JP2004233464A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which precisely corrects images for each image formation, obtains stable images for a long term, shortens time required for control, and prevents productivity from decreasing. <P>SOLUTION: Toner images are formed on an image carrier 4 by a first development means in succession so that transfer is carried out at a first recording medium 6A and a second recording medium 6B on a recording-material carrier 5 in this order. Before the second recording medium 6B with the toner image transferred on it by the first development means is passed through a transfer section, the second development means is moved to a development section by a moving means so that transfer is carried out at the second recording medium 6b and the first recording medium 6A on the recording-medium carrier 5 in this order. Then toner images are formed in succession on the image carrier 4 by the second development means 4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００６５】
光量／濃度変換部（ＬＯＧ変換部）２０６は、ルックアップテーブルＲＯＭにより構成され、Ｒ４、Ｇ４、Ｂ４の輝度信号がＭ０、Ｃ０、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、Ｍ０、Ｃ０、Ｙ０の画像信号を遅延させる。
【００６６】
マスキング及びＵＣＲ回路２０８は、入力されたＭ１、Ｃ１、Ｙ１の３原色信号により黒信号（Ｋ）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、Ｍ２、Ｃ２、Ｙ２、Ｋ２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。
【００６７】
γ補正回路２０９は、リーダ部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。
【００６８】
このように処理されたＭ４、Ｃ４、Ｙ４、Ｋ４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。
【００６９】
また、リーダ部Ａは、リーダ部内の制御を行うＣＰＵ２１４、ＲＡＭ２１５、ＲＯＭ２１６を有しており、更に、操作部２１７、表示器２１８を備えている。
【００７０】
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。
【００７１】
図３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、（Ｍ）、（Ｃ）、（Ｙ）、（Ｋ）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。
【００７２】
（プリンタ部Ｂ）
図１において、帯電手段８は、コロナ帯電器であり、バイアスを印加することで、像担持体である感光体ドラム４の表面を一様に負極性に帯電させる。
【００７３】
画像データは、プリンタ画像処理部１０９に含まれるレーザドライバ及びレーザ光源１１０を介してレーザ光に変換され、そのレーザ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。レーザ光の走査により潜像が形成された感光体ドラム４は、図中に示す矢印の方向に回転する。感光体ドラム４は、ホームポジションを持ち、エンコーダなどを利用することによって回転動作中に位置情報を得ることが可能な構成となっている。
【００７４】
現像装置は、互いに異なる色のトナーを収容し像担持体上に形成された潜像を現像部で現像する複数の現像手段と、複数の現像手段を収容しその一つが現像部に択一的に位置するように移動させる移動手段とを有し、上記静電潜像を可視像化するものである。現像装置は、本実施例では、マゼンタ、シアン、イエロー、ブラック各色の現像器３Ｍ、３Ｃ、３Ｙ、３Ｋを収納する回転式現像装置３とされる。
【００７５】
４つの現像器３Ｍ、３Ｃ、３Ｙ、３Ｋは、回転可能な回転式現像装置３内に着脱可能に保持されており、画像形成の際には回転式現像装置３に保持された状態で回転軸を中心に回転し、例えばマゼンタトナー現像器３Ｍが感光体ドラム４に対向した位置に停止し、マゼンタトナー現像器内の、現像剤担持体としての現像スリーブが感光体ドラム４に対して微小間隔（４００μｍ程度）をもって対向し、感光体ドラム上に対して可視像の形成を行う。異なる色のトナー像、例えばシアントナー像やイエロートナー像の現像を行う際には、同様に現像装置３が回転駆動の後、所定の現像器が感光体ドラムに対向した位置で停止して現像が行われる。
【００７６】
以上の現像動作が終了すると、回転式現像装置内のあらゆる色の現像器内のスリーブが感光体ドラム４に当接しない位置まで回転式現像装置が離間し、この位置をホームポジションとする。このようにホームポジションを設定することで、不用意に回転式現像装置内のトナーが感光体ドラム表面に付着するのを防ぐとともに、回転式現像装置内に収納されている他の色の現像器内に混入することを防ぐことができる。
【００７７】
無端状の記録材担持体としての、樹脂シートが張設された転写ドラム５上には、吸着手段をもって、記録材６を担持、搬送することが可能である。また、転写ドラム５は、画像形成時、一方向にのみ回転可能に支持され、図示しないモーターによって回転駆動される。
【００７８】
上記構成は、一色目を転写した後に転写ドラムが逆回転することによって二色目を転写し、以降転写ドラムの順回転と逆回転を繰り返し各色を転写するようなスイッチバック方式などの構成と比較して、色ズレの軽減やモーターのコストダウン、機構の簡易化といったメリットもある。
【００７９】
クリーニング装置９は、現像器によって可視化された像が転写ドラム５上の記録材６に転写された後、感光体ドラム４上の残トナーをクリーニングするものであり、廃トナーはクリーニング容器に蓄えられ、満杯になった段階で交換処理される。
【００８０】
定着器７は、記録材６上のトナー像を加熱定着させるものであり、記録材６に熱を加えるための定着ローラと、記録材を定着ローラに圧接させるための加圧ローラの２本のローラで構成されている。
【００８１】
また、像担持体としての感光体ドラム４上に形成された検出用のトナー像であるトナーパッチパターンを読み取る、即ち、トナーパッチパターンの反射光量（濃度）を検出するための検出手段としての、ＬＥＤ光源１０（約９６０ｎｍに主波長をもつ）とフォトダイオード１１から成る光学読み取り装置（フォトセンサ）４０を設けている。感光体ドラム４の表面電位は、表面電位センサ１２で計測される。
【００８２】
（画像形成シーケンス）
ここで、本実施例の画像形成のシーケンスについて説明する。
【００８３】
感光体ドラム４と転写ドラム５は、共にプロセススピード２６５ｍｍ／ｓで図示した矢印方向へ回転する。直径６０ｍｍの感光体ドラム４は１回転当たり０．７１秒で回転し、直径１６０ｍｍの転写ドラム５は１．９秒で１回転する。
【００８４】
なお、感光体ドラム４と転写ドラム５の周速は完全に一致していなくても良く、転写効率を向上させるためにどちらか一方の周速を他方に対して所定量速くするか、或いは、遅くする構成であっても良い。
【００８５】
ユーザーがコピーのスタートスイッチを操作すると、図２６に示すように、転写ドラム５のシート保持面Ａ、Ｂのそれぞれに対応した所定のタイミングで、露光装置から感光体ドラム４に対する静電潜像の書き込みがなされ、これら静電潜像はマゼンタ現像器３Ｍによって現像される。現像された二つのマゼンタトナー像は、図２５に示す転写ドラム５のシート保持面Ａの先端基準ＰＡ及びシート保持面Ｂの先端基準ＰＢに合致して保持された第１と第２の二枚の記録材６Ａ、６Ｂに相次いで転写される。
【００８６】
このとき、記録材６Ｂの後端と記録材６Ａの先端の間隔は、（１６０×π―４２０）／２より、およそ４１．２ｍｍであり、転写ドラム５は外周で４１．２ｍｍだけ回転するのに要する時間はおよそ０．１６秒である。
【００８７】
回転式現像装置３を回転して、続くシアン現像器３Ｃを用いて現像を行うことを考える。
【００８８】
実施例における回転式現像装置３は直径が１４０ｍｍであり、回転交換時の駆動速度は２２０ｍｍ／ｓｅｃであるので、現像器の回転交換に必要な時間は（１４０×π／４）／２２０より、およそ０．５秒であり、現像器を回転交換していると、記録材６Ｂの後端の通過後、記録材６Ａの先端部を通過してしまい、シアン像を現像、転写することができない。
【００８９】
そこで、本実施例では、ここで転写ドラム５を空回転させ、次の第１の記録材６Ａをスキップし、第２の記録材６Ｂ、第１の記録材６Ａの順にシアン像の現像、転写を行う構成とする。
【００９０】
すなわち、転写ドラム５の１．５回転サイクル毎にシート保持面Ａ、Ｂに保持された保持された二枚の記録材６Ａ、６Ｂに同一色のトナー像を連続して転写することができ、この１．５回転サイクルを繰り返す毎に、マゼンタ、シアン、イエロー及びブラックのトナー像が転写ドラム５のシート保持面Ａ、Ｂに保持された二枚の記録材６Ａ、６Ｂにそれぞれ転写される。
【００９１】
もちろん、この転写ドラム５の空回転時間中も回転速度は画像形成時と同速度が維持されるものとする。即ち、転写ドラム５は無端状で、画像形成時は一方向にしか回転せず、また、空回転時は感光体ドラム４と転写ドラム５のスピードは減速されずにそのままのスピードが維持される。
【００９２】
この構成により、転写ドラム５上では記録材６Ｂの後端と６Ａの先端の間隔４１．２ｍｍに加え、記録材６Ａの領域２１０ｍｍを空回転させる時間が生じ、回転式現像装置３を回転する余裕を得ることができる。
【００９３】
さらに、この転写ドラム５の空回転時間を利用して本実施例では、マゼンタ現像器３Ｍは、二つのマゼンタトナー像に続いて、濃度検知用のトナー画像となる所定のパッチパターンを現像した後に、回転式現像装置３が９０°回転して現像器の交換が行われ、シアン現像器３Ｃが感光体ドラム４との対向位置に設定される。
【００９４】
シート保持面Ａに対応した次の転写ドラム５の半回転サイクルでは露光装置の感光体ドラム４への書き込みは行わず、転写ドラム５は記録材６Ａ、６Ｂを保持したまま空回転する。この時間帯にフォトセンサ４０は、感光体ドラム４の表面を検知してその読み取った感光体ドラム表面からの反射出力を下地出力データとして記憶する。この際に、感光体ドラム表面の反射出力と感光体ドラムの位置情報を共に記憶する。
【００９５】
ここで、本実施例の構成では、感光体ドラム４の周長は記録材上の画像形成領域よりも短いため、転写ドラム５の空回転サイクル中に感光体ドラムは一周以上回転でき、感光体ドラム表面の反射出力は感光体ドラム一周分以上検出することができる。
【００９６】
そして、空回転に係るシート保持面Ａに対応した転写ドラム５の半回転サイクルが終了すると、転写ドラム５の次の１回転サイクルにおいて、シート保持面Ｂとシート保持面Ａに対応した露光が行われる。これにより、感光体ドラム４上にはシアンに対応した二つの静電潜像が相次いで書き込まれ、これら静電潜像はシアン現像器３Ｃによって現像される。このようにして形成されたシアンの二つのトナー像は、転写ドラム５のシート保持面Ｂ及びシート保持面Ａに保持された二枚の記録材６Ａ、６Ｂに相次いで転写される。
【００９７】
このように、本実施例のシーケンスでは、前後する転写ドラム５の半回転サイクル毎にトナー像を形成してこれを転写ドラム５のシート保持面Ａ、Ｂに保持された二枚の記録材に連続して転写し、その次の半回転サイクル中に現像器の交換を行うと同時に感光体ドラム表面をフォトセンサ４０で検知して下地出力データとして記憶する。
【００９８】
これにより、転写ドラム５の１．５回転サイクル毎に二枚の記録材に同一色のトナー像を連続して転写することができ、この１．５回転サイクルを繰り返す毎に、マゼンタ、シアン、イエローおよびブラックのトナー像がシート保持面Ａ、Ｂに保持された二枚の記録材６Ａ、６Ｂにそれぞれ転写される。
【００９９】
従って、転写ドラム５の５．５回転で二枚の記録材６Ａ、６Ｂ上に４色のトナー像による重ね合わせトナー像が形成され、ブラックのトナー像の転写が終了した記録材６Ａ、６Ｂは相次いで転写ドラム５から剥離され、定着器７を経て排出トレイに排出される。
【０１００】
毎サイクルの転写ドラム５の空回転中にフォトセンサ４０によって検出され記憶される感光体ドラム表面一周分の下地出力データは、感光体ドラムの位置情報を元にその位置ごとに、毎回の平均値をとってもよいし、次々に最新の値として更新されていく構成としてもよい。
【０１０１】
以上、本実施例３のシーケンスでは、各色でのトナー像を現像し、後述する第２の制御用のパッチパターンを現像した後に、回転式現像装置３を回転させ現像器３Ｍ、３Ｃ、３Ｙ、３Ｋを交換し、その時間は転写ドラム５の空回転時間とし、さらにこの時間中に感光体ドラム上の下地を一周分以上検知することができ、さらに位置情報と共に記憶するため、後述するトナーパッチを検出して画像情報を補正する第２の制御手段を行う前に改めて感光体ドラム上の下地を検知する手間がなくなり、時間的にも短縮することができる。さらに現像器３の交換によって生じる振動が静電潜像の書き込みに影響を及ぼすことも避けることができる。
【０１０２】
（プリンタ制御部（プリンタ画像処理部）１０９）
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。
【０１０３】
プリンタ制御部、即ち、プリンタ画像処理部１０９は、ＣＰＵ２８、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、リーダ部Ａ及びプリンタエンジン部１００と通信できるように構成され、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、一次帯電器８、レーザ光源１０１、表面電位センサ１２、現像器３を制御している。又、プリンタエンジン部１００には、機内の空気中の水分量を測定する環境センサ３３が備えられている。
【０１０４】
表面電位センサ１２が現像装置３より上流側に設けられており、一次帯電器８のグリッド電位、現像装置３の現像バイアスは後述のようにＣＰＵ２８により制御される。
【０１０５】
（階調画像を得る画像信号処理回路）
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。
【０１０６】
画像の輝度信号がＣＣＤ１０５で得られ、リーダ画像処理部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。
【０１０７】
図６に、階調が再現される様子を４限チャートで示す。
【０１０８】
第Ｉ象限は、原稿濃度を濃度信号に変換するリーダ部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。
【０１０９】
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。
【０１１０】
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。
【０１１１】
ＬＵＴ２５は、後に述べる演算結果により生成される。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、レーザのＯＮ／ＯＦＦを制御するレーザドライバ２７に送られる。本実施例では、Ｍ、Ｃ、Ｙ、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。
