Belt unit, transfer device, and image forming apparatus

Abstract

To prevent the occurrence of damage including cracks in a transfer belt to extend its life.SOLUTION: A transfer belt unit 1 as a belt unit comprises: a drive roller 61 that rotates a transfer belt 7; a counter roller 62 that is arranged on the downstream side of the drive roller 61; and a cleaning roller 70 that is opposite to the counter roller 62 with the transfer belt 7 therebetween. The transfer belt 7 has projections 72 projecting toward its inner periphery at both ends. The counter roller 62 is provided such that the ends of a body are located on the inside in an axial direction X of the projections 72 with respect to the transfer belt 7. The cleaning roller 70 is provided such that the ends of a body are located on the inside in the axial direction X of the ends of the body of the counter roller 62.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a belt unit, a transfer device including the belt unit, and an image forming apparatus. [Background technology]

[0002] In an electrophotographic image forming apparatus, an electrostatic latent image corresponding to the image to be printed is formed on a photosensitive drum, and is visualized and developed with supplied toner. The toner image formed on the photosensitive drum is transferred to a transfer belt, for example, and then transferred from the transfer belt to paper, and then fixed to the paper by a fixing unit.

[0003] In this type of image forming device, the transfer belt is formed in a ring shape, and is stretched around a drive roller, a driven roller, etc. to move in a circular motion, and is configured to transfer a toner image onto paper when passing between the photosensitive drum and the transfer roller. However, the transfer belt has a problem in that it is prone to a phenomenon called skew or meandering, in which the transfer belt moves in one direction of the roller shaft of the drive roller, etc., while it is moving.

[0004] To address such problems, for example, Patent Document 1 discloses providing a rib member called a bead on the transfer belt to prevent the transfer belt from skewing, etc. The rib member is formed in a strip shape along the inner circumferential surface of the belt body of the transfer belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-76999 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the conventional transfer belt, the rib member is attached to the belt body with an adhesive. However, since the rib member is subjected to a large load, there is a risk that cracks may easily occur near the adhesive portion during long-term use.

[0007] In addition, there is a problem that the rib member provided on the transfer belt is likely to ride up on each roller that stretches the transfer belt. For example, the drive roller disclosed in the above-mentioned Patent Document 1 is wound with urethane rubber on the entire outer circumference and is made of a material with a high friction coefficient, so there was a problem that the rib member was likely to ride up on the drive roller for a long time.

[0008] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a belt unit that can prevent damage such as cracks from occurring in the transfer belt, enable stable operation for a long period of time, and increase production efficiency, as well as a transfer device and an image forming apparatus that are equipped with such a belt unit. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the present invention comprises a circular belt stretched by a plurality of tension rollers arranged parallel to each other and having an axle portion and a body portion, a drive roller which is one of the plurality of tension rollers and rotates the belt, an inner roller which is one of the plurality of tension rollers and is arranged downstream in the rotation direction of the belt relative to the drive roller so that the belt is wound around the body portion, and an outer roller which abuts the outer peripheral surface of the belt and is arranged to sandwich the belt between the inner roller, wherein the belt has protrusions protruding inward at both ends in the width direction of the belt which coincide with the axial direction of the tension rollers, the ends of the body portion of the inner roller are arranged so as to be located more inward in the axial direction than the protrusions relative to the belt, and the ends of the body portion of the outer roller are arranged so as to be located more inward in the axial direction than the ends of the body portion of the inner roller.

[0010] More specific examples of the belt unit having the above configuration include the following: That is, in the belt unit having the above configuration, it is preferable that a body portion of the inner roller abuts against the inner circumferential surface of the belt, and the axial length of the body portion is shorter than the axial distance between the protrusions, and a body portion of the outer roller abuts against the belt, and the axial length of the body portion is shorter than the axial length of the body portion of the inner roller.

[0011] In addition, in the belt unit having the above configuration, it is preferable that the drive roller abuts against the inner peripheral surface of the belt at the body portion, and the outer roller is arranged upstream of the inner roller in the rotation direction so that the belt is located on the inner side of a plane formed by a tangent connecting the outer peripheral surface of the body portion of the drive roller and the outer peripheral surface of the body portion of the inner roller.

[0012] In the belt unit having the above-described configuration, it is preferable that the inner roller is provided such that the length of the body portion in the axial direction is the longest among the plurality of tension rollers.

[0013] In the belt unit having the above configuration, the body of the outer roller may have an inclined portion at both ends in the axial direction such that the diameter of the outer peripheral surface becomes smaller from the inside to the outside in the axial direction of the body. Also, the belt may have a seam along the width direction of the belt.

