JP4167002B2

JP4167002B2 - Developing device and image forming apparatus

Info

Publication number: JP4167002B2
Application number: JP2002114973A
Authority: JP
Inventors: 隆程島; 信貴竹内; 康雄三好; 一郎門田; 洋志中井
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-04-17
Filing date: 2002-04-17
Publication date: 2008-10-15
Anticipated expiration: 2022-04-17
Also published as: JP2003307924A

Description

【０００１】
【発明の属する技術分野】
本発明は、現像装置、特に現像ローラの軸方向に平行に配設され互いに逆の方向に現像剤を搬送する２つの現像剤搬送部材を備えた現像装置及びこれを有する画像形成装置に関する。
【０００２】
【従来の技術】
複写機、ファクシミリ、プリンタ等の画像形成装置には一般に、感光体等の像担持体を現像するための現像装置を有している。現像装置として、トナーとキャリアよりなる２成分現像剤を用いる２成分現像方式の装置が知られており、この現像装置では、現像剤撹拌部分でキャリアとトナーを十分に混合した現像剤を、現像ローラに供給し、現像ローラにより現像剤を像担持体としての感光体と対向する領域に搬送して、感光体表面の静電潜像にトナーを付着させて現像する。
【０００３】
現像剤を撹拌混合し、現像ローラに供給する現像剤撹拌部の構成は、従来様々な構成が用いられているが、現在では、現像ローラの横方向や下方に、撹拌搬送スクリュを水平方向に２本配置する構成が主流である。その一例として、図６に、像担持体としての感光体ドラム２０５に対向配設された現像ローラ２０１の斜め下方に水平方向に２本の攪拌搬送スクリュ２０２、２０３を配設した現像装置２００を示す。
【０００４】
このような構成の現像装置２００では、２本のスクリュ２０２、２０３の間に仕切り板２０４を設け、２本のスクリュ２０２、２０３は互いに反対の方向に現像剤を搬送し、仕切り板２０４のない両端部分で現像剤の受け渡しを行なうことで、現像剤を循環させている。現像ローラ２０１から離れて配置された第１スクリュ２０２では、その搬送方向上流側で、トナーを補給され、トナーとキャリアを混合しながら搬送して、第１スクリュ２０２の下流側で、現像ローラ２０１に近く配置された第２スクリュ２０３に現像剤を受け渡す。
【０００５】
第２スクリュ２０３は現像ローラ２０１への現像剤の供給、現像ローラ２０１からの現像剤の回収を行ないながら、現像剤を搬送し、その下流側で、第１スクリュ２０２に現像剤を受け渡す。現像ローラ２０１は、図示しない複数の磁極を配置した図示しないマグネットローラを内部に有し、固定されたマグネットローラの周囲を図示しない円筒状のスリーブが回転する構成となっている。第２スクリュ２０３に対向する部分では現像剤の汲み上げを行う機能と、現像を終了した現像剤を切り離す機能とが必要であり、マグネットローラにはその機能を果たすように磁極が設けられている。
【０００６】
しかし、このような構成の現像装置２００では現像ローラ２０１、撹拌スクリュ２０２、２０３の２本が横方向に並んでいるために縦方向の大きさは小さくできるが、横方向の大きさは小さくすることが難しい。昨今、電子写真方式を用いた画像形成装置ではカラー化が進んでいるが、その生産性を向上させるためには、イエロー、マゼンタ、シアン、ブラックの各色毎に、４個の像担持体としての感光体ドラムを用いて画像を形成するタンデム方式を採用することが効果的である。
【０００７】
タンデム方式では４個の感光体ドラムを横方向に並べて、各ドラムに帯電装置等の作像装置を設けることになり、現像装置も各ドラムに対して設けることとなる。画像形成装置を小さくするためには、各ドラムの間隔を狭める必要があるがその為には現像装置も水平方向の大きさを小さくする必要があり、上述した２本のスクリュを水平方向に並べる方式の現像装置では省スペース化に限界がある。
【０００８】
特開平１１−２０２６２７号公報においては、上下に配置された撹拌スクリュと供給スクリュとにより現像剤を循環させる現像装置が開示されている。またこの現像装置では、撹拌スクリュが供給スクリュより大きい搬送能力を発揮するようにし、現像剤の総量を減らし撹拌スクリュが部分的にしか浸かっていない状態にしても現像剤のバランスが保たれ、スクリュの駆動トルクを低減するとともに現像剤の寿命を長くするようになっている。
【０００９】
【発明が解決しようとする課題】
しかし、特開平１１−２０２６２７によって開示されたかかる現像装置では、現像ローラの横にスクリュを２本、縦方向に並べた構成としており、横方向の省スペース化が図れるものの、現像後、トナー濃度の少なくなった現像剤と、トナー濃度の高い現像剤が同時に現像ローラに汲み上げられることになり、現像ローラ上の現像剤のトナー濃度が均一にならず、画像濃度にムラが生じやすく均一な画像が得られ難いという不具合がある。
【００１０】
また、同様の不具合が、上スクリュによって撹拌される現像剤と、下スクリュによって撹拌される現像剤とが所々で入れ替わってしまうため、現像剤が均一に撹拌されにくいことからも生じる。さらに、帯電の不充分なトナーがあるためにハーフトーン画像部の粒状性が悪化したり、地肌部にトナーが付着する地肌汚れや、キャリアからトナーが遊離してしまうことによるトナー飛散等の不具合を生じるという不具合もある。
【００１１】
本発明は、現像ローラの軸方向に平行に配設され互いに逆の方向に現像剤を搬送する２つの現像剤搬送部材を備えた現像装置であって、水平方向の大きさを小さくした上で、高画質が得られ、現像剤へのストレスが少なく、帯電を十分に行い安定した現像性能が得られる現像装置及びこれを有する画像形成装置を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上記目的を達成するため、請求項１記載の発明は、像担持体を現像する現像ローラと、上記現像ローラの軸と平行に配設されこの軸の一方向に現像剤を搬送する第１現像剤搬送部材と、上記現像ローラの軸と平行に配設されこの軸の他方向に現像剤を搬送する第２現像剤搬送部材と、上記第１現像剤搬送部材と、上記第２現像剤搬送部材との間に配設され、上記第１現像剤搬送部材の周囲の空間と、上記第２現像剤搬送部材の周囲の空間とを遮蔽する仕切り板とを有する現像装置において、上記現像ローラは、現像剤を汲み上げる現像剤汲み上げ部と、この現像剤汲み上げ部の上方に位置し現像剤を離す現像剤離し部とを有し、上記第１現像剤搬送部材を、上記現像剤汲み上げ部近傍に配置し、上記第２現像剤搬送部材を、上記現像剤離し部近傍に配置し、上記第１現像剤搬送部材の回転方向を、上記現像ローラの回転方向と同じとし、上記第２現像剤搬送部材の回転方向を、上記現像ローラの回転方向と逆とし、上記第１現像剤搬送部材の周囲の空間においては、現像剤が上記現像ローラに寄せられながら上記第１現像剤搬送部材によって上記一方向に搬送され、上記第２現像剤搬送部材の周囲の空間においては、現像剤が上記現像ローラから離されながら上記第２現像剤搬送部材によって上記他方向に搬送され、上記仕切り板は、上記第１現像剤搬送部材の周囲の空間と、上記第２現像剤搬送部材の周囲の空間とを連通する連通口であって、上記第１現像剤搬送部材の現像剤の搬送方向の下流部分の、上記現像ローラから離れた位置の同仕切り板を残しつつ、同下流部分の上記現像ローラ寄りの位置に形成された連通口を有することを特徴とする。
【００１３】
請求項２記載の発明は、請求項１記載の現像装置において、上記第２現像剤搬送部材の現像剤の搬送方向の上流部分において、現像剤へのトナー補給を行うことを特徴とする。
【００１４】
請求項３記載の発明は、請求項１または２記載の現像装置において、上記現像ローラと上記仕切り板との間隔を０．２ｍｍ〜１ｍｍの範囲としたことを特徴とする。
【００１５】
請求項４記載の発明は、請求項３記載の現像装置において、上記仕切り板は、上記現像ローラの回転方向における、上記現像剤離し部の下流側且つ上記現像剤汲み上げ部の上流側の、上記現像ローラへの現像剤の付着量が少ない領域で、上記現像ローラに対向していることを特徴とする。
【００１６】
請求項５記載の発明は、請求項３または４記載の現像装置において、上記仕切り板は、上記現像ローラの回転方向における、上記現像剤離し部の下流側且つ上記現像剤汲み上げ部の上流側の、上記現像ローラ表面の磁束密度が１０ｍＴ以下の領域で、上記現像ローラに対向していることを特徴とする。
【００１９】
請求項６記載の発明は、請求項１ないし５の何れか１つに記載の現像装置において、上記第１現像剤搬送部材と、上記第２現像剤搬送部材とは、その軸を中心とした回転により現像剤を搬送する形状をなしており、上記第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、上記第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくしたことを特徴とする。
【００２０】
請求項７記載の発明は、請求項１ないし６の何れか１つに記載の現像装置を有する画像形成装置にある。
【００２１】
【実施例】
図１に本発明を適用した現像装置及びこの現像装置を有する画像形成装置の概略を示す。画像形成装置は複写機、ファクシミリ、プリンタ等周知のものであり、本発明を適用した現像装置を用いることができるタイプの画像形成装置であればどのようなものでも良い。本実施例の画像形成装置はカラー画像を形成するものであるが、単色の画像を形成するものであっても良い。
【００２２】
画像形成装置２０は、一般にコピー等に用いられる普通紙と、ＯＨＰシートや、カード、ハガキといった９０Ｋ紙、坪量約１００ｇ／ｍ^２相当以上の厚紙や、封筒等の、普通紙よりも熱容量が大きないわゆる特殊シートとの何れをもシート状の記録媒体として用いることが可能である。以下これらを記録媒体と記載する。
【００２３】
