JP3692823B2

JP3692823B2 - Development device

Info

Publication number: JP3692823B2
Application number: JP06961299A
Authority: JP
Inventors: 英明田中
Original assignee: Fuji Xerox Co Ltd; Fujifilm Business Innovation Corp
Current assignee: Fujifilm Business Innovation Corp
Priority date: 1999-03-16
Filing date: 1999-03-16
Publication date: 2005-09-07
Anticipated expiration: 2019-03-16
Also published as: JP2000267416A

Description

【０００１】
【発明の属する技術分野】
本発明は、磁性キャリアとこの磁性キャリアに静電的に吸着されるトナ−とを含む現像剤を用い、像担持体上に形成された静電潜像にトナーを選択的に転移させてその静電潜像を可視化する現像装置に関する。
【０００２】
【従来の技術】
近年、トナ−および磁性キャリアからなる二成分現像剤を像担持体に供給してその像担持体に形成された静電潜像を現像する現像装置に関して、装置の小型化、低コスト化を図るために、トナ−濃度センサなどを有する複雑なトナ−濃度制御機構を設けずにトナ−濃度を制御する技術が提案されている。
【０００３】
例えば、特開昭６３−４２７８号公報には、現像剤搬送方向に対して、トナ−供給口より下流側で現像剤層厚規制部材の上流側に現像剤遮蔽部材を設け、現像剤層厚規制部材で規制されて溢れた現像剤を現像剤遮蔽部材で遮蔽することにより現像剤の体積を変化させ、この体積変化した現像剤でトナー供給口を覆うことによりトナーの取り込み量を制御してトナー濃度を安定して維持する技術が提案されている。
【０００４】
また、特開平８−１８５０５１号公報には、所定量の現像剤を滞留する現像剤滞留部を設け、その現像剤滞留部の、嵩変化する現像剤で、トナ−供給口を塞ぐことによりトナーの取り込みを調整して、トナー濃度を制御する技術が提案されている。
【０００５】
さらに、特開平９−３１１５５１号公報には、現像剤層厚規制部材で溢れてＵタ−ンする現像剤にトナ−を接触させ、重力を利用して一緒に搬送することで現像剤室にトナーを取り込み、その現像剤室の現像剤の体積変化に応じた濃度のトナ−を現像ロールに供給する技術が提案されている。
【０００６】
【発明が解決しようとする課題】
しかしながら、特開昭６３−４２７８号公報に提案された技術では、取り込まれたトナ−は現像剤層厚規制部材手前までほとんど攪拌されずに搬送され、その現像剤層厚規制部材を通過する際に、強い圧力で攪拌、帯電が行なわれるため、トナーの均一な分散や適切な帯電が得られなかったり、現像剤がすぐに劣化してしまい、かぶりや濃度ムラ、トナ−汚れが発生するという問題がある。
【０００７】
また、特開平８−１８５０５１号公報に提案された技術では、嵩の増加により現像剤滞留部の入口は塞がれるものの、移動する磁気ブラシがトナ−と接触しているため、トナ−は現像剤層の移動と共に搬送される。従って、トナ−の取り込みは完全には停止せず、トナ−の消費がほとんど行なわれない画像が連続した場合にはトナ−濃度が高くなってかぶりが発生するという問題がある。
【０００８】
さらに、特開平９−３１１５５１号公報に提案された技術では、現像剤層厚規制部材で現像領域に進むことを阻止され押し戻されてＵタ−ンした現像剤にトナ−が補給される。Ｕタ−ンした現像剤の固まりは、地表プレ−トが移動するがごとくゆっくりと全体で移動するため、現像剤に乗って一緒に運ばれて取り込まれるトナ−は非常にゆっくりと取り込まれ、また搬送中はほとんど攪拌されることはなく、従ってトナ−が現像剤の隙間に固まりで入り込んだままの状態で搬送される。ようやく、現像ロ−ル表面の磁気ブラシに接触すると、トナ−の固まりを抱き込んだ状態で現像ロールを構成するスリ−ブ上を搬送されるが、磁気ブラシの上層部にはＵタ−ンした現像剤が乗っているため、下層部の現像剤は十分に攪拌されずに搬送される。そのため、スリ−ブ上のトナ−の減少に対して、レスポンスが遅く、濃度が回復するまでには時間がかかるという問題がある。さらに、磁性キャリアとの混合攪拌および帯電も不十分なため、濃度低下やかぶり、あるいはトナ−の固まりが直接現像されてしまうというような画像欠陥が発生する。
【０００９】
本発明は、上記事情に鑑み、複雑なトナー制御機構を用いることなく簡素な構成でトナー濃度を制御することができ、常に安定した画像濃度が得られる現像装置を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成する本発明の現像装置は、磁性キャリア粒子とこの磁性キャリア粒子に静電的に吸着されるトナ−とを含む現像剤を用い、像担持体上に形成された静電潜像に上記トナ−を選択的に転移させてその静電潜像を可視化する現像装置において、
回転方向に複数の磁極が配置されて水平な回転軸のまわりに回転することにより交番磁界を発生させる交番磁界発生手段を備え、表面に現像剤を担持して搬送する、表面がロール状の現像剤搬送体と、
上記現像剤搬送体の、その現像剤搬送体により現像剤が下向きに搬送される部分に隣接した位置に、現像剤の一部を溜めて形成した現像剤溜り部と、
補給トナーを貯えて、その補給トナーを、上記現像剤溜り部を挟んだ、上記現像剤搬送体に対向した側からその現像剤溜り部に補給するトナー貯蔵部と、
下端が上記現像剤溜り部に位置するように立設され、上記トナー貯蔵部の補給トナーと上記現像剤溜り部の現像剤との接触を制限する仕切り板とを備えたことを特徴とする。
【００１２】
また、上記仕切り板が、少なくとも下端部に磁性材料を含む部分を備えたものであることが好ましい。
【００１３】
さらに、上記トナー貯蔵部が、上記現像剤溜り部の隣接部分に、その現像剤溜り部に向って補給トナーを滑落させるとともに、上記現像剤溜り部に供給された補給トナーの嵩が増加するに従ってその補給トナーを上記交番磁界発生手段から離すための斜面を有するものであることも好ましい形態である。
【００１４】
また、上記現像剤搬送体が、円筒スリーブと、その円筒スリーブ内で回転する固定磁石とを有するものであってもよい。
【００１５】
さらに、上記現像剤搬送体が、表面に円周方向全周にわたって複数の磁極が形成された回転ロールであってもよい。
【００１６】
【発明の実施の形態】
以下、本発明の実施形態について説明する。
【００１７】
図１は、本発明の第１実施形態の現像装置を用いた画像形成装置の概略構成図である。
【００１８】
図１に示す画像形成装置には、像担持体としての感光体ドラム１が備えられている。この感光体ドラム１は、導電性材料からなる円筒部材１ａと、その円筒部材１ａの表面に形成された薄層の感光体層１ｂから構成されている。感光体層１ｂとしては、例えば負帯電の有機感光体が用いられる。この感光体ドラム１は、図示しない駆動手段によって矢印Ａ方向に回転駆動される。
【００１９】
また感光体ドラム１の周囲には、その回転方向に沿って、帯電器２と、露光手段３と、感光体ドラム１に対向して配置された円筒部材からなる現像ロ−ル２１を有する現像装置４と、転写前コロトロン５と、転写コロトロン６と、剥離コロトロン７と、クリ−ナ８と、光除電器９とが備えられている。現像装置４は、本発明の第１実施形態の現像装置であり、詳細は後述する。
【００２０】
このように構成された画像記録装置において、感光体ドラム１が矢印Ａ方向に回転駆動され、帯電器２によって感光体ドラム１の表面が所定の電圧に一様に帯電される。次いで、感光体ドラム１の表面に、露光手段３により画像に対応した露光が行なわれて静電潜像が形成される。感光体ドラム１の表面に形成された静電潜像は、現像装置４によってトナ−が現像され、顕像化される。その際、現像ロ−ル２１には、図示しない現像バイアス用の電源によって現像バイアスが印加される。
【００２１】
感光体ドラム１上に形成されたトナ−像は、必要に応じて転写前コロトロン５によって帯電を受け、次いで転写コロトロン６の帯電によって記録用紙１０上に転写される。さらに、この記録用紙１０は、剥離コロトロン７の帯電によって感光体ドラム１の表面から剥離される。次いで、この記録用紙１０は、図示しない定着器へと搬送され、記録用紙１０上にトナ−像が定着されて画像形成が終了する。
【００２２】
一方、トナ−像の転写および記録用紙１０の剥離工程が終了した感光体ドラム１の表面は、クリ−ナ８によって残留トナ−が清掃され、さらに光除電器９による露光を受けて残留電荷が除電され、次の画像形成工程に備えられる。
【００２３】
尚、露光手段３としては、画像情報に応じた露光が可能なものであれば任意の露光手段を使用することができ、例えばレ−ザ−書き込み装置、ＬＥＤアレイ、一様光源と液晶マイクロシャッタ−からなる液晶ライトバルブ等任意のものを目的に応じて使用することができる。また、この露光手段３は、画像部露光を行なうものであっても、非画像部(背景部)露光を行なうものでもあっても良く、必要に応じて適宜選択することができる。
【００２４】
次に、図１に示す画像形成装置を構成する本発明の第1実施形態の現像装置４について、図２を参照して説明する。
【００２５】
図２は、本発明の第１実施形態の現像装置の概略構成図である。
【００２６】
この現像装置４には、磁性キャリア粒子とこの磁性キャリア粒子に静電適に吸着されるトナーとを含む現像剤３６を収容するハウジング２０が備えられている。このハウジング２０内には、周面に現像剤３６を担持して感光体ドラム１との対向領域に搬送する現像ロ−ル２１と、その現像ロ−ル２１に近接して対向配置され現像領域を通過した現像剤３６を現像ロ−ル２１から回収する現像剤回収ロ−ル２２が備えられている。またハウジング２０内には、現像ロ−ル２１と所定間隔をおいて対向配置され、表面に現像剤３６を担持して現像ロ−ル２１と対向する位置に搬送する、表面がロ−ル状の層形成ロ−ル２３（本発明にいう現像剤搬送体の一例）が備えられている。さらにハウジング２０内には、層形成ロ−ル２３の、その層形成ロ−ル２３により現像剤３６が下向きに搬送される部分に隣接した位置に、現像剤３６の一部を溜めて形成した現像剤溜り部１００が備えられている。またハウジング２０内には、補給トナー３５を貯えて、その補給トナー３５を、現像剤溜り部１００を挟んだ、層形成ロ−ル２３に対向した側からその現像剤溜り部１００に補給するトナー貯蔵部３４も備えられている。このトナー貯蔵部３４は、現像剤溜り部１００の隣接部分に、その現像剤溜り部１００に向って補給トナー３５を滑落させるとともに、この現像剤溜り部１００に供給された補給トナーの嵩が増加するに従ってその補給トナーを、後述する磁界発生部材２３ｂから離すための斜面である現像剤溜り形成部材３２を有する。またこのトナー貯蔵部３４には、そのトナー貯蔵部３４の補給トナー３５を、現像剤溜り形成部材３２を介して現像剤溜り部１００に接触するように導くトナー搬送部材３３が備えられている。
