Belt unit, transfer apparatus, and image forming apparatus

Abstract

A belt unit includes a belt member configured to be entrained around a plurality of support rotating bodies including a first support rotating body and a second support rotating body; a tension applying mechanism configured to apply tension in a traveling direction of the belt member; and a belt displacement restriction mechanism configured to restrict axial displacement of the belt member by tilting an axis of the first support rotating body. One end portion of each rotation shaft of the first and second support rotating bodies is supported by a common first supporting member, and another end portion of each of the rotation shafts of the first and second support rotating bodies is supported by a common second supporting member. Both end portions of a rotation shaft of either the first or the second support rotating body are movably supported relative to the first and second supporting members.

Description

BELT UNIT, TRANSFER APPARATUS, AND IMAGE FORMING APPARATUS

[0001] The present invention relates to a belt unit, a transfer apparatus, and an image forming apparatus.

[0002] Conventionally, belt units including a belt that is entrained around a plurality of rollers and driven to travel are known. In such a belt unit, belt displacement, in which a belt moves in an axial direction while being driven to travel, may occur due to the parallelism or an outer diameter deviation of a plurality of rollers around which the belt is entrained, a circumferential length deviation of the belt, or the like. There is known a technique by which, when such belt displacement occurs, a shaft tilting member causes one of the plurality of rollers around which the belt is entrained to be tilted relative to the other rollers in the axial direction, thereby applying a moving force to the belt in a direction opposite to a direction in which the belt has displaced (see Patent Documents 1 to 3, for example).

[0003] [NPL 1] Japanese Patent No. 6628141 [NPL 2] Japanese Unexamined Patent Application Publication No. 2017-58651 [NPL 3] Japanese Patent No.6691682

[0004] In the techniques described in Patent Documents 1 to 3, one roller (displacement control roller or tension roller) is tilted in order to control belt displacement, but an external force acting in the axial direction is also applied to the tilted roller itself. Therefore, a restricting member that restricts axial movement of the roller (displacement control roller or tension roller) and a supporting member that rotatably supports the roller are brought into contact with each other and slide, and unanticipated friction and wear occur between them. As a result, the positioning accuracy of the roller in the axial direction tends to be decreased.

[0005] Such a tendency toward decreased positioning accuracy becomes more pronounced because, if there is a difference in the positional relationship or parallelism between the displacement control roller or the tension roller and a backup roller adjacent thereto, a belt displacement force is generated to a greater extent, and as the belt displacement force increases, an axial displacement force of the displacement control roller or the tension roller also increases. As a result, sliding wear of the restricting member that restricts axial movement of the displacement control roller or the tension roller occurs more than anticipated.

[0006] If the displacement control roller or the tension roller is displaced in the axial direction more than anticipated due to wear of the restricting member being more than anticipated, a shaft tilting member on the opposite side comes into contact with the displacement control roller or the tension roller, thereby causing the displacement control roller or the tension roller to be tilted. Therefore, a force that accelerates belt displacement in a direction opposite to a direction in which the belt is originally intended to be returned acts on the belt. As a result, a load applied to an end portion of the belt becomes larger than anticipated, thereby causing the belt to be damaged.

[0007] It is an object of the present invention to provide a belt unit, a transfer apparatus, and an image forming device that solve the above-described problems and can perform belt displacement control satisfactorily over a long period of time even when an external force in the axial direction acts on a roller that controls the belt displacement.

[0008] A belt unit according to the present invention includes: a belt member configured to be entrained around a plurality of support rotating bodies and driven to travel by rotation of the plurality of support rotating bodies, the plurality of support rotating bodies including a first support rotating body and a second support rotating body disposed adjacent to the first support rotating body; a tension applying mechanism configured to apply tension in a traveling direction of the belt member; and a belt displacement restriction mechanism configured to restrict axial displacement of the belt member by tilting an axis of the first support rotating body, wherein one end portion of each rotation shaft of the first support rotating body and the second support rotating body is supported by a common first supporting member, and another end portion of each of the rotation shafts of the first support rotating body and the second support rotating body is supported by a common second supporting member, and both end portions of a rotation shaft of either the first support rotating body or the second support rotating body are movably supported relative to the first supporting member and the second supporting member.

[0009] According to the present invention, belt displacement control can be performed satisfactorily over a long period of time.

