Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-11
2001-06-26
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S014000, C347S016000
Reexamination Certificate
active
06250737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording method and apparatus, which record an image on a recording medium by ejecting ink droplets according to image data.
2. Related Background Art
With spread of copying machines, information equipment such as wordprocessors, computers, and the like, and communication equipment, an apparatus for performing digital image recording using an ink jet recording head has become increasingly popular as one of recording apparatuses for such equipment. A recording apparatus of this type uses a head prepared by integrating a plurality of ink ejection orifices and ink channels as a recording head (to be referred to as a multi-head hereinafter) in which a plurality of recording elements are integrated and aligned for the purpose of an increase in recording speed. Furthermore, a color recording apparatus normally comprises a plurality of multi-heads.
Unlike in a monochrome printer for printing characters alone, when a color image is to be printed, various characteristics such as color development characteristics, gradation characteristics, uniformity, and the like are required. In particular, as for the uniformity, a small variation in units of nozzles, which is generated during a multi-head manufacturing process, influences the ejection amount or ejection direction of an ink of each nozzle, and consequently deteriorates image quality as a density nonuniformity of a printed image.
An example of the density nonuniformity will be explained below with reference to
FIGS. 71A
to
72
C. In
FIG. 71A
, a multi-head
91
is constituted by eight multi-nozzles
92
for ejecting ink droplets
93
. Normally, the multi-nozzles
92
ideally eject the ink droplets in a uniform amount and in a uniform direction, as shown in FIG.
71
A. If such ejection is performed, dots having a uniform size land on a sheet surface, as shown in
FIG. 71B
, and a uniform image free from the density nonuniformity can be obtained as a whole (FIG.
71
C).
However, in practice, each nozzle suffers from a variation, as described above. If a print operation is performed in the same manner as described above, ink droplets having various sizes are ejected from the nozzles in various directions, as shown in
FIG. 72A
, and land on a sheet surface, as shown in FIG.
72
B. As shown in
FIG. 72B
, a blank portion, which does not satisfy an area factor of 100%, conversely, a portion where dots unnecessarily overlap each other, and a white line (at the center of
FIG. 72B
) periodically appear in the head main scan direction. The group of dots which landed in the state shown in
FIG. 72B
has a density distribution shown in
FIG. 72C
in the nozzle alignment direction, and consequently, such a phenomenon is normally observed as a density nonuniformity by human eye.
As a countermeasure against such density nonuniformity, the following method has been proposed. The method will be described below with reference to
FIGS. 73A
to
74
C. According to this method, in order to complete a print area shown in
FIGS. 71A
to
72
C, the multi-head
91
is scanned (main scan) three times, and a half area in units of four pixels is completed by two passes. In this case, the eight nozzles of the multi-head are divided into two groups respectively including upper four nozzles and lower four nozzles. Dots to be printed by one nozzle in a single scan are obtained by thinning out given image data to about a half according to a predetermined image data arrangement. In the second scan, dots corresponding to the remaining half image data are printed, thus completing the area in units of four pixels. The above-mentioned recording method will be referred to as a divisional recording method hereinafter.
When such a recording method is used, even if a head equivalent to the multi-head shown in
FIG. 72A
is used, since the influence of the nozzles to a printed image is reduced to half, an image shown in
FIG. 73B
is printed, and black and white lines observed in
FIG. 72B
do not become conspicuous. Therefore, the density nonuniformity is remarkably eliminated as compared to
FIG. 72C
, as shown in FIG.
73
C.
Upon execution of such recording, image data is divisionally thinned out to predetermined complementary arrangements in the first and second scans. As the image data arrangement (thinning pattern), a checker pattern in which dots are printed on every other pixels in the vertical and horizontal directions is normally used, as shown in FIG.
74
A. Therefore, a unit print area (in units of four pixels) is completed by the first scan for printing dots in a checker pattern and the second scan for printing dots in a reverse checker pattern.
FIGS. 74A
,
74
B, and
74
C explain how to complete a predetermined record area using the checker and reverse checker patterns by the multi-head having eight nozzles like in
FIGS. 71A
to
73
C. In the first scan, dots are recorded in a checker pattern
using lower four nozzles (FIG.
74
A). In the second scan, a sheet is fed by four pixels (½ the head length), and dots are recorded in a reverse checker pattern ◯ (FIG.
74
B). Furthermore, in the third scan, the sheet is fed by four pixels (½ the head length), and dots are recorded in the checker pattern again (FIG.
74
C). In this manner, when the sheet feed operation in units of four pixels, and recording operations of the checker and reverse checker patterns are alternately performed, a record area in units of four pixels is completed for each scan.
As described above, since the print area is completed by two different groups of nozzles, a high-quality image free from the density nonuniformity can be obtained.
Such a recording method has already been disclosed in Japanese Laid-Open Patent Application No. 60-107975 and U.S. Pat. No. 4,967,203, and these references describe that this method is effective to remove the density nonuniformity and connection lines. The former reference discloses that “the invention is characterized by comprising means for forming an overlapping portion by overlapping two adjacent main scans by setting a sheet feed width of each main scan to be smaller than the width of the main scan, and means for printing dots of the overlapping portion so as not to overlap each other in the two main scans”. According to this reference, as described above, a thinning mask is defined as one for “alternately printing odd and even rows in every other columns” in one case. However, in another case, odd rows are printed in the first scan, and even rows are printed in the second scan. In still another case, odd and even rows are randomly printed in each scan. Thus, the thinning mask and the sheet feed width are not completely limited.
In contrast to this, the latter U.S. Pat. No. 4,967,203 discloses that
“a) in the first pass, dots are printed at alternate pixel positions, which are not two-dimensionally adjacent to each other, of only the upper half of a first band,
b) in the second pass, dots are printed on pixel positions, which are not printed in the first pass, in the first band, and at alternate pixel positions, which are not two-dimensionally adjacent to each other, in the lower half of the first band, and
c) in the third pass, dots are printed at pixel positions, which are not printed in the first and second passes, in the first band, and at the same time, the first pass print operation in the next band.” In this manner, in this reference, a thinning mask used in divisional recording is limited to an alternate pixel arrangement in which pixels are not two-dimensionally adjacent to each other.
As an arrangement to be additionally described in this reference, a recording method wherein a pseudo pixel (super pixel) as a group of several pixels is formed for the purpose of gradation expression and multi-color expression, and an alternate thinning print operation at two-dimensionally non-adjacent pixel positions in units of pseudo pixels (super pixels) is disclosed. It is described that according to this method, “once a system for real
Gotoh Fumihiro
Hirabayashi Hiromitsu
Koitabashi Noribumi
Matsubara Miyuki
Nagoshi Shigeyasu
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hallacher Craig A.
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