンタトナー画像の各組の色ずれ補正量ＭＨ［０］，ＭＨ［１］，ＭＨ［２］，ＭＨ［３］は、下記の数１１で示す式により求めることができる。この数１１で示す式により求めた各組の色ずれ補正量ＭＨ［０］，ＭＨ［１］，ＭＨ［２］，ＭＨ［３］の平均値がマゼンタトナー画像の色ずれ補正量（画素数）となる。
【００９５】
【数１１】

【００９６】
副走査タイミング制御部５０４および主走査タイミング制御部５０５は、補正演算部５３０で求めた色ずれ補正量に基づいて各色の色ずれ補正を実行するものである。すなわち、斜め方向の色ずれ補正をする場合は、ブラックトナー画像を除いたカラートナー画像につき上記の数７で示す式により求めた色ずれ補正量ＹＡ′、ＣＡ′およびＭＡ′の補正を行うことになる。この場合、主走査方向の領域を補正量ＹＡ′、ＣＡ′およびＭＡ′の値に応じて略等間隔の複数に分割し、この分割した領域を単位として斜め方向に階段状に補正を行うことになる。なお、今までにすでに色ずれ補正を行っている場合は、上述の再算出した色ずれ補正量に基づいて補正を行うようにすればよい。
【００９７】
例えば、主走査方向の画素数が７１６８で、色ずれ補正量が副走査方向に１ライン分（あるいは１画素分）あったとすると、図６に概念的に示すように、画像メモリ５０２（図３）に記憶されている画像データの読み出し位置が７１６８×１／２の位置にきたとき、その傾き方向に応じて前のラインあるいは後のラインのアドレスに読み出しアドレスを切り換えるようにすればよい。
【００９８】
また、主走査方向の画素数が７１６８で、色ずれ補正量が副走査方向に３ライン分（あるいは３画素分）あったとすると、図７に概念的に示すように、画像メモリ５０２に記憶されている画像データの読み出し位置が７１６８×１／４、７１６８×２／４および７１６８×３／４の各位置にきたとき、その傾き方向に応じて前のラインあるいは後のラインのアドレスに順次読み出しアドレスを切り換えるようにすればよい。なお、通常、画像メモリ５０２に記憶されている画像データは数ライン分ごとにラインバッファに取り込まれることになるので、この場合はラインバッファから画像データを読み出すときに読み出しアドレスを切り換えるようにすればよい。
【００９９】
また、副走査方向の色ずれ補正をする場合は、ブラックトナー画像を除いたカラートナー画像につき、副走査ずれ補正部５３３で算出した色ずれ補正量に基づいて画像データの書き出しタイミングを調整するようにすればよい。例えば、図８に示すタイムチャートに基づいて説明すると、マゼンタトナー画像（Ｍ）については、基準となる副走査方向の画像有効区間信号の立下りから時間ａが経過したときに画像データの書き出しが実行され、シアントナー画像（Ｃ）については、マゼンタトナー画像（Ｍ）の副走査方向の画像有効区間信号の立下りから時間ｂが経過したときに画像データの書き出しが実行される。
【０１００】
また、イエロートナー画像（Ｙ）については、シアントナー画像（Ｃ）の副走査方向の画像有効区間信号の立下りから時間ｃが経過したときに画像データの書き出しが実行され、ブラックトナー画像（Ｋ）については、イエロートナー画像（Ｙ）の副走査方向の画像有効区間信号の立下りから時間ｄが経過したときに画像データの書き出しが実行される。
【０１０１】
また、主走査方向の色ずれ補正をする場合は、ブラックトナー画像および各カラートナー画像につき、ＬＥＤプリントヘッドからなる露光部２２７（図１）の主走査方向（ライン方向）の左右両側の端部に挿入する余白部分を形成するための白画素量（白画素の個数）を主走査ずれ補正部５３４で算出した色ずれ補正量に応じて調整するようにしている。例えば、図９に示すタイムチャートに基づいて説明すると、読み出しクロック信号に同期して設定される露光部２２７の主走査方向における有効画像区間（有効画像区間信号（Ｐ）のＯＮ区間）内の端部（例えば、符号ｔで示す区間）に挿入する白画素量を主走査ずれ補正部５３４で算出した色ずれ補正量に応じて調整することで画像メモリ５０２から読み出された画像データを主走査方向に移動させ、これにより色ずれ補正を行うようにしている。
【０１０２】
なお、露光部２２７の主走査方向の端部に挿入する白画素量は、主走査ずれ補正部５３４で算出した色ずれ補正量と、画像のセンター位置を調整するために露光部２２７の主走査方向の端部に挿入される白画素量とから設定されることになる。この白画素は、露光部２２７に“０”の画像データを送出することで生成されるものである。
【０１０３】
そして、本発明は、上記のような補正演算部５３０による色ずれの補正量算出、並びに副走査タイミング制御部５０４および主走査タイミング制御部５０５によるタイミング制御を前提とするものであり、かかる制御が実行され得る状態で、レジストマークに異常が検出された場合に色ずれ制御が適正に行われなくなるという課題を、センサ制御部５２０の第１および第２サンプリング処理部５２１，５２２による第１および第２レジストマーク６１，６２の適否判定データの採取、並びに得られたデータに基づく第１および第２レジストマーク異常判定部５２３，５２４による判定結果に基づいて以下に説明するように適正に対処することで解決するものである。
【０１０４】
以下、本発明の作用について図１０を基に説明する。図１０は、レジストマークの異常検出と、異常が検出された場合の対応を説明するためのフローチャートである。ステップＳ１では、第１および第２フォトセンサ２４５１，２４５２のＬＥＤ光量等の調整を行う。ステップＳ２では第１および第２レジストマーク６１，６２の形成を行う。
【０１０５】
ついで、ステップＳ３で第１および第２フォトセンサ２４５１，２４５２により、第１および第２レジストマーク６１，６２の読み取りを行う。この読み取りデータよりステップ４でまず第１レジストマークが異常か正常かが判定される。この判定方法を図１１を用いて説明する。レジストマークは図２で示したように各色１ライン毎に形成された４本のラインを１単位として形成される（たとえば図２のＬ１、Ｌ２）。従って、Ｐ波出力が１本、Ｓ波出力として３本の合計４本の出力が得られる。第１レジストマーク異常判定部５２３はこの本数をカウントし
所定の本数と同じかどうかを判定する。この場合４本であれば正常と判定する。
【０１０６】
もしレジストマークが図１１のＡのＫ２のように作成されなかったときは、Ｐ波がＰｔｈを越えないため３本しかカウントされず異常と判定される。また、図１１のＢのＭ１のようにレジストマークの中心にトナーが載らなかったときはマークの両端においてＳｔｈを越え中心ではＳｔｈを下回りＭ１部では２本分カウントされてしまう。この結果総数は５本となり異常と判定される。この判定方式については以下同様である。
【０１０７】
そして、ステップＳ４で第１レジストマークが異常でない（すなわち正常）と判定されたとき（Ｓ４でＮＯ）には、ステップＳ５で第２レジストマークが異常であるか否かが判定される。この判定の結果、第２レジストマークが異常でない（すなわち正常）と判定された場合（すなわち、第１および第２レジストマークの双方が正常と判定された場合）、傾きずれ補正部５３２による傾きずれ（斜め色ずれ）の補正値の算出（Ｓ６）、副走査ずれ補正部５３３による副走査方向の色ずれの補正値の算出（Ｓ７）、主走査ずれ補正部５３４による主走査方向の色ずれの補正値の算出（Ｓ８）が実行される。
【０１０８】
これに対し、ステップＳ５で第２レジストマークが異常と判定された場合（すなわち、第１レジストマークが正常で第２レジストマークが異常の場合）、傾きずれの補正値を算出することなく、副走査方向の色ずれの補正値の算出（Ｓ１７）、主走査方向の色ずれの補正値の算出（Ｓ１８）が順次実行され、その後、センサ異常通知部５１２によって第２レジストマークが異常である旨の通知がなされる（Ｓ１９）。
【０１０９】
一方、前記ステップＳ４において第１レジストマークが異常と判定された場合（Ｓ４でＹＥＳ）、第２レジストマークが異常であるか否かが判定され（Ｓ９）、第２レジストマークが異常でない場合（すなわち、第２レジストマークは正常であるが第１レジストマークが異常な場合）、傾きずれの補正値を算出することなく、副走査方向の色ずれの補正値の算出（Ｓ２７）、主走査方向の色ずれの補正値の算出（Ｓ２８）が順次実行され、その後、センサ異常通知部５１２によって第１フォトセンサ２４５１が異常である旨の通知がなされる（Ｓ２９）。
【０１１０】
前記ステップＳ９で第２レジストマークが異常と判定された場合（すなわち第１および第２レジストマークの双方が異常の場合）、ステップＳ３９においてセンサ異常通知部５１２によるセンサ異常発生の報知が行われるのみで、色ずれ補正のためのアクションはなにも行われない。
【０１１１】
なお、図１０には記載がないが、ステップＳ８、ステップＳ１９、ステップＳ２９の後、副走査タイミング制御部５０４および主走査タイミング制御部５０５による制御の基に、具体的に色ずれの補正が実行される。
【０１１２】
本発明の画像形成装置１０は、以上詳述したように、転写ベルト２４３により搬送される用紙Ｐに対して異なる色のトナー画像を重ねて転写する画像形成部２２と、用紙Ｐ上に転写されるトナー画像の色ずれ量検出用のレジストマークを画像形成部２２により転写ベルト２４３上に形成させるパターンジェネレータ４２と、転写ベルト２４３上に形成されたレジストマークの位置を検出するための反射型フォトセンサ２４５（第１および第２フォトセンサ２４５１，２４５２）と、これらから出力される検出信号に基づいて色ずれ補正量を算出する色ずれ補正量算出手段（傾きずれ補正部５３２、副走査ずれ補正部５３３および主走査ずれ補正部５３４）とが備えられてなるものであり、第１および第２レジストマークの異常を判定する第１および第２レジストマーク異常判定部５２３，５２４が備えられ、色ずれ補正量算出手段は、第１および第２レジストマーク異常判定部５２３，５２４が異常と判定した方の反射型フォトセンサ２４５の検出信号を採用することなく残りの反射型フォトセンサ２４５の検出信号に基づいて色ずれの補正を行うものである。
【０１１３】
したがって、２台の反射型フォトセンサ２４５（第１および第２フォトセンサ２４５１，２４５２）に対応したレジストマークのいずれかが異常になっても、色ずれ補正量算出手段は、残りのレジストマークの反射型フォトセンサ２４５による検出結果に基いて色ずれ補正量を算出し、この算出結果に基いて色ずれ補正が実行されるため、用紙Ｐに可能な限り色ずれ補正の施されたカラー画像を形成させることができる。したがって、全く色ずれ補正が行われない場合に比較してより良好なカラー画像を用紙Ｐに形成させることができる。
【０１１４】
また、第１および第２レジストマーク異常判定部５２３，５２４は、レジストマークが線状パターンからなり、前記線状パターンの本数が所定の数だけ出力されたときレジストマークを正常と判別し、これ以外のとき異常と判別するするようにしているため、レジストマークの本数を計測するという簡単な操作で当該レジストマークの正常・異常が判別され、装置コストの低減化に貢献することができる。
【０１１５】
また、レジストマークは、副走査方向に沿って所定の間隔をおいて形成されるとともに、副走査方向に対して斜めに延びるように形成された斜め線Ｌ１と、主走査方向に延びるように形成された横線Ｌ２とからなり、反射型フォトセンサ２４５は、レジストマークに対応して一対で設けられ、色ずれ補正量算出手段は、主走査方向の色ずれ補正量を反射型フォトセンサ２４５から出力される検出信号に基づいて算出される斜め線Ｌ１の間隔および横線Ｌ２の間隔と、予めそれぞれの間隔に対応して設定された各基準値とを比較することにより算出するようにしているため、色ずれ補正の精度を向上させることができる。
【０１１６】
また、第１および第２レジストマークのいずれか一方が第１および第２レジストマーク異常判定部５２３，５２４のいずれかにより異常と判定された場合、色ずれ補正量算出手段は、他方の検出信号に基づいて色ずれ補正量を算出する一方、双方が第１および第２レジストマーク異常判定部５２３，５２４により異常と判定された場合、色ずれ補正量の算出を中止されるため、第１および第２レジストマークのいずれか一方が異常と判定されても、他方のレジストマークのみを用いることでそれなりの色ずれ補正を行うことができる。そして、第１および第２レジストマークの双方が異常と判定されたときには、色ずれ補正が中止されるため、レジストマークが異常であるにも拘らず、異常なままで色ずれ補正を行うことによって逆に色ずれが増幅されるような不都合の発生を防止することができる。
【０１１７】
そして、制御部５０の管理部５１０には、異常判定手段が異常と判定したレジストマークを特定して通知するレジストマーク異常通知部５１２が設けられているため、この通知によってどのレジストマークが異常になっているかを知ることができる。
【０１１８】
しかも、レジストマーク異常通知部５１２は、専用のモード設定により異常判定手段が異常と判定したレジストマークに係る情報を出力するようにしているため、レジストマークの異常を一般のユーザーに意識させることを抑制した状態で、専門の技術者に知らせることができ、無駄な混乱を避けることができる。
【０１１９】
本発明は、上記の実施形態に限定されるものではなく、以下の内容をも包含するものである。
【０１２０】
（１）上記実施形態では、斜め方向の色ずれ補正を行う場合、ブラックトナー画像を基準に各カラートナー画像の色ずれ補正を行うようにしているが、これに限るものではない。例えば、ブラックトナー画像および各カラートナー画像のそれぞれについて、それぞれの初期設定位置に対する色ずれ補正量を求め、この求めた色ずれ補正量に基づいて色ずれ補正を行うようにしてもよい。
【０１２１】
（２）上記実施形態では、副走査方向の色ずれ補正を行う場合、ブラックトナー画像を基準に各カラートナー画像の色ずれ補正を行うようにしているが、これに限るものではない。例えば、ブラックトナー画像および各カラートナー画像のそれぞれについて、それぞれの初期設定位置に対する色ずれ補正量を求め、この求めた色ずれ補正量に基づいて色ずれ補正を行うようにしてもよい。
【０１２２】
（３）上記実施形態では、所定の計算式に基づいて色ずれ補正量を算出するようにしているが、こうすることに限定されるものではなく、制御部５０の所定の記憶部に記憶させたテーブルを用いて色ずれ補正量を求めるようにしてもよい。要は、補正演算部５３０が計算式やテーブル等から色ずれ補正量を算出する機能を有しておればよいのである。
【０１２３】
（４）上記の実施形態では、画像形成装置１０として、画像形成ユニット２２１〜２２４を転写ベルト２４３の移送方向に沿って配設する方式（いわゆるタンデム方式）が採用されているが、これに限るものではなく、例えば、用紙を搬送する状画像担持体としての回転ドラムの回転方向に沿って画像形成ユニット２２１〜２２４を配設するようにしたものであってもよい。
【０１２４】
（５）上記実施形態では、色ずれを検出するためのレジストマークは、転写ベルト２４３の幅方向両端部に形成されたものであるが、レジストマークを転写ベルト２４３の幅方向の両端部に設けることに限定されるものではなく、例えば、転写ベルト２４３の幅方向における一方端部側にのみ形成することも可能であり、転写ベルト２４３の幅方向の中央部に設けてもよい。
【０１２５】
（６）上記実施形態では、色ずれを検出するためのレジストマークは、副走査方向に対して斜めに形成された線状パターンからなる斜め線Ｌ１と、主走査方向に沿って形成された線状パターンからなる横線Ｌ２とから構成されているが、これに限るものではない。例えば、線状パターンからなる斜め線Ｌ１と線状パターンからなる横線Ｌ２とも副走査方向に対して斜めに形成されていてもよい。要は、斜め線Ｌ１を構成する線状パターンと横線Ｌ２を構成する線状パターンとが互いに異なる角度を有するように形成されておればよい。
【０１２６】
（７）上記実施形態では、色ずれを検出するためのレジストマークはパターンジェネレータ４２を用いて形成されたものであるが、これに限るものではない。例えば、制御部５０の記憶部に線状パターンからなる斜め線Ｌ１と横線Ｌ２との組み合わせからなる画像データとして記憶させておき、この画像データを読み出すことで転写ベルト２４３面にレジストマークを形成するようにすることもできる。
【０１２７】
（８）上記実施形態では、露光部２２７はＬＥＤプリントヘッドから構成されたものであるが、これに限定されるものではない。例えば、レーザ光走査型のものであってもよい。
【０１２８】
（９）上記実施形態では、画像形成装置１０はカラープリンタであるが、これに限るものではない。例えば、カラー複写機やカラーファクシミリ等の他の構成であってもよい。
【０１２９】
【発明の効果】
本発明の画像形成装置によれば、色ずれ補正量算出手段は、異常判定手段が異常と判定したレジストマークの検出信号を採用することなく残りのレジストマークの検出信号に基づいて色ずれの補正を行うようにしているため、複数存在するレジストマークのいずれかが異常になっても、色ずれ補正量算出手段は、残りのレジストマークによる検出結果に基いて色ずれ補正量を算出し、この算出結果に基いて色ずれ補正が実行される。したがって、用紙に可能な限り色ずれ補正の施されたカラー画像を形成させることができ、全く色ずれ補正が行われない場合に比較して用紙により良好なカラー画像を印刷することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る色ずれ補正方法が適用されるデジタルカラー画像形成装置の内部構成を概略的に示す説明図である。
【図２】感光体ドラムを含めた状態の転写搬送部の平面視の説明図である。
【図３】種々の変動要因による色ずれ量の検出動作およびその色ずれ補正動作を説明するための制御構成を示すブロック図である。
【図４】反射型フォトセンサの出力波形を説明するための説明図である。
【図５】反射型フォトセンサのＰ波出力の重心を求める説明のための説明図である。
【図６】斜め方向の色ずれ補正を説明するための説明図である。
【図７】斜め方向の他の色ずれ補正を説明するための説明図である。
【図８】副走査方向の色ずれ補正を説明するためのタイムチャートである。
【図９】主走査方向の色ずれ補正を説明するためのタイムチャートである。
【図１０】レジストマークの異常検出と、異常が検出された場合の対応を説明するためのフローチャートである。
【図１１】レジストマークの出力波形を説明するための説明図である。
【符号の説明】
１０ 画像形成装置 １２ 本体部
１４ 用紙排出部 １８ 筐体
２０ 給紙カセット ２２ 画像形成部
２２１〜２２４ 第１〜第４画像形成ユニット
２２５ 感光体ドラム ２２６ 帯電部
２２７露光部 ２２８ 現像部
２２９ クリーニング部 ２３０ 転写部
２４ 転写搬送部 ２４１ 従動ローラ
２４２ 駆動ローラ ２４３ 転写ベルト
２４４ 転写ローラ ２４５ 反射型フォトセンサ
２４５１ 第１フォトセンサ ２４５２ 第２フォトセンサ
２４６ ブレード ２６ 定着ユニット
２６１ 熱遮蔽ボックス ２６２ 定着ローラ
２６３ 加圧ローラ ２６４ ブレード
２６５ 後搬送路 ２８ 第１の搬送路
２８１ 搬送ローラ対 ２８２ レジストローラ対
２８３ タイミングセンサ ４０ 画像入力部
４１ スキャナ ４２パターンジェネレータ
４３ レジストマーク入力部 ４４ レジストマーク生成部
５０ 制御部 ５００ 画像制御部
５０１ メモリ書込処理部 ５０２ 画像メモリ
５０３ メモリ読出処理部 ５０４ 副走査タイミング制御部
５０５ 主走査タイミング制御部
５１０ 管理部 ５１１ 補正実行管理部
５１２ レジストマーク異常通知部
５２０ センサ制御部
５２１ 第１サンプリング処理部
５２２ 第２サンプリング処理部
５２３ 第１レジストマーク異常判定部
５２４ 第２レジストマーク異常判定部
５２５ 第１レジストマーク位置算出部
５２６ 第２レジストマーク位置算出部
５３０ 補正演算部 ５３１ 補正方法選択部
５３２ 傾きずれ補正部 ５３３ 副走査ずれ補正部
５３４ 主走査ずれ補正部 Ｌ１，Ｌ１′ 斜め線
Ｌ２，Ｌ２′ 横線
６１ 第１レジストマーク ６２ 第２レジストマーク[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a full-color printer or a full-color copying machine having a plurality of image forming units that transfer toner images of different colors onto a sheet in a multiplex manner, and to an image forming apparatus having a color misregistration correction function. Things.
[0002]
[Prior art]
Conventionally, four image forming units including photoreceptor drums for individually forming four color toner images of yellow, magenta, cyan and black are arranged along a transport direction on a transfer belt for transporting a sheet. A tandem-type full-color printer or full-color copier configured to form a color image by superimposing and transferring toner images of each color formed on a photosensitive drum onto a sheet conveyed by a transfer belt. And the like are known.
[0003]
In such a tandem-type image forming apparatus, when forming a high-accuracy color image on a sheet, it is necessary to transfer toner images of each color onto the sheet so that color shift does not occur mutually. Mounting error of the exposure unit including the LED print head for forming an electrostatic latent image on the surface, mounting error of the image forming unit including the photoconductor drum, rotation speed error of the photoconductor drum, etc. A color shift inevitably occurs due to various fluctuation factors such as a minute change in the distance between image forming units due to an environmental change and a deformation of the image forming unit itself.
[0004]
For this reason, for example, a registration mark composed of a linear pattern of each color is formed on the surface of the transfer belt by an image forming unit, and the position of the registration mark is detected by a mark detection unit installed on the downstream side. The color misregistration correction is performed based on the position information of the registration mark detected in (1) (for example, see Patent Document 1).
[0005]
By the way, in such color misregistration correction, the registration mark may not be able to output a correct detection signal due to scratches and dirt on the transfer belt. If color misregistration correction is continued in this state, an abnormal image is transferred to the paper. Would. In order to avoid such an inconvenience, a detecting means for detecting an abnormality in the registration mark is adopted when an abnormality occurs in the registration mark. When the detecting means detects an abnormality in the registration mark, the location where the abnormality has occurred is stored, and In order to avoid this, a registration mark has been developed (for example, see Patent Document 2).
[0006]
[Patent Document 1]
JP-A-13-171170 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-13767
[Problems to be solved by the invention]
However, there is a high possibility that scratches and dirt on the transfer belt will occur over the entire circumference of the transfer belt, and in this case, there is no place to create a registration mark, and it becomes impossible to perform color misregistration correction. For this reason, when the color shift correction is not entirely performed, a new problem to be solved is that an image without the color shift correction is output.
[0008]
The present invention has been made in view of such circumstances, and even if an error occurs in a registration mark, color shift correction is performed as much as possible, thereby solving the problem that correction is not performed at all. It is an object of the present invention to provide an image forming apparatus capable of performing the above.
