JP2008145637A

JP2008145637A - Image forming apparatus

Info

Publication number: JP2008145637A
Application number: JP2006331444A
Authority: JP
Inventors: Yoshihiro Ando; 由博安藤
Original assignee: Kyocera Mita Corp
Current assignee: Kyocera Document Solutions Inc
Priority date: 2006-12-08
Filing date: 2006-12-08
Publication date: 2008-06-26

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that is free from image failure and conveyance failure by preventing a fluctuation in the speed of paper conveyance relative to an intermediate transfer body by a simple configuration. <P>SOLUTION: The linear velocity Vc of an intermediate transfer belt 8 is made lower than the linear velocity Vr of a pair of registration rollers 12b but made higher than the linear velocity Vt of a pair of fixing rollers 13. In addition, the linear velocity Vr of the pair of registration rollers 12b is set smaller than a value obtained by adding a difference between the longest and shortest conveyance distances a and b, respectively, from the transfer position to the fixing position to the linear velocity Vt of the pair of fixing rollers 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、画像形成装置に関し、特にモノクロ画像形成装置、及び中間転写体上にトナー像が順次形成されるカラー画像形成装置における記録媒体の搬送速度設定に関するものである。 The present invention relates to an image forming apparatus, and more particularly to a monochrome image forming apparatus and a recording medium conveyance speed setting in a color image forming apparatus in which toner images are sequentially formed on an intermediate transfer member.

従来、種々の画像形成装置が提案されているが、その中に、複数の画像形成部により各色のトナー像を順次重ね合わせてフルカラー画像を形成するタンデム型のカラー画像形成装置がある。さらに、タンデム型のカラー画像形成装置には、各画像形成部において像担持体上に形成されたトナー像を、無端状の搬送ベルトにより搬送されてくる記録媒体に順次転写する直接転写方式と、無端状の中間転写ベルト上にトナー像を順次重ね合わせた（一次転写した）後、記録媒体に一度に転写（二次転写）する中間転写方式とがある。 Conventionally, various image forming apparatuses have been proposed. Among them, there is a tandem type color image forming apparatus that forms a full color image by sequentially superimposing toner images of respective colors by a plurality of image forming units. Further, the tandem color image forming apparatus includes a direct transfer system that sequentially transfers a toner image formed on an image carrier in each image forming unit to a recording medium conveyed by an endless conveyance belt; There is an intermediate transfer system in which toner images are sequentially superimposed (primary transfer) on an endless intermediate transfer belt and then transferred (secondary transfer) to a recording medium at once.

図８は、従来の中間転写方式のカラー画像形成装置における二次転写機構周辺の拡大図である。中間転写ベルト８は、矢印方向に回転する駆動ローラ１１により図中時計回りに回動する。２０ａ、２０ｂはレジストローラ対１２ｂを通過した用紙Ｐを転写ニップ部に導くための転写ガイド部材であり、２１ａ、２１ｂはトナー像が転写された用紙Ｐを定着ニップ部に導くための定着ガイド部材である。 FIG. 8 is an enlarged view around a secondary transfer mechanism in a conventional intermediate transfer type color image forming apparatus. The intermediate transfer belt 8 is rotated clockwise in the figure by a driving roller 11 that rotates in the direction of the arrow. Reference numerals 20a and 20b denote transfer guide members for guiding the paper P that has passed through the registration roller pair 12b to the transfer nip portion. Reference numerals 21a and 21b denote fixing guide members for guiding the paper P to which the toner image has been transferred to the fixing nip portion. It is.

転写ローラ９は導電性のゴムローラで構成され、図示しないチャージャによりトナーと逆極性の所定の転写バイアスが印加される。この転写バイアスは転写ローラ９を介して中間転写ベルト８にも印加され、中間転写ベルト８上のトナー像を静電的に引き付けて用紙Ｐ上に転写する。転写ローラ９、駆動ローラ１１、レジストローラ対１２ｂ、及び定着ローラ対１３を矢印方向に回転させて用紙Ｐを転写ニップ部及び定着ニップ部に順次搬送しながら、中間転写ベルト８上に形成されたフルカラー画像の用紙Ｐ上への転写及び定着が行われる。 The transfer roller 9 is composed of a conductive rubber roller, and a predetermined transfer bias having a polarity opposite to that of the toner is applied by a charger (not shown). This transfer bias is also applied to the intermediate transfer belt 8 via the transfer roller 9, and the toner image on the intermediate transfer belt 8 is electrostatically attracted and transferred onto the paper P. The transfer roller 9, the drive roller 11, the registration roller pair 12 b, and the fixing roller pair 13 are rotated on the intermediate transfer belt 8 while sequentially rotating the paper P to the transfer nip portion and the fixing nip portion. Transfer and fixing of the full-color image onto the paper P is performed.

上述したようなカラー画像形成装置においては、二次転写を安定して行うために、中間転写ベルト８の線速と用紙Ｐの搬送速度を等しくする必要がある。そのため、レジストローラ対１２ｂ、中間転写ベルト８（＝転写ローラ９）、及び定着ローラ対１３の線速をそれぞれＶｒ、Ｖｃ、Ｖｔとすると、Ｖｒ＝Ｖｃ＝Ｖｔとなるように設定されていた。 In the color image forming apparatus as described above, it is necessary to make the linear speed of the intermediate transfer belt 8 equal to the conveyance speed of the paper P in order to stably perform the secondary transfer. Therefore, if the linear speeds of the registration roller pair 12b, the intermediate transfer belt 8 (= transfer roller 9), and the fixing roller pair 13 are Vr, Vc, and Vt, respectively, Vr = Vc = Vt.

しかし、装置の使用環境による中間転写ベルト８の周長や転写ローラ９、レジストローラ対１２ｂ、定着ローラ対１３の外径変化、用紙サイズや紙質のバラツキ等により、転写ニップ部における用紙搬送速度が変動するという問題点があった。二次転写時の用紙速度が変動した場合、転写ニップ部で中間転写ベルト８と用紙との摩擦が生じ、転写位置ずれや画像の擦れ等の転写不良が発生する。また、中間転写ベルト８と用紙との摩擦は中間転写ベルト８の回転にも影響を与えるため、二次転写中に中間転写ベルト８上に次のトナー像を形成する連続印刷時においてジッターによる横スジやピッチむら、色ずれ等が生じ、画像品質の低下の原因となる。 However, the sheet conveyance speed in the transfer nip portion is affected by the peripheral length of the intermediate transfer belt 8 depending on the use environment of the apparatus, the outer diameter change of the transfer roller 9, the registration roller pair 12b, the fixing roller pair 13, the variation in the sheet size and paper quality, and the like. There was a problem that it fluctuated. When the paper speed at the time of secondary transfer fluctuates, friction occurs between the intermediate transfer belt 8 and the paper at the transfer nip portion, and transfer defects such as transfer position deviation and image friction occur. In addition, since the friction between the intermediate transfer belt 8 and the paper also affects the rotation of the intermediate transfer belt 8, lateral printing due to jitter occurs during continuous printing in which the next toner image is formed on the intermediate transfer belt 8 during the secondary transfer. Streaks, pitch irregularities, color misregistration, and the like occur, causing a reduction in image quality.

