JP3656812B2

JP3656812B2 - Development device

Info

Publication number: JP3656812B2
Application number: JP18976799A
Authority: JP
Inventors: さえ子戸田; 哲夫丹田; 誠浜口; 寿向高
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 1999-07-02
Filing date: 1999-07-02
Publication date: 2005-06-08
Anticipated expiration: 2019-07-02
Also published as: JP2001022184A

Description

【０００１】
【発明の属する技術分野】
本発明は、現像剤(トナー)を用いて複写機、プリンタ、ＦＡＸなどの電子写真現像法により現像を行う現像装置に関し、特に現像担持体としてＮ極とＳ極を着磁した固定マグネットローラを内包する回転スリーブを用いた現像装置に関するものである。
【０００２】
【従来の技術】
現像剤担持体としてＮ極とＳ極を複数着磁した固定マグネットローラを内包する回転スリーブを用い、回転スリーブ上に形成させる磁気的担持力を利用して現像剤の容器内に集積した現像剤を担持しながら、層厚規制部材を利用して層厚規制を行った後、感光体への現像位置に導くようにした現像装置は周知である。
【０００３】
そして、特に、２成分現像方式での多色現像の場合は、各色（イエロー、マゼンタ、シアン、ブラック）毎の現像装置を必要とし、現像を行っている現像装置以外の現像装置から現像剤が混入するのを遮断する必要がある。
従来現像剤混入遮断手段として、現像を行っていない現像装置を回転や後退させる退避機構を設けた現像装置がある。
また、装置の小型化をはかるため回転スリーブ上の、現像位置より回転方向上流側にゴムブレード等の規制板を接触させ、現像剤の混入を遮断させる方法がある。(特開昭59-60453号、特開平6-242666号公報参照)。
【０００４】
【発明が解決しようとする課題】
しかし、上記退避型の現像装置は現像器を退避させる空間や複雑な機構を必要とすることから装置の大型化やコストアップにつながるという問題がある。
また、上記接触ブレード方式では、回転トルクが大きくなってしまうために省電力化が難しいという問題や、ブレードが回転スリーブに圧接しているときに擦り傷が生じ、回転スリーブから離間しているときでも現像剤の通過による摩擦が生じるために、ブレードの耐久性の面で問題があり、さらに、現像ローラとブレード間を通過する際に現像剤を傷めてしまうために現像剤が劣化してしまうという問題もあった。
【０００５】
本発明は上記問題に鑑みてなされたものであり、現像を行っている現像装置以外の現像装置から現像剤が混入するのを防止する画像形成装置を提供することを目的とする。
また、本発明の他の目的は、現像装置から感光体ローラ側への搬送を完全に遮断し、現像剤の劣化防止やブレードの長寿命化が図れる画像形成装置を提供することである。
また、本発明の他の目的は、回転スリーブ内の固定マグネットローラと、それに対面して配置される可動マグネットの磁気的拘束力を利用して簡素化、高速化、小型化、コストダウンが図れる画像形成装置を提供することである。
【０００６】
【課題を解決させるための手段】
本発明は、Ｎ極とＳ極を着磁した複数の永久磁石を有する固定マグネットローラを内包する回転スリーブを感光体ドラムに対面配置し、前記回転スリーブにより前記感光体ドラム上の現像位置へ現像剤を導く現像装置において、
前記回転スリーブと外周同士を所定間隙有して前記現像位置より前記回転スリーブの回転方向上流側に配置した固定スリーブと、
該固定スリーブ内に配置され、現像時に位置する第１停止位置と非現像時に位置する第２停止位置との間を回動可能な１極以上の可動マグネットと、
前記固定スリーブと前記回転スリーブとの最近接点を挟んで、前記回転スリーブ内の前記現像位置側に配置された前記固定マグネットローラの第１極と、反現像位置側に配置された前記固定マグネットローラの第２極とを備え、
前記第１極の垂直磁力を６００ガウス以上（望ましくは７００〜８００ガウス）、前記第２極の垂直磁力を３００ガウス以上（望ましくは３５０〜７００ガウス）、前記回転スリーブと固定スリーブの最近接点における前記固定マグネットローラの前記回転スリーブ表面での水平磁力が４５０ガウス以下（望ましくは２００〜４００ガウス）に設定するとともに、回転スリーブと固定スリーブの最近接点から、垂直磁力０のガウス点が±２０°以内にあるか若しくは±２０°の範囲を超える場合は穂切り時の可動マグネットを前記最近接点位置と一致する角度に停止するように構成し、
現像時には、前記可動マグネットが前記第２停止位置より離間する前記第１停止位置にあって、前記固定マグネットローラ側への前記可動マグネットの磁力を不作用とし、前記固定マグネットローラの磁力を利用して前記回転スリーブ上に担持させた現像剤を前記固定スリーブの周面と接触させて層厚規制した後前記現像位置に導き、
非現像時は、前記可動マグネットが前記回転スリーブと接近する側に回動して前記第２停止位置に停止し前記固定マグネットローラ側に前記可動マグネットの磁力を作用させ、前記現像位置側へ現像剤の供給を遮断するとともに、前記現像位置への現像剤の供給を停止し、前記回転スリーブ上の現像剤を回収させるように構成したことを特徴とする。
【０００７】
請求項１記載の発明に係る現像装置は、Ｎ極とＳ極を着磁した固定マグネットローラを内包する回転スリーブと、前記回転スリーブと外周同志を所定間隙有して前記現像位置より前記回転スリーブの回転方向上流側に配置した、回動可能でかつ非現像位置で停止可能な１極以上の可動マグネットを内包した固定スリーブとより構成することを第１の特徴とする。
このように構成することにより、現像剤搬送のために回転するのは前記回転スリーブのみであって、前記回転スリーブの外周と前記固定スリーブの外周とは機械的に精度よく設定配置することができ、一定した現像剤の層厚規制が可能である。
【０００８】
また、現像時に位置する第１停止位置と非現像時に位置する第２停止位置との間を回動可能な１極以上の可動マグネットが前記固定スリーブ内に配置され、該可動マグネットは前記固定スリーブと前記回転スリーブとの最近接点を挟んで、前記回転スリーブ内の前記現像位置側に配置された前記固定マグネットローラの第１極と、反現像位置側に配置された前記固定マグネットローラの第２極とを備え、
現像時には、前記可動マグネットが前記第２停止位置より離間する前記第１停止位置にあって、前記固定マグネットローラ側への前記可動マグネットの磁力を不作用とし、前記固定マグネットローラの磁力を利用して前記回転スリーブ上に担持させた現像剤を前記固定スリーブの周面と接触させて層厚規制した後前記現像位置に導き、
非現像時は、前記可動マグネットが前記回転スリーブと接近する側に回動して前記第２停止位置に停止し前記固定マグネットローラ側に前記可動マグネットの磁力を作用させ、前記現像位置側へ現像剤の供給を遮断するとともに、前記現像位置への現像剤の供給を停止し、前記回転スリーブ上の現像剤を回収させるように構成したことが第２の特徴である。
【０００９】
非現像時は、前記可動マグネットの磁力が前記固定マグネットローラ側に作用し、前記可動マグネットと前記固定マグネットローラの第１極間の磁力と、前記可動マグネットと前記第２極間の磁力が、感光体ドラム側の現像位置への現像剤の搬送を遮断する。
【００１０】
また、前記第１極の垂直磁力を６００ガウス以上（望ましくは７００〜８００ガウス）、前記第２極の垂直磁力を３００ガウス以上（望ましくは３５０〜７００ガウス）、前記回転スリーブと固定スリーブの最近接点における前記固定マグネットローラの前記回転スリーブ表面での水平磁力が４５０ガウス以下（望ましくは２００〜４００ガウス）に設定したことが第３の特徴である。
