JP2010256798A - Belt device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt device which can be applied to even an image forming apparatus provided with an endless belt as a conveying belt or an intermediate transfer belt, while preventing undesired deformation, etc. of the endless belt caused by its biasing and to provide the image forming apparatus provided with the belt device. <P>SOLUTION: A driven roller 13 is inclined by movement of the inner circumferential edge 43 of the driven roller 13 along the inclined surface 42 of an inclination member 32. Force for returning the endless belt 14 to the right side is applied to the endless belt 14 by the inclination. The magnitude of the force is greater as the inclination of the driven roller 13 is greater. Consequently, the biasing of the endless belt 14 and the driven roller 13 is stopped when the force applied to the endless belt 14 by the error due to a configuration and the force applied to the endless belt 14 by the inclination of the driven roller 13 are balanced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a belt device and an image forming apparatus including the belt device.

As an electrophotographic color printer, a so-called tandem type printer is known in which four photosensitive drums corresponding to yellow, magenta, cyan, and black are arranged in parallel.
This tandem type color printer is usually provided with an endless belt. The endless belt is wound around a plurality of rollers including a driving roller and a driven roller, and is disposed so as to contact each photosensitive drum. When the driving roller is rotationally driven, the endless belt travels around and the driven roller rotates following the endless belt. For example, the paper is supplied onto the endless belt, and the paper passes sequentially between the photosensitive drums and the endless belt by the endless belt traveling around. When the toner image passes through the photosensitive drum, the toner image is transferred onto the paper so that a color image is formed on the paper.

As a general problem that a belt device having such an endless belt has, there is a problem that the endless belt is displaced during its round running.
That is, due to structural errors such as variations in the shape of each roller (eccentricity, difference in circumferential length at both ends in the axial direction, etc.) and difference in circumferential length at both ends in the width direction of the endless belt, the endless belt runs around its circumference. Sometimes force in the width direction is applied. When a force in the width direction is applied to the endless belt, the endless belt is shifted to one side in the width direction. Normally, the driven roller is provided with a detent member for preventing the endless belt from being displaced. However, when the deviation toward the one side in the width direction increases, the contact portion of the endless belt with the detent member. There is a risk that the endless belt may be deformed and eventually damaged by this load.

  As a configuration to prevent deformation of the endless belt, a roller-shaped moving body is provided between the driving roller and the driven roller in contact with the inner surface of the endless belt, and the opposite side of the endless belt to the moving body In addition, there has been proposed a configuration in which a substantially conical taper member whose diameter increases toward the outer side in the width direction (axial direction) is provided so as to come into contact with the outer edge of the moving body (see, for example, Patent Document 1).

  In the configuration according to this proposal, a force due to a structural error is applied to the endless belt, and when the moving body moves to one side in the width direction together with the endless belt, the outer peripheral end surface of the moving body rides on the peripheral surface of the taper member. As a result, the moving body is inclined so that the end of the endless belt on one side (one side in the width direction) is lifted. Due to the inclination of the moving body, a force to be returned to the other side in the width direction is applied to the endless belt, and the magnitude of the force increases as the inclination of the moving body increases. Therefore, the deviation of the endless belt and the moving body stops when the force applied to the endless belt due to the structural error balances with the force applied to the endless belt due to the inclination of the moving body. As a result, the endless belt runs around in a stable state.

JP-A-10-227342

  However, the configuration proposed in Patent Document 1 is an image forming apparatus provided with an endless belt as a conveying belt for conveying paper to a photosensitive drum, and the endless belt as an intermediate transfer belt to which a toner image is transferred from the photosensitive drum. The image forming apparatus provided cannot be applied as it is. This is because, in order to satisfactorily form an image (toner image) on a sheet or an endless belt, the outer surface of the endless belt must be brought into stable contact with the photosensitive drum between the driving roller and the driven roller. This is because when the moving body is inclined, a difference occurs in the contact state of the endless belt with the photosensitive drum in the width direction.

