Note: Descriptions are shown in the official language in which they were submitted.
~224~
MDH 00l P2 -l-
FLUID JET PRI~T HEAD AND METHOD OF MAKING
Background of_the Invention
The present application relates to fluid jet
print heads and, more particularly, to a stimulation
arrangement of the type which produces pressure
varicosities in the individual fluid jets, resulting in
substantially uniform breakup of the jets into streams of
drops.
Ink jet printers~ incorporating fluid jet print
heads, are known which have an orifice structure defining
a plurality of orifices. The orifices receive an
electrically conductive recording fluid, such as for
e~ample a water-base ink, from a pressurized fluid supply
manifold and eject the fluid in one or more rows of
parallel streams. As the streams break up into drops, the
drops are selectively cnarged and deflected, with some of
the drops being deposited on a print receiving medium and
the balance of the drops being caught by an appropriate
catcher structure.
Charging of the drops is accomplished by
selectively applying charging voltages to charge
electrodes positioned near each of the streams. The fluid
flowing through each orifice emerges as a fluid filament.
Drops break away from the tip of the fluid filament and
carry charges related to the voltage of the associated
charge electrode at the instant of drop formation. Each
drop is then subjected to an electrostatic field which
deflects the drop by a distance proportional to the
magnitude of the charge which it carries. Drops may thus
be deflected to one or more print positions and, when a
drop is not to be deposited on the print receiving medium,
deflected to an adjacent catcher structure.
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~d~
MDH OOl P2 -2-
With print heads of the type used in ink jet
printers, it is necessary to control drop formation since
if left to natural stimulating disturbances, ~he fluid
filaments would break up erratically into drops of various
sizes at irregular intervals. Such erratic drop formation
would prevent proper charging and deflection of the
drops. Accordingly, it is customary to apply a
stimulating disturbance to all of the fluid streams to
produce jets of uniformly sized and reg~larly spaced drops.
Various types of stimulation arrangements have
been suggested. U.S. patent No. 3/739~393~ issued June
12, 1973, to Lyon et al, discloses an ink jet print head
in which the fluid orifices are defined by a thin,
relatively flexible orifice plate. A piezoelectric
transducer contacts the orifice plate at one end and
produces a series of bending waves which travel
longitudinally along the plate. Dampers at each end of
the orifice plate dampen the traveling waves and prevent
wave reflection. The bending waves in the orifice plate
produce an oscillatory movement of the orifices which, in
turn, causes pressure varicosities in the fluid filaments
emerging from the orifices. ~s a consequence, the fluid
filaments break up into relatively uniform jet drop
streams.
It will be appreciated that break up of the drop
streams is nonsynchronous in a print head employing
traveling wave stimulation. The print head, therefore,
cannot be operated at its maximum printing resolution
since the precise time of drop formation for each stream
will be unknown and charge voltages must be supplied ~o
the charge electrodes for sufficient time periods to
MDH 001 P2 -3-
insure tnat they result in appropriate charging of at
least one drop. As a consequence more than one drop is
usually charged in succession and partially charged drops,
formed during charge voltage transition periods, are
commonly formed.
One solution to these problems is to apply drop
stimulating disturbances to all filaments in synchronism.
If all of the jets have the same diameter ana velocity,
and stimulating disturbances are applied to the jets
simultaneously, all filaments will generate drops in
synchronism. Such synchronized drop generation greatly
simplifies the application of charge signals to the charge
electrodes, because the timing for each of the jets is
precisely the same. Additionally, charge voltage
transitions can be timed to occur between drop
forma-tions. The number of partially charged drops is
therefore substantially reduced. Providing such preclse
synchronized stimulation to all of the jet drop streams in
a long row of streams is not a simple matter, however.
U.S. patent No. 4,095,232, issued June 13, 1978,
to Cha, discloses a print head in which stimulation is
provided by flexing a pressure plate mounted on the
opposite side of the fluid manifold Erom the orifice
plate. A plurality of piezoelectric transducers are
positioned along the length of the pressure plate on the
opposite side thereof from the manifold. The transducers
are stimulated in unison so as to produce oscillation of
the pressure plate which is in phase along its entire
length. This approach requires a substantial amount of
mounting structure for the transducers and, additionally,
requires that all of the transducers operate in precise
MDH 001 P2 -4- ~
synchronization and at substantially the same amplitude.
