JPH04362677A - Image forming device - Google Patents

Abstract

PURPOSE:To surely transfer a form a transfer part to a fixing part and to prevent the occurrence of winkles by disposing a transfer device so as to be adjacent to, at least, one supporting roller of a belt photosensitive body rotating supported between two supporting rollers, and adopting a constitution so that the diameter of the supporting roller in the vicinity of the transfer device is different on the central part and the end part in a longitudinal direction. CONSTITUTION:The form P is subjected to the transfer of toner on the down surface, then, separate from the belt photosensitive body and carried to the downstream side. However, the supporting roller 18 in the vicinity of the transfer device supporting the belt photosensitive body is in a convex crown shape, so that the form P has firmness via the belt photosensitive body, and simultaneously, is surely separated. Further, the form P having the firmness is carried to a fixing device 11 along an exit side guide 10. But, the exit side guide 10 is flat, so that the leading edge side of the form P having in contact with the exit side guide 10 is along a flat shape. Therefore, the form P reasonably and flatly enters the fixing nip of the fixing device 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus in which an image is formed on the bottom surface of a sheet of paper and the image is conveyed to a fixing device.

0002

2. Description of the Related Art A laser printer, which is an electrophotographic image forming apparatus, uses a drum photoreceptor 2 as a latent image carrier charged by a charging device 1, as shown in an example in FIG.
is irradiated with light from the optical device 3 to form an electrostatic latent image,
A toner is brought into contact with the electrostatic latent image by the developing device 4 to form a visible image, and the paper P fed from the paper feed cassette 5 by the paper feed roller 6 via the entrance guide 7 is placed on the visible image. are overlapped at the right timing by the registration rollers 8, the toner is transferred to the bottom surface of the paper P by the transfer device 9, the paper P after the toner transfer is separated from the drum photoreceptor 2, and then heated by the exit guide 10. The paper P is guided to a roller-type fixing device 11 to fix the toner, and is ejected onto a paper ejection tray 13 through a paper ejection roller 12.
The residual toner on the drum photoreceptor 2 after separation is removed by a cleaning device 14 having a cleaning blade, and the residual charge on the drum photoreceptor 2 is removed by a static eliminator 15.
(Japanese Unexamined Patent Publication No. 2-291350).

Furthermore, in the above laser printer,
In order to convey the toner image formed on the bottom surface of the paper P from the transfer unit to the fixing unit, the output side guide 10 is recessed upward in a direction perpendicular to the conveyance direction of the paper P. By aligning the paper P along the guide 10, the paper P
The user is allowed to enter the fixing device 11 while sitting down.

0004

However, in the case of the laser printer described above, the guide 10 on the exit side of the drum photoreceptor 2
Since this method uses a concave shape formed in the paper to give the paper P a stiffness, it is possible to prevent the paper P from sagging in front of the fixing device 11. cannot be obtained, and as a result, the paper P
There is a problem in that wrinkles are likely to occur.

On the other hand, there is a conventional method in which a suction device is used to suction the paper from above while guiding and transporting the paper.
In the case of this method, there is a problem that the structure becomes complicated and the cost increases.

[0006] Therefore, the present invention has been devised to make it possible to reliably transport paper on which a toner image is formed on the bottom surface from the transfer section to the fixing section without using a suction device, and to prevent wrinkles from forming on the paper. This is what I am trying to do.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention transfers a toner image formed on the surface of a latent image carrier to the lower surface of a sheet of paper using a transfer device, and then transfers the sheet of paper to a fixing device. In an electrophotographic image forming apparatus configured to be conveyed, at least two latent image carriers are used as the latent image carrier.
A belt photoreceptor rotatably supported between book support rollers is used, a transfer device is placed close to one of the support rollers, and the support roller close to the transfer device is placed between the central and end portions in the longitudinal direction. The configuration has a shape with a diameter difference.

Further, the transfer device may be an elastic roller type transfer device, and the transfer device may be arranged in pressure contact with the belt photoreceptor.

