U.S. patent number 3,885,172 [Application Number 05/427,144] was granted by the patent office on 1975-05-20 for sonic transducer.
This patent grant is currently assigned to Continental Can Company, Inc.. Invention is credited to Donald E. Miller.
United States Patent |
3,885,172 |
Miller |
May 20, 1975 |
Sonic transducer
Abstract
My invention is a transducer having a resonating element and a
power generating element. The acoustic length of the resonating
element is made the same as the acoustic length of the power
generating element. Each is made to be a length one half wave
(.lambda./2) when the transducer operates at a given frequency. In
this way, the ends of the resonating element and the power
generating element are attached to each other and there is little
stress at the point of attachment.
Inventors: |
Miller; Donald E. (Mt.
Prospect, IL) |
Assignee: |
Continental Can Company, Inc.
(New York, NY)
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Family
ID: |
26898733 |
Appl.
No.: |
05/427,144 |
Filed: |
December 21, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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203587 |
Dec 1, 1971 |
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Current U.S.
Class: |
310/325 |
Current CPC
Class: |
B06B
1/0618 (20130101); H04R 17/00 (20130101); H04R
17/08 (20130101) |
Current International
Class: |
B06B
1/06 (20060101); H04R 17/00 (20060101); H04R
17/04 (20060101); H04R 17/08 (20060101); H04r
017/00 () |
Field of
Search: |
;310/8.2,8.3,8.7,9.1,26 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Budd; Mark O.
Attorney, Agent or Firm: Diller, Brown, Ramik &
Wight
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of copending application Ser.
No. 203,587, filed Dec. 1, 1971 and now abandoned.
Claims
What is claimed is:
1. A transducer assembly comprising:
a force generating assembly comprising;
a first tubular means including a sleeve means at a first end and
having an internal threaded portion at said first end and a flat
portion at a second end;
a first annular electrostrictive element mounted adjacent said flat
portion of said first tubular means and having an outside diameter
about equal to the outside diameter of said first tubular means and
an inside diameter greater than the least internal diameter of said
first tubular means, dimensioned so that the cross-sectional area
of said element multiplied by the modulus of elasticity of the
element about equals the cross-sectional area of said sleeve means
multiplied by the modulus of elasticity of said sleeve means;
a flat electrically conductive disk having an outside diameter
greater than that of said electrostrictive element and an inside
diameter about that of the inside diameter of said electrostrictive
element;
a second annular electrostrictive element mounted adjacent said
flat electrically conductive disk and constructed nearly identical
to said first annular electrostrictive element, and
a second tubular means including a sleeve means at a first end and
having an internal threaded portion at said first end and a flat
portion at a second end adjacent said second electrostrictive
element, dimensioned so that the cross-sectional area of said
element multiplied by the modulus of elasticity of the element
about equals the cross-sectional area of said sleeve means
multiplied by the modulus of elasticity of said sleeve means;
and
a tensioning stud of about the same material and cross-sectional
area as said first and second tubular means and having a first
threaded end and a seconded threaded end and fitting through said
first and second force transmitting sleeve, said first and second
electrostrictive elements and said flat electrically conductive
disk with its first end threaded into said first end of said first
sleeve and its second end threaded into said second end of said
second sleeve whereby said first and second tubular means, said
first and second annular spacer, said first and second
electrostrictive element and said conductive disk are pressed
against each other and placed in compressive strain whereby the
resonant frequencies, phases and amplitudes of the stud and force
generating assemblies are matched.
2. A transducer assembly as set forth in claim 1 in which each said
first means comprises;
a tapered sleeve means having an internal threaded portion at a
first end and a flat portion at a second end; and
a flat annular disk mounted adjacent each said second end of said
tapered tubular means whereby one side of said annular disk is in
contact with said flat portion of said second end
a flat annular disk mounted adjacent each said second end of said
tapered tubular means whereby one side of said annular disk is in
contact with said flat portion of second end.
3. A transducer assembly as set forth in claim 2 further
comprising;
a tubular spacer made of an electrically insulating material and
mounted about said stud and between said stud and the inside of
said annular electrostrictive element whereby said electrostricitve
elements are electrically insulated from said tensioning stud.
4. A transducer assembly as set forth in claim 2 further
comprising;
a first groove extending completely around an inner shoulder of
said flat annular disk;
a second groove extending around the inner shoulder of said flat
section of said tapered sleeve means and of the same external
diameter as said groove in said flat annular disk; and
a centering ring of size to fit snugly into said first and second
groove whereby said flat annular disk and said tubular means may be
turned relative to each other without changing the lateral distance
between the tensioning stud and the tubular sleeve.
