IMPRIMANTE AU JET D'ENCRE A TETE UNIQUE MULTI-ORIFICE

MULTI-JET SINGLE HEAD INK JET PRINTER

Abrégé anglais

26
Abstract
In a jet type printing system a plurality of ink jets are
provided in line in the direction of carriage movement. The ink jets
are deflected to print in a conventional manner and also pass by
charging electrodes which charge individual droplets as they are
broken off from the jets. The charging electrodes are provided with a
charge to produce scanning transverse to the direction of carriage
movement such that if no charge is provided, ink will be caught in a
catcher and returned to the ink reservoir for reuse. By interlining
the lines a faster more effective printing occurs. Interlining may be
done in accordance with several stated methods. An alternative
provides ink jets one above the other with deflection means causing
deflection to occur in opposite directions so that one effectively
scans up and the other scans down, this alternative preferably
employing a pair of ink catchers for the respective jets.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A multi-ink jet printer providing interlacing
of print lines comprising:
an ink chamber and an array of nozzle orifices
generally aligned on an axis substantially parallel to
the relative print direction,
means to apply pressure to the ink chamber to
force ink out through each of said nozzle orifices in a
thin filament, including means acting on the ink to
break the filament into droplets of predetermined size,
each droplet producing a dot of predetermined size in a
raster of dots forming a printed character,
deflection plates between which all of the
droplets pass in droplet paths from the respective
nozzle orifices each in paths transverse to an
electrostatic field created by the deflection plates,
deflection voltage supply means connected to the
deflection plates to impose an electrostatic field
between the deflection plates,
charging electrode means fixed relative to each
nozzle orifice in position adjacent to the breaking
point of ink filament associated with the respective
nozzle orifices along the droplet paths from that
nozzle,
a source of voltage connected to the respective
charging electrode means each of which in turn is
capable of inducing electrostatic charge on the
individual droplets as they break off from the filament
emerged from the nozzle orifice associated with the
charging electrode, causing the droplets to be
deflected into paths determined by their charge as they
pass through the field imposed by the deflection
plates, such that the range of possible deflection is
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sufficient to permit the printing of one line of a
predetermined width on receiving medium,
voltage switching means applying selected voltage
in a prearranged order to each charging electrode as
individual droplets break off from ink filaments
adjacent the charging electrode to induce a charge of
predetermined magnitude on each droplet causing each
droplet to follow a particular path to a predetermined
position on a receiving medium,
ink collector means positioned for collection of
non-print ink droplets for all jets generated by a
particular level of voltage, and
means for supporting the receiving medium and said
array of nozzle orifices for relative movement in a
direction substantially parallel to said axis of said
array of nozzle orifices.
2. The multi-ink jet printer of claim 1 in which
the nozzle orifices and related structure are
stationary and the means supporting the receiving
medium is movable relative thereto.
3. The multi-ink jet printer of claim 1 in which
the nozzle orifices and related structure are on a
carriage movable relative to the means supporting the
receiving medium, and means for advancing the receiving
medium in increments of predetermined width.
4. The ink jet printer of claim 1 in which the
ink collector means is connected by recirculation means
back to the ink chamber.
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5. The ink jet printer of claim 1 in which
electrostatic means is interposed between adjacent
charging electrodes to isolate charge effects imposed
on droplets of one stream from droplets of another.
6. The ink jet printer of claim 1 in which the
means to apply pressure to the reservoir to force ink
out through the orifices is constant pressure or
constant flow means and the means acting on the ink to
break the filaments into droplets is an acoustic wave
generator positioned relative to the ink chamber and
nozzle orifices to generate acoustic waves of the same
amplitude and the same phase.
7. The ink jet printer of claim 1 in which the
means to apply pressure to the reservoir includes means
for recirculating ink from the ink collector means and
applying constant pressure or constant flow
characteristics to the ink and the means acting on the
ink to break the filament into droplets includes a
plurality of acoustic wave generating means positioned
relative to the ink chamber and the nozzle orifices
such that acoustic waves generated are of the same
amplitude and the same phase.
8. The ink jet printer of claim 1 in which a
plurality of charge rings are molded in a single
insulating block and conductive members are placed
between the charge electrodes and are grounded
electrically to afford electrostatic shielding to
isolate charge effects imposed on droplets of one
stream of droplets of another.
-21-

9. The ink jet printer of claim 1 in which the
charging electrode means are supported in common
insulating structure.
10. The ink jet printer of claim 9 in which the
charging electrode means are each ring-shaped,
U-shaped, or semicircular shaped, and each charging
electrode being precision-formed to be identical to one
another.
11. A multi-ink jet printer providing interlacing
of dotted lines in a matrix print format for marking a
receiving medium comprising:
an array of nozzle orifices aligned along an axis
and connected to an ink source,
means to apply pressure to the ink source to force
ink out through each of said nozzle orifices in a thin
filament, including means acting on the ink to break
the filament into droplets of predetermined size,
droplets issuing from a respective one of said nozzle
orifices capable of producing one of the dotted columns
in the matrix print format,
means for establishing an electrostatic field
having a direction substantially perpendicular to said
axis of said array of nozzle orifices through which all
of said droplets pass, each droplet path being
transverse to the direction of the electrostatic
field,
charging electrode means positioned adjacent to
each nozzle orifice for individually charging said
droplets,
a signal source connected to said charging
electrode for selectively inducing electrostatic
charges on said individual droplets as they break off,
-22-

