Note: Descriptions are shown in the official language in which they were submitted.
105009~
The invention relates to marking of recording surfaces.
The prior art, typified by UK patent nos
1,148,771 and 1,064,344 discloses the marking of recording
surfaces responsive to electrical signals by means of
ink jets and styli.
One method of marking so disclosed operates
with physical contact between a liquid fed stylus and
the recording surface, said physical contact being
interrupted in accordance with a signal. Interruption
of physical contact is hard to control with high speeds
and with a fast flow of intelligence requires a highly
damped non-elastic mechanical system. The large
amount of distortion free power required to operate such
a system at higher speeds, such as lO kcs or higher,
results in high initial cost and a very low level of
operating efficiency.
Another marking device so disclosed is
commonly referred to as an 'ink spitter' or 'ink jet'
and includes devices in which liquid is transferred across
a gap from a point or orifice on to the recording surface
responsive directly to an electrical force or to controlled
pressure in the feed system. Such devices are limited
by the energy required to move a particle across a gap.
Factors such as inertia and surface tension must be over-
come, both being extremely difficult at high frequency
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rates. For example, in drops of sizes suitable for
recording purposes, it is estimated that the potential
required to move the drops across a one mil gap at 10 kcs
is in the range of 30,000 volts/cm, which is also about
the potential required to produce undesirable air break-
down. If it is also necessary to completely overcome
surface tenstion by electrical potential, the useable
frequency is greatly reduced.
Another category of such marking devices so
disclosed is one in which a liquid fed stylus is maintained
in constant contact with the recording surface and is moved
relative to the recording sheet in order to record
information. Such a device provides a continuous mark
on the recording surface at all times when the stylus
and the recording surface are in contact. Such a device
is fairly limited in practical application to oscillogra-
phic use, and it becomes quite complex to control a
continuously mar~ing stylus through the tortuous configu-
rations necessary for most sophisticated writing.
Disclosed in UK patent no 1,064,344 is a
stylus marking device capable of fast turn on and inter-
ruption of liquid flow from a stylus which is in continuous
contact with the recording surface. Such a device
contemplates the liquid being held in the stylus while
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a high voltage signal across the stylus and recording
sheet is applied in order to effect rapid flow of the
liquid. Removal of the high voltage signal results
in interruption of the liquid flow, although the stylus
remains in contact with the recording surface. Although
capable of solving many of the prior art problems, such
a device in general application requires a high voltage
supply and embodies a single stylus in contact with a
recording surface which is rotated many times as the
stylus moves across the surface so that eventually the
point of the stylus covers most of the surfaces area.
Such methods are generally so slow as to be undesirable
and require undesirably high voltages.
Also known in the prior art is the device and
method disclosed in US patent no 2,143,376 wherein
recording fluid is held in an open ended container and
drawn therefrom on to a recording surface interposed
between the open ended fluid container and a conductive
element when electrical energy is applied to the conductive
element. A series of such fluid containing containers
and matching conductive elements may be arranged across
the path of a recording surface so as to simultaneously
mark at least portions of a line on a recording surface
as the surface moves between the fluid containers and the
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conductive elements. Such a device is subject to
limitations of speed and definition~ The clarity
and resolution of the images produced by such a marking
device are physically limited by the number of sets of
open ended fluid containers and conductive elements which
may be placed side by side in line across the paper path.
The voltage requirements of such a device are found to
be undesirably high for many applications.
There is also known in the prior art, the
apparatus for marking a recording surface described in
US patent 2,600,129 wherein a fine stream of charged
liquid particles are produced by creating a DC field
between a nozzle or a point protruding from a liquid
supply and an external annular electrode through which
the stream passes. The external annular electrode has a
focusing effect which allows the use of a comparatively small
potential to move a stream of liquid particles over
comparatively great distances; however, in many embodi-
ments it is inconvenient to place an anular electrode
between the source of the stream of particles and the
recording surface. If, for example, the droplets are
sought to emanate from a row of adjacent sources to
selectively mark portions of a moving recording surface,
the definition of the image thus created may be limited
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by the spacing between the sources required by the matching
series of annular electrodes. It may also be inconvenient
at times to be limited to the use of a direct current
in order to establish a field.
In the marking of recording surfaces, especially
in response to electrical impulses such as those provided
by computers or facsimile devices it is often desirable
to mark the recording surface as it moves past a row of
closely spaced sources of liquid droplets which may be
activated and inactivated rapidly so as to produce a high
resolution image at high speed.
