JP2004157162A

JP2004157162A - Development device and image forming apparatus

Info

Publication number: JP2004157162A
Application number: JP2002319944A
Authority: JP
Inventors: Yoshie Iwakura; 良恵岩倉; Minoru Tomii; 稔冨依; Susumu Murakami; 進村上; Hideshi Izumi; 英志泉
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2002-11-01
Filing date: 2002-11-01
Publication date: 2004-06-03

Abstract

<P>PROBLEM TO BE SOLVED: To prevent development and density inhomogeneities which are caused by a belt member. <P>SOLUTION: If temperature in the vicinity of a belt 34 detected by a temperature sensor 41 falls within a normal-temperature range, a control part 42 rotates a drive roller 32 in order to rotate and advance the belt member 34 and place the area 34a of the belt member 34 upon a carrier 35. If the temperature detected in the vicinity of the belt 34 is in a low-temperature range, the control part 42 rotates and advances the belt member 34 in order to place the area 34b of the belt member 34 upon the carrier 35. Further, if the temperature detected in the vicinity of the belt 34 is in a high-temperature range, the control part 42 rotates and advances the belt member 34 in order to place the area 34c of the belt member 34 upon the carrier 35. Thus, even if the temperature of the belt 34 changes, the value of the volume resistance of each area of the belt member 34 which is placed upon the carrier 35 is always kept constant at approximately 10x10<SP>14</SP>Ωcm. Accordingly, the electric field of a travelling wave transmitted through the belt member 34 stabilizes and the amount of developer carried on the belt member 34 also stabilizes. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、進行波電界により現像剤を搬送し、この現像剤により静電潜像を現像する現像装置及び画像形成装置に関する。
【０００２】
【従来の技術】
電子写真方式を採用した複写機やプリンタ等の画像形成装置においては、例えば特許文献１に記載の技術の様に現像剤をベルト部材に一旦付着させて、現像剤をベルト部材により搬送し、現像剤をベルト部材から像担持体へと供給するというベルト現像方式のものがある。
【０００３】
また、近年は、現像剤を像担持体近傍まで搬送し、現像剤を像担持体上の静電潜像へと飛翔させて、この静電潜像を現像するという非接触方式の現像装置が注目されている。この非接触方式には、パウダークラウド方法、ジャンピング方法、電界カーテン（進行波電界）を利用した方法等がある。
【０００４】
進行波電界を利用した方法は、例えば特許文献２及び特許文献３等に記載されている。これらにおいては、現像剤の搬送路に多数の電極を埋設し、これらの電極に多相の交流電圧を印加して、進行波電界を発生させ、この進行波電界により搬送路上の現像剤を像担持体まで搬送する。現像剤は、像担持体近傍まで搬送されると、像担持体の静電潜像へと飛翔し、静電潜像に付着する。これにより、像担持体上の静電潜像が現像される。
【０００５】
ところが、特許文献２や特許文献３では、搬送路の除電や清掃等を格別に行っておらず、このために搬送路の電荷により進行波電界が乱されたり、搬送路に現像剤が固着してしまい、これらが像担持体と搬送路間の現像電界や現像材の搬送に悪影響を与えて、現像むら及び画像の濃度むらを引き起こした。
【０００６】
このため、本発明の発明者等は、搬送路に重ねられる無端状ベルト部材を設けて、この無端状ベルト上で現像剤を搬送し、この無端状ベルトを移動させることにより現像剤の搬送面を変更してリフレッシュし、この搬送面の除電及び清掃を行い、これにより搬送面の帯電や現像材の固着を防止するという現像装置を提案している（特許文献４等を参照）。
【０００７】
尚、特許文献４の現像装置では、ベルト部材の移動速度を現像剤の搬送速度よりも十分に低く設定し、現像剤の搬送を進行波電界により行ない、ベルト部材により搬送面のリフレッシュのみを行なっている。従って、このベルト部材は、上記ベルト現像方式のベルト部材とは明らかに異なるものである。
【０００８】
【特許文献１】
特開平６−３０８８１３号公報
【特許文献２】
特公平５−３１１４６号公報
【特許文献３】
特公平５−３１１４７号公報
【特許文献４】
特願２０００−２８３０８７号
【０００９】
【発明が解決しようとする課題】
しかしながら、特許文献４に記載の現像装置では、搬送路の帯電や現像剤の固着を防止することができても、進行波電界がベルト部材を透過するため、ベルト部材の抵抗値の変動やベルト部材の帯電により、進行波電界が不安定になって、ベルト部材上での現像剤の搬送量が安定化せず、現像むら及び画像の濃度むらを引き起こした。
【００１０】
そこで、本発明は、上記従来の問題点に鑑みてなされたものであり、ベルト部材が原因となって、現像むら及び濃度むらを引き起こすことがない現像装置及び画像形成装置を提供することを目的とする。
【００１１】
【課題を解決するための手段】
上記課題を解決するために、本発明は、複数の電極を有する搬送路と、搬送路に重ねられるベルト部材とを備え、多相の交流電圧を搬送路の各電極に印加して、進行波電界を形成し、この進行波電界により現像剤をベルト部材上で像担持体へと搬送して、この現像剤を像担持体に供給することにより像担持体上の静電潜像を現像する現像装置において、ベルト部材が現像剤の搬送方向に連なる複数の領域に区分され、各領域の抵抗値が相互に異なり、各領域のいずれかが搬送路に重ねられている。
【００１２】
この様な構成の本発明によれば、ベルト部材が現像剤の搬送方向に連なる複数の領域に区分され、各領域の抵抗値が相互に異なる。そして、ベルト部材が現像剤の搬送方向に適宜に移動されて、ベルト部材の各領域のいずれかが搬送路に重ねられる。このため、各領域の抵抗値のいずれかを選択して、この選択した抵抗値の領域を搬送路に重ねることができる。これにより、現像剤の搬送面をリフレッシュすると同時に、ベルト部材上の進行波電界のレベル変動を抑えることができ、ベルト部材上での現像剤の搬送量を安定化して、現像むら及び画像の濃度むらを防止することができる。
【００１３】
また、本発明においては、ベルト部材が３つの領域に区分され、一定温度での各領域の抵抗値が相互に１桁ずつ異なっている。
【００１４】
ベルト部材近傍の温度は、ベルト部材近傍の温度に応じて変動する。このため、ベルト部材の各領域の抵抗値の抵抗値を１桁ずつ異ならせ、ベルト部材近傍の温度が高温範囲、常温範囲、及び低温範囲のいずれに入るかにより、ベルト部材の各領域のいずれかを現像剤の搬送面に重ね合わせれば、この搬送面に重なるベルト部材領域の抵抗値の変動を抑えることができる。
【００１５】
更に、本発明においては、ベルト部材近傍の温度を検出する温度検出手段と、温度検出手段により検出された温度に応じてベルト部材を移動させ、ベルト部材の各領域のいずれかを搬送路に重ねる制御手段とを備えている。
【００１６】
この様にベルト部材の近傍の温度を検出し、この検出された温度に応じてベルト部材を移動されば、ベルト部材の近傍の温度が変動しても、現像剤の搬送面に重なるベルト部材領域の抵抗値の変動を抑えることができる。
【００１７】
また、本発明においては、複数の印字モードのいずれかを選択するモード選択手段と、モード選択手段により選択された印字モードに応じて、ベルト部材を移動させ、ベルト部材の各領域のいずれかを搬送路に重ねる制御手段とを備えている。
【００１８】
複数の印字モードとしては、例えばテキストを現像するモード、写真画像を現像するモード等があり、前者のモードでは、濃い目の現像が好まれ、後者のモードでは、薄めの現像が好まれる。このため、選択された印字モードに応じて、ベルト部材を移動させて、現像剤の搬送面に重なるベルト部材領域の抵抗値を適宜に設定し、ベルト部材上の進行波電界のレベルを調節して、ベルト部材上での現像剤の搬送量を変更し、現像濃度を調節している。
【００１９】
次に、本発明は、複数の電極を有する搬送路と、搬送路に重ねられるベルト部材とを備え、多相の交流電圧を搬送路の各電極に印加して、進行波電界を形成し、この進行波電界により現像剤をベルト部材上で像担持体へと搬送して、この現像剤を像担持体に供給することにより像担持体上の静電潜像を現像する現像装置において、ベルト部材は、現像が行われているときに停止され、現像が行われていないときに移動されて、搬送路に重ねられる該ベルト部材の領域を更新される。
【００２０】
この様な構成の本発明によれば、現像が行われていないときに移動されて、搬送路に重ねられる該ベルト部材の領域を更新している。このため、現像剤の搬送面に重なるベルト部材の領域が一度に完全にリフレッシュされることになる。これにより、進行波電界の変動を抑え、ベルト部材上での現像剤の搬送量を安定化させ、現像むら及び画像の濃度むらを防止することができる。
【００２１】
また、本発明においては、静電潜像の現像回数を計数する計数手段と、計数手段により計数された現像回数が予め設定された閾値に達すると、ベルト部材を移動させ、搬送路に重ねられる該ベルト部材の領域を更新する制御手段とを備えている。
【００２２】
ここでは、静電潜像の現像回数が多くなる程、現像剤の搬送面に重なるベルト部材の領域の帯電量が増大するため、この現像回数が閾値に達したときに、ベルト部材を移動させ、搬送路に重ねられるベルト部材の領域を更新している。
【００２３】
更に、本発明においては、ベルト部材の電位を検出する電位検出手段と、電位検出手段により検出された電位が予め設定された閾値に達すると、ベルト部材を移動させ、搬送路に重ねられる該ベルト部材の領域を更新する制御手段とを備えている。
【００２４】
この様に搬送路に重ねられるベルト部材の電位が閾値に達したときに、つまり帯電量が増大したときにベルト部材を移動させ、搬送路に重ねられるベルト部材の領域を更新しても良い。
【００２５】
次に、本発明は、複数の電極を有する搬送路と、搬送路に重ねられるベルト部材とを備え、多相の交流電圧を搬送路の各電極に印加して、進行波電界を形成し、この進行波電界により現像剤をベルト部材上で像担持体へと搬送して、この現像剤を像担持体に供給することにより像担持体上の静電潜像を現像する現像装置において、ベルト部材が現像剤の搬送速度よりも低い移動速度で移動され、ベルト部材の抵抗値が１０×１０＾１０Ωｃｍ〜１０×１０＾１４Ωｃｍである。
【００２６】
ベルト部材を現像剤の搬送速度よりも低い移動速度で常に移動させる場合でも、ベルト部材の抵抗値を１０×１０＾１０Ωｃｍ〜１０×１０＾１４Ωｃｍに設定すれば、ベルト部材の帯電を防止することができ、ベルト部材上で現像剤を搬送するのに必要な進行波電界を十分に維持することができる。
【００２７】
また、本発明においては、ベルト部材の比誘電率が２〜５である。
【００２８】
ベルト部材の比誘電率を２〜５に維持すれば、ベルト部材の帯電を防止し、かつベルト部材の電位を適宜に保つことができる。
【００２９】
更に、本発明においては、ベルト部材の厚みが２０μｍ〜１００μｍである。
【００３０】
ベルト部材の厚みを２０μｍ〜１００μｍに設定すれば、ベルト部材の柔軟性と強度を共に得ることができる。
【００３１】
次に、本発明の画像形成装置は、本発明の現像装置を備えている。
【００３２】
この様な本発明の画像形成装置においても、本発明の現像装置と同様の作用及び効果を達成することができる。
【００３３】
【発明の実施の形態】
以下、本発明の実施形態を添付図面を参照して詳細に説明する。
【００３４】
図１は、本発明の現像装置の第１実施形態を適用した画像形成装置を示す側面図である。この画像形成装置は、電子写真方式により画像を形成するものであり、感光体ドラム１１の周辺に、現像装置１２、転写装置１３、クリーニング装置１４、除電装置１５、帯電装置１６、露光装置１７等を感光体ドラム１１の回転方向の上流側から順に配置している。また、記録用紙Ｐの搬送方向下流側には、定着装置１８を配置している。記録用紙Ｐは、感光体ドラム１１と転写装置１３間を通過し、定着装置１８へと搬送される。
【００３５】
この画像形成装置では、感光体ドラム１１を矢印Ｂの方向に回転させつつ、感光体ドラム１１の表面を帯電装置１６により均一に帯電させる。そして、画像を示す印字データに従って露光装置１７から感光体ドラム１１へと出射される光ビームを変調しつつ、この光ビームにより感光体ドラム１１の表面を走査し、感光体ドラム１１上に静電潜像を形成する。更に、現像剤を現像装置１２により静電潜像に付着させて、現像剤像を形成し、この現像剤像を転写装置１３により感光体ドラム１１からＰＰＣ用紙等の記録用紙Ｐへと転写し、記録用紙Ｐ上の現像剤像を定着装置１８により加熱及び加圧して定着させる。この後、感光体ドラム１１上の残留現像剤をクリーニング装置１４により除去して、感光体ドラム１１をクリーニングし、感光体ドラム１１の表面の残留電荷を除電装置１５により除電する。
【００３６】
感光体ドラム１１は、例えばアルミニウム等の金属ドラムの外周に、アモルファスシリコン（ａ−Ｓｉ）、セレン（Ｓｅ）、有機光半導体（ＯＰＣ）等からなる薄膜状の光導電層を形成したものである。
【００３７】
帯電装置１６は、例えばタングステンワイヤ等の帯電線、金属製のシールド板、グリッド板からなるコロナ帯電器、あるいは帯電ローラや帯電ブラシ等を備えている。露光装置１７は、光ビームを出射する半導体レーザや発光ダイオード、光ビームの走査機構等を備えている。転写装置１３は、コロナ帯電器、あるいは帯電ローラや帯電ブラシ等を備えている。クリーニング装置１４は、感光体ドラム１１の表面に摺接するクリーニングブレード等である。除電装置１５は、除電ランプ等である。
