Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-02-05
2004-09-14
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000
Reexamination Certificate
active
06789867
ABSTRACT:
This application is based on Japanese Patent Application Nos. 2001-030187 and 2001-030189 filed Feb. 6, 2001 and 2002-27473 filed Feb. 4, 2002, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method which create color images of high quality on a print medium by ejecting different kinds of ink from a plurality of print heads. More particularly, the invention relates to improvements on an ink jet printing apparatus and an ink jet printing method which form a printed image by performing a single print scan (one pass) or multiple print scans (multiple passes) over one print area.
The present invention is applicable to all devices that use such print media as paper, cloth, leather, non-woven cloth, OHP sheet and even metal. Applicable devices include, for example, office equipment such as printers, copying machines and facsimiles and industrial manufacturing devices.
2. Description of the Related Art
Because of its advantages such as low noise, low running cost and the ease with which the apparatus can be reduced in size and with which color printing can be introduced, the ink jet printing method has found wide uses in printers, copying machines and facsimiles.
Generally, a color ink jet printing apparatus prints color images using four colors of ink, i.e., three color inks—cyan, magenta and yellow—plus a black ink.
In the conventional ink jet printing apparatus, to obtain color images with high color saturation without a spread of ink requires the use of dedicated paper that has an ink absorbing layer. This increases the printing cost. To solve this problem, a printing apparatus has been developed in recent years which is made applicable to inexpensive “plain paper” used in large volumes in printers and copying machines by improving the inks used. However, the print quality on the “plain paper” has not yet attained a satisfactory level. The most notable factors for this are color deviations due to differences in the order of ink ejection and in the ejection time. These cause problems such as density and color deviations or deviations in the feed direction (sub-scan direction) and transverse direction (main scan direction in which the print heads are scanned) of the print medium.
Further, in the ink jet printing apparatus there are growing user needs for the printer ability to print at high speed.
When printing is done with emphasis placed on high speed, the multipass printing, which is intended to realize high quality printing, is not performed but a so-called one-pass printing is effective which prints one line in one pass. The number of passes for printing means the number of times that the carriages is scanned to complete one line.
The reason for choosing the one-pass printing is that, because the print head has a fixed number of nozzles, the greater number of passes results in a smaller feed distance that the paper is fed at one time and the fewer passes result in a larger feed. For example, if a 2-pass printing currently adopted can be changed to a one-pass printing, this can simply increase the print speed two-fold. That is, the smaller the number of passes in the multipass printing, the smaller the number of carriage scans (number of scans over a predetermined area of the print medium) and the greater the distance that the paper is fed at one time. As a result, the time it takes for one sheet to be printed decreases.
By performing a bidirectional printing in which printing is done in both the forward and backward passes of the print heads, idle scanning can be eliminated, further increasing the print speed.
For example,
FIGS. 1A
to
1
C show comparison between different printing methods using the same print head and the same number of scans. Here, the width of the print head is defined to be one line.
FIG. 1A
shows a printed state after three scans have been performed by a 2-pass bidirectional printing. The example shown here represents a case where an image is completed by two passes with 50% duty printing performed in each pass.
FIG. 1A
shows a print area under consideration divided into four areas each corresponding to one-half of the print width of the print head H. In a first scan in the forward direction, the top area in
FIG. 1A
is printed with a 50% duty by using the lower half of the print head H. In a second scan in the backward direction, the top area of
FIG. 1A
is printed by using the upper half of the print head H and at the same time the second area from the top is printed with a 50% duty by the lower half of the print head H. This second scan completes the printing on the top area of FIG.
1
A. In a third scan in the forward direction, the second area from the top is printed by the upper half of the print head H, completing the printing on this area. At the same time, the lower half of the print head H prints on the third area from the top with a 50% duty. If the area corresponding to the print width of the print head H is taken as one line, the execution of three scans completes one line and leaves one line half-finished, as described above. Although the example of
FIG. 1A
shows a bidirectional printing, if the printing is done in one of the forward and backward directions, there is an idle scan, which do not execute printing, between the successive scans. The completed area therefore is 0.5 line.
In the 1-pass unidirectional printing shown in
FIG. 1B
, three scans produce two lines of print-completed area. Here, there is one scan that does not execute printing (which in
FIG. 1B
corresponds to a backward idle scan following the forward scan). In a 1-pass bidirectional printing shown in
FIG. 1C
, three scans produce three lines of print-completed area and this method carries out the most efficient printing operation. For high speed printing, this is an effective method.
When a conventional ink jet printing apparatus forms an image of multiple colors by 1-pass bidirectional printing, however, a problem arises that the density deviations and color deviations due to differences in the order of ink ejection and in the ejection time degrade the image quality as described below.
Difference in the Order of Ejection
When print heads of different color inks are arranged in the transverse direction (main scan direction), because the order of ejecting the inks during the forward pass differs from that during the return pass, a hue difference may occur between the printing in the forward pass and the printing in the backward pass.
For example, when a blue, a secondary color, is formed, there are two different processes, as shown in
FIGS. 2A and 2B
. In the first case magenta is printed first producing a blue with a strong hue of magenta. In the second case cyan is printed first to produce a blue with a strong hue of cyan. This may be explained as follows. The hue depends on the characteristics of inks and paper, and the ink printed first is adsorbed first by paper fibers and the subsequently printed ink sinks under the first printed ink. The coloring component of the first printed ink exists mostly at or near the surface of the print medium and thus the intensity of the color of that ink, i.e., the density of that ink, is relatively high.
In a state where such a phenomenon occurs, if the 1-pass bidirectional printing as shown in
FIG. 1C
is performed, bands of different hues are printed alternately in the forward pass (during which the print head moves from left to right) and backward pass, as shown in
FIG. 3. A
first print head H
1
and a second print head H
2
eject magenta and cyan inks, respectively, with the magenta ink printed first in the forward pass and the cyan ink printed first in the backward pass. The difference in hue caused by the alternating order of ink ejection make the printed area look like a pattern of two bands of different hues alternating every scan.
Variations in Print Time
When print heads of different color inks are arranged in the vertical direction (sub-scan direction), t
Chikuma Toshiyuki
Iwasaki Osamu
Nishikori Hitoshi
Otsuka Naoji
Sugimoto Hitoshi
Dudding Alfred E
Meier Stephen D.
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