JP6684463B2

JP6684463B2 - Transfer device and image forming device

Info

Publication number: JP6684463B2
Application number: JP2016008762A
Authority: JP
Inventors: 春樹永田; 敦司永田; 長谷川　亮; 亮長谷川; 賢二本城
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2016-01-20
Filing date: 2016-01-20
Publication date: 2020-04-22
Anticipated expiration: 2036-01-20
Also published as: JP2017129723A

Description

本発明は、転写装置及び画像形成装置に関するものである。 The present invention relates to a transfer device and an image forming device.

従来、画像形成装置の転写装置として、像担持体と転写部材とで形成した転写部に記録媒体を挟み込み、像担持体上から画像を転写するものが知られている。 2. Description of the Related Art Conventionally, as a transfer device of an image forming apparatus, there is known a transfer device in which a recording medium is sandwiched between transfer portions formed by an image carrier and a transfer member and an image is transferred from the image carrier.

特許文献１に記載の画像形成装置には、係る転写装置であって、感光体から中間転写ベルトに一次転写されトナー像を、記録媒体である用紙に二次転写する二次転写装置が設けられている。この二次転写装置は、中間転写ベルトおもて面に接する二次転写ローラと、二次転写ローラと対向し中間転写ベルト裏面に接する二次転写対向ローラとを有する。また、前記二次転写装置は、二次転写ローラの中間転写ベルトに対する加圧力を変更可能な加圧機構を備え、表面粗さが大きい記録材への画像形成時には二次転写部の圧力を高め、表面粗さが小さい記録材への画像形成時には二次転写部の圧力を低くする。これにより、幅広い種類の記録材について、それぞれ適した二次転写圧で二次転写して良好な転写効率を得ることとしている。 The image forming apparatus described in Patent Document 1 is provided with a secondary transfer device that is such a transfer device that secondarily transfers a toner image that is primarily transferred from a photoconductor to an intermediate transfer belt onto a sheet that is a recording medium. ing. This secondary transfer device has a secondary transfer roller that contacts the front surface of the intermediate transfer belt, and a secondary transfer counter roller that faces the secondary transfer roller and contacts the back surface of the intermediate transfer belt. Further, the secondary transfer device is provided with a pressure mechanism capable of changing the pressure applied to the intermediate transfer belt by the secondary transfer roller, and increases the pressure of the secondary transfer portion when forming an image on a recording material having a large surface roughness. When the image is formed on the recording material having a small surface roughness, the pressure at the secondary transfer portion is lowered. As a result, a wide variety of recording materials are subjected to secondary transfer at suitable secondary transfer pressures to obtain good transfer efficiency.

しかしながら、二次転写圧を変化させると、中間転写ベルト上から用紙上に転写した画像の用紙搬送方向における長さが、二次転写圧ごとで異なる画像倍率変動が生じてしまう。 However, if the secondary transfer pressure is changed, the length of the image transferred from the intermediate transfer belt onto the sheet in the sheet conveying direction varies depending on the secondary transfer pressure, and the image magnification varies.

上記課題を解決するために、本発明は、表面移動可能な像担持体と、前記像担持体と当接し該像担持体から記録媒体に画像を転写する転写部を形成する回転可能な転写部材と、前記転写部材を回転駆動させるための転写部材駆動手段と、前記転写部における転写圧を変更する転写圧変更手段とを備えた転写装置において、前記転写圧の大きさに応じて前記転写部材の回転速度を変更するように前記転写部材駆動手段を制御する転写部材駆動制御手段を有し、前記転写圧変更手段により、所定の転写圧よりも小さい第一転写圧から該所定の転写圧以下であって該第一転写圧よりも大きい第二転写圧へと、転写圧を変更した際に、前記第一転写圧のときよりも前記転写部材の回転速度を速くすることを特徴とする。 In order to solve the above problems, the present invention provides a rotatable transfer member that forms a surface-movable image carrier and a transfer unit that is in contact with the image carrier and transfers an image from the image carrier to a recording medium. A transfer member driving unit for rotating the transfer member, and a transfer pressure changing unit for changing the transfer pressure in the transfer unit. the have a transfer member driving control means for controlling said transfer member drive means so as to change the rotational speed, by the transfer pressure changing means, said predetermined transfer pressure or under a small first transfer pressure than the predetermined transfer pressure In addition, when the transfer pressure is changed to the second transfer pressure larger than the first transfer pressure, the rotation speed of the transfer member is made higher than that at the first transfer pressure .

以上、本発明によれば、転写圧を変化させたときの画像倍率変動を低減させることができるという優れた効果がある。 As described above, according to the present invention, there is an excellent effect that it is possible to reduce the fluctuation of the image magnification when the transfer pressure is changed.

二次転写圧の変化に応じて二次転ローラ駆動モータの回転速度を変更することによる、二次転写圧変化時の画像倍率調整制御について示したフローチャート。6 is a flowchart showing image magnification adjustment control when the secondary transfer pressure changes by changing the rotation speed of the secondary transfer roller drive motor according to the change in the secondary transfer pressure. 実施形態に係るプリンタの概略構成図。1 is a schematic configuration diagram of a printer according to an embodiment. 二次転写部における二次転写圧を変更させる二次転写圧変更機構の説明図。Explanatory drawing of the secondary transfer pressure change mechanism which changes the secondary transfer pressure in a secondary transfer part. 二次転写ローラによって用紙が搬送される様子について説明した図。FIG. 6 is a diagram illustrating a state where a sheet is conveyed by a secondary transfer roller. 二次転写圧を変化させた場合における画像倍率変動の実験結果を示すグラフ。6 is a graph showing the experimental results of image magnification variation when the secondary transfer pressure is changed. 二次転写ローラが圧縮された状態を示す図。FIG. 6 is a diagram showing a state in which the secondary transfer roller is compressed. 二次転写ローラに歪が発生した状態を示す図。FIG. 6 is a diagram showing a state in which distortion has occurred in the secondary transfer roller. 用紙銘柄×××の設定値を保存する用紙ＤＢを本体メモリに作成する場合の説明図。Explanatory drawing at the time of creating the paper DB which stores the setting value of paper brand XXX in the main body memory. 通紙条件に応じて、用紙設定パラメータＮｏ．１００転写圧可変設定を任意の値に設定する場合の説明図。Depending on the paper passing conditions, the paper setting parameter No. Explanatory drawing when setting 100 transfer pressure variable setting to an arbitrary value. 印刷する用紙をセットする用紙収容部に用紙ＤＢ００２を設定する場合の説明図。Explanatory drawing in the case of setting paper DB002 in the paper storage part which sets the paper to print. 用紙収容部に設定されている用紙ＤＢを参照する場合の説明図。Explanatory drawing when referring to the paper DB set in the paper storage unit. 用紙ＤＢ００２の中の用紙設定パラメータＮｏ．１００の設定値を参照する場合の説明図。Paper setting parameter No. in paper DB002. Explanatory drawing at the time of referring to the set value of 100.

以下、本発明を適用した画像形成装置として、電子写真方式のプリンタ（以下、単にプリンタという）の一実施形態について説明する。まず、本実施形態に係るプリンタの基本的な構成について説明する。 An embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described below as an image forming apparatus to which the present invention is applied. First, the basic configuration of the printer according to this embodiment will be described.

図２は、本実施形態に係るプリンタ１００の概略構成図である。プリンタ１００は、記録媒体である用紙Ｐに転写するトナー像を担持するトナー像担持体が中間転写体としての中間転写ベルト７となっているカラー画像形成装置である。プリンタ１００は、中間転写ベルト７の走行方向に沿って四個の画像形成ユニット１Ｙ、Ｍ、Ｃ、Ｋが配置された四連タンデム型のカラー画像形成装置である。図中及び説明において、各符号の添え字Ｙ、Ｃ、Ｍ、Ｋは、それぞれ、イエロー用、シアン用、マゼンタ用、ブラック用の部材であることを示すものである。四つの画像形成ユニット１Ｙ、Ｍ、Ｃ、Ｋの構成は使用するトナーの色が異なる点以外はほぼ同様であるので、以下の説明では色分け用の添え字（Ｙ、Ｃ、Ｍ、Ｋ）を適宜省略して説明する。なお、プリンタ１００内には、プリンタ１００の種々の制御を司る制御部３０が設けられており、制御部３０は演算手段であるＣＰＵ（ＣｅｎｔｒａｌＰｒｏｃｅｓｓｉｎｇＵｎｉｔ）３１や、記憶手段であるメモリ３２などを有している FIG. 2 is a schematic configuration diagram of the printer 100 according to the present embodiment. The printer 100 is a color image forming apparatus in which a toner image carrier that carries a toner image to be transferred onto a sheet P that is a recording medium is an intermediate transfer belt 7 that serves as an intermediate transfer member. The printer 100 is a four-series tandem type color image forming apparatus in which four image forming units 1Y, M, C and K are arranged along the running direction of the intermediate transfer belt 7. In the drawings and in the description, the subscripts Y, C, M, and K of the reference numerals indicate members for yellow, cyan, magenta, and black, respectively. The configuration of the four image forming units 1Y, M, C, and K is almost the same except that the colors of the toners used are different. Therefore, in the following description, the subscripts (Y, C, M, and K) for color classification are used. The description will be omitted as appropriate. A control unit 30 that controls various controls of the printer 100 is provided in the printer 100. The control unit 30 includes a CPU (Central Processing Unit) 31 that is a calculation unit, a memory 32 that is a storage unit, and the like. Have

