Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-08-29
2003-08-05
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S041000
Reexamination Certificate
active
06601939
ABSTRACT:
This application is based on Patent Application Nos. 2000-261645 filed Aug. 30, 2000 and 2001-215789 filed Jul. 16, 2001 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 a printing method and a printing apparatus, and is particularly suited for the application to a printing apparatus by the ink jet method. More particularly, the present invention intends to solve a granular impression of image and a color tone irregularity caused by the ejection order of color inks which are becoming problematic in case where the divided printing, for instance in a bi-directional printing, is performed applying a plurality of times of main scanning according to a pixel arrangement, in a complementary relation for a same image area in a so-called serial type color inkjet printing apparatus. In addition to general printing apparatus, the present invention can also be applied to copying machines, facsimiles with a communication system, word processors with a printer, and industrial printing apparatus combined with a variety of processing devices.
2. Description of the Related Art
An image printing apparatus of so-called serial scan type, which executes the print operation while scanning a print head, or a printing unit, over a print medium, has found a variety of image forming applications. The ink jet printing apparatus in particular has in recent years achieved high resolution and color printing, making a significant image quality improvement, which has resulted in a rapid spread of its use. Such an apparatus employs a so-called multi-nozzle head that has an array of densely arranged nozzles for ejecting ink droplets. Images with still higher resolution has now been made possible by increasing the nozzle density and reducing the amount of ink per dot. Further, to realize an image quality approaching that of silver salt picture, various technologies have been developed, including the use of pale or light color ink with reduced density in addition to four basic color inks (cyan, magenta, yellow and black). A print speed reduction problem, which is feared to arise as the picture quality advances, is dealt with by increasing the number of print elements, improving the drive frequency and employing a bi-directional printing technique, thus realizing a satisfactory throughput.
FIG. 45
schematically shows a general construction of a printer that uses the multi-nozzle for printing. In the figure, reference number
1901
represents head cartridges corresponding to four inks, black (K), cyan (C), magenta (M) and yellow (Y). Each head cartridge
1901
consists of an ink tank
1902
T filled with a corresponding color ink and a head unit
1902
H having an array of many nozzles for ejecting the ink supplied from the ink tank onto a print medium
1907
.
FIG. 46
schematically shows the head unit
1902
H in the Z direction for illustrating representing the nozzle array thereof. In this example, ejection openings
2001
are arrayed in one line.
In
FIG. 45
, designated
1903
is a paper feed roller which, in cooperation with an auxiliary roller
1904
, clamps a print medium (print paper)
1907
and rotates in the direction of arrow in the figure to feed the print paper
1907
in the Y direction as required. Denoted
1905
is a pair of paper supply rollers that clamp the print paper
1907
and carries it toward the print position. The paper supply rollers
1905
also keep the print paper
1907
flat and tight between the supply rollers and the feed rollers
1903
,
1904
.
Designated
1906
is a carriage that supports the four head cartridges
1901
and moves them in a main scan direction during the print operation. When the printing is not performed or during an ink ejection performance recovery operation for the head unit
1902
H, the carriage
1906
is set at a home position h indicated by a dotted line.
The carriage
1906
, which was set at the home position h before the print operation, starts moving in the X direction upon reception of a print start command and at the same time the head unit
1902
H ejects ink from a plurality of nozzles (n nozzles) formed therein according to print data to perform printing over a band of a width corresponding to the length of the nozzle array. When the printing is done up to the X-direction end of the print paper
1907
, the carriage
1906
returns to the home position h in the case of one-way printing and resumes printing in the X direction. In the case of bi-directional printing, the carriage
1906
also performs printing while it is moving in a −X direction toward the home position h. In either case, after one print operation (one scan) in one direction has been finished before the next print operation is started, the paper feed roller
1903
is rotated a predetermined amount in the direction of arrow in the figure to feed the print paper
1907
in the Y direction a predetermined distance (corresponding to the length of the nozzle array). By repeating the one-scan print operation and the print paper feeding by a predetermined distance, data for one sheet of paper is printed.
Unlike a monochromatic printing that prints only characters such as letters, numbers and symbols, the color image printing must meet various requirements such as color development, grayscale characteristic and uniformity. As to the uniformity in particular, slight variations among individual nozzles that are produced during the manufacture of a multi-nozzle head formed integrally with many nozzles (in this specification the nozzle generally refers to an ejection opening, a liquid passage communicating with the ejection opening and an element for generating energy used to eject ink) influence the amounts of ink ejected from the individual nozzles and the directions of ink ejection during printing and eventually degrade the image quality in the form of density variations of the printed image.
Detailed examples will be explained by referring to
FIGS. 47A-47C
,
48
A-
48
C and
49
A-
49
C. In
FIG. 47A
, designated
3001
is a multi-nozzle head with a construction similar to the one shown in
FIG. 46
, which is shown to have only eight nozzles
3002
for simplicity. Denoted
3003
are ink droplets ejected from the nozzles
3002
. It is ideal that the ink droplets are ejected in equal amounts and in the same direction. If ink ejection is done in this manner, ink dots of equal sizes land on the print medium, as shown in
FIG. 47B
, resulting in a uniform density distribution with no unevenness in density (FIG.
47
C).
In reality, however, individual nozzles have their own variations and if the printing is done in a manner described above, the ink droplets ejected from individual nozzles vary in size and direction as shown in
FIG. 48A
, forming ink dots on the paper surface as shown in FIG.
48
B. From this figure it is seen that a blank part appears cyclically in the head main scan direction, dots overlap excessively in other parts, or a white line occurs at the central part in the figure. The ink dots printed in this way produce a density distribution in the direction of nozzle arrangement or nozzle column as shown in
FIG. 48C
, which is perceived as unevenness in density by normal human eye.
To deal with the problem of the unevenness in density, the following method has been proposed.
This method will be explained by referring to
FIGS. 49A
to
49
C. Although the head
3001
is scanned three times as shown in
FIG. 14A
to complete the print in an area similar to that shown in
FIGS. 47A-47C
and
FIGS. 48A-48C
, an area of four pixels, one-half the vertically arranged eight pixels, is completed with two scans (passes). In this case, the eight nozzles of the head
3001
is divided into two halves, upper four nozzles and lower four nozzles, and the number of dots formed by one nozzle in one scan is equal to the image data culled to one-half according to a predetermined image data arrangement. During the second scan, dots are embedded at the remaining half of the image data to complete t
Edamura Tetsuya
Fujita Miyuki
Kawatoko Norihiro
Konno Yuji
Maeda Tetsuhiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Lamson
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