Note: Descriptions are shown in the official language in which they were submitted.
2n6~05
ULTRASONIC TRAI~SDUCER
TECHNICAL F I ELD
The present invention relates to a method for
rneasuring 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, or alternatively for measuring the
position of a surface on or in proximity to the member.
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 sha~t rotates eccentrically, or it might depend upon the
det~ction of an abnormal temperature rise of the bearing.
~ach 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
quantitatively the amount of wear that has occurred, the wall
thickness remaining or the amount of material which has been
removed.
~ ther approaches have been devised to measure the
thickness o~ a workpiece or wear member, and by measuring
such thickness, the amount of wear which has occurred can be
~ `;
2068~0~
calsulated. lrhese approaches have numerous commercial and/or
industrial applications, however, their use ior measuring the
thickness of or wear which has occurred to a work surface in-
situ i5 cost prohibitive. In addition, these approacles
typically utilize devices fabricated from materials which
]imit their applications to an operating environment having a
tem~erature of normally less than 75C, and cause the
resulting readings to be dependent upon the temperature of
t'ne operating environment. It has also been found that the
matQrials utilized for these devices cannot withstand severe
opera-ting environments which further limits the applications
in which they can be used. Thus, these devices and
rneasurement techniques are not usable for measuring and/or
monitoring the thickness of or wear which has occurred to
work surfaces, such as a sleeve bearing, in an elevated
ternperature operating environment such as might exist in
rotating equipment. This inability to measure and/or monitor
wear in-situ can result in coskly machine downti~e 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,
bra]ce discs or pads, clutch plates and sealing mernbers.
Ideally, the resulting device could also be used for
measuring other physical properties (such as temperature or
pressure) of the member, in-situ, and positional properties
of the member relative to other members or surfaces defining
same.
2 ~ 0 ~
SU_ ARY OF THE INVENTION
The present inven-tion provides an ultrasonic
piezoelectric transducer that can be mounted within the wall
of a wear member, such as a sleeve or thrust bearing, brake
disc ox 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 and/or pressure, can be made in-situ.
T`ne transducer, which is an integral part of the member in
which it is mounted, includes an outer sleeve which is
threadedly received in a blind bore within the wear member, a
piezoelectric element which is positioned within the blind
bore, and spacer means inLerposed 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
hetween 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
exp~rimentally that this transducer can readily measure the
wall thickness of and/or the amount 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
2068~0~
that other physical properties such as strain resulting from
stress being applied to the wear member can be monitored with
th~ transducer. It has also been found that the transducer
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.
Alternatively, the position oE the shaft relative to a wear
surface can be determined, i.e., the oil film between the
wear surface and the outer periphery of the shaft can be
"jumped" to determine the position of the shaft. 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 alternate 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.
206830~
. .
Regardless of the embodiment utilized, a separate
t~.ansducer may be placed in the same environment as the other
transducers to provide a relative time reference or a
: plurality of relative time references for temperature
compensation. Several embodiments of relative time
references are disclosed.
13R EF DESCRIPTION OF THE D A~INGS
Figure 1 is a partial cross-sectional view of an
ultra~sonic piezoelectric transducer embodying the invention
of this disclosure and installed in a wear member.
Figure 2 is a partial cross-sectional view o~ a
plurality of ultrasonic piezoelectric transducers embodying
the invention of this disclosure and installed in and around
the periphery of a wear memher, such as a sleeve bearing.
Figure 3 is a paxtial cross-sectional view of a
mounting ring for retaining one or more ultrasonic
piezoelectric transducers 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 tha-t it is a
partial cross-sectional view of an ultrasonic piezoelectric
transducer which may provide 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
ref~rence for temperature compensation.
Figure 7 illustrates an interrogating pulse to and a
return "echo" pulse from an ultrasonic piezoelectric
tran.sducer embodying the invention of this disclosure.
2068~05
Figure ~ is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer
ins,alled in a wear member and which provides a relative time
reference for temperature compensation.
Figure 9 is a partial cross-sectional view of another
embodimen-t of an ultr~sonic 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 wèar member and which provides a relative time
reference for temperature compensation.
