JP4230163B2 - Gradation correction method for optical writing apparatus and image forming apparatus using the same - Google Patents

Description

したがって、本実施形態では、図８のように出力されたテストパターンにおいて、最大点灯時間を基に割り振られた階調表現にて形成されるパターンデータ物のなかから階調が識別可能となる低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１０”とを求め、階調表現しても識別が困難な低濃度限界の階調パターン“４”以下の低濃度域の階調数『４』と高濃度限界の階調パターン“１０”以上の高濃度域の階調数『５』とを、それぞれ減らした少ない階調数「２」と「３」とで粗く割り振るのに対し、その減らした階調数「４」によって増える階調数「６＋４＝１０」によって、低濃度限界の階調パターン“４”から高濃度限界の階調パターン“１０”までの中間域（ＬＥＤ書込みヘッド２２７の有効な点灯時間）での階調数“６”が細かく割り振りし、この割り振られた各階調「１０」に対応するＬＥＤ書込みヘッド２２７の点灯時間をＬＥＤ書込みヘッド２２７の有効な点灯時間（低濃度限界の階調パターン“４”および高濃度限界の階調パターン“１０”を画像形成する際のＬＥＤ書込みヘッド２２７の点灯時間）に基づいて設定されることになり、プリンタ２２の画像形成特性に応じて最も良好な階調表現を得ることができる。
【００４７】
また、高濃度限界の階調パターンを画像形成する際の光書込み装置の点灯時間以降に割り振られる階調数を、低濃度限界の階調パターンを画像形成する際の光書込み装置の点灯時間までの範囲に割り振られる階調数よりも多くしている場合には、両領域とも階調表現時の識別性の最も困難な領域であることから、低濃度限界の階調パターンまでの領域では、書込み光を少し照射しても色材（トナー）が付着できない領域があり、付着できる所より階調を割り当てるため高濃度限以降の階調数より少なくてもよいが、かなり広い領域である高濃度限界の階調パターン以降へ割り振る階調数が、低濃度限界の階調パターンまでの点灯時間を割り振る階調数よりも多く設定されることによって、階調表現を良好に行なうことが可能となる。しかも、これらの領域では、目視では階調を識別し難いが、多色画像を形成する場合には、色味の微妙な変化を再現することが可能となる。
また、高濃度限界の階調パターン以降の領域において、ベタ画像では濃度の識別が困難であるものの、線画像や点画像では線の太さや点の大きさが変化するので、低濃度限界の階調パターンまでの範囲に割り振られる階調数より高濃度限界の階調パターン以降の範囲に割り振られる階調数を多くすることで、良好な画像再現を行うことが可能となる。
本実施の形態では、図８のように出力されたテストパターンにおいて、高濃度限界の階調パターン“１０”を画像形成する際のＬＥＤ書込みヘッド２２７の点灯時間以降に割り振られる階調数「３」が、低濃度限界の階調パターン“４”を画像形成する際のＬＥＤ書込みヘッド２２７の点灯時間までの範囲に割り振られる階調数「２」よりも多くなっているので、両領域とも階調表現時の識別性の最も困難な領域であることから、低濃度限界の階調パターン“４”までの領域では、ＬＥＤ書込みヘッド２２７の出射光が少し照射しても色材（トナー）が付着できない領域があり、付着できる所より階調を割り当てるため高濃度限以降の階調数「３」より少ない「２」でもよいが、かなり広い領域である高濃度限界の階調パターン“１０”以降へ割り振る階調数「３」が、低濃度限界の階調パターン“４”までの点灯時間を割り振る階調数「２」よりも多く設定されることによって、階調表現を良好に行なうことができる。
【００４８】
しかも、高濃度限界の階調パターン“１０”以降の領域において、ベタ画像では濃度の識別が困難であるものの、線画像や点画像では線の太さや点の大きさが変化するので、低濃度限界の階調パターン“４”までの範囲に割り振られる階調数「２」より高濃度限界の階調パターン“１０”以降の範囲に割り振られる階調数「３」を多くすることで、良好な画像再現を行うことができる。
つまり、高濃度限界の階調パターンを画像形成する際の光書込み装置の点灯時間以降に割り振る階調数を、低濃度限界の階調パターンを画像形成する際の光書込み装置の点灯時間までの範囲に割り振る階調数よりも多くすることで、書込み光が少し照射しても色材が付着し難い低濃度限界の階調パターンまでの領域での階調数を減らして、色材が付着できる高濃度限界以降の階調パターンの階調数を多くし、階調表現を良好に行なうことができる。しかも、目視では階調を識別し難い領域においても、多色画像を形成する場合に色味の微妙な変化を再現することができる。更に、高濃度限界の階調パターン以降の領域において線の太さや点の大きさが変化する線画像や点画像を、良好に画像再現することができる。
【００４９】
そして、相隣なる２階調で１つの階調パターンを記録用紙に画像形成したパターンデータ物を適用し、ハイライト側を０、ダーク側を１５とすると、全部で１６階調のそれぞれ隣り合う２階調毎にグループ化しそのグループパターンの階調を１段階毎に変化（０と１、１と２、・・・、１４と１５）させ、主走査方向にグループパターンを形成し、副走査方向に１５本のグループパターン（テストパターン）を形成しているので、階調パターンでの階調の異なる模様の境界を目視によって確認することで、微妙な階調差を識別することができ、最適な点灯時間を容易に求めることができる。
【００５０】
更に、相隣なる２階調の模様を副走査方向において三角形状にラインを分割し、それらの領域の中に２階調を交互に割り当てているので、例えば四角形状の短冊状の階調パターンのように、階調パターンの境界線がつながってしまうために、残像によって階調表現（濃度差）されていないにもかかわらず、階調表現されているように錯覚し誤った判断を行なうことが防止され、模様による錯覚に陥ることもなく、正確な判別を行なうことができ、階調の異なる模様の輪郭を見ることで階調差を容易に識別することができる。
【００５１】
＜第２の実施の形態＞
次に、本発明の第２の実施形態を図１５および図１６に基づいて説明する。
【００５２】
この実施形態では、多色画像形成を行う際の光走査ユニットの階調補正方法を多色画像形成装置において実行させるようにしている。なお、光走査ユニットを除くその他の構成は上記第１の実施形態の場合と同じであり、同じ部分については同一の符号を付してその詳細な説明は省略する。
【００５３】
つまり、図１５において、多色画像形成装置Ｘ′内には、転写搬送ベルト機構３１が設けられている。この転写搬送ベルト機構３１は、その一側（図１５では左側）に回動自在に支持された駆動ローラ３１１と、他側（図１５では右側）に回動自在に支持された従動ローラ３１２と、この両ローラ３１１，３１２間に張架され、図１５中に示す矢印Ｚ方向に駆動する無端の転写搬送ベルト３１３とを備えている。この転写搬送ベルト３１３は、厚さ１００μｍ程度のフイルムを用いて無端状に形成されている。そして、上記転写搬送ベルト３１３の表面上に記録材料としての記録用紙Ｐを静電吸着させることによって、レジストローラ３１０，３１０から供給される記録用紙Ｐを他側（上流側）から一側（下流側）に搬送するようになされている。転写紙搬ベルト機構３１の記録用紙Ｐ搬送方向下流側（図１５は左側）には定着装置３２が設けられ、この定着装置３２によって、記録用紙Ｐに転写形成されたトナー像を記録用紙Ｐ上に定着させることが行われる。定着装置３２は、熱ヒートローラ３２１と、加圧ローラ３２２とを上下に備え、転写紙搬ベルト機構３１（転写搬送ベルト３１３）上を搬送された記録用紙Ｐを熱ヒートローラ３２１と加圧ローラ３２２との間のニップを介して通過させるようにしている。なお、３１４は、転写搬送ベルト３１３の表面に残存するトナーをクリーニングするクリーニングユニットである。
【００５４】
また、転写搬送ベルト機構３１の上方には、画像形成部としての第１の画像形成ステーションＳ１、第２の画像形成ステーションＳ２、第３の画像形成ステーションＳ３および第４の画像形成ステーションＳ４がそれぞれ転写搬送ベルト３１３に近接して記録用紙搬送経路上流側（図１５は右側）から順に所定間隔置きに並設されている。この場合、転写搬送ベルト３１３上の記録用紙Ｐは、第１の画像形成ステーションＳ１、第２の画像形成ステーションＳ２、第３の画像形成ステーションＳ３および第４の画像形成ステーションＳ４に順次搬送されることになる。
【００５５】
各画像形成ステーションＳ１〜Ｓ４は、実質的に同一構成となり、図１５中に示す矢印Ｆ方向にそれぞれ回転する像担持体としての感光体ドラム３３ａ〜３３ｄを具備している。この各感光体ドラム３３ａ〜３３ｄの周囲には、各感光体ドラム３３ａ〜３３ｄを帯電し、各感光体ドラム３３ａ〜３３ｄの外周面上に静電潜像を形成する帯電器３４ａ〜３４ｄと、感光体ドラム３３ａ〜３３ｄの外周面上に形成された静電潜像をトナーにより可視像に現像する現像装置３５ａ〜３５ｄと、感光体ドラム３３ａ〜３３ｄの外周面上に現像されたトナー像（可視像）を記録用紙Ｐに転写する転写ローラ３６ａ〜３６ｄと、感光体ドラム３３ａ〜３３ｄの外周面上に残留するトナーを除去するクリーニング装置３７ａ〜３７ｄとが感光体ドラム３３ａ〜３３ｄの回転方向（矢印Ｆ方向）に沿って順次設けられている。
【００５６】
上記転写ローラ３６ａ〜３６ｄには、トナー像を印加する高電圧｛トナーの帯電極性（−）とは逆極性（＋）の高電圧｝が印加されている。この転写ローラ３６ａ〜３６ｄは、直径８ｍｍ〜１０ｍｍの金属（例えばステンレス）軸をベースとし、その表面を導電性の弾性材（例えばＥＰＤＭ、発泡ウレタンなど）によって覆ってなる。そして、この導電性の弾性材により、記録用紙Ｐに対して均一に高電圧を印加することができるようになっている。
【００５７】
また、各感光体ドラム３３ａ〜３３ｄの上方には、光書込み装置としての光走査ユニット３８ａ〜３８ｄが設けられている。この光走査ユニット３８ａ〜３８ｄは、外部から伝達された画像情報に基づいて、たとえばレーザーなどの光によって、帯電している感光体ドラム３３ａ〜３３ｄの表面上に画像を書き込む。これによって、感光体ドラム３３ａ〜３３ｄ上に静電潜像が形成される。
【００５８】
上記転写搬送ベルト３１３の搬送方向最上流側に位置する第１の画像形成ステーションＳ１の光走査ユニット３８ａにはカラー原稿画像の黒色成分像に対応する画素信号が入力され、次の第２の画像形成ステーションＳ２の光走査ユニット３８ｂにはカラー原稿画像のシアン色成分像に対応する画素信号が入力され、さらに次の第３の画像形成ステーションＳ３の光走査ユニット３８ｃにはカラー原稿画像のマゼンタ色成分像に対応する画素信号が入力され、最下流側に位置する第４の画像形成ステーションＳ４の光走査ユニット３８ｄにはカラー原稿画像のイエロー色成分像に対応する画素信号が入力されるようになされている。これにより、色変換された原稿画像情報に対応する静電潜像が各感光体ドラム３３ａ〜３３ｄの外周面上に形成される。
【００５９】
第１の画像形成ステーションＳ１の現像装置３５ａには黒色のトナーが収容され、第２の画像形成ステーションＳ２の現像装置３５ｂにはシアン色のトナーが収容され、第３の画像形成ステーションＳ３の現像装置３５ｃにはマゼンタ色のトナーが収容され、さらに、第４の画像形成ステーションＳ４の現像装置３５ｄにはイエロー色のトナーが収容されている。各感光体ドラム３３ａ〜３３ｄの外周面上の静電潜像は、これら各色のトナーにより可視像に現像され、これにより、原稿画像情報が各色のトナーによってトナー像として再現されるようになっている。
【００６０】
第１の画像形成ステーションＳ１と転写搬送ベルト３１３との間には記録用紙吸着用帯電器３１５が設けられている。この記録用紙吸着用帯電器３１５は、転写搬送用ベルト３１３の表面を帯電するものであり、多色画像形成装置本体Ｘａ′の下部に設けられた給紙カセット３１９から給紙機構（図示せず）によって供給された記録用紙Ｐを転写搬送用ベルト３１３上に確実に吸着させることによって、第１の画像形成ステーションＳ１から第４の画像形成ステーションＳ４までの間で記録用紙Ｐをズレさせずに搬送するようにしている。
【００６１】
一方、第４の画像形成ステーションＳ４と定着装置３２との間には、除電用放電器３１６が駆動ローラ３１１のほぼ真上に位置して設けられている。この除電用放電器３１６には、転写搬送用ベルト３１３に静電吸着されている記録用紙Ｐを転写搬送用ベルト３１３から分離するための交流電流が印加されている。
【００６２】
そして、記録用紙Ｐは、上記給紙カセット３１９からピックアップローラ３００により１枚ずつ送り出されて給紙機構の記録用紙搬送経路Ｓのガイド内に供給されると、その記録用紙Ｐの先端部分がセンサ（図示せず）により検知され、このセンサから出力される検知信号に基づいて一対のレジストローラ３１０，３１０により一旦停止される。このレジストローラ３１０，３１０により一旦停止された記録用紙Ｐは、各画像形成ステーションＳ１〜Ｓ４とタイミングをとって、図１の矢印Ｚ方向に回転している転写搬送ベルト３１３上に受け渡される。このとき、転写搬送ベルト３１３には記録用紙吸着用帯電器３１５による所定の帯電が施されているため、記録用紙Ｐは、各画像形成ステーションＳ１〜Ｓ４を通過する間、安定して搬送供給される。
