JP3707505B2 - Optical printer - Google Patents

Description

【００３１】
パッチ生成はＹＭＣＫの各色について、変調処理部２０７でＲＯＭ３０２から表１の露光条件に対応するデータを読み出し、切り替え部５０５を経てレーザドライバ２０８に送られ、ＹＭＣＫのパッチが次々に中間転写体１０６上に形成される。ただし、４色のパッチが形成されても、給紙手段１１１は駆動されず、被転写材への２次転写も行われない。
【００３２】
中間転写体１０６上に４色のグラデーションパッチが形成されると、パッチ読取りのステップへ進む。１次転写部で４色目のＫのパッチを転写された中間転写体１０６はそのまま送られて、パッチセンサ１２２の対向部へ至る。各色のパッチは中間転写体が送られることによりＬＥＤとフォトセンサを組合せたパッチセンサ１２２で読み取られる。読みとった値はＡ／Ｄ変換器３０４でＡ／Ｄ変換されて、画像処理部２００のＣＰＵ３０１へ送られる。
【００３３】
センサ１２２で読みとられた後、中間転写体１０６上のパッチは１次転写ローラ１０７に転写時とは別のバイアスをかけることにより感光体１０１へそのほとんどが逆転写され、残りはクリーナ１１９で中間転写体１０６から除去される。
【００３４】
ＬＵＴ選択部５０１で、送られたパッチの値に従ってＬＵＴを決定するのが最後のステップである。その値により入力画像データとレーザ光変調のパラメータを対応付ける、前述のＬＵＴ５０２を選択する。表２〜４はその選択の仕方を示す、濃度と選ぶべきＬＵＴの対応を示す表である。表２はＡパッチ用、表３はＢパッチ用、表４はＣパッチ用の対応表である。
【００３５】
【表２】

【００３６】
【表３】

【００３７】
【表４】

【００３８】
また、図１２はＬＵＴ選択の手順を示したものである。まず、イエロー（Ｙ）のＡパッチの濃度測定結果と表２のインデックスを比較し、最も近いインデックスを求める（Ｓ１）。そして、そのインデックスに対応するＬＵＴの番号を同表から読み出す（Ｓ２）。これをＢ、Ｃパッチについても繰り返し、Ａ、Ｂ、Ｃパッチそれぞれから３つのＬＵＴ番号を求める（Ｓ３）。次にこれら３つのＬＵＴ番号を平均し、その平均値に最も近い番号のＬＵＴをＹ用のＬＵＴとして選択する（Ｓ４）。このＳ１〜Ｓ４のステップを残りの色（ＭＣＫ）についても繰り返し、各色のＬＵＴを選択する。選択されるＬＵＴは各色別に用意されＲＯＭ３０２中に格納されている。このようにＬＵＴを色別に用意するのは、各色で露光条件に対する濃度の出力特性が異なるからである。
【００３９】
以上のようにして、ＬＵＴとして適切なものが選択されてパッチ生成モードを抜ける。
【００４０】
次に露光条件を決定づけるＬＵＴ５０２について説明する。 ＬＵＴはデータ変換部５０３で用いられ、画像データの表わす目標画像濃度に対して、露光強度とパルス幅に対応するデータを出力するものである。図７は本実施例のＬＵＴ５０２の内容を示すグラフで、横軸にＬＵＴの入力となる画像濃度、縦軸に露光強度をとってある。このグラフは入力画像データの表わす画像濃度に対して、ＬＵＴにより対応づけられている露光強度とパルス幅の組み合わせ中の露光強度をプロットし、同じパルス幅のものを線で結んだものである。図中実線部が実際にＬＵＴに設定されている組合せの部分、破線部はＬＵＴに設定されていない組合せの部分である。例えば、出力目標濃度１．０が入力されると、それに対してはＬＵＴにはパルス幅７／８で強度６０％の組合せが設定されており、８／８と３２％の組合せは設定されていない。このＬＵＴでは、出力目標濃度が最低濃度から上昇してゆくと、最初パルス幅１／８強度６２％からスタートしてパルス幅１／８のまま強度が増えてゆき、目標濃度０．１８で強度が１００％に達すると、次の濃度０．１８４に対してはパルス幅２／８強度５７％の組合せとなり、再び強度が増やされてゆく。このように、最高濃度の１．４６までの各濃度に対して、パルス幅と強度の組合せが図中の実線で示されるように設定されている。
【００４１】
一方、表１に示した、パッチ信号発生部から出力される、パッチを生成するための露光強度とパルス幅についても同様にプロットしたのが図中Ｐｐ１〜Ｐｐ３である。
【００４２】
このように、パッチは通常画像形成モードで出力される濃度域、すなわち０．１３〜１．４６の間の濃度のものを形成する。つまり、パッチと同じ濃度の画像を通常画像形成モードで出力する。しかし、その同じ濃度を出力するための露光強度とパルス幅の組み合わせは、パッチ生成時と通常の画像生成時では異なっている。さらに、画像形成時の露光強度のグラフはパッチ形成時のグラフより上側にある。つまり、パッチと同じ濃度の画像を形成する際の露光強度は、パッチ生成時に用いられる露光強度より大きい。
【００４３】
また、図８は、横軸は図７と同じだがパルス幅を縦軸にとったものである。画像形成時のパルス幅のグラフは、Ｐｐ１〜Ｐｐ３で表わされるパッチ生成時のパルス幅のグラフより下側にある。つまり、パッチと同じ濃度の画像を形成する際のパルス幅は、パッチ生成時に用いられるパルス幅より狭い。
【００４４】
パッチの濃度測定の結果切り替えられるＬＵＴはもちろん相互に異なっており、それらについて図７、８と同様のグラフを描けば多少の上下はするが、パッチ形成時のグラフとの上下関係は入れ替わらない。
【００４５】
また、図９はＬＵＴ５０２で指定されている露光強度とパルス幅の組合せをプロットしたもので、実線で示される組合せが通常画像形成に用いられる。一方、パッチ生成に用いられる組合せは、同図中点Ｐｐ１〜Ｐｐ３で示されている。この図からわかるように、通常画像形成に用いられる組合せのうちパルス幅が８／８のものは、パッチ生成に用いられる組合せとパルス幅が等しいが、露光強度は５０％以上で、パッチ生成に用いられる４１％以下の組合せと比較して、露光強度が強い。また、通常画像形成に用いられる組合せのうち露光強度が１６％、２８％、４１％のものは、パルス幅が１／８の時に見られるが、これらはパッチ生成に用いられるパルス幅が８／８で露光強度が１６％、２８％、４１％のものと比べて、露光強度は同じだが、パルス幅が短い。
【００４６】
このように、本実施例の光プリンタでは画像形成時にはパッチと同じ濃度を出力するときに、パッチ生成時より狭いパルス幅で強い強度で出力する。このように構成したので、パッチ生成時には環境変動により濃度が大きく変動して、パッチ濃度測定による環境変動の検出精度が高まる。また、画像形成時には環境変動による濃度変動が少ないので、パッチ濃度による画像形成条件の補正後に環境変動あっても出力画像の濃度変動が抑えられる。
【００４７】
この理由を図１０を用いて説明する。図１０（ａ）は強度が強くパルス幅が短いレーザ光と、強度が弱くパルス幅が長い光による露光後の感光体の表面電位を示す図であり、図１０（ｂ）は表面電位に対する出力濃度の関係（γ特性）を示す図である。図１０（ａ）に示す様に、強度が強くパルス幅が短いレーザ光で形成された潜像と、強度が弱くパルス幅が長い光によるものは、電位分布が異なる。図１０（ａ）中右側に示した狭いパルス幅での潜像では、図１０（ｂ）に示す様にパルス中央部の表面電位Ｖ２で出力濃度が飽和する。環境が変動すると図１０（ｂ）の矢印のように現像特性が変動するが、狭いパルス幅で強い強度での潜像の電位Ｖ２では環境が変動しても出力濃度が飽和した部分に入っているので、環境変動が少ない。一方広いパルス幅で弱い強度での潜像の電位Ｖ１はγ特性の過渡領域にあるため、環境変動により濃度が図中Ａ点からＢ点へと大きく変化してしまう。このためにパッチ形成時と画像形成時で環境による濃度変動量が異なるのである。
