Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to apparatus for applying
fluid droplets to a writing surface, and more particularly to
improvement to a mechanism for writing on paper with an ejected
colored liquid.
The speed of recording data on paper in, for example,
a data processing system is limited for one thing by the capa-
bility of the writing mechanism, which in many cases is substan-
tially less than that of the data processing system.
Because of the high speed capability of the ink ejec-
tion type writing mechanism, many proposals have been made inwhich the liquid is discharged onto the paper by application of
electrical pulses, the liquid being ejected in a series of pulsed
droplets. The speed of the writing mechanism is in turn largely
determined by the capability of the liquid responding to the
rapidly occurring electrical pulses. However, the voltage of the
electrical pulses must be high enough to overcome the resistance
offerred by the liquid due to its surface tension and viscosity.
The range of voltage necessary for driving the writing unit
(dynamic range of a writing mechanism) is therefore determined by
the resistance of the liquid to the applied pulses. Prior art
writing mechanisms have a narrow dynamic range. This resulted in
liquid droplets of comparatively
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large size and therefore satisfactory gradation of image cannot
be obtained on the writing surface.
Because of the high operating speed of the writing
mechanism, the liquid droplets are ejected onto a sheet of paper
which is wrapped around a roller revolving at a high speed.
Since a series of droplets is formed upon ejection in response
to a single electrical pulse, they tend to land on different
localities of the writing surface, thus causing a blur on the
image. Furthermore, the high speed revolution of the roller
creates a whirl of wind at the surface which would cause disper-
sion of the ejected droplets.
Therefore, an object ofthe present invention is to
provide an improved liquid applying apparatus which assures a
wider dynamic range than is available by the prior art apparatus
to thereby decrease the size of droplets to be deposited on the
writing surface.
Another object is to provide an improved liquid apply-
ing apparatus in which liquid droplets ejected in response to a
single pulse are accelerated by a stream of air so that they land
on the writing surface at substantially the same instant of time.
A specific object of the invention is to provide a
liquid applying apparatus having a pneumatic chamber connected to
a source of pressurized air and an improved
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arrangement for connecting a liquid supply container with
the source of pressurized air.
~ ccording to the present invention there is provided
an apparatus for applying liquid droplets to a surface
comprising, a housing including a first liquid chamber for
containing a liquid to be applied to a surface and having an
associated piezoelectric device for generating short-duration
rises of the pressure of liquid in the first liquid chamber,
a second liquid chamber communicating with the first liquid
chamber through a connecting channel and having a first dis-
charge channel for droplets of said liquid to leave the
apparatus, the first discharge channel being in alignment
with the connecting channel and in close proximity thereto
so that a short-duration pressure rise in the first liquid
chamber causes a series of liquid droplets to be expelled
through the first discharge channel, the second liquid chamber
having a first intake channel connected to a liquid supply
source, a pneumatic chamber substantially divided into an
inner, disc-like portion formed with a second discharge channel
and an outer, annular portion formed with a second intake
channel connected to a source of pressurized air, the second
discharge channel being in alignment with the first discharge
channel and in close proximity thereto, and means for providing
communication for the liquid supply source with the air supply
source to increase the static pressure in the liquid in the
liquid supply source to such a degree that the static pressure
in the first discharge channel is substantially equal to the
static pressure in the space between the first and second
discharge channels.
The cross-sectional area of the air discharge channels
is preferably selected in relation to the cross-sectional
area of the liauid
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di~charge channel in order that a laminar air flow iY
formed at the exit thereofO
The ~ource of pre~urized air i9 in communication
with the liquid supply container to increa~e the pres-
sure in the liquid in relation to the air pre~sure.
Thi~ prevents the intru~ion of air into the liquid
chamber portion.
