JPH0635242A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] Cleaning of a transfer member in a contact type transfer device can be performed reliably in a short time, and stable and good transfer is always performed to obtain a high quality image. An image forming apparatus capable of performing the above is provided. [Configuration] The primary charging device 2 is turned on in order to set the potential of the photosensitive drum 1 to the cleaning potential V ₀ during the pre-rotation, the paper interval, and the post-rotation period. While the transfer roller 12 is not cleaned, the surface potential of the photosensitive drum 1 is set to zero by turning on the blank exposure device 16 using an LED having a fast rise time. on the other hand,
The blank exposure device 16 is turned off only during the cleaning of the transfer roller 12, and the area of the photosensitive drum 1 that is primarily charged has a predetermined rise time (t ₁ ) and fall time (t ₂ ) of substantially zero. Of cleaning potential V ₀ .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic type or electrostatic recording type image forming apparatus, and more particularly to a visible image formed on an image carrier, that is, a toner image, on a transfer roller. The present invention relates to an image forming apparatus which obtains an image by transferring to a transfer material by a contact type transfer device using such a transfer member.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a latent image is formed on an image carrier, the latent image is visualized as a toner image by a developing device, and then the toner image is visualized. An image can be obtained by transferring a toner image onto a transfer material such as paper. As a transfer device for transferring the toner image onto the transfer material, a corona transfer device has heretofore been widely used.

A corona transfer device is effective as a means for transferring a toner image formed on an image carrier onto a transfer material.
It requires a high-voltage power source and has problems such as generation of ozone due to corona discharge. In contrast to such a corona transfer device, a contact type transfer device configured to transfer a toner image to a transfer material by applying a voltage to a transfer member such as a transfer roller and bringing the transfer member into contact with the transfer material is used. In addition, since it has the advantages that it can lower the voltage of the power supply and that it produces a small amount of ozone, it has been attracting attention as a transfer device in recent years, and research into its practical application is underway.

[0004]

However, for example, in an image forming apparatus using a transfer roller as a transfer member, the transfer roller is urged into contact with the image carrier, so that the transfer material is If not,
The transfer roller comes into direct contact with the image carrier,
The residual toner on the surface of the image carrier adheres to the surface of the transfer roller. Also, it is observed that toner adheres to the transfer roller due to various other causes. Therefore, if an image is formed in this state, there is a problem that the surface resistance value of the transfer roller varies, and good transfer cannot be performed.

Therefore, during the non-image forming period, a bias voltage having a reverse polarity to the transfer voltage is applied to the transfer roller to clean the transfer roller. In order to further improve the cleaning performance, it has been proposed that the image carrier has a predetermined potential when passing through the area of the transfer roller. For this reason, the image carrier is set to a predetermined potential by, for example, energizing a primary charging device for forming a latent image. There is a problem that the carrier does not reach a predetermined potential and the transfer roller is not sufficiently cleaned in the rising and falling regions. To solve this problem,
In order to complete the cleaning, it was necessary to lengthen the voltage application time of the charging device accordingly.

Therefore, an object of the present invention is to make it possible to clean the transfer member in the contact type transfer device in a short time and reliably, and always perform stable and good transfer.
An object of the present invention is to provide an image forming apparatus capable of obtaining a high quality image.

[0007]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
A latent image is formed on the image carrier, a toner image is formed by developing the latent image with a developer, and a transfer voltage is applied to the toner image by applying a transfer voltage to a transfer member in contact with the transfer material. In an image forming apparatus that obtains an image by transferring to a transfer material, at the time of cleaning the transfer member, a cleaning voltage having the same polarity as that of a developer is applied to the transfer member, and at the same time, the cleaned transfer of the image carrier is performed. in a region facing the member, the rise time (t ₁₎ and fall time (t ₂₎ to form a predetermined cleaning potential that is substantially zero (V _0), and the cleaning potential (V ₀₎ The image forming apparatus is characterized in that the size of the charged area on the surface of the image carrier is substantially the same as that of the transfer member cleaning area.

According to a preferred aspect of the present invention, in the area of the image carrier facing the transfer member to be cleaned, the image carrier is precharged to a predetermined potential over an area wider than the cleaning area. After that, it is formed by exposing and discharging so as to have substantially the same size as the cleaning region of the transfer member.

According to another preferred embodiment, the AC bias voltage applied for development is adjusted in accordance with the timing when the area of the image carrier facing the transfer member to be cleaned passes a development site. OFF, and
The DC bias voltage is maximized.

Further, the transfer member may be provided with a resistance measuring device capable of being brought into contact with and separated from the transfer member.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 shows a schematic structure of an electrophotographic apparatus which is an embodiment of the image forming apparatus of the present invention. In this embodiment, the image carrier 1 is a drum type electrophotographic photosensitive member, that is, a photosensitive drum, which has a conductive base layer 1b made of aluminum or the like and a photoconductive layer 1a formed on the outer peripheral surface thereof as a basic constituent layer. To be done.
The photosensitive drum 1 is rotationally driven around the support shaft 1d in the clockwise direction in the drawing at a predetermined peripheral speed.

