JP2022173663A - Belt device and image forming apparatus - Google Patents

Abstract

To provide a belt device that can reduce the generation of wrinkles in a belt compared to before.SOLUTION: A belt device comprises an endless belt member and a plurality of support rotating bodies that support the belt member in a tensioned state. At least one support rotating body 42 has a crown shape, and the at least one support rotating body 42 applies, to the belt, a force to extend to both outer sides in a width direction. The support rotating body 42 in the crown shape applies the extending force F2 in grooves 42c formed in a roller surface part.SELECTED DRAWING: Figure 4

Description

The present invention relates to belt devices and image forming apparatuses.

Conventionally, a belt device is known that includes an endless belt member and a plurality of supporting rotating bodies that stretch and support the belt member.
For example, Patent Document 1 describes an image forming apparatus using such a belt device as an intermediate transfer belt device. This image forming apparatus is a tandem type color image forming apparatus, and at least one driven roller of an electrostatic conveying belt device for conveying paper has a crown shape (a shape in which the outer diameter at the center in the width direction is larger than the outer diameter at both ends). ). It is said that the winding portion of the belt has a straight shape in a state where the crown-shaped roller is bent by the tension of the belt, and a constant tension in the thrust direction can be obtained.

However, there remains a possibility that the belt may be wrinkled.

In order to solve the above-described problems, the present invention provides a belt device comprising an endless belt member and a plurality of support rotors for supporting the belt member with tension, wherein at least one support rotor has a crown shape. and at least one supporting rotating body is characterized in that it imparts a force to expand the belt to both lateral sides in the width direction.

According to the present invention, the generation of wrinkles in the belt can be suppressed as compared with the conventional art.

1 is a schematic configuration diagram of a color printer according to an embodiment; FIG. FIG. 4 is an explanatory diagram of an intermediate transfer unit of the same color printer; FIG. 4 is an explanatory diagram of rollers of the intermediate transfer unit; Explanatory drawing of the example which provides a groove|channel in the same roller. FIG. 4 is an explanatory diagram of an example in which grooves are provided in a straight-shaped roller; FIG. 4 is an explanatory diagram of a roller provided with a crown according to another embodiment;

[Embodiment 1]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments according to the present invention will be sequentially described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a color printer 1 exemplified as one embodiment of the image forming apparatus of the present invention. This color printer 1 is of a quadruple tandem type intermediate transfer system that forms a color image from four color toners of yellow, magenta, cyan and black. In the figure, Y, M, C, and K are suffixes assigned to components associated with the colors yellow, magenta, cyan, and black.

The color printer 1 is provided with a new toner storage unit 19 for individually storing four colors of new toner in the upper part of the front 2A side of an image forming apparatus main body (hereinafter referred to as "apparatus main body") 2 which is a housing. there is Approximately in the center of the apparatus main body 2, there are four image forming units (image forming units) 3Y, 3M, 3C, and 3K serving as a plurality of image forming portions for forming monochromatic toner images from four color toners, and a beltless image forming unit. An intermediate transfer unit 4, which is both a unit and a transfer device, is arranged. The image forming units 3Y, 3M, 3C, and 3K are arranged below the intermediate transfer unit 4. As shown in FIG. An optical unit 5 as exposure means is arranged below the imaging units 3Y, 3M, 3C, and 3K.

The image forming units 3Y, 3M, 3C, and 3K are provided with drum-shaped photoconductors 30Y, 30M, 30C, and 30K as image carriers on which electrostatic latent images are formed by exposure light emitted from the optical unit 5, respectively. ing. The image forming units 3Y, 3M, 3C, and 3K include charging means 31Y, 31M, 31C, and 31K, developing means 32Y, 32M, 32C, and 32K, and cleaning units 33Y and 33M around the photoreceptors 30Y, 30M, 30C, and 30K. , 33C, 33K and a static elimination unit. The image forming units 3Y, 3M, 3C, and 3K execute an electrophotographic process using these means to form monochromatic toner images on the photoreceptors 30Y, 30M, 30C, and 30K, respectively.

The intermediate transfer unit 4 includes a plurality of rollers 41, 42, 43, and 44 as supporting rotating bodies and a transfer belt 45, which is an endless belt member and serves as a transfer body, wound around the rollers 41, 42, 43, and 44. As shown in FIG. Rollers 41 and 42 positioned on one side (left side in the figure) in the width direction of the intermediate transfer unit 4 indicated by an arrow W and a roller 43 positioned on the other side (right side in the figure) are driven rollers. and the roller 44 arranged above the roller 43 is a driving roller. The intermediate transfer unit 4 is configured such that the transfer belt 45 rotates and conveys in the counterclockwise direction in the drawing by rotating the roller 44 .

