Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-03-26
2001-12-11
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S065000
Reexamination Certificate
active
06328435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head and an ink jet recording device.
2. Description of the Related Art
As a typical desktop nonimpact recording device, an ink jet recording device is now receiving attention for reasons of simple manufacturing and easy realization of full-color recording. The ink jet recording device has a recording head provided with a plurality of pressure chambers. A piezoelectric element or a resistive heating element, for example, as an actuator is built in each pressure chamber. Each pressure chamber is partially defined by a nozzle plate. The nozzle plate is formed with a plurality of nozzles respectively corresponding to the pressure chambers.
Ink is supplied from a common ink chamber through a plurality of ink supply channels respectively to the pressure chambers. When the actuator is driven, a pressure wave is generated in the corresponding pressure chamber to eject ink droplets from the corresponding nozzle, thus effecting dot recording on a recording medium such as a sheet of paper. In an existing ink jet head, the ratio of the mass of ink in each nozzle and the mass of ink in each ink supply channel is preferably set in the range of about 1:1 to about 1:2. Further, the diameter of each nozzle is preferably set to about 30 &mgr;m in consideration of printing speed, resolution, etc.
In the case of deciding the dimensions of each ink supply channel so as to meet the above conditions, the length of each ink supply channel is set to less than 100 &mgr;m provided that the sectional shape of each ink supply channel is circular or square. If the length of each ink supply channel is not less than 100 &mgr;m and the sectional shape thereof is square, the viscosity of ink in each ink supply channel is too small, causing a reduction in balance between the ink mass in each nozzle and the ink mass in the corresponding ink supply channel. Accordingly, in the case of setting the length of each ink supply channel to not less than 100 &mgr;m, the sectional shape of each ink supply channel is set oblong.
FIGS. 1A and 1B
illustrate a prior art ink jet head having short ink supply channels each having a length less than 100 &mgr;m. Reference numeral
1
denotes a pressure chamber plate formed with a common ink chamber
2
and a plurality of pressure chambers
3
. Each pressure chamber
3
is connected through an ink supply channel
4
to the common ink chamber
2
. A nozzle plate
6
having a plurality of nozzles
7
is bonded to the pressure chamber plate
1
. Reference numeral
8
denotes an ink droplet ejected from one of the nozzles
7
. In the case that the thickness of a partition wall
5
formed between the common ink chamber
2
and each pressure chamber
3
, that is, the length of each ink supply channel
4
is set to less than 100 &mgr;m as mentioned above, good flying characteristics or frequency characteristics of ink can be realized by setting the sectional shape of each ink supply channel
4
substantially square. However, in the case of integrally forming the common ink chamber
2
, the pressure chambers
3
, and the ink supply channels
4
on the pressure chamber plate
1
, the manufacture of the ink jet head becomes difficult with the thickness of the partition wall
5
set to less than 100 &mgr;m.
FIGS. 2A and 2B
illustrate another prior art ink jet head having long ink supply channels each having a length not less than 100 &mgr;m. As shown in
FIG. 2A
, the length of each ink supply channel
4
′, that is, the thickness of a partition wall
5
′ is set to not less than 100 &mgr;m. In this case, the sectional shape of each ink supply channel
4
′ is set oblong as shown in
FIG. 2B
in consideration of the balance between the ink mass in each nozzle
7
and the ink mass in the corresponding ink supply channel
4
′.
As mentioned previously, in the case of integrally forming the common ink chamber, the pressure chambers, and the ink supply channels on the pressure chamber plate, the manufacture of the ink jet head becomes very difficult with the length of each ink supply channel, or the thickness of the partition wall between the common ink chamber and each pressure chamber set to less than 100 &mgr;m. Further, in the case of setting the length of each ink supply channel to not less than 100 &mgr;m, the sectional shape of each ink supply channel
4
′ becomes oblong as shown in
FIG. 2B
in consideration of the balance between the ink mass in each nozzle and the ink mass in the corresponding ink supply channel. However, when the sectional shape of each ink supply channel is oblong, a turbulent flow is likely to generate in each ink supply channel, causing a deterioration in flying characteristics or frequency characteristics of ink.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ink jet head which can be easily manufactured and can improve the flying characteristics of ink.
In accordance with an aspect of the present invention, there is provided an ink jet head comprising a piezoelectric element having a displacing portion; a pressure chamber plate bonded to the piezoelectric element for defining a common ink chamber and a plurality of pressure chambers in cooperation with the piezoelectric element; and a nozzle plate bonded to the piezoelectric element and the pressure chamber plate and having a plurality of nozzles respectively communicating with the plurality of pressure chambers; each of the plurality of pressure chambers being connected to the common ink chamber through a plurality of ink supply channels each having a substantially square cross-section.
Preferably, the displacing portion of the piezoelectric element comprises a plurality of individual electrodes embedded in the piezoelectric element and a plurality of ground electrodes embedded in the piezoelectric element in alternate relationship with the plurality of individual electrodes; each of the plurality of individual electrodes being connected to drive means. Preferably, the pressure chamber plate is formed by molding a thermosetting resin containing a filler, and the thermosetting resin has a coefficient of linear expansion of 15×10
−6
/° C. or less. More preferably, the thermosetting resin is a thermosetting epoxy resin, and the filler is silica (SiO
2
). More preferably, 70-80 wt. % of silica is mixed in the thermosetting epoxy resin.
In accordance with another aspect of the present invention, there is provided an ink jet recording device comprising a housing; a platen mounted to the housing; a guide member mounted to the housing so as to extend substantially in parallel to the platen; a carriage movably mounted on the guide member; first drive means for driving the carriage; and a plurality of ink jet heads mounted on the carriage; each of the plurality of ink jet heads comprising a piezoelectric element having a displacing portion; a pressure chamber plate bonded to the piezoelectric element for defining a common ink chamber and a plurality of pressure chambers in cooperation with the piezoelectric element; a nozzle plate bonded to the piezoelectric element and the pressure chamber plate and having a plurality of nozzles respectively communicating with the plurality of pressure chambers; second drive means connected to the displacing portion of the piezoelectric element; and control means connected to the second drive means for controlling the second drive means; each of the plurality of pressure chambers being connected to the common ink chamber through two ink supply channels each having a substantially square cross-section.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.
REFERENCES:
patent: 4367480 (1983-01-01), Kotoh
patent: 5774145 (1998-0
Iwaishi Akira
Kawamura Takumi
Miyaki Akihiko
Ono Masahiro
Sasaki Masayuki
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Ltd.
Nguyen Thinh
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