JP4194130B2

JP4194130B2 - Color image forming apparatus

Info

Publication number: JP4194130B2
Application number: JP09668998A
Authority: JP
Inventors: 健彦鈴木; 俊明宮代; 鶴谷　　貴明; 和弘船谷
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1998-03-25
Filing date: 1998-03-25
Publication date: 2008-12-10
Anticipated expiration: 2018-03-25
Also published as: JPH11272093A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真方式の複写機やレーザプリンタ等のカラー画像形成装置に関するものである。
【０００２】
【従来の技術】
図８は、従来のカラー画像形成装置を示す概略図である。
【０００３】
カラー画像形成装置は、像担持体として感光ドラム１を有し、この感光ドラム１は、図示しない駆動手段によって矢印方向に回転され、その回転過程で感光ドラム１に当接した一次帯電ローラ２により表面が一様に帯電される。ついで、露光装置３によりイエローの画像模様に従ったレーザ光Ｌが感光ドラム１の表面に照射され、感光ドラム１の表面に静電潜像が形成される。
【０００４】
回転支持体１１に４個の現像器４ａ、４ｂ、４ｃ、４ｄが支持されており、感光ドラム１の回転が進むと、回転支持体１１の回転により、イエロートナーを収容した現像器４ａが感光ドラム１と対向した位置（現像位置）に移動し、このように選択された現像器４ａにより感光ドラム１上の潜像が現像される。潜像は現像によりイエロートナー像として可視化される。
【０００５】
感光ドラム１に隣接して、感光ドラム１と略同速度で矢印方向に回転する中間転写ベルト５が設置されており、感光ドラム１上に形成されたイエロートナー像は、１次転写バイアスを印加した１次転写ローラ８ａにより、中間転写ベルト５の表面に転写される（１次転写）。以上の行程をイエロー、マゼンタ、シアン、ブラックの４色について行うことにより、中間転写ベルト５上に４色のトナー像を重ね合わせて転写したカラー画像が形成される。
【０００６】
つぎに転写材カセット１２内からピックアップローラ１３によって転写材が取り出され、所定のタイミングで中間転写ベルト５に供給される。これと同時に２次転写バイアスを印加された２次転写ローラ８ｂが転写材を挟んで中間転写ベルト５に当接し、中間転写ベルト５上の４色のトナー像が転写材の表面に一括して転写される（２次転写）。
【０００７】
このようにして４色のトナー像を転写された転写材は、搬送ベルト１４によって定着装置６まで搬送され、そこで加熱および加圧によりトナーが転写材に溶融固定されて、カラーの定着画像が得られる。４色のトナー像の転写が終了して、中間転写ベルト５の表面に残留した２次転写残りのトナーは、クリーニングローラ１５により電荷が付与された後、１次転写ローラ８ａにより感光ドラム１上に逆転写され、中間転写ベルト５から除去される。一方、感光ドラム１上の１次転写残りトナーおよび逆転写された２次転写残りトナーは、クリーニング装置の公知のブレード手段７により感光ドラム１から除去される。
【０００８】
【発明が解決しようとする課題】
ところで、上記の中間転写ベルト５は、高温高湿環境下や長期間の使用による抵抗変動で、ベルトの時定数τが下がる。ここで、時定数τとは、ベルトをＶo （Ｖ）に帯電して、それがＶo ／ｅ（Ｖ）（ｅは自然対数の底）に減衰するまでの時間である。
【０００９】
この中間転写ベルト５の時定数が下がると、ドラムゴーストが発生する問題があった。
【００１０】
すなわち、２色目以降の１次転写の際、中間転写ベルト５上に前色までの１次転写により所定の電荷が保持されており、中間転写ベルト５上の電位が下がっているので、これを前提に２色目以降の１次転写バイアスを決定している。中間転写ベルト５の時定数τが低下すると、中間転写ベルト５上に所定の電荷が保持できなくなり、中間転写ベルト５上の電位が高くなる。従って、上記で決定した転写バイアスと同一のバイアスを印加しても、所望の電位差以上の電位差になり、このため感光ドラム１へ過剰な電流が流れてしまい、ドラムゴーストが発生する。
【００１１】
また、中間転写ベルト５の時定数τが顕著に低下すると、トナーの飛び散り等の不具合も発生し、画質が劣化する。
【００１２】
このように、中間転写ベルト５の寿命を決める主たる要因は、中間転写ベルト５の時定数τの低下である。従って、時定数が所定値に低下したら、中間転写ベルト５の寿命をユーザーに知らせることが望ましい。
【００１３】
しかしながら、従来は、プリント枚数や中間転写ベルトの回転数等の予め定めた条件が所定値に達したことにより、中間転写ベルト５が寿命に至ったものとしてユーザーに知らせていた。しかし、中間転写ベルト５の時定数の低下は、使用環境や使用モード等によって変動する。このため、正常にプリントできるにもかかわらず、中間転写ベルト５を交換してしまうことがあった。
【００１４】
本発明の目的は、中間転写体の時定数τが下がっても、ドラムゴーストのない高品質の画像を得ることができ、また中間転写体の寿命告知を使用環境や使用モード等によらずに常に最適時期に行うことを可能としたカラー画像形成装置を提供することである。
【００１５】
【課題を解決するための手段】