そこで、転写ニップ部における用紙速度の変動を抑制して安定した転写を行う方法が提案されており、例えば特許文献１には、レジストローラ対、搬送ベルト、定着ローラ対による記録媒体（用紙）の搬送速度をそれぞれ検知するとともに、搬送ベルトによる搬送速度をレジストローラ対による搬送速度よりも所定速度だけ遅く、且つ定着ローラ対による搬送速度よりも所定速度だけ速くすることにより、画像転写部での記録媒体の引っ張りや弛みを抑制してトナー像の転写位置ずれを防止する方法が開示されている。 In view of this, there has been proposed a method of performing stable transfer while suppressing fluctuations in the paper speed at the transfer nip. For example, Patent Document 1 discloses a recording medium (paper) formed by a pair of registration rollers, a conveyance belt, and a fixing roller. Each of the conveyance speeds is detected, and the conveyance speed by the conveyance belt is slower than the conveyance speed by the registration roller pair by a predetermined speed, and is made faster than the conveyance speed by the pair of fixing rollers by a predetermined speed. A method for preventing a transfer position shift of a toner image by suppressing pulling or loosening of a medium is disclosed.

また、特許文献２には、各感光体ドラムの線速及び搬送ベルトの周速を検知するとともに、検知結果に基づいてＬＥＤの発光タイミングを制御することにより、各色のトナー像の色重ね精度を確保して色ずれを防止する方法が開示されている。 In Patent Document 2, the linear speed of each photosensitive drum and the peripheral speed of the conveyor belt are detected, and the light emission timing of the LED is controlled based on the detection result, thereby improving the color overlay accuracy of the toner images of the respective colors. A method for ensuring and preventing color misregistration is disclosed.

しかしながら、特許文献１及び２の方法では、レジストローラ、搬送ベルト及び定着ローラ対の速度をそれぞれ検知するためのセンサが必要となり、装置のコストアップに繋がる上、制御機構も複雑なものとなる。 However, the methods of Patent Documents 1 and 2 require sensors for detecting the speeds of the registration roller, the conveyance belt, and the fixing roller pair, respectively, leading to an increase in cost of the apparatus and a complicated control mechanism.

また、特許文献２の方法では、各色のトナー像を直接転写するタイプのカラー画像形成装置において感光体及び搬送ベルトの速度変動による色ずれは効果的に防止できるものの、中間転写方式のカラー画像形成装置に適用した場合、二次転写での中間転写体の線速に対する用紙速度の変動を抑制することはできなかった。 Further, according to the method of Patent Document 2, although color misregistration due to fluctuations in the speed of the photoreceptor and the conveyor belt can be effectively prevented in a color image forming apparatus of a type that directly transfers toner images of each color, color image formation by an intermediate transfer method is possible. When applied to the apparatus, fluctuations in the paper speed relative to the linear speed of the intermediate transfer member in the secondary transfer could not be suppressed.

なお、ここでは複数色のそれぞれに対応した複数の感光体（像担持体）を用い、中間転写体の送りに同期させてカラー画像を順次形成した後、記録媒体上に一度に転写する中間転写方式のカラー画像形成装置の二次転写機構における不具合について説明したが、転写位置ずれや画像の擦れに関しては、中間転写体を用いない直接転写方式の画像形成装置においても事情は同じである。
特開２００４−１５１３８３号公報特開平１０−３１３３８号公報 Here, a plurality of photoconductors (image carriers) corresponding to each of a plurality of colors are used, a color image is sequentially formed in synchronization with the feeding of the intermediate transfer member, and then transferred onto a recording medium at a time. Although the problems in the secondary transfer mechanism of the color image forming apparatus of the type have been described, the situation with respect to the transfer position shift and image rubbing is the same in the direct transfer type image forming apparatus that does not use the intermediate transfer member.
JP 2004-151383 A Japanese Patent Laid-Open No. 10-31338

本発明は、上記問題点に鑑み、中間転写体に対する用紙搬送速度の変動を簡単な構成により防止し、画像不良や搬送不良の発生しないカラー画像形成装置を提供することを目的とする。 In view of the above problems, an object of the present invention is to provide a color image forming apparatus that prevents fluctuations in the sheet conveyance speed with respect to the intermediate transfer member with a simple configuration and does not cause image defects or conveyance defects.

上記目的を達成するために本発明は、像担持体と現像装置とを含む複数の画像形成部と、像担持体に当接して回転駆動され前記画像形成部によりトナー像が順次積層される中間転写体と、該中間転写体に所定の圧力で当接して記録媒体を挿通させる転写ニップ部を形成するとともに前記中間転写体上に形成されたトナー像を記録媒体上に一度に転写する転写ローラと、前記転写ニップ部に所定のタイミングで記録媒体を給送するレジストローラ対と、前記転写ローラにより転写されたトナー像を記録媒体上に定着させる定着ローラ対と、を備えた画像形成装置において、前記レジストローラ対の線速をＶｒ、前記転写ニップ部における前記中間転写体の線速をＶｃ、前記定着ローラ対の線速をＶｔとしたとき、以下の条件式（１）を満たすことを特徴としている。
Ｖｔ＜Ｖｃ＜Ｖｒ＜Ｖｔ＋（ａ−ｂ）・・・（１）
ただし、
ａ：転写ニップ部から定着ローラ対のニップ部までの最長搬送距離、
ｂ：転写ニップ部から定着ローラ対のニップ部までの最短搬送距離、
である。 In order to achieve the above object, the present invention provides a plurality of image forming units including an image carrier and a developing device, and an intermediate in which toner images are sequentially laminated by the image forming unit in contact with the image carrier. A transfer roller that forms a transfer body and a transfer nip portion that contacts the intermediate transfer body with a predetermined pressure and allows the recording medium to pass therethrough and that transfers a toner image formed on the intermediate transfer body onto the recording medium at a time An image forming apparatus comprising: a registration roller pair that feeds the recording medium to the transfer nip portion at a predetermined timing; and a fixing roller pair that fixes the toner image transferred by the transfer roller onto the recording medium. When the linear velocity of the registration roller pair is Vr, the linear velocity of the intermediate transfer member at the transfer nip portion is Vc, and the linear velocity of the fixing roller pair is Vt, the following conditional expression (1) is satisfied. It is characterized in.
Vt <Vc <Vr <Vt + (ab) (1)
However,
a: The longest conveyance distance from the transfer nip portion to the nip portion of the fixing roller pair,
b: the shortest transport distance from the transfer nip portion to the nip portion of the fixing roller pair,
It is.

