Note: Descriptions are shown in the official language in which they were submitted.
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APPARAq'US AND METHOD FOR DROP DEFLECTION
Background of the Invention
The present invention relates to the field of
drop deflection and has specific application to a record-
ing or printing device in which one or more jets of ink
are controlled to enable drops to be directed from each
jet drop stream to a plurality of print positions on a
moving print receiving medium. Further application may be
made to drop dispensers or to particle separation.
A number of prior art jet printers have provided
for servicing a plurality of print positions on a print
receiving medium with each of a plurality of jets. Such
printers have generally been relatively complicated in
that a charge electrode assembly has been required for
selective charging of drops in the jet drop streams, with
the charge electrode assembly being separate from the
deflection electrode assembly which provides a field to
deflect charged drops in each jet drop stream. In one
type of jet printer, shown in U.S. Patent No. 3,739,395,
issued June 12, 1973, to King, a plurality of jets,
arranged in a row perpendicular to the direction of move-
ment of the print receiving medium, are selectively charged
on a binary basis. Two pairs of deflection electrodes,
associated with each jet, generate orthogonal deflection
fields through which the drops in each jet pass. The
uncharged drops pass through the fields in a straight
trajectory and a strike catcher extending beneath the row
ox jets The first deflection electrode pair provides a
static electrical field which deflects the charged jet
drops in a direction substantially perpendicular to the
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row of jets such that they do not strike the catcher.
Thereafter, the charged drops pass through a field provided
by the second pair of electrodes and are laterally deflect-
ed in a direction parallel to the row of jets such that
they strike the print receiving web at one of a plurality
of print positions on the web. A cyclically varying poten-
tial is applied to the second pair of electrodes such that
a cyclically varying electric field deflects charged drops
to the print positions in a repeated sequence. props are
in the cyclically varying deflection field for a substan-
tial period of time, and some are exposed to the deflection
field as it initially increases and then decreases. In
some cases, the field may totally reverse during the time
that a drop traverses the field. As a result, it may be
difficult to produce deflection of the drops to preferred
print positions.
In a different type of ink jet printer, such as
shown in U.S. Patent No. 4,307,407, issued December 22,
1981, to Donahue et al, drops are subjected to a static
deflection field to produce deflection to various print
positions. The charge level carried by the drops is
selected to produce deflection to the desired print
positions or to a catcher structure. A charge electrode
plate, separate from the balance of the printer structure,
is required in the Donahue et al device to accomplish
charging of the drops. In this device, as in most other
prior art printers, drops are charged by applying an
electric charge potential to a charge electrode positioned
adjacent the fluid filament from which the drops are
formed The print head and the fluid filament are electri-
gaily grounded and, as a consequence, an electrical charge,
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proportional in amplitude to the electric charge potential
on the charge electrode but opposite in polarity, is formed
on the end of the fluid filament. This electric charge is
carried away by a drop as the drop separates from the end
of the fluid filament. An insulating space, downstream
from the charge electrodes, must be provided to separate
the fluid filaments from the deflection field or fields.
This results in a fairly long drop path from the point of
drop break off to the print receiving medium. This
substantial distance can accentuate errors where the fluid
filament is initially crooked due to imperfections in the
print head.
Typical prior art in the areas of drop dispensing
and particle separating is shown in Fulwyler U.S. Patent
3,380,584 and in Robertson U.S. Patent 3,647,138.
Summary of the Invention
This invention provides a method of drop deflec-
tion wherin drops of conductive liquid are selectively
charged and thereafter deflected by a common static
electrical field. The electrical field is applied
sidewardly across a continuously flowing stream of conduc-
tive liquid in a region extending downstream from the
point of drop breakoff. The stream is connected to a
source of reference potential, and drop charging is accom-
plished by changing the potential of the applied field at
the drop breakoff location while maintaining a constant
field strength throughout Such potential changing may be
accomplished by making equal adjustments to the potentials
applied to two field generating electrodes positioned on
opposite sides of the stream. Since the field strength is
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not changed, variable drop charging may be accomplished
without affecting the deflection force applied to
previously generated drops. Thus a single field may be
used for charging and deflection.
An ink jet printer in accordance with this
invention includes print head means foz generating a jet
drop stream directed generally toward a print receiving
medium. A fluid filament emerges from the print head
means and breaks up into the stream of ink drops. A pair
of electrodes is positioned on opposite sides of the fluid
filament above the point of drop formation and extends
along the path of the jet drop stream for a substantial
distance beyond the point of break up of the filament. A
means is provided for supplying a first deflection
potential to a first of the pair of electrodes and for
supplying a second deflection potential of different
magnitude to a second of the pair of electrodes such that
an electric field between the pair of electrodes is
produced. The stream of fluid is connected to a source of
reference potential. A selective charging means simul-
taneously shifts the first and second deflection potentials
by equal amounts in dependence upon the print position to
which a drop then being formed is to be deflected. Drops
are charged in dependence upon the field potential level
at the end of the fluid filament, while a constant field
strength is maintained between the electrodes. Charged
drops are deflected in a manner which is unaffected by
shifting of the first and second deflection potentials.
