JP4235334B2 - Image forming apparatus - Google Patents

Description

Ｂ）帯電バイアス印加系
図４は帯電ローラ２に対する帯電バイアス印加系のブロック回路図である。
【００６６】
電源Ｓ１から直流電圧に周波数ｆの交流電圧を重畳した所定の振動電圧（バイアス電圧Ｖｄｃ＋Ｖａｃ）が芯金２ａを介して帯電ローラ２に印加されることで、回転する感光体ドラム１の周面が所定の電位に帯電処理される。
【００６７】
帯電ローラ２に対する電圧印加手段である電源Ｓ１は、直流（ＤＣ）電源１１と交流（ＡＣ）電源１２を有している。
【００６８】
１３は制御回路であり、上記電源Ｓ１のＤＣ電源１１とＡＣ電源１２をオン・オフ制御して帯電ローラ２に直流電圧と交流電圧のどちらか、若しくはその両方の重畳電圧を印加するように制御する機能と、ＤＣ電源１１から帯電ローラ２に印加する直流電圧値と、ＡＣ電源１２から帯電ローラ２に印加する交流電圧のピーク間電圧値を制御する機能を有する。
【００６９】
１４は感光体１を介して帯電ローラ２に流れる交流電流値を測定する手段としての交流電流値測定回路である。この回路１４から上記の制御回路１３に測定された交流電流値情報が入力する。
【００７０】
１５はプリンタが設置されている環境を検知する手段としての環境センサー（温度計と湿度計）である。この環境センサー１５から上記の制御回路１３に検知された環境情報が入力する。
【００７１】
そして、制御回路１３は交流電流値測定回路１４から入力の交流電流値情報、更には環境センサー１５から入力の環境情報から、印字工程の帯電工程における帯電ローラ２に対する印加交流電圧の適切なピーク間電圧値の演算・決定プログラムを実行する機能を有する。
【００７２】
Ｃ）交流電圧のピーク間電圧の制御方法
次に、印字時に帯電ローラ２に印加する交流電圧のピーク間電圧の制御方法を述べる。
【００７３】
本発明者らは、種々の検討により、以下の定義により数値化した放電電流量が実際のＡＣ放電の量を代用的に示し、感光体ドラムの削れ、画像流れ、帯電均一性と強い相関関係があることを見出した。
【００７４】
すなわち図５に示すように、ピーク間電圧Ｖｐｐに対して交流電流Ｉａｃは放電開始電圧Ｖｔｈ×２（Ｖ）未満（未放電領域）で線形の関係にあり、それ以上から放電領域に入るにつれ徐々に電流の増加方向にずれる。放電の発生しない真空中での同様の実験においては直線が保たれたため、これが、放電に関与している電流の増分△Ｉａｃであると考える。
【００７５】
よって、放電開始電圧Ｖｔｈ×２（Ｖ）未満のピーク間電圧Ｖｐｐに対して電流Ｉａｃの比をαとしたとき、放電による電流以外の、接触部へ流れる電流（以下、ニップ電流）などの交流電流はα・Ｖｐｐとなり、放電開始電圧Ｖｔｈ×２（Ｖ）以上の電圧印加時に測定されるＩａｃと、このα・Ｖｐｐの差分、
式１・・・△Ｉａｃ＝Ｉａｃ−α・Ｖｐｐ
から△Ｉａｃを放電の量を代用的に示す放電電流量と定義する。
【００７６】
この放電電流量は一定電圧または一定電流での制御下で帯電を行った場合、環境、耐久を進めるにつれ変化する。これはピーク間電圧と放電電流量の関係、交流電流値と放電電流量との関係が変動しているからである。
【００７７】
ＡＣ定電流制御方式では、帯電部材から被帯電体に流れる総電流で制御している。この総電流量とは、上記のように、ニップ電流α・Ｖｐｐと非接触部で放電することで流れる放電電流量△Ｉａｃの和になっており、定電流制御では実際に被帯電体を帯電させるのに必要な電流である放電電流だけでなく、ニップ電流も含めた形で制御されている。
【００７８】
そのため、実際に、放電電流量は制御できていない。定電流制御において同じ電流値で制御していても、帯電部材の材質の環境変動によって、ニップ電流が多くなれば当然放電電流量は減り、ニップ電流が減れば放電電流量は増えるため、ＡＣ定電流制御方式でも完全に放電電流量の増減を抑制することは不可能であり、長寿命を目指したとき、感光体ドラムの削れと帯電均一性の両立を実現することは困難であった。
【００７９】
そこで、本発明者らは、常に所望の放電電流量を得るため、以下の要領で制御を行った。
【００８０】
所望の放電電流量をＤとしたときに、この放電電流量Ｄとなるピーク間電圧を決定する方法を説明する。
【００８１】
本実施例では印字準備回転動作時において制御回路１３で印字工程時の帯電工程における帯電ローラ２に対する印加交流電圧の適切なピーク間電圧値の演算・決定プログラムを実行させている。
【００８２】
具体的に、図６のＶｐｐ−Ｉａｃグラフと、図７の制御フロー図を参照して説明する。
【００８３】
制御回路１３はＡＣ電源１２を制御して図６に示すように、帯電ローラ２に放電領域であるピーク間電圧（Ｖｐｐ）を３点、未放電領域であるピーク間電圧を３点、順次に印加し、その時の感光体１を介して帯電ローラ２に流れる交流電流値が交流電流値測定回路１４で測定されて制御回路１３に入力する。
【００８４】
次に制御回路１３は、上記測定された各３点の電流値から、最小二乗法を用いて、放電、未放電領域のピーク間電圧と交流電流の関係を直線近似し、以下の式２と式３を算出する。
【００８５】
式２・・・放電領域の近似直線 ：Ｙ_α＝αＸ＋Ａ
式３・・・未放電領域の近似直線 ：Ｙ_β＝βＸ＋Ｂ
その後、上記の式２の放電領域の近似直線と、式３の未放電領域の近似直線の差分が、放電電流量Ｄとなるピーク間電圧Ｖｐｐを式４によって決定する。
【００８６】
式４・・・Ｖｐｐ＝（Ｄ−Ａ＋Ｂ）／（α−β）
ここで、請求項に記載した、未放電領域と放電領域でのピーク間電圧（Ｖｐｐ）−交流電流（Ｉａｃ）関数fI1(Vpp)とfI2(Vpp)はそれぞれ上記式３のＹ_β＝βＸ_β＋Ｂと式２のＹ_α＝αＸ_α＋Ａに対応している。また請求項に記載した定数Ｄは上記の所望の放電電流量Ｄと対応している。
【００８７】
よって、請求項に記載したfI2(Vpp)−fI1(Vpp)＝Ｄは
Ｙ_α−Ｙ_β＝（αＸ_α＋Ａ）−（βＸ_β＋Ｂ）＝Ｄ
となる。
【００８８】
また、fI2(Vpp)−fI1(Vpp)＝Ｄから式４の
Ｖｐｐ＝（Ｄ−Ａ＋Ｂ）／（α−β）
の誘導は次のとおりである。
【００８９】
fI2(Vpp)−fI1(Vpp)＝Ｙ_α−Ｙ_β＝Ｄ
（αＸ_α＋Ａ）−（βＸ_β＋Ｂ）＝Ｄ
今、ＤとなるＸの値を探しており、その点をＶｐｐとすると、
（αＶｐｐ＋Ａ）−（βＶｐｐ＋Ｂ）＝Ｄ
よって、Ｖｐｐ＝（Ｄ−Ａ＋Ｂ）／（α−β）となる。
【００９０】
そして、帯電ローラ２に印加するピーク間電圧を上記の式４で求めたＶｐｐに切り替え、定電圧制御し、前記した印字工程へと移行する。
【００９１】
この様に、毎回、印字準備回転時において、印字時に所定の放電電流量を得るために必要なピーク間電圧を算出し、印字中には求めたピーク間電圧を定電圧制御で印加することで、帯電ローラ２の製造ばらつきや材質の環境変動に起因する抵抗値のふれや、本体装置の高圧ばらつきを吸収し、確実に所望の放電電流量を得ることが可能となった。
【００９２】
この制御下で、耐久検討を行なったところ、どの環境下でも像担持体としての感光体ドラムの劣化・削れを発生させず、従来の定電流制御と比較して約１０％の感光体ドラムの長寿命化を実現可能とした。
【００９３】
本実施例では帯電ローラに印加する交流電圧のピーク間電圧を切り替えることで放電電流量を制御したが、これに限らず、逆に交流電流を印加することで交流電圧のピーク間電圧を測定し（図４中の交流電流値測定回路１４をピーク間電圧値測定回路に変更）、印字時には所望の放電電流量を得るに必要な交流電流を常に印加できるようにＡＣ電源の出力交流電流を制御回路１３で定電流制御することも可能である。
【００９４】
さらに、本実施例では所望の放電電流量Ｄ、印字準備回転時に印加するピーク間電圧値を各環境一定にしたが、環境センサー（温度計と湿度計）１５が設置されている装置においては、環境ごとでそれぞれの値を可変することで、さらに安定した均一帯電を行なうことが可能となる。
【００９５】
かくして、印字準備回転中に未放電領域で数点、放電領域で数点、順次、ピーク間電圧を帯電ローラ２に印加し、交流電圧値を測定し、印字中に印加するピーク間電圧を決定することで、常に所望の放電電流量を得られるピーク間電圧または交流電流を印加することで、感光体の劣化・削れと帯電均一性を両立させることができ、長寿命化、高画質化が実現可能となった。
【００９６】
さらに、製造時のばらつきも吸収できることから、材料、精度に関しても許容範囲が広がることで、製造時のコストダウンも行なえ製品を安価にユーザーに提供することが可能となる。
【００９７】
〈実施例２〉（図８）
本実施例は、１点制御、定電圧制御の系である。図８に示すように、画像形成装置は、印字準備回転時に、帯電ローラに放電領域であるピーク間電圧（Ｖｐｐ）を２点、未放電領域であるピーク間電圧を１点、順次、帯電ローラ印加し、その時の交流電流値を測定する。ピーク間電圧と交流電流の関係はピーク間電圧がゼロの時、交流電流値もゼロとなるよう予め設定されている。
【００９８】
次に画像形成装置は、放電領域では測定値２点から、未放電領域では測定値と０点とを用いて、ピーク間電圧と交流電流の関係を直線近似し、以下の式２と式３を算出する。
【００９９】
式２・・・放電領域の近似直線 ：Ｙ_α＝αＸ_α＋Ａ
式３・・・未放電領域の近似直線 ：Ｙ_β＝βＸ_β
その後、放電領域の近似直線Ｙ_αと未放電領域の近似直線Ｙ_βの差分が、放電電流量Ｄとなるピーク間電圧Ｖｐｐを式４によって決定する。