また本発明は、像担持体と現像装置とを含む画像形成部と、像担持体に所定の圧力で当接して記録媒体を挿通させる転写ニップ部を形成するとともに像担持体上に形成されたトナー像を記録媒体上に転写する転写ローラと、前記転写ニップ部に所定のタイミングで記録媒体を給送するレジストローラ対と、前記転写ローラにより転写されたトナー像を記録媒体上に定着させる定着ローラ対と、を備えた画像形成装置において、前記レジストローラ対の線速をＶｒ、前記転写ニップ部における像担持体の線速をＶｄ、前記定着ローラ対の線速をＶｔとしたとき、以下の条件式（２）を満たすことを特徴としている。
Ｖｔ＜Ｖｄ＜Ｖｒ＜Ｖｔ＋（ａ−ｂ）・・・（２）
ただし、
ａ：転写ニップ部から定着ローラ対のニップ部までの最長搬送距離、
ｂ：転写ニップ部から定着ローラ対のニップ部までの最短搬送距離、
である。 Further, the present invention forms an image forming portion including an image carrier and a developing device, a transfer nip portion that contacts the image carrier with a predetermined pressure and allows a recording medium to pass therethrough, and is formed on the image carrier. A transfer roller for transferring the toner image onto the recording medium, a pair of registration rollers for feeding the recording medium to the transfer nip portion at a predetermined timing, and a fixing for fixing the toner image transferred by the transfer roller onto the recording medium. In the image forming apparatus including the roller pair, when the linear velocity of the registration roller pair is Vr, the linear velocity of the image carrier in the transfer nip portion is Vd, and the linear velocity of the fixing roller pair is Vt, It satisfies the conditional expression (2).
Vt <Vd <Vr <Vt + (ab) (2)
However,
a: The longest conveyance distance from the transfer nip portion to the nip portion of the fixing roller pair,
b: the shortest transport distance from the transfer nip portion to the nip portion of the fixing roller pair,
It is.

本発明の第１の構成によれば、レジストローラの線速Ｖｒと、中間転写体の線速Ｖｃと、定着ローラ対の線速Ｖｔとが条件式（１）を満たすことにより、転写位置ずれや画像の擦れ等の転写不良、及び連続印刷時のピッチむらやジッターによる色ずれを抑制して高画質な画像形成を可能とし、且つジャムやスキュー等の発生し難い安定した用紙搬送も実現することができる。 According to the first configuration of the present invention, when the linear velocity Vr of the registration roller, the linear velocity Vc of the intermediate transfer member, and the linear velocity Vt of the fixing roller pair satisfy the conditional expression (1), the transfer position shift is performed. Suppresses transfer defects such as image rubbing and color misalignment due to pitch unevenness and jitter during continuous printing, enables high-quality image formation, and realizes stable paper transport that is unlikely to cause jamming or skewing. be able to.

また、本発明の第２の構成によれば、レジストローラの線速Ｖｒと、像担持体の線速Ｖｄと、定着ローラ対の線速Ｖｔとが条件式（２）を満たすことにより、転写位置ずれや画像の擦れ等の転写不良を抑制して高画質な画像形成を可能とし、且つジャムやスキュー等の発生し難い安定した用紙搬送も実現することができる。 Further, according to the second configuration of the present invention, the linear velocity Vr of the registration roller, the linear velocity Vd of the image carrier, and the linear velocity Vt of the fixing roller pair satisfy the conditional expression (2). Transfer defects such as misalignment and image rubbing can be suppressed, high-quality image formation can be performed, and stable paper conveyance that does not easily cause jamming or skewing can be realized.

以下、図面を参照しながら本発明の実施形態について説明する。図１は、本発明の第１実施形態に係る画像形成装置の構成を示す側面断面図である。画像形成装置（カラープリンタ）１００本体内には４つの画像形成部Ｐａ、Ｐｂ、Ｐｃ及びＰｄが、搬送方向上流側（図４では右側）から順に配設されている。これらの画像形成部Ｐａ〜Ｐｄは、異なる４色（シアン、マゼンタ、イエロー及びブラック）の画像に対応して設けられており、それぞれ帯電、露光、現像及び転写の各工程によりシアン、マゼンタ、イエロー及びブラックの画像を順次形成する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing the configuration of the image forming apparatus according to the first embodiment of the present invention. In the main body of the image forming apparatus (color printer) 100, four image forming portions Pa, Pb, Pc and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 4). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

この画像形成部Ｐａ〜Ｐｄには、各色の可視像（トナー像）を担持する感光体ドラム１ａ、１ｂ、１ｃ及び１ｄが配設されており、これらの感光体ドラム１ａ〜１ｄ上に形成されたトナー像が、駆動手段（図示せず）により図１において時計回りに回転し、各画像形成部に隣接して移動する中間転写ベルト８上に順次転写された後、転写ローラ９において用紙Ｐ上に一度に転写され、さらに、定着部７において用紙Ｐ上に定着された後、装置本体より排出される構成となっている。感光体ドラム１ａ〜１ｄを図１において反時計回りに回転させながら、各感光体ドラム１ａ〜１ｄに対する画像形成プロセスが実行される。 Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 that moves adjacent to each image forming unit. The image is transferred onto P at a time, and further fixed on the paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

トナー像が転写される用紙Ｐは、装置下部の用紙カセット１６内に収容されており、給紙ローラ１２ａ及びレジストローラ対１２ｂを介して転写ローラ９へと搬送される。中間転写ベルト８には誘電体樹脂製のシートが用いられ、その両端部を互いに重ね合わせて接合しエンドレス形状にしたベルトや、継ぎ目を有しない（シームレス）ベルトが用いられる。また、転写ローラ９の下流側には中間転写ベルト８表面に残存するトナーを除去するためのクリーニングブレード１９が配置されている。 The paper P to which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the transfer roller 9.