The stream of fluid is preferably grounded, and the first
and ; second deflection potentials are preferably of
opposite polarity.
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The selective charging means includes means for
generating a cyclically varying drop charge potential
signal having a plurality of discrete print potential
levels, each of which is associated with a respective one
of the print positions, and switch means for selectively
superimposing the cyclically varying drop charge potential
signal on the first and second deflection potentials such
that the potential of the electric field at the end of the
fluid filament is selectively varied to induce charging of
drops to print charge levels, but the field strength
experienced subsequently by the drops as they pass between
the electrodes remains substantially constant.
The printer may further include drop catcher means
for catching drops carrying a catch charge level. The
selective charging means further comprises means for
supplying a catch potential level to the switch means such
that the switch means selectively superimposes the cycli-
cally varying drop charge potential signal and the catch
potential level on the first and second deflection levels
to produce charging of drops to the catch charge level and
the print charge levels.
The electric field may be non-parallel with
respect to the direction of movement of the print receiving
medium.
The printer may provide for directing drops from
each of a plurality of jet drop streams to a plurality of
print positions on a moving print receiving medium. The
print head means generates a plurality of jet drop streams
arranged in a row and directed generally toward the print
receiving medium, with the streams emerging from the print
head means as electrically grounded fluid filaments which
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break up into the streams of ink drops. A plurality of
pairs of electrodes are provided, each such electrode pair
being positioned on opposite sides of a corresponding one
of the fluid filaments, above the point of drop formation
thereof, and extending along the path of the jet drop
stream emanating from the filament for a substantial
distance beyond the point of break up of the filament. A
means for supplying a first deflection potential of a
first polarity to a first one of each of the pairs of
electrodes and for supplying a second deflection potential
of a second polarity, opposite to the first polarity, to a
second one of each of the pairs of electrodes produces an
electric field between each of the pairs of electrodes. A
selective charging means shifts the first and second
deflection potentials supplied to each of the pairs of
electrodes by equal amounts in dependence upon the print
position to which a drop then being formed from the corres-
ponding fluid filament is to be deflected, whereby drops
are charged in dependence upon the field potential level
at the end of each of the fluid filaments and a uniform
field is maintained between each of the pairs of elec-
trodes~ The charged drops are laterally deflected in a
manner which is unaffected by shifting of the first and
second deflection potentials.
The selective charging means may include means
for generating a cyclically varying drop charge potential
signal having a plurality of discrete print potential
levels, each of which i5 associated with a respective one
of the print positions, and a switch means for selectively
superimposing the cyclically varying charge potential
signal on the first and second deflection potentials
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supplied to each of the pairs of electrodes. The potential
of the electric field at the end of each of the fluid
filaments is selectively varied to induce charging to
print charge levels, but the field strength experienced
subsequently by the drops as they pass between the elec-
trodes remains substantially constant. The printer may
further include a drop catcher means for catching drops
carrying a catch charge level.
The selective charging means may further comprise
means for supplying a catch potential level to the switch
means such that the switch means selectively superimposes
the cyclically varying drop charge potential signal and
the catch potential level on the first and second deflec-
tion levels supplied to each of the pairs of electrodes to
produce charging of drops to the catch charge level and
the print charge levels.
The drop catcher means may extend generally
parallel to and to one side of the row of jet drop streams
and the printer may further include means for producing a
secondary deflection field ox a strength sufficient to
deflect drops carrying a catch charge level to the catcher-
means. The electric fields between each of the pairs of
electrodes extend generally parallel to the row and the
secondary deflection field extends generally perpendicular
to the row.
Accordingly, it is an object of the present
invention to provide an ink jet printer in which drops
from at least one jet drop stream are selectively charged
by use of the same electrode structure which provides a
deflection field of substantially constant field strength
tv provide such a printer in which a cyclically varying
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charging signal is'superimposed on first and second deflec-
tion potentials of equal magnitude and opposite polarity
with such deflection potentials being applied to deflection
electrodes positioned on opposite sides of the jet drop
stream; and to provide such a printer in which a catch
potential level may be selectively superimposed on the
deflection potentials to produce charging of drops for
deflection to a catcher.
Other objects and advantages of the invention
will be apparent from the following description, the
accompanying drawings and the appended claims.
