JP2004184463A - Method for deciding light receiving width for alignment pattern detecting sensor, alignment pattern detecting sensor, method for forming alignment pattern and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately detect color slippage with a simple and inexpensive configuration. <P>SOLUTION: An alignment pattern Pm is constituted by successively forming patches obtained by making the relational positional relation of the line images of two colors deviate by an arbitrary amount, wherein a plurality of lines formed by overlapping the line image Bk of black, which is a reference color and the line image C of a color other than a reference color, for instance, cyan as one patch. The light receiving width of an alignment pattern detecting means is formed so as to satisfy the relation of (light receiving width)>(line width)/(5.0627×(write density (dpi))<SP>-0.5331</SP>) in the relationship between the write density of an image forming apparatus and the line width of each patch constituting the alignment pattern. Further, a factor originating from the relationship between the line width deteriorating the linearity of two straight lines for the arbitrary shift amount of the line image of the color other than the reference color and the light receiving width is reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

ここで、受光幅は３ｍｍであるから、

となるので、ライン幅は１１．８ｄｏｔ以下に設定しなければならない。このようなライン幅と受光幅との関係が解像度との関係においてあるが故に、ライン幅を２４ｄｏｔとした実験結果（図３９）では位置ずれ量の計算結果が３４．７４μｍと、検出誤差最大許容値以上となり、上記関係を満足するライン幅１１．８ｄｏｔ以下の条件であるライン幅１０ｄｏｔラインとした実験結果（図４０）では計算結果が１２．９１μｍと位置ずれ量が検出誤差最大許容値以下で算出できたものと考えられる。
【００６２】
ただ実際には、ライン幅は補正すべき装置の最大ずれ量に基づき決定されるために、上記式よりライン幅／受光幅比を求めた後、最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、受光幅を決定される順序が正しい。
以下に、補正すべき装置の最大ずれ量から必要なライン幅を求める方法を示す。
今、２つの近似直線より交点計算を行う事を考えた場合、例えば図３９の例では、中央パッチのずれ量がほぼゼロであったために、パッチ：Ｐ６が出力電圧の極小値となったが、もし仮に主走査方向のずれ量が１２ｄｏｔ程度あった場合には、図１６に示すような出力となる。
この場合には、かろうじて極小値を中心とした前後の極大値データまでの点（Ｐ４〜Ｐ１３）を使い、交点計算ができるが、もしずれ量が図１７に示すように、その倍の２４ｄｏｔあった場合には、交点計算が不能となる。
従って、ライン幅は補正すべき機械の最大ずれ量の２倍以上である事が望ましい。
【００６３】
すなわち、下記式を満たすようにする。
［ライン幅］＞２×［補正すべき最大ずれ量］
上記式より、装置のもつ最大ずれ量が５ｄｏｔであった場合、

となり、１ｄｏｔ＝４２．３μｍ（６００ｄｐｉ）で計算すると、４２３μｍ以上となる。
ここで、６００ｄｐｉの場合のライン幅／受光幅比は

であるために、

でなければならないことが判る。
逆に、このように設定することにより、位置ずれ誤差を最大許容値以下に抑えることが可能となる。
【００６４】
これまでの検討では、２色の重ね合わせパターンを位置合わせパターン検知センサで検知する場合において、位置合わせパターンのライン幅及び受光幅（又は受光径）は、画像形成装置の書き込み密度及び画像形成装置の補正すべき最大ずれ量に対し、どのような根拠に基づき設定すればよいかについて理論的に考えてきた。
しかしながら、このようにして条件設定した場合においても、実際に実験を行った結果では位置ずれ検出誤差が大きくなる場合があった。その実験結果を図１８に示す。
図１８のグラフは、図２で示したようなＢｋラインとカラーラインの重ね合わせパターンで、各色のライン幅を１０００μｍとし、Ｂｋラインに対しカラーラインを１００μｍずつずらしたパッチを２１個形成してなる位置合わせパターンを転写ベルト１８上に形成し、２００万画素ＣＣＤ搭載デジタルマイクロスコープにて各パッチのシアン（Ｃ）とＢｋとの線幅比を測定し、「横軸のカラーラインの任意のシフト量」に対してプロットしたものである。
極大値近傍では「横軸のカラーラインの任意のシフト量」に対する線幅比の変化率が減少してしまっていることが判る。
図１９は、各色のライン幅を５００μｍとし、Ｂｋラインに対しカラーラインを１０μｍずつずらしたパッチをセンサで検出したたもので、横軸のシフト量と縦軸のセンサ出力電圧との関係を示すグラフである。本図からも極大値近傍及び極小値近傍で直線性が悪化していることが判る。
【００６５】
このようなことを調べたのは、実際に、図３に示した位置合わせパターン検知センサ４０にて測定される出力電圧が、極大値近傍において飽和してしまう結果を示していたからであるが、実験の結果、図１８又は図１９に示すように、実際の転写ベルト１８上に形成されたパッチでも飽和してしまっていることが確認された。
従って、この極大値近傍の出力の飽和現象は、センサ側の問題ではなく、パターン形成をしている画像形成装置側の問題であるといえる。
このような結果となった理由は、Ｂｋ、Ｃライン共に狙いのライン幅（＝１０００μｍ）に対し太りが生じてしまっていたからであることがデジタルマイクロスコープによる観察で確認できた。
このような現象が生じる原因にはトナー濃度の影響等が挙げられるが、特にラインのエッジ効果の生じやすい２成分方式の現像装置を使った場合には顕著となる。
【００６６】
なお、今回の結果では、図２０に示すように、Ｂｋライン、Ｃラインが共にライン太りしていたために、このような出力の飽和が極大値側のみに現れた。図２０に示すように、共にライン太りが生じている場合、Ｃラインを図２０（ａ）に示すパッチＡの状態から図２０（ｂ）に示すパッチＢの状態にシフトしても、Ｂｋライン間におけるＣラインには変化が生じず出力は同じとなり、検知することができない。
この実験則を踏まえれば、もし仮にＢｋのトナー濃度が非常に高く、その結果Ｂｋラインのみがライン太りが生じ、逆にカラーのトナー濃度が非常に低く、潜像に対し忠実な線幅のラインを形成した場合には、極小値近傍で同様の出力の飽和現象が発生するものと推定できる。
すなわち、図２１に示すように、Ｃラインを図２１（ａ）に示すパッチＡの状態から図２１（ｂ）に示すパッチＢの状態にシフトしても、ＣラインのシフトはＢｋラインの範囲内でなされるために変化は生じず出力は同じとなり、検知することができない。
【００６７】
従って、近似直線を求めるのに用いるデータ点は、画像形成装置の持つ固有の特性による影響を極力排除するために、極大値及び極小値又はそれらの近傍のデータを除外するのが望ましい。具体的には、例えば、複数パッチの出力の最大値と最小値より、（最大値＋最小値）／２±（最大値−最小値）×０．４のデータのみを計算に用いるようにする。
従来技術においては、連続したパッチの全点データより２つの近似直線を求め、交点計算を行う事によりずれ量を算出しており、上記のような交点近傍で生じる出力の飽和現象については論じられていない。
従って、従来技術においては、このような極値近傍で生じる出力の飽和現象により、２つの近似式の決定係数Ｒ^２が悪化する場合があり、それにより交点計算により求まる位置ずれ量には誤差が生じてしまう場合があるといえる。
【００６８】
また、本実施形態では、位置合わせパターンＰｍが形成される転写ベルト１８には、明度Ｌ^＊（ＪＩＳＺ８７２９）＝１．７のポリイミド製のベルトを用いている。これを含む上記のような構成とした理由について以下にさらに詳述する。
（位置合わせパターンの構成について）
図２２は、図３に示した位置合わせパターン検知センサ４０のベルト地肌部、Ｂｋベタパッチ部、Ｃ（シアン）パッチ部の正反射光出力電圧を、横軸のＬＥＤ電流に対してプロットしたグラフである。
ここで例えば、転写ベルト地肌部の出力電圧が４．０ｖとなるＬＥＤ電流設定（＝３７ｍＡ）時の各パッチ部の出力電圧を見てみると、表１に示すような結果となる。
【００６９】
【表１】

【００７０】
ここで、図２２の位置合わせパターンを正反射光出力で読むことを考えると、Ｐ１、及びＰ１３の面積比は、黒ライン×５０％＋カラーライン×５０％であり、Ｐ７の面積比は、黒ライン×５０％＋カラーライン×５０％であるために、各パッチ部のセンサ出力はおよそ、以下の通りとなる。
（「Ｂｋライン群」が「カラーライン群」の上に形成されている場合）
Ｐ１、Ｐ１３の出力電圧＝０．１２（Ｂｋベタ）×０．５＋１．９１（Ｃベタ）×０．５＝１．０１５ｖ
Ｐ７の出力電圧＝０．１２（Ｂｋベタ）×０．５＋４．０（ベルト部）×０．５＝２．０６ｖ
（「Ｂｋライン群」が「カラーライン群」の下に形成されている場合）
Ｐ１、Ｐ１３の出力電圧＝０．１２（Ｂｋベタ）×０．５＋１．９１（Ｃベタ）×０．５＝１．０１５ｖ
Ｐ７の出力電圧＝１．９１（Ｃベタ）×０．５＋４．０（ベルト部）×０．５＝２．９５５ｖ
【００７１】
各パッチの出力電圧を、「横軸のカラーラインの任意のシフト量」に対しプロットすると、図２３に示すような結果となる。図２３より、以下のことが判る。
（正反射光により検知を行った場合）
（ａ）出力電圧は２色ラインが完全に重なり合ったパッチ（Ｐ７）にて最大となり、その出力電圧はほとんどベルト地肌部からの出力によって決まる。
（ｂ）「黒ライン群」が「カラーライン群」に対して上である場合の方が、下である場合に比べ最小値（Ｐ１、Ｐ１３）と最大値（Ｐ７）との出力差が小さくなる。
このように、正反射光による検知を行った場合の極大値（Ｐ７）の出力は、ベルト地肌部からの出力（∝光沢度）によって決まるために、
（ｃ）経時的な摩耗、又は部分的なキズ等により、光沢度が低下すると、その部分の出力は低下してしまう。換言すれば、経時的な摩耗によるベルト劣化により検知ができなくなるために、これによりベルト寿命が決まる。
【００７２】
つまり、図２で示したＰ２〜Ｐ１２のように、部分的にベルト面が露出しているパッチ部の正反射光出力電圧は、ベルト光沢度、又は表面粗さＲｚ等で表される表面形状特性のノイズの影響を受けやすいために、例えば、Ｐ６パッチの地肌部にキズがあると、これと鏡像関係にあるＰ８とで出力が異なってしまい、結果として計算によって求まる交点位置がずれるという結果が生じてしまう。
【００７３】
これに対し、拡散反射光による検知を行った場合には、転写ベルト１８の表面の粗さの影響をほとんど受けることなく位置ずれ量の検知ができる。
図２４は、図３で示した位置合わせパターン検知センサ４０のベルト地肌部、Ｂｋベタ部、Ｃ（シアン）ベタ部の拡散反射光出力電圧を、横軸のＬＥＤ電流に対しプロットしたものである。
正反射光出力が図２６に示す通り、被検知物体（位置合わせパターンが形成された転写ベルト１８）の光沢度との相関が高いのに対し、拡散反射光出力は図２７に示す通り、被検知物体の明度Ｌ^＊との相関が高く光沢度との相関は無いために、本実施形態におけるカラープリンタに搭載されたＬ^＊＝１．７の転写ベルト１８は、黒トナーとほぼ同じ出力特性を持つ。図２７から明らかなように、明度Ｌ^＊が約４０まで直線性が得られ、明度Ｌ^＊が２０まではその直線性が極めて高い。
ここで、先と同様に以下２つのケースについて考えてみると、各部出力電圧は表２に示すような結果となる。
【００７４】
【表２】

【００７５】
（「Ｂｋライン群」が「カラーライン群」の上に形成されている場合）
Ｐ１、Ｐ１３の出力電圧＝０．１６（Ｂｋベタ）×０．５＋３．４２（Ｃベタ）×０．５＝１．７９ｖ
Ｐ７の出力電圧＝０．１６（Ｂｋベタ）×０．５＋０．０７（ベルト部）×０．５＝０．１１５ｖ
（「Ｂｋライン群」が「カラーライン群」の下に形成されている場合）
Ｐ１、Ｐ１３の出力電圧＝０．１６（Ｂｋベタ）×０．５＋３．４２（Ｃベタ）×０．５＝１．７９ｖ
Ｐ７の出力電圧＝３．４２（Ｃベタ）×０．５＋０．０７（ベルト部）×０．５＝１．７４５ｖ
【００７６】
各パッチの出力電圧を、「横軸のカラーラインの任意のシフト量」に対しプロットすると、図２５のような結果となる。図２５より、以下のことが判る。
（拡散反射光により検知を行った場合）
（ａ）出力電圧は２色ラインが完全に重なり合ったパッチ（Ｐ７）にて最小となり、その出力電圧は「カラーライン群」の出力電圧によって決まる。
（ｂ）「黒ライン群」が「カラーライン群」に対し上である場合の方が、下である場合に比べ最大値（Ｐ１、Ｐ１３）と最小値（Ｐ７）との出力差を大きく取れる。
このように、拡散反射光による検知を行った場合の最大値（Ｐ７）の出力は、「カラーライン群」からの出力（∝明度）によって決まるために、
（ｃ）経時的な摩耗、又は部分的なキズ等による影響を全く受ける事がない。換言すれば、検知性能がベルト劣化に依存しないために、転写ベルトの長寿命化が達成可能となる。
【００７７】
以上より、基準色である黒のライン像と基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンを、この位置合わせパターンを検知するための位置合わせパターン検知センサにて検知することを考えた場合、転写ベルトの摩耗、又は部分的なキズ等の経時的な変動要因の影響を全く受けることのない検知を行うためには、
（１）拡散光出力による検知をすることが望ましく、
（２）基準色である黒ライン像の作像順序が、転写体上での色重ねの最終色であることが望ましく、
（３）位置合わせパターンを形成する転写体の明度（Ｌ^＊）が４０以下、好ましくは２０以下であることが望ましい、ということができる。
【００７８】
なお、図２６に示した結果は、４２種類もの光沢度及び明度の異なる転写ベルトについて、ＬＥＤ電流Ｉｆ＝２０ｍＡ固定としたときの正反射光出力値を、横軸の転写ベルト表面の６０°光沢度に対してプロットしたものである。またこの図に示す光沢度測定値は、日本電色社製の光沢度計ＰＧ−１を使い、測定角度６０°の条件で測定した値である。
図２７に示した結果は、図２６に示したものと同じ４２種類のベルトについて、ＬＥＤ電流２０ｍＡ固定としたときの拡散反射光出力を、横軸の転写ベルト表面の明度Ｌ^＊に対してプロットしたものである。なお、この図に示す明度測定値は、Ｘ−Ｒｉｔｅ社製のＸ−Ｒｉｔｅ９３８を使い、光源Ｄ５０、視野角２°の条件で測定した値である。
【００７９】
上述した本発明の手法による効果確認のための実験を図２８に示す。なお、各出力電圧のサンプリングは、本画像形成装置（カラープリンタ）の線速１２５ｍｍ／ｓｅｃに対し、５００Ｓａｍｐｌｉｎｇ／ｓｅｃにて行った。
全パッチの出力電圧と、全パッチの出力電圧値から求めた２直線の傾き、ｙ切片、ＲＳＱ（＝決定係数）及び交点計算結果を表３に示す。
【００８０】
【表３】

【００８１】
このように、上記実験では、図１３に示したシミュレーションによる受光径３ｍｍ、ライン幅２５０μｍ（＝約６ｄｏｔライン）の位置ずれ量検出誤差最大値５．１５μｍに対し、位置ずれ量２．８３μｍという結果が得られた。
ただ、図２８のグラフをみれば判る通り、やはり極値付近のデータは出力が飽和している傾向が見られる。
そこで、極値及び極値近傍のデータを除いた点で交点計算を行った結果を表４に示す。
【００８２】
【表４】

