Note: Descriptions are shown in the official language in which they were submitted.
Back~round~of the Invention
The-need for high quality printers with changeable
formats has been evidénced in recent years.~ Developments
~have proceeded with respect to ink jet technologies to
- ~ ~ answer this needr A technology that has been the subject of
~considerable development effort is the electrostatic pres-
sure system. The major types of electrostatic pressure
systems are the deflected type such as taught by Sweet, U.S.
20 Patent 3,596,275, and the binary type such as taught by
Sweet et al, U.S. Patent 3,373,437.
Both types of systems project;one or more streams o~
ink which are perturbated to break into streams of drops.
In the de~lected type of sy tem, each drop in a single
stream of ink drops is selectively charged at drop breakoff
~ ~ and passed through a uniform deflection field to impact
-; various locations on a recording medium in accordance with
the quantum of the-charge. Thus, by applying suitable
~ charging signals to the drops, a visible human-readable
printed record may be formed on the recording medium. The
binary type of system employs a pluralit~ of jets
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1 in one or more rows, selectively charc~inq dro~s at dro~ brea'f~off
2 with a single charge amplitude to be deflected by a constant
3 field to an ink drop catcher. The uncharqed drops continue
4 along the original jet stream paths to impact a recordina
medium. A visible human-readable printed record may thus be
6 formed by leaving uncharged those drops re~uired for printinq
7 during relative head to record medium motion~
8 Both types of electrostatic pressure ink jet systems
7 9 are highly dependent upon insuring that the drops receive only
the intended charge so that the drops are then deflected a
11 predetermined lateral distance. The drop formation by pertur-
12 bating the jet streams generally results in the formation of
13 both individual drops and at least temporary satellite drops
14 which subsequently merge with one of the adjacent drops. The
perturbation may be by varying the pressure of the ink prior
16 to ejection from a nozzle, by vibrating the nozzler or by other
17 suitable means. The perturbation introduces varicosities into
18 the stream filament which gradually increase to form drops and
19 to pinch off the ink stream between drops. The pinchinq off
is called drop breakoff.
. .
21 It has been observed that the satellites are formed
22 from a li~uid ligament portion of the ~et stream interconnecting
23 two large varicosities in the stream which become drops.
24 The ink employed in electrostatic ink jet is electrically
conductive. Drops are charged by exposing the drop stream to
26 a selected charge signal at an adjacent charae electrode at the
27 point of drop breakoff. The ink is grounded inside the head, but
28 the pinched portion of the stream becomes, in effect, an open
29 circuit as breakoff occurs such that the ink beyond the break-
off point retains a charge.
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1 Any ligament which becomes a satellite may first break
off at the front and temporarily remain a part of the stream
; or may first break off at the rear and temporarily be a part
of the drop it follows.
In the situations where breakoff occurs at rear of the
ligament first, the satellite will be charged by the same
signal as the drop it follows, whether the charge signal is
then switched prior to or subsequent to the breakoff at the
front of the ligament. If the satellite subsequently merges
with the preceding drop (forward merge), the resultant drop
will be properly charged. However, if the satellite merges
with the succeeding drop (rearward merge), a portion of the
charge intended for the preceding drop is transferred by the
satellite to the succeeding drop.
In the situations where breakoff first occurs at the
front of the ligament, the relative timing of rear breakoff
and charge voltage switching becomes important. If the
charge signal is switched prior to rear breakoff of the
ligament, the satellite will be charged differently than the
preceding drop. If the satellite subsequently forward
merges, charge transfer will occur. Charge transfer will
not occur if the satellite rearward merges. If the charge
signal is switched subsequent to rear breakoff of the liga-
ment, the satellite will then be charged the same as the
preceding drop. Thus, charge transfer will not occur upon
a forward merge of the satellite, and charge transfer will
occur upon a rearward merge of the satellite.
The aforementioned U.S. Patent 3,928,855 broadly
describes satellite control using asymmetric perturbation.