【００１１】
そして、前記可動マグネットの前記固定スリーブ表面での、前記固定マグネットの第２極と相反する磁極の垂直磁力は３００ガウス以上（望ましくは３００〜４５０ガウス）、かつその両端に現れる磁極の垂直磁力は１５０ガウス以下（望ましくは１００ガウス以下）と設定することも本発明の有効な手段である。
【００１２】
現像剤搬送区間の一つである、層厚規制区域の前記回転スリーブと前記固定スリーブとの最短近接位置を挟んで、固定マグネットローラの第１極と第２極は現像時において現像剤を搬送するために相反する極が配置され、前記固定マグネットローラの第１極と第２極との間の搬送磁力により現像剤は現像位置に搬送される。一方、可動マグネットの主極と前記第１極間のシールド磁力と、前記主極と前記第２極間の拘束磁力によって前記搬送磁力を止めれば、現像剤の搬送は遮断される。
【００１３】
前記第１極と前記第２極の垂直磁力が同じでも極間角度が狭いと、搬送磁力が大きくなり、前記可動マグネットの磁力を上げねば現像剤の搬送を遮断することはできない。
また、前記第１極と第２極の極間角度が大き過ぎると前記固定マグネットローラの磁極配置の角度バランスが悪くなることや、可動マグネット主極と前記第１極及び第２極、またはこれらの極間が遠ざかり、前記シールド磁力と拘束磁力も弱くなる。
また、穂切り時は、可動マグネットの主極と第２極は吸引しあうので、両磁力が大きすぎるとマグネットを支持する部材が引き合いに負けて撓み、マグネットがスリーブ部材に当接する。
また、第１極の磁力が小さ過ぎるとシールド磁力が弱くなり現像剤の遮断ができない。
よって、上記磁力が望ましい。
【００１４】
本発明は上述のように、現像を行っている現像装置以外の現像装置から現像剤が混入するのを防止する画像形成装置を提供することができる。
そして、本発明は、現像装置を移動しないで、回転スリーブ内の固定マグネットローラと、それに対面して配置される可動マグネットの磁気的拘束力を利用して現像剤の搬送及び遮断を行っているので、画像形成装置の簡素化、高速化、小型化、コストダウンを図れることができる。
【００１５】
また、現像スリーブに現像剤遮断用ブレードを用いないで、現像装置から感光体ローラ側への搬送を完全に磁力により遮断するので、現像スリーブが回転しても固定スリーブが不動であるために、遮断時においては現像剤の移動が少なく、現像剤の劣化防止を図るとともに、前記現像スリーブや前記現像剤遮断用ブレードの摩耗等による現像装置の短命化を防止し、現像装置の長寿命化を図ることができる。
【００１６】
【発明の実施の形態】
以下、図面に基づいて本発明の実施の形態を例示的に詳しく説明する。但しこの実施の形態に記載されている構成部品の寸法、材質、形状、その相対配置などは特に特定的な記載がない限りは、この発明の範囲をそれのみに限定する趣旨ではなく単なる説明例に過ぎない。
【００１７】
図１は、本発明にお実施の形態にかかる画像形成装置全体の断面図を示す。以下、本発明の実施の形態を図面に基づいて詳細に説明する。
図示しない給紙カセット、感光体ドラム１、光走査ユニット２、帯電器３、現像剤容器を含んだ４個の現像装置４〜７、中間転写体１２、２次転写ローラ１３、定着器１４、画像が転写された記録媒体８を前記２次転写ローラ１３から定着器１４に搬送する無端ベルトを用いた搬送装置９等よりなる。
【００１８】
印刷時は各色毎に、感光体ドラム１を帯電器３によって帯電し、光走査ユニット２から露光、各現像装置４〜７で現像した画像を中間転写体１２に転写し、図示しない給紙カセットから搬送される記録媒体８に２次転写ローラ１３で転写し、定着器１４で加熱・加圧して定着させ排紙を行う。
【００１９】
本発明に係る実施の形態の構成を詳細に説明する。
図２は、現像装置４の感光体ドラム１へ現像剤を飛翔する現像位置近傍を示す断面図であり、Ｎ極とＳ極に着磁した永久磁石を有する固定マグネットローラ２０、該固定マグネットローラ２０を内包する回転スリーブ２１、該回転スリーブ２１の現像位置Ａより回転方向上流側に配置する固定スリーブ２２、該固定スリーブ２２の中心を中心軸２３ａとして回動可能な主極がＳ極、その両端に現れる副極がＮ極の可動マグネット２３を配置してなる。
【００２０】
可動マグネット２３は図３及び図４に示すように、中心軸２３ａの軸心２３ｅとして断面扇形に形成され、軸心２３ｅから半径ｒを有する外周面２３ｄを円周面としてＳ極に、軸心２３ｅから角度θを有して形成される扇形斜面２３ｂ及び２３ｃがそれぞれＮB及びＮAのＮ極となるように磁化されている。
【００２１】
現像中の現像装置４は、可動マグネット２３が図２（Ａ）の様に固定マグネットローラ２０の磁力に影響を与えない位置で停止している場合には、固定マグネットローラ２０の磁力を利用して回転スリーブ２１上に担持させた現像剤２４を固定スリーブ２２の周面と接触させて層厚規制した後、感光体ドラム１への現像位置Ａに導くことが出来る。(以下図２（Ａ）の現像器の状態を穂出しと呼ぶ)
なお、現像剤の層厚規制は回転スリーブ２１と固定スリーブ２２との距離ｄで決まる。
【００２２】
しかし現像を行っている以外の現像装置５〜７がそれぞれ有する回転スリーブ２１へ現像剤を供給すると、その現像剤が他の穂出し中の現像器に混入したり感光体ドラム１上のトナー像を乱す。これを防ぐために、図２（Ｂ）のように可動マグネット２３を回転スリーブ２１の最近接点付近に移動させると、現像を行っている以外の現像装置が現像剤を回転スリーブへ供給するのを遮断することが出来る。（以下図２（Ｂ）の現像器の状態を穂切りと呼ぶ）
【００２３】
以下、図２を用いて現像装置の動作を説明する。
図２（Ａ）の穂出し状態のとき、回転スリーブ２１と固定スリーブ２２の最近接点（以下ブレード位置と呼ぶ）では、磁力線は、磁石内を回転スリーブ２１の第１極(Ｓ極)から第２極（Ｎ極）に向い、磁石外を第２極（Ｎ極）から第１極（Ｓ極）に向けて発生し、閉じた環状をなす。
【００２４】
また、現像位置Ａに対向して配置されている第３極（Ｎ極）と第１極（Ｓ極）とは、磁力線は、磁石内を第１極（Ｓ極）から第３極（Ｎ極）に向い、磁石外を第３極（Ｎ極）から第１極（Ｓ極）に向けて発生し、閉じた環状をなす。
これらの磁力線に沿って、現像剤は回転スリーブ２１の回転による搬送力で第１極を経由して現像位置Ａへと運ばれ、感光体ドラム１の潜像を現像する。
【００２５】
現像後においては、図２（Ｂ）に示すように可動マグネット２３が回転し、この主極(Ｓ極)がブレード位置０゜で停止する。このとき可動マグネット２３のＳ極と回転スリーブ２１の第１極の間は反発磁界による磁気シールド（以下シールド磁力と呼ぶ）を作り、回転スリーブ２１上の現像剤はこの磁界を境に現像位置Ａ側とブレード位置より内側に分離される(図２（Ｂ））。
【００２６】
分離後、現像位置Ａ側の現像剤は回転スリーブ２１の回転により現像装置４内に回収される。また、回動マグネット２３の主極（Ｓ極）から回転スリーブ２１の第２極への吸引磁界（以下拘束磁力と呼ぶ）が同時に生じており、ブレード位置より内側の現像剤はこの両極の間で拘束される。
【００２７】
これらのシールド磁力と拘束磁力が回転スリーブ２１の第２極と第１極間の搬送磁力である磁力線を遮断するので第２極と第１極間に磁力線が通らず、現像剤は回転スリーブ上を搬送される事なく図２（Ｃ）状態で止まる。こうして現像剤を他の現像装置へ混入させることや感光体上のトナー画像を乱すのを防ぐことが出来る。
【００２８】
次に、固定マグネット２０及び可動マグネット２３の条件を種々変えて、穂切りの有無を測定した測定データを表１及び表２に示す。尚、表１及び表２に穂切り結果が良好であったものを実施例として、また、表３及び表４は穂切りができなかったもの、及び、不安定であったものを含み、比較例として記載する。
【００２９】
【表１】

