JP3698176B2

JP3698176B2 - Image forming apparatus

Info

Publication number: JP3698176B2
Application number: JP32086595A
Authority: JP
Inventors: 信正阿部
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 1995-12-08
Filing date: 1995-12-08
Publication date: 2005-09-21
Anticipated expiration: 2015-12-08
Also published as: JPH09160384A

Description

【０００１】
【発明の属する技術分野】
本発明は、現像剤により潜像担持体の潜像を可視化するための現像ローラを有する現像装置が潜像担持体に対して離間する位置と当接する位置に移動可能な現像装置移動手段を備えた画像形成装置に関する。
【０００２】
【従来の技術】
電子写真プロセスを利用したカラー画像形成が可能な画像形成装置として、装置内に複数の現像装置を有し、所望の色彩の現像装置を選択して現像位置まで移動経路を経て移動させて現像を行う画像形成装置が提案されている。
【０００３】
この方式の画像形成装置の従来技術として、例えば、特開昭６３−２２０２６７号公報が挙げられ、複数の現像装置を備え、潜像担持体に対して黒現像装置専用と黒以外の色の現像装置専用の計２ヶ所の現像位置を有し、黒以外の色の現像装置が選択され、選択された現像装置が現像位置まで移動経路を経て移動する際、移動経路に近い現像装置の色から順に潜像形成して現像を行うというものであった。
【０００４】
【発明が解決しようとする課題】
しかしながら、前述の特開昭６３−２２０２６７号公報に開示されるような画像形成装置では、黒と単色（例えば、シアン、マゼンタ、イエロー）による２色の画像形成では高速出力が可能となるが、フルカラーの画像形成では、現像位置にある現像装置を入れ換える際、現像位置から待機位置までの移動経路が一つしか存在しないので、現像位置に存在した現像装置が待機位置へ移動するまで次の現像装置を現像位置に移動させることができず、つまり、現像装置の切り換えに時間を要し、高速出力ができないという問題点があった。
【０００５】
一般的に電子写真プロセスを用いてフルカラー画像を形成する場合、シアン、マゼンタ、イエロー、ブラックのトナーを備えた現像装置を用い、感光体に対して４回画像形成を行うことが必要であり、モノクロ画像を形成するに比べて出力に要する時間が４倍必要である。しかし、前述の従来技術のように実際の画像形成に要する時間は現像装置の切り換え時間がさらに上乗せされるため、画像形成時間が長くなり、高速出力の妨げとなっている。
【０００６】
また、前記従来技術では現像装置を装置本体外部に収納するため、装置外部で所望の現像装置の選択動作を行った後に本体内部へ移送するため、現像装置移動機構と移動経路が複雑かつ大規模となり、装置の小型化の妨げとなっている。
【０００７】
本発明は上述した従来技術に鑑みてなされたものであり、現像装置を待機位置から現像位置まで移動するための時間が画像出力に要する時間に含まれないようにし、高速出力が可能なカラー画像形成装置を提供することを第１の目的とし、また、現像装置の移動機構を簡便かつ小型な構成とし、コンパクトなカラー画像形成装置を提供することを第２の目的としている。
【０００８】
【課題を解決するための手段】
上記目的を達成するために、本発明の請求項１記載の画像形成装置は、帯電、画像露光が行われて静電潜像が形成される潜像担持体と、表面に現像剤を担持して前記潜像担持体と当接しながら前記潜像担持体上の静電潜像を顕像化する現像ローラをそれぞれ備えた複数の現像装置と、前記現像装置をその前記現像ローラが前記潜像担持体に当接する現像位置と前記潜像担持体から離間する待機位置とに移動させる現像装置移動手段とを有する画像形成装置において、前記現像装置移動手段が、前記複数の現像装置をそれぞれ前記現像位置または前記待機位置に案内する各現像装置ごとに設けられた現像装置案内手段と、前記複数の現像装置をそれぞれ対応する前記現像装置案内手段に沿って移動させて前記潜像担持体に対して離接させる駆動手段とによって構成され、前記駆動手段の内１つの駆動手段が、前記複数の現像装置の内の２つの現像装置をそれぞれ対応する前記現像装置案内手段に沿って移動させて前記潜像担持体に対して交互に離接させる単一の駆動手段であり、前記２つの現像装置の前記各現像ローラがそれぞれ前記潜像担持体と当接する前記現像位置が略同一位置に設定されており、前記２つの現像装置のそれぞれの前記現像装置案内手段が、対応する現像装置の現像ローラを略同一位置に設定された前記現像位置に案内する現像装置案内手段であることを特徴とする。
【０００９】
また、請求項２記載の画像形成装置は、前記単一の駆動手段は正逆回転が可能で、前記単一の駆動手段が一方向に回転することで前記２つの現像装置の一方が前記潜像担持体から離間し、かつ前記２つの現像装置の他方が前記潜像担持体と当接し、前記単一の駆動手段が逆方向に回転することで前記２つの現像装置の他方が前記潜像担持体から離間し、かつ前記２つの現像装置の一方が前記潜像担持体と当接することを特徴とする。
【００１０】
また、請求項３記載の画像形成装置は、前記２つの現像装置の各現像装置案内手段が、それぞれ対応する現像装置端部の両側に設けた一対の凸部と、装置本体側に設けて前記凸部と係合する一対の現像装置案内溝とからなり、前記駆動手段が、前記各現像装置案内手段のそれぞれの前記凸部と係合する溝部を有するカム部材と、前記カム部材を駆動する正逆回転可能なモータとからなることを特徴とする。
【００１１】
更に、請求項４記載の画像形成装置は、前記現像装置移動手段を複数備えていることを特徴とする。
更に、請求項５記載の画像形成装置は、前記現像装置移動手段を２つ備えているとともに前記現像装置を４つ備え、前記４つの現像装置の内２つの現像装置が前記２つの現像装置移動手段の内１つの現像装置移動手段で移動可能とされ、また、前記４つの現像装置の内他の２つの現像装置が前記２つの現像装置移動手段の内他の１つの現像装置移動手段で移動可能とされていることを特徴とする。
【００１２】
【発明の実施の形態】
以下、実施例に基づき本発明を詳しく説明する。
【００１３】
図１は本発明の画像形成装置の実施例の全体構成を示す装置断面図であり、カラー画像記録が可能なプリンタ装置である。この第１の実施例の概略動作を図１で説明する。
【００１４】
図１において、潜像担持体である感光体１はニッケル電鋳管または表面にアルミ層をコーティングしたポリエチレンテレフタレート樹脂などの無端ベルト基材上に有機感光体を塗布して構成され、その内周に当接して矢印Ａ方向に回転する感光体駆動ローラ２によって回転駆動される。なお、感光体１はベルト状とせず、アルミパイプ材の表面に有機感光体を直接塗布し、感光体駆動ローラ２を廃止しても良い。感光体１の外周には、帯電手段として帯電ローラ３が配置され、図示しない高圧電源から約−１２００Ｖの電圧が印加され、感光体１に当接回転しながら感光体１の表面を一様に帯電させる。ここで、本例では帯電手段として帯電ローラ２を用いたが、コロナ帯電器を用いることも可能である。
【００１５】
帯電手段によって表面が一様に帯電された感光体１は、露光手段であるレーザー走査光学系４によって第１色目として例えばブラックの画像情報に応じて選択的に走査露光され、ブラック用の静電潜像が形成される。本例では露光手段としてレーザー走査光学系３を用いたが、ＬＥＤアレイまたは液晶シャッタ等で構成した露光用光学系を露光手段として用いることも可能である。
【００１６】
レーザー走査光学系４の感光体回転方向下流側には、感光体１を感光体駆動ローラ２に当接させる方向に付勢する感光体補助ローラ５が配置され、感光体補助ローラ５からの駆動力を円滑に感光体１へ伝達すると同時に、後述する現像装置の離接動作によって感光体１上の露光位置がずれることを防止している。
