Ink jet printerhead with a plurality of nozzles and two...

Incremental printing of symbolic information – Ink jet – Ejector mechanism

Reexamination Certificate

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C347S048000

Reexamination Certificate

active

06511157

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ink jet print head. More specifically, it relates to an ink jet print head in which ink droplets are jetted out through orifices by increasing inner pressure of an ink chamber and fixed on a recording medium such as paper or transparent film, enabling very fine printing with high resolution.
2. Description of the Background Art
In a conventional ink jet printer disclosed in Japanese Patent Publication No. 53-12138/1978 (corresponding to U.S. Pat. No. 3,946,398), a piezo vibrator is provided facing an ink chamber, the piezo vibrator is deformed by applying an electric signal thereto so as to reduce volume of the ink chamber and increase inner pressure of the ink chamber, whereby an ink droplet is ejected from an orifice. In this method, it is necessary to provide piezo vibrators same in number as the corresponding ink ejecting channels (number of orifices). Therefore, it is difficult to reduce the size and highly dense arrangement of orifices is limited.
Ink jet print heads of other types include ones in which wall surface of an ink chamber is deformed inward to cause pressure to eject ink droplets by electrostatic force or magnetic force.
However, these methods suffer from problems that the generated pressure is too small or that the head becomes too large when necessary high pressure is to be generated.
FIG. 15
shows a schematic structure of a conventional serial print type ink jet printer. A pair of guiding rods
7
and
8
are provided parallel to a platen
6
around which a sheet of paper, not shown, is wound and fed. Along guiding rods
7
and
8
, a carriage
4
is reciprocally attached. A head body
1
is mounted on carriage
4
, and an ink tank
2
is mounted on body
1
. Head body
1
ejects and fixes ink droplets onto the sheet of paper fed by platen
6
, whereby printing is-done. Reference numeral
5
denotes a maintenance station.
FIG. 16
is a perspective view showing schematically a conventional serial print type ink jet print head. There is a nozzle
3
on the front end surface of head body
1
on which ink tank
2
is mounted.
FIG. 17
is a partially exploded perspective view showing, in enlargement, an internal structure of nozzle
3
, and
FIG. 18
is a cross section thereof. In nozzle
3
, a number of mutually parallel partitions
15
are formed continuously and integrally from an inner bottom surface, a filter
12
is provided at a rear portion between adjacent ones of partitions
15
,
15
and front end side of each partition
15
is formed to have a triangular plate shape
15
a
and faces a front surface of nozzle
3
. An upper surface of the group of partitions
15
is covered and tightly sealed by a pressure chamber ceiling
16
which is integral with nozzle
3
, and by adjacent partitions
15
,
15
, filter
12
and pressure chamber ceiling
16
, a number of ink pressure chambers
11
are formed parallel to each other. Because of the triangular plate
15
a,
the front end side of each ink pressure chamber
11
is tapered, and opened as an orifice
10
at the front surface of nozzle
3
. Behind the group of partitions
15
and the group of filters
12
, there is formed a common ink feed path
13
surrounded by the inner bottom surface of nozzle
3
and pressure chamber ceiling
16
. The common ink feed path
13
is communicated with ink tank
2
shown in FIG.
16
and receives ink supply from ink tank
2
. Further, this ink feed path is communicated with each ink pressure chamber
11
with each filter
12
interposed, and supplies ink to each ink pressure chamber
11
. A piezo vibrator
14
is bonded on an upper surface of pressure chamber ceiling
16
at a position corresponding to each ink pressure chamber
11
. Between each piezo vibrator
14
and pressure chamber ceiling
16
which is at the ground potential, a series circuit including a power supply
17
and a switch
18
is connected individually.
The operation will be described in the following. As shown in
FIG. 18
, ink pressure chamber
11
is filled with ink
19
. When switch
18
is off as shown in
FIG. 18A
, voltage is not supplied from power supply
17
to piezo vibrator
14
. Accordingly, piezo vibrator
14
is not driven and hence it is kept flat. Therefore, inner pressure of ink pressure chamber
11
does not change, and equilibrium between each of ambient pressure, surface tension and ink pressure is kept at orifice
10
. Accordingly, ink droplet is not ejected from orifice
10
.
When switch
18
is turned on as shown in
FIG. 18B
, a voltage is supplied to piezo vibrator
14
from power supply
17
, piezo vibrator
14
is deformed curved with the central portion projecting downward, pressure chamber ceiling
16
deforms curved downward with respect to ink pressure chamber
11
at a position corresponding to the driven piezo vibrator
14
, a volume of the corresponding ink pressure chamber
11
reduces and inner pressure of ink pressure chamber
11
increases. As a result, ink
19
is forced out from orifice
10
as an ink droplet
19
a,
which jets toward a recording medium, not shown.
However, in the ink jet print head in accordance with the prior art shown in the figures, means for supplying ink uniformly to respective ink pressure chambers
11
from common ink feed path
13
is not provided. Therefore, the amount of ink
19
in respective ink pressure chambers
11
and hence inner pressure of these chambers differ from each other, and as a result, ink droplets
19
a
ejected from orifices
10
may have different sizes.
SUMMARY OF THE INVENTION
The present invention was made in view of the foregoing and its object is to provide an ink jet print head by which ink droplets ejected from all orifices are adapted to have approximately uniform size. A further object is to enable simple switching between ink droplet ejecting state and non-ejecting state. A still further object is to enable simple adjustment of the size of the ejected ink droplets.
According to an aspect of the present invention, the above described objects can be attained by an ink jet print head including a plurality of ink chambers partitioned from each other, each having, at a front end portion, an orifice; a common pressure chamber connected to the plurality of ink chambers through a first filter; a common ink feed path connected to the common pressure chamber through a second filter; a pressure generating member provided on a wall surface of the common pressure chamber; and a movable wall provided in each of the plurality of ink chambers and deformable in a direction increasing volume of the ink chamber; in which a pressure wave generated by the drive of the pressure generating member in the common pressure chamber is transmitted to each of the plurality of ink chambers through the first filter, which pressure wave is absorbed when the movable wall is deformed, and it causes an ink droplet to be ejected from the orifice when the movable wall is not deformed.
Preferably, the pressure generating member of the ink jet print head is driven periodically, and whether the ink droplet is to be ejected or not is switched by changing timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member.
More preferably, the ink jet print head adjusts the size of the ejected ink droplets by changing the timing of deformation of the movable wall in the direction increasing the volume of the ink chamber with respect to the timing of driving the pressure generating member when the ink droplets are to be ejected.
More preferably, the ink jet print head further includes a highly resilient member for receiving deformation of the movable wall.
In accordance with the present invention, the common pressure chamber is separated from the common ink feed path by the second filter, and pressure wave generated by driving the pressure generating member in the common pressure chamber is supplied to each of the ink chambers through the first filter. Therefor

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