Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-10-25
2004-03-30
Stephens, Juanita (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S071000
Reexamination Certificate
active
06712454
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2001-328765 filed on Oct. 26, 2002, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus in which ink droplets are ejected from nozzles so as to record characters or graphics.
2. Description of the Related Art
Drop-on-demand type ink jet systems are generally known well (JP-A-Hei.53-12138 and JP-A-Hei.10-193587). In the drop-on-demand type ink jet systems, a pressure generating member such as a piezoelectric actuator is used to generate a pressure wave (acoustic wave) in a pressure generating chamber filled with ink, so that an ink droplet is ejected from a nozzle communicating with the pressure generating chamber by the pressure wave.
FIG. 23
shows an example of an ejector in an ink jet recording apparatus known in these official gazettes. An ejector
10
is constituted by a common flow path
4
, an air damper
26
, an ink supply path
5
, a diaphragm plate
8
, a piezoelectric actuator
3
, a pressure generating chamber
1
and a nozzle
2
. Generally, one ejector
10
has one nozzle
2
. Generally, one ejector
10
has one nozzle
2
. The nozzle
2
for ejecting ink and the ink supply path
5
for introducing ink from an ink tank (not shown) through the common flow path
4
communicate with the pressure generating chamber
1
. The air damper
26
is provided on the common flow path
4
so as to absorb the pressure. In addition, the diaphragm plate
6
is provided on the bottom surface of the pressure generating chamber
1
, and the piezoelectric actuator
7
is attached to the outside of the diaphragm plate
6
.
To eject an ink droplet
8
, the piezoelectric actuator
7
displaces the diaphragm plate
6
to change the volume of the pressure generating chamber
1
to thereby generate a pressure wave. By this pressure wave, a part of ink charged into the pressure generating chamber
1
is jetted to the outside through the nozzle
2
so as to fly as the ink droplet
8
. The flying ink droplet
8
lands on a recording medium such as a recording paper so as to form a recording dot. Such a recording dot is formed repeatedly in accordance with image data. Thus, characters or graphics are recorded on the recording medium.
FIG. 24
schematically show the meniscus operation of the nozzle
2
before and after ejecting the ink droplet
8
. As shown in
FIG. 24A
, a meniscus
9
is substantially flat initially. When the pressure generating chamber
1
is compressed, the meniscus
9
moves toward the outside of the nozzle
2
so as to eject the ink droplet
8
(FIG.
24
B). Immediately after the ink droplet
8
is ejected, the ink volume inside the nozzle
2
is reduced so that the meniscus
9
is formed into a concave shape (FIG.
24
C). The value y shown in
FIG. 24C
designates the displacement of the meniscus
9
after the ejection. The concave meniscus
9
undergoes the states shown in
FIGS. 24D and 24E
by the effect of the surface tension of the ink, and returns to the opening portion of the nozzle
2
gradually. Thus, in a short time, the meniscus
9
recovers its condition before the ejection (FIG.
24
F).
FIG. 25
shows the positional change of the meniscus
9
immediately after the ejection of the ink droplet
8
. The meniscus
9
making a large retreat (y=−60 &mgr;m) immediately after the ejection (t=0) returns to its initial position (y=0) while swinging as shown in FIG.
25
. The return behavior of the meniscus
9
after the ejection of the ink droplet
8
is referred to as “refill”, and time for the meniscus
9
to return to the opening surface of the nozzle
2
for the first time after the ejection of the ink droplet
8
is referred to as “refill time” (t
r
).
In ink jet recording heads, the number of nozzles
2
is a parameter having the greatest influence on the recording speed. As the number of the nozzles
2
is increased, the number of dots that can be formed per unit time is increased so that the recording speed can be enhanced. Therefore, in a typical ink jet recording apparatus, a multi-nozzle type recording head in which a plurality of ejectors
10
have been interconnected one another is often adopted.
FIG. 26
shows a recording head in which ejectors
10
are aligned one-dimensionally. The recording head is constituted by an ink tank
20
, ink conduits
18
a
and
18
b
, a filter
19
and the ejectors
10
. The ink tank
20
is connected to a common flow path
4
through the ink conduits
18
a
and
18
b
and the filter
19
. The plurality of ejectors
10
communicate with the common flow path
4
.
However, in such a structure in which the ejectors
10
are aligned one-dimensionally, the number of the ejectors
10
cannot be increased much. It is said that the upper limit of the number of ejectors
10
is typically about 100. Therefore, some ink jet recording heads in which the number of ejectors is increased by arraying ejectors two-dimensionally in a matrix (hereinafter, referred to as “matrix-array head”) have been heretofore proposed (JP-A-Hei.1-208146, JP-A-Hei.10-508808, etc.).
FIG. 27
shows an example of a matrix-array head. The matrix-array head differs from the recording head in
FIG. 26
in that a second common flow path
16
is provided newly and there are a plurality of common flow paths
4
. Each of common flow paths
4
communicate with the second common flow path
16
, and a plurality of ejectors
10
are connected to each of the common flow paths
4
. Such a matrix-array head structure is very effective in increasing the number of ejectors
10
. For example, when the number of common flow paths
4
is set at 26 and 10 ejectors
10
are connected to each of the common flow paths
4
, 260 ejectors
10
can be arrayed.
FIG. 28
shows an ink jet recording head disclosed in JP-A-Hei.10-508808.
FIG. 28A
shows the section of ejectors
10
, and
FIG. 28B
shows the schematic arrangement of the ejectors
10
. As shown in
FIG. 28A
, the ink jet recording head is constituted by pressure generating chambers
1
, nozzles
2
, communication paths
3
, ink supply paths
5
, a diaphragm plate
6
, piezoelectric actuators
7
and flow paths
23
. This ink jet recording head is formed by laminating a nozzle plate
11
, a flow path plate
25
and the diaphragm plate
6
to one another. Partition walls
27
are thick enough not to transmit the pressure in the pressure generating chambers
1
to the flow paths
23
. As shown in
FIG. 28B
, the flow paths
23
communicate with the flow paths
24
. The flow paths
23
correspond to the common flow paths
4
in
FIG. 27
, and the flow paths
24
correspond to the second common flow path
16
.
In the related-art matrix-array heads as shown in
FIGS. 27 and 28
, however, there are some problems. As for the first problem, the interval (nozzle pitch Pc) of nozzles
2
having a common flow path
4
therebetween cannot be set to be small. As a result, the array density of the ejectors
10
(the number of nozzles per unit area) cannot be made very high.
FIG. 29
shows an equivalent electric circuit of the matrix-array head. The signs m, r, c, and &PHgr; designate inertance [kg/m
4
], acoustic resistance [Ns/m
5
], acoustic capacitance [m
5
/N] and pressure [Pa], respectively, and suffixes d, c, i, n, p and p′ designate a driving portion, a pressure generating chamber, an ink supply path, a nozzle, a common flow path and a second common flow path, respectively. In the matrix-array head having the ejectors
10
arrayed two-dimensionally, as shown in
FIG. 29
, a large number of ejectors
10
communicate with one another through the common flow paths
4
and the second common flow path
16
. Therefore, when the number of ejectors
10
communicating with one and the same common flow path
4
is large, it is necessary to suppress crosstalk (pressure interference) or the like between the ejectors
10
clo
Morgan & Lewis & Bockius, LLP
Stephens Juanita
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