[0010] Fig. 1 is a schematic block diagram illustrating an image forming apparatus according to an embodiment of the present invention;Fig. 2A is a schematic side view of an intermediate transfer unit during full color printing;Fig. 2B is a schematic side view illustrating a state in which full color printing transitions to monochrome printing;Fig. 3A is a cross-sectional view of a belt unit according to a first embodiment of the present invention;FIG. 3B is a side view of a tension roller and a backup roller of the belt unit according to the first embodiment of the present invention during monochrome printing;FIG. 3C is a side view of the tension roller and the backup roller of the belt unit according to the first embodiment of the present invention during full color printing;Fig. 4A is a side view of a belt unit according to a second embodiment of the present disclosure;Fig. 4B is a view including a plan view and a side view of the belt unit according to the second embodiment of the present invention, in which the side view illustrates the backup roller in a pivoting state;Fig. 5A is a cross-sectional view when belt displacement and displacement of a tension roller have started in a belt unit of Related Art 1;Fig. 5B is a cross-sectional view in which the belt displacement and the displacement of the tension roller have advanced in the belt unit of Related Art 1;Fig. 5C is a view including a plan view and a side view of the belt unit of Related Art 1, in which the side view illustrates a backup roller in a pivoting state;Fig. 6A is a side view of a belt unit of Related Art 2; andFig. 6B is a view including a plan view and a side view of the belt unit of Related Art 2, in which the side view illustrates a backup roller in a pivoting state.

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions thereof will be simplified or omitted as appropriate.

[0012] ● Image Forming Apparatus

[0013] Embodiments according to the present invention will be described below in order with reference to the drawings. Fig. 1 illustrates a quadruplet tandem color printer 1 that is an example of an image forming apparatus according to an embodiment of the present invention and is an intermediate-transfer-type printer forming a color image using four color toners of yellow, magenta, cyan, and black. In the drawings, suffixes Y, M, C, and K are appended to components relating to colors of yellow, magenta, cyan, and black, respectively.

[0014] Four process cartridge units 3Y, 3M, 3C, and 3K, which serve as an image forming part that forms yellow, magenta, cyan, and black toner images using the four color toners, respectively, and an intermediate transfer unit 4 are arranged in substantially a central portion of the color printer 1.

[0015] The process cartridge units 3Y, 3M, 3C, and 3K are disposed below the intermediate transfer unit 4. Further, an optical unit 5 serving as an exposure unit is disposed below the process cartridge units 3Y, 3M, 3C, and 3K.

[0016] The process cartridge units 3Y, 3M, 3C, and 3K include drum-shaped photoconductors 30Y, 30M, 30C, and 30K, respectively, as image bearers, on each of which an electrostatic latent image is formed by exposure light emitted from the optical unit 5. The process cartridge units 3Y, 3M, 3C, and 3K respectively include charging units 31Y, 31M, 31C, and 31K, developing units 32Y, 32M, 32C, and 32K, cleaning units 33Y, 33M, 33C, and 33K, and discharging units. The charging units, the developing units, the cleaning units, and the discharging units are arranged around the photoconductors 30Y, 30M, 30C, and 30K, respectively. The process cartridge units 3Y, 3M, 3C, and 3K perform an electrophotographic image forming process using these units to respectively form single color toner images on the photoconductors 30Y, 30M, 30C, and 30K.

[0017] The intermediate transfer unit 4 includes a plurality of rollers 40, 41, 42, 43, 44, and 47 serving as a plurality of rotation supporting members, and an endless transfer belt 45 serving as an intermediate transfer body and entrained around the plurality of rollers. The intermediate transfer unit 4 is configured such that, by rotationally driving the roller 41, the transfer belt 45 is rotated counterclockwise as indicated by an arrow in Fig. 1.

[0018] Primary transfer rollers 6Y, 6M, 6C, and 6K serving as primary transfer members are arranged inside the loop of the transfer belt 45 so as to face the photoconductors 30Y, 30M, 30C, and 30K, respectively. The primary transfer rollers 6Y, 6M, 6C, and 6K press the transfer belt 45 toward the photoconductors 30Y, 30M, 30C, and 30K, respectively. Primary transfer parts 7Y, 7M, 7C, and 7K where toner images on the photoconductors are transferred to the transfer belt 45 are formed between the photoconductors 30Y, 30M, 30C, and 30K and the transfer belt 45, respectively. A primary transfer bias is applied to the primary transfer parts 7Y, 7M, 7C, and 7K.

[0019] A secondary transfer part 8 is formed downstream of the primary transfer parts 7Y, 7M, 7C and 7K in the conveyance direction of the belt. The secondary transfer part 8 is formed between the transfer belt 45 and a secondary transfer roller 9, which serves as a secondary transfer member disposed to face a drive roller 44 and in contact with the transfer belt 45. A secondary transfer bias is applied to the secondary transfer part 8. The drive roller 44 serves as a fourth support rotating body and can be rotationally driven by a drive unit or a driver.