  Therefore, the object of the present invention can be applied to an image forming apparatus provided with an endless belt as a transport belt or an intermediate transfer belt while preventing an undesired deformation caused by the deviation of the endless belt. Another object is to provide a belt device and an image forming apparatus including the belt device.

  In order to achieve the above-mentioned object, the invention according to claim 1 is a belt device, wherein the peripheral surface is in contact with the inner surface of the endless belt and the endless belt, and the endless belt is driven to rotate. In the width direction of the endless belt with respect to the driven roller, a driving roller to which force is input, a cylindrical driven roller whose outer peripheral surface is in contact with the inner surface of the endless belt and rotates as the endless belt rotates. A regulating member for regulating the movement of the driven roller, and an inclined member having an inclined surface that comes into contact with the inner peripheral edge of the driven roller and inclines away from the drive roller toward the outer side in the width direction. .

The invention described in claim 2 is the invention described in claim 1, further comprising a shaft inserted into the space in the driven roller, and the inclined member is provided on the shaft. .
According to a third aspect of the present invention, in the second aspect of the present invention, the shaft is biased, and the biasing force causes the driven roller to be pressed against the inner surface of the endless belt via the inclined member. It is characterized by further providing a biasing member.

The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the endless belt is wound around the drive roller and the driven roller, and the drive roller and the driven roller It has the feature that it has two flat parts extended flatly between.
According to a fifth aspect of the present invention, there is provided an image forming apparatus, wherein the belt device according to the fourth aspect and the outer surface of the one flat portion of the endless belt are disposed in contact with each other, and a developer is formed on the peripheral surface. And a plurality of photosensitive drums for carrying an image.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the object to be removed is removed from the outer surface of the endless belt, arranged in contact with the flat portion different from the flat portion with which the photosensitive drum contacts. It is further characterized by further including a cleaning device.
A seventh aspect of the present invention is the sheet conveying belt according to the fifth or sixth aspect, wherein the endless belt is a sheet conveying belt for conveying a sheet onto which a developer image on the peripheral surface of the photosensitive drum is transferred. It is characterized by being.

  The invention according to claim 8 is a belt device, comprising: an endless belt; a driving roller having a peripheral surface in contact with an inner surface of the endless belt, and a rotational driving force for causing the endless belt to run around; A cylindrical member whose outer peripheral surface is in contact with the inner surface of the endless belt, a regulating member for regulating movement of the endless belt in the width direction relative to the cylindrical member, and an inner circumferential edge of the cylindrical member. And an inclined member having an inclined surface which is inclined so as to be separated from the drive roller toward the outer side in the width direction.

  According to the first aspect of the present invention, the driving roller and the driven roller are provided inside the endless belt so that the outer peripheral surfaces of the driving roller and the driven roller are in contact with the inner surface of the endless belt. The driven roller is formed in a cylindrical shape. An inclined member is provided in association with the cylindrical driven roller. The inclined member has an inclined surface that is inclined so as to be farther from the driving roller toward the outer side in the width direction, and the inclined surface is disposed so as to contact the inner peripheral edge of the driven roller. Further, a regulating member is provided, and movement of the endless belt in the width direction relative to the driven roller is regulated by the regulating member.

  When the drive roller is driven to rotate, the endless belt travels around and the driven roller rotates along with the endless belt. At this time, a force in the width direction is applied to the endless belt due to structural errors such as variations in the shapes of the driving roller and the driven roller and a difference in circumferential length at both ends in the width direction of the endless belt. Since the movement in the width direction of the endless belt with respect to the driven roller is restricted, when a force in the width direction is applied to the endless belt, the endless belt is shifted to one side in the width direction together with the driven roller. Then, the inner peripheral edge of the driven roller moves on the inclined surface, and the driven roller is inclined so that one end portion in the width direction is separated from the driving roller. Due to the inclination of the driven roller, a force to be returned to the other side in the width direction is applied to the endless belt, and the magnitude of the force increases as the inclination of the driven roller increases. Accordingly, the deviation of the endless belt and the driven roller stops when the force applied to the endless belt due to the structural error balances with the force applied to the endless belt due to the inclination of the driven roller. As a result, the endless belt runs around in a stable state.