causing them to be deflected into paths determined by
their charge level as they pass through said
electrostatic field, such that the range of possible
deflection is sufficient to permit the printing of a
matrix print format of a predetermined height on the
receiving medium,
switching means for switching said signal source
in a prearranged order to apply a selected voltage to
each charging electrode means as individual droplets
break off to induce a charge of predetermined magnitude
on each droplet to cause each droplet to be directed to
a predetermined position on the receiving medium
whereby each dotted line of the matrix print format is
marked by droplets issuing from one of said nozzle
orifices only and the respective dotted lines are
interlaced until each matrix print format is completed,
and
means for supporting the receiving medium and said
array of nozzle orifices for relative movement in a
direction substantially parallel to said axis of said
array of nozzle orifices.
12. An ink jet printer in a serial printer
configuration in which nozzle orifices are aligned
substantially parallel to the relative print direction
and in the same plane along which relative movement
occurs between the receiving medium and the nozzle
orifice array including droplet charging means and
deflection means, the path of droplets produced from
different nozzle orifices at any given time lying in
parallel planes transverse to deflection plates, such
that the droplets from one nozzle orifice impinging
receiving medium supported in their paths form lines of
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predetermined width parallel to and interlaced with
lines formed by droplets from the other nozzle
orifices.
13. The ink jet printer of claim 12 in which the
spacing of the nozzle orifices is such that lines drawn
by droplets from the respective orifices are interlaced
with one another.
14. An ink jet printer comprising:
an ink chamber having at least two matched orifice
nozzles so one orifice is above the character printing
and the other orifice lies below the character
printing,
means to apply pressure to the ink chamber to
force ink out through each of said orifice nozzles in a
thin filament, including means acting on the ink to
break the filament into droplets of predetermined size,
each droplet producing a dot of predetermined size in a
raster of dots forming a printed character,
deflection plates between which all of the
droplets pass in droplet paths from the respective
orifice nozzles each in paths transverse to the
deflection plates,
deflection voltage supply means connected to the
deflection plates to impose an electrostatic field
between the deflection plates,
charging electrode means fixed relative to each
orifice nozzle in position adjacent to the respective
orifice nozzles along the droplet paths from that
nozzle, and
a source of voltage connected to the respective
charging electrode means each of which in turn is
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capable of inducing electrostatic charge on the
individual droplets as they break off from the filament
emerged from the orifice nozzle associated with the
charging electrode, causing them to be deflected into
paths determined by their charge as they pass through
the field imposed by the deflection plates, imposing a
positive signal upon one stream of droplets and a
negative signal upon the other so that the droplets are
deflected in opposite directions, and are interlaced to
form a desired mark, or a character.
15. The ink jet printer of claim 14 in which
separate ink collector means positioned above and below
respective orifices are employed to collect the
non-print ink droplets from the respective orifices.
16. The ink jet printer of claim 14 in which said
orifice nozzles are in two rows of ink jet nozzle
orifice arrays located above and below the print area,
each array of nozzle orifices aligned in an axis
substantially parallel to each other, the signals for
the charging electrodes having opposite polarities
between the two rows of orifice nozzles so that print
droplets from said two rows of orifice nozzles are
deflected in opposite direction into the print area and
are interlaced to form a predetermined character or
image, and means for supporting the receiving medium
and said arrays of nozzle orifices for relative
movement in a direction substantially parallel to the
axis of said arrays of nozzle orifices.
17. The method of printing with a multi-ink jet
printer to accomplish proper line interlace within a
given character where the printer has an array of
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nozzles parallel to the relative print direction, means
for generating sequentially timed droplets from the
nozzles, individual means for each nozzle for omitting
or imposing different charges upon the droplets in
accordance with instructions from a memory and means
for deflecting droplets on which a charge has been
imposed to permit drawing a line comprising:
generating droplets from adjacent nozzles,
charging droplets in accordance with selected
character patterns of characters selected from memory,
deflecting charged droplets to draw parallel lines
or partial lines needed for selected characters, such
that the kth jet of an n jet array will print every
(mn + k)th line where m is an integer, and
timing delay between the droplet line patterns for
adjacent nozzles to (D+1/R)10V seconds where R is the
resolution defined in dots per millimeter and D is the
spacing in millimeters between adjacent nozzles and "V"
is the relative print speed in cm./sec. so that
interlaced lines properly complete the selected
characters.
18. The method of printing with a multi-ink jet
printer having an array of nozzles parallel to the
relative print direction, means for generating
sequentially timed droplets from the nozzles,
individual means for each nozzle for omitting or
imposing different charges upon the droplets in
accordance with instructions from a memory and means
for deflecting droplets on which a charge has been
imposed to permit drawing a line comprising:
generating droplets from adjacent nozzles,
charging droplets in accordance with selected
character patterns of characters selected from memory,
-26-

