JP2004053748A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for forming an excellent image on recording material without being affected by the fluctuation of the resistance value of an ionic conductive transfer roller caused by environmental fluctuation such as temperature and humidity and electric conduction drift. <P>SOLUTION: After paper P reaches (S601) the transfer roller, the mean value Iz(n) of a transfer current required for one rotation of the transfer roller is calculated on the basis of the result of detection by a transfer roller current detection part 207 (S606), and compared with the mean value Iz(n-1) of the transfer current calculated previously. When the absolute value of the difference between them is equal to or below a specified value (YES in S608), it is determined that the resistance value of the transfer roller has fluctuated, and transfer voltage V0 and print transfer voltage Vt are corrrespondingly corrected (S609 and S610). <P>COPYRIGHT: (C)2004,JPO

Description

【００７８】
比較例１では、連続通紙の４〜７枚目で文字画像に軽微だがトナー飛び散りが発生した。トナー飛び散りが発生したのは、通電ドリフトによってイオン導電性転写ローラの抵抗値が上昇し、トナー保持電荷不足を起こしたためである。また、連続通紙の１２０枚目くらいからハーフトーン画像に黒点が見え始めた。この現象が起こったのは、定着装置１１から発生する水蒸気と熱によって転写ローラ９の抵抗値が下がったために、電荷が局所的に紙を突き抜けて感光ドラム１上に放電跡を生じたためである。通紙中に流れる電流値をモニタした結果、比較例１におけるレーザビームプリンタＡでは、１５０枚通紙する間に流れる電流値が大きく変動していたが、実施例１では電流はほとんど安定していた。実施例１では、１５０枚を通じて、画像に問題がなかった。
【００７９】
次に、紙ＰとしてＸｘ４０２４，坪量７５ｇと、封筒Ｃｏｍ１０を１枚づつ交互に、それぞれ５０枚通紙する実験２を行った。評価結果を表２に示す。
【００８０】
【表２】

【００８１】
比較例１では、実験１と同様に初期において通電ドリフトによるトナー保持電荷不足によりトナー飛び散りが発生した。また、定電流制御を用いる比較例２では、封筒通紙の際に、非通紙部に電流が流れ込み、転写電圧不足となってトナー飛び散りおよび転写抜けが発生した。
【００８２】
実施例１のレーザビームプリンタＡでは、Ｘｘ４０２４，封筒ともに良好な画像を得ることができた。
【００８３】
以上の実験が示すように、本実施例ではイオン導電性転写ローラの通電ドリフト、温湿度変動の影響を解消し、良好な画像を提供することができる。
【００８４】
すなわち、記録材への転写動作中に、転写部材に流れる転写電流を検知し、転写部材の抵抗検知を行ってプリント転写電圧を補正することにより、単位時間当たりのプリント出力枚数を落とすことなく、転写動作中の転写部材の抵抗値変動による画像への影響を補正し、良好な画像を形成する画像形成装置を提供することができる。
【００８５】
（実施例２）
本実施例でも、実施例１と同様のハードウエア構成の画像形成装置であるレーザビームプリンタＡを用いる。
【００８６】
本実施例は、プリント中の転写ローラ平均電流値と、全画像領域に対するトナー像の印字率をモニタし、転写電圧の補正を行うものである。
【００８７】
プリント中の転写電流値は、転写ローラ抵抗値，紙の抵抗値に加えて、画像上のトナー抵抗によっても変動する。トナー抵抗は全画像領域に対するのトナー像の印字率、すなわちレーザビームスキャナ３のレーザ点灯比率にほぼ比例する。通常、文字画像における全画像領域に対するトナー像の印字率は平均で約５％程度、ハーフトーン画像では約５０％、べた黒画像では、ほぼ１００％となる。
【００８８】
本実施例では、トナー抵抗を考慮することによって、より正確で誤検知の少ない転写電圧補正を行う。つまり、実施例１においてはトナー抵抗を示すトナー像の印字率にかかわらず転写電圧の補正を行なっていたが、トナー像の印字率が大きく変動すると転写ローラ９の抵抗値変動が少ない場合でも誤って転写電圧の補正をしてしまう可能性がある。実施例２は実施例１と異なり、トナー像の印字率が所定値以内でありトナー抵抗による変動が少ない場合に限定して転写ローラ９の抵抗値変動にもとづく転写電圧の補正を行なうものである。
【００８９】
図７に示すように、通紙時のプリント転写電圧印加中に、レーザスキャナ３のレーザ点灯比率を転写ローラ１周毎にモニタして、平均化した転写ローラ電流平均値Ｉｚ（ｎ）と、転写ローラ１周分におけるレーザスキャナ３のレーザ点灯比率Ｌｚ（ｎ）をプリンタ制御部２０２のメモリに記憶する。レーザ点灯比率Ｌｚ（ｎ）は、感光ドラム１の表面の画像領域をレーザビームで走査する時間に対するレーザスキャナ３の点灯時間を表すものであり、前述のようにトナー像を現像する領域が多いほどレーザスキャナ３が点灯する時間も長くなる。走査時間に対してレーザがオン状態となっている（点灯している）時間を不図示の計時手段により計時することでレーザ点灯比率を算出できる。
【００９０】
以下、本実施例における制御を図８および図９のフローチャートを用いて説明する。なおプリント開始からプリント終了に到るまでの制御全体は図５のフローチャートと同様であり、図８および図９は図５における転写電圧制御（ステップＳ５１５）の詳細を示すフローチャートである。図５のフローチャートについては実施例１にて説明したので説明を省略する。
【００９１】
ステップＳ８０１では、紙Ｐが転写ローラ９に到達したか否かを判定する。この判定はＴＯＰセンサ１５により紙Ｐの先端が検出されてから紙Ｐの搬送速度に応じた所定時間が経過したか否かで判断する。
【００９２】
紙Ｐが転写ローラ９に到達したことに応じて、ステップＳ８０２ではプリント転写電圧Ｖｔの印加を開始する。
【００９３】
ステップＳ８０３では転写ローラ１周分において転写ローラ電流検知部２０７にて検知される転写ローラ電流値を平均化して転写電流平均値Ｉｚ（１）を算出し、その値をステップＳ８０４にてプリンタ制御部２０２が有するメモリに記憶させる。
【００９４】
ステップＳ８０５では転写ローラ１周分において全画像領域に対するレーザ点灯比率Ｌｚ（１）を算出する。レーザ点灯比率Ｌｚ（１）もＩｚ（１）と同様にステップＳ８０６にてプリンタ制御部２０２が有するメモリに記憶させる。
【００９５】
図８のステップＳ８０７〜ステップＳ８０９および図９のステップＳ９０１〜ステップＳ９１４は、ｎ回目に算出した転写電流平均値Ｉｚ（ｎ）をその前回算出したＩｚ（ｎ−１）と比較して転写電圧Ｖ０およびプリント転写電圧Ｖｔを補正する処理を行っている。この処理を紙Ｐが転写ローラ９を通過するまで繰り返すことで、通紙中の転写ローラ９の抵抗値変動による画質への悪影響を防止するものである。
【００９６】
ステップＳ８０７でｎ＝２を設定しているが、このｎは転写ローラに紙Ｐが到達してからの転写ローラ９の回転数を示すものであり、ステップＳ８０３からステップＳ８０６では既に１回転目の処理を行っているので２を設定している。
【００９７】
ステップＳ８０８でｍ＝１をステップＳ８０９ではＭ＝１を設定しているが、ｍおよびＭはレーザ点灯比率が所定値以内か否かを判定するためのものであるが、詳しくは後述する。
【００９８】
ステップＳ９０１ではｎ回転目の転写ローラ１周分の転写電流平均値Ｉｚ（ｎ）を算出し、ステップＳ９０２においてＩｚ（ｎ）をプリンタ制御部２０２のメモリに記憶させる。
【００９９】
ステップＳ９０３ではｎ回転目の転写ローラ１周分において全画像領域に対するレーザ点灯比率Ｌｚ（ｎ）を算出する。レーザ点灯比率Ｌｚ（ｎ）もＩｚ（ｎ）と同様にステップＳ９０４にてプリンタ制御部２０２が有するメモリに記憶させる。
【０１００】
ステップＳ９０５ではｎ回転目の転写ローラ１周分におけるレーザ点灯比率（Ｌｚ（ｎ））と、それ以前に算出したレーザ点灯比率（Ｌｚ（ｎ−１）、Ｌｚ（ｎ−２）、・・・、Ｌ（ｎ−ｍ）、・・・、Ｌ（１））との差分の絶対値が所定値以内か否かを判定し、所定値以内であればステップＳ９０６〜Ｓ９０８の転写電圧補正処理へ進む。ステップＳ９０５でレーザ点灯比率の比較することで、トナー像の印字率の変化が大きい場合に誤って転写電圧の補正を行わないようにしている。すなわち、ｎ回転目の転写ローラ１周分におけるレーザ点灯比率（Ｌｚ（ｎ））と同じような（差分の絶対値が所定範囲内の）ｎ−ｍ回転目における転写電流平均値Ｉｚ（ｎ−ｍ）を用いて転写電圧Ｖ０の補正をすることで転写ローラ９の抵抗値変動に応じた転写電圧の補正を行うことができる。なお、ステップＳ９１０でｍ＝ｍ＋１とし、ステップＳ９１０でｍ＞Ｍか否かの判断をすることで、ｎ回転目のレーザ点灯比率Ｌｚ（ｎ）を１回転目のＬｚ（１）まで（ｎ−１）回転目、（ｎ−２）回転目、・・・、（ｎ−ｍ）回転目、・・・、１回点目と順を追って比較する処理が可能となる。