【００４８】
このような環境変動を考慮したＬＵＴの作成方法として、より直接的に環境変動特性を測定して作成する方法をとることができる。次の実施例は、このようにして作成したＬＵＴを用いた光プリンタの例である。環境に対する安定性とは、環境が変化したときに画像濃度がどれだけ変化するかということであるから、画像濃度Ｄを温度Ｔと湿度Ｈの関数として見て、ｄＤ＝（∂Ｄ／∂Ｔ）ｄＴ＋（∂Ｄ／∂Ｈ）ｄＨの大小により評価できる。ｄＤが大きいということは環境が変化したときの濃度の変動が大きいということなので、これを「環境変動度」と呼ぶことにして、露光強度とパルス幅とパルス密度からなる露光条件が与えられると、その各組合せに対して、各環境毎にこの環境変動度を求めることができる。
【００４９】
本実施例では、次のようにして環境変動度を求めた。露光条件としては、露光強度が０〜２５５、パルス幅が０〜７の範囲から組合せて用いた。各組合せに対して、温湿度を１０℃２０％ＲＨから、温度を５℃刻み、湿度を２０％ＲＨ刻みで３５℃８０％ＲＨまで変化させた環境下で画像形成する。形成された画像濃度は、プリンタ内のパッチ濃度センサで読みとらせて濃度値を求め、出力された画像濃度も別途測定する。各組合せの各温湿度環境に対する環境変動度は、その温湿度環境から５℃ずれた環境、２０％ＲＨずれた環境それぞれでの出力濃度との濃度差を足し合わせて求める。
【００５０】
図１１（ａ）はこのようにして得られた、標準環境（２０℃６０％ＲＨ）での出力濃度と環境変動度の関係を露光強度とパルス幅の組合せ毎に示した図であり、（ｂ）は（ａ）同様の条件について出力濃度の代わりにパッチセンサで読みとった濃度をとったものである。線群は同じパルス幅で強度を変化させたものである。この他の環境についても同様な図を作成できる。（ａ）の出力濃度に比べ（ｂ）のパッチセンサの濃度が高く出ているのは、パッチが比較的反射率の低い中間転写体上に生成されているからである。もちろんパッチセンサの特性を調整したり、中間転写体の反射率を調整すれば、（ａ）と（ｂ）の濃度をほぼ等しくできるが、ここではそのような調整は行なわなかった。さて、ＬＵＴを作成する際にはこの（ａ）図を用いて、同じ濃度を出力できる組合せの中で最も環境変動度が小さくなるように露光条件を選んで、その環境用のＬＵＴを作成する。（ａ）で実線で示した部分が実際のＬＵＴに登録された部分である。一方、パッチ生成のためには（ｂ）を用いて、環境変動度が最大となるように露光条件を選ぶ。本実施例では（ｂ）でプロットしたｄ１〜ｄ９点の組合せのように露光条件を選んだ。これらの露光条件による出力濃度は（ａ）中のｅ１〜ｅ９に対応する。こうすることで、５℃と２０％ＲＨの環境変動による出力濃度差の和が、パッチ生成モードで用いられる組合せでは、通常画像形成モードで用いられる組合せに比べて、大きくなっている。
【００５１】
なお、所定温湿度変動として、温度が５℃、湿度が２０％ＲＨの変化を採用したが、この温度と湿度の変動量の比率は例えば通常プリンタが使用されるようなオフィスでの環境変動傾向を参考にして、水蒸気の分圧が一定という条件で温度に対応して湿度の変化量を定めることもできる。これをより簡便にして、異なる環境として、３０℃８５％ＲＨの高温高湿環境、２０℃５０％ＲＨの標準環境、１０℃１５％ＲＨの低温低湿環境とすることもできる。
【００５２】
また、パッチ生成のための組合せを求めるため、パッチセンサで読みとらせた値を用いたが、出力濃度を用いて組合せを求めても同様の結果が得られる。しかし、パッチセンサの値を用いれば、パッチ測定の結果からどのＬＵＴを選択するかという判断部に用いられる情報が同時に得られ便利である。
【００５３】
さて、光プリンタ、特にカラーの光プリンタでは前述したように中間調の再現が重要である。これまで説明してきた光プリンタでも強度変調と４ビット（９段階）のパルス幅変調を組み合わせることで５ビット（３２段階）の中間調を表現できるが、画素サイズを大きくすることによりパルス幅の変調数を大きくできて中間調の再現をさらに改善することができる。例えば、これまで６００ｄｐｉ当たり８分割できていたのだから、６００ｄｐｉの画素の３つ分の幅の画素とすれば、パルス幅は画素当たり８×３＝２４分割でき、２５段階のパルス幅変調ができるようになる。以下、このような光プリンタの例について説明する。
【００５４】
本実施例は、画像処理部２００の内、レーザドライバ２０８と、変調処理部２０７で用いられるＬＵＴ５０２の構成が、先ほどの実施例と異なる。なお、電子写真プロセス部は前述の実施例と同じなので説明を省略する。
【００５５】
図１３は本実施例の変調処理部２０７の構成を示すブロック図である。本実施例ではＣＰＵ１３０１から強度信号とパルス幅信号の他に、２ビットのパルス密度信号が出力される。
【００５６】
図１４は本実施例のレーザドライバ２０８の構成を示すブロック図である。コード変換器１４０４にはパルス幅信号とパルス密度信号が与えられ、パルススタートタイミングとストップタイミング及び画素周期を示すデータが出力される。これらのタイミングデータはそれぞれラッチ１４０５、１４０６、１４０７に保持される。カウンタ１４１１は６００ｄｐｉの１画素の１／８時間の周期を持つクロック信号をカウントし、カウント信号を比較器１４０８、１４０９、１４１０に出力する。カウンタ１４１１のカウントがラッチ１４０５に保持されたパルススタートタイミングに達すると、比較器１４０８が出力してフリップフロップ１４１２をセットする。カウントがラッチ１４０６のパルスストップタイミングに達すると、比較器１４０９の出力によりフリップフロップ１４１２はリセットされる。カウントがラッチ１４０７の画素周期タイミングに達すると、比較器１４１０が出力して、カウンタ１４１１、及びラッチ１４０５〜１４０７をリセットする。このようにして、パルス密度信号に対応する頻度で強度とパルス幅の変調された信号を半導体レーザに出力できるのである。
【００５７】
表５は本実施例のＬＵＴ５０２の一部分を示したものである。データ変換部５０３に入力される画像データに対して強度、パルス幅、パルス密度が設定されている。データ変換部５０３ではこの表に従って画像データを変換する。
【００５８】
【表５】

【００５９】
パッチ信号発生器５０４は強度２５％、パルス幅７／８、パルス密度６００パルス／インチ（ｐｐｉ）のパッチ生成信号を発生する。この組合せはＬＵＴには設定されておらず画像形成には用いられないが、仮にこの組み合わせで画像形成した場合には出力濃度は０．６となる。出力濃度０．６の画像を通常画像形成モードで出力する際には、パルス密度は２００パルス／インチとなっており、パッチのパルス密度が、画像形成に用いられるパルス密度より高い。また、このパッチ生成に用いられるパルス密度は、画像形成で用いられるパルス密度の最高密度である。
【００６０】
図１５は図１０同様の、潜像の表面電位とγ特性を示す図である。パルス密度が高い場合には、空白部の電位Ｖ３が現像γ特性の過渡領域に位置し、環境変動を受けやすい。このように、パッチの環境変動度を同じ濃度の通常画像の環境変動度より大きくしているのである。前出の実施例では、潜像の中央部の電位（図１０中Ｖ２）をγ特性の過渡領域にすることで環境変動度を大きくしたが、本実施例の方法は空白部の電位を過渡領域にするのである。