deflecting charged droplets to draw parallel lines
or partial lines needed for selected characters, such
that the kth jet of an n jet array will print every
(mn + k)th line where m is an integer, and
subjecting droplets generated from a lagging
adjacent jet to form adjacent interlaced lines in a
character to a spacial delay of (DR+1) dotted lines
wherein D is the spacing between centers of adjacent
nozzles in millimeters and R is resolution in dots per
millimeter, and repeating the process along each line
of characters.
19. A method of ink jet printing using two jet
heads wherein droplest are generated by a jet orifice
structure and deflected by deflection means onto a
receiving medium to print an nth line in a character,
while a second jet parallel to the relative print
direction prints at the (n+1)th line, after a timed
delay of (D+1/R)/10V seconds or a spacial delay of
(RD+1) dotted lines, where resolution is R dots per
millimeter, D represents spacing between centers of
adjacent nozzles in millimeters, and V is the relative
printing velocity in cm/sec.
20. A method of ink jet printing using two jet
heads wherein droplets are generated by a jet orifice
structure and deflected by defelection means onto a
receiving medium to print at the 2(2n)th line in a
character, while a second jet parallel to the relative
print direction prints at the 2(2n+1)th line, after a
timed delay of (D+2/R)/10V seconds or a spacial delay
of (DR+2) dotted lines, where resolutions is R dots per
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millimeter, D represents spacing between centers of
adjacent nozzles in millimeters, and V is the relative
print velocity in cm/sec.
21. A multi-ink jet printer of claims 1, 11 or 12,
containing n nozzle orifices aligned in one or two arrays
with axis (or axes) substantially parallel to the relative
print direction, printing in a constant relative print
velocity mode, the deflection electric field must be tilted
by an angle .THETA., satisfying the following relationships-
<IMG>, and
the relative print velocity V = <IMG> cm/sec,
where .THETA. is the angle between the direction of deflection
electric field and the normal of relative print direction,
n is the number of nozzle orifices in the print head, N
is the total number of possible print droplets generated
per orifice per second, Nv is the number of possible print
positions available in the vertical direction, and Rv and
Rh are resolutions in dots/mm. in the vertical and horizontal
directions, respectively.
22. A multi-ink jet printer of claims 14 or 16,
containing n nozzle orifices aligned in one or two arrays
with axis (or axes) substantially parallel to the relative
print direction, printing in a constant relative print
velocity mode, the deflection electric field must be tilted
by an angle .THETA., satisfying the following relationships:
<IMG> , and
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the relative print velocity V = <IMG> cm/sec,
where .THETA. is the angle between the direction of deflection
electric field and the normal of relative print direction,
n is the number of nozzle orifices in the print head, N
is the total number of possible print droplets generated
per orifice per second, Nv is the number of possible print
positions available in the vertical direction, and Rv and
Rh are resolutions in dots/mm. in the vertical and horizontal
directions, respectively.
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Description

~2~5~Z
A MULTI-JET SINGLE ~nEAD INK JET PRINTER
m e present invention relates to the use of more than one jet in
a single head ink jet printer to accomplish faster and more effective
printing, while maintaining an excellent print qualit~ for serial
printers. m e multi-jet nozzles are aligned in a straight line
parallel to the prunting direction, while droplets from each jet (or
nozzle) are deflected under ~le deflection electric field in a direc-
tlon perpendicular to the printing direction. ~n interlacing tech
nique is used to assure quality as good as that of a single continuous
jet printer, but it yields a print speed n-times faster, where n is
the nu~ber of nozzles in the ink jet array printer. The present
invention also relates to the method of producing that printing.
~.".
:

~ 25Z;~
State of the Art
At the present time there are available from various sources
continuous single jet printer devices. Such a printer has an ink
reservoir which is under a constant pressure of typically 16 to 80
pounds per square inch. The pressure causes the ink filament ejected
from a small orifice of 20 to 50 microns in diameter toward a small
well-defined area of the paper to be printed which paper is supported
a fixed distance from the nozzle on a suitable platen. Under the
stimulation of an ultrasonic wave, the filament is broken into a
stream of well-defined ink droplets at a rate equal to the requency
of the superimposed ultrasonic wave. Through charge induction,
droplets are charged one by one before break-up and the amount of
charge causes each droplet to deflect generally perpendicular to the
printing direction in proportion to the charge imposed. The droplet
is deflected under the influence of an electrostatic field produced ~y
deflection means to a predetermined position. In the course of each
of the successive deflections a straight line, generally perpendicular
to the print direction (usually a vertical line), or parts of a line,
is drawn so that by drawing a series of closely spaced verticall~
oriented segments of lines the desired character is completed. The
charge imposed on the droplets is varied in a predetermined stepwise
fashion, but for eaGh droplet there is the option of putting the
char~e at a level which causes the droplet to be directed to a gutter
or ink catcher ra~her than impinging upon the paper.
Typically, these non-printing droplets are not charged and only
the droplets used to draw the successive vertical line segments are
charged. Successive vertical lines are drawn as a carriage supporting
at least the ink jet orifice and charging electrode moves transverse
to the jet deflection, usually horizontally across a line on the paper
on the plat2n for a serial printer. The charge potential for succes-
sive droplets is increased or decreased in generally fixed prede-
termined steps so that if all of the droplets are allowed to impinge
the paper, they will together draw a vertical line. Characters are
produced by moving the carriage horizontally effectively drawing a
successive sequence of vertical line segments at predetermined po-
sitions which are needed to form the sequence of selected characters.
Particle charge information for each possible character capable of

522
being pxinted is stored in a m~mory which typically at each voltage
will either allow that deflection voltage to be imposed on the charg-
ing electrode or typically in most printers cQmpletely removes voltage
to allcw the ink to be caught in the ink gutter positioned to catch
uncharged particles and recirculate them to the reservoir for reuse.
In the prior art, it has been understood that there can be
electrostatic interaction between adjacent ink droplets but there is a
certain tolerance to error which can be accommcdated to the droplet
placement. This is preferably less than 30 ~icrons for a resolution
of 240 dots per inch (or lO dots/mm.) and less than 25 u for 300
dots/inch printing (or 12 dots/mm.). In the prior art, various
tec~miques were employed f~r munimiæing this error. One of these was
the use of guard drops as taught by U.S. Patent No. 3~562~757/ issued
February, 1971, to V. Bischoff. Also, there are charge compensation
schemes such as illustrated by U.S. Patent No. 3,828,354, issued
~ugust 6, 1974, to H. T. Hilton. However, such knGwn processes have
also reduced the number of printing droplets by a factor of 2 to 3
depending, for example, upon the number of non-charged droplets placed
between the printing droplets. If every other droplet is not charged,
the printing speed is reduced by a factor of 2. If only every other
third droplet is potentially capable of charge, printing speed is
reduced b~ a factor of 3.
An ink jet printer of the present invention may be of the type
shown in U.S. Patent No. 3,596,275, issued July 27, 1971, to R. G.
Sweet or U.S. Patent No. 3,298,030, issued January, 1967, to A. Lewis
and D. Brown. The process has produced 240 dots/inch (or 10 dots/mm.)
printing at 92 characters per second at 12 pitch.
m ere ls another approach using ink jet array. Numerous closely
packed ink jet nozzles æ e aligned in a straight line perpendicular to
the printing direction. The non-charged droplets are used to print on
paper; while the non-printing droplets are charged and deflected into
a common gutter and are recirculated into its ink system. The process
was first taught in U.S. patent No. 3,373,437, issued March 12, 1968,
to R. G. Sweet and R. C. Cumming. The process has been further
developed at Mead Corporation as tau~ht in U.S. patent No. 3,586,907
to D. R. Beam et al, U.S. patent No. 3,714,928 to R. P. Taylor, U.S.
patent No. 3,836~913 to M. Burnett et al, and U.S. Patent No.
4,010,477 to J. A. Frey.