  Since the one end portion in the width direction of the driven roller is inclined so as to be separated from the driving roller, the flatness is the inclination of the driven roller when the endless belt extends flatly between the driving roller and the driven roller. Will not be damaged. Therefore, when this belt device is applied to an image forming apparatus provided with an endless belt as a conveying belt or an intermediate transfer belt, the endless belt is arranged so that a portion where the flatness of the endless belt is ensured contacts the photosensitive drum. By disposing, the endless belt can be brought into contact with the photosensitive drum uniformly in the width direction (without causing a difference in contact state).

Therefore, the present invention can be applied to an image forming apparatus provided with an endless belt as a conveyance belt or an intermediate transfer belt while preventing an undesired deformation due to the deviation of the endless belt.
According to invention of Claim 2, the axis | shaft penetrated by the space in a driven roller is provided. In this case, by providing the inclined member on the shaft, the inclined surface of the inclined member can be reliably brought into contact with the inner peripheral edge of the driven roller.

According to the third aspect of the present invention, the urging member for urging the shaft is provided. The driven roller is pressed against the inner surface of the endless belt through the inclined member by the biasing force of the biasing member. Thereby, tension can be applied to the endless belt.
According to the fourth aspect of the present invention, the endless belt is wound around the drive roller and the driven roller. In the endless belt, two flat portions extending flat are formed between the driving roller and the driven roller. Therefore, when the belt device is applied to an image forming apparatus including an endless belt as a conveyance belt or an intermediate transfer belt, the width direction of the endless belt with respect to the photosensitive drum, regardless of which of the two flat portions contacts the photosensitive drum. A uniform contact state can be obtained.

  According to the fifth aspect of the present invention, the plurality of photosensitive drums are arranged in contact with the outer surface of one flat portion of the endless belt, so that each photosensitive drum and the endless belt are uniformly contacted in the width direction. Can be made. Therefore, the developer image carried on the peripheral surface of each photosensitive drum can be satisfactorily transferred to the sheet or endless belt conveyed by the endless belt. Further, since the flatness of the flat portion of the endless belt is ensured, the developer images transferred from the respective photosensitive drums can be accurately superimposed on the sheet or the endless belt. As a result, it is possible to form a good developer image with no positional deviation on the sheet or the endless belt.

  According to the invention described in claim 6, the cleaning device for removing the object to be removed from the outer surface of the endless belt is provided. The cleaning device is disposed in contact with a flat portion different from the flat portion with which the photosensitive drum contacts. Thereby, a cleaning apparatus and an endless belt can be made to contact uniformly in the width direction. As a result, the removal target can be satisfactorily removed from the outer surface of the endless belt.

According to the seventh aspect of the present invention, it is possible to form a good developer image with no positional deviation on the sheet.
According to the eighth aspect of the present invention, the drive roller and the cylindrical member are provided inside the endless belt so that the outer surface of the drive roller and the cylindrical member is in contact with the inner surface of the endless belt. An inclined member is provided in association with the cylindrical member. The inclined member has an inclined surface that is inclined so as to be farther from the drive roller toward the outer side in the width direction, and the inclined surface is disposed so as to contact the inner peripheral edge of the cylindrical member. In addition, a regulating member is provided, and movement of the endless belt in the width direction relative to the cylindrical member is regulated by the regulating member.

