JP2013148648A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a peripheral speed difference of a second roll due to a shaft distortion in an endless belt that is supported by a first roll corresponding to a transfer roll and by the second roll corresponding to a peeling roll.SOLUTION: The diameter of a secondary transfer roll 216 at the center portion in the rotation axis direction is configured to be smaller than the diameter at both end portions in accordance with the maximum deflection amount of a peeling roll 218, and the thickness of a secondary transfer belt 217 at the center portion in a direction parallel to the rotation axis of the secondary transfer roll 216 is configured to be larger than the thickness at both end portions. With this, contact pressure applied to the secondary transfer roll 216 and secondary transfer belt 217 becomes uniform in a contact zone when an image is transferred to a sheet, and a circumferential difference in the secondary transfer belt 217 is eliminated so as to eliminate the peripheral speed difference.

Description

  The present invention relates to a transfer device and an image forming apparatus.

  In an image forming apparatus that employs an intermediate transfer method, there is a problem that paper after secondary transfer is stuck to the intermediate transfer belt and paper jamming is likely to occur. On the other hand, a technique for suppressing the occurrence of paper jam by providing a peeling roll for peeling the paper after the secondary transfer from the intermediate transfer belt is widely known. In such a configuration, an endless belt is stretched between the secondary transfer roll and the peeling roll. For example, Patent Document 1 discloses a biasing force applied to an endless belt due to a speed difference between one end side and the other end side of the endless belt in order to suppress a belt walk in a portion where the endless belt in the peeling roll is stretched. Techniques for adjusting are described.

Japanese Patent Laid-Open No. 2007-025440

  An object of the present invention is to provide a circumferential speed difference caused by the deflection of the shaft of the second roll in the endless belt supported by the first roll corresponding to the transfer roll and the second roll corresponding to the peeling roll. It is to reduce.

  The transfer device according to claim 1 is rotated in a state in which both end portions in the width direction are in contact with an endless belt having a thickness smaller than a thickness of a central portion between both end portions and a transfer medium on which an image is transferred. A first roll in which the image is transferred from the transfer medium to a recording medium conveyed to a contact area with the transfer medium and the endless belt is stretched over the endless belt in the rotation axis direction. A first roll having a radius at both ends of a region in contact with the first roll larger than the radius of the central portion between the two ends, and the end roll provided at a position spaced apart from the first roll and the endless A second roll on which a belt is stretched, and a difference between a radius of both ends of the region in contact with the endless belt in the first roll and a radius of the central portion, and the both ends of the endless belt The difference between the thickness and the thickness of the center portion of both, characterized in that it is a magnitude of the predetermined range from the amount of deflection of the second roll.

  The transfer device according to claim 2, wherein the difference between the radius of both ends of the region in contact with the endless belt in the first roll and the radius of the central portion is the thickness of the both ends of the endless belt and the center. The size is within a range determined in advance from the difference from the thickness of the part.

    The image forming apparatus according to claim 3 forms an electrostatic latent image by exposing the image carrier, a charging unit for charging the image carrier, and the image carrier charged by the charging unit. A developing means for developing the electrostatic latent image formed by the exposing means to form an image on the surface of the image carrier, a transfer medium to which the image is transferred, and a Transfer means for transferring an image formed on the surface to the transfer medium, a transfer device according to claim 1 or 2 for transferring the image transferred to the transfer medium to a recording medium, and the image transferred to the recording medium And fixing means for fixing the image on the recording medium.

According to the first aspect of the present invention, in the endless belt supported by the first roll corresponding to the transfer roll and the second roll corresponding to the peeling roll, the radius and the center of the both ends of the first roll Compared to the case where the difference between the radius and the difference between the thickness of both end portions and the thickness of the center portion of the endless belt are not within the predetermined range from the deflection amount of the second roll. Thus, the peripheral speed difference caused by the deflection of the shaft of the second roll can be reduced.
According to invention of Claim 2, the difference of the radius of the said center part in the said 1st roll and the radius of the said both ends is the thickness of the said both ends of the said endless belt, and the thickness of the said center part. In the endless belt supported by the second roll corresponding to the first roll corresponding to the transfer roll and the second roll corresponding to the first roll corresponding to the transfer roll, the first end corresponding to the transfer roll is compared with the case where there is no configuration having a size within a predetermined range. The difference in peripheral speed due to the deflection of the shaft of the second roll can be further reduced.
According to invention of Claim 3, in the endless belt which the 1st roll corresponding to a transfer roll and the 2nd roll corresponding to a peeling roll support, the radius of the both ends in a 1st roll, and the center part Compared to the case where the difference between the radius and the difference between the thickness of both end portions and the thickness of the center portion of the endless belt are not within the predetermined range from the deflection amount of the second roll. Thus, the peripheral speed difference caused by the deflection of the shaft of the second roll can be reduced.