[0014] In order to achieve the above object, a transfer device equipped with the belt unit is also within the scope of the technical idea of ​​the present invention. That is, it is preferable that the transfer device further includes a transfer roller that is one of the plurality of tension rollers, the belt is a transfer belt, and the outer roller is a cleaning roller that cleans the transfer belt. Also, an image forming apparatus equipped with the transfer device is also within the scope of the technical idea of ​​the present invention.

[0015] By satisfying the above-mentioned specific features, it is possible to provide a belt unit that prevents damage such as cracks from occurring in the protruding portions of the belt and enables stable running for a long period of time, as well as a transfer device and an image forming apparatus that are equipped with such a belt unit. Effect of the Invention

[0016] According to the present invention, it is possible to prevent damage such as cracks from occurring in a belt that is stretched by a plurality of tension rollers and has protrusions, thereby enabling the belt to run stably and have a long life. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing a transfer device provided in the image forming apparatus. [Diagram 3] 3 is a perspective view showing the transfer device as viewed from the opposite side of FIG. 2. FIG. [Figure 4] 2 is a side view showing the transfer device as viewed in the direction of the arrow A in FIG. 1. [Diagram 5] 5 is a cross-sectional view taken along line BB in FIG. [Figure 6] 2 is a perspective view showing a tension roller and a transfer belt in a transfer belt unit provided in the transfer device. FIG. [Figure 7] FIG. 2 is a partially cutaway perspective view of a transfer belt in the transfer belt unit; [Figure 8A] FIG. 4 is a side view of the transfer belt as viewed in the axial direction. [Figure 8B] 8B is a cross-sectional view taken along CC in FIG. 8A. [Figure 9] 7 is an explanatory diagram showing a schematic configuration of the transfer belt unit shown in FIG. 6 as viewed in the axial direction. FIG. [Figure 10] FIG. 10 is a partial cross-sectional view taken along the line DD in FIG. [Figure 11] 10 is a partial cross-sectional view taken along the E-E cross section of FIG. 9. [Figure 12A]6 is an explanatory diagram showing a comparison of axial lengths of a plurality of tension rollers in the transfer belt unit; FIG. [Figure 12B] 5 is an explanatory diagram showing an opposing roller and a cleaning roller in the transfer belt unit; FIG. [Figure 13] FIG. 11 is a perspective view showing a transfer belt unit according to a reference example. [Figure 14] 14 is an explanatory diagram showing a schematic configuration of the transfer belt unit shown in FIG. 13 as viewed in the axial direction. FIG. [Figure 15] 15 is a partial cross-sectional view taken along the line FF in FIG. 14. [Figure 16] FIG. 11 is a partial cross-sectional view showing the configurations of an opposing roller, a cleaning roller, and a transfer belt in a transfer belt unit according to a second embodiment of the present invention. [Figure 17] FIG. 11 is a partial cross-sectional view showing another configuration of the counter roller, the cleaning roller, and the transfer belt in the transfer belt unit according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A belt unit and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[0019] (Embodiment 1) 1 is a schematic cross-sectional view of an image forming apparatus 10 according to a first embodiment of the present invention. In this embodiment, a case in which the present invention is applied to an image forming apparatus 10 that outputs a monochrome image will be described.

[0020] This image forming apparatus 10 obtains image data read from an original or image data received from an external source, and forms a monochrome image represented by this image data on paper. Image forming apparatus 10 is broadly composed of an automatic document feeder (ADF) 101, an image reading device 102, an image forming unit 103, a paper transport unit 104, and a paper feed unit 105. In addition, in image forming apparatus 10, an internal paper discharge space is formed between image reading device 102 and image forming unit 103, and a paper discharge tray 43 is disposed therein.

[0021] When at least one document is set on the document tray 11, the document transport unit 101 pulls out the document from the document tray 11 one by one, transports the document, and guides the document onto a first platen glass 23 of the image reading device 102 so that the document passes through the first platen glass 23.

[0022] In the image reading device 102, an optical unit consisting of a first scanning unit 21 and a second scanning unit 22 is disposed below a first platen glass 23, and when a document passes over the first platen glass 23, the document surface is exposed to light by the light source of the first scanning unit 21, and the mirrors of the first scanning unit 21 and the second scanning unit 22 guide the reflected light from the document surface to an imaging lens 24, which forms an image of the document surface on a CCD (Charge Coupled Device) 25. The CCD 25 repeatedly reads the image of the document surface in the main scanning direction and outputs image data indicating the image of the document surface.