If one or more of the transducers operate slightly off
frequency, or at a lower amplitude, i~ is possible that
traveling waves may be produced which move along the
pressure plate, causing nonsynchronous drop generationO
Additionally, the stimulation amplitude may vary along the
length of the print head, producing fluid filaments of
differing lengths.
U.S. patent No. 4,138,687, issued February 6,
1979, to Cha et al, discloses a print head having an
elongated piston mounted in the upper portion of the fluid
manifold. A number of piezoelectric transducers are
mounted along the length of the piston to produce vertical
movement thereof and stimulation of fluid jets. The
piston has a plurality of transverse slits along its
length which are alternately cut from opposite upper and
lower surfaces. The slits are more than one-half of the
height of the piston such that there are no horizontal
planes through the piston which are not cut by at least
some o~ the slits~ These slits minimize wave propagation
along the piston which would otherwise cause deterioration
of the stimulation process.
It will be appreciated that prior art mounting
structures for piezoelectric transducers used in a print
head having a stimulation piston or pressure plate
arrangement are relatively complicated and add
substantially to ~he cost, size, and weight of the print
head. It will be appreciated, also, that multiple
transducer stimulators in the prior art have been subject
to operating difficulties when the amplitudes of the
vibrations produced by the transducers have not been
substantially uniform.
MDH OOl P2 -5-
Accordingly, it is seen that there is a need for
a stimulation arrangement not having the limitations
associated with prior art fluid jet stimulation devices.
Summary of the Invention
A fluid jet print head for producing a plurality
of jet drop streams of fluid includes a manifold means
defining an elongated cavity therein, and an orifice plate
defining a plurality of orifices arranged in at least one
row. The orifice plate is mounted on the manifold means
such that the orifices communicate with the cavity and the
row of orifices extends in a direction generally parallel
to the direction of elonga~ion of the cavityO A
stimulator means is mounted in the cavity and is spaced
from the orifice plate so as to define a fluid reservoir
therebetween. The stimulator means includes a plurality
of piezoelectric means which, when electrically excited,
produce pressure waves of substantially uniform phase
front which travel through fluid in the reservoir toward
the orifice plate and which cause break up into jet drop
streams of fluid flowing through the orifices. The
stimulator means further includes acoustic isolation
material surrounding the plurality of piezoelectric means
and providing a means of supporting the piezoelectric
means in the cavity. ~ave propagation along the
stimulation means in a direction parallel to the row of
orifices is thereby prevented. The acoustic isolation
material may comprise a polyurethane foam material.
The piezoelectric means may include an elonsated
transducer defining a plurality of slots, extending
alternately from opposite sides of the transducer
partially therethrough and being substantially
~2~ 0
MDH 001 P2 -6-
perpendicular to said row of orifices. The stimulator
means may further include electrode means in contact wi~h
the side of the piezoelectric means adjacent the reservoir
and with the opposite side of the piezoelectric means.
The print head may further include electrical signal
generator means connected to the electrode means, whereby
a fluctuating electrical signal is impressed across the
piezoelectrc means, producing waves of a corresponding
frequency in the fluid in the reservoir.
The stimulator means may further include sealing
means extending across each slot adjacent the reservoir so
as to seal the slots and prevent flow of fluid from the
reservoir into the slots. The sealing means may further
extend across the surface of said acoustic isolation
material on the side thereof adjacent said reservoir,
whereby the sealing means prevents fluid in the reservoir
from contacting the acoustic isolation material.
The stimulator means may include electrode means
mounted on opposing surfaces of the elongated transducer.
The opposing surfaces extend along the length of the
transducer and are substantially normal to the orifice
plate. An electrical signal generator means may be
connected between the electrode means, whereby a
fluctuating electrical signal is impressed across the
piezoelectric means, producing waves of a corresponding
frequency in the fluid in the reservoir. The plurality of
piezoelectric means may be potted into place in the cavity
by the acoustical isolation material. The acoustical
isolation material covers the electrode means such that
the electrode means are electrically isolated from fluid
in the reservoir.
MDH OOl P2 -7~
The plurality of piezoelectric means may include
a plurality of transducers arranged in at least one
transducer row and extending in a direction substantially
parallel to the row of orifices. The transducers are
uniformly spaced apart and acoustic isolation material
surrounds each of the transducers on the sides thereof
generally perpendicular to the orifice plate, whereby the
transducers are acoustically isolated. The stimulator
means may include electrode means in contact with the side
of each of the transducers adjacent the reservoir and with
the opposite side thereof. Alternatively, the stimulator
means may include electrode means mounted on opposing
surfaces of each of the transducers, with the opposing
surfaces being substantially normal to the orifice plate.
