JPH08160779A - Image forming device - Google Patents

Abstract

PURPOSE: To use a clean transfer roller at all times while maintaining an ordinary copying-speed CONSTITUTION: In the case an electric field for transferring toner to a photosensitive drum 1 from a transfer roller 6 is generated by a control power source 11, a small original is placed on an original platen, and a transfer material P of the same size as the original is manually inserted and fed with the pressure plate of the origian platen open, the sufficient clearing away of soil on the transfer roller 6 is not always achieved. In such a case, the cleaning conditions of the electric field for transferring the toner to the photosensitive drum 1 from the transfer roller 6 is changed. Also, in the case of supplying a transfer material P such as paper in a cassette or in a roll, the transfer roller 6 is cleaned while the ordinary copying-speed is maintained.

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 copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, non-contact type transfer charging means has been widely used in image forming apparatuses such as copying machines. In this system, the toner image on the image carrier is transferred onto a transfer material by utilizing, for example, corona discharge of a corona charger, which is arranged so as to face the surface of the image carrier in a non-contact state.

However, this transfer means must apply a considerably high voltage to the corona charger in order to generate a corona discharge, which requires a high voltage power supply.
There is also a problem that ozone is generated by corona discharge.

For this reason, in recent years, an image forming apparatus has been developed which uses a contact charging type transfer means which only needs to apply a relatively low voltage.

In this method, a transfer member such as a conductive roller or a conductive brush is brought into contact with the image carrier, the transfer material is fed to a transfer portion which is a transfer nip portion between the two, and the back surface of the transfer material is contacted. By applying a bias voltage to the transfer member, the back surface of the transfer material is contact-charged to a predetermined polarity for transfer, and the toner image on the image carrier is electrically attracted to the surface of the transfer material and transferred. It is a thing.

In the contact charging type transfer means of such an image forming apparatus, since the voltage applied to the transfer member may be a relatively low voltage and the current may be relatively small, it is possible to reduce the size and weight of the power source. Therefore, there is an advantage that a low-cost image forming apparatus that produces a small amount of ozone can be obtained.

In such an image forming apparatus, when the toner image formed on the image carrier is larger than the size of the transfer material to which the image is transferred, it is directly transferred to the transfer member protruding from the transfer material. , Or if a jam occurs, the transfer material is not fed to the transfer nip portion, so that all the toner images on the image carrier are transferred to the transfer member, and the transfer member is significantly contaminated and the back surface of the transfer material that follows. However, there is a problem in that the transfer is soiled or the transfer bias is substantially insufficient to cause transfer failure.

Therefore, in order to avoid such a problem, a bias voltage having a reverse polarity to that at the time of transfer is applied to the transfer roller at the time of non-transfer to transfer the toner to the image carrier and clean the transfer roller. Means have been proposed.

Further, especially after cleaning after jamming (Japanese Patent Laid-Open No. 1-316775), in addition to applying the reverse polarity bias for cleaning the normal toner, the same polarity bias for cleaning the reverse toner may be further added. It has been proposed (JP-A-3-69978).

[0010]

However, in the image forming apparatus of the above-mentioned conventional example, especially in a machine having a high copy speed, when copying is continuously performed, it is possible to sufficiently secure the cleaning time of the transfer roller between each copy. However, there is a problem that the transfer roller cannot always be used in a clean state because the cleaning roller does not have a sufficient cleaning time in the non-transfer time.

The present invention has been made to solve the above problems, and provides an image forming apparatus in which a transfer roller is always used in a clean state while maintaining a normal copy speed. With the goal.

[0012]

To achieve the above object, in an image forming apparatus according to the present invention, an image carrier on which a charged toner image is formed, and an image carrier which is in contact with the image carrier are used. A transfer member that forms a transfer nip portion with the image carrier, and a charged toner is applied to the image carrier by inserting a transfer material into the transfer nip portion and applying a transfer voltage to the transfer member. An image is transferred onto the transfer material, and a power supply for applying a voltage to the transfer member and a voltage applied to the power supply is controlled when the transfer material is not inserted into the transfer nip portion. A control device that forms a cleaning electric field for transferring the unnecessary charged toner that has adhered to the image carrier, and a plurality of transfer material supply mechanisms that supply the transfer material in different supply states toward the transfer nip portion. When Wherein the control unit, by another of the transfer material feed mechanism, and changing the cleaning electric field.

For example, the control device may change the strength of the cleaning electric field.

Further, for example, the control device may change the application time of the cleaning electric field.

Further, for example, the control device may change the number of times the cleaning electric field is applied.

