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The present invention relates generally to ink jet printers including printheads
and, more particularly, to such a printer including a method of effectively removing
bubbles from such printhead during periodic maintenance of the printhead.
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An ink jet printer of the so-called "drop-on-demand" type has at least one
printhead from which droplets of ink are directed towards a recording medium. Within
the printhead, the ink may be contained in a plurality of channels and energy pulses are
used to cause the droplets of ink to be expelled, as required, from orifices at the ends
of the channels.
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In a thermal ink jet printer, the energy pulses are usually produced by resistors,
each located in a respective one of the channels, which are individually addressable by
current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any
one of the channels, ink bulges from the channel orifice or nozzle until the current pulse
has ceased and the bubble begins to collapse. At that stage, the ink within the channel
retracts and separates from the bulging ink which forms a droplet moving in a direction
away from the channel and towards a recording medium. The channel is then refilled
by capillary action, drawing ink from a supply container.
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One particular example of a type of thermal ink jet printer is described in U.S.
Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads,
each with its own ink supply cartridge, mounted on a reciprocating carriage. The
channel orifices or nozzles in each printhead are aligned perpendicular to the line of
movement of the carriage and a swath of information is printed on the stationary
recording medium as the carriage is moved in one direction. The recording medium is
then stepped, perpendicular to the line of carriage movement, by a distance equal to the
width of the printed swath and the carriage is then moved in the reverse direction to
print another swath of information.
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It has been recognized that there is a need to maintain the ink ejecting orifices
of an ink jet printer, for example, by periodically cleaning the orifices when the printer
is in use, and/or by capping the printhead when the printer is out of use or is idle for
extended periods. The capping of the printhead is intended to prevent the ink in the
printhead from drying out. There is also a need to prime a printhead before use, to
ensure that the printhead channels are completely filled with ink and contain no
contaminants or bubbles. Maintenance and/or priming stations for the printheads of
various types of ink jet printers are described in, for example, U.S. Patent 4,863,717 and
the removal of gas from the ink reservoir of a printhead during printing is described in
U.S. Patent. 4,679,059. All of these patents are hereby incorporated by reference.
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Bubbles in different locations of the ink path that feeds the thermal ink jet
printhead can range from harmless to very problematic. Removing these bubbles can
be very difficult and requires the removal of large amounts of ink in order to "pull" the
air bubble out. The problem is that bubbles are difficult to break up and pull through
the small nozzles of the printhead.
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Air bubbles in the print head, especially those near the nozzles can and do
restrict fluid flow to the nozzles. This is especially apparent when printing high area
coverage regions at high frequency, and at elevated temperatures. The air bubble will
cause 2-8 adjacent nozzles or jets to intermittently misfire, causing highly noticeable
horizontal white streaks across the image. It has been found that the size of the air
bubble relative to the printhead or die reservoir volume directly influences the nature
of the print quality defect. Small bubbles will not cause any problems. Medium
bubbles may cause 1 or 2 jets to misfire. Large bubbles may cause a large bank of jets
to poorly fire.
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Conventional methods for removing air bubbles involve applying a vacuum
force to the print head for extracting ink and air from the printhead through the
apertures or openings of the nozzles. However, as the resolution of inkjet devices
increases, the apertures of the nozzles are becoming significantly smaller and smaller,
thereby limiting the ability of ink to flow during such a vacuum operation. For
example, it has been found that when conventionally applying a vacuum pressure of
about 300 mmHg to the front face or nozzle face of a printhead, large problem bubbles
are difficult to remove.
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In accordance with the present invention, there is provided a simultaneous push-pull
method of removing bubbles from the nozzles of a powerable ink jet printhead.
The method includes the steps of providing a printhead capping member including side
walls, a bottom wall, a vacuuming path through said bottom wall, and a capping recess
defined by the side walls and the bottom wall; applying power to the powerable ink jet
printhead for forcibly pushing and ejecting drops of liquid ink in an ink ejecting
direction through nozzles in the nozzle face and into the capping recess; and
simultaneously applying a vacuum force through the capping recess to the nozzle face
for additively pulling and moving ink in the ink channels through the nozzles and in the
ink ejecting direction, thereby effectively priming the nozzles in the nozzle face by
removing ink and undesirable bubbles from the ink channels.
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Embodiments of the present invention will now be described, by way of
example, with reference to the accompanying drawings in which:
- FIG. 1 is a schematic elevational view of a liquid ink printer including a
controller for application of the method of the present invention; and
- FIG. 2 is a schematic illustration of a capping member in sealing engagement
with the nozzle face of an ink jet printhead for application of the method of the present
invention.