【０１０１】
ステップＳ９０７では、転写電圧値Ｖ０に今回取得した転写電流平均値Ｉｚ（ｎ）に対する（ｎ−ｍ）回転目に取得した転写電流平均値Ｉｚ（ｎ−ｍ）の比率を乗じることでＶ０を補正している。つまり転写電流平均値が小さくなれば、転写電圧値Ｖ０が大きくなるよう補正する。
【０１０２】
ステップＳ９０８では、補正された新たな転写電圧値Ｖ０を用いて新たなプリント転写電圧値Ｖｔを算出する。
【０１０３】
ステップＳ９１４では、紙Ｐが転写ローラを通過したか否かをステップＳ８０１と同様にＴＯＰセンサ１５の出力にもとづいて判定し、通過した場合は図５のフローチャートへ復帰する。
【０１０４】
図５のステップＳ５１６では次にプリントすべきページがあるか否かを判定して次ページがあればステップＳ５１５の転写電圧制御を再び行なう。すなわちステップＳ５１５の転写電圧制御はプリントすべき紙Ｐの１枚ごとに実行する制御であり連続プリントが終了するまでこの処理を繰り返す。
【０１０５】
以下、具体例で説明する。
【０１０６】
本実施例の画像形成装置であるレーザビームプリンタＡにおいては、実施例１と同様のイオン導電性転写ローラを用いているので、転写ローラ９についての詳細な説明は省略する。
【０１０７】
レーザスキャナ３により潜像形成が開始されると、プリンタ制御部２０２は転写ローラ１周の周期３００ｍｓｅｃ．毎にレーザ点灯比率Ｌｚ（ｎ）をプリンタ制御部２０２が有するメモリに記憶する。感光ドラム１上に形成されたトナー像と同期して紙Ｐが転写ニップＴに通紙され、プリント転写電圧Ｖｔが印加される。転写電流検知部２０７は、レーザスキャナ３のレーザ点灯比率をモニタした周期（３００ｍｓｅｃ．）と同期して、電流の平均値Ｉｚ（ｎ）をモニタして記憶する。
【０１０８】
本実施例では、転写ローラ周期でモニタされたレーザスキャナ３のレーザ点灯比率Ｌｚ（ｎ）と平均電流値Ｉｚ（ｎ）から、紙の切り替わりおよびトナー像の切り替わりを識別し、転写ローラ抵抗値の変動検知を検知するとともにその変動が所定値以内の場合だけ転写バイアスの補正を行う。
【０１０９】
モニタされたレーザスキャナ３のレーザ点灯比率Ｌｚ（ｎ）が、前周までのＬｚ（ｎ−１）、または前々周のＬｚ（ｎ−２）、Ｌｚ（ｎ−３）…、Ｌｚ（ｎ−ｍ）、…、Ｌｚ（１）との差が、５％（ステップＳ９０５におけるＣ）以内であれば、ほぼ同等のトナー抵抗をもつ画像と判断できる。ｎ回転目のレーザ点灯比率Ｌｚ（ｎ）を、最前のメモリデータＬｚ（１）まで比較して５％以内の条件に合わなければ、比較できる画像がないことからバイアス補正を行わない。
【０１１０】
モニタされた平均電流値Ｉｚ（ｎ）と、トナー抵抗がほぼ同等と判断された領域である（ｎ−ｍ）回転目では、平均電流値Ｉｚ（ｎ）と平均電流値Ｉｚ（ｎ−ｍ）との差の絶対値が、通電ドリフトおよび環境変動によって起こりうる変動率０．９％／３００ｍｓｅｃ．以内であり、かつこの間に転写電圧の補正切り替えがなければ、紙Ｐの材質の変化などの影響ではなく転写ローラ９の抵抗変動と判断できる。電流値の変動率が指定条件Ｂ以上であれば（ステップＳ９０６でＮＯ）、紙種の切り換え、またはイレギュラーな放電などによる影響と考えられ、その抵抗変動が無視できないことから転写電圧補正を行わない。
【０１１１】
電流値の変動率が指定条件Ｂ以内であれば、下式のように、Ｉｚ（ｎ）とＩｚ（ｎ−ｍ）との差に比例して、抵抗値対応転写電圧値Ｖ０、およびプリント転写電圧値Ｖｔを補正する。なお右辺におけるＶ０は補正前の値であり、左辺におけるＶ０が補正後の値である。
補正後　Ｖ０＝Ｉｚ（ｎ−ｍ）／Ｉｚ（ｎ）×Ｖ０
補正後　Ｖｔ＝α×Ｖ０＋β
【０１１２】
本実施例では、通紙中の転写ローラ電流値と画像の印字率によって転写電圧補正制御を行うため、文字画像と写真画像が混じった複合画像でも、正確な転写電圧補正制御が可能である。
【０１１３】
本実施例の効果を、通紙実験にて確認した。ＮｅｅｎａＢｏｎｄ，坪量６０ｇ、開封直後で水分量が５．０％の紙Ｐを連続１５０枚通紙した。プリントする画像は、図１０のような文字画像と写真画像からなる複合画像とした。レーザビームプリンタＡとして、実施例２におけるもの、実施例２と同構成で転写電圧補正を行わない比較例１を用いた。通紙環境は、雰囲気温度１０℃、湿度１５％の低温低湿環境である。印字された画像を評価した結果を表３に示す。
【０１１４】
【表３】

【０１１５】
比較例１では、連続通紙の４〜７枚目で文字画像に軽微だがトナー飛び散りが発生した。また、１２０枚目くらいから写真画像に黒点が見え始めた。本実施例におけるレーザビームプリンタＡでは、１５０枚を通じて、画像に問題がなかった。
【０１１６】
以上の実験が示すように、本実施例ではイオン導電性転写ローラの通電ドリフト，温湿度変動の影響を解消し、良好な画像を提供することができる。
【０１１７】
すなわち、本実施例によれば、トナー抵抗を考慮することによって、より正確で誤検知の少ない転写電圧補正を行うことにより、良好な画像を形成する画像形成装置を提供することができる。
【０１１８】
【発明の効果】
以上説明したように、本発明によれば、温度、湿度等の環境変動や通電ドリフトに起因する転写部の抵抗値変動による影響を受けることなく良好な画像を記録材上に形成する画像形成装置を提供することができる。
【０１１９】
また、本発明は、イオン導電性転写部材を用いた画像装置において、温度、湿度等の環境変動や通電ドリフトに起因する転写部の抵抗値変動による影響を受けることなく良好な画像を記録材上に形成する画像形成方法を提供することができる。
【図面の簡単な説明】
【図１】レーザビームプリンタＡの概略構成を示す断面図
【図２】レーザビームプリンタＡの制御ブロック図
【図３】ＡＴＶＣ抵抗検知制御における転写電圧および検知電流を示す図
【図４】転写中における転写ローラ電流値を示す図
【図５】実施例１の制御全体を示すフローチャート
【図６】実施例１の転写電圧制御を示すフローチャート
【図７】転写中におけるレーザ点灯比率を示す図
【図８】実施例２の転写電圧制御を示すフローチャート（その１）
【図９】実施例２の転写電圧制御を示すフローチャート（その２）
【図１０】確認実験で用いられた画像を示す図
【図１１】転写ローラの構成を示す斜視図
【符合の説明】
Ａ　レーザビームプリンタ
１　感光ドラム
２　帯電装置
３　レーザスキャナ
４　現像装置
９　転写ローラ
１１　定着装置
２０１　画像処理制御部
２０２　プリンタ制御部
２０６　転写電圧印加部
２０７　転写ローラ電流検知部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus such as a copying machine or an LBP (laser beam printer), and an image forming method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus such as an electrophotographic copying machine or an LBP includes an electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier generally having a rotary drum type, and charging and image exposure. Forming a toner image as a transferable image corresponding to the target image information by an image forming process unit of development, transferring the toner image to a recording material side by a transfer unit, and further introducing the recording material to a fixing unit. The toner image is thermally fixed as a permanent fixed image on a recording material surface and output as an image formed product (copy, print). After the transfer of the toner image to the recording material, the photosensitive drum is repeatedly subjected to an image forming process by removing and removing residual adhesion contaminants such as transfer residual toner and paper dust remaining on the surface thereof.