画像形成装置２０は、原稿画像に応じて各色ごとの画像を形成する作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫと、作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫに対向して配置された転写装置２２と、各作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫと転写装置２２とが対向する転写領域に各種記録媒体を供給する記録媒体供給手段としての給紙カセット２３、２４、３３と、給紙カセット２３、２４、３３から搬送されてきた記録媒体を作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫによる作像のタイミングにあわせて供給するレジストローラ３０とを有している。
【００２４】
また、画像形成装置２０は、作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫのそれぞれに備えられた後述する感光体ドラム２５Ｃ、２５Ｙ、２５Ｍ、２５ＢＫと転写装置２２との対向位置である転写領域３５Ｃ、３５Ｙ、３５Ｍ、３５ＢＫのうちの少なくとも１つの転写領域においてトナー像を転写された後の記録媒体の定着を行う定着装置１と、筐体３１と、筐体３１の上部に配設された、定着装置１を通過しトナー像が定着した記録媒体を積載するための排紙トレイ３２とを有している。
【００２５】
また、画像形成装置２０は、給紙カセット２３、２４、３３それぞれから記録媒体を送り出すピックアップローラ４０、４１、４２と、給紙カセット２３、２４、３３から搬送されてきた記録媒体をレジストローラ３０に向けて搬送するローラ構造４４と、排紙トレイ３２に向け筐体３１外部へ記録媒体を排出する排出ローラ４５と、定着装置１により定着された記録媒体を排出ローラ４５に向けて搬送するローラ構造４３とを有している。
【００２６】
転写装置２２は、画像形成装置２０が図の左右方向において小型になるよう、斜め方向に配設され、矢印Ｂで示すシート状媒体搬送方向が斜め方向となっている。これにより、画像形成装置２０は、図の左右方向における筐体３１の幅が、Ａ３サイズのシート状媒体の長手方向の長さよりも僅かに長い大きさとなっている。すなわち、画像形成装置２０は、内部にシート状媒体を収容するために最低限必要な大きさとされることで大幅に小型化されている。
【００２７】
各作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫはそれぞれシアン、イエロー、マゼンタ、ブラックの各色の現像を行うものであり、用いるトナーの色が異なるが、その構成はほぼ同様であるから、作像装置２１ＢＫの構成を各作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫの代表として説明する。作像装置２１ＢＫは、像担持体である静電潜像担持体としての感光体ドラム２５ＢＫ、感光体ドラム２５ＢＫの回転方向Ａにおいて順に配置されている帯電装置２７ＢＫ、現像装置２６ＢＫ、クリーニング装置２８ＢＫ等を有し、帯電装置２７ＢＫと現像装置２６ＢＫとの間で露光光２９ＢＫを受ける周知の構成である。静電潜像担持体はドラム状でなく、ベルト状としても良い。以下、作像装置について、色を区別しないときには末尾に付したＣ、Ｙ、Ｍ、ＢＫのアルファベットを省略して説明する。
【００２８】
図２に示すように、現像装置２６は、現像ケーシング５１と、感光体ドラム２５を現像する現像ローラ５２と、現像ローラ５２の軸５３と平行に配設され軸５３の一方向すなわち紙面手前側に現像剤を搬送する第１現像剤攪拌搬送部材としての第１現像剤搬送部材５４と、軸５３と平行に配設され軸５３の他方向すなわち紙面奥側に現像剤を搬送する第２現像剤攪拌搬送部材としての第２現像剤搬送部材５５とを有している。
【００２９】
現像装置２６はまた、第１現像剤搬送部材５４と第２現像剤搬送部材５５との間に配設され、第１現像剤搬送部材５４の周囲の空間と第２現像剤搬送部材５５の周囲の空間とを遮蔽する、現像ケーシング５１と一体の仕切り板５６と、図２において時計回りに回転する現像ローラ５２の回転方向Ｃにおける、現像ローラ５２と第２現像剤搬送部材５４との対向領域の下流側において、現像ローラ５２に汲み上げられた現像剤を規制する、現像ローラ５２の下方に配設された現像剤規制部材５７とを有している。
【００３０】
現像ローラ５２は、現像剤を引き付け現像剤を汲み上げる現像剤汲み上げ部６１と、現像剤汲み上げ部６１の上方に位置し現像剤を離す現像剤離し部６２とを有している。第１現像材搬送部材５４は現像剤汲み上げ部６１の近傍において現像剤汲み上げ部６１に対向する位置に配設されており、第２現像材搬送部材５５は現像剤離し部６２の近傍において現像剤離し部６２に対向する位置に配設されている。なお、図２において、符号３６はクリーニング装置２８に備えられたクリーニングブレードを、符号３７は転写装置２２に備えられた転写ベルトを示している。
【００３１】
現像ローラ５２は、円周方向に複数の磁石を配置した図示しないマグネットローラを内部に有し、その周囲を図示しない円筒状のスリーブが回転する構成となっている。スリーブはアルミ等の非磁性の金属で形成されている。マグネットローラは、各磁石が所定の方向を向くように固定されており、その周囲をスリーブが回転して、磁石によって引き付けた現像剤を搬送していく。現像装置２６では、現像ローラ５２が感光体ドラム２５に対向する部分において、現像ローラ５２表面が下方から上方に向けて移動する構成としている。
【００３２】
図３に示すように、現像ローラ５２は、内部にＰ１、Ｐ２、Ｐ３、Ｐ４、Ｐ５の５つの磁石を有し、５つの磁極が生じるようになっている。現像ローラ５２と感光体ドラム２５とが対向する部分にＰ１極と称する磁極が位置し、以下現像ローラ回転方向Ｃに沿って、Ｐ２、Ｐ３、Ｐ４、Ｐ５極の各磁極が配設されている。極性はＰ１極から順に、Ｎ、Ｓ、Ｎ、Ｎ、Ｓ極としているが、これらは各極が反対の極性であっても構わない。現像ローラ５２と感光体ドラム２５は直接には接触せずに、一定の間隔を保持して対向しており、この対向領域が現像ニップ領域３８を形成している。
【００３３】
現像ローラ５２は、Ｐ１極で現像剤を穂立ちさせ、現像剤を感光体ドラム２５に接触させることで、感光体ドラム２５表面の潜像にトナーを付着させて顕像化する。現像ローラ５２には所定のバイアスを印加しており、現像ローラ５２と感光体ドラム２５表面に形成された静電潜像との電位差により、トナーを潜像部分に付着させている。
【００３４】
Ｐ２極は現像後の現像剤を搬送し、現像ケーシング５１内に引き入れる。Ｐ３、Ｐ４極は同極性として、Ｐ３極とＰ４極との間で、現像ローラ５２の周囲に引き寄せていた現像剤を現像ローラ５２から引き離す、剤離し、の機能を担っている。現像剤汲み上げ部６１はＰ４極により、現像剤離し部６２はＰ３極により形成されている。
【００３５】
感光体ドラム２５にトナーを付着させた後の現像剤は、トナー濃度が下がっている為、現像ローラ５２から離れずに再度現像ニップ領域３８に搬送され現像に供されると狙いの画像濃度を得ることが出来ないという不具合が生じるため、このように現像後の領域で、現像ローラ５２から現像剤を離す構成となっている。
【００３６】
仕切り板５６は、現像ローラ５２の回転方向Ｃにおける、現像剤汲み上げ部６１の上流側且つ現像剤離し部６２の下流側の、Ｐ３極とＰ４極との間で形成される、現像ローラ５２への現像剤の付着量が少ない領域３９で、現像ローラ５２に対向するように配設されている。かかる領域３９は、現像ローラ５２の表面の磁束密度が１０ｍＴ以下となる領域であって、現像材の付着量が少なくなっている。
【００３７】
仕切り板５６は、現像ケーシング５１本体から領域３９に向けて突設されており、その先端部における現像ローラ５２との間隔は０．２ｍｍとされている。かかる間隔は０．２ｍｍ〜１ｍｍの間で設定することができる。したがって、仕切り板５６により、現像後の現像剤を現像ローラ５２から良好には分離することができるようになっている。
【００３８】
このように、仕切り板５６は、現像ローラ５２から離され第２現像剤搬送部材５５により撹拌搬送される現像剤が再度現像ローラ５２に引き付けられて、第１現像剤搬送部材５４により撹拌される空間へ移動するのを防止するものであり、また、第２現像剤搬送部材５５が撹拌搬送する現像剤を下から支えて現像剤搬送経路を形成する機能をも有している。
【００３９】
現像ローラ５２から分離された現像後の現像剤には、第２現像剤搬送部材５５による現像剤の搬送方向における上流部分すなわち図２、３における紙面手前側の部分で、狙いのトナー濃度となるようにトナー補給が行われ、狙いのトナー帯電量になるように、第２現像剤搬送部材５５及び第１現像剤搬送部材５４にて十分に撹拌混合され、この現像剤はＰ４極により現像ローラ５２に汲上げられる。
【００４０】
Ｐ４極の磁力により現像ローラに引き付けられた現像剤は現像剤規制部材５７を通過することにより、所定の厚さに整えられて、磁気ブラシを形成しながら現像ニップ領域３８に搬送される。Ｐ５極は現像剤規制部材５７通過後からＰ１極までの間で搬送を行う極としての機能、及び、現像剤規制部材５７に対向する部分で現像剤を穂立ちさせることにより、現像剤の層厚を安定させる機能を担っている。
【００４１】
図４に示すように、第１現像剤搬送部材５４は、回転軸６３を中心とした回転により現像剤を搬送する形状をなしており、本例においては回転軸６３の回りにスパイラル６５を設けたスクリュ形状をしており、現像ローラ５２と同方向Ｄに回転することによりその軸方向のうち図２、３における紙面の奥側から手前側に向けた方向Ｆに向けて現像剤を搬送する。
【００４２】
スクリュは、被搬送物を軸方向に送りながら、回転方向に寄せる作用があるので、第１現像剤搬送部材５４は現像剤を現像ローラ５２に寄せながら搬送することになり、現像ローラ５２への連続した現像剤供給が可能になる。回転軸６３を中心とした回転により現像剤を搬送する形状としては、スパイラルでなく、回転軸６３に対して傾斜した斜板を回転軸６３の軸方向に多数並設した形状であっても良い。
【００４３】
第２現像剤搬送部材５５は、回転軸６４を中心とした回転により現像剤を搬送する形状をなしており、本例においては回転軸６４の回りにスパイラル６６を設けたスクリュ形状をしており、現像ローラ５２と逆方向Ｅに回転することによりその軸方向のうち図２、３における紙面の手前側から奥側に向けた方向Ｆと逆の方向Ｇに向けて現像剤を搬送する。
【００４４】
これにより、第２現像剤搬送部材５５は現像剤を現像ローラ５２から離れた方向に寄せながら搬送するので、一度現像ローラ５２から離れた現像剤が現像ローラ５２に再度付着して第１現像剤搬送部材５４の領域に搬送されることを防ぐ。回転軸６４を中心とした回転により現像剤を搬送する形状としては、スパイラルでなく、回転軸６４に対して傾斜した斜板を回転軸６４の軸方向に多数並設した形状であっても良い。
