JP2000305337A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of an image deviation between respective colors and a blurring of image. SOLUTION: In this device, a driving roll 11 is installed on the upstream side in a moving direction of a carrying belt 2 from a transfer position of a 1st color toner image on photoreceptors 10Y, 10M, 10C and 10K, and a following roll 12 to impart tensional force to the carrying belt 2 is installed on the downstream side from a transfer position of a last color toner on photoreceptors 10Y, 10M, 10C and 10K in the moving direction of the carrying belt 2. Then, a cleaning member 9a is provided in a section where the carrying belt 2 is moved from the following roll 12 to the driving roll 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a printer or a copying machine for sequentially transferring toner images of respective colors on a plurality of photosensitive members onto a sheet conveyed by a conveying belt.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, a plurality of photosensitive members are opposed to a transport belt (also referred to as a transfer belt) for transporting sheets such as plain paper and OHP sheets. A full-color image is formed by forming toner images of magenta, cyan, and black colors and sequentially transferring the toner images of each color on the plurality of photoconductors onto a sheet conveyed by the conveyance belt. There is a color electrophotographic apparatus called a tandem type.

Conventionally, in a tandem type color electrophotographic apparatus, one driving roller and one or a plurality of driven rollers are used to drive a conveying belt, and one driving roller is used to apply tension to the conveying belt. Usually, the driven roller is configured to be movable. Further, the drive roller is located downstream of the position where the final color toner image (the toner image transferred last on the paper) of the toner images of each color on the plurality of photoconductors is transferred on the paper in the moving direction of the transport belt. And a driven roller for applying tension to the transport belt transfers the first color toner image (the first toner image to be transferred to the sheet) of the toner images of each color on the plurality of photoconductors to the sheet. The cleaning member that is disposed upstream of the position with respect to the moving direction of the transport belt and that cleans the transport belt is a section where the transport belt returns (a section where the drive roller returns to the driven roller) or the transport belt is wound around the driven roller. In a section where toner images of each color are sequentially transferred from a plurality of photoconductors to a sheet in a section, the conveyor belt is generally used in a state where the transport belt is tighter.

Japanese Utility Model Publication No. 6-43813, Utility Model Registration No. 2531020 and Japanese Patent No. 2743359 disclose an electrophotograph of a system in which images of respective colors are sequentially superimposed and transferred from a drum-shaped photosensitive member onto paper. In the apparatus, it is described that a transfer speed of a transfer transfer member including a transfer drum and a transfer belt for transferring a sheet is set to be higher than a peripheral speed of a photoconductor by a predetermined speed.

Japanese Utility Model Publication No. 6-43813, Utility Model Registration No. 2531020, and Patent No. 274335
In any of the publications, when trying to make the peripheral speed of the photoconductor and the conveyance speed of the transfer conveyance member the same, the frictional force between the photoconductor and the transfer conveyance member fluctuates due to the eccentricity of the photoconductor. If the toner image is displaced and the peripheral speed of the photoconductor is faster than the transfer speed of the transfer conveyance member, the paper is slackened and the toner image is displaced. It is described that it is better to increase the speed than the peripheral speed.

In a tandem-type color electrophotographic apparatus, with respect to driving of a transfer belt, a drive roller is used to drive a final color toner image of a toner image of each color on a plurality of photoconductors (a toner image to be finally transferred to paper). And a driven roller for applying tension to the transfer belt is a first roller of a toner image of each color on a plurality of photoconductors. Generally, the toner image of the color (the first toner image to be transferred to the sheet) is disposed upstream of the transfer belt in the moving direction of the transfer belt. Is more stable when the transfer belt is in contact with the photosensitive member without sagging of the transfer belt.