[0003]
As a transfer unit for transferring a toner image from a photosensitive drum to a recording material used in the above-described image forming apparatus, there is an advantage that the conveyance path of the recording material can be simplified and stabilized at the same time. A contact rotating type transfer in which a voltage is applied and a recording material is sandwiched and conveyed at a transfer portion which is a nip portion with the photosensitive drum to electrostatically transfer the toner image on the photosensitive drum side to the recording material side. Transfer means using a member, a so-called transfer roller, is frequently used.
[0004]
The resistance value of the transfer roller is 1 × 10 ⁶ ~ 1 × 10 ¹⁰ (Ω), and as shown in FIG. 11, an elastic layer 118 is provided on the outer peripheral surface of a conductive core 117, and the elastic layer 118 has conductivity (FIG. 11). Transfer roller 116) has recently been proposed. The transfer roller 116 is roughly classified into the following two types depending on how the elastic layer 118 has conductivity. That is, (1) a transfer roller having electronic conductivity, (hereinafter, referred to as an electronic conductive transfer roller), and (2) a transfer roller having ion conductivity (hereinafter, referred to as an ion conductive transfer roller).
[0005]
The transfer roller (1) has an elastic layer 118 as shown in FIG. 11 and a conductive filler dispersed in the elastic layer 118. For example, a conductive filler such as carbon or metal oxide is used as the transfer roller. Examples include dispersed EPDM rollers and urethane rollers.
[0006]
The transfer roller of (2) is a material in which the elastic layer 118 contains an ion conductive material. For example, a material in which a material such as urethane has conductivity or a surfactant is dispersed in the elastic layer 118. One.
[0007]
In general, it is known that the resistance value of the transfer roller is easily changed according to the temperature and humidity of the ambient environment, and the change in the resistance value of the transfer roller may cause poor transfer, explosion scattering, paper marks, and the like. There is concern.
[0008]
Therefore, in order to prevent the occurrence of transfer defects and paper marks caused by fluctuations in the resistance value of the transfer roller, the resistance value of the transfer roller is measured, and the transfer voltage applied to the transfer roller is appropriately adjusted according to the measurement result. "Applied transfer voltage control" is employed. As such an applied transfer voltage control means, there is ATVC control (Active Transfer Voltage Control) disclosed in JP-A-2-123385.
[0009]
The ATVC control optimizes a voltage applied to a transfer roller when transferring a toner image to a recording material, and controls so as to prevent transfer failure and occurrence of paper marks. In the ATVC control, a desired constant current is applied from the transfer roller to the photosensitive drum during the multi-rotation process before the image forming apparatus, and the voltage value at that time is maintained to measure the resistance value of the transfer roller and record the toner image. When transferring to a material, a constant transfer voltage according to the resistance value is applied to the transfer roller.
[0010]
In order to accurately detect the transfer roller resistance value and determine the optimal applied transfer voltage by the above-described ATVC control, it is necessary to monitor the resistance value for one round of the transfer roller and obtain an average value thereof. A problem may occur because the transfer roller resistance has a voltage dependency. That is, the transfer roller resistance value is measured from the voltage value detected at the time when a constant current is applied to the transfer roller, but a voltage value close to the voltage value applied when transferring the toner image to the recording material is generated. If the constant current value is not set, the resistance value of the transfer roller cannot be measured accurately. Therefore, the ATVC control or the like is generally performed during the pre-rotation where there is enough time in the image forming process.
[0011]
In the transfer process in the image forming apparatus, if the transfer current becomes excessive, an image defect occurs due to a discharge trace remaining on the photosensitive drum. If the transfer current is insufficient, problems such as poor transfer and explosion and scattering of toner occur. To cope with this problem, the electronic conductive transfer roller imparts conductivity by dispersing the conductive filler as described above, and therefore suppresses partial resistance unevenness due to rubber distortion or the like generated when the core metal is pressed. It is difficult. If the resistance unevenness of the transfer roller is large, the value of the current flowing to the transfer roller when the recording material passes through the transfer roller becomes different depending on the longitudinal direction (axial direction) and the rotation direction of the transfer roller. In some cases, the transfer current is excessive, while in the other, the transfer current is insufficient, and the transfer current value is not uniform, making it difficult to provide a good image. Further, even when the resistance value unevenness is small, a discharge of a transfer bias occurs in a very small area on the surface of the transfer roller, and a current flows intensively, so that a discharge mark remains on the photosensitive drum and an image defect occurs. Conversely, poor transfer occurs where no transfer current flows.
[0012]
On the other hand, the ion conductive transfer roller is characterized in that discharge in a small area is unlikely to occur due to the electric conduction characteristics of ion conductivity. Further, resistance value unevenness due to transfer roller distortion is unlikely to occur, so that resistance value unevenness can be suppressed to within 1.5. For this reason, in the electronic conductive transfer roller, it is difficult to obtain an image margin of 100 mm / sec. Even at the above transfer speed, a good image can be obtained by the ion conductive transfer roller.
[0013]
[Problems to be solved by the invention]
(Ionic conductivity problem)
As described above, the resistance of the transfer roller generally varies according to the temperature and humidity of the atmospheric environment. However, the resistance of the transfer roller also varies due to heat and water vapor generated during continuous printing in the fixing device. In addition, the ion conductive transfer roller has a characteristic of an energization drift in which the resistance value during energization changes with time. In a transfer roller having a poor conduction drift characteristic, the resistance value continues to increase for several tens of seconds from the start of bias application, and the resistance value of the transfer roller fluctuates even during printing of one sheet. Due to these characteristics, during continuous printing, a deviation from the transfer roller resistance value monitored by the ATVC control performed during the previous rotation occurs, and it becomes impossible to apply an optimal constant voltage bias to the transfer paper.
[0014]
(Problem of constant current control)
The transfer control of the image forming apparatus is roughly classified into constant current control and constant voltage control. The constant current control, which controls the voltage so that the current value is constant, does not cause problems due to the energization drift of the transfer roller and fluctuations in temperature and humidity. However, when small-sized paper such as envelopes is passed, the resistance value is higher than that of the paper passing section. The transfer current flows into the non-sheet passing portion having a low value, and the transfer current is insufficient in the sheet passing portion. This problem can be solved by setting the control current value for passing small-sized paper larger than that for plain paper. However, means for setting that small-size paper is to be printed before passing or means for identifying that small-size paper is passed is required, leading to an increase in the cost and size of the apparatus. It is not preferable for an image forming apparatus for personal and small offices.