Block diagram showing hardware configuration of image forming apparatus The figure which shows an example of the structure of an image formation part Sectional view of the secondary transfer roll, the secondary transfer belt, and the flexing peeling roll in the conventional example viewed perpendicularly to the paper transport direction Sectional view of the secondary transfer roll, the secondary transfer belt, and the peeling roll that is warped in the present embodiment as viewed perpendicular to the paper conveyance direction A diagram showing the measurement results from experiments

<Embodiment>
FIG. 1 is a block diagram illustrating a hardware configuration of the image forming apparatus 10. The image forming apparatus 10 is configured as a computer having a control unit 100, an image forming unit 200, a storage unit 300, a communication unit 400, and a UI (User Interface) unit 500. Each part is electrically connected by a bus. The control unit 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit connected to the control unit 100 by executing a control program stored in the ROM or the storage unit 300.

  The image forming unit 200 is a unit that forms an image through each process of electrophotography such as charging, exposure, development, transfer, and fixing. The image forming unit 200 applies conditions according to these steps, and forms an image represented by the image data on a sheet. The image forming unit 200 is a unit that forms a color image in the present embodiment, but may be a unit that forms a monochrome image.

  The storage unit 300 is a storage device such as a hard disk and stores a control program, for example. The communication unit 400 acquires image data and the like by communicating with a client terminal such as a personal computer operated by the user under the control of the control unit 100. The UI unit 500 includes, for example, a touch screen and keys. The UI unit 500 supplies a signal corresponding to a user operation content to the control unit 100. The control unit 100 determines the operation content based on this signal, and executes, for example, an image forming process or displays an image on the touch screen.

  FIG. 2 is a diagram illustrating an example of the structure of the image forming unit 200. The image forming unit 200 illustrated in FIG. 2 forms an image using toner of four colors of yellow (Y), magenta (M), cyan (C), and black (K) by a so-called intermediate transfer method. is there. The image forming unit 200 includes toner cartridges 211Y, 211M, 211C, and 211K, transfer units 212Y, 212M, 212C, and 212K, an exposure device 213, an intermediate transfer belt 214, a plurality of support rolls 215, and a secondary transfer roll. 216, a secondary transfer belt 217, a peeling roll 218, a plurality of conveying rolls 219, and a fixing device 220.

  Note that among the components shown in FIG. 2, those with the alphabet (Y, M, C, or K) at the end of the reference sign indicate that the component corresponds to one of the above four colors. ing. Although these components are different in the color of the toner to be used, the main components and functions are common. Therefore, in the following description, when it is not necessary to distinguish these components from each other, they are collectively referred to as “toner cartridge 211” and “transfer unit 212” by omitting the suffix. It shall be.

  The toner cartridge 211 is means for storing toner of each color and supplying it to the developing unit of the transfer unit 212 as necessary. The transfer unit 212 includes a photosensitive drum as an image holding member, a charger for charging the photosensitive drum, a developing unit, a primary transfer roll, and the like, and intermediately transfers toner images of each color formed on the surface of the photosensitive drum. 2 is an example of a transfer unit that transfers to a belt 214; The exposure device 213 is an example of an exposure unit that exposes a photosensitive drum to form an electrostatic latent image. The developing device is an example of a developing unit that develops the electrostatic latent image formed by the exposure device 213 and forms an image on the surface of the photosensitive drum.