画像形成ユニット１は、像担持体としての感光体２を備え、この感光体２の周りには、感光体クリーニングブレード６、帯電器３、露光装置４、現像器５等が配置されている。フルカラー画像形成時は、イエロー用画像形成ユニット１Ｙ、マゼンタ用画像形成ユニット１Ｍ、シアン用画像形成ユニット１Ｃ、ブラック用画像形成ユニット１Ｋの順で可視像を形成する。そして、各色の可視像が中間転写ベルト７に順次重ねて転写されることでフルカラー画像が形成される。中間転写ベルト７は、駆動ローラ８、テンションローラ９及び二次転写対向ローラ１６等の複数の張架ローラにより張架されており、中間転写駆動モータ４０によって駆動ローラ８が回転駆動することによって図２中の矢印で示すように時計回り方向に表面移動する。プリンタ１００では、中間転写ベルト７のプロセス速度は、４１５［ｍｍ／ｓｅｃ］に調整されている。中間転写ベルト７の内側には、従動ローラである四つの一次転写ローラ１０Ｙ、Ｍ、Ｃ、Ｋ及びブラシ対向ローラ１４を備えている。中間転写ベルト７の幅方向（図２中の紙面手間奥方向）の両端には中間転写ベルトユニット側板を備え、中間転写ベルト７の内側の各ローラは、中間転写ベルトユニット側板によって各軸受やアームを介して中間転写ベルト７の両側より支持されている。 The image forming unit 1 includes a photoconductor 2 as an image carrier, and a photoconductor cleaning blade 6, a charging device 3, an exposure device 4, a developing device 5 and the like are arranged around the photoconductor 2. When forming a full-color image, a visible image is formed in the order of the yellow image forming unit 1Y, the magenta image forming unit 1M, the cyan image forming unit 1C, and the black image forming unit 1K. Then, the visible images of the respective colors are sequentially transferred onto the intermediate transfer belt 7 so that a full-color image is formed. The intermediate transfer belt 7 is stretched around a plurality of tension rollers such as a drive roller 8, a tension roller 9 and a secondary transfer counter roller 16, and is driven by the intermediate transfer drive motor 40 to rotate the drive roller 8. The surface moves clockwise as indicated by the arrow in 2. In the printer 100, the process speed of the intermediate transfer belt 7 is adjusted to 415 [mm / sec]. Inside the intermediate transfer belt 7, four primary transfer rollers 10Y, M, C, K which are driven rollers and a brush facing roller 14 are provided. Intermediate transfer belt unit side plates are provided at both ends in the width direction of the intermediate transfer belt 7 (in the depth direction of the paper surface in FIG. 2). It is supported from both sides of the intermediate transfer belt 7 via.

一次転写ローラ１０は感光体２と中間転写ベルト７との接触部に配置されており、一次転写ローラ１０には所定の転写バイアスが印加される。本実施形態では＋１８００［Ｖ］の転写バイアスが印加されるように設定されている。ウレタンゴムよりなるベルトクリーニングブレード１１は中間転写ベルト７に押し当てられ、トナーを堰き止めて清掃する構成となっている。プリンタ１００では、クリーニングし易くするために、固形潤滑剤１２を潤滑剤塗布部材であるブラシローラ１３によって削り、中間転写ベルト７の表面に潤滑剤を塗布する。 The primary transfer roller 10 is arranged at a contact portion between the photoconductor 2 and the intermediate transfer belt 7, and a predetermined transfer bias is applied to the primary transfer roller 10. In the present embodiment, the transfer bias of +1800 [V] is set to be applied. The belt cleaning blade 11 made of urethane rubber is pressed against the intermediate transfer belt 7 to block and clean the toner. In the printer 100, in order to facilitate cleaning, the solid lubricant 12 is scraped by the brush roller 13 which is a lubricant applying member, and the lubricant is applied to the surface of the intermediate transfer belt 7.

四つの一次転写ローラ１０Ｙ、Ｍ、Ｃ、Ｋのうちカラー用の三つの一次転写ローラ１０Ｙ、Ｍ、Ｃは、一次転写接離機構で中間転写ベルト７と接離可能となっている。ブラックトナーのみで画像形成を行うモノクロモード時には、ブラック用の一次転写ローラ１０Ｋは中間転写ベルト７と当接した状態となっている。そして、カラー用の三つの一次転写ローラ１０Ｙ、Ｍ、Ｃは、中間転写ベルト７から離間した状態となっている。フルカラーモード時には、ブラック用の一次転写ローラ１０Ｋと、カラー用の三つの一次転写ローラ１０Ｙ、Ｍ、Ｃとが、図２で示すように中間転写ベルト７に当接する。そして、中間転写ベルト７を押し伸ばした状態でそれぞれの感光体２Ｙ、Ｍ、Ｃ、Ｋに中間転写ベルト７が当接して巻き付くようになっている。 Of the four primary transfer rollers 10Y, M, C, K, three primary transfer rollers 10Y, M, C for color can be brought into contact with and separated from the intermediate transfer belt 7 by a primary transfer contact / separation mechanism. In the monochrome mode in which an image is formed only with black toner, the black primary transfer roller 10K is in contact with the intermediate transfer belt 7. The three primary transfer rollers 10Y, M, C for color are separated from the intermediate transfer belt 7. In the full color mode, the primary transfer roller 10K for black and the three primary transfer rollers 10Y, M, C for color contact the intermediate transfer belt 7 as shown in FIG. Then, the intermediate transfer belt 7 is in contact with and wound around each of the photoconductors 2Y, M, C, and K in a state where the intermediate transfer belt 7 is extended.

図２に示すように、中間転写ベルト７の下方には、二次転写対向ローラ１６と中間転写ベルト７を挟んで対向する二次転写ローラ１５を備えた二次転写ユニット３００を備える。中間転写ベルト７を挟んで二次転写対向ローラ１６と二次転写ローラ１５とが対向する二次転写部では、二次転写ローラ１５が電気的に接地され、二次転写対向ローラ１６に二次転写バイアス電源によって二次転写バイアスが印加される。これにより、中間転写ベルト７上のトナーを二次転写対向ローラ１６側から二次転写ローラ１５側に向けて静電移動させる二次転写電界が形成される。 As shown in FIG. 2, below the intermediate transfer belt 7, a secondary transfer unit 300 including a secondary transfer counter roller 16 and a secondary transfer roller 15 that faces the intermediate transfer belt 7 with the intermediate transfer belt 7 interposed therebetween is provided. In the secondary transfer portion where the secondary transfer counter roller 16 and the secondary transfer roller 15 face each other with the intermediate transfer belt 7 sandwiched therebetween, the secondary transfer roller 15 is electrically grounded, and the secondary transfer counter roller 16 is subjected to the secondary transfer. A secondary transfer bias is applied by the transfer bias power source. As a result, a secondary transfer electric field is formed that electrostatically moves the toner on the intermediate transfer belt 7 from the secondary transfer counter roller 16 side toward the secondary transfer roller 15 side.

二次転写ユニット３００の下方には、用紙Ｐを収容する用紙収容部１２１（本体トレイ）を備える。なお、用紙収容部１２１（本体トレイ）を複数設けても良い。用紙収容部１２１の上部には、給紙ピックアップローラ１２２が設けられており、この給紙ピックアップローラ１２２は、用紙収容部１２１に収容されている用紙Ｐのうち最上段にある用紙Ｐを一枚ずつ取り出し、給紙搬送路１２３に送り出す。このように、給紙ピックアップローラ１２２によって給紙搬送路１２３に送り出された用紙Ｐは、搬送ローラ対１２５によって二次転写部に向けて搬送されるが、この途中のレジストローラ対１２４で用紙先端を挟み込んで、用紙Ｐの搬送が一旦停止される。レジストローラ対１２４は、中間転写ベルト７上のトナー像が形成されている部分が、二次転写部に到達されるタイミングで、用紙Ｐを二次転写部に向けて送り出すものである。レジストローラ対１２４によって送り出された用紙Ｐは、二次転写部で中間転写ベルト７上のトナー像が転写され、定着装置２００に向けて搬送される。そして、定着装置２００において熱や圧力によってトナー像が定着された用紙Ｐは、排紙トレイ１５０に排紙される。 Below the secondary transfer unit 300, a paper storage unit 121 (main body tray) that stores the paper P is provided. A plurality of paper storage units 121 (main body trays) may be provided. A paper feed pickup roller 122 is provided above the paper storage unit 121. The paper feed pickup roller 122 is one of the uppermost sheets of the paper P stored in the paper storage unit 121. They are taken out one by one and sent out to the paper feeding and conveying path 123. As described above, the sheet P sent to the sheet feeding / conveying path 123 by the sheet feeding pickup roller 122 is conveyed toward the secondary transfer portion by the pair of conveying rollers 125. The sheet P is sandwiched and the conveyance of the sheet P is temporarily stopped. The registration roller pair 124 feeds the paper P toward the secondary transfer portion at the timing when the portion of the intermediate transfer belt 7 on which the toner image is formed reaches the secondary transfer portion. The toner image on the intermediate transfer belt 7 is transferred at the secondary transfer portion of the paper P sent out by the registration roller pair 124, and is conveyed toward the fixing device 200. Then, the paper P on which the toner image has been fixed by heat and pressure in the fixing device 200 is discharged to the paper discharge tray 150.