[0020] A plurality of trays 10 storing recording materials P are arranged below the optical unit 5. The recording materials P stored in the trays 10 are separated one by one from the trays 10 by a group of rollers 11, which perform feeding and separation of the recording materials P, and are conveyed toward the secondary transfer part 8.

[0021] In the secondary transfer part 8, the toner images transferred onto the transfer belt 45 at the primary transfer parts 7Y, 7M, 7C, and 7K are transferred onto a recording material P. The recording material P onto which the toner images are transferred is conveyed to a fixing device 12 disposed downstream of the secondary transfer part 8 in the conveyance direction of the recording material. The fixing device 12 applies heat and pressure to the recording material P to fix the toner images on the recording material P, and conveys the recording material P toward an ejection port 13.

[0022] The recording material P conveyed to the ejection port 13 is ejected by a roller pair 15 and stacked on an ejection tray 14 provided at an upper portion of an apparatus body 1a. After the toner images are transferred, for example, residual toner and paper dust are removed from the transfer belt 45 by a belt cleaner 16.

[0023] The process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4 are supported by the apparatus body 1a such that the process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4 are attachable to and detachable from the front side of the apparatus body 1a and are slidable relative to the apparatus body 1a. The process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4 are disposed adjacent to each other in the apparatus body 1a.

[0024] In the present embodiment, slight gaps are formed at a boundary 100 between upper portions of the process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4. With the slight gaps, the process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4 are disposed so as not to contact each other and interfere with each other when the process cartridge units 3Y, 3M, 3C, and 3K and the intermediate transfer unit 4 are attached to and detached from the apparatus body 1a.

[0025] ● Movements of Primary Transfer Rollers Figs. 2A and 2B are schematic side views of the intermediate transfer unit 4 illustrating movements of the primary transfer rollers 6Y, 6M, 6C, and 6K during monochrome printing and full color (FC) printing. A sensor facing member 46, a toner abnormality detection sensor 49, and a cleaning blade 48 are disposed on the upper path of the transfer belt 45.

[0026] As illustrated in Fig. 2A, in full color (FC) printing, all the primary transfer rollers 6Y, 6M, 6C, and 6K are in a lowered position and are in contact with the respective photoconductors 30Y, 30M, 30C, and 30K via the transfer belt 45. Thus, toner images formed on the surfaces of the photoconductors 30Y, 30M, 30C, and 30K are transferred to the transfer belt 45 as a full color image.

[0027] Conversely, in monochrome printing, the primary transfer rollers 6Y, 6M, and 6C other than the black primary transfer roller 6K move upward to be spaced apart from the photoconductors 30Y, 30M, and 30C as indicated by a dashed line in Fig. 2B. Therefore, only a monochrome image formed on the surface of the black photoconductor 30K is transferred to the transfer belt 45.

[0028] The tension of the transfer belt 45 tends to chang due to upward and downward movements of the primary transfer rollers 6Y, 6M, and 6C between monochrome printing and full color printing as described above. Such a change in the tension of the transfer belt 45 can easily lead to conveyance failure of the transfer belt 45 and resultant transfer failure. For this reason, a backup roller 42 disposed between a tension roller 41 configured to control belt displacement and a transfer unit (primary transfer roller 6Y) located closest to the backup roller 42 optimally adjusts the tension of the transfer belt 45, thereby effectively suppressing the conveyance failure and the transfer failure of the transfer belt 45.

[0029] ● First Embodiment A belt unit or a transfer apparatus according to a first embodiment of the present invention will be described with reference to Figs. 3A to 3C. Fig. 3A is a cross-sectional view taken along the line 3A-3A of Fig. 3B.

[0030] As illustrated in Fig. 3A, a belt contact member 50 having a flange portion 50a is inserted onto a rotation shaft 41a of the tension roller 41 so as to be movable in the axial direction. When the transfer belt 45 contacts the flange portion 50a of the belt contact member 50 due to displacement of the transfer belt 45 in a direction indicated by an arrow, the belt contact member 50 is pushed by the transfer belt 45 and moves to the right together with a support rotating body displacement member 51, which is included in a belt displacement restriction mechanism.

[0031] Upon the movement of the support rotating body displacement member 51 to the right, an inclined portion 51a of the support rotating body displacement member 51 contacts a guide member 55 integrated with a body frame 57, and pushes down the rotation shaft 41a. As a result, the tension on the front side of the transfer belt 45 decreases and the tension on the rear side increases. As a result, the transfer belt 45 moves toward the rear side on which the tension is relatively high. In this manner, the displacement of the transfer belt 45 is suppressed within a certain range (excessive displacement is suppressed).

[0032] The rotation shaft 41a of the tension roller 41 is rotatably supported by a supporting member 53. The supporting member 53 is movably disposed in an elongated hole 60a formed in a shaft supporting member 60.

