JP3891294B2

JP3891294B2 - Image forming apparatus

Info

Publication number: JP3891294B2
Application number: JP2003193331A
Authority: JP
Inventors: 稔岸上
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2003-07-08
Filing date: 2003-07-08
Publication date: 2007-03-14
Anticipated expiration: 2023-07-08
Also published as: JP2005031167A

Description

【０００１】
【技術分野】
本発明は、ロータリー現像装置の現像色切り換え動作により複数の現像器が順次現像位置に回転移動して像担持体上に形成された潜像を現像し転写位置で媒体に転写して画像を形成するように構成した画像形成装置に関する。
【０００２】
【従来の技術】
ロータリー現像方式を採用した画像形成装置では、潜像が形成される像担持体と、現像ローラを有し現像剤を搬送して潜像を現像する複数の現像器と、複数の現像器を外周に沿って支持して像担持体に対向する現像位置に回転移動するロータリー現像装置とを備えた画像形成装置では、従来、現像動作を行う現像器は、現像位置において、ロータリー現像装置の回転中心と現像ローラの回転中心と感光体の回転中心が一直線上になるようにロータリー現像装置の位置決めを行い、現像動作を行うようになっている（例えば、特許文献１、２参照）。
【０００３】
【特許文献１】
特許第２６４９０３３号公報
【０００４】
【特許文献２】
特開２００３−５４８４号公報
【０００５】
【発明が解決しようとする課題】
しかし、上記従来装置のように現像位置において、現像動作を行う現像器が、ロータリー現像装置の回転中心と現像ローラの回転中心と感光体の回転中心が一直線上になるようにロータリー現像装置を位置決めしていることにより、幾つかの課題が生じている。
【０００６】
例えば現像動作が終了し、次の色の現像器を現像位置に回転移動させるためにロータリー現像装置が現像色切り換え動作により回転すると、それまで現像動作をしていた現像器が感光体に押し当てられている押圧力は、最大値から移動開始と共に減少し始め、現像ローラが感光体から完全に離れてゼロになる。なお、現像位置での現像ローラと感光体との距離を決める方法には種々あるが、非接触現像方式の例では、現像ローラと同軸上に現像ローラよりやや大きい径のコロを配設し、このコロを感光体に当接することで現像ローラと感光体との隙間を決定する構成がある。この構成の場合には、先の押圧力の減少に当てはめると、現像位置からロータリー現像装置が回転して暫くしコロが感光体表面から離れると、押圧力が０になる。なお、このコロについて、特許文献２では、図２、図３の現像ローラ２２の端部に輪状の部材で示されている。
【０００７】
現像器を感光体に押し当てる押圧力が変化すると、感光体を駆動する際の付加が変動する。これが感光体の回転ムラを発生させ、画像ムラ等の画像欠陥を生じることになる。また、感光体を装置本体に装着する場合には、一定のガタを有する。このガタは、嵌合させて装着する構造上である程度必要とされるものである。現像器を感光体に押し当てると、感光体はこのガタの範囲でロータリー現像装置の回転中心と現像ローラの回転中心と感光体の回転中心を結ぶ直線上で感光体が現像ローラとは反対の方向に移動することになる。先の問題と同様に、ロータリー現像装置が回転を始め、押圧力が減少すると、感光体はガタの範囲で先の方向とは反対の方向に移動することが可能である。このように感光体の位置が変化すると１次転写ローラと感光体との間で画像が歪（転写ズレ）を生じる不具合が発生する。
【０００８】
【課題を解決するための手段】
本発明は、上記課題を解決するものであって、感光体の回転ムラを低減して、回転ムラによる露光ズレ、転写ズレをなくし、画像ムラ、画像不良をなくすと共に、現像色切り換え動作時間の短縮を図るものである。
【０００９】
そのために本発明は、潜像が形成される像担持体と、該像担持体に前記潜像を形成する潜像形成手段と、現像ローラを有し現像剤を搬送して前記潜像を現像する複数の現像器と、前記複数の現像器を外周に沿って揺動可能に支持し所定方向に回転して前記像担持体に対向する現像位置に前記複数の現像器が順次移動するロータリー現像装置とを備え、前記ロータリー現像装置の現像色切り換え動作により前記複数の現像器が順次前記現像位置に回転移動して前記像担持体上に形成された潜像を現像し転写位置で媒体に転写して画像を形成するように構成した画像形成装置において、前記ロータリー現像装置は、前記現像位置の前記現像器に対して、前記ロータリー現像装置の回転中心と前記像担持体の回転中心とを結ぶ直線上より前記ロータリー現像装置の回転方向の下流側で前記現像ローラ又は前記現像ローラの両端に配設されたコロを前記像担持体に押し当て、かつ、前記現像ローラの回転中心と前記像担持体の回転中心とを結ぶ直線に対して、所定の角度だけ前記像担持体の回転方向の下流側に向けて前記現像ローラを前記像担持体に押し当てるように、前記現像ローラを前記像担持体に押し当てる位置に対して現像器揺動支点が位置決めされることを特徴とする。
【００１１】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照しつつ説明する。図１は本発明に係る画像形成装置の実施の形態を示す図である。図中、１はロータリー現像装置、２は現像器、３は感光体、４は中間転写媒体、５は露光装置、６はプロセスユニット、７は１次転写装置、８は２次転写装置、９は給紙トレイ、１０は給紙ローラ、１１はレジローラ、１２は紙搬送ユニット、１３は定着ユニット、１４は排紙トレイ、１５は扉体を示す。
【００１２】
本実施形態の画像形成装置は、図１に示すようにハウジングの上部に形成された排紙トレイ１４と、ハウジングの前面に開閉自在に挿着された扉体１５を有する。ハウジング内には、複数の現像器２を搭載したロータリー現像装置１、潜像が形成され現像されてトナー像が形成される感光体３、感光体３を露光して潜像を形成する露光装置５、無端状のベルトからなりトナー像が転写される中間転写媒体４、露光装置５による潜像の形成を制御するプロセスユニット６、感光体３上のトナー像を中間転写媒体４に１次転写する１次転写装置７、中間転写媒体４のトナー像を記録媒体（紙等）に２次転写する２次転写装置８、記録媒体を収容する給紙トレイ９、記録媒体上のトナー像を定着する定着ユニット１３、各駆動モータやバイアスを制御する制御ユニットなどが配設されている。また、扉体１５内には給紙トレイ９から記録媒体を２次転写装置８を通して定着ユニット１３に搬送する紙搬送ユニット１２が配設されている。そして、各ユニットは、本体に対して着脱可能な構成であり、メンテナンス時等には一体的に取り外して修理または交換を行うことが可能な構成になっている。
