JP2004348016A - Image control method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image control method and an image forming apparatus in which gradation control for interpolation to obtain a value that is more approximate to an actual value can be exerted with a smaller number of patches and without complex calculations and image stabilization can be achieved. <P>SOLUTION: Polynomial interpolation of order determined in consideration of image gradation property is used for interpolation between reading data. Further, the number of the gradations of the image pattern is determined in order to use the polynomial interpolation of order determined in consideration of the image gradation property. In order to increase the accuracy of the polynomial interpolation, the output signal value of the image pattern is determined in numerical analysis, thereby increasing the accuracy of the gradation control and stabilizing an image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２４】
光量／濃度変換部（ＬＯＧ変換部）２０６はルックアップテーブル（ＬＵＴ）ＲＯＭにより構成され、Ｒ４、Ｇ４、Ｂ４の輝度信号がＣ０、Ｍ０、Ｙ０の濃度信号に変換される。ライン遅延メモリ２０７は、不図示の黒文字判定部で、Ｒ４、Ｇ４、Ｂ４信号から生成されるＵＣＲ、ＦＩＬＴＥＲ、ＳＥＮ等の判定信号までのライン遅延分だけ、Ｃ０、Ｍ０、Ｙ０の画像信号を遅延させる。
【００２５】
マスキング及びＵＣＲ回路２０８は、入力されたＹ１、Ｍ１、Ｃ１の３原色信号により黒信号（Ｂｋ）を抽出し、更に、プリンタ部Ｂでの記録色材の色濁りを補正する演算を施して、Ｙ２、Ｍ２、Ｃ２、Ｂｋ２の信号を各読み取り動作の度に順次、所定のビット幅（８ｂｉｔ）で出力する。
【００２６】
γ補正回路２０９は、リーダー部Ａにおいて、プリンタ部Ｂの理想的な階調特性に合わせるべく濃度補正を行う。また、空間フィルタ処理部（出力フィルタ）２１０は、エッジ強調又はスムージング処理を行う。
【００２７】
このように処理されたＭ４、Ｃ４、Ｙ４、Ｂｋ４の面順次の画像信号は、プリンタ制御部１０９に送られ、プリンタ部ＢでＰＷＭによる濃度記録が行われる。
【００２８】
また、２１４はリーダー部内の制御を行うＣＰＵ、２１５はＲＡＭ、２１６はＲＯＭである。２１７は操作部であり、表示器２１８を有する。
【００２９】
図３は、図２に示す画像処理部１０８における各制御信号のタイミングを示す図である。同図において、ＶＳＹＮＣ信号は、副走査方向の画像有効区間信号であり、論理“１”の区間において、画像読み取り（スキャン）を行って、順次、（Ｃ）、（Ｍ）、（Ｙ）、（Ｂｋ）の出力信号を形成する。また、ＶＥ信号は、主走査方向の画像有効区間信号であり、論理“１”の区間において主走査開始位置のタイミングをとり、主にライン遅延のライン計数制御に用いられる。そして、ＣＬＯＣＫ信号は画素同期信号であり、“０”→“１”の立ち上がりタイミングで画像データを転送するのに用いられる。
【００３０】
次にプリンタ部Ｂの説明を行う。
【００３１】
図１において感光ドラム４は、１次帯電器８により、一様に帯電される。
【００３２】
画像データは、プリンタ画像処理部１０９に含まれるレーザードライバ及びレーザー光源１１０を介してレーザー光に変換され、そのレーザー光はポリゴンミラー１及びミラー２により反射され、一様に帯電された感光体ドラム４上に照射される。
【００３３】
レーザー光の走査により潜像が形成された感光ドラム４は、図中に示す矢印の方向に回転する。
【００３４】
すると、現像器３により各色ごとの現像が順次なされる。
【００３５】
本実施例では、現像方式として、２成分系を用いており、感光体ドラム４のまわりに、各色の現像器３が上流よりブラック（Ｂｋ）、イエロー（Ｙ）、シアン（Ｃ）、マゼンタ（Ｍ）の順で配置され、画像信号に応じた現像器が、その感光ドラム上に作られた潜像領域を現像するタイミングで、現像動作を行うようになっている。
【００３６】
一方、転写紙６は転写ドラム５に巻き付けられてＭ、Ｃ、Ｙ、Ｂｋの順番に１回ずつ回転し、計４回回転して各色のトナー画像が転写紙６上に多重に転写される。
【００３７】
転写が終了すると、転写紙６を転写ドラム５から分離し、定着ローラー対７によって定着され、フルカラー画像プリントが完成する。
【００３８】
また、感光ドラム４の現像器３の上流側に表面電位センサ１２を配置している。
【００３９】
また、感光体ドラム４上の転写残トナーをクリーニングするためのクリーナー９と、後述する、感光体ドラム４上に形成されたトナーパッチパターンの反射光量を検出するための、ＬＥＤ光源１０（約９６０ｎｍに主波長をもつ）とフォトダイオード１１を設けている。フォトダイオード１１はＬＥＤ光源からの光の正反射（鏡面反射）の方向に設けている。
【００４０】
図４は本実施例による画像形成装置の構成ブロック図を示す。
【００４１】
プリンタ画像処理部１０９はＣＰＵ２８及び、ＲＯＭ３０とＲＡＭ３２、テストパターン記憶部３１、濃度換算回路４２及びＬＵＴ２５より成り立ち、リーダー部Ａ、プリンタエンジン部１００と通信できるようになっている。
【００４２】
プリンタエンジン部１００において、感光体ドラム４の回りに配置されている、ＬＥＤ１０とフォトダイオード１１から成る、光学読み取り装置４０、１次帯電器８、レーザー１０１、表面電位センサ１２、現像器３を制御している。
【００４３】
また、機内の空気中の水分量を測定する環境センサ２１３が備えられている。
【００４４】
表面電子センサ１２は、現像器３より上流側に設けられており、１次帯電器８のグリッド電位、現像器３の現像バイアスはＣＰＵ２８により制御される。
【００４５】
図５は本実施例による階調画像を得る画像信号処理回路を示す。
【００４６】
画像の輝度信号がＣＣＤ１０５で得られ、リーダー画像処理部１０８において面順次の画像信号に変換される。この画像信号は、初期設定時のプリンタのγ特性が入力された画像信号によって表される、原画像の濃度と出力画像の濃度が一致するように、ＬＵＴ２５にて濃度特性が変換される。
【００４７】
図６に階調が再現される様子を４限チャートで示す。