【００６１】
また、Ｖ３はパルス密度が高いほど絶対値が大きくなり（図（ａ）中下側へ移動する）、環境変動度が大きくなる。従って、パッチはプリンタの最高パルス密度で生成するとなおよい。
【００６２】
なお、以上濃度を検出するとして説明したが、輝度や明度を検出するようにしても良い。輝度を用いる場合には、受光量を対数変換するステップが不要となるという効果がある。明度を用いる場合には、明度は人間の視覚特性と対応するので、ＬＵＴ選択時の誤差の影響を視覚上最小にすることができるという効果がある。
【００６３】
【発明の効果】
本発明の光プリンタによれば、露光条件として露光強度とパルス幅を変調するとともに、パッチを生成してその濃度測定結果によりプリンタの動作条件を調整するので、環境が変動しても画質の変動が抑えられる。
【００６４】
また、本発明の光プリンタによれば、パッチを生成するときの露光条件と通常の画像を形成するときの露光条件で、環境に対する濃度の変動量が異なるので、パッチによる濃度測定の精度が高まり、わずかな環境変動を検出して補正することができるとともに、通常の画像形成時の濃度変動をさらに抑えることができる。
以上
【図面の簡単な説明】
【図１】本発明に係わる光プリンタの主要断面図。
【図２】プリンタ外部のコンピュータなどのホストから送られたデータに対して、画像処理部２００で行う処理を示すブロック図。
【図３】変調処理部２０７の構成を示すブロック図。
【図４】レーザドライバ２０８の構成を示すブロック図。
【図５】変調処理部２０７で行われる処理の構成を示すブロック図。
【図６】パッチ生成モードへ切り替える方法を示すフローチャート。
【図７】実施例のＬＵＴ５０２の内容を示すグラフ。
【図８】実施例のＬＵＴ５０２の内容を示すグラフ。
【図９】ＬＵＴ５０２で指定されている露光強度とパルス幅の組合せをプロットしたグラフ。
【図１０】強度が強くパルス幅が短いレーザ光と、強度が弱くパルス幅が長い光による露光後の感光体の表面電位及び、表面電位に対する出力濃度の関係（γ特性）を示すグラフ。
【図１１】出力濃度と環境変動度の関係を露光強度とパルス幅の組合せ毎に示したグラフ。
【図１２】ＬＵＴ選択の手順を示したフローチャート。
【図１３】実施例の変調処理部２０７の構成を示すブロック図。
【図１４】実施例のレーザドライバ２０８の構成を示すブロック図。
【図１５】潜像の表面電位とγ特性を示すグラフ。
【図１６】パルス幅と強度に対する出力濃度を示すグラフ。
【符号の説明】
１００ 電子写真プロセス部
１０１ 感光体
１０２ 帯電ローラ
１０３ 露光手段
１０４ 折り返しミラー
１０５Ｙ イエロー現像器
１０５Ｍ マゼンタ現像器
１０５Ｃ シアン現像器
１０５Ｋ ブラック現像器
１０６ 中間転写体
１０７ １次転写ローラ
１０８ １次転写用電源
１０９ 感光体クリーナー
１１０ 除電ランプ
１１１ 給紙手段
１１２ 給紙カセット
１１３ 転写材
１１４ レジストローラ対
１１５ 駆動ローラ
１１６ ２次転写ローラ
１１７ ２次転写用電源
１１８ テンションローラ
１１９ 中間転写体クリーナ
１２０ 定着手段
１２１ 演算手段
１２２ パッチセンサ
２００ 画像処理部
２０１ ホスト
２０２ コード解釈部
２０３ メモリ
２０４ 色変換部
２０５ 多値化処理部
２０６ 色切り替え部
２０７ 変調処理部
２０８ レーザドライバ
３０１、１３０１ ＣＰＵ
３０２、１３０２ ＲＯＭ
３０３、１３０３ ＲＡＭ
３０４ Ａ／Ｄ変換器
４０１ 半導体レーザ
４０２ レーザパワーコントロール回路
４０３ センサ
４０４ コード変換器
４０５、４０６、１４０５、１４０６、１４０７ ラッチ、
４０７、４０８、１４０８、１４０９、１４１０ 比較器
４０９、１４１２ フリップフロップ
４１０、１４１１ カウンタ
５０１ ＬＵＴ選択部
５０２ ＬＵＴ
５０３ データ変換部
５０４ パッチ信号発生部
５０５ 切り替え部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical printer that forms an image on a recording material such as paper or OHP using an electrophotographic method, such as a copying machine, a printer, and a facsimile, and in particular, generates a patch under a predetermined condition and detects its density. The present invention relates to an optical printer that adjusts printer operating conditions such as exposure conditions, development bias, and charging bias.
[0002]
[Prior art]
Conventional optical printers such as laser beam printers and LED printers modulate the pulse width or the exposure intensity to form a halftone image. However, in the case of the type that modulates the pulse width, there is a problem that if the speed of the printer is increased, the modulation of the pulse width must be increased accordingly. On the other hand, the type that modulates the exposure intensity has a problem that the density of the output image is easily affected by the environmental fluctuation of the printer.
[0003]
On the other hand, in the apparatus disclosed in US Pat. No. 5,371,524, the pulse width is determined by the upper 2 bits and the exposure intensity is determined by the lower 6 bits of the 8-bit digital image data given to each pixel. Thus, both the pulse width and the exposure intensity are modulated. This makes it possible to increase the speed and make it less susceptible to environmental fluctuations.