The surface of the photosensitive drum 1 is uniformly primary-charged with a predetermined polarity and potential by a primary charging device 2 which is a charging roller in this embodiment. The charging roller 2 is composed of a central core metal 2c, a conductive layer 2b formed on the outer periphery thereof, and resistance layers 2a ₁ and 2a ₂ formed on the outer periphery thereof, and is arranged in parallel with the photosensitive drum 1. Both ends of the cored bar 2c are rotatably supported by bearing members (not shown), and a predetermined pressing force is applied to the photosensitive drum 1 by pressing means (not shown). The photosensitive drum 1 is driven to rotate as the photosensitive drum 1 is rotationally driven.

A predetermined DC bias voltage is applied to the charging roller 2 from the power source 3 through the core metal 2c, and the peripheral surface of the photosensitive drum 1 is charged to a predetermined polarity and potential.

The photosensitive drum 1, which is uniformly primary-charged by the charging roller 2, is exposed with target image information by an exposure device 10 such as a laser beam scanning exposure device, and its peripheral surface is electrostatically charged corresponding to the target image information. A latent image is formed. The latent image is then visualized as a toner image by the developing device 11. It is preferable that a DC voltage on which an AC voltage is superimposed is applied as a developing bias voltage to the developing sleeve 11a, which is the developer conveying means of the developing device 11.

This toner image is then transferred to the transfer material 14 by the transfer device 12. The transfer material 14 is synchronized with the rotation of the photosensitive drum 1 from a paper feeding device (not shown) so that the transfer material 14 and the transfer device 12 are synchronized with each other at an appropriate timing.
It is conveyed to the transfer section between the.

In this embodiment, the transfer means 12 is the transfer material 14
Is a transfer roller that contacts the back surface of the roller and rotates. By applying a voltage having a polarity opposite to that of the toner to the transfer roller 12,
The toner image on the surface of the photosensitive drum 1 is transferred to the surface of the transfer material 14. In this embodiment, as the transfer roller 12, EPDM, SBR, BR or the like having a single foam or continuous foam having a roller diameter of 20 mm and a resistance value of about 10 ⁷ to 10 ¹⁰ Ω,
The one processed into a length of about 300 mm was used.

The transfer material 14 to which the toner image has been transferred is separated from the photosensitive drum 1, is conveyed to a fixing device (not shown), undergoes image fixing, and is discharged outside the machine. Further, in an apparatus that also forms an image on the back surface of the transfer material, the transfer material is transported to a re-conveying unit to the transfer unit.

After the image is transferred, the photosensitive drum 1 after the image transfer is cleaned by a cleaning device 13 to remove adhered contaminants such as toner remaining after transfer, and is further discharged by a discharging and exposing device 15 for use in the next image forming process.

Before explaining the operation sequence of the present invention for the electrophotographic apparatus having the above-mentioned structure, an example of the operation sequence which has been conventionally performed will be described with reference to FIG. The operation sequence of FIG. 5 shows the case of continuous printing of two sheets. Based on the print start signal, the rotation drive of the photosensitive drum 1 of the apparatus which has been in the standby state until then is started, and the pre-rotation period starts. In this pre-rotation period, in order to clean the transfer roller 12, a bias voltage having a reverse polarity to that at the time of transfer is applied to the transfer roller 12 for a predetermined time, that is, a time required for the transfer roller 12 to rotate once or twice. As a result, the toner adhering to the surface of the transfer roller 12 is not transferred to the photosensitive drum 1.
The transfer roller is returned to the upper position, and the transfer roller is cleaned.
Further, in order to further improve the cleaning performance, the corresponding area on the photosensitive drum 1 at the time of cleaning the transfer roller is set to a predetermined potential (hereinafter, referred to as “cleaning potential”), preferably equal to or lower than the potential at the time of image formation. In order to charge, the voltage application to the primary charging device 2 is turned on at a predetermined timing. Until the cleaning of the transfer roller 12 is completed, the image formation of the first sheet is completed, and the image formation of the second sheet is performed (hereinafter, referred to as “paper interval”), the same method as above is used. The transfer roller 12 is cleaned. After the image formation of the final print, which is the second print in this embodiment, is completed, the photosensitive drum 1 enters the post-rotation period.
At this time as well, the transfer roller 1 is similarly subjected to the same method as described above.
2. Cleaning is performed.

When an image is formed in such an operation sequence, particularly when a plurality of sheets are continuously copied, cleaning failure of the transfer roller occurs between sheets, and a good transferred image is obtained.
That is, there were cases where images could not be obtained.