【００４８】
第Ｉ象限は、原稿濃度を濃度信号に変換するリーダー部Ａの読み取り特性を示し、第ＩＩ象限は濃度信号をレーザー出力信号に変換するためのＬＵＴ２５の変換特性を示し、第ＩＩＩ象限はレーザー出力信号から出力濃度に変換するプリンタ部Ｂの記録特性を示し、第ＩＶ象限は原稿濃度から出力濃度の関係を示すこの画像形成装置のトータルの階調再現特性を示している。
【００４９】
階調数は８ｂｉｔのデジタル信号で処理しているので、２５６階調である。 この画像形成装置では、第ＩＶ象限の階調特性をリニアにするために、第ＩＩＩ象限のプリンタ特性がリニアでない分を第ＩＶ象限のＬＵＴ２５によって補正している。
【００５０】
ＬＵＴ２５は後に述べる演算結果により生成される。
【００５１】
ＬＵＴ２５にて濃度変換された後、パルス巾変調（ＰＷＭ）回路２６により信号がドット巾に対応した信号に変換され、レーザーのＯＮ／ＯＦＦを制御するレーザードライバ２７に送られる。
【００５２】
本実施例では、Ｙ、Ｍ、Ｃ、Ｋの全色とも、パルス巾変調処理による階調再現方法を用いた。
【００５３】
そして、レーザー１１０の走査により感光体ドラム４上にはドット面積の変化により、所定の階調特性を有する潜像が形成され、現像、転写、定着という過程をへて階調画像が再生される。
【００５４】
に、画像安定化を達成する制御系について説明する。
本制御は、感光ドラム４上のパッチパターン濃度を検出し、前述のＬＵＴ２５を作り直すことにより、画像安定化を達成する。
【００５５】
図７は感光ドラム４に相対するＬＥＤ１０とフォトダイオード１１から成るフォトセンサ４０からの信号を処理する処理回路を示す。フォトセンサ４０に入射された感光ドラム４からの近赤外光は、フォトセンサ４０により電気信号に変換され、電気信号はＡ／Ｄ変換回路４１により０〜５Ｖの出力電圧を０〜２５５レベルのデジタル信号に変換される。そして、濃度換算回路４２により濃度に変換される。
【００５６】
なお、本実施例で使用したトナーは、イエロー、マゼンタ、シアンの色トナーで、スチレン系共重合樹脂をバインダーとし、各色の色材を分散させて形成されている。
【００５７】
また、感光ドラム４はＯＰＣドラムであり、近赤外光の反射率（９６０ｎｍ）は約４０％であり、反射率が同程度であれば、アモルファスシリコン系ドラム等であってもかまわない。
【００５８】
また、本実施例で使用したフォトセンサ４０は、感光ドラム４からの正反射光のみを検出するよう構成されている。
【００５９】
感光ドラム４上の濃度を各色の面積階調により段階的に変えていった時の、フォトセンサ４０出力と出力画像濃度との関係を図８に示す。
【００６０】
トナーが感光体ドラム４に付着していない状態におけるフォトセンサ４０の出力を５Ｖ、すなわち、２５５レベルに設定した。
【００６１】
図８からわかるように、各トナーによる面積被覆率が大きくなり画像濃度が大きくなるにしたがい、感光ドラム４単体よりフォトセンサ４０出力が小さくなる。
【００６２】
これらの特性から、各色専用のセンサ出力信号から、濃度信号に変換するテーブル４２ａを持つことにより、各色とも精度良く濃度信号を読み取ることができる。
【００６３】
制御に用いるパッチパターンは、ＬＵＴ２５を作用させずに、パターンジェネレータ２９から発生させる。
【００６４】
パッチパターンは、図９に示すように、レーザー出力信号を、１６，６４，１２８，１９２，２４０レベルとした階調パッチパターンとした。
【００６５】
ここで、上記の５パッチとしたのは、後述するように６次の多項式で補間するためであり、それらのレーザー出力信号値は数値解析的に多項式補間の精度が上がるように決めた。
【００６６】
１パッチ（図９のａ）あたりの読むポイントは６ポイントであり、得られた信号を平均する。ポイント数はセンサ、画像形成装置によって最適化するのが好ましい。
【００６７】
各パッチ毎に６ポイントの値が平均された、信号を、先に示した光学濃度への変換方法により、濃度値に直し、それを出力濃度として、横軸にレーザー出力レベルをプロットしたのが、図１０である。
【００６８】
図１９に示した５点をもとに、本実施例では紙のベース濃度０．０５のレーザー出力レベルを０レベル、この画像形成装置の最大濃度１．６のレーザー出力レベルを２５５とし、レーザー出力レベル０〜２５５における濃度値を１つの多項式にあてはめることで、補間し求める。
【００６９】
補間には次式に示すラグランジュの多項式を用いる
【外２】

【００７０】
本実施例においてパッチパターンの階調数５つとした理由は、前述したように、補間に６次式を用いるためである。上式はパッチパターンの５つのレベルと、０レベル、２５５レベルの計７レベルの濃度値を変数とすると６次式となる。
【００７１】
本実施例において６次の多項式を補間に用いた理由は、本実施例で用いた画像形成装置の階調特性が、使用条件によらず常に６次式で良く近似できるからである。電子写真の場合、このようなケースが多く見られる。
【００７２】
また、さらにパッチパターンのレーザー出力信号値も、６次式の補間が安定に精度よく行われるように、良く知られている次式を参考に決めている。
区間［ａ、ｂ］において
【外３】

【００７３】
補間した結果を図１１に示す。
【００７４】
このように、画像形成装置の階調特性に適した次数の補間式を決め、補間制御を考慮して、制御のための、パッチパターンの数とレーザー出力信号を決めることで、精度良く、濃度データ間の補間が行える。
【００７５】
ＬＵＴ２５の内容は、図Ｂの濃度レベルを入力レベル（図６の濃度信号軸）に、レーザー出力レベルを出力レベル（図６のレーザー出力信号軸）に座標を入れ換えるだけで、簡単に作成できる。パッチに対応しない濃度レベルについては、補間演算により値を求める。
【００７６】
本制御系のフローを図１２を用いて説明する。この制御はＣＰＵ２８により実現される。
【００７７】
メイン電源スイッチをオン（Ｓ２０１）にした時に、定着ローラーの温度が１５０℃以下であった場合、制御系による制御が行われるように設定している（Ｓ２０２）。
【００７８】
定着温度が１５０℃以下の場合、定着ローラー温度が所定の温度になり、レーザー温度も温調点に達し、コントラスト電位を設定するために、電位データを測定する電位測定制御をおこない、トナートリボが安定するまで、現像器を空回転して、スタンバイ状態になるまで待つ（Ｓ２０３）。
【００７９】
スタンバイ状態になったところで、Ｙ、Ｍ、Ｃ、Ｂｋの各色毎のパッチパターンを感光ドラム上に形成して、フォトセンサ４０で検知する（Ｓ２０４）。
フォトセンサ４０で得られた信号は、前述した変換テーブル４２ａにより、濃度信号に変換される（Ｓ２０５）。
【００８０】
選られた濃度信号より、前述した方法により、ＬＵＴ２５を作成し、設定する（Ｓ２０６）。
【００８１】
以上により、画像安定化を達成する制御が終了する。
【００８２】
制御が終了したら、“コピーできます”のメッセージを上述の操作パネル上に表示し、コピースタンバイとなる（Ｓ２０７）。
【００８３】
以上で、本制御系による制御が完了する。
【００８４】
通常この画像形成装置は、電源を夜間切り、朝入れるケースが多く、従って制御系は、１日に１回は起動されることになる場合が多い。
【００８５】
（実施例２）
本実施例は実施例１でのパッチパターンをＬＵＴ２５を作用させて出力した場合の実施例である。
【００８６】