The satellite control results in drop generation without
satellite generation or with forward or rearward merge of
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1 satellites. However, the embodiment of the aforementioned
U.S. Patent 3,928,855 concerns magnetic ink jet which employs
magnetic deflection of ferrofluid drops. Hence, the drops
are not charged and charge transfer is not a concern. The
aforementioned U.S. Patent therefore describes no method or
apparatus specifically arranged for preventing charge
transfer.
Satellite control has also been a subject of Keur et al,
U.S. Patent 3,683,396, which claims a reduction of a satel-
lite problem by designing the nozzle structure to have a
mechanical resonance at the drop generation frequency. This
however specifically assumes that a ligament first breaking
off at the rear will forward merge and vice versa, a condi-
tion that is not assured.
Stauffer, U.S. Patent 3,334,351, also references
satellite control thorugh the use of two separate vibration
means acting in different directions to thereby impart a
rolling motion to the ink drops to induce a merging of any
satellites. The problem of possible charge transfer through
merger of satellites and drops is not considered, however.
The result of charge transfer is that the drops
receive or lose unintended charges and are therefore impro-
perly deflected by the constant deflection field. For
example, in the binary type of system, an "uncharged" drop
receiving some charge by charge transfer may be deflected
slightly by the deflection field and impact the recording
medium at an unintended location. A "charged" drop losing
some charge may be insufficiently deflected and impact a
gutter or drop catcher at an unintended point and splatter ~
or bounce off and impact the recording medium. The deflec- -
tion error may involve 25% of the total deflection distance.
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1 Summary of the Invention
2 It is therefore an object of -the present invention to
3 provide an improved method and apparatus for control of satellites
4 in a fluid jet stream.
In accordance with the present invention, there is
provided for a fluid jet head including an inlet for pressurized
7 fluid, a manifold cavity communicating with the inlet, and at
8 least one nozzle orifice communicating with the manifold cavity
9 for projecting a fluid stream therefrom, the improvement of an
electromechanical transducer for perturbatinq the fluid stream
11 to break the fluid stream into a stream of drops and an electric
12 signal generation means for supplying to the transaucer a funda-
13 mental sine wave at the drop repetition rate and a secona harmonic
14 of the fundamental at the selected amplitude and phase with
respect to the fundamental that causes ligaments forminq satel-
16 lite drops to first break from the fluid stream at the end
17 opposite the drop with which the satellite merqes. Thus, the
18 amplitude and phase are selected which cause the liqament
19 forming a forward merging satellite to break irst at the
end closest the fluid stream, and vice versa.
21 An advantage of the invention is that the control over
22 charge transfer is particularly useful in multi~orifice heaas
23 which have slightly differing charges is maintained larqely
24 independently of fine mechanical and fluid characteristic
considerations.
26 , The foregoing and other objects, features a~d advantages
27 of the invention will be ap~arent from the following more
28 particular description of preferred embodiments of the invention,
29 as illustrated in the accompanying drawinqs.
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1 Brief Descri~tion of the Drawinqs
2 FIGURE 1 is a frontal and partiall~ schematic view of
3 an exemplary electrostatic ink jet head and electrode assembly
4 for implementing the present invention;
FIGURE 2 is a cross section view through the electro-
6 static ink jet asse~ly of Figure 1;
7 FIGURE 3 is another cross section view through the
8 electrostatic ink jet assembly of Figure 1 with a partial.