【０１００】
式４・・・Ｖｐｐ＝（Ｄ−Ａ）／（α−β）
そして、帯電部材に印加するピーク間電圧を求めたＶｐｐに切り替え（Ｖｐｐで定電圧制御）、前記した画像形成動作へと移行する。
【０１０１】
このような制御構成にすることで実施例１と同様の効果を少ない測定点で得ることが可能となる。
【０１０２】
本実施例のような１点制御系に関して、より広義なものとして、ここではゼロでなくてもよく、例えばあるＶｐｐの時に流れる電流量が予め分かっていれば、その点と測定点を用いてピーク間電圧と交流電流の関係を求めることも可能であり、少なくとも一点を測定すれば、ピーク間電圧と交流電流の関係が得られる。
【０１０３】
〈実施例３〉（図９）
本実施例は、３点制御、定電流制御の系であり、所望の放電電流量をＤとしたときに、この放電電流量Ｄとなる交流電流値を決定する方法を説明する。
【０１０４】
図９に示すように、画像形成装置は、印字準備回転時に、帯電ローラに放電領域である交流電流（Ｉａｃ）を３点、未放電領域である交流電流を３点、順次、帯電ローラ印加し、その時のピーク間電圧値を測定する。
【０１０５】
次に画像形成装置は、測定された各３点の電流値から、最小二乗法を用いて、放電、未放電領域でのピーク間電圧と交流電流の関係を直線近似し、以下の式２と式３を算出する。
【０１０６】
式２・・・放電領域の近似直線 ：Ｙ_α＝αＸ_α＋Ａ
式３・・・未放電領域の近似直線 ：Ｙ_β＝βＸ_β＋Ｂ
その後、放電領域の近似直線Ｙ_αと未放電領域の近似直線Ｙ_βの差分が、放電電流量Ｄとなる交流電流（Ｉａｃ）を式４によって決定する。
【０１０７】
Ｄとなる交流電流値をＩａｃ１とし、そのときのピーク間電圧をＶｐｐとすると、式２と式３は、
Ｉａｃ１＝αＶｐｐ＋Ａ・・・式ａ
Ｉａｃ２＝βＶｐｐ＋Ｂ・・・式ｂ
となる。ここで、Ｉａｃ２は未放電領域の近似直線Ｙ_βでのＶｐｐとなる交流電流値である。
【０１０８】
Ｉａｃ１＝Ｉａｃ２＋Ｄ・・・式ｃ
式ａ、ｂ、ｃから、放電電流量Ｄとなる交流電流（Ｉａｃ）は、式４で決定される。
【０１０９】
式４・・・Ｉａｃ＝（αＤ＋αＢ−βＡ）／（α−β）
そして、帯電部材に印加する交流電流を求めたＩａｃに切り替え、Ｉａｃで定電流制御し、前記した画像形成動作へと移行する。
【０１１０】
〈実施例４〉（図１０）
本実施例は、１点制御、定電流制御の系であり、所望の放電電流量をＤとしたときに、この放電電流量Ｄとなる交流電流値を決定する方法を説明する。
【０１１１】
図１０に示すように、画像形成装置は、印字準備回転時に、帯電ローラに放電領域である交流電流（Ｉａｃ）を２点、未放電領域である交流電流を１点、順次、帯電ローラに印加し、その時のピーク間電圧値を測定する。
【０１１２】
次に画像形成装置は、放電領域では測定値２点から、未放電領域では測定値と０点とを用いて、ピーク間電圧と交流電流の関係を直線近似し、以下の式２と式３を算出する。
【０１１３】
式２・・・放電領域の近似直線 ：Ｙ_α＝αＸ_α＋Ａ
式３・・・未放電領域の近似直線 ：Ｙ_β＝βＸ_β
その後、放電領域の近似直線Ｙ_αと未放電領域の近似直線Ｙ_βの差分が、放電電流量Ｄとなる交流電流（Ｉａｃ）を式４によって決定する。
【０１１４】
Ｄとなる交流電流値をＩａｃ１とし、そのときのピーク間電圧をＶｐｐとすると、式２と式３は、
Ｉａｃ１＝αＶｐｐ＋Ａ・・・式ａ
Ｉａｃ２＝βＶｐｐ ・・・式ｂ
となる。ここで、Ｉａｃ２は未放電領域の近似直線Ｙ_βでのＶｐｐとなる交流電流値である。
【０１１５】
Ｉａｃ１−Ｉａｃ２＝Ｄ・・・式ｃ
式ａ、ｂ、ｃから、放電電流量Ｄとなる交流電流（Ｉａｃ）は、式４で決定される。
【０１１６】
式４・・・Ｉａｃ＝（αＤ−βＡ）／（α−β）
そして、帯電部材に印加する交流電流を求めたＩａｃに切り替え、Ｉａｃで定電流制御し、前記した画像形成動作へと移行する。
【０１１７】
〈実施例５〉（図１１）
図１１は本実施例における画像形成装置の概略構成模型図である。本例の画像形成装置は、転写方式電子写真プロセス利用、接触帯電方式、反転現像方式、クリーナーレス、最大通紙サイズがＡ３サイズのレーザビームプリンタである。
【０１１８】
前記の実施例１のプリンタと共通する構成部材・部分には同じ符号を付して再度の説明を省略し、実施例１のプリンタとは異なる構成部材・部分・事項について説明する。
【０１１９】
（１）プリンタの全体的概略構成
本実施例のプリンタにおいて、像担持体としての感光体ドラム１は外径５０ｍｍである。
【０１２０】
現像手段である現像装置４は二成分磁気ブラシ現像方式の反転現像装置であり、感光体ドラム１面に形成された静電潜像はこの現像装置４により順次にトナー像として本例の場合は負に摩擦帯電されたトナー（ネガトナー）により反転現像されていく。現像容器４ａに収容の現像剤４ｅは二成分現像剤である。４ｆは現像容器４ａ内の底部側に配設した現像剤攪拌部材、４ｇはトナーホッパーであり、補給用トナーを収容させてある。
【０１２１】
現像容器４ａ内の二成分現像剤４ｅはトナーと磁性キャリアの混合物であり、現像剤攪拌部材４ｆにより攪拌される。本例においてトナーの平均粒径は６μｍ、磁性キャリアの抵抗は約１０¹³Ωｃｍ、粒径は約４０μｍである。トナーは磁性キャリアとの摺擦により負極性に摩擦帯電される。
【０１２２】
現像スリーブ４ｂは感光体ドラム１との最近接距離（Ｓ−Ｄｇａｐと称する）を３５０μｍに保たせて感光体ドラム１に近接させて対向配設してある。この感光体ドラム１と現像スリーブ４ａとの対向部が現像部ｃである。現像スリーブ４ｂは現像部ｃにおいて感光体ドラム１の進行方向とは逆方向に回転駆動される。この現像スリーブ４ｂの外周面に該スリーブ内のマグネットローラ４ｃの磁力により現像容器４ａ内の二成分現像剤４ｅの一部が磁気ブラシ層として吸着保持され、該スリーブの回転に伴い回転搬送され、現像剤コーティングブレード４ｄにより所定の薄層に整層され、現像部ｃにおいて感光体ドラム１の面に対して接触して感光体ドラム面を適度に摺擦する。現像スリーブ４ｂには電源Ｓ２から所定の現像バイアスが印加される。
【０１２３】
而して、回転する現像スリーブ４ｂの面に薄層としてコーティングされ、現像部ｃに搬送された現像剤中のトナー分が現像バイアスによる電界によって感光体ドラム１面に静電潜像に対応して選択的に付着することで静電潜像がトナー画像として現像される。本例の場合は感光体ドラム１面の露光明部にトナーが付着して静電潜像が反転現像される。
【０１２４】
現像部ｃを通過した現像スリーブ４ｂ上の現像剤薄層は引き続く現像スリーブの回転に伴い現像容器４ａ内の現像剤溜り部に戻される。
【０１２５】
現像容器４ａ内の二成分現像剤４ｅのトナー濃度を所定の略一定範囲内に維持させるために、現像容器４ａ内の二成分現像剤４ｅのトナー濃度が不図示の例えば光学式トナー濃度センサーによって検知され、その検知情報に応じてトナーホッパー４ｇが駆動制御されて、トナーホッパー内のトナーが現像容器４ａ内の二成分現像剤４ｅに補給される。二成分現像剤４ｅに補給されたトナーは攪拌部材４ｆにより攪拌される。
【０１２６】
（２）クリーナーレスシステム
本例のプリンタはクリーナーレスであり、転写材Ｐに対するトナー画像転写後の感光体ドラム１面に若干量残留する転写残トナーを除去する専用のクリーニング装置は具備させていない。転写後の感光体ドラム１面上の転写残トナーは引き続く感光体ドラム１の回転に伴い帯電部ａ、露光部ｂを通って現像部ｃに持ち運ばれて、現像装置３により現像同時クリーニング（回収）される。
【０１２７】
現像同時クリーニングは、転写後の感光体上の転写残トナーを次工程以降の現像工程時、即ち引き続き感光体を帯電し、露光して静電潜像を形成し、該静電潜像の現像工程過程時にかぶり取りバイアス（現像装置に印加する直流電圧と感光体の表面電位間の電位差であるかぶり取り電位差Ｖback）によって、トナーで現像されるべきではない感光体面部分上に存在する転写残トナーは現像装置に回収する方法である。この方法によれば、転写残トナーは現像装置に回収されて次工程以降の静電潜像の現像に再用されるため、廃トナーをなくし、またメンテナンスに手を煩わせることも少なくすることができる。またクリーナーレスであることで画像形成装置の小型化にも有利である。
【０１２８】
８はトナー帯電制御手段であり、転写部ｄよりも感光体ドラム回転方向下流側で、帯電部ａよりも感光体ドラム回転方向上流側の位置に配設してある。このトナー帯電制御手段７は、適度の導電性を持ったブラシ形状部材（補助ブラシ）であり、ブラシ部を感光体ドラム１面に接触させて配設してあり、負極性の電圧が電源Ｓ４より印加されている。ｆはブラシ部と感光体ドラム１面の接触部である。トナー帯電制御手段７を通過する感光体ドラム１上の転写残トナーはその帯電極性が正規極性である負極性に揃えられる。
【０１２９】
すなわち、転写工程後の感光体ドラム１面上の転写残トナーには画像部で転写し切れなかった負極性トナー、現像時に非画像部に付着した正極性のカブリトナー、転写の正極性の電圧に影響され極性が正極性に反転してしまったトナーが含まれる。このような転写残トナーは上記のトナー帯電制御手段８によりその帯電極性が一様に負極性に揃えられる。本実施例では、トナー帯電制御手段８には転写後の感光体に対して放電がおこる電圧である−１０００Ｖを印加した。これにより、トナー帯電制御手段８を通過する転写残トナーには放電および直接電荷注入により電荷付与がなされ、負極性に揃えられる。
【０１３０】