Brief Description of the Drawings
Fig. 1 is a sectional view of the ink jet printer
of the present invention taken in a plane generally perpen-
dicular to the row of jet drop streams;
Fig. 2 is a partial enlarged sectional view taken
generally along line 2-2 in Fig. l;
Fig. 3 is an enlarged partial sectional view taken
in a plane corresponding generally to Fig. 1,
Fig. 4 is a perspective view of a portion of the
deflection electrode arrangement of the printer;
Fig. 5 is a view taken generally along line 5-5
in Fig. 3;
Fig. 6 is an electrical schematic representation
of the switching arrangement associated with the deflec-
tion electrodes; and
Fig. 7 illustrates the wave shape of the cycli-
cally varying drop charge potential signal which is super-
imposed selectively on the first and second deflection
potentials.
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Detailed Description of the Preferred Embodiment
Reference is now made to Fig. 1 which is a
sectional view of the ink jet printer of the present
invention. A print head means 10 is provided for generat-
ing a plurality of jet drop streams 12 directed toward a
continuously moving print receiving medium 14. The streams
12 are arranged in a row extending generally perpendicular
to the plane of the sectional view of Fig. 1 and this row,
in turn, is substantially perpendicular to the direction
of movement of the print receiving medium 14. The print
head means includes an upper assembly 16 and a lower
assembly 18 which are held together by clamping bars 20,
extending the length of the print head means 10, and
threaded bolts 22~ Gasket 24 provides a fluid tight seal
between the upper assembly 16 and the lower assembly 18,
which assemblies together form a fluid receiving manifold
26. An orifice plate 28 extends the length of the manifold
26 and defines a plurality of orifices 30 from which fluid
filaments 41 emerge. Fluid drops periodically separate
from the ends of the fluid filaments, thereby forming the
jet drop streams
In order to increase the uniformity of drop size
and the regularity of drop formation, any of a number of
jet stimulation techniques may be used. One such
technique, disclosed in U.S. Patent No. 3,701,998, issued
October 31, 1972, to Mathis, is to provide mechanical
stimulation to the orifice plate at one end of the print
head means 10, causing bending waves to travel along the
length of the orifice plate These bending waves create
pressure varicosities in the fluid filaments emerging from
the orifices 30, thus stimulating the formation of drops
from the tips of the filaments.
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As illustrated more fully in Figs. 2-4, the
orifice plate 28 is positioned above a deflection electrode
plate 36 having notches 38 defined therein which partially
surround each of the jet drop streams 12~ A plurality of
pairs of electrodes 40 are positioned on opposite sides of
corresponding ones of the fluid filaments 41 above the
point of drop formation and extending along the path of
the jet drop stream 12 for a substantial distance. When
first and second deflection potentials of opposite polarity
are supplied to opposing electrodes 40, an electric field
is produced which extends between the pair of electrodes
in a direction substantially parallel to the row of jet
drop stream~O As shown in Fig. 4, conductors 42, which
may be printed circuit conductors on the surface of plate
36, provide a means for connecting each pair of electrodes
to first and second deflection potentials, respectively.
The deflection potentials are of equal magnitude but
opposite in polarity. This produces a deflection field
having a zero potential or ground plane Zp located
precisely halfway between the electrodes 40. Zero
potential plane Zp, when thus positioned, coincides
precisely with the associated fluid filamentt as shown in
Fig. 2. Since the fluid filament 41 is electrically
grounded, no potential difference exists between the
filament and the field potential and, therefore, drops
formed from the filament 41 are uncharged and pass
downward through the deflection field unaffected by the
field.
The present invention recognizes and takes advan-
tage of the fact that the amount of deflection experienced
by charged drops is a function of field strength, while
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charging of the drops by the field i6 a function of field
potential in the region of the fluid filament. Field
strength is directly proportional to the voltage differen-
tial between opposing electrodes 40 and inJersely propor-
tional Jo the spacing between the electrodes. Since the
electrodes remain a fixed distance apart, if the potential
difference between the plates is held constant, a field of
constant strength will result. The field is directed
sidewardly of the fluid filament.
As an example, if the voltage on both of the elec-
trodes is simultaneously raised by ~10 volts, the field
strength and the force exerted on the drops in the field
will be unaltered. The zero potential ground plane will
be shifted, however, toward one of the electrodes 40.
This, in turn, will result in the fluid filament 41 being
positioned in the field in a region of non-zero field
potential. As a consequence, an electric charge will form
on the end of the fluid filament. The magnitude of the
charge will be directly related to the magnitude of the
field in the region of the fluid filament, but will be of
opposite polarity. When a drop is formed from the end of
the filament, this drop will carry away with it a substan-
tial charge. The drop will then experience a lateral,
deflecting force produced by the field between plates 40,
such that the trajectory of the drop will be deflected.
