JP3955698B2 - Image forming apparatus - Google Patents

Description

【００４４】
この表１に示した例では、出力値Ｖｓｐ／Ｖｓｇと、これに対応するＰ目標値との比較に基づいて、Ｐパターンにおける画像濃度の濃淡を判定させている。この出力値Ｖｓｇとはトナー像を形成していない状態の感光ドラム１の地肌部を検知したときのＰセンサ８からの出力値であり、この検知はＰパターン検知に先立って行われる。なお、表１及び後述の表６におけるＳは、トナー濃度ＴＣが１［ｗｔ％］上昇するときの出力値ＶＴの変化量であるＴセンサ感度を示している。
【００４５】
表１において、例えば、Ｖｓｐ／ＶｓｇがＰ目標値より大きい、即ち、Ｐパターンの画像濃度が目標よりも薄いにもかかわらず、ΔＶＴが０よりも大きい、即ち、トナー濃度ＴＣが高いと判断される場合には、制御部１０に対してこのときのトナー濃度ＴＣを、低いか又は通常であると判断させるように基準値ＶＴｒｅｆを補正させる必要がある。そこで、このような場合には、補正後のＶＴｒｅｆ（＝前回までの基準値ＶＴｒｅｆ＋補正量ΔＶＴｒｅｆ）を補正前よりも小くするように、表１に示したデータベースからマイナス極性のΔＶＴｒｅｆを選択して基準値ＶＴｒｅｆを補正させるように制御部１０を構成している。このようにＶＴｒｅｆを補正させると、トナー濃度ＴＣをそれまでより低く維持するようにトナー補給を実行させ、画像濃度を高めることができる。
【００４６】
また例えば、Ｖｓｐ／ＶｓｇがＰ目標値より小さい、即ち、Ｐパターンの画像濃度が目標よりも濃いにもかかわらず、ΔＶＴが０よりも小さい、即ち、トナー濃度ＴＣが低いと判断される場合には、制御部１０に対してこのときのトナー濃度ＴＣを高いか又は通常であると判断させるように基準値ＶＴｒｅｆを補正させる必要がある。そこで、このような場合には、補正後の基準値ＶＴｒｅｆを補正前よりも高くするように、表１に示したデータベースからプラス極性のΔＶＴｒｅｆを選択して基準値ＶＴｒｅｆを補正させるように制御部１０を構成している。
【００４７】
しかしながら、このような基準値ＶＴｒｅｆの補正を実施させていても、トナー濃度ＴＣの過多によって感光体ドラム１や転写紙５の非画像部に地汚れを生じたり、トナー濃度ＴＣの不足によって画像濃度の著しい低下や感光体ドラム１へのキャリア付着を生じたりする場合がある。
【００４８】
例えば、連続プリント動作を実施したり、画像面積率の高い画像をプリントアウトしたりすると、トナー補給装置７によるトナー補給速度が現像装置３内のトナー濃度ＴＣの低下速度に追いつかない場合がある。このような場合には、トナーカートリッジ７ａに十分量のトナーが収容されているにもかかわらず、トナー濃度が一時的に低下することになる。そして、この低下の度合いが大きいと、画像濃度の著しい低下やキャリア付着を生ずる。
【００４９】
また例えば、現像剤の劣化等により現像装置３の現像能力が大きく低下している場合には、基準濃度がかなり高く維持される。このような場合には、目標の濃度が形成される代わりに、地汚れを引き起こす場合がある。
【００５０】
図３はＰセンサ８の出力特性と、現像装置３の現像特性とを示すグラフであり、図中左側のグラフは前者の特性を示し、図中右側のグラフは後者の特性を示している。図示の例では、感光体ドラム１と現像スリーブ３ａとの間に電位差４００［Ｖ］の現像ポテンシャルが生ずることによりＰパターンが形成される。また、Ｐパターンを検知するＰセンサ８からの出力Ｖｓｐの値と、出力Ｖｓｇの値との比率Ｖｓｐ／Ｖｓｇが１／１０になったときに、Ｐパターンの画像濃度ＩＤが基準濃度になる。よって、Ｖｓｐ／Ｖｓｇを１／１０にするようなトナー濃度であれば、現像装置３の現像特性は曲線Ａに示すような状態になり、６００［Ｖ］の現像ポテンシャルで形成される出力画像の濃度が目標ＩＤになる。一方、環境変化等の原因により、現像装置３の現像特性が曲線Ｂに示すような状態に変化した場合には、トナー濃度を増加させて現像特性を曲線Ａに示すような状態に復帰させれば目標ＩＤの画像を得ることができる。しかし、曲線Ｂを曲線Ａに示す状態にすべくトナー濃度を増加させ過ぎると、目標濃度の画像が形成される代わりに、地汚れを引き起こしてしまうのである。
【００５１】
そこで、制御部１０は、予め設定された上下限値を機能させながら基準値ＶＴｒｅｆを補正するのである。このように基準値ＶＴｒｅｆを補正すると、地汚れを生じさせない範囲で基準濃度を増加させ、且つ画像濃度の著しい低下やキャリア付着を生じない範囲で該基準濃度を低下させることができる。
【００５２】
なお、Ｐパターンの画像濃度が目標よりも濃いにもかかわらず、ΔＶＴが０よりも大幅に小さいと判断される場合には、装置が未使用状態で長期間放置された可能性が高い。長期間の放置により、トナー帯電量Ｑ／Ｍが不足することに起因してＰパターンの画像濃度が目標よりも濃くなる一方で、現像剤中におけるトナーの嵩密度が低下することに起因して出力ＶＴの値が本来よりも低くなっている可能性が高いからである。このような場合（以下、攪拌要求ケースという）には、現像剤の攪拌に伴ってトナーの摩擦帯電と拡散とが進行するので、Ｐセンサ８からの出力Ｖｓｐ、及びＴセンサからの出力ＶＴは、やがて正常な値に安定してくるとともに、現像装置３の現像能力も復帰してくる。従って、攪拌要求ケースのときには、トナー濃度をあまり変化させずに画像形成を実施させることが望ましい。しかし、攪拌要求ケースのときには、トナー濃度が一定であっても出力ＶＴが現像剤の攪拌に伴って変化してしまう。具体的には、本プリンタの場合には、トナー濃度が一定であっても出力ＶＴが現像剤の攪拌に伴って低下してくる。このような状況下で、画像形成に伴ってトナーが消費されてもトナー濃度を一定に維持させるようにするためには、基準値ＶＴｒｅｆをプリント動作に伴って低下させて行く必要がある。そこで、制御部１０は、攪拌要求ケースの場合には、一旦補正した基準値ＶＴｒｅｆをプリント動作に伴って元の基準値ＶＴｒｅｆまで徐々に低下させて行く第２補正を実施する。
【００５３】
次に示す表２及び表３は、攪拌要求ケース用の第２補正で補正量ΔＶＴｒｅｆを決定させるべくデータ記憶部１１に格納しているデータベースの一例である。
【表２】

【表３】

【００５４】
この第２補正において、制御部１０は、まず、表２に示したデータベースを用いて、ΔＶＴの値に応じた値の攪拌時間Ｔ［ｓｅｃ］と補正量ΔＶＴｒｅｆとを選択する。例えば、ΔＶＴ＝−０．４［Ｖ］である場合には、攪拌時間Ｔとして２００［ｓｅｃ］を選択するとともに、補正量ΔＶＴｒｅｆとして０．２［Ｖ］を選択する。そして、元の基準値ＶＴｒｅｆに補正量ΔＶＴｒｅｆを加算して基準値ＶＴｒｅｆを補正する。次に、以降のプリント動作の実施時間が攪拌時間Ｔに到達するまでの間において、表３に示したデータベースを用いて、残り攪拌時間Ｔｒに応じた値の補正量ΔＶＴｒｅｆを選択しながら、元の基準値ＶＴｒｅｆに補正量ΔＶＴｒｅｆを加算して基準値ＶＴｒｅｆの補正を繰り返す。表３に示したように、第２補正においては、残り攪拌時間Ｔｒが少なくなるほど、元の基準値ＶＴｒｅｆに加算される補正量ΔＶＴｒｅｆは小さくる。このため、第２補正においては、最初に補正された基準値ＶＴｒｅｆがプリント動作に伴って元の基準値ＶＴｒｅｆまで徐々に低下して行くことになる。
【００５５】
なお、表２における攪拌時間は現像動作に伴う攪拌動作の駆動時間を示すものであり、現像動作とは個別に実施される攪拌動作の駆動時間を示すものではない。また、残り攪拌時間についても同様である。
【００５６】
次に示す表４は、トナー補給時間ｔを決定するためにデータ記憶部１１に格納しているデータベースである。
【表４】

【００５７】
