JP2014224941A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device configured to reduce, in a balanced manner, shock jitter to be generated when a tip of a recording medium enters a secondary transfer nip, shock jitter to be generated when a rear end of the recording medium exits the secondary transfer nip, and impact to be generated when a separated secondary transfer roller comes into contact with a secondary transfer opposite roller via an intermediate transfer belt without reducing productivity in passing the recording medium, and to provide an image forming apparatus.SOLUTION: A distance between the shafts of a secondary transfer roller 19 and a secondary transfer opposite roller 11 to be generated when a tip of a recording medium P is supplied into a secondary transfer nip is controlled to be smaller than a distance between the shafts to be generated when a rear end of the recording medium P is discharged from the secondary transfer nip.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a transfer device installed therein, and in particular, an intermediate transfer belt is installed. The present invention relates to a transfer device and an image forming apparatus.

Conventionally, in an image forming apparatus such as a copying machine or a printer, a tandem type color image forming apparatus provided with an intermediate transfer belt (transfer apparatus) is known (for example, see Patent Document 1).
Specifically, four photosensitive drums (image carriers) are arranged side by side so as to face the intermediate transfer belt (belt member). On these four photosensitive drums, black (black), yellow, magenta, and cyan toner images are formed, respectively. Then, the toner images of the respective colors formed on the respective photosensitive drums are primarily transferred while being superimposed on the intermediate transfer belt. Further, the toner images of a plurality of colors carried on the intermediate transfer belt are color images at the position of the secondary transfer nip formed by the secondary transfer roller contacting the secondary transfer counter roller via the intermediate transfer belt. Is secondarily transferred onto the recording medium.

On the other hand, in Patent Document 1, in order to reduce the shock jitter that occurs when the leading edge of the recording medium enters the secondary transfer nip and the shock jitter that occurs when the trailing edge of the recording medium leaves the secondary transfer nip. In addition, the secondary transfer roller is moved relative to the secondary transfer counter roller at a timing immediately before the leading edge of the recording medium enters the secondary transfer nip and at a timing immediately before the trailing edge of the recording medium leaves the secondary transfer nip. A technique for relatively separating a predetermined distance is disclosed.
Further, in Patent Document 1, both rollers are brought into contact with each other from the separated state in order to reduce an impact when the secondary transfer roller in the separated state comes into contact with the secondary transfer counter roller via the intermediate transfer belt. A technique for decelerating the rotational speed of a cam that is shifted to a state is disclosed.

  The technique disclosed in Patent Document 1 described above reduces the rotational speed of the cam that shifts the secondary transfer roller and the secondary transfer counter roller from the separated state to the contact state. There was a possibility that the performance would deteriorate.

  Such a problem is not limited to the transfer device (image forming device) using the intermediate transfer belt, and the image forming device transfers the image at the position of the transfer nip onto the recording medium conveyed toward the transfer nip. In this case, the transfer roller is configured to contact the transfer counter roller via a belt member (for example, a photosensitive belt) to form a transfer nip, or the transfer roller is a rotating body (for example, The intermediate transfer drum, etc.) may be generated even if the transfer nip is formed.

  The present invention has been made to solve the above-described problems. A shock jitter generated when the leading edge of the recording medium enters the secondary transfer nip without lowering the productivity during sheet passing; The balance between the shock jitter that occurs when the trailing edge of the recording medium comes out of the secondary transfer nip and the impact that occurs when the secondary transfer roller that has been in a separated state contacts the secondary transfer counter roller via the intermediate transfer belt. It is an object of the present invention to provide a transfer device and an image forming apparatus that are well reduced.

  According to a first aspect of the present invention, a transfer device is stretched around a plurality of roller members, travels in a predetermined traveling direction, and an image formed on the surface of the image carrier is subjected to primary transfer. An intermediate transfer belt, and a secondary transfer nip formed in contact with the outer peripheral surface of the intermediate transfer belt, and carried on the intermediate transfer belt on a recording medium conveyed toward the secondary transfer nip. A secondary transfer roller for secondary transfer of the transferred image, a secondary transfer counter roller that is one of the plurality of roller members and that faces the secondary transfer roller via the intermediate transfer belt, Variable means for changing a distance between the axes of the secondary transfer roller and the secondary transfer counter roller, and the variable means is configured to change the second when the leading edge of the recording medium is fed into the secondary transfer nip. A secondary transfer roller and the secondary transfer counter roller; The distance between the axes is controlled to be smaller than the distance between the axes of the secondary transfer roller and the secondary transfer counter roller when the trailing edge of the recording medium is sent out from the secondary transfer nip. It is.

  In the present invention, the distance between the axes of the secondary transfer roller and the secondary transfer counter roller when the leading edge of the recording medium is fed into the secondary transfer nip is sent from the secondary transfer nip to the trailing edge of the recording medium. The distance is controlled so as to be smaller than the distance between the axes. As a result, the shock jitter that occurs when the leading edge of the recording medium enters the secondary transfer nip and the shock that occurs when the trailing edge of the recording medium slips out of the secondary transfer nip without lowering the productivity during paper feeding. Provided is a transfer device and an image forming apparatus in which the jitter and the impact when the separated secondary transfer roller comes into contact with the secondary transfer opposing roller via the intermediate transfer belt are reduced in a balanced manner. be able to.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. FIG. 2 is a configuration diagram illustrating a transfer device installed in the image forming apparatus of FIG. 1. It is the schematic which looked at a part of transfer device in the width direction. FIG. 6 is a schematic diagram illustrating the contact and separation operation of the secondary transfer roller when passing thin paper. FIG. 6 is a schematic diagram illustrating the contact and separation operation of the secondary transfer roller when a thick sheet is passed. It is a table | surface figure which shows an experimental condition and an experimental result. FIG. 10 is a schematic diagram illustrating a contact / separation operation of a secondary transfer roller when a thin sheet is passed as a modification. It is a figure which shows the eccentric cam as a modification.

Embodiment.
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIGS.
FIG. 1 is a block diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing an image forming unit thereof.
As shown in FIG. 1, an intermediate transfer belt device 15 as a transfer device is installed in the center of the image forming apparatus main body 100. Further, image forming portions 6Y, 6M, 6C, and 6K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8 (belt member) of the intermediate transfer belt device 15. Yes.