【００１７】
感光体補助ローラ５の感光体回転方向下流側には、現像剤としてそれぞれブラック、シアン、マゼンタ、イエローのトナーを貯蔵し、感光体１に対して離接自在な現像装置６、７、８、９が配置されている。
【００１８】
ここで、各現像装置の構成を図２で説明する。図２はブラック現像装置６の構成を示す断面図である。図２において、現像装置内に充填されたトナー（図示せず）の凝集を防ぎ、図２の奥行き方向に均等に堆積させることを目的としてアジテータ１０の回転で攪拌される。供給ローラ１１は軸部材の外周に導電性弾性体を配置したローラであり、矢印Ｃ方向に回転しながら現像ローラ１２に押圧され、トナーを摩擦帯電しながら現像ローラ１２に供給する。トナーが供給された現像ローラ１２は矢印Ｄ方向に回転し、一端が現像装置ケース１３に固定された板バネ１４の自由端側に固定された規制部材１５が現像ローラ１２に圧接することでトナー層の厚さを適量に規制する。なお、現像ローラ１２としては金属ローラの表面にゴム等の弾性部材を設けたり、金属ローラの表面に適当な面粗度の表面処理を加えて構成し、規制部材１５としてはゴム、樹脂、金属などで構成することができる。このような構成の現像装置を感光体１に当接させ、必要に応じて感光体１と現像ローラー１２の間に電位差を設けることで感光体上の潜像がトナーによて顕像化される。また、他の色の現像装置７、８、９も構成は同一である。
【００１９】
図１に戻り、レーザー走査光学系４で形成されたブラック用の静電潜像は感光体１の矢印Ａ方向への回転に伴い、予め二点鎖線位置から矢印Ｂ方向に移動して感光体１と圧接されたブラック現像装置６によって現像され、ブラックのトナー像が形成される。この時、他の色の現像装置７、８、９は感光体１から離間されている。
【００２０】
現像装置の感光体回転方向下流側には、感光体１に隣接して中間転写媒体１６が転写媒体ローラ１７、１８、１９に掛け回されており、図示しない駆動源によって感光体１の周速度と同一速度で駆動されている。中間転写媒体１６はポリエステル、ポリカーボネート、ポリエチレンテレフタレート等の材質に対してカーボン等の導電剤を付与し、適度の導電抵抗を有する導電性フィルムとして構成してある。転写媒体ローラ１７または１８は図示しない高圧電源に接続され、図示しないスイッチ手段で選択的に高電圧が印加される。また、感光体１は転写媒体ローラ１７および１８間に支持された中間転写媒体８と一次転写部２０で当接している。前述のように、感光体１の表面に形成されたブラックのトナー像は感光体１の矢印Ａ方向への回転に伴って一次転写部２０に至る。この時、転写媒体ローラ１７または１８には図示しない高圧電源から約＋２０００Ｖの電圧が印加され、一次転写部２０で感光体１の表面に形成されたブラックのトナー像が中間転写媒体１６に転写される。
【００２１】
中間転写媒体１６にブラックのトナー像を転写した感光体１は更に矢印Ａ方向へ回転し、クリーナーブレード等で構成された感光体クリーナ２１によって感光体１の表面に残留するトナーが掻き取られ、更に、除電器２２によって感光体１の表面を一様に露光して感光体１上の残存電荷が除去され、再び画像形成が可能となる。
【００２２】
所望のブラックのトナー像が中間転写媒体１６にすべて転写されると、ブラック現像装置６は矢印Ｂとは逆方向に移動し、当初の待機位置に退避する。
【００２３】
引き続き、第１色目と同様の手順で第２色目から第４色目の画像（マゼンタ、シアン、イエロー）が中間転写媒体１６上に順次重ね合わせて記録される。
【００２４】
中間転写媒体１６へのカラートナー像の重ね合わせが終了すると、記録シート載置台２３に積み重ねて載置された記録シート２４は、給紙ローラ２５で給送が開始され、図示しない摩擦分離式または爪分離式の１枚分離手段で最上部の１枚のみが給送される。１枚分離して給送された記録シート２４の搬送方向先端は図示しないクラッチ手段で駆動が一時的に解除されて停止したレジストローラ２６に至る。記録シート２４は搬送方向先端がレジストローラ２６のニップ部と当接することで斜め送りが補正され、中間転写媒体１６に重ね合わされたカラートナー像の位置と同期してレジストローラ２６が図示しないクラッチ手段によって駆動を開始することで二次転写部２７の方向に給送が再開される。これにより、記録シート２４は二次転写部２７に至る。
【００２５】
二次転写部２７に記録シート２４の先端が進入すると、二次転写ローラ２８には図示しない高圧電源から約−２０００Ｖの電圧が印加され、中間転写媒体１６の表面に形成されたカラートナー像が記録シート２４の表面に転写される。カラートナー像の転写を終えた中間転写媒体１６にはクリーナーブレード等で構成された転写媒体クリーナ２９が矢印Ｅ方向へ移動して当接し、中間転写媒体１６の表面に残留したトナーが掻き取られ、掻き取りが終了すると転写媒体クリーナ２９は矢印Ｅとは逆方向へ移動して退避する。
【００２６】
カラートナー像が転写された記録シート２４は、ベルト搬送装置３０によって搬送され、内部に棒状のハロゲンランプ３１を備えたヒートローラ３２と、ヒートローラ３２に加圧当接して回転する加圧ローラ３３、３４で構成された定着装置に至り、カラートナー像が転写された記録シート２４が加熱加圧しながら挟持搬送されてトナー像が定着される。トナー像が定着された記録シート２４は排紙ローラ群３５によって装置外部へと排出され、カラー画像記録が完了する。
【００２７】
次に、各現像装置が感光体１に対して離接動作を行う移動手段について説明する。図３は本画像形成装置のブラック現像装置６およびシアン現像装置７の離接動作機構の構造を示す部分断面斜視図であり、各構成部材の係合を説明するために各構成部材を軸方向に分散して配置してある。図３において、各構成部材を保持するサイドフレーム３６には現像装置ガイド３７、３８、３９が配置してあり、現像装置ガイド３７には現像装置案内溝４０および４１が、現像装置ガイド３８には現像装置案内溝４２が、現像装置ガイド３９には現像装置案内溝４３を設けてある。ブラック現像装置６の端部には突起４４および４５が設けられ、突起４４は現像装置案内溝４０と、突起４５は現像装置案内溝４２と係合し、ブラック現像装置６は現像装置案内溝４０および４２の方向に平行移動可能に保持される。同様にシアン現像現像装置７も突起４６および４７が現像装置案内溝４１および４３と係合し、現像装置案内溝４１および４３の方向に平行移動可能に保持される。
【００２８】
一方、ブラック現像装置６の端部にはガイド軸４８が設けられ、サイドフレーム３６に設けた位置案内溝４９と係合し、かつ、軸先端がカム部材５０に設けた溝部５１と係合するように配置してある。同様にシアン現像装置７の端部にもガイド軸５２が設けられ、サイドフレーム３６に設けた位置案内溝５３と係合し、かつ、軸先端がカム部材５０に設けた溝部５１と係合するように配置してある。カム部材５０はモータ５４によって正逆回転駆動可能であり、カム部材の回転によってブラック現像装置６およびシアン現像装置７が移動する。また、図３とは反対のサイドフレーム側にも同様に各現像装置を保持する機構が設けてあり、カム部材５０の外周に設けた伝達歯車５５および伝達軸５６で反対側に設けたカム部材に駆動力を伝達することでブラック現像装置６およびシアン現像装置の移動を円滑に行うことができる。
【００２９】
即ち、突起４４、４５、４６、４７とガイド軸４８、５２と現像装置案内溝４０、４１、４２、４３と位置案内溝４９、５３が本発明の現像装置案内手段であり、カム部材５０およびモータ５４が本発明の駆動手段であり、伝達歯車５５および伝達軸５６は駆動手段の補助機構である。
【００３０】