[0016]

Based on the above configuration, in a copying machine as an image forming apparatus, a transfer material supply mechanism such as a manual sheet feeding mechanism or a multi-size sheet feeding mechanism is installed directly in the image forming apparatus main body. , Such as cassette paper feeding, the transfer material is once installed in another unit, and roll paper feeding or the like is used to feed a fixed size transfer material. In the latter two cases, it is easy to detect the size of the transfer material, and even if the original image is wider than the transfer material width,
Since the potential of the transfer member is controlled according to the transfer material size,
There is no developer, and therefore it is easy to prevent the transfer member from becoming dirty. Also, since the transfer material is solid, there are few jams.

On the other hand, in the case of a transfer material supply mechanism such as manual paper feeding, it is difficult to detect what kind of transfer material is supplied. Particularly when a small original is placed and a transfer material of the same size as the small original is supplied with the pressure plate of the original table opened, the transfer roller other than the transfer nip portion becomes dirty. Therefore, the transfer roller needs to be cleaned, and jams are relatively frequent.

Therefore, for example, when the transfer material is supplied by a transfer material supply mechanism such as cassette paper feeding or roll paper feeding, the cleaning condition of the transfer member is changed so as to maintain the normal image forming speed, and the manual paper feeding is performed. In the case of the transfer material supply by the transfer material supply mechanism, the cleaning condition is sufficiently obtained to surely remove the dirt on the transfer member.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. <Embodiment 1> FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. This embodiment is an electrophotographic image forming apparatus and is a charging device for charging an image carrier. A contact charging type is used for both the apparatus and the transfer apparatus for transferring the toner image on the image carrier to the transfer material.

This image forming apparatus is equipped with a sightseeing drum 1 as an image carrier rotatably supported by an image forming apparatus body (not shown) (hereinafter simply referred to as "apparatus body"). The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member having a conductive base 1b made of aluminum or the like and a photoconductive layer 1a formed on the outer periphery thereof as a basic structure. The photosensitive drum 1 has a support shaft 1c at its center, and is rotated about the support shaft 1c in the direction of arrow R1 by a driving means (not shown).

A primary charging device is arranged above the photosensitive drum 1. This primary charging device is for uniformly and uniformly charging the surface of the photosensitive drum 1 to a predetermined potential with a predetermined polarity, and is configured as a roller as a whole, and is a charging member (hereinafter referred to as a contact member) which is in contact with the surface of the photosensitive drum 1. Charging roller 2). The charging roller 2 includes a conductive roller (core bar) 2c arranged at the center, a conductive layer 2b formed on the outer periphery thereof, and a resistance layer 2a formed on the outer periphery thereof.
₂ and 2a ₁ . The charging roller 2 is arranged parallel to the photosensitive drum 1, and the core metal 2
Both ends of c are rotatably supported by bearing members (not shown). The bearing members at both ends are urged toward the photosensitive drum 1 by pressing means (not shown), so that the resistance layer 2a _{1 on} the surface of the charging roller 2 presses the surface of the photosensitive drum 1 with a predetermined pressing force. Has been pressed.
The charging roller 2 is driven to rotate in the direction of arrow R2 as the photosensitive drum 1 rotates in the direction of arrow R1. The core metal 2c of the charging roller 2 is in contact with the electric contact 10a connected to the power source 10. A bias voltage is applied to the charging roller 2 by the power source 10, and thereby the surface of the photosensitive drum 1 is uniformly and uniformly contact-charged.

An exposure means 3 is arranged downstream of the charging roller 2 in the rotation direction of the photosensitive drum 1. The exposure unit 3 performs, for example, slit exposure of an original image and forms an electrostatic latent image according to image information on the surface of the photosensitive drum 1 by this exposure.

A developing device (developing means) 5 having a developing container 5b for accommodating a developer (toner) and a developing sleeve 5a for adhering the toner to an electrostatic latent image is arranged on the downstream side of the exposing means 3. Has been done. The toner in the developing container 5b is rotated by the developing sleeve 5a in the direction of arrow R5,
The toner is applied to the surface of the photosensitive drum 1 with a predetermined thickness, and is transferred from the developing sleeve 5a onto the photosensitive drum 1 at the developing position facing the surface of the photosensitive drum 1, and adheres to the electrostatic latent image on the photosensitive drum 1. It is like this. Toner is attached to the electrostatic latent image to form a visible image (toner image). The toner is charged to have a predetermined polarity.