[0004]
[Problems to be solved by the invention]
However, simply assigning the upper bits and lower bits to the pulse width and intensity is improved compared to the type that modulates only the exposure intensity, but there is still a problem that the output image fluctuates due to environmental fluctuations. It was.
[0005]
The present invention has been made in view of these problems, and an object of the present invention is to provide an image forming apparatus that can cope with high speed and can maintain stable image quality even when the environment fluctuates. is there.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, an optical printer of the present invention is an optical printer that obtains an output image by developing a latent image obtained by irradiating light on a photoconductor with toner and transferring it onto a recording material. The image forming apparatus has a normal image forming mode for forming an image based on image data given from the outside of the printer and a patch generation mode for adjusting the operating conditions of the printer. Light is applied to the photoconductor according to the exposure conditions given for each pixel. Exposure as an exposure condition of the exposure unit in the normal image formation mode based on the result of density measurement by the exposure unit for irradiation, the density measurement unit for measuring the density of the patch formed in the patch generation mode, and the density measurement unit Control means for modulating intensity and pulse width, said control means for adjusting exposure light according to a signal representing exposure intensity and pulse width, density measurement Based on the result of density measurement by the stage, a determination means for determining a rule for converting pixel data into a combination of exposure intensity and pulse width, and pixel data is converted into a combination of exposure intensity and pulse width according to the rule determined by the determination means. Conversion means for outputting a first signal representing the signal, signal generating means for generating a second signal representing the exposure light intensity and pulse width for forming the patch, the first signal in the normal image forming mode, and the patch generation mode. Comprises a switching means for sending a second signal to the exposure control means, and a combination of exposure intensity and pulse width represented by the first signal when outputting an image having the same density as the patch. The first image by Combination of exposure intensity and pulse width represented by the second signal The second image, and the density fluctuation amounts ΔD1 and ΔD2 with respect to the predetermined temperature and humidity fluctuations of the respective images are in a relationship of ΔD1 <ΔD2. Features.
[0010]
Furthermore, the optical printer of the present invention is characterized in that at least one of the first signals corresponding to various pixel data has the same exposure intensity as that of the second signal and only a pulse width is short.
[0011]
Furthermore, the optical printer of the present invention is characterized in that at least one of the first signals corresponding to various pixel data has the same pulse width as that of the second signal and only the exposure intensity is high.
[0012]
In the optical printer of the present invention, the conversion unit converts the pixel data into a combination of exposure intensity, pulse width, and pulse density according to the rule determined by the determination unit, and at a first frequency according to the pulse density. A conversion means for outputting a first signal representing the exposure intensity and the pulse width and a second signal representing the exposure intensity and the pulse width for forming the patch are generated at a second frequency corresponding to a predetermined pulse density. A signal generation unit; and a switching unit configured to send a first signal to the exposure unit in the normal image formation mode and a second signal in the patch generation mode. The first generation unit outputs an image having the same density as the patch. The pulse density corresponding to the frequency is lower than the pulse density corresponding to the second frequency.
[0013]
Furthermore, the optical printer of the present invention is characterized in that the pulse density corresponding to the second frequency is the same as the highest density of the pulse density corresponding to the first frequency output from the conversion means.
[0014]
[Action]
FIG. 16A shows the output density when an image is formed while changing the intensity by fixing the laser beam to a certain pulse width, and a to h are each 1/8 pixel pulse width. 2/8 pixel,..., 8/8 (1) pixel width. As can be seen from the figure, for example, when a density of 0.8 is obtained, even if the pulse width is 8/8 and the intensity is 25%, the pulse width is 7/8 and the intensity is 32%, 6/8 is 48%, or 5 / The same density of 0.8 can be output even with a combination of 8 and 82%.
[0015]
FIG. 16 (b) is a graph similar to FIG. 16 (a), but simultaneously shows the output density when the environment where the apparatus is placed is different in the case of e of pulse width 5/8 and h of 8/8. It is. In a combination of a pulse width of 5/8 and an intensity of 82% that can output a density of 0.8, the output density changes by ΔDe = 0.03 when the environment changes from low temperature and low humidity to high temperature and high humidity. On the other hand, in the combination of the pulse width of 8/8 and the intensity of 25% that have been able to output the same concentration of 0.8, the concentration change when changing from low temperature and low humidity to high temperature and high humidity is ΔDh = 0.3. As described above, the amount of environmental change varies depending on the combination of the laser intensity and the pulse width.
[0016]
The present invention utilizes this relationship, and generates a patch for adjusting the printer operating conditions with a combination of an intensity and a pulse width (for example, a combination of the above-described pulse width 8/8 and an intensity of 25%) that causes large environmental fluctuations. The detection accuracy is increased. In addition, by setting the image forming condition based on the detection result, it is possible to appropriately cope with slight environmental fluctuations. Furthermore, by using a combination that reduces environmental fluctuations (for example, the combination of the above pulse width 5/8 and intensity 82%) for actual image formation, environmental stability, especially in one screen where patch generation is not possible on the way. Concentration stability against environmental fluctuations can be increased.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a main sectional view of an optical printer according to the present invention. Such optical printers are roughly divided into an electrophotographic process unit 100 and an image processing unit 200 (described in FIG. 2) described later. The configuration of the electrophotographic process unit 100 and the operation during image formation will be described with reference to FIG. The charging roller 102 charges the photosensitive member 101 to a uniform potential (for example, −700 V). A laser beam having a resolution of 600 dpi (dot per inch) formed by the exposure unit 103 is guided onto the photoconductor 101 by the folding mirror 104 to form an electrostatic latent image. Next, of the one-component contact type developing device 105 that can be contacted / separated in the direction of the arrow in FIG. The toner is reversely developed and visualized on the photosensitive member 101. The visualized yellow toner is obtained by dispersing the carbon in ETFE (ethylene tetrafluoroethylene copolymer) and the intermediate transfer member 106 adjusted to an appropriate resistance on the primary transfer roller 107 and the primary transfer power source 108. Thus, a bias having a polarity opposite to that of the toner is applied, and the toner is transferred by the action of the electric field. The untransferred toner on the photoconductor 101 is collected by a photoconductor cleaner 109 that is cleaned by bringing the blade into contact therewith, and then the photoconductor potential is reset by the charge eliminating lamp 110. The same operation is repeated for the magenta developing unit 105M, the cyan developing unit 105C, and the black developing unit 105K in synchronization with the position of the intermediate transfer member 106 and the light emission timing of the exposure unit 103, whereby each color toner is transferred onto the intermediate transfer member 106. Are superimposed to form a full color image. During this time, the secondary transfer roller 116 and the intermediate transfer body cleaner 119 are in a separated state. On the other hand, the recording material 113 such as paper or OHP is conveyed from the paper feeding cassette 112 to the registration roller pair 114 by the paper feeding means 111 and then synchronized with the full color image on the intermediate transfer member 106 and the driving roller 115. The sheet is conveyed to a secondary transfer portion formed by a secondary transfer roller 116 that can be contacted and separated in the middle arrow direction. In the secondary transfer portion, the secondary transfer roller 116 contacts the intermediate transfer member 106 in synchronization with the recording material 113 to form and press the nip portion and calculate the voltage obtained from the primary transfer power source 108. The voltage determined in 121 is constant voltage controlled by the secondary transfer power source 117, and a full color toner image is formed on the transfer material 113 by the action of the electric field. Thereafter, the recording material 113 is fixed by the fixing unit 120 and discharged out of the apparatus.
