Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
1998-08-31
2001-01-16
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Feeding
Separators
C271S109000, C271S117000, C271S119000
Reexamination Certificate
active
06173951
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sheet feeder provided in an image forming device such as a copy machine, laser printer, and facsimile machine, and more particularly, to a sheet feeder for feeding stacked sheets of a recording medium one sheet at a time.
An example of a conventional sheet feeding device provided in image forming devices such as copy machines, laser printers, and facsimile devices is shown in FIG.
10
. This sheet feeding device is provided with a feed roller
1
and a separating pad
3
opposite the feed roller
1
for conveying a sheet
2
of a recording medium one sheet at a time from a stack of sheets. The separating pad
3
is inset into a depression formed in a sheet receiving portion
5
of a separating pad holder
4
. The separating pad holder
4
is urged toward the feed roller
1
by a spring
7
interposed between a fixed stop member
6
and the bottom surface of the sheet receiving portion
5
. The feed roller
1
is formed of an elastic material in an approximate D-shape and includes a circumferential surface portion
8
for contacting and conveying the sheet
2
and a cutout surface portion
9
formed by cutting away a portion of the circumferential surface portion
8
. Rollers
10
are rotatably mounted on both ends of the feed roller
1
. Both of the rollers
10
are formed with a radius slightly smaller than the radius of the circumferential surface portion
8
. Hence, when the circumferential surface portion
8
is conveying the sheet
2
, the rollers
10
do not contact the sheet
2
. However, when the circumferential surface portion
8
has completed conveying the sheet
2
and the cutout surface portion
9
opposes the sheet
2
, the peripheral surfaces of the two rollers
10
contact the sheet
2
and oppose the urging force of the separating pad
3
, thereby forming a space between the cutout surface portion
9
and the sheet
2
to prevent the cutout surface portion
9
from contacting the sheet
2
.
Guide rollers
12
and
13
are positioned downstream of the feed roller
1
and convey the sheet
2
after the circumferential surface portion
8
has completed conveying the sheet
2
. Although not shown in the drawings, each time the feed roller
1
conveys a sheet
2
, the rotation of the feed roller
1
is suspended for a predetermined period when the cutout surface portion
9
is brought into confrontation with the sheet
2
and the two rollers
10
separate the cutout surface portion from the sheet. In this case, the rollers
10
contact and rotate on the top surface of the sheet
2
, while the guide rollers
12
and
13
convey the sheet
2
, thereby allowing only one sheet
2
to be conveyed at a time.
However, when conveying the sheet
2
in this way, the circumferential surface portion
8
and the rollers
10
contact the sheet
2
and separating pad
3
at different heights, because the radius of the two rollers
10
is smaller than the radius of the circumferential surface portion
8
. This difference in radii creates a bump when the sheet
2
and separating pad
3
change from contacting the rollers
10
to contacting the circumferential surface
8
and vice versa, causing the separating pad
3
to move upward and downward.
SUMMARY OF THE INVENTION
If the difference in radii is large, then when the sheet
2
and separating pad
3
contacted by the two rollers
10
comes in contact with the circumferential surface portion
8
of the feed roller
1
, the circumferential surface portion
8
pushes down on the sheet
2
and separating pad
3
due to the difference in radii, causing a large fluctuation in pressure at that moment. This fluctuation in pressure invites a plurality of sheets
2
, sometimes referred to as doubles, to be fed simultaneously between the circumferential surface portion
8
and the separating pad
3
, particularly when the sheet
2
recording medium is thin or lightweight. On the other hand, if the difference in radii is small, the circumferential surface portion
8
does not push very strongly on the sheet
2
or separating pad
3
, but the pressure needed to convey the sheet
2
is low, inviting the occurrence of empty feeds, in which the sheet
2
is not fed. This is particularly common when the sheet
2
is thick or heavy.
Hence, this construction for conveying a sheet of recording medium by a feed roller having a circumferential surface portion and a cutout surface portion has conflicting properties, in that feeding of doubles can occur easily if the difference in radii described above is large, while empty feeds can occur if the difference is small. As a result, it is not possible to design a device that can reliably feed sheets regardless of the thickness and weight of the sheet, thereby lowering the degree of freedom in design.
In view of the foregoing, it is an object of the present invention to provide a sheet feeder configured with the feed roller having the circumferential surface portion and the cutout surface portion and capable of reliably feeding sheets of a recording medium regardless of the thickness, weight, and other qualities of the recording medium.
This and other objects of the present invention will be attained by providing a sheet feeder for feeding each sheet of recording medium, the sheet feeder includes a feed roller, a separating pad, a space forming member, and means for changing a distance. The feed roller has a roller shaft defining an axial center and a roller body provided with a circumferential surface portion having a first radius for contacting and conveying a sheet of a recording medium, and a cutout surface portion formed by cutting out a portion of the circumferential surface portion. The separating pad opposes the feed roller and is urged toward the feed roller for interposing the sheet between the separating pad and the feed roller. The space forming member has a contact portion contacting the sheet and the separating pad and forms a space between the cutout surface portion and the separating pad when the cutout surface portion is opposite to the separating pad. The space forming member is provided around the roller shaft. The distance changing means is adapted for changing a distance from the axial center to the contact portion. The changing means is provided in association with the space forming member and the roller shaft.
In another aspect of the invention, there is provided an image forming device includes a casing, at least one cassette, the sheet feeder, a pair of guide rollers, and an image forming unit. The casing has at least one cassette accommodating section. The at least one cassette maintains a stack of sheets and is detachably mounted on the at least one cassette accommodating section. The sheet feeder is provided immediately downstream of the at least one cassette, the sheet feeder includes the above described feed roller, the separation pad, the space forming member, and means for changing the distance from the axial center to the contact portion. The pair of guide rollers are provided immediately downstream of the sheet feeder for conveying each sheet fed by the sheet feeder. The image forming unit is positioned downstream of the pair of guide rollers for forming an image on the sheet fed by the pair of guide rollers. The image forming unit includes a photosensitive drum and a transfer roller in confronting relation to the photosensitive drum.
REFERENCES:
patent: 5244191 (1993-09-01), Kanekura
patent: 5570876 (1996-11-01), Samii
patent: 5582399 (1996-12-01), Sugiura
patent: 5934664 (1999-08-01), Murayama et al.
Asada Tetsuo
Inoue Mitsuaki
Makino Kazumasa
Brother Kogyo Kabushiki Kaisha
Martin Brett C.
Oliff & Berridg,e PLC
Walsh Donald P.
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