上述した帯電工程では、転写残トナーの上から感光体ドラム１面上を帯電処理する。転写残トナーの極性は負極性に一様に揃えられているため、負極性の直流電圧を印加されている帯電ローラ２へのトナー付着はない。露光工程においても転写残トナー上から露光を行なうが、転写残トナーの量は少ないため、大きな影響は現れない。現像工程においては、感光体ドラム１上の未露光部に存在する転写残トナーは、電界の関係上現像器に回収される。
【０１３１】
前述したように現像スリーブ２ｂと感光体ドラム１との最近接距離（Ｓ−Ｄｇａｐ）は３５０μｍであり、この距離を保つことで現像スリーブ４ｂ上に形成された二成分現像剤の磁気ブラシが感光体ドラム１表面と適度に摺擦し感光体ドラム１上の転写残トナーの現像同時回収が行なわれる。また転写残トナーの回収に有利であるように、現像スリーブ４ｂは現像部ｃにおいて感光体ドラム１の表面の進行方向とは逆方向に回転させている。
【０１３２】
（３）交流電圧のピーク間電圧の制御
クリーナーレスシステムにおいて、ＡＣ帯電方式を用いた場合、次の問題がおこる。すなわちＡＣ帯電により発生した放電生成物に起因した画像流れ、ボケである。
【０１３３】
接触帯電によるＡＣ帯電方式の場合も、コロナ帯電器による帯電処理との対比において発生オゾン量は少ないが皆無ではないので、多少ながら放電生成物による悪影響がある。画像形成装置にあっては、像担持体としての感光体面に放電生成物が付着し、さらに吸湿することで感光体表面が低抵抗化して潜像の解像力低下し、また上記のようなクリーナーレスの構成を採用した画像形成装置では、クリーニング装置による感光体の刷新効果が望めなく、ボケ、画像流れ等が発生しやすくなる。
【０１３４】
上記の問題と帯電均一性を両立させるには、常に所望の放電電流量を得る必要があり、そのためには本発明である帯電ローラへの印加電圧制御手段を用いる必要がある。
【０１３５】
本実施例の交流電圧のピーク間電圧制御は、次のように行っている。
【０１３６】
印字準備回転中に未放電領域で３点、放電領域で３点、順次、ピーク間電圧を帯電ローラ２に印加し、交流電圧値を測定し、印字中に印加するピーク間電圧を決定する。印加するピーク間電圧の算出方法は実施例１に示した方法と同様である。
【０１３７】
本実施例で用いた装置本体には環境センサ１５（図４）を設けており、各環境で、印字準備回転中に印加するピーク間電圧を可変し、帯電ローラの抵抗が低下するＨ／Ｈ環境ではＬ／Ｌ環境と比較し、約１０％低いピーク間電圧をそれぞれ印加している。これによって、実際に印字時に印加するピーク間電圧に近い値で測定することができ、さらに確実に所望の放電電流量を得ることが可能となった。
【０１３８】
また、放電電流量Ｄの値も環境ごとに可変とし、Ｌ／Ｌ環境に比べ、帯電安定性を得るのに必要な放電電流量が小さくかつ画像流れの発生しやすいＨ／Ｈ環境において、Ｌ／Ｌ環境での設定放電電流量Ｄの約２／３に下げる制御を行った。それにより、上記の問題に対しても、Ｈ／Ｈ環境ではＬ／Ｌ環境の約２／３倍にすることで、Ｈ／Ｈ環境では画像流れ、ボケの発生を確実に防ぎ、Ｌ／Ｌ環境では砂地を発生させることなく安定した均一帯電を行うことが可能となった。
【０１３９】
上記制御を行うことで、帯電ローラ製造ばらつきや材質の環境変動に起因する抵抗値のフレや、本体装置の高圧ばらつきを吸収し、さらに帯電ローラが汚れたときにおいても確実に所望の放電電流量を得ることができるという、実施例１と同様の効果だけでなく、同時に環境制御を行なうことで、各環境において必要かつ最小限の放電電流量できめ細かい制御を行うことが可能である。
【０１４０】
かくして、クリーナーレス装置に用いた場合においても、長期にわたり画像流れ、帯電不良、融着、画像メモリーなどの問題が発生することなく、安定して高画質・高品質を保つことが可能となった。
【０１４１】
実施例２〜４のような制御方法を採択することも勿論できる。
【０１４２】
〈その他〉
１）実施例においては、モノカラー（単色）での印字動作についてのみ述べたが、本発明はこれに限るものではなく、フルカラーの印字動作においても同様の効果を発揮することが可能である。
【０１４３】
２）実施例においてはプリンタの非画像形成時である印字準備回転動作期間において、印字工程の帯電工程における印加交流電圧の適切なピーク間電圧値または交流電流値の演算・決定プログラムの実行は実施例のプリンタのように印字準備回転動作期間に限られるものではなく、他の非画像形成時、すなわち初期回転動作時、紙間工程時、後回転工程時とすることもできるし、複数の非画像形成時に実行させるようにすることもできる。
【０１４４】
３）像担持体は表面抵抗が１０⁹ 〜１０¹⁴Ω・ｃｍの電荷注入層を設けた直接注入帯電性のものであってもよい。電荷注入層を用いていない場合でも、例えば電荷輸送層が上記の抵抗範囲にある場合も同等の効果がえられる。表層の体積抵抗が約１０¹³Ω・ｃｍであるアモルファスシリコン感光体もよい。
【０１４５】
４）可撓性の接触帯電部材は帯電ローラの他に、ファーブラシ、フェルト、布などの形状・材質のものも使用可能である。また各種材質のものの組み合わせでより適切な弾性、導電性、表面性、耐久性のものを得ることもできる。
【０１４６】
５）接触帯電部材や現像部材に印加する振動電界の交番電圧成分（ＡＣ成分、周期的に電圧値が変化する電圧）の波形としては、正弦波、矩形波、三角波等適宜使用可能である。直流電源を周期的にオン／オフすることによって形成された矩形波であってもよい。
【０１４７】
６）像担持体としての感光体の帯電面に対する情報書き込み手段としての像露光手段は実施例のレーザ走査手段以外にも、例えば、ＬＥＤのような固体発光素子アレイを用いたデジタル露光手段であってもよい。ハロゲンランプや蛍光灯等を原稿照明光源とするアナログ的な画像露光手段であってもよい。要するに、画像情報に対応した静電潜像を形成できるものであればよい。
【０１４８】
７）像担持体は静電記録誘電体などであってもよい。この場合は該誘電体面を一様に帯電した後、その帯電面を除電針ヘッドや電子銃等の除電手段で選択的に除電して目的の画像情報に対応した静電潜像を書き込み形成する。
【０１４９】
８）静電潜像のトナー現像方式・手段は任意である。反転現像方式でも正規現像方式でもよい。
【０１５０】
一般的に、静電潜像の現像方法は、非磁性トナーについてはこれをブレード等でスリーブ等の現像剤担持搬送部材上にコーティングし、磁性トナーについてはこれを現像剤担持搬送部材上に磁気力によってコーティングして搬送して像担持体に対して非接触状態で適用し静電潜像を現像する方法（１成分非接触現像）と、上記のように現像剤担持搬送部材上にコーティングしたトナーを像担持体に対して接触状態で適用し静電潜像を現像する方法（１成分接触現像）と、トナー粒子に対して磁性のキャリアを混合したものを現像剤（２成分現像剤）として用いて磁気力によって搬送して像担持体に対して接触状態で適用し静電潜像を現像する方法（２成分接触現像）と、上記の２成分現像剤を像担持体に対して非接触状態で適用し静電潜像を現像する方法（２成分非接触現像）との４種顛に大別される。
【０１５１】
９）転写手段は実施形態例のローラ転写に限られず、ブレード転写、ベルト転写、その他の接触転写帯電方式であってもよいし、コロナ帯電器を使用した非接触転写帯電方式でもよい。
【０１５２】
１０）転写ドラムや転写ベルトなどの中間転写体を用いて、単色画像形成ばかりでなく、多重転写等により多色、フルカラー画像を形成する画像形成装置にも本発明は適用できる。
【０１５３】
【発明の効果】
以上のように本発明によれば、像担持体の帯電を該像担持体に近接又は接触配置され電圧が印加された帯電手段により行う画像形成装置について、環境や製造時による帯電部材の抵抗値のばらつき等にかかわらず、過剰放電を起こさせず常に一定量の放電を生じさせて像担持体の劣化、トナー融着、画像流れ等の問題なく均一な帯電を行なえるように帯電手段に印加する電圧・電流を適切に制御することができ、またこれにより長期にわたり高画質、高品質を安定して維持させることができる。
【図面の簡単な説明】
【図１】 実施例１の画像形成装置の概略構成模型図
【図２】 感光体の層構成模型図
【図３】 画像形成装置の動作シーケンス図
【図４】 帯電バイアス印加系のブロック回路図
【図５】 放電電流量の測定概略図
【図６】 印字準備回転中に測定するピーク間電圧と交流電流量の関係図
【図７】 帯電制御フロー図
【図８】 実施例２における印字準備回転中に測定するピーク間電圧と交流電流量の関係図
【図９】 実施例３における印字準備回転中に測定するピーク間電圧と交流電流量の関係図
【図１０】 実施例４における印字準備回転中に測定するピーク間電圧と交流電流量の関係図
【図１１】 実施例５の画像形成装置（クリーナーレス）の概略構成模型図
【符号の説明】
１・・感光体ドラム（像担持体）、２・・帯電ローラ、３・・レーザビームスキャナ、４・・現像装置、５・・転写ローラ、６・・定着装置、７・・クリーニング装置、８・・トナー帯電制御手段、Ｓ１〜Ｓ４・・バイアス電圧印加電源、１１・・ＤＣ電源、１２・・ＡＣ電源、１３・・制御回路、１４・・交流電圧値またはピーク間電圧値の測定回路、１５・・環境センサー[0001]
BACKGROUND OF THE INVENTION
  The present invention, PaintingThe present invention relates to an image forming apparatus.