表４に示すように、ΔＶＴがマイナスのとき、即ち、トナー濃度ＴＣが基準濃度を下回っているときにトナー補給がなされる。そして、決定されるトナー補給時間ｔは、出力ＶＴの値がマイナス側に大きくなる（トナー濃度が低くなる）ほど延長される。このようなトナー補給時間ｔの決定により、適切な量のトナーが現像装置３に補給されてトナー濃度ＴＣが基準濃度まで回復する。なお、本プリンタにおいては、Ｓ（Ｔセンサ感度）＝０．４［ｗｔ％／Ｖ］のＴセンサ３ｄを使用している。
【００５８】
なお、本プリンタは、出荷直後の初期トナー投入時には、まず、供給ローラ７ｄ、トナー搬送スクリュー３ｂ、３ｃの回転駆動を所定時間実施して、現像装置３内のトナー濃度が約４．５［ｗｔ％］になるようなトナー補給を行う。次いで、供給ローラ７ｄを停止させるとともに、トナー搬送スクリュー３ｂ、３ｃの回転駆動を継続してＴセンサ３ｄの出力ＶＴの値を安定化させた後、基準値ＶＴｒｅｆを２．５［Ｖ］に設定するように構成されている。
【００５９】
ところで、従来、以上の構成のプリンタにおいては、基準値ＶＴｒｅｆの第２補正中に地汚れを引き起こすという問題を生ずる場合があった。本発明者らはこの問題について鋭意研究した結果、第２補正時に基準値ＶＴｒｅｆに対して閾値が機能することにより地汚れが生じていたことを見出した。そこで、本プリンタは、次のような特徴的は制御を実施することで、第２補正中に生ずる地汚れを低減している。
【００６０】
以下、この特徴的な制御について説明する。
図４から図９までは、制御部１０のプリント制御の要部を示すフローチャートである。以下、これらの図を参照しながら、このプリント制御について説明する。
図４において、制御部１０は、メインスイッチをＯＮされると（ｓ１）、まず、トナー付着のない感光体ドラム１の非画像部を検知するＰセンサ８の出力Ｖｓｇを所定の値に設定する（ｓ２）。そして、感光体ドラム１にＰパターンを形成させた後（ｓ３）、今度は該Ｐパターンを検知するＰセンサ８からの出力Ｖｓｐの値を検出する（ｓ４）。次いで、Ｖｓｐ／Ｖｓｇを演算した後（ｓ５）、現像装置３内の現像剤を検知するＴセンサ３ｄからの出力ＶＴの値を検出する（ｓ６）。そして、ΔＶＴ（ＶＴｒｅｆ−ＶＴ）を演算した後（ｓ７）、ｓ８、ｓ９の制御を実行する。
【００６１】
これらｓ８、ｓ９の制御においては、攪拌要求ケース用の制御の必要性が判断される。表１に示したように、この制御が実施される必要があるケースは、「ΔＶＴ<−０．３」&「（Ｖｓｐ／Ｖｓｇ）<０．１３」の条件を具備したときである。従って、制御部１０は、これらｓ８、ｓ９において、「ΔＶＴ<−０．３」&「（Ｖｓｐ／Ｖｓｇ）<０．１３」であるか否かを判定し、そうである場合には制御を攪拌モード処理に進める。また、そうでない場合には、制御を通常モード処理に進める。
【００６２】
図５は、この通常モード処理の制御内容を示すフローチャートである。図示のように、制御部１０は制御を通常モード処理に進めると、まず、基準値ＶＴｒｅｆに基づいて、表１から補正量ΔＶＴｒｅｆを決定する（Ｏｓ１）。そして、この補正量ΔＶＴｒｅｆの加算により基準値ＶＴｒｅｆを補正した後（Ｏｓ２）、補正した基準値ＶＴｒｅｆに対して上限値１．１［Ｖ］と下限値２．８［Ｖ］とを機能させる（Ｏｓ３〜Ｏｓ６）。具体的には、Ｏｓ３〜Ｏｓ６の制御において、基準値ＶＴｒｅｆは１．１を下回る場合には上限値である１．１に補正され、２．８を超える場合には、２．８に補正される。このため、基準値ＶＴｒｅｆは最終的に１．１〜２．８［Ｖ］の範囲内で補正されることになる。このような補正により、本プリンタは地汚れを生じさせない範囲でトナーの基準濃度を増加させ、且つ形成画像の著しい低下やキャリア付着を生じない範囲で該基準濃度を低下させることができる。
【００６３】
制御部１０は、このようにして基準値ＶＴｒｅｆを補正すると、次に、プリント命令の有無があるまで待機し（Ｏｓ７でＮ）、プリント命令がなされた時点（Ｏｓ７でＹ）で制御を通常モード用プリント処理に進める。
【００６４】
一方、上述のように現像剤の状態が攪拌要求ケースである場合には、制御部１０は制御を攪拌モード処理に進める。
図６は、この攪拌モード処理の制御内容を示すフローチャートである。図示のように、制御部１０は制御を攪拌モード処理に進めると、まず、基準値ＶＴｒｅｆに基づいて、表２から攪拌時間Ｔ及び補正量ΔＶＴｒｅｆを決定する（Ｋｓ１）。そして、この補正量ΔＶＴｒｅｆの加算により元の基準値ＶＴｒｅｆを補正した後（Ｋｓ２）、残り攪拌時間Ｔｒを攪拌時間Ｔと同等の値に設定する（Ｋｓ３）。次いで、プリント命令の有無があるまで待機し（Ｋｓ４でＮ）、プリント命令がなされた時点（Ｋｓ４でＹ）で制御を攪拌モード用プリント処理に進める。
【００６５】
図５と図４とを比較すると、通常処理モードでは基準値ＶＴｒｅｆに閾値としての上下限を機能させていたのに対し、攪拌モード処理では該上下限を機能させていないことがわかる。このように、攪拌モード処理において、上下限を機能させないで基準値ＶＴｒｅｆを補正すると、基準値ＶＴｒｅｆを補正すべき値に確実に変化させる。
【００６６】
例えば、攪拌モードにおいて、上下限を機能させないで基準値ＶＴｒｅｆ（２．５［Ｖ］）の補正を実施した場合、出力ＶＴ＝３．２［Ｖ］、出力Ｖｓｐ／Ｖｓｇ＝０．０７のときには、ΔＶＴ＝２．５−３．２＝−０．７［Ｖ］となる。そして、上記Ｋｓ１で表２より６００［ｓｅｃ］の攪拌時間Ｔと０．６［Ｖ］の補正量ΔＶＴｒｅｆが選択され、上記Ｋｓ２で基準値ＶＴｒｅｆが２．５＋０．６＝３．１に補正される。このように基準値ＶＴｒｅｆが補正されると、ΔＶＴは３．１−３．２＝−０．１［Ｖ］になるので、以降の制御において２．４［ｓｅｃ］のトナー補給が実施される（表４参照）。
【００６７】
一方、攪拌モードにおいて、上下限を機能させて基準値ＶＴｒｅｆ（２．５［Ｖ］）の補正を実施した場合、上記Ｋｓ２で補正された基準値ＶＴｒｅｆ＝３．１［Ｖ］が、上限値の機能により２．８［Ｖ］に修正されてしまう。このように修正されると、ΔＶＴは２．８−３．２＝−０．４［Ｖ］になるので、以降の制御において１秒ＯＮ／２秒ＯＦＦの間欠補給が連続的に継続され、トナー濃度ＴＣが著しく増加してしまう。そして、このようなトナー濃度ＴＣの著しい増加が、地汚れを引き起こすことになる。
【００６８】
図７は、上記攪拌モード処理におけるプリント処理の制御内容を示すフローチャートである。図示のように、制御部１０は制御を攪拌モード用プリント処理に進めると、まず、一回分のプリント動作を開始させてから（Ｋｓ５）、攪拌動作を開始させる（Ｋｓ６）。この攪拌動作とは、具体的には、トナー搬送スクリュー３ｂ、３ｃを回転駆動させることである。次いで、制御部１０は、残り攪拌時間Ｔｒのカウントダウンを開始した後に（Ｋｓ７）、出力ＶＴの値を検出する（Ｋｓ８）。そして、「ΔＶＴ＝ＶＴｒｅｆ−ＶＴ」の演算結果と、上記表４とに基づいてトナー供給時間ｔを決定した後（Ｋｓ９）、トナー補給を開始させる（Ｋｓ１０）。
【００６９】
制御部１０は、トナー補給を開始した後、一回分のプリント動作を終了すると（Ｋｓ１１）、次に、累積プリント回数を示す変数であるＰＣに１を加算する（Ｋｓ１２）。そして、攪拌動作を終了した後に（Ｋｓ１３）、残り攪拌時間Ｔｒのカウントダウンを終了する（Ｋｓ１４）。なお、この時点で残り攪拌時間Ｔｒが０までカウントダウンされていない場合には、以降のプリント動作において、攪拌モード用の制御が継続されることになる。
【００７０】
次に制御部１０は、予定数のプリント動作を行ったか否かについて判定し、連続プリント命令を受けたことによりまだ次のプリント動作が残っている場合（Ｋｓ１５でＮ）には、制御をＫｓ１５ａに進める。また、次のプリント動作が残っていない場合（Ｋｓ１５でＹ）には、制御をＫｓ１６に進める。
【００７１】