【００４５】
第２現像剤搬送部材５５の現像剤搬送方向下流側、すなわち図２、３の紙面における現像装置２０奥側では、仕切り板５６を設けないことで、あるいは、仕切り板５６の一部に開口を設けることで、第１現像剤搬送部材５４の周囲の空間と第２現像剤搬送部材５５の周囲の空間とを連通する連通口６７が設けてあり、第２現像剤搬送部材５５により搬送された現像剤が、下方に位置する第１現像剤搬送部材５４の搬送経路へと落下していくようになっている。
【００４６】
現像装置２６のように、現像剤搬送部材５５、５４を上下に配置した現像装置では、上下の現像剤搬送部材５５、５４の間で現像剤の移動を行うことになる。上方の現像剤搬送部材５５から、下方の現像剤搬送部材５４への現像剤の移動は上述のように自由落下で良いが、下方から上方への移動に関してはその為の機構が必要になる。
【００４７】
しかし現像装置２６は、現像ローラ５２が下方の現像剤搬送部材５４から現像剤を汲上げ、上方の現像剤撹拌部材５５周囲の空間に現像剤を離すので、下方から上方への現像剤の移動は現像ローラ５２が行うことになり、特別な現像剤汲上げ機構は必要なく、水平方向の寸法を小さくした現像装置を、簡単な構成で実現するものである。
【００４８】
現像装置２６内の現像剤は、現像動作を繰り返すうちにトナーが消費されていくので、現像装置２６外部から現像装置２６内の現像剤に対してトナーを補給する必要がある。よって現像装置２６においては、上述したように、現像ローラ５２から現像剤が離される領域の近傍に配置した第２現像剤搬送部材５５の搬送方向上流部でトナー補給を行なうようになっている。
【００４９】
そして、第２現像剤搬送部材５５による現像剤搬送経路では、現像ローラ５２から離れた現像剤を回収するのみで、現像ローラ５２へのトナー供給は行なわないので、補給されたトナーは現像ローラ５２から離れた現像剤中で撹拌混合されながら、現像装置２６の奥側まで搬送された後、連通口６７を経て、第１現像剤搬送部材５４の搬送経路に落下し、第１現像剤搬送部材５４により手前側に搬送されながら現像ローラ５２に供給され現像に使用される。
【００５０】
現像剤は、現像装置２６内で撹拌を受ける事により劣化していく。キャリアは表面のコート膜が削れていったり、トナーの樹脂成分が表面に付着していくことによって、初期の性能が発揮できないようになっていく。トナーは周囲に付着している添加物が埋没していくことによって、その性能が落ちていく。これら現像剤の劣化は、剤中トナー濃度が低い状態で撹拌を受けた場合のほうが、トナー濃度が高い状態で撹拌された場合よりも促進されやすい。
【００５１】
また、現像装置２６内のどの部分で劣化を促進するストレスを受けるかという点では、現像ローラ５２と現像剤規制部材５７の間の狭い間隔を通過する際に最もストレスを受け、スクリュ形状をなす第１現像剤搬送部材５４、第２現像剤搬送部材５５に当接する部分でのストレスは殆どない。現像装置２６では、現像後にトナー濃度の下がった現像剤は、現像ローラ５２から離した後、スクリュ形状をなす第１現像剤搬送部材５４、第２現像剤搬送部材５５でのみ撹拌し、トナー補給された現像剤と混合した後に、現像ローラ５２に供給されるから、トナー濃度の下がった状態で現像ローラと現像剤規制部材の間隙を通過するようなことはないので、現像剤の劣化を促進することがなく、現像剤劣化が抑制されるので、安定した画質を長期にわたって維持することが可能となっている。
【００５２】
現像装置２６では、第１現像剤搬送部材５４で搬送される現像剤は、Ｆ方向に向けて搬送されながら、現像ローラ５２に汲み上げられる。現像ローラ５２に汲み上げられた現像剤は、感光体ドラム２５に接触して現像に供された後、現像装置２６内で現像ローラ５２から離され、第２現像剤搬送部材５５により、Ｇ方向へ向けて搬送される。このような現像剤循環では、第１現像剤搬送部材５４によりＦ方向先端側まで搬送される前に、現像に使用され、第２現像剤搬送部材５５によりＧ方向へ戻される現像剤が多くなり、現像剤が奥側に溜まる傾向にある。そして、Ｆ方向下流まで現像剤が到達しないと、第１現像剤搬送部材５４のＦ方向下流側端部部分では現像ローラ５２上に現像剤が汲み上げられないという不具合が生じてしまう。
【００５３】
そのため、現像装置２６では、第１現像剤搬送部材５４の現像剤搬送能力を、第２現像剤搬送部材５５の現像剤搬送能力よりも大きくすることで、現像ローラ５２の軸方向、言い換えると現像装置２６の奥行き方向における現像剤のバランスをとるようになっている。すなわち、第１現像剤搬送部材５４の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材５５の単位時間あたりの現像剤の搬送量よりも大きくし、第１現像剤搬送部材５４の現像剤の搬送速度を、第２現像剤搬送部材５５の現像剤の搬送速度よりも大きくしている。
【００５４】
具体的には、第１現像剤搬送部材５４の外径すなわちスパイラル６５の外径を、第２現像剤搬送部材５５の外径すなわちスパイラル６６の外径よりも大きくし、第１現像剤搬送部材５４のピッチ、すなわちスパイラル６５のピッチを、第２現像剤搬送部材５５のピッチ、すなわちスパイラル６６のピッチよりも大きくし、第１現像剤搬送部材５４の回転数を、第２現像剤搬送部材５５の回転数よりも大きくしている。その他、第１現像剤搬送部材５４により現像剤が搬送される空間の容積を、第２現像剤搬送部材５５により現像剤が搬送される空間の容積よりも大きくしてもよい。これらは少なくとも１つあるいはこれらの各組み合わせで用いることができる。
【００５５】
このように、第１現像剤搬送部材５４の現像剤搬送能力を大きくした場合、第１現像剤搬送部材５４の下流部まで搬送されてきた現像剤がすべて現像ローラ５２に汲み上げられていれば、現像装置２６の奥行き方向の現像剤バランスは問題ない。しかし、現像装置２６の傾斜、現像剤の流動性により、現像剤の搬送量は変わるので、第１現像剤搬送部材５４の下流部での現像剤汲上げ不足、言い換えると現像剤汲み上げ不良を防ぐには、第１現像剤撹拌搬送部材の搬送能力は、第１現像剤搬送部材５４の下流部に現像剤が溜まる程度に設定した方が良い。
【００５６】
ところが、現像剤が手前側に多く溜まった場合に逃げ場がないと、第１現像剤搬送部材５４の負荷トルクが増大したり、ロックしたりする場合がある。そこで、図４に示すように、仕切り板５６の、Ｆ方向の下流部分に、第１現像剤搬送部材５４の周囲の空間と、第２現像剤搬送部材５５の周囲の空間とを連通する連通口６８を設け、第１現像剤搬送部材５４の下流部に現像剤が溜まった場合の現像剤の逃げ場を作っている。これにより、第１現像剤搬送部材５４の下流部に現像剤が溜まり気味になった場合には、連通口６８を経て、上方の第２現像剤搬送部材５５周囲の空間に現像剤が移動していくので、第１現像剤搬送部材５４の負荷トルク増大、ロックが防止されている。
【００５７】
連通口６８は、仕切り板５６における、現像ローラ５２寄りの位置に形成し、現像ローラ５２から離れた位置における仕切り板５６は残してある。このようにすることで、第１現像剤搬送部材５４により現像ローラ５２に寄せられながら、上方に溢れてきた現像剤を、第２現像剤搬送部材５５により仕切り板５６の上面に乗せ、現像ローラ５２から離しながら、Ｇ方向に向けて搬送することができる。
【００５８】
本実施例は以上の構成により、画像形成装置２０の電源が投入されると、画像形成が可能な状態となり、操作者が画像形成を開始する周知の操作を行うと、感光体ドラム２５Ｃの方向Ａへの回転にともない、感光体ドラム２５Ｃは帯電装置２７Ｃより表面を一様に帯電され、露光光２９Ｃにより原稿画像に応じた静電潜像が形成される。
【００５９】
現像装置２６Ｃに備えられた現像ローラ５２Ｃにより現像装置２６Ｃ内の現像剤が感光体ドラム２５Ｃと対向する現像ニップ領域３８へ搬送され、感光体ドラム２５Ｃ表面に形成されている静電潜像に現像剤中のトナーが付着して顕像化し、現像が行われる。感光体ドラム２５Ｃ上に形成されたトナー像が、感光体ドラム２５Ｃと転写装置２２とが対向する転写領域３５Ｃにおいて、転写装置２２上を矢印Ｂ方向に搬送される記録媒体上に転写され、記録媒体上の画像となる。
【００６０】
転写後に記録媒体に転写されずに感光体ドラム２５Ｃ上に残留しているトナーがクリーニング装置２８Ｃに備えられたクリーニングブレード３６Ｃによって掻き取られて感光体２５Ｃがクリーニングされ、クリーニング装置２８Ｃを通過した感光体ドラム２５Ｃの表面は、その後、再び帯電装置２７Ｃにより一様に帯電され、次の画像形成工程を繰り返す。
【００６１】
シアンのトナーが転写された記録媒体は、転写装置２２により矢印Ｂ方向に搬送されつつ、作像装置２１Ｃにおける上述の作像工程と同様の作像工程を行う作像装置２１Ｙ、２１Ｍ、２１ＢＫにより順次それぞれイエロー、マゼンタ、ブラックのトナー像を適宜転写され、画像形成に必要なすべてのトナー像を転写された後、転写装置２２から定着装置１に受け渡され、記録媒体上のトナー像の記録媒体への定着が行われる。定着後の記録媒体はローラ構造４３、排出ローラ４５を経て、排紙トレイ３２上に積載される。
【００６２】
以上本発明を適用した現像装置及び画像形成装置について説明したが、作像装置２１は図５に示すような構成とすることができる。現像ローラ５２と感光体ドラム２５とが対向する現像ニップ領域３８で、感光体ドラム２５表面の移動方向Ａに対して現像ローラ５２表面の移動方向Ｃを同方向とする現像方式を順現像、感光体ドラム２５表面の移動方向Ａに対して現像ローラ５２表面の移動方向Ｃを逆方向とする現像方式を逆現像と称するが、図５に示した作像装置２１は、図１等に示した逆現像を行う作像システムによる作像装置２１と異なり、順現像となるように適用した作像システムを採用したものである。
【００６３】
この例においては、転写装置２２における転写ベルト３７の搬送方向Ｂも図１等に示したものと逆になっている。各作像装置２１Ｃ、２１Ｙ、２１Ｍ、２１ＢＫの配設位置も、図１等に示した場合においては転写装置２２の上方としていたが、この例においては、その逆の転写装置２２の下方となっている。その他、図２と同様の構成には同じ符号を付して説明を省略する。
【００６４】
【発明の効果】