上記目的は、本発明にかかるカラー画像形成装置にて達成される。要約すれば、本発明は、像担持体と、中間転写体と、前記像担持体を一様に帯電する帯電手段と、帯電した前記像担持体を露光し、現像して各色のトナー像が得られるたびに、そのトナー像を前記中間転写体に重ね合わせて転写する１次転写手段と、前記中間転写体に転写された各色のトナー像を一括して転写材に転写する２次転写手段とを有するカラー画像形成装置において、複数の定電圧電源と、前記複数の定電圧電源からの電圧の印加により前記中間転写体に電圧を印加し、前記中間転写体に電荷を付与する複数の電荷付与手段と、前記複数の電荷付与手段による電圧の印加によって発生する前記中間転写体に流れる電流を検知する電流検知手段とを有し、前記電荷付与手段により前記中間転写体の回動過程で前記中間転写体の同一箇所に連続して複数回電圧を印加し、前記電流検知手段によって複数回検知したそれぞれの電流値に応じて、前記１次転写手段に印加する１次転写バイアスを制御することを特徴とするカラー画像形成装置である。
【００１６】
本発明の一実施態様によれば、前記電荷付与手段が２つであり、前記１次転写手段が前記電荷付与手段の一方を兼ね、前記２次転写手段が前記電荷付与手段の他方を兼ねる。
【００１７】
本発明の他の実施態様によれば、前記帯電手段とは別の第２の帯電手段と、第２の帯電手段からの帯電バイアスの印加により、前記中間転写体上の２次転写残りのトナーに電荷を付与するクリーニング部材とがさらに設置され、前記電荷を付与された２次転写残りのトナーは、前記１次転写手段によるトナー像の中間転写体への転写と同時に像担持体に逆転写されるようになっており、そして前記電荷付与手段が２つであり、前記第２の帯電手段が前記電荷付与手段の一方を兼ね、前記１次転写手段が前記電荷付与手段の他方を兼ねる。
本発明の他の実施態様によれば、前記帯電手段とは別の第２の帯電手段と、第２の帯電手段からの帯電バイアスの印加により、前記中間転写体上の２次転写残りのトナーに電荷を付与するクリーニング部材とがさらに設置され、前記電荷を付与された２次転写残りのトナーは、前記１次転写手段によるトナー像の中間転写体への転写と同時に像担持体に逆転写されるようになっており、そして前記電荷付与手段が２つであり、前記第２の帯電手段が前記電荷付与手段の一方を兼ね、前記２次転写手段が前記電荷付与手段の他方を兼ねる。
【００１８】
【発明の実施の形態】
以下、本発明の実施例を図面に即して詳細に説明する。
【００１９】
実施例１
図１は、本発明のカラー画像形成装置の要部を示す概略図である。本発明は、中間転写体である中間転写ベルト５に電圧を印加して、そのときの電流値から中間転写ベルト５の時定数τを推定し、１次転写ローラ８ａに印加する１次転写バイアス等を制御することが大きな特徴である。本発明のカラー画像形成装置の構成自体は、図８に示した従来のカラー画像形成装置と基本的に同じであるので、以下必要に応じて図８を援用して説明する。
【００２０】
図８の従来のカラー画像形成装置では、１色目から４色目までのトナー像を１色目から４色目まで予め決められた転写バイアスにより、順次中間ベルト５上に１次転写していく。このときの転写バイアスは、中間転写ベルト５の表面電位と感光ドラム１の表面電位（暗部電位ＶD ）の電位差が所定の電位になるように設定する。１色目の転写前には中間転写ベルト５上には前残留電荷がないように除電されているので、印加された１色目の転写バイアスＶt1が中間転写ベルト５の表面電位となるため、差分Ｖt1−ＶD が所定の値になるようにＶt1を設定する。２色目転写時には、中間転写ベルト５上には１色目転写時に与えられた電荷（転写バイアスとは逆極性）が残っているため、中間転写ベルトの表面電位は印加された２色目の転写バイアスよりも低くなる（Ｖt2−ΔＶ1 ）。従って、Ｖt2−ΔＶ1 −ＶD が所定の値になるようにＶt2を設定する。同様に、３色目、４色目の転写バイアスも、前色までの残留電荷を考慮して設定している。
【００２１】
しかし、中間転写ベルト５はプリント枚数が進むにつれて表面に窒素酸化物等が付着し、それが吸湿することにより徐々に表面抵抗が下がり、時定数τも低下してしまう。これは、雰囲気の温湿度によっても変わり、高温高湿環境が最も顕著である。
【００２２】
このように、中間転写ベルト５の時定数が下がると、電荷保持能力が低下してしまう。これにより、前色までの残留電荷が減るため、所望の電位差よりも大きな電位差が発生し、転写電流が増加してしまう。転写電流が増加する、すなわち感光ドラム１が付与される電荷が増加すると、感光ドラム１の次回の帯電で所望の電位に帯電されず、ドラムゴーストが発生する。
【００２３】
そこで、本実施例では、図１に示すように、中間転写ベルト５に電荷を付与する手段として接離可能な電荷付与ローラ１６を設置し、中間転写体５が２回転する間に、定電圧電源２２からの電荷付与ローラ１６への電圧の印加によって、電荷付与ローラ１６で中間転写ベルト５の同一箇所に電圧を連続的に２回印加して中間転写ベルト５に２回電荷を付与し、そのとき中間転写ベルト５に流れる各電流値を電源２２に接続された電流検知手段２４により検知した。そして検知した２回分の電流値のそれぞれに応じて、ＣＰＵ２０により中間転写ベルト５の時定数τを推定し、これに基づき１次転写電源１８により１次転写ローラ８ａに印加する１次転写バイアスを制御するようにした。
【００２４】
本実施例によれば、中間転写ベルト５は、体積抵抗１０⁵ Ωｃｍ以下のＮＢＲ（ニトリルゴム）を厚さ１ｍｍ、幅２３０ｍｍ、周長１４０πｍｍの円筒状にシームレス成形し、その上に高抵抗の誘電体層を厚さ５０μｍ程度にコートして構成した。１次転写ローラ８ａには、体積抵抗１０⁵ Ωｃｍ以下のＥＰＤＭによる直径１４ｍｍ、幅２２０ｍｍのローラを用いた。電荷付与ローラ１６には、体積抵抗１０⁷ 〜１０⁸ ΩｃｍのＥＰＤＭによる直径１８ｍｍ、幅２２０ｍｍのローラを用いた。
【００２５】
１次転写バイアスを印加したときの中間転写ベルト５の時定数τの変化に対する転写電流Ｉt の変化を図２に示す。図２において、Ｉt1、Ｉt2、Ｉt3、Ｉt4は、１色目、２色目、３色目および４色目の転写電流で、それぞれ１次転写バイアスとして１００Ｖ、５５０Ｖ、７００Ｖおよび８５０Ｖを印加した。