An electrically grounded catcher 46 of conven-
tional construction is provided beneath the deflection
electrode plate to catch selected drops and prevent them
from striking the print receiving medium. The catcher 46
extends parallel to the row of jet drop streams and is
positioned on one side of the row. A surface 48 is struck
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by drops deflected to the catcher 46. The drops run down
surface 48 and are ingested into a vacuum cavity 50. A
catch electrode 52 extends along the row of jet drop
streams, directly opposite the surface 48. A relatively
high D.C. voltage is supplied to electrode 52 to produce a
secondary deflection field of a strength sufficient to
deflect drops carrying a catch charge level to the catcher
46.
It will be appreciated that the deflection
between electrodes 40 will be substantially parallel to
the row of jet drop streams, while the deflection between
catcher 46 and deflection electrode 52 will be generally
perpendicular to the row of jet drop streams. As seen in
Fig. 5, therefore, the drops are initially deflected
laterally between opposing electrodes 40 and, subsequently,
are deflected between catcher 46 and electrode 52 to
produce a skewed row of print positions associated with
each jet drop stream. Drops 54 are uncharged drops which
pass downward, unaffected by either of the fields. Drops
56 illustrate the final position of drops which carry an
intermediate charge level These are deflected laterally
slightly by the field between electrodes 40 and, there-
after, are deflected by the secondary field between
electrode 52 and catcher 46 in an orthogonal direction.
Finally, drops 58 carry a higher charge level and are
therefore deflected more by both of the fields. Drops 60
carry a catch charge level which is greater than any of
the print charge levels and they are deflected sufficient-
ly such that they strike the surface 48 of catcher 46 and
are prevented from being deposited on the print receiving
medium 14.
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Figs. 6 and 7 illustrate schematically the control
circuitxy associated with one jet drop stream, it being
understood that additional circuitry is required for each
of the jet drop streams. D.C. potential sources 62 and 64
are connected in series to provide a first deflection
potential TV of a first polarity to a first one of a pair
of electrodes 40, and a second deflection potential -Y of
a second polarity, opposite to the first polarity, to a
second one of the pair of electrodes 40~ A stairstep
o generator circuit 66 provides a cyclically varying drop
charge potential signal, illustrated in Fig. 7, which has
a plurality of discrete print potential levels. Each of
the potential levels is associated with a respective one
of the print positions serviced by the jet drop stream.
This stairstep signal when applied to line 68 by switch 70
shifts the first and second deflection potentials by equal
amounts. As a consequence, the drops then being produced
by the fluid filament will be charged to successive print
charge levels and appropriately deflected to the various
print positions. Switch 70 may be switched under control
of control input 72 so that line 68 is connected to line
74. A catch potential level VD is continuously applied
to line 74 and, if connected via switch 70 to line 68,
produces a shift ox the potentials on electrodes 40 suffi-
cient to produce a catch charge level on the drop or drops
then being formed. As a consequence, these drops will be
caught by catcher 46.
It may be seen, therefore, that this arrangement
will produce the deposit of drops from a jet in a cyclical
fashion at each of the print positions serviced by the jet.
It is understood that sinc2 the print receiving medium is
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continuously transported past the printer a line of drops
from each of the print positions will result. By control-
ling the deposit of drops along these lines, a print image
is formed on the print receiving medium. As is clear from
Fig. 5, a substantial gap exists between the print posi-
tions serviced by adjacent jets. Ink may be deposited on
the print receiving medium in the gap areas between jets
by a second printer positioned elsewhere along the path of
the print receiving medium. although a multiple jet
printer is illustrated in the accompanying drawings, it
will be appreciated that the present invention will also
find application with single jet printers.
It will also be appreciated that pairs of cooper-
ating electrodes 40 need not be connected to sources of
opposite polarity. It is only necessary that the sources
have different magnitudes and that these magnitudes be
adjusted by like amounts so as to maintain a constant
strength field therebetween. Likewise it is not necessary
that the fluid filament be grounded. So long as the fila-
ment is electrically conductive, the tip thereof will carry
an electrical charge corresponding to the difference
between its own potential and the potential of the
surrounding electrical field. The resulting charged drops
will be subjected to an unchanging electrical field in
accordance with this invention and will be deflected to
the desired locations. The catcher, of course, may be
positioned at any one of those desired locations consis-
tent with geometrical constraints.
The disclosed apparatus and method have appli-
cations other than ink jet printing. For example, utility
may be found as a particle separator for any of the uses
mentloned in Fulwyler U.S. Patent ~,380,584.
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While the form of apparatus herein described
constitutes a preferred embodiment of this invention, it
is to be understood what the invention is not limited to
this precise form of apparatus, and that changes may be
made therein without departing from the scope of the
invention which is defined in the appended claims.
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
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