[0009]
[Means for Solving the Problems]
An image forming unit having an exposure unit for exposing a photosensitive drum, and transferring toner images of different colors onto a sheet conveyed by an image carrier in a superimposed manner. Mark forming control means for forming the registration marks for detecting the color misregistration amount of the toner image transferred to the image carrier in a plurality of rows on the image carrier by the image forming unit; A plurality of mark detection means provided corresponding to the registration mark for detecting the position of the registration mark; and a color misregistration correction amount for calculating a color misregistration correction amount based on a detection signal output from each mark detection means. An image forming apparatus comprising: a calculation unit; a registration mark abnormality determination unit configured to determine whether the registration mark is abnormal; Calculating means is characterized in that said abnormality judgment means performs a correction of color shift on the basis of the detection signals excluding the detection signal of the registration mark is determined to be abnormal.
[0010]
According to the present invention, even if any one of the plurality of registration marks becomes abnormal, the color misregistration correction amount calculating means excludes the registration mark that has been detected abnormally based on the detection result of the remaining registration marks. Since the color misregistration correction amount is calculated and the color misregistration correction is executed based on the calculation result, a color image on which the color misregistration correction is performed as much as possible is formed on the sheet. Therefore, a better color image is printed on the paper as compared with the case where no color misregistration correction is performed.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, the registration mark is formed of a linear pattern, and the registration mark abnormality determination unit determines that the number of the linear pattern is a predetermined number from the mark detection unit. When output, the registration mark is determined to be normal, and otherwise, it is determined to be abnormal.
[0012]
According to the present invention, the normality / abnormality of the registration mark is determined by a simple operation of measuring the number of registration marks output from the mark detection means, which contributes to simplification of the abnormality determination processing.
[0013]
According to a third aspect of the present invention, in the first or second aspect of the present invention, a pair of the mark detection units are provided so as to face each other in the width direction of the image carrier, and each of the registration marks is a pair of mark detection units. The registration marks in each row are formed in two rows so as to correspond to the respective means, and the registration marks in each row are formed so as to extend obliquely to the sub-scanning direction and to extend in the main scanning direction. The second color pattern, and the color misregistration correction amount calculating means calculates a color misregistration correction amount between the first linear patterns calculated based on a detection signal output from the mark detecting means. By comparing any one of the interval, the interval between the second linear patterns, and the interval between the first and second linear patterns with each reference value set in advance corresponding to each interval. Also calculate It is characterized in that it.
[0014]
According to the present invention, since the registration mark is formed of the first and second linear patterns and is provided at a predetermined interval along the sub-scanning direction, a large amount of information (data ) Can be obtained, and the accuracy of the color misregistration correction is improved.
[0015]
According to a fourth aspect of the present invention, in the invention of the third aspect, one of the registration marks formed in two rows corresponding to the pair of mark detection means is abnormal by the registration mark abnormality determination means. When the determination is made, the color shift correction amount calculating means calculates the color shift correction amount based on the other registration mark.
[0016]
According to the present invention, even if any one of the pair of registration marks is determined to be abnormal by the abnormality determining means, it is possible to perform appropriate color misregistration correction by using only the other registration mark. When both registration marks are determined to be abnormal, the color misregistration correction is stopped. The occurrence of inconvenience such as amplification is prevented.
[0017]
According to a fifth aspect of the present invention, in the first aspect of the present invention, there is provided an abnormality notifying means for notifying when the registration mark abnormality determining means determines that there is an abnormality. It is.
[0018]
According to the present invention, it is possible to know which registration mark has become abnormal by the notification of the abnormality notifying means.
[0019]
According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the abnormality notifying unit outputs information relating to the mark detecting unit that has been determined to be abnormal by the abnormality determining unit by setting a dedicated mode. That is.
[0020]
According to the present invention, it is possible to notify a specialized technician in a state where the abnormality of the registration mark is suppressed from being made conscious by a general user, and unnecessary confusion can be avoided.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an explanatory diagram schematically showing an internal configuration of a digital color image forming apparatus to which a color misregistration correction method according to an embodiment of the present invention is applied, and FIG. 2 is a diagram showing a state including a photosensitive drum. FIG. 3 is an explanatory diagram of a transfer conveyance unit in a plan view. First, as shown in FIG. 1, the image forming apparatus 10 constitutes a tandem-type color printer, and includes a main body 12 for printing a color image on paper (transfer paper) and an upper part of the main body 12. And a paper discharge unit 14 from which the paper on which the color image is printed by the main body unit 12 is discharged.
[0022]
The main body 12 includes a paper feed cassette 20 disposed at a lower part in the housing 18, an image forming unit 22 disposed at an upper part in the housing 18, and a lower part of the image forming unit 22 in the housing 18. , A fixing unit 26 disposed downstream of the transfer transport unit 24 in the housing 18, and a transfer unit 24 disposed between the sheet cassette 20 and the transfer transport unit 24. A first transport path 28 and a second transport path 30 disposed between the fixing unit 26 and the sheet discharge unit 14 are provided.
[0023]
The paper feed cassette 20 is configured so that the paper P can be replenished by being pulled out of the housing 18, and the paper P accumulated inside is fed one by one by a paper feed roller (not shown). It is fed out to the side of one transport path 28. Note that a predetermined number of the paper feed cassettes 20 are provided corresponding to the size of the paper.
[0024]
The image forming unit 22 is configured to multiplexly form a plurality of toner images on a sheet, and includes a first image forming unit 221 for forming a magenta toner image and a second image forming unit 222 for forming a cyan toner image. And a third image forming unit 223 for forming a yellow toner image and a fourth image forming unit 224 for forming a black toner image are arranged at predetermined intervals along the sheet conveying direction.
[0025]
Each of the image forming units 221 to 224 includes a photoconductor drum 225, a charging unit 226 provided to face the peripheral surface of the photoconductor drum 225, and a peripheral portion of the photoconductor drum 225 downstream of the charging unit 226. An exposure unit 227 provided with an LED print head having, for example, 7168 pixels in the line direction, disposed opposite to the surface, and a downstream side of the exposure unit 227 facing the peripheral surface of the photosensitive drum 225; And a cleaning unit 229 disposed downstream of the developing unit 228 and opposed to the peripheral surface of the photosensitive drum 225. Further, a transfer unit 230 is formed by disposing a transfer roller 244 to be described later facing the developing unit 228 and the cleaning unit 229 on the peripheral surface of the photosensitive drum 225.
[0026]
Each photosensitive drum 225 is configured to rotate clockwise in FIG. 1 by a drive motor (not shown). Each of the developing units 228 has a toner box at the top. The toner box of the first image forming unit 221 contains magenta toner, the toner box of the second image forming unit 222 contains cyan toner, the toner box of the third image forming unit 223 contains yellow toner, and the fourth image. Black toner is stored in the toner box of the forming unit 224.
[0027]
The transfer conveyance unit 24 includes a driven roller 241 disposed near the first image forming unit 221, a driving roller 242 disposed near the fourth image forming unit 224, the driven roller 241 and the driving roller A transfer belt (shape image carrier) 243 disposed across the transfer belt 242 and four transfer rollers disposed so as to be able to be pressed against the developing unit 227 of each photosensitive drum 225 via the transfer belt 243. 244 and a pair of reflective photosensors (mark detection means) 245 (first photosensor 2451 and second photosensor 2452 (FIG. 2)) disposed at a position below the drive roller 242 and close to the transfer belt 243. And a blade 246 disposed at a position downstream of the reflection type photosensor 245 and in contact with the transfer belt 243. The reflection type photo sensor 245 includes a light emitting element such as an LED and a light receiving element such as a photodiode.
[0028]
In the transfer conveyance section 24, the paper conveyed from the first conveyance path 28 is electrostatically attracted onto a transfer belt 243 circulating in a counterclockwise direction by driving a drive motor (not shown), and is conveyed downstream. The toner image is transferred to the sheet at the position of the transfer unit 230 of each of the image forming units 221 to 224. The transfer belt 243 is made of a heat-resistant synthetic resin material such as a polyimide resin whose surface is coated with silicone or the like.
[0029]
Further, a pair of reflective photosensors 245 provided in the transfer conveyance section 24 are disposed at both ends in the width direction (main scanning direction) orthogonal to the transfer direction of the transfer belt 243, and are provided at both ends of the transfer belt 243. It constitutes a registration sensor (that is, mark detection means) for detecting a registration mark described later formed in each area by each of the image forming units 221 to 224. The pair of reflection-type photosensors 245 are arranged such that the first photosensor 2451 which is one of them is located on the left side (downward in FIG. 2) toward the downstream side (left side in FIG. 2) of the transfer belt 243, The other second photosensor 2452 is disposed on the opposite side. In addition, a first registration mark 61 is formed at a position corresponding to the first photosensor, and a second registration mark 62 is formed at a position corresponding to the second photosensor.
[0030]
The first and second photosensors 2451 and 2452 each include a light emitting unit (light transmitting unit) including a light emitting diode such as an LED that transmits light toward a registration mark position described later on the transfer belt 243, and a transfer belt. A light receiving unit including a photodiode or the like that receives reflected light reflected at a registration mark position described later on the H.243, and a detection circuit unit that converts the amount of reflected light received by the light receiving unit into a voltage value. . The first and second photosensors 2451 and 2452 each provide a P-wave output that provides a large output for a black toner image and a large output for a color toner image of magenta, cyan, and yellow toners. The S wave output can be detected.
