JP2007025215A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus reducing image degradation caused by the deterioration in developer and the occurrence of toner scattering or the like by reducing stress imposed on developer in a tandem type color electrophotographic system. <P>SOLUTION: In the image forming apparatus, a photoreceptor 1 is driven synchronously with the rotation of an intermediate transfer body 4. A developer carrier having a driving source separately from the photoreceptor 1 and performing rotating operation, forms an image on the photoreceptor 1, then stops while the photoreceptor 1 is driven, and performs reverse rotating operation just before it stops. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an electrophotographic image forming apparatus such as a printer, a copying machine, and a FAX.

A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photoconductor, and a toner is attached by these developing devices to form a composite toner image on the photoconductor, and the toner image is transferred. A so-called one-drum type that records a color image on transfer paper and a plurality of photoconductors arranged side by side are each provided with a developing device, and a monochromatic toner image is formed on each photoconductor, and the monochromatic toner images thereof. There is a so-called tandem type in which a combined color image is recorded on a transfer paper by sequentially transferring images.
Comparing the 1-drum type and the tandem type, the former has only one photoconductor, so that there is an advantage that it can be relatively downsized and cost can be reduced. (4 times) Since the image formation is repeated to form a full-color image, there is a drawback that it is difficult to increase the speed of image formation, while the latter has the disadvantage of increasing the size and cost. There is an advantage that speeding up is easy.
Recently, tandem type has been attracting attention because the demand for full-color monochrome speed is desired.

FIG. 1 is a schematic configuration diagram of a conventional tandem color electrophotographic apparatus.
The tandem type color electrophotographic apparatus includes a direct transfer system in which an image on each photoconductor is sequentially transferred onto a transfer sheet conveyed by a conveyance belt by a transfer device, and each photoconductor 1 as shown in FIG. The indirect transfer method in which the image on the intermediate transfer body 4 is sequentially transferred to the intermediate transfer body 4 once by the primary transfer apparatus 2 and then transferred onto the transfer paper by the secondary transfer apparatus 5 at once. is there. The transfer device is a transfer conveyance belt, but there is also a roller-shaped method.
Comparing the direct transfer method and the indirect transfer method, the former has to arrange the paper feeding device 6 on the upstream side of the tandem type image forming apparatus T on which the photoconductors 1 are arranged, and the fixing device 7 on the downstream side. There is a disadvantage that the transfer paper is increased in the conveyance direction.
On the other hand, the latter can set the secondary transfer position relatively freely. The paper feeding device 6 and the fixing device 7 can be disposed so as to overlap the tandem type image forming apparatus T, and there is an advantage that downsizing is possible.

For these reasons, recently, among the tandem type color electrophotographic apparatuses, the indirect transfer type has been attracting attention. In this type of color electrophotographic apparatus, as shown in FIG. 1, the transfer residual toner remaining on the photoconductor 1 after the primary transfer is removed by the photoconductor cleaning device 8 to clean the surface of the photoconductor 1. In preparation for the second image formation.
Further, the transfer residual toner remaining on the intermediate transfer body 4 after the secondary transfer is removed by the intermediate transfer body cleaning device 9 to clean the surface of the intermediate transfer body 4 to prepare for the image formation again.
In such an image forming apparatus, if each color photoconductor 1 is not rotated while the intermediate transfer body 4 is rotating, the photoconductor 1 and the intermediate transfer body 4 are rubbed at the nip portion and the surface layer is damaged. Therefore, the intermediate transfer member 4 and the photosensitive members 1 of the respective colors are rotated in the same time in synchronization.

If the developer carrying member is stopped while the photosensitive member is rotating, the toner at the tip of the tip formed by the carrier is separated from the carrier while being rubbed against the photosensitive member. As a result, the carrier on which the toner is not adhered and the photoconductor are rubbed, and the surface layer of the photoconductor is damaged. For this reason, problems such as shortening of the life of the photosensitive member occur, and therefore, the developer carrying member must be rotated as much as possible while the photosensitive member is rotating.
As described above, since the photosensitive member must be rotated while the intermediate transfer member is rotating, the developer carrying member must be rotated as much as possible while the intermediate transfer member is rotating. The intermediate transfer member is rotated until the transfer residual toner of the image secondarily transferred onto the transfer paper is cleaned by the cleaning unit. Therefore, in the tandem type electrophotographic apparatus, while the one-color image is formed on the photosensitive drum. Compared to the one-drum type, which only needs to rotate the developer carrier, the developer carrier is rotated for a considerably long time. That is, the time for rotating the developer carrying member for one image is longer than that for the one-drum type. The longer the developer carrying body is rotated, the more stress is applied to the developer, and the developer is more likely to deteriorate.