【００３０】
【表２】

【００３１】
【表３】

【００３２】
【表４】

【００３３】
上述の表１及び表２のデータから、本実施例１〜１０では、可動マグネットと第１極間のシールド磁力及び可動マグネットと第２極間の拘束磁力が第１極と第２極間の水平磁力を完全に防ぐので、完全に現像剤を遮断する事が出来た。
【００３４】
一方、比較例１は実施例１と第１極及び第２極の垂直磁力は同じ位だが、水平磁力が５５０Ｇと高い。同様に比較例２〜比較例４も第１極，第２極の垂直磁力と極間角度が狭いため水平磁力が８４０Ｇ、６５０Ｇ，６００Ｇと高くなっている。このため、可動マグネット２３と第１極間のシールド磁力及び可動マグネット２３と第２極間の拘束磁力が水平磁力を完全に防ぐことが出来ず、現像剤が回
転スリーブ２１上を磁力線に沿って搬送されるため現像位置Ａ側に漏れてきた。
【００３５】
また、比較例５においては、固定マグネット２０の第１極の磁力は７４０Ｇ、第２極は４６０Ｇと実施例７，８の第１極及び第２極の値と同じである。
そして、実施例７，８の可動マグネット２３の主極は４００Ｇ、副極はそれぞれ１５０，８０ガウスである。これらは、可動マグネットの主極(Ｓ極)から副極Ｎ_Ａへの磁力線が小さいため現像剤を遮断することができた。
しかしながら、比較例５は可動マグネットの副極が１７０Ｇと高い。この場合、シールド磁力により分離された現像剤が可動マグネット２３の主極(Ｓ極)から副極Ｎ_Ａへの磁力線に沿って移動し、副極Ｎ_Ａ部分に蓄積される。副極Ｎ_Ａ部分に一定量以上現像剤が溜まると、現像剤は副極Ｎ_Ａから回転スリーブ２１上の第１極への磁力線に沿って移動するので完全に穂切りすることが出来なかった。
【００３６】
また、比較例６と比較例７については、実施例４と比較例６の固定マグネット、実施例６と比較例７の固定マグネットは、それぞれ第１極が６００Ｇ、第２極が４４０Ｇ、第１極が６５０Ｇ、第２極が４３０Ｇと同じである。
そして、実施例４及び６とも可動マグネット２３の副極が８０Ｇであり可動マグネット副極Ｎ_Ａが小さいと穂切りできるが、比較例６，７の場合副極Ｎ_Ａが１５０Ｇあるため穂切りできなかった。
【００３７】
また、実施例１〜９においては、各実施例ともに、回転スリーブ２１と固定スリーブ２２の最近接点（ブレード位置）から、垂直磁力０のガウス点は、表１に記載するように、２０°以内にあり、前記ブレード位置から、垂直磁力０のガウス点が近接している。
この垂直磁力０ガウス点が本実施例の範囲を超える場合は、表３及び表４に示すように、可動マグネット２３と第１極間の磁力と前記可動マグネット２３と第２極間の磁力、第２極と第１１間の水平磁力の関係がバランスを保てなくなるため穂切りが不安定、もしくは穂切りできなくなる。
【００３８】
同様の理由で、穂切り時の可動マグネットの停止位置が表２に開示している範囲を超えると穂切りできなくなる。（表４の−５０°〜５０°とは表２に開示している範囲を超えた部分を指す。即ち−５０°〜５０°（−５°〜５°及び−１０°〜−３０°を除く）である。）
例えば、実施例１０においては、ブレード位置から、垂直磁力０のガウス点は±２０°の範囲を超えて−３０°〜３０°（ここで表１及び表３に示す−３０°〜３０°とは−３０°〜−２０°と、２０°〜３０°の（−３０°〜３０°（±２０°の範囲を除く））の範囲であったが、その場合は表２に示すように穂切り時の可動マグネットは、前記最近接点（ブレード位置）と一致する角度に停止する必要がある。
【００３９】
そして、回転スリーブ２１と固定スリーブ２２の最近接点（ブレード位置）から垂直磁力０ガウス点が離れると最近接点での垂直磁力が大きくなり、現像時にスリーブ間を通過する現像剤の圧力が高くなりトルクアップを招くことからも好ましくない。
また、穂切り時の可動マグネットの停止位置が極端に第１極や第２極に近いとマグネット同士の反発や吸引による部材の反りを生じるため、好ましくない。
【００４０】
なお、可動マグネット２３の主極の磁力を上げればシールド磁力、拘束磁力が強くなり水平磁力を遮断する力も強くなるが、可動マグネット２３と固定マグネット２０間の吸引磁力によるマグネットや部材の反りが生じやすくなるので出来るだけ低磁力が望ましい。
また、本実施の形態の磁力関係が成立していれば回転スリーブの外径は特に指定しないが、好ましくは１５〜２５mmである。
【００４１】
また、図４に示すように半径ｒを一定とし、断面扇形状に形成した可動マグネット２３の角度θを変えて形成し、主極（Ｓ極）と主極両端（ＮA、ＮB極）を測定し、表５の結果を得た。
【００４２】
【表５】