The piezoelectric means may include a plurality
of transducers arranged in two parallel transducer rows
which extend in a direction substantially parallel to the
row of orifices.
The fluid jet print head may further include
electrical signal generator means for electrically
exciting the plurality of piezoelectric means. The
generator means has means for providing an alternating
drive signal, and attenuator means for supplying the
alternating drive signal to the piezoelectric means to
produce proper break up of the jet drop streams along the
length of the print head. The attenuator means may
comprise a plurality of capacitors. Each of the
capacitors electrically connects the means for providing
an alternating drive signal to an associated one of the
piezoelectric means.
MDH OOl P2 -8- ~2~
A method of making an elongated piezoelectric
stimulator according to the present invention comprises
the steps of:
(a) plating a sheet o piezoelectric material on
opposing surfaces with an electrically conductive
material,
(b) cutting a strip having the desired length
and height for the transducer, and
(c) cutting slots alternately from opposite,
unplated sides of the strip, with the slots being spaced
uniformly along the length of the strip.
A method of electrically tuning the stimulator of
a fluid jet print head constructed according to the
present invention includes the steps of:
(a) applying a drive signal to all of the
piezoelectric means,
(b) monitoring the fluid filament length of a
jet closest to the first of the piezoelectric means while
adjusting the current supplied thereto in order to
determine the optimum current level to be applied to the
first of said piezoelectric means,
(c) repeating step (b) for each of the remaining
piezoelectric means, and
(d) connecting impedances of appropriate
amplitudes in series with each of the piezoelectric means
such that the piezoelectric means may be driven by a
single drive signal source with each of the piezoelectric
means receiving its respective optimum current level.
The step of connecting impedances may include the
step of connecting a capacitor of a desired impedance in
series with each of said piezoelectric means.
MDH OOl P2 -9-
Accordingly, it is an object of the present
invention to provide a fluid jet print head having a
stimulation arrangement including a plurality of
piezoelectric means mounted by acoustic isolation
material; to provide such a print head in which the
plurality of piezoelectric means are defined by an
elongated transducer; to provide such a print head in
which the transducer defines a plurality of slots
extending alternately from opposite sides of the
transducer partially therethrough and being substantially
perpendicular to the row of orifices; to provide such a
print head in which an electrical signal generator may be
connected between a plurality of electrodes on the
transducer; to provide such a print head in which the
plurality of piezoelectric means includes a plurality of
transducers arranged in at least one transducer row
extending in a direction substantially parallel to the row
of orifices and in which the acoustic isolation material
surrounds each of the transducers on the sides thereof
generally perpendicular to the orifice plate and the fluid
within the print head reservoir, to provide such a print
head in which sealing material in each of the slots
prevents fluid flow from the reservoir into the slots; to
provide such a print head in which the drive circuitry
supplying driving signals to the plurality of
piezoelectric means includes means for attenuating the
drive signal supplied to each piezoelectric means to
optimize operation thereof; to provide a method for
determining the attenuation required for each such
piezoelectric means and the component values of impedances
which, connected in series with the piezoelectric means
MDH 001 P2 -10~ B~
provide such attenuation; and to provide such a print head
in which the sealing material separates the reservoir from
the transducer means.
Other objects and advantages of the invention
will be apparent from the following description, the
accompanying drawings and the appended claims.
Brief Description of the Drawings
Fig. 1 is an exploded perspective view,
illustrating a first embodiment of the present invention;
Fig. 2 is a sectional view taken generally along
line 2-2 in Fig. l;
Fig. 3 is an enlarged partial sectional view,
similar to Fig. 2;
Fig. 4 is a perspective view of the piezoelectric
means incorporated in the first embodiment of the
invention;
Fig. 5 is a sectional view, similar to Fig. 2,
illustrating a second embodiment of the present invention;
Fig. 6 is a perspective view of the piezoelectric
means incorporated in the second embodiment of the
invention;
Fig. 7 is a perspective view, with portions
broken away, of stimulator means incorporated in a third
embodiment of the invention;
Fig. ~ is a perspective view, similar to Fig. 7,
illustrating a variation of the stimulator means which may
be used in the third embodiment;
Fig 9 is a front view of the piezoelectric means
incorporated in a further embodiment of the invention;
Fig. 10 is a plan view of the piezoelectric means
of Fig. 9; and
Fig. 11 is an electrical schematic diagram
illustrating tuning of the piezoelectric means.
