JP2007316218A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed so that the ability to convey transfer paper is stable and abnormal images and wrinkles in transfer paper are prevented by precisely disposing an intermediate transfer belt and members for conveying transfer paper. <P>SOLUTION: The image forming apparatus has an intermediate transfer belt unit 10. The unit 10 includes: a secondary transfer counter roller 7 located opposite to or downstream of a secondary transfer roller 6 that transfers a toner image on the intermediate transfer belt 11 to the transfer paper P; and a follower roller 9 located upstream of the secondary transfer counter roller 7. The follower roller 9 is not positioned by the intermediate transfer belt unit 10 but positioned by the main body of the image forming apparatus together with the secondary transfer counter roller 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, an LED printer, and a facsimile machine having an intermediate transfer belt unit stretched over a plurality of rollers.

Today, in an image forming apparatus, it is necessary to convey transfer paper at a high speed due to an increase in output speed, and therefore, belt units having high running stability are increasing. Further, due to an increase in demand for full-color output, a tandem type color image forming apparatus that can obtain an output speed comparable to that of a monochrome image has attracted attention, and a belt unit is also used as the image forming unit.
The belts of these belt units deteriorate with time, and in particular, a transfer belt or the like that affects image formation deteriorates the image quality due to belt deterioration. Therefore, it is necessary to replace the belt unit every time it is used.
The conventional belt unit uses a rigid frame such as sheet metal front and rear side plates and aluminum extruded stays, and belt replacement has been performed by users and service personnel with specialized knowledge.
However, since the number of image forming apparatuses that replace the belt unit with the current belt unit is increased so that even a general user can easily replace the belt unit, a resin frame is increasingly used to reduce the weight of the belt unit and reduce the cost. Further, since the thickness of the belt unit is reduced due to downsizing of the belt unit and layout restrictions, the rigidity of the belt unit is likely to be lowered.

Since the intermediate transfer belt unit is a resin frame, its rigidity is weak, it is deformed by bending, etc., the positional relationship between the intermediate transfer belt and the secondary transfer roller is shifted, and the parallelism and left / right magnification error are distorted. An image, an image with a different density difference between right and left, or the like is output, or the transfer paper does not stably enter the fixing device, causing problems such as wrinkles.
In the transfer unit in the belt-type photosensitive unit, a primary transfer roller is disposed at a position facing the belt-type photosensitive unit with the intermediate transfer belt interposed therebetween. Further, a guide member and a tension roller, which are pressing members, are arranged upstream of the secondary transfer roller.
Thus, when the tension roller for applying tension to the intermediate transfer belt is disposed upstream of the secondary transfer counter roller, the pressing member for stabilizing the position of the transfer nip or the intermediate transfer belt between the two rollers. May have been added.

However, in such a configuration, the intermediate transfer belt and the transfer material are likely to be misaligned due to twisting of the unit, etc., so that the parallelism and the left / right magnification error are out of order, or the difference in density between the left and right And the like, and the transfer material does not enter the fixing portion stably, and thus wrinkles occur.
As a means for solving this problem, there is a means for receiving and positioning the secondary transfer roller by the intermediate transfer belt unit. However, the positional relationship with a roller attached to another main body such as a registration roller is not improved. There is also a problem that transportability is not stable.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to form an image which prevents the occurrence of abnormal images and wrinkles of transfer paper by arranging the intermediate transfer belt and a member for transferring the transfer paper with high accuracy to stabilize the transfer of the transfer paper. To provide an apparatus.

In order to solve the above-mentioned problems, the invention according to claim 1 is an image forming apparatus having an intermediate transfer belt unit, wherein the intermediate transfer belt unit transfers a toner image on the intermediate transfer belt to transfer paper. A secondary transfer counter roller positioned opposite to or downstream of the secondary transfer roller, and a driven roller positioned upstream of the secondary transfer counter roller; the driven roller is not positioned in the intermediate transfer belt unit; The image forming apparatus is positioned by the main body of the image forming apparatus together with the secondary transfer counter roller.
According to a second aspect of the present invention, the secondary transfer counter roller positioned opposite or downstream of the secondary transfer roller is a driving roller that rotates the intermediate transfer belt by obtaining a driving force from the main body. Item 5. An image forming apparatus according to Item 1.
According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the rotational speed of the driven roller is detected.
According to a fourth aspect of the present invention, when the pressing member for optimally maintaining the position of the intermediate transfer belt with respect to the transfer paper is located upstream of the secondary transfer counter roller, the secondary transfer roller The image forming apparatus according to claim 1, wherein both of the pressing members are positioned on the main body.
The invention according to claim 5 is any one of claims 1 to 4, wherein the three components of the secondary transfer counter roller, the driven roller upstream thereof, and the secondary transfer roller are positioned by a single positioning member. The image forming apparatus described in item 1 is characterized.