本発明によれば、像担持体を現像する現像ローラと、上記現像ローラの軸と平行に配設されこの軸の一方向に現像剤を搬送する第１現像剤搬送部材と、上記現像ローラの軸と平行に配設されこの軸の他方向に現像剤を搬送する第２現像剤搬送部材と、上記第１現像剤搬送部材と、上記第２現像剤搬送部材との間に配設され、上記第１現像剤搬送部材の周囲の空間と、上記第２現像剤搬送部材の周囲の空間とを遮蔽する仕切り板とを有する現像装置において、上記現像ローラは、現像剤を汲み上げる現像剤汲み上げ部と、この現像剤汲み上げ部の上方に位置し現像剤を離す現像剤離し部とを有し、上記第１現像剤搬送部材を、上記現像剤汲み上げ部近傍に配置し、上記第２現像剤搬送部材を、上記現像剤離し部近傍に配置し、上記第１現像剤搬送部材の回転方向を、上記現像ローラの回転方向と同じとし、上記第２現像剤搬送部材の回転方向を、上記現像ローラの回転方向と逆とし、上記第１現像剤搬送部材の周囲の空間においては、現像剤が上記現像ローラに寄せられながら上記第１現像剤搬送部材によって上記一方向に搬送され、上記第２現像剤搬送部材の周囲の空間においては、現像剤が上記現像ローラから離されながら上記第２現像剤搬送部材によって上記他方向に搬送され、上記仕切り板は、上記第１現像剤搬送部材の周囲の空間と、上記第２現像剤搬送部材の周囲の空間とを連通する連通口であって、上記第１現像剤搬送部材の現像剤の搬送方向の下流部分の、上記現像ローラから離れた位置の同仕切り板を残しつつ、同下流部分の上記現像ローラ寄りの位置に形成された連通口を有するので、現像ローラの軸方向に平行に配設され互いに逆の方向に現像剤を搬送する２つの現像剤搬送部材を備え、水平方向の大きさを小さくすることができ、また、下方の現像剤搬送部材から上方の現像剤搬送部材への現像剤の汲上げを現像ローラで行えるので、汲上げ機構も必要なく簡単な構成で、小型とすることができ、さらに、水平方向のコンパクト化を図った上で、現像ローラに対してトナーとキャリアを十分に撹拌混合した現像剤のみを供給し、現像直後のトナー濃度の下がった現像剤が直ぐに供給されることがないので、狙いの帯電量を持ったトナーを現像に用いるので、高画質の画像形成に寄与することができ、また、第１現像剤搬送部材の搬送方向下流側の現像剤汲上げ不良を防ぐ為に、第１現像剤搬送部材の搬送方向下流側に溜まり気味に設定した場合に、現像剤が溜まりすぎて、第１現像剤撹拌搬送部材の負荷トルク増大や、ロックが生じるのを防止し、各部材の劣化等の不具合を防止でき、現像装置を長寿命とすることができるとともに、第１現像剤撹拌搬送部材の回転により、現像剤を現像ローラに掃き寄せながら軸方向に搬送することになるので現像ローラへの現像剤供給をスムーズに行なうことができ、画像濃度ムラを抑制して高画質の画像形成に寄与することができ、現像ローラに寄せられながら搬送された現像剤であって、第１現像剤搬送部材周囲の空間から連通口を介して上側の第２現像剤搬送部材周囲の空間に溢れてきた現像剤を、仕切り板上に乗せ、第２現像剤撹拌搬送部材の回転により、現像剤を現像ローラから離れた部分に掃き寄せながら軸方向に搬送することで、現像ローラから離された現像剤が現像ローラに引き寄せられるのを防ぐことができ、現像ローラから離しながら搬送し、確実に第２現像剤搬送部材による現像剤の搬送経路に保持して第２現像剤搬送部材により搬送できるから、現像剤の攪拌循環をスムーズに行うことができる現像装置を提供することができる。
【００６５】
第２現像剤搬送部材の現像剤の搬送方向の上流部分において、現像剤へのトナー補給を行うこととすれば、現像ローラへの現像剤供給を行なわない第２現像剤搬送部材の上流部分にトナーを補給することで補給されたトナーと現像剤との撹拌時間を稼げること、また、第２現像剤搬送部材の搬送経路には現像直後でトナー濃度の下がった現像剤があるため補給トナーとキャリア表面とが接触することが多いことから、トナーをキャリアと十分に撹拌混合し、トナーの帯電を効率的に行なうことができるから、帯電量を立ち上げてから現像に用いることができ、高画質の画像形成に寄与することができる現像装置を提供することができる。
【００６６】
現像ローラと仕切り板との間隔を０．２ｍｍ〜１ｍｍの範囲としたこととすれば、現像ローラと仕切り板との間隙を現像剤が通過することを抑制し、トナー濃度の下がった現像剤が現像ローラと現像剤規制部材の空隙を通過せず、第２現像剤搬送部材による撹拌を受けるだけなので、キャリア、トナーにかかるストレスが押さえられ、劣化を抑制できるので、現像剤の性能を長期にわたった維持することが可能で、高寿命、高耐久な現像装置を提供することができる。
【００６７】
仕切り板が、現像ローラの回転方向における、現像剤離し部の下流側且つ現像剤汲み上げ部の上流側の、現像ローラへの現像剤の付着量が少ない領域で、現像ローラに対向していることとすれば、現像ローラと仕切り板との対抗領域に存する現像剤が少ないから、トナー濃度の下がった現像剤が現像ローラと現像剤規制部材の空隙を通過せず、第２現像剤搬送部材による撹拌を受けるだけなので、キャリア、トナーにかかるストレスが押さえられ、劣化を抑制できるので、現像剤の性能を長期にわたった維持することが可能で、高寿命、高耐久にすることができる現像装置を提供することができる。
【００６８】
仕切り板が、現像ローラの回転方向における、現像剤離し部の下流側且つ現像剤汲み上げ部の上流側の、現像ローラ表面の磁束密度が１０ｍＴ以下の領域で、現像ローラに対向していることとすれば、現像ローラと仕切り板との対抗領域に引き寄せられる現像剤が少ないから、トナー濃度の下がった現像剤が現像ローラと現像剤規制部材の空隙を通過せず、第２現像剤搬送部材による撹拌を受けるだけなので、キャリア、トナーにかかるストレスが押さえられ、劣化を抑制できるので、現像剤の性能を長期にわたった維持することが可能で、高寿命、高耐久にすることができる現像装置を提供することができる。
【００７１】
第１現像剤搬送部材と、第２現像剤搬送部材とが、その軸を中心とした回転により現像剤を搬送する形状をなしており、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくしたこととすれば、現像剤へのストレスが少ないとともに、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７２】
第１現像剤搬送部材の現像剤の搬送速度を、第２現像剤搬送部材の現像剤の搬送速度よりも大きくしたこととすれば、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくし、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７３】
第１現像剤搬送部材の外径を、第２現像剤搬送部材の外径よりも大きくしたこととすれば、第１現像剤搬送部材、第２現像剤搬送部材の外径の関係を設定することで、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくし、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７４】
第１現像剤搬送部材のピッチを、第２現像剤搬送部材のピッチよりも大きくしたこととすれば、第１現像剤搬送部材、第２現像剤搬送部材のピッチの関係を設定することで、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくし、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７５】
第１現像剤搬送部材の回転数を、第２現像剤搬送部材の回転数よりも大きくしたこととすれば、第１現像剤搬送部材、第２現像剤搬送部材の回転数の関係を設定することで、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくし、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７６】
第１現像剤搬送部材により現像剤が搬送される空間の容積を、第２現像剤搬送部材により現像剤が搬送される空間の容積よりも大きくしたこととすれば、第１現像剤搬送部材、第２現像剤搬送部材の周囲の空間の容積の関係を設定することで、第１現像剤搬送部材の単位時間あたりの現像剤の搬送量を、第２現像剤搬送部材の単位時間あたりの現像剤の搬送量よりも大きくし、第１の現像剤撹拌搬送部材の搬送方向下流側の現像剤が少なくなることを防止して、現像剤を手前側まで行き渡らせ、現像ローラへの現像剤汲上げ不良を防止し、画像濃度ムラを抑制して高画質の画像形成に寄与することができる現像装置を提供することができる。
【００７７】
本発明に係る画像形成装置によれば、かかる効果を奏する現像装置を備えた画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明を適用した現像装置及びこの現像装置を備えたカラー画像形成が可能な画像形成装置の概略を示す側面図である。
【図２】図１に示した作像装置の側面図である。
【図３】図１に示した作像装置における、磁極と、現像剤汲み上げ部、現像剤離し部、第１現像剤搬送部材、第２現像材搬送部材、仕切り板との位置関係を示す側面図である。
【図４】図１に示した現像装置の斜視図である。
【図５】作像装置の別の構成例を示した側面図である。
【図６】現像ローラの軸方向に平行に配設され互いに逆の方向に現像剤を搬送する２つの現像剤搬送部材を備えた従来の現像装置の側面図である。
【符号の説明】
２０画像形成装置
２５、２５Ｃ、２５Ｙ、２５Ｍ、２５ＢＫ像担持体
５２現像ローラ
５３現像ローラの軸
５４第１現像剤搬送部材
５５第２現像剤搬送部材
５６仕切り板
６１現像剤汲み上げ部
６２現像剤離し部
６８連通口
Ｃ現像ローラの回転方向
Ｄ第１現像剤搬送部材の回転方向
Ｅ第２現像剤搬送部材の回転方向
Ｆ現像ローラの軸の一方向、第１現像剤搬送部材の現像材の搬送方向
Ｇ現像ローラの軸の他方向、第２現像剤搬送部材の現像材の搬送方向[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device, and in particular, a developing device provided with two developer conveying members that are arranged in parallel to the axial direction of the developing roller and convey the developer in opposite directions. And image forming apparatus having the same About.