ここで、ブラック現像装置６およびシアン現像装置７の配置と現像装置案内溝４０、４１、４２、４３、位置案内溝４９、５３の好適な位置関係を図４に示す。図４において、ブラック現像装置６およびシアン現像装置７の現像ローラ１２は略同一位置のブラック・シアン現像ローラ当接位置５９で感光体１と当接する。これによってどちらの現像装置の現像ローラが感光体１に当接しても感光体１の弾性変形する位置が略同一となり、かつ、各現像ローラが感光体１に与える駆動特性も略同一とすることができ、圧接現像条件の均一化と安定化が実現できる。また、現像装置案内溝４０、４１、４２、４３および位置案内溝４９、５３の配置方向としては感光体１のブラック・シアン現像ローラ当接位置５９における法線Ｋに対する現像装置案内溝４０、４２および位置案内溝４９の配置角度αと現像装置案内溝４１、４３および位置案内溝５３の配置角度βが４５゜以下であることが望ましい。配置角度βを４５゜以下とすることで現像装置が離接する際に感光体１の回転方向に与える力が現像ローラの当接方向に与える力よりも小さくすることができ、現像ローラが感光体１と離接する際に現像ローラの食い込みや感光体１の振動が発生しにくくなる。また、マゼンタ・イエロー現像ローラ当接位置６０は、感光体１の長軸方向中心線Ｌに対してブラック・シアン現像ローラ当接位置５９と線対称の位置（角度γが等しい）に設けることで感光体１の弾性変形と現像ローラが感光体１に与える駆動特性をブラック・シアン現像ローラ当接位置５９と同一にすることができる。
【００３１】
さらに、図５から図７によってブラック現像装置６およびシアン現像装置７の感光体１に対する離接動作についてもう少し詳しく説明する。
【００３２】
図５は装置全体が停止状態または待機状態または現像装置交換状態におけるブラック現像装置６とシアン現像装置７の位置を示す画像形成装置の部分断面図である。この状態でブラック現像装置６はバネ５７によって矢印Ｆ方向に付勢され、突起４４および４５が現像装置案内溝４０および４２と係合して位置決めされ、現像ローラ１２は感光体１と大きく離間している。同様にシアン現像装置７もバネ５８によって矢印Ｇ方向に付勢され、突起４６および４７が現像装置案内溝４１および４３と係合して位置決めされ、現像ローラ１２は感光体１と大きく離間している。この状態では各現像装置のアジテータ１０、供給ローラ１１、現像ローラ１２は停止状態である。
【００３３】
次に、図６はブラック現像装置６が現像状態、シアン現像装置７が待機状態である場合のブラック現像装置６とシアン現像装置７の位置を示す画像形成装置の部分断面図である。前述の画像形成が開始され、感光体１上に形成されたブラック用の静電潜像がブラック・シアン現像ローラ当接位置５９に至る前に、モータ５４によってカム部材５０が矢印Ｈ方向に回転し、溝部５１がガイド軸４８を移動させ、バネ５７の付勢に抗してブラック現像装置６は矢印Ｂ方向に移動しつつ、アジテータ１０、供給ローラ１１、現像ローラ１２が回転を開始してブラック現像装置６の現像ローラ１２が当接位置５９で感光体１と当接し、ブラック用の静電潜像を現像する。一方、シアン現像装置７は溝部５１がガイド軸５２に作用せず、突起４６および４７が現像装置案内溝４１および４３と係合しているためにカム部材５０が回動せても移動しない。この時、アジテータ１０、供給ローラ１１、現像ローラ１２は停止状態である。ブラック用の静電潜像の現像が終了すると、カム部材５０がモーター５４によって矢印Ｈとは反対方向に回転し、ブラック現像装置６は図５の状態へ復帰しつつ、ブラック現像装置６のアジテータ１０、供給ローラ１１、現像ローラ１２が停止する。
【００３４】
次に、図７はブラック現像装置６が待機状態、シアン現像装置７が現像状態である場合のブラック現像装置６とシアン現像装置７の位置を示す画像形成装置の部分断面図である。感光体１上に形成されたシアン用の静電潜像がブラック・シアン現像ローラ当接位置５９に至る前に、モータ５４によってカム部材５０が矢印Ｉ方向に回転し、溝部５１がガイド軸５２を移動させ、バネ５８の付勢に抗してシアン現像装置７は矢印Ｊ方向に移動しつつ、アジテータ１０、供給ローラ１１、現像ローラ１２が回転を開始してシアン現像装置７の現像ローラ１２が当接位置５９で感光体１と当接し、シアン用の静電潜像を現像する。一方、ブラック現像装置６は溝部５１がガイド軸４８に作用せず、突起４４および４５が現像装置案内溝４０および４２と係合しているためにカム部材５０が回動せても移動せず、アジテータ１０、供給ローラ１１、現像ローラ１２は停止状態である。シアン用の静電潜像の現像が終了すると、カム部材５０がモーター５４によって矢印Ｉとは反対方向に回転し、シアン現像装置７は図５の状態へ復帰しつつ、シアン現像装置７アジテータ１０、供給ローラ１１、現像ローラ１２が停止する。
【００３５】
マゼンタ現像装置８およびイエロー現像装置９に関してもブラック現像装置６およびシアン現像装置７と同様の構造で感光体１に対して各現像ローラが離接するように構成してあり、説明は省略する。なお、各色現像装置の配置は上記の位置に限定されるものではなく、４色の現像装置の配置を任意に入れ換えても良い。
【００３６】
以上のような構成とすることにより、４色の現像装置を２色づつに分割し、各２色の現像装置を１つのモータの正逆転動作で移動させることで各現像装置の現像ローラを感光体１に対して離接させることが可能となる。
【００３７】
本例のような画像形成装置では効率良く画像形成を行って短時間に画像形成出力を得ることを目的として、例えば、第１色目の現像が終了して第１色目の現像装置が潜像担持体から離間し、第２色目の現像装置が潜像担持体に当接する際に、帯電、潜像記録、潜像担持体からのトナー像の転写などの動作が継続中である場合が多い。このようなカラー画像形成装置の現像装置に一成分圧接現像方式を適応した場合には、各色の現像ローラが感光体に当接する際の衝撃が画質に悪影響を与えることが実験的に明らかであった。そこで、各色の現像ローラの周速度と、各現像装置の離接動作を行うモータの回転速度を適宜制御することで、現像ローラが感光体１と当接する際の衝撃を低減させることにした。本発明における各現像ローラの周速度制御と各現像装置の離接動作を行うモータの回転速度制御を示すタイミングチャートを図８に示す。
【００３８】
図８において、感光体１が回転を開始し所定周速度Ｖ１に達するとレーザー走査光学系が回転動作を開始し、走査光学系が所定の回転速度に到達するとＴＢｋの間でブラック潜像を感光体１上に書き込む。また、ブラック現像装置７とシアン現像装置８を移動させるモータがＴＲ１の間にスローアップ、スローダウンしながら回転し、ブラック現像ローラが感光体１に当接する。これに先立ってブラック現像ローラは周速度が感光体と等速度のＶ１で回転を開始し、現像ローラの周速度がＶ１の状態で現像ローラと感光体１が当接する。ブラック現像ローラと感光体１が当接後、感光体１のブラック潜像の先端が現像位置に至る前に現像ローラの周速度は好適な現像状態を得るためにＶ１からＶ２へ徐々に加速され、ＴＤ１の間でブラック潜像を現像する。ブラックの現像が終了すると現像ローラの周速度は再びＶ２からＶ１へ徐々に減速され、ＴＲ３の間にブラック現像装置７とシアン現像装置８を移動させるモータがＴＲ１とは逆方向にスローアップ、スローダウンしながら回転することでブラック現像ローラが感光体１から離間し、離間後に停止する。
【００３９】
一方、マゼンタ現像装置８とイエロー現像装置９を移動させるモータがＴＤ１の途中のＴＲ２の間でスローアップ、スローダウンしながら回転し、ブラック現像ローラの感光体１からの離間を待たずに感光体１方向への移動を開始し、ブラック現像現像ローラが離間開始直後に感光体１に当接する。当接前後にマゼンタ現像ローラにはブラック現像ローラと同様の速度制御がなされＴＭの間に走査光学系が書き込んだマゼンタ潜像をＴＤ２の間で現像する。マゼンタの現像が終了し、ＴＲ４の間にマゼンタ現像装置８とイエロー現像装置９を移動させるモータがＴＲ２とは逆方向にスローアップ、スローダウンしながら回転することでマゼンタ現像ローラが感光体１から離間する。その際にもマゼンタ現像ローラにはブラック現像ローラと同様の速度制御がなされ、離間後に停止する。
【００４０】
同様に、マゼンタ現像ローラが離間開始直後にＴＲ３で移動したシアン現像ローラが感光体１と当接し、ＴＣの間に走査光学系が書き込んだシアン潜像をＴＤ３の間で現像して、ＴＲ５の間に感光体１から離間し、シアン現像ローラが離間開始直後にＴＲ４で移動したイエロー現像ローラが感光体１と当接し、ＴＹの間に走査光学系が書き込んだイエロー潜像をＴＤ４の間で現像して、ＴＲ６の間に感光体１から離間する。この一連の動作で得られた各色のトナー像を図１の中間転写媒体１６上に重ねて転写することでフルカラー画像が得られる。
