Note: Descriptions are shown in the official language in which they were submitted.
~32~6~
ULTRASONIC TRANSDUCER
TECHNICAL FIELD
The present invention relates to a methoa for
measuring and/or monitoring the amount of material which has
been removed from a member through wear, machining, etc., and
more particularly to an ultrasonic piezoelectric transducer
for measuring and/or monitoring the amount of material which
has been removed from a member and other physical properties
of the member in-situ.
BACKGROUND ART
Various approaches have been devised for detecting,
monitoring and measuring the amount of wear which has
occurred to a wear member. For example, in the area of
rotating equipment, a number of electrical devices are
available to detect and monitor bearing wear. These devices
are based upon a number of detection techniques. Thus, wear
detection might depend upon the completion of an electrical
circuit through the bearing when there is excessive bearing
wear, or it might depend upon the generation of a voltage if
the shaft rotates eccentrically, or it might depend upon the
detection of an abnormal temperature rise of the bearing.
Each of these approaches has some inherent disadvantages with
respect to accuracy and does not measure actual bearing wear,
bearing wall thickness or the amount of material which has
been removed from the bearing, i.e., each approach is
responsive to bearing wear but does not measure
quan-titatively the amount of wear that has occurred, the wall
thickness remaining or the amount of material which has been
~removed.
Other approaches have been devised to measure the
thickness of a workpiece or wear member, and by measuring
such thickness, the amount of wear which has occurred can be
132~ ~8
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calculated. These approaches have numerous commercial and/or
industrial applications, however, their use for measuring the
thickness of or wear which has occurred to a work surface in-
situ is cost prohibitive. In addition, these approachestypically utilize devices fabricated from materials which
limit their applications to an operating environment having a
temperature of normally less than 75C, and cause the
resulting readings to be dependent upon the temperature of
the operating environment. It has also been found that the
materials utilized for these devices cannot withstand severe
operating environments which further limits the applications
in which they can be used. Thus, these devices and
measurement techniques are not usable for measuring and/or
lS monitoring the thickness of or wear which has occurred to
work surfaces, such as a sleeve bearing, in an elevated
temperature operating environment such as might exist in
rotating equipment. This inability to measure and/or monitor
wear in-situ can result in costly machine downtime to inspect
the condition of the bearings. Alternatively, this inability
can result in unnecessary damage to the rotating equipment
due to bearing failure which was not promptly detected.
Because of the foregoing, it has become desirable to
develop a device which can be utilized to measure and/or
monitor in-situ the thickness of, the amount of wear which
has occurred to, and the amount of material which has been
removed from a member such as sleeve or thrust bearings,
brake discs or pads, clutch plates and sealing members.
Ideally, the resulting device could also be used for
measuring other physical properties of the member, in-situ.
SUMMARY OF THE INVENTION
~ The present invention provides an ultrasonic
piezoelectric transducer that can be mounted within the wall
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of a wear member, such as a sleeve or thrust bearing, brake
disc or pad, clutch plate or sealing device, so that
measurements of wall thickness, the amount of materiaL which
has been removed through wear, and other physical properties
such as temperature, can be made in-situ. The transducer,
which is an integral part of the member in which it is
mounted, includes an outer sleeve which is threadedly
rec,eived in a blind bore within the wear member, a
piezoelectric element which is positioned within the blind
bore, and spacer means interposed between the end of the
outer sleeve and the piezoelectric element. The spacer means
and the end of the outer sleeve have complementary
configurations permitting the spacer means to align itself
within the end of the outer sleeve and apply a substantially
uniform compressive force to the piezoelectric element. The
application of such a substantially uniform compressive force
causes a firm, electrical and acoustical contact to be formed
between the piezoelectric element and the bottom of the blind
bore which insures a highly accurate measurement of the wall
thickness between the bottom of the blind bore and the inner
surface of the wear member. For example, it has been found
experimentally that this transducer can readily measure the
wall thickness of and/or the amoùnt of material which has
been removed from the wall of a bronze bearing at
temperatures over 300F with a repeatability in the sub-
micron range utilizing state-of-the-art electronics. The
transducers can also be located in a pre-determined
arrangement around the periphery of the wear member so that
wear and/or material removed can be measured and/or monitored
around the periphery thereof. In addition, it has been found
that other physical properties such as strain resulting from
~stress being applied to the wear member can be monitored with
the transducer. It has also been found that the transducer
~2 ~J~
can be utilized to determine local temperatures within the
wear member and, in the case of rotating machinery, the
relative vibration and alignment between the shaft and the
member can be measured and/or monitored with the transducer.
It has been further found that if ball bearings are being
utilized, each ball exhibits specific pressure
characteristics which change due to wear or fracture, and
that these pressure characteristics can be measured and/or
monitored with the transducer.
In an alternate embodiment of the invention, a
mounting ring is provided to position one or more transducers
against the outer surface of the wear member. In this
embodiment, the piezoelectric elements contact the outer
surface of the wear member and the total thickness of the
wear member is measured.
In still another alternatè embodiment of the
invention, the blind bores within the wear member are
replaced with though bores to reduce production costs. A
transducer assembly is received within each of the through
bores so that its end is flush with the inner surface of the
wear member. In this embodiment, the end of the transducer
assembly is actually an integral part of the wear surface and
the thickness of the end of the transducer assembly is being
measured.