【００４３】
表５に示す結果から、実施例Ａは、マグネット角度θが６０゜で、固定スリーブ表面での可動マグネット主極Ｓ極の垂直磁力が４００ガウスのとき、副極のＮA,B 極の垂直磁力が８０ガウスであったために、磁力線に沿って現像剤が副極へ移動することは無く良好な穂切り結果が得られた。
また、実施例Ｂも、実施例Ａよりマグネット角度θが９０゜と狭くなったためにマグネットが小型となり、よって、固定スリーブ表面での可動マグネット主極Ｓ極の垂直磁力が３００ガウスとなったが、副極のＮA,B 極の垂直磁力が８０ガウスであったために、磁力線に沿って現像剤が副極へ移動することは無く良好な穂切り結果が得られた。
【００４４】
これに対して、比較例Ｂは、マグネットの角度θが２２０゜であり、固定スリーブ表面での可動マグネット主極Ｓ極の垂直磁力が６００ガウスあったが、副極のＮA,B 極の垂直磁力が１５０ガウスであったために、副極磁力に現像剤が捕らえられ穂切りが不安定であった。
また、比較例Ａは、マグネットの角度θが９０゜と狭くなったためにマグネットが小型となり、よって、固定スリーブ表面での可動マグネット主極Ｓ極の垂直磁力が４００ガウスあったが、副極のＮA,B 極の垂直磁力が１５０ガウスであったために、副極磁力に現像剤が捕らえられ穂切りが不安定であった。
【００４５】
【発明の効果】
以上、詳細に説明したように本発明の現像装置によれば、穂切り時に固定マグネットローラと可動マグネットローラ間のホールド磁力と拘束磁力が完全に固定マグネットローラの水平磁力を遮断するように構成したので、現像を行っている以外の現像装置から現像剤が混入するのを遮断することができる。
また、現像剤の混入を遮断するのに磁気拘束力を利用しているので、従来のようにゴムブレードを回転スリーブに接触させて現像剤を遮断する必要がなく、ブレードと現像剤の摩擦によるブレードや現像剤の劣化が無くなり、ブレードの耐久性向上により現像装置の耐久性を上げることができる。
また、現像剤の混入を遮断するのに磁気拘束力を利用しているので現像装置を退避させる空間や複雑な機構を必要とせず、装置の簡素化、高速化、小型化、コストダウンをすることができる。
等の種々の著効を有す。
【図面の簡単な説明】
【図１】本発明の実施の形態に係る要部構成を示す断面図である。
【図２】現像状態を説明する説明図である（Ａ）。現像装置が穂切りを始めた状態を示す説明図である（Ｂ）。現像装置の穂切り状態を示す概略図である（Ｃ）。
【図３】可動マグネットの形状を示す斜視図である。
【図４】可動マグネットの断面図である。
【符号の説明】
１感光体ドラム
２０固定マグネットローラ
２１回転スリーブ
２２固定スリーブ
２３可動マグネット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing apparatus that performs development using a developer (toner) by an electrophotographic developing method such as a copying machine, a printer, and a FAX, and in particular, a fixed magnet roller having a north pole and a south pole magnetized as a developing carrier. The present invention relates to a developing device using a rotating sleeve included therein.
[0002]
[Prior art]
A developer carrying a rotating sleeve containing a fixed magnet roller having a plurality of N poles and S poles as a developer carrying member, and using the magnetic carrying force formed on the rotating sleeve, the developer accumulated in the developer container A developing device is known in which the layer thickness is regulated using a layer thickness regulating member while being carried, and then guided to the development position on the photosensitive member.
[0003]
In particular, in the case of multi-color development by the two-component development method, a developing device for each color (yellow, magenta, cyan, black) is required, and the developer is supplied from a developing device other than the developing device that performs the development. It is necessary to block contamination.
2. Description of the Related Art Conventionally, there is a developing device provided with a retracting mechanism that rotates or retracts a developing device that is not performing development as a developer mixing blocking means.
In order to reduce the size of the apparatus, there is a method in which a regulating plate such as a rubber blade is brought into contact with the rotating sleeve on the upstream side of the developing position in the rotating direction to block the mixing of the developer. (See JP-A-59-60453 and JP-A-6-242666).
[0004]
[Problems to be solved by the invention]
However, since the retractable developing device requires a space for retracting the developing device and a complicated mechanism, there is a problem that the device is increased in size and cost.
In the contact blade method, the problem is that it is difficult to save power because the rotational torque increases, and even when the blade is pressed against the rotating sleeve, scratches occur and the blade is separated from the rotating sleeve. Since friction occurs due to the passage of the developer, there is a problem in terms of durability of the blade, and further, the developer deteriorates because the developer is damaged when passing between the developing roller and the blade. There was also a problem.
[0005]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that prevents a developer from being mixed in from a developing device other than a developing device that performs development.
Another object of the present invention is to provide an image forming apparatus capable of completely blocking the conveyance from the developing device to the photosensitive roller side, thereby preventing the deterioration of the developer and extending the life of the blade.
Another object of the present invention is to simplify, increase the speed, reduce the size, and reduce the cost by using the magnetic force of the fixed magnet roller in the rotating sleeve and the movable magnet arranged to face the fixed magnet roller. An image forming apparatus is provided.
[0006]
[Means for solving the problems]
In the present invention, a rotating sleeve containing a fixed magnet roller having a plurality of permanent magnets magnetized with an N pole and an S pole is disposed facing the photosensitive drum, and development is performed to the developing position on the photosensitive drum by the rotating sleeve. In the developing device for guiding the agent,
A fixed sleeve disposed on the upstream side in the rotation direction of the rotary sleeve with a predetermined gap between the rotary sleeve and the outer periphery;
One or more movable magnets disposed within the fixed sleeve and capable of rotating between a first stop position located during development and a second stop position located during non-development;
A first pole of the fixed magnet roller disposed on the developing position side in the rotating sleeve and the fixed magnet roller disposed on the anti-development position side with the closest contact point between the fixed sleeve and the rotating sleeve interposed therebetween. The second pole of
The vertical magnetic force of the first pole is 600 gauss or more (preferably 700 to 800 gauss), the vertical magnetic force of the second pole is 300 gauss or more (preferably 350 to 700 gauss), and the closest contact point between the rotating sleeve and the fixed sleeve. The horizontal magnetic force of the fixed magnet roller on the surface of the rotating sleeve is set to 450 gauss or less (preferably 200 to 400 gauss), and the Gauss point of zero vertical magnetic force is ± 20 ° from the closest contact point between the rotating sleeve and the fixed sleeve. If it is within or exceeds the range of ± 20 °, the movable magnet at the time of cutting is configured to stop at an angle that coincides with the position of the closest point,
At the time of development, the movable magnet is in the first stop position separated from the second stop position, the magnetic force of the movable magnet toward the fixed magnet roller is made inactive, and the magnetic force of the fixed magnet roller is used. The developer carried on the rotating sleeve is brought into contact with the peripheral surface of the fixed sleeve to regulate the layer thickness and then led to the developing position,
