JP3594214B2

JP3594214B2 - Multiple image forming device

Info

Publication number: JP3594214B2
Application number: JP34882497A
Authority: JP
Inventors: 沢秀雄相
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1997-12-18
Filing date: 1997-12-18
Publication date: 2004-11-24
Anticipated expiration: 2017-12-18
Also published as: JPH11184214A

Description

【０００１】
【発明の属する技術分野】
本発明は、感光体を帯電する帯電手段と、感光体上に画像情報に応じた光を照射して静電潜像を形成するための露光手段と、感光体上に形成された静電潜像をトナ−で現像するための現像手段を含む画像形成手段を２以上備え、それぞれの画像形成手段で同一感光体上に複数の画像、例えば異なる色の２以上の画像、を形成する複数画像形成装置に関する。
【０００２】
【従来の技術】
例えば２色画像画像形成装置では、１つの画像形成手段にて黒画像を形成し、もう１つの画像形成手段にて赤，青など、黒色とは異なる色画像を形成する。３色画像形成装置では例えばイエロ−画像，マゼンタ画像およびシアン画像を形成する。４色画像形成装置では例えばブラック画像，イエロ−画像，マゼンタ画像およびシアン画像を形成する。
【０００３】
同一の感光体上に選択的に又は順次に画像を形成する場合、感光体の移動方向に関して下流側にある帯電器が上流側で先行して形成される画像のトナ−で汚れる。この汚れにより下流側の帯電器が放電ムラを生じて下流側で形成する画像に黒筋が現われる。
【０００４】
特開平８−１４６７１９号公報に開示の多色画像形成装置は、感光体移動の上流側に第１帯電器を、下流側に第２帯電器を備える２色画像形成装置において、上流側で第１色の画像（第１画像）を形成し下流側で第２色の画像（第２画像）を形成する２色画像形成時に、第１画像のトナーが第２帯電器のグリッドやシールド部に付着するのを防止するため、第２帯電器のグリッド，シールドに感光体上のトナー層電位と同等以上の電圧を印加する。すなわち、第２色の画像を形成するときに、感光体上のトナー層電位よりも同等以上の電圧を第２帯電器のグリッド，シールドに印加する。
【０００５】
特開平９−１１４１８７号公報に開示の画像形成装置は、上流側で第１画像を形成し下流側では第２画像を形成しない第１画像形成時に、第２帯電器を感光体から退避させる方向に移動させ、第２帯電器へのトナー付着を防止する機構を備えている。
【０００６】
【発明が解決しようとする課題】
前記特開平８−１４６７１９号公報の多色画像形成装置は、第１画像と第２画像を並行して形成するときの、第１画像のトナ−による第２帯電器の汚れは防止されるが、第１画像を形成し第２画像を形成しないときに、第２帯電器が第１画像のトナ−で汚れる。感光体上のトナー像は、反転現像により現像されているため、感光体との静電気力が弱く、感光体近傍にアース部材が有ればアース部材に向かって逆飛翔してしまう。これによって、第１画像を形成し第２画像を形成しないときに第２帯電器が汚れる。また、上流側現像器から飛散、又は落下してくるトナーによる、下流側第２帯電器の汚れは防止できず、結果的には、下流側帯電器のワイヤー汚れ，グリッド汚れが発生し、放電ムラとなってしまう。
【０００７】
前記特開平９−１１４１８７号によれば、単色画像形成時に使用していない下流側第２帯電器を感光体から退避させる方向に移動させるので、たしかにアース部材と感光体との距離が広ければトナーの逆飛翔現象は防止可能となる。しかし、帯電器を移動させるための機構が必要となり、コストアップとなり又、装置自体も大型化してしまう欠点を有している。
【０００８】
本発明は、上流側で第１画像を形成し下流側では第２画像を形成しない時においても、下流側第２帯電器のトナ−汚れを防止することを目的とする。
【０００９】
【課題を解決するための手段】
（１）本発明は、感光体(1)を帯電するための第１帯電手段(2)と、感光体上に画像情報に応じた光を照射して静電潜像を形成するための第１露光手段(3)と、感光体上に形成された静電潜像をトナ−で現像するための反転現像方式の第１現像手段(4)を含む第１画像形成手段(2〜4)；および、感光体(1)を帯電するための第２帯電手段(5)と、感光体上に画像情報に応じた光を照射して静電潜像を形成するための第２露光手段(6)と、感光体上に形成された静電潜像を現像するための第２現像手段(7)を含み、感光体(1)の移動方向に関して第１画像形成手段(2〜4)の下流側にある第２画像形成手段(5〜7)；を少くとも備える複数画像形成装置において、
第１画像形成手段 (2 〜 4) で作像するが第２画像形成手段 (5 〜 7) では作像しない作像モ− ドのとき、第２帯電手段 (5) の汚れを防止するために第１画像形成手段が感光体上に形成するトナ−と同極性の、放電開始電圧以下の電圧を第２帯電手段 (5) に印加し、第２画像形成手段 (5 〜 7) を用いて画像を形成する作像モ−ドのときは、潜電潜像を形成するための電圧を第２帯電手段 (5) に印加する付勢制御手段(16,17,Hw2a,Hw2b)、を備えることを特徴とする。
【００１０】
なお、理解を容易にするためにカッコ内には、図面に示し後述する実施例の対応要素の符号又は対応事項を、参考までに付記した。
【００１１】
