Note: Descriptions are shown in the official language in which they were submitted.
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FLUID JET PRINT HEAD AND STIMULATOR T~IERE~'OR
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Backyround of the Invention
This invention relates generally to fluid jet
printing and, more particularly, to a fluid jet print head
and stimulator which are si~nple in construction and which
provide reliable drop breakup.
~ et drop printers are known in which a plurality
of streams of drops are produced by a single fluid jet
print head. The print head includes a manifold, definin~
a fluid receivin~ reservoir, and an orifice plate,
defining a plurality of orifices which communicate with
said reservoir. As ink is applied under pressure to the
fluid receiving reservoir, it flows throu~h the orifices
in the orifice plate and emerges from the orifices as
continuously flowing fluid filaments. The filaments tend
to break up into drops of irregular and unpredictable size
and spacing. Such jet drop streams are generally
unacceptable for purposes of printing. It is known that
to enhance drop formation, mechanical disturbances may be
produced in the fluid or the print head structure and
coupled to the fluid filaments.
One exceptionally effective prior art technique
for producing uniform drop breakup is shown in U. S.
Patent No. 3,701,9~8, issued October 31, 1972, to Mathis,
and assigned to the assignee of the present invention. In
the ~lathis printer, a pro~e, coupled to an
electromechanical transducer, extendin~ into the fluid
receiving cavity of the print head, contacts the interior
surface of the orifice plate at one end of the plate. The
electromechanical transducer vibrates the probe and the
orifice plate is caused to vibrate at the point of probe
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contact. This, in turn, produces ~ending waves which
travel along the length of the orifice plate. The bending
waves produce surface vibrations on the fluid filaments
which result in drop breakup in the desired manner.
The prior art printers which operate on the basis
of traveliny wave stimulation of this type have included
relatively complicated piezoelectric, electromechanical
transducers in the stimulator structures. ~ot only are
such transducer devices expensive, but they are also
somewhat unreliable. Further, the amplitude of the
mechanical vibration produced may vary. Accordingly, it
is seen that there is a need for a fluid jet print head~
and a stimulator therefor, which are simple in
construction, and reliable in operation and which provide
for vibrational amplitude monitoring.
Summary of the Invention
. .
A fluid jet print head for producing a plurality
of jet drop streams includes Manifold means definin~ a
fluid receiving reservoir to wnich fluid may be applied
under pressure. An orifice plate means is mounted on the
manifold means and defines a plurality of orifices which
communicate ~ith the fluid receiving reservoir such that
fluid from the reservoir flows throuyh the orifices and
emerges therefrom as fluid filaments. A stimulator means
is mounted in contact with the orifice plate means for
vibrating the orifice plate means to produce a series of
bending waves w~lich travel along the orifice plate means
and break up the fluid filaments into drops of
substantially uniform size and spacing.
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The stimulator means includes a stimulator member
of the length which is substantially equal to n~/2, where
n is a positive integer and ~ is the wavelength of an
acoustic wave traveling along the stimulator member. ~ i5
equal to (Y/P )1/2/f, where Y is Young's modulus, P is
the density of the stimulator member, and f is the
frequency of acoustic waves generated in the member. The
member contacts the orifice plate means at one end oE the
member.
The stimulator means further includes
piezoelectric crystal means, mounted on the stimulator
member, for alternately compressing and extending in a
direction parallel to the axis of elonyation of the member
when driven by an electrical drive signal so as to produce
acoustic waves in the member. Mounting means sup~ort the
stimulator member at a nodal plane therealong. A driver
means applies the electrical drive signal to the
piezoelectric crystal means at the frequency f.
The length of the print head may be such that n
is greater than or equal to 2. The stimulator means may
contact the orifice plate means inside the manifold means,
entering the manifold means through an opening includiny a
seal. The seal contacts the stimulator member at a nodal
plane along the stimulator member.
The piezoelectrical crystal means may include a
pair of piezoelectric crystals mounted on opposite sides
of the Member, the piezoelectric crystals being of the
length which is less than or equal to 1/2 ~ .
The stimulator member may be of a length equal to
1/2~. The stimulator means may further include a pin,
mounted on the end of the member, in direct contact with
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the orifice plate rneans. The pin has a cross-sectiona~
area, taken in a plane perpendicular to the axis of
elongation of the member, which is substantially less than
the cross-sectional area of the member taken in a parallel
plane.
The stimulator means may further comprise a
feedback transducer means which is mounted at the end of
the member, opposite the end which contacts the orifice
plate means, and uhich provides an electrical si-Jnal
~roportional in frequency and amplitude to the frequency
and amplitude of the acoustic waves passing t~lrough the
member.
The stimulator member may be tapered to~ard the
end thereof which contacts the orifice plate means such
that the member contacts the orifice plate means
substantially at a point.
