Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-02-12
2003-02-11
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S085000, C347S089000, C347S084000, C347S029000, C347S030000, C347S086000, C347S092000
Reexamination Certificate
active
06517189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing device including a print head formed with a plurality of nozzles for selectively ejecting ink droplets onto a recording medium based on print data so as to form images on the recording medium, and also to an ink supply method for supplying the print head with ink.
2. Related Art
There has been provided a conventional ink jet print device that performs an image forming operation for forming images on a recording medium. Main components of such a conventional ink jet print device are shown in FIG.
8
. As shown in
FIG. 8
, the ink jet print device includes a print head
301
formed with several hundreds of nozzles
302
(only one is shown in FIG.
8
), a common ink chamber
307
, a supply path
308
, and a sub ink tank
309
. A motor (not shown) is provided for reciprocally moving the print head
301
in a direction that is perpendicular to the sheet surface of
FIG. 8. A
recording medium
313
is placed in confrontation with the nozzles
302
.
Each nozzle
302
includes an orifice
303
, an ink chamber
305
, and a restrictor
306
, all are in fluid communication with one another. The restrictor
306
regulates the amount of ink that is supplied from the common ink chamber
307
into the ink chamber
305
. A recording medium
313
is placed in confrontation with the orifices
314
. A piezoelectric element
304
is mounted on a partition wall of the ink chamber
305
. The piezoelectric element
304
is an energy generating member that is deformed and undeforms based on driving signals.
The sub ink tank
309
is connected to a pressure pump
311
via a deformable duct
312
, and further to a main ink tank
310
.
With this configuration, the image forming operation is performed by selectively ejecting an ink droplet
314
through the orifices onto the recording medium
313
while reciprocally moving the print head
301
. The ink droplet
314
is ejected through the orifice
303
in the following manner.
That is, first, the piezoelectric element
304
is deformed based on a driving signal, so that the volume of the ink channel
305
increases. As a result, internal pressure of the ink channel
305
decreases, and ink in the common ink chamber
307
is introduced into the ink chamber
305
through the ristrisctor
306
. Next, the deformation of the piezoelectric element
304
is released. The volume of the ink chamber
305
drops to its initial amount, so the internal pressure of the ink chamber
305
increases. As a result, an ink droplet
314
is ejected through the orifice
303
. Each time an ink droplet
314
is ejected, ink in the sub ink tank
306
is introduced into the common ink chamber
307
through the supply path
308
to supplement the consumed ink.
In the above-described print head, ink level in the ink tank
309
is set lower than the position of the orifice
303
by a level difference Ho in a vertical direction. In this way, ink in the ink chamber
305
is prevented from leaking through the orifice
303
. Also, a sensor
315
is provided to the sub ink tank
309
for detecting the remaining amount of ink in the sub ink tank
309
. As the ink is consumed, the ink level is lowered and the level difference Ho increases. When the sensor
315
detects that the level difference Ho becomes greater than a predetermined height, then the pressure pump
311
supplies ink from the main ink tank
310
into the sub ink tank
309
. That is, the pressure pump
311
sucks up the ink from the main ink tank
310
, and then applies pressure to the sucked-ink. As a result, a predetermined amount of ink is supplied into the sub ink tank
309
via the duct
312
.
Also, the ink in the sub ink tank
309
is exposed to the ambient air through openings
399
. Because the sub ink tank
309
is not sealed off from the outside, pressure applied to the nozzle
302
will not greatly fluctuate even when the print head
301
is reciprocally moved. Also, because the main ink tank
310
, which has relatively a large volume, is not mounted on the print head
301
, the motor for driving the print head
301
can be smaller.
However, in the above-described ink jet print device, when the piezoelectric elements increase and decrease the internal pressure of the ink chamber
305
for ejecting the ink droplet
314
, air bubbles are generated in the ink in the nozzles
302
. Such air bubbles prevent proper ink ejection, so degrade image quality.
Because the print head
301
is formed with a large number of nozzles
302
, image forming can be performed at high speed. However, when the print head
301
is formed with a larger number of nozzles
302
, air bubbles are more likely to be generated.
Also, when the print head
301
is reciprocally moved, the velocity of the print head
301
is repeatedly accelerated and decelerated. This acceleration and deceleration changes pressure applied to the ink in the print head
301
, especially when the moving direction of the print head
301
is reversed. As a result, air bubbles are easily generated.
Moreover, air bubbles are also generated in the main ink tank
310
and the duct
312
. When these air bubbles are supplied to the print head
301
along with ink, the air bubbles also prevent proper ink ejection.
In order to overcome the above-described problems, the ink jet print device executes a purging operation for forcefully removing such air bubbles. During the purging operation, first, the print head
301
is moved to a predetermined purging position that is outside of a recording region. A purging mechanism
320
is provided in the purging position, and includes a cap
321
, a suction pump
322
, and a purge tank
325
. The cap
321
includes a seal member
323
. Then, the cap
321
is lifted up and seals the print head
301
. In this condition, the suction pump
322
sucks up and removes air bubbles along with ink from the nozzles
302
.
However, it is difficult to remove air bubbles from the common ink chamber
307
, a connecting portion between the ristrictor
306
and the common ink chamber
307
, a connection portion between the common ink chamber
307
and the supply path
308
, and the supply path
308
even in the above-described purging operation. In order to remove these air bubbles, it is conceivable to use a suction pump with greater power. It is also conceivable to drive the suction pump
322
for a increased time duration. However such operations increase the size of the ink jet print device and also decrease the printing speed. Also, the amount of ink consumed during the purging operation increases, which is uneconomical.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above problems, and to provide an ink supply method for reliably removing air bubbles remaining in print head without wasting ink, and also to provide an ink jet print device that performs the ink supply method.
In order to achieve the above and other objectives, there is provided an ink jet print device including a head, a sub ink tank, a main ink tank, a first switching valve, and a second switching valve. The head is formed with a plurality of nozzles and a common ink chamber in fluid communication with each of the nozzles. Each nozzle is formed with an orifice through which an ink droplet is ejected. The common ink chamber has a first end and a second end. The sub ink tank stores ink and supplies the ink to the nozzles. The main ink tank stores ink and supplies the ink to the sub ink tank. The first switching valve is provided to the first end of the common ink chamber, and is selectively switched to an opening condition where the common ink chamber is in fluid connection with the sub ink tank and a closed condition where the common ink chamber is in fluid disconnection from the sub ink tank. The second switching valve is provided to the second end of the common ink chamber. The second switching valve is selectively switched to a first condition where the common ink chamber is in fluid connection with the sub ink tank and fluid disconnectio
Kagami Takashi
Ogawa Toshitaka
Tobita Satoru
Barlow John
Hitachi Koki Co,. Ltd.
Tran Ly T
Whitham Curtis & Christofferson, P.C.
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