In the inner loop of the transfer belt 45, primary transfer rollers 6Y, 6M, 6C and 6K as primary transfer members are arranged at positions facing the photoreceptors 30Y, 30M, 30C and 30K. The primary transfer rollers 6Y, 6M, 6C, and 6K press the transfer belt 45 toward the photoreceptors 30Y, 30M, 30C, and 30K. , primary transfer portions 7Y, 7M, 7C, and 7K for transferring the toner images on the photoreceptors to the transfer belt 45 are formed. A transfer bias for primary transfer is supplied to the primary transfer portions 7Y, 7M, 7C, and 7K.

A secondary transfer portion 8 is formed downstream of the primary transfer portions 7Y, 7M, 7C, and 7K in the belt conveying direction. The secondary transfer portion 8 is formed between the transfer belt 45 and a secondary transfer roller 9 as a secondary transfer member that is arranged to face the roller 44 and contacts the transfer belt 45 . A transfer bias for secondary transfer is supplied to the secondary transfer portion 8 .

A plurality of trays 10 containing recording materials P are provided below the optical unit 5 . The recording material P accommodated in the tray 10 is separated into one sheet from the tray 10 by a roller group 11 for feeding and separating, and conveyed toward the secondary transfer portion 8 . In the secondary transfer portion 8, the toner images transferred to the transfer belt 45 by the primary transfer portions 7Y, 7M, 7C, and 7K are transferred onto the recording material P. As shown in FIG. The recording material P onto which the toner image has been transferred is conveyed to a fixing device 12 arranged downstream of the secondary transfer portion 8 in the recording material conveying direction.

The fixing device 12 applies heat and pressure to the recording material P to fix the toner image on the recording material P, and conveys the toner image toward the discharge port 13 . The recording material P conveyed to the discharge port 13 is discharged by a roller pair 15 and stacked on a discharge tray 14 formed in the upper portion of the apparatus main body 2 . After transferring the toner image, the transfer belt 45 is cleaned by the belt cleaning means 16 to remove residual toner, paper dust, and the like.

FIG. 2 is an explanatory diagram of a support structure for the transfer belt 45 of the intermediate transfer unit 4. As shown in FIG. FIG. 2(a) shows a full-color mode state in which the primary transfer rollers 6Y, 6M, 6C, and 6K are positioned at the primary transfer portion forming positions for all colors. In FIG. 2B, only the black primary transfer roller 6K is positioned at the primary transfer portion forming position, and the primary transfer rollers 6Y, 6M, and 6C of the other colors are positioned away from the photoreceptors 30Y, 30M, and 30C. Indicates the state of the monochrome mode to be taken. Broken lines indicate rollers and belts that are positioned differently from the full-color mode. The double-headed arrow line segments show the displacement of the roller as it assumes different positions between the modes. FIG. 2(c) is an explanatory diagram of the pushing amount S2 of the roller 42 with respect to the natural position of the belt in the monochrome mode.

In the example shown in FIG. 2, the primary transfer rollers 6Y, 6M, 6C and the roller 42 are driven and controlled by motors so that they take different positions (set different belt track paths) between modes. It is held by a contact/separation mechanism driven by a cam or the like. The roller 41 is a tension imparting member that applies tension to the transfer belt 45 from the inside toward the outside by means of a compression coil spring 48 as an urging means (the transfer belt 45 is stretched). It is freely supported by the side plate. The roller 42 functions as a backup roller, and the roller 43 constitutes an entrance roller for the secondary transfer portion 8 .

Toner image detecting means 50 for detecting the toner image on the transfer belt 45, and a sensor facing member 46 arranged in the inner loop of the transfer belt 45 for stabilizing the surface position of the belt facing the toner image detecting means 50. Prepare. A pressing roller 47 is provided outside the transfer belt 45 and close to the toner image detecting means 50 as a pressing member that is movable in the direction of advancing and retreating with respect to the surface of the transfer belt 45 .

In the color printer 1 of the present embodiment, the transfer belt 45 as an endless belt member and a plurality of rollers 41, 42, 43, and 44 that support the transfer belt 45 are provided in the intermediate transfer unit as a belt device. , the roller 42 as a supporting rotating body is crown-shaped. FIG. 3 is an explanatory diagram of the roller 42. As shown in FIG. 3A is a perspective view, FIG. 3B is a bottom view, and FIGS.