¦ 9 schematic showing;
FIGURE 4 is an isometric view of the nozzle plate of
11 the electrostatic ink jet assembly of Fiqure 1;
12 FIGURE 5 is an isometric view of the charqe plate of
13 the electrostatic ink~jet assembly of Figure 1,
14 FIGURE 6 is a schematic circuit diaaram of an electric
signal generator in accordance with the present invention-
16 FIGURE 7 shows multiple fluid jet drop streams generated
17 with only the fundamental frequencyJ
lR FIGURE 8 shows multiple fluid jet drop streams generated
13 in accordance with the present invention;
FIGURE 9 is a cross-section view of a sinqle nozzle
21 ink jet head for implementing the present invention
22 FIGURE 10 shows single fluid jet drop streams generated
23 with only the fundamental frequency;
24 FIGURE 11 shows single fluid jet drop streams generated
~ 25 in accordance with the present invention;
26 FIGURE 12 is a schematic circuit diaaram of an alternative
27 electric signal generator in accordance with the present invention:
2~ FIGURE 13 is a detailed circuit diaqram of the attenuators
29 of Figure 12; and
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~ GURE 14 is a detailed circuit diaqram of the inteqrators
2 of Figure 12;
3 Description of the Preferred ~mbodiments
_ _ _ _ _ _ ... .. .. . . ..
4 Referring to Figures 1 throuqh 3, an ink jet head assembly
is shown for an eleckrostatic pressure ink jet s~stem of the
6 binary type. The head assembly includes a cavity plate 10 having
7 a manifold cavity 11 formed therein. Mounted wi~hin the manifold
8 are a piezoelectric crystal 12 and a nozzle plate 13. Referrinq
9 additionally to Figure 4, the nozzle plate includes two rows 14
ànd 15 of closely spaced ink jet orifices. The piezoelectric
11 crystal 12 is mounted on a mounting plate 16, which is clamped
12 to the cavity plate 10. A sealing ring 17 is mounted in slot
13 18 to provide a fluid seal of manifold 11 between cavity plate
14 10 and piezoelectric crystal 12. A charqe plate 20 is mounted
on cavity plate 10 and is provided with two rows of charge
16 electrodes 21 and 22, each charge electrode being aliqned with
17 a corresponding orifice of nozzle plate 13. The charge plate
18 is illustrated in detail in Figure 5. Also aligned wi-th orifices
19 14 and 15 and charge electrodes 21 and ~2 r are oPenings 23 and 24
in cavity plate 10. These openings allow passaqe of ink jet
21 streams from the orifice plate, ~s shown in Figure 5 r the charge
22 plate 20 is also provided with a series of conductive lands 25,
23 each of which individually connects a charge electrode to a sepa-
24 rate data source.
Referring to Figure 3, pressurized ink from fluid
26 supply system 26 is supplied via line 27 to connector 28 for
27 transmission through passage 29 in mounting block 16 and cavity
28 plate 10 to the interior of cavity 11. Passage 29 is sealed
29 at the juncture between mounting block 16 and cavity plate 10
~o by means of O-ring 33.
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1 The pressurized ink in manifold 11 is then ejected
2 through orifices 14 and 15 of nozzle plate 13. The piezoelectric
3 crystal driver 12 is then perturbated as will be explained to
vary the internal volume of cavity ll. This perturbates the
ink pressure, causing the ink jet streams emanating from ori~ices
14 and 15 to break into streams of uniformly sized drops. The
7 ink emanates from orifices 14 and 15 in the form of filaments
8 passing through openings 23 and 24 with the perturbations increas-
g ing as the distance from orifice plate 13 increases. At some
point within the charge electrodes 21 or 22, the drops break off
11 from the filaments. The ink in cavity 11 is grounded through
12 cavity plate lO to grounding terminal 34. Selected ones of the
13 charge electrodes 21 or 22 may be given a voltaqe signal, which
14 induces a corresponding signal in the filament within the corre-
sponding charge electrode. At the moment of drop breakoff, the
16 conductive path between the drop or drop-and-liqament and the
17 grounded stream is broken. The drop or drop-and-liqament thus
18 retains a charge corresponding to the applied volta~e of the
l9 charge electrode.
Uncharged drops proceed alona paths 30 and 31 to impact
21 a recording medium 32. A high voltaqe deflection plate 35 is
22 positioned intermediate the two drop flow paths 30 and 31.