次に、画像形成部Ｐａ〜Ｐｄについて説明する。回転自在に配設された感光体ドラム１ａ〜１ｄの周囲及び下方には、感光体ドラム１ａ〜１ｄを帯電させる帯電器２ａ、２ｂ、２ｃ及び２ｄと、各感光体ドラム１ａ〜１ｄに画像情報を露光する露光ユニット４と、感光体ドラム１ａ〜１ｄ上にトナー像を形成する現像ユニット３ａ、３ｂ、３ｃ及び３ｄと、感光体ドラム１ａ〜１ｄ上に残留した現像剤（トナー）を除去するクリーニング部５ａ、５ｂ、５ｃ及び５ｄが設けられている。 Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing units 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

ユーザにより画像形成開始が入力されると、先ず、帯電器２ａ〜２ｄによって感光体ドラム１ａ〜１ｄの表面を一様に帯電させ、次いで露光ユニット４によって光照射し、各感光体ドラム１ａ〜１ｄ上に画像信号に応じた静電潜像を形成する。現像ユニット３ａ〜３ｄには、それぞれシアン、マゼンタ、イエロー及びブラックの各色のトナーが補給装置（図示せず）によって所定量充填されている。このトナーは、現像ユニット３ａ〜３ｄにより感光体ドラム１ａ〜１ｄ上に供給され、静電的に付着することにより、露光ユニット４からの露光により形成された静電潜像に応じたトナー像が形成される。 When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing units 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing units 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

そして、中間転写ベルト８に所定の転写電圧で電界が付与された後、中間転写ローラ６ａ〜６ｄにより感光体ドラム１ａ〜１ｄ上のシアン、マゼンタ、イエロー、及びブラックのトナー像が中間転写ベルト８上に転写（一次転写）される。これらの４色の画像は、所定のフルカラー画像形成のために予め定められた所定の位置関係をもって形成される。その後、引き続き行われる新たな静電潜像の形成に備え、感光体ドラム１ａ〜１ｄの表面に残留したトナーがクリーニング部５ａ〜５ｄにより除去される。 After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transferred (primary transfer) on top. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

中間転写ベルト８は、上流側のテンションローラ１０と下流側の駆動ローラ１１とに掛け渡されており、駆動モータ（図示せず）による駆動ローラ１１の回転に伴い中間転写ベルト８が時計回りに回転を開始すると、用紙Ｐがレジストローラ１２ｂから所定のタイミングで中間転写ベルト８に隣接して設けられた転写ローラ９へ搬送され、中間転写ベルト８とのニップ部（転写ニップ部）においてフルカラー画像が転写（二次転写）される。トナー像が転写された用紙Ｐは定着部７へと搬送される。 The intermediate transfer belt 8 is stretched between an upstream tension roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the sheet P is conveyed from the registration roller 12b to the transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is formed at the nip portion (transfer nip portion) with the intermediate transfer belt 8. Is transferred (secondary transfer). The paper P on which the toner image is transferred is conveyed to the fixing unit 7.

定着部７に搬送された用紙Ｐは、定着ローラ対１３のニップ部（定着ニップ部）を通過する際に加熱及び加圧されてトナー像が用紙Ｐの表面に定着され、所定のフルカラー画像が形成される。フルカラー画像が形成された用紙Ｐは、複数方向に分岐した分岐部１４によって搬送方向が振り分けられる。用紙Ｐの片面のみに画像を形成する場合は、そのまま排出ローラ１５によって排出トレイ１７に排出される。 The sheet P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13 to fix the toner image on the surface of the sheet P, and a predetermined full-color image is formed. It is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

一方、用紙Ｐの両面に画像を形成する場合は、定着部７を通過した用紙Ｐの一部を一旦排出ローラ１５から装置外部にまで突出させる。その後、用紙Ｐは排出ローラ１５を逆回転させることにより分岐部１４で用紙搬送路１８に振り分けられ、画像面を反転させた状態で転写ローラ９に再搬送される。そして、中間転写ベルト８上に形成された次の画像が転写ローラ９により用紙Ｐの画像が形成されていない面に転写され、定着部７に搬送されてトナー像が定着された後、排出トレイ１７に排出される。 On the other hand, when forming images on both sides of the paper P, a part of the paper P that has passed through the fixing unit 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the transfer roller 9 with the image surface reversed. Then, the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P where the image is not formed by the transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. 17 is discharged.

図２は、第１実施形態の画像形成装置における二次転写機構周辺の構成を示す拡大図であり、図３は図２における転写−定着間の拡大図である。図１及び従来例の図８と共通する部分には同一の符号を付して説明を省略する。 FIG. 2 is an enlarged view showing a configuration around the secondary transfer mechanism in the image forming apparatus of the first embodiment, and FIG. 3 is an enlarged view between the transfer and fixing in FIG. Portions common to FIG. 1 and FIG. 8 of the conventional example are denoted by the same reference numerals and description thereof is omitted.

図２において、レジストローラ対１２ｂの線速Ｖｒが中間転写ベルト８の線速Ｖｃ以下である場合、レジスト−転写間で用紙Ｐが引っ張られ、定着ローラ対１３の線速Ｖｔが中間転写ベルト８の線速Ｖｃ以上である場合、転写−定着間で用紙Ｐが引っ張られてしまい、いずれも中間転写ベルト８と用紙Ｐとの擦れが発生して転写位置ずれや擦れ等の転写不良の原因となる。また、連続画像形成時においては中間転写ベルト８の速度変動によりピッチむらやジッターが発生して色ずれの原因にもなる。そこで、本発明においては、中間転写ベルト８の線速Ｖｃが、レジストローラ対１２ｂの線速Ｖｒよりも小さく、且つ定着ローラ対１３の線速Ｖｔよりも大きくなるように設定されている。 In FIG. 2, when the linear velocity Vr of the registration roller pair 12 b is equal to or lower than the linear velocity Vc of the intermediate transfer belt 8, the sheet P is pulled between registration and transfer, and the linear velocity Vt of the fixing roller pair 13 is changed to the intermediate transfer belt 8. When the linear velocity Vc is equal to or higher than the linear velocity Vc, the paper P is pulled between the transfer and fixing, and both of them cause friction between the intermediate transfer belt 8 and the paper P and cause transfer defects such as transfer position deviation and friction. Become. Further, during continuous image formation, the unevenness of the pitch and the jitter are generated due to the speed fluctuation of the intermediate transfer belt 8, which may cause color misregistration. Therefore, in the present invention, the linear velocity Vc of the intermediate transfer belt 8 is set to be smaller than the linear velocity Vr of the registration roller pair 12 b and larger than the linear velocity Vt of the fixing roller pair 13.