Regardless of the embodiment utilized, a separate
transducer may be placed in the same environment as the other
transducers to provide a relative time reference for
temperature compensation. Several embodiments of relative
time references are disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial cross-sectional view of an
ultrasonic piezoelectric transducer embodying the invention
of this disclosure and installed in a wear member.
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Figure 2 is a partial cross-sectional view of a
plurality of ultrasonic piezoelectric transducers embodying
the invention of this disclosure and installed in and around
the periphery of a wear member, such as a sleeve bearing.
Figure 3 is a partial cross-sectional view of a
mounting ring for retaining one or more ultrasonic
piezoelectric transdusers against the outer surface of a wear
member, such as a sleeve bearing or a ball bearing.
Figure 4 is a partial cross-sectional view of an
alternate embodiment of an ultrasonic piezoelectric
transducer embodying the invention of this disclosure and
installed in a wear member.
Figure 5 is similar to Figure 4 in that it is a
partial cross-sectional view of an ultrasonic piezoelectric
transducer which provides a relative time reference for
temperature compensation.
Figure 6 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
Figure 7 illustrates an interrogating pulse to and a
return "echo" pulse from an ultrasonic piezoelectric
transducer embodying the invention of this disclosure.
Figure 8 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
Figure 9 is a partial cross-sectional view oE another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
Figure 10 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
~ 3~s'~
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Figure 11 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
Figure 12 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a relative time
reference for temperature compensation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings where the illustrations
are for the purpose of describing the preferred embodiment of
the present invention and are not intended to limit the
invention hereto, Figure 1 is a cross-sectional view of the
transducer 10 installed in a wear member 12, such as a sleeve
or thrust bearing, clutch plate, brake disc or pad, sealing
member, valve or the like, in order to measure and/or monitor
the thickness of, the amount of wear which has occurred to,
and the amount of material which has been removed from the
wear member. The transducer 10 is comprised of an outer
sleeve 14, an aligning and electrically insulating spacer 16
received within the end of the outer sleeve, and a
piezoelectric element 18.
The outer sleeve 14 is typically fabricated from round
tubing, such as brass tubing or the like, which has threads
formed adjacent to one end thereof. Typically, the tubing
material has the same or similar thermal expansion properties
as that of the wear member 12 to maintain a firm contact
therewith. This firm contact is provided by the threads 20
which engage complementary threads provided in the wear
member 12, as hereinafter described. The threads 20 also
permit the adjustment of the outer sleeve 14 within the wear
member 12 to optimize the operation of the transducer 10 as
~2 ~ $.~
discussed later. It should be noted that other approaches
are possible for the adjustable attachment of the outer
sleeve 14 to the wear member 12, such as a bracket
arrangement (not shown) that is adjustable with respect to
the wear member 12 and which retains the sleeve 14. The end
22 of the outer sleeve 14 has an indentation provided therein
forming a surface 24 connecting the end 22 of the sleeve 14
with the inner cireumferential wall 26 of the sleeve. This
indentation may have a curved eonfiguration, sueh as
semispherieal or parabolie, or it may have a conieal
eonfiguration whieh is preferred to permit alignment of the
spacer 16 therein.
The aligning and electrically insulating spacer 16 is
fabricated from a ceramic or ceramic-like material that is
eapable of sustaining hiqh temperatures and high pressures.
For example, pyrolytie boron nitride or another eeramic-like
material can be used for the spacer 16. The particular
eeramie or eeramic like-material utilized for the spacer 16
is seleeted to properly eompensate for the thermal expansion
properties of the other eomponents eomprising the transducer
and the wear member 12 so that the spacer 16 will maintain
a substantially uniform eompressive foree on the
piezoelectric element 18 over a broad operating temperature
range. The spaeer 16 typieally has a eonieal eonfiguration
that is eomplementary to that of the indentation formed in
the end 22 of the outer sleeve 14. The spaeer 16 is reeeived
within the indentation so that the outer surfaee 28 defining
its eonieal eonfiguration eontacts the surface 24 formed by
the indentation. The use of eonieal surfaees 24, 28 formed
on the outer sleeve 14 and the spaeer 16, respectively
permits the alignment of the spacer 16 within the outer
sleeve 14 through elastie deformation of the spacer 16 and
the indentation formed in the end 22 of the outer sleeve 14.
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In contrast, self-alignment of the spacer 16 within the outer
sleeve 14 can be achieved by using a semi-spherical or
parabolic configuration for the surfaces 24, 28 formed on the
end 22 of the outer sleeve 14 and the spacer 16,
respectively. It should be noted that regardless of the
shape of the complementary configurations used for the spacer
16 and the indentation in the end 22 of the outer sleeve 14,
a precise fit of the spacer 16 within the indentation is not
necessary since any variations in size or shape will be
compensated for by the elastic deformation of the spacer 16
and the indentation and/or by the self-alignment of the
complementary curved surfaces. The alignment of the spacer
16 within the outer sleeve 14, whether by elastic deformation
of the spacer 16 and the indentation in the end 22 of the
outer sleeve 14 or by self-alignment through complementary
curved surfaces, is necessary to ensure the application of a
uniform compressive force on the piezoelectric element 18.