【００１３】
像担持体である感光体３は、薄肉円筒状の導電性基材と、その表面に形成された感光層とを有する。その感光体３の外周には、回転方向に沿って感光体３を一様に帯電するための帯電装置（図示せず）、感光体３上に潜像を形成するための露光装置５、潜像を現像するためのロータリー現像装置１、感光体３上のトナー像が転写される中間転写媒体４、及び中間転写媒体４にトナー像を１次転写する１次転写装置７、１次転写後の感光体３の表面をクリーニングするクリーナ（図示せず）などが配設されている。そして、感光体３上に露光装置５により形成された潜像をロータリー現像装置１により現像してトナー像を形成し、形成されたトナー像を１次転写装置７により中間転写媒体４上に転写して、さらに２次転写装置８により記録媒体（紙等）に転写する。
【００１４】
上記構成の画像形成装置によるフルカラーの画像形成では、露光装置５にプロセスユニット６からの画像形成信号が入力されると、制御ユニットによる駆動モータやバイアスの制御にしたがい、感光体３、ロータリー現像装置１、中間転写媒体４が回転駆動される。そして、感光体３は、外周面が帯電装置によって一様に帯電され、ロータリー現像装置１は、第１色、例えばイエローＹのトナー像を形成するため、現像色切り換え動作により、イエローＹ用の現像器２がロータリー現像装置１の回転中心と感光体３の回転中心とを結ぶ直線上からさらに越えて回転移動し、ロータリー現像装置１の回転移動する方向の下流側で現像ローラ又は現像ローラの両端に配設されたコロ（以下、同じ）が感光体３に当接して停止する。現像器２の現像ローラが回転駆動されると同時に、まず、感光体３の表面に露光装置５によって第１色、イエローＹの画像情報に応じた選択的な露光がなされ、感光体３上にイエローＹの潜像が形成される。そのイエローＹの潜像は、現像器２によって現像されて感光体３上にトナー像が形成される。
【００１５】
ロータリー現像装置１は、現像器２によりイエローＹの潜像の後端が現像され現像が終了すると、直ちに、つまりそのトナー像の後端が１次転写装置７に達する以前に、次の第２色、例えばブラックＫのトナー像を形成するための現像色切り換え動作を開始する。この現像色切り換え動作により、ブラックＫ用の現像器２の現像ローラは、ロータリー現像装置１の回転中心と感光体３の回転中心とを結ぶ直線上からさらに越えて回転移動し、ロータリー現像装置１の回転移動する方向の下流側で感光体３に当接して停止する。
【００１６】
この間、１次転写装置７には、トナーの帯電極性と逆極性の１次転写電圧が印加され、感光体３上に形成されたトナー像は、１次転写装置７で中間転写媒体４上に転写される。２次転写装置８は、中間転写媒体４から離間されている。
【００１７】
第２色の現像色切り換え動作が終了して、ブラックＫ用の現像器２の現像ローラが感光体３に当接して停止すると、感光体３の表面に露光装置５によって第２色、ブラックＫの画像情報に応じた選択的な露光がなされ、感光体３上にブラックＫの潜像が形成される。このような一連の処理が画像形成信号の第２色目、第３色目、第４色目に対応して繰り返して実行されることにより、各画像形成信号の内容に応じたイエローＹ、ブラックＫ、シアンＣ、マゼンタＭからなる４色のトナー像が感光体３から順次中間転写媒体４上において重ね合わされて転写され、フルカラー画像が形成される。
【００１８】
そして、フルカラー画像が２次転写装置８に達するタイミングで、給紙トレイ９の記録媒体（紙等）が搬送通路から給紙ローラ１０、レジローラ１１を通して２次転写装置８に搬送され、２次転写装置８が中間転写媒体４に押圧されるとともに２次転写電圧が印加されて、中間転写媒体４上の４色のフルカラートナー像が２次転写装置８で記録媒体上に転写される。このようにしてフルカラートナー像が転写された記録媒体は紙搬送ユニット１２により定着ユニット１３まで搬送されると、定着ユニット１３により記録媒体上のフルカラートナー像が加熱加圧されて定着され、排紙トレイ１４に排紙される。
【００１９】
図２はロータリー現像装置が現像色切り換え動作により回転移動して位置決めされ現像ローラが感光体に当接している状態を示す図、図３はロータリー現像装置が現像色切り換え動作により回転移動し現像ローラが感光体から離れる位置を示す図、図４は現像ローラがロータリー現像装置の回転中心と感光体の回転中心を結ぶ直線上にある状態を示す図である。図中、２１はロータリー現像装置駆動モータ、２２は駆動モータ歯車、２３はロータリー現像装置回転歯車、２４は現像ローラ、２５は現像器揺動支点、２６はロータリーフレーム、２７は当接バネ、２８、２９は現像器揺動規制部、３１〜３３は回転中心を示す。
【００２０】
ロータリー現像装置１は、図２に示すように外周に沿ってロータリー現像装置回転歯車２３を有し、このロータリー現像装置回転歯車２３に駆動モータ歯車２２が噛合してロータリー現像装置駆動モータ２１により図示反時計周りを回転方向として回転駆動される。そして、ロータリー現像装置１に着脱可能に搭載された現像器２は、ロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上に対し、ロータリー現像装置１の回転中心３１とと現像ローラ２４の回転中心３３を結ぶ直線が回転角Ｂ°だけ回転方向の下流側で現像ローラ２４が感光体３に押し当てるように位置決めされる。
【００２１】
現像器２は、現像器揺動支点２５を支点として、揺動可能に装着され、その揺動は、現像器２側の現像器揺動規制部２８とロータリーフレーム２６側の現像器揺動規制部２９により規制され、ロータリーフレーム２６に設けられた当接バネ２７により感光体３の方向に付勢され、所定の押圧力で感光体３に当接するようになっている。
【００２２】
そして、ロータリー現像装置駆動モータ２１により現像色切り換え動作を開始して、ロータリー現像装置１が回転移動すると、現像動作が終了した現像器２では、図３に示す回転角Ａ°から現像器２側の現像器揺動規制部２８とロータリーフレーム２６側の現像器揺動規制部２９により揺動が規制されて、現像ローラ２４が感光体３から離れる。そして、次の現像動作を行う現像器２は、ロータリー現像装置１の回転移動と共に現像ローラ２４が感光体３に当接して、図４に示すようにロータリー現像装置１の回転中心３２と感光体３の回転中心３２とを結ぶ直線Ｌ上に達し、さらに回転移動した後、図２に示す回転角Ｂ°だけ回転方向の下流側で現像ローラ２４が感光体３に当接するように位置決めされる。
【００２３】