これによれば、第１画像形成手段(2〜4)のみで画像を形成する作像モ−ド（単色黒記録モ−ド）のときに、第２帯電手段 (5) にトナ−と同極性の電圧 (-1 〜 -2KV) を印加するので、感光体から第２帯電手段 (5) への逆飛翔トナーが押さえられ、第２帯電手段 (5) のトナ−汚れによる画像上の黒筋発生が防止される。複雑な構成を必要とせず、低コストにて汚れ防止が行なわれる。又、第２帯電手段 (5) に印加する電圧を、放電開始電圧以下に押さえるので、オゾンの発生量は少い。
【００１２】
【発明の実施の形態】
（２）第２帯電手段(5)は放電ワイヤを備える帯電器であり、前記付勢制御手段(16,17,Hw2a,Hw2b)は、第１画像形成手段（2〜4）で作像するが第２画像形成手段 (5 〜 7) では作像しない作像モ−ドのとき、第２帯電手段(5)の放電ワイヤのトナ−汚れを防止するために第１画像形成手段（ 2 〜 4 ）が感光体上に形成するトナ−と同極性の、コロナ放電開始電圧以下の電圧を第２帯電手段(5)の放電ワイヤに印加し、第２画像形成手段(5 〜 7)を用いて画像を形成する作像モ−ドのときは、潜電潜像を形成するための電圧を第２帯電手段 (5) の放電ワイヤに印加する。
【００１３】
第１画像形成手段(2〜4)のみで画像を形成する作像モ−ド（単色黒記録モ−ド）のときに、第２帯電手段(5)の放電ワイヤにトナ−と同極性の電圧(-1〜-2KV)を印加するので、感光体から第２帯電手段(5)の放電ワイヤへの逆飛翔トナーが押さえられ、放電ワイヤのトナ−汚れによる画像上の黒筋発生が防止される。複雑な構成を必要とせず、低コストにて汚れ防止が行なわれる。又、第２帯電手段(5)の放電ワイヤに印加する電圧を、コロナ放電開始電圧以下に押さえるので、オゾンの発生量は少い。
【００１４】
（３）第２帯電手段は放電ワイヤ，グリッドおよびシ−ルドを備える帯電器であり、付勢制御手段は、第１画像形成手段のみにより画像を形成する作像モ−ドのとき、第１画像形成手段が感光体上に形成するトナ−と同極性の、絶対値が、放電ワイヤ印加電圧＞グリッド印加電圧≧シ−ルド印加電圧、なる関係の電圧を、放電ワイヤ，グリッドおよびシ−ルドに印加する。第２帯電手段の放電ワイヤ，グリッドおよびシ−ルドのトナ−汚れが防止されると共に、放電ワイヤに印加する電圧を最も高くする事により、画像にもっとも現れる放電ムラによる黒筋を防止する効果が高い。
【００１５】
（４）第２画像形成手段 (5 〜 7) による静電潜像形成用の電圧を発生する主電源回路，第２帯電手段 (5) の放電ワイヤのトナ−汚れを防止するための、第１画像形成手段 (2 〜 4) が感光体上に形成するトナ−と同極性の、コロナ放電開始電圧以下の電圧を発生する補助電源回路、および、前記主電源回路および補助電源回路が発生する電圧の一方を選択的に第２帯電手段 (5) の放電ワイヤに印加する切換リレーを備え、前記付勢制御手段は前記切換リレーを用いて、第１画像形成手段 (2 〜 4) のみで画像を形成する作像モ−ドのとき前記コロナ放電開始電圧以下の電圧を第２帯電手段の放電ワイヤに印加し、第２画像形成手段 (5 〜 7) を用いて画像を形成する作像モ−ドのときは前記、潜電潜像を形成するための電圧を第２帯電手段 (5) の放電ワイヤに印加する、上記（２）又は（３）に記載の複数画像形成装置。
【００１６】
本発明の他の目的および特徴は、図面を参照した以下の実施例の説明より明らかになろう。
【００１７】
【実施例】
図１に本発明の一実施例の主要部を示す。感光体１は、図中の矢印方向に回転する。
（１）単色黒記録モ−ドの画像形成：
スコロトロン方式の第１帯電器２は感光体ドラムをマイナス帯電し、第１露光装置３が画像情報によって変調されたレ−ザビ−ムを帯電面に照射する。これにより画像を表わす静電潜像が感光体ドラム１の表面に形成される。２成分磁気ブラシ現像方式の第１現像器４が静電潜像にトナ−を与えて、感光体ドラム１上の静電潜像を反転現像により顕像化する。この実施例では、第１現像器４には黒色現像剤が収納されており、感光体ドラム１上の静電潜像は黒色トナ−により黒画像に顕像化する。
【００１８】
感光体ドラム１上の黒画像が、レジストロ−ラ８で送られる図示しない転写紙に、転写帯電器９で転写され、転写紙は分離帯電器１０で感光体ドラム１から分離されて搬送ベルト１１で図示しない定着器に送られる。
【００１９】
この単色記録モ−ドでは、スコロトロン方式の第２帯電器５には、感光体ドラムの黒画像が到達する直前から通過終了直後まで、黒画像のトナ−の第２帯電器５への逆飛翔を防止するために、第２帯電器５の放電ワイヤには、コロナ放電開始電圧以下の−１〜−２ＫＶの電圧が印加され、グリッドおよびシールド部には、−８９０Ｖ前後の電圧が印加される。グリッドとシールドに印加される電圧は、グリッド電圧の方がシールド電圧よりも高いか又は、同等の電圧である。
【００２０】
第２露光装置は露光しない状態になっており、この実施例では赤色現像剤を収納した第２現像器７は、非磁性非接触１成分現像方式の現像器であり、感光体ドラム１の表面より離れた位置に退避している。
【００２１】
（２）単色赤記録モ−ドの画像形成：
第１帯電器２が感光体ドラム１を均一にマイナス帯電させる。第１露光装置３は露光しない状態になっている。第１現像器４は第２現像器７に駆動を与えるため回転しているが、現像バイアスがＯＮされているため、感光体ドラム１を現像しない。
【００２２】
スコロトロン方式の第２帯電器５が更に感光体ドラム１をマイナス帯電する。このとき、第２帯電器５には、上述の単色黒記録モ−ドの画像形成のときとは異なる電圧が印加される。具体的には、放電ワイヤには−４．５〜−６ＫＶ、グリッドおよびシールド部には、−８９０Ｖの電圧が印加される。
【００２３】
第２露光装置６が画像情報によって変調されたレ−ザビ−ムを帯電面に照射する。これにより画像を表わす静電潜像が感光体ドラム１の表面に形成される。第２現像器７が図示していない移動手段により、感光体ドラム１表面に近い現像位置に駆動されて、現像を行う。この実施例では、第２現像器７には赤色トナ−が収納されており、感光体ドラム１上の静電潜像は赤色トナ−により赤画像に顕像化する。