2522
In ~his approach, an array with up to 1200 nozzles have been
aligned in a 25 cm. head in a direction perpendicular ~o the print
direction. Since each nozzle is a single continuous jet and is
printing in a binary mcde, a paper roll up to 10 1/2 inches width has
been printed after passin~ under the print head only once at a speed
in excess o~ 1000 feet per minute whi.ch is the fastest electronic
printer ever built to date.
m e approach has all nozzles share a comnon ir~ system, a common
ink reservoir, a ccmmon deflection electrode, and a common ink collec-
tor. m e cost is substantially less than those of 1200 single contin-
uous ~ets.
Limited b~ hcw closely we can pack nozzles per milli~ter and by
jet straightness cbtained by today's fabrication technology (1 to 1/2
milliradian), the print quality has not exceeded an equivalent of 240
dots/inch (or 10 dots/mm.).

~2~3Z522
Pr ent Invention
~ he present invention is directed to a print head containing from
2 to n jets. All jets are aligned in a straight line parallel to the
printing dixection. Each jet deflection is in a direction perpendicu-
lar to the print direction. Proper delay is provided to each jet
during printing to maintain a good printing qualit~ y -the use of
the rnultiple jets the printing speed will be increased 2 to n tLmes
faster depending upon the number of jets used. At 12 characters per
inch printing, a high resolution character needs 640 print droplets at
10 dots/mm (or 240 dots/inch) resolu~ion; and needs 1000 print
A ~ J o~
dro~lets at 12 dots/mm. (or ~re-t~*YS4iR.-) resolution. While at 5
dots/mm. (or 120 dots~inch) resolution, only 160 print droplets are
sufficient to for~ a character. A typical continuous ink jet operates
at about 100,000 droplets a second. Hence, a typical single
continuous jet printer prints about 50 characters per second at 12
dots/mm. resolution; c~bout 80 characters per second at 10 dots/mm.
resolution; and about 310 characters per second at 5 dots/mm.
resolution. m e follcwing table lists the printing speeds as a
~unction of process and a number of jets:

~L2~ 2
Table I Printing Speed Vs Nu~ber of Jets per Head
at 13~,000 droplets/second
Number of Jets/Head 1 2 4 n
2-guard-drop 44 cps 88 cps 176cps 44n cps
12 scheme
dots/mnl-guard-drop 66 cps 132 cps 264cps 66n cps
scheme
2-guard-drop 68 cps 136 cps 272cps 68n cps
scheme
dots/mnl-guard-drop 103 cps 206 cps 412cps 103n cps
scheme
2-guard-drop 275 cps 550 cps llOOcps275n cps
scheme
dots/m~Ll-guard-drop412 cps 825 cps1650 cps412n cps
scheme
At 12 dots/ron., a single continuous jet printer has a quality and
speed comparable with that of a daisywheel printer. m ere is very
little price performance advantage over a daisywheel printer. By
adding multi-no~zle to the print head, the present invention off~rs a
printing speed increase by n-times (where n is the number of nozzles
in a single print head), w~Lile maintaining ~he same high resolution
quality. Furtherm~re, the additional structure required in accordance
with the present invention is relatively nominalO The parts are known
and easily fabricated and many parts can be used in cor~Lon such as the
ink system, the deflection plates, the gutter and recirculation
system. Hence, the process is cost effective.
The following are the descriptions of this invention.
m e present invention has the ink jet nozzles aligned in a
straight line and is in parallel with the relative print direction.
Each nozzle is capable of producing a stream of ink droplets. Each
droplet is properly charged to a pre-determined level and is able to
be deflected by the deflection electric field to a maximum deflection
of at least 1.35 times the character height perpendicular to the print