[0018]
The electrophotographic process unit 100 is further provided with a patch sensor 122 at a position facing the surface of the intermediate transfer member 106 downstream from the primary transfer roller. The patch sensor 122 is a sensor in which an LED and a photo sensor are combined. The read value is A / D converted and sent to the image processing unit 200.
[0019]
The optical printer of this embodiment has a normal image forming mode and a patch generation mode as operation modes. In the normal image forming mode, an image is formed and output based on data sent from a host such as a personal computer outside the printer. In the patch generation mode, an image is formed based on data inside the printer, and the density of the formed image is measured by the patch sensor 122 in the printer without being output to the outside of the printer.
[0020]
Next, processing performed by the image processing unit 200 will be described. FIG. 2 is a block diagram showing processing performed by the image processing unit 200 on data sent from a host such as a computer outside the printer. Data sent from the host 201 includes a code for controlling the printer, a character code, vector data, and image data. The sent data is interpreted by the code interpretation unit 202 as to which type of data, and is converted into a bitmap if necessary. The image data and the bitmap-converted image data are stored in the memory 203 as 8-bit RGB information. The stored data is read out for each pixel in synchronization with the printing operation, converted into CMYK data by the color conversion processing unit 204, converted into 5-bit data for each color by the multi-value processing unit 205, and a color switching unit. In 206, the developing device is selected, and only the image data of the color being printed is sent to the modulation processing unit 207, where it is converted into a signal indicating the exposure intensity and pulse width, and sent to the laser driver 208.
[0021]
FIG. 3 is a block diagram illustrating a configuration of the modulation processing unit 207. The modulation processing unit 207 includes a CPU 301, a ROM 302 and a RAM 303 that can exchange data with the CPU 301, and a peripheral circuit (not shown) for driving them. The CPU 301 receives the single color image data selected by the color switching unit 206, the mode signal indicating the normal image formation mode or the patch generation mode, and the detection signal from the patch sensor 122 via the A / D converter 304. An intensity signal and a pulse width signal are output. In the optical printer of this embodiment, the image data input to the CPU 301 is 5 bits for each color, the output intensity data is 8 bits, and the pulse width data is 4 bits.
[0022]
FIG. 4 is a block diagram showing the configuration of the laser driver 208. The laser driver 208 includes a laser power control circuit 402 for controlling the intensity of the semiconductor laser 401, a sensor 403 for monitoring the output of the semiconductor laser 401, and circuit portions 404 to 410 for generating a pulse corresponding to the pulse width signal. It is configured. The code converter 404 receives the 4-bit pulse width signal output from the modulation processing unit 207 as an address, and outputs two 4-bit signals. Each signal is data indicating the timing for starting and stopping the pulse in one pixel period. Each data is held in latches 405 and 406 for one pixel period. The counter 410 counts clock signals having a period of 1/8 hour of one pixel. The count signal is input to the comparators 407 and 408, and when the start timing held in the latch 405 is reached, the comparator 407 outputs and sets the flip-flop 409. When the counter output reaches the stop timing, the flip-flop 409 is reset by the output of the comparator 408. Thus, the output of the flip-flop 409 becomes a pulse having a width corresponding to the pulse width signal, and is input to the laser power control circuit 402. By setting the start timing and stop timing according to the pulse width in this way, the dots formed by the exposure pulse are aligned with the center position of each pixel.
[0023]
The laser power control circuit 402 compares the signal obtained by D / A converting the level of the input intensity signal and adjusting the level with the signal returned from the sensor 403, and compares the level of the laser according to the exposure intensity signal. Generate drive current. Further, the laser power control circuit 402 turns on / off the output by a pulse output from the flip-flop 409. Thus, the laser 401 is driven by a signal in which both the exposure intensity and the pulse width are modulated.
[0024]
In this embodiment, the circuit portion for generating the pulse corresponding to the pulse width signal is a synchronous digital circuit as described above, but it is obtained by D / A conversion of the pulse width signal. A pulse having a predetermined width may be generated by comparing the level and the level of the reference triangular wave. In addition, the laser power control circuit uses a type that can be turned on / off by inputting a pulse signal. However, the one that can only perform power control is used, and on / off based on the pulse width is the generated pulse and the output of the power control circuit. May be performed by connecting them with an AND circuit. Here, in order to modulate the exposure intensity, a method of changing the driving current of the semiconductor laser is adopted here, but this method can also be applied to the case of exposing with an LED. In addition to this method, an optical element capable of changing the transmittance in the middle of the optical path may be provided to change the characteristics thereof.
[0025]
FIG. 5 is a block diagram illustrating a configuration of processing performed by the modulation processing unit 207. The modulation processing unit 207 includes a lookup table (LUT) selection unit 501, a data conversion unit 503, a patch signal generation unit 504, and a switching unit 505, all of which are the CPU 301, ROM 302, and RAM 303 shown in FIG. It is realized by software processing executed on a circuit consisting of
[0026]
The lookup table (LUT) selection unit 501 selects an appropriate LUT from the LUT 502 that matches each environmental condition stored in the ROM 302 based on the output from the patch sensor 122 and refers to the data conversion unit 503. To be set in the RAM 303. A data conversion unit 503 receives image data from the color switching unit 206 and converts the image data into exposure intensity and pulse width signals using the LUT set in the RAM 303. The patch signal generator 504 reads out and outputs exposure intensity and pulse width data used when generating a patch from the ROM 302. The switching unit 505 switches between the output from the data conversion unit 503 and the output from the patch signal generation unit 504 based on the information about the normal image formation mode or the patch generation mode.
[0027]
Since the patch signal generation unit 504 of this embodiment stores the patch data in a memory area different from that of the image data, the data being received and the patch data are not mixed and the memory management is easy. Further, since this memory area can be managed by a CPU different from the CPU that receives and develops image data from the host, the processing is performed in parallel and the processing speed can be increased.
[0028]
Next, a method for switching to the patch generation mode will be described with reference to FIG. When receiving data from the host computer, the optical printer according to the present embodiment analyzes the contents by the code analysis unit 202, and continues processing in the case of character code or vector data, and in the case of image data, the patch. Enter production mode. In the case of image data, since the amount of data is generally large and it takes time to communicate data, there is a certain amount of time from when data is received until when printing is actually started. By generating a patch during this period, it is possible to adjust the printer operating conditions without increasing the time until image output. Furthermore, image data is often a natural image, and reproduction of a halftone density portion is more important in terms of image quality than a line drawing such as a graph described by vector data. In the optical printer of this embodiment, since the adjustment process of the printer operating conditions is performed before the output of the image data, the reproduction of the halftone can be stabilized.