[0002]
[Prior art]
An image forming apparatus such as a copying machine, a facsimile machine, or a printer generally has a developing device for developing an image carrier such as a photosensitive member. As a developing device, a two-component developing type device using a two-component developer composed of toner and carrier is known. In this developing device, a developer in which a carrier and toner are sufficiently mixed in a developer stirring portion is developed. The developer is supplied to the roller, and the developer is conveyed to a region facing the photoconductor as the image carrier by the developing roller, and the toner is attached to the electrostatic latent image on the surface of the photoconductor for development.
[0003]
Various configurations of a developer agitating unit that agitates and mixes the developer and supplies the developer to the developing roller have been used in the past, but at present, the agitating and conveying screw is disposed in the horizontal direction or below the developing roller. A configuration in which two are arranged is the mainstream. As an example, FIG. 6 shows a developing device 200 in which two agitating and conveying screws 202 and 203 are disposed in a horizontal direction obliquely below a developing roller 201 disposed to face a photosensitive drum 205 as an image carrier. Show.
[0004]
In the developing device 200 having such a configuration, the partition plate 204 is provided between the two screws 202 and 203, and the two screws 202 and 203 convey developer in opposite directions, and there is no partition plate 204. The developer is circulated by delivering the developer at both ends. The first screw 202 arranged away from the developing roller 201 is replenished with toner on the upstream side in the transport direction, transports the toner and the carrier while mixing, and develops on the downstream side of the first screw 202. The developer is transferred to the second screw 203 arranged close to.
[0005]
The second screw 203 transports the developer while supplying the developer to the developing roller 201 and collecting the developer from the developing roller 201, and delivers the developer to the first screw 202 on the downstream side. The developing roller 201 has a magnet roller (not shown) in which a plurality of magnetic poles (not shown) are arranged, and a cylindrical sleeve (not shown) rotates around the fixed magnet roller. The part facing the second screw 203 needs to have a function of pumping up the developer and a function of separating the developer that has been developed, and the magnet roller is provided with a magnetic pole so as to perform the function.
[0006]
However, in the developing device 200 having such a configuration, since the developing roller 201 and the stirring screws 202 and 203 are arranged in the horizontal direction, the size in the vertical direction can be reduced, but the size in the horizontal direction is reduced. It is difficult. In recent years, image forming apparatuses using an electrophotographic method have been colorized, but in order to improve the productivity, four image carriers are provided for each color of yellow, magenta, cyan, and black. It is effective to employ a tandem method in which an image is formed using a photosensitive drum.
[0007]
In the tandem system, four photosensitive drums are arranged in the horizontal direction, and an image forming device such as a charging device is provided for each drum, and a developing device is also provided for each drum. In order to reduce the size of the image forming apparatus, it is necessary to reduce the interval between the drums. To that end, the developing apparatus also needs to be reduced in size in the horizontal direction, and the above-described two screws are arranged in the horizontal direction. There is a limit to space saving in this type of developing device.
[0008]
Japanese Patent Application Laid-Open No. 11-202627 discloses a developing device in which a developer is circulated by means of a stirring screw and a supply screw arranged above and below. Also, in this developing device, the balance of the developer is maintained even when the stirring screw exhibits a larger conveying capacity than the supply screw, the total amount of developer is reduced, and the stirring screw is only partially immersed, and the screw is maintained. The driving torque of the developer is reduced and the life of the developer is extended.
[0009]
[Problems to be solved by the invention]
However, such a developing device disclosed in Japanese Patent Laid-Open No. 11-202627 has a configuration in which two screws are arranged in the vertical direction on the side of the developing roller, and space saving in the horizontal direction can be achieved. The developer with less toner and the developer with high toner concentration are simultaneously pumped up to the developing roller, so that the toner concentration of the developer on the developing roller is not uniform and the image density is likely to be uneven and a uniform image There is a problem that it is difficult to obtain.
[0010]
Further, the same problem arises because the developer stirred by the upper screw and the developer stirred by the lower screw are interchanged in some places, so that the developer is not easily stirred uniformly. In addition, due to insufficiently charged toner, the graininess of the halftone image part deteriorates, the background is contaminated with the toner on the background, or the toner is scattered from the carrier when the toner is released. There is also a defect that causes.
[0011]
The present invention is a developing device provided with two developer conveying members that are arranged in parallel to the axial direction of the developing roller and convey the developer in opposite directions, with the horizontal size being reduced. , Developing device that provides high image quality, low stress on the developer, and sufficient charging to provide stable development performance And image forming apparatus having the same The purpose is to provide.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 includes a developing roller for developing the image carrier, and a first developing unit that is arranged in parallel with the axis of the developing roller and conveys the developer in one direction of the axis. A developer transport member, a second developer transport member disposed in parallel with the axis of the developing roller and transporting the developer in the other direction of the shaft, the first developer transport member, and the second developer transport. A developing device having a partition plate disposed between the first developer transporting member and a partition plate that shields the space surrounding the first developer transporting member and the space surrounding the second developer transporting member; A developer pumping unit that pumps up the developer, and a developer release unit that is located above the developer pumping unit and separates the developer, and the first developer transporting member is located in the vicinity of the developer pumping unit. And arranging the second developer conveying member with the developer separating portion. Place near, The rotation direction of the first developer conveying member is the same as the rotation direction of the developing roller, the rotation direction of the second developer conveying member is opposite to the rotation direction of the developing roller, In the space around the first developer conveying member, the developer is conveyed in the one direction by the first developer conveying member while being brought close to the developing roller, and the space around the second developer conveying member. The developer is transported in the other direction by the second developer transport member while being separated from the developing roller, and the partition plate includes a space around the first developer transport member and the second development. A communication port that communicates with the space around the agent conveying member, while leaving the partition plate at a position away from the developing roller in the downstream portion of the first developer conveying member in the developer conveying direction, It has a communication port formed at a position near the developing roller in the downstream portion.
[0013]
According to a second aspect of the present invention, in the developing device according to the first aspect, toner is supplied to the developer at an upstream portion of the second developer conveying member in the developer conveying direction.
[0014]
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the distance between the developing roller and the partition plate is in a range of 0.2 mm to 1 mm.
[0015]
According to a fourth aspect of the present invention, in the developing device according to the third aspect, the partition plate is located on the downstream side of the developer separating portion and the upstream side of the developer pumping portion in the rotation direction of the developing roller. It is characterized in that it faces the developing roller in a region where the amount of developer adhering to the developing roller is small.
[0016]
According to a fifth aspect of the present invention, in the developing device according to the third or fourth aspect, the partition plate is located on the downstream side of the developer separating portion and the upstream side of the developer pumping portion in the rotation direction of the developing roller. The surface of the developing roller faces the developing roller in a region where the magnetic flux density is 10 mT or less.
[0019]
Claim 6 The invention described in claim 1 to claim 1 5 In the developing device according to any one of the above, the first developer transport member and the second developer transport member are configured to transport the developer by rotation about its axis, The developer transport amount per unit time of the first developer transport member is larger than the developer transport amount per unit time of the second developer transport member.
[0020]
Claim 7 The invention described in claim 1 to claim 1 6 An image forming apparatus having the developing device according to any one of the above.
[0021]
【Example】
FIG. 1 shows an outline of a developing device to which the present invention is applied and an image forming apparatus having the developing device. The image forming apparatus is a well-known apparatus such as a copying machine, a facsimile machine, or a printer, and any image forming apparatus that can use a developing device to which the present invention is applied may be used. The image forming apparatus of the present embodiment forms a color image, but may form a single color image.
[0022]
The image forming apparatus 20 includes plain paper generally used for copying and the like, 90K paper such as an OHP sheet, a card, and a postcard, and a basis weight of about 100 g / m. ² Any of so-called special sheets having a larger heat capacity than plain paper, such as considerably thicker paper or envelopes, can be used as the sheet-like recording medium. These are hereinafter referred to as recording media.
[0023]
The image forming apparatus 20 includes image forming apparatuses 21C, 21Y, 21M, and 21BK that form an image for each color according to a document image, and a transfer apparatus 22 that is disposed to face the image forming apparatuses 21C, 21Y, 21M, and 21BK. Sheet cassettes 23, 24, 33 serving as recording medium supply means for supplying various recording media to a transfer area where the image forming devices 21C, 21Y, 21M, 21BK and the transfer device 22 face each other; , 24, and 33, and a registration roller 30 that supplies the recording medium in accordance with the timing of image formation by the image forming apparatuses 21C, 21Y, 21M, and 21BK.
[0024]
In addition, the image forming apparatus 20 includes a transfer region 35C, which is a position where a later-described photosensitive drum 25C, 25Y, 25M, 25BK provided in each of the image forming devices 21C, 21Y, 21M, and 21BK and the transfer device 22 are opposed to each other. The fixing device 1 that fixes the recording medium after the toner image is transferred in at least one transfer region of 35Y, 35M, and 35BK, a casing 31, and a fixing unit that is disposed above the casing 31. A paper discharge tray 32 for stacking a recording medium that has passed through the apparatus 1 and has a toner image fixed thereon.
[0025]
In addition, the image forming apparatus 20 includes pickup rollers 40, 41, and 42 that feed recording media from the paper feed cassettes 23, 24, and 33, and a recording medium that is conveyed from the paper feed cassettes 23, 24, and 33, and registration rollers 30. A roller structure 44 that conveys the recording medium toward the paper discharge tray 32, a discharge roller 45 that discharges the recording medium to the outside of the housing 31, and a roller that conveys the recording medium fixed by the fixing device 1 toward the discharge roller 45. Structure 43.