【００６３】
各画像形成ステーションＳ１〜Ｓ４においては、各色のトナー像がそれぞれ形成され、転写搬送ベルト３１３により静電吸着されて搬送される記録用紙Ｐの支持面上で各画像形成ステーションＳ１〜Ｓ４のトナー像が重ね合わされて画像が転写される。そして、第４の画像形成ステーションＳ４による画像の転写が完了すると、記録用紙Ｐは、その先端部分から順次除電用放電器３１６により転写搬送ベルト３１３上から剥離され、定着装置３２へと導かれる。この定着装置３２においてトナー画像が定着された記録用紙Ｐは、排出ローラ４１，４１により画像形成装置本体Ｘａ′の側面中央部位にある排紙トレイ４２または画像形成装置本体Ｘａ′の上面にある排紙トレイ４３に搬送方向切換ゲート４４により振り分けられて画像形成装置Ｘ′外に排出される。
【００６４】
また、上記画像形成装置Ｘ′は、上述の如く第１〜第４の画像形成ステーションＳ１〜Ｓ４のすべての感光体ドラム３３ａ〜３３ｄを転写搬送用ベルト３１３上の記録用紙Ｐに対し順に接触させて画像を転写する多色画像形成と、最上流側の第１の画像形成ステーションＳ１の感光体ドラム３３ａのみを転写搬送用ベルト３１３上の記録用紙Ｐに対し接触させて画像を転写する単色画像形成とが選択的に行えるようになっている。
【００６５】
そして、多色画像形成装置Ｘ′のプリンタ制御部２２４においても、ＬＥＤ発光素子の点灯時の光出力を変化させることなく、点灯時間の長さを変化させることによって、図１６に示すように、Ｋ・Ｃ・Ｍ・Ｙそれぞれの１６段階の階調パターンで画像を形成、つまり各色成分毎に１６段階の階調を表現する点灯時間制御が行われている。
【００６６】
図１６に示すパターンでは、Ｋ・Ｃ・Ｍ・Ｙそれぞれの階調補正用に区切られていて、一枚の出力用紙で複数の光走査ユニット３８ａ〜３８ｄの階調補正ができるようになっている。それぞれの２階調組み合わせ部分の境界が区別できる、つまり階調の識別できる範囲を各色毎にパターン番号で選択し、各画像形成ステーションＳ１〜Ｓ４の光走査ユニット３８ａ〜３８ｄ毎のＬＥＤ書込みヘッド２２７の有効点灯時間を設定し、階調補正を行なう。この場合には、各色成分ごとに補正値として有効点灯時間の値を操作パネルより入力する。これにより、目視では階調を識別し難い単色画像に比べて多色画像での色味の微妙な変化が再現され、各成分色の階調を良好に表現することができる。
【００６７】
しかも、複数の階調パターンを各色成分毎に記録部材に並べて画像形成したパターンデータ物を用いることで、各色毎に並んだ階調パターンから、複数並んだ画像形成ステーションＳ１〜Ｓ４それぞれの階調を識別できる範囲と有効点灯時間が同時に求められることになり、各色毎の階調補正が一度のパターンデータ物の出力により設定され、色再現に優れた多色画像形成装置Ｘ′を提供することができる。
【００６８】
【発明の効果】
以上のように、本発明によれば、以下のような効果が発揮される。先ず、最大点灯時間を基に割り振った階調表現にて形成する画像形成物のなかから低濃度限界の階調パターンと高濃度限界の階調パターンとを求め、低濃度限界の階調パターン以下の低濃度域の階調数と高濃度限界の階調パターン以上の高濃度域の階調数とを、それぞれ減らした少ない階調数で粗く割り振るのに対し、その減らした階調数によって増える階調数で低濃度限界の階調パターンから高濃度限界の階調パターンまでの中間域での階調数を細かく割り振りし、この割り振った各階調に対応する光書込み手段の点灯時間を光書込み手段の有効な点灯時間に基づいて設定することで、画像形成部の画像形成特性に応じて最も良好な階調表現を得ることができる。
【００７０】
さらに、相隣なる２階調で１つの階調パターンを記録部材に画像形成した画像形成物を適用し、その相隣なる階調パターンの階調を１段階毎に変化させて全階調域全ての階調パターンを画像形成するので、微妙な階調差を目視によって識別することができ、最適な点灯時間を容易に求めることができる。
【００７１】
しかも、相隣なる２階調の模様を三角形状の階調パターンとすることで、階調表現されているように錯覚し誤った判断を防止して正確な判別を行なうことができ、階調の異なる模様の輪郭を見ることで階調差を容易に識別することができる。
【００７２】
更に、光書込み装置の階調補正方法を画像形成装置に実行することで、光書込み装置の最適な階調補正を画像形成装置の画像形成特性に応じて行え、階調性に優れた画像を提供することができる。
【００７３】
また、複数の光書込み手段によって複数の階調パターンで単色および多色の画像を形成することで、複数個並んだ画像形成部それぞれの画像形成特性に応じた光書込み装置の最適な階調補正を行え、各画像形成部の階調のバラツキを抑えて、階調性と色再現に優れた画像を形成することができる。
【００７４】
しかも、複数の階調パターンを各色成分毎に記録部材に並べて画像形成した画像形成物を用いることで、各色毎に並んだ階調パターンから、複数並んだ画像形成部それぞれの階調を識別できる範囲と有効点灯時間が同時に求められることになり、各色毎の階調補正が一度のパターンデータ物の出力により設定され、色再現に優れた多色画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係る光走査ユニットの階調補正方法を実行する画像形成装置の内部を正面から見た断面図である。
【図２】同じくプリンタ制御部および制御対象を示すブロック構成図である。
【図３】同じくＬＥＤ書込みヘッドおよび感光体ドラム付近の斜視図である。
【図４】同じくプリンタ制御部による光走査ユニットの階調補正方法の流れを示すフローチャート図である。
【図５】同じく副走査方向に１５本のグループパターンを短冊状に形成したパターンデータ物を示す図である。
【図６】同じく副走査方向に１５本のグループパターンを三角形状に形成したパターンデータ物を示す図である。
【図７】同じく最大点灯時間を階調番号毎に均等に分割して示す図である。
【図８】同じく低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１０”とで表されるパターンデータ物を示す図である。
【図９】同じく低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１１”とで表されるパターンデータ物を示す図である。
【図１０】同じく操作部の正面図である。
【図１１】同じく低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１０”とで表されるパターンデータ物に基づいて割り振られた各階調に対応するＬＥＤ書込みヘッドの点灯時間を設定する階調補正の説明図である。
【図１２】同じく低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１１”とで表されるパターンデータ物に基づいて割り振られた各階調に対応するＬＥＤ書込みヘッドの点灯時間を設定する階調補正の説明図である。
【図１３】同じく低濃度限界の階調パターン“４”と高濃度限界の階調パターン“１０”とで表されるパターンデータ物に基づいて割り振られた各階調に対応するＬＥＤ書込みヘッドの最大点灯時間を階調番号毎に均等に分割して示す図である。
【図１４】同じく階調補正された階調番号に対するＬＥＤ書込みヘッドの点灯時間の特性を示す特性図である。
【図１５】本発明の第２の実施形態に係る光走査ユニットの階調補正方法を実行する多色画像形成装置の要部を正面から見た断面図である。
【図１６】同じく副走査方向に各色毎に１５本のグループパターンを短冊状に形成したパターンデータ物を示す図である。
【符号の説明】
２００ 感光体ドラム（像担持体）
２２ プリンタ（画像形成部）
２２２ 光走査ユニット（光書込み装置）
２２４ プリンタ制御部（制御手段）
２２７ ＬＥＤ書込みヘッド（光書込み手段）
２９０ パターンデータ記憶部（記憶部）
２９１ 操作部（選択手段）
３３ａ〜３３ｄ 感光体ドラム（像担持体）
３８ａ〜３８ｄ 光走査ユニット（光書込み装置）
Ｐ 記録用紙（記録部材）
Ｘ 画像形成装置
Ｘ′ 多色画像形成装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradation correction method for an optical writing apparatus provided with optical writing means for writing an image on an image carrier based on image information, and an electrophotographic image forming apparatus using the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that includes an image forming station including a photosensitive drum, a writing device, and a developing device is used. In this device, an optical writing technique is often used as a writing device, and recently, a solid scanning optical writing device such as an LED array head is often used to reduce the size of the device.
[0003]
In such an optical writing device, the lighting time control or the light output control is performed to form an image with a plurality of gradation patterns, that is, to express gradation.
[0004]
Furthermore, in an image forming apparatus that forms a multicolor image by superimposing a plurality of component color images, it is necessary to write an image for each color component, and a plurality of image forming units that form each color component image are used side by side. ing.
[0005]
[Problems to be solved by the invention]
However, in the case of performing gradation expression of the optical writing device by equally dividing the maximum lighting time by the optical writing device, when the gradation pattern of each optical pattern is simply formed by dividing the maximum lighting time equally. Even if the lighting time of the optical writing means is set, all the gradations cannot be expressed well with all the lighting times set. This is because, in a highlight portion having a low density (for example, white), the density does not appear when the lighting time is short (developer, for example, toner is difficult to adhere), and thus a density difference cannot be obtained. This is because a high dark portion (for example, black) is solid black even if the lighting time is different, and the density difference cannot be recognized. For this reason, there is a problem that a region in which a difference in gradation pattern cannot be distinguished occurs, and satisfactory gradation expression cannot be performed.
