Image forming apparatus

Abstract

To effectively prevent dangling of a belt, while increasing an effect of regulating belt skew.SOLUTION: An image forming apparatus 100 has a plurality of stretch rollers that stretch an intermediate transfer belt 2, and that are arranged so that respective rotation axis directions extend along predetermined directions (roller axial direction, belt width direction). A first stretch roller 1 is provided with a first regulation part 8a that is in contact with a rib 6 to regulate the movement of the rib 6 in the predetermined directions. A second stretch roller 110 is provided with a second regulation part 9a that is in contact with the rib 6 to regulate the movement of the rib 6 in the predetermined directions, and a third regulation part 10a that is in contact with the rib 6 to regulate the movement of the rib 6 in a radial direction of the second stretch roller 110. An end of the second regulation part 9a on the end side of the intermediate transfer belt 2 in the predetermined directions, is located closer to the center of the intermediate transfer belt 2 in the predetermined directions than an end of the first regulation part 8a on the end side of the intermediate transfer belt 2 in the predetermined directions.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, printer, facsimile machine, or multifunction machine that uses an electrophotographic or electrostatic recording method, or that has a plurality of functions selected from these. [Background technology]

[0002] Conventionally, image forming apparatuses such as electrophotographic copying machines have widely used an intermediate transfer method in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer belt at a primary transfer unit, and then the toner image is secondarily transferred to a recording material such as paper at a secondary transfer unit. The intermediate transfer belt is an endless belt that is stretched over multiple tension rollers (drive rollers, tension rollers, support rollers, etc.) and stretched with a predetermined tension.

[0003] In an image forming apparatus with such a configuration, a phenomenon called "belt deviation" may occur, in which the intermediate transfer belt moves in the width direction (a direction substantially perpendicular to the conveyance direction) as it is conveyed (circulated). When this occurs, the edge of the intermediate transfer belt in the width direction may come into contact with other components, causing problems such as damage.

[0004] Therefore, as described in Patent Document 1, image forming devices sometimes employ a rib regulation system in which a rib is provided on the inner peripheral surface of the widthwise end of the intermediate transfer belt, and a regulating member that can come into contact with the rib is provided at the end of the tension roller in the direction of the rotation axis, thereby regulating the belt shift. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-247634 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the rib-regulating system uses only one roller to regulate belt deviation, the belt may become misaligned across the width between the roller that regulates the belt deviation and a distant roller that does not regulate the belt deviation, resulting in twisting. To address this issue, adding a second roller to regulate belt deviation can be considered to enhance the belt deviation regulation effect. However, when regulating belt deviation using the rib-regulating system, the rib may receive a reaction force from the regulating member, causing the belt to ripple. Therefore, simply increasing the number of rollers that regulate belt deviation is difficult to achieve the desired results.

[0007] Furthermore, even if the rib regulation method regulates belt misalignment, it does not regulate belt sagging. "Belt sagging" is a phenomenon in which the widthwise edge of the belt bends in the radial direction of the tension roller. This occurs when the belt becomes prone to bending due to loosening of belt tension caused by belt twisting or when the belt edge moves away from the position where it is supported by the tension roller in the widthwise direction. When belt sagging occurs, stress concentrates in the bent part of the belt, which can cause belt damage.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to effectively suppress sagging of the belt while enhancing the effect of restricting belt deviation. [Means for solving the problem]

[0009] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including an image carrier that carries a toner image, an endless intermediate transfer belt that transports the toner image that has been primarily transferred from the image carrier in a primary transfer section to a recording material in a secondary transfer section for secondary transfer, and a plurality of tension rollers that tension the intermediate transfer belt, including a first tension roller and a second tension roller, and that are arranged so that the directions of the rotation axes of the plurality of tension rollers are along a predetermined direction, wherein the intermediate transfer belt has a rib that extends along the circumferential direction on an inner peripheral surface of an end portion in the width direction, and the first tension roller has a first regulating portion that comes into contact with the rib and regulates movement of the rib in the predetermined direction at an end portion in the predetermined direction. The second tension roller is provided with a second regulating portion at its end in the predetermined direction, which contacts the rib to regulate movement of the rib in the predetermined direction, and a third regulating portion at its end in the predetermined direction, which contacts the rib to regulate movement of the rib in the radial direction of the second tension roller, the third regulating portion being located on the end side of the intermediate transfer belt in the predetermined direction relative to the second regulating portion, and the end of the second regulating portion on the end side of the intermediate transfer belt in the predetermined direction is located closer to the center of the intermediate transfer belt in the predetermined direction than the end of the first regulating portion on the end side of the intermediate transfer belt in the predetermined direction. [Effects of the Invention]

[0010] According to the present invention, it is possible to effectively suppress sagging of the belt while enhancing the effect of restricting belt deviation. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic cross-sectional view of an image forming unit. [Figure 3] FIG. 2 is an enlarged perspective view of the vicinity of an end of a tension roller in a secondary transfer unit. [Figure 4] FIG. 2 is a schematic perspective view showing a cross section of an intermediate transfer belt. [Figure 5] FIG. 4 is a cross-sectional view showing a deviation regulating portion of the tension roller. [Figure 6] FIG. 2 is a perspective view of a first restricting member. [Figure 7] 4 is a cross-sectional view showing a deviation restricting portion and a sagging restricting portion of the drive roller. FIG. [Figure 8] FIG. 3 is a perspective view of a second restricting member in the first embodiment. [Figure 9] FIG. 10 is a cross-sectional view showing a deviation regulating portion of a drive roller in a comparative example. [Figure 10] 3A and 3B are a top view of an intermediate transfer unit and a cross-sectional view showing the positional relationship between first, second, and third regulating portions. [Figure 11] 10 is a cross-sectional view showing a shift regulation portion and a sagging regulation portion of a drive roller in a second embodiment. FIG. [Figure 12] FIG. 10 is a perspective view of a second restricting member and a third restricting member in the second embodiment. [Figure 13] FIG. 10 is a front view of a second restricting member in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0013] [Example 1] 1. Overall configuration and operation of the image forming apparatus First, the overall configuration and operation of the image forming apparatus of this embodiment will be described. Figure 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem-type full-color printer that employs an intermediate transfer system and is capable of forming full-color images using an electrophotographic system.