The present invention will be under~tood from the
following description when read in conjunction with
the accompanying drawing~, in which;
Fig. 1 is a cro~s-~ectional view of one embodiment
of li4uid applying apparatus according to the pre~ent
invention;
Fig. 2 i8 a cros~-sectional view of one embodiment
f liquid applying apparatUJ according to the invention
~howing a connection of an air intske channel to the
pneumatic chamber portion;
~ig. 3 is a cross-sectional view taken along the
line~ 3-3 of Fig. 2;
Fig. 4 is a -~chematic functional block diagram
of a Yource of pres~urized air employed in the embodi-
ment of Fig. 1;
Fig. 5 i~ a cross-sectional view of one embodiment
of a humidifier of Fig. 4;
Fig. 6 is a cro~s-sectional view of another
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embodiment of the humidifier of ~ig. 4;
Fig. 7 i~ a graph ahowing a relation between the
diameter of liquid di~charge channel and the air
pressure;
Fig~ 8 is a graph showing a relation between the
diameters of liquid and air di~charge channelY;
Fig. 9 is a graph ~howing a relation between the
thicknes~ of diqc-like chamber and the optical density
of an image produced on the ~urface; and
Figo 10 is a cross-sectional view qhowing the flow
of air from the disc-like chamber to the atmosphere.
Referring now to Fig. 1 apparatus of the present
invention is qhown and compriqe~ generally a liquid
applying unit 10, a liquid supply container 11 and a
pneumatic pressure producing mean~ 12. The liquid
applying unit 10 compri~es an outer chamber portion 14
an inner chamber portion 15 and a pneumatic chamber
portion which include~ an intake channel 13 connected
to the pressure producing means 12 via a conduit 26,
an annular chamber portion 13' and a disc-like chamber
portion 13" which is in communication with the atmosphere
via a diqcharge channel 19. The thickness of the disc-
like chamber portion 13" is substantially smaller than
the depth, or axial dimengion of the annular chamber
portion 13'. The outer and inner chamber-q 14 and 15
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are in communication through a connecting channel 16
which is provided in a dividing plate 17 situated
between and forming the ~eparation of the liquid
chamber into the chamber portions 14 and 15. The con-
necting channel 16 i~ positioned in the dividing plate17 so that it is directly opposite to and axially
aligned with a discharge channel 18 which is provided
at the outer end of the outer liquid chamber 14 and
opens to the atmo~phere from the outer chamber portion
14 through the dischar$e channel 19. The discharge
channel 19 is axially aligned with the discharge
channel 18. A circular metal plate or membrane 20 i~
fastened to the wall 15' of the inner chamber portion
15. The dividing plate 17 has an intake channel 21
which opens into the outer liquid chamber 14 and i4
in communication with the fluid container 11 via a
conduit 22. The container may be disposed at a lower
level than the discharge channel 18 becau~e of the
capillary forces existing in the channel~ communicat-
ing with the outer chamber portion 14. A piezoelectriccrystal 23 i~ attached to the metal membrane 20 in any
conventional manner. Conductive wires 24 are provided,
one being electrically connected to the metal membrane
20 and the other to the piezoelectric crystal 23. The
wires 24 supply control pulses to the crystal 23. The
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Inner liquid chamber portion 15 has its one end
oppo~ite to the outer chamber portion 14 a larger
diameter portion 15" which i~ in contact with the
metal membrane 20. The cros~-sectional area of the
discharge channel 18 is substantially 9maller than the
cro~s-~ectional area of the larger diameter portion
15", and slightly smaller than the cross-sectional
area of the di~charge channel 19.
When the cry~tal 23 i~ activated by a pulse, fluid
i~ discharged from the inner chamber portin 15 through
the connecting channel 16, through the fluid layer in
the outer chamber portion 14 and further through the
di~charge channel~ 18 and 19 whereupon it is applied
to a writing ~urface. When the voltage pulse drops to
zero the direction of the fluid stream in the connect-
ing channel 16 i8 reversed and fluid is now sucked in
through the outer chamber portion 14 from the container
11 via the intake channel 21.