【００４１】
なお、図８では現像ローラの離接動作時に感光体に与える衝撃が最小となるように各現像ローラの周速度と感光体の周速度を等速にして離接動作を行う構成としたが、各現像ローラの周速度と感光体の周速度が完全に一致した状態で現像ローラと感光体が離接すると、現像かぶりが顕著となる場合があり、このような場合には各現像ローラの周速度を感光体の周速度よりも１０％程度速くすることでかぶりを軽減することができる。従って、感光体と離接する際の各現像ローラの周速度は感光体の周速度と必ずしも完全に一致させずに略等速であれば良い。
【００４２】
図８で説明した手順で本例の装置を動作させることにより、例えば第１の現像位置で１色目の現像中に２色目の現像装置を第２の現像位置に近接させる予備動作を行い、第１の現像位置で１色目の現像が終了すると、直ちに第２の現像位置で２色目の現像を開始することができる。また、２色目の現像中に１色目の現像装置の待機位置への退避動作と３色目の現像装置を第１の現像位置に近接させる予備動作を行い、第２の現像位置で２色目の現像が終了すると、直ちに第１の現像位置で３色目の現像を開始することができる。従って、前記従来技術に比較して現像装置を切り換えるための時間が画像形成の時間に上乗せされないので、画像の高速出力が可能となる。
【００４３】
さらに、現像装置案内手段と駆動手段を図３のような構成とすることで、図８のＴＲ３およびＴＲ４で示すように、同一集団内の現像装置６、７または８、９を入れ換える際にモータを一方向に回転させるだけで入れ換え動作を行わせることができ、コンパクトで簡便な構成と単純な駆動制御方法で現像装置入れ換え動作が実現できる。
【００４４】
また、現像ローラと感光体を離接する際に各現像装置の現像ローラの周速度を一旦、感光体の周速度と略同一としてから現像ローラを徐々に感光体と離接させることにより、現像ローラの離接動作時に感光体へ与える衝撃が大幅に軽減され、現像ローラの離接動作に伴う色ズレや画像ブレなどの画質劣化が防止できる。また、現像ローラが感光体と離接する際の周速差で現像ローラ上のトナーを飛散させることもなく、装置内部を浮遊トナーで汚染することもない。
【００４５】
さらに、現像前後に現像ローラの周速度を感光体と略等速度、あるいは、感光体の周速度よりも速い速度に徐々に増減速させることで、変速時に感光体に与える衝撃も極めて軽微となり、かぶりがなく、かつ、充分な画像濃度を有する高画質な画像を得ることができる。
【００４６】
【発明の効果】
以上述べたように、本発明の画像形成装置によれば、請求項１の構成により、２つの現像装置を現像装置案内手段に沿って単一の駆動手段で、それぞれの現像ローラが潜像担持体に当接する現像位置に対して交互に離接移動させることで現像装置移動機構の構成を簡便にすることができる。
しかも、２つの現像装置のそれぞれの現像ローラが潜像担持体に当接する各現像位置が略同一位置に設定されているので、２つの現像装置の内どちらの現像装置の現像ローラが潜像担持体に当接しても潜像担持体の弾性変形する位置が略同一となり、かつ、各現像ローラが潜像担持体に与える駆動特性も略同一とすることができ、圧接現像条件の均一化と安定化が実現できる。
【００４７】
また、請求項２の構成により、２つの現像装置を入れ換える際に駆動手段を一方向に回転させるだけで入れ換え動作を行わせることができ、単純な駆動制御方法で現像装置入れ換え動作を実現することができる。
【００４８】
また、請求項３の構成により、現像装置装置案内手段と駆動手段をコンパクトで簡便な構成で実現することができる。
【００４９】
さらに、請求項４または５の構成とすることで、現像装置を待機位置から現像位置まで移動するための時間を画像出力に要する時間に含めずにフルカラーの画像形成が行えるので、カラー画像の高速出力が可能となる。
【図面の簡単な説明】
【図１】本発明の画像形成装置の実施例の全体構成を示す装置断面図である。
【図２】本発明の実施例におけるブラック現像装置６の構成を示す断面図である。
【図３】本発明の実施例におけるブラック現像装置６およびシアン現像装置７の離接動作機構の構造を示す部分断面斜視図である。
【図４】本発明の実施例におけるブラック現像装置６およびシアン現像装置７の配置と現像装置案内溝４０、４１、４２、４３、位置案内溝４９、５３の好適な位置関係を示す部分断面図である。
【図５】本発明の実施例で装置が停止状態または待機状態または現像装置交換状態における部落現像装置６とシアン現像装置７の位置を示す部分断面図である。
【図６】本発明の実施例でブラック現像装置６が現像状態、シアン現像装置７が待機状態である場合のブラック現像装置６とシアン現像装置７の位置を示す部分断面図である。
【図７】本発明の実施例でブラック現像装置６が待機状態、シアン現像装置７が現像状態である場合のブラック現像装置６とシアン現像装置７の位置を示す部分断面図である。
【図８】本発明の実施例における各現像ローラの周速度制御と各現像装置の離接動作を行うモータの回転速度制御を示すタイミングチャートである。
【符号の説明】
１…感光体（潜像担持体）
２…感光体駆動ローラ
３…帯電ローラ
４…レーザー走査光学系
５…感光体補助ローラ
６…ブラック現像装置
７…シアン現像装置
８…マゼンタ現像装置
９…イエロー現像装置
１０…アジテータ
１１…供給ローラ
１２…現像ローラ
１３…現像装置ケース
１４…板バネ
１５…規制部材
１６…中間転写媒体
１７、１８、１９…転写媒体ローラ
２０…一次転写部
２１…感光体クリーナ
２２…除電器
２３…記録シート載置台
２４…記録シート
２５…給紙ローラ
２６…レジストローラ
２７…二次転写部
２８…二次転写ローラ
２９…転写媒体クリーナ
３０…ベルト搬送装置
３１…ハロゲンランプ
３２…ヒートローラ
３３、３４…加圧ローラ
３５…排紙ローラ群
３６…サイドフレーム
３７、３８、３９…現像装置ガイド
４０、４１、４２、４３…現像装置案内溝
４４、４５、４６、４７…突起
４８、５２…ガイド軸
４９、５３…位置案内溝
５０…カム部材
５１…溝部
５４…モータ
５５…伝達歯車
５６…伝達軸
５７、５８…バネ
５９…ブラック・シアン現像ローラ当接位置
６０…マゼンタ・イエロー現像ローラ当接位置[0001]
BACKGROUND OF THE INVENTION
The present invention includes a developing device moving means capable of moving a developing device having a developing roller for visualizing a latent image on a latent image carrier with a developer to a position where the developing device is in contact with a position separated from the latent image carrier. The present invention relates to an image forming apparatus.
[0002]
[Prior art]
As an image forming apparatus capable of forming a color image using an electrophotographic process, the apparatus has a plurality of developing devices, and a developing device of a desired color is selected and moved to a developing position through a moving path for development. An image forming apparatus to perform has been proposed.