Figure 11 is a partial cross-sectional view of another
em~odiment of an ultrasonic pie7oelectric 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
embodimen-t of an ultrasonic piezoelectric transducer
insl:alled in a wear member and which provides a relative time
~, reference for temperature compensation.
1, Figure 13 is a partial cross-sectional view of another
ernbodiment of an ultrasonic piezoelectric transducer
installed in a wear member and which provides a plurality of
relative time references for temperature compensation.
Figure 14 is a partial cross-sectional view of a
piezoelectric ultrasonic transducer, similar to the
transducer shown in Figure 9, installed in a wear member and
illustrates the position of the transducer relative to a
rotating shaft.
Figure 15 illustrates a first pressure pulse and a
secvnd pressure pulse having an opposite polarity, said
pressure pulses being produced by the piezoelectric element
within the transducer shown in Figure 14, and shows the
2~68~0~
respective "echo" return pressure pulses from a slot within
the transducex, the end of the transducer, and the surface of
the ro-tating shaft.
Figure 15 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer, similar
to the transducer shown in Figure 9, installed in a wear
member and illustrates the position of the transducer
relative to a rotating shaft.
Figure 17 illustrates a pressure pulse produced by the
pie30electric element within the transducer shown in Figure
16, and shows the respective "echo" return pressure pulses
from lhe top surface of a slot within the transducer, the
bottom surface of the slot, the end of the transducer, and
the surface of the rotating shaft.
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, sealiny
mernber, 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
pie~oelectric 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
206~50~
as that o.E the wear member l2 to maintain a firm contact
therewith. This firm contact is provided by the threads 20
whicl1 enga~e complementary threads provided in the wear
member 12, as hereinafter described. The threads 20 also
perinit the adjustment of the outer sleeve 1~ within the wear
mem~er 12 to optimize the operation of the transducer 10 as
discussed later. It should be noted that other approaches
are possible for the adjustable attachment of the outer
sleeve 14 to the ~1ear member 12, such as a bracket
arL^angernent (not shown) that is adjustable with respect to
the wear member 12 and which retains the sleeve 14. The end
22 o f the outer sleeve 1~ has an indentation provided therein
-Eorming a surace 24 connecting the end 22 of the sleeve 14
wi-th the inner circumferential wall 26 of the sleeve. This
inc1entation may have a curved configuration, such as
se.nispnerical or parabolic, or it may have a conical
con.i~uration which is preferred to permit aligmnent oE the
spacer 16 therein.
;The aligning and electrically insulating spacer 16 is
fa.o.7:icated from a ceramic or ceramic-like material that is
capable of sustaining high temperatures and high pressures.
For exanple, pyrolytic boron nitride or another ceramic-like
material can be used for the spacer 16. The particular
ceramic or ceramic like-material utilized for the spacer 16
is selected to properly compensate for the thermal expansion
properties of the other components comprising the transducer
1~ and the ~ear member 12 so that the spacer 15 will maintain
a substantially uniform compressive force on the
piezoelectric element 18 over a broad operating temperature
range. The spacer 16 typically has a conical confiyuration
tha, i.s complementary to that of the indentation formed in
the end 22 of the outer sleeve 14. The spacer 16 is received
wit~lin the indentation so that the outer surf~ce 28 definin~
.
2~8~5
.. g
its conical configuration contacts the sur~ace 24 formed by
the indentation. The use of conical surfaces 24, 28 formed
on the outer sleeve 14 and the spacer 16, respectively
pex~.nits the alignment of the spacer 16 ~ithin the outer
sleeve 14 through elastic deformation of the spacer 16 and
the in~entation formed in the end 22 of the outer sleeve 14.
In contrast, selE-aligmnent of the spacer 16 within the outer
s3.eeve 14 can be achieved by using a semi-spherical or
parabolic configuration for the surfaces 24, 28 forlned on the
end 22 of the outer sleeve 14 and the spacer 16,
respectively. It should be noted that regardless of the
sllape 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 hy 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
within the outer sleeve 14, whether by elastic deformation
of the spacer 16 and the indentation in the end 22 of the
outPr 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 uniforn 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
2~6~05
- 1 O-
si~nal than if complemelltary 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
~enerally results in a higher signal to noise ratio than if
complementary curved configurations are used for same. In
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 oE 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
member 12. The blind bore 36 is of a predetsrmined depth and
has a substantially flat surface 42 at the bottom thereoE.