このような中間転写ユニットを用いた転写装置において、二次転写の際には、二次転写部Ｎに用紙Ｐが進入して、中間転写ベルト７上のトナー像を用紙Ｐ上に転写をする。その際に、用紙Ｐの表面線速と中間転写ベルト７の表面線速が等しければ、用紙Ｐの単位時間あたりに進む距離と中間転写ベルト７の単位時間あたりに進む距離が等しくなる。そのため、中間転写ベルト７上のトナー像の大きさと等しい大きさで用紙Ｐに二次転写されることになる。しかし、用紙Ｐの表面線速が中間転写ベルト７の表面線速よりも速い場合、用紙Ｐの単位時間あたりに進む距離が中間転写ベルト７の単位時間あたりに進む距離よりも長くなる。そのため、中間転写ベルト７上のトナー像を用紙Ｐに二次転写する際にトナー像が長くなり、理想倍率よりも長い側に画像倍率変動が発生する。一方、用紙Ｐの表面線速が中間転写ベルト７の表面線速よりも遅い場合、用紙Ｐの単位時間当たりに進む距離が中間転写ベルト７の単位時間あたりに進む距離よりも短くなる。そのため、中間転写ベルト７上のトナー像を用紙Ｐに二次転写する際にトナー像が短くなり、理想倍率よりも短い側に画像倍率変動が発生する。 In the transfer device using such an intermediate transfer unit, at the time of the secondary transfer, the paper P enters the secondary transfer portion N to transfer the toner image on the intermediate transfer belt 7 onto the paper P. . At that time, if the surface linear velocity of the paper P and the surface linear velocity of the intermediate transfer belt 7 are equal, the distance traveled per unit time of the paper P is equal to the distance traveled per unit time of the intermediate transfer belt 7. Therefore, the toner image on the intermediate transfer belt 7 is secondarily transferred to the paper P in a size equal to that of the toner image. However, when the surface linear velocity of the paper P is faster than the surface linear velocity of the intermediate transfer belt 7, the distance traveled per unit time of the paper P is longer than the distance traveled per unit time of the intermediate transfer belt 7. Therefore, when the toner image on the intermediate transfer belt 7 is secondarily transferred to the paper P, the toner image becomes long, and the image magnification fluctuation occurs on the side longer than the ideal magnification. On the other hand, when the surface linear velocity of the paper P is slower than the surface linear velocity of the intermediate transfer belt 7, the distance traveled per unit time of the paper P is shorter than the distance traveled per unit time of the intermediate transfer belt 7. Therefore, when the toner image on the intermediate transfer belt 7 is secondarily transferred to the paper P, the toner image becomes short, and the image magnification fluctuation occurs on the side shorter than the ideal magnification.

中間転写ベルト７と二次転写ローラ１５の駆動はそれぞれ独立しており、中間転写ベルト７は常に等速で動作するように、制御部３０によって中間転写駆動モータ４０が制御されている。また、二次転写ローラ１５は用紙Ｐの表面線速を中間転写ベルト７の表面線速と等しい速度となるように、制御部３０によって二次転写ローラ駆動モータ５０が制御されている。すなわち、用紙Ｐの厚み分だけ二次転写ローラ１５の回転速度を遅くすることによって、どの紙厚でもできる限り理想倍率となるように、二次転写ローラ１５の駆動部の回転速度によって調整している。 The intermediate transfer belt 7 and the secondary transfer roller 15 are driven independently of each other, and the control unit 30 controls the intermediate transfer drive motor 40 so that the intermediate transfer belt 7 always operates at a constant speed. Further, the secondary transfer roller drive motor 50 is controlled by the controller 30 so that the surface linear velocity of the paper P of the secondary transfer roller 15 becomes equal to the surface linear velocity of the intermediate transfer belt 7. That is, by adjusting the rotational speed of the secondary transfer roller 15 by the rotational speed of the secondary transfer roller 15, the rotational speed of the secondary transfer roller 15 is reduced by the thickness of the paper P so that the ideal magnification is obtained as much as possible for any paper thickness. There is.

図３は、二次転写部Ｎにおける二次転写圧を変更させる二次転写圧変更機構２０の説明図である。本実施形態のプリンタ１００は、二次転写圧の大きさを変更する二次転写圧変更機構２０を備えている。用紙Ｐの種類に応じた二次転写圧設定値をメモリ３２に予め記憶させておき、用紙Ｐの種類に応じて制御部３０が前記二次転写転写圧設定値を用いて二次転写圧変更機構２０を制御して、二次転写圧の大きさを変更することができる。なお、画像形成に用いる用紙Ｐの種類に関する情報としては、例えば、プリンタ１００に設けられた操作パネル６０からユーザーが設定したものを用いれば良い。 FIG. 3 is an explanatory diagram of the secondary transfer pressure changing mechanism 20 that changes the secondary transfer pressure in the secondary transfer portion N. The printer 100 of the present embodiment includes a secondary transfer pressure changing mechanism 20 that changes the magnitude of the secondary transfer pressure. The secondary transfer pressure set value corresponding to the type of the paper P is stored in the memory 32 in advance, and the control unit 30 changes the secondary transfer pressure using the secondary transfer transfer pressure set value according to the type of the paper P. By controlling the mechanism 20, the magnitude of the secondary transfer pressure can be changed. As the information regarding the type of the paper P used for image formation, for example, information set by the user from the operation panel 60 provided in the printer 100 may be used.

二次転写ローラ１５と二次転写対向ローラ１６とは、中間転写ベルト７を挟んで二次転写ローラ１５が下側で二次転写対向ローラ１６が上側に位置するように対向配置されている。二次転写ローラ１５には、付勢手段である二次転写加圧バネ１８によって二次転写対向ローラ１６に向かうような付勢力が加わっている。二次転写加圧バネ１８は、二次転写ローラ１５の回転軸を回転可能に支持する二次転写回転軸支持部材１７を二次転写対向ローラ１６に向けて押し上げることで付勢力を作用させる。付勢手段としては、例えば、圧縮バネや引っ張りバネなどが挙げることができ、本実施形態の二次転写加圧バネ１８では圧縮バネを用いている。この二次転写加圧バネ１８によって二次転写ローラ１５から用紙Ｐや中間転写ベルト７に対して所定の転写圧を付加することができる。 The secondary transfer roller 15 and the secondary transfer counter roller 16 are arranged so that the secondary transfer roller 15 is located on the lower side and the secondary transfer counter roller 16 is located on the upper side with the intermediate transfer belt 7 interposed therebetween. A biasing force is applied to the secondary transfer roller 15 by a secondary transfer pressure spring 18 which is a biasing means so as to move toward the secondary transfer counter roller 16. The secondary transfer pressure spring 18 applies a biasing force by pushing up the secondary transfer rotation shaft support member 17 that rotatably supports the rotation shaft of the secondary transfer roller 15 toward the secondary transfer counter roller 16. Examples of the urging means include a compression spring and a tension spring, and the secondary transfer pressure spring 18 of the present embodiment uses a compression spring. A predetermined transfer pressure can be applied from the secondary transfer roller 15 to the paper P or the intermediate transfer belt 7 by the secondary transfer pressure spring 18.

次に、二次転写圧変更機構２０について説明する。二次転写圧変更機構２０は、ステッピングモータ２６やカム部材２１などで構成され、この二次転写圧変更機構２０によって二次転写ローラ１５を、中間転写ベルト７に対して一定範囲内で自由に移動させることができる構成となっている。二次転写対向ローラ１６の軸方向両端部には、二次転写対向ローラ１６と同軸上にカム部材２１が設置されている。二次転写ローラ１５の軸方向両端部には、二次転写ローラ１５の回転を妨げないように玉軸受２２が取り付けられており、この玉軸受２２にカム部材２１を突き当てるような構成となっている。カム部材２１が取り付けられている回転軸２１ａがステッピングモータ２６からの回転駆動力により回転すると、カム部材２１も同じタイミング、且つ、同じ角度で回転する構成となっている。具体的には、カム部材２１と回転軸２１ａとがＤカット型や小判型等の形状が一致する穴形状と軸形状とで嵌め合わされて取り付けられている。 Next, the secondary transfer pressure changing mechanism 20 will be described. The secondary transfer pressure changing mechanism 20 is composed of a stepping motor 26, a cam member 21, etc., and the secondary transfer pressure changing mechanism 20 allows the secondary transfer roller 15 to freely move within a certain range with respect to the intermediate transfer belt 7. It can be moved. Cam members 21 are installed coaxially with the secondary transfer counter roller 16 at both axial ends of the secondary transfer counter roller 16. Ball bearings 22 are attached to both axial ends of the secondary transfer roller 15 so as not to hinder the rotation of the secondary transfer roller 15, and the cam member 21 is abutted against the ball bearings 22. ing. When the rotary shaft 21a to which the cam member 21 is attached is rotated by the rotational driving force from the stepping motor 26, the cam member 21 is also rotated at the same timing and the same angle. Specifically, the cam member 21 and the rotary shaft 21a are fitted and attached by a hole shape and a shaft shape that match the shape of a D-cut type or an oval type.

カム部材２１の形状は、カム部材２１の回転中心と外形部とを結んだ距離の最も短い部分が、二次転写対向ローラ１６の直径よりも短くなるような形状である。また、カム部材２１の回転中心と外形部とを結んだ距離の最も長い部分が、二次転写対向ローラ１６の直径よりも長くなるような形状である。回転軸２１ａは、ステッピングモータ２６により自由に回転を制御できるような構成となっている。 The shape of the cam member 21 is such that the shortest distance between the rotation center of the cam member 21 and the outer shape portion is shorter than the diameter of the secondary transfer counter roller 16. In addition, the longest distance between the center of rotation of the cam member 21 and the outer shape is longer than the diameter of the secondary transfer counter roller 16. The rotation shaft 21a is configured so that its rotation can be freely controlled by the stepping motor 26.

本実施形態のプリンタ１００では、ステッピングモータ２６の回転軸に固定された出力プーリー２３及び回転軸２１ａに固定された入力プーリー２４は、その周面に歯車のような歯が付いたプーリーである。これらのプーリーの周面は歯付ベルトからなる駆動伝達ベルト２５の内周面と噛み合う構成である。そして、出力プーリー２３及び入力プーリー２４と駆動伝達ベルト２５とを介することによって、ステッピングモータ２６の回転駆動力が回転軸２１ａに伝達される。そして、カム部材２１を回転させることにより、中間転写ベルト７に対して二次転写ローラ１５が遠ざかるほど転写圧が小さくなり、中間転写ベルト７に対して二次転写ローラ１５を近づけるほど転写圧が大きくなる。 In the printer 100 of the present embodiment, the output pulley 23 fixed to the rotary shaft of the stepping motor 26 and the input pulley 24 fixed to the rotary shaft 21a are pulleys having teeth like gears on their peripheral surfaces. The peripheral surfaces of these pulleys are in mesh with the inner peripheral surface of the drive transmission belt 25, which is a toothed belt. Then, the rotation driving force of the stepping motor 26 is transmitted to the rotation shaft 21 a through the output pulley 23, the input pulley 24, and the drive transmission belt 25. By rotating the cam member 21, the transfer pressure decreases as the secondary transfer roller 15 moves away from the intermediate transfer belt 7, and the transfer pressure decreases as the secondary transfer roller 15 moves closer to the intermediate transfer belt 7. growing.

