Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-11-17
2002-04-16
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06371603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet recording head, and especially to the ink-jet recording head which can realize the higher density arrangement of ink nozzles.
2. Description of the Related Art
A non-impact recording method attracts public attention because this method is excellent in negligibly small noise at the time of recording. The ink-jet recording method included in the non-impact recording method has the advantages that a high speed recording is possible directly on a recording medium by using a simple mechanism. An ordinary paper can be used as the recording medium.
The ink-jet recording method is conducted by directly adhering ink droplets ejected from a recording head directly onto recording paper for recording letters and fingers. The ink-jet recording method has the advantages of conducting the recording without special fixation treatment to the ordinary paper in addition to conducting the high speed recording. A variety of ink-jet printers are proposed and commercialized.
A main stream of the ink-jet printers in recent days includes a piezoelectric element which converts an electric signal into mechanical energy as a pressure applying means for ejecting ink hereinafter referred to as “piezoelectric type”. Still another embodiment of such printers includes a heater converting an electric signal into thermal energy as the pressure-applying means (hereinafter referred to as “thermal type”). The basic structures and operations of both of the printers of the piezoelectric type and the thermal type are not different except for the pressure-generation system, and only the piezoelectric type will be described.
A conventional ink-jet recording head of the piezoelectric type is described in JP-A-3(1991)-15555, and the configuration of the ink-jet recording head described therein is shown in FIG.
1
. The ink-jet recording head includes a nozzle plate
11
having ink nozzles
10
, and an ink pool
15
is defined by the nozzle plate
11
, an ink pool plate
12
and an ink supply plate
13
. A plurality of pressure chambers
18
are defined by a pressure chamber plate
16
and a vibration plate
17
. Each of the pressure chambers
18
is communicated to the ink pool
15
through an ink supply port
19
, and the vibration plate
17
includes stripe piezoelectric elements
20
each corresponding to each of the pressure chambers
18
. Although each of the components is shown as a single element in
FIG. 1
, one or more plates may be integrally formed. Signal lines for transmitting electric signals to the piezoelectric elements
20
and ink paths for filling ink in the ink pool
15
are omitted in the drawings.
The operational principle in accordance with the Juniomoruv effect in the ink-jet recording head will be described referring to
FIGS. 2A and 2B
. Each of the piezoelectric elements
20
includes a first electrode
22
a
on a side in contact with the vibration plate
17
and a second electrode
22
b
on the reverse side, and the piezoelectric elements
20
have a polarization directed in the plate thickness direction (in the direction “P” in FIG.
2
A). The vibration plate
17
to which each of the first electrode
22
a
of the piezoelectric elements
20
is communicated and a switching circuit
23
to which each of the second electrodes
22
b
is communicated are communicated to one and the other terminals of a driving source
24
, respectively.
When the switching circuit
23
is turned on upon the input of a print order, a voltage is applied to the corresponding piezoelectric elements
20
from the driving source
24
, and the piezoelectric elements
20
becomes contracted in the direction (in the direction “e” in
FIG. 2B
) perpendicular to the plate thickness direction due to the piezoelectric transversal effect. At this stage, an amount of the distortion at the first electrode
22
a
side of the piezoelectric elements
20
is smaller because the first electrode
22
a
side is fixed to the vibration plate
17
and has an electric charge. Thereby, the amounts of the distortion of the both surfaces of the piezoelectric elements
20
are different, and the piezoelectric elements
20
flexibly deforms in the plate thickness direction (in the direction “f” in
FIG. 2B
) to reduce the volume of the corresponding pressure chamber
18
thereby increasing the inner pressure of the pressure chamber
18
.
In
FIG. 3A
showing the sectional view at the time of the operation of the ink-jet recording head in accordance with the above operation principle, the ink is filled in the ink pool
15
, the ink supply port
19
, the pressure chambers
18
and the ink nozzles
10
. When the switching circuit
23
(
FIGS. 2A and 2B
) is turned on in accordance with the printing order under the circumstance, the ink in the printing chamber
18
is pressurized by the piezoelectric elements
20
(arrow “g”) as shown in
FIG. 3B
to be ejected through the ink nozzle
10
because the pressure is open to the ink nozzle
10
and the ink supply path
19
(arrows “k” and “m”).
When the switching circuit
23
(
FIGS. 2A and 2B
) is turned off as shown in
FIG. 3C
, the internal of the pressure chamber
18
returns to the initial state as shown in
FIG. 3A
because the application of the pressure by the piezoelectric elements
20
is released (arrow “h”). At this stage, the pressure chamber
18
is refilled with the ink flowing from the ink pool
15
side by the ejection through the ink supply port
19
as shown by an arrow “n” to complete the series of operations. The series of the operations are repeated at the high speed to conduct the printing.
In the conventional ink-jet recording head, the reduction of the recording head area viewed from the ink ejection side is limited because a plurality of the pressure chambers
18
are flatly arranged and a minimum head width is desired which equals to the sum of the widths of the pressure chambers
18
and the intervals between the adjacent pressure chambers
18
. Therefore, an area occupied by the pressure chambers increases with the increase of the number of the ink nozzles for responding to the high density, and the demand for the higher density of the ink nozzles and the miniaturization of the recording head are trade-off.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide an ink-jet recording head which promotes a higher density of ink nozzles while realizing smaller dimensions for the ink-jet recording head.
The present invention provides an ink-jet recording head including: an ink pool; a plurality of pressure chambers each communicated to the ink pool; a plurality of ink nozzles each communicated to a corresponding one of the pressure chambers; and a plurality of piezoelectric elements each for ejecting ink droplets through a corresponding one of the ink nozzles by exerting a pressure to a corresponding one of the pressure chambers; the pressure chambers and the piezoelectric element being alternately stacked.
In accordance with the present invention, the pressure chambers are stacked with one another viewed from the ink ejection side because the pressure chambers having the piezoelectric element are arranged vertically or stepwise. Thereby, when the number of ink nozzles is increased for responding to the demand for a higher density, the area occupied by the pressure chambers can be reduced. A particularly advantageous structure of the recording head includes ink nozzles communicating with end zones of respective pressure chambers. Accordingly, the smaller dimensions and the higher density can be realized for the recording head.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.
REFERENCES:
patent: 4455560 (1984-06-01), Louzil
patent: 5872580 (1999-02-01), Ochi et al.
patent: 3-15555 (1991-01-01), None
Dickstein , Shapiro, Morin & Oshinsky, LLP
NEC Corporation
Nguyen Judy
LandOfFree
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