TRANSFER DEVICE AND IMAGE FORMING APPARATUS

A transfer device includes: an endless transfer belt that circulates and receives an image; one image carrier that carries an image and is in contact with an outer circumferential surface of the transfer belt from above; another image carrier that carries an image and is in contact with the outer circumferential surface of the transfer belt from below; one transfer roller that holds the transfer belt with respect to the one image carrier to transfer the image carried on the one image carrier to the transfer belt, the one transfer roller including one cylindrical roller part; and another transfer roller that holds the transfer belt with respect to the other image carrier to transfer the image carried on the other image carrier to the transfer belt, the other transfer roller including another cylindrical roller part. The one roller part and the other roller part protrude at central portions thereof in the axial direction with respect to ends thereof in the axial direction. The amount of protrusion at the central portion of the other roller part is smaller than the amount of protrusion at the central portion of the one roller part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2023-130496 filed Aug. 9, 2023.

BACKGROUND

(i) Technical Field

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

(ii) Related Art

An image forming apparatus described in Japanese Unexamined Patent Application Publication No. 2009-80325 includes multiple image forming units, a transfer belt member, multiple stretching members, first transfer members, a second transfer member, and a fixing unit.

The image forming units form visible images by allowing charged developer to adhere to electrostatic latent images. The visible images formed by the image forming units are transferred to the transfer belt member. The transfer belt member is stretched over the stretching members. The first transfer members transfer the visible images formed by the image forming units to the transfer belt member. The second transfer member transfers the visible image transferred to the transfer belt member to a recording medium. The fixing unit fixes the visible image transferred to the recording medium. The image forming units are arranged in two or more transfer areas defined by the transfer belt member and the stretching members.

SUMMARY

A transfer device includes multiple image carriers arranged side-by-side in a direction in which the transfer belt runs, and transfer rollers disposed on the other side of the transfer belt from the image carriers.

At this time, one transfer roller and another transfer roller may be provided. The one transfer roller is disposed on the other side of the transfer belt from one image carrier that is in contact with the outer circumferential surface of the transfer belt from above. The other transfer roller is disposed on the other side of the transfer belt from another image carrier that is in contact with the outer circumferential surface of the transfer belt from below.

With this structure, when the shape of the one transfer roller and the shape of the other transfer roller are the same, a difference occurs between: the pressure generated between the one transfer roller and the one image carrier at the central portion in the axial direction; and the pressure generated between the other transfer roller and the other image carrier at the central portion in an axial direction, due to deflection of the transfer rollers caused by gravity.

Aspects of non-limiting embodiments of the present disclosure relate to reducing the difference between: the pressure generated between the one transfer roller and the one image carrier at the central portion in the axial direction; and the pressure generated between the other transfer roller and the other image carrier at the central portion in the axial direction, compared with a case where the shape of the one transfer roller and the shape of the other transfer roller are the same.

According to an aspect of the present disclosure, there is provided a transfer device including: an endless transfer belt that circulates and receives an image; one image carrier that carries an image and is in contact with an outer circumferential surface of the transfer belt from above; another image carrier that carries an image and is in contact with the outer circumferential surface of the transfer belt from below; one transfer roller that holds the transfer belt with respect to the one image carrier to transfer the image carried on the one image carrier to the transfer belt, the one transfer roller including one cylindrical roller part; and another transfer roller that holds the transfer belt with respect to the other image carrier to transfer the image carried on the other image carrier to the transfer belt, the other transfer roller including another cylindrical roller part. The one roller part and the other roller part protrude at central portions thereof in the axial direction with respect to ends thereof in the axial direction. The amount of protrusion at the central portion of the other roller part is smaller than the amount of protrusion at the central portion of the one roller part.

DETAILED DESCRIPTION

An example of transfer device and an example of image forming apparatus according to an exemplary embodiment of the present disclosure will be described with reference toFIGS.1to6. In the drawings, the arrow H indicates the apparatus top-bottom direction (vertical direction), the arrow W indicates the apparatus width direction (horizontal direction), and the arrow D indicates the apparatus depth direction (horizontal direction).

Image Forming Apparatus

An image forming apparatus10according to this exemplary embodiment is an electrophotographic image forming apparatus that forms a toner image on a sheet member P, serving as a recording medium. As illustrated inFIG.1, the image forming apparatus10includes a storage section20, a transport section30, an image forming section40, and a fixing device50.

