Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-11-02
2003-04-29
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06554396
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an ink-jet printing apparatus and method and, more particularly, to an inkjet printing apparatus in which a carriage mounting an ink-jet printhead having a plurality of print elements arrayed in at least two rows for performing printing by discharging ink from the print elements is scanned back and forth above a print medium in a direction cross to the direction in which the print elements are arrayed to thereby print on the print medium, and to a printing method using this apparatus.
BACKGROUND OF THE INVENTION
A printer for recording information such as desired characters and images on a sheet-like print medium such as paper or film is available as an information output apparatus in a word processor, personal computer and facsimile machine, etc.
Though a variety of printing methods implemented by such a printer are known, the ink-jet method in particular has been the focus of attention in recent years because it is capable of printing on a print medium such as printing paper without making mechanical contact with the medium, because color printing can be performed with ease and because printing can be performed silently. From the viewpoint of low cost and small size, a widely employed printing technique is serial printing in which the ink-jet printing apparatus is fitted with a printhead for discharging ink in accordance with the desired print information and printing is carried out while the printhead is scanned back and forth at right angles to the direction in which the print medium such as printing paper is fed.
Recent improvements in the performance of such ink-jet printers have made it possible to achieve a high printing speed on a par with that of laser printers. An increase in the processing speed of personal computers and the spread of the Internet have led to ever greater demand for the printing of color images at higher and higher speeds.
One ink-jet technique is the bubble jet printing technique in which ink droplets are discharged from orifices by the pressure of bubbles produced by rapidly heating and vaporizing ink by means of a heating element. A bubble produced in a bubble jet printhead having such a structure is cooled by the surrounding ink so that the ink vapor within the bubble is condensed back into liquid form and vanishes.
Ink expended by discharge is replenished via an ink supply path from an ink tank containing the ink.
FIG. 9
is a diagram illustrating an example of the arrangement of nozzles
4
in such an ink-jet printhead. A row of even-numbered nozzles
4
is disposed on the left side of an ink supply path
105
and a row of odd-numbered nozzles
4
is disposed on the right side of the ink supply path
105
. Ink is supplied from the ink supply path
105
via an ink flow path
5
provided in correspondence with each nozzle
4
.
A known ink-jet printing technique other than the above-described bubble jet printing technique is the bubble through jet printing technique through which bubbles produced by rapidly heating and vaporizing ink by means of a heating element are discharged upon being passed through the outside air.
FIGS. 3A
to
3
D and
FIGS. 3E
to
3
H illustrate the manner in which droplets are discharged in accordance with the bubble jet and bubble through jet techniques, respectively. The shape of the discharged ink varies in a time series as indicated by
FIGS. 3A
to
3
D and
FIGS. 3E
to
3
H.
Ink that has been discharged from the nozzle
4
leaves a tail immediately after being discharged, as in
FIGS. 3A and 3E
. A main droplet then starts to form at the leading edge in
FIGS. 3B and 3F
, the ink splits into a main droplet and satellites, as shown in
FIGS. 3C and 3G
, at the moment surface tension attempting to coalesce the ink is overcome, and the ink finally splits into a main droplet
31
and satellites
32
, as indicated in
FIGS. 3D and 3H
.
The printhead which discharges ink by the above-described techniques will be described with reference to
FIGS. 4A
to
4
C in regard to a case where the printhead is mounted on a transported carriage and a printing operation is carried out by moving the carriage back and forth in a direction cross to the direction in which the print medium is transported.
As illustrated in
FIG. 4A
, an ink droplet discharged from each ink nozzle of an even-numbered nozzle row and an ink droplet discharge from each nozzle of an odd-numbered nozzle row of each chip of a printhead IJH comprises a main droplet
78
i
(
i
=1~n), which impacts upon a print surface
76
a
of paper
76
serving as an example of a print medium to thereby form the main portion of one pixel constituting an image or character, and a satellite
78
ai
(
i
=1~n), which is the remainder of the discharged main droplet
78
i
. The satellite
88
ai
flies is a fixed direction in dependence upon the release characteristics of the ink droplet, e.g., the printhead characteristics (the shape of the ink nozzle and the properties of the ink fluid).
In a case where the printhead IJH travels in the direction indicated by arrow F in
FIG. 4A
, e.g., in the forward direction, the impact position of the satellite
78
ai
relative to the main droplet
78
i
will be on the side opposite that of the direction of travel when the flying direction of the satellite
78
ai
, which has been discharged from the nozzle of the row of even-numbered nozzles, relative to the main droplet
78
i
is opposite the direction indicated by arrow F.
Accordingly, if the structure of the printhead is such that the arrays of the nozzles on the sides of the even and odd numbers are substantially symmetrical with respect to the centrally located ink supply path, as illustrated in
FIG. 9
, the direction in which the satellite
78
ai
from the nozzle of the odd-numbered nozzle row flies relative to the main droplet
78
i
will be diagonally away from the main droplet
78
i
in a direction the same as that indicated by arrow F, so that the impact position of the satellite
78
ai
relative to the main droplet
78
i
will be on the side of the direction of travel.
As a result, a portion
82
ai
formed by the satellite
78
ai
discharged from the nozzle of the even-numbered nozzle row is formed so as to overlap and become included within a portion
80
i formed by the main droplet
78
i
that has impacted the printing surface
76
a
, as depicted in FIG.
4
B. On the other hand, a portion
82
ai
formed by the satellite
78
ai
discharged from the nozzle of the odd-numbered nozzle row is formed outside the portion
80
i
formed by the main droplet
78
i
that has impacted the printing surface
76
a
, as depicted in FIG.
4
C.
Further, in a case where the printhead IJH travels in the direction indicated by arrow R in
FIG. 4A
, e.g., in the reverse direction, the portion
82
ai
formed by the satellite
78
ai
discharged from the nozzle of the even-numbered nozzle row is formed outside the portion
80
i
, as shown in FIG.
4
C. On the other hand, the portion
82
ai
formed by the satellite
78
ai
discharged from the nozzle of the odd-numbered nozzle row is formed so as to overlap and become included within a portion
80
i
formed by the main droplet
78
i
that has impacted the printing surface
76
a
, as depicted in FIG.
4
B.
If the printhead prints a character or the like on a printing surface by being moved in the forward and reverse directions, the character is formed mostly by the main droplets
78
i
, and the satellites
78
ai
are mostly covered by the main droplets. However, the portion
82
ai
formed as shown in
FIG. 4C
at the edge portion of a printed character by a satellite not covered by the portion
80
i
formed by the main droplet will have an influence upon print quality. This portion appears as edge roughness at several parts of the printed character.
FIGS. 5A and 5B
illustrate examples of edge roughness when characters are printed, in which
FIG. 5A
represents roughness due to printing in the forward direction and
FIG. 5B
roughness due to printing in the reverse direction. Such edge roughne
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