[0014] Here, with regard to the image forming apparatus 100 and its elements, the front side of the paper in Fig. 1 is referred to as the "front side (front side)," and the back side of the paper in Fig. 1 is referred to as the "rear side (rear side)." The direction connecting the front side and the rear side (the direction perpendicular to the paper in Fig. 1) is assumed to be approximately parallel to the rotation axis direction of the photosensitive drum 103 and the tension roller of the intermediate transfer belt 2, which will be described later. Furthermore, with regard to the image forming apparatus 100 and its elements, "up" and "down" refer to up and down in the direction of gravity (vertical direction), but do not mean only directly above and directly below, but also include above and below a horizontal plane that passes through a reference position or element.

[0015] The image forming apparatus 100 has four image forming units 109Y, 109M, 109C, and 109K that form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively, as multiple image forming units. These image forming units 109Y, 109M, 109C, and 109K are arranged along the moving direction of the primary transfer surface of the intermediate transfer belt 2, which will be described later.

[0016] For example, when forming a full-color image, in image forming unit 109Y, a yellow toner image is formed on photosensitive drum 103Y and then transferred onto intermediate transfer belt 2. In image forming unit 109M, a magenta toner image is formed on photosensitive drum 103M and then transferred and superimposed on the yellow toner image on intermediate transfer belt 2. Similarly, in image forming units 109C and 109K, a cyan toner image and a black toner image are formed on photosensitive drums 103C and 103K, respectively, and then these are transferred and superimposed in order on the previously transferred toner images on intermediate transfer belt 2. The image forming operations in image forming units 103Y, 103M, 103C, and 103K will be described later.

[0017] The four color toner images carried on the intermediate transfer belt 2 are transported to a secondary transfer section T2 and are collectively (secondarily) transferred onto a recording material P. Sheet-like recording materials (recording media, transfer materials, sheets) P ​​such as paper or plastic sheets are stored in a recording material cassette 120 serving as a recording material storage section. The recording materials P stored in the recording material cassette 120 are separated one by one by a separation roller 121 serving as a feeding member and transported to registration rollers 122 serving as a transport member. The registration rollers 122 transport the recording material P to the secondary transfer section T2 in synchronization with the toner images on the intermediate transfer belt 2.

[0018] A secondary transfer roller 111, a roller-type secondary transfer member serving as a secondary transfer unit, is disposed on the outer peripheral surface of the intermediate transfer belt 2, facing a drive roller 110, which is one of the tension rollers of the intermediate transfer belt 2. The secondary transfer roller 111 contacts the intermediate transfer belt 2 on the drive roller 110 to form a secondary transfer portion T2. ​​The recording material P, onto which the four-color toner image has been secondarily transferred after passing through the secondary transfer portion T2, is separated by curvature from the intermediate transfer belt 2 and conveyed to a fixing device 112 serving as a fixing unit. The fixing device 112 fixes (melts and adheres) the image onto the recording material P by applying heat and pressure to the recording material P at a nip portion between a fixing roller 112a and a pressure roller 112b. The recording material P, onto which the image has been fixed by the fixing device 112, is discharged (output) to the outside of the apparatus main body 123 of the image forming apparatus 100.

[0019] 2. Image forming section Next, the image forming operations in image forming units 109Y, 109M, 109C, and 109K will be described. Image forming units 109Y, 109M, 109C, and 109K have substantially the same configuration, except that they use different toner colors: yellow, magenta, cyan, and black, respectively. Therefore, elements having the same or corresponding functions or configurations for each color will be described collectively, with the suffixes Y, M, C, and K omitted from the reference numerals indicating that the element is for one of the colors. Figure 2 is a schematic cross-sectional view of image forming unit 109.

[0020] The image forming unit 109 includes a photosensitive drum 103, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as an image carrier. The image forming unit 109 also includes a charging roller 104, an exposure device 105, a developing device 106, a primary transfer roller 107, and a drum cleaning device 108, which are arranged around the photosensitive drum 103. The charging roller 104 is a roller-type charging member and is an example of a charging means. In this embodiment, the exposure device 105 is configured as a laser scanner and is an example of an exposure means. The exposure device 105 is not limited to a laser scanner and may be, for example, one that uses an LED as a light source. The exposure device 105 may also be configured as a common unit that exposes the photosensitive drums 103 of multiple image forming units 109. The developing device 106 is an example of a developing means that develops an electrostatic image (electrostatic latent image) using toner as a developer. The primary transfer roller 107 is a roller-type primary transfer member and is an example of a primary transfer means. The primary transfer roller 107 also constitutes an intermediate transfer unit 124, which will be described later. The drum cleaning device 108 is of a blade cleaning type in this embodiment, and is an example of a photosensitive member cleaning means.

[0021] The photosensitive drum 103 has a photosensitive layer formed on its surface, and is driven to rotate in the direction of arrow R1 (clockwise) at a predetermined peripheral speed (process speed) by a driving force transmitted from a driving motor (not shown) constituting a driving means. The surface of the rotating photosensitive drum 103 is charged by a charging roller 104 to a predetermined potential of a predetermined polarity (negative polarity in this embodiment).

[0022] The charged surface of the photosensitive drum 103 is scanned and exposed by the exposure device 105, forming an electrostatic image on the photosensitive drum 103. The exposure device 105 scans a laser beam with a rotating mirror to write an electrostatic image of an image onto the surface of the photosensitive drum 103. The electrostatic image formed on the photosensitive drum 103 is developed (visualized) by the development device 106, which supplies toner as a developer and forms a toner image (toner image, developer image) on the photosensitive drum 103. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 103 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 103, where the absolute value of the potential has been reduced by exposure after being uniformly charged (reverse development method). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative polarity.

[0023] The toner image formed on the photosensitive drum 103 is primarily transferred onto the intermediate transfer belt 2 at the primary transfer portion T1. During the primary transfer, a primary transfer voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the primary transfer roller 107. Toner remaining on the surface of the photosensitive drum 103 after the primary transfer (primary transfer residual toner) is removed and collected from the surface of the photosensitive drum 103 by a drum cleaning device 108. The drum cleaning device 108 rubs a cleaning blade against the surface of the photosensitive drum 103 to collect the primary transfer residual toner from the surface of the photosensitive drum 103.

[0024] 3. Intermediate transfer unit Next, a description will be given of the intermediate transfer unit 124 in this embodiment. Figure 3 is a perspective view of a part of the intermediate transfer unit 124 in this embodiment (near an end of a tension roller 1, which will be described later).