[0031]
The blade 246 is for scraping off extraneous matter such as toner on the transfer belt 243, and is formed to have a length substantially equal to the width direction dimension of the transfer belt 243. It is arranged in a state where it abuts. The blade 246 is separated from the transfer belt 243 when it is not necessary to perform the operation of scraping off the deposits, and contacts the surface of the transfer belt 243 only when it becomes necessary to perform the operation of scraping off the deposits. You may make it contact.
[0032]
The fixing unit 26 (FIG. 1) heats the paper P on which the respective toner images formed on the surface of the photosensitive drum 225 of the image forming unit 22 are multiplex-transferred to perform a fixing process on the paper P. There is a heat shield box 261, a fixing roller 262 provided above the heat shield box 261 and having a built-in heater, and a heat shield box 261 provided at a lower part of the heat shield box 261 in pressure contact with the fixing roller 262. The pressure roller 263 and the fixing roller 262 are disposed upstream (to the right in FIG. 1) of the fixing roller 262 and the pressure roller 263 in the heat shielding box 261, and transfer the sheet P conveyed from the transfer conveyance unit 24 to the fixing roller 262. A pre-conveying path 264 for guiding between the pressure rollers 263 and a downstream side of the fixing roller 262 and the pressure roller 263 in the heat shielding box 261 are provided. And a conveying path 265 after guiding the to the sheet in the second conveyance path 30.
[0033]
The first transport path 28 transports the paper P fed from the paper feed cassette 20 to the transfer transport unit 24 side. The first transport path 28 includes a plurality of transport roller pairs 281 arranged at predetermined positions, A registration roller pair 282 is provided in front of the unit 24 and takes timing of an image forming operation and a sheet feeding operation of the image forming unit 22. The plurality of transport roller pairs 281 and the pair of registration rollers 282 are rotationally driven by respective drive motors (not shown) via electromagnetic clutches. A timing sensor 283 composed of a photo interrupter or the like is provided in front of the pair of registration rollers 282. When the leading edge of the sheet is conveyed to the pair of registration rollers 282, an output signal from the timing sensor 283 is output. Then, the conveyance of the sheet is temporarily stopped based on this.
[0034]
The second transport path 30 transports the sheet subjected to the fixing process by the fixing unit 26 toward the sheet discharge unit 14. A plurality of transport roller pairs 301 are disposed at a predetermined position, and the second transport path 30 has an exit side. Is provided with a discharge roller pair 302. The transport roller pair 301 and the discharge roller pair 302 are rotatably driven by a drive motor (not shown) via an electromagnetic clutch.
[0035]
The paper discharge unit 14 is formed on the upper surface of the housing 18 surrounding the main body unit 12, and the paper on which the image has been formed is transported from the second transportation path 30 on the back side. Are sequentially accumulated.
[0036]
The image forming apparatus 10 configured as described above transmits a print instruction signal including various print information such as paper size information and print copy number information and image data to be printed from an external device such as an externally connected personal computer. Then, it operates as follows.
[0037]
That is, in each of the photosensitive drums 225 of the image forming unit 22, an electrostatic area is formed on the surface by the charging unit 226, and the electrostatic area is exposed by the output light from the exposure unit 227 and transmitted from an external device. An electrostatic latent image is formed based on the received image data, and then a toner image is formed by the developing unit 228. Further, the fixing roller 262 of the fixing unit 26 is energized by applying a voltage to a built-in heater by a voltage supply unit (not shown), and the heating of the surface of the fixing roller 262 is controlled so as to be a fixing-possible temperature.
[0038]
On the other hand, a sheet of a designated size is fed out from the sheet feeding cassette 20, conveyed to a position short of the registration roller pair 282 by the first conveying path 28, and temporarily stopped. Then, the sheet P conveyed to a position before the pair of registration rollers 282 is conveyed to the transfer conveyance unit 24 after timing of the image forming operation of the image forming unit 22 is set, and the image forming units 221 to 224 As a result, the toner image on the peripheral surface of each photosensitive drum 225 is sequentially transferred to the paper P. That is, the toner image on the peripheral surface of each photosensitive drum 225 is transferred onto the paper P in a state where the magenta toner, the cyan toner, the yellow toner, and the black toner are superimposed on the paper P in this order.
[0039]
Then, the paper P on which the toner image has been transferred is conveyed into the fixing unit 26, and while being heated by the fixing roller 262, is nipped by the fixing roller 262 and the pressure roller 263, and conveyed to the downstream side. The sheet is discharged to the sheet discharge unit 14 by the transport path 30. After the transfer of the toner image to the paper P, the toner remaining on the surface of each photosensitive drum 225 is removed by a predetermined process in the cleaning unit 229. By repeating this operation sequentially, printing on a predetermined number of sheets of paper P is executed.
[0040]
Here, the image forming apparatus 10 performs color shift in the main scanning direction (a direction orthogonal to the transfer direction of the transfer belt 243, that is, a width direction of the transfer belt 243) caused by an attachment error of the exposure unit 227 including the LED print head. The sub-scanning direction (the same direction as the transfer direction of the transfer belt 243, that is, transfer) caused by an attachment error of the first to fourth image forming units 221 to 224, a rotational speed error of a drive motor for rotationally driving the respective photosensitive drums 225, and the like. The color misregistration in the longitudinal direction of the belt 243 and the oblique direction (main scanning direction and sub-scanning direction) caused by the mounting error (tilt) of the first to fourth image forming units 221 to 224 and the skew of the transfer belt 243. (A direction between them) is detected, and color shift correction (registration correction) based on the detected color shift is performed.
[0041]
FIG. 3 is a block diagram showing a control configuration for explaining the operation of detecting the amount of color misregistration due to these various fluctuation factors and the operation of correcting the color misregistration. That is, the first to fourth image forming units 221 to 224 are connected to the control unit 50 via an interface circuit (not shown), and the first to fourth image forming units 221 to 224 are mounted on the transfer belt 243. Is performed based on a control signal from the control unit 50. A drive motor 33 for rotating the drive roller 242 is connected to the control unit 50 via an interface circuit (not shown). The drive motor 33 transfers the transfer belt 243 during the image forming operation on the transfer belt 243. The operation is executed in synchronization with the image forming operation based on a control signal from the control unit 50.
[0042]
The control unit 50 includes a first unit sensor 34 for detecting the insertion / removal operation of the first to fourth image forming units 221 to 224 (removal operation with respect to the main body unit 12), and a transfer / conveyance unit including the transfer belt 243. A second unit sensor 36 for detecting the insertion / removal operation and a temperature / humidity sensor 38 for detecting ambient temperature and humidity are connected via an interface circuit (not shown).
[0043]
The control unit 50 includes an image input unit 40 for reading an image of a document and inputting the image to the control unit 50, a pattern generator 42 for forming a registration mark described later on the surface of the transfer belt 243, A registration mark input unit 43 for reading a registration mark attached to the surface of the transfer belt 243 by the generator 42 and inputting it to the control unit 50 is connected via an interface circuit (not shown). The image input unit 40 has a scanner 41, and reading of a document image is performed by the scanner 41. The registration mark input unit 43 has a mark generation unit 44. When a mark generation signal from the registration mark generation unit 44 is input to the control unit 50, the first to fourth image forming units 221 to 224 are driven. Four linear registration marks are formed on the surface of the orbiting transfer belt 243 at positions corresponding to the first and second photosensors.
[0044]
Further, the control unit 50 controls an image control unit 500 that controls image data input via the scanner 41, and manages a trigger for starting correction execution, replacing an image forming unit, and detecting a registration mark abnormality. A control unit 510 for notifying, a sensor control unit 520 for processing a detection signal from the reflection type photosensor 245, a correction operation unit 530 for specifically executing correction of color misregistration, and control of driving of the image forming unit 22. An image forming unit control unit 540 is provided.
[0045]
The image control unit 500 includes a memory writing processing unit 501, an image memory 502, a memory reading processing unit 503, a sub-scanning timing control unit 504, and a main scanning timing control unit 505.
[0046]
The memory write processing unit 501 performs processing necessary for storing image data of a document read by the scanner 41 in the image memory 502. The image memory 502 sequentially stores the image data input from the memory writing processing unit 501. The memory read processing unit 503 plays a role of reading image data to be subjected to print processing from the image memory 502 based on a predetermined operation signal and preparing the image data so as to be provided for print processing.
[0047]
The sub-scanning timing control unit 504 outputs a control signal for correcting a color shift in the sub-scanning direction of the print image of the paper P in cooperation with the correction calculation unit 530 to the image forming unit control unit 540. With this control signal, the synchronization timing between the sheet P sent by the rotation of the transfer belt 243 and the toner image on the peripheral surface of the photosensitive drum 225 is adjusted.
[0048]
The main scanning timing control unit 505 outputs, to the image forming unit control unit 540, a control signal for correcting a color shift of the print image of the paper P in the main scanning direction in cooperation with the correction calculation unit 530. The position of the electrostatic image formed on the peripheral surface of the photosensitive drum 225 in the main scanning direction is adjusted by the control signal.
[0049]
