JPH0446282Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> This invention relates to a paper conveying device near a transfer section in an image forming apparatus such as an electrostatic electrophotographic copying machine.

<Summary of the invention> This invention uses a transfer section that includes a paper transport roller that transports the paper before transfer to the photoreceptor drum and a peeling roller that peels the paper after transfer from the photoreceptor drum and transports the paper. When the trailing edge of the paper is removed from the paper transport roller, the paper is transported without shifting the contact surface with the photoreceptor drum, thereby preventing the occurrence of transfer misalignment.

<Prior Art and Its Disadvantages> In electrostatic electrophotographic copying machines and the like, a peeling device for peeling the transferred paper from the photoreceptor drum is formed in the transfer portion of the photoreceptor drum. A device that has a relatively simple structure and reliably peels off the paper has been adopted as a device that uses a peeling roller to forcibly peel the paper.

Copying machines in which the peeling roller is provided at one end of the photosensitive drum in such a peeling device have the following problems.

FIG. 5 is a bottom view of the transfer section of the photoconductor drum (the transfer charger is omitted).The paper conveyance roller 2 that conveys the paper before transfer to the photoconductor drum 6 is provided just before the transfer section. It is being The paper before being transferred is sent to the transfer section by this paper transport roller. The paper conveyance speed at this time is the same as the peripheral speed of the photosensitive drum, and the toner image is transferred onto the paper by the transfer charger. When the transferred paper reaches the position of the peeling roller 7, it is peeled off. At this time, the peeling roller 7, the photosensitive drum 6, and the paper transport roller 2 all transport the paper in synchronization, so that stable transfer is performed.

However, after that, the moment the trailing edge of the paper comes off the paper conveyance roller, the paper conveyance roller acts to push out the trailing edge of the sheet. At this time, the end of the paper in contact with the peeling roller is sandwiched between the peeling roller and the photoreceptor drum and is being conveyed at a constant speed. Since the contact area (distance) with the drum 6 is small, it is greatly influenced by the paper transport roller. On the other hand, the paper is free on the side where the peeling roller is not installed, so
It is in contact with the photoreceptor drum over a wide area (distance) due to the action of static electricity. Therefore, it is hardly affected by the paper conveyance roller. As a result, a rotational moment is applied to the paper the moment the trailing edge of the paper comes off the paper conveyance roller, causing misalignment at the contact surface between the paper and the photosensitive drum. For example, there were cases where bleeding occurred in a wedge-shaped area as shown in FIG.

<Purpose of the invention> The purpose of this invention is to prevent the entire paper from being affected even if the paper is ejected at the moment the trailing edge of the paper comes off the paper transport roller in the above-mentioned situation. An object of the present invention is to provide a paper conveying device that can prevent misalignment.

<Structure and effects of the invention> This invention includes a photoreceptor drum, and a peeling roller that is provided at an end of the photoreceptor drum and contacts the photoreceptor drum to peel off the paper on which the toner image has been transferred from the photoreceptor drum. and a paper transport roller that transports the paper before being transferred to the photoreceptor drum. It is characterized by having a diameter larger than that of other parts of the conveying roller.

With the above configuration, the end portion of the sheet conveying roller facing the peeling roller with the photosensitive drum in between is conveyed faster than the other portion. As a result, the paper on the side facing the peeling roller across the photosensitive drum is curved from the time when the leading edge of the paper contacts the photosensitive drum until the trailing edge of the paper comes off the paper transport roller. Therefore, even if the paper is ejected at the moment when the trailing edge of the paper comes off the paper transport roller, the curved portion cushions the effect, so no rotational moment is generated on the paper.
Transfer misalignment can be prevented.

<Example> FIG. 1 is a diagram showing the configuration of the vicinity of a transfer section of an image forming apparatus using a paper conveyance device according to an example of this invention.

In the figure, 6 is a photoreceptor drum, and a peeling roller 7 and paper conveyance rollers 1 and 2 are provided with this photoreceptor drum in between. Paper transport roller 1
and 2 convey the paper 9 before transfer toward the photosensitive drum 6 along the guide plates 3 and 4.

A transfer charger 5 transfers the toner image already formed on the photosensitive drum 6 onto the paper by applying corona discharge to the paper 9 in contact with the photosensitive drum 6. Since the photosensitive drum 6 and the paper transport rollers 1 and 2 are driven synchronously,
The paper is conveyed to the left in contact with the photoreceptor drum without shifting.

The release tape 8 is fixed at a position where it contacts the end of the photoreceptor drum 6. On the other hand, the peeling roller 7 is in contact with the peeling tape 8, but also with the photosensitive drum 6, and is rotated by the photosensitive drum 6 in the direction of the arrow in the figure. The leading edge of the transported paper is transported along the release tape 8 and separated from the photosensitive drum 6 along the guide member 10. The peeled paper is conveyed as it is by the peeling roller 7 and the photosensitive drum 6.