【０１１２】
そして、レーザ光源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。
【０１１３】
（第１の制御系）
次に、リーダ部Ａ、プリンタ部Ｂの双方を含む系の画像再現特性の安定化に関する第１の制御系について説明する。
【０１１４】
まず、リーダ部Ａを用いてプリンタ部Ｂのキャリブレーションについて、図７のフロー図を用いて説明する。このフローは、リーダ部Ａを制御するＣＰＵ２１４（図２）とプリンタ部Ｂを制御するＣＰＵ２８（図４、図５）により実現される。
【０１１５】
操作部２１７（図２）上に設けられた、自動階調補正というモード設定ボタンを押すことで、本制御がスタートする。なお、本実施例では、表示器２１８（図２）は、図８〜図１０に示す様なプシュセンサつきの液晶操作パネル（タッチパネルディスプレイ）で構成されている。
【０１１６】
図７のステップＳ５１において、表示器２１８上に、テストプリント１のプリントスタートボタン８１が現れ（図８（ａ））、それを押すことで図１１に示すテストプリント１の画像がプリンタ部Ｂによりプリントアウトされる。テストプリント１は記録材である用紙６に所定の画像パターンが形成され定着処理されたものである。
【０１１７】
このとき、テストプリント１を形成するための用紙の有無をＣＰＵ２１４が判断し、ない場合は図８（ｂ）に示すような警告表示を行う。
【０１１８】
このテストプリント１の形成時にはコントラスト電位（後述する）は、環境に応じた標準状態のものを初期値として登録しておき、これを用いる。
【０１１９】
また、本実施例に用いた画像形成装置は、複数の用紙カセットを備え、Ｂ４、Ａ３、Ａ４、Ｂ５等複数種の用紙サイズが選択可能となっている。
【０１２０】
しかし、この制御で使用するプリント用紙は、後の読み取り作業時に、縦置き、横置きの間違えによるエラーを避けるために、一般で言われているラージサイズ紙を用いている。すなわち、Ｂ４、Ａ３、１１×１７、ＬＧＲを用いるように、設定されている。
【０１２１】
図１１のテストパターン１には、Ｍ、Ｃ、Ｙ、Ｋ４色分の中間階調濃度による、帯状のパターン６１を形成する。
【０１２２】
このパターン６１を目視で検査することにより、スジ状の異常画像、濃度ムラ、色ムラがないことを確認する。このパターンはスラスト方向に、パッチパターン６２、及び階調パターン７１、７２（図１２）をカバーするようにＣＣＤセンサ１０５の主走査方向のサイズが設定されている。
【０１２３】
異常が認められる場合には、再度テストプリント１のプリントを行い、再度異常が認められた場合にはサービスマンコールとする。
【０１２４】
なお、この帯パターン６１をリーダ部Ａで読み取り、そのスラスト方向の濃度情報により、以後の制御を行うかどうかの可否判断を自動で下すことも可能である。
【０１２５】
一方パターン６２はＭ、Ｃ、Ｙ、Ｋの各色の最大濃度パッチで、濃度信号値で２５５レベルを用いる。
【０１２６】
図７のステップＳ５２では、このテストプリント１の画像を、原稿台ガラス１０２上に図１３のようにのせて、図９の（ａ）に示される読み取りスタートボタン９１を押す。このとき、図９（ａ）に示す操作者用のガイダンス表示が現れる。
【０１２７】
図１３は、原稿台１０３を上部から見た図であり、左上のくさび型マークＴが原稿台１０２の原稿突き当て用のマークであり、帯パターン６１が、突き当てマークＴ側にくるようにして、なおかつ、表裏を間違えないように、操作パネル上で上述のようなメッセージを表示する（図９（ａ））。このようにすることで、置き間違えによる制御エラーを防ぐようにした。
【０１２８】
リーダ部Ａにより、パターン６２を読み取る際に、突き当てマークＴから徐々に走査し、一番最初の濃度ギャップ点Ａがパターン６１の角で得られるので、その座標ポイントから、相対座標で、パターン６２の各パッチの位置を割り出して、パターン６２の濃度値を読み取る。
【０１２９】
読み取り中は図９（ｂ）に示す表示が行われ、テストプリント１の向きや位置が不正確で読み取り不能のときは図９（ｃ）に示すメッセージを表し、操作者が置きなおして、読み込みキー９２を押すことにより再度読み取りを行う。
【０１３０】
得られたＲＧＢ値より、光学濃度の換算するためには、下式（２）を用いる。市販の濃度計と同じ値にするために、補正係数（ｋ）で調整している。
【０１３１】
【数２】

【０１３２】
また、別にＬＵＴを用いてＲＧＢの輝度情報からＭＣＹＫの濃度情報に変換してもよい。
【０１３３】
次に、得られた濃度情報から、最大濃度を補正する方法を説明する。
【０１３４】
図１５に相対ドラム表面電位と上述の演算により得られた画像濃度の関係を示す。
【０１３５】
その時点で用いたコントラスト電位、すなわち、現像バイアス電位と一次帯電された後レーザ光を用いて最大レベルを打った時の感光体ドラムの表面電位との差が、Ａという設定で得られた最大濃度ＤＡであった場合、最大濃度の濃度域では、相対ドラム表面電位に対して画像濃度が実線Ｌに示すように、リニアに対応することがほとんどである。
【０１３６】
ただし、２成分現像系では、現像器内のトナー濃度が変動して、下がってしまった場合、破線Ｎのように、最大濃度の濃度域で、非線形特性になってしまう場合もある。
【０１３７】
従って、ここでは、最終的な最大濃度の目標値を１．６としているが、０．１のマージンを見込んで、１．７を最大濃度をあわせる制御の目標値に設定して制御量を決定する。
【０１３８】
ここでのコントラスト電位Ｂは、次式（３）を用いて求める。
【０１３９】
Ｂ＝（Ａ＋Ｋａ）×１．７／ＤＡ （３）
【０１４０】
ここで、Ｋａは補正係数であり、現像方式の種類によって値を最適化するのが好ましい。
【０１４１】
実際には、電子写真方式では、環境によって、コントラスト電位Ａの設定は、環境に応じて変えないと画像濃度が合わず、先に説明した、機内の水分量をモニタする環境センサ３３（図４）の出力によって、図１６のように設定を変えている。
【０１４２】
従って、コントラスト電位を補正する方法として次式の補正係数Ｖｃｏｎｔ．ｒａｔｅｌを、バックアップされたＲＡＭ３２に保存しておく。
【０１４３】
Ｖｃｏｎｔ．ｒａｔｅｌ＝Ｂ／Ａ
【０１４４】
画像形成装置が３０分毎に、環境（水分量）の推移を、モニタし、その検知結果に基づいてＡの値を決定する度に、Ａ×Ｖｃｏｎｔ．ｒａｔｅｌを算出して、コントラスト電位を求める。
【０１４５】
コントラスト電位から、グリッド電位と現像バイアス電位を求める方法を簡単に説明する。
【０１４６】
図１７にグリッド電位と感光体ドラムとの関係を示す。グリッド電位を−２００Ｖにセットして、レーザ光のレベルを最低にして走査したときの表面電位Ｖ_Ｌ並びにレーザ光のレベルを最高にしたときの表面電位Ｖ_Ｈを表面電位センサ１２（図１、図４）で測定する。同様にグリッド電位を−４００ＶにしたときのＶ_ＬとＶ_Ｈを測定する。−２００Ｖのデータと−４００Ｖのデータを、補間、外挿することで、グリッド電位と表面電位との関係を求めることができる。
【０１４７】
この電位データを求めるための制御を電位測定制御とよぶ。
【０１４８】
Ｖ_Ｌから画像上にカブリトナーが付着しないように設定されたＶｂｇ（ここでは１００Ｖに設定）の差を設けて、現像バイアスＶＤＣを設定する。
【０１４９】
コントラスト電位Ｖｃｏｎｔは、現像バイアスＶＤＣとＶ_Ｈの差分電圧であり、このＶｃｏｎｔが大ほど、最大濃度が大きくとれるのは、上述した通りである。
【０１５０】
計算で求めたコントラスト電位Ｂにするためには、図１７の関係より、何ボルトのグリッド電位が必要か、そして何ボルトの現像バイアス電位が必要かは、計算で求めることができる。
【０１５１】
図７のステップＳ５３では最大濃度を最終的な目標値より、０．１高くなるようにコントラスト電位を求め、このコントラスト電位が得られるように、グリッド電位及び現像バイアス電位をＣＰＵ２８（図４、図５）がセットする。
【０１５２】
ステップＳ５４にて、求めたコントラスト電位が、制御範囲にあるかどうかを判断して、制御範囲からはずれている場合には、現像器等に異常があるものと判断して、対応する色の現像器をチェックするように、サービスマンにわかるように、エラーフラグをたてておき、所定のサービスモードでそのエラーフラッグをサービスマンが見られるようにする。
【０１５３】
ここでは、そのような異常時には制御範囲ぎりぎりの値にリミッターをかけて、修正制御して（ステップＳ５５）、制御は継続させる。
【０１５４】
以上の様に、ステップＳ５３で求めたコントラスト電位になれるように、ＣＰＵ２８によりグリッド電位と現像バイアス電位の設定を行う。
【０１５５】
図２４に、濃度変換特性図を示す。本実施例での最大濃度を最終目標値より高めに設定する最大濃度制御により第ＩＩＩ象限のプリンタ特性図は実線Ｊのようになる。
【０１５６】
もし仮に、このような制御を行わないときには、破線Ｈのような１．６に達しないプリンタ特性になる可能性もある。破線Ｈの特性の場合ＬＵＴ２５をいかように設定しても、ＬＵＴ２５は最大濃度を上げる能力は持ち合わせていないので、濃度ＤＨと１．６の間の濃度は再現不可能となる。
【０１５７】
実線Ｊの様に最大濃度をわずかに越える設定になっていれば、確実に、第ＩＶ象限のトータル階調特性で、濃度再現域は保証することができる。
【０１５８】
次に、図１０（ａ）のように操作パネル上に、テストプリント２の画像のプリントスタートボタン１５０が現れ、それを押すことで図１２のテストプリント２の画像がプリントアウトされる（ステップＳ５６）。プリント中は図１０（ｂ）のような表示となる。テストプリント２もテストプリント１と同様に記録材である用紙６に所定の画像パターンが形成され定着処理されたものである。
【０１５９】
テストプリント２は図１２に示すように、Ｍ、Ｃ、Ｙ、Ｋの各色、４列１６行の全部で６４階調分のグラデーションのパッチ群により成り立ち、ここで、６４階調分は、全部で２５６階調あるうちの、濃度の低い領域を重点的にレーザ出力レベルを割り当ててあり、高濃度領域は、レーザ出力レベルをまびいてある。このようにすることにより、特にハイライト部における階調特性を良好に調整することができる。
【０１６０】
図１２には、解像度２００ｌｐｉ（ｌｉｎｅｓ／ｉｎｃｈ）のパッチ７１と、４００ｌｐｉ（ｌｉｎｅｓ／ｉｎｃｈ）のパッチ７２が示される。各解像度の画像を形成するためには、パルス幅変調回路２６（図４、図５）において、処理の対象となっている画像データとの比較に用いられる三角波の周期を複数用意することによって実現できる。
【０１６１】
なお、本画像形成装置は、階調画像は２００ｌｐｉの解像度で、文字等の線画像は４００ｌｐｉの解像度で、作成している。この２種類の解像度で同一の階調レベルのパターンを出力しているが、解像度のちがいで、階調特性が大きく異なる場合には、解像度に応じて先の階調レベルを設定するのがより好ましい。
【０１６２】
また、テストプリント２は、ＬＵＴ２５を作用させずに、パターンジェネレータ２９（図４、図５）から発生させる。
【０１６３】
図１４は、テストプリント２の出力を、原稿台ガラス１０２上に置いたときに、上方から見た模式図であり、左上のくさび型マークＴが原稿台の原稿突き当て用のマークであり、Ｋのパターンが、突き当てマークＴ側にくるようにして、なおかつ、表裏を間違えないように操作パネル上でメッセージを表示した（図１０の（ｃ））。このようにすることで、置き間違えによる制御エラーをふせぐようにした。
【０１６４】
リーダ部Ａにて、パターンを読み取る際に、突き当てマークＴから徐々に走査し、一番最初の濃度ギャップ点Ｂが得られるので、その座標ポイントから、相対座標でパターンの各色パッチの位置を割り出して、読み取るようにした（ステップＳ５７）。
【０１６５】
１パッチ（図１２の７３）当たりの読むポイントは図１８のように、パッチの内部を、読み取りポイント（ｘ）を１６ポイントとり、得られた信号を平均する。ポイント数は読み取り装置、画像形成装置によって最適化するのが好ましい。
【０１６６】
各パッチ毎に１６ポイントの値が平均された、ＲＧＢ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、横軸にレーザ出力レベルをプロットしたのが、図１９である。
【０１６７】
更に、右の縦軸のように、紙のベース濃度、本例では０．０８を０レベルに、この画像形成装置の最大濃度として設定している１．６０を２５５レベルに正規化している。
【０１６８】
得られたデータがＣ点のように、特異的に濃度が高かったり、Ｄ点のように、低かったりした場合には、原稿台ガラス１０２上に汚れがあったり、テストパターン上に不良があったりすることがあるので、データ列に連続性が保存されるように、傾きにリミッターをかけ、補正を行う。ここでは具体的には傾きが３以上の時は、３に固定し、マイナス値の時は、その前のレベルと同じ濃度レベルにしている。
【０１６９】
ＬＵＴ２５の内容は前述したように、図１９の濃度レベルを入力レベル（図６の濃度信号軸）に、レーザ出力レベルを出力レベル（図６のレーザ出力信号軸）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。
【０１７０】
このときに、入力レベル０レベルに対して、出力レベルは０レベルになるように、制限条件を設けている。
【０１７１】
そして、ステップＳ５８で上述の様に作成した変換内容をＬＵＴ２５に設定する。
【０１７２】
以上で、読取装置（リーダ部）Ａを用いた第１の制御系によるコントラスト電位制御とγ変換テーブル作成が完了する。上述の処理中には、図１０（ｄ）のような表示が行われ、完了すると図１０（ｅ）のように表示される。
【０１７３】
（第２の制御系）
第２の制御系は、通常画像形成中に行う画像制御として、プリンタ部Ｂ単独の画像再現特性の安定化するもので、感光体ドラム４上のパッチパターン濃度を検出し、前述のＬＵＴ２５を補正することにより、画像安定化を達成する。
【０１７４】
図２０は、感光体ドラム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（図１）からの信号を処理する処理回路を示す。フォトセンサ４０に入射された感光体ドラム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。
【０１７５】
本実施例で使用したフォトセンサ４０は、感光体ドラム４からの正反射光のみを検出するよう構成されている。
【０１７６】
感光体ドラム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２１に示す。
【０１７７】
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。
【０１７８】
図２１から分かるように、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、感光体ドラム４単体よりフォトセンサ４０の出力が小さくなる。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（図２０）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。
【０１７９】
ここで、本実施例では、前述した問題点にあるように、感光体ドラム４の表面性の劣化やフォトセンサ４０表面の窓汚れ、フォトセンサ４０を構成するＬＥＤ１０の光量低下などの要因によりトナーパッチのフォトセンサ出力は耐久により変動することが予想されるため、フォトセンサ４０から得られた出力に対して、あらかじめ検出され記憶された下地出力データから下地補正係数を算出し補正出力を演算する。すなわち、
下地補正係数＝１／下地出力データ
補正出力＝フォトセンサ出力×下地補正係数
ここで使用される下地出力データは、前述の通常画像形成中に記憶された下地出力データを使用する。
【０１８０】
この際に、前述のように下地出力データは感光体ドラム上の位置情報と共に記憶されている。図２８に示すように、補正出力の演算を行う場合には、実際に検出するトナーパッチが形成された感光体ドラム表面の位置を検出して、あらかじめ記憶された感光体ドラム一周分の下地出力データから、トナーパッチ形成位置に該当する位置の下地出力データを読み出して補正出力演算を行う構成とする。これによりトナーパッチが形成される位置と同じ位置の感光体ドラム表面の反射光量を下地データとして使用できるため、耐久によって感光体ドラム表面に局所的な劣化やトナー付着などが発生した場合でも補正精度を保つことができる。
【０１８１】
第２の制御系は第１の制御系により達成された色再現性の安定維持が目的であるため、第１の制御系による制御の終了直後の状態を目標値として設定する。目標値設定のフローを図２２に示す。