露光装置５により画像情報に応じた選択的な露光をして感光体３上に潜像を形成しているとき、先に述べた嵌合・装着のため有する構造上のガタにより感光体３に移動が生じたり、回転ムラが生じたりすると、露光ズレなどによる画像ムラ、画像不良が生じる。また、感光体３上に形成されたトナー像を１次転写装置７で中間転写媒体４上に転写しているときにも、同様に、感光体３に移動、回転ムラが生じると、転写ズレなどによる画像ムラ、画像不良が生じる。この感光体３の移動、回転ムラは、感光体３が受ける外力の変動が大きいほど、また、その絶対値が大きいほど生じやすくなる。
【００２４】
感光体２に現像ローラ２４を押し当てる押圧力は、その外力の１つであり、現像ローラ２４が図４に示すロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上にあるときに最大値となり、感光体３に回転ムラを生じさせやすい。また、ロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上で現像ローラ２４を感光体３に押し当てるようにした場合であっても、実際には現像器２の揺動に伴ってその直線Ｌ上から左右に僅かな揺れが生じると、現像ローラ２４と感光体３との押し当て部接線方向に対して、押圧力の分力が感光体３の回転方向に作用したり逆回転方向に作用したりすることになり、これもまた、感光体３に回転ムラを生じさせやすい要因である。
【００２５】
本実施形態のように現像動作を行う現像位置で、図２に示すようにロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上より回転角Ｂ°だけ回転方向の下流側で現像ローラ２４を感光体３に押し当てるようにすると、図４に示すようにロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上で現像ローラ２４を感光体３に押し当てる場合に比べて押圧力を小さくすることができる。しかも、押圧力の分力が感光体３の回転方向に作用したり逆回転方向に作用したりすることはなく、一定の方向に作用させることができる。これらのことから、現像ローラ２４を感光体３に押し当てることにより感光体３の移動、回転ムラを生じるのを低減することができる。
【００２６】
現像ローラ２４を感光体３に押し当てる位置を、図２に示す回転方向の下流側とは逆に、回転方向の上流側とした場合にも、上記と同様ではあるが、この場合には、ロータリー現像装置１の現像色切り換え動作を開始した直後、現像ローラ２４がロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上を通過する間に押圧力が最も大きな変動を与える。すなわち、ロータリー現像装置１の現像色切り換え動作を開始した直後から感光体３に現像ローラ２４を押し当てる押圧力が増大して直線Ｌ上で最大となり、それから低減して零になる。しかも、先にも述べたように押圧力が最大となる直線Ｌ上を通過する前後で、押圧力の分力が感光体３の回転方向に対して反転する。つまり、ブレーキ成分から加速成分に切り替わり、最も感光体３に回転ムラが生じやすくなる。
【００２７】
そのため、感光体３上のトナー像を１次転写装置７により中間転写媒体４上に転写しているときに、このようなロータリー現像装置１の現像色切り換え動作を行うと、感光体３の移動、回転ムラによる転写ムラがより悪化することになる。この場合には、現像動作が終了しても、転写終了までこのようなロータリー現像装置１の現像色切り換え動作が行えない。このことは、次の現像色の画像形成のための動作に速やかに移行できないことになる。
【００２８】
本実施形態の図２に示すようにロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上より回転角Ｂ°だけ回転方向の下流側で現像ローラ２４を感光体３に押し当てて現像を行うことにより、感光体３上に形成された潜像の後端を現像器２が現像すると直ぐ次色現像器２を現像位置に移動させるためのロータリー現像装置１の現像色切り換えを開始することができる。そのことにより、現像色切り換え動作を開始した直後の、回転方向の上流側で現像ローラ２４を感光体３に押し当てて現像を行う場合のような感光体３の移動、回転ムラを生じさせることがなくなり、１次転写での転写ズレをなくすことができる。
【００２９】
近年、画像形成装置は、印字速度の高速化が求められることから、ロータリー現像装置１を採用する画像形成装置では、各色現像器２を交換するロータリー現像装置１の現像色切り換え動作に要する時間の短縮、回転速度の向上が求められると共に、中間転写媒体４上における画像と画像の間隔（紙間）の短縮も求められている。本実施形態では、感光体３上に形成された潜像の後端を現像器２が現像すると、現像後のトナー像がまだ１次転写装置７により中間転写媒体４上に転写中であっても、すぐに次色の現像器２を速やかに現像位置に移動するためのロータリー現像装置２の現像色切り換え動作を開始することができる。
【００３０】
また、本実施形態の図２に示すようにロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上より回転角Ｂ°だけ回転方向の下流側で現像ローラ２４を感光体３に押し当てて現像を行う場合には、ロータリー現像装置１の現像色切り換え動作の終了間際において、押圧力が最大となる直線Ｌ上を通過するため、このときに感光体３に最も大きな移動、回転ムラが生じることになる。最もこの時点までには、トナー像の後端が１次転写装置７で中間転写媒体４上に転写され１次転写は終了しているので、転写に悪影響を与えることは回避することができる。一方、感光体３上に潜像を形成するための露光装置５による画像情報に応じた選択的な露光の開始は、上記現像色切り換え動作の終了間際において、押圧力が最大となる直線Ｌ上を通過するときに生じる感光体３の移動、回転ムラによる悪影響を受けないため、ロータリー現像装置１の現像色切り換え動作が終了した後に行うことが望ましい。
【００３１】
本実施形態の図２に示すようにロータリー現像装置１の回転中心３１と感光体３の回転中心３２とを結ぶ直線Ｌ上より回転角Ｂ°だけ回転方向の下流側で現像ローラ２４を感光体３に押し当てて現像を行うことは、見方を変えれば感光体３に対して感光体３の回転中心３２方向より回転方向の下流側に向けて現像ローラ２４を押し当てることでもある。このことにより、先に述べた押圧力を低減、緩和し、ロータリー現像装置１の現像色切り換え動作直後の押圧力の変動を低減、緩和することができる。そのためには、現像ローラ２４の回転中心３３と感光体３の回転中心３２とを結ぶ直線に対して、現像ローラ２４の回転中心３３から感光体３の回転中心３２より所定の角度だけ感光体３の回転方向の下流側に向けて現像ローラ２４を感光体３に押し当てるように、現像ローラ２４を感光体３に押し当てる位置に対して現像器揺動支点２５の位置を設定することである。