【００２７】
またこの現像装置４には、下端が現像剤溜り部１００に位置するように立設され、トナー貯蔵部３４の補給トナー３５と現像剤溜り部１００の現像剤３６との接触を制限する仕切り板３１が備えられている。
【００２８】
図３は、図２に示す現像ロール周面の部分拡大断面図である。
【００２９】
現像ロ−ル２１は、図３に示すように、導電性基体２１ａと、その導電性基体２１ａ上に積層された磁気記録層２１ｂから構成されている。導電性基体２１ａには、図示しない現像バイアス電源により、現像バイアス電圧が印加される。また、磁気記録層２１ｂには、現像ロ−ル２１の全周にわたって磁性キャリアが一層程度しか保持できない微少ピッチでＳ極とＮ極とが交互に着磁されている。
【００３０】
磁気記録層２１ｂには、磁性材料としてγ−Ｆｅ₂Ｏ₃が、また結着樹脂としてポリウレタンが使用されており、この磁気記録層２１ｂの層厚は５０μｍである。
【００３１】
図４は、現像ロ−ルを構成する磁気記録層の着磁方法の一例を示す図である。
【００３２】
現像ロ−ル２１を構成する磁気記録層２１ｂの着磁は、図４に示すように、現像ロ−ル２１の周面に近接して配置された磁気記録用ヘッド２４によって行なわれる。
【００３３】
この磁気記録用ヘッド２４は、軟磁性材料からなる、両端部が所定の間隔を置いて並列配置された形状のコア部材２５と、このコア部材２５に巻回されたコイル２６とを有し、上記コア部材２５の両端部が現像ロ−ル２１の周面に近接するように配置される。コイル２６には、図示しない磁化信号発生装置を介して電源から磁化電流が供給されるようになっており、コイル２６に電流が流れると、コア２６内に磁束２７が発生する。この磁束２７はコア部材２５の先端から磁気記録層２１ｂ内を通過する。コイル２６へ供給される磁化電流は磁化信号発生装置を介して断続的または適宣電流の方向を変えて供給され、現像ロ−ル２１が図４に示す矢印Ａ方向に回転駆動されて磁気記録層２１ｂが所定の着磁パタ−ンに磁化される。尚、現像ロ−ル２１は表面に磁界が及んで磁性キャリアを保持しながら感光体ドラム１（図２参照）と電位差が設けられればよく、基体上に磁気記録層を積層した上に導電性材料の薄層を蒸着などにより形成したものでも構わない。
【００３４】
再び図２に戻って説明を続ける。図２に示す現像剤回収ロ−ル２２は、中空の一部が歪んだ形状を有する円筒状の非磁性導電性スリ−ブ２２ａと、その内側に位置する磁界発生部材２２ｂから構成される。この磁界発生部材２２ｂは、異なる極性の磁極が全周にわたって交互に着磁され、外側の固定されたスリ−ブ２２ａとは独立して回転することができるように設けられている。
【００３５】
また、層形成ロ−ル２３は、周回可能に支持された中空円筒状のスリ−ブ２３ａと，そのスリ−ブ２３ａ内で回転する磁界発生部材２３ｂとを有する。この磁界発生部材２３ｂは、本発明にいう交番磁界発生手段に相当するものであり、回転方向に複数の磁極が配置されて水平な回転軸のまわりに回転することにより交番磁界を発生する。この磁界発生部材２３ｂは、隣接する磁極間で形成される磁界によって現像剤３６の磁気ブラシをスリ−ブ２３ａ表面に形成する。層形成ロ−ル２３では、磁界発生部材２３ｂのみ、または磁界発生部材２３ｂとスリ−ブ２３ａとの双方が互いに異なる方向に回転することにより、スリ−ブ２３ａ表面に交番磁界を発生させてトナ−３５を磁性キャリアと均一に混合・摩擦帯電しながら磁気ブラシを層形成ロ−ル２３と所定間隔おいて配置された現像ロ−ル２１と対向する位置まで搬送してその磁気ブラシの先端を現像ロ−ル２１表面に接触させて現像剤層を形成する。層形成ロ−ル２３の磁極ピッチは、搬送・撹拌性能が良好な１〜６ｍｍ程度が好ましく、現像ロ−ル２１の磁極ピッチよりも大きい方がよい。本実施形態では、スリ−ブ２３ａとしては直径が１８ｍｍの部材が用いられ、また磁界発生部材２３ｂとしてはスリ−ブ２３ａ周面上で磁極間ピッチが約５ｍｍとなる間隔でＮ極とＳ極が交互に着磁された磁石ロ−ルが用いられる。各磁極ともスリ−ブ２３ａ上での垂直方向の磁束密度ピ−ク値は５０ｍＴであり、スリ−ブ２３ａと磁界発生部材２３ｂは、図示する方向にそれぞれ回転する。
【００３６】
現像剤溜まり形成部材３２は、先端部が層形成ロ−ル２３に所定間隔をおいて対向して配置されており、溜まった現像剤３６を、層形成ロ−ル２３上の現像剤嵩が少なくなった時に戻せる状態で保持する。この現像剤溜り形成部材３２は、先端部から斜度が設られて上方に向けてトナ−貯蔵部３４近くまで延びた形状であり、これによりその現像剤溜り形成部材３２に沿って現像剤溜り部１００が形成される。現像剤溜り形成部材３２の斜度は１５°〜６０°が好ましい。また、現像剤溜り形成部材３２が層形成ロ−ル２３と最も近接して現像剤溜り部１００を作り始めるポイント（位置）は、層形成ロ−ル２３の中心を通る水平な直線に対して上下に０°〜７５°の角度内に収まる位置が好ましく、さらに好ましくは０°〜４５°の角度内に収まる位置が良い。
【００３７】
仕切り板３１は、下端が層形成ロ−ル２３から所定距離離れた位置に、かつ所定の高さ位置で現像剤溜り部１００の現像剤に接触するように、また現像剤溜まり形成部材３２の先端部と所定の隙間をあけて上方に延びるように設けられており、下端近傍は層形成ロ−ル２３の磁界がおよぶ範囲内にある。具体的には、この下端は、層形成ロ−ル２３から４ｍｍ離れた位置に、現像剤溜り形成部材３２の先端部と２ｍｍ隙間をあけて設けられており、材料は例えば非磁性のリン青銅が用いられる。
【００３８】
トナ−搬送部材３３は、トナー貯蔵部３４内のトナ−３５を攪拌するとともに、現像剤溜り部１００近傍にトナ−３５を搬送するように針金状の回転部材が用いられる。
【００３９】
本実施形態の現像装置４は、層形成ロール２３と、現像剤溜り部１００と、トナー貯蔵部３４とを備えたものであり、この現像装置４では、現像領域を通過した現像剤３６により現像剤溜まり部１００が形成され、その現像剤溜り部１００の一部がトナ−貯蔵部３４のトナ−３４に接触する。トナ−３４に接触した現像剤３６は、トナ−濃度に応じて動きが制御される。例えば、トナ−濃度が低い場合には、磁界発生部材２３ｂの交番磁界が作用して、現像剤３６が磁気的に転がり移動するため、この現像剤３６に接触したトナ−３５は固まりであっても細かくほぐされ、現像剤３６の溜りの中に攪拌されながら取り込まれる。このとき、現像剤３６は少数の磁性キャリア単位で転がり移動するため、取り込まれたどのトナ−粒子も磁性キャリアの表面に接触する機会が多く、すぐに均一に分散し、現像に適したレベル近くまで帯電が立ち上がり、磁性キャリア表面に付着してトナ−補給された均一な現像剤になる。
【００４０】
一方、トナ−濃度が高くなってくると、トナ−３５に接触した現像剤３６に働く交番磁界が弱まってトナ−３５に接触した現像剤３６の動きが鈍くなり、トナ−３５の取り込みが少なくなり、ついにはトナ−３５に接触した現像剤３６に交番磁界が及ばなくなり、その現像剤３６の動きが停止するため、トナ−３５の取り込みが完全に停止する。この状態では、現像装置４が作動していてもトナ−３５は取り込まれないため、トナ−消費量がほとんどないような画像が続いてもトナ−濃度が上昇してかぶりを発生することがない。
【００４１】
この結果、トナ−消費量に応じてトナ−３５を現像剤３６に必要量だけ供給することができ、従ってトナ−濃度をほぼ一定に保つことができ、攪拌不足による帯電不良、かぶり、濃度むら、トナ−汚れといったことがなく、安定した画像が得られる。また、取り込み性、攪拌性が高く、現像剤３６に大きなストレスとなる圧力をかけることなくトナ−３５の取り込み、攪拌、帯電立ち上げを短時間にできるため、トナ−消費量の多い画像や、現像剤量をあまり多く使えない小型の現像装置では特に有効である。
【００４２】
また、本実施形態の現像装置４では、下端が現像剤溜り部１００に位置するように立設され、トナ−貯蔵部３４のトナ−３５と現像剤溜り部１００の現像剤３６との接触を制限する仕切り板３１が設けられており、仕切り板３１で仕切られた現像剤溜り部１００の、現像領域から遠い側の領域にトナ−３５が供給され、そのトナ−３５が現像剤溜り部１００に接触する。トナ−濃度が低い場合は、仕切り板３１の下端にちょうど接するかもしくは隙間ができる嵩で、現像剤溜り部１００の、仕切り板３１の下端近傍の現像剤３６が、交番磁界の影響を受けて、キャリア数粒単位で活発に転がり移動している。このため、現像剤３６に接触したトナ−３５は現像剤３６にほぐされ、混合攪拌されながら仕切り板３１の下端をすり抜けて一緒に搬送されて取り込まれ、十分に帯電され磁性キャリア表面に付着して、均一に分散する。
【００４３】
トナ−濃度が高くなると、現像剤溜り部１００の嵩が増加し、その現像剤溜り部１００と仕切り板３１の間にあった隙間が塞がれる。トナ−３５は現像剤溜り部１００と仕切り板３１の囲まれた領域のみに供給され、さらに嵩が増加すると仕切り板３１に沿ってトナ−３５と接触する位置が移動し、磁界発生部材２３ｂから離れていくため、現像剤３６に及ぶ交番磁界が仕切り板３１の下端よりも次第に弱くなり、ついには現像剤３６を磁気的に動かすことができない部分に現像剤３６とトナ−３５が接触する位置が移動すると、トナ−３５と接触する現像剤３６は全く動かなくなり、トナ−３５の取り込みが完全に停止する。
【００４４】
一方、トナ−３５の消費に伴い、トナ−濃度が低下してくると、再び現像剤溜り部１００の嵩が低下し、現像剤３６がトナ−３５と接触する位置が仕切り板３１の下端に近づき、磁界発生部材２３ｂに近づくため、現像剤３６に働く交番磁界も強まって、転がり移動を始め、トナ−３５の取り込みを再開する。
【００４５】