実施例１と同一な部分は省略し、異なる部分のみ説明する。
【００８７】
本実施例の制御に用いるパッチパターンはＬＵＴ２５を作用させて形成する。
【００８８】
ＬＵＴ２５は階調特性を線形にする役割をもつため、ＬＵＴ２５を作用させて形成したパッチパターンの階調特性は、多くの場合、線形に近い形となる。この場合に、データ間の補間に最適な多項式の次数は、この画像形成装置の階調特性の変動パターンを考慮して決める。
【００８９】
本実施例で用いた画像形成装置の階調特性変動パターンは、３次式により精度よく近似されるため、実施例１と同様な方法により、パッチパターンをレーザー出力レベル６４、１９２の２階調とした。
【００９０】
本実施例において、レーザー出力レベルを横軸にとり、パッチパターンの出力濃度をプロットし、３次式で補間した結果が図１４である。
【００９１】
これより、実施例１と同様な方法を用いてＬＵＴを作成するが、このＬＵＴはＬＵＴ２５を作用させた状態で作成したものであるため、ＬＵＴ２５に設定するのではなく、もうひとつ別のＬＵＴとして設定する。画像を形成するときは、濃度信号にこの２つのＬＵＴを作用させて出力信号とする。
【００９２】
本実施例のように、ＬＵＴ２５を作用させてパッチパターンを形成することにより、パッチパターンを２つにすることができ、制御時間の短縮や、トナー使用料の削減などの点で、有利となる。
【００９３】
制御時間が短ければ、制御頻度を増やすことも可能になる。
【００９４】
本実施例では実施例１と同様の高精度な階調制御が、少ないパッチ数で行え、より高精度な画像安定化が達成できる。
【００９５】
（実施例３）
本実施例は実施例２での多項式補間に用いる多項式の次数を、パッチパターンの画像情報より自動的に決める場合の実施例である。
【００９６】
実施例２と同一な部分は省略し、異なる部分のみ説明する。
【００９７】
本実施例の制御では、ＬＵＴ２５を作用させて、レーザー出力レベル６４、１９２の２階調のパッチパターンを形成し、濃度を読み取る。
【００９８】
ここで、レーザー出力レベル６４のパッチパターンの計測濃度値と、目標濃度値（ＬＵＴ２５により、達成させる濃度値）との差が、０．２以内であれば、実施例２と同様に、３次式を用いて補間を行い、計測濃度値と目標濃度値の濃度差が０．２を超えれば、６次式を用いて補間を行うように、ＣＰＵ２８により制御される。
【００９９】
６次式を用いる場合は、さらにレーザー出力レベル１６、１２８、２４０のパッチパターンを形成し、その後にＬＵＴの作成を行う。
【０１００】
本実施例では、画像形成装置の階調特性の変動が小さいときには、制御時間の短縮できる３次の多項式補間を用い、階調特性の変動が大きいときには、高精度な６次の多項式補間を用いることにより、複雑な変動を起こす画像形成装置において、より適切な制御が行え、高精度な画像安定化が達成できる。
【０１０１】
また画像形成装置の画像安定化が達成されることにより、複数の画像形成装置を用いて出力を行うクラスタプリンティングにおいて、装置間の初期状態をあわせておけば、その後どの装置により出力された画像も同じ色にすることができる。
【０１０２】
【発明の効果】
以上説明したように、本発明によると、少ないパッチ数で、複雑な計算を用いることなく、より実際に近い値を得る補間を行う階調制御が可能となり、画像安定化を達成する画像制御方法および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】実施例１の構成断面図。
【図２】実施例１のリーダー画像処理部１０８の構成ブロック図。
【図３】実施例１のリーダー画像処理部１０８のタイミングを示す図。
【図４】実施例１の制御ブロック図。
【図５】実施例１を示すブロック図。
【図６】階調再現特性を示す４限チャート図。
【図７】フォトセンサ４０から濃度変換までのフロー図。
【図８】フォトセンサ出力と画像濃度の関係を示す図。
【図９】実施例１におけるパッチパターンを示す図。
【図１０】実施例１におけるパッチパターンの読み取り例を示す図。
【図１１】図１０におけるデータ間を補間した結果を示す図。
【図１２】実施例１の制御系のフロー図。
【図１３】実施例２における３次式での補間結果を示す図。
【符号の説明】
３ 現像器
４ 感光ドラム
７ 定着ローラー
８ １次帯電器
１０ ＬＥＤ
１１ フォトダイオード
１２ 表面電位センサ
２５ γ−ＬＵＴ
２９ パターンジェネレータ
３３ 環境（水分量）センサ
１００ プリンタエンジン
１０５ ＣＣＤセンサ
１０９ プリンタ制御部
１１０ 半導体レーザー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image control method and an image forming apparatus for forming an image in a copying machine, a laser beam printer, or the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a method (image control method) for adjusting image processing characteristics of an image forming apparatus such as a copying machine or a printer, the following method is known (for example, see Patent Documents 1 and 2).
[0003]
First, the image forming apparatus is activated, and after the warm-up operation is completed, a specific patch pattern (image pattern) is formed on an image carrier such as a photosensitive drum. The density of the formed patch pattern is read, and the operation of a circuit for determining image forming conditions, such as a γ correction circuit, is changed based on the read density value to stabilize the quality of the formed image. Let me.
[0004]
Furthermore, even when the gradation characteristic changes due to a change in environmental conditions, a specific pattern is formed on the image carrier again, read, and fed back to a circuit for determining image forming conditions, such as a γ correction circuit. Accordingly, the image quality can be stabilized in accordance with the variation amount of the environmental condition.
