JP5114866B2 - Image forming apparatus - Google Patents

Image forming apparatus Download PDF

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JP5114866B2
JP5114866B2 JP2006123924A JP2006123924A JP5114866B2 JP 5114866 B2 JP5114866 B2 JP 5114866B2 JP 2006123924 A JP2006123924 A JP 2006123924A JP 2006123924 A JP2006123924 A JP 2006123924A JP 5114866 B2 JP5114866 B2 JP 5114866B2
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transfer
image forming
forming apparatus
voltage
color
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JP2007298541A (en
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尚寿 藤田
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Fujifilm Business Innovation Corp
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Fuji Xerox Co Ltd
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Description

本発明は画像形成装置に関し、特に複数の像担持体上に形成された静電潜像をトナーによって現像し転写媒体に転写することによって画像を形成する画像形成装置に関する。   The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by developing an electrostatic latent image formed on a plurality of image carriers with toner and transferring the image onto a transfer medium.

従来より、レーザプリンタやファクシミリ装置、複写機等の画像形成装置には、像担持体としての感光体ドラムを備え、感光体ドラムの表面を均一に帯電させ、その後に画像データに基づく光ビームを照射して感光体ドラム上に静電潜像を形成し、所定極性に帯電されたトナーを用いて静電潜像を現像し、感光体ドラム上で現像された画像を転写ロールなどの転写手段を用いて転写媒体(用紙))に転写し、画像を形成するものがある。   Conventionally, image forming apparatuses such as laser printers, facsimile machines, and copiers have been provided with a photosensitive drum as an image carrier, and the surface of the photosensitive drum is uniformly charged, and then a light beam based on the image data is emitted. Irradiating to form an electrostatic latent image on the photosensitive drum, developing the electrostatic latent image using toner charged to a predetermined polarity, and transferring the image developed on the photosensitive drum to a transfer means such as a transfer roll Is used to form an image by transferring to a transfer medium (paper).

このとき帯電されたトナーを忠実に用紙に転写するためには、転写手段に所定の転写電界を発生させ、転写バイアス制御により転写電界を安定させる必要がある。   In order to faithfully transfer the charged toner to the paper at this time, it is necessary to generate a predetermined transfer electric field in the transfer unit and stabilize the transfer electric field by transfer bias control.

転写バイアス制御の方法は大別すると定電流制御と定電圧制御にわけられる。文献などで既に良く知られているように両者は一長一短で、どちらが良いとは一概に言えないが、次のような特徴がある。定電流制御は制御が簡単である一方で、電流漏れが発生してしまうと必要最低限の転写電界が得られず転写不良を招きやすい。また、小サイズの転写媒体の転写性に弱い。   The transfer bias control methods are roughly classified into constant current control and constant voltage control. As is well known in the literature, both are merits and demerits, and it cannot be generally said which is better, but it has the following characteristics. The constant current control is easy to control. On the other hand, if current leakage occurs, the minimum required transfer electric field cannot be obtained, and transfer failure tends to occur. In addition, the transfer property of a small-size transfer medium is weak.

これに対して定電圧制御は制御が複雑になるが、電流漏れには比較的強い。小サイズの転写媒体には強いが、想定外のメディアが搬送されると電圧制御が対応しきれないことがある。   In contrast, the constant voltage control is complicated in control, but is relatively resistant to current leakage. Although it is strong against small-size transfer media, voltage control may not be able to cope with unexpected media being conveyed.

ここで、複数の感光体ドラム/転写手段を転写媒体の搬送路に沿って設けた用紙搬送タンデム型カラー機の場合を考えると、白黒機のように最上流の転写ロールとレジロール間での電流漏れだけでなく、転写ロール相互間でも電流漏れが発生しやすく、転写制御が不安定になりやすい。そのため、定電圧制御を採用する方が安定した転写性を確保しやすいという特徴がある。そこでタンデム型の画像形成装置において、少なくとも1つの転写手段で印字前に定電流制御を行い、その時の出力電圧に応じて用紙内の転写電圧を決定し、定電圧を印加する構成が提案されている(例えば、特許文献1参照)。   Here, considering the case of a paper transport tandem type color machine in which a plurality of photosensitive drums / transfer means are provided along the transfer medium transport path, the current between the most upstream transfer roll and registration roll as in a black and white machine is considered. In addition to leakage, current leakage is likely to occur between transfer rolls, and transfer control tends to become unstable. Therefore, there is a feature that it is easier to ensure stable transferability when the constant voltage control is adopted. Therefore, in a tandem type image forming apparatus, a configuration is proposed in which constant current control is performed before printing by at least one transfer unit, the transfer voltage in the sheet is determined according to the output voltage at that time, and the constant voltage is applied. (For example, refer to Patent Document 1).

しかし、上記の例で開示されているように、印字前に印加電圧を定電流制御することで、用紙内に印加する転写電圧としてある程度適正な電圧を選択できることになるが、定電圧制御のベースは予測制御であるが故に、想定外の用紙が搬送されて来た時は用紙内での転写電圧調整が必要となる。   However, as disclosed in the above example, by controlling the applied voltage at a constant current before printing, an appropriate voltage can be selected as a transfer voltage applied to the paper. Since this is predictive control, when an unexpected sheet is conveyed, it is necessary to adjust the transfer voltage within the sheet.

既に転写電圧処理が開始されている状態で、用紙内で電圧調整を行う所謂 On paper feedback を行った場合、例えばカラー画像の形成時に任意の一色で電圧調整を行うと用紙内で転写条件が変動し濃度むらが発生し、2次色、3次色では色むらとなってしまう。   When the so-called On paper feedback is performed to adjust the voltage in the paper when the transfer voltage processing has already started, the transfer condition varies within the paper if the voltage is adjusted with an arbitrary color when forming a color image, for example. Density unevenness occurs, and color unevenness occurs in the secondary color and tertiary color.

そこで本発明では転写電圧を用紙内で調整しても色むらの目立たない画像形成装置を提供することを目的とする。
特開平11−119562号公報
Accordingly, an object of the present invention is to provide an image forming apparatus in which unevenness in color is not noticeable even when a transfer voltage is adjusted in a sheet.
JP 11-119562 A

本発明は上記事実を考慮し、簡素な構成で色むらの目立たない画像形成装置を提供することを目的とする。   In view of the above facts, an object of the present invention is to provide an image forming apparatus that has a simple configuration and does not show uneven color.