The background of the crown-shaped roller 42 is as follows. In the intermediate transfer unit 4, color misregistration occurs due to deflection of rollers upstream of each primary transfer portion. In the color printer 1, the roller (roller 42 in the illustrated example) on the upstream side of the uppermost stream of the image forming unit is flexed by the belt tension, and the belt moves along the flexure. is transcribed. Since the deflection amount of the belt is different for each color, color misregistration occurs.

In order to prevent this color misregistration, the roller 42, which is a roller supporting the belt portion immediately before the most upstream primary transfer portion in the belt moving direction, has a crown shape. A roller 42 is a backup roller that supports the belt from the inside, and is also a belt position adjustment roller that determines the position of the belt entering the most upstream image forming unit. It can be said that it is a belt adjustment roller in the sense that it determines appropriate belt positions for both full-color mode and mono-color mode. By giving the roller 42 a shape that cancels the amount of deflection of the roller 42 (adding a crown) in advance, the deflection of the belt in the image forming unit is canceled and color misregistration is prevented.

FIG. 3( c ) shows the wrap region 70 of the transfer belt 45 around the roller 42 and the belt tension T passing through the center of the wrap region and the center of the roller 42 . Due to this tension, the axial central portion of the roller (hereinafter referred to as the central portion) bends so that it is located further inside the belt than the axial ends thereof (hereinafter referred to as both ends). FIG. 3(b) shows a state where both end portions 42a with a small outer diameter and the central portion 42b with a large outer diameter are aligned with each other when there is no bending. When the roller 42 bends due to the belt tension, the central portion 42b is positioned inside the belt as shown in FIG.

Due to this crown shape, it was possible to cancel the color shift due to bending and improve the color matching. However, the crown-shaped roller creates a speed difference between the center and the ends of the belt. Specifically, the distance from the center of rotation to the belt contact area is large at the center and smaller at the ends than at the center. occur. Due to this difference in speed, the ends of the belt tend to move toward the center, causing problems such as wrinkles and image distortion on the belt. A dashed arrow F1 in FIG. 3(b) indicates a force acting to bias the belt toward the center. A force is applied to the belt toward the center. Arrow A indicates the direction and orientation of rotation of the surface of the roller.

When the belt is wrinkled, the wrinkles cause areas where the toner image is placed and areas where it is not, resulting in an abnormal image. This abnormal image appears conspicuously when the wrinkles of the belt are broken.

When a crown-cancelling force is applied to the crowned roller 42 by belt tension, there is no longitudinal deviation in the distance from the rotation center to the belt contact portion at the center of the belt winding portion. However, it is not possible to eliminate the deviation of the distance from the rotation center to the belt contact portion in the entire belt winding region that is deviated from the belt winding center.

Also, if the tension is not at the target value, there will be a speed difference between the belt center and the edge, causing wrinkles and image distortion. Since the crown shape of the part is canceled, no velocity difference occurs).

Furthermore, in the color printer 1, the positions of the rollers 42 are switched between when printing in the full-color mode and when printing in the monochrome mode.

That is, the amount of pushing (deflection) of the belt by the backup roller differs between the monochrome mode and the full-color mode. For example, the belt extrusion amount S1 shown in FIG. 2A is different from the belt extrusion amount S2 shown in FIG. 2C. Therefore, the load applied from the belt to the roller 42 is also different, and the deflection amount of the roller 42 is different between the monochrome mode and the full-color mode. If the amount of crown is adjusted to match the load in the full-color mode, the crown remains in the monochromatic mode, resulting in wrinkles.

In order to avoid wrinkles caused by the different positions of the rollers 42 between modes, it is conceivable to separate the backup roller from the belt in the monochrome mode. Become.

In such a configuration in which the roller 42 is released in the monochrome mode, switching from the monochrome mode to the full-color mode is performed while the intermediate transfer belt is rotating in order to reduce the printing time and the waiting time after printing. , performs a switching operation. During the switching operation (during the operation of changing the belt trajectory setting), the belt tension is not the target load, and the amount of cancellation of the crown shape of the roller 42 is different from the appropriate amount. As a result, there is a speed difference between the center and the ends of the belt, which causes the belt to be distorted, causing belt wrinkles and image distortion when printing in the full-color mode after switching from the monochrome mode.