【００２４】
感光体ドラム１上の赤画像が、レジストロ−ラ８で送られる図示しない転写紙に、転写帯電器９で転写され、転写紙は分離帯電器１０で感光体ドラム１から分離されて搬送ベルト１１で図示しない定着器に送られる。
【００２５】
（３）２色記録モ−ドの画像形成：
感光体ドラム１は第１帯電器２によりマイナスに帯電され、第１露光装置３により静電潜像が形成され、第１現像器４が静電潜像を黒色トナ−で顕像化し、これにより黒画像（第１画像）が感光体ドラム１上に形成される。つぎに、第２帯電器５が、黒画像の上から、感光体ドラム１をマイナスに帯電させる。このとき第２帯電器５に、上述の単色赤記録モ−ドの画像形成のときと同じ値の電圧が印加される。第２露光装置６が、黒画像形成部以外の部分を画像情報に基づいて露光して静電潜像を形成し、第２現像器７がこの静電潜像を赤色トナ−で顕像化し、赤画像（第２画像）を生成する。
【００２６】
感光体ドラム１上の黒画像（第１画像）および赤画像（第２画像）が、レジストロ−ラ８で送られる図示しない転写紙に、転写帯電器９で転写され、転写紙は分離帯電器１０で感光体ドラム１から分離されて搬送ベルト１１で図示しない定着器に送られる。
【００２７】
（４）第２帯電器５に印加する電圧の切換え：
第２帯電器５の放電ワイヤには、切換リレ−１７を介して、単色黒記録モ−ドのときには補助電源回路Ｈｗ２ｂが発生する電圧（−１〜−２ＫＶ）が、また単色赤記録モ−ドおよび２色記録モ−ドのときには主電源回路Ｈｗ２ａが発生する帯電電圧（−４．５〜−６ＫＶ）が印加される。切換リレ−１７は、その電気コイルに通電がないＯＦＦのときには主電源回路Ｈｗ２ａを第２帯電器５の放電ワイヤに接続しているが、電気コイルに通電があるＯＮのときには補助電源回路Ｈｗ２ｂを第２帯電器５の放電ワイヤに接続する。
【００２８】
上述の各モ−ドのときの、第１帯電器２および第２帯電器５に電圧を印加する電源回路の電圧発生（ＯＮ）／非発生（ＯＦＦ）の組合せを、次の表１に示す。
【００２９】
【表１】

【００３０】
感光体ドラム１周りには上述の画像形成要素の他に、転写済の感光体面を掃除するクリ−ニング装置１２，感光体面を除転する除電ランプ１３，画像濃度を検出するための反射型光センサ１４，転写紙の非分離（ペ−パジャム）を検出するための紙センサ１５ならびに図示しないイレ−サなども設けられている。これらは公知のものであり、本発明の実施に直接には関係しないため、説明は省略する。
【００３１】
図示しないオペレ−タ操作ボ−ドおよびホストコンピュ−タからの指示入力に応答して上述の（１）〜（３）の画像形成を制御するプリントコントロ−ラ１６は、各種センサからの電気信号を処理し、各種電気的アクチュエ−タ（電気モ−タ，ソレノイド，クラッチ）に通電する入，出力電気回路およびマイクロコンピュ−タを含み、指示入力によって指定される作像モ−ド，用紙サイズ，プリント枚数，画像処理パラメ−タ等の作像条件に従って、感光体ドラム１の所定小回転量を１単位とする、ドラム回転同期パルスのカウント値対各電気要素のオン／オフのスケジュ−ル（タイミング）と、その繰返し回数を設定する。このタイミング設定の中の、帯電器に関するタイミング設定項目を図２に示す。
【００３２】
図２を参照すると、帯電器（チャ−ジャ）の設定においては、指示入力によって表わされる作像モ−ドおよび用紙サイズ（画像形成サイズ）に従って、第１画像形成用の帯電器２のオン／オフタイミングを定め（ＴＤ１）、第２画像形成用の帯電器５のオン／オフタイミングを定め（ＴＤ２）、転写帯電器９のオン／オフタイミングを定め、また、分離帯電器１０のオン／オフタイミングを定める。なお、帯電器が出力電圧可変型のものである場合には、オンタイミングに出力電圧指定デ−タが割り宛てられ、電源回路（Ｈｗ１，Ｈｇ１，Ｈｗ２ａ，Ｈｗ２ｂ，Ｈｇ２，Ｈｗ３，Ｈｗ４）にはオンタイミングに出力電圧指定デ−タが与えられ、電源回路は指定デ−タに対応する電圧を発生し出力する。
【００３３】
この実施例では、第１帯電器２の放電ワイヤ、および、グリッド，シ−ルド部に帯電電圧を与える帯電電源回路Ｈｗ１およびＨｇ１，第２帯電器５の放電ワイヤ、および、グリッド，シ−ルド部に帯電電圧を与える主電源回路Ｈｗ２ａおよびＨｇ２、ならびに、第２帯電器５の放電ワイヤ１に、コロナ放電開始電圧以下の電圧を与える補助電源回路Ｈｗ２ｂは、いずれも出力電圧を手動調整するための可変抵抗器を含むものであり、それぞれ所定範囲内で出力電圧を調整しうる。これらの電源回路に関して本実施例では、プリントコントロ−ラ１６はオン／オフタイミングのみを定め、出力電圧の指定又は調整は行なわない。
【００３４】
図３に、第２帯電器５のオン／オフタイミングの設定（ＴＤ２）の内容を示す。ここでプリントコントロ−ラ１６は、入力指定が表わす作像モ−ドに対応して、それが単色赤記録モ−ドあるいは２色記録モ−ドのときには、プリントスタ−トに応じた画像形成動作開始タイミングを起点とした、第２帯電器５のオンタイミングに、主電源回路Ｈｗ２ａをＯＮ（電圧発生），補助電源回路Ｈｗ２ｂをＯＦＦ（非発生）、および、切換リレ−１７をＯＦＦ（Ｈｗ２ａの電圧を放電ワイヤに供給）にするデ−タを宛て、そして、用紙サイズで定まる第２帯電器５のオフタイミングに、主電源回路Ｈｗ２ａをＯＦＦ（非発生），補助電源回路Ｈｗ２ｂをＯＦＦ（非発生）、および、切換リレ−１７をＯＦＦにするデ−タを宛てる（ステップＳ２１〜２４）。
【００３５】