~Z~i2;2
direction. In other words, each nozzle in the ink jet printer prints
exactly like the ink jet printer described ln the Sw~et patent and
Lewis and Brown patent. ~1hen multi-nozzle print head i5 used as
described, each nozzle will print a portion oE the vertical matrices.
The vertical matrices pr mted by different nozzles in the array will
interlace to form a high resolution character.
~ or example, if the array head contains t~ nozzles, jet "l" will
print every even number of vertical matrices, while the jet "2" will
print every odd number of vertical matrices. ~here is a time delay
for jet "2" with respect to jet "l" by (d -~ l/R)/lOV seconds where:
d is the inter jet spacing in mm.,
R is the resolution in dots/mm., and
V is the printer head speed in cm./sec; or a
spacial delay of (dR + l) dotted lines.
It will then be understood that the distance between centers of
two nozzles must be a multiple integer of the inter dot distance
between centers for the given resolution.
If three nozzles are used, each nozzle prints only every third
vertical matrices, i.e.,
jet "1" prints ~m + l)th dotted line;
jet "2" prints (~m + 2)th dotted line;
jet "3" prints (3m + 3)th dotted line; where m is an integer.
The time delays with respect to je~ "l" are, (d + l/R3/lOV seconds for
Sec~c,,~, ~
2 jet "27'; c~nd (2d + 2/R)lOV~sceff~ for jet "3", or there are spacial
delays with respect to jet i'l" by (d~ dotted lines for jet "2",
and (2dR + 2) dotted lines for jet "3".
A In ~eneral, if there ar~ n nozzles in a single head separated by
a distance d between centers (d is also an integer of l/R), each
noz~le will prunt every nth dotted line c~part. In particukar, the Kth
jet in the array will print every (mn + K~th dotted line, while the
first jet will print every (mn ~ l)th dotted line, where ~tis an
integer. m ere exists a time delay for the ~th jet with re.spect to
the first jet by (K-l) [d _ l/R]/lOV second, or a spacial delay of
(K-l) [dR _ l] dotted lines.
Let us now examine the electrostatic interaction between charged
droplets on flight between two adjacent jets which could effect the
droplet placement error. Electrosta-tic Coulomb force between two
charged particles of adjacent jets is

F = K qlq2
r2
where q is the charge con-tained in the droplet "i", r is the distance
between the droplets of adjacent jets, and K is a constant. Note that
the closest distance between charged droplets from 2 adjacents jets is
the distance between the jet nozzles which as a practical proposition
is taken to be 1 - 3 mm. At 132,000 droplets/sec. and a droplet
velocity of 2000 cm./sec.~ the inter-droplet spacing for a single jet
is .152 millimeters, the inter-droplet spacing is 7 to 20 times closer
than the inter-jet spacing. Since Coulomb force is inversely
proportional to -the square of the distance, correction due to adjacent
jet is very small. ~ence, one can ignore both the electrostatic
correction as ~ell as the aerodynamic wake effect for droplets between
jets.
More specifically, the ink jet printer apparatus of the present
invention employs an ink chamber or reservoir having cat least two
matched orifice noæzles aligned parallel to one another. Means of
constant pressure or of constant flow is en~)loyed to apply pressure to
the reservoir to force ink out through each of said orifices in a thin
fila~ent, including means acoustic energy means generating waves of
the same phase being preferred, acting on the ink to break the
fiL~ment into droplets of predetermined size~ each droplet being of a
size to produce a dot of predetermined size m a raster of dots
formlng a printed character. Deflection plates are positioned so ~at
all of the droplets pass in droplet paths from the respective nozzles
each in planes transverse to the deflection platesO Deflection
voltage supply means is connected to the deflection plates to impose
an electrostatic field between the deflection plates. Charging
electrode means is fixed relative to each orifice nozzle in position
adjacent to the respective ori~ice nozzles along the droplet paths
from that nozzle. Electrostatic shielding means may be interposed
between adjacent charging e]Rctrodes to isolate charge effects i~posed
on drople~s of one stream from droplets of another. A source of
voltage is connected to the respective charging electrode means. Each
charging electrode, in turn, is capable of inducing electrostatic
charge on the individual droplets as they break off from the ink
filan~lt emerging from the orifice associated with the charging

~2S2Z
electrode. The droplets are then deflected into paths determined b~v
their respective charges as they pass through -the field im~osed by the
deflection plates. Voltage switching means ls provided for applying
in a prearranged order selected voltages ~which may include zero
voltage) to each charging electrode~ as the individual droplets pass
throughO The selected level of voltage induces charge on each droplet
determined by and different for each voltage and causes that droplet
to follow a predetermined droplet path. Each droplet haviny the same
charge will follow ~he same path, different frcm paths followed by
droplets having other charges but all of which droplet paths lie in a
common plane transverse to the deflection plates. Ink collector means
is pssitioned for collection of non-print ink droplets for all nozzles
moving along the predictable paths generated hy a particular selected
level of voltage typically at zero potential. Means is supplied for
supporting paper in position such that droplets moving along paths in
a plane from an orifice nozzle will impinge the supported paper at
points along a line opposite that orifice nozzle and parallel to a
line opposite another orifice nozzle upon which droplets from said
other nozzle impinge. Carriage is also pro~ided fvr moving the
orifice nozzles and charging electrode means relative to the means
supporting the paper transverse to the plane of dr~plet paths from a
particular nozzle.
The method of the present invention invol~7es eith~r manually or
autQmatically, as by computer, delaying the printing of intermediate
lines until the seco~d nozzle orifice catches up with the position
adjacent to that the first nozzle orifice was in when it printed the
line adjacent to which the new line is to be printed by the second
nozzle. In accordance with the present invention, the pattern of dots
in the (2n ~ l)th dotted line printed by the second jet is delayed
frcm the time of the printing of the 2nth dotted line by the first jet
by (d + l/R)/lOV seconds where "d" is in the inter-jet spacing in
mill~meters, "V" is the print speed in cm./ æc., and "R" is resolution
in dots per millimeter~ m e spacial delay is expressed ~dR ~ 13
dotted lines.