[0005]
[Patent Document 1]
JP 04-267272 A [Patent Document 2]
JP 06-198973 A
[Problems to be solved by the invention]
However, in the above-described conventional example, since the gradation characteristics of the image forming apparatus are not linear (particularly highlight), when the density data is interpolated by an approximate expression, the actual density differs from the actual density. If the gradation data is fed back to the image forming conditions, there is a disadvantage that an optimum image cannot be obtained. In order to increase the accuracy, it is conceivable to increase the number of patches. However, there is a problem that the control time increases and the frequency of control cannot be increased.
[0007]
In order to solve the above-described problem, the present invention enables gradation control for performing interpolation to obtain a value closer to the actual value with a small number of patches and without using a complicated calculation, thereby achieving image stabilization. It is an object to provide an image control method and an image forming apparatus.
[0008]
[Means for Solving the Problems]
The present invention has been made in view of the above circumstances, and has an image forming unit that forms an image on an image carrier, an optical detection unit that detects density and gradation of the image on the image carrier, Forming at least one or more image patterns for determining image characteristics on the image carrier, comprising: density adjusting means for adjusting the density; and tone adjusting means for adjusting the tone characteristics of the image. The read image pattern is read by the optical detection means, and an image control method for controlling image forming conditions based on the read image information determines an interpolation between read data in consideration of a gradation characteristic of an image. Using a degree polynomial interpolation, further determining the number of gradations of the image pattern in order to use a degree polynomial interpolation determined in consideration of the gradation characteristics of the image, and increasing the degree of precision of the polynomial interpolation in advance. If this is characterized in that to determine the output signal values of the image pattern numerically, the image signal formed by the image forming means, may be assumed to be converted image signals according to the correction information.
[0009]
Further, the order polynomial interpolation determined in consideration of the gradation characteristics may be an order polynomial interpolation automatically determined based on image information of the image pattern.
[0010]
Also, an image carrier, image forming means for forming an image on the image carrier, transfer means for transferring the image on the image carrier to a recording material, and recording the image transferred on the recording material. In an image forming apparatus including a fixing unit for fixing a material, image density adjustment and image gradation adjustment can be performed by the above-described image control method.
