CA2024831A1 - Non-invasive torquemeter - Google Patents
Non-invasive torquemeterInfo
- Publication number
- CA2024831A1 CA2024831A1 CA 2024831 CA2024831A CA2024831A1 CA 2024831 A1 CA2024831 A1 CA 2024831A1 CA 2024831 CA2024831 CA 2024831 CA 2024831 A CA2024831 A CA 2024831A CA 2024831 A1 CA2024831 A1 CA 2024831A1
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- Prior art keywords
- patch
- birefringent
- photoelastic material
- light
- torque
- Prior art date
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- Abandoned
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- 238000005259 measurement Methods 0.000 claims abstract description 8
- 230000002596 correlated effect Effects 0.000 claims abstract 2
- 238000005286 illumination Methods 0.000 claims description 24
- 229920006335 epoxy glue Polymers 0.000 claims description 5
- 239000004568 cement Substances 0.000 claims description 4
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- 230000001070 adhesive effect Effects 0.000 claims description 3
- 238000010183 spectrum analysis Methods 0.000 claims description 3
- 230000006870 function Effects 0.000 claims description 2
- 238000012986 modification Methods 0.000 abstract description 2
- 230000004048 modification Effects 0.000 abstract description 2
- 238000012360 testing method Methods 0.000 description 10
- 230000003068 static effect Effects 0.000 description 9
- 239000004593 Epoxy Substances 0.000 description 3
- 238000013461 design Methods 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
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- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
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- 230000010363 phase shift Effects 0.000 description 1
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- Force Measurement Appropriate To Specific Purposes (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
ABSTRACT
In the past in order to measure the applied forces to an object contactwith the object, modification of the object, or adding a heavy or a bulky addition to the object was necessary. In the described method and apparatus for the non-invasive measurement of torque induced strain in an object, the photoelastic properties of certain materials is utilized.
By attaching a small lightweight patch of photoelastic material to an object in such a manner as to allow it to be strained with the object, applied forces can be monitored, by observing the changes in the optical characteristics of the strained patch. The observed changes can then be correlated into a value for the applied forces at a remote location.
Since all that is necessary for observation is fiber optic cables, this measurement system is almost completely non-obtrusive.
In the past in order to measure the applied forces to an object contactwith the object, modification of the object, or adding a heavy or a bulky addition to the object was necessary. In the described method and apparatus for the non-invasive measurement of torque induced strain in an object, the photoelastic properties of certain materials is utilized.
By attaching a small lightweight patch of photoelastic material to an object in such a manner as to allow it to be strained with the object, applied forces can be monitored, by observing the changes in the optical characteristics of the strained patch. The observed changes can then be correlated into a value for the applied forces at a remote location.
Since all that is necessary for observation is fiber optic cables, this measurement system is almost completely non-obtrusive.
Description
( ( ~/ - I
This invention is concerned with devices used to measure a torque applied to an object, such as a shaft, which may be either static or moving. A
device to measure the applied substantially torsional force is described which uses photoelastic material to detect the amount of torque induced strain at a preselected locus on the surface of the object. By observing the changes in the optical behaviour of the photoelastic material the applied torque can be measured.
In the past in order to measure accurately the torque applied to an object some form of contact with the object has been necessary, for example, the commonly used variable resistance electrical strain gauges. Static tests were used to measure strain between selected points, such as over the length of the ob~ect. These tests would allow for accurate analysis of the behaviour of an object under static conditions and permit determination of a maximum safe load. They do not permit evaluation of the object either under dynamic test conditions, or in its conditions of use. Electronic measurement of strain can be made in both static and dynamic situations, but these devices require some form of electrical connection with the object being tested. Whilst such connections can be easily made for static testing, the need for reliable electrical contacts with the object results in difficulties when trying to measure torque induced strain either under dynamic conditions or within a normal working environment. The use of slip ring contacts seems to have overcome some of these problems but such systems are bulky and present the designer with added complications and maintenance considerations.