[0033] A restricting member 54 is disposed on the rotation shaft 41a of the tension roller 41 projecting outward of the body frame 57. The restricting member 54 restricts the axial movement of the rotation shaft 41a.

[0034] An elastically deformable intermediate member 59 is disposed between the restricting member 54 and the shaft supporting member 60. The intermediate member 59 prevents wear of the restricting member 54.

[0035] As illustrated in Fig. 4B, the shaft supporting member 60 is disposed to be pivotable in the up-down direction about a fulcrum 60b. The fulcrum 60b is axially supported by the body frame 57.

[0036] In the belt unit or the transfer apparatus according to the first embodiment, as illustrated in Figs. 3B and 3C, the tension roller 41, which serves as a first support rotating body, and the backup roller 42, which serves as a second support rotating body, are rotatably supported by one (common) supporting member 80. That is, a front end portion of the rotation shaft 41a of the tension roller 41 and a front end portion of a rotation shaft 42a of the backup roller 42 are rotatably supported by the supporting member 80, which serves as a first supporting member. The supporting member 80 supports the rotation shaft 41a between the intermediate member 59 and the shaft supporting member 60.

[0037] Similarly, rear end portions of the rotation shafts 41a and 42a of the tension roller 41 and the backup roller 42 are rotatably supported by a supporting member (not illustrated in detail), which serves as a second supporting member. The supporting member 80 on the front side and the supporting member on the rear side have the same shape.

[0038] An elongated hole 80a is formed in one end portion (a left end portion) of the supporting member 80 in the longitudinal direction of the supporting member 80 (the traveling direction of the transfer belt 45). The rotation shaft 41a of the tension roller 41 is rotatably inserted into the elongated hole 80a. The rotation shaft 41a is movable in the longitudinal direction of the elongated hole 80a.

[0039] Conversely, an axial hole is formed in the other end portion of the supporting member 80, and the rotation shaft 42a of the backup roller 42 can be rotatably inserted into the axial hole. The supporting member serving as the second supporting member on the rear side have the same configuration as that of the supporting member 80 on the front side.

[0040] The distance between the tension roller 41 and the backup roller 42 changes as the rotation shaft 41a of the tension roller 41 moves in the elongated hole 80a. Fig. 3B illustrates a state in which the tension roller 41 and the backup roller 42 are closest to each other, and Fig. 3C illustrates a state in which the tension roller 41 and the backup roller 42 are farthest apart from each other.

[0041] The rotation shaft 42a of the backup roller 42 is supported by the tip of a support arm 70 that is pivotable about the fulcrum 70a. In monochrome printing, the support arm 70 rotates upward as illustrated in Fig. 3B to pull up the transfer belt 45, which serves as a belt member. As a result, the transfer belt 45 is inclined upward to the left as indicated by the dashed line in Fig. 2B.

[0042] In full color (FC) printing, the support arm 70 rotates downward as illustrated in Fig. 3C to push down the transfer belt 45. As a result, the transfer belt 45 is horizontal as indicated by a solid line in Fig. 2A.

[0043] In this manner, the tension roller 41 and the backup roller 42 are rotatably supported by the one (common) supporting member 80, and the tension roller 41 is configured to be moveable toward or away from the backup roller 42. Thus, it is possible to adjust, that is, increase or decrease, the tension of the transfer belt 45 on the front side and the rear side of the belt unit.

[0044] That is, by moving the tension roller 41 toward the backup roller 42 as illustrated in Fig. 3B, the tension of the transfer belt 45 can be decreased. Further, by moving the tension roller 41 away from the backup roller 42 as illustrated in Fig. 3C, the tension of the transfer belt 45 can be increased.

[0045] The rotation shaft 41a of the tension roller 41 is tilted by the support rotating body displacement member 51, which is included in the belt displacement restriction mechanism, along with belt displacement of the transfer belt 45. Further, the rotation shaft 41a of the tension roller 41 is biased to the left in Fig. 3C by a tension spring 61, which serves a first spring of a tension applying mechanism.

[0046] The rotation shaft 41a is slidably disposed in the elongated hole 60a of the shaft supporting member 60 (see Fig. 4B). The shaft supporting member 60 is disposed to be pivotable in the up-down direction about the fulcrum 60b. A clockwise rotational moment about the fulcrum 60b is applied to the shaft supporting member 60 by the tensile force of a biasing spring 52, which serves as a second spring of the tension applying mechanism.

[0047] The pivotal position of the shaft supporting member 60 is stabilized by the balance between the clockwise rotational moment and a counterclockwise rotational moment generated by the tension of the transfer belt 45. Note that the fixed end of the biasing spring 52 is coupled to the guide member 55.