[0015]
(Problem with constant voltage control)
In the constant voltage control in which a predetermined constant voltage is applied during the paper passing, since the transfer omission does not occur when the small size paper is passed, image forming without means for identifying that the small size paper is passed is not performed. In devices, constant voltage control is often used. However, in an image forming apparatus that performs constant voltage control, when the fluctuation amount of the energization drift (the change over time in the resistance value of the transfer roller) is large and the period from the start of energization to the convergence of the resistance value of the transfer roller is long. Since the resistance value of the transfer roller continues to increase during the paper passing, the amount of current continues to decrease, and the transfer current value at the rear end of the paper becomes smaller than that at the front end of the paper. In the transfer process in the image forming apparatus, when the transfer current is excessive, a discharge mark is left on the photosensitive drum to cause an image failure, and when the transfer current is insufficient, problems such as transfer failure and explosion and scattering of toner occur. If the current value change range during paper passing is larger than the current value change range of a good image, the current will be excessive at the leading edge of the paper, or the current will be insufficient at the rear end of the paper and the second and subsequent sheets, resulting in image failure. I do.
[0016]
During the non-sheet-passing time other than the pre-rotation, that is, during the period after the trailing end of the preceding recording material passes through the transfer roller and the leading end of the succeeding recording material is conveyed to the transfer roller, the recording material flows to the transfer roller by ATVC control or the like. Control for detecting the transfer roller resistance value by monitoring the current or the voltage value during the constant current control can be performed. By controlling in this way, the transfer roller resistance value during continuous paper passing can be detected and the print application bias can be corrected. As the sampling period, a high-pressure stabilization time and a time in which the timing at which the leading and trailing ends of the recording material pass through the transfer nip are added. In an image forming apparatus that requires a high-speed print output number, there is a demand that the conveyance interval of the recording material be as short as possible in order to increase the output number of the recording material per unit time. It is difficult to accurately detect the resistance value between the recording materials.
[0017]
During continuous printing, the time from when the trailing edge of the preceding recording material passes through the specified number of prints or at predetermined time intervals until the leading edge of the succeeding recording material is conveyed to the transfer roller is extended longer than usual. Although there is a method of detecting the resistance value, it is not desirable to maintain the number of printouts per unit time. For example, in an image forming apparatus having an output capacity of 20 sheets / minute in A4 size, every 20 sheets from when the trailing edge of the preceding recording material passes to when the leading edge of the succeeding recording material is conveyed to the transfer roller. If the resistance value detection is performed by extending the time by 5 seconds, the number of output sheets drops to 18 sheets / minute.
[0018]
In such a method of detecting the resistance value between the time when the trailing edge of the preceding recording material passes through the transfer roller and the time when the leading edge of the succeeding recording material is conveyed to the transfer roller, the above-described transfer roller due to the current drift is used. Inability to respond to fluctuations in resistance.
[0019]
(Object of the invention)
The present invention has been made in view of the above problems, and a good image can be formed on a recording material without being affected by environmental fluctuations such as temperature and humidity and fluctuations in the resistance value of a transfer unit caused by a current drift. It is an object to provide an image forming apparatus that can be formed.
[0020]
Further, the present invention provides an image forming apparatus using an ion-conductive transfer member, which can print a good image without being affected by environmental fluctuations such as temperature and humidity and fluctuations in the resistance value of a transfer section caused by an electric current drift. It is an object to provide an image forming method that can be formed thereon.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the image forming apparatus is configured as in the following (1) to (6), and the image forming method is configured as in the following (7) to (9).
[0022]
(1) an image holding unit that holds a toner image corresponding to image information;
A transfer unit that rotates while being in contact with the image bearing unit to transfer the toner image carried by the image bearing unit to a recording material;
Transfer voltage applying means for applying a transfer voltage for electrostatically transferring the toner image to the transfer unit,
Transfer current detecting means for detecting a transfer current flowing through the transfer member,
A control unit that controls a transfer voltage applied by the transfer voltage application unit in accordance with the transfer current detected by the transfer current detection unit when transferring the toner image onto the recording material.
[0023]
(2) The image forming apparatus according to (1), wherein the control unit corrects the transfer voltage applied by the transfer voltage application unit when a variation value of the transfer current detected by the transfer current detection unit is within a predetermined value. apparatus.
[0024]
(3) current value calculating means for calculating an average value of the transfer current detected by the transfer current detecting means during a predetermined period,
The fluctuation value is a value corresponding to a difference between the first transfer current average value calculated in the first predetermined period by the calculation means and the second transfer current average value calculated in the second predetermined period. The image forming apparatus according to (2).
[0025]
(4) The image forming apparatus according to (3), wherein the predetermined period is a period required for the transfer unit to make one rotation.
[0026]
(5) charging means for charging the image bearing surface of the image bearing unit to a predetermined potential;
Irradiating means for irradiating light in an on state or an off state according to the image information to form an electrostatic latent image according to the image information on the image bearing surface charged by the charging means,
An irradiation ratio calculation unit that calculates an irradiation ratio of an ON state and an ob state of light emitted by the irradiation unit,
The control unit may control the transfer voltage applied by the transfer voltage application unit when the change value of the irradiation ratio calculated by the irradiation ratio calculation unit is within a predetermined value. The image forming apparatus as described in the above.
[0027]
(6) The image according to any one of (1) to (5), wherein the transfer unit has an ion conductive transfer member composed of NBR rubber, epichlorohydrin, an epichlorohydrin copolymer, and the like. Forming equipment.
[0028]
(7) An image forming method in an image forming apparatus using an ion conductive transfer member,
A step A of detecting a transfer current value flowing through the ion-conductive transfer member during a transfer operation to a recording material;
A step B of correcting a transfer voltage applied to the ion-conductive transfer member during paper passing based on the transfer current value detected in the step A;
An image forming method comprising:
[0029]
(8) An image forming method in an image forming apparatus using an ion conductive transfer member,
Step C of detecting a printing rate of the transferable image formed on the image carrier;
A step D of detecting a transfer current value flowing through the ion-conductive transfer member during a transfer operation to a recording material;
Correcting a transfer voltage to be applied to the ion-conductive transfer member during paper passing based on the printing rate detected in the step C and the transfer current value detected in the step D;
An image forming method comprising:
[0030]
(9) In the image forming method according to the above (7) or (8),
The image forming method, wherein the transfer current value is an average current value for one rotation of the ion-conductive transfer member.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to examples of an image forming apparatus. The present invention is not limited to the form of the apparatus, but can be implemented in the form of a method, supported by the description of the embodiments.
[0032]
【Example】
(Example 1)
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a laser beam printer A that is an “image forming apparatus” using electrophotography according to a first embodiment. FIG. 2 is a control block diagram of the laser beam printer A. Hereinafter, an overall configuration and an image forming process in the laser beam printer A will be described with reference to FIGS.
[0033]
An image processing control unit 201 expands image information transmitted from an external device such as a host computer, stores the image information in a built-in memory, and issues a print instruction at the start of printing to a printer control unit 202 that controls each unit of the laser beam printer A. Send to Note that the image information stored in the memory is transmitted to scanner control means (not shown) for controlling the laser beam scanner 3. However, when the printer control unit 202 controls the scanner control means, the image information is processed together with a print instruction. When the image processing control unit 201 controls the scanner control unit, the image data is transmitted from the control unit 201 to the printer control unit 202, and is read from the built-in memory and used. Note that the image processing control unit 201 has been described as processing for expanding information transmitted from the host computer into printable image information that can be handled by the laser beam scanner 3, but the image processing control unit 201 can print from an external device such as the host computer. When the image information is sent directly, the image information is stored in a built-in memory without performing the expansion processing.