[0023] When an original document is placed on the second platen glass 26 on the top surface of the image reading device 102, the first scanning unit 21 and the second scanning unit 22 are moved in the sub-scanning direction while maintaining a predetermined speed relationship relative to each other, and the first scanning unit 21 exposes the original document surface on the second platen glass 26. The first scanning unit 21 and the second scanning unit 22 further reflect the reflected light from the original document surface and direct it to the imaging lens 24, and the imaging lens 24 forms an image of the original document surface on the CCD 25.

[0024] The image data output from the CCD 25 is subjected to various image processing by a control circuit such as a microcomputer, and then output to the image forming unit 103. A photoconductor drum 31 serving as an image carrier is disposed approximately in the center of the image forming unit 103. Around the photoconductor drum 31, a charging unit 32, an optical scanning unit 33, a developing unit (developing device) 34, a transfer device 100, and a cleaning unit 35 are disposed.

[0025] The charging unit 32 uniformly charges the surface of the photoconductor drum 31. The optical scanning unit 33 inputs image data, and while modulating the intensity of the light beam according to the image data, scans the light beam on the uniformly charged photoconductor drum 31 to write an electrostatic latent image. The developing unit 34 visualizes the electrostatic latent image on the photoconductor drum 31 with a developer (toner) to form a developer image on the photoconductor drum 31. The transfer device 100 includes a transfer belt unit 1, and transfers the developer image on the photoconductor drum 31 onto the paper while sandwiching and transporting the paper between the transfer device 100 and the photoconductor drum 31. The cleaning unit 35 removes the developer remaining on the photoconductor drum 31 so that a new developer image can be formed on the photoconductor drum 31.

[0026] A fixing device 36 is disposed above the image forming section 103. The fixing device 36 sandwiches the paper onto which the image has been transferred between a fixing roller 361, which has an internal heat source, and a pressure roller 362, and fixes the image by heat and pressure. After fixing, the paper is transported by paper transport rollers, and is discharged by paper discharge rollers 41 to a paper discharge tray 43 in the internal paper discharge space.

[0027] When forming images on both sides of the paper, the paper is reversed and transported in the opposite direction by the paper discharge rollers 41, then transported to the reverse transport path 44, where it is turned over and transported again to the image forming unit 103, where the developer image is transferred and fixed on the reverse side. The paper is discharged from the paper discharge rollers 41 to the paper discharge tray 43.

[0028] The paper feed unit 105 includes a paper feed tray 51, and separates and supplies paper one by one from the paper feed tray 51. The paper is temporarily stopped by a registration roller 42, which is provided in front of the photosensitive drum 31 and the transfer belt unit 1 among the paper transport rollers, and is supplied between the photosensitive drum 31 and the transfer belt unit 1 in accordance with the timing of transfer, and the developer image on the photosensitive drum 31 is transferred to the paper.

[0029] (Transfer device and transfer belt unit) Next, the transfer device 100 and the transfer belt unit 1 provided in the image forming apparatus 10 will be described.

[0030] Fig. 2 is a perspective view showing a transfer device 100 provided in an image forming apparatus 10 of this embodiment, and Fig. 3 is a perspective view of the transfer device 100 as viewed from the opposite side of Fig. 2. Fig. 4 is a side view showing the transfer device 100 as viewed in the direction of the arrow A in Fig. 1, and Fig. 5 is a cross-sectional view taken along line BB in Fig. 4. Fig. 4 is also a side view as viewed from a direction perpendicular to the axial direction X shown in Fig. 3.

[0031] A transfer device 100 of an image forming apparatus 10 is provided with a transfer belt unit 1 as an example of a belt unit according to the present invention. The transfer belt unit 1 includes a plurality of tension rollers 6 and a transfer belt (belt) 7 that is tensioned by the plurality of tension rollers 6.

[0032] As shown in FIG. 1, the transfer belt 7 is an annular belt arranged opposite the photosensitive drum 31, and is arranged to form a nip between the transfer belt 7 and the photosensitive drum 31. Also, as shown in FIG. 5, the multiple tension rollers 6 include multiple rollers arranged in contact with the inner circumferential surface of the transfer belt 7. In the illustrated embodiment, the multiple tension rollers 6 include a drive roller 61, an opposing roller (inner surface roller) 62, a driven roller 63, a pre-transfer roller 64, and a transfer roller 65 arranged in this order from the drive roller 61 along the belt rotation direction R. Also, a cleaning roller (outer surface roller) 70 arranged in contact with the outer circumferential surface of the transfer belt 7 is included as one of the multiple tension rollers 6 that tension the transfer belt 7. As described later, each of these multiple tension rollers 6 has a shaft portion that serves as a rotation center and a cylindrical (columnar) body portion around the shaft portion.