The intermediate transfer belt 214 is a unit that holds the toner image transferred by the transfer unit 212. That is, the intermediate transfer belt 214 is an example of a transfer medium to which a toner image is transferred. The intermediate transfer belt 214 is supported by a plurality of support rolls 215 and moves while circling in a direction indicated by an arrow A1 in the drawing. The secondary transfer roll 216 is a means for transferring the toner image transferred to the intermediate transfer belt 214 onto a sheet, and is an example of a first roll according to the present invention. The paper is an example of a recording medium according to the present invention. The secondary transfer belt 217 is an endless belt stretched between the secondary transfer roll 216 and the peeling roll 218, and is an example of an endless belt according to the present invention. As the secondary transfer roll 216 is driven, the secondary transfer belt 217 moves while rotating in the direction indicated by the arrow A2 in the drawing. A region where the intermediate transfer belt 214 supported by the support roll 215 is in contact with the secondary transfer belt 217 supported by the secondary transfer roll 216 is referred to as a contact region. In this contact area, the image is transferred from the intermediate transfer belt 214 to the sheet. The peeling roll 218 is provided at a position spaced apart from the secondary transfer roll 216 and rotates as the secondary transfer belt 217 rotates. When the sheet conveyed in close contact with the secondary transfer belt 217 moves to the position of the peeling roll 218, the sheet is peeled off from the secondary transfer belt 217 due to the rigidity of the sheet itself. The peeling roll 218 is an example of a second roll according to the present invention. The transport roll 219 is a means for transporting the paper along a route along the broken line arrow A3 in the drawing. The fixing device 220 is an example of a fixing unit that fixes the toner image on the paper by heating and pressing the paper on which the toner image is transferred by the secondary transfer roll 216.
The above is the description of the configuration of the image forming apparatus 10.

  Here, a phenomenon that occurs in the secondary transfer roll 216, the secondary transfer belt 217, and the peeling roll 218 will be described. First, in the secondary transfer roll 216 and the peeling roll 218, the end located on the back side of the image forming apparatus 10 in the rotation axis direction is referred to as the IN side end, and the end located on the front side is the OUT side end. The center position between the IN side end portion and the OUT side end portion is referred to as a center portion. Similarly, also in the secondary transfer belt 217, an end located on the back side of the image forming apparatus 10 in the rotation axis direction of the secondary transfer roll 216 and the peeling roll 218 is referred to as an IN side end and is located on the front side. The end is called the OUT side end, and the center position is called the center. Hereinafter, when both the IN side end and the OUT side end are shown, they are referred to as both ends. The central part is between these ends. Here, “between both ends” is a range that does not include both ends.

In the image forming apparatus 10, when the peeling roll 218 is made of a material having lower bending rigidity than the secondary transfer roll 216 due to manufacturing cost and installation space, the peeling is caused by the tension of the secondary transfer belt 217. The shaft of the roll 218 is bent.
FIG. 3 is a view of the secondary transfer roll 216, the secondary transfer belt 217, and the peeling roll 218 that has been bent in the conventional example as seen from a direction parallel to the rotation axes of the secondary transfer roll 216 and the peeling roll 218. . A secondary transfer belt 217 is stretched between the secondary transfer roll 216 and the peeling roll 218. As shown in FIG. 3, the peeling roll 218 is pulled and bent in a direction approaching the secondary transfer roll 216 by the tension of the secondary transfer belt 217. The amount of bending at this time is referred to as the amount of bending D. When the peeling roll 218 is bent, the length of the outer periphery of the secondary transfer belt 217 varies depending on each position in the belt width direction. Specifically, the length of the outer periphery of the secondary transfer belt 217 is shorter at the center than at both ends. Hereinafter, the difference in the length of the outer circumference between the both end portions and the central portion is referred to as the outer circumferential difference.

  When the secondary transfer roll 216 and the peeling roll 218 rotate in such a state where the outer peripheral lengths are different, the difference in the speed in the circumferential direction of the secondary transfer belt 217 at each position in the width direction of the secondary transfer belt 217 (hereinafter, referred to as the following) , Called peripheral speed difference). Specifically, the peripheral speed at the center of the secondary transfer belt 217 is slower than the peripheral speed at both ends by the shorter outer circumference. When such a peripheral speed difference occurs, a difference in length (hereinafter, referred to as a magnification difference) of an image formed on the sheet in the sheet conveyance direction occurs between both end portions and the center portion, which adversely affects image quality. . Specifically, in the image formed on the paper, the length of the image at both ends is longer than the length of the image at the center. In the present embodiment, the following structure is adopted for the secondary transfer roll 216 and the secondary transfer belt 217 so that such a problem does not occur.