At the time of non-development, the movable magnet rotates to the side closer to the rotating sleeve, stops at the second stop position, applies the magnetic force of the movable magnet to the fixed magnet roller side, and develops to the development position side. The supply of the developer is cut off, the supply of the developer to the developing position is stopped, and the developer on the rotating sleeve is collected.
[0007]
A developing device according to a first aspect of the present invention is a rotating sleeve containing a fixed magnet roller magnetized with an N pole and an S pole, and the rotating sleeve from the developing position with a predetermined gap between the rotating sleeve and an outer periphery. And a fixed sleeve containing a movable magnet having one or more poles that can be rotated and stopped at a non-developing position.
With this configuration, only the rotating sleeve rotates to convey the developer, and the outer periphery of the rotating sleeve and the outer periphery of the fixed sleeve can be set and arranged mechanically with high accuracy. A constant developer layer thickness can be regulated.
[0008]
A movable magnet having one or more poles capable of rotating between a first stop position positioned during development and a second stop position positioned during non-development is disposed in the fixed sleeve, and the movable magnet is disposed in the fixed sleeve. A first pole of the fixed magnet roller disposed on the developing position side in the rotating sleeve and a second pole of the fixed magnet roller disposed on the counter-developing position side with the closest contact point between the rotating sleeve and the rotating sleeve. With poles,
At the time of development, the movable magnet is in the first stop position separated from the second stop position, the magnetic force of the movable magnet toward the fixed magnet roller is made inactive, and the magnetic force of the fixed magnet roller is used. The developer carried on the rotating sleeve is brought into contact with the peripheral surface of the fixed sleeve to regulate the layer thickness and then led to the developing position,
At the time of non-development, the movable magnet rotates to the side closer to the rotating sleeve, stops at the second stop position, applies the magnetic force of the movable magnet to the fixed magnet roller side, and develops to the development position side. The second feature is that the supply of the developer is cut off, the supply of the developer to the developing position is stopped, and the developer on the rotating sleeve is collected.
[0009]
During non-development, the magnetic force of the movable magnet acts on the fixed magnet roller side, the magnetic force between the movable magnet and the first pole of the fixed magnet roller, and the magnetic force between the movable magnet and the second pole, The conveyance of the developer to the developing position on the photosensitive drum side is blocked.
[0010]
Further, the vertical magnetic force of the first pole is 600 gauss or more (preferably 700 to 800 gauss), the vertical magnetic force of the second pole is 300 gauss or more (preferably 350 to 700 gauss), and the rotating sleeve and the stationary sleeve are recently installed. The third feature is that the horizontal magnetic force on the surface of the rotating sleeve of the fixed magnet roller at the contact point is set to 450 gauss or less (preferably 200 to 400 gauss).
[0011]
The perpendicular magnetic force of the magnetic pole opposite to the second pole of the fixed magnet on the surface of the fixed sleeve of the movable magnet is 300 gauss or more (preferably 300 to 450 gauss), and the perpendicular magnetic force of the magnetic pole appearing at both ends thereof is Setting it to 150 gauss or less (preferably 100 gauss or less) is also an effective means of the present invention.
[0012]
The first and second poles of the fixed magnet roller convey the developer during development across the shortest proximity position between the rotating sleeve and the fixed sleeve in the layer thickness regulation area, which is one of the developer conveying sections. In order to achieve this, opposite poles are arranged, and the developer is transported to the development position by the transport magnetic force between the first and second poles of the fixed magnet roller. On the other hand, if the conveyance magnetic force is stopped by the shield magnetic force between the main pole of the movable magnet and the first pole and the binding magnetic force between the main pole and the second pole, the conveyance of the developer is blocked.
[0013]
Even if the perpendicular magnetic force of the first pole and the second pole is the same, if the angle between the poles is narrow, the transport magnetic force becomes large, and the transport of the developer cannot be blocked unless the magnetic force of the movable magnet is increased.
In addition, if the angle between the first pole and the second pole is too large, the angle balance of the magnetic pole arrangement of the fixed magnet roller is deteriorated, the movable magnet main pole and the first pole and the second pole, or these The distance between the poles is increased, and the shielding magnetic force and binding magnetic force are also weakened.
Further, since the main pole and the second pole of the movable magnet attract each other at the time of trimming, if both magnetic forces are too large, the member that supports the magnet loses the bend and bends, and the magnet contacts the sleeve member.
On the other hand, if the magnetic force of the first pole is too small, the shield magnetic force becomes weak and the developer cannot be blocked.
Therefore, the above magnetic force is desirable.
[0014]
As described above, the present invention can provide an image forming apparatus that prevents a developer from being mixed in from a developing device other than a developing device that performs development.
In the present invention, the developer is transported and blocked using the magnetic restraint force of the fixed magnet roller in the rotating sleeve and the movable magnet arranged facing the fixed magnet roller without moving the developing device. Therefore, it is possible to simplify, increase the speed, reduce the size, and reduce the cost of the image forming apparatus.
[0015]
In addition, since the developer sleeve is not used for the developing sleeve and the conveyance from the developing device to the photosensitive roller side is completely blocked by magnetic force, the fixed sleeve does not move even if the developing sleeve rotates. At the time of shut-off, there is little movement of the developer, so that the deterioration of the developer is prevented, and the life of the developing device is prevented by shortening the life of the developing device due to wear of the developing sleeve or the developer blocking blade. Can be planned.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.