~2~S~2
- 10
Drawings of the Present Invention
.
The present invention will be better understood by
reference to the accompanying drawings in which:
Fig. 1 is a side elevational view of a two jet version
of the present invention in a partial sectional view or in
the section as taken through the charging electrode ring and
deflecting plate along the paths from one orifice;
Fig. 2 is a plan view from above partially in section
showing a sec~ion through the jet path at orifice level at
both orifices and ~he bottom plate of the deflection plates;
Fig. 3 is an alternative construction shown in a view
similar to that of Fig. l;
Fig~ 4 is a detail view taken along line 4-4 of Fig. 3
showing a modified ink collector means;
Fig. 5 is a side sectional view of printer head in
Fig. l;
Fig. 6 is a sectional view taken along line 6-6 of Fig. 5;
Fig. 7 is a front view of the ink jet head as seen from
line 7-7 of Fig. 6;
Fig. 8 is a sectional view taken along line 8-8 of
Fig. 5;
Fig. 9 is a schematic drawing representing a five jet
version of the present invention;
FigO 10 is a side sectional view across any one of the
jets in Fig. 9;
Fig. 11 illustrates how a letter "Ti' is printed by the
five jet printer; and
Figs. 12a, b and c are ~ragmentary perspective views of
different configurations of charging electrodes~

~Z~2S;Z:~
11
~cl ______ odiments of the Present Invention
-
Referring how to the drawings, Figs. 1 and 2, 5, 6, 7 and 8
illustrate a preferred embodiment. Much of the system is known to be
conventional. Much of it has been shown in schematic form since the
actual physical form is well known. Thus, for example, in Figs. 1 and
2, the ink chamber 10 is shcwn schematically. The orifice nozzles
through which ink filaments are ejected from the reservoir are best
seen as nozzles 12a and 12b in an orifice plate 12 The use of two
nozzles in this configuration is new. A support structure 18 of
insulating material supports ring charging electrodes 16a and 16b,
between which is provided a conductive electrostatic shield 14 of
conductive material.
Considering Figs. 5 and 6 briefly, it will be seen that the
reservoir structure is more representative of an actual form which
would be emp]oyed. The reservoir pro~ides a cone-shaped cavity in a
block 20 provided with a cylindrical extension 20a the outside surface
of which is threaded to engage the threads of a cap 22. 'rhe cap
closes the narrow end of the conical cavity and is provided with the
orifices 12a and 12b on an orifice plate 12. Ink is fed into the
cavity 10 through a conduit 24, preferc~31y from a sump fed from the
return means from the gutter ~to be described) through a sultable pump
which supplies pressure at a constant rc~te, typically about 16 to 80
pounds per square inch. The ink is fed into the ink chamber by way of
a cavity 26 adjacent -to back plate 28 mounted on the reservoir plate
20 using a sealing gasket 30 and suitable fasteners and supp~rting an
ultrasonic transducer 32. A fiL~ment of ink on the order of 20 to 30
microns in diameter is ejected under the pressure through the orifice
nozzle and is broken into well-defined ink droplets in the charge
rings 16 at a rate equal to the rate of the frequency of the
ultrasonic source, thus, enabling each individual droplet to be
separately and differently chc~rged by the charging means 14~
Specifically the two jets involved here are charged hy the
charging ring electrodes 16a and 16b which surround the paths of the
droplets close to the orifice and before they are deflected hy the
electrostatic plates 34a and 34b. The a~ount of deflection of an
individual droplet depends upon the charge imposed upon that droplet
by its charginy ring electrode 16a or 16b. In the usual
configuration, uncharged droplets are allcwed to proceed undeflected

~2~S~
12
through the electrosta-tic field between the plates 34a and 34b into
the gutter or catcher 36~ They are returned by drain 38 to a sump and
by the pump back to the reservoir ~hrough the line 24 as described all
in conventional manner~ If instead of not being charged the droplets
are charged, the electrostatic field will act upon them to deflect
them. The arrangements shown in the drawings requires an upward
deflection such that the greater the charge, the more uE~7ard the
deflection would be. By varying the amount of charge in steps, a line
of dots can be drawn by successive droplets on a piece of paper 40
carried on a platen 42 on a printer. The ink must pass through an
elon~ated slot 44a in a shield 44 and the slot is gauged to permit the
full length of the character to be dra~n or printed on the paper 40.
In pra~tice, a_though the~ are shown as elements broken-away,
suggesting their extension the length of the platen, the deflection
electrodes 34a and 34b may be short and carried on the print head
carriage or may be made optionally long and extend the length of the
printer platen. The same is true of the catcher or gutter 36. l'he
rest of the structure, -the charging electrodes 16a and 16b and their
support ~ are effectively mechanically integral with the reservoir
and orifices and are part of the laterally moving print head which
moves parallel to the length of the platen. m e print head therefore
is designed to sequentially print as it moves along the structure,
parallel to the platen.
Some dimensions actually used in a two jet construction are
helpful in visualizing the size of the structure. The t~ orifice
nozzles located along the horizontal diame~er (or axis) are spaced on
the order of 3 to 4 mm apart. The tip of the cone in the ink chamber
10 is elongatRd in the horizontal direction, the direction of head
traverse to a dimension of 6 mm as opposed to 3 mm in the vertical
dimension. The elongated cone tip is recommended to focus the
acoustic energy and to assure an efficient non-perturbed acoustic wave
reaching at the orifice nozzles with identical energy density and at
identical phase. The back of the cone has a diameter of 8 mm and is
closed by a stainless steel plate 28 with a circular disc transducer
32, 8-10 mm in diametRr, mounted in the other side of the rnetal cover
for stirnulation. For maxir~Im kransfer of acoustic energy, the
distance between the orifice plate and the back plate for stirnulation
should be (2m + 1) ~/4 where ~ is the acoustic wave length of the