【００３８】
尚、感光体ドラム１１、及び各装置１３〜１８として、他の方式のものを適用しても構わない。
【００３９】
次に、本実施形態の現像装置１２は、図２に示す様に現像剤を収容した現像槽２０、進行波電界を発生して現像剤を搬送する現像剤搬送部２１、現像剤を現像槽２０から現像剤搬送部２１へと供給する供給ローラ２３、ブレード２６、現像槽２０内の現像剤を攪拌しつつ供給ローラ２３へと移動させるミキシングパドル２４、及び現像剤搬送部２１から現像槽２０へと現像剤を回収する回収ローラ２５等を備えている。
【００４０】
現像槽２０は、感光体ドラム１１の側方に対向する開口部２０ａを有しており、この開口部２０ａに現像剤搬送部２１を設けている。従って、現像槽２０の開口部２０ａが現像剤搬送部２１により塞がれており、この内側が現像剤の貯蔵庫となる。
【００４１】
供給ローラ２３は、現像剤搬送部２１の下端に沿って配置されており、回転自在に支持されて、図示しないモータ等により反時計回りに回転駆動され、現像剤を現像剤搬送部２１のベルト部材３４へと供給する。この現像剤の供給に際し、供給ローラ２３は、その電位及び現像剤への圧接により現像剤を帯電しつつ、ベルト部材３４に付着する現像剤の層厚を規制する。この供給ローラ２３の材質としては、例えばシリコーン、ウレタン、ＥＰＤＭ（エチレン−プロピレン−ジエン−メチレン共重合体）等のソリッドゴムや発泡ゴム等を挙げることができる。また、供給ローラ用バイアス直流電圧を供給ローラ２３に印加して、供給ローラ２３の電位を設定することから、カーボンブラックやイオン導電剤等を添加して、供給ローラ２３に導電性を付与しても良い。
【００４２】
ブレード２６は、薄板状であって、供給ローラ２３に摺接し、ブレード用バイアス直流電圧を印加され、現像剤の電荷量や層厚を規制する。このブレード２６の材質は、供給ローラ２３と同じであっても、また異なっていても構わない。
【００４３】
回収ローラ２５は、現像剤搬送部２１の上端に沿って配置されており、回転自在に支持されて、図示しないモータ等により反時計回りに回転駆動される。回収ローラ２５は、現像剤搬路２１のベルト部材３４に摺接して、ベルト部材３４を除電したり、ベルト部材３４上の残留現像剤を掻き取って、ベルト部材３４をクリーニングし、現像剤を現像槽２０へと回収する。この回収ローラ２５の材質は、特に限定されないが、例えば供給ローラ２３と同じで構わない。
【００４４】
尚、供給ローラ２３及び回収ローラ２５を現像剤搬送部２１に対して非接触としたり、これらのローラの代わりに、回転しないそれぞれの部材を適用しても構わない。
【００４５】
現像剤搬送部２１は、現像槽２０の開口部２０ａに固定された支持体３１と、現像槽２０の内側に設けられた駆動ローラ３２及び従動ローラ３３と、支持体３１、駆動ローラ３２、及び従動ローラ３３の外周に掛け渡されたベルト部材３４と、感光体ドラム１１に対向する支持体３１の表面に設けられた搬送体３５とを備えている。
【００４６】
支持体３１は、感光体ドラム１１側で、若干傾斜した緩やかな曲面を描いており、この曲面に沿って搬送体３５を設け、搬送体３５を感光体ドラム１１に対向させている。この支持体３１の材質としては、ＡＢＳ（アクリロニトリルブタジエンスチレン：Ａｃｒｙｌｏｎｉｔｌｅ−Ｂｕｔａｄｉｅｎｅ−Ｓｔｙｒｅｎｅ）樹脂等を挙げることができる。
【００４７】
尚、感光体ドラム１１側の支持体３１の面が半円弧状であっても、略平面状であっても構わない。
【００４８】
駆動ローラ３２は、図示しない駆動機構により所定の周速度で回転駆動され、ベルト部材３４を同速度で回転移動する。この駆動ローラ３２は、例えばＳＵＳや鉄等の金属ローラ、あるいは金属ローラの周囲をゴム、フィルム、スポンジ等により被ったものである。
【００４９】
従動ローラ３３は、ベルト部材３４が回転移動するときにのみ、図示しないバネ等により駆動ローラ３２に押し付けられて、駆動ローラ３２との間にベルト部材３４を挟み込んだ状態で、駆動ローラ３２と共に回転し、ベルト部材３４を滑らかに回転移動させる。この従動ローラ３３も、駆動ローラ３２と同様に、例えばＳＵＳや鉄等の金属ローラ、あるいは金属ローラの周囲をゴム、フィルム、スポンジ等により被ったものである。
【００５０】
尚、従動ローラ３３の代わりに、もう１つの駆動ローラを設け、２つの駆動ローラを相互に押し付けて、これらの駆動ローラ間にベルト部材３４を挟み込んでも構わない。
【００５１】
ベルト部材３４は、搬送体３５の帯電を防止したり、現像剤が搬送体３５に固着することを防止する。このベルト部材３４の厚みは、後で述べる搬送体３５上の各電極間ピッチに応じて５μｍ乃至２００μｍに設定され、望ましくは１０μｍ乃至１００μｍに設定される。このベルト部材３４の材質としては、ポリイミド、ＰＥＴ（ポリエチレンテレフタレート）、ポリ４フッ化エチレン、ポリフッ化エチレンプロピレン、ＰＴＦＥ（ポリテトラフルオロエチレン）等の有機絶縁材料、シリコン、イソプレン、ブタジエン等のゴム材料等を挙げることができる。
【００５２】
搬送体３５は、例えば図３に示す様にポリイミド等からなる厚み２５μｍ程度の基材３５ａ上に、発生電極体（ＦＰＣベルト）を形成し、その上にポリイミド等からなる厚み２５μｍ程度の表面保護層３５ｂを積層した構造を有する。発生電極体（ＦＰＣベルト）は、厚み１８μｍ程度の銅箔からなり、複数の進行波発生電極３６を形成する。
【００５３】
尚、図３においては、搬送体３５を簡略化して平板状のものとして示している。
【００５４】
搬送体３５において、各進行波発生電極３６は、例えば約４０μｍ〜２５０μｍの幅を有し、５０ｄｐｉ〜３００ｄｐｉ（約５００μｍ〜約８５μｍ）の間隔を開けて平行に配置され、支持体３１の下端から上端にかけて設けられている。また、各進行波発生電極３６は、３本又は４本程度を１組として、複数組に分けられている。そして、各組毎に、多相の交流電圧がそれぞれの進行波発生電極３６に印加される。例えば、４本の各進行波発生電極３６を１組とし、４相の交流電圧を印加する場合は、図４（ａ）〜（ｄ）に示す様な４相の交流電圧Ｖａｃ１〜Ｖａｃ４が多相交流電源３７から４本の各進行波発生電極３６にそれぞれ印加される。これにより、進行波電界が形成される。
【００５５】
各進行波発生電極３６を支持体３１の下端から上端にかけて設けているので、進行波電界が支持体３１の下端から上端にかけて形成される。この進行波電界は、現像剤を支持体３１の下端から上端へと矢印Ｃの方向に搬送する。４相の交流電圧は、各進行波発生電極３６間で絶縁破壊が発生しない様に、例えば１００Ｖ〜３ｋＶ程度に設定される。また、その周波数は、１００Ｈｚ〜５ｋＨｚ程度に設定される。更に、４相の交流電圧及びその周波数は、各進行波発生電極３６の形状、現像剤の搬送速度、現像剤の性質等に応じて適宜に設定される。
【００５６】
先に述べた様に供給ローラ２３は、現像剤を現像槽２０から現像剤搬送部２１のベルト部材３４へと供給する。そして、進行波電界は、現像剤をベルト部材３４上で搬送体３５の下端から上端へと搬送する。更に、回収ローラ２５は、現像剤をベルト部材３４から現像槽２０へと回収する。
【００５７】
尚、ベルト部材３４上の現像剤の搬送速度は、例えばベルト部材３４上の現像剤を検出する一対の赤外線センサを設け、各赤外線センサによる現像剤のそれぞれの検出時間とそれぞれの検出箇所間の距離に基づいて求めたり、高速度ビデオカメラを用いて計測する方法がある（ＩＳ＆ＴｓＮＩＰ１５：１９９９ＩｎｔｅｒｎａｔｉｏｎａｌＣｏｎｆｅｒｅｎｃｅｏｎＤｉｇｉｔａｌＰｒｉｎｔｉｎｇＴｅｃｈｎｏｌｏｇｉｅｓｐ．２６２−２６５を参照）。
【００５８】
一方、多相交流電源３７の４相の交流電圧Ｖａｃ１〜Ｖａｃ４に対して現像用バイアス直流電源３８の現像用バイアス直流電圧を重畳しており、感光体ドラム１１と搬送体３５が接近した現像領域Ａ（図１に示す）で、現像用バイアス直流電圧による現像電界を形成している。この現像電界により現像剤がベルト部材３４から感光体ドラム１１上の静電潜像へと飛翔し、現像剤が静電潜像に付着して、現像剤像が形成される。
【００５９】
さて、本実施形態では、ベルト部材３４として、図５に示す様に現像剤の搬送方向に連なる複数の領域３４ａ，３４ｂ，３４ｃに区分され、各領域３４ａ，３４ｂ，３４ｃの体積抵抗値が相互に異なり、各領域３４ａ，３４ｂ，３４ｃのいずれかが搬送体３５に重ねられて接するものを適用している。このベルト部材３４は、各領域３４ａ，３４ｂ，３４ｃに対応するそれぞれのベルト部材の各端部を接着剤等により相互に接着したり、該各端部を重ね合わせて高温圧着することにより形成される。
【００６０】
また、ベルト部材３４近傍の温度を検出する温度センサ４１、及びベルト部材３４の駆動ローラ３２を駆動制御する制御部４２を設けている。制御部４２は、温度センサ４１により検出された温度に応じて、駆動ローラ３２を回転駆動して、ベルト部材３４を回転移動させ、ベルト部材３４の各領域３４ａ，３４ｂ，３４ｃのいずれかを搬送体３５に重ねる。
【００６１】
ここで、ベルト部材３４の温度をＴとすると、Ｔ＜１５℃となる低温範囲、１５℃≦Ｔ≦２８℃となる常温範囲、及びＴ＞２８℃となる高温範囲を定める。また、ベルト部材３４の各領域３４ａ，３４ｂ，３４ｃとして、常温一定で、１０×１０＾１４Ωｃｍ、１０×１０＾１３Ωｃｍ、１０×１０＾１５Ωｃｍという各体積抵抗値を有するそれぞれの材質のものを適用する。
【００６２】
ベルト部材３４の体積抵抗値は、先に述べた様に有機絶縁材料やゴム材料等であり、ベルト部材３４の温度Ｔが低温範囲から常温範囲に変動したり、常温範囲から高温範囲へと変動すると、ベルト部材３４の体積抵抗値が１桁低下する。あるいは、ベルト部材３４の温度Ｔが高温範囲から常温範囲に変動したり、常温範囲から低温範囲へと変動すると、ベルト部材３４の体積抵抗値が１桁上昇する。従って、ベルト部材３４の温度Ｔが常温範囲に入るときには、ベルト部材３４の領域３４ａの体積抵抗値が約１０×１０＾１４Ωｃｍに維持され、ベルト部材３４の温度Ｔが低温範囲に入るときには、ベルト部材３４の領域３４ｂの体積抵抗値が約１０×１０＾１４Ωｃｍに上昇し、ベルト部材３４の温度Ｔが高温範囲に入るときには、ベルト部材３４の領域３４ｃの体積抵抗値が約１０×１０＾１４Ωｃｍに低下する。
【００６３】
そこで、制御部４２は、温度センサ４１により検出されたベルト３４近傍の温度が常温範囲に入れば、駆動ローラ３２を回転駆動して、ベルト部材３４を回転移動させ、ベルト部材３４の領域３４ａを搬送体３５に重ね、また検出されたベルト３４近傍の温度が低温範囲に入れば、ベルト部材３４を回転移動させて、ベルト部材３４の領域３４ｂを搬送体３５に重ね、更に検出されたベルト３４近傍の温度が高温範囲に入れば、ベルト部材３４を回転移動させて、ベルト部材３４の領域３４ｃを搬送体３５に重ねる。これにより、ベルト３４の温度Ｔが変動しても、搬送体３５に重なるベルト部材３４の領域の体積抵抗値が約１０×１０＾１４Ωｃｍと常に一定となる。
【００６４】
こうして搬送体３５に重なるベルト部材３４の領域の体積抵抗値を一定に保持すると、ベルト部材３４を透過する進行波電界が安定化し、ベルト部材３４上での現像剤の搬送量が安定化する。
【００６５】
実験により、搬送体３５に重なるベルト部材３４の領域の体積抵抗値が約１０×１０＾１４Ωｃｍのときに、各進行波発生電極３６に印加される４相の交流電圧を１００Ｖ〜３ＫＶに設定すると、感光体ドラム１１上のべた領域で現像剤濃度が１．３５以上になり、べた領域としての現像剤濃度を確保し得ることが分かった。
【００６６】
すなわち、本実施形態では、現像用バイアス直流電圧を１００Ｖ〜３ＫＶに設定することを前提として、搬送体３５に重なるベルト部材３４の領域の体積抵抗値を約１０×１０＾１４Ωｃｍと常に一定に維持し、これによりベルト部材３４上での現像剤の搬送量を安定化させ、現像むら及び画像の濃度むらを防止している。
【００６７】
尚、搬送体３５に重なるベルト部材３４の領域の体積抵抗値を約１０×１０＾１４Ωｃｍに維持しているが、現像剤の種類やベルト部材の材質等に応じて、この一定に維持される体積抵抗値を変更しても構わない。
【００６８】
ところで、ベルト３４の温度に応じて、ベルト部材３４を回転移動させる代わりに、複数の印字モードのいずれが選択されたかに応じて、ベルト部材３４を回転移動させ、ベルト部材３４の各領域３４ａ，３４ｂ，３４ｃのいずれかを搬送体３５に重ねても良い。ただし、ベルト３４の温度が略一定であることを前提とする。
【００６９】
ここでは、複数の印字モードとして、通常の濃度となる通常印字モード、高濃度となるテキスト印字モード、及び低濃度となる写真印字モードを設定する。そして、画像形成装置において、ユーザの操作入力により通常印字モードが選択されると、これに応答して制御部４２は、駆動ローラ３２を回転駆動して、ベルト部材３４を回転移動させ、ベルト部材３４の領域３４ａを搬送体３５に重ねる。この状態では、ベルト部材３４の領域３４ａの体積抵抗値が約１０×１０＾１４Ωｃｍであることから、ベルト部材３４を透過する進行波電界が通常のレベルとなり、ベルト部材３４上での現像剤の搬送量が通常となり、画像の濃度が通常のレベルとなる。
【００７０】
また、ユーザの操作入力によりテキスト印字モードが選択されると、これに応答して制御部４２は、ベルト部材３４を回転移動させ、ベルト部材３４の領域３４ｃを搬送体３５に重ねる。この状態では、ベルト部材３４の領域３４ｃの体積抵抗値が約１０×１０＾１５Ωｃｍであることから、ベルト部材３４を透過する進行波電界が高いレベルとなり、ベルト部材３４上での現像剤の搬送量が多くなり、画像の濃度が高くなる。
【００７１】
更に、ユーザの操作入力により写真印字モードが選択されると、これに応答して制御部４２は、ベルト部材３４を回転移動させ、ベルト部材３４の領域３４ｂを搬送体３５に重ねる。この状態では、ベルト部材３４の領域３４ｂの体積抵抗値が約１０×１０＾１３Ωｃｍであることから、ベルト部材３４を透過する進行波電界が低いレベルとなり、ベルト部材３４上での現像剤の搬送量が少なくなり、画像の濃度が低くなる。
【００７２】
この様にベルト部材３４の各領域３４ａ，３４ｂ，３４ｃのいずれかを搬送体３５に重ねることにより、通常印字モード、テキスト印字モード、及び写真印字モードを選択的に設定することができる。従来は、画像の濃度を調節するために、現像領域Ａの現像用バイアス直流電圧を変更したり、露光装置１７から感光体ドラム１１へと出射される光ビームの強度を変更したり、感光体ドラム１１の帯電電位を変更していたが、これらの変更を行なわなくても、ベルト部材３４を移動させるだけで、画像の濃度を調節することが可能となる。
【００７３】
一般に、有機絶縁材料やゴム材料等の誘電体フィルムからなるベルト部材３４は、その抵抗値と比誘電率が反比例の関係にある。つまり、ベルト部材３４の絶縁性が高くなる程、誘電率が低くなって１に近づき、ベルト部材３４の絶縁性が低くなる程、誘電率が高くなる（導体に近くなる程、比誘電率が高くなる。金属は数千である。）。
【００７４】
従って、ベルト部材３４の各領域３４ａ，３４ｂ，３４ｃの体積抵抗値が１０×１０＾１４Ωｃｍ、１０×１０＾１３Ωｃｍ、１０×１０＾１５Ωｃｍに基づいて、該各領域３４ａ，３４ｂ，３４ｃの比誘電率を２，３，１と定義することができる。そして、該各領域３４ａ，３４ｂ，３４ｃ別に、ベルト部材３４上の進行波電界に対応するベルト部材３４上の電位Ｖｓを次式（１）から求めることができる。
【００７５】
【数１】