[0034]
The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow by a main motor 203 controlled by a printer control unit 202. Note that the main motor 203 rotationally drives devices related to paper conveyance such as the transfer roller 9 and the fixing device 11 in addition to the photosensitive drum 1.
[0035]
The charging device 2, which is a contact charging member, charges the peripheral surface of the photosensitive drum 1 to have a predetermined polarity and potential based on an instruction from the printer control unit 202 (primary charging).
[0036]
The laser beam scanner 3 as an image exposure unit outputs a laser beam L on / off modulated in accordance with image information input from an external device such as an image scanner (not shown) or a host computer, and outputs the laser beam L to the photosensitive drum 1. The upper charging processing surface is scanned and exposed. This scanning exposure forms an electrostatic latent image on the surface of the photosensitive drum 1 according to the image information.
[0037]
In the developing device 4, a developer (toner) is attached from the developing sleeve 4a to the surface of the photosensitive drum 1, and the electrostatic latent image is visualized as a toner image.
[0038]
A recording material (hereinafter, referred to as paper) P is stored in the paper feed cassette 5, and the solenoid 204 transmits the driving force of the main motor 203 to the paper feed roller 6 based on a paper feed start signal from the printer control unit 202. The sheets P in the sheet cassette 5 are fed one by one. Thereafter, the paper P is conveyed by the registration roller 7, and is introduced at a predetermined timing into a transfer portion T, which is a contact nip portion between the photosensitive drum 1 and the transfer roller 9, through a TOP sensor 15 provided in a paper path 8 a. You. Here, the timing at which the TOP sensor 15 detects the leading end of the paper P so that the leading end of the toner image formed on the surface of the photosensitive drum 1 and the timing at which the leading end of the paper P reaches the transfer site T are synchronized. Based on this, the timing of scanning exposure of the photosensitive drum 1 by the laser scanner 3 is controlled. Note that signals from various sensors of the laser beam printer A such as the TOP sensor 15 are input to the printer control unit 202 via the sensor input unit 205.
[0039]
The paper P introduced into the transfer site T is nipped and conveyed by the photosensitive drum 1 and the transfer roller 9 at the transfer site T. At this time, a transfer voltage controlled to a predetermined value is applied to the transfer roller 9 from a transfer voltage control unit.
[0040]
The details of the transfer roller 9 and the transfer voltage control will be described later. By applying a transfer voltage having a polarity opposite to that of the toner to the transfer roller 9, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the surface of the paper P at the transfer portion T.
[0041]
The paper P on which the toner image has been transferred at the transfer portion T is separated and conveyed from the photosensitive drum 1, and conveyed to the fixing device 11 through the paper path 8b, where the toner image is fixed on the paper P while being heated and pressed. Receive.
[0042]
On the other hand, the surface of the photosensitive drum 1 after the transfer and separation is subjected to cleaning of the transfer residual toner and paper dust by the cleaning device 10 and is repeatedly subjected to an image forming process.
[0043]
The paper P that has passed through the fixing device 11 is guided toward the paper path 8 c and is discharged from the paper discharge port 13 onto the paper discharge tray 14.
[0044]
The transfer voltage control of the transfer roller 9 in the present embodiment is performed according to the detection of the transfer roller resistance value. That is, for example, the transfer roller resistance value detected in the transfer roller resistance value detection performed during the pre-rotation processing (stabilization processing of the surface potential of the photosensitive drum 1, the transfer roller cleaning processing, etc.) performed prior to the start of printing. The transfer voltage of the transfer roller during paper passing is controlled by the constant voltage control according to. For example, the above-mentioned ATVC control is used as this control.
[0045]
In the present embodiment, description will be made assuming that control is performed using ATVC control. In the ATVC control, the transfer voltage application unit 206 performs constant current control for controlling the transfer roller 9 to have a predetermined current value during the pre-rotation process, and monitors the voltage applied to the transfer roller 9 during the constant current control. Thus, the voltage value V0 corresponding to the transfer roller resistance value is determined.
[0046]
3-a in FIG. 3 shows the voltage applied to the transfer roller 9 until the voltage value V0 corresponding to the transfer roller resistance value is determined, and 3-b shows the transfer voltage applied as in 3-a. 9 shows a current value detected by the transfer roller current detection unit 207 when the operation is performed.
[0047]
In the ATVC resistance detection control, first, an initial transfer voltage Vp is applied for a time T1, and a current value flowing during the T1 is monitored. The value of the detected current Ip1 is compared with a target current value It by a CPU (not shown) of the printer control unit 202, and a transfer voltage value V1 to be applied next time is determined. Specifically, a transfer voltage value larger than Vp is applied if Ip1 is smaller than It, and a transfer voltage value smaller than Vp is applied if Ip1 is larger than It such that the transfer roller current value Ip2 detected next time becomes equal to the target current value It. I do. Next, the determined transfer voltage V1 is applied for a time T2, and the current value Ip2 is monitored again. This is repeated n times, and after detecting the current value Ipn and determining the transfer voltage value Vpn so that the target current value It flows, the transfer voltage values V1 to Vn stored in the memory of the printer control unit 202 are averaged. To determine the resistance-corresponding voltage V0. In FIG. 3, V0 is determined after adjusting the transfer voltage four times with n = 4.
[0048]
Based on V0 obtained by the ATVC voltage detection control, a print transfer voltage Vt to be applied at the time of printing is determined by the following control formula, and constant voltage control is performed.
Vt = α × V0 + β
Note that α and β are correction coefficients set according to the specifications of the apparatus, the material characteristics of members constituting the image forming process such as the photosensitive drum 1, and the like. For example, α = 1.5, β = 1.0 [ kV].
[0049]
As described above, the transfer voltage V0 according to the transfer roller resistance value is set during the execution of the pre-rotation processing executed prior to the start of printing, and the photosensitive drum 1 is set using the print transfer voltage Vt calculated from V0. The transfer control according to the resistance value of the transfer roller 9 can be performed by transferring the toner image on the surface of the sheet to the paper P.
[0050]
However, as described above, the resistance value of the transfer roller 9 can fluctuate due to temperature and humidity, etc., and therefore, in this embodiment, even during the transfer of the toner image by the transfer roller 9, the transfer voltage V0 and the print transfer voltage calculated therefrom. Vt is corrected.
[0051]
FIG. 4 is a diagram showing a transfer roller current value during transfer. As will be described later, during transfer in which a print transfer voltage is applied, the transfer roller current average value Iz (n) for one round of the transfer roller is detected. To correct the print transfer voltage Vt.
[0052]
Hereinafter, the control in the present embodiment will be described with reference to the flowcharts of FIGS. FIG. 5 is a flowchart showing the overall control of this embodiment from the start of printing to the end of printing, and FIG. 6 is a flowchart showing details of the transfer voltage control (step S515) in the flowchart of FIG.
[0053]
After the power is turned on to the laser beam printer A and a predetermined initialization process (such as a process of raising the fixing device 11 to a predetermined temperature) is performed and the laser beam printer A enters a standby state in which an image can be formed, FIG. In step S501, the printer control unit 202 determines whether a print instruction has been received from the image processing control unit 201. If the print instruction has been received, the process proceeds to step S502.
[0054]
In step S502, a pre-rotation process such as a process for stabilizing the surface potential of the photosensitive drum 1 and a process for cleaning the transfer roller is started.
[0055]
In step S503, the initial transfer voltage Vp is applied, and the transfer roller current value Ip1 detected with respect to the applied Vp is detected in step S504.
[0056]
In step S505, the transfer voltage V1 is calculated by comparing the detected transfer roller current value Ip1 with the target current value It.
[0057]
In steps S506 to S511, the process of comparing the detected transfer roller current value Ipn with the target current value It to calculate the transfer voltage Vn is repeated, and the same process is performed N times including the processes in steps S504 to S505. Is to be repeated. That is, by setting n = 2 in step S502 and adding 1 to n in step S510, the transfer voltages V2, V3,... Are repeatedly calculated. In step S511, it is determined whether the process of calculating the transfer voltage Vn has been performed a predetermined number of N times. If YES, the process proceeds to step S512.