【０１８２】
第１の制御系による制御の終了した時点で、Ｍ、Ｃ、Ｙ、Ｋの各色毎のパッチパターンを感光体ドラム上に形成して、フォトセンサ４０で検知する。
【０１８３】
ここで、パッチのレーザ出力は、各色とも濃度信号（図６の濃度信号軸）で１２８レベルを用いる。この際、ＬＵＴ２５の内容ならびに、コントラスト電位の設定は、第１の制御系で得たものを用いる。このときの濃度値Ｄ１２８を第２の制御系の目標値とし、バックアップしておく。目標値は第１の制御系による制御が行われるごとに更新される。
【０１８４】
第２の制御系は、通常画像形成中に非画像領域に形成したパッチ濃度を検出し、第１の制御系で得たγＬＵＴを随時補正していく制御である。前述したシーケンスに従い、通常画像形成中に感光体ドラム４上の非画像領域上にパッチを形成する。パッチのレーザ出力は、目標値設定時と同様であることが重要であり、各色とも濃度信号（図６の濃度信号軸）で１２８レベルを用いる。この際、ＬＵＴ２５の内容ならびに、コントラスト電位の設定は、その時点での通常画像形成時と同様とする。すなわち、第１の制御系で得たものを、前回までの第２の制御系により補正したものを用いる。
【０１８５】
濃度信号１２８は、１．６を２５５に正規化した濃度スケールでパッチ出力濃度がＤ１２８になるように制御されているが、プリンタの画像特性は不安定であり、常に変化を起こす可能性をもつため、測定した結果がＤ１２８になるわけではなく、ΔＤだけずれている場合がある。
【０１８６】
このΔＤに基づき、第２の制御系では第１の制御系で作成したＬＵＴ２５（γＬＵＴ）を補正する。
【０１８７】
図２３に、本実施例の場合の、濃度信号１２８において出力濃度がΔＤＸずれた場合の、一般的な濃度信号０〜２５５までにおける出力濃度の変化に対応するγＬＵＴ補正テーブルを示す。これを予めもっておき、制御時には、γＬＵＴ補正テーブルの濃度信号１２８での値がΔＤになるようγ補正テーブルを規格化し、これを打ち消すように形成したＬＵＴを、ＬＵＴ２５に足すことでＬＵＴ２５を補正する。ＬＵＴ２５を書き換えるタイミングは各色ごとに異なり、書き換え準備ができた段階で、その色のレーザ書き込みが行われていない間のＴＯＰ信号により行う。
【０１８８】
本実施例では、画像処理装置のメインスイッチＯＮ時、又は、メインスイッチＯＮ後一定時間経過後、又は、環境変動を検出する不図示の温度センサ、湿度センサによるセンサ出力に応じて補正用の第２の制御系を実施している。
【０１８９】
第１の制御系は、人の作業がともなうので、頻繁に行うことは想定しにくいため、画像形成装置の設置作業にサービスマンが第１の制御系を実効し、画像に問題が生じなければ、第２の制御系で、短期間内は特性を自動的に維持させ、長期間で徐々に変化したものに対しては、第１の制御系でキャリブレーションを行うという役割分担ができ、結果として画像形成装置の寿命まで、階調特性を維持することができるようになる。
【０１９０】
以上、本実施例において、第１の制御手段である自動階調補正を実施しそれで作成されたＬＵＴに基づき、感光体ドラム上に形成された基準濃度取得用の第２の制御であるトナーパッチ読込みを行いパッチセンサの基準濃度とし、それに基づいて、転写体（転写ドラム）５の１回転サイクル中にトナー像を転写させた後、次の転写体の回転サイクル中に回転式現像装置を回転させ現像器の交換を行う画像形成装置の転写体の空回転サイクル中に補正用の感光体ドラム下地を感光体ドラム一周に渡って検知してその位置情報と共に記憶しておき、それによって補正された第２の制御のトナーパッチ濃度値との変化量に応じて、自動階調補正で作成したＬＵＴを補正していくことで、自動階調補正で得られた画像濃度特性を長期的に維持することができる。
【０１９１】
また、本実施例では、図１に示すような転写ドラムをもつ構成の画像形成装置について述べたが、他にも転写ベルトの構成や、図２７に示すような中間転写体５１を備えた構成でも同様の効果が得られ適用可能である。
【０１９２】
図２７に示す実施例の画像形成装置は、中間転写体５１を用いる以外は、図１を参照して説明した画像形成装置と同様の構成とされ、従って、同様の構成及び作用をなす部材には同じ参照番号を付し、詳しい説明は省略する。
【０１９３】
図２７の実施例においても、上記説明した実施例と同様の構成とすることにより同様の効果が得られる。
【０１９４】
【発明の効果】
以上説明したように、本発明は、転写体を用いて記録材上に多重転写を行うか、又は、中間転写体を用いて該中間転写体上に積層したトナー像を記録材に一括して２次転写を行い、現像手段が回転式現像装置から構成され、転写体又は中間転写体の１回転サイクル中にトナー像を転写させた後、次の転写体又は中間転写体の回転サイクル中に回転式現像装置を回転させ現像器の交換を行う画像形成装置において、転写体又は中間転写体の空回転サイクル中に像担持体表面上に形成されたトナーパッチを光学的検出手段によって読み取り、その読み取った画像情報と基準画像情報の差異に基づいて画像形成条件を補正する構成により、画像形成毎に精度よく画像補正を行うことができ、長期にわたって安定した画像を得ることが可能となる。
【０１９５】
また、本発明は、転写体を用いて記録材上に多重転写を行うか、又は、中間転写体を用いて中間転写体上に積層したトナー像を一括して記録材に２次転写を行い、現像手段が回転式現像装置から構成され、転写体又は中間転写体の１回転サイクル中にトナー像を転写させた後、次の転写体又は中間転写体の回転サイクル中に回転式現像装置を回転させ現像器の交換を行う画像形成装置において、転写体又は中間転写体の空回転サイクル中に下地補正用データとして像担持体表面を光学的検出手段によって読み取ることにより、第２の制御系を行う前に改めて下地補正用のデータを取る必要がなくなり、第２の制御系に要する時間を短縮することが可能となる。
【図面の簡単な説明】
【図１】本発明に係る画像形成装置の一実施例の概略構成図である。
【図２】画像形成装置におけるリーダ画像処理部の構成ブロック図である。
【図３】画像形成装置におけるリーダ画像処理部のタイミングを示す図である。
【図４】画像形成装置の制御ブロック図である。
【図５】画像形成装置の制御ブロック図である。
【図６】階調再現特性を示す４限チャート図である。
【図７】画像形成装置の第１の制御系のフロー図である。
【図８】画像形成装置における表示器の表示内容を示す図である。
【図９】画像形成装置における表示器の表示内容を示す図である。
【図１０】画像形成装置における表示器の表示内容を示す図である。
【図１１】テストプリント１の例を示す図である。
【図１２】テストプリント２の例を示す図である。
【図１３】原稿台でのテストプリント１の置き方を示す図である。
【図１４】原稿台でのテストプリント２の置き方を示す図である。
【図１５】相対ドラム表面電位と画像濃度の関係を示す図である。
【図１６】絶対水分量とコントラスト電位の関係を示す図である。
【図１７】グリッド電位と表面電位の関係を示す図である。
【図１８】パッチパターンの読み取りポイントを示す図である。
【図１９】テストプリント２の読み取り例を示す図である。
【図２０】フォトセンサから濃度変換までのフロー図である。
【図２１】フォトセンサ出力と画像濃度の関係を示す図である。
【図２２】目標値設定のフロー図である。
【図２３】γＬＵＴ補正ｔａｂｌｅを説明する図である。
【図２４】濃度変換特性を示す図である。
【図２５】本実施例における転写ドラムのシート保持面の領域を示す図である。
【図２６】画像形成動作を示すタイミングチャートである。
【図２７】本発明に係る画像形成装置の他の実施例の概略構成図である。
【図２８】下地検知を説明する概略構成図である。
【符号の説明】
１ ポリゴンミラー（露光装置）
２ 反射ミラー
３ 回転式現像装置
３Ｍ、３Ｃ、３Ｙ、３Ｋ 現像器
４ 感光体ドラム（像担持体）
５ 転写ドラム（転写体）
６ 記録材
８ １次帯電器（帯電手段）
１０ ＬＥＤ
１１ フォトダイオード
１２ 表面電位センサ
４０ フォトセンサ
５１ 中間転写体
１００ プリンタエンジン
１０５ ＣＣＤセンサ
１０８ リーダ画像処理部
１０９ プリンタ制御部
１１０ 半導体レーザ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multicolor image forming apparatus for obtaining an image by transferring a toner image of each color component onto a recording material by an appropriate image forming process such as an electrophotographic system or an electrostatic recording system, and relates to a color copying machine. And a color laser beam printer.
[0002]
[Prior art]
Conventionally, an apparatus as shown in FIG. 1 has been used as a color image forming apparatus. That is, in the printer section B, the developing means is the rotary developing device 3, and includes a magenta toner developing device 3M, a cyan toner developing device 3C, a yellow toner developing device 3Y, and a black toner developing device 3K. The rotary developing device 3 is rotatably supported by a rotation support device (not shown), and the above-described color toner developing devices 3M, 3C, 3Y, and 3K sequentially face a photosensitive drum 4 as an image carrier. The development with the toner of each color is performed.
[0003]
The photoconductor drum 4 is driven to rotate at a predetermined angular velocity, and the surface of the photoconductor drum is uniformly charged by the charging unit 8.
[0004]
Next, an exposure apparatus whose ON / OFF is controlled in accordance with image data of the first color (for example, magenta), that is, a laser beam by a printer control unit 109, a laser driver and a laser light source 110, a polygon mirror 1, a reflection mirror 2, and the like. Is exposed and scanned to form an electrostatic latent image of the first color on the photosensitive drum 4, and is developed and visualized by the magenta toner developing unit 3M of the first color.
[0005]
The visualized first toner image is transferred onto the recording material 6 adsorbed on the surface of the transfer drum 5 which is driven to rotate while being pressed against the photosensitive drum 4 with a predetermined pressing force.
[0006]
The transfer process is repeated for other toners (cyan, yellow, and black) in the same manner, and each time, a toner image of each color toner included in each developing unit is placed on the same recording material 6 carried on the transfer drum 5. A color image is formed by sequential transfer and lamination, is fixed by the fixing device 7, and is discharged outside the image forming apparatus.
[0007]
In the above-described color image forming apparatus, in order to obtain a full-color image, it is necessary to transfer the toner image on the recording material 6 by the number of each color component. Therefore, in the above-described configuration, the transfer drum 5 rotates several times. Otherwise, a full-color image cannot be obtained, and there is a problem that the full-color image forming speed is lower than a single-color image that can be obtained by one rotation of the transfer drum 5.
[0008]
On the other hand, the speed has been improved by transferring two images at a time on the transfer drum so that two full-color images can be obtained simultaneously by driving the transfer drum in one sequence. That is, as shown in FIG. 25, the two recording materials 6A and 6B are simultaneously carried on the peripheral surface of the transfer drum 5, and therefore, the transfer drum 5 is simultaneously driven on the two recording materials 6A and 6B for one rotation. One full color image can be transferred.
[0009]
In addition, when a color image is formed, the rotation of the rotary developing device is exchanged using the time required to pass through one of the two image forming areas on the transfer drum for the rotation of the rotary developing device. An image forming apparatus that performs an operation has also been devised.