[0006]
Therefore, the effective lighting time that can express the gradation pattern, that is, the effective lighting time of the optical writing means when forming the low density limit gradation pattern and the high density limit gradation pattern that can distinguish the density difference is set. Thus, even if the number of gradations expressing the effective lighting time is simply divided equally, a sufficiently smooth gradation cannot be obtained.
[0007]
The present invention has been made in view of the above points, and an object of the present invention is to obtain an optimum gradation by obtaining an effective lighting time of the optical writing unit in accordance with characteristics at the time of image formation. An object of the present invention is to provide a gradation correction method for an optical writing device and an image forming apparatus using the same.
[0008]
[Means for Solving the Problems]
  To achieve the above object, the gradation correction method for an optical writing device according to one aspect of the present invention includes optical writing means for writing an image on an image carrier based on image information, and the lighting time of the optical writing means is set. As a gradation correction method of an optical writing apparatus that forms an image with a plurality of gradation patterns by controlling, one gradation pattern is composed of two gradations that are adjacent to each other. And by changing the gradation of the adjacent gradation pattern for each step, an image formed product imaged on the recording member so as to be the gradation pattern of all the gradation areas is created, From this image formationThe gradation difference is visuallyidentificationWasLow density limit gradation pattern andThe gradation difference was identified visually.Select the gradation pattern for the high density limit and select the gradation pattern for the low density limit.While roughly allocating the gradation corresponding to the lighting time of the optical writing means with a small number of gradations reduced from the number of gradations up to the gradation pattern of the low density limit,After the high density limit gradation patternThe gradation corresponding to the lighting time of the optical writing means in the above is calculated from the number of gradations after the gradation pattern of the high density limit.Roughly assigning with the reduced number of gradations, while increasing the number of gradations with the reduced number of gradations, from the low density limit gradation pattern to the high density limit gradation patternGray scale corresponding to the lighting time of the optical writing meansAre finely allocated, and the low density limit gradation pattern andthe aboveWhen forming high density limit gradation patternsthe aboveBased on the lighting time of the optical writing means, it corresponds to each of the allocated gradationsthe aboveThe lighting time of the optical writing means is set.
  The gradation correction method for an optical writing device according to another aspect of the present invention includes optical writing means for writing an image on an image carrier based on image information, and controls the lighting time of the optical writing means. As a gradation correction method for an optical writing apparatus that forms an image with a plurality of gradation patterns, a plurality of gradation patterns stored in advance are converted into one gradation pattern by two adjacent gradations. By changing the gradations of adjacent gradation patterns step by step, the gradation number is assigned to each gradation pattern so that all gradation patterns can be obtained in all gradation areas. Create an image-formed product that has been imaged, and use this image-formed productThe gradation difference is visuallyidentificationWasLow density limit gradation patternAs the pattern number corresponding to the input pattern number is input, the gradation pattern at the low density limit corresponding to the input pattern number is selected and the gradation difference is visually identified.High density limit gradation patternVs.By entering the corresponding pattern number, A high density limit gradation pattern corresponding to the input pattern numberSelect the gradation pattern of the low density limitWhile roughly allocating the gradation corresponding to the lighting time of the optical writing means with a small number of gradations reduced from the number of gradations up to the gradation pattern of the low density limit,After the high density limit gradation patternThe gradation corresponding to the lighting time of the optical writing means in the above is the gradation pattern after the gradation pattern of the high density limitWhile the rough allocation is performed with a small number of gradations reduced from the number of gradations, the gradation pattern from the low density limit to the gradation pattern with the high density limit is increased by the number of gradations increased by the reduced number of gradations.Gray scale corresponding to the lighting time of the optical writing meansAre finely allocated, and the low density limit gradation pattern andthe aboveWhen forming high density limit gradation patternsthe aboveBased on the lighting time of the optical writing means, it corresponds to each of the allocated gradationsthe aboveThe lighting time of the optical writing means is set.