[0058]
In step S512, the transfer voltage values calculated N times from V1 to VN are averaged to determine a transfer voltage V0 corresponding to the resistance value of the transfer roller 9. In step S513, the print transfer voltage Vt is determined using the V0.
[0059]
In step S514 after determining the transfer voltage V0 and the print transfer voltage Vt, it is determined whether or not the pre-rotation processing has been completed, and if it has been completed, the process proceeds to the transfer voltage control in step S515.
[0060]
Next, a description will be given with reference to FIG. 6 which is a flowchart showing the transfer voltage control.
[0061]
In step S601, it is determined whether the paper P has reached the transfer roller 9. This determination is made based on whether or not a predetermined time according to the transport speed of the paper P has elapsed since the top end of the paper P was detected by the TOP sensor 15.
[0062]
In response to the paper P reaching the transfer roller 9, the application of the print transfer voltage Vt is started in step S602.
[0063]
In step S603, the transfer roller current value detected by the transfer roller current detection unit 207 for one rotation of the transfer roller is averaged to calculate a transfer current average value Iz (1), and the value is calculated in step S604 by the printer control unit. The data is stored in the memory of the memory 202.
[0064]
In steps S605 to S612, a process of correcting the transfer voltage V0 and the print transfer voltage Vt by comparing the transfer current average value Iz (n) calculated at the n-th time with the previously calculated Iz (n-1) is performed. . This process is repeated until the paper P passes through the transfer roller, thereby preventing a change in the resistance value of the transfer roller 9 during the paper feeding from affecting the image quality.
[0065]
By setting n = 2 in step S605 and adding 1 to n in step S611, in step S608, transfer is performed as Iz (2) -Iz (1), Iz (3) -Iz (2),. The comparison of the current average value is repeated. In step S608, if the absolute value of the difference between the transfer current average value Iz (n) acquired this time and the transfer current average value Iz (n-1) acquired last time is B or less, the transfer current average value The process proceeds to step S609 assuming that the change is caused by the change in the resistance value of the transfer roller 9.
[0066]
In step S609, V0 is corrected by multiplying the transfer voltage value V0 by the ratio of the previously obtained transfer current average value Iz (n-1) to the transfer current average value Iz (n) obtained this time. That is, if the transfer current average value is smaller than the previous time, the correction is performed so that the transfer voltage value V0 increases.
[0067]
In step S610, a new print transfer voltage value Vt is calculated using the corrected new transfer voltage value V0.
[0068]
In step S612, whether or not the paper P has passed the transfer roller 9 is determined based on the output of the TOP sensor 15 as in step S601. If the paper P has passed, the process returns to the flowchart of FIG.
[0069]
In step S516 in FIG. 5, it is determined whether there is a page to be printed next. If there is a next page, the transfer voltage control in step S515 is performed again. That is, the transfer voltage control in step S515 is control executed for each sheet of paper P to be printed, and this process is repeated until continuous printing is completed.
[0070]
Hereinafter, a specific example will be described.
[0071]
In the laser beam printer A, which is the image forming apparatus of the present embodiment, the transport speed of the paper P is 100 mm / sec. In this case, an ion conductive transfer roller is used as the transfer roller 9.
[0072]
The ion conductive transfer roller used in this embodiment is a blend of NBR rubber and epichlorohydrin rubber, and has an initial resistance of 2.0 when a voltage of 2 kV is applied in an environment of a temperature of 23.5 ° C. and a humidity of 60%. × 10 ⁸ Ω. The ratio of the maximum resistance value to the minimum resistance value in one rotation of the transfer roller is about 1.2 times, and the time required for the transfer roller 9 to make one rotation is 300 msec. The length of one circumference of the transfer roller is 30 mm. When the transfer roller used in this embodiment is left in a high-temperature and high-humidity environment with an ambient temperature of 32.5 ° C. and a humidity of 80%, the transfer roller in a low-temperature and low-humidity environment with an ambient temperature of 10 ° C. and a humidity of 15% is used. It increases about 50 times. When paper P having a moisture content of 5.0% is continuously passed immediately after opening in a low-temperature and low-humidity environment, a maximum of 5% / sheet is generated by steam and heat generated when the fixing device 11 heats and fixes the paper P. Experimental results show that the resistance value of the transfer roller 9 decreases. In addition, it is known that the resistance value of the transfer roller 9 increases at a rate of 3% / sheet at a maximum and 10% / sheet at a maximum due to the energization drift. The transfer roller 9 is not limited to the blend of the NBR rubber and the epichlorohydrin rubber, but may be made of NBR rubber, epichlorohydrin, epichlorohydrin copolymer, or the like.
[0073]
When the printer control unit 202 receives a print instruction from the image processing control unit 201, the latent image formation is started by the laser scanner 3 and the paper P passes through the transfer nip T in synchronization with the toner image formed on the photosensitive drum 1. The paper is fed and the application of the print transfer voltage Vt is started. The printer control unit 202 sets a period of 300 msec. The transfer current average value Iz (n) is detected every time, and the detection result is stored in the memory.
[0074]
The difference between the detected average current value Iz (n) for one rotation of the transfer roller and the average current value Iz (n-1) of the previous one rotation indicates a variation rate of 0. 9% / 300 msec. (B in step S608) (YES in step S608 in FIG. 6), and if there is no correction switching of the transfer voltage during this period, it can be determined that the resistance value of the transfer roller 9 has fluctuated. If the rate of change of the current value is equal to or greater than the designated condition B (NO in step S608), it is considered that the change is caused by switching the paper type or irregular discharge, and the transfer voltage correction is performed because the resistance change cannot be ignored. Absent.
[0075]
If the variation rate of the current value is within the designated condition B, the transfer voltage value V0 corresponding to the resistance value and the print transfer in proportion to the difference between Iz (n) and Iz (n-1) as shown in the following equation. The voltage value Vt is corrected. Note that V0 on the right side is a value before correction, and V0 on the left side is a value after correction.
After correction V0 = Iz (n-1) / Iz (n) × V0
Vt = α × V0 + β after correction
[0076]
The effect of this example was confirmed in a paper passing experiment. NeenaBond, basis weight 60 g, 150 sheets of paper P having a water content of 5.0% immediately after opening were continuously passed. A laser beam printer A according to the first embodiment, a comparative example 1 having the same configuration as in the first embodiment and not performing the transfer voltage correction, and a comparative example in which the transfer voltage is controlled at a constant current so that the current value is constant at 3.5 μA Two types of apparatuses were used. The paper passing environment is a low-temperature, low-humidity environment with an ambient temperature of 10 ° C. and a humidity of 15%. Table 1 shows the results of evaluation of the printed image.
[0077]
[Table 1]

[0078]
In Comparative Example 1, although the character image was slight on the fourth to seventh sheets of continuous paper passing, toner scattering occurred. The toner scattering occurred because the resistance value of the ion-conductive transfer roller increased due to the current-carrying drift, resulting in insufficient toner holding charge. Also, black spots began to appear in the halftone image from about the 120th sheet of continuous paper feeding. This phenomenon occurred because the resistance value of the transfer roller 9 was lowered by the water vapor and heat generated from the fixing device 11, so that electric charges locally penetrated the paper and generated a discharge mark on the photosensitive drum 1. . As a result of monitoring the current value flowing during paper passing, the current value flowing during 150-sheet passing varied greatly in the laser beam printer A in Comparative Example 1, but the current was almost stable in Example 1. Was. In Example 1, there was no problem with the image after 150 sheets.
[0079]
Next, an experiment 2 was performed in which Xx4024 as the paper P and a basis weight of 75 g and 50 sheets of the envelope Com10 were alternately passed one by one. Table 2 shows the evaluation results.
[0080]
[Table 2]

[0081]
In Comparative Example 1, as in Experiment 1, toner scattering occurred due to a shortage of toner holding charge due to an electric current drift. Further, in Comparative Example 2 using the constant current control, when the envelope was passed, the current flowed into the non-sheet passing portion, the transfer voltage became insufficient, and toner scattering and transfer omission occurred.