[0048] Conventionally, if there is a difference in the positional relationship / parallelism between the tension roller 41 and the backup roller 42 on the front side and the rear side, a displacement force of the transfer belt 45 would be generated to a greater extent, and as the belt displacement force increases, an axial displacement force of the tension roller 41 would also increase. In the first embodiment of the present invention, because the rotation shafts 41a and 42a of the tension roller 41 and the backup roller 42 are rotatably supported by the one (common) supporting member 80, an error in the positional relationship / parallelism between the two rollers is suppressed.

[0049] Further, because the rotation shaft 41a of the tension roller 41 is movably disposed in the elongated hole 80a of the supporting member 80, the center-to-center distance between the tension roller 41 and the backup roller 42 can be changed. Therefore, it is possible to appropriately manage the tension of the transfer belt 45, thereby preventing belt damage, preventing the formation of roller marks on the belt, and avoiding the occurrence of abnormal images at the positions of the roller marks.

[0050] The supporting member 80 can also be provided with an adjustment unit that can adjust the parallelism between the tension roller 41 and the backup roller 42. The parallelism between the tension roller 41 and the backup roller 42 can be reliably maintained by such an adjustment unit.

[0051] ● Second Embodiment Next, a belt unit or a transfer apparatus according to a second embodiment of the present invention will be described with reference to Figs. 4A and 4B. Similar to the first embodiment, in the second embodiment, the tension roller 41 and the backup roller 42 are rotatably supported by one (common) supporting member 80.

[0052] However, in the second embodiment, instead of the rotation shaft 41a of the tension roller 41, the rotation shaft 41a of the backup roller 42 is movably supported. That is, an elongated hole 80b is formed in the other end portion of the supporting member 80 in the longitudinal direction of the supporting member 80 (the traveling direction of the transfer belt 45).

[0053] The rotation shaft 42a of the backup roller 42 is rotatably inserted into the elongated hole 80b. An axial hole into which the rotation shaft 41a of the tension roller 41 can be rotatably inserted is formed in one end portion of the supporting member 80. Similar to the first embodiment, in the second embodiment, the rotation shafts 41a and 42a of the tension roller 41 and the backup roller 42 are also rotatably supported by the one (common) supporting member 80, and thus an error in the positional relationship / parallelism between the two rollers can be suppressed.

[0054] In addition, because the rotation shaft 42a of the backup roller 42 is movably disposed in the elongated hole 80b of the supporting member 80, the center-to-center distance between the tension roller 41 and the backup roller 42 can be changed. Therefore, it is possible to appropriately manage the tension of the transfer belt 45, thereby preventing belt damage, preventing the formation of roller marks on the belt, and avoiding the occurrence of abnormal images at the positions of the roller marks.

[0055] The rotation shaft 42a of the backup roller 42 is supported by the tip of the support arm 70 that is pivotable about the fulcrum 70a. In monochrome printing, the support arm 70 rotates upward to pull up the transfer belt 45, and in full color (FC) printing, the support arm 70 rotates downward to push down the transfer belt 45.

[0056] A guided pin 70b is provided at a position slightly below an intermediate portion of the support arm 70. When the support arm 70 pivots in the up-down direction, the guided pin 70b is guided by a guide portion 72.

[0057] In the second embodiment, a driven roller 82, which serves as a third support rotating body, is rotatably supported by a longitudinal intermediate portion of the supporting member 80. The driven roller 82 contacts the inner surface of the transfer belt 45 at an intermediate position between the tension roller 41 and the backup roller 42.

[0058] Therefore, the travel path of the transfer belt 45 between the tension roller 41 and the backup roller 42 can be stabilized by the driven roller 82. By stabilizing the travel path of the transfer belt 45, the tension of the transfer belt 45 can be stabilized on the front side and the rear side, and thus excessive displacement of the transfer belt 45 and excessive movement of the tension roller 41 can be suppressed. The driven roller 82 can also be disposed on the supporting member 80 according to the first embodiment illustrated in Figs. 3A to 3C.

[0059] The driven roller 82 can be positioned as close as possible to the position of the tension roller 41 with high accuracy (with strict tolerance). That is, the distance between the tension roller 41 and the driven roller 82 can be set to L1 with high accuracy on the front side and the rear side.

[0060] Accordingly, even when a deviation occurs in the parallelism between the tension roller 41 and the backup roller 42 as indicated by center-to-center distances L5 < L6 in Fig. 4B, the displacement force of the belt can be canceled (offset) by the displacement force of the driven roller 82, thereby preventing or minimizing displacement of the tension roller 41. Further, by disposing the driven roller on the member supported by the backup roller 42, the parallelism can be adjusted not only in the full color (FC) printing mode but also in the monochrome printing mode.