FIG. 2 is a schematic perspective view showing the relationship between the paper transport roller, the paper, and the photosensitive drum.

As shown in the figure, paper 9 is held between paper transport rollers 1 and 2 and is transported in the direction of photoreceptor drum 6, but the paper transport speed on the front frame side is
If vf is the paper conveyance speed on the rear frame side, and vr is the paper conveyance speed on the rear frame side, the paper is conveyed in the relationship vf/vr by the action of the paper conveyance roller 1, as will be described later.

FIG. 3 is a diagram showing the shapes of paper conveyance rollers 1 and 2.

As shown in the figure, the upper paper transport roller 1 has grooves d1 and d2 for mounting a paper detection switch, and is the paper transport roller on the side facing the peeling roller across the photosensitive drum, that is, on the rear frame side. The diameter of the end portion (portion A in the figure) is slightly larger than the diameter of the other portion of the paper conveying roller 1 (portion indicated by dimension B in the figure). For example, A is
16.2mm, B is 16.0mm. Because of this relationship, the end portion (A portion) of the paper transport roller transports the paper slightly faster than the other portions. As a result, the paper in the area indicated by a in FIG. 2 is curved. Therefore, even if the paper is ejected at the moment it comes off the paper transport rollers 1 and 2, the force will be absorbed by the curvature of the paper, and the contact surface between the photosensitive drum and the paper will not shift.

Note that the paper conveyance speed of the paper conveyance roller other than section A is the same as the circumferential speed of the photoreceptor drum, so section b of the paper shown in Fig. 2 is not curved, but as mentioned above, it is Since a certain paper edge is in contact with the photoreceptor drum over a wide area, the contact surface will not shift even if the above-mentioned force is applied.

Figure 4 shows the results of an experiment in which the amount of transfer misalignment generated when changing the dimensions of the end portion (A section) of the paper conveyance roller 1 is divided into the rear frame side, center, and front frame side of the paper. .

When the diameter of part A is 16 mm, which is the same as the diameter of the other parts, the rear frame side, that is, the side where the peeling roller is provided, is particularly deviated greatly. Conversely, the diameter of part A
If you set it to 16.4mm or more, the front frame side of the paper will shift significantly. This is because when the trailing edge of the paper comes off the paper conveyance roller, the rear frame side of the paper comes off quickly.
This is thought to have occurred because the front frame side was extremely backward.

The dimensions of the end of the paper transport roller that should be made thicker need to be determined appropriately based on the distance between the paper transport roller and the transfer section of the photoreceptor drum, the transport speed, and the adsorption force between the photoreceptor and the paper at the transfer section. There is.

Note that by making section A of the paper transport roller thicker than the other parts to increase the paper transport speed, the leading edge of the paper is aligned between these paper transport rollers 1 and 2, and then the photoreceptor drum However, since the distance between the transfer section and the paper conveyance roller is short, this error does not substantially pose a problem.

In the embodiment, only the end portion (portion A) of the paper conveyance roller is made thicker than the other portions, but the diameter of the paper conveyance roller may be configured to change continuously along its axis. In addition, in the embodiment, only the upper roller of the paper conveyance roller is made thicker at its end, but the lower roller (see 2 in Figure 3) is also made thicker at its end. You may.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration near the transfer section of an image forming apparatus using the paper transport device of this invention, FIG. 2 is a schematic perspective view showing the relationship between the paper transport roller, the paper, and the photosensitive drum, and FIG. The figure shows the structure of the paper conveyance roller, and FIG. 4 shows the situation in which transfer misalignment occurs when the shape of the paper conveyance roller is changed.
FIG. 5 is a bottom view of the transfer unit with the transfer charger removed, showing the contact state between the photosensitive drum and the paper, and FIG. 6 is a diagram showing the location where wedge-shaped transfer deviation occurs. . 1, 2... Paper transport roller, 5... Transfer charger, 6... Photosensitive drum, 7... Peeling roller,
8...Peeling tape, 9...Paper.

Claims (1)

[Claims for Utility Model Registration] A photoreceptor drum; a peeling roller provided at an end of the photoreceptor drum that contacts the photoreceptor drum and peels off the paper to which the toner image has been transferred from the photoreceptor drum; In an image forming apparatus having a paper transport roller that transports the paper before being transferred to the photoreceptor drum, the diameter of the end of the paper transport roller facing the peeling roller with the photoreceptor drum in between is defined as the diameter of the paper transport roller. A paper conveyance device characterized by having a diameter larger than that of other parts.