【００２６】
図２から明らかなように、各色とも中間転写ベルト５の時定数τが小さくなるほど多く、また転写電流は３色目、４色目と後の色ほど多く、時定数τの変化に対する転写電流の差分は３色目、４色目で特に大きく、４色目が最も大きい。ドラムゴーストは、転写電流が９μＡを超える３色目、４色目で発生した。
【００２７】
５００Ｖの電圧を印加した電荷付与ローラ１６により中間転写ベルト５の同一箇所に２回連続して電荷を付与したときの時定数τに対する転写電流Ｉ1 、Ｉ2 の変化を図３に示す。
【００２８】
図３に示されるように、この場合も、図２の転写電流の変化と同様の傾向を示していることが分かる。また、２つの電流値の比Ｉ2 ／Ｉ1 は、時定数τが大きくなるほど小さくなるような相関があることが分かる。
【００２９】
そこで、本実施例では、１色目、２色目、３色目、４色目の１次転写バイアスＶt10 、Ｖt20 、Ｖt30 、Ｖt40 を以下のように設定した。
【００３０】
Ｖt10 ＝１００（Ｖ）
Ｖt20 ＝５００＋１００×（１−Ｉ2 ／Ｉ1 ）（Ｖ）
Ｖt30 ＝５５０＋３００×（１−Ｉ2 ／Ｉ1 ）（Ｖ）
Ｖt40 ＝６００＋５００×（１−Ｉ2 ／Ｉ1 ）（Ｖ）
【００３１】
これにより、転写電流Ｉt10 、Ｉt20 、Ｉt30 、Ｉt40 は図４のようになり、時定数τが下がっても、転写電流が９μＡを超えることがなくなり、ドラムゴーストを防止することができる。
【００３２】
以上では、電流の測定を２回行ったが、３回以上行うことができるのはいうまでもない。
【００３３】
実施例２
前述したように、中間転写ベルト５の時定数τが下がると転写電流が多くなり、次回の帯電で感光ドラム１が所望の電位まで達せず、ドラムゴーストが発生する。つまり、ドラムゴーストは帯電能力以上の電荷が転写により付与されることにより発生する。そこで、本実施例では、転写電流が多い（中間転写ベルトの時定数τが低い）ときに、帯電能力を上げてやるように帯電ローラ２の帯電バイアスを制御した。
【００３４】
従来、帯電バイアスはＶdc＝−５５０Ｖの直流成分にＶpp＝２．０ｋＶ、周波数１．２ｋＨz の交流成分を重畳したものを用いていた。このバイアスでは、転写電流が９μＡ以上になると、ドラムゴーストが発生した。
【００３５】
帯電バイアスのＶppを変更し、転写電流に対するドラムゴーストの発生状況を実験した結果を表１に示す。表１において、符号の○はドラムゴーストが発生しないことを示し、×はドラムゴーストが発生することを示す。
【００３６】
【表１】

【００３７】
表１によれば、Ｖppを高くすることによって帯電能力が上がっていることが分かる。
【００３８】
これを踏まえて、本実施例では、図５に示すように、電荷付与ローラ１６により電圧を中間転写ベルト５の同一箇所に連続して印加し、その各印加時、中間転写ベルト５に流れる電流値を電流検知手段２４で検知し、ＣＰＵ２０により中間転写ベルト５の時定数τを推定する。そして、それに基づき帯電バイアス電源２６により帯電ローラ２に印加する帯電バイアスのＶppを制御する。
【００３９】
実施例１で説明したように、転写電流は中間転写ベルト５の時定数τと相関があり、τは実施例１と同様に電荷付与ローラ１６から中間転写ベルト５の同一箇所に２回連続して電圧を印加したときの各電流値Ｉ1 、Ｉ2 の比Ｉ2 ／Ｉ1 で推定することができる。
【００４０】
そこで、本実施例では、帯電バイアスのＶppを以下のように設定した。
【００４１】
Ｖpp＝２．６−１．２×（１−Ｉ2 ／Ｉ1 ）（ｋＶ）
これにより、中間転写ベルト５の時定数τが低下しても、ドラムゴーストを防止することができる。
【００４２】
本実施例では、帯電バイアスのＶppを変更したが、ＡＣ電流値やあるいはＶdcや周波数を変更することによっても、同様の効果を得ることができる。
【００４３】
実施例３
本実施例では、中間転写ベルト５の時定数τが所定の範囲から外れた場合に、中間転写ベルト５の寿命に関する信号を出力するようにした。
【００４４】
詳述すると、中間転写ベルト５の寿命は時定数τの低下に基づいている。中間転写ベルト５のτが著しく低下すると、前述したドラムゴーストだけでなく飛び散り等の不具合も発生し、画質に大きな影響を与えるため、所望のτになったら寿命をユーザーに知らせていた。
【００４５】
しかし、時定数τの低下は使用環境、使用モード等によってその速度が変わるが、従来はその中で最も速い条件でのプリント枚数を持って寿命としていた。従って、ほとんどの場合、中間転写ベルト５が依然として使用可能な状態であるにもかかわらず、寿命となってしまっていた。
【００４６】
本実施例では、上記不具合を解決するために、図１等において、ＣＰＵ２０に中間転写ベルト５の寿命に関する図示しない報知手段を設置し、上述した方法で中間転写ベルト５の時定数τを推定し、この値が所定の範囲から外れた場合、報知手段に中間転写ベルト５が寿命に達する旨のメッセージを表示して、ユーザーに告知するようにした。
【００４７】
本実施例によれば、これにより、使用環境、使用モードに応じて、中間転写ベルト５の最終的な交換時期を常に適切に知らせることができる。
【００４８】
実施例４
本実施例では、図６に示すように、１次転写ローラ８ａに１次転写バイアスを印加する１次転写電源１８に電流検知手段２４を接続し、１次転写ローラ８ａにより中間転写ベルト５の同一箇所に２回連続して電圧を印加し、電流検知手段２４によりそれぞれの電流値を検知して、中間転写ベルト５の時定数τを推定し、１次転写バイアスを制御するようにした。
【００４９】