The management unit 510 includes a correction execution management unit 511 and a registration mark abnormality notification unit 512. The correction execution management unit 511 specifically manages a trigger (start) for starting correction execution or replacing an image forming unit based on detection signals from the first unit sensor 34, the second unit sensor 36, and the like. Yes, the registration mark abnormality notification unit 512 outputs a display signal indicating that a registration mark abnormality has occurred to a display member (not shown) of an operation panel for performing a normal printing operation, which is located at an appropriate position of the housing 18. Is what you do. Such registration mark abnormality information cannot be known by a normal operation performed by a normal user. However, a maintenance person needs to perform a dedicated mode setting performed through an operation panel or the like, or to a deep portion in the housing 18. The information can be obtained by operating a specific operation button.
[0050]
The sensor control unit 520 is provided corresponding to the first sampling processing unit 521 corresponding to the first photosensor 2451, the second sampling processing unit 522 corresponding to the second photosensor 2452, and the first sampling processing unit 521. The first registration mark abnormality determination unit 523 provided, the second registration mark abnormality determination unit 524 provided corresponding to the second sampling processing unit 522, and the position of the registration mark detected by the first photosensor 2451 are calculated. And a second registration mark position calculation unit 526 that calculates the position of the registration mark detected by the second photosensor 2452.
[0051]
The first and second sampling processing units 521 and 522 output control signals for turning on and off the power supply to the first and second photosensors 2451 and 2452, respectively, and perform A / A of the detection signal of each sensor. It performs D conversion (conversion from an analog signal to a digital signal).
[0052]
The first and second registration mark abnormality determination units 523 and 524 determine abnormality and normality of the first and second registration marks 61 and 62, respectively, based on digital signals from the first and second sampling processing units 521 and 522. Is what you do. The details of this determination will be described later.
[0053]
The first and second registration mark position calculation units 525 and 526 calculate the position of each registration mark from data on the registration mark sampled after the sampling processing by the first and second sampling processing units 521 and 522. is there.
[0054]
The correction operation unit 530 corrects the shift of the transferred image by each of the first to fourth image forming units 221 to 224 based on the image data of the registration mark on the surface of the transfer belt 243 read by the registration mark input unit 43. And has a correction method selection unit 531, a tilt shift correction unit 532, a sub-scan shift correction unit 533, and a main scan shift correction unit 534.
[0055]
The correction method selection unit 531 determines the type of color shift to be corrected based on the determination results of the first and second registration mark abnormality determination units 523 and 524, and performs the color shift correction on the first and second registration mark abnormalities. The user selects which of the registration marks 61 and 62 is to be used.
[0056]
The tilt shift correcting unit 532 updates an address when writing image data to the image memory 502 based on the tilt color shift amount detected by the reflection type photo sensor 245, and thereby corrects the tilt color shift. .
[0057]
The sub-scanning deviation correction unit 533 adjusts the timing of writing image data in the sub-scanning direction with respect to the peripheral surface of the photosensitive drum 225 based on the amount of color deviation in the sub-scanning direction detected by the reflection type photosensor 245. The sub-scanning timing control unit 504 outputs a control signal corrected toward the image forming unit control unit 540 based on the correction signal output from the sub-scanning deviation correcting unit 533. Reference numeral 22 outputs an image on which the color shift in the sub-scanning direction has been corrected to the paper P.
[0058]
The main scanning shift correction unit 534 adjusts the timing of writing image data in the main scanning direction with respect to the peripheral surface of the photosensitive drum 225 based on the amount of color shift in the main scanning direction detected by the reflection type photo sensor 245. The main scanning timing control unit 505 outputs a control signal corrected to the image forming unit control unit 540 based on the correction signal output from the main scanning shift correction unit 534. Means that an image in which color misregistration in the main scanning direction has been corrected is output to the paper P.
[0059]
Next, the registration mark will be described in detail. As shown in FIG. 2, the registration mark is formed at one end (lower side in FIG. 2) of the transfer belt 243 in the width direction (main scanning direction) by an oblique line L1 composed of a linear pattern of four colors having a predetermined width. And a horizontal line L2 (vertically oriented in FIG. 2) formed of a four-color linear pattern having a predetermined width and disposed on the upstream side (right side in FIG. 2) of the diagonal line L1. At the other end (upper side in FIG. 2) of the transfer belt 243 in the width direction (main scanning direction), an oblique line L1 ′ composed of a linear pattern of four colors having a predetermined width is formed. A horizontal line L2 'formed of a linear pattern of four colors having a predetermined width and arranged at an upstream side (right side in FIG. 2) of the diagonal line L1' is formed alternately at a predetermined interval. It is. Each of these linear patterns has a width of, for example, 1.35 mm.
[0060]
Here, the oblique lines L1 and L1 ′ are formed at positions facing each other in the width direction (main scanning direction) of the transfer belt 243, and the horizontal lines L2 and L2 ′ are formed in the width direction of the transfer belt 243 (main scanning direction). Direction). In addition, one diagonal line L1 on one end side and one horizontal line L2 subsequent thereto constitute one set, and one diagonal line L1 'on the other end side and one horizontal line L2' subsequent thereto. One set is composed. In this embodiment, four sets of diagonal lines L1 and horizontal lines L2 and four sets of diagonal lines L1 'and horizontal lines L2' are formed.
[0061]
Each of the oblique lines L1 and L1 'is a black toner image formed by the fourth image forming unit 224 from the downstream side (left side in the figure) to the upstream side (right side in the figure) in the transfer direction of the transfer belt 243. The first linear pattern K1, the second linear pattern Y1 which is a yellow toner image formed by the third image forming unit 223, and the third linear pattern C1 which is a cyan toner image formed by the second image forming unit 222 And the fourth linear pattern M1 which is a magenta toner image formed by the first image forming unit 221 is arranged at a predetermined interval at an angle of 45 ° with respect to the sub-scanning direction (or the main scanning direction) in that order. It was formed.
[0062]
Similarly, the horizontal lines L2 and L2 'extend from the downstream side (left side in the drawing) to the upstream side (right side in the drawing) of the transfer direction of the transfer belt 243 in the same manner as the diagonal lines L1 and L1'. A first line K2 which is a black toner image formed by the second image forming unit 224, a second line Y2 which is a yellow toner image formed by the third image forming unit 223, and a cyan toner image formed by the second image forming unit 222. And the fourth line M2, which is a magenta toner image formed by the first image forming unit 221, is formed at a predetermined interval along the sub-scanning direction in this order. Things.
[0063]
Note that, of the first and second photosensors 2451 and 2452, the first photosensor 2451 is located at a position where the substantially central position in the main scanning direction of the oblique line L1 and the horizontal line L2 of the registration mark at one end can be detected. The second photosensor 2452 is provided at a position where the substantially center position in the main scanning direction of the oblique line L1 'and the horizontal line L2' of the registration mark at the other end can be detected.
[0064]
The sensor control unit 520 also controls the registration mark measurement operation by the first and second photosensors 2451 and 2452. For example, after a falling edge of a synchronization signal is detected, a count start instruction is issued, The distance (mm) from the exposure position of the first image forming unit 221 to the photosensitive drum 225 to the detection position of the registration mark by the first and second photosensors 2451 and 2452, and the peripheral speed (mm / s) of the transfer belt 243 From the time when the measurement start timing (ms) obtained based on the above is reached, the four sets of each oblique line L1, L1 'and each horizontal line L2, L2' pass through the detection positions of the first and second photosensors 2451, 452. Until the end, the outputs from the first and second photosensors 2451 and 2452 are obtained every predetermined time (for example, every 1 ms). Those were Unishi.
[0065]
From the first and second photosensors 2451 and 2452, as shown in FIG. 4, the detection values of the P-wave output and the S-wave output of the reflected light can be obtained corresponding to the linear patterns of four colors. ing. Here, for the first linear patterns K1 and K2, which are black toner images, the output value of the P-wave output is larger than that of the S-wave output. For the second, third and fourth linear patterns Y1, Y2, C1, C2 and M1, M2, which are color toner images, the S-wave output is larger than the P-wave output. Is obtained, the S-wave output is used when calculating the positions of the second, third, and fourth linear patterns Y1, Y2, C1, C2 and M1, M2.
[0066]
Then, the first and second registration mark position calculation units 525 and 526 convert the plurality of output values of each linear pattern obtained from the first and second photosensors 2451 and 2452 at predetermined time intervals (for example, every 1 ms). An operation for calculating the position of each linear pattern on the transfer belt 243 is performed based on the calculation. Note that the outputs from the first and second photosensors 2451 and 2452 have a downwardly convex waveform for the P-wave output and an upwardly convex waveform for the S-wave output for each linear pattern. It becomes what has.
[0067]
Here, if the color unevenness of the linear pattern or the transfer unevenness of the transfer belt does not occur, the minimum value (in the case of the black toner image) or the maximum value (in the case of the color toner image) of the waveform is obtained to obtain the predetermined width. The position of each linear pattern can be determined, but if the waveform is distorted due to color unevenness of the linear pattern or transfer unevenness of the transfer belt, etc., an accurate position may be determined depending on the minimum or maximum value of the waveform. Can not be sought. For this reason, in the present embodiment, the center of gravity of each waveform is obtained in order to always obtain the accurate position of each linear pattern, and this center of gravity is used as the position of the linear pattern. In the present embodiment, the position of each linear pattern is represented by the elapsed time (ms) after the count start instruction based on the clock signal is performed.
[0068]
Since the center of gravity has a downwardly convex waveform as shown in FIG. 5 in the case of P-wave output, for example, a preset threshold value of the output value P [n] obtained every predetermined time (for example, every 1 ms) For those less than or equal to Pth (P [n] ≦ Pth) (that is, those within the range of count values m to p (ms)), the product of the count value and the output value corresponding to the count value is calculated for each count value. And the sum is divided by the sum of the output value of each count value. That is, the center of gravity GP of the P-wave output can be obtained by the following equation (1).
[0069]
(Equation 1)