[0011]
In this case, the image carrier may be a photosensitive drum in the form of a drum having a photosensitive layer on the surface, a photosensitive sheet in the form of a sheet having a photosensitive layer on the surface, or a photosensitive belt in the form of a belt having a photosensitive layer on the surface, or The transfer member may be a transfer member to which the toner image is transferred from the body, or an intermediate transfer member to which the toner image is transferred from the photosensitive member.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
(Example 1)
FIG. 1 shows a configuration diagram of the present embodiment.
[0014]
A full-color image forming method will be described.
[0015]
A document 101 placed on a platen glass 102 is illuminated by a light source 103 and is imaged on a CCD sensor 105 via an optical system 104. The CCD sensor 105 generates red, green, and blue color component signals for each line sensor using a group of red, green, and blue CCD line sensors arranged in three rows.
[0016]
These reading optical system units scan the document in the direction of the arrow to convert the document into an electric signal data sequence for each line.
[0017]
Further, an attachment member 107 for abutting the position of the original on the original platen glass 102 to prevent the original from being placed obliquely, a CCD member 105 for determining the white level of the CCD sensor 105 on the original platen glass surface, A reference white plate 106 for shading the sensor 105 in the thrust direction is provided.
[0018]
The image signal obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108, sent to the printer unit B, and processed by the printer control unit 109.
[0019]
Next, the image processing unit 108 will be described.
[0020]
FIG. 2 is a block diagram illustrating a flow of an image signal in the image processing unit 108 of the reader unit A according to the present embodiment. As shown in the figure, an image signal output from the CCD sensor 105 is input to an analog signal processing unit 201, where gain adjustment and offset adjustment are performed, and then an A / D converter 202 outputs 8 bits for each color signal. Are converted into digital image signals R1, G1, and B1. Thereafter, the signal is input to the shading correction unit 203, and a known shading correction is performed for each color using a read signal of the reference white plate 106.
[0021]
The clock generation unit 211 generates a clock for each pixel. The main scanning address counter 212 counts clocks from the clock generation unit 211 and generates a one-line pixel address output. Then, the decoder 213 decodes the main scanning address from the main scanning address counter 212, and outputs a line drive CCD drive signal such as a shift pulse or a reset pulse, or a VE indicating an effective area in a one-line read signal from the CCD. A signal and a line synchronization signal HSYNC are generated. The main scanning address counter 212 is cleared by the HSYNC signal, and starts counting the main scanning addresses of the next line.
[0022]
Since the line sensors of the CCD sensor 105 are arranged at a predetermined distance from each other, the line delay circuit 204 in FIG. 2 corrects a spatial shift in the sub-scanning direction. Specifically, in the sub-scanning direction with respect to the B signal, each of the R and G signals is line-delayed in the sub-scanning direction to match the B signal.
[0023]
The input masking unit 205 converts a read color space determined by the spectral characteristics of the R, G, and B filters of the CCD sensor into an NTSC standard color space, and performs a matrix operation as shown in the following equation.
[Outside 1]

[0024]
The light quantity / density conversion unit (LOG conversion unit) 206 is configured by a look-up table (LUT) ROM, and converts the luminance signals of R4, G4, and B4 into density signals of C0, M0, and Y0. The line delay memory 207 delays the C0, M0, and Y0 image signals by the line delay from the R4, G4, and B4 signals to the determination signals such as UCR, FILTER, and SEN in a black character determination unit (not shown). Let it.
[0025]
The masking and UCR circuit 208 extracts a black signal (Bk) from the input three primary color signals of Y1, M1, and C1, and further performs an operation of correcting color turbidity of a recording color material in the printer unit B. The signals of Y2, M2, C2, and Bk2 are sequentially output at a predetermined bit width (8 bits) for each reading operation.
[0026]
The γ correction circuit 209 performs density correction in the reader unit A so as to match the ideal gradation characteristics of the printer unit B. The spatial filter processing unit (output filter) 210 performs edge enhancement or smoothing processing.
[0027]
The M4, C4, Y4, and Bk4 frame-sequential image signals thus processed are sent to the printer control unit 109, and the printer unit B performs density recording by PWM.
[0028]
Reference numeral 214 denotes a CPU for controlling the inside of the reader unit, 215 denotes a RAM, and 216 denotes a ROM. An operation unit 217 has a display 218.
[0029]
FIG. 3 is a diagram showing the timing of each control signal in the image processing unit 108 shown in FIG. In the figure, a VSYNC signal is an image valid section signal in the sub-scanning direction, and performs image reading (scanning) in a logical "1" section to sequentially perform (C), (M), (Y), (Bk) output signal is formed. The VE signal is an image valid section signal in the main scanning direction, takes the timing of the main scanning start position in the section of logic "1", and is mainly used for line counting control of line delay. The CLOCK signal is a pixel synchronization signal, and is used to transfer image data at the rising timing of “0” → “1”.
[0030]
Next, the printer section B will be described.
[0031]
In FIG. 1, the photosensitive drum 4 is uniformly charged by the primary charger 8.
[0032]
The image data is converted into laser light via a laser driver and a laser light source 110 included in the printer image processing unit 109, and the laser light is reflected by the polygon mirror 1 and the mirror 2 and is uniformly charged. 4 is illuminated.
[0033]
The photosensitive drum 4 on which the latent image has been formed by the scanning of the laser beam rotates in the direction of the arrow shown in the figure.
[0034]
Then, development for each color is sequentially performed by the developing device 3.
[0035]
In the present embodiment, a two-component system is used as a developing method, and a developing unit 3 of each color is provided around a photosensitive drum 4 with black (Bk), yellow (Y), cyan (C), magenta ( M), and the developing device according to the image signal performs the developing operation at the timing of developing the latent image area formed on the photosensitive drum.