また、上記仕切り板３１が、少なくとも下端部に磁性材料を含む部分を備えていると、遮蔽効果により、仕切り板３１下端部以上に現像剤溜り部１００の嵩が増加した時に、現像剤に働く交番磁界が急激に減衰するため、トナーの取込み制御を敏感にすることができる。
【００４６】
さらに、本実施形態の現像装置４では、磁界発生部材２３ｂに所定間隔を置いて対向し、現像剤３６の一部をせき止めてそこから所定角度で磁界発生部材２３ｂから離れていくように延びた斜面である現像剤溜り形成部材３２が設けられている。このため、トナ−３５が取り込まれトナ−濃度が上昇し現像剤溜り部１００が増えるに従い、その現像剤溜り形成部材３２に沿って現像剤溜り部１００が広がり、磁界発生部材２３ｂから離れて交番磁界による現像剤３６の移動が起こらなくなる。現像剤３６の動きが止まれば、現像剤３６に接触しているトナ−３５は取り込まれなくなり、トナ−濃度は上昇しなくなる。一方、トナ−３５が消費されてトナ−濃度が低下すると、循環する現像剤３６全体の嵩が減少するため、磁界発生部材２３ｂから十分に離れて交番磁界で動くことのなかった現像剤３６は現像剤溜り形成部材３２に沿って磁界発生部材２３ｂに近づき、トナ−３５と現像剤３６との接触界面が移動する。すると、トナ−３５と接触している現像剤３６が、交番磁界で再び転がり移動しはじめるため、トナ−３５が取り込まれトナ−濃度が保たれる。
【００４７】
従って、本実施形態の現像装置４では、トナ−濃度が常に一定に保たれ、攪拌、帯電が不十分で濃度ムラやかぶりが発生することがなく、良好な画像を安定して得ることができる。
【００４８】
次に現像剤の流れについて説明する。
【００４９】
現像領域を通過して現像ロ−ル２１に担持された現像剤層は、現像剤回収ロ−ラ２２と対向する位置に搬送される。現像剤回収ロ−ル２２は、現像ロ−ル２１に対して近接対向して配置されており、現像剤回収ロ−ル２２内部の磁界発生部材２２ｂの強力な磁力により現像ロ−ル２１上のほとんどの現像剤が回収されて、現像剤回収ロ−ル２２上に移動する。現像剤回収ロ−ル２２上に移動した現像剤は、磁界発生部材２２ｂの回転にともなってスリ−ブ２２ａ上を時計方向に移動し、そのスリ−ブ２２ａの、磁界発生部材２２ｂからの距離が遠くなる部分に到達した際に磁気拘束力が弱まってスリ−ブ２２ａから落下し、現像剤回収ロ−ル２２の下に位置する層形成ロ−ル２３上に付着して搬送される。層形成ロ−ル２３上の現像剤３６は、磁界発生部材２３ｂとスリ−ブ２３ａの回転により反時計方向に搬送され、その現像剤３６の一部が現像剤溜り形成部材３２によってせき止められて現像剤溜り部１００を形成する。現像剤溜り部１００は、現像剤溜まり形成部材３２に沿って移動し、トナ−貯蔵部３４内のトナ−搬送部材３３によって運ばれてきた補給用トナ−３５に接触する。この時点では、現像剤溜り部１００表面の現像剤３６は層形成ロ−ル２３に十分近いため、層形成ロ−ル２３内の回転する磁界発生部材２３ｂによる交番磁界により転動しながらスリ−ブ２３ａ側に移動しており、現像剤溜り部１００に接触したトナ−３５は次々に取り込まれ、スリ−ブ２３ａ側に搬送されながら、磁性キャリアと混合・攪拌され、帯電付与される。
【００５０】
一方、現像剤溜り形成部材３２によってせき止められずに通過した他の現像剤は、スリ−ブ２３ａ上で磁界の変動とともに撹拌・帯電が行なわれながら現像ロ−ル２１と対向する領域に搬送されて現像ロ−ル２１と対向する近傍に到達する。現像ロ−ル２１と層形成ロ−ル２３は、層形成ロ−ル２３上の現像剤穂立ち(磁極上高さ)よりも若干狭い間隙をおいて対向して配置されており、現像ロ−ル２１と対向する近傍に搬送された現像剤層の先端が現像ロ−ル２１表面に接触する。ここで、層形成ロ−ル２３上の現像剤は、現像ロ−ル２１と対向する領域では、現像ロ−ル２１の搬送方向と異なる方向に搬送されるため、現像ロ−ル２１表面は層形成ロ−ル２３との最近接位置から離れる方向に移動する。従って、現像ロ−ル２１表面近傍だけに現像剤３６が吸着されて現像ロ−ル２１の表面の移動とともに搬送される。また、現像ロ−ル２１表面近傍に到達できなかった現像剤３６は、取り残され、層形成ロ−ル２３と現像ロ−ル２１が近接対向する手前の領域に滞留して、現像ロ−ル２１表面に接触する機会に備えられる。滞留して溜まりを形成し、現像ロ−ル２１表面に接触する機会が与えられた現像剤３６により、現像ロ−ル２１の表面は常に覆われるため、現像ロ−ル２１表面に形成する現像剤層が不足することはない。さらに、現像ロ−ル２１表面の磁気記録層２１ｂは着磁間隔が１００μｍと小さな間隔となっているので、過剰に供給された現像剤３６の内、現像ロ−ル２１表面近傍の現像剤３６だけに強い磁気拘束力が働き、その上層部の現像剤３６には磁気拘束力がほとんど働かない上、層形成ロ−ル２３により搬送された現像剤３６が現像ロ−ル２１上に供給され層形成される領域では、現像剤３６が現像ロ−ル２１から離れる方向に重力が働くので、現像ロ−ル２１の、磁性キャリアに働く磁気拘束力による現像剤３６のうち重力に打ち勝った磁気拘束力による現像剤３６だけが搬送される。従って、例えばしっかりと表面が現像ロ−ル２１表面に接している磁性キャリアは現像ロ−ル２１から離脱することなく搬送されるが、現像ロ−ル２１表面に直接接触できず磁性キャリア上に乗った状態の磁性キャリアは脱落して現像剤溜まり部１００に留まるか、または落下して層形成ロ−ル２３上に戻されるため、現像ロ−ル２１の移動とともに搬送される現像剤層は、磁性キャリアがほほ１層の均一な薄層となる。
【００５１】
現像ロ−ル２１上に形成された均一な現像剤薄層は、現像ロ−ル２１の回転に伴って、感光体ドラム１と対向する現像領域へと搬送され、磁性キャリアに付着したトナ−３５のみが感光体ドラム１上の静電潜像に転移して現像される。尚、現像剤層は感光体ドラム１に対して非接触状態に保持される。
【００５２】
次にトナ−補給機構について説明する。
【００５３】
現像によりトナ−３５が消費され、トナ−濃度が低下すると前述したようにしてトナ−３５が取り込まれるが、トナ−消費量が減ったりあるいは十分にトナ−３５が補給されてトナ−濃度が高くなると、現像剤溜り部１００の嵩が増加し、現像剤溜り部１００は仕切り板３１の下端に接触し補給トナ−３５は仕切り板３１と現像剤溜まり形成部材３２とで囲まれた領域に供給される。現像剤溜り部１００が仕切り板３１の下端にようやく接触する高さでは、現像剤溜り部１００表面の現像剤３６は層形成ロ−ル２３の交番磁界の影響で、転がり移動しており、一部の現像剤３６はトナ−３５を取り込み、仕切り板３１の下端をすり抜けてスリ−ブ２３ａ側に搬送される。さらに、現像剤溜り部１００の高さが上昇してくると、現像剤溜り部１００の表面は層形成ロ−ル２３から離れるため現像剤３６におよぶ交番磁界が弱くなり、現像剤３６の磁界による動きが鈍くなり、ついには全く動かなくなる。従って、現像剤３６の動きにより取り込まれていたトナ−３５は、現像剤溜り部１００表面の現像剤３６の動きとともに、取り込み量、取り込みスピ−ドが共に低下し、ついには全く取り込まれなくなる。
【００５４】
トナ−３５の取り込みが停止した状態で現像によりトナ−３５が消費されることでトナ−濃度が低下しはじめると、現像剤溜り部１００の嵩が減少して高さが低下して交番磁界の影響領域に入るため、再び現像剤３６が動きはじめて、トナ−３５の取り込みが再開される。従って、トナ−濃度センサなどを有する複雑なトナ−濃度制御機構を設けることなく簡素な構成でトナ−濃度を一定に保つことができる。
【００５５】
尚、本実施形態で用いられる二成分現像剤３６は、非磁性のポリエステル系トナ−とフェライト系磁性キャリアとを混合したものであるが、他の材料からなるトナ−と磁性キャリアを用いることもできる。トナ−は重合法によるものであってもよく、あるいは混連粉砕法によるものであってもよいが、流動性の高い球形形状の方が好ましい。トナ−の形状をほぼ球形とすることで、流動性が増し、現像剤としての流動性も向上し、トナ−供給部でのトナ−や現像剤の移動が均一性よく滑らかになるため、トナ−取り込みの制御を精度よく行なうことができる。
【００５６】
また、現像剤３６の磁性キャリアは１０⁶/(４π)Ａ／ｍの磁界中における磁化が４５ＫＡ／ｍ以上３６０ＫＡ／ｍ以下となるものを用いるのが望ましい。
【００５７】
また、仕切り板３１の形状はこれに限定されるものではなく、高さ方向に交番磁界が少なくとも一旦弱まる形状のものであればよい。
【００５８】
さらには現像方式も本方式に限定されるものではなく、トナ−供給部が同様の構成であれば通常の磁気ブラシ現像など他の現像方式にも適用できることは言うまでもない。
【００５９】
次に、本実施形態の現像装置４を用いて印字画像密度の異なる画像をそれぞれ連続してプリントした場合の濃度維持性についてテストした結果を示す。
【００６０】
印字パタ−ンは、前半が白紙で後半がベタ画像(像密度約５０％)のものと、前半が白紙で後半が文字(像密度約２％)のものとの２種類を用い、それぞれの印字パタ−ンで１００枚連続で印字した。この時の現像ロ−ル２１上のトナ−濃度推移を図５に示す。
【００６１】
図５は、本発明の第１実施形態の現像装置を用いて密度の異なる画像をそれぞれ連続してプリントした場合の現像ロ−ル上の現像剤のトナ−濃度変化を示す図である。
【００６２】
この現像装置４では、トナ−消費量に応じて消費した量のトナ−３５がすぐに補給されるため、図５に示すように、印字パタ−ンによらず、トナ−濃度が安定して一定に保たれ、両印字パタ−ンとも濃度低下や地肌かぶりが発生せず、良好な画質を安定して得ることができる。
【００６３】
尚、本実施形態の現像装置４では、本発明にいう現像剤搬送体は、円筒状のスリーブ２３ａと、そのスリーブ２３内で回転する磁界発生部材２３ｂとを有する層形成ロール２３の例で説明したが、これに限られるものではなく、本発明にいう現像剤搬送体は、表面に円周方向全周にわたって複数の磁極が形成された回転ロールであってもよい。
【００６４】
図６は、本発明の第２実施形態の現像装置における、トナ−供給部の概略構成図である。
【００６５】
この現像装置４００には、交番磁界を発生させて現像剤を担持して搬送する現像剤担持ロ−ル４５（本発明にいう現像剤搬送体の一例）と、現像剤担持ロ−ル４５上を循環する現像剤の一部をせき止めて現像剤溜り部２００を形成する現像剤溜り形成部材４２と、現像剤溜り部２００の現像剤にトナ−を供給するようにトナ−を搬送するトナ−搬送部材４３と、補給トナ−を蓄えるトナ−貯蔵部４４と、トナ−搬送部材４３により搬送され、現像剤溜り部２００に接触するトナ−が現像剤溜り部２００と接触できる領域を制限する仕切り板４１とが備えられている。