There are at present several methods (discussed in a paper entitled "Rotorshaft Torquemeter" by R. B. Bossler, Presented at the 35th Annual National Forum of the American Helicopter Society, May 1979) of measuring torque to within 2% involving limited or no contact. One of these, phase displacement, is obtrusive to the shaft being tested. Telemetric transmitters are problematic due to noise. Mercury transmitters are problematic in their bulk and weight. Though capacitative transmitters are smaller than rotational transmitters both remain obtrusive. Though telemetric torque meters are presently in use in helicopter shafts, it would greatly simplify design if a less obtrusive torque meter could be used.
This invention is concerned with devices used to measure a torque applied to an object, such as a shaft, which may be either static or moving. A
device to measure the applied substantially torsional force is described which uses photoelastic material to detect the amount of torque induced strain at a preselected locus on the surface of the object. By observing the changes in the optical behaviour of the photoelastic material the applied torque can be measured.
In the past in order to measure accurately the torque applied to an object some form of contact with the object has been necessary, for example, the commonly used variable resistance electrical strain gauges. Static tests were used to measure strain between selected points, such as over the length of the ob~ect. These tests would allow for accurate analysis of the behaviour of an object under static conditions and permit determination of a maximum safe load. They do not permit evaluation of the object either under dynamic test conditions, or in its conditions of use. Electronic measurement of strain can be made in both static and dynamic situations, but these devices require some form of electrical connection with the object being tested. Whilst such connections can be easily made for static testing, the need for reliable electrical contacts with the object results in difficulties when trying to measure torque induced strain either under dynamic conditions or within a normal working environment. The use of slip ring contacts seems to have overcome some of these problems but such systems are bulky and present the designer with added complications and maintenance considerations.
There are at present several methods (discussed in a paper entitled "Rotorshaft Torquemeter" by R. B. Bossler, Presented at the 35th Annual National Forum of the American Helicopter Society, May 1979) of measuring torque to within 2% involving limited or no contact. One of these, phase displacement, is obtrusive to the shaft being tested. Telemetric transmitters are problematic due to noise. Mercury transmitters are problematic in their bulk and weight. Though capacitative transmitters are smaller than rotational transmitters both remain obtrusive. Though telemetric torque meters are presently in use in helicopter shafts, it would greatly simplify design if a less obtrusive torque meter could be used.
2~2~ 3~
In 1959 F. Zandman proposed (Product Engineering, March 2, 1959, Vol 30p.43~ a torque meter using the photoelastic properties of some materials.
The device as described requires two different photoelastic patch areas on a rotating shaft each of which must be illuminated. One of the patches is connected to the shaft in such a way as to be unstrained, and i8 used as a base comparison. The other is connected to the shaft in such a way as to be strained under a torque condition. The light beams reflected off each patch area are combined in order to form an interference pattern which is observed. A mechanical screw is used to perform the opto-mechanical compensation. This device is slow and is obtrusive. It would also appear that the device as described cannot be used in an environment of operation.
It is also a disadvantage of the Zandman system that two photoelastic patches are required, together with a coherent split light beam system involving a mechanical splitter in order to provide one value. It is therefore desirable to be able to measure torque photoelastically by a technique not requiring these complications.
It is therefore desirable to be able to measure torque in a rotating ormoving object, such as a shaft, without any physical connection having to be made to the object itself. Furthermore, it is desirable to be able to measure torque in such a rotating or moving object without having to make any modifications at all to the object: that is, by a non-obtrusive method. In addition to eliminating the difficulties of maintaining adequate electrical contacts, such a method also allows for shapes other than simple cylinders and the like better to be accommodated.
It is also desirable to be able to measure the applied torque in a moving or rotating object either under predefined test conditions or during use in its intended environment.
It is also desirable to be able to measure torque in a rotating shaft without having to attach to the shaft any significant amount of weight or bulk, and allowing the shaft to remain one piece along all axes in order to facilitate design.