[0036]
On the other hand, the transfer paper 6 is wound around the transfer drum 5 and rotates once in the order of M, C, Y, and Bk, and rotates four times in total, so that the toner images of each color are transferred onto the transfer paper 6 in a multiplex manner. .
[0037]
When the transfer is completed, the transfer paper 6 is separated from the transfer drum 5 and fixed by the fixing roller pair 7 to complete a full-color image print.
[0038]
Further, a surface potential sensor 12 is arranged on the photosensitive drum 4 on the upstream side of the developing device 3.
[0039]
Also, a cleaner 9 for cleaning the transfer residual toner on the photosensitive drum 4 and an LED light source 10 (about 960 nm) for detecting the amount of reflected light of a toner patch pattern formed on the photosensitive drum 4, which will be described later. Having a main wavelength) and a photodiode 11. The photodiode 11 is provided in the direction of regular reflection (specular reflection) of light from the LED light source.
[0040]
FIG. 4 is a block diagram showing a configuration of the image forming apparatus according to the present embodiment.
[0041]
The printer image processing unit 109 includes the CPU 28, the ROM 30 and the RAM 32, the test pattern storage unit 31, the density conversion circuit 42, and the LUT 25, and can communicate with the reader unit A and the printer engine unit 100.
[0042]
In the printer engine unit 100, the optical reading device 40, the primary charger 8, the laser 101, the surface potential sensor 12, and the developing device 3, which are arranged around the photosensitive drum 4 and include the LED 10 and the photodiode 11, are controlled. are doing.
[0043]
Further, an environment sensor 213 for measuring the amount of water in the air in the machine is provided.
[0044]
The surface electronic sensor 12 is provided upstream of the developing device 3, and the grid potential of the primary charger 8 and the developing bias of the developing device 3 are controlled by the CPU 28.
[0045]
FIG. 5 shows an image signal processing circuit for obtaining a gradation image according to the present embodiment.
[0046]
A luminance signal of the image is obtained by the CCD 105 and is converted into a frame-sequential image signal by the reader image processing unit 108. The density characteristic of this image signal is converted by the LUT 25 so that the density of the original image and the density of the output image, which are represented by the input image signal of the γ characteristic of the printer at the time of initial setting, match.
[0047]
FIG. 6 is a four-limit chart showing how the gradation is reproduced.
[0048]
The first quadrant indicates the reading characteristics of the reader unit A for converting the original density into a density signal, the second quadrant indicates the conversion characteristics of the LUT 25 for converting the density signal into a laser output signal, and the third quadrant indicates the laser output. The recording characteristics of the printer unit B for converting a signal into an output density are shown, and the fourth quadrant shows the total tone reproduction characteristics of the image forming apparatus showing the relationship between the original density and the output density.
[0049]
Since the number of gradations is processed by an 8-bit digital signal, there are 256 gradations. In this image forming apparatus, in order to make the gradation characteristic of the IV quadrant linear, the printer characteristic of the III quadrant is corrected by the LUT 25 of the IV quadrant to the extent that the printer characteristic is not linear.
[0050]
The LUT 25 is generated based on a calculation result described later.
[0051]
After the density conversion by the LUT 25, the signal is converted into a signal corresponding to the dot width by a pulse width modulation (PWM) circuit 26, and sent to a laser driver 27 for controlling ON / OFF of the laser.
[0052]
In the present embodiment, a tone reproduction method using pulse width modulation processing is used for all colors of Y, M, C, and K.
[0053]
A latent image having a predetermined gradation characteristic is formed on the photosensitive drum 4 by a change in the dot area by the scanning of the laser 110, and the gradation image is reproduced through a process of development, transfer and fixing. .
[0054]
Next, a control system for achieving image stabilization will be described.
This control achieves image stabilization by detecting the patch pattern density on the photosensitive drum 4 and recreating the LUT 25 described above.
[0055]
FIG. 7 shows a processing circuit for processing a signal from a photosensor 40 including an LED 10 and a photodiode 11 facing the photosensitive drum 4. The near-infrared light from the photosensitive drum 4 incident on the photosensor 40 is converted into an electric signal by the photosensor 40, and the electric signal is output from an output voltage of 0 to 5 V by an A / D conversion circuit 41 to a level of 0 to 255. It is converted to a digital signal. Then, the density is converted into a density by the density conversion circuit 42.
[0056]
The toner used in the present embodiment is a yellow, magenta, or cyan color toner, which is formed by using a styrene-based copolymer resin as a binder and dispersing color materials of each color.
[0057]
The photosensitive drum 4 is an OPC drum, and has a reflectance (960 nm) of near-infrared light of about 40%. If the reflectance is almost the same, an amorphous silicon-based drum or the like may be used.
[0058]
Further, the photo sensor 40 used in this embodiment is configured to detect only the regular reflection light from the photosensitive drum 4.
[0059]
FIG. 8 shows the relationship between the output of the photosensor 40 and the output image density when the density on the photosensitive drum 4 is changed stepwise according to the area gradation of each color.
[0060]
The output of the photosensor 40 in a state where the toner did not adhere to the photosensitive drum 4 was set to 5 V, that is, to the 255 level.
[0061]
As can be seen from FIG. 8, as the area coverage by each toner increases and the image density increases, the output of the photosensor 40 becomes smaller than that of the photosensitive drum 4 alone.
[0062]
From these characteristics, by having a table 42a for converting a sensor output signal dedicated to each color into a density signal, the density signal can be read with high accuracy for each color.
[0063]
The patch pattern used for the control is generated by the pattern generator 29 without operating the LUT 25.