MDH 001 P2 ~ 2Z~ ~
Detailed Description of the Prefer~ed Embodiments
The present invention relates to a fluid jet
print head, such as may be utilized in an ink ~et printing
system for producing a plurality of jet drop streams, and
more particularly to a print head including an improved
drop stimulation arrangement. As seen in Figs. 1 and 2,
the fluid jet print head has a manifold means, including
upper manifold portion 10 and lower manifold portion 12,
which defines an elongated cavity 14 therein. Manifold
10 portions 10 and 12 are held together by bolts 16,
compressing a sealing ring 18 therebetween which provides
a fluid-tight seal.
The print head further includes an orifice plate
20 which defines a plurality of orifices 22 which are
arranged in at least one relatively long row. Orifice
plate 20 is mounted on the bottom of manifold portion 12
by an adhesive or, alternatively, by soldering or other
appropriate means. The orifices 22 communicate with
cavity 14 and the row of orifices extends generally
parallel to the direction of elongation of the cavity 14.
A stimulator means 24 is mounted in cavity 14
and, as shown in Figs. 2 and 3, is spaced from orifice
plate 20 by a distance D of approximately 1/2 wavelength
of the stimulation waves through the fluid used by the
print head. The stimulator 24 and the orifice plate 20
define a fluid reservoir 26 therebetween. Stimulator
means 24 includes a plurality of piezoelectric means which
are defined by elongated transducer 27 and which lengthen
and contract vertically when electrically excited with an
oscillating signal. The stimulator means further includes
MDH 001 P2 -12- ~2~
acoustic isolation material 28 which surrounds the
piezoelectric means and provides a means of supporting the
piezoelectric means in the cavity 14.
The oscillatory movement of the bottom surfaces
of the piezoelectric means produces pressure waves of
substantially uniform phase front in the fluid in the
reservoir 26. These waves travel downward through the
fluid and are coupled to the fluid filaments flowing
through the orifices 22 causing them to break up into jet
drop streams. The transducer 27, constructed of a ceramic
piezoelectric material, changes dimension when subjected
to an appropriate voltage differential. The transducer 27
vibra~es vertically in response to an oscilla~ing
excitation signal produced by an electrical signal
generator 29 at a frequency corr~sponding to the output
frequency of the generator.
As seen in Fig. 2, the fluid filaments break up
into a series of relatively uniform, evenly spaced drops
31. As a result of the substantially uniform phase front
of the waves in the f luid, the filament stimulation is
synchroni~ed and drops in each of the jet drop streams are
produced in synchronization. In a known manner, these
drops may be electrically charged by means o~ charge
electrodes, adjacent the tips of the fluid filaments, to
which charge voltages are applied during the formation of
the drops. Since the drops are formed in synchronization,
the charge voltages may be applied to the electrodes in
synchronization, producing controlled, precise charging of
individual drops in the streams. After charging, drops 31
are deflected by an electrical field or fields to a
catcher or, alternately, to a print receiving medium~ as
is known in the art.
MDH OOl P2 -l3- ~2~
Fluid is supplied to the reservoir 26 via fluid
supply inlet 32 which, as shown in Fig. 2, extends
downward through upper manifold portion lO and a support
plate 33, attached to manifold portion lO by bolts 34.
Inlet 32 terminates in a channel 36 which extends
substantially the entire length of the reservoir 26. A
similar channel 3~ communicates with the reservoir 26 and
a fluid outlet 40 and provides a means of removing fluid
from the print head or during cross flushing at shutdown.
As seen in Fig. 4, the elongated transducer 27
defines a plurality of slots 42 which extend alternately
from opposite sides of the transducer partially
therethrough so as to define the plurality of
piezoelectric means. Each of the slots is substantially
perpendicular to the row of orifices when the transducer
is positioned in cavity 14, as shown in Fig. l. Slots ~2
may be formed by cutting a block of piezoelectric
material, leaving approximately .05 inch between the end
of the slot and the opposite face of the block. In one
transducer constructed according to the present invention,
slots cut from the same side were spaced apart by a
distance of approximately .25 inches.