【００３２】
なお、本発明は、上記実施の形態に限定されるものではなく、種々の変形が可能である。例えば上記実施の形態では、潜像形成手段として感光体を露光して静電潜像を形成する露光装置で説明したが、書込電極を用いたものその他潜像形成手段でも同様であることは勿論のことである。
【００３３】
【発明の効果】
以上の説明から明らかなように、本発明によれば、潜像が形成される像担持体と、該像担持体に潜像を形成する潜像形成手段と、現像ローラを有し現像剤を搬送して潜像を現像する複数の現像器と、複数の現像器を外周に沿って揺動可能に支持し所定方向に回転して像担持体に対向する現像位置に複数の現像器が順次移動するロータリー現像装置とを備え、ロータリー現像装置の現像色切り換え動作により複数の現像器が順次現像位置に回転移動して像担持体上に形成された潜像を現像し転写位置で媒体に転写して画像を形成するように構成した画像形成装置において、ロータリー現像装置は、現像位置の現像器に対して、ロータリー現像装置の回転中心と像担持体の回転中心とを結ぶ直線上よりロータリー現像装置の回転方向の下流側で現像ローラ又は現像ローラの両端に配設されたコロを像担持体に押し当て、かつ、現像ローラの回転中心と像担持体の回転中心とを結ぶ直線に対して、所定の角度だけ像担持体の回転方向の下流側に向けて現像ローラを像担持体に押し当てるように、現像ローラを像担持体に押し当てる位置に対して現像器揺動支点が位置決めされるので、像担持体に対する現像器の押圧力を軽減、緩和して像担持体の回転ムラを低減することができ、回転ムラによる露光ズレ、転写ズレをなくし、画像ムラ、画像不良をなくすことができる。
【００３４】
本発明によれば、ロータリー現像装置は、潜像の後端を現像した後、その現像したトナー像の後端まで転写位置で媒体に転写される前に、ロータリー現像装置の現像色切り換え動作を開始することができるので、現像されたトナー像の転写が終了するまで待つことなく次の現像色の現像器を現像位置に移動するための現像色切り換え動作時間の短縮を図り、像担持体の回転ムラを低減して、回転ムラによる転写ズレをなくし、画像ムラ、画像不良をなくすことができる。また、潜像形成手段は、ロータリー現像装置の現像色切り換え動作により次の現像器が現像位置に回転移動した後に潜像の形成を開始することができ、ロータリー現像装置の現像色切り換え動作中に像担持体に回転ムラが生じても、その影響を受けないように回避し、回転ムラによる露光ズレをなくし、画像ムラ、画像不良をなくすことができる。さらに、現像器は、揺動可能に支持されて像担持体の回転中心より像担持体の回転方向の下流側に向けて付勢されるように揺動支点を有し１つの付勢部材（バネ２７）により付勢されるので、より簡単な機構でスムーズに揺動でき、像担持体に対する現像器の押圧力を軽減、緩和して像担持体の回転ムラを低減することができ、回転ムラによる露光ズレ、転写ズレをなくし、画像ムラ、画像不良をなくすことができる。
【図面の簡単な説明】
【図１】本発明に係る画像形成装置の実施の形態を示す図である。
【図２】ロータリー現像装置が現像色切り換え動作により回転移動して位置決めされ現像ローラが感光体に当接している状態を示す図である。
【図３】ロータリー現像装置が現像色切り換え動作により回転移動し現像ローラが感光体から離れる位置を示す図である。
【図４】現像ローラがロータリー現像装置の回転中心と感光体の回転中心を結ぶ直線上にある状態を示す図である。
【符号の説明】
１…ロータリー現像装置、２…現像器、３…感光体、４…中間転写媒体、５…露光装置、６…プロセスユニット、７…１次転写装置、８…２次転写装置、９…給紙トレイ、１０…給紙ローラ、１１…レジローラ、１２…紙搬送ユニット、１３…定着ユニット、１４…排紙トレイ、１５…扉体[0001]
【Technical field】
In the present invention, a developing image is switched by a rotary developing device, and a plurality of developing devices are sequentially rotated to a developing position to develop a latent image formed on an image carrier and transfer it to a medium at a transfer position to form an image. The present invention relates to an image forming apparatus configured as described above.
[0002]
[Prior art]
In an image forming apparatus adopting a rotary developing system, an image carrier on which a latent image is formed, a plurality of developing units that have a developing roller and convey the developer to develop the latent image, and a plurality of developing units In a conventional image forming apparatus having a rotary developing device that is rotated along and moved to a developing position facing the image carrier, a developing device that performs a developing operation has conventionally been at the rotation position of the rotary developing device at the developing position. The rotary developing device is positioned so that the rotation center of the developing roller and the rotation center of the photosensitive member are in a straight line, and the developing operation is performed (see, for example, Patent Documents 1 and 2).
