JP4019739B2 - Image forming apparatus and method - Google Patents

Description

【００８８】
図７の動作において、ＣＰＵ１１１は、垂直同期信号Ｖsyncごとに温度センサ６および湿度センサ７からの入力データを取り込んで、１次転写バイアスの出力値の変更が必要か否かを判定している。
【００８９】
図７において、時刻ｔ１，ｔ２，ｔ３，ｔ４，ｔ５，ｔ６，ｔ７にそれぞれ垂直同期信号Ｖsyncが出力される。時刻ｔ１の垂直同期信号Ｖsyncの立下り時点から所定時間Ｔ１後に１枚目の画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、１枚目の画像信号に対応する静電潜像の形成が開始されるとともに、現像バイアスがオンにされる。また、時刻ｔ１の垂直同期信号Ｖsyncの立下り時点から所定時間Ｔ２後に２枚目の画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、２枚目の画像信号に対応する静電潜像の形成が開始される。
【００９０】
そして、時刻ｔ１から所定時間Ｔ３後には２次転写が行われていないので、環境条件の変化に応じて、１次転写バイアス生成回路１１６の出力値がＶ１１からＶ１２に変更される。
【００９１】
これによって、トナー像Ｋ１が、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の下流側であるサブ領域７６Ａに１次転写され、トナー像Ｋ２が、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の上流側であるサブ領域７６Ｂに１次転写される。
【００９２】
一方、給紙カセット３から転写紙４が２次転写部３７に向けて所定速度で搬送される。そして、時刻ｔ１から所定時間後の時刻ｔ１５に２次転写ローラ用離接クラッチがオンにされて、２次転写ローラ３５が中間転写ベルト３１に当接する。次いで、時刻ｔ１から所定時間後の時刻ｔ１６，ｔ１７に２次転写バイアス生成回路１１７から２次転写ローラ３５への２次転写バイアスの印加がそれぞれオンにされ、これによって、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の下流側であるサブ領域７６Ａに１次転写されているトナー像Ｋ１が１枚目の転写紙４に転写され、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の上流側であるサブ領域７６Ｂに１次転写されているトナー像Ｋ２が２枚目の転写紙４に転写される。そして、このトナー像Ｋ１，Ｋ２が転写紙４に定着され、転写紙４が排出される。
【００９３】
次いで、垂直同期信号Ｖsyncが出力される時刻ｔ２の時点で、環境条件により１次転写バイアスの出力値の変更が必要であるか否かが判定されるとともに、変更が必要であれば、時刻ｔ２から所定時間Ｔ３後に２次転写バイアスがオンにされているか否かが判定される。
【００９４】
図７では出力値の変更が必要であり、また時刻ｔ２から所定時間Ｔ３後に２次転写バイアスはオンになる。従って、時刻ｔ２の時点では画像形成が行われず、次に垂直同期信号Ｖsyncが出力される時刻ｔ３まで待機する。そして、この時刻ｔ３から所定時間後に３，４枚目の画像形成のためのトナー像Ｋ３，Ｋ４が形成され、時刻ｔ３から所定時間Ｔ３後に１次転写バイアスの出力値がＶ１２からＶ１３に変更されて、以下、上述したのと同様の動作が行われる。
【００９５】
続いて、大サイズの転写紙４に対する画像形成が行われるが、上述したのと同様に、時刻ｔ４から所定時間Ｔ３後に２次転写バイアスがオンになっていることが判定できるので、１次転写バイアスの出力値の変更が行えないため、時刻ｔ４の時点では画像形成が行われず、次に垂直同期信号Ｖsyncが出力される時刻ｔ５まで待機する。
【００９６】
そして、時刻ｔ５の垂直同期信号Ｖsyncの立下り時点から所定時間Ｔ１後に画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、その画像信号に対応する静電潜像の形成が開始されるとともに、現像バイアスがオンにされる。
【００９７】
時刻ｔ５から所定時間Ｔ３後には２次転写が行われていないので、環境条件の変化に応じて、１次転写バイアス生成回路１１６の出力値がＶ１３からＶ１２に変更される。
【００９８】
一方、給紙カセット３から転写紙４が２次転写部３７に向けて所定速度で搬送される。そして、時刻ｔ５から所定時間後の時刻ｔ１８に２次転写バイアス生成回路１１７から２次転写ローラ３５への２次転写バイアスの印加がオンにされ、これによって、中間転写ベルト３１の転写許可領域７６に１次転写されているトナー像Ｋ５が転写紙４に転写される。そして、このトナー像Ｋ５が転写紙４に定着され、転写紙４が排出される。
【００９９】
続いて、垂直同期信号Ｖsyncが出力される時刻ｔ６の時点で、時刻ｔ６から所定時間Ｔ３後に２次転写バイアスがオンにされているか否かが判定され、図７では時刻ｔ６から所定時間Ｔ３後に２次転写バイアスはオフになるので、時刻ｔ６から所定時間後に次の画像形成のためのトナー像Ｋ６が形成され、時刻ｔ６から所定時間Ｔ３後に１次転写バイアスの出力値がＶ１２からＶ１１に変更されて、以下、上述したのと同様の動作が行われる。そして、トナー像Ｋ６の２次転写が終了し、２次転写バイアスがオフにされた後の時刻ｔ１９に２次転写ローラ用離接クラッチがオンにされて、２次転写ローラ３５が中間転写ベルト３１から離間する。
【０１００】
このように、図７の動作によれば、図６の場合と同様に、非画像領域としての転写禁止領域７５が１次転写部１４を通過中に、１次転写バイアスの出力値の変更が完了するようにしているので、１次転写開始前に確実に当該出力値の変更を行うことができる。
【０１０１】
また、図６の場合と同様に、２次転写が行われていないときに１次転写バイアスの出力値の変更を行うようにしているので、１次転写バイアスの変更が２次転写に悪影響を及ぼして転写紙４上に転写される画質が劣化するのを未然に防止することができる。
【０１０２】
また、垂直同期信号Ｖsyncの検出時点でそのまま画像形成を継続し、必要な１次転写バイアスの出力値の変更が２次転写中であるために行えない場合には、トナー像が無駄に形成されることになるが、図７の動作によれば、バイアス変更条件に応じて１次転写バイアスの出力値の変更が必要であるか否かを垂直同期信号Ｖsyncの検出時点で判定するようにしているので、無駄なトナー像の形成を未然に防止することができる。
【０１０３】
次に、図８を参照して、本プリンタのさらに別の動作について説明する。図８はエンジン部１の各部の状態の時間変化を示すタイミングチャートで、２枚取り可能なサイズのモノクロ画像形成を４枚行う場合を示しており、図７と同一タイミングには同一符号を付している。なお、図８でも、図６と同様に、便宜上、画像信号は画像要求信号Ｖreqに同期してオンにされるように記載している。
【０１０４】
なお、図８では、図７と同様に、温度および湿度の環境条件に応じて１次転写バイアスを変更するようにしている。また、図８では、図７と同様に、モノクロ画像（例えばＫ）の形成が行われるので、ロータリー現像部２０は現像ユニット２Ｋのままとなることから画像形成が終了するまで現像バイアスのオンが継続され、トナー像の重ね合わせがないことから画像形成が終了するまで２次転写ローラ３５の中間転写ベルト３１への当接状態が維持される。また、温度・湿度に応じた１次転写バイアスの出力値は、例えば上記表１に示す値が用いられる。
【０１０５】
図８において、時刻ｔ１，ｔ２，ｔ３，ｔ４にそれぞれ垂直同期信号Ｖsyncが出力される。時刻ｔ１の垂直同期信号Ｖsyncの立下り時点から所定時間Ｔ１後に１枚目の画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、１枚目の画像信号に対応する静電潜像の形成が開始されるとともに、現像バイアスがオンにされる。また、時刻ｔ１の垂直同期信号Ｖsyncの立下り時点から所定時間Ｔ２後に２枚目の画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、２枚目の画像信号に対応する静電潜像の形成が開始される。
【０１０６】
そして、時刻ｔ１から所定時間Ｔ３後には２次転写が行われていないので、環境条件の変化に応じて、１次転写バイアス生成回路１１６の出力値がＶ１１からＶ１２に変更される。
【０１０７】
これによって、トナー像Ｋ１が、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の下流側であるサブ領域７６Ａに１次転写され、トナー像Ｋ２が、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の上流側であるサブ領域７６Ｂに１次転写される。
【０１０８】
一方、給紙カセット３から転写紙４が２次転写部３７に向けて所定速度で搬送される。そして、時刻ｔ１から所定時間後の時刻ｔ２１に２次転写ローラ用離接クラッチがオンにされて、２次転写ローラ３５が中間転写ベルト３１に当接する。次いで、時刻ｔ１から所定時間後の時刻ｔ２２，ｔ２３に２次転写バイアス生成回路１１７から２次転写ローラ３５への２次転写バイアスの印加がそれぞれオンにされ、これによって、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の下流側であるサブ領域７６Ａに１次転写されているトナー像Ｋ１が１枚目の転写紙４に転写され、中間転写ベルト３１の転写許可領域７６のうち回転駆動方向７２の上流側であるサブ領域７６Ｂに１次転写されているトナー像Ｋ２が２枚目の転写紙４に転写される。そして、このトナー像Ｋ１，Ｋ２が転写紙４に定着され、転写紙４が排出される。
【０１０９】
続いて、次に垂直同期信号Ｖsyncが出力される時刻ｔ２の時点で、転写紙４のサイズに応じて予め設定されている２次転写バイアスの印加時間に基づき、時刻ｔ２から所定時間Ｔ３後に２次転写バイアスがオンにされているか否かが判定される。図８では時刻ｔ２から所定時間Ｔ３後に２次転写バイアスはオンになるので、時刻ｔ２の時点では画像形成が行われずに待機し、さらに、時刻ｔ２から所定時間Ｔ２後に２次転写バイアスはオンにされているか否かが判定される。
【０１１０】
図８では時刻ｔ２から所定時間Ｔ２後に２次転写バイアスはオフにされているので、転写許可領域７６のうち回転駆動方向７２の上流側であるサブ領域７６Ｂに１次転写すべく、時刻ｔ２から所定時間Ｔ２経過後に画像要求信号Ｖreqが出力され、この画像要求信号Ｖreqの立下りに同期して、３枚目の画像信号に対応する静電潜像の形成が開始されてトナー像Ｋ３が形成される一方、時刻ｔ２から所定時間Ｔ４後に１次転写バイアスの出力値がＶ１２からＶ１３に変更されてトナー像Ｋ３の１次転写が行われ、続いて２次転写が行われる。
