Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 BACKGROUND OF THE INVENTION
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2 Field of Invention
3 The field of the present invention relates
4 generally to ink jet apparatus, and more specifically
5 to a method for operating an ink jet apparatus for
6 providing selective control within a range of either the
7 volume of the ink droplets ejected by the apparatus
8 and/or the amount of ink striking a desired point on a
9 recording medium.
The design of practical ink jet devices and
11 apparatus for producing a single droplet of ink on
12 demand is relatively new in the art. In prior drop on
13 demand ink jet apparatus, the volume of each individual
14 ink droplet is typically dependent upon the geometry of
15 the ink jet apparatus, the type of ink used, and the
16 magnitude of the pressure force developed within the ink
17 chamber of the ink jet rejecting an ink droplet from an
18 associated orifice. The effective diameter and design
19 of the orifice, the volume and configuration of the ink
20 chamber associated with the orifice, the transducer
21 design, and the method of coupling the transducer to the
22 ink chamber, are all factors determining the volume of
23 individual ink droplets ejected from the orifice.
24 Typically, once the mechanical design of an ink jet
25 apparatus it frozen, control over the volume of the
26 ejected ink droplets can only be obtained over a narrow
27 range by varying the amplitude of the electrical pulses
I or dry voltage applied to the individual transducers of
29 the ink jet apparatus or array.
The present inventor discovered that by
31 operating the transducer of an ink jet in an iterative
32 manner, for causing a plurality of successively higher,
I I
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1 lower, or equal velocity ink droplets or some combine-
2 lion thereof, to be ejected from the orifice of the ink
3 jet, within a time period permitting the droplets to
4 either merge in flight prior to striking a recording
5 medium, or to each strike the recording medium at the
6 same point, that broader control of the boldness and
7 toning of printing could be obtained. The volume of ink
8 striking a recording medium at a given point is thereby
9 partly determined by the number of ink droplets merged
10 prior to striking or at the point of striking.
11 In the drawing, wherein like items have common
12 reference designations:
13 Figure 1 is a sectional view of an illustrated
14 ink jet apparatus;
Figure 2 is an enlarged view of a portion of
16 the section shown in Figure l;
;
17 Figure 3 is an exploded projectile or pie-
18 tonal view of the ink jet apparatus, including the
19 embodiments shown in Figures 1 and 2;
Figure 4 is a partial sectional/schematic
21 diagram view of the transducer shown in Figure l and 3,
22 with the transducer in the de-energized state;
23 Figure 5 is a partial sectional/schematic
24 diagram or view of the transducer of Figure 4 in the
25 energized state;
26 Figure 6 shows the wave shapes for electrical
27 pulses of one embodiment of the invention;
28 Figure 7 shows a typical ejection of an ink
29 droplet from an orifice;
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Figure 8 shows the ejection of an ink droplet
from an orifice at a time when the previously ejected
ink droplet is still in flight;
Figure 9 shows the merging of two ink droplets
while in flight.
Figure 10 shows a typical ink droplet formed
after the merger of a number of ink droplets just prior
to striking a recording medium;
Figure 11 shows the wave shapes for electrical
pulses for another embodiment of the invention;
Figure 12 shows the wave shapes for electrical
pulses for yet another embodiment of the invention; and
Figures 13, 14 and 15 show wave shapes for
other embodiments of the invention.
The resent invention was discovered during
development of improved methods for operating the thus-
trative~ ink jet apparatus of Canadian Patent No.
1,174,516 which is shown in Figures through S. However,
the present inventor believes that the various embody-
mints of his invention illustrated and claimed herein
are applicable for use with a broad range of ink jet
apparatus (especially drop on demand ink jet apparatus).
Accordingly, the ink jet apparatus to be discussed here-
in is presented for purposes of illustration of the
method of the present invention, and is not meant to
be limiting. Also, only the basic mechanical features
and operation of this apparatus are discussed in the
following paragraphs, and reference is made to the pro-
piously mentioned patent for greater details concerning
this apparatus. The reference designations used in
Figures 1 through 5 are the same as used in the patent,
in order to facilitate any referencing back to that
; patent that may issue therefrom.
:
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With reference to Figures 1 through 3, the
illustrative ink jet apparatus includes a chamber 200
having an orifice 202 for ejecting droplets of ink in
response to the state of energization of a transducer
204 for each jet in an array of such jets (see Fig. 3).