Furthermore, in an electrophotographic image forming apparatus, the toner image formed on the surface of the latent image carrier is transferred to the lower surface of the sheet by a transfer device, and then the sheet is conveyed to the fixing device. A belt photoreceptor rotatably supported between at least two support rollers is used as a latent image carrier, and an elastic roller is used as a transfer device, and the elastic roller has a diameter at the center and end portions in the longitudinal direction. The belt may have a different shape and be pressed against the belt photoreceptor.

0010

[Function] Since the diameter of the transfer device proximal support roller is different between the center and the end in the longitudinal direction, when the paper passes through this roller, it is stiffened and separated reliably, improving conveyance. It will be done.

[0011] Furthermore, if the transfer device is an elastic roller type,
The adhesion of the paper to the belt photoreceptor is improved, and transfer is performed more reliably.

Furthermore, by making the diameter of the elastic roller different between the center and the end in the longitudinal direction, even if the transfer device proximal support roller is a straight type, it is possible to stiffen the paper and transfer is performed reliably.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show an embodiment of the present invention,
Similar to the laser printer shown in FIG. 6, in an image forming apparatus configured to convey an image while forming and holding an image on the lower surface of a sheet P, an endless belt photoreceptor 16 is used as a latent image carrier, and the belt photoreceptor 16 is used as a latent image carrier. The body 16 is rotatably supported in the counterclockwise direction in FIG. 1 between two support rollers 17 and 18, which are a drive roller and an idle roller, and
The developing device 9 is disposed close to one of the support rollers 18, and the diameter of the center portion in the longitudinal direction of the developing device proximal support roller 18 is 0.4 to 1 mm larger than the diameter of the end portions. It has a convex crown shape (drum shape), and further,
An exit guide 10 for guiding the paper P after the image transfer to the fixing device 11 has a flat shape in a direction perpendicular to the paper conveyance direction. Reference numeral 19 denotes a belt stopper member attached to the width end of the back side of the belt photoreceptor 16, and reference numeral 20 denotes a backing material placed on the back side of the belt photoreceptor 16 in correspondence with the blade of the cleaning device 14. Note that in Figure 1, Figure 6
The same reference numerals indicate the same parts.

The paper P fed from the paper feed cassette 5 and superimposed on the belt photoreceptor 2 with the timing set by the registration roller 8 is transferred from the belt photoreceptor 2 after the toner is transferred to the lower surface by the transfer device 9. The paper P is separated and conveyed downstream, but at this time, since the transfer device proximity support roller 18 that supports the belt photoreceptor 2 has a convex crown shape, the paper P passes through the belt photoreceptor 2 and becomes stiff. and ensure separation. Further, the stiffened paper P is guided along the exit guide 10 and transferred to the fixing device 11.
At this time, since the output side guide 10 has a flat shape, the leading edge side of the paper P that contacts the output side guide 10 is aligned with the flat shape. P is allowed to enter the fixing nip of the fixing device 11 in a flat plane without any force. Therefore, the paper P is prevented from being wrinkled as in the case where the paper P is forced to enter the fixing nip in a piled state, as in the past.

FIG. 3 shows another embodiment of the present invention.
In a configuration similar to that of the embodiment shown in FIG. (state).

The embodiment shown in FIG. 3 also provides the same effects as the embodiment shown in FIG.

Next, FIG. 4 shows still another embodiment of the present invention. That is, in the above embodiment, a corona discharge type was used as the transfer device 9, but in this embodiment, the transfer device 9 is provided with a rubber layer 9b around the outer periphery of a metal shaft 9a, and This uses an elastic roller system in which a voltage is applied to 9a.

In the embodiment shown in FIG. 4, since the rubber layer 9b is pressed against the surface of the belt photoreceptor 16, the adhesion of the paper P is improved compared to the above embodiments. As a result, image transfer can be performed more reliably, and image unevenness can be prevented. Although FIG. 4 shows a convex crown-shaped transfer device proximal support roller 18, it may also have a concave crown shape.