[0010]
Further, the following method is known as a method (image control method) for adjusting the image processing characteristics of an image forming apparatus such as a copying machine or a printer having such a configuration.
[0011]
First, after starting the image forming apparatus, after the warm-up operation is completed, a specific pattern is formed, the density of the pattern is read, and image forming conditions such as a γ correction circuit are determined based on the read density value. The quality of the image formed is stabilized by changing the operation of the circuit that performs the operation.
[0012]
Further, even when the gradation characteristic changes due to a change in the environmental condition, the specific pattern is formed and read again, and the image is fed back to a circuit for determining the image forming condition such as a γ correction circuit. The image quality can be stabilized in accordance with the amount of fluctuation of.
[0013]
Further, when the image forming apparatus has been used for a long period of time, there may be a case where the density obtained by reading the pattern on the image carrier and the density of the actually printed out image do not match. Therefore, there is also known a method of forming a specific pattern on a recording material and correcting an image forming condition based on the density value.
[0014]
Further, a circuit that forms a specific pattern in the non-image area during the image forming operation, reads the density of the pattern, and determines an image forming condition such as a γ correction circuit for each image forming operation based on the read density value. There is also known a method of accurately correcting a constantly changing image characteristic by changing the operation of (1).
[0015]
[Problems to be solved by the invention]
However, in recent years, the color image forming apparatus has been required to have improved productivity and further space saving. For this reason, in the color image forming apparatus having the above configuration, the driving speed of the transfer drum (hereinafter referred to as “process When the speed is increased, the peripheral length of the transfer drum that is rotationally driven during rotation exchange of the rotary developing device becomes longer than the interval between the electrostatic latent images when developing the image. There is a possibility that it will. Further, if the diameter of the transfer drum is reduced for the purpose of saving space, the interval between the electrostatic latent images is reduced.
[0016]
Furthermore, as the process speed is increased, the rotating operation of the rotary developing device must be performed immediately after an image is formed on the photosensitive drum, and a specific pattern for image correction is formed in the non-image area. There is no longer enough time to perform, and as a result, it becomes impossible to accurately correct image characteristics that change every time for each image formation, and a stable image cannot be obtained. there were.
[0017]
Therefore, for the purpose of solving the above problems, multiple transfer is performed on a recording material using a transfer body, or a toner image laminated on the intermediate transfer body is collectively used on a recording material using an intermediate transfer body. The secondary transfer is performed, and the developing means is constituted by a rotary developing device. After the toner image is transferred during one rotation cycle of the transfer body or the intermediate transfer body, the rotation cycle of the next transfer body or the intermediate transfer body is performed. In an image forming apparatus in which a rotary developing device is rotated to replace a developing device, a toner patch formed during an idle rotation cycle of a transfer body or an intermediate transfer body is read by optical detection means, and the read image information is read. An image forming apparatus that corrects image forming conditions based on a difference between the image forming apparatus and the reference image information has been devised.
[0018]
However, in the image forming apparatus having such a configuration, as the durability increases, a change in surface properties due to a factor such as a scratch or abrasion of the photosensitive drum serving as an image carrier, or a decrease in reflectance due to adhesion of toner on the photosensitive drum surface or the like. It is known to happen. That is, since the result of density detection greatly differs depending on the reflectance of the base (reflectance for light used for density detection), there is a problem that the measured density value changes with time.
[0019]
Therefore, a method of forming a specific pattern on a photoconductor drum, reading the reflectance of the background on the photoconductor drum before reading the density of the pattern, and performing the background correction using the read result. However, in this case, it is necessary to read the base in the same manner before the operation of forming and reading a specific pattern, which takes extra time, resulting in a decrease in productivity. There was a problem that would.
[0020]
In addition, a method has been proposed in which the surface of the photosensitive drum at a position different from the position where a specific toner pattern is formed is detected in advance, and the background is corrected. It is difficult to cope with a change in surface properties due to deterioration of the surface of the body drum or adhesion of toner, and there has been a problem in correction accuracy.
[0021]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, it is possible to accurately perform image correction for each image formation, obtain a stable image for a long time, and reduce the time required for control. It is an object of the present invention to provide an image forming apparatus that can be shortened and does not reduce productivity.
[0022]
Another object of the present invention is to perform multiple transfer onto a recording material using a transfer body, or to perform secondary transfer of a toner image laminated on an intermediate transfer body to a recording material at once using an intermediate transfer body. The developing means is constituted by a rotary developing device, and after the toner image is transferred during one rotation cycle of the transfer body or the intermediate transfer body, the rotary development is performed during the rotation cycle of the next transfer body or the intermediate transfer body. In an image forming apparatus in which the developing device is replaced by rotating the device, optically detecting the entire circumference of the photosensitive drum surface on which the toner image has not been developed while the rotating developing device is rotating and the developing device is being replaced. By means of reading by means and storing the position information together with the position information, it is not necessary to newly obtain data for base correction before performing the second control system, and the time required for the second control system can be reduced. Image forming equipment An object of the present invention is to provide a.