Such a substantially uniform compressive force also minimizes
the possibility of damaging the piezoelectric element 18
through the application of a nonuniform compressive force
thereto. Even though both of the foregoing approaches apply a
substantially uniform compressive force to the piezoelectric
element 18, it has been found that the use of an appropriate
conical configuration for the spacer 16 and the indentation
in the end 22 of the outer sleeve 14 is easier to implement
and may result in a substantially higher absorption and
obliteration of spurious echoes from the primary ultrasonic
signal than if complementary curved configurations are used
for the spacer 16 and the indentation in the end 22 of the
outer sleeve 14. Thus, the use of a conical configuration
for the spacer 16 and the end 22 of the outer sleeve 14
generally results in a higher signal to noise ratio than if
complementary curved configurations are used for same. In
~ 3 h ~ r~ ~3
_9 _
summary, the spacer 16 is necessary in this structure in
order to provide a substantially uniform compressive force to
the piezoelectric element 18 and to absorb and obliterate
spurious echoes. Regardless of the configuration utilized
for the spacer 16, an aperture 30 is formed therethrough.
This aperture is sufficiently large to permit the passage of
an electric conductor therethrough.
The wear member 12 is provided with a blind bore 36
therein. The blind bore 36 is located so as to be
substantially perpendicular to the outer and inner surfaces
38, 40, respectively of the member 12. If the member 12 is a
sleeve bearing, the blind bore 36 is directed radially
inwardly so as to be normal to the inner surface 40 of the
rnember 12. The blind bore 36 is of a predetermined depth and
has a substantially flat surface 42 at the bottom thereof.
The distance between the flat surface 42 and the inner
surface 40 of the member 12 is the distance to be measured
and/or monitored. The blind bore 36 may also have threads 44
formed therein which terminate adjacent to the bottom
thereof.
The piezoelectric element 18 is a standard state-of-
the-art device and typically has a round disc-like shape. The
element 18 can be formed from commercially available
piezoelectric transducer material, such as PZT-5H available
from Vernitron, Inc. of Bedford, Ohio. The size of the
element 18 is a function of the overall size of the
transducer 10, however, an element having a diameter of 0.080
inch and a thickness of .003 inch has been tested
experimentally with excellent results. The diameter of the
element 18 is slightly less than the diameter of the blind
bore 36 provided in the wear member 12. The element 18 is re-
sponsive to a short voltage pulse, such as a 200 volt DC
pulse of 10 nanosecond duration, and converts the voltage
--1 0-- ~ ~ 2 ~
pulse into a pressure pulse which is applied to the surface
of the material whose thickness is to be measured and/or
monitored. Similarly, the piezoelectric element 18 converts
the "echo" return pressure pulse from the opposite surface of
the material whose thickness is being monitored into a
voltage pulse for measurement purposes. The substantially
uniform compressive force applied to the piezoelectric
element 18 by the spacer 16 ensures that the element 18 is
firmly "seated" within the blind bore 36 for the proper
transmission of the voltage pulse into the element 18 and the
reception of the reflected "echo" pulse by the element.
In order to assemble the transducer 10, the
piezoelectric element 18 is received within the blind bore 3G
and positioned so that one side 46 thereof contacts the flat
surface 42 at the bottom of the blind bore 36. Inasmuch as
the diameter of the element 18 is only slightly less than the
diameter of the blind bore 36, the center of the element 18
and the center of the flat surface 42 at the bottom of the
blind bore 36 will substantially coincide, however, such
coincidence is not necessary for the proper operation of the
transducer 10. The other side 48 of the piezoelectric
element 18 may be electrically connected to an electrical
conductor 50. The electrical conductor 50 is received
through the aperture 30 provided in the spacer 16, and the
spacer 16 is received in the blind bore 36 so that its base
32 contacts the side 48 of the piezoelectric element 18 which
is mechanically and electrically connected to the electrical
conductor 50. The threads 20 on the outer sleeve 24 are
coated with an adhesive, such as Loctite, and the sleeve 14
is threadedly advanced into the wear member 12 until the
conical surface 24 provided on its end 22 engages the outer
surface 28 of the spacer 16. Further advancement of the
outer sleeve 14 into the wear member 12 causes the elastic
C~ ~
deformation of the spacer 16 and the indentation in the end
22 of the outer sleeve 14, and the application of a
substantially uniform compressive force by the base 32 of the
spacer 16 to the side 48 of the piezoelectric element 18. If
complementary curved configurations, such as semispherical or
parabolic, are used for the spacer 16 and the indentation in
the end 22 of the outer sleeve 14, the spacer 16 will self-
align itself within the indentation in the end 22 of the
outer sleeve 14 so that its base 32 will apply a
substantially uniform compressive force to the side 48 of the
piezoelectric element 18. Regardless of the shape of the
spacer 16 and the indentation in the end 22 of the outer
sleeve 14, the outer sleeve 14 is threadedly advanced into
the wear member 12 by manually rotating the outer sleeve 14
until a snug fit exists between the indentation provided in
its end 22 and the outer surface 28 of the spacer 16, and
between the base 32 of the spacer 16 and the side 48 of the
piezoelectric element 18. In order to ensure that such a
snug fit exists, the foregoing advancement of the outer
sleeve 14 into the wear member 12 is monitored by a pulser-
receiver device and an oscilloscope (all not shown). With
this apparatus a sequence of short voltage pulses is applied
by the pulser to the transducer 10 while the outer sleeve 14
is being threadedly advanced into the wear member 12 so that
the sleeve 14 can be rotationally adjusted until the optimum
return "echo" pulse, shown on the oscilloscope, is recorded
by the receiver. In this manner, a snug fit between the
foregoing components is assured and the transducer 10 and the
wear member 12 are "matched" to provide the optimum return
"echo" pulse with respect to shape, amplitude and signal to
noise ratio. This snug fit is retained through the use of
the aforementioned adhesive, such as Loctite, on the threads
of the outer sleeve 14, thus preventing any further movement
~3
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of the outer sleeve 14 with respect to the wear member 12.
