JP4328101B2

JP4328101B2 - Printing control method and image forming apparatus

Info

Publication number: JP4328101B2
Application number: JP2003022917A
Authority: JP
Inventors: 政義中山; 輝章三矢; 久雄岡田; 夏城栗林; 啓介窪田
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2003-01-31
Filing date: 2003-01-31
Publication date: 2009-09-09
Anticipated expiration: 2023-01-31
Also published as: JP2004233704A

Description

【０００１】
【発明の属する技術分野】
本発明は、プリンタ、ファクシミリ、複写機等のトナー等の着色粒子を用いて画像を顕像化させる電子写真方式の印刷制御方法及び画像形成装置に関するものである。
【０００２】
【従来の技術】
以下、従来の印写方法について説明する。電子写真方式を用いた記録装置は、着色粒子を記録体表面に画像として顕像化させる印写工程と顕像化された着色粒子画像を記録体に移して固着させる定着工程から成る。着色粒子には電子写真専用のトナーと呼ばれる粉末が用いられる。帯電工程において、感光体はその表面の全面が一旦帯電され、続いて露光工程において光を照射することにより部分的な電荷放電が行われる。ここに、感光体表面には帯電領域と放電領域による電位コントラストが形成され、これを静電潜像と呼ぶ。
【０００３】
次の現像工程では、まず、着色粒子であるトナー粒子を帯電させる。トナーの帯電方法にはキャリアビーズを用いる二成分現像方法やトナーと部材などとの摩擦により帯電を行う一成分現像方法がある。一方、静電潜像の顕像化の方式として、バイアス現像と呼ばれる方法がよく用いられる。バイアス現像では、現像ローラにバイアス電圧を印加し、感光体表面に形成された潜像電位と現像ローラとの間に発生する電界の作用により帯電されたトナー粒子を現像ローラ表面の現像剤から分離して感光体表面に移動させ、作像が行われる。潜像電位（すなわち感光体の像形成部分の電位）として、前述の帯電電位を用いてもよいし、放電電位を用いてもよい。一般に、潜像電位として帯電電位を用いる方法を正規現像法、放電電位を用いる方法を反転現像法と呼ぶ。
【０００４】
バイアス現像には、現像ローラに直流電圧のみを印加するものと、直流電圧に交流電圧を重畳して印加するものがある。直流電圧に交流電圧を重畳して印加するものは、直流電圧だけの現像バイアスが印加されたものに比べて、感光体上の潜像により多くのトナーを供給でき、画像濃度を上昇させる利点を持っている（例えば特許文献1参照）。
【０００５】
帯電電位と放電電位のうち潜像電位として用いられない側の電位を背景電位と呼ぶ。現像ローラのバイアス電圧の直流電圧は帯電電位と放電電位の中間に設定され、潜像電位との差を現像電位差と呼ぶ。同様に、背景電位との差を背景電位差と呼ぶ。現像電位差が大きければ形成される電界（現像電界と呼ぶ）が強くなるので現像性能が高くなる。一方、背景電位差は画像の背景部の画質に影響し、背景電位差が少ないと背景部へのかぶりが増える。ところで、トナーの帯電量は現像性能と密接な関係にある。トナーの帯電量が大きい程、同一現像電界強度での現像性能は低下する。
【０００６】
次に、現像性能の経時的変動について説明する。現像性能の経時的変動要因は、現像剤の帯電量の変動によるものと、現像電界の変動によるものに大別される。一般的にトナーの帯電量は雰囲気の湿度に対して変動しやすく、湿度が低いと増加し、湿度が高いと低下する性質がある。また、２成分現像の場合は攪拌部材との摩擦等により、経時的にトナー及びキャリアビーズの表面の状態が変化して、トナーの帯電量が変化する。
【０００７】
一方、露光により形成された放電領域の電位は、感光体の温度変化、雰囲気の湿度変化、経時的な膜厚の変化により、露光光量が一定にもかかわらず変動する。この放電領域の電位の変動は、露光での光量を十分に与えないようにして完全に放電しきっていない中間の電位領域を設けた場合などに著しい。
【０００８】
ところで、線画像や網点などは、電界の周辺効果の影響が大きく、ソリッド領域（ベタ画像部）の内部に発生する現像電界（平行電界）よりも現像電界の強度が大きい。以後、平行電界に対し、周辺効果の影響により、平行電界よりも強度が大きい電界を周辺電界と呼ぶ。感光体の膜厚が経時的に変化すると、同一の現像電位差下でも、平行電界及び、周辺電界の強度が変化するとともに、平行電界と周辺電界の強度の比率も変化する。
【０００９】
経時的に画質を一定にするためには、上記した現像剤の帯電量の変動による現像性能の変化及び現像電界の変動を補正する必要がある。
【００１０】
現像剤の帯電量の変化に伴って生じる印刷画像の濃度変動を補正するため、画像形成に先立って、レーザ書き込みユニットによって感光体上にテストパッチ潜像を形成し、このテストパッチ潜像を現像機によって現像してテストパッチ像としたのち、クリーニング装置の上流側に設けた光学式画像濃度センサーにより、そのテストパッチ像の反射濃度（画像濃度）を測定し、反射濃度（画像濃度）が既定値からずれている場合は、現像バイアス、帯電器のグリット電圧、トナーの補給等を制御する方法が知られている。
【００１１】
また、現像電界の変動の補正方法として、電位センサーにより感光体表面の電位を検出し、かつ何らかの方法で感光体の膜厚を検出して、現像電界を一定にするようレーザの光量を変化させ、感光体表面の電位を制御する方法が知られている（例えば特許文献２参照）。
【００１２】
さらに、上記、光学式画像濃度センサーによる制御と、感光体電位センサーによる制御を併用した方法も知られている。
【特許文献１】
特開昭６２−２８９５８号公報
【特許文献２】
特開平１１−１５２１４号公報
【００１３】
【発明が解決しようとする課題】
上記従来の技術では、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合、面積率１００％（ベタ部）および、０〜５０％の低面積率の階調濃度変動は比較的小さくなるように補正することができるが、面積率５０〜９０％の高面積率の階調濃度変動は補正することができないという問題があった。
【００１４】
本発明の目的は、電子写真の記録装置において、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合にも、低面積率から高面積率の全ての階調濃度を補正することができる印写制御方法を提供することにある。
【００１５】
【課題を解決するための手段】