FIG. 2 shows an example of a conventional tandem type color electrophotographic apparatus. This tandem type color electrophotographic apparatus has a configuration in which image forming units of four colors are arranged in a passage path of a sheet conveyed by being electrostatically attracted and conveyed by a conveying belt, and has four colors, for example, yellow (hereinafter referred to as Y). , Magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as K) images are transferred to the photoconductors 10Y, 10M,
Image forming unit 1 formed on each of 10C and 10K
Y, 1M, 1C, and 1K, an endless transport belt 2 that transports the paper, a paper feed device including a paper feed cassette 3 and a paper feed roller 4 in which the paper is stored, a registration roller pair 5, and an image forming unit 1Y, 1M, 1C, 1K, photoconductors 10Y, 10
Transfer chargers 6Y, 6M, 6C, and 6K as transfer means for sequentially transferring images of respective colors formed on N, 10C, and 10K onto a sheet on the conveyance belt 2 and a fixing device 7
And a cleaning device 9 for cleaning the conveyor belt 2 and the like.
Y, 10M, 10C, and 10K.

The conveyor belt 2 is stretched over a plurality of rollers 11 to 13, and usually a plurality of photosensitive members 10Y, 10M,
Of the toner images of each color on 10C and 10K, the toner image of the first color (the Y toner image that is first transferred to the sheet) is arranged on the upstream side in the moving direction of the transport belt 2 from the position where the toner image is transferred to the sheet The driven roller 12 is used as a driven roller, and the final color toner image (the last toner image to be transferred onto the paper) of the toner images of each color on the plurality of photoconductors 10Y, 10M, 10C, and 10K.
The roller 11 disposed on the downstream side in the moving direction of the transport belt 2 from the position where the toner image) is transferred to the sheet is a driving roller.

A driving source 14 is connected to the driving roller 11,
The driven roller 12 is provided with a pressure spring 15 for applying tension to the conveyor belt 2, and the driven roller 12 is pressed to the right side in FIG. The drive roller 11 is rotationally driven by a drive source 14 in the direction of arrow D to rotate the transport belt 2 in the direction of arrow E. As the photoconductors 10Y, 10M, 10C, and 10K, for example, drum-shaped photoconductors are used, and the photoconductors 10Y, 10M, 10C, and 10K are driven to rotate in the direction of arrow F by a photoconductor driving unit (not shown). Here, the photoconductor 10
It is said that when the peripheral speed f of Y, 10M, 10C, and 10K satisfies f <e with respect to the moving speed e of the transport belt 2, the occurrence of misregistration of each color image is small.

In each of the image forming units 1Y, 1M, 1C, and 1K, the surface of each of the photoconductors 10Y, 10M, 10C, and 10K is a charger 16Y, 1 whose surface is a charger.
6M, 16C, 16K, which is charged to give a uniform charging potential, and is a writing unit 1 comprising a laser optical system.
The images (each color separation component) are written by being exposed by 7Y, 17M, 17C, and 17K to form an electrostatic latent image, and are developed by developing units 18Y, 18M, 18C, and 18K.
The toner images of the respective colors Y, M, C, and K are developed with the toners of the respective colors M, C, and K.

On the other hand, the paper is fed one by one from a paper feed cassette 3 to a pair of registration rollers 5 by a paper feed roller 4, and the pair of registration rollers 5 is exposed to the photoconductors 10Y, 10M, 10C, 10C.
The sheet is sent out to the transport belt 2 in synchronization with each color toner image on K. The transport belt 2 is driven by a driving roller 11
Is driven by the driven roller 12 with a constant tension, and the paper sent from the registration roller pair 5 is attracted by electrostatic and conveyed.

Sheets conveyed while being attracted to the conveyor belt 2 by static electricity are photosensitive members 10Y, 10M, 10C, 10C.
The transfer toners 6Y, 6M, and 6 for the respective color toner images on K
The full-color image is formed by being sequentially transferred by superimposition by C and 6K, separated from the transport belt 2 and passed between the fixing roller 7a and the pressure roller 7b of the fixing device 7 to fix the full-color image. Will be discharged later.