In essence, the transducer 10 becomes permanently affixed to
and an integral part of the wear member 12, and the snug fit
between the indentation in the end 22 of the outer sleeve 14
and the outer surface 2B of the spacer 16 is maintained
throughout the life of the device.
Since the piezoelectric element 18 is somewhat
deformable under a compressive force, the application of a
substantially uniform compressive force thereto results in a
firm, optimum electrical and acoustical contact between the
side 46 of the element 18 and the flat surface 42 at the
bottom of the blind bore 36. By providing such a firm,
optimum electrical and acoustical contact with the flat
surface 42 of the blind bore 36, any signals emanating from
the piezoelectric element 18 will be properly directed toward
the inner surface 40 of the wear member 12 to be measured
and/or monitored, and the wear member 12 will provide the
proper electrical ground for the system. Thus, the surfaces
24, 28 compensate for deviations in manufacturing tolerances
in the components involved, and the possibility that the
blind bore 36 may not be positioned exactly normal to the
inner surface 40 of the wear member 12. Both of these
conditions could result in the piezoelectric element 18 not
firmly contacting the flat surface 42 of the blind bore 36
which, in turn, could result in inaccurate measurements
and/or system malfunctions. After the transducer 10 has been
assembled and installed in the wear member 12, the area 52
enclosed by the inner circumferential wall 26 of the outer
sleeve 14 and containing the electrical conductor 50 may be
filled with a dense insulating and dampening material such as
epoxy, e.g., Duro epoxy, loaded with tungsten for application
temperatures less than 400F. or loaded ceramic adhesive for
temperatures in excess of 400F. This electric insulation
~ 2 ~L~3 tJ(3
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material and the spacer 16 preferably match the acoustical
impedance of the piezoelectric element 18 and help suppress
spurious echoes from interfering with the primary
measurement.
The wear member 12 may have a configuration that is
either flat, such as a brake disc, clutch plate, face type
seal or thrust bearing, or circular, such as a sleeve bearing
or ring type seal. In any case, a plurality of transducers
can be utilized to measure and/or monitor wear at various
locations on the wear member 12. If a sleeve bearing is
utilized, the plurality of transducers 10 can be placed
within the outer bearing wall and around the periphery of the
bearing, as shown in Figure 2. In this manner, the thickness
of, the amount of wear which has occurred to, and the amount
of material which has been removed from the bearing can be
measured and/or monitored at various locations around the
periphery thereof. Thus, by placing the transducer 10 within
one or more blind bores 36 within the bearing, wear can be
measured and/or monitored in situ, eliminating costly
periodic machine downtime to inspect the condition of the
bearing. Machine downtime would only occur when a transducer
indicates that sufficient wear has occurred to justify the
replacement of the bearing.
Alternatively, rather than placing a plurality of
transducers 10 within the blind bores provided in the outer
bearing wall, a mounting attachment 54, such as a ring as
shown in Figure 3, can be used to retain the transducers 10
in a radially spaced apart relationship. In such an
arrangement, the mounting attachment 54 is slipped over the
sleeve bearing 56 and the piezoelectric elements 18 firmly
contact the outer surface of the bearing wall. Thus, no
blind bores, which could damage the bearing or affect its
performance, are required in the bearing wall. The foregoing
is particularly important in the case of ball bearings. In
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the arrangement shown in Figure 3, the radius of the
curvature of the bearing 56 is substantially greater than the
diameter of each piezoelectric element 18. Since a
substantial compresslve force is being applied to each
element 18 by its associated spacer 16, it has been found
that sufficient surface contact exists between each element
18 and the outer surface of the bearing 56 to produce very
accurate distortionless measurements of wall thickness. Thus,
by using this apparatus, the thickness of, the amount of wear
which has occurred to, the rate of wear of, and the amount of
material which has been removed from the bearing wall can be
measured and/or monitored at various locations on the
bearing. From the foregoing, it is apparent that the
mounting attachment 54 can also be used to measure the wall
thickness or the overall thickness of a non-wear cylindrical
member, such as a machine member, by slipping the mounting
attachment 54 over the non-wear member and positioning the
piezoelectric elements 18 so that they firmly contact the
outer surface of the non-wear member at specific locations
thereon. Thus, the transducer 10 can be utilized for
precision in-processing gauging or in-process measuring of
strain.