請求項1に記載の画像形成装置は、感光体上に形成されたトナー画像を、転写電圧を印加した転写手段で用紙上に転写するトナー画像形成装置を用紙搬送方向に複数備えたタンデム方式のカラー画像形成装置であって、前記転写手段に印加する転写電圧をそれぞれ独立して制御する制御手段と、Y色トナー画像形成装置の前記転写手段に設けられ該転写手段に対する電圧印加時に電流を検知する検知手段とを備え、前記Y色トナー画像形成装置は用紙搬送方向上流端に設けられ、前記制御手段は前記用紙が前記Y色転写位置に到着する前に前記Y色トナー画像形成装置にて前記転写手段に所定の電圧を印加し、前記検知手段にて検知された前記転写手段に流れる電流が、一定範囲の値に収まるようにY色トナー転写電圧を仮決めしたのち、 前記用紙の先端が前記Y色トナー画像形成装置から次のトナー画像形成装置に搬送される前に前記転写手段に前記仮決めしたY色電圧を印加し、前記転写手段に流れる電流が一定範囲の値に収まるように前記Y色トナー転写電圧の補正を行うことを特徴とする。 The image forming apparatus according to claim 1 is a tandem type image forming apparatus including a plurality of toner image forming apparatuses in a sheet conveying direction that transfer a toner image formed on a photoreceptor onto a sheet by a transfer unit to which a transfer voltage is applied. A color image forming apparatus, wherein a control unit that independently controls a transfer voltage applied to the transfer unit and a current that is provided in the transfer unit of the Y color toner image forming apparatus and detects a current when a voltage is applied to the transfer unit And the Y color toner image forming apparatus is provided at the upstream end in the paper conveyance direction, and the control means is provided at the Y color toner image forming apparatus before the paper arrives at the Y color transfer position. A predetermined voltage is applied to the transfer unit, and the Y-color toner transfer voltage is temporarily determined so that the current flowing through the transfer unit detected by the detection unit falls within a certain range. Before the leading edge of the recording paper is conveyed from the Y color toner image forming apparatus to the next toner image forming apparatus, the provisionally determined Y color voltage is applied to the transfer means, and the current flowing through the transfer means is within a certain range. The Y color toner transfer voltage is corrected so as to be within the value .

上記構成の発明では、転写電圧を用紙内で変化させても目立たないY色で転写手段に流れる電流が一定範囲の値に収まるように用紙内最適電圧を見積もり印加することで適正な転写電圧の設定と調整を行うので、色むらの目立たない電圧調整ができる。 In the invention having the above-described configuration, the optimum transfer voltage is estimated by applying the estimated optimum voltage in the sheet so that the current flowing in the transfer means in Y color that is inconspicuous even if the transfer voltage is changed in the sheet falls within a certain range . Since setting and adjustment are performed, voltage adjustment without noticeable color unevenness can be performed.

請求項2に記載の画像形成装置は、前記用紙の先端が前記Y色トナー画像形成装置の転写手段にニップされ、前記仮決めされた前記Y色トナー転写電圧が前記転写手段に印加されることで前記検知手段にて検知される電流が、一定範囲の値に収まるように前記Y色トナー転写電圧の補正量を決定することを特徴とする。 The image forming apparatus according to claim 2, wherein a leading end of the paper is nipped by a transfer unit of the Y color toner image forming apparatus, and the temporarily determined Y color toner transfer voltage is applied to the transfer unit. The correction amount of the Y color toner transfer voltage is determined so that the current detected by the detection means falls within a certain range of values .

上記構成の発明では、転写電圧を用紙内で変化させても目立たないY色で用紙先端にて用紙の抵抗を検知し適正な転写電圧の設定と調整を行うので、色むらの目立たない電圧調整ができる。   In the invention of the above configuration, the resistance of the paper is detected at the front end of the paper with the Y color that is not noticeable even if the transfer voltage is changed in the paper, and an appropriate transfer voltage is set and adjusted, so that the voltage adjustment that does not make color unevenness noticeable Can do.

請求項3に記載の画像形成装置は、前記補正されたY色トナー転写電圧に基づいて用紙搬送方向下流の転写電圧を決定することを特徴とする。   According to a third aspect of the present invention, the image forming apparatus determines a transfer voltage downstream in the sheet conveyance direction based on the corrected Y toner transfer voltage.

上記構成の発明では、転写電圧を用紙内で変化させても目立たないY色で適正な転写電圧の設定と調整を行い、その他の色のトナーに対しては、その他のトナー画像形成装置に用紙が到達する前に、Y色トナー画像形成装置で把握した用紙の情報を反映して転写電圧を決めることができるので、その他の色トナー転写中は電圧を固定することができ色むらを目立ちにくくできる。   In the invention of the above configuration, an appropriate transfer voltage is set and adjusted in Y color that is not noticeable even if the transfer voltage is changed in the paper, and other toner image forming apparatuses are used for other color toners. Since the transfer voltage can be determined by reflecting the paper information grasped by the Y color toner image forming apparatus before the toner reaches, the voltage can be fixed during the transfer of the other color toners, and the color unevenness is hardly noticeable. it can.