The photoreceptor 10Y, 1 on which the transfer of the toner image has been completed
On the surfaces of 0M, 10C, and 10K, residual toner is cleaned and collected by photoconductor cleaning devices 19Y, 19M, 19C, and 19K. The charge remaining on the surface of the conveyor belt 2 is removed by the charge eliminator 8 in preparation for the next image forming operation, and the surface is cleaned by the cleaning member 9 a of the cleaning device 9. The cleaning member 9a is a cleaning blade 9a formed of urethane rubber, and is provided on the backup roller 13 rotatably supported by the transport belt 2a.
At a constant contact pressure.

[0014]

In a tandem type color electrophotographic apparatus, an image shift (color shift) between respective colors tends to occur, and prevention of the color shift is an important technical problem. Causes of the color misregistration include a color misregistration caused by a mechanical assembly error and component precision, a color misregistration due to thermal expansion and deformation of the component, and the like. For example, when the tension of the transport belt fluctuates, the transport belt expands and contracts, and the image transfer position from each photoconductor to the paper fluctuates, or the paper slightly shifts and the image transfer position fluctuates. A positional shift occurs between the superimposed color images.

In the case of a blade cleaning system in which a urethane sheet in the form of a plate is used as a cleaning blade and this is brought into contact with the conveyor belt to clean the conveyor belt, the frictional resistance between the cleaning blade and the conveyor belt is reduced by the conveyor belt. May vary depending on the surface condition of the toner and the amount of toner remaining on the transport belt. When there is such a load fluctuation of the transport belt, the tension applied to the transport belt within the range where image transfer is performed fluctuates, and the elongation amount of the transport belt fluctuates. For this reason, the positions at which the toner images of each color are transferred from the photoconductor to the paper are shifted, and image transfer shift occurs.

Further, since the diameter of the driving roller for driving the conveyor belt and the diameter of the drum-shaped photoconductor slightly vary depending on the processing accuracy, it is impossible to keep the peripheral speed of the photoconductor and the moving speed of the conveyor belt at exactly the same speed. It is impossible, and there is a difference between the peripheral speed of the photoconductor and the moving speed of the transport belt. For this reason, if the photoconductor, the paper, and the transport belt come into close contact with each other due to the electrostatic force when the toner images of the respective colors are transferred from the photoconductor to the paper, the transport belt is pulled or pushed back by the photoconductor. The transfer position of the toner image of each color from the paper to the paper shifts, and the transfer of the image occurs. Further, if the difference between the peripheral speed of the photoconductor and the moving speed of the transport belt is too large, image blur occurs.

According to the first aspect of the present invention, the positional deviation between the superimposed color images caused by the expansion and contraction of the conveyor belt caused by the fluctuation of the frictional load applied to the conveyor belt by the cleaning member for cleaning the conveyor belt. It is an object of the present invention to provide an electrophotographic apparatus that can prevent such an electrophotographic apparatus.

According to a second aspect of the present invention, there is provided an electrophotographic apparatus capable of preventing a transfer belt from being loosened due to a frictional force between a photoreceptor and a sheet and preventing a positional shift between superimposed color images. The purpose is to provide.

According to a third aspect of the present invention, there is provided an electrophotographic apparatus capable of preventing an image from being blurred due to an excessively large difference between the peripheral speed of the photosensitive member and the moving speed of the conveyor belt. Aim.

[0020]

According to a first aspect of the present invention, a plurality of photoconductors are opposed to a conveyor belt that conveys a sheet, and each of the photoconductors is provided on the plurality of photoconductors. In an electrophotographic apparatus for forming a toner image and transferring the toner images of each color on the plurality of photoconductors sequentially on paper conveyed by the conveyance belt, a driving roller for rotating the conveyance belt, The toner image of the first color among the toner images of each color on the plurality of photoconductors is arranged on the upstream side in a moving direction of the transport belt from a position where the toner image of the first color is transferred to a sheet, and tension is applied to the transport belt. And a driven roller for transferring the final color toner image of the respective color toner images on the plurality of photoconductors to a position downstream of the transfer belt in the moving direction of the transfer belt. Clean the belt A cleaning member that is one in which the conveyor belt is provided in the section which moves the driving roller from the driven roller.