23 Grounded deflection electrodes 37 and 38 are positioned respec-
24 tively on the opposite sides of drop paths 31 and 32 from hiqh
voltage deflection electrode 35. Deflection electrodes 37, 38
26 curve away from the drop paths and terminate in openin~s 41 and27 42 which communicate with cavities 43 and 44. The cavities
28 further communicate with tubes 45 and 46 which are connected to
29 a vacuum source 50 by, respectively, lines 52 and 53.
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1 Electrostatic fields established between electrode 35
2 and electrodes 37 and 38 thus cause charged drops to be deflected
3 from normal uncharged drop paths 30 and 31 to contact, respectively,
4 electrodes 37 and 38. Electrodes 37 and 38 therefore also serve
as gutters to intercept the drops which are deflected and not used
6 for recording pur~oses. The intercepted drops flow to the ends
7 of their respective electrodes and are drawn through the respec-
8 tive opening 41 or 42 into cavity 43 or 44 by the vacuum source
9 50~ Accumulated ink is drawn from cavity 43 or 44 through the
respective tube 45, 46 to the vacuum source 50. The ink may then
11 be recycled for subsequent recording use. In the example shown,
12 high voltage electrode 35 is hollow, havinq each side covered by
13 a fine mist screen 63. Thus, any ink mist is drawn throuqh the
14 screen and through a hollowed out screw 68 containing a passage
70 sealed from the atmosphere by O-ring seal 72. Passage 70
16 also communicates with tube 71 which is connected to vacuum
17 source 50 by line 73. Any ink mist is thus drawn therethrough
18 into the vacuum system 50.
19 Proper electrical considerations require that high voltage
electrode 35 be insulated from the grounded electrodes and
21 support structure by means of insulators. This is accomplishea
22 b~ forming mounting blocks 78 and 79 from an insulating material
23 and by connecting vacuum line 73 to the vacuum system 50 separately
24 from lines 52 and 53 to prevent a short circuit through the con-
ductive ink. Further, charge electrode plate 20 is made of an
26 insulating material, such as plastic, to prevent conduction be-
27 tween various ones of the lands 25 or to prevent conduction be-
28 tween various ones of the charge electrodes 21 and 22. The lands
29 may further be covered by an insulative and protective coating.
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1 Referrinq now in more detail to the ink iet perturhation,
2 piezoelectric driver 12 is held between cavity plate 10 and
3 mounting block 16 by the pressure of sealinq rinq 17. A cavity
4 80 is formed in mountinq block 16 behind the crvstal driver. A
wire 81 is connected between drive input 82 and the rear face of
6 the piezoelectric crystal driver 12. The front face of the crystal
7 driver is in contact with the electrically conductive ink in
8 cavity 11. The ink thus forms a conductive path between the face
9 of the crystal driver and mountinq block 10, which is qrounded at
terminal 34. Thus, any electrical perturbation a~pearinq at input
11 82 is applied between the rear face of the Piezoelectric crystal
12 driver 12 and the grounded front face thereof.
13 As previously discussed, perturhation of the ink, such
14 as pressure perturbation due to the chan~e in volume of ca~7itY 11
by e~pansion and contraction of piezoelectric crystal driver 12,
1~ introduces varicosities into the ink jet stream which ~radually
17 increase to form drops and to pinch off the ink stream hetween
18 drops. The pinching off is called drop break-off.
19 Referrinq to Fiqure 7, a pluralitv of ink jet streams are
shown emanating from a multi-orifice head. In the example shown,
21 the ink in the head is pressurized at approximately 22.5 psi and
22 issued from orifices of approximately 1 s~. mil area with an
23 80Khz perturbation rate. Each of the fluid filaments comprises
24 a series of ever larqer varicisities 90 and 91 connected by
ligaments 92. When a satellite 93 is formed, the liqament pinches
26 or breaks off generally first at one end and then at the other
27 end. As discussed extensively ahove, the particular se~uence of
28 front and rear breakoff and switchinq of the charae siqnal deter-
29 mines whether the satellite 93 has the same charae as the preced-
ing drop 94 or whether it has the same charge as the succeedinq
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l drop 91. Whether or not charqe transfer oCCUr.C, then de~ends upon
2 whether the satellite 93 forward meraes with drop 9~ or whether
3 it rearward merqes with droP 91.