【０１１１】
上記所定時間Ｔ４は、中間転写ベルト３１のサブ領域７６Ｂにタイミングが合うように形成された感光体１１上のトナー像の先端（回転駆動方向７２の下流端）が１次転写部１４に到達するまで（すなわち非画像領域としてのトナー像が転写されていないサブ領域７６Ａが１次転写部１４を通過中）に、中間転写ベルト３１に対して印加される１次転写バイアスの変更が完了するように予め設定されている。
【０１１２】
次いで、次に垂直同期信号Ｖsyncが出力される時刻ｔ３において、環境条件が変化して１次転写バイアスの出力値の変更が必要であるか否かが判定され、ここでは出力値の変更が必要でないと判定される。そして、時刻ｔ３から所定時間Ｔ１後に４枚目の画像要求信号Ｖreqが出力され、これによってトナー像Ｋ４が形成される。ここで、時刻ｔ３から所定時間Ｔ３後には、２次転写が実行中であるが、環境条件が変化しておらず、１次転写バイアスの出力値を変更しないので、そのまま画像形成動作が行われる。なお、上述したように、出力値は変更しないが、時刻ｔ３から所定時間Ｔ３後に前回と同一データが制御データとしてＣＰＵ１１１からＤ／Ａ変換部１２１に送出される。
【０１１３】
そして、このトナー像Ｋ４の２次転写が終了し、２次転写バイアスがオフにされた後の時刻ｔ２４に２次転写ローラ用離接クラッチがオンにされて、２次転写ローラ３５が中間転写ベルト３１から離間する。
【０１１４】
このように、図８の動作によれば、図６の場合と同様に、２次転写が行われていないときに１次転写バイアスの出力値の変更を行うようにしているので、１次転写バイアスの変更が２次転写に悪影響を及ぼして転写紙４上に転写される画質が劣化するのを未然に防止することができる。
【０１１５】
また、図８の動作によれば、次の垂直同期信号Ｖsyncまで待機せず、非画像領域としてのトナー像が転写されていないサブ領域７６Ａが通過する分だけ待機するようにしているので、その分だけ図７の動作に比べてスループットを向上することができる。
【０１１６】
また、図８の動作によれば、バイアス変更条件に応じて１次転写バイアスの出力値の変更が必要であるか否かを垂直同期信号Ｖsyncの検出時点で判定するようにしているので、環境条件に変化がなく、１次転写バイアスの出力値の変更を行わない場合には、そのまま画像形成を継続することができ、これによってスループットの低下を未然に防止することができる。
【０１１７】
なお、本発明は上記実施形態に限定されるものではなく、その趣旨を逸脱しない限りにおいて上述したものに対して種々の変更を加えることが可能である。
【０１１８】
例えば、上記実施形態では、継ぎ目７１で継ぎ合わされた無端ベルトからなる中間転写ベルト３１を用いているが、本発明の中間転写媒体はこれに限られず、例えば継ぎ目の無いシームレスの無端ベルトからなる中間転写ベルトや、円筒状の中間転写ドラムを用いてもよい。この場合には、ベルトクリーナ３３の当接および離間領域を転写禁止領域７５に設定すればよい。
【０１１９】
また、上記実施形態の図６の動作では、１〜４番目の全ての１次転写において１次転写バイアスの出力値を変更しているが、これに限られない。例えば１〜３番目の１次転写は同一値とし、４番目の１次転写バイアスの出力値のみ変更するようにしてもよい。また、１番目の１次転写バイアスの出力値のみ変更し、２〜４番目の１次転写は同一値としてもよい。
【０１２０】
また、上記実施形態ではカラープリンタとしているが、図７、図８の動作はこれに限られず、モノクロプリンタに適用することができる。また、上記実施形態では１つの感光体を備え、中間転写ベルト３１を連続回転させてトナー像を重ね合わせる方式のカラープリンタとしているが、図７、図８の動作はこれに限られず、中間転写ベルトに沿って並んで配置された複数の感光体を備えるいわゆるタンデム方式のカラープリンタに適用することができる。
【０１２１】
また、図９に示すような形態を採用してもよい。中間転写ベルト３１の全長をＬ０（図４参照）とし、図９に示すように、回転駆動方向７２における転写禁止領域７５の寸法をＬ１とし、転写許可領域７６の寸法をＬ２とし（すなわちＬ０＝Ｌ１＋Ｌ２）、１次転写部１４と２次転写部３７との間の距離をＬ３としたときに、図９の形態は、
Ｌ１＞Ｌ３
に設定している。
【０１２２】
そして、ＣＰＵ１１１は、転写禁止領域７５が１次転写部１４および２次転写部３７の双方を通過中に１次転写バイアスの出力値を変更する制御を行う。この変形形態によれば、１次転写の出力値の変更が２次転写中に行われるのを確実に避けることができる。従って、制御構成を簡素なものとすることができる。
【０１２３】
また、上記実施形態では、ホストコンピュータなどの外部装置より与えられた画像を転写紙に印刷するプリンタを用いて説明しているが、本発明はこれに限られず、複写機やファクシミリ装置などを含む一般の電子写真方式の画像形成装置に適用することができる。
【０１２４】
【発明の効果】
以上説明したように、請求項１，６の発明によれば、中間転写媒体上にトナー像が転写されていない非画像領域が１次転写部を通過中であって、２次転写が行われていないときに、１次転写バイアスの出力値を変更するようにしているので、上記出力値の変更が２次転写中に行われるのを確実に避けることができ、これによって、上記出力値の変更による影響が２次転写に及ぶのを未然に防止することができる。また、基準信号の出力時点から、非画像領域が１次転写部を通過し終わるまでに１次転写バイアスの出力値の変更が行われるように予め設定された経過時間後に、１次転写バイアスの出力値を変更するようにしているので、基準信号に基づく計時により容易に、上記出力値の変更が２次転写中に行われるのを避けることができる。また、バイアス変更条件の変化により１次転写バイアスの出力値の変更が必要であるか否かを基準信号の出力時点に判定し、上記出力値の変更が必要であると判定されたときに、当該出力時点から前記経過時間後に２次転写が行われているか否かを当該出力時点に判定して、その出力時点から前記経過時間後に２次転写が行われていると判定されたときは、予め設定された待機時間だけ次のトナー像形成を待機するようにしているので、バイアス変更条件に合わない上記出力値で１次転写を行ったり、トナーを無駄に消費するような事態を避けることができる。
【０１２５】
また、請求項２の発明によれば、雰囲気温度および雰囲気湿度の少なくとも一方の値に応じて１次転写バイアスの出力値を変更するようにしているので、雰囲気温度や雰囲気湿度などの環境条件による転写効率の変化による影響を低減し、感光体から中間転写媒体への１次転写を好適に行うことが可能になる。
【０１２６】
また、請求項３の発明によれば、１番目のトナー像の１次転写時と最後のトナー像の１次転写時とで１次転写バイアスの出力値を変更するようにしているので中間転写媒体上のトナー像の厚さによる転写効率の変化に拘わらず感光体から中間転写媒体への１次転写を好適に行うことが可能になる。
【０１２９】
また、請求項４の発明によれば、待機時間は、少なくとも次の基準マークが検出されるまでの時間であるとしているので、基準信号に基づく計時により、容易かつ確実に、上記出力値の変更が２次転写中に行われるのを避けることができる。
【０１３０】
また、請求項５の発明によれば、待機時間は、中間転写媒体が少なくとも１つのサブ領域分だけ回転駆動する時間であるとしているので、中間転写媒体が一周する時間だけ待機するのに比べてスループットの低下を抑制することができる。
【図面の簡単な説明】
【図１】 本発明に係る画像形成装置の一実施形態であるプリンタの内部構成を示す図である。
【図２】 同プリンタの電気的構成を示すブロック図である。
【図３】 中間転写ベルトの断面図である。
【図４】 （Ａ）（Ｂ）は中間転写ベルトの展開図である。
【図５】 転写バイアス生成回路の構成例を模式的に示す図である。
【図６】 動作を説明するためのエンジン部の各部の状態の時間変化を示すタイミングチャートである。
【図７】 別の動作を説明するためのエンジン部の各部の状態の時間変化を示すタイミングチャートである。
【図８】 さらに別の動作を説明するためのエンジン部の各部の状態の時間変化を示すタイミングチャートである。
【図９】 変形形態を示す図である。
【符号の説明】
４ 転写紙
６ 温度センサ
７ 湿度センサ
１１ 感光体
１４ １次転写部
３１ 中間転写ベルト（中間転写媒体）
３１Ａ バイアス印加部材（１次転写バイアス印加手段）
３２ 垂直同期センサ（基準検出手段）
３７ ２次転写部
７２ 回転駆動方向
７３ 回転軸方向
７５ 転写禁止領域
７６ 転写許可領域
７６Ａ，７６Ｂ サブ領域
８２ 導電層
１１０ エンジン制御部
１１１ ＣＰＵ（バイアス制御手段、トナー像形成制御手段、バイアス変更判定手段、２次転写判定手段）
１１６ １次転写バイアス生成回路（１次転写バイアス印加手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming technique such as a printer, a copying machine, and a facsimile machine.
[0002]
[Prior art]
Conventionally, an electrostatic latent image formed on a photosensitive member by an exposure unit is attached with toner by a developing unit to form a toner image, the toner image is transferred to a transfer sheet, and the toner image on the transfer sheet is transferred by a fixing unit. An electrophotographic image forming apparatus for fixing to the transfer paper is known. In particular, as an apparatus capable of forming a color image, a toner image formed on a photoreceptor is primarily transferred to an intermediate transfer medium, There is known an image forming apparatus in which a primary transfer toner image on an intermediate transfer medium is secondarily transferred onto a transfer sheet.