[0025] The image forming apparatus 100 has an intermediate transfer unit 124 as a belt conveying device disposed to face four photosensitive drums 103Y, 103M, 103C, and 103K. The intermediate transfer unit 124 has a frame 31, an intermediate transfer belt 2, a drive roller 110, a tension roller 1, a first auxiliary roller 113, a second auxiliary roller 114, and primary transfer rollers 107Y, 107M, 107C, and 107K. The intermediate transfer unit 124 also has a belt cleaning device 102. The frame 31 is a frame member (frame body) that rotatably supports the drive roller 110 and other components. The intermediate transfer unit 124 is configured by assembling these elements together. The intermediate transfer unit 124 as a replaceable unit is removable (attachable and detachable) as a unit from the apparatus main body (housing structure) 123 of the image forming apparatus 100.

[0026] Intermediate transfer belt 2, which is an endless belt serving as an intermediate transfer body, is stretched and stretched around a plurality of tension rollers, namely, drive roller 110, tension roller 1, and first and second auxiliary rollers 113 and 114, and is tensioned with a predetermined tension. The rotational axes of drive roller 110, tension roller 1, and first and second auxiliary rollers 113 and 114, which are tension rollers for intermediate transfer belt 2, are approximately parallel to each other. In other words, the plurality of tension rollers that stretch intermediate transfer belt 2 are arranged so that the rotational axes thereof are aligned in a predetermined direction.

[0027] Furthermore, primary transfer rollers 107Y, 107M, 107C, and 107K are disposed on the inner circumferential surface of the intermediate transfer belt 2, corresponding to the photosensitive drums 103Y, 103M, 103C, and 103K, respectively. The primary transfer rollers 107 press the intermediate transfer belt 2 toward the photosensitive drums 103, forming primary transfer portions (primary transfer nips) T1, which are contact portions between the photosensitive drums 103 and the intermediate transfer belt 2. In this embodiment, the primary transfer rollers 107 are formed as sponge rollers, and are pressed (urged) against the inner circumferential surface of the intermediate transfer belt 2 by a pressure mechanism (not shown), and come into contact with the photosensitive drums 103 via the intermediate transfer belt 2.

[0028] The driving roller 110 is driven to rotate by a driving force transmitted from a driving motor (not shown) constituting a driving means. The driving force is transmitted from the driving roller 110 to the intermediate transfer belt 2, which rotates (moves orbitally, runs) in the direction of arrow R2 in the drawing (counterclockwise direction) at a peripheral speed (process speed) corresponding to the peripheral speed of the photosensitive drum 103.

[0029] A secondary transfer roller (secondary outer transfer roller) 111 is disposed on the outer peripheral surface of the intermediate transfer belt 2, facing the drive roller 110. The secondary transfer roller 111 contacts the surface (outer peripheral surface) of the intermediate transfer belt 2 and forms a secondary transfer portion (secondary transfer nip) T2 between itself and the drive roller 110. That is, the drive roller 110 sandwiches the intermediate transfer belt 2 between itself and the secondary transfer roller 111, forming the secondary transfer portion T2. ​​In this way, the drive roller 110 also functions as an opposing roller (secondary inner transfer roller) facing the secondary transfer roller 111 across the intermediate transfer belt 2. During secondary transfer, a secondary transfer voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 111. The drive roller 110 is electrically grounded (connected to ground). In addition, a secondary transfer voltage of the same polarity as the normal charging polarity of the toner may be applied to the inner secondary transfer roller corresponding to the drive roller 110 in this embodiment, and the outer secondary transfer roller corresponding to the secondary transfer roller 111 in this embodiment may be electrically grounded.

[0030] The first and second auxiliary rollers 113 and 114 form a surface (primary transfer surface) onto which the toner image of the intermediate transfer belt 2 is primarily transferred. The second auxiliary roller 114 has a crown shape in which the outer diameter is greatest at approximately the center in the direction of the rotation axis and gradually decreases toward both ends in the direction of the rotation axis. This is to prevent the tension of the intermediate transfer belt 2 from bending the center in the direction of the rotation axis of the second auxiliary roller 114 and causing wrinkles in the center of the intermediate transfer belt 2 in the width direction (the direction approximately perpendicular to the moving direction of the surface).

[0031] The tension roller 1 is rotatably supported by tension roller bearing members 35 at both ends of the tension roller 1 in the direction of its rotation axis. The tension roller bearing members 35 are attached to the frame 31 so as to be movable (slidable). The tension roller bearing members 35 at both ends of the tension roller 1 in the direction of its rotation axis are biased (pressurized) from the inner circumferential surface toward the outer circumferential surface of the intermediate transfer belt 2 by the biasing force (pressure force, compression force) of tension springs 21 serving as biasing means. The tension springs 21 are compression springs serving as biasing members. The tension roller bearing members 35 are moved (slid) from the inner circumferential surface toward the outer circumferential surface of the intermediate transfer belt 2 in the biasing direction of the tension springs 21. As a result, the tension roller 1 biases the intermediate transfer belt 2 from the inner circumferential surface toward the outer circumferential surface of the intermediate transfer belt 2, thereby applying tension to the intermediate transfer belt 2.

[0032] 4 is a schematic perspective view showing a cross section (a cross section substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 2) of the end in the width direction of the intermediate transfer belt 2 on the rear side of the image forming apparatus 100. Note that while only the end on the rear side of the intermediate transfer belt 2 is shown in FIG. 4, in this embodiment the end on the front side also has the same configuration (symmetrical with respect to the center in the width direction of the intermediate transfer belt 2).

[0033] In this embodiment, the inner circumferential surface 2a of the intermediate transfer belt 2 is provided with ribs (protruding members) 6 protruding from the inner circumferential surface 2a at both ends in the width direction. In this embodiment, the ribs 6 have a substantially rectangular cross section substantially perpendicular to the extension direction, and are fixed to the inner circumferential surface 2a of the intermediate transfer belt 2 by adhesive. Note that the means for fixing the ribs 6 is not limited to adhesive, and the ribs 6 can be fixed to the inner circumferential surface 2a of the intermediate transfer belt 2 by any fixing means, such as adhesive, welding, or integral molding. In this manner, the intermediate transfer belt 2 is provided with ribs 6 extending along the circumferential direction on the inner circumferential surface at the ends in the width direction. In this embodiment, the ribs 6 are provided around the entire circumference of the intermediate transfer belt 2. The ribs 6 are typically formed continuously in the circumferential direction of the intermediate transfer belt 2, but may be divided into multiple segments in the circumferential direction of the intermediate transfer belt 2.