Due to resource conservation and weight reduction of materials, the diameter of the roller is reduced and the wall thickness of the hollow pipe roller is reduced.

In this embodiment, at least one belt support rotating body imparts force to the belt to spread outward in the width direction in order to prevent problems caused by the speed difference between the center and the end of the belt of the crown-shaped rollers. That is, a force directed outward in the width direction is applied to the belt. The support roller that imparts the spreading force may be a roller driven by the belt or a roller driving the belt. It is preferable that the support rotator is adjacent to the crown-shaped support rotator from the downstream side or the upstream side in the belt moving direction. Most preferably, the crown-shaped supporting rotor itself imparts a force to spread the belt to both sides in the width direction.

The following methods are mentioned as a method of giving an expanding force. In this method, grooves formed on the surface of the roller apply a spreading force. A groove slanted in the axial direction of the roller is provided from the center toward the outside. The grooves are in opposite directions for the rollers driven by the belt and the rollers for driving the belt. Due to the inclination of the groove, a force is applied to the belt in the direction of the roller axis according to the inclination. By directing the belt outward in the axial direction of the roller with this force, the central portion of the belt is pulled, so wrinkles can be suppressed.

FIG. 4 is an explanatory diagram of an example in which grooves 42c inclined in the roller axial direction are provided in the crown-shaped roller 42 from the center toward the outside. FIG. 4(a) is a perspective view of the roller 42, and FIG. 4(b) is a bottom view. As shown in FIG. 4B, it is possible to apply to the belt a force F2 that spreads in the opposite direction to the force F1 that bends the belt due to the speed difference between the center and the end of the crown-shaped roller.

FIG. 5 is an explanatory view of an example in which a straight-shaped belt entrainment roller is provided with grooves inclined in the roller axial direction from the center toward the outside. FIG. 5(a) is a perspective view of the roller, and FIG. 5(b) is a bottom view. As shown in FIG. 5(b), a spreading force F2 can be applied to the belt by the grooves of the roller.

As for the method of applying force to the outside of the belt, there is a method of applying a spreading force to portions having different coefficients of friction formed on the roller surface, in addition to the grooves. Specifically, for example, the inclined shape is provided with a material (for example, rubber) having a higher coefficient of friction than the surface of the roller. This shape of the roller can also be applied to the roller itself, which has a larger outer diameter at the center than at the ends, and can also be applied to other rollers in contact with the belt. It may be applied not only to a single roller but also to a plurality of rollers. Preferably, a roller to which a stronger belt tension is applied is more effective.

By giving the roller itself a shape that imparts force to the belt to expand outward, the roller (for example, a straight roller) that does not give a speed difference between the center and the edge of the belt gives only a force toward the edge of the belt. can be done. Therefore, it is possible to suppress wrinkles and image distortion due to the belt moving toward the center due to the speed difference.

Further, if a configuration is adopted in which force is applied to both ends of the belt at a position close to the roller 42, image distortion can be effectively suppressed. Preferably, the backup roller itself is configured to cancel the speed difference. Further, the position close to the backup roller is preferably a portion as close as possible, such as the next roller, in the downstream. Even in the upstream configuration, wrinkles and image distortion due to speed differences can be canceled by applying a force in the direction of stretching the belt in advance to the belt with an outward force.

[Embodiment 2]
In the above embodiment, at least one support rotor is crown-shaped, and the at least one support rotor imparts force to the belt to spread outward in the width direction. In place of at least one supporting rotating body imparting a force to expand the belt to both lateral sides in the width direction, at least one supporting rotating body has a central portion in the width direction or both ends in other locations in the width direction. A material having a larger coefficient of friction with the back surface of the belt may be employed. That is, in the belt device according to the second embodiment, at least one supporting rotating body has a crown shape, and the central portion or both ends in the width direction have a larger coefficient of friction with the back surface of the belt than other portions in the width direction. It is a thing.

FIG. 6 shows a crowned roller 42 with different coefficients of friction between the central portion 42d and the end belts. By configuring the rollers 42 of the color printer 1 in this manner, belt wrinkles can be suppressed. By lowering the coefficient of friction of the roller 42 other than the central portion, the portion other than the central portion of the roller slides on the belt. Therefore, by driving only at the central portion, the linear velocity in the longitudinal direction of the belt is determined by the diameter of the central portion of the roller, and the force in the longitudinal direction of the belt is less likely to be received. As a result, the force directed toward the longitudinal central portion of the belt can be canceled, so longitudinal strain is less likely to occur and wrinkles of the belt are less likely to occur.