The invention according to claim 6 is characterized in that the pressing member is attached to the positioning member.
The invention according to claim 7 is the image forming apparatus according to claim 5 or 6, wherein when the intermediate transfer belt unit is attached to and detached from the main body, the secondary transfer roller held by the positioning member can be attached and detached together. Features.
The invention according to claim 8 is characterized in that the urging means for urging the secondary transfer roller is released by opening and closing the main body cover.
The invention according to claim 9 is an intermediate transfer unit of a tandem type in which the intermediate transfer belt unit superimposes images of continuous image carriers on the intermediate transfer belt and transfers them onto transfer paper. The image forming apparatus according to any one of 1 to 8, is characterized.

  According to the present invention, since the intermediate transfer belt and the member that conveys the transfer paper are arranged with high accuracy, the transferability of the transfer paper is stabilized, and the occurrence of abnormal images and wrinkles of the transfer material can be prevented. it can.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of a color copying machine as an image forming apparatus. In FIG. 1, a process for obtaining a color image will be described first.
The color copying machine 1 includes a transfer belt unit 10 having an intermediate transfer belt 11 and four image stations. Each image station has 15Y, 15C, 15M, and 15Bk as image carriers (hereinafter referred to as photosensitive drums). is doing. The intermediate transfer belt 11 is stretched around the driving roller 7, the tension roller 8, and the driven rollers 9 and 13.
Around the photosensitive drums 15Y, 15C, 15M, and 15Bk, there are dedicated charging devices 16Y, 16C, 16M, and 16Bk, developing devices 14Y, 14C, 14M, and 14Bk, and cleaning devices 17Y, 17C, 17M, and 17Bk, respectively. Yes. The developing devices 14Y, 14C, 14M, and 14Bk are supplied with yellow (Y), cyan (C), magenta (M), and black (Bk) toners by a predetermined supply amount for each color.
When the transfer paper P is fed from the paper feed cassette 2 by the paper feed roller 3 and the leading edge of the transfer paper P reaches the registration roller pair 5 through the transport roller pair 4, it is detected by a sensor (not shown). The transfer paper P is conveyed to the nip portion between the secondary transfer roller 6 and the intermediate transfer belt 11 by the registration roller pair 5.

The photosensitive drums 15Y, 15C, 15M, and 15Bk uniformly pre-charged by the charging devices 16Y, 16C, 16M, and 16Bk are exposed by laser beams 18Y, 18C, 18M, and 18Bk from an optical writing device (not shown). As a result of scanning, electrostatic latent images are formed on the photosensitive drums 15Y, 15C, 15M, and 15Bk.
The electrostatic latent images are developed by the developing devices 14Y, 14C, 14M, and 14Bk for the respective colors, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 15Y, 15C, 15M, and 15Bk. Next, a voltage is applied to the primary transfer rollers 12Y, 12C, 12M, and 12Bk, and the toner on the photosensitive drums 15Y, 15C, 15M, and 15Bk is sequentially transferred onto the intermediate transfer belt 11.
At this time, the image forming operation for each color is executed while shifting the timing from the upstream side to the downstream side so that the toner image is transferred to the same position on the intermediate transfer belt 11. The image formed on the intermediate transfer belt 11 is conveyed to the position of the secondary transfer roller 6 and is secondarily transferred to the transfer paper P.
The transfer paper P on which the toner images of the respective colors are transferred is conveyed to the fixing device 19 and thermally fixed, and is discharged through the paper discharge roller 20. The residual toner on the photosensitive drums 15Y, 15C, 15M, and 15Bk is cleaned by the respective cleaning devices 17Y, 17C, 17M, and 17Bk.
Thereafter, the charging devices 16Y, 16C, 16M, and 16Bk in which the bias of the alternating current component is applied to the direct current are charged at the same time as the charge removal to prepare for the next image formation. The residual toner on the intermediate transfer belt 11 is cleaned by the intermediate transfer belt cleaning device 21 to prepare for the next image forming process.

FIG. 2 is a schematic view showing an intermediate transfer unit in the belt type photoreceptor unit. In FIG. 2, a primary transfer roller 29 is disposed at a position facing the belt-type photosensitive unit 30 with the intermediate transfer belt 21 interposed therebetween.
The intermediate transfer belt 21 is stretched between a driving roller 22 and a belt cleaning unit facing roller 23 facing the belt cleaning unit 24 and a secondary transfer facing roller 26. A transfer inlet guide member 28 and a tension roller 27 that are pressing members are disposed upstream of the secondary transfer roller 25.
As described above, when the tension roller 27 for applying tension to the intermediate transfer belt 21 is disposed upstream of the secondary transfer counter roller 26, the position of the transfer nip or the intermediate transfer belt 21 is stabilized between the two rollers. The pressing member 28 may be added.