[0034] In this embodiment, reinforcing tape (reinforcing member) 7 is provided on the outer peripheral surface 2b of the intermediate transfer belt 2 at both ends in the width direction. In this embodiment, the reinforcing tape 7 is fixed to the outer peripheral surface 2b of the intermediate transfer belt 2 by adhesion. Note that the means for fixing the reinforcing tape 7 is not limited to adhesion, and the reinforcing tape 7 can be fixed to the outer peripheral surface 2b of the intermediate transfer belt 2 by any fixing means such as adhesion, welding, integral molding, etc.

[0035] In this embodiment, the rib 6 and the reinforcing tape 7 are respectively positioned slightly inward from the edges of both ends of the intermediate transfer belt 2. In addition, in this embodiment, the rib 6 and the reinforcing tape 7 are positioned so that they at least partially overlap each other in the width direction of the intermediate transfer belt 2 (particularly in this embodiment, the area of ​​the reinforcing tape 7 includes the area of ​​the rib 6).

[0036] In this embodiment, the intermediate transfer belt 2 is made of a resin belt having a base layer of polyimide (PI). In this embodiment, the intermediate transfer belt 2 has a tensile elastic modulus E of 18000 N / cm 2 and a thickness of 0.08 mm. The intermediate transfer belt 2 is preferably made of a resin with relatively high rigidity, such as polyvinylidene fluoride (PVDF), polyamide, polyimide resin (PI), polyethylene terephthalate (PET), or polycarbonate (PC). The thickness of the intermediate transfer belt 2 is preferably in the range of 0.02 mm to 0.50 mm. If the intermediate transfer belt 2 is too thin, it may not have sufficient durability against abrasion, and if it is too thick, it may be difficult to bend on the drive roller 110, tension roller 1, and first and second auxiliary rollers 113 and 114, resulting in deformation or crease.

[0037] In this embodiment, the rib 6 is made of a material mainly composed of urethane rubber. In this embodiment, the reinforcing tape 7 is made of the same material as the intermediate transfer belt 2. The materials of the intermediate transfer belt 2, the rib 6, and the reinforcing tape 7 are not particularly limited.

[0038] In this embodiment, the belt cleaning device 102 is a blade cleaning device and is an example of an intermediate transfer member cleaning means. The belt cleaning device 102 rubs a cleaning blade 102b against the surface of the intermediate transfer belt 2 to remove and collect deposits, such as toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 2 after the secondary transfer. The cleaning blade 102b is in contact with the area where the intermediate transfer belt 2 is wound around the tension roller 1. The tip of the cleaning blade 102b faces in the counter direction relative to the moving direction of the surface of the intermediate transfer belt 2 (the free end is located upstream of the fixed end in the moving direction of the surface of the intermediate transfer belt 2). The belt cleaning device 102 contacts the tip of the cleaning blade 102b against the surface (outer periphery) of the intermediate transfer belt 2 to collect deposits, such as secondary transfer residual toner. In this embodiment, the cleaning blade 102b is made of urethane rubber. This urethane rubber has a JIS-A hardness of 75 degrees and a thickness of 2 mm. In this embodiment, the cleaning blade 102b has a contact angle of 25° and a contact pressure of 3 N / m (30 gf / cm). However, the configuration of the belt cleaning device 102 is not limited to this.

[0039] 4. Overview of belt deviation and belt sagging regulation in this embodiment As mentioned above, if there is only one roller that regulates belt misalignment (herein, simply referred to as "misalignment regulation"), the effect of regulating belt misalignment may not be sufficient. Furthermore, even if misalignment is regulated using a rib regulation method, belt sagging (herein, simply referred to as "sagging regulation") is not regulated. In particular, in the secondary transfer section, if belt sagging occurs, the belt surface (secondary transfer surface) at the secondary transfer section may become distorted, potentially affecting the image. Therefore, in addition to regulating belt misalignment, it is necessary to regulate belt sagging, particularly in the secondary transfer section.

[0040] Therefore, in this embodiment, the shift regulation is performed by two rollers, and further, the shift regulation portion and the sagging regulation portion are provided on the same roller. In this embodiment, the shift regulation portion of the second roller (second tension roller) of the two rollers is provided on the inside in the rotation axis direction of the roller (toward the center in the width direction of the intermediate transfer belt 2) of the shift regulation portion of the first roller (first tension roller). This allows the shift regulation portion of the first roller to primarily regulate the shift, and the shift regulation portion of the second roller to secondary regulate the shift, thereby suppressing rippling of the belt surface on the second roller. However, on the second roller, the belt is more likely to sag than on the first roller due to loosening of the belt tension when the belt twists between the first and second rollers. Therefore, in this embodiment, the second roller is further provided with a sagging regulation portion. This enhances the belt shift regulation effect while effectively suppressing belt sagging. In this embodiment, the second roller is a roller that forms the secondary transfer portion, which makes it possible to prevent the belt surface from rippling due to shift regulation and to prevent the belt surface from becoming distorted due to sagging, particularly at the secondary transfer portion.

[0041] 5. Leaning and sagging control parts Next, the shift restriction portion and the droop restriction portion in this embodiment will be described in detail.

[0042] In this embodiment, the tension roller 1 is the first regulating roller (first tension roller), and the drive roller 110 is the second regulating roller (second tension roller). FIG. 5 is a cross-sectional view showing a shift regulation portion at the end of the tension roller 1, which is the first regulating roller, in the direction of its rotation axis (showing a cross section of the intermediate transfer belt 2 and other components and a side view of the tension roller 1 and other components). FIG. 6 is a perspective view of a first regulating member 8 provided at the end of the tension roller 1, in the direction of its rotation axis. FIG. 7 is a cross-sectional view showing a shift regulation portion and a sagging regulation portion at the end of the drive roller 110, which is the second regulating roller, in the direction of its rotation axis (showing a cross section of the intermediate transfer belt 2 and other components and a side view of the drive roller 110 and other components). FIG. 8 is a perspective view of a second regulating member 9 provided at the end of the drive roller 110, in the direction of its rotation axis. In this embodiment, the shift regulation portions at both ends of the tension roller 1 in the direction of its rotation axis have the same configuration (symmetrical with respect to the center of the tension roller 1 in the direction of its rotation axis). Similarly, in this embodiment, the shift regulation portion and sagging regulation portion at both ends of the drive roller 110 in the rotational axis direction are identical in configuration (symmetrical with respect to the center of the drive roller 110 in the rotational axis direction). Therefore, the following description will mainly focus on the configuration at one end. Also, the rotational axis direction of the tension rollers (drive roller 110, tension roller 1, first and second auxiliary rollers 113, 114) of the intermediate transfer belt 2 is also simply referred to as the "roller axis direction." Also, the radial direction of the tension rollers (drive roller 110, tension roller 1, first and second auxiliary rollers 113, 114) of the intermediate transfer belt 2 is also simply referred to as the "roller radial direction."