入力指定が表わす作像モ−ドが単色黒記録モ−ドのときには、第２帯電器５の上述のオンタイミングに、主電源回路Ｈｗ２ａをＯＦＦ（非発生），補助電源回路Ｈｗ２ｂをＯＮ（電圧発生）、および、切換リレ−１７をＯＮ（Ｈｗ２ｂの電圧を放電ワイヤに供給）にするデ−タを宛て、そして、用紙サイズで定まる第２帯電器５のオフタイミングに、主電源回路Ｈｗ２ａをＯＦＦ（非発生），補助電源回路Ｈｗ２ｂをＯＦＦ（非発生）、および、切換リレ−１７をＯＦＦにするデ−タを宛てる（ステップＳ２５，Ｓ２６）。
【００３６】
各電気要素のオン／オフのタイミング（スケジュ−ル）と、その繰返し回数を設定し、画像形成動作を開始するとプリントコントロ−ラ１６は、設定したタイミングで各電気要素をオン／オフし、これを設定した回数分（プリント指定枚数分）繰返す。これによって、第１帯電器２および第２帯電器５は、指定作像モ−ドに対応して表１に示すようにＯＮ／ＯＦＦが制御される。
【００３７】
単色黒記録モ−ドでは、感光体ドラム１上に形成された黒画像のトナーは、ネガポジ現像の為、感光体ドラム１との付着力が弱く、近傍にあるアース部材に逆飛翔してしまう。従来であれば、第２帯電器５は、単色黒記録モ−ドではアース状態となっていた為、その放電ワイヤ，グリッドおよびシ−ルド部にトナーが付着し、放電ムラの原因となるが、本発明では、第２帯電器５に補助電源回路Ｈｗ２ｂが発生する電圧を印加する事により、逆飛翔するトナーが第２帯電器５へ付着するのが防止される。２色記録モ−ドおよび単色赤記録モ−ドのときは、第２帯電器５に画像形成用の高圧電圧が主電源回路２ａから印加され、しかも第２帯電器５のグリッド，シールド部にも電圧が印加されるので、第２帯電器５への逆飛翔現象は発生しない。
【００３８】
上述の本発明の実施例の場合と、従来の条件の場合において、単色黒記録モ−ドで実際にランニングテストを行い、第２帯電器５の放電ワイヤ汚れによる黒筋発生枚数を比較すると以下の様な値となり、本発明の効果が明らかに認められる。
【００３９】
ランニングは、Ａ４Ｙ６％チャートの連続コピーとした(各条件とも２台ラン)。
１．第２帯電器５がアース状態の場合：２０Ｋ，３０Ｋ枚にて黒筋発生（Ｋは×1000を意味する），
２．第２帯電器５のグリッド，シールド部に電圧印加：５Ｋ，１０Ｋ枚にて黒筋発生，
３．第２帯電器５の放電ワイヤ，グリッド，シールド部に電圧印加（本発明の実施例）：１００Ｋ枚コピーにおいても、黒筋発生せず。
【００４０】
感光体ドラム１に形成された黒画像のトナーは、アース部材に向かって逆飛翔し、感光体ドラム１の周りに発生している気流に乗り、より遠くまで付着する。上記１．の場合は、第２帯電器５の放電ワイヤ，グリッド，シールド部がすべてアース状態となっている為、感光体ドラム１に最も近接したグリッド，シールド部から、トナー付着が始まり、グリッドのトナー補獲作用が少なくなると、より奥側にある帯電ワイヤーに付着し放電ムラとなる。上記２．の場合には、感光体ドラム１に最も近接しているグリッド，シールド部にトナーと同極性の電圧が印加されている為、グリッド，シールド部にはトナーが捕獲されず、アース状態である放電ワイヤに向かってトナーが逆飛翔する為、より早い枚数にて放電ムラが発生する。上記３．の場合には、第２帯電器５の放電ワイヤ，グリッド，シールド部のすべてにトナーと同極性の電圧が印加されており、かつ放電ワイヤの印加電圧がグリッド，シールド部に印加される電圧よりも高い為、より帯電ワイヤーにトナー付着しずらい条件である為、１００Ｋ枚コピーにおいても、黒筋の発生が防止できたものである。
【００４１】
なお、２色画像形成を例にして実施例を説明してきたが、３以上の画像形成手段を備える３色以上の多色画像形成装置に対しても本発明は有効である。また、各画像形成手段にて形成する画像色は任意であり、上述の実施例の黒および赤に限る必要はない。
【図面の簡単な説明】
【図１】本発明の一実施例の主要部を示すブロック図である。
【図２】図１に示すプリントコントロ−ラ１６の、帯電器付勢タイミング設定の項目を示すフロ−チャ−トである。
【図３】図２に示す「チャ−ジャ５のＯＮ／ＯＦＦタイミング設定」（ＴＤ３）の内容を示すフロ−チャ−トである。
【符号の説明】
１：感光体ドラム２：第１帯電器
３：第１露光装置４：第１現像器
５：第２帯電器６：第２露光装置
７：第２現像器８：レジストロ−ラ
９：転写帯電器１０：分離帯電器
１１：搬送ベルト１２：クリ−ニング装置
１３：除電ランプ１４：反射型光センサ
１５：ペ−パセンサ１６プリントコントロ−ラ
１７：切換リレ− Ｈｗ１〜Ｈｗ４，Ｈｇ１，Ｈｇ２：電源回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging unit for charging a photoconductor, an exposure unit for irradiating light on the photoconductor in accordance with image information to form an electrostatic latent image, and an electrostatic latent image formed on the photoconductor. A plurality of image forming units including two or more image forming units including a developing unit for developing an image with toner, wherein a plurality of images, for example, two or more images of different colors, are formed on the same photosensitive member by the respective image forming units. It relates to a forming apparatus.