[0023]
Another object of the present invention is to perform multiple transfer onto a recording material using a transfer body, or to perform secondary transfer of a toner image laminated on an intermediate transfer body to a recording material at once using an intermediate transfer body. The developing means is constituted by a rotary developing device, and after the toner image is transferred during one rotation cycle of the transfer body or the intermediate transfer body, the rotary development is performed during the rotation cycle of the next transfer body or the intermediate transfer body. In the image forming apparatus in which the developing device is replaced by rotating the apparatus, the second control is performed by reading the surface of the image bearing member as background correction data by the optical detecting means during the idle rotation cycle of the transfer member or the intermediate transfer member. It is an object of the present invention to provide an image forming apparatus which eliminates the necessity of re-acquiring data for background correction before performing the system, and can reduce the time required for the second control system.
[0024]
[Means for Solving the Problems]
The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus having the following configuration.
[0025]
(1) An image carrier, a plurality of developing means for accommodating toners of different colors and developing a latent image formed on the image carrier by a developing section, and a plurality of developing means, one of which is a developing section Transfer means for moving the recording medium so as to be positioned as an alternative, and a recording material carrier for carrying the recording material, wherein the toner image is transferred from the image carrier to a plurality of recording materials on the recording material carrier. In an image forming apparatus that forms a plurality of toner images on a recording material by repeating a process of transferring
A first developing unit sequentially forming toner images on the image carrier so that transfer is performed in the order of a first recording material and a second recording material on the recording material carrier;
Before the second recording material to which the toner image has been transferred by the first developing unit passes through the transfer section, the second recording material on the recording material carrier, the first recording material, An image characterized in that a second developing means is moved to the developing section by the moving means so that transfer is performed in order, and a toner image is sequentially formed on the image carrier by the second developing means. Forming equipment.
[0026]
(2) detecting means for detecting the density of the toner image for detection by a detecting unit, wherein the first developing means includes the first recording material and the second recording material on the recording material carrier The toner image for detection is formed after the toner image is formed on the image carrier so that the transfer is performed in the following order, and before the toner image is moved by the moving means. 1) The image forming apparatus.
[0027]
(3) The image forming apparatus according to (2), further including a correcting unit that corrects an image forming condition based on the density detected by the detecting unit.
[0028]
(4) The correction means has a first control system for controlling image forming conditions based on the density of the toner image for detection detected by the detection means, and controls the image by the first control system. After completion of the above, a toner image for detection is formed again, and the density is detected by the detecting means. Based on the detected density, a toner image for detection is formed during normal image formation, and the detecting means is used. And a second control system that further corrects image forming conditions corrected by image control by the first control system based on a difference between the detected density and the reference density. The image forming apparatus according to the above (3).
[0029]
(5) The image forming apparatus according to any one of (2) to (4), wherein the detection unit detects a density of the toner image for detection formed on the image carrier.
[0030]
(6) The image forming apparatus according to any one of (1) to (5), further including an image carrier position information detecting unit that detects position information of the image carrier.
[0031]
(7) Before the toner image for detection is formed, the detecting means reflects light reflected from an area on the image carrier on which no image is carried while the moving means is moving the developing means. Is detected in advance, the image forming apparatus according to the above (6).
[0032]
(8) The image forming apparatus according to (7), wherein the detected reflected light is detected for the entire area in the circumferential direction of the image carrier.
[0033]
(9) The image forming apparatus according to (8), wherein the detected reflected light is stored together with position information on the image carrier detected by the image carrier position information detecting means.
[0034]
(10) The image forming apparatus according to (9), wherein the output of the detection unit is corrected using the detected reflected light.
[0035]
(11) The second developing unit forms a toner image on the image carrier such that the transfer is performed in the order of the second recording material and the first recording material on the recording material carrier. The image forming apparatus according to any one of the above (7) to (10), wherein the toner image for detection is formed later and before being moved by the moving means.
[0036]
(12) The plurality of developing means and the moving means are constituted by a rotary developing device containing a plurality of developing devices rotatably supported on the image carrier, and a peripheral length of the recording material carrier. Is L (mm), the moving speed of the recording material carrier is Vtr (mm / s), the number of recording materials carried on the recording material carrier is n (sheets), and the length of the image forming area on the recording material. Is P (mm), the diameter of the rotary developing device is R (mm), the rotational speed of the rotary developing device is Vrt (mm / s), and the number of developing devices housed in the rotary developing device is N ( ),
(L−n × P) × (1 / n) × (1 / Vtr) <πR × (1 / N) × (1 / Vrt) <P × (1 / Vtr)
The image forming apparatus according to any one of the above (1) to (11), wherein the following relational expression is satisfied.
[0037]
(13) The image forming apparatus according to any one of (1) to (12), wherein the length of the image forming area on the recording material is longer than the circumference of the image carrier.
[0038]
(14) An image carrier, a plurality of developing means for accommodating toners of different colors and developing a latent image formed on the image carrier with a developing section, and a plurality of developing means, one of which is a developing section A transfer unit for moving the toner image so that the toner image is alternatively located, and an intermediate transfer body, and repeating the process of transferring the toner image from the image carrier to a plurality of positions on the intermediate transfer body by the transfer unit. In the image forming apparatus, after forming a plurality of toner images on the intermediate transfer body, the plurality of toner images on the intermediate transfer body are respectively transferred to a plurality of recording materials.
A first developing unit sequentially forms a toner image on the image carrier so that transfer is performed in the order of a first position and a second position on the intermediate transfer body,
Before the second position to which the toner image is transferred by the first developing unit passes through the transfer portion, transfer is performed in the order of the second position on the intermediate transfer member and the first position. As described above, the image forming apparatus is characterized in that the second developing means is moved to the developing section by the moving means, and a toner image is sequentially formed on the image carrier by the second developing means.
[0039]
(15) A detecting unit for detecting the density of the toner image for detection by a detecting unit, wherein the first developing unit transfers the first position and the second position on the intermediate transfer body in this order. (14) wherein the toner image for detection is formed after the toner image is formed on the image carrier so that the toner image is formed, and before the toner image is moved by the moving means. Image forming device.
[0040]
(16) The image forming apparatus according to the above (15), further comprising a correcting unit that corrects an image forming condition based on the density detected by the detecting unit.
[0041]
(17) The correction unit has a first control system that controls image forming conditions based on the density of the toner image for detection detected by the detection unit, and performs image control by the first control system. After completion of the above, a toner image for detection is formed again, and the density is detected by the detecting means. Based on the detected density, a toner image for detection is formed during normal image formation, and the detecting means is used. And a second control system that further corrects image forming conditions corrected by image control by the first control system based on a difference between the detected density and the reference density. The image forming apparatus according to the above (16).
[0042]
(18) The image forming apparatus according to any one of (15) to (17), wherein the detection unit detects the density of the toner image for detection formed on the image carrier.
[0043]
(19) The image forming apparatus according to any one of (14) to (18), further including an image carrier position information detecting unit that detects position information of the image carrier.
[0044]
(20) Before the toner image for detection is formed, the detecting means reflects light reflected from an area on the image carrier on which no image is carried while the moving means moves the developing means. The image forming apparatus according to (19), wherein the image forming apparatus detects in advance.
[0045]
(21) The image forming apparatus according to (20), wherein the detected reflected light is detected for the entire area in the circumferential direction of the image carrier.
[0046]
(22) The image forming apparatus according to (21), wherein the detected reflected light is stored together with position information on the image carrier detected by the image carrier position information detecting means.
[0047]
(23) The image forming apparatus according to (22), wherein the output of the detection unit is corrected using the detected reflected light.
[0048]
(24) The second developing means may form a toner image on the image carrier such that transfer is performed in the order of the second position and the first position on the intermediate transfer member. The image forming apparatus according to any one of (20) to (23), wherein the toner image for detection is formed before being moved by the moving means.
[0049]
(25) The plurality of developing means and the moving means are constituted by a rotary developing device containing a plurality of developing devices rotatably supported on the image carrier, and the peripheral length of the intermediate transfer is set to L. (Mm), the moving speed of the intermediate transfer body is Vtr (mm / s), the number of image forming areas transferred on the intermediate transfer body is n (pieces), and the length of the image forming area on the recording material is P (mm). When the diameter of the rotary developing device is R (mm), the rotation speed of the rotary developing device is Vrt (mm / s), and the number of developing devices housed in the rotary developing device is N (unit). To
(L−n × P) × (1 / n) × (1 / Vtr) <πR × (1 / N) × (1 / Vrt) <P × (1 / Vtr)
The image forming apparatus according to any one of the above (14) to (24), wherein the following relational expression is satisfied.
[0050]
(26) The image forming apparatus according to any one of (14) to (25), wherein the length of the image forming area on the recording material is longer than the circumference of the image carrier.
[0051]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.
[0052]
Example 1
In this embodiment, in an image forming apparatus having a rotary developing device, stable image formation can be performed for a long period of time, and toner is transferred during one rotation cycle of a transfer body as a recording material carrier. Thereafter, a toner image (toner patch) for detection is formed during the next idle rotation cycle of the transfer body, the density is read by the detecting means, and the image forming conditions are corrected based on the difference between the read density and the reference density. is there.
[0053]
FIG. 1 shows a schematic configuration of an electrophotographic color image forming apparatus according to an embodiment of the present invention. The configuration has been schematically described above in relation to the description of the prior art. explain.
[0054]
As shown in FIG. 1, the color image forming apparatus of the present embodiment has a reader unit A and a printer unit B.
[0055]
(Leader A)
In the reader unit A, a document 101 placed on a document table glass 102 is illuminated by a light source 103, and a document image is formed on a CCD sensor 105 via an optical system 104. The CCD sensor 105 generates red, green, and blue color component signals of an original image for each line sensor by using a group of red, green, and blue CCD line sensors arranged in three rows.
[0056]
The reading optical system units 103 to 105 convert original image information into an electric signal data sequence for each line by sub-scanning the original surface in the direction of the arrow.
[0057]
An abutting member 107 for abutting the position of the document 101 on the platen glass 102 to prevent the document 101 from being skewed, and for determining a white level of the CCD sensor 105 on the platen glass surface. A reference white plate 106 for shading the CCD sensor 105 in the thrust direction is provided.
[0058]
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.
[0059]
(Reader image processing unit 108)
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.
[0060]
As shown in FIG. 2, the image signal output from the CCD sensor 105 is input to an analog signal processing unit 201, where the image signal is subjected to gain adjustment and offset adjustment. 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.
[0061]
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.
[0062]
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.
[0063]
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.
[0064]
(Equation 1)

[0065]
The light quantity / density conversion unit (LOG conversion unit) 206 is configured by a look-up table ROM, and converts R4, G4, and B4 luminance signals into M0, C0, and Y0 density signals. The line delay memory 207 delays the M0, C0, and Y0 image signals by a black character determination unit (not shown) by a line delay from the R4, G4, and B4 signals to the determination signals such as UCR, FILTER, and SEN. Let it.
[0066]
The masking and UCR circuit 208 extracts a black signal (K) from the input three primary color signals M1, C1, and Y1, and further performs an operation to correct the color turbidity of the recording color material in the printer unit B. The signals of M2, C2, Y2, and K2 are sequentially output with a predetermined bit width (8 bits) for each reading operation.
[0067]
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.
[0068]
The thus processed M4, C4, Y4, and K4 frame-sequential image signals are sent to the printer control unit 109, and the printer unit B performs density recording by PWM.
[0069]
The reader unit A has a CPU 214 for controlling the inside of the reader unit, a RAM 215, and a ROM 216, and further includes an operation unit 217 and a display 218.
[0070]
FIG. 3 is a diagram showing the timing of each control signal in the image processing unit 108 shown in FIG.
[0071]
In FIG. 3, a VSYNC signal is an image valid section signal in the sub-scanning direction, and performs image reading (scanning) in a section of logic "1" to sequentially perform (M), (C), (Y), The output signal of (K) is formed. The VE signal is an image effective 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”.