Ｋｓ１５ａに制御を進めた場合、制御部１０は残り攪拌時間Ｔｒの値と表３とに基づいて、新たなΔＶＴｒｅｆを決定した後、メインスイッチがＯＦＦされる前まで使用していた元の基準値ＶＴｒｅｆにこのΔＶＴｒｅｆを加算して基準値ＶＴｒｅｆを更新する（Ｋｓ１５ｂ）。このとき、残り攪拌時間Ｔｒの減少分に応じて、基準値ＶＴｒｅｆは元の基準値に近づいて低下することになる。更に、制御部１０は、制御を上述のＫｓ５にループさせて次のプリント動作を開始する。
【００７２】
Ｋｓ１６に制御を進めた場合、即ち、次のプリント命令を受けていない場合、制御部１０はトナー補給を終了したか否かについて判定する。トナー補給時間ｔの長さによっては、プリント動作中にトナー補給が完了しない場合がある。そこで、制御部１０は、このような判定を行い、「完了していない」と判定した場合には（Ｋｓ１６でＮ）には、トナー補給を継続させるＫｓ１７に制御を進めた後、Ｋｓ１６にループさせる。このようなループにより、トナー補給が完了していない場合には、トナー補給が完了するまで制御が先のステップに進まないようになっている。
【００７３】
制御部１０は、補給動作を完了させた場合、又は補給動作がプリント動作中で完了していた場合には（Ｋｓ１６でＹ）、次に、残り攪拌時間をゼロまでカウントダウンしているか否かについて判定する（Ｋｓ１８）。そして、ゼロまでカウントダウンしている場合には（Ｋｓ１８でＹ）、制御をメインフローにリターンさせる。このリターンにより、攪拌モード処理が終了する。そして、通常は、以降の制御において、上記ｓ８、ｓ９で「ΔＶＴ<−０．３」&「（Ｖｓｐ／Ｖｓｇ）<０．１３」という条件が「否」と判定されて通常モード処理が実施される。
【００７４】
また、制御部１０は、上記Ｋｓ１８において、ゼロまでカウントダウンしていないと判断した場合には（Ｋｓ１８でＮ）、攪拌モード処理を継続すべく制御を上記Ｋｓ５（図４参照）にループさせる。このループにより、以降の制御において、プリント命令を受信すると、攪拌モード処理を継続して実施する。従って、攪拌モード処理は、残り攪拌時間Ｔｒがゼロまでカウントダウンされるまで継続される。
【００７５】
図８は、上記通常モード処理におけるプリント処理の制御内容を示すフローチャートである。この通常モード用プリント処理においては、残り攪拌時間Ｔｒを考慮しない制御が実施される以外は、図８に示した攪拌モード用プリント処理の制御とほぼ同様であるので説明を省略する。
【００７６】
以上、本実施形態のプリンタによれば、基準値ＶＴｒｅｆの第２補正中に上限値を機能させることにより生ずるトナーの過補給を回避するので、第２補正中に生ずる地汚れを低減することができる。
【００７７】
次に、この実施形態のプリンタに、より特徴的な構成を付加した実施例のプリンタについて説明する。
図９は本実施例のプリンタにおける攪拌モード処理の制御内容を部分的に示すフローチャートである。図示のように、このプリンタの制御部１０は、Ｋｓ１４とＫｓ１５との間（図７における点Ａ）において、Ｋｓ１４ａの制御を実施する。このＫｓ１４では、残り攪拌時間Ｔｒのカウントダウン値についてゼロに達しているか否かを判定し、「達していない」と判定した（Ｋｓ１４ａでＮ）場合には制御をＫｓ１５に進めて攪拌モード処理の制御を継続する。一方、「達した」と判定した場合（Ｋｓ１４ａでＹ）には、例え連続プリント動作中であっても、制御をＫｓ１５に進めることなくメインフローにリターンさせる。
【００７８】
上記表３に示したように、残り攪拌時間Ｔｒがゼロに達した時点で、基準値ＶＴｒｅｆの第２補正は終了し、基準値ＶＴｒｅｆは第２補正前の値に戻っている。しかし、このとき、トナー帯電量Ｑ／Ｍの影響などでトナーの嵩密度が十分に回復していないと、基準値ＶＴｒｅｆは実状にそぐわない値になっている場合がある。そして、このことにより、上記Ｋｓ１５以降に出力されるプリントアウト画像において、地汚れを生ずるおそれがある。そこで、制御部１０は、上記Ｋｓ１４ａで基準値ＶＴｒｅｆの第２補正を終了している（Ｔｒ＝０）と判定した場合には、制御をメインフローにリターンさせる。このようにリターンさせると、第２補正終了後の初めのプリント動作に先立って、Ｐパターンを形成し、このＰパターンについてのＶｓｐ／Ｖｓｇ及び出力ＶＴに基づいて基準値ＶＴｒｅｆを補正することができる。そして、このことにより、第２補正後の基準値ＶＴｒｅｆ基準値が実状にそぐわない値になっていても、初めのプリント動作に先立って適正な値に補正することができる。
【００７９】
以上、本実施例のプリンタによれば、第２補正後の基準値ＶＴｒｅｆが実状にそぐわない値であっても、初めのプリント動作に先立って適正な値に補正されるので、第２補正後に生ずる地汚れを低減することができる。
【００８０】
なお、上記実施形態及び実施例において、感光体ドラム１から転写紙５にトナー像を直接転写する構成のプリンタについて説明したが、中間転写体を介して転写紙５に転写する構成の画像形成装置についても本発明の適用が可能である。
【００８１】
また、現像装置を１つだけ備えるプリンタについて説明したが、リボルバ現像ユニットなど、複数の現像器を備える画像形成装置についても本発明の適用が可能である。
【００８２】
また、所定信号出力手段としてＰセンサを備えるプリンタについて説明したが、例えば湿度センサなど、他の所定信号出力手段を備える画像形成装置についても本発明の適用が可能である。
【００８３】
【発明の効果】
請求項１の発明によれば、下限値や上限値を機能させながら、該下限値や上限値の機能に起因して第２補正中に生ずる画像形成物質の過補給を回避するので、下限値や上限値を機能させながら第２補正中に生ずる地汚れを低減することができるという優れた効果がある。
【図面の簡単な説明】
【図１】実施形態に係るプリンタの作像部分を示す概略構成図。
【図２】同プリンタのＴセンサの出力特性を示すグラフ。
【図３】同プリンタのＰセンサの出力特性と、現像装置の現像特性とを示すグラフ。
【図４】同プリンタの制御部におけるプリント制御の要部を示すフローチャート。
【図５】同プリント制御の通常モード処理の制御内容を示すフローチャート。
【図６】同プリント制御の攪拌モード処理の制御内容を示すフローチャート。
【図７】同攪拌モード処理のプリント処理の制御内容を示すフローチャート。
【図８】同通常モード処理のプリント処理の制御内容を示すフローチャート。
【図９】実施例のプリンタにおける攪拌モード処理の制御内容を部分的に示すフローチャート。
【図１０】Ｔセンサの出力ＶＴの値とプリントアウト回数（又は攪拌動作時間）との関係を示すグラフ。
【符号の説明】
１ 感光体ドラム
２ 帯電装置
３ 露光装置
５ 給紙トレイ
６ レジストローラ
７ 搬送装置
８ 転写装置
９ 定着装置
１０ 排紙トレイ
１１ クリーニング装置
２０ スキャナー部
２１ 画像処理部
２２ プリンタ部
３０ 湿度センサー
３１ 温度センサー
１００ 現像装置
１０１ 現像ケーシング
１０２ トナー収容部
１０３ 第１搬送ローラ
１０５ 第２搬送ローラ
２００ 第１搬送ローラバイアス切替スイッチ
２０２ ＭＰＵ
２０３ 回収バイアス切替スイッチ[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus such as a copying machine, a facsimile, and a printer using the image forming method, and more particularly, a density signal output unit that changes the value of an output signal according to the density of an image forming substance in a developer. The present invention relates to improvement of reference value correction means for correcting the reference value.