[0002]
[Prior art]
For example, in a two-color image forming apparatus, a black image is formed by one image forming unit, and a color image different from black, such as red and blue, is formed by another image forming unit. The three-color image forming apparatus forms, for example, an yellow image, a magenta image, and a cyan image. The four-color image forming apparatus forms, for example, a black image, a yellow image, a magenta image, and a cyan image.
[0003]
When an image is selectively or sequentially formed on the same photoconductor, a charger located downstream with respect to the moving direction of the photoconductor is contaminated with toner of an image formed earlier on the upstream. Due to this stain, the charger on the downstream side causes discharge unevenness, and black streaks appear on the image formed on the downstream side.
[0004]
A multicolor image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-146719 discloses a two-color image forming apparatus having a first charger upstream of the movement of a photoconductor and a second charger downstream thereof. When forming a one-color image (first image) and forming a second-color image (second image) on the downstream side, when forming a two-color image, the toner of the first image is applied to the grid and shield portion of the second charger. To prevent adhesion, a voltage equal to or higher than the potential of the toner layer on the photoconductor is applied to the grid and shield of the second charger. That is, when forming a second color image, a voltage equal to or higher than the potential of the toner layer on the photoconductor is applied to the grid and shield of the second charger.
[0005]
An image forming apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 9-114187 discloses a direction in which a second charger is retracted from a photoconductor at the time of forming a first image on an upstream side and not forming a second image on a downstream side. And a mechanism for preventing toner from adhering to the second charger.
[0006]
[Problems to be solved by the invention]
The multicolor image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-146719 prevents contamination of the second charger by toner of the first image when forming the first image and the second image in parallel. When the first image is formed and the second image is not formed, the second charger is stained with the toner of the first image. Since the toner image on the photoreceptor is developed by reversal development, the electrostatic force with the photoreceptor is weak, and if there is a grounding member near the photoreceptor, the toner image will fly backward toward the grounding member. As a result, the second charger is soiled when the first image is formed and the second image is not formed. Further, the contamination of the downstream second charger by the toner scattered or dropped from the upstream developing device cannot be prevented. As a result, wire contamination and grid contamination of the downstream charger occur, and discharge unevenness occurs. Will be.
[0007]
According to Japanese Patent Application Laid-Open No. Hei 9-114187, the downstream second charger, which is not used for forming a single-color image, is moved in a direction to retreat from the photoconductor, so that if the distance between the ground member and the photoconductor is large, toner Reverse flight phenomenon can be prevented. However, a mechanism for moving the charger is required, which leads to an increase in cost and an increase in the size of the apparatus itself.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to prevent toner contamination of the downstream second charger even when the first image is formed on the upstream side and the second image is not formed on the downstream side.
[0009]
[Means for Solving the Problems]
(1) The present invention provides a first charging unit (2) for charging a photoreceptor (1), and a first charging unit (2) for irradiating light on a photoreceptor in accordance with image information to form an electrostatic latent image. (1) First image forming means (2-4) including an exposing means (3) and a reversal developing type first developing means (4) for developing an electrostatic latent image formed on a photoreceptor with toner. And second charging means (5) for charging the photoreceptor (1), and second exposure means for irradiating light on the photoreceptor in accordance with image information to form an electrostatic latent image ( 6), and a second developing means (7) for developing the electrostatic latent image formed on the photoconductor, and the first image forming means (2-4) with respect to the moving direction of the photoconductor (1). A plurality of image forming apparatuses including at least downstream second image forming means (5 to 7);
First image forming means (2-4) in the image forming Suruga second image forming means (5-7) in no imaging Sakuzomo - when de, to prevent contamination of the second charging unit (5) Then, a voltage having the same polarity as the toner formed on the photoreceptor by the first image forming means and equal to or lower than the discharge starting voltage is applied to the second charging means (5) , and the second image forming means (5 to 7) is used. In the image forming mode in which the image is formed by using the image forming apparatus, the energizing control means (16, 17, Hw2a, Hw2b) for applying a voltage for forming a latent latent image to the second charging means (5) is provided. It is characterized by having.
[0010]
In addition, in order to facilitate understanding, in the parentheses, reference numerals or corresponding items of the corresponding elements of the embodiment shown in the drawings and described later are added for reference.
[0011]
According to this, in the image forming mode (monochromatic black recording mode ) in which an image is formed only by the first image forming means (2 to 4) , the second charging means (5) is the same as the toner. Since a polarity voltage (-1 to -2 KV) is applied , the toner that flies backward from the photoconductor to the second charging means (5) is suppressed, and black on the image due to toner contamination of the second charging means (5). Streaks are prevented. Dirt prevention is performed at low cost without requiring a complicated configuration. Further, since the voltage applied to the second charging means (5) is kept below the discharge starting voltage, the amount of ozone generated is small.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
(2) a second charging unit (5) is a charging device comprising a discharge wire, the biasing control means (16,17, Hw2a, Hw2b) is imaged by the first image forming means (2-4) In the image forming mode in which the image is not formed by the second image forming means (5 to 7) , the first image forming means ( 2 to 2 ) is used to prevent the discharge wire of the second charging means (5) from being stained by toner. 4 ) Applying a voltage of the same polarity as the toner formed on the photoreceptor but lower than the corona discharge starting voltage to the discharge wire of the second charging means (5) , and using the second image forming means (5 to 7) In the image forming mode in which the latent image is formed, a voltage for forming a latent electrostatic latent image is applied to the discharge wire of the second charging means (5) .