  Referring to FIG. 2, an image forming unit 6Y corresponding to yellow includes a photosensitive drum 1Y as an image carrier, a charging unit 4Y disposed around the photosensitive drum 1Y, a developing unit 5Y, and a cleaning unit 2Y. , And a static elimination unit (not shown). Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1Y, and a yellow image is formed on the photosensitive drum 1Y.

  The other three image forming units 6M, 6C, and 6K have substantially the same configuration as that of the image forming unit 6Y corresponding to yellow except that the color of the toner used is different. A corresponding image is formed. Hereinafter, description of the other three image forming units 6M, 6C, and 6K will be omitted as appropriate, and only the image forming unit 6Y corresponding to yellow will be described.

Referring to FIG. 2, photoconductor drum 1Y is rotated counterclockwise by a drive motor (not shown). Then, the surface of the photosensitive drum 1Y is uniformly charged at the position of the charging unit 4Y (a charging process).
Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and an electrostatic latent image corresponding to yellow is formed by exposure scanning at this position (in the exposure process). is there.).

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the developing portion 5Y, and the electrostatic latent image is developed at this position to form a yellow toner image (developing process).
Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the intermediate transfer belt 8 (belt member) and the primary transfer roller 9Y, and the toner image on the photosensitive drum 1Y is transferred onto the intermediate transfer belt 8 at this position. Transferred (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the cleaning unit 2Y, and untransferred toner remaining on the photosensitive drum 1Y at this position is collected in the cleaning unit 2Y by the cleaning blade 2a (cleaning). Process.)
Finally, the surface of the photosensitive drum 1Y reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

The image forming process described above is performed in the other image forming units 6M, 6C, and 6K in the same manner as the yellow image forming unit 6Y. That is, a laser beam L based on image information is irradiated from the exposure unit 7 disposed above the image forming unit onto the photosensitive drums 1M, 1C, and 1K of the image forming units 6M, 6C, and 6K. Is done. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven.
Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are superimposed on the intermediate transfer belt 8 and primarily transferred. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 3, the intermediate transfer belt device 15 (transfer device) includes an intermediate transfer belt 8, four primary transfer rollers 9Y, 9M, 9C, and 9K, a driving roller 12A, and a secondary transfer counter roller 11. , Tension rollers 12B to 12D, cleaning counter roller 13, intermediate transfer cleaning unit 10, secondary transfer roller 19, and the like. The intermediate transfer belt 8 is stretched and supported by a plurality of roller members 11, 12 </ b> A to 12 </ b> D, 13 and is moved endlessly in the direction of the arrow in FIG. 3 by the rotational drive of one roller member (drive roller 12 </ b> A). .

The four primary transfer rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 between the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. Then, a transfer voltage (transfer bias) opposite to the polarity of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow, and sequentially passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 8.

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer counter roller 11 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 8 are transferred onto a recording medium P such as transfer paper conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning unit 10. At this position, the untransferred toner on the intermediate transfer belt 8 is removed.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed. The configuration and operation of the intermediate transfer belt device 15 as a transfer device will be described in more detail later with reference to FIGS.

Here, referring to FIG. 1, the recording medium P conveyed to the position of the secondary transfer nip is fed from a sheet feeding unit 26 disposed below the apparatus main body 100 to a sheet feeding roller 27 and a registration roller pair 28. Etc., which are conveyed via
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the rollers of the registration roller pair 28.

  The recording medium P conveyed to the registration roller pair 28 (timing roller pair) temporarily stops at the position of the roller nip of the registration roller pair 28 whose rotation driving has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt and the pressure roller.
Thereafter, the recording medium P is discharged out of the apparatus by a pair of discharge rollers (not shown). The recording medium P discharged out of the apparatus by the pair of paper discharge rollers is sequentially stacked on the stack unit as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Next, the configuration and operation of the developing unit (developing device) in the image forming unit will be described in more detail with reference to FIG.
The developing unit 5Y includes a developing roller 51Y that faces the photosensitive drum 1Y, a doctor blade 52Y that faces the developing roller 51Y, two transport screws 55Y disposed in the developer containing unit, and an opening in the developer containing unit. A toner replenishment path 43Y that communicates with each other via a toner density, a density detection sensor 56Y that detects a toner density in the developer, and the like. The developing roller 51Y includes a magnet fixed inside, a sleeve rotating around the magnet, and the like. In the developer accommodating portion, a two-component developer composed of a carrier and toner is accommodated.

The developing unit 5Y configured as described above operates as follows.
The sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. The developer carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. Here, the developer in the developing section 5Y is adjusted so that the ratio of toner in the developer (toner concentration) falls within a predetermined range.
Thereafter, the toner replenished in the developer accommodating portion circulates through the two separated developer accommodating portions while being mixed and stirred together with the developer by the two conveying screws 55Y (movement in the direction perpendicular to the paper surface of FIG. 2). .) The toner in the developer is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

  The developer carried on the developing roller 51Y is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. The developer on the developing roller 51Y is conveyed to a position facing the photosensitive drum 1Y (development area) after the developer amount is made appropriate at this position. The toner is attracted to the latent image formed on the photosensitive drum 1Y by the electric field formed in the development area. Thereafter, the developer remaining on the developing roller 51Y reaches the upper portion of the developer accommodating portion as the sleeve rotates, and is detached from the developing roller 51Y at this position.

Next, the intermediate transfer belt device 15 (transfer device) in the present embodiment will be described in detail with reference to FIGS.
FIG. 3 is a configuration diagram showing an intermediate transfer belt device 15 as a transfer device. 4A is a schematic diagram showing a state in which the secondary transfer roller 19 is in contact with the secondary transfer counter roller 11 via the intermediate transfer belt 8 in the width direction, and FIG. 3 is a schematic view showing a state in which a secondary transfer roller 19 is separated from a secondary transfer counter roller 11 and an intermediate transfer belt 8 in a width direction. FIG. FIG. 5 is a schematic diagram showing the contact / separation operation of the secondary transfer roller 19 when the thin paper is passed, and FIG. 6 is a schematic diagram showing the contact / separation operation of the secondary transfer roller when the thick paper is passed. FIG. 7 is a table showing experimental conditions and experimental results.

