Advancing material of indeterminate length – Means to engage longitudinally spaced modifications in material – With additional means to restrict material movement
Reexamination Certificate
1998-10-15
2001-01-23
Jillions, John M. (Department: 3653)
Advancing material of indeterminate length
Means to engage longitudinally spaced modifications in material
With additional means to restrict material movement
C226S074000, C226S195000
Reexamination Certificate
active
06176411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a paper transfer apparatus incorporated in an electrophotographic printer used for printing selected images on elongated paper.
2. Description of the Related Art
To describe the overall arrangements of a typical paper transfer apparatus, reference is first made to
FIG. 1
of the accompanying drawings. As shown in
FIG. 1
, a paper transfer apparatus may include a paper hopper
11
, a pair of paper tractors
2
(only one is shown), a photosensitive drum
12
, an image transferring unit
13
, a discharge or scuff roller
16
, a pinch roller
17
and a paper stacker
18
.
The paper hopper
11
accommodates elongated paper P in an alternately folded manner. The elongated paper is formed with a series of feed holes arranged along each longitudinal edge of the paper. After being pulled out from the paper hopper
11
, the paper P is brought into engagement with the tractors
2
. The two tractors
2
are spaced from each other by a predetermined distance in a widthwise direction of the elongated paper P. Each of the tractors
2
includes an endless belt
21
formed with a plurality of projections
22
. In operation, these projections come into engagement with the feed holes of the paper P. Thus, when the endless belts
21
are rotated, the paper P is caused to advance along a transfer path.
The photosensitive drum
12
has a cylindrical side surface on which electrostatic latent images are produced by an electrostatic latent image forming unit
14
. Thus produced latent images are made visible or developed by a developing unit
15
. Specifically, the latent images on the photosensitive drum
12
are changed to toner images by the developing unit. Then, the toner images are transferred onto the paper P by the transferring unit
13
. Thereafter, the transferred toner images are thermally fixed to the paper by an image fixing unit
19
. Then, the paper P, held between the discharge roller
16
and the pinch roller
17
, is moved further along the transfer path. Finally, the paper P is received in the stacker
18
in an alternatively folded manner.
For performing high-quality printing, the transferring operation for the elongated paper needs to be synchronized to the rotation of the photosensitive drum
12
. For attaining such synchronous operation, according to the arrangements shown in
FIG. 1
, use is made of the tractors
2
and the discharge roller
16
associated with the pinch roller
17
. The tractors
2
, arranged at an upstream point of the transfer path, are capable of moving the elongated paper at a rate equal to the peripheral speed of the photosensitive drum
12
rotated. The discharge roller
16
together with the pinch roller
17
, arranged at a downstream point of the transfer path, is capable of applying a pulling force to the paper P in the transferring direction. For generating appropriate tension in the elongated paper P located between the tractors
2
and the discharge roller
16
, the discharge roller
16
is caused to rotate at a rate greater than the predetermined transfer speed of the paper P (i.e., the peripheral speed of the photosensitive drum).
A conventional electrophotographic printer incorporating a paper transfer apparatus having the above arrangements has been found disadvantageous in the following points.
Specifically, as the thickness of the elongated paper used for a conventional printer is reduced, the feed holes of the paper tend to be more easily broken when the paper goes through the tractors
2
. Even if such a breakage does not occur, the paper may be prematurely jerked out of engagement with the tractors
2
. These anomalies will lead to defective printing results such as images printed at unintended locations on the paper.
The inventor of the present invention has found out that the above anomalies are caused by the following phenomena. First, as the thickness of the paper becomes smaller, the paper will be more strongly attached to the photosensitive drum
12
due to the corona discharge occurring at the time of image transfer. Second, as the rotational speed of the photosensitive drum
12
is increased for enabling more effective printing, it becomes harder for the elongated paper to be detached from the photosensitive drum
12
after the developed images are transferred onto the paper. This is because sufficient air cannot flow in between the photosensitive drum
12
and the paper as the rotational speed of the photosensitive drum is increased. As a result, even after the image transfer is finished, the paper is not detached immediately but will remain to be attached to the photosensitive drum for a while, as shown in FIG.
8
. This means that the elongated paper is forced to move downstream to a greater extent than is originally expected. In such an instance, the feed holes of the paper may be broken or the paper may prematurely come out of engagement with the tractors
2
, as stated above.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a paper transfer apparatus capable of overcoming the disadvantages described above.
According to the present invention, there is provided a paper transfer apparatus incorporated in an electrophotographic printer having a photosensitive drum for printing on elongated paper transferred along a transfer path extending via the photosensitive drum, the paper transfer apparatus comprising:
a discharge roller for pulling the elongated paper in a transferring direction, the discharge roller being spaced downstream from the photosensitive drum; and
a traction mechanism for advancing the elongated paper along the transfer path, the traction mechanism being spaced upstream from the photosensitive drum;
wherein the traction mechanism is provided with braking means for applying friction to the elongated paper.
As previously stated, since the elongated paper is forcefully pulled in the transferring direction, the feed holes of the paper may be broken, or the paper may unduly come off the traction mechanism without taking any countermeasures. However, according to the present invention, use is made of a traction mechanism provided with braking means for applying friction to the elongated paper. By canceling out the forced pull with the friction, it is possible to prevent the feed holes of the paper from being broken or to prevent the paper from being unduly brought out of engagement with the traction mechanism. As a result, anomalies such as positionally improper printing is advantageously avoided even when relatively thin paper is used. Here, it should be noted that when the friction applied by the braking means is adjusted to be equal to the forced pull, the friction does not interfere with-the normal operation of the traction mechanism.
According to a preferred embodiment, the traction mechanism comprises at least one tractor which includes: a support base provided with an upper surface for supporting the elongated paper; a front and a rear pulleys rotatably supported by the support base; an endless belt held in engagement with the front and the rear pulleys, the endless belt being provided with a plurality of projections coming into engagement with feed holes of the elongated paper; and a tractor lid pivotably supported by the support base, the tractor lid being pivotable between an open position where the endless belt is exposed and a closed position where the tractor lid is held in facing relation to the endless belt; and
wherein the braking means comprises a presser member supported by the tractor lid, the presser member being arranged to apply a predetermined pressing force to the elongated paper when the tractor lid is in the closed position.
Conventionally, use has been made of a tractor lid. However, the conventional tractor lid is used only for preventing recording paper from prematurely coming out of engagement with the tractors, but has never been used for supplying friction to the paper. It should be noted that such a friction supply arrangement has conventionally been regarded
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Jillions John M.
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