請求項4に記載の画像形成装置は、感光体上に形成されたトナー画像を、転写電圧を印加した転写手段で用紙上に転写するトナー画像形成装置を用紙搬送方向に複数備えたタンデム方式のカラー画像形成装置であって、前記転写手段に印加する転写電圧はそれぞれ独立して制御する制御手段と、K色トナー画像形成装置よりも用紙搬送方向上流に設けられた第1のトナー画像形成装置の転写手段に設けられ該転写手段に対する電圧印加時に電流を検知する検知手段とを備え、前記制御手段は前記用紙が前記第1のトナー画像形成装置に搬送される前に前記第1のトナー画像形成装置にて前記転写手段に所定の電圧を印加し、前記検知手段にて検知された前記転写手段に流れる電流が、一定範囲の値に収まるように第1のトナー転写電圧を仮決めしたのち、前記用紙の先端が前記第1のトナー画像形成装置から次のトナー画像形成装置に搬送される前に前記転写手段に前記仮決めした第1のトナー転写電圧を印加し、前記転写手段に流れる電流が一定範囲の値に収まるように前記第1のトナー転写電圧の補正を行うことを特徴とする。 The image forming apparatus according to claim 4 is a tandem type image forming apparatus including a plurality of toner image forming apparatuses in a sheet conveying direction that transfer a toner image formed on a photoreceptor onto a sheet by a transfer unit to which a transfer voltage is applied. A color image forming apparatus, wherein the transfer voltage applied to the transfer means is controlled independently, and the first toner image forming apparatus provided upstream of the K color toner image forming apparatus in the paper conveying direction. Detecting means for detecting a current when a voltage is applied to the transfer means, and the control means includes the first toner image before the sheet is conveyed to the first toner image forming apparatus. wherein a predetermined voltage is applied to the transfer means in forming apparatus, current flowing through the transfer unit is detected by said detecting means, tentatively determine a first toner transfer voltage to fit a range of values And then it was to apply a first toner transfer voltage the temporarily determined on the transfer unit before the leading end of the sheet is conveyed from the first toner image forming apparatus to the next toner image forming apparatus, the transfer means The first toner transfer voltage is corrected so that the current flowing through the toner falls within a certain range .

上記構成の発明では、K色よりも上流側に設けられた色の転写手段に流れる電流が、一定範囲の値に収まるように用紙内最適電圧を見積もり印加することで適正な転写電圧の設定と調整を行うので、K色において濃度むらの目立たない電圧調整ができる。 In the invention with the above configuration, an appropriate transfer voltage is set by estimating and applying the optimum voltage in the sheet so that the current flowing through the color transfer means provided on the upstream side of the K color falls within a certain range of values. Since the adjustment is performed, the voltage adjustment in which the density unevenness is not conspicuous in the K color can be performed.

請求項5に記載の画像形成装置は、前記用紙の先端が前記第1のトナー画像形成装置の転写手段にニップされ、前記仮決めされた転写電圧が前記転写手段に印加されることで前記検知手段にて検知される電流が、一定範囲の値に収まるように前記前記第1のトナー転写電圧の補正量を決定することを特徴とする。 6. The image forming apparatus according to claim 5, wherein the leading edge of the sheet is nipped by a transfer unit of the first toner image forming apparatus, and the provisional determined transfer voltage is applied to the transfer unit. The correction amount of the first toner transfer voltage is determined so that the current detected by the means falls within a certain range of values .

上記構成の発明では、K色よりも上流側に設けられた色で用紙先端にて用紙の抵抗を検知し前記転写手段に流れる電流が一定範囲の値に収まるように適正な転写電圧の設定と調整を行うので、K色において濃度むらの目立たない電圧調整ができる。 In the invention having the above-described configuration, an appropriate transfer voltage is set so that the resistance of the sheet is detected at the leading end of the sheet with a color provided upstream of the K color, and the current flowing through the transfer unit falls within a certain range. Since the adjustment is performed, the voltage adjustment in which the density unevenness is not conspicuous in the K color can be performed.

請求項6に記載の画像形成装置は、前記補正された第1のトナー転写電圧に基づいてK色トナー画像形成装置の転写電圧を決定することを特徴とする。   According to a sixth aspect of the present invention, the transfer voltage of the K-color toner image forming apparatus is determined based on the corrected first toner transfer voltage.

上記構成の発明では、K色よりも上流側に設けられた色で適正な転写電圧の設定と調整を行い、K色のトナーに対しては、Kのトナー画像形成装置に用紙が到達する前に、第1のトナー画像形成装置で把握した用紙の情報を反映して転写電圧を決めることができるので、K色トナー転写中は電圧を固定することができ、濃度むら発生を防ぐことができる。   In the invention of the above configuration, an appropriate transfer voltage is set and adjusted with the color provided upstream of the K color, and before the paper reaches the K toner image forming apparatus for the K color toner. In addition, since the transfer voltage can be determined by reflecting the information on the paper grasped by the first toner image forming apparatus, the voltage can be fixed during the transfer of the K color toner, and uneven density can be prevented. .

本発明は上記構成としたので、簡素な構成で色むらの目立たない画像形成装置とすることができた。   Since the present invention has the above-described configuration, an image forming apparatus that has a simple configuration and does not notice uneven color can be obtained.

<基本構成>
図1には本発明に係る画像形成装置を備えた画像形成装置が示されている。
<Basic configuration>
FIG. 1 shows an image forming apparatus including an image forming apparatus according to the present invention.

図1は本発明に係る画像形成装置を備えたフルカラーレーザビームプリンタを示すものである。   FIG. 1 shows a full-color laser beam printer provided with an image forming apparatus according to the present invention.

この画像形成装置10は、図1に示すように、イエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)用の各感光体ドラム32Y〜32Kを有する現像装置30Y〜30Kと、これら感光体ドラム32Y〜32K に接触する一次帯電用の帯電ロールと、イエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色のレーザ光31Y〜31Kを照射するROS(Raster Output Scanner)20とで、その主要部が構成されている。   As shown in FIG. 1, the image forming apparatus 10 includes developing devices 30Y to 30K having photosensitive drums 32Y to 32K for yellow (Y), magenta (M), cyan (C), and black (K). ROS which irradiates the charging rolls for primary charging contacting these photosensitive drums 32Y to 32K and laser beams 31Y to 31K of yellow (Y), magenta (M), cyan (C) and black (K). (Raster Output Scanner) 20 and its main part are configured.

現像装置30Y〜30K、および定着器34は用紙Pの搬送経路、すなわち搬送ベルト22に沿って略鉛直方向に下から上へと配置されている。これにより装置を小型化し、かつ用紙Pの排出トレイをアクセスしやすい装置上部に設ける構成とすることができる。   The developing devices 30 </ b> Y to 30 </ b> K and the fixing device 34 are arranged from the bottom to the top in a substantially vertical direction along the transport path of the paper P, that is, the transport belt 22. As a result, the apparatus can be downsized and the discharge tray for the paper P can be provided at the top of the apparatus where it can be easily accessed.