ただし、ｅが搬送体３５の各進行波発生電極３６の印加電圧、ｄｇがベルト部材３４上の空隙、ｄ１が搬送体３５の表面保護層３５ｂの厚み、ｄ２がベルト部材３４の厚み、ｅ１が搬送体３５の表面保護層３５ｂの比誘電率、ｅ２がベルト部材３４の該各領域３４ａ，３４ｂ，３４ｃの比誘電率である。
例えば、ｅ＝１０００Ｖ、ｄｇ＝１００μｍ、ｄ１＝２５μｍ、ｄ２＝５０μｍ、ｅ１＝２とする。更に、先に述べた様に領域３４ａの比誘電率ｅ２＝２とすると、ベルト部材３４上の電位Ｖｓ＝２７２Ｖとなり、領域３４ｂの比誘電率ｅ２＝３とすると、ベルト部材３４上の電位Ｖｓ＝２５０Ｖとなり、領域３４ｃの比誘電率ｅ２＝１とすると、ベルト部材３４上の電位Ｖｓ＝３３３Ｖとなる。
また、ベルト部材３４上の電位Ｖｓがベルト部材３４上の電界Ｅに比例するため（Ｖｓ＝Ｅ＊ｄ）、電位Ｖｓが低くなる程、進行波電界も低くなる。
この様な関係から、ベルト部材３４の絶縁性が高くなる程、誘電率が低くなって、進行波電界のレベルが高くなり、またベルト部材３４の絶縁性が低くなる程、誘電率が高くなって、進行波電界のレベルが低くなることは明らかである。
【００７６】
このため、ベルト部材３４の各領域３４ａ，３４ｂ，３４ｃのいずれかを搬送体３５に重ねることにより、ベルト部材３４上の進行波電界のレベルを調節して、ベルト部材３４上での現像剤の搬送量を調節し、通常印字モード、テキスト印字モード、及び写真印字モードを選択的に設定することができる。
【００７７】
図６は、本発明の現像装置の第２実施形態を簡略化して示す側面図である。本実施形態の現像装置１２Ａでは、図２及び図５の装置におけるベルト部材３４の代わりに、ベルト部材３４Ａを用い、ベルト部材３４Ａの表面電位を検出する電位検出センサ５１を設けている。ベルト部材３４Ａは、全周にわたって、厚み、体積抵抗値、及び比誘電率等が一様なものである。また、現像領域Ａの下流側に電位検出センサ５１を設置しているが、非現像領域であれば、如何なる箇所に電位検出センサ５１を設置しても構わない。
【００７８】
尚、図６の現像装置１２Ａの細部は、図２の装置と同様であり、現像槽２０、現像剤搬送部２１、供給ローラ２３、ブレード２６、ミキシングパドル２４、及び回収ローラ２５等を備えている。
【００７９】
本実施形態の現像装置１２Ａでは、電位検出センサ５１の検出出力を制御部４２に加えている。制御部４２は、電位検出センサ５１の検出出力によって示されるベルト部材３４Ａの表面電位と予め設定された閾値を比較し、ベルト部材３４Ａの表面電位が閾値に達すると、駆動ローラ３２を回転駆動して、ベルト部材３４Ａを回転移動させ、搬送体３５に重なり合うベルト部材３４Ａの領域を更新する。
【００８０】
ベルト部材３４Ａの表面電位が上昇すると、ベルト部材３４Ａに対する現像剤の付着力が上昇し、ベルト部材３４Ａから感光体ドラム１１への現像剤の供給量が不足して、現像むら及び画像の濃度むらが発生する。また、ベルト部材３４Ａの摩擦帯電によりベルト部材３４Ａ近傍の電界強度が５．０×１０＾６Ｖ／ｍになると、ベルト部材３４Ａ上での現像剤の搬送が不安定になり、やはり現像むら及び画像の濃度むらが発生する。例えば、ベルト部材３４Ａの厚みをｔとし、ベルト部材３４Ａの表面電位をＶｓとし、ベルト部材３４Ａ近傍の電界強度をＥｓとすると、電界強度Ｅｓを次式（２）で表わすことができる。
【００８１】
Ｅｓ＝Ｖｓ／ｔ ……（２）
上式（２）によれば、ベルト部材３４Ａの厚みｔが２０μｍであって、ベルト部材３４Ａの表面電位が１２０Ｖに達したときに、ベルト部材３４Ａ近傍の電界強度Ｅｓ＝Ｖｓ／ｔ＝６．０×１０＾６Ｖ／となり、ベルト部材３４Ａ上での現像剤の搬送が不安定になる。
【００８２】
そこで、ベルト部材３４Ａの表面電位と比較される閾値として、電界強度５．０×１０＾６Ｖ／ｍとベルト部材３４Ａの厚みｔ＝２０μｍとの積（Ｅｓ・ｔ）を設定し、電位検出センサ５１の検出出力によって示されるベルト部材３４Ａの表面電位Ｖｓが該閾値に達したときに、ベルト部材３４Ａを回転移動させ、搬送体３５に重なり合うベルト部材３４Ａの領域を更新する。これにより、未帯電のベルト部材３４Ａの領域が搬送体３５に重なり合い、ベルト部材３４Ａ上での現像剤の搬送量が安定化し、現像むら及び画像の濃度むらが防止される。
【００８３】
一方、ベルト部材３４Ａの表面電位は、記録用紙の印字枚数の増加に伴って上昇して行く。このため、ベルト部材３４Ａの表面電位を検出する代わりに、記録用紙の印字枚数を計数し、この計数値が予め設定された閾値に達したときに、ベルト部材３４Ａを回転移動させ、搬送体３５に重なり合うベルト部材３４Ａの領域を更新しても良い。記録用紙の印字枚数と比較される閾値は、ベルト部材３４Ａの厚み、搬送体３５の各進行波発生電極３６の印加電圧、感光体ドラム１１の表面電位等に応じて設定される。
【００８４】
また、搬送体３５に重なり合うベルト部材３４Ａの領域を更新するために、ベルト部材３４Ａを回転移動させるタイミングは、記録用紙の非現像時に行なう。これは、記録用紙の現像時にベルト部材３４Ａを回転移動させると、ベルト部材３４Ａの下流側のみが更新された状態が発生し、このときにベルト部材３４Ａの上流側と下流側間で表面電位の差が生じて、現像むらが生じるためである。
【００８５】
ベルト部材３４Ａの領域は、搬送体３５から一旦外れても、ベルト部材３４Ａの領域の更新の繰り返しにより搬送体３５に再び重ねられる。従って、ベルト部材３４Ａの領域が繰り返し使用されることになるが、未使用期間中に、ベルト部材３４Ａの領域の電位が自然放電により低下したり、該領域の電位が接地部材を介しての放電により低下し、該領域の電位が０Ｖとなり、該領域の電位履歴が消去されてから、該領域が搬送体３５に再び重ねられることになる。接地部材としては、駆動ローラ３２や従動ローラ３３等がある。
【００８６】
ベルト部材３４Ａは、先に述べた様に全周にわたって、厚み、体積抵抗値、及び比誘電率等が一様なものである。例えば、体積抵抗値Ｒは、１０×１０＾１０Ωｃｍ≦Ｒ≦１０×１０＾１４Ωｃｍの範囲で設定するのが好ましい。体積抵抗値Ｒが１０×１０＾１０Ωｃｍ未満である場合は、ベルト部材３４Ａを透過する進行波電界のレベルが低下し、ベルト部材３４Ａ上での現像剤の搬送量が少なくなって、画像の濃度が低くなってしまう（べた領域で現像剤濃度が１．３５未満となる）。また、体積抵抗値Ｒが１０×１０＾１４Ωｃｍよりも高い場合は、帯電したベルト部材３４Ａの電荷が接地点に流れず、ベルト部材３４Ａの領域の電位が長期間高く維持され続けてしまい、ベルト部材３４Ａ上での現像剤の搬送量が不安定となり、現像むら及び画像の濃度むらが発生する。
【００８７】
次の表１及び表２は、ベルト部材３４Ａの体積抵抗値Ｒに対する画像濃度及び除電性能を実験により評価して示すものである。これらの表１及び表２からも明らかな様にベルト部材３４Ａの体積抵抗値Ｒを１０×１０＾１０Ωｃｍ≦Ｒ≦１０×１０＾１４Ωｃｍの範囲で設定するのが好ましい。
【００８８】
【表１】