[0064]
As shown in FIG. 9, the patch pattern was a gradation patch pattern in which the laser output signal was at 16, 64, 128, 192, 240 levels.
[0065]
Here, the above-mentioned five patches are used for interpolation by a sixth-order polynomial as described later, and their laser output signal values are determined numerically so that the accuracy of the polynomial interpolation is increased.
[0066]
The number of reading points per patch (a in FIG. 9) is 6, and the obtained signals are averaged. It is preferable that the number of points is optimized by the sensor and the image forming apparatus.
[0067]
The signal obtained by averaging the values of 6 points for each patch was converted into a density value by the conversion method to the optical density described above, and the resulting output density was plotted with the laser output level on the horizontal axis. FIG.
[0068]
Based on the five points shown in FIG. 19, in this embodiment, the laser output level at the paper base density of 0.05 is set to 0 level, the laser output level of the maximum density 1.6 of this image forming apparatus is set to 255, Interpolation is obtained by applying the density values at the output levels 0 to 255 to one polynomial.
[0069]
The Lagrange polynomial shown in the following equation is used for interpolation.

[0070]
The reason why the number of gradations of the patch pattern is five in the present embodiment is that, as described above, the sixth order equation is used for interpolation. The above equation is a sixth-order equation when the five levels of the patch pattern, the 0 level, and the 255 levels, which are a total of 7 levels of density values, are variables.
[0071]
The reason why the sixth-order polynomial is used for the interpolation in the present embodiment is that the gradation characteristics of the image forming apparatus used in the present embodiment can always be approximated well by the sixth-order expression regardless of the use conditions. In the case of electrophotography, such cases are often observed.
[0072]
Further, the laser output signal value of the patch pattern is determined with reference to the following well-known equation so that the interpolation of the 6-order equation can be performed stably and accurately.
In section [a, b]

[0073]
FIG. 11 shows the result of the interpolation.
[0074]
As described above, the interpolation formula of the order suitable for the gradation characteristics of the image forming apparatus is determined, and the number of the patch patterns and the laser output signal for the control are determined in consideration of the interpolation control. Interpolation between data can be performed.
[0075]
The contents of the LUT 25 can be easily created simply by replacing the coordinates of the density level of FIG. B with the input level (density signal axis of FIG. 6) and the coordinates of the laser output level with the output level (laser output signal axis of FIG. 6). For a density level that does not correspond to a patch, a value is obtained by interpolation.
[0076]
The flow of this control system will be described with reference to FIG. This control is realized by the CPU 28.
[0077]
If the temperature of the fixing roller is 150 ° C. or less when the main power switch is turned on (S201), the control by the control system is set (S202).
[0078]
When the fixing temperature is 150 ° C or lower, the fixing roller temperature reaches the predetermined temperature, the laser temperature also reaches the temperature control point, and the potential measurement control for measuring the potential data is performed to set the contrast potential. Until the operation, the developing device idles and waits until it enters the standby state (S203).
[0079]
In the standby state, a patch pattern for each of the colors Y, M, C, and Bk is formed on the photosensitive drum, and is detected by the photosensor 40 (S204).
The signal obtained by the photo sensor 40 is converted into a density signal by the above-described conversion table 42a (S205).
[0080]
From the selected density signal, the LUT 25 is created and set by the method described above (S206).
[0081]
Thus, the control for achieving the image stabilization ends.
[0082]
When the control is completed, a message "Copy is possible" is displayed on the operation panel, and the copy standby mode is set (S207).
[0083]
Thus, the control by the present control system is completed.
[0084]
Usually, this image forming apparatus is often turned off at night and turned on in the morning, and therefore the control system is often started once a day.
[0085]
(Example 2)
This embodiment is an embodiment in the case where the patch pattern in the first embodiment is output by operating the LUT 25.
[0086]
The same parts as those in the first embodiment are omitted, and only different parts will be described.
[0087]
The patch pattern used in the control of this embodiment is formed by operating the LUT 25.
[0088]
Since the LUT 25 has a role of making the gradation characteristics linear, the gradation characteristics of the patch pattern formed by operating the LUT 25 are almost linear in many cases. In this case, the order of the optimal polynomial for interpolation between data is determined in consideration of the variation pattern of the gradation characteristics of the image forming apparatus.
[0089]
Since the gradation characteristic variation pattern of the image forming apparatus used in this embodiment is approximated with high accuracy by a cubic expression, the patch pattern is converted into the two gradations of the laser output levels 64 and 192 in the same manner as in the first embodiment. And
[0090]
FIG. 14 shows a result obtained by plotting the output densities of the patch patterns on the horizontal axis and plotting the output densities of the patch patterns using the cubic equation in this embodiment.
[0091]
From this, an LUT is created using the same method as in the first embodiment. However, since this LUT is created with the LUT 25 acting, it is not set in the LUT 25, but as another LUT. Set. When forming an image, the two LUTs are applied to the density signal to produce an output signal.
[0092]
By forming the patch pattern by operating the LUT 25 as in the present embodiment, two patch patterns can be formed, which is advantageous in terms of shortening the control time and reducing the toner usage fee. .
[0093]
If the control time is short, the control frequency can be increased.
[0094]
In the present embodiment, high-precision gradation control similar to that of the first embodiment can be performed with a small number of patches, and more accurate image stabilization can be achieved.
[0095]
(Example 3)
This embodiment is an embodiment in which the order of the polynomial used for the polynomial interpolation in the second embodiment is automatically determined from the image information of the patch pattern.
[0096]
The same parts as in the second embodiment are omitted, and only different parts will be described.
[0097]
In the control of this embodiment, the LUT 25 is operated to form a two-tone patch pattern with laser output levels 64 and 192, and the density is read.