[0003]
[Patent Document 1]
Japanese Patent No. 2649033 [0004]
[Patent Document 2]
Japanese Patent Laid-Open No. 2003-5484
[Problems to be solved by the invention]
However, at the development position as in the above-described conventional device, the developing device that performs the developing operation positions the rotary developing device so that the rotation center of the rotary developing device, the rotation center of the developing roller, and the rotation center of the photosensitive member are in a straight line. As a result, several problems arise.
[0006]
For example, when the developing operation is completed and the rotary developing device is rotated by the developing color switching operation in order to rotate the developing device for the next color to the developing position, the developing device that has been operating until then presses against the photoreceptor. The applied pressing force starts to decrease from the maximum value as the movement starts, and the developing roller is completely separated from the photosensitive member and becomes zero. Although there are various methods for determining the distance between the developing roller and the photosensitive member at the developing position, in the non-contact developing method example, a roller having a slightly larger diameter than the developing roller is disposed coaxially with the developing roller, There is a configuration in which a gap between the developing roller and the photosensitive member is determined by contacting the roller with the photosensitive member. In the case of this configuration, when applied to the decrease in the previous pressing force, the pressing force becomes zero when the rotary developing device rotates from the developing position and the roller moves away from the surface of the photosensitive member for a while. In addition, this roller is shown in Patent Document 2 by a ring-shaped member at the end of the developing roller 22 in FIGS.
[0007]
When the pressing force that presses the developing device against the photoconductor changes, the addition when driving the photoconductor fluctuates. This causes rotation unevenness of the photosensitive member and causes image defects such as image unevenness. Further, when the photosensitive member is attached to the apparatus main body, it has a certain amount of play. This play is required to some extent on the structure for fitting and mounting. When the developing unit is pressed against the photosensitive member, the photosensitive member is opposite to the developing roller on a straight line connecting the rotation center of the rotary developing device, the rotation center of the developing roller, and the rotation center of the photosensitive member within the range of the backlash. Will move in the direction. Similar to the previous problem, when the rotary developing device starts rotating and the pressing force decreases, the photosensitive member can move in the direction opposite to the previous direction within the range of play. When the position of the photoconductor changes in this way, there arises a problem that an image is distorted (transfer shift) between the primary transfer roller and the photoconductor.
[0008]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, and reduces the rotation unevenness of the photosensitive member, eliminates the exposure shift and transfer shift due to the rotation unevenness, eliminates the image unevenness and the image defect, and reduces the development color switching operation time. It is intended to shorten.
[0009]
Therefore, the present invention provides an image carrier on which a latent image is formed, a latent image forming unit that forms the latent image on the image carrier, and a developer roller that conveys a developer to develop the latent image. A plurality of developing units, and a rotary development in which the plurality of developing units are supported so as to be swingable along an outer periphery and rotated in a predetermined direction so that the plurality of developing units sequentially move to a developing position facing the image carrier. And the plurality of developing devices sequentially rotate and move to the developing position by the developing color switching operation of the rotary developing device to develop the latent image formed on the image carrier and transfer it to the medium at the transfer position. In the image forming apparatus configured to form an image, the rotary developing device connects the rotation center of the rotary developing device and the rotation center of the image carrier with respect to the developing device at the development position. The rotor from a straight line -The developing roller or rollers disposed at both ends of the developing roller on the downstream side in the rotation direction of the developing device are pressed against the image carrier, and the rotation center of the developing roller and the rotation center of the image carrier The developing roller is pressed against the image carrier so that the developing roller is pressed against the image carrier by a predetermined angle toward the downstream side in the rotation direction of the image carrier with respect to a straight line connecting The developing device swinging fulcrum is positioned with respect to the position .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. In the figure, 1 is a rotary developing device, 2 is a developing device, 3 is a photoreceptor, 4 is an intermediate transfer medium, 5 is an exposure device, 6 is a process unit, 7 is a primary transfer device, 8 is a secondary transfer device, 9 Is a paper feed tray, 10 is a paper feed roller, 11 is a registration roller, 12 is a paper transport unit, 13 is a fixing unit, 14 is a paper discharge tray, and 15 is a door.
[0012]
As shown in FIG. 1, the image forming apparatus according to the present embodiment includes a paper discharge tray 14 formed on an upper portion of a housing, and a door body 15 that is openably and detachably inserted on the front surface of the housing. In the housing, a rotary developing device 1 having a plurality of developing devices 2 mounted thereon, a photosensitive member 3 on which a latent image is formed and developed to form a toner image, and an exposure device that exposes the photosensitive member 3 to form a latent image. 5. Intermediate transfer medium 4 consisting of an endless belt to which a toner image is transferred, a process unit 6 for controlling the formation of a latent image by the exposure device 5, and a toner image on the photoreceptor 3 to the intermediate transfer medium 4. Primary transfer device 7, secondary transfer device 8 for secondary transfer of the toner image of the intermediate transfer medium 4 to a recording medium (such as paper), paper feed tray 9 for storing the recording medium, and fixing the toner image on the recording medium A fixing unit 13, a drive motor, a control unit for controlling the bias, and the like are disposed. A paper transport unit 12 that transports the recording medium from the paper feed tray 9 to the fixing unit 13 through the secondary transfer device 8 is disposed in the door body 15. Each unit is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.
[0013]
The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photoconductor 3, a charging device (not shown) for uniformly charging the photoconductor 3 along the rotation direction, an exposure device 5 for forming a latent image on the photoconductor 3, a latent image A rotary developing device 1 for developing an image, an intermediate transfer medium 4 to which a toner image on a photoreceptor 3 is transferred, and a primary transfer device 7 for primary transfer of the toner image to the intermediate transfer medium 4 after primary transfer A cleaner (not shown) for cleaning the surface of the photosensitive member 3 is disposed. The latent image formed by the exposure device 5 on the photosensitive member 3 is developed by the rotary developing device 1 to form a toner image, and the formed toner image is transferred onto the intermediate transfer medium 4 by the primary transfer device 7. Then, the image is further transferred to a recording medium (paper or the like) by the secondary transfer device 8.