【００８３】
このように、極値及び極値近傍のデータ点を直線近似式算出のデータ点から除外することにより、直線性を表す近似直線の決定係数Ｒ^２（＝ＲＳＱ）を０．９７１３から０．９９９９（Ｐ１〜Ｐ７）に、０．９７０３から０．９９９８（Ｐ７〜Ｐ１３）に、という具合に大幅に改善でき、その結果として、より高精度な位置ずれ量検知が可能となることが確認できた。
なお、この実験においても、転写ベルト１８上に作成した位置合わせパターンの中央パッチＰ７の位置ずれ量を２００万画素ＣＣＤ搭載デジタルマイクロスコープにて観察し、ずれ量がゼロであることを確認した。
【００８４】
以上の結果から、基準色である黒のライン像と基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、この位置合わせパターンを検知するための位置合わせパターン検知手段と、この位置合わせパターン検知手段からの出力信号から基準色と基準色以外との位置ずれ量とその方向を判断し、その位置ずれ量を補正する補正手段を備えた画像形成装置において、
▲１▼位置合わせパターンのライン幅を、位置合わせパターン検知手段の受光幅と画像形成装置の書き込み密度との関係において
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{−０．５３３１}）
の関係を満足するように、位置合わせパターンの各パッチを構成するライン幅を設定することにより、出力の非線形性による位置ずれ量検出誤差を最大許容値以下とすることができ、また、
▲２▼交点計算に用いるデータ点から極値又はその近傍のデータを除外することにより、交点計算に用いる２つの近似直線の直線性が改善されるので、その結果として直線近似式算出に使うデータ点数、すなわちパターン数を各直線ともに最小で２点まで（全体のパッチ数は４つまで）減らすことができる。
すなわち、通常のプリント動作とは関係のない、すなわち、生産性に寄与しない位置ずれ調整動作の処理時間を大幅に短縮することが可能となる。
また、このようなセンサ（従来と同様の位置合わせパターン検知センサ４０）を用いた場合でも、高精度な位置ずれ量検知が可能となることから、従来のエッジ検出方式に対し約１／１００の低サンプリング周波数によるサンプリングで十分な位置ずれ量検知が可能となる。
【００８５】
上述した位置合わせパターン検知センサ４０及び手法に基づく位置ずれ補正は、位置ずれ量補正手段によってなされる。この位置ずれ量補正手段４６を図５に基づいて説明する。
位置合わせパターン検知センサ４０ａ、４０ｂ、４０ｃの発光部である発光ダイオード４０Ａは発光量制御部４７により発光量を制御され、出力側であるフォトダイオード４０Ｂはアンプ４８、フィルタ４９、Ａ／Ｄ変換器５０、ＦＩＦＯメモリ５１を介してＩ／Ｏポート５４に接続されている。
位置合わせパターン検知センサ４０ａ、４０ｂ、４０ｃから得られた検知信号は、アンプ（ＡＭＰ）４８によって増幅され、フィルタ４９を通過してＡ／Ｄ変換器５０によってアナログデータからデジタルデータへと変換される。
データのサンプリングはサンプリング制御部５２によって制御され、サンプリングされたデータはＦＩＦＯメモリ５１に格納される。サンプリング制御部５２、書込制御基板５３はＩ／Ｏポート５４に接続されている。
【００８６】
Ｉ／Ｏポート５４、ＣＰＵ５５、ＲＯＭ５６、ＲＡＭ５７はデータバス５８とアドレスバス５９により接続されている。
ＲＯＭ５６には、位置合わせパターンＰｍの位置ずれ量を演算するためのプログラムを始め、各種のプログラムが格納されている。位置合わせパターンＰｍの位置ずれ量を演算するためのプログラムには、上述した交点計算に用いるデータ点から極値データ等を除外する等の条件が盛り込まれている。
アドレスバス５９によって、ＲＯＭアドレス、ＲＡＭアドレス、各種入出力機器の指定を行っている。
ＣＰＵ５５は、位置合わせパターン検知センサ４０ａ、４０ｂ、４０ｃからからの検知信号を定められたタイミングでモニタし、位置合わせパターン検知センサ４０ａ、４０ｂ、４０ｃの発光ダイオード４０Ａの劣化等が起こっても確実に位置合わせパターンＰｍの検知が行えるように、発光ダイオード４０Ａの発光量を発光量制御部４７によって制御し、フォトダイオード４０Ｂからの受光信号の出力レベルが常に一定となるようにする。
【００８７】
また、ＣＰＵ５５は、位置合わせパターン（後述する副走査方向の位置ずれ検知を目的とした位置合わせパターンを含む）の検知結果から求めた補正量に基づき、主、副レジストの変更及び倍率誤差に基づき画周波数を変更するために書込制御基板５３に対してその設定を行う。
書込制御基板５３には、出力周波数を非常に細かく設定できるデバイス、例えばＶＣＯ（Ｖｏｌｔａｇｅ Ｃｏｎｔｒｏｌｌｅｄ Ｏｓｃｉｌｌａｔｏｒ）を利用したクロックジェネレータ等を、基準色を含め各色に対して備えている。この出力を画像クロックとして用いている。また、ＣＰＵ５５は、位置合わせパターンの検知結果から求めた補正量に基づき、光書き込みユニット１６内の図示しないスキュー調整用のステッピングモータの制御も行っている。
位置合わせパターン検知センサ４０ａ、４０ｂ、４０ｃを除く上記各要素により位置ずれ量補正手段４６が構成されている。位置ずれ量補正手段４６は、カラープリンタのメインコントローラが兼ねることができる。
【００８８】
上記位置ずれ量補正手段４６による位置ずれ調整動作は、▲１▼電源投入時、▲２▼光学系の温度変化が所定値（例えば５ｄｅｇ）以上あった場合、▲３▼ある一定枚数以上のプリントジョブがあったジョブ終了時のいずれかの条件に一致したときに実行される。
上記第１の実施形態では、主走査方向の色ずれを検知するための位置合わせパターンについて述べたが、副走査方向（転写ベルト１８の進行方向と同方向）の色ずれを検知する場合には、図２９に示すような位置合わせパターンＰｓが転写ベルト１８上に、例えば図４で示した場合と同様の態様で形成される。
位置合わせパターンＰｓは位置合わせパターンＰｍと同様に、基準色である黒のライン像Ｂｋと該基準色以外の色、例えばシアンのライン像Ｃとを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成して構成されている。
また、位置合わせパターンの走査方向に対する向き（角度）は、図３０に示すように、どのようであってもよく、位置合わせパターン検知センサ４０の受光面形状も円形状のみならず、楕円であっても四角形であっても同様である。
【００８９】
本発明は、ビームスプリッタを用いることにより、光をＰ波、Ｓ波の成分に分解するような構成のセンサの受光面形状及びセンサのパターン走査方向の配置に対しても有効である（第２の実施形態）。
その一例を図３１に基づいて説明する。本実施形態における位置合わせパターン検知手段としての位置合わせパターン検知センサ６０は、１つの発光部としての発光ダイオード（以下、ＬＥＤという）６１と、３つの受光部としてのフォトダイオード（以下、ＰＤという）６２、６３、６４と、２つの偏光ビームスプリッタ（以下、ＰＢＳという）６５、６６を有している。
【００９０】
ＬＥＤ６１から放射された投光６７の偏光状態はランダムであるが、ＰＢＳ６５によって、入射面に対して垂直方向に振動する光成分（Ｓ波光）と、入射面に対して平行方向に振動する光成分（Ｐ波光）とに分離される。Ｓ波光６８はＰＢＳ６５で反射してＰＤ６２に入射し、Ｐ波光６９はＰＢＳ６５を透過して転写ベルト１８の位置合わせパターンに投光される。
位置合わせパターンから反射したＰ波光６９は乱反射によって偏光状態がランダムになり、ＰＢＳ６６によってＰ波光７０とＳ波光７１に分離される。Ｐ波光７０はＰＢＳ６６を透過してＰＤ６３に入射し、Ｓ波光７１はＰＢＳ６６で反射してＰＤ６４に入射する。
本実施形態では、受光部としてのＰＤ６２、６３、６４は、拡散反射光ではなく拡散反射成分を受光する。
【００９１】
上記各実施形態では、４連タンデム直接転写方式のカラー画像形成装置での適用例を示したが、図３２に示すように、４連タンデム構成で中間転写体へ転写した後転写紙へ一括転写する方式のカラー画像形成装置においても同様に実施できる（第３の実施形態）。
本実施形態では上述した位置合わせパターンＰｍ、Ｐｓが中間転写体としての中間転写ベルト２上に形成され、これを支持ローラ２Ｂの近傍に配置された位置合わせパターン検知センサ４０により検知する。位置ずれ量補正手段は第１の実施形態と同様である。
【００９２】
以下に、本実施形態における画像形成装置としてのタンデム型のカラー複写機の構成及び動作の概要を説明する。カラー複写機１は、装置本体中央部に位置する画像形成部１Ａと、該画像形成部１Ａの下方に位置する給紙部１Ｂと、画像形成部１Ａの上方に位置する画像読取部１Ｃを有している。
画像形成部１Ａには、水平方向に延びる転写面を有する転写体としての中間転写ベルト２が配置されており、該中間転写ベルト２の上面には、色分解色と補色関係にある色の画像を形成するための構成が設けられている。すなわち、補色関係にある色のトナー（イエロー、マゼンタ、シアン、ブラック）による像を担持可能な像担持体としての感光体３Ｙ、３Ｍ、３Ｃ、３Ｂが中間転写ベルト２の転写面に沿って並置されている。
【００９３】
各感光体３Ｙ、３Ｍ、３Ｃ、３Ｂはそれぞれ同じ反時計回り方向に回転可能なドラムで構成されており、その周りには、回転過程において画像形成処理を実行する帯電手段としての帯電装置４、各感光体３Ｙ、３Ｍ、３Ｃ、３Ｂ上に画像情報に基づいて電位Ｖ_Ｌの静電潜像を形成するための露光手段としての光書込装置５、各感光体３上の静電潜像を該静電潜像と同極性のトナーで現像する現像手段としての現像装置６、一次転写手段としての転写バイアスローラ７、印加電圧部材１５、クリーニング装置８が配置されている。各符号に付記しているアルファベットは、感光体３と同様、トナーの色別に対応している。各現像装置６にはそれぞれのカラートナーが収容されている。
中間転写ベルト２は、複数のローラ２Ａ〜２Ｃに掛け回されて感光体３Ｙ、３Ｍ、３Ｃ、３Ｂとの対峙位置において同方向に移動可能な構成を備えている。転写面を支持するローラ２Ａ、２Ｂとは別のローラ２Ｃは、中間転写ベルト２を挟んで２次転写装置９に対向している。図３２中、符号１０は中間転写ベルト２を対象としたクリーニング装置を示している。
【００９４】
感光体３Ｙの表面が帯電装置４Ｙにより一様に帯電され、画像読取部１Ｃからの画像情報に基づいて感光体３Ｙ上に書き込み密度（＝解像度）６００ｄｐｉで静電潜像が形成される。該静電潜像はイエローのトナーを収容した２成分（キャリアとトナー）現像装置６Ｙによりトナー像として可視像化され、該トナー像は第１の転写工程として、中間転写ベルト２上に、転写バイアスローラ７Ｙに印加された電圧による電界で引き付けられて転写される。
印加電圧部材１５Ｙは感光体３Ｙの回転方向における転写バイアスローラ７Ｙの上流側に設けられている。印加電圧部材１５Ｙにより、中間転写ベルト２に感光体３Ｙの帯電極性と同極性で且つ絶対値がベタ時Ｖ_Ｌより大きい電圧を印加し、転写領域にトナー像が入る以前に感光体３Ｙから中間転写ベルト２へトナーが転写することを防止して、感光体３Ｙから中間転写ベルト２へのトナーの転写時のチリによる乱れを防止する。
【００９５】
他の感光体３Ｍ、３Ｃ、３Ｂでもトナーの色が異なるだけで同様の画像形成がなされ、それぞれの色のトナー像が中間転写ベルト２上に順に転写されて重ね合わせられる。
転写後感光体３上に残留したトナーはクリーニング装置８により除去され、また、転写後図示しない除電ランプにより感光体３の電位が初期化され、次の作像工程に備えられる。
２次転写装置９は、帯電駆動ローラ９Ａ及び従動ローラ９Ｂに掛け回されて中間転写ベルト２と同方向に移動する転写ベルト９Ｃを有している。転写ベルト９Ｃを帯電駆動ローラ９Ａにより帯電させることで、中間転写ベルト２に重畳された多色画像あるいは担持されている単一色の画像を転写材としての用紙２８に転写することができる。
【００９６】
２次転写位置には給紙部１Ｂから用紙２８が給送されるようになっている。給紙部１Ｂには用紙２８が積載収容される複数の給紙カセット１Ｂ１と、給紙カセット１Ｂ１に収容された用紙２８を最上のものから順に１枚ずつ分離して給紙する給紙コロ１Ｂ２と、搬送ローラ対１Ｂ３と、２次転写位置の上流に位置するレジストローラ対１Ｂ４等が設けられている。
給紙カセット１Ｂ１から給紙された用紙２８は、レジストローラ対１Ｂ４で一旦停止され、斜めずれ等を修正された後、中間転写ベルト２上のトナー像の先端と搬送方向先端部の所定位置とが一致するタイイングでレジストローラ対１Ｂ４により２次転写位置に送られる。装置本体の右側には起倒可能に手差しトレイ２９が設けられており、該手差しトレイ２９に収容された用紙２８は給紙コロ３１により給送された給紙カセット１Ｂ１からの用紙搬送路と合流する搬送路によりレジストローラ対１Ｂ４に向けて送られる。
【００９７】
光書込装置５では、画像読取部１Ｃからの画像情報あるいは図示しないコンピュータから出力される画像情報により書き込み光が制御されて感光体３Ｙ、３Ｍ、３Ｃ、３Ｂに対して画像情報に応じた書き込み光を出射して静電潜像を形成するようになっている。
画像読取部１Ｃは、自動原稿給送装置１Ｃ１と、原稿載置台としてのコンタクトガラス８０を有するスキャナ１Ｃ２等を有している。自動原稿給送装置１Ｃ１は、コンタクトガラス８０上に繰り出される原稿を反転可能な構成を有し、原稿の表裏各面での走査が行えるようになっている。
光書込装置５により形成された感光体３上の静電潜像は現像装置６によって可視像処理され、中間転写ベルト２に１次転写される。中間転写ベルト２に対して各色毎のトナー像が重畳転写されると、２次転写装置９により用紙２８上に一括して２次転写される。２次転写された用紙２８は定着装置１１へ送られ、ここで熱と圧力により未定着画像を定着される。２次転写後の中間転写ベルト２上の残留トナーは、クリーニング装置１０により除去される。
【００９８】
定着装置１１を通過した用紙２８は、定着装置１１の下流側に設けられた搬送路切り換え爪１２により、排紙トレイ２７に向けた搬送路と反転搬送路ＲＰとに選択的に案内される。排紙トレイ２７に向けて搬送された場合には、排紙ローラ対３２により排紙トレイ２７上に排出され、スタックされる。反転搬送路ＲＰへ案内された場合には反転装置３８により反転され、再度レジストローラ対１Ｂ４に向けて送られる。
【００９９】
以上の構成により、カラー複写機１では、コンタクトガラス８０上に載置された原稿を露光走査することにより、あるいはコンピュータからの画像情報により、一様に帯電された感光体３に対して静電潜像が形成され、該静電潜像が現像装置６によって可視像処理された後、トナー像が中間転写ベルト２に１次転写される。
中間転写ベルト２に転写されたトナー像は、単一画像の場合にはそのまま給紙部１Ｂから繰り出された用紙２８に転写される。多色画像の場合には１次転写が繰り返されることにより重畳された後、用紙２８に一括して２次転写される。
２次転写後の用紙２８は定着装置１１により未定着画像を定着された後、排紙トレイ２７に排出され、あるいは反転されて両面画像形成のために再度レジストローラ対１Ｂ４に向けて送られる。
【０１００】
また、１つ感光体ドラムとリボルバー方式の現像装置を用いて各色のトナー像を形成し、各トナー像を中間転写体に重ね合わせ転写した後、シート状記録媒体としての転写紙上に一括転写する方式のカラー画像形成装置においても同様に実施することができる（第４の実施形態）。その一例を図３３に示す。
本実施形態では、上述した位置合わせパターンＰｍ、Ｐｓが中間転写体としての中間転写ベルト４２６上に形成され、これを駆動ローラ４４４の近傍に配置された位置合わせパターン検知センサ４０により検知する。位置ずれ量補正手段は第１の実施形態と同様である。
【０１０１】
以下に、本実施形態における画像形成装置としてのカラー複写機の構成の概要を説明する。
カラー複写機において、露光手段としての書き込み光学ユニット４００は、カラースキャナ２００からのカラー画像データを光信号に変換して原稿画像に対応した光書き込みを行い、像担持体である感光体ドラム４０２上に書き込み密度（＝解像度）６００ｄｐｉにて静電潜像を形成する。
該書き込み光学ユニット４００は、レーザーダイオード４０４、ポリゴンミラー４０６とその回転用モータ４０８、ｆ／θレンズ４１０や反射ミラー４１２等により構成されている。
感光体ドラム４０２は、矢印で示すように反時計回りの向きに回転され、その周囲には、感光体クリーニングユニット４１４、除電ランプ４１６、電位センサ４２０、回転式現像装置４２２のうちの選択された現像器、現像濃度パターン検知器４２４、中間転写体としての中間転写ベルト４２６等が配置されている。
【０１０２】
回転式現像装置４２２は、ブラック用現像器４２８、シアン用現像器４３０、マゼンタ用現像器４３２、イエロー用現像器４３４と、各現像器を回転させる図示しない回転駆動部を有している。各現像器は、キャリアとトナーとの混合現像剤が入った、いわゆる２成分現像方式の現像器であり、上記実施形態で示した現像装置４と同様の構成を有している。磁性キャリアの条件や仕様等も同様である。
待機状態では、回転式現像装置４２２は、ブラック現像の位置にセットされており、コピー動作が開始されると、カラースキャナ２００で所定のタイミングからブラック画像のデータの読み取りがスタートし、この画像データに基づいてレーザ光による光書き込み・静電潜像（ブラック潜像）の形成が始まる。
【０１０３】
このブラック潜像の先端部から現像するために、ブラック用現像器４２８の現像位置に潜像先端部が到達する前に、現像スリーブを回転開始してブラック潜像をブラックトナーで現像する。感光体ドラム４０２にはマイナス極性のトナーが作像される。
そして、以後、ブラック潜像領域の現像動作を続けるが、潜像後端部がブラック現像位置を通過した時点で、速やかにブラックのための現像位置から次の色の現像位置まで、回転式現像装置４２２が回転する。当該動作は、少なくとも、次の画像データによる潜像先端部が到達する前に完了させる。
像形成サイクルが開始されると、まず、感光体ドラム４０２は矢印で示すように反時計回りの向きに、中間転写ベルト４２６は時計回りの向きに、図示しない駆動モータによって回転させられる。中間転写ベルト４２６の回転に伴って、ブラックトナー像形成、シアントナー像形成、マゼンタトナー像形成、イエロートナー像形成が行われ、最終的にブラック（Ｂｋ）、シアン（Ｃ）、マゼンタ（Ｍ）、イエロー（Ｙ）の順に、中間転写ベルト４２６上に重ねられ（１次転写）、トナー像が形成される。
【０１０４】
中間転写ベルト４２６は、感光体ドラム４０２に対向する１次転写電極ローラ４５０、駆動ローラ４４４、２次転写ローラ４５４に対向する２次転写対向ローラ４４６、中間転写ベルト４２６の表面を清掃するクリーニング手段４５２に対向するクリーニング対向ローラ４４８Ａの各支持部材間に張架されており、図示しない駆動モータにより駆動制御されるようになっている。
感光体ドラム４０２に順次形成されるブラック、シアン、マゼンタ、イエローの各トナー像が中間転写ベルト４２６上で正確に順次位置合わせされ、これによって４色重ねのベルト転写画像が形成される。このベルト転写画像は２次転写対向ローラ４４６により用紙に一括転写される。
【０１０５】
給紙バンク４５６内の各記録紙カセット４５８、４６０、４６２には装置本体内のカセット４６４に収容された用紙のサイズとは異なる各種サイズの用紙が収容されており、これらのうち、指定されたサイズ紙の収容カセットから、該指定された用紙が給紙コロ４６６によってレジストローラ対４７０方向に給紙・搬送される。図３３において、符号４６８はＯＨＰ用紙や厚紙等のための手差し給紙トレイを示す。
像形成が開始される時期に、用紙は上記いずれかのカセットの給紙口から給送され、レジストローラ対４７０のニップ部で待機する。そして、２次転写対向ローラ４４６に中間転写ベルト４２６上のトナー像の先端がさしかかるときに、丁度用紙先端がこの像先端に一致するようにレジストローラ対４７０が駆動され、用紙と像のレジスト合わせが行われる。
【０１０６】
このようにして、用紙が中間転写ベルト４２６と重ねられて、トナーと同極性の電圧が印加される２次転写対向ローラ４４６の下を通過する。このとき、トナー画像が用紙に転写される。続いて、用紙は除電され、中間転写ベルト４２６から剥離して紙搬送ベルト４７２に移る。
中間転写ベルト４２６から４色重ねトナー像を一括転写された用紙は、紙搬送ベルト４７２によりベルト定着方式の定着装置４７０へ搬送され、この定着装置４７０で熱と圧力によりトナー像を定着される。定着を終えた用紙は排出ローラ対４８０で機外へ排出され、図示しないトレイにスタックされる。これにより、フルカラーコピーが得られる。
【０１０７】
本発明における上述した位置合わせパターン検知センサは、２色の重ね合わせパッチを複数形成することにより構成される位置合わせパターンを検出することにより、位置ずれ量を検知、補正を行う画像形成装置であれば、どれでも適用できるために、インクジェット装置の位置ずれ検知センサとしても適用可能である（第５の実施形態）。
その一例を図３４乃至図３６に基づいて説明する。
【０１０８】
まず、図３４に基づいて画像形成装置としてのインクジェット記録装置５００の概略構成及び印字機能を説明する。インクジェット記録装置５００は、装置本体５０１の内部に、主走査方向に移動可能なキャリッジ、キャリッジに搭載したインクジェットヘッドからなる記録ヘッド、記録ヘッドへのインクを供給するインクカートリッジ等で構成される印字機構部５０２等を有している。
装置本体５０１の下方部にはシート状記録媒体としての用紙５０３を積載収容可能な給紙カセット５０４が設けられており、該給紙カセット５０４は前方側（図中左側）から装置本体５０１に対して着脱自在に設けられている。
装置本体５０１の前面には手差しトレイ５０５が開閉自在に設けられており、給紙カセット５０４又は手差しトレイ５０５から給紙される用紙５０３を搬送して印字機構部５０２により書き込み密度（＝解像度）６００ｄｐｉにて所定の画像を記録した後、装置本体５０１の後面側に設けられた排紙トレイ５０６に排紙するようになっている。装置本体５０１の上面は上カバー５０７が開閉自在に設けられている。
【０１０９】
印字機構部５０２では、図示しない左右の側板間に支持された主ガイドロッド５０８と従ガイドロッド５０９によりキャリッジ５１０が主走査方向（紙面垂直方向）に摺動自在に保持されており、該キャリッジ５１０の下面側には、イエロー（Ｙ）、シアン（Ｃ）、マゼンタ（Ｍ）、ブラック（Ｂｋ）の各色のインク滴を吐出するノズルを有するインクジェットヘッドからなる記録ヘッド５１１が設けられている。キャリッジ５１０の上側には記録ヘッド５１１に各色のインクを供給するための各インクカートリッジ５１２が交換可能に設けられている。
記録ヘッド５１１としては、各色のインク滴を吐出する複数個のヘッドを主走査方向に並べて配置したもの、あるいは各色のインク滴を吐出するノズルを有する１個のヘッドを用いたものでもよい。
【０１１０】
記録ヘッド５１１の下方には、該記録ヘッド５１１による印写位置に対して用紙５０３を副走査方向に搬送するために、搬送ローラ５１３と従動ローラ５１４の間に用紙５０３を静電吸着して搬送する搬送ベルト５１５が掛け回されている。搬送ベルト５１５は中間ローラ５１６によってテンションを付与されている。搬送ベルト５１５を挟んで搬送ローラ５１３と対向する位置には、搬送ベルト５１５を帯電させるためのバイアスローラ５１７が配設されている。搬送ベルト５１５の平面起点部付近には、用紙５０３を搬送ベルト５１５側に押し付ける押さえローラ５１８が配設されている。ここで、搬送ベルト５１５の平面起点部とは、搬送ベルト５１５の記録ヘッド５１１側で該記録ヘッド５１１と平行になる部分の用紙搬送方向上流側、具体的には搬送ローラ５１３から搬送ベルト５１５１が離れる部分を意味している。
【０１１１】
給紙カセット５０４に収容された用紙５０３は、給紙コロ５１９及びフリクションパッド５２０により最上のものから順に１枚ずつ分離され、湾曲したガイド部材５２１によりバイアスローラ５１７と搬送ベルト５１５のニップ部に向けて搬送される。
搬送ベルト５１５の用紙搬送方向下流側上方には、用紙５０３に形成される位置合わせパターンＰｍを検知する位置合わせパターン検知センサ４０が設けられている。位置ずれ量補正手段は第１の実施形態と同様である。
図３５は搬送ベルト５１５周辺の拡大図であるが、図３４で示した押さえローラ５１８に代えて板状の抑え部材５２２を設けてもよい。
図３６に示すように、位置合わせパターンが形成される転写体としての用紙５０３上に例えば図３７で示した位置合わせパターンＰｋが形成され、これを位置合わせパターン検知センサ４０で検知して色ずれを補正する。
【０１１２】
【発明の効果】
請求項１記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成する位置合わせパターンを検知する位置合わせパターン検知センサの受光幅決定方法において、上記位置合わせパターンのライン幅と、画像形成装置の書き込み密度及び位置合わせパターン検知センサの受光幅との相関関係を実験的に導出し、導出された結果に基づいて上記受光幅を決定することとしたので、基準色以外の色のライン像の任意のシフト量に対する２直線の直線性を悪化させているライン幅、受光幅との関係による要因を低減でき、直線性の向上、すなわち位置合わせパターン検知精度の向上を図ることができる。
【０１１３】
請求項２記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンを検知する位置合わせパターン検知センサの受光幅決定方法において、上記位置合わせパターンを構成する各パッチのライン幅と、画像形成装置の書き込み密度及び位置合わせパターン検知センサの受光幅との相関関係を実験的に導出し、導出された結果に基づいて上記受光幅を決定することとしたので、基準色以外の色のライン像の任意のシフト量に対する２直線の直線性を悪化させているライン幅、受光幅との関係による要因を低減でき、直線性の向上、すなわち位置合わせパターン検知精度の向上を図ることができる。
【０１１４】
請求項３記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知するための位置合わせパターン検知センサと、該位置合わせパターン検知センサからの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知センサの受光幅を、上記画像形成装置の書き込み密度及び上記位置合わせパターンのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定することとしたので、基準色以外の色のライン像の任意のシフト量に対する２直線の直線性を悪化させているライン幅、受光幅との関係による要因を最大許容値以下とすることができる。その結果、
▲１▼：従来のエッジ検出方式に比べ、約１／１００の低サンプリング周波数でも高精度な検知が可能となる。
▲２▼：▲１▼の結果として、サンプリング以降の処理回路部も高速化する必要がなくなるために、エレキハードウエア構成を大幅にコストダウン可能となる。
▲３▼：２直線の直線性が大幅に改善されるので、位置合わせパターンを構成するパッチ数を大幅に減らすことが可能となる。
▲４▼：▲３▼の結果として、位置ずれ調整のように、通常プリントとは関係のない調整に要する処理時間を大幅に短縮できるので、生産性を大幅に向上することができる。
【０１１５】
請求項４記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知するための位置合わせパターン検知センサと、該位置合わせパターン検知センサからの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知センサの受光幅を、上記画像形成装置の書き込み密度及び上記位置合わせパターンを構成する各パッチのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定することとしたので、請求項３記載の発明と同様の効果を得ることができる。
【０１１６】
請求項５記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知するための位置合わせパターン検知センサと、該位置合わせパターン検知センサからの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、受光幅を決定することとしたので、位置ずれ検知の精度を高めることができる。
【０１１７】
請求項６記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知するための位置合わせパターン検知センサと、該位置合わせパターン検知センサからの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、受光幅を決定することとしたので、位置ずれ検知の精度を高めることができる。
【０１１８】
請求項７記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成する位置合わせパターンを所定の受光幅により検知する位置合わせパターン検知センサにおいて、上記所定の受光幅が、画像形成装置の書き込み密度及び上記位置合わせパターンのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１１９】
請求項８記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンを所定の受光幅により検知する位置合わせパターン検知センサにおいて、上記所定の受光幅が、画像形成装置の書き込み密度及び上記位置合わせパターンを構成する各パッチのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１２０】
請求項９記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成する位置合わせパターンを所定の受光幅により検知する位置合わせパターン検知センサにおいて、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、画像形成装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記所定の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１２１】
請求項１０記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンを所定の受光幅により検知する位置合わせパターン検知センサにおいて、［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、画像形成装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記所定の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１２２】
請求項１１記載の発明によれば、基準色のライン像と該基準色以外の色のライン像とを重ねて形成する位置合わせパターンの形成方法において、上記ライン像のライン幅を、画像形成装置の有する最大ずれ量の２倍以上とすることとしたので、交点計算が不能となることを防止できる。
【０１２３】
請求項１２記載の発明によれば、基準色である黒のライン像と該基準色以外のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンの形成方法において、上記ライン像のライン幅を、画像形成装置の有する最大ずれ量の２倍以上とすることとしたので、交点計算が不能となることを防止できる。
【０１２４】
請求項１３記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を順次転写体上に重ねて転写した後、シート状記録媒体に一括転写することによりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンのライン幅との関係において、以下の関係を
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１２５】
請求項１４記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を順次転写体上に重ねて転写した後、シート状記録媒体に一括転写することによりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンを構成する各パッチのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１２６】
請求項１５記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を転写体上に担持されたシート状記録媒体上に順次重ねて転写することによりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１２７】
請求項１６記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を転写体上に担持されたシート状記録媒体上に順次重ねて転写することによりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンを構成する各パッチのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１２８】
請求項１７記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を順次転写体上に重ねて転写した後、シート状記録媒体に一括転写することによりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１２９】
請求項１８記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を順次転写体上に重ねて転写した後、シート状記録媒体に一括転写することによりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１３０】
請求項１９記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を転写体上に担持されたシート状記録媒体上に順次重ねて転写することによりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１３１】
請求項２０記載の発明によれば、複数の像担持体を有し、各像担持体上に形成されたトナー像を転写体上に担持されたシート状記録媒体上に順次重ねて転写することによりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１３２】
請求項２１記載の発明によれば、請求項１４、１６、１８又は２０記載の画像形成装置において、基準色である黒ライン像の作像順序は、上記転写体上での色重ねの最終色である構成としたので、高いＳＮ比が得られ、検知精度を向上させることができる。
【０１３３】
請求項２２記載の発明によれば、請求項１３乃至２１のうちの何れか１つに記載の画像形成装置において、上記位置合わせパターンを形成する上記転写体の明度（Ｌ^＊）が４０以下、好ましくは２０以下である構成としたので、高いＳＮ比が得られ、検知精度を向上させることができる。
【０１３４】
請求項２３記載の発明によれば、請求項１３乃至２１のうちの何れか１つに記載の画像形成装置において、上記位置合わせパターンの基準色ライン像に対する基準色以外のライン像の任意のシフト量に対する上記位置合わせパターン検知手段からの出力信号が１つ以上の極値を持ち、任意のシフト量を横軸としたときに、上記位置ずれ量補正手段は、上記極値に対し両側に形成される２直線の交点を算出することにより基準色に対する基準色以外の色の位置ずれ量とその方向を判断するものであって、その交点算出には極値又は極値近傍におけるデータ点を計算に使わない構成としたので、位置合わせパターン検知手段の出力電圧の極大値又は極小値近傍における飽和現象による直線性悪化を排除でき、近似直線の直線性をより高められるので、位置ずれ検知精度を向上させることができる。
【０１３５】
請求項２４記載の発明によれば、請求項２３記載の画像形成装置において、２成分現像方式の現像装置を有している構成としたので、位置合わせパターンの形成におけるライン太り又は細りが生じやすいので、特に、近似直線の直線性をより高めて位置ずれ検知精度を向上させる効果を発揮させることができる。
【０１３６】
請求項２５記載の発明によれば、インクジェット方式によりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１３７】
請求項２６記載の発明によれば、インクジェット方式によりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、上記位置合わせパターン検知手段の受光幅が、装置の書き込み密度及び上記位置合わせパターンを構成する各パッチのライン幅との関係において、以下の関係
［受光幅］＞［ライン幅］／（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）
を満たすように決定されている構成としたので、請求項３記載の発明と同様の効果を得ることができる。
【０１３８】
請求項２７記載の発明によれば、インクジェット方式によりカラー画像を得る画像形成装置であって、基準色のライン像と該基準色以外の色のライン像とを重ねて形成された位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の像と該基準色以外の色の像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【０１３９】
請求項２８記載の発明によれば、インクジェット方式によりカラー画像を得る画像形成装置であって、基準色である黒のライン像と該基準色以外の色のライン像とを重ねて形成された複数ラインを１つのパッチとし、２色のライン像の相対的位置関係を任意量ずつずらしたパッチを連続的に形成してなる位置合わせパターンと、該位置合わせパターンを検知する位置合わせパターン検知手段と、該位置合わせパターン検知手段からの出力信号に基づいて上記基準色の黒のライン像と該基準色以外の色のライン像との位置ずれ量とその方向を判断し該位置ずれ量を補正する位置ずれ量補正手段を有する画像形成装置において、
［ライン幅／受光幅］＜（５．０６２７×［書き込み密度（ｄｐｉ）］^{− ０．５３３１}）の式よりライン幅／受光幅比を求めた後、装置の有する最大ずれ量から必要なライン幅を算出し、ライン幅／受光幅比より、上記位置合わせパターン検知手段の受光幅が決定されている構成としたので、位置ずれ検知の精度を高めることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態における画像形成装置としてのカラープリンタの概要正面図である。
【図２】主走査方向の位置ずれ検知用の位置合わせパターンの概要平面図である。
【図３】位置合わせパターンの走査方向に対する位置合わせパターン検知センサの配置関係を示す概要平面図である。
【図４】転写ベルト上における位置合わせパターンの形成位置と位置合わせパターン検知センサとの位置関係を示す概要平面図である。
【図５】位置ずれ量補正手段を示すブロック図である。
【図６】顕微鏡観察による各パッチのＢｋラインに対するカラーライン幅の実測値を示すグラフである。
【図７】位置合わせパターン検知センサの受光面形状が円形であることにより生じる面積増分の非線形性を示す図である。
【図８】位置合わせパターン検知センサの受光面形状が円形であることにより生じる面積増分の非線形性を示す図である。
【図９】円形の受光面内における長方形の面積を求める図である。
【図１０】受光面内に占めるカラーライン像の面積値を各パッチの出力値とするシミュレーション計算によるグラフ及びＢｋライン中心と受光面中心との位置関係を示す図である。
【図１１】受光面内に占めるカラーライン像の面積値を各パッチの出力値とするシミュレーション計算によるグラフ及びＢｋライン中心と受光面中心との位置関係を示す図である。
【図１２】受光面内に占めるカラーライン像の面積値を各パッチの出力値とするシミュレーション計算によるグラフ及びＢｋライン中心と受光面中心との位置関係を示す図である。
【図１３】Ｂｋライン中心の受光面中心からのずれ量に対する検出誤差を示すグラフである。
【図１４】ライン幅／受光径比に対する検出誤差を示すグラフである。
【図１５】解像度とライン幅／受光幅比の最大許容値の関係を示すグラフである。
【図１６】Ｂｋラインに対するカラーラインのシフト量と拡散光出力電圧との関係を示すグラフで、１２ｄｏｔのずれが生じた場合の状態を示す図である。
【図１７】Ｂｋラインに対するカラーラインのシフト量と拡散光出力電圧との関係を示すグラフで、２４ｄｏｔのずれが生じた場合の状態を示す図である。
【図１８】転写ベルト上の位置合わせパターンのずれ量の実測結果を示すグラフである。
【図１９】転写ベルト上の位置合わせパターンのずれ量のセンサによる実測結果を示すグラフである。
【図２０】ＢｋラインとＣラインが共にライン太りを生じている状態を示す図である。
【図２１】Ｂｋラインのみにライン太りが生じている状態を示す図である。
【図２２】ＬＥＤ発光電流と正反射光出力との関係を示すグラフである。
【図２３】正反射光により検知を行った場合の位置ずれパターン出力を示すグラフである。
【図２４】ＬＥＤ発光電流と拡散反射光出力との関係を示すグラフである。
【図２５】拡散反射光により検知を行った場合の位置ずれパターン出力を示すグラフである。
【図２６】転写ベルト表面の光沢度とセンサ出力との関係を示すグラフである。
【図２７】転写ベルト表面の明度と拡散光出力との関係を示すグラフである。
【図２８】Ｂｋラインに対するカラーラインのシフト量と拡散反射光出力電圧との関係を示すグラフである。
【図２９】副走査方向の位置ずれ検知用の位置合わせパターンの概要平面図である。
【図３０】位置合わせパターンの走査方向に対する向き（角度）の変化を示す図である。
【図３１】第２の実施形態における位置合わせパターン検知センサの構成を示す図である。
【図３２】第３の実施形態における画像形成装置としてのカラー複写機の概要正面図である。
【図３３】第４の実施形態における画像形成装置としてのカラー複写機の概要正面図である。
【図３４】第５の実施形態における画像形成装置としてのインクジェット記録装置の概要正面図である。
【図３５】図３４における搬送ベルト周辺の拡大図である。
【図３６】インクジェット記録装置における位置合わせパターンの形成と位置合わせパターン検知センサの位置関係を示す概要平面図である。
【図３７】２色のラインの重ね合わせにより構成される位置合わせパターンの概要平面図である。
【図３８】位置合わせパターンの走査方向に対する従来の光学センサの各素子の配置を示す概要平面図である。
【図３９】従来の光学センサを用いた場合のライン幅が２４ｄｏｔの位置ずれパターンの出力電圧と交点計算結果を示すグラフである。
【図４０】従来の光学センサを用いた場合のライン幅が１０ｄｏｔの位置ずれパターンの出力電圧と交点計算結果を示すグラフである。
【符号の説明】
Ｐｍ、Ｐｓ 位置合わせパターン
４０、６０ 位置合わせパターン検知手段としての位置合わせパターン検知センサ
７０２ 受光部としてのフォトトランジスタ
４６ 位置ずれ量補正手段
Ｂｋ 黒のライン像[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for forming a color image such as a copier, a printer, a facsimile, a plotter, an ink jet recording apparatus, an alignment pattern detection sensor used in the image forming apparatus, and a light receiving width of the alignment pattern detection sensor. And a method for forming an alignment pattern.
[0002]
[Prior art]
Until now, a single photosensitive drum and a revolver type developing device have been used to form toner images of each color, and each toner image has been superimposed and transferred onto an intermediate transfer member, and then collectively transferred onto transfer paper as a sheet-shaped recording medium. Transfer type color image forming apparatuses have been the mainstream.
On the other hand, due to the recent trend toward higher speeds and higher functions of color image output apparatuses, a plurality of image forming units each including a photoconductor (image carrier) and a corresponding developing device are opposed to the transfer belt by color. The so-called quadruple tandem type color image forming apparatus, which is arranged side by side at a set position and sequentially transfers a toner image on an image carrier onto a transfer paper or a transfer belt, has become the mainstream.
[0003]
The color image forming apparatus of this type has an advantage that the printing speed can be increased because the toner images formed on the image carriers of the respective colors can be transferred simultaneously. Compared to the drum intermediate transfer type color image forming apparatus, the method is disadvantageous in terms of color misregistration between colors.
A number of correction methods have been proposed for this technical problem of color misregistration. For example, Japanese Patent Publication No. Hei 7-19084 discloses that a line image of each color is formed on a transfer belt, the passage of the line image is detected by a detection sensor, and the deviation amount of the passage timing of the line image of each color from the ideal is determined. A technique has been disclosed in which the amount of misregistration of each color is ascertained by measurement and correction is performed.
[0004]
Since such a method is a method of detecting the edge of the pattern passing through the detection sensor, the detection accuracy is determined by the sampling frequency. That is, if the resolution is 600 dpi and the correction unit is 42.3 μm (= 25.4 / 600 × 1000), the detection is performed at least ±± (= 21.7 μm) or less of the correction unit. If the linear velocity of the line image on the transfer belt is 125 mm / sec, it can be detected, and the following equation is obtained: [sampling frequency] = [linear velocity] / [25.4 / resolution dpi / 2] The minimum required sampling frequency is calculated to be 6 kHz or more. In this case (= 6 kHz), the detection accuracy (= detection error) is 21.7 μm.
If this numerical value is directly fed back to the displacement correction, there may be no problem with such a sampling frequency, but when it is necessary to use this detection result (= x μm) for other calculations, for example, Such detection is performed at both left and right ends in the paper transport direction, and skew correction or magnification error correction is performed based on the detection results at both ends, because higher detection accuracy is required. If, for example, 2 μm is required as the detection accuracy, the sampling frequency needs to be very high, such as 60 kHz.
[0005]
As described above, since the required sampling frequency is proportional to the linear velocity and the resolution, the processing block after data sampling also needs a high processing speed capable of coping with the high-speed sampling. However, there is a problem that the speed increases substantially in proportion to the speeding up of the apparatus.
As a detection means for improving the detection accuracy of the edge of the pattern, a method of detecting with a high-precision, high-resolution CCD sensor has been proposed, but even when such a detection means is used, Problems such as the complexity of the apparatus and the increase in cost were unavoidable.
[0006]
To cope with such a problem, for example, Japanese Patent No. 3254244 discloses a relative position between a toner image pattern formed by superimposing a toner image of a second color on a toner image of a first color and a pattern of two colors. The average density of the toner image pattern formed at the timing when the relationship is shifted by a predetermined amount is detected by an optical sensor, and the position shift amount and the direction of the position shift between the first color and the second color are determined from the signal output. A technique for determining and correcting is disclosed.
In this technique, the amount of displacement is detected not by detecting the edge of the pattern image (line image), but by detecting the average output signal of the optical sensor of the entire pattern. Detection is possible at a sampling frequency of about 500 Hz or less (every 2 msec), that is, about 1/100 of the sampling frequency as compared with that described in Japanese Patent Publication No. Hei 7-19084.
[0007]
Therefore, even when the displacement detection method described in Japanese Patent No. 3254244 is used, if the detection accuracy at the same level as the technology described in Japanese Patent Publication No. Hei 7-19084 is obtained, more hardware is required for detecting the displacement. Since it can be configured at low cost, it is possible to significantly reduce costs.
Japanese Patent Application Laid-Open Nos. 10-329381, 2000-81745, 2001-209223, and 2002-40746 disclose similar methods to the displacement detection method described in Japanese Patent No. 3254244. And Japanese Patent Application Laid-Open No. 2002-229280.