[0029]
The patch generation mode is performed in three steps: a step of generating a patch on the intermediate transfer member 106, a step of reading the density of the patch, and a step of determining the LUT. The step of generating the patch is basically the same as the normal printing operation except that the image is not transferred to the transfer material. The patch forms a gradation patch group of each color including a low density patch in order to stabilize a halftone level important for gradation reproduction. In the optical printer of this embodiment, pulse widths are shown in Table 1 in order to generate patches corresponding to output densities of 0.15, 0.6, and 1.2 (referred to as A patch, B patch, and C patch, respectively). The patch is generated by setting as follows. In actual image output, in order to obtain these output densities, the combination used for patch generation is not used as will be described later.
[0030]
[Table 1]

[0031]
For each color of YMCK, the modulation processing unit 207 reads out data corresponding to the exposure conditions shown in Table 1 from the ROM 302 and sends the data to the laser driver 208 via the switching unit 505. The YMCK patches are successively transferred to the intermediate transfer member 106. Formed. However, even if the four-color patch is formed, the paper feeding unit 111 is not driven and the secondary transfer to the transfer material is not performed.
[0032]
When the four-color gradation patch is formed on the intermediate transfer member 106, the process proceeds to the patch reading step. The intermediate transfer body 106 to which the K-color patch of the fourth color is transferred at the primary transfer portion is sent as it is, and reaches the opposite portion of the patch sensor 122. Each color patch is read by a patch sensor 122 that combines an LED and a photosensor by sending an intermediate transfer member. The read value is A / D converted by the A / D converter 304 and sent to the CPU 301 of the image processing unit 200.
[0033]
After being read by the sensor 122, most of the patches on the intermediate transfer member 106 are reversely transferred to the photosensitive member 101 by applying a bias different from that at the time of transfer to the primary transfer roller 107, and the rest is the cleaner 119. It is removed from the intermediate transfer member 106.
[0034]
In the last step, the LUT selection unit 501 determines the LUT according to the sent patch value. The LUT 502 described above that associates the input image data with the laser light modulation parameter according to the value is selected. Tables 2 to 4 are tables showing the correspondence between the density and the LUT to be selected. Table 2 is for A patch, Table 3 is for B patch, and Table 4 is for C patch.
[0035]
[Table 2]

[0036]
[Table 3]

[0037]
[Table 4]

[0038]
FIG. 12 shows the LUT selection procedure. First, the density measurement result of the yellow (Y) A patch is compared with the index shown in Table 2 to obtain the closest index (S1). Then, the LUT number corresponding to the index is read from the table (S2). This is repeated for the B and C patches, and three LUT numbers are obtained from each of the A, B, and C patches (S3). Next, these three LUT numbers are averaged, and the LUT having the number closest to the average value is selected as the LUT for Y (S4). The steps S1 to S4 are repeated for the remaining colors (MCK), and the LUT for each color is selected. The selected LUT is prepared for each color and stored in the ROM 302. The reason why the LUT is prepared for each color is that the output characteristics of the density with respect to the exposure conditions differ for each color.
[0039]
As described above, an appropriate LUT is selected and the patch generation mode is exited.
[0040]
Next, the LUT 502 that determines the exposure conditions will be described. The LUT is used in the data conversion unit 503 and outputs data corresponding to the exposure intensity and the pulse width for the target image density represented by the image data. FIG. 7 is a graph showing the contents of the LUT 502 of this embodiment, with the horizontal axis representing the image density serving as the input of the LUT and the vertical axis representing the exposure intensity. This graph plots the exposure intensity in the combination of the exposure intensity and the pulse width correlated by the LUT against the image density represented by the input image data, and connects the same pulse width with a line. In the figure, the solid line portion is the portion of the combination that is actually set in the LUT, and the broken line portion is the portion of the combination that is not set in the LUT. For example, when an output target density of 1.0 is input, a combination of 60% intensity with a pulse width of 7/8 is set in the LUT, and a combination of 8/8 and 32% is set. Absent. In this LUT, when the output target density increases from the lowest density, the intensity starts with the pulse width 1/8 intensity 62% and increases with the pulse width 1/8, and the intensity reaches the target density 0.18. Reaches 100%, the next density of 0.184 is a combination of 2/8 pulse width and 57% intensity, and the intensity is increased again. Thus, for each density up to the maximum density of 1.46, the combination of pulse width and intensity is set as indicated by the solid line in the figure.
[0041]
On the other hand, the exposure intensities and pulse widths for generating patches output from the patch signal generator shown in Table 1 are also plotted in the same manner as Pp1 to Pp3 in the figure.
[0042]
As described above, the patch forms a density range output in the normal image forming mode, that is, a density between 0.13 and 1.46. That is, an image having the same density as the patch is output in the normal image forming mode. However, the combination of the exposure intensity and the pulse width for outputting the same density differs between the patch generation and the normal image generation. Furthermore, the graph of the exposure intensity at the time of image formation is above the graph at the time of patch formation. That is, the exposure intensity at the time of forming an image having the same density as the patch is higher than the exposure intensity used when generating the patch.
[0043]
In FIG. 8, the horizontal axis is the same as FIG. 7, but the pulse width is taken on the vertical axis. The graph of the pulse width at the time of image formation is below the graph of the pulse width at the time of patch generation represented by Pp1 to Pp3. That is, the pulse width when an image having the same density as the patch is formed is narrower than the pulse width used when the patch is generated.
[0044]
Of course, the LUTs that are switched as a result of the patch density measurement are different from each other. If the same graphs as those shown in FIGS. 7 and 8 are drawn, they may move up and down slightly, but the vertical relationship with the graph at the time of patch formation does not change. .
[0045]
FIG. 9 is a plot of the combination of exposure intensity and pulse width specified in the LUT 502, and the combination indicated by the solid line is used for normal image formation. On the other hand, combinations used for patch generation are indicated by points Pp1 to Pp3 in the figure. As can be seen from this figure, among the combinations used for normal image formation, those with a pulse width of 8/8 have the same pulse width as the combination used for patch generation, but the exposure intensity is 50% or more. Compared with the combination of 41% or less used, the exposure intensity is strong. Further, among combinations used for normal image formation, those with exposure intensity of 16%, 28%, and 41% are seen when the pulse width is 1/8, but these have a pulse width used for patch generation of 8 / 8, the exposure intensity is the same, but the pulse width is shorter than those of exposure intensity of 16%, 28%, and 41%.
[0046]
As described above, in the optical printer of this embodiment, when the same density as that of the patch is output at the time of image formation, it is output with a stronger intensity with a narrower pulse width than that at the time of patch generation. With this configuration, when the patch is generated, the density greatly fluctuates due to the environmental fluctuation, and the detection accuracy of the environmental fluctuation due to the patch density measurement is increased. In addition, since there are few density fluctuations due to environmental fluctuations during image formation, density fluctuations in the output image can be suppressed even if there are environmental fluctuations after correcting the image forming conditions based on the patch density.
