Typewriting machines – Sheet or web – Including sheet guide
Reexamination Certificate
1999-09-21
2001-11-06
Hilten, John S. (Department: 2854)
Typewriting machines
Sheet or web
Including sheet guide
C400S624000, C271S264000
Reexamination Certificate
active
06312178
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to media handling apparatus, and more particularly to techniques for reducing trailing edge print defects in printing devices with media-handling rollers.
BACKGROUND OF THE INVENTION
Inkjet printers typically have an input media source such as a media stack in an input tray, an output tray, a media path between the input source and the output tray, and an inkjet printing apparatus located along the media path at a print area. The printing apparatus can comprise one or more inkjet printheads with nozzle arrays which emit droplets of ink onto the print media at the print area. A media handling apparatus is provided to pick the input media from the input source, feed the picked medium along the media path to the print area, and eject the picked medium onto the output tray after printing operations on the medium are completed.
In a typical sheet-fed printer using print media in sheet form, such as paper, a pick roller is employed to pick the top sheet of print media from the input tray and advance the picked sheet along the media path toward the printing apparatus. This is illustrated in the diagrammatic view of
FIG. 1
, wherein the pick roller
10
with associated pinch roller
13
has picked the sheet
12
from an input source (not shown), and pulled the sheet around the input guide
15
with curved guide surface
15
A. The sheet handling apparatus further typically includes a feed or drive roller
14
and a forward pinch roller
16
which create a nip into which the leading edge of the picked sheet is fed by the pick roller along guide
18
. The print zone at which printing operations are conducted is typically located on the media path just downstream of the pinch roller
16
. Stresses are applied to the picked sheet at the print zone for media shape control and wet cockle control.
A problem arises in that the trailing edge
12
A of the picked sheet is unconstrained after leaving the pick roller. Because of the stresses applied to the picked sheet in the print zone, the unconstrained shape of the sheet after leaving the pick roller is significantly rotated about the forward pinch roller
16
. This is illustrated in
FIG. 1
, in which the constrained state prior to leaving the pick roller
10
and pinch roller
13
is indicated as sheet
12
with trailing edge
12
A, and the unconstrained state is indicated as sheet
12
′ with trailing edge
12
A′. This results in a rapid print medium shape change in stiff media that can cause an effective overfeed as seen by the print head just downstream of the nip between the drive roller and pinch roller. The effective overfeed causes a print defect, known as a “bottom of form” (BOF) print defect. This print defect is often quite visible on images printed on premium photo paper, for example.
Another cause of print defects for media handling apparatus incorporating separate roller wheels instead of solid rollers, is that, as the print medium is compressed under pinch rollers, energy is stored in the medium by deforming the print medium around the rollers. This is illustrated in the cross-section view of
FIG. 2
, taken transversely to the media path. Here the pick roller structure and the pinch roller structure is defined by three spaced pick roller wheel/pinch wheel pairs,
10
A/
13
A,
10
B/
13
B and
10
C/
13
C. The deformation of the medium
12
in the regions between the wheel pairs is illustrated in exaggerated form in FIG.
2
. This deformation can cause overfeeding, especially on stiff medias, when the trailing edge of the medium leaves the nip between the drive and pinch rollers.
These print defects will generally be described as “trailing edge” print defects, i.e. those print defects occurring when the trailing edge of the print media passes some point, e.g. a pinch point or the pick roller.
It would therefore be an advantage to provide a technique to minimize or eliminate trailing edge print defects in printing systems using media handling apparatus with one or more rollers.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention, a media handling system is described for handling sheets of media. The system includes a pick roller having a circumferential media-contacting surface and arranged for rotation about a roller axis to contact and pick a sheet from an input source. A drive roller is arranged for rotation about a drive roller axis, with a media path extending between the pick roller and the drive roller. A first guide structure is positioned along a first longitudinal edge of the media path and providing a first media guide surface. A second guide structure is positioned along a second longitudinal edge of the media path and provides a second media guide surface. The first and second guide surfaces are positioned to constrain the movement of a media sheet in the media path between the pick roller and the drive roller, thereby alleviating trailing edge print defects.
REFERENCES:
patent: 5177547 (1993-01-01), Kanemitsu et al.
patent: 5192141 (1993-03-01), Chung et al.
patent: 5940106 (1999-08-01), Walker
patent: 5975778 (1999-11-01), Kanemitsu
patent: 6120201 (2000-09-01), McKay et al.
patent: 0737589 (1996-10-01), None
patent: 0816107 (1998-01-01), None
European Search Report dated Mar. 16, 2001 re European Patent Application 00307498.6-2304-.
Patent Abstracts of Japan, vol. 012, No. 105 (M-681), Apr. 6, 1988.
Davis Robert D.
Schwiebert William H.
Sunada Craig D.
Hewlett--Packard Company
Hilten John S.
Williams Kevin D.
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