Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-05-28
2004-09-28
Meier, Stephen (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S071000
Reexamination Certificate
active
06796637
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART
The present invention relates to piezoelectric/electrostrictive actuators and methods for manufacturing the same. More particularly, it relates to a piezoelectric/electrostrictive film-type actuator which is used for a dislocation control device, a solid-state device motor, an ink-jet head, a relay, a switch, a shutter, a pump, a fin, and so on, which operates in response to a dislocation of an element and which serves as a transducer for converting mechanical energy into and from electrical energy, so as to achieve a quicker response, a higher energy conversion efficiency, and a larger bending dislocation, and it relates to methods for manufacturing the piezoelectric/electrostrictive actuator.
Piezoelectric/electrostrictive actuators which serve as a mechanism for increasing a pressure in a pressurized chamber formed in a base of the actuator and which change the volume of the pressurized chamber in response to a dislocation of a piezoelectric/electrostrictive element disposed on a wall of the pressurized chamber have been recently known. Such piezoelectric/electrostrictive actuators are used for, for example, an ink pump of a print head of an ink-jet printer and the like, for discharging an ink particle (ink droplet) from a nozzle communicating with the pressurized chamber by increasing the pressure in the pressurized chamber filled with ink in response to a dislocation of the piezoelectric/electrostrictive element, and thus for performing printing.
An example of an ink-jet print head using piezoelectric/electrostrictive actuators as shown in
FIGS. 4 and 5
is disclosed in JP-A-06-40035.
An ink-jet print head
140
has an ink nozzle member
142
and a piezoelectric/electrostrictive actuator
145
integrally bonded with the nozzle member, and has a configuration in which ink fed in cavities
146
formed in the piezoelectric/electrostrictive actuator
145
is discharged from nozzles
154
formed in the ink nozzle member
142
.
More particularly, the piezoelectric/electrostrictive actuator
145
has a ceramic base
144
and piezoelectric/electrostrictive elements
178
integrally formed with the ceramic base
144
. The ceramic base
144
has a closing plate
166
, a connecting plate
168
, and a spacer plate
170
interposed between the closing plate and the connecting plate, these plates having a thin flat shape and being integrally formed.
The connecting plate
168
has first communication openings
172
and second communication openings
174
formed at positions corresponding to communication holes
156
and orifices
158
, respectively, formed in an orifice plate
150
. While the first communication opening
172
has substantially the same or a little larger inner diameter than that of the communication hole
156
, the second communication opening
174
has a larger diameter than that of the orifice
158
by a predetermined amount.
Also, the spacer plate
170
has a plurality of long rectangular windows
176
formed therein. The spacer plate
170
is overlaid on the connecting plate
168
so that one of the first communication openings
172
and one of the second communication openings
174
formed in the connecting plate
168
are opened to the corresponding window
176
.
Furthermore, the spacer plate
70
has the closing plate
166
and the connecting plate
168
overlaid on the respective surfaces thereof so that the closing plate
166
covers the windows
176
. Thus, the ceramic base
144
has the cavities
146
formed therein which communicate with the outside via the first and second communication openings
172
and
174
.
In such a piezoelectric/electrostrictive film-type actuator
145
, in order to provide a larger dislocation so as to discharge a larger droplet, it is effective to make the closing plate
166
serving as upper walls as well as diaphragms of the cavities
146
thinner and also the short sides of the rectangular cavities
146
wider; however, this configuration leads to a decrease in the stiffness of the closing plate
166
, resulting in a deterioration in the quick response of the actuator
145
.
In order to increase the stiffness so as to achieve a quicker response, it is effective to make the closing plate
166
thicker and also the short sides of the long rectangular windows
176
(cavities
146
) shorter; however, making the closing plate
166
thicker leads to thicker diaphragms, resulting in a small dislocation of the diaphragms, thereby causing a problem in that a required volume of a droplet is not discharged. In other words, it is difficult to achieve a large dislocation and a quick response, at the same time, of the piezoelectric/electrostrictive actuators by only optimizing the dimensions of the actuators when further improved performances of the actuators are required.
To solve these problems, the same applicant has proposed a piezoelectric/electrostrictive film-type actuator, in PCT Application No. PCT/JP02/02290, wherein piezoelectric/electrostrictive elements, each having a plurality of layers of piezoelectric/electrostrictive films and electrode films laminated therein, are disposed on a base. The proposed actuator is the same as a piezoelectric/electrostrictive film-type actuator
71
, shown in
FIG. 7
, wherein a piezoelectric/electrostrictive element
78
having electrode films
73
,
75
, and
77
and a plurality of (i.e., two-layered) piezoelectric/electrostrictive films
79
laminated therein is disposed on a ceramic base
44
having a cavity
46
therein. When compared to a piezoelectric/electrostrictive element having a single-layered piezoelectric/electrostrictive film, the piezoelectric/electrostrictive element
78
increases a response speed because of its higher stiffness and also produces a larger force as a whole since the element
78
is driven by the plurality of piezoelectric/electrostrictive films, thereby achieving a relatively large dislocation despite its high stiffness. As a result, when the actuator is applied, for example, to an ink-jet print head, the actuator discharges a required volume of a droplet more quickly.
SUMMARY OF THE INVENTION
It is an object of the present invention to fully complement the foregoing proposal. That is to say, it has been found that when the proposed piezoelectric/electrostrictive element having a plurality of layers of piezoelectric/electrostrictive films and electrode films laminated therein is manufactured by firing all together after the piezoelectric/electrostrictive films and the electrode films are laminated, the upper surface of the piezoelectric/electrostrictive films, i.e., the piezoelectric/electrostrictive film in the uppermost layer is likely to be partially decomposed in firing, thereby causing different phases such as decomposed portions
80
illustrated in the piezoelectric/electrostrictive film-type actuator
71
shown in
FIG. 7
to be produced, and leading to the likelihood of withstand voltage deterioration.
More particularly, for example, in PZT typically used as a piezoelectric material, Pb acting as a component of PZT and having a high vapor pressure property evaporates in firing, and thus a PZT crystal is decomposed, resulting in crater-like traces in which glass-like material (different from PZT) mainly including Zr and Ti resides. Since these portions have a reduced thickness of the piezoelectric/electrostrictive film and contain substances having different dielectric constants, the element is likely to have an electric field concentration during polarization or when a driving voltage is applied, thereby causing an electrical breakdown, that is, causing a problem of a reduced withstand voltage.
It has also been found that the piezoelectric/electrostrictive film in the lowermost layer closest to the ceramic base experiences an anti-shrinkage resistance most from the ceramic base (i.e., a closing plate) in firing shrinkage, and also experiences a heat stress most from the ceramic base (i.e., the closing plate) due to a difference in thermal expansion and shrinkage in cooling down after firing, thereby preventing
Kitagawa Mutsumi
Takahashi Nobuo
Takeuchi Yukihisa
Do An H.
Meier Stephen
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