[0002]
[Prior art]
In an image forming apparatus using a two-component developer (hereinafter simply referred to as a developer) composed of a magnetic carrier and a toner as an image forming substance, the toner concentration, which is the image forming substance concentration in the developer, is developed by the developing apparatus. This is one of the main factors that influence ability. Therefore, in order to form an image having a stable density, it is desirable to keep the toner density in the two-component developer in the developing device constant.
[0003]
However, the developing capability of the developing device greatly depends on changes in the environment such as humidity and temperature, changes in the characteristics of the developer over time (for example, deterioration), changes in development conditions, and the like in addition to the toner concentration. For this reason, the image density cannot be stabilized simply by keeping the toner density constant.
[0004]
Therefore, conventionally, in order to stabilize the image density, an output value from an optical sensor (hereinafter referred to as a P sensor) serving as an adhesion amount signal output means and a permeability sensor (hereinafter referred to as T sensor) serving as a density signal output means. Various image forming apparatuses that determine a toner density value to be kept constant based on an output value from a sensor (for example, Japanese Patent Laid-Open Nos. 5-134548, 8-110700, and 8) are known. -202137, JP-A-9-211911, etc.).
[0005]
In this type of image forming apparatus, for example, a toner density (hereinafter referred to as a reference density) to be maintained constant is determined as follows. That is, first, the developer in the developing device is detected by the T sensor while forming a reference image on the photosensitive member as the latent image carrier, and the value of the output VT from the T sensor at this time is measured. Then, while detecting the reference image by the P sensor, the value of the output Vsp from the P sensor is measured. Next, based on the output VT value and the Vsp value, the reference value VTref is corrected (hereinafter simply referred to as reference value correction) so that the toner adhesion amount as the image forming substance adhesion amount can be set to the target adhesion amount. . Specifically, a correction amount ΔVTref with respect to the previous reference value VTref is determined based on the value of the output VT and the value of Vsp, and the reference value correction is performed by adding the correction amount ΔVTref. Then, the toner supply to the developing device is controlled so that the value of the output VT from the T sensor reaches the corrected reference value VTref. In such a series of controls, the correction amount ΔVTref determined based on the value of the output VT that changes in accordance with the change in the toner density and the value of the output Vps that changes in accordance with the change in the toner adhesion amount is changed to VTref. By adding (or subtracting), the reference density of the toner in the developing device is changed. Then, by changing the reference density in this way, the image density can be stabilized while maintaining the developing ability constant.
[0006]
However, even if such a reference value correction is performed, a so-called background smear that causes toner to adhere to the non-image portion of the latent image carrier or the output document due to excessive toner density, or image density due to insufficient toner density. In some cases, and the carrier may adhere to the latent image carrier. For example, when the developing ability of the developing device is greatly reduced due to deterioration of the developer or the like, the toner density is significantly increased by correcting the reference value. Then, instead of forming an image having a target density, there is a case where background staining occurs due to such a significant increase in toner density. Further, for example, when the developing ability of the developing device is greatly increased for some reason, the toner density is remarkably lowered by the reference value correction. In this way, when the toner density is significantly reduced, an image with a high image area ratio that consumes a large amount of toner is formed, or when the toner replenishment capability is reduced due to a shortage of toner remaining in the toner cartridge containing the replenishment toner. In some cases, the toner density is insufficient and the image density may be significantly reduced or carrier adhesion may occur.
[0007]
In view of this, an image forming method in which a threshold value is provided for the reference value VTref of the T sensor in order to reduce the occurrence of such background contamination, image density reduction, and carrier adhesion has been known (for example, Japanese Patent Laid-Open No. 8-202137). As described in). According to this image forming method, by correcting the reference value in a range that does not reach a preset threshold value, the toner density is increased in a range that does not cause background contamination, or the image density is significantly reduced and carrier adhesion occurs. The toner density can be lowered within the range where it is not. Thus, it is possible to reduce the occurrence of scumming as described above, or to significantly reduce the image density and the occurrence of carrier adhesion.
[0008]
On the other hand, if the image forming apparatus is left unused for a long period of time in a high temperature and high humidity environment such as a summer vacation, the toner charge amount of the developer is reduced and the bulk density of the toner in the developer is reduced. End up. When the power of the image forming apparatus is turned on in such a state, the toner whose electrostatic adhesion with the carrier is weakened due to insufficient charge amount easily adheres to the latent image carrier, and the density of the reference image Is higher than the target. On the contrary, the output VT from the T sensor becomes lower as the bulk density of the toner decreases even if the toner concentration of the developer is the same. Therefore, the comparison result between the value of the output VT and the reference value VTref is The toner density decreases. When normal reference value correction is performed in such a state, the reference value VTref is corrected so as to reduce the toner density. However, as the image forming operation proceeds, the charge amount of the toner gradually increases due to the stirring operation of the developing device. Even though the density of the output image is lowered due to this increase, the toner density is kept lower than usual until the next reference value correction is performed. If the toner density is kept low in this way, the density of the output image is remarkably lowered or carrier adhesion occurs. Therefore, when the toner charge amount is gradually stabilized with the progress of the stirring operation of the developing device (hereinafter referred to as a stirring request case), it is desirable to perform a reference value correction different from normal. Specifically, it is desirable to perform a reference value correction that does not change the toner density so much. However, in the case where the agitation is required, the toner bulk density gradually increases as the agitation operation of the developing device progresses, so the output VT changes as the agitation operation proceeds even if the toner concentration is constant. Resulting in. In order to maintain the toner density constant under such circumstances, it is desirable that the corrected reference value VTref be brought closer to the reference value VTref before correction as the developing device stirs. This is because by changing the reference value VTref in accordance with the change in the output VT accompanying the stirring operation, the toner density can be kept constant even if the output VT changes.
[0009]
Therefore, conventionally, an image forming apparatus that corrects the reference value VTref in a stirring request case by a method different from usual is known. In this type of image forming apparatus, first, a variable is added to correct the original reference value VTref. Then, the correction of the original reference value VTref is repeated as appropriate while gradually reducing the variable to be added to the original reference value VTref before correction as the stirring operation accompanying development proceeds. By repeating such correction, the corrected reference value VTref can be brought closer to the original reference value VTref before correction as the stirring operation proceeds.
[0010]
[Problems to be solved by the invention]
By the way, conventionally, in the image forming apparatus in which the threshold value is provided for the reference value VTref as described above, when the correction of the reference value VTref in the stirring request case (hereinafter referred to as the second correction) is performed, In some cases, it causes a problem of causing dirt. Therefore, as a result of intensive studies on this problem, the present inventors have found that such scumming was generated for the following reasons. That is, the cause of the background contamination is that the threshold functions when the second correction of the reference value VTref is performed. As described above, in the case of the stirring request case, it is desirable to control so that the toner density does not change so much. However, for example, in the case of using a T sensor that decreases the value of the output VT as the toner density increases, if the upper limit as the threshold value functions in the second correction, the reference value VTref is more than the value to be corrected. Lower. If the reference value VTref is lowered in this way, the toner replenishment amount becomes excessive, resulting in background smearing.
[0011]
Further, in the conventional image forming apparatus in which the threshold value of the reference value VTref is provided, there is a case in which the problem of causing background smearing occurs even after the second correction. Therefore, as a result of intensive studies on this problem, the present inventors have found that such scumming was generated for the following reasons. That is, the cause of this background contamination is that the reference value VTref after the second correction is not suitable for the reason described below.