  FIG. 4 is a view of the secondary transfer roll 216, the secondary transfer belt 217, and the peeling roll 218 that is bent in the present embodiment as viewed perpendicularly to the sheet conveyance direction. As shown in FIG. 4, the secondary transfer roll 216 has a reverse crown shape. Specifically, the radius of the central portion of the secondary transfer roll 216 is smaller than the radii of both ends of the region in contact with the secondary transfer belt 217. Hereinafter, the radii of both end portions of the secondary transfer roll 216 in contact with the secondary transfer belt 217 are simply referred to as the radii of both end portions. Correspondingly, the thickness of the central portion of the secondary transfer belt 217 is larger than the thickness of both end portions. That is, as shown in FIG. 4, the radius of the central portion of the secondary transfer roll 216 is smaller than the radius of the both end portions by a difference Diff at the maximum, and the thickness of the central portion of the secondary transfer belt 217 is The difference Diff is maximum as compared with the thicknesses of the both ends. In FIGS. 3 and 4, the belt thickness and the radius size of the secondary transfer roll are expressed in excess of the actual size so that the difference in belt thickness can be easily understood. Further, the radius of the secondary transfer roll 216 changes so as to gradually decrease from the end portion toward the center portion, and the thickness of the secondary transfer belt 217 increases gradually from the end portion toward the center portion. To change.

  At this time, the line segments L1 and L2 shown in FIG. 4 are in a state of being nearly parallel as compared to FIG. Here, the line segment L1 is a line segment connecting the contact points between the plane passing through the rotation axes of the secondary transfer roll 216 and the peeling roll 218 and the outer peripheral surface of the secondary transfer belt 217 on the peeling roll 218 side. A line segment L2 is a line segment connecting a contact point between the plane passing through the rotation axes of the secondary transfer roll 216 and the peeling roll 218 and the outer peripheral surface of the secondary transfer belt 217 on the secondary transfer roll 216 side. When the line segments L1 and L2 are parallel, the distance from the line segment L1 to L2 is substantially the same at each position in the width direction of the secondary transfer belt 217, so the length of the outer periphery of the secondary transfer belt 217 is also approximately the same. This is the same, and the difference in outer circumference is smaller than in FIG. Here, “substantially the same” means the same degree that the above-described magnification difference does not occur or an allowable magnification difference can occur.

  As described above, when the peeling roll 218 bends due to the tension of the secondary transfer belt 217, a difference in outer periphery occurs depending on the position in the width direction of the secondary transfer belt 217, causing the above-described problem of magnification difference. Therefore, in this embodiment, in order to eliminate the difference in the outer periphery, the central portion is configured to be thicker than both end portions of the secondary transfer belt 217 corresponding to the bending of the peeling roll 218. In this case, by aligning the curve formed by the bent peeling roll 218 with the curve formed by the inner peripheral side in the cross section of the secondary transfer belt 217, the above-described line segment L1 is rotated by the secondary transfer roll 216. Parallel to the axial direction.

  However, since the secondary transfer roll 216 does not bend, the center portion of the secondary transfer belt 217 in contact with the secondary transfer roll 216 rises more than the both ends due to the thickness. The outer periphery of the part becomes longer than the outer periphery of both ends. That is, as described above, the secondary transfer belt 217 on the secondary transfer roll 216 side is in a state where the central portion is raised, and therefore, when contacting the intermediate transfer belt 214, the secondary transfer belt 217 is applied to the central portion of the secondary transfer belt 217. Pressure becomes higher than both ends. As a result, the contact pressure applied to the secondary transfer roll 216 and the secondary transfer belt 217 in the contact area is not uniform in the width direction of the secondary transfer belt 217. If the contact pressure at the time of transfer is not uniform in the width direction of the secondary transfer belt 217, image quality may be adversely affected, such as unevenness in image density in the width direction.

  Therefore, in the present embodiment, the secondary transfer roll 216 is further formed in a reverse crown shape. The reverse crown shape of the roll is a shape in which the diameter of both end portions of the roll is smaller than the diameter of the central portion. The radius of the secondary transfer roll 216 having a reverse crown shape decreases from the both end portions toward the central portion. By making the radius difference between the central portion and both end portions of the secondary transfer roll 216 in accordance with the difference in thickness between the central portion and both end portions of the secondary transfer belt 217, the reverse crown of the secondary transfer roll 216 is obtained. The curve formed by the shape matches the curve formed by the inner peripheral side in the cross section of the secondary transfer belt 217. Thereby, as shown in FIG. 4, the line segment L2 becomes substantially parallel to the line segment L1, and the difference in outer periphery is eliminated. Here, the difference in radius between both ends and the center of the secondary transfer roll 216 having an inverted crown shape and the difference in thickness between the ends and the center of the secondary transfer belt 217 are both the secondary transfer roll 216. This is a size within a predetermined range from the deflection amount Dmax of the shaft which is the rotation axis of the shaft. Here, the “bending amount Dmax” is determined from the line segment L3 connecting the contact points P1 and P2 between the widthwise end of the secondary transfer belt 217 on the inner side of the secondary transfer belt 217 and the peeling roll 218 on the peeling roll 218 side. Expressed by the maximum distance to. The “predetermined range” means a range in which the above-described magnification difference does not occur or an allowable magnification difference can occur, and is specified in advance by experiment or calculation. . With such a configuration, the difference in outer periphery of the secondary transfer belt 217 is eliminated, so that the difference in peripheral speed between the peripheral speed at the center of the secondary transfer belt 217 and the peripheral speed at both ends is reduced. As a result, the contact pressure applied to the secondary transfer roll 216 and the secondary transfer belt 217 approaches a uniform state in the contact area described above, and a difference in magnification in the sheet conveyance direction of the image formed on the sheet is suppressed. The