すなわち、前の実施例１では、電荷付与ローラ１６、つまり電流測定用の電荷付与手段を設置していたが、本実施例では、１次転写ローラ８ａに電荷付与手段に兼ねさせて、特別な電荷付与手段を設置することを省略した。これにより、コストアップをすることなく、実施例１と同様な効果を発揮することができる。
【００５０】
本実施例では、１次転写ローラ８ａが電荷付与手段を兼ねたが、２次転写ローラ８ｂや中間転写ベルト５のクリーニングローラ１５に電荷付与手段を兼ねさせてもよく、同様な効果を得ることができる。
【００５１】
実施例５
本実施例では、図７に示すように、１次転写ローラ８ａと２次転写ローラ８ｂのそれぞれを電荷付与手段とし、１次転写電源１８からの１次転写ローラ８ａへの電圧の印加、２次転写電源２８からの２次転写ローラ８ｂへの電圧の印加により、中間転写ベルト５の同一箇所に連続して電圧を印加する。そしてそれぞれの電流検知手段２４、３０により得られた各電流値から、ＣＰＵ２０により中間転写ベルト５の時定数τを推定し、それに基づき電源１８により１次転写ローラ８ａに印加する１次転写バイアスを制御するようにした。
【００５２】
前の実施例１〜４では、１つの電荷付与手段により２回の電流測定を行っていたため、少なくとも中間転写ベルト５を２回転させる必要があったが、本実施例では、中間転写ベルト５の１回転で２回の電流測定が可能なため、制御工程の時間短縮が図れる。
【００５３】
本実施例では、電流検知を行って１次転写ローラ８ａの１次転写バイアスを制御したが、帯電ローラ２の帯電バイアス制御や、中間転写ベルト５の寿命決定を行ってもよい。
【００５４】
また本実施例では、１次転写ローラ８ａと２次転写ローラ８ｂのそれぞれに電荷付与手段を兼ねさせたが、電荷付与手段の１つを中間転写ベルト５のクリーニングローラ１５で代用してもよい。さらに３つ以上の電荷付与手段を用いることもできる。
【００５５】
本発明における電流検知は、画像形成行程の先頭の非画像部で毎回プリント中に行うのが好ましいが、電源投入時やジャム処理後の作動状態復帰時の前回転のときに行っても、あるいは濃度制御の前後で行ってもよい。
【００５６】
【発明の効果】
以上説明したように、本発明によれば、複数の定電圧電源と、複数の定電圧電源からの電圧の印加により中間転写体に電圧を印加し、中間転写体に電荷を付与する複数の電荷付与手段と、複数の電荷付与手段による電圧の印加によって発生する中間転写体に流れる電流を検知する電流検知手段とを有し、電荷付与手段により中間転写体の回動過程で中間転写体の同一箇所に連続して複数回電圧を印加し、電流検知手段によって複数回検知したそれぞれの電流値に応じて、１次転写手段に印加する１次転写バイアスを制御するようにしたので、中間転写体の時定数τが下がっても、ドラムゴーストが発生するのを防止することができる。
【００５８】
また、複数の電荷付与手段を設置して、中間転写体の同一箇所に連続して複数回電圧を印加するようにしたので、１次転写バイアス制御等の時間を短縮することができる。さらに、１次転写手段、２次転写手段もしくは中間転写体のクリーニング手段に電荷付与手段を兼ねさせた場合には、コストを上昇することなく、１次転写バイアス制御等を実施することができる。
【図面の簡単な説明】
【図１】本発明のカラー画像形成装置の一実施例における要部を示す概略構成図である。
【図２】図１の要部に設置された中間転写ベルトに１次転写バイアスを印加したときの中間転写ベルトの時定数τの変化に対する転写電流Ｉt の変化を示す図である。
【図３】図１の要部に設置された電荷付与ローラにより中間転写ベルトの同一箇所に２回連続して電荷を付与したときの時定数τに対する転写電流Ｉ1 、Ｉ2 の変化を示す図である。
【図４】図１の実施例における制御を行ったときの中間転写ベルトの時定数τに対する転写電流の変化を示す図である。
【図５】本発明の他の一実施例における要部を示す概略構成図である。
【図６】本発明のさらに他の一実施例における要部を示す概略構成図である。
【図７】本発明のさらに他の一実施例における要部を示す概略構成図である。
【図８】従来のカラー画像形成装置を示す概略図である。
【符号の説明】
１感光ドラム
２帯電ローラ
５中間転写ベルト
８ａ１次転写ローラ
８ｂ２次転写ローラ
１６電荷付与ローラ
１８、２２、２６、２８電源
２０ＣＰＵ
２４、３０電流検知手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus such as an electrophotographic copying machine or a laser printer.
[0002]
[Prior art]
FIG. 8 is a schematic view showing a conventional color image forming apparatus.
[0003]
The color image forming apparatus has a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotated in a direction indicated by an arrow by a driving unit (not shown), and a primary charging roller 2 that contacts the photosensitive drum 1 in the rotation process. The surface is uniformly charged. Next, the exposure device 3 irradiates the surface of the photosensitive drum 1 with laser light L according to the yellow image pattern, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.