[0009]
By this specific matter, the low density limit gradation pattern and the high density limit gradation pattern that makes it possible to distinguish the gradation from among the image formations formed by the gradation expression assigned based on the maximum lighting time. The number of gradations in the low density region below the low density limit gradation pattern and the number of gradations in the high density region above the high density limit gradation pattern, which are difficult to identify even if the gradation is expressed, In contrast to the rough allocation with a reduced number of gradations, the intermediate range from the low density limit gradation pattern to the high density limit gradation pattern with the number of gradations increased by the reduced gradation number (of the optical writing device). The number of gradations in the effective lighting time) is finely allocated, and the lighting time of the light writing means corresponding to each assigned gradation is set to the effective lighting time of the light writing means (low density limit gradation pattern and high density). Image formation of limit gradation patterns It would be set based on the lighting time) of the optical writing means when that, it becomes possible to obtain the best gray scale representation according to the image formation characteristics of the image forming unit.
[0012]
  furtherBy applying an image formed product in which one gradation pattern is formed on a recording member with two adjacent gradations, and changing the gradation of the adjacent gradation pattern for each step, all gradations are obtained. All gradation patterns are imagedBecauseBy visually confirming the boundary between patterns having different gradations in the gradation pattern, it is possible to identify a subtle gradation difference and to easily obtain the optimum lighting time.
[0013]
Moreover, when two adjacent gradation patterns are triangular gradation patterns, the boundary lines of the gradation patterns are connected as in the case of, for example, a square gradation pattern. Even though there is no tone expression (density difference), it is possible to prevent the user from making an illusion that the tone is expressed and making an erroneous determination. For this reason, accurate discrimination can be performed without falling into the illusion of a pattern, and a gradation difference can be easily identified by looking at the outline of a pattern having different gradations.
[0014]
In particular, the following configuration is listed as a method of using the gradation correction method of an optical writing device in an image forming apparatus.
[0015]
  That meansThe image forming unit includes a selection unit, and the image forming unit includes:Optical writing means for writing an image on an image carrier based on image informationOptical writing deviceAn optical writing device that forms an image with a plurality of gradation patterns by controlling the lighting time of the optical writing means, and a plurality of gradations that form one gradation pattern with two adjacent gradations A storage unit for storing patterns in advance;And control meansThe plurality of gradation patterns in the storage unitThe gradation pattern once written on the image carrier after the optical writing means is written on the image carrier.Create an image by forming an image on a recording memberThe selecting means is the aboveFrom the image formation created by the image forming unit, select the low density limit gradation pattern with the visually identified gradation difference and the high density limit gradation pattern with the visually identified gradation difference.The control means isThe number of gradations corresponding to the lighting time of the optical writing means up to the gradation pattern of the low density limit selected by the selection means is reduced from the number of gradations up to the gradation pattern of the low density limit. In addition to rough allocation, the gradation corresponding to the lighting time of the optical writing means after the gradation pattern of the high density limit is coarsened with a small number of gradations reduced from the number of gradations after the gradation pattern of the high density limit. On the other hand, the gradation corresponding to the lighting time of the optical writing means from the low density limit gradation pattern to the high density limit gradation pattern is finely allocated with the number of gradations increased by the reduced number of gradations. And corresponding to each of the allocated gradations based on the lighting time of the optical writing means when forming the gradation pattern of the low density limit and the gradation pattern of the high density limit. To set the lighting time of the serial light writing meansThe
[0016]
By this specific matter, the optimum gradation correction of the optical writing apparatus is performed according to the image forming characteristics of the image forming apparatus, and it becomes possible to provide an image with excellent gradation.
[0017]
  Also,The above constituting the optical writing deviceOptical writing meansMultipleIn the case where a monochromatic image and a multicolor image are formed with a plurality of gradation patterns by each of the optical writing means, the optical writing device according to the image forming characteristics of each of the plural image forming units arranged Optimal gradation correction is performed, and it is possible to form an image excellent in gradation and color reproduction by suppressing gradation variation in each image forming unit.
[0018]
  Furthermore,Image formationA plurality of gradation patterns are arranged on a recording member for each color component to form an image.StuffIn this case, a range in which the gradation of each of the plurality of image forming units arranged and the effective lighting time are simultaneously obtained from the gradation pattern arranged for each color, and gradation correction for each color is performed once. It is possible to provide a multicolor image forming apparatus which is set by the output of the image forming unit and has excellent color reproduction.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0020]
<First Embodiment>
FIG. 1 is a schematic configuration diagram showing the inside of an image forming apparatus that executes a gradation correction method of an optical scanning unit as an optical writing apparatus according to the first embodiment of the present invention. The image forming apparatus X is a multi-function type and has functions as a copying machine, a printing machine, and a facsimile machine. The image forming apparatus X includes a printer 22 as an image forming unit, a scanner 23, an automatic document feeder 24, a paper discharge processing device 25, and a multistage paper feeding device 26. Hereinafter, the configuration of each unit will be described.
[0021]
The automatic document feeder 24 conveys and positions a document placed on a document set tray (not shown) on the platen glass 230, and conveys a document whose image has been read by the scanner 23 to a document discharge tray (not shown). Then, it comes to discharge. Further, one side (the one side on the back side in FIG. 1) of the automatic document feeder 24 is pivotally supported so that a document that cannot be transported can be placed on the platen glass 230, and the entire device 24 can be opened and closed. ing.
[0022]
The scanner 23 can select and set either the automatic reading mode or the manual operation reading mode. When the former automatic reading mode is selected, the scanner 23 reads an image of the original in conjunction with the conveyance of the original onto the platen glass 230 by the automatic original conveying device 24. When the latter manual operation reading mode is selected, the scanner 23 reads the image of the document placed on the platen glass 230 in response to the manual operation. In either mode, the first and second scanning units 231 and 232 are moved while maintaining a predetermined speed relationship with each other, and the image of the document placed on the platen glass 230 is moved by the first scanning unit 231. After exposure, the first and second scanning units 231 and 232 guide reflected light from the document to the lens 233, and the lens 233 forms an image of the document on a photoelectric conversion element (CCD) 234. The CCD 234 repeatedly scans and reads an image of a document in the main scanning direction, and outputs image data based on the document image. The scanner 23 is configured to attach a type of recording paper as a recording member based on image data based on the original image.
[0023]
The printer 22 inputs image data from the scanner 23 and image data from an external device (for example, a personal computer), and records an image indicated by the image data on a recording sheet. LED writing as optical writing means An optical scanning unit 222 having a head 227 is provided.
[0024]
The printer 22 also includes a printer control unit 224 as control means. As shown in FIG. 2, the printer control unit 224 functions as an interface for controlling the electrophotographic process unit 220 (see FIG. 1) and receiving image data from an external device. An image data input unit 225 for inputting the original image read as image data, and an image data storage unit 226 for performing predetermined image processing on the image data input to the image data input unit 225 and storing the image data. ing.
[0025]
As shown in FIG. 1, the electrophotographic process unit 220 includes a photosensitive drum 200 as an image carrier, a charger 201, an optical scanning unit 222 as an optical writing device, a developing unit 202, a transfer unit 203, and a cleaning unit. 204, a static elimination unit 205, and the like. The photosensitive drum 200 is rotated in one direction by a drum motor (not shown). The charger 201 uniformly charges the surface of the photosensitive drum 200. The developing unit 202 supplies toner to the surface of the photoreceptor 200. The toner adheres to the electrostatic latent image on the surface of the photosensitive drum 200, and a toner image is formed. The transfer unit 203 superimposes the conveyed recording paper and the photosensitive drum 200 to transfer the toner image from the photosensitive drum 200 to the recording paper. The cleaning unit 204 removes toner remaining on the surface of the photosensitive drum 200. The neutralization unit 205 removes the charge on the surface of the photosensitive drum 200.
[0026]
A fixing device 230 is disposed on the downstream side of the electrophotographic process unit 220. The fixing device 230 heats and pressurizes the recording paper to fix the toner image on the recording paper. The recording sheet on which the toner image has been fixed is conveyed by each discharge roller 219 and delivered to the paper discharge processing device 25.
[0027]
Further, when an image is recorded on the back side of the recording paper, the conveyance of the recording paper is temporarily stopped and the recording paper is conveyed to the printer 22 in the reverse direction. In the printer 22, the branching claw 252 is rotated, the recording paper is guided to the reversing conveyance path (not shown) by the branching claw 252, and the recording paper is conveyed again to the electrophotographic process 220 through the reversing conveyance path. By inverting the front and back of the recording paper, an image is recorded on the back of the recording paper. The recording paper on which the images are recorded in this way is conveyed by each discharge roller 219 and delivered to the paper discharge processing device 25.