[0003]
In this image forming apparatus, when forming a color image, for example, toner images of different colors are sequentially formed on a photoconductor, and a plurality of colors are formed by primary transfer to an intermediate transfer medium every time a toner image of each color is formed. A color toner image on which the toner images are superimposed is formed on an intermediate transfer medium, and the color toner image is secondarily transferred onto a transfer sheet to obtain a color image. In addition, this image forming apparatus can perform single color printing using a specific color, in many cases, black toner among a plurality of colors.
[0004]
By the way, the primary transfer is performed, for example, by applying a primary transfer bias between the intermediate transfer medium and the photosensitive member, and the secondary transfer is opposed to the intermediate transfer medium with the transfer paper interposed therebetween, for example. This is performed by applying a secondary transfer bias between the intermediate transfer medium and the arranged secondary transfer member.
[0005]
In this case, conventionally, the output value of the primary transfer bias is different for each color, or the output values of the primary transfer bias and the secondary transfer bias are changed according to environmental conditions such as temperature and humidity. Is known.
[0006]
[Problems to be solved by the invention]
When the primary transfer bias is controlled at a constant voltage, the potential difference in the primary transfer portion is kept constant, so even if the output value of the secondary transfer bias changes during the application of the primary transfer bias. The change has little influence on the primary transfer.
[0007]
On the other hand, if the output value of the primary transfer bias changes during application of the secondary transfer bias, the electric field between the intermediate transfer medium and the secondary transfer member changes, so that the secondary transfer becomes unstable. There is a fear. In particular, when the intermediate transfer medium is composed of a plurality of layers including a conductive layer, the application of the primary transfer bias to the intermediate transfer medium is not limited to the primary transfer part, and the intermediate transfer medium includes a secondary transfer part. Therefore, the influence of the change in the output value of the primary transfer bias on the secondary transfer is great.
[0008]
Therefore, the material of the toner of each color is different, and the transfer efficiency varies depending on the fact that the toner of each color is laminated on the intermediate transfer medium or the temperature / humidity changes. Therefore, the primary transfer is performed according to each condition. Although it is preferable to change the output value of the bias, it is desirable to set the change timing so as not to adversely affect the secondary transfer. However, the output value of the primary transfer bias needs to be determined before the primary transfer is started.
[0009]
The present invention has been made in view of the above problems, and in the case where the intermediate transfer medium is composed of a plurality of layers including a conductive layer, the change in the output value of the primary transfer bias adversely affects the secondary transfer. An object of the present invention is to provide an image forming apparatus and method capable of preventing the above.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the invention described in claim 1 includes an intermediate transfer medium including a plurality of layers including a conductive layer,By developing meansA toner image is formed on the photoreceptor, and the toner image on the photoreceptor is primarily transferred to the rotating intermediate transfer medium in a primary transfer portion, and the toner image on the intermediate transfer medium is transferred to a transfer paper in the secondary transfer portion. In the image forming apparatus configured to perform secondary transfer, the intermediate transfer medium performs primary transfer of a toner image set in a transfer permission area where the primary transfer of the toner image is permitted and the rotation axis direction. With a prohibited transcription area,Reference detection means for detecting a reference mark provided on the intermediate transfer medium and outputting a reference signal; toner image formation control means for controlling toner image formation on the photoconductor based on the reference signal;A primary transfer bias applying means for applying a preset primary transfer bias to the conductive layer of the intermediate transfer medium; and a non-image area where no toner image is transferred onto the intermediate transfer medium. The output value of the primary transfer bias is changed in accordance with a predetermined bias changing condition when passing and no secondary transfer is performed.The output value after a preset elapsed time so that the output value is changed from when the reference signal is output until the non-image area passes through the primary transfer portion. ChangeWith bias control meansThe bias change determining means for determining whether or not the output value needs to be changed according to the bias changing condition at the output time of the reference signal, and the bias change determining means if the output value needs to be changed. And a secondary transfer determination unit that determines, at the output time, whether or not secondary transfer is performed after the elapsed time from the output time, and the toner image formation control unit includes the output When the secondary transfer determination unit determines that the secondary transfer is performed after the elapsed time from the time, the next toner image formation is waited for a preset standby time.It is characterized by(Claim 1).
[0011]
According to this configuration, since the primary transfer bias set in advance is applied to the conductive layer of the intermediate transfer medium including a plurality of layers including the conductive layer, the primary transfer bias is an intermediate transfer medium including the secondary transfer unit. It will be applied to the whole. Accordingly, when the output value of the primary transfer bias is changed, if the output value is changed during the secondary transfer, the influence of the change will affect the secondary transfer. When the non-image area to which the toner image is not transferred is passing through the primary transfer portion and the secondary transfer is not performed, the output value of the primary transfer bias is changed according to a predetermined bias changing condition. Therefore, since the change of the output value is performed before the start of the primary transfer, the primary transfer is suitably performed and it can be reliably avoided that the transfer is performed during the secondary transfer. It is possible to prevent the influence of the change of the output value from affecting the secondary transfer.
[0012]
In the configuration of the first aspect, the non-image area may be a transfer prohibited area, or may be an area including the transfer prohibited area where the toner image is not transferred.
[0013]
  Further, according to this configuration, when a reference mark provided on the intermediate transfer medium is detected, a reference signal is output, and a toner image is formed on the photoconductor based on the reference signal, while the output of the reference signal is performed. The output value of the primary transfer bias is changed after a preset time so that the output value is changed from the time point until the non-image area passes through the primary transfer portion. The change of the output value is easily performed before the start of the primary transfer by timing based on the signal.
[0014]
  Further, according to this configuration, it is determined at the output time of the reference signal whether or not the output value of the primary transfer bias is necessary according to the bias change condition, and it is determined that the output value needs to be changed. At this time, it is determined at the output time whether or not secondary transfer is performed after the elapsed time from the output time. When it is determined that the secondary transfer is performed after the elapsed time from the output time, the next toner image formation is waited for a preset waiting time. That is, even if it is determined that the output value of the primary transfer bias needs to be changed, the output value is not changed during the secondary transfer, but the output value of the primary transfer bias is changed in this way. When it is not, the formation of a toner image on the photosensitive member is awaited. Accordingly, since the secondary transfer is in progress and the output value of the primary transfer bias according to the bias change condition is not changed, the toner image formation is not waited for, and thus the bias change condition is not met. If the primary transfer is performed with the output value or the primary transfer is stopped after the toner image is formed, the toner is wasted, but according to this configuration, such a situation can be avoided. It will be.
[0015]
  Further, the bias control means may use at least one value of an atmospheric temperature and an atmospheric humidity as the bias changing condition.
[0016]
  According to this configuration, since the output value of the primary transfer bias is changed according to the ambient temperature, the ambient humidity, or both, the influence due to the change in transfer efficiency due to the environmental conditions such as the ambient temperature and the ambient humidity is reduced. In addition, primary transfer from the photosensitive member to the intermediate transfer medium can be suitably performed.
[0017]
The developing means sequentially forms toner images of different colors on the photoreceptor, and the intermediate transfer medium forms toner images of each color so that the toner images of the respective colors overlap on the intermediate transfer medium. The bias control means uses the order of the toner images superimposed on the intermediate transfer medium as the bias changing condition, and uses the order of the first toner image and the last transfer of the toner image. The output value of the primary transfer bias may be changed depending on the primary transfer of the toner image.
[0018]
According to this configuration, the toner images of different colors are sequentially formed on the photosensitive member, and the toner images of the respective colors overlap each other on the intermediate transfer medium so that the primary image is transferred from the photosensitive member to the intermediate transfer medium every time the toner image of each color is formed. Transcribed. Here, the order of the toner images superimposed on the intermediate transfer medium is used as the bias changing condition, and the primary transfer bias is changed during the primary transfer of the first toner image and the primary transfer of the last toner image. By changing the output value, primary transfer is suitably performed regardless of the change in transfer efficiency due to the thickness of the toner image on the intermediate transfer medium.
[0019]
  Further, the waiting time may be a time until at least the next reference mark is detected by the reference detection means.
[0020]
  According to this configuration, by setting at least the time until the next reference mark is detected as the standby time, the output value can be easily and reliably changed during the secondary transfer by measuring the time based on the reference signal. Can be avoided.
[0021]
  Further, the transfer permission area of the intermediate transfer medium includes a plurality of sub areas to which a toner image of a predetermined size is transferred, and the waiting time is equal to at least one sub area of the intermediate transfer medium. It may be the time for rotational driving (claim 5).
[0022]
  According to this configuration, the time during which the intermediate transfer medium is driven to rotate by at least one sub-region is set as the standby time, thereby suppressing a decrease in throughput as compared with the case where the intermediate transfer medium waits for one round. Is possible.
[0023]
  The invention according to claim 6 includes an intermediate transfer medium including a plurality of layers including a conductive layer, forms a toner image on a photoreceptor, and rotates the toner image on the photoreceptor in a primary transfer portion. In an image forming method in which a primary transfer is performed on an intermediate transfer medium, and a toner image on the intermediate transfer medium is secondarily transferred onto a transfer sheet in a secondary transfer unit, the intermediate transfer medium is a primary transfer of a toner image. Is provided with a transfer permission area in which the toner image is permitted and a transfer prohibition area in which the primary transfer of the toner image set in the rotation axis direction is prohibited. The toner image is transferred onto the intermediate transfer medium. When a non-image area that has not been passed through the primary transfer portion and secondary transfer has not been performed, from the output point of the reference signal by detecting the reference mark provided on the intermediate transfer medium, The non-image area is the 1 In until you have passed through the transfer sectionPrimary transfer biasAfter an elapsed time set in advance so that the output value is changed, it is applied to the conductive layer of the intermediate transfer medium according to a predetermined bias changing condition.SaidWhen the output value of the primary transfer bias is changed, and it is determined that the output value needs to be changed according to the bias change condition at the output time of the reference signal, after the elapsed time from the output time. Whether or not secondary transfer is being performed is determined at the output time point, and when it is determined that secondary transfer is being performed after the elapsed time from the output time point, the reference time is set for a preset standby time. It waits for the next toner image formation on the said photoconductor based on the signal (Claim 6).
