JP2002072617A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce color slurring in the belt width direction without an increase in cost by a simple device structure. SOLUTION: This image forming device having a typical structure, is provided with an endless belt 8 stretched around plural rollers, and plural image forming stations 2 respectively forming the image on the endless belt 8 or a sheet S transported by the endless belt 8. The peripheral length of the roller stretching the endless belt 8 thereon, is respectively set to the reciprocal number of the integer of the distance between image forming stations for each color.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a belt driving device having an endless belt stretched around at least two belt stretching rollers and rotating.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method or an electrostatic recording method for an image forming process, a cylindrical photosensitive drum is used as an image bearing member, and the photosensitive drum is charged around the photosensitive drum. A type in which peripheral devices such as a container, an exposure unit, a developing unit, and a cleaning unit, a recording material transport mechanism (recording material transport unit), and the like are well known.

In recent years, in order to further improve the functions of a photosensitive drum, a recording material conveying mechanism, and the like, an endless belt has been adopted as a photosensitive member instead of the photosensitive drum.
An image forming apparatus using an endless belt as a sheet conveying mechanism has been developed.

In such an image forming apparatus using an endless belt for the photosensitive member and the sheet conveying mechanism, many functions can be improved, but the driving which is a disadvantage peculiar to the belt mechanism is achieved. The endless belt sometimes shifts or meanders with respect to the reference trajectory.

Therefore, conventionally, when the endless belt has shifted or meandered, as one of means for correcting these problems, a deviation regulating rib is provided on the endless belt, or the endless belt is suspended and suspended. Or the accuracy of the rollers, such as the degree of parallelism and the twist of the rollers.

[0006]

However, the above conventional method has the following problems. There is a limit to the straightness of the deviation control rib, and even if the deviation control rib with good straightness can be attached to the endless belt, the deviation of the endless belt applied to the deviation control rib during rotation of the endless belt If the force is not always constant, meandering occurs in accordance with the cycle of the shift force change.

Further, in order to make the above-mentioned deviation force constant, it is necessary to improve the parallelism between the rollers on which the endless belt is stretched, the accuracy of the roller runout, and the like, but this is also limited.

Usually, a roller for controlling the peripheral length is used to absorb the peripheral length difference (variation due to mass production) of the endless belt, but the roller changes in accordance with the peripheral length difference in the belt width direction of the endless belt. As a result, the rollers on which the endless belt is stretched lose their parallelism. As a result, meandering occurs in the endless belt, causing color misregistration in the belt width direction orthogonal to the sheet conveying direction.

Accordingly, an object of the present invention is to reduce color misregistration in the belt width direction with a simple configuration without increasing the cost of the apparatus.

[0010]

In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an endless belt stretched by a plurality of rollers, the endless belt or the endless belt. In an image forming apparatus having a plurality of image forming means for forming an image on a conveyed sheet, a peripheral length of a roller which stretches the endless belt is set to be an integral number of a distance between image forming means for each color. It was characterized in that.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus according to the first embodiment, FIG. 2 is a configuration diagram of a sheet conveying device, and FIG. 3 is a graph showing a meandering amount of the endless belt generated by a roller that stretches the endless belt.

As shown in FIG. 1, the image forming apparatus according to the present embodiment is a color laser beam printer employing an electrophotographic image forming process. The sheets S stacked on the feed cassette 4 are separated one by one by a pickup roller 5 and sent out to a feed roller 6. The sheet S sent to the feeding roller is fed to a recording material conveying unit and an endless belt 8 which is a transfer belt.

On the other hand, uniformly charged photosensitive drums 1a,
In 1b, 1c and 1d, the surfaces of the photosensitive drums are exposed by scanner units 3a, 3b, 3c and 3d each constituted by a rotating polygon mirror and a reflecting mirror, and latent images are respectively formed. Each latent image is developed by developing units 7a, 7b, 7c, and 7d for applying yellow, magenta cyan, and black toners, and is converted into a visible image. Then, this visible image is transferred onto the sheet S conveyed by the endless belt 8.

[0015] As shown in FIG. 2, the endless belt 8 is formed of a film-like member having a thickness of about 150μm which gave a volume resistivity of less than e.g. 10 ¹² Qcm, downstream constituting the belt suspension KaiCho portion material It is wound around the drive roller 9c on the side and the driven rollers 9a and 9b and the tension roller 9d on the upstream side, and moves in the direction (arrow X direction) for conveying the sheet.
The volume resistivity was measured using a high resistance meter R834 manufactured by ADVANTEST, using a measurement probe conforming to JIS method K6911.
0 is a value obtained by applying 100 V.

