Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-07-09
2003-05-06
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C029S025350
Reexamination Certificate
active
06557986
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink jet head for use in ink jet printers and to a method for the manufacture of such an ink jet head. The technical field of the present invention pertains particularly to an ink jet head of the type of emitting ink by a piezoelectric actuator having a structure-improved vibration plate.
BACKGROUND ART
In recent years, the ink jet printer has been used widely for business/home use. In order to meet recent demands for noise reduction, printing quality improvement, et cetera, several methods have been proposed for ink jet heads for use in ink jet printers. Generally, ink jet heads can be classified roughly into the following two types.
In the first type, a portion of a flowpath or a portion of an ink chamber is formed, as a pressure chamber, by a piezoelectric actuator having a piezoelectric element. Then, a pulse-like voltage is applied to the piezoelectric element, thereby causing the piezoelectric actuator to undergo deformation. As a result, the pressure chamber is so deformed that its volume is reduced. This generates in the pressure chamber a pressure pulse which forces droplets of ink to be emitted from a nozzle in communication with the pressure chamber.
In the second type, a heat generating resistor is disposed in a flowpath. A pulse-like voltage is applied to the heat generating resistor. The heat generating resistor generates heat, thereby bringing the ink in the flowpath to the boil to generate vapor bubbles. Droplets of the ink are emitted from a nozzle by the pressure of the generated vapor bubbles.
The present invention pertains to the first type. Therefore, the first type is further described in detail. Referring to
FIGS. 9 and 10
, there is shown an ink jet head as an example of the first type. This ink jet head is provided with a head main body
101
in which a plurality of recessed portions
102
for pressure chambers are formed. Each recessed portion
102
has a supply opening
102
a
for supplying ink and an emission opening
102
b
for emitting the ink. The recessed portions
102
of the head main body
101
are arranged such that they are spaced at specified intervals in one direction.
The head main body
101
is made up of a pressure chamber component
105
defining sidewalls of the recessed portion
102
, an ink flowpath component
106
defining a bottomwall of the recessed portion
102
and formed by lamination of a plurality of thin plates, and a nozzle plate
113
. Formed in the ink flowpath component
106
are an ink flowpath
107
for supply which is connected to the supply opening
102
a
of the recessed portion
102
and an ink flowpath
108
for emission which is connected to the emission opening
102
b
of the recessed portion
102
. Each ink flowpath
107
is connected to an ink supply chamber
110
extending in the direction in which the recessed portions
102
are arranged. The ink supply chamber
110
is connected to an ink supply aperture
111
formed through the pressure chamber component
105
and the ink flowpath component
106
and connected to an ink tank (not shown). Formed through the nozzle plate
113
is a nozzle aperture
114
connected to the ink flowpath
108
.
A piezoelectric actuator
121
is provided atop the pressure chamber component
105
of the head main body
101
in a corresponding fashion to the recessed portion
102
. Each piezoelectric actuator
121
has a vibration plate
122
blocking up the recessed portion
102
of the head main body
101
to form, together with the recessed portion
102
, a pressure chamber
103
. This vibration plate
122
is common to all the piezoelectric actuators
121
, serving also as a lower electrode common to all piezoelectric elements
123
which will be described later. Each piezoelectric actuator
121
has a piezoelectric element
123
provided at a portion of the top surface of the vibration plate
122
corresponding to the pressure chamber
103
and an upper electrode
124
provided atop the piezoelectric element
123
for the application of voltage to the piezoelectric element
123
.
In the piezoelectric actuator
121
, when a pulse-like voltage is applied, through the vibration plate
122
acting as a lower electrode and the upper electrode
124
, to the piezoelectric element
123
, the piezoelectric element
123
shrinks in a direction perpendicular to its thickness direction, whereas neither the vibration plate
122
nor the upper electrode
124
shrinks. As a result, a portion of the vibration plate
122
corresponding to the piezoelectric element
123
is deflected and deformed by the so-called bimetal effect, being formed into a convex shape toward the pressure chamber
103
. This deflection/deformation generates a pressure in the inside of the pressure chamber
103
. By this pressure, the ink in the pressure chamber
103
is emitted outside from the nozzle aperture
114
by way of the emission opening
102
b
and the ink flowpath
108
.
Recently, various attempts have been made for further improvements in order to meet severe demands for size/weight reduction, drive voltage reduction, noise reduction, cost reduction, and improvement in ink emission controllability. With a view to achieving further miniaturization and high performance, there has been made the attempt that the vibration plate and the piezoelectric element are formed of thin films capable of easily being subjected to fine processing (capable of easily being down-sized and precisely processed).
However, if reduction in film thickness is tried by simply employing materials, shapes, and configurations of conventional piezoelectric actuators, this will produce problems such as the occurrence of cracking in the vibration plate, piezoelectric element, or upper electrode, film debonding, film expansion, at the time of manufacture, therefore leading to the drop in ink jet head productivity.
Additionally, also at the time when the ink jet head is in use, such simple reduction in film thickness inevitably results in the drop in mechanical strength because the thickness of each portion is thin. Therefore, cracking is likely to occur in the vibration plate which frequently undergoes deformation, thereby reducing the life of the ink jet head. Therefore, there have been demands for the realization of an ink jet head which is miniaturized and achieves high performance in ink emission amount controllability and, in addition, which provides longer life because of excellent component strength and is easy to manufacture.
Bearing in mind the above points, the present invention was made. Accordingly, an object of the present invention is to provide an ink jet head of the type that ink in a pressure chamber is emitted by a piezoelectric actuator which is miniaturized and improved in productivity and reliability as high as possible by providing a devised structure for a vibration plate of the piezoelectric actuator.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, in the present invention the vibration plate is made up of at least two layers having different Young's moduli. Alternatively, the vibration plate is made up of at least one compressive residual stress layer having a compressive residual stress and at least one tensile residual stress layer having a tensile residual stress.
The present invention provides an ink jet head comprising:
a head main body with a recessed portion for a pressure chamber formed therein, the recessed portion having a supply opening for supplying ink and an emission opening for emitting the ink; and
a piezoelectric actuator including a vibration plate blocking up the recessed portion of the head main body so as to form, together with the recessed portion, the pressure chamber, a piezoelectric element provided on a portion of a side of the vibration plate opposite the head main body and corresponding to the pressure chamber, and an electrode, provided at a side of the piezoelectric element opposite the vibration plate, for the application of voltage to the piezoelectric element, wherein, when a voltage is applied, through the e
Kanno Isaku
Matsuo Koji
Tomita Kenji
Watanabe Osamu
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