Here, in the case where the position shift correction based on the output signal from the optical sensor of the superposition pattern of the two-color toner image disclosed in Japanese Patent No. 3254244 is considered, the maximum correction which must be temporarily corrected If the amount is ± 10 dots, if 21 patterns are formed in which the relative positional relationship between the two colors is shifted by one dot, the amount of misalignment correction and its direction can be determined by reading its extreme value. However, if such a large number of patterns are created, not only the amount of wasteful toner consumption is increased, but also the time required for the automatic adjustment of the positional deviation is undesirably increased.
To cope with this problem, for example, Japanese Patent Application Laid-Open No. 10-329381 discloses a method of calculating the position shift amount with higher accuracy by calculating the intersection of two straight lines when the vertical axis is the reflection optical density with respect to the print position parameter on the horizontal axis. The method of detecting is shown.
[0008]
[Patent Document 1]
Japanese Patent Publication No. 7-19084
[Patent Document 2]
Japanese Patent No. 3254244
[Patent Document 3]
JP-A-6-1002
[Patent Document 4]
JP-A-10-329381
[Patent Document 5]
JP 2000-81745 A
[Patent Document 6]
JP 2001-209223 A
[Patent Document 7]
JP-A-2002-40746
[Patent Document 8]
JP 2002-229280 A
[Patent Document 9]
JP 2001-212115 A
[Patent Document 10]
JP-A-2002-62707
[Patent Document 11]
JP-A-5-100556
[Patent Document 12]
JP 2002-148890 A
[Patent Document 13]
JP-A-2002-6580
[Patent Document 14]
JP 2000-35704 A
[0009]
[Problems to be solved by the invention]
According to the method disclosed in JP-A-10-329381, even when the maximum correction amount is ± 10 dots, it is not necessary to form 21 patterns, and it is appropriately several dots at a time, for example, two dots at a time. It is only necessary to form 11 shifted patterns, and if it is a pattern shifted by 5 dots, it is sufficient to form 5 patterns. Therefore, the number of patterns is greatly reduced, and the time required for positional deviation adjustment is greatly reduced. While shortening, more accurate positional deviation correction can be realized.
Since the misregistration adjustment is an operation that is not related to the normal printing operation, the longer the processing time, the longer the time required for the first printing, and in consideration of productivity, if such an adjustment time is short, Shorter is better.
However, when the amount of displacement is obtained by calculating the intersection of two straight line approximation formulas, or when the amount of displacement is obtained by arithmetic processing with a resolution equal to or less than the amount of shift of the line by other methods, An output characteristic in which the sensor output signal increases or decreases linearly with respect to an arbitrary predetermined shift amount, that is, the determination coefficient R of each approximate expression of two straight lines²Must be obtained as close as possible to a straight line.
[0010]
Therefore, whether the density detection and the intersection calculation of the two-color superimposed patterns disclosed so far can provide the same detection accuracy as the edge detection method disclosed in Japanese Patent Publication No. Hei 7-19084? In order to verify, in a one-drum intermediate transfer belt type color image forming apparatus (writing density: 600 dpi) as shown in FIG. 33, as shown in FIG. 37, the reference color black (Bk) and another color (for example, Each color line of a patch formed by superimposition of two color lines of cyan (c) is constituted by superimposition of one line, which is the minimum number of lines, as one patch, and the relative positional relationship between the two colors FIG. 38 shows a detection pattern (positioning pattern) Pk for detecting a positional deviation in the main scanning direction, which is formed by continuously shifting 13 by an arbitrary amount to form 13 pieces (P1 to P13) in the main scanning direction. UNA read in a conventional optical sensor (alignment pattern detection sensor), plots the output voltage of each patch for any shift other than the reference color lines, were intersection calculations.
Here, an experiment was performed with two levels of 24 dots and 10 dots as the level of the line width of two colors. Here, the reason why the one-drum intermediate transfer type image forming apparatus is used is to eliminate the influence of the apparatus as much as possible from the verification results. Also, the pattern used for the verification is the main scanning pattern for the same reason.
[0011]
In FIG. 37, each patch is arranged along the scanning direction of the optical sensor, that is, along the moving direction of the transfer belt, and in order to detect a color shift in the main scanning direction, a color other than the reference color is set in a direction orthogonal to the direction. Are shifted by an arbitrary amount.
In FIG. 38, the optical sensor includes an LED (light emitting diode) 700, a regular reflection light receiving element 701, and a diffused light (hereinafter, also referred to as diffuse reflection light) light receiving element 702, and these elements are provided on a support substrate 703. Supported. These elements are actually arranged in a plane substantially perpendicular to the plane of movement of the alignment pattern. However, in FIG. 38B, reference numeral 700a denotes the spot shape of the LED 700, 701a denotes the spot shape of the regular reflection light receiving element 701, and 702a denotes the spot shape of the diffused light receiving element 702.
[0012]
FIG. 39 shows the result when the line width is 24 dots, and FIG. 40 shows the result when the line width is 10 dots.
As shown in FIG. 39, when the line width is set to 24 dots, the approximate straight line obtained from the plot points on the minus side with respect to the extreme value is R.²= 0.9275, and the approximate straight line obtained from the plot point on the plus side with respect to the extreme value is R²= 0.9555, an output characteristic that was hardly a straight line was obtained.
Also, as a result of calculating the intersection from the two approximate straight lines, a position shift amount = 34.74 μm (= 0.82 dot) was obtained.
On the other hand, when the line width is set to 10 dots, as shown in FIG.²= 0.9909, and the approximate straight line obtained from the plot point on the plus side with respect to the extreme value is R²= 0.9985, it was found that characteristics close to a straight line could be obtained.
Further, as a result of calculating the intersection from these two approximate straight lines, the amount of displacement was 12.91 μm (= 0.30 dots). The experimental conditions are as follows.
[0013]
[Detailed parameters of detection pattern of result shown in FIG. 39]
Line width: 24 dots (= 25.4 / 600 × 1000 × 24 = 1.016 mm): common setting for Bk line and color line
Arbitrary shift amount: 4 dots (= 25.4 / 600 × 1000 × 4 = 169.3 μm)
Total number of patches: 13 patches (P1 and P13 do not completely overlap, and P7 both overlap completely)
Number of line repetitions: 1
[Detailed parameters of detection pattern of result shown in FIG. 40]
Line width: 10 dots (= 25.4 / 600 × 1000 × 10 = 0.423 mm): common setting for Bk line and color line
Arbitrary shift amount: 1 dot (= 25.4 / 600 × 1000 × 1 = 42.3 μm)
Total number of patches: 21 patches (P1 and P21 both overlap completely, P11 both overlap completely)
Number of line repetitions: 1
[Detection sensor] (= detailed specification of sensor shown in Fig. 38)
Light emitting side
Element: GaAs infrared light emitting diode (peak emission wavelength: λp = 950 nm), top view type
Spot diameter: 1.0mm
Light receiving side
Element: Si photo transistor (peak spectral sensitivity: λp = 800 nm), top view type
Spot diameter
Specularly reflected light receiving side: 1.0mm
Diffuse reflected light receiving side: 3.0mm
Detection distance: 5 mm (distance from upper part of sensor to detection target surface (patch))
[Line speed]
245mm / sec
[Sampling frequency]
500 Sampling / sec
In this experiment, an alignment pattern was formed on the transfer belt such that the center of the Bk line substantially coincided with the center of the sensor light receiving surface.
[0014]
As described above, it has been confirmed that the linearity, which is the basis of the intersection calculation, changes due to the difference in line width. This means that there is room for improving the positional deviation detection accuracy by a method of forming an alignment pattern or the like. In other words, this means that there is room for improving the displacement detection accuracy without increasing the accuracy or the like of the detection sensor, that is, without increasing the cost.
Therefore, the present invention uses an alignment pattern detection sensor that can detect color misregistration with high accuracy easily and at low cost, a method for determining a sensor light receiving width of alignment pattern detection, a method for forming an alignment pattern, and the alignment pattern. The main purpose is to provide an image forming apparatus.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the light reception of the alignment pattern detection sensor for detecting an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color is performed. In the width determination method, the correlation between the line width of the alignment pattern, the writing density of the image forming apparatus, and the light receiving width of the alignment pattern detection sensor is experimentally derived, and the light receiving width is determined based on the derived result. Was decided. Here, "experimental" refers to a concept that includes both actual experiments and computer simulations (the same applies hereinafter).
[0016]
According to the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. In a method for determining a light receiving width of an alignment pattern detection sensor for detecting an alignment pattern formed by continuously forming patches shifted by an arbitrary amount, a line width of each patch constituting the alignment pattern and a line width of an image forming apparatus. The correlation between the writing density and the light receiving width of the alignment pattern detection sensor was experimentally derived, and the light receiving width was determined based on the derived result.
[0017]
According to a third aspect of the present invention, there is provided an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection sensor for detecting the alignment pattern. A position shift amount correcting unit that determines a position shift amount and a direction of an image of the reference color and an image of a color other than the reference color based on an output signal from the alignment pattern detection sensor and corrects the position shift amount. In the image forming apparatus having means, the light receiving width of the alignment pattern detection sensor is determined so as to satisfy the following relationship in relation to the writing density of the image forming apparatus and the line width of the alignment pattern. did.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0018]
According to the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. An alignment pattern formed by continuously forming patches shifted by an arbitrary amount; an alignment pattern detection sensor for detecting the alignment pattern; and the reference signal based on an output signal from the alignment pattern detection sensor. In the image forming apparatus, the position of the color image and the image of a color other than the reference color are determined and the direction thereof, and the image forming apparatus includes a position shift amount correcting unit for correcting the position shift amount. The width is determined so as to satisfy the following relationship in relation to the writing density of the image forming apparatus and the line width of each patch constituting the alignment pattern. It was.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0019]
According to a fifth aspect of the present invention, there is provided an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection sensor for detecting the alignment pattern. A position shift amount correcting unit that determines a position shift amount and a direction of an image of the reference color and an image of a color other than the reference color based on an output signal from the alignment pattern detection sensor and corrects the position shift amount. [Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount, and the light receiving width is determined from the line width / light receiving width ratio.
[0020]
According to the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. An alignment pattern formed by continuously forming patches shifted by an arbitrary amount; an alignment pattern detection sensor for detecting the alignment pattern; and the reference signal based on an output signal from the alignment pattern detection sensor. In an image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of a color image and an image of a color other than the reference color and corrects the position shift amount, [line width / light receiving width] < (5.0627 × [writing density (dpi)]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount, and the light receiving width is determined from the line width / light receiving width ratio.
[0021]
According to a seventh aspect of the present invention, in the positioning pattern detection sensor for detecting a positioning pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color with a predetermined light receiving width, The light receiving width is determined so as to satisfy the following relationship with the writing density of the image forming apparatus and the line width of the alignment pattern.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0022]
In the invention according to claim 8, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. In a positioning pattern detection sensor for detecting a positioning pattern formed by continuously forming patches shifted by an arbitrary amount by a predetermined light receiving width, the predetermined light receiving width is determined by the writing density of the image forming apparatus and the positioning pattern. Is determined so as to satisfy the following relationship with respect to the line width of each patch constituting.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0023]
According to a ninth aspect of the present invention, in the alignment pattern detecting sensor for detecting an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color with a predetermined light receiving width, / Light receiving width] <(5.0627 × [writing density (dpi)]^{− 0.5331}After calculating the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount of the image forming apparatus, and the predetermined light receiving width is determined from the line width / light receiving width ratio. , Is adopted.
[0024]
According to the tenth aspect, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. In a positioning pattern detection sensor that detects a positioning pattern formed by continuously forming patches shifted by an arbitrary amount by a predetermined light receiving width, [line width / light receiving width] <(5.0627 × [writing density (dpi) )]^{− 0.5331}After calculating the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount of the image forming apparatus, and the predetermined light receiving width is determined from the line width / light receiving width ratio. , Is adopted.
[0025]
According to an eleventh aspect of the present invention, in the method for forming an alignment pattern in which a line image of a reference color and a line image of a color other than the reference color are formed so as to overlap with each other, the line width of the line image is provided by the image forming apparatus. It was decided to be at least twice the maximum deviation amount.
[0026]
In a twelfth aspect of the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined. In a method of forming an alignment pattern by continuously forming patches shifted by an arbitrary amount, the line width of the line image is set to be at least twice the maximum shift amount of the image forming apparatus.
[0027]
In the invention according to the thirteenth aspect, a plurality of image carriers are provided, and the toner images formed on each image carrier are successively superimposed and transferred on a transfer member, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image, comprising: an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and an alignment pattern detecting means for detecting the alignment pattern And a position for correcting the positional deviation amount by judging the positional deviation amount and the direction between the line image of the reference color and the line image of a color other than the reference color based on the output signal from the alignment pattern detecting means. In the image forming apparatus having the shift amount correcting unit, the light receiving width of the alignment pattern detecting unit has the following relationship with the writing density of the device and the line width of the alignment pattern. Plus is determined as, adopts a configuration that.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0028]
According to the fourteenth aspect of the present invention, the image forming apparatus has a plurality of image carriers, and the toner images formed on each image carrier are sequentially transferred onto the transfer body in a superimposed manner, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image, wherein a plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color as one patch are used as one patch. A positioning pattern formed by continuously forming patches whose relative positional relationship is shifted by an arbitrary amount; a positioning pattern detecting means for detecting the positioning pattern; and an output signal from the positioning pattern detecting means. In the image forming apparatus, the image forming apparatus further includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color and corrects the position shift amount. Rank Receiving width of the combined pattern detection means are taken in the relationship between the line width of each patch constituting the writing density and the alignment pattern of the device, it is determined so as to satisfy the following relation, the configuration of.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0029]
According to the present invention, a plurality of image carriers are provided, and a toner image formed on each image carrier is successively superimposed and transferred onto a sheet-like recording medium carried on a transfer body. An image forming apparatus for obtaining an image, comprising: a registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and a registration pattern detection unit for detecting the registration pattern. A position shift amount correcting unit that determines a position shift amount and a direction of an image of the reference color and an image of a color other than the reference color based on an output signal from the alignment pattern detection unit and corrects the position shift amount. In the image forming apparatus having the means, the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship in relation to the writing density of the apparatus and the line width of the alignment pattern. It is, adopts a configuration that.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0030]
According to the sixteenth aspect of the present invention, the color image forming apparatus includes a plurality of image carriers, and the toner images formed on the respective image carriers are sequentially transferred onto a sheet-shaped recording medium carried on a transfer body. An image forming apparatus for obtaining an image, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positions of the two color line images are determined. Based on a positioning pattern formed by continuously forming patches whose target positional relationship is shifted by an arbitrary amount, a positioning pattern detecting means for detecting the positioning pattern, and an output signal from the positioning pattern detecting means. In the image forming apparatus, the image forming apparatus includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color and corrects the position shift amount. Combination Receiving width of the allowed pattern detection means are taken in the relationship between the line width of each patch constituting the writing density and the alignment pattern of the device, it is determined so as to satisfy the following relation, the configuration of.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0031]
According to the seventeenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on each image carrier are sequentially transferred onto a transfer body in a superimposed manner, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image, comprising: an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and an alignment pattern detecting means for detecting the alignment pattern And a position for correcting the positional deviation amount by judging the positional deviation amount and the direction between the line image of the reference color and the line image of a color other than the reference color based on the output signal from the alignment pattern detecting means. In an image forming apparatus having a shift amount correcting unit, [line width / light receiving width] <(5.0627 × [writing density (dpi)])^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0032]
According to the eighteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on each of the image carriers are successively superimposed on a transfer body and transferred, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image, wherein a plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color as one patch are used as one patch. A positioning pattern formed by continuously forming patches whose relative positional relationship is shifted by an arbitrary amount; a positioning pattern detecting means for detecting the positioning pattern; and an output signal from the positioning pattern detecting means. In the image forming apparatus having position shift amount correction means for determining the position shift amount and direction of the black line image of the reference color and the line image of a color other than the reference color and correcting the position shift amount, Rye Width / receiving width] <(5.0627 × [writing density (dpi)]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0033]
According to the nineteenth aspect of the present invention, the image forming apparatus includes a plurality of image carriers, and the toner images formed on the respective image carriers are sequentially transferred onto a sheet-like recording medium carried on a transfer body by transferring the toner images. An image forming apparatus for obtaining an image, comprising: a registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and a registration pattern detection unit for detecting the registration pattern. A position shift amount correcting unit that determines a position shift amount and a direction of an image of the reference color and an image of a color other than the reference color based on an output signal from the alignment pattern detection unit and corrects the position shift amount. [Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0034]
According to the twentieth aspect of the present invention, the color image forming apparatus includes a plurality of image carriers, and the toner images formed on the respective image carriers are sequentially transferred onto a sheet-shaped recording medium carried on a transfer body. An image forming apparatus for obtaining an image, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positions of the two color line images are determined. Based on a positioning pattern formed by continuously forming patches whose target positional relationship is shifted by an arbitrary amount, a positioning pattern detecting means for detecting the positioning pattern, and an output signal from the positioning pattern detecting means. In an image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color and corrects the position shift amount, width Receiving width] <(5.0627 × [writing density (dpi)]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0035]
According to a twenty-first aspect of the present invention, in the image forming apparatus according to the fourteenth aspect, the image forming order of the black line image as the reference color is the final color of the color superposition on the transfer body. , Is adopted.
[0036]
According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to thirteenth aspects, the brightness (L) of the transfer body on which the alignment pattern is formed is formed.^*) Is 40 or less, preferably 20 or less.
[0037]