[0024]
  According to this configuration, since the primary transfer bias set in advance is applied to the conductive layer of the intermediate transfer medium including a plurality of layers including the conductive layer, the primary transfer bias is an intermediate transfer medium including the secondary transfer unit. It will be applied to the whole. Accordingly, when the output value of the primary transfer bias is changed, if the output value is changed during the secondary transfer, the influence of the change will affect the secondary transfer. When the non-image area to which the toner image is not transferred is passing through the primary transfer portion and the secondary transfer is not performed, the output value of the primary transfer bias is changed according to a predetermined bias changing condition. Therefore, since the change of the output value is performed before the start of the primary transfer, the primary transfer is suitably performed and it can be reliably avoided that the transfer is performed during the secondary transfer. It is possible to prevent the influence of the change of the output value from affecting the secondary transfer.
[0025]
  Further, according to this configuration, when a reference mark provided on the intermediate transfer medium is detected, a reference signal is output, and a toner image is formed on the photoconductor based on the reference signal, while the output of the reference signal is performed. The output value of the primary transfer bias is changed after a preset time so that the output value is changed from the time point until the non-image area passes through the primary transfer portion. The change of the output value is easily performed before the start of the primary transfer by timing based on the signal.
[0026]
  Further, according to this configuration, it is determined at the output time of the reference signal whether or not the output value of the primary transfer bias is necessary according to the bias change condition, and it is determined that the output value needs to be changed. At this time, it is determined at the output time whether or not secondary transfer is performed after the elapsed time from the output time. When it is determined that the secondary transfer is performed after the elapsed time from the output time, the next toner image formation is waited for a preset waiting time. That is, even if it is determined that the output value of the primary transfer bias needs to be changed, the output value is not changed during the secondary transfer, but the output value of the primary transfer bias is changed in this way. When it is not, the formation of a toner image on the photosensitive member is awaited. Accordingly, since the secondary transfer is in progress and the output value of the primary transfer bias according to the bias change condition is not changed, the toner image formation is not waited for, and thus the bias change condition is not met. If the primary transfer is performed with the output value or the primary transfer is stopped after the toner image is formed, the toner is wasted, but according to this configuration, such a situation can be avoided. It will be.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
First, the configuration of a printer that is an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a diagram showing the internal configuration of the printer, FIG. 2 is a block diagram showing the electrical configuration of the printer, FIGS. 3 and 4 are sectional views and development views of the intermediate transfer belt, respectively, and FIG. 5 is a transfer bias generation circuit. It is a figure which shows typically the example of a structure.
[0030]
This printer forms a full color image by superposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K), or uses only black (K) toner, for example. A monochrome image is formed. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 causes each part of the engine unit 1 to respond to the control signal from the main control unit 100. And an image corresponding to the image signal is printed out on the transfer paper 4 conveyed from the paper feed cassette 3 disposed below the apparatus main body 2.
[0031]
The engine unit 1 includes a photoconductor unit 10, a rotary developing unit 20, an intermediate transfer unit 30, a fixing unit 40, and an exposure unit 50. The photoconductor unit 10 includes a photoconductor 11, a charging unit 12, and a cleaning unit 13. A rotary developing unit 20 includes a yellow developing unit 2Y containing yellow toner, a magenta developing unit 2M containing magenta toner, and cyan. The intermediate transfer unit 30 includes an intermediate transfer belt 31, a vertical synchronization sensor 32, a belt cleaner 33, a pair of gate rollers 34, 2 and the like. A next transfer roller 35, a photoreceptor driving motor 36, and the like are provided. The seven units 10, 2Y, 2M, 2C, 2K, 30, 40 are each configured to be detachable from the apparatus main body 2.
[0032]
The printer is configured to primarily transfer the toner image on the photoconductor 11 to the intermediate transfer belt 31 and secondarily transfer the primary transfer toner image to the transfer paper 4 under predetermined bias changing conditions. Accordingly, the output value of the primary transfer bias is changed and, as will be described later, the change is not performed during the execution of the secondary transfer.
[0033]
The photoconductor 11 of the photoconductor unit 10 is moved in the direction of arrow 5 by the photoconductor drive motor 36 in a state where the seven units 10, 2Y, 2M, 2C, 2K, 30, 40 are mounted on the apparatus main body 2. Rotate. Around the photoreceptor 11, a charging unit 12, a rotary developing unit 20, and a cleaning unit 13 are arranged along the rotation direction 5.
[0034]
The charging unit 12 includes a wire electrode to which a high voltage of a predetermined level is applied, and uniformly charges the outer peripheral surface of the photoreceptor 11 by, for example, corona discharge. The cleaning unit 13 is disposed on the upstream side of the charging unit 12 in the rotation direction 5 of the photoconductor 11 and remains on the outer peripheral surface of the photoconductor 11 after the primary transfer of the toner image from the photoconductor 11 to the intermediate transfer belt 31. The surface of the photoreceptor 11 is cleaned by scraping off the toner.
[0035]
The exposure unit 50 is reflected by a laser light source 51 made of, for example, a semiconductor laser, a polygon mirror 52 that reflects laser light from the laser light source 51, a scanner motor 53 that rotates the polygon mirror 52 at high speed, and the polygon mirror 52. A lens unit 54 for focusing the laser light, a plurality of reflection mirrors 55, a horizontal synchronization sensor 56, and the like are provided. The laser beam 57 reflected by the polygon mirror 52 and emitted through the lens unit 54 and the reflection mirror 55 is scanned in the main scanning direction (direction perpendicular to the paper surface of FIG. 1) on the surface of the photoreceptor 11. Then, an electrostatic latent image corresponding to the image signal is formed on the surface of the photoreceptor 11. At this time, the horizontal synchronization sensor 56 obtains a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal. The exposure unit 50 functions as an exposure unit.
[0036]
The rotary developing unit 20 develops the toner of each color by attaching it to the electrostatic latent image. The yellow developing unit 2Y, the magenta developing unit 2M, the cyan developing unit 2C, and the black developing unit 2K of the rotary developing unit 20 are provided to be rotatable about the axis, and these developing units 2Y, 2M, 2C, and 2K are determined in advance. The plurality of positions are movably disposed, and are selectively disposed at the contact position and the separation position with respect to the photoconductor 11. Then, a developing bias in which an alternating current component is superimposed on a direct current component or a direct current component is applied, and the toner of the color adheres to the surface of the photosensitive member 11 from the developing unit in contact with the photosensitive member 11. The rotary developing unit 20 functions as a developing unit.
[0037]
The intermediate transfer belt 31 of the intermediate transfer unit 30 is stretched around a plurality of rollers, and is rotationally driven together with the photosensitive member 11 by the photosensitive member driving motor 36. As shown in the cross-sectional view of FIG. 3, the intermediate transfer belt 31 includes a plurality of layers having a resistance layer 81 on the surface, an intermediate conductive layer 82, and a base material portion 83 as a lower layer. The resistance layer 81 is made of a synthetic resin (for example, urethane resin) having a predetermined thickness (for example, 20 μm), and is made of conductive particles (for example, SnO).₂) 84, fluororesin (for example, polytetrafluoroethylene) particles 85, and the like. By including the conductive particles 84, the resistance value of the resistance layer 81 is 10⁸-10¹⁴The frictional resistance is suppressed by including the fluororesin particles 85 and the intermediate transfer belt 31 is prevented from being locked by the belt cleaner 33 (described later).
[0038]
The conductive layer 82 is formed by vapor deposition of aluminum, for example. The base material portion 83 has a predetermined thickness (for example, 100 μm) and is formed of a synthetic resin (for example, polyethylene terephthalate). In this manner, the cost is reduced by separating the resistance layer 81 and the conductive layer 82 which are layers that perform an electrical function and the base material portion 83 that is a layer for giving mechanical strength.
[0039]
Further, as shown in the development view of FIG. 4, the intermediate transfer belt 31 is an endless belt formed by joining substantially rectangular sheet bodies at a seam 71 and has a total length L0. In FIG. 4, an arrow 72 indicates the rotational drive direction, and an arrow 73 indicates the rotational axis direction. The intermediate transfer belt 31 is provided with a protrusion 74 on one end side (the upper side in FIG. 4) in the rotation axis direction 73.
[0040]
The intermediate transfer belt 31 has a transfer prohibition area 75 and a transfer permission area 76. The transfer prohibition area 75 is set from one end to the other end in the rotation axis direction 73 within a predetermined size range on both sides of the joint 71, and primary transfer of the toner image is prohibited. The transfer permission area 76 is an area other than the transfer prohibition area 75 and is set to a rectangular area excluding one end and the other end in the rotation axis direction 73. The transfer permission area 76 has a size larger than the A3 size in the long side direction in the rotation driving direction 72. As shown in FIG. 4A, an A3 size image 77 having a long side direction in the rotational drive direction 72 can be transferred. Further, as shown in FIG. 4B, the transfer permission area 76 is divided into two sub areas 76A and 76B, and the A4 size is one side of the intermediate transfer belt 31 and the short side direction in the rotational drive direction 72. The two images 78 can be transferred.
[0041]
As shown in FIG. 4, the conductive layer 82 is exposed on the surface at the other end side (the lower side in FIG. 4) of the intermediate transfer belt 31 in the rotation axis direction 73. A primary transfer bias is applied to the exposed portion via a bias applying member 31A (see FIG. 2), and the toner image on the photoconductor 11 is primarily applied to the intermediate transfer belt 31 by the primary transfer bias. The contact position of the photosensitive member 11 to the intermediate transfer belt 31 is set in the primary transfer portion 14.