【００６６】
現像剤担持ロ−ル４５は、Ｓ極とＮ極が交互に着磁され回転可能な磁石ロ−ル４５ｂを内蔵し、外側に非磁性スリ−ブ４５ａを回転可能に設けた構成であり、磁石ロ−ル４５ｂを回転することで、スリ−ブ４５ａ表面に交番磁界を発生させ、スリ−ブ４５ａ上に現像剤を担持して混合攪拌しながら搬送する。
【００６７】
現像剤溜り形成部材４２は、先端部が現像剤担持ロ−ル４５に所定間隔をおいて対向して配置されており、この先端部でせき止めた現像剤を現像剤溜り形成部材４２の面に沿って保持する。この現像剤溜り形成部材４２の形状は、図６に示すように、せき止めた現像剤がある程度の量貯蔵され、所定量以上の嵩に対して斜面に沿って現像剤担持ロ−ル４５から離れるように上昇していく形状である。
【００６８】
トナ−搬送部材４３は、トナ−貯蔵部４４内のトナ−を攪拌するとともに、現像剤溜り部２００近傍にトナ−を搬送するように針金状の回転部材が用いられている。
【００６９】
仕切り板４１は、非磁性板４１ａと、その非磁性板４１ａの片面に貼り付けられた磁性板４１ｂから構成されている。この仕切り板４１により、現像剤溜り部２００のうち、その仕切り板４１で仕切られてトナ−と接触する側の現像剤が受ける磁石ロ−ル４５ｂによる交番磁界を、現像剤の嵩が仕切り板４１の下端以上の場合に遮断または弱めることができ、従ってトナ−取り込みの制御を敏感に行なうことができる。現像剤量が少なく、トナ−濃度による現像剤溜り部２００の嵩の変化が小さい小型現像装置では特に有効である。
【００７０】
次に、この現像装置４００のトナ−補給部の作用について説明する。
【００７１】
トナ−濃度が十分に高い時には現像剤溜り部２００の表面は仕切り板４１の下端に接触しており、トナ−貯蔵部４４から供給されたトナ−は、仕切り板４１よりもトナ−貯蔵部４４側に達した現像剤のみに接触する。トナ−に接触する現像剤は仕切り板４１を挟んで交番磁界を発生する現像剤担持ロ−ル４５と対向しているため、仕切り板４１の磁性板４１ｂで交番磁界が遮断あるいは弱められ、交番磁界が及ばずほとんど動かないためトナ−は取り込まれない。
【００７２】
トナ−が消費されると、現像剤担持ロ−ル４５周りの全現像剤の嵩が減少するため、現像剤溜り形成部材４２によって形成された現像剤溜り部２００もトナ−の消費によって水位が低下する。現像剤溜り部２００とトナ−が接触する位置が仕切り板４１の下端近辺まで下がってくると、仕切り板４１に遮断されない強い交番磁界がトナ−と接触する現像剤に及ぶ様になり、トナ−に接触する現像剤が転がり移動するため、トナ−が取り込まれる。
【００７３】
トナ−の取り込みが続くと、現像剤溜り部２００の嵩が再び上昇するため、交番磁界が遮断される所定水位以上で現像剤の動きが急激に鈍くなってトナ−取り込みが停止してトナ−濃度が一定に保たれる。
【００７４】
この現像装置４００を用いて第１実施形態と同様の連続プリントを実施したところ、トナ−濃度が安定して一定に保たれ、濃度低下やかぶりのない良好な画質が安定して得られた。
【００７５】
図７は、仕切り板の各種形態を示す図である。
【００７６】
図７（ａ）には、前述した図６に示す仕切り板４１が示されている。また、図７（ｂ）には、非磁性板４６ａと、その非磁性板４６ａの先端に継ぎ足された磁性板４６ｂからなる仕切り板４６が示されている。さらに、図７（ｃ）には、全体が磁性板からなる仕切り板４７が示されている。このように、少なくとも下端部に磁性材料を含む部分を備えた仕切り板４６，４７を用いても、仕切り板４１を用いた場合と同様の効果を得ることができる。
【００７７】
図８は、本発明の第３実施形態の現像装置における、トナ−供給部の概略構成図である。
【００７８】
この現像装置５００におけるトナ−供給部には、図６に示す現像剤担持ロ−ル４５と同様、Ｓ極とＮ極が交互に着磁された磁石ロ−ル５５ｂを内蔵し、外側に非磁性スリ−ブ５５ａを回転可能に設けた構成の現像剤担持ロ−ル５５が備えられている。またこのトナ−供給部には、現像剤溜り形成部材５２と、その現像剤溜り形成部材５２の斜面に先端部が垂直に対向した仕切り板５１が備えられている。このような形状を有する仕切り板５１を備えることにより、その仕切り板５１と現像剤溜り形成部材５２との隙間変動が小さく抑えられ、ＴＣ（トナー濃度）制御を精度よく行なうことができる。即ち、仕切り板５１の下端部が、磁石ロ−ル５５ｂから離れる方向に設けられているため、トナ−と接触する現像剤の動きを現像剤嵩の増減に応じて細かく制御することができる。従って、トナ−濃度が目標レベルに対して、大幅に低い時にはトナ−と接触する現像剤が強い交番磁界の影響を受けて激しく動くため、トナ−を短時間に多く取り込むことができ、これによりトナ−濃度が上昇して、目標レベルに近づくに従い、トナ−と接触する現像剤の位置が上昇して徐々に交番磁界の影響が弱まるため、現像剤の動きも徐々に小さくなり、取り込むトナ−量も徐々に少なく制御される。その結果、目標トナ−濃度に対して精度よく、最小の時間でトナ−濃度を調整することが可能となる。
【００７９】
このようなトナ−供給部を有する現像装置５００を用いて第１実施形態と同様の連続プリントを実施したところ、トナ−濃度が安定して一定に保たれ、濃度低下やかぶりのない良好な画質が安定して得られた。
【００８０】
図９は、本発明の第４実施形態の現像装置における、トナ−供給部の概略構成図である。
【００８１】
この現像装置６００におけるトナ−供給部には、図８に示す現像剤担持ロ−ル５５と同様、磁石ロ−ル６５ｂを内蔵し、外側に非磁性スリ−ブ６５ａを回転可能に設けた構成の現像剤担持ロ−ル６５が備えられいる。またこのトナ−供給部には、現像剤溜り形成部材６２と、その現像剤溜り形成部材６２の斜面側に傾いた方向に延びた構造の仕切り板６１が備えられている。このような形状を有する仕切り板６１を備えることにより、現像剤溜り部の嵩が増加してトナ−との接触位置が上昇するほど急激に交番磁界から遠ざかるため、トナ−取り込みを敏感に行なうことができる。
【００８２】
このようなトナ−供給部を有する現像装置６００を用いて第１実施形態と同様の連続プリントを実施したところ、トナ−濃度が安定して一定に保たれ、濃度低下やかぶりのない良好な画質が安定して得られた。
【００８３】
【発明の効果】
以上説明したように、本発明の現像装置によれば、複雑なトナ−濃度制御機構を設けずに簡素な構成でトナ−消費に応じた量のトナ−を取り込み、短時間で磁性キャリアと混合攪拌、帯電を行なうことができる。このため、濃度低下、濃度ムラ、かぶりのないトナ−濃度が安定した画質が得られ、特に現像剤の循環経路が短かい構成の小型の現像装置に好適である。
【図面の簡単な説明】
【図１】本発明の第１実施形態の現像装置を用いた画像形成装置の概略構成図である。
【図２】本発明の第１実施形態の現像装置の概略構成図である。
【図３】図２に示す現像ロール周面の部分拡大断面図である。
【図４】現像ロ−ルを構成する磁気記録層の着磁方法の一例を示す図である。
【図５】本発明の第１実施形態の現像装置を用いて密度の異なる画像をそれぞれ連続してプリントした場合の現像ロ−ル上の現像剤のトナ−濃度変化を示す図である。
【図６】本発明の第２実施形態の現像装置における、トナ−供給部の概略構成図である。
【図７】仕切り板の各種形態を示す図である。
【図８】本発明の第３実施形態の現像装置における、トナ−供給部の概略構成図である。
【図９】本発明の第４実施形態の現像装置における、トナ−供給部の概略構成図である。
【符号の説明】
１感光体ドラム
１ａ円筒部材
１ｂ感光体層
２帯電器
３露光手段
４，４００，５００，６００現像装置
５転写前コロトロン
６転写コロトロン
７剥離コロトロン
８クリ−ナ
９光除電器
１０記録用紙
２０ハウジング
２１現像ロ−ル
２１ａ導電性基体
２１ｂ磁気記録層
２２現像剤回収ロ−ル
２２ａ，２３ａ，４５ａ，５５ａ，６５ａスリ−ブ
２２ｂ，２３ｂ磁界発生部材
２３層形成ロ−ル
２４磁気記録用ヘッド
２５コア部材
２６コイル
２７磁束
３１，４１，４６，４７，５１，６１仕切り板
３２，４２，５２，６２現像剤溜り形成部材
３３，４３トナ−搬送部材
３４，４４トナ−貯蔵部
３５補給トナ−
３６現像剤
４１ａ，４６ａ非磁性板
４１ｂ，４６ｂ磁性板
４５，５５，６５現像剤担持ロ−ル
４５ｂ，５５ｂ，６５ｂ磁石ロ−ル
１００，２００現像剤溜り部[0001]
BACKGROUND OF THE INVENTION
The present invention uses a developer containing a magnetic carrier and a toner electrostatically attracted to the magnetic carrier, and selectively transfers toner to an electrostatic latent image formed on an image carrier. The present invention relates to a developing device for visualizing an electrostatic latent image.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with respect to a developing device that supplies a two-component developer comprising a toner and a magnetic carrier to an image carrier and develops an electrostatic latent image formed on the image carrier, the device is reduced in size and cost. Therefore, a technique for controlling the toner concentration without providing a complicated toner concentration control mechanism having a toner concentration sensor or the like has been proposed.