感光体ドラム32Y、32M、32C、32Kは、共通の接平面を有するように一定の間隔をおいて配置されている。各色毎の画像情報に応じた信号は、図示しない画像処理ユニットによりROS20に入力される。このレーザ光学ユニットでは、イエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色のレーザ光が変調され、対応する色の感光体ドラム32Y〜32Kに照射される。   The photoconductor drums 32Y, 32M, 32C, and 32K are arranged at regular intervals so as to have a common tangential plane. A signal corresponding to the image information for each color is input to the ROS 20 by an image processing unit (not shown). In this laser optical unit, laser light of each color of yellow (Y), magenta (M), cyan (C), and black (K) is modulated and irradiated to the corresponding photosensitive drums 32Y to 32K.

上記各感光体ドラム32Y〜32Kでは、周知の電子写真方式による各色毎の画像形成プロセスが行なわれる。まず、上記感光体ドラム32Y〜32Kとしては例えばOPC感光体を用いた感光体ドラムが用いられ、これらの感光体ドラム32Y〜32Kは回転駆動される。上記感光体ドラム32Y〜32Kの表面は帯電ロールによってDC電圧を印加することで例えば約−300V程度に帯電される。   Each of the photosensitive drums 32Y to 32K is subjected to an image forming process for each color by a known electrophotographic method. First, as the photosensitive drums 32Y to 32K, for example, photosensitive drums using OPC photosensitive members are used, and these photosensitive drums 32Y to 32K are driven to rotate. The surfaces of the photosensitive drums 32Y to 32K are charged to about −300 V, for example, by applying a DC voltage by a charging roll.

表面電位を印加された感光体ドラム32Y〜32Kの表面には、露光装置としてのROS20によってイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色に対応したレーザ光31Y〜31Kが照射され、各色毎の入力画像情報に応じた静電潜像が形成される。ROS20でレーザ光31Y〜31Kが照射され、画像が書き込まれることにより、感光体ドラム32Y〜32K上の画像露光部の表面電位は画線部、すなわち露光した箇所が除電され静電潜像が形成される。   Laser light 31Y corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is applied to the surface of the photosensitive drums 32Y to 32K to which the surface potential is applied by the ROS 20 as an exposure device. ˜31K is irradiated, and an electrostatic latent image corresponding to input image information for each color is formed. By irradiating the laser beams 31Y to 31K with the ROS 20 and writing an image, the surface potential of the image exposure portion on the photosensitive drums 32Y to 32K is removed from the image line portion, that is, the exposed portion, and an electrostatic latent image is formed. Is done.

次いで、上記感光体ドラム32Y〜32Kの表面に形成されたイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色に対応した静電潜像は、対応する色の現像装置30Y〜30Kによって現像され、感光体ドラム32Y〜32K上にイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色のトナー像として現像され可視化される。   Next, the electrostatic latent images corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) formed on the surfaces of the photosensitive drums 32Y to 32K are developed with the corresponding colors. The images are developed by the devices 30Y to 30K, and are developed and visualized as toner images of yellow (Y), magenta (M), cyan (C), and black (K) on the photosensitive drums 32Y to 32K.

各現像装置30Y〜30Kには、それぞれ色の異なったイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)色のトナー及びキャリアからなる現像剤が充填されている。これらの現像装置30Y〜30Kは、図示しないトナー補給装置からトナーが補給され、補給されたトナーは各現像装置30Y〜30K内部のオーガーで充分にキャリアと攪拌されて摩擦帯電される。   Each of the developing devices 30Y to 30K is filled with a developer including yellow (Y), magenta (M), cyan (C), and black (K) toners and carriers of different colors. The developing devices 30Y to 30K are replenished with toner from a toner replenishing device (not shown), and the replenished toner is sufficiently agitated with the carrier by the augers inside the developing devices 30Y to 30K and frictionally charged.

キャリアと攪拌されて摩擦帯電され現像ロール33上に供給されたトナーは、マグネットロールの磁力によって、キャリアとトナーで構成された磁気ブラシを形成する。この磁気ブラシが感光体ドラム32Y〜32Kと接触している。現像ロール33に現像バイアス電圧を印加して、現像ロール33上のトナーを感光体ドラム32Y〜32K上に形成された静電潜像にトナーを転写することにより、イエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色のトナー画像が形成される。   The toner agitated with the carrier, frictionally charged, and supplied onto the developing roll 33 forms a magnetic brush composed of the carrier and the toner by the magnetic force of the magnet roll. This magnetic brush is in contact with the photosensitive drums 32Y to 32K. By applying a developing bias voltage to the developing roll 33 and transferring the toner on the developing roll 33 to the electrostatic latent images formed on the photosensitive drums 32Y to 32K, yellow (Y), magenta (M ), Cyan (C), and black (K) toner images are formed.

このトナー画像が図示しないトレイから給送され、アイドルロール24に懸架された搬送ベルト22上を搬送される用紙P上に転写されることで、用紙P上にカラー画像が形成される。すなわち、上記各感光体ドラム30Y〜30K上に形成されたイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)の各色のトナー像が用紙P上に位置合わせを行い、重ねてそれぞれ転写される。   This toner image is fed from a tray (not shown) and transferred onto the paper P conveyed on the conveyance belt 22 suspended on the idle roll 24, whereby a color image is formed on the paper P. That is, the yellow (Y), magenta (M), cyan (C), and black (K) toner images formed on the respective photoconductive drums 30Y to 30K are aligned on the paper P and overlapped. Are each transcribed.

用紙Pが吸着ロール24にて搬送ベルト22に吸着保持され、感光体ドラム32Yとのニップ位置まで搬送されると、搬送ベルト22を挟んで感光体ドラム32Yと対向する位置にある転写ロール(=BTR)28Yによって用紙Pは感光体ドラム32Yに向けて押圧され、同時に帯電したY色トナーは転写ロール28Yに印加された所定の転写電圧によって用紙Pに転写される。   When the sheet P is sucked and held on the transport belt 22 by the suction roll 24 and transported to the nip position with the photosensitive drum 32Y, the transfer roll (== the position facing the photosensitive drum 32Y across the transport belt 22). (BTR) 28Y presses the paper P toward the photosensitive drum 32Y, and the Y toner charged at the same time is transferred to the paper P by a predetermined transfer voltage applied to the transfer roll 28Y.