[0003]
As a prior art of this type of image forming apparatus, for example, Japanese Patent Laid-Open No. 63-220267 can be cited, which is provided with a plurality of developing devices and is dedicated to a black developing device and develops a color other than black for a latent image carrier. There are a total of two development positions dedicated to the device. When a development device of a color other than black is selected and the selected development device moves to the development position via the movement path, the color of the development apparatus close to the movement path is selected. A latent image was formed in order and developed.
[0004]
[Problems to be solved by the invention]
However, in the image forming apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-220267, high-speed output is possible in two-color image formation using black and single colors (for example, cyan, magenta, and yellow). In full-color image formation, when the developing device at the development position is replaced, there is only one movement path from the development position to the standby position. Therefore, the next development is performed until the development device existing at the development position moves to the standby position. There is a problem that the apparatus cannot be moved to the developing position, that is, it takes time to switch the developing apparatus and high-speed output cannot be performed.
[0005]
In general, when a full-color image is formed using an electrophotographic process, it is necessary to perform image formation four times on a photoreceptor using a developing device including cyan, magenta, yellow, and black toners. The time required for output is four times longer than that for forming a monochrome image. However, the time required for actual image formation as in the above-described prior art is further increased by the switching time of the developing device, so that the image formation time becomes long and hinders high-speed output.
[0006]
Further, since the developing device is housed outside the apparatus main body in the prior art, the developing apparatus moving mechanism and the moving path are complicated and large-scale because it is transferred to the main body after selecting the desired developing apparatus outside the apparatus. This hinders downsizing of the apparatus.
[0007]
The present invention has been made in view of the above-described prior art, and prevents a time required for moving the developing device from the standby position to the developing position from being included in the time required for image output, so that a color image capable of high-speed output is provided. It is a first object to provide a forming apparatus, and a second object is to provide a compact color image forming apparatus with a simple and compact moving mechanism of a developing device.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention comprises a latent image carrier on which electrostatic latent images are formed by charging and image exposure, and a developer carried on the surface. A plurality of developing devices each including a developing roller that visualizes the electrostatic latent image on the latent image carrier while being in contact with the latent image carrier, and the developing roller includes the developing roller. In the image forming apparatus, the developing device moving means moves the developing device to the developing position, and the developing device moving means moves the developing device to a standby position separated from the latent image carrier. A developing device guide means provided for each developing device that guides to the position or the standby position, and the plurality of developing devices are moved along the corresponding developing device guide means to move relative to the latent image carrier. Drive to separate The driving means is configured such that one of the driving means moves the two developing devices of the plurality of developing devices along the corresponding developing device guide means to the latent image carrier. A single driving unit that alternately contacts and separates the developing rollers, and the developing positions at which the developing rollers of the two developing devices come into contact with the latent image carrier are set at substantially the same position. The developing device guide means of each of the developing devices is a developing device guide means for guiding the developing roller of the corresponding developing device to the developing position set at substantially the same position.
[0009]
Further, in the image forming apparatus according to claim 2, the single driving unit can rotate forward and reverse, and one of the two developing devices can move to the latent image by rotating the single driving unit in one direction. The other of the two developing devices is separated from the image carrier, and the other of the two developing devices is in contact with the latent image carrier, and the other driving device rotates in the reverse direction so that the other of the two developing devices is the latent image. It is separated from the carrier, and one of the two developing devices is in contact with the latent image carrier.
[0010]
According to a third aspect of the present invention, in the image forming apparatus, the developing device guides of the two developing devices are provided on a pair of convex portions provided on both sides of the corresponding developing device end and on the apparatus main body side, respectively. The drive unit includes a pair of developing device guide grooves that engage with the convex portion, and the driving unit drives the cam member with a cam member having a groove portion that engages with the convex portion of each of the developing device guide units. It consists of a motor that can rotate forward and reverse.
[0011]
Furthermore, the image forming apparatus according to claim 4 is provided with a plurality of the developing device moving means.
Further, the image forming apparatus according to claim 5 includes the two developing device moving means and the four developing devices, and two of the four developing devices move the two developing devices. The two developing devices can be moved by one developing device moving means, and the other two developing devices of the four developing devices can be moved by the other developing device moving means of the two developing device moving means. It is made possible.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on examples.
[0013]
FIG. 1 is a cross-sectional view showing the overall configuration of an embodiment of an image forming apparatus according to the present invention, which is a printer apparatus capable of recording color images. The schematic operation of the first embodiment will be described with reference to FIG.
[0014]
In FIG. 1, a photoreceptor 1 as a latent image carrier is formed by coating an organic photoreceptor on an endless belt base material such as a nickel electroformed tube or a polyethylene terephthalate resin whose surface is coated with an aluminum layer. Is driven to rotate by a photosensitive member driving roller 2 that rotates in the direction of arrow A. The photoconductor 1 may not be formed in a belt shape, and an organic photoconductor may be directly applied to the surface of an aluminum pipe material, and the photoconductor drive roller 2 may be eliminated. A charging roller 3 is disposed on the outer periphery of the photosensitive member 1 as a charging unit, and a voltage of about −1200 V is applied from a high-voltage power source (not shown), and the surface of the photosensitive member 1 is made uniform while rotating in contact with the photosensitive member 1. Charge. Here, in this example, the charging roller 2 is used as the charging means, but a corona charger can also be used.
[0015]
The photosensitive member 1 whose surface is uniformly charged by the charging unit is selectively scanned and exposed as a first color according to, for example, black image information by the laser scanning optical system 4 serving as an exposure unit. A latent image is formed. In this example, the laser scanning optical system 3 is used as the exposure means. However, an exposure optical system constituted by an LED array or a liquid crystal shutter can also be used as the exposure means.
[0016]
On the downstream side of the laser scanning optical system 4 in the rotation direction of the photosensitive member, a photosensitive member auxiliary roller 5 that urges the photosensitive member 1 in a direction to contact the photosensitive member driving roller 2 is disposed. The force is smoothly transmitted to the photosensitive member 1 and at the same time, the exposure position on the photosensitive member 1 is prevented from being shifted due to the separating operation of the developing device described later.
[0017]
On the downstream side of the photoconductor auxiliary roller 5 in the photoconductor rotation direction, black, cyan, magenta, and yellow toners are stored as developers, respectively, and developing devices 6, 7, 8, 9 is arranged.
[0018]
Here, the configuration of each developing device will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the configuration of the black developing device 6. In FIG. 2, the agitator 10 is agitated for the purpose of preventing toner (not shown) filled in the developing device from aggregating and depositing it uniformly in the depth direction of FIG. The supply roller 11 is a roller in which a conductive elastic body is disposed on the outer periphery of the shaft member. The supply roller 11 is pressed by the developing roller 12 while rotating in the direction of arrow C, and supplies toner to the developing roller 12 while being frictionally charged. The developing roller 12 supplied with the toner rotates in the direction of arrow D, and the regulating member 15 fixed to the free end side of the leaf spring 14 having one end fixed to the developing device case 13 comes into pressure contact with the developing roller 12 so that the toner is supplied. Regulate the layer thickness to an appropriate amount. The developing roller 12 is constructed by providing an elastic member such as rubber on the surface of the metal roller, or by adding surface treatment with an appropriate surface roughness to the surface of the metal roller, and the regulating member 15 is made of rubber, resin or metal. Etc. can be configured. The developing device having such a configuration is brought into contact with the photosensitive member 1 and, if necessary, a potential difference is provided between the photosensitive member 1 and the developing roller 12 so that the latent image on the photosensitive member is visualized with toner. The The other color developing devices 7, 8, and 9 have the same configuration.
[0019]
Returning to FIG. 1, the electrostatic latent image for black formed by the laser scanning optical system 4 moves in advance in the direction of arrow B from the position of the two-dot chain line in accordance with the rotation of the photosensitive member 1 in the direction of arrow A. The black toner image is developed by the black developing device 6 brought into pressure contact with 1 to form a black toner image. At this time, the developing devices 7, 8, 9 of other colors are separated from the photosensitive member 1.