[0033] A driving force is transmitted from a rotation driving unit (not shown) to the shaft portion 612 via a driving gear 611 (see FIG. 4), and the driving roller 61 is rotationally driven. As a result, the driving roller 61 rotates (circulates) the transfer belt 7 in the belt rotation direction R.

[0034] The opposing roller 62 and the pre-transfer roller 64 are disposed downstream of the driving roller 61 in the belt rotation direction R, and are provided so as to provide an appropriate tension to the transfer belt 7. The driven roller 63 is rotated in association with the movement of the transfer belt 7 in the belt rotation direction R caused by the rotational drive of the driving roller 61. A paper feed guide member 8 is provided on the outer circumferential side of the transfer belt 7 that contacts the driven roller 63, spaced apart from the transfer belt 7. The paper feed guide member 8 guides the paper that has been transported from the paper feed tray 51 to the registration roller 42, as shown in FIG. 1, between the photosensitive drum 31 and the transfer belt unit 1.

[0035] A cleaning roller (outer surface roller) 70 is provided at a position facing the opposing roller 62. The cleaning roller 70 is disposed at a position facing the opposing roller 62 with the transfer belt 7 sandwiched therebetween. As shown in FIG. 3, the cleaning roller 70 includes a cylindrical body portion 701 and a shaft portion 702. Both ends of the shaft portion 702 are rotatably supported by bearing portions 704, and the bearing portions 704 are biased toward the transfer belt 7 by spring members 703. As a result, the cleaning roller 70 rotates in contact with the outer peripheral surface of the transfer belt 7, and is configured to clean the outer peripheral surface (surface) of the transfer belt 7.

[0036] The transfer roller 65 is disposed at a position corresponding to the photosensitive drum 31 with the transfer belt 7 sandwiched therebetween. The transfer belt 7 transfers the developer image on the photosensitive drum 31 onto the paper while conveying the paper sandwiched between the transfer belt 7 and the photosensitive drum 31. The transfer roller 65 abuts against the nip between the photosensitive drum 31 and the transfer belt 7 from the inner peripheral side of the transfer belt 7.

[0037] 6 is a perspective view showing the tension rollers 6 and the transfer belt 7 in the transfer belt unit 1. Each of the tension rollers 6 has a shaft portion (such as the shaft portion 631 of the driven roller 63 shown in FIG. 6) and a cylindrical body portion (such as the body portion 601 of the driven roller 63 shown in FIG. 6) provided around the shaft portion. As shown in FIG. 6, the tension rollers 6 include the shaft portion 612 of the drive roller 61, the shaft portion 621 of the counter roller 62, the shaft portion 702 of the cleaning roller 70, the shaft portion 631 of the driven roller 63, the shaft portion 641 of the pre-transfer roller 64, and the shaft portion 651 of the transfer roller 65, which are all arranged in parallel to one another along the axial direction X of the shaft portion 612 of the drive roller 61. Drive roller 61, opposing roller 62, driven roller 63, pre-transfer roller 64, and transfer roller 65 support transfer belt 7 from the inner periphery side, tensioning the transfer belt 7, and rotate about their axes to move transfer belt 7 in belt rotation direction R. Cleaning roller 70 is disposed so as to tension transfer belt 7 from the outer periphery side of transfer belt 7 and sandwich transfer belt 7 between itself and opposing roller 62.

[0038] 7, 8A, and 8B show the transfer belt 7 in the transfer belt unit 1. Of these, Fig. 7 is a perspective view showing the transfer belt 7 with a part cut away, Fig. 8A is a side view showing the transfer belt 7 in the axial direction X, and Fig. 8B is a cross-sectional view taken along line CC in Fig. 8A.

[0039] The transfer belt 7 has a belt body 71 and protrusions (beads) 72 formed integrally at both ends of the belt body 71. The belt body 71 is formed in an annular shape, and its inner circumferential surface becomes a contact surface with each of the rollers, namely, the drive roller 61, the counter roller 62, the driven roller 63, the pre-transfer roller 64, and the transfer roller 65. In the following description, the surface of the annular transfer belt 7 on which the multiple tension rollers 6 are arranged and facing inward is referred to as the inner circumferential surface of the belt body 71, and the surface facing outward and with which the cleaning roller 70 comes into contact is referred to as the outer circumferential surface of the belt body 71.