FIG. 5 is a diagram illustrating a measurement result by an experiment in the present embodiment.
In the figure, the values of the central portion and the end portion of the thickness of the secondary transfer belt 217 and the diameter of the secondary transfer roll 216 are described in units of mm (millimeters). Here, the end portion is simply described on the assumption that the diameters of both ends are the same, but an average of the diameter of the IN side end and the diameter of the OUT side end may be used. Further, regarding the secondary transfer belt 217, the difference between the two obtained by subtracting the thickness of the end portion from the thickness of the central portion is expressed in mm. Further, for the secondary transfer roll 216, a value that is half of the difference between the diameter of the center portion and the diameter of the end portion is expressed in mm. That is, the “radius difference” is a difference between the radius of the central portion and the radius of the end portion of the secondary transfer roll 216.

  In addition, “transfer unevenness” and “magnification difference” are shown as measurement results. “Transfer unevenness” represents the degree of transfer unevenness. That is, when “transfer unevenness” is “◯”, it indicates that there is no transfer unevenness on the paper, and “Δ” indicates that an acceptable range of transfer unevenness occurs. “Δ−” represents an allowable range but is not desirable as compared with “Δ”. “X” indicates that an unacceptable range of transfer unevenness has occurred on the paper. The evaluation here is based on visual judgment. The “magnification difference” is the difference between the width of the image formed on the IN side edge in the paper conveyance direction and the width of the image formed on the OUT side edge in the paper conveyance direction. ) Shown in units. In the figure, if the magnification difference is in the range of “−100 to +100 μm”, “◯” means that there is no problem, and if it is in the range of “−200 to −100 μm” and “+100 to +200 μm”, it is acceptable. “Δ” which means that the level is possible, and “X” which means that there is a problem in other ranges.

  In Embodiments 1 and 2, the thickness of the central portion of the secondary transfer belt 217 is thicker than the end portion, and the diameter of the central portion of the secondary transfer roll 216 is smaller than the diameter of the end portion. In Examples 1 and 2 described above, both “transfer unevenness” and “magnification difference” are good results. Hereinafter, the difference in thickness between the central portion and the end portion of the secondary transfer belt 217 is referred to as a belt thickness difference. Further, hereinafter, the difference in radius between the central portion and the end portion of the secondary transfer roll 216 is referred to as a roll radius difference.

  In Example 3, the difference in belt thickness is thicker at the center than at the end, and the radius difference between rolls is narrower at the center than at the end. In Example 3, compared with Examples 1 and 2, the radius difference between the rolls is smaller than the difference in belt thickness. In such a case, as shown in FIG. In Example 4, the belt thickness difference is thicker at the center than at the end, and the roll radius difference is narrower at the center than at the end. In Example 4, compared to Examples 1 and 2, the difference in the belt thickness and the difference in the radius of the roll are large. In such a case, as shown in the drawing, there is a slight difference in magnification within an allowable range. In Example 5, the difference in belt thickness is thicker at the center than at the end, and the radius difference of the roll is narrower at the center than at the end. In Example 5, as compared with Examples 1 and 2, the roll radius difference is larger than the belt thickness difference. In such a case, as shown in the drawing, there is a slight difference in magnification within an allowable range.

  In Comparative Example 1, the difference in the belt thickness is thicker at the center than at the end, and the difference in the radius of the roll is slightly different between the center and the end. In such a case, an unacceptable range of transfer unevenness occurs, and an unacceptable range of magnification difference occurs. In Comparative Example 1, the secondary transfer roll 216 is substantially cylindrical, and the secondary transfer belt 217 is thicker at the center than at the end. Therefore, when the secondary transfer belt 217 is stretched over the secondary transfer roll 216 and used, a crown shape corresponding to the thickness of the central portion of the secondary transfer belt 217 is exhibited. In this case, as is clear from the experimental results, a magnification difference in the paper conveyance direction occurs.