  When the drive roller is rotationally driven, the endless belt travels around and the cylindrical member rotates following the round travel of the endless belt. At this time, a force in the width direction is applied to the endless belt due to structural errors such as variations in the shapes of the driving roller and the cylindrical member and a difference in circumferential length between both ends of the endless belt in the width direction. Since the movement of the endless belt in the width direction relative to the cylindrical member is restricted, when a force in the width direction is applied to the endless belt, the endless belt is shifted to one side in the width direction together with the cylindrical member. Then, the inner peripheral edge of the cylindrical member moves on the inclined surface, and the one end in the width direction of the cylindrical member is inclined so as to be separated from the drive roller. Due to the inclination of the cylindrical member, a force to be returned to the other side in the width direction is applied to the endless belt, and the magnitude of the force increases as the inclination of the cylindrical member increases. Accordingly, the deviation of the endless belt and the cylindrical member stops when the force applied to the endless belt due to structural errors balances with the force applied to the endless belt due to the inclination of the cylindrical member. As a result, the endless belt runs around in a stable state.

  Since the one end in the width direction of the cylindrical member is inclined so as to be separated from the driving roller, the flatness is cylindrical when the endless belt extends flat between the driving roller and the cylindrical member. It is not damaged by the inclination of the member. Therefore, when this belt device is applied to an image forming apparatus provided with an endless belt as a conveying belt or an intermediate transfer belt, the endless belt is arranged so that a portion where the flatness of the endless belt is ensured contacts the photosensitive drum. By disposing, the endless belt can be brought into contact with the photosensitive drum uniformly in the width direction (without causing a difference in contact state).

  Therefore, the present invention can be applied to an image forming apparatus provided with an endless belt as a conveyance belt or an intermediate transfer belt while preventing an undesired deformation due to the deviation of the endless belt.

FIG. 1 is a side sectional view of a color printer according to an embodiment of the present invention. FIG. 2 is a side view of the belt unit. FIG. 3 is a plan view of the belt unit. FIG. 4 is a plan sectional view of the belt unit. FIG. 5 is a side view of the belt unit and shows a state in which the belt unit is being driven. FIG. 6 is a plan view of the belt unit, showing a state in which the belt unit is being driven. FIG. 7 is a plan sectional view of the belt unit and shows a state in which the belt unit is being driven. FIG. 8 is a plan sectional view of a belt unit according to the second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1. 1 is a side sectional view of a color printer according to an embodiment of the present invention.
A color printer 1 as an example of an image forming apparatus is a tandem color printer. A drum unit 3 is mounted in the main body casing 2 of the color printer 1. The drum unit 3 is detachable from the main casing 2 by opening a cover 4 provided on the front surface of the main casing 2.

The drum unit 3 includes four photosensitive drums 5. The four photosensitive drums 5 are provided corresponding to the respective colors of black, yellow, magenta, and cyan, and in the conveying direction of the paper P by the endless belt 14 described later, black, yellow, magenta, cyan, and the like in this order from the upstream side. Arranged in parallel at intervals.
The drum unit 3 includes a scorotron charger 6 and a developing cartridge 7 corresponding to each photosensitive drum 5. The developing cartridge 7 has a developing roller 8 for supplying toner (developer) to the photosensitive drum 5 and a box shape for containing the toner inside, and the developing roller 8 is exposed at a lower end part of the peripheral surface. And a housing 9 that is held in a state of being. Each developing cartridge 7 is detachably attached to the drum unit 3.

Above the drum unit 3, an exposure device 10 that emits four laser beams corresponding to each color is arranged.
As the photosensitive drum 5 rotates, the surface of the photosensitive drum 5 is uniformly charged by the discharge from the scorotron charger 6 and then selectively exposed by the laser beam from the exposure device 10. By this exposure, electric charges are selectively removed from the surface of the photosensitive drum 5, and an electrostatic latent image is formed on the surface of the photosensitive drum 5. When the electrostatic latent image faces the developing roller 8, toner is supplied from the developing roller 8 to the electrostatic latent image. As a result, a toner image is formed on the surface of the photosensitive drum 5.