FIG. 3 is a schematic plan view showing the positional relationship between the intermediate transfer belt and the front and rear side plates of the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a side view showing the front plate of FIG.
1, 3, and 4, the intermediate transfer belt unit 10 includes a drive roller 7 that drives the intermediate transfer belt 11 and serves as a reference for the intermediate transfer belt unit 10, a tension roller 8 that applies tension to the intermediate transfer belt 11, The driven rollers 9 and 13 are included.
The intermediate transfer belt unit 10 also includes a primary transfer roller 12 that transfers an image on the photoconductor 15 onto the intermediate transfer belt 11, a slave reference shaft 31 that is a slave reference of the intermediate transfer belt unit 10, the above-described components and the like. It comprises a front plate 32 and a rear plate 33 that hold the subunits. The image on the intermediate transfer belt 11 is transferred onto the transfer paper P by the secondary transfer roller 6.
The driven roller (transfer entrance roller) 9 is not completely positioned by the front side plate 32 and the rear side plate 33, and is free in the holding portion (holding hole) 34 of the front side plate 32, and the image forming apparatus main body. When mounted on the main body, the driving roller 7 and the entrance roller 9 are positioned on the main body front side plate (or face plate) and the main body rear side plate (not shown). The secondary reference shaft 31 is also held by the main body.
As shown in FIGS. 1, 3, and 4, the secondary transfer counter roller 7 is a driving roller. A secondary transfer counter roller 7 positioned opposite or downstream of the secondary transfer roller 6 is a driving roller that rotates the intermediate transfer belt 11 by obtaining a driving force from the main body.
By using the driving roller 7 as a roller disposed opposite or downstream of the secondary transfer roller 6 (FIG. 1), the transfer paper P is not conveyed due to expansion / contraction of the intermediate transfer belt 11 or displacement of the roller and the intermediate transfer belt. It is possible to reduce the stabilization, and the transfer paper P can be transported stably.

FIG. 5 is a schematic plan view showing the positional relationship between the intermediate transfer belt and the front and rear plates of the second embodiment of the image forming apparatus according to the present invention. In FIG. 5, an encoder disk 36 with a slit is attached on the axis of the transfer entrance roller 9, and the rotation speed of the encoder disk 36 with the slit is detected by a sensor 37 attached to the front side plate 32. The rotational speed is fed back to a drive motor (not shown).
In this way, by detecting the rotational speed of the driven roller 9 located immediately downstream of the drive roller 7 and feeding it back to the travel of the drive roller 9, the color shift and position of the image due to the expansion and contraction of the intermediate transfer belt 11. The influence on the deviation can be reduced.
In the example of the belt-type photosensitive unit shown in FIG. 2, a pressing member (transfer entrance guide member) 28 is provided downstream of the driving roller 22. If the positional relationship between the transfer entrance guide plate 28 and each roller is deviated, the transfer paper conveyance becomes unstable, so that an image in which the parallelism and the left / right magnification error are distorted easily occurs.

In the conventional means, when the transfer inlet guide plate 28 is attached to the intermediate transfer belt unit side, the positional accuracy with the roller in the intermediate transfer belt unit is obtained, but the positional accuracy with the roller on the main body side is difficult to obtain. If the transfer inlet guide plate 28 is attached to the main body, the opposite is true, and in either case, the transfer paper is misaligned.
In the present invention, the pressing member 28 is not positioned in the intermediate transfer belt unit like the transfer entrance roller 9 in FIG. 4, but is positioned together with the driving roller 7 by the image forming apparatus main body.
Since the positional accuracy of the secondary transfer counter roller 7, the upstream driven roller (transfer entrance roller) 9, and the three rollers of the secondary transfer roller 6 can be increased, the transportability of the transfer paper is stabilized. It is possible to prevent the occurrence of abnormal images and wrinkles on transfer paper.

FIG. 6 is a schematic view showing a positioning plate fixed to the main body rear side plate. 5 and 6, a positioning plate 38 is fixed to a main body rear side plate (not shown), and the driving roller 7 is held by the reference hole 39 and the inlet roller 9 is held by the reference hole 40.
The secondary transfer roller 6 is regulated by a guide-shaped portion 41 and pressed against the intermediate transfer belt 11 by an urging member (not shown). The main body front side plate (or face plate) not shown also has a positioning plate that is symmetrical to the positioning plate 38.
According to the above configuration, the secondary transfer roller 6, the secondary transfer counter roller 7, and the driven roller 9 upstream thereof can be positioned with higher accuracy. Can be small.