[0012]
10 is a graph showing the relationship between the value of the output VT of the T sensor and the number of printouts (in the case of the curves A ′ and A ″, the stirring operation time). As shown by the curve B in FIG. The T sensor that detects the developer in the normal state before being left out outputs a substantially constant VT even when the number of printouts increases, and is supplied with toner of approximately the same amount as the toner consumption associated with the printouts. On the other hand, in the agitation request case, if the same amount of toner as the toner consumption is supplied and the toner density is stabilized, the value of the output VT gradually decreases as shown by the curve A. Then, it reaches a value equivalent to that of the curve B and stabilizes, and therefore, in the agitation request case, the reference value VTref is gradually lowered by the second correction as shown by the curve A. The reference value VTref as shown by the curve A. Reduce However, if the toner charge amount at the start of printout has not decreased so much due to a short developer leaving period, etc., As shown by the curve A ″, the bulk density of the toner recovers early. Further, when the toner charge amount at the start of the printout is remarkably reduced due to a long developer leaving period, the toner bulk density is recovered as shown by a curve A ′. It becomes difficult. Among these, when the bulk density of the toner is difficult to recover, the value of the output VT greatly exceeds the reference value VTref after the second correction. As a result, the toner density is kept high until the next reference value correction (normal correction) is performed. That is, as a result of the reference value VTref after the second correction becoming inaccurate, the toner density is kept high. As a result of the toner density being kept high in this way, background staining has occurred.
[0013]
The present invention has been made in view of the above problems. Eyes The target is to provide an image forming method and an image forming apparatus capable of reducing the background contamination generated during the second correction while functioning the threshold value.
[0015]
[Means for Solving the Problems]
Up Note In order to achieve the objective, the invention of claim 1 includes a latent image carrier that carries a latent image; Using a developer consisting of a toner that is an image forming substance and a magnetic carrier, The latent image toner A developing device for developing the latent image by attaching the toner to the developing device toner Replenishing means for replenishing the developer in the developer in the developing device toner Density signal output means for outputting a signal having a value corresponding to the density; The output value of the adhesion amount signal is changed according to the toner adhesion amount with respect to the reference image developed on the latent image carrier. Predetermined signal output means Corrugation amount signal output means Replenishment control means for controlling the operation of the replenishment means based on the comparison result between the output value from the concentration signal output means and the reference value; and Adhesion amount signal The reference value is preset based on the output value of From lower limit to upper limit range Inside First reference value correcting means for correcting with Although the image density of the reference image is determined to be higher than a predetermined target density based on the output value of the adhesion amount signal, the output value from the density signal output means is compared with the reference value. If it is determined that the toner density is lower than the target density, the reference value is corrected instead of the first reference value correcting means. Image forming apparatus comprising second reference value correcting means The second reference value correction means corrects the reference value without limitation of the range based on the adhesion amount signal and then gradually approaches the pre-correction value. It is something that is repeatedly corrected regardless of the signal. It is characterized by this.
[0019]
this In the invention, along with the progress of the stirring operation of the developing device toner When the second correction of the reference value occurs, such as a stirring request case that stabilizes the charge amount of Lower limit or upper limit The reference value is corrected without causing the function to function. like this Based on When the reference value is corrected, the reference value is surely changed to the value to be corrected, and during the second correction Lower limit or upper limit Caused by functioning toner Can be avoided. Also, By first reference value correction means When implementing the correction, Lower limit or upper limit By reducing the occurrence of background stains or reducing the significant density drop that occurs in the formed image. Lower limit or upper limit Can function effectively.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic printer (hereinafter referred to as a printer) which is an image forming apparatus will be described.
[0023]
First, the basic configuration of this printer will be described.
FIG. 1 is a schematic configuration diagram showing an image forming portion of the printer according to the present embodiment. The printer is rotatably mounted with a photosensitive drum 1 as a latent image carrier on which an electrostatic latent image is formed, and is driven clockwise in the figure by a drive system (not shown). Around the photosensitive drum 1, there are a charging roller 2, a developing device 3, a transfer roller 4, a cleaning device 5, a static elimination lamp 6 as a static elimination device, a reflection photosensor as an adhesion amount signal output means, and the like. A sensor 8 and an optical writing unit (not shown) are disposed. Further, the developing device 3 is provided with a toner replenishing device 7 as a replenishing unit for replenishing the developing device 3 with toner as an image forming material.
[0024]
The surface of the photosensitive drum 1 is neutralized by passing through a position facing the neutralizing lamp 6 in accordance with the clockwise rotation in the drawing. Then, after being in contact with the charging roller 6 and uniformly charged, a part of the light is exposed by irradiation with the writing light L emitted from the optical writing unit. By this exposure, the surface of the photosensitive drum 1 carries an electrostatic latent image. Then, when the electrostatic latent image passes through a position (development position) facing the developing device 3 as the photosensitive drum 1 rotates, toner as an image forming material is attached and developed into a toner image. The
[0025]
On the other hand, from a paper supply unit (not shown), the transfer paper 5 is discharged toward the registration roller pair 9 at the timing when the toner image passes the position (transfer position) facing the transfer roller 4. The transfer paper 5 thus discharged passes through the registration roller pair 9 and is then sent to the transfer position. At this transfer position, the toner image is sandwiched between the photosensitive drum 1 and the transfer roller 4 so as to be superimposed on the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 4 by a bias applying means (not shown), and a transfer electric field generated by a potential difference between the transfer roller 4 and the photosensitive drum 1 is formed at the transfer position. The toner image on the photosensitive drum 1 is transferred onto the transfer paper 5 by receiving a synergistic action such as a transfer electric field and pressure at the transfer position.
[0026]
The transfer paper 5 onto which the toner image has been transferred passes through the transfer position in accordance with the rotation of the photosensitive drum 1 and the transfer roller 4 that rotates counterclockwise in the figure, and then is sent to a fixing device (not shown). Then, heat and pressure are applied in the fixing device, whereby the toner image is fixed. Further, the transfer paper 5 on which the toner image is fixed in this way is discharged out of the apparatus by a discharge means (not shown) to become a printout paper.
[0027]
The residual toner remaining on the surface of the photosensitive drum 1 after passing through the transfer position is mechanically scraped and removed from the surface when the toner is conveyed to a position facing the cleaning device 5. . Then, the surface of the photosensitive drum 1 that has passed the position facing the cleaning device 5 is again discharged by the discharging light lamp 6 and is prepared for the next image formation.
[0028]
The toner replenishing device 7 is a toner cartridge 7a serving as a container, a stirring member 7b that is rotationally driven by a motor 7c to stir the toner in the toner cartridge 7a, and a motor 7e that is rotationally driven to develop the toner in the toner cartridge 7a. 3 is provided with a supply roller 7d and the like.
[0029]
The developing device 3 is a two-component developing device using, for example, a two-component developer composed of a negatively chargeable toner and a magnetic carrier, and includes a developing sleeve 3a, toner conveying screws 3b and 3c, and density signal output means. A T sensor 3d and the like are provided.
[0030]
The T sensor 3d is provided on the bottom wall portion below the toner conveying screw 3c and detects the developer present around the toner conveying screw 3c.
[0031]
The toner conveying screws 3b and 3c are each driven to rotate by a drive system (not shown). A partition wall (not shown) is provided between the toner conveying screws 3b and 3c, and a storage space for storing the developer in the developing device 3 is individually secured around the partition wall. However, the partition wall is not provided in a region corresponding to the vicinity of both ends of the toner conveying screws 3b and 3c (near the front end and near the rear end in the figure), and the two storage spaces communicate with each other in the vicinity of both ends. It is supposed to be.
[0032]
The toner supplied from the toner replenishing device 7 into the developing device 3 falls into the accommodation space on the toner conveying screw 3c side, and a two-component developer (hereinafter simply referred to as developer) around the toner conveying screw 3c. Contact). Then, along with the rotation of the toner conveying screw 3c, it is conveyed to the back side in the figure while being mixed and stirred with the developer. During this conveyance, the toner is rubbed against the magnetic carrier, the toner conveyance screw 3c, and the like, and is charged to, for example, a negative polarity.
[0033]
The developer transported to the far end in the drawing by the toner transport screw 3c is transferred to the accommodation space on the toner transport screw 3b side through the communication space between the toner transport screws 3b and 3c, and the toner transport screw 3c. This time, it is conveyed to the front side in the figure by the rotation of 3b. This conveyance further promotes charging of the toner in the developer.
[0034]
In the accommodation space on the toner conveying screw 3b side, a roller-shaped developing sleeve 3a is arranged in parallel with the toner conveying screw 3b. The developing sleeve 3a includes, for example, a magnet roller (not shown) having five magnetic poles and a cylindrical nonmagnetic pipe covering the magnetic roller, and only the nonmagnetic pipe is driven to rotate counterclockwise in the figure by a driving system (not shown). It has come to be. The non-magnetic pipe draws and carries the developer conveyed to the front side in the drawing by the toner conveying screw 3b by the magnetic force generated by the magnet roller as it rotates. The developer thus carried is conveyed to a developing position that is a position facing the photosensitive drum 1 as the nonmagnetic pipe rotates.