Instead of the exposure device 10, four LED arrays may be provided corresponding to each photosensitive drum 5.
Below the drum unit 3, a belt unit 11 as an example of a belt device is disposed. The belt unit 11 includes a driving roller 12 and a driven roller 13 that are arranged at intervals in the direction in which the photosensitive drums 5 are arranged. An endless belt 14 is wound around the driving roller 12 and the driven roller 13. The driving roller 12 and the driven roller 13 have the same outer diameter. As a result, the endless belt 14 is spaced in the vertical direction between the driving roller 12 and the driven roller 13 with the same interval as the outer diameter of the driving roller 12 and the driven roller 13, and the photosensitive drums 5 are arranged in the horizontal direction (horizontal direction). ) Have two flat portions 14A, 14B.

Inside the endless belt 14, four transfer rollers 15 and one recovery transfer roller 16 are provided.
The four transfer rollers 15 are respectively arranged at positions facing the photosensitive drum 5 with the flat portion 14A on the upper side of the endless belt 14 interposed therebetween, and are in contact with the inner surface of the flat portion 14A.

The collection transfer roller 16 is disposed at a position facing a collection roller 22 described later across the flat portion 14B on the lower side of the endless belt 14, and is in contact with the inner surface of the flat portion 14B. A predetermined bias is applied to the collection transfer roller 16 or the collection transfer roller 16 is connected to the ground.
At the bottom of the main casing 2, a paper feed cassette 17 that houses paper P as an example of a sheet is disposed. The paper P stored in the paper feed cassette 17 is conveyed onto the endless belt 14 by various rollers. The paper P conveyed on the endless belt 14 sequentially passes between the endless belt 14 and each photosensitive drum 5 as the endless belt 14 travels. Each transfer roller 15 is supplied with a negative transfer current having a polarity opposite to the charging polarity of the surface of the photosensitive drum 5. The toner image on the surface of the photosensitive drum 5 is attracted to the transfer roller 15 and transferred to the paper P passing between the photosensitive drum 5 and the conveyance belt 11.

A fixing device 18 is provided downstream of the belt unit 11 in the conveyance direction of the paper P. The sheet P on which the toner image is transferred is conveyed to the fixing device 18. In the fixing device 18, the toner image is fixed on the paper P by heating and pressing. The paper P on which the toner image is fixed is discharged to a paper discharge tray 19 on the upper surface of the main casing 2 by various rollers.
On the other hand, a cleaning device 20 is disposed at a position between the belt unit 11 and the paper feed cassette 17. The cleaning device includes a collection box 21 and a collection roller 22.

The collection box 21 has an opening that opens toward the belt unit 11.
The collection roller 22 closes the opening formed in the collection box 21 and is disposed at a position facing the collection transfer roller 16 with the lower portion of the endless belt 14 interposed therebetween.
After the transfer of the toner image from the photosensitive drum 5 to the paper P, the removal target such as residual toner adhering to the surface of the photosensitive drum 5 and paper dust of the paper P is transferred to the rotation of the photosensitive drum 5 and the transfer roller 15. Is transferred from the surface of the photosensitive drum 5 onto the endless belt 14. Then, the removal object transferred onto the endless belt 14 is recovered by the potential difference between the recovery transfer roller 16 and the recovery roller 22 when the endless belt 14 is opposed to the recovery roller 22 by running of the endless belt 14. To be recovered. The object to be removed collected by the collection roller 22 is stored in the collection box 21.

In the description of the present embodiment, the side where the cover 4 is provided (the right side in FIG. 1) is the front side (front side), and the opposite side (the left side in FIG. 1) is the rear side (back side). In addition, when the color printer 1 is viewed from the front side, the left and right reference is used. Hereinafter, the left-right direction may be referred to as the width direction.
2. Belt Unit FIG. 2 is a side view of the belt unit. FIG. 3 is a plan view of the belt unit. FIG. 4 is a plan sectional view of the belt unit.

