Electrophotography – Document handling – Copy
Reexamination Certificate
2001-02-26
2002-09-03
Chen, Sophia S. (Department: 2852)
Electrophotography
Document handling
Copy
Reexamination Certificate
active
06445903
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus having mechanism by which sheets transported one by one are switch-backed, which is typified by a printer, a copier, or the like.
2. Description of the Related Art
An image forming apparatus typified by a printer, a copier, or the like, which can perform automatic duplex printing by switch-backing and reversing sheets transported one by one, has been put to practical use. In such an image forming apparatus, a sheet handling device such as a finisher having an after treatment device that connects to a back stage of the image forming apparatus such as a stacker having a paper tray, a stapler or the like requires a function of exhausting a sheet of which one side has been already printed in a state where its printed side is faced downward (hereinafter referred to as face-down exhaust) in order to readily make up print pages. Further, in case that sheets having binding holes are used, in order to exhaust the sheets in such a manner that the binding-hole directions at the one-sided printing time and at the two-sided printing time are fitted to each other, there is required a function of selectively switching that the sheet of which one side has been already printed is exhausted face-down, and the sheet of which two sides have been already printed is exhausted in a state where the last printed side is faced upward to be exhausted (hereinafter referred to as a face-up exhaust). Accordingly, in a recent image forming apparatus, a sheet reversing device, which has the function of reversing the surface of the already printed sheet and the rear surface and the function of selectively switching the face-up exhaust and the face-down exhaust, is necessary and indispensable in a last paper exhausting section.
FIG. 4
shows one example of the constitution of a paper feeding section in the conventional image forming apparatus that satisfies the above functions. In
FIG. 4
, a fixing device
9
provided in an image forming apparatus
1
is composed of a heat roller
9
a
and a pressure roller
9
b
that are pressure welded to each other, and a toner image transferred onto a sheet is fixed by this device
9
. Reference numeral
10
is a gate and has a function of switching the directions of a sheet to be transported. A sheet transporting passage
12
connecting the fixing device
9
and a paper outlet
11
of the image forming apparatus to each other is referred to as a sheet feeding passage. Further, reference numeral
13
a
is referred to as a pull-in passage and diverges from the sheet feeding passage
12
on the downstream side in the sheet transporting direction in relation to the fixing device
9
, and the sheet fed out from the fixing device
9
by the switching control of the gate
10
is selectively pulled in it. Further, reference numeral
13
b
is referred to as a reversed sheet exhausting passage and diverges from a midway divergent point P of the pull-in passage
13
a
, and its end joins the sheet feeding passage
12
on the upstream side of the sheet outlet
11
in the image forming apparatus
1
. In
FIG. 4
, reference numeral
15
is a feed roller pair provided in the front stage of the gate
10
, reference numeral
16
is a discharge roller pair in the back stage of the gate
10
, and reference numeral
17
is a drive roller of a feed roller pair that is provided on the pull-in passage
13
a
and the reversed sheet exhausting passage
13
b
. Reference numerals
17
and
17
a
constitute an induction roller pair by which the sheet inducted to the pull-in passage
13
a
is put in, and reference numerals
17
and
17
b
constitute a feed roller pair for feeding out the sheet reversed and transported from the reversed sheet exhausting passage
13
b
. Reference numeral
18
is a reversal roller pair that is provided on the pull-in passage
13
a
and can switch its rotation to forward rotation/reverse rotation.
Under the above constitution, in case that the already printed sheet is exhausted face-up, the sheet fed out from the fixing device
9
is intactly exhausted along the sheet feeding passage
12
from the paper outlet
11
, and fed out to a sheet handling device
2
. Further, in case that the already printed sheet is exhausted face-down, the sheet fed out from the fixing device
9
is pulled in the pull-in passage
13
a
by guide of the gate
10
, the reversal roller pair
18
is rotated in the opposite direction to the direction at the pulling-in time at a timing when a sheet rear end reaches the divergent point P in the pull-in passage
13
a
, and the sheet is transported from the reversed sheet exhausting passage
13
b
to the discharge roller pair
16
side and exhausted from the paper outlet
11
to be fed out to the sheet handling device
2
side.
In the above conventional art, in a device that transports sheets at a high speed, such a state occurs frequently that while a preceding sheet is reversed and transported on the reversed sheet exhausting passage
13
b
, a succeeding sheet is inducted to the pull-in passage
13
a
. In case that the sheet that is being reversed and transported and the succeeding sheet cross on the pull-in passage
13
a
, the following problem occurs.
In case that the rear end of the sheet during reversal passes through the reversal roller pair
18
and the succeeding sheet achieves the reversal roller pairs
18
before the rotation of the reversal roller pair
18
is switched to the forward rotation, the succeeding sheet stops in a state where its leading end portion cannot enter in the reversal roller pair
18
, so that sheet jam occurs.
In order to solve the above problem, in the conventional image forming apparatus, the following methods are proposed and executed. As a first method, the induction roller pair
17
,
17
a
is constituted by the drive roller different from the drive roller of the feed roller pair
17
,
17
b
, the transporting velocity at the downstream of the sheet reversing device is heightened, and the reverse rotation velocity of the reversal roller pair
18
is made speedier than the forward rotation velocity thereof thereby to quickly exhaust the reversed sheet. As a second method, nip release mechanism that releases a nip of the reversal roller pair is provided, the nip is released before the succeeding sheet reaches the reversal roller, and two sheets that move in the opposite direction to each other can be existed between the reversal roller pair
18
. As a third method, the distance between the preceding sheet and the succeeding sheet is made large.
However, according to the conventional first method, the transporting velocity at the downstream of the sheet reversing device becomes so high in the device transporting the sheets at the high speed that the driving force necessary for sheet transportation becomes large. Further, since consumption of the abrasive system of the sheet transporting device is severe, reliability of the device lowers. Further, since the velocity of the sheet exhausted from the sheet outlet
11
is different between a case that the sheet is reversed and a case that the sheet is not reversed, the sheet handling device
2
must correspond to the velocity of two kinds, so that the constitution of the device becomes complicated. Further, according to the conventional second method, the nip release mechanism so constituted that the drive roller constituting the reversal roller pair
18
is fixed and a pinch roller opposed to the drive roller is constituted separably in relation to the drive roller is simple and cheap in constitution. However, since the drive roller is exposed on the transporting passage, in case that the sheet that moves in the direction opposite to the rotational direction of the aforesaid drive roller passes, the sheet leading end is bent or stained due to action of the relative motion between the drive roller and the sheet, so that there is fear that bad influences on the succeeding sheet transportation and on the print quality occur. As a method for solving this fear, th
Hashimoto Yasushi
Miwa Masato
Terakado Akira
Chen Sophia S.
Hitachi Koki Co,. Ltd.
Tran Hoan
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