Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-04-02
2001-11-27
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06322198
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrostatic inkjet head having a pair of spaced electrodes.
BACKGROUND OF THE INVENTION
Japanese Patent Laid-Open Publications Nos. 6-340069 and 7-246706 each disclose an electrostatic inkjet head generally illustrated in FIG.
8
. The inkjet head, generally indicated by reference numeral
70
, includes three major parts; cover plate
72
, channel plate
74
and substrate
76
. These parts are assembled and fixed to each other. The channel plate
74
made from a silicon plate is formed with a number of grooves on an upper surface thereof by etching. The grooves are covered with the cover plate
72
, so that defined are ink-channels
78
for receiving ink, nozzles
80
for ejecting ink in the form of droplets, reservoir
82
for the accommodation of supplemental ink, and ink-inlets
84
for connecting ink-channels
78
to the reservoir
82
.
Thinned portions of the channel plate
74
underlying the ink-channels
78
are diaphragms
86
, each of which bears a common electrode
88
on one surface thereof confronting to the substrate
76
. For each diaphragm
86
, the substrate
76
is formed with a recess
90
adjacent to the diaphragm
86
. Also, a driving electrode
92
is mounted on a bottom of each recess
90
leaving a gap between the common and driving electrodes,
88
and
92
, respectively.
In operation, when a voltage is applied between the common and driving electrodes,
88
and
92
, an electric attraction force is generated between the electrodes, which biases the thinned diaphragm
86
to bend toward the substrate
76
. The displacement of the diaphragm
86
increases a volume of the ink-channel
78
, which draws supplemental ink from the reservoir
82
through corresponding ink-inlet
84
. Then, when the voltage application is turned off, the displaced diaphragm
86
returns its original position shown in FIG.
8
. This pressurizes the ink in the ink-channel
78
, ejecting an ink-droplet
94
through the nozzle
80
.
As shown in
FIG. 9
, the bent diaphragm
86
presents the maximum displacement at its central portion
87
a
. That is, the central portion
87
a
provides the minimum gap between the driving electrode
90
and the diaphragm
86
when the diaphragm is deformed.
Generally, the electrostatic attraction force to be generated between two opposing electrodes is inversely proportional to the second power of the distance between the electrodes. This means that the central portion
87
a
that defines the minimum gap between the electrodes is subject to the maximum electrostatic attraction force, which in turn accelerates the displacement of the central portion
87
a
. Therefore, the central portion
87
a
is subject to the maximum stress whenever the voltage is applied between the electrodes. This deteriorates a durability of the diaphragm
86
as well as the head
70
.
In addition, in the electrostatic inkjet head, the electrostatic attraction force generated between the opposing electrodes varies with the voltage applied between the electrodes. Ideally, the size of the ink-droplet or amount of ink to be ejected can be controlled by changing the voltage applied. However, this requires a plurality of voltage drivers, for example, low-voltage, middle-voltage, and high-voltage drivers. Disadvantageously, a cost of the driver increases exponentially with the voltage that the driver can supply. This means that incorporating plural voltage drivers in the inkjet head results in a drastic increase in cost of the inkjet head. Alternatively, it appears to be possible to change the amount of ink to be ejected by changing an opposing area of the electrodes. Practically, however, it is not effective for the high-density inkjet head to change the area of the opposing electrodes for the purpose of increasing the amount of ink to be ejected.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide an improved inkjet head capable of overcoming at least one of the above mentioned problems. To achieve the object, according to one aspect of the present invention, an inkjet head includes a first and second electrode. The first electrode is supported by a substrate and the second electrode is supported by a diaphragm so that the second electrode is spaced apart from the first electrode. A drive circuit is connected with the first and second electrodes for applying a voltage between the first and second electrodes so that an electrostatic attraction force is generated between the first and second electrodes. The electrostatic attraction force results in a displacement of the diaphragm toward the substrate and the displacement is utilized for an ejection of ink. Further, the first and second electrodes are positioned so that, when the voltage is turned off, opposing central portions of the first and second electrodes define a gap that is greater than that defined by opposing end portions of the first and second electrodes. Due to this, when the voltage is turned on, the opposing central portions of the first and second electrodes define another gap that is substantially equal to that defined by the opposing end portions of the first and second electrodes.
With this arrangement, when the voltage is applied between the opposing first and second electrodes so that the diaphragm deforms or bends toward the substrate, a nearly constant gap is defined between the first and second electrode. This results in that a nearly uniform stress is generated in the entire diaphragm rather than being provided with any stress concentration which would deteriorate the diaphragm. Therefore, the durability of the diaphragm as well as the inkjet head is extended so much.
Also, the uniformity of the electrostatic force increases a displacement of peripheral portion of the diaphragm, which in turn increase an amount of ink to be ejected.
Further, according to another aspect of the present invention, an inkjet head includes first and second electrode. The first electrode is supported by a substrate and the second electrode is supported by a diaphragm so that the second electrode is spaced apart from the first electrode. A drive circuit is connected with the first and second electrodes for applying a voltage between the first and second electrodes so that an electrostatic attraction force is generated between the first and second electrodes. The electrostatic attraction force results in a displacement of the diaphragm toward the substrate and the displacement is utilized for an ejection of ink. Also, the first electrode and/or second electrode is divided into plural parts so that each of the plural parts of the first electrode and/or second electrode are each electrically disconnected from another part and the plural parts take different distances from the other electrode. Each of the divided parts may be overlapped entirely or partially with another part. The neighboring overlapped parts may be electrically disconnected by an insulative material disposed between them.
With this arrangement, simply by selecting one or more divided parts and then applying the parts with a voltage, the electrostatic attraction force can be changed. This in turn varies an amount of ink to be ejected. Therefore, the amount of ink to be ejected can be changed by the use of cheap and lower-voltage driver even in the high-density inkjet head having a great number of nozzles for ejecting ink.
REFERENCES:
patent: 6000785 (1999-12-01), Sakai et al.
patent: 6-340069 (1994-12-01), None
patent: 7-246706 (1995-09-01), None
patent: 9-039235 (1997-02-01), None
Fujii Yasuhisa
Higashino Kusunoki
Sando Yasuhiro
Takata Hisashi
Barlow John
Gordon Raquel Yvette
Minolta Co. , Ltd.
Sidley Austin Brown & Wood
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