上記目的は、感光体と、グリッドを備えた帯電器と、露光手段と、現像機と、制御手段と、前記感光体上に形成されたテストパッチを検知するセンサとを有し、前記露光装置は前記制御手段によって露光量が調整され、前記現像機には直流電圧と交流電圧とが印加されており、前記帯電器と前記露光装置とを用いて前記感光体上に背景領域と画像領域を形成させる電子写真の画像形成装置の印写制御方法において、ベタ画像の内部を印刷するのに調整する露光量である第１露光量と、ベタ画像の内部以外の周辺部、線画像および網点画像を印刷するのに調整する露光量である第２露光量とを設け、前記制御手段によって、前記第１露光量で前記感光体上にベタ画像のテストパッチ潜像を作成し、前記直流電圧と前記グリッドに印加されるグリッド電圧との差を一定にし、前記直流電圧と前記グリッド電圧とを変化させた後、前記ベタ画像のテストパッチ潜像を前記現像機によって現像してベタ画像のテストパッチであるベタ画像パッチを作成し、前記センサで前記ベタ画像パッチの内部の画像濃度を測定することで、予め定めたベタ画像の画像濃度にするための前記直流電圧の電圧値と、前記グリッド電圧の電圧値とを決定する第１調整を行い、前記第１調整を行った後、前記第２露光量を変化させ、前記感光体上に面積率が一定の網点画像のテストパッチである第１網点画像パッチを作成し、前記センサで前記第１網点画像パッチの画像濃度を測定することで、予め定めた網点画像の画像濃度の範囲内にするための第２露光量を決定する第２調整を行い、前記第２調整を行った後、前記感光体上に面積率が６０〜８０％のうちどれか一定の面積率の網点画像のテストパッチである第２網点画像パッチを作成し、前記センサで前記第２網点画像パッチの画像濃度を測定することで得られた測定結果画像濃度と、予め定めた網点画像の画像濃度の範囲とで比較を行い、前記測定結果画像濃度が予め定めた網点画像の画像濃度の範囲内であるとき、前記制御手段は制御を終了し、前記測定結果画像濃度が予め定めた網点画像の画像濃度の範囲外であるとき、前記交流電圧の振幅を変化させ、前記第１調整および前記第２調整を再度繰り返すことにより達成される。
【００１６】
【発明の実施の形態】
以下、本発明の一実施例を図１〜図１０を用いて説明する。
【００１７】
図１は本実施例の記録装置の断面を模式的に表した図である。１は感光体ドラム、２はスコロトロン帯電器、３は現像機、４は記録紙、５は転写機、６は定着機、７はクリーナ、８は露光装置、９は制御装置、１０は光学式画像濃度センサーである。
【００１８】
スコロトロン帯電器２により一様に帯電された感光体ドラム１表面に、画像信号に基き露光装置８によって６００ｄｐｉの解像度で潜像が形成される。この後、直流電圧に交流電圧を重畳したバイアスが印加された現像機３によりトナーを現像する。現像バイアスに重畳する交流電圧の周波数は２〜１６ｋＨｚ、振幅Ｖｐｐは０．４〜２．０ｋＶが好ましく、波形は矩形波、正弦波、三角波等が使用される。感光体ドラム１の表面に現像されたトナーは、転写機５によって記録紙４に転写される。この後、転写されたトナー画像は定着機６で加熱融解され記録紙４に定着する。また、転写されずに感光体ドラム１表面に残存したトナーはクリーナ７により回収され、一連のプロセスを終了する。本実施例では、露光装置８によって感光体上に予め定めた画像パターンのテストパッチ潜像を形成し、このテストパッチ潜像を現像機３によって現像してテストパッチ像としたのち、光学式画像濃度センサー１０により、そのテストパッチ像の反射濃度を検出し、その検出値に基づいて制御装置９により、スコロトロン帯電器のグリット電圧Ｖg、現像バイアスの直流電圧Ｖb、交流電圧の振幅Ｖｐｐを調節することができる。
【００１９】
図２は、ソリッド画像を現像するときに発生する現像電界と、網点や線画像などを現像するときに発生する現像電界を横軸を感光体上の位置として模式的に表した図である。３０がソリッド画像を現像するときに発生する現像電界にあたり、３１が網点や線画像などを現像するときに発生する現像電界にあたる。ソリッド画像の内部は、電界の周辺効果の影響を受けない領域であり、この領域に発生する現像電界を平行電界と呼び、図２中に３２で示している。一方、ソリッド画像の端部および、網点や線画像は、電界の周辺効果の影響を受け、平行電界よりも強い電界が発生する。このソリッド画像の端部および、網点や線画像に発生する現像電界を周辺電界と呼び、図２中に３３で示している。この周辺電界によって、網点や線画像は、ソリッド画像の内部に比べ多くのトナーが現像される。
【００２０】
本記録装置では、画像信号を露光前にメモリに取り込み、パターンマッチング手法により全ての画像の白紙部と隣接する予め定めた画素数の部分を検出する。そして、白紙部と隣接する予め定めた画素数の部分は露光量Ｅ2で露光し、またそれ以外については露光量Ｅ1で露光するよう露光制御手段９によりコントロールする。
【００２１】
前記白紙部と隣接する予め定めた画素数はソリッド画像の端部に発生する周辺電界の幅に相当する画素数以下に設定する。本実施例では、ソリッド画像の端部に約２００μｍの幅に渡って周辺電界が発生しており、６００ｄｐｉの解像度では、約５ｄｏｔの画素数に相当する。この周辺電界を平行電界と同じ強さにするためには、周辺電界が発生している５ｄｏｔの画素を予め定めた画素数とする必要があるが、周辺電界の変動を補正するためには、それ以下の画素数で、網点や線画像の画質を安定化できることが実験によってわかっており、本実施例では、前記白紙部と隣接する予め定めた画素数を２ｄｏｔに設定している。図３にランダムな画像パターンにつき、前記検出された白紙部と隣接する２ドット幅の部分を３５でそれ以外の部分を３４で示す。前記検出された白紙部と隣接する２ドット幅の部分３５は画像の幅の小さい領域およびソリッド画像の端部であり、周辺電界が支配的な領域である。次に、露光量Ｅ1と露光量Ｅ2の関係について述べる。図４は感光体ドラム１の光応答特性を示す図である。横軸Ｅは露光量であり、感光体ドラム１に投入された光エネルギーにて示してある。縦軸は露光後一定時間における感光体ドラム１の電位である。縦軸のＶ0は現像における背景電位を示す。縦軸のＶr1は露光量Ｅ1に対応した感光体１での電位、Ｖr2は露光量Ｅ2に対応した感光体１での電位である。Ｖbは現像機のバイアス電圧であり、Ｖb−Ｖr1、Ｖb−Ｖr2がそれぞれ現像電位差である。
【００２２】
すなわち、電界周辺効果が強く作用するソリッド領域の端部、線画像、網点に対しては現像電位にＶb−Ｖr2を用い、ソリッド領域（ベタ画像）に対しては現像電位にＶb−Ｖr1を用いる。
【００２３】
図５は、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合の、階調カーブの変動を示す図であり、１４が現像ギャップが適正な場合の階調カーブ、１５が適正な現像ギャップよりも現像ギャップが狭い場合の階調カーブ、１６が適正な現像ギャップよりも現像ギャップが広い場合の階調カーブである。
【００２４】
図６は、平行電界によって現像される画像（ソリッド画像）のテストパッチ像を画像濃度センサーで検知し、該画像濃度センサーによる検知濃度が、予め定めた値になるように現像バイアスの直流電圧を調整し、前記現像バイアスの直流電圧の条件を維持したもとで、周辺電界によって感光体上に現像される画像（面積率が５０％の網点画像）のテストパッチ像を画像濃度センサーで検知し、該画像濃度センサーによる検知濃度が予め定めた値となるように、白紙部と隣接する数ドット幅の画像領域を露光する照射光量Ｅ2を調整し、階調性の補正を行った場合の階調カーブである。
【００２５】
この制御方法では、図６に示したように、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合、面積率１００％（ソリッド画像）の濃度および、面積率０〜５０％の低面積率の階調濃度は補正することができるが、面積率５０〜９０％の高面積率の階調濃度の変動を十分に補正することができない。
【００２６】