図４は二次転写ローラ１５によって用紙Ｐが搬送される様子について説明した図である。図のように、二次転写部Ｎに用紙Ｐが進入して、中間転写ベルト７上のトナー像を用紙Ｐ上に転写をする。その際に、用紙Ｐの表面線速と中間転写ベルト７の表面線速とが等しければ、用紙Ｐの単位時間あたりに進む距離と、中間転写ベルト７の単位時間あたりに進む距離とが等しくなる。そのため、中間転写ベルト７上のトナー像の大きさと等しい大きさで、用紙Ｐにトナー像が転写されることになる。 FIG. 4 is a diagram illustrating how the sheet P is conveyed by the secondary transfer roller 15. As shown in the figure, the paper P enters the secondary transfer portion N, and the toner image on the intermediate transfer belt 7 is transferred onto the paper P. At that time, if the surface linear velocity of the paper P and the surface linear velocity of the intermediate transfer belt 7 are equal, the distance traveled per unit time of the paper P is equal to the distance traveled per unit time of the intermediate transfer belt 7. . Therefore, the toner image is transferred onto the paper P with a size equal to that of the toner image on the intermediate transfer belt 7.

これに対し、用紙Ｐの表面線速が中間転写ベルト７の表面線速よりも速い場合には、用紙Ｐの単位時間あたりに進む距離が、中間転写ベルト７の単位時間あたりに進む距離よりも長くなる。そのため、中間転写ベルト７上から用紙Ｐ上に転写されたトナー像の用紙搬送方向における長さが、中間転写ベルト７上よりも長くなり、理想倍率よりも長い側に画像倍率変動が発生する。一方、用紙Ｐの表面線速が中間転写ベルト７の表面線速よりも遅い場合には、用紙Ｐの単位時間当たりに進む距離が、中間転写ベルト７の単位時間あたりに進む距離よりも短くなる。そのため、中間転写ベルト７上から用紙Ｐ上に転写されたトナー像の用紙搬送方向における長さが、中間転写ベルト７上よりも短くなり、理想倍率よりも短い側に画像倍率変動が発生する。 On the other hand, when the surface linear velocity of the paper P is faster than the surface linear velocity of the intermediate transfer belt 7, the distance traveled per unit time of the paper P is greater than the distance traveled per unit time of the intermediate transfer belt 7. become longer. Therefore, the length of the toner image transferred from the intermediate transfer belt 7 onto the paper P in the paper transport direction is longer than that on the intermediate transfer belt 7, and the image magnification fluctuation occurs on the side longer than the ideal magnification. On the other hand, when the surface linear velocity of the paper P is slower than the surface linear velocity of the intermediate transfer belt 7, the distance traveled per unit time of the paper P is shorter than the distance traveled per unit time of the intermediate transfer belt 7. . Therefore, the length of the toner image transferred from the intermediate transfer belt 7 onto the paper P in the paper transport direction is shorter than that on the intermediate transfer belt 7, and the image magnification fluctuation occurs on the side shorter than the ideal magnification.

図５は、二次転写圧を変化させた場合における画像倍率変動の実験結果を示すグラフである。なお、図５に示すグラフの横軸は二次転写圧である。また、縦軸は理想倍率に対する画像倍率変動であり、＋側に倍率誤差が発生している場合は、理想の画像倍率に対して長い側に画像倍率変動しており、−側に倍率誤差が発生している場合は、理想の画像倍率に対して短い側に画像倍率変動をしていることを示す。 FIG. 5 is a graph showing experimental results of image magnification variation when the secondary transfer pressure is changed. The horizontal axis of the graph shown in FIG. 5 is the secondary transfer pressure. Further, the vertical axis represents the image magnification variation with respect to the ideal magnification. When a magnification error occurs on the + side, the image magnification varies on the longer side of the ideal image magnification, and the magnification error appears on the-side. If it occurs, it means that the image magnification is changing to a side shorter than the ideal image magnification.

図５からわかるように、所定の二次転写圧よりも低圧の範囲では、二次転写圧が大きいほど、中間転写ベルト７から用紙Ｐに転写された画像の用紙搬送方向における長さが、中間転写ベルト７上よりも短くなる。これは、図６に示すように、二次転写ローラ１５の二次転写圧がかかっている部分が二次転写圧によって圧縮され、その部分におけるローラ半径ｒ２が、二次転写圧がかかっていない部分におけるローら半径ｒ１よりも短くなり、用紙表面速度が遅くなるためである。そのため、前記低圧の範囲では、二次転写圧が大きくなるにつれて画像倍率が小さく。 As can be seen from FIG. 5, in the range lower than the predetermined secondary transfer pressure, the larger the secondary transfer pressure is, the longer the length in the sheet transport direction of the image transferred from the intermediate transfer belt 7 to the sheet P becomes. It becomes shorter than that on the transfer belt 7. This is because, as shown in FIG. 6, the part of the secondary transfer roller 15 on which the secondary transfer pressure is applied is compressed by the secondary transfer pressure, and the roller radius r2 at that part is not applied with the secondary transfer pressure. This is because the radius from the Lo et al. In the portion becomes shorter than the radius r1 and the sheet surface speed becomes slow. Therefore, in the low pressure range, the image magnification decreases as the secondary transfer pressure increases.

一方、所定の二次転写圧よりも高圧の範囲では、二次転写圧が大きいほど、中間転写ベルト７から用紙Ｐに転写された画像の用紙搬送方向における長さが、中間転写ベルト７上よりも長くなる。図７に示す二次転写ローラ１５のローラ半径ｒ１，ｒ２，ｒ３は、ｒ２＜ｒ１＜ｒ３の関係を満たし、図７に示すように、二次転写圧により一定以上圧縮された二次転写ローラ１５は、それ以上圧縮することができず歪を発生させ、ローラ半径が通常よりも長くなる。これにより、用紙表面速度が速くなるため、前記高圧の範囲では、二次転写圧が大きくなるにつれて画像倍率が大きくなる。 On the other hand, in a range higher than the predetermined secondary transfer pressure, as the secondary transfer pressure is higher, the length of the image transferred from the intermediate transfer belt 7 to the paper P in the paper transport direction is larger than that on the intermediate transfer belt 7. Also becomes longer. The roller radii r1, r2, r3 of the secondary transfer roller 15 shown in FIG. 7 satisfy the relationship of r2 <r1 <r3, and as shown in FIG. 7, the secondary transfer roller compressed by a certain amount or more by the secondary transfer pressure. No. 15 cannot be compressed any more and causes distortion, and the roller radius becomes longer than usual. As a result, the surface speed of the paper is increased, and thus the image magnification increases as the secondary transfer pressure increases in the high pressure range.

ここで、二次転写圧を変化させる目的としては、例えば、用紙Ｐの表面上に凹凸状のパターンが形成されているような凹凸紙では、二次転写圧を増加させたほうが凹部におけるトナーの転写性が良化する。そのため、二次転写圧を高くしたほうが、用紙Ｐ上で良好な画像を得ることができる。逆に、キャストコート紙のような超平滑紙では、転写圧性確保には高い二次転写圧は必要がなく、二次転写圧が高すぎると、トナーの凝縮による文字虫食いや、二次転写部Ｎへの用紙突入時の衝撃が引き起こす横スジの異常画像（ショックジター）が発生する。そのため、二次転写圧を低くしたほうが、用紙Ｐ上で良好な画像を得ることができる。このように、紙種に応じて二次転写圧を変化させることにより、紙種対応力の向上を図ることができるが、図５に示すように二次転写圧を変化させると、画像倍率変動が発生してしまうため問題となっていた。 Here, for the purpose of changing the secondary transfer pressure, for example, in the case of uneven paper in which an uneven pattern is formed on the surface of the paper P, increasing the secondary transfer pressure causes the toner in the recesses to increase. Transferability is improved. Therefore, it is possible to obtain a good image on the paper P by increasing the secondary transfer pressure. On the other hand, with ultra-smooth paper such as cast coated paper, a high secondary transfer pressure is not required to secure transfer pressure.If the secondary transfer pressure is too high, it causes worming due to toner condensation and secondary transfer area. An abnormal image of horizontal stripes (shock jitter) caused by the impact when the paper enters N is generated. Therefore, the lower the secondary transfer pressure is, the better image can be obtained on the paper P. In this way, by changing the secondary transfer pressure according to the paper type, it is possible to improve the paper type adaptability, but if the secondary transfer pressure is changed as shown in FIG. Is a problem because it occurs.

そこで、本実施形態においては、二次転写圧を変化させた際の画像倍率変動を抑制するために、二次転写圧の大きさに応じて二次転写ローラ１５の回転速度を変更する。なお、前記所定の二次転写圧は、二次転写ローラ１５の圧縮限界における二次転写圧の値であって、前記所定の二次転写圧よりも小さい二次転写圧の範囲（前記低圧の範囲）では、二次転写ローラ１５が上述したように圧縮変形する。また、前記所定の二次転写圧よりも大きい二次転写圧の範囲（前記高圧の範囲）では、上述したように二次転写ローラ１５が歪み変形する。 Therefore, in the present embodiment, the rotational speed of the secondary transfer roller 15 is changed according to the magnitude of the secondary transfer pressure in order to suppress the image magnification variation when the secondary transfer pressure is changed. The predetermined secondary transfer pressure is a value of the secondary transfer pressure at the compression limit of the secondary transfer roller 15, and is a range of the secondary transfer pressure smaller than the predetermined secondary transfer pressure (the low transfer pressure In the range), the secondary transfer roller 15 is compressed and deformed as described above. Further, in the range of the secondary transfer pressure (the high pressure range) larger than the predetermined secondary transfer pressure, the secondary transfer roller 15 is distorted and deformed as described above.