【００８９】
【表２】

また、ベルト部材３４Ａの比誘電率ｅは、２≦ｅ≦５の範囲で設定するのが好ましい。比誘電率ｅが２未満である場合は、体積抵抗値Ｒが高すぎる場合と同様に、帯電したベルト部材３４Ａの電荷が接地点に流れず、ベルト部材３４Ａ上での現像剤の搬送量が不安定となり、現像むら及び画像の濃度むらが発生する。また、比誘電率ｅが５よりも高い場合は、体積抵抗値Ｒが低すぎる場合と同様に、ベルト部材３４Ａを透過する進行波電界のレベルが低下し、ベルト部材３４Ａ上での現像剤の搬送量が少なくなって、画像の濃度が低くなってしまう（べた領域で現像剤濃度が１．３５未満となる）。その上、比誘電率ｅが５よりも高い場合は、帯電によりベルト部材３４Ａの表面電位が上昇することがなく、このために先に述べた様にベルト部材３４Ａの表面電位が閾値まで上昇したときに、搬送体３５に重なり合うベルト部材３４Ａの領域を更新するのであれば、搬送体３５に重なり合うベルト部材３４Ａの領域が更新されることがなくなり、ベルト部材３４Ａの特定の領域だけが使用され続け、該特定の領域でベルト部材３４Ａの亀裂や摩耗が発生する。
【００９０】
次の表３及び表４は、ベルト部材３４Ａの比誘電率ｅに対する除電性能及びベルト部材３４Ａの劣化特性を実験により評価して示すものである。これらの表３及び表４からも明らかな様にベルト部材３４Ａの比誘電率ｅを２≦ｅ≦５の範囲で設定するのが好ましい。
【００９１】
【表３】

【００９２】
【表４】

また、ベルト部材３４Ａの厚みｔは、２０μｍ≦ｔ≦１００μｍ範囲で設定するのが好ましい。厚みｔが２０μｍ未満の場合は、ベルト部材３４Ａの強度が低下し、耐久性に劣る。また、厚みｔが１００μｍよりも厚い場合は、ベルト部材３４Ａの剛性が高くなり過ぎて、ベルト部材３４Ａと搬送体３５間の密着性が低下したり、駆動ローラ３２や従動ローラ３３によるベルト部材３４Ａの駆動にむらが発生する。
【００９３】
次の表５及び表６は、ベルト部材３４Ａの厚みｔに対するベルト部材３４Ａの強度及びベルト部材３４Ａと搬送体３５間の密着性を実験により評価して示すものである。これらの表５及び表６からも明らかな様にベルト部材３４Ａの厚みｔを２０μｍ≦ｔ≦１００μｍ範囲で設定するのが好ましい。
【００９４】
【表５】