  In Comparative Example 2, the belt thickness difference is thicker at the center than at the end, and the roll radius difference is thicker at the center than at the end. In such a case, an unacceptable range of transfer unevenness occurs, but an unacceptable range of magnification difference occurs. In Comparative Example 2, the secondary transfer roll 216 has a crown shape, and when the secondary transfer belt 217 is stretched over and used, the central portion is further increased by the thickness of the central portion of the secondary transfer belt 217. Becomes thicker. In this case as well, as is clear from the experimental results, a magnification difference in the paper transport direction occurs.

  In Comparative Example 3, the belt thickness difference is thicker at the center than at the end, and the roll radius difference is narrower at the center than at the end. In Comparative Example 3, the difference in roll radius is larger than the difference in belt thickness. In such a case, the secondary transfer belt 217 does not come into contact with the central portion of the secondary transfer roll 216. In such a case, an unacceptable range of transfer unevenness occurs, and an unacceptable range of magnification difference occurs. In Comparative Example 4, the difference in belt thickness is thinner at the center than at the end, and the radius difference between the rolls is thicker at the center than at the end. That is, the comparative example 4 has a configuration opposite to the configuration in the present embodiment. In such a case, unacceptable range of transfer unevenness and magnification difference occur.

The difference in thickness between the central portion and both end portions of the secondary transfer belt 217 is preferably within a range determined in advance from the radial difference between the central portion and both end portions of the secondary transfer roll 216. The predetermined range obtained by the above-described experiment is preferably “± 0.15 mm”, and the allowable range of the limit is “± 0.25 mm”. This can be expressed, for example, by the following equation (1).
(| Secondary transfer roll shaft end diameter−secondary transfer roll shaft center diameter |) / 2− (| secondary transfer belt center thickness−secondary transfer belt end thickness |) = (− 0. (15mm, + 0.15mm) (1)

  Note that the roll radius difference and the belt thickness difference shown in FIG. 5 are merely examples, and appropriate values differ depending on the size, shape, material, and the like of the secondary transfer roll 216, the peeling roll 218, and the secondary transfer belt 217. .

  According to this embodiment, as the outer peripheral difference of the secondary transfer belt 217 is eliminated, the contact pressure in the contact area becomes uniform, and the peripheral speed difference in the secondary transfer belt 217 is eliminated. In addition, since only the shapes of the secondary transfer roll 216 and the secondary transfer belt 217 are devised, there is no need to separately provide a driving device that performs control for eliminating the peripheral speed difference, for example.

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 100 ... Control part, 200 ... Image forming part, 300 ... Memory | storage part, 400 ... Communication part, 500 ... UI part, Toner cartridge ... 211, Transfer unit ... 212, Exposure apparatus ... 213, Intermediate transfer belt 214, support roll 215, secondary transfer roll 216, secondary transfer belt 217, peeling roll 218, transport roll 219, fixing device 220, density sensor 221

Claims (3)

An endless belt in which the thickness of both end portions in the width direction is smaller than the thickness of the central portion between the both end portions,
The image is rotated in contact with the transfer medium to which the image has been transferred, and the image is transferred from the transfer medium to a recording medium conveyed to a contact area with the transfer medium. A first roll in which the radius of both ends of the region in contact with the endless belt in the rotation axis direction is larger than the radius of the central portion between the both ends,
A second roll provided at a position spaced apart from the first roll and rotating and on which the endless belt is stretched;
The difference between the radius of the both ends of the region in contact with the endless belt in the first roll and the radius of the central portion, and the difference between the thickness of the both ends of the endless belt and the thickness of the central portion, Is a size within a predetermined range from the amount of deflection of the second roll. The difference between the radius of the both ends of the region in contact with the endless belt in the first roll and the radius of the center is determined in advance from the difference between the thickness of the both ends of the endless belt and the thickness of the center. The transfer device according to claim 1, wherein the size is within a range. An image carrier,
Charging means for charging the image carrier;
Exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image formed by the exposure means to form an image on the surface of the image carrier;
A transfer medium on which the image is transferred;
Transfer means for transferring an image formed on the surface of the image carrier to the transfer medium;
The transfer device according to claim 1 or 2, wherein the image transferred to the transfer medium is transferred to a recording medium;
An image forming apparatus comprising: fixing means for fixing the image transferred to the recording medium to the recording medium.

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