CA2068505C - Ultrasonic transducer - Google Patents

Abstract

ULTRASONIC TRANSDUCER

ABSTRACT OF THE DISCLOSURE

An ultrasonic piezoelectric transducer and a method for measuring and/or monitoring various physical properties of a member, in-situ, are disclosed. The transducer includes a sleeve which is received in a blind bore provided in the member, a piezoelectric element positioned within the blind bore, and an aligning spacer means interposed between the end of the sleeve and the piezoelectric element. By the application of appropriate voltage pulses to the piezoelectric element causing interrogating signals to be applied to the member, and the measurement of the time interval between the application of an interrogating signal and the receipt of a return signal from the member, various physical properties of the member and structural information regarding same can be determined.

Description

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 ~ `;

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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.

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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.

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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~

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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 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 .. ~ . .

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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~

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 : : .

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2~68~05 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 - 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, ' ., . . '' ~ ~' ::~

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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~

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~

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~

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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.

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~ 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~

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 ~

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 ;, ' ' 2068~05 120 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~

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~

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 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 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 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 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.

Claims (12)

1. An ultrasonic transducer device for measuring the thickness of a member comprising a piezoelectric element, means for biasing said piezoelectric element against the member whose thickness is to be measured, said biasing means comprising a sleeve having a recess provided in one end thereof and spacer means received within said recess in said sleeve, said spacer means operatively contacting said piezoelectric element, and means for producing a plurality of reference thicknesses, said reference thickness producing means being received within the member whose thickness is to be measured and being formed from a material having an acoustical velocity differing from the acoustic velocity of the member whose thickness is to be measured, said reference thickness producing means and said wear surface intercepting signals produced by said piezoelectric element in response to actuation thereof and producing return signals differing in time relative to one another.

2. The transducer device as defined in claim 1 wherein the acoustic velocity of said material comprising said reference thickness producing means is less than the acoustic velocity of the member whose thickness is to be measured.

3. The transducer device as defined in claim 1 wherein at least one of the surfaces defining said reference thickness producing means is substantially parallel to a wear surface on the member whose thickness is to be measured.

4. The transducer device as defined in claim 1 wherein said piezoelectric element has a pair of faces, one of said pair of faces being in operative engagement with a surface of the member whose thickness is to be measured and with said reference thickness producing means, the other of said pair of faces being contacted by said biasing means.

5. An ultrasonic transducer device for measuring the thickness of a member comprising, in combination, a piezoelectric element, a member whose thickness is to be measured, means for biasing said piezoelectric element against said member whose thickness is to be measured, said biasing means comprising a sleeve having a recess provided in one end thereof and spacer means received within said recess in said sleeve, said spacer means operatively contacting said piezoelectric element, and means for producing a plurality of reference thicknesses, said reference thickness producing means being received within said member whose thickness is to be measured and being formed from a material having an acoustic velocity that differs from the acoustic velocity of said member whose thickness is to be measured, said reference thickness producing means and said wear surface intercepting signals produced by said piezoelectric element in response to actuation thereof and producing return signals differing in time relative to one another.

6. The combination as defined in claim 5 wherein the acoustic velocity of said material comprising said reference thickness producing means is less than the acoustic velocity of said member whose thickness is to be measured.

7. The combination as defined in claim 5 wherein at least one of the surfaces defining said reference thickness producing means is substantially parallel to a wear surface on said member whose thickness is to be measured.

8. The combination as defined in claim 5 wherein said piezoelectric element has a pair of faces, one of said pair of faces being in operative engagement with a surface of said member whose thickness is to be measured and with said reference thickness producing means, the other of said pair of faces being contacted by said biasing means.

9. A method for measuring the thickness of a member in-situ through the use of an ultrasonic transducer device comprising a piezoelectric element, means for biasing said piezoelectric element against the member whose thickness is to be measured, said biasing means comprising a sleeve having a recess provided in one end thereof and spacer means received within said recess in said sleeve, said spacer means operatively contacting said piezoelectric element, and means for producing a plurality of reference thicknesses, said reference thickness producing means being formed from a material having an acoustic velocity that differs from the acoustic velocity of the member whose thickness is to be measured, said method comprising the steps of:
applying a pulse to said ultrasonic transducer device causing said piezoelectric element to transmit an interrogating signal into the member whose thickness is to be measured;
receiving a return signal from at least one of the surfaces defining said reference thickness producing means and from the end of the member whose thickness is to be measured in response to said interrogating signal;

processing said return signals to eliminate the effects thereon of any temperature gradients which exist in the member whose thickness is to be measured; and determining the thickness of the member from said processed return signals.

10. The method as defined in claim 9 wherein the acoustic velocity of each material comprising said reference thickness producing means is less than the acoustic velocity of the member whose thickness is to be measured.

11. A method for determining the position of a member through the use of an ultrasonic transducer device comprising a piezoelectric element, a reference member, means for biasing said piezoelectric element against a surface of said reference member, said biasing means comprising a sleeve having a recess provided in one end thereof and spacer means received within said recess in said sleeve, said spacer means operatively contacting said piezoelectric element, and means for producing a plurality of reference thicknesses, said reference thickness producing means being formed from material having an acoustic velocity that differs from the acoustic velocity of said reference member, said method comprising the steps of:
locating said ultrasonic transducer device in proximity to the member whose position is to be determined;
applying a pulse to said ultrasonic transducer device causing said piezoelectric element to transmit an interrogating signal into said reference member and into the member whose position is to be determined;

receiving a return signal from at least one of the surfaces defining said reference thickness producing means and from the end of said reference member and from the member whose position is to be determined;
processing said return signals to eliminate the return signal produced from said end of said reference member; and determining the position of the member from said processed return signals.

12. The method as defined in claim 11 wherein the acoustic velocity of said material comprising said reference thickness producing means is less than the acoustic velocity of said reference member.