Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
2000-07-17
2002-01-29
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Feeding
Separators
Reexamination Certificate
active
06341774
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 USC 119 and contains subject matter related to Japanese Patent Application No. 11-202550 filed in the Japanese Patent Office on Jul. 16, 1999, the entire contents of which are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding device for use in an image forming apparatus such as a copying machine, a facsimile, a laser printer, or similar image forming apparatus.
2. Discussion of the Background
FIG. 5
is a schematic cross-sectional view illustrating a conventional sheet feeding device of an image forming apparatus, such as a laser printer.
FIG. 6
is a cross-sectional view illustrating a part in the vicinity of a sheet feeding roller of the conventional sheet feeding device of FIG.
5
. The image forming apparatus in
FIG. 5
includes a sheet feeding roller
1
, a sheet feeding cassette
2
, a cassette bottom plate
3
, a pair of sheet conveying rollers
4
, sheets
5
, an image forming section
6
, a fixing section
7
, a sheet discharging section
8
, and a sheet discharging tray
9
. The sheet feeding cassette
2
is configured so that it can be removed from the image forming apparatus by being drawn out to the right-hand side as seen in FIG.
5
.
As illustrated in
FIG. 6
, the sheet feeding device includes a friction pad
10
at a lower portion of the sheet feeding roller
1
to separate a top sheet from the rest of the stack of sheets
5
in the sheet feeding cassette
2
. The sheets
5
in the sheet feeding cassette
2
are fed through the conventional sheet feeding device via a friction pad sheet separating method. The friction pad
10
is attached to a friction pad pedestal
11
that is biased by a spring
12
to protrude upwardly. However, the friction pad pedestal
11
is prevented from protruding too far past a predetermined extent by a hook pawl
11
a
which is provided at a lower end portion of the friction pad pedestal
11
and is caught by a part of a holding section
2
a
of the sheet feeding cassette
2
.
Operations of the sheet feeding device will now be described. First, the sheet feeding roller
1
rotates when a clutch (not shown) is turned on by a driving device (not shown), and thereby starts to feed the sheets
5
. Then, a top sheet is separated from the rest of the sheets
5
in the sheet feeding cassette
2
by the friction pad
10
which is pressed by the sheet feeding roller
1
. The top sheet is then conveyed to the sheet conveying rollers
4
which are disposed downstream of the sheet feeding roller
1
in the sheet conveying direction. After the leading edge of the top sheet reaches a nip portion between the sheet conveying rollers
4
, the driving of the sheet feeding roller
1
is stopped when the clutch is turned off by the driving device. Subsequently, the sheet feeding roller
1
is rotated together with the top sheet conveyed by the sheet conveying rollers
4
. When the trailing edge of the top sheet passes through a nip portion between the sheet feeding roller
1
and the friction pad
10
, the rotation of the sheet feeding roller
1
is stopped.
In the above-described operations of the sheet feeding device, a load or force F is received by the top sheet of the sheets
5
when the top sheet of the sheets
5
is pulled out from the sheet feeding cassette
2
by the sheet conveying rollers
4
under the condition that the sheet feeding roller
1
is not driven. The load F is a sum of a load Fp and a load Ff and a load Fk. The load Fp is received by the top sheet of the sheets
5
when the cassette bottom plate
3
presses the top sheet of the sheets
5
against the sheet feeding roller
1
. The load Ff is received by the top sheet of the sheets
5
when the top sheet of the sheets
5
is pressed against at the nip between the sheet feeding roller
1
and the friction pad
10
. The load Fk is a sum of a load received by the top sheet of the sheets
5
when the top sheet of the sheets
5
is bent along a curved sheet conveying path, another load received by the top sheet of the sheets
5
when the sheet feeding roller
1
is rotated together with the top sheet of the sheets
5
conveyed by the sheet conveying rollers
4
, and other loads.
In the above-described sheet feeding device, the load Fp is in a range of about 150 gf to 250 gf, the load Ff is in a range of about 250 gf to 400 gf, and the load Fk is in a range of about 50 gf~150 gf. Therefore, the load F is in a range of about 450 gf~800 gf. Because the sheet conveying rollers
4
pull out the top sheet of the sheets
5
from the sheet feeding cassette
2
against the above-described load, the following problems typically occur. First, the sheet conveying rollers
4
are likely to be worn due to heavy load. Second, if rubber of superior wear resistance is used for the sheet conveying rollers
4
so as to improve the wear resistance of the sheet conveying rollers
4
, an increase in cost will result. Third, in order to convey the top sheet of the sheets
5
with a stable speed, it may be necessary to increase the sheet conveying force of the sheet conveying rollers
4
. However, for this reason, a roller holding section for the sheet conveying rollers
4
may need to be of sturdy construction, and the load of the motor may increase. Thus, both an increased cost and size of the image forming apparatus may result.
In order to reduce the above-described load received by a sheet when the sheet is conveyed by the sheet conveying rollers
4
, a conventional sheet feeding roller, having a cross-sectional shape which is approximately a partly cut-off circle (e.g., a semicircle), is known. As illustrated in
FIGS. 7A through 7D
, a sheet feeding roller
20
has a cross-sectional shape of a partly cut-off circle including an arc portion
22
and a chord portion
21
. It is configured so that after one rotation of the sheet feeding roller
20
, the sheet feeding roller
20
does not contact the friction pad
10
and the stack of sheets
5
in the sheet feeding cassette
2
.
As illustrated in
FIG. 7A
, when the sheet feeding roller
20
is in a standby condition, the sheet feeding roller
20
is held such that the chord portion
21
of the sheet feeding roller
20
faces both the friction pad
10
and the stack of sheets
5
in the sheet feeding cassette
2
. In this standby condition, the hook pawl
11
a
, which is provided at a lower end portion of the friction pad pedestal
11
, is caught by the portion of the holding section
2
a
provided at the rear end of the sheet feeding cassette
2
, so that the friction pad
10
is not elevated to a higher position. Thereby, a gap is formed between the upper surface of the friction pad
10
and the chord portion
21
of the sheet feeding roller
20
. Moreover, when the sheet feeding roller
20
is in the standby condition, the cassette bottom plate
3
is locked by a locking mechanism (not shown), so that the sheets
5
in the sheet feeding cassette
2
are not elevated to a higher position. Thereby, the gap formed between the surface of the sheets
5
and the chord portion
21
of the sheet feeding roller
20
remains the same.
In the sheet feeding device including the sheet feeding roller
20
having a cross-sectional shape of a partly cut-off circle, when the feeding of the top sheet of the sheets
5
is begun, the sheet feeding roller
20
starts its one full rotation under the action of a one-rotation clutch (not shown). When the sheet feeding roller
20
starts to rotate, the cassette bottom plate
3
is unlocked by releasing the locking mechanism immediately before the arc portion
22
of the sheet feeding roller
20
contacts the top sheet of the sheets
5
. Subsequently, the arc portion
22
contacts the top sheet of the sheets
5
in the sheet feeding cassette
2
, and a few sheets of the sheets
5
start to be fed by the sheet feeding roller
20
as the sheets
5
are pressed against the sheet feeding roller
20
by a biasing force of a spring
23
serving as a bottom p
Bower Kenneth W
Ellis Christopher P.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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