[0017]
FIG. 1 is a cross-sectional view of the entire image forming apparatus according to an embodiment of the present invention. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A sheet feeding cassette (not shown), a photosensitive drum 1, an optical scanning unit 2, a charger 3, four developing devices 4 to 7 including a developer container, an intermediate transfer member 12, a secondary transfer roller 13, a fixing device 14, The recording medium 8 having the image transferred thereon is composed of a conveying device 9 using an endless belt for conveying the recording medium 8 from the secondary transfer roller 13 to the fixing device 14.
[0018]
At the time of printing, the photosensitive drum 1 is charged by the charger 3 for each color, and the image exposed by the optical scanning unit 2 and developed by the developing devices 4 to 7 is transferred to the intermediate transfer body 12, and a paper feeding cassette (not shown) Then, the image is transferred to the recording medium 8 conveyed by the secondary transfer roller 13 and fixed by heating and pressurizing by the fixing device 14 to be discharged.
[0019]
The configuration of the embodiment according to the present invention will be described in detail.
FIG. 2 is a cross-sectional view showing the vicinity of the developing position where the developer flies to the photosensitive drum 1 of the developing device 4, and includes a fixed magnet roller 20 having permanent magnets magnetized on the N pole and the S pole, and the fixed magnet roller. A rotation sleeve 21 containing the rotation sleeve 21, a fixed sleeve 22 disposed upstream of the developing position A of the rotation sleeve 21 in the rotation direction, and a main pole rotatable about the center of the fixed sleeve 22 as a central axis 23a. A sub-pole that appears at both ends is arranged with an N-pole movable magnet 23.
[0020]
As shown in FIGS. 3 and 4, the movable magnet 23 is formed in a sector fan shape as an axial center 23e of the central shaft 23a, and an outer peripheral surface 23d having a radius r from the axial center 23e is a circumferential surface on the S pole. Fan-shaped inclined surfaces 23b and 23c formed at an angle θ from 23e are magnetized so as to be the N poles of NB and NA, respectively.
[0021]
The developing device 4 under development uses the magnetic force of the fixed magnet roller 20 when the movable magnet 23 is stopped at a position that does not affect the magnetic force of the fixed magnet roller 20 as shown in FIG. Then, after the developer 24 carried on the rotating sleeve 21 is brought into contact with the peripheral surface of the fixed sleeve 22 to regulate the layer thickness, the developer 24 can be guided to the developing position A on the photosensitive drum 1. (Hereinafter, the state of the developing device in FIG. 2A is called heading)
The developer layer thickness regulation is determined by the distance d between the rotating sleeve 21 and the fixed sleeve 22.
[0022]
However, if the developer is supplied to the rotating sleeves 21 included in the developing devices 5 to 7 other than the developing device, the developer is mixed into other developing devices in the head and the toner image on the photosensitive drum 1. Disturb. In order to prevent this, when the movable magnet 23 is moved to the vicinity of the closest contact point of the rotating sleeve 21 as shown in FIG. 2B, the developing device other than the developing unit is prevented from supplying the developer to the rotating sleeve. I can do it. (Hereinafter, the state of the developing unit in FIG.
[0023]
Hereinafter, the operation of the developing device will be described with reference to FIG.
2A, at the closest point of contact between the rotating sleeve 21 and the fixed sleeve 22 (hereinafter referred to as the blade position), the lines of magnetic force pass through the magnet from the first pole (S pole) of the rotating sleeve 21. It is directed to the 2 pole (N pole), and the outside of the magnet is generated from the second pole (N pole) to the first pole (S pole) to form a closed ring.
[0024]
In addition, the third pole (N pole) and the first pole (S pole) arranged opposite to the development position A are magnetic lines of force in the magnet from the first pole (S pole) to the third pole (N). It is generated from the third pole (N pole) to the first pole (S pole), and forms a closed ring.
Along the magnetic force lines, the developer is transported to the development position A via the first pole by the conveying force generated by the rotation of the rotary sleeve 21 and develops the latent image on the photosensitive drum 1.
[0025]
After development, the movable magnet 23 rotates as shown in FIG. 2B, and the main pole (S pole) stops at the blade position 0 °. At this time, a magnetic shield (hereinafter referred to as a shield magnetic force) is formed between the S pole of the movable magnet 23 and the first pole of the rotating sleeve 21, and the developer on the rotating sleeve 21 develops at the developing position A with this magnetic field as a boundary. It is separated from the side and the inside of the blade position (FIG. 2B).
[0026]
After the separation, the developer on the developing position A side is collected in the developing device 4 by the rotation of the rotating sleeve 21. Further, an attraction magnetic field (hereinafter referred to as binding magnetic force) from the main pole (S pole) of the rotating magnet 23 to the second pole of the rotating sleeve 21 is generated at the same time, and the developer inside the blade position is between these poles. It is restrained by.
[0027]
Since these shield magnetic force and restraining magnetic force block the magnetic force line that is the transfer magnetic force between the second pole and the first pole of the rotating sleeve 21, the magnetic force line does not pass between the second pole and the first pole, and the developer is on the rotating sleeve. Is stopped in the state of FIG. In this way, it is possible to prevent the developer from being mixed into another developing device and to disturb the toner image on the photoreceptor.
[0028]
Next, Table 1 and Table 2 show measurement data obtained by changing the conditions of the fixed magnet 20 and the movable magnet 23 and measuring the presence / absence of ear cutting. Tables 1 and 2 show examples in which panning results were good, and Tables 3 and 4 included those that could not be trimmed and those that were unstable. It is described as an example.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
[Table 3]