[0042]
1 and 2, the vertical synchronization sensor 32 includes a photo interrupter having, for example, a light emitting unit (for example, an LED) and a light receiving unit (for example, a photodiode) disposed to face each other, and the rotation shaft of the rotating intermediate transfer belt 31 is rotated. It is arranged on one end side in the direction 73 and detects the passage of the protrusion 74, and this detection signal is used as a vertical synchronization signal (reference signal) serving as a reference for image formation control by the engine control unit 110. The belt cleaner 33 is disposed so as to be switchable between a contact state (solid line in FIG. 1) and a separation state (broken line in FIG. 1) with the cleaner separating clutch. The residual toner on the transfer belt 31 is scraped off. The gate roller pair 34 is driven to rotate when the driving force of the transport system driving motor 60 is transmitted by turning on the gate clutch.
[0043]
The secondary transfer roller 35 is switched between a contact state (solid line in FIG. 1) and a separation state (broken line in FIG. 1) with the intermediate transfer belt 31 by the secondary transfer roller separation / contact clutch. A predetermined secondary transfer bias is applied to the secondary transfer roller 35 in contact with the intermediate transfer belt 31, and the primary transfer toner image on the intermediate transfer belt 31 is transferred to the transfer paper while conveying the transfer paper 4. 4, the contact position is set in the secondary transfer portion 37.
[0044]
The fixing unit 40 includes a heating roller 41 and a pressure roller 42, and fixes the toner image on the transfer paper 4 to the transfer paper 4 while conveying the transfer paper 4 by a heat roller fixing method, and constitutes a fixing unit. To do.
[0045]
From the front end (right end in FIG. 1) of the paper feed cassette 3, a half-moon pickup roller 61 and a feed roller pair 62 are disposed, and the gate roller pair 34, the secondary transfer roller 35, and the fixing unit 40 are arranged. Further, a pair of conveying rollers 63 and a pair of discharging rollers 64 are disposed so as to form a conveying path for the transfer paper 4 (a chain line in FIG. 1).
[0046]
The pickup roller 61 is driven by a pickup solenoid. The feed roller pair 62, the gate roller pair 34, the secondary transfer roller 35, the heating roller 41 of the fixing unit 40, the transport roller pair 63, and the discharge roller pair 64 are respectively the same transport system driving motor via a driving force transmission mechanism. 60. The feed roller pair 62 is driven to rotate by the driving force of the conveyance system driving motor 60 being transmitted when the feed clutch is turned on. The transfer paper 4 is conveyed at a predetermined conveyance speed by the conveyance system driving motor 60. The feed roller pair 62, the gate roller pair 34, the transport roller pair 63, and the discharge roller pair 64 constitute transport means for the transfer paper 4.
[0047]
The engine unit 1 also includes a temperature sensor 6 that detects the atmospheric temperature and a humidity sensor 7 that detects the atmospheric humidity. The temperature sensor 6 and the humidity sensor 7 constitute temperature detection means and humidity detection means as environmental condition detection means, respectively.
[0048]
In FIG. 2, the main control unit 100 includes an interface 102 that transmits and receives control signals between the CPU 101 and an external device such as a host computer, and an image for storing an image signal given through the interface 102. And a memory 103. When the CPU 101 receives a print command signal including an image signal from an external device via the interface 102, the CPU 101 converts the job data into a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110.
[0049]
The engine control unit 110 includes a CPU 111, a ROM 112, a RAM 113, and the like. The ROM 112 stores a control program of the CPU 111 and the like, and the RAM 113 temporarily stores control data of the engine unit 1, a calculation result by the CPU 111, and the like.
[0050]
The CPU 111 receives a vertical synchronization signal Vsync from the vertical synchronization sensor 32 as an input signal from the engine unit 1, a horizontal synchronization signal Hsync from the horizontal synchronization sensor 56, and the ambient temperature and ambient humidity from the temperature sensor 6 and the humidity sensor 7. Receive information on environmental conditions. The CPU 111 controls the operation of each unit of the engine unit 1 based on these input signals and the control program.
[0051]
That is, the CPU 111 sends a control signal to the motor drive circuit 114 that drives the photoconductor drive motor 36 to rotate the photoconductor 11 and the intermediate transfer belt 31 in synchronization. In addition, a control signal is sent to the motor drive circuit 115 that drives the transport system driving motor 60 to control the transport of the transfer paper 4 from the paper feed cassette 3.
[0052]
Further, the CPU 111 sends a control signal to a drive circuit that drives the cleaner separating clutch, and controls the separation and contact of the belt cleaner 33 with respect to the intermediate transfer belt 31. Further, a control signal is sent to a drive circuit that drives the secondary transfer roller separation clutch, and the separation and contact of the secondary transfer roller 35 with respect to the intermediate transfer belt 31 are controlled.
[0053]
Further, the CPU 111 receives, for example, the operation content for the operation keys of the operation display panel 8 disposed on the surface of the apparatus main body 2 and controls the display content of the display unit. In addition, when forming two or more images of a size that can be taken by two CPUs (for example, a size of A4 size or less which is the short side direction in the rotational drive direction 72), the CPU 111 forms a sub area in the transfer permission area 76. Image formation on the photoconductor 11 is controlled so that the toner images are transferred to 76A and 76B, respectively.
[0054]
In addition, the CPU 111 sends a control signal to a primary transfer bias generation circuit 116 that generates a primary transfer bias, and controls application of the primary transfer bias to the intermediate transfer belt 31. In addition, the CPU 111 sends a control signal to a secondary transfer bias generation circuit 117 that generates a secondary transfer bias, and controls application of the secondary transfer bias to the secondary transfer roller 35.
[0055]
Here, as shown in FIG. 5, the CPU 111 sends control data to the D / A converter 121 of the primary transfer bias generation circuit 116. The D / A conversion unit 121 controls the drive unit 122 based on control data input from the CPU 111, and performs primary transfer by constant voltage (for example, a voltage value set in advance within a range of about 50 to 400V). The application of bias is controlled.
[0056]
In addition, the CPU 111 sends control data to the D / A conversion unit 123 of the secondary transfer bias generation circuit 117. The D / A conversion unit 123 controls the drive unit 124 based on control data input from the CPU 111, and takes into account a lower limit voltage (for example, a voltage value set in advance within a range of about 500 to 3000 V). Application of the secondary transfer bias is controlled by constant current control (for example, a current value set in advance within a range of about 1 to 100 μA). That is, voltage control is performed until the lower limit voltage is reached, and then constant current control is performed.
[0057]
In FIG. 5, a load 125 is equivalently composed of a resistance component such as the photoreceptor 11 and the bias applying member 31A, and a load 126 is equivalently composed of a resistance component such as the secondary transfer roller 35 and the intermediate transfer belt 31. Is done.
[0058]
The CPU 111 sets a predetermined bias changing condition when a non-image area where no toner image is transferred onto the intermediate transfer belt 31 is passing through the primary transfer unit 14 and secondary transfer is not performed. Accordingly, the output value of the primary transfer bias for the D / A converter 121 is changed.
[0059]
Here, the “non-image area” is, for example, the transfer prohibited area 75, and may be simply an area where the toner image is not transferred and including the transfer prohibited area 75. Further, “the non-image area is passing through the primary transfer unit 14” means, for example, that the rear end of the transfer prohibition area 75, that is, the front end of the transfer permission area 76 (downstream end in the rotational driving direction 72) is the primary transfer section 14. Say the state before reaching.
[0060]
Further, as the predetermined bias changing condition, the environmental conditions of the atmospheric temperature and the atmospheric humidity obtained by the temperature sensor 6 and the humidity sensor 7 are used. Further, as a predetermined bias changing condition, the order of primary transfer of toner to be superimposed on the intermediate transfer belt 31 in the case of color image formation is used, and the output value of the primary transfer bias is set for each primary transfer of the toner image. change.
[0061]
Note that the CPU 111 sends control data to the D / A converter 121 of the primary transfer bias generation circuit 116 even when the output value of the primary transfer bias does not need to be changed due to the bias change condition. As a result, even when the control data of the D / A converter 121 is garbled due to noise or the like, it is possible to prevent the operation of the primary transfer bias generation circuit 116 from continuing the abnormal data.
[0062]
The intermediate transfer belt 31 corresponds to an intermediate transfer medium, and the bias applying member 31A and the primary transfer bias generating circuit 116 correspond to a primary transfer bias applying unit. The CPU 111 corresponds to a bias control unit, a toner image formation control unit, a bias change determination unit, and a secondary transfer determination unit.
[0063]
Next, the operation of this printer will be described with reference to FIG. FIG. 6 is a timing chart showing the time change of the state of each part of the engine unit 1 and shows a case where four color images having a size that can be taken by two sheets are formed. For each primary transfer of each toner image to be superimposed, FIG. The output value of the primary transfer bias is changed. The image signal receives the image request signal Vreq and is turned on in synchronization with the rotating intermediate transfer belt 31. The on timing is delayed by a predetermined time from the image request signal Vreq. However, in FIG. It is described that it is turned on in synchronization with the image request signal Vreq.
[0064]
When a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 starts operation of each unit of the engine unit 1 in response to the control signal from the main control unit 100. To do. At this time, if the size of the transfer paper 4 loaded in the paper feed cassette 3 does not match the size instructed by the print command signal, a message prompting the user to replace the paper feed cassette is displayed on the operation display panel 8. To do. In FIG. 1, the printer is provided with one paper feed cassette 3, but the printer is not limited to this, and may be provided with a plurality of paper feed cassettes.
[0065]
When the size of the transfer paper 4 loaded on the paper feed cassette 3 matches the size specified by the print command signal, the exposure unit is placed on the surface of the photoconductor 11 uniformly charged by the charging unit 12. An electrostatic latent image corresponding to the image signal is formed by the laser beam 57 from 50, and the electrostatic latent image is developed by the rotary developing unit 20 to form a toner image. The toner image on the photoreceptor 11 is Primary transfer is performed on the intermediate transfer belt 31 in the primary transfer unit 14.