【００９５】
【表６】

ここで、上記表１〜表４に従って、体積抵抗値Ｒを１０×１０＾１０Ωｃｍ≦Ｒ≦１０×１０＾１４Ωｃｍの範囲で設定し、比誘電率ｅを２≦ｅ≦５の範囲で設定した場合は、ベルト部材３４Ａが帯電しても、自然放電や接地部材を介しての放電が速やかに行なわれ、搬送体３５に重なり合うベルト部材３４Ａの領域全体の電位が常に安定化する。このため、記録用紙の非現像時にだけ、ベルト部材３４Ａを回転移動させて、搬送体３５に重なり合うベルト部材３４Ａの領域を更新する代わりに、記録用紙の現像時に、ベルト部材３４Ａを現像剤の搬送速度よりも十分に遅い速度で回転移動させて、搬送体３５に重なり合うベルト部材３４Ａの領域を徐々に更新しても、該領域全体の電位が常に安定化し、ベルト部材３４Ａ上での現像剤の搬送量が安定化し、現像むら及び画像の濃度むらが防止される。ベルト部材３４Ａの回転移動速度は、現像剤の搬送速度の１／１００〜１／１０程度に設定される。
【００９６】
特に、１５℃〜２８℃の室内に画像形成装置を設置することを前提とすると、体積抵抗値Ｒを１０×１０＾１０Ωｃｍ≦Ｒ≦１０×１０＾１２Ωｃｍの範囲で設定するのが最適である。体積抵抗値Ｒが１０×１０＾１０Ωｃｍ未満である場合は、ベルト部材３４Ａを透過する進行波電界のレベルが低下し、ベルト部材３４Ａ上での現像剤の搬送量が少なくなって、画像の濃度が低くなってしまう。また、体積抵抗値Ｒが１０×１０＾１２Ωｃｍよりも高い場合は、帯電したベルト部材３４Ａの電位が低下するのに時間を要してしまい、ベルト部材３４Ａの上流側と下流側間で電位差が生じ、現像むら及び画像の濃度むらが発生する。
【００９７】
ただし、体積抵抗値Ｒを１０×１０＾１０Ωｃｍ≦Ｒ≦１０×１０＾１２Ωｃｍの範囲で設定したとしても、劣悪な使用環境や数百枚の連続印字等の過酷な使用条件では、搬送体３５に重なり合うベルト部材３４Ａの領域の電位が不安定になり、ベルト部材３４Ａ上での現像剤の搬送量が不安定となる。このため、ベルト部材３４Ａを十分に遅い速度で回転移動させて、搬送体３５に重なり合うベルト部材３４Ａの領域を徐々に更新するときの条件を特定しておき、この条件から外れるときには、ベルト部材３４Ａの表面電位や記録用紙の印字枚数に応じて、記録用紙の非現像時に、搬送体３５に重なり合うベルト部材３４Ａの領域を更新する。これにより、ベルト部材３４Ａ上での現像剤の搬送量を常に安定化させることが可能になる。
【００９８】
尚、本発明は上記各実施形態に限定されるものではなく、多様に変形することができる。例えば、感光体ドラム１１の代わりに、感光体ベルト等を用いても良い。更に、電子写真方式の画像形成装置に限定されず、イオンフロー方式の様に誘電体上に静電潜像を直接形成する画像形成装置や、トナージェット方式の様に複数の開口部を有する電極に電圧を印加して、空間に静電潜像を形成し、現像剤を記録媒体に飛翔させて画像形成を直接行なう画像形成装置にも、本発明の現像装置を適用することができる。
【００９９】
【発明の効果】
以上説明した様に本発明によれば、ベルト部材が現像剤の搬送方向に連なる複数の領域に区分され、各領域の抵抗値が相互に異なる。そして、ベルト部材が現像剤の搬送方向に適宜に移動されて、ベルト部材の各領域のいずれかが搬送路に重ねられる。このため、各領域の抵抗値のいずれかを選択して、この選択した抵抗値の領域を搬送路に重ねることができる。これにより、現像剤の搬送面をリフレッシュすると同時に、進行波電界の変動を抑えることができ、ベルト部材上での現像剤の搬送量を安定化して、現像むら及び画像の濃度むらを防止することができる。
【０１００】
また、現像が行われていないときに移動されて、搬送路に重ねられる該ベルト部材の領域を更新している。このため、現像剤の搬送面に重なるベルト部材の領域が一度に完全にリフレッシュされることになり、これにより進行波電界の変動を抑え、ベルト部材上での現像剤の搬送量を安定化させ、現像むら及び画像の濃度むらを防止することができる。
【０１０１】
更に、ベルト部材が現像剤の搬送速度よりも低い移動速度で常に移動させる場合は、ベルト部材の抵抗値を１０×１０＾１０Ωｃｍ〜１０×１０＾１４Ωｃｍに設定して、ベルト部材の帯電を防止し、ベルト部材上で現像剤を搬送するのに必要な進行波電界を十分に維持している。
【図面の簡単な説明】
【図１】本発明の現像装置の第１実施形態を適用した画像形成装置を示す側面図である。
【図２】第１実施形態の現像装置を示す側面図である。
【図３】図２の現像装置における搬送体を部分的に拡大して示す図である。
【図４】（ａ）〜（ｄ）は、図２の現像装置における搬送体の各進行波発生電極に印加される４相の交流電圧波形を示す図である。
【図５】図２の現像装置を簡略化して示す側面図である。
【図６】本発明の現像装置の第２実施形態を簡略化して示す側面図である。
【符号の説明】
１１感光体ドラム
１２現像装置
１３転写装置
１４クリーニング装置
１５除電装置
１６帯電装置
１７露光装置
１８定着装置
２０現像槽
２１現像剤搬送部
２３供給ローラ
２４ミキシングパドル
２５回収ローラ
３１支持体
３２駆動ローラ
３３従動ローラ
３４ベルト
３５搬送体
３６進行波発生電極
３７多相交流電源
３８現像用バイアス直流電源
４１温度センサ
４２制御部
５１電位検出センサ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a developing device that transports a developer by a traveling wave electric field and develops an electrostatic latent image with the developer, and an image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, a developer is once adhered to a belt member, and the developer is conveyed by the belt member and developed, as in the technique described in Patent Document 1, for example. There is a belt developing type in which an agent is supplied from a belt member to an image carrier.
[0003]
In recent years, a non-contact type developing device that transports a developer to the vicinity of an image carrier, flies the developer to an electrostatic latent image on the image carrier, and develops the electrostatic latent image has been developed. Attention has been paid. The non-contact method includes a powder cloud method, a jumping method, a method using an electric field curtain (a traveling wave electric field), and the like.
[0004]
Methods using a traveling wave electric field are described in, for example, Patent Documents 2 and 3 and the like. In these, a large number of electrodes are embedded in a developer transport path, and a multi-phase AC voltage is applied to these electrodes to generate a traveling-wave electric field, and the developer on the transport path is imaged by the traveling-wave electric field. It is transported to the carrier. When the developer is transported to the vicinity of the image carrier, the developer flies to the electrostatic latent image on the image carrier and adheres to the electrostatic latent image. Thereby, the electrostatic latent image on the image carrier is developed.
[0005]
However, in Patent Literature 2 and Patent Literature 3, static elimination or cleaning of the transport path is not particularly performed. For this reason, the traveling-wave electric field is disturbed by the charge in the transport path, or the developer adheres to the transport path. These adversely affect the developing electric field between the image carrier and the transport path and the transport of the developer, causing uneven development and uneven image density.
[0006]
For this reason, the inventors of the present invention provide an endless belt member that is superimposed on the conveyance path, conveys the developer on the endless belt, and moves the endless belt to transfer the developer. The developing device has been proposed in which the transfer surface is changed and refreshed, and the transfer surface is neutralized and cleaned, thereby preventing charging of the transfer surface and sticking of the developer (see Patent Document 4 and the like).
[0007]
In the developing device of Patent Document 4, the moving speed of the belt member is set sufficiently lower than the conveying speed of the developer, the conveying of the developer is performed by the traveling wave electric field, and only the refreshing of the conveying surface is performed by the belt member. ing. Therefore, this belt member is clearly different from the belt member of the belt developing system.
[0008]
[Patent Document 1]
JP-A-6-308813
[Patent Document 2]
Japanese Patent Publication No. 5-31146
[Patent Document 3]
Japanese Patent Publication No. 5-31147
[Patent Document 4]
Japanese Patent Application No. 2000-283087
[0009]
[Problems to be solved by the invention]
However, in the developing device described in Patent Document 4, even if the charging of the conveyance path and the sticking of the developer can be prevented, the traveling wave electric field passes through the belt member, so that the resistance value of the belt member changes and Due to the charging of the member, the traveling wave electric field became unstable, and the transport amount of the developer on the belt member was not stabilized, resulting in uneven development and uneven image density.
[0010]
Therefore, the present invention has been made in view of the above-described conventional problems, and has as its object to provide a developing device and an image forming apparatus that do not cause uneven development and uneven density due to a belt member. And
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention includes a transport path having a plurality of electrodes, and a belt member superimposed on the transport path, and applies a multi-phase AC voltage to each electrode of the transport path to form a traveling wave. An electric field is formed, the developer is conveyed to the image carrier on the belt member by the traveling wave electric field, and the developer is supplied to the image carrier to develop the electrostatic latent image on the image carrier. In the developing device, the belt member is divided into a plurality of regions connected in the direction of transport of the developer, each region has a different resistance value, and any one of the regions is overlapped on the transport path.
[0012]
According to the present invention having such a configuration, the belt member is divided into a plurality of regions connected in the developer conveying direction, and the resistance values of the respective regions are different from each other. Then, the belt member is appropriately moved in the developer conveying direction, and any one of the regions of the belt member is overlapped on the conveying path. For this reason, it is possible to select any one of the resistance values of the respective regions and to overlap the region of the selected resistance value on the transport path. This makes it possible to refresh the developer transport surface and at the same time suppress the level fluctuation of the traveling wave electric field on the belt member, stabilize the transport amount of the developer on the belt member, and develop uneven development and image density. Unevenness can be prevented.
[0013]
Further, in the present invention, the belt member is divided into three regions, and the resistance value of each region at a constant temperature is different from each other by one digit.
[0014]
The temperature near the belt member varies according to the temperature near the belt member. For this reason, the resistance value of the resistance value of each area of the belt member is changed by one digit, and depending on whether the temperature near the belt member falls within the high temperature range, the normal temperature range, or the low temperature range, By superposing this on the conveying surface of the developer, the fluctuation of the resistance value of the belt member region overlapping the conveying surface can be suppressed.
[0015]
Further, in the present invention, the temperature detecting means for detecting the temperature in the vicinity of the belt member, and the belt member is moved according to the temperature detected by the temperature detecting means, and any one of the regions of the belt member is overlapped on the transport path. Control means.
[0016]
As described above, if the temperature near the belt member is detected and the belt member is moved according to the detected temperature, even if the temperature near the belt member fluctuates, the belt member area that overlaps the developer conveyance surface is changed. Of the resistance value can be suppressed.
[0017]
Further, in the present invention, a mode selecting means for selecting any one of a plurality of printing modes, and the belt member is moved according to the printing mode selected by the mode selecting means, and any one of the respective regions of the belt member is moved. Control means for superimposing on the transport path.
[0018]
The plurality of printing modes include, for example, a mode for developing a text, a mode for developing a photographic image, and the like. In the former mode, darker development is preferred, and in the latter mode, lighter development is preferred. Therefore, the belt member is moved in accordance with the selected printing mode, the resistance value of the belt member region overlapping the developer conveying surface is appropriately set, and the level of the traveling wave electric field on the belt member is adjusted. Thus, the amount of the developer transported on the belt member is changed to adjust the developing density.
[0019]
Next, the present invention includes a transport path having a plurality of electrodes, and a belt member superimposed on the transport path, applying a polyphase AC voltage to each electrode of the transport path to form a traveling wave electric field, In a developing device which transports a developer to an image carrier on a belt member by the traveling wave electric field and supplies the developer to the image carrier, the electrostatic latent image on the image carrier is developed. The member is stopped when development is being performed and moved when development is not being performed to update the area of the belt member that overlaps the transport path.
[0020]
According to the present invention having such a configuration, the belt member is moved when development is not being performed, and the area of the belt member that is superimposed on the transport path is updated. For this reason, the region of the belt member overlapping the developer conveying surface is completely refreshed at a time. Thus, the fluctuation of the traveling wave electric field can be suppressed, the amount of the developer transported on the belt member can be stabilized, and uneven development and uneven image density can be prevented.
[0021]
Further, in the present invention, a counting means for counting the number of developments of the electrostatic latent image, and when the number of developments counted by the counting means reaches a preset threshold, the belt member is moved and overlapped on the transport path. Control means for updating the area of the belt member.
[0022]
Here, as the number of times of development of the electrostatic latent image increases, the charge amount in the region of the belt member overlapping with the developer transport surface increases, so that when the number of times of development reaches the threshold, the belt member is moved. The area of the belt member to be superimposed on the transport path is updated.
[0023]
Further, in the present invention, the potential detecting means for detecting the potential of the belt member, and when the potential detected by the potential detecting means reaches a preset threshold, the belt member is moved, and the belt Control means for updating the region of the member.
[0024]
As described above, when the potential of the belt member superimposed on the transport path reaches the threshold value, that is, when the charge amount increases, the belt member may be moved to update the area of the belt member superimposed on the transport path.
[0025]
Next, the present invention includes a transport path having a plurality of electrodes, and a belt member superimposed on the transport path, applying a polyphase AC voltage to each electrode of the transport path to form a traveling wave electric field, In a developing device which transports a developer to an image carrier on a belt member by the traveling wave electric field and supplies the developer to the image carrier, the electrostatic latent image on the image carrier is developed. The member is moved at a moving speed lower than the conveying speed of the developer, and the resistance value of the belt member is 10 × 10 ＾ 10 Ωcm to 10 × 10 ＾ 14 Ωcm.