[0028]
In addition, a paper feeding unit 260 is provided below the printer 22. The sheet feeding unit 260 stacks and stores recording sheets, and separates and removes the recording sheets one by one from the sheet storing cassette 261 and supplies the recording sheets to the electrophotographic process unit 220. A take-out unit 262. The recording sheet taken out by the take-out unit 262 is conveyed to the transfer unit 203 and further conveyed by the discharge rollers 219 via the fixing device 230. The recording sheet is conveyed with a center reference that is aligned with respect to the center of the fixing device 230 with respect to the center orthogonal to the conveyance direction. The paper storage cassette 261 can be pulled out from the image forming apparatus main body Xa, and the recording paper can be supplied to the paper storage cassette 261 in the pulled-out state.
[0029]
A duplex unit 255 is provided below the sheet feeder 260. The duplex unit 255 communicates with a reversing conveyance path 256 that reverses the recording sheet, and is used when image formation is performed on both sides of the recording sheet. The duplex unit 255 can be replaced with a normal paper cassette, and the duplex unit 255 can be replaced with a normal paper cassette.
[0030]
The paper discharge processing device 25 receives the recording paper from the printer 22 and performs post-processing on the recording paper. Examples of the post-processing include stapling processing and sorting processing. The recording sheet subjected to this processing is discharged to one of a plurality of discharge trays 256 and 259.
[0031]
The printer 22 and the paper feeding unit 260 are placed on the multi-stage paper feeding device 26. The scanner 23 and the automatic document feeder 24 are placed on a system rack 27. At the bottom of the multi-stage sheet feeding device 26, each moving roller 269 and each fixed portion (not shown) are provided. The multi-stage sheet feeding device 26 can be moved by screwing each fixed portion into the bottom of the multi-stage sheet feeding device 26, separating each fixed portion from the floor surface, and supporting the multi-stage sheet feeding device 26 by each moving roller 269. it can. In this state, the multi-stage paper feeding device 26, the printer 22 and the paper discharge processing device 25 are moved and arranged inside the system rack 27. Thereafter, the multi-stage sheet feeding device 26 is fixed by rotating and projecting the fixing portions 268 and bringing the fixing portions 268 into contact with the floor surface.
[0032]
The multi-stage paper feeding device 26 is an option and is detachable from the image forming apparatus X. In the multistage sheet feeding device 26, a plurality of types of recording sheets are stored in the respective sheet storage cassettes 262 and 263. In the multi-stage sheet feeding device 26 of the present embodiment, an upper cassette 262 that is positioned above and can accommodate a relatively large size (for example, A3 size) recording sheet, and a lower side of the upper cassette 262 are arranged side by side. And a lower cassette 263 capable of storing recording paper of a frequently used size (for example, A4 size).
[0033]
A paper guide passage 265 extending in the vertical direction is provided inside the multi-stage paper feeding device 26, and the recording paper taken out from each cassette 261, 262, 263 is supplied to the printer 22 through the paper guide passage 265. It has become so. A paper receiving opening (not shown) is formed on the lower surface of the printer 22 at a position corresponding to the paper guide path 265, and the recording paper passing through the paper guiding path 265 passes through the paper receiving opening and is guided to the printer 22. It has come to be. Note that the upper cassette 261 can be pulled out from the paper supply device frame 266 toward the front side in the drawing, and the recording paper can be replenished in the pulled-out state.
[0034]
As shown in FIG. 2, a paper feed mechanism 28 that supplies recording paper from the paper feed cassettes 261, 262, 263, a charger 201 that charges the photosensitive drum 200, and an outer peripheral surface of the photosensitive drum 200 A developing unit 202 that develops the upper electrostatic latent image into a visible image, a transfer unit 203 that transfers the visible image on the outer peripheral surface of the photosensitive drum 200 to a recording sheet, and a toner image transferred and formed on the recording sheet A fixing device 230 for fixing the image on the recording paper and an optical scanning unit 222 (LED writing head 227) for writing on the outer peripheral surface of the photosensitive drum 200 are connected to the printer control unit 224 so that signals can be input and output. It is controlled by a command from the printer control unit 224. In addition, the printer control unit 224 is connected so that a signal from the pattern data storage unit 290 can be input, and can call up 16-step gradation patterns stored in advance in the pattern data storage unit 290. Further, the printer control unit 224 is connected so that a command signal from the operation unit 291 (see FIG. 10) can be input.
[0035]
As a characteristic part of the present invention, as shown in FIG. 3, the LED writing head 227 emits emitted light in accordance with image data read from the image data storage unit 226 or image data transferred from an external device. The surface of the photosensitive drum 200 is repeatedly scanned in the main scanning direction by the light emitting diode array light source 227a to be formed and the light (light image) emitted from the light emitting diode array light source 227a, and an electrostatic latent image is formed on the surface of the photosensitive drum 200. A lens array 227b (for example, a SELFOX lens) for imaging. The LED writing head 227 is turned on based on the image data, and writes on the photosensitive drum 200 line by line. The number of LED light emitting elements of the light emitting diode array light source 227a corresponds to the resolution of an image formed by the image forming apparatus X. For example, in the case of an A3 width (297 mm) with a resolution of 600 dpi, about 7000 are used.
[0036]
The maximum lighting time per LED light emitting element of the light emitting diode array light source 227a is limited by the process speed. In addition, enormous voltages are required to light a large number of LED light emitting elements simultaneously, and in fact, a large number of LED light emitting elements are divided into several groups, and the LED light emitting elements of each group are sequentially lighted. There are further restrictions there. In this case, the lighting time possible per LED light emitting element is set as the maximum lighting time.
[0037]
Further, the printer control unit 224 forms an image with a 16-step gradation pattern by changing the length of the lighting time without changing the light output when the LED light-emitting element is turned on, that is, the 16-step gradation. Lighting time control that expresses the key is performed.
[0038]
Next, an example of the gradation correction method of the optical scanning unit 222 by the printer control unit 224 will be described based on the flowchart of FIG.
[0039]
First, in step ST1 of the flowchart of FIG. 4, a 16-step gradation pattern stored in advance in the pattern data storage unit 290 of the image forming apparatus X is called, and the 16-step gradation as shown in FIGS. By patterning the pattern on the recording paper P, a pattern data object as an image formed object is created. These gradation patterns are created by lighting time control. As shown in FIG. 7, the maximum lighting time is equally divided and the lighting time is changed for each gradation to control the gradation pattern. Expresses gradation. Since the LED writing head 227 used here is capable of expressing 16 gradations, description will be given with a pattern of 16 gradations. It is possible to create. For example, if the controllable gradation expression number is 32, it is possible to create a gradation pattern by dividing the lighting time of the LED light emitting element into 32, and the controllable level of the LED writing head can be created. It will be sufficient to correspond to the number of key expressions.
[0040]
In this 16-gradation pattern, if the highlight side is 0 and the dark side is 15, a total of 16 gradations are grouped into two adjacent gradations, and the gradation of the group pattern is changed for each step. (0, 1, 1, 2,..., 14 and 15), a group pattern is formed in the main scanning direction, and 15 group patterns (test patterns) are formed in the sub scanning direction. Further, in the sub-scanning direction, lines are divided into strips in FIG. 5 and triangles in FIG. 6, and two gradations are alternately allocated in these regions. Each test pattern is numbered from 1 to 15 as a pattern number. In addition, although the pattern this time comprised what was comprised by the triangle and the square as shown in FIG.5 and FIG.6, as long as the boundary can be made, of course, you may use another shape. Further, in gradation grouping, two gradations are selected, but any number of gradation groups may be used as long as the gradation identification range can be selected. In addition, if there are a large number of gradation expressions that can be controlled and it is difficult to create a gradation pattern using all gradations, select only the gradations near the boundary where gradation identification is possible. A gradation pattern may be created by
[0041]
Next, in step ST2, a pattern data product created by forming an image of a 16-step gradation pattern on a recording sheet is visually compared, and a gradation pattern that can distinguish the boundary between two gradation combination portions, that is, Select the range that can be identified by the pattern number attached to the test pattern.
[0042]
Here, when the test pattern as shown in FIG. 5 is output and the pattern data object is visually identified, the identifiable range of the gradation may be widely judged due to the effect of the pattern having a low pattern number. . This is because the gradation boundary lines are arranged in a straight line, which causes an illusion that it is determined that even a pattern that cannot be actually identified can be identified. When the test pattern of FIG. 6 is used, these illusions are unlikely to occur and are considered suitable for visual judgment.
[0043]
Thereafter, in step ST3, the pattern number is input to the operation unit 291 of the image forming apparatus X shown in FIG. Specifically, in the present embodiment, assuming that the image formation output from FIG. 6 is the one shown in FIGS. 8 and 9, in this test pattern, the pattern number that can identify the boundary is “ Since “4” is changed to “10” and “4” is changed to “11” in FIG. 9, the pattern number for identifying each boundary, that is, the gradation pattern number “4” at the low density limit and the level at the high density limit. The key pattern number “10” or “11” is input to the operation unit 291.