%5~2~
13
ink, and m is an integer. Other than two orifice nozzles at the
orifice plate and an elongated cone tip, the head structure remains
identical with that of a single jet head structure.
Charging electrodes 16a and 16b consist of two metal rings with
1.0 mm inner diameter. The thickness of the charging electrode or the
~ I ~g iu ~v~
length of each ring is about 0.9 to ~ r. I~he distance hetween
centers of the charging rings is identical to the distance bet~en
centers of the orifice nozzles.
Both the orifice nozzles 12a and 12b and tw~ charging rings 16a
and 16b are located an equal distance above the bottom of the
deflection plates 34a.
In operation nozzles 12a and 12b produce jets that are as close
to identical twins as possible. As the printer head traverses along
its carrier rod (not shown), for example, from left to right~ for any
given spot on the paper, jet a will reach there first, while jet b is
3 mm. away. m e printed dot fron a droplet in jet a will be 3mm. away
frcm the one in jet b, plus additional error caused by the jet
straightness. Hence jet straightness is a major concern for a high
resolution printing ink jet array. For a printing resolution of 300
dots per inch, the droplet placernent error should be within 25
microns. The corresponding jet straightness is less than 1
milliradian.
For a given vertical printed dotted line, there are 40 printing
positions vertically for each jet. Signal voltage plus the charge
compensation control are used to assure that droplet is placed within
a 25 micron radius of th~ predetermined spot position.
In a regular text printing mode with a resolution of 300 dots per
inch ~or 12 dots/mm.), jet a will print the 2nth dotted line, while
jet b will print the (2n ~ l)th dotted line. m ere is a delay of 3 x
12 + 1 dotted lines between jets, or a time delay of ~3 + 1/12~/1 W
seconds before jet b starts printing next to the dotted line prin~ed
by jet a, t~here "V" is the velocity of the carrier in cm./second. For
bi-directional priNting, jet a lags behind jet b by 3 x 12 ~ 1 dotted
lines or lags by a time of (3 ~ 1/123/lOV seconds.
For a resolution of 240 dots/inch (or 10 dots/mm), each jet
prints 32 positions. Jet a prints the even num~er 2n th dotted lines
and jet b prints the odd (2n-l)th dotted lines. Time delay between
these two jets is (3 + 1/10~/lOV seconds or 3 x lO + 1 dotted lines.

~ZC~i22
14
In general, if "d" is the inter-jet spacing in mm. and resolution is R
dots/mm., then ~he time delay between two jets is
(d + l/R)/lOV seconds;
or a spacial delay of
(dR + 1) dotted lines.
In a draft printing m~de, the electronics takes a slightly
different sequence. ~et a will print at the 2(2m)th dotted lines;
while jet b prLnts at the 2(m - l)th dotted lines. All odd number of
dotted lines are omitted. The time delay between two jets is always
~ d ~ 2/R)/lOV seconds;
or a spacial delay of
(dR -~ 2) dotted lines away.
"d'ir "R" and "V'l have been defined in Section (1).
Since each jet is basically the same as a regular single
continuous jet used in regular printing, droplet charging, charge
compensation, and guard drop scheme are the same. To m mimize the
cross talk between jets, electrostatic shieldin~ between charging
electrodes is reccmmended.
Referring now to Fig. 9, a conflguration is shcwn in which a
5-noææle jet configuration is employed. I~he structure is very similar
as that for the 2-jet array shown in Figs. 1, 2, 5 through 8 and
therefore similar numbers with the addi-tion of prim~s thereto are
employed in the structure. The ink reservoir 10' is modified somewhat
A m sh~pe and3~10,n~ated within plate 20' in order to acc~n}date ~hree
transducers ~, 32b', 32c'. The back plate 28' supports the
transducers distributed lon~itudinally and the transducers are
interconnected in such a way that they will be cumulative or additive
in their effect rather than counteracting the effect of other
transducers. Specifically, they all act to generate a pulse which is
in phase and they are selected to be of such a frequency as to avoid
standing waves or other effects counterproductive to the generation of
the droplets. The orifice plate 12' in this case has five separate
orifices 12a', 12b', 12c', 12d', and 12e'. m e o~ifices are carefully
aligned so that they produce jets which are directed in parallel
paths. The jets pass through charging rings 16a', 16b', 16c', 16d',
and 16e' and they are each supp~rted on an insulating charge plate
18'. Fig. 9 is a sectional view through the structure so that only
the lower deflection plate 34b' is seen but it will be understood that

~2~Z5i~:Z
an upper de1ection plate 34a' is also employed as in the prior
structure. Furthe~more, an ink collector means 35' is positioned so
that if no charge is placed upon the droplets, they will be collected
by the collection means. However, as in the prior arrangements, if
charges are placed upon the droplets, -they will be suitably deflected
onto paper 40' on a platen 42'.
Fig. 11 ~shows a typical pattern printed by the 5-nozzle printer
of Fig. 9 to print a character "T'l. Jet "1" prints the 1st, 6th,
11th, 16th and 21st dotted lines; jet "2" prints the 2nd, 7th, 12th,
17th, and 22nd dotted lines; ...; and jet "5" prints the 5th, 10th,
15th, 20th, and 25th dotted lines. The interlacing of all printed
dotted lines forms the character "T"~ Note that all 5 nozzles must be
identical in every practical meansO Jet straightness must be within
acceptable level. The interlacing scheme blends all 5 jet printin~ in
every portion of the character. Hence, it produces a more ho~cgeneous
appearance, and every slight misalignment will be averaged out. me
vertical positional accuracy are precisely taken care of by electronic
compensation on the amount of charge given to each individual droplet.
Note that the printing sequence by the 5-jet array is shcwn on
the top of Fig. 11 where kth jet prints every (5m + K)th dotted lines,
if we choose a time delay for the Kth jet with respect to the 1st jet
by (K-l) (d + l/R)/lOV seconds, where d, R, m, and V are as defined
above. m e corresponding spacial delay is (K-l~ (dR + 1) dotted lines
for th Kth jet. Another printing sequence is shcwn in the bottcm of
Fi~. 11 where the Kth jet prints every (5m - K)th dotted lines, if we
choose the tume delay for the Kth jet with respec-t to the first jet by
(~-1) (d - l/R)/lOV s conds. m e corresponding spacial delay is (K-l)
(dR ~ 1) dotted lines.
~ laracter printing is done through a character generator on a ROM
chip. The signal frGm each dotted column will first go through a
specific shift register to provide a proper spacial delay (or time
delay) before being sent to the driving electronics for the Kth jet
charge electrcde. In Fig. 9 the printer head assembly starts with a
transducer array 32a', 32b', 32c' of rectangular shape mounted on a
back plate 28' opposite to the rectangular pads 31a', 31b' and 31c'.
A transducer array is necess~ry when the total length of the ink ~et
array exceeds A/2, the half acoustic wavelength of the ink. The
acoustic wave generated by the transducer array must have the same