In addition to being able to measure and/or monitor
the thickness of, the amount of wear which has occurred to,
and the amount of material which has been removed from a
wear member in-situ, the construction of the transducer 10
provides another advantage in that no buffer element is
required between the piezoelectric element 1~ and the wall
whose thickness is being measured and/or monitored, i.e., the
distance between the flat surface 42 of the blind bore 36 and
the inner surface 40 of the wear member 12. Typically, in
prior art devices such a buffer element is required fcr
mechanical support, impedance matching and sealing of the
3 3 3
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transducer, however, its use greatly attenuates and degrades
the primary pulses produced by the transducer and the
reflected "echo" pulses received by the transducer. Inasmuch
as the transducer 10 requires no buffer element, such signal
attenuation and degradation does not occur. In addition,
because of the absence of a buffer element, a firm electrical
and acoustical contact can be made by the piezoelectric
element 18 directly to the wall whose thickness is being
measured and/or monitored, and the resulting measurements
have a much higher degree of accuracy than those resulting
from prior art devices. For example, measurements with a
repeatability in the submicron range utilizing state-of-the-
art electronics have been achieved. And lastly, due to the
inherent simplicity of the structure of the transducer, it is
substantially less costly to produce than the prior art
devices.
In an alternate embodiment of the invention, as shown
in Figure 4, the blind bore 36 in the wear member 12 is
replaced with a through bore 60 connecting the outer and
inner surfaces 38, 40 of the member 12. The through bore 60
may have threads 62 formed therein. A transducer 64
comprising an outer sleeve 14, a spacer 16~ and a
piezoelectric element 18 is received within a blind bore 66
in a wear reference member 68 which may have threads 70
formed on the outer surface thereof. The wear reference
member 68 is received within the through bore 60 so that its
end 72 is substantially flush with the inner surface 40 of
the wear member 12. The inner surface 40 of the wear member
12 is then machined to ensure that the end 72 of the wear
reference member 68 is flush with the inner surface 40. It
should be noted that the material utilized for the wear
reference member 68 may be the same as or may be different
from the material comprising the wear member 12 inasmuch as
.~J~ l3~3
-16-
only the thickness of the end oE the reference member 68 is
belng monitored and/or measured. The operation of this
embodiment is similar to the previous embodiment utilizing a
blind bore, however, it is easier and less costly to
produce.
With any of the foregoing embodiments, it might be
desired to compensate for the temperature and pressure of the
environment and the strains existing on the transducer. Such
compensation can be accomplished by using a transducer that
provides a relative time reference, such as transducer 80,
shown in Figure 5. The structure of this transducer 80 is
similar to transducer 10, in that it comprised of an outer
sleeve 14, a spacer 16, and a piezoelectric element 18,
however, the foregoing components are received in a blind
bore 82 provided in a reference member 84, which is similar
to wear reference member 68. The material utilized for the
reference member 84 is the same as or similar to the material
for the wear member 12 if a blind bore 36 is utilized in the
member 12, or the same as or similar to the material for the
wear reference member 68 if a through bore 60 is provided in
the wear member 12. The assembly of the transducer 80 and
the reference member 84 is placed within the same
temperature, pressure or material environment as the other
transducers 10, though not necessarily contacting the wear
member 12. By monitoring the measurements of the reference
distance, produced by the transducer 80, the measurements
produced by the transducer 10 can be adjusted to compensate
for possible measurement variations caused by operating
environment changes.
Another embodiment of a transducer that provides a
relative time reference is transducer 90 shown in Figure
6. The structure of this transducer is similar to the
transducer 80 in that it is comprised of an outer sleeve 14,
a spacer 16, a piezoelectric element 18, and an electrical
.
.
CJ? ((3
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conductor 50, however, the foregoing components are received
in a blind bore 36 provided in the wear member 12. The
electrical conductor 50 is attached to a disc-shaped
electrical connector 92 which is interposed between the base
32 of spacer 16 and the top surface 94 of a reference
acoustical member 96 having a cylindrical configuration. The
bottom surface 98 of the reference acoustical member 96
firmly contacts the other side 48 of the piezoelectric
10 element 18. The diameters of the disc-shaped electrical
connector 92 and the reference acoustical melnber 96 are
similar and are slightly less than the diameter of the blind
bore 36 permitting the easy insertion therein. The reference
acoustical member 96 is formed from the same material as, or
15 similar material to, the material comprising the wear member
12. A recess 100, which is preferably cylindrical in
configuration, is provided in the top surface 94 of the
reference acoustical member 96 and is concentric with the
center of the reference member 96 leaving the area between
20 the diameter of the recess 100 and the outer diameter of the
reference member 96 in contact with the bottom surface of the
electrical connector 92. A low impedance acoustical material
102 may be provided in the recess 100 or the recess 100 may
be left empty in which case it would have approximately a
25 zero impedance. The low impedance of the recess 100 provides
a relatively large reflection coefficient for any pressure
wave intercepted thereby. Such a relatively large reflection
coefficient is beneficial for the operation of this
transducer 90, hereinafter described.
