JP2000233845A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing formation of a poor image. SOLUTION: A guide part 2 is provided at the downstream of paired regist rollers 24 and 25 feeding a sheet S to a pressure contacting part N1 between an image carrier 11 and a contact type transfer means, and the sheet S is thereby guided by the guide part 2 to a pressure-contacting part N1 of the image carrier 11 and the contact type transfer means. A carrying path R is provided between the pressure contacting part N1 of the image carrier 11 and the contact type transfer means and each of the paired regist rollers 24 and 25, and a part of the carrying path R is formed up by the guide part 2, and the carrying path R is allowed to be flexed in such a way that the guide part 2 intersects with a straight line A which connects the pressure contacting part N1 of the image carrier 11 and the contact type transfer means with the pressure contacting part N2 of the paired regist rollers 24 and 25. When the sheet S passes through the flexed transfer path R, the waving in the carrying direction of the sheet is so devised as to be removed out.

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 such as an electrophotographic apparatus typified by a copying machine and an LBP, and more particularly to an image forming apparatus having a contact-type transfer device.

[0002]

2. Description of the Related Art Conventionally, in a general image forming apparatus such as a copying machine, an image bearing device is used as a transfer device for transferring a toner image on a rotating image carrier onto a sheet material while carrying the toner image on the surface. A so-called corona discharger that applies a high voltage to a discharge wire facing a body is widely used.

[0003] However, since this corona discharger is based on air discharge, it often generates ozone and the like which are unfavorable to the human body. Therefore, it is necessary to add a special mechanism for removing ozone and the like. This has led to an increase in the complexity and size of the device.

Therefore, instead of such a corona discharger, a contact-type transfer device that generates less ozone has been studied.
It has been put to practical use. Here, the contact-type transfer device includes an image carrier, a transfer roller that rotates while being pressed against the image carrier,
A transfer member such as a transfer belt and a transfer drum; a transfer member such as a sheet of paper; and a transfer bias applied to the transfer member by applying a transfer bias to the transfer member. To transfer a toner image formed on the surface of the image carrier to a transfer material.

[0005] Such a transfer device requires a relatively low transfer bias and a low capacity as compared with the case where a corona discharger is used, so that the transfer device is compact and generates almost no ozone. It has made it possible to provide a forming device.

FIG. 4 is a longitudinal sectional view of a copying machine as an example of an image forming apparatus provided with such a conventional contact-type transfer device. In this copying machine, a photosensitive drum is driven by a primary charger 13. 11 is uniformly charged, and then exposed
As a result, the photosensitive drum 11 is exposed, and an electrostatic latent image is formed on the photosensitive drum 11. Then, the electrostatic latent image is developed by the developing device 14 and visualized as a toner image.

On the other hand, sheets (not shown) accommodated in the tray 21 are fed one by one by a feed roller 22 and conveyed to a pair of registration rollers 24 and 25 along a guide 23. Then, the registration roller pairs 24 and 25 rotate in accordance with the image on the photosensitive drum 11 to transfer the sheet to the transfer guide 1.
When the sheet is conveyed to the transfer nip along 6, the transfer roller 15 transfers the toner image on the photosensitive drum 11 onto the sheet.

The sheet on which the toner image has been transferred is
Thereafter, the toner image is conveyed to the fixing device 26, the toner image is fixed by the fixing device 26, and then discharged from the fixing device 26.

In the transfer process of the contact type transfer device, the sheet S is linearly conveyed from the pair of registration rollers 24 and 25 to the transfer guide 16 as shown in FIG. I am trying to. Then, the position of the transfer guide 16 and the registration roller pair 24, so that the sheet S can be guided linearly in this manner.
The nip angle of 25 and the position of the transfer roller 16 with respect to the photosensitive drum 11 are adjusted.

[0010]

However, in an image forming apparatus having such a conventional transfer device, a transfer bias is applied to the sheet S while being pressed against the transfer roller 15. At this time, the sheet is also conveyed to the transfer nip N1 between the transfer roller 15 and the photosensitive drum 11 by nipping and conveying the pair of registration rollers 24 and 25. That is, the transfer process includes two roller pairs 11, 15, 24,
25 is carried out.

For this reason, for example, the registration roller pair 24,
When the transfer speed of the transfer roller 25 is higher than that of the transfer roller 15, as shown in FIG.
Between 24 and 25, a loop occurs in the sheet S. In addition, when the sheet S is thin paper and the registration roller pairs 24 and 25 are configured by intermittent arrangement of short rubber rollers as shown in FIG. Is "wavy".