The distance between the flat suxface 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 fro~ commercially available
piezoelectric transducer material, such as PZT-5EI available
from Vernitron, Inc. of Bedford, Ohio. The size of the
ele~nent 18 is a function of the overall size of the
transducer 10, however, an element havin~ a diameter of 0.080
.. ~ . .
., :;
:: :
2~687~5
inch and a thickness of .003 inch has been tested
e~p~rimentally with excellent results. The dlameter 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 volta~e
pul,e into a pressure pulse (often referred to as a "stress
pulse") which is applied to the surface of the material whose
thic~ness is to be measured and/or monitored. Similarly, the
piezoelectric element 18 converts the "echo" return pressure
2ulse from the opposite surface of the material whose
thickness is being monitored into a voltage pulse for
measurement purposes. The substantially uniforrn compressive
force applied to the piezoelectric element 18 by the spacer
16 ensllres 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 36
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 sli~htly 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
elerl1ent 18 may be electrically connected to an electrical
conductor 50. The electrical conductor 50 is received
throu(~h the aperture 30 provided in the spacer 16, and the
spacer 16 is received in the blind bore 36 so that its base
2068~0~
-12-
32 contacts the side 48 of the piezoelectric element 1 a 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
deformation of the spacer 16 and the indentation in the end
22 of the outer sleeve 14, and the application of a
sub.qtantially uniform compressive Eorce 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
pie%oelectric 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
bet~een the base 32 of the spacer 16 and the side 48 of tile
piezoelectric element 18. In order to ensure that such a
snuy 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
: : .
-
.
2~68~05
-13-
return "echo" pulse, shown on the oscilloscope, is recorded
by the receiver. In this manner, a snug fit netween the
foregoing components is assured and the transducer 10 and the
wear member 12 are "matched" to provide the optimum return
"echo" pulse with respec-t to shape, amplitude and signal to
noise ratio. This snug fit is retained through the use of
the aorementioned adhesive, such as Loctite, on the threads
of the outer sleeve 14, thus preventing any further movement
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 28 of the spacer 16 is maintained
-throllghout 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
andlor 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
. .
2068~05
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
epo~y, e.g., Duro epoxy, loaded with tungsten for application
temperatures less than 400F. or loaded ceramic adhesive for
temperatures in excess of 400~. This electric insulation
material and the spacer 16 preferably match the acoustical
impedance of the piezoelectric element 18 and he]p 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
utili~ed, 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 Inore 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.
~ lternatively, rather than placing a plurality of
transducers 10 within the blind bores provided in the outer
2068505
-15-
- bearing wall, a mounting attachment 54, such as a ring as
sho~n in Figure 3, can be used to retain the transducers 10
in a radially spaced apart relationship. In such an
arrangement, the mountin~ attachment 54 is slipped over the
sleeve bearing 56 and the piezoelectrlc elements 18 firmly
con~act 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
the arrangement shown in Figure 3, the radius of the
curvature of the bearing 56 is substantially greater than the
diameter o~ each piezoelectric element 18. Since a
substantial compressive force is being applied to each
element 18 by its associated spacer 16, it has been found
tha~ sufficient surface contact e~ists between each element
b 18 and the outer surface of the bearing 56 to produce very
accura-te distortionless measurements of wall thickness. Thus,
by using this apparatus, the thickness of, the amount of wear
~hich 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
mem~er, 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,
'
., . . '' ~ ~'
::~
20~85~
-16-
and the amount of material which has been removed from a
wear member in-situ, the construction oE the transducer 10
provldes another advantage in that no buffer element is
re-~uired between the piezoelectric element 18 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 bufLer element is required for
mech;lnical s-lpport, impedance matching and sealing of the
transducer, however, its use greatly attenuates and degrades
the primary pulses produced by the transducer and the
re~lected "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
fron1 prior ar-t devices. For example, measurements with a
repeatahility 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 memher 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
2068~0~
-17-
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 ~0. It
should be noted that the material utilized for the wear
reference member 68 is not critical inasmuch as only the
thickness of the end of the reference member 68 i5 being
monltored 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.