The transducer 204 expands and contracts (in directions
indicated by the arrows in Fig. 2) along its axis of
elongation, and the movement is coupled to the chamber
200 by coupling means 206 which includes a foot 207,
a visco-elas-tic material 208 juxtaposed to the foot 207,
and a diaphragm 210 which is reloaded to the position
shown in Figures 1 and 2.
Ink flows into the chamber 200 from an unpres-
surized reservoir 212 through restricted inlet means
provided by a restricted opening 214. The inlet 214
comprises an opening in a restructure plate 216 (see Fig.
3). As shown in Figure 2, the reservoir 212 which is
formed in a chamber plate 220 includes a tapered edge
222 leading into the inlet 214. As shown in Fig. 3,
the reservoir 212 is supplied with a feed tube 223 and
a vent tube 225. The reservoir 212 is compliant by Yin-
tune of the diaphragm 210, which is in communication with
the ink through a large opening 227 in the restructure
plate 216 which is juxtaposed to an area of relief 229
in the plate 226.
One extremity of each one of the transducers
204 is guided by the cooperation of a foot 207 with a
hole 224 in a plate 226. As shown, the feet 207 are
slide ably retained within the holes 224. The other
extremities of each one of the transducers 204 are
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1 compliantly mounted in a block 228 by means of a come
2 pliant or elastic material 230 such as silicon rubber.
3 The compliant material 230 is located in slots 232
4 (see Fig. 3) so as to provide support for the other
extremities of the transducers 204~ Electrical contact
6 with the transducers 204 is also made in a compliant
7 manner by means of a compliant printed circuit 234,
8 which is electrically coupled by suitable means such
9 as solder 236 to an electrode 260 of the transducers
204. Conductive patterns 238 are provided on the
11 printed circuit 234.
12 The plate 226 (see Figures 1 and 3) includes
13 holes 224 at the base of a slot 237 which receive the
14 feet 207 of the transducers 204, as previously men-
toned. The plate 226 also includes a receptacle 239
16 for a heater sandwich 240, the latter including a heater
17 element 242 with coils 244, a hold down plate 246,
18 a spring 248 associated with the plate 246, and a
19 support plate 250 located immediately beneath the heater
240. The slot 253 is for receiving a thermistor 252,
21 the latter being used to provide monitoring of the
22 temperature of the heater element 242. The entire
23 heater 240 is maintained within the receptacle in the
24 plate 226 by a cover plate 254.
As shown in Fig. 3, the variously described
26 components of the ink jet apparatus are held together
27 by means of screws 256 which extend upwardly through
28 openings 257, and screws 258 which extend downwardly
29 through openings 259, the latter to hold a printed
circuit board 234 in place on the plate 228. The dashed
31 lines in Fig. 1 depict connections 263 to the printed
32 circuits 238 on the printed circuit board 234. The
33 connections 263 connect a controller 261 to the ink jet
34 apparatus, for controlling the operation of the latter.
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1 The controller 261 is programmed to at an
2 appropriate time, via its connection to the printed
3 circuits 238, apply a voltage to a selected one or ones
4 of the hot electrodes 260 of the transducers 204. The
applied voltage causes an electric field to be produced
transverse to the axis of elongation of the selected
7 transducers 204, causing the transducers 204 to contract
8 along their elongated axis. When a particular trays-
9 dicer 204 so contracts upon energization (see Fig. 5),
the portion of the diaphragm 210 located below the foot
11 207 of the transducer 204 moves in the direction of
12 the contracting transducer 204, thereby effectively
13 expanding the volume of the associated chamber 200. As
14 the volume of the particular chamber 200 is so expanded,
a negative pressure is initially created within the
16 chamber, causing ink therein to tend to move away from
17 the associated orifice 202, while simultaneously per-
18 milting ink from the reservoir 212 to flow through the
13 associated restricted opening or inlet 214 into the
chamber 200. Given sufficient time, the newly supplied
21 ink completely fills the expanded chamber and orifice,
22 providing a "fill before fire" cycle. Shortly there-
23 after, the controller 261 is programmed to remove the
24 voltage or drive signal from the particular one or ones
of the selected transducers 204, causing the transducer
26 204 or transducers 204 to return to their deenergized
27 states as shown in Fig. 4. Specifically, the drive
28 signals are terminated in a step like fashion, causing
29 the transducers 204 to very rapidly expand along
their elongated axis, whereby via the visco-elastic
31 material 208 the feet 207 of the transducers 204 push
32 against the area of the diaphragm 210 beneath them,
33 causing a rapid contraction or reduction of the volume
34 of the associated chamber or chambers 200. In turn,
this rapid reduction in the volume of the associated
36 chambers 200, creates a pressure pulse or positive
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I pressure disturbance within the chambers 200, causing an
2 ink droplet to be ejected from the associated orifices
3 202. Note that as shown in Figure 5, when a given
4 transducer 204 is so energized, it both contracts or
reduces its length and increases its thickness. However,
6 the increase in thickness is of no consequence to the
7 illustrated ink jet apparatus, in that the changes in
8 length of the transducer control the operation of the
g individual ink jets of the array. Also note, that with
present technology, by energizing the transducers for
11 contraction along their elongated axis, accelerated
12 aging of the transducers 204 is avoided, and in extreme
13 cases, depolarization is also avoided.