Here, if the sheet S enters the transfer process in the state of "waving", a state in which the sheet S does not adhere to the transfer roller 15 locally may occur. When the sheet S does not adhere to the transfer roller 15 as described above,
In some cases, the image on the sheet that has undergone the transfer process locally includes an image defect portion caused by a transfer defect such as “missing” or “unevenness”. In addition, the inventors are particularly concerned with the latter half of the sheet S in the conveying direction (200 m from the leading end of the sheet).
m), it is confirmed that this phenomenon appears remarkably.

Although it is conceivable to prevent the formation of a loop that causes this abnormal image by improving the dimensional accuracy of the diameter of the conveying roller, the registration rollers 24 and 25 also have a small diameter as the machine becomes smaller. Was used, and the use conditions were in accordance with it, and this was not possible.

For example, φ10 ± 0.03 mm, rotation speed 60
When the sheet is conveyed at a speed of about 32 mm / sec at a setting of rpm, a difference of about 1.6 mm in the conveyance amount occurs in the calculation in order to convey A4 length (297 mm) by the upper and lower tolerance rollers. . The 1.6 mm difference in the conveyance amount is the cause of the loop generated between the registration roller and the transfer unit.

Here, it is impractical to improve the dimensional tolerance to ± 0.03 mm or more in consideration of productivity, and it is possible to prevent transfer failure when using a small-diameter (about φ10) roller in addition to improving the accuracy. Has been an important technical issue.

Accordingly, the present invention has been made in view of such a situation, and has as its object to provide an image forming apparatus capable of preventing occurrence of an image defect.

[0017]

SUMMARY OF THE INVENTION According to the present invention, there is provided an image bearing member which rotates while holding a toner image on a surface thereof, rotates while being pressed against the image bearing member, and is fed into a pressure contact portion with the image bearing member. Contact transfer means for applying an electrostatic charge to the sheet to be transferred to transfer the toner image onto the sheet, and a sheet in contact with the press-contact portion between the image carrier and the contact transfer means in synchronization with the movement of the toner image. An image forming apparatus provided with a pair of registration rollers for feeding a sheet, a guide unit provided downstream of the pair of registration rollers, for guiding a sheet to a press-contact portion between the image carrier and the contact-type transfer unit; A conveying path provided between the registration roller pair and a pressure contact portion between the body and the contact-type transfer unit, and a part of the conveying path is formed by the guide section, and the guide section and Contact with the image carrier It is characterized in that a straight line connecting the contact portion between the contact portion between the transfer means and the pair of registration rollers is to meet.

Further, the present invention is characterized in that a part of the guide portion protrudes into the transport path so that the guide portion and the straight line intersect.

Further, according to the present invention, another part of the transport path is formed by a casing of a process cartridge provided with the image carrier, and a part of the casing intersects the straight line with the casing of the process cartridge. Are projected into the transport path.

Further, the present invention is characterized in that the amount of protrusion of the guide portion into the conveyance path is variable so as to change the amount of intersection between the guide portion and the straight line according to the thickness of the sheet. Things.

Further, according to the present invention, when the sheet is nipped and conveyed, the registration roller includes a lever which rotates in accordance with the movement of one of the registration rollers in a separating direction, and the guide portion is provided at a rotation end of the lever. And the amount of projection of the guide portion is changed in accordance with the rotation of the lever.

Further, according to the present invention, the projecting amount of the guide portion is
The thickness is inversely proportional to the thickness of the sheet.

Further, as in the present invention, a guide portion is provided downstream of a pair of registration rollers for feeding a sheet to a press contact portion between the image carrier and the contact transfer device, and the guide portion allows the image carrier and the contact transfer device to be provided. The sheet is guided to the press-contact part of. Further, a conveyance path is provided between the registration roller pair and the press-contact portion between the image carrier and the contact transfer means, and a part of the conveyance path is formed by a guide. The transport path is bent so that a straight line connecting the pressure contact portion between the contact roller and the contact transfer means and the pressure contact portion of the registration roller pair intersects. Then, when the sheet passes through the bent conveyance path, the waving in the sheet conveyance direction is removed.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged sectional view of a transfer section of the image forming apparatus according to the first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a process cartridge provided with at least a photosensitive drum 11, a developing device 14, and a toner container 14a;
The lower surface 3 of the casing 3 is a main body housing portion.