2~2~(,31 Furthermore, in many applications it is desirable to be able to measurethe torque applied to an object in its environment of use on an on-going real-time basis. Such measurements would allow temporarily exceeding a safe loading factor, for example, in an emergency situation.
Alternatively, such data would allow prediction of approaching catastrophe and the control of the power being applied to the object to produce the observed torque to limit that observed torque to within acceptable values.
The invention herein described broadly utilises the photoelasticproperties of certain materials in order to facilitate the non-invasive measurement of torque induced strain in an object such as a shaft. A
small, lightweight patch or band of birefringent photoelastic material with a reflective backing is attached to a pre-chosen locus on the surface of the object at the point the torque induced strain is to be measured.
As the object deflects under torque induced strain, the birefringent photoelastic material similarly deforms thus causing changes in its optical properties. By observing these changes in optical properties the applied torque can be readily derived. As the only "contact" required with the object is the ability to illuminate the patch of strained birefringent photoelastic material, and to capture at least some of the light reflected from it, no physical connection with the object is needed.
The use of fiber optics allows both the source of light, and the analyzer means used to observe changes in optical properties in the birefringent photoelastic material to be remote from the object itself. Further, the distance between the ends of the fiber optics cables and the patch also often can be kept quite short, thus facil~tating measurements in a condition of use environment. The system may be used under static or dynamic test conditions, but is especially useful as it permits measurements in many cases in the environment of use.
Thus in a first broad aspect this invention seeks to provide a method for measuring a substantially torsional force applied to an object which comprises in combination:
(i) fixedly applying to a preselected locus on the surface of the object a suitable sized patch of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
2024~,3~
(iii)illuminating at least some of the strained patch with a single beam illumination means;
~iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
~v) correlating the observed changes with the known properties of the birefringent photoelastic material; and (vi) deriving a value for the substantially torsional force from the correlation data.
In a more detailed embodiment, this invention seeks to provide a methodfor measuring a substantially torsional force applied to an object, which comprises in combination:
(i) fixedly applying to a preselected locus on the surface of the object a patch of a birefringent photoelastic material of known photoelastic properties;
~ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least a portion of the strained patch with a single beam illumination means;
(iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
(v~ correlating the observed changes in the at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with an electronic fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic signal correspondlng to th~ applied torque; and (vii)processing the obtained electronic signal to provide a value for the applied substantially torsional force.
In a second more detailed embodiment, this invention seeks to provide amethod for measuring a substantially torsional force applied to an object, such as a shaft transmitting a power load, which comprises in combination, ~2'~3~
(i) fixedly applying to a preselected locus on ehe surface of the object a patch in the form of a continous strip or ring of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least a portion of the strained patch with a single beam illumination means;
(iv) observing changes related to at least torque induced strains in at least some of the light reflected from ehe strained birefringent photoelastic material which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in the at least some of the light reflected with the known properties of the birefringent photoelastic material by means of a spectral analysis means thereby providing an electronic slgnal; and (vi) processing the obtained electronic signal to provide a value for the applied force.
Preferably, the suitable illumination means provides circularly polarized light.
Preferably, the suieable illumination means provides continuous light.
Alternatively, the suitable illumination means provides stroboscopic light.
Preferably the birefringent photoelastic material is a plastic to facilitate molding and affixing.
Preferably, the birefringent photoelastic material is fixedly applied to the object by means of a reflective glue or cement such as an epoxy glue which provides a reflective surface between the patch and the object.
Preferably, the method is used in an environment of dynamic use under dynamic load.
Preferably, the method is used in an environment of static use under static load.
