Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-10-23
2002-03-26
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06362844
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink-jet printer head of the piezoelectric type.
BACKGROUND OF THE INVENTION
An ink-jet printer head of the thermal-bubble type is conventionally used to jet the ink onto a medium to form an image thereon. The printer head of the type typically generates a large driving force. i.e. about 40 atmosphere pressures, onto the ink droplet being jetted. At the moment the ink droplet leaves the printer head, a droplet trailing phenomenon is observed. Therefore, ink-jet printer of the type wastes ink, and has difficulty in controlling the desired shape and size of the ink droplet. In addition, lower resolution printing quality is also the drawback with the thermal-bubble type ink-jet printer.
The piezoelectric type is another category of the ink-jet printer head which utilizes a piezoelectric ceramic plate as an actuator for driving the ink. The driving force of such type is about 4 atmosphere pressures, which is much smaller than one generated by the thermal-bubble type. Due to the characteristic of driving mechanism, the size of the ink droplet is smaller and the droplet trailing phenomenon is substantially reduced. In addition, the piezoelectric type printer head saves ink and has a higher resolution compared with the thermal-bubble ink-jet type.
The characteristics of the piezoelectric ceramic plate is introduced in the following by referencing FIG.
1
. As well known in the arts, the piezoelectric ceramic plate is made with one predetermined polarization direction. For piezoelectric material whose polarization direction is d
31
, the deformation of the piezoelectric material will be in X direction, when an electric field is applied in Z direction. On the other hand, for piezoelectric material whose polarization direction is d
33
, the deformation of the piezoelectric material will be in Z direction, when the applied electric field is in Z direction. Two well known conventional approaches are used to operate the piezoelectric type printer head. The first one involves utilizing a multi-layer piezoelectric ceramic plate as an actuator to jet the ink as shown in FIG.
2
. Referring to
FIG. 2
, the multi-layer, i.e. 8 layers, piezoelectric ceramic plate
20
is disposed in a housing with the bottom end fixed and the upper end free to move. The polarization direction of each layer of the piezoelectric ceramic plate
20
is d
33
. The positive electrodes for each layer within the multi-layer ceramic plate
20
together form a comb configuration denoted as
100
. The negative electrodes for each layer within the multi-layer ceramic plate
20
together form a comb configuration denoted as
200
.
Initially when a first voltage is applied across the positive and negative electrodes, the electric field generated will make each layer deform and cause the multi-layer piezoelectric plate
20
to move downwards. The rubber pad
21
moves downwards accordingly. The space of the ink tank
23
becomes larger and the ink flows from the ink container
24
into the ink tank
23
via the passage
25
. Afterwards when a second voltage is applied across the positive and negative electrodes, the direction of the electric field generated will be opposite, and each layer deforms in the opposite direction and causes the multi-layer piezoelectric plate
20
to move upwards. The rubber pad
21
moves upwards accordingly. The ink tank
23
will become smaller, and the pressure inside the ink tank
23
will force the ink to be jetted from the ink tank
23
via the outlet
22
.
In the structure of
FIG. 2
, the multi-layer piezoelectric ceramic plate
20
is positioned under the outlet
22
with the upper end moves in a vertical direction. The amount of the displacement &Dgr;X of the upper end of the multi-layer piezoelectric ceramic plate
20
is calculated by the following equation: &Dgr;X=d
33
*V*n, wherein d
33
is the piezoelectric parameter, V is the voltage applied across two electrodes, and n is the number of the layers within the multi-layer piezoelectric ceramic plate
20
. Due to its multi-layer structure, the multi-layer piezoelectric ceramic plate in
FIG. 2
has a larger displacement when applied with a voltage, and results in a larger driving force to the ink. However, the manufacturing of multi-layer piezoelectric ceramic plate
20
and the electrodes is difficult and costly.
The second approach performs the function through another way. The walls of the ink tank are formed by piezoelectric ceramic segments. When the walls of the ink tank are applied with a voltage, the shape of the ink tank will be changed and thus the ink will be jetted out of the ink tank.
FIG. 3
a
shows a cross-sectional view of the structure in which the side walls of the ink tank
302
deforms in response to the voltage applied across the corresponding electrodes. The shown cross section is perpendicular to the longitudinal dimension (into the paper) of the ink tanks
301
,
302
,
303
. The structure includes a plurality of single-layer piezoelectric ceramic segments
321
,
322
,
323
,
324
which are formed by a diamond cutting process on a single sheet of piezoelectric ceramic plate. After the cutting procedure, corresponding side walls of two successive piezoelectric ceramic segments, i.e.
322
,
323
, constitute one ink tank
302
therebetween. The electrodes
39
on the inner surface of each ink tank are respectively formed by an electrodeless nickel plating process. A sheet of glass or ceramic plate
34
is covered and connected onto the upper surface of the piezoelectric ceramic segments to totally enclose the tank space. Two voltages A, B shown in FIG.
3
(
b
) are applied across the respective electrodes to create corresponding deformation as desired. As a result, the right side wall of the tank
302
deforms rightwards and the left side wall of the tank
302
deforms leftwards. Therefore, the size of the ink tank
302
increases due to the deformation. The space of the ink tanks
302
increases, and the ink will be drawn from an ink container (not shown) into the ink tank
302
. Afterwards, the voltage A drops sharply to a negative value and the voltage B elevates sharply to a positive value. Due to this opposite action, the dimension of the tank
302
decreases due to the deformation of the piezoelectric ceramic segments
322
,
323
in a reverse direction. As the space of the ink tank
302
decreases, the ink is jetted from the ink tank
302
via an outlet
31
. The plastic substrate
38
is made of soft and resilient material which also helps the ink tank
302
generate the driving force. Since the electrodeless plating process is used to manufacture the electrodes
39
, its endurance against the ink erosion is enhanced. However, this second approach of the piezoelectric type printer head is complex in structure and in manufacturing. More details regarding the second approach disclosed in FIG.
3
(
a
) can be found in U.S. Pat. No. 5,327,627.
SUMMARY OF THE PRESENT INVENTION
The main object of the present invention is to provide a ink-jet printer head of the piezoelectric ceramic type which has a simple structure and is easy to manufacture.
In the present invention, the printer head includes a deformable polymer membrane, an ink tank and a dual-layer piezoelectric ceramic plate. The dual-layer piezoelectric ceramic plate is mounted on the deformable polymer membrane which functions to apply a perturbation force to the ink within the ink tank. The dual-layer of the piezoelectric ceramic plate includes an top layer and a bottom layer, both of which have same polarization direction. One end of the piezoelectric ceramic plate is fixed to the membrane and the other end is free to vibrate. When a voltage is applied across two electrodes at the fixed end of the dual-layer piezoelectric ceramic plate, the free end of the dual-layer piezoelectric ceramic plate vibrates. Through the deformable membrane, a perturbation force is created and drives the ink to be jetted outside the ink tank via an outlet.
REFERENCES:
patent: 4520374 (1985-05-01), Koto
p
Liu Ru-Shi
Lu Yu-Yang
Shieh Shen-Jye
Yang Ying-Jay
Acer Peripherals Inc.
Barlow John
Fulbright & Jaworski L.L.P.
Stewart Jr. Charles W.
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