[0026]
Even when the belt member is constantly moved at a lower moving speed than the developer conveying speed, the belt member can be prevented from being charged by setting the resistance value of the belt member to 10 × 10 ＾ 10Ωcm to 10 × 10 ＾ 14Ωcm. Therefore, the traveling wave electric field required for transporting the developer on the belt member can be sufficiently maintained.
[0027]
In the present invention, the relative permittivity of the belt member is 2 to 5.
[0028]
If the relative dielectric constant of the belt member is maintained at 2 to 5, the charging of the belt member can be prevented, and the potential of the belt member can be appropriately maintained.
[0029]
Further, in the present invention, the thickness of the belt member is 20 μm to 100 μm.
[0030]
When the thickness of the belt member is set to 20 μm to 100 μm, both flexibility and strength of the belt member can be obtained.
[0031]
Next, the image forming apparatus of the present invention includes the developing device of the present invention.
[0032]
Such an image forming apparatus of the present invention can also achieve the same functions and effects as those of the developing apparatus of the present invention.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0034]
FIG. 1 is a side view showing an image forming apparatus to which a first embodiment of the developing device of the present invention is applied. The image forming apparatus forms an image by an electrophotographic method. A developing device 12, a transfer device 13, a cleaning device 14, a static elimination device 15, a charging device 16, an exposure device 17, etc. are formed around a photosensitive drum 11. Are arranged in order from the upstream side in the rotation direction of the photosensitive drum 11. Further, a fixing device 18 is arranged on the downstream side in the transport direction of the recording paper P. The recording paper P passes between the photosensitive drum 11 and the transfer device 13 and is conveyed to the fixing device 18.
[0035]
In this image forming apparatus, the surface of the photosensitive drum 11 is uniformly charged by the charging device 16 while rotating the photosensitive drum 11 in the direction of arrow B. The light beam emitted from the exposure device 17 to the photosensitive drum 11 is modulated according to print data indicating an image, and the surface of the photosensitive drum 11 is scanned by the light beam. Form a latent image. Further, the developer is adhered to the electrostatic latent image by the developing device 12 to form a developer image, and the developer image is transferred from the photosensitive drum 11 to the recording paper P such as PPC paper by the transfer device 13. The fixing device 18 fixes the developer image on the recording paper P by heating and pressing. Thereafter, the residual developer on the photoconductor drum 11 is removed by the cleaning device 14 to clean the photoconductor drum 11, and the residual charge on the surface of the photoconductor drum 11 is discharged by the discharging device 15.
[0036]
The photoconductor drum 11 has a thin-film photoconductive layer made of amorphous silicon (a-Si), selenium (Se), organic optical semiconductor (OPC), or the like formed on the outer periphery of a metal drum such as aluminum. .
[0037]
The charging device 16 includes, for example, a charging wire such as a tungsten wire, a metal shield plate, a corona charger formed of a grid plate, or a charging roller or a charging brush. The exposure device 17 includes a semiconductor laser, a light emitting diode, and a light beam scanning mechanism that emit a light beam. The transfer device 13 includes a corona charger, a charging roller, a charging brush, and the like. The cleaning device 14 is a cleaning blade or the like that slides on the surface of the photosensitive drum 11. The static elimination device 15 is a static elimination lamp or the like.
[0038]
It should be noted that other types may be used as the photosensitive drum 11 and the devices 13 to 18.
[0039]
Next, as shown in FIG. 2, the developing device 12 of the present embodiment includes a developer tank 20 containing a developer, a developer transport unit 21 that generates a traveling wave electric field and transports the developer, and a developer tank. A supply roller 23, a blade 26, a mixing paddle 24 for moving the developer in the developer tank 20 to the supply roller 23 while stirring the developer, and a developer tank 20 from the developer transport section 21 to the developer transport section 21. And a collection roller 25 for collecting the developer.
[0040]
The developing tank 20 has an opening 20 a facing the side of the photosensitive drum 11, and a developer conveying section 21 is provided in the opening 20 a. Therefore, the opening 20a of the developing tank 20 is closed by the developer conveying section 21, and the inside of the opening 20a becomes a developer storage.
[0041]
The supply roller 23 is disposed along the lower end of the developer transport unit 21, is rotatably supported, is driven to rotate counterclockwise by a motor (not shown), and transfers the developer to the belt of the developer transport unit 21. Supply to the member 34. When supplying the developer, the supply roller 23 regulates the layer thickness of the developer attached to the belt member 34 while charging the developer by its potential and pressure contact with the developer. Examples of the material of the supply roller 23 include silicone, urethane, solid rubber such as EPDM (ethylene-propylene-diene-methylene copolymer), foamed rubber, and the like. In addition, since the supply roller 23 is applied with the supply roller bias DC voltage to set the potential of the supply roller 23, carbon black or an ionic conductive agent is added to impart conductivity to the supply roller 23. Is also good.
[0042]
The blade 26 is in the form of a thin plate, is in sliding contact with the supply roller 23, is applied with a bias DC voltage for the blade, and regulates the charge amount and the layer thickness of the developer. The material of the blade 26 may be the same as or different from that of the supply roller 23.
[0043]
The collection roller 25 is disposed along the upper end of the developer transport unit 21, is rotatably supported, and is driven to rotate counterclockwise by a motor (not shown) or the like. The collection roller 25 slides on the belt member 34 of the developer carrying path 21 to remove electricity from the belt member 34, scrape off residual developer on the belt member 34, clean the belt member 34, and remove the developer. Collected in the developing tank 20. The material of the collection roller 25 is not particularly limited, but may be the same as, for example, the supply roller 23.
[0044]
Note that the supply roller 23 and the collection roller 25 may be in non-contact with the developer transport unit 21, or non-rotating members may be used instead of these rollers.
[0045]
The developer transport unit 21 includes a support 31 fixed to the opening 20a of the developing tank 20, a driving roller 32 and a driven roller 33 provided inside the developing tank 20, a support 31, a driving roller 32, A belt member 34 wrapped around the outer periphery of the driven roller 33, and a transport body 35 provided on the surface of the support 31 facing the photosensitive drum 11.
[0046]
The support 31 has a slightly inclined gentle curved surface on the photoconductor drum 11 side, and a carrier 35 is provided along the curved surface, and the carrier 35 is opposed to the photoconductor drum 11. Examples of the material of the support 31 include ABS (acrylonitrile-butadiene-styrene) resin and the like.
[0047]
The surface of the support 31 on the photosensitive drum 11 side may have a semi-circular shape or a substantially planar shape.
[0048]
The drive roller 32 is driven to rotate at a predetermined peripheral speed by a drive mechanism (not shown), and rotates the belt member 34 at the same speed. The drive roller 32 is, for example, a metal roller such as SUS or iron, or a roller covered with rubber, a film, a sponge, or the like.
[0049]
The driven roller 33 is pressed against the driving roller 32 by a spring or the like (not shown) only when the belt member 34 rotates and rotates together with the driving roller 32 while the belt member 34 is sandwiched between the driven roller 33 and the driving roller 32. Then, the belt member 34 is smoothly rotated and moved. Similarly to the drive roller 32, the driven roller 33 is, for example, a metal roller such as SUS or iron, or a metal roller covered with rubber, a film, a sponge, or the like.
[0050]
Note that another driving roller may be provided instead of the driven roller 33, and the two driving rollers may be pressed against each other, and the belt member 34 may be sandwiched between these driving rollers.
[0051]
The belt member 34 prevents the carrier 35 from being charged and prevents the developer from sticking to the carrier 35. The thickness of the belt member 34 is set to 5 μm to 200 μm, and desirably 10 μm to 100 μm, according to the pitch between the electrodes on the carrier 35 described later. Examples of the material of the belt member 34 include organic insulating materials such as polyimide, PET (polyethylene terephthalate), polytetrafluoroethylene, polyfluoroethylene propylene, and PTFE (polytetrafluoroethylene), and rubber materials such as silicon, isoprene, and butadiene. And the like.
[0052]
As shown in FIG. 3, for example, as shown in FIG. 3, a carrier 35 is formed by forming a generating electrode body (FPC belt) on a base material 35a made of polyimide or the like and having a thickness of about 25 μm, and then protecting the surface of the material made of polyimide or the like to a thickness of about 25 μm. It has a structure in which the layers 35b are stacked. The generating electrode body (FPC belt) is made of a copper foil having a thickness of about 18 μm, and forms a plurality of traveling wave generating electrodes 36.
[0053]
In FIG. 3, the carrier 35 is simplified and shown as a flat plate.
[0054]
In the carrier 35, each traveling wave generating electrode 36 has, for example, a width of about 40 μm to 250 μm, and is arranged in parallel at an interval of 50 dpi to 300 dpi (about 500 μm to about 85 μm). It is provided over the upper end. Further, each traveling wave generating electrode 36 is divided into a plurality of sets, with about 3 or 4 electrodes as one set. Then, a polyphase AC voltage is applied to each traveling wave generating electrode 36 for each set. For example, when four traveling wave generating electrodes 36 are used as one set and a four-phase AC voltage is applied, there are many four-phase AC voltages Vac1 to Vac4 as shown in FIGS. A phase alternating current power supply 37 applies a voltage to each of the four traveling wave generating electrodes 36. Thereby, a traveling wave electric field is formed.
[0055]
Since each traveling wave generating electrode 36 is provided from the lower end to the upper end of the support 31, a traveling wave electric field is formed from the lower end to the upper end of the support 31. This traveling wave electric field transports the developer from the lower end to the upper end of the support 31 in the direction of arrow C. The four-phase AC voltage is set to, for example, about 100 V to 3 kV so that dielectric breakdown does not occur between the traveling wave generating electrodes 36. Further, the frequency is set to about 100 Hz to 5 kHz. Further, the four-phase AC voltage and its frequency are appropriately set according to the shape of each traveling wave generating electrode 36, the transport speed of the developer, the properties of the developer, and the like.
[0056]
As described above, the supply roller 23 supplies the developer from the developing tank 20 to the belt member 34 of the developer transport unit 21. The traveling wave electric field transports the developer on the belt member 34 from the lower end to the upper end of the transport body 35. Further, the collecting roller 25 collects the developer from the belt member 34 to the developing tank 20.
[0057]
In addition, the conveyance speed of the developer on the belt member 34 is, for example, provided with a pair of infrared sensors for detecting the developer on the belt member 34, and between the respective detection time of the developer by each infrared sensor and each detection location. There is a method of obtaining the distance based on the distance or measuring using a high-speed video camera (see IS & Ts NIP 15: 1999 International Conference on Digital Printing Technologies p. 262-265).
[0058]
On the other hand, the developing bias DC voltage of the developing bias DC power supply 38 is superimposed on the four-phase AC voltages Vac1 to Vac4 of the polyphase AC power supply 37, so that the developing area in which the photosensitive drum 11 and the carrier 35 are close to each other. At A (shown in FIG. 1), a developing electric field is formed by a developing bias DC voltage. The developer flies from the belt member 34 to the electrostatic latent image on the photosensitive drum 11 by the developing electric field, and the developer adheres to the electrostatic latent image to form a developer image.
[0059]
In this embodiment, the belt member 34 is divided into a plurality of