[0061] ● Related Art 1 Next, Related Art 1 will be described with reference to Figs. 5A to 5C. Fig. 5A is a cross-sectional view when belt displacement and displacement of a tension roller 41 have started in Related Art 1. The cross-sectional view is taken along the line 5A-5A of Fig. 5C. Further, Fig. 5B is a cross-sectional view in which the belt displacement and the displacement of the tension roller 41 have advanced.

[0062] A belt contact member 50 including a flange portion 50a is inserted onto a rotation shaft 41a of the tension roller 41 so as to be movable in the axial direction. When a transfer belt 45 contacts the flange portion 50a of the belt contact member 50 due to displacement of the transfer belt 45 in a direction indicated by an arrow, the belt contact member 50 is pushed by the transfer belt 45 and moves to the right together with a support rotating body displacement member 51.

[0063] Upon the movement of the support rotating body displacement member 51 to the right, an inclined portion 51a of the support rotating body displacement member 51 contacts a guide member 55 integrated with a body frame 57, and pushes down the rotation shaft 41a as illustrated in Fig. 5B. As a result, the tension on the front side of the transfer belt 45 decreases and the tension on the rear side increases. As a result, the transfer belt 45 moves toward the rear side on which the tension is relatively high. In this manner, the displacement of the transfer belt 45 is suppressed within a certain range (excessive displacement is suppressed).

[0064] The rotation shaft 41a of the tension roller 41 is rotatably supported by a supporting member 53. The supporting member 53 is movably disposed in an elongated hole 60a formed in a shaft supporting member 60.

[0065] A restricting member 54 is disposed on the rotation shaft 41a of the tension roller 41 projecting outward of the body frame 57. The restricting member 54 restricts the axial movement of the rotation shaft 41a.

[0066] An elastically deformable intermediate member 59 is disposed between the restricting member 54 and the shaft supporting member 60. The intermediate member 59 prevents wear of the restricting member 54.

[0067] As illustrated in Fig. 5C, the shaft supporting member 60 is disposed to be pivotable in the up-down direction about a fulcrum 60b. The fulcrum 60b is axially supported by the body frame 57.

[0068] In Related Art 1, the tension roller 41 and a backup roller 42 are arranged so as to be independently movable. Therefore, as indicated by center-to-center distances L2 < L3 in Fig. 5C, a difference easily occurs in the positional relationship or the parallelism between the tension roller 41 and the backup roller 42 on the front side and the rear side. It is difficult to suppress an error in the positional relationship or the parallelism between the two rollers. Therefore, as the belt displacement force increases, the axial displacement force of the tension roller 41 also increases, and thus the collision force and friction force between the restricting member 54 and the intermediate member 59 increase.

[0069] If the restricting member 54 wears more than anticipated and the tension roller 41 is displaced more than anticipated, a support rotating body displacement member 51 on the opposite side comes into contact with a guide member 55, and the opposite side of the tension roller 41 is tilted. This generates a force that accelerates the belt displacement in a direction opposite to a direction in which the transfer belt 45 is intended to be returned. Thus, a load on the belt end becomes larger than anticipated, and the transfer belt 45 is damaged.

[0070] ● Related Art 2 Next, Related Art 2 will be described with reference to Figs. 6A and 6B. Fig. 6A illustrates a side view of a belt unit. Fig. 6B illustrates a view including a plan view and a side view of the belt unit, in which the side view illustrates a backup roller in a pivoting state.

[0071] In Related Art 2, in order to improve Related Art 1, rotation shafts 41a and 42a of a tension roller 41 and a backup roller 42 are rotatably supported by one (common) supporting member 80. However, the positions of the rotation shafts 41a and 42a are fixed, and thus a center-to-center distance L4 does not change between the front side and the rear side of a belt unit. Therefore, when the rotation shafts 41a and 42a are tilted, as illustrated in Fig. 6B, the two shafts are tilted while maintaining a parallel state with the center-to-center distance L4.

[0072] Because the rotation shafts 41a and 42a are integrally supported, the positional relationship (parallelism) with respect to the tension roller 41 remains unchanged even if either the front side or the rear side of the backup roller 42 deviates from a target position. Therefore, the belt displacement force can be suppressed.

[0073] However, in a case where the center-to-center distance L4 is fixed, there is a high possibility that the tension of a transfer belt 45 cannot be appropriately managed. If the tension of the transfer belt 45 cannot be appropriately managed, a roller mark (an indentation) remains on the transfer belt 45. In particular, if the belt unit or a transfer apparatus is used as an image forming apparatus after being left for a long period of time, an abnormal image may be generated at the position of the roller mark. In addition, if the tension of the transfer belt 45 cannot be appropriately managed, a tension difference occurs in the feed direction or between the left and right sides of the transfer belt 45. This tension difference accelerates displacement of the transfer belt 45 and displacement of the roller, and sliding wear of the member (restricting member 54) that restricts the axial movement of the roller may occur to a greater extent than anticipated.

