Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-04-13
2001-02-27
Yockey, David F. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06193354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printer or recorder for forming an image by ejecting ink from its ink jet head. Specifically, the invention relates to an ink jet printer which makes it possible to suck and remove bad or defective ink, foreign substances, air bubbles, and/or the like from the ink jet head with the head nozzle capped.
2. Description of Related Art
A conventional ink jet printer of this type includes an ink jet head, which has a nozzle for ejecting ink and ink chambers storing ink behind the nozzle. By generating pressure vibration in one or more the ink chambers, it is possible to eject ink from the nozzle to form an image on a recording medium.
The printer also includes a cap for covering the outer side of the nozzle airtightly. The printer further includes a suction device, which may be a suction pump, for developing negative pressure in the cap in airtight contact with the nozzle to suck ink from the nozzle. The negative pressure developed in the cap covering the nozzle can suck and remove bad ink, foreign substances, air bubbles and/or the like from the nozzle. It is therefore possible to prevent defective ejection of ink from the nozzle so that a clear image can be formed.
On the other hand, negative pressure is applied always to the ink chambers and the nozzle. This negative pressure prevents ink from leaking from the nozzle, and allows ink to be ejected only when pressure vibration develops in one or more of the chambers. This prevents recording media from staining or spotting. The negative pressure may, however, worsen the suction and removal with the pump for the reason stated below.
FIGS. 5A-5D
of the accompanying drawings show the suction and removal process as part of the maintenance of a conventional ink jet printer. The printer includes an ink jet head
73
, which includes a nozzle plate
75
having a nozzle
75
a
for ejecting ink. The head
73
has ink chambers
77
a
storing ink behind the nozzle plate
75
. The chambers
77
a
are connected to the nozzle
75
a.
The head
73
also includes actuators
77
including piezoelectric elements. Each of the actuators
77
is associated with one of the chambers
77
a.
The head
73
further includes a manifold
79
connected to the chambers
77
a.
The manifold
79
is also connected through a tube (not shown) or the like to an ink tank (not shown) for supplying the chambers
77
a
with ink. When one or more of the actuators
77
are energized to generate pressure vibrations in the associated chambers
77
a,
ink is ejected from the nozzle
75
a.
This printer also includes a cap
83
for compressively contacting the nozzle surface
75
b
of the nozzle plate
75
to airtightly cover the outer side of the nozzle
75
a.
The cap
83
has a suction port
83
a
connected to a suction pump (not shown). When the pump is driven, negative pressure develops in the cap
83
.
As shown in
FIG. 5A
, air bubbles
99
may be produced in the ink chambers
77
a.
As shown in
FIG. 5B
, it is possible to suck and remove the bubbles
99
together with ink by capping the nozzle
75
a
with the cap
83
and driving the pump.
On the other hand, negative pressure is applied always to the ink chambers
77
a
and nozzle
75
a.
Immediately after the pump stops, as shown in
FIG. 5C
, this negative pressure may draw back into the ink jet head
73
some of the bubbles
99
sucked already into the cap
83
. Even after the suction ends and the cap
83
separates from the head
73
, as shown in
FIG. 5D
, air bubbles
99
remain in the head, and may cause defective ejection of ink from the nozzle
75
a.
Not only the bubbles
99
but also foreign substances and/or solidified ink may be drawn back into the head
73
, and cause defective ejection of ink.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an ink jet recorder in which air bubbles etc. can be removed securely from the ink jet head with the nozzle capped airtightly, to prevent the head from ejecting ink defectively.
In accordance with the invention, an ink jet recorder is provided, which includes an ink jet head having a nozzle for ejecting ink. The head also has ink passages formed in it and communicating with the nozzle. The nozzle can be capped with a suction cap. The recorder also includes a suction pump for sucking ink from the nozzle through the cap to purge the nozzle. The recorder further includes an ink supply for supplying the head with ink. A pressure control unit is provided or interposed between the supply and the head to control the pressure applied to the ink in the nozzle.
The pressure control unit applies positive pressure to the ink in the nozzle at least just before purging finishes, that is to say, before the suction cap is separated from the ink jet head. This prevents the air bubbles, the foreign substances and/or the like sucked already into the cap by the suction pump from flowing back into the head. Consequently, the ink jet recorder can prevent defective ejection of ink, particularly just after the purging.
When the suction cap is separated from the ink jet head during the purging, the suction pump may be either stopped or kept driven to suck the ink remaining in the cap (sucking ink and air to keep the head clean).
While the nozzle is not capped, the pressure control unit may apply negative pressure to the ink in the nozzle to maintain the menisci of ink in the nozzle.
The pressure control unit may include an ink tank in liquid communication with the ink passages in the ink jet head. The unit may also include a tank height adjuster for adjusting the height of the tank relatively to the front end of the nozzle. By using the tank and the height adjuster, it is possible to simplify the structure of the control unit and make the pressure control easy. The height adjuster can make the ink surface in the tank higher than that in the nozzle to produce a head difference for applying positive pressure to the ink in the nozzle so that the ink can be discharged from the nozzle. The adjuster can also make the ink surface in the tank lower than that in the nozzle to apply negative pressure to the ink in the nozzle so that the menisci of ink can be maintained well in the nozzle.
The pressure control unit may instead be a pump provided between the ink supply and the ink jet head.
The ink jet recorder may also include a controller for controlling the driving of the tank height adjuster and the suction pump. The controller may be a microcomputer for batch control of the operation of the recorder.
The ink jet recorder may further include a detector for detecting the ink level in the ink tank. On the basis of the result of the detection by the detector, the controller may control the tank height adjuster in such a manner that the ink surface in the ink tank is positioned at a predetermined level relative to the front end of the nozzle.
The ink supply may be an ink cartridge, which can be replaced by the user. The cartridge may contain ink and be sealed. The cartridge may be larger in volume than the ink tank. The ink tank may be open so that the ink in it may be exposed to the atmosphere. In this case, it is preferable that the tank be as small as possible in volume to prevent the ink from oxidizing or altering otherwise in quality. If the tank is small, however, the ink jet recorder can record only a small number of images continuously. By making the cartridge (main ink tank) larger than the tank, it is possible to replenish ink all times from the cartridge and therefore perform continuous recording even if the tank is small. Because the cartridge is closed, the ink in it is inhibited from altering in quality.
The side walls of the ink passages may be made of piezoelectric material. The invention can be also applied to bubble jet type ink jet recorders.
REFERENCES:
patent: 4359744 (1982-11-01), Salmre
patent: 4367479 (1983-01-01), Bower
patent: 4558326 (1985-12-01), Kimura
patent: 4590494 (1986-05-01), Ichihashi et al.
patent: 4947191 (1990-08-01), Nozawa et al.
patent: 52489
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Stewart Jr. Charles W.
Yockey David F.
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