regions

34a, 34b, and 34c that are continuous in the developer transport direction as shown in FIG. 5, and the volume resistance values of the

respective regions

34a, 34b, and 34c are mutually different. Unlike the above, one in which any one of the

regions

34a, 34b, and 34c overlaps and comes into contact with the carrier 35 is applied. The belt member 34 is formed by bonding the respective ends of the respective belt members corresponding to the

respective regions

34a, 34b, and 34c to each other with an adhesive or the like, or by laminating the respective ends and performing high-temperature pressing. You.
[0060]
Further, a temperature sensor 41 for detecting a temperature near the belt member 34 and a control unit 42 for controlling the drive of the drive roller 32 of the belt member 34 are provided. The control unit 42 drives the driving roller 32 to rotate and move the belt member 34 according to the temperature detected by the temperature sensor 41, and conveys any one of the

regions

34a, 34b and 34c of the belt member 34. Lay on body 35.
[0061]
Here, assuming that the temperature of the belt member 34 is T, a low temperature range where T <15 ° C., a normal temperature range where 15 ° C. ≦ T ≦ 28 ° C., and a high temperature range where T> 28 ° C. are determined. Further, as the

respective regions

34a, 34b, 34c of the belt member 34, materials having respective volume resistance values of 10 × 10 ＾ 14Ωcm, 10 × 10 ＾ 13Ωcm, and 10 × 10 ＾ 15Ωcm at room temperature are applied. I do.
[0062]
The volume resistance value of the belt member 34 is an organic insulating material or a rubber material as described above, and the temperature T of the belt member 34 varies from a low temperature range to a normal temperature range or from a normal temperature range to a high temperature range. Then, the volume resistance value of the belt member 34 decreases by one digit. Alternatively, when the temperature T of the belt member 34 changes from the high temperature range to the normal temperature range or from the normal temperature range to the low temperature range, the volume resistance value of the belt member 34 increases by one digit. Therefore, when the temperature T of the belt member 34 falls within the normal temperature range, the volume resistance value of the region 34a of the belt member 34 is maintained at about 10 × 10 ＾ 14 Ωcm. When the volume resistance of the region 34b of the member 34 rises to about 10 × 10 ＾ 14 Ωcm and the temperature T of the belt member 34 enters the high temperature range, the volume resistance of the region 34c of the belt member 34 becomes about 10 × 10 ＾ 14 Ωcm. To decline.
[0063]
Then, when the temperature near the belt 34 detected by the temperature sensor 41 falls within the normal temperature range, the control unit 42 drives the drive roller 32 to rotate, and rotates the belt member 34 to move the area 34a of the belt member 34. If the detected temperature in the vicinity of the belt 34 falls within the low temperature range, the belt member 34 is rotated to move the area 34b of the belt member 34 onto the transport body 35, and the detected belt 34 When the nearby temperature falls within the high temperature range, the belt member 34 is rotated and the region 34c of the belt member 34 is superimposed on the carrier 35. As a result, even if the temperature T of the belt 34 fluctuates, the volume resistance value in the region of the belt member 34 that overlaps the conveyor 35 is always constant at about 10 × 10 ＾ 14 Ωcm.
[0064]
When the volume resistance value of the region of the belt member 34 overlapping the conveying member 35 is kept constant in this manner, the traveling wave electric field passing through the belt member 34 is stabilized, and the amount of the developer transported on the belt member 34 is stabilized.
[0065]
According to an experiment, when the volume resistance of the region of the belt member 34 overlapping the carrier 35 is about 10 × 10 ＾ 14 Ωcm, the four-phase AC voltage applied to each traveling wave generating electrode 36 is set to 100 V to 3 KV. It was found that the developer concentration in the solid region on the photosensitive drum 11 was 1.35 or more, and that the developer concentration in the solid region could be secured.
[0066]
That is, in the present embodiment, on the assumption that the developing bias DC voltage is set to 100 V to 3 KV, the volume resistance value of the region of the belt member 34 overlapping the carrier 35 is always kept constant at about 10 × 10 ＾ 14 Ωcm. This stabilizes the transport amount of the developer on the belt member 34, thereby preventing uneven development and uneven image density.
[0067]
Although the volume resistance value of the belt member 34 overlapping the transporting body 35 is maintained at about 10 × 10 ＾ 14 Ωcm, it is maintained at a constant value depending on the type of the developer and the material of the belt member. The volume resistance value may be changed.
[0068]
By the way, instead of rotating the belt member 34 in accordance with the temperature of the belt 34, the belt member 34 is rotated in accordance with which of the plurality of print modes is selected, and the

respective regions

34a, 34a, Either 34b or 34c may be superimposed on the carrier 35. However, it is assumed that the temperature of the belt 34 is substantially constant.
[0069]
Here, as the plurality of print modes, a normal print mode having a normal density, a text print mode having a high density, and a photo print mode having a low density are set. Then, in the image forming apparatus, when the normal print mode is selected by a user's operation input, in response to this, the control unit 42 drives the driving roller 32 to rotate, and the belt member 34 is rotationally moved. The area 34 a of 34 is superimposed on the carrier 35. In this state, since the volume resistance of the region 34a of the belt member 34 is about 10 × 10 ＾ 14 Ωcm, the traveling wave electric field transmitted through the belt member 34 becomes a normal level, and the developer on the belt member 34 The transport amount becomes normal, and the image density becomes a normal level.
[0070]
When the text printing mode is selected by a user's operation input, in response to this, the control unit 42 rotates and moves the belt member 34 so that the area 34c of the belt member 34 overlaps the transport body 35. In this state, since the volume resistance value of the region 34c of the belt member 34 is about 10 × 10 ＾ 15Ωcm, the traveling wave electric field transmitted through the belt member 34 is at a high level, and the developer is transported on the belt member 34. The amount increases and the density of the image increases.
[0071]
Further, when the photo print mode is selected by a user's operation input, in response to this, the control unit 42 rotates the belt member 34 and overlaps the area 34b of the belt member 34 with the carrier 35. In this state, since the volume resistance of the region 34b of the belt member 34 is about 10 × 10 ＾ 13 Ωcm, the traveling wave electric field transmitted through the belt member 34 is at a low level, and the developer is conveyed on the belt member 34. The amount is reduced and the density of the image is reduced.
[0072]
As described above, by superimposing any one of the

regions

34a, 34b, and 34c of the belt member 34 on the carrier 35, the normal print mode, the text print mode, and the photo print mode can be selectively set. Conventionally, in order to adjust the image density, the developing bias DC voltage in the developing area A is changed, the intensity of the light beam emitted from the exposure device 17 to the photosensitive drum 11 is changed, Although the charging potential of the drum 11 has been changed, the density of the image can be adjusted only by moving the belt member 34 without making these changes.
[0073]
In general, the resistance value and the relative permittivity of the belt member 34 made of a dielectric film such as an organic insulating material or a rubber material are in an inversely proportional relationship. That is, as the insulation of the belt member 34 increases, the dielectric constant decreases and approaches 1, and as the insulation of the belt member 34 decreases, the dielectric constant increases. High, thousands of metals.)
[0074]
Therefore, based on the volume resistance value of each

region

34a, 34b, 34c of the belt member 34 being 10 × 10１０14Ωcm, 10 × 10、１０13Ωcm, and 10 × 10 ＾ 15Ωcm, the relative dielectric constant of each

region

34a, 34b, 34c The rate can be defined as 2,3,1. Then, the potential Vs on the belt member 34 corresponding to the traveling wave electric field on the belt member 34 can be obtained from the following equation (1) for each of the

regions

34a, 34b, 34c.
[0075]
(Equation 1)

Here, e is the applied voltage of each traveling wave generating electrode 36 of the carrier 35, dg is the gap on the belt member 34, d1 is the thickness of the surface protection layer 35b of the carrier 35, d2 is the thickness of the belt member 34, and e1 is the thickness of the belt member 34. The relative dielectric constant of the surface protection layer 35b of the carrier 35 and e2 are the relative dielectric constants of the

respective regions

34a, 34b and 34c of the belt member 34.
For example, e = 1000 V, dg = 100 μm, d1 = 25 μm, d2 = 50 μm, and e1 = 2. Furthermore, as described above, when the relative dielectric constant e2 of the region 34a is set to e2 = 2, the potential Vs on the belt member 34 becomes 272V, and when the relative dielectric constant e2 of the region 34b is set to 3, the potential Vs on the belt member 34 becomes Vs. = 250V, and the relative permittivity e2 of the region 34c is 1, the potential Vs on the belt member 34 is 333V.
Further, since the potential Vs on the belt member 34 is proportional to the electric field E on the belt member 34 (Vs = E * d), the lower the potential Vs, the lower the traveling wave electric field.
From such a relationship, the higher the insulating property of the belt member 34, the lower the dielectric constant, the higher the level of the traveling wave electric field, and the lower the insulating property of the belt member 34, the higher the dielectric constant. Thus, it is clear that the level of the traveling wave electric field is reduced.
[0076]
Therefore, by superimposing any one of the

regions

34a, 34b, 34c of the belt member 34 on the carrier 35, the level of the traveling wave electric field on the belt member 34 is adjusted, and the developer on the belt member 34 By adjusting the carry amount, a normal print mode, a text print mode, and a photo print mode can be selectively set.
[0077]
FIG. 6 is a simplified side view showing a second embodiment of the developing device of the present invention. In the developing device 12A of this embodiment, a belt member 34A is used instead of the belt member 34 in the devices of FIGS. 2 and 5, and a potential detection sensor 51 for detecting the surface potential of the belt member 34A is provided. The belt member 34A has a uniform thickness, volume resistivity, relative dielectric constant, and the like over the entire circumference. Further, although the potential detection sensor 51 is provided on the downstream side of the development area A, the potential detection sensor 51 may be provided at any place in the non-development area.
[0078]
The details of the developing device 12A in FIG. 6 are the same as those in the device in FIG. 2, and include a developing tank 20, a developer conveying section 21, a supply roller 23, a blade 26, a mixing paddle 24, a collection roller 25, and the like. I have.
[0079]
In the developing device 12A of the present embodiment, the detection output of the potential detection sensor 51 is added to the control unit 42. The control unit 42 compares the surface potential of the belt member 34A indicated by the detection output of the potential detection sensor 51 with a preset threshold value, and when the surface potential of the belt member 34A reaches the threshold value, drives the drive roller 32 to rotate. Then, the belt member 34A is rotationally moved to update the area of the belt member 34A that overlaps the transport body 35.
[0080]
When the surface potential of the belt member 34A rises, the adhesive force of the developer to the belt member 34A increases, and the supply amount of the developer from the belt member 34A to the photosensitive drum 11 becomes insufficient, causing uneven development and uneven image density. Occurs. Further, when the electric field intensity near the belt member 34A becomes 5.0 × 10 ＾ 6 V / m due to frictional charging of the belt member 34A, the transport of the developer on the belt member 34A becomes unstable. Concentration unevenness occurs. For example, assuming that the thickness of the belt member 34A is t, the surface potential of the belt member 34A is Vs, and the electric field intensity near the belt member 34A is Es, the electric field intensity Es can be expressed by the following equation (2).
[0081]
Es = Vs / t (2)
According to the above equation (2), when the thickness t of the belt member 34A is 20 μm and the surface potential of the belt member 34A reaches 120 V, the electric field intensity Es = Vs / t = 6. 0 × 10 ＾ 6 V /, and the conveyance of the developer on the belt member 34A becomes unstable.
[0082]
Therefore, as the threshold value to be compared with the surface potential of the belt member 34A, the product (Es · t) of the electric field strength 5.0 × 10 ＾ 6 V / m and the thickness t = 20 μm of the belt member 34A is set, and the potential detection sensor is used. When the surface potential Vs of the belt member 34A indicated by the detection output of 51 reaches the threshold value, the belt member 34A is rotated and the area of the belt member 34A that overlaps the transport body 35 is updated. As a result, the area of the uncharged belt member 34A overlaps with the transport body 35, the transport amount of the developer on the belt member 34A is stabilized, and uneven development and uneven image density are prevented.
[0083]
On the other hand, the surface potential of the belt member 34A increases with an increase in the number of printed sheets of recording paper. For this reason, instead of detecting the surface potential of the belt member 34A, the number of printed sheets is counted, and when the counted value reaches a preset threshold, the belt member 34A is rotated and moved, and May be updated. The threshold value to be compared with the number of printed sheets of recording paper is set according to the thickness of the belt member 34A, the voltage applied to each traveling wave generating electrode 36 of the carrier 35, the surface potential of the photosensitive drum 11, and the like.
[0084]
In order to update the area of the belt member 34A that overlaps the transport body 35, the timing of rotating the belt member 34A is performed when the recording paper is not developed. This is because, when the belt member 34A is rotated during the development of the recording paper, a state occurs in which only the downstream side of the belt member 34A is updated. At this time, the surface potential of the belt member 34A is changed between the upstream side and the downstream side. This is because a difference occurs and uneven development occurs.
[0085]
Even if the area of the belt member 34A is once removed from the transport body 35, the area of the belt member 34A is repeatedly superimposed on the transport body 35 by repeatedly updating the area of the belt member 34A. Therefore, the region of the belt member 34A is repeatedly used. However, during the unused period, the potential of the region of the belt member 34A decreases due to spontaneous discharge or the potential of the region decreases due to the discharge through the ground member. , The potential of the region becomes 0 V, the potential history of the region is erased, and then the region is superimposed on the carrier 35 again. As the grounding member, there are a driving roller 32, a driven roller 33, and the like.
[0086]
The belt member 34A has a uniform thickness, volume resistivity, relative dielectric constant, and the like over the entire circumference as described above. For example, the volume resistance value R is preferably set in the range of 10 × 10 ＾ 10 Ωcm ≦ R ≦ 10 × 10 ＾ 14 Ωcm. When the volume resistance value R is less than 10 × 10Ω10 Ωcm, the level of the traveling wave electric field passing through the belt member 34A decreases, the amount of the developer transported on the belt member 34A decreases, and the density of the image decreases. (Developer concentration is less than 1.35 in a solid area). When the volume resistance value R is higher than 10 × 10 ＾ 14 Ωcm, the charge of the charged belt member 34A does not flow to the ground point, and the potential of the belt member 34A is maintained at a high level for a long time. The transport amount of the developer on the member 34A becomes unstable, and uneven development and uneven image density occur.
[0087]
Tables 1 and 2 below show the image density and the static elimination performance with respect to the volume resistance value R of the belt member 34A evaluated by experiments. As is apparent from Tables 1 and 2, it is preferable to set the volume resistance value R of the belt member 34A in the range of 10 × 10 ＾ 10Ωcm ≦ R ≦ 10 × 10 ＾ 14Ωcm.
[0088]
[Table 1]