A high-friction member is placed or coated on the central portion 42d (only the central portion is wrapped with rubber or coated or painted with a high-friction coefficient member). A material with a relatively high coefficient of friction may be placed in the middle or both ends, or a material with a relatively low coefficient of friction may be placed elsewhere. A low friction coating such as a DLC coating can be used.

Specific examples of the roller 42 include the following. A metal roller made of nickel-plated SUM material (sulfur and sulfur composite free-cutting steel) is provided with a thick material such as rubber in the center and having a higher coefficient of friction with paper than plating. By providing a rubber thickness corresponding to the deflection of the roller 42 during printing in the full-color mode, it is possible to suppress belt wrinkles and abnormal images while suppressing color misregistration due to the deflection of the roller 42 . In this case, the roller is preferably a straight roller having a large central portion formed by a rubber layer, thereby reducing unnecessary shaving of metal and saving resources.

As described above, Embodiment 1 includes a plurality of image carriers that carry toner images, a rotatable intermediate transfer member, and a plurality of image carriers that are arranged to face the plurality of image carriers, and the intermediate transfer member. and a secondary transfer roller for transferring the toner image on the intermediate transfer member to a transfer material, wherein the intermediate transfer member is transferred by the plurality of primary transfer rollers. After the toner images are sequentially superimposed thereon, the toner images are transferred from the intermediate transfer body to the transfer material by the secondary transfer roller, and a belt position adjustment roller is provided upstream of the primary transfer roller, and the belt position adjustment roller is 1. An image forming apparatus, wherein the belt position adjusting roller is arranged upstream of the most upstream of image formation on a plurality of image carriers, and the outer diameter of the belt position adjusting roller at the center in the axial direction is larger than the outer diameter at both ends in the axial direction. It can be said that the position adjustment roller itself is configured to apply a force in the direction of pulling the belt to both ends.

Further, the second embodiment includes a plurality of image carriers that carry toner images, a rotatable intermediate transfer member, and a plurality of image carriers that are arranged to face the plurality of image carriers, and transfer from the image carriers to the intermediate transfer member. a plurality of primary transfer rollers for transferring a toner image; and a secondary transfer roller for transferring the toner image on the intermediate transfer member to a transfer material; After the toner images are sequentially superimposed on each other, the toner images are transferred from the intermediate transfer member to the transfer material by the secondary transfer roller, and a belt position adjustment roller is provided upstream of the primary transfer roller, and the belt position adjustment roller is 1. An image forming apparatus arranged upstream of image formation on a plurality of image bearing members, and characterized in that the outer diameter of the belt position adjusting roller at the center in the axial direction is larger than the outer diameter at both ends in the axial direction. It can be said that the friction between the adjusting roller and the belt is different between the central portion and the non-central portion.

In any of the embodiments, the crown shape is adopted for the belt position adjusting roller, but the crown shape may be adopted for other belt supporting rotating bodies. Also, the present invention can be applied to a belt device in another part of the image forming apparatus, or to a belt device used in devices other than the image forming apparatus.

In order to solve the problems caused by forming at least one rotary support into a crown shape, the following other methods are conceivable, but the above embodiments are superior to these methods. That is, the following [1] to [3] are conceivable.
[1] The crown is canceled by inverting the crown of the rollers other than the backup roller that is essential.
[2] Giving the belt a shape/configuration that applies an outward force.
[3] Giving the rollers a shape and configuration that applies an outward force.

In [1], the reverse crown shape of the roller always causes a speed difference, resulting in color shift. (The speed difference due to the reverse crown is required during monochrome printing when the backup roller is in contact with the belt in monochrome mode, and when switching the backup roller due to the change between full-color printing and monochrome printing. The crown shape of the backup roller Since it varies depending on the shape, the inverted crown shape cannot be determined unconditionally.)

Regarding [2], Patent Document 2 discloses that when a crown is attached to the drive roller to prevent the belt from twisting, the linear speed of the belt at the center becomes faster than that at the ends due to the crown, causing the belt to bend and bend at the center. , the image is distorted. In order to solve this problem, the belt is shaped and reinforced obliquely in the traveling direction so that the driving roller in the straight portion does not shift, and a configuration is described in which force is applied to both ends of the belt. .

