Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-10-13
2001-06-05
Metjahic, Safet (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06243114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to ink jet heads and, more particularly, to an ink jet head for use in an ink jet printer constructed such that a piezoelectric plate member is deformed to have a dome configuration so as to cause the volume of a pressure chamber to vary and cause the ink in the pressure chamber to be ejected.
There is a demand for an ink jet printer to have an improved printing resolution and printing speed. In order to meet such a demand, the operation for deforming the piezoelectric plate member to bulge into a dome configuration should be performed efficiently.
2. Description of the Related Art
FIG. 1A
is a partial front sectional view of an ink jet head
10
showing a pressure chamber
11
of a plurality of pressure chambers provided in the ink jet head
10
;
FIG. 1B
is a partial enlarged view of the ink jet head
10
of
FIG. 1A
;
FIG. 1C
is a lateral sectional view of the ink jet head
10
of
FIG. 1A
; and
FIG. 1D
is a bottom view of the ink jet head
10
of FIG.
1
A.
In the ink jet head
10
, the volume of the pressure chamber
11
containing the ink is cyclically reduced and restored by cyclically deforming an oscillating plate
13
(for example, a stainless plate of a thickness of 20 &mgr;m) and returning it to an original state. When the volume of the pressure chamber
11
is reduced, ink particles
15
(approximately 80 pl) are ejected from a nozzle
14
. When the volume of the pressure chamber
11
is restored to an original level, the ink inside a common passage
16
is supplied to the pressure chamber
11
via an ink supplying passage
17
.
The ink jet head
10
further comprises barriers
20
and
21
, a top plate
22
, a nozzle plate
23
and a piezoelectric plate member
25
.
The piezoelectric plate member
25
has a common electrode
26
on the upper surface thereof and an individual electrode
27
on the lower surface thereof. The piezoelectric plate member
25
is attached to the lower surface of the oscillating plate
13
via a adhesive layer
28
. The oscillating plate
13
and the piezoelectric plate member
25
are integral with each other so as to form a flat bimorph element
29
.
The pressure chamber
11
generally has a rectangular solid configuration. The oscillating plate
13
constitutes a bottom plate for the pressure chamber
11
and has all four sides thereof adhesively attached to the chamber
11
.
As shown in
FIG. 1D
, the common electrode
26
and the individual electrode
27
both have a rectangular configuration of a size that corresponds to the size of the bottom of the pressure chamber
11
.
A voltage is applied across the individual electrode
27
and the common electrode
26
so that the piezoelectric plate member
25
is polarized in a direction of the thickness thereof.
The piezoelectric plate member
25
has a piezoelectric constant d33 in a direction of the polarization (that is, in the direction of the thickness) of the piezoelectric plate member
25
, and a piezoelectric constant d31 in a direction perpendicular to the direction of polarization (that is, in the direction along the plane). Distortion caused by expansion and contraction of the piezoelectric plate member
25
is determined by the intensity of the electric field exerted on the piezoelectric plate member
25
×piezoelectric constant.
Generally, the piezoelectric constant d33 is larger than the piezoelectric constant d31 such that d33 may be twice as large as d31.
The ink jet head
10
is capable of printing at a resolution of 300 dpi. A distance a between the adjacent nozzles
14
(equal to a distance between the barriers
20
and
21
) is 0.339 mm. An area S
1
of a bottom of the pressure chamber
11
is a×b.
A description will now be given of bulging distortion the bimorph element
29
.
When a switch
40
shown in
FIG. 1A
is closed, a voltage from a power source
41
is applied to the individual electrode
27
so that an electric field
42
indicated by the arrows is produced between the individual electrode
27
and the common electrode
26
of the piezoelectric plate member
25
in the direction of the thickness of the bimorph
29
. As a result, the piezoelectric plate member
25
expands in a direction indicated by an arrow
43
and contracts in a direction indicated by an arrow
44
in a plane direction perpendicular to the direction of the electric field
42
. Due to the contraction of the piezoelectric plate member
25
in the plane direction, the bimorph element
29
bulges into a dome configuration, as indicated by the alternate long and two short dashes line. When the switch
40
is grounded, the electric field
42
is removed so that the distortion due to the contraction and the expansion is gone. The bimorph element
29
is restored to a flat state due to elasticity of the oscillating plate
13
.
Since d31<d33, the efficiency of contraction of the piezoelectric plate member
25
in the direction along the plane is lower than the corresponding efficiency in the direction of the polarization. The efficiency with which the bimorph element
29
is bulged into a dome configuration is not satisfactory.
As a result, the ink particles
15
ejected from the nozzle
14
may be insufficient in volume for proper printing, if the pressure chamber
11
is relatively small. For this reason, reduction of the size of the pressure chamber
11
is difficult. Thus, the goals of improving the printing resolution and printing speed are difficult to achieve.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide an ink jet head in which the aforementioned problems are eliminated.
Another and more specific object is to provide an ink jet head with which the printing resolution and the printing speed are improved.
The aforementioned objects can be achieved by an ink jet head comprising: a pressure chamber containing ink; a piezoelectric plate member which constitutes a portion of a wall of the pressure chamber and bulges to cause distortion when a voltage is applied to the piezoelectric plate member; a first set of electrodes; and a second set of electrodes; wherein the first set of electrodes and the second set of electrodes being arranged such that an electric field produced in the piezoelectric plate member is orientated so as to have components in a direction along a plane of the piezoelectric plate member so that distortion in the direction along a plane of the piezoelectric plate member due to the components causes the piezoelectric plate member to bulge.
According to the ink jet head of the present invention, the piezoelectric plate member is distorted depending on the piezoelectric constant d33. Distortion that depends on the piezoelectric constant d33 takes place more efficiently than that of the piezoelectric constant d31. Accordingly, given that the same voltage as used in the related art is used, the degree of bulging is improved. Thus, given the same amount of ejection of ink particles, the pressure chamber can be reduced in size so that the nozzle pitch is reduced and the printing resolution is increased from the current 300 dpi. By reducing the size of the pressure chamber, the size of the piezoelectric plate member corresponding to one pressure chamber is reduced so that the natural frequency of the piezoelectric plate member can be increased. Thus, the frequency of the driving signal from the driving circuit can be increased. By increasing the frequency of the driving signal, the printing speed can be improved.
Another aspect of the ink jet head of the invention is that, given the same amount of ejection of ink particles, the voltage from the power source can be reduced so that the power consumption can be reduced. The cost of fabricating the driving circuit can be reduced.
In further accordance with the present invention, each of the first set of electrodes and each of the second set of electrodes may be alternately arranged on the same surface of the piezoelectric plate member at predetermined intervals so that the elec
Kawamura Takumi
Miyaki Akihiko
Ono Masahiro
Yano Akio
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Gordon Raquel Yvette
Metjahic Safet
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