Reference numeral 2 denotes a transfer guide which is a guide portion disposed on the main body housing.
And the lower surface 1A of the casing of the process cartridge 1.
And a pair of registration rollers 24 and 25
And a transfer path R between the photosensitive drum 11 and a transfer nip N1 between the transfer roller 15 serving as a contact transfer means.

In the figure, the upper end of the transfer guide 2 indicated by the reference numeral C and the lower end of the lower surface 1A of the process cartridge 1 indicated by the reference numeral B are paired with registration roller pairs 24, 25.
Of the photosensitive drum 11 and the transfer nip N1 of the transfer roller 15 so as to intersect a straight line A connecting the photosensitive drum 11 and the transfer nip N1 of the transfer roller 15.

The upper end C of the transfer guide 2
By making the lower end B of the lower surface 1A of the process cartridge 1 intersect with the straight line A, the lower end B of the process cartridge 1 and the upper end C of the transfer guide 2 have a transport path R
Has a bent shape.

Here, by bending the conveyance path R in this manner, the sheet S conveyed by the pair of registration rollers 24 and 25 comes into contact with the two protruding portions B and C, and the protruding portions B and C cause “ I'm sick. " Then, by squeezing the sheet S in this manner, the "undulating" state of the sheet S can be removed, and the sheet S without undulating can enter the transfer nip portion N1.

As described above, by bending the transport path R so that the straight line A intersects the transfer guide 2 and the lower surface 1A of the process cartridge 1, the sheet S in the middle of transport can be squeezed, and The sheet S from which the waviness has been removed can enter the transfer nip portion N1. As a result, it is possible to prevent the occurrence of image defects such as "transfer".

By protruding the lower surface 1A of the casing of the process cartridge 1 as in the present embodiment, the transport path R can be bent at a more appropriate position with respect to the transfer nip portion N1, and a more effective effect can be obtained. Thus, the state of the sheet can be stabilized.

Next, a second embodiment of the present invention will be described.

FIG. 2 is an enlarged view of the transfer section of the image forming apparatus according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

In the figure, reference numeral 4 denotes a pair of levers for holding a transfer guide 2 'to be described later, and the levers 4 are rotatably held by a shaft support 5 formed integrally with the main body housing 3. And is urged by a tension spring 6 in a counterclockwise direction. The shaft support 5 of the lever 4 is provided with a pair of registration rollers 24, as shown in FIG.
25, and the ends of the levers 4 and 4 on the registration roller side are arranged so as to contact the shaft 25a of the registration upper roller 25 from below.

Here, the urging force of the tension spring 6 is set such that the lever 4 slightly contacts the shaft 25a of the registration upper roller 25 from below. For example, in the case of FIG. 3, the load at the time of operation of the tension spring 6 is 1 g, and the distance between the tension spring 6 and the center of rotation of the lever 4 is 30 m.
m, the distance between the contact point of the upper registration roller and the rotation center is 3 mm, and the lever 4 is connected to the shaft 2 of the upper registration roller 25.
It is configured to contact 5a with 10 g from below.

On the other hand, a transfer guide 2 'is rotatably held at the other end of the levers 4, 4. In this embodiment, locking pins 41 are protruded from the ends of the levers 4 and 4, respectively, and the transfer guide 2 'has an elongated hole 2a for locking the locking pins 41. Is provided. Further, one end of the transfer guide 2 is rotatably held by a shaft support 2 </ b> A formed integrally with the main body housing 3.

The one end of the transfer guide 2 is rotatably held by the shaft support 2A, and the locking pins 41 of the levers 4 and 4 are locked in the elongated holes 2a. , 4 rotate, the transfer guide 2 'also rotates.

With the above configuration,
When the sheet is conveyed, the sheet is nipped between the pair of registration rollers 24 and 25, and when the registration upper roller 25 moves upward (separating direction) by the thickness of the sheet (about 0.1 to 0.2 mm), Following this, the lever 4 rotates counterclockwise by the urging force of the tension spring 6, and the transfer guide 2 'also rotates following this.

Incidentally, the transfer failure due to the state of the sheet such as the waving described above often depends on the strength of the sheet, ie, the thickness thereof. Must be provided in the transport path to correct the sheet before transfer.