[0070]
Since the S wave output has an upwardly convex waveform, the output value S [n] obtained every predetermined time (for example, every 1 ms) is equal to or more than a predetermined threshold value Sth (S [n]). ≧ Sth) (that is, those within the range of count values m to p (ms)), the product of the count value and the output value corresponding to the count value is summed for each count value, and this summed value is calculated for each count value. It can be obtained as a value obtained by dividing the output value of the count value by the total value. That is, the center of gravity GS of the S-wave output can be obtained by the following equation (2). These calculated centroids GP and GS are stored in a storage unit such as a RAM that constitutes the control unit 50 each time they are calculated. For this reason, compared to the case where all of the output values P [n] and S [n] are stored in the storage unit, and thereafter the centroids GP and GS are calculated, the storage unit may have a smaller storage capacity.
[0071]
(Equation 2)

[0072]
The correction amount for the color shift (position shift) of each linear pattern is calculated by the correction calculation unit 530. That is, regarding the color misregistration of each linear pattern, the position of each linear pattern K2, Y2, C2, M2 of the horizontal lines L2, L2 'on the left and right sides facing each other is detected, and the amount of color misregistration in the oblique direction (inclination direction) is detected. (I.e., if it is oblique, there is a difference between the detection time of one horizontal line L2 and the detection time of the other horizontal line L2 '). The amount of color shift in the sub-scanning direction can be detected by detecting the interval in the sub-scanning direction between the linear patterns K2, Y2, C2, and M2 of the horizontal lines L2, L2 ', and at least one of the left and right sides facing each other. Of the same colors of the linear patterns K1, Y1, C1, M1 of the set of oblique lines L1 (or L1 ') and the linear patterns K2, Y2, C2, M2 of the horizontal lines L2 (or L2') are detected. Leading by It is possible to detect the amount of color shift in the inspection direction (because the distance between the oblique line L1 and the horizontal line L2 changes if the resist pattern is shifted in the width direction). The color shift correction amount (the number of lines or the number of pixels) is obtained from the number or the number of pixels.
[0073]
In the present embodiment, in the case of performing the color shift correction in the oblique direction and the case of performing the color shift correction in the sub-scanning direction, the fourth image forming unit 224 uses the fourth image forming unit 224 in order to suppress an image defect caused by the color shift correction. The formed black toner image is not corrected, and color misregistration correction is performed so that the color toner images formed by the first to third image forming units 221 to 223 are aligned with the positions of the black toner images.
[0074]
Next, the color shift correction in the oblique direction (tilt color shift correction) performed by the tilt shift correction unit 532 will be described in detail. The amount of color shift in the oblique direction (the number of lines or the number of pixels) is the sum KA of the amount of color shift of the second linear pattern K2, which is a black toner image of the horizontal lines L2 and L2 'on the left and right sides facing each other, and the color The sums YA, CA, and MA of the color shift amounts of the second linear patterns Y2, C2, and M2, which are toner images, are respectively obtained. Differences between the sums of the color shift amounts YA, CA, and MA are obtained, and these differences are used as color shift correction amounts (the number of lines or the number of pixels) of each color toner image.
[0075]
That is, the number of pixels in the main scanning direction (line direction) of the exposure unit 227 including the LED print head is N (for example, N = 7168), and the distance (number of pixels) between the pair of first and second photosensors 2451 and 2452. (For example, D = 5184 pixels), the peripheral speed of the transfer belt 243 is S (mm / s) (for example, S = 116 mm / s), and the width of one pixel is G (mm) (for example, G = 0. 0423 mm), and the positions of the four second linear patterns K2, which are black toner images at one end, are sequentially designated as K21F, K22F, K23F, and K24F from the downstream side to the upstream side, and the other side. Assuming that the positions of the four second linear patterns K2, which are black toner images at the end, are K21R, K22R, K23R, and K24R in order from the downstream side to the upstream side, black toner Sum KA of the color shift amount of the second linear pattern K2 is an image can be determined according to the equation shown in Equation 3 below.
[0076]
[Equation 3]