[0043] 5 and 6, a first regulating member 8 is provided at the end of the tension roller 1 in the rotational axis direction. The first regulating member 8 has a first regulating portion 8a that comes into contact with the side surface 6b or edge portion 6c of the rib 6 to regulate movement of the rib 6 in the roller axis direction.

[0044] 7 and 8, a second regulating member 9 is provided at the end of the drive roller 110 in the rotational axis direction. The second regulating member 9 has a second regulating portion 9a that contacts the side surface 6b or edge portion 6c of the rib 6 to regulate movement of the rib 6 in the roller axis direction. The second regulating member 9 also has a third regulating portion 10a that contacts the inner peripheral surface 6a of the rib 6 to regulate movement of the rib 6 radially inward of the roller. In this embodiment, the second regulating member 9 including the second regulating portion 9a and the third regulating portion 10a is integrally formed. The rib 6 is positioned outward in the roller axis direction from the first regulating portion 8a and the second regulating portion 9a.

[0045] In this embodiment, the first regulating portion 8a and the second regulating portion 9a are configured with tapered surfaces inclined with respect to the rotation axes of the tension roller 1 and the drive roller 110 (extensions of the outer circumferential surfaces of the tension roller 1 and the drive roller 110), respectively. Also, in this embodiment, the third regulating portion 10a is configured with a surface along the inner circumferential surface 6a of the rib 6. In particular, in this embodiment, the third regulating portion 10a is configured with a cylindrical surface that is approximately parallel to the rotation axis of the drive roller 110 (extensions of the outer circumferential surface of the drive roller 110). Also, in this embodiment, the second regulating portion 9a is positioned closer to the center in the width direction of the intermediate transfer belt 2 (inner in the roller axial direction) than the third regulating portion 10a.

[0046] That is, in this embodiment, the first regulating portion 8a has a tapered surface that gradually increases in diameter from the end side in the width direction of the intermediate transfer belt 2 toward the center side in the width direction of the intermediate transfer belt 2 and is approximately concentric with the tension roller 1. Also, in this embodiment, the second regulating portion 9a has a tapered surface that gradually increases in diameter from the end side in the width direction of the intermediate transfer belt 2 toward the center side in the width direction of the intermediate transfer belt 2 and is approximately concentric with the drive roller 110. Also, in this embodiment, the third regulating portion 10a has a diameter smaller than the outer diameter Dr of the drive roller 110 and is a cylindrical surface that is approximately concentric with the drive roller 110.

[0047] The first restricting portion 8a and the second restricting portion 9a contact at least one of the edge portion 6c and the side surface 6b of the rib 6. The side surface 6a of the rib 6 is the inner side surface in the roller axial direction among the side surfaces that intersect with the inner peripheral surface 6a of the rib 6. The edge portion 6c of the rib 6 is an edge portion formed by the inner peripheral surface 6a of the rib 6 and the side surface 6b of the rib 6. In addition, the third restricting portion 10a contacts the inner peripheral surface 6a of the rib 6.

[0048] In this embodiment, the first regulating member 8 is rotatable relative to the tension roller 1 and is supported by a rotation shaft 1a that protrudes from the end of the tension roller 1 in the direction of its rotation axis. Similarly, the second regulating member 9 is rotatable relative to the drive roller 110 and is supported by a rotation shaft 110a that protrudes from the end of the drive roller 110 in the direction of its rotation axis.

[0049] The outer surface and outer diameter of the tension roller 1 and the drive roller 110 refer to the main parts of the tension roller 1 and the drive roller 110, i.e., the parts around which the intermediate transfer belt 2 is wound (the parts that come into contact with the inner surface 2a of the intermediate transfer belt 2).

[0050] In this embodiment, the first and second restricting members 8 and 9 are each made of a sliding grade of POM. However, the materials of the first and second restricting members 8 and 9 are not particularly limited.

[0051] In this embodiment, the first and second restricting portions 8a and 9a are tapered surfaces (inclined surfaces) that are angled at 60° with respect to the rotation axes of the tension roller 1 and the drive roller 110, respectively. The angle of the tapered surfaces is not limited to this and is typically 30° or greater and less than 90°, and preferably 45° or greater and 75° or less. The first and second restricting portions 8a and 9a, which have a relatively low coefficient of friction, prevent the ribs 6 from riding over the tension roller 1 and the drive roller 110, thereby restricting the intermediate transfer belt 2 from shifting toward the belt. The tapered surfaces do not necessarily have to have a linear cross-sectional shape and may have a curved cross-sectional shape. In this embodiment, the minimum diameter of the second restricting portion 9a is approximately the same as the outer diameter D3 of the third restricting portion 10a.

[0052] The third regulating portion 10a has a cylindrical surface substantially concentric with the drive roller 110. The outer diameter D3 of the third regulating portion 10a is substantially the same as or smaller than the inner diameter of the rib 6. The inner diameter of the rib 6 is the diameter of a circle inscribed in the inner circumferential surface 6a of the rib 6 at the position where the intermediate transfer belt 2 is wound around the drive roller 110. Considering the tolerances of the rib 6 and the second regulating member 9, it is preferable that the outer diameter D3 of the third regulating portion 10a be slightly smaller than the inner diameter of the rib 6, for example, by approximately 1.0 mm. Furthermore, the third regulating portion 10a has a surface that conforms to the inner circumferential surface 6a of the rib 6 to keep the rib 6 substantially parallel to the rotation axis of the drive roller 110. In this embodiment, the inner circumferential surface 6a of the rib 6 is substantially parallel to the rotation axis of the drive roller 110. Therefore, it is preferable that the third regulating portion 10a is approximately parallel to the rotation axis of the drive roller 110 (the plane of the intermediate transfer belt 2). However, due to factors such as the fitting tolerance between the second regulating member 9 and the rotation shaft portion 110a of the drive roller 110, the third regulating portion 10a may be inclined up to about 1.3° with respect to the rotation axis of the drive roller 110. Here, the case where there is an inclination of the above tolerance is also considered to be approximately parallel.