例えば、前記所定の二次転写圧よりも小さい変更前二次転写圧から前記所定の二次転写圧以下であって変更前二次転写圧よりも大きい変更後二次転写圧へと、二次転写圧を変更した際には、変更前二次転写圧のときよりも二次転写ローラ１５の回転速度を速くする。また、前記所定の二次転写圧よりも小さい変更前二次転写圧から前記所定の二次転写圧以上であって変更前二次転写圧よりも大きい変更後二次転写圧へと、二次転写圧を変更した際に、変更前二次転写圧のときよりも二次転写ローラ１５の回転速度を遅くする。また、前記所定の二次転写圧よりも大きい変更前二次転写圧から前記所定の二次転写圧以下であって変更前二次転写圧よりも小さい変更後二次転写圧へと、二次転写圧を変更した際に、変更前二次転写圧のときよりも二次転写ローラ１５の回転速度を遅くする。また、前記所定の二次転写圧よりも大きい変更前二次転写圧から前記所定の二次転写圧以上であって変更前二次転写圧よりも小さい変更後二次転写圧へと、二次転写圧を変更した際に、変更前二次転写圧のときよりも二次転写ローラ１５の回転速度を速くする。 For example, from the secondary transfer pressure before change, which is smaller than the predetermined secondary transfer pressure, to the secondary transfer pressure after change, which is less than or equal to the predetermined secondary transfer pressure and larger than the secondary transfer pressure before change, When the transfer pressure is changed, the rotation speed of the secondary transfer roller 15 is made faster than when the secondary transfer pressure before change is used. In addition, the secondary transfer pressure before change, which is smaller than the predetermined secondary transfer pressure, is changed to the secondary transfer pressure after change, which is equal to or higher than the predetermined secondary transfer pressure and is larger than the secondary transfer pressure before change. When the transfer pressure is changed, the rotation speed of the secondary transfer roller 15 is made slower than when the secondary transfer pressure before the change. In addition, the secondary transfer pressure before change, which is larger than the predetermined secondary transfer pressure, is changed to the secondary transfer pressure after change, which is less than or equal to the predetermined secondary transfer pressure and smaller than the secondary transfer pressure before change, When the transfer pressure is changed, the rotation speed of the secondary transfer roller 15 is made slower than when the secondary transfer pressure before the change. In addition, the secondary transfer pressure before the change, which is larger than the predetermined secondary transfer pressure, is changed to the secondary transfer pressure after the change, which is equal to or more than the predetermined secondary transfer pressure and is smaller than the secondary transfer pressure before the change. When the transfer pressure is changed, the rotation speed of the secondary transfer roller 15 is made faster than when the secondary transfer pressure before change is used.

表１に、二次転写圧を変化させた際の画像倍率変動を抑制するために、二次転写圧と、二次転写ローラ駆動の回転速度調整量との関係を示す。 Table 1 shows the relationship between the secondary transfer pressure and the rotational speed adjustment amount for driving the secondary transfer roller in order to suppress the change in image magnification when the secondary transfer pressure is changed.

なお、本実施形態においては、変更前の二次転写圧を前記所定の二次転写圧よりも大きな５０［Ｎ］としている。そして、その二次転写圧５０［Ｎ］から二次転写圧の大きさを任意の値変化させた場合の画像倍率変動に応じて、その変動分を二次転写ローラ１５の駆動部の回転速度を変化させることで補正するような制御を実施する。 In the present embodiment, the secondary transfer pressure before the change is set to 50 [N], which is higher than the predetermined secondary transfer pressure. Then, in accordance with a change in the image magnification when the magnitude of the secondary transfer pressure is changed from the secondary transfer pressure 50 [N] by an arbitrary value, the changed amount is the rotational speed of the drive unit of the secondary transfer roller 15. Is controlled by changing

例えば、二次転写圧を５０［Ｎ］から１００［Ｎ］へと変化させた場合、互いに同じ二次転写ローラ１５の回転速度で二次転写を行うと、二次転写圧５０［Ｎ］のときに比べて二次転写圧１００［Ｎ］のときのほうが、画像倍率が０．０５５［％］大きくなる。そのため、二次転写圧を５０［Ｎ］から１００［Ｎ］へと変化させた場合、二次転写ローラ１５の駆動部を二次転写圧５０［Ｎ］のときに比べて−０．０５５［％］遅くするように制御する。これにより、画像倍率が−０．０５５［％］短くなるため、二次転写圧を５０［Ｎ］から１００［Ｎ］へと変化させた場合でも、画像倍率変動を抑制することができる。また、二次転写圧を５０［Ｎ］から１００［Ｎ］以外の他の二次転写圧に変化させた場合でも同様に、二次転写圧を変化させたときに生じ得る画像倍率変動分だけ、二次転写ローラ１５の回転速度を変化させることで、二次転写圧変化による画像倍率変動を抑制できる。このような制御を実施することで、二次転写圧を変化させる機構をもつ画像形成装置において、二次転写圧変化における画像倍率変動を抑制することができる。 For example, when the secondary transfer pressure is changed from 50 [N] to 100 [N] and the secondary transfer is performed at the same rotation speed of the secondary transfer roller 15, the secondary transfer pressure of 50 [N] is The image magnification is 0.055 [%] higher when the secondary transfer pressure is 100 [N] than when. Therefore, when the secondary transfer pressure is changed from 50 [N] to 100 [N], the drive unit of the secondary transfer roller 15 is -0.055 [compared to when the secondary transfer pressure is 50 [N]. %] Control to slow down. As a result, the image magnification is reduced by -0.055 [%], so that the variation in the image magnification can be suppressed even when the secondary transfer pressure is changed from 50 [N] to 100 [N]. Further, even when the secondary transfer pressure is changed from 50 [N] to another secondary transfer pressure other than 100 [N], similarly, only the image magnification variation that can occur when the secondary transfer pressure is changed. By changing the rotation speed of the secondary transfer roller 15, it is possible to suppress a change in image magnification due to a change in secondary transfer pressure. By performing such control, in the image forming apparatus having the mechanism for changing the secondary transfer pressure, it is possible to suppress the image magnification variation due to the change in the secondary transfer pressure.

本実施形態では、二次転写ローラ１５の硬度が高く堅いハードコートローラでの制御の一例を示したが、二次転写圧に応じた画像倍率変動量は、二次転写ローラ１５の硬度や、二次転写ローラ１５に対向する二次転写対向ローラ１６の硬度に依存する。そのため、画像倍率変動量は、図５や表１などに示されるような値に限定されるものではない。また、二次転写ローラ１５の圧縮や歪の他に、用紙Ｐが二次転写部Ｎでつぶれ紙厚が変化すると、用紙Ｐの表面速度が変化してくる。これは、二次転写圧が高いほど用紙Ｐに圧縮や歪が発生し紙厚が変化するために用紙Ｐの表面速度が変化する。この二次転写圧による用紙Ｐの厚み変化は、紙厚が厚いほど圧縮量や歪量が増えるため、二次転写圧増加による用紙Ｐの表面速度の変化が大きくなる。また、密度が低い用紙Ｐほど二次転圧増加による用紙Ｐの圧縮量が大きい。そのため、二次転写圧の変化に伴う二次転写ローラ１５の駆動線速調整量を、用紙Ｐの厚みや密度に応じて変化させることで、二次転写圧を変化させた際の画像倍率変動を、より高精度に補正することができる。 In the present embodiment, an example of control with a hard coat roller having a high hardness of the secondary transfer roller 15 is shown, but the image magnification variation amount according to the secondary transfer pressure is It depends on the hardness of the secondary transfer counter roller 16 that opposes the secondary transfer roller 15. Therefore, the image magnification variation amount is not limited to the values shown in FIG. 5 and Table 1. In addition to the compression and distortion of the secondary transfer roller 15, when the paper P is crushed at the secondary transfer portion N and the paper thickness changes, the surface speed of the paper P also changes. This is because the higher the secondary transfer pressure is, the more the compression or distortion occurs in the sheet P and the sheet thickness changes, so that the surface speed of the sheet P changes. With respect to the change in the thickness of the paper P due to the secondary transfer pressure, since the compression amount and the distortion amount increase as the paper thickness increases, the change in the surface speed of the paper P due to the increase in the secondary transfer pressure increases. Further, the lower the density of the paper P, the greater the amount of compression of the paper P due to the increase in the secondary rolling pressure. Therefore, by changing the drive linear velocity adjustment amount of the secondary transfer roller 15 according to the change of the secondary transfer pressure according to the thickness and the density of the paper P, the image magnification variation when the secondary transfer pressure is changed. Can be corrected with higher accuracy.

表２に、転写圧可変設定と二次転写ローラ駆動モータの回転速度調整設定値との関係を示す。 Table 2 shows the relationship between the transfer pressure variable setting and the rotation speed adjustment setting value of the secondary transfer roller drive motor.