According to one aspect of the invention there
is provided a method of propelling droplets of marking
liquid which comprises:
(a) providing supply of marking liquid;
(b) positioning a shaft electrode so that a
propellent end thereof extends to a position
just above the operative surface level of the
marking liquid supply; and
~c) establishing a field between the shaft
electrode and at least one external electrode
sufficient to cause droplets to be propelled from
the marking liquid source covering the shaft
electrode onto a record receiving means.
Such a method provides droplets which are quickly
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responsive to electrical input and which are suitable
to mark a recording surface with a high degree of resolution.
The marking droplets may be, for example, propelled to the
recording surface directly from a row of closely spaced
independently driven shaft electrodes; or, if desired,
the droplets may be deflected by an electric field prior
to striking the recording surface.
According to another aspect of the invention
there is provided an apparatus for marking a recording
surface responsive to electrical input which comprises:
(a) a container for holding a supply of
marking liquid;
(b) a shaft electrode positioned in the supply
of marking liquid so that a propellent end thereof
protrudes to a position just above the operative
surface level of the marking liquid;
(c) a second electrode positioned so that a
field may be created between it and said shaft
electrode sufficient to cause a stream of drop-
lets to emanate therefrom whenever a sufficient
field is established between the electrodes; and
(d~ a means for creating such a field between
said electrodes.
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A marking method and apparatus according to the
present invention will now be described by way of example
and with reference to the accompanying drawings wherein:
Fig 1 shows in cross-section one embodiment of
an apparatus for performing the present invention.
Fig 2 shows in cross section the embodiment of
Fig 1 wherein the marking liquid covers the tip of the
shaft electrode.
Fig 3 shows in cross section the embodiment of
Figs 1 and 2 wherein a stream of droplets of marking
liquid are propelled from the shaft electrode to a recording
surface.
Fig 4 shows in cross section an apparatus for
performing the method of the present invention wherein a
preferred shaft electrode is used.
Fig 5 shows in cross section an apparatus for
performing the method of the present invention wherein
the field is established between the shaft electrode and
the marking liquid container.
Fig 6 shows schematically a means for marking
a recording surface in imagewise fashion using the method
of the present invention.
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Fig 7 shows schematically an alternative means
for making a recording surface by the method of the present
invention wherein deflecting electrodes are employed to
change the path of the marking liquid droplets.
Referring more specifically to Fig 1 there is
shown in cross section an open ended container 1 which
holds a supply of marking liquid 2. A shaft electrode 3
is positioned in the supply of marking liquid 2 in such a
way that one end referred to as a propellent end, 3a
protrudes to a position just above the operative surface
level thereof. Positioned above the protruding end 3a
of the shaft electrode 3 is a second electrode 4.
The shaft electrode 3 and the second electrode 4
may be made from any suitable conductive material.
Typically the electrodes are formed from conductive materials
such as aluminium, copper and steel.
The protruding end 3a of the shaft electrode 3
may be positioned so that it protrudes any suitable distance
from the operative surface level of the supply of marking liquid 2.
Typically the protruding end 3a extends at least about 0.020
inch above the surface of the supply of marking liquid 2.
Surprisingly it is observed that the movement of the droplets
is unstable when the protruding end 3a extends less than
about 0.020 inch above the surIace of the marking liquid 2.
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That is the droplets are either not formed or are
formed at irregular intervals and have irregular sizes~
However, distances of at least about 0.020 inch are
observed to produce droplets of substantially regular
size and spacing. It will be apparent to those skilled
in the art that the maximum distance which the protruding
end 3a may extend above the surface of the supply of
marking liquid 2 is largely dependant upon such factors
as the shape of the protruding end and the viscosity
of the marking liquid 2. Such maximum distance will
vary from case to case and may be optimized by experi-
mentation in each case.
The shaft electrode 3 may be of any suitable
shape and diameter. Typically the shaft electrode 3
has a diameter of from about 0.001 to about 0.010 inch,
although a preferred shaft electrode 3 diameter is about
0.005 inch at its protruding end 3a because of the size
of the droplet thus produced. The shaft electrode
typically has a non-pointed protruding end 3a. It may
be flat as shown in Fig 1 or rounded, although a rounded
protruding end 3a is preferred because the droplets
formed by such a shaft electrode 3 are found to be more
accurately directed. It is observed that the droplets
produced by a flat electrode eminate from various points
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on the flat surface and thus are not as well directed as
the droplets produced by a rounded electrode end. An
optimum configuration for the protruding end 3a of the
shaft electrode 3 is a rounded surface which is covered
with insulating material over its protruding portion.
