Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-09-19
2004-11-02
Lee, Susan (Department: 2852)
Electrophotography
Image formation
Transfer
C399S101000
Reexamination Certificate
active
06813463
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial no. 2001-287021, filed on Sep. 20, 2001, and 2002-078952, filed on Mar. 20, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to an image forming device, such as a copying machine, a printer, or a facsimile. More particularly, the invention relates to a tandem type image forming device, wherein after a first transfer stage at which a toner images on plural image supporters disposed along an intermediate transfer belt are sequentially composed on the intermediate transfer belt at a first transfer section where the intermediate transfer belt and each image supporter are oppositely arranged, the composite toner image transferred on the intermediate transfer belt is collectively transferred on a transfer material at a secondary transfer section where the intermediate transfer belt and the transfer material are oppositely arranged.
2. Description of Related Art
As described above, the tandem-type image forming device has the following advantages. A large amount of color documents were handled and this would continue in increasing volume for many more years, and therefore, demands for a compact and high-speed image forming device, such as a full color printer and a full color copying machine, etc. is highly desirable
For the color image forming device, in general there are two types, namely, a one drum type image forming device and a tandem type image forming device. The color image forming device of one drum type comprises a plurality of developing units disposed around one photoreceptor (the image supporter) for forming toner images in different colors. Thereafter, a composite toner image is formed on the photoreceptor by using the developing units, and then the composite toner image on the photoreceptor is transferred onto a recording medium, such as a paper or an OHP sheet, to form a color image. On the other hand, tandem-type color image forming device comprises a plurality of image forming units each of which includes a photoreceptor and an image forming means. The single-color toner image for each color is respectively formed on each image forming unit. These single-color toner images are overlapped and transferred onto a recording medium transported by a transferring/transporting belt, or onto an intermediate transfer belt, so as to form a composite color image.
The one drum image forming device can be more compact since one photoreceptor is included, and advantageously, the cost can be reduced. However, because one photoreceptor is usedperform for several times (usually, 4 times) of image forming processes to form a full color image, therefore the image formation with a high speed is very difficult. In contrast, the tandem-type image forming device has drawbacks in being large in size and high cost, but has advantages in the image formation with a high speed. Recently, since the need for a high speed or a faster and full color forming device is highly demanded, skilled people pay more attention on the above tandem-type image forming device.
For the tandem-type image forming device, there are a direct transfer type and an indirect transfer type. The tandem-type image forming device of direct transfer type transfers sequentially the image on the photoreceptor of each image forming unit onto the recording medium that is transported by the transferring/transporting belt. On the other hand, for the tandem-type image forming device of indirect transfer type, a first transfer stage is first performed so that the image on the photoreceptor of each image forming unit is sequentially overlapped onto the intermediate transfer belt. Next, the secondary transfer stage is performed so that the first transferred image on the intermediate transfer belt is wholly transferred onto the recording medium.
Referring to
FIGS. 17 and 18
, generally, in the tandem-type image forming device of direct transfer type, each of the image forming units is disposed side by side in the horizontal direction along the transferring/transporting belt. In this way, the paper feeding device for feeding the recording medium is disposed at the upmost upstream side of the transferring/transporting belt. Therefore, the perimeter of the horizontal portion where the recording medium on the transferring/transporting belt is transported gets longer, but however such a image forming device has a drawback, in that the device main body gets larger along the horizontal direction.
In order to prevent the device main body from becoming large along the horizontal direction, it is necessary that the fixing device has to be disposed in the vicinity of a separating section at which the recording medium where the composite toner image is transferred thereon is separated from the transferring/transporting belt. However, in such a configuration, it is very difficult to maintain a sufficient gap at which the recording medium that is separated from the transferring/transporting belt possesses a margin to bend between the separating section and the fixing device.
Therefore, in the above structure where the separating section and the fixing device are formed nearby, it is easy that the transferred image is adversely affected by an impact when the tip of the recording medium enters the fixing device (the thicker the recording medium is, the larger the impact is), or by a speed difference between the fixing device's transporting speed and the transferring/transporting belt's transporting speed. In contrast, in the tandem-type image forming device of intermediate transfer type, the position of the secondary transfer device can be more freely selected. Therefore, in the tandem-type image forming device of intermediate transfer type, the paper-feeding device and the fixing device can be disposed under the intermediate transfer belt, and advantageously, the device main body can be more compact along the horizontal direction. In addition, the device can maintain a sufficient gap at which the recording medium that is separated from the intermediate transfer belt can be bent between the fixing device and the separating section of the intermediate transfer belt. As described, since the tandem-type image forming device of intermediate transfer type possesses a margin capable of disposing the fixing device, it almost has no influence on the image formation of fixing device. For reasons as described above, skilled people in the field have paid much attention on the tandem-type image forming device of intermediate transfer type.
In the aforementioned image forming device, after the composite toner image on the intermediate transfer belt
10
of the secondary transfer device is collectively transferred on the transfer S, it is necessary to exactly separate the transfer paper S from the intermediate transfer belt
10
at the separating section. The separating ability of the transfer paper S at the separating section is also affected by the material of the intermediate transfer belt
10
and the entrance angle of the recording medium (the transfer paper S), but is largely affected by the winding angle &thgr; with respect to the supporting roller
16
of the intermediate transfer belt
10
at the separating section. If the intermediate transfer belt
10
's the winding angle &thgr; with respect to the supporting roller
16
forming the separating section is small, the separating ability of the transfer paper S at the separating section gets worse. In the worst situation, the transfer paper is not separated at the separating section, and then is transported and gets wounded on the intermediate transfer belt
10
. Therefore, for the image forming device using the intermediate transfer belt
10
, it is necessary to form a separating charger or a separating claw in order to separate the transfer paper S smoothly at the separating section according to the conventional art.
In order to improve the separating ability of the transfer material at the separating section of the intermediate tra
Lee Susan
Ricoh & Company, Ltd.
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