Thus, for example, Patent Document 1 discloses a technique for extending the life of a developer by automatically changing the developer so that the magnetization amount of the magnetic carrier is within a predetermined range.
However, it is possible to extend the life of the developer by automatically changing the developer, but there is a problem that a mechanism for automatic change is necessary and the apparatus becomes large and the cost becomes high.

JP 2004-145115 A

  In view of the above-described problems, the present invention provides an image forming apparatus that reduces the stress applied to the developer and reduces the occurrence of image deterioration, toner scattering, and the like due to the deterioration of the developer without increasing the size of the apparatus. The task is to do.

In order to solve the above problems, the present invention has the following features.
1. The image forming apparatus of the present invention includes a plurality of image carriers arranged in parallel and a plurality of developer carriers that form toner images on each image carrier using a two-component developer. Each developer carrier is driven by a separate drive from the image carrier that forms the image, and the toner image formed on each image carrier is primarily transferred onto the intermediate transfer member. In an image forming apparatus that forms a plurality of color images by superimposing them, the image carrier is driven in synchronization with the rotation of the intermediate transfer member, and the developer carrier having a separate drive is formed on the image carrier after image formation. The image carrier is stopped while being driven, and a reverse rotation operation is performed immediately before the image carrier is stopped.
2. Further, the reverse rotation operation of the developer carrying member is performed after the rear end of the toner image on the image carrying member is primarily transferred onto the intermediate transfer member.
3. Further, the plurality of developer carriers may be driven in plural, and the developer carrier that forms an image on a later image carrier may be driven in a predetermined manner after the start of driving the image carrier. It is characterized by being driven after time.

  According to the present invention, it is possible to provide an image forming apparatus that can reduce the stress applied to the developer and reduce the occurrence of image deterioration, toner scattering, and the like due to the deterioration of the developer at low cost without increasing the size of the apparatus.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a conventional tandem color electrophotographic apparatus. In the first embodiment, the Y, C, and M photoconductors 1 are removed from the intermediate transfer member 4 from the state shown in FIG. 1 so that the Y, C, and M photoconductors 1 are not rotated in the Bk single color printing operation. Keep them apart. Therefore, driving of the Bk photoconductor and driving of the Y, C, and M photoconductors are performed separately, and the Bk developing unit and the photoconductor unit are driven by different motors (not shown). The Y, C, and M photoconductor units are driven by the same motor (not shown), and the Y, C, and M developing units are driven by the same different motor. In this embodiment, such a driving method is used. However, in other methods, if at least one developing unit and a developing unit formed thereby are driven separately, the present invention is implemented. it can.

FIG. 2 is a diagram illustrating an example of a timing chart of the electrophotographic apparatus. The intermediate transfer motor rotates until the transfer residual toner after the image superimposed on the intermediate transfer member is transferred onto the transfer paper is cleaned by the cleaning unit. The motor for driving the Bk photoconductor unit and the Y, C, M photoconductor unit driving motor (hereinafter referred to as “YCM photoconductor motor”) are rotated for the same time in synchronization with the rotation of the intermediate transfer member.
The developer carrying member is preferably rotated while the photosensitive member is rotating as much as possible. Therefore, the developer carrying member is rotated as shown in FIG. The rotation of the Bk developer carrier is controlled by turning the Bk development motor on and off, and the Y, C, and M developer carriers are driven by the Y, C, and M developer carrier motors (hereinafter referred to as “YCM”). The rotation is controlled by turning on / off the "developing motor". The toner images of the respective colors are formed on the Y, C, M, and Bk photoconductors while being shifted by a predetermined timing, and the color image is formed on the intermediate transfer member at the timing shown in FIG. Writing with a laser diode (LD) is performed.