It is believed the insulating tip of the protruding end
has a beneficial effect on the direction and concentration
of the lines of force between the shaft electrode 3 and
the second electrode 4. Such an embodiment is described
in greater detail in connection with Fig 4.
Although it is not essential, open ended con-
tainer 1 may function as an external electrode as explained
in greater detail in connection with the following illustrations.
The marking liquid 2 may be any suitable liquid.
Typically, it is a relatively insulating liquid having a
viscosity of less than about 50 cps and a dielectric
constant of from about 2 to about 3. The desirable
resistivity of the marking liquid varies with the diameter
of the shaft electrode. Generally, as the diameter of the
shaft electrode becomes smaller the desired resistivity
of the marking liquid is reduced. For example, satisfactory
results have been obtained using a shaft electrode with a
diameter of about 0.005 inch with a marking liquid having
a resistivity of about 10 ohm cm, said marking liquid
comprising light mineral oil having a viscosity of about
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30 cps with 5 wt percent Antoron, a dispersant which is
commercially available from General Analine Film Limited
which is added to increase the conductivity. Th~ marking
liquid may be colored with, for example, a suitable
amount of carbon black or some other suitable dye or
pigment to enhance its marking ability.
Referring more specifically to Fig 2 there is
shown the embodiment of Fig l wherein an electrical poten-
tial is established between the shaft electrode 3 and the
second electrode 4. The marking liquid 2 has been drawn
by the field to cover the protruding propellent end 3a
of the shaft electrode 3. Although in this illustration
the marking liquid 2 is drawn to cover the protruding end
3a of the shaft electrode 3 by the field, it is to be
understood that the marking liquid could be so drawn by
surface tension.
Although the function of the liquid covering the
protruding end 3a of the shaft electrode 3 is not completely
understood it is known to be important to the proper
functioning of the method of the present invention that
an amount of the marking liquid cover the protruding
propellent end 3a. It is believed that the liquid so drawn
may have a beneficial effect on the concentration and
direction of the lines of force between the shaft electrode 3
and the external electrode 4 in addition to serving as a
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supply for the droplets to be formed.
Re~erring more specifically now to Fig 3 there
is shown in cross section an apparatus for performing
the method the present invention wherein a stream of
droplets 5 are moving from the protruding end 3a of the
shaft electrode 3 toward the external electrode 4.
The stream of droplets 5 strikes and adheres to a recording
surface 6. Although the recording surface 6 of Fig 3
is shown to be moving in a path defined by rollers 7 and
7a, it is to be understood that the recording surface may
be stationery. Any suitable material may be used for the
recording surface. Typically, plain paper is used.
Any suitable potential of either alternating
or direct current may be established between the shaft
electrode 3 and the external electrode 4 depending primarily
upon the distance through which the droplets are sought
to be propelled and the diameter of the protruding end 3a
of the shaft electrode 3. It is observed that the potential
necessary to produce a satisfactory stream of droplets is
somewhat dependant upon the geometry of the protruding end 3a.
Typically a potential of from about 14,000 v/cm to about
30,000 v/cm may be used to propell the droplets when, for
example, a rounded shaft electrode 3 having a protruding
propellent end 3a diameter of about 0.005 inch is used.
It is understood that as the diameter of the protruding end 3a
decreases a smaller potential will be sufficient to propell the
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stream of droplets 5 toward the recording surface 6.
Additionally, a smaller potential may be used if the
protruding end 3a is rounded than if it is flat; however,
it is observed that a pointed protruding end is not useful.
A pointed protruding end tends to so concentrate the
potential charge that it effects air breakdown before
the droplets are created. This is thought to be caused
by the undesirably high concentration of charge at the
point and by the absence of sufficient marking liquid to
cover the site of concentrated charge on the pointed
protruding end of a shaft electrode.
It is also observed that potentials of greater
than about 30,000 v/cm undesirably tend to result in air
breakdown between the electrodes even when a shaft electrode
with a flat protruding end is used.
It is observed that when a suitable potential
is applied to an apparatus such as that described in
connection with Figs 1, 2 and 3 there results immediate
propulsion of a stream of regularly sized and spaced droplets
away from the shaft electrode. The steam of droplets is
also observed to cease immediately upon the removal of
sufficient potential. The droplets have a size related
somewhat to the diameter of the protruding end 3a of the
shaft electrode 3.
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Smaller electrode ends are observed to produce
generally smaller droplets than those produced by larger
electrodes. For example, it is observed
that a shaft electrode having a protruding end with a
diameter of about 0.005 inch and having a potential of
about 20,000 v/cm applied will produce droplets of a
suitable marking liquid having a diameter of about 0.005
inch and a spacing between droplets of about 0.005 inch.