[0044]
Then, in step ST4, correction is performed based on the pattern number input in step ST3, and the lighting time of the LED writing head 227 is set for each gradation. Based on this pattern number, the gradation distinguishable range is limited, and the lighting time in that range is defined as the effective lighting time. In other words, the effective lighting time of the LED writing head 227 is “4” to “10” in the case of FIG. 8 as the pattern number of the test pattern, and “4” to “11” in the case of FIG. The lighting time corresponding to each gradation is obtained by using the lighting times as effective lighting times. Thereby, the effective lighting time of the LED writing head 227 is set, and gradation correction as shown in FIGS. 11 and 12 is performed.
[0045]
Specifically, as shown in Table 1 below, in the test pattern output as shown in FIG. 8, the levels up to the gradation pattern “4” of the low density limit before correction as shown in FIG. The number of gradations “4” and the number of gradations “5” after the gradation pattern “10” of the high density limit before correction are reduced by two from each number of gradations, and the smaller number of gradations “2” and “ 3 ”and make a rough allocation. On the other hand, the gradation number “6 + 4 = 10”, which is increased by “4” by the gradation numbers “4-2 = 2” and “5-3 = 2” reduced by two, the low density limit before correction. The gradation number “6” from the gradation pattern “4” to the gradation pattern “10” at the high density limit is finely assigned and corrected. Then, based on the lighting time of the LED writing head 227 when the low density limit gradation pattern “4” and the high density limit gradation pattern “10” are formed as shown in FIG. The lighting time of the LED writing head 227 corresponding to each allocated gradation is set. In this case, in the test pattern output as shown in FIG. 8, the number of gradations “3” allocated after the lighting time of the LED writing head 227 when forming the gradation pattern “10” of the high density limit is The number of gradations is larger than the number of gradations “2” allocated to the range up to the lighting time of the LED writing head 227 when the gradation pattern “4” of the low density limit is formed.
[0046]
[Table 1]

Therefore, in the present embodiment, in the test pattern output as shown in FIG. 8, the gradation can be identified from among the pattern data objects formed by the gradation expression allocated based on the maximum lighting time. The density limit gradation pattern “4” and the high density limit gradation pattern “10” are obtained, and the low density range gradation pattern “4” or less that is difficult to identify even if the gradation is expressed. The number of gradations “4” and the number of gradations “5” in the high density region above the gradation pattern “10” of the high density limit are roughly allocated with the reduced numbers of gradations “2” and “3”, respectively. On the other hand, an intermediate area from the low density limit gradation pattern “4” to the high density limit gradation pattern “10” by the gradation number “6 + 4 = 10” increased by the reduced gradation number “4”. Gradation at (effective lighting time of LED writing head 227) “6” is finely allocated, and the lighting time of the LED writing head 227 corresponding to each allocated gradation “10” is set to the effective lighting time of the LED writing head 227 (the gradation pattern “4” of the low density limit and the high The density limit gradation pattern “10” is set based on the lighting time of the LED writing head 227 when forming an image), and the best gradation expression is obtained according to the image forming characteristics of the printer 22. be able to.
[0047]
  Also,The number of gradations allocated after the lighting time of the optical writing device when forming an image of the high density limit gradation pattern, the range from the lighting time of the optical writing device when forming the image of the low density limit gradation pattern If the number of gradations is larger than the number of gradations assigned to each of the areas, both areas are the most difficult areas to distinguish when representing gradations. There is a region where the colorant (toner) cannot adhere even if it is irradiated a little, and the number of gradations after the high density limit may be less than the high density limit to assign the gradation from where it can adhere, but the high density limit, which is a fairly wide area By setting the number of gradations to be assigned to the gradation pattern after this number more than the number of gradations to which the lighting time up to the gradation pattern of the low density limit is assigned, gradation expression can be performed satisfactorily. In addition, in these areas, it is difficult to visually identify the gradation, but when a multicolor image is formed, it is possible to reproduce a subtle change in color.
Also, in the area after the gradation pattern of the high density limit, although it is difficult to identify the density in the solid image, the line thickness and the point size change in the line image and the point image. By increasing the number of gradations allocated to the range after the gradation pattern of the high density limit, compared to the number of gradations allocated to the range up to the tone pattern, it is possible to perform good image reproduction.
In this embodiment,In the test pattern output as shown in FIG. 8, the number of gradations “3” assigned after the lighting time of the LED writing head 227 when forming the gradation pattern “10” of the high density limit is the low density limit. Since the number of gradations “4” is larger than the number of gradations “2” assigned to the range up to the lighting time of the LED writing head 227 when forming the image of the gradation pattern “4”, both regions are discriminating at the time of gradation expression. In the region up to the low density limit gradation pattern “4”, there is a region where the color material (toner) cannot adhere even if the emitted light of the LED writing head 227 is slightly irradiated. The number of gradations allocated to the high density limit gradation pattern “10” or later, which is a considerably wide area, may be “2” which is less than the number of gradations “3” after the high density limit in order to assign the gradation from the place where it can be attached. " "Is by being set larger than the number of gradations" 2 "to allocate the lighting time to the gradation pattern" 4 "of the low concentration limit, it is possible to perform gradation expression good.
[0048]
  In addition, in the area after the gradation pattern “10” of the high density limit, although it is difficult to identify the density in the solid image, the line thickness and the dot size change in the line image and the point image. Good by increasing the number of gradations “3” allocated to the range after the gradation pattern “10” of the high density limit to the number of gradations “2” allocated to the range up to the limit gradation pattern “4”. Image reproduction can be performed.
In other words, the number of gradations assigned after the lighting time of the optical writing device when forming an image of the high density limit gradation pattern is equal to the lighting time of the optical writing device when forming the image of the low density limit gradation pattern. By increasing the number of gradations to be assigned to the range, the coloring material adheres by reducing the number of gradations in the area up to the low density limit gradation pattern where coloring material is difficult to adhere even if the writing light is irradiated a little. The number of gradations of the gradation pattern after the high density limit that can be increased is increased, and gradation expression can be performed well. In addition, even in a region where it is difficult to visually identify the gradation, it is possible to reproduce a subtle change in color when forming a multicolor image. In addition, it is possible to satisfactorily reproduce a line image or a point image in which the thickness of the line or the size of the point changes in the area after the gradation pattern of the high density limit.
[0049]
Then, applying a pattern data object in which one gradation pattern is formed on a recording sheet with two adjacent gradations, if the highlight side is 0 and the dark side is 15, each of the 16 gradations is adjacent to each other. By grouping every two gradations, the gradation of the group pattern is changed for each step (0, 1, 1, 2,..., 14 and 15), and a group pattern is formed in the main scanning direction. Since 15 group patterns (test patterns) are formed in the direction, it is possible to identify a subtle gradation difference by visually confirming the boundary between patterns having different gradations in the gradation pattern. The optimum lighting time can be easily obtained.
[0050]
Further, since the adjacent two-gradation patterns are divided into triangles in the sub-scanning direction and two gradations are alternately allocated in these areas, for example, a rectangular strip-shaped gradation pattern In this way, the boundary line of the gradation pattern is connected, so even if the gradation expression (density difference) is not expressed by the afterimage, the illusion that the gradation expression is expressed and an erroneous determination is made. Therefore, accurate discrimination can be performed without falling into the illusion of the pattern, and the gradation difference can be easily identified by looking at the outline of the pattern with different gradation.
[0051]
<Second Embodiment>
Next, a second embodiment of the present invention will be described with reference to FIGS.
[0052]
In this embodiment, the multi-color image forming apparatus executes the gradation correction method of the optical scanning unit when performing multi-color image formation. The other configurations except for the optical scanning unit are the same as those in the first embodiment, and the same portions are denoted by the same reference numerals and detailed description thereof is omitted.
[0053]
That is, in FIG. 15, a transfer conveyance belt mechanism 31 is provided in the multicolor image forming apparatus X ′. The transfer / conveying belt mechanism 31 includes a driving roller 311 that is rotatably supported on one side (left side in FIG. 15), and a driven roller 312 that is rotatably supported on the other side (right side in FIG. 15). And an endless transfer / conveying belt 313 which is stretched between the rollers 311 and 312 and is driven in an arrow Z direction shown in FIG. This transfer / conveying belt 313 is formed endlessly using a film having a thickness of about 100 μm. Then, the recording paper P as a recording material is electrostatically adsorbed on the surface of the transfer conveyance belt 313, whereby the recording paper P supplied from the registration rollers 310, 310 is moved from the other side (upstream side) to one side (downstream). Side). A fixing device 32 is provided on the downstream side (left side in FIG. 15) of the transfer paper transport belt mechanism 31 in the recording paper P conveyance direction. The toner image transferred and formed on the recording paper P by the fixing device 32 It is made to fix to. The fixing device 32 includes a heat heat roller 321 and a pressure roller 322 above and below, and the recording paper P transported on the transfer paper transport belt mechanism 31 (transfer transport belt 313) is subjected to the heat heat roller 321 and the pressure roller. It is made to pass through the nip with 322. Reference numeral 314 denotes a cleaning unit that cleans toner remaining on the surface of the transfer conveyance belt 313.