5. A transducer assembly as set forth in claim 2 in which said
tensioning stud comprises;
an elongated stud the cross-section of which has at least one flat
portion.
6. A transducer assembly as set forth in claim 5 in which each of
said first and second annular disks comprises;
a flat disk having a circular exterior with at least one flat
portion on its inner circumference to match with said flat portion
on said elongated stud.
7. A transducer assembly as set forth in claim 6 in which each said
tensioning stud and annular disk comprise;
at least six flat matching portions on each said tensioning stud
and annular disk.
8. A transducer assembly as set forth in claim 6 in which said
threads on said first and second end of said tensioning stud
further comprise;
threads cut in one direction on said stud whereby when said first
and second tapered tubular means are rotated in the same direction
about said stud said tubular means turn against said flat annular
disk and said first and second tapered tubular means are moved
toward each other to finally place said tensioning stud in tension
and said first and second sleeve, said first and second
electrostrictive elements and said conductive disk in compressive
strain.
9. A transducer assembly as set forth in claim 2 in which;
the distance from said conductive disk to said threaded end of said
first tubular sleeve means is the same as the distance from said
conductive disk to said threaded end of said second tubular sleeve
means.
10. An ultrasonic welding apparatus comprising in combination;
a transducer having a first force transmitting sleeve means having
a first flat end and a second internally thread end,
a first annular electrostrictuve element mounted adjacent said
first sleeve means, and having an outside diameter about equal to
the outside diamater of said first sleeve means and an inside
diameter greater than the least internal diameter of said first
sleeve means, whereby the cross-sectional area of said element
multiplied by the modulus of elasticity of the element about equals
the cross-sectional area of said sleeve means multiplied by the
modulus of elasticity of said sleeve means,
a flat elelctrically conductive disk having an outside diamter
greater than that of said electrostrictive element and an inside
diameter equal to that of the inside diameter of said
electrostrictive element,
a second annular electrostrictive element mounted adjacent said
flat disk and having the same dimensions as said first annular
electrostatic element,
a second force transmitting sleeve means having a first flat end
and a second end with internal threads,
a tensioning stud having a first threaded end and a second threaded
end and fitting through said first and second force transmitting
sleeve, said first and second electrostrictive elements and said
flat electrically conductive disk with its first and its second end
threaded into said second end of said second sleeve whereby said
first and second tubular sleeve, said first and second annular
spacer, said first and second electrostrictive element and said
conductive disk are pressed against each other and placed in
compressive strain,
a horn having,
a head adapted to be attached to said first end of said tensioning
stud end of a length equal to half the length of said
transducer,
a flange attached to said head at its most remote point from said
tensioning stud and adapted to be attached to a first point,
and
a stem attached to said head at a point remote from said tensioning
stud whereby power generated in said transducer may be applied to
an object through said strain.
11. An ultrasonic transducer assembly comprising, in
combination:
a tubular force-generating component of sandwich construction and
including electrostrictive means located in the central region
along the axis of said tubular force-generating component and a
pair of sleeve members forming the opposite ends of said tubular
force-generating component whereby maximum axial vibrational
displacement of selected frequency is effected at the free ends of
said sleeve member in response to excitation of said
electrostrictive means, said free ends of the sleeve members being
internally threaded; and
a stud disposed coaxially within and essentially coextensive in
length with said tubular force-generating component, said stud
being threadedly engaged at its opposite ends to the respective
free ends of said sleeve members and being pretensioned to place
said tubular force-generating component in compression;
the cross-sectional dimensions of said tubular force-generating
component and of said stud being cooperatively related to produce
vibrational displacements of the respective threadedly joined
portions of said stud and of said force-generating component which
are substantially in phase at said selected frequency and of
substantially equal amplitudes whereby minimally to stress such
threadedly joined portions.
12. An ultrasonic transducer assembly as defined in claim 11
wherein the product of the modulus of elasticity of said
electrostrictive means and its cross-sectional area is
substantially equal to the product of the modulus of elasticity and
the cross-sectional area of each sleeve member.
Description
This invention relates to ultrasonic tranducers and pertains to a
novel form of transducer for transforming electrical energy into
ultrasonic energy.
In the last decade, many sonic and ultrasonic transducers have been
proposed. Typical of these are the patents to James Byron Jones et
al., U.S. Pat. No. 3,283,182; John N. Antonevich, U.S. Pat. No.