[0014]
In full-color image formation by the image forming apparatus having the above-described configuration, when an image formation signal is input from the process unit 6 to the exposure device 5, the photoconductor 3 and the rotary developing device are controlled according to control of the drive motor and bias by the control unit. 1. The intermediate transfer medium 4 is driven to rotate. The outer peripheral surface of the photosensitive member 3 is uniformly charged by the charging device, and the rotary developing device 1 forms a toner image of the first color, for example, yellow Y. The developing device 2 rotates and moves further beyond the straight line connecting the rotation center of the rotary developing device 1 and the rotation center of the photosensitive member 3, and the developing roller or the developing roller of the developing device 2 is located downstream in the rotational movement direction of the rotary developing device 1. Rollers disposed at both ends (hereinafter the same) contact the photoreceptor 3 and stop. At the same time as the developing roller of the developing device 2 is driven to rotate, the surface of the photosensitive member 3 is first subjected to selective exposure according to the image information of the first color and yellow Y by the exposure device 5, so A yellow Y latent image is formed. The yellow Y latent image is developed by the developing device 2 to form a toner image on the photoreceptor 3.
[0015]
As soon as the rear end of the yellow Y latent image is developed by the developing unit 2 and development is completed, the rotary developing device 1 immediately after that, that is, before the rear end of the toner image reaches the primary transfer device 7, The developing color switching operation for forming a color, for example, a black K toner image is started. By this developing color switching operation, the developing roller of the black K developing device 2 rotates and moves further beyond the straight line connecting the rotation center of the rotary developing device 1 and the rotation center of the photosensitive member 3. And abut against the photosensitive member 3 on the downstream side in the rotational movement direction.
[0016]
During this time, a primary transfer voltage having a polarity opposite to the toner charging polarity is applied to the primary transfer device 7, and the toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer medium 4 by the primary transfer device 7. Transcribed. The secondary transfer device 8 is separated from the intermediate transfer medium 4.
[0017]
When the developing color switching operation for the second color is completed and the developing roller of the black K developing device 2 comes into contact with the photosensitive member 3 and stops, the second color, black K is applied to the surface of the photosensitive member 3 by the exposure device 5. The black K latent image is formed on the photoreceptor 3 by selective exposure according to the image information. Such a series of processing is repeatedly executed corresponding to the second color, the third color, and the fourth color of the image forming signal, so that yellow Y, black K, cyan corresponding to the contents of each image forming signal. Four-color toner images composed of C and magenta M are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer medium 4 to form a full-color image.
[0018]
Then, at the timing when the full-color image reaches the secondary transfer device 8, the recording medium (paper or the like) in the paper feed tray 9 is conveyed from the conveyance path to the secondary transfer device 8 through the paper supply roller 10 and the registration roller 11. The apparatus 8 is pressed against the intermediate transfer medium 4 and a secondary transfer voltage is applied, and the four color full-color toner images on the intermediate transfer medium 4 are transferred onto the recording medium by the secondary transfer apparatus 8. When the recording medium to which the full color toner image is transferred in this manner is conveyed to the fixing unit 13 by the paper conveying unit 12, the full color toner image on the recording medium is heated and pressed by the fixing unit 13, and is fixed. The paper is discharged to the tray 14.
[0019]
FIG. 2 is a diagram showing a state in which the rotary developing device is rotated and moved by the developing color switching operation and is positioned, and the developing roller is in contact with the photosensitive member. FIG. 3 is a drawing in which the rotary developing device is rotated and moved by the developing color switching operation. FIG. 4 is a diagram illustrating a state where the developing roller is on a straight line connecting the rotation center of the rotary developing device and the rotation center of the photosensitive member. In the figure, 21 is a rotary developing device drive motor, 22 is a drive motor gear, 23 is a rotary developing device rotating gear, 24 is a developing roller, 25 is a developing device swinging fulcrum, 26 is a rotary frame, 27 is a contact spring, 28 , 29 is a developer swing restricting portion, and 31 to 33 are rotation centers.
[0020]
As shown in FIG. 2, the rotary developing device 1 has a rotary developing device rotating gear 23 along the outer periphery, and a driving motor gear 22 meshes with the rotary developing device rotating gear 23 and is illustrated by the rotary developing device driving motor 21. It is driven to rotate in the counterclockwise direction. The developing device 2 detachably mounted on the rotary developing device 1 has a rotational center of the rotary developing device 1 with respect to a straight line L connecting the rotational center 31 of the rotary developing device 1 and the rotational center 32 of the photosensitive member 3. The developing roller 24 is positioned so that the straight line connecting 31 and the rotation center 33 of the developing roller 24 presses the photoreceptor 3 on the downstream side in the rotation direction by the rotation angle B °.
[0021]
The developing device 2 is slidably mounted with the developing device rocking fulcrum 25 as a fulcrum. The rocking of the developing device 2 is restricted by the developing device rocking restricting portion 28 on the developing device 2 side and the developing device rocking restriction on the rotary frame 26 side. It is regulated by the portion 29 and is urged in the direction of the photoreceptor 3 by a contact spring 27 provided on the rotary frame 26 so as to contact the photoreceptor 3 with a predetermined pressing force.
[0022]
When the developing color switching operation is started by the rotary developing device driving motor 21 and the rotary developing device 1 is rotated, the developing device 2 that has completed the developing operation has the developer 2 side from the rotation angle A ° shown in FIG. The developing device swing restricting portion 28 and the developing device swing restricting portion 29 on the rotary frame 26 side restrict the swing, so that the developing roller 24 is separated from the photoreceptor 3. In the developing device 2 that performs the next developing operation, the developing roller 24 comes into contact with the photosensitive member 3 as the rotary developing device 1 rotates, and the rotational center 32 of the rotary developing device 1 and the photosensitive member as shown in FIG. After reaching a straight line L connecting to the rotation center 32 of 3 and further rotating, the developing roller 24 is positioned so as to come into contact with the photoreceptor 3 on the downstream side in the rotation direction by the rotation angle B ° shown in FIG. .