[0035]
A developing bias is applied to the developing sleeve 3a from a power source (not shown), and a developing electric field (developing potential) is formed between the photosensitive drum 1 and the developing sleeve 3a by this application. The toner in the developer that has been transported to the developing position as the developing sleeve 3a rotates is separated from the magnetic carrier by the action of the developing electric field and adheres to the electrostatic latent image on the photosensitive drum 1. The electrostatic latent image is developed by this adhesion.
[0036]
Next, control means of the printer will be described.
The control unit 10 has functions as a replenishment control unit, a first reference value correction unit, and a second reference value correction unit, each drive system including the motors 7c and 7e, various sensors including the T sensor 3d and the P sensor 8, A data storage unit 11 including a RAM and a ROM, an operation display unit including a touch panel, and the like are connected. This control unit 10 is based on image information sent from a personal computer (not shown) or the like, and is based on the static elimination lamp 6, the charging roller 2, the optical writing unit, the developing device 3, the developing bias applying means, the paper feeding unit, the transfer unit The printing operation is performed by controlling the driving of the bias applying means and the transfer roller. Further, based on the P pattern data stored in the data storage unit 11, a P pattern as a reference image is formed in a non-image area of the photosensitive drum 1 at a predetermined timing.
[0037]
The data storage unit 11 stores data used by the control unit 10 such as a reference value VTref that is an output target of the T sensor 3d.
[0038]
The controller 10 measures the value of the output VT from the T sensor 3d when the transfer paper 5 passes the transfer position in accordance with the printing operation. Then, based on the value of the output VT and the reference value VTref stored in the data storage unit 11, ΔVT (= VTref−VT) that is the difference between the two is calculated.
[0039]
FIG. 2 is a graph showing output characteristics of the T sensor 3d. The T sensor 3d in this printer is composed of a magnetic permeability sensor or the like that detects the magnetic permeability, and has a characteristic of decreasing the value of the output VT as the toner concentration TC of the developer increases as shown in the figure. . Accordingly, as the value of ΔVT, which is the solution of “VTref−VT”, increases toward the minus side, the toner density of the developer is lower than the target density.
[0040]
When the control unit 10 determines that the toner density of the developer is lower than the target density based on the calculation result of ΔVT, the control unit 10 determines the toner replenishment time t (drive time of the motor 7c) according to the calculation result. To do. Then, the motor 7c is driven to rotate based on the determined toner replenishment time t, so that a required amount of toner is replenished into the developing device 3.
[0041]
Next, reference value correction control for correcting the reference value VTref will be described.
The P sensor 8 is composed of a light emitting unit made of a light emitting diode or the like and a light receiving unit made of a photo sensor such as a phototransistor. Irradiation light from the light emitting unit is irradiated onto the photosensitive drum 1 at a predetermined position, and the amount of reflected light is detected by the light receiving unit. The detection result is output as a DC voltage from the P sensor 8 and input to the control unit 10 via an A / D converter (not shown). Since the amount of reflected light varies depending on the toner adhesion amount M / A per unit area in the P pattern formation region on the photosensitive drum 1, the value of the output Vsp from the P sensor 8 also varies depending on the toner adhesion amount M / A. . The printer uses a P sensor 8 that decreases the output value Vsp as the toner adhesion amount M / A increases.
[0042]
The data storage unit 11 stores an output target value (hereinafter referred to as a P target value) from the P sensor 8 that detects the P pattern. The control unit 10 determines the density of the image density in the P pattern based on the P target value and the value of the output Vsp for the P pattern on the photosensitive drum 1. Further, based on this determination result and the value of the output VT from the T sensor 3d, a correction amount ΔVTref for the reference value VTref used until the previous time is determined. Then, the reference value VTref is corrected by adding the correction amount ΔVTref. By such correction, the developing density of the developing device 3 is stabilized by changing the reference density.
[0043]
Table 1 shown below is an example of a database stored in the data storage unit 11 in order to determine the correction amount ΔVTref.
[Table 1]

[0044]
In the example shown in Table 1, the density of the image density in the P pattern is determined based on the comparison between the output value Vsp / Vsg and the corresponding P target value. This output value Vsg is an output value from the P sensor 8 when the background portion of the photosensitive drum 1 in a state where no toner image is formed, and this detection is performed prior to the P pattern detection. Note that S in Table 1 and Table 6 described later indicates T sensor sensitivity, which is the amount of change in the output value VT when the toner concentration TC increases by 1 [wt%].
[0045]
In Table 1, for example, it is determined that ΔVT is larger than 0, that is, the toner density TC is high, even though Vsp / Vsg is larger than the P target value, that is, the image density of the P pattern is lower than the target. In this case, it is necessary to correct the reference value VTref so that the control unit 10 determines that the toner density TC at this time is low or normal. Therefore, in such a case, ΔVTref having a negative polarity is selected from the database shown in Table 1 so that VTref after correction (= reference value VTref until the previous time + correction amount ΔVTref) is made smaller than before correction. Thus, the control unit 10 is configured to correct the reference value VTref. When VTref is corrected in this way, toner replenishment can be executed to maintain the toner density TC lower than before, and the image density can be increased.
[0046]
For example, when Vsp / Vsg is smaller than the P target value, that is, it is determined that ΔVT is smaller than 0, that is, the toner density TC is low, even though the image density of the P pattern is higher than the target. Needs to correct the reference value VTref so that the controller 10 determines that the toner density TC at this time is high or normal. Therefore, in such a case, the control unit selects the positive polarity ΔVTref from the database shown in Table 1 and corrects the reference value VTref so that the corrected reference value VTref is higher than that before the correction. 10 is constituted.
[0047]
However, even if the correction of the reference value VTref is performed, the toner density TC is excessive and the non-image portion of the photosensitive drum 1 and the transfer paper 5 is soiled, or the toner density TC is insufficient to cause the image density. In some cases, and the carrier adheres to the photosensitive drum 1 in some cases.
[0048]
For example, when a continuous printing operation is performed or an image with a high image area ratio is printed out, the toner replenishing speed by the toner replenishing device 7 may not catch up with the decreasing speed of the toner density TC in the developing device 3. In such a case, the toner density temporarily decreases even though a sufficient amount of toner is stored in the toner cartridge 7a. When the degree of the reduction is large, the image density is significantly reduced and carrier adhesion occurs.
[0049]
Further, for example, when the developing ability of the developing device 3 is greatly reduced due to the deterioration of the developer or the like, the reference density is maintained fairly high. In such a case, instead of forming a target density, it may cause background contamination.
[0050]
FIG. 3 is a graph showing the output characteristics of the P sensor 8 and the development characteristics of the developing device 3. The left graph in the figure shows the former characteristics, and the right graph in the figure shows the latter characteristics. In the example shown in the figure, a P pattern is formed when a developing potential having a potential difference of 400 [V] is generated between the photosensitive drum 1 and the developing sleeve 3a. Further, when the ratio Vsp / Vsg between the value of the output Vsp from the P sensor 8 that detects the P pattern and the value of the output Vsg becomes 1/10, the image density ID of the P pattern becomes the reference density. Therefore, if the toner density is set to Vsp / Vsg 1/10, the developing characteristics of the developing device 3 are as shown by the curve A, and the output image formed with a developing potential of 600 [V] is obtained. The density becomes the target ID. On the other hand, when the development characteristics of the developing device 3 change to the state shown by the curve B due to environmental changes or the like, the toner density can be increased to restore the development characteristics to the state shown by the curve A. Thus, an image with a target ID can be obtained. However, if the toner density is increased too much to bring the curve B into the state shown by the curve A, an image having a target density is formed instead of causing a background stain.
[0051]
Therefore, the control unit 10 corrects the reference value VTref while causing the preset upper and lower limit values to function. When the reference value VTref is corrected in this way, the reference density can be increased within a range that does not cause background contamination, and the reference density can be decreased within a range where no significant decrease in image density or carrier adhesion occurs.