According to a second aspect of the present invention, in the electrophotographic apparatus according to the first aspect, at the position where the toner images of each color are transferred from the plurality of photoconductors to a sheet, the plurality of the plurality of photoconductors are moved relative to the moving speed of the conveyor belt. The moving speed of the photosensitive member surface is set to be higher.

According to a third aspect of the present invention, in the electrophotographic apparatus according to the second aspect, at the position where the toner images of each color are transferred from the plurality of photoconductors to the sheet, the plurality of the plurality of photoconductors are moved relative to the moving speed of the conveyor belt. The moving speed of the photosensitive member surface is set to be higher by 0% to 3%.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is an example of a tandem type color electrophotographic apparatus, in which a cleaning member for cleaning a conveyor belt expands and contracts due to a change in frictional load applied to the conveyor belt. In order to prevent the positional deviation between the superimposed color images caused by the above, the driving roller for rotating the transport belt is replaced with the driving roller of the toner image of each color on the plurality of photoconductors, contrary to the related art. A driven roller for applying tension to the transport belt is disposed upstream of the position where the first color toner image is transferred to the sheet with respect to the moving direction of the transport belt. The transfer roller is disposed downstream of the position where the final color toner image is transferred onto the sheet in the moving direction of the transport belt, and the driven roller is provided with a tension mechanism that applies tension to the transport belt. A cleaning member comprising a cleaning boot de for cleaning the one in which the conveyor belt is provided in the section which moves the driving roller from the driven roller.

Thus, in this embodiment, in the range from the driving roller corresponding to the image transfer section to the driven roller, the tension of the transport belt is only the tension generated by the tension mechanism, and the transport belt is varied due to the load fluctuation of the cleaning board. Is no longer fluctuated.

Further, an electric field is applied when the toner image on the photosensitive member is transferred to the sheet, so that the photosensitive member, the sheet, and the transport belt are in a state of being attracted to each other. Here, if the moving speed of the surface of the photoconductor and the moving speed of the conveyor belt (= moving speed of the paper) completely match, no frictional force is generated between the photoconductor and the conveyor belt due to the speed difference. Actually, there are variations in the diameter of the photoconductor, variations in the outer shape of the conveyance belt driving roller, and uneven rotation of the drive unit that drives the photoconductor and the conveyance belt. It is difficult to match.

In the case where the speed of the photosensitive member surface becomes faster or slower than the moving speed of the conveyor belt due to the uneven rotation, the frictional force between the conveyor belt and the photosensitive member surface is caused by the driving roller It acts alternately in the direction of pulling and the direction of loosening with respect to the side, resulting in an unstable movement speed of the transport belt. Further, in the case where the speed of the photosensitive member surface is slower than the moving speed of the transfer belt, the frictional force between the transfer belt and the photosensitive member surface acts in a direction to loosen the transfer belt with respect to the drive roller side. The result is that the rollers are pulled and the position of the conveyor belt becomes unstable.

On the other hand, in the case where the speed of the photosensitive member surface is higher than the moving speed of the transfer belt, the frictional force between the transfer belt and the photosensitive member surface acts in a direction in which the transfer belt is constantly pulled toward the drive roller side. Therefore, the moving speed of the transport belt is stabilized. The friction between the conveyor belt and the photoreceptor surface that occurs here is kinetic friction, and is substantially constant regardless of whether the difference between the moving speed of the conveyor belt and the speed of the photoreceptor surface is large or small, and is stable. .

For the above reasons, by increasing the moving speed of the surface of the photosensitive member rather than the moving speed of the conveying belt, the moving speed and elongation of the conveying belt are kept constant, and the conveying force is caused by the frictional force between the photosensitive member and the paper. Eliminate the slack of the belt,
It is possible to prevent misalignment between the superimposed color images.

The rate at which the speed of the photosensitive member surface is increased with respect to the moving speed of the conveying belt is such that the moving speed of the conveying belt and the speed of the photosensitive member surface fluctuate periodically due to uneven rotation and eccentricity of the shaft. In this case, even when the conveying belt has the maximum speed and the photosensitive member surface has the minimum speed, the speed of the photosensitive member surface needs to be higher than the moving speed of the conveying belt. That is, it is necessary that the average speed of the surface of the photosensitive member is higher than the moving speed of the conveyor belt.