Storage Section and Transport Section

The storage section20includes a storage member22that stores sheet members P, and a feed roller24that feeds the sheet members P stored in the storage member22to a sheet transport path32. The transport section30includes multiple transport rollers34that transport the sheet members P along the transport path32.

Image Forming Section

The image forming section40includes toner-image forming units60that form toner images, and a transfer device70that transfers the toner images formed by the toner-image forming units60to a sheet member P.

Toner-Image Forming Unit

The toner-image forming units60include toner-image forming units60Y,60M,60C, and60K corresponding to a total of four colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). Note that alphabet letters appended to the reference signs may be omitted when Y, M, C, and K are not distinguished from one another.

The toner-image forming units60Y and60M have basically the same structure except for the toners used. The toner-image forming units60C and60K have basically the same structure except for the toners used.

As illustrated inFIGS.1and2, the toner-image forming units60Y and60M are arranged side-by-side along a horizontal portion of a transfer belt71provided in the transfer device70. As illustrated inFIGS.1and3, the toner-image forming units60C and60K are arranged side-by-side along an inclined portion of the transfer belt71provided in the transfer device70.

As illustrated inFIG.2, the toner-image forming units60Y and60M include photosensitive members61Y and61M that rotate in the arrow A01direction and are in contact with the outer circumferential surface of the transfer belt71from above, and charging devices62Y and62M that charge the photosensitive members61Y and61M.

The toner-image forming units60Y and60M also include exposure devices63Y and63M that radiate light onto the photosensitive members61Y and61M charged by the charging devices62Y and62M to form electrostatic latent images, and developing devices64Y and64M that develop the electrostatic latent images with toner to form toner images.

As illustrated inFIG.3, the toner-image forming units60C and60K include photosensitive members61C and61K that rotate in the arrow A02direction and are in contact with the outer circumferential surface of the transfer belt71from below, and charging devices62C and62K that charge the photosensitive members61C and61K.

The toner-image forming units60C and60K include exposure devices63C and63K that radiate light onto the photosensitive members61C and61K charged by the charging devices62C and62K to form electrostatic latent images, and developing devices64C and64K that develop the electrostatic latent images with toner to form toner images.

Transfer Device

As illustrated inFIG.1, the transfer device70includes the photosensitive members61Y,61M,61C, and61K, the transfer belt71, multiple rollers72, first transfer rollers73Y,73M,73C, and73K, a second transfer roller76, and a removal blade78. As described, the photosensitive members61Y,61M,61C, and61K constitute the transfer device70and, at the same time, constitute the toner-image forming unit60.

In this structure, the first transfer rollers73Y,73M,73C, and73K transfer the toner images held on the photosensitive members61Y,61M,61C, and61K to the running transfer belt71. Furthermore, the second transfer roller76transfers the toner image transferred to the transfer belt71to a sheet member P being transported. The transfer device70will be described in detail below.

Fixing Device

As illustrated inFIG.1, the fixing device50includes a heating roller50athat rotates, and a pressure roller50bthat is rotated by the heating roller50aand presses the sheet member P against the heating roller50awhile nipping the sheet member P between the heating roller50aand the pressure roller50b. The fixing device50is an example of fixing unit.

With this structure, the fixing device50applies heat and pressure to the sheet member P having the toner image transferred thereto to fix the toner image to the sheet member P. The sheet member P having the toner image fixed thereto is discharged to the outside of a housing10aof the image forming apparatus10.

Relevant Part Structure

Next, the transfer device70will be described. As described above, the transfer device70includes the photosensitive members61Y,61M,61C, and61K, the transfer belt71, the rollers72, the first transfer rollers73Y,73M,73C, and73K, the second transfer roller76, and the removal blade78. The photosensitive members61Y and61M are an example of one image carrier, and the photosensitive members61C and61K are an example of another image carrier. The first transfer rollers73Y and73M are an example of one transfer roller, and the first transfer rollers73C and73K are an example of another transfer roller.

Photosensitive Member

The photosensitive members61Y,61M,61C, and61K have a circular cross section. All the photosensitive members61Y,61M,61C, and61K have the same outer diameter. In other words, the photosensitive members61Y,61M,61C, and61K all have the same shape.