[0032]
[Table 4]

[0033]
From the data of Table 1 and Table 2 described above, in Examples 1 to 10, the shielding magnetic force between the movable magnet and the first pole and the binding magnetic force between the movable magnet and the second pole are between the first pole and the second pole. Since the horizontal magnetic force is completely prevented, the developer can be completely blocked.
[0034]
On the other hand, in Comparative Example 1, the first and second poles have the same vertical magnetic force as in Example 1, but the horizontal magnetic force is as high as 550G. Similarly, in Comparative Examples 2 to 4, the vertical magnetic force of the first pole and the second pole and the angle between the poles are narrow, so the horizontal magnetic force is as high as 840G, 650G, and 600G. For this reason, the shielding magnetic force between the movable magnet 23 and the first pole and the restraining magnetic force between the movable magnet 23 and the second pole cannot completely prevent the horizontal magnetic force, and the developer moves on the rotating sleeve 21 along the magnetic force line. Since it was conveyed, it leaked to the developing position A side.
[0035]
In Comparative Example 5, the magnetic force of the first pole of the fixed magnet 20 is 740 G, and the second pole is 460 G, which is the same as the values of the first pole and the second pole of Examples 7 and 8.
In the seventh and eighth embodiments, the movable magnet 23 has a main pole of 400 G and sub-poles of 150 and 80 gauss, respectively. They were able to block the developer for magnetic field lines from the main pole of the movable magnet (S-pole) to Fukukyoku N _A is small.
However, in Comparative Example 5, the secondary pole of the movable magnet is as high as 170G. In this case, the developer separated by shielding the magnetic force is moved along the magnetic field lines from the main pole of the movable magnet 23 (S pole) to Fukukyoku N _A, it is stored in Fukukyoku N _A portion. When Fukukyoku N _A portion more than a certain amount to the developer is accumulated, the developer could not be completely inoperative position so moves along the magnetic field lines from Fukukyoku N _A to the first pole of the rotating sleeve 21 .
[0036]
As for Comparative Example 6 and Comparative Example 7, the fixed magnets of Example 4 and Comparative Example 6 and the fixed magnets of Example 6 and Comparative Example 7 have a first pole of 600G, a second pole of 440G, and a first magnet, respectively. The pole is 650G and the second pole is the same as 430G.
Then, the sub-electrode in Example 4 and 6 both movable magnet 23 can be inoperative position and a is a small movable magnet Fukukyoku N _A 80G, can bristle cutting for Fukukyoku N _A is 150G in Comparative Examples 6 and 7 There wasn't.
[0037]
In each of Examples 1 to 9, the Gauss point of zero perpendicular magnetic force is within 20 ° from the closest point (blade position) between the rotating sleeve 21 and the fixed sleeve 22 in each example, as shown in Table 1. And a Gauss point with zero perpendicular magnetic force is close to the blade position.
When this perpendicular magnetic force 0 Gauss point exceeds the range of the present embodiment , as shown in Tables 3 and 4, the magnetic force between the movable magnet 23 and the first pole and the magnetic force between the movable magnet 23 and the second pole, Since the relationship of the horizontal magnetic force between the second pole and the eleventh cannot be balanced, the trimming is unstable or cannot be trimmed.
[0038]
For the same reason, when the stop position of the movable magnet at the time of trimming exceeds the range disclosed in Table 2, it becomes impossible to perform the trimming. (-50 ° to 50 ° in Table 4 refers to a portion exceeding the range disclosed in Table 2. That is, −50 ° to 50 ° (-5 ° to 5 ° and −10 ° to −30 ° are used). Except)).)
For example, in Example 10, from the blade position, the Gauss point of zero perpendicular magnetic force exceeds the range of ± 20 ° to −30 ° to 30 ° (here, −30 ° to 30 ° shown in Table 1 and Table 3). Was in the range of -30 ° to -20 ° and 20 ° to 30 ° (-30 ° to 30 ° (excluding the range of ± 20 °)). The movable magnet at the time of cutting needs to stop at an angle that coincides with the closest point (blade position) .
[0039]
When the perpendicular magnetic force 0 gauss point moves away from the closest contact (blade position) between the rotating sleeve 21 and the fixed sleeve 22, the perpendicular magnetic force at the closest contact increases, and the pressure of the developer passing between the sleeves during development increases and the torque increases. It is not preferable because it causes an increase.
Further, it is not preferable that the stop position of the movable magnet at the time of trimming is extremely close to the first pole or the second pole, because repulsion between the magnets or warping of the member due to suction occurs.
[0040]
If the magnetic force of the main pole of the movable magnet 23 is increased, the shielding magnetic force and the binding magnetic force are increased and the horizontal magnetic force is also blocked. However, the magnet or member is warped by the attractive magnetic force between the movable magnet 23 and the fixed magnet 20. Since it becomes easy, low magnetic force is desirable.
Moreover, if the magnetic force relationship of this Embodiment is materialized, the outer diameter of a rotation sleeve will not be specified in particular, However, Preferably it is 15-25 mm.
[0041]
In addition, as shown in FIG. 4, the radius r is constant, and the movable magnet 23 formed in a sectional fan shape is formed by changing the angle θ to measure the main pole (S pole) and both ends of the main pole (NA and NB poles). The results shown in Table 5 were obtained.
[0042]
[Table 5]