2~2~,3~
Preferably the method is used in test environments providing both sta,ic and dynamic testing, In a second broad aspect this invention seeks to provide an apparatus for measuring a substantially torsional force applied to an object comprising in combination, (i~ a patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the surface of the object;
(iii)an illumination means adapted to illuminate the patch with suitable light;
(iv)an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and to pass it to the correlation means;
(v) a correlation means adapted to receive the at least some light passed from the observation means, and to convert it into an input signal adapted to act as the input into a signal processor means;
(vi) a signal processor means adapted to receive the input signal and provide an appropriate output signal to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
In a more detailed embodiment this invention seeks to provide an apparatus for measuring a substantially torsional force applied to an object, such as a shaft transmitting a power load, comprising in combination, (i) a patch in the form of a continuous strip or ring of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object;
(iii)an illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and pass it to the analyzer means;
2 0 ~
(v) an analyzer means adapted to receive the at least some light passed from the observation means and convert it into an input signal adapted to act as the input into a processor means;
(vi) a processor means adapted to receive the input signal and provide an output signal indicative of the observed torque to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
In a second more detailed embodiment this invention seeks to provide anapparatus for measuring a torque applied to an object, such as a shaft transmitting a power load, comprising in combination, (i) a patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object;
(iii)at least one illumination means adapted to illuminate at least some of the patch with suitable light;
(iv) at least one observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and pass it to the analyzer means;
(v) at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into an input signal adapted to act as the input into a processor means and relating to at least the torque induced strain;
(vi) a processor means adapted to receive the input signal and process sa~d signal in order to provide an appropriate output signal relating to at least the torque induced strain to the output means;
and (vii)an output means adapted to provide in a readable form an output related to the observed value for the induced strain.
Preferably, the illumination means consists of an circularly polarizedlight source.
Preferably, the illumination means consists of a continuous light source.
2Q2~31 Alternatively the illumination means may consist of a stroboscopic light source.
Preferably, the photoelastic material is a plastic.
Preferably, the observation means includes fiber optic cables and suitable optics.
Preferably, the analyzer means includes an optical analyzer/detector, a fringe counter means, and an analog to digital converter.
Alternatively, the analyzer means includes a spectral analysis means.
Preferably, the affixing means is a reflective epoxy glue or cement.
Preferably, the output means includes a display means, a storage means, a display/storage means, or both a display and a storage means, in which the storage and display functions can be seperate (such as in a personal computer memory and a video display) or combined (such as a chart recorder trace or a data logger).
The invention will now be described by way of reference to the attachedfigures in which:
FIGURE 1 represents a complete system overview in the form of a block diagram;
FIGURE 2 represents a preferred embodiment of the invention.
FIGURE 3 represents an alternate embodiment of the invention.
The invention in its broadest embodiment comprises at least one illumination means 1, at least one patch of birefringent photoelastic material 5 affixedly attached to the object 20 to which the applied torque is being measured, at least one observation means 3, at least one analyzer means 17, at least one processor means 9, and at least one output means 10 .
The illumination means 1 includes a light source 19 and a polarizer 2.
The light emitted by the light source 19 is circularly polarized by the polarizer 2 before it reaches the birefringent photoelastic material 5.
~2l.~33 ~
Once it has passed through the birefringent photelastic material 5, it is reflected off the affixing means 6 back through the birefringent photelastic material 5. An observation means 3 receives the reflected light waves which contain a phase shift. The reflected light is analyzed by an optical analyzer 4 and a fringe pattern is produed. The analyzer means 17 comprises a fringe counting analyzer means 7 and an analog to digital converter 8. The fringe counting analyzer means 7 can then calculates the fringe orderJ and the offset from the last fringe boundary, and the analog to digital converter 8 then converts the results lnto an electronic signal which will act as the input to the processor means 9.
In the processor, it is converted into a value for applied torque based on the known photoelastic properties of the test object and of the birefringent photoelastic material. This value is passed to the output means 10 which typically may comprises a display means 11, a storage means 12, and a feedback means 13.
The display means 11 can comprise a digital display, an LED device, a light, a bell, a printer, a chart recorder, a meter, a buzzer, a television display, or any other suitable audio visual display means.
The storage means 12 can comprise a printer, a chart recorder, a magnetic disk, an optical disk, a random access memory, an electronic memory, a magnetic tape, a videotape, and any other suitable storage means.
