Electrophotography – Document handling – Copy
Reexamination Certificate
2000-03-08
2002-03-12
Brase, Sandra (Department: 2852)
Electrophotography
Document handling
Copy
C271S228000, C399S394000
Reexamination Certificate
active
06356735
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a sheet transport device for transporting each sheet to a specified target location. More particularly, the invention is concerned with a sheet transport device for an image-forming apparatus which makes it possible to transfer an image to an exact position even onto a sheet of maximum size having cutoff margins around a maximum image area, as well as with an image-forming apparatus employing the sheet transport device.
Generally, processes performed by an image-forming apparatus using electrophotographic technology are such that an electrostatic latent image corresponding to an image signal, for instance, is formed on a latent image carrier, such as a photosensitive drum, and a toner image obtained by developing the latent image is transferred onto a sheet of paper or other material, directly or indirectly by way of an intermediate image transfer device.
In this kind of image-forming apparatus, the maximum sheet size that can be used is determined by the maximum image area of the latent image carrier like a photosensitive drum on which the latent image is produced. The maximum sheet size thus determined is A3 size as defined in a Japanese Industrial Standard (JIS), for example.
To transfer an image to an exact position on a sheet, the sheet is usually aligned with a specific reference position. For example, this sheet alignment operation is achieved by a leading edge registration method in which the sheet is fed to am image transfer part after its leading edge has been correctly positioned, or by a side edge registration method in which the sheet is fed to the image transfer part after its side edge has been set to a specific side reference position.
The leading edge registration method is associated with a problem that when images are formed on both sides of the sheet, they tend to be incorrectly aligned with each other. This is because the sheet is likely to be fed obliquely in the leading edge registration method. Compared to this, the sheet is always lined up with the side reference position in the side edge registration method. Therefore, the side edge registration method is preferable in that it helps reduce misalignments of images formed on both sides of the sheet.
Also known in the prior art is an oblique feed correction technique used in sheet transport processes. This technique aligns each sheet with a specific side reference position by moving a registration roller, for instance, in a direction perpendicular to a sheet transport direction. Examples of the oblique feed correction technique are described in Japanese Laid-open Patent Publications No. 59-4552, No. 61-249063 and No. 63-185758, and Japanese Patent No. 2632405.
To further improve the performance of this kind of image-forming apparatus, those provided with various aftertreatment devices, such as a stapler, a puncher and a binder, have thus far been proposed.
Under such circumstances, the inventor of the present invention fitted aftertreatment devices like a trimmer to an image-forming apparatus and examined the possibility of providing a high-accuracy printing system. Test results have proved that to obtain a maximum image area equal to JIS A3 size (297 mm wide), for example, the printing system must be able to handle a sheet as large as A3 broad size (320 mm wide), for example, which is larger than the A3 size, and trim the sheet of the A3 broad size after an image has been fixed onto it to produce a print of the standard A3 size.
To meet such requirements, there is no way but to make the maximum image area that can be handled by the image-forming apparatus larger than usable sheet sizes.
To enlarge the maximum image area, however, it is inevitable for the apparatus to become large-sized, and this would result in an increase in product cost. Moreover, development efforts for increasing the maximum image area would be enormous and time-consuming.
The maximum image area of existing image-forming apparatus designed to handle A3 size sheets is naturally the A3 size. Thus, none of the existing image-forming apparatus can handle A3 broad size sheets without extensive design change. Although the A3 broad size is only 23 mm wider than the A3 size, increasing the maximum image area of the existing image-forming apparatus by this amount would involve almost the same man-hours as would be required for developing a new image-forming apparatus. In addition, such a modification would make it necessary to redesign or newly develop almost every component.
Even when the A3 broad size sheet is used, however, a final image is not formed throughout its entire surface area but in the area of the A3 size, because portions of the sheet around the central A3 area where the image is formed serve simply as cutoff margins.
In this situation, the inventor has reached the conclusion that an image-forming apparatus intending to handle the A3 broad size sheet need not necessarily provide a maximum image area as large as the A3 broad size but may be so constructed that it can transfer an image exactly onto the central A3 area of the A3 broad size sheet by using a readily available image-forming module capable of handling the standard A3 size sheet.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and provide a sheet transport device image-forming module, wherein the sheet transport device makes it possible to transfer an image to an exact position even on a sheet of maximum size having cutoff margins around a maximum image area of the image-forming module. The invention also provides an image-forming apparatus employing the sheet transport device.
According to an aspect of the invention, a sheet transport device comprises a registration/transport member
2
provided in a sheet path upstream of a target location P for correctly positioning a sheet
1
in a sheet transport direction and transporting it toward the target location P, and a sheet alignment mechanism
3
provided in the sheet path upstream of the target location P for moving the sheet
1
in a direction perpendicular to the sheet transport direction to align the sheet
1
to a reference position predefined for each set of sheet information, as shown in FIG.
1
.
While the aforementioned construction of the sheet transport device of the invention is applicable to a wide range of sheet transport devices in which the sheet
1
of paper or other material is transported toward the target location P, it is particularly effective when implemented in an image-forming apparatus which requires a high positioning accuracy of the sheet
1
in the sheet transport direction.
According to another aspect of the invention, an image-forming apparatus comprises an image carrier
5
which carries an image T formed on its image transfer part, a sheet transport device
6
which transports a sheet
1
to the image transfer part of the image carrier
5
, and an image transfer element
7
which transfers the image T on the image carrier
5
onto the sheet
1
at the image transfer part, the sheet transport device
6
including a registration/transport member
2
provided in a sheet path upstream of the image transfer part for correctly positioning the sheet
1
in a sheet transport direction and transporting it toward the image transfer part, and a sheet alignment mechanism
3
provided in the sheet path upstream of the image transfer part for moving the sheet
1
in a direction perpendicular to the sheet transport direction to align the sheet
1
to a reference position predefined for each set of sheet information, as shown in FIG.
1
.
While a typical example of the registration/transport member
2
that can be used in the aforementioned sheet transport device and image-forming apparatus would be a driving roller (registration drive roller) associated with a driven roller (registration idle roller) which is pressed against the driving roller to nip and transport the sheet
1
, the invention is not limited to this arrangement. For example, the registration/transport
Brase Sandra
Fuji 'Xerox Co., Ltd.
LandOfFree
Sheet transport device and an image-forming apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sheet transport device and an image-forming apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sheet transport device and an image-forming apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2850061