4 In the example of Fiqure 7, the timina of the front and
rear breakoff of liqament 96 from drops 97 an~ 9R to form
6 satellite 99 is considerahly different from the timina o the
7 front and rear breakoff of liqaments g2 from droPs 90 and 91 to
8 form satellites 9~. The timinq of the charae sianals is the
9 same for each stream, howe~rer. Thus, some satellites mav have
the same charge as the succeedinq drop. Charqe transfer may
ll therefore occur in some, but not all, of the streams if all
12 the satellites rearward merqe or if all the satellites forward
13 mer~e.
14 Char~e transfer causes droPs to be incorrectly charqed
and incorrectly deflected by the constant electrostatic deflec-
16 tion field.
17 Referrinq to Fiqure 2, drops intende~ to be uncharaed
18 which acquire some charqe throuqh the effect of charae transfer
l9 will not proceed alonq ~aths 3~ or 31 directlv to the recor~ina
medium 32, but will be deflecte~ outwardlY t~A7ard the aroun~e~
21 deflection plates 37 and 38. By beinq displaced in o~osite
22 directions to incorrectly imPact the recordina medium 32, the
23 drops adversely effect print quality. Charqed drops which lose
24 a portion of their charqe throuqh charqe transfer but ac~uire a
correspondinq amount of uncharqed fluid from the merqina satellite.
26 retain the proper mass but have an im~roper charae. Such drops
27 are deflected by the constant deflection fiel~ towards the grounded
28 deflection plates 37 and 38 by a smaller amount than oriainallv
29 intended. Rather than beinq properly intercepted by electrodes
37 and 38 which serve as qutter~s, the droPs may splatter or bounce
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1 off to partially or whol.ly impact recordinq me-li.um 32 to ~urther
2 have a deleterious effect upon the print quality.
3 Mer~er of ligaments 92 or 96 without charae tran.sfer is
4 accomplished by ap~lyina the fundamental and a small amount o:F
second harmonic thereof as the drive siqnal to input 82 of the
6 perturbation means. A preferred emhodiment of circuitrv for ac-
7 complishin~ this function is illustrated in Fiqure 6. An oscil-
8 lator 110 o~erates at 32 times the ~undamental fre~uenc~ of lf,
9 which may comprise 100KHz. The oscillator out~ut is su~plied
to the input of counter 111 and to AN~ inverter 112. Counter
11 111 is a four-position recyclable, binarv counter. The outPuts
12 from the four staqes are supplied on cable 114 to excluslve OR
13 115. The output of the counter on cable 114 thus continuallY
14 cyclically counts from 0 to 15, recvclinq at the 2f rate. ~ire
118 is connected to the fourth staae of the counter 111. The
16 fourth stage goes on at the count of 8 and qoes off when the
17 counter recycles to zero. Thus, the counter produces a s~uaxe
18 wave of frequency 2f on line 118, which is su~lie~ to attenuator
19 120.
Attenuator 120 is preset to control the am~litude level
21 of the 2f square wave. The attenuate~ s~uare wave is su~lied
22 on line 121 to filter 122. The filter is extremely narrow
23 and centered on the second harmonic fre~uency so a.s to shape
24 the square wave from attenuator 120 into a ~ine wave~ The
second harmonic sine wave is su~plied on line 124 to analoa
26 adder or summer 125.