The drive roller 12 has a drive roller main body 35 and a drive roller shaft 36 that is inserted into the drive roller main body 35 so as not to be relatively rotatable.
The drive roller body 35 is formed in a cylindrical shape.
The drive roller shaft 36 extends in the width direction on the central axis (rotation axis) of the drive roller body 35. Both end portions of the drive roller shaft 36 protrude from the drive roller body 35 to the outside in the width direction and are rotatably supported by an outer frame (not shown) of the belt unit 11. Both end portions of the drive roller shaft 36 further protrude outward in the width direction from the outer frame, and a rotational driving force is input to one of the protruding portions from a motor (not shown). When a rotational driving force is input from the motor to the driving roller shaft 36, the driving roller body 35 rotates integrally with the driving roller shaft 36.

  The driven roller 13 is formed in a cylindrical shape having the same outer diameter as that of the drive roller body 35. The driven roller 13 is provided so as to be movable in the width direction with respect to an outer frame (not shown) of the belt unit 11 and to be rotatable about its central axis. At both ends of the driven roller 13, flanges 39 are formed as an example of hook-shaped restricting members protruding in the radial direction from the peripheral surface of the driven roller 13. The flange 39 restricts the movement of the endless belt 14 in the width direction with respect to the driven roller 13.

A driven roller shaft 29 as an example of a shaft extending in the width direction is inserted into the space in the driven roller 13. Both end portions of the driven roller shaft 29 protrude outward in the width direction from the driven roller 13.
A biased member 30 is attached to a portion protruding from the driven roller 13 at both ends of the driven roller shaft 29 so as not to be relatively rotatable. The biased member 30 is formed in a rectangular shape in side view.

One end of a coil spring 31 as an example of a biasing member is connected to each biased member 30. The coil spring 31 is disposed so as to extend in the front-rear direction, and the other end is connected to an outer frame (not shown) of the belt unit 11. The coil spring 31 is provided in a compressed state and biases the biased member 30 forward by its elastic force.
Inclined members 32 are attached to both ends of the driven roller shaft 29 so as not to rotate relative to the respective biased members 30 in the width direction. The inclined member 32 is rotationally symmetric with respect to the rotational axis of the driven roller shaft 29, and is formed in a substantially conical shape with a taper on the inner side in the width direction. Thereby, the peripheral surface 41 of the inclined member 32 includes an inclined surface 42 that is inclined with respect to the width direction so as to be farther from the driving roller 12 toward the outer side in the width direction. The outer end in the width direction of the inclined member 32 has substantially the same diameter as the inner diameter of the driven roller 13. The inner end in the width direction of the inclined member 32 has a diameter smaller than the inner diameter of the driven roller 13 and enters the inner side of the driven roller 13.

Since the biased member 30 is fixed to the driven roller shaft 29 and the biased member 30 is biased forward by the coil spring 31, as shown in FIG. The included inclined surface 42 abuts against the inner peripheral edge 43 at both ends of the driven roller 13. As a result, the driven roller 13 is urged forward, and tension is applied to the endless belt 14 wound around the driven roller 13 and the driving roller 12.
3. Driving of Belt Unit FIG. 5 is a side view of the belt unit. The state during driving of the belt unit is shown. FIG. 6 is a plan view of the belt unit, showing a state in which the belt unit is being driven. FIG. 7 is a plan sectional view of the belt unit and shows a state in which the belt unit is being driven.

When a rotational driving force from a motor (not shown) is input to the drive roller shaft 36 and the drive roller main body 35 is rotationally driven, the endless belt 14 travels around. The driven roller 13 is driven to rotate.
At this time, due to structural errors such as variations in the shapes of the driving roller 12 and the driven roller 13 and differences in circumferential lengths at both ends in the width direction of the endless belt 14, a force in the width direction is applied to the endless belt 14 during its circular travel. . Since the movement of the endless belt 14 in the width direction with respect to the driven roller 13 is restricted by the flange 39, when a force in the width direction is applied to the endless belt 14, the endless belt 14 and the driven roller 13 on one side in the width direction (FIG. 6). In the example shown in FIG.