[0023]
When a latent image is formed on the photosensitive member 3 by selectively exposing according to image information by the exposure device 5, the photosensitive member 3 is exposed to the above-described structural backlash for fitting and mounting. When movement occurs or rotation unevenness occurs, image unevenness due to exposure misalignment or the like, or image failure occurs. Similarly, when the toner image formed on the photoconductor 3 is transferred onto the intermediate transfer medium 4 by the primary transfer device 7, similarly, if the photoconductor 3 is moved and rotated, uneven transfer occurs. This causes image unevenness and image defects. The movement and rotation unevenness of the photosensitive member 3 is more likely to occur as the fluctuation of the external force received by the photosensitive member 3 increases and as the absolute value increases.
[0024]
The pressing force that presses the developing roller 24 against the photosensitive member 2 is one of the external forces, and the developing roller 24 is a straight line connecting the rotation center 31 of the rotary developing device 1 and the rotation center 32 of the photosensitive member 3 shown in FIG. When it is on L, the maximum value is obtained, and rotation unevenness is likely to occur in the photosensitive member 3. Even if the developing roller 24 is pressed against the photosensitive member 3 on the straight line L connecting the rotational center 31 of the rotary developing device 1 and the rotational center 32 of the photosensitive member 3, the developing device 2 is actually used. When a slight swaying from side to side occurs along the straight line L, the component force of the pressing force is in the direction of rotation of the photosensitive member 3 with respect to the tangential direction of the pressing portion between the developing roller 24 and the photosensitive member 3. This also acts in the reverse rotation direction, which is also a factor that easily causes rotation unevenness in the photosensitive member 3.
[0025]
At the developing position where the developing operation is performed as in the present embodiment, as shown in FIG. 2, the rotational direction is the rotational angle B ° from the straight line L connecting the rotational center 31 of the rotary developing device 1 and the rotational center 32 of the photosensitive member 3. When the developing roller 24 is pressed against the photosensitive member 3 on the downstream side of the developing roller 24, the developing roller 24 is on a straight line L connecting the rotation center 31 of the rotary developing device 1 and the rotation center 32 of the photosensitive member 3 as shown in FIG. The pressing force can be reduced as compared with the case where is pressed against the photosensitive member 3. In addition, the component force of the pressing force does not act in the rotation direction of the photosensitive member 3 or acts in the reverse rotation direction, and can be applied in a certain direction. For these reasons, it is possible to reduce the occurrence of uneven movement and rotation of the photosensitive member 3 by pressing the developing roller 24 against the photosensitive member 3.
[0026]
Even when the position where the developing roller 24 is pressed against the photosensitive member 3 is opposite to the downstream side in the rotational direction shown in FIG. 2 and the upstream side in the rotational direction, it is the same as described above. Immediately after starting the developing color switching operation of the rotary developing device 1, the pressing force is greatest while the developing roller 24 passes on the straight line L connecting the rotation center 31 of the rotary developing device 1 and the rotation center 32 of the photosensitive member 3. Give fluctuations. That is, immediately after the developing color switching operation of the rotary developing device 1 is started, the pressing force that presses the developing roller 24 against the photosensitive member 3 increases, reaches a maximum on the straight line L, and then decreases to zero. In addition, as described above, the component force of the pressing force is reversed with respect to the rotation direction of the photosensitive member 3 before and after passing through the straight line L where the pressing force is maximum. That is, the brake component is switched to the acceleration component, and the rotation unevenness is most likely to occur in the photoreceptor 3.
[0027]
Therefore, when the developing color switching operation of the rotary developing device 1 is performed while the toner image on the photosensitive member 3 is transferred onto the intermediate transfer medium 4 by the primary transfer device 7, the movement of the photosensitive member 3 is performed. The transfer unevenness due to the rotation unevenness is further deteriorated. In this case, even if the developing operation is completed, the developing color switching operation of the rotary developing device 1 cannot be performed until the transfer is completed. This means that it is not possible to quickly shift to the operation for forming the next developed color image.
[0028]
As shown in FIG. 2 of the present embodiment, the developing roller 24 is arranged on the downstream side in the rotational direction by a rotational angle B ° from a straight line L connecting the rotational center 31 of the rotary developing device 1 and the rotational center 32 of the photosensitive member 3. Of the rotary developing device 1 for moving the next color developing device 2 to the developing position as soon as the developing device 2 develops the rear end of the latent image formed on the photoreceptor 3 by pressing against the developing device 3. Development color switching can be started. As a result, immediately after the development color switching operation is started, the movement and rotation unevenness of the photosensitive member 3 is caused as in the case where development is performed by pressing the developing roller 24 against the photosensitive member 3 on the upstream side in the rotation direction. This eliminates the transfer deviation in the primary transfer.
[0029]
In recent years, since the image forming apparatus is required to increase the printing speed, in the image forming apparatus employing the rotary developing device 1, the time required for the development color switching operation of the rotary developing device 1 for replacing each color developing device 2 is reduced. There is a demand for shortening and an improvement in rotation speed, and a reduction in the interval between images (intermediate paper) on the intermediate transfer medium 4 is also required. In this embodiment, when the developing device 2 develops the rear end of the latent image formed on the photoreceptor 3, the developed toner image is still being transferred onto the intermediate transfer medium 4 by the primary transfer device 7. However, the developing color switching operation of the rotary developing device 2 for quickly moving the developing device 2 of the next color to the developing position can be started immediately.
[0030]
Also, as shown in FIG. 2 of the present embodiment, the developing roller 24 is moved downstream in the rotation direction by a rotation angle B ° from a straight line L connecting the rotation center 31 of the rotary developing device 1 and the rotation center 32 of the photosensitive member 3. When the development is performed by pressing against the photoreceptor 3, the development passes through the straight line L where the pressing force is maximum at the end of the development color switching operation of the rotary developing device 1. Large movement and rotation unevenness occur. Up to this point, the trailing edge of the toner image is transferred onto the intermediate transfer medium 4 by the primary transfer device 7 and the primary transfer is completed, so that it is possible to avoid adversely affecting the transfer. On the other hand, the selective exposure start according to the image information by the exposure device 5 for forming a latent image on the photosensitive member 3 is performed on the straight line L where the pressing force becomes maximum immediately before the end of the development color switching operation. Therefore, it is desirable to carry out the operation after the developing color switching operation of the rotary developing device 1 is completed.