[0089]
[Table 2]

Further, the relative permittivity e of the belt member 34A is preferably set in a range of 2 ≦ e ≦ 5. When the relative permittivity e is less than 2, the charged charge of the belt member 34A does not flow to the ground point, and the transport amount of the developer on the belt member 34A is reduced, as in the case where the volume resistance value R is too high. It becomes unstable, causing uneven development and uneven image density. Further, when the relative permittivity e is higher than 5, the level of the traveling wave electric field transmitted through the belt member 34A decreases as in the case where the volume resistance value R is too low, and the developer on the belt member 34A The transport amount is reduced, and the density of the image is reduced (the developer density is less than 1.35 in a solid area). In addition, when the relative dielectric constant e is higher than 5, the surface potential of the belt member 34A does not increase due to charging, and therefore, the surface potential of the belt member 34A increases to the threshold as described above. At this time, if the area of the belt member 34A overlapping the carrier 35 is updated, the area of the belt member 34A overlapping the carrier 35 is not updated, and only a specific area of the belt member 34A is continuously used. The belt member 34A is cracked or worn in the specific area.
[0090]
Tables 3 and 4 below show the static elimination performance with respect to the relative dielectric constant e of the belt member 34A and the deterioration characteristics of the belt member 34A evaluated by experiments. As is clear from Tables 3 and 4, it is preferable to set the relative dielectric constant e of the belt member 34A in the range of 2 ≦ e ≦ 5.
[0091]
[Table 3]

[0092]
[Table 4]

Further, it is preferable that the thickness t of the belt member 34A is set in a range of 20 μm ≦ t ≦ 100 μm. If the thickness t is less than 20 μm, the strength of the belt member 34A decreases, and the durability is poor. When the thickness t is greater than 100 μm, the rigidity of the belt member 34A becomes too high, and the adhesion between the belt member 34A and the transport body 35 is reduced, and the belt member 34A by the driving roller 32 and the driven roller 33 is used. Drive is uneven.
[0093]
The following Tables 5 and 6 show the strength of the belt member 34A with respect to the thickness t of the belt member 34A and the adhesion between the belt member 34A and the transporting body 35 evaluated by experiments. As is apparent from Tables 5 and 6, it is preferable to set the thickness t of the belt member 34A in the range of 20 μm ≦ t ≦ 100 μm.
[0094]
[Table 5]

[0095]
[Table 6]

Here, according to Tables 1 to 4, the volume resistance value R was set in the range of 10 × 10 ＾ 10 Ωcm ≦ R ≦ 10 × 10 ＾ 14 Ωcm, and the relative permittivity e was set in the range of 2 ≦ e ≦ 5. In this case, even if the belt member 34A is charged, a spontaneous discharge or a discharge via the grounding member is quickly performed, and the potential of the entire region of the belt member 34A that overlaps the transport body 35 is always stabilized. Therefore, instead of rotating the belt member 34A only when the recording sheet is not developed and updating the area of the belt member 34A that overlaps the transport body 35, the belt member 34A is transported by the developer during the development of the recording sheet. Even when the belt member 34A is rotated at a speed sufficiently lower than the speed to gradually update the area of the belt member 34A that overlaps the transport body 35, the potential of the entire area is always stabilized, and the developer on the belt member 34A The transport amount is stabilized, and uneven development and uneven image density are prevented. The rotational movement speed of the belt member 34A is set to approximately 1/100 to 1/10 of the developer conveyance speed.
[0096]
In particular, assuming that the image forming apparatus is installed in a room at 15 ° C. to 28 ° C., it is optimal to set the volume resistance value R in the range of 10 × 10１０10 Ωcm ≦ R ≦ 10 × 10 ＾ 12 Ωcm. . When the volume resistance value R is less than 10 × 10Ω10 Ωcm, the level of the traveling wave electric field passing through the belt member 34A decreases, the amount of the developer transported on the belt member 34A decreases, and the density of the image decreases. Will be lower. When the volume resistance R is higher than 10 × 10 ＾ 12 Ωcm, it takes time for the potential of the charged belt member 34A to decrease, and the potential difference between the upstream side and the downstream side of the belt member 34A is reduced. This causes uneven development and uneven image density.
[0097]
However, even if the volume resistance value R is set in the range of 10 × 10 ＾ 10 Ωcm ≦ R ≦ 10 × 10 ＾ 12 Ωcm, in a severe use condition such as an inferior use environment or continuous printing of several hundred sheets, the carrier 35 may be used. The potential of the area of the belt member 34A that overlaps with the belt member becomes unstable, and the transport amount of the developer on the belt member 34A becomes unstable. For this reason, the condition for rotating the belt member 34A at a sufficiently low speed and gradually updating the area of the belt member 34A overlapping the carrier 35 is specified. When the recording paper is not developed, the area of the belt member 34A that overlaps the transport body 35 is updated in accordance with the surface potential of the recording paper and the number of printed sheets. Thus, the transport amount of the developer on the belt member 34A can be constantly stabilized.
[0098]
Note that the present invention is not limited to the above embodiments, and can be variously modified. For example, a photosensitive belt or the like may be used instead of the photosensitive drum 11. Further, the image forming apparatus is not limited to the electrophotographic image forming apparatus, and may be an image forming apparatus that directly forms an electrostatic latent image on a dielectric material such as an ion flow method, or an electrode having a plurality of openings such as a toner jet method. The developing device of the present invention can also be applied to an image forming apparatus in which an electrostatic latent image is formed in a space by applying a voltage to the developer and a developer is caused to fly on a recording medium to directly form an image.
[0099]
【The invention's effect】
As described above, according to the present invention, the belt member is divided into a plurality of regions connected in the developer conveying direction, and the resistance values of the respective regions are different from each other. Then, the belt member is appropriately moved in the developer conveying direction, and any one of the regions of the belt member is overlapped on the conveying path. For this reason, it is possible to select any one of the resistance values of the respective regions and to overlap the region of the selected resistance value on the transport path. This makes it possible to refresh the developer transport surface and at the same time suppress fluctuations in the traveling wave electric field, stabilize the transport amount of the developer on the belt member, and prevent uneven development and uneven image density. Can be.
[0100]
Further, the belt member is moved when development is not being performed, and updates the area of the belt member that is superimposed on the transport path. Therefore, the area of the belt member that overlaps the developer conveying surface is completely refreshed at a time, thereby suppressing the fluctuation of the traveling wave electric field and stabilizing the amount of the developer conveyed on the belt member. In addition, uneven development and uneven image density can be prevented.
[0101]
Further, when the belt member is constantly moved at a moving speed lower than the transport speed of the developer, the resistance value of the belt member is set to 10 × 10 ＾ 10Ωcm to 10 × 10 ＾ 14Ωcm to prevent charging of the belt member. In addition, the traveling wave electric field necessary for transporting the developer on the belt member is sufficiently maintained.
[Brief description of the drawings]
FIG. 1 is a side view showing an image forming apparatus to which a first embodiment of a developing device of the present invention is applied.
FIG. 2 is a side view illustrating the developing device according to the first embodiment.
FIG. 3 is a partially enlarged view showing a conveyance body in the developing device of FIG. 2;
4 (a) to 4 (d) are diagrams showing four-phase AC voltage waveforms applied to each traveling wave generating electrode of a carrier in the developing device of FIG. 2;
FIG. 5 is a side view schematically showing the developing device of FIG. 2;
FIG. 6 is a simplified side view showing a second embodiment of the developing device of the present invention.
[Explanation of symbols]
11 Photoconductor drum
12 Developing device
13 Transfer device
14 Cleaning device
15 Static eliminator
16 Charging device
17 Exposure equipment
18 Fixing device
20 Developing tank
21 Developer transport section
23 Supply roller
24 mixing paddles
25 Collection roller
31 Support
32 drive roller
33 driven roller
34 belt
35 Carrier
36 Traveling wave generating electrode
37 polyphase AC power supply
38 DC bias power supply for development
41 Temperature sensor
42 control unit
51 Potential detection sensor

Claims

A transport path having a plurality of electrodes, and a belt member superposed on the transport path, a multi-phase AC voltage is applied to each electrode of the transport path to form a traveling wave electric field, and the developer is Is transported to an image carrier on a belt member, and the developer is supplied to the image carrier to develop an electrostatic latent image on the image carrier.
A developing device, wherein a belt member is divided into a plurality of regions connected in a developer conveying direction, resistance values of the respective regions are different from each other, and any one of the regions is overlapped on a conveying path.

2. The developing device according to claim 1, wherein the belt member is divided into three regions, and the resistance values of the respective regions at a constant temperature are different from each other by one digit.

Temperature detection means for detecting a temperature near the belt member;
3. The developing device according to claim 1, further comprising a control unit configured to move the belt member according to the temperature detected by the temperature detection unit and overlap any one of the regions of the belt member on the conveyance path. 4. .

Mode selection means for selecting any of a plurality of print modes, and control means for moving the belt member according to the print mode selected by the mode selection means, and superimposing any one of the belt member areas on the transport path. The developing device according to claim 1, further comprising:

A transport path having a plurality of electrodes, and a belt member superposed on the transport path, a multi-phase AC voltage is applied to each electrode of the transport path to form a traveling wave electric field, and the developer is Is transported to an image carrier on a belt member, and the developer is supplied to the image carrier to develop an electrostatic latent image on the image carrier.
The developing device is characterized in that the belt member is stopped when the development is being performed, and is moved when the development is not being performed to update an area of the belt member that is superimposed on the transport path.

Counting means for counting the number of developments of the electrostatic latent image,
6. A control means for moving the belt member when the number of developments counted by the counting means reaches a preset threshold value, and updating a region of the belt member superimposed on the conveyance path. 3. The developing device according to claim 1.

Potential detecting means for detecting the potential of the belt member,
6. A control means for moving a belt member when a potential detected by the potential detecting means reaches a preset threshold value, and updating a region of the belt member superimposed on a transport path. 3. The developing device according to claim 1.

A transport path having a plurality of electrodes, and a belt member superposed on the transport path, a multi-phase AC voltage is applied to each electrode of the transport path to form a traveling wave electric field, and the developer is Is transported to an image carrier on a belt member, and the developer is supplied to the image carrier to develop an electrostatic latent image on the image carrier.
A developing device, wherein the belt member is moved at a moving speed lower than the transport speed of the developer, and the resistance value of the belt member is 10 × 10 ＾ 10 Ωcm to 10 × 10 ＾ 14 Ωcm.

The developing device according to claim 8, wherein the relative permittivity of the belt member is 2 to 5.

The developing device according to claim 8, wherein the belt member has a thickness of 20 μm to 100 μm.

An image forming apparatus comprising the developing device according to claim 1.