また、定着ガイド部材２１ａは定着ガイド部材２１ｂに対し凹状に湾曲しており、用紙Ｐの弛みをある程度吸収可能となっている。しかし、レジストローラ対１２ｂの線速Ｖｒが定着ローラ対１３の線速Ｖｔよりも所定速度以上大きい場合、レジスト−転写間で用紙Ｐが定着ガイド部材２１ａ、２１ｂの弛み許容範囲を超えて弛んでしまい、シワや転写不良が発生する。また、用紙のスキューやジャムも発生し易くなる。 Further, the fixing guide member 21a is concavely curved with respect to the fixing guide member 21b, and can absorb the slackness of the paper P to some extent. However, when the linear velocity Vr of the registration roller pair 12b is larger than the linear velocity Vt of the fixing roller pair 13 by a predetermined speed or more, the sheet P is slackened beyond the allowable range of looseness of the fixing guide members 21a and 21b between registration and transfer. As a result, wrinkles and transfer defects occur. Also, paper skew and jamming are likely to occur.

ここで、図３に示すように、転写ニップ部Ｎ１と定着ニップ部Ｎ２との間を用紙Ｐが通過する際、用紙Ｐが定着ガイド部材２０ａに沿って最大量弛んだ状態では、用紙Ｐの搬送距離は転写ニップ部Ｎ１から定着ニップ部Ｎ２までの最長距離ａ（図の破線）となる。また、用紙Ｐが引っ張られた状態では、用紙Ｐの搬送距離は転写ニップ部Ｎ１から定着ニップ部Ｎ２までの最短距離ｂ（図の実線）となる。つまり、用紙Ｐの弛み許容範囲は最長距離ａから最短距離ｂまでの範囲である。 Here, as shown in FIG. 3, when the sheet P passes through between the transfer nip portion N1 and the fixing nip portion N2, the sheet P is in a state where the sheet P is slackened along the fixing guide member 20a, and the sheet P The transport distance is the longest distance a (broken line in the figure) from the transfer nip portion N1 to the fixing nip portion N2. When the paper P is pulled, the transport distance of the paper P is the shortest distance b (solid line in the figure) from the transfer nip portion N1 to the fixing nip portion N2. That is, the slack allowable range of the paper P is a range from the longest distance a to the shortest distance b.

従って、レジストローラ対１２ｂの線速Ｖｒを、定着ローラ対１３の線速Ｖｔに転写−定着間の最長搬送距離ａと最短搬送距離ｂの差を加えた値よりも小さくなるように設定しておけば、用紙Ｐは定着ローラ対１３に引っ張られることなく、且つ許容範囲内の弛みをもって転写−定着間を通過可能となる。即ち、Ｖｒ、Ｖｃ及びＶｔの関係をまとめると、条件式（１）のようになる。
Ｖｔ＜Ｖｃ＜Ｖｒ＜Ｖｔ＋（ａ−ｂ）・・・（１） Accordingly, the linear velocity Vr of the registration roller pair 12b is set to be smaller than a value obtained by adding the difference between the longest conveyance distance a and the shortest conveyance distance b between the transfer and fixing to the linear velocity Vt of the fixing roller pair 13. In this case, the paper P can pass between the transfer and fixing without being pulled by the fixing roller pair 13 and with a slack within an allowable range. That is, the relationship between Vr, Vc, and Vt is summarized as conditional expression (1).
Vt <Vc <Vr <Vt + (ab) (1)

Ｖｒ、Ｖｃ、及びＶｔを上記条件式（１）の範囲に設定することにより、転写不良やジッターによる色ずれを低減して高画質な画像形成を可能とし、同時にジャムやスキュー等の発生し難い安定した用紙搬送も実現する。Ｖｒ、Ｖｃ、及びＶｔの設定は、中間転写ベルト８の周長や、テンションローラ１０、駆動ローラ１１レジストローラ対１２ｂ、定着ローラ対１３の外径の設定により行うか、或いはそれらを回転駆動するモータの回転速度の調整により行われる。 By setting Vr, Vc, and Vt within the range of the conditional expression (1), it is possible to reduce the color misregistration due to transfer failure and jitter, and to form a high-quality image, and at the same time, it is difficult for jamming and skew to occur. Stable paper conveyance is also realized. Vr, Vc and Vt are set by setting the circumference of the intermediate transfer belt 8, the outer diameter of the tension roller 10, the driving roller 11, the resist roller pair 12b, and the fixing roller pair 13, or rotationally driving them. This is done by adjusting the rotation speed of the motor.

ここで、二次転写時における用紙Ｐの搬送速度は、転写ローラ９の外径や転写ニップ部Ｎ２における中間転写ベルト８の曲率等、画像形成装置の仕様によって決まる固有値である。そして、用紙Ｐの弛み許容量の最大値も、例えば搬送速度の数％というように装置毎に個別に設定される。従って、定着ガイド部材２０ａは、内面の長さ、即ち最長搬送距離ａが、搬送速度から算出される弛み許容量の最大値を超えない範囲となるように設計される。 Here, the conveyance speed of the paper P at the time of secondary transfer is an eigenvalue determined by the specifications of the image forming apparatus such as the outer diameter of the transfer roller 9 and the curvature of the intermediate transfer belt 8 at the transfer nip portion N2. The maximum allowable slack amount of the paper P is also set individually for each apparatus, for example, several percent of the conveyance speed. Therefore, the fixing guide member 20a is designed so that the length of the inner surface, that is, the longest transport distance a does not exceed the maximum value of the allowable slack amount calculated from the transport speed.

なお、上記実施形態では中間転写体として中間転写ベルト８を用いているが、図４に示すように、線速Ｖｃで回動する中間転写ドラム２３を用いることもできる。この場合にも、条件式（１）を満たすようにＶｒ、Ｖｃ及びＶｔを設定することにより、転写位置ずれや画像の擦れ等の転写不良を効果的に抑制できる。中間転写ドラム２３としては、例えば発泡ウレタンに導電性ゴムを被覆したものが用いられる。 In the above embodiment, the intermediate transfer belt 8 is used as the intermediate transfer member. However, as shown in FIG. 4, an intermediate transfer drum 23 that rotates at a linear velocity Vc can also be used. Also in this case, by setting Vr, Vc, and Vt so as to satisfy the conditional expression (1), transfer defects such as transfer position shift and image rubbing can be effectively suppressed. As the intermediate transfer drum 23, for example, urethane foam coated with conductive rubber is used.