Slots 42 reduce substantially the possibility of
wave movement or bending along the length of the
transducer 27. Additionally, the acoustic isolation
material, which may for example be a polyurethane foam
material, provides a means of supporting the piezoelectric
transducer so that vibrations are not coupled to the
manifold portion lO. Thus, unwanted wave transmission
through the transducer or associated support structure is
minimized, and generally undistorted downward traveling
waves are produced in the fluid in reservoir 26.
MDH OOl P2 -14-
In order to provide for electrical stimulation of
the plurality of piezoelectric means the electrical signal
generator 29 is coupled by means of conductor 44 to a
plurality of electrodes 46. Each electrode 46 is
associated with and provides a means of energizing a
respective one of the piezoelectric means, i.e. that
section of the transducer defining the particular
piezoelectric means. As shown in Fig. 4, the electrodes
46 may be connected in parallel by conductors 48 which
bridge the slots 42. These electrodes may be plated onto
the piezoelectric material prior to cutting slots ~2.
Conductor 50 provides a means of electrically
connecting the generator 28 to conductive fluid in
reservoir 26 via electrically conductive manifold portion
12. The fluid contacts the surfaces 30 on the bottom of
the transducer and efEectively acts as a second set of
electrodes, opposing electrodes 46. The fluctuating
potential difference between electrodes 46 and the fluid
contacting the opposite side of the transducer produces
the desired fluctuating voltage potential across the
transducer, causing the piezoelectric means to vibrate
vertically.
As shown in Figs. l and 2, the acoustical
isolation material7 which is of low density, surrounds the
transducer 27, effectively isolating it from manifold
portion lO. Further, the material 28 pots the transducer
27 into position in the cavity 14, since it is bonded to
both the transducer 27 and the manifold portion lO. A
sealing means, such as a room-temperature vulcanized
silicone 53, extends across and into slots 42, as
indicated at 54, so as to seal the slots 42 and prevent
~DH 001 P2 -15
flow of fluid from the reservoir 26 into the slots. The
room temperature vulcanized silicone material 53 also
covers the acoustic isolation material 28. This prevents
the fluid in the reservoir from contacting the acoustic
isolation material in the instance where a porous foam is
utilized. It should be noted, however, that material 53
does not cover surfaces 30, thereby permitting electrical
contact between these surfaces and the fluid. Also
provided in cavity 14 is a layer of epoxy 55 which acts as
a backing material for the stimulator means while, at the
same time, sealing the stimulator transducer 27 and the
slots 42 defined therein from atmosphere.
Figs~ 5 and 6 illustrate a second embodiment of
the present invention. With the exception of the
construction of the stimulator means and the connection of
generator 29 thereto, the print head is of the same
construction as that illustrated in the embodiment of
Figs. 1-4. As a consequence, corresponding reference
numerals have been utilized to indicate identical print
head elements in the two embodiments.
In this embodiment, the plurality of
piezoelectric means are defined by an elongated transducer
56. Electrically conductive coatings 58 and 60 on
opposing surfaces of the elongated transducer 56 provide
the electrodes for the piezoelectric means. Since
coatings 58 and 60 are electrically continuous along the
length of the transducer, the plurality of piezoelectric
means are effectively connected in parallel.
As seen in Fig. 5, when the stimulator means is
mounted in cavity 14 by acoustic isolation material 28,
the opposing surfaces, bearing coatings 58 and 60, extend
, ... ~", ~ ~ . ...
~DH 001 P2 -16~
along the length of the transducer 56 and are generally
normal to the orifice plate 20. Coatings 58 and 60 define
serpentine electrodes which cover substantially all of the
lateral surfaces of piezoelectric transducer 56 except for
uncoated area 62 which extends along the lo~er sides of
transducer 56. As may be seen in Fig. 5, acoustical
isolation material 28 therefore completely covers
electrodes 58 and 60 and prevents any contact of these
electrodes by electrically conductive fluid in reservoir
26. This is desirable since silicone material 53 is used
to seal the slots 42 but does not ccver the entire lower
surface of the stimulator means~
Electrical conductors 64 and 66 are electrically
connected to generator 29 and provide the necessary
15 excitation signal to electroaes 58 and 60. Transducer 56
is formed of a piezoelectric material of the type which
vibrates in a direction transverse to the electrical
voltage difference applied thereacross. As a consequence,
transducer 56 vibrates vertically and stimulation of drop
breakup is provided by waves generated in the fluid in
reservoir 26, in the same manner as discussed previouslyO
The transducer 56 may advantageously be
fabricated from a sheet of ceramic piezoelectric material
of a thickness equal to the desired width C of the
transducer. An electrically conductive coating is formed
on opposite faces by plating or other appropriate
techniques. Next, the sheet is cut into a strip having
the desired length and height for the transducer.