All of these rollers 9a to 9d are rotatably held at both ends between bearings (not shown) and are disposed substantially in parallel. The drive roller 9c is formed of a metal roller having a rubber layer having a large friction coefficient on its surface, and has a diameter of 30 mm. The drive roller 9c is driven to rotate at a predetermined speed in a sheet conveying direction by a drive source. The driven roller 9b regulates a problem such as a deviation or meandering of the endless belt 8. The tension roller 9d is a roller for urging the endless belt 8 to stretch the endless belt 8, and is always urged by a spring in the direction in which the endless belt 8 is stretched. Driven roller 9a,
9b is a metal roller of SUS or the like, and the bearings at both ends are fixed at predetermined positions.

When the driving roller 9c is driven to rotate in the direction in which the sheet is conveyed by the driving source, the driving force is transmitted to the endless belt 8 by the frictional force between the outer peripheral surface of the driving roller 9c and the inner peripheral surface of the endless belt 8, The endless belt 8 is rotatably driven in a direction for conveying a sheet between four members of a driving roller 9c, driven rollers 9a and 9b, and a tension roller 9d.

A tension roller 9d for controlling the circumferential length is used to absorb a circumferential length difference (such as variation due to mass production) in the belt width direction (arrow Y direction) of the endless belt 8 perpendicular to the sheet conveying direction. I have. Therefore, when there is a difference in the circumferential length of the endless belt 8 in the belt width direction, the tension roller 9d and the other rollers 9a to 9c that stretch the endless belt 8 are not necessarily parallel.

During the rotation of the endless belt, the distance between the rollers changes due to the run-out of each of the rollers 9a to 9d. Therefore, the position of the tension roller 9d fluctuates in accordance with the swing cycle of each roller, and the parallelism between the tension roller 9d and the other rollers 9a to 9c that stretch the endless belt changes periodically. . As a result, a biasing force of each roller in the swing cycle is generated on the endless belt 8, and the endless belt 8 is meandering.

The peripheral length of the driving roller 9c and the driven roller 9b is equal to the interval H (distance between image forming units of each color) between the image forming stations 2 as image forming units. Further, the driven roller 9a and the tension roller 9d
Means that the circumference of the roller is equal to the distance H between the image forming stations.
Is equal to one half of

FIG. 3 shows that the position of the tension roller 9d fluctuates in accordance with the swing cycle of each of the driven rollers 9a and 9b, the driving roller 9c, and the tension roller 9d, so that the tension roller 9d and the other rollers 9a to 9c are parallel. 6 is a graph showing the amount of meandering of the endless belt 8 when changes periodically.

The Y-axis indicates the meandering amount of the endless belt, and the X-axis indicates the amount of advance of the endless belt. In addition, the driven roller 9b has a period of 1 / 4π, the driven roller 9a has a period of 1 / 2π, and the tension roller 9d has a period of 1 / 4π with respect to the driving roller 9c.

The driving roller 9c and the driven roller 9b have a circumferential length of the roller equal to the interval H between the image forming stations, and the driven roller 9a and the tension roller 9d are
The circumference of the roller is equal to 1 / 2H. Therefore, the cycle of the composite wave of each roller meandering amount is the interval H between the image forming stations. That is, due to the meandering of the endless belt, the transfer position of the image in the belt width direction orthogonal to the sheet conveyance direction changes sinusoidally with respect to the ideal transfer position. Since the meandering amount is always the same, there is no relative color shift of each color on the image.

The sheet S to which the toner image has been transferred is peeled off from the photosensitive drum 1d by a separation charger, and is fixed to a fixing roller pair.
Conveyed to 10. On the other hand, the photosensitive drums 1a to 1d are provided with a cleaning device provided in contact with the photosensitive drums 1a to 1d.
The toner remaining on the surfaces of the photosensitive drums 1a to 1d is scraped off by 11 to prepare for the next image formation. Fixing roller pair 10
The toner image is fixed on the sheet S conveyed by the fixing roller pair 10 and discharged by the discharge roller pair 12 to the outside of the image forming apparatus.

With the above-described configuration, meandering caused by compounding due to runout and eccentricity of each roller is canceled by setting the cycle of the meandering to the interval H between the image forming stations. Thus, color shift in the belt width direction can be reduced with a simple configuration without increasing the cost of the apparatus.