図５は、本発明の第２実施形態に係る画像形成装置の側面断面図である。第１実施形態の図１と共通する部分には同一の符号を付して説明を省略する。図５において、画像形成装置１００はモノクロプリンタであり、ブラックの画像を形成する画像形成部Ｐｄのみを備えている。また、中間転写ベルト８や中間転写ドラム２３等の中間転写体は設けられておらず、感光体ドラム１ｄ上に形成されたトナー像は、転写ローラ９により用紙カセット１６から搬送される用紙Ｐ上に直接転写される。 FIG. 5 is a side sectional view of an image forming apparatus according to the second embodiment of the present invention. Portions common to FIG. 1 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In FIG. 5, the image forming apparatus 100 is a monochrome printer, and includes only an image forming unit Pd that forms a black image. Further, no intermediate transfer member such as the intermediate transfer belt 8 or the intermediate transfer drum 23 is provided, and the toner image formed on the photosensitive drum 1d is transferred onto the paper P conveyed from the paper cassette 16 by the transfer roller 9. Directly transcribed into

本実施形態においても、感光体ドラム１ｄの線速Ｖｄが、レジストローラ対１２ｂの線速Ｖｒよりも小さく、且つ定着ローラ対１３の線速Ｖｔよりも大きくなるように設定するとともに、レジストローラ対１２ｂの線速Ｖｒを、定着ローラ対１３の線速Ｖｔに転写−定着間の最長搬送距離ａと最短搬送距離ｂの差を加えた値よりも小さくなるように、即ち、Ｖｒ、Ｖｄ及びＶｔが条件式（２）
Ｖｔ＜Ｖｄ＜Ｖｒ＜Ｖｔ＋（ａ−ｂ）・・・（２）
を満たすように設定しておけば、第１実施形態と同様に転写位置ずれや画像の擦れ等の転写不良を効果的に抑制できる。Ｖｒ、Ｖｄ、Ｖｔ、及び最長搬送距離ａの設定方法については第１実施形態と同様であるため説明を省略する。 Also in the present embodiment, the linear velocity Vd of the photosensitive drum 1d is set to be smaller than the linear velocity Vr of the registration roller pair 12b and larger than the linear velocity Vt of the fixing roller pair 13, and the registration roller pair The linear velocity Vr of 12b is made smaller than the value obtained by adding the difference between the longest conveyance distance a and the shortest conveyance distance b between the transfer and fixing to the linear velocity Vt of the fixing roller pair 13, that is, Vr, Vd and Vt. Is conditional expression (2)
Vt <Vd <Vr <Vt + (ab) (2)
If it is set so as to satisfy, transfer defects such as transfer position shift and image rubbing can be effectively suppressed as in the first embodiment. The method for setting Vr, Vd, Vt, and the longest transport distance a is the same as that in the first embodiment, and a description thereof will be omitted.

その他、本発明は上記実施形態に限定されず、本発明の趣旨を逸脱しない範囲で種々の変更が可能である。例えば第１実施形態では、感光体ドラム及び現像装置を備えた複数の画像形成部を中間転写体に沿って配置したタンデム方式のカラー画像形成装置を例に挙げて説明したが、現像ユニット内に複数の現像カートリッジを備え、現像ユニットを回転させて感光体ドラムに対向する現像カートリッジを切り換えるロータリー式のカラー画像形成装置や、感光体ドラムの周囲に４つの現像装置が固定されたシングルドラム式のカラー画像形成装置にも全く同様に適用できる。 In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the first embodiment, a tandem color image forming apparatus in which a plurality of image forming units including a photosensitive drum and a developing device are arranged along an intermediate transfer member has been described as an example. A rotary type color image forming apparatus having a plurality of developing cartridges and switching a developing cartridge facing the photosensitive drum by rotating the developing unit, or a single drum type in which four developing devices are fixed around the photosensitive drum The present invention can be applied to a color image forming apparatus in exactly the same manner.

また、上記実施形態ではカラー及びモノクロプリンタについて説明したが、本発明はプリンタに限らず、複写機やファクシミリ等、電子写真プロセスを用いる種々の画像形成装置に適用できるのはもちろんである。 In the above-described embodiment, the color and monochrome printers have been described. However, the present invention is not limited to the printer, and can be applied to various image forming apparatuses using an electrophotographic process such as a copying machine and a facsimile.

図１に示した中間転写式のカラー画像形成装置を用いて画像形成を行った場合の、レジストローラ対、中間転写ベルト及び定着ローラ対の線速と色ずれ及び画像伸縮との関係を調査した。試験条件としては、転写ニップ部から定着ニップ部までの最長搬送距離ａを８９ｍｍ、最短搬送距離ｂを８４ｍｍ、定着ローラ対の線速Ｖｔを１４８ｍｍ／ｓｅｃ、中間転写ベルトの線速Ｖｃを１４９ｍｍ／ｓｅｃに固定した。そして、レジストローラ対の線速Ｖｒを１４７ｍｍ／ｓｅｃから１５５ｍｍ／ｓｅｃまで、１ｍｍ／ｓｅｃずつ段階的に変化させてテスト画像を形成して色ずれ及び画像伸縮の有無を評価した。評価方法としては、形成されたテスト画像を目視により観察し、色ずれ量が１００μｍ以下、画像伸縮量が±２ｍｍ以内を適正範囲とした。結果を図６及び図７に示す。 When the image was formed using the intermediate transfer type color image forming apparatus shown in FIG. 1, the relationship between the linear velocity of the registration roller pair, the intermediate transfer belt and the fixing roller pair, the color shift, and the image expansion and contraction was investigated. . As test conditions, the longest conveyance distance a from the transfer nip portion to the fixing nip portion is 89 mm, the shortest conveyance distance b is 84 mm, the linear velocity Vt of the fixing roller pair is 148 mm / sec, and the linear velocity Vc of the intermediate transfer belt is 149 mm / sec. It was fixed to sec. Then, the linear velocity Vr of the registration roller pair was changed stepwise by 1 mm / sec from 147 mm / sec to 155 mm / sec to form a test image, and the presence / absence of color shift and image expansion / contraction was evaluated. As an evaluation method, the formed test image was visually observed, and the color misregistration amount was 100 μm or less and the image expansion / contraction amount was within ± 2 mm. The results are shown in FIGS.