  Referring to FIG. 3, the intermediate transfer belt device 15 (transfer device) includes an intermediate transfer belt 8 as a belt member, four primary transfer rollers 9Y, 9M, 9C, and 9K, a driving roller 12A, and a secondary transfer counter roller. 11, tension rollers 12 </ b> B to 12 </ b> D, a cleaning counter roller 13, an intermediate transfer cleaning unit 10, a secondary transfer roller 19, and the like.

  The intermediate transfer belt 8 as a belt member is disposed so as to face the photosensitive drums 1Y, 1M, 1C, and 1K as four image carriers that respectively carry toner images of respective colors. The intermediate transfer belt 8 is stretched and supported mainly by six roller members (a driving roller 12A, a secondary transfer counter roller 11, tension rollers 12B to 12D, and a cleaning counter roller 13).

In the present embodiment, the intermediate transfer belt 8 includes PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. in a single layer or multiple layers. A conductive material such as carbon black is dispersed. The intermediate transfer belt 8 is adjusted so that the volume resistivity is in the range of 10 ⁷ to 10 ¹² Ωcm, and the surface resistivity on the back side of the belt is in the range of 10 ⁸ to 10 ¹² Ωcm. The intermediate transfer belt 8 is set to have a thickness in the range of 80 to 100 μm. In the present embodiment, the thickness of the intermediate transfer belt 8 is set to 90 μm.
If necessary, a release layer can be coated on the surface of the intermediate transfer belt 8. At that time, materials used for the coating are ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (four A fluororesin such as fluorinated ethylene-hexafluoropropylene copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.
Further, as a method for manufacturing the intermediate transfer belt 8, there are a casting method, a centrifugal molding method, and the like, and a step of polishing the surface is performed as necessary.

  The primary transfer rollers 9Y, 9M, 9C, and 9K face the corresponding photosensitive drums 1Y, 1M, 1C, and 1K through the intermediate transfer belt 8, respectively. More specifically, the yellow transfer roller 9Y faces the yellow photosensitive drum 1Y via the intermediate transfer belt 8, and the magenta transfer roller 9M contacts the magenta photosensitive drum 1M via the intermediate transfer belt 8. The cyan transfer roller 9C faces the cyan photosensitive drum 1C via the intermediate transfer belt 8, and the black (black) transfer roller 9K passes through the intermediate transfer belt 8 for black (black). For example).

The drive roller 12A is rotationally driven by a drive motor (not shown). As a result, the intermediate transfer belt 8 travels in a predetermined traveling direction (clockwise in FIG. 3). In the present embodiment, the traveling speed (process linear speed) of the intermediate transfer belt 8 is set to be about 415 mm / second.
The secondary transfer counter roller 11 is in contact with the secondary transfer roller 19 via the intermediate transfer belt 8. The three tension rollers 12 </ b> B to 12 </ b> D are in contact with the inner peripheral surface or the outer peripheral surface of the intermediate transfer belt 8. An intermediate transfer cleaning unit 10 (cleaning blade) is installed between the secondary transfer counter roller 11 and the tension roller 12B so as to face the cleaning counter roller 13 with the intermediate transfer belt 8 interposed therebetween.

Here, in the intermediate transfer belt device 15 (image forming apparatus 100) in the present embodiment, variable means 30 to 32, 35 that change the inter-axis distance between the secondary transfer roller 19 and the secondary transfer counter roller 11, 36 is provided.
In detail, referring to FIG. 4, the secondary transfer counter roller 11 around which the intermediate transfer belt 8 is wound is rotatably held on a frame (not shown) of the apparatus 15. In addition, eccentric cams 30 are rotatably installed at both ends of the width direction of the secondary transfer counter roller 11 (the left-right direction in FIG. 4 and the vertical direction in FIG. 3). . These eccentric cams 30 (arranged so that the eccentric phases of the two eccentric cams 30 coincide with each other) are connected by a connection shaft (not shown), and a shaft portion 30a ( A pulley is installed on the eccentric shaft). A timing belt 31 is stretched between the pulley of the eccentric cam 30 and the pulley installed on the shaft portion 32a of the drive motor 32 (stepping motor).
On the other hand, at both ends in the width direction of the secondary transfer roller 19, there are abutting portions 35 (ball bearings having an outer diameter smaller than the outer diameter of the secondary transfer roller 19) that can contact the eccentric cam 30. is set up. Further, compression springs 36 (biasing members) for urging the secondary transfer roller 19 toward the secondary transfer counter roller 11 are installed at shaft portions at both ends in the width direction of the secondary transfer roller 19.

With such a configuration, the secondary transfer roller 19 is brought into contact with the secondary transfer counter roller 11 (intermediate transfer belt 8) by changing the posture of the eccentric cam 30 in the rotational direction by the rotational drive of the drive motor 32. 4A (the state shown in FIG. 4A) and the secondary transfer roller 19 separated from the secondary transfer counter roller 11 (intermediate transfer belt 8) (the state shown in FIG. 4B). Can be switched between.
Specifically, when the eccentric cam 30 is in the rotational direction as shown in FIG. 4A, the eccentric cam 30 does not interfere with the abutting portion 35, and the secondary transfer roller is urged by the urging force of the compression spring 36. 19 is urged upward, and the secondary transfer roller 19 comes into contact with the secondary transfer counter roller 11 (intermediate transfer belt 8). On the other hand, when the eccentric cam 30 is in the rotational direction as shown in FIG. 4B, the eccentric cam 30 pushes the abutting portion 35 to resist the urging force of the compression spring 36. The secondary transfer roller 19 is pushed down, and the secondary transfer roller 19 is separated from the secondary transfer counter roller 11 (intermediate transfer belt 8).