[0031]
As shown in FIG. 2 of the present embodiment, the developing roller 24 is arranged on the downstream side in the rotational direction by a rotational angle B ° from a straight line L connecting the rotational center 31 of the rotary developing device 1 and the rotational center 32 of the photosensitive member 3. In other words, the development roller 24 is pressed against the photosensitive member 3 from the direction of the rotation center 32 toward the downstream side in the rotation direction. As a result, the pressing force described above can be reduced and reduced, and fluctuations in the pressing force immediately after the developing color switching operation of the rotary developing device 1 can be reduced and reduced. For this purpose, the photosensitive member 3 has a predetermined angle from the rotational center 33 of the developing roller 24 to the rotational center 32 of the photosensitive member 3 with respect to a straight line connecting the rotational center 33 of the developing roller 24 and the rotational center 32 of the photosensitive member 3. The position of the developer swinging fulcrum 25 is set with respect to the position where the developing roller 24 is pressed against the photosensitive member 3 so that the developing roller 24 is pressed against the photosensitive member 3 toward the downstream side in the rotation direction. .
[0032]
In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the exposure apparatus that exposes the photosensitive member to form an electrostatic latent image as the latent image forming unit has been described. However, the same applies to other latent image forming units using write electrodes. Of course.
[0033]
【The invention's effect】
As is apparent from the above description, according to the present invention, an image carrier on which a latent image is formed, a latent image forming unit that forms a latent image on the image carrier, a developing roller, and a developer. A plurality of developing units that convey and develop a latent image, and a plurality of developing units that sequentially support the plurality of developing units so as to be swingable along the outer periphery and rotate in a predetermined direction to face the image carrier. A rotary developing device that moves, and by developing color switching operation of the rotary developing device, a plurality of developing devices sequentially rotate to the developing position to develop the latent image formed on the image carrier and transfer it to the medium at the transfer position In the image forming apparatus configured to form an image, the rotary developing device is configured to perform rotary development from a straight line connecting the rotation center of the rotary developing device and the rotation center of the image carrier with respect to the developing device at the development position. Present downstream of the machine rotation direction Pressing a roller disposed at opposite ends of the roller or the developing roller to the image carrier, and, with respect to a straight line connecting the centers of rotation and the image bearing member of the developing roller, the predetermined angle only the image bearing member The developing device swinging fulcrum is positioned relative to the position where the developing roller is pressed against the image carrier so that the developing roller is pressed against the image carrier toward the downstream side in the rotation direction. Can reduce and mitigate the pressing force of the image carrier to reduce the rotation unevenness of the image carrier, eliminate the exposure shift and transfer shift due to the rotation unevenness, and eliminate the image unevenness and the image defect.
[0034]
According to the present invention, the rotary developing device performs the developing color switching operation of the rotary developing device after developing the trailing end of the latent image and before transferring the developed toner image to the medium at the transfer position. Since it can be started, it is possible to shorten the developing color switching operation time for moving the developing device for the next developing color to the developing position without waiting until the transfer of the developed toner image is completed. Rotational unevenness can be reduced, transfer deviation due to rotational unevenness can be eliminated, and image unevenness and image defects can be eliminated. The latent image forming means can start the formation of the latent image after the next developing device has been rotated to the developing position by the developing color switching operation of the rotary developing device, and during the developing color switching operation of the rotary developing device. Even if rotation unevenness occurs in the image carrier, it can be avoided so as not to be affected by it, exposure deviation due to rotation unevenness can be eliminated, and image unevenness and image defects can be eliminated. Further, the developing device is supported in a swingable manner and has a swing fulcrum so as to be biased toward the downstream side in the rotation direction of the image carrier from the rotation center of the image carrier. Since it is urged by the spring 27), it can be smoothly swung by a simpler mechanism, and the pressing force of the developing device against the image carrier can be reduced and relaxed to reduce rotation unevenness of the image carrier, Exposure deviation and transfer deviation due to unevenness can be eliminated, and image unevenness and image defects can be eliminated.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a diagram illustrating a state in which a rotary developing device is rotated and positioned by a developing color switching operation and a developing roller is in contact with a photosensitive member.
FIG. 3 is a diagram illustrating a position where a rotary developing device is rotated by a developing color switching operation and a developing roller is separated from a photosensitive member.
FIG. 4 is a diagram illustrating a state where the developing roller is on a straight line connecting the rotation center of the rotary developing device and the rotation center of the photosensitive member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Rotary developing device, 2 ... Developing device, 3 ... Photoconductor, 4 ... Intermediate transfer medium, 5 ... Exposure device, 6 ... Process unit, 7 ... Primary transfer device, 8 ... Secondary transfer device, 9 ... Paper feed Tray, 10 ... feed roller, 11 ... registration roller, 12 ... paper transport unit, 13 ... fixing unit, 14 ... discharge tray, 15 ... door

Claims

An image carrier on which a latent image is formed; a latent image forming unit that forms the latent image on the image carrier; and a plurality of developing units that have a developing roller and transport the developer to develop the latent image. A rotary developing device that supports the plurality of developing units so as to be swingable along an outer periphery, rotates in a predetermined direction, and sequentially moves the plurality of developing units to a developing position facing the image carrier, By the developing color switching operation of the rotary developing device, the plurality of developing devices sequentially rotate to the developing position, develop the latent image formed on the image carrier, and transfer the image to a medium at the transfer position to form an image. In the image forming apparatus configured as described above,
The rotary developing device is arranged on the downstream side of the rotation direction of the rotary developing device with respect to the developing device at the developing position from a straight line connecting the rotation center of the rotary developing device and the rotation center of the image carrier. A developing roller or rollers disposed at both ends of the developing roller are pressed against the image carrier, and a predetermined angle with respect to a straight line connecting the rotation center of the development roller and the rotation center of the image carrier The developer oscillating fulcrum is positioned relative to the position where the developing roller is pressed against the image carrier so that the developing roller is pressed against the image carrier toward the downstream side in the rotational direction of the image carrier. an image forming apparatus characterized in that it is.