[0066]
That is, the intermediate transfer belt 31 is rotated at a predetermined peripheral speed by the photosensitive member driving motor 36, and as shown in FIG. 6, the vertical synchronization signal Vsync is generated at times t1, t2, t3, t4, t5, t6, and t7, respectively. Is output. The first image request signal Vreq is output after a predetermined time T1 from the falling point of the vertical synchronization signal Vsync at times t1, t2, t3, and t4. The first image request signal Vreq is synchronized with the falling of the image request signal Vreq. Formation of an electrostatic latent image corresponding to the image signal is started, and the developing bias is turned on. The second image request signal Vreq is output after a predetermined time T2 (> T1) from the falling point of each vertical synchronizing signal Vsync, and the second image is synchronized with the falling edge of the image request signal Vreq. Formation of an electrostatic latent image corresponding to the signal is started.
[0067]
Then, the developing unit of the rotary developing unit 20 is switched at times t1, t2, t3, and t4, and toner images of the respective colors are formed on the photoconductor 11 and sequentially transferred onto the intermediate transfer belt 31 sequentially. At this time, the output value of the primary transfer bias generation circuit 116 is changed after a predetermined time T3 from time t1, t2, t3, t4.
[0068]
In the present embodiment, the first transfer bias (here, Y) is set to a voltage V1 (eg, V1 = 220V), and the second (here, C) is set to a voltage V2 (eg, V2 = 245V). The third (here, M) is set to the voltage V3 (for example, V3 = 270V), and the last (here, the fourth and K) is set to the voltage V4 (for example, V4 = 300V).
[0069]
During the predetermined time T3, the front end (downstream end in the rotational drive direction 72) of the toner image on the photoconductor 11 formed so that the timing coincides with the sub area 76A of the intermediate transfer belt 31 reaches the primary transfer unit 14. Until the change of the primary transfer bias applied to the intermediate transfer belt 31 is completed (ie, the transfer prohibited area 75 as a non-image area is passing through the primary transfer unit 14). . Further, since the secondary transfer is not performed after the predetermined time T3 from the times t1, t2, t3, and t4, the output values of the primary transfer bias are changed to V1, V2, V3, and V4, respectively.
[0070]
During this time, the secondary transfer roller 35 is separated from the intermediate transfer belt 31, so that the toner images of the respective colors are superimposed on the intermediate transfer belt 31. The developing bias is turned off after a predetermined time determined in advance by the transfer paper size from the falling point of each vertical synchronization signal Vsync at times t1, t2, t3, and t4.
[0071]
As a result, the color image obtained by superimposing the toner images Y1, C1, M1, and K1 is primarily transferred to the sub area 76A on the downstream side in the rotational driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31, and the toner is transferred. The color image obtained by superimposing the images Y2, C2, M2, and K2 is primarily transferred to the sub area 76B that is upstream of the rotation driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31.
[0072]
On the other hand, the uppermost transfer sheet 4 in the bundle of transfer sheets stacked on the sheet feeding cassette 3 is taken out by the pickup roller 61, conveyed at a predetermined speed by the feed roller pair 62, and nipped by the gate roller pair 34. Then, the gate clutch is turned on in synchronization with the toner image on the intermediate transfer belt 31, and the transfer paper 4 is conveyed from the gate roller pair 34 toward the secondary transfer unit 37 at a predetermined speed.
[0073]
Then, at time t11 after a predetermined time from time t4, the secondary transfer roller separating clutch is turned on, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, the application of the secondary transfer bias from the secondary transfer bias generation circuit 117 to the secondary transfer roller 35 is turned on at time t12 after a predetermined time from time t4.
[0074]
As a result, the color image on which the toner images Y1, C1, M1, and K1 are superimposed and transferred primarily to the sub area 76A on the downstream side in the rotational driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31 is superimposed. The image is transferred to the first transfer paper 4.
[0075]
The gate clutch is temporarily turned off after the first transfer sheet 4 is carried out, and the application time of the secondary transfer bias is set in advance according to the size of the transfer sheet 4. At this time, the next transfer paper 4 is taken out by the pickup roller 61, conveyed at a predetermined speed by the feed roller pair 62, and nipped by the gate roller pair 34.
[0076]
After the gate clutch and the secondary transfer bias application are turned off, the gate clutch is turned on at the timing of the next toner image and the next transfer paper 4 is conveyed, and the secondary transfer is performed at a time t13 after a predetermined time from the time t4. Bias application is turned on. Then, when the set application time of the secondary transfer bias elapses, the application of the secondary transfer bias is turned off, and then the secondary transfer roller separating clutch is turned on at time t14 after a predetermined time from time t4. As a result, the secondary transfer roller 35 is separated from the intermediate transfer belt 31.
[0077]
As a result, a color image in which the toner images Y2, C2, M2, and K2 are superimposed and transferred primarily to the sub area 76B on the upstream side in the rotation driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31 is superimposed. It is transferred to the second transfer paper 4.
[0078]
In the fixing unit 40, the toner image is fixed to the transfer paper 4 while the transfer paper 4 is conveyed. The transfer paper 4 is further transported by a transport roller pair 63 and is discharged by a discharge roller pair 64 to a paper discharge section 9 provided at the upper part of the apparatus main body 2.
[0079]
Subsequently, the third and fourth sheets of images are formed on the photoconductor 11, but the application time of the secondary transfer bias is set in advance according to the size of the transfer paper 4, so that the vertical synchronization signal Vsync is next. It is possible to determine whether or not the secondary transfer bias is turned on after a predetermined time T3 from the time t5 at the time t5 when is output. Here, in FIG. 6, since the secondary transfer bias is on at a time after a predetermined time T3 from time t5, the output value of the primary transfer bias is not changed. It waits for image formation until the output time t6.
[0080]
Then, toner images Y3 and Y4 for forming the third and fourth images are formed after a predetermined time from time t6, and the output value of the primary transfer bias is changed to V1 after a predetermined time T3 from time t6. Thereafter, the same operation as described above is performed.
[0081]
As described above, according to the operation of FIG. 6, the change of the output value of the primary transfer bias is completed while the transfer prohibited area 75 as the non-image area passes through the primary transfer unit 14. The output value can be reliably changed before the start of primary transfer.
[0082]
Further, since the primary transfer bias is changed for each primary transfer of the toner image, the toner of each color corresponding to the transfer efficiency of the toner that changes according to the thickness of the toner on the intermediate transfer belt 31. Is preferably primary-transferred onto the intermediate transfer belt 31, whereby a high-quality color image can be obtained on the transfer paper 4.
[0083]
In addition, since the output value of the primary transfer bias is changed when the secondary transfer is not performed, the change of the primary transfer bias adversely affects the secondary transfer and is transferred onto the transfer paper 4. It is possible to prevent deterioration of the image quality.
[0084]
Next, another operation of the printer will be described with reference to FIG. FIG. 7 is a timing chart showing temporal changes in the state of each part of the engine unit 1. After four monochrome image formations of a size that can be taken by two sheets are performed, the size of only one sheet (for example, A3 size) is subsequently available. The case where two monochrome images are formed is shown, and the same reference numerals are given to the same timings as in FIG. In FIG. 7, as in FIG. 6, for convenience, the image signal is described as being turned on in synchronization with the image request signal Vreq.
[0085]
In FIG. 7, the primary transfer bias is changed under the environmental conditions of temperature and humidity. For convenience of explanation, the output value is always changed at the change timing of the primary transfer bias, assuming that the environmental conditions have changed. ing. In FIG. 7, it is assumed that the printer includes two paper feed cassettes 3 in which transfer papers 4 of the above sizes are accommodated. In FIG. 7, since a monochrome image (for example, K) is formed, the rotary developing unit 20 remains in the developing unit 2K. Therefore, the developing bias is kept on until the image formation is completed, and the toner images are overlapped. Since there is no alignment, the contact state of the secondary transfer roller 35 to the intermediate transfer belt 31 is maintained until the image formation is completed.
[0086]
Table 1 shows an example of the output value of the primary transfer bias according to the environmental conditions of temperature and humidity in the operation of FIG. In Table 1, TP represents temperature and HM represents humidity. Since the transfer efficiency decreases as the temperature and humidity become higher, as shown in Table 1, the output value of the primary transfer bias is increased as the temperature and humidity become higher.
[0087]
[Table 1]

[0088]
In the operation of FIG. 7, the CPU 111 fetches input data from the temperature sensor 6 and the humidity sensor 7 for each vertical synchronization signal Vsync, and determines whether or not the output value of the primary transfer bias needs to be changed.
[0089]
In FIG. 7, the vertical synchronization signal Vsync is output at times t1, t2, t3, t4, t5, t6, and t7, respectively. The first image request signal Vreq is output after a predetermined time T1 from the falling point of the vertical synchronization signal Vsync at time t1, and corresponds to the first image signal in synchronization with the falling edge of the image request signal Vreq. The formation of the electrostatic latent image is started and the developing bias is turned on. The second image request signal Vreq is output after a predetermined time T2 from the falling point of the vertical synchronization signal Vsync at time t1, and the second image signal is synchronized with the falling edge of the image request signal Vreq. The corresponding electrostatic latent image is formed.
[0090]
Then, since the secondary transfer is not performed after the predetermined time T3 from the time t1, the output value of the primary transfer bias generation circuit 116 is changed from V11 to V12 according to the change of the environmental condition.
[0091]
As a result, the toner image K1 is primarily transferred to the sub-area 76A downstream of the rotation driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31, and the toner image K2 is transferred to the intermediate transfer belt 31. The primary transfer is performed on the sub-region 76B on the upstream side of the rotational drive direction 72 of 76.
[0092]
On the other hand, the transfer paper 4 is conveyed from the paper feed cassette 3 toward the secondary transfer unit 37 at a predetermined speed. Then, at time t15 after a predetermined time from time t1, the secondary transfer roller separating clutch is turned on, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, the application of the secondary transfer bias from the secondary transfer bias generation circuit 117 to the secondary transfer roller 35 is turned on at times t16 and t17 after a predetermined time from the time t1, whereby the transfer of the intermediate transfer belt 31 is performed. The toner image K1 primarily transferred to the sub area 76A downstream of the rotation drive direction 72 in the permission area 76 is transferred to the first transfer sheet 4 and is included in the transfer permission area 76 of the intermediate transfer belt 31. The toner image K2 that has been primarily transferred to the sub-region 76B on the upstream side in the rotational driving direction 72 is transferred to the second transfer paper 4. Then, the toner images K1 and K2 are fixed on the transfer paper 4, and the transfer paper 4 is discharged.