In the present embodiment, the variable means 30 to 32, 35, 36 are the secondary transfer roller 19 when the leading end of the recording medium P (the leading end in the transport direction) is fed into the secondary transfer nip. Between the secondary transfer roller 19 and the secondary transfer opposite roller 11 when the rear end of the recording medium P (the rear end in the transport direction) is sent from the secondary transfer nip. It is controlled so as to be smaller than the inter-axis distance with the facing roller 11.
Specifically, as shown in FIGS. 5A and 5C, the variable means 30 to 32, 35, and 36 perform secondary transfer when the leading end of the recording medium P is fed into the secondary transfer nip. The separation amount H1 between the roller 19 and the secondary transfer counter roller 11 is the separation amount H2 between the secondary transfer roller 19 and the secondary transfer counter roller 11 when the trailing edge of the recording medium P is sent from the secondary transfer nip. Is controlled so as to be smaller (H1 <H2).
Further, as shown in FIGS. 5A to 5C, the variable means 30 to 32, 35, and 36 include the secondary transfer roller 19 when the leading end of the recording medium P is fed into the secondary transfer nip. The distance between the axes of the secondary transfer counter roller 11 (see FIG. 5A) and the secondary transfer roller 19 and the secondary transfer when the trailing edge of the recording medium P is sent from the secondary transfer nip. The distance between the axes of the counter roller 11 (see FIG. 5C) and the secondary transfer rollers 19 and 2 when the image is secondarily transferred onto the recording medium P in the secondary transfer nip. The distance is controlled to be larger than the distance between the axes of the next transfer counter roller 11 (see FIG. 5B).

Specifically, referring to FIG. 5, the eccentric cam 30 installed on the secondary transfer counter roller 11 has two top dead centers (first top dead center) so that the above-described three inter-axis distances can be formed. Point A and second top dead center C.) and one bottom dead center B.
In the eccentric cam 30, the bottom dead center B is a region on the outer peripheral surface formed so that the distance from the rotation shaft 30a is the shortest. The distance from the rotating shaft 30a to the bottom dead center B is M2, the radius of the secondary transfer counter roller is X1, the radius of the secondary transfer roller is X2, and the radius of the abutting portion 35 (ball bearing) is N. In this case, the relationship X1 + X2 ≧ M2 + N is established. As a result, as shown in FIG. 5B, when the bottom dead center B of the eccentric cam 30 faces the abutting portion 35, the secondary transfer roller 19 becomes the secondary transfer counter roller 11 (intermediate transfer belt 8). Is pressed with a predetermined pressure (a desired secondary transfer nip is formed).
On the other hand, the first top dead center A is a region on the outer peripheral surface formed so as to have the longest distance from the rotation shaft 30a. The radius of the abutting portion 35 (ball bearing) is set such that the distance from the rotary shaft 30a to the first top dead center A is M1, the radius of the secondary transfer counter roller is X1, and the radius of the secondary transfer roller is X2. When N is N, the relationship X1 + X2 <M1 + N is established. As a result, as shown in FIG. 5C, when the first top dead center A of the eccentric cam 30 comes into contact with the abutting portion 35, the secondary transfer roller 19 is moved to the secondary transfer counter roller 11 (intermediate transfer). The belt 8) is separated by a relatively large separation amount H2.
The second top dead center C (medium dead center) is an area on the outer peripheral surface formed so that the distance from the rotation shaft 30a is next to the first top dead center A. Then, the distance from the rotary shaft 30a to the second top dead center C is M3, the radius of the secondary transfer counter roller is X1, the radius of the secondary transfer roller is X2, and the radius of the abutting portion 35 (ball bearing) When N is N, the relationship X1 + X2 <M3 + N (<M1 + N) is established. As a result, as shown in FIG. 5A, when the second top dead center C of the eccentric cam 30 comes into contact with the abutting portion 35, the secondary transfer roller 19 is moved to the secondary transfer counter roller 11 (intermediate transfer). The belt 8) is separated by a relatively small separation amount H1 (<H2).

Then, by the variable means 30 to 32, 35, and 36 configured in this way, when the recording medium P passes through the secondary transfer nip, the interaxial distance between the secondary transfer roller 19 and the secondary transfer counter roller 11 is reached. Will be varied as follows.
First, as shown in FIG. 5A, immediately before the leading edge of the recording medium P enters the secondary transfer nip, the secondary transfer roller 19 moves against the secondary transfer counter roller 11 (intermediate transfer belt 8). Control is performed so as to be separated by a relatively small separation amount H1 (<H2).
Thus, when the leading edge of the recording medium P enters the secondary transfer nip, a gap is formed between the secondary transfer roller 19 and the secondary transfer counter roller 11 (intermediate transfer belt 8). It is possible to reliably reduce the occurrence of shock jitter due to an impact when the leading edge of the recording medium P enters between the secondary transfer roller 19 and the secondary transfer counter roller 11 in the pressure contact state (secondary transfer nip). . Such a shock jitter is mainly performed on the upstream side because an instantaneous speed difference occurs in the traveling speed of the intermediate transfer belt 8 due to an impact when the leading edge of the recording medium P enters the secondary transfer nip. An abnormal image (horizontal streak image) produced by affecting the primary transfer process at the position of the primary transfer nip (which is the primary transfer process in the image forming process for the recording medium P that continues next during continuous paper feeding). Accordingly, it is an abnormal image (transfer misalignment image) generated by affecting the secondary transfer process performed at the position of the secondary transfer nip.

Then, at the timing after the leading edge of the recording medium P reaches the secondary transfer nip, the image area of the recording medium P (the central area where the image can be formed, not the margin area at the front and rear end portions and the both end portions). 5) at a timing before reaching the secondary transfer nip, the secondary transfer roller 19 is pressed against the secondary transfer counter roller 11 (intermediate transfer belt 8) with a predetermined pressure as shown in FIG. 5B. (A desired secondary transfer nip is formed).
At this time, the secondary transfer roller 19 moves from the relatively small separation amount H1 toward the secondary transfer counter roller 11, so that the impact when the both rollers 11 and 19 move (collision) is extremely low. Can be small. Then, the image carried on the intermediate transfer belt 8 is secondarily transferred to the image area of the recording medium P in a state where a desired secondary transfer nip is formed.