[0077]
Further, the positions of the four second linear patterns Y2, which are yellow toner images on one end side, are sequentially set as Y21F, Y22F, Y23F, and Y24F from the downstream side to the upstream side, and the positions on the other end side. Assuming that the positions of the four second linear patterns Y2 that are yellow toner images are Y21R, Y22R, Y23R, and Y24R in order from the downstream side to the upstream side, the second linear patterns Y2 that are yellow toner images The total sum YA of the color misregistration amounts can be obtained by the following equation (4).
[0078]
(Equation 4)

[0079]
Further, the positions of the four second linear patterns C2, which are cyan toner images on one end side, are C21F, C22F, C23F, and C24F in order from the downstream side to the upstream side, and the positions on the other end side. Assuming that the positions of the four second linear patterns C2 that are cyan toner images are C21R, C22R, C23R, and C24R in order from the downstream side to the upstream side, the positions of the second linear patterns C2 that are cyan toner images are The sum CA of the color misregistration amounts can be obtained by the following equation (5).
[0080]
(Equation 5)

[0081]
Further, the positions of the four second linear patterns M2, which are the magenta toner images at one end, are set to M21F, M22F, M23F, and M24F in order from the downstream side to the upstream side, and at the other end side. Assuming that the positions of the four second linear patterns M2 that are magenta toner images are M21R, M22R, M23R, and M24R in order from the downstream side to the upstream side, the positions of the second linear patterns M2 that are cyan toner images are The total sum MA of the color misregistration amounts can be obtained by the following equation (6).
[0082]
(Equation 6)

[0083]
Therefore, the color shift amount YA 'of the yellow toner image with respect to the black toner image, the color shift amount CA' of the cyan toner image, and the color shift amount MA 'of the magenta toner image are obtained by the following equations. Can be. YA ', CA', and MA 'obtained by the equation shown in Expression 7 are the color misregistration correction amounts of the color toner images. If the color misregistration correction has already been performed so far, the color misregistration correction amount to be actually corrected may be recalculated from the current color misregistration correction amount and the previous color misregistration correction amount. .
[0084]
(Equation 7)

[0085]
Next, color shift correction in the sub-scanning direction performed by the sub-scanning shift correcting unit 533 will be described in detail. As described above, the amount of color misregistration (the number of lines or the number of pixels) in the sub-scanning direction is, as described above, the distance in the sub-scanning direction between the linear patterns K2, Y2, C2, and M2 of the horizontal lines L2 and L2 'on the left and right sides. In this embodiment, the color shift of each linear pattern Y2, C2, and M2 is determined by the distance between each linear pattern Y2, C2, and M2 of the color toner image and the linear pattern K2 of the black toner image. The amount is detected. That is, regarding the linear pattern Y2 of the color toner image, the color is determined by the difference between the position of the linear pattern Y2 and the position of the linear pattern K2 of the black toner image, which is a reference value (initial setting value). The deviation amount is obtained.
[0086]
Regarding the linear patterns C2 and M2 of the other color toner images, the reference values (initial setting values) of the intervals determined from the positions of the linear patterns C2 and M2 and the position of the linear pattern K2 of the black toner image are also used. The amount of color misregistration can be obtained from the difference between. However, since the obtained color shift amount includes the color shift amount in the oblique direction, the corrected color shift amount in the oblique direction is the color shift correction amount in the sub-scanning direction. For this reason, it is necessary to previously obtain the amount of color shift correction in the oblique direction for the linear patterns Y2, C2, and M2 of the color toner image by using the mathematical formula shown in the above-described “Formula 7”.
[0087]
Finally, a description will be given of the color misregistration correction in the main scanning direction performed by the main scanning misalignment correction unit 534. In the present embodiment, the amount of color misregistration (the number of pixels) in the main scanning direction is determined by each linear pattern of the same color of diagonal lines L1 and horizontal lines L2 on one end side (the same set of K1 and K2 for black toner images, The difference between the reference value (initial setting value) of the interval between the same set of Y1 and Y2 for the yellow toner image, the same set of C1 and C2 for the cyan toner image, and the same set of M1 and M2 for the magenta toner image. I want to ask.
[0088]
That is, the peripheral speed of the transfer belt 243 is S (mm / s) (for example, S = 116 mm / s), the width of one pixel is G (mm) (for example, G = 0.0423 mm), While the reference value (the number of lines) of the interval between the linear pattern of the line L1 and the linear pattern of the horizontal line L2 is Q (for example, Q = 864 lines), each of the four black toner images on one end side is a black toner image. Assuming that the positions of the first linear pattern K1 and the second linear pattern K2 are K11F, K12F, K13F, K14F and K21F, K22F, K23F, and K24F in order from the downstream side to the upstream side, respectively, The set of color misregistration correction amounts KH [0], KH [1], KH [2], KH [3] can be obtained by the following equation (8). The average value of the color misregistration correction amounts KH [0], KH [1], KH [2], and KH [3] of each set obtained by the equation shown in Expression 8 is the color misregistration correction amount (the number of pixels) of the black toner image. ).
[0089]
(Equation 8)

[0090]
Further, the positions of the four first linear patterns Y1 and the second linear patterns Y2, which are yellow toner images on one end side, are sequentially shifted from the downstream side to the upstream side to Y11F, Y12F, Y13F, and Y11F. Assuming that Y14F and Y21F, Y22F, Y23F, and Y24F, the color misregistration correction amounts YH [0], YH [1], YH [2], and YH [3] of each set of the yellow toner image are represented by the following Expression 9. It can be obtained by an equation. The average value of the color misregistration correction amounts YH [0], YH [1], YH [2], and YH [3] of each set obtained by the equation shown in Expression 9 is the color misregistration correction amount (pixel number) of the yellow toner image. ).
[0091]
(Equation 9)

[0092]
Further, the positions of the four first linear patterns C1 and the second linear patterns C2, which are cyan toner images on one end side, are respectively arranged from the downstream side to the upstream side in the order of C11F, C12F, C13F, and C11F. Assuming that C14F and C21F, C22F, C23F, and C24F, the color misregistration correction amounts CH [0], CH [1], CH [2], and CH [3] of each set of the cyan toner image are represented by the following Expression 10. It can be obtained by an equation. The average value of the color misregistration correction amounts CH [0], CH [1], CH [2], and CH [3] of each set obtained by the equation shown in Expression 10 is the color misregistration correction amount (the number of pixels) of the cyan toner image. ).
[0093]
(Equation 10)