14 For purposes of illustration, assume that the
pulses shown in Figure 6 are applied via controller 261
16 to one of the transducer 204. As shown the first and
17 second pulses 1 and 3 respectively each have an expo-
18 nential leading eye and a substantially linear trailing
19 edge, respectively, peak amplitudes + Al, + V2 volts
respectively, and pulse widths of To, To, respectively.
21 Note that the shapes of the pulses 1,3, respectively,
22 may be other than as illustrated herein, depending upon
23 the particular ink jet device being driven and the
24 particular application. In this example, the peak
amplitude plus + V2 of pulse 3 is greater than the peak
26 amplitude Al of pulse 1, and the fall time for the
27 trailing edge of pulse 3 is less than the fall time
28 for the trailing edge of pulse 1. Since the degree of
29 contraction of the selected transducer 204 is directly
related within a range to the amplitude of the pulse
31 applied to the transducer, the greater the amplitude,
32 the greater the degree of contraction. Accordingly,
33 upon termination of a particular operating or control
34 pulse/ the magnitude of the pressure disturbance pro-
duped in the associated chamber 200 will be directly
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1 related within a range to the amplitude of the previous-
2 lye applied control pulse. Also, the greater the slope
3 or the less the fall time of the trailing edge of the
4 control pulse, the more rapid the expansion or elonga-
lion of the selected transducer 204 to its rest state
6 upon termination of the control pulse. Correspondingly,
7 the greater the rate of expansion of the transducer 204,
8 the greater the magnitude of the resulting pressure
g disturbance within the associated chamber 200. Assume
that the amplitudes + Al and + V2 of pulses 1,3, respect
11 lively, are large enough to ensure ejection of a ink
12 droplet from associated orifice 202 upon termination
13 of these pulses, respectively.
14 With reference to Figure 7, assume that pulse
1 is applied to a selected one of transducers 204. Upon
16 termination of pulse 1, a typical ink droplet 5 will be
17 ejected from the associated orifice 202. Substantially
18 upon the termination of pulse 1, assume that pulse 3 is
19 applied to the selected transducer 204. Shortly after
the termination of pulse 3, a second ink droplet 7 will
21 be ejected from the associated orifice 202 as shown in
22 Figure 8, for example. Ink droplet 7 will have a
23 substantially greater velocity than the air-borne ink
24 droplet 5 because the amplitude of pulse 3 is greater of
that than pulse 1 and the fall time of pulse 3 is less
26 than that of pulse 1. Note that as previously explained
27 though, the velocity of the second ink droplet 7 will be
28 greater than that of ink droplet 5 so long as at least
29 one of either the amplitude of pulse 3 is greater than
that of pulse 1 even if the fall times of these pulses
31 are equal, or the fall time of pulse 3 is less than
32 that of pulse 1 even if their amplitudes are equal.