[0026]
The transfer device 22 is arranged in an oblique direction so that the image forming apparatus 20 is small in the left-right direction in the drawing, and the sheet-like medium conveyance direction indicated by an arrow B is an oblique direction. Thus, in the image forming apparatus 20, the width of the casing 31 in the left-right direction in the figure is slightly longer than the length in the longitudinal direction of the A3 size sheet-like medium. That is, the image forming apparatus 20 is greatly reduced in size by being the minimum size required to accommodate the sheet-like medium therein.
[0027]
Each of the image forming devices 21C, 21Y, 21M, and 21BK develops each color of cyan, yellow, magenta, and black, and uses different toner colors, but the configuration is almost the same. The configuration of 21BK will be described as a representative of the image forming devices 21C, 21Y, 21M, and 21BK. The image forming device 21BK includes a photosensitive drum 25BK as an electrostatic latent image carrier that is an image carrier, a charging device 27BK, a developing device 26BK, a cleaning device 28BK, and the like that are sequentially arranged in the rotation direction A of the photosensitive drum 25BK. And has a well-known configuration for receiving the exposure light 29BK between the charging device 27BK and the developing device 26BK. The electrostatic latent image carrier may be a belt shape instead of a drum shape. Hereinafter, the image forming apparatus will be described by omitting the C, Y, M, and BK alphabets attached to the end when the colors are not distinguished.
[0028]
As shown in FIG. 2, the developing device 26 includes a developing casing 51, a developing roller 52 that develops the photosensitive drum 25, and a shaft 53 that is disposed in parallel with the shaft 53 of the developing roller 52. A first developer conveying member 54 as a first developer agitating and conveying member that conveys the developer to the second axis, and a second developer that is arranged in parallel with the shaft 53 and conveys the developer in the other direction of the shaft 53, that is, the back side of the paper surface. And a second developer conveying member 55 as an agent stirring and conveying member.
[0029]
The developing device 26 is also disposed between the first developer transport member 54 and the second developer transport member 55, and the space around the first developer transport member 54 and the periphery of the second developer transport member 55. A partition plate 56 integral with the developing casing 51, and a facing region between the developing roller 52 and the second developer conveying member 54 in the rotation direction C of the developing roller 52 that rotates clockwise in FIG. And a developer regulating member 57 disposed below the developing roller 52 for regulating the developer pumped up by the developing roller 52.
[0030]
The developing roller 52 has a developer pumping unit 61 that attracts the developer and pumps up the developer, and a developer releasing unit 62 that is located above the developer pumping unit 61 and separates the developer. The first developer conveying member 54 is disposed near the developer pumping portion 61 at a position facing the developer pumping portion 61, and the second developer conveying member 55 is a developer near the developer separating portion 62. It is disposed at a position facing the separating portion 62. In FIG. 2, reference numeral 36 denotes a cleaning blade provided in the cleaning device 28, and reference numeral 37 denotes a transfer belt provided in the transfer device 22.
[0031]
The developing roller 52 has a magnet roller (not shown) in which a plurality of magnets are arranged in the circumferential direction, and a cylindrical sleeve (not shown) rotates around the magnet roller. The sleeve is made of a nonmagnetic metal such as aluminum. The magnet roller is fixed so that each magnet faces a predetermined direction, and a sleeve rotates around the magnet roller to convey the developer attracted by the magnet. The developing device 26 is configured such that the surface of the developing roller 52 moves from below to above in a portion where the developing roller 52 faces the photosensitive drum 25.
[0032]
As shown in FIG. 3, the developing roller 52 has five magnets P1, P2, P3, P4, and P5 inside, and generates five magnetic poles. A magnetic pole called a P1 pole is located at a portion where the developing roller 52 and the photosensitive drum 25 are opposed to each other, and P2, P3, P4, and P5 magnetic poles are arranged along the developing roller rotation direction C. . The polarities are the N, S, N, N, and S poles in order from the P1 pole, but these poles may have opposite polarities. The developing roller 52 and the photosensitive drum 25 are not in direct contact with each other but are opposed to each other while maintaining a certain distance, and this facing region forms a developing nip region 38.
[0033]
The developing roller 52 causes the developer to rise at the P1 pole and brings the developer into contact with the photosensitive drum 25, thereby attaching the toner to the latent image on the surface of the photosensitive drum 25 to make a visible image. A predetermined bias is applied to the developing roller 52, and the toner is adhered to the latent image portion by the potential difference between the developing roller 52 and the electrostatic latent image formed on the surface of the photosensitive drum 25.
[0034]
The P2 pole conveys the developed developer and draws it into the developing casing 51. The P3 and P4 poles have the same polarity, and the P3 and P4 poles have the functions of separating the developer attracted to the periphery of the developing roller 52 from the developing roller 52 and separating the developer. The developer pumping portion 61 is formed by the P4 pole, and the developer separating portion 62 is formed by the P3 pole.
[0035]
Since the developer after the toner is adhered to the photosensitive drum 25 has a reduced toner density, the developer is transported to the development nip region 38 again without being separated from the developing roller 52 and used for development. Since there is a problem that the developer cannot be obtained, the developer is separated from the developing roller 52 in the post-development region.
[0036]
The partition plate 56 is formed between the P3 pole and the P4 pole on the upstream side of the developer pumping portion 61 and the downstream side of the developer separating portion 62 in the rotation direction C of the developing roller 52. The developer 39 is disposed so as to face the developing roller 52 in the region 39 where the developer adhesion amount is small. Such a region 39 is a region where the magnetic flux density on the surface of the developing roller 52 is 10 mT or less, and the amount of developer attached is small.
[0037]
The partition plate 56 protrudes from the main body of the developing casing 51 toward the region 39, and the distance from the developing roller 52 at the tip is 0.2 mm. Such an interval can be set between 0.2 mm and 1 mm. Therefore, the partition plate 56 can separate the developed developer from the developing roller 52 satisfactorily.
[0038]
As described above, the partition plate 56 is separated from the developing roller 52 and the developer stirred and conveyed by the second developer conveying member 55 is attracted to the developing roller 52 again and is stirred by the first developer conveying member 54. The second developer transport member 55 also has a function of supporting the developer agitated and transported from below to form a developer transport path.
[0039]
The developed developer separated from the developing roller 52 has a target toner concentration in the upstream portion in the developer transport direction by the second developer transport member 55, that is, the portion on the front side in FIG. Thus, the toner is replenished and sufficiently agitated and mixed by the second developer conveying member 55 and the first developer conveying member 54 so that the target toner charge amount is obtained. It is pumped up to 52.
[0040]
The developer attracted to the developing roller by the magnetic force of the P4 pole passes through the developer regulating member 57, is adjusted to a predetermined thickness, and is conveyed to the developing nip region 38 while forming a magnetic brush. The P5 pole functions as a pole for carrying between the P1 pole after passing through the developer regulating member 57, and the developer layer is formed by making the developer spike at a portion facing the developer regulating member 57. It plays a function of stabilizing the thickness.
[0041]
As shown in FIG. 4, the first developer conveying member 54 has a shape that conveys the developer by rotation around the rotation shaft 63. In this example, a spiral 65 is provided around the rotation shaft 63. By rotating in the same direction D as the developing roller 52, the developer is transported in the axial direction toward the direction F from the back side to the front side in FIGS. .
[0042]
Since the screw has an effect of moving the object to be conveyed in the axial direction while moving the object to be conveyed in the axial direction, the first developer conveying member 54 conveys the developer while bringing the developer closer to the developing roller 52. Continuous developer supply becomes possible. The shape in which the developer is conveyed by rotation about the rotation shaft 63 may be a shape in which a large number of swash plates inclined with respect to the rotation shaft 63 are arranged in parallel in the axial direction of the rotation shaft 63 instead of the spiral. .
[0043]
The second developer conveying member 55 has a shape that conveys the developer by rotation about the rotation shaft 64. In this example, the second developer conveyance member 55 has a screw shape in which a spiral 66 is provided around the rotation shaft 64. By rotating in the direction E opposite to the developing roller 52, the developer is conveyed in a direction G opposite to the direction F from the front side to the back side in FIG.
[0044]
As a result, the second developer conveying member 55 conveys the developer in a direction away from the developing roller 52, so that the developer once separated from the developing roller 52 adheres again to the developing roller 52 and becomes the first developer. It is prevented from being conveyed to the area of the conveying member 54. The shape in which the developer is conveyed by rotation around the rotation shaft 64 may be a shape in which a large number of swash plates inclined with respect to the rotation shaft 64 are arranged in parallel in the axial direction of the rotation shaft 64 instead of the spiral. .
[0045]
On the downstream side in the developer conveying direction of the second developer conveying member 55, that is, on the back side of the developing device 20 on the paper surface of FIGS. 2 and 3, the partition plate 56 is not provided or an opening is formed in a part of the partition plate 56. By providing, a communication port 67 that communicates the space around the first developer conveying member 54 and the space around the second developer conveying member 55 is provided, and the communication is performed by the second developer conveying member 55. The developer falls to the transport path of the first developer transport member 54 located below.
[0046]
In the developing device in which the developer conveying members 55 and 54 are arranged vertically like the developing device 26, the developer is moved between the upper and lower developer conveying members 55 and 54. The developer may move freely from the upper developer conveying member 55 to the lower developer conveying member 54 as described above, but a mechanism for that is necessary for the upward movement from the lower side.
[0047]
However, in the developing device 26, the developing roller 52 pumps up the developer from the lower developer conveying member 54 and releases the developer into the space around the upper developer stirring member 55, so that the developer moves from the lower side to the upper side. Therefore, the developing roller 52 does not require a special developer pumping mechanism, and a developing device having a small horizontal dimension can be realized with a simple configuration.
[0048]
Since the developer in the developing device 26 is consumed while the developing operation is repeated, it is necessary to replenish the toner in the developing device 26 from the outside of the developing device 26. Therefore, in the developing device 26, as described above, toner is replenished at the upstream portion in the transport direction of the second developer transport member 55 disposed in the vicinity of the region where the developer is separated from the developing roller 52.