~ ith any of the foregoing embodiments, it might be
desired to compensate for the temperature and pressure of the
environrnent 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,
shot~n 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 6a if a through bore 50 is provided in
the wear member 12. The assembly of the transducer 80 and
the refereIlce memher 84 is placed within the same
temp~rature, pressure or material environment as the other
transducers 10, though not necessarily con-tacting the wear
member 12. By monitoring the measurements of the reference
2068~0~
-18-
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 e-nbodiment 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 ~0 in that it is comprised of an outer sleeve 14,
a spacer 16, a piezoelectric element 18, and an electrical
conductor 50, however, the fore~oing 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 34 of a reEerence
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
element 18. The diameters of the disc-shaped electrical
connector 92 and the reference acoustical member 96 are
similar and are slightly less than the diameter of the blind
bore 36 permitting the easy insertion therein. The reLerence
acoustical member 96 is formed from the same material as, or
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
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
zero impedance. The low impedance of the recess 100 provides
2~8505
a relatively large reElection coefficient for any pressure
wave intercepted thereby. Such a relatively large reElection
coeffisient is beneficial for the operation of this
transd~cer 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 (stress pulses) which are
transmitted in opposite directions--one pressure pulse being
transmitted 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
4~ oE the element 18. The pressure pulse transmitted into
the wear member 12 is reflected by the inner surface 40 oE
the wear member 12 back toward the one side 46 of the
piezoelectric elsment 18 and is intercepted by same.
Sinilarly, the pressure pulse transmitted into the reference
acoustical member 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
reFerel1ce acoustical member 96 varies independently of wear
and is typically affected 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
reEerence parameter. Thus, in essence, one pressure pulse
"monitors" 'he 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"
2068~0~
-20-
.
the latter thickness through elapsed pulse tra~el 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,
compensatioII 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
etween the reference acoustical member 96 and the portion
oE the wear rnernber 12 whose thickness is being monitored or
measured, and using the piezoelectric element to
simultaneously transmit oressure pulses in opposite
dire~tions is that signal degradation is minimized and a
high signal-to-noise ratlo is maintained. For example, if
the reference acoustical member is located on the same side
of the piezoPlectric element as the portion of the wear
rnember whose thickness is heing monitored or measured, i.e.~
the referellce acoustical member is interposed between the
piezoele~tric element and the "monitored or measured" portion
of the wear member, pressure pulses only in one direction
are required. ~owever, each pressure pulse must pass through
the re~erence acoustical member, the portion of the wear
me,nber 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
amp1itudP 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.
: . . ,
I' ' . ~ ~
.~ .
. : ,,
,. , :
.. .
. .
2068505
-21-
~ s previously indicated, physical properties other
than the thic]cness 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. ~y such monitoring,
appropriate means can be taken to minimize and/or control
SUC31 stress within the wear member. It has also been found
that local temperature within the wear member can be
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 heing 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
exp~rimentally, that the ratios tl, and thus tl-t, are
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
:
: :.
`~
2~850~
relatively independen-t of ternpe.rature and pressure, the time
~ and the time .interval t1-t are each a function of
tetnperature. 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
mem~er 12 can be util.ized 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 txansducer 80, as in Figure 5, and the resulting
temperature can be substituted in the functional relationship
l~etween 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
andJor 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
reference transducer by incorporating a relative time
reference into the transducer. The foregoing is accom~lished
in the alternate embodiment of the transducer 110 shown in
Figure B. The structure of this transducer 110 is similar to
the transducer 64 shown in Figure 4 in that it is comprised
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
cent:rally located tip 112 protruding therefrom. As in Figure
4, the wear reference member 68 is received within the
tl-rough bore 60 in the wear member 12, however, its end 72 is
not flush with the inner surface 40 of the wear member 12.