[0054]
Above the transfer / conveying belt mechanism 31, there are a first image forming station S1, a second image forming station S2, a third image forming station S3, and a fourth image forming station S4 as image forming units. In proximity to the transfer conveyance belt 313, they are arranged in parallel at predetermined intervals in order from the upstream side of the recording paper conveyance path (right side in FIG. 15). In this case, the recording paper P on the transfer conveyance belt 313 is sequentially conveyed to the first image forming station S1, the second image forming station S2, the third image forming station S3, and the fourth image forming station S4. It will be.
[0055]
Each of the image forming stations S1 to S4 has substantially the same configuration, and includes photosensitive drums 33a to 33d as image carriers that rotate in the direction of arrow F shown in FIG. Around the photosensitive drums 33a to 33d, chargers 34a to 34d for charging the photosensitive drums 33a to 33d and forming electrostatic latent images on the outer peripheral surfaces of the photosensitive drums 33a to 33d; Developing devices 35a to 35d for developing the electrostatic latent images formed on the outer peripheral surfaces of the photosensitive drums 33a to 33d into visible images with toner, and toner images developed on the outer peripheral surfaces of the photosensitive drums 33a to 33d. Transfer rollers 36a to 36d that transfer (visible image) to the recording paper P and cleaning devices 37a to 37d that remove toner remaining on the outer peripheral surfaces of the photosensitive drums 33a to 33d are the photosensitive drums 33a to 33d. They are sequentially provided along the rotation direction (arrow F direction).
[0056]
A high voltage {a high voltage having a polarity (+) opposite to the toner charging polarity (-)} for applying a toner image is applied to the transfer rollers 36a to 36d. The transfer rollers 36a to 36d are based on a metal (for example, stainless steel) shaft having a diameter of 8 mm to 10 mm, and the surface thereof is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). The conductive elastic material can uniformly apply a high voltage to the recording paper P.
[0057]
Further, optical scanning units 38a to 38d as optical writing devices are provided above the respective photosensitive drums 33a to 33d. The optical scanning units 38a to 38d write images on the surfaces of the charged photosensitive drums 33a to 33d, for example, with light such as a laser, based on image information transmitted from the outside. As a result, electrostatic latent images are formed on the photosensitive drums 33a to 33d.
[0058]
A pixel signal corresponding to the black component image of the color original image is input to the optical scanning unit 38a of the first image forming station S1 located on the most upstream side in the transport direction of the transfer transport belt 313, and the next second image. The pixel signal corresponding to the cyan component image of the color original image is input to the optical scanning unit 38b of the forming station S2, and the magenta color of the color original image is further input to the optical scanning unit 38c of the next third image forming station S3. A pixel signal corresponding to the component image is input, and a pixel signal corresponding to the yellow color component image of the color original image is input to the optical scanning unit 38d of the fourth image forming station S4 located on the most downstream side. Has been made. Thereby, electrostatic latent images corresponding to the color-converted document image information are formed on the outer peripheral surfaces of the respective photosensitive drums 33a to 33d.
[0059]
The developing device 35a of the first image forming station S1 stores black toner, the developing device 35b of the second image forming station S2 stores cyan toner, and the developing of the third image forming station S3. The device 35c contains magenta toner, and the developing device 35d of the fourth image forming station S4 contains yellow toner. The electrostatic latent images on the outer peripheral surfaces of the respective photosensitive drums 33a to 33d are developed into visible images by the toners of the respective colors, whereby the document image information is reproduced as toner images by the toners of the respective colors. ing.
[0060]
A recording paper suction charger 315 is provided between the first image forming station S 1 and the transfer conveyance belt 313. The recording paper suction charger 315 charges the surface of the transfer / conveying belt 313 and feeds a paper feed mechanism (not shown) from a paper feed cassette 319 provided at the bottom of the multicolor image forming apparatus main body Xa ′. ) Is securely adsorbed onto the transfer / conveying belt 313, so that the recording paper P is not displaced between the first image forming station S1 and the fourth image forming station S4. I am trying to carry it.
[0061]
On the other hand, between the fourth image forming station S <b> 4 and the fixing device 32, a discharger 316 for neutralization is provided almost directly above the drive roller 311. An AC current for separating the recording paper P electrostatically attracted to the transfer / conveyance belt 313 from the transfer / conveyance belt 313 is applied to the discharger 316 for charge removal.
[0062]
When the recording paper P is fed one by one from the paper feeding cassette 319 by the pickup roller 300 and supplied into the guide of the recording paper transport path S of the paper feeding mechanism, the leading end portion of the recording paper P is detected by the sensor. (Not shown) and is temporarily stopped by the pair of registration rollers 310 and 310 based on a detection signal output from the sensor. The recording paper P that has been temporarily stopped by the registration rollers 310 and 310 is delivered to the transfer conveyance belt 313 that rotates in the direction of arrow Z in FIG. 1 in time with the image forming stations S1 to S4. At this time, since the transfer conveyance belt 313 is predeterminedly charged by the recording sheet adsorption charger 315, the recording sheet P is stably conveyed and supplied while passing through the image forming stations S1 to S4. The
[0063]
In each of the image forming stations S1 to S4, toner images of the respective colors are formed, and the toner images of the image forming stations S1 to S4 are formed on the support surface of the recording paper P that is electrostatically attracted and transported by the transfer transport belt 313. Are superimposed and the image is transferred. When the transfer of the image by the fourth image forming station S4 is completed, the recording paper P is sequentially peeled from the transfer conveyance belt 313 from the front end portion thereof by the discharger 316 for discharging, and guided to the fixing device 32. The recording paper P on which the toner image has been fixed in the fixing device 32 is discharged by the discharge rollers 41 and 41 on the upper surface of the image forming apparatus main body Xa ′. The paper tray 43 is sorted by the transport direction switching gate 44 and discharged out of the image forming apparatus X ′.
[0064]
Further, as described above, the image forming apparatus X ′ causes all the photosensitive drums 33a to 33d of the first to fourth image forming stations S1 to S4 to contact the recording paper P on the transfer / conveying belt 313 in order. And a single color image for transferring an image by bringing only the photosensitive drum 33a of the first image forming station S1 on the most upstream side into contact with the recording paper P on the transfer conveying belt 313. Formation can be performed selectively.
[0065]
Further, in the printer control unit 224 of the multicolor image forming apparatus X ′, as shown in FIG. 16, by changing the length of the lighting time without changing the light output when the LED light emitting element is turned on, Light-up time control is performed to form an image with 16-step gradation patterns of K, C, M, and Y, that is, to express 16 steps of gradation for each color component.
[0066]
The pattern shown in FIG. 16 is divided for K, C, M, and Y gradation correction, and the gradation correction of a plurality of optical scanning units 38a to 38d can be performed with one output sheet. Yes. The boundary between the two gradation combination portions can be distinguished, that is, the range in which the gradation can be identified is selected by the pattern number for each color, and the LED writing head 227 for each of the optical scanning units 38a to 38d of each of the image forming stations S1 to S4. The effective lighting time is set and gradation correction is performed. In this case, an effective lighting time value is input from the operation panel as a correction value for each color component. As a result, a subtle change in color tone in a multicolor image is reproduced as compared with a monochromatic image in which it is difficult to visually distinguish the gradation, and the gradation of each component color can be expressed well.
[0067]
In addition, by using a pattern data product in which a plurality of gradation patterns are arranged on a recording member for each color component to form an image, the gradation of each of the plurality of image forming stations S1 to S4 arranged from the gradation pattern arranged for each color is used. A multi-color image forming apparatus X ′ that is excellent in color reproduction, in which tone range correction for each color is set by a single output of pattern data objects, and an effective lighting time is required at the same time. Can do.
[0068]
【The invention's effect】
As described above, according to the present invention, the following effects are exhibited. First, a low density limit tone pattern and a high density limit tone pattern are obtained from the image formation formed by the tone expression assigned based on the maximum lighting time. The number of gradations in the low density region and the number of gradations in the high density region above the gradation pattern at the high density limit are roughly allocated with the reduced number of gradations, respectively, but increases with the reduced number of gradations. The number of gradations in the middle range from the low density limit gradation pattern to the high density limit gradation pattern is finely allocated and the lighting time of the optical writing means corresponding to each allocated gradation is optically written. By setting based on the effective lighting time of the means, it is possible to obtain the best gradation expression according to the image forming characteristics of the image forming unit.
[0070]
  furtherApplying an image formed by forming one gradation pattern on a recording member with two adjacent gradations, and changing the gradation of the adjacent gradation pattern for each step, all the gradation areas Image of the gradation patternofWith subtle gradation differenceVisuallyThe optimum lighting time can be easily obtained.