図７に、直流電圧だけの現像バイアスを印加した場合と、直流電圧に交流電圧を重畳した現像バイアスを印加した場合の階調カーブの比較を示す。１９が直流電圧だけの現像バイアスを印加した場合の階調カーブであり、２０、２１が直流電圧に交流電圧を重畳した現像バイアスを印加した場合の階調カーブである。ここで、２０よりも、２１の方が交流電圧の振幅Ｖｐｐが大きい場合に相当する。２２は直流電圧だけの現像バイアスを印加した場合の階調カーブと直流電圧に交流電圧を重畳した現像バイアスを印加した場合の階調カーブの交差する点である。現像バイアスに交流電圧を重畳して印加すると、面積率１００％のソリッド画像の画像濃度が増加するだけでなく、比較的面積率の大きい画像の現像性が増加し、面積率の小さい画像の現像性が低下するため、階調カーブの傾きが変化する。交流電圧を重畳して印加した場合に、階調カーブの傾きが変化する割合は、交流電圧の振幅Ｖｐｐが大きい程大きい。
【００２７】
直流電圧だけの現像バイアスを印加した場合の階調カーブと交流電圧を重畳して印加した場合の階調カーブの交差する点２２の画像面積率は、現像バイアスの直流電圧Ｖｂと、感光体上の電位潜像の関係によって決まる。現像電位差と背景電位差が等しい場合には、交差点は、画像の面積率が５０％付近の点になり、現像電位差が背景電位差よりも大きくなる程、交差点は、面積率の低い方にシフトする。例えば、帯電電位−６００Ｖ、放電電位−５０Ｖ、現像バイアスの直流電圧Ｖｂが−４００Ｖの場合、交差点は面積率が３０％付近の点になる。画像面積率が５０％以下の比較的面積率が小さい部分は、元々周辺電界による現像が支配的なため、交流電圧の振幅Ｖｐｐを変化させた場合の、画像濃度の変化は小さい、一方、画像面積率が５０％以上の比較的面積率の大きい部分は、交流電圧の振幅Ｖｐｐを変化させた場合の画像濃度の変化が大きい。
【００２８】
次に、本発明の印写制御方法について説明する。
【００２９】
（手順１）
先ず、ある交流電圧の振幅Ｖｐｐの条件（制御開始時は設計中心値）において、一定露光量Ｅ1で、感光体上にソリッド画像のテストパッチ潜像を数個作成する。
次に、現像バイアスの直流電圧Ｖbとスコロトロン帯電器のグリット電位Ｖgの差を例えば１５０Ｖに一定にしたまま、Ｖb及びＶgを５０Ｖおきに数点変化させて該テストパッチ潜像を現像し、テストパッチ像とする。次に、光学式画像濃度センサー１０で該ソリッド画像のテストパッチ像の内部（平行電界によって現像されている領域）の画像濃度を測定し、図９に示した現像バイアスの直流電圧Ｖbとソリッド画像濃度の関係を得る。図９より、目標とするソリッド画像濃度３６となる現像バイアスの直流電圧Ｖbの値を一次近似により決定する。スコロトロン帯電器のグリット電位ＶgはＶb＋１５０Ｖに決定する。
【００３０】
（手順２）
手順１で決定した現像バイアスの直流電圧Ｖb及びスコロトロン帯電器のグリット電位Ｖgの条件において、露光量Ｅ2を変化させながら感光体上に周辺電界による現像が主たる画像のテストパッチ潜像を数個作成する。テストパッチ潜像は一定面積率（例えば５０％）の網点画像を用いる。該テストパッチ潜像を現像してテストパッチ像とした後、光学式画像濃度センサー１０で該テストパッチ像の画像濃度を測定し、図１０に示した露光量Ｅ2と網点画像濃度の関係を得る。図１０より、目標とする網点画像濃度３７となる露光量Ｅ2の値を一次近似により決定する。
【００３１】
（手順３）
手順１、２で決定した現像バイアスの直流電圧Ｖb、スコロトロン帯電器のグリット電位Ｖg、露光量Ｅ2の条件において、画像面積率７０％の網点画像のテストパッチ潜像を作成し、該テストパッチ潜像を現像してテストパッチ像とした後、光学式画像濃度センサー１０で該網点画像のテストパッチ像の画像濃度を測定し、予め定めた画像濃度の範囲と比較を行う。
【００３２】
（手順４）
画像面積率７０％の網点の画像濃度が予め定めた画像濃度の範囲内に入っていた場合には、制御を終了する。一方、画像面積率７０％の網点の画像濃度が、予め定めた画像濃度の範囲よりも小さい場合には、交流電圧の振幅Ｖｐｐを増加させ、逆に、画像面積率７０％の網点画像が予め定めた画像濃度の範囲よりも大きい場合には、交流電圧の振幅Ｖｐｐを減少させる。
【００３３】
手順４において、画像面積率７０％の網点の画像濃度が予め定めた画像濃度の範囲内に入るまで、（手順１）〜（手順４）を繰り返す。
【００３４】
（手順４）での交流電圧の振幅Ｖｐｐの変更幅は、予め、交流電圧の振幅Ｖｐｐの変更幅と、画像濃度の変化の割合のデータを得ておき、これに基づいて、交流電圧の振幅Ｖｐｐの変更幅を決めて行うことにより、７０％の網点の画像濃度を、予め定めた画像濃度の範囲内に早く収束させることができる。
【００３５】
図１０は、上記説明した本発明の印写制御方法を用いて、階調性の補正を行った場合の階調カーブである。平行電界によって現像される画像（ソリッド画像）のテストパッチ像を画像濃度センサーで検知し、該画像濃度センサーによる検知濃度が、予め定めた値になるように現像バイアスの直流電圧を調整し、前記現像バイアスの直流電圧の条件を維持したもとで、周辺電界によって感光体上に現像される画像（面積率が５０％の網点画像）のテストパッチ像を画像濃度センサーで検知し、該画像濃度センサーによる検知濃度が予め定めた値となるように、白紙部と隣接する数ドット幅の画像領域を露光する照射光量Ｅ2を調整して階調性の補正を行った場合には、図６に示したように、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合に面積率５０〜９０％の高面積率の階調濃度の変動を十分に補正することができなかったのに対し、本発明の印写制御方法を用いて、階調性の補正を行った場合は、面積率５０〜９０％の高面積率の階調濃度も補正することができる。
【００３６】
また、本実施例では、画像面積率７０％の網点の画像濃度を予め定めた画像濃度に調整した例について説明したが、ここで用いる画像面積率は、現像ギャップが変動したときに大きく変動する画像面積率（６０〜８０％）であれば、同様の効果が得られる。
【００３７】
以上説明した印写制御を、装置の製造時および、現像ギャップが変動する可能性がある作業（例えば、現像機の交換、修理等）の後に行うことにより、感光体と現像ローラの間隔距離（現像ギャップ）のばらつきによる階調濃度の変動を補正することができる。
【００３８】
また、手順１、２のみを、画像形成装置の電源投入時および、その後、印刷ジョブの切れ目を見計らって定期的に行う。これにより、環境変動もしくは経時的な現像剤の帯電量の変化及び、感光体特性の変化が発生しても、全ての画像パターン対して経時的に安定な画質を保つことができる。
【００３９】
また、本実施例では、画像信号を露光前にメモリに取り込み、パターンマッチング手法により全ての画像の白紙部と隣接する予め定めた画素数の部分を検出し、白紙部と隣接する予め定めた画素数の部分は露光量Ｅ2で露光し、またそれ以外については露光量Ｅ1で露光するよう露光を制御した例について説明したが、全ての画像パターンを同一光量で露光する画像形成装置においても、（手順２）を省略して、（手順１）（手順３）（手順４）を行うことにより、感光体と現像ローラの間隔距離（現像ギャップ）のばらつきによる階調濃度の変動を補正することができる。
【００４０】
【発明の効果】
以上述べたように本発明によれば、感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合にも、低面積率から高面積率の全ての階調濃度を補正することができる画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施形態にかかる記録装置の模式図である。
【図２】本発明の実施形態におけるソリッド画像を現像するときに発生する現像電界と、網点や線画像などを現像するときに発生する現像電界の模式図である。
