Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2003-03-25
2004-06-29
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06755506
ABSTRACT:
This application claims priority from Japanese Patent Application No. 2002-084407 filed Mar. 25, 2002, which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet print head and an ink jet printing apparatus for ejecting ink onto a print medium to form an image thereon.
2. Description of the Related Art
An ink jet printing apparatus forms an image on a print medium by ejecting ink droplets from a print head mounted in an apparatus body onto the print medium, with the ink droplets adhering to the print medium and fixing in it to produce their intended colors. Recent years have seen a proliferation of a so-called serial scan type ink jet printing apparatus. In this type, an image is formed by alternately repeating two operations—a printing scan for scanning the print head over the print medium to eject ink onto the medium and a paper feed for moving the print medium or the print head relative to each other in a direction perpendicular to a printing scan direction. The serial scan type ink jet printing apparatus, however, has the following drawback.
In the serial scan type apparatus, a single printing scan can only produce an image of a predetermined printing width for at least one color of ink (this single printing operation is referred to also as a “one-pass printing”). Hence, to form an image over the entire print medium requires performing a plurality of printing scans. When in such a system an image of high duty is to be formed, a problem may occur that a boundary portion between an image area formed on the print medium in a certain printing scan and an adjoining image area formed in another printing scan appears light in density.
This problem is considered to occur in the following mechanism.
FIGS. 7A
to
7
D are schematic views showing how an image of high duty is formed during the one-pass printing, as seen in the print head scanning direction. In the figure, reference number
1
represents a print head,
2
a print medium, and e a column of nozzles (also referred to as a “column of ejection openings”) for ejecting ink droplets.
FIG. 7A
shows ink droplets adhering to a print medium which were ejected in one printing scan. In the figure, p
1
denotes an ink adhering to the print medium. With the elapse of time the ink on the print medium soaks into the medium and fixes there.
FIG. 7B
illustrates this state and p
2
denotes the ink that has soaked into the print medium and fixed there. After the printing scan, the print medium is fed in a direction perpendicular to the printing scan direction of the print head (this operation is called a line feed) and the next printing scan is performed.
FIG. 7C
shows a state in which the line feed and the second printing scan have been performed. In the figure, a distance that the print medium was fed is indicated by an arrow. This line feed distance is equal to the length of the nozzle column of the print head. Ink droplets adhering to the print medium that were ejected in the second printing scan are indicated by p
3
.
FIG. 7D
shows a state in which the ink that landed on the print medium during the second printing scan has soaked and fixed with elapse of time. As shown by p
1
of FIG.
7
A and p
3
of
FIG. 7C
, the ink that has just landed on the print medium and has not yet soaked into and fixed in the print medium forms an ink surface that is low at ends and bulges at a center. This is a common phenomenon produced by a surface tension of the ink. In this state, the ink penetrates and fixes in the print medium. Therefore, as indicated by p
2
and p
4
of
FIGS. 7B and 7D
, in an image area formed by each printing scan, an amount of ink that fixes at the end portions is less than at other portions and the color of that portions tends to be lighter. Thus, when the printing scan is repeated a plurality of times to form an image of high duty, the end portions of an image area formed by each printing scan appear light. That is, the boundary portions between adjoining image areas are printed lighter than other portions, giving rise to a problem of light stripes showing up in the printed image. In the case of a black ink in particular, since its penetration capability is generally low, it tends to produce a greater density difference between a dot center and a dot end than do color inks. This may result in boundary portions between adjoining image areas printed by different printing scans appearing lighter and in the worst case showing up as white horizontal stripes.
A possible measure to deal with this problem may involve making the line feed distance shorter than the printing width or nozzle column length of the print head. One such example is to design a nozzle-to-nozzle interval (nozzles may also be referred to as “ejection openings”) somewhat longer than normal. As a result, the length of the nozzle column used for the one-pass printing becomes somewhat longer than the line feed distance, producing the following advantages.
FIGS. 8A
to
8
D show dots ejected from a nozzle column with a longer-than-normal nozzle-to-nozzle interval. In the figure, reference numeral
1
represents a print head,
2
a print medium and e a nozzle column for ejecting ink droplets.
FIG. 8A
shows ink droplets adhering to the print medium which were ejected in one printing scan. In the figure, p
1
denotes an ink adhering to the print medium. With the elapse of time the ink on the print medium soaks into the print medium and fixes there.
FIG. 8B
illustrates this state and p
2
denotes the ink that has soaked into the print medium and fixed there. After the first printing scan, the print medium is fed (line feed) in a direction perpendicular to the printing scan direction of the print head and the next printing scan is performed. Because the nozzle-to-nozzle interval of the print head is set somewhat longer than normal, the line feed distance is shorter than the nozzle column length e.
FIG. 8C
shows a state in which the line feed and the second printing scan have been performed. In the figure, a distance that the print medium was fed is indicated by an arrow and, as described above, is somewhat shorter than the nozzle column length e of the print head. Ink droplets adhering to the print medium that were ejected in the second printing scan are indicated by p
3
. Then, the ink that landed on the print medium during the second printing scan also sinks and fixes in the print medium over time, as shown in FIG.
8
D.
Since the line feed distance shown in
FIG. 7C
is equal to the nozzle column length or a difference between the line feed distance and the nozzle column length is smaller than that of
FIG. 8C
, a comparison between FIG.
8
D and
FIG. 7D
shows that an overlap between p
2
and p
4
is somewhat larger in
FIG. 8D
than in FIG.
7
D. Thus, as shown in
FIG. 8D
, the above-described problem that a boundary portion between an image area formed on the print medium by a printing scan and an adjoining image area formed by another printing scan appears lighter than other portions is less likely to occur.
Printing apparatus capable of printing color inks as well as black ink are available in recent years. Some of these printing apparatus have a black ink nozzle column set longer than other color ink nozzle columns in order to reduce a time taken by the printing operation using only the black ink as in a document printing. In this arrangement, when printing is done using only the black ink, all the nozzles of the black ink nozzle column are used, whereas during color printing, only that part of the black ink nozzle column which is almost equal in length to other color ink nozzle columns is used. In such a printing apparatus, in which the length of that nozzle portion in the entire nozzle column which is used for printing is changed according to an image being formed, a problem may arise that lighter horizontal stripes will show up in a printed image at boundaries between adjoining image areas formed on a print medium by separate printing scans, depending on the leng
Chikuma Toshiyuki
Iwasaki Osamu
Nishikori Hitoshi
Otsuka Naoji
Seki Satoshi
Canon Kabushiki Kaisha
Nguyen Thinh
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