On the other hand, in the case of thick paper which is unlikely to cause transfer failure, there is a risk of causing a jam at a bent portion due to the effect of “strain”. Become.

For this reason, in the present embodiment, the transfer guide 2 'is rotated while being in inverse proportion to the thickness of the sheet. That is, when a thick sheet is conveyed, for example, the transfer guide 2 ′, which was at the position where the protrusion amount indicated by the solid line is large, is rotated about the shaft support 2 A to the position where the protrusion amount is small as indicated by the broken line. I try to lower it.

By changing the amount of projection of the transfer guide 2 'according to the thickness of the sheet, the lower end B of the lower surface 1A of the process cartridge 1 and the upper end C of the transfer guide 2' are formed. The degree of bending of the conveyance path R can be changed according to the thickness of the sheet.

That is, the transport path R can be bent more when transporting thin paper that is likely to be partially uneven, and the degree of bending can be reduced in the case of thick paper in which the harmful effects of jams are concerned. .

[0045]

As described above, according to the present invention, the guide portion forming a part of the transport path, the press contact portion between the image carrier and the contact transfer device, and the press contact portion between the registration roller pair are connected. The conveying path is bent so as to intersect with a straight line, and when passing through the bent conveying path, the corrugation in the conveying direction of the sheet is removed, so that the image carrier and the contact-type transfer unit are kept in a stable state with the sheet. Into the press-contact part of
Image defects can be prevented from occurring.

Further, by changing the degree of bending of the conveyance path according to the thickness of the sheet, it is possible to more reliably prevent the occurrence of image defects and the occurrence of jams.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a transfer unit of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a transfer unit of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a perspective view of a transfer unit of the image forming apparatus.

FIG. 4 is a longitudinal sectional view of a copying machine as an example of an image forming apparatus provided with a conventional contact-type transfer device.

FIG. 5 is an enlarged sectional view of a transfer section of the conventional copying apparatus.

FIG. 6 is a diagram illustrating a state where a loop occurs in a sheet in a transfer unit of the conventional copying apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Process cartridge 2, 2 'Transfer guide 3 Main body housing part 4 Lever 11 Photosensitive drum 15 Transfer roller 24, 25 Registration roller pair N1 Transfer nip part N2 Nip part of registration roller pair A Nip part of registration roller pair and transfer nip part B Lower end of lower surface of process cartridge C Upper end of transfer guide R Transport path S Sheet

Claims (6)

[Claims] 1. An image bearing member, which rotates while holding a toner image on a surface thereof, and applies an electrostatic charge to a sheet which is rotated while being pressed against the image bearing member and fed into a pressure contact portion with the image bearing member. Contact transfer means for transferring the toner image onto the sheet, and a pair of registration rollers for feeding a sheet to a press contact portion between the image carrier and the contact transfer means in synchronization with the movement of the toner image. In the image forming apparatus, a guide portion provided downstream of the pair of registration rollers and guiding a sheet to a press contact portion between the image carrier and the contact transfer device; and the image carrier and the contact transfer device. And a conveying path provided between the registration roller pair and the registration roller pair, and a part of the conveying path is formed by the guide portion,
An image forming apparatus, wherein a straight line connecting the guide portion, a pressure contact portion between the image carrier and the contact transfer device, and a pressure contact portion of the registration roller pair intersects with each other. 2. The image forming apparatus according to claim 1, wherein a part of the guide section protrudes into the conveyance path so that the guide section and the straight line intersect. 3. A process cartridge according to claim 1, wherein the other portion of the transport path is formed of a casing of a process cartridge having the image carrier, and a portion of the casing is transported so that the casing of the process cartridge intersects the straight line. The image forming apparatus according to claim 1, wherein the image forming apparatus protrudes into a road. 4. The amount of projection of the guide portion into the conveyance path is variable so that the amount of intersection between the guide portion and the straight line is changed according to the thickness of the sheet. The image forming apparatus as described in the above. 5. When the sheet is nipped and conveyed, the registration roller includes a lever that rotates with movement of one of the registration rollers in a separating direction, and the guide portion is provided at a rotation end of the lever. The image forming apparatus according to claim 4, wherein an amount of protrusion of the guide portion is changed according to rotation of the lever. 6. The sheet according to claim 4, wherein the amount of protrusion of the guide portion is inversely proportional to the thickness of the sheet.
Or the image forming apparatus according to 5.