Printing method and a printing apparatus

Details Printing method and a printing apparatus Printing method and a printing apparatus

2000-08-17

2002-12-10

Nguyen, Lamson D. (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S015000, C347S043000, C358S001200

Reexamination Certificate

active

06491373

ABSTRACT:

This application is based on Japanese Patent Application No. 11-237299 (1999) filed Aug. 24, 1999, 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 adjusting the positions of ink dots in a printing apparatus of an ink jet system. 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. 19
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
.
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 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.
In the above serial type ink jet printer, various provisions have been made as to the construction of the head unit or the printing method in order to realize an image printing with higher resolution.
For example, the manufacture of the multi-nozzle head inevitably places a limit on the density of the nozzles in a single nozzle array.
FIG. 20A
shows an example head that realizes a higher nozzle density. This head has two columns of nozzles extending in the Y direction and spaced a distance px (corresponding to a predetermined number of pixels) apart in the X direction. The two nozzle columns, each consisting of many nozzles arranged at a predetermined pitch py in the Y direction, are shifted from each other by a distance py/
2
in the Y direction. This arrangement of the nozzles realizes a resolution two times higher than that achieved by a single nozzle column. When this head is applied to the apparatus shown in
FIG. 19
, the heads having the construction shown in
FIG. 20A
for one color can be arranged in parallel in the X direction for six colors. In this arrangement, simply adjusting the ejection timings of the two nozzle columns can achieve a color printing with two times the resolution of the single nozzle column.
In other technologies, such as U.S. Pat. No. 4,920,355 and Japanese Patent Application Laid-open No. 7-242025 (1995), a high resolution printing is realized by setting the paper feed distance for each print scan to a predetermined number of pixels less than the length of the column of nozzles while leaving the multi-nozzle arrangement at a low resolution. Such a printing method is hereinafter called an interlace printing method.
The interlace printing method will be briefly explained by referring to FIG.
21
. Here let us take up an example case where an image with resolution of 1200 DPI (dots/inch) is printed by using a head H with nozzles arranged at a pitch of 300 DPI. For the sake of simplicity, it is assumed that the head has nine nozzles and that the distance of the paper feed carried out after each print scan is nine pixels at 1200-DPI resolution. The rasters printed in the forward pass are shown as solid lines and the rasters printed in the backward pass are shown as dashed lines. These two kinds of lines are formed alternately.
While in this example the paper is fed a fixed distance of 9 pixels at 1200-DPI resolution, other arrangements may be made in the interlace printing. The interlace printing method does not need to have a constant paper feed distance at all times as long as a picture is printed with a plurality print scans arranged at a pitch finer than the arrangement pitch of the nozzles themselves. In either base, an image can be printed with a higher resolution than he nozzle arrangement resolution.
By the various methods explained above, it has been realized to print an image with resolutions higher than a nozzle array.
On the other hand, a printing resolution of a printer is not necessarily equal to an input resolution from a host device as an image data supply source. Recent printers permit printing according to plural input resolutions. For example, when high speed processing is desired, it is possible even for a printer with a resolution of 1200 DPI to reduce a transmission time from the host device if an image data is inputted with a resolution of 300 DPI. In such a case, 17 levels which can be expressed by 4×4 pixels, in practice, are reduced to 2 levels.
Moreover, even if a printing of high quality image is required, it becomes a burden for the host device to transmit an image data of 1200 DPI. In this case, a method h

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