[0072]
(Printer B)
In FIG. 1, a charging unit 8 is a corona charger, and applies a bias to uniformly charge the surface of the photosensitive drum 4 as an image carrier to a negative polarity.
[0073]
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 on the photosensitive drum. 4 is illuminated. 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. The photosensitive drum 4 has a home position, and is configured to be able to obtain position information during a rotation operation by using an encoder or the like.
[0074]
The developing device contains a plurality of developing units that contain toners of different colors and develops a latent image formed on the image carrier in a developing unit, and a plurality of developing units that contain one of the developing units. And a moving means for moving the electrostatic latent image to a visible position. In this embodiment, the developing device is a rotary developing device 3 that accommodates the developing devices 3M, 3C, 3Y, and 3K for each of magenta, cyan, yellow, and black.
[0075]
The four developing units 3M, 3C, 3Y, and 3K are detachably held in a rotatable rotary developing device 3, and the rotary shaft is held in the rotary developing device 3 during image formation. , For example, the magenta toner developing device 3M stops at a position facing the photosensitive drum 4, and the developing sleeve as a developer carrier in the magenta toner developing device (About 400 μm), and a visible image is formed on the photosensitive drum. When developing a toner image of a different color, for example, a cyan toner image or a yellow toner image, similarly, after the developing device 3 is driven to rotate, a predetermined developing device is stopped at a position facing the photosensitive drum, and the development is performed. Is performed.
[0076]
When the above-described developing operation is completed, the rotary developing device is separated to a position where the sleeves in the developing devices of all colors in the rotary developing device do not contact the photosensitive drum 4, and this position is set as a home position. By setting the home position in this way, it is possible to prevent the toner in the rotary developing device from inadvertently adhering to the surface of the photosensitive drum, and to use other color developing devices accommodated in the rotary developing device. It can be prevented from being mixed in.
[0077]
The recording material 6 can be held and conveyed by a suction means on the transfer drum 5 on which a resin sheet is stretched as an endless recording material carrier. The transfer drum 5 is rotatably supported in only one direction during image formation, and is rotated by a motor (not shown).
[0078]
The above configuration is compared with a configuration such as a switchback method in which the second color is transferred by rotating the transfer drum in the reverse direction after transferring the first color, and thereafter, the transfer drum is repeatedly rotated forward and backward to transfer each color. In addition, there are advantages such as reduction of color shift, reduction of motor cost, and simplification of mechanism.
[0079]
The cleaning device 9 cleans the residual toner on the photosensitive drum 4 after the image visualized by the developing device is transferred to the recording material 6 on the transfer drum 5, and the waste toner is stored in a cleaning container. Is exchanged when it becomes full.
[0080]
The fixing device 7 heats and fixes the toner image on the recording material 6, and includes two fixing rollers for applying heat to the recording material 6 and a pressure roller for pressing the recording material against the fixing roller. It is composed of rollers.
[0081]
In addition, a toner patch pattern, which is a toner image for detection, formed on the photosensitive drum 4 as an image carrier is read, that is, as a detection unit for detecting the amount of reflected light (density) of the toner patch pattern, An optical reading device (photosensor) 40 including an LED light source 10 (having a main wavelength of about 960 nm) and a photodiode 11 is provided. The surface potential of the photosensitive drum 4 is measured by a surface potential sensor 12.
[0082]
(Image formation sequence)
Here, an image forming sequence of the present embodiment will be described.
[0083]
Both the photosensitive drum 4 and the transfer drum 5 rotate at a process speed of 265 mm / s in the direction of the arrow shown in the figure. The photosensitive drum 4 having a diameter of 60 mm rotates at 0.71 seconds per rotation, and the transfer drum 5 having a diameter of 160 mm rotates once at 1.9 seconds.
[0084]
The peripheral speed of the photosensitive drum 4 and the peripheral speed of the transfer drum 5 do not need to completely coincide with each other. In order to improve the transfer efficiency, one of the peripheral speeds is increased by a predetermined amount with respect to the other, or It may be configured to be slow.
[0085]
When the user operates the copy start switch, as shown in FIG. 26, the exposure device transfers the electrostatic latent image from the exposure device to the photosensitive drum 4 at a predetermined timing corresponding to each of the sheet holding surfaces A and B of the transfer drum 5. Writing is performed, and these electrostatic latent images are developed by the magenta developing device 3M. The two developed magenta toner images are first and second sheets held in conformity with the leading edge reference PA of the sheet holding surface A and the leading edge reference PB of the sheet holding surface B of the transfer drum 5 shown in FIG. Are sequentially transferred to the recording materials 6A and 6B.
[0086]
At this time, the interval between the rear end of the recording material 6B and the front end of the recording material 6A is approximately 41.2 mm from (160 × π−420) / 2, and the transfer drum 5 rotates by 41.2 mm on the outer periphery. Is about 0.16 seconds.
[0087]
It is assumed that the rotary developing device 3 is rotated and development is performed using the subsequent cyan developing device 3C.
[0088]
Since the rotary developing device 3 in the embodiment has a diameter of 140 mm and a driving speed at the time of rotation exchange of 220 mm / sec, the time required for the rotation exchange of the developing device is (140 × π / 4) / 220. When the rotation of the developing device is changed, it is about 0.5 second, and after passing the rear end of the recording material 6B, it passes through the front end of the recording material 6A, and the cyan image cannot be developed and transferred. .
[0089]
Therefore, in the present embodiment, the transfer drum 5 is idled here, the next first recording material 6A is skipped, and the cyan image is developed and transferred in the order of the second recording material 6B and the first recording material 6A. Is performed.
[0090]
That is, the toner image of the same color can be continuously transferred to the two recording materials 6A and 6B held on the sheet holding surfaces A and B every 1.5 rotation cycles of the transfer drum 5, Each time the 1.5 rotation cycle is repeated, magenta, cyan, yellow and black toner images are transferred to the two recording materials 6A and 6B held on the sheet holding surfaces A and B of the transfer drum 5, respectively.
[0091]
Of course, it is assumed that the rotation speed is maintained at the same speed as during image formation even during the idle rotation time of the transfer drum 5. That is, the transfer drum 5 is endless, rotates only in one direction during image formation, and maintains the same speed during idle rotation without reducing the speed of the photosensitive drum 4 and the transfer drum 5. .
[0092]
With this configuration, in addition to the interval of 41.2 mm between the rear end of the recording material 6B and the front end of 6A on the transfer drum 5, a time for idling the area 210mm of the recording material 6A is generated, and there is room for rotating the rotary developing device 3. Can be obtained.
[0093]
Further, in the present embodiment, using the idle rotation time of the transfer drum 5, the magenta developing unit 3M develops a predetermined patch pattern that becomes a toner image for density detection after two magenta toner images. Then, the rotary developing device 3 rotates 90 ° to replace the developing device, and the cyan developing device 3C is set at a position facing the photosensitive drum 4.
[0094]
In the next half rotation cycle of the transfer drum 5 corresponding to the sheet holding surface A, writing to the photosensitive drum 4 of the exposure device is not performed, and the transfer drum 5 idles while holding the recording materials 6A and 6B. During this time period, the photo sensor 40 detects the surface of the photosensitive drum 4 and stores the read reflection output from the photosensitive drum surface as background output data. At this time, the reflection output of the photoconductor drum surface and the position information of the photoconductor drum are both stored.
[0095]
Here, in the configuration of the present embodiment, since the circumferential length of the photosensitive drum 4 is shorter than the image forming area on the recording material, the photosensitive drum can rotate one or more turns during the idle rotation cycle of the transfer drum 5, and The reflection output on the drum surface can be detected for one or more rounds of the photosensitive drum.
[0096]
Then, when the half rotation cycle of the transfer drum 5 corresponding to the idle rotation of the sheet holding surface A is completed, the exposure corresponding to the sheet holding surface B and the sheet holding surface A is performed in the next one rotation cycle of the transfer drum 5. Is As a result, two electrostatic latent images corresponding to cyan are successively written on the photosensitive drum 4, and these electrostatic latent images are developed by the cyan developing device 3C. The two cyan toner images thus formed are successively transferred to the sheet holding surface B and the two recording materials 6A and 6B held on the sheet holding surface A of the transfer drum 5.
[0097]
As described above, in the sequence of the present embodiment, a toner image is formed every half rotation cycle of the transfer drum 5 before and after, and the toner image is formed on the two recording materials held on the sheet holding surfaces A and B of the transfer drum 5. The transfer is continuously performed, and during the next half rotation cycle, the developing device is replaced. At the same time, the surface of the photosensitive drum is detected by the photo sensor 40 and stored as background output data.
[0098]
Thereby, the toner image of the same color can be continuously transferred to the two recording materials every 1.5 rotation cycles of the transfer drum 5. Each time the 1.5 rotation cycle is repeated, magenta, cyan, The yellow and black toner images are transferred to the two recording materials 6A and 6B held on the sheet holding surfaces A and B, respectively.
[0099]
Therefore, a superimposed toner image of four color toner images is formed on the two recording materials 6A and 6B by the 5.5 rotation of the transfer drum 5, and the recording materials 6A and 6B on which the transfer of the black toner image is completed are formed. Subsequently, the sheet is peeled off from the transfer drum 5 and discharged to a discharge tray via a fixing device 7.
[0100]
The background output data for one round of the photosensitive drum surface detected and stored by the photo sensor 40 during the idle rotation of the transfer drum 5 in each cycle is an average value for each position based on the position information of the photosensitive drum. Or may be configured to be updated as the latest value one after another.
[0101]
As described above, in the sequence of the third embodiment, after developing the toner image of each color and developing the second control patch pattern described later, the rotary developing device 3 is rotated to develop the developing devices 3M, 3C, 3Y, 3K is exchanged, and the time is set to the idle rotation time of the transfer drum 5. During this time, the base on the photosensitive drum can be detected for one or more rotations. Before performing the second control means for detecting the image information and correcting the image information, there is no need to detect the background on the photosensitive drum again, and the time can be shortened. Further, it is possible to prevent the vibration generated by replacing the developing device 3 from affecting the writing of the electrostatic latent image.
[0102]
(Printer control unit (printer image processing unit) 109)
FIG. 4 is a configuration block diagram of the image forming apparatus according to the present embodiment.
[0103]
The printer control unit, that is, 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 is configured to be able to communicate with the reader unit A and the printer engine unit 100. The printer engine unit 100 controls the optical reading device 40 including the LED 10 and the photodiode 11 disposed around the photosensitive drum 4, the primary charger 8, the laser light source 101, the surface potential sensor 12, and the developing device 3. ing. Further, the printer engine unit 100 is provided with an environment sensor 33 for measuring the amount of moisture in the air in the machine.
[0104]
The surface potential 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 as described later.
[0105]
(Image signal processing circuit for obtaining a gradation image)
FIG. 5 shows an image signal processing circuit for obtaining a gradation image according to the present embodiment.
[0106]
A luminance signal of the image is obtained by the CCD 105, and is converted into a frame-sequential image signal in 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.
[0107]
FIG. 6 is a four-limit chart showing how the gradation is reproduced.
[0108]
The first quadrant indicates the reading characteristics of the reader unit A for converting the document 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.
[0109]
The number of gradations is 256 since the processing is performed using an 8-bit digital signal.
[0110]
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.
[0111]
The LUT 25 is generated based on a calculation result described later. After the density conversion by the LUT 25, the signal is converted by a pulse width modulation (PWM) circuit 26 into a signal corresponding to the dot width, and sent to a laser driver 27 for controlling ON / OFF of the laser. In the present embodiment, a gradation reproduction method by pulse width modulation processing is used for all colors of M, C, Y, and K.