On the other hand, if the difference between the moving speed of the conveyor belt and the speed of the photosensitive member surface is too large, image blurring occurs, and strictly depends on the width of the contact width between the photosensitive member and paper. However, according to experiments, usually, the difference in the speed of the photosensitive member surface with respect to the moving speed of the conveyor belt is 0 to 3%, which is a range in which image blur does not occur. Therefore, the appropriate range of the difference between the speed of the photosensitive member surface and the moving speed of the conveyor belt is 0 to 3%.

FIG. 1 shows an embodiment of the present invention. This embodiment is an embodiment of the invention according to claims 1 to 3, and FIG.
1 has the same configuration as that of the conventional tandem type color electrophotographic apparatus, and the same portions are denoted by the same reference numerals and description thereof is omitted. In this embodiment, the difference from the conventional tandem-type color electrophotographic apparatus shown in FIG. 2 will be described. In driving the conveyor belt 2, the driving roller 11 is driven by a plurality of photoconductors 10Y, 10M, 10C, 10K on the Y,
Of the M, C, and K toner images, the first color Y toner image (the toner image that is first transferred to the sheet) is located upstream of the position in which the transfer belt 2 moves in the moving direction of the transport belt 2. Driven roller 1 for applying tension to the conveyor belt 2
Reference numeral 2 transfers the K toner image of the final color (the toner image to be finally transferred to the paper) among the toner images of the Y, M, C, and K colors on the plurality of photoconductors 10Y, 10M, 10C, and 10K to the paper. It is arranged downstream from the position with respect to the moving direction of the conveyor belt.

Further, the transport belt 2 is attached to the driven roller 12.
A pressure spring 15 is provided as a tension mechanism for applying tension to the driven roller 12, and the driven roller 12 is moved by the pressure spring 15 as shown in FIG.
At the left side (in the direction of increasing the tension of the conveyor belt 2)
Press. Therefore, the cleaning blade 9a for cleaning the transport belt 2 is provided in a section where the transport belt 2 moves from the driven roller 12 to the drive roller 11.

With this configuration, the frictional force generated between the cleaning blade 9a and the transport belt 2 acts as tension only between the cleaning blade 9a and the drive roller 11, and the toner image is transferred within the range (drive range). (Range from the roller 11 to the cleaning blade 9a) is not affected by the fluctuation of the frictional force between the cleaning blade 9a and the conveyor belt 2. Further, the tension of the transport belt 2 in this range is controlled by the pressing force of the pressure spring 15 and has little fluctuation. Therefore, the amount of elongation of the transport belt 2 is constant and stable, and the image shift between the colors can be kept small.

The drive roller 11 is driven to rotate in the direction of arrow A by the drive source 14, and the conveyor belt 2 moves in the direction of arrow B, and the photosensitive members 10Y, 10M, 10C, and 10K.
Is rotated in the direction of arrow C, and the moving speed b of the conveyor belt 2 and the moving speed (peripheral speed) c of the surfaces of the photoconductors 10Y, 10M, 10C, and 10K are set to be c> b. Thereby, the frictional force generated between the photoconductors 10Y, 10M, 10C, and 10K and the sheet acts to pull the conveyor belt 2 leftward in FIG. And the displacement of the conveyor belt 2 is reduced. As a result, it is possible to keep the displacement of the image small.

The plurality of photoconductors 10Y, 10M, 10
At the position where the toner images of the respective colors are transferred from C and 10K to the sheet, a plurality of photoconductors 1
0Y, 10M, 10C, 10K The moving speed of the surface is
% To 3% larger. Thereby, the photoconductor 10
The difference between the peripheral speeds of Y, 10M, 10C, and 10K and the moving speed of the conveyor belt 2 is too large to prevent the image from being blurred.