[0002]
  More specifically, an image forming apparatus in which charging of the image carrier is performed by a charging unit that is arranged in proximity to or in contact with the image carrier and to which a voltage is applied.In placeRelated.
[0003]
[Prior art]
Conventionally, for example, as a method of charging the surface of an image carrier as a charged body such as a photoreceptor or a dielectric in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a high voltage is applied to a thin corona discharge wire. Corona charging, which is non-contact charging, in which charging is performed by causing the generated corona to act on the surface of the image carrier, is generally used.
[0004]
In recent years, from the viewpoints of low-pressure process, low ozone generation, and low cost, a roller-type or blade-type charging member is brought into contact with the surface of the image carrier, and a voltage is applied to the charging member to Contact charging methods for charging are becoming mainstream. In particular, a roller-type charging member can perform stable charging over a long period of time.
[0005]
The voltage applied to the charging member may be only a DC voltage, but charging can be performed uniformly by applying an oscillating voltage and alternately causing discharge to the plus side and minus side.
[0006]
For example, a vibration in which an alternating voltage having a peak-to-peak voltage that is twice or more the discharge start threshold voltage (charging start voltage) of the object to be charged when a DC voltage is applied and a DC voltage (DC offset bias) are superimposed. It is known that applying a voltage has the effect of leveling the charge of the object to be charged and performs uniform charging.
[0007]
The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. The oscillating voltage is a rectangular wave voltage formed by periodically turning on / off the DC voltage, or the same output as the superimposed voltage of the AC voltage and the DC voltage by periodically changing the value of the DC voltage. Including.
[0008]
As described above, a contact charging method in which an oscillating voltage is applied to the charging member for charging is hereinafter referred to as an “AC charging method”. A contact charging method in which only a DC voltage is applied for charging is referred to as a “DC charging method”.
[0009]
However, in the AC charging method, compared to the DC charging method, the amount of discharge to the image carrier increases, so that the image carrier deterioration such as scraping of the image carrier is promoted, and in the high temperature and high humidity environment due to the discharge product. Abnormal images such as image flow may occur.
[0010]
In order to improve this problem, it is necessary to minimize the discharge that occurs alternately on the positive side and the negative side by applying the minimum necessary voltage.
[0011]
However, in reality, the relationship between the voltage and the discharge amount is not always constant, and changes depending on the film thickness of the photosensitive layer and dielectric layer of the image carrier, the environmental variation of the charging member and air, and the like. In a low-temperature and low-humidity environment (L / L), the material dries and the resistance value rises, making it difficult to discharge. Therefore, in order to obtain uniform charging, a peak-to-peak voltage above a certain value is required. Even at the lowest voltage value at which charging uniformity can be obtained in the environment, if the charging operation is performed in a high-temperature and high-humidity environment (H / H), the material absorbs moisture and the resistance value decreases. Will cause a discharge. As a result, when the discharge amount increases, problems such as image flow / blurring, toner fusion, and image carrier scraping / shortening due to deterioration of the surface of the image carrier occur.
[0012]
  Increase / decrease in discharge due to this environmental changeTheIn addition to the “AC constant voltage control method” in which a constant AC voltage is always applied in order to suppress the above, “AC constant current control to control the alternating current value that flows by applying an AC voltage to the charging member” "Method" has been proposed. According to this AC constant current control system, the peak voltage value of the AC voltage is increased in an L / L environment where the material resistance increases, and conversely, the peak voltage value is decreased in an H / H environment where the material resistance decreases. Therefore, increase / decrease in discharge can be suppressed as compared with the AC constant voltage control method.
[0013]
Here, the charging member does not necessarily need to be in contact with the surface of the image carrier, and as long as the dischargeable region determined by the voltage between the gap and the correction Paschen curve is reliably ensured between the charging member and the image carrier, For example, they may be arranged close to each other in a noncontact manner with a gap (gap) of several tens of μm (proximity charging). In the present invention, this proximity charging is also included in the category of contact charging.
[0014]
[Problems to be solved by the invention]
However, when aiming to further extend the life of the image carrier, even in the AC constant current control system, the variation in the resistance value due to manufacturing variation and contamination of the charging member, the capacitance fluctuation of the image carrier due to durability, the main body high voltage device It is not perfect for suppressing the increase and decrease of the discharge amount due to the variation of the current. In order to suppress the increase / decrease in the discharge amount, it is necessary to take measures to suppress the manufacturing variation of the charging member and the environmental fluctuation and to eliminate the high-voltage fluctuation, thereby increasing the cost.
[0015]
Accordingly, the present invention relates to an image forming apparatus in which charging of an image carrier is performed by a charging means that is placed close to or in contact with the image carrier and to which a voltage is applied, regardless of variations in the resistance value of the charging member depending on the environment and manufacturing. The voltage and current to be applied to the charging means are set so that a constant amount of discharge is always generated without causing excessive discharge and uniform charging can be performed without problems such as deterioration of the image carrier, toner fusion, and image flow. The purpose is to appropriately control, thereby stably maintaining high image quality and high quality over a long period of time.
[0016]
[Means for Solving the Problems]
  The present invention is characterized by the following means and configuration.PaintingAn image forming apparatus.
[0017]
  (1) In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier.
  The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
  For charging meansat leastAC powerPressureMeans for applying;
  Apply to charging meansExchangeCurrent-to-peak voltagePower ofControl pressure valuecontrolMeans,
bandMeans for measuring an alternating current value flowing through the electric means;
  Environment detection means for detecting the environment in which the image forming apparatus is installed;
  When the DC voltage is applied to the charging member and the discharge start voltage to the image carrier when Vth is Vth,The control means includesCharging means for non-image formation1Peak-to-peak voltage less than twice Vth above pointAC voltage withCurrent value when2Peak-to-peak voltage more than twice Vth above pointAC voltage withMeasure the current value when applyingApplied to obtain an approximate line of the relationship between voltage and current, determine a peak-to-peak voltage of the AC voltage applied to the charging means during image formation from the approximate line, and obtain the approximate line during non-image formation The peak-to-peak voltage of the AC voltage is smaller when the environment detected by the environment detection unit is a high temperature and high humidity environment than when the environment is a low temperature and low humidity environment.
[0018]
  (2) A peak-to-peak voltage-alternating current function obtained by connecting 0 to a current value when a peak-to-peak voltage less than twice Vth of one point is applied to the charging means with D being a predetermined constant. By comparing fI1 (Vpp) with the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of at least two points is applied.
    fI2 (Vpp) −fI1 (Vpp) = D
The peak-to-peak voltage value to be determined is determined, and the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled at a constant voltage based on the determined peak-to-peak voltage value.Image forming apparatus.
[0019]
  (3) The peak-to-peak voltage-alternating current function fI1 (Vpp) obtained from the current value when D is a predetermined constant and a voltage less than twice the Vth of at least two points is applied to the charging means. And the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when at least two times the peak-to-peak voltage of Vth is applied.
    fI2 (Vpp) −fI1 (Vpp) = D
The peak-to-peak voltage value to be determined is determined, and the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled at a constant voltage based on the determined peak-to-peak voltage value.Image forming apparatus.
[0021]
  (4)From the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the alternating current value during non-image formation, fI2 ( Vpp) −fI1 (Vpp) = D, and the constant D used when determining the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is changed for each environment detected by the environment detection unit. As described in (2) or (3)Image forming apparatus.
[0023]
  (5)In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
  The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
  Means for applying at least an alternating current to the charging means;
  Means for controlling the AC current value applied to the charging means;
  Means for measuring the peak-to-peak voltage value of the alternating voltage applied to the charging means;
  Environment detection means for detecting the environment in which the image forming apparatus is installed;
When the DC voltage is applied to the charging member and the discharge start voltage to the image carrier when Vth is Vth,The control means includesCharging means for non-image formation1The voltage value when an alternating current is applied that has a peak-to-peak voltage less than twice Vth above the point2Measure the peak-to-peak voltage value of the AC voltage when an AC current that has a peak-to-peak voltage more than twice the Vth above the pointA step of obtaining an approximate line of the relationship between voltage and current, determining an alternating current applied to the charging unit during image formation from the approximate line, and determining an alternating current applied to the charging unit during image formation from the approximate line When the environment detected by the environment detection means is a high temperature and high humidity environment, the alternating current applied to obtain the approximate line during non-image formation is made smaller than when the environment is a low temperature and low humidity environment. An image forming apparatus.
[0024]
  (6)The peak-to-peak voltage obtained by connecting 0 to the voltage value when an alternating current value that gives a peak-to-peak voltage less than twice the Vth of one point is applied to the charging means with D being a predetermined constant. The current function fI1 (Vpp) and the peak-to-peak voltage-AC current function fI2 (Vpp) obtained from the voltage value when an alternating current value that is at least two times the peak-to-peak voltage of Vth is applied. By comparing,
    fI2 (Vpp) = fI1 (Vpp) + D
The AC current value is determined, and the AC current value to be applied to the charging unit during image formation is controlled by constant current based on the determined AC current value.(5)Described inImage forming apparatus.
[0025]
  (7)D is a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 () obtained from the voltage value when an alternating current value that is less than twice the Vth of at least two points is applied to the charging means. Vpp) and the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the voltage value when applying an alternating current value that is at least two times the peak-to-peak voltage of Vth at least two points ,
    fI2 (Vpp) = fI1 (Vpp) + D
The AC current value is determined, and the AC current value to be applied to the charging unit during image formation is controlled by constant current based on the determined AC current value.(5)Described inImage forming apparatus.
[0027]
  (8)It has an environment detection means that detects the environment where the image forming apparatus is installed, and the peak-to-peak voltage-AC current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value of the AC voltage during non-image formation From the above, it is characterized in that the constant D used when determining the alternating current applied to the charging means at the time of image formation is changed for each environment detected by the environment detection means by fI2 (Vpp) = fI1 (Vpp) + D. Do(6) or (7)Described inImage forming apparatus.
