Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
2000-07-27
2001-12-18
Bollinger, David H. (Department: 3651)
Sheet feeding or delivering
Feeding
Separators
C271S119000, C271S124000
Reexamination Certificate
active
06331002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding apparatus for separating sheets stacked on a sheet stacking portion one by one and for feeding the separated sheet to an image forming apparatus.
2. Related Background Art
Among conventional image forming apparatus such as printers, copying machines, facsimiles and the like, there is an image forming apparatus in which an image is formed on a thick sheet such as a post card and an envelope or a special sheet such as a plastic thin plate, as well as a plain paper. In such an image forming apparatus, the feeding of the sheet to an image forming portion is effected by manual sheet insertion one by one or is effected by a sheet feeding apparatus automatically and continuously.
FIG. 10
shows a schematic construction of a printer as an example of an image forming apparatus having such a sheet feeding apparatus. In
FIG. 10
, a sheet P fed by a sheet feeding apparatus
1
A for feeding sheets to printing means
4
one by one is conveyed while being pinched between conveying rollers
2
,
3
, and, after printing is effected by the printing means
4
, the sheet is discharged out of the apparatus by discharge rollers
5
,
6
.
Such a sheet feeding apparatus
1
A is disclosed in Japanese Utility Model Publication No. 8-3396, for example, and
FIG. 11
shows a construction of such an apparatus.
In
FIG. 11
, a sheet feeding roller
10
having a D-shaped cross-section has a cylindrical portion
10
a
and a straight portion
10
b
. Incidentally, a shaft
10
c
of the sheet feeding roller
10
is supported by a guide block
11
. Further, a cassette
12
has therein a stacking plate
12
a
on which a plurality of sheets are set in a stacked condition. By a biasing force of a spring
12
c
for biasing the stacking plate
12
a
, a sheet stack P stacked (rested) on the stacking plate is biased toward the sheet feeding roller
10
.
A separation pad
13
attached to a bracket
13
a
is disposed in a rotational movement path of the cylindrical portion
10
a
of the sheet feeding roller
10
and is biased the shaft
10
c
of the sheet feeding roller along a guide
15
by means of a spring
14
.
An idle (idler) roller
16
is rotatably attached to the guide block
11
, and a movable idle roller
17
is attached in an elongated groove
11
a
of the guide block
11
via a shaft
17
a
for shifting movement. The movable idle roller
17
is biased toward the separation pad
13
by a spring
18
to abut against the separation pad
13
. Incidentally, a biasing force F
2
of the spring
18
is selected to be smaller than a biasing force F
1
of the spring
14
of the separation pad
13
(i.e., F
1
>F
2
).
Further, when it is assumed that a friction force between the cylindrical portion
10
a
of the sheet feeding roller
10
and an uppermost sheet P
1
in the sheet stack is f
1
, a friction force between a next sheet P
2
and the separation pad
13
is f
2
, and a friction force between the uppermost sheet P
1
and the next sheet P
2
is f
3
, coefficients of friction of the sheet feeding roller
10
and the separation pad
13
are selected to satisfy the following relationship:
f
1
>
f
2
>
f
3
.
Now, a sheet feeding operation of the sheet feeding apparatus
1
A will be explained.
In a waiting condition, as shown in
FIG. 11
, the straight portion
10
b
of the sheet feeding roller
10
is opposed to the sheet stack P so that the sheet feeding roller
10
is not contacted with the sheet P. Further, since the biasing force F
2
of the spring
18
of the movable idle roller
17
is smaller than the biasing force F
1
of the spring
14
of the separation pad
13
, the movable idle roller
17
is pushed upwardly by the separation pad
13
so that the shaft
17
a
abut against an upper end of the elongated groove
11
a.