[0053] When the intermediate transfer belt 2 moves in the width direction while it is running, at least one of the edge portion 6c or the side surface 6b of the rib 6 comes into contact with the first regulating portion 8a and the second regulating portion 9a (mainly the first regulating portion 8a in this embodiment, as will be described later). This regulates the position of the intermediate transfer belt 2 in the width direction, making it possible to prevent the belt from shifting. As a result, it is possible to prevent problems such as damage caused by the edge portion of the intermediate transfer belt 2 coming into contact with other members.

[0054] Furthermore, while the intermediate transfer belt 2 is running, the inner peripheral surface 6a of the rib 6 comes into contact with the third regulating portion 10a, thereby preventing the widthwise ends of the intermediate transfer belt 2 from bending inward in the radial direction of the roller, thereby preventing the belt from sagging. As a result, it is possible to prevent damage to the intermediate transfer belt 2 caused by bending of the widthwise ends of the intermediate transfer belt 2 and the influence on images caused by disturbance of the surface (secondary transfer surface) of the intermediate transfer belt 2 at the secondary transfer portion T2.

[0055] FIG. 9 is a cross-sectional view of a deviation regulating unit when the second regulating member 9 does not include the third regulating portion 10a (comparative example). The cross-section of the intermediate transfer belt 2 and the side of the drive roller 110 are shown. As shown in FIG. 9, while the intermediate transfer belt 2 is running, the widthwise ends of the intermediate transfer belt 2 tend to bend radially toward the roller, which can cause the belt to sag. The intermediate transfer belt 2 is prone to bending radially toward the roller due to a loosening of tension in the intermediate transfer belt 2 caused by twisting of the intermediate transfer belt 2 or the end of the intermediate transfer belt 2 moving away from the position where it is supported by the tension roller in the widthwise direction. If the intermediate transfer belt 2 is transported in this state, stress concentration can cause fatigue in the bent portion, leading to cracks and potentially damage to the intermediate transfer belt 2. This phenomenon becomes more pronounced when the intermediate transfer belt 2 is thinned or hardened by applying a coating agent to its surface. Furthermore, if the belt sags at the secondary transfer portion T2, the secondary transfer surface becomes distorted, which affects the image.

[0056] Therefore, as in this embodiment, it is desirable to provide not only a shift regulation portion but also a sagging regulation portion (the third regulation portion 10a in this embodiment), particularly at the end portion in the rotational axis direction of the drive roller 110 that forms the secondary transfer portion T2.

[0057] Next, the positional relationship between the first, second, and third regulating portions 8a, 9a, and 10a will be described. Figure 10 is a top view of the intermediate transfer unit 124 and a cross-sectional view showing the positional relationship between the first, second, and third regulating portions 8a, 9a, and 10a.

[0058] In the deviation prevention portion, the rib 6 may receive a reaction force from the prevention member, which may cause the intermediate transfer belt 2 to ripple. Therefore, in this embodiment, as shown in FIG. 10 , the second outer end surface 9b, which is the outer end surface of the second prevention member 9a in the roller axial direction, is located more inward in the roller axial direction (closer to the center in the width direction of the intermediate transfer belt 2) than the first outer end surface 8b, which is the outer end surface of the first prevention member 8a in the roller axial direction. The first outer end surface 8b can be considered to be the end of the first prevention member 8a closer to the end of the intermediate transfer belt 2 in the roller axial direction. The second outer end surface 9b can be considered to be the end of the second prevention member 9a closer to the end of the intermediate transfer belt 2 in the roller axial direction. In this embodiment, the position of the first prevention member 8 in the rotational axis direction of the tension roller 1 is determined by a bearing (not shown) provided on the rotational shaft portion 1a of the tension roller 1. Similarly, in this embodiment, the position of the second regulating member 9 in the direction of the rotation axis of the drive roller 110 is determined by a bearing (not shown) provided on the rotation shaft portion 110a of the drive roller 110. In this configuration, the first regulating member 8 and the second regulating member 9 may each move in the direction of the roller axis due to backlash. The first regulating member 8 and the second regulating member 9 are configured so that the positional relationship between the first outer end surface 8b and the second outer end surface 9b is maintained even if there is a change in position due to such backlash.

[0059] As a result, the first restricting portion 8a first contacts the side surface 6b or edge portion 6c of the rib 6 to actively restrict the belt shift, and the second restricting portion 9a supplementarily restricts the belt shift. In other words, if the side surface 6b or edge portion 6c of the rib 6 contacts the first restricting portion 8a and the belt shift continues in the same direction, the side surface 6b or edge portion 6c of the rib 6 contacts the second restricting portion 9a. As a result, the drive roller 110 forming the secondary transfer surface can restrict the belt shift, enhancing the belt shift restriction effect, while reducing the reaction force that the rib 6 receives from the restricting member at the portion wrapped around the drive roller 110 forming the secondary transfer surface. This reduces the risk of the secondary transfer surface becoming wavy, which can affect the image.

[0060] The distance X1 between the first outer end face 8b and the second outer end face 9b in the roller axial direction (the distance by which the second outer end face 9b is retracted inward in the roller axial direction from the first outer end face 8b) can be set appropriately depending on the tendency for belt deviation and waviness to occur, etc. Although not limited thereto, the distance X1 can be, for example, about 0.5 mm or more and 3.0 mm or less, and is 0.9 mm in this embodiment.

[0061] 10, in this embodiment, the third outer end surface 10b, which is the outer end surface of the third regulating portion 10a in the roller axial direction, is located further outward in the roller axial direction than the first outer end surface 8b, which is the outer end surface of the first regulating portion 8a in the roller axial direction. The third outer end surface 10b can be said to be the end of the third regulating portion 10a on the end side of the intermediate transfer belt 2 in the roller axial direction. The first regulating member 8 and the second regulating member 9 are configured so that the positional relationship between the first outer end surface 8b and the third outer end surface 10b is maintained even if there is a change in position due to the play as described above.

[0062] As a result, even when the intermediate transfer belt 2 is shifted most to one side, the inner peripheral surface 6a of the rib 6 can abut against the third regulating portion 10a without falling off from the third regulating portion 10a. In other words, even when the intermediate transfer belt 2 is shifted most to the right side in FIG. 10 (at this time, shift regulation is performed at the left end of the intermediate transfer belt 2 in the figure), the inner peripheral surface 6a of the rib 6 at the right end of the intermediate transfer belt 2 in the figure can abut against the third regulating portion 10a without falling off from the third regulating portion 10a. As a result, sagging of the belt can be reliably suppressed.