It is to be understood that the rising of the
marking liquid 2 to cover the protruding end 3a of the shaft
electrode 3 as shown in Fig 2 may occur almost simultane-
ously with the start of the flow of droplets therefrom.
Alternatively, however, especially in embodiments wherein
it is desireable to produce intermittant bursts of droplets
from the shaft electrode, as exemplified by the embodiment
of Fig 6, a potential may be maintained on the shaft electrode
sufficient to maintain a covering of marking liquid over
the protruding end at all times.
Referring more specifically to Fig 4, there is
shown a preferred embodiment of an apparatus for performing
the method of the present invention. In Fig 4 the shaft
electrode 3 is formed from a conductive metal and has a
rounded protruding end 3a which is covered with an insulating
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material 8. Any suitable insulating material may be
used. Typically insulating paints and varnishes are
used as insulators.
The marking material container 1 of Fig 4 has a
generally circular cross section along line 4-4 and is
electrically connected with the second electrode 4 so that
the container 1 and the second electrode 4 act together to
establish a field with the shaft electrode.
Although not completely understood it is
believed that the insulated, shaped protruding end 3a of
the shaft electrode 3 and the establishing of a potential
between the shaft electrode 3, the container 1 and the
second electrode 4 cause a field having lines of force
which aid in directing the stream of droplets 5 toward a
very localiæed area on the recording surface 6.
Referring now to Fig 5 there is shown an alternative
apparatus for performing the method of the present invention.
In this embodiment the potential is applied between a shaft
electrode 3 and the conductive container 1 which becomes
in effect the second electrode. It is observed that the
application of a sufficient potential established between
the shaft electrode and the container 1 will cause a
stream of droplets 5 of substantially regular size and
spacing to move away from the protruding propellent end 3a
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of the shaft electrode 3 with sufficient velocity and
volume to mark the recording material 6. Although
satisfactory in its operation, it is observed that the
path of the droplet stream 5 i5 slightly less regular
when compared with the paths of the droplet streams of Fig
3 and 4, causing corresponding loss in resolution on the
recording material.
Referring to Fig 6 there is shown schematically
an apparatus for marking a recording surface 6, said
apparatus making use of the present invention. Droplet
supply 8 is a row of shaft electrodes positioned in marking
material containers and electrically connected to external
electrode 4 substantially in accordance, for example9 with
the embodiments of Figs 3 or 4. Electrical potential
sufficient to cause a stream of droplets to move in a
desirably straight path from each of the shaft electrodes
in the droplet source 8 toward the external electrode 4
is supplied by electrical input generator 9. Electrical
input generators such as computers and facsimile apparatus
are well known in the art, and any suitable such device
may be used.
As the recording surface 6 moves past the drop-
let source 8 the electrical input apparatus 9 syncrynously
provides a potential between selected shaf~ electrodes and
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the external electrode so that droplets are moved to
mark the recording surface and meaningful information
produced thereon.
Referring more specifically to Fig 7, there is
shown schematically yet another method of marking a recording
surface 6 using the method of the present invention. A
shaft electrode 3 is positioned in a supply of marking
liquid 2 and a charge sufficient to cause a stream of
droplets 5 to move from the shaft electrode 3 toward the
recording surface 6 is established between the shaft
electrode and an external electrode which, by way of
example in this illustration is the marking liquid container
1.
In the embodiment of Fig 7 a pair of directional
electrodes 11 are placed on either side of the path of the
s~ream of droplets 5. The directional electrodes 11 are
driven by an electrical input means 10, which may be, for
example, a computer or a facsimile device. Such devices
are well known in the art and any suitable such device
may be used. The field applied by the directional
electrodes 11 is such that it may change the direction of
the stream of droplets 5 sufficient to effect writing
on the recording surface 6.
The field established by the directional electrodes
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11 is believed to be effective to change the direction
of movement of the stream of droplets 5 because of the
charge which is observed to be resident on each droplet
as it moves away from the shaft electrode. It will be
apparent to those skilled in the art that the amount of
such charge is dependant upon factors such as the con-
ductivity of the marking liquid, the amount of potential
applied between the electrodes and the profile of the
protruding end of the shaft electrode. In a typical
example a marking liquid having a conductivity of about
ohm cm which is propelled from a shaft electrode
having a rounded protruding end with a diameter of about
0.003 inch by a potential of about 20,000 v/cm will
have a charge of about 10 coulombs.
While particular embodiments of the invention
have been described above, it will be appreciated that
various modifications may be made by one skilled in the
art without departing from the scope of the invention
as defined in the appended claims.
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