When the sheet feeding operation is started, the sheet feeding roller
10
is rotated in a direction shown by the arrow, and, by contacting the circular portion
10
a
with the uppermost sheet P
1
in the sheet stack P, the uppermost sheet P
1
is sent toward the separation pad
13
. In this case, due to the friction force between the sheet P
1
and the next sheet P
2
, the next sheet P
2
may be sent together with the uppermost sheet P
1
. However, the next sheet P
2
is separated from the uppermost sheet P
1
by the separation pad
13
in the following manner, and only the uppermost sheet P
1
is fed.
When a leading end of the next sheet P
2
abut against the separation pad
13
, the movement of the next sheet is prevented to primarily separate the next sheet from the uppermost sheet P
1
. Further, as mentioned above, since the friction force f
1
between the cylindrical portion
10
a
of the sheet feeding roller
10
and the uppermost sheet P
1
, the friction force f
2
between the next sheet P
2
and the separation pad
13
and the friction force f
3
between the uppermost sheet P
1
and the next sheet P
2
are selected to satisfy the relationship f
1
>f
2
>f
3
, as the sheet feeding roller is rotated, when both the uppermost sheet P
1
and the next sheet P
2
are pinched between the cylindrical portion
10
a
of the sheet feeding roller
10
and the separation pad
13
, the next sheet P
2
a prevented from being moved by the friction force f
2
between the separation pad
13
and the next sheet and is secondarily separated from the uppermost sheet P
1
, with the result that only the uppermost sheet P
1
is fed.
Thereafter, when the sheet feeding roller
10
is further rotated, the sheet feeding roller
10
is returned to the waiting condition where the separation pad
13
is not urged by the cylindrical portion
10
a
, as shown in FIG.
11
. Incidentally, in this case, due to the difference between the biasing forces F
1
, F
2
of the springs
14
,
18
, a separation pad
13
is stopped in a condition that the movable idle roller
17
is pushed upwardly until the shaft
17
a
abuts against the upper end of the elongated groove
11
a.
By the way, since the separation pad
13
is disposed in the rotational movement path of the cylindrical portion
10
a
of the sheet feeding roller
10
, as the cylindrical portion
10
a
is rotated, the separation pad
13
is pushed downwardly by the cylindrical portion
10
a
. Since the movable idle roller
17
is biased toward the separation pad
13
by the spring
18
, even when the separation pad
13
is pushed downwardly, the movable idle roller abuts against the separation pad
13
, and this abutment aids the separating operation.
Further, by adopting the arrangement in which the movable idle roller
17
is biased toward the separation pad
13
to pinch the sheet P
1
between the movable idle roller and the separation pad
13
, even when the friction force acts between the uppermost sheet P
1
and the next sheet P
2
, while the sheet P
1
is being conveyed by the conveying rollers
2
,
3
, the next sheet P
2
can be prevented from being sent together with the uppermost sheet P
1
.
By the way, when such a conventional sheet feeding apparatus is used in the printer as shown in
FIG. 10
, the fed sheet P
1
is conveyed while being pinched between the conveying rollers
2
,
3
and is printed by the printing means
4
. In this case, when the conveyance of the sheet P
1
by the conveying rollers
2
,
3
is started, normally, the sheet P
1
is not completely left from the sheet feeding apparatus
1
A. That is to say, a trailing end portion of the sheet P
1
is pinched between the separation pad
13
and the movable idle roller
17
, and the sheet P
1
is conveyed by the conveying rollers
2
,
3
in this condition.
Accordingly, the sheet P
1
is conveyed by the conveying rollers
2
,
3
in a condition that the sheet is subjected to load due to the pinching (in a condition that the load acts on the trailing end of the sheet) until the trailing end of the sheet leaves the nip between the separation pad
13
and the movable idle roller
17
.
As mentioned above, since the separation pad
13
serves to prevent double-feeding by pinching the she
Asai Yasuyuki
Katayanagi Jun
Sonoda Shinya
Yanagi Haruyuki
Yoshino Hiroshi
Bollinger David H.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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