Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-07-31
2002-04-09
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S068000, C347S071000, C347S072000
Reexamination Certificate
active
06367916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to an inkjet head to be used for an inkjet type printer or the like, more specifically to an inkjet head having piezoelectric device to apply positive pressure or negative pressure to ink to control ink ejection.
2. Description of the Related Art
FIG. 1
shows the configuration of a conventional inkjet head. In such an inkjet head, an ink passage
103
and a plurality of ink chambers
105
(one of which is depicted) are formed on a plate portion
104
. Ink is supplied from the ink passage
103
to the ink chambers
105
, and then, a piezoelectric element
101
applies pressure to the ink, so that the ink is ejected through an ink nozzle
102
.
The ink ejecting action of the inkjet head is further explained with reference to FIG.
2
.
FIG. 2
is a sectional view taken substantially along the line II—II of FIG.
1
. As shown in
FIG. 2
, electrodes
106
to be negatively charged and electrodes
107
to be positively charged are mounted on the piezoelectric element
101
. These electrodes
106
and
107
are located at positions corresponding to the ink chambers
105
, respectively. By using the electrodes
106
and
107
, an electric field whose direction is perpendicular to the polarization direction of the piezoelectric element
101
is applied to the piezoelectric element
101
in order to distort the piezoelectric element
101
in a shear mode (thickness shear mode). Namely, when the electric field is applied, the piezoelectric element
101
deflects inwardly into the ink chambers
105
, and pressure is applied to the ink within the ink chambers
105
. In such a manner, the ink ejection can be realized. In addition, the shear mode means a mode of distortion that occurs by applying an electric field whose direction is perpendicular to the polarization direction of a piezoelectric element.
Furthermore, an ink ejecting action of another inkjet head using the shear mode is explained with reference to FIG.
3
.
FIG. 3
is a sectional view of the inkjet head. As shown in
FIG. 3
, electrodes
202
to be positively charged and electrodes
203
to be negatively charged are mounted on a piezoelectric element
201
. The electrodes
202
are located at positions corresponding to ink chambers
205
formed on a plate portion
204
, respectively. The electrodes
203
are located at positions corresponding to side wall portions, respectively. By using the electrodes
202
and
203
, an electric field whose direction is perpendicular to the polarization direction of the piezoelectric element
201
is applied to the piezoelectric element
201
in order to distort the piezoelectric element
201
in the shear mode. Thus, it is possible to apply pressure to ink within the ink chambers
205
to eject the ink.
Moreover, an ink ejecting action of an inkjet head using a distortion mode other than the shear mode is explained with reference to FIG.
4
.
FIG. 4
is a sectional view of the inkjet head. As shown in
FIG. 4
, a diaphragm
303
is disposed on ink chambers
304
formed on a plate portion
305
as an upper wall. Laminated piezoelectric members are mounted on the surface of the diaphragm
303
. Each of the laminated piezoelectric members is formed of a plurality of piezoelectric elements
301
and a plurality of electrode layers
302
. The piezoelectric elements
301
and the electrode layers
302
are alternately laminated. By using the electrode layers
302
, an electric field whose direction is parallel to the polarization direction of the piezoelectric elements
301
is applied to the piezoelectric elements
301
in order to distort the piezoelectric elements
301
in an expansion mode (longitudinal vibration mode). Thus, it is possible to apply pressure to ink within the ink chambers
304
to eject the ink. In addition, the expansion mode means a mode of distortion that occurs by applying an electric field whose direction is parallel to the polarization direction of a piezoelectric element.
However, in the inkjet head using the shear mode shown in
FIG. 2
or
FIG. 3
, distortion of the piezoelectric element
101
or
201
is relatively small. Therefore, it is required to apply a high voltage to the piezoelectric element
101
or
201
in order to obtain sufficient distortion to realize optimum ink ejection.
On the other hand, in the inkjet head using the expansion mode shown in
FIG. 4
, distortion of the each laminated piezoelectric member is relatively large. Therefore, sufficient distortion can be obtained by a low voltage. However, the diaphragm
303
is made of a soft elastic material so as not to restrict distortion of each piezoelectric element
301
. Therefore, pressure which has been applied to ink within the ink chambers
304
is reduced due to the soft elasticity of the diaphragm
303
.
Furthermore, in the inkjet head using the expansion mode shown in
FIG. 4
, the plate portion
305
, the diaphragm
303
, the piezoelectric elements
301
, and so on are separated as independent parts, respectively. When assembling the inkjet head, these parts are accurately bonded to each other at the predetermined positions by using adhesive. Therefore, if the size of an inkjet head is reduced, the manufacture of the inkjet head is difficult.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a piezoelectric device which can be distorted largely and dynamically by low electric energy to thereby control ink ejection efficiently.
It is a second object of the present invention to provide a piezoelectric device which can be simplified its construction and its manufacturing process, providing large and dynamic distortion by low electric energy.
It is a third object of the present invention to provide an inkjet head which can be simplified its construction and its manufacturing process, improving ink ejection performance.
According to the present invention, the above mentioned objects can be achieved by a piezoelectric device for applying pressure to ink within a plurality of ink chambers formed in an inkjet head to control ejection of the ink, the piezoelectric device being mounted on a plate body of the inkjet head on which the plurality of ink chambers and a plurality of peripheral portions are alternately arranged, the piezoelectric device having: a base piezoelectric layer whose underside is fixed onto the plate body, and covering over the ink chambers and the peripheral portions, the base piezoelectric layer being polarized in a direction of its thickness; an electric field applying device for applying an electric field to the base piezoelectric layer, a direction of the electric field intersecting a polarization direction of the base piezoelectric layer; and a plurality of piezoelectric members arranged on an upside of the base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Each of the piezoelectric members has a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately laminated. Each of the piezoelectric layers is polarized in a direction of its thickness such that respective polarization directions of the piezoelectric layers are reversed for each of the piezoelectric layers.
In this piezoelectric device, when voltages having certain polarities are supplied to the electric field applying device, the electric field applying device generates an electric field whose direction intersects the polarization direction of the base piezoelectric layer, and applies the electric field to the base piezoelectric layer. Therefore, the base piezoelectric layer is distorted in a shear mode. As a result, the base piezoelectric layer protrudes to the inside of the ink chambers.
Furthermore, when voltages having a certain polarities are supplied to the respective electrode layers of each piezoelectric member, the electric field whose direction is parallel to the polarization direction of each of the piezoelectric layers of the piezoelectric member is
Barlow John
Brother Kogyo Kabushiki Kaisha
Do An H.
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