[0013]
Sakuzomo to form an image in only the first image forming means (2-4) - de (monochrome black recording mode - de) when, the discharge wire of the second charging unit (5) toner - the same polarity since application of a voltage (-1～- 2 KV), reverse flying toner is pressed from the photoconductor to the discharge wire of the second charging unit (5), discharge wire of toner - black muscle occurs in the image due to contamination Is prevented. Dirt prevention is performed at low cost without requiring a complicated configuration. Further, since the voltage applied to the discharge wire of the second charging means (5) is suppressed to be equal to or lower than the corona discharge starting voltage, the amount of generated ozone is small.
[0014]
(3) The second charging means is a charger having a discharge wire, a grid and a shield, and the bias control means is a first charging means in the image forming mode for forming an image only by the first image forming means. The absolute value of the polarity of the toner formed on the photoreceptor by the image forming means, and the absolute value of the voltage is such that discharge wire applied voltage> grid applied voltage ≧ shield applied voltage, the discharge wire, grid and shield are applied. Is applied. Toner contamination of the discharge wire, grid and shield of the second charging means is prevented, and the highest voltage applied to the discharge wire prevents black streaks due to discharge unevenness which appear most in an image. high.
[0015]
(4) A main power supply circuit for generating a voltage for forming an electrostatic latent image by the second image forming means (5 to 7) , and a second power supply circuit for preventing toner stains on a discharge wire of the second charging means (5) . toner first image forming means (2-4) is formed on the photosensitive member - the auxiliary power supply circuit for generating the same polarity, the voltage below the corona discharge starting voltage, and the main power supply circuit and the auxiliary power supply circuit generates A switching relay for selectively applying one of the voltages to the discharge wire of the second charging means (5) , wherein the energizing control means uses the switching relay and controls only the first image forming means (2 to 4) ; In an image forming mode for forming an image, a voltage lower than the corona discharge starting voltage is applied to the discharge wire of the second charging means, and an image is formed using the second image forming means (5 to 7). mode - wherein when the de, applying a voltage to form the latent electrostatic latent image on the second discharge wire of the charging means (5) That, a plurality image forming apparatus according to (2) or (3).
[0016]
Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.
[0017]
【Example】
FIG. 1 shows a main part of an embodiment of the present invention. The photoconductor 1 rotates in the direction of the arrow in the figure.
(1) Image formation in single-color black recording mode:
A scorotron first charger 2 negatively charges the photosensitive drum, and a first exposure device 3 irradiates a charged surface with a laser beam modulated by image information. As a result, an electrostatic latent image representing an image is formed on the surface of the photosensitive drum 1. A first developing device 4 of a two-component magnetic brush developing system gives toner to the electrostatic latent image to visualize the electrostatic latent image on the photosensitive drum 1 by reversal development. In this embodiment, the first developing device 4 contains a black developer, and the electrostatic latent image on the photosensitive drum 1 is visualized into a black image by a black toner.
[0018]
The black image on the photosensitive drum 1 is transferred to a transfer paper (not shown) fed by a registration roller 8 by a transfer charger 9, and the transfer paper is separated from the photosensitive drum 1 by a separation charger 10 and conveyed by a conveyor belt 11. Is sent to a fixing device (not shown).
[0019]
In the single-color recording mode, the toner of the black image flies back to the second charger 5 from immediately before the black image on the photosensitive drum reaches the end of the passage to the second charger 5 of the scorotron system. In order to prevent this, a voltage of −1 to −2 KV or less, which is equal to or lower than the corona discharge starting voltage, is applied to the discharge wire of the second charger 5, and a voltage of about −890 V is applied to the grid and the shield part. . The voltage applied to the grid and the shield is such that the grid voltage is higher than or equal to the shield voltage.
[0020]
The second exposure device is in a non-exposure state. In this embodiment, the second developing device 7 containing the red developer is a non-magnetic non-contact one-component developing type developing device. It has been evacuated to a more distant position.
[0021]
(2) Image formation in monochromatic red recording mode:
The first charger 2 uniformly and negatively charges the photosensitive drum 1. The first exposure device 3 is not exposed. The first developing device 4 is rotating to give a drive to the second developing device 7, but does not develop the photosensitive drum 1 because the developing bias is ON.
[0022]
The scorotron-type second charger 5 further negatively charges the photosensitive drum 1. At this time, a different voltage is applied to the second charger 5 than in the above-described monochrome image forming mode. Specifically, a voltage of -4.5 to -6 KV is applied to the discharge wire, and a voltage of -890 V is applied to the grid and the shield portion.
[0023]
The second exposure device 6 irradiates the charged surface with a laser beam modulated by image information. As a result, an electrostatic latent image representing an image is formed on the surface of the photosensitive drum 1. The second developing device 7 is driven by a moving unit (not shown) to a developing position near the surface of the photosensitive drum 1 to perform development. In this embodiment, a red toner is stored in the second developing unit 7, and the electrostatic latent image on the photosensitive drum 1 is visualized as a red image by the red toner.
[0024]
The red image on the photosensitive drum 1 is transferred to a transfer paper (not shown) sent by a registration roller 8 by a transfer charger 9, and the transfer paper is separated from the photosensitive drum 1 by a separation charger 10 and conveyed by a conveyor belt 11. Is sent to a fixing device (not shown).
[0025]
(3) Image formation in two-color recording mode:
The photoreceptor drum 1 is negatively charged by a first charger 2, an electrostatic latent image is formed by a first exposure device 3, and a first developing device 4 visualizes the electrostatic latent image with a black toner. As a result, a black image (first image) is formed on the photosensitive drum 1. Next, the second charger 5 charges the photosensitive drum 1 negatively from above the black image. At this time, a voltage having the same value as that in the above-described image formation in the monochromatic red recording mode is applied to the second charger 5. The second exposure device 6 forms an electrostatic latent image by exposing portions other than the black image forming portion based on the image information, and the second developing device 7 visualizes the electrostatic latent image with a red toner. , A red image (second image).