3,370,186; and Lewis Balamuth, U.S. Pat. No. 3,578,996. These
devices use a shaft or sleeve to hold the transducer in
compression. The devices developed, so far as known in the art,
have usually had large stresses at the point of attachment between
the shaft and the resonating end of the transducer. A shaft is
oridinarily a stud or screw used to pull the elements of the
transducer together so that the electrostrictive elements are
placed in initial compression. Transducer failure is frequent in
the area where the threads of the stud match with threads in the
power generation part of the transducer itself.
It is an object of my invention to provide a transducer having a
maximum displacement amplitude at its ends.
It is a further object of my invention to provide a transducer
wherein the stress at the end threads is minimized.
It is a final object of my invention to provide a transducer
wherein the power generating assembly is of the same acoustic
length as the resonant tensioning stud.
In brief, my invention is a transducer assembly having a resonating
stud and a power generating assembly. The acoustic length of the
resonating stud is made the same as the acoustic length of the
power generating assembly. Each is constructed to be of length
equal to one half wave (.lambda./2) if the transducer operates at a
given constant frequency. In this way, the ends of the resonating
stud and the ends of the power generating element may be attached
to each other with little dynamic stress at the points of
attachment during operation.
A better understanding of an embodiment of my invention may be had
by reference to the accompanying illustrations and the following
description wherein like reference numerals refer to like
parts.
FIG. 1 shows a cross-sectional view of a transducer of my
invention.
FIG. 2 shows a horn attached to my transducer.
FIG. 3 shows a cross-sectional view of my transducer taken along
the line 2--2 of FIG. 2.
The principles of my invention are applicable to more than one type
of transducer. However, shown in FIG. 1 is an embodiment of my
invention. The transducer of FIG. 1 has a central stud mounted so
that is passes through the other elements of the transducer
assembly and binds them together under a compressive force. When
assembled, the stud itself is in tension. This stud is made of a
material which can stand considerable tensile force, such as
steel.
Threads are cut into the exterior surface of the stud at each end
of the stud. These threads lock with internal threads of the
tubular means which is part of the force generating assembly. A
section of this stud next to the threaded section is undercut to an
amount slightly in excess of the depth of the thread and extends
part way toward the center of the stud. The purpose of this
undercut is to avoid the stress concentration which exists at the
termination of a thread when that termination occurs within the
body of the stud.
In the ordinary transducer assembly, considerable stresses are
applied to the threads of a stud such as the stud shown in FIGS.
1-3. Every sharp corner serves as a focal point for strain and
breakage is frequently found at these focal points. By undercutting
the stud portion adjacent the threads to an amount slightly in
excess of the thread depth, a concentration of forces is avoided at
the point where the thread and the thread undercut come together.
By this means, breakage of the stud in the area near the threads is
minimized. This area has been a frequent point of breakage in prior
assemblies.
Broadly speaking, the tensioning stud is a resonating system and
the rest of the transducer assembly is a force generating assembly
which is designed to oscillate at the same frequency as the
tensioning stud.
The force generating assembly 1 of the transducer 30 shown in FIG.
1 has annular elements 2, 3 made of a ceramic or any other commonly
used piezoelectric or polarized electrostrictive material. Located
centrally of the two annular electrostrictive elements is a flat
electrically conductive disk 4 having a hole 5 through its center.
The disk is positioned between the annular electrostrictive
elements 2, 3 and in intimate contact with them along its sides 6,
7. Adjacent each electrostrictive element on its outerside are flat
annular disks 8, 9 made of steel or the like. Each flat annular
disk is preferably made of the same material as are the tapered
tubular means or sleeve means 10, 11 which lie just outside of it.
The sleeve is taken as including the flat annular disk. Tensioning
stud 12 runs through the entire assembly. The stud may have an
irregular cross-section, such as a hexagonal cross-section. The
flat annular disk is made to fit snugly about the stud. The
hexagonal cross-section of the hole 13 in the disc prevents
relative turning between the stud 12 and disk 8, 9. Both sides 14,
15 of each flat annular disk are smooth so that on one side there
is a close contact with each annular electrostrictive element 2, 3
and on the other side, there is a close contact with the flat end
16, 17 of the sleeve means. The sleeve means has a flat end 16, 17
which is shown in contact with the annular disks 8, 9 and at the
other end, it has internal threads 18 for matching with the threads
19 of the tensioning stud 12. A tubular spacer 20 made of an
electrically nonconducting material such as nylon is placed in the
space between the annular electrostrictive elements 8, 9 and the
outer part of the tensioning stud 12. Tubular spacer 20 extends
from one flat annular disk 8 to the other 9. Centering rings 21, 22
made of a resilient metal fit into grooves 23, 24 in the flat
annular disk and also fit into another set of grooves 25, 26 in the
inner edge of the tubular means as shown in FIG. 1. Each centering
ring fits snugly into the grooves and extends completely around the
interior of the flat annular disk and the sleeve means.