【図３】本発明の実施形態におけるランダムな画像パターンを用いて白紙部と隣接する２ドット幅の部分と、それ以外の部分を示す説明図である。
【図４】本発明の実施形態における感光体ドラムの光応答特性を示す説明図である。
【図５】本発明の実施形態における感光体と現像ローラの間隔距離（現像ギャップ）が製品毎にばらついた場合の、階調カーブの変動を示す図である。
【図６】本発明の実施形態における現像バイアス（直流電圧）、感光体表面電位、白紙部と隣接する数ドット幅の画像領域を露光する照射光量を調整して、階調性の補正を行った場合の階調カーブである。
【図７】本発明の実施形態における直流電圧だけの現像バイアスを印加した場合と、直流電圧に交流電圧を重畳した現像バイアスを印加した場合の階調カーブの比較を示す図である。
【図８】本発明の実施形態におけるテストパッチ像検出にて得られる現像バイアスの直流電圧Ｖbとソリッド画像濃度の関係を示す説明図である。
【図９】本発明の実施形態におけるテストパッチ像検出にて得られる露光量Ｅ2と網点画像濃度の関係を示す説明図である。
【図１０】本発明の印写制御方法を用いて、階調性の補正を行った場合の階調カーブを示す図である。
【符号の説明】
１…感光体ドラム、２…スコロトロン帯電器、３…現像機、４…記録紙、５…転写機、６…定着機、７…クリーナ、８…露光装置、９…制御装置、１０…光学式画像濃度センサー、１４…現像ギャップが適正な場合の階調カーブ、１５…適正な現像ギャップよりも現像ギャップが狭い場合の階調カーブ、１６…適正な現像ギャップよりも現像ギャップが広い場合の階調カーブ、１９…直流電圧だけの現像バイアスを印加した場合の階調カーブ、２０、２１…直流電圧に交流電圧を重畳した現像バイアスを印加した場合の階調カーブ、２２…直流電圧だけの現像バイアスを印加した場合の階調カーブと交流電圧を重畳して印加した場合の階調カーブの交差する点、３０…ソリッド画像を現像するときに発生する現像電界、３１…網点や線画像などを現像するときに発生する現像電界、３２…平行電界、３３…周辺電界。３４…露光量Ｅ1での露光部分、３５…露光量Ｅ2での露光部分、３６…目標のソリッド画像濃度、３７…目標の網点画像濃度、Ｖ0…帯電電位または背景電位、Ｖg…スコロトロン帯電器のグリッド電位、Ｖb…現像バイアス電位、Ｖr1、Ｖr2…放電電位または画像部電位。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic printing control method and an image forming apparatus in which an image is visualized using colored particles such as toner of a printer, a facsimile machine, a copying machine or the like.
[0002]
[Prior art]
Hereinafter, a conventional printing method will be described. A recording apparatus using an electrophotographic method includes a printing process in which colored particles are visualized as an image on the surface of a recording medium, and a fixing process in which the visualized colored particle images are transferred to the recording medium and fixed. As the colored particles, a powder called toner exclusively for electrophotography is used. In the charging process, the entire surface of the photoconductor is once charged, and subsequently, partial charge discharge is performed by irradiating light in the exposure process. Here, a potential contrast is formed between the charged area and the discharged area on the surface of the photoreceptor, which is called an electrostatic latent image.
[0003]
In the next development step, first, toner particles that are colored particles are charged. The toner charging method includes a two-component developing method using carrier beads and a one-component developing method in which charging is performed by friction between the toner and a member. On the other hand, a method called bias development is often used as a method for developing an electrostatic latent image. In bias development, a bias voltage is applied to the developing roller, and the charged toner particles are separated from the developer on the surface of the developing roller by the action of an electric field generated between the latent image potential formed on the surface of the photoreceptor and the developing roller. Then, it is moved to the surface of the photoconductor to form an image. As the latent image potential (that is, the potential of the image forming portion of the photoconductor), the above-described charging potential or the discharge potential may be used. In general, a method using a charging potential as a latent image potential is called a normal development method, and a method using a discharge potential is called a reversal development method.