According to a twenty-third aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to thirteenth aspects, an image forming apparatus according to any one of the thirteenth to twenty-first aspects is provided for an arbitrary shift amount of a line image other than a reference color with respect to a reference color line image of the alignment pattern. When the output signal from the alignment pattern detecting means has one or more extreme values and an arbitrary shift amount is set on the horizontal axis, the positional shift amount correcting means is formed on both sides of the extreme value. By calculating the intersection of the two straight lines, the amount of misregistration and the direction of the color other than the reference color with respect to the reference color are determined, and the calculation of the intersection uses an extreme value or a data point near the extreme value. There is a configuration that does not exist.
[0038]
According to a twenty-fourth aspect of the present invention, in the image forming apparatus according to the twenty-third aspect, the image forming apparatus includes a developing device of a two-component developing system.
[0039]
The invention according to claim 25 is an image forming apparatus for obtaining a color image by an ink-jet method, comprising: an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; Positioning pattern detecting means for detecting a positioning pattern; and determining a displacement amount and a direction between the image of the reference color and an image of a color other than the reference color based on an output signal from the positioning pattern detecting means. In an image forming apparatus having a position shift amount correcting unit for correcting the position shift amount, the light receiving width of the alignment pattern detecting unit is determined by the following relationship between the writing density of the device and the line width of the alignment pattern. It is configured to be determined to satisfy the relationship.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0040]
According to an embodiment of the present invention, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color are formed. An alignment pattern formed by continuously forming patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount as one patch, an alignment pattern detecting means for detecting the alignment pattern, A position shift for correcting the position shift amount by judging a position shift amount and a direction between a black line image of the reference color and a line image of a color other than the reference color based on an output signal from the alignment pattern detecting means. In an image forming apparatus having an amount correcting means, the light receiving width of the alignment pattern detecting means is determined by the writing density of the apparatus and the line of each patch constituting the alignment pattern. In relation to the width, adopts a decision has been that, as configured to meet the following relationship.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
[0041]
The invention according to claim 27 is an image forming apparatus which obtains a color image by an ink jet method, wherein an alignment pattern formed by overlapping a line image of a reference color and a line image of a color other than the reference color, Positioning pattern detecting means for detecting a positioning pattern; and determining a displacement amount and a direction between the image of the reference color and an image of a color other than the reference color based on an output signal from the positioning pattern detecting means. In the image forming apparatus having the displacement amount correcting means for correcting the displacement amount, [line width / light receiving width] <(5.0627 × [writing density (dpi)])^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0042]
According to a twenty-eighth aspect of the present invention, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color are formed. An alignment pattern formed by continuously forming patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount as one patch, an alignment pattern detecting means for detecting the alignment pattern, A position shift for correcting the position shift amount by judging a position shift amount and a direction between a black line image of the reference color and a line image of a color other than the reference color based on an output signal from the alignment pattern detecting means. In the image forming apparatus having the amount correcting unit, [line width / light receiving width] <(5.0627 × [writing density (dpi)])^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. Has been adopted.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of a four-tandem direct transfer type color printer as an image forming apparatus according to the present embodiment will be described with reference to FIG.
The color printer has three paper feed trays, one manual feed tray 36, two paper feed cassettes 34 (first paper feed tray), and 34 (second paper feed tray). The not-shown transfer paper as a sheet-shaped recording medium is separated one by one by a feed roller 37 in order from the uppermost one, and is conveyed toward the registration roller pair 23. The transfer paper fed from the first paper feed tray 34 or the second paper feed tray 34 is separated one by one by the paper feed roller 35 from the top one to the registration roller pair 23 via the transport roller pair 39. It is conveyed toward.
The fed transfer paper is temporarily stopped by the pair of registration rollers 23, and after the skew is corrected, the leading end of an image formed on the photosensitive drum 14Y located at the most upstream position, which will be described later, and the transfer direction of the transfer paper. At a timing when the position coincides with the predetermined position, the sheet is conveyed toward the transfer belt 18 by rotating the registration roller pair 23 by turning on a registration clutch (not shown).
When the transfer paper passes through a paper suction nip constituted by the transfer belt 18 and a paper suction roller 41 in contact with the transfer belt 18, the transfer paper is electrostatically attracted to the transfer belt 18 by a bias applied to the paper suction roller 41, It is transported at a process linear speed of 125 mm / sec.
[0044]
Transfer brushes 21B, 21C, 21M, and 21Y, which are arranged at positions opposed to the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors with the transfer belt 18 interposed therebetween, transfer toner onto the transfer paper that is attracted to the transfer belt 18. By applying a transfer bias (plus) having a polarity opposite to the charging polarity (minus), the toner images of the respective colors formed on the photosensitive drums 14B, 14C, 14M, and 14Y become yellow (Y) and magenta (M). ), Cyan (C), and black (Bk) in this order.
The transfer paper that has undergone the transfer process of each color is separated from the transfer belt 18 by a curvature at the position of the drive roller 19 on the downstream side, and is conveyed to the fixing device 24. By passing through a fixing nip formed by a fixing belt 25 and a pressure roller 26 in the fixing device 24, the toner image is transferred to a transfer sheet by heat and pressure. The transfer paper on which the fixing has been performed is discharged to an FD (face-down) tray 30 formed on the upper surface of the apparatus main body in the case of the single-sided printing mode.
When the double-sided printing mode is selected in advance, the transfer paper exiting the fixing device 24 is sent to a reversing unit (not shown). 33. The transfer paper is re-fed from the double-sided conveyance unit 33, and is conveyed to the registration roller pair 23 via the conveyance roller pair 39. Thereafter, the sheet passes through the fixing device 24 through the same operation as in the one-sided printing mode, and is discharged to the FD tray 30.
[0045]
Next, a configuration and an image forming operation in the image forming unit of the color printer will be described in detail.
Since the image forming section has the same configuration and operation for each color, the configuration and operation for forming a yellow image will be described as a representative, and the other portions will be denoted by the reference numerals corresponding to the respective colors and description thereof will be omitted.
Around the photosensitive drum 14Y located on the most upstream side in the transfer paper transport direction, there are provided an image forming unit 12Y having a charging roller 42Y and a cleaning unit 43Y, a developing unit 13Y, an optical writing unit 16, and the like.
At the time of image formation, the photosensitive drum 14Y is driven to rotate clockwise by a main motor (not shown), is discharged by an AC bias (DC component is zero) applied to the charging roller 42Y, and has a surface potential of approximately -50 V. Potential.
[0046]
Next, the photosensitive drum 14Y is uniformly charged to a potential substantially equal to a DC component by applying a DC bias in which an AC bias is superimposed on the charging roller 42Y, and has a surface potential of approximately -500v to -700v (target charging). The potential is determined by the process controller).
Digital image information sent from a controller unit (not shown) as a print image is converted into a binarized LD light emission signal for each color, and a cylinder lens, a polygon motor, an fθ lens, first to third mirrors, and WTL The exposure light 16Y is irradiated onto the photosensitive drum 14Y by the optical writing unit 16 having a lens or the like. The drum surface potential of the irradiated portion becomes approximately −50 V, and an electrostatic latent image corresponding to image information is formed at a writing density (= resolution) of 600 dpi.
[0047]
The electrostatic latent image corresponding to the yellow image information on the photosensitive drum 14Y is visualized by the developing unit 13Y. By applying DC (−300 to −500 V) with an AC bias superimposed on the developing sleeve 44Y of the developing unit 13Y, the toner (Q / M: −20 to −30 μC / g) is developed to form a toner image. The developing unit 13Y is a so-called two-component developing type developing device containing a mixed developer of a carrier and a toner. The formed toner images on the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors are transferred onto the transfer paper attracted onto the transfer belt 18 by the transfer bias.
[0048]
In the color printer according to the present embodiment, a color misregistration adjustment operation is performed prior to the above-described image forming operation. In the color misregistration adjustment operation, an alignment pattern described later is formed on the transfer belt 18, and the alignment pattern is read (detected) by an alignment pattern detection sensor (hereinafter, also simply referred to as a sensor) 40 as an alignment pattern detection unit. To do).
The alignment pattern detection sensor 40 is disposed on the lower surface side of the transfer belt 18 facing the photosensitive drum 14B.
[0049]
As shown in FIG. 2, a registration pattern Pm for detecting a displacement in the main scanning direction overlaps a black line image Bk as a reference color with a color other than the reference color, for example, a cyan line image C. Are formed as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount (an arbitrary shift amount) are continuously formed. It is not intended to limit the reference color to black (the same applies to other embodiments described below).
Here, the “arbitrary shift amount” includes that the shift amount between P1 and P2 is 50 μm and the shift amount between P2 and P3 is not always constant such as 20 μm.
In the present embodiment, the alignment pattern Pm has a configuration in which one patch overlaps a 250 μm color line other than the reference color with a black line having the same width as this patch. The entire configuration is made up of 13 patches in which the color line C is shifted by 40 μm from the line.
Here, the meaning of "continuously forming patches" means that the patches are arranged along the scanning direction (the traveling direction of the transfer belt 18), and the arrangement is, for example, P1, P11, P2, and P10. Even if the order is different, the meaning is included continuously. Further, it is assumed that even if the interval between P1 and P2 and the interval between P2 and P3 are different, they are continuously included.
[0050]
The alignment pattern detection sensor 40 as the alignment pattern detection means in the present embodiment has the same configuration as the conventional sensor shown in FIG. That is, as shown in FIG. 3, a light emitting diode (LED) 40A as a light emitting section, a regular reflection light receiving element (phototransistor) 40B as a light receiving section, and a diffused light receiving element (phototransistor) 40C as a light receiving section. These elements are supported by a support substrate 40D. Reference numeral 40A-1 indicates the spot shape of the LED 40A, 40B-1 indicates the spot shape of the regular reflection light receiving element 40B, and 40C-1 indicates the spot shape of the diffused light receiving element 40C. The specifications of the alignment pattern detection sensor 40 are as follows.
[Detection sensor] (= Detailed specification of sensor shown in Fig. 3)
Light emitting side
Element: GaAs infrared light emitting diode (peak emission wavelength: λp = 950 nm), top view type
Spot diameter: 1.0mm
Light receiving side
Element: Si photo transistor (peak spectral sensitivity: λp = 800 nm), top view type
Spot diameter
Specularly reflected light receiving side: 1.0mm
Diffuse reflected light receiving side: 3.0mm
Detection distance: 5 mm (distance from upper part of sensor to detection target surface (patch))
[0051]
As shown in FIG. 4, the alignment pattern Pm is formed at three positions on both sides and the center of the transfer belt 18, and correspondingly, the alignment pattern detection sensor 40 is also supported by a support substrate (not shown). (40a, 40b, 40c) are provided, and two sensors arranged on both sides of the transfer belt 18 detect a shift amount of the alignment pattern Pm for detecting a shift in the main scanning direction shown in FIG. Thereby, the main scanning deviation and the magnification error are corrected. Further, the three sensors arranged on both sides and the center of the transfer belt 18 detect the amount of misalignment of the alignment pattern Ps for detecting the misalignment in the sub-scanning direction shown in FIG. And skew correction.
[0052]
The color printer as the image forming apparatus according to the present embodiment has a writing density of 600 dpi. Correspondingly, the line width of each patch of the alignment pattern Pm and the light receiving width of the alignment pattern detection sensor 40 are set so as to satisfy the following relationship.
[Line width / light receiving width] <5.0627 × [writing density]^-0.5331
[Left side] = [line width / light receiving width] = [0.25 / 3.0] = 0.0833
[Right side] = 5.0627 × [Write density]^-0.5331= 0.167
∴ Satisfies [left side] <[right side].
[0053]
Next, the reason for setting the above conditions in the correlation between the line width, the light receiving width, and the writing density, that is, the background and grounds for conceiving and realizing the present invention will be described.
As shown in FIG. 39, in the displacement detection by the conventional optical sensor, an output characteristic that is hardly a straight line was obtained.
However, as a result of measuring the actual shift amount of the alignment pattern created on the transfer belt 18 with a digital microscope equipped with a 2 million pixel CCD, as shown in FIG. 6, a pattern with a line width of 24 dots was obtained. The shift amount at P7 where these two lines completely overlap was almost zero.
The approximate straight line obtained from the plot points on the minus side with respect to the extreme value is R²= 0.9988, and the approximate straight line obtained from the plot point on the plus side with respect to the extreme value is R²= 0.9996, an infinitely straight line (R²= 1).
Further, as a result of calculating the intersection from these two straight lines, the amount of displacement was 4.13 μm, which was almost a value close to the actual value (= 0). The shift amount on the transfer belt 18 was measured in the same manner for the pattern having the line width of 10 dots, and the shift amount was almost zero.
[0054]
As described above, the displacement amount of the pattern on the transfer belt by the digital microscope is almost zero in any of the two line width levels, whereas the displacement amount calculated from the output of the displacement detection sensor is: When the line width is 24 dots, the displacement amount is 34.74 μm, and the maximum permissible value of the detection error at 600 dpi (= ± 25.4 / resolution dpi × 1000/2 [μm] = ± 21.2 [μm]) It is considered that the difference between the two (24-dot pattern and 10-dot pattern) is due to the measurement system.
FIGS. 7 and 8 show the relationship between the light receiving diameter of the sensor and the pattern in order to consider the difference between the two.
The patches P1 to P3 shown in FIG. 7 are configured by 24 dot lines, and the patches P1 to P3 illustrated in FIG. 8 are configured by 10 dot lines. The line shift amounts of P1 to P2 and P2 to P3 are both set to 4 dots for the same comparison.
In the experiment, the center of the Bk line coincides with the center of the light receiving surface in both the 24-dot patch and the 10-dot line patch.
[0055]
Since it is considered that the diffused light output voltage of the sensor has a certain correlation with the increase in the area of the color line portion in the light receiving surface, the difference in the amount of shift between adjacent patches (4 dots in this case) increases the area increase. If is constant, it should be linear.
However, as is clear from FIG. 7, in the case of a 24 dot line having a large line width, the effect of the circular light receiving surface appears strongly, and therefore, “the change amount of the area (P2 -1) "and" Amount of change in area (P3-1) with respect to shift of color line 4dot of P2 to P3 "are larger in the latter. In other words, it is understood that it is not linear.
This is because when the light receiving surface is circular, the line width is wide (it does not mean that the light receiving width <line width) for a certain light receiving width (in this case, the light receiving diameter of the light receiving sensor). Means that it is easily affected by the shape of the light receiving surface.
[0056]
When measuring with a digital microscope, an enlarged photograph of the patch image observed with the digital microscope is imported to a personal computer in TIFF format without considering the circular light receiving surface shape, and a part of the patch is converted into a rectangular area. It is probable that the circular effect (non-linearity of output) did not appear because the intersection was calculated by cutting and calculating the area ratio of the color line / Bk line in the region.
Photoshop 5.5 manufactured by Adobe was used as image processing software based on measurement with a digital microscope.
From the above experimental results, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined by an arbitrary amount. A positioning pattern formed by continuously forming shifted patches, a positioning pattern detecting sensor (positioning pattern detecting means) for detecting the positioning pattern, and an output signal from the positioning pattern detecting sensor. In the case where an image forming apparatus provided with a correcting unit that determines the amount of misalignment between the reference color and the color other than the reference color and its direction and corrects the amount of misalignment, detects the amount of misalignment with a resolution equal to or less than an arbitrary shift amount As an example of the calculation algorithm, the method of calculating the intersection using two approximation formulas has been described above. However, the present invention is not limited to this, and is simply performed by comparing the difference output of each patch. It is possible to detect the amount of deviation with a resolution equal to or less than the shift amount by processing.) In order to ensure the required detection accuracy, the distance between the line width of the alignment pattern and the light receiving width of the alignment pattern detection sensor must be set. Need to satisfy a certain relationship.
[0057]
To derive this relationship, it is assumed that the diffused light output of the alignment pattern detection sensor has a linear relationship with the area of the color line image on the light receiving surface. Calculate the area of the color line image occupying the light receiving surface of the alignment pattern detection sensor of each of the patches, and perform a simulation calculation using this area value as the output value of each patch by combining the following error conditions. Was.
In addition, a calculation for obtaining a detection error of the displacement amount is also performed by calculating an intersection of two straight lines obtained when the area value is plotted with respect to the “shift amount of the color line image with respect to the reference color (black) on the horizontal axis”. Was.
[0058]
[a formula]
As shown in FIG. 9, the rectangular area S of one section located at a distance a from the center of the light receiving surface is S = 2 × [a × tan (acos (a / 1.5))] × (25. 4/600) as a function of the distance a from the center of the light receiving surface.
[Calculation condition]
Pattern configuration: a configuration in which the repetition of the Bk line and the color line is regarded as one patch, and a plurality of patches in which the color line is shifted by an arbitrary amount are formed continuously.
Sensor light receiving diameter: 3.0mm diameter
[Error factors and levels]
Line width (Bk, Color): 3 dots, 6 dots, 12 dots, 18 dots, 24 dots (* Calculated here: 1 dot = 42.3 μm (600 dpi))
Light receiving diameter center position with respect to Bk line center: 1 to 48 dots
[0059]
FIG. 10 to FIG. 12 show examples of calculation results by the above simulation. These results are obtained when the line width of Bk and color is set to 24 dots (= 1.016 mm) with respect to the sensor light receiving diameter: 3 mm.
FIG. 10A shows the result when the center of the Bk line coincides with the center of the sensor light receiving surface, and FIG. 10B shows the positional relationship. FIG. 11A shows a case where the center of the Bk line and the center of the light receiving surface of the sensor are shifted by 12 dots, and FIG. 11B is a diagram showing the positional relationship.
FIG. 12A shows the result when the center of the Bk line and the center of the light receiving surface of the sensor are shifted by 36 dots, and FIG. 12B shows the positional relationship. 3 is a diagram showing a positional relationship in the case of a patch P1 in FIG. 2.
[0060]
The same intersection calculation as above was also performed for line widths: 3 dots, 6 dots, 12 dots, and 18 dots. The result is shown in FIG. The horizontal axis in FIG. 13 is the “shift amount of the center of the Bk line with respect to the center of the light receiving surface” taken up as an error factor, and the vertical axis shows the result of the intersection calculation at that time.
From this result, it can be seen that the detection error increases as the line width increases.
However, since the result shown in FIG. 13 is a result under the condition that the light receiving width (= light receiving diameter) is fixed at 3 mm, in FIG. 14, the ratio of the line width to the light receiving width is plotted on the horizontal axis and the vertical axis is plotted on the vertical axis. 13, the maximum detection error on the plus side and the maximum detection error on the minus side are plotted.
[0061]
As described above, since the maximum allowable value of the detection error is determined by the resolution (= writing density), the horizontal axis represents the resolution (= writing density), and the vertical axis represents the maximum value of the vertical axis shown in FIG. The “line width / light receiving width ratio” of each resolution obtained from the detection error was plotted. (* Maximum allowable value of detection error = ± 25.4 / resolution dpi × 1000/2 [μm])
From the graph shown in FIG. 15, it can be seen that the line width / light receiving diameter ratio must satisfy the following relationship with respect to the writing density (= resolution) of the color image forming apparatus.
[Line width / light receiving width] <5.0627 × [writing density (dpi)]^-0.5331
Based on this relationship, since the writing density of the color printer shown in FIG. 1 is 600 dpi,