これを各色ごとに、すなわち用紙Pの搬送経路に沿ってM→C→Kと繰り返すことにより、用紙P上には、Y単色像上にシアン(C)、マゼンタ(M)、ブラック(K)色をそれぞれ重ねた四重色像として最終的なフルカラートナー像が形成されることになる。   By repeating this for each color, that is, M → C → K along the conveyance path of the paper P, on the paper P, cyan (C), magenta (M), and black (K) on the Y monochromatic image. A final full-color toner image is formed as a quadruple color image in which the colors are superimposed.

最後に、用紙P上に形成されたイエロー(Y)、マゼンタ(M)、シアン(C)、ブラック(K)のフルカラートナー像は定着器34によって熱溶着されることで用紙P上に定着され、一連の画像形成プロセスが完了する。   Finally, full-color toner images of yellow (Y), magenta (M), cyan (C), and black (K) formed on the paper P are fixed on the paper P by heat welding by the fixing unit 34. A series of image forming processes is completed.

ここで、本発明の実施形態においては、定着された用紙は、反転経路23を通過して吸着ロール22の手前まで戻り、後端から用紙Pを再度搬送ベルト22に吸着させることで、用紙Pの二面、すなわち画像形成が行われていない面にもトナー画像形成を行うことができる、所謂両面プリンタの構成となっている。   Here, in the embodiment of the present invention, the fixed sheet passes through the reversing path 23 and returns to the front of the suction roll 22, and the sheet P is again attracted to the transport belt 22 from the rear end. This is a so-called double-sided printer configuration in which toner image formation can be performed on the two surfaces, that is, the surface on which image formation is not performed.

<転写電圧制御>
図2には本発明に係る転写ロールに印加される転写電圧の制御方法が示されている。
<Transfer voltage control>
FIG. 2 shows a method for controlling the transfer voltage applied to the transfer roll according to the present invention.

図中、Vtr_simp(BTR)は一面印刷時に転写ロール28に印加する電圧であり、Vtr_dup(BTR)は二面印刷時に転写ロール28に印加する電圧であり、Vpg(BTR)は用紙間で転写ロール28に印加する電圧、同様に Vtr_simp(ESA)は一面印刷時に吸着ロール26に印加する電圧であり、Vtr_dup(ESA)は二面印刷時に転写ロール28に印加する電圧であり、Vpg(ESA)は用紙間で吸着ロール28に印加する電圧である。   In the figure, Vtr_simp (BTR) is a voltage applied to the transfer roll 28 during one-side printing, Vtr_dup (BTR) is a voltage applied to the transfer roll 28 during two-side printing, and Vpg (BTR) is a transfer roll between sheets. Similarly, Vtr_simp (ESA) is a voltage applied to the suction roll 26 during one-side printing, Vtr_dup (ESA) is a voltage applied to the transfer roll 28 during two-side printing, and Vpg (ESA) is This is a voltage applied to the suction roll 28 between sheets.

裏表両面の転写性を適正にするには、Vtr_simp(BTR)とVtr_dup(BTR)の値を変える必要がある。具体的には、一面(最初に画像形成を行う面)よりも二面(裏面)に画像形成を行う際の転写電圧を高めに設定する。また、Vpg(BTR)は用紙P内に印加する転写電圧よりも低くすることで、感光体ドラム32への転写履歴をなくすことができる。   In order to make the transferability of both the front and back sides appropriate, it is necessary to change the values of Vtr_simp (BTR) and Vtr_dup (BTR). Specifically, the transfer voltage at the time of image formation on two surfaces (back surface) is set higher than one surface (surface on which image formation is first performed). Further, by making Vpg (BTR) lower than the transfer voltage applied to the sheet P, the transfer history to the photosensitive drum 32 can be eliminated.

図2に示すように、まず前処理部40では転写ロール28Yにて疑似定電流処理を行いシステム抵抗を検知する。   As shown in FIG. 2, the pre-processing unit 40 first performs pseudo constant current processing with the transfer roll 28Y to detect system resistance.

すなわち、転写ロール28Yにまず所定の電圧V0を印加し、その際に流れる電流が一定の値に収まっているか否かを図示しない電流モニタにて検知する。このとき、多くの電流が流れすぎて感光体ドラム32Yに履歴を残さないように、最初は小さめの電圧から始めて段々と電圧をあげる方向で調整を行う。電流検知→電圧補正を繰り返し、予め設定されている狙いの電流値に収束させるまで処理を繰り返す。   That is, a predetermined voltage V0 is first applied to the transfer roll 28Y, and it is detected by a current monitor (not shown) whether or not the current flowing at that time falls within a certain value. At this time, the adjustment is performed in such a way that the voltage is gradually increased starting from a small voltage so that a large amount of current flows and no history is left in the photosensitive drum 32Y. The current detection → voltage correction is repeated, and the process is repeated until it converges to a preset target current value.

このとき、転写ロール28と吸着ロール26間で電流の行き来(電流漏れ)があると、正確に上記の処理すなわち転写ロール28の擬似定電流制御が行えなくなるので、吸着ロール26に印加する電圧の初期値 V0(ESA)は低めの電圧とする。   At this time, if there is a current flow (current leakage) between the transfer roll 28 and the suction roll 26, the above process, that is, the pseudo constant current control of the transfer roll 28 cannot be performed accurately. The initial value V0 (ESA) is a lower voltage.

電流が一定の値に収まっていれば、。擬似定電流制御は終了する。電流が少ない場合は印加電圧を上げて再度電流を検知し、電流が多い場合は印加電圧を下げて再度電流を検地する。この操作を、転写ロール28Yに流れる電流が一定の値に収まるまで続けることによって用紙間で転写ロール28に印加する電圧Vpg(BTR)が決定される。ここまでが前処理部40で行われる操作である。   If the current is within a certain value. The pseudo constant current control ends. When the current is small, the applied voltage is increased and the current is detected again. When the current is large, the applied voltage is decreased and the current is detected again. By continuing this operation until the current flowing through the transfer roll 28Y falls within a certain value, the voltage Vpg (BTR) to be applied to the transfer roll 28 between sheets is determined. This is the operation performed by the preprocessing unit 40.