図５で示したような二次転写圧を変化させた際の画像倍率変動量と、その画像倍率変動量を補正できる二次転写駆動モータの回転速度とを、予め実験で取得しておく。例えば、二次転写圧が７５［Ｎ］のときは、二次転写圧が５０［Ｎ］のときと比べて、画像倍率が０．０１５［％］大きくなる。そのため、二次転写圧が７５［Ｎ］のときにおける二次転写ローラ１５の駆動モータの回転速度を、二次転写圧が５０［Ｎ］のときよりも遅くしないと、二次転写圧が５０［Ｎ］のときと７５［Ｎ］のときとで画像倍率が変化してしまう。 The amount of change in image magnification when the secondary transfer pressure is changed as shown in FIG. 5 and the rotation speed of the secondary transfer drive motor that can correct the amount of change in image magnification are acquired in advance by experiments. For example, when the secondary transfer pressure is 75 [N], the image magnification is 0.015 [%] higher than when the secondary transfer pressure is 50 [N]. Therefore, if the rotation speed of the drive motor of the secondary transfer roller 15 when the secondary transfer pressure is 75 [N] is not slower than when the secondary transfer pressure is 50 [N], the secondary transfer pressure is 50. The image magnification changes between [N] and 75 [N].

そこで、二次転写圧が７５［Ｎ］のときに二次転写圧が５０［Ｎ］と画像倍率が等しくなるような二次転写ローラ駆動モータ５０の回転速度を実験で予め求めておく。通常であれば、二次転写ローラ駆動モータ５０の回転速度を一定パーセント変化させた際の用紙Ｐの表面速度の変化量は一致するため、変化した画像倍率パーセント分だけ二次転写ローラ駆動モータ５０の回転速度を、画像倍率の変化を打ち消す側に変化させればよい。ところが、二次転写ローラ駆動モータ５０の回転速度を一定パーセント変化させた際の用紙Ｐの表面速度の変化量は、用紙Ｐのスリップなどの影響により、必ずしも一致するとは限らない。そのため、各二次転写圧での画像倍率を一定とするための二次転写ローラ駆動モータ５０の回転速度を予め実験によって求めておく必要がある。そして、実験で求めた各二次転写圧での画像倍率を一定とするための二次転写ローラ駆動モータ５０の回転速度を示したのが表２である。この表２に示したような設定値を、プリンタ内のメモリ３２に保存しておく。これにより、プリンタが画像形成動作を実行する前に、設定した二次転写圧に応じて二次転写ローラ駆動モータ５０の回転速度を変化させることで、二次転写圧を変動させた際にも、用紙Ｐ上に転写された画像の画像倍率を常に一定にすることができる。 Therefore, the rotational speed of the secondary transfer roller drive motor 50 that makes the image magnification equal to the secondary transfer pressure of 50 [N] when the secondary transfer pressure is 75 [N] is obtained in advance by an experiment. Normally, the amount of change in the surface speed of the paper P when the rotational speed of the secondary transfer roller drive motor 50 is changed by a certain percentage is the same, so the secondary transfer roller drive motor 50 is changed by the changed image magnification percentage. It suffices to change the rotation speed of to the side that cancels the change in the image magnification. However, the amount of change in the surface speed of the paper P when the rotation speed of the secondary transfer roller drive motor 50 is changed by a certain percentage is not always the same due to the influence of slip of the paper P and the like. Therefore, the rotational speed of the secondary transfer roller drive motor 50 for keeping the image magnification at each secondary transfer pressure constant needs to be obtained in advance by experiments. Then, Table 2 shows the rotational speed of the secondary transfer roller drive motor 50 for keeping the image magnification at each secondary transfer pressure constant, which is obtained by the experiment. The setting values as shown in Table 2 are stored in the memory 32 in the printer. As a result, by changing the rotation speed of the secondary transfer roller drive motor 50 according to the set secondary transfer pressure before the printer executes the image forming operation, even when the secondary transfer pressure is changed. The image magnification of the image transferred on the paper P can always be made constant.

本実施形態では、二次転写圧が段階的に変化するため、その二次転写圧に対応した二次転写ローラ駆動モータ５０の回転速度設定値をテーブルでメモリ領域に記憶させる例を示したが、これに限るものではない。すなわち、二次転写圧に対応した二次転写ローラ駆動モータ５０の回転速度設定値を、テーブルではなく、二次転写圧に応じた関数として設定しメモリ領域に記憶させてもよい。例えば、二次転写圧をカムなどによって無段階に変化させることが可能な場合には、二次転写圧に応じた二次転写ローラ駆動モータ５０の回転速度設定値をテーブルで設定すると、データ量が膨大になってしまう。そのため、二次転写圧Ｎに応じた二次転写ローラ駆動線速Ｖが一対一で決まるような関数式を作成し、プリンタ内部のメモリ領域に保存させるほうが望ましい。例えば、本実施形態においては、数１に示すような関係式をプリンタ内部のメモリ領域に記憶することで実現できる。 In the present embodiment, since the secondary transfer pressure changes stepwise, an example in which the rotation speed setting value of the secondary transfer roller drive motor 50 corresponding to the secondary transfer pressure is stored in a memory area in a table has been described. , But not limited to this. That is, the rotation speed setting value of the secondary transfer roller drive motor 50 corresponding to the secondary transfer pressure may be set not as a table but as a function according to the secondary transfer pressure and stored in the memory area. For example, when the secondary transfer pressure can be changed steplessly by a cam or the like, if the rotation speed setting value of the secondary transfer roller drive motor 50 corresponding to the secondary transfer pressure is set in the table, the data amount Will be huge. Therefore, it is desirable to create a functional expression that determines the secondary transfer roller drive linear velocity V according to the secondary transfer pressure N on a one-to-one basis and store it in a memory area inside the printer. For example, in the present embodiment, it can be realized by storing the relational expression shown in Formula 1 in the memory area inside the printer.

図１は、二次転写圧の変化に応じて二次転ローラ駆動モータの回転速度を変更することによる、二次転写圧変化時の画像倍率調整制御について示したフローチャートである。まず、通紙前準備を開始し（Ｓ１）、印刷する用紙（例えば、用紙銘柄×××）を選択して（Ｓ２）、図８のように用紙銘柄×××の設定値を保存する用紙ＤＢ（例えば、用紙ＤＢ００２）をメモリ３２に作成する（Ｓ３）。そして、用紙ＤＢ００２の中の転写圧可変設定値（例えば、用紙設定パラメータＮｏ．１００転写圧可変設定）を参照する（Ｓ４）。そして、図９のように、通紙条件に応じて、用紙設定パラメータＮｏ．１００転写圧可変設定を任意の値（例えば、モード３：５０［Ｎ］）に設定する（Ｓ５）。そして、図１０のように、印刷する用紙Ｐをセットする用紙収容部１２１に用紙ＤＢ００２を設定する（Ｓ６）。これにより、通紙前準備が終了し（Ｓ７）、用紙収容部１２１からの通紙による印刷準備を開始する（Ｓ８）。まず、図１１のように、用紙収容部１２１に設定されている用紙ＤＢ（用紙収容部１２１＝用紙ＤＢ００２）を参照する（Ｓ９）。そして、図１２のように、用紙ＤＢ００２の中の用紙設定パラメータＮｏ．１００の設定値（モード３：５０［Ｎ］）を参照する（Ｓ１０）。用紙設定パラメータＮｏ．１００の設定値に応じて、二次転写圧を設定する（Ｓ１１）。転写圧可変時の二次転写ローラ駆動モータ５０の回転速度調整設定値テーブルを参照して、二次転写ローラ駆動モータ５０の回転速度を設定する（Ｓ１２）。これにより、用紙収容部１２１からの通紙による印刷準備を終了する（Ｓ１３）。その後、中間転写ベルト７から用紙への画像の転写を開始するために、用紙収容部１２１から二次転写部Ｎに向けて通紙を行ない（Ｓ１４）、その後、用紙への画像の転写を終了する（Ｓ１５）。 FIG. 1 is a flowchart showing the image magnification adjustment control when the secondary transfer pressure changes by changing the rotation speed of the secondary transfer roller drive motor according to the change of the secondary transfer pressure. First, the paper preparation is started (S1), the paper to be printed (for example, paper brand XXX) is selected (S2), and the paper brand XXX setting value is stored as shown in FIG. A DB (for example, paper DB002) is created in the memory 32 (S3). Then, the transfer pressure variable setting value in the paper DB 002 (for example, the paper setting parameter No. 100 transfer pressure variable setting) is referred to (S4). Then, as shown in FIG. 9, the sheet setting parameter No. The 100 transfer pressure variable setting is set to an arbitrary value (for example, mode 3:50 [N]) (S5). Then, as shown in FIG. 10, the paper DB 002 is set in the paper storage unit 121 for setting the paper P to be printed (S6). As a result, the pre-sheet passing preparation is completed (S7), and the printing preparation by the sheet passing from the sheet storage section 121 is started (S8). First, as shown in FIG. 11, the paper DB (paper storage unit 121 = paper DB002) set in the paper storage unit 121 is referred to (S9). Then, as shown in FIG. 12, the paper setting parameter No. The set value of 100 (mode 3: 50 [N]) is referred to (S10). Paper setting parameter No. The secondary transfer pressure is set according to the set value of 100 (S11). The rotation speed of the secondary transfer roller drive motor 50 is set with reference to the rotation speed adjustment setting value table of the secondary transfer roller drive motor 50 when the transfer pressure is variable (S12). As a result, the preparation for printing by passing the paper from the paper storage unit 121 is completed (S13). After that, in order to start the transfer of the image from the intermediate transfer belt 7 to the paper, the paper is passed from the paper storage unit 121 to the secondary transfer unit N (S14), and then the transfer of the image to the paper is completed. Yes (S15).

