Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-04-11
2004-02-03
Meier, Stephen D. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06685305
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording head and an ink jet recording apparatus used this head, which records characters and images on a recording medium by making ink drops eject from nozzles.
DESCRIPTION OF THE RELATED ART
In Japanese Patent Publication No. SHO 53-12138 and Japanese Patent Application Laid-Open No. HEI 10-193587, an ink jet recording head being a drop on demand type has been disclosed. The ink jet recording head ejects ink drops from nozzles connected to pressure chambers by making pressure waves (acoustic waves) generate in the pressure chambers in which ink was filled, by using electromechanical transducers such as piezoelectric actuators as their pressure generating means.
FIG. 1
is a sectional view showing a structure of a conventional ink jet recording head. In
FIG. 1
, a nozzle
52
for ejecting ink drops
57
, and an ink supplying path
54
, which supplies ink to a pressure chamber
51
through a common ink path
53
from an ink tank (not shown), are connected to the pressure chamber
51
. The bottom surface of the pressure chamber
51
is covered with a vibration plate
55
, and an air damper
58
is on the common ink path
53
.
In order to make the ink drops
57
eject from the nozzle
52
connected to the pressure chamber
51
, mechanical displacement is generated at the vibration plate
55
by a piezoelectric actuator
56
positioned on the outside of the vibration plate
55
. And pressure waves (acoustic waves) are generated in the pressure chamber
51
by changing the volume of the pressure chamber
51
by this mechanical displacement of the vibration plate
55
. With these pressure waves, a part of the ink filled in the pressure chamber
51
is ejected through the nozzle
52
and the ejected ink becomes the ink drops
57
. The ink drops
57
hit a recording medium such as a piece of paper and recording dots made of the ink drops
57
are formed on the paper. By repeating this process to form the recording dots based on inputted image data, characters and images are recorded on the recording medium.
At the conventional ink jet recording head mentioned above, a parameter, which decides its recording speed, is the number of nozzles. The more the number of nozzles is, the more the number of dots, which can be formed per unit time, is, and the recording speed increases. In order to meet this requirement, in a normal type ink jet recording apparatus, a multi nozzle type recording head, in which plural ink jet mechanisms (ejectors) are connected, is used. In this, the ejector is composed of the nozzle
52
, the pressure chamber
51
, the vibration plate
55
, the piezoelectric actuator
56
, and the ink supplying path
54
.
FIG. 2
is a perspective view showing a basic structure of a conventional multi nozzle type ink jet recording head. In
FIG. 2
, an ink tank
67
is connected to a common ink path
63
through a filter
66
, and plural pressure chambers
61
are connected to this common ink path
63
through ink supplying paths (not shown), and each of the plural pressure chambers
68
provides a nozzle
62
. However, at this structure, in which ejectors
68
are arrayed in a one-dimensional way, the maximum number of ejectors
68
is limited to about
100
pieces, and this number cannot be increased so largely.
In Japanese Patent No. 2806386 and Japanese Patent Application Laid-Open No. HEI 10-508808, in order to increase the number of nozzles, an ink jet recording head, in which ejectors are arrayed in a two-dimensional matrix, has been disclosed. Hereinafter this ink jet recording head is referred to as a matrix head.
FIG. 3
is a perspective view showing a basic structure of a conventional matrix head for an ink jet recording head. In
FIG. 3
, the common ink path is composed of a common ink main path
73
and plural common ink branch paths
78
, and six ejectors are connected to each of the plural common ink branch paths
78
. And ink is supplied to the common ink main path
73
from an ink tank
77
through a filter
76
. This matrix head structure has a great advantage to increase the number of ejectors, in this, each of the ejectors provides a pressure chamber
71
, a nozzle
72
, a part of the common ink branch paths
78
, a vibration plate (not shown), and a piezoelectric actuator (not shown). In
FIG. 3
, there are six common ink branch paths
78
and six pressure chambers
71
for each of the six common ink branch paths
78
, therefore the total number of ejectors is
36
. For example, when the number of the common ink branch paths
78
is 26 and 10 pressure chambers
71
are disposed in each of the common ink branch paths
78
, 260 ejectors can be arrayed in the matrix head. In
FIG. 3
, Pn shows the distance between adjacent two ejectors, and Pc shows the distance between adjacent two common ink branch paths
78
.
FIG. 4
is a diagram showing a conventional matrix head for an ink jet recording head. And in FIG.
4
(
a
), a sectional view of the conventional matrix head is shown, and in FIG.
4
(
b
), a plane view of the conventional matrix head is shown. This structure is shown in the Japanese Patent Application Laid-Open No. HEI 10-508808. In
FIG. 4
, an ink path A
81
shows a common ink branch path and an ink path B
88
shows a common ink main path, and an ink path plate
89
is actually formed by a multi layered structure of plural plates. In
FIG. 4
, an ejector is composed of a nozzle
82
, a pressure chamber
83
, a vibration plate
87
, a piezoelectric actuator
84
, and an ink supplying path
85
.
FIG. 5
is a sectional view showing another conventional matrix head for an ink jet recording head. In
FIG. 5
, in addition to the structure shown in
FIG. 4
, an air damper plate
99
and an air damper
98
are provided. And in
FIG. 5
, a common ink branch path
91
, a nozzle
92
, a pressure chamber
93
, a piezoelectric actuator
94
, an ink supplying path
95
, a nozzle plate
96
, and a vibration plate
97
are further shown.
At the matrix head mentioned above, in which the ejectors are arrayed in a two-dimensional matrix, there is an advantage to increase the number of nozzles (ejectors). However, in order to realize a stable ejection of ink from nozzles at an actual matrix head, the common ink path must be designed suitably.
FIG. 6
is an equivalent circuit of the conventional matrix head for the ink jet recording head. As shown in
FIG. 6
, each of many ejectors
101
is connected to one of common ink branch paths
102
, and each of the common ink branch paths
102
is connected to a common ink main path
103
. Therefore, in order to prevent that pressure wave interference (crosstalk) between ejectors
101
is generated, and also to prevent that refilling time is increased, at the time when many ejectors
101
eject ink at the same time, it is necessary to obtain large acoustic capacitance at each of the common ink branch paths
102
. In this, the refilling time is the time to refill ink in nozzles after ink drops were ejected from the nozzles. In
FIG. 6
, “m” shows inertance Kg/m
4
, “r” shows acoustic resistance Ns/m
5
, “c” shows acoustic capacitance m
5
/N, and &phgr; shows pressure Pa. Further, each of suffixes shows as follows: “d” shows a driving section, “c” shows a pressure chamber, “i” shows an ink supplying path, “n” shows a nozzle, “p” shows a common ink branch path, and “p′” shows a common ink main path.
According to the study, when the acoustic capacitance of the common ink branch path is set to satisfy the condition c
p
>10 c
n
, it is possible to prevent the crosstalk from generating and the refilling time from increasing. In this, the c
p
is the acoustic capacitance of the common ink branch path per one ejector, and the c
n
is the acoustic capacitance of one nozzle. When the diameter of the nozzle is defined as d
n
m, and the surface tension of ink is defined as &sgr; N/m, the c
n
can be approximated by an equation (1). In this, in the following equation (1), the C
n
shows in =.
c
n
=
π
d
n
4
48
σ
(
1
)
At a
Do An H.
Fuji 'Xerox Co., Ltd.
Meier Stephen D.
Scully Scott Murphy & Presser
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