[0052]
If it is determined that ΔVT is significantly smaller than 0 even though the image density of the P pattern is higher than the target, there is a high possibility that the apparatus has been left unused for a long time. The image density of the P pattern becomes darker than the target due to the toner charge amount Q / M being insufficient after being left for a long time, while the toner bulk density in the developer is lowered. This is because the possibility that the value of the output VT is lower than the original value is high. In such a case (hereinafter referred to as an agitation request case), the toner is triboelectrically charged and diffused as the developer is agitated. Therefore, the output Vsp from the P sensor 8 and the output VT from the T sensor are Eventually, the normal value is stabilized, and the developing ability of the developing device 3 is restored. Therefore, in the case of the stirring request case, it is desirable to perform image formation without changing the toner density so much. However, in the stirring request case, the output VT changes as the developer is stirred even if the toner concentration is constant. Specifically, in the case of this printer, the output VT decreases with stirring of the developer even if the toner concentration is constant. Under such circumstances, the reference value VTref needs to be lowered with the printing operation in order to keep the toner density constant even when the toner is consumed as the image is formed. Therefore, in the case of the agitation request case, the control unit 10 performs the second correction in which the corrected reference value VTref is gradually lowered to the original reference value VTref along with the printing operation.
[0053]
Tables 2 and 3 shown below are examples of databases stored in the data storage unit 11 in order to determine the correction amount ΔVTref by the second correction for the stirring request case.
[Table 2]

[Table 3]

[0054]
In the second correction, the control unit 10 first selects a stirring time T [sec] and a correction amount ΔVTref corresponding to the value of ΔVT using the database shown in Table 2. For example, when ΔVT = −0.4 [V], 200 [sec] is selected as the stirring time T, and 0.2 [V] is selected as the correction amount ΔVTref. Then, the correction value ΔVTref is added to the original reference value VTref to correct the reference value VTref. Next, while the execution time of the subsequent printing operation reaches the stirring time T, using the database shown in Table 3, while selecting the correction amount ΔVTref of the value according to the remaining stirring time Tr, The correction amount ΔVTref is added to the reference value VTref and the correction of the reference value VTref is repeated. As shown in Table 3, in the second correction, the correction amount ΔVTref added to the original reference value VTref decreases as the remaining stirring time Tr decreases. For this reason, in the second correction, the reference value VTref corrected first is gradually lowered to the original reference value VTref along with the printing operation.
[0055]
The stirring time in Table 2 indicates the driving time of the stirring operation accompanying the developing operation, and does not indicate the driving time of the stirring operation performed separately from the developing operation. The same applies to the remaining stirring time.
[0056]
Table 4 shown below is a database stored in the data storage unit 11 in order to determine the toner replenishment time t.
[Table 4]

[0057]
As shown in Table 4, the toner is replenished when ΔVT is negative, that is, when the toner density TC is lower than the reference density. The determined toner replenishment time t is extended as the value of the output VT increases to the minus side (toner density decreases). By determining the toner replenishment time t, an appropriate amount of toner is replenished to the developing device 3 and the toner density TC is restored to the reference density. In the printer, the T sensor 3d with S (T sensor sensitivity) = 0.4 [wt% / V] is used.
[0058]
When the initial toner is supplied immediately after shipment, the printer first rotates the supply roller 7d and the toner conveying screws 3b and 3c for a predetermined time so that the toner concentration in the developing device 3 is about 4.5 [wt]. %] Is applied. Next, the supply roller 7d is stopped and the rotation of the toner conveying screws 3b and 3c is continued to stabilize the value of the output VT of the T sensor 3d, and then the reference value VTref is set to 2.5 [V]. Is configured to do.
[0059]
Conventionally, in the printer having the above-described configuration, there has been a case in which a background stain is caused during the second correction of the reference value VTref. As a result of diligent research on this problem, the present inventors have found that background contamination has occurred due to the threshold functioning with respect to the reference value VTref during the second correction. In view of this, this printer reduces the background stains that occur during the second correction by performing the following characteristic control.
[0060]
Hereinafter, this characteristic control will be described.
4 to 9 are flowcharts showing the main part of the print control of the control unit 10. Hereinafter, this print control will be described with reference to these drawings.
In FIG. 4, when the main switch is turned on (s1), the control unit 10 first sets the output Vsg of the P sensor 8 that detects the non-image portion of the photosensitive drum 1 without toner adhesion to a predetermined value. (S2). After the P pattern is formed on the photosensitive drum 1 (s3), the value of the output Vsp from the P sensor 8 that detects the P pattern is detected (s4). Next, after calculating Vsp / Vsg (s5), the value of the output VT from the T sensor 3d that detects the developer in the developing device 3 is detected (s6). And after calculating (DELTA) VT (VTref-VT) (s7), control of s8 and s9 is performed.
[0061]
In the control of s8 and s9, the necessity of control for the stirring request case is determined. As shown in Table 1, the case where this control needs to be implemented is “ΔVT <-0.3 "&" (Vsp / Vsg) <0.13 ”. Therefore, the control unit 10 determines that “ΔVT” in these s8 and s9. <-0.3 "&" (Vsp / Vsg) It is determined whether or not <0.13 ”, and if so, the control proceeds to the stirring mode process. Otherwise, control proceeds to normal mode processing.
[0062]
FIG. 5 is a flowchart showing the control contents of the normal mode process. As shown in the figure, when the control unit 10 proceeds to the normal mode process, first, based on the reference value VTref, the correction amount ΔVTref is determined from Table 1 (Os1). Then, after correcting the reference value VTref by adding the correction amount ΔVTref (Os2), the upper limit value 1.1 [V] and the lower limit value 2.8 [V] are caused to function on the corrected reference value VTref ( Os3 to Os6). Specifically, in the control of Os3 to Os6, when the reference value VTref is less than 1.1, it is corrected to the upper limit value 1.1, and when it exceeds 2.8, it is corrected to 2.8. The For this reason, the reference value VTref is finally corrected within the range of 1.1 to 2.8 [V]. By such correction, the printer can increase the reference density of toner within a range that does not cause background contamination, and can reduce the reference density within a range where a formed image is not significantly lowered and carrier adhesion does not occur.
[0063]
When the control unit 10 corrects the reference value VTref in this manner, the control unit 10 then waits until there is a print command (N in Os7), and the control is performed in the normal mode when the print command is issued (Y in Os7). Proceed to print processing.
[0064]
On the other hand, when the developer state is the stirring request case as described above, the control unit 10 advances the control to the stirring mode process.
FIG. 6 is a flowchart showing the control content of the stirring mode process. As illustrated, when the control proceeds to the stirring mode process, the control unit 10 first determines the stirring time T and the correction amount ΔVTref from Table 2 based on the reference value VTref (Ks1). Then, after correcting the original reference value VTref by adding the correction amount ΔVTref (Ks2), the remaining stirring time Tr is set to a value equivalent to the stirring time T (Ks3). Next, the process waits until there is a print command (N at Ks4), and when the print command is issued (Y at Ks4), the control is advanced to the agitation mode print process.
[0065]
When FIG. 5 and FIG. 4 are compared, it can be seen that the upper and lower limits as the threshold value are made to function as the reference value VTref in the normal processing mode, whereas the upper and lower limits are not made to function in the stirring mode processing. Thus, in the stirring mode process, if the reference value VTref is corrected without causing the upper and lower limits to function, the reference value VTref is reliably changed to a value to be corrected.
[0066]
For example, when the reference value VTref (2.5 [V]) is corrected without operating the upper and lower limits in the stirring mode, when the output VT = 3.2 [V] and the output Vsp / Vsg = 0.07 ΔVT = 2.5−3.2 = −0.7 [V]. Then, a stirring time T of 600 [sec] and a correction amount ΔVTref of 0.6 [V] are selected from Table 2 with Ks1, and the reference value VTref is corrected to 2.5 + 0.6 = 3.1 with Ks2. The When the reference value VTref is corrected in this way, ΔVT becomes 3.1-3.2 = −0.1 [V], so that toner supply of 2.4 [sec] is performed in the subsequent control. (See Table 4).
[0067]
On the other hand, when the reference value VTref (2.5 [V]) is corrected by operating the upper and lower limits in the stirring mode, the reference value VTref = 3.1 [V] corrected by Ks2 is the upper limit value. Is corrected to 2.8 [V]. When corrected in this way, ΔVT becomes 2.8−3.2 = −0.4 [V], and therefore, in the subsequent control, intermittent replenishment of 1 second ON / 2 seconds OFF is continuously continued. The toner density TC is remarkably increased. Such a significant increase in the toner concentration TC causes scumming.
[0068]
FIG. 7 is a flowchart showing the control contents of the printing process in the stirring mode process. As shown in the figure, when the control proceeds to the stirring mode printing process, the control unit 10 first starts a printing operation for one time (Ks5) and then starts the stirring operation (Ks6). Specifically, the stirring operation is to rotate the toner conveying screws 3b and 3c. Next, after starting the countdown of the remaining stirring time Tr (Ks7), the control unit 10 detects the value of the output VT (Ks8). Then, after the toner supply time t is determined based on the calculation result of “ΔVT = VTref−VT” and Table 4 above (Ks9), toner supply is started (Ks10).