As illustrated inFIG.2, the photosensitive members61Y and61M are in contact with the outer circumferential surface of the transfer belt71from above. As illustrated inFIG.3, the photosensitive members61C and61K are in contact with the outer circumferential surface of the transfer belt71from below.

Transfer Belt, Rollers, Second Transfer Roller, and Removal Blade

As illustrated inFIG.1, the transfer belt71is an endless belt wound around the rollers72in an inverted triangular form. The toner-image forming units60Y and60M are arranged side-by-side along the horizontal portion on the upper side of the transfer belt71, and the toner-image forming units60C and60K are arranged side-by-side along the inclined portion of the transfer belt71on one side (right side inFIG.1) in the apparatus width direction. The transfer belt71runs in the arrow B direction when at least one of the rollers72is rotationally driven.

The second transfer roller76is disposed on the other side of the transfer belt71from the roller72(the roller72ainFIG.1) that is disposed so as to push outward an inclined portion of the transfer belt71on the other side (left side inFIG.1) in the apparatus width direction. The second transfer roller76transfers a toner image, which has been transferred to the transfer belt71, to a sheet member P being transported, at a transfer position NT.

The removal blade78is disposed on the other side of the transfer belt71from the roller72(the roller72binFIG.2) around which a portion of the transfer belt71on the other side in the apparatus width direction is wound. The removal blade78removes substance deposited on the transfer belt71from the transfer belt71.

First Transfer Rollers

As illustrated inFIG.2, the first transfer rollers73Y and73M are disposed on the other side of the transfer belt71from the photosensitive members61Y and61M so as to hold the transfer belt71with respect to the photosensitive members61Y and61M from below the transfer belt71.

What is meant by that the first transfer rollers73Y and73M hold the transfer belt71with respect to the photosensitive members61Y and61M from below the transfer belt71is that the first transfer rollers73Y and73M are disposed below the photosensitive members61Y and61M, respectively, when viewed from the apparatus depth direction. Specifically, the first transfer rollers73Y and73M are disposed below the photosensitive members61Y and61M in a state in which line segments L1connecting the centers C of the first transfer rollers73Y and73M and the centers C of the photosensitive members61Y and61M are inclined at at least 15° with respect to the horizontal direction. In this exemplary embodiment, for example, the line segments L1are inclined by 90° with respect to the horizontal direction.

As illustrated inFIG.4, the first transfer rollers73Y and73M include elastic cylindrical roller parts80Y and80M, and shafts82Y and82M made of stainless steel and inserted through the roller parts80Y and80M so as to protrude outside from the ends of the roller parts80Y and80M.

The first transfer rollers73Y and73M are rotatably supported by support members98disposed at the ends of the shafts82Y and82M. This allows the first transfer rollers73Y and73M to be rotated by the running transfer belt71.

Meanwhile, as illustrated inFIG.3, the first transfer rollers73C and73K are disposed on the other side of the transfer belt71from the photosensitive members61C and61K so as to hold the transfer belt71with respect to the photosensitive members61C and61K from above the transfer belt71.

What is meant by that the first transfer rollers73C and73K hold the transfer belt71with respect to the photosensitive members61C and61K from above the transfer belt71is that the first transfer rollers73C and73K are disposed above the photosensitive members61C and61K, respectively, when viewed from the apparatus depth direction. Specifically, the first transfer rollers73C and73K are disposed above the photosensitive members61C and61K in a state in which line segments L2connecting the centers C of the first transfer rollers73C and73K and the centers C of the photosensitive members61C and61K are inclined at at least 15° with respect to the horizontal direction. In this exemplary embodiment, for example, the line segments L2are inclined at 65° with respect to the horizontal direction.

As illustrated inFIG.5, the first transfer rollers73C and73K include clastic cylindrical roller parts80C and80K, and shafts82C and82K made of stainless steel and are inserted through the roller parts80C and80K so as to protrude outside from the ends of the roller parts80C and80K.

The first transfer rollers73C and73K are rotatably supported by support members98disposed at the ends of the shafts82C and82K. This allows the first transfer rollers73C and73K to be rotated by the running transfer belt71.