The feedback means 13 may comprise any suitable control means having as at least one input thereto a signal from or generated by or as a result of a signal from or generated by the processor means 9.
The processor means 9 may comprise markings on a metering device, a comparison means, a microprocessor devise, or any other means of rendering the input signal readable.
In one preferred embodiment, shown as FIGURE 2, the invention comprises a stroboscopic light source 19 and a patch of birefringent photoelastic plastic material such as epoxy applied to the object 20, such as a shaft, with reflective adhesive 6 such as epoxy glue. A fiber optic cable containing at least two fibers 14 and 34 serves to transmlt the light.
_ g _ 2 1~ 2 ~
Fiber 14 is used to transmit the polarized light from the light source 19 to the object 20 allowing for the other components to remain at a remote location. The observation means 3 includes fiber 34, which transmits the reflected light back to the remote location where it is analyzed by the optical analyzer 4, The fringe pattern which results is passed to the fringe counting analyzer means 7. The value calculated is digitized by an A/D converter 8 in the analyzer means. A processor means 9 receives all the data and calculates the applied substantially torsional force as well as any information desired by the user or necessary for feedback. This information is transmitted to an output means 10. For testing purposes the processor means 9 and the output means 10 can be in the form of what is commonly referred to as a personal computer.
It would be prefererable to measure a substantially torsional force with the fewest other force components. One method to accomplish this is by locating the point at which the torsional force is the greatest contributor (by percentage~ to the measured value. This can be accomplished by using more than one illumination means at appropriate locations in order to facillitate the selection of the value relating most closely to pure torque.
This simple system can be expanded relatively easily 80 that a torque can be measured at more than one point. The optical properties of the patch 5 can be viewed at more than one point by using a plurality of pairs of optical fibers 14 and 34. The resulting light beams are analyzed by either a multiple channel analyzer means 17, or by several optical analyzers. Similarly, several output means 10, or a multiple channel means is also then necessary to deal with the plurality of signals being developed, In FIGURE 3, a further embodiment for measuring the applied strain in an object such as an aircraft wing 20als shown. The birefringent photoelastic coating 5 is applied fixedly in the form of a patch to the inside of the wing assembly 20a using reflective epoxy 6a. At least one illumination means 1 emits light which passes through the birefringent photoelastic plastic material 5 and is reflected off the reflective epoxy 6a back through the birefringent photoelastic plastic material 5. Even though the wing is static, the applied strain can be analyzed and used to ~02~
predict failure by avoiding the on~et of meta]. fatigue or to improve maintenance.
In 1959 F. Zandman proposed (Product Engineering, March 2, 1959, Vol 30p.43~ a torque meter using the photoelastic properties of some materials.
The device as described requires two different photoelastic patch areas on a rotating shaft each of which must be illuminated. One of the patches is connected to the shaft in such a way as to be unstrained, and i8 used as a base comparison. The other is connected to the shaft in such a way as to be strained under a torque condition. The light beams reflected off each patch area are combined in order to form an interference pattern which is observed. A mechanical screw is used to perform the opto-mechanical compensation. This device is slow and is obtrusive. It would also appear that the device as described cannot be used in an environment of operation.
It is also a disadvantage of the Zandman system that two photoelastic patches are required, together with a coherent split light beam system involving a mechanical splitter in order to provide one value. It is therefore desirable to be able to measure torque photoelastically by a technique not requiring these complications.
It is therefore desirable to be able to measure torque in a rotating ormoving object, such as a shaft, without any physical connection having to be made to the object itself. Furthermore, it is desirable to be able to measure torque in such a rotating or moving object without having to make any modifications at all to the object: that is, by a non-obtrusive method. In addition to eliminating the difficulties of maintaining adequate electrical contacts, such a method also allows for shapes other than simple cylinders and the like better to be accommodated.
It is also desirable to be able to measure the applied torque in a moving or rotating object either under predefined test conditions or during use in its intended environment.