[0074] ● Summary Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be appropriately modified within the technical concept of the present invention. As the belt displacement restriction mechanism, instead of the above-described restriction method using the support rotating body displacement member 51 and the like, any other restriction method having the same or a similar belt displacement restriction effect may be adopted. Further, as the tension applying mechanism, instead of the biasing method using the biasing spring 52 and the tension spring 61, any other biasing method having the same or a similar tension applying effect can be adopted. Further, the position of the backup roller 42 is not limited to the downstream side of the tension roller 41, and the backup roller 42 can be disposed on the upstream side of the tension roller 41. In this case, the tension roller 41 may be a drive roller instead of a driven roller.

[0075] The present invention can be applicable to, for example, a combination of the following clauses 1 to 12. <Clause 1> A belt unit including: a belt member configured to be entrained around a plurality of support rotating bodies and driven to travel by rotation of the plurality of support rotating bodies, the plurality of support rotating bodies including a first support rotating body and a second support rotating body disposed adjacent to the first support rotating body; a tension applying mechanism configured to apply tension in a traveling direction of the belt member; and a belt displacement restriction mechanism configured to restrict axial displacement of the belt member by tilting an axis of the first support rotating body, wherein one end portion of each rotation shaft of the first support rotating body and the second support rotating body is supported by a common first supporting member, and another end portion of each of the rotation shafts of the first support rotating body and the second support rotating body is supported by a common second supporting member, and both end portions of a rotation shaft of either the first support rotating body or the second support rotating body are movably supported relative to the first supporting member and the second supporting member. <Clause 2> The belt unit according to clause 1, wherein a direction in which the both end portions of the rotation shaft of either the first support rotating body or the second support rotating body are movable relative to the first support member and the second support member is a direction in which the first support member and the second support member approach or separate from each other. <Clause 3>The belt unit according to clause 1 or 2, wherein both end portions of a third support rotating body of the plurality of support rotating bodies are supported by longitudinal intermediate portions of the first support member and the second support member, respectively. <Clause 4> The belt unit according to any one of clauses 1 to 3, wherein a fourth support rotating body, of the plurality of support rotating bodies, disposed at one end portion of the belt member in the traveling direction is rotationally driven by a driver, the first support rotating body is rotatably disposed to be driven at another end portion of the belt member in the traveling direction, and the second support rotating body is disposed downstream of the first support rotating body. <Clause 5> The belt unit according to any one of clauses 1 to 4, wherein the second support rotating body is pivotably supported in a direction in which tension of the belt member is increased or decreased. <Clause 6> The belt unit according to any one of clauses 1 to 5, wherein the belt displacement restriction mechanism includes a belt contact member provided on the rotation shaft of the first support rotating body, and configured to, when an end portion of the belt member moves in an axial direction of the rotation shaft of the first support rotating body, come into contact with the end portion of the belt member and be movable in the axial direction together with the belt member; a support rotating body displacement member provided on the rotation shaft of the first support rotating body, configured to be movable in the axial direction in accordance with movement of the belt contact member, and having an inclined surface for displacing the first support rotating body; and a guide member configured to restrict a movement direction of the support rotating body displacement member by contacting the inclined surface; a supporting member disposed movably in a tension direction of the belt member with respect to a shaft supporting member pivotably disposed at each end portion of the first support rotating body, and configured to rotatably support the rotation shaft of the first support rotating body; and a restriction member configured to restrict axial movement of the rotation shaft of the first support rotating body. <Clause 7> The belt unit according to any one of clauses 1 to 6, wherein the tension applying mechanism includes a first spring disposed between the shaft supporting member and the supporting member, and a second spring configured to bias the shaft supporting member, and a pivot position of the shaft supporting member is stabilized by a balance between a biasing force of the first spring and a biasing force of the second spring. <Clause 8> A transfer apparatus comprising: the belt unit of any one of clauses 1 to 7, wherein the belt member forms an intermediate transfer belt, and the plurality of support rotating bodies include a plurality of primary transfer rollers configured to transfer toner images onto the intermediate transfer belt and a secondary transfer roller configured to transfer the toner images transferred onto the intermediate transfer belt onto a transfer material. <Clause 9> An image forming apparatus comprising: the transfer apparatus of clause 8.

[0076] This application is based on and claims priority to Japanese Patent Application No. 2025-044871, filed on March 19, 2025, the entire contents of which are incorporated herein by reference.