Accordingly, it is an object of the present
invention to provide a fluid jet print head, and a
stimulator therefor, in whicll the stimulator includes an
elongated member of a length substantially equal to an
integer half wavelength of acoustic waves of a specific
frequency in the member, a transducer arrangement for
producing acoustic waves in the member in response to an
A.C. drive signal, and means for applying the A. C. drive
signal at the predetermined frequency to the transducer;
to provide such a print head and stimulator therefor in
which the transducer means includes a pair of
piezoelectric transducers which are bonded to opposite
sides of the stimulator member, with the transducers
extending in opposite directions from a nodal plane
parallel to the axis of elongation of the member; to
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MDF nos P2 -5-
provide such a print head and stimulator therefor in which
the stiMulator member is Mounted at a nodal plane
therealong/ which nodal plane may coincide with the plane
from which the pie~oelectric transducers extend; to
provide such a print head and stimulator therefor in which
the stimulator contacts the interior of the urint head
structure, entering the print head throuyh an opening
which is sealed by a seal surrounding the member and
contacting the member at a nodal plane, to provide such a
print head and stimulator therefor in which a relatively
thin pin, having a cross-sectional area substantially less
than the cross-sectional area of the stimulator member,
extends into the print head and contacts the print head
structure; and to provide such a print head and stimulator
therefor in whic~l a sensor is mounted on the member to
provide an electrical feedback signal proportional in
amplitude and frequency to the acoustic waves which pass
along the member.
Other objects and advantayes of the invention
will be apparent from the following description, the
accompanying drawings and the appended claims.
~rief Description of the Drawings
Fig. 1 is a perspective view of a first
embodiment of the print head and stimulator of the present
invention, with portions broken away to reveal interior
structure
Fig. 2 is a sectional view of the stimulator of
Fiy. 1, taken through the center of the stimulator in a
plane parallel to the axis of elongation thereof;
Fig. 3 is a sectional view taken generally along
line 3-3 in Fig. 2; and
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Fig. 4 is an enlarc3ed perspective view of a
second embodiment of the ~resent invention, with portions
broken away and in section.
Detailed Description of the Preferred ~rnbodiments
Fi(Js. 1, 2 and 3 illustrate a fluid jet print
head and stimulator therefor constructed according to a
first em~odiment of the present invention. The print head
includes a manifold means consisting of an upper rnanifold
element 10, a lower manifold element 12, and a gasket 14
therebetween The manifold means defines a fluid
receiving reservoir 16 to which fluid may be applied under
pressure via fluid inlet tube 18. Fluid may be removed
from reservoir 16 through outlet tube 20 during cleaning
operations or prior to extended periods of print head
shutdown.
An orifice plate 22 is mounted on the manifold
means. The plate is formed of a metal material and is
relatively thin so as to be somewhat ~lexible. Orifice
plate 22 is bonded to the manifold element 12~ as for
example by solder or by an adhesive, such that it closes
and defines one wall of the reservoir 16. Orifice plate
22 defines a plurality of orifices 24 which are arranged
in at least one row and which communicate with the
reservoir 16 such that fluid in the reservoir 16 flows
through the orifices 24 and emeryes therefrom as fluid
filaments.
As is known, the fluid filaments, left to
naturally occurring random stimulating disturbances, will
tend to break up into drops of non-uniform size and
spacing. In order to improve the uniformity of breakup, a
stimulator means 26 mounted in contact with the orifice
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plate 22 vibrates the orifice plate to produce a series of
bending waves ~7hich travel along the orifice plate 22 in a
direction generally parallel to the ro~ of orifices.
The stimulator means 26 includes a stimulator
member 28, configured as a thin metal rod. The type of
metal for the stimulator member 28 is selected to be
compatible with the fluid supplied to reservoir 16. The
stimulator member 28 is of a lenyth L which is
substantially equal to n~/2, ~here n is a positive integer
and ~ is the wavelength of an acoustic wave traveliny
along the stimulator member 28. As is known, the
~avelength of such a wave, traveling along a thin rod, is
substantially equal to (y/p )l/2/f~ where Y is Young's
modulus, P is the density of the stimulator member
material, and f is the frequency of acoustic waves
generated in the member.
The end 30 of member 28 is tapered so that the
member 28 contacts the orifice plate 22 substantially at a
point. As is known, such point contact on the center line
of the orifice plate 22 insures that bending waves of a
first order are generated in the orifice plate 22, and
that satisfactory stimulation is obtained.
The stimulator means 26 further includes
piezoelectric crystal means, comprising piezoelecteic
crystals 32 and 34, which are mounted on the stimulator
member 28. The crystals 32 and 34 each include a thin,
electrically conductive layer on their outer surfaces to
~hich conductors 36 and 38 are electrically connected.