Here, since the light receiving width is 3 mm,

Therefore, the line width must be set to 11.8 dots or less. Since the relationship between the line width and the light receiving width is related to the resolution, the calculation result of the displacement amount is 34.74 μm in the experimental results (FIG. 39) in which the line width is 24 dots, and the maximum allowable detection error is obtained. In the experimental results (FIG. 40) in which the line width is 10 dots and the line width is 11.8 dots or less that satisfies the above relationship, the calculation result is 12.91 μm, and the displacement is less than the maximum allowable value of the detection error. It is probable that the calculation was successful.
[0062]
However, actually, since the line width is determined based on the maximum deviation amount of the device to be corrected, after calculating the line width / light receiving width ratio from the above equation, the necessary line width is calculated from the maximum deviation amount, The order in which the light receiving width is determined is correct from the line width / light receiving width ratio.
Hereinafter, a method for obtaining a necessary line width from the maximum deviation amount of the device to be corrected will be described.
Now, when calculating the intersection from two approximate straight lines, for example, in the example of FIG. 39, since the shift amount of the central patch was almost zero, the patch: P6 became the minimum value of the output voltage. If the shift amount in the main scanning direction is about 12 dots, the output is as shown in FIG.
In this case, the point of intersection can be calculated using the points (P4 to P13) before and after the local minimum data centering on the local minimum value, but as shown in FIG. In this case, the intersection calculation becomes impossible.
Therefore, it is desirable that the line width be at least twice the maximum displacement of the machine to be corrected.
[0063]
That is, the following equation is satisfied.
[Line width]> 2 × [maximum deviation to be corrected]
From the above equation, if the maximum deviation amount of the device is 5 dots,

Calculating with 1dot = 42.3 μm (600 dpi), it becomes 423 μm or more.
Here, the line width / light receiving width ratio in the case of 600 dpi is

To be

It turns out that it must be.
Conversely, by setting in this way, it is possible to suppress the displacement error to the maximum allowable value or less.
[0064]
In the previous studies, when a two-color superposition pattern is detected by a positioning pattern detection sensor, the line width and light receiving width (or light receiving diameter) of the positioning pattern are determined by the writing density of the image forming apparatus and the image forming apparatus. We have theoretically considered what grounds should be set for the maximum deviation to be corrected.
However, even when the conditions are set in this manner, there is a case where the error of detecting the displacement becomes large as a result of the actual experiment. FIG. 18 shows the experimental results.
The graph of FIG. 18 is a superposition pattern of the Bk line and the color line as shown in FIG. 2, in which the line width of each color is 1000 μm, and 21 patches are formed by shifting the color line by 100 μm with respect to the Bk line. Is formed on the transfer belt 18 and the line width ratio between cyan (C) and Bk of each patch is measured with a digital microscope equipped with a 2 million pixel CCD, and “an arbitrary color line on the horizontal axis is measured. The shift amount is plotted.
In the vicinity of the maximum value, it can be seen that the rate of change of the line width ratio with respect to “arbitrary shift amount of the horizontal color line” has decreased.
FIG. 19 shows the relationship between the shift amount on the horizontal axis and the sensor output voltage on the vertical axis, where the line width of each color is set to 500 μm, and a patch in which the color line is shifted by 10 μm from the Bk line is detected by the sensor. It is a graph. It can also be seen from this figure that the linearity has deteriorated near the local maximum value and the local minimum value.
[0065]
The reason for examining this fact is that the output voltage actually measured by the alignment pattern detection sensor 40 shown in FIG. 3 was shown to be saturated near the local maximum value. As a result, as shown in FIG. 18 or 19, it was confirmed that the patches formed on the actual transfer belt 18 were saturated.
Therefore, it can be said that the saturation phenomenon of the output near the maximum value is not a problem on the sensor side, but a problem on the image forming apparatus side performing pattern formation.
It was confirmed by observation with a digital microscope that the reason for such a result was that both the Bk and C lines were thicker than the target line width (= 1000 μm).
The cause of such a phenomenon includes the influence of the toner density and the like, but is particularly remarkable when a two-component type developing device in which an edge effect of a line easily occurs is used.
[0066]
In this result, as shown in FIG. 20, since both the Bk line and the C line are thickened, such output saturation appears only on the local maximum value side. As shown in FIG. 20, when both lines are thickened, even if the line C is shifted from the state of patch A shown in FIG. 20A to the state of patch B shown in FIG. There is no change in the C line between the outputs, the output is the same, and it cannot be detected.
Based on this experimental rule, if the toner density of Bk is very high, as a result, only the Bk line causes line thickening, and on the contrary, the color toner density is very low, and the line width is faithful to the latent image. Is formed, it can be estimated that a similar output saturation phenomenon occurs near the minimum value.
That is, as shown in FIG. 21, even if the C line is shifted from the state of the patch A shown in FIG. 21A to the state of the patch B shown in FIG. 21B, the shift of the C line is within the range of the Bk line. Since no change is made, the output is the same and cannot be detected.
[0067]
Therefore, it is desirable that the data points used for obtaining the approximate straight line exclude the local maximum value and the local minimum value or data in the vicinity thereof in order to minimize the influence of the inherent characteristics of the image forming apparatus. Specifically, for example, only the data of (maximum value + minimum value) / 2 ± (maximum value−minimum value) × 0.4 from the maximum value and the minimum value of the output of a plurality of patches is used for the calculation. .
In the related art, two approximate straight lines are obtained from all point data of continuous patches, and the amount of deviation is calculated by performing intersection calculation. The output saturation phenomenon that occurs near the intersection as described above is discussed. Not.
Therefore, in the prior art, such a saturation phenomenon of the output that occurs near the extreme value causes the determination coefficient R of the two approximate expressions.²May worsen, which may cause an error in the displacement amount obtained by the intersection calculation.
[0068]
In the present embodiment, the transfer belt 18 on which the alignment pattern Pm is formed has a lightness L.^*(JISZ8729) = A belt made of polyimide of 1.7 is used. The reason for adopting the above configuration including this will be described in more detail below.
(About the configuration of the alignment pattern)
FIG. 22 is a graph in which the regular reflection light output voltage of the belt background portion, the Bk solid patch portion, and the C (cyan) patch portion of the alignment pattern detection sensor 40 shown in FIG. 3 is plotted against the LED current on the horizontal axis. is there.
Here, for example, when looking at the output voltage of each patch when the LED current is set (= 37 mA) at which the output voltage of the background portion of the transfer belt is 4.0 V, the result shown in Table 1 is obtained.
[0069]
[Table 1]