In this embodiment, as compared with the conventional tandem type color electrophotographic apparatus shown in FIG.
By performing image transfer on the slack side of, it may be seemingly unstable, but the tension of the conveyor belt 2 can be sufficiently controlled by the strength of the pressure spring 15, and the unstable Absent.

According to this embodiment, with the above-described configuration, even if the frictional force between the transport belt 2 and the cleaning blade 9a changes depending on the amount of the residual toner on the transport belt 2, The tension applied to the conveyor belt 2 changes only in the portion between the cleaning blade 9a and the drive roller 11, and the K image of the final color is transferred to the sheet from the position where the Y image of the first color is transferred to the sheet. Between the positions, the tension of the conveyor belt 2 is
2 and there is no change. Therefore, the elongation of the conveyor belt 2 also becomes a constant value and does not fluctuate, and it is possible to prevent image displacement. Further, the transport belt 2 is not loosened due to the frictional force between the photoconductors 10Y, 10M, 10C, and 10K and the sheet, so that image misalignment can be prevented. Further, it is possible to prevent the image from being blurred due to the difference between the peripheral speed of the photoconductors 10Y, 10M, 10C, and 10K and the moving speed of the conveyor belt 2 being too large.

The present invention is not limited to the above-described embodiment. For example, the photosensitive member may be a belt-like member, and two or three colors may be transferred from the photosensitive member to the paper on the conveying belt. The present invention can be similarly applied to an electrophotographic apparatus in which toner images are sequentially superimposed and transferred.

[0039]

As described above, according to the first aspect of the present invention, even if the frictional force between the transport belt and the cleaning member changes depending on the amount of the residual toner on the transport belt, the transport belt is not affected. This tension changes only in the portion between the cleaning member and the drive roller,
At the position where the image is transferred from the photoreceptor to the paper, the tension of the transport belt is only the tension generated by the driven roller and does not change. Therefore, the elongation of the transport belt does not fluctuate as a constant value, and the displacement of the image can be prevented.

According to the second aspect of the present invention, the conveyance belt does not become loose due to the frictional force between the photosensitive member and the sheet, and the displacement of the image can be prevented.

According to the third aspect of the invention, it is possible to prevent the image from being blurred due to the difference between the peripheral speed of the photosensitive member and the moving speed of the conveyor belt being too large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

FIG. 2 is a schematic view showing an example of a conventional tandem type color electrophotographic apparatus.

[Explanation of symbols]

 1Y, 1M, 1C, 1K Image forming unit 9a Cleaning blade 10Y, 10M, 10C, 10K Photoconductor 11 Drive roller 12 Follower roller 15 Pressure spring

Claims (3)

[Claims] A plurality of photoconductors are opposed to a conveyance belt for conveying a sheet, toner images of respective colors are formed on the plurality of photoconductors, and the toner images of respective colors on the plurality of photoconductors are formed. In an electrophotographic apparatus for sequentially transferring images onto a sheet conveyed by a conveyance belt, a driving roller for rotating the conveyance belt is provided with a toner of a first color among toner images of respective colors on the plurality of photoconductors. A driven roller for arranging a tension on the transport belt is disposed on the upstream side in a moving direction of the transport belt from a position at which the image is transferred to a sheet, and a driven roller among the toner images of each color on the plurality of photoconductors is provided. And a cleaning member for cleaning the transport belt is disposed downstream of the position where the final color toner image is transferred to the sheet in the moving direction of the transport belt. Electrophotographic apparatus, characterized in that provided in the section which moves the drive roller. 2. The electrophotographic apparatus according to claim 1, wherein the moving speed of the surface of the plurality of photosensitive members relative to the moving speed of the transport belt at a position where the toner images of each color are transferred from the plurality of photosensitive members to a sheet. An electrophotographic apparatus characterized in that the value of (1) is set larger. 3. The moving speed of the surface of the plurality of photoconductors with respect to the moving speed of the transport belt at a position where a toner image of each color is transferred from the plurality of photoconductors to a sheet of paper. An electrophotographic apparatus characterized in that 0% to 3% is set to be larger.