Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-11-12
2002-04-02
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S070000
Reexamination Certificate
active
06364468
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink-jet head for jetting ink by using a piezoelectric effect of a piezoelectric device and a method of manufacturing the same.
Recently, ink-jet printers are widely used in offices and households. Various systems have been proposed for ink-jet heads used in the ink-jet printers in order to meet recent demands for low noise and high print quality. In general, the systems for the ink-jet heads can be roughly divided into the following two systems:
In a first system, part of an ink passage and an ink chamber is formed into a pressure chamber by using a piezoelectric actuator having a piezoelectric device, and a pulse voltage is applied to the piezoelectric device so as to deform the piezoelectric actuator. Thus, the pressure chamber is deformed to have a smaller volume, thereby generating a pressure pulse within the pressure chamber. By using the pressure pulse, ink drops are jetted through a nozzle hole communicating with the pressure chamber.
In a second system, an exothermic resistance is provided in an ink passage, and a pulse voltage is applied to the exothermic resistance so as to generate heat therein. Thus, ink contained in the passage is boiled with vapor bubble generated. By using the pressure of the vapor bubble, ink drops are jetted through a nozzle hole.
The present invention relates to an ink-jet head of the first system, and hence, this system will be further described in detail.
FIGS. 7 through 9
show an exemplified conventional ink-jet head of the first system, and the ink-jet head comprises a head body
101
including a plurality of pressure chamber concaves
102
each having a supply port
102
a
for supplying ink and a discharge port
102
b
for discharging ink. The concaves
102
of the head body
101
are arranged along one direction at predetermined intervals.
The head body
101
includes a pressure chamber part
105
forming the side walls of the concaves
102
, an ink passage part
106
forming the bottoms of the concaves
102
and including plurality of thin plates adhered to one another, and a nozzle plate
113
. Within the ink passage part
106
, an ink supply passage
107
communicating with the supply port
102
a of each concave
102
and an ink discharge passage
108
communicating with the discharge port
102
b
of each concave
102
are formed. Each ink supply passage
107
communicates with an ink supply chamber
110
extending in the direction of arranging the concaves
102
, and the ink supply chamber
110
communicates with an ink supply hole
111
formed in the pressure chamber part
105
and the ink passage part
106
and connected with an external ink tank (not shown). In the nozzle plate
113
, nozzle holes
114
respectively connected with the ink discharge passages
108
are formed.
On the upper surface of the pressure chamber part
105
of the head body
101
, a piezoelectric actuator
121
is disposed. The piezoelectric actuator
121
includes one common electrode
122
of Cr that covers all the concaves
102
of the head body
101
so as to form pressure chambers
103
together with the concaves
102
and is shared by all piezoelectric devices
123
described below. The common electrode
122
also works as the so-called vibration plate. Furthermore, the piezoelectric actuator
121
includes the piezoelectric devices
123
of lead zirconate titanate (PZT) disposed on the upper surface of the common electrode
122
correspondingly to the respective pressure chambers
103
, and an individual electrode
124
of Pt disposed on each piezoelectric device
123
for applying a voltage to the corresponding piezoelectric device
123
together with the common electrode
122
.
When a pulse voltage is applied between the common electrode
122
and each individual electrode
124
, each piezoelectric device
123
shrinks in a lateral direction perpendicular to a thickness direction, but the common electrode
122
and the individual electrode
124
do not shrink. Therefore, a portion of the common electrode
122
corresponding to the piezoelectric device
123
is deformed into a convex projecting toward the pressure chamber
103
due to the so-called bimetal effect. This deformation causes a pressure within the pressure chamber
103
, and owing to the pressure, ink contained in the pressure chamber
103
is jetted from the nozzle hole
114
through the discharge port
102
b
and the ink discharge passage
108
.
In the ink-jet head for jetting ink by using the piezoelectric actuator
121
as described above, various improvements have been recently made so as to meet strict demands for compactness and light weight, a low driving voltage, low noise, low cost, and high controllability in jetting ink. In order to attain further compactness and higher performance, the common electrode
122
, the piezoelectric devices
123
and the individual electrodes
124
can be formed from thin films easily subjected to refined processes.
In this case, for example, a method of manufacturing an ink-jet head shown in FIGS.
10
(
a
) through
10
(
g
) can be adopted. In FIGS.
10
(
a
) through
10
(
g
), the ink-jet head is shown upside down, namely, inversely to that shown in
FIGS. 7 and 8
.
Specifically, a Pt film
142
is formed on the entire surface of a supporting substrate
141
of MgO as is shown in FIG.
10
(
a
), and then, the Pt film
142
is patterned (separated), thereby forming a plurality of individual electrodes
124
as is shown in FIG.
10
(
b
).
Subsequently, a PZT film
143
is formed on the entire supporting substrate
141
bearing the individual electrodes
124
as is shown in FIG.
10
(
c
), and the PZT film
143
is patterned into the same shape as the Pt film
142
. Thus, a plurality of piezoelectric devices
123
are formed as is shown in FIG.
10
(
d
).
Next, on the piezoelectric devices
123
, a common electrode
122
(of a Cr film) is formed as is shown in FIG.
10
(
e
), and the common electrode
122
is fixed on a pressure chamber part
105
as is shown in FIG.
10
(
f
).
Then, the supporting substrate
141
is melted and removed by using heated phosphoric acid or the like, and the pressure chamber part
105
is fixed on an ink passage part
106
and a nozzle plate
113
previously integrated as is shown in FIG.
10
(
g
). Thereafter, wiring of the individual electrodes
124
and other necessary processes are conducted, resulting in completing the ink-jet head.
In the above-described method of manufacturing an ink-jet head, however, it is particularly difficult to form the common electrode
122
in the shape of a thin film. Specifically, in a method where the common electrode
122
is formed by adhering a previously formed Cr film onto the piezoelectric devices
123
with an adhesive, the film is so thin that it is difficult to adhere it onto the piezoelectric devices
123
. On the other hand, in a method in which the common electrode
122
is directly formed on the piezoelectric devices
123
by sputtering or the like, good adhesion can be attained and the thickness can be very small. However, the common electrode
122
cannot be formed into a flat shape on the entire surface of the supporting substrate
141
because the portion thereof on the supporting substrate
141
where the individual electrodes
124
and the piezoelectric devices
123
are not formed is placed at a lower level. Specifically, a portion of the common electrode
122
corresponding to an interval between the piezoelectric devices
123
can be formed in a lower level down to the surface of the supporting substrate
141
as is shown in FIG.
11
(
a
). As a result, portions of the common electrode
122
corresponding to the respective piezoelectric devices
123
can be separated from one another. Alternatively, the portion of the common electrode
122
corresponding to the interval between the piezoelectric devices
123
can be largely bent toward the supporting substrate
141
as is shown in FIG.
11
(
b
). When the common electrode
122
is separated as described above, it is troublesome because the separat
Kanno Isaku
Tanoue Hidetoshi
Tomita Kenji
Watanabe Osamu
Harness & Dickey & Pierce P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Nguyen Thinh
LandOfFree
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