Image forming apparatus with an intermediate transfer body...

Electrophotography – Control of electrophotography process – Control of transfer

Reexamination Certificate

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C399S302000, C399S308000

Reexamination Certificate

active

06256461

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus of the type transferring a toner image from an image carrier to a sheet-like recording medium by way of an intermediate transfer body.
An electrophotographic image forming apparatus of the type transferring a toner image from a photoconductive drum to a paper or similar sheet-like recording medium by way of an intermediate transfer belt is conventional. It is a common practice with this type of apparatus to set various image forming conditions on the basis of a reference mark or marks provided on the belt. Japanese Patent Laid-Open Publication No. 7-36249, for example, teaches a color image forming apparatus capable of causing an intermediate transfer belt to run at a constant speed by sensing a plurality of marks provided on the belt. Japanese Patent Laid-Open Publication No. 7-325455 discloses a color image forming apparatus in which a reference mark is formed on a photoconductive belt and then transferred to an intermediate transfer belt for the purpose of accurately matching the image areas of the two belts.
Further, Japanese Patent Laid-Open Publication No. 8-101554 proposes a multicolor image forming apparatus including a plurality of sensing means provided on an intermediate transfer belt for sensing changes ion dimension ascribable to temperature or humidity. Moreover, Japanese Patent Laid-Open Publication No. 10-104970 discloses a color image forming apparatus in which a bias is not applied at a reference mark position in order to form an attractive image.
In an image forming process effected with an intermediate transfer belt provided with a single mark (marker hereinafter) as a reference for the start of image formation, every time the belt makes one turn, a single image forming period exists on the belt, and an image transferring period occurs slightly later than the image forming period. This brings about a problem that whatever the image size may be, the printing speed is fixed. Further, when marker sensing means senses the marker of the belt, image formation on a photoconductive drum including in image forming means starts on the elapse of a preselected period of time. Subsequently, as soon as the leading edge of an image on the drum reaches a preselected position in a preselected period of time, the image is transferred from the drum to the belt. In this case, even in a repeat print mode, the next image is not formed until the marker passes the marker sensing means. As a result, the image forming means remains in a stand-by state between the transfer of an image to the belt and the next image forming operation.
Assume that a single marker is provided on the intermediate transfer belt. Then, whenever the apparatus is in a stand-by state, the belt with the single marker remains stationary at the same position. Therefore, in the case where the belt is passed over rollers, the belt is apt to deform. Moreover, because image transfer starts at the same position at all times, deterioration and therefore wear is likely to concentrate at a particular portion of the belt.
Furthermore, to form a color image, the interval between the sensing of the marker and the start of the next image formation must be set beforehand by taking account of a period of time necessary for, e.g., the switching of a developing color. This cannot be done without resorting to a large counter capable of counting a long period of time with accuracy. In addition, irregularities in the movement of the belt accumulate between the sensing of the marker and the start of the next image formation, preventing toner images of different colors from being transferred in accurate register with each other.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an image forming apparatus capable of protecting an intermediate transfer belt from local deterioration.
It is another object of the present invention to provide an image forming apparatus capable of protecting an intermediate transfer body from early wear.
It is still another object of the present invention to provide an image forming apparatus promoting the efficient use of an intermediate transfer body.
It is yet another object of the present invention to provide an image forming apparatus capable of reducing an image forming time.
It is a further object of the present invention to provide an image forming apparatus capable of efficiently printing an image in accordance with the image size, protecting an intermediate transfer body local deformation, and obviating early deterioration ascribable to such deformation.
In accordance with the present invention, an image forming apparatus includes an image forming section for forming a toner image on an image carrier. The toner image is transferred from the image carrier to an intermediate transfer body. A transferring device transfers the toner image from the intermediate transfer body to a sheet-like recording medium. A storage stores the frequency of use of each of a plurality of regions of the intermediate transfer body. A selector selects, in accordance with the frequencies of use stored in the storage, a transfer start position on the intermediate transfer body where the transfer of the toner image to the intermediate transfer body should start.
Also, in accordance with the present invention, an image forming apparatus includes a plurality of image forming sections. Each image forming section includes a respective image carrier for forming a toner image thereon, a respective optical writing device for optically writing a latent image on the image carrier, at least two developing devices each for developing the latent image with toner of particular color, and a switching device for selecting one of the two developing devices. The toner image is transferred to an intermediate image transfer body. A transferring device transfers a composite toner image from the intermediate transfer body to a sheet-like recording medium. A storage stores the frequency of use of each of a plurality of regions of the intermediate transfer body. A selector selects, in accordance with the frequencies of use stored in the storage, a transfer start position where the transfer of the toner image to the intermediate transfer body should start.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:
FIG. 1
is a timing chart demonstrating the operation of a conventional image forming apparatus;
FIG. 2
is a graph showing a relation between the position on an intermediate transfer belt and the frequency of use of the belt particular to the apparatus shown in
FIG. 1
;
FIG. 3
is a fragmentary view showing an image forming apparatus in accordance with the present invention;
FIG. 4
is an isometric view showing an arrangement around an intermediate transfer belt included in the apparatus of
FIG. 3
;
FIG. 5
is an isometric view showing sensing means included in the apparatus of
FIG. 3
;
FIG. 6
is a circuit diagram showing marker sensing circuitry associated with the sensing means;
FIG. 7
is a timing chart representative of the operation of the apparatus of
FIG. 3
;
FIGS. 8
,
9
and
10
are graphs showing a relation between a position on the intermediate transfer belt and the frequency of use of the belt unique to the apparatus of
FIG. 3
;
FIGS. 11A through 11E
are timing charts demonstrating an image forming process including intermediate image transfer;
FIG. 12
is a timing chart showing a relation between the rotation of the belt and the image forming period;
FIG. 13
is a block diagram schematically showing a control system included in the apparatus of
FIG. 3
;
FIGS. 14 through 16
are flowcharts relating to control over the belt using markers; and
FIGS. 17 and 18
are front views each showing a particular configuration of the apparatus.


REFERENCES:
patent: 4615607 (1986-10-01), Yanagawa et al.
patent: 5337136 (1994-08-01), Knapp et a

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