[0003]
For example, in Japanese Patent Application Laid-Open No. 63-4278, a developer shielding member is provided on the downstream side of the toner supply port on the upstream side of the developer layer thickness regulating member with respect to the developer conveying direction. By controlling the developer overflowed by the regulating member by changing the volume of the developer by shielding it with the developer shielding member, and by covering the toner supply port with the developer whose volume has changed, the toner intake amount is controlled. A technique for stably maintaining the toner concentration has been proposed.
[0004]
Japanese Patent Laid-Open No. 8-185051 provides a developer retaining portion that retains a predetermined amount of developer, and the toner retaining portion closes the toner supply port with the developer that changes in volume. There has been proposed a technique for controlling the toner density by adjusting the uptake of toner.
[0005]
Further, Japanese Patent Application Laid-Open No. 9-311551 discloses that a toner is brought into contact with a developer overflowing with a developer layer thickness regulating member and U-turned, and conveyed together using gravity to enter the developer chamber. There has been proposed a technique for taking in toner and supplying a toner having a density corresponding to a change in the volume of the developer in the developer chamber to a developing roll.
[0006]
[Problems to be solved by the invention]
However, in the technique proposed in Japanese Patent Laid-Open No. 63-4278, the taken toner is transported to the front of the developer layer thickness regulating member with almost no stirring, and passes through the developer layer thickness regulating member. In addition, since stirring and charging are performed with a strong pressure, uniform dispersion of toner and proper charging cannot be obtained, or the developer deteriorates quickly, resulting in fogging, uneven density, and toner stains. There's a problem.
[0007]
Further, in the technique proposed in Japanese Patent Application Laid-Open No. 8-185505, although the entrance of the developer retaining portion is blocked by the increase in volume, the moving magnetic brush is in contact with the toner, so that the toner is developed. It is conveyed with the movement of the agent layer. Therefore, toner taking-in does not stop completely, and there is a problem that the toner density becomes high and fogging occurs when images with little toner consumption are continuous.
[0008]
Further, in the technique proposed in Japanese Patent Application Laid-Open No. 9-311551, the developer layer thickness regulating member is prevented from proceeding to the developing region and is pushed back to supply toner to the U-turned developer. The U-turned developer lump moves slowly as a whole as the ground plate moves, so the toner carried along with the developer is taken in very slowly, Further, the toner is hardly agitated during the conveyance, so that the toner is conveyed in a state of being stuck in the gaps between the developers. Finally, when it comes into contact with the magnetic brush on the surface of the developing roller, it is transported on the sleeve constituting the developing roll while holding the toner mass, but the upper part of the magnetic brush has a U-turn. Since the developed developer is placed, the lower layer developer is transported without being sufficiently stirred. Therefore, there is a problem that the response is slow with respect to the decrease in toner on the sleeve, and it takes time until the concentration is restored. Further, since mixing and stirring with the magnetic carrier and charging are insufficient, an image defect such as a decrease in density, fogging, or toner mass is directly developed.
[0009]
In view of the above circumstances, an object of the present invention is to provide a developing device that can control the toner density with a simple configuration without using a complicated toner control mechanism and can always obtain a stable image density.
[0010]
[Means for Solving the Problems]
  The developing device of the present invention that achieves the above object uses an electrostatic latent image formed on an image carrier using a developer containing magnetic carrier particles and a toner electrostatically adsorbed to the magnetic carrier particles. In the developing device for selectively transferring the toner to the surface and visualizing the electrostatic latent image,
  Developing with an alternating magnetic field generating means for generating an alternating magnetic field by rotating around a horizontal rotation axis with a plurality of magnetic poles arranged in the rotation direction, and carrying and transporting the developer on the surface. Agent carrier,
  A developer reservoir formed by accumulating a part of the developer at a position adjacent to a portion where the developer is conveyed downward by the developer conveyance body of the developer conveyance body;
  A toner storage unit for storing replenishment toner and replenishing the replenishment toner to the developer reservoir from a side facing the developer transport body with the developer reservoir sandwiched therebetween;,
  A partition plate is provided so that a lower end thereof is positioned so as to be positioned in the developer reservoir, and a partition plate that restricts contact between the replenishment toner of the toner storage unit and the developer of the developer reservoir is provided.
[0012]
Moreover, it is preferable that the said partition plate is provided with the part containing a magnetic material in a lower end part at least.
[0013]
Further, the toner storage unit slides the replenishment toner toward the developer reservoir in the adjacent portion of the developer reservoir, and the volume of the replenishment toner supplied to the developer reservoir increases. It is also preferable that the replenishment toner has a slope for separating it from the alternating magnetic field generating means.
[0014]
The developer transport body may include a cylindrical sleeve and a fixed magnet that rotates within the cylindrical sleeve.
[0015]
Further, the developer transport body may be a rotary roll having a plurality of magnetic poles formed on the surface over the entire circumference.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0017]
FIG. 1 is a schematic configuration diagram of an image forming apparatus using the developing device according to the first embodiment of the present invention.
[0018]
The image forming apparatus shown in FIG. 1 includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 includes a cylindrical member 1a made of a conductive material and a thin photosensitive layer 1b formed on the surface of the cylindrical member 1a. For example, a negatively charged organic photoreceptor is used as the photoreceptor layer 1b. The photosensitive drum 1 is rotationally driven in the direction of arrow A by a driving unit (not shown).
[0019]
Further, around the photosensitive drum 1, a developing device having a developing roller 21 made up of a charger 2, an exposing unit 3, and a cylindrical member disposed so as to face the photosensitive drum 1 along the rotation direction thereof. An apparatus 4, a pre-transfer corotron 5, a transfer corotron 6, a peeling corotron 7, a cleaner 8, and an optical static eliminator 9 are provided. The developing device 4 is a developing device according to the first embodiment of the present invention, and details will be described later.
[0020]
In the image recording apparatus configured as described above, the photosensitive drum 1 is rotationally driven in the direction of arrow A, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined voltage by the charger 2. Next, the exposure unit 3 performs exposure corresponding to the image on the surface of the photosensitive drum 1 to form an electrostatic latent image. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 4 to be visualized. At this time, a developing bias is applied to the developing roll 21 by a developing bias power source (not shown).
[0021]
The toner image formed on the photosensitive drum 1 is charged by the pre-transfer corotron 5 as necessary, and then transferred onto the recording paper 10 by charging of the transfer corotron 6. Further, the recording paper 10 is peeled from the surface of the photosensitive drum 1 by charging of the peeling corotron 7. Next, the recording paper 10 is conveyed to a fixing device (not shown), and a toner image is fixed on the recording paper 10 to complete image formation.
[0022]
On the other hand, the remaining toner is cleaned by the cleaner 8 on the surface of the photosensitive drum 1 after the transfer of the toner image and the peeling process of the recording paper 10 is completed, and the residual charge is exposed by the light neutralizer 9. The charge is removed and it is prepared for the next image forming process.
[0023]
As the exposure means 3, any exposure means can be used as long as exposure according to image information is possible. For example, a laser writing device, an LED array, a uniform light source, and a liquid crystal micro shutter. Any liquid crystal light valve made of-can be used according to the purpose. Further, the exposure means 3 may perform image portion exposure or non-image portion (background portion) exposure, and can be appropriately selected as necessary.
[0024]
Next, the developing device 4 of the first embodiment of the present invention constituting the image forming apparatus shown in FIG. 1 will be described with reference to FIG.
[0025]
FIG. 2 is a schematic configuration diagram of the developing device according to the first embodiment of the present invention.
[0026]
The developing device 4 includes a housing 20 that houses a developer 36 including magnetic carrier particles and toner that is electrostatically adsorbed to the magnetic carrier particles. In the housing 20, a developing roller 21 that carries a developer 36 on its peripheral surface and transports it to a region facing the photosensitive drum 1, and a developing region that is disposed in close proximity to the developing roller 21. A developer collecting roll 22 for collecting the developer 36 that has passed through the developing roll 21 is provided. In the housing 20, the developing roller 21 is disposed opposite to the developing roller 21 at a predetermined interval, and the developer 36 is carried on the surface and conveyed to a position facing the developing roller 21. The layer forming roll 23 (an example of the developer conveying member referred to in the present invention) is provided. Further, a part of the developer 36 is accumulated in the housing 20 at a position adjacent to a portion of the layer forming roll 23 where the developer 36 is conveyed downward by the layer forming roll 23. A developer reservoir 100 is provided. In the housing 20, the replenishment toner 35 is stored, and the replenishment toner 35 is replenished to the developer reservoir 100 from the side facing the layer forming roll 23 with the developer reservoir 100 interposed therebetween. A reservoir 34 is also provided. The toner storage unit 34 slides the replenishment toner 35 toward the developer reservoir 100 at an adjacent portion of the developer reservoir 100 and increases the volume of the replenishment toner supplied to the developer reservoir 100. The developer reservoir forming member 32 is an inclined surface for separating the replenished toner from a magnetic field generating member 23b described later. Further, the toner storage unit 34 is provided with a toner conveying member 33 that guides the replenishing toner 35 of the toner storage unit 34 through the developer storage forming member 32 so as to come into contact with the developer storage unit 100.