[0063] The distance X2 between the first outer end surface 8b and the third outer end surface 10b in the roller axial direction (the distance by which the third outer end surface 10b protrudes further outward in the roller axial direction than the first outer end surface 8b) can be set appropriately depending on the tendency of belt misalignment. It is desirable that even when the intermediate transfer belt 2 is most misaligned to one side, at least half of the width of the inner circumferential surface 6a of the rib 6 overlaps with the third restricting portion 10a in the roller axial direction. In this embodiment, even when the intermediate transfer belt 2 is most misaligned to one side, at least 70% of the width of the inner circumferential surface 6a of the rib 6 overlaps with the third restricting portion 10a in the roller axial direction. In this embodiment, the width of the rib 6 in the roller axial direction (the width of the inner circumferential surface 6a) is approximately 3 mm.

[0064] 7, in this embodiment, the outer diameters of the drive roller 110, the second regulating member 9a, and the third regulating member 10a are, in descending order of size, Dr, D2, D3 (Dr>D2>D3). This results in a dimensional relationship in which, when tension is applied to the intermediate transfer belt 2 by the tension roller, the inner peripheral surface 2a of the intermediate transfer belt 2 does not contact the outer peripheral surface 9c of the second regulating member 9a, and the inner peripheral surface 6a of the rib 6 contacts the third regulating member 10a. As a result, damage to the intermediate transfer belt 2 caused by friction between the inner peripheral surface 2a of the intermediate transfer belt 2 and the second regulating member 9 during the running of the intermediate transfer belt 2 can be suppressed, while also suppressing belt sagging.

[0065] In this embodiment, the first regulating member 8 and the second regulating member 9 are attached so as to be rotatable relative to the tension roller 1 and the drive roller 110, respectively, but they may also be attached in a fixed manner so as not to rotate relative to each other.

[0066] Furthermore, as in this embodiment, a sagging restriction portion may be provided on the drive roller 110 as the second tension roller, and a sagging restriction portion may also be provided on the tension roller 1 as the first tension roller. In this case, the width of the sagging restriction portion provided on the tension roller 1 in the roller axial direction may be shorter than the width of the sagging restriction portion provided on the drive roller 110 in the roller axial direction. This is because the tension roller 1 is designed to actively restrict shift, making belt sagging less likely to occur than the drive roller 110.

[0067] As described above, in this embodiment, the image forming apparatus 100 includes an image carrier (photosensitive drum) 103 that carries a toner image, an endless intermediate transfer belt 2 that transports the toner image that has been primarily transferred from the image carrier 103 at a primary transfer portion T1 to a recording material P for secondary transfer at a secondary transfer portion T2, and a plurality of tension rollers that tension the intermediate transfer belt 2, including a first tension roller (tension roller) 1 and a second tension roller (drive roller) 110, and the plurality of tension rollers are arranged so that the directions of the rotation axes of the respective tension rollers are along a predetermined direction (the roller axis direction, the width direction of the intermediate transfer belt 2). The intermediate transfer belt 2 has ribs 6 that extend along the circumferential direction on the inner peripheral surface of the end portion in the width direction, and the first tension roller 1 has ribs 6 that extend along the circumferential direction in the predetermined direction. A first regulating portion 8a is provided at the end of the second tension roller 110, which contacts the rib 6 and regulates movement of the rib 6 in the specified direction, and a second regulating portion 9a is provided at the end of the second tension roller 110 in the specified direction, which contacts the rib 6 and regulates movement of the rib 6 in the specified direction, and a third regulating portion 10a is provided at the end of the second tension roller 110 in the specified direction, which contacts the rib 6 and regulates movement of the rib 6 in the radial direction, the third regulating portion 10a being located on the end side of the intermediate transfer belt 2 in the specified direction relative to the second regulating portion 9a, and the end of the second regulating portion 9a on the end side of the intermediate transfer belt 2 in the specified direction is located closer to the center of the intermediate transfer belt 2 in the specified direction than the end of the first regulating portion 8a on the end side of the intermediate transfer belt 2 in the specified direction. In this embodiment, the end of the third regulating portion 10a on the end side of the intermediate transfer belt 2 in the predetermined direction is located closer to the end of the intermediate transfer belt 2 in the predetermined direction than the end of the first regulating portion 8a on the end side of the intermediate transfer belt 2 in the predetermined direction. In this embodiment, the outer diameter of the portion of the second tension roller 110 that contacts the inner circumferential surface of the intermediate transfer belt 2 is defined as Dr, the outer diameter of the second regulating portion 9a is defined as D2, and the outer diameter of the third regulating portion 10a is defined as D3. In this embodiment, the first regulating member 8 having the first regulating portion 8a is attached to the first tension roller 1. In this embodiment, the first regulating member 8 is attached to the first tension roller 1 so as to be rotatable relative to the first tension roller 1.In this embodiment, a second regulating member 9 having a second regulating portion 9a and a third regulating portion 10a is attached to a second tension roller 110. In this embodiment, the second regulating member 9 is attached so as to be rotatable relative to the second tension roller 110. In this embodiment, the second tension roller 110 is a tension roller that forms the secondary transfer portion T2.

[0068] As described above, according to this embodiment, it is possible to effectively prevent the belt from sagging while enhancing the effect of restricting the belt deviation.

[0069] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of the image forming apparatus of embodiment 1, and detailed descriptions thereof will be omitted.

[0070] The shift regulation portion and the droop regulation portion in this embodiment will be described. FIG. 11 is a cross-sectional view showing the shift regulation portion and the droop regulation portion at the end of the rotation axis direction of the drive roller 110 in this embodiment (a cross section of the intermediate transfer belt 2 and the like and a side view of the drive roller 110 and the like are shown). FIG. 12 is a perspective view of the second regulation member 9 and the third regulation member 10 provided at the end of the rotation axis direction of the drive roller 110 in this embodiment. In this embodiment, the configuration of the first regulation member 8 provided on the tension roller 1 is the same as in the first embodiment. In this embodiment, the shift regulation portion and the droop regulation portion at both end of the rotation axis direction of the drive roller 110 are the same configuration (symmetrical with respect to the center of the rotation axis direction of the drive roller 110). Therefore, the following description will mainly focus on the configuration on one end side.