33 Accordingly, either amplitude control of the control
34 pulses, or trailing edge fall time control of the
control pulses or a combination of the two can be used
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1 to produce a higher velocity second droplet 7 as thus-
2 treated in Figure 8, for example. By properly control-
3 lying the pulse parameters, the velocity of the second
4 ink droplet 7 can be made high enough to cause droplet
7 to catch up with droplet 5 while each is air-borne,
6 causing these droplets to begin to merge together as
7 shown in Figure 9. Assuming sufficient flight time, the
8 merger of droplets 5 and 7 may result in a droplet shape
9 as shown in Figure 10 prior to the merged droplets
striking a recording medium. Alternatively depending
11 upon the relative speeds (successively higher or lower)
12 of the droplets and movement of the recording media, the
13 droplets can be made to strike the recording media at
14 the same point or spot, without merging while air-borne,
thereby obtaining the same result. In this manner, the
16 size of the ink droplet or volume of ink striking a
17 recording media at a particular point is substantially
18 increased relative to using only a single droplet, and
19 such control of the volume of ink directly provides
control of the boldness of printing. Typical values for
21 the parameters of pulses 1,3 used by the inventor in
22 conducting his experiments, were 28 volts and 30 volts
23 for Al, V2, respectively; 60 microseconds for each
24 one of the pulse widths To and To; and fall times of
2 microseconds and 1 microsecond for pulses 1,3, respect
26 lively. The viscosity of the ink in this example was 12
27 centipoise. For the particular ink jet device operated
28 by the present inventor, the approximate diameter of
29 droplet 5 was 108 miss, for the second ink droplet 7 was
2.2 miss, and for the merged ink droplet 9 was 4.0 miss.
31 Other ink droplet diameters or volumes may be obtained
32 within a range via control of the amplitudes and fall
33 times of pulses 1 and 3, as previously mentioned.
34 Within a range, control of the size of ink
droplets ejected from the ink jet device can be con-
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1 trolled by adjusting the amplitudes and fall times of
2 the control pulses applied to the ink jet device. The
3 range of control of the volume of ink or ultimate ink
4 droplet size striking a recording media is substantially
extended via another embodiment of the present invention
6 for merging a plurality of ink droplets in flight or at the point of striking a recording media.
8 In Figure 11, the amplitudes Al, V2 of
9 pulses 11, 13, respectively, are shown to be equal
(typically 30 volts, for example). In this example, the
11 trailing edge of pulse 11 is about 10 microseconds
12 in fall time, whereas the trailing edge of pulse 13 has
13 a fall time of about 1 microsecond. Accordingly, the
14 ink droplet resulting from the application of pulse 11
to a selected transducer 204 will have a velocity that
16 is substantially slower than the velocity of the follow-
17 in ink droplet resulting from the application of pulse
18 3 to the transducer 204. Accordingly, only fall time
19 control is being used to adjust the velocities of the
ink droplets resulting from the application of pulses 1
21 and JO In this example, it is assumed that the second
22 ejected higher velocity ink droplet will merge with the
23 first ejected ink droplet while air-borne or at the
24 point of striking a recording media, as previously
described.
26 In Figure 12, a third control or firing pulse
27 15 has been added following the termination of pulse 13.
28 In one experiment with a given ink jet device, the
29 present inventor set the amplitude of pulses 11, 13, 15
all at 30 volts (+ Al, V2 and V3 all equal 30 volts),
31 with pulses 11, 13 and 15 typically having exponential
32 fall times of 10 microseconds, 5 microseconds and 1
33 microsecond, respectively; and pulse widths of 60
34 microseconds, 40 microseconds and 30 microseconds,
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1 respectively, for example. When applied to a selected
2 transducer 204 of the given ink jet device, pulse 11
3 caused a first ink droplet to be ejected, pulse 13
4 caused a second ink droplet of greater velocity than the
first to be ejected, and pulse 15 caused a third ink
droplet of even greater velocity to be ejected, whereby
7 all of these ink droplets were of such relative vowels-
8 ties that they merged in flight prior to striking a
g recording media. In this manner, an even greater range
of control can be obtained for adjusting the size of an
11 ink droplet in an ink jet system. Depending upon the
12 distance of the selected ink jet orifice 202 from
13 the recording medium, the relative speeds of movement of
14 the recording medium and/or the ink jet head, and the
design of the particular ink jet device, it is possible
16 that an even greater number of ink droplets can be
17 ejected at correspondingly greater velocities in order
18 to permit merger in flight or at the point of striking,
lo providing even greater control of ink droplet size from
one marking position to another on a recording medium.
21 Note that in practice, an ink droplet is not
22 ejected immediately after the termination of a portico-
23 far firing pulse. For example, if the pulses lo off Figure 6 are applied to a transducer 204 of the ink jet
device used by the present inventor in his experiments,
26 an ink droplet 5 is ejected 4 microseconds after the
27 termination of pulse 1, and the second ink droplet is
28 ejected 3 microseconds after the termination of pulse
29 3. The velocity of the first ejected ink droplet was
measured to be 3.5 meters per second and of the second
31 ejected ink droplet 5.0 meters per second.