[0034]
<Operation>
That is, the present invention controls the peak-to-peak voltage or current of the AC voltage applied to obtain a desired discharge in contact charging by the AC charging method. In other words, by measuring the relationship between voltage and current during non-image formation, the peak-to-peak voltage or the peak discharge voltage can always be obtained regardless of the environment, variations in manufacturing of the charging member, variations in the main body high voltage device, etc. An alternating current can be applied. As a result, it has become possible to perform image formation without causing problems due to excessive discharge and insufficient discharge, which are concerns of conventional AC constant voltage control and AC constant current control.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1> (FIGS. 1 to 7)
FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer having a transfer type electrophotographic process, a contact charging method, a reverse development method, and a maximum sheet passing size of A3 size.
[0036]
(1) Overall schematic configuration of the printer
a) Image carrier
Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. This photosensitive drum 1 is a negatively charged organic photoconductor (OPC), has an outer diameter of 25 mm, and rotates in the counterclockwise direction indicated by an arrow with a process speed (peripheral speed) of 100 mm / sec around the center support shaft. Driven.
[0037]
As shown in the layer configuration model diagram of FIG. 2, the photosensitive drum 1 has an undercoat layer 1b that suppresses light interference and improves the adhesion of the upper layer on the surface of an aluminum cylinder (conductive drum base) 1a. The photocharge generation layer 1c and the charge transport layer 1d are coated in order from the bottom.
[0038]
b) Charging means
Reference numeral 2 denotes a contact charging device (contact charger) as charging means for uniformly charging the peripheral surface of the photosensitive drum 1, and in this example, a charging roller (roller charger).
[0039]
The charging roller 2 holds both ends of the cored bar 2a rotatably by bearing members (not shown), and is urged in the direction of the photosensitive drum by a pressing spring 2e to be applied to the surface of the photosensitive drum 1. It is brought into pressure contact with a predetermined pressing force, and rotates following the rotation of the photosensitive drum 1. A pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a.
[0040]
  A charging bias voltage of a predetermined condition is applied to the metal core 2a of the charging roller 2 from the power source S1, so that the peripheral surface of the rotating photosensitive drum 1 is uniformly contact-charged to have a negative polarity in this example.The
[0041]
The configuration of the charging roller 2 and the charging control method will be described in detail in section (3).
[0042]
c) Information writing means
Reference numeral 3 denotes an exposure apparatus as information writing means for forming an electrostatic latent image on the surface of the charged photosensitive drum 1, and this example is a laser beam scanner using a semiconductor laser. A laser beam modulated in response to an image signal sent from a host device such as an image reading device (not shown) to the printer side is output to perform laser scanning on the uniformly charged surface of the rotating photosensitive drum 1 at the exposure position b. Exposure L (image scanning exposure) is performed. By this laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is lowered, so that an electrostatic latent image corresponding to the scanned and exposed image information is sequentially formed on the surface of the rotating photosensitive drum 1. It will be done.
[0043]
d) Development means
Reference numeral 4 denotes a jumping developing device (developing device) in the present example as developing means for supplying a developer (toner) to the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. The electrostatic latent image formed on the surface of the photosensitive drum 1 is reversely developed with the one-component magnetic toner (negative toner) negatively charged by the developing device 4.
[0044]
4a is a developing container, 4b is a non-magnetic developing sleeve, and this developing sleeve 4b is rotatably arranged in the developing container 4a with a part of its outer peripheral surface exposed to the outside. 4c is a non-rotating magnet roller fixedly inserted in the developing sleeve 4b, 4d is a developer coating blade, 4e is a one-component magnetic toner as a developer contained in the developing container 4a, and S2 is a developing for the developing sleeve 4b. This is a bias application power source.
[0045]
Accordingly, the surface of the developing sleeve 4b rotating in the counterclockwise direction indicated by the arrow is coated as a thin layer, and the one-component magnetic toner conveyed to the developing unit c is electrostatically latentized on the surface of the photosensitive drum 1 by the electric field due to the developing bias. The electrostatic latent image is developed as a toner image by selectively adhering to the image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.
[0046]
The developer thin layer on the developing sleeve 4b that has passed through the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.
[0047]
e) Transfer means, fixing means, cleaning means
Reference numeral 5 denotes a transfer device, and this example is a transfer roller. The transfer roller 5 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, and the pressure nip portion is a transfer portion d. A transfer material (a member to be transferred, a recording material) P is fed to the transfer portion d from a paper feeding mechanism portion (not shown) at a predetermined control timing.
[0048]
The transfer material P fed to the transfer portion d is nipped and conveyed between the rotating photosensitive drum 1 and the transfer roller 5, and during that time, the transfer roller 5 has a negative polarity that is the normal charging polarity of the toner from the power source S 3. When a positive transfer bias having a reverse polarity is applied, the toner image on the surface side of the photosensitive drum 1 is sequentially electrostatically transferred onto the surface of the transfer material P that is nipped and conveyed by the transfer portion d. .
[0049]
The transfer material P which has received the transfer of the toner image through the transfer portion d is sequentially separated from the surface of the rotating photosensitive drum 1 and conveyed to the fixing device 6 (for example, a heat roller fixing device) to receive the toner image fixing process. Output as an image formed product (print, copy).
[0050]
Reference numeral 7 denotes a cleaning device. The surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is rubbed by the cleaning blade 7a to be cleaned to remove the transfer residual toner, and repeatedly used for image formation. The e is a photosensitive drum surface contact portion of the cleaning blade 7a.
[0051]
(2) Printer operation sequence
FIG. 3 is an operation sequence diagram of the printer.
[0052]
a. Initial rotation operation (front multiple rotation process)
This is a start operation period (start operation period, warming period) when the printer is started. When the power switch is turned on, the photosensitive drum is rotationally driven, and a preparatory operation of a predetermined process device such as starting up the fixing device to a predetermined temperature is executed.
[0053]
b. Print preparation rotation operation (pre-rotation process)
Print signal-This is a preparatory rotation operation period before image formation from when the image formation (printing) process operation is actually performed, and is executed following the initial rotation operation when a print signal is input during the initial rotation operation. Is done. When the print signal is not input, the main motor is temporarily stopped after the initial rotation operation is completed, and the photosensitive drum is stopped from rotating. The printer is kept in a standby (standby) state until the print signal is input. When the print signal is input, the print preparation rotation operation is executed.
[0054]
In the present embodiment, during this printing preparation rotation operation period, an appropriate peak-to-peak voltage value (or alternating current value) calculation / determination program for the applied alternating voltage in the charging step of the printing step is executed. This will be described in detail in section (3) below.
[0055]
c. Printing process (image forming process, image forming process)
When the predetermined print preparation rotation operation is completed, an image forming process for the rotating photosensitive drum is subsequently executed, and the toner image formed on the surface of the rotating photosensitive drum is transferred to a transfer material, and the fixing process of the toner image by the fixing device is performed. The image formation is printed out.
[0056]
In the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined set number of prints n.
[0057]
d. Paper gap process
In the continuous printing mode, after the trailing edge of one transfer material passes the transfer position d, the recording paper is not passed through the transfer position until the leading edge of the next transfer material reaches the transfer position d. It is a state period.
[0058]
e. Post-rotation operation
This is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while even after the last transfer material printing step is completed to rotate the photosensitive drum.
[0059]
f. stand-by
When the predetermined post-rotation operation is completed, the drive of the main motor is stopped, the rotation of the photosensitive drum is stopped, and the printer is kept in a standby state until the next print start signal is input.
[0060]
In the case of printing only one sheet, after the printing is completed, the printer goes into a standby state through a post-rotation operation.
[0061]
When the print start signal is input in the standby state, the printer proceeds to the pre-rotation process.
[0062]
The printing process of c is the time of image formation, and the initial rotation operation of a, the pre-rotation operation of b, the paper gap process of d, and the post-rotation operation of e are non-image formation.
[0063]
(3) Detailed description of charging means
A) Charging roller 2
The longitudinal length of the charging roller 2 as the contact charging member is 320 mm. As shown in the layer configuration model diagram of FIG. 1, the lower layer 2b, the intermediate layer 2c, and the surface layer 2d are disposed around the core metal (support member) 2a. Is a three-layer structure in which are sequentially stacked from the bottom. The lower layer 2b is a foamed sponge layer for reducing charging noise, the intermediate layer 2c is a conductive layer for obtaining a uniform resistance as a whole of the charging roller, and the surface layer 2d has defects such as pinholes on the photosensitive drum 1. This is a protective layer provided to prevent the occurrence of leaks even if there is.
[0064]
More specifically, the specification of the charging roller 2 of this example is as follows.
[0065]

B) Charging bias application system
FIG. 4 is a block circuit diagram of a charging bias application system for the charging roller 2.
[0066]
A predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage of frequency f on a DC voltage from the power source S1 is applied to the charging roller 2 through the core metal 2a, so that the peripheral surface of the rotating photosensitive drum 1 is It is charged to a predetermined potential.
[0067]
A power source S 1 that is a voltage application unit for the charging roller 2 includes a direct current (DC) power source 11 and an alternating current (AC) power source 12.
[0068]
Reference numeral 13 denotes a control circuit which controls the DC power supply 11 and the AC power supply 12 of the power supply S1 so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 2. And a function of controlling the DC voltage value applied to the charging roller 2 from the DC power source 11 and the peak-to-peak voltage value of the AC voltage applied from the AC power source 12 to the charging roller 2.
[0069]
Reference numeral 14 denotes an AC current value measurement circuit as means for measuring the AC current value flowing through the charging roller 2 via the photosensitive member 1. The measured AC current value information is input from the circuit 14 to the control circuit 13.
[0070]
Reference numeral 15 denotes an environment sensor (thermometer and hygrometer) as means for detecting the environment where the printer is installed. The detected environmental information is input from the environmental sensor 15 to the control circuit 13.
[0071]
Then, the control circuit 13 determines from the AC current value information input from the AC current value measurement circuit 14 and further from the environmental information input from the environmental sensor 15 between appropriate peaks of the AC voltage applied to the charging roller 2 in the charging process of the printing process. It has a function of executing a voltage value calculation / determination program.