[0027]
The developing device 4 is a partition plate that is erected so that its lower end is positioned in the developer reservoir 100 and restricts the contact between the replenishment toner 35 in the toner reservoir 34 and the developer 36 in the developer reservoir 100. 31 is provided.
[0028]
3 is a partially enlarged cross-sectional view of the circumferential surface of the developing roll shown in FIG.
[0029]
As shown in FIG. 3, the developing roll 21 includes a conductive substrate 21a and a magnetic recording layer 21b laminated on the conductive substrate 21a. A developing bias voltage is applied to the conductive substrate 21a by a developing bias power source (not shown). The magnetic recording layer 21b is alternately magnetized with S and N poles at a very small pitch that can hold only about one layer of magnetic carrier over the entire circumference of the developing roll 21.
[0030]
The magnetic recording layer 21b has γ-Fe as a magnetic material.₂O_ThreeHowever, polyurethane is used as the binder resin, and the thickness of the magnetic recording layer 21b is 50 μm.
[0031]
FIG. 4 is a diagram showing an example of a method for magnetizing the magnetic recording layer constituting the developing roll.
[0032]
Magnetization of the magnetic recording layer 21b constituting the developing roll 21 is performed by a magnetic recording head 24 disposed close to the peripheral surface of the developing roll 21, as shown in FIG.
[0033]
The magnetic recording head 24 includes a core member 25 made of a soft magnetic material and having both ends arranged in parallel at a predetermined interval, and a coil 26 wound around the core member 25. Both end portions of the core member 25 are disposed so as to be close to the peripheral surface of the developing roll 21. A magnetizing current is supplied to the coil 26 from a power source via a magnetizing signal generator (not shown). When a current flows through the coil 26, a magnetic flux 27 is generated in the core 26. The magnetic flux 27 passes through the magnetic recording layer 21 b from the tip of the core member 25. The magnetizing current supplied to the coil 26 is supplied intermittently or by changing the direction of the appropriate current through the magnetizing signal generator, and the developing roller 21 is rotationally driven in the direction of arrow A shown in FIG. The layer 21b is magnetized to a predetermined magnetization pattern. The developing roll 21 may be provided with a potential difference from the photosensitive drum 1 (see FIG. 2) while a magnetic field is applied to the surface to hold the magnetic carrier. A thin layer of material may be formed by vapor deposition or the like.
[0034]
Returning to FIG. 2 again, the description will be continued. The developer recovery roll 22 shown in FIG. 2 includes a cylindrical non-magnetic conductive sleeve 22a having a hollow part with a distorted shape, and a magnetic field generating member 22b located inside the cylindrical non-magnetic conductive sleeve 22a. The magnetic field generating member 22b is provided such that magnetic poles of different polarities are alternately magnetized over the entire circumference and can rotate independently of the outer fixed sleeve 22a.
[0035]
Further, the layer forming roll 23 includes a hollow cylindrical sleeve 23a supported so as to be capable of rotating, and a magnetic field generating member 23b rotating within the sleeve 23a. The magnetic field generating member 23b corresponds to the alternating magnetic field generating means referred to in the present invention, and generates an alternating magnetic field by rotating around a horizontal rotation axis with a plurality of magnetic poles arranged in the rotating direction. The magnetic field generating member 23b forms a magnetic brush of the developer 36 on the surface of the sleeve 23a by a magnetic field formed between adjacent magnetic poles. In the layer forming roll 23, only the magnetic field generating member 23b, or both the magnetic field generating member 23b and the sleeve 23a rotate in different directions, thereby generating an alternating magnetic field on the surface of the sleeve 23a. The magnetic brush is conveyed to a position facing the developing roll 21 arranged at a predetermined distance from the layer forming roll 23 while uniformly mixing and frictionally charging -35 with the magnetic carrier, and the tip of the magnetic brush is moved. A developer layer is formed in contact with the surface of the development roll 21. The magnetic pole pitch of the layer forming roll 23 is preferably about 1 to 6 mm with good conveyance / stirring performance, and is preferably larger than the magnetic pole pitch of the developing roll 21. In the present embodiment, a member having a diameter of 18 mm is used as the sleeve 23a, and the magnetic pole generating member 23b is an N pole and an S pole at intervals of about 5 mm on the circumferential surface of the sleeve 23a. A magnet roll in which are alternately magnetized is used. Each magnetic pole has a vertical magnetic flux density peak value of 50 mT on the sleeve 23a, and the sleeve 23a and the magnetic field generating member 23b rotate in the directions shown in the drawing.
[0036]
The developer reservoir forming member 32 is disposed so that the tip portion thereof is opposed to the layer forming roll 23 with a predetermined interval, and the developer volume on the layer forming roll 23 is increased by the accumulated developer 36. Hold in a state where it can be returned when it is low. The developer pool forming member 32 has a shape that is inclined from the front end and extends upward to the vicinity of the toner storage section 34, whereby the developer pool forming member 32 is formed along the developer pool forming member 32. Part 100 is formed. The inclination of the developer pool forming member 32 is preferably 15 ° to 60 °. The point (position) at which the developer pool forming member 32 starts to form the developer pool portion 100 closest to the layer forming roll 23 is relative to a horizontal straight line passing through the center of the layer forming roll 23. A position that falls vertically within an angle of 0 ° to 75 ° is preferable, and a position that falls within an angle of 0 ° to 45 ° is more preferable.
[0037]
The partition plate 31 has a lower end positioned at a predetermined distance from the layer forming roll 23 and in contact with the developer in the developer reservoir 100 at a predetermined height. It is provided so as to extend upward with a predetermined gap from the front end portion, and the vicinity of the lower end is within the range covered by the magnetic field of the layer forming roll 23. Specifically, the lower end is provided at a position 4 mm away from the layer forming roll 23 with a 2 mm gap from the tip of the developer reservoir forming member 32, and the material is, for example, nonmagnetic phosphor bronze Is used.
[0038]
The toner conveying member 33 is a wire-like rotating member that agitates the toner 35 in the toner storage unit 34 and conveys the toner 35 to the vicinity of the developer reservoir 100.
[0039]
The developing device 4 of the present embodiment includes a layer forming roll 23, a developer reservoir 100, and a toner storage unit 34. In the developing device 4, development is performed by the developer 36 that has passed through the development region. The agent reservoir 100 is formed, and a part of the developer reservoir 100 contacts the toner 34 of the toner reservoir 34. The movement of the developer 36 in contact with the toner 34 is controlled according to the toner density. For example, when the toner concentration is low, the alternating magnetic field of the magnetic field generating member 23b acts to cause the developer 36 to roll and move magnetically, so that the toner 35 in contact with the developer 36 is a lump. Then, it is finely loosened and taken into the reservoir of developer 36 while being stirred. At this time, since the developer 36 rolls and moves in a small number of magnetic carrier units, there are many opportunities for any incorporated toner particles to come into contact with the surface of the magnetic carrier. The toner is charged up to the surface of the magnetic carrier and becomes a uniform developer replenished with toner.
[0040]
On the other hand, as the toner density increases, the alternating magnetic field acting on the developer 36 that contacts the toner 35 weakens, and the movement of the developer 36 that contacts the toner 35 becomes dull, and the toner 35 is less taken up. Finally, the alternating magnetic field does not reach the developer 36 in contact with the toner 35, and the movement of the developer 36 is stopped, so that the toner 35 is completely taken in. In this state, the toner 35 is not taken in even if the developing device 4 is operated. Therefore, even if an image with little toner consumption continues, the toner density does not increase and fog does not occur. .
[0041]
As a result, the toner 35 can be supplied to the developer 36 in a required amount according to the toner consumption amount, so that the toner concentration can be kept almost constant, and charging failure, fogging, and uneven density due to insufficient stirring. Stable images can be obtained without toner stains. Further, since the toner 35 can be taken in, stirred and charged in a short time without applying a stress that causes great stress to the developer 36, the toner 36 can be taken in a large amount of toner. This is particularly effective in a small-sized developing device that cannot use a large amount of developer.
[0042]
Further, in the developing device 4 of this embodiment, the lower end is erected so as to be positioned in the developer reservoir 100, and the toner 35 in the toner reservoir 34 and the developer 36 in the developer reservoir 100 are brought into contact with each other. A partition plate 31 to be restricted is provided, and the toner 35 is supplied to a region far from the development region of the developer reservoir 100 partitioned by the partition plate 31, and the toner 35 is supplied to the developer reservoir 100. To touch. When the toner concentration is low, the developer 36 is in contact with the lower end of the partition plate 31 or has a gap so that the developer 36 near the lower end of the partition plate 31 of the developer reservoir 100 is affected by the alternating magnetic field. The carrier is actively rolling and moving in units of several grains. For this reason, the toner 35 coming into contact with the developer 36 is loosened by the developer 36, passed through the lower end of the partition plate 31 while being mixed and stirred, taken together, and charged enough to adhere to the surface of the magnetic carrier. And disperse uniformly.
[0043]
As the toner concentration increases, the bulk of the developer reservoir 100 increases, and the gap between the developer reservoir 100 and the partition plate 31 is closed. The toner 35 is supplied only to the region surrounded by the developer reservoir 100 and the partition plate 31, and when the bulk is further increased, the position in contact with the toner 35 moves along the partition plate 31, and the magnetic field generating member 23b As the distance increases, the alternating magnetic field reaching the developer 36 gradually becomes weaker than the lower end of the partition plate 31, and finally the position where the developer 36 and the toner 35 come into contact with a portion where the developer 36 cannot be moved magnetically. When the toner moves, the developer 36 coming into contact with the toner 35 stops moving at all, and the toner take-up is completely stopped.
[0044]
On the other hand, when the toner concentration decreases with the consumption of the toner 35, the bulk of the developer reservoir 100 decreases again, and the position where the developer 36 contacts the toner 35 is at the lower end of the partition plate 31. As it approaches and approaches the magnetic field generating member 23b, the alternating magnetic field acting on the developer 36 also strengthens, starts rolling, and resumes the toner 35 taking-in.