  As a result, the inner peripheral edge 43 of the driven roller 13 moves on the inclined surface 42. Specifically, as shown in FIG. 7, the inner peripheral edge 43 on the left side of the driven roller 13 moves leftward on the inclined surface 42 of the left inclined member 32 and moves away from the driving roller 12. Go. The right inner peripheral edge 43 of the driven roller 13 moves leftward on the inclined surface 42 of the right inclined member 32 and approaches the driving roller 12. Therefore, the driven roller 13 is inclined so that the left end portion thereof is separated from the driving roller 12 and the right end portion thereof approaches the driving roller 12.

Due to the inclination of the driven roller 13, a force returning to the right side is applied to the endless belt 14. The magnitude of this force increases as the inclination of the driven roller 13 increases. Therefore, the deviation of the endless belt 14 and the driven roller 13 stops when the force applied to the endless belt 14 due to a structural error and the force applied to the endless belt 14 due to the inclination of the driven roller 13 are balanced. As a result, the endless belt 14 runs around in a stable state.
4). As described above, since the left end portion of the driven roller 13 is inclined so as to be separated from the driving roller 12, the flatness of the flat portion 40 of the endless belt 14 is not impaired by the inclination of the driven roller 13. Therefore, the endless belt 14 is arranged so that the flat portion 40 of the endless belt 14 contacts the photosensitive drum 5, so that the endless belt 14 is made uniform in the width direction with respect to the photosensitive drum 5 (difference in contact state). Without contact).

Therefore, the present invention can be applied to the color printer 1 including the endless belt 14 as a paper transport belt while preventing an undesired deformation due to the deviation of the endless belt 14.
A driven roller shaft 29 is inserted into the space in the driven roller 13. Since the inclined member 32 is provided on the driven roller shaft 29, the inclined surface 42 of the inclined member 32 can be reliably brought into contact with the inner peripheral edge 43 of the driven roller 13.

Further, a coil spring 31 for urging the driven roller shaft 29 is provided. The driven roller 13 is pressed against the inner surface of the endless belt 14 via the inclined member 32 by the biasing force of the coil spring 31. Thereby, tension can be applied to the endless belt 14.
The endless belt 14 is wound around the drive roller 12 and the driven roller 13. In the endless belt 14, two flat portions 14 </ b> A and 14 </ b> B that extend flatly are formed between the driving roller 12 and the driven roller 13. Therefore, even if any of the two flat portions 14A and 14B is brought into contact with the photosensitive drum 5, a uniform contact state in the width direction of the endless belt 14 with respect to the photosensitive drum 5 can be obtained.

  Further, by arranging the plurality of photosensitive drums 5 in contact with the outer surface of the flat portion 14A on the upper side of the endless belt 14, each photosensitive drum 5 and the endless belt 14 can be uniformly contacted in the width direction. . Therefore, the toner image carried on the surface of each photosensitive drum 5 can be satisfactorily transferred onto the paper P or the endless belt 14 conveyed by the endless belt 14. Further, since the flatness of the flat portion 14A of the endless belt 14 is ensured, the toner images transferred from the respective photosensitive drums 5 can be accurately superimposed on the paper P or the endless belt 14. As a result, it is possible to form a good toner image with no positional deviation on the paper P or the endless belt 14.

Further, a cleaning device 20 is provided for removing the object to be removed from the outer surface of the endless belt 14. The cleaning device 20 is disposed in contact with a lower flat portion 40 different from the flat portion 40 with which the photosensitive drum 5 contacts. Thereby, the cleaning apparatus 20 and the endless belt 14 can be made to contact uniformly in the width direction. As a result, the object to be removed can be favorably removed from the outer surface of the endless belt 14.
5). In the above embodiment, the driven roller shaft 29 and the inclined member 32 are not relatively rotatable, and the driven roller shaft 29 and the biased member 30 are not relatively rotatable. The inclined member 32 may be relatively rotatable, and the driven roller shaft 29 and the biased member 30 may not be relatively rotatable. Further, the driven roller shaft 29 and the inclined member 32 may not be relatively rotatable, the driven roller shaft 29 and the biased member 30 may be relatively rotatable, or the driven roller shaft 29 and the inclined member 32 may be The driven roller shaft 29 and the biased member 30 may be relatively rotatable.
6). Second Embodiment FIG. 8 is a plan sectional view of a belt unit according to a second embodiment of the present invention. In FIG. 8, parts corresponding to the parts shown in FIG. 4 are denoted by the same reference numerals as those parts. In the following description, only the differences between the configuration shown in FIG. 8 and the configuration shown in FIG. 4 will be described, and the description of each part given the same reference numeral will be omitted.