~Z~Z5i'~2
16
amplitude and-phase to avoid generating a longitudinal acoustic
standing wave along the direction of the orifices. Transducers
are mounted by epoxy or by mechanical means on the back plate
28', which may be a flat thin plate, or with a number of corres-
ponding pads. The structure separates the transducer array from
direct contact with ink, while transmitting acoustic energy
effectively to the ink chamber.
The ink chamber contains ink inlet 24' and an ink outlet
25', preferably with a controlled valve (not shown). The
tapered slot shape ink chamber block has transducer array
mounted on the larger crosssect-on end, and the orifice plate
at the tapered end. Mechanical clamping, solderin~, or gluing
by epoxy are methods of mounting. A tapered shaped ink chamber
is to focus the acoustic energy toward the orifice plate. The
length of the ink chamber should be at least ~/2 longer than the
total length of the orifice array. The width of the slot in
the ink chamber should not exceed half wavelength ~/2 to avoid
higher order standing wave generation. For the best stimulation,
the depth of ink chamber between the back plate and the orifice
plate should be kept at (2m + 1) ~/4, where m is an integer and
~ is the acoustic wavelength of the ink at the stimulation
frequency.
The fabrication of the orifice plate 12' is one of the most
critical parts of the ink jet printer. Although it is possible
to drill a series of identical holes on a thin metal plate,
(preferably a 5+ to i0 mils stainless or nickel plate) it is
better recommended to use photo-fabrication process to control
precisely the dimension and the shape. Silicon single crystal
wafer can be made as an orifice plate through oxidation then
preferentially etch nozzles at predetermined positions using
photo-resist. One can also use electroform process to fabricate
a precision orifice plate, where a photoresist image is first
made on a conductive substrate before electrodeposition. Care
must be exercised to assure perfectly round holes with identical
dimensions to minimize the droplet placement error.
The charge plate 18' has equal number of holes lined-up
concentrically with the orifices as shown in Fig. ]2a.

~)25~
16a
Conductive rings 16a', 16b', 16c', 16d' and 16e' are made on
the holes in the charge plate and is individually connected
to the driving circuit for charging electrode. Electrostatic
shields between nearest charge rings are recommended though
not necessary. ~nother configuration of . O . . . . . ~ . .

~z~z~z;~
17
the charge plate consists of an array of conductive U-shaped ehannels
18a (see Fig. 12b) or semi~circles 18b (see Fig. 12e) on the charge
plate. Each channel is connected to the driving electronic eircuit.
Although the former eonfiguration has superior shielding against
cross-talk between jets, the latter has advantages in operation
espeeially during the start-up and shut dc~n.
m e width of the defleetion plates and eatcher 36' have to be
widened to cover beyond the entire jet array in the present invention.
Ctherwise, they are identical with that of a sin~le jet printer. I`he
ink chamber, defleetion plates, eateher and ink system ineluding pump,
filtration, ink supply and -tubings are eommon to all jets.
Attention is now directed to Figs. 3 and 4 which shows a modified
construction wherein two jets are employed but the jets are provided
one above the other instead of in lateral alignment.
Fig. 3 is the side view of another type of 2-jet configuration,
where tw~ jets are aligned 3 to 6 mm apart one on each side of
printing area. The eh æ ge eleetrodes for jet a and jet b have
opposite polarities. Under the deflection eleetrie field given in
Fig. 3, charged droplets from jet a will be posikively "~" charged,
hence cleflected dc ~ ward; while droplets frc~n jet b will be negati~ely
charged "-" and are deflected upward. A dual catcher is shc~n in Fig.
4 whieh is a seetional view frc~ line 4-4 in Fig. 3. The upper
cateher eatehes the non-print droplets from jet a and the lower
eateher eatehes the non-print droplets frcxn jet b. The aperkure
between the eateher fingers is the window for printing. It is at
least 0~1 ineh in height. One may interlaee droplets frc)m jet a to
droplets frc~n jet b to form a single line (eaeh jet needs only 1/2 the
n~nber of steps per vertical line), or interlace the dotted lines
printed by each jet to form a eharaeter. In either seheme, the 2-jet
head printer will print twiee the speed of a single jet printerO
Furthermore, the jet a and jet b in FigO 3 may be r~plaeed by ~w~
rows of ink jet array, eaeh array is parallel to the print direetion.
Row a is loeated above the print area and row b is located below the
print area. The polarities of the matehed charge eleetrodes for row a
is opposite to that of row b so that the print droplets from eaeh row
of ink jet array are defleeted in opposite direction into the print
area to form the predetermined eharacters or in~ages. Using the
interlacing schemes described previously, high resolution images ean

z~zz
-
18
be obta med at a printing speed n times faster ~han a single jet
printer, where n is the total number of jets in the print head.