When the present inventors pursued this point, as shown in FIG. 6, it takes a rising time (t ₀ ) until the potential of the photosensitive drum 1 reaches the cleaning potential V _0. Therefore, it is found that the photosensitive drum 1 does not reach the cleaning potential V ₀ at the initial stage of cleaning, and a cleaning failure occurs particularly when cleaning is required in time, such as between sheets. It was

Therefore, according to the present invention, as shown in FIG. 7, the rise time (t ₁ ) and the fall time (t 1
₂ ) is substantially zero, and especially the rise time (t ₁ )
Is set to substantially zero, the potential of the photosensitive drum 1 is immediately set to the cleaning potential V ₀ . An example of the operation sequence for that is shown in FIG.

In this embodiment, the primary charging device 2 is turned on in order to set the potential of the photosensitive drum 1 to the cleaning potential V ₀ during the pre-rotation, the paper interval and the post-rotation. When the transfer roller 12 is not cleaned,
By turning on the blank exposure device 16 using an LED having a fast rise time, the surface potential of the photosensitive drum 1 is made zero.

On the other hand, by turning off the blank exposure device 16 only during the cleaning of the transfer roller 12, the area of the photosensitive drum 1 which is primary charged can maintain a predetermined cleaning potential V _0, and when copying a plurality of sheets. It is possible to reliably perform the cleaning between the sheets. According to the present embodiment, as shown in FIG. 7, the photosensitive drum 1 is formed with a predetermined cleaning potential V ₀ whose rise time (t ₁ ) and fall time (t ₂ ) are substantially zero. To be done.

FIG. 3 shows another embodiment of the operation sequence of the present invention. According to this embodiment, when the area of the photosensitive drum 1 set to the cleaning potential V ₀ , that is, the drum area of the photosensitive drum 1 corresponding to the cleaning area of the transfer roller 12 passes through the portion of the developing device 11, development is performed. By making the AC component of the bias voltage OFF and making the DC component maximum, it is possible to prevent the fog toner from adhering to the photosensitive drum 1 from the developing device 11. As a result, according to this embodiment, the cleaning property of the transfer roller 12 can be more reliably maintained as compared with the embodiment shown in FIG.

FIG. 3 shows still another embodiment of the operation sequence of the present invention. According to this embodiment, as shown by the alternate long and short dash line in FIG. The resistance measuring device 20 contacts the surface of the transfer roller 12 in synchronization with the application of the cleaning bias voltage to the transfer roller 12, and thereby the resistance value of the transfer roller can be measured. According to this embodiment, the cleaning time t _CL of the transfer roller 12 is continued until the value measured by the resistance measuring device 20 reaches a predetermined value. Therefore, in this embodiment, even when the transfer roller 12 is heavily soiled, the cleaning can be reliably performed.

[0028]

As described above, according to the image forming apparatus of the present invention, the cleaning potential V _{0 of the} surface of the image carrier facing the cleaning of the transfer member such as the transfer roller is set to the rising time (t ₁ ) And the fall time (t ₂ ) can be set to a predetermined potential with substantially zero, and the cleaning potential charging area on the surface of the image carrier having the cleaning potential V ₀ has the same size as the transfer member cleaning area. With such a configuration, the transfer member can be reliably cleaned, and a stable and good image can always be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention.

2 is an example of an operation sequence of the image forming apparatus of FIG.

FIG. 3 is another example of the operation sequence of the image forming apparatus in FIG.

4 is still another embodiment of the operation sequence of the image forming apparatus of FIG.

FIG. 5 is an example of an operation sequence of a conventional image forming apparatus.

FIG. 6 is a diagram showing a temporal transition of a potential on a photosensitive drum during cleaning of a conventional transfer roller.

FIG. 7 is a diagram showing a temporal transition of the potential on the photosensitive drum during cleaning of the transfer roller in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging device 10 Exposure device 11 Developing device 12 Transfer member 14 Transfer material 16 Blank exposure device

Claims (4)

[Claims] 1. A latent image is formed on an image bearing member, a toner image is formed by developing the latent image with a developer, and the toner image is applied with a transfer voltage to a transfer member in contact with a transfer material. By doing so, in the image forming apparatus that obtains an image by transferring to the transfer material, during cleaning of the transfer member,
A cleaning voltage having the same polarity as that of the developer is applied to the transfer member, and at the same time, a rising time (t) is applied to a region of the image carrier facing the transfer member to be cleaned.
₁ ) and the fall time (t ₂ ) form a predetermined cleaning potential (V ₀ ) which is substantially zero, and the size of the charged area on the surface of the image carrier having the cleaning potential (V ₀ ). The image forming apparatus is substantially the same as the transfer member cleaning area. 2. An area of the image carrier facing the transfer member to be cleaned is pre-charged to a predetermined potential over an area wider than the cleaning area, and then the transfer member is cleaned. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed by exposing and discharging so as to have substantially the same size as the area. 3. An AC bias voltage applied for development is turned off and a DC bias voltage is applied in accordance with the timing when a region of the image carrier facing the transfer member to be cleaned passes a development site. The image forming apparatus according to claim 1 or 2, characterized in that 4. The image forming apparatus according to claim 1, wherein the transfer member is provided with a resistance measuring device that can be brought into contact with and separated from the transfer member.