[0004]
There are two types of bias development: one that applies only a DC voltage to the developing roller, and one that applies an AC voltage superimposed on the DC voltage. Compared with a DC voltage that is applied with an AC voltage superimposed, it can supply more toner to the latent image on the photoreceptor, and has the advantage of increasing the image density, compared to a DC voltage applied with a development bias of only DC voltage. Have (see, for example, Patent Document 1).
[0005]
Of the charging potential and the discharging potential, the potential that is not used as the latent image potential is called a background potential. The DC voltage of the developing roller bias voltage is set between the charging potential and the discharging potential, and the difference from the latent image potential is called the developing potential difference. Similarly, the difference from the background potential is called the background potential difference. If the development potential difference is large, the electric field formed (referred to as the development electric field) becomes strong, so that the development performance is enhanced. On the other hand, the background potential difference affects the image quality of the background portion of the image. If the background potential difference is small, the fogging of the background portion increases. Incidentally, the toner charge amount is closely related to the development performance. The larger the toner charge amount, the lower the development performance at the same development electric field strength.
[0006]
Next, changes in development performance over time will be described. Factors that cause changes in development performance over time are roughly classified into those caused by fluctuations in the charge amount of the developer and those caused by fluctuations in the developing electric field. In general, the charge amount of toner tends to fluctuate with respect to the humidity of the atmosphere, and increases when the humidity is low, and decreases when the humidity is high. In the case of two-component development, the surface state of the toner and carrier beads changes with time due to friction with the stirring member, and the charge amount of the toner changes.
[0007]
On the other hand, the potential of the discharge region formed by exposure varies due to a change in the temperature of the photoconductor, a change in humidity of the atmosphere, and a change in film thickness over time, regardless of the exposure light amount being constant. This variation in potential in the discharge region is significant when an intermediate potential region that is not completely discharged is provided so as not to give a sufficient amount of light during exposure.
[0008]
By the way, line images, halftone dots, and the like are greatly affected by the peripheral effect of the electric field, and the intensity of the developing electric field is larger than the developing electric field (parallel electric field) generated inside the solid region (solid image portion). Hereinafter, an electric field whose intensity is larger than that of the parallel electric field due to the influence of the peripheral effect is referred to as a peripheral electric field. When the film thickness of the photoconductor changes with time, the parallel electric field and the intensity of the peripheral electric field change as well as the ratio of the intensity of the parallel electric field and the peripheral electric field even under the same development potential difference.
[0009]
In order to make the image quality constant over time, it is necessary to correct the change in the development performance and the change in the development electric field due to the change in the charge amount of the developer.
[0010]
Prior to image formation, a test patch latent image is formed on the photoconductor by a laser writing unit to develop the developed test patch latent image in order to correct the density fluctuation of the printed image that accompanies changes in the charge amount of the developer. The test patch image is developed by a machine and the reflection density (image density) of the test patch image is measured by an optical image density sensor provided upstream of the cleaning device. In the case where the value deviates from the value, a method for controlling the developing bias, the grit voltage of the charger, the replenishment of toner, and the like is known.
[0011]
Also, as a method for correcting fluctuations in the development electric field, the potential of the surface of the photoconductor is detected by a potential sensor, and the film thickness of the photoconductor is detected by some method, and the amount of laser light is changed so that the development electric field is constant. A method for controlling the potential of the photoreceptor surface is known (see, for example, Patent Document 2).
[0012]
Furthermore, a method is also known in which the control using the optical image density sensor is combined with the control using the photoreceptor potential sensor.
[Patent Document 1]
Japanese Patent Laid-Open No. 62-28958 [Patent Document 2]
Japanese Patent Laid-Open No. 11-15214
[Problems to be solved by the invention]
In the above conventional technique, when the distance between the photosensitive member and the developing roller (development gap) varies from product to product, the gradation density variation of 100% area ratio (solid portion) and a low area ratio of 0 to 50% occurs. Although it can be corrected to be relatively small, there is a problem that gradation density variation with a high area ratio of 50 to 90% cannot be corrected.
[0014]
The object of the present invention is to correct all gradation densities from a low area ratio to a high area ratio even when the distance between the photosensitive member and the developing roller (development gap) varies from product to product in an electrophotographic recording apparatus. It is to provide a printing control method that can be performed.
[0015]
[Means for Solving the Problems]
The above object includes a photoconductor, a charger provided with a grid, an exposure unit, a developing device, a control unit, and a sensor for detecting a test patch formed on the photoconductor, and the exposure apparatus. The exposure amount is adjusted by the control means, and a DC voltage and an AC voltage are applied to the developing machine, and a background area and an image area are formed on the photoconductor using the charger and the exposure device. In a printing control method of an electrophotographic image forming apparatus to be formed, a first exposure amount that is an exposure amount adjusted to print the inside of a solid image, a peripheral portion other than the inside of the solid image, a line image, and a halftone dot A second exposure amount that is an exposure amount to be adjusted to print an image, and the control means creates a solid test patch latent image on the photoconductor with the first exposure amount, and the DC voltage And the grid applied to the grid A solid image patch, which is a solid image test patch, by developing the solid image test patch latent image with the developing device after changing the DC voltage and the grid voltage to be constant. The voltage value of the DC voltage and the voltage value of the grid voltage for making a predetermined solid image density are determined by creating and measuring the image density inside the solid image patch with the sensor After the first adjustment is performed, the second exposure amount is changed, and a first halftone dot image patch that is a test patch of a halftone dot image having a constant area ratio is formed on the photoconductor. The second adjustment is performed to determine the second exposure amount to be within the range of the image density of the predetermined halftone image by creating and measuring the image density of the first halftone image patch by the sensor. After performing the second adjustment A second halftone dot image patch, which is a test patch of a halftone dot image having an area ratio of 60% to 80%, is created on the photosensitive member, and the second halftone dot image patch is formed by the sensor. The measurement result image density obtained by measuring the image density is compared with a predetermined image density range of the halftone image, and the measurement result image density is a predetermined image density range of the halftone image. The control means terminates the control, and when the measurement result image density is outside the range of the image density of the predetermined halftone image, the amplitude of the alternating voltage is changed, and the first adjustment and This is achieved by repeating the second adjustment again.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0017]
FIG. 1 is a diagram schematically showing a cross section of the recording apparatus of this embodiment. 1 is a photosensitive drum, 2 is a scorotron charger, 3 is a developing machine, 4 is recording paper, 5 is a transfer machine, 6 is a fixing machine, 7 is a cleaner, 8 is an exposure device, 9 is a control device, and 10 is an optical type. It is an image density sensor.