次に用紙内電圧決定部42にて、予測制御や用紙Pの先端抵抗検知によりY色の転写バイアス電圧を決定する。   Next, the in-paper voltage determining unit 42 determines the Y-color transfer bias voltage by predictive control or detection of the leading edge resistance of the paper P.

予測制御とは、前処理部で決定されたVpg(BTR)をもとにY色転写電圧を印加してしまう制御方法で、例えばVtr_simp(BTR)= Vpg(BTR)+α、Vtr_dup(BTR)= Vpg(BTR)+β (α、βは定数、α<β)などと定義する。先端抵抗検地とは、用紙先端近傍の極短い範囲の用紙先端が転写ロールにニップしている時とニップしていない時の電流差ΔIを利用してY色転写電圧を決定する制御である。例えばVtr_simp(BTR)= f(ΔI)*Vpg(BTR) (f(ΔI)は△Iの関数)と定義する。   Predictive control is a control method in which a Y-color transfer voltage is applied based on Vpg (BTR) determined by the preprocessing unit. For example, Vtr_simp (BTR) = Vpg (BTR) + α, Vtr_dup (BTR) = Vpg (BTR) + β (α and β are constants, α <β). The leading edge resistance detection is control for determining the Y color transfer voltage by using the current difference ΔI between when the leading end of the sheet in the vicinity of the leading end of the sheet is nipped with the transfer roll and when it is not nipped. For example, Vtr_simp (BTR) = f (ΔI) * Vpg (BTR) (f (ΔI) is a function of ΔI).

用紙Pの先端が転写ロールにニップしてから前述の仮決め電圧を転写ロール28Yに印加し、流れる電流を電流モニタにて検知することで、Y色転写時の電流値を検出することができる。   After the leading edge of the paper P is nipped to the transfer roll, the above-mentioned provisional voltage is applied to the transfer roll 28Y, and the current value detected by the current monitor can be detected by the current monitor. .

このとき転写ロール28Yに流れる電流が一定範囲の値に収まっていれば、用紙Pを含めた電気抵抗もまた所定の値に収まっているので、この時点で印加した電圧をY色トナーの転写電圧と決定する。   At this time, if the current flowing through the transfer roll 28Y falls within a certain range of values, the electrical resistance including the paper P also falls within a predetermined value. Therefore, the voltage applied at this time is set to the transfer voltage of the Y toner. And decide.

電流が一定範囲の値に収まっていない場合、例えば電流が少ない場合は用紙Pを含めた電気抵抗が想定以上に大きいためであるので、印加電圧を上げて再度電流を検知する。この操作を、電流が一定範囲の値に収まるまで続けることによってY色トナーの転写電圧が決定される。決定したY色トナーの転写電圧を基に、各色バイアス決定部44にてY色に続くMCK色のトナー画像についての転写電圧をも決定するようにすれば、任意の用紙Pについて適正な転写電圧を各色で印加することができる。例えば、MCKの転写電圧は、Y色転写電圧に対して下流にいくほど徐々に電圧を上げていくように設定する。   If the current does not fall within a certain range, for example, if the current is small, the electrical resistance including the paper P is larger than expected, so the applied voltage is increased and the current is detected again. By continuing this operation until the current falls within a certain range of values, the transfer voltage of the Y color toner is determined. If the transfer voltage for the MCK color toner image subsequent to the Y color is also determined by each color bias determination unit 44 based on the determined transfer voltage for the Y color toner, an appropriate transfer voltage for any paper P can be obtained. Can be applied in each color. For example, the MCK transfer voltage is set so that the voltage gradually increases as it goes downstream with respect to the Y color transfer voltage.

前述のように、既にY色で転写処理が開始されている状態で、一枚の用紙P内で転写電圧の調整を行う所謂 On paper feedback を行った場合、例えばY色画像の形成時に一枚の用紙P内で電圧調整を行うと用紙P内で転写条件が変動するので、Y色トナーの転写量が変化してY色画像の濃度むらが発生する。これはYMCK4色の、どの転写段階で電圧調整を行ったとしても、一枚の用紙Pの中で転写電圧調整を行う以上は当該色画像の濃度むら発生は避けることはできない。   As described above, when the so-called On paper feedback is performed in which the transfer voltage is adjusted in one sheet P in the state where the transfer process has already been started in the Y color, for example, one sheet is formed when a Y color image is formed. When the voltage adjustment is performed within the paper P, the transfer condition varies within the paper P, so that the transfer amount of the Y color toner changes and the density unevenness of the Y color image occurs. Even if the voltage adjustment is performed at any transfer stage of the four colors of YMCK, the density unevenness of the color image cannot be avoided as long as the transfer voltage adjustment is performed on one sheet of paper P.

しかし転写されたトナー画像を人間が目視にて観察した場合、MCKの各色に比較してY色における色むらは最も目立たない。すなわち、色むらの発生は避けることはできないが、最も目立たないY色において色むらを発生させ、他の3色MCKでの色むら発生を避けることができる。   However, when the transferred toner image is visually observed by a human, the color unevenness in the Y color is the least noticeable compared to each color of MCK. That is, the occurrence of color unevenness cannot be avoided, but the color unevenness is generated in the least noticeable Y color, and the occurrence of color unevenness in the other three colors MCK can be avoided.

これにより本発明では、用紙Pを感光体ドラム32Yと転写ロール28Yとでニップした状態で、仮決め電圧を転写ロール28Yに印加し、流れる電流を電流モニタにて検知することで、Y色トナー転写時の転写電圧を調整/決定する。   Accordingly, in the present invention, the Y-color toner is detected by applying the provisional voltage to the transfer roll 28Y while the paper P is nipped between the photosensitive drum 32Y and the transfer roll 28Y and detecting the flowing current with a current monitor. Adjust / determine the transfer voltage during transfer.

すなわち用紙PがM色トナー画像の転写位置に到達する間に転写電圧の調整/決定が行われるので、Y色に続くMCK色のトナー画像転写時には転写電圧の調整が行われる必要はなく、そのためMCK色のトナー画像内での画像むらの発生を防ぐことができる。   That is, since the transfer voltage is adjusted / determined while the paper P reaches the transfer position of the M color toner image, it is not necessary to adjust the transfer voltage when transferring the MCK color toner image following the Y color. It is possible to prevent the occurrence of image unevenness in the MCK color toner image.