On the other hand, a stream of air is supplied
by constant pre~sure from the pressure producing means
12 to the annular chamber portion 13' through the
intake channel 13. The air stream diverges as it
flows through the annular path of the chamber portion
13' and converges a~ it flows into the disc-like
chamber portion 13" and then escapes through the
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di.~charge channel 19 at a high speed. The pre~4ure
at which the air is supplied is adjusted such that the
pre~sure in the di~c-like chamber portion 13"
equal~ the pressure in the liquid in the di~charge
channel 18 to permit the liquid to be sucked out there-
from overcoming the surface tension and visco~ity
associated with the liquid (Fig. 10) and that the
velocity of the air at the exit of the discharge channel
~9 i9 greater than the speed at which the liquid is
discharged ~o that the discharged liquid i~ accelerated
by the air stream. Since the liquid breaks up into a
serie~ of droplets of decreasing qize upon di~charge,
the droplets of smaller size are accelerated at a
higher ~peed than the droplets of larger ~ize ~o that
they land on the writing surface at sub~tantially the
same inAtant of time.
The axial direction of the intake channel 13 may
preferably be tangential to the periphery of the
anllu]ar chamber portion 13' aY illu~trated in FigY. 2
and 3 90 that a circular flow of air i9 formed in the
annular chamber portion 13' a~ indicated by the arrow
in ~ig. 3 and that the air flow~ into the di~c-like
chamber portion 13" in a spiral form radially inwardly
toward the discharge channel 19.
Exemplary dimen~ion~ of the liquid applying unit
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lO which provide~ a laminar flow at the outlet of the
discharge channel 19 are as follows:
Outer diameter of annular
chamber portion 13' ...... 20 mm
Width of annular chamber
portion 13' (W) ..... 1 - 4 mm
Depth of annular chamber
portion 13' (D) ..... 0.5 - 2 mm
Thickness (T) of disc-like
chamber portion 13" ..... 10 - 100 ~m
Diameter of discharge
channel 18 ..... 40 ~m
Diameter of discharge
channel 19 ..... 100 - 150 ~m
Pneumatic pressure in
disc-like chamber portion ...... 100 - 1000 mm Aq
Hecause there i-q no axial component in the spiral
air flow in the disc-like chamber portion 13", the air
may be sucked into the outer chamber portion 14 and
further into the inner chamber portion 15 through the
discharge channel 18 from the disc-like chamber portion
13" and prevents Yati~factory ejection of liquid. In
order to prevent 4uch air intruYion, the liquid con-
tainer 11 i~ communicated with the pre~sure producing
means 12 via a conduit 27.
The preYsure producing mean~ 12 compri~e~, a~
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~hown in Fig. 4, a pump 30, an air filter 31 connected
to the outlet of` the pump unit 30 to filter out any
foreign particles and to dampen oscillations of air
flow which might be generated from the pump 30. The
outlet of the filter 31 is preferably connected to a
humidifier 32 to impart moisture to the air to be
supplied to the liquid applying unit 10. The outlet
of the humidifier 32 iJ also connected to a pressure
regulating means such as a valve 33, the outlet of the
valve 33 being connected to the liquid supply container
S~ j G
11 via the conduit 27. The~pressure in the liquid in
5~ c
the container 11, and hence the\pre~sure in the liquid
in the discharge channel 18, are thereby increased,
and regulated manually by the valve means 33 such that
the pressure in the liquid in the discharge channel 18
eqllal J the presAure in the air chamber 13~.
During the intervals when the control pulses are
not Yupplied to the crystal 23, the surface area of
the liquid in the discharge channel 18 is likely to
be dried up to thereby increase its visco~ity. The
humidifier 32 keeps it~ liquidity by providing moi~ture
to the air stream. A~ illustrated in Fig. 5, the
humidifier 32 compri~es a housing 34, a porous member
3; ~uch as ~ponge or fibrous material which divides
the interior of the housing into an inlet chamber 36
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and nn outlet chamber 37. A water supply pipe 38 is
connected to the side wall of the housing 34 to fill
a lower portion of the housing 34 with water. The
lower part of the porous member 35 i~ immersed in the
water so that water permeates throughout the porous
material by absorption. The inlet chamber 36 is in
communication by a conduit 39 with the filter 31 and
the outlet chamber 37 ia connected by a conduit 40 to
the intake channel 13 of the liquid applying unit 10.