[0018]
A latent image is formed on the surface of the photosensitive drum 1 uniformly charged by the scorotron charger 2 with a resolution of 600 dpi by the exposure device 8 based on the image signal. Thereafter, the toner is developed by the developing machine 3 to which a bias in which an AC voltage is superimposed on a DC voltage is applied. The frequency of the alternating voltage superimposed on the developing bias is preferably 2 to 16 kHz, the amplitude Vpp is preferably 0.4 to 2.0 kV, and the waveform is rectangular, sine, triangular, or the like. The toner developed on the surface of the photosensitive drum 1 is transferred to the recording paper 4 by the transfer machine 5. Thereafter, the transferred toner image is heated and melted by the fixing device 6 and fixed on the recording paper 4. Further, the toner remaining on the surface of the photosensitive drum 1 without being transferred is collected by the cleaner 7 and the series of processes is completed. In this embodiment, a test patch latent image having a predetermined image pattern is formed on the photosensitive member by the exposure device 8, and this test patch latent image is developed by the developing device 3 to form a test patch image. The reflection density of the test patch image is detected by the density sensor 10, and the grit voltage Vg of the scorotron charger, the DC voltage Vb of the developing bias, and the amplitude Vpp of the AC voltage are adjusted by the control device 9 based on the detected value. be able to.
[0019]
FIG. 2 is a diagram schematically showing a developing electric field generated when developing a solid image and a developing electric field generated when developing a halftone dot or a line image with the horizontal axis as a position on the photosensitive member. . 30 corresponds to a developing electric field generated when developing a solid image, and 31 corresponds to a developing electric field generated when developing a halftone dot or a line image. The interior of the solid image is an area that is not affected by the peripheral effect of the electric field. The developing electric field generated in this area is called a parallel electric field, and is indicated by 32 in FIG. On the other hand, the edge of the solid image, the halftone dot, and the line image are affected by the peripheral effect of the electric field, and an electric field stronger than the parallel electric field is generated. The developing electric field generated at the edge of the solid image and the halftone dot or line image is called a peripheral electric field, and is indicated by 33 in FIG. Due to this peripheral electric field, more toner is developed in the halftone dots and line image than in the solid image.
[0020]
In this recording apparatus, an image signal is taken into a memory before exposure, and a portion having a predetermined number of pixels adjacent to a blank portion of all images is detected by a pattern matching method. The portion of the predetermined number of pixels adjacent to the blank paper portion is exposed with the exposure amount E2, and the other portions are controlled by the exposure control means 9 so as to be exposed with the exposure amount E1.
[0021]
The predetermined number of pixels adjacent to the blank paper portion is set to be equal to or less than the number of pixels corresponding to the width of the peripheral electric field generated at the edge of the solid image. In this embodiment, a peripheral electric field is generated at the end of the solid image over a width of about 200 μm, which corresponds to a pixel number of about 5 dots at a resolution of 600 dpi. In order to make this peripheral electric field the same strength as the parallel electric field, it is necessary to set the number of pixels of 5 dots where the peripheral electric field is generated to a predetermined number of pixels. In order to correct the fluctuation of the peripheral electric field, Experiments have shown that the image quality of halftone dots and line images can be stabilized with a smaller number of pixels. In this embodiment, the predetermined number of pixels adjacent to the blank page is set to 2 dots. FIG. 3 shows a 2-dot-width portion adjacent to the detected blank paper portion as 35 and the other portion as 34 for a random image pattern. The two-dot width portion 35 adjacent to the detected blank paper portion is a region having a small image width and an end portion of the solid image, and is a region in which the peripheral electric field is dominant. Next, the relationship between the exposure dose E1 and the exposure dose E2 will be described. FIG. 4 is a diagram showing the light response characteristics of the photosensitive drum 1. The horizontal axis E is the exposure amount and is indicated by the light energy input to the photosensitive drum 1. The vertical axis represents the potential of the photosensitive drum 1 at a fixed time after exposure. V0 on the vertical axis represents the background potential during development. Vr1 on the vertical axis is the potential on the photoreceptor 1 corresponding to the exposure amount E1, and Vr2 is the potential on the photoreceptor 1 corresponding to the exposure amount E2. Vb is a bias voltage of the developing machine, and Vb-Vr1 and Vb-Vr2 are development potential differences.
[0022]
That is, Vb-Vr2 is used as the developing potential for the edge, line image, and halftone of the solid region where the electric field peripheral effect acts strongly, and Vb-Vr1 is used as the developing potential for the solid region (solid image). Use.
[0023]
FIG. 5 is a diagram showing the fluctuation of the gradation curve when the distance between the photosensitive member and the developing roller (development gap) varies from product to product. Reference numeral 14 denotes a gradation curve when the development gap is appropriate. Is a gradation curve when the development gap is narrower than the appropriate development gap, and 16 is a gradation curve when the development gap is wider than the appropriate development gap.
[0024]
FIG. 6 shows a test patch image of an image developed by a parallel electric field (solid image) detected by an image density sensor, and the DC voltage of the development bias is set so that the detected density by the image density sensor becomes a predetermined value. The image density sensor detects a test patch image of an image (a halftone dot image with an area ratio of 50%) developed on the photoconductor by the peripheral electric field while adjusting and maintaining the DC bias condition of the development bias. When the gradation amount is corrected by adjusting the irradiation light amount E2 for exposing an image area having a width of several dots adjacent to the blank paper portion so that the detection density by the image density sensor becomes a predetermined value. It is a gradation curve.
[0025]
In this control method, as shown in FIG. 6, when the distance between the photosensitive member and the developing roller (development gap) varies from product to product, the density of the area ratio 100% (solid image) and the area ratio 0-50. %, The gradation density of the low area ratio can be corrected, but the fluctuation of the gradation density of the high area ratio of 50 to 90% cannot be sufficiently corrected.
[0026]
FIG. 7 shows a comparison of gradation curves when a developing bias of only a DC voltage is applied and when a developing bias in which an AC voltage is superimposed on the DC voltage is applied. 19 is a gradation curve when a developing bias of only a DC voltage is applied, and 20 and 21 are gradation curves when a developing bias in which an AC voltage is superimposed on a DC voltage is applied. Here, 21 corresponds to the case where the amplitude Vpp of the AC voltage is larger than 20. Reference numeral 22 denotes a point where a gradation curve when a developing bias of only a DC voltage is applied and a gradation curve when a developing bias in which an AC voltage is superimposed on the DC voltage are applied intersect. When an AC voltage is superimposed and applied to the developing bias, not only the image density of a solid image with an area ratio of 100% increases, but also the developability of an image with a relatively large area ratio increases, and an image with a small area ratio is developed. The slope of the gradation curve changes due to a decrease in the characteristics. When the AC voltage is applied in a superimposed manner, the rate at which the gradient of the gradation curve changes increases as the amplitude Vpp of the AC voltage increases.