[0094]
Further, the positions of the four first linear patterns M1 and the second linear patterns M2, which are the magenta toner images at one end, are respectively set from M11F, M12F, M13F to M11F from the downstream side to the upstream side. Assuming that M14F and M21F, M22F, M23F, and M24F, the color misregistration correction amounts MH [0], MH [1], MH [2], and MH [3] of each set of the magenta toner images are represented by the following Expression 11. It can be obtained by an equation. The average value of the color misregistration correction amounts MH [0], MH [1], MH [2], and MH [3] of each set obtained by the equation shown in Expression 11 is the color misregistration correction amount (pixel number) of the magenta toner image. ).
[0095]
(Equation 11)

[0096]
The sub-scanning timing control unit 504 and the main-scanning timing control unit 505 execute color misregistration correction for each color based on the color misregistration correction amount obtained by the correction calculation unit 530. In other words, when correcting the color shift in the oblique direction, the color shift correction amounts YA ', CA', and MA 'obtained by the above equation (7) are corrected for the color toner image excluding the black toner image. become. In this case, the area in the main scanning direction is divided into a plurality of substantially equal intervals according to the values of the correction amounts YA ', CA', and MA ', and the divided areas are used as a unit to perform stepwise correction in an oblique direction. become. If the color shift correction has already been performed, the correction may be performed based on the recalculated color shift correction amount.
[0097]
For example, if the number of pixels in the main scanning direction is 7168 and the amount of color misregistration correction is one line (or one pixel) in the sub-scanning direction, the image memory 502 (FIG. 3) is conceptually shown in FIG. When the read position of the image data stored in ()) is at the position of 7168 × 1/2, the read address may be switched to the address of the previous line or the next line according to the inclination direction.
[0098]
Assuming that the number of pixels in the main scanning direction is 7168 and the amount of color misregistration correction is for three lines (or three pixels) in the sub-scanning direction, the color shift is stored in the image memory 502 as conceptually shown in FIG. When the read position of the image data is at each position of 7168 × 1/4, 7168 × 2/4 and 7168 × 3/4, it is sequentially read to the address of the previous line or the next line according to the inclination direction. The address may be switched. Normally, the image data stored in the image memory 502 is fetched into the line buffer every several lines. In this case, the read address is switched when reading the image data from the line buffer. Good.
[0099]
In the case of correcting the color misregistration in the sub-scanning direction, the writing timing of the image data is adjusted based on the color misregistration correction amount calculated by the sub-scanning misregistration correction unit 533 for the color toner image excluding the black toner image. What should I do? For example, as described with reference to a time chart shown in FIG. 8, for the magenta toner image (M), the writing of the image data is started when the time a has elapsed since the fall of the reference image valid section signal in the sub-scanning direction. For the cyan toner image (C), writing of image data is executed when the time “b” has elapsed from the fall of the image effective section signal in the sub-scanning direction of the magenta toner image (M).
[0100]
For the yellow toner image (Y), image data is written out when the time c has elapsed from the fall of the image effective section signal in the sub-scanning direction of the cyan toner image (C), and the black toner image (K) With regard to ()), writing of image data is executed when a time d has elapsed from the fall of the image effective section signal in the sub-scanning direction of the yellow toner image (Y).
[0101]
When correcting color misregistration in the main scanning direction, the left and right ends of the exposure unit 227 (FIG. 1) composed of an LED print head in the main scanning direction (line direction) are used for the black toner image and each color toner image. The amount of white pixels (the number of white pixels) for forming a blank portion to be inserted into the image data is adjusted according to the color shift correction amount calculated by the main scanning shift correction unit 534. For example, a description will be given based on a time chart shown in FIG. 9. An edge in an effective image section (ON section of the effective image section signal (P)) in the main scanning direction of the exposure unit 227 set in synchronization with the read clock signal. By adjusting the amount of white pixels to be inserted into a section (for example, a section indicated by a symbol t) in accordance with the amount of color shift correction calculated by the main scan shift corrector 534, the image data read from the image memory 502 is main-scanned. In this direction, thereby performing color misregistration correction.
[0102]
The amount of white pixels to be inserted at the end of the exposure unit 227 in the main scanning direction is determined by the amount of color shift correction calculated by the main scan shift correction unit 534 and the amount of white scan by the exposure unit 227 to adjust the center position of the image. This is set based on the amount of white pixels inserted at the end in the direction. The white pixels are generated by sending image data of “0” to the exposure unit 227.
[0103]
The present invention is based on the above-described calculation of the amount of color misregistration correction by the correction calculation unit 530 and the timing control by the sub-scanning timing control unit 504 and the main scanning timing control unit 505. The problem that the color misregistration control is not properly performed when an abnormality is detected in the registration mark in a state in which the registration mark can be executed is solved by the first and second sampling processing units 521 and 522 of the sensor control unit 520. (2) To collect appropriateness determination data of the registration marks 61 and 62, and to take appropriate measures as described below based on the determination results by the first and second registration mark abnormality determination units 523 and 524 based on the obtained data. Is the solution.
[0104]
Hereinafter, the operation of the present invention will be described with reference to FIG. FIG. 10 is a flowchart for explaining the detection of a registration mark abnormality and the correspondence when an abnormality is detected. In step S1, adjustment of the LED light amount and the like of the first and second photosensors 2451 and 2452 is performed. In step S2, first and second registration marks 61 and 62 are formed.
[0105]
Next, in step S3, the first and second registration marks 61 and 62 are read by the first and second photo sensors 2451 and 2452. At step 4 it is first determined from the read data whether the first registration mark is abnormal or normal. This determination method will be described with reference to FIG. As shown in FIG. 2, the registration mark is formed with four lines formed for each line of each color as one unit (for example, L1 and L2 in FIG. 2). Accordingly, one P-wave output and three S-wave outputs are obtained, for a total of four outputs. The first registration mark abnormality determination unit 523 counts this number and determines whether the number is equal to a predetermined number. In this case, if the number is four, it is determined to be normal.
[0106]
If the registration mark is not created like K2 in FIG. 11A, only three waves are counted because the P wave does not exceed Pth, and it is determined that the mark is abnormal. Further, when the toner is not placed at the center of the registration mark like M1 in FIG. 11B, the mark exceeds Sth at both ends of the mark and falls below Sth at the center, and two marks are counted in the M1 portion. As a result, the total number becomes five, and it is determined that there is an abnormality. This determination method is the same in the following.
[0107]
When it is determined in step S4 that the first registration mark is not abnormal (that is, normal) (NO in S4), it is determined in step S5 whether the second registration mark is abnormal. As a result of this determination, when it is determined that the second registration mark is not abnormal (that is, normal) (that is, when both the first and second registration marks are determined to be normal), the inclination deviation correction unit 532 performs the inclination deviation. Calculation of the correction value of (oblique color shift) (S6), calculation of the correction value of the color shift in the sub-scanning direction by the sub-scanning shift correcting unit 533 (S7), and calculation of the color shift in the main scanning direction by the main scanning shift correcting unit 534. Calculation of the correction value (S8) is performed.
[0108]
On the other hand, when it is determined in step S5 that the second registration mark is abnormal (that is, when the first registration mark is normal and the second registration mark is abnormal), the sub-registration correction value is calculated without calculating the tilt deviation correction value. The calculation of the correction value of the color shift in the scanning direction (S17) and the calculation of the correction value of the color shift in the main scanning direction (S18) are sequentially performed, and thereafter, the sensor error notification unit 512 indicates that the second registration mark is abnormal. Is notified (S19).
[0109]
On the other hand, if it is determined in step S4 that the first registration mark is abnormal (YES in S4), it is determined whether the second registration mark is abnormal (S9), and if the second registration mark is not abnormal (S9). That is, when the second registration mark is normal but the first registration mark is abnormal), the correction value of the color shift in the sub-scanning direction is calculated without calculating the correction value of the tilt shift (S27), and the main scanning direction is calculated. The correction value of the color misregistration (S28) is sequentially executed, and thereafter, the sensor abnormality notification unit 512 notifies the first photosensor 2451 that the first photosensor 2451 is abnormal (S29).
[0110]
If it is determined in step S9 that the second registration mark is abnormal (that is, if both the first and second registration marks are abnormal), only the sensor abnormality notification unit 512 notifies the sensor abnormality occurrence in step S39. No action is taken for color misregistration correction.
[0111]
Although not shown in FIG. 10, after step S8, step S19, and step S29, color shift correction is specifically executed based on the control by the sub-scanning timing control unit 504 and the main scanning timing control unit 505. Is done.
[0112]
As described in detail above, the image forming apparatus 10 of the present invention includes an image forming unit 22 that superimposes and transfers toner images of different colors on the paper P conveyed by the transfer belt 243, and that is transferred onto the paper P. Generator 42 for forming a registration mark for detecting the amount of color misregistration of the toner image on transfer belt 243 by image forming unit 22 and a reflective photodetector for detecting the position of the registration mark formed on transfer belt 243. A sensor 245 (first and second photosensors 2451 and 2452) and a color shift correction amount calculating means (tilt shift corrector 532, sub-scan shift correction) for calculating a color shift correction amount based on detection signals output from these sensors; And a main scanning deviation correcting unit 534). The first unit 533 determines whether the first and second registration marks are abnormal. And a second registration mark abnormality determination unit 523, 524, and the color misregistration correction amount calculation unit detects the reflection type photo sensor 245 that the first and second registration mark abnormality determination units 523, 524 have determined to be abnormal. The color misregistration is corrected based on the detection signals of the remaining reflection type photosensors 245 without using any signals.
[0113]
Therefore, even if any of the registration marks corresponding to the two reflection-type photosensors 245 (the first and second photosensors 2451 and 2452) becomes abnormal, the color misregistration correction amount calculation means calculates the remaining registration marks. The color misregistration correction amount is calculated based on the detection result of the reflection type photosensor 245, and the color misregistration correction is executed based on the calculation result. Can be formed. Therefore, a better color image can be formed on the paper P as compared with the case where no color misregistration correction is performed.
[0114]
In addition, the first and second registration mark abnormality determination units 523 and 524 determine that the registration mark is normal when the registration mark is formed of a linear pattern and a predetermined number of the linear patterns are output. Otherwise, it is determined that the registration mark is abnormal. Therefore, the normality / abnormality of the registration mark can be determined by a simple operation of measuring the number of registration marks, thereby contributing to a reduction in apparatus cost.
[0115]
Further, the registration marks are formed at predetermined intervals along the sub-scanning direction, and are formed so as to extend obliquely with respect to the sub-scanning direction and to extend in the main scanning direction. The reflection type photosensor 245 is provided in a pair corresponding to the registration mark, and the color misregistration correction amount calculating means outputs the color misregistration correction amount in the main scanning direction from the reflection type photosensor 245. Since the distance between the diagonal lines L1 and the distance between the horizontal lines L2 calculated based on the detected signals is compared with each reference value set in advance corresponding to each of the distances, the calculation is performed. The accuracy of color misregistration correction can be improved.
[0116]
When one of the first and second registration marks is determined to be abnormal by one of the first and second registration mark abnormality determination units 523 and 524, the color misregistration correction amount calculating unit outputs the other detection signal. When the first and second registration mark abnormality determination units 523 and 524 determine that both are abnormal, the first and second registration mark abnormality determination units 523 and 524 stop calculating the color deviation correction amount. Even if it is determined that one of the second registration marks is abnormal, it is possible to perform a proper color shift correction by using only the other registration mark. When it is determined that both the first and second registration marks are abnormal, the color misregistration correction is stopped. Therefore, the color misregistration correction is performed with the registration mark abnormal even though the registration mark is abnormal. Conversely, it is possible to prevent inconvenience such as amplifying the color shift.
[0117]
The management unit 510 of the control unit 50 is provided with a registration mark abnormality notification unit 512 for identifying and notifying the registration mark determined to be abnormal by the abnormality determination unit. You can know if it is.
[0118]
In addition, the registration mark abnormality notification unit 512 outputs information on the registration mark determined to be abnormal by the abnormality determination unit by setting a dedicated mode, so that the general user can be made aware of the registration mark abnormality. In a suppressed state, a professional engineer can be notified and unnecessary confusion can be avoided.
[0119]
The present invention is not limited to the above embodiments, but also includes the following contents.
[0120]
(1) In the above embodiment, when the color shift correction in the oblique direction is performed, the color shift correction of each color toner image is performed based on the black toner image. However, the present invention is not limited to this. For example, for each of the black toner image and each of the color toner images, a color misregistration correction amount for each of the initial setting positions may be obtained, and color misregistration correction may be performed based on the obtained color misregistration correction amounts.
[0121]
(2) In the above embodiment, when color shift correction in the sub-scanning direction is performed, color shift correction of each color toner image is performed based on the black toner image, but the present invention is not limited to this. For example, for each of the black toner image and each of the color toner images, a color misregistration correction amount for each of the initial setting positions may be obtained, and color misregistration correction may be performed based on the obtained color misregistration correction amounts.
[0122]
(3) In the above-described embodiment, the color misregistration correction amount is calculated based on a predetermined calculation formula. However, the present invention is not limited to this, and may be stored in a predetermined storage unit of the control unit 50. Alternatively, the color misregistration correction amount may be obtained using the table. The point is that the correction operation unit 530 only needs to have a function of calculating the color misregistration correction amount from a calculation formula, a table, or the like.
[0123]
(4) In the above-described embodiment, a method in which the image forming units 221 to 224 are disposed along the transfer direction of the transfer belt 243 (a so-called tandem method) is adopted as the image forming apparatus 10, but is not limited thereto. Instead, for example, the image forming units 221 to 224 may be arranged along the rotation direction of a rotating drum as an image carrier for conveying a sheet.
[0124]
(5) In the above embodiment, the registration marks for detecting color misregistration are formed at both ends in the width direction of the transfer belt 243, but the registration marks are provided at both ends in the width direction of the transfer belt 243. However, the present invention is not limited to this. For example, the transfer belt 243 may be formed only at one end in the width direction, or may be provided at the center of the transfer belt 243 in the width direction.
[0125]
(6) In the above embodiment, the registration marks for detecting the color misregistration include the oblique line L1 formed of a linear pattern formed obliquely with respect to the sub-scanning direction and the line formed along the main scanning direction. And the horizontal line L2 formed in a shape pattern, but is not limited to this. For example, both the oblique line L1 formed of a linear pattern and the horizontal line L2 formed of a linear pattern may be formed obliquely with respect to the sub-scanning direction. In short, it is only necessary that the linear pattern forming the oblique line L1 and the linear pattern forming the horizontal line L2 have different angles.
[0126]
(7) In the above embodiment, the registration mark for detecting the color misregistration is formed using the pattern generator 42. However, the present invention is not limited to this. For example, the storage unit of the control unit 50 stores the image data as a combination of the oblique line L1 and the horizontal line L2 formed of a linear pattern, and reads out the image data to form a registration mark on the surface of the transfer belt 243. You can also do so.
[0127]
(8) In the above embodiment, the exposure unit 227 is configured by an LED print head, but is not limited to this. For example, a laser beam scanning type may be used.
[0128]
(9) In the above embodiment, the image forming apparatus 10 is a color printer, but is not limited to this. For example, another configuration such as a color copying machine or a color facsimile may be used.
[0129]
【The invention's effect】
According to the image forming apparatus of the present invention, the color misregistration correction amount calculating means corrects the color misregistration based on the detection signals of the remaining registration marks without employing the detection signals of the registration marks determined to be abnormal by the abnormality determining means. Therefore, even if any of the plurality of registration marks becomes abnormal, the color misregistration correction amount calculation means calculates the color misregistration correction amount based on the detection result of the remaining registration marks, and Color misregistration correction is performed based on the calculation result. Therefore, it is possible to form a color image on which the color misregistration correction is performed as much as possible on the sheet, and it is possible to print a better color image on the sheet as compared with a case where the color misregistration correction is not performed at all.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing an internal configuration of a digital color image forming apparatus to which a color misregistration correction method according to an embodiment of the present invention is applied.
FIG. 2 is an explanatory plan view of a transfer conveyance unit including a photosensitive drum.
FIG. 3 is a block diagram illustrating a control configuration for explaining a color misregistration amount detection operation due to various fluctuation factors and a color misregistration correction operation;
FIG. 4 is an explanatory diagram for explaining an output waveform of a reflection type photo sensor.
FIG. 5 is an explanatory diagram for explaining the calculation of the center of gravity of the P-wave output of the reflection type photosensor.
FIG. 6 is an explanatory diagram for explaining color shift correction in an oblique direction.
FIG. 7 is an explanatory diagram for explaining another color shift correction in an oblique direction.
FIG. 8 is a time chart for explaining color misregistration correction in the sub-scanning direction.
FIG. 9 is a time chart for explaining color shift correction in the main scanning direction.
FIG. 10 is a flowchart for explaining detection of an abnormality in a registration mark and correspondence when an abnormality is detected.
FIG. 11 is an explanatory diagram for explaining an output waveform of a registration mark.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 image forming apparatus 12 main body section 14 paper discharge section 18 housing 20 paper feed cassette 22 image forming sections 221 to 224 first to fourth image forming units 225 photosensitive drum 226 charging section 227 exposure section 228 developing section 229 cleaning section 230 Transfer Unit 24 Transfer Conveying Unit 241 Driven Roller 242 Drive Roller 243 Transfer Belt 244 Transfer Roller 245 Reflective Photosensor 2451 First Photosensor 2452 Second Photosensor 246 Blade 26 Fixing Unit 261 Heat Shield Box 262 Fixing Roller 263 Pressure Roller 264 Blade 265 Rear transport path 28 First transport path 281 Transport roller pair 282 Register roller pair 283 Timing sensor 40 Image input unit 41 Scanner 42 Pattern generator 43 Registration mark input unit 44 Registrar Image generation unit 50 control unit 500 image control unit 501 memory write processing unit 502 image memory 503 memory read processing unit 504 sub-scanning timing control unit 505 main scanning timing control unit 510 management unit 511 correction execution management unit 512 registration mark abnormality notification unit 520 Sensor control unit 521 First sampling processing unit 522 Second sampling processing unit 523 First registration mark abnormality determination unit 524 Second registration mark abnormality determination unit 525 First registration mark position calculation unit 526 Second registration mark position calculation unit 530 Calculation unit 531 Correction method selection unit 532 Tilt deviation correction unit 533 Sub-scan deviation correction unit 534 Main scanning deviation correction unit L1, L1 'Diagonal line L2, L2' Horizontal line 61 First registration mark 62 Second registration mark