[0004]
Four developing

devices

4 a, 4 b, 4 c, 4 d are supported on the rotating support 11. When the rotation of the photosensitive drum 1 proceeds, the developing device 4 a containing yellow toner is exposed to light by the rotation of the rotating support 11. The latent image on the photosensitive drum 1 is developed by the developing device 4a thus moved to a position facing the drum 1 (developing position). The latent image is visualized as a yellow toner image by development.
[0005]
An intermediate transfer belt 5 that rotates in the direction of the arrow at substantially the same speed as the photosensitive drum 1 is installed adjacent to the photosensitive drum 1, and a primary transfer bias is applied to the yellow toner image formed on the photosensitive drum 1. The image is transferred onto the surface of the intermediate transfer belt 5 by the primary transfer roller 8a (primary transfer). By performing the above process for four colors, yellow, magenta, cyan, and black, a color image is formed by superimposing and transferring the four color toner images on the intermediate transfer belt 5.
[0006]
Next, the transfer material is taken out from the transfer material cassette 12 by the pickup roller 13 and supplied to the intermediate transfer belt 5 at a predetermined timing. At the same time, the secondary transfer roller 8b to which the secondary transfer bias is applied contacts the intermediate transfer belt 5 with the transfer material interposed therebetween, and the four color toner images on the intermediate transfer belt 5 are collectively applied to the surface of the transfer material. Transferred (secondary transfer).
[0007]
The transfer material onto which the four color toner images have been transferred in this manner is conveyed to the fixing device 6 by the conveyance belt 14, where the toner is melted and fixed to the transfer material by heating and pressurization, and a color fixed image is obtained. It is done. After the transfer of the four color toner images is completed, the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 5 is charged by the cleaning roller 15 and then transferred onto the photosensitive drum 1 by the primary transfer roller 8a. And transferred from the intermediate transfer belt 5. On the other hand, the primary transfer residual toner and the reversely transferred secondary transfer residual toner on the photosensitive drum 1 are removed from the photosensitive drum 1 by known blade means 7 of the cleaning device.
[0008]
[Problems to be solved by the invention]
By the way, the intermediate transfer belt 5 has a belt time constant τ that decreases due to resistance fluctuations caused by high-temperature and high-humidity environment or long-term use. Here, the time constant τ is the time until the belt is charged to Vo (V) and attenuated to Vo / e (V) (e is the base of natural logarithm).
[0009]
When the time constant of the intermediate transfer belt 5 is lowered, there is a problem that drum ghost is generated.
[0010]
That is, at the time of primary transfer for the second and subsequent colors, a predetermined charge is held on the intermediate transfer belt 5 by the primary transfer up to the previous color, and the potential on the intermediate transfer belt 5 is lowered. The primary transfer bias for the second and subsequent colors is determined on the premise. When the time constant τ of the intermediate transfer belt 5 decreases, a predetermined charge cannot be held on the intermediate transfer belt 5 and the potential on the intermediate transfer belt 5 increases. Therefore, even if the same bias as the transfer bias determined above is applied, the potential difference becomes equal to or greater than a desired potential difference, and an excessive current flows to the photosensitive drum 1 to generate drum ghost.
[0011]
In addition, when the time constant τ of the intermediate transfer belt 5 is remarkably reduced, problems such as toner scattering occur and image quality deteriorates.
[0012]
Thus, the main factor that determines the life of the intermediate transfer belt 5 is a decrease in the time constant τ of the intermediate transfer belt 5. Therefore, it is desirable to inform the user of the life of the intermediate transfer belt 5 when the time constant decreases to a predetermined value.
[0013]
However, conventionally, the user has been informed that the intermediate transfer belt 5 has reached the end of its life because predetermined conditions such as the number of prints and the number of rotations of the intermediate transfer belt have reached a predetermined value. However, the decrease in the time constant of the intermediate transfer belt 5 varies depending on the use environment, the use mode, and the like. For this reason, the intermediate transfer belt 5 may be replaced even though printing can be performed normally.
[0014]
It is an object of the present invention to obtain a high-quality image without drum ghost even when the time constant τ of the intermediate transfer member is lowered, and to notify the life of the intermediate transfer member regardless of the use environment or use mode. It is an object of the present invention to provide a color image forming apparatus that can always be performed at an optimum time.
[0015]
[Means for Solving the Problems]
The above object is achieved by a color image forming apparatus according to the present invention. In summary, the present invention includes an image bearing member, and the intermediate transfer member, a charging means for uniformly charging said image bearing member, exposing the charged the image bearing member, a toner image of each and developed color each time the resulting thereof and a toner image primary transfer means for transferring superimposed on the intermediate transfer member, second transfer means for transferring to the transfer material at once the color toner images transferred to the intermediate transfer member in the color image forming apparatus having the door, and a plurality of constant voltage power supply, voltage is applied to the intermediate transfer member by applying a voltage from the plurality of constant voltage power supply, a plurality of charge imparting a charge to said intermediate transfer member and applying means, and a current detecting means for detecting a current flowing through the intermediate transfer member caused by application of a voltage by the plurality of charging unit, said at turning the course of the intermediate transfer member by said charging unit Same part of intermediate transfer member And a voltage is applied a plurality of times continuously, and a primary transfer bias applied to the primary transfer unit is controlled in accordance with each current value detected a plurality of times by the current detection unit. Forming device.
[0016]
According to an embodiment of the present invention, there are two charge applying units, the primary transfer unit also serves as one of the charge providing units, and the secondary transfer unit also serves as the other of the charge providing units.