すなわち、本実施形態においては、図１のフローチャートにしたがって、通紙前に印刷用紙に応じた各種パラメータを保存できる保存領域（例：用紙ＤＢ）に二次転写圧可変のパラメータを保存する。その二次転写圧可変のパラメータをプリンタ本体は参照して、印刷前に二次転写圧を所定の設定された二次転写圧へと変更する。そして、表２のような二次転写圧可変設定と二次転ローラ駆動モータの回転速度設定値との関係を示すテーブルまたは関数にしたがって、二次転写ローラ駆動モータ５０の回転速度を変化させる。そして、その状態で通紙、印刷を行うことで、二次転写圧を変化させたときでも、画像倍率が変化することなく一定の画像倍率で印刷することができる。 That is, in the present embodiment, according to the flowchart of FIG. 1, the secondary transfer pressure variable parameter is stored in a storage area (eg, paper DB) in which various parameters corresponding to the print paper can be stored before the paper is passed. The printer main body refers to the variable parameter of the secondary transfer pressure to change the secondary transfer pressure to the predetermined secondary transfer pressure before printing. Then, the rotation speed of the secondary transfer roller drive motor 50 is changed according to a table or a function showing the relationship between the secondary transfer pressure variable setting and the rotation speed setting value of the secondary transfer roller drive motor as shown in Table 2. Then, by performing sheet passing and printing in that state, it is possible to print at a constant image magnification without changing the image magnification even when the secondary transfer pressure is changed.

以上に説明したものは一例であり、次の態様毎に特有の効果を奏する。
（態様Ａ）
表面移動可能な中間転写ベルト７などの像担持体と、前記像担持体と当接し該像担持体から記録媒体に画像を転写する二次転写部Ｎなどの転写部を形成する回転可能な二次転写ローラ１５などの転写部材と、前記転写部材を回転駆動させるための二次転写ローラ駆動モータ５０などの転写部材駆動手段と、前記転写部における転写圧を変更する二次転写圧変更機構２０などの転写圧変更手段とを備えた転写装置において、前記転写圧の大きさに応じて前記転写部材の回転速度を変更するように前記転写部材駆動手段を制御する制御部３０などの転写部材駆動制御手段を有する。
（態様Ａ）においては、転写部で像担持体上から記録媒体上に転写した画像の記録媒体搬送方向の長さが、基準の転写圧で転写したときの画像よりも長くなるような転写圧の場合は、転写部材の回転速度を基準の転写圧のときよりも遅くする。これにより、基準の転写圧での回転速度で転写部材を回転させた場合よりも、記録媒体表面速度が遅くなるので、その分、記録媒体に転写された画像の記録媒体搬送方向の長さが長くなるような画像倍率変動を低減させることができる。また、転写部で像担持体上から記録媒体上に転写した画像の記録媒体搬送方向の長さが、基準の転写圧で転写したときの画像よりも短くなるような転写圧の場合は、転写部材の回転速度を基準の転写圧のときよりも速くする。これにより、基準の転写圧での回転速度で転写部材を回転させた場合よりも、記録媒体表面速度が速くなるので、その分、記録媒体に転写された画像の記録媒体搬送方向の長さが短くなるような画像倍率変動を低減させることができる。よって、転写部材駆動制御手段により転写部材駆動手段を制御して、転写圧の大きさに応じて転写部材の回転速度を変更することで、転写圧を変化させたときの画像倍率変動を低減させることができる。
（態様Ｂ）
（態様Ａ）において、前記転写圧変更手段により、所定の転写圧よりも小さい第一転写圧から該所定の転写圧以下であって該第一転写圧よりも大きい第二転写圧へと、転写圧を変更した際に、前記第一転写圧のときよりも前記転写部材の回転速度を速くする。なお、前記所定の転写圧は、転写部材の圧縮限界における転写圧の値であって、所定の転写圧よりも小さい転写圧の範囲では、転写部材が圧縮変形する。（態様Ｂ）においては、転写圧を大きくしたことにより、転写部材が圧縮され転写部材の半径が短くなることで、記録媒体搬送速度が低下する。それに伴い画像が短くなる画像倍率変動分を、転写部材の回転速度を速くすることで抑制し、画像倍率変動を改善することができる。
（態様Ｃ）
（態様Ａ）において、前記転写圧変更手段により、所定の転写圧よりも小さい第一転写圧から該所定の転写圧以上であって該第一転写圧よりも大きい第二転写圧へと、転写圧を変更した際に、前記第一転写圧のときよりも前記転写部材の回転速度を遅くする。なお、前記所定の転写圧は、転写部材の圧縮限界における転写圧の値であって、所定の転写圧よりも大きい転写圧の範囲では、転写部材が歪み変形する。（態様Ｃ）においては、転写部材の圧縮限界を超えるまで転写圧を大きくしたことにより、転写部材が圧縮限界を超えて歪みが発生し、転写部材のニップ部周囲が長くなることで、記録媒体搬送速度が増加する。それに伴い画像が長くなる画像倍率変動分を、転写部材の回転速度を遅くすることで抑制し、画像倍率変動を改善することができる。
（態様Ｄ）
（態様Ａ）において、前記転写圧変更手段により、所定の転写圧よりも大きい第一転写圧から該所定の転写圧以下であって該第一転写圧よりも小さい第二転写圧へと、転写圧を変更した際に、前記第一転写圧のときよりも前記回転部材の回転速度を遅くする。なお、前記所定の転写圧は、転写部材の圧縮限界における転写圧の値であって、所定の転写圧よりも小さい転写圧の範囲では、転写部材が圧縮変形する。（態様Ｄ）においては、転写圧を小さくしたことにより、転写部材の圧縮が解放され転写部材の半径が大きくなることにより、記録媒体搬送速度が増加する。それに伴い画像が長くなる画像倍率変動分を、転写部材の回転速度を遅くすることで抑制し、画像倍率変動を改善することができる。
（態様Ｅ）
（態様Ａ）において、前記転写圧変更手段により、所定の転写圧よりも大きい第一転写圧から該所定の転写圧以上であって該第一転写圧よりも小さい第二転写圧へと、転写圧を変更した際に、前記第一転写圧のときよりも前記回転部材の回転速度を速くする。なお、前記所定の転写圧は、転写部材の圧縮限界における転写圧の値であって、所定の転写圧よりも大きい転写圧の範囲では、転写部材が歪み変形する。（態様Ｅ）においては、転写部材の圧縮限界を超えるまで大きくした転写圧を小さくしたことにより、転写部材の圧縮限界を超えて発生していた歪みが低減し、その歪によって長くなっていた転写部材のニップ部周囲が短くなることで、記録媒体搬送速度が低下する。それに伴い画像が短くなる画像変動倍率分を、転写部材の回転速度を速くすることで抑制し、画像倍率変動を改善することができる。
（態様Ｆ）
（態様Ｂ）乃至（態様Ｅ）のいずれかにおいて、前記転写圧変更手段により転写圧を前記第一転写圧から前記第二転写圧へと変更した際における、前記転写部材の回転速度を、前記記録媒体の厚さに応じて変化させる。これによれば、上記実施形態について説明したように、記録媒体の厚みに応じて、転写圧を変化させた際の画像倍率変動を、より高精度に補正することができる。
（態様Ｇ）
（態様Ｂ）乃至（態様Ｅ）のいずれかにおいて、前記転写圧変更手段により転写圧を前記第一転写圧から前記第二転写圧へと変更した際における前記転写部材の回転速度を、前記記録媒体の密度に応じて変化させる。これによれば、上記実施形態について説明したように、記録媒体の密度に応じて、転写圧を変化させた際の画像倍率変動を、より高精度に補正することができる。
（態様Ｈ）
（態様Ａ）乃至（態様Ｇ）のいずれかにおいて、前記像担持体を表面移動させるための中間転写駆動モータ４０などの像担持体駆動手段と、前記像担持体駆動手段を制御する制御部３０などの像担持体駆動制御手段と、前記転写圧に応じた転写部材回転速度設定値を記憶するメモリ３２などの記憶手段とを有しており、像担持体表面移動速度と転写部材回転速度それぞれが、前記像担持体駆動制御手段と前記転写部材駆動制御手段とによって独立して調整可能であって、前記転写部材駆動制御手段は、前記転写圧の大きさに応じた前記記憶手段に記憶された前記転写部材回転速度設定値となるように、前記転写部材駆動手段を制御する。これによれば、上記実施形態について説明したように、画像倍率変動を改善できる。
（態様Ｉ）
像担持体の表面に形成した画像を、転写手段を用いて記録媒体へ転写することにより、該記録材上に画像を形成する画像形成装置において、前記転写手段として、（態様Ａ）乃至（態様Ｈ）のいずれか一記載の転写装置を用いる。これによれば、上記実施形態について説明したように、記録媒体上に転写された画像の転写圧を変化させた際における画像倍率変動を抑制し、良好な画像形成を行うことができる。 What has been described above is an example, and unique effects are obtained for each of the following aspects.
(Aspect A)
An image carrier such as an intermediate transfer belt 7 whose surface is movable, and a rotatable two roller that forms a transfer unit such as a secondary transfer unit N that contacts the image carrier and transfers an image from the image carrier to a recording medium. A transfer member such as the next transfer roller 15, a transfer member driving unit such as a secondary transfer roller drive motor 50 for rotationally driving the transfer member, and a secondary transfer pressure changing mechanism 20 for changing the transfer pressure at the transfer portion. In a transfer device including a transfer pressure changing unit such as a transfer member driving unit that controls the transfer member driving unit so as to change the rotational speed of the transfer member according to the magnitude of the transfer pressure. It has a control means.
In (Aspect A), the transfer pressure is such that the length of the image transferred on the recording medium from the image carrier at the transfer portion in the recording medium conveyance direction is longer than the image when transferred at the reference transfer pressure. In the case of 1, the rotation speed of the transfer member is made slower than that at the standard transfer pressure. As a result, the surface speed of the recording medium becomes slower than when the transfer member is rotated at the rotational speed at the standard transfer pressure, and the length of the image transferred to the recording medium in the recording medium conveyance direction is correspondingly reduced. It is possible to reduce the image magnification variation that becomes long. If the transfer pressure of the image transferred from the image carrier to the recording medium at the transfer unit is shorter than the image when transferred at the standard transfer pressure, the transfer The rotation speed of the member is made higher than that at the standard transfer pressure. As a result, the surface speed of the recording medium becomes faster than when the transfer member is rotated at the rotational speed at the standard transfer pressure, and the length of the image transferred to the recording medium in the recording medium conveyance direction is correspondingly increased. It is possible to reduce the image magnification variation that becomes short. Therefore, by controlling the transfer member drive unit by the transfer member drive control unit and changing the rotational speed of the transfer member according to the magnitude of the transfer pressure, it is possible to reduce the image magnification variation when the transfer pressure is changed. be able to.
(Aspect B)
In (Aspect A), the transfer pressure changing unit transfers a first transfer pressure lower than a predetermined transfer pressure to a second transfer pressure lower than the predetermined transfer pressure and higher than the first transfer pressure. When the pressure is changed, the rotation speed of the transfer member is made higher than that at the first transfer pressure. The predetermined transfer pressure is a value of the transfer pressure at the compression limit of the transfer member, and the transfer member is compressed and deformed in the range of the transfer pressure smaller than the predetermined transfer pressure. In (Aspect B), by increasing the transfer pressure, the transfer member is compressed and the radius of the transfer member is shortened, so that the recording medium conveyance speed is reduced. It is possible to suppress the image magnification variation due to which the image is shortened by increasing the rotation speed of the transfer member, and improve the image magnification variation.
(Aspect C)
In (Aspect A), the transfer pressure changing unit transfers a first transfer pressure lower than a predetermined transfer pressure to a second transfer pressure higher than the predetermined transfer pressure and higher than the first transfer pressure. When the pressure is changed, the rotation speed of the transfer member is made slower than that at the first transfer pressure. The predetermined transfer pressure is a value of the transfer pressure at the compression limit of the transfer member, and the transfer member is distorted and deformed in the range of the transfer pressure higher than the predetermined transfer pressure. In (Aspect C), since the transfer pressure is increased until the compression limit of the transfer member is exceeded, the transfer member exceeds the compression limit, distortion occurs, and the circumference of the nip portion of the transfer member becomes long, so that the recording medium Transport speed increases. It is possible to suppress the image magnification variation caused by the lengthening of the image by slowing the rotation speed of the transfer member, and improve the image magnification variation.
(Aspect D)
In (Aspect A), the transfer pressure changing unit transfers a first transfer pressure higher than a predetermined transfer pressure to a second transfer pressure lower than the predetermined transfer pressure and lower than the first transfer pressure. When the pressure is changed, the rotation speed of the rotating member is made slower than that at the first transfer pressure. The predetermined transfer pressure is a value of the transfer pressure at the compression limit of the transfer member, and the transfer member is compressed and deformed in the range of the transfer pressure smaller than the predetermined transfer pressure. In (Aspect D), by reducing the transfer pressure, the compression of the transfer member is released and the radius of the transfer member is increased, so that the recording medium conveyance speed is increased. It is possible to suppress the image magnification variation caused by the lengthening of the image by slowing the rotation speed of the transfer member, and improve the image magnification variation.
(Aspect E)
In (Aspect A), the transfer pressure changing unit transfers a first transfer pressure higher than a predetermined transfer pressure to a second transfer pressure higher than the predetermined transfer pressure and lower than the first transfer pressure. When the pressure is changed, the rotation speed of the rotating member is made higher than that at the first transfer pressure. The predetermined transfer pressure is a value of the transfer pressure at the compression limit of the transfer member, and the transfer member is distorted and deformed in the range of the transfer pressure higher than the predetermined transfer pressure. In (Embodiment E), the transfer pressure increased to exceed the compression limit of the transfer member is reduced, so that the distortion that has occurred beyond the compression limit of the transfer member is reduced, and the transfer that is lengthened by the distortion is performed. By shortening the circumference of the nip portion of the member, the recording medium conveyance speed decreases. It is possible to suppress the image variation magnification, which shortens the image accordingly, by increasing the rotation speed of the transfer member, and improve the image magnification variation.
(Aspect F)
In any one of (Aspect B) to (Aspect E), the rotational speed of the transfer member when the transfer pressure is changed from the first transfer pressure to the second transfer pressure by the transfer pressure changing unit is It is changed according to the thickness of the recording medium. According to this, as described in the above embodiment, it is possible to more accurately correct the image magnification variation when the transfer pressure is changed according to the thickness of the recording medium.
(Aspect G)
In any one of (Aspect B) to (Aspect E), the rotational speed of the transfer member when the transfer pressure is changed from the first transfer pressure to the second transfer pressure by the transfer pressure changing unit is the recording speed. It is changed according to the density of the medium. According to this, as described in the above embodiment, it is possible to more accurately correct the image magnification variation when the transfer pressure is changed according to the density of the recording medium.
(Aspect H)
In any one of (Aspect A) to (Aspect G), an image carrier driving unit such as an intermediate transfer driving motor 40 for moving the surface of the image carrier, and a control unit 30 for controlling the image carrier driving unit. And an image carrier drive control unit, and a storage unit such as a memory 32 that stores a transfer member rotational speed setting value corresponding to the transfer pressure. Is adjustable independently by the image carrier drive control means and the transfer member drive control means, and the transfer member drive control means is stored in the storage means according to the magnitude of the transfer pressure. Further, the transfer member driving means is controlled so that the transfer member rotation speed setting value is obtained. According to this, as described in the above embodiment, it is possible to improve the image magnification variation.
(Aspect I)
In an image forming apparatus for forming an image on a recording material by transferring an image formed on the surface of an image carrier to a recording medium by using a transfer unit, the transfer unit includes (Aspect A) to (Aspect) The transfer device according to any one of H) is used. According to this, as described in the above embodiment, it is possible to suppress the image magnification variation when the transfer pressure of the image transferred onto the recording medium is changed, and perform good image formation.