[0093]
Next, at time t2 when the vertical synchronization signal Vsync is output, it is determined whether or not the output value of the primary transfer bias needs to be changed according to environmental conditions. It is determined whether or not the secondary transfer bias is turned on after a predetermined time T3.
[0094]
In FIG. 7, the output value needs to be changed, and the secondary transfer bias is turned on after a predetermined time T3 from time t2. Accordingly, image formation is not performed at time t2, and the process waits until time t3 when the vertical synchronization signal Vsync is output next time. Then, toner images K3 and K4 for forming the third and fourth images are formed after a predetermined time from time t3, and the output value of the primary transfer bias is changed from V12 to V13 after a predetermined time T3 from time t3. Thereafter, the same operation as described above is performed.
[0095]
Subsequently, an image is formed on the large-size transfer paper 4. As described above, since it can be determined that the secondary transfer bias is turned on after a predetermined time T3 from time t4, the primary transfer is performed. Since the bias output value cannot be changed, image formation is not performed at time t4, and the process waits until time t5 when the vertical synchronization signal Vsync is next output.
[0096]
Then, the image request signal Vreq is output after a predetermined time T1 from the falling point of the vertical synchronization signal Vsync at time t5, and the electrostatic latent image corresponding to the image signal is synchronized with the falling edge of the image request signal Vreq. As the formation starts, the developing bias is turned on.
[0097]
Since the secondary transfer is not performed after the predetermined time T3 from the time t5, the output value of the primary transfer bias generation circuit 116 is changed from V13 to V12 according to the change of the environmental condition.
[0098]
  On the other hand, the transfer paper 4 is conveyed from the paper feed cassette 3 toward the secondary transfer unit 37 at a predetermined speed. Then, the application of the secondary transfer bias from the secondary transfer bias generation circuit 117 to the secondary transfer roller 35 is turned on at time t18 after a predetermined time from time t5, whereby the transfer permission area 76 of the intermediate transfer belt 31 is turned on. Toner image K that is primarily transferred to5Is transferred to the transfer paper 4. The toner image K5Is fixed to the transfer paper 4, and the transfer paper 4 is discharged.
[0099]
Subsequently, at time t6 when the vertical synchronization signal Vsync is output, it is determined whether or not the secondary transfer bias is turned on after a predetermined time T3 from time t6. In FIG. 7, after a predetermined time T3 from time t6. Since the secondary transfer bias is turned off, a toner image K6 for the next image formation is formed after a predetermined time from time t6, and the output value of the primary transfer bias is changed from V12 to V11 after a predetermined time T3 from time t6. Thereafter, the same operation as described above is performed. Then, at time t19 after the secondary transfer of the toner image K6 is completed and the secondary transfer bias is turned off, the secondary transfer roller contact clutch is turned on, and the secondary transfer roller 35 is moved to the intermediate transfer belt. Separated from 31.
[0100]
As described above, according to the operation of FIG. 7, as in the case of FIG. 6, the output value of the primary transfer bias is changed while the transfer prohibited area 75 as the non-image area passes through the primary transfer unit 14. Since the process is completed, the output value can be reliably changed before the start of the primary transfer.
[0101]
Similarly to the case of FIG. 6, since the output value of the primary transfer bias is changed when the secondary transfer is not performed, the change of the primary transfer bias adversely affects the secondary transfer. It is possible to prevent the image quality transferred onto the transfer paper 4 from being deteriorated.
[0102]
Further, when the image formation is continued as it is when the vertical synchronization signal Vsync is detected and the required primary transfer bias output value cannot be changed because of the secondary transfer, a toner image is formed wastefully. However, according to the operation of FIG. 7, it is determined at the time of detection of the vertical synchronization signal Vsync whether or not the output value of the primary transfer bias is necessary according to the bias change condition. Therefore, it is possible to prevent the formation of a useless toner image.
[0103]
Next, still another operation of the printer will be described with reference to FIG. FIG. 8 is a timing chart showing the time change of the state of each part of the engine unit 1, and shows a case where four monochrome images having a size capable of taking two sheets are formed. The same timing as in FIG. is doing. In FIG. 8, as in FIG. 6, for convenience, the image signal is described as being turned on in synchronization with the image request signal Vreq.
[0104]
In FIG. 8, as in FIG. 7, the primary transfer bias is changed according to the environmental conditions of temperature and humidity. Further, in FIG. 8, since a monochrome image (for example, K) is formed as in FIG. 7, since the rotary developing unit 20 remains in the developing unit 2K, the development bias is turned on until the image formation is completed. Since the toner images are not superimposed, the contact state of the secondary transfer roller 35 to the intermediate transfer belt 31 is maintained until the image formation is completed. Further, as the output value of the primary transfer bias according to the temperature and humidity, for example, the values shown in Table 1 are used.
[0105]
In FIG. 8, the vertical synchronization signal Vsync is output at times t1, t2, t3, and t4, respectively. The first image request signal Vreq is output after a predetermined time T1 from the falling point of the vertical synchronization signal Vsync at time t1, and corresponds to the first image signal in synchronization with the falling edge of the image request signal Vreq. The formation of the electrostatic latent image is started and the developing bias is turned on. The second image request signal Vreq is output after a predetermined time T2 from the falling point of the vertical synchronization signal Vsync at time t1, and the second image signal is synchronized with the falling edge of the image request signal Vreq. The corresponding electrostatic latent image is formed.
[0106]
Then, since the secondary transfer is not performed after the predetermined time T3 from the time t1, the output value of the primary transfer bias generation circuit 116 is changed from V11 to V12 according to the change of the environmental condition.
[0107]
As a result, the toner image K1 is primarily transferred to the sub-area 76A downstream of the rotation driving direction 72 in the transfer permission area 76 of the intermediate transfer belt 31, and the toner image K2 is transferred to the intermediate transfer belt 31. The primary transfer is performed on the sub-region 76B on the upstream side of the rotational drive direction 72 of 76.
[0108]
On the other hand, the transfer paper 4 is conveyed from the paper feed cassette 3 toward the secondary transfer unit 37 at a predetermined speed. Then, at time t21, which is a predetermined time after time t1, the secondary transfer roller separating clutch is turned on, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, the application of the secondary transfer bias from the secondary transfer bias generation circuit 117 to the secondary transfer roller 35 is turned on at times t22 and t23 after a predetermined time from the time t1, whereby the transfer of the intermediate transfer belt 31 is performed. The toner image K1 primarily transferred to the sub area 76A downstream of the rotation drive direction 72 in the permission area 76 is transferred to the first transfer sheet 4 and is included in the transfer permission area 76 of the intermediate transfer belt 31. The toner image K2 that has been primarily transferred to the sub-region 76B on the upstream side in the rotational driving direction 72 is transferred to the second transfer paper 4. Then, the toner images K1 and K2 are fixed on the transfer paper 4, and the transfer paper 4 is discharged.
[0109]
Subsequently, at the time t2 when the vertical synchronization signal Vsync is next output, 2 is applied after a predetermined time T3 from the time t2 based on the application time of the secondary transfer bias set in advance according to the size of the transfer paper 4. It is determined whether or not the next transfer bias is turned on. In FIG. 8, since the secondary transfer bias is turned on after a predetermined time T3 from the time t2, the image forming apparatus does not perform image formation at the time t2, and the secondary transfer bias is turned on after the predetermined time T2 from the time t2. It is determined whether or not it has been done.
[0110]
In FIG. 8, since the secondary transfer bias is turned off after a predetermined time T2 from time t2, from the time t2 in order to perform primary transfer to the sub area 76B upstream of the rotation drive direction 72 in the transfer permission area 76. The image request signal Vreq is output after the predetermined time T2 has elapsed, and in synchronization with the fall of the image request signal Vreq, formation of an electrostatic latent image corresponding to the third image signal is started to form a toner image K3. On the other hand, after a predetermined time T4 from time t2, the output value of the primary transfer bias is changed from V12 to V13, the primary transfer of the toner image K3 is performed, and then the secondary transfer is performed.
[0111]
During the predetermined time T4, the front end (downstream end in the rotational drive direction 72) of the toner image on the photoconductor 11 formed so that the timing coincides with the sub area 76B of the intermediate transfer belt 31 reaches the primary transfer unit 14. The change in the primary transfer bias applied to the intermediate transfer belt 31 is completed until the sub-region 76A to which the toner image as the non-image region is not transferred passes through the primary transfer unit 14. Is set in advance.
[0112]
Next, at time t3 when the vertical synchronization signal Vsync is next output, it is determined whether the environmental condition has changed and the output value of the primary transfer bias needs to be changed. Here, the output value needs to be changed. It is determined that it is not. Then, after a predetermined time T1 from time t3, the fourth image request signal Vreq is output, thereby forming a toner image K4. Here, after the predetermined time T3 from the time t3, the secondary transfer is being executed, but the environmental condition has not changed and the output value of the primary transfer bias is not changed, so the image forming operation is performed as it is. . As described above, the output value is not changed, but the same data as the previous time is sent from the CPU 111 to the D / A converter 121 as control data after a predetermined time T3 from time t3.
[0113]
Then, at time t24 after the secondary transfer of the toner image K4 is completed and the secondary transfer bias is turned off, the secondary transfer roller separation clutch is turned on, and the secondary transfer roller 35 is intermediately transferred. Separated from the belt 31.
[0114]
As described above, according to the operation of FIG. 8, as in the case of FIG. 6, the output value of the primary transfer bias is changed when the secondary transfer is not performed. It is possible to prevent the change in the bias from adversely affecting the secondary transfer and the deterioration of the image quality transferred onto the transfer paper 4 from occurring.
[0115]
Further, according to the operation of FIG. 8, since it does not wait until the next vertical synchronization signal Vsync, it waits only for the passage of the sub area 76A to which the toner image as the non-image area is not transferred. Compared with the operation of FIG. 7, the throughput can be improved by that much.