20685~
-23-
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
su.rface 40 of the wear member 12 and substantially parallel
to the end 72 oE -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 o the wear reference member
68 can be accurately measured and acts as a reference
distance. Since the end 72 oE the wear reference member 68
i5 not subjected to wear, the distance x is affected only by
chan~e.s in the tenpera-ture 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
chan~e 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 Lhe voltage pulse into
a pressure pulse (stress 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 reflscted 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 bac~ 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 ti.ne between the
transmission of the initial pressure pulse and the receipt
of each of the two "echo" return pressure pulses can be
deter~nined. The elapsed time between the transmission of the
initial pxessure pulse and the receipt of the "echo" return
'
2 ~ o ~
-24-
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 ths 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
surEace. Inasmuch as the temperature of the bottom portion
118 of the wear ref~rence 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 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 rnanner, temperature compensation can be easily
accomplished without the use of a reference acoustical member
and/or a separate reference transducer.
~ n 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
nwnerals and will not be discussed further. This transducer
120 differs fro~ 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 oi 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
;, ' '
2068~05
-25-
120 further differs in that the wear reference member 68 does
not have a centrally located tip 112. In this case, the
dist~nce x (the reference distance) is between the bottom
surface 116 of ~lind 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
volta~e into a pressure pulse (stress pulse) which is
transmitted into the bottom portion 118 of the wear reference
nember 68. The foregoing pressure pulse is reflected by the
top surface 124 of the slot 122 and the end 72 of the wear
reEerence member 68 resulting in two "echo" return pressure
pulses which are separated. By measuring the elapsed times
bet~een 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 6~ can be
accurately determined.
~ n alternate embodiment of the transducer 120, shown
in Figure 9, is transducer 130, illustrated in Figure 10.
Here a~ain, 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
differs from transducer 120 in that the horizontal slot 122
is replaced by a circumferential horizontal 510t 132 which is
substantially parallel to but spaced apart from the end 72 of
the wear reference member 6a. The top surface 134 of the
circumferential horizontal slot 132 forms a plane wl1ich is
opposite a portion of the piezoelectric element 18 to
int~rcept and reElect a portion of the pressure pulses
tr~nsrnitted thereby. In this case, the distance x (the
.
20~850~
-26-
reference distance) is between the bottom surface 116 of the
b1.Lnd bore 66 and the top surface 134 of the circumferential
ho.:izontal .slot 132 and the distance y is between the bottom
surface 116 of the blind bore 66 and the end 72 of the wear
.reEerence member 68. As in the previous embodiments, the top
surEace 134 of the circumEerential horizont;ll slot 132 and
the end 72 of the wear reference member 58 produce separate
"echo" return pressure pulses in response to a pressure
pul,e from the pie%oelectric element 18. Similarly, as in
the previous embodiments, by measuring and comparing the
elapsed times ~etween the transmission of the initial
p,essure pulse and the receipt of each of the two "echo"
re~urn pressure pulses, tempera-ture compensation can be
accornplished and an accurate de-termination of the wear which
llas occur~ed to the end 72 of the wear reference member 68
can be made.
A still another alternate embodiment of the transducer
, shown in Figure 8, is transducer 149, illustrated in
Figure 11. Here a~ain, those elements which are similar to
the elements shown in Figure 8 carry the same reference
numerals and will not be discussed further. This transducer
140 differs rom transducer 110 in that the centrally located
tip 112 on txansducer 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
weal- 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
difference) is hetween the bottom surface 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 since it is from the bottosn surface 116 of the blind
..
2068~0~
--27--
bore S6 to the end 72 of the weaL 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 sur~ace 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 cornparing 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 de-termined.
~ nother alternate embodiment of transducer 1 1 0, shown
in Figure 8, is transducer 1 50, illustrated in Figure 12. As
in the all of the previous embodiments, those elements which
are similar to the elements shown in Figure 8 carry the same
ref erence 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 circulnferential 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 ref lect a portion of the pressure pulses
transmitted thereby. In this case, the distance x (the
re,erence distance) is between the bottom surface 116 of the
blind bore 66 and the top surface 154 of the circumferential
poclcet 152. The distance y is the same as in Figure a in
that it is from the bottom surface 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 ( stress pulse) by the piezoelectric element 18
2~68~05
-28-
into the bottom portion 118 of the wear reference member 6~
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
oE the centrally located tip 112. Here again, by measuring
the elapsed times between the transmission oE 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
detersnination of the wear which has occurred to the end 114
of the centrally located tip 112 can be made.