27 ~xclusive OR circuitr~ 115 com~rises four se~arate
28 exclusive OR circuits, each of which is connected to one of
29 the wires in cable 114 and a corresPondin~ one of the wire.s
of cable 127. Circuit 128 comprises four 1 or 0 preset input.s
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1 to be supplied on four lines 127. These pre.set inPuts rePresent
a binary count whose variance Erom the binary count of 8 is the
; 3 phase variance between the lf freauency and the 2f sianal on
4 line 118. Thus, each binary count difference rePresents 1/16th
of a 180 phase shift, with preset inputs less than 8 represent~
~ 6 ing a negative shift of the 2f freauency with respect to the lf
: 7 frequency, and preset inputs qreater than 8 rePreSentina a po.si-
8 tive phase shift of the 2f fre~uency with resPect to lf. Thus,
9 when counter 111 reaches the count represented ~Y the preset inPut.s
of circuitry 128, exclusive OR circuits 115 all pro~7i~e positi~Te
11 inputs on cable 130 to and inverter 112~ Simultaneously, oscillator
12 110 provides an input siqnal at input 131 of AN~ inverter 112.
13 AND inverter 112 therefore provides neqative goina outPUt pulse on
14 line 133 to flip-flop 134 for the half-cycle duration of oscillator
110. At the next cycle of oscillator 110, counter 111 moves to the
16 next binary state to terminate the output of at least one of the
17 exclusive OR's of circuitry 115. Thus, n-, further output is
18 supplied from A~D inverter 112 until counter 111 has made another
19 complete cycle to the count of preset inPuts 128~ Flip-flop 134
changes state in resPonse to each input pulse aPPearina on line
21 133, thereby underqoin~ a complete cvcle for every t~7O cycles
22 of counter 111. The flip-flop therefore serves as a fre~uencv
23 divider to produce a fre~uencv one-half that o the 2f fre~uency
24 on line 118~ Flip-flop 134 may be initially set in a 180 Pha.se
~ 25 shift from that of the 2f freauency by the original initialization
26 setting of the flip-floP.
27 This lf frequency output from flip-flop 134 is supPlied
28 on line 138 to attenuator 140. Attenuator 140 sets the level
29 of the lf square wave output of flip-floP 134 at the desired
level, ~hich is substantially greater than the 2f output of
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1 attenuator 120. The output of attenuator 140 sup~lled on line
2 141 to filter 142. Filter 142 also has very narrow freauency
3 pass characteristics to convert the sauare wave siqnal on line
4 141 to a sine wave on line 144. Analoq adder 125 therefore
combines the sine waves appearinq on lines 144 and 124 to produce
6 the combined fundamental and second harmonic comhined drive sianal
7 on line 150. The combined drive siqnal on line 150 is then
8 supplied to drive input 82 in Fiqure 2 to o~erate the piezoelect-
9 ric crystal driver 12 in accordance with the su~plied sianals.
Alternatively, analog adder 125 may also include an am~lifier so
11 as to provide an input siqnal to terminal 82 which is pro~erlv
12 matched to the specific driver.
13 An example of multiple ink jet streams driven both with
14 a fundamental and a second harmonic com~risinq an amplitude of 1
volt as compared to 8~ volts for the fundamental siqnal, and at
16 a phase shift of 158 with respect to the fundamental are shown
17 in Figure 8. When controlled in this manner, each liaament 160
18 first breaks off from the succeedina drop 161 to thereby as~ume
19 the same charqe as the precedinq drop 162, and then forward merqes
with the same preceding drop.
21 Therefore, whether or not a momentary satellite is formed,
22 the ligament 160 forward meraes with the same dro~ with wwhich it
23 was associated ~Ihen the charqe was acquired at charqe electxodes
24 21 or 22 in Fiqures 1 and 2. As the result of use of the subject
inventionj no charqe transfer cccurs.
26 The invention is equally aavantaaeous in sinale nozzle
27 heads as it is in multi-orifice heads of Fiaures 1-5. Sinqle
28 nozzle heads are most often used in deflected tvpe of electro-
29 static pressure fluid jet systems, such as tauqht by Sweet,
above. The adverse effects of charqe transfer may be even more
SA974044 -14-
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important in this type of system which often finally controls
2 the charging of individual droPs by separatinq dro~s that im~act
3 adjacent spots by only three volts at the charae electro~e while
4 charging drops over a range greater than 250 volts. In such
systems, drops having no charqe are quttered whereas the variahly
6 charged drops are swept in a sinqle column to form various part.s
7 of the printed characters within the column. Thus, charqe trans-
8 fer from an uncharged to charqed dro~ or vice versa can very
g seriously affect placement of the drop on the recor~ina medium.