The photosensitive drum 1 on the downstream side of the developing device 5.
A roller-shaped transfer member (hereinafter, referred to as “transfer roller”) 6 that is a contact charging type transfer unit is disposed below. The transfer roller 6 is composed of a conductor roller (core bar) 6a connected to a power source 11 and a conductive layer 6b formed in a cylindrical shape on the outer surface thereof. Transfer roller 6
Are arranged parallel to the photosensitive drum 1 and the core metal 6
Both ends of a are rotatably supported by bearing members (not shown) in the direction of arrow R6. The bearing member is urged toward the photosensitive drum 1 by a pressing member such as a spring (not shown), and thus the conductive layer 6b of the transfer roller 6 is formed.
Is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force, and a transfer nip portion N is formed between the photosensitive drum 1 and the transfer roller 6. To the transfer nip portion N, the transfer material P conveyed in the arrow K1 direction by a paper feeding mechanism described later is supplied in synchronization with the rotation of the photosensitive drum 1.
The transfer material P is nipped and conveyed at the transfer nip portion N. At this time, the surface side of the transfer material P is on the photosensitive drum 1.
Further, the back side contacts the transfer roller 6.

When the transfer material P passes through the transfer nip portion N,
A bias voltage having a polarity opposite to the polarity of the toner is applied to the back surface of the transfer material P by the power supply 11, whereby the toner image on the photosensitive drum 1 is transferred to the front surface of the transfer material P. Further, the power supply 11 includes a control device 12 that controls the applied voltage and forms a cleaning electric field for transferring the unnecessary charged toner adhering to the transfer roller 6 to the photosensitive drum 1 when the transfer material P is not inserted. It is connected.

The transfer material P having the toner image transferred thereto is separated from the photosensitive drum 1 and conveyed to an image fixing means (not shown) where the toner image is fixed and then a final copy of the apparatus main body. Either it is discharged to the outside, or in the case of multiplex copying or double-sided copying, it is sent again to the image forming section including the photosensitive drum 1, the exposing means 3, the developing device 5 and the like via the re-conveying means.

The photosensitive drum 1 after the toner image transfer is
The cleaner 7 removes adhered substances such as residual toner, and the charge is removed by the charge eliminator 9 before being used in the next image forming process.

In the above-mentioned structure, the conductive layer 6b of the transfer roller 6 has EPDM, SBR, or single-cell type open-cell type, so that the resistance value thereof is about 10 ⁷ to 10 ¹⁰ Ω · cm.
A BR or the like processed into a roller diameter of 20 mm and a length of about 300 mm was used. Further, the transfer material P is transferred from the photosensitive drum 1.
The drive system of the photosensitive drum 1 and the drive system of the transfer roller 6 are installed independently of each other in order to prevent a hollow portion when the toner image is transferred to the transfer roller 6.

In the first embodiment, a manual sheet feeding mechanism 51 and a cassette sheet feeding mechanism 53 are provided as a transfer material feeding mechanism. In the case of manual sheet feeding, the transfer material P is first transferred to the manual sheet feeding mechanism 51. When inserted, the detection sensor 51b detects the presence of the transfer material P, the paper feed roller 51a rotates, and the transfer material P is conveyed via the guide 54a. After that, the registration roller 5
The timing is set to 2 and the sheet is conveyed to the transfer nip portion N via the guide 55.

Further, in the case of cassette sheet feeding, by inputting a copy start signal, the sheet feeding roller 53a rotates, and the transfer material P is conveyed through the rollers 53c and the guide 54b. After that, the registration roller 52 takes the timing, and the sheet is conveyed to the transfer nip portion N via the guide 55.

The cleaning sequence of the transfer roller 6 in the first embodiment is shown in FIG. Here, an example of regular development using positively charged toner will be shown.

While the transfer material P is passing through the transfer nip portion N (FIG. 2), a negative bias voltage is applied to the transfer roller 6 from the control power source 11 so that the positively charged toner is transferred to the transfer material P. It is applied to the core metal 6a. After that, during non-transfer, first, regular toner cleaning (in FIG. 2) is performed by applying a reverse polarity bias voltage by the control power supply 11 so as to transfer the toner from the transfer roller 6 to the photosensitive drum 1. After that, reverse toner cleaning (FIG. 2) in which a bias voltage of the same polarity is applied by the control power supply 11 is performed. In the case of normal cassette feeding, cleaning is performed for a necessary and minimum time, and in the case of manual feeding, as shown in FIG. 3, regular toner cleaning (see FIG.
Cleaning time) and the reverse toner cleaning (of FIG. 3) are extended.

In this way, in the case of the paper feed which is apt to be stained, the application time required for cleaning the transfer roller 6, the applied voltage and the number of times of application are changed so as not to reduce the copy speed during normal use. First, perform cleaning.