[0026]
A black image (first image) and a red image (second image) on the photosensitive drum 1 are transferred to a transfer paper (not shown) fed by a registration roller 8 by a transfer charger 9, and the transfer paper is separated by a separation charger. At 10, the photosensitive drum 1 is separated from the photosensitive drum 1 and sent to a fixing device (not shown) by a conveyor belt 11.
[0027]
(4) Switching of voltage applied to second charger 5:
The voltage (-1 to -2 KV) generated by the auxiliary power supply circuit Hw2b in the monochromatic black recording mode and the monochromatic red recording mode are applied to the discharge wire of the second charger 5 via the switching relay 17. In the two-color recording mode, the charging voltage (-4.5 to -6 KV) generated by the main power supply circuit Hw2a is applied. The switching relay 17 connects the main power supply circuit Hw2a to the discharge wire of the second charger 5 when the electric coil is turned off and the auxiliary power supply circuit Hw2b is connected when the electric coil is turned on. Connected to the discharge wire of the second charger 5.
[0028]
Table 1 below shows combinations of voltage generation (ON) / non-generation (OFF) of the power supply circuit for applying a voltage to the first charger 2 and the second charger 5 in each mode described above. .
[0029]
[Table 1]

[0030]
Around the photoreceptor drum 1, in addition to the above-described image forming elements, a cleaning device 12 for cleaning the transferred photoreceptor surface, a neutralizing lamp 13 for revolving the photoreceptor surface, and a reflection type light for detecting an image density. A sensor 14, a paper sensor 15 for detecting non-separation (paper jam) of transfer paper, an eraser (not shown), and the like are also provided. Since these are publicly known and are not directly related to the implementation of the present invention, description thereof will be omitted.
[0031]
The print controller 16 which controls the image formation of the above (1) to (3) in response to an operator operation board (not shown) and an instruction input from the host computer provides electric signals from various sensors. , Including input and output electric circuits and microcomputers for energizing various electric actuators (electric motors, solenoids, clutches), image forming mode specified by instruction input, paper size The count value of the drum rotation synchronizing pulse and the ON / OFF schedule of each electric element, with the predetermined small rotation amount of the photosensitive drum 1 as one unit according to image forming conditions such as the number of prints, image processing parameters, and the like. (Timing) and the number of repetitions are set. FIG. 2 shows timing setting items for the charger in the timing setting.
[0032]
Referring to FIG. 2, in setting the charger (charger), the first image forming charger 2 is turned on / off in accordance with the image forming mode and the paper size (image forming size) indicated by the instruction input. The off timing is determined (TD1), the on / off timing of the second image forming charger 5 is determined (TD2), the on / off timing of the transfer charger 9 is determined, and the on / off of the separation charger 10 is determined. Determine the timing. If the charger is of a variable output voltage type, output voltage designation data is assigned to the ON timing, and the power supply circuit (Hw1, Hg1, Hw2a, Hw2b, Hg2, Hw3, Hw4) is supplied to the power supply circuit. Output voltage designation data is given at the on timing, and the power supply circuit generates and outputs a voltage corresponding to the designated data.
[0033]
In this embodiment, the discharge wires of the first charger 2 and the charging power supply circuits Hw1 and Hg1 for applying a charging voltage to the grid and shield portions, the discharge wires of the second charger 5, and the grid and shield portions The main power supply circuits Hw2a and Hg2 for applying a charging voltage to the unit and the auxiliary power supply circuit Hw2b for applying a voltage equal to or lower than the corona discharge start voltage to the discharge wire 1 of the second charger 5 are used for manually adjusting the output voltage. And the output voltage can be adjusted within a predetermined range. In this embodiment, with respect to these power supply circuits, the print controller 16 determines only the ON / OFF timing and does not specify or adjust the output voltage.
[0034]
FIG. 3 shows the contents of the setting (TD2) of the ON / OFF timing of the second charger 5. Here, the print controller 16 corresponds to the image forming mode indicated by the input designation, and when the mode is the monochromatic red recording mode or the two-color recording mode, the image formation corresponding to the print start is performed. The main power supply circuit Hw2a is turned on (voltage generation), the auxiliary power supply circuit Hw2b is turned off (non-generation), and the switching relay 17 is turned off (Hw2a) at the on timing of the second charger 5 starting from the operation start timing. The main power supply circuit Hw2a is turned off (non-generated), and the auxiliary power supply circuit Hw2b is turned off (at the off timing of the second charger 5 determined by the paper size). Non-occurrence) and data for turning off the switching relay 17 (steps S21 to S24).
[0035]
When the image formation mode indicated by the input designation is the monochromatic black recording mode, the main power supply circuit Hw2a is turned off (not generated) and the auxiliary power supply circuit Hw2b is turned on (voltage) at the above-described ON timing of the second charger 5. The main power supply circuit Hw2a is turned on when the switching relay 17 is turned on (the voltage of Hw2b is supplied to the discharge wire), and when the second charger 5 is turned off according to the paper size. OFF (not generated), data for turning off the auxiliary power supply circuit Hw2b (not generated), and turning off the switching relay 17 are sent (steps S25 and S26).
[0036]
The on / off timing (schedule) of each electric element and the number of repetitions are set, and when the image forming operation is started, the print controller 16 turns on / off each electric element at the set timing. Is repeated for the set number of times (for the specified number of prints). As a result, ON / OFF of the first charger 2 and the second charger 5 is controlled as shown in Table 1 corresponding to the designated image forming mode.