[0116]
Further, according to the operation of FIG. 8, since it is determined at the time of detection of the vertical synchronization signal Vsync whether or not it is necessary to change the output value of the primary transfer bias according to the bias change condition. When there is no change in the conditions and the output value of the primary transfer bias is not changed, image formation can be continued as it is, thereby preventing a reduction in throughput.
[0117]
The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention.
[0118]
For example, in the above embodiment, the intermediate transfer belt 31 composed of an endless belt joined by a joint 71 is used. However, the intermediate transfer medium of the present invention is not limited to this, and for example, an intermediate composed of a seamless endless belt without a joint. A transfer belt or a cylindrical intermediate transfer drum may be used. In this case, the contact and separation area of the belt cleaner 33 may be set as the transfer prohibition area 75.
[0119]
In the operation of FIG. 6 in the above embodiment, the output value of the primary transfer bias is changed in all of the first to fourth primary transfers, but is not limited thereto. For example, the first to third primary transfer may be the same value, and only the output value of the fourth primary transfer bias may be changed. Further, only the output value of the first primary transfer bias may be changed, and the second to fourth primary transfer may have the same value.
[0120]
In the above embodiment, the color printer is used. However, the operations in FIGS. 7 and 8 are not limited to this, and can be applied to a monochrome printer. In the above embodiment, the color printer has a single photoconductor and continuously rotates the intermediate transfer belt 31 to superimpose the toner images. However, the operations in FIGS. 7 and 8 are not limited to this, and the intermediate transfer is not limited thereto. The present invention can be applied to a so-called tandem color printer including a plurality of photoconductors arranged side by side along a belt.
[0121]
Moreover, you may employ | adopt a form as shown in FIG. The total length of the intermediate transfer belt 31 is L0 (see FIG. 4). As shown in FIG. 9, the dimension of the transfer prohibition area 75 in the rotational drive direction 72 is L1, and the dimension of the transfer permission area 76 is L2 (that is, L0 = L1 + L2) When the distance between the primary transfer portion 14 and the secondary transfer portion 37 is L3, the form of FIG.
L1> L3
Is set.
[0122]
Then, the CPU 111 performs control to change the output value of the primary transfer bias while the transfer prohibited area 75 passes through both the primary transfer unit 14 and the secondary transfer unit 37. According to this modification, it is possible to reliably avoid changing the output value of the primary transfer during the secondary transfer. Therefore, the control configuration can be simplified.
[0123]
In the above embodiment, a printer that prints an image supplied from an external device such as a host computer on transfer paper is described. However, the present invention is not limited to this, and includes a copying machine, a facsimile machine, and the like. The present invention can be applied to a general electrophotographic image forming apparatus.
[0124]
【The invention's effect】
  As explained above, claims 1 and6According to the invention, the non-image area where the toner image is not transferred onto the intermediate transfer medium1Pass through the next transfer sectionNo secondary transfer is being performedSince the output value of the primary transfer bias is sometimes changed, it is possible to reliably avoid the change of the output value during the secondary transfer, and thereby the change of the output value. It is possible to prevent the influence from affecting the secondary transfer.In addition, after the preset time has elapsed so that the output value of the primary transfer bias is changed from when the reference signal is output until the non-image area passes through the primary transfer portion, the primary transfer bias is changed. Since the output value is changed, it is possible to easily avoid the change of the output value during the secondary transfer by counting based on the reference signal. Further, it is determined at the time of output of the reference signal whether or not the change of the output value of the primary transfer bias is necessary due to the change of the bias change condition, and when it is determined that the change of the output value is necessary, Whether the secondary transfer is performed after the elapsed time from the output time is determined at the output time, and when it is determined that the secondary transfer is performed after the elapsed time from the output time, Since the next toner image formation is waited for a preset waiting time, it is possible to avoid a situation in which primary transfer is performed at the output value that does not meet the bias change condition or toner is consumed wastefully. Can do.
[0125]
According to the second aspect of the present invention, the output value of the primary transfer bias is changed according to at least one of the atmospheric temperature and the atmospheric humidity, so that it depends on the environmental conditions such as the atmospheric temperature and the atmospheric humidity. The influence due to the change in transfer efficiency is reduced, and the primary transfer from the photoreceptor to the intermediate transfer medium can be suitably performed.
[0126]
According to the invention of claim 3, since the output value of the primary transfer bias is changed between the primary transfer of the first toner image and the primary transfer of the last toner image, intermediate transfer is performed. Regardless of the change in transfer efficiency due to the thickness of the toner image on the medium, primary transfer from the photoreceptor to the intermediate transfer medium can be suitably performed.
[0129]
  Claims4According to the invention, since the waiting time is at least the time until the next reference mark is detected, the change of the output value can be easily and reliably performed during the secondary transfer by measuring the time based on the reference signal. Can be avoided.
[0130]
  Claims5According to the invention, since the standby time is a time during which the intermediate transfer medium is driven to rotate by at least one sub-region, a decrease in throughput is suppressed as compared with a case where the intermediate transfer medium waits for one round. can do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the printer.
FIG. 3 is a cross-sectional view of an intermediate transfer belt.
4A and 4B are development views of the intermediate transfer belt.
FIG. 5 is a diagram schematically illustrating a configuration example of a transfer bias generation circuit.
FIG. 6 is a timing chart showing temporal changes in the state of each part of the engine part for explaining the operation.
FIG. 7 is a timing chart showing temporal changes in the state of each part of the engine part for explaining another operation.
FIG. 8 is a timing chart showing temporal changes in the state of each part of the engine unit for explaining still another operation.
FIG. 9 is a diagram showing a modification.
[Explanation of symbols]
4 Transfer paper
6 Temperature sensor
7 Humidity sensor
11 photoconductor
14 Primary transfer section
31 Intermediate transfer belt (intermediate transfer medium)
31A Bias applying member (primary transfer bias applying means)
32 Vertical synchronization sensor (reference detection means)
37 Secondary transfer section
72 Rotation drive direction
73 Rotational axis direction
75 Transcription prohibited area
76 Transcription permitted area
76A, 76B Sub-region
82 Conductive layer
110 Engine control unit
111 CPU (bias control means, toner image formation control means, bias change determination means, secondary transfer determination means)
116 Primary transfer bias generation circuit (primary transfer bias applying means)

Claims (6)

An intermediate transfer medium comprising a plurality of layers including a conductive layer is provided, a toner image is formed on the photosensitive member by a developing means , and the toner image on the photosensitive member is primary-transferred to the rotating intermediate transfer medium in a primary transfer portion. In an image forming apparatus in which a toner image on the intermediate transfer medium is secondarily transferred to a transfer paper in a secondary transfer unit,
The intermediate transfer medium includes a transfer permission area in which primary transfer of a toner image is permitted and a transfer prohibition area in which primary transfer of a toner image set in the rotation axis direction is prohibited. ,
A reference detection means for detecting a reference mark provided on the intermediate transfer medium and outputting a reference signal;
Toner image formation control means for controlling toner image formation on the photoconductor based on the reference signal;
Primary transfer bias applying means for applying a preset primary transfer bias to the conductive layer of the intermediate transfer medium;
When the non-image area where no toner image is transferred onto the intermediate transfer medium is passing through the primary transfer portion and secondary transfer is not performed, the primary transfer is performed according to a predetermined bias change condition. An output value of the transfer bias is changed, and is set in advance so that the output value is changed from the time when the reference signal is output until the non-image area passes through the primary transfer portion. Bias control means for changing the output value after an elapsed time ;
Bias change determination means for determining at the time of output of the reference signal whether or not the output value needs to be changed according to the bias change condition;
When the bias change determination unit determines that the output value needs to be changed, the secondary transfer determines whether the secondary transfer is performed after the elapsed time from the output time. Determination means,
When the secondary transfer determination unit determines that the secondary transfer is performed after the elapsed time from the output time point, the toner image formation control unit forms the next toner image for a preset standby time. image forming apparatus characterized by waiting for a.   The image forming apparatus according to claim 1, wherein the bias control unit uses at least one of an ambient temperature and an ambient humidity as the bias change condition. The developing means sequentially forms toner images of different colors on the photoreceptor, and the intermediate transfer medium is formed each time a toner image of each color is formed so that the toner images of the respective colors overlap on the intermediate transfer medium. The primary transfer
The bias control means uses the order of the toner images superimposed on the intermediate transfer medium as the bias changing condition, and performs the first toner image primary transfer and the last toner image primary transfer. The image forming apparatus according to claim 1, wherein an output value of the primary transfer bias is changed. 4. The image forming apparatus according to claim 1, wherein the standby time is at least a time until the next reference mark is detected by the reference detection unit. The transfer permission area of the intermediate transfer medium includes a plurality of sub areas to which toner images of a predetermined size are transferred,
The image forming apparatus according to claim 1, wherein the standby time is a time during which the intermediate transfer medium is driven to rotate by at least one sub-region . An intermediate transfer medium comprising a plurality of layers including a conductive layer is formed, a toner image is formed on a photoconductor, and the toner image on the photoconductor is primarily transferred to the intermediate transfer medium rotating in a primary transfer portion, and then secondary In an image forming method in which a toner image on the intermediate transfer medium is secondarily transferred onto a transfer sheet in a transfer unit,
The intermediate transfer medium includes a transfer permission area in which primary transfer of a toner image is permitted and a transfer prohibition area in which primary transfer of a toner image set in the rotation axis direction is prohibited. ,
When a non-image area in which no toner image is transferred onto the intermediate transfer medium is passing through the primary transfer portion and secondary transfer is not performed, a reference mark provided on the intermediate transfer medium is After an elapse time that is set in advance so that the output value of the primary transfer bias is changed from the output time point of the reference signal by detection until the non-image area finishes passing through the primary transfer portion, change the output value of the primary transfer bias applied to the conductive layer of the intermediate transfer medium in accordance with a predetermined bias change condition,
When it is determined that the output value needs to be changed according to the bias change condition at the output time of the reference signal, it is determined whether secondary transfer is performed after the elapsed time from the output time. Determine at the time of the output,
When it is determined that the secondary transfer is performed after the lapse of time from the output time, the next toner image formation on the photoconductor based on the reference signal is waited for a preset standby time. An image forming method.

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