Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-12-21
2003-10-21
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S104000, C400S636000
Reexamination Certificate
active
06634745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording medium.
2. Description of the Related Art
In general, an ink jet recording apparatus as one type of image forming apparatus has a recording head which discharges ink droplets to form and record on a recording medium characters, images and so forth (collectively referred to as an “image” hereinafter). The term “recording medium” is used in this specification to generally encompass web or sheet-type media which have small thicknesses and on which images are formable by an ink. Thus, the recording medium may be a sheet of plain paper, a sheet of resinous recording medium as a substitute for the plain paper, a postcard, an envelope, a label, and so on. In this specification, the term “sheets” is used to encompass all such possible recording media.
Ink jet recording apparatuses offer various advantages such as ease of miniaturization of recording heads, capability of recording fine images at high speed, low running cost, reduced noise level due to non-impact nature, and ease of recording color images with multiple color inks.
In general, an ink jet recording apparatus is configured such that a recording medium sheet is fed from a sheet feed section onto a platen which opposes a recording head and which supports the recording medium sheet at the reverse side thereof while the recording head records an image on the obverse side of the recording medium sheet. The recording medium sheet carrying the image recorded thereon is ejected from the apparatus through an ejecting section which is disposed at the downstream end as viewed in the direction of convey of the recording medium sheet.
To be more specific, reference is made to
FIG. 8
which shows an overall arrangement of a known ink jet recording apparatus generally denoted by
1
,
FIG. 9
which is a sectional view of the ink jet recording apparatus
1
, and
FIG. 10
which shows a portion of the apparatus
1
including a recording medium sheet ejecting section denoted by
4
. In
FIG. 10
, components such as a conveyor roller
36
, a pinch roller
37
, spurs
42
, an ejecting roller
41
, as well as a sheet P, are schematically shown in a perspective view. Since
FIG. 10
is a schematic illustration, the dimensional relationships between the components in this Figure do not exactly conform with those in FIG.
9
. Reference is made also to
FIG. 11
which is a sectional view taken along the line C—C of FIG.
10
.
Referring to
FIGS. 8
to
11
, a stack of recording medium sheets P is placed on a sheet feed section
2
, and the recording medium sheets are fed by a sheet feed roller
22
in one-by-one fashion starting from the topmost sheet toward a position where a recording head
7
is located. The sheet P is nipped between the pinch roller
37
and the conveyor roller
36
which is driven by power derived from a drive source which is not shown, and is conveyed to a recording start position on a platen
34
.
The recording head
7
is detachably secured to a carriage
50
which is carried by a guide shaft
81
for reciprocal movement along the guide shaft
81
in directions which cross the direction of convey of the sheet P. Thus, the recording head
7
performs recording of images on the sheet P which is being conveyed, while moving in directions that cross the direction of movement of the sheet P.
The ejection roller
41
is driven by the conveyor roller
36
through a transmission roller
40
. The ejection roller
41
has a plurality of roller elements
41
a
which are made of an elastomer or a rubber and which are arranged in the direction of width of the sheet P so as to convey the sheet P.
There are a plurality of spurs
42
each of which is held in pressure contact with the associated roller element
41
a.
Each spur
42
rotates in contact with the recording medium sheet which carries an image formed thereon. In order to prevent transfer of the ink, therefore, the spur
42
has a plurality of radial projections with pointed ends.
The recording sheet medium P is pinched between and conveyed by the conveyor roller
36
and the pinch roller
37
, until its leading end is caught between the ejection roller
41
and the spur
42
. The sheet P, after its trailing end has cleared the nip between the conveyor roller
36
and the pinch roller
37
, is conveyed by the ejection roller
41
and the spur
42
. The sheet P is then ejected onto and received by a sheet ejection tray
100
.
The upper surface of the platen
34
has a plurality of ribs
34
a
which project therefrom and which extend in the direction of movement of the sheet P. The ribs are arranged at intervals in a direction which crosses the direction of movement of the sheet P. Each rib
34
a
is aligned with one of the spurs
42
which is disposed downstream of the rib
34
a,
as viewed in the direction of movement of the sheet P. In other words, each rib
34
and the associated spur
42
are disposed on a common straight line which extends in the direction of movement of the sheet P. With this arrangement, crests of waviness of the recording medium sheet, which occur when the sheet P is wetted by the ink, are flattened by the effect of the spurs
42
. This waviness will be referred to as “cockling”, hereinafter. In addition, the sheet P is caused to cockle downward at portions thereof not supported by the ribs, so that floating of the sheet P is minimized while the sheet passes through the recording section.
The cockling of the sheet P occurs at regular portions thereof due to the regular arrangement of the ribs
34
a.
This means that the distance between the sheet P and the recording head
7
regularly varies along the breadth of the sheet P, which if not corrected may degrade the quality of the recorded image. In order to obviate this problem, the discharge of the ink from the recording head
7
is performed so as to compensate for any influence caused by the presence of the ribs the height of which is known, whereby any degradation of the image quality which otherwise may be caused by the presence of the ribs is effectively corrected.
The problem of cockling is serious particularly when an image is “painted” with a dye color ink which is permeable to the material of the recording medium sheet. In order that images of high quality are stably formed with this type of ink, it is necessary to strictly maintain a constant gap between the sheet P and the recording head, thereby minimizing undesirable effects of cockling.
Image recording apparatuses also have recently been proposed which use pigment-type black ink in order to increase the density of black color of images. A considerably long time is required for this type of ink to be dried and fixed after being deposited on a recording medium sheet. A problem is therefore encountered with the use of this type of ink. It is assumed here that two recording medium sheets, a first sheet and a second sheet, are successively ejected. In such a case, the leading end of the second sheet rubs the ink which is still wet on the first sheet which has been ejected. Consequently, the image on the first recording medium sheet is fouled. The phenomenon of fouling the image on the leading recording medium sheet is generally referred to as “smear”.
The image forming apparatus shown in
FIG. 9
has sheet supporting members
47
which are provided in the sheet ejection section
4
and which serve as means for preventing smearing. The sheet supporting members
47
serve to support the sheet P after recording so as to prolong the time required for the sheet P to land on a sheet ejection tray
200
after the discharged ink is deposited on the sheet P. A subsequent sheet P, i.e., the second sheet, is then ejected to fall onto the recording medium sheet when the ink on the preceding recording sheet medium P, i.e., the first sheet, has been dried, thus preventing smearing of the image on the first sheet.
Hitherto, the sheet supporting members
47
are arranged in the direction of breadth of the sheet P,
Barlow John
Do An H.
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