[0037]
In the monochromatic black recording mode, the black image toner formed on the photosensitive drum 1 has a weak adhesion to the photosensitive drum 1 due to negative-positive development, and flies back to a nearby ground member. . In the prior art, the second charger 5 is grounded in the single-color black recording mode, so that toner adheres to the discharge wire, grid, and shield portion, which causes uneven discharge. According to the present invention, the voltage generated by the auxiliary power supply circuit Hw2b is applied to the second charger 5, so that the toner that flies backward is prevented from adhering to the second charger 5. In the two-color recording mode and the monochromatic red recording mode, a high voltage for image formation is applied to the second charger 5 from the main power supply circuit 2a. Since the voltage is also applied to the second charging device 5, the reverse flying phenomenon to the second charger 5 does not occur.
[0038]
A running test was actually performed in the single-color black recording mode under the above-described embodiment of the present invention and under the conventional conditions, and the number of black streaks caused by the discharge wire contamination of the second charger 5 was compared. And the effect of the present invention is clearly recognized.
[0039]
The running was a continuous copy of the A4Y6% chart (two runs for each condition).
1. When the second charger 5 is in the ground state: black streaks occur at 20K and 30K sheets (K means × 1000),
2. Voltage applied to grid and shield of second charger 5: Black streaks occurred at 5K and 10K sheets,
3. Voltage application to discharge wire, grid and shield part of second charger 5 (Embodiment of the present invention): Black streaks did not occur even after copying 100K sheets.
[0040]
The toner of the black image formed on the photosensitive drum 1 flies back toward the ground member, rides on the airflow generated around the photosensitive drum 1, and adheres farther. The above 1. In the case of (2), since the discharge wire, grid, and shield of the second charger 5 are all in the ground state, the toner starts to adhere from the grid and shield closest to the photosensitive drum 1, and the toner of the grid is supplemented. When the catching action is reduced, it adheres to the charging wire on the deeper side, resulting in uneven discharge. The above 2. In the case of (1), since a voltage having the same polarity as that of the toner is applied to the grid and the shield portion closest to the photosensitive drum 1, the toner is not captured by the grid and the shield portion, and the discharge is in the ground state. Since the toner flies backward toward the wire, discharge unevenness occurs at an earlier number. 3 above. In the case of (1), a voltage having the same polarity as that of the toner is applied to all of the discharge wire, grid and shield of the second charger 5, and the applied voltage of the discharge wire is lower than the voltage applied to the grid and shield. Therefore, black streaks can be prevented even when copying 100K sheets because toner is more difficult to adhere to the charging wire.
[0041]
Although the embodiment has been described by taking two-color image formation as an example, the present invention is also effective for a multi-color image forming apparatus of three or more colors provided with three or more image forming units. Further, the image color formed by each image forming means is arbitrary, and need not be limited to black and red in the above-described embodiment.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main part of an embodiment of the present invention.
FIG. 2 is a flowchart showing items for setting a charging device activation timing of the print controller 16 shown in FIG. 1;
FIG. 3 is a flowchart showing the contents of “ON / OFF timing setting of charger 5” (TD3) shown in FIG. 2;
[Explanation of symbols]
1: photosensitive drum 2: first charging device 3: first exposure device 4: first developing device 5: second charging device 6: second exposure device 7: second developing device 8: resist roller 9: transfer charging Device 10: Separation charger 11: Conveying belt 12: Cleaning device 13: Static elimination lamp 14: Reflection type optical sensor 15: Paper sensor 16 Print controller 17: Switching relay Hw1-Hw4, Hg1, Hg2: Power supply circuit

Claims

First charging means for charging the photoreceptor, first exposure means for irradiating light on the photoreceptor in accordance with image information to form an electrostatic latent image, and a photoreceptor formed on the photoreceptor; A first image forming means including a first developing means of a reversal developing system for developing an electrostatic latent image with a toner; a second charging means for charging a photosensitive member; Second exposure means for forming an electrostatic latent image by irradiating the photoreceptor with light, and second developing means for developing the electrostatic latent image formed on the photoreceptor. A second image forming unit at least downstream of the first image forming unit;
In an image forming mode in which an image is formed by the first image forming means but is not formed by the second image forming means, the first image forming means forms on the photosensitive member to prevent the second charging means from being stained. In the image forming mode in which a voltage having the same polarity as the toner and not higher than the discharge starting voltage is applied to the second charging means and an image is formed using the second image forming means, a latent image latent image is formed. A plurality of image forming apparatuses, comprising: an urging control unit that applies a voltage to the second charging unit .

The second charging means is a charger having a discharge wire, and the urging control means is configured to generate a second image when the image is formed by the first image forming means but not by the second image forming means . A voltage equal to or lower than the corona discharge starting voltage and having the same polarity as the toner formed on the photoreceptor by the first image forming means is applied to the discharge wire of the second charging means in order to prevent toner stain on the discharge wire of the charging means. 2. The image forming apparatus according to claim 1 , wherein a voltage for forming a latent latent image is applied to a discharge wire of the second charging unit in an image forming mode in which an image is formed using the second image forming unit. Multiple image forming apparatus.

The second charging means is a charger having a discharge wire, a grid and a shield, and the bias control means is a first image forming means in an image forming mode in which an image is formed only by the first image forming means. Is applied to the discharge wire, the grid and the shield, the absolute value of which is the same as that of the toner formed on the photoreceptor, and whose absolute value is such that the discharge wire applied voltage> the grid applied voltage ≧ the shield applied voltage. The multiple image forming apparatus according to claim 2 .

A main power supply circuit for generating a voltage for forming an electrostatic latent image by the second image forming means, and a first image forming means for preventing a discharge wire of the second charging means from being stained by toner are formed on the photosensitive member. An auxiliary power supply circuit for generating a voltage equal to or lower than the corona discharge start voltage and having the same polarity as the toner, and selectively applying one of the voltages generated by the main power supply circuit and the auxiliary power supply circuit to the discharge wire of the second charging means A switching relay that switches the voltage below the corona discharge start voltage in an image forming mode in which an image is formed only by the first image forming means by using the switching relay. In the image forming mode in which an image is formed using the second image forming means, the voltage for forming the latent image is applied to the discharge wire of the second charging means. , double of claim 2 or claim 3 Image forming apparatus.