Finally, slots 42 are cut from opposite sides of the
strip. Uncoated areas 62 may be formed by machining or
other techniques, such as etching.
MDH 001 P2 -17- ~2~4~8~
Fig. 7 illustrates the piezoelectric means
incorporated in a third embodiment of the fluid jet print
head. The balance of the print head structure is
identical to that shown in Figs. 1-6, and is therefore
omitted. The piezoelectric means include a plurality of
transducers 68 which are arranged in at least one
transducer row. The transducer row extends in a direction
substantially parallel to the row of orifices when the
stimulator means is positioned in the print head
manifold. The transducers 68 are uniformly spaced apart
and are each surrounded by acoustic isolation material 28
on the sides of the transducers which are generally
perpendicular to the orifice plate. The acoustical
isolation material 28 is bonded to all four side surfaces
of the transducers 68 and to the manifold portion 10 which
defines the cavity in which the stimulator means is
positioned. As a consequence, the acoustical isolation
material 28 effectively isolates each of the transducers
68 from the balance of the print head structure and from
the other transducers in the row, while providing a means
of supporting the transducers in their operating positions.
The stimulator means further includes electrode
means, comprising electrodes 70 and 72 which are
positioned on opposing surfaces of each of the transducers
68. The opposing surfaces, as illustrated, are
substantially normal to the orifice plate when the
stimulator means is mounted in the manifold. The
electrodes 70 and 72 may comprise thin layers of metal
which are plated onto the desired surfaces of the
transducers. As illustrated, an electrical conductor 74
extends between and is electrically connected to each of
MDH 001 P2 -18~
the electrodes 70. Similarly, an electrical conductor 76
extends between and is electrically connected to each of
the electrodes 72. When an oscillating electrical
potential from an electrical signal generator is placed
across conductors 74 and 76, the transducers 68 vibrate
vertically in response to the electrical fields between
the opposing electrode 70 and 72.
The electrodes 70 and 72 are insulated from the
fluid in the print head reservoir by terminating their
lower edges above the bottom surface of the stimulator
means, such that the acoustical isolation material covers
the electrodes 70 and 72 and electrically isolates them
from fluid in the reservoir. A room temperature
vulcanizing material may be used to seal the bottom
surface of the material 28 from the fluid in the reservoir.
It will be appreciated that if piezoelectric
transducers are utilized which vibrate in a direction
parallel to the electrical field placed thereacross,
electrodes 70 and 72 may be eliminated and electrodes may
be positioned on the top surfaces of the transducers 68 in
a fashion similar to that shown in Fig. 4. In such an
arrangement, the bottom surfaces of the transducers are
exposed to the fluid in the reservoir which acts as the
second set of opposing electrodes. The electrical signal
generator means is connected between the electrodes on the
tops of the transducers and the electrically conductive
manifold defining the reservoir, such that the
piezoelectric material is electrically stimulated.
Reference is now made to Fig. 8, which is a view,
similar to Fig. 7, illustrating a variation in the
construction of the stimulator means. Specifically,
MDH OOl P2 -l9-
transduers 68 and 68' are positioned in a pair of
transducer rows. When the stimulator means of Fig. 8 is
mounted in the print head, both of the transducer rows
extend generally parallel to the row of orifices. The
electrical conductors 74 and 74' are electrically
connected to one side of the electrical signal generator
means, while the electrical conductors 76 and 76' are
electrically connected to the other side of the electrical
signal generator means. As a consequence, all of the
transducers 68 and 68' vibrate in synchronism, producing
waves in the fluid which have a substantially uniform
phase front. The acoustical isolation material 28
provides a support arrangement for the transducers 68 and
68', as well as providing isolation between the
transducers and the associated print head mounting
structure.