[0072]
C) AC voltage peak-to-peak voltage control method
Next, a method for controlling the peak-to-peak voltage of the AC voltage applied to the charging roller 2 during printing will be described.
[0073]
Based on various studies, the inventors have shown that the amount of discharge current quantified according to the following definition represents the actual amount of AC discharge, and has a strong correlation with the photoconductor drum scraping, image flow, and charging uniformity. Found that there is.
[0074]
That is, as shown in FIG. 5, the alternating current Iac is in a linear relationship with the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) (undischarged region), and gradually increases from that point toward the discharge region. In the direction of increasing current. In a similar experiment in a vacuum where no discharge occurs, a straight line is maintained, so this is considered to be the increment ΔIac of the current involved in the discharge.
[0075]
Therefore, when the ratio of the current Iac to the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) is α, AC current such as current flowing to the contact portion (hereinafter referred to as nip current) other than current due to discharge The current becomes α · Vpp, and the difference between Iac measured when a voltage higher than the discharge start voltage Vth × 2 (V) is applied, and this α · Vpp,
Formula 1... ΔIac = Iac−α · Vpp
To ΔIac is defined as a discharge current amount that indicates the amount of discharge instead.
[0076]
The amount of discharge current changes as the environment and durability are increased when charging is performed under the control of a constant voltage or a constant current. This is because the relationship between the peak-to-peak voltage and the discharge current amount and the relationship between the alternating current value and the discharge current amount are fluctuating.
[0077]
In the AC constant current control method, control is performed with the total current flowing from the charging member to the member to be charged. As described above, the total current amount is the sum of the nip current α · Vpp and the discharge current amount ΔIac that flows by discharging at the non-contact portion. In constant current control, the charged object is actually charged. In addition to the discharge current, which is the current required for the control, the nip current is controlled.
[0078]
For this reason, the amount of discharge current cannot actually be controlled. Even if the constant current control is performed with the same current value, the discharge current amount naturally decreases as the nip current increases due to the environmental variation of the charging member material, and the discharge current amount increases as the nip current decreases. Even with the current control method, it is impossible to completely suppress the increase / decrease in the amount of discharge current, and it has been difficult to achieve both the shading of the photosensitive drum and the charging uniformity when aiming for a long life.
[0079]
Therefore, the present inventors performed control in the following manner in order to always obtain a desired discharge current amount.
[0080]
A method of determining the peak-to-peak voltage that becomes the discharge current amount D when the desired discharge current amount is D will be described.
[0081]
In this embodiment, the control circuit 13 executes an appropriate peak-to-peak voltage value calculation / determination program for the charging roller 2 in the charging process during the printing process during the printing preparation rotation operation.
[0082]
Concretely, it demonstrates with reference to the Vpp-Iac graph of FIG. 6, and the control flowchart of FIG.
[0083]
As shown in FIG. 6, the control circuit 13 controls the AC power source 12 so that the charging roller 2 has three points of peak-to-peak voltage (Vpp) that is a discharge region and three points of peak-to-peak voltage that is an undischarged region. The alternating current value flowing through the charging roller 2 through the photosensitive member 1 at that time is measured by the alternating current value measuring circuit 14 and input to the control circuit 13.
[0084]
Next, the control circuit 13 linearly approximates the relationship between the peak-to-peak voltage in the discharged and undischarged regions and the alternating current from the measured current values at the three points using the least square method, Equation 3 is calculated.
[0085]
Equation 2 ... Approximate straight line of discharge area: Y_α= ΑX + A
Equation 3 ... Approximate straight line of undischarged area: Y_β= ΒX + B
After that, the peak-to-peak voltage Vpp at which the difference between the approximate straight line of the discharge area of Expression 2 and the approximate straight line of the undischarged area of Expression 3 becomes the discharge current amount D is determined by Expression 4.
[0086]
Formula 4... Vpp = (D−A + B) / (α−β)
Here, the peak-to-peak voltage (Vpp) -alternating current (Iac) functions fI1 (Vpp) and fI2 (Vpp) in the undischarged region and the discharged region described in the claims are Y in the above equation 3, respectively._β= ΒX_β+ B and Y in Equation 2_α= ΑX_αCorresponds to + A. The constant D described in the claims corresponds to the desired discharge current amount D.
[0087]
Therefore, fI2 (Vpp) −fI1 (Vpp) = D described in the claim is
Y_α-Y_β= (ΑX_α+ A)-(βX_β+ B) = D
It becomes.
[0088]
Further, fI2 (Vpp) −fI1 (Vpp) = D
Vpp = (D−A + B) / (α−β)
Induction is as follows.
[0089]
fI2 (Vpp) −fI1 (Vpp) = Y_α-Y_β= D
(ΑX_α+ A)-(βX_β+ B) = D
Now looking for the value of X that becomes D, and if that point is Vpp,
(ΑVpp + A) − (βVpp + B) = D
Therefore, Vpp = (D−A + B) / (α−β).
[0090]
Then, the peak-to-peak voltage applied to the charging roller 2 is switched to Vpp obtained by the above equation 4, the constant voltage control is performed, and the process proceeds to the above-described printing process.
[0091]
  In this way, every time during the print preparation rotation, it is predetermined at the time of printing.ofBy calculating the peak-to-peak voltage necessary for obtaining the amount of discharge current and applying the obtained peak-to-peak voltage with constant voltage control during printing, resistance due to manufacturing variations of the charging roller 2 and environmental changes in the material It is possible to absorb the fluctuation of the value and the high voltage variation of the main body device, and to obtain a desired discharge current amount with certainty.
[0092]
When durability was examined under this control, no deterioration or abrasion of the photosensitive drum as an image carrier occurred in any environment, and about 10% of the photosensitive drum compared with the conventional constant current control. Long service life can be realized.
[0093]
In this embodiment, the discharge current amount is controlled by switching the peak-to-peak voltage of the AC voltage applied to the charging roller. However, the present invention is not limited to this, and conversely, the peak-to-peak voltage of the AC voltage is measured by applying the AC current. (The AC current value measurement circuit 14 in FIG. 4 is changed to a peak-to-peak voltage value measurement circuit), and the output AC current of the AC power supply is controlled so that an AC current necessary for obtaining a desired discharge current amount can always be applied during printing. It is also possible to perform constant current control with the circuit 13.
[0094]
Furthermore, in this embodiment, the desired discharge current amount D and the peak-to-peak voltage value applied during the print preparation rotation are made constant in each environment. However, in the apparatus in which the environment sensor (thermometer and hygrometer) 15 is installed, By varying the respective values for each environment, it is possible to perform more stable and uniform charging.
[0095]
Thus, during printing preparation rotation, several points in the undischarged area and several points in the discharging area are sequentially applied to the charging roller 2 to measure the AC voltage value, and the peak-to-peak voltage applied during printing is determined. By applying a peak-to-peak voltage or an alternating current that can always obtain the desired amount of discharge current, it is possible to achieve both deterioration and shaving of the photoconductor and charging uniformity, extending the life and improving the image quality. It became feasible.
[0096]
Furthermore, since variations at the time of manufacturing can be absorbed, the permissible range of materials and accuracy is widened, so that the cost of manufacturing can be reduced and products can be provided to users at low cost.
[0097]
<Example 2> (FIG. 8)
This embodiment is a one-point control and constant voltage control system. As shown in FIG. 8, the image forming apparatus is configured to sequentially charge the charging roller with two points of peak-to-peak voltage (Vpp) that is a discharge region and one point of peak-to-peak voltage that is an undischarged region. Apply and measure the alternating current value at that time. The relationship between the peak-to-peak voltage and the alternating current is set in advance so that when the peak-to-peak voltage is zero, the alternating current value is also zero.
[0098]
Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current using the measurement value 2 points in the discharge region and the measurement value 0 point in the non-discharge region. Is calculated.
[0099]
Equation 2 ... Approximate straight line of discharge area: Y_α= ΑX_α+ A
Equation 3 ... Approximate straight line of undischarged area: Y_β= ΒX_β
After that, the approximate straight line Y of the discharge region_αAnd the approximate straight line Y of the undischarged area_βThe peak-to-peak voltage Vpp at which the discharge current amount D becomes the D current is determined by Equation 4.
[0100]
Formula 4... Vpp = (D−A) / (α−β)
Then, the peak-to-peak voltage applied to the charging member is switched to Vpp obtained (constant voltage control using Vpp), and the process proceeds to the image forming operation described above.
[0101]
By adopting such a control configuration, it is possible to obtain the same effect as in the first embodiment with a small number of measurement points.
[0102]
As for the one-point control system as in this embodiment, as a broader meaning, it may not be zero here. For example, if the amount of current flowing at a certain Vpp is known in advance, that point and the measurement point are used. It is also possible to obtain the relationship between the peak-to-peak voltage and the alternating current, and the relationship between the peak-to-peak voltage and the alternating current can be obtained by measuring at least one point.
[0103]
<Example 3> (FIG. 9)
The present embodiment is a system of three-point control and constant current control, and a method of determining an alternating current value that becomes the discharge current amount D when D is a desired discharge current amount will be described.
[0104]
As shown in FIG. 9, the image forming apparatus sequentially applies the charging roller to the charging roller with three points of alternating current (Iac) that is a discharge region and three points of alternating current that is an undischarged region to the charging roller during print preparation rotation. Measure the peak-to-peak voltage at that time.
[0105]
Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current in the discharged and undischarged regions from the measured current values at the three points using the least square method, Equation 3 is calculated.
[0106]
Equation 2 ... Approximate straight line of discharge area: Y_α= ΑX_α+ A
Equation 3 ... Approximate straight line of undischarged area: Y_β= ΒX_β+ B
After that, the approximate straight line Y of the discharge region_αAnd the approximate straight line Y of the undischarged area_βThe AC current (Iac) which becomes the discharge current amount D is determined by the equation (4).
[0107]
If the alternating current value for D is Iac1, and the peak-to-peak voltage at that time is Vpp, then Equations 2 and 3 are
Iac1 = αVpp + A Expression a
Iac2 = βVpp + B Formula b
It becomes. Here, Iac2 is an approximate straight line Y of the undischarged region._βIt is an alternating current value which becomes Vpp at.
[0108]
Iac1 = Iac2 + D (Formula c)
From the equations a, b, and c, the alternating current (Iac) that becomes the discharge current amount D is determined by the equation 4.