[0045]
Further, if the partition plate 31 includes a portion containing a magnetic material at least at the lower end, it acts on the developer when the bulk of the developer reservoir 100 increases beyond the lower end of the partition plate 31 due to the shielding effect. Since the alternating magnetic field is rapidly attenuated, toner intake control can be made sensitive.
[0046]
Further, in the developing device 4 of the present embodiment, the magnetic field generating member 23b is opposed to the magnetic field generating member 23b at a predetermined interval, and a part of the developer 36 is damped and extends from the magnetic field generating member 23b at a predetermined angle therefrom. A developer reservoir forming member 32 that is an inclined surface is provided. Therefore, as the toner 35 is taken in and the toner density increases and the developer reservoir 100 increases, the developer reservoir 100 spreads along the developer reservoir forming member 32 and is separated from the magnetic field generating member 23b. The developer 36 is not moved by the magnetic field. If the movement of the developer 36 stops, the toner 35 in contact with the developer 36 is not taken in, and the toner density does not increase. On the other hand, when the toner 35 is consumed and the toner density is lowered, the total volume of the developer 36 that circulates decreases. Therefore, the developer 36 that is sufficiently separated from the magnetic field generating member 23b and does not move in the alternating magnetic field is Along the developer pool forming member 32, the magnetic field generating member 23b is approached, and the contact interface between the toner 35 and the developer 36 moves. As a result, the developer 36 in contact with the toner 35 begins to roll and move again in the alternating magnetic field, so that the toner 35 is taken in and the toner density is maintained.
[0047]
Therefore, in the developing device 4 of the present embodiment, the toner density is always kept constant, the stirring and charging are insufficient, density unevenness and fog do not occur, and a good image can be stably obtained. .
[0048]
Next, the flow of the developer will be described.
[0049]
The developer layer carried on the developing roller 21 through the developing region is conveyed to a position facing the developer collecting roller 22. The developer collection roll 22 is disposed in close proximity to the development roll 21, and on the development roll 21 by the strong magnetic force of the magnetic field generating member 22 b inside the developer collection roll 22. Most of the developer is collected and moved onto the developer collection roll 22. The developer that has moved onto the developer collecting roller 22 moves clockwise on the sleeve 22a as the magnetic field generating member 22b rotates, and the distance of the sleeve 22a from the magnetic field generating member 22b. When it reaches a farther portion, the magnetic restraining force is weakened and falls from the sleeve 22a, and is transported while adhering onto the layer forming roll 23 located under the developer recovery roll 22. The developer 36 on the layer forming roll 23 is conveyed counterclockwise by the rotation of the magnetic field generating member 23b and the sleeve 23a, and a part of the developer 36 is blocked by the developer pool forming member 32. A developer reservoir 100 is formed. The developer reservoir 100 moves along the developer reservoir forming member 32 and comes into contact with the replenishing toner 35 carried by the toner conveying member 33 in the toner reservoir 34. At this point, since the developer 36 on the surface of the developer reservoir 100 is sufficiently close to the layer forming roll 23, the developer 36 is rolled while being rolled by an alternating magnetic field generated by the rotating magnetic field generating member 23b in the layer forming roll 23. The toner 35 which has moved to the side of the groove 23a and has come into contact with the developer reservoir 100 is successively taken in, mixed and stirred with a magnetic carrier while being conveyed to the side of the sleeve 23a, and charged.
[0050]
On the other hand, the other developer that has passed without being blocked by the developer pool forming member 32 is conveyed to a region facing the developing roller 21 while being stirred and charged along with the fluctuation of the magnetic field on the sleeve 23a. As a result, it reaches the vicinity facing the developing roll 21. The developing roller 21 and the layer forming roller 23 are arranged to face each other with a gap slightly narrower than the developer spike (the height on the magnetic pole) on the layer forming roller 23. The tip of the developer layer conveyed to the vicinity facing the roll 21 comes into contact with the surface of the development roll 21. Here, the developer on the layer forming roll 23 is transported in a direction different from the transport direction of the developing roller 21 in the region facing the developing roller 21, so that the surface of the developing roller 21 is It moves in a direction away from the closest position with the layer forming roll 23. Accordingly, the developer 36 is adsorbed only in the vicinity of the surface of the developing roller 21 and is conveyed along with the movement of the surface of the developing roller 21. Further, the developer 36 that could not reach the vicinity of the surface of the developing roller 21 is left behind and stays in a region in front of the layer forming roller 23 and the developing roller 21 that are in close proximity to each other. 21 is provided for the opportunity to contact the surface. Since the surface of the development roll 21 is always covered by the developer 36 that has been retained to form a pool and given the opportunity to contact the surface of the development roll 21, the development formed on the surface of the development roll 21. There is no shortage of drug layers. Further, since the magnetic recording layer 21b on the surface of the developing roller 21 has a small magnetization interval of 100 μm, the developer 36 in the vicinity of the surface of the developing roller 21 out of the excessively supplied developer 36. The magnetic binding force acts only on the upper layer of the developer 36, and the magnetic binding force hardly acts on the developer 36 in the upper layer portion, and the developer 36 conveyed by the layer forming roll 23 is supplied onto the developing roll 21. In the region where the layer is formed, gravity acts in a direction in which the developer 36 moves away from the developing roll 21, so that the magnetic force that has overcome the gravity of the developer 36 due to the magnetic binding force acting on the magnetic carrier of the developing roll 21. Only the developer 36 due to the restraining force is conveyed. Therefore, for example, the magnetic carrier whose surface is firmly in contact with the surface of the developing roller 21 is transported without detaching from the developing roller 21, but cannot be brought into direct contact with the surface of the developing roller 21 and is on the magnetic carrier. The magnetic carrier in the fallen state falls off and stays in the developer reservoir 100, or falls and returns onto the layer forming roll 23, so that the developer layer conveyed along with the movement of the developing roll 21 is The magnetic carrier becomes a uniform thin layer of about one layer.
[0051]
The uniform developer thin layer formed on the developing roller 21 is conveyed to the developing region facing the photosensitive drum 1 as the developing roller 21 rotates, and the toner adhered to the magnetic carrier. Only 35 is transferred to the electrostatic latent image on the photosensitive drum 1 and developed. Note that the developer layer is held in a non-contact state with respect to the photosensitive drum 1.
[0052]
Next, the toner supply mechanism will be described.
[0053]
When the toner 35 is consumed by development and the toner density decreases, the toner 35 is taken in as described above. However, the toner consumption is reduced or the toner 35 is sufficiently replenished to increase the toner density. As a result, the bulk of the developer reservoir 100 increases, the developer reservoir 100 contacts the lower end of the partition plate 31, and the replenishment toner 35 is supplied to the region surrounded by the partition plate 31 and the developer reservoir forming member 32. Is done. At a height at which the developer reservoir 100 finally comes into contact with the lower end of the partition plate 31, the developer 36 on the surface of the developer reservoir 100 is rolling and moving under the influence of the alternating magnetic field of the layer forming roll 23. Part of the developer 36 takes in the toner 35, passes through the lower end of the partition plate 31, and is conveyed to the sleeve 23 a side. Further, when the height of the developer reservoir 100 is increased, the surface of the developer reservoir 100 is separated from the layer forming roll 23, so that the alternating magnetic field exerted on the developer 36 is weakened, and the magnetic field of the developer 36 is reduced. The movement due to becomes dull and finally stops moving at all. Therefore, the toner 35 taken in by the movement of the developer 36 is reduced in both the amount and speed of loading as the developer 36 on the surface of the developer reservoir 100 moves, and finally is not taken in at all.
[0054]
When toner 35 is consumed by development in a state in which toner 35 intake is stopped, the toner density starts to decrease, the volume of developer reservoir 100 decreases, the height decreases, and the alternating magnetic field is reduced. In order to enter the affected area, the developer 36 starts to move again, and the toner 35 is taken in again. Therefore, the toner concentration can be kept constant with a simple configuration without providing a complicated toner concentration control mechanism having a toner concentration sensor or the like.
[0055]
The two-component developer 36 used in this embodiment is a mixture of a non-magnetic polyester toner and a ferrite magnetic carrier. However, a toner and a magnetic carrier made of other materials may be used. it can. The toner may be obtained by a polymerization method or a mixed pulverization method, but a spherical shape with high fluidity is preferred. By making the shape of the toner almost spherical, the fluidity is increased, the fluidity as a developer is improved, and the toner and the developer in the toner supply section move smoothly and uniformly. -Accumulation control can be performed.
[0056]
The magnetic carrier of the developer 36 is 10⁶It is desirable to use one having a magnetization of 45 KA / m or more and 360 KA / m or less in a magnetic field of / (4π) A / m.
[0057]
In addition, the shape of the partition plate 31 is not limited to this, and may be any shape as long as the alternating magnetic field weakens at least once in the height direction.
[0058]
Further, the developing system is not limited to this system, and it is needless to say that the developing system can be applied to other developing systems such as normal magnetic brush development as long as the toner supply unit has the same configuration.
[0059]
Next, the result of testing the density maintenance property when images having different print image densities are successively printed using the developing device 4 of the present embodiment is shown.
[0060]
There are two types of print patterns: the first half is blank and the second half is a solid image (image density is about 50%), and the first half is white and the second half is text (image density is about 2%). 100 sheets were continuously printed with the print pattern. The transition of toner density on the developing roller 21 at this time is shown in FIG.
[0061]
FIG. 5 is a graph showing changes in the toner density of the developer on the developing roll when images having different densities are successively printed using the developing device according to the first embodiment of the present invention.
[0062]
In this developing device 4, the toner 35 consumed in accordance with the toner consumption is immediately replenished. Therefore, as shown in FIG. 5, the toner density is stable regardless of the printing pattern. It is kept constant, and both print patterns do not cause a decrease in density or background fogging, and a good image quality can be stably obtained.
[0063]
In the developing device 4 of the present embodiment, the developer conveying body referred to in the present invention is described with an example of a layer forming roll 23 having a cylindrical sleeve 23 a and a magnetic field generating member 23 b that rotates in the sleeve 23. However, the present invention is not limited to this, and the developer transport body referred to in the present invention may be a rotating roll having a plurality of magnetic poles formed on the surface over the entire circumference.
[0064]
FIG. 6 is a schematic configuration diagram of a toner supply unit in the developing device according to the second embodiment of the present invention.
