Sheet feeding or delivering – Delivering – With transfer means between conveyor and receiver
Reexamination Certificate
2001-03-14
2003-09-16
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Delivering
With transfer means between conveyor and receiver
Reexamination Certificate
active
06619657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a curl correction device for correcting the curl of a curled sheet, and to an image forming apparatus having the curl correction device, such as a copying machine, a printer, a facsimile apparatus or a composite apparatus composed of such apparatuses.
2. Description of Related Art
Image forming apparatuses, such as a copying machine, a printer, a facsimile apparatus, etc., which are arranged to form images on sheets have recently come to be popularly used. These apparatuses are forming images by various methods. Among the known image forming methods, an electrophotographic method whereby a toner image is transferred to and fixed on a sheet is widely employed. The electrophotographic-type image forming apparatus is provided with a thermal fixing device for fixing a toner image to a sheet after the toner image is transferred to the sheet. Further, since energy saving is vary important these days, a two-sided printing function is becoming indispensable to an image forming apparatus.
A laser beam printer of the electrophotographic type is described below, by way of example, as one of the conventional image forming apparatuses having the two-sided printing function, with reference to
FIGS. 14
to
17
.
As shown in
FIG. 14
, the conventional image forming apparatus includes, within an image forming apparatus body
1
, sheet cassettes
20
each of which is arranged as a sheet housing part to allow sheets P stacked therein, an image forming part
2
which is arranged as an image forming means to form a toner image on a sheet P, and a fixing part
3
which is arranged to fix the toner image formed on the sheet P.
Further, the image forming apparatus is provided with a sheet conveying path
21
which is formed to extend from the sheet cassette
20
up to the image forming part
2
, and a two-sided-print conveying path
4
which is arranged, as a sheet reconveying path, to feed the image forming part
2
again with the sheet P, after the sheet P has passed the fixing part
3
, for the purpose of printing on both sides of the sheet P. Further, on the downstream side of the fixing part
3
, there are provided a sheet delivery path
6
for delivering a sheet P to the outside of the apparatus, and a sheet inverse conveying path
7
for leading the sheet P to the two-sided-print conveying path
4
. These conveying paths
6
and
7
are arranged in such a way as to fork away from each other.
Conveying path change-over levers (not shown) are arranged respectively at a fork point between the sheet delivery path
6
and the sheet inverse conveying path
7
and at a confluence point between the sheet inverse conveying path
7
and the two-sided-print conveying path
4
. The sheet conveying paths are arranged to be switched from one path over to another by these conveying path change-over levers under control signals from control means (not shown) which is arranged to control the whole image forming apparatus.
Each of the sheet conveying paths is provided with pairs of conveying rollers
22
for conveying the sheet. A pickup roller
23
is arranged to pick up from each of the sheet cassettes
20
a sheet P which is located uppermost among the sheets P stacked at the sheet cassette
20
. A pair of registration rollers
24
are arranged to intermittently feed a transfer part
5
of the image forming part
2
with the sheets P at a predetermined timing. A pair of delivery rollers
25
are arranged to discharge and deliver to the outside a sheet P having passed through the fixing part
3
. A belt conveyer part
26
is composed of a plurality of belts and a plurality of pulleys which are arranged to feed the fixing part
3
with a sheet P after an image is formed on the sheet P through the image forming part
2
.
In the image forming apparatus, a sheet P which is located uppermost among the sheets P stacked at each of the sheet cassettes
20
is picked up by the pickup roller
23
. The sheet P picked up is transported along the sheet conveying path
21
by the conveying roller pairs
22
which are disposed after the pickup roller
23
. With the sheet P transported in this manner, the registration roller pair
24
intermittently feeds the transfer part
5
of the image forming part
2
with the sheet P. After a toner image is transferred to the upper surface of the sheet P by the transfer part
5
, the sheet P is conveyed to the fixing part
3
by means of the belt conveyer part
26
.
At the fixing part
3
, the sheet P is heated and pressed to have the toner image fixed thereto. In the case of ordinary printing only on one side of the sheet P, the sheet P is discharged and delivered to the outside by the delivery roller pair
25
after the fixing process.
In a case where the apparatus is used for printing on both sides of the sheet P, on the other hand, the sheet P having passed through the fixing part
3
is led by the conveying path change-over lever (not shown) to the sheet inverse conveying path
7
which branches downward after the fixing part
3
. While the sheet P is on the movement from the sheet inverse conveying path
7
to the two-sided-print conveying path
4
, the moving direction of the sheet P is reversed to move the sheet P further on the two-sided-print conveying path
4
in a state of having its image-formed side facing upward. Then, the sheet P is shifted from the two-sided-print conveying path
4
again to the sheet conveying path
21
. On the sheet conveying path
21
, the main surface side of the sheet P is inverted to have its image-formed side facing upward. In this state, the sheet P is intermittently conveyed to the transfer part
5
of the image forming part
2
. After a toner image is transferred to the upper surface of the sheet P, the sheet P is subjected to the toner image fixing process at the fixing part
3
and is then delivered to the outside by the delivery roller pair
25
.
The electrophotographic image forming apparatus has a problem in that the sheet P is curled by heat when the sheet P passes through the fixing part
3
. This is called heat curl. After heating by the fixing device
3
, the sheet P is curled also while it is passing through a bent part A or B of the conveying path. In a case where the sheet P comes to the two-sided-print conveying path
4
, the upper side (image-formed surface) of the sheet P tends to be curled into an upward protruding shape, as shown in FIG.
17
. In a case where the image forming apparatus is used for printing on two sides of the sheet P, in order to prevent inadequate image transfer, the curl must be removed before the sheet P is fed to the image forming part
2
. To meet this requirement, as shown in
FIG. 14
, a curl correction mechanism
200
is arranged on the two-sided-print conveying path
4
to correct the protruding curl by retrorsely imparting a curl to the sheet P in the reverse direction.
The curl correction mechanism
200
includes, as shown in
FIG. 16
, an endless belt
214
arranged to convey the sheet P, stretching shafts
211
and
212
arranged to revolvably stretch the endless belt
214
, and a pressing roller
213
which is rotatively arranged to push the stretched endless belt
214
from outside. The curl correction mechanism
200
is thus arranged to convey the sheet P in a state of having the sheet P sandwiched or pinched between the endless belt
214
and the pressing roller
213
.
At the curl correction mechanism
200
, the sheet P is caused to pass through a path formed approximately in a V shape jointly by the endless belt
214
and the pressing roller
213
of the curl correction mechanism
200
shown in
FIGS. 14 and 16
. By this arrangement, the upward curl of the sheet P is corrected to prevent inadequate image transfer to the second surface of the sheet P.
The conventional image forming apparatus arranged as described above has presented a problem in the following point.
If the retrorse curl imparted to the sheet P is too strong, the curl correction becomes excessive to bring forth a downward protruding curl
Horikoshi Jun
Suzuki Kenji
Ellis Christopher P.
Ridley Richard
LandOfFree
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