The tensioning stud has at least one flat portion 27 on its
exterior to match with a flat portion of the interior of each of
the flat annular disks. The matching flat portions prevent relative
turning of these elements. In practice, the stud is made hexagonal
and the interior of the flat annular disks 8, 9 is made hexagonal.
The purpose of the matching hexagonal parts of the stud and the
flat annular disk is so that the sleeve means may be turned
independently of the stud 12, flat annular disks 8, 9 and annular
electrostrictive elements 2, 3. In practice, one of the sleeve
means is screwed onto a stud until its threaded end is about flush
with the stud end. The stud is recessed a bit to allow later
torquing of the horn up against the sleeve. A set screw 28 in the
side of the sleeve means is tightened and the sleeve means and stud
are fixed in position relative to each other. Next the transducer
is assembled as shown in FIG. 1 and the second sleeve means is
rotated until it puts the electrostrictive elements into the
requisite compression. As the transducer elements approach each
other, the centering rings 21, 22 center the flat annular disks and
the force transmitting sleeve means relative to each other because
each centering ring 21, 22 falls into the grooves 23-26 in the disk
and tapered tubular means. The flat annular disk is held from
turning by the hexagonal stud. The disk may slide longitudinally on
the stud. The tapered sleeve means is turned until the desired
tension and compression is put upon the resonating structure and
the force generating assembly respectively.
The relative dimensions of the force transmitting sleeve 10, 11,
the flat annular disks 8, 9 and the annular electrostrictive
elements 2, 3 are of considerable consequence for the following
reasons. If stud dimensions deviate substantially from a half wave
length, considerable stress must be applied to the end of the stud
to force oscillation of the stud. If such a stud is used as a
preloading stud, the nominal dynamic stress in the threaded
portions 19 at its ends will be undesirably high. On the other
hand, if the tensioning stud is made approximately one half wave
length long, then a way must be found to make the body of the
transducer to resonate at the same length and frequency. If these
two bodies, both being one half wave length long, resonate at the
same length and the same frequency, there there is a minimum of
dynamic stress at the ends of the stud. This is because each end of
the tensioning stud is in phase with the corresponding end of the
force generating assembly.
The resonant length of most conventionally designed transducers is
considerably less than a half wave length. These transducers use
steel, stainless steel, tatanium, or other suitable stud materials.
The reason is that the elastic modulus of the ceramic
electrostrictive element is substantially lower than that of the
metallic elements which make up the rest of the transducer.
Furthermore, in most conventional designs, the cross-sectional area
of the electrostrictive element (area of the ceramic material) is
smaller than the cross-sectional area of the end sleeves. This
brings about a situation in which the transmitter body may be
considered as a bar with a short zone at midlength which is very
low in stiffness.
In the present invention, the zone of the electrostrictive element
is made as stiff as the remainder of the transducer body by
proportioning the cross-sectional areas of the tubular means 10, 11
and the annular electrostrictive element 8, 9 inversely as their
moduli of elasticity, so that
Area.sub.ee .times. E.sub.ee = Area.sub.SM .times. E.sub.SM
where
Area.sub.ee = area of the annular electrostrictive element taken
across its axis,
E.sub.ee = modulus of elasticity of the electrostrictive
element.
Area.sub.SM = the cross-sectional area of the sleeve means taken
along a line perpendicular to its direction of vibration.
and,
E.sub.SM = the modulus of eleasticity of the sleeve means.
When the conditions above are met, the length of both the stud 12
and the force generating assembly 1 shown in FIGS. 1 and 3 may be
constructed very close to one half wave length and the distance
from the flat electrically conductive disk 4 to each end of the
transducer may be constructed very close to one quarter wave
length. Within the scope of this invention, a variety of materials
may be used.
