Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-05-01
2003-07-29
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06598958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for ejecting liquid, which is applicable to, for example, an ink jet type print head and a spraying/coating apparatus.
2. Description of the Background Art
FIG. 18
is a sectional view showing a structure of a conventional liquid ejector, which is introduced in Japanese Patent Application Laid-Open No. 10-278253, for example. A cavity is provided on an ink tank
10
for storing ink
30
. The cavity communicates with an opening
19
opened on the ink tank
10
and has a parabolic reflecting wall
11
as an inner wall which locates a focal point
12
in the vicinity of the opening
19
. The cavity is also opened at the opposite side of the opening
19
, where a piezoelectric transducer
20
is provided to vibrate the ink
30
. The vibration is carried out by connecting an ac source
25
between a surface of a piezoelectric vibration excitor
29
forming the piezoelectric transducer
20
and an electrode
21
for preventing leakage of the ink
30
from the cavity through wirings
24
and
23
, respectively.
In such a liquid ejector, the vibration of the piezoelectric transducer
20
provides acoustic wave
26
for the ink
30
stored in the cavity in almost plane form. The acoustic wave
26
propagates within the ink
30
and reaches the reflecting wall
11
to be focused onto the focal point
12
. Since the focal point
12
is positioned near the opening
19
, the acoustic energy of the ink
30
at this point increases in density so that an ink droplet
31
is ejected.
A leading path
13
which supplies the ink
30
into the cavity is provided on the reflecting wall
11
and near the piezoelectric transducer
20
so as not to impair the function of reflecting the acoustic wave
26
.
However, this arrangement easily causes an air bubble
30
a
to remain in the cavity, especially on the opposite side of the leading path
13
near the piezoelectric transducer
20
when the ink
30
is supplied from the leading path
13
into the cavity surrounded by the reflecting wall
11
. The occurrence of the bubble
30
a
may impair the propagation of the acoustic wave
26
and the reflection at the reflecting wall
11
at the position, which may result in decrease in the acoustic energy at focusing. That is, it is a first problem that the presence of the bubble
30
a
makes it difficult to control a droplet to be ejected and worsens the ejection efficiency.
Since the focal point
12
is provided in the vicinity of the opening
19
, the leading path
13
on the opposite side of the opening
19
is placed at a position where the reflecting wall
11
with a parabolic surface extends wide open. This causes a mechanism for supplying the ink to the leading path
13
to be provided outside the maximum diameter of the cavity, resulting in a second problem that is to be a factor of preventing miniaturization of the device.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a liquid ejector comprising at least one acoustic conductor for propagating acoustic wave including a first surface and an outer surface for reflecting the acoustic wave given to the first surface and focusing it onto a focal point. The liquid ejector further comprises a supplying path for supplying liquid to be ejected from the outside of the acoustic conductor to the focal point. The “outside of the acoustic conductor” indicates portions other than the acoustic conductor, and includes a form that the “outside” is surrounded by the acoustic conductor.
According to a second aspect of the present invention, in the liquid ejector of the first aspect, in cross section of the at least one acoustic conductor, the outer surface presents a parabola having a focus on the focal point, and the acoustic wave is supplied in parallel with an axis of the parabola.
According to a third aspect of the present invention, in the liquid ejector of the first aspect, in cross section of the at least one acoustic conductor, the outer surface presents an ellipse having a first focus on the focal point, and the acoustic wave is supplied radially at a second focus of the ellipse.
According to a fourth aspect of the present invention, in the liquid ejector of the first aspect, the supplying path is arranged outside the outer surface.
According to a fifth aspect of the present invention, in the liquid ejector of the fourth aspect, the at least one acoustic conductor includes a plurality of acoustic conductors, and the supplying path is used in common for the plurality of acoustic conductors.
According to a sixth aspect of the present invention, in the liquid ejector of the fifth aspect, the supplying path extends in a direction that the plurality of acoustic conductors are arranged.
According to seventh and tenth aspects of the present invention, in the liquid ejector of the fourth or ninth aspect, the at least one acoustic conductor further comprises a second surface arranged closer to the first surface than the focal point, a boundary between the liquid to be ejected and the second surface is perpendicular to a traveling direction of the acoustic wave reflected at the outer surface.
According to eighth and eleventh aspects of the present invention, in the liquid ejector of the seventh or tenth aspect, in cross section of the at least one acoustic conductor, the outer surface presents a parabola having a focus on the focal point, and the second surface presents an arc shape being convex to the first surface.
According to a ninth aspect of the present invention, in the liquid ejector of the first aspect, the at least one acoustic conductor further comprises an inner surface separated from the outer surface, and the supplying path is formed by the inner surface.
According to a twelfth aspect of the present invention, in the liquid ejector of the eleventh aspect, in the cross section where the outer surface presents the parabola, an intersection of the first surface and the parabola is taken as a first intersection, an intersection of the arc and a line connecting the first intersection and the focus of the parabola is taken as a second intersection, and the inner surface is positioned closer to the axis than a line passing through the second intersection in parallel with the axis.
According to a thirteenth aspect of the present invention, in the liquid ejector of the ninth aspect, the outer surface presents a parabola in cross section having a focus on the focal point, and the inner surface is provided in the vicinity of an axis of the parabola.
According to a fourteenth aspect of the present invention, in the liquid ejector of the thirteenth aspect, the inner surface presents a line in cross section of the at least one acoustic conductor.
According to a fifteenth aspect of the present invention, in the liquid ejector of the ninth aspect, the at least one acoustic conductor is liquid being filled in between a body surrounding the at least one acoustic conductor and the supplying path.
According to a sixteenth aspect of the present invention, the liquid ejector of the first or fourteenth aspect further comprises a protecting member being in contact with the outer surface of the at least one acoustic conductor and having an acoustic impedance larger than that of the at least one acoustic conductor.
According to a seventeenth aspect of the present invention, in the liquid ejector of the sixteenth aspect, the protecting member is thicker than the wavelength of the acoustic wave in the at least one acoustic conductor.
According to an eighteenth aspect of the present invention, in the liquid ejector of the first aspect, the outer surface has a diameter decreasing from the focal point toward an opening for ejecting the liquid to be ejected.
In the liquid ejector of the first to third aspects, focusing of the acoustic wave results in increase in the acoustic energy to eject the liquid to be ejected. Further, there is no need to provide an inner wall combining the function of storing the liquid to be ejected with that of reflecting the acoust
Aizawa Jyun-ichi
Fukumoto Hiroshi
Takeda Munehisa
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