[0017]
According to another embodiment of the present invention, a secondary transfer remaining toner on the intermediate transfer member by applying a second charging unit different from the charging unit and a charging bias from the second charging unit. And a secondary transfer residual toner to which the charge is applied is reversely transferred to the image carrier simultaneously with the transfer of the toner image to the intermediate transfer member by the primary transfer unit. In addition, there are two charge applying units, the second charging unit also serves as one of the charge providing units, and the primary transfer unit also serves as the other of the charge providing units.
According to another embodiment of the present invention, a secondary transfer remaining toner on the intermediate transfer member by applying a second charging unit different from the charging unit and a charging bias from the second charging unit. And a secondary transfer residual toner to which the charge is applied is reversely transferred to the image carrier simultaneously with the transfer of the toner image to the intermediate transfer member by the primary transfer unit. In addition, there are two charge applying units, the second charging unit also serves as one of the charge providing units, and the secondary transfer unit also serves as the other of the charge providing units.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
Example 1
FIG. 1 is a schematic view showing a main part of a color image forming apparatus of the present invention. In the present invention, a voltage is applied to the intermediate transfer belt 5 as an intermediate transfer member, the time constant τ of the intermediate transfer belt 5 is estimated from the current value at that time, and the primary transfer bias applied to the primary transfer roller 8a. It is a great feature to control etc. The configuration itself of the color image forming apparatus of the present invention is basically the same as that of the conventional color image forming apparatus shown in FIG. 8, and will be described below with reference to FIG. 8 as necessary.
[0020]
In the conventional color image forming apparatus shown in FIG. 8, the toner images of the first color to the fourth color are sequentially primary-transferred onto the intermediate belt 5 by the predetermined transfer bias from the first color to the fourth color. The transfer bias at this time is set so that the potential difference between the surface potential of the intermediate transfer belt 5 and the surface potential of the photosensitive drum 1 (dark portion potential VD) becomes a predetermined potential. Before the transfer of the first color, the intermediate transfer belt 5 is neutralized so that there is no previous residual charge. Therefore, the applied transfer bias Vt1 of the first color becomes the surface potential of the intermediate transfer belt 5, so the difference Vt1 -Vt1 is set so that -VD becomes a predetermined value. At the time of the second color transfer, the electric charge (polarity opposite to the transfer bias) applied at the time of the first color transfer remains on the intermediate transfer belt 5, so that the surface potential of the intermediate transfer belt is greater than the applied transfer bias of the second color. (Vt2−ΔV1). Therefore, Vt2 is set so that Vt2−ΔV1−VD becomes a predetermined value. Similarly, the transfer bias for the third color and the fourth color is also set in consideration of the residual charge up to the previous color.
[0021]
However, as the number of printed sheets advances, nitrogen oxide or the like adheres to the surface of the intermediate transfer belt 5, and when it absorbs moisture, the surface resistance gradually decreases and the time constant τ also decreases. This also varies depending on the temperature and humidity of the atmosphere, and a high-temperature and high-humidity environment is most prominent.
[0022]
As described above, when the time constant of the intermediate transfer belt 5 is lowered, the charge holding ability is lowered. As a result, the residual charge up to the previous color is reduced, a potential difference larger than the desired potential difference is generated, and the transfer current is increased. When the transfer current increases, that is, the charge applied to the photosensitive drum 1 increases, the photosensitive drum 1 is not charged to a desired potential by the next charging, and a drum ghost is generated.
[0023]
Therefore, in this embodiment, as shown in FIG. 1, a charge applying roller 16 that can be contacted and separated is provided as a means for applying charge to the intermediate transfer belt 5, and a constant voltage is applied while the intermediate transfer member 5 rotates twice. By applying a voltage from the power supply 22 to the charge applying roller 16, the charge applying roller 16 continuously applies a voltage twice to the same portion of the intermediate transfer belt 5 to apply a charge to the intermediate transfer belt 5 twice. At this time, each current value flowing through the intermediate transfer belt 5 was detected by the current detection means 24 connected to the power source 22. Then, the CPU 20 estimates the time constant τ of the intermediate transfer belt 5 according to each of the detected current values, and based on this, the primary transfer bias applied to the primary transfer roller 8a by the primary transfer power source 18 is estimated. I tried to control it.
[0024]
According to this embodiment, the intermediate transfer belt 5 is formed by seamlessly molding NBR (nitrile rubber) having a volume resistance of 10 ⁵ Ωcm or less into a cylindrical shape having a thickness of 1 mm, a width of 230 mm, and a circumferential length of 140πmm, and a high resistance. A dielectric layer was coated to a thickness of about 50 μm. As the primary transfer roller 8a, a roller having a diameter of 14 mm and a width of 220 mm by EPDM having a volume resistance of 10 ⁵ Ωcm or less was used. As the charge application roller 16, a roller having a diameter of 18 mm and a width of 220 mm by EPDM having a volume resistance of 10 ⁷ to 10 ⁸ Ωcm was used.
[0025]
FIG. 2 shows changes in the transfer current It with respect to changes in the time constant τ of the intermediate transfer belt 5 when the primary transfer bias is applied. In FIG. 2, It1, It2, It3, and It4 are transfer currents of the first, second, third, and fourth colors, and 100 V, 550 V, 700 V, and 850 V were applied as primary transfer biases, respectively.
[0026]
As is clear from FIG. 2, the color transfer current increases as the time constant τ of the intermediate transfer belt 5 decreases for each color, and the transfer current increases as the third color, the fourth color, and the subsequent colors. The third color and the fourth color are particularly large, and the fourth color is the largest. Drum ghosts occurred in the third and fourth colors where the transfer current exceeded 9 μA.
[0027]
FIG. 3 shows changes in the transfer currents I1 and I2 with respect to the time constant .tau. When the electric charge application roller 16 to which a voltage of 500 V is applied applies electric charges to the same portion of the intermediate transfer belt 5 twice in succession.