[0020]
An intermediate transfer medium 16 is wound around transfer medium rollers 17, 18, and 19 adjacent to the photoconductor 1 on the downstream side of the developing device in the rotation direction of the photoconductor, and the peripheral speed of the photoconductor 1 is driven by a drive source (not shown). Are driven at the same speed. The intermediate transfer medium 16 is configured as a conductive film having an appropriate conductive resistance by applying a conductive agent such as carbon to a material such as polyester, polycarbonate, or polyethylene terephthalate. The transfer medium roller 17 or 18 is connected to a high voltage power source (not shown), and a high voltage is selectively applied by a switch means (not shown). The photosensitive member 1 is in contact with the intermediate transfer medium 8 supported between the transfer medium rollers 17 and 18 at the primary transfer portion 20. As described above, the black toner image formed on the surface of the photoreceptor 1 reaches the primary transfer portion 20 as the photoreceptor 1 rotates in the direction of arrow A. At this time, a voltage of about +2000 V is applied to the transfer medium roller 17 or 18 from a high voltage power source (not shown), and the black toner image formed on the surface of the photoreceptor 1 is transferred to the intermediate transfer medium 16 by the primary transfer unit 20. The
[0021]
The photosensitive member 1 having the black toner image transferred to the intermediate transfer medium 16 further rotates in the direction of arrow A, and the toner remaining on the surface of the photosensitive member 1 is scraped off by the photosensitive member cleaner 21 constituted by a cleaner blade or the like. Further, the surface of the photosensitive member 1 is uniformly exposed by the static eliminator 22 to remove the residual charges on the photosensitive member 1, and image formation can be performed again.
[0022]
When all of the desired black toner image is transferred to the intermediate transfer medium 16, the black developing device 6 moves in the direction opposite to the arrow B and retracts to the initial standby position.
[0023]
Subsequently, the second to fourth color images (magenta, cyan, and yellow) are sequentially superimposed and recorded on the intermediate transfer medium 16 in the same procedure as the first color.
[0024]
When the superimposition of the color toner image on the intermediate transfer medium 16 is finished, the recording sheet 24 stacked and placed on the recording sheet placing table 23 is started to be fed by the paper feed roller 25, and is not shown in a friction separation type or not shown. Only the uppermost sheet is fed by the nail separation type single sheet separating means. The leading end in the conveyance direction of the recording sheet 24 that has been separated and fed by one sheet reaches a registration roller 26 that has been temporarily stopped by a clutch means (not shown) and stopped. The recording sheet 24 has its front end in the conveying direction abutting against the nip portion of the registration roller 26 to correct the oblique feeding, and the registration roller 26 is not shown in the clutch means in synchronization with the position of the color toner image superimposed on the intermediate transfer medium 16. Thus, the feeding is resumed in the direction of the secondary transfer unit 27 by starting driving. As a result, the recording sheet 24 reaches the secondary transfer portion 27.
[0025]
When the leading edge of the recording sheet 24 enters the secondary transfer portion 27, a voltage of about −2000 V is applied to the secondary transfer roller 28 from a high voltage power source (not shown), and a color toner image formed on the surface of the intermediate transfer medium 16 is formed. It is transferred to the surface of the recording sheet 24. A transfer medium cleaner 29 composed of a cleaner blade or the like moves in the direction of arrow E and contacts the intermediate transfer medium 16 after the color toner image has been transferred, and the toner remaining on the surface of the intermediate transfer medium 16 is scraped off. When the scraping is completed, the transfer medium cleaner 29 moves in the direction opposite to the arrow E and retracts.
[0026]
The recording sheet 24 to which the color toner image has been transferred is conveyed by a belt conveying device 30, a heat roller 32 having a rod-shaped halogen lamp 31 therein, and a pressure roller 33 that rotates in pressure contact with the heat roller 32. , 34, the recording sheet 24 to which the color toner image has been transferred is nipped and conveyed while being heated and pressed to fix the toner image. The recording sheet 24 on which the toner image is fixed is discharged to the outside of the apparatus by a discharge roller group 35, and the color image recording is completed.
[0027]
Next, a moving unit in which each developing device performs a contact / separation operation with respect to the photoreceptor 1 will be described. FIG. 3 is a partial cross-sectional perspective view showing the structure of the separation / contact operation mechanism of the black developing device 6 and the cyan developing device 7 of the image forming apparatus. Are distributed. In FIG. 3, developing device guides 37, 38, and 39 are arranged on the side frame 36 that holds each component, the developing device guide 37 includes developing device guide grooves 40 and 41, and the developing device guide 38 includes The developing device guide groove 42 is provided, and the developing device guide 39 is provided with a developing device guide groove 43. Protrusions 44 and 45 are provided at the end of the black developing device 6. The protrusion 44 engages with the developing device guide groove 40, the protrusion 45 engages with the developing device guide groove 42, and the black developing device 6 has the developing device guide groove 40. And 42 so as to be movable in parallel. Similarly, the protrusions 46 and 47 engage with the developing device guide grooves 41 and 43 in the cyan developing and developing device 7 and are held so as to be movable in the direction of the developing device guide grooves 41 and 43.
[0028]
On the other hand, a guide shaft 48 is provided at the end of the black developing device 6, engages with a position guide groove 49 provided in the side frame 36, and a shaft tip engages with a groove 51 provided in the cam member 50. It is arranged as follows. Similarly, a guide shaft 52 is provided at the end of the cyan developing device 7, and engages with a position guide groove 53 provided in the side frame 36, and a shaft tip engages with a groove 51 provided in the cam member 50. It is arranged as follows. The cam member 50 can be driven forward and backward by a motor 54, and the black developing device 6 and the cyan developing device 7 are moved by the rotation of the cam member. Similarly, a mechanism for holding each developing device is also provided on the side frame side opposite to FIG. 3, and a cam member provided on the opposite side by a transmission gear 55 and a transmission shaft 56 provided on the outer periphery of the cam member 50. The black developing device 6 and the cyan developing device can be moved smoothly by transmitting the driving force to.
[0029]
That is, the protrusions 44, 45, 46, 47, the guide shafts 48, 52, the developing device guide grooves 40, 41, 42, 43 and the position guide grooves 49, 53 are the developing device guide means of the present invention, and the cam member 50 and The motor 54 is the driving means of the present invention, and the transmission gear 55 and the transmission shaft 56 are auxiliary mechanisms of the driving means.
[0030]
Here, FIG. 4 shows a preferred positional relationship between the arrangement of the black developing device 6 and the cyan developing device 7 and the developing device guide grooves 40, 41, 42, 43 and the position guide grooves 49, 53. In FIG. 4, the developing roller 12 of the black developing device 6 and the cyan developing device 7 contacts the photosensitive member 1 at a black / cyan developing roller contact position 59 at substantially the same position. As a result, the position at which the photosensitive member 1 is elastically deformed is substantially the same regardless of which developing roller of the developing device comes into contact with the photosensitive member 1, and the driving characteristics that each developing roller applies to the photosensitive member 1 are also substantially the same. And uniform and stable pressure development conditions. The developing device guide grooves 40, 41, 42, 43 and the position guide grooves 49, 53 are arranged in the developing device guide grooves 40, 42 with respect to the normal K at the black / cyan developing roller contact position 59 of the photoreceptor 1. It is desirable that the arrangement angle α of the position guide groove 49 and the arrangement angle β of the developing device guide grooves 41 and 43 and the position guide groove 53 are 45 ° or less. By setting the arrangement angle β to 45 ° or less, the force applied in the rotation direction of the photosensitive member 1 when the developing device is separated from and contacting can be made smaller than the force applied in the contact direction of the developing roller. It is difficult for the developing roller to bite and the photosensitive member 1 to vibrate when it is in contact with the 1. Further, the magenta / yellow developing roller contact position 60 is provided in a line-symmetrical position (the angle γ is equal) to the black / cyan developing roller contact position 59 with respect to the longitudinal center line L of the photoreceptor 1. The elastic deformation of the photosensitive member 1 and the driving characteristics given to the photosensitive member 1 by the developing roller can be made the same as the black / cyan developing roller contact position 59.