[0047]
The reason for this will be described with reference to FIG. FIG. 10A is a diagram showing the surface potential of the photosensitive member after exposure by laser light having a high intensity and a short pulse width and light having a low intensity and a long pulse width, and FIG. 10B shows an output with respect to the surface potential. It is a figure which shows the relationship (gamma characteristic) of density | concentration. As shown in FIG. 10A, the potential distribution differs between a latent image formed with laser light having a high intensity and a short pulse width, and a light image having a low intensity and a long pulse width. In the latent image with a narrow pulse width shown on the right side in FIG. 10A, the output density is saturated at the surface potential V2 at the center of the pulse as shown in FIG. 10B. When the environment fluctuates, the development characteristics fluctuate as shown by the arrows in FIG. 10B. However, the potential V2 of the latent image with a narrow pulse width and strong intensity enters the portion where the output density is saturated even if the environment fluctuates. As a result, there is little environmental fluctuation. On the other hand, since the potential V1 of the latent image with a wide pulse width and weak intensity is in the transient region of the γ characteristic, the density greatly changes from the point A to the point B in the figure due to environmental fluctuations. For this reason, the amount of density fluctuation due to the environment differs between patch formation and image formation.
[0048]
As a method of creating an LUT in consideration of such environmental fluctuations, a method of measuring and creating environmental fluctuation characteristics more directly can be used. The following embodiment is an example of an optical printer using the LUT created as described above. The stability to the environment means how much the image density changes when the environment changes. Therefore, when the image density D is seen as a function of the temperature T and the humidity H, dD = (∂D / ∂T ) It can be evaluated by the magnitude of dT + (∂D / ∂H) dH. When dD is large, the variation in density when the environment changes is large, so this is called “environmental variation”, and given an exposure condition consisting of exposure intensity, pulse width, and pulse density. For each combination, the degree of environmental variation can be obtained for each environment.
[0049]
In this example, the degree of environmental variability was determined as follows. As exposure conditions, a combination of exposure intensity from 0 to 255 and pulse width from 0 to 7 was used. For each combination, images are formed in an environment where the temperature and humidity are changed from 10 ° C. and 20% RH to a temperature of 5 ° C. and the humidity is changed from 20 ° C. to 35 ° C. and 80% RH. The formed image density is read by a patch density sensor in the printer to obtain a density value, and the output image density is also measured separately. The degree of environmental variability for each temperature / humidity environment of each combination is obtained by adding the density differences from the output density in the environment deviated by 5 ° C. and the environment deviated by 20% RH from the temperature / humidity environment.
[0050]
FIG. 11A is a diagram showing the relationship between the output density and the environmental variation in the standard environment (20 ° C., 60% RH) obtained for each combination of exposure intensity and pulse width. b) shows the density read by the patch sensor instead of the output density under the same conditions as in (a). The line group is one in which the intensity is changed with the same pulse width. Similar diagrams can be created for other environments. The reason why the density of the patch sensor of (b) is higher than the output density of (a) is because the patch is generated on an intermediate transfer member having a relatively low reflectance. Of course, the density of (a) and (b) can be made substantially equal by adjusting the characteristics of the patch sensor or adjusting the reflectance of the intermediate transfer member, but such adjustment was not performed here. When creating an LUT, using this figure (a), an exposure condition is selected so as to minimize the degree of environmental variation among combinations that can output the same density, and an LUT for that environment is created. . A portion indicated by a solid line in (a) is a portion registered in an actual LUT. On the other hand, for patch generation, the exposure condition is selected using (b) so that the degree of environmental variation is maximized. In this embodiment, the exposure conditions are selected like the combination of d1 to d9 plotted in (b). The output density under these exposure conditions corresponds to e1 to e9 in (a). By doing so, the sum of the output density differences due to environmental fluctuations of 5 ° C. and 20% RH is larger in the combination used in the patch generation mode than in the combination used in the normal image forming mode.
[0051]
As the predetermined temperature / humidity fluctuation, a change of temperature 5 ° C. and humidity 20% RH is adopted, but the ratio of the fluctuation amount of the temperature and humidity is, for example, an environmental fluctuation tendency in an office where a normal printer is used. As a reference, the amount of change in humidity can also be determined according to temperature under the condition that the partial pressure of water vapor is constant. This can be made simpler and different environments can be a high temperature and high humidity environment of 30 ° C. and 85% RH, a standard environment of 20 ° C. and 50% RH, and a low temperature and low humidity environment of 10 ° C. and 15% RH.
[0052]
Further, in order to obtain a combination for generating a patch, a value read by the patch sensor is used. However, a similar result can be obtained even if a combination is obtained using the output density. However, if the value of the patch sensor is used, it is convenient to simultaneously obtain information used by the determination unit as to which LUT is selected from the patch measurement result.
[0053]
In an optical printer, particularly a color optical printer, halftone reproduction is important as described above. Even the optical printers described so far can express halftones of 5 bits (32 steps) by combining intensity modulation and 4 bits (9 steps) of pulse width modulation, but by increasing the pixel size, modulation of the pulse width is possible. The number can be increased to further improve halftone reproduction. For example, since it has been divided into 8 per 600 dpi so far, if the width is 3 pixels of 600 dpi pixels, the pulse width can be divided into 8 × 3 = 24 per pixel, and 25 steps of pulse width modulation can be performed. It becomes like this. Hereinafter, an example of such an optical printer will be described.
[0054]
In the present embodiment, the configuration of the LUT 502 used in the laser driver 208 and the modulation processing unit 207 in the image processing unit 200 is different from the previous embodiment. Since the electrophotographic process unit is the same as that in the above-described embodiment, the description thereof is omitted.
[0055]
FIG. 13 is a block diagram showing the configuration of the modulation processing unit 207 of this embodiment. In this embodiment, the CPU 1301 outputs a 2-bit pulse density signal in addition to the intensity signal and the pulse width signal.
[0056]
FIG. 14 is a block diagram showing the configuration of the laser driver 208 of this embodiment. The code converter 1404 is supplied with a pulse width signal and a pulse density signal, and outputs data indicating the pulse start timing, stop timing, and pixel period. These timing data are held in latches 1405, 1406, and 1407, respectively. The counter 1411 counts a clock signal having a 1/8 hour period of one pixel of 600 dpi, and outputs the count signal to the comparators 1408, 1409, and 1410. When the count of the counter 1411 reaches the pulse start timing held in the latch 1405, the comparator 1408 outputs and sets the flip-flop 1412. When the count reaches the pulse stop timing of the latch 1406, the flip-flop 1412 is reset by the output of the comparator 1409. When the count reaches the pixel cycle timing of the latch 1407, the comparator 1410 outputs and resets the counter 1411 and the latches 1405 to 1407. In this way, a signal whose intensity and pulse width are modulated can be output to the semiconductor laser at a frequency corresponding to the pulse density signal.
[0057]
Table 5 shows a part of the LUT 502 of this embodiment. The intensity, pulse width, and pulse density are set for the image data input to the data conversion unit 503. The data converter 503 converts the image data according to this table.
[0058]
[Table 5]

[0059]
The patch signal generator 504 generates a patch generation signal having an intensity of 25%, a pulse width of 7/8, and a pulse density of 600 pulses / inch (ppi). This combination is not set in the LUT and is not used for image formation. However, if an image is formed with this combination, the output density is 0.6. When an image having an output density of 0.6 is output in the normal image forming mode, the pulse density is 200 pulses / inch, and the pulse density of the patch is higher than the pulse density used for image formation. The pulse density used for patch generation is the highest pulse density used for image formation.