[0028]
As shown in FIG. 3, it can be seen that this case also shows the same tendency as the change in the transfer current in FIG. It can also be seen that the ratio of the two current values I2 / I1 has a correlation that decreases as the time constant τ increases.
[0029]
Therefore, in this embodiment, the primary transfer biases Vt10, Vt20, Vt30, and Vt40 for the first color, the second color, the third color, and the fourth color are set as follows.
[0030]
Vt10 = 100 (V)
Vt20 = 500 + 100 × (1−I 2 / I 1) (V)
Vt30 = 550 + 300 × (1−I 2 / I 1) (V)
Vt40 = 600 + 500 × (1-I2 / I1) (V)
[0031]
As a result, the transfer currents It10, It20, It30, and It40 are as shown in FIG. 4, and even if the time constant τ decreases, the transfer current does not exceed 9 μA, and drum ghosting can be prevented.
[0032]
In the above, the current measurement was performed twice, but it goes without saying that it can be performed three or more times.
[0033]
Example 2
As described above, when the time constant τ of the intermediate transfer belt 5 decreases, the transfer current increases, and the photosensitive drum 1 does not reach a desired potential at the next charging, and a drum ghost is generated. That is, the drum ghost is generated when a charge exceeding the charging capability is applied by transfer. Therefore, in this embodiment, the charging bias of the charging roller 2 is controlled so as to increase the charging capability when the transfer current is large (the time constant τ of the intermediate transfer belt is low).
[0034]
Conventionally, a charging bias in which an AC component of Vpp = 2.0 kV and a frequency of 1.2 kHz is superimposed on a DC component of Vdc = −550 V has been used. With this bias, when the transfer current was 9 μA or more, drum ghost was generated.
[0035]
Table 1 shows the results of experiments on the occurrence of drum ghost with respect to the transfer current by changing the charging bias Vpp. In Table 1, the symbol ◯ indicates that drum ghost is not generated, and x indicates that drum ghost is generated.
[0036]
[Table 1]

[0037]
According to Table 1, it can be seen that the charging ability is increased by increasing Vpp.
[0038]
Based on this, in this embodiment, as shown in FIG. 5, a voltage is continuously applied to the same portion of the intermediate transfer belt 5 by the charge applying roller 16, and the current flowing through the intermediate transfer belt 5 at each application is applied. The value is detected by the current detector 24, and the CPU 20 estimates the time constant τ of the intermediate transfer belt 5. Based on this, the charging bias power supply 26 controls the charging bias Vpp applied to the charging roller 2.
[0039]
As described in the first exemplary embodiment, the transfer current has a correlation with the time constant τ of the intermediate transfer belt 5, and τ continues twice from the charge applying roller 16 to the same portion of the intermediate transfer belt 5 as in the first exemplary embodiment. Thus, it can be estimated by the ratio I2 / I1 of the current values I1, I2 when a voltage is applied.
[0040]
Therefore, in this embodiment, Vpp of the charging bias is set as follows.
[0041]
Vpp = 2.6-1.2.times. (1-I @ 2 / I @ 1) (kV)
As a result, even if the time constant τ of the intermediate transfer belt 5 decreases, drum ghost can be prevented.
[0042]
In this embodiment, the charging bias Vpp is changed, but the same effect can be obtained by changing the AC current value, Vdc, or frequency.
[0043]
Example 3
In this embodiment, when the time constant τ of the intermediate transfer belt 5 is out of a predetermined range, a signal relating to the life of the intermediate transfer belt 5 is output.
[0044]
More specifically, the life of the intermediate transfer belt 5 is based on a decrease in the time constant τ. When the τ of the intermediate transfer belt 5 is remarkably lowered, not only the drum ghost described above but also problems such as scattering are generated, and the image quality is greatly affected.
[0045]
However, although the speed of the time constant τ varies depending on the use environment, use mode, etc., conventionally, the lifetime is determined with the number of prints under the fastest condition. Therefore, in most cases, the intermediate transfer belt 5 has reached the end of its life even though it is still usable.
[0046]
In this embodiment, in order to solve the above problem, in FIG. 1 and the like, a notifying means (not shown) relating to the life of the intermediate transfer belt 5 is installed in the CPU 20, and the time constant τ of the intermediate transfer belt 5 is estimated by the method described above. When this value is out of the predetermined range, a message indicating that the intermediate transfer belt 5 has reached the end of its life is displayed on the notification means to notify the user.
[0047]
According to the present embodiment, this makes it possible to always appropriately notify the final replacement time of the intermediate transfer belt 5 according to the use environment and the use mode.
[0048]
Example 4
In this embodiment, as shown in FIG. 6, a current detecting means 24 is connected to a primary transfer power source 18 for applying a primary transfer bias to the primary transfer roller 8a, and the intermediate transfer belt 5 is moved by the primary transfer roller 8a. A voltage was applied to the same location twice in succession, and each current value was detected by the current detection means 24, the time constant τ of the intermediate transfer belt 5 was estimated, and the primary transfer bias was controlled.
[0049]
That is, in the previous embodiment 1, the charge applying roller 16, that is, the charge applying means for measuring the current, is installed. In this embodiment, the primary transfer roller 8a is also used as the charge applying means, and is special. The installation of charge imparting means was omitted. Thereby, the effect similar to Example 1 can be exhibited, without raising a cost.
[0050]
In the present embodiment, the primary transfer roller 8a also serves as the charge application unit, but the secondary transfer roller 8b and the cleaning roller 15 of the intermediate transfer belt 5 may also serve as the charge application unit, and the same effect can be obtained. Can do.