At this time, the first transfer rollers73Y and73M supported at support points, which are the support members98, sag due to gravity, as indicated by a two-dot chain line inFIG.4. Hence, the distance between the first transfer rollers73Y and73M and the photosensitive members61Y and61M at the central portions thereof in the axial direction is larger than that in the case where the first transfer rollers do not sag. Meanwhile, the first transfer rollers73C and73K supported at support points, which are the support members98, sag due to gravity, as indicated by a two-dot chain line inFIG.5. Hence, the distance between the first transfer rollers73C and73K and the photosensitive members61C and61K at the central portions thereof in the axial direction is larger than that in the case where the first transfer rollers do not sag.

The two-dot chain lines inFIGS.4and5representing the sag are exaggerated for better understanding of the sag.

For these reasons, the pressure generated between the first transfer rollers73Y and73M and the photosensitive members61Y and61M at the central portions thereof in the axial direction may be weaker than the pressure generated between the first transfer rollers73C and73K and the photosensitive members61C and61K at the central portions thereof in the axial direction.

However, as illustrated inFIG.6A, in the first transfer rollers73Y and73M, the outer diameter of the central portion of the roller parts80Y and80M in the axial direction is larger than the outer diameter of the ends of the roller parts80Y and80M in the axial direction. The outer circumferential surfaces of the roller parts80Y and80M are each formed of a single convex surface. As described, the outer circumferential surfaces of the roller parts80Y and80M have a positive crown shape. The ends of the roller parts80in the axial direction are the ends of the outer circumferential surfaces of the roller parts80in the axial direction. The central portion of the roller parts80in the axial direction is the portion where the distance from one end in the axial direction and the distance from the other end in the axial direction are equal.

Meanwhile, as illustrated inFIG.6B, in the first transfer rollers73C and73K, the outer diameter of the central portion of the roller parts80C and80K in the axial direction is smaller than the outer diameter of the ends of the roller parts80C and80K in the axial direction. The outer circumferential surfaces of the roller parts80C and80K are each formed of a single concave surface. As described, the outer circumferential surfaces of the roller parts80C and80K have a negative crown shape. The outer diameter of the ends of the roller parts80C and80K in the axial direction is equal to the outer diameter of the ends of the roller parts80Y and80M in the axial direction. The crown shapes illustrated inFIGS.6A and6Bare exaggerated for better understanding of the crown shapes.

Furthermore, the distance (D1inFIG.4) between the center of the shafts82Y and82M, at the portion supported by the support member98, and the axis of the photosensitive members61Y and61M is shorter than the distance (D2inFIG.5) between the center of the shafts82C and82K, at the portion supported by the support member98, and the axis of the photosensitive members61C and61K. The distances D1and D2may be measured by using, for example, a three-dimensional measurement device.

As described above, in the first transfer rollers73Y and73M of the transfer device70, the outer diameter of the central portion of the roller parts80Y and80M in the axial direction is larger than the outer diameter of the ends of the roller parts80Y and80M in the axial direction. Furthermore, in the first transfer rollers73C and73K, the outer diameter of the central portion of the roller parts80C and80K in the axial direction is smaller than the outer diameter of the ends of the roller parts80C and80K in the axial direction. Hence, compared with the case where the shape of the roller parts80Y and80M of the first transfer rollers73Y and73M and the shape of the roller parts80C and80K of the first transfer rollers73C and73K are the same, the difference between: the pressure generated between the first transfer rollers73Y and73M and the photosensitive members61Y and61M at the central portions thereof in the axial direction; and the pressure generated between the first transfer rollers73C and73K and the photosensitive members61C and61K at the central portions thereof in the axial direction, is small.

In the transfer device70, the outer circumferential surfaces of the roller parts80Y and80M and the outer circumferential surfaces of the roller parts80C and80K are curved surfaces. Thus, compared with the case where the roller parts include steps, the pressure generated between the first transfer roller73and the photosensitive member61gradually changes in the axial direction.

Furthermore, in the transfer device70, the outer circumferential surfaces of the roller parts80Y and80M have a positive crown shape, and the outer circumferential surfaces of the roller parts80C and80K have a negative crown shape. In other words, the amount of protrusion of the roller parts80Y and80M is positive, and the amount of protrusion of the roller parts80C and80K is negative. Hence, compared with a case where the amount of protrusion of both roller parts is positive or a case where the amount of protrusion of both roller parts is negative, the difference between: the pressure generated between the first transfer rollers73Y and73M and the photosensitive members61Y and61M at the central portions thereof in the axial direction; and the pressure generated between the first transfer rollers73C and73K and the photosensitive members61C and61K at the central portions thereof in the axial direction, is small. At this time, the magnitude of the amount of protrusion is not the magnitude of absolute values, but the magnitude including positive and negative values.