Operationally, a short voltage pulse is applied to
the piezoelectric element 18 via the electrical conductor 50,
the electrical connector 92 and the reference acoustical
member 96. The piezoelectric element 18 converts the voltage
pulse into two pressure pulses which are transmitted in
opposite directions--one pressure pulse being transmitted
r~ 'r
-18-
into the wear member 12 via the one side 46 of the element 18
and the other pressure pulse being transmitted into the
reference acoustical member 96 via the other side 48 of the
5 element 18. The pressure pulse transmitted into the wear
member 12 is reflected by the inner surface 40 of the wear
member 12 back toward the one side 46 of the piezoelectric
element 18 and is intercepted by same. Similarly, the
pressure pulse transmitted into the reference acoustical
lO mernber 96 is reflected by the low impedance acoustical
material 102 in the recess 100 back toward the other side 48
of the piezoelectric element 18 and is intercepted by same.
Inasmuch as the thickness of the reference acoustical member
96 varies independently of wear and is typically affected
15 only by variations in temperature, the elapsed time between
the transmission of the initial pressure pulse and the
receipt of the "echo" return pressure pulse can be
determined and utilized as a temperature reference
parameter. Thus, in essence, one pressure pulse "monitors"
the thickness of the wear member 12 and the other pressure
pulse "monitors" the thickness of the reference acoustical
member 96 between the top surface of the piezoelectric
element 18 and the bottom of the recess 100 containing the
low impedance material 102. By "measuring" the latter
thickness through elapsed pulse travel time, compensation can
be made for variations in the thickness of the wear member 12
resulting from temperature variations. In addition, through
manipulation of the resulting pulse travel time data and
calibration as a function of pressure, compensation can be
made for variations in the thickness of the wear member 12
resulting from variations in the pressure to which the member
12 is subjected.
The advantage of interposing the piezoelectric element
18 between the reference acoustical member 96 and the portion
of the wear member 12 whose thickness is being monitored or
-1 9-
measured, and uslng the piezoelectric element to
simultaneously transmit pressure pulses in opposite
directions is that signal degradation is minimized and a
high signal-to-noise ratio is maintained. For example, if
the reference acoustical member is located on the same side
of the piezoelectric element as the portion of the wear
member whose thickness is being monitored or measured, i.e.,
the reference acoustical member is interposed between the
piezoelectric element and the "monitored or measured" portion
of the wear member, pressure pulses only in one direction
are required. However, each pressure pulse must pass through
the reference acoustical member, the portion of the wear
member whose thickness is being monitored or measured, and
the interface therebetween. The end result is significant
degradation and attenuation of the signal and substantial
differences in the amplitude of the "echo" return pulses from
the foregoing interface and the inner surface of the wear
member. Such signal degradation and differences in pulse
amplitude results in inaccuracies in elapsed travel time
measurements, low signal-to-noise ratios, and inaccuracies in
the "temperature compensations" made for variations in the
thickness of the wear member.
As previously indicated, physical properties other
than the thickness of, the amount of wear has occurred to,
and the amount of material which has been removed from the
wear member can be measured and/or monitored by the
transducer 10. For example, it has also been found that
strain due to stress being applied to the wear member can be
readily monitored by one or more transducers mounted within
or attached to the wear member. By such monitoring,
appropriate means can be taken to minimize and/or control
such stress within the wear member. It has also been found
that local temperature within the wear member can be
~ ~ 2 1 ~ r
-20-
determined with one or more transducers and, in the case of
rotating equipment, the relative vibration and alignment
between the shaft and the wear member can be measured and/or
monitored by the transducers. It has been further found that
if ball bearings are being utilized, the pressure
characteristics of each ball can be measured and/or monitored
by a transducer to determine ball wear or fracture.
Another approach for obtaining temperature
compensation when using the transducer 10 or for measuring
temperature of the wear member 12 with the transducer 10 is
shown in Figure 7 which illustrates an interrogating voltage
pulse which is applied to the transducer 10 and the resulting
return "echo" voltage pulse produced by the same transducer.
The return voltage pulse is defined by a first zero crossing
point corresponding to time t and a second zero crossing
point corresponding to time t1. It has been found
experimentally, that the ratios tl, and thus tl-t, are
t t
relatively independent of temperature and pressure variations
to which the transducer and the wear member may be subjected
and these ratios remain substantially constant unless wear
has occurred. Even though the foregoing ratios are
relatively independent of temperature and pressure, the time
t and the time interval t1-t are each a function of
temperature Thus, if the temperature of the wear member 12
is initially determined, and time t and the time interval
t1-t are measured at the time of initial temperature
determination, a measurement of time t and the time interval
t1-t after a temperature change has occurred to the wear
member 12 can be utilized to determine the temperature of the
transducer 10 or the wear member 12. Alternatively, the
temperature of the wear member 12 can be determined by using
a reference transducer 80, as in Figure 5, and the resulting
~.J,~
-21-
temperature can be substituted in the functional relationship
between temperature, pressure and the time interval t1-t to
determine pressure. Thus, the time t and the time interval
t1-t can be utilized to determine the wear, temperature
and/or the pressure to which the transducer and/or wear
member are being subjected.
