Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-01-23
2003-04-15
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06547375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet head and a method of manufacturing the ink-jet head. The ink-jet head has an electrode formed on an inner surface of a diaphragm in an ink chamber, and a drive voltage is applied to the electrode according to image data to cause shear deformation of the diaphragm and accordingly cause a pressure change within the ink chamber. Ink drops are thus selectively ejected from respective ink chambers.
2. Description of the Background Art
Nonimpact printers such as ink-jet printer are appropriate for color printing and increasing number of gray-scale levels, and the nonimpact printers replacing impact printers have rapidly been widespread in recent years. A nonimpact printer of drop-on-demand type employs Kaiser method using a piezoelectric element or employs thermal jet method using a heating element for ejecting required ink only when a print is made. This drop-on-demand type printer is advantageous particularly in printing efficiency, production cost and running cost for example, and thus is in the mainstream of the nonimpact printers.
According to the Kaiser method, the volume of the piezoelectric element outside an ink chamber changes to deform a part of a wall forming the ink chamber so that ink is ejected therefrom. This Kaiser printer is difficult to decrease in size and inappropriate for enhancement of resolution. According to the thermal jet method, heating of the heating element causes air bubbles in the ink contained in an ink chamber and the pressure of the air bubbles causes ink to be ejected. The ink is repeatedly subjected to heating and cooling and thus the ink must have a high endurance, and the heating element has a short lifetime and a high power consumption.
In order to overcome these disadvantages, an ink-jet printer utilizes shear deformation of piezoelectric material forming an ink chamber, the shear deformation resulting in a change in pressure of ink within the ink chamber, and accordingly ink is ejected. In this type of ink-jet printer, a plurality of groove-shaped ink chambers partitioned by diaphragms are formed on a substrate of piezoelectric material, and a drive voltage is applied to an electrode formed on an inner surface of the diaphragm in the ink chamber to cause shear mode deformation of the diaphragm of piezoelectric material. Then, the pressure of ink which fills the ink chamber changes to eject ink drops from the ink chamber. The ink-jet printer of this type is suitable for increase in the density of nozzles, decrease of power consumption and higher frequency of the drive voltage.
Referring to
FIGS. 6 and 7
, a conventional ink-jet head formed of piezoelectric material includes a plurality of groove-shaped ink chambers
104
partitioned by diaphragms
103
that are formed on the upper surface of a substrate
101
of piezoelectric material which is polarized in the direction of thickness. The ink-jet head further includes a cover plate
102
where an ink supply opening
121
and a common ink chamber
122
to be placed on the upper surface of ink chambers
104
, and a nozzle plate
109
where a nozzle
110
communicating with the front side of each ink chamber
104
is formed. Cover plate
102
and nozzle plate
109
are attached to substrate
101
. An electrode
105
is formed on an upper half of the inner surface, in the direction of depth, of each diaphragm
103
in ink chamber
104
.
Ink chamber
104
includes a shallow-groove region
106
on the back side of region A of a constant depth with region B therebetween. The bottom surface in the cross section of region B is in the shape of arc corresponding to the diameter of a dicing blade used for dicing for forming ink chamber
104
on substrate
101
. Shallow-groove region
106
is used as a region for connecting the electrode electrically to an external driving circuit. An electrode
108
of a flexible substrate for example has one end connected to the external driving circuit, and the other end thereof is connected to electrode
105
formed on shallow-groove region
106
via a bonding wire or anisotropic conductive film (ACF).
In the conventional ink-jet head shown in
FIGS. 6 and 7
, the cross sectional bottom surface of ink chamber
104
in region B is in the shape of arc. In region B communicating with common ink chamber
122
, the upper surfaces of diaphragms
103
are not joined to cover plate
102
. Therefore, even if a drive voltage is applied to electrode
105
, no shear deformation occurs in diaphragms
103
in region B and accordingly no pressure for ejecting ink is generated. In other words, region B is an unnecessary part which does not contribute to the essential ink-ejecting function. Rather, region B impedes shear deformation of diaphragms
103
in region A.
Formation of electrode
105
is also necessary in region B. Then, the capacitance of electrode
105
increases, which causes delay in rise and fall of a drive voltage and accordingly results in increase of power consumption. In addition, the length of region B in the direction from the front side to the back side of substrate
101
is determined depending on the diameter of the dicing blade used for dicing and on the depth of ink chamber
104
. For example, if the dicing blade of 52 mm in diameter is used for forming ink chamber
104
of 360 &mgr;m in depth, the length of region B is approximately 4.3 mm which is equal to or greater than the length of region A. Then, the material cost increases due to the increased area of substrate
101
.
In order to eliminate the region in the ink chamber that is unnecessary for generation of pressure by which ink is ejected, an ink-jet head structure is proposed according to which the ink chamber has a constant depth over the entire length in the direction from the front to the back side of the substrate. Referring to
FIG. 8
which is an exploded perspective view of such a structure viewed from the back side thereof, a cover plate
202
has no ink supply opening and no common ink chamber. Instead, a manifold
260
has an ink supply opening
261
and a common ink chamber
262
formed therein and is joined to the back side of a substrate
201
. An electrode
205
is formed on an inner surface of each diaphragm
203
in an ink chamber
204
. Respective electrodes
205
of ink chambers
204
are separately formed and continue to the back side of substrate
201
where the back end surfaces of diaphragms
203
are located. On the back side of substrate
201
, electrodes
205
are electrically connected to an external driving circuit.
In this conventional ink-jet head, from which eliminated the region of the ink chamber that is unnecessary for generation of pressure causing ejection of ink, the electrodes are formed from the inner surfaces of diaphragms to the back surface of the substrate, the back surface being orthogonal to the inner surfaces. Therefore, it is likely that the electrode has an insufficient thickness at the right-angled corner where the inner surface of the diaphragm and the back surface of the substrate meet. When the ink-jet head is assembled, the electrode at the corner is readily separated by being touched or hit with another component. Consequently, the electrode is broken and no shear deformation can be caused in the diaphragm even if a drive voltage is applied thereto. A resultant problem is accordingly that ink cannot correctly be ejected.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an ink-jet head and a manufacturing method thereof, the ink-jet head eliminating any region in an ink chamber that is unnecessary for generation of pressure which causes ink ejection while surely preventing an electrode from being broken, and being able to correctly ejecting ink according to a drive voltage.
The present invention is structured as detailed below for achieving the object above.
(1) According to the present invention, an ink-jet head includes a substrate of piezoelectric material and a plurality of groove-shaped ink chambers each having respective
Isono Hitoshi
Nakajima Yoshinori
Conlin David G.
Dike Bronstein Roberts & Cushman
Nguyen Judy
Sharp Kabushiki Kaisha
Tucker David A.
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