[0027]
The image area ratio at the point 22 where the gradation curve when the development curve of only the direct current voltage is applied and the gradation curve when the alternating current voltage is applied in an overlapping manner is the development bias direct current voltage Vb and on the photoreceptor. It is determined by the relationship of the potential latent image. When the development potential difference and the background potential difference are equal, the intersection is a point where the area ratio of the image is near 50%, and the intersection shifts to the lower area ratio as the development potential difference becomes larger than the background potential difference. For example, when the charging potential is −600 V, the discharge potential is −50 V, and the DC voltage Vb of the developing bias is −400 V, the intersection is a point with an area ratio of about 30%. In a portion with a relatively small area ratio of 50% or less, the development by the peripheral electric field is primarily dominant. Therefore, the change in the image density when the amplitude Vpp of the AC voltage is changed is small. A portion with a relatively large area ratio of 50% or more has a large change in image density when the amplitude Vpp of the AC voltage is changed.
[0028]
Next, the printing control method of the present invention will be described.
[0029]
(Procedure 1)
First, several solid test patch latent images are created on the photosensitive member with a constant exposure amount E1 under the condition of the amplitude Vpp of a certain AC voltage (design center value at the start of control).
Next, while the difference between the DC voltage Vb of the developing bias and the grit potential Vg of the scorotron charger is kept constant, for example, 150V, the test patch latent image is developed by changing Vb and Vg at several points every 50V. Let it be a patch image. Next, the image density inside the test patch image of the solid image (area developed by the parallel electric field) is measured by the optical image density sensor 10, and the development bias DC voltage Vb and the solid image shown in FIG. 9 are measured. Get the concentration relationship. From FIG. 9, the value of the DC voltage Vb of the developing bias that becomes the target solid image density 36 is determined by linear approximation. The grit potential Vg of the scorotron charger is determined to be Vb + 150V.
[0030]
(Procedure 2)
Several test patch latent images of an image mainly developed by a peripheral electric field are formed on the photosensitive member while changing the exposure amount E2 under the conditions of the DC voltage Vb of the developing bias determined in the procedure 1 and the grid potential Vg of the scorotron charger. To do. As the test patch latent image, a halftone image having a constant area ratio (for example, 50%) is used. After developing the test patch latent image to obtain a test patch image, the optical image density sensor 10 measures the image density of the test patch image, and the relationship between the exposure amount E2 and the halftone dot image density shown in FIG. obtain. From FIG. 10, the value of the exposure amount E2 to be the target halftone image density 37 is determined by linear approximation.
[0031]
(Procedure 3)
A test patch latent image of a halftone dot image with an image area ratio of 70% is created under the conditions of the DC voltage Vb of the developing bias determined in steps 1 and 2, the grit potential Vg of the scorotron charger, and the exposure amount E2, and the test patch After developing the latent image into a test patch image, the optical image density sensor 10 measures the image density of the test image of the halftone image and compares it with a predetermined image density range.
[0032]
(Procedure 4)
If the image density of a halftone dot with an image area ratio of 70% is within a predetermined image density range, the control is terminated. On the other hand, when the image density of a halftone dot with an image area ratio of 70% is smaller than a predetermined image density range, the amplitude Vpp of the AC voltage is increased, and conversely, a halftone dot image with an image area ratio of 70%. Is larger than a predetermined image density range, the AC voltage amplitude Vpp is decreased.
[0033]
In Procedure 4, (Procedure 1) to (Procedure 4) are repeated until the image density of a halftone dot having an image area ratio of 70% falls within a predetermined image density range.
[0034]
The change width of the amplitude Vpp of the AC voltage in (Procedure 4) is obtained in advance by obtaining data on the change width of the AC voltage amplitude Vpp and the change rate of the image density. By determining the change width of Vpp, it is possible to quickly converge the image density of halftone dots within a predetermined image density range.
[0035]
FIG. 10 is a gradation curve when gradation correction is performed using the above-described printing control method of the present invention. A test patch image of an image developed by a parallel electric field (solid image) is detected by an image density sensor, and the DC voltage of the development bias is adjusted so that the detected density by the image density sensor becomes a predetermined value, A test patch image of an image (a halftone dot image with an area ratio of 50%) developed on the photosensitive member by a peripheral electric field is detected by an image density sensor while maintaining the condition of the DC voltage of the developing bias. When the tone correction is performed by adjusting the irradiation light amount E2 for exposing the image area of several dots width adjacent to the blank paper portion so that the density detected by the density sensor becomes a predetermined value, FIG. As shown in FIG. 5, when the distance between the photosensitive member and the developing roller (development gap) varies from product to product, it is possible to sufficiently correct the variation in gradation density with a high area ratio of 50 to 90%. Not On the other hand, when gradation correction is performed using the printing control method of the present invention, gradation density with a high area ratio of 50 to 90% can be corrected.
[0036]
In this embodiment, an example in which the image density of a halftone dot having an image area ratio of 70% is adjusted to a predetermined image density has been described. However, the image area ratio used here varies greatly when the development gap varies. If the image area ratio is 60 to 80%, the same effect can be obtained.
[0037]
The above-described printing control is performed at the time of manufacture of the apparatus and after an operation (for example, replacement or repair of the developing machine) in which the development gap may fluctuate, so that the distance between the photosensitive member and the developing roller ( Variations in gradation density due to variations in development gap) can be corrected.
[0038]
Further, only the procedures 1 and 2 are periodically performed when the image forming apparatus is turned on and thereafter after a break in the print job. As a result, stable image quality can be maintained over time for all image patterns even if environmental fluctuations or changes in developer charge amount over time and changes in photoreceptor characteristics occur.
[0039]
Further, in this embodiment, an image signal is taken into a memory before exposure, a portion having a predetermined number of pixels adjacent to the blank portion of all images is detected by a pattern matching method, and a predetermined pixel adjacent to the blank portion is detected. The example in which the exposure is controlled so that the number of portions are exposed with the exposure amount E2 and the other portions are exposed with the exposure amount E1 has been described. However, in the image forming apparatus that exposes all image patterns with the same light amount, By omitting step 2) and performing steps (1), (step 3), and (step 4), it is possible to correct gradation density variations due to variations in the distance between the photosensitive member and the developing roller (developing gap). it can.