Temperature compensation can also be achieved without
the use of a reference acoustical member or a separate
lO reference transducer by incorporating a relative time
reference into the transducer. The foregoing is accomplished
in the alternate embodiment of the transducer 110 shown in
Figure 8. The structure of this transducer 110 is similar to
the transducer 64 shown in Figure 4 in that it is comprised
15 of an outer sleeve 14, a spacer 16, a piezoelectric element
18, an electrical conductor 50, all of which are received
within a blind bore 66 in a wear reference member 68,
however, the end 72 of the wear reference member 68 has a
centrally located tip 112 protruding therefrom. As in Figure
4, the wear reference member 68 is received within the
through bore 60 in the wear member 12, however, its end 72 is
not flush with the inner surface 40 of the wear member 12.
The end 72 of the wear reference member 68 forms a plane
which is opposite a portion of the piezoelectric element 18
to intercept and reflect a portion of the pressure pulses
transmitted thereby. The end 114 of the centrally located
tip 112 is machined to ensure that it is flush with the inner
surface 40 of the wear member 12 and substantially parallel
to the end 72 of the wear reference member 68. In this
embodiment, the distance x between the bottom surface 116 of
the blind bore 66 and the end 72 of the wear reference member
68 can be accurately measured and acts as a reference
distance. Since the end 72 of the wear reference member 68
is not subjected to wear, the distance x is affected only by
-22-
changes in the temperature of transducer 110. The distance y
between the bottom surface 116 of the blind bore 66 and the
end 114 of the centrally located tip 112 is subject to
S change due to wear and variations in transducer temperature.
Operationally, a short voltage pulse is applied to the
piezoelectric element 18 via the electrical conductor 50.
The piezoelectric element 18 converts the voltage pulse into
a pressure pulse which is transmitted into the bottom portion
118 of the wear reference member 68 via the one side 46 of
the element 18. The pressure pulse that is transmitted is
reflected by the end 72 of the wear reference member 68 and
by the end 114 of the centrally located tip 112 resulting in
two "echo" return pressure pulses being transmitted back
toward the one side 46 of the piezoelectric element 18 which
intercepts same. Appropriate means (not shown) are utilized
to separate these two "echo" return pressure pulses. In
addition, the elapsed time between the transmission of the
initial pressure pulse and the receipt of each of the two
"echo" return pressure pulses can be determined. The elapsed
time between the transmission of the initial pressure pulse
and the receipt of the "echo" return pressure pulse from the
end 72 of the wear reference member 68 is representative of
distance x which changes with temperature but is unaffected
by wear since it is not a wear surface. The elapsed time
between the transmission of the initial pressure pulse and
the receipt of the "echo" return pressure pulse from the end
114 of centrally located tip 112 is representative of the
distance y which changes with temperature and wear since the
end 114 of tip 112 is a wear surface. Inasmuch as the
temperature of the bottom portion 118 of the wear reference
member 68 and the centrally located tip 112 are substantially
the same, by comparing the elapsed times between the
transmission of the initial pressure pulse and the receipt of
~ '~ '3 ~ ~1 Q
--23--
each of the two "echo" return pressure pulses, compensation
can be made for the operating temperature of the transducer
110 and a very accurate indication of the amount of wear
which has occurred to the end 114 of centrally located tip
112 can be determined. In this manner, temperature
compensation can be easily accomplished without the use of a
reference acoustical member and/or a separate reference
transducer.
An alternate embodiment of the transducer 110, shown
in Figure 8, is transducer 120, illustrated in Figure 9. In
this embodiment, those elements which are similar to the
elements shown in Figures 4 and 8 carry the same reference
numerals and will not be discussed further. This transducer
120 differs from transducer 110 in that the wear reference
member 68 has a horizontal slot 122 passing partially
therethrough. The horizontal slot 122 is substantially
parallel to but spaced apart from the end 72 of the wear
reference member 68. The top surface 124 of the horizontal
slot 122 forms a plane which is opposite a portion of the
piezoelectric element 18 to intercept and reflect a portion
of the pressure pulses transmitted thereby. This transducer
120 further differs in that the wear reference member 68 does
not have a centrally located tip 112. In this case, the
distance x ~the reference distance) is between the bottom Sor~c~
116 of blind bore 66 and the top surface 124 of the slot 122
and the distance y is between bottom surface 116 of blind
bore 66 and the end 72 of the wear reference member 68. As
in the previous embodiment, a short voltage pulse is applied
to the piezoelectric element 18 which converts the voltage
into a pressure pulse which is transmitted into the bottom
portion 118 of the wear reference member 68. The foregoing
pressure pulse is reflected by the top surface 124 of the
slot 122 and the end 72 of the wear reference member 68
:~ 3 2 ~ $ ~, ~
-24-
resulting in two "echo" return pressure pulses which are
separated. By measuring the elapsed times between the
transmission of the initial pressure pulse and the receipt of
each of the two "echo" return pressure pulses, and by
comparing these elapsed times, compensation for temperature
can be made so that the wear which has occurred to the end
72 of the wear reference member 68 can be accurately
determined.
lOAn alternate embodiment of the transducer 1Z0, shown
in Figure 9, is transducer 130, illustrated in Figure 10.