~ n alternate embodiment of the transducer 120, shown
in ~igure 9, is transducer 200, illustrated in Figur~ 13. In
this em~odiment, those elements which are similar to the
elements shown in Figures 4 and 9 carry the same reference
numerals and will not be discussed further. This transducer
200 differs from transducer 120 in that the wear reference
member 68 has an additional horizontal slot 202 provided
therein. The horizontal slot 202 is substantially parallel
to horizontal slot 122 but is spaced apart therefrom. In
addition, the horizontal slot 202 is substantially parallel
to and spaced apart from the end 72 of the wear reference
member 68. The horizontal slot 202 can be placed on the same
side of wear reference member 6~ as slot 122 or can be offset
therefrom; the only requirement being that the horizontal
slot 202 is substantially parallel to the horizontal slot 122
and to the end 72 of the wear reference member 6~. In
addition, the width and depth of the horizontal slot 202 can
be the same as or different from the respective width and
depth of the horizontal slot 122. The top surfaces 124 and
204 oE the horizontal slots 122 and 202, respectively, form
planes which are opposite a portion of the piezoelectric
,
2~68~05
-29-
elemellt 1~ to int~rcept and re~lect a portion of the pressure
pulses transmitted thereby. In this case, the distance x
(Lhe first reference distance) i~ between the bottom surface
116 of the blind bore 66 and the top surface 12~ of the slot
22, the distance y (the second reference distance) is hetween
the bottom surface 116 of the blind bore 66 and the top
surface 204 of the slot 202; and the distance z is between
the bottom surface 116 of the blind bore 66 and the end 72 of
the wear xeference member 68.
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 (stress pulse) which is transmitted into the
bottom portion 118 of the wear reference member 68 via the
one side ~6 of the element 18. The foregoing pressure pulse
is reflected by the top surface 124 of the slot 122, by the
top surface 204 of the slot 202 and by the end 72 of the wear
reEerence member 68 resulting in three "echo" return
pressure pulses being transmitted back toward the one side 46
of the piezoelectric element which intercepts same.
Appropriate means (not shown) are utilized to separate these
three "echo" return pressure pulses. In addition, the
elapsed time between the transmission of the initial pressure
pul,e and the receipt of each of the three "echo" return
pre~sure pulses can be determined. ~y measuring the elapsed
times between the transmission of the initial pressure pulse
and the receipt of each of the three "echo" return pressure
pul,es, and by comparing these elapsed times, the temperature
gradient which exists between the bottom surface 116 of the
blind bore 66 and the end 72 of the wear reference member 68
or between the bottom surface 116 of the blind bore 66 and
each of the slots 122 and 202, or be-tween each of the
foregoing slots 122 and 202, or between each of the foregoing
2068505
-30-
slots 122 and 202 and the end 72 of the wear reference member
6~ can be determined. With the use of the foregoing
determinations, compensation for temperature can be made so
that the w~ar which has occurred to the end 72 of the wear
reference member 6~ can be accurately determined, and through
interpolation and extrapolation techniques, the temperature
of the surface defining the end 72 can be deternlined with a
very high degree of accuracy. Thus, remote sensing of the
temperature of the wear surface can be effected without the
use of a temperature sensing device, such as a thermocouple.
It should be noted that the foregoing embodiments
o:E transducers (Figures 8 through 13) and the waveform
~ .strated 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 transducex. It should be further noted
that the foregoing structures shown in these Figures
illustrate typ.ical 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
ach:ieved without the use of a reference acoustical member or
a separate reference transducer. P~egardless of the structure
uti-ized, the objective is to provide a relative time
reference surface as close as possible to the wear member
sur~ace being monitored so that wear can be accurately
de-terlnined .
