Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-11-15
2004-03-09
Nguyen, Judy (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06702414
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink jet recording device, in particular, to a method for driving an ink jet recording head that ejects minute ink droplets from nozzles and prints characters and images, and to an ink jet recording device.
BACKGROUND ART
Concerning an ink jet recording device that ejects minute ink droplets from nozzles and prints characters and images, for example, as disclosed in Japanese Patent Application Laid-Open No. SHO53-12138 and Japanese Patent Application Laid-Open No. HEI10-193587, a drop-on-demand type ink jet is well known, in which a pressure wave (acoustic wave) is generated in a pressure generating chamber filled with ink by using a driving device such as a piezoelectric actuator that converts electric energy into mechanical energy such as vibration, and an ink droplet is ejected from a nozzle connected to the pressure generating chamber.
FIG. 13
is a diagram showing an example of a recording head in an ink jet recording device well known by the above described patent applications, etc. A nozzle
62
for ejecting ink and an ink supply channel
64
for leading ink from an ink tank (not shown) through a common ink chamber
63
are connected to a pressure generating chamber
61
. Further, a diaphragm
65
is set at the bottom of the pressure generating chamber.
When ejecting ink droplets, the diaphragm
65
is displaced by a piezoelectric actuator
66
set to the outside of the pressure generating chamber
61
, and volume in the pressure generating chamber
61
is changed. Thereby, a pressure wave is generated in the pressure generating chamber
61
. By the pressure wave, a part of the ink which fills the inside of the pressure generating chamber
61
is ejected outward through the nozzle
62
as an ink droplet
67
. The ejected ink droplet reaches the surface of a recording medium such as recording paper, and forms a recording dot. By repeating the formation of the recording dot based on image data, characters and images are recorded on the recording paper.
In order to acquire high image quality using this kind of ink jet recording head, it is necessary to make the diameter of an ejected ink droplet very small. Namely, in order to obtain a smooth image with low granularity, it is necessary to make the recording dot (pixel) formed on the recording paper as small as possible. For that purpose, the diameter of the ejected ink droplet has to be set smaller.
Generally, when the dot diameter becomes 40 &mgr;m or less, the granularity of the image decreases to a large extent. Further, when it becomes 30 &mgr;m or less, it becomes difficult to visually recognize each dot even at a highlight section of the image, and thereby, the image quality can be drastically improved. The relationship between the ink droplet diameter and the dot diameter depends on the flying speed of the ink droplet (droplet velocity), the physical property of the ink (e.g. viscosity and surface tension), the kind of the recording paper, etc. Nevertheless, the dot diameter generally becomes approximately twice as large as the ink droplet diameter. Therefore, in order to obtain the dot diameter not exceeding 30 &mgr;m, it is necessary to set the ink droplet diameter to 15 &mgr;m or less.
Incidentally, in this specification, the drop diameter is defined as the diameter of one spherical ink droplet in the same amount as the total amount of the ink (including satellites) ejected at a time.
The most effective means of reducing the ink droplet diameter includes a reduction of a nozzle diameter.
However, because of the limit of manufacturing technology, and problems in reliability such as clogging of a nozzle, etc., the lower limit of the nozzle diameter is 20 to 25 &mgr;m for actual use, and thereby, it is difficult to obtain an 15 &mgr;m level ink droplet only by the reduction of the nozzle diameter. Consequently, there have been made some attempts to reduce the ejecting ink droplet diameter by driving methods, and some efficient methods have been proposed.
As a driving method for realizing the ejection of a minute droplet with an ink jet recording head, there is known a driving method in which a pressure generating chamber is once inflated just before ejection, and the ejection is conducted from the state where a meniscus at a nozzle opening section is pulled toward the side of the pressure generating chamber (for example, Japanese Patent Application Laid-Open No. SHO55-17589).
An example of a driving waveform used in this kind of driving method is shown in FIG.
14
.
While the relationship between a driving voltage and operation of a piezoelectric actuator varies according to the configuration and the polarized direction of the actuator, it is assumed in this specification that, when the driving voltage is increased, the volume of the pressure generating chamber is reduced, and contrary, when the driving voltage is reduced, the volume of the pressure generating chamber is increased.
The driving waveform shown in
FIG. 14
comprises a voltage changing section
141
for inflating the pressure generating chamber and a voltage changing section
142
for subsequently compressing the pressure generating chamber and ejecting ink droplets.
FIGS.
15
(
a
) to
15
(
d
) are pattern diagrams showing the movement of the meniscus at the nozzle opening section when applying the driving waveform shown in FIG.
14
.
In an initial state, the meniscus is formed of a flat shape (FIG.
15
(
a
)). When the pressure generating chamber
61
is expanded just before the ejection, the central part of the meniscus is pulled toward the pressure generating chamber
61
, and thereby, the shape of the meniscus becomes concave as shown in FIG.
15
(
b
).
From this state, when the pressure generating chamber
61
is compressed by the voltage changing section
142
, the central part of the meniscus is pushed out of the nozzle
41
, and a thin liquid column
43
is formed as shown in FIG.
15
(
c
). Subsequently, as shown in FIG.
15
(
d
), the tip of the liquid column
43
is separated, and an ink droplet
44
is formed.
The droplet diameter of the ink droplet
44
is approximately the same as that of the formed liquid column
43
, and is smaller than that of the nozzle
41
. Namely, by using that kind of driving method, it is possible to eject ink droplets smaller than the nozzle in diameter.
Incidentally, as described above, the driving method in which minute droplet ejection is conducted by controlling the meniscus shape just before the ejection will be hereinafter referred to as a “meniscus control method” in this specification.
As described above, by using the meniscus control method, it becomes possible to eject ink droplets smaller than the nozzle in diameter. However, when using the driving waveform as shown in
FIG. 14
, approximately 25 &mgr;m is the smallest limit to the droplet diameter obtained in actuality, which cannot be enough to meet recent increasing needs for higher image quality.
Consequently, the present inventor proposed, in Japanese Patent Application Laid-Open No. HEI10-318443, a driving waveform as shown in
FIG. 16
as a driving method for enabling further minute droplets to be ejected. This driving waveform comprises a voltage changing section
151
for pulling in the meniscus just before the ejection, a voltage changing section
152
for compressing the pressure generating chamber and forming the liquid column, a voltage changing section
153
for early separating the droplet from the tip of the liquid column, and a voltage changing section
154
for controlling reverberation of the pressure wave remaining after the ink droplet ejection.
Namely, the driving waveform of
FIG. 16
is such that pressure wave control aiming at the early separation of the ink droplet and the reverberation control is added to the conventional meniscus control method, and thereby, it becomes possible to eject an ink droplet having an approximately 20 &mgr;m droplet diameter stably.
In addition, the present inventor developed an ejection method utilizing natural vibration of a piezoelectric actu
Do An H.
Fuji 'Xerox Co., Ltd.
McGinn & Gibb PLLC
Nguyen Judy
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