[0109]
Formula 4... Iac = (αD + αB−βA) / (α−β)
Then, the AC current applied to the charging member is switched to the obtained Iac, the constant current is controlled by the Iac, and the process proceeds to the above-described image forming operation.
[0110]
<Example 4> (FIG. 10)
The present embodiment is a one-point control and constant current control system, and a method of determining an alternating current value that becomes the discharge current amount D when the desired discharge current amount is D will be described.
[0111]
As shown in FIG. 10, the image forming apparatus sequentially applies two points of alternating current (Iac) that is a discharge area to the charging roller and one point of alternating current that is an undischarged area to the charging roller during print preparation rotation. Then, the peak-to-peak voltage value at that time is measured.
[0112]
Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current using the measurement value 2 points in the discharge region and the measurement value 0 point in the non-discharge region. Is calculated.
[0113]
Equation 2 ... Approximate straight line of discharge area: Y_α= ΑX_α+ A
Equation 3 ... Approximate straight line of undischarged area: Y_β= ΒX_β
After that, the approximate straight line Y of the discharge region_αAnd the approximate straight line Y of the undischarged area_βThe AC current (Iac) which becomes the discharge current amount D is determined by the equation (4).
[0114]
If the alternating current value for D is Iac1, and the peak-to-peak voltage at that time is Vpp, then Equations 2 and 3 are
Iac1 = αVpp + A Expression a
Iac2 = βVpp Formula b
It becomes. Here, Iac2 is an approximate straight line Y of the undischarged region._βIt is an alternating current value which becomes Vpp at.
[0115]
Iac1-Iac2 = D... Formula c
From the equations a, b, and c, the alternating current (Iac) that becomes the discharge current amount D is determined by the equation 4.
[0116]
Formula 4... Iac = (αD−βA) / (α−β)
Then, the AC current applied to the charging member is switched to the obtained Iac, the constant current is controlled by the Iac, and the process proceeds to the above-described image forming operation.
[0117]
<Example 5> (FIG. 11)
FIG. 11 is a schematic configuration model diagram of the image forming apparatus in the present embodiment. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a contact charging method, a reversal development method, cleaner-less, and a maximum sheet passing size of A3 size.
[0118]
Constituent members / portions common to the printer of the first embodiment are denoted by the same reference numerals and description thereof is omitted, and constituent members / portions / items different from those of the printer of the first embodiment are described.
[0119]
(1) Overall schematic configuration of the printer
In the printer of this embodiment, the photosensitive drum 1 as an image carrier has an outer diameter of 50 mm.
[0120]
The developing device 4 which is a developing means is a reversal developing device of a two-component magnetic brush developing system, and the electrostatic latent image formed on the surface of the photosensitive drum 1 is sequentially converted into a toner image by the developing device 4 in this example. Reversal development is performed by negatively charged toner (negative toner). The developer 4e accommodated in the developing container 4a is a two-component developer. Reference numeral 4f denotes a developer stirring member disposed on the bottom side in the developing container 4a, and 4g denotes a toner hopper which accommodates replenishing toner.
[0121]
The two-component developer 4e in the developing container 4a is a mixture of toner and a magnetic carrier and is stirred by the developer stirring member 4f. In this example, the average particle diameter of the toner is 6 μm, and the resistance of the magnetic carrier is about 10¹³Ωcm, particle size is about 40 μm. The toner is triboelectrically charged to negative polarity by rubbing with the magnetic carrier.
[0122]
The developing sleeve 4b is disposed opposite to the photosensitive drum 1 so that the closest distance (referred to as S-Dgap) to the photosensitive drum 1 is maintained at 350 μm. A facing portion between the photosensitive drum 1 and the developing sleeve 4a is a developing portion c. The developing sleeve 4b is driven to rotate in the direction opposite to the traveling direction of the photosensitive drum 1 in the developing portion c. A part of the two-component developer 4e in the developing container 4a is adsorbed and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 4b by the magnetic force of the magnet roller 4c in the sleeve, and is rotated and conveyed as the sleeve rotates. A predetermined thin layer is formed by the developer coating blade 4d, and in contact with the surface of the photosensitive drum 1 at the developing portion c, the surface of the photosensitive drum is appropriately rubbed. A predetermined developing bias is applied to the developing sleeve 4b from the power source S2.
[0123]
Thus, the toner in the developer coated as a thin layer on the surface of the rotating developing sleeve 4b and conveyed to the developing unit c corresponds to the electrostatic latent image on the surface of the photosensitive drum 1 by the electric field due to the developing bias. As a result, the electrostatic latent image is developed as a toner image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.
[0124]
The developer thin layer on the developing sleeve 4b that has passed through the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.
[0125]
In order to maintain the toner concentration of the two-component developer 4e in the developing container 4a within a predetermined substantially constant range, the toner concentration of the two-component developer 4e in the developing container 4a is adjusted by, for example, an optical toner concentration sensor (not shown). The toner hopper 4g is driven and controlled according to the detected information, and the toner in the toner hopper is supplied to the two-component developer 4e in the developing container 4a. The toner supplied to the two-component developer 4e is stirred by the stirring member 4f.
[0126]
(2) Cleanerless system
The printer of this example is cleanerless, and is not provided with a dedicated cleaning device that removes a small amount of transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. After the transfer, the untransferred toner on the surface of the photosensitive drum 1 is carried to the developing portion c through the charging portion a and the exposing portion b as the photosensitive drum 1 continues to rotate. Recovered).
[0127]
Simultaneous development cleaning is the process of developing the electrostatic latent image by transferring the residual toner on the photosensitive member after transfer to the subsequent development step, that is, continuously charging the photosensitive member and exposing it to light. Residual transfer toner present on the surface of the photoreceptor that should not be developed with toner due to fog removal bias (fogging potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor) during the process. Is a method of collecting in a developing device. According to this method, the transfer residual toner is collected by the developing device and reused for development of the electrostatic latent image in the subsequent process, so that waste toner is eliminated and maintenance work is reduced. Can do. In addition, the cleaner-less configuration is advantageous for downsizing the image forming apparatus.
[0128]
A toner charging control unit 8 is disposed at a position downstream of the transfer portion d in the photosensitive drum rotation direction and at a position upstream of the charging portion a in the photosensitive drum rotation direction. This toner charge control means 7 is a brush-shaped member (auxiliary brush) having moderate conductivity, and is arranged with the brush portion in contact with the surface of the photosensitive drum 1, and a negative voltage is applied to the power source S4. Is applied. f is a contact portion between the brush portion and the photosensitive drum 1 surface. The untransferred toner on the photosensitive drum 1 that passes through the toner charge control means 7 is aligned to a negative polarity whose charge polarity is normal.
[0129]
That is, the transfer residual toner on the surface of the photosensitive drum 1 after the transfer process includes a negative toner that cannot be completely transferred in the image portion, a positive fog toner that adheres to the non-image portion during development, and a positive transfer voltage. The toner whose polarity is reversed to positive polarity due to the influence of the toner is included. Such a transfer residual toner is uniformly charged to a negative polarity by the toner charge control means 8 described above. In this embodiment, the toner charge control means 8 is applied with −1000 V, which is a voltage at which discharge occurs on the transferred photoreceptor. As a result, the transfer residual toner that passes through the toner charge control means 8 is given a charge by discharging and direct charge injection, and is made negative in polarity.
[0130]
In the charging process described above, the surface of the photosensitive drum 1 is charged from above the untransferred toner. Since the polarity of the transfer residual toner is uniformly uniform to the negative polarity, the toner does not adhere to the charging roller 2 to which the negative DC voltage is applied. Even in the exposure process, the exposure is performed from the transfer residual toner, but since the amount of the transfer residual toner is small, there is no significant influence. In the developing process, the transfer residual toner present in the unexposed portion on the photosensitive drum 1 is collected by the developing device due to the electric field.
[0131]
As described above, the closest distance (S-Dgap) between the developing sleeve 2b and the photosensitive drum 1 is 350 μm, and by keeping this distance, the magnetic brush of the two-component developer formed on the developing sleeve 4b is exposed to light. The transfer residual toner on the photosensitive drum 1 is simultaneously recovered by rubbing moderately with the surface of the photosensitive drum 1. Further, the developing sleeve 4b is rotated in the direction opposite to the traveling direction of the surface of the photosensitive drum 1 in the developing portion c so as to be advantageous for collecting the transfer residual toner.
[0132]
(3) Control of peak voltage of AC voltage
When the AC charging method is used in the cleanerless system, the following problems occur. That is, image flow and blur caused by discharge products generated by AC charging.
[0133]
In the case of the AC charging method using contact charging, the amount of generated ozone is small in comparison with the charging process using a corona charger, but it is not completely absent. In the image forming apparatus, the discharge product adheres to the surface of the photoconductor as the image carrier, and further absorbs moisture, thereby reducing the resistance of the photoconductor surface and reducing the resolution of the latent image. In the image forming apparatus adopting the above configuration, the effect of renewing the photosensitive member by the cleaning device cannot be expected, and blurring, image flow, and the like are likely to occur.
[0134]
In order to achieve both the above-described problem and charging uniformity, it is necessary to always obtain a desired amount of discharge current, and for this purpose, it is necessary to use the means for controlling the voltage applied to the charging roller according to the present invention.
[0135]
The peak-to-peak voltage control of the AC voltage in the present embodiment is performed as follows.
[0136]
During printing preparation rotation, three points in the non-discharge region and three points in the discharge region are sequentially applied to the charging roller 2 to measure the AC voltage value, and the peak-to-peak voltage applied during printing is determined. The calculation method of the applied peak-to-peak voltage is the same as the method shown in the first embodiment.
[0137]
The apparatus main body used in this embodiment is provided with an environmental sensor 15 (FIG. 4). In each environment, the peak-to-peak voltage applied during printing preparation rotation is varied, and the resistance of the charging roller is reduced. In the environment, a peak-to-peak voltage which is about 10% lower than that in the L / L environment is applied. As a result, it was possible to measure at a value close to the peak-to-peak voltage actually applied at the time of printing, and it became possible to obtain a desired amount of discharge current more reliably.
[0138]
Further, the value of the discharge current amount D is also variable for each environment, and in an H / H environment where the amount of discharge current necessary for obtaining charging stability is small and image flow is likely to occur compared to the L / L environment, the L Control was performed to reduce the set discharge current amount D in the / L environment to about 2/3. As a result, even for the above problem, in the H / H environment, about 2/3 times the L / L environment, the image flow and the blurring are reliably prevented in the H / H environment. In the environment, it became possible to carry out stable and uniform charging without generating sand.