It is also desirable to be able to measure torque in a rotating shaft without having to attach to the shaft any significant amount of weight or bulk, and allowing the shaft to remain one piece along all axes in order to facilitate design.
2~2~(,31 Furthermore, in many applications it is desirable to be able to measurethe torque applied to an object in its environment of use on an on-going real-time basis. Such measurements would allow temporarily exceeding a safe loading factor, for example, in an emergency situation.
Alternatively, such data would allow prediction of approaching catastrophe and the control of the power being applied to the object to produce the observed torque to limit that observed torque to within acceptable values.
The invention herein described broadly utilises the photoelasticproperties of certain materials in order to facilitate the non-invasive measurement of torque induced strain in an object such as a shaft. A
small, lightweight patch or band of birefringent photoelastic material with a reflective backing is attached to a pre-chosen locus on the surface of the object at the point the torque induced strain is to be measured.
As the object deflects under torque induced strain, the birefringent photoelastic material similarly deforms thus causing changes in its optical properties. By observing these changes in optical properties the applied torque can be readily derived. As the only "contact" required with the object is the ability to illuminate the patch of strained birefringent photoelastic material, and to capture at least some of the light reflected from it, no physical connection with the object is needed.
The use of fiber optics allows both the source of light, and the analyzer means used to observe changes in optical properties in the birefringent photoelastic material to be remote from the object itself. Further, the distance between the ends of the fiber optics cables and the patch also often can be kept quite short, thus facil~tating measurements in a condition of use environment. The system may be used under static or dynamic test conditions, but is especially useful as it permits measurements in many cases in the environment of use.
Thus in a first broad aspect this invention seeks to provide a method for measuring a substantially torsional force applied to an object which comprises in combination:
(i) fixedly applying to a preselected locus on the surface of the object a suitable sized patch of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
2024~,3~
(iii)illuminating at least some of the strained patch with a single beam illumination means;
~iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
~v) correlating the observed changes with the known properties of the birefringent photoelastic material; and (vi) deriving a value for the substantially torsional force from the correlation data.
In a more detailed embodiment, this invention seeks to provide a methodfor measuring a substantially torsional force applied to an object, which comprises in combination:
(i) fixedly applying to a preselected locus on the surface of the object a patch of a birefringent photoelastic material of known photoelastic properties;
~ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least a portion of the strained patch with a single beam illumination means;
(iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
(v~ correlating the observed changes in the at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with an electronic fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic signal correspondlng to th~ applied torque; and (vii)processing the obtained electronic signal to provide a value for the applied substantially torsional force.
In a second more detailed embodiment, this invention seeks to provide amethod for measuring a substantially torsional force applied to an object, such as a shaft transmitting a power load, which comprises in combination, ~2'~3~
(i) fixedly applying to a preselected locus on ehe surface of the object a patch in the form of a continous strip or ring of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least a portion of the strained patch with a single beam illumination means;
(iv) observing changes related to at least torque induced strains in at least some of the light reflected from ehe strained birefringent photoelastic material which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in the at least some of the light reflected with the known properties of the birefringent photoelastic material by means of a spectral analysis means thereby providing an electronic slgnal; and (vi) processing the obtained electronic signal to provide a value for the applied force.
Preferably, the suitable illumination means provides circularly polarized light.
Preferably, the suieable illumination means provides continuous light.
Alternatively, the suitable illumination means provides stroboscopic light.
Preferably the birefringent photoelastic material is a plastic to facilitate molding and affixing.
Preferably, the birefringent photoelastic material is fixedly applied to the object by means of a reflective glue or cement such as an epoxy glue which provides a reflective surface between the patch and the object.
Preferably, the method is used in an environment of dynamic use under dynamic load.
Preferably, the method is used in an environment of static use under static load.