Specifically, the shock jitter (speed fluctuation of the intermediate transfer belt 8) when the recording medium P enters the secondary transfer nip is determined by the amount of separation (gap) between the secondary transfer roller 19 and the secondary transfer counter roller 11. Experiments have confirmed that the larger the setting, the easier the suppression. However, as the distance between the secondary transfer roller 19 and the secondary transfer counter roller 11 increases, the secondary transfer roller 19 is brought into pressure contact with the secondary transfer counter roller 11 during the secondary transfer process so that a desired secondary transfer nip is formed. When forming, the impact due to the collision of the secondary transfer roller 19 with the secondary transfer counter roller 11 is increased, the speed fluctuation of the intermediate transfer belt 8 is also increased, and a large shock jitter (the front end entering the secondary transfer nip). Which occurs with almost the same mechanism as time). Also, the time from when the leading edge of the recording medium P reaches the secondary transfer nip to when the secondary transfer process to the image area of the recording medium P is started at the secondary transfer nip is extremely short (particularly process). When the recording medium P enters the secondary transfer nip, the distance between the rollers 11 and 19 is set to be large when the recording medium P enters the secondary transfer nip. It is difficult to control the two rollers 11 and 19 so that they slowly come into contact with each other over a period of time until the operation starts (productivity decreases).
For these reasons, in the present embodiment, when the shock jitter, the secondary transfer counter roller 11 and the secondary transfer roller 19 collide with each other when the leading edge of the recording medium P enters the secondary transfer nip (from the separated state) When the leading edge of the recording medium P enters the secondary transfer nip, it is balanced so that both of the shock jitter and the shock jitter in the contact state do not become too large exceeding the allowable limit. The distance H1 between the transfer roller 19 and the secondary transfer counter roller 11 is set to be relatively small.

Then, the timing after the image area of the recording medium P (the area where image formation is possible, not the blank area) passes through the secondary transfer nip, and the rear end of the recording medium P passes through the secondary transfer nip. At the timing before passing, as shown in FIG. 5C, the secondary transfer roller 19 has a relatively large separation H2 (> H1) with respect to the secondary transfer counter roller 11 (intermediate transfer belt 8). It is controlled to be separated.
As described above, when the trailing edge of the recording medium P leaves the secondary transfer nip, a gap is formed between the secondary transfer roller 19 and the secondary transfer counter roller 11 (intermediate transfer belt 8). Shock jitter due to impact when the trailing edge of the recording medium P comes out between the secondary transfer roller 19 and the secondary transfer counter roller 11 in the pressure contact state (secondary transfer nip) (when the leading edge enters the secondary transfer nip) Can be reliably reduced.)
After that, in preparation for the secondary transfer process of the next transported recording medium P, the secondary transfer roller 19 is controlled to be separated from the secondary transfer counter roller 11 again by a relatively small separation amount H1. (Transition from the state of FIG. 5C to the state of FIG. 5A).

Specifically, the shock jitter (speed fluctuation of the intermediate transfer belt 8) when the trailing edge of the recording medium P leaves the secondary transfer nip is the amount of separation (gap) between the secondary transfer roller 19 and the secondary transfer counter roller 11. Experiments have confirmed that the larger the value is, the more it can be suppressed. On the other hand, when the secondary transfer roller 19 and the secondary transfer counter roller 11 shift from the contact state to the separation state, the collision of both rollers 11 and 19 as in the transition from the separation state to the contact state occurs.・ Shock jitter due to impact hardly occurs. In addition, since the time from when the trailing edge of the recording medium P passes through the secondary transfer nip to when the leading edge of the next recording medium P reaches the secondary transfer nip is relatively long, the recording medium P is in the secondary transfer nip. When the distance between the rollers 11 and 19 is set large, the distance between the paper and the next recording medium P is used, and the leading edge of the next recording medium P enters the secondary transfer nip. It is relatively easy to control the distance between the rollers 11 and 19 to be variable.
For these reasons, in the present embodiment, in order to reliably reduce the shock jitter when the trailing edge of the recording medium P is removed from the secondary transfer nip with a margin, the trailing edge of the recording medium P is disposed at the secondary transfer nip. The separation amount H2 between the secondary transfer roller 19 and the secondary transfer counter roller 11 when moving out is set to be relatively large.

Here, in this embodiment, the control by the variable means 30 to 32, 35, and 36 as described in FIGS. 5A to 5C is performed on the recording medium P conveyed toward the secondary transfer nip. This is done only when the thickness is below a predetermined value.
Specifically, only when the thickness of the recording medium P to be conveyed is detected by the thickness detection means and the detection result is a predetermined value or less (in this embodiment, the basis weight is 157 gsm or less). Control (the contact / separation control described with reference to FIGS. 5A to 5C) is performed such that the amount of separation when the front end enters is small and the amount of separation when the rear end is removed is large.
Such control is performed because the recording medium P (thick paper) whose thickness exceeds a predetermined value (basis weight is 157 gsm) is shock jitter when the recording medium P enters the secondary transfer nip. The former is dominant when compared with the shock jitter at the time of collision between the secondary transfer counter roller 11 and the secondary transfer roller 19 (when shifting from the separated state to the contact state). This is because it is considered to be. Such a phenomenon has been experimentally confirmed as will be described later. In other words, in order to reduce the shock jitter at the time of tip entry, the distance between the rollers 11 and 19 at the time of tip entry is set as large as possible when the shock jitter at the time of tip entry and both rollers 11 and 19 collide. The generation of shock jitter can be reduced as a whole, rather than the balance between the shock jitter and the distance between the rollers 11 and 19 being set small.

  For this reason, in the present embodiment, the thickness of the recording medium P conveyed toward the secondary transfer nip exceeds a predetermined value (in this embodiment, the basis weight is 157 gsm). As shown in FIG. 6, the axial distance (separation amount H2) between the secondary transfer roller 19 and the secondary transfer counter roller 11 when the leading edge of the recording medium P is fed into the secondary transfer nip, 2 The distance between the secondary transfer roller 19 and the secondary transfer counter roller 11 (separation amount H2) when the trailing edge of the recording medium P is sent from the secondary transfer nip is conveyed toward the secondary transfer nip. The distance between the axes of the secondary transfer roller 19 and the secondary transfer counter roller 11 when the trailing edge of the recording medium P is sent out from the secondary transfer nip when the thickness of the recording medium P to be recorded is less than a predetermined value Variable means 30 to 32 so as to be equal to (separation amount H2), And controls the 5,36.