１画像形成ユニット
２感光体
３帯電器
４露光装置
５現像器
６感光体クリーニングブレード
７中間転写ベルト
８駆動ローラ
９テンションローラ
１０一次転写ローラ
１１ベルトクリーニングブレード
１２固形潤滑剤
１３ブラシローラ
１４ブラシ対向ローラ
１５二次転写ローラ
１６二次転写対向ローラ
１７二次転写回転軸支持部材
１８二次転写加圧バネ
２０二次転写圧変更機構
２１カム部材
２１ａ回転軸
２２玉軸受
２３出力プーリー
２４入力プーリー
２５駆動伝達ベルト
２６ステッピングモータ
３０制御部
３１ＣＰＵ
３２メモリ
４０中間転写駆動モータ
５０二次転写ローラ駆動モータ
６０操作パネル
１００プリンタ
１２１用紙収容部
１２２給紙ピックアップローラ
１２３給紙搬送路
１２４レジストローラ対
１２５搬送ローラ対
１５０排紙トレイ
２００定着装置
３００二次転写ユニット 1 Image Forming Unit 2 Photoconductor 3 Charging Device 4 Exposure Device 5 Developing Device 6 Photoconductor Cleaning Blade 7 Intermediate Transfer Belt 8 Drive Roller 9 Tension Roller 10 Primary Transfer Roller 11 Belt Cleaning Blade 12 Solid Lubricant 13 Brush Roller 14 Brush Opposite Roller 15 Secondary Transfer Roller 16 Secondary Transfer Opposing Roller 17 Secondary Transfer Rotating Shaft Supporting Member 18 Secondary Transfer Pressing Spring 20 Secondary Transfer Pressure Changing Mechanism 21 Cam Member 21a Rotating Shaft 22 Ball Bearing 23 Output Pulley 24 Input Pulley 25 Drive Transmission belt 26 Stepping motor 30 Control unit 31 CPU
32 memory 40 intermediate transfer drive motor 50 secondary transfer roller drive motor 60 operation panel 100 printer 121 paper storage unit 122 paper feed pickup roller 123 paper feed transport path 124 registration roller pair 125 transport roller pair 150 discharge tray 200 fixing device 300 two Next transfer unit

特開２０１２−１２８２２９号公報JP 2012-128229 A

Claims

An image carrier whose surface is movable,
A rotatable transfer member that is in contact with the image carrier and forms a transfer unit that transfers an image from the image carrier to a recording medium;
Transfer member driving means for rotating the transfer member,
In a transfer device including a transfer pressure changing unit that changes the transfer pressure in the transfer unit,
Have a transfer member driving control means for controlling said transfer member drive means so as to change the rotational speed of the transfer member in accordance with the magnitude of the transfer pressure,
When the transfer pressure is changed by the transfer pressure changing unit from a first transfer pressure smaller than a predetermined transfer pressure to a second transfer pressure which is less than the predetermined transfer pressure and larger than the first transfer pressure. The transfer device is characterized in that the rotation speed of the transfer member is made higher than that at the first transfer pressure .

The transfer device according to claim 1 ,
By the transfer pressure changing means, wherein to a predetermined said from the first transfer pressure greater than transfer pressure predetermined transfer pressure or higher at a lower than the first transfer pressure second transfer pressure, when changing the transfer pressure In addition, the transfer device is characterized in that the rotation speed of the transfer member is made higher than that at the first transfer pressure .

In the transfer device of one according to 請 Motomeko 1 or 2,
Image carrier driving means for moving the image carrier on the surface;
Image carrier drive control means for controlling the image carrier drive means,
And a storage unit that stores a transfer member rotation speed setting value according to the transfer pressure,
Each of the image carrier surface moving speed and the transfer member rotation speed can be independently adjusted by the image carrier drive control means and the transfer member drive control means,
The transfer member drive control unit controls the transfer member drive unit so that the transfer member rotation speed setting value stored in the storage unit according to the magnitude of the transfer pressure is achieved. apparatus.

In an image forming apparatus for forming an image on the recording medium by transferring the image formed on the surface of the image carrier to a recording medium using a transfer unit,
Image forming apparatus, characterized in that as the transfer means, using a transfer device according to any one of claims 1 to 3.