[0082]
In the laser beam printer A of Example 1, good images could be obtained for both the Xx4024 and the envelope.
[0083]
As shown in the above experiments, in the present embodiment, it is possible to eliminate the effects of the current drift of the ion-conductive transfer roller and fluctuations in temperature and humidity, and provide a good image.
[0084]
That is, during the transfer operation to the recording material, the transfer current flowing through the transfer member is detected, the resistance of the transfer member is detected, and the print transfer voltage is corrected, so that the number of printouts per unit time is not reduced. It is possible to provide an image forming apparatus that forms an excellent image by correcting the influence on the image due to the change in the resistance value of the transfer member during the transfer operation.
[0085]
(Example 2)
In this embodiment, a laser beam printer A which is an image forming apparatus having the same hardware configuration as that of the first embodiment is used.
[0086]
In the present embodiment, the transfer roller average current value during printing and the printing rate of the toner image over the entire image area are monitored, and the transfer voltage is corrected.
[0087]
The transfer current value during printing varies depending on the toner resistance on the image in addition to the transfer roller resistance value and the paper resistance value. The toner resistance is substantially proportional to the printing rate of the toner image over the entire image area, that is, the laser lighting ratio of the laser beam scanner 3. Normally, the printing rate of the toner image over the entire image area of the character image is about 5% on average, about 50% for a halftone image, and about 100% for a solid black image.
[0088]
In the present embodiment, the transfer voltage is corrected more accurately and with less erroneous detection by considering the toner resistance. That is, in the first embodiment, the transfer voltage is corrected irrespective of the printing rate of the toner image indicating the toner resistance. However, if the printing rate of the toner image fluctuates greatly, the transfer voltage is erroneously changed even when the resistance value of the transfer roller 9 is small. There is a possibility that the transfer voltage is corrected. The second embodiment differs from the first embodiment in that the transfer voltage is corrected based on the change in the resistance value of the transfer roller 9 only when the printing ratio of the toner image is within a predetermined value and the change due to the toner resistance is small. .
[0089]
As shown in FIG. 7, during application of the print transfer voltage during paper passing, the laser lighting ratio of the laser scanner 3 is monitored for each rotation of the transfer roller, and an averaged transfer roller current average value Iz (n) is obtained. The laser lighting ratio Lz (n) of the laser scanner 3 for one rotation of the transfer roller is stored in the memory of the printer control unit 202. The laser lighting ratio Lz (n) represents the lighting time of the laser scanner 3 with respect to the time for scanning the image area on the surface of the photosensitive drum 1 with a laser beam, and as described above, the larger the area where the toner image is developed, the larger the area. The time during which the laser scanner 3 is turned on also becomes longer. The laser lighting ratio can be calculated by measuring the time during which the laser is in the ON state (lighting) with respect to the scanning time by a timing unit (not shown).
[0090]
Hereinafter, the control in this embodiment will be described with reference to the flowcharts of FIGS. 8 and 9. Note that the entire control from the start of printing to the end of printing is the same as the flowchart in FIG. 5, and FIGS. 8 and 9 are flowcharts showing the details of the transfer voltage control (step S515) in FIG. Since the flowchart of FIG. 5 has been described in the first embodiment, description thereof will be omitted.
[0091]
In step S801, it is determined whether the paper P has reached the transfer roller 9. This determination is made based on whether or not a predetermined time according to the transport speed of the paper P has elapsed since the top end of the paper P was detected by the TOP sensor 15.
[0092]
In response to the paper P reaching the transfer roller 9, in step S802, application of the print transfer voltage Vt is started.
[0093]
In step S803, the transfer roller current value detected by the transfer roller current detection unit 207 for one round of the transfer roller is averaged to calculate a transfer current average value Iz (1), and the value is calculated in step S804 by the printer control unit. The data is stored in the memory of the memory 202.
[0094]
In step S805, the laser lighting ratio Lz (1) with respect to the entire image area for one rotation of the transfer roller is calculated. The laser lighting ratio Lz (1) is also stored in the memory of the printer control unit 202 in step S806, similarly to Iz (1).
[0095]
Steps S807 to S809 in FIG. 8 and steps S901 to S914 in FIG. 9 compare the transfer current average value Iz (n) calculated at the n-th time with the previously calculated Iz (n-1), and determine the transfer voltage V0. And a process of correcting the print transfer voltage Vt. This process is repeated until the paper P passes through the transfer roller 9, thereby preventing a change in the resistance value of the transfer roller 9 during paper feeding from affecting the image quality.
[0096]
In step S807, n = 2 is set. This n indicates the number of rotations of the transfer roller 9 after the paper P reaches the transfer roller. In steps S803 to S806, the first rotation has already been performed. Since processing is being performed, 2 is set.
[0097]
Although m = 1 is set in step S808 and M = 1 is set in step S809, m and M are used to determine whether the laser lighting ratio is within a predetermined value, which will be described in detail later.
[0098]
In step S901, the transfer current average value Iz (n) for one rotation of the transfer roller at the nth rotation is calculated, and in step S902, Iz (n) is stored in the memory of the printer control unit 202.
[0099]
In step S903, the laser lighting ratio Lz (n) for the entire image area in one rotation of the transfer roller at the nth rotation is calculated. The laser lighting ratio Lz (n) is also stored in the memory of the printer control unit 202 in step S904, similarly to Iz (n).
[0100]
In step S905, the laser lighting ratio (Lz (n)) for one rotation of the transfer roller at the n-th rotation and the laser lighting ratios (Lz (n−1), Lz (n−2),. , L (nm),..., L (1)), it is determined whether or not the absolute value is within a predetermined value, and if it is within the predetermined value, the process proceeds to the transfer voltage correction processing in steps S906 to S908. move on. By comparing the laser lighting ratios in step S905, the transfer voltage is not erroneously corrected when the change in the printing ratio of the toner image is large. That is, the transfer current average value Iz (n−n−n) at the (n−m) th rotation which is similar to the laser lighting ratio (Lz (n)) for one rotation of the transfer roller at the nth rotation (the absolute value of the difference is within a predetermined range) By correcting the transfer voltage V0 using m), the transfer voltage can be corrected according to the change in the resistance value of the transfer roller 9. By setting m = m + 1 in step S910 and determining whether m> M in step S910, the laser lighting ratio Lz (n) at the n-th rotation is increased up to Lz (1) at the first rotation (n− 1) Rotation, (n−2) th rotation,..., (N−m) th rotation,.
[0101]
In step S907, the transfer voltage value V0 is corrected by multiplying the transfer voltage value V0 by the ratio of the transfer current average value Iz (nm) acquired at the (nm) th rotation to the transfer current average value Iz (n) acquired this time. are doing. That is, the correction is performed so that the transfer voltage value V0 increases when the transfer current average value decreases.
[0102]
In step S908, a new print transfer voltage value Vt is calculated using the corrected new transfer voltage value V0.
[0103]
In step S914, whether or not the paper P has passed the transfer roller is determined based on the output of the TOP sensor 15, as in step S801. If the paper P has passed, the process returns to the flowchart in FIG.
[0104]
In step S516 in FIG. 5, it is determined whether there is a page to be printed next. If there is a next page, the transfer voltage control in step S515 is performed again. That is, the transfer voltage control in step S515 is control executed for each sheet of paper P to be printed, and this process is repeated until continuous printing is completed.
[0105]
Hereinafter, a specific example will be described.
[0106]
In the laser beam printer A, which is the image forming apparatus of the present embodiment, the same ionic conductive transfer roller as that of the first embodiment is used, so that the detailed description of the transfer roller 9 is omitted.
[0107]
When the formation of a latent image by the laser scanner 3 is started, the printer control unit 202 sends a cycle of one rotation of the transfer roller 300 msec. The laser lighting ratio Lz (n) is stored in the memory of the printer control unit 202 for each time. The paper P is passed through the transfer nip T in synchronization with the toner image formed on the photosensitive drum 1, and a print transfer voltage Vt is applied. The transfer current detection unit 207 monitors and stores the average value Iz (n) of the current in synchronization with the cycle (300 msec.) In which the laser lighting ratio of the laser scanner 3 is monitored.