  Specifically, when the thick paper is passed, first, as shown in FIG. 6A, the secondary transfer roller 19 is moved to the secondary transfer counter roller 11 immediately before the leading edge of the recording medium P enters the secondary transfer nip. Is controlled to be separated by a large separation amount H2 (which is the same size as the separation amount H2 in the state of FIG. 5C). Then, as shown in FIG. 6B, at the timing after the leading edge of the recording medium P reaches the secondary transfer nip and before the image area of the recording medium P reaches the secondary transfer nip, The secondary transfer roller 19 is controlled so as to come into pressure contact with the secondary transfer counter roller 11 with a predetermined pressure. Then, as shown in FIG. 6C, the timing after the image area of the recording medium P passes through the secondary transfer nip and before the trailing edge of the recording medium P passes through the secondary transfer nip. Thus, the secondary transfer roller 19 is controlled to be separated from the secondary transfer counter roller 11 by a large separation amount H2 (which is the same size as the separation amount H2 in the state of FIG. 5C). .

  The thickness detecting means for detecting the thickness of the recording medium P is a recording medium input by a user from an operation panel (not shown) of the image forming apparatus 100, a personal computer connected to the image forming apparatus 100, or the like. Those based on the information of P can be used, and a thickness detection sensor (which detects the paper thickness directly in the conveyance path from the paper feeding unit 26 or the paper feeding unit 26 to the secondary transfer nip, can be used. , Known ones can be used).

  Further, when the above-described control is performed, the stiffness of the recording medium P is weak when passing the recording medium P having a very thin thickness (for example, an ultrathin paper having a basis weight of 53 gsm or less). For this reason, it is assumed that neither the shock jitter at the front end entry nor the shock jitter at the rear end removal will exceed the allowable range. In such a case, when the thickness of the transported recording medium P is in a predetermined value range (basis weight is 53 to 157 gsm), the separation amount when the leading edge enters is small, and the separation amount when the trailing edge is removed is large. When such control (the contact / separation control described with reference to FIGS. 5A to 5C) is performed, and the thickness of the recording medium P being conveyed exceeds a predetermined value range (when the basis weight exceeds 157 gsm). ) Is controlled such that the separation amount when the front end enters and the separation amount when the rear end is removed (the contact / separation control described in FIGS. 6A to 6C) is performed. When the thickness of the recording medium P is less than the predetermined value range (when the basis weight is less than 53 gsm), the control is performed so that both the rollers 11 and 19 are not separated when the leading end enters and when the trailing end slips out (FIG. 5B). It is preferable to perform control to maintain the pressure contact state.

FIG. 7 is a table showing a part of the conditions and results of an experiment conducted by the present inventor in order to confirm the effect of the present invention.
The experiment of FIG. 7 includes the time when the leading edge enters when the recording medium P having a different thickness (basis weight) is passed (including the time when the secondary transfer roller 19 and the secondary transfer counter roller 11 collide). This is a measurement of the magnitude of the speed fluctuation of the intermediate transfer belt 8 when the trailing edge is missing. In FIG. 7, “No separation” is the case where the secondary transfer roller 19 and the secondary transfer counter roller 11 are not separated (the state in FIG. 5B), and “small separation amount”. Is the case where the separation amount between the secondary transfer roller 19 and the secondary transfer counter roller 11 is set small (the separation amount H1 shown in FIG. 5A), and “large separation amount” is the secondary transfer. This is the case where the separation amount between the roller 19 and the secondary transfer counter roller 11 is set large (the separation amount H2 shown in FIG. 5C). In FIG. 7, “◯” indicates a good result that the speed fluctuation of the intermediate transfer belt 8 does not reach 2 mm / second, and “Δ” indicates that the speed fluctuation of the intermediate transfer belt 8 is about 2 to 3 mm / second. The result is not good but not so bad, and “x” is a result that a large shock jitter occurs when the speed fluctuation of the intermediate transfer belt 8 is 4 mm / second or more. FIG. 7A shows the experimental results when using paper 1 having a basis weight of 53 gsm (“copy printing paper 45 kg” manufactured by Ricoh), and FIG. 7B shows paper 2 having a basis weight of 128 gsm. FIG. 7 (C) shows a paper 3 having a basis weight of 279 gsm (“OK Special Art Post 279” manufactured by Oji Paper Co., Ltd.). It is an experimental result when using.

  7A to 7C also show that when the thickness of the recording medium P to be conveyed is equal to or less than a predetermined value, the separation amount when the leading edge enters is small and the separation amount when the trailing edge is missing is large. When such a control (the contact / separation control described in FIGS. 5A to 5C) is performed and the thickness of the recording medium P to be conveyed exceeds a predetermined value, By performing the control (the contact / separation control described with reference to FIGS. 6A to 6C) such that the separation amount when the trailing edge comes out is increased, the thickness of the recording medium P to be conveyed is affected. It can be seen that the generation of large shock jitter can be reduced overall. In performing such control, the “basis weight 157 gsm” as the “predetermined value” described above is determined by the experimental results of FIG. 7 and the additional experiments and predictions associated therewith.

In the present embodiment, the secondary transfer roller 19 is configured to be separated from the secondary transfer counter roller 11 when the front end enters and the rear end is removed.
On the other hand, the pressure contact force (nip pressure) of the secondary transfer roller 19 against the secondary transfer counter roller 11 (intermediate transfer belt 8) when the front end enters and the rear end slips out is the pressure contact force during the secondary transfer process. It can also be configured to be smaller than (nip pressure).
Specifically, referring to FIG. 8, the variable means 30 to 32, 35, and 36 are the secondary transfer roller 19 and the secondary transfer counter roller 11 when the leading edge of the recording medium P is fed into the secondary transfer nip. Is pressed between the secondary transfer roller 19 and the secondary transfer counter roller 11 when the trailing edge of the recording medium P is sent out from the secondary transfer nip. It is controlled to be larger than the force W3 (see FIG. 8C) (W1> W3). Further, the variable means 30 to 32, 35, and 36 are configured so that the pressure contact force W1 between the secondary transfer roller 19 and the secondary transfer counter roller 11 when the leading edge of the recording medium P is fed into the secondary transfer nip, 2 The pressure contact force W3 between the secondary transfer roller 19 and the secondary transfer counter roller 11 when the trailing edge of the recording medium P is sent out from the secondary transfer nip is 2 images on the recording medium P in the secondary transfer nip. The pressure is controlled to be smaller than the pressure contact force W0 (see FIG. 8B) between the secondary transfer roller 19 and the secondary transfer counter roller 11 during the next transfer (W0>W1> W3). is there.).