Claims (6)

An image forming unit having an exposure unit for exposing the photosensitive drum and transferring a toner image of a different color in a superimposed manner on a sheet conveyed by the image carrier, and a color of the toner image transferred on the sheet Mark forming control means for forming a plurality of rows of registration marks for detecting a shift amount on the image carrier by the image forming unit, and detecting positions of the registration marks formed in a plurality of rows on the image carrier. A plurality of mark detection means provided corresponding to the registration marks, and a color shift correction amount calculation means for calculating a color shift correction amount based on a detection signal output from each mark detection means. The image forming apparatus further includes a registration mark abnormality determination unit that determines an abnormality of the registration mark. An image forming apparatus characterized in that to correct the color shift on the basis of the detection signals excluding the detection signal of the registration marks is constant means determines an abnormality. The registration mark is formed of a linear pattern, and the registration mark abnormality determination unit determines that the registration mark is normal when the number of the linear patterns is output from the mark detection unit by a predetermined number. The image forming apparatus according to claim 1, wherein the image forming apparatus determines the abnormality. A pair of the mark detecting means is provided so as to oppose each other in the width direction of the image carrier, and each of the registration marks is formed in two rows so as to correspond to the pair of mark detection means, respectively. Is composed of a first linear pattern formed to extend obliquely to the sub-scanning direction and a second linear pattern formed to extend in the main scanning direction. And means for calculating the amount of color misregistration correction between the first linear pattern, the distance between the second linear patterns, and the first and second distances calculated based on the detection signal output from the mark detecting means. The image according to claim 1, wherein the image is calculated by comparing any one of the intervals between the linear patterns with each reference value set in advance corresponding to each interval. Forming equipment When one of the registration marks formed in two rows corresponding to the pair of mark detection means is determined to be abnormal by the registration mark abnormality determination means, the color misregistration correction amount calculation means determines the other. 4. The image forming apparatus according to claim 3, wherein a color misregistration correction amount is calculated based on the registration mark. The image forming apparatus according to any one of claims 1 to 4, further comprising an abnormality notifying unit configured to notify when the registration mark abnormality determining unit determines that the registration mark is abnormal. 6. The image forming apparatus according to claim 5, wherein the abnormality notifying unit outputs information relating to the registration mark detecting unit that has been determined to be abnormal by the abnormality determining unit by setting a dedicated mode.

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