In this embodiment, the transfer roller is used as the transfer member, but any brush, blade, film or the like which presses the photosensitive drum 1 to apply the transfer bias may be used. Similar results are obtained with members.

Further, in the present embodiment, not only the regular development but also
Similar effects can be obtained in reversal development. Second Embodiment Next, a second embodiment in which the magnitude of the transfer cleaning bias is changed will be described with reference to FIGS. 4 and 5.

As a transfer material supply mechanism, FIG. 4 shows a case of cassette sheet feeding, and FIG. 5 shows a case of manual sheet feeding. In this example, in the case of cassette feeding, the cleaning bias is low, and the rising time and load are reduced. <Embodiment 3> FIGS. 6 and 7 show Embodiment 3 in which a part of the cleaning bias for transfer is omitted. FIG. 6 shows the case of cassette feeding, and only non-transferred toner is cleaned. In FIG. 7, the regular toner and the reversal toner of the manual feed are cleaned. <Embodiment 4> FIGS. 8 and 9 also show an example in which a part of the transfer cleaning bias is omitted. FIG. 8 shows the cleaning of the transfer roller 6 in the case of cassette sheet feeding and during non-transfer when the transfer material does not pass. Instead, the toner is transferred from the transfer roller 6 to the photosensitive drum 1 at the time of multi-rotation before and after the multi-rotation, and cleaning is performed. In FIG. 9, the transfer roller 6 is cleaned by transferring the toner from the transfer roller 1 to the photosensitive drum 6 at the time of non-transfer when the transfer material does not pass in the case of manual feeding.

In any of the above-described embodiments, even if the transfer roller is significantly contaminated, the developer is transferred from the contact charging type transfer means to the image carrier, so that the transfer material on which an image is subsequently formed is formed. The transfer roller can always be used in a clean state while maintaining a normal image forming speed without being stained.

[0038]

As described above, since the transfer member cleaning electric field is controlled in accordance with the transfer material supply mechanism used in the image forming apparatus, the normal speed and load required for image formation can be maintained. In addition, when a transfer material supply mechanism such as manual paper feeding is used, it is possible to clean the dirt by changing the cleaning electric field when it is assumed that the transfer member is heavily soiled.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a cleaning sequence diagram when a cassette is fed to a transfer roller according to the first exemplary embodiment.

FIG. 3 is a cleaning sequence diagram when manually feeding the transfer roller of the first embodiment.

FIG. 4 is a cleaning sequence diagram in which a bias is changed when a cassette is fed to a transfer roller according to a second exemplary embodiment.

FIG. 5 is a cleaning sequence diagram in which a bias is changed when a sheet is manually fed to a transfer roller according to a second exemplary embodiment.

FIG. 6 is a cleaning sequence diagram in which a part of the bias when the cassette is fed to the transfer roller of the third embodiment is omitted.

FIG. 7 is a cleaning sequence diagram in which a part of bias is manually omitted when manually feeding the transfer roller in the third embodiment.

FIG. 8 is a cleaning sequence diagram when a cassette is fed to a transfer roller according to a fourth exemplary embodiment.

FIG. 9 is a cleaning sequence diagram in the case where the transfer roller of the fourth embodiment is manually fed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 image carrier (photosensitive drum) 5 developing means (developing device) 6 transfer member (transfer roller) 11 power supply 12 control device 51 transfer material supply mechanism (manual paper feeding mechanism) 53 transfer material supply mechanism (cassette paper feeding mechanism) N Transfer nip P Transfer material

Claims (4)

[Claims] 1. A transfer member, comprising: an image carrier on which a charged toner image is formed; and a transfer member which is in contact with the image carrier and forms a transfer nip portion between the image carrier and the transfer member. In an image forming apparatus that transfers a charged toner image onto the image carrier by inserting a transfer material into the nip portion and applying a transfer voltage to the transfer member, applying a voltage to the transfer member. Control for controlling a voltage applied to the power source and a cleaning electric field for transferring unnecessary charged toner adhering to the transfer member to the image carrier when the transfer material is not inserted into the transfer nip portion. An apparatus and a plurality of transfer material supply mechanisms that respectively supply transfer materials in different supply states toward the transfer nip portion, and the control device cleans the transfer material according to the transfer material supply mechanism. Changing the electric field, the image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, wherein the control device changes the strength of the cleaning electric field. 3. The image forming apparatus according to claim 1, wherein the control device changes an application time of the cleaning electric field. 4. The image forming apparatus according to claim 1, wherein the control device changes the number of times the cleaning electric field is applied.