An example of a sinqle nozzle ink jet head is illustrated
11 in Figure 9. The head includes a head body 170 with a cavity 171
12 formed therein. A jewel nozzle 172 havina an orifice 173 is
13 cemeted to the face of the head body 170 overlayina and sealina
14 cavity 171~ A piezoelectric driver 174 is secured aqàinst mounting
block 175 and within the cavity. An O-rinq 17~ provides a fluid
16 seal of the cavity between the piezoelectric crystal driver 174
17 and head body 170. Pressurized fluid is supplied from a pressure
18 source to input 177 and transmitted by passaae 178 into cavity
19 171, for e~ection through orifice 173 of nozz~e 172. Pin 179
provides a means for electrically connectinq the rear of piezo-
21 electric crystal driver 174 to the piezoelectric drive line 15n
22 of the driving circuit. The other si~e of the piezoelectric
23 crystal driver is grounded through the ink in cavity 171 and
24 head body 170 to a groundinq point, such as post 180.
Therefore, application of the drive siqnal from the
26 circuitry of Figure 6 to pin 179 perturbates piezoelectric crystal
27 driver 174, 204, which further perturbates the pressure of the
28 fluid in cavity 171 to produce ink jet streams such as shown
29 in Figure 11.
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1 As previously discussed, perturhation of the ink, such
2 as pressure perturbation due to the chance in volume of cavity 171
3 by expansion and contraction of piezoelectric crystal driver 172,
4 introduces varicosities into the ink jet stream which ~radually
increase to form drops and to pinch off the ink stream between
6 drops. The pinching off is called drop breakoff.
7 Referring to Fiaure 10, the fluid filament perturbated
by only the fundamental comprises a series of even larger vari-
9 cosities 190 and 191 connected by ligaments 192. The portion
of a ligament connectinq it to the adjacent drops ultimately
11 pinches off generally first at one end and then at the other end
12 to form a satellite drop 194. One of the charqe electro~es may
13 expose the drop stream to a selected charae sianal at the instant
14 of drop breakoff. The ink is grounded by h~ad hody 170 ! but the
1~ pinched portion of the stream brakes the conductive path as
16 breakoff occurs s~lch that the ink beyond the breakoff point re-
17 tains a charge. Thus, liqament 192 first breaks off from the
18 preceding drop 193 and secondly from the succeeding drop 191.
19 Thus, satellite 194 and drop 193 may both carry a charqe based
on the same charge signal, dependinq uPon the timinq of the charqe
21 signal. I~ satellite 194 merqes with drop 143 prior to enterinq
22 the deflection field formed by deflection plates, no charqe trans-
23 fer occurs and the resultant merged drop is pro~erly deflected.
24 Ligament 197 also breaks off first with respect to the
precedinq drop 198 and secondly from the succeedina drop 199 to
26 form satellite 200. The satellite 200 and the succeedina drop
27 198 may thus be similarly charqed, aqain dependina uPon the
28 timing of the charge siqnal. The satellite, however, does not
29 rearwardly merge into the succeedinq drop, but rather merqes
with preceding drop 201. The charqe, or lack of charqe, intended
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1 for succeedin~ drop 198 is therefore -transferred to precedi.n~ drop
2 201. Both drops 201 and 198 will thérefore be incorrectly char~ed
3 and incorrectly deflected by the constant electrostatic deflec-
4 tion field.
Figure 11 illustra-tes examples of ink jet streams
6 corresponding to those of Fiqure 10, but driven both with a
7 fundamental and a second harmonic comprising an amplitude 3 per-
8 cent that of the fundamental signal and at a phase shift of 180
9 with respect to the fundamental. When controlled in this manner,
each ligament 210-212 first breaks off from the succeedinq drop
11 220-221 to thereby assume the same charqe as the precedin~ drop
12 230-232, and then forward merqes with the same precedinq drop.
