Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-10-25
2004-09-21
Pham, Hai (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S040000, C347S019000
Reexamination Certificate
active
06793320
ABSTRACT:
This application is based on Patent Application No. 2000-335179 filed Nov. 1, 2000 in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing method and apparatus on a multi-path printing system in which a desired image is formed completely on a printing medium by a plurality of scanning movements of a printing head on the same printing area of the printing medium.
2. Description of the Related Art
FIGS. 1A
,
1
B, and
1
C are schematic diagrams that illustrate a transport stage for transporting a printing medium in a typical serial type printing apparatus.
In those figures, the reference numeral
509
denotes a printing medium (e.g., a sheet of paper or a plastic sheet). The printing medium
509
can be fed in a sub-scan direction from the right side to the left side as indicated by the arrow in each figure. In other words, the printing medium
508
receives the sheet-feed force when it is sandwiched between the transport roller
501
and the pinch roller
503
. The transport roller
501
can be driven by a sheet-feed motor (not shown). The pinch roller
502
is pressed against that transport roller
501
by the spring pressure, so that it can be rotated together with the transport roller
501
. The sheet-ejection rollers
503
,
504
are also arranged as a two-stage sheet-ejection roller so that they work together with the transport roller
501
. In addition, sheet-ejection spurs
505
,
506
are pressed against the rollers
503
,
504
by the spring pressures, respectively.
The feed amount of the printing medium
508
(the amount by which, or rate at which, it is fed) due to the rotational movements of the sheet-ejection rollers
503
,
504
is adjusted to about 100.3% of the feed amount of the printing medium
508
due to the rotational movement of the transport roller
501
because the printing medium swells due to the application of ink upon printing in an ink jet printing system. If the feed amount of the printing medium
508
defined by the sheet-ejection rollers
503
,
504
were set to the same level as that due to the transport roller
501
, the swell amount of the printing medium
508
would accumulate, causing a failed sheet-feed between these rollers.
In the sheet-feed stage shown in
FIG. 1A
, the printing medium
508
becomes caught between the rollers using the upper portions of the sheet-ejection rollers
503
,
504
, and the transport roller
501
, respectively. If the printing medium
508
did not swell under the condition shown in
FIG. 1A
, the printing medium
508
would slip over the contacted surfaces of the respective sheet-ejection rollers
503
,
504
. In this case, therefore, the feed amount of the printing medium
508
could depend on the transport thereof by the transport roller
501
.
Furthermore, the reference numeral
507
denotes a printing head that performs a printing scan in the direction perpendicular to the plane of each of
FIGS. 1A
,
1
B, and
1
C (i.e., main-scan direction). The reference numeral
509
denotes a printing area of the printing medium
508
to be printed by the printing head
507
.
FIG. 1A
illustrates the state in which two distinctive sheet-feed forces are being applied on the printing medium
508
by the transport roller
501
and sheet-ejection rollers
503
,
504
, respectively.
FIG. 1B
illustrates a moment when the rear end of the printing medium
508
has left the space between the pinch roller
502
and the transport roller
501
.
FIG. 1C
illustrates the state in which the sheet-feed force is being applied to the printing medium
508
only by the sheet-ejection rollers
503
,
504
.
Referring now to
FIG. 2
, a two-path printing system will be described as an example of the conventional multi-path printing system, in which image formation is completed by moving the printing head
507
through two scans in forming each pixel.
The printing head
507
in
FIG. 2
relatively moves towards the bottom of the figure with respect to the printing medium
508
, which is intermittently transported in the sub-scan direction. As the present example is the two-path printing system, as those of the steps S
201
to S
207
(shown as successive head positions in FIG.
2
.), the position of the printing head
507
in the sub-scan direction relatively deviates downward by one-half of a printing element width in the sub-scan direction. An image can be formed on each of the printing areas P
0
to P
14
on the printing medium
508
by two printing scans of the printing head
507
. In the figure, “A
2
” denotes a mask that allows 50% of image data to remain. “B
2
” denotes a mask that interpolates the image data that mask A
2
excludes.
The images are formed on the printing medium
508
one after another by alternately repeating: the printing scan of the printing head
507
on the basis of image data thinned out by alternately using the masks A
2
and B
2
; and the transport of the printing medium
508
in the sub-scan direction by shifting it by one-half of the printing element width of the printing head
507
. More specifically, in the step S
201
, the printing scan is performed on the basis of the image data thinned out using the mask A
2
, and thereafter, the printing medium
508
is fed in the sub-scan direction by one-half of the printing element width. Subsequently, in the step S
202
, the printing scan is performed on the basis of image data thinned out using the mask B
2
, and thereafter, the printing medium
508
is fed in the sub-scan direction by one-half of the printing element width. Thereafter, the same procedure is successively repeated to form images on the printing medium
508
in succession.
In the multi-path printing system of
FIG. 2
, for example, the following description relates to a period at step S
204
, which corresponds to the state shown in
FIG. 1A and a
period at step S
205
, which corresponds to the state shown in FIG.
1
B. In this case, during the transport of the printing medium
508
from S
204
to S
205
, the rear end of the printing medium
508
moves through a point PA between the steps S
204
and S
205
, where it emerges from the grip of the pinch roller
502
(i.e., comes into the state shown in FIG.
1
B).
The printing head
507
may be an ink jet print head having a plurality of printing elements that eject ink from their nozzles. In this example, the number of nozzles is 256 with 1200-dot/inch resolution. In this case, it is possible to form ink dots uniformly on the printing medium
508
as shown in
FIG. 3
under the condition at step S
204
, which corresponds to the state shown in FIG.
1
A. In the state of
FIG. 1A
, the printing medium
508
may be intermittently fed in the sub-scan direction to distances of about 2700 &mgr;m, that correspond to 128 nozzles. In the period at S
205
, which corresponds to the state shown in
FIG. 1C
, the feed amount of the printing medium
508
may be about 2708 &mgr;m, corresponding to about 100.3% of about 2700 &mgr;m. As a result, as shown in
FIG. 4
, each of the positions on which ink dots have been formed deviates by about 8 &mgr;m from its ideal position in the sub-scan direction, where that deviation corresponds to the difference between the feed amounts of the printing medium
508
obtained at the states shown in FIG.
1
A and FIG.
1
C. Furthermore, if the printing medium
508
is shifted from the state of
FIG. 1A
to the state of FIG.
1
C through the state of
FIG. 1B
, the feed amount of the printing medium
508
may be further increased by about 8 &mgr;m in addition to the mentioned difference in feed amount of 8 &mgr;m. Because it is conceivable that the difference between the feed amounts of the sheet-ejection rollers
503
,
504
and the transport roller
501
cannot be substantially removed by the slippage of the sheet-ejection rollers
503
,
504
, the stresses stored in the printing medium
508
and the sheet-ejection rollers
503
,
504
are released at the instant when the printing medium
508
comes off the p
Iwasaki Osamu
Otsuka Naoji
Takahashi Kiichiro
Teshigawara Minoru
Nguyen Lam
Pham Hai
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