本発明において転写ロール28は4本の抵抗値ばらつきを抑えたいため、抵抗値ばらつきが少ないイオン導電性の転写ロールを用いることが望ましい。また、装置内外の温湿度などの環境条件や、処理枚数などの条件の影響を加味するために温湿度センサや処理カウンタなどの検知手段で得られた数値をファクタとして加えてもよい
なお、本実施形態では吸着ロール26に印加される電圧は、メディア(用紙P)の種類(厚紙、OHPなど)や環境(温湿度、処理枚数など)を考慮に入れ、用紙Pの吸着力やプレ帯電性(OHPのような高抵抗用紙を転写前にプレ帯電することで転写性を向上させる)が最適になるような値を出力する。
In the present invention, the transfer roll 28 is desirably an ion conductive transfer roll having a small resistance value variation in order to suppress variations in the resistance value of the four rollers. In addition, in order to take into account the influence of environmental conditions such as temperature and humidity inside and outside the device and conditions such as the number of processed sheets, numerical values obtained by detection means such as temperature and humidity sensors and processing counters may be added as factors. In the embodiment, the voltage applied to the suction roll 26 takes into consideration the type of media (paper P) (thick paper, OHP, etc.) and the environment (temperature, humidity, number of processed sheets, etc.), and the suction power and pre-charging property of the paper P. A value is output that optimizes (highly resistive paper such as OHP is precharged before transfer to improve transferability).

また本発明では上記のような転写電圧制御方法としたことで、定電流回路を必要としないので簡素な構成の画像形成装置とすることができる。   Further, according to the present invention, since the transfer voltage control method is used as described above, a constant current circuit is not required, so that an image forming apparatus having a simple configuration can be obtained.

<黒むら防止>
通常、K(墨)色のトナー画像を形成する現像装置30Kは、用紙Pの搬送方向最も下流に設けられる。最下流に配置すれば、未定着像が他のドラムと接触することがなく、他のドラムへのトナー戻りを回避することができるためである。
<Black unevenness prevention>
Usually, the developing device 30K that forms a K (black) toner image is provided on the most downstream side in the conveyance direction of the paper P. This is because if it is arranged on the most downstream side, the unfixed image does not come into contact with other drums, and toner return to the other drums can be avoided.

このとき、前述のように例えば搬送方向上流側にあるY色の現像装置30において、用紙Pを感光体ドラム32Yと転写ロール28Yとでニップした状態で、仮決め電圧を転写ロール28Yに印加し、流れる電流を転写ロール28Yにて検知することで、Y色転写時の転写電圧を調整/決定しておけば、少なくともK色トナー画像の転写中に転写電圧を調整する必要はない。   At this time, for example, in the Y-color developing device 30 on the upstream side in the transport direction as described above, a temporarily determined voltage is applied to the transfer roll 28Y while the paper P is nipped between the photosensitive drum 32Y and the transfer roll 28Y. If the transfer voltage at the Y color transfer is adjusted / determined by detecting the flowing current with the transfer roll 28Y, it is not necessary to adjust the transfer voltage at least during the transfer of the K color toner image.

すなわち、K色の現像装置30Kよりも搬送方向上流側に設けられた、YMC何れかの色の現像装置において(上流側であればY色に限定する必要はない)転写電圧を調整/決定することにより、K色の現像装置30Kにおいて転写電圧の調整を行う必要がないので、K色のトナー画像内における色むらの発生を防ぐことができる。つまりK色の現像装置30Kにおける転写電圧は、用紙Pが搬送された時点で既に決定されているので調整の必要はなく、転写電圧変動によるK色の濃度むら発生を防ぐことができる。   That is, the transfer voltage is adjusted / determined in any of the YMC developing devices provided upstream of the K-color developing device 30K in the transport direction (they need not be limited to the Y color as long as they are upstream). As a result, there is no need to adjust the transfer voltage in the K color developing device 30K, so that it is possible to prevent color unevenness in the K color toner image. That is, the transfer voltage in the K-color developing device 30K has already been determined when the paper P is transported, so there is no need for adjustment, and unevenness in the density of K color due to variations in the transfer voltage can be prevented.

これは4色フルカラーのトナー画像形成時のみならず、通常のオフィス用途などで最も多用されるK色の単色画像形成時において画像むらの発生自体を防ぐことができるので他の色における濃度むら発生防止よりも更に効果は大きい。   This can prevent image unevenness itself when forming a single color image of K color, which is most frequently used in normal office applications, as well as when forming a four-color full-color toner image. More effective than prevention.

<その他>
以上、本発明の実施例について記述したが、本発明は上記の実施例に何ら限定されるものではなく、本発明の要旨を逸脱しない範囲において種々なる態様で実施し得ることは言うまでもない。
<Others>
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to said Example at all, and can implement in a various aspect in the range which does not deviate from the summary of this invention.

すなわち本実施形態では4色フルカラーレーザビームプリンタを例に挙げたが、これに限定せず例えば3色以下または5色以上のプリンタでもよいことは言うまでもない。   That is, in this embodiment, a four-color full-color laser beam printer has been described as an example. However, the present invention is not limited to this, and it is needless to say that a printer having three colors or less or five colors or more may be used.

本発明に係る画像形成装置を示す断面図である。1 is a cross-sectional view illustrating an image forming apparatus according to the present invention. 本発明に係る画像形成装置の転写電圧決定までの手順を示す図である。It is a figure which shows the procedure until transfer voltage determination of the image forming apparatus which concerns on this invention.