図６から明らかなように、Ｖｒが１５０〜１５２ｍｍ／ｓｅｃの範囲、即ちＶｒ、Ｖｃ、及びＶｔの関係が条件式（１）を満たす場合は色ずれ量は１００μｍ以下であり、適正範囲内となっていた。一方、Ｖｒが１５３〜１５５ｍｍ／ｓｅｃの範囲、即ちＶｒがＶｔ＋（ａ−ｂ）を超える場合は、転写−定着間の用紙の撓みが最長搬送距離ａ以上となるため、適正範囲を超える１４０〜１８０μｍの色ずれが観察された。逆に、Ｖｒが１４７〜１４９ｍｍ／ｓｅｃの範囲、即ちＶｒがＶｃよりも小さい場合は、転写−定着間で用紙が引っ張られるため、適正範囲を超える１２０〜１６０μｍの色ずれが観察された。 As is apparent from FIG. 6, when the Vr is in the range of 150 to 152 mm / sec, that is, when the relationship between Vr, Vc, and Vt satisfies the conditional expression (1), the color misregistration amount is 100 μm or less, It was. On the other hand, when Vr is in the range of 153 to 155 mm / sec, that is, when Vr exceeds Vt + (a−b), the deflection of the sheet between the transfer and fixing becomes longer than the longest conveyance distance a, and thus exceeds 140 to exceed the appropriate range. A color shift of 180 μm was observed. On the contrary, when Vr is in the range of 147 to 149 mm / sec, that is, when Vr is smaller than Vc, the sheet is pulled between the transfer and fixing, and thus a color shift of 120 to 160 μm exceeding the appropriate range was observed.

また、図７から明らかなように、Ｖｒ、Ｖｃ、及びＶｔの関係が条件式（１）を満たす場合は画像伸縮量も−１ｍｍ、１ｍｍ、及び２．５ｍｍであり、適正範囲である±２ｍｍ以内にほぼ収まっていた。一方、ＶｒがＶｔ＋（ａ−ｂ）を超える場合は適正範囲を超える３．５ｍｍ以上の画像の伸びが観察された。逆に、ＶｒがＶｃよりも小さい場合は適正範囲を超える−３ｍｍ以上の画像の縮みが観察された。 As is clear from FIG. 7, when the relationship between Vr, Vc, and Vt satisfies the conditional expression (1), the image expansion and contraction amounts are also −1 mm, 1 mm, and 2.5 mm, which is an appropriate range of ± 2 mm. Was almost within. On the other hand, when Vr exceeds Vt + (a−b), an image elongation of 3.5 mm or more exceeding the appropriate range was observed. On the contrary, when Vr is smaller than Vc, shrinkage of an image of −3 mm or more exceeding the proper range was observed.

以上の結果より、レジストローラ対の線速Ｖｒ、中間転写ベルトの線速Ｖｃ、定着ローラ対の線速Ｖｔが、Ｖｔ＜Ｖｃ＜Ｖｒ＜Ｖｔ＋（ａ−ｂ）の関係を満たすことにより、色ずれ及び画像伸縮を効果的に防止できることが確認された。なお、ここには記載しないが、図５に示すような直接転写方式の画像形成装置を用いて条件式（２）を満たすようにレジストローラ対の線速Ｖｒ、像担持体の線速Ｖｄ、定着ローラ対の線速Ｖｔを設定することにより、同様に画像伸縮を防止する効果が得られることが確認されている。 From the above results, the linear velocity Vr of the registration roller pair, the linear velocity Vc of the intermediate transfer belt, and the linear velocity Vt of the fixing roller pair satisfy the relationship of Vt <Vc <Vr <Vt + (ab). It was confirmed that displacement and image expansion / contraction can be effectively prevented. Although not described here, the linear velocity Vr of the registration roller pair, the linear velocity Vd of the image carrier, and the linear velocity Vd of the image carrier so as to satisfy the conditional expression (2) using an image forming apparatus of a direct transfer type as shown in FIG. It has been confirmed that the effect of preventing image expansion and contraction can be obtained by setting the linear velocity Vt of the fixing roller pair.

本発明は、像担持体と現像装置とを含む複数の画像形成部と、像担持体に当接して回転駆動され画像形成部によりトナー像が順次積層される中間転写体と、該中間転写体に所定の圧力で当接して記録媒体を挿通させる転写ニップ部を形成するとともに中間転写体上に形成されたトナー像を記録媒体上に一度に転写する転写ローラと、転写ニップ部に所定のタイミングで記録媒体を給送するレジストローラ対と、転写ローラにより転写されたトナー像を記録媒体上に定着させる定着ローラ対と、を備えた画像形成装置において、レジストローラ対の線速をＶｒ、転写ニップ部における中間転写体の線速をＶｃ、定着ローラ対の線速をＶｔとしたとき、Ｖｔ、Ｖｃ、Ｖｒの順に大きく、且つ転写ニップ部から定着ローラ対のニップ部までの最長搬送距離をａ、最短搬送距離をｂとしたとき、ＶｒがＶｔ＋（ａ−ｂ）を超えないこととする。 The present invention relates to a plurality of image forming units including an image carrier and a developing device, an intermediate transfer member in which toner images are sequentially stacked by the image forming unit in contact with the image carrier, and the intermediate transfer member. A transfer nip that forms a transfer nip that contacts the recording medium with a predetermined pressure and transfers a toner image formed on the intermediate transfer member onto the recording medium at a time, and a predetermined timing at the transfer nip. In the image forming apparatus including the registration roller pair for feeding the recording medium and the fixing roller pair for fixing the toner image transferred by the transfer roller on the recording medium, the linear velocity of the registration roller pair is Vr, the transfer When the linear velocity of the intermediate transfer member at the nip portion is Vc and the linear velocity of the fixing roller pair is Vt, the longest conveyance from the transfer nip portion to the nip portion of the fixing roller pair is the largest in order of Vt, Vc, Vr. When the distance was a, the shortest transport distance is b, and the Vr does not exceed Vt + (a-b).

また本発明は、像担持体と現像装置とを含む画像形成部と、像担持体に所定の圧力で当接して記録媒体を挿通させる転写ニップ部を形成するとともに像担持体上に形成されたトナー像を記録媒体上に転写する転写ローラと、転写ニップ部に所定のタイミングで記録媒体を給送するレジストローラ対と、転写ローラにより転写されたトナー像を記録媒体上に定着させる定着ローラ対と、を備えた画像形成装置において、レジストローラ対の線速をＶｒ、転写ニップ部における像担持体の線速をＶｄ、定着ローラ対の線速をＶｔとしたとき、Ｖｔ、Ｖｄ、Ｖｒの順に大きく、且つ転写ニップ部から定着ローラ対のニップ部までの最長搬送距離をａ、最短搬送距離をｂとしたとき、ＶｒがＶｔ＋（ａ−ｂ）を超えないこととする。 Further, the present invention forms an image forming portion including an image carrier and a developing device, a transfer nip portion that contacts the image carrier with a predetermined pressure and allows a recording medium to pass therethrough, and is formed on the image carrier. A transfer roller for transferring the toner image onto the recording medium, a pair of registration rollers for feeding the recording medium to the transfer nip portion at a predetermined timing, and a pair of fixing rollers for fixing the toner image transferred by the transfer roller onto the recording medium And Vt, the linear velocity of the image carrier at the transfer nip portion is Vd, and the linear velocity of the fixing roller pair is Vt, Vt, Vd, Vr. It is assumed that Vr does not exceed Vt + (ab), where a is the longest transport distance from the transfer nip portion to the nip portion of the fixing roller pair, and b is the shortest transport distance.

