Photocopying – Using microcapsules – Sheet feeding
Reexamination Certificate
1999-06-24
2001-11-27
Adams, Russell (Department: 2851)
Photocopying
Using microcapsules
Sheet feeding
C355S024000, C355S023000
Reexamination Certificate
active
06323939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile and the like, and more particularly, it relates to an image forming apparatus having a sheet re-feeding apparatus for re-feeding a sheet to permit formation an image on a second surface of the sheet having a first surface on which an image was already formed.
2. Related Background Art
In the past, image forming apparatuses such as copying machines, printers, facsimiles and the like, having a both-face mode for forming images on both surface of a single sheet are already known.
FIG. 7
shows an entire construction of a conventional image forming apparatus having a both-face mode.
At left and right parts of a lowermost portion of a main body
2
of an image forming apparatus
1
, there are provided deck cases (sheet stacking means)
3
a
,
3
b
disposed side by side. For example, these deck cases
3
a
,
3
b
are capable of containing of about 1500 small size sheets (such as A4 size sheets) which are frequently used.
In
FIG. 7
, sheets P in the right deck case
3
a
are supplied and separated at a sheet supply portion
31
a
, and the separated sheet is directed into a registration introduction path (sheet convey path)
5
b
through a sheet feed path
5
d.
In
FIG. 7
, sheets P in the left deck case
3
b
are supplied and separated at a sheet supply portion
31
b
, and the separated sheet is directed into the registration introduction path
5
b
through a sheet feed path
5
a.
The sheet P introduced into the registration introduction path
5
b
is passed through an introduction path
5
c
and is conveyed to an image forming portion (transfer portion)
11
through a pair of registration rollers
10
.
The sheet P on which an image was formed (transferred) in the image forming portion
11
is conveyed to a fixing device
15
through a convey portion
13
. In the fixing device
15
, heat and pressure are applied to the sheet to fix a toner image to the sheet P.
A pair of sheet discharge rollers
17
are disposed at a downstream side of the fixing device
15
. A flapper
16
for switching the sheet P having a first surface on which the image was formed toward a reversing introduction path
18
is disposed between the fixing device and the pair of sheet discharge rollers
17
.
In a both-face mode, after the image was formed on the first surface of the sheet, the sheet P is guided into the reversing introduction path
18
by the flapper
16
, and the reversing a front surface and a rear surface of the sheet is effected in a reversing portion
19
, and then, the sheet is conveyed to a re-feed path
20
. When the sheet P is entered into the re-feed path
20
, the sheet was turned over.
The sheet P is conveyed through the re-feed path
20
. When a leading end of the sheet P reaches a sheet sensor
20
b
, the fact that the sheet P reached an end of the re-feed path
20
is detected by the sheet sensor
20
b.
As a result, command is emitted from a control means (not shown) to a drive means (not shown) of the re-feed path
20
, so that the drive means is temporarily stopped to temporarily stop the sheet P at a waiting position
20
p
spaced apart from the sheet sensor
20
b
by several ten millimeters in a downstream direction. Thereafter, the sheet P having the first surface on which the image was formed is fed into the registration introduction path
5
b
again through a junction
5
bj
to the registration introduction path
5
b
at a predetermined timing after a new sheet P was supplied from the sheet feed path
5
a
or
5
d.
Thereafter, similar to the formation of the image on the first surface, an image is formed on a second surface of that sheet P, and then, the sheet is discharged out of the image forming apparatus by the pair of sheet discharge rollers
17
. In this way, the image forming apparatus
1
shown in
FIG. 1
can form the images on both surfaces of the sheet P.
The image forming apparatus
1
serves to alternately send a sheet P fed from the deck
3
a
and having a first surface on which an image is to be formed and a sheet fed from the re-feed path
20
and having the first surface on which the image was formed to the image forming portion
11
. That is to say, the sheet P having the first surface on which the image is to be formed and the sheet P having the first surface on which the image was formed and the second surface on which the image is to be formed are alternately introduced into the registration introduction path
5
b
(this is referred to as “alternate feeding” hereinafter).
Accordingly, the flapper
16
can effect the re-feed guide of the sheet having the first surface on which the image was formed and the second surface on which the image is to be formed and the discharge guide of the sheet P having both surfaces on which the images were formed alternately for each sheet.
Incidentally, above the reversing portion
19
and the re-feed path
20
, there are disposed cassettes
4
b
,
4
a
(stacked vertically) capable of selectively containing large size sheets (such as A3 size sheets) and small size sheets (such as A4 size sheets). For example, the cassettes
4
b
,
4
a
can contain about 500 sheets P.
By the way, in case of the above-mentioned conventional image forming apparatus
1
, a both-face unit
21
including the reversing portion
19
and the re-feed path
20
, and the sheet feed path
5
a
for the left deck case
3
b
are designed so that they can be retracted forwardly (toward a front side of the main body) independently.
Thus, if the sheet P is jammed, when the jam treatment is being effected by retracting either the both-face unit
21
or the sheet feed path
5
a
, the other cannot be retracted for the jam treatment.
That is to say, the conventional image forming apparatus
1
has a disadvantage that the sheet feed path
5
a
and the both-face unit
21
cannot be retracted simultaneously.
Further, comparing the installation position of the left deck case
3
b
with the installation position of the right deck case
3
b
with respect to the waiting position
20
p
for the sheet P to be re-fed, since the left deck case
3
b
is more spaced apart from the waiting position than the right deck case, when the alternate feeding is effected by using the left deck case
3
b
, the stopping time of the re-fed sheet P is increased accordingly.
Accordingly, in the conventional image forming apparatus
1
, in the case where the small size sheets (such as A4 size sheets) in the deck case are copied by several hundred sheets, when the sheets P in the right deck case
3
a
are copied, since the sheets can be copied with substantially the same sheet-to-sheet interval, the both-face copying productivity is good, but, when the sheets P in the left deck case
3
b
are copied, the sheet-to-sheet interval (sheet interval) is increased, with the result that the both-face copying productivity is worsened.
To solve this problem, it is considered that a conveying speed of the sheet P supplied from the left deck case
3
b
. In this case, however, it is required that the conveying speed must be increased by several times in order to make the sheet-to-sheet interval for the sheets supplied from the left deck case substantially the same as the sheet-to-sheet interval for the sheets supplied from the right deck case
3
a
, with the result that control becomes complicated and/or conveying performance becomes unstable.
Accordingly, an object of the present invention is to provide an image forming apparatus in which (1) a re-feed path and a sheet feed path can be retracted simultaneously, and (2) even when a sheet is fed either one of sheet stacking means arranged side by side, a both-face image processing time for the sheet becomes substantially the same, and any loss of productivity does not occur in feed position switching.
SUMMARY OF THE INVENTION
To achieve the above object, the present invention relates to an image forming apparatus comprising a plurality of sheet stacking means for stacking sheets, a plurality
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kim Peter B.
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