The pressuri~ed air is admitted into the inlet chamber
36 from the filter 31 and moiAture laden air emerges
from the outlet chamber 37.
An alternative arrangement of the humidifier 32
i9 illustrated in Fig. 6. The housing 41 is partially
filled with water supplied from pipe 42. A porous
porcelain or porous glass member 43 i9 disposed at the
lower part of the housing spaced from its bottom wall
41a defining a lower chamber 45. A porous member 44
such aA sponge or fibrous material is preferably
provided in a position above the surface of` the water
defining an upper chamber 46. The lower chamber 45 is
connected to the fulter 31 through conduits 47 and 48
and the upper chamber 46 is connected to the intake
channel 13 of the unit 10 via conduit and f`urther con-
nected to the presYure regulating means 33 via a conduit
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~(). When air is admitted into the lower chamber 45
rrom filter 31, the air will be forced into the water
through the porous glasY 43 and emerges as air bubble~
which float upward to the surface. The porous member
44 ab~orb~ the Yplashe~ cauYed by the upward flow of
tlle bubble~, but admit~ moi~ture laden air to pass
therethrough to the outlet chamber 46.
Experiments were conducted to aqYure ~ati~factory
operation of the liquid applying unit of the inventinn.
In Fig. 7 the relation between the air pres~ure
and the diameter (d) of diYcharge channel 18 is il-
illu~trated. In thi~ experiment, it wa~ assumed that
the diameter of discharge channel 19 iY approximately
2d + 20~m and the thicknes~ of the disc-like chamber
13" i~ 20 ~m. The lower limit of the air pressure
required to provide a laminar flow at the exit of
di~charge channel 19 follow~ the curve which decays
in a manner similar to an exponential curve with the
increa~e in the diameter of di~charge channel, 18.
Fig. ô ~hows the relation between the diameters
of discharge channels 18 and 19, and indicates that
a wider range of diameters iY available for the outer
discharge channel 19 when the inner discharge channel
1~ has a smaller diameter than when it ha~ a larger
diameter.
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Fig. 9 shows the relation between optical density and
the thickness of disc-like chamber 13" and indicates that at a
smaller thickness value the optical density of the image produced
on the writing surface by deposition of droplets is smaller than
at a larger thickness value. Good gradation of images was ob-
tained for the thickness value ranging from 10 to 20 ~m. The
thickness value in the range from 40 to 100 ~m was found suitable
for two-valued image reproduction, such as black-and-white docu-
ments.
By formation of a high speed laminar air flow at the
exit of the liquid discharge channel 18, the following advantages
are provided:
1) A series of droplets of decreasing size is acceler-
ated by the air stream so that the droplets of smaller size are
accelerated at a higher speed because of their small inertia than
the droplets of larger size. They land on the writing surface
substantially at the same instant of time on substantially the
same locality of the surface. This increases the resolution of
the image produced.
2) The liquid in the inner discharge channel 18 is
prevented from being dried because of the moisture provided by
the humidifier.
3) Because
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the static pressure at the exit side of the discharge channel
18 is balanced against the static pressure in the liquid, -~
this contributes to the lowering of surface tension of the
boundary surface layer of the liauid in the discharge channel
18 and as a result facilitates the ejection of li~uid droplets
to the atmosphere. Therefore, the threshold value at which
the droplets of the smallest size are ejected is lowered.
4) The air stream serves to avoid objectionable
effect caused by high speed rotation of a paper drum or roller
by guiding the discharged droplets to the paper surface at a
high speed which in some cases reaches 80 meters per second.
5) Because the discharged liquid droplets are guided
by the air stream, the distance travelled by the droplets can
be increased to advantage to allow the spacing between the
li~uid ejection apparatus and the writing surface.
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