これにより、転写ニップ部における転写位置ずれや用紙の擦れ等の転写不良を低減して高画質な画像を形成し、且つジャムやスキュー等の発生し難い安定した用紙搬送も実現する画像形成装置の提供が可能となる。また、中間転写ベルトを用いる中間転写方式のカラー画像形成装置においては、連続印刷時におけるピッチむらやジッターによる色ずれの発生も抑制できる。 As a result, an image forming apparatus capable of forming a high-quality image by reducing transfer defects such as a transfer position shift and paper rubbing in the transfer nip portion, and realizing stable paper conveyance that is unlikely to cause a jam or a skew. Provision is possible. In addition, in an intermediate transfer type color image forming apparatus using an intermediate transfer belt, occurrence of color misregistration due to pitch unevenness and jitter during continuous printing can be suppressed.

は、本発明の第１実施形態に係るカラー画像形成装置の構成を示す側面断面図である。These are side surface sectional drawings which show the structure of the color image forming apparatus which concerns on 1st Embodiment of this invention. は、第１実施形態の画像形成装置の二次転写機構周辺を示す拡大図である。FIG. 2 is an enlarged view showing the periphery of a secondary transfer mechanism of the image forming apparatus according to the first embodiment. は、図２における転写−定着間の構成を示す拡大図である。FIG. 3 is an enlarged view showing a configuration between transfer and fixing in FIG. 2. は、第１実施形態の画像形成装置において、中間転写ドラムを用いた構成を示す二次転写機構周辺の拡大図である。FIG. 2 is an enlarged view of a periphery of a secondary transfer mechanism showing a configuration using an intermediate transfer drum in the image forming apparatus of the first embodiment. は、本発明の第２実施形態に係るモノクロ画像形成装置の構成を示す側面断面図である。These are side surface sectional drawings which show the structure of the monochrome image forming apparatus which concerns on 2nd Embodiment of this invention. は、実施例においてレジストローラ対の線速を変化させた場合の色ずれ量との関係を示すグラフである。These are graphs showing the relationship with the amount of color misregistration when the linear velocity of the registration roller pair is changed in the embodiment. は、実施例においてレジストローラ対の線速を変化させた場合の画像伸縮量との関係を示すグラフである。These are graphs showing the relationship with the amount of image expansion and contraction when the linear velocity of the registration roller pair is changed in the embodiment. は、従来の中間転写方式のカラー画像形成装置における二次転写機構周辺の構成を示す拡大図である。FIG. 5 is an enlarged view showing a configuration around a secondary transfer mechanism in a conventional intermediate transfer type color image forming apparatus.

Explanation of symbols

１ａ〜１ｄ感光体ドラム（像担持体）
２ａ〜２ｄ帯電器
３ａ〜３ｄ現像ユニット
４露光ユニット
５ａ〜５ｄクリーニング部
６ａ〜６ｄ中間転写ローラ
８中間転写ベルト（中間転写体）
７定着部
９転写ローラ
１２ｂレジストローラ対
１３定着ローラ対
１６用紙カセット
１９ベルトクリーニングブレード
２０ａ、２０ｂ転写ガイド部材
２１ａ、２０ｂ定着ガイド部材
２３中間転写ドラム（中間転写体）
１００画像形成装置
Ｐａ〜Ｐｄ画像形成部
Ｎ１転写ニップ部
Ｎ２定着ニップ部 1a to 1d Photosensitive drum (image carrier)
2a to 2d Charger 3a to 3d Developing unit 4 Exposure unit 5a to 5d Cleaning unit 6a to 6d Intermediate transfer roller 8 Intermediate transfer belt (intermediate transfer member)
DESCRIPTION OF SYMBOLS 7 Fixing part 9 Transfer roller 12b Registration roller pair 13 Fixing roller pair 16 Paper cassette 19 Belt cleaning blade 20a, 20b Transfer guide member 21a, 20b Fixing guide member 23 Intermediate transfer drum (intermediate transfer body)
100 Image forming apparatus Pa to Pd Image forming portion N1 Transfer nip portion N2 Fixing nip portion

Claims

A plurality of image forming units including an image bearing member and a developing device; an intermediate transfer member that is rotationally driven in contact with the image bearing member and in which toner images are sequentially stacked by the image forming unit; A transfer nip is formed to contact with pressure and allow the recording medium to pass therethrough, and a toner image formed on the intermediate transfer member is transferred onto the recording medium at a time, and at a predetermined timing to the transfer nip. In an image forming apparatus comprising: a registration roller pair for feeding a recording medium; and a fixing roller pair for fixing the toner image transferred by the transfer roller on the recording medium.
When the linear velocity of the registration roller pair is Vr, the linear velocity of the intermediate transfer member at the transfer nip portion is Vc, and the linear velocity of the fixing roller pair is Vt, the following conditional expression (1) is satisfied. An image forming apparatus.
Vt <Vc <Vr <Vt + (ab) (1)
However,
a: The longest conveyance distance from the transfer nip portion to the nip portion of the fixing roller pair,
b: the shortest transport distance from the transfer nip portion to the nip portion of the fixing roller pair,
It is.

An image forming unit including an image carrier and a developing device, and a transfer nip portion that is brought into contact with the image carrier with a predetermined pressure to allow the recording medium to pass therethrough and a toner image formed on the image carrier are recorded on the recording medium A transfer roller for transferring up, a registration roller pair for feeding a recording medium to the transfer nip portion at a predetermined timing, and a fixing roller pair for fixing the toner image transferred by the transfer roller onto the recording medium. In the provided image forming apparatus,
When the linear velocity of the registration roller pair is Vr, the linear velocity of the image carrier in the transfer nip portion is Vd, and the linear velocity of the fixing roller pair is Vt, the following conditional expression (2) is satisfied: Image forming apparatus.
Vt <Vd <Vr <Vt + (ab) (2)
However,
a: The longest conveyance distance from the transfer nip portion to the nip portion of the fixing roller pair,
b: the shortest transport distance from the transfer nip portion to the nip portion of the fixing roller pair,
It is.