[0098]
Here, if the difference between the measured density value of the patch pattern of the laser output level 64 and the target density value (the density value achieved by the LUT 25) is within 0.2, the third order is performed as in the second embodiment. The interpolation is performed using the equation, and if the density difference between the measured density value and the target density value exceeds 0.2, the CPU 28 is controlled to perform the interpolation using the sixth order equation.
[0099]
When the sixth order equation is used, patch patterns of laser output levels 16, 128, and 240 are further formed, and then an LUT is created.
[0100]
In this embodiment, when the variation of the gradation characteristic of the image forming apparatus is small, a third-order polynomial interpolation that can reduce the control time is used. When the variation of the gradation characteristic is large, a highly accurate sixth-order polynomial interpolation is used. Accordingly, more appropriate control can be performed in an image forming apparatus that causes complicated fluctuations, and highly accurate image stabilization can be achieved.
[0101]
Also, by achieving image stabilization of an image forming apparatus, in cluster printing in which output is performed using a plurality of image forming apparatuses, if the initial state between the apparatuses is matched, an image output by any apparatus thereafter can be used. Can be the same color.
[0102]
【The invention's effect】
As described above, according to the present invention, it is possible to perform gradation control for performing interpolation to obtain a value closer to the actual value with a small number of patches and without using complicated calculations, and an image control method for achieving image stabilization. And an image forming apparatus.
[Brief description of the drawings]
FIG. 1 is a configuration sectional view of a first embodiment.
FIG. 2 is a block diagram illustrating a configuration of a reader image processing unit according to the first embodiment.
FIG. 3 is a diagram showing the timing of a leader image processing unit according to the first embodiment.
FIG. 4 is a control block diagram according to the first embodiment.
FIG. 5 is a block diagram showing the first embodiment.
FIG. 6 is a fourth-limit chart showing gradation reproduction characteristics.
FIG. 7 is a flowchart from the photo sensor 40 to the density conversion.
FIG. 8 is a diagram illustrating a relationship between a photo sensor output and an image density.
FIG. 9 is a diagram illustrating a patch pattern according to the first embodiment.
FIG. 10 is a diagram illustrating an example of reading a patch pattern according to the first embodiment.
FIG. 11 is a diagram showing a result of interpolation between data in FIG. 10;
FIG. 12 is a flowchart of a control system according to the first embodiment.
FIG. 13 is a diagram illustrating a result of interpolation using a cubic expression in the second embodiment.
[Explanation of symbols]
3 developing device 4 photosensitive drum 7 fixing roller 8 primary charger 10 LED
11 Photodiode 12 Surface potential sensor 25 γ-LUT
29 pattern generator 33 environment (moisture content) sensor 100 printer engine 105 CCD sensor 109 printer controller 110 semiconductor laser

Claims (12)

Image forming means for forming an image on an image carrier; optical detecting means for detecting the density and gradation of the image on the image carrier; density adjusting means for adjusting the image density; A tone adjusting unit for adjusting the image characteristics, forming at least one image pattern for determining image characteristics on the image carrier, reading the formed image pattern by the optical detecting unit, and reading the read image pattern; In an image control method for controlling image forming conditions based on image information obtained, polynomial interpolation of an order determined in consideration of gradation characteristics of an image is used for interpolation between read data, and further, gradation characteristics of the image are further reduced. The number of tones of the image pattern is determined to use polynomial interpolation of an order determined by taking into account, and the output signal value of the image pattern is numerically determined to increase the accuracy of the polynomial interpolation. Image control method according to claim. An image carrier, an image forming unit for forming an image on the image carrier, a transfer unit for transferring the image on the image carrier to a recording material, and an image transferred to the recording material on the recording material. Fixing means for fixing, wherein image density adjustment and image gradation adjustment are performed by the image control method according to claim 1.
An image forming apparatus comprising: 3. The image control method according to claim 1, wherein the order polynomial interpolation determined in consideration of the gradation characteristics is an order polynomial interpolation automatically determined based on image information of the image pattern. Image forming device. 3. The image control method and image forming apparatus according to claim 1, wherein interpolation between data is performed by applying the entire output signal value range to one polynomial. The image control method and the image forming apparatus according to claim 1, wherein the image forming condition is γLUT correction. 3. The image control method and image forming apparatus according to claim 1, wherein the polynomial interpolation is Lagrange interpolation. 3. The image control method according to claim 1, wherein the degree polynomial determined in consideration of the gradation characteristics of the image is a third-order, fourth-order, fifth-order, or sixth-order polynomial. And an image forming apparatus. In the polynomial interpolation, when a sixth-order polynomial is used for interpolation, the output signal of the image pattern is 0, 16, 64, 128, 192, 240, 255 in 256 values (8 bits) from 0 to 255. 3. The image control method and image forming apparatus according to claim 1, wherein a tone pattern is the image pattern. In the polynomial interpolation, when a third-order polynomial is used for interpolation, a gradation pattern in which an output signal of an image pattern is 0, 64, 192, or 255 in 256 values (8 bits) from 0 to 255 is converted to the image pattern. 3. The image control method and image forming apparatus according to claim 1, wherein: 3. The image control method and image forming apparatus according to claim 1, wherein said optical detection means is a regular reflection type sensor. The image signal formed by the image forming unit is an image signal converted according to the correction information,
3. An image control method and an image forming apparatus according to claim 1, wherein: 3. The image control method and image forming apparatus according to claim 1, wherein the image carrier is a photoconductor having a photosensitive layer on a surface or an intermediate transfer body.

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