[0077] 1: color printer 3Y, 3M, 3C, 3K: process cartridge unit 4: intermediate transfer unit 5: optical unit 6Y, 6M, 6C, 6K: primary transfer roller 8: secondary transfer part 10: tray 11: group of rollers 12: fixing device 13: ejection port 14: ejection tray 15: roller pair 16: belt cleaner 30Y, 30M, 30C, 30K: photoconductor 31Y, 31M, 31C, 31K: charging unit 32Y, 32M, 32C, 32K: developing unit 33Y, 33M, 33C, 33K: cleaning unit 41: tension roller (first support rotating body) 41a: rotation shaft 42: backup roller (second support rotating body) 42a: rotation shaft 44: drive roller (fourth support rotating body) 45: transfer belt (belt member) 50: belt contact member 50a: flange portion 51: support rotating body displacement member (belt displacement restriction mechanism) 51a: inclined portion 52: biasing spring 53: supporting member 54: restricting member 55: guide member 57: body frame 59: intermediate member 60: shaft supporting member 60a: elongated hole 60b: fulcrum 61: tension spring 70: support arm 70a: fulcrum 70b: guided pin 72: guide portion 80: supporting member 80a, 80b: elongated hole 82: driven roller (third support rotating body) 100: boundary L1 to L6: center-to-center distance P: recording material

Claims

A belt unit comprising:a belt member configured to be entrained around a plurality of support rotating bodies and driven to travel by rotation of the plurality of support rotating bodies, the plurality of support rotating bodies including a first support rotating body and a second support rotating body disposed adjacent to the first support rotating body;a tension applying mechanism configured to apply tension in a traveling direction of the belt member; anda belt displacement restriction mechanism configured to restrict axial displacement of the belt member by tilting an axis of the first support rotating body, whereinone end portion of each rotation shaft of the first support rotating body and the second support rotating body is supported by a common first supporting member, and another end portion of each of the rotation shafts of the first support rotating body and the second support rotating body is supported by a common second supporting member, andboth end portions of the rotation shaft of either the first support rotating body or the second support rotating body are movably supported relative to the first supporting member and the second supporting member.The belt unit according to claim 1, wherein a direction in which the both end portions of the rotation shaft of either the first support rotating body or the second support rotating body are movable relative to the first support member and the second support member is a direction in which the first support member and the second support member approach or separate from each other.The belt unit according to claim 1 or 2, wherein both end portions of a third support rotating body of the plurality of support rotating bodies are supported by longitudinal intermediate portions of the first support member and the second support member, respectively.The belt unit according to any one of claims 1 to 3, wherein a fourth support rotating body, of the plurality of support rotating bodies, disposed at one end portion of the belt member in the traveling direction is rotationally driven by a driver, the first support rotating body is rotatably disposed to be driven at another end portion of the belt member in the traveling direction, and the second support rotating body is disposed downstream of the first support rotating body.The belt unit according to any one of claims 1 to 4, wherein the second support rotating body is pivotably supported in a direction in which tension of the belt member is increased or decreased.The belt unit according to any one of claims 1 to 5, whereinthe belt displacement restriction mechanism includesa belt contact member provided on the rotation shaft of the first support rotating body, and configured to, when an end portion of the belt member moves in an axial direction of the rotation shaft of the first support rotating body, come into contact with the end portion of the belt member and be movable in the axial direction together with the belt member;a support rotating body displacement member provided on the rotation shaft of the first support rotating body, configured to be movable in the axial direction in accordance with movement of the belt contact member, and having an inclined surface for displacing the first support rotating body; anda guide member configured to restrict a movement direction of the support rotating body displacement member by contacting the inclined surface;a supporting member disposed movably in a tension direction of the belt member with respect to a shaft supporting member pivotably disposed at each end portion of the first support rotating body, and configured to rotatably support the rotation shaft of the first support rotating body; anda restriction member configured to restrict axial movement of the rotation shaft of the first support rotating body.The belt unit according to any one of claims 1 to 6, whereinthe tension applying mechanism includesa first spring disposed between the shaft supporting member and the supporting member, anda second spring configured to bias the shaft supporting member, anda pivot position of the shaft supporting member is stabilized by a balance between a biasing force of the first spring and a biasing force of the second spring.A transfer apparatus comprising:the belt unit of any one of claims 1 to 7, whereinthe belt member forms an intermediate transfer belt, andthe plurality of support rotating bodies include a plurality of primary transfer rollers configured to transfer toner images onto the intermediate transfer belt and a secondary transfer roller configured to transfer the toner images transferred onto the intermediate transfer belt onto a transfer material.An image forming apparatus comprising:the transfer apparatus of claim 8.

Images