Here again, those elements which are similar to the elements
shown in Figures 4, 8 and 9 carry the same reference numerals
and will not be discussed further. This transducer 130
15differs from transducer 120 in that the horizon-tal slot 122
is replaced by a circumferential horizontal slot 132 which is
substantially parallel to but spaced apart from the end 72 of
the wear reference member 68. The top surface 134 of the
circumferential horizontal slot 132 forms a plane which is
opposite a portion of the piezoelectric element 18 to
intercept and reflect a portion of the pressure pulses
transmitted thereby. In this case, the distance x (the
su~
reference distance) is between the bottom~116 of the blind
bore 66 and the top surface 134 of the circumferential
horizontal slot 132 and the distance y is between the bottoms~h~
116 of the blind bore 66 and the end 72 of the wear reference
member 68. As in the previous embodiments, the top surface
134 of the circumferential horizontal slot 132 and the end 72
of the wear reference member 68 produce separate "echo"
return pressure pulses in response to a pressure pulse from
the piezoelectric element 18. Similarly, as in the previous
embodiments, by measuring and comparing the elapsed times
between the transmission of the initial pressure pulse and
the receipt of each of the two "echo" return pressure pulses,
~2~
-25-
temperature compensation can be accomplished and an accurate
determination of the wear which has occurred to the end 72 of
the wear reference member 68 can be made.
A still another alternate embodiment of the transducer
110, shown in Figure 8, is transducer 140, illustrated in
Figure 11. Here again, those elements which are similar to
the elements shown in Figure 8 carry the same reference
numerals and will not be discussed further. Thls transducer
140 differs from transducer 110 in that the centrally located
tip 112 on transducer 110 is replaced by a centrally located
recess 142. The top surface 144 of the centrally located
recess 142 is substantially parallel to the end 72 of the
wear reference member 68 and forms a plane which is opposite
a portion of the piezoelectric element 18 to intercept and
reflect a portion of the pressure pulses transmitted
thereby. In this case, the distance x (the reference
5~''ra C~
difference) is between the bottom~116 of the blind bore 66
and the top surface 144 of the centrally located recess 142
and the distance y is similar to that in Figures 9 and 10
s~r~ce
since it is from the bottom~116 of the blind bore 66 to the
end 72 of the wear reference member 68. As in all of the
previous embodiments, the transmission of a pressure pulse by
the piezoelectric element 18 results in two "echo" return
pressure pulses, one "echo" return pulse from the top surface
144 of the centrally located recess 142 and the other "echo"
return pressure pulse from the end 72 of the wear reference
member 68. By measuring and comparing the elapsed times
between the transmission of the initial pressure pulse and
the receipt of each of the two "echo" return pressure pulses,
compensation can be made for temperature so that the wear
which has occurred to the end 72 of the wear reference member
68 can be accurately determined.
~ v 2 ~
-26-
Another alternate embodiment of transducer 110, shown
in Figure 8, is transducer 150, illustrated in Figure 12. As
in the all of the previous embodiments, those elements which
5 are similar to the elements shown in Figure 8 carry the same
reference numerals and will not be discussed further. The
transducer 150 differs from transducer 110 in that the end 72
of the wear reference member 68 has a clrcumferential pocket
152 formed therein with the tip 112 protruding substantially
centrally therefrom. The top surface 154 of the
circumferential pocket 152 is substantially parallel to the
end 114 of the centrally located tip 112 and forms a plane
which is opposite a portion of the piezoelectric element 18
to intercept and reflect a portion of the pressure pulses
transmitted thereby. In this case, the distance x (the
5 V~;~ce.
reference distance) is between the bottom~116 of the blind
bore 66 and the top surface 154 of the circumferential pocket
152. The distance y is the same as in Figure 8 in that it is
50/~a~,e.
from the bottom~l~ 116 of blind bore 66 to the end 114 of the
centrally located tip 112. As in all of the other previous
embodiments, the transmission of a pressure pulse by the
piezoelectric element 18 into the bottom portion 118 of the
wear reference member 68 causes two "echo" return pressure
pulses to be formed--one "echo" return pressure pulse being
reflected by the top surface 154 of the circumferential
pocket 152 and the other "echo" return pressure pulse being
reflected from the end 114 of the centrally located tip 112.
Here again, by measuring the elapsed times between the
transmission of the initial pressure pulse and the receipt of
each of the two "echo" return pressure pulses, and by
comparing these elapsed times, temperature compensation can
be accomplished and an accurate determination of the wear
which has occurred to the end 114 of the centrally located
tip 112 can be made.
-27-
It should be noted that the foregoing embodiments
of transducers (Figures 8 through 12) and the waveform
illustrated in Figure 7 show that temperature compensation
can be readily achieved without the use of a reference
acoustical member, such as an interposing buffer or a
separate reference transducer. It should be further noted
that the foregoing structures shown in these Figures
illustrate typical structures, and many other structures are
obtainable and can be used to achieve the same result. Thus,
the structures are representative structures and, in no way,
illustrate all of the structures which can be produced to
obtain a transducer in which temperature compensation can be
achieved without the use of a reference acoustical member or
a separate reference transducer. Regardless of the structure
utilized, the objective is to provide a relative time
reference surface as close as possible to the wear member
surface being monitored so that wear can be accurately
determined.
Certain modifications and improvements will occur to
those skilled in the art upon reading the foregoing. It
should be understood that all such modifications and
improvements have been deleted herein for the sake of
conciseness and readability, but are properly within the
scope of the following claims.