[0040] As shown in FIG. 6, the transfer belt 7 has protruding portions 72 protruding inward at both ends in the width direction of the transfer belt 7 that coincide with the axial direction X of the plurality of tension rollers 6. As shown in FIG. 7, the protruding portions 72 are provided at both ends in the axial direction X to protrude from the inner circumferential surface of the belt body 71, and have a rectangular cross-sectional shape in the illustrated embodiment. The opposing side surfaces of these two protruding portions 72 are provided so as to be perpendicular to the shaft portion 612 of the drive roller 61. The provision of such protruding portions 72 is intended to suppress phenomena such as skewing and meandering in which the running transfer belt 7 moves in one direction of each shaft portion of the plurality of tension rollers 6.

[0041] 7, the transfer belt 7 can be manufactured into a ring shape by joining two end faces in a direction perpendicular to the axial direction X, that is, both ends provided in the injection direction. Therefore, a parting line (seam) along the axial direction X is formed at one point on the transfer belt 7, but by manufacturing the transfer belt 7 in this manner, it is possible to increase productivity and reduce manufacturing costs.

[0042] The transfer belt 7 is formed of a material such as chloroprene rubber, and preferably has a volume resistivity of 10 Log Ω·cm. The outer peripheral surface of the belt body 71 is preferably fluorine-coated. As shown in FIG. 8B, the width w of the protruding portion 72 in the direction along the axial direction X is preferably about 2 mm. The protruding amount t of the protruding portion 72 from the inner peripheral surface of the belt body 71 is preferably about 1.5 mm toward the inner peripheral side. In contrast, the thickness of the belt body 71 is preferably about 0.5 mm.

[0043] In the transfer belt unit 1, the transfer belt 7 is sandwiched between an opposing roller 62, which is disposed downstream of a driving roller 61 in the belt rotation direction R, and a cleaning roller 70. Here, the inner surface of one of the protrusions 72 provided at both ends of the transfer belt 7 abuts against the roller end of the opposing roller 62, thereby regulating deviation of the transfer belt 7.

[0044] Fig. 9 is an explanatory diagram showing a schematic configuration of the transfer belt unit 1 shown in Fig. 6 as viewed in the axial direction X. Fig. 10 is a partial cross-sectional view taken along the line DD in Fig. 9, and Fig. 11 is a partial cross-sectional view taken along the line EE in Fig. 9.

[0045] In this embodiment, the counter roller 62 is disposed downstream of the driving roller 61 in the belt rotation direction R of the transfer belt 7 so that the transfer belt 7 is wound around the body 601 of the counter roller 62. As shown in FIG. 9, in the transfer belt unit 1, the transfer belt 7 is disposed so that the transfer belt 7 is wound around the body 601 of the counter roller 62 at a predetermined angle. That is, the trajectory of the rotational movement of the transfer belt 7 in the belt rotation direction R is formed on the inner side of a plane formed by a tangent line connecting the outer peripheral surface of the body of the driving roller 61 and the outer peripheral surface of the body of the counter roller 62. In the embodiment shown in FIG. 9, the trajectory of the rotational movement of the transfer belt 7 is formed on the inner side of a plane including the tangent line T shown by a two-dot chain line.

[0046] 9, in the transfer belt unit 1, the cleaning roller 70 is disposed closer to the drive roller 61 than the opposing roller 62. In other words, the cleaning roller 70 is disposed upstream of the opposing roller 62 in the belt rotation direction R.

[0047] 10, the body 601 of the opposing roller 62 is provided in contact with the inner circumferential surface of the transfer belt 7. The end of the body 601 of the opposing roller 62 is provided so as to be located inside the protruding portion 72 in the axial direction X with respect to the transfer belt 7 (to the right in FIG. 10). Therefore, the length of the body 601 of the opposing roller 62 in the axial direction X is set shorter than the distance in the axial direction X between the protruding portions 72 at both ends of the transfer belt 7. The opposing roller 62 is formed to have a length such that the end of the body 601 is in contact with the inner surface of the protruding portion 72 or is not in contact with the protruding portion 72.

[0048] Further, the body 701 of the cleaning roller 70 is provided in contact with the outer peripheral surface of the transfer belt 7. An end of the body 701 of the cleaning roller 70 is provided to be located more inward in the axial direction X than an end of the body 601 of the opposing roller 62. Therefore, the length of the body 701 of the cleaning roller 70 in the axial direction X is set shorter than the length of the body 601 of the opposing roller 62 in the axial direction X.

[0049] The cleaning roller 70 acts to press the transfer belt 7 down toward the opposing roller 62 side beyond the tangent line T connecting the outer circumferential surface of the trunk of the drive roller 61 and the outer circumferential surface of the trunk of the opposing roller 62. As shown in Fig. 6, the cleaning roller 70 and the transfer belt 7 act on the upstream side of the opposing roller 62 in the belt rotation direction R such that the trunk 701 of the cleaning roller 70 presses the belt main body 71 toward the inner circumference.