符号の説明Explanation of symbols

10 画像形成装置
20 ROS
24 アイドルロール
26 吸着ロール
28 転写ロール
30 現像装置
32 感光体ドラム
34 定着器
10 image forming apparatus 20 ROS
24 Idle Roll 26 Adsorption Roll 28 Transfer Roll 30 Developing Device 32 Photosensitive Drum 34 Fixing Device

Claims (6)

感光体上に形成されたトナー画像を、転写電圧を印加した転写手段で用紙上に転写するトナー画像形成装置を用紙搬送方向に複数備えたタンデム方式のカラー画像形成装置であって、
前記転写手段に印加する転写電圧をそれぞれ独立して制御する制御手段と、
Y色トナー画像形成装置の前記転写手段に設けられ該転写手段に対する電圧印加時に電流を検知する検知手段とを備え、
前記Y色トナー画像形成装置は用紙搬送方向上流端に設けられ、
前記制御手段は前記用紙が前記Y色転写位置に到着する前に前記Y色トナー画像形成装置にて前記転写手段に所定の電圧を印加し、前記検知手段にて検知された前記転写手段に流れる電流が、一定範囲の値に収まるようにY色トナー転写電圧を仮決めしたのち、
前記用紙の先端が前記Y色トナー画像形成装置から次のトナー画像形成装置に搬送される前に前記転写手段に前記仮決めしたY色電圧を印加し、前記転写手段に流れる電流が一定範囲の値に収まるように前記Y色トナー転写電圧の補正を行うことを特徴とする画像形成装置。
A tandem type color image forming apparatus provided with a plurality of toner image forming apparatuses in a sheet conveying direction for transferring a toner image formed on a photoreceptor onto a sheet by a transfer unit to which a transfer voltage is applied,
Control means for independently controlling the transfer voltage applied to the transfer means;
A detection unit provided in the transfer unit of the Y color toner image forming apparatus and detecting a current when a voltage is applied to the transfer unit;
The Y color toner image forming apparatus is provided at the upstream end in the paper conveyance direction,
The control unit applies a predetermined voltage to the transfer unit in the Y-color toner image forming apparatus before the sheet reaches the Y-color transfer position, and flows to the transfer unit detected by the detection unit. After tentatively determining the Y toner transfer voltage so that the current falls within a certain range ,
Before the leading edge of the sheet is conveyed from the Y color toner image forming apparatus to the next toner image forming apparatus, the provisionally determined Y color voltage is applied to the transfer means, and the current flowing through the transfer means is within a certain range. An image forming apparatus that corrects the Y-color toner transfer voltage so as to fall within the range .
前記用紙の先端が前記Y色トナー画像形成装置の転写手段にニップされ、前記仮決めされた前記Y色トナー転写電圧が前記転写手段に印加されることで前記検知手段にて検知される電流が、一定範囲の値に収まるように前記Y色トナー転写電圧の補正量を決定することを特徴とする請求項1に記載の画像形成装置。 The leading edge of the sheet is nipped by the transfer unit of the Y color toner image forming apparatus, and the current detected by the detection unit is applied by applying the temporarily determined Y color toner transfer voltage to the transfer unit. The image forming apparatus according to claim 1 , wherein the correction amount of the Y color toner transfer voltage is determined so as to fall within a certain range of values . 前記補正されたY色トナー転写電圧に基づいて用紙搬送方向下流の転写電圧を決定することを特徴とする請求項2に記載の画像形成装置。   The image forming apparatus according to claim 2, wherein a transfer voltage downstream in the sheet conveyance direction is determined based on the corrected Y color toner transfer voltage. 感光体上に形成されたトナー画像を、転写電圧を印加した転写手段で用紙上に転写するトナー画像形成装置を用紙搬送方向に複数備えたタンデム方式のカラー画像形成装置であって、
前記転写手段に印加する転写電圧はそれぞれ独立して制御する制御手段と、
K色トナー画像形成装置よりも用紙搬送方向上流に設けられた第1のトナー画像形成装置の転写手段に設けられ該転写手段に対する電圧印加時に電流を検知する検知手段とを備え、
前記制御手段は前記用紙が前記第1のトナー画像形成装置に搬送される前に前記第1のトナー画像形成装置にて前記転写手段に所定の電圧を印加し、前記検知手段にて検知された前記転写手段に流れる電流が、一定範囲の値に収まるように第1のトナー転写電圧を仮決めしたのち、
前記用紙の先端が前記第1のトナー画像形成装置から次のトナー画像形成装置に搬送される前に前記転写手段に前記仮決めした第1のトナー転写電圧を印加し、前記転写手段に流れる電流が一定範囲の値に収まるように前記第1のトナー転写電圧の補正を行うことを特徴とする画像形成装置。
A tandem type color image forming apparatus provided with a plurality of toner image forming apparatuses in a sheet conveying direction for transferring a toner image formed on a photoreceptor onto a sheet by a transfer unit to which a transfer voltage is applied,
Control means for independently controlling the transfer voltages applied to the transfer means;
A detection unit provided in a transfer unit of the first toner image forming apparatus provided upstream of the K-color toner image forming apparatus in the paper conveyance direction and detecting a current when a voltage is applied to the transfer unit;
The control means applies a predetermined voltage to the transfer means in the first toner image forming apparatus before the paper is conveyed to the first toner image forming apparatus, and is detected by the detection means. After tentatively determining the first toner transfer voltage so that the current flowing through the transfer means falls within a certain range of values ,
Before the leading edge of the paper is transported from the first toner image forming apparatus to the next toner image forming apparatus, the temporarily transferred first toner transfer voltage is applied to the transfer means, and the current flowing through the transfer means The image forming apparatus is characterized in that the first toner transfer voltage is corrected so as to fall within a certain range of values .
前記用紙の先端が前記第1のトナー画像形成装置の転写手段にニップされ、前記仮決めされた転写電圧が前記転写手段に印加されることで前記検知手段にて検知される電流が、一定範囲の値に収まるように前記前記第1のトナー転写電圧の補正量を決定することを特徴とする請求項4に記載の画像形成装置。 A current detected by the detection unit is fixed within a certain range when the leading end of the sheet is nipped by the transfer unit of the first toner image forming apparatus and the temporarily determined transfer voltage is applied to the transfer unit. 5. The image forming apparatus according to claim 4, wherein the correction amount of the first toner transfer voltage is determined so as to fall within a value of 5 . 前記補正された第1のトナー転写電圧に基づいてK色トナー画像形成装置の転写電圧を決定することを特徴とする請求項5に記載の画像形成装置。   6. The image forming apparatus according to claim 5, wherein a transfer voltage of the K-color toner image forming apparatus is determined based on the corrected first toner transfer voltage.
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