[0065]
The developing device 400 includes a developer carrying roll 45 (an example of a developer carrying body according to the present invention) that generates and carries an alternating magnetic field and carries the developer, and the developer carrying roll 45. A developer reservoir forming member 42 that blocks a part of the developer circulating through the developer to form the developer reservoir 200, and a toner that conveys the toner so as to supply the toner to the developer in the developer reservoir 200. A transport member 43, a toner storage unit 44 for storing replenishment toner, and a partition that limits a region in which a toner that is transported by the toner transport member 43 and contacts the developer reservoir 200 can contact the developer reservoir 200. A plate 41 is provided.
[0066]
The developer carrying roll 45 has a structure in which a S-pole and a N-pole are alternately magnetized and rotatable, and a non-magnetic sleeve 45a is rotatably provided outside. By rotating the magnet roll 45b, an alternating magnetic field is generated on the surface of the sleeve 45a, and the developer is carried on the sleeve 45a and conveyed while mixing and stirring.
[0067]
The developer reservoir forming member 42 is disposed so that the tip portion thereof is opposed to the developer carrying roll 45 at a predetermined interval, and the developer blocked by the tip portion is placed on the surface of the developer reservoir forming member 42. Hold along. As shown in FIG. 6, the developer pool forming member 42 has a shape in which a certain amount of the clogged developer is stored and separated from the developer carrying roll 45 along the slope with respect to a predetermined volume or more. It is a shape that rises like this.
[0068]
As the toner conveying member 43, a wire-like rotating member is used so as to agitate the toner in the toner storage unit 44 and convey the toner to the vicinity of the developer reservoir 200.
[0069]
The partition plate 41 includes a nonmagnetic plate 41a and a magnetic plate 41b attached to one surface of the nonmagnetic plate 41a. By this partition plate 41, an alternating magnetic field generated by the magnet roll 45b received by the developer on the side of the developer reservoir 200 that is partitioned by the partition plate 41 and in contact with the toner, the bulk of the developer is the partition plate. If it is above the lower end of 41, it can be blocked or weakened, so that toner uptake can be controlled sensitively. This is particularly effective in a small-sized developing device in which the developer amount is small and the change in the bulk of the developer reservoir 200 due to toner density is small.
[0070]
Next, the operation of the toner replenishing portion of the developing device 400 will be described.
[0071]
When the toner concentration is sufficiently high, the surface of the developer reservoir 200 is in contact with the lower end of the partition plate 41, and the toner supplied from the toner storage unit 44 is more than the toner storage unit 44 than the partition plate 41. Only contact the developer that has reached the side. Since the developer contacting the toner is opposed to the developer carrying roll 45 that generates an alternating magnetic field across the partition plate 41, the alternating magnetic field is blocked or weakened by the magnetic plate 41b of the partition plate 41, and the alternating Since the magnetic field does not reach and hardly moves, the toner is not captured.
[0072]
When the toner is consumed, the bulk of all the developer around the developer carrying roll 45 is reduced. Therefore, the water level of the developer reservoir 200 formed by the developer reservoir forming member 42 is also reduced by the consumption of the toner. descend. When the position where the developer reservoir 200 and the toner contact is lowered to the vicinity of the lower end of the partition plate 41, a strong alternating magnetic field that is not blocked by the partition plate 41 reaches the developer contacting the toner. Since the developer in contact with the toner rolls and moves, the toner is taken in.
[0073]
When toner is continuously taken in, the bulk of the developer reservoir 200 rises again, so that the developer moves abruptly at a predetermined water level where the alternating magnetic field is cut off, and toner take-in stops and the toner is stopped. Concentration is kept constant.
[0074]
When the same continuous printing as in the first embodiment was performed using the developing device 400, the toner density was stably kept constant, and good image quality without density reduction and fogging was stably obtained.
[0075]
FIG. 7 is a diagram showing various forms of the partition plate.
[0076]
FIG. 7A shows the partition plate 41 shown in FIG. 6 described above. FIG. 7B shows a partition plate 46 including a nonmagnetic plate 46a and a magnetic plate 46b joined to the tip of the nonmagnetic plate 46a. Further, FIG. 7C shows a partition plate 47 that is entirely made of a magnetic plate. As described above, even when the partition plates 46 and 47 having a portion including a magnetic material at least at the lower end are used, the same effect as that obtained when the partition plate 41 is used can be obtained.
[0077]
FIG. 8 is a schematic configuration diagram of a toner supply unit in the developing device according to the third embodiment of the present invention.
[0078]
In the toner supply section of the developing device 500, similarly to the developer carrying roll 45 shown in FIG. 6, a magnet roll 55b in which S poles and N poles are alternately magnetized is built in and is not on the outside. A developer carrying roll 55 having a structure in which a magnetic sleeve 55a is rotatably provided is provided. Further, the toner supply section includes a developer pool forming member 52 and a partition plate 51 whose front end portion is vertically opposed to the inclined surface of the developer pool forming member 52. By providing the partition plate 51 having such a shape, the variation in the gap between the partition plate 51 and the developer reservoir forming member 52 is suppressed to be small, and TC (toner concentration) control can be performed with high accuracy. That is, since the lower end portion of the partition plate 51 is provided in a direction away from the magnet roll 55b, the movement of the developer that comes into contact with the toner can be finely controlled according to the increase or decrease in the developer volume. Therefore, when the toner density is significantly lower than the target level, the developer in contact with the toner moves violently under the influence of a strong alternating magnetic field, so that a large amount of toner can be taken in a short time. As the toner density rises and approaches the target level, the position of the developer in contact with the toner rises, and the influence of the alternating magnetic field gradually weakens. The amount is gradually controlled to be small. As a result, it is possible to adjust the toner density with a minimum time with high accuracy with respect to the target toner density.
[0079]
When the same continuous printing as in the first embodiment was performed using the developing device 500 having such a toner supply unit, the toner density was stably maintained constant, and good image quality without reduction in density and fogging was obtained. Was obtained stably.
[0080]
FIG. 9 is a schematic configuration diagram of a toner supply unit in the developing device according to the fourth embodiment of the present invention.
[0081]
As in the developer carrying roller 55 shown in FIG. 8, the toner supply unit in the developing device 600 has a built-in magnet roller 65b and a nonmagnetic sleeve 65a provided rotatably on the outside. The developer carrying roll 65 is provided. The toner supply section is provided with a developer reservoir forming member 62 and a partition plate 61 having a structure extending in a direction inclined toward the slope side of the developer reservoir forming member 62. By providing the partition plate 61 having such a shape, the toner reservoir portion is rapidly moved away from the alternating magnetic field as the bulk of the developer reservoir increases and the contact position with the toner rises. Can do.
[0082]
When the same continuous printing as in the first embodiment was performed using the developing device 600 having such a toner supply unit, the toner density was stably maintained constant, and good image quality with no density reduction or fogging was obtained. Was obtained stably.
[0083]
【The invention's effect】
As described above, according to the developing device of the present invention, an amount of toner corresponding to the toner consumption is taken in with a simple configuration without providing a complicated toner density control mechanism, and mixed with the magnetic carrier in a short time. Stirring and charging can be performed. Therefore, it is possible to obtain a stable image quality with low density, uneven density, and no fogging toner density, and it is particularly suitable for a small-sized developing device having a short developer circulation path.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus using a developing device according to a first embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a developing device according to the first embodiment of the present invention.
3 is a partially enlarged cross-sectional view of a peripheral surface of a developing roll shown in FIG.
FIG. 4 is a diagram showing an example of a method for magnetizing a magnetic recording layer constituting a developing roll.
FIG. 5 is a graph showing changes in the toner density of the developer on the developing roll when images having different densities are successively printed using the developing device according to the first embodiment of the present invention.
FIG. 6 is a schematic configuration diagram of a toner supply unit in a developing device according to a second embodiment of the present invention.
FIG. 7 is a view showing various forms of a partition plate.
FIG. 8 is a schematic configuration diagram of a toner supply unit in a developing device according to a third embodiment of the present invention.
FIG. 9 is a schematic configuration diagram of a toner supply unit in a developing device according to a fourth embodiment of the present invention.
[Explanation of symbols]
1 Photosensitive drum
1a Cylindrical member
1b Photoreceptor layer
2 Charger
3 Exposure means
4,400,500,600 Developing device
5 Corotron before transfer
6 Transcription corotron
7 Peeling corotron
8 Cleaner
9 Light static eliminator
10 Recording paper
20 Housing
21 Development Roll
21a Conductive substrate
21b Magnetic recording layer
22 Developer collection roll
22a, 23a, 45a, 55a, 65a Sleeve
22b, 23b Magnetic field generating member
23 Layer formation roll
24 Magnetic recording head
25 Core material
26 coils
27 Magnetic flux
31, 41, 46, 47, 51, 61 Partition plate
32, 42, 52, 62 Developer reservoir forming member
33, 43 Toner conveying member
34, 44 toner storage
35 Supply Toner
36 Developer
41a, 46a Non-magnetic plate
41b, 46b Magnetic plate
45, 55, 65 Developer carrying roll
45b, 55b, 65b Magnet Roll
100, 200 Developer reservoir

Claims

Using a developer containing magnetic carrier particles and a toner electrostatically attracted to the magnetic carrier particles, the toner is selectively transferred to an electrostatic latent image formed on an image carrier. In a developing device for visualizing an electrostatic latent image,
Developing with an alternating magnetic field generating means for generating an alternating magnetic field by rotating around a horizontal rotation axis with a plurality of magnetic poles arranged in the rotation direction, and carrying and transporting the developer on the surface. An agent carrier;
A developer reservoir formed by accumulating a part of the developer at a position adjacent to a portion of the developer transport body where the developer is transported downward by the developer transport body;
A toner storage unit for storing replenishment toner and replenishing the replenishment toner to the developer reservoir from the side facing the developer transport body with the developer reservoir sandwiched therebetween ;
Development comprising a partition plate standing upright so that a lower end thereof is positioned in the developer reservoir, and restricting contact between the replenishing toner in the toner reservoir and the developer in the developer reservoir apparatus.

The developing device according to claim 1 , wherein the partition plate includes a portion including a magnetic material at least at a lower end portion .

The toner storage unit slides the replenishment toner toward the developer reservoir in a portion adjacent to the developer reservoir, and the replenishment toner is supplied as the volume of the replenishment toner supplied to the developer reservoir increases. 3. The developing device according to claim 1 , further comprising a slope for separating the toner from the alternating magnetic field generating means .

4. The developing device according to claim 1, wherein the developer transport body includes a cylindrical sleeve and a fixed magnet that rotates in the cylindrical sleeve . 5.

The developer transport member is a developing device according to any one of the preceding claims, characterized in that a rotating roll in which a plurality of magnetic poles are formed over the circumferential entire periphery to the surface 3.