[0031]
Further, the contact / separation operation of the black developing device 6 and the cyan developing device 7 with respect to the photoreceptor 1 will be described in more detail with reference to FIGS.
[0032]
FIG. 5 is a partial cross-sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the entire apparatus is in a stopped state, a standby state, or a developing device replacement state. In this state, the black developing device 6 is biased in the direction of arrow F by the spring 57, and the protrusions 44 and 45 are positioned by engaging with the developing device guide grooves 40 and 42, so that the developing roller 12 is largely separated from the photoreceptor 1. ing. Similarly, the cyan developing device 7 is also urged in the direction of arrow G by the spring 58, the protrusions 46 and 47 are positioned by engaging with the developing device guide grooves 41 and 43, and the developing roller 12 is greatly separated from the photoreceptor 1. Yes. In this state, the agitator 10, the supply roller 11, and the developing roller 12 of each developing device are in a stopped state.
[0033]
Next, FIG. 6 is a partial sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the developing state and the cyan developing device 7 is in the standby state. Before the image formation is started and before the electrostatic latent image for black formed on the photosensitive member 1 reaches the black / cyan developing roller contact position 59, the cam member 50 is rotated in the direction of arrow H by the motor 54. Then, the groove 51 moves the guide shaft 48, the black developing device 6 moves in the arrow B direction against the bias of the spring 57, and the agitator 10, supply roller 11, and developing roller 12 start rotating. The developing roller 12 of the black developing device 6 comes into contact with the photosensitive member 1 at the contact position 59 and develops the black electrostatic latent image. On the other hand, since the groove 51 does not act on the guide shaft 52 and the protrusions 46 and 47 are engaged with the developing device guide grooves 41 and 43, the cyan developing device 7 does not move even if the cam member 50 rotates. At this time, the agitator 10, the supply roller 11, and the developing roller 12 are in a stopped state. When the development of the electrostatic latent image for black is completed, the cam member 50 is rotated in the direction opposite to the arrow H by the motor 54, and the black developing device 6 returns to the state shown in FIG. 10. The supply roller 11 and the developing roller 12 are stopped.
[0034]
Next, FIG. 7 is a partial sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the standby state and the cyan developing device 7 is in the developing state. Before the cyan electrostatic latent image formed on the photoreceptor 1 reaches the black / cyan developing roller contact position 59, the motor 54 rotates the cam member 50 in the direction of arrow I, and the groove 51 forms the guide shaft 52. The cyan developing device 7 moves in the direction of arrow J against the bias of the spring 58, and the agitator 10, supply roller 11, and developing roller 12 start to rotate, and the developing roller 12 of the cyan developing device 7 is moved. Comes into contact with the photosensitive member 1 at the contact position 59 and develops the electrostatic latent image for cyan. On the other hand, in the black developing device 6, the groove 51 does not act on the guide shaft 48 and the protrusions 44 and 45 are engaged with the developing device guide grooves 40 and 42, so that the black developing device 6 does not move even when the cam member 50 rotates. The agitator 10, the supply roller 11, and the developing roller 12 are in a stopped state. When the development of the electrostatic latent image for cyan is completed, the cam member 50 is rotated in the direction opposite to the arrow I by the motor 54, and the cyan developing device 7 returns to the state shown in FIG. The supply roller 11 and the developing roller 12 are stopped.
[0035]
The magenta developing device 8 and the yellow developing device 9 have the same structure as that of the black developing device 6 and the cyan developing device 7 so that the developing rollers are in contact with and separated from the photosensitive member 1, and description thereof is omitted. The arrangement of each color developing device is not limited to the above position, and the arrangement of the four color developing devices may be arbitrarily replaced.
[0036]
With the above configuration, the four-color developing device is divided into two colors, and each two-color developing device is moved by the forward / reverse operation of one motor to sensitize the developing roller of each developing device. It can be separated from the body 1.
[0037]
In an image forming apparatus such as this example, for the purpose of efficiently forming an image and obtaining an image forming output in a short time, for example, the development of the first color is completed and the developing device of the first color carries the latent image When the developing device for the second color moves away from the body and contacts the latent image carrier, operations such as charging, latent image recording, and transfer of the toner image from the latent image carrier are often continued. When the one-component pressure contact developing method is applied to the developing device of such a color image forming apparatus, it is experimentally clear that the impact when the developing roller of each color comes into contact with the photoreceptor adversely affects the image quality. It was. Therefore, the impact when the developing roller comes into contact with the photosensitive member 1 is reduced by appropriately controlling the peripheral speed of the developing roller of each color and the rotational speed of the motor that performs the contact / separation operation of each developing device. FIG. 8 is a timing chart showing the peripheral speed control of each developing roller and the rotational speed control of a motor that performs the contact / separation operation of each developing device in the present invention.
[0038]
In FIG. 8, when the photosensitive member 1 starts rotating and reaches a predetermined peripheral speed V1, the laser scanning optical system starts rotating, and when the scanning optical system reaches a predetermined rotating speed, the black latent image is exposed between TBk. Write on body 1. Further, a motor for moving the black developing device 7 and the cyan developing device 8 rotates while slowing up and slowing down during TR1, and the black developing roller comes into contact with the photosensitive member 1. Prior to this, the black developing roller starts rotating at a peripheral speed V1 equal to that of the photosensitive member, and the developing roller and the photosensitive member 1 come into contact with each other while the peripheral speed of the developing roller is V1. The peripheral speed of the developing roller is gradually accelerated from V1 to V2 in order to obtain a suitable developing state before the black developing roller and the photosensitive member 1 come into contact and before the leading edge of the black latent image on the photosensitive member 1 reaches the developing position. The black latent image is developed between TD1 and TD1. When the black development is completed, the peripheral speed of the developing roller is gradually reduced again from V2 to V1, and the motor that moves the black developing device 7 and the cyan developing device 8 between TR3 slows up and slows in the direction opposite to TR1. By rotating while down, the black developing roller is separated from the photoreceptor 1 and stops after the separation.
[0039]
On the other hand, a motor for moving the magenta developing device 8 and the yellow developing device 9 rotates while slowing up and slowing down between TR2 in the middle of TD1, and the photosensitive member without waiting for the black developing roller to be separated from the photosensitive member 1. The movement in one direction is started, and the black developing roller comes into contact with the photoreceptor 1 immediately after the start of separation. Before and after the contact, the magenta developing roller is controlled at the same speed as the black developing roller, and the magenta latent image written by the scanning optical system during TM is developed during TD2. When magenta development is completed, the motor that moves the magenta developing device 8 and the yellow developing device 9 during TR4 is rotated while slowing up and slowing down in the direction opposite to TR2, so that the magenta developing roller is moved from the photoreceptor 1. Separate. At that time, the magenta developing roller is controlled at the same speed as the black developing roller and stops after being separated.
[0040]
Similarly, the cyan developing roller moved in TR3 immediately after the separation start of the magenta developing roller comes into contact with the photosensitive member 1, and the cyan latent image written by the scanning optical system during TC is developed during TD3. The yellow developing roller that is separated from the photosensitive member 1 and moved by TR4 immediately after the separation of the cyan developing roller comes into contact with the photosensitive member 1, and the yellow latent image written by the scanning optical system during TY is transferred between TD4. Develop and separate from the photoreceptor 1 during TR6. A full-color image is obtained by transferring the toner images of the respective colors obtained by this series of operations on the intermediate transfer medium 16 of FIG.
[0041]
In FIG. 8, the separation operation is performed by setting the circumferential speed of each developing roller and the circumferential speed of the photosensitive member to be constant so that the impact given to the photosensitive member during the separation operation of the developing roller is minimized. If the developing roller and the photosensitive member are in contact with each other in a state where the peripheral speed of each developing roller and the photosensitive member are completely coincident with each other, the development fog may become prominent. The fog can be reduced by making the speed about 10% faster than the peripheral speed of the photoreceptor. Accordingly, the peripheral speed of each developing roller at the time of contacting / separating with the photosensitive member does not necessarily coincide completely with the peripheral speed of the photosensitive member, and may be substantially constant.