With respect to the embodiments of Figs. 1-6, it
is preferred that the height A (Fig. 4) be no greater than
one-half of the wavelength of the waves in the elongated
transducer 27 so that it will act as a good piston
radiator. Any greater height may tend to produce bowing
of the transducer. The space B between alternate slots 42
and the width C of the transducer 27 are preferably
limited to one-sixth to one-eighth of the wavelength of
the vibrations in the transducer 27. Such dimensional
limitations ensure that substantial wave movement along
the length of the transducer is not produced.
Similarly, with respect to the height of
transducers 68 and 68' in the embodiments of Figs. 7 and
8, it is preferred that this dimension not exceed one-half
wavelength, while the other two dimensions of each of the
M~H 001 P2 -20- ~2~
transducers should be approximately one-sixth to
one-eighth wavelength. The spacing between adjacent
transducers in a transducer row is preferably on the order
of one-thirtieth of a wavelength. While greater spacing
between adjacent transducers increases the isolation of
each of the transducers, substantially greater spacing
between transducers results in production of a wave in the
fluid which does not have a uniform phase front. If the
transducers are spaced too far apart, each transducer
tends to produce separate waves which interfere with those
produced by other transducers in the row.
Reference is now made to Figs. 9 and 10 which
illustrate a stimulator means constructed in a manner
similar to that of the stimulator of Fig. 6. In the
stimulator arrangement of Figs. 9 and 10, however, the
electrically conductive coating 58 has been cut
mechanically, or etched, at points 80. Similarly,
electrically conduc~ive coating 60 has been cut
mechanically, or etched, at points along the transducer
opposite points 80. The effect of this is to divide the
transducer electrically into sections 82, 84, 86, 88, 90,
92, 94, and 96. These eight sections each approximately
are one-half to one wavelength long and are individually
connected to conductors 98, 100, 102, 104, 106, 108, 110,
and 112, respectively. Although eight sections are shown
for purposes of illustration, a stimulator arrangement may
be constructed according to the present invention with a
great many more sections. As shown in Fig. 10 an
electrical conductor 114 electrically connects the
sections of coating 60 together. This conductor 114 is
not required, however, if cuts in the electrically
MDH 001 P2 -21-
conductive layex 60 are not made. In such a case, layer
60 provides a continuous electrically conductive coating
along the entire length of the transducer and only a
single electrical connection need be made to the coating
at any point along the transducer.
The arrangement of Figs. 9 and 10 permits the
separate sections of the transducer to be driven by a
single drive signal which is selectively attenuated for
the optimum driving amplitude for each such section. As
shown in Fig. 11, an electrical signal generator means for
electrically exciting the plurality of piezoelectric means
includes means 116 for providing an alternating drive
signal and an attenuator means, including capacitors 118,
120, 122, 124, 126, 128, and 130, for supplying the
alternating drive signal to the piezoelectric means. The
amplitude of the drive signal is set for each such
piezoelectric means to produce proper break up of the jet
drop streams along the length of the print head.
Capacitors are utilized to attenuate the driving
current since sections 82-96 are generally capacitive in
nature. As a consequence, capacitors 118-130 provide
relatively little phase shift in the driving current
applied to the respective transducer sections.
It has been found that the values of the various
capacitors needed for a specific print head may be
determined experimentally in a one-pass testing
procedure. The print head, including the stimulator
means, is operated and a jet stream generally below a
transducer section of interest is observed. The sections
82-96 are each electrically connected in series with one
ohm resistors, but with no capacitive attenuation being
MDH OOl P2 -22- ~2~
provided. A volt meter is placed across the one ohm
resistor connected to the section of interest to monitor
driving current. The driving voltage across the section
of interest and the one ohm resistor is varied and the
drive current for the section which results in a fluid
filament of minimum length and optimum break up of the jet
drop stream is determined.
This operation is repeated for each of the
transducer sections, with a jet drop stream roughly in the
center of the transducer section being monitored for
minimum filament length and optimum break off. The
section of the transducer requiring the most drive
current, in Fig. ll section 86, is then operated without
attenuation. The balance of the sections have capacitors
inserted electrically in series to reduce the drive
current to the level which was found during testing to
provide optimum break off.
While the forms of apparatus and the methods of
making herein described constitute preferred embodiments
Of the invention, it is to be understood that the
invention is not limited to these precise forms of
apparatus, and that changes may be made therein withcut
departing from the scope of the invention.
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
