Arrangement for multi-orifice ink jet print head

Recording arrangement in which a row of ink jet nozzles is inclined with respect to the relative motion of a recording surface to permit the variously and selectively charged drops from each nozzle to be deflected by a single pair of planar electrostatic deflection plates common to all nozzles and parallel to the row so that each nozzle is capable of producing marks at regularly spaced locations along a plurality of parallel rows. Also disclosed is a method of determining the angle of inclination. The inclination angle, nozzle spacing, and deflection levels are preferably chosen so that marks can be placed at all possible data points by a single row of nozzles in a single recording pass. The disclosed method also provides for recording in either direction, the use of two or more parallel nozzle rows, and for the interlacing of drop marks at the recording surface.

BACKGROUND OF THE INVENTION 
High speed ink jet printing employs multiple nozzles, each producing a 
stream of drops that are selectively deflected to designated data points 
on a recording surface. Usually, the plurality of nozzles is arranged in a 
row transverse to the relatively moving recording surface and each nozzle 
has its own drop charging ring and its own set of deflection plates to 
appropriately direct the drop to their respective data points. Unwanted 
drops are directed to a catcher or gutter for accumulation and possible 
reuse. 
The arrangement shown in U.S. Pat. No. 3,786,517 to K. A. Krause, shows a 
typical transverse orientation of a nozzle plurality. The number of 
nozzles and their controls is optional and can be the number required to 
record a full line on the record surface. Many deflection levels are 
necessary to record with the resolution desired. These numerous deflection 
levels add greatly to the control signal complexity because of 
compensation to counteract adverse effects of charge interaction and 
aerodynamics. 
A somewhat similar arrangement is shown in U.S. Pat. No. 3,739,395 to K. O. 
King in which a plurality of transverse rows are used, each offset 
slightly from the preceding in order to cover all data points along the 
width of the recording surface. The streams can be deflected in two 
orthogonal directions; each nozzle in a row has an individual pair of 
deflection electrodes and all of the nozzles in a row have a pair of 
common deflection electrodes at right angles with respect to the 
individual pairs. Deflection by the common electrode is in the direction 
of motion. 
In both of the foregoing patents there is difficulty in making the 
necessary structure sufficiently small to cover all desired data points on 
a recording surface. In addition, the control of the drop charging and 
deflection signals becomes exceedingly complex. 
Another transverse arrangement of nozzles is shown in U.S. Pat. No. 
3,871,004 and uses selectively operable deflection electrodes to move ink 
drops a single level of deflection above or below the nozzle with respect 
to motion of the nozzle row. The drops are generated only on demand and 
are not selectively charged, but are deflected by the presence of a 
switched attracting field. Each electrode is discretely contoured adjacent 
each nozzle. 
A different approach has been to increase the number of nozzles in the 
transverse row and provide one nozzle per line of data points so that the 
control is binary with the drops being either allowed to reach the 
recording surface or deflected to a gutter. This arrangement is 
illustrated in U.S. Pat. No. 3,373,437 to R. G. Sweet et al. Such an 
arrangement has not been acceptable, however, because the nozzles cannot 
be placed sufficiently close together to meet the resolution requirements. 
Quality printing requires approximately 240 pels or print elements per 
inch or more. 
Another proposed solution is that described in a U.S. patent Application 
entitled "Multi-Nozzle Ink Jet Print Head Apparatus," Ser. No. 671,920, 
filed Mar. 29, 1976, by K. A. Krause and assigned to the assignee of the 
present application. In that application, multiple rows of nozzles are 
inclined with respect to the relative document-to-print head motion so 
that drops from a series of nozzles are able to impact the recording 
surface in an overlapping or contacting manner to produce a line segement. 
The inclination of the nozzle rows is relatively steep because the 
nozzles, due to structural limitations, cannot be placed sufficiently 
close to one another. In order to produce a linear mark extending across 
the width of the recording surface, numerous nozzle series must be 
accurately positioned and controlled. One nozzle is needed for each row of 
print elements or data points in the printed line. 
Another proposed solution has been disclosed in a U.S. patent application 
entitled "Multi-Nozzle Ink Jet Printer And Method of Printing," Ser. No. 