The inner surfaces of the crystals are in contact with and
are grounded by the member 28. Member 28, in turn, may be
yrounded through orifice plate 22 or through yround
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MDF 008 P2 -8-
cond~ctor 40. The crystals 32 and 34 are configured such
that they tend to compress or extend in a direction
parallel to the axis of elongation of the member 28 when a
fluctuating electrical potential is placed across the
crystals As a consequence, when an A.C. electrical drive
signal is applied to lines 36 and 38 by driver circuit
means 40, the crystals 32 and 34 produce acoustic ~JaVes in
the stimulator member 28. The circuit 40 supplies an
electrical drive signal at a frequency f, as specified
above in relation to the length of the member 28.
In the embodiment illustrated in Figs. 1-3, the
stimulator member is substantially equal in length to one
wavelength, that is, n is equal to 2. The member 28
extends into the manifold means through an opening 44
defined by element 10. The member 28 contacts the orifice
plate 22 inside the reservoir 16. A seal, such as o-ring
46 surrounds the member 28, contacting the member 28 and
element 10.
The stimulator means is mounted by tapered pins
48 which enyage generally conical detents 50 in the sides
of member 28. The pins 48 and detents 50 provide a
pivotal mounting which restricts movement of member 28
vertical. As may be noted, the detents 50 are positioned
1/4~ f rom the upper end oE the member 28, as seen in
~ig. 2, while the O-ring 46 contacts the member 28
substantially 1/4~ from the lower end of the member 28.
It will be appreciated that since crystals 32 and 34
extend above and below the detents 50 by substantially
equal distances, pins 48 support the stimulator means in a
nodal plane. Since the ring 46 contacts the member 28
1/2~ below the pins 48, O-ring 46 also contacts the
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MDF 008 P2 -9-
member 28 at a nodal plane. Thus substantial damping
between the member 28 and the ring 46 does not occur.
Additionally, the end of 30 of the member 28 is 1/4
below a nodal plane and therefor at an anti-node,
producing maximum amplitude mechanical stimulation for
generation of the bending waves in the orifice plate 22.
It will be understood that it is desirable to limit the
length Lc of the crystals 32 and 34 to 1/2~ or less. I~
the length of the crystals is greater than this, their
vibratory motion will tend to counteract formation of
standing waves in the member 28 and the production oE
nodal planes.
It will be appreciated that member 28 could be
substantially lonyer than illustrated. The length of the
member can be increased in multiples of 1/2 wavelength
with predictable harmonic progressions. In any event,
however, it is desirable that the mounting for the member
28 be at a nodal plane and that sealing also occur at a
nodal plane so that vibrational energy is not lost through
the sealing or the mounting structures and that the member
28 contacts the orifice plate 22 at an anti-node.
An additional pair of piezoelectric crystals 52
may also be mounted on the member 28. Crystals 52 act as
sensors and provide an electrical ~eedback si~nal on line
54 which is proportional in frequency and amplitude to the
frequency and amplitude of the acoustic waves traveling
through the member 28. The feedbac~ signal on line 54 may
be used by the driver circuit 40 to control the frequency
and amplitude of the drive signal applied on lines 36 and
38.
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Fi~. ~ illustrates a second embodiment of the
present invention in which the elements corresponding to
the those in the first embodiment have been designated by
the same numerals as those used in Figs. 1-3. The
stimulator member 28 of Fig. 4, rectangular in
cross-section, is substantially 1/2 wavelength long, that
is, L e~uals 1/2~ . Piezoelectric crystals 32 and 34
(not shown) are mounted on opposing faces of the member
28.
A vibration transmission pin 56 is mounted on one
end of the member and is preferably pressed into a hole in
the end of the member or is rnachined on the end of the
mem~er. The pin ~6 directly transmits the movemellt of the
lower end of the member 28 to the orifice plate 22. The
pin 56 has a cross-sectional area, ta~en in a plane
substantially perpendicular to the direction of the
elon~Jation of member 28, which is substantially less than
the cross-sectional area of the member. ThUS, the
acoustic waves in the member 28 do not pass through pin
56, but rather are reflected back toward the nodal plane
which passes through pins 48. The length of pin 56 is not
related to the frequency of operation of the stimulator
means, since the pin acts merely as a means of
transmitting the vibrations from the anti-node at the end
of member 28 to the plate 22. The pin 56 passes through
opening 44 and is engaged by a small diameter O-ring 58
which prevents leakaye of fluid from reservoir 16.
Preferably, an automatic gain control in the driver
circuit allows the stimulation amplitude to be held
constant, regardless of the degree of damping provided by
O-ring 58.
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A single piezoelectric transducer 60 is mounted
on a side of the member 28 other than the sides upon which
the piezoelectric transducers 32 and 34 are mounted.
Transducer 60 provides a feedback signal on line 54 which
may be used by a driver circuit to control operation of
the stimulator.
While the forms of apparatus herein described
constitute preferred embodiments of this 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 without departing from the scope of the
invention which is defined in the appended claims.