It has been found that transducer 140, illustrated in
Figure 11, and possibly some of the other transducers
described herein, can be utillzed to determine the position
of a rotating shaft relative to a non-wear surface, e.g., the
toU surface 144 of recess 142. In this case, the pressure
2~68505
pulse transmitted by the piezoelectric element 18 will "jump
thn gap" between the top surface 144 of recess 142 and the
surface of the shaft resul-ting in an additional "echo"
return pressure pulse from the surface of the shaft. By
comparing the additional "echo" return pressure pulse with
the foregoing two "echo" return pressure pulse;, the position
of the shaft relative to the end 72 of the wear reference
member 68 and the thickness of the oil film therebetween can
be determined. ~Ct has been found experimentally that oil
film thickness of less than .002 in. to more than .040 in.
can be measured.
Another approach for "jumping the gap" between the end
72 o the wear reference member 68 and the surface of a shaft
is illustrated in Figures 14 and 15. Figure 14 illustrates
the transducer 120, as shown in Figure 9, mounted so as to be
in close proximity to a shaft 210. In this case, the
pressure pulse (s~ress pulse) produced hy the piezoelectric
element 1~ 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, the end 72
of the wear reference member 68 and the surface 212 of the
shaft 210 resulting in a waveform that has three distinct
"echo" return pressure pulses which are separated from one
another wi-th respect to time. In addition, multiple "echo"
return pressure pulses of a smaller magnitude are produced as
the "echo" return pressure pulse from the surface 212 of the
shaft 210 is reflected back and forth between the surface 212
of the shaft 210 and the end 72 of the wear reference member
68. The foregoing "echo" return pressure pulses are
illustrated in Figure 15 and designated as pulses L, E and S
froJ,~ surface 124 of the slot 122, end 72 of the wear
reference member 68 and surface 212 oE the shaft 210,
respectively. ~ultiple pressure pulses S1~ S2, etc.
2~8~05
--32--
resul-ting froM the "echo" return pressure pulse S frorn the
surface 212 of the sha-Et 210 being reflected back and forth
between the surface 212 and the end 72 oE the wear reference
memb~r 68 are also illustrated. In order to efEectively
"juln~ the gap" and monitor the position of the shaft 210,
such positlon being represented by pulse S from the surface
212 oE shaft 210, pulse E should be made to effectively
vanish, i.e., it should be cancelled, due to its close
proY.imity to pulS8 S in the resulting waveform. Cancellation
or subtraction of pulse E can be accomplished by having the
piezoelectric element 18 produce a pressure pulse (stress
pulse) of a polarity opposite to that which was ori~inally
produced and to transmit this pressure pulse of opposite
polarity into the bottom portion 118 of the wear reference
member 68 resulting in the production of "echo" return
pressure pulses L', E' and S' from surface 124 of slot 122,
end 72 of wear reference member 68 and surface 212 of shaft
210, respectively. Multiple pressure pulses S1, S2, etc.
resulting from the "echo" return pressure pulse S' being
refl~cted back and forth between the surface 212 of the shaft
~10 and the end 72 of the wear reference member 68 are
similarly illustrated. ~he timing of the transmission and
the amplitude o the pressure pulse of opposite polarity into
the botto!n portion 118 of the wear reference member 68 can be
adjusted so that "echo" return pressure pulse E from the end
72 of the wear reference member 68 is "cancellPd" by the
"echo" return pressure pulse L' frorn the surface 124 of the
slot 122. In this manner, the only remaining "echo" return
pressure pulses will be pulse L from surfacs 124 of slot 122,
!?Ul~g S, S1l S2, etc. and S', S1r S2, etc. from surface 212
oE shaft 210 and pulse E' from end 72 of wear reference
rnemb~r 68. By deterrnining the elapsed time between "echo"
return pressure pulses L and S, the position of the shaft 210
;
,- . . . .
`
2~68~05
with respect to the slot 122 in the wear reference member 68
can be determined very accurately. In this way, ths orbit of
the shaft 210 can be monitored continuously even when the oil
Eilm between the wear reference member 68 and the shaft 210
is very thin.