[0051]
Example 5
In this embodiment, as shown in FIG. 7, each of the primary transfer roller 8a and the secondary transfer roller 8b is used as a charge applying unit, and voltage application from the primary transfer power supply 18 to the primary transfer roller 8a is performed. By applying a voltage from the secondary transfer power supply 28 to the secondary transfer roller 8b, a voltage is continuously applied to the same portion of the intermediate transfer belt 5. The CPU 20 estimates the time constant τ of the intermediate transfer belt 5 from the current values obtained by the current detection means 24 and 30, and based on the estimated time constant τ, the primary transfer bias applied to the primary transfer roller 8 a by the power source 18 is based on the estimated time constant τ. I tried to control it.
[0052]
In the previous Examples 1 to 4, since the current measurement was performed twice by one charge applying unit, it was necessary to rotate the intermediate transfer belt 5 at least twice, but in this example, the intermediate transfer belt 5 Since current can be measured twice in one rotation, the time required for the control process can be shortened.
[0053]
In this embodiment, the current detection is performed to control the primary transfer bias of the primary transfer roller 8a. However, the charging bias control of the charging roller 2 and the life of the intermediate transfer belt 5 may be determined.
[0054]
In this embodiment, each of the primary transfer roller 8a and the secondary transfer roller 8b is also used as a charge applying unit. However, one of the charge applying units may be replaced by the cleaning roller 15 of the intermediate transfer belt 5. . Further, three or more charge imparting means can be used.
[0055]
The current detection in the present invention is preferably performed during printing every time at the top non-image portion of the image forming process, but it may be performed at the time of pre-rotation when the power is turned on or when the operation state is restored after jam processing, or You may carry out before and after density control.
[0056]
【The invention's effect】
As described above, according to the present invention, a plurality of constant voltage power supplies and a plurality of charges for applying a voltage to the intermediate transfer body by applying voltages from the plurality of constant voltage power supplies and applying a charge to the intermediate transfer body. And a current detecting means for detecting a current flowing in the intermediate transfer member generated by applying a voltage from a plurality of charge applying means, and the intermediate transfer member is identical in the rotation process of the intermediate transfer member by the charge applying means. Since the primary transfer bias applied to the primary transfer unit is controlled according to the respective current values detected by the current detection unit a plurality of times , and the intermediate transfer member The drum ghost can be prevented from occurring even when the time constant τ decreases.
[0058]
Further, by installing a plurality of charging unit. Thus applying a plurality of times voltages in succession at the same position of the intermediate transfer member, it is possible to shorten the primary transfer bias control of the time. Further, when the primary transfer unit, the secondary transfer unit or the intermediate transfer member cleaning unit is also used as the charge applying unit, the primary transfer bias control and the like can be performed without increasing the cost.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a main part in an embodiment of a color image forming apparatus of the present invention.
FIG. 2 is a diagram showing a change in transfer current It with respect to a change in time constant τ of the intermediate transfer belt when a primary transfer bias is applied to the intermediate transfer belt installed in the main part of FIG. 1;
3 is a graph showing changes in transfer currents I1 and I2 with respect to time constant τ when a charge is applied to the same portion of the intermediate transfer belt twice in succession by a charge application roller installed in the main part of FIG. is there.
4 is a diagram illustrating a change in transfer current with respect to a time constant τ of the intermediate transfer belt when the control in the embodiment of FIG. 1 is performed.
FIG. 5 is a schematic configuration diagram showing a main part in another embodiment of the present invention.
FIG. 6 is a schematic configuration diagram showing a main part in still another embodiment of the present invention.
FIG. 7 is a schematic configuration diagram showing a main part in still another embodiment of the present invention.
FIG. 8 is a schematic view showing a conventional color image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 5 Intermediate transfer belt 8a Primary transfer roller 8b Secondary transfer roller 16

Charging roller

18, 22, 26, 28 Power supply 20 CPU
24, 30 Current detection means

Claims

An image bearing member, and the intermediate transfer member, a charging means for uniformly charging said image bearing member, exposing the charged the image bearing member, each time a toner image of each and developed color is obtained, and the toner image a primary transfer unit that transfers superimposed on the intermediate transfer member, in the color image forming apparatus and a secondary transfer means for transferring to the transfer material at once the color toner images transferred to the intermediate transfer member a plurality of constant voltage power supply, voltage is applied to the intermediate transfer member by applying a voltage from the plurality of constant voltage power supply, a plurality of charge applying means for applying a charge to said intermediate transfer member, said plurality of charge and a current detecting means for detecting a current flowing through the intermediate transfer member caused by application of a voltage by the applying means, continuously at the same position of the intermediate transfer member by said charging unit in rotation process of the intermediate transfer body And multiple times voltage Applied to the current in accordance with respective current values detected a plurality of times by detecting means, a color image forming apparatus characterized by controlling the primary transfer bias applied to the primary transfer unit.

The charging unit is two is, the primary transfer means also serves as one of the charging unit, a color image forming apparatus according to claim 1 wherein the second transfer means also serve as the other of said charge applying means.

A second charging unit different from the charging unit, and a cleaning member for applying a charge to the secondary transfer residual toner on the intermediate transfer member by applying a charging bias from the second charging unit are further provided. The secondary transfer residual toner to which the charge is applied is reversely transferred to the image carrier simultaneously with the transfer of the toner image to the intermediate transfer member by the primary transfer unit, and the charge application means is two is, the second charging means serves one of the charging unit, a color image forming apparatus according to claim 1 wherein the first transfer means also serves as the other of said charge applying means.

A second charging unit different from the charging unit, and a cleaning member for applying a charge to the secondary transfer residual toner on the intermediate transfer member by applying a charging bias from the second charging unit are further provided. The secondary transfer residual toner to which the charge is applied is reversely transferred to the image carrier simultaneously with the transfer of the toner image to the intermediate transfer member by the primary transfer unit, and the charge application means are among 2, wherein one of the doubles of the second charging means the charging unit, a color image forming apparatus according to claim 1 wherein the second transfer means also serve as the other of said charge applying means.