[0050] 11, the body 701 of the cleaning roller 70 presses the inside position of the end of the transfer belt 7 downward in the figure (toward the inner circumference of the belt main body 71). As a result, the protrusion 72 warps toward the outer circumference of the belt main body 71 and is separated from the roller end of the opposing roller 62 by an opening angle δ, resulting in an open posture with a gap between the opposing roller 62 and the belt main body 71.

[0051] Therefore, even if the transfer belt 7 is misaligned and the protruding portion 72 comes into contact with the body portion 601 of the opposing roller 62 when the transfer belt 7 is rotated, the belt body 71 deforms so as to be warped toward the outer periphery as shown in Fig. 11, and an appropriate escape (warping) can be provided on the protruding portion 72 side. This can reduce the stress acting on the base P of the protruding portion 72, and can prevent stress concentration from occurring at the base P, thereby preventing damage from occurring between the protruding portion 72 and the belt body 71. Therefore, even the transfer belt 7 having a parting line can have a sufficiently long life.

[0052] In this manner, the transfer belt 7 moves in the belt rotation direction R with the tip of the protruding portion 72 expanded by the opening angle δ, toward the opposing roller 62. The protruding portion 72 is unlikely to ride up onto the end of the body portion 601 of the opposing roller 62.

[0053] More specifically, as shown in FIG. 9, the cleaning roller 70 is disposed at an angle α between a straight line (normal line) connecting the rotation center of the opposing roller 62 (the axis of the shaft 621) and the rotation center of the cleaning roller 70 (the axis of the shaft 702) and a normal line of the opposing roller 62 perpendicular to a tangent line T connecting the driving roller 61 and the opposing roller 62. When the angle α is close to 0 degrees, the opening angle δ of the tip of the protrusion 72 becomes small, and when the angle α is close to 90 degrees, the opening angle δ of the tip of the protrusion 72 becomes large, but the larger the angle α, the larger the bending of the transfer belt 7 becomes, and the larger the load on the transfer belt becomes. Therefore, by appropriately setting the angle α, it is possible to effectively prevent the protrusion 72 from riding up. In addition, since the cleaning roller 70 acts to press down the transfer belt 7, the winding angle β of the transfer belt 7 around the opposing roller 62 becomes large. This leads to an increase in the angle γ between the tangent (s1) of the cleaning roller 70 at the center of winding with the transfer belt 7 and the tangent (s2) of the opposing roller 62 and the driven roller 63. That is, the area of ​​the protruding portion 72 facing the end of the body part 601 of the opposing roller 62 becomes larger. Therefore, even if the protruding portion 72 comes into contact with the end of the body part 601 of the opposing roller 62, the protruding portion 72 is unlikely to ride up onto the opposing roller 62.

[0054] 10 and 11, the trunk 701 of the cleaning roller 70 is not present on the outer circumferential surface of the belt body 71 at a position corresponding to the protruding portion 72 (the surface opposite the protruding portion 72 of the transfer belt 7 in the figures). Therefore, in the region corresponding to the winding angle β, the end of the belt body 71 warps toward the outer circumferential side between the cleaning roller 70 and the opposing roller 62, and is appropriately relieved, so that it is possible to prevent stress from concentrating on the base P of the protruding portion 72.

[0055] 12A is an explanatory diagram for comparing the lengths of the multiple tension rollers 6 in the transfer belt unit 1 in the axial direction X, and FIG. 12B is an explanatory diagram showing the length of the cleaning roller 70 relative to the opposing roller 62 in the axial direction X. As shown in FIG.

[0056] The lengths in the axial direction X of the transfer belt 7, the opposing roller 62, the transfer roller 65, and the driven roller 63 constituting the transfer belt unit 1 will be compared. As shown in Fig. 12A, the transfer belt 7 has the trunks of multiple tension rollers 6 disposed between the protrusions 72 at both ends (inter-bead distance D). Therefore, the length (width) L7 of the transfer belt 7 is longer than the length of the trunks of the tension rollers 6.

[0057] Among the multiple tension rollers 6, the length of the body in the axial direction X is the longest, which is the length L62 of the opposing roller 62. For example, the length L7 of the transfer belt 7 is 324 mm, whereas the inter-bead distance D is 318.5 mm and the length L62 of the body of the opposing roller 62 is 315 mm. Also, for example, the length L65 of the body of the transfer roller 65 is 309 mm. Note that although the illustration of the pre-transfer roller 64, which is one of the multiple tension rollers 6, is omitted in FIG. 12A, the length of its body is shorter than the length L62 of the body of the opposing roller 62.