[0071]
Moreover, by making the adjacent two-gradation pattern a triangular gradation pattern, it is possible to perform an accurate determination while preventing an illusion that the gradation is expressed and making an erroneous determination. The gradation difference can be easily identified by looking at the contours of different patterns.
[0072]
Furthermore, by executing the gradation correction method of the optical writing apparatus on the image forming apparatus, the optimum gradation correction of the optical writing apparatus can be performed according to the image forming characteristics of the image forming apparatus, and an image having excellent gradation characteristics can be obtained. Can be provided.
[0073]
In addition, by forming single-color and multi-color images with a plurality of gradation patterns by a plurality of optical writing means, the optimum gradation correction of the optical writing apparatus according to the image forming characteristics of each of the plurality of image forming units arranged side by side Thus, it is possible to form an image excellent in gradation and color reproduction while suppressing variations in gradation of each image forming unit.
[0074]
In addition, by using an image formed product in which a plurality of gradation patterns are arranged on a recording member for each color component to form an image, the gradation of each of the plurality of arranged image forming units can be identified from the gradation pattern arranged for each color. The range and the effective lighting time are obtained at the same time, and gradation correction for each color is set by outputting the pattern data object once, so that a multicolor image forming apparatus excellent in color reproduction can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an interior of an image forming apparatus that executes a gradation correction method for an optical scanning unit according to a first embodiment of the present invention, as viewed from the front.
FIG. 2 is a block diagram showing a printer control unit and a control target.
FIG. 3 is a perspective view of the vicinity of an LED writing head and a photosensitive drum.
FIG. 4 is a flowchart showing the flow of the gradation correction method for the optical scanning unit by the printer controller.
FIG. 5 is a diagram showing a pattern data object in which 15 group patterns are similarly formed in a strip shape in the sub-scanning direction.
FIG. 6 is a diagram showing a pattern data object in which 15 group patterns are similarly formed in a triangular shape in the sub-scanning direction.
FIG. 7 is a diagram showing the maximum lighting time equally divided for each gradation number.
FIG. 8 is a diagram showing pattern data objects similarly represented by a gradation pattern “4” at a low density limit and a gradation pattern “10” at a high density limit.
FIG. 9 is a diagram showing pattern data objects similarly represented by a low density limit gradation pattern “4” and a high density limit gradation pattern “11”.
FIG. 10 is a front view of the operation unit.
FIG. 11 shows the lighting of the LED write head corresponding to each gradation allocated based on the pattern data object represented by the gradation pattern “4” of the low density limit and the gradation pattern “10” of the high density limit. It is explanatory drawing of the gradation correction which sets time.
FIG. 12 shows the lighting of the LED write head corresponding to each gradation allocated based on the pattern data object represented by the gradation pattern “4” of the low density limit and the gradation pattern “11” of the high density limit. It is explanatory drawing of the gradation correction which sets time.
FIG. 13 shows the maximum LED writing head corresponding to each gradation allocated based on the pattern data object represented by the gradation pattern “4” of the low density limit and the gradation pattern “10” of the high density limit. It is a figure which divides | segments lighting time equally and divided | segmented for every gradation number.
FIG. 14 is a characteristic diagram showing the characteristics of the lighting time of the LED writing head with respect to the gradation number subjected to the same gradation correction.
FIG. 15 is a cross-sectional view of a main part of a multicolor image forming apparatus that executes a gradation correction method for an optical scanning unit according to a second embodiment of the present invention, as viewed from the front.
FIG. 16 is a diagram showing a pattern data object in which 15 group patterns are formed in a strip shape for each color in the sub-scanning direction.
[Explanation of symbols]
200 Photosensitive drum (image carrier)
22 Printer (image forming unit)
222 Optical scanning unit (optical writing device)
224 Printer control unit (control means)
227 LED writing head (optical writing means)
290 Pattern data storage unit (storage unit)
291 Operation unit (selection means)
33a to 33d Photosensitive drum (image carrier)
38a to 38d Optical scanning unit (optical writing device)
P Recording paper (recording member)
X image forming device
X 'Multicolor image forming apparatus

Claims (6)

Tone correction of an optical writing device comprising optical writing means for writing an image on an image carrier based on image information, and controlling the lighting time of the optical writing means to form an image with a plurality of gradation patterns In the method
By making a plurality of gradation patterns stored in advance into one gradation pattern with two adjacent gradations, and changing the gradation of the adjacent gradation patterns for each step, all gradation areas An image formed product is formed by forming an image on a recording member so as to have a gradation pattern of
From these image formed products, a low density limit gradation pattern in which a gradation difference is visually identified and a high density limit gradation pattern in which a gradation difference is visually identified are selected, respectively.
The gradation corresponding to the lighting time of the light writing means up to the low density limit gradation pattern is roughly allocated with a small number of gradations reduced from the number of gradations up to the low density limit gradation pattern, and the high density The gradation corresponding to the lighting time of the optical writing means after the density limit gradation pattern is roughly assigned with a small number of gradations reduced from the number of gradations after the high density limit gradation pattern. Finely assign gradations corresponding to the lighting time of the optical writing means from the low density limit gradation pattern to the high density limit gradation pattern with the number of gradations increased by the reduced number of gradations,
The lighting time of the light writing means corresponding to each of the allocated gradations based on the lighting time of the light writing means when forming the low density limit gradation pattern and the high density limit gradation pattern. A gradation correction method for an optical writing device, wherein: Tone correction of an optical writing device comprising optical writing means for writing an image on an image carrier based on image information, and controlling the lighting time of the optical writing means to form an image with a plurality of gradation patterns In the method
By making a plurality of gradation patterns stored in advance into one gradation pattern with two adjacent gradations, and changing the gradation of the adjacent gradation patterns for each step, all gradation areas And forming an image formed product by forming an image on a recording member with each gradation pattern having a pattern number attached thereto,
By inputting a pattern number corresponding to the low density limit gradation pattern in which the gradation difference is visually identified from the image formed product, the low density limit level corresponding to the input pattern number is input. A tone number is selected and a pattern number corresponding to a high density limit tone pattern whose tone difference is visually identified is input, whereby a high density limit tone corresponding to the input pattern number is input. Select a pattern,
The gradation corresponding to the lighting time of the light writing means up to the low density limit gradation pattern is roughly allocated with a small number of gradations reduced from the number of gradations up to the low density limit gradation pattern, and the high density The gradation corresponding to the lighting time of the optical writing means after the density limit gradation pattern is roughly assigned with a small number of gradations reduced from the number of gradations after the high density limit gradation pattern. Finely assign gradations corresponding to the lighting time of the optical writing means from the low density limit gradation pattern to the high density limit gradation pattern with the number of gradations increased by the reduced number of gradations,
The lighting time of the light writing means corresponding to each of the allocated gradations based on the lighting time of the light writing means when forming the low density limit gradation pattern and the high density limit gradation pattern. A gradation correction method for an optical writing device, wherein: In the gradation correction method of the optical writing device according to claim 1 or 2,
The gradation correction method for an optical writing device, wherein the gradation pattern is a triangular pattern of two adjacent gradations. In the image forming apparatus using the gradation correction method of the optical writing device according to any one of claims 1 to 3,
An image forming unit and a selection unit;
The image forming unit
Optical writing device der having an optical writing means for writing an image on the image carrier based on image information, to form an image in the plurality of gradation patterns by controlling the lighting time of the light writing means Optical writing device,
A storage unit that stores in advance a plurality of gradation patterns that are one gradation pattern with two adjacent gradations;
Control means ,
The plurality of gradation patterns in the storage unit are temporarily written on the image carrier by the optical writing means, and then the gradation patterns written on the image carrier are imaged on a recording member to form an image formed product. And
The selection means includes a low density limit tone pattern in which a tone difference is visually identified and a high density limit tone in which a tone difference is visually identified from among the image formed products created by the image forming unit. Select each gradation pattern ,
The control means reduces the gradation corresponding to the lighting time of the light writing means up to the low density limit gradation pattern selected by the selection means from the number of gradations up to the low density limit gradation pattern. The number of gradations corresponding to the lighting time of the optical writing means after the gradation pattern of the high density limit is reduced from the number of gradations after the gradation pattern of the high density limit. Corresponding to the lighting time of the light writing means from the low density limit gradation pattern to the high density limit gradation pattern with the number of gradations increased by the reduced number of gradations while roughly allocating with a small number of gradations The gradations to be assigned are finely assigned, and the assigned light levels are determined based on the lighting time of the optical writing means when forming the low density limit tone pattern and the high density limit tone pattern. An image forming apparatus comprising a benzalkonium set the lighting time of the light writing means corresponding to each tone was. The image forming apparatus according to claim 4, wherein
An image forming apparatus comprising a plurality of the optical writing means constituting the optical writing apparatus, wherein each of the optical writing means forms a single color image and a multicolor image with a plurality of gradation patterns. . In the image forming apparatus according to claim 5,
The image forming apparatus is an image forming apparatus in which a plurality of gradation patterns are arranged on a recording member for each color component to form an image.

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