As shown in FIG. 2, the developing unit is driven for a considerably longer time than the actual image forming time. In a one-drum type electrophotographic apparatus, the developing unit is usually disposed at a position where it contacts the photoconductor, which is slightly longer than the time for forming a toner image on the photoconductor. Is driven for a very long time in a tandem type electrophotographic apparatus. For this reason, the stress applied to the developer increases with the same number of prints.
In the first embodiment, the stress applied to the developer is reduced as follows. When the developer carrying member is rotated in the normal rotation direction, the developer that has consumed the toner after passing through the developing nip is temporarily returned to the container of the developing unit, and the developer circulating in the developing unit and Agitated and freshly pumped in front of the development doctor. In the portion where the developer is once returned to the container of the developing unit, almost no magnetic force acts on the developer. For this reason, when the developer carrying member is rotated in the reverse direction, the developer cannot be pumped up after being separated, so that there is no agent in the developing nip portion. In such a state, even if the photosensitive member is rotated with the developer carrying member stopped, the photosensitive member is not damaged by the developing spikes.

  FIG. 3 is a diagram showing an example of a timing chart of the electrophotographic apparatus of the present invention. As shown in the timing chart of FIG. 3, by rotating the Bk developing motor after image formation on the Bk photoconductor and the YCM developing motor after image forming on the M photoconductor for a short time, and then stopping them. The driving time of the developing unit can be shortened without damaging the surface layer of the photoreceptor.

(Embodiment 2)
In the present embodiment, the reverse rotation timing of the developer carrier in the first embodiment is changed. When the developer carrier is rotated in the reverse direction, the rotation of the developer carrier is braked in the state where the developer head is in contact with the photosensitive member at first, and the developer carrier rotates in the reverse direction. Although it is a short time until disappearance, the speed of the photosensitive member is fluctuated. At this time, if the toner image on the photosensitive member is being transferred onto the intermediate transfer member, density unevenness occurs in the toner image on the intermediate transfer member. For this reason, the time (A and B in FIG. 3) from when the toner image is formed on the photosensitive member to when the developing motor is rotated in the reverse direction is transferred to the intermediate transfer member 1. After the next transfer is completed, the developing motor is set to rotate in the reverse direction. Thereby, density unevenness can be prevented.

(Embodiment 3)
FIG. 4 is a view showing another example of the timing chart of the electrophotographic apparatus of the present invention. If the developer is not in the development nip before the image forming operation is completed, the developer carrier can be stopped for the first time at the start of the next image formation (Bk development in FIG. 4). motor). By doing so, the driving time can be greatly reduced compared to the driving time of the developing motor in the timing chart shown in FIG. However, before the image is formed on the photosensitive member, the developer carrier is pre-rotated so that the state of the developing head is constant and the toner charge amount becomes a desired value. The YCM development motor cannot be stopped much before image formation. However, since the color image forming apparatus normally uses a large amount of Bk single color printing, it is a great effect to shorten the driving time of the developing motor of the Bk unit.

It is a schematic block diagram of the conventional tandem type color electrophotographic apparatus. It is a figure which shows an example of the timing chart of an electrophotographic apparatus. It is a figure which shows an example of the timing chart of the electrophotographic apparatus of this invention. It is a figure which shows another example of the timing chart of the electrophotographic apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Primary transfer apparatus 4 Intermediate transfer body 5 Transfer apparatus 6 Paper feeder 7 Fixing apparatus 8 Photoconductor cleaning apparatus 9 Intermediate transfer body cleaning apparatus T Tandem type image forming apparatus

Claims (3)

A plurality of image carriers arranged in parallel;
A plurality of developer carriers that form toner images with a two-component developer on each image carrier;
At least one developer carrier is configured to be driven by a separate drive from the image carrier that forms an image by the developer carrier,
In an image forming apparatus that forms a plurality of color images by primarily transferring and superimposing a toner image formed on each image carrier onto an intermediate transfer member,
The image carrier is driven in synchronization with the rotation of the intermediate transfer member,
An image forming apparatus, wherein the developer carrier having a separate drive stops while the image carrier after image formation is being driven on the image carrier, and performs a reverse rotation operation immediately before stopping. In the image forming apparatus according to claim 1,
The image forming apparatus, wherein the reverse rotation operation of the developer carrying member is performed after the trailing edge of the toner image on the image carrying member is primarily transferred onto the intermediate transfer member. In the image forming apparatus according to claim 1,
The plurality of developer carriers are driven by a plurality of drives,
An image forming apparatus comprising: a developer carrying member that forms an image on a later image carrier in a predetermined order after the start of driving the image carrier.

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