[0069]
After starting the toner supply, the control unit 10 ends the printing operation for one time (Ks11). Next, the control unit 10 adds 1 to PC which is a variable indicating the cumulative number of printing (Ks12). Then, after the stirring operation is finished (Ks13), the countdown of the remaining stirring time Tr is finished (Ks14). If the remaining stirring time Tr is not counted down to 0 at this time, the control for the stirring mode is continued in the subsequent printing operation.
[0070]
Next, the control unit 10 determines whether or not a predetermined number of printing operations have been performed. If the next printing operation still remains after receiving a continuous printing command (N in Ks15), the control is performed by Ks15a. Proceed to If the next printing operation does not remain (Y in Ks15), the control proceeds to Ks16.
[0071]
When the control is advanced to Ks15a, the control unit 10 determines a new ΔVTref based on the value of the remaining stirring time Tr and Table 3, and then uses the original reference value before the main switch is turned off. The reference value VTref is updated by adding this ΔVTref to VTref (Ks15b). At this time, the reference value VTref approaches the original reference value and decreases according to the decrease in the remaining stirring time Tr. Further, the control unit 10 loops the control to the above-described Ks5 and starts the next printing operation.
[0072]
When the control is advanced to Ks16, that is, when the next print command is not received, the control unit 10 determines whether or not the toner replenishment is finished. Depending on the length of the toner replenishment time t, toner replenishment may not be completed during the printing operation. Therefore, the control unit 10 makes such a determination, and if it is determined that “not completed” (N in Ks16), the control proceeds to Ks17 for continuing toner supply, and then loops to Ks16. Let By such a loop, when the toner supply is not completed, the control does not proceed to the previous step until the toner supply is completed.
[0073]
When the replenishment operation is completed or when the replenishment operation is completed during the printing operation (Y in Ks16), the control unit 10 next determines whether or not the remaining stirring time is counted down to zero. Determine (Ks18). If the countdown is zero (Y in Ks18), the control is returned to the main flow. With this return, the agitation mode process ends. Usually, in the subsequent control, “ΔVT” at s8 and s9. <-0.3 "&" (Vsp / Vsg) The condition of <0.13 ”is determined as“ No ”, and normal mode processing is performed.
[0074]
Further, when the control unit 10 determines that the countdown to zero is not completed in Ks18 (N in Ks18), the control unit 10 loops the control to Ks5 (see FIG. 4) to continue the stirring mode process. By this loop, when a print command is received in the subsequent control, the stirring mode process is continued. Therefore, the stirring mode process is continued until the remaining stirring time Tr is counted down to zero.
[0075]
FIG. 8 is a flowchart showing the control contents of the printing process in the normal mode process. The normal mode print process is substantially the same as the control of the agitation mode print process shown in FIG. 8 except that the control without taking into account the remaining agitation time Tr is performed, and thus the description thereof is omitted.
[0076]
As described above, according to the printer of the present embodiment, the toner is prevented from being oversupplied by causing the upper limit value to function during the second correction of the reference value VTref, so that the background stains generated during the second correction can be reduced. it can.
[0077]
Next, an example printer in which a more characteristic configuration is added to the printer of this embodiment will be described.
FIG. 9 is a flowchart partially showing the control contents of the stirring mode processing in the printer of this embodiment. As shown in the figure, the control unit 10 of this printer performs control of Ks14a between Ks14 and Ks15 (point A in FIG. 7). In this Ks14, it is determined whether or not the countdown value of the remaining stirring time Tr has reached zero. If it is determined that it has not reached (N in Ks14a), the control proceeds to Ks15 to control the stirring mode process. Continue. On the other hand, if it is determined that “reached” (Y in Ks14a), the control is returned to the main flow without proceeding to Ks15 even during the continuous printing operation.
[0078]
As shown in Table 3 above, when the remaining stirring time Tr reaches zero, the second correction of the reference value VTref ends, and the reference value VTref returns to the value before the second correction. However, at this time, if the bulk density of the toner is not sufficiently recovered due to the influence of the toner charge amount Q / M, the reference value VTref may be a value that does not match the actual state. As a result, the printout image output after Ks15 may cause a background stain. Therefore, if the control unit 10 determines that the second correction of the reference value VTref is completed at Ks14a (Tr = 0), the control unit 10 returns the control to the main flow. By returning in this way, a P pattern is formed prior to the first printing operation after the end of the second correction, and the reference value VTref can be corrected based on Vsp / Vsg and the output VT for this P pattern. . As a result, even if the reference value VTref after the second correction is a value that does not match the actual value, it can be corrected to an appropriate value prior to the first printing operation.
[0079]
As described above, according to the printer of this embodiment, even if the reference value VTref after the second correction is a value that does not match the actual state, it is corrected to an appropriate value prior to the first printing operation, and thus occurs after the second correction. Soil can be reduced.
[0080]
In the above-described embodiments and examples, the printer having a configuration in which the toner image is directly transferred from the photosensitive drum 1 to the transfer paper 5 has been described. The present invention can also be applied to.
[0081]
Further, the printer having only one developing device has been described, but the present invention can also be applied to an image forming apparatus having a plurality of developing devices such as a revolver developing unit.
[0082]
Further, the printer including the P sensor as the predetermined signal output unit has been described. However, the present invention can also be applied to an image forming apparatus including another predetermined signal output unit such as a humidity sensor.
[0083]
【The invention's effect】
Claim 1's According to the invention, Lower limit or upper limit While functioning Lower limit or upper limit In order to avoid oversupply of the image forming substance that occurs during the second correction due to the function of Lower limit or upper limit There is an excellent effect that it is possible to reduce background stains occurring during the second correction while functioning.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming portion of a printer according to an embodiment.
FIG. 2 is a graph showing output characteristics of a T sensor of the printer.
FIG. 3 is a graph showing output characteristics of a P sensor of the printer and development characteristics of a developing device.
FIG. 4 is a flowchart illustrating a main part of print control in the control unit of the printer.
FIG. 5 is a flowchart showing control details of normal mode processing of the print control.
FIG. 6 is a flowchart showing control contents of agitation mode processing of the print control.
FIG. 7 is a flowchart showing control contents of print processing in the stirring mode processing.
FIG. 8 is a flowchart showing control details of print processing in the normal mode processing;
FIG. 9 is a flowchart partially showing the control content of the stirring mode process in the printer of the embodiment.
FIG. 10 is a graph showing the relationship between the value of the output VT of the T sensor and the number of printouts (or the stirring operation time).
[Explanation of symbols]
1 Photosensitive drum
2 Charging device
3 Exposure equipment
5 Paper tray
6 Registration roller
7 Transport device
8 Transfer device
9 Fixing device
10 Output tray
11 Cleaning device
20 Scanner section
21 Image processing unit
22 Printer section
30 Humidity sensor
31 Temperature sensor
100 Developer
101 Development casing
102 Toner container
103 1st conveyance roller
105 Second transport roller
200 First transport roller bias switch
202 MPU
203 Recovery bias selector switch

Claims (1)

A latent image carrier for carrying a latent image;
A developing device that develops the latent image by attaching the toner to the latent image using a developer composed of toner that is an image forming substance and a magnetic carrier ;
Supply means for supplying toner to the developing device;
A density signal output means for outputting a signal having a value corresponding to the toner density in the developer in the developing device;
And the predetermined signal output means serving adhesion amount signal output means for changing the output value of the coating weight signals in accordance with the amount of adhered toner with respect to the developed reference image in the latent image bearing member,
Replenishment control means for controlling the operation of the replenishment means based on the comparison result between the output value from the concentration signal output means and the reference value;
A first reference value correction means for correcting in the range up to the upper limit value from the lower limit value previously set the reference value based on the output value of the coating weight signals,
Although the image density of the reference image is determined to be higher than a predetermined target density based on the output value of the adhesion amount signal, the output value from the density signal output means is compared with the reference value. An image forming apparatus comprising: a second reference value correcting unit that corrects the reference value instead of the first reference value correcting unit when the toner density is determined to be lower than the target density based on the first reference value correcting unit ;
Regardless of the adhesion amount signal, the second reference value correction means corrects the reference value without limitation of the range based on the adhesion amount signal and gradually approaches the value before correction. An image forming apparatus characterized by being repeatedly corrected .

Images