13 Therefore, each momentary satellite forward merqes with
14 the same drop with which it was associated when the charae was
acquired. As the result of use of the subject invention, no
16 charge transfer occurs.
17 Another way of statinq the situation is that the dro~
1~ and the ligament which merges with the drop break off from the
19 stream filament as a unit.
An alternative circuit to that shown in Fiqure 6 is
21 illustrated in Figure 12. The circuit of Figure 12 differs from
22 that of Figure 6 primarily by beinq adjustable to allow tests to
23 be run on a specific head to determine the optimum amplitudes of
24 the fundamental and second harmonics and the optimum relative
phase. A substantial portion of the circuitry in Figure 12 is,
26 however, identical to that in Fiqure 6 and therefore retains the
27 same number as in Fiqure 6. Referrinq specifically to the dif-
28 ferences, preset inputs 128 of Figure 6 are rePlaced by switches
29 251-254 in Figure 12. These switches comprise the various binary
counts and are individually settable in the closed position to
SA974~44 -17-
~8~Z,~2
1 connect with ground terminal 255 or -to the open position, repre-
2 senting respectively a binary 1 or a 0. Any oE 16 phase anqles
3 may therefore be set by the binary number represented by the
4 settings of the switches 251-254. The outputs of the switches
are supplied on wires representinq cable 127 and supplied to
6 exclusive OR circuit 115. Operation of the oscillator 110,
7 counter 111, exclusive OR 150 and inverter 112, and fli~-flop
8 135 are precisely the same as discussed with respect to Fiqure 6.
9 In Figure 12, lines 118 and 138 are sup~lied to attenuators
258 and 259 respectively. Other inputs to the attenuators are
11 supplied by switches 260 and 261 respectively. The attenuators
12 158 and 159 are identical and are illustrated in detail in Fiqure
13 13. The attenuators include a potentiometer 262 for individually
14 adjusting the attenuation of the input signal at input 118 or 138.
Switch 260 or 261 may be selectively closed to kill the output
16 signal entirely. The output siqnal is supplied on lines 264 or
17 265 to differential amplifier 267 for transmission on lines 268
18 to integrator 269. These circuits together convert the current
19 input on lines 264, 265 to a voltaqe si~nal and convert the re-
sultant signal to a combined and summed set of sine waves at the
21 fundamental and second harmonic freauencies to be suP~lied on
22 drive output 150. Differential amplifier 267 and inteqrator
23 269 are illustrated in specific detail in Fiqure 14.
24 In tests conducted with piezoelectric drivers and various
types of fluid jet heads, charge transfer and satellite generation
26 have been controlled through application of a second harmonic
27 frequency of amplitudes ranginq between 1% and 10% of the funda-
28 mental frequency and at various phase anqles ranging from 90 to
29 180 with respect to the fundamental. The variations in phase
SA974044 -18-
~ZZ~3Z
1 angle are attributed to the differing characteristics of the
2 specific heads.
3 The ranges in phase and amplitude are largely the result
4 of various head designs and resonances, with each head apparently
having an experimentally obtained optimum. In some heads the
6 invention also works where a rearward merger takes place. In
7 such cases, the optimum point is in the situation where the
8 ligament and succeeding drop break off from the filament as a
g unit. This means that the succeeding drop breaks from the front
of the following ligament and either the leadinq liqament does
11 not form a temporary satellite, or the leading liqament breaks
12 from the succeeding drop only after that drop has broken from
13 the stream filament.
14 While the invention has been particularly shown and
described with reference to preferred embodiments thereof, it
16 will be understood by those skilled in the art that the fore-
17 going and other changes in form and details may be made therein
18 without departing from the spirit and scope of the invention.
19 What is claimed is:
21
22
23
24
26
27
28
29
SA974044 -19-