2~2~,3~
Preferably the method is used in test environments providing both sta,ic and dynamic testing, In a second broad aspect this invention seeks to provide an apparatus for measuring a substantially torsional force applied to an object comprising in combination, (i~ a patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the surface of the object;
(iii)an illumination means adapted to illuminate the patch with suitable light;
(iv)an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and to pass it to the correlation means;
(v) a correlation means adapted to receive the at least some light passed from the observation means, and to convert it into an input signal adapted to act as the input into a signal processor means;
(vi) a signal processor means adapted to receive the input signal and provide an appropriate output signal to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
In a more detailed embodiment this invention seeks to provide an apparatus for measuring a substantially torsional force applied to an object, such as a shaft transmitting a power load, comprising in combination, (i) a patch in the form of a continuous strip or ring of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object;
(iii)an illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and pass it to the analyzer means;
2 0 ~
(v) an analyzer means adapted to receive the at least some light passed from the observation means and convert it into an input signal adapted to act as the input into a processor means;
(vi) a processor means adapted to receive the input signal and provide an output signal indicative of the observed torque to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
In a second more detailed embodiment this invention seeks to provide anapparatus for measuring a torque applied to an object, such as a shaft transmitting a power load, comprising in combination, (i) a patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object;
(iii)at least one illumination means adapted to illuminate at least some of the patch with suitable light;
(iv) at least one observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and pass it to the analyzer means;
(v) at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into an input signal adapted to act as the input into a processor means and relating to at least the torque induced strain;
(vi) a processor means adapted to receive the input signal and process sa~d signal in order to provide an appropriate output signal relating to at least the torque induced strain to the output means;
and (vii)an output means adapted to provide in a readable form an output related to the observed value for the induced strain.
Preferably, the illumination means consists of an circularly polarizedlight source.
Preferably, the illumination means consists of a continuous light source.
2Q2~31 Alternatively the illumination means may consist of a stroboscopic light source.
Preferably, the photoelastic material is a plastic.
Preferably, the observation means includes fiber optic cables and suitable optics.
Preferably, the analyzer means includes an optical analyzer/detector, a fringe counter means, and an analog to digital converter.
Alternatively, the analyzer means includes a spectral analysis means.
Preferably, the affixing means is a reflective epoxy glue or cement.
Preferably, the output means includes a display means, a storage means, a display/storage means, or both a display and a storage means, in which the storage and display functions can be seperate (such as in a personal computer memory and a video display) or combined (such as a chart recorder trace or a data logger).
The invention will now be described by way of reference to the attachedfigures in which:
FIGURE 1 represents a complete system overview in the form of a block diagram;
FIGURE 2 represents a preferred embodiment of the invention.
FIGURE 3 represents an alternate embodiment of the invention.
The invention in its broadest embodiment comprises at least one illumination means 1, at least one patch of birefringent photoelastic material 5 affixedly attached to the object 20 to which the applied torque is being measured, at least one observation means 3, at least one analyzer means 17, at least one processor means 9, and at least one output means 10 .
The illumination means 1 includes a light source 19 and a polarizer 2.
The light emitted by the light source 19 is circularly polarized by the polarizer 2 before it reaches the birefringent photoelastic material 5.
~2l.~33 ~
Once it has passed through the birefringent photelastic material 5, it is reflected off the affixing means 6 back through the birefringent photelastic material 5. An observation means 3 receives the reflected light waves which contain a phase shift. The reflected light is analyzed by an optical analyzer 4 and a fringe pattern is produed. The analyzer means 17 comprises a fringe counting analyzer means 7 and an analog to digital converter 8. The fringe counting analyzer means 7 can then calculates the fringe orderJ and the offset from the last fringe boundary, and the analog to digital converter 8 then converts the results lnto an electronic signal which will act as the input to the processor means 9.
In the processor, it is converted into a value for applied torque based on the known photoelastic properties of the test object and of the birefringent photoelastic material. This value is passed to the output means 10 which typically may comprises a display means 11, a storage means 12, and a feedback means 13.
The display means 11 can comprise a digital display, an LED device, a light, a bell, a printer