Another approach for cancelling "echo" return pressure
pulse ~ involves having the piezoelectric element 18 produce
a pressure pulse (stress pulse), transmitting the foregoing
pressure pulse into the bottom portion 11~ of the wear
reference member 68, receiving the "echo" return pressure
pulse L from surface 124 of the slot 122, inverting "echo"
return pressure pulse L, delaying the inverted "echo" return
pressure pulse ~, and then adding the delayed inverted "echo"
returll pressure pulse L to "echo" return pressure pulse E to
cancel same. A still another approach involves transmitting
a pressure pulse into the bottom portion 118 of the wear
reference member 68 when a shaft is not present, receiving
the "echo" return pressure pulse E from the end 72 of the
wear reference member 68, inverting the pulse E and storing
it in memory, and then adding the inverted "echo return
pressure pulse E to the "echo" return pressure pulse E when
the shaft is present to cancel this latter pressure pulse.
Alternatively, with the shaft present and by using digital
methods the "echo" return pressure pulse E can be placed in
memory and then subtracted from itself to effectively cancel
same.
The transducer can also be designed so as to
"mechanically" cancel the "echo" return pressure pulse from
the end of the wear reference member. Figure 16 illustrates
a transducer 220 which can "mechanically" cancel the
foregoing pressure pulse. Those elements of transducer 220,
which is an alternate embodiment of Figure 9, that are
similar to the elements shown in Figure 9 carry the same
2~8~5
reference numerals and will not be discussed further.
Transducer 220 differs from transducer 120 in that horizontal
slot 122 is filled with an acoustically conducting material
222 that differs from the material comprising the wear
referetlce member 68. In this manner, a first "echo" return
pressure pulse is received from the top surface 124 of the
slot 122 and a second "echo" return pressure pulse from the
bottom surface 224 of the slot 122. The material 222 which
fills slot 122 should have an acoustic velocity that is
lower than the acoustic velocity of the material comprising
the wear reference member 68. ~y selecting a material having
a lower acoustic velocity and by utili~ing the parameters
that define same, the "echo" return pressure pulse from
bottom surface 224 of slot 122 can effectively cancel the
"echo" return pressure pulse from the end 72 oE the wear
reference member 68. Operationally, the pressure pulse
(s~ress pulse) produced by the piezoelectric element 18 is
transmitted into the bottom portion 118 of the wear reference
member 6~. The foregoing pressure pulse is reflected by the
top surface 124 of the slot 122, the ~ottom surface 224 of
the slot 122, the end 72 of the wear re'erence member 68 and
the surface 212 of the shaft 210 resulting in a waveform that
has four distinct "ec'no" return pressure pulses that are
separated from one another with respect to time. The
foregoing "echo" return pressure pulses are illustrated in
Fiyure 17 and designated as pulses L, M, E and S from top
surface 124 of the slot 122, bottom surface 224 of the slot
122, end 72 of the wear reference member 68 and surface 212
of the shaft 210, respectively. In order to effectively "jump
the gap" and monitor the position of the shaft 210, such
posi~ion being represented by pulse S from the surface 212 of
the shaft 210, pulse E should be cancelled because of its
close proximity to pulse S in the resulting waveform.
2068~0~
Cancellation of pulse E can be accomplished by varying the
distance between the top surface 124 and the bottom surface
224 of the slot 122 and/or the type of material 222 used
therein so that pulse M from the bottom surface 224 of the
slot 122 substantially coincides, in time, with pulse E from
the end 72 of the wear reference member 68. Since pulse M
from the bottom surface 224 of slot 122 is of opposite
polarity to pulse E from the end 72 of the wear reference
member 68, pulse E is effectively cancelled, thus permitting
an accurate measurement of pulse S from surface 212 of the
shaft 210. 13y determining the elapsed time between "echo"
return pressure pulses L and S, the position of the shaft 210
with respect to wear reference member 68 can be determined
very accurately. In this manner, the orbit of the shaft 210
can be monitored continuously even when the oil film between
the wear reference member 68 and the shaft 210 is very thin.
Thus, it is apparent that the position of the shaft 210
and/or the thickness of the oil film between end of the wear
reference member 68 and the shaft 210 can be readily
determined electrically or mechanically.
The foregoing illustrations of methods or approaches
for "cancelling" the "echo" return pressure pulse E in order
to monitor the position of the shaft 210 should not be
considered to be the only approaches to effectively cancel
this pulse, but merely illustrate some of the approaches
that can be utilized. Other approaches are available to
accomplish the same result, viz., the cancellation of "echo"
return pressure pulse E.
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.