[0058] 12B, cleaning roller 70 disposed on the outer periphery of transfer belt 7 may be shorter than opposing roller 62 having length L62 in the axial direction X by a maximum difference in body length W1. Body 701 of cleaning roller 70 abuts against the outer periphery of transfer belt 7, and is shorter than the length of the body of opposing roller 62 in the axial direction X. This configuration also makes it difficult for protrusion 72 to ride over the body of opposing roller 62.

[0059] Here, the transfer belt unit 1 according to the first embodiment will be compared with a transfer belt unit 90 of a reference example. Fig. 13 to Fig. 15 show the transfer belt unit 90 as a reference example, Fig. 13 is a perspective view showing the transfer belt unit 90 of the reference example, and Fig. 14 is an explanatory diagram showing a schematic configuration of the transfer belt unit 90 shown in Fig. 13 as viewed in the axial direction X. Fig. 15 is a partial cross-sectional view at the FF cross section in Fig. 14.

[0060] In the transfer belt unit 90 of the reference example, a drive roller 610, an opposing roller 620, a driven roller 630, a pre-transfer roller 640, and a transfer roller 650 are provided in this order in the belt rotation direction R on the inner peripheral side of a transfer belt 710.

[0061] 15, the end of the body of the opposing roller 620 is provided so as to be located more inward in the axial direction X than the protruding portion 712 of the transfer belt 710, while the end of the body of the cleaning roller 720 is provided so as to be located more outward in the axial direction X than the end of the body of the opposing roller 620. The body of the cleaning roller 720 is provided longer in the axial direction X than the body of the opposing roller 620. The body of the cleaning roller 720 of the reference example is provided longer than the end of the body 701 of the cleaning roller 70 according to this embodiment, which is indicated by the two-dot chain line in the figure.

[0062] In this case, as shown in Fig. 14, the counter roller 620 is not disposed so as to be wound around the transfer belt 710. The cleaning roller 720 is disposed at a position where a tangent line connecting the cleaning roller 720 and the driving roller 610 and a straight line (normal line) connecting the rotation center of the cleaning roller 720 and the rotation center of the counter roller 620 intersect at right angles. Also, a winding angle β1 of the transfer belt 710 to the counter roller 620 is smaller than the winding angle β in this embodiment shown in Fig. 9. An angle γ1 between a tangent line (s3) of the cleaning roller 720 at the winding center with the transfer belt 710 and a tangent line (s4) between the counter roller 620 and the driven roller 630 is smaller than the angle γ shown in Fig. 9.

[0063] 15, the roller portion of the cleaning roller 720 is in contact with the outer circumferential surface of the belt main body 711 (the surface opposite to the protruding portion 712 of the transfer belt 710 in the figure). Between the cleaning roller 720 and the opposing roller 620, there is no escape route for the belt main body 711 at a position corresponding to the protruding portion 712, and the base P1 of the protruding portion 712 is always in contact with the roller end of the opposing roller 620.

[0064] As a result, when the transfer belt 710 passes between the opposing roller 620 and the cleaning roller 720, stress concentration occurs at the base P1 of the protrusion 712, making it easy for cracks to occur at the base P1 of the protrusion 712. In particular, in the transfer belt 710 having a parting line, cracks are easy to occur from the protrusion 712 on the parting line.

[0065] In contrast to this, in the transfer belt unit 1 according to this embodiment, as described above, the belt body 71 at the position corresponding to the protruding portion 72 can move appropriately toward the outer periphery between the cleaning roller 70 and the opposing roller 62, so that it is possible to prevent stress from concentrating on the base P of the protruding portion 72 and prevent cracks from occurring in the protruding portion 72. Therefore, it is possible to enhance the effect of preventing skew in the transfer belt 7 and to extend the life of the transfer belt 7.

[0066] (Embodiment 2) 16 and 17 are partial cross-sectional views showing the configurations of the opposing roller 62, the cleaning roller 70, and the transfer belt 7 in the transfer belt unit 1 according to the second embodiment of the present invention, and correspond to FIG. 12B.

[0067] In the transfer belt unit 1, the multiple tension rollers 6 including the cleaning roller 70 are not limited to the configuration shown in the embodiment 1, and can be embodied in various other forms. For example, the cleaning roller 70 may be configured to have inclined portions 705 at both ends in the axial direction X.

[0068] In the example shown in Fig. 16, the cleaning roller 70 has an end of a body portion 701 chamfered to form an inclined portion 705. In the example shown in Fig. 17, the cleaning roller 70 has a gentle taper toward the end of the body portion 701 to form an inclined portion 705. In either case, the cleaning roller 70 is provided with an inclined portion 705 such that the diameter of the body portion 701 decreases toward the end.