Because of the presence of the changes of area of the cross-section
along the length of the stud, the resonant length of the stud will
not be quite the same as for a resonant bar of uniform
cross-section even though the average cross-sectional area is
identical. As one method of construction, the force generating
assembly can be made to resonate at about the same length as the
stud by turning the end sleeves down on a lathe to achieve an
appropriate cross-sectional area so that the stud and force
generating assembly resonate in phase. As a metter of practice, the
amount of sleeve material that must be machined off is small.
Since the force generating system 1 is matched with the resonant
oscillating stud 12 as to acoustic length, an end of this system
may be used for transmitting energy to a horn. Such a device 29 is
shown assembled in FIG. 2. The center zone of the transducer
assembly 30, i.e. the electrostrictive element 2, 3, is longer than
in conventional transducers and stud 12 and force generating system
1 are perfectly matched as to acoustical length. The total length
of the transducer assembly 30 is greater than in a conventional
transducer. The additional transducer length allows a greater
displacement of each end of the transducer assembly. There is
induced a larger oscillation amplitude at the same maximum stress
in consequence of the greater length of the transducer assembly. It
can be shown theoretically that of two transducers operating at the
same resonant frequency, the one having the longer sleeves exhibits
the larger displacement amplitude.
The horn 31 shown in FIG. 2 has a transducer 30 of my invention
attached to it. The transducer 30 is threaded onto the stud 32 and
fits snugly against the horn 31. The transducer assembly and horn
are a total of one wave length from the tip of the blade to the
distal end of the transducer. The distance from the tip 32 of the
horn blade 33 to the point 35 of attachment is about one-quarter
wave length of the horn to the base assembly. The distance from the
point 35 to the point of attachment 34 between the horn and the
transducer is about one-quarter wave length. As indicated above in
the preceding paragraphs, the distance between the force
transmitting end 36 of the transducer and the flat electrically
conductive disk 4 is about one-quarter wave length and from the
flat electrically conductive disk 4 to the distal end 37 of the
transducer assembly is likewise about one-quarter wave length.
Thus, it is readily apparent that the length of the transducer
assembly 30 plus the horn 31 is one full wave length. When the
transducer assembly and horn are supported in this fashion, the
points of maximum displacement of the transducer assembly are at
the ends 36, 37 of the transducer and at the end 32 of blade 33 of
the horn. The horn is hung or supported by the flanged portion 38
at its midpoint, this being a point of maximum stress and minimum
displacement.
The end view of my transducer taken along the line 3--3 of FIG. 2
has a cut-away section. The stud 12 shown in FIGS. 1 and 3 is
hexagonal in its center section 39 and is shown in FIG. 3 as
matching with the interior hexagonal shape of the hole 13 through
the flat annular disks. The lower portion of the end view of FIG. 3
shows the lower part of the end view of the transducer. The end of
stud 12 is shown as rounded and the hexagonal cross-section 40 of
the outer tubular element 10, 11 is shown. Concentric with the flat
annular disks 8, 9 and extending exterior to the disk flat to the
tubular section is the insulating annulus 20 (not shown in FIG. 3).
The electrically conductive disk 4 is shown extending beyond
annulus 20. The only real criterion for the electrically conductive
disk is that it be located between the annular electrostrictive
elements 2, 3 so that the potential applied to disk 4 is applied
laterally equally to each of the elements 2, 3 in order that
electrical energy is delivered equally to the elements. For this
reason, even though an annular electrically conducting disk is
shown extending well beyond the annular electrostrictive elements
2, 3, it is necessary only that the disk extend outwardly to such
an extent that an electrical attachment may be made to it so as to
bring electric potential across the electrostrictive elements.
Annular disk 4 is shown as large and may be used to radiate heat or
to be a radiating and cooling surface since considerable heat may
be generated by the annular electroscrictive elements.
Some of the advantages of my device are that a larger oscillation
amplitude displacement is possible because with a longer
transducer, the displacement at the ends of the transducer assembly
is greater. Another advantage is that because of the correspondence
of resonance between the tension stud and the force generating
system, cracking of the stud or transducer assembly near the ends
of the transducer assembly structure is reduced to a minimum.
Cracks appear mostly because of localized stresses brought about by
forced stud displacement and high dynamic stress. These cracks
cause early failure of the assembly because the phase displacement
of the ends of the transducer assembly is the same in both the stud
and force generating assembly. Undercutting at the ends of the stud
provides a means for avoiding localization of any stress which may
be applied at the ends of the stud and transducer assembly.
The foregoing is a description of an illustrative embodiment of the
invention and it is applicant's invention in the appended claims to
cover all forms which fall within the scope of the invention.
* * * * *