[0040]
【The invention's effect】
As described above, according to the present invention, even when the distance between the photosensitive member and the developing roller (development gap) varies from product to product, all gradation densities from a low area ratio to a high area ratio can be corrected. It is possible to provide an image forming apparatus capable of
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a recording apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a developing electric field generated when developing a solid image and a developing electric field generated when developing a halftone dot or a line image according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram showing a 2-dot-width portion adjacent to a blank paper portion and other portions using a random image pattern according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram showing optical response characteristics of a photosensitive drum according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a change in a gradation curve when an interval distance (development gap) between a photoconductor and a developing roller in an embodiment of the present invention varies for each product.
FIG. 6 illustrates gradation bias correction by adjusting a developing bias (DC voltage), a photoreceptor surface potential, and an irradiation light amount for exposing an image area having a width of several dots adjacent to a blank paper portion in the embodiment of the present invention. It is a gradation curve in the case of.
FIG. 7 is a diagram showing a comparison of gradation curves when a developing bias of only a DC voltage is applied and when a developing bias in which an AC voltage is superimposed on the DC voltage is applied in the embodiment of the present invention.
FIG. 8 is an explanatory diagram showing a relationship between a DC voltage Vb of a developing bias obtained by test patch image detection and a solid image density in the embodiment of the present invention.
FIG. 9 is an explanatory diagram showing a relationship between an exposure amount E2 obtained by test patch image detection and a halftone image density in the embodiment of the present invention.
FIG. 10 is a diagram showing a gradation curve when gradation correction is performed using the printing control method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Scorotron charger, 3 ... Developing machine, 4 ... Recording paper, 5 ... Transfer machine, 6 ... Fixing machine, 7 ... Cleaner, 8 ... Exposure device, 9 ... Control device, 10 ... Optical type Image density sensor, 14 ... gradation curve when development gap is appropriate, 15 ... gradation curve when development gap is narrower than appropriate development gap, 16 ... floor when development gap is wider than appropriate development gap Tone curve, 19: gradation curve when a development bias of only DC voltage is applied, 20, 21: gradation curve when a development bias in which AC voltage is superimposed on DC voltage is applied, 22: development of only DC voltage The point where the gradation curve when the bias is applied and the gradation curve when the alternating voltage is applied are crossed, 30 ... the development electric field generated when developing a solid image, 31 ... the halftone dot or line image Developing an electric field generated when developing the 32: parallel electric field, 33 ... fringe field. 34 ... exposure portion at exposure amount E1, 35 ... exposure portion at exposure amount E2, 36 ... target solid image density, 37 ... target dot image density, V0 ... charge potential or background potential, Vg ... scorotron charger Grid potential, Vb: development bias potential, Vr1, Vr2: discharge potential or image portion potential.

Claims

A photosensitive member, a charger provided with a grid, an exposure unit, a developing device, a control unit, and a sensor for detecting a test patch formed on the photosensitive member, wherein the exposure apparatus includes the control unit; The exposure amount is adjusted by the apparatus, and a DC voltage and an AC voltage are applied to the developing machine, and an electrophotographic image forming a background area and an image area on the photoconductor using the charger and the exposure device. In the image forming apparatus printing control method,
A first exposure amount that is an exposure amount that is adjusted to print the inside of the solid image, and a second exposure that is an exposure amount that is adjusted to print a peripheral portion other than the inside of the solid image, a line image, and a halftone image. The amount and
The control means creates a solid test patch latent image on the photoconductor with the first exposure amount, makes the difference between the DC voltage and the grid voltage applied to the grid constant, After changing the grid voltage, the solid image test patch latent image is developed by the developing device to create a solid image patch, which is a solid image test patch, and the sensor includes a solid image patch inside the solid image patch. By measuring the image density, a first adjustment for determining the voltage value of the DC voltage and the voltage value of the grid voltage to obtain a predetermined solid image density is performed,
After performing the first adjustment, the second exposure amount is changed, and a first halftone dot image patch which is a test patch of a halftone dot image having a constant area ratio is created on the photoconductor, and the sensor uses the sensor. By measuring the image density of the first halftone image patch, and performing a second adjustment for determining a second exposure amount to be within a predetermined image density range of the halftone image,
After performing the second adjustment, a second halftone image patch, which is a test patch of a halftone image having an area ratio of 60% to 80%, is created on the photoconductor, and the sensor And comparing the measurement result image density obtained by measuring the image density of the second halftone dot image patch with the predetermined image density range of the halftone dot image,
When the measurement result image density is within a predetermined image density range of the halftone image, the control means ends the control,
When the measurement result image density is outside a predetermined halftone dot image density range, the amplitude of the AC voltage is changed, and the first adjustment and the second adjustment are repeated again. Control method.

A photosensitive member, a charger provided with a grid, an exposure unit, a developing device, a control unit, and a sensor for detecting a test patch formed on the photosensitive member, wherein the exposure apparatus includes the control unit; The exposure amount is adjusted by the apparatus, and a DC voltage and an AC voltage are applied to the developing machine, and an electrophotographic image forming a background area and an image area on the photoconductor using the charger and the exposure device. In the image forming apparatus,
A first exposure amount that is an exposure amount that is adjusted to print the inside of the solid image, and a second exposure that is an exposure amount that is adjusted to print a peripheral portion other than the inside of the solid image, a line image, and a halftone image. The amount and
The control means creates a solid test patch latent image on the photoconductor with the first exposure amount, makes the difference between the DC voltage and the grid voltage applied to the grid constant, After changing the grid voltage, the solid image test patch latent image is developed by the developing device to create a solid image patch, which is a solid image test patch, and the sensor includes a solid image patch inside the solid image patch. By measuring the image density, a first adjustment for determining the voltage value of the DC voltage and the voltage value of the grid voltage to obtain a predetermined solid image density is performed,
After performing the first adjustment, the second exposure amount is changed, and a first halftone dot image patch which is a test patch of a halftone dot image having a constant area ratio is created on the photoconductor, and the sensor uses the sensor. By measuring the image density of the first halftone image patch, and performing a second adjustment for determining a second exposure amount to be within a predetermined image density range of the halftone image,
After performing the second adjustment, a second halftone image patch, which is a test patch of a halftone image having an area ratio of 60% to 80%, is created on the photoconductor, and the sensor And comparing the measurement result image density obtained by measuring the image density of the second halftone dot image patch with the predetermined image density range of the halftone dot image,
When the measurement result image density is within a predetermined image density range of the halftone image, the control means ends the control,
When the measurement result image density is outside the range of the image density of a predetermined halftone image, control is performed to change the amplitude of the AC voltage and repeat the first adjustment and the second adjustment again. Image forming apparatus.