[0049]
In the developer transport path by the second developer transport member 55, only the developer separated from the developing roller 52 is collected and toner is not supplied to the developing roller 52. The developer is transported to the back side of the developing device 26 while being agitated and mixed in the developer away from the developer, and then dropped into the transport path of the first developer transport member 54 via the communication port 67, and the first developer transport member The toner is supplied to the developing roller 52 while being conveyed to the front side by 54 and used for development.
[0050]
The developer deteriorates by receiving stirring in the developing device 26. The carrier is not able to exhibit its initial performance due to the coating film on the surface being scraped or the resin component of the toner adhering to the surface. The performance of the toner decreases as the additive adhering to the periphery is buried. The deterioration of the developer is more easily promoted when stirring is performed in a state where the toner concentration in the agent is low than when stirring is performed in a state where the toner concentration is high.
[0051]
Further, in terms of which part in the developing device 26 is subjected to stress that promotes deterioration, it is most stressed when passing through a narrow space between the developing roller 52 and the developer regulating member 57 and forms a screw shape. There is almost no stress at the portion in contact with the first developer conveying member 54 and the second developer conveying member 55. In the developing device 26, the developer whose toner density has been reduced after development is separated from the developing roller 52, and is then stirred only by the first developer conveying member 54 and the second developer conveying member 55 having a screw shape to replenish the toner. Since it is supplied to the developing roller 52 after being mixed with the developed developer, it does not pass through the gap between the developing roller and the developer regulating member in a state where the toner density is lowered, thus promoting the deterioration of the developer. Therefore, the deterioration of the developer is suppressed, so that stable image quality can be maintained for a long time.
[0052]
In the developing device 26, the developer conveyed by the first developer conveying member 54 is pumped up to the developing roller 52 while being conveyed in the F direction. The developer pumped up by the developing roller 52 is brought into contact with the photosensitive drum 25 for development, and then separated from the developing roller 52 in the developing device 26, and in the G direction by the second developer conveying member 55. It is conveyed toward. In such developer circulation, the developer used for development before being transported to the front end side in the F direction by the first developer transport member 54 and returned to the G direction by the second developer transport member 55 is increased. The developer tends to accumulate on the back side. If the developer does not reach the downstream in the F direction, there is a problem that the developer cannot be pumped onto the developing roller 52 at the downstream end portion of the first developer conveying member 54 in the F direction.
[0053]
For this reason, in the developing device 26, the developer conveying capability of the first developer conveying member 54 is made larger than the developer conveying capability of the second developer conveying member 55, so that the developing roller 52 in the axial direction, in other words, development. The developer is balanced in the depth direction of the device 26. That is, the developer transport amount per unit time of the first developer transport member 54 is made larger than the developer transport amount per unit time of the second developer transport member 55, and the first developer transport member 54. The developer transport speed of the second developer transport member 55 is set higher than the developer transport speed of the second developer transport member 55.
[0054]
Specifically, the outer diameter of the first developer conveying member 54, that is, the outer diameter of the spiral 65 is made larger than the outer diameter of the second developer conveying member 55, that is, the outer diameter of the spiral 66, and the first developer conveying member. 54, that is, the pitch of the spiral 65 is made larger than the pitch of the second developer conveying member 55, that is, the pitch of the spiral 66, and the rotational speed of the first developer conveying member 54 is set to the second developer conveying member 55. It is larger than the number of revolutions. In addition, the volume of the space where the developer is conveyed by the first developer conveying member 54 may be larger than the volume of the space where the developer is conveyed by the second developer conveying member 55. These can be used in at least one or a combination thereof.
[0055]
In this way, when the developer transport capability of the first developer transport member 54 is increased, if all the developer transported to the downstream portion of the first developer transport member 54 is pumped up to the developing roller 52, There is no problem in the developer balance in the depth direction of the developing device 26. However, since the developer transport amount changes depending on the inclination of the developing device 26 and the developer fluidity, insufficient pumping of the developer in the downstream portion of the first developer transport member 54, in other words, poor pumping of the developer is prevented. In this case, it is preferable to set the conveyance capability of the first developer agitating / conveying member so that the developer is accumulated in the downstream portion of the first developer conveying member 54.
[0056]
However, if a large amount of developer accumulates on the near side and there is no escape, the load torque of the first developer conveying member 54 may increase or lock. Therefore, as shown in FIG. 4, communication that connects the space around the first developer transport member 54 and the space around the second developer transport member 55 to the downstream portion of the partition plate 56 in the F direction. An opening 68 is provided to create a place for the developer to escape when the developer accumulates in the downstream portion of the first developer conveying member 54. As a result, when the developer accumulates in the downstream portion of the first developer conveying member 54 and becomes slightly wet, the developer moves to the space around the upper second developer conveying member 55 through the communication port 68. Therefore, an increase in load torque and locking of the first developer conveying member 54 are prevented.
[0057]
The communication port 68 is formed at a position near the developing roller 52 in the partition plate 56, and the partition plate 56 at a position away from the developing roller 52 remains. In this way, the developer overflowed upward while being brought to the developing roller 52 by the first developer conveying member 54 is placed on the upper surface of the partition plate 56 by the second developer conveying member 55, and the developing roller The sheet can be conveyed in the G direction while being separated from 52.
[0058]
According to the present embodiment, when the image forming apparatus 20 is turned on, the image forming apparatus 20 is ready for image formation. When the operator performs a known operation for starting image formation, the direction of the photosensitive drum 25C is set. With rotation to A, the surface of the photosensitive drum 25C is uniformly charged by the charging device 27C, and an electrostatic latent image corresponding to the document image is formed by the exposure light 29C.
[0059]
The developing roller 52C provided in the developing device 26C transports the developer in the developing device 26C to the developing nip region 38 facing the photosensitive drum 25C, and develops the electrostatic latent image formed on the surface of the photosensitive drum 25C. The toner in the agent adheres to become a visible image and is developed. The toner image formed on the photoconductive drum 25C is transferred onto a recording medium conveyed in the direction of arrow B on the transfer device 22 in a transfer area 35C where the photoconductive drum 25C and the transfer device 22 face each other. It becomes an image on the medium.
[0060]
After transfer, the toner remaining on the photosensitive drum 25C without being transferred to the recording medium is scraped off by a cleaning blade 36C provided in the cleaning device 28C, and the photosensitive member 25C is cleaned, and the photosensitive member that has passed through the cleaning device 28C. Thereafter, the surface of the body drum 25C is uniformly charged again by the charging device 27C, and the next image forming process is repeated.
[0061]
The recording medium onto which the cyan toner has been transferred is conveyed in the direction of arrow B by the transfer device 22 and is subjected to image forming devices 21Y, 21M, and 21BK that perform an image forming process similar to the image forming step described above in the image forming device 21C. The yellow, magenta, and black toner images are sequentially transferred appropriately, and all the toner images necessary for image formation are transferred, and then transferred from the transfer device 22 to the fixing device 1 to record the toner image on the recording medium. Fixing to the medium is performed. The recording medium after fixing is stacked on the paper discharge tray 32 through the roller structure 43 and the discharge roller 45.
[0062]
Although the developing device and the image forming apparatus to which the present invention has been applied have been described above, the image forming device 21 can be configured as shown in FIG. In the developing nip region 38 where the developing roller 52 and the photosensitive drum 25 face each other, a developing method in which the moving direction C of the developing roller 52 surface is the same as the moving direction A of the photosensitive drum 25 surface is forward developed and photosensitive A developing method in which the moving direction C of the surface of the developing roller 52 is opposite to the moving direction A of the surface of the body drum 25 is referred to as reverse development. The image forming device 21 shown in FIG. Unlike the image forming apparatus 21 using an image forming system that performs reverse development, an image forming system that is applied so as to perform forward development is employed.
[0063]
In this example, the transfer direction B of the transfer belt 37 in the transfer device 22 is also opposite to that shown in FIG. The arrangement positions of the image forming devices 21C, 21Y, 21M, and 21BK are also above the transfer device 22 in the case shown in FIG. 1 and the like, but in this example, they are below the opposite transfer device 22. ing. The other components similar to those in FIG.
[0064]
【The invention's effect】
According to the present invention, the developing roller that develops the image carrier, the first developer conveying member that is disposed in parallel with the axis of the developing roller and conveys the developer in one direction of the axis, and the developing roller A second developer transport member disposed in parallel with the shaft and transporting the developer in the other direction of the shaft; the first developer transport member; and the second developer transport member. In the developing device having a partition plate that shields a space around the first developer conveying member and a space around the second developer conveying member, the developing roller draws up the developer. And a developer separating section that is located above the developer pumping section and separates the developer, and the first developer transport member is disposed in the vicinity of the developer pumping section, and the second developer transport section The member is disposed in the vicinity of the developer separating portion, The rotation direction of the first developer conveying member is the same as the rotation direction of the developing roller, the rotation direction of the second developer conveying member is opposite to the rotation direction of the developing roller, In the space around the first developer conveying member, the developer is conveyed in the one direction by the first developer conveying member while being brought close to the developing roller, and the space around the second developer conveying member. The developer is transported in the other direction by the second developer transport member while being separated from the developing roller, and the partition plate includes a space around the first developer transport member and the second development. A communication port that communicates with the space around the agent conveying member, while leaving the partition plate at a position away from the developing roller in the downstream portion of the first developer conveying member in the developer conveying direction, Since it has a communication port formed at a position near the developing roller in the downstream portion, it is provided with two developer conveying members that are arranged in parallel to the axial direction of the developing roller and convey the developer in opposite directions, Horizontal The developer can be reduced in size, and the developer can be pumped from the lower developer transport member to the upper developer transport member by the developing roller. Further, the developer in which the toner density is reduced immediately after development by supplying only the developer in which the toner and the carrier are sufficiently stirred and mixed to the developing roller after the horizontal direction is made compact. Since the toner having the target charge amount is used for development because the toner is not supplied immediately, it is possible to contribute to the formation of a high-quality image, and the downstream side in the transport direction of the first developer transport member. In order to prevent poor developer pumping, when the first developer conveying member is set to the downstream side in the conveying direction, the developer is excessively accumulated and the load torque of the first developer agitating and conveying member increases, The lock occurs Preventing, can prevent a problem such as deterioration of the members, with the developing device can be a long life, By rotating the first developer agitating and conveying member, the developer is transported in the axial direction while sweeping the developer to the developing roller, so that the developer can be smoothly supplied to the developing roller and image density unevenness can be suppressed. Can contribute to high-quality image formation, A developer that is conveyed while being brought close to the developing roller and that overflows from the space around the first developer conveying member to the space around the upper second developer conveying member through the communication port is partitioned. On the board The developer separated from the developing roller is prevented from being attracted to the developing roller by transporting the developer in the axial direction while sweeping the developer away from the developing roller by the rotation of the second developer stirring and conveying member. It is possible, Since the developer can be transported while being separated from the developing roller, and can be reliably transported by the second developer transport member while being held in the developer transport path by the second developer transport member, the developer can be smoothly circulated. An apparatus can be provided.
