Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-01-21
2002-05-14
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06386682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink-jet head using electrostatic force for a driving source for ejecting ink.
An ink-jet head for ejecting ink by pressurization and printing the ejected ink on recording paper has a bubble type which generates a bubble with a heating element to jet ink. In the bubble-type ink-jet head
1
, a heating element
5
is provided in a nozzle
3
as shown in FIG.
51
and ink
7
is supplied to the rear part of the nozzle
3
(an upper part in
FIG. 51
) from an ink cartridge not shown. When the heating element
5
is heated, a bubble
9
is generated in the nozzle
3
and ink pushed out by the bubble
9
is ejected toward recording paper not shown as an ink droplet
7
a
. When driving voltage is turned off, the bubble
9
disappears, ink
7
flows into the nozzle
3
by capillarity. Repeating it, printing on the recording paper is performed.
An ink-jet head also has a piezoelectric element type using a piezoelectric element and others for a driving source for ejecting ink. In the piezoelectric element-type ink-jet head
11
, as shown in
FIG. 52
, a pin
15
is fixed to the end of a piezoelectric element
13
the base end of which is fixed and the end of the pin
15
is inserted in a nozzle
17
. An ink passage
19
is connected to the nozzle
17
and ink
7
is supplied to the ink passage
19
from an ink cartridge not shown. When a driving pulse is applied to the piezoelectric element
13
, the piezoelectric element
13
is displaced and the pin
15
is moved in the nozzle
17
so that the ink passage
19
is opened or closed. The ink
7
is sucked by reduced pressure in the nozzle
17
and is ejected as an ink droplet
7
a
because the pin
15
enters the nozzle
17
again.
However, as the above bubble-type ink-jet head is required to heat ink instantaneously and generate a bubble, there is disadvantage that driving power is large. There is a problem that as time required since a driving pulse is applied to a heating element until a bubble is generated is delayed due to various factors such as the exoergic efficiency of a heating element, thermal conductivity between the heating element (a solid) and ink (fluid) and the temperature dependency characteristics of ink itself, it is difficult to improve the responsibility.
In the meantime, there is disadvantage that in the piezoelectric element-type ink-jet head, high driving voltage is required to acquire physical quantity such as pressure and oscillation. There is also a problem that the sensitivity of conversion is relatively low and it is thus Difficult to improve the responsibility. Further, there is a problem that as the ink-jet head is required to have resonant structure with deforming material if the ink-jet head is integrated with the deforming material, the design is difficult. It is also expected that the ink-jet head is connected to an electronic circuit to be an integrated circuit by forming a piezoelectric element on the same substrate, however, in this case, there is a problem that micronization and integration is difficult by a method of forming a thick film and the formation of a piezoelectric film itself is difficult by a method of forming a thin film.
To solve such problems, there is proposed an ink-jet head wherein ink is ejected by deforming a diaphragm wall, which constitutes a part of an ink chamber, by electrostatic force (Maxwell stress).
For example, U.S. Pat. No. 4,520,375 discloses an ink-jet head wherein ink is ejected by providing a parallel flat diaphragm made of a semiconductor on one side of an ink chamber and pressurizing after reducing pressure by electrostatic force.
Unexamined Japanese Patent Publication No. Hei 5-50601 discloses an ink-jet head provided with plural nozzle apertures, plural ejecting chamber communicating with each nozzle aperture and a diaphragm for deforming a part of the ejecting chamber wherein ink is ejected by deforming the diaphragm with electrostatic force so that the ejecting chamber is under reduced pressure and pressurizing the ejecting chamber when the diaphragm is restored afterward.
Unexamined Japanese Patent Publication No. Hei 6-106725 discloses an ink-jet head wherein ink is ejected from the end of a nozzle by forming a nozzle with a rigid electrode and an elastic electrode opposite, making ink with a high dielectric constant flow into the nozzle and applying voltage between both electrodes to deform the elastic electrode in the direction of the rigid electrode with electrostatic attraction.
The ink-jet heads according to these methods have advantages that driving voltage can be reduced, compared with the above bubble-type and the above piezoelectric element type, high speed driving is enabled, large scale integration is enabled, the degree of freedom in selecting the material of the element is high, the design is easy and in addition, a driving circuit can be integrated by forming the ink-jet head with a semiconductor such as silicon.
However, for these ink-jet heads, means for achieving high speed ejecting and efficient ejecting is not referred. The control of gradation and the correction of the quantity of ink when multiple nozzles are provided are also not referred.
There are the following problems to realize the above high speed ejecting and the above efficient ejecting:
That is, in an ink chamber, an ink ejection port and an ink supply port exist. There occurs a problem that as simultaneously, ink reversely flows toward a reservoir from the ink supply port if the ink chamber is pressurized and ink is ejected from the ink ejection port, energy efficiency for ejecting ink is bad (efficient ejecting cannot be executed) and ink cannot be ejected at high speed. To solve the problem, the passage resistance of the ink supply port is required to be set to a higher value, compared with that of the ink ejection port.
In the meantime, there occurs a problem that when the passage resistance of an ink supply port is high if an ink chamber is decompressed and ink is supplied from the ink supply port, ink supply speed is reduced and ink cannot be supplied at high speed. In this case, bubbles may invade from an ink ejection port. To solve the problem, the passage resistance of the ink supply port is required to be reduced, compared with that of the ink ejection port.
Since these conditions conflict with each other, in the related arts, a neutral value is acquired based upon both compromised values and the passage resistance of an ink supply port and an ink ejection port is determined.
To solve such a problem, Unexamined Japanese Patent Publication No. Hei 9-141855 discloses an ink-jet head wherein an ink supply port is tapered, however, there is a limit in effect because passage resistance is controlled every direction in which ink flows, depending upon only the shape of a passage.
There are the following problem in relation to the control of gradation:
That is, heretofore, there has been known a method of controlling the gradation by varying directly the concentration or the area of an ink droplet to vary the quantity of ejected ink by means of controlling the degree of pressurization (value, applied time, or the number of pulses of voltage). However, in the case of an ink-jet head, as the volume of an ink chamber is very large, compared with the volume of a ejected ink droplet, it is difficult to control the quantity of an ink droplet precisely.
To solve these problems, Unexamined Japanese Patent Publication No. Hei 9-193385 discloses an ink-jet head wherein the control of gradation and correction in ejecting from plural nozzles are enabled by means of pressurizing by a single piezoelectric element and plural buckled valve means based upon generated heat. However, pressurizing by a piezoelectric element has a problem that a response is slow as described above and driving voltage is high. A built-in assembly of a piezoelectric element costs high and is not suitable for large scale integrated multi-nozzle. The buckled valve depends upon thermal expansion, is slow in a response, and the reliability and the life
Fuji Photo Film Co. , Ltd.
Gordon Raquel Yvette
Sughrue & Mion, PLLC
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