[0108]
In the present embodiment, paper switching and toner image switching are identified from the laser lighting ratio Lz (n) and the average current value Iz (n) of the laser scanner 3 monitored in the transfer roller cycle, and the transfer roller resistance value is determined. When the fluctuation is detected, the transfer bias is corrected only when the fluctuation is within a predetermined value.
[0109]
The monitored laser lighting ratio Lz (n) of the laser scanner 3 is Lz (n−1) up to the previous circumference, or Lz (n−2), Lz (n−3),. If the difference from −m),..., Lz (1) is within 5% (C in step S905), it can be determined that the image has substantially the same toner resistance. If the laser lighting ratio Lz (n) at the n-th rotation does not meet the condition of 5% or less compared to the memory data Lz (1) at the front, bias correction is not performed because there is no comparable image.
[0110]
The average current value Iz (n) and the average current value Iz (n-m) at the (nm) th rotation, which is a region where the toner resistance is determined to be substantially equal to the monitored average current value Iz (n). And the absolute value of the difference from the fluctuation rate of 0.9% / 300 msec. If it is within the range, and if there is no transfer switching of the transfer voltage during this time, it can be determined that the resistance of the transfer roller 9 is not a change due to a change in the material of the paper P or the like. If the variation rate of the current value is equal to or more than the designated condition B (NO in step S906), it is considered that the influence is caused by switching of the paper type or irregular discharge, and the transfer voltage correction is performed because the resistance variation cannot be ignored. Absent.
[0111]
If the variation rate of the current value is within the designated condition B, the transfer voltage value V0 corresponding to the resistance value and the print transfer in proportion to the difference between Iz (n) and Iz (nm) as shown in the following equation. The voltage value Vt is corrected. Note that V0 on the right side is a value before correction, and V0 on the left side is a value after correction.
After correction V0 = Iz (nm) / Iz (n) × V0
Vt = α × V0 + β after correction
[0112]
In this embodiment, since the transfer voltage correction control is performed based on the transfer roller current value and the printing rate of the image during paper passing, accurate transfer voltage correction control is possible even for a composite image in which a character image and a photographic image are mixed.
[0113]
The effect of this example was confirmed in a paper passing experiment. NeenaBond, basis weight 60 g, 150 sheets of paper P having a water content of 5.0% immediately after opening were continuously passed. The image to be printed was a composite image composed of a character image and a photographic image as shown in FIG. As the laser beam printer A, the laser beam printer according to the second embodiment and the comparative example 1 having the same configuration as the second embodiment and not performing the transfer voltage correction were used. The paper passing environment is a low-temperature, low-humidity environment with an ambient temperature of 10 ° C. and a humidity of 15%. Table 3 shows the results of evaluation of the printed image.
[0114]
[Table 3]

[0115]
In Comparative Example 1, although the character image was slight on the fourth to seventh sheets of continuous paper passing, toner scattering occurred. Black spots began to appear in the photographic image from the 120th sheet. In the laser beam printer A according to the present embodiment, there was no problem in the image over 150 sheets.
[0116]
As shown in the above experiments, in the present embodiment, it is possible to eliminate the effects of the current-carrying drift of the ion-conductive transfer roller and the temperature and humidity fluctuations, and to provide a good image.
[0117]
That is, according to the present embodiment, it is possible to provide an image forming apparatus that forms a good image by performing the transfer voltage correction more accurately and with less erroneous detection by considering the toner resistance.
[0118]
【The invention's effect】
As described above, according to the present invention, an image forming apparatus that forms a good image on a recording material without being affected by environmental fluctuations such as temperature and humidity and fluctuations in the resistance value of a transfer unit due to an electric current drift Can be provided.
[0119]
Further, the present invention provides an image apparatus using an ion-conductive transfer member, which can print a good image on a recording material without being affected by environmental fluctuations such as temperature and humidity and fluctuations in the resistance value of a transfer section caused by an electric current drift. An image forming method can be provided.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a schematic configuration of a laser beam printer A.
FIG. 2 is a control block diagram of a laser beam printer A.
FIG. 3 is a diagram showing a transfer voltage and a detection current in ATVC resistance detection control.
FIG. 4 is a diagram showing a transfer roller current value during transfer.
FIG. 5 is a flowchart showing the overall control of the first embodiment.
FIG. 6 is a flowchart illustrating transfer voltage control according to the first embodiment.
FIG. 7 is a diagram showing a laser lighting ratio during transfer.
FIG. 8 is a flowchart illustrating transfer voltage control according to the second embodiment (part 1).
FIG. 9 is a flowchart illustrating transfer voltage control according to the second embodiment (part 2);
FIG. 10 is a diagram showing an image used in a confirmation experiment.
FIG. 11 is a perspective view illustrating a configuration of a transfer roller.
[Description of sign]
A Laser beam printer
1 Photosensitive drum
2 Charging device
3 laser scanner
4 Developing device
9 Transfer roller
11 Fixing device
201 Image processing control unit
202 Printer control unit
206 Transfer voltage application section
207 Transfer roller current detector

Claims (9)

An image holding unit that holds a toner image corresponding to the image information;
A transfer unit that rotates while being in contact with the image bearing unit to transfer the toner image carried by the image bearing unit to a recording material;
Transfer voltage applying means for applying a transfer voltage for electrostatically transferring the toner image to the transfer unit,
Transfer current detecting means for detecting a transfer current flowing through the transfer member,
A control unit that controls a transfer voltage applied by the transfer voltage application unit in accordance with the transfer current detected by the transfer current detection unit when the toner image is transferred to the recording material. Image forming device. 2. The image according to claim 1, wherein the control unit corrects the transfer voltage applied by the transfer voltage application unit when a variation value of the transfer current detected by the transfer current detection unit is within a predetermined value. Forming equipment. A current value calculating means for calculating an average value of the transfer current detected by the transfer current detecting means for a predetermined period,
The fluctuation value is a value corresponding to a difference between the first transfer current average value calculated in the first predetermined period by the calculation means and the second transfer current average value calculated in the second predetermined period. The image forming apparatus according to claim 2, wherein: The image forming apparatus according to claim 3, wherein the predetermined period is a period required for the transfer unit to make one rotation. A charging unit that charges an image bearing surface of the image bearing unit to a predetermined potential; and a charging unit that charges the image bearing surface charged by the charging unit according to the image information to form an electrostatic latent image corresponding to the image information. Irradiation means for irradiating light in an on state or an off state,
An irradiation ratio calculation unit that calculates an irradiation ratio between an on state and an off state of light emitted by the irradiation unit,
5. The method according to claim 1, wherein the control unit controls the transfer voltage applied by the transfer voltage applying unit when a variation value of the irradiation ratio calculated by the irradiation ratio calculation unit is within a predetermined value. An image forming apparatus according to any one of the above. 6. The image forming apparatus according to claim 1, wherein the transfer unit has an ion conductive transfer member made of NBR rubber, epichlorohydrin, epichlorohydrin copolymer, or the like. apparatus. An image forming method in an image forming apparatus using an ion conductive transfer member,
A step A of detecting a transfer current value flowing through the ion-conductive transfer member during a transfer operation to a recording material;
A step B of correcting a transfer voltage applied to the ion-conductive transfer member during paper passing based on the transfer current value detected in the step A;
An image forming method comprising: An image forming method in an image forming apparatus using an ion conductive transfer member,
Step C of detecting a printing rate of the transferable image formed on the image carrier;
A step D of detecting a transfer current value flowing through the ion-conductive transfer member during a transfer operation to a recording material;
Correcting a transfer voltage to be applied to the ion-conductive transfer member during paper passing based on the printing rate detected in the step C and the transfer current value detected in the step D;
An image forming method comprising: The image forming method according to claim 7, wherein
The image forming method according to claim 1, wherein the transfer current value is an average current value for one rotation of the ion conductive transfer member.

Images