Then, the variable control of the pressing force shown in FIGS. 8A to 8C is the same as the variable control of the separation amount described above with reference to FIGS. This is done only when is below a predetermined value. That is, when the thickness of the recording medium P exceeds a predetermined value, the pressure contact force is W3 (the pressure contact force W3 in the state shown in FIG. 8C) when the leading edge enters, and the pressure contact force is increased during the secondary transfer process. W0 (the pressure contact force W0 in the state of FIG. 8B) is controlled, and the pressure contact force is controlled to be W3 (the pressure contact force W3 in the state of FIG. 8C) when the rear end is pulled out. .
Even when such a pressure contact variable control is performed, an experimental result almost similar to the experimental result shown in FIG. 7 can be obtained, so that the same effect as that of the present embodiment can be obtained. it can.
The roller portions of the secondary transfer roller 19 and the secondary transfer counter roller 11 are formed in a drum shape (the outer diameter of the central portion in the width direction is larger than the outer diameter of both end portions in the width direction). When the same distance between the axes is controlled, the pressure control shown in FIGS. 8A to 8C is performed at the central portion in the width direction, and FIG. It may occur that the control of the separation amount shown in A) to (C) is performed.

When the variable control of the pressing force shown in FIG. 8 is performed, an eccentric cam 30 having a relatively small difference in height between the top dead centers A and C and the bottom dead center B as shown in FIG. 9 can be used. .
In such an eccentric cam 30, the first top dead center A (a region that abuts against the abutting portion 35 in FIG. 8C) and the second top dead center C (projected in FIG. 8A). It is preferable to set the distance (the distance along the outer peripheral surface) to be short. Specifically, the interval between the first top dead center A and the second top dead center C (angle around the rotation shaft 30a) is R [deg], and the angular velocity of the drive motor 32 is Q [deg / sec]. Assuming that the paper interval between the recording medium P and the recording medium P during continuous paper feeding is F [mm], and the process linear velocity (conveying speed of the recording medium P) is S [mm / sec],
R / Q <F / S
It is preferable that the relationship is established. As a result, the pressure contact force (distance between the shafts) of both rollers 11 and 19 after the trailing edge of the recording medium P passes through the secondary transfer nip and before the leading edge of the next recording medium P reaches the secondary transfer nip. ) Can be smoothly performed without lowering productivity (conveying speed of the recording medium P).

  As described above, in this embodiment, the distance between the axes of the secondary transfer roller 19 and the secondary transfer counter roller 11 when the leading edge of the recording medium P is fed into the secondary transfer nip is the secondary transfer nip. The distance is controlled to be smaller than the distance between the axes when the trailing edge of the recording medium P is sent out from the transfer nip. As a result, the shock jitter that occurs when the leading edge of the recording medium P enters the secondary transfer nip and the trailing edge of the recording medium P come out of the secondary transfer nip without lowering the productivity during paper passing. The generated shock jitter and the impact when the secondary transfer roller 19 in the separated state comes into contact with the secondary transfer counter roller 11 via the intermediate transfer belt 8 can be reduced in a balanced manner.

In the present embodiment, the present invention is applied to a transfer device (intermediate transfer belt device 15) using the intermediate transfer belt 8 as a belt member. In contrast, a transfer device (image forming apparatus) using a photosensitive belt (which functions as the photosensitive drum in the present embodiment and is an endless belt-shaped photosensitive body) as a belt member. The present invention can also be applied to.
In such a case, a transfer roller that contacts the outer peripheral surface of the belt member to form a transfer nip and transfers an image carried on the belt member onto a recording medium conveyed toward the transfer nip, and the belt member A transfer counter roller facing the transfer roller via the belt member, and a variable means for changing the distance between the axes of the transfer roller and the transfer counter roller. The variable means is configured such that the distance between the axes of the transfer roller and the transfer counter roller when the leading edge of the recording medium is fed into the transfer nip is the same as that when the trailing edge of the recording medium is sent from the transfer nip. It is controlled to be smaller than the distance between the axes of the transfer roller and the transfer counter roller.
And even if it is such a case, the effect similar to this Embodiment can be acquired.

Furthermore, the present invention can also be applied to an image forming apparatus provided with a rotating body (for example, an intermediate transfer drum or a photosensitive drum) on which an image is carried.
In such a case, a transfer roller that contacts the outer peripheral surface of the rotating body to form a transfer nip and transfers an image carried on the rotating body onto a recording medium conveyed toward the transfer nip, and the rotating body Variable means for varying the distance between the shaft and the transfer roller. The variable means is configured such that the center distance between the transfer roller and the rotating body when the leading end of the recording medium is fed into the transfer nip is rotated with the transfer roller when the trailing end of the recording medium is sent from the transfer nip. It will be controlled to be smaller than the distance between the body and the axis.
And even if it is such a case, the effect similar to this Embodiment can be acquired.