In the belt unit 51 shown in FIG. 8, the driven roller shaft 29 is non-rotatably supported by an outer frame (not shown) of the belt unit 51. Then, instead of the inclined member 32 shown in FIG. 4, inclined members 52 are attached to both ends of the driven roller shaft 29 so as not to be relatively rotatable.
The inclined member 52 is formed in a substantially trapezoidal shape in plan view. The outer end in the width direction of the inclined member 52 is formed in a cylindrical shape having an outer diameter that is substantially the same as the inner diameter of the driven roller 13. The inner end in the width direction of the inclined member 52 is formed in a shape that tapers toward the inner side in the width direction, and an inclined surface 53 that inclines with respect to the width direction so as to move away from the driving roller 12 toward the outer side in the width direction. Is formed.

  Even with such a configuration, the belt unit 51 can achieve the same effects as the belt unit 11.

DESCRIPTION OF SYMBOLS 1 Color printer 5 Photosensitive drum 12 Drive roller 13 Drive roller 14 Endless belt 14A Flat part 14B Flat part 20 Cleaning device 29 Drive roller axis 31 Coil spring 32 Inclined member 39 Flange 42 Inclined surface 52 Inclined member 53 Inclined surface P Paper

Claims (8)

Endless belt,
A driving roller that receives a rotational driving force for making a circumferential surface contact the inner surface of the endless belt and causing the endless belt to travel around;
A cylindrical follower roller whose outer peripheral surface is in contact with the inner surface of the endless belt, and that rotates as the endless belt rotates.
A regulating member for regulating movement of the endless belt in the width direction relative to the driven roller;
A belt device comprising: an inclined member abutting on an inner peripheral edge of the driven roller and having an inclined surface that is inclined so as to be separated from the drive roller toward the outer side in the width direction. A shaft inserted into the space in the driven roller;
The belt device according to claim 1, wherein the inclined member is provided on the shaft.   The belt device according to claim 2, further comprising a biasing member that biases the shaft and presses the driven roller against the inner surface of the endless belt via the inclined member by the biasing.   The endless belt has two flat portions wound around the drive roller and the driven roller and extending flatly between the drive roller and the driven roller. The belt device according to one item. A belt device according to claim 4;
An image forming apparatus comprising: a plurality of photosensitive drums arranged in contact with an outer surface of one of the flat portions of the endless belt and carrying a developer image on a peripheral surface thereof.   The image forming apparatus according to claim 7, further comprising a cleaning device that is disposed in contact with the flat portion different from the flat portion with which the photosensitive drum contacts, and for removing a removal target from an outer surface of the endless belt. .   The image forming apparatus according to claim 5, wherein the endless belt is a sheet conveying belt for conveying a sheet onto which a developer image on the circumferential surface of the photosensitive drum is transferred. Endless belt,
A driving roller that receives a rotational driving force for making a circumferential surface contact the inner surface of the endless belt and causing the endless belt to travel around;
A cylindrical member whose outer peripheral surface is in contact with the inner surface of the endless belt;
A regulating member for regulating movement of the endless belt in the width direction with respect to the cylindrical member;
A belt device comprising: an inclined member that abuts an inner peripheral edge of the cylindrical member and has an inclined surface that is inclined so as to move away from the drive roller toward the outer side in the width direction.

Images