[0060]
FIG. 15 is a diagram showing the surface potential and γ characteristics of the latent image, similar to FIG. When the pulse density is high, the potential V3 of the blank portion is located in the transition region of the development γ characteristic and is susceptible to environmental fluctuations. In this way, the environmental variation degree of the patch is made larger than that of the normal image having the same density. In the previous embodiment, the potential of the environment is increased by setting the potential at the center of the latent image (V2 in FIG. 10) to the transient region of the γ characteristic. Make it an area.
[0061]
In addition, the absolute value of V3 increases as the pulse density increases (moves downward in the figure (a)), and the degree of environmental variation increases. Therefore, it is even better to generate the patch at the highest pulse density of the printer.
[0062]
In addition, although demonstrated as detecting a density | concentration above, you may make it detect a brightness | luminance and a brightness. When luminance is used, there is an effect that a step of logarithmically converting the amount of received light is not necessary. When the brightness is used, the brightness corresponds to the human visual characteristic, so that the effect of the error at the time of selecting the LUT can be minimized.
[0063]
【The invention's effect】
The present invention With this optical printer, the exposure intensity and pulse width are modulated as exposure conditions, and patches are generated and the printer's operating conditions are adjusted based on the density measurement results. It is done.
[0064]
Also, The present invention According to the optical printer, since the amount of variation in density with respect to the environment differs between the exposure condition for generating a patch and the exposure condition for forming a normal image, the accuracy of density measurement with the patch increases, and the slight environment Variations can be detected and corrected, and density variations during normal image formation can be further suppressed.
that's all
[Brief description of the drawings]
FIG. 1 is a main cross-sectional view of an optical printer according to the present invention.
FIG. 2 is a block diagram showing processing performed by the image processing unit 200 on data sent from a host such as a computer outside the printer.
3 is a block diagram showing the configuration of a modulation processing unit 207. FIG.
4 is a block diagram showing a configuration of a laser driver 208. FIG.
FIG. 5 is a block diagram showing a configuration of processing performed by a modulation processing unit 207;
FIG. 6 is a flowchart illustrating a method for switching to a patch generation mode.
FIG. 7 is a graph showing the contents of an LUT 502 according to the embodiment.
FIG. 8 is a graph showing the contents of an LUT 502 according to the embodiment.
FIG. 9 is a graph plotting combinations of exposure intensity and pulse width specified by LUT502.
FIG. 10 is a graph showing the surface potential of a photoconductor after exposure with laser light having a high intensity and a short pulse width and light having a low intensity and a long pulse width, and the relationship (γ characteristic) of the output density to the surface potential.
FIG. 11 is a graph showing the relationship between output density and environmental variation for each combination of exposure intensity and pulse width.
FIG. 12 is a flowchart showing a procedure for selecting an LUT.
FIG. 13 is a block diagram illustrating a configuration of a modulation processing unit 207 according to the embodiment.
FIG. 14 is a block diagram illustrating a configuration of a laser driver 208 according to the embodiment.
FIG. 15 is a graph showing the surface potential and γ characteristics of a latent image.
FIG. 16 is a graph showing output density with respect to pulse width and intensity.
[Explanation of symbols]
100 Electrophotographic process department
101 photoconductor
102 Charging roller
103 Exposure means
104 Folding mirror
105Y Yellow developer
105M Magenta developer
105C cyan developer
105K black developer
106 Intermediate transfer member
107 Primary transfer roller
108 Power supply for primary transfer
109 Photoconductor cleaner
110 Static elimination lamp
111 Paper feeding means
112 Paper cassette
113 Transfer material
114 Registration Roller Pair
115 Drive roller
116 Secondary transfer roller
117 Power supply for secondary transfer
118 Tension roller
119 Intermediate transfer member cleaner
120 fixing means
121 Calculation means
122 Patch sensor
200 Image processing unit
201 hosts
202 Code interpretation part
203 memory
204 color converter
205 Multi-value processor
206 Color switching part
207 Modulation processor
208 Laser driver
301, 1301 CPU
302, 1302 ROM
303, 1303 RAM
304 A / D converter
401 Semiconductor laser
402 Laser power control circuit
403 sensor
404 code converter
405, 406, 1405, 1406, 1407 latch,
407, 408, 1408, 1409, 1410 comparators
409, 1412 flip-flop
410, 1411 counter
501 LUT selection part
502 LUT
503 Data converter
504 Patch signal generator
505 switching unit

Claims (5)

In an optical printer that obtains an output image by developing a latent image obtained by irradiating light on a photoreceptor with toner and transferring it onto a recording material, an image is usually formed based on image data given from the outside of the printer An image forming mode and a patch generation mode for adjusting the operating conditions of the printer are formed in the patch generation mode, and an exposure unit for irradiating light to the photoconductor according to the exposure condition given for each pixel. Density measuring means for measuring the density of the patch, and control means for modulating exposure intensity and pulse width as exposure conditions of the exposure means in the normal image formation mode based on the result of density measurement by the density measuring means, The control means exposes the pixel data based on the result of density measurement by the exposure control means and density measurement means for modulating the exposure light according to the signal representing the exposure intensity and pulse width. Determining means for determining a rule for conversion to a combination of degree and pulse width; and converting means for converting pixel data into a combination of exposure intensity and pulse width and outputting a first signal representing the rule according to the rule determined by the determining means And a signal generating means for generating a second signal representing the exposure light intensity and pulse width for forming the patch, a switching means for sending the first signal to the exposure control means in the normal image forming mode and the second signal in the patch generation mode. , And a first image obtained by combining the exposure intensity and pulse width represented by the first signal when outputting an image having the same density as the patch, and a second image obtained by combining the exposure intensity and pulse width represented by the second signal . An optical printer characterized in that the density fluctuation amounts ΔD1 and ΔD2 with respect to the predetermined temperature and humidity fluctuations of each image have a relationship of ΔD1 <ΔD2 . At least one of the first signals corresponding to various pixel data, optical printer according to claim 1, wherein the only the pulse width is short in the same exposure intensity and the second signal. At least one of the first signals corresponding to various pixel data, optical printer according to claim 1, wherein the only exposure intensity with the same pulse width as the second signal is high. The converting means converts the pixel data into a combination of exposure intensity, pulse width, and pulse density according to the rule determined by the determining means, and expresses the exposure intensity and pulse width at a first frequency according to the pulse density. Conversion means for outputting one signal, signal generation means for generating a second signal representing exposure intensity and pulse width for forming a patch at a second frequency corresponding to a predetermined pulse density, and a normal image forming mode Has a switching means for sending the first signal to the exposure means in the patch generation mode, and the pulse density corresponding to the first frequency when outputting an image having the same density as the patch is optical printer according to any one of claims 1 to 3, characterized in that less than a pulse density corresponding to the second frequency. The optical printer according to claim 4 , wherein a pulse density corresponding to the second frequency is the same as a maximum pulse density corresponding to the first frequency output from the conversion unit.

Images