[0042]
By operating the apparatus of this example according to the procedure described in FIG. 8, for example, a preliminary operation is performed in which the developing device for the second color is brought close to the second developing position during the development of the first color at the first developing position. When the first color development is completed at the first development position, the second color development can be started immediately at the second development position. In addition, during the development of the second color, the first color developing device is retracted to the standby position, and the preliminary operation of bringing the third color developing device close to the first developing position is performed, and the second color developing is performed at the second developing position. When the process is finished, the development of the third color can be started immediately at the first development position. Accordingly, since the time for switching the developing device is not added to the time for image formation as compared with the prior art, high-speed image output is possible.
[0043]
Further, the developing device guide means and the driving means are configured as shown in FIG. 3, so that when the developing devices 6, 7 or 8, 9 in the same group are replaced, as shown by TR3 and TR4 in FIG. It is possible to perform the replacement operation only by rotating in one direction, and the development device replacement operation can be realized with a compact and simple configuration and a simple drive control method.
[0044]
Further, when the developing roller and the photosensitive member are separated from each other, the circumferential speed of the developing roller of each developing device is temporarily made substantially the same as the circumferential speed of the photosensitive member, and then the developing roller is gradually separated from and brought into contact with the photosensitive member. The impact on the photosensitive member during the contact / separation operation is greatly reduced, and image quality deterioration such as color shift and image blur due to the contact / separation operation of the developing roller can be prevented. Further, the toner on the developing roller is not scattered due to the difference in peripheral speed when the developing roller comes in contact with the photoreceptor, and the interior of the apparatus is not contaminated with floating toner.
[0045]
Furthermore, by gradually increasing or decreasing the peripheral speed of the developing roller to approximately the same speed as the photosensitive member before or after development, or to a speed faster than the peripheral speed of the photosensitive member, the impact applied to the photosensitive member at the time of shifting becomes extremely light, It is possible to obtain a high-quality image having no fog and having a sufficient image density.
[0046]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, according to the configuration of claim 1, the two developing devices are moved along the developing device guide means by a single driving means, and each developing roller carries a latent image. The structure of the developing device moving mechanism can be simplified by moving the developing device in contact with the body alternately.
In addition, since the developing positions at which the developing rollers of the two developing devices come into contact with the latent image carrier are set at substantially the same position, the developing roller of either of the two developing devices carries the latent image. The position where the latent image carrier is elastically deformed even when abutting on the body can be made substantially the same, and the driving characteristics given to each latent image carrier by each developing roller can be made almost the same, making the pressure development conditions uniform. Stabilization can be realized.
[0047]
According to the second aspect of the present invention, when the two developing devices are switched, it is possible to perform the switching operation only by rotating the driving means in one direction, and to realize the developing device switching operation by a simple drive control method. Can do.
[0048]
According to the third aspect of the present invention, the developing device guide unit and the driving unit can be realized with a compact and simple configuration.
[0049]
Furthermore, by adopting the structure of claim 4 or 5, full-color image formation can be performed without including the time required for moving the developing device from the standby position to the developing position in the time required for image output. Output is possible.
[Brief description of the drawings]
FIG. 1 is an apparatus cross-sectional view illustrating an overall configuration of an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing a configuration of a black developing device 6 in an embodiment of the present invention.
FIG. 3 is a partial cross-sectional perspective view showing the structure of a separation / contact operation mechanism of a black developing device 6 and a cyan developing device 7 in an embodiment of the present invention.
FIG. 4 is a partial sectional view showing a preferred positional relationship between the arrangement of the black developing device 6 and the cyan developing device 7 and the developing device guide grooves 40, 41, 42, 43 and the position guide grooves 49, 53 in the embodiment of the present invention. It is.
FIG. 5 is a partial cross-sectional view showing positions of a part developing device 6 and a cyan developing device 7 when the apparatus is in a stopped state, a standby state, or a developing device replacement state in the embodiment of the present invention.
FIG. 6 is a partial cross-sectional view showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the developing state and the cyan developing device 7 is in the standby state in the embodiment of the present invention.
7 is a partial cross-sectional view showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the standby state and the cyan developing device 7 is in the developing state in the embodiment of the present invention. FIG.
FIG. 8 is a timing chart showing the peripheral speed control of each developing roller and the rotational speed control of a motor that performs the contact / separation operation of each developing device in an embodiment of the present invention.
[Explanation of symbols]
1 ... Photoconductor (latent image carrier)
2 ... Photoconductor drive roller
3 ... Charging roller
4 ... Laser scanning optical system
5 ... Photoreceptor auxiliary roller
6 ... Black developing device
7 ... Cyan developing device
8. Magenta developing device
9 ... Yellow developing device
10 ... Agitator
11 ... Supply roller
12 ... Developing roller
13 ... Developer case
14 ... leaf spring
15 ... Regulating member
16: Intermediate transfer medium
17, 18, 19 ... transfer medium roller
20 ... Primary transfer section
21. Photoconductor cleaner
22 ... Static eliminator
23 ... Recording sheet placement table
24 ... Recording sheet
25. Paper feed roller
26 ... Registration roller
27. Secondary transfer section
28 ... Secondary transfer roller
29. Transfer medium cleaner
30 ... Belt conveyor
31 ... Halogen lamp
32 ... Heat roller
33, 34 ... pressure roller
35 ... Discharge roller group
36 ... side frame
37, 38, 39 ... developing device guide
40, 41, 42, 43 ... developing device guide groove
44, 45, 46, 47 ... projections
48, 52 ... Guide shaft
49, 53 ... Position guide groove
50. Cam member
51 ... Groove
54 ... Motor
55 ... Transmission gear
56 ... Transmission shaft
57, 58 ... Spring
59: Black / cyan developing roller contact position
60: Magenta yellow developing roller contact position

Claims

Charging a latent image bearing member and image exposure is performed the electrostatic latent image is formed and, the latent image carrier carrying a developer on the surface and in contact with the electrostatic latent image on the latent image bearing member moving a plurality of developing devices to a developing roller with each for visualizing, said developing device to a waiting position where the developing roller that is separated from the latent image bearing member and a developing position abutting on the latent image bearing member An image forming apparatus having a developing device moving means
The developing device moving means, said plurality of developing devices to a developing unit guide means provided for each of the developing devices respectively guided to the developing position or the standby position, the developing device corresponding plurality of developing devices, respectively Drive means for moving along the guide means to separate from and contact the latent image carrier ,
One driving means among the driving means moves two developing devices out of the plurality of developing devices along the corresponding developing device guide means so as to alternately come in contact with the latent image carrier. A single drive means
The developing positions at which the developing rollers of the two developing devices come into contact with the latent image carrier are set at substantially the same position,
Each of the developing device guide means of the two developing devices is a developing device guide means for guiding the developing roller of the corresponding developing device to the developing position set at substantially the same position. .

The single driving means can be rotated forward and backward, and when the single driving means rotates in one direction, one of the two developing devices is separated from the latent image carrier, and the two developing devices the other device is in contact with the latent image carrier, the other of said single said two developing apparatus by driving means rotates in the opposite direction away from the latent image bearing member, and the two developing The image forming apparatus according to claim 1, wherein one of the apparatuses contacts the latent image carrier .

Each developing device guide means of the two developing devices includes a pair of convex portions provided on both sides of the corresponding developing device end portion, and a pair of developing device guide grooves provided on the apparatus main body side and engaged with the convex portions. Ri Do from the said drive means includes a cam member having a groove for engagement with each of the convex portions of the respective developing devices guiding means, that consisting of a forward and reverse rotatable motor for driving said cam member The image forming apparatus according to claim 1 or 2,

The developing device that has a plurality of moving means image forming apparatus according to claim 1 or 2 or 3, wherein the.

Wherein comprising four said developing device with has two developing device moving means, the four two developing device of the developing device is movable in one developing device moving means of said two developing device moving means The other two developing devices of the four developing devices can be moved by another developing device moving means of the two developing device moving means. 5. The image forming apparatus according to 4.