[0112]
Then, a latent image having a predetermined gradation characteristic is formed on the photosensitive drum 4 by the change of the dot area by the scanning of the laser light source 110, and the gradation image is reproduced through the processes of development, transfer and fixing. You.
[0113]
(First control system)
Next, a first control system related to stabilization of image reproduction characteristics of a system including both the reader unit A and the printer unit B will be described.
[0114]
First, the calibration of the printer unit B using the reader unit A will be described with reference to the flowchart of FIG. This flow is realized by the CPU 214 (FIG. 2) for controlling the reader unit A and the CPU 28 (FIGS. 4 and 5) for controlling the printer unit B.
[0115]
This control is started by pressing a mode setting button called automatic gradation correction provided on the operation unit 217 (FIG. 2). In this embodiment, the display 218 (FIG. 2) is configured by a liquid crystal operation panel (touch panel display) with a push sensor as shown in FIGS.
[0116]
In step S51 of FIG. 7, a print start button 81 of test print 1 appears on the display 218 (FIG. 8A), and by pressing it, the image of test print 1 shown in FIG. Printed out. The test print 1 is one in which a predetermined image pattern is formed on a sheet 6 as a recording material and subjected to a fixing process.
[0117]
At this time, the CPU 214 determines whether or not there is a sheet for forming the test print 1, and if there is no sheet, a warning display as shown in FIG.
[0118]
When the test print 1 is formed, a contrast potential (described later) in a standard state corresponding to the environment is registered as an initial value and used.
[0119]
The image forming apparatus used in the present embodiment includes a plurality of paper cassettes, and can select a plurality of types of paper sizes such as B4, A3, A4, and B5.
[0120]
However, the printing paper used in this control uses large-size paper, which is generally referred to, in order to avoid an error due to a mistake in vertical or horizontal placement in a later reading operation. That is, it is set so that B4, A3, 11 × 17, and LGR are used.
[0121]
In the test pattern 1 of FIG. 11, a band-shaped pattern 61 is formed with intermediate gradation densities for four colors of M, C, Y, and K.
[0122]
By visually inspecting the pattern 61, it is confirmed that there is no streak-like abnormal image, density unevenness, and color unevenness. In this pattern, the size of the CCD sensor 105 in the main scanning direction is set so as to cover the patch pattern 62 and the gradation patterns 71 and 72 (FIG. 12) in the thrust direction.
[0123]
If an abnormality is found, the test print 1 is printed again, and if an abnormality is found again, a serviceman call is made.
[0124]
It is also possible to read the band pattern 61 by the reader unit A and automatically determine whether or not to perform subsequent control based on the density information in the thrust direction.
[0125]
On the other hand, the pattern 62 is a maximum density patch of each color of M, C, Y, and K, and uses 255 levels of density signal values.
[0126]
In step S52 of FIG. 7, the image of the test print 1 is placed on the platen glass 102 as shown in FIG. 13, and the reading start button 91 shown in FIG. 9A is pressed. At this time, a guidance display for the operator shown in FIG. 9A appears.
[0127]
FIG. 13 is a view of the platen 103 viewed from above. The wedge-shaped mark T at the upper left is a mark for abutting the document on the platen 102, and the band pattern 61 is located on the side of the abutting mark T. In addition, the above-mentioned message is displayed on the operation panel so that the front and the back are not mistaken (FIG. 9A). By doing so, a control error due to misplacement is prevented.
[0128]
When reading the pattern 62 by the reader unit A, the scanning is gradually performed from the abutting mark T, and the first density gap point A is obtained at the corner of the pattern 61. The position of each patch 62 is determined, and the density value of the pattern 62 is read.
[0129]
During the reading, the display shown in FIG. 9B is performed. When the orientation and position of the test print 1 are incorrect and the reading is impossible, the message shown in FIG. 9C is displayed. By pressing the key 92, reading is performed again.
[0130]
The following equation (2) is used to convert the optical density from the obtained RGB values. In order to obtain the same value as that of a commercially available densitometer, it is adjusted by the correction coefficient (k).
[0131]
(Equation 2)

[0132]
Alternatively, RGB luminance information may be converted to MCYK density information using a separate LUT.
[0133]
Next, a method of correcting the maximum density from the obtained density information will be described.
[0134]
FIG. 15 shows the relationship between the relative drum surface potential and the image density obtained by the above calculation.
[0135]
The difference between the contrast potential used at that time, that is, the developing bias potential and the surface potential of the photosensitive drum when the maximum level was hit by using the laser beam after the primary charging was obtained by setting A as the maximum. In the case of the density DA, the image density generally corresponds linearly to the relative drum surface potential as indicated by the solid line L in the maximum density range.
[0136]
However, in the two-component developing system, when the toner density in the developing device fluctuates and drops, nonlinear characteristics may occur in the density range of the maximum density as indicated by a broken line N.
[0137]
Therefore, in this case, the final target value of the maximum density is 1.6, but the control amount is determined by setting 1.7 as the target value of the control for adjusting the maximum density in consideration of a margin of 0.1. I do.
[0138]
Here, the contrast potential B is obtained using the following equation (3).
[0139]
B = (A + Ka) × 1.7 / DA (3)
[0140]
Here, Ka is a correction coefficient, and it is preferable to optimize the value according to the type of the developing method.
[0141]
Actually, in the electrophotographic system, depending on the environment, the setting of the contrast potential A does not match the image density unless it is changed in accordance with the environment, and the environment sensor 33 (FIG. ), The settings are changed as shown in FIG.
[0142]
Therefore, as a method of correcting the contrast potential, the correction coefficient Vcont. The ratel is stored in the backed-up RAM 32.
[0143]
Vcont. ratel = B / A
[0144]
Every 30 minutes, the image forming apparatus monitors the transition of the environment (moisture content), and every time the image forming apparatus determines the value of A based on the detection result, A × Vcont. The contrast potential is obtained by calculating the rate.
[0145]
A method for obtaining the grid potential and the developing bias potential from the contrast potential will be briefly described.
[0146]
FIG. 17 shows the relationship between the grid potential and the photosensitive drum. The grid potential is set to -200 V, and the surface potential V when scanning is performed with the level of the laser beam minimized. _L And the surface potential V when the laser light level is maximized. _H Is measured by the surface potential sensor 12 (FIGS. 1 and 4). Similarly, when the grid potential is -400 V, V _L And V _H Is measured. The relationship between the grid potential and the surface potential can be obtained by interpolating and extrapolating -200 V data and -400 V data.
[0147]
Control for obtaining this potential data is called potential measurement control.
[0148]
V _L The developing bias VDC is set by providing a difference of Vbg (here, set to 100 V) set so that fog toner does not adhere to the image.
[0149]
The contrast potential Vcont is equal to the developing bias VDC and V _H As described above, as Vcont increases, the maximum density can be increased.
[0150]
In order to obtain the calculated contrast potential B, from the relationship shown in FIG. 17, how many volts of the grid potential is required and how many volts of the developing bias potential are required can be obtained by calculation.
[0151]
In step S53 of FIG. 7, a contrast potential is obtained so that the maximum density becomes 0.1 higher than the final target value, and the grid potential and the developing bias potential are set to the CPU 28 (FIGS. 5) is set.
[0152]
In step S54, it is determined whether or not the obtained contrast potential is within the control range. If the contrast potential is out of the control range, it is determined that there is an abnormality in the developing device or the like, and the development of the corresponding color is performed. An error flag is set so that the serviceman can check the device so that the serviceman can see the error flag in a predetermined service mode.
[0153]
Here, in the case of such an abnormality, a limiter is applied to a value at the very end of the control range to perform correction control (step S55), and the control is continued.
[0154]
As described above, the grid potential and the developing bias potential are set by the CPU 28 so that the contrast potential obtained in step S53 can be obtained.
[0155]
FIG. 24 shows a density conversion characteristic diagram. According to the maximum density control for setting the maximum density higher than the final target value in the present embodiment, the printer characteristic diagram in the third quadrant is as shown by a solid line J.
[0156]
If such control is not performed, the printer characteristic may not reach 1.6 as indicated by the broken line H. In the case of the characteristic indicated by the broken line H, no matter how the LUT 25 is set, since the LUT 25 does not have the ability to increase the maximum density, the density between the density DH and 1.6 cannot be reproduced.
[0157]
If the setting slightly exceeds the maximum density as indicated by the solid line J, the density reproduction range can be reliably guaranteed with the total gradation characteristics of the fourth quadrant.
[0158]
Next, a print start button 150 for the image of test print 2 appears on the operation panel as shown in FIG. 10A, and the image of test print 2 in FIG. 12 is printed out by pressing the button (step S56). ). During printing, the display is as shown in FIG. Similarly to the test print 1, the test print 2 is formed by forming a predetermined image pattern on a sheet 6 as a recording material and performing a fixing process.
[0159]
As shown in FIG. 12, the test print 2 is composed of a gradation group of 64 gradations in all of M, C, Y, and K, 4 columns and 16 rows. The laser output level is assigned with emphasis on the low density area of the 256 gradations, and the laser output level is spread over the high density area. This makes it possible to satisfactorily adjust the gradation characteristics particularly in the highlight portion.
[0160]
FIG. 12 shows a patch 71 having a resolution of 200 lpi (lines / inch) and a patch 72 having a resolution of 400 lpi (lines / inch). In order to form an image of each resolution, the pulse width modulation circuit 26 (FIGS. 4 and 5) is realized by preparing a plurality of periods of the triangular wave used for comparison with the image data to be processed. it can.
[0161]
In this image forming apparatus, a gradation image is created at a resolution of 200 lpi, and a line image such as a character is created at a resolution of 400 lpi. Although the same gradation level pattern is output at these two resolutions, if the gradation characteristics are greatly different due to the difference in resolution, it is more preferable to set the preceding gradation level according to the resolution. preferable.
[0162]
The test print 2 is generated from the pattern generator 29 (FIGS. 4 and 5) without operating the LUT 25.
[0163]
FIG. 14 is a schematic view of the output of the test print 2 viewed from above when the output of the test print 2 is placed on the platen glass 102. A wedge-shaped mark T at the upper left is a mark for abutting the document on the platen. The message is displayed on the operation panel so that the pattern of K is on the side of the abutting mark T and that the front and back are correct (FIG. 10 (c)). By doing so, a control error due to misplacement is prevented.
[0164]
When reading the pattern, the reader unit A gradually scans from the abutting mark T to obtain the first density gap point B. From the coordinate point, the position of each color patch of the pattern is determined by relative coordinates. It was determined and read (step S57).
[0165]
As for the reading points per patch (73 in FIG. 12), as shown in FIG. 18, 16 reading points (x) are taken inside the patch, and the obtained signals are averaged. It is preferable that the number of points is optimized by the reading device and the image forming device.
[0166]
The RGB signal in which the values of 16 points were averaged for each patch was converted into a density value by the conversion method to the optical density described above, and the laser output level was plotted on the horizontal axis with the output density as the output density. FIG.
[0167]
Further, as shown on the right vertical axis, the base density of the paper, in this example, 0.08 is normalized to the 0 level, and 1.60, which is set as the maximum density of the image forming apparatus, is normalized to the 255 level.
[0168]
If the obtained data has a specific high density like point C or a low density like point D, there is no stain on the platen glass 102 or no defect on the test pattern. Therefore, the inclination is limited and corrected so that continuity is preserved in the data sequence. Here, specifically, when the inclination is 3 or more, it is fixed at 3, and when the inclination is a negative value, the density level is the same as the previous level.
[0169]
As described above, the contents of the LUT 25 are simply changed by simply changing the coordinates of the density level in FIG. 19 to the input level (density signal axis in FIG. 6) and the laser output level to the output level (laser output signal axis in FIG. 6). Can be created. For a density level that does not correspond to a patch, a value is obtained by interpolation.
[0170]
At this time, a limiting condition is set so that the output level becomes 0 level with respect to the input level 0 level.