In the transfer devices70, the outer diameter of the photosensitive members61Y and61M and the outer diameter of the photosensitive members61C and61K are the same.

Furthermore, in the transfer device70, the distance (D1inFIG.4) between the center of the shafts82Y and82M, at the portion supported by the support member98, and the axis of the photosensitive members61Y and61M is shorter than the distance (D2inFIG.5) between the center of the shafts82C and82K, at the portion supported by the support member98, and the axis of the photosensitive members61C and61K.

The image forming apparatus10includes the transfer device70.

Although a specific exemplary embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to this exemplary embodiment, and it is apparent to those skilled in the art that various other exemplary embodiments are possible within the scope of the present disclosure. For example, although the outer circumferential surfaces of the roller parts80are curved surfaces in the exemplary embodiment, the roller parts may have corners, steps, or the like. In that case, however, the advantage provided by the roller parts80having curved outer circumferential surfaces is not obtained.

In the exemplary embodiment described above, the amount of protrusion of the roller parts80Y and80M is positive, and the amount of protrusion of the roller parts80C and80K is negative. Instead, the amount of protrusion of both roller parts may be positive, the amount of protrusion of both roller parts may be negative, or the amount of protrusion of either the roller parts80Y and80M or the roller parts80C and80K may be zero. However, in that case, the advantage provided by the roller parts80Y and80M having positive amount of projection and the roller parts80C and80K having negative amount of projection is not obtained.

Furthermore, in the above-described exemplary embodiment, the distance (D1inFIG.4) between the center of the shafts82Y and82M, at the portion supported by the support member98, and the axis of the photosensitive members61Y and61M is shorter than the distance (D2inFIG.5) between the center of the shafts82C and82K, at the portion supported by the support member98, and the axis of the photosensitive members61C and61K. However, the distances D1and D2may be equal. In that case, however, the advantage provided by the distance D1being shorter than the distance D2is not obtained.

Although not particularly described in the above-described exemplary embodiment, the pressure generated between the second transfer roller76and the roller72ais higher than the pressure generated between the first transfer rollers73and the photosensitive members61.

APPENDIX

A transfer device including: an endless transfer belt that circulates and receives an image; one image carrier that carries an image and is in contact with an outer circumferential surface of the transfer belt from above; another image carrier that carries an image and is in contact with the outer circumferential surface of the transfer belt from below; one transfer roller that holds the transfer belt with respect to the one image carrier to transfer the image carried on the one image carrier to the transfer belt, the one transfer roller including one cylindrical roller part; and another transfer roller that holds the transfer belt with respect to the other image carrier to transfer the image carried on the other image carrier to the transfer belt, the other transfer roller including another cylindrical roller part, wherein the one roller part and the other roller part protrude at central portions thereof in an axial direction with respect to ends thereof in the axial direction, and the amount of protrusion at the central portion of the other roller part is smaller than the amount of protrusion at the central portion of the one roller part.

The transfer device according to (((1))), wherein the outer circumferential surface of the one roller part and the outer circumferential surface of the other roller part are curved surfaces.

The transfer device according to (((1))) or (((2))), wherein the amount of protrusion of the one roller part is positive, and the amount of protrusion of the other roller part is negative.

The transfer device according to any one of (((1))) to (((3))), wherein the outer diameter of the one image carrier and the outer diameter of the other image carrier are the same.

The transfer device according to any one of (((1))) to (((4))), wherein the one transfer roller includes one shaft member inserted through the first roller part and protruding from both ends of the first roller part, the other transfer roller includes another shaft member inserted through the other roller part and protruding from both ends of the other roller part, and the distance between the center of the one shaft member, at a portion where the one shaft member is supported, and the axis of the one image carrier is shorter than the distance between the center of the other shaft member, at a portion where the other shaft member is supported, and the axis of the other image carrier.

An image forming apparatus including: the transfer device according to any one of (((1))) to (((5))); and a fixing unit that fixes the image transferred to a recording medium by the transfer device to the recording medium.