32 With reference to Figure 13, the combination
33 of wave shapes shown cause the ink jet apparatus to emit
I two droplets which merge at a common point of striking
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1 on a print medium to produce dots varying in diameter
2 from 5.3 to 5.6 milliinches, for producing very bold
3 print. Typically, To, To, To, and To are 80, 4, 18 and
4 6 microseconds, respectively, with the amplitudes of
pulses 17 and 19 at 110 volts, and pulse 21 at about
6 73 volts, for producing the previous dot diameter range
7 on a particular type of paper (~ammermill XEROCOPY,
8 manufactured by Hammer mill Papers Co., Inc., Erie, PA),
g using an ink having a wax base. The type ox paper and
ink formulation affects the dot diameter in a given
11 application. Typically, the fall time of pulses 17 and
12 19 are 9 microseconds and 1.0 microseconds, respectively
13 Under the conditions indicated above, shortly after
I termination of pulse 17, a first droplet having a
velocity ranging from 8 to 10 meters per second was
16 produced. Also, the combination of pulses 19 and 21,
17 caused a second droplet to be produced about 2 micro-
18 seconds after the termination of pulse 19. Pulse 21
19 is not of sufficient amplitude to cause a third droplet
to be produced, but does cause the second droplet to
21 break off earlier from the orifice of the ink jet rota-
22 live to operating without pulse 21. Also, pulse 21
23 permits higher frequency operation of the ink jet
24 apparatus, and reduced ink bobbing problems at the
orifice. Using the pulse time periods and amplitudes
26 mentioned above, the velocity of the second droplet is
27 typically 6 to 8 meters per second. The slower velocity
28 of the second droplet relative to the first droplet is
29 caused by the presence of pulse 21. In this example,
by increasing the amplitude of pulse 19, the velocity
31 of the second droplet can be increased Also, by
32 varying the delay time To between the termination of
33 pulse 17 and initiation of pulse 19, the boldness can be
34 modulated within a range.
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1 In Figure 14, by using only pulse 17 to
2 operate the ink jet apparatus, dots having a diameter
3 range of 3.3 to 3.5 milliinches can be obtained. Such
4 dot diameters produce much less bold print relative to
operating the ink jet apparatus via the combination of
6 pulses 17, 19, and 21.
7 With reference to Figure 15, the combination
8 of pulses 17 and 21, as shown, operated the ink jet for
9 producing ink droplets having diameters ranging from 2.9
to 3.0 milliinches. This combination produces a very
11 light print
12 By using various combinations of the waveforms
13 of Figures 13, 14, and 15, desired shading can be
14 accomplished. Such shading is known as half-toning.
Note that with respect to Figure 13, that although the
16 second droplet is lower in velocity than the first
17 droplet, they are merged at a common point of impact as
18 the point medium.
19 As previously mentioned, depending upon the
relative speeds of the ink droplets, the ink jet head,
21 and the recording medium, the droplets can be made to
22 strike the recording medium at substantially the same
23 spot or point, and are thereby merged at that point for
I producing a desired dot size. Accordingly, the shapes
of the waveforms used to drive the ink jet apparatus can
26 be designed to cause successively produced ink droplets
27 to have successively higher or lower relative velocities,
28 or some combination thereof, so long as system timing
29 permits the droplets to strike the recording medium at
substantially the same point. In this manner, one
31 droplet or a plurality of ink droplets can be selective-
32 lye chosen for printing a dot of desired boldness at a
33 point on a recording medium
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1 The controller 261 can be provided via hard-
2 wired logic, or by a microprocessor programmed for
3 providing the necessary control functions, or by same
4 combination of the two, for example. Note that a
Wavetek Model 175 wave shape generator, manufactured by
6 Wavetek~ San Diego, California, was used by the present
7 inventor to obtain the wave shapes shown in Figures 6,
8 11, 12, 13, 14, and 15. In a practical system, a
g controller 261 would typically be designed for providing
the necessary wave shapes and functions, as previously
11 mentioned, for each particular application.
12 Although particular embodiments of the present
13 inventive method for operating an ink jet apparatus for
14 extending the range of control of the volume of ink or
ink droplet diameter striking a recording media at a
16 given point have been shown and described, other embody-
17 mints, which fall within the true spirit and scope of
18 the appended claims may occur to those of ordinary skill
19 in the art.