[0071] 11 and 12, a second regulating member 9 having a second regulating portion 9a and a third regulating member 10 having a third regulating portion 10a are provided as separate bodies. The second regulating member 9 and the third regulating member 10 are each supported by a rotation shaft portion 110a of the drive roller 110 so as to be rotatable relative to the drive roller 110.

[0072] Integrating the second regulating portion 9a and the third regulating portion 10a as in the first embodiment has the advantage of simplifying the configuration. However, portions with different radii, such as the inner circumferential surface 6a of the rib 6, the side surface 6b of the rib 6, and the inner circumferential surface 2a of the intermediate transfer belt 2, run coaxially in different regions in the width direction of the intermediate transfer belt 2. Therefore, when the second regulating portion 9a and the third regulating portion 10a rotate integrally, the intermediate transfer belt 2 runs at slightly different peripheral speeds relative to the second regulating portion 9a and the third regulating portion 10a in the respective regions with different radii. As a result, a load may be generated due to friction between the inner circumferential surface 6a of the rib 6, the side surface 6b of the rib 6, and the second regulating portion 9a and the third regulating portion 10a.

[0073] In contrast, in this embodiment, the second and third restricting portions 9a and 10a are separate and can rotate independently, which further reduces the effect of the load caused by the friction. As a result, the stability of the image and the durability of the intermediate transfer belt 2 and the ribs 6 can be further improved.

[0074] In the configuration shown in Figure 11, a gap is provided between the second regulating member 9 and the second regulating member 10, but even if the second regulating member 9 and the third regulating member 10 are separate, they may be arranged adjacent to each other with substantially no gap, as in the configuration shown in Figure 7.

[0075] FIG. 13 is a front view of the second regulating member 9 in this embodiment. As shown in FIG. 13, in this embodiment, the second regulating member 9 has a shape that is symmetrical with respect to a plane that is approximately perpendicular to the rotational axis direction of the drive roller 110. This allows the second regulating member 9 to be attached to either of the two end portions of the drive roller 110 in the rotational axis direction without specifying the orientation. As a result, when assembling the intermediate transfer unit 124, in the process of attaching the second regulating member 9 to the drive roller 110, there is no need to align the attachment orientation of the second regulating member 9, allowing for smooth attachment and preventing incorrect assembly. This effect is particularly noticeable when the second regulating member 9 is thin and its shape is difficult to distinguish.

[0076] In this manner, in this embodiment, the second regulating member 9 having the second regulating portion 9a and the third regulating member 10 having the third regulating portion 10a are each attached so as to be rotatable relative to the second tension roller 110. Also, in this embodiment, the second regulating member 9 has a shape that is symmetrical with respect to a plane that is approximately perpendicular to the roller axial direction.

[0077] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the second regulating portion 9a and the third regulating portion 10a are separate bodies, which further reduces the influence on the running of the intermediate transfer belt 2. This makes it possible to further improve the stability of the image and the durability of the belt. [Explanation of symbols]

[0078] 1 Tension roller 2 Intermediate transfer belt 6. Ribs 6a Inner surface of rib 6b Side of rib 7 Reinforcement tape 8 First restricting member 8a First Regulatory Section 8b Outer end surface of the first restricting portion 9 Second restricting member 9a Second Regulatory Section 9b Outer end surface of the second restricting portion 10. Third Regulating Member 10a Third Regulatory Section 10b Outer end surface of the third restricting portion 100 Image forming device 110 Drive roller 111 Secondary transfer roller 124 Intermediate transfer unit

Claims

1. an image carrier that carries a toner image; an endless intermediate transfer belt that conveys the toner image that has been primarily transferred from the image carrier at the primary transfer unit so that the toner image can be secondarily transferred onto a recording material at the secondary transfer unit; a plurality of tension rollers for tensioning the intermediate transfer belt, the tension rollers including a first tension roller and a second tension roller, the plurality of tension rollers being arranged such that the rotation axes of the respective tension rollers are aligned in a predetermined direction; and the intermediate transfer belt is provided with a rib extending in a circumferential direction on an inner peripheral surface of an end portion in a width direction, the first tension roller is provided with a first restriction portion at an end portion in the predetermined direction, the first restriction portion contacting the rib to restrict movement of the rib in the predetermined direction; the second tension roller is provided with a second regulating portion at an end in the predetermined direction, the second regulating portion contacting the rib to regulate movement of the rib in the predetermined direction, and a third regulating portion contacting the rib to regulate movement of the rib in the radial direction of the second tension roller, the third regulating portion being located closer to the end of the intermediate transfer belt in the predetermined direction than the second regulating portion; An image forming apparatus characterized in that the end of the second regulating portion on the end side of the intermediate transfer belt in the specified direction is located closer to the center of the intermediate transfer belt in the specified direction than the end of the first regulating portion on the end side of the intermediate transfer belt in the specified direction.

2. 2. The image forming apparatus according to claim 1, wherein the end of the third regulating portion on the end side of the intermediate transfer belt in the predetermined direction is located closer to the end of the intermediate transfer belt in the predetermined direction than the end of the first regulating portion on the end side of the intermediate transfer belt in the predetermined direction.

3. 2. The image forming apparatus according to claim 1, wherein when the outer diameter of the portion of the second tension roller that contacts the inner surface of the intermediate transfer belt is Dr, the outer diameter of the second regulating portion is D2, and the outer diameter of the third regulating portion is D3, the relationship Dr > D2 > D3 is satisfied.

4. 2. The image forming apparatus according to claim 1, wherein a first regulating member having the first regulating portion is attached to the first tension roller.

5. 5. The image forming apparatus according to claim 4, wherein the first regulating member is attached so as to be rotatable relative to the first tension roller.

6. 2. The image forming apparatus according to claim 1, wherein a second regulating member including the second regulating portion and the third regulating portion is attached to the second tension roller.

7. 7. The image forming apparatus according to claim 6, wherein the second regulating member is attached so as to be rotatable relative to the second tension roller.

8. 2. The image forming apparatus according to claim 1, wherein a second regulating member having the second regulating portion and a third regulating member having the third regulating portion are each attached so as to be rotatable relative to the second tension roller.

9. 9. The image forming apparatus according to claim 8, wherein the second regulating member has a shape that is symmetrical with respect to a plane that is substantially perpendicular to the predetermined direction.

10. 10. The image forming apparatus according to claim 1, wherein the second tension roller is a tension roller that forms the secondary transfer portion.

Images