[0043]
From the results shown in Table 5, in Example A, when the magnet angle θ is 60 ° and the vertical magnetic force of the movable magnet main pole S pole on the surface of the fixed sleeve is 400 gauss, the vertical magnetic forces of the secondary poles NA and B poles Was 80 gauss, so that the developer did not move to the sub pole along the magnetic field lines, and a good trimming result was obtained.
Also in Example B, the magnet angle θ is 90 ° narrower than in Example A, so the magnet becomes smaller, and the vertical magnetic force of the movable magnet main pole S pole on the surface of the fixed sleeve is 300 gauss. Since the perpendicular magnetic force of the NA and B poles of the secondary pole was 80 gauss, the developer did not move to the secondary pole along the magnetic field lines, and a good panning result was obtained.
[0044]
On the other hand, in Comparative Example B, the magnet angle θ is 220 ° and the vertical magnetic force of the movable magnet main pole S pole on the surface of the fixed sleeve is 600 gauss. Since the magnetic force was 150 gauss, the developer was caught by the subpolar magnetic force, and the ear cutting was unstable.
In Comparative Example A, the magnet becomes smaller because the angle θ of the magnet is as narrow as 90 °. Therefore, the perpendicular magnetic force of the movable magnet main pole S pole on the surface of the fixed sleeve was 400 gauss. Since the perpendicular magnetic force of the NA and B poles was 150 gauss, the developer was caught by the subpolar magnetic force and the ear cutting was unstable.
[0045]
【The invention's effect】
As described above in detail, according to the developing device of the present invention, the hold magnetic force and the binding magnetic force between the fixed magnet roller and the movable magnet roller are completely cut off from the horizontal magnetic force of the fixed magnet roller at the time of trimming. Therefore, it is possible to prevent the developer from being mixed in from a developing device other than the developing device.
In addition, since the magnetic restraint force is used to block the mixing of the developer, it is not necessary to block the developer by bringing the rubber blade into contact with the rotating sleeve as in the prior art, and the friction between the blade and the developer is not necessary. The blade and the developer are not deteriorated, and the durability of the developing device can be improved by improving the durability of the blade.
In addition, the magnetic restraint force is used to block the mixing of the developer, so there is no need for a space for retracting the developing device or a complicated mechanism, and the device is simplified, speeded up, miniaturized, and reduced in cost. be able to.
It has various effects such as.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a main part configuration according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining a development state (A). It is explanatory drawing which shows the state which the developing apparatus started the ear cutting (B). FIG. 2C is a schematic diagram showing a cutting state of the developing device (C).
FIG. 3 is a perspective view showing a shape of a movable magnet.
FIG. 4 is a cross-sectional view of a movable magnet.
[Explanation of symbols]
1 Photosensitive drum 20 Fixed magnet roller 21 Rotating sleeve 22 Fixed sleeve 23 Movable magnet

Claims

Development in which a rotating sleeve containing a fixed magnet roller having a plurality of permanent magnets magnetized with N and S poles is arranged facing the photosensitive drum, and the developer is guided to the developing position on the photosensitive drum by the rotating sleeve. In the device
A fixed sleeve disposed on the upstream side in the rotation direction of the rotary sleeve with a predetermined gap between the rotary sleeve and the outer periphery;
One or more movable magnets disposed within the fixed sleeve and capable of rotating between a first stop position located during development and a second stop position located during non-development;
A first pole of the fixed magnet roller disposed on the developing position side in the rotating sleeve and the fixed magnet roller disposed on the anti-development position side with the closest contact point between the fixed sleeve and the rotating sleeve interposed therebetween. The second pole of
The first pole of the vertical force 600 gauss or more on the second electrode of the vertical force 300 gauss or more on the horizontal force at the rotating sleeve surface of the fixed magnet roller in the closest point of the fixed sleeve and the rotary sleeve 450 and sets under gauss or less, from the closest point between the rotating sleeve fixed sleeve, the movable magnet when inoperative position when Gauss point of the vertical force 0 is beyond the scope of any or ± 20 ° is within ± 20 ° Configured to stop at an angle coinciding with the closest point position,
At the time of development, the movable magnet is in the first stop position separated from the second stop position, the magnetic force of the movable magnet toward the fixed magnet roller is made inactive, and the magnetic force of the fixed magnet roller is used. The developer carried on the rotating sleeve is brought into contact with the peripheral surface of the fixed sleeve to regulate the layer thickness and then led to the developing position,
At the time of non-development, the movable magnet rotates to the side closer to the rotating sleeve, stops at the second stop position, applies the magnetic force of the movable magnet to the fixed magnet roller side, and develops to the development position side. A developing device characterized in that the supply of the developer is cut off, the supply of the developer to the developing position is stopped, and the developer on the rotating sleeve is collected.

In the fixed sleeve surface of the movable magnet, characterized in that the second pole to the vertical force of the opposite pole is 300 gauss or more on, and the vertical force is 150 gauss or less of a magnetic pole appearing at both ends of the fixed magnet The developing device according to claim 1.