In this embodiment, the secondary transfer roller 19 is separated from the secondary transfer counter roller 11 (intermediate transfer belt 8) by the variable means. On the other hand, the secondary transfer opposing roller 11 (intermediate transfer belt 8) can be separated from the secondary transfer roller 19 by a variable means.
Further, in the present embodiment, compression springs 36 (biasing members) are installed at the shaft portions at both ends in the width direction of the secondary transfer roller 19 so that the secondary transfer roller 19 is directed to the secondary transfer counter roller 11 alone. And configured to be energized. On the other hand, a tension spring (biasing member) that urges the secondary transfer unit including the secondary transfer roller 19 toward the intermediate transfer belt 8 together with the unit is installed to transfer the secondary transfer roller 19 to the secondary transfer. It can also comprise so that it may bias toward the opposing roller 11. FIG.
Furthermore, in this embodiment, ball bearings having an outer diameter smaller than the outer diameter of the secondary transfer roller 19 are brought into contact with the eccentric cam 30 at both ends in the width direction of the secondary transfer roller 19 as the contact portions 35. The inter-axis distance between the secondary transfer roller 19 and the secondary transfer counter roller 11 is variable. On the other hand, a ball bearing having an outer diameter larger than the outer diameter of the secondary transfer roller 19 is brought into contact with the eccentric cam 30 at both end portions in the width direction of the secondary transfer roller 19 as the contact portions 35. The distance between the shafts of the transfer roller 19 and the secondary transfer counter roller 11 can be varied.
Even in such a case, the same effect as in the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1Y, 1M, 1C, 1K photosensitive drum (image carrier),
8 Intermediate transfer belt (belt member),
11 Secondary transfer counter roller,
15 Intermediate transfer belt device (transfer device, belt device),
19 Secondary transfer roller,
30 Eccentric cam,
30a rotation axis,
100 Image forming apparatus body (apparatus body), P recording medium,
A 1st top dead center, B bottom dead center, C 2nd top dead center.

JP 2011-133653 A

Claims (9)

An intermediate transfer belt that is stretched around a plurality of roller members, travels in a predetermined traveling direction, and an image formed on the image carrier on the surface thereof is primarily transferred;
A secondary transfer nip is formed in contact with the outer peripheral surface of the intermediate transfer belt, and an image carried on the intermediate transfer belt is secondarily transferred onto a recording medium conveyed toward the secondary transfer nip. A secondary transfer roller;
A secondary transfer opposing roller that is one of the plurality of roller members and faces the secondary transfer roller via the intermediate transfer belt;
Variable means for varying an inter-axis distance between the secondary transfer roller and the secondary transfer counter roller;
With
The variable means is configured such that the distance between the axes of the secondary transfer roller and the secondary transfer counter roller when the leading edge of the recording medium is fed into the secondary transfer nip is from the secondary transfer nip to the recording medium. A transfer device controlled to be smaller than an inter-axis distance between the secondary transfer roller and the secondary transfer counter roller when the rear end is sent out.   The variable means is configured so that a pressure contact force between the secondary transfer roller and the secondary transfer counter roller when the leading edge of the recording medium is fed into the secondary transfer nip is changed from the secondary transfer nip to the rear of the recording medium. 2. The transfer device according to claim 1, wherein the transfer device is controlled to be larger than a pressure contact force between the secondary transfer roller and the secondary transfer counter roller when the end is fed.   The variable means is configured such that when the leading edge of the recording medium is fed into the secondary transfer nip, the amount of separation between the secondary transfer roller and the secondary transfer counter roller is from the secondary transfer nip to the rear of the recording medium. 3. The transfer device according to claim 1, wherein the transfer device is controlled to be smaller than a separation amount between the secondary transfer roller and the secondary transfer counter roller when the end is fed. .   When the thickness of the recording medium conveyed toward the secondary transfer nip is equal to or less than a predetermined value, the variable means is configured to change the secondary when the leading end of the recording medium is fed into the secondary transfer nip. The distance between the axes of the transfer roller and the secondary transfer counter roller is the distance between the secondary transfer roller and the secondary transfer counter roller when the trailing edge of the recording medium is sent out from the secondary transfer nip. The transfer device according to claim 1, wherein the transfer device is controlled to be smaller than the transfer device.   When the thickness of the recording medium conveyed toward the secondary transfer nip exceeds the predetermined value, the secondary transfer roller and the 2 when the leading edge of the recording medium is fed into the secondary transfer nip The inter-axis distance between the secondary transfer counter roller and the inter-axis distance between the secondary transfer roller and the secondary transfer counter roller when the trailing edge of the recording medium is sent out from the secondary transfer nip, The secondary transfer roller and the secondary transfer when the trailing edge of the recording medium is sent out from the secondary transfer nip when the thickness of the recording medium conveyed toward the secondary transfer nip is a predetermined value or less. The transfer device according to claim 4, wherein the transfer device is controlled so as to be equal to an inter-axis distance with the opposite roller.   The variable means includes a distance between the axes of the secondary transfer roller and the secondary transfer counter roller when the leading edge of the recording medium is fed into the secondary transfer nip, and the recording medium from the secondary transfer nip. The distance between the axes of the secondary transfer roller and the secondary transfer counter roller when the trailing edge is sent out is the above-mentioned when the image is secondarily transferred onto the recording medium in the secondary transfer nip. The transfer device according to claim 1, wherein the transfer device is controlled to be larger than an inter-axis distance between a secondary transfer roller and the secondary transfer counter roller.   An image forming apparatus comprising the transfer device according to claim 1. A belt member that is stretched around a plurality of roller members, travels in a predetermined traveling direction, and carries an image on its surface;
A transfer roller that abuts on the outer peripheral surface of the belt member to form a transfer nip and transfers an image carried on the belt member onto a recording medium conveyed toward the transfer nip;
A transfer facing roller that is one of the plurality of roller members and faces the transfer roller via the belt member;
Variable means for varying an inter-axis distance between the transfer roller and the transfer counter roller;
With
The variable means is configured such that an inter-axis distance between the transfer roller and the transfer counter roller when the leading edge of the recording medium is fed into the transfer nip is determined when a trailing edge of the recording medium is fed from the transfer nip. An image forming apparatus controlled to be smaller than an inter-axis distance between the transfer roller and the transfer counter roller. A rotating body that rotates in a predetermined traveling direction and carries an image on its surface;
A transfer roller for contacting the outer peripheral surface of the rotating body to form a transfer nip, and transferring an image carried on the rotating body onto a recording medium conveyed toward the transfer nip;
Variable means for varying an inter-axis distance between the rotating body and the transfer roller;
With
The variable means is configured such that an inter-axis distance between the transfer roller and the rotating body when the leading end of the recording medium is fed into the transfer nip is the same as that when the trailing end of the recording medium is fed from the transfer nip. An image forming apparatus controlled to be smaller than a distance between axes of a transfer roller and the rotating body.

Images