In the present embodiment, the roller around which the endless belt is stretched has a circumferential length of H or 1/2 H. However, the roller may be any integer number of the distance between the image forming means of each color. Is D, the same effect can be obtained as long as it has a relationship of πD = H / α (α is an integer).

In this embodiment, the winding angle of the endless belt 8 around the driven roller 9a is about 2 degrees.
0 degrees, which is smaller than other rollers. For this reason, a change in the endless belt stretching distance due to the run-out of the driven roller 9a is small, and a change in the position of the tension roller 9d is small. Further, the biasing force of the endless belt 8 due to the parallelism between the tension rollers is reduced, and the meandering of the endless belt 8 is reduced.

Further, the influence of the winding angle of the endless belt 8 on the tension roller on the meandering of the endless belt 8 was investigated. As for the rollers other than the tension roller 9d, the rollers having actual roller runout accuracy within ± 0.5 mm were used. In this case, the influence of the belt meandering caused by the roller runout was not observed within the winding angle of 70 degrees. On the other hand, when the wrapping angle was set to 80 degrees, the influence of the run-out of the roller (color shift in the cycle of the roller set to 80 degrees) was confirmed on the image.

For this reason, the driven roller 9a having a winding angle of 70 degrees or less is not affected by the belt meandering caused by the roller run-out, and the peripheral length of the roller is set to be an integral number of the distance between the image forming means of each color. No need to do. Therefore, only the driven roller 9b and the driving roller 9c whose wrapping angle with the endless belt 8 is 70 degrees or more, and the tension roller 9d for urging the endless belt 8 to stretch the endless belt 8 have the peripheral length of each color. The same effect can be obtained even if the distance between the image forming means is 1 / integer.

[0030]

As is apparent from the above description, in the image forming apparatus according to the first aspect of the present invention, the circumferential length of the roller on which the endless belt is stretched is substantially an integer of the distance between the image forming stations. I'm making it one-third. This makes it possible to cancel the meandering caused by the runout and eccentricity of each roller due to the distance between the image forming stations, and correct the color shift in the belt width direction without increasing the precision of the parts.

In the image forming apparatus according to a second aspect of the present invention, among the rollers for stretching the endless belt, at least the roller for applying tension to the endless belt and the winding angle between the endless belt and the endless belt are adjusted. The circumferential length of the roller, which is 70 degrees or more, is set to be approximately an integral number of the distance between the image forming stations of each color. This makes it possible to cancel the meandering caused by the runout and eccentricity of each roller by the distance between the image forming stations, and to correct the color shift in the belt width direction without increasing the precision of the parts.

Japanese Patent Publication No. 6-13373 discloses that the color shift in the sub-scanning direction is improved by setting the pitch between the drums to be equal to or a multiple of the circumference of the drive roller. This patent improves color misregistration in the main scanning direction by matching the belt meandering period with the drum pitch by setting the pitch between drums equal to or an integer multiple of the circumference of each roller on which the belt is stretched. Is what you do.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a configuration diagram of a sheet conveying device.

FIG. 3 is a graph showing a meandering amount of the endless belt generated by a roller that stretches the endless belt.

[Explanation of symbols]

H: distance between image forming stations (distance between image forming means for each color) S: sheets 1a to d: photosensitive drums 2: image forming stations (image forming means) 3a to d: scanner unit 4: feeding cassette 5: pickup Roller 6: Feeding rollers 7a-d: Developing device 8: Endless belt 9a, b: Followed roller 9c: Driving roller 9d: Tension roller 10: Fixing roller pair 11: Cleaning device 12: Discharge roller pair

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takemoto Miyamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H030 AA01 AB02 BB44 BB46 2H032 AA15 BA18 BA19 BA23 3F049 AA02 BA11 DA03 LA01 LB03

Claims (2)

[Claims] 1. An image forming apparatus comprising: an endless belt stretched by a plurality of rollers; and a plurality of image forming means for forming an image on the endless belt or a sheet conveyed by the endless belt. The circumference of the roller that stretches the belt
An image forming apparatus characterized in that the distance between image forming means for each color is set to a fraction of an integer. 2. The method according to claim 1, wherein at least one of the rollers extending around the endless belt has a winding angle of at least 70 degrees with respect to the endless belt, and the roller is used to stretch the endless belt. 2. The image forming apparatus according to claim 1, wherein the peripheral length of the roller for urging the endless belt is a fraction of the distance between the image forming units of each color.