FIG. 5 shows still another embodiment of the present invention, in which an elastic roller type transfer device 9 is placed in pressure contact with the surface of the belt photoreceptor 2, similar to the embodiment shown in FIG. In the configuration, the rubber layer 9b constituting the transfer device 9 has a convex crown shape (or concave crown shape) with a diameter difference of 0.4 to 1 mm between the center and end portions in the longitudinal direction, and is located close to the transfer device. The support roller 18 has a straight shape, and is further arranged so that the center of the roller of the transfer device 9 is shifted upstream by an appropriate distance l from the center of the transfer device proximal support roller 18.

In the case of the embodiment shown in FIG.
is shifted upstream with respect to the transfer device proximal support roller 18, so that the belt photoreceptor 2 can be deformed into a concave (or convex) shape by pressing the transfer device 9 into contact with it, thereby changing the shape of the belt photoreceptor 2. Since the paper P can be made to follow the paper P, it is possible to ensure the transfer and the reliable conveyance by stiffening the paper P, as in the case of the embodiment shown in FIG.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, the number of support rollers for wrapping the belt photoreceptor 2 may be three or more; Of course, various changes can be made within the scope.

[0022]

As described above, according to the image forming apparatus of the present invention, the transfer device is disposed close to one support roller of the belt photoreceptor rotatably supported between at least two support rollers. Since the diameter of the transfer device proximal support roller is configured to be different at the longitudinal center and at the ends, it is possible to bend the paper in the width direction through deformation of the belt photoreceptor. Not only can separation from the photoreceptor be ensured, but the paper can also be stiffened, and can be reliably transported to the fixing device without using a suction device, thereby preventing the occurrence of fixation wrinkles. I can do it,
This is particularly advantageous in the case of devices of the top transport type.

Furthermore, by using an elastic roller type transfer device and placing it in pressure contact with the belt photoreceptor, transfer can be performed more reliably and image unevenness can be prevented.

Furthermore, the shape of the transfer device proximal support roller can be changed by using an elastic roller type for the transfer device and placing it in pressure contact with the belt photoreceptor with a difference in diameter between the center portion in the longitudinal direction and the width end portion. It is possible to ensure the transfer and the stiffness of the paper and ensure the transportability without causing any problems.

[Brief explanation of drawings]

FIG. 1 is an overall schematic diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an enlarged sectional view of a support roller section showing the main part of FIG. 1;

FIG. 3 is an enlarged sectional view of a support roller section showing another embodiment of the present invention.

FIG. 4 shows still another embodiment of the present invention, (A)
(B) is an enlarged sectional view of the support roller portion, and (B) is a schematic side view.

FIG. 5 shows still another embodiment of the present invention, (A)
(B) is an enlarged sectional view of the support roller portion, and (B) is a schematic side view.

FIG. 6 is a schematic diagram of a laser printer that is an example of an image forming apparatus.

[Explanation of symbols]

9 Transfer device 11 Fixing device 16 Belt photoreceptor (latent image carrier) P Paper

Claims (3)

[Claims] 1. An electrophotographic image forming apparatus in which a toner image formed on the surface of a latent image carrier is transferred to the lower surface of a sheet of paper by a transfer device and then the sheet of paper is conveyed to a fixing device. A belt photoreceptor rotatably supported between at least two support rollers is used as a latent image carrier, a transfer device is disposed close to one of the support rollers, and the transfer device proximal support roller is An image forming apparatus characterized by having a configuration having a diameter difference between a central portion and an end portion in a direction. 2. The image forming apparatus according to claim 1, wherein the transfer device is an elastic roller type transfer device, and the transfer device is arranged in pressure contact with the belt photoreceptor. 3. In an electrophotographic image forming apparatus, the toner image formed on the surface of the latent image carrier is transferred to the lower surface of the paper by a transfer device, and then the paper is conveyed to the fixing device. A belt photoreceptor rotatably supported between at least two support rollers is used as a latent image carrier, and an elastic roller is used as a transfer device,
An image forming apparatus characterized in that the elastic roller has a shape having a diameter difference between a center portion and an end portion in the longitudinal direction and is pressed against the belt photoreceptor.