[0069] This makes it possible to disperse the stress acting on the contact surface between the inner circumferential surface of the transfer belt 7 and the cleaning roller 70, thereby enabling the life of the transfer belt 7 to be further extended.

[0070] (Other embodiments) The belt unit, transfer device, and image forming apparatus according to the present invention can be embodied in various forms other than the above-mentioned embodiment. For example, in the transfer belt unit 1 according to the above-mentioned embodiment, the transfer belt 7 in which the protruding portion 72 is integrally formed with the belt body 71 is shown, but the belt unit according to the present invention is not limited to this, and may be configured such that the protruding portion is integrally joined to the belt body formed into a ring shape by extrusion molding or the like. According to the present invention, the stress acting on the base P of the protruding portion 72 can be alleviated, and stress concentration at the base P can be avoided, so that the life of the transfer belt 7 can be extended even if the transfer belt 7 is formed in this way.

[0071] In addition, the image forming apparatus including the belt unit or transfer device according to the present invention may be a color image forming apparatus or a monochrome image forming apparatus. The image forming apparatus may be a multifunction machine having a copy function, a printer function, a scanner function, a facsimile function, etc. Therefore, in the image forming apparatus, the configuration of the belt unit including the belt having the protrusions is not limited to being applied to the transfer belt unit 1, but may also be applied to the belt unit of other conveying system units such as an intermediate transfer unit or a secondary transfer unit. Therefore, the above embodiment is merely an example and is not limiting.

[0072] It should be noted that the present invention can be modified in various ways within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0073] 1 Transfer belt unit (belt unit) 6 Tension roller 601 Torso 61 Drive roller 62 Counter roller (inner roller) 63 Driven roller 64 Pre-transfer roller 65 Transfer roller 70 Cleaning roller (outer roller) 701 Torso 702 Shaft 703 Spring parts 704 Bearings 705 Inclined section 7 Transfer belt (belt) 71 Belt body 72 Protrusion 8 Paper feed guide member 10 Image forming device 100 Transfer device 101 Document transport section 102 Image reading device 103 Image forming section 104 Paper transport section 105 Paper feed section 31 Photoconductor drum (image carrier) R Belt rotation direction

Claims

1. a circular belt stretched by a plurality of tension rollers arranged parallel to each other and having a shaft portion and a body portion; a drive roller which is one of the plurality of tension rollers and rotates the belt; an inner roller which is one of the plurality of tension rollers and is disposed downstream of the driving roller in a rotation direction of the belt such that the belt is wound around the body portion; an outer roller that is disposed in contact with an outer peripheral surface of the belt and sandwiches the belt between the outer roller and the inner roller; The belt has protrusions protruding toward the inner periphery at both ends in a width direction of the belt, the protrusions being aligned with an axial direction of the tension roller, the driving roller abuts against an inner circumferential surface of the belt at the trunk portion, an end portion of a body portion of the inner roller is provided so as to be located more inward in the axial direction than the protruding portion with respect to the belt; the outer roller is disposed upstream of the inner roller in the direction of rotation so that the belt is positioned on the inner side of a plane formed by a tangent line connecting the outer peripheral surface of the barrel of the drive roller and the outer peripheral surface of the barrel of the inner roller, a belt unit comprising: an outer roller having a body portion, the outer roller having a body portion that is disposed inward in the axial direction with respect to an end of the body portion of the inner roller;

2. 2. The belt unit according to claim 1, a body portion of the inner roller abuts against an inner circumferential surface of the belt, and a length of the body portion in the axial direction is shorter than a distance between the protrusions in the axial direction; A belt unit comprising: a body portion of the outer roller that contacts the belt; and a length of the body portion in the axial direction that is shorter than a length of the body portion of the inner roller.

3. 3. The belt unit according to claim 1, The belt unit is characterized in that the inner roller has a body portion with a longest axial length among the plurality of tension rollers.

4. The belt unit according to any one of claims 1 to 3, A belt unit characterized in that the body portion of the outer roller is provided with inclined portions at both ends in the axial direction such that the diameter of the outer surface becomes smaller as it goes from the inside to the outside of the body portion in the axial direction.

5. The belt unit according to any one of claims 1 to 4, The belt unit is characterized in that the belt has a seam along a width direction of the belt.

6. A transfer device including the belt unit according to any one of claims 1 to 5, A transfer roller is one of the plurality of tension rollers, the belt is a transfer belt, The transfer device according to claim 1, wherein the outer roller is a cleaning roller for cleaning the transfer belt.

7. An image forming apparatus comprising the transfer device according to claim 6.

Images