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While the present invention will be described in connection with a preferred
embodiments thereof, it will be understood that it is not intended to limit the invention
to those embodiments. On the contrary, it is intended to cover all alternatives,
modifications, and equivalents as may be included within the spirit and scope of the
invention as defined by the appended claims.
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For a general understanding of the features of the present invention, reference
is made to the drawings. In the drawings, like reference numerals have been used
throughout to identify identical elements.
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Referring now to FIG. 1, there is shown a schematic elevational view of a liquid
ink printer 10, for instance, an ink jet printer. As shown, the liquid ink or ink jet printer
10 incorporates an input tray 12 containing sheets of a sheet of paper 14 to be printed
upon by the printer 10. Single sheets of the sheet of paper 14 are removed from the
input tray 12 by a pickup device 16 and fed by feed rollers 18 to a transport mechanism
20. The transport mechanism 20 moves the sheet by a feed belt or belts 22 driven by
one of support rollers 24 beneath a liquid ink printhead assembly 26. The printhead
assembly 26 as is well known, includes an ink supply (not labeled) attached for example
to the printhead support or coupled to associated printheads through appropriate supply
tubing.
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The printhead assembly 26 includes printheads 28 which, for example, can be
reciprocating printheads, or partial, or page width array, printheads supported in a
printing position by a printhead support (not shown) in a confronting relation with the
belt 22. During printing, the printheads 28 image-wise deposit droplets of liquid ink
onto the sheet of paper 14 as the is carried by the belt 22 past and beneath the plurality
of printheads 28. As is well known, each of the printheads 28 includes an array of print
nozzles, for instance, staggered or linear arrays, having a length sufficient to image-wise
deposit droplets of ink as above, within a printing zone that lies below the printheads
and is crossed the sheet of paper 14. As the sheet of paper 14 is moved through the
printing zone, the printheads 28 print or record a liquid ink image on the sheet of paper
14.
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After printing or recording of the liquid ink image as above within the printing
zone, the sheet of paper 14 is then carried by the belt 22 through a dryer assembly 32
for drying the liquid ink image thereon. From the dryer assembly 32, the sheet of paper
14, with a dried ink image thereon is moved to an output tray 33.
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As shown, a controller 34 controls the operation of various aspects of the printer
10, including the transport mechanism 20, the dryer assembly 32 and the maintenance
operation including a simultaneous push-pull method of air bubble removal in
accordance with the present invention. The transport mechanism 20 for example
includes the pickup device 16, the feed roller 18, the belt 22 and the drive rollers 24.
In addition, the controller 34 controls the movement of the printhead assembly 26,
printing by the printheads 28 as would be understood by one skilled in the art.
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The controller 34 is preferably a self-contained, dedicated mini-computer having
a central processor unit (CPU), electronic storage, and a display or user interface (UI).
With the help of sensors and connections (not shown), the controller 34 reads, captures,
prepares and manages the flow of data for the image being printed by the printheads 28.
In addition, the controller 34 is the main multi-tasking processor for operating and
controlling all of the other machine subsystems and printing operations.
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At the completion of a printing job or when otherwise necessary, such as during
a power failure, the printhead assembly 26, is moved away from the belt 22 in the
directions of an arrow 36. A vacuum assembly 60 including a molded capping member
52 is moved beneath the printhead assembly 26, in the directions of the arrow 40 for
capping the printheads 28 of the printhead assembly 26. Once the capping member 52
is positioned directly beneath the printhead assembly 26, the printhead assembly 26 is
moved towards the belt 22 and into sealing engagement with a raised membrane 50 on
the molded capping member 52 for effective priming by application of the simultaneous
push-pull method of the present invention (to be described in detail below).
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When the printhead assembly 26, has been capped, and fully primed as above,
and is again needed for another printing job, it is moved away from the belt 22 and the
vacuum assembly 60 is then moved away from the printhead assembly 26 such that the
printhead assembly 26 can be repositioned appropriately with respect to the belt 22 for
printing on the recording sheets 14.
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Referring to FIGS. 1-2 and in particular to FIG. 2, the printhead assembly 26
includes for example, a reciprocating printhead 28, that has been moved into a capping
position against the capping member 52 of the vacuum assembly 60. As shown, the
raised membrane 50, preferably a low (20-30 shore "A") durometer silicone rubber
joined to the molded capping member 52 seals against a nozzle face 29 of each
printhead 28. As further shown, the capping member 52 includes a substrate 54 and a
capping chamber or recess 56 that terminates at a base 62 having an orifice into a
vacuuming path 58 therethrough.