[0070]
Here, considering that the alignment pattern of FIG. 22 is read with regular reflection light output, the area ratio of P1 and P13 is black line × 50% + color line × 50%, and the area ratio of P7 is Since black line × 50% + color line × 50%, the sensor output of each patch section is approximately as follows.
(When "Bk line group" is formed on "Color line group")
Output voltage of P1 and P13 = 0.12 (Bk solid) x 0.5 + 1.91 (C solid) x 0.5 = 1.015v
P7 output voltage = 0.12 (Bk solid) × 0.5 + 4.0 (belt) × 0.5 = 2.06v
(When “Bk line group” is formed below “Color line group”)
Output voltage of P1 and P13 = 0.12 (Bk solid) x 0.5 + 1.91 (C solid) x 0.5 = 1.015v
P7 output voltage = 1.91 (solid C) × 0.5 + 4.0 (belt) × 0.5 = 2.955v
[0071]
If the output voltage of each patch is plotted against “arbitrary shift amount of the color line on the horizontal axis”, a result as shown in FIG. 23 is obtained. The following can be seen from FIG.
(When detection is performed using specular reflection light)
(A) The output voltage is maximum at the patch (P7) where the two color lines completely overlap, and the output voltage is almost determined by the output from the belt background.
(B) The output difference between the minimum value (P1, P13) and the maximum value (P7) is smaller when the "black line group" is above the "color line group" than when it is below. Become.
As described above, the output of the maximum value (P7) when the detection is performed by the specular reflection light is determined by the output from the belt background (∝ gloss).
(C) When the glossiness is reduced due to abrasion with time or partial scratches, the output of that portion is reduced. In other words, the belt cannot be detected due to deterioration of the belt due to abrasion with time, and this determines the life of the belt.
[0072]
That is, like P2 to P12 shown in FIG. 2, the specular reflected light output voltage of the patch portion where the belt surface is partially exposed is the surface shape expressed by the belt glossiness or the surface roughness Rz. For example, if the background portion of the P6 patch has a flaw, the output is different from that of P8 which has a mirror image relationship because the characteristic portion is susceptible to the influence of noise. As a result, the intersection position obtained by calculation is shifted. Will occur.
[0073]
On the other hand, when the detection is performed by the diffuse reflection light, the displacement amount can be detected without being substantially affected by the roughness of the surface of the transfer belt 18.
FIG. 24 is a diagram in which the diffuse reflected light output voltage of the belt background portion, the Bk solid portion, and the C (cyan) solid portion of the alignment pattern detection sensor 40 shown in FIG. 3 is plotted against the LED current on the horizontal axis. .
As shown in FIG. 26, the regular reflection light output has a high correlation with the glossiness of the detected object (the transfer belt 18 on which the alignment pattern is formed), while the diffuse reflection light output has a high correlation with the detected object as shown in FIG. Lightness L of detected object^*Is high and has no correlation with the glossiness.^*= 1.7 has almost the same output characteristics as the black toner. As is clear from FIG.^*To about 40, and the lightness L^*Up to 20, the linearity is extremely high.
Here, when the following two cases are considered in the same manner as above, the output voltages of the respective parts are as shown in Table 2.
[0074]
[Table 2]

[0075]
(When "Bk line group" is formed on "Color line group")
Output voltage of P1 and P13 = 0.16 (Bk solid) × 0.5 + 3.42 (C solid) × 0.5 = 1.79v
P7 output voltage = 0.16 (Bk solid) × 0.5 + 0.07 (belt) × 0.5 = 0.115 v
(When “Bk line group” is formed below “Color line group”)
Output voltage of P1 and P13 = 0.16 (Bk solid) × 0.5 + 3.42 (C solid) × 0.5 = 1.79v
Output voltage of P7 = 3.42 (solid C) × 0.5 + 0.07 (belt) × 0.5 = 1.745v
[0076]
When the output voltage of each patch is plotted against “arbitrary shift amount of the color line on the horizontal axis”, a result as shown in FIG. 25 is obtained. The following can be seen from FIG.
(When detection is performed using diffuse reflection light)
(A) The output voltage is minimized at the patch (P7) where the two color lines completely overlap, and the output voltage is determined by the output voltage of the “color line group”.
(B) The output difference between the maximum value (P1, P13) and the minimum value (P7) can be larger when the "black line group" is above the "color line group" than when it is below. .
As described above, the output of the maximum value (P7) when the detection is performed by the diffuse reflection light is determined by the output (∝lightness) from the “color line group”.
(C) There is no influence of wear over time or partial scratches. In other words, since the detection performance does not depend on the belt deterioration, it is possible to achieve a longer life of the transfer belt.
[0077]
As described above, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. Considering that an alignment pattern formed by continuously forming an alignment pattern is detected by an alignment pattern detection sensor for detecting the alignment pattern, the transfer belt may be worn over time or may be partially damaged. In order to perform detection without being affected by dynamic factors at all,
(1) It is desirable to detect by diffused light output,
(2) It is desirable that the image forming order of the black line image as the reference color is the final color of the color superimposition on the transfer body,
(3) The brightness (L) of the transfer member forming the alignment pattern^*) Is desirably 40 or less, preferably 20 or less.
[0078]
The results shown in FIG. 26 show that the specular light output value when the LED current If was fixed at 20 mA for 42 types of transfer belts having different glossiness and lightness was the 60 ° gloss of the transfer belt surface on the horizontal axis. It is plotted against degrees. The measured gloss value shown in this figure is a value measured using a gloss meter PG-1 manufactured by Nippon Denshoku Co., Ltd. at a measurement angle of 60 °.
The results shown in FIG. 27 show that, for the same 42 types of belts as those shown in FIG. 26, the diffuse reflected light output when the LED current was fixed at 20 mA was the lightness L of the transfer belt surface on the horizontal axis.^*Is plotted against. The lightness measurement values shown in this figure are values measured using X-Rite 938 manufactured by X-Rite under the conditions of a light source D50 and a viewing angle of 2 °.
[0079]
FIG. 28 shows an experiment for confirming the effect by the above-described method of the present invention. The sampling of each output voltage was performed at 500 sampling / sec with respect to the linear velocity of the image forming apparatus (color printer) of 125 mm / sec.
Table 3 shows the output voltages of all the patches, the slopes of two straight lines obtained from the output voltage values of all the patches, the y-intercept, the RSQ (= determination coefficient), and the intersection calculation results.
[0080]
[Table 3]

[0081]
As described above, in the above experiment, as a result of the simulation shown in FIG. 13, the positional deviation amount is 2.83 μm with respect to the maximum positional deviation amount detection error of 3.15 μm with the light receiving diameter of 3 mm and the line width of 250 μm (= about 6 dots line). was gotten.
However, as can be seen from the graph of FIG. 28, the output near the extreme value also tends to be saturated.
Therefore, Table 4 shows the result of performing the intersection calculation at points excluding the extremum and data near the extremum.
[0082]
[Table 4]