It is considered effective to apply force to both ends of the belt by means of shape/reinforcing members, but there are the following problems. Addition of shape or reinforcement to the belt causes color unevenness due to uneven electrical resistance of the belt. This is because, when a transfer current is applied to the belt, if there are places where the current easily flows and places where the current does not easily flow due to reinforcing materials, the transfer will be different. In addition, since the thickness of the belt increases due to the reinforcement, the thickness variation increases (generally, since the thickness variation is determined by the ratio of the thickness, the tolerance increases as the thickness increases). Color misregistration is aggravated by surface linear velocity variations on the driving roller due to the thickness variations.

Regarding [3], Patent Document 2 describes a configuration in which a spiral groove is formed in a straight drive roller to prevent the belt from shifting, and a configuration in which force is applied to both ends of the belt. However, if the point of forming a spiral groove in the driving roller is simply applied to the color printer 1 having the crown-shaped roller 42 of the first embodiment, the following problem remains. That is, the crown-shaped roller 42 is arranged for the purpose of securing the belt winding state with the photosensitive member at the most upstream of the image forming station, so it is arranged at the upstream of the most upstream of the image forming station. Therefore, as shown in FIG. 1, the drive roller is in a position opposed to the roller 42 (a position 180 degrees opposite on the belt path), and the distance between them is large. Due to the distance, distortion is likely to occur, and the distortion accumulates as the belt rotates many times, resulting in image distortion and wrinkles.

1 : color printer 2 : main body 2A : front 3 : image forming unit 4 : intermediate transfer unit 5 : optical unit 6 : primary transfer roller 7 : primary transfer section 8 : secondary transfer section 9 : secondary transfer roller 10 : Tray 11 : Roller group 12 : Fixing device 13 : Discharge port 14 : Discharge tray 15 : Roller pair 16 : Belt cleaning means 19 : New toner storage section 30 : Photoreceptor 31 : Charging means 32 : Developing means 33 : Cleaning section 41 : Roller 42 : Roller 42a : Both ends 42b : Central portion 42c : Groove 43 : Roller 44 : Roller 45 : Transfer belt 46 : Sensor facing member 47 : Pressing roller 48 : Compression coil spring 50 : Toner image detection means 70 : Wrapping area A : Arrow F1 : Force F2 : Force P : Recording material S1 : Pushing amount S2 : Pushing amount T : Belt tension

Japanese Patent Application Laid-Open No. 2003-345142 JP-A-2002-357960

Claims (10)

In a belt device comprising an endless belt member and a plurality of supporting rotating bodies that stretch and support the belt member,
1. A belt device, wherein at least one support rotor is crown-shaped, and the at least one support rotor imparts a force to expand the belt to both lateral sides in the width direction. The belt device according to claim 1,
A belt device according to claim 1, wherein the support roller that applies the spreading force is a support rotator adjacent to the crown-shaped support rotator from the downstream side or the upstream side in the belt moving direction. The belt device according to claim 1,
A belt device according to claim 1, wherein said crown-shaped supporting rotor imparts force to the belt to spread it outward in the width direction. In the belt device according to any one of claims 1 to 3,
A belt device, characterized in that grooves formed on the surface of a roller apply the spreading force. In the belt device according to any one of claims 1 to 3,
A belt device, wherein the spreading force is applied to portions having different coefficients of friction formed on the surface of the roller. In a belt device comprising an endless belt member and a plurality of supporting rotating bodies that stretch and support the belt member,
1. A belt device, wherein at least one supporting rotating body is crown-shaped, and a central portion or both ends thereof in the width direction have a greater coefficient of friction with the back surface of the belt than other portions in the width direction. In the belt device according to claim 6,
A belt device characterized in that a material having a relatively large coefficient of friction is arranged at the central portion or both ends, or a material having a relatively small coefficient of friction is arranged at the other portion. In an image forming apparatus equipped with a belt device,
An image forming apparatus employing the belt device according to any one of claims 1 to 7 as a belt device. In the image forming apparatus according to claim 8,
The provided belt device is a belt device in which a plurality of image forming units face each other,
wherein the crown-shaped support rotator is a support rotator supporting a portion of the belt immediately before the image forming unit facing the most upstream image forming unit in the belt moving direction among the plurality of image forming units. Device. The image forming apparatus according to claim 9,
An image forming apparatus comprising a plurality of belt trajectory settings having mutually different tensions associated with a support rotating body that supports the immediately preceding belt portion, and driving the belt during an operation of changing the belt trajectory setting.

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