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As further shown, the molded capping member 52 includes the bottom wall 62,
and side walls 64, 66 defining the capping chamber or recess 56, as well as, the
vacuuming path 58 from the vacuum device 70 into the capping chamber or recess 56.
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The simultaneous push-pull method of removing bubbles from the nozzles
includes the steps of providing the printhead capping member 52, applying power
through the power and controller connector 74 to the powerable ink jet printhead for
forcibly pushing and ejecting drops of liquid ink, in an ink ejecting direction 76,
through nozzles in the nozzle face 29 and into the capping recess 56. The method then
includes the step of simultaneously applying a vacuum force from the vacuum device
70 through the capping recess 56 to the nozzle face 29 for additively pulling and
moving ink in the ink channels 80 through the nozzles and in a vacuum pull direction
78 that is the same as the ink ejecting direction 76. This thereby effectively primes the
nozzles in the nozzle face 29 by removing ink and undesirable bubbles from the ink
channels 80.
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The step of applying power to the powerable printhead preferably comprises
sequentially firing the nozzles in the nozzle face one at a time or a group at a time. The
valve 72 to the vacuuming path 58 is maintained in an open position while power is
being applied to the printhead to fire the nozzles, and a vacuum force is being
simultaneously applied in a push-pull manner to additively remove bubbles from the
printhead.
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As shown, the vacuum applying device or pump 70 is connected to the
vacuuming path 58, through the valve 72, for applying a vacuum suction force to
nozzles in the nozzle face 29. Power, preferably full power is applied through a power
and controller connector 74. The power and controller connector 74 is connected to the
printhead 28 and to its controller and drivers 34, for controllably and forcibly firing and
ejecting drops of ink from the ink channels 80 through nozzles in the nozzle face 29.
The full power ejection of ink drops through the nozzles when simultaneously
combined with the vacuum suction force, effectively function to push-pull and suck out
ink and bubbles from within the channels, thereby effectively priming the nozzles in the
nozzle face 29.
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The simultaneous push-pull method of removing bubbles from the powerable
(powerable meaning simply that the printhead can be powered up to fire or eject drops
of ink) printhead 28 thus includes providing a printhead capping member 52 including
a bottom wall 62 and side walls 64, 66 defining a capping recess 56 defined by the
bottom wall, the side walls, and the nozzle face 29. The method also includes applying
power to the powerable ink jet printhead 28 for forcibly pushing and ejecting drops of
liquid ink in an ink ejecting direction 76 through nozzles in the nozzle face 29, and into
the capping recess 56. Importantly, the method then includes simultaneously applying
a vacuum force from the device 70 through the capping recess 56 to the nozzle face 29
for additively pulling and moving ink in the ink channels 80 through the nozzles and
in the ink ejecting direction 76. This thereby effectively primes the nozzles in the
nozzle face 29 by removing ink and undesirable bubbles from the ink channels.
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It is recalled that ordinarily, removing bubbles from the ink path of a printhead
can be very difficult and requires the removal of large amounts of ink in order to "pull"
the bubble out. The problem is that bubbles are difficult to break up and pull through
the small nozzles of the printhead. The simultaneous push-pull method of the present
invention effectively removes bubbles from even deep within ink channels connected
to the nozzles in the nozzle face. The result is a bubble free ink path.
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To recap, the present invention utilizes printing or full power ink drop ejection
in conjunction with vacuum force pulling or priming to effectively remove offending
air bubbles from the printhead. The printing or full power drop ejection operates to
distort the air bubbles sufficiently such that the simultaneous application of vacuum can
easily remove even large bubbles.
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As can be seen, there has been provided a simultaneous push-pull method of
removing bubbles from the nozzles of a powerable ink jet printhead. The method
includes the steps of providing a printhead capping member including side walls, a
bottom wall, a vacuuming path through said bottom wall, and a capping recess defined
by the side walls and the bottom wall; applying power to the powerable ink jet
printhead for forcibly pushing and ejecting drops of liquid ink in an ink ejecting
direction through nozzles in the nozzle face and into the capping recess; and
simultaneously applying a vacuum force through the capping recess to the nozzle face
for additively pulling and moving ink in the ink channels through the nozzles and in the
ink ejecting direction, thereby effectively priming the nozzles in the nozzle face by
removing ink and undesirable bubbles from the ink channels.
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While the embodiment disclosed herein is preferred, it will be appreciated from
this teaching that various alternative, modifications, variations or improvements therein
may be made by those skilled in the art, which are intended to be encompassed by the
following claims.