[0083]
As described above, by excluding the extreme points and the data points near the extreme values from the data points of the calculation of the linear approximation formula, the determination coefficient R of the approximate straight line representing the linearity is obtained.²(= RSQ) from 0.9713 to 0.9999 (P1 to P7), from 0.9703 to 0.9998 (P7 to P13), and as a result, a more accurate position It was confirmed that the displacement can be detected.
Also in this experiment, the amount of misalignment of the center patch P7 of the alignment pattern created on the transfer belt 18 was observed with a digital microscope equipped with a 2 million pixel CCD, and it was confirmed that the amount of misalignment was zero.
[0084]
From the above results, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are regarded as one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. Alignment pattern formed by successively forming patches, alignment pattern detection means for detecting the alignment pattern, and a reference color and a color other than the reference color based on an output signal from the alignment pattern detection means. In an image forming apparatus including a correction unit that determines a position shift amount and a direction thereof and corrects the position shift amount,
{Circle around (1)} The line width of the alignment pattern is determined by the relationship between the light receiving width of the alignment pattern detection means and the writing density of the image forming apparatus.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^-0.5331)
By setting the line width constituting each patch of the alignment pattern so as to satisfy the relationship, the positional deviation amount detection error due to the nonlinearity of the output can be set to a maximum allowable value or less.
{Circle around (2)} By excluding extreme values or data in the vicinity thereof from the data points used for the intersection calculation, the linearity of the two approximate straight lines used for the intersection calculation is improved. As a result, the data used for the linear approximation expression calculation is obtained. The number of points, that is, the number of patterns can be reduced to a minimum of two points for each straight line (the total number of patches is reduced to four).
That is, it is possible to greatly reduce the processing time of the misregistration adjustment operation which is not related to the normal printing operation, that is, does not contribute to the productivity.
Further, even when such a sensor (positioning pattern detection sensor 40 similar to the conventional one) is used, it is possible to detect the amount of positional deviation with high accuracy, so that it is about 1/100 of the conventional edge detection method. Sampling at a low sampling frequency makes it possible to detect a sufficient amount of displacement.
[0085]
The misregistration correction based on the above-described registration pattern detection sensor 40 and the method is performed by the misregistration amount correcting means. The displacement amount correcting means 46 will be described with reference to FIG.
The light emitting diode 40A, which is the light emitting unit of the alignment pattern detection sensors 40a, 40b, 40c, has its light emission controlled by a light emission control unit 47, and the output photodiode 40B has an amplifier 48, a filter 49, and an A / D converter. 50, connected to the I / O port 54 via the FIFO memory 51.
Detection signals obtained from the alignment pattern detection sensors 40a, 40b, 40c are amplified by an amplifier (AMP) 48, passed through a filter 49, and converted from analog data to digital data by an A / D converter 50. .
The sampling of data is controlled by the sampling control unit 52, and the sampled data is stored in the FIFO memory 51. The sampling control unit 52 and the write control board 53 are connected to an I / O port 54.
[0086]
The I / O port 54, the CPU 55, the ROM 56, and the RAM 57 are connected by a data bus 58 and an address bus 59.
The ROM 56 stores various programs including a program for calculating the amount of displacement of the alignment pattern Pm. The program for calculating the amount of displacement of the alignment pattern Pm includes conditions such as excluding extreme value data and the like from the data points used in the above-described intersection calculation.
The address bus 59 specifies a ROM address, a RAM address, and various input / output devices.
The CPU 55 monitors the detection signals from the alignment pattern detection sensors 40a, 40b, 40c at a predetermined timing, and ensures that even if the light emitting diode 40A of the alignment pattern detection sensors 40a, 40b, 40c is deteriorated, etc. The light emission amount of the light emitting diode 40A is controlled by the light emission amount control unit 47 so that the alignment pattern Pm can be detected, so that the output level of the light receiving signal from the photodiode 40B is always constant.
[0087]
In addition, the CPU 55 determines a main / sub registration based on a correction amount obtained from a detection result of a positioning pattern (including a positioning pattern for detecting a positional deviation in the sub-scanning direction described later) and based on a magnification error. The setting is performed on the write control board 53 to change the image frequency.
The write control board 53 includes a device capable of setting the output frequency very finely, for example, a clock generator using a VCO (Voltage Controlled Oscillator) for each color including the reference color. This output is used as an image clock. The CPU 55 also controls a skew adjustment stepping motor (not shown) in the optical writing unit 16 based on the correction amount obtained from the detection result of the alignment pattern.
The above-described elements other than the alignment pattern detection sensors 40a, 40b, and 40c constitute a positional deviation amount correction unit 46. The position shift amount correcting means 46 can also serve as the main controller of the color printer.
[0088]
The position shift adjustment operation by the position shift amount correcting means 46 includes (1) when the power is turned on, (2) when the temperature change of the optical system is a predetermined value (for example, 5 deg) or more, and (3) printing of a certain number of sheets or more. Executed when any of the conditions at the end of the job in which the job was completed match.
In the first embodiment, the alignment pattern for detecting the color shift in the main scanning direction has been described. However, in the case where the color shift in the sub-scanning direction (the same direction as the traveling direction of the transfer belt 18) is detected, 29 is formed on the transfer belt 18 in the same manner as in the case shown in FIG. 4, for example.
Similar to the positioning pattern Pm, the positioning pattern Ps includes a plurality of lines formed by superimposing a black line image Bk as a reference color and a color other than the reference color, for example, a cyan line image C, as one patch. And patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount are continuously formed.
The orientation (angle) of the alignment pattern with respect to the scanning direction may be any as shown in FIG. 30, and the shape of the light receiving surface of the alignment pattern detection sensor 40 is not only circular but also elliptical. The same applies to the case of a rectangular shape.
[0089]
The present invention is also effective for the shape of the light receiving surface of the sensor configured to decompose light into P-wave and S-wave components and the arrangement of the sensor in the pattern scanning direction by using the beam splitter (second example). Embodiment).
One example will be described with reference to FIG. The alignment pattern detection sensor 60 as an alignment pattern detection unit in the present embodiment includes a light emitting diode (hereinafter, referred to as LED) 61 as one light emitting unit and a photodiode (hereinafter, referred to as PD) as three light receiving units. 62, 63, 64, and two polarizing beam splitters (hereinafter, referred to as PBS) 65, 66.
[0090]
Although the polarization state of the light projection 67 emitted from the LED 61 is random, the PBS 65 causes a light component (S-wave light) that vibrates in a direction perpendicular to the incident surface and a light component that vibrates in a direction parallel to the incident surface. (P-wave light). The S-wave light 68 is reflected by the PBS 65 and is incident on the PD 62, and the P-wave light 69 is transmitted through the PBS 65 and projected on the alignment pattern of the transfer belt 18.
The P-wave light 69 reflected from the alignment pattern has a random polarization state due to irregular reflection, and is separated into a P-wave light 70 and an S-wave light 71 by the PBS 66. The P-wave light 70 passes through the PBS 66 and enters the PD 63, and the S-wave light 71 is reflected by the PBS 66 and enters the PD 64.
In the present embodiment, the PDs 62, 63, and 64 serving as light receiving units receive diffuse reflection components instead of diffuse reflection light.
[0091]
In each of the above embodiments, an example of application in a four-tandem direct transfer type color image forming apparatus has been described. However, as shown in FIG. 32, the image is transferred to an intermediate transfer body in a four-tandem configuration and then transferred collectively to transfer paper. The present invention can be similarly applied to a color image forming apparatus of the following method (third embodiment).
In the present embodiment, the above-described alignment patterns Pm and Ps are formed on the intermediate transfer belt 2 as an intermediate transfer body, and are detected by an alignment pattern detection sensor 40 arranged near the support roller 2B. The displacement correcting means is the same as in the first embodiment.
[0092]
An outline of the configuration and operation of a tandem-type color copying machine as an image forming apparatus according to the present embodiment will be described below. The color copying machine 1 has an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit 1C located above the image forming unit 1A. are doing.
In the image forming section 1A, an intermediate transfer belt 2 as a transfer body having a transfer surface extending in the horizontal direction is arranged. On the upper surface of the intermediate transfer belt 2, an image of a color having a complementary color relationship with the color separation color is provided. Are provided. That is, the photoconductors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image with toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the intermediate transfer belt 2. Have been.
[0093]
Each of the photoconductors 3Y, 3M, 3C, and 3B is formed of a drum that is rotatable in the same counterclockwise direction. Around the charging device 4, a charging device 4 serving as a charging unit that performs an image forming process in a rotation process is provided. The potential V is set on each of the photoconductors 3Y, 3M, 3C and 3B based on the image information._LAn optical writing device 5 as an exposure device for forming an electrostatic latent image, and a developing device as a developing device for developing the electrostatic latent image on each photoconductor 3 with toner having the same polarity as the electrostatic latent image. 6, a transfer bias roller 7 as a primary transfer unit, an applied voltage member 15, and a cleaning device 8 are arranged. The alphabet attached to each code corresponds to the color of the toner similarly to the photoconductor 3. Each developing device 6 contains a respective color toner.
The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and move in the same direction at a position facing the photoconductors 3Y, 3M, 3C, and 3B. A roller 2C different from the rollers 2A and 2B supporting the transfer surface is opposed to the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. In FIG. 32, reference numeral 10 denotes a cleaning device for the intermediate transfer belt 2.
[0094]
The surface of the photoconductor 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photoconductor 3Y at a writing density (= resolution) of 600 dpi based on image information from the image reading unit 1C. The electrostatic latent image is visualized as a toner image by a two-component (carrier and toner) developing device 6Y containing yellow toner, and the toner image is transferred onto the intermediate transfer belt 2 as a first transfer step. The transfer is performed by being attracted by an electric field due to the voltage applied to the transfer bias roller 7Y.
The applied voltage member 15Y is provided on the upstream side of the transfer bias roller 7Y in the rotation direction of the photoconductor 3Y. The applied voltage member 15Y causes the intermediate transfer belt 2 to have the same polarity as the charging polarity of the photoreceptor 3Y and an absolute value of V_LA larger voltage is applied to prevent the toner from transferring from the photoconductor 3Y to the intermediate transfer belt 2 before the toner image enters the transfer area. Prevent turbulence caused by dust.
[0095]
Similar image formation is performed on the other photoconductors 3M, 3C, and 3B except for the color of the toner, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.
After the transfer, the toner remaining on the photoconductor 3 is removed by the cleaning device 8, and after the transfer, the potential of the photoconductor 3 is initialized by a discharging lamp (not shown) to prepare for the next image forming process.
The secondary transfer device 9 has a transfer belt 9C that is wrapped around a charging drive roller 9A and a driven roller 9B and moves in the same direction as the intermediate transfer belt 2. By charging the transfer belt 9C by the charging drive roller 9A, a multicolor image or a single-color image carried on the intermediate transfer belt 2 can be transferred onto a sheet 28 as a transfer material.
[0096]
The sheet 28 is fed from the sheet feeding section 1B to the secondary transfer position. A plurality of sheet cassettes 1B1 in which sheets 28 are stacked and stored in the sheet feeding section 1B, and a sheet feeding roller 1B2 which separates and feeds the sheets 28 stored in the sheet cassette 1B1 one by one from the top. , A pair of conveying rollers 1B3, a pair of registration rollers 1B4 located upstream of the secondary transfer position, and the like.
The sheet 28 fed from the sheet feeding cassette 1B1 is temporarily stopped by the pair of registration rollers 1B4, and after correcting the oblique displacement or the like, the sheet 28 on the intermediate transfer belt 2 and the predetermined position of the tip in the conveyance direction are adjusted. Are sent to the secondary transfer position by the registration roller pair 1B4 with the matching tying. A manual feed tray 29 is provided on the right side of the apparatus main body so as to be able to be turned upside down. The paper 28 stored in the manual feed tray 29 joins the paper transport path from the paper feed cassette 1B1 fed by the paper feed roller 31. Then, the sheet is sent toward the registration roller pair 1B4 through the transfer path.
[0097]
In the optical writing device 5, writing light is controlled by image information from the image reading unit 1C or image information output from a computer (not shown) to write the photosensitive members 3Y, 3M, 3C, and 3B according to the image information. Light is emitted to form an electrostatic latent image.
The image reading unit 1C includes an automatic document feeder 1C1, a scanner 1C2 having a contact glass 80 as a document table, and the like. The automatic document feeder 1C1 has a configuration in which a document fed out onto the contact glass 80 can be inverted, and can scan each side of the document.
The electrostatic latent image on the photoconductor 3 formed by the optical writing device 5 is subjected to visible image processing by the developing device 6, and is primarily transferred to the intermediate transfer belt 2. When the toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt 2, they are collectively and secondarily transferred onto the paper 28 by the secondary transfer device 9. The secondary-transferred sheet 28 is sent to the fixing device 11, where an unfixed image is fixed by heat and pressure. The residual toner on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10.
[0098]
The sheet 28 that has passed through the fixing device 11 is selectively guided to a conveyance path toward the paper discharge tray 27 and a reversing conveyance path RP by a conveyance path switching claw 12 provided on the downstream side of the fixing apparatus 11. When the sheet is conveyed toward the sheet discharge tray 27, the sheet is discharged onto the sheet discharge tray 27 by the sheet discharge roller pair 32 and stacked. When the sheet is guided to the reversing conveyance path RP, the sheet is reversed by the reversing device 38 and sent again to the registration roller pair 1B4.
[0099]
With the above configuration, the color copier 1 performs electrostatic scanning on the uniformly charged photoreceptor 3 by exposing and scanning the original placed on the contact glass 80 or by image information from a computer. After the latent image is formed and the electrostatic latent image is subjected to a visible image processing by the developing device 6, the toner image is primarily transferred to the intermediate transfer belt 2.
In the case of a single image, the toner image transferred to the intermediate transfer belt 2 is directly transferred to the sheet 28 fed from the sheet feeding unit 1B. In the case of a multicolor image, after the primary transfer is repeated and superimposed, the secondary transfer is collectively performed on the paper 28.
After the secondary transfer, the sheet 28 after the unfixed image is fixed by the fixing device 11 is discharged to the sheet discharge tray 27 or inverted and sent again to the registration roller pair 1B4 for double-sided image formation.
[0100]
Further, a toner image of each color is formed by using one photosensitive drum and a revolver type developing device, and each toner image is superimposedly transferred onto an intermediate transfer member, and then transferred collectively onto transfer paper as a sheet-shaped recording medium. The present invention can be similarly implemented in a color image forming apparatus of the system (fourth embodiment). An example is shown in FIG.
In the present embodiment, the above-described alignment patterns Pm and Ps are formed on an intermediate transfer belt 426 as an intermediate transfer body, and are detected by an alignment pattern detection sensor 40 arranged near a driving roller 444. The displacement correcting means is the same as in the first embodiment.
[0101]
Hereinafter, an outline of a configuration of a color copying machine as an image forming apparatus according to the present embodiment will be described.
In a color copier, a writing optical unit 400 as an exposure unit converts color image data from the color scanner 200 into an optical signal to perform optical writing corresponding to a document image, and performs an optical writing on a photosensitive drum 402 as an image carrier. An electrostatic latent image is formed at a writing density (= resolution) of 600 dpi.
The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 thereof, an f / θ lens 410, a reflection mirror 412, and the like.
The photoconductor drum 402 is rotated in a counterclockwise direction as indicated by an arrow, and a photoconductor cleaning unit 414, a static elimination lamp 416, a potential sensor 420, and a rotary developing device 422 are selected around the photoconductor drum 402. A developing device, a developing density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer body, and the like are arranged.
[0102]
The rotary developing device 422 includes a black developing device 428, a cyan developing device 430, a magenta developing device 432, a yellow developing device 434, and a rotation drive unit (not shown) for rotating each developing device. Each developing device is a so-called two-component developing type developing device containing a mixed developer of a carrier and a toner, and has the same configuration as the developing device 4 described in the above embodiment. The same applies to the conditions and specifications of the magnetic carrier.
In the standby state, the rotary developing device 422 is set at the position of black development, and when a copying operation is started, reading of black image data is started at a predetermined timing by the color scanner 200, and this image data is read. , The formation of the optical writing / electrostatic latent image (black latent image) by the laser beam starts.
[0103]
In order to develop from the leading end of the black latent image, before the leading end of the latent image reaches the developing position of the black developing device 428, the rotation of the developing sleeve is started to develop the black latent image with black toner. An image of negative polarity toner is formed on the photosensitive drum 402.
Thereafter, the developing operation of the black latent image area is continued, but when the rear end of the latent image passes the black developing position, the rotary developing operation is promptly performed from the developing position for black to the developing position for the next color. The device 422 rotates. This operation is completed at least before the leading end of the latent image based on the next image data arrives.
When the image forming cycle is started, first, the photosensitive drum 402 is rotated in a counterclockwise direction as indicated by an arrow, and the intermediate transfer belt 426 is rotated in a clockwise direction by a drive motor (not shown). As the intermediate transfer belt 426 rotates, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), and magenta (M) , Yellow (Y) in this order on the intermediate transfer belt 426 (primary transfer) to form a toner image.
[0104]
The intermediate transfer belt 426 includes a primary transfer electrode roller 450 facing the photosensitive drum 402, a driving roller 444, a secondary transfer facing roller 446 facing the secondary transfer roller 454, and a cleaning unit that cleans the surface of the intermediate transfer belt 426. It is stretched between the respective support members of the cleaning opposing roller 448A opposing the 452, and is driven and controlled by a drive motor (not shown).
The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image. This belt transfer image is collectively transferred to the sheet by the secondary transfer opposing roller 446.
[0105]
Each of the recording paper cassettes 458, 460, and 462 in the paper supply bank 456 stores various sizes of paper different from the size of the paper stored in the cassette 464 in the apparatus main body. The designated sheet is fed and conveyed from the size paper storage cassette toward the registration roller pair 470 by the sheet feeding roller 466. In FIG. 33, reference numeral 468 denotes a manual paper feed tray for OHP paper, thick paper, and the like.
At the time when the image formation is started, the paper is fed from the paper feed port of any one of the cassettes, and waits at the nip portion of the pair of registration rollers 470. When the leading end of the toner image on the intermediate transfer belt 426 approaches the secondary transfer opposing roller 446, the registration roller pair 470 is driven so that the leading end of the sheet coincides with the leading end of the image, and the registration of the sheet and the image is adjusted. Is performed.
[0106]
In this way, the sheet is superimposed on the intermediate transfer belt 426 and passes under the secondary transfer opposing roller 446 to which a voltage having the same polarity as that of the toner is applied. At this time, the toner image is transferred to the paper. Subsequently, the paper is discharged, separated from the intermediate transfer belt 426 and moved to the paper transport belt 472.
The sheet on which the four-color superimposed toner image has been collectively transferred from the intermediate transfer belt 426 is conveyed by a paper conveying belt 472 to a fixing device 470 of a belt fixing system, and the fixing device 470 fixes the toner image by heat and pressure. The sheet on which fixing has been completed is discharged out of the apparatus by a discharge roller pair 480 and stacked on a tray (not shown). Thereby, a full-color copy is obtained.
[0107]
The above-described registration pattern detection sensor according to the present invention is an image forming apparatus that detects and corrects a displacement amount by detecting a registration pattern formed by forming a plurality of overlapping patches of two colors. Since any of them can be applied, it can also be applied as a position shift detection sensor of an inkjet device (fifth embodiment).
One example will be described with reference to FIGS.
[0108]
First, a schematic configuration and a printing function of an inkjet recording apparatus 500 as an image forming apparatus will be described with reference to FIG. The inkjet recording apparatus 500 includes a printing mechanism including a carriage movable in the main scanning direction, a recording head including an inkjet head mounted on the carriage, an ink cartridge for supplying ink to the recording head, and the like inside an apparatus main body 501. It has a part 502 and the like.
A sheet cassette 504 capable of stacking and storing sheets 503 as sheet-shaped recording media is provided below the apparatus main body 501. The sheet cassette 504 is moved from the front side (left side in the figure) to the apparatus main body 501. It is provided detachably.
A manual feed tray 505 is provided on the front surface of the apparatus main body 501 so as to be openable and closable. After recording a predetermined image, the sheet is discharged to a sheet discharge tray 506 provided on the rear side of the apparatus main body 501. An upper cover 507 is provided on the upper surface of the apparatus main body 501 so as to be freely opened and closed.
[0109]
In the printing mechanism 502, a carriage 510 is slidably held in a main scanning direction (a direction perpendicular to the paper surface) by a main guide rod 508 and a sub guide rod 509 supported between left and right side plates (not shown). A recording head 511 including an inkjet head having nozzles for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk) is provided on the lower surface side of the recording head 511. Above the carriage 510, each ink cartridge 512 for supplying each color ink to the recording head 511 is replaceably provided.
As the recording head 511, a head in which a plurality of heads for ejecting ink droplets of each color are arranged in the main scanning direction or a single head having a nozzle for ejecting ink droplets of each color may be used.
[0110]
Below the recording head 511, the sheet 503 is electrostatically attracted and conveyed between the conveying roller 513 and the driven roller 514 in order to convey the sheet 503 in the sub-scanning direction to the printing position by the recording head 511. Transport belt 515 is wound around. The conveyor belt 515 is tensioned by an intermediate roller 516. A bias roller 517 for charging the transport belt 515 is provided at a position facing the transport roller 513 with the transport belt 515 interposed therebetween. A pressing roller 518 for pressing the sheet 503 against the conveying belt 515 is provided near the plane starting point of the conveying belt 515. Here, the plane starting point of the transport belt 515 is defined as an upstream side in the sheet transport direction of a portion of the transport belt 515 parallel to the recording head 511 on the recording head 511 side, specifically, the transport belt 5151 from the transport roller 513. It means the part that leaves.
[0111]
The paper 503 stored in the paper feed cassette 504 is separated one by one from a top one by a paper feed roller 519 and a friction pad 520, and directed toward a nip portion of a bias roller 517 and a transport belt 515 by a curved guide member 521. Transported.
An alignment pattern detection sensor 40 that detects an alignment pattern Pm formed on the paper 503 is provided above the transport belt 515 on the downstream side in the paper transport direction. The displacement correcting means is the same as in the first embodiment.
FIG. 35 is an enlarged view of the vicinity of the transport belt 515. However, a plate-shaped suppressing member 522 may be provided instead of the pressing roller 518 shown in FIG.
As shown in FIG. 36, for example, an alignment pattern Pk shown in FIG. 37 is formed on a sheet 503 as a transfer body on which an alignment pattern is formed, and the alignment pattern Pk is detected by the alignment pattern detection sensor 40 and color misregistration is performed. Is corrected.
[0112]
【The invention's effect】
According to the first aspect of the present invention, in the method for determining a light receiving width of a positioning pattern detection sensor for detecting a positioning pattern formed by overlapping a line image of a reference color and a line image of a color other than the reference color, The line width of the alignment pattern and the correlation between the writing density of the image forming apparatus and the light receiving width of the alignment pattern detection sensor were experimentally derived, and the light receiving width was determined based on the derived result. Therefore, it is possible to reduce a factor due to the relationship between the line width and the light receiving width that deteriorates the linearity of the two straight lines with respect to an arbitrary shift amount of the line image of the color other than the reference color, and to improve the linearity, that is, to detect the alignment pattern. Accuracy can be improved.
[0113]
According to the second aspect of the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two-color line images. In a method for determining a light receiving width of an alignment pattern detection sensor for detecting an alignment pattern formed by continuously forming patches in which the relationship is shifted by an arbitrary amount, the line width of each patch constituting the alignment pattern and the image formation Since the correlation between the writing density of the device and the light receiving width of the alignment pattern detection sensor was experimentally derived, and the light receiving width was determined based on the derived result, a line image of a color other than the reference color was determined. Can be reduced due to the relationship between the line width and the light receiving width, which are deteriorating the linearity of the two straight lines with respect to an arbitrary shift amount. It is possible to improve the.
[0114]
According to the third aspect of the present invention, an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection for detecting the alignment pattern A position shift amount for correcting the position shift amount by determining a position shift amount and a direction between the image of the reference color and an image of a color other than the reference color based on an output signal from the sensor and the alignment pattern detection sensor; In the image forming apparatus having the amount correcting means, the light receiving width of the alignment pattern detection sensor is expressed by the following relationship in relation to the writing density of the image forming apparatus and the line width of the alignment pattern.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Is determined so as to satisfy the condition, the factor due to the relationship between the line width and the light receiving width that deteriorates the linearity of the two straight lines with respect to an arbitrary shift amount of the line image of the color other than the reference color is equal to or less than the maximum allowable value. It can be. as a result,
{Circle around (1)} Compared with the conventional edge detection method, highly accurate detection can be performed even at a low sampling frequency of about 1/100.
{Circle around (2)} As a result of {circle around (1)}, it is not necessary to increase the speed of the processing circuit section after sampling, so that the cost of the electric hardware configuration can be greatly reduced.
{Circle around (3)} Since the linearity of the two straight lines is greatly improved, the number of patches constituting the alignment pattern can be significantly reduced.
{Circle around (4)} As a result of {circle around (3)}, the processing time required for adjustment that is not related to normal printing, such as positional deviation adjustment, can be greatly reduced, so that productivity can be greatly improved.
[0115]
According to the fourth aspect of the present invention, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two color line images. Based on an alignment pattern formed by continuously forming patches whose relationship is shifted by an arbitrary amount, an alignment pattern detection sensor for detecting the alignment pattern, and an output signal from the alignment pattern detection sensor. An image forming apparatus comprising: a position shift amount correcting unit that determines a position shift amount and a direction thereof between the image of the reference color and an image of a color other than the reference color and corrects the position shift amount. Of the light receiving width of the image forming apparatus and the line width of each patch constituting the alignment pattern,
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Therefore, the same effect as the third aspect of the invention can be obtained.
[0116]
According to the fifth aspect of the present invention, an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection for detecting the alignment pattern A position shift amount for correcting the position shift amount by determining a position shift amount and a direction between the image of the reference color and an image of a color other than the reference color based on an output signal from the sensor and the alignment pattern detection sensor; In an image forming apparatus having an amount correcting unit,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}), The line width / light receiving width ratio is calculated, then the required line width is calculated from the maximum deviation amount, and the light receiving width is determined from the line width / light receiving width ratio. Can be increased.
[0117]
According to the invention described in claim 6, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two color line images. Based on an alignment pattern formed by continuously forming patches whose relationship is shifted by an arbitrary amount, an alignment pattern detection sensor for detecting the alignment pattern, and an output signal from the alignment pattern detection sensor. An image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color and corrects the position shift amount.
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}), The line width / light receiving width ratio is calculated, then the required line width is calculated from the maximum deviation amount, and the light receiving width is determined from the line width / light receiving width ratio. Can be increased.
[0118]
According to the seventh aspect of the present invention, in the positioning pattern detecting sensor for detecting a positioning pattern formed by superposing a line image of a reference color and a line image of a color other than the reference color with a predetermined light receiving width. The relationship between the predetermined light receiving width and the writing density of the image forming apparatus and the line width of the alignment pattern is as follows.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0119]
According to the invention described in claim 8, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two-color line images. In an alignment pattern detection sensor for detecting an alignment pattern formed by continuously forming patches whose relationship is shifted by an arbitrary amount by a predetermined light receiving width, the predetermined light receiving width is determined by the writing density of the image forming apparatus and the position. In relation to the line width of each patch making up the matching pattern, the following relationship
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0120]
According to the ninth aspect of the present invention, there is provided an alignment pattern detection sensor for detecting an alignment pattern formed by overlapping a line image of a reference color and a line image of a color other than the reference color with a predetermined light receiving width,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After calculating the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount of the image forming apparatus, and the predetermined light receiving width is determined from the line width / light receiving width ratio. With the configuration, it is possible to enhance the accuracy of the positional deviation detection.
[0121]
According to the tenth aspect, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two-color line images. In an alignment pattern detection sensor that detects an alignment pattern formed by continuously forming patches in which the relationship is shifted by an arbitrary amount by a predetermined light receiving width, [line width / light receiving width] <(5.0627 × [writing density] (Dpi)]^{− 0.5331}After calculating the line width / light receiving width ratio from the formula (2), the required line width is calculated from the maximum deviation amount of the image forming apparatus, and the predetermined light receiving width is determined from the line width / light receiving width ratio. With the configuration, it is possible to enhance the accuracy of the positional deviation detection.
[0122]
According to an eleventh aspect of the present invention, in the method for forming an alignment pattern in which a line image of a reference color and a line image of a color other than the reference color are formed so as to overlap with each other, the line width of the line image is set to an image forming apparatus. Since the maximum deviation amount is set to be twice or more, it is possible to prevent the intersection calculation from being disabled.
[0123]
According to the twelfth aspect, a plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and the relative positions of the two-color line images. In the method of forming an alignment pattern formed by continuously forming patches in which the relationship is shifted by an arbitrary amount, the line width of the line image is set to be at least twice the maximum shift amount of the image forming apparatus. In addition, it is possible to prevent the intersection calculation from becoming impossible.
[0124]
According to the thirteenth aspect of the present invention, the image forming apparatus has a plurality of image carriers, and the toner images formed on each image carrier are sequentially transferred onto the transfer member in a superimposed manner, and then are collectively transferred to a sheet-shaped recording medium. An image forming apparatus that obtains a color image by the above-described method, comprising: a registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and a registration pattern for detecting the registration pattern. Detecting a position shift amount and a direction between the line image of the reference color and a line image of a color other than the reference color based on an output signal from the detection unit and the alignment pattern detection unit and correcting the position shift amount In the image forming apparatus having the position shift amount correcting means, the light receiving width of the alignment pattern detecting means has the following relationship in relation to the writing density of the apparatus and the line width of the positioning pattern. The
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined to be satisfied, the same effect as the third aspect of the invention can be obtained.
[0125]
According to the fourteenth aspect of the present invention, the image forming apparatus has a plurality of image carriers, and the toner images formed on the respective image carriers are sequentially transferred onto the transfer body in a superimposed manner, and then are collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image by using a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color as one patch, and forming a two-color line An alignment pattern formed by continuously forming patches in which the relative positional relationship between images is shifted by an arbitrary amount; alignment pattern detection means for detecting the alignment pattern; and an output signal from the alignment pattern detection means. The image forming apparatus includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color based on the position shift amount and corrects the position shift amount. ,Up Receiving width of the alignment pattern detecting means, in relation to the line width of each patch constituting the writing density and the alignment pattern of the device, the following relationship
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0126]
According to the fifteenth aspect, a plurality of image carriers are provided, and the toner images formed on each of the image carriers are sequentially transferred onto a sheet-like recording medium carried on a transfer body. An image forming apparatus that obtains a color image by using an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection that detects the alignment pattern Means for determining the amount of misalignment and the direction of the image of the reference color and the image of a color other than the reference color based on the output signal from the alignment pattern detecting means, and correcting the amount of misalignment. In an image forming apparatus having an amount correcting unit, the light receiving width of the alignment pattern detecting unit is determined by the following relationship between the writing density of the device and the line width of the alignment pattern.
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0127]
According to the sixteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on each of the image carriers are sequentially transferred onto a sheet-like recording medium carried on a transfer body. A plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color as one patch, and a two-color line image An alignment pattern formed by continuously forming patches in which the relative positional relationship is shifted by an arbitrary amount; an alignment pattern detection means for detecting the alignment pattern; and an output signal from the alignment pattern detection means. In the image forming apparatus, the image forming apparatus includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color based on the position shift amount and corrects the position shift amount. Above rank Receiving width of the combined pattern detection means, in relation to the line width of each patch constituting the writing density and the alignment pattern of the device, the following relationship
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0128]
According to the seventeenth aspect of the present invention, the image forming apparatus has a plurality of image carriers, and the toner images formed on each image carrier are sequentially superimposed on the transfer body and transferred, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus that obtains a color image by the above-described method, comprising: a registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and a registration pattern for detecting the registration pattern. Detecting a position shift amount and a direction between the line image of the reference color and a line image of a color other than the reference color based on an output signal from the detection unit and the alignment pattern detection unit and correcting the position shift amount In the image forming apparatus having the position shift amount correcting means,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[0129]
According to the eighteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on each image carrier are successively superimposed on a transfer body and transferred, and then collectively transferred to a sheet-shaped recording medium. An image forming apparatus for obtaining a color image by using a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color as one patch, and forming a two-color line An alignment pattern formed by continuously forming patches in which the relative positional relationship between images is shifted by an arbitrary amount; alignment pattern detection means for detecting the alignment pattern; and an output signal from the alignment pattern detection means. The image forming apparatus includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color based on the position shift amount and corrects the position shift amount. ,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[0130]
According to the nineteenth aspect of the present invention, a plurality of image carriers are provided, and the toner images formed on each of the image carriers are sequentially transferred onto a sheet-like recording medium carried on a transfer body. An image forming apparatus that obtains a color image by using an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, and an alignment pattern detection that detects the alignment pattern Means for determining the amount of misalignment and the direction of the image of the reference color and the image of a color other than the reference color based on the output signal from the alignment pattern detecting means, and correcting the amount of misalignment. In an image forming apparatus having an amount correcting unit,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[0131]
According to the twentieth aspect of the present invention, the image forming apparatus has a plurality of image carriers, and the toner images formed on the respective image carriers are sequentially transferred onto the sheet-shaped recording medium carried on the transfer body. A plurality of lines formed by superposing a black line image as a reference color and a line image of a color other than the reference color as one patch, and a two-color line image An alignment pattern formed by continuously forming patches in which the relative positional relationship is shifted by an arbitrary amount; an alignment pattern detection means for detecting the alignment pattern; and an output signal from the alignment pattern detection means. In the image forming apparatus, the image forming apparatus includes a position shift amount correcting unit that determines a position shift amount and a direction of the black line image of the reference color and a line image of a color other than the reference color based on the position shift amount and corrects the position shift amount.
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[0132]
According to the twenty-first aspect, in the image forming apparatus according to the fourteenth aspect, the image forming order of the black line image as the reference color is a final color of the color overlap on the transfer body. Therefore, a high SN ratio can be obtained, and the detection accuracy can be improved.
[0133]
According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to thirteenth aspects, the lightness (L) of the transfer body on which the alignment pattern is formed is formed.^*) Is 40 or less, preferably 20 or less, so that a high SN ratio can be obtained and the detection accuracy can be improved.
[0134]
According to a twenty-third aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to thirteenth aspects, any shift of a line image other than a reference color with respect to a reference color line image of the alignment pattern is performed. When the output signal from the alignment pattern detecting means with respect to the amount has one or more extreme values and an arbitrary shift amount is set on the horizontal axis, the positional deviation amount correcting means forms the extreme values on both sides. By calculating the intersection of the two straight lines, the amount of misregistration of the color other than the reference color with respect to the reference color and the direction thereof are determined. For the calculation of the intersection, a data point at or near an extreme value is calculated. Is not used, it is possible to eliminate linearity deterioration due to the saturation phenomenon near the local maximum value or local minimum value of the output voltage of the alignment pattern detecting means, and it is possible to further improve the linearity of the approximate straight line. , It is possible to improve the positional deviation detection accuracy.
[0135]
According to the twenty-fourth aspect of the present invention, the image forming apparatus according to the twenty-third aspect has a configuration in which the developing device of the two-component developing system is used. Therefore, in particular, the effect of improving the linearity of the approximate straight line and improving the positional deviation detection accuracy can be exhibited.
[0136]
According to the twenty-fifth aspect of the present invention, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color is provided. Positioning pattern detecting means for detecting the positioning pattern; and a positional deviation amount and a direction of the reference color image and an image of a color other than the reference color based on an output signal from the positioning pattern detecting means. In the image forming apparatus having a position shift amount correcting unit that determines the position shift amount and corrects the position shift amount, the light receiving width of the alignment pattern detection unit is determined based on a relationship between a writing density of the device and a line width of the alignment pattern. The following relationship
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0137]
According to the twenty-sixth aspect of the present invention, there is provided an image forming apparatus for obtaining a color image by an ink-jet method, wherein a plurality of line images formed by superposing a black line image as a reference color and a line image other than the reference color are formed. A positioning pattern formed by continuously forming patches in which the line is regarded as one patch and the relative positional relationship between the two color line images is shifted by an arbitrary amount, and a positioning pattern detecting means for detecting the positioning pattern; Determining the amount of misalignment and the direction between the black line image of the reference color and the line image of a color other than the reference color based on the output signal from the alignment pattern detecting means, and correcting the amount of misalignment. In an image forming apparatus having a displacement amount correcting means, the light receiving width of the positioning pattern detecting means is determined by the writing density of the device and the size of each patch constituting the positioning pattern. In relation to the in-width, the following relationship:
[Light receiving width]> [Line width] / (5.0627 × [Write density (dpi)])^{− 0.5331})
Since the configuration is determined so as to satisfy the following, the same effect as the invention according to claim 3 can be obtained.
[0138]
According to the invention according to claim 27, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color is provided. Positioning pattern detecting means for detecting the positioning pattern; and a positional deviation amount and a direction of the reference color image and an image of a color other than the reference color based on an output signal from the positioning pattern detecting means. [Line width / light receiving width] <(5.0627 × [writing density (dpi)]) in the image forming apparatus having the position shift amount correcting means for determining the position shift amount and correcting the position shift amount.^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[0139]
According to the invention described in claim 28, there is provided an image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of black line images as a reference color and a line image of a color other than the reference color are formed so as to overlap with each other. A positioning pattern formed by continuously forming patches in which the line is regarded as one patch and the relative positional relationship between the two color line images is shifted by an arbitrary amount, and a positioning pattern detecting means for detecting the positioning pattern; Determining the amount of misalignment and the direction between the black line image of the reference color and the line image of a color other than the reference color based on the output signal from the alignment pattern detecting means, and correcting the amount of misalignment. In an image forming apparatus having a displacement correcting unit,
[Line width / light receiving width] <(5.0627 × [writing density (dpi)]]^{− 0.5331}After determining the line width / light receiving width ratio from the formula (1), the required line width is calculated from the maximum deviation amount of the apparatus, and the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. With this configuration, it is possible to improve the accuracy of the positional deviation detection.
[Brief description of the drawings]
FIG. 1 is a schematic front view of a color printer as an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic plan view of a registration pattern for detecting a displacement in the main scanning direction.
FIG. 3 is a schematic plan view showing an arrangement relationship of an alignment pattern detection sensor with respect to a scanning direction of the alignment pattern.
FIG. 4 is a schematic plan view showing a positional relationship between a position at which a positioning pattern is formed on a transfer belt and a positioning pattern detection sensor.
FIG. 5 is a block diagram showing a displacement amount correcting unit.
FIG. 6 is a graph showing actual measurement values of a color line width with respect to a Bk line of each patch by microscopic observation.
FIG. 7 is a diagram showing a non-linearity of an area increment caused by a circular light receiving surface shape of the alignment pattern detection sensor.
FIG. 8 is a diagram showing a non-linearity of an area increment caused by a circular light receiving surface shape of the alignment pattern detection sensor.
FIG. 9 is a diagram for obtaining a rectangular area within a circular light receiving surface.
FIG. 10 is a graph illustrating a simulation calculation using the area value of a color line image occupying the light receiving surface as an output value of each patch, and a diagram illustrating a positional relationship between a Bk line center and the light receiving surface center.
11A and 11B are a graph obtained by a simulation calculation using an area value of a color line image occupying the light receiving surface as an output value of each patch, and a diagram illustrating a positional relationship between a Bk line center and a light receiving surface center.
12A and 12B are a graph obtained by a simulation calculation using an area value of a color line image occupying the light receiving surface as an output value of each patch, and a diagram showing a positional relationship between a Bk line center and a light receiving surface center.
FIG. 13 is a graph showing a detection error with respect to a shift amount of the center of the Bk line from the center of the light receiving surface.
FIG. 14 is a graph showing a detection error with respect to a line width / light receiving diameter ratio.
FIG. 15 is a graph showing a relationship between resolution and a maximum allowable value of a line width / light receiving width ratio.
FIG. 16 is a graph illustrating a relationship between a shift amount of a color line with respect to a Bk line and a diffused light output voltage, and is a diagram illustrating a state where a shift of 12 dots occurs.
FIG. 17 is a graph showing a relationship between a shift amount of a color line with respect to a Bk line and a diffused light output voltage, showing a state where a shift of 24 dots occurs.
FIG. 18 is a graph showing actual measurement results of a displacement amount of an alignment pattern on a transfer belt.
FIG. 19 is a graph showing a measurement result of a displacement amount of an alignment pattern on a transfer belt by a sensor.
FIG. 20 is a diagram illustrating a state in which both the Bk line and the C line are thickened.
FIG. 21 is a diagram illustrating a state in which line thickening occurs only in the Bk line.
FIG. 22 is a graph showing a relationship between an LED emission current and a regular reflection light output.
FIG. 23 is a graph showing a positional shift pattern output when detection is performed using specularly reflected light.
FIG. 24 is a graph showing the relationship between LED emission current and diffuse reflected light output.
FIG. 25 is a graph showing a positional shift pattern output when detection is performed by diffuse reflection light.
FIG. 26 is a graph showing the relationship between the glossiness of the transfer belt surface and the sensor output.
FIG. 27 is a graph showing the relationship between the brightness of the transfer belt surface and the diffused light output.
FIG. 28 is a graph showing a relationship between a shift amount of a color line with respect to a Bk line and a diffuse reflection light output voltage.
FIG. 29 is a schematic plan view of an alignment pattern for detecting a positional shift in the sub-scanning direction.
FIG. 30 is a diagram showing a change in the direction (angle) of the alignment pattern with respect to the scanning direction.
FIG. 31 is a diagram illustrating a configuration of an alignment pattern detection sensor according to a second embodiment.
FIG. 32 is a schematic front view of a color copying machine as an image forming apparatus according to a third embodiment.
FIG. 33 is a schematic front view of a color copying machine as an image forming apparatus according to a fourth embodiment.
FIG. 34 is a schematic front view of an ink jet recording apparatus as an image forming apparatus according to a fifth embodiment.
FIG. 35 is an enlarged view of the vicinity of the conveyance belt in FIG. 34;
FIG. 36 is a schematic plan view showing a positional relationship between formation of a positioning pattern and a positioning pattern detection sensor in the ink jet recording apparatus.
FIG. 37 is a schematic plan view of an alignment pattern formed by superimposing two color lines.
FIG. 38 is a schematic plan view showing an arrangement of each element of a conventional optical sensor with respect to a scanning direction of an alignment pattern.
FIG. 39 is a graph showing an output voltage of a misregistration pattern having a line width of 24 dots and an intersection calculation result when a conventional optical sensor is used.
FIG. 40 is a graph showing an output voltage of a misregistration pattern having a line width of 10 dots and a calculation result of an intersection when a conventional optical sensor is used.
[Explanation of symbols]
Pm, Ps Positioning pattern
40,60 Alignment pattern detection sensor as alignment pattern detection means
702 Phototransistor as light receiving part
46 Position shift amount correction means
Bk black line image