FIG. 7 is a schematic view showing a modification of the positioning plate fixed to the main body rear side plate of FIG. FIG. 8 is a side view showing another example of the front side plate of FIG. With reference to FIGS. 5, 7, and 8, the positioning plate 38 ′ holds the driving roller 7 in the reference hole 39 and holds the inlet roller 9 in the reference hole 40.
The secondary transfer roller 6 is regulated by a guide-shaped portion 41 so that the positioning plate 38 ′ cannot be removed by a stopper 42 protruding from both inner walls. The positioning plate 38 ′ is attached to the rear plate 33 side of the intermediate transfer belt unit, and a symmetrical positioning plate is attached to the front plate 32 side (FIG. 8). The shaft of the driving roller 7, the shaft of the entrance roller 9, and the slave reference shaft 31 protruding from the positioning plate 38 ′ are positioned on the main body.
Since the intermediate transfer belt unit 10 and the secondary transfer roller 6 are integrated, it is difficult to remove the transfer paper sandwiched between the jams. However, since the bias of the secondary transfer roller 6 is released by opening and closing the cover of the image forming apparatus main body (not shown), the transfer paper between the intermediate transfer belt 11 and the secondary transfer roller 6 can be easily removed. Can do. That is, the urging means for urging the secondary transfer roller is configured to be released by opening and closing the main body cover.
Further, since the intermediate transfer belt unit and the secondary transfer roller 6 are detached as a unit, the replacement work is facilitated. Further, according to the present invention, the above-described means improves the color misregistration and positional misalignment of the image forming apparatus employing the tandem intermediate transfer belt unit and the image forming apparatus employing the one-drum intermediate transfer belt unit. Can do.

1 is a schematic diagram illustrating an overall configuration of a color copying machine that is an image forming apparatus. FIG. 2 is a schematic diagram illustrating an intermediate transfer unit in a belt-type photosensitive unit. 1 is a schematic plan view showing a positional relationship between an intermediate transfer belt and front and rear side plates of a first embodiment of an image forming apparatus according to the present invention. It is a side view which shows the front side board of FIG. FIG. 6 is a schematic plan view showing a positional relationship between an intermediate transfer belt and front and rear side plates of a second embodiment of an image forming apparatus according to the present invention. It is the schematic which shows the positioning board fixed to a main body rear side board. It is the schematic which shows the modification of the positioning plate fixed to the main body rear side board of FIG. It is a side view which shows the other example of the front side board of FIG.

Explanation of symbols

1 Image forming device (color copier)
6 Secondary transfer roller 7 Secondary transfer counter roller (drive roller)
9 Driven roller (transfer entrance roller)
DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt unit 11 Intermediate transfer belt 14 Developing device 15 Image carrier (photosensitive drum)
28 Pressing member (transfer inlet guide member)
31 Subordinate shaft 32 Front side plate 33 Rear side plate 36 Encoder disk 37 Sensor 38 Positioning plate 38 'Positioning plate P Transfer paper

Claims (9)

  In the image forming apparatus having an intermediate transfer belt unit, the intermediate transfer belt unit includes an intermediate transfer belt, a secondary transfer roller that transfers a toner image on the intermediate transfer belt to transfer paper, and the secondary transfer roller. Or a secondary transfer counter roller positioned downstream and a driven roller positioned upstream of the secondary transfer counter roller. The driven roller is not positioned in the intermediate transfer belt unit, and the secondary transfer counter roller is positioned. An image forming apparatus characterized by being positioned by a main body of the image forming apparatus together with a counter roller.   The image forming apparatus according to claim 1, wherein the secondary transfer counter roller is a driving roller that rotates the intermediate transfer belt by obtaining a driving force from the image forming apparatus main body.   The image forming apparatus according to claim 1, further comprising a configuration for detecting a rotation speed of the driven roller.   When there is a pressing member for optimally maintaining the position of the intermediate transfer belt with respect to the transfer paper upstream of the secondary transfer counter roller, both the secondary transfer roller and the pressing member are the main body of the image forming apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is positioned at the position.   5. The image forming apparatus according to claim 1, wherein the secondary transfer opposing roller, the driven roller upstream thereof, and the secondary transfer roller are positioned by a single positioning member. .   The image forming apparatus according to claim 5, wherein the pressing member is attached to the positioning member.   7. The structure according to claim 5 or 6, wherein when the intermediate transfer belt unit is attached to or detached from the main body of the image forming apparatus, the secondary transfer roller held by the positioning member can be attached and detached together. Image forming apparatus.   8. The image forming apparatus according to claim 7, wherein the biasing means for biasing the secondary transfer roller is released by opening and closing the main body cover.   9. The intermediate transfer belt unit according to claim 1, wherein the intermediate transfer belt unit is a tandem type intermediate transfer unit that superimposes images on a plurality of image carriers on the intermediate transfer belt and transfers the images onto a transfer sheet. The image forming apparatus according to claim 1.

Images