[0065]
If toner is supplied to the developer in the upstream portion of the second developer transport member in the developer transport direction, the developer is not supplied to the developing roller in the upstream portion of the second developer transport member. Replenishing toner can increase the agitation time between the replenished toner and the developer, and the transport path of the second developer transport member includes a developer whose toner concentration has decreased immediately after development. Since the toner surface often comes into contact with the carrier, the toner can be sufficiently agitated and mixed with the carrier, and the toner can be charged efficiently. A developing device that can contribute to image formation with high image quality can be provided.
[0066]
If the distance between the developing roller and the partition plate is in the range of 0.2 mm to 1 mm, the developer is prevented from passing through the gap between the developing roller and the partition plate, and the developer having a lowered toner concentration Since it does not pass through the gap between the developing roller and the developer regulating member and is only agitated by the second developer conveying member, stress applied to the carrier and toner can be suppressed and deterioration can be suppressed, so that the performance of the developer can be prolonged. It is possible to provide a developing device that can be maintained for a long time and has a long life and high durability.
[0067]
The partition plate faces the developing roller in a region where the amount of developer adhering to the developing roller is small in the rotation direction of the developing roller, on the downstream side of the developer separating portion and the upstream side of the developer pumping portion. In this case, since there is little developer in the opposing region between the developing roller and the partition plate, the developer whose toner concentration has been reduced does not pass through the gap between the developing roller and the developer regulating member, and the second developer conveying member Since it only receives agitation, stress applied to the carrier and toner can be suppressed and deterioration can be suppressed, so that the performance of the developer can be maintained over a long period of time, and the developing device can have a long life and high durability. Can be provided.
[0068]
The partition plate faces the developing roller in a region where the magnetic flux density on the surface of the developing roller is 10 mT or less, downstream of the developer separating portion and upstream of the developer pumping portion in the rotation direction of the developing roller. If so, the amount of the developer attracted to the opposing area between the developing roller and the partition plate is small, so that the developer whose toner concentration has been lowered does not pass through the gap between the developing roller and the developer regulating member, and the second developer conveying member Since it only receives agitation, stress applied to the carrier and toner can be suppressed and deterioration can be suppressed, so that the performance of the developer can be maintained over a long period of time, and the developing device can have a long life and high durability. Can be provided.
[0071]
The first developer conveying member and the second developer conveying member are configured to convey the developer by rotation about its axis, and the developer per unit time of the first developer conveying member If the transport amount is larger than the transport amount of the developer per unit time of the second developer transport member, the stress on the developer is small and the first developer agitating transport member is downstream in the transport direction. Prevents the developer on the side from decreasing, spreads the developer to the near side, prevents poor developer pumping to the developing roller, and suppresses uneven image density, contributing to high-quality image formation It is possible to provide a developing device that can
[0072]
Assuming that the developer transport speed of the first developer transport member is greater than the developer transport speed of the second developer transport member, the developer transport per unit time of the first developer transport member The amount of developer is larger than the amount of developer transported per unit time of the second developer transport member, and the developer on the downstream side in the transport direction of the first developer agitating transport member is prevented from being reduced. It is possible to provide a developing device capable of contributing to high-quality image formation by spreading the agent to the near side, preventing poor pumping of the developer to the developing roller, and suppressing image density unevenness.
[0073]
If the outer diameter of the first developer conveying member is made larger than the outer diameter of the second developer conveying member, the relationship between the outer diameters of the first developer conveying member and the second developer conveying member is set. Thus, the developer transport amount per unit time of the first developer transport member is made larger than the developer transport amount per unit time of the second developer transport member, and the first developer stirring transport member Prevents the developer on the downstream side in the transport direction from decreasing, spreads the developer to the near side, prevents poor pumping of the developer to the developing roller, suppresses uneven image density, and prevents high-quality images. A developing device that can contribute to formation can be provided.
[0074]
Assuming that the pitch of the first developer conveying member is larger than the pitch of the second developer conveying member, by setting the relationship between the pitches of the first developer conveying member and the second developer conveying member, The transport amount of the developer per unit time of the first developer transport member is made larger than the transport amount of the developer per unit time of the second developer transport member, and the transport direction of the first developer stirring transport member Prevents the developer on the downstream side from decreasing, spreads the developer to the near side, prevents poor pumping of the developer to the developing roller, and suppresses uneven image density, contributing to high-quality image formation It is possible to provide a developing device capable of performing the above.
[0075]
If the number of rotations of the first developer conveying member is made larger than the number of rotations of the second developer conveying member, the relationship between the number of rotations of the first developer conveying member and the second developer conveying member is set. Thus, the developer transport amount per unit time of the first developer transport member is made larger than the developer transport amount per unit time of the second developer transport member, and the first developer stirring transport member Prevents the developer on the downstream side in the transport direction from decreasing, spreads the developer to the near side, prevents poor pumping of the developer to the developing roller, suppresses uneven image density, and prevents high-quality images. A developing device that can contribute to formation can be provided.
[0076]
If the volume of the space in which the developer is conveyed by the first developer conveying member is made larger than the volume of the space in which the developer is conveyed by the second developer conveying member, the first developer conveying member, By setting the relationship of the volume of the space around the second developer transport member, the developer transport amount per unit time of the first developer transport member can be set as the development amount per unit time of the second developer transport member. This is larger than the amount of developer transported, prevents the developer on the downstream side in the transport direction of the first developer agitating / conveying member from being reduced, spreads the developer to the near side, and pumps the developer onto the developing roller. Thus, it is possible to provide a developing device that can prevent a rise failure and suppress uneven image density and contribute to high-quality image formation.
[0077]
According to the image forming apparatus of the present invention, the image forming apparatus including the developing device that exhibits such an effect. Can be provided.
[Brief description of the drawings]
FIG. 1 is a side view showing an outline of a developing device to which the present invention is applied and an image forming device equipped with the developing device and capable of forming a color image.
2 is a side view of the image forming apparatus shown in FIG. 1. FIG.
3 is a side view showing the positional relationship between the magnetic pole, the developer pumping unit, the developer separating unit, the first developer transport member, the second developer transport member, and the partition plate in the image forming apparatus shown in FIG. 1; FIG.
4 is a perspective view of the developing device shown in FIG. 1. FIG.
FIG. 5 is a side view showing another configuration example of the image forming apparatus.
FIG. 6 is a side view of a conventional developing device provided with two developer conveying members that are arranged in parallel to the axial direction of the developing roller and convey the developer in opposite directions.
[Explanation of symbols]
20 Image forming apparatus
25, 25C, 25Y, 25M, 25BK Image carrier
52 Development roller
53 Developing roller shaft
54 First developer transport member
55 Second developer transport member
56 Partition plate
61 Developer pumping section
62 Developer separation part
68 Communication port
C Development roller rotation direction
D Direction of rotation of the first developer conveying member
E Direction of rotation of the second developer conveying member
F One direction of the axis of the developing roller, the developer transport direction of the first developer transport member
G The other direction of the axis of the developing roller, the developer conveying direction of the second developer conveying member

Claims

A developing roller for developing the image carrier;
A first developer conveying member disposed in parallel with the axis of the developing roller and conveying the developer in one direction of the axis;
A second developer conveying member disposed parallel to the axis of the developing roller and conveying the developer in the other direction of the axis;
A space between the first developer transport member and the second developer transport member, and a space around the first developer transport member and a space around the second developer transport member. In a developing device having a partition plate for shielding,
The developing roller has a developer pumping unit that pumps up the developer, and a developer releasing unit that is located above the developer pumping unit and separates the developer,
The first developer conveying member is disposed in the vicinity of the developer pumping portion,
The second developer conveying member is disposed in the vicinity of the developer separating portion,
The rotation direction of the first developer conveying member is the same as the rotation direction of the developing roller,
The rotation direction of the second developer conveying member is opposite to the rotation direction of the developing roller,
In the space around the first developer conveying member, the developer is conveyed in the one direction by the first developer conveying member while being brought close to the developing roller,
In the space around the second developer conveying member, the developer is conveyed in the other direction by the second developer conveying member while being separated from the developing roller,
The partition plate is a communication port that communicates a space around the first developer conveying member and a space around the second developer conveying member, and the partition plate is configured to communicate the developer of the first developer conveying member. A developing device having a communication port formed at a position near the developing roller in the downstream portion while leaving the partition plate at a position away from the developing roller in the downstream portion in the transport direction.

2. The developing device according to claim 1, wherein toner is supplied to the developer in an upstream portion of the second developer transport member in the developer transport direction.

3. The developing device according to claim 1, wherein a distance between the developing roller and the partition plate is in a range of 0.2 mm to 1 mm.

4. The developing device according to claim 3, wherein the partition plate adheres the developer to the developing roller on the downstream side of the developer separating portion and the upstream side of the developer pumping portion in the rotation direction of the developing roller. A developing device, wherein the developing device is opposed to the developing roller in a small amount region.

5. The developing device according to claim 3, wherein the partition plate is a magnetic flux density on the surface of the developing roller on the downstream side of the developer separating portion and the upstream side of the developer pumping portion in the rotation direction of the developing roller. Is a developing device characterized by facing the developing roller in a region of 10 mT or less.

6. The developing device according to claim 1 , wherein the first developer conveying member and the second developer conveying member are configured to convey the developer by rotation about its axis. and none of, characterized in that the the amount of the developer conveyed per unit time of the first developer conveying member, is larger than the amount of the developer conveyed per unit time of the second developer conveying member Development device.

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