Claims (28)

In a light-receiving width determination method of an alignment pattern detection sensor that detects an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color,
The correlation between the line width of the alignment pattern and the light receiving width of the writing pattern and the alignment pattern detection sensor of the image forming apparatus is experimentally derived, and the light receiving width is determined based on the derived result. A method for determining the light receiving width of the alignment pattern detection sensor which is a feature. A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount are successive. In a method for determining a light receiving width of an alignment pattern detection sensor for detecting an alignment pattern formed in an
The correlation between the line width of each patch constituting the alignment pattern, the writing density of the image forming apparatus and the light receiving width of the alignment pattern detection sensor is experimentally derived, and the light receiving width is determined based on the derived result. The method for determining the light receiving width of the alignment pattern detection sensor, characterized in that: A registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, a registration pattern detection sensor for detecting the registration pattern, and a registration pattern detection sensor. An image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color based on the output signal and corrects the position shift amount.
A light receiving width of the alignment pattern detection sensor, which is determined so as to satisfy the following relationship in relation to a writing density of the image forming apparatus and a line width of the alignment pattern. Method for determining the light receiving width.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount are successive. An alignment pattern formed in a predetermined manner, an alignment pattern detection sensor for detecting the alignment pattern, and an image of the reference color and a color other than the reference color based on an output signal from the alignment pattern detection sensor. An image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of the image of the color and corrects the position shift amount,
The light receiving width of the alignment pattern detection sensor is determined so as to satisfy the following relationship in relation to the writing density of the image forming apparatus and the line width of each patch constituting the alignment pattern. A method for determining the light receiving width of the alignment pattern detection sensor.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) A registration pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, a registration pattern detection sensor for detecting the registration pattern, and a registration pattern detection sensor. An image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color based on the output signal and corrects the position shift amount.
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is calculated from the maximum deviation amount. A light receiving width is determined based on a line width / light receiving width ratio. A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount are successive. An alignment pattern formed in a predetermined manner, an alignment pattern detection sensor for detecting the alignment pattern, and an image of the reference color and a color other than the reference color based on an output signal from the alignment pattern detection sensor. An image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of the image of the color and corrects the position shift amount,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is calculated from the maximum deviation amount. A light receiving width is determined based on a line width / light receiving width ratio. An alignment pattern detection sensor for detecting an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color by a predetermined light receiving width,
An alignment pattern detection sensor, wherein the predetermined light receiving width is determined so as to satisfy the following relationship in relation to the writing density of the image forming apparatus and the line width of the alignment pattern.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch. In a positioning pattern detection sensor that detects a positioning pattern formed in a predetermined manner by a predetermined light receiving width,
The alignment pattern, wherein the predetermined light receiving width is determined so as to satisfy the following relationship in relation to the writing density of the image forming apparatus and the line width of each patch constituting the alignment pattern. Detection sensor.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An alignment pattern detection sensor for detecting an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color by a predetermined light receiving width,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), a necessary value is obtained from the maximum displacement amount of the image forming apparatus. An alignment pattern detection sensor, wherein a line width is calculated, and the predetermined light receiving width is determined from a line width / light receiving width ratio. A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch. In a positioning pattern detection sensor that detects a positioning pattern formed in a predetermined manner by a predetermined light receiving width,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), a necessary value is obtained from the maximum displacement amount of the image forming apparatus. An alignment pattern detection sensor, wherein a line width is calculated, and the predetermined light receiving width is determined from a line width / light receiving width ratio. In a method of forming an alignment pattern in which a line image of a reference color and a line image of a color other than the reference color are overlapped and formed,
A method of forming an alignment pattern, wherein the line width of the line image is at least twice the maximum deviation amount of the image forming apparatus. A plurality of lines formed by superimposing a black line image as a reference color and a line image other than the reference color are defined as one patch, and patches in which the relative positional relationship between the two color line images is shifted by an arbitrary amount are successive. In a method of forming an alignment pattern, a line width of the line image is twice or more a maximum shift amount of the image forming apparatus. An image forming apparatus having a plurality of image carriers, and sequentially transferring the toner images formed on each image carrier on a transfer body, and then collectively transferring the toner images to a sheet-shaped recording medium to obtain a color image. An alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, alignment pattern detection means for detecting the alignment pattern, and alignment pattern detection means Image forming apparatus which has a displacement amount correcting means for judging a displacement amount and a direction of a line image of the reference color and a line image of a color other than the reference color based on an output signal from the controller and correcting the displacement amount. In the device,
An image forming apparatus, wherein the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship with the writing density of the device and the line width of the alignment pattern.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus having a plurality of image carriers, and sequentially transferring the toner images formed on each image carrier on a transfer body, and then collectively transferring the toner images to a sheet-shaped recording medium to obtain a color image. A plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined by an arbitrary amount. A positioning pattern formed by continuously forming shifted patches; positioning pattern detecting means for detecting the positioning pattern; and a black line of the reference color based on an output signal from the positioning pattern detecting means. In an image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of an image and a line image of a color other than the reference color and corrects the position shift amount,
An image characterized in that the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship in relation to the writing density of the device and the line width of each patch constituting the alignment pattern. Forming equipment.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus having a plurality of image carriers, and obtaining a color image by sequentially superimposing and transferring the toner images formed on each image carrier onto a sheet-shaped recording medium carried on a transfer body. An alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, an alignment pattern detection unit for detecting the alignment pattern, and an alignment pattern detection unit. An image forming apparatus having a position shift amount correcting means for determining a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color based on the output signal of the reference color and correcting the position shift amount.
An image forming apparatus, wherein the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship with the writing density of the device and the line width of the alignment pattern.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus having a plurality of image carriers, and obtaining a color image by sequentially superimposing and transferring the toner images formed on each image carrier onto a sheet-shaped recording medium carried on a transfer body. A plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. An alignment pattern formed by successively forming patches, alignment pattern detection means for detecting the alignment pattern, and a black line image of the reference color based on an output signal from the alignment pattern detection means. And an image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of a line image of a color other than the reference color and the direction thereof, and corrects the position shift amount.
An image characterized in that the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship in relation to the writing density of the device and the line width of each patch constituting the alignment pattern. Forming equipment.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus having a plurality of image carriers, and sequentially transferring the toner images formed on each image carrier on a transfer body, and then collectively transferring the toner images to a sheet-shaped recording medium to obtain a color image. An alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, alignment pattern detection means for detecting the alignment pattern, and alignment pattern detection means Image forming apparatus which has a displacement amount correcting means for judging a displacement amount and a direction of a line image of the reference color and a line image of a color other than the reference color based on an output signal from the controller and correcting the displacement amount. In the device,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. An image forming apparatus having a plurality of image carriers, and sequentially transferring the toner images formed on each image carrier on a transfer body, and then collectively transferring the toner images to a sheet-shaped recording medium to obtain a color image. A plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is determined by an arbitrary amount. A positioning pattern formed by continuously forming shifted patches; positioning pattern detecting means for detecting the positioning pattern; and a black line of the reference color based on an output signal from the positioning pattern detecting means. In an image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of an image and a line image of a color other than the reference color and corrects the position shift amount,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. An image forming apparatus having a plurality of image carriers, and obtaining a color image by sequentially superimposing and transferring the toner images formed on each image carrier onto a sheet-shaped recording medium carried on a transfer body. An alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color, an alignment pattern detection unit for detecting the alignment pattern, and an alignment pattern detection unit. An image forming apparatus having a position shift amount correcting means for determining a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color based on the output signal of the reference color and correcting the position shift amount.
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. An image forming apparatus having a plurality of image carriers, and obtaining a color image by sequentially superimposing and transferring the toner images formed on each image carrier onto a sheet-shaped recording medium carried on a transfer body. A plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch, and the relative positional relationship between the two color line images is shifted by an arbitrary amount. An alignment pattern formed by successively forming patches, alignment pattern detection means for detecting the alignment pattern, and a black line image of the reference color based on an output signal from the alignment pattern detection means. And an image forming apparatus having a position shift amount correcting unit that determines a position shift amount and a direction of a line image of a color other than the reference color and the direction thereof, and corrects the position shift amount.
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. The image forming apparatus according to claim 14, 16, 18, or 20,
An image forming apparatus according to claim 1, wherein the image forming order of the black line image as the reference color is the final color of the color superposition on the transfer body. The image forming apparatus according to any one of claims 13 to 21,
An image forming apparatus, wherein the lightness (L ^* ) of the transfer body for forming the alignment pattern is 40 or less, preferably 20 or less. The image forming apparatus according to any one of claims 13 to 21,
An output signal from the alignment pattern detecting means for an arbitrary shift amount of a line image other than the reference color with respect to the reference color line image of the alignment pattern has one or more extreme values, and the arbitrary shift amount is represented by a horizontal axis. Then, the position shift amount correction means determines the position shift amount and direction of a color other than the reference color with respect to the reference color by calculating the intersection of two straight lines formed on both sides with respect to the extreme value. An image forming apparatus characterized in that an extremum or a data point near an extremum is not used in the calculation of the intersection. The image forming apparatus according to claim 23,
An image forming apparatus comprising a two-component developing type developing device. An image forming apparatus for obtaining a color image by an inkjet method, comprising: an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and an alignment detecting the alignment pattern. A pattern detecting unit and a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color are determined based on an output signal from the alignment pattern detecting unit, and the position shift amount is corrected. In an image forming apparatus having a displacement correcting unit,
An image forming apparatus, wherein the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship with the writing density of the device and the line width of the alignment pattern.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch and two colors are formed. An alignment pattern formed by continuously forming patches in which the relative positional relationship of the line images is shifted by an arbitrary amount, an alignment pattern detection unit for detecting the alignment pattern, and an output from the alignment pattern detection unit An image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of a black line image of the reference color and a line image of a color other than the reference color based on a signal and corrects the position shift amount. At
An image characterized in that the light receiving width of the alignment pattern detecting means is determined so as to satisfy the following relationship in relation to the writing density of the device and the line width of each patch constituting the alignment pattern. Forming equipment.
[Light receiving width]> [line width] / (5.0627 × [writing density (dpi)] ^{− 0.5331} ) An image forming apparatus for obtaining a color image by an inkjet method, comprising: an alignment pattern formed by superimposing a line image of a reference color and a line image of a color other than the reference color; and an alignment detecting the alignment pattern. A pattern detecting unit and a position shift amount and a direction of the image of the reference color and an image of a color other than the reference color are determined based on an output signal from the alignment pattern detecting unit, and the position shift amount is corrected. In an image forming apparatus having a displacement correcting unit,
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio. An image forming apparatus for obtaining a color image by an ink jet method, wherein a plurality of lines formed by superimposing a black line image as a reference color and a line image of a color other than the reference color are defined as one patch and two colors are formed. An alignment pattern formed by continuously forming patches in which the relative positional relationship of the line images is shifted by an arbitrary amount, an alignment pattern detection unit for detecting the alignment pattern, and an output from the alignment pattern detection unit An image forming apparatus including a position shift amount correcting unit that determines a position shift amount and a direction of a black line image of the reference color and a line image of a color other than the reference color based on a signal and corrects the position shift amount. At
After calculating the line width / light receiving width ratio from the formula [line width / light receiving width] <(5.0627 × [writing density (dpi)] ^{− 0.5331} ), the necessary line width is obtained from the maximum deviation amount of the apparatus. Wherein the light receiving width of the alignment pattern detecting means is determined from the line width / light receiving width ratio.

Images