[0171]
Then, the conversion contents created as described above are set in the LUT 25 in step S58.
[0172]
Thus, the control of the contrast potential and the creation of the γ conversion table by the first control system using the reader (reader unit) A are completed. During the above-described processing, a display as shown in FIG. 10D is performed, and when it is completed, a display as shown in FIG. 10E is displayed.
[0173]
(Second control system)
The second control system stabilizes the image reproduction characteristics of the printer unit B alone as image control performed during normal image formation, detects the patch pattern density on the photosensitive drum 4, and corrects the LUT 25 described above. By doing so, image stabilization is achieved.
[0174]
FIG. 20 shows a processing circuit for processing a signal from a photosensor 40 (FIG. 1) including the LED 10 and the 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 converted into an output voltage of 0 to 5 V by an A / D conversion circuit 41 to a level of 0 to 255. Is converted to a digital signal. Then, the density is converted into a density by the density conversion circuit 42.
[0175]
The photo sensor 40 used in the present embodiment is configured to detect only regular reflection light from the photosensitive drum 4.
[0176]
FIG. 21 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.
[0177]
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.
[0178]
As can be seen from FIG. 21, 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. From these characteristics, by having a table 42a (FIG. 20) dedicated to each color for converting a sensor output signal into a density signal, the density signal can be read with high accuracy for each color.
[0179]
Here, in the present embodiment, as described above, the toner is deteriorated due to factors such as deterioration of the surface properties of the photosensitive drum 4, dirt on the surface of the photosensor 40, and a decrease in the amount of light of the LED 10 constituting the photosensor 40. Since the photosensor output of the patch is expected to fluctuate due to durability, a base correction coefficient is calculated from the base output data detected and stored in advance for the output obtained from the photosensor 40 to calculate the correction output. . That is,
Background correction coefficient = 1 / Background output data
Correction output = photosensor output x background correction coefficient
The background output data used here uses the background output data stored during the above-described normal image formation.
[0180]
At this time, the background output data is stored together with the position information on the photosensitive drum as described above. As shown in FIG. 28, when calculating the correction output, the position of the surface of the photosensitive drum on which the toner patch to be actually detected is formed is detected, and the pre-stored base output for one rotation of the photosensitive drum is stored. The configuration is such that the base output data at the position corresponding to the toner patch formation position is read from the data and the correction output operation is performed. As a result, the amount of reflected light on the surface of the photoconductor drum at the same position as the position where the toner patch is formed can be used as background data. Therefore, even if local deterioration or toner adhesion occurs on the surface of the photoconductor drum due to durability, correction accuracy can be improved. Can be kept.
[0181]
Since the second control system aims at maintaining stable color reproducibility achieved by the first control system, the state immediately after the end of the control by the first control system is set as a target value. FIG. 22 shows a flow of the target value setting.
[0182]
When the control by the first control system is completed, a patch pattern for each of the colors M, C, Y, and K is formed on the photosensitive drum, and is detected by the photosensor 40.
[0183]
Here, the laser output of the patch uses a density signal (density signal axis in FIG. 6) of 128 levels for each color. At this time, the contents of the LUT 25 and the setting of the contrast potential use those obtained by the first control system. The density value D128 at this time is set as a target value of the second control system and is backed up. The target value is updated each time control is performed by the first control system.
[0184]
The second control system is a control for detecting a patch density formed in a non-image area during normal image formation, and correcting the γLUT obtained by the first control system as needed. According to the above-described sequence, a patch is formed on a non-image area on the photosensitive drum 4 during normal image formation. It is important that the laser output of the patch is the same as when the target value is set. For each color, 128 levels are used as the density signal (density signal axis in FIG. 6). At this time, the contents of the LUT 25 and the setting of the contrast potential are the same as those at the time of normal image formation. That is, a value obtained by the first control system and corrected by the second control system up to the previous time is used.
[0185]
The density signal 128 is controlled so that the patch output density becomes D128 on a density scale obtained by normalizing 1.6 to 255. However, the image characteristics of the printer are unstable, and there is a possibility that the density is constantly changed. Therefore, the measured result is not always D128, and may be shifted by ΔD.
[0186]
Based on this ΔD, the second control system corrects the LUT 25 (γLUT) created by the first control system.
[0187]
FIG. 23 shows a γLUT correction table corresponding to a change in output density from general density signals 0 to 255 when the output density is shifted by ΔDX in the density signal 128 in the present embodiment. This is stored in advance, and at the time of control, the γ correction table is standardized so that the value of the density signal 128 of the γ LUT correction table becomes ΔD, and an LUT formed so as to cancel this is added to the LUT 25 to correct the LUT 25. . The timing at which the LUT 25 is rewritten differs for each color. When the LUT 25 is ready for rewriting, the LUT 25 is rewritten by a TOP signal while laser writing of the color is not performed.
[0188]
In the present embodiment, when the main switch of the image processing apparatus is turned on, or after a lapse of a fixed time after the main switch is turned on, or in response to a sensor output from a temperature sensor and a humidity sensor (not shown) for detecting an environmental change, a third correction is performed. Two control systems are implemented.
[0189]
Since the first control system involves human work, it is difficult to assume that the first control system is frequently performed. Therefore, if a serviceman executes the first control system in the installation work of the image forming apparatus, and there is no problem with the image, In the second control system, the characteristics can be automatically maintained for a short period of time, and for the one that gradually changes over a long period of time, the first control system can perform the calibration. As a result, the gradation characteristics can be maintained until the life of the image forming apparatus.
[0190]
As described above, in the present embodiment, the toner patch which is the second control for acquiring the reference density formed on the photosensitive drum based on the LUT created by performing the automatic gradation correction as the first control means and based on the LUT created by the automatic control. After the reading, the toner image is transferred during one rotation cycle of the transfer body (transfer drum) 5 based on the reference density of the patch sensor, and the rotary developing device is rotated during the next rotation cycle of the transfer body. During the idle rotation cycle of the transfer body of the image forming apparatus in which the developing device is replaced, the base of the photosensitive drum for correction is detected over the entire circumference of the photosensitive drum and stored together with the position information, and the correction is performed by the correction. The image density characteristics obtained by the automatic gradation correction are maintained for a long time by correcting the LUT created by the automatic gradation correction according to the amount of change from the toner patch density value of the second control. To do It can be.
[0191]
Further, in this embodiment, the image forming apparatus having the transfer drum as shown in FIG. 1 has been described. However, in addition, the structure of the transfer belt and the structure having the intermediate transfer body 51 as shown in FIG. However, similar effects can be obtained and applied.
[0192]
The image forming apparatus of the embodiment shown in FIG. 27 has the same configuration as that of the image forming apparatus described with reference to FIG. 1 except that the intermediate transfer body 51 is used. Are denoted by the same reference numerals, and detailed description is omitted.
[0193]
Also in the embodiment of FIG. 27, similar effects can be obtained by adopting the same configuration as the above-described embodiment.
[0194]
【The invention's effect】
As described above, the present invention performs multiple transfer onto a recording material using a transfer body, or collectively transfers a toner image laminated on the intermediate transfer body using an intermediate transfer body onto a recording material. The secondary transfer is performed, and the developing unit is constituted by a rotary developing device. After the toner image is transferred during one rotation cycle of the transfer body or the intermediate transfer body, the developing unit is rotated during the rotation cycle of the next transfer body or the intermediate transfer body. In an image forming apparatus in which a rotary developing device is rotated to replace a developing device, a toner patch formed on an image carrier surface during an idle rotation cycle of a transfer body or an intermediate transfer body is read by an optical detection unit, With the configuration in which the image forming condition is corrected based on the difference between the read image information and the reference image information, the image can be accurately corrected for each image formation, and a long-term stable image can be obtained.
[0195]
Further, the present invention provides a method of performing multiple transfer onto a recording material using a transfer body, or performing a secondary transfer onto a recording material collectively using a toner image laminated on an intermediate transfer body using an intermediate transfer body. The developing means comprises a rotary developing device, and after transferring the toner image during one rotation cycle of the transfer member or the intermediate transfer member, the rotary developing device is rotated during the rotation cycle of the next transfer member or the intermediate transfer member. In the image forming apparatus in which the developing unit is rotated and rotated, the second control system is read by reading the surface of the image carrier as the base correction data by the optical detection means during the idle rotation cycle of the transfer body or the intermediate transfer body. It is not necessary to newly acquire the data for the background correction before performing, and it is possible to reduce the time required for the second control system.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of a reader image processing unit in the image forming apparatus.
FIG. 3 is a diagram illustrating a timing of a reader image processing unit in the image forming apparatus.
FIG. 4 is a control block diagram of the image forming apparatus.
FIG. 5 is a control block diagram of the image forming apparatus.
FIG. 6 is a fourth-limit chart showing gradation reproduction characteristics.
FIG. 7 is a flowchart of a first control system of the image forming apparatus.
FIG. 8 is a diagram illustrating display contents of a display device in the image forming apparatus.
FIG. 9 is a diagram illustrating display contents of a display device in the image forming apparatus.
FIG. 10 is a diagram illustrating display contents of a display device in the image forming apparatus.
FIG. 11 is a diagram showing an example of test print 1.
FIG. 12 is a diagram illustrating an example of a test print 2.
FIG. 13 is a diagram showing how to place a test print 1 on a document table.
FIG. 14 is a diagram showing how to place a test print 2 on a document table.
FIG. 15 is a diagram showing a relationship between relative drum surface potential and image density.
FIG. 16 is a diagram showing a relationship between an absolute water content and a contrast potential.
FIG. 17 is a diagram showing a relationship between a grid potential and a surface potential.
FIG. 18 is a diagram showing read points of a patch pattern.
FIG. 19 is a diagram illustrating an example of reading a test print 2.
FIG. 20 is a flowchart from the photo sensor to the density conversion.
FIG. 21 is a diagram showing a relationship between a photo sensor output and an image density.
FIG. 22 is a flowchart for setting a target value.
FIG. 23 is a diagram illustrating a γLUT correction table.
FIG. 24 is a diagram showing density conversion characteristics.
FIG. 25 is a diagram illustrating a region of a sheet holding surface of a transfer drum in the present embodiment.
FIG. 26 is a timing chart illustrating an image forming operation.
FIG. 27 is a schematic configuration diagram of another embodiment of the image forming apparatus according to the present invention.
FIG. 28 is a schematic configuration diagram illustrating background detection.
[Explanation of symbols]
1 polygon mirror (exposure device)
2 Reflection mirror
3 Rotary developing device
3M, 3C, 3Y, 3K developer
4 Photoconductor drum (image carrier)
5 Transfer drum (transfer)
6 Recording materials
8 Primary charger (charging means)
10 LED
11 Photodiode
12 Surface potential sensor
40 Photo sensor
51 Intermediate transfer member
100 Printer Engine
105 CCD sensor
108 Reader image processing unit
109 Printer control unit
110 semiconductor laser

Claims (1)

An image carrier, a plurality of developing means for accommodating toners of different colors and developing a latent image formed on the image carrier with a developing section, and a plurality of developing means accommodated and one of the developing means is selected as a developing section; Transfer means for moving the recording medium so as to be positioned at a predetermined position, and a recording material carrier for carrying the recording material, and the transfer unit transfers the toner image from the image carrier to a plurality of recording materials on the recording material carrier. An image forming apparatus that forms a plurality of toner images on a recording material by repeating the steps of
A first developing unit sequentially forming toner images on the image carrier so that transfer is performed in the order of a first recording material and a second recording material on the recording material carrier;
Before the second recording material to which the toner image has been transferred by the first developing unit passes through the transfer section, the second recording material on the recording material carrier, the first recording material, An image characterized in that a second developing means is moved to the developing section by the moving means so that transfer is performed in order, and a toner image is sequentially formed on the image carrier by the second developing means. Forming equipment.

Images