[0139]
By performing the above control, it absorbs fluctuations in resistance values due to manufacturing variations of the charging roller and environmental variations of materials, and high-pressure variations in the main unit, and even when the charging roller becomes dirty, the desired amount of discharge current is ensured. In addition to the same effects as in the first embodiment, it is possible to perform detailed control with the minimum and necessary discharge current amount in each environment by simultaneously performing environmental control.
[0140]
Thus, even when used in a cleaner-less device, it has become possible to stably maintain high image quality and high quality without causing problems such as image flow, charging failure, fusion, and image memory over a long period of time. .
[0141]
Of course, it is possible to adopt the control method as in the second to fourth embodiments.
[0142]
<Others>
1) In the embodiments, only the printing operation in mono color (single color) has been described. However, the present invention is not limited to this, and the same effect can be exhibited in the full color printing operation.
[0143]
2) In the embodiment, an appropriate peak-to-peak voltage value or AC current value calculation / determination program is executed in the charging process of the printing process during the printing preparation rotation operation period when the printer is not forming an image. It is not limited to the print preparation rotation operation period as in the case of the example printer, but can be used during other non-image formation, that is, during the initial rotation operation, during the inter-sheet process, during the post-rotation process, It can also be executed at the time of image formation.
[0144]
3) The image carrier has a surface resistance of 10⁹ -10¹⁴A direct injection charging type having a charge injection layer of Ω · cm may be used. Even when the charge injection layer is not used, for example, the same effect can be obtained when the charge transport layer is in the above resistance range. The volume resistance of the surface layer is about 10¹³An amorphous silicon photoreceptor having Ω · cm may be used.
[0145]
4) In addition to the charging roller, a flexible contact charging member having a shape or material such as a fur brush, felt, or cloth can be used. Further, a combination of various materials can provide more appropriate elasticity, conductivity, surface property, and durability.
[0146]
5) As the waveform of the alternating voltage component (AC component, voltage whose voltage value periodically changes) of the oscillating electric field applied to the contact charging member and the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off a DC power supply.
[0147]
6) In addition to the laser scanning unit of the embodiment, the image exposure unit as the information writing unit for the charged surface of the photoconductor as the image carrier is a digital exposure unit using a solid light emitting element array such as an LED. May be. An analog image exposure unit using a halogen lamp or a fluorescent lamp as a document illumination light source may be used. In short, any device capable of forming an electrostatic latent image corresponding to image information may be used.
[0148]
7) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged, the charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information. .
[0149]
8) The toner developing method and means for the electrostatic latent image are arbitrary. A reversal development method or a regular development method may be used.
[0150]
In general, the electrostatic latent image is developed by coating a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and magnetic toner on a developer carrying member. A method of developing and developing an electrostatic latent image by coating and transporting by force and applying to the image carrier in a non-contact state, and coating on the developer carrying member as described above A method for developing an electrostatic latent image by applying toner in contact with an image carrier (one-component contact development), and a developer obtained by mixing a magnetic carrier with toner particles (two-component developer) And a method of developing the electrostatic latent image by conveying it by magnetic force and applying it in contact with the image carrier (two-component contact development), and applying the above two-component developer to the image carrier. Apply electrostatic latent image in contact It is roughly divided into four 顛 the method (two-component non-contact development) to the image.
[0151]
9) The transfer means is not limited to the roller transfer in the embodiment, but may be a blade transfer, belt transfer, other contact transfer charging method, or a non-contact transfer charging method using a corona charger.
[0152]
10) The present invention can be applied not only to the formation of a single color image by using an intermediate transfer member such as a transfer drum or a transfer belt, but also to an image forming apparatus that forms a multicolor, full color image by multiple transfer or the like.
[0153]
【The invention's effect】
As described above, according to the present invention, with respect to an image forming apparatus in which charging of an image carrier is performed by a charging unit that is close to or in contact with the image carrier and to which a voltage is applied, the resistance value of the charging member depending on the environment and manufacturing time. Regardless of the variation in color, etc., a constant amount of discharge is always generated without causing excessive discharge, and applied to the charging means so that uniform charging can be performed without problems such as deterioration of the image carrier, toner fusion, and image flow. The voltage and current to be controlled can be appropriately controlled, and the high image quality and high quality can be stably maintained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a model diagram of the layer structure of the photoreceptor.
FIG. 3 is an operation sequence diagram of the image forming apparatus.
FIG. 4 is a block circuit diagram of a charging bias application system.
[Figure 5] Measurement schematic of discharge current amount
Fig. 6 Relationship between peak-to-peak voltage and AC current measured during printing preparation rotation
[Fig. 7] Charge control flow chart
FIG. 8 is a relationship diagram between the peak-to-peak voltage and the amount of alternating current measured during the print preparation rotation in the second embodiment.
FIG. 9 is a graph showing the relationship between the peak-to-peak voltage and the amount of alternating current measured during printing preparation rotation in Example 3.
FIG. 10 is a graph showing the relationship between the peak-to-peak voltage and the amount of alternating current measured during printing preparation rotation in Example 4.
FIG. 11 is a schematic configuration model diagram of an image forming apparatus (cleaner-less) according to a fifth embodiment.
[Explanation of symbols]
1 .... photosensitive drum (image carrier) 2 .... charging roller 3 .... laser beam scanner 4 .... developing device 5 .... transfer roller 6 .... fixing device 7 .... cleaning device 8 .. Toner charging control means, S1 to S4 .. Bias voltage application power supply, 11. DC power supply, 12. AC power supply, 13. Control circuit, 14. AC voltage value or peak-to-peak voltage measurement circuit, 15. Environment sensor

Claims (8)

In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
It means for applying at least AC voltage to the charging means,
And control means for controlling the voltage values of the peak-to-peak voltage of the applied to that ac voltage to the charging means,
It means for measuring the alternating current flowing through the strip conductor means,
Environment detection means for detecting the environment in which the image forming apparatus is installed;
When the DC voltage is applied to the charging member and the discharge start voltage to the image carrier when Vth is Vth, the control means sets the charging means to the charging means at least twice Vth at the time of non-image formation. and a current value when an AC voltage is applied with a peak voltage of less than the current value when an AC voltage is applied with a peak-to-peak voltage twice or more than 2 points of Vth is measured, the voltage and current Determining an approximate line of the relationship, determining a peak-to-peak voltage of the AC voltage applied to the charging unit during image formation from the approximate line, and performing a peak of the AC voltage applied to determine the approximate line during non-image formation The inter-voltage is made smaller when the environment detected by the environment detection means is a high temperature and high humidity environment than when the environment is a low temperature and low humidity environment. D is a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 (Vpp obtained by connecting 0 to the current value when a peak-to-peak voltage less than twice Vth at one point is applied to the charging means. ) And the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when at least two times the peak-to-peak voltage of Vth is applied.
fI2 (Vpp) −fI1 (Vpp) = D
Determining the peak-to-peak voltage value to be, by the determined peak-to-peak voltage value, the image according to the peak voltage of the AC voltage applied to the charging means during image formation in claim 1, characterized in that a constant voltage control Forming equipment . Let D be a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 (Vpp) obtained from the current value when at least two points or more of the peak-to-peak voltage less than twice Vth are applied to the charging means; By comparing the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of two or more points is applied,
fI2 (Vpp) −fI1 (Vpp) = D
Determining the peak-to-peak voltage value to be, by the determined peak-to-peak voltage value, the image according to the peak voltage of the AC voltage applied to the charging means during image formation in claim 1, characterized in that a constant voltage control Forming equipment . From the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the alternating current value during non-image formation, fI2 ( Vpp) −fI1 (Vpp) = D, and the constant D used when determining the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is changed for each environment detected by the environment detection unit. The image forming apparatus according to claim 2 or 3. In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
Means for applying at least an alternating current to the charging means;
Means for controlling the AC current value applied to the charging means;
Means for measuring the peak-to-peak voltage value of the alternating voltage applied to the charging means;
Environment detection means for detecting the environment in which the image forming apparatus is installed;
When the DC voltage is applied to the charging member and the discharge start voltage to the image carrier when Vth is Vth, the control means sets the charging means to the charging means at least twice Vth at the time of non-image formation. and the voltage value at the time of applying an alternating current at a peak voltage of less than, and measuring the peak voltage value of the AC voltage when applying an alternating current at a peak voltage of more than 2 times the two or more points Vth Then, an approximate line of the relationship between voltage and current is obtained, an AC current applied to the charging unit during image formation is determined from the approximate line, and an AC current applied to the charging unit during image formation is determined from the approximate line. When the environment detected by the environment detection means is a high-temperature and high-humidity environment, the alternating current applied to perform the process and obtain the approximate line at the time of non-image formation is smaller than in the low-temperature and low-humidity environment. A picture characterized by Forming apparatus. The peak-to-peak voltage obtained by connecting 0 to the voltage value when an alternating current value that gives a peak-to-peak voltage less than twice the Vth of one point is applied to the charging means with D being a predetermined constant. The current function fI1 (Vpp) and the peak-to-peak voltage-AC current function fI2 (Vpp) obtained from the voltage value when an alternating current value that is at least two times the peak-to-peak voltage of Vth is applied. By comparing,
fI2 (Vpp) = fI1 (Vpp) + D
6. The image forming apparatus according to claim 5 , wherein an alternating current value to be determined is determined, and the alternating current value applied to the charging unit during image formation is controlled by constant current based on the determined alternating current value . D is a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 () obtained from the voltage value when an alternating current value that is less than twice the Vth of at least two points is applied to the charging means. Vpp) and the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the voltage value when applying an alternating current value that is at least two times the peak-to-peak voltage of Vth at least two points ,
fI2 (Vpp) = fI1 (Vpp) + D
6. The image forming apparatus according to claim 5 , wherein an alternating current value to be determined is determined, and the alternating current value applied to the charging unit during image formation is controlled by constant current based on the determined alternating current value. It has an environment detection means that detects the environment where the image forming apparatus is installed, and the peak-to-peak voltage-AC current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value of the AC voltage during non-image formation From the above, it is characterized in that the constant D used when determining the alternating current applied to the charging means at the time of image formation is changed for each environment detected by the environment detection means by fI2 (Vpp) = fI1 (Vpp) + D. The image forming apparatus according to claim 6 or 7 .

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