646,130, filed Jan. 2, 1976 by D. F. Jensen, et al., and assigned to the 
assignee of the present application. In that application, a series of ink 
jet nozzles are arranged in a row inclined to the relative motion between 
the print head and recording surface. The drops in the stream from each 
nozzle are selectively controlled to impact the recording surface at 
different levels of deflection. Each nozzle is capable of printing a 
plurality of lines of data points, and each nozzle has its own deflection 
means. When recording occurs during continuous relative motion, each 
deflection means must be individually tailored to lead the approaching 
desired data point to accurately place the ultimate mark. 
The known ink jet printers require either individual deflection devices for 
each ink stream, are limited to a single level of deflection, or can 
deflect only along the direction of relative motion. In addition, these 
printers either do not have to consider a compensation for relative motion 
between the ink streams and recording surface, or they have adjustments in 
the structure or signals individual to each stream. 
It is accordingly a primary object of this invention to provide an 
arrangement of common planar electrodes capable of deflecting the ink 
streams of a plurality of nozzles each to a plurality of levels of 
deflection during continuous relative motion with respect to the recording 
surface. 
Another object of this invention is to provide an arrangement of a 
plurality of ink jet nozzles and charging means with a pair of common 
electrodes capable of deflecting the drops in each nozzle stream to a 
plurality of levels of deflection which includes compensation via 
electrode orientation for relative motion between the nozzles and the 
recording surface. 
Yet another object of this invention is to provide a method of determining 
the inclination of a row of nozzles and deflection electrodes with respect 
to a recording surface which includes compensation by a common electrode 
adjustment for relative motion of the nozzles and surface and permits 
selection of different matrical arrangements of drop placement on the 
surface. 
A still further object of this invention is to provide an electrostatically 
deflected ink jet recording arrangement for a plurality of nozzles aligned 
in one or more parallel rows inclined with respect to the relative motion 
of the recording surface, each nozzle of which can record a plurality of 
parallel rows of drops at predetermined data points on an orthogonal grid 
on the recording surface. 
SUMMARY OF THE INVENTION 
The foregoing objects are attained in accordance with the invention by 
arranging a plurality of nozzles in a row with each nozzle having a drop 
charging means and all nozzles being located so as to direct their streams 
in parallel between a single pair of planar, parallel electrostatic 
deflection plates toward a recording surface. As the drops issue 
concurrently from all nozzles, the drops or group of drops selected for 
recording are charged according to the desired level of deflection and, 
due to the electrostatic field of the electrodes, are deflected along 
trajectories normal to the longitudinal axis of the electrodes to a 
respective data point on the recording surface. Uncharged drops are not 
deflected and are caught in a gutter for reuse. 
The row or rows of nozzles and parallel electrode pair are inclined with 
respect to the direction of relative motion. Each nozzle is then able to 
print a row of marks during recording surface movement for each level of 
deflection. Since the deflection of any charged drops is normal to the 
electrodes and those drops require finite flight time to reach respective 
data points on the recording surface, the angle of inclination according 
to the invention requires a consideration of several factors. Among these 
are the data point pattern and spacing desired, the number of levels of 
deflection to be recorded by each nozzle, the orthogonal nozzle spacing, 
and the number of drops generated by a nozzle as movement occurs between 
recordable data points in a row in the direction of travel. These 
relationships are integer values or integer multiples of the data point 
spacing in the same coordinate direction. 
An inclined nozzle row with means to achieve multiple levels of deflection 
permits simplification of the recording structure and allows greater 
nozzle spacing. Nozzle row inclination is readily adaptable to different 
drop frequencies and recording velocities and can be adjusted to 
accommodate a variety of orthogonal data point spacings. Printing can be 
done in either a forward or reverse raster and the drops can be deposited 
by interlacing, if desired. 
The foregoing and other objects, features and advantages of the invention 
will be apparent from the following more particular description of 
preferred embodiments of the invention, as illustrated in the accompanying 
drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a plurality of nozzles 10, 11 and 12 receive ink from 
pressurized manifold 13 which is replenished via supply tube 14. The ink 
within manifold 13 is subjected to cyclic pressure disturbances by any of 
several well known means, not shown. Then, as the ink issues in respective 
streams 15, 16 and 17 from each of the nozzles, the stream cross-sections 
are not uniform and the streams break up at a common, and preferably 
constant, frequency into individual drops 18 within a stream charge ring 
19 to which electrical signals are selectively applied by a character 
generator 23. As each drop breaks off from the stream, it carries a charge 
proportional to the signal on the charge ring at the time of break-off and 
travels between a pair of electrostatic deflection electrodes or plates 20 
and 21 which have a constant high voltage thereacross. One of the 
deflection plates, in this instance plate 20, has a gutter 22 for catching 
unwanted drops. For example, in this embodiment, drops which are to be 
discarded into the gutter are not given any charge; hence, the drops will 
not be deflected by the electrostatic field between plates 20 and 21 and 
will pass directly into gutter 22. Each charged drop, however, will 
continue toward the recording paper sheet 26, moved by rollers 24, and 
will impact the sheet at a selected spot, according to the magnitude of 
its charge, nozzle position, and time of charging. Drops may, of course, 
receive other charges for opposite deflection. 
In this illustration, the drops in each of the three streams are 
selectively charged with one of three different voltages by the respective 
charge rings so that the drops are deflected to one of three sets of 
horizontal lines on the recording surface. For example, drop stream 15 
from nozzle 10 is used to record the bottom three rows 1-3 of marks of the 
character "2" while stream 16 from nozzle 11 records the middle three rows 
4-6 and stream 17 from nozzle 12 records the top three mark rows 7-9. The 
charging signals are applied to the charge rings in synchronization with 
drop frequency and break-off in each stream to produce the required 
deflection. Fewer or additional levels of deflection can be used, if 
required. 
In this description, the term "data point" is intended to mean a possible 
mark location and, in the illustration, is each intersection of uniformly 
spaced orthogonal rows and columns in which the horizontal or "X" 
dimension between adjacent intersections is equal to the vertical or "Y" 
dimension between adjacent intersections. This results in a square matrix 
of data points. However, as described herinafter data points can also be 
recorded having different X and Y dimensions. 
In the figure, the row of nozzzles 10-12 are arranged along a line that is 
inclined with respect to the direction of motion of the recording sheet 
26, indicated by the arrow. As charged ink drops enter the electrostatic 
field between the parallel electrodes 20 and 21, they will be deflected in 
a direction normal to the longitudinal axis of the electrodes. Therefore, 
deflection with respect to the nozzle will occur along a line that is also 
inclined with respect to the direction of relative motion of the recording 
surface. Drops are selected or charged according to the need for a mark at 
a particular data point. Such selection is under the control of the 
character generator. 
Referring to FIG. 2, there is shown a portion of sheet 26 having 
intersecting, orthogonal grid lines thereon which define possible data 
points for recording marks by impacting ink drops. Each data point, 
separated by horizontal distance X and vertical distance Y, is intended as 
a possible site for drop placement and is recordable in this figure in a 
single pass between the row of nozzles 10, 11, and 12 and recording sheet 
26. Data points intended for recording by each nozzle are indicated by 
solid circles and ink drops for producing respective marks are indicated 
by solid dots, as viewed from the nozzle. Relative sizes of drops and 
marks and the grid have been distorted for purposes of explanation. 
Practically, the X and Y spacings between grid intersections may 
approximate 0.1 mm. or less. In this example, the proper motion is in the 
horizontal direction indicated by the arrow. 
The recording of each data point on a square grid requires the least 
deflection when the data points lie at an angle of 45.degree. with respect 
to the direction of motion of recording surface 26. At this angle, the 
data points at each successive level of deflection are displaced an X 
unit, the miminum, along the axis of relative motion between the recording 
surface and nozzles. During the horizontal movement of sheet 26 from one 
vertical column of data points to the next, each nozzle must be capable of 
producing sufficient drops for all assigned data points. 
In this figure, nozzles 10, 11 and 12 are indicated by "+" and each must 
have the capability of producing a series of at least three recordable 
drops or drop groups during the time required for horizontal motion 
between columns of data points. Therefore, a mark pattern is shown which 
represents the three possible marks formed by drops from each nozzle while 
the paper advances one X unit. In this description "series of drops" and 
"a series of marks" refers to all drops generated or marks recordable 
during the recording surface advance of one X unit. 
The actual motion between the recording surface and printing means requires 
compensation, and this is shown in FIG. 2. The drops, as they are 
generated, must be aimed to lead their corresponding mark sites because of 
the relative motion during drop flight time and because of the delay due 
to successive generation of drops or groups of drops from a nozzle. Since 
the flight time of each drop is approximately the same, the compensating 
lead of each drop for recording surface motion during droplet flight time 
is the same. Therefore, translating the nozzles and drops with respect to 
the recorded marks along the axis of relative motion has the same effect 
as changing the flight time of all drops. This, however, does not alter 
the angular relationships between the nozzles, marks and drops. 
Accordingly, each nozzle 10, 11 and 12, is located on lines 25 through the 
marks to be formed by drops from the respective nozzles. Each nozzle is 
illustrated as capable of recording three horizontal rows of data points. 
Uncharged drops that are not to be deflected are caught in a gutter. Drops 
are shown fully deflected as they would pass through the plane of the 
recording medium, but leading the actual point of impact as of the time of 
generation. 
The required compensation for successively generating drops while the 
recording surface is moving means that the ink drops from a nozzle will 
have to be actually deflected along lines 27 slightly in advance of the 
intended respective data points. As the charged drops enter the 
electrostatic field between electrodes 20 and 21, their direction of 
deflection will be parallel to the potential gradient and normal to the 
electrode axes. Therefore, parallel electrodes 20 and 21 must be 
repositioned at an angle .phi. with respect to the nozzle row to provide 
for the necessary lead of those drops intended for marking. This 
divergence between the nozzle row and the deflection electrodes results in 
increasing the electrode spacing to accommodate the nozzle row, 
necessitating excessive voltages between the electrodes. An alternative to 
the increased electrode spacing is to provide individual electrodes for 
each nozzle but these electrodes produce distorted electrostatic fields. 
The provision of a compensating lead angle for generation of successive 
drops, however, is possible when nozzles 11 and 12 are repositioned at 
greater distances than their original spacing and the levels of deflection 
and drop frequency are considered. Certain dimensional relations may then 
be established to permit the angle .theta. to be varied for both a square 
grid or other arrangement. A nozzle spacing which still permits the 
deflection electrodes to be parallel to the nozzle row and at an 
acceptable separation is shown in FIG. 3. The data points lie at the 
intersections of orthogonal lines as in FIG. 2 and form a square grid. The 
marks formed by the nozzles during a drop series also lie at an angle of 
45.degree. with respect to the direction of relative motion. Nozzles 10, 
11, and 12, however, have been shifted along the horizontal. 
Since the recording apparatus is to be capable of marking at all data 
points, adjacent nozzles are to leave no horizontal row of data points 
non-recordable. This dictates that the number of levels of deflection 
available, which is an integer value, be equal to or greater than the 
number of horizontal rows between nozzles. In this case, three or more 
levels of deflection are required. Extra drops, shown in broken lines, 
would be discarded and the potential superfluous marks, also shown in 
broken lines, would not be recorded. The successive positions of the 
printhead during the generation of a drop series is represented by 
intervals 28 in FIG. 3 to the right of nozzle 10. In order to maintain the 
accuracy of drop placement at each data point required of each nozzle, the 
numbered intervals must be an integer value; otherwise, fractional 
intervals will occur resulting in erroneous placement. It will be noted 
that each successive drop or drop group from nozzle 10 occurs at an 
interval 28 later than its predecessor but still leads its respective data 
point by a constant value. The illustrated sequence of successively 
greater deflection values for each drop is commonly referred to as forward 
rastering, while the deflection of drops in a series to successively 
decreasing deflection levels is reverse rastering. Reverse rastering is 
discussed later herein. 
The horizontal spacing of adjacent nozzles can vary considerably when the 
nozzles are in a common row. There is a limitation, however, in that the 
horizontal spacing, must be such as to maintain the uniformity of the 
vertical spacings from nozzle to nozzle. Thus, only certain relationships 
of the vertical and horizontal dimensions are operable to define an 
acceptable angle of .theta., the angle between the nozzle row and path of 
motion. 
The determination of the angle .theta. must also involve for consideration 
the number of drops generated in the series including any discarded drops 
and the distance traveled by the nozzle row during each generated drop 
series. For the deflection electrodes to be parallel to the nozzle row, 
lines 27 through the drops must be perpendicular to the nozzle row. The 
value of .theta. for the angle of inclination is then determined from 
these relationships by the following simultaneous equations: 
EQU Tan .theta. = LY/MX (1) 
and 
EQU Tan .theta. = (N-K)X/NY (2) 
where X and Y are the respective horizontal and vertical separations 
between adjacent data points, M and L are the respective number of data 
points between adjacent nozzles along the path of relative motion and an 
axis normal thereto, N is the number of data points possible to mark with 
each drop series generated, and K is the number of data points of relative 
movement along the path of motion during the generation of the series of 
drops necessary to mark N data points. Each of the values L, M, N and K 
must be integers. The values of N and K determine the relationship between 
the drop rate and the relative velocity of the nozzle row with respect to 
recording surface. Equations 1 and 2 can be combined to yield the 
following reltionship as seen in FIG. 3: 
EQU ly/mx = (n-k)x/ny (3) 
frequently data points will be at the intersections of equally spaced 
orthogonal axes. This results in the "X" and "Y" terms dropping out of the 
foregoing equations. When other grid proportions are desired, the "X" and 
"Y" terms express the ratio of the two respective dimensions. 
Likewise in most applications, K will probably be equal to 1, since 
coverage of all data points will be accomplished in a single pass between 
nozzle row and recording surface. A single pass eliminates the potential 
misplacement of drops due to misalignment of two or more nozzle rows, dual 
passes, or errors in signal or drop generation frequency. However, in 
those instances when the recording velocity is too fast for a single 
nozzle row and the available drop rate, then K may be a larger integer 
value. 
Considering equation (3) there are three groups of solutions: X = Y, L = N, 
and X = Y when L = N. The last is a special situation and perhaps the most 
efficient in terms of marks versus drops generated. 
The number of drops N in a series can be equal to the number of levels used 
for deflection or the number of drops can be larger. For example, in FIG. 
3, N = 4 and three levels of deflection are used. Thus, the fourth or 
extra drop is discarded, that is, not charged and directed to the gutter. 
It should be noted that successive drops can be similiarly charged as 
groups and used to form a single mark. For instance, two or three drops or 
more may be used for each mark, or two or more drops may be generated for 
each drop used to form a mark and the extra drops in each group discarded. 
However, the number of drop groups generated during KX motion must be 
equal to an integer value in order to maintain placement accuracy. 
The direction of relative motion between nozzles 10, 11, 12 and recording 
sheet 26 can be reversed while maintaining forward rastering. The effect 
of this change is illustrated in FIG. 4. Data points to be recorded again 
lie along a line through the intersections of diagonal data points. The 
nozzles are again positioned with respect to the marks so that line 27 
through the drops intersects line 25 through the marks at the respective 
nozzles. The deflected drops must lead the ultimate respective marks to 
compensate for the relative motion. The effect of the direction change is 
to require that the value K be added to the value N in equation (3) rather 
than subtracted so that the equation will appear thus: 
EQU LY/MX = (N+K)X/NY (4) 
again the constraint is the values L, M, N and K be integers. However, 
because of the condition that N be equal to or greater than L, there is no 
obvious solution to equation (4) with integer values of L, M, N and K 
where X = Y. Therefore, for this orientation the data points and the two 
orthogonal directions must be in the ratio: 
EQU X/Y = [M(N+K)/LN].sup.1/2 (5) 
this is evident in FIG. 4 where X and Y distances are unequal. 
The direction of relative motion can be reversed with the angles of nozzle 
row inclination merely by using reverse rastering of the drops. This is 
illustrated in FIG. 5 where nozzles 10 and 11 are inclined along the same 
angle as in FIG. 3, but the movement of sheet 26 is in the opposite 
direction. The first drop of a series N, theoretically destined for the 
cross-hatched mark 30 for nozzle 10 or mark 35 for nozzle 11 is actually 
discarded, then drops 31, 32, and 33 and drops 36, 37, and 38 are 
generated with each successive drop in a series carrying less charge and 
impacting sheet 26 at the coincident and corresponding marks. The drops of 
a series are each generated after successive intervals 28 and are 
deflected along lines 27 normal to the nozzle row. The use of forward and 
reverse rastering allows marks to be recorded in either direction without 
changing the inclination of the printhead and deflection apparatus. 
In FIG. 5, the nozzles and drops have been translated with respect to the 
marks so that the line 27 through the drops intersects line 25 through the 
marks at the theoretical location of the first marks 30 and 35. This has 
been done to illustrate the geometric relationship. When the direction of 
both the raster and printhead travel has changed, the timing of a drop 
series will require some minor adjustment but the remaining angular 
relationships still hold. 
A refinement in the deflection of drops to multiple levels is that of 
interlacing. This refinement improves drop placement accuracy by further 
separating drops in flight to avoid charge and aerodynamic interaction in 
which the charges and aerodynamic turbulence of neighboring drops are 
sufficient to modify the trajectories of drops from that which is desired. 
Interlacing is accomplished by avoiding the placement of successively 
charged drops at adjacent mark positions. 
An inclined orifice row with multi-level drop deflection is adaptable to 
drop interlacing as seen in FIG. 6. Interlacing is of doubtful benefit 
with fewer than 5 deflection levels and is illustrated in the figure as 
comprising a series of six drops. Only nozzles 10 and 11 are shown which 
lie along an inclined row at an angle .theta. with respect to the travel 
of sheet 26. The X and Y dimensions will be noted as unequal. This has 
been done merely for convenience of illustration. With the deflection 
plates parallel to the nozzle row, drops are deflected normal to the row 
along respective lines 40, and are generated at intervals 28 during the 
movement of the sheet through distance KX. The drops designated 1-6 in 
order of generation form two sub-series of marks. For example, drops 1, 3, 
and 5 form a first sub-series and drops 2, 4, and 6 form a second 
sub-series. From the designated mark locations, it will be seen that the 
marks resulting from one sub-series is offset with respect to those of the 
second sub-series by a fraction of the distance KX moved during generation 
of the entire series of six drops. The amount of offset for interlacing 
may be expressed as: 
EQU Offset = (KX/N)[N/J - 1] (6) 
where KX is the distance moved during the generation of a drop series, N is 
the number of drops generated in the series, and J is the number of drops 
in each sub-series. It will be noted that interlacing can be extended to 
more than two sub-series and that each will be offset with respect to the 
others. 
The determination of the angle of inclination when using interlacing is 
similar to equations (1) and (2) except that it may be determined using 
the data points of a sub-series along a line parallel to the direction of 
motion. The combined result would be: 
EQU JY/MX = (J-K)X/LY (7) 
since the direction of the printhead velocity with respect to the recording 
medium and the sequence of mark generation (away from the nozzle) are the 
same as in FIG. 3, it is appropriate to compare equation (7) with equation 
(3). It is seen that the two equations are identical when N = J. 
During printing with an inclined row of nozzles and multiple levels of 
deflection, the selection of recordable points is somewhat complex. Each 
nozzle can place a drop or drops in a different vertical row for each 
level of deflection during the generation of a single series of drops. For 
example, the nozzles will move three columns while printing a vertical 
line segment with one nozzle as shown in FIG. 1. Each nozzle will generate 
a single mark at a different deflection level for each column moved. Drops 
for all other levels will be discarded. Thus, the charging control for the 
drops requires consideration of the necessary omissions. 
As mentioned above, the amount of movement of a nozzle row during 
generation of the series of drops for printing at all levels of deflection 
can be equal to the spacing of adjacent grid columns or some multiple 
thereof. For example, if the value K were 2, the printhead could 
incorporate two parallel nozzle rows separated by some integer value of 
the column-to-column distance and each nozzle would then produce its 
series of N drops during the movement of the head over the new K value. An 
alternative would be to make two or more sweeps of the single nozzle row 
over the same recorded line but displaced in time of drop placement to 
record in areas left blank during the first pass. 
In all examples, the printing means has been depicted as fixed in position 
with respect to the recording medium. All the relationships discussed 
above hold if the recording medium is fixed and the printing means moves 
when the relative velocity is the same. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details may be made therein without departing from the spirit and scope of 
the invention.