Electrophotography – Document handling – Copy
Reexamination Certificate
2002-03-01
2004-08-17
Beatty, Robert (Department: 2852)
Electrophotography
Document handling
Copy
Reexamination Certificate
active
06778806
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-forming apparatus used advantageously for printers or copying machines. In particular, the present invention relates to an electrophotographic image-forming apparatus.
2. Description of the Related Art
Electrophotographic image-forming apparatus have been used in various kinds of printers or copying machines.
FIG. 10
of the accompanying drawings shows the basic structure of a conventional image-forming apparatus. The illustrated apparatus includes an image-forming unit
71
to print images on continuous recording paper P, and a paper transfer mechanism
73
to draw out paper P from the paper hopper
72
and feed it to the image-forming unit
71
.
The paper transfer mechanism
73
includes scuff rollers
74
, back-tension rollers
75
, a sub-tractor
76
and a main tractor
77
. The scuff rollers
74
exert a forward pulling force on the paper P, while the back-tension rollers
75
exert a backward pulling force (tension) on the paper P. The sub-tractor
76
and the main tractor
77
regulate the transfer speed of the paper P. Each of the tractors
76
,
77
includes a pair of tractor belts
77
a
from which a plurality of tractor pins
77
b
project. In a paper feeding operation, the pins
77
b
are brought into engagement with indexing holes of the paper P.
FIG. 11
shows a typical indexing hole (reference numeral
78
) having a serrated circumference.
The image-forming unit
71
includes a rotatable photosensitive drum
81
upon which an electrostatic latent image is produced. Around the drum
81
are provided a pre-charger
82
, a laser emitter
83
, a developer
84
, a transfer charger
85
, an AC discharger
86
, a toner cleaner
87
and an LED discharger
88
. The functions of these components are as follow. The pre-charger
82
uniformly charges the image-forming surface of the drum
81
. The laser emitter
83
irradiates the charge surface with a laser beam to produce an electrostatic latent image in conformity with the original. The latent image is made visible as a toner image by the developer
84
. Then, the toner image is transferred onto the paper P by the transfer charger
85
. The transferred image is fused to the paper P by application of e.g. heat or pressure from a fixing unit (not shown). The remnant charge on the drum surface is removed by the dischargers
86
and
88
, while the remnant toner is removed by the cleaner
87
.
In operation, the scuff rollers
74
and the drum
81
are responsible for the forward movement of the paper P, while the back-tension rollers
75
exert a backward force on the paper P so that the paper P is appropriately stretched. To avoid exertion of an unduly strong pulling force on the paper P, the scuff rollers
74
can slip on the paper P. This arrangement is advantageous to avoiding the breakage of the paper P at an indexing hole
78
for example.
While the conventional apparatus is functional, it has the following disadvantage.
In the conventional apparatus, the photosensitive drum
81
can exert a forward pulling force on the paper P while it is held in contact with the paper P. However, at an initial stage of the printing operation where the drum
81
has not come into contact with the paper P yet, the paper P is pulled forward only by the action of the scuff rollers
74
. In this situation, the back-tension rollers
75
may pull the paper P backward with a stronger force than the scuff rollers
74
pull the paper P forward. As a result, the paper P may shift backward relative to the main tractor
77
, whereby the tractor pins
77
b
come into contact with the front portion of the indexing holes
78
(see FIG.
11
).
When the drum
81
is held in contact with the paper P, on the other hand, the paper P is pulled forward more strongly by the combination of the scuff rollers
74
and the drum
81
, whereby the tractor pin
77
b
is shifted relatively backward in the indexing hole
78
. Thus, as shown in
FIG. 12
, the pin
77
b
comes into contact with the rear portion of the hole
78
.
Disadvantageously, as seen from
FIGS. 11 and 12
, the tractor pin
77
b
can shift by a maximum distance (A) through the printing session. This deviation may cause a shear in printing, and therefore should be avoided.
SUMMARY OF THE INVENTION
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide an image-forming apparatus which does not suffer the positional deviation of the recording paper relative to the tractor pins.
According to a first aspect of the present invention, there is provided an image-forming apparatus including: a photosensitive member on which an electrostatic latent image is produced; scuff rollers that move recording paper along a transfer path; a tractor disposed upstream of the transfer path from the scuff rollers, the tractor moving the recording paper at a predetermined transfer speed; back-tension rollers disposed upstream from the tractor, the back-tension rollers exerting a tension on the recording paper; and a speed controller that adjusts a transfer speed of the recording paper. The speed controller makes greater the circumferential speed of the back-tension rollers than the transfer speed by the tractor during a period after the recording paper is started to move along the transfer path and before image-printing is begun.
Preferably, the speed controller may make smaller the circumferential speed of the back-tension rollers than the transfer speed by the tractor after the image-printing is begun.
Preferably, the apparatus of the present invention may further include a transfer charger for transferring a toner image onto the recording paper. After a predetermined period of time passes since a beginning of transfer by the transfer charger, the speed controller makes smaller the circumferential speed of the back-tension rollers than the transfer speed by the tractor.
According to a second aspect of the present invention, there is provided an image-forming apparatus including: an image-forming unit that prints an image on recording paper; scuff rollers that move the recording paper along a transfer path; a tractor disposed upstream of the transfer path from the scuff rollers, the tractor moving the recording paper at a predetermined transfer speed; back-tension rollers disposed upstream from the tractor for exerting a tension on the recording paper; and a pressure controller that adjusts a pressing force acting on the recording paper. During a period after the recording paper is started to move along the transfer path and before image-printing is begun, the pressure controller prevents the back-tension rollers from exerting a pressing force on the recording paper.
Preferably, the pressure controller may control the back-tension rollers after the image-printing is begun, so that the back-tension rollers exert a pressing force on the recording paper.
Preferably, the apparatus of the present invention may further include a transfer charger for transferring a toner image onto the recording paper. The pressure controller may cause the back-tension rollers to exert a pressing force on the recording paper after a predetermined period of time passes since the beginning of image transfer performed by the transfer charger.
Preferably, the apparatus of the present invention may further include a mechanism for changing the position of the back-tension rollers. The pressure controller controls the position-changing mechanism to cause the back-tension rollers to selectively exert a pressing force on the recording paper.
Preferably, the back-tension rollers may include a drive roller and a follower roller which faces the drive roller and is moved by the position-changing mechanism.
According to a third aspect of the present invention, there is provided an image-forming apparatus including: an image-forming unit provided with a photosensitive member on which an electrostatic latent image is produced; scuff rollers that move recording paper along a
Beatty Robert
Fuji Xerox, Ltd.
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Image-forming apparatus with reduced deviation of continuous... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image-forming apparatus with reduced deviation of continuous..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image-forming apparatus with reduced deviation of continuous... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3307867