Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-12-18
2003-04-22
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S070000, C347S071000, C310S328000, C310S330000
Reexamination Certificate
active
06550897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inkjet recording head and an inkjet recording apparatus for carrying out the recording of characters and images with jetted droplets of ink.
2. Description of the Related Art
An inkjet recording head is used for printing characters and images onto a sheet of recording paper or the like by adhering droplets of inks onto the paper. The droplets of ink are selectively jetted from a plurality of nozzles while reciprocally moving the head in the main scanning direction as well as moving the recording paper in a sub-scanning direction orthogonal to the main scanning direction.
FIGS. 19
to
21
are diagrams showing a structure of a general inkjet recording head according to a conventional technique.
FIG. 19
is a exploded perspective diagram,
FIG. 20
is a cross-sectional diagram of a portion near one pressure chamber, and
FIG. 21
is a top plan perspective diagram of a main portion (piezoelectric actuators and pressure chambers). As shown in FIG.
19
and
FIG. 20
, the inkjet recording head is constructed of a nozzle plate
21
, a supply-path plate
22
, a pressure chamber plate
23
, and a diaphragm
4
, which are laminated in this order. Based on these plates and the diaphragm, there are formed plural ink paths extending from an ink pool
10
to nozzles
1
via supply paths
11
and pressure chambers
2
, respectively.
Specifically, the plural nozzles
1
for jetting droplets of ink are formed in one line on the nozzle plate
21
with piercing through this plate. On the supply-path plate
22
, there is formed each of the supply paths
11
that connects between a corresponding pressure chamber
2
and the ink pool
10
, and each of through-holes
12
that connects between a corresponding one of the pressure chambers
2
and a corresponding one of the nozzles
1
. Each of the supply paths
11
and through-holes
12
pierces through the supply-path plate
22
. The pressure chamber plate
23
has the single ink pool
10
and the pressure chambers
2
corresponding to the respective nozzles
1
, formed with piercing through this pressure chamber
23
. Piezoelectric actuators
5
are connected to the diaphragm
4
corresponding to the respective pressure chambers
2
by a conductive adhesive. Electrode films are provided on both sides of each piezoelectric actuator
5
, and an electrode film on the free surface side functions as an individual electrode
9
. The diaphragm
4
made of a metal material also works as an electrode common to each piezoelectric actuator
5
.
As shown in FIG.
20
and
FIG. 21
, each piezoelectric actuator
5
is shaped like a plate having a constant width, and this consists of a driving section
6
and an electrode pad section
7
. The driving section
6
is positioned in an area corresponding to a corresponding pressure chamber
2
, and the electrode pad section
7
is positioned in an area corresponding to a side wall
3
of the pressure chamber
2
.
An electrical connection (not shown) from an external driving circuit to the individual electrodes
9
is made by the electrode pad section
7
. When a potential difference is applied as a driving signal between both electrodes (the individual electrodes
9
and the diaphragm
4
) of a piezoelectric actuator
5
, the driving section
6
of the piezoelectric actuator
5
and an area of the diaphragm
4
corresponding to this driving section
6
are deformed. As a result, the ink in a corresponding pressure chamber
2
is compressed, and a droplet of ink is jetted from the corresponding nozzle
1
. When the deformation is larger, it becomes possible to increase the jetted volume of ink. After the droplets of ink has been jetted, the ink is replenished from the ink pool
10
to the corresponding pressure chamber
2
via the corresponding supply path
11
.
An electrical connection to the individual electrode
9
by the electrode pad section
7
provided in the piezoelectric actuator
5
has an advantage that no wiring is needed to provide an electrical connection to the driving section
6
. With this arrangement, it is possible to prevent a constraint in the flexure deformation and the occurrence of variation in the deformation, which would be developed by the wiring at the time of driving. Further, the electrical connection made by the electrode pad section has another advantage as follows. The electrode pad section is not destroyed even when excessive pressure is applied to the electrode pad section in the electrical connection process, as the electrode pad section is located on the side wall of the pressure chamber and has high rigidity. In other words, it is possible to prevent the inkjet apparatus from being destroyed due to flexure caused by applying pressure.
As shown in
FIGS. 19
to
21
, conventionally the plane view of the pressure chamber has a rectangular shape. This has two reasons. One is that it has been desired to make the pitch between the nozzles as narrow as possible (that is, to make the short side of a rectangular shorter) so as to achieve high-resolution printing. The other reason is that it has been desired to make the flexure area of the diaphragm as large as possible (that is, to increase the long side thereof as much as possible) so as to secure the volume of an ink droplet required for the high-resolution printing. The piezoelectric actuator is shaped like a rectangular shape having a constant width to match the pressure chamber that has a rectangular shape.
As explained above, conventionally, a high-resolution inkjet recording head has been realized in a simple structure, by using a pressure chamber having a rectangular plan shape.
In recent years, a high speed has also been required for the inkjet recording head. In order to realize high-speed inkjet recording, it is effective to increase the number of nozzles. This is because when the number of nozzles is larger, it becomes possible to increase the number of ink droplets (dots of an image) that can be formed on the recording paper per unit time.
However, when only the number of nozzles is increased, the total size of the head becomes larger, and this brings about a problem of increase in the manufacturing cost of the head. Therefore, in the case of increasing the number of nozzles, it is necessary to take into account how to dispose as large number of nozzles as possible within a constant head area. In other words, how to increase the density of nozzles becomes a most important issue.
The pressure chamber occupies most of the area of each nozzle. Therefore, in order to realize the improvement in the nozzle density, it becomes essential to reduce the plane area of each pressure chamber. When the area of the plane of the pressure chamber is reduced, the flexure deformation of the driving section is lowered. As a result, the volume of a jetted ink droplet becomes smaller, resulting in reduced density of printed characters and images.
In other words, in order to realize the high-speed inkjet printing it is essential to increase the flexure deformation of the driving section even if the plane area of the pressure chamber is reduced, that is, to increase the driving efficiency per unit area.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an inkjet recording head allowing a high driving efficiency per unit area.
It is another object of the present invention to provide an inkjet recording head capable of preventing a variation in the driving efficiency even when a position of a piezoelectric actuator has deviated.
It is still another object of the present invention to provide an inkjet recording head that has high precision and high reliability, which can be manufactured at low cost in a simplified manufacturing process.
In order to solve the above problems, the inventors have carried out analysis and research focusing attention on the plane shape of a pressure chamber. On the condition that pressure chambers having rectangular plane shapes of the same plane areas but having different aspect ratios (the ratio of height
Nakamura Hirofumi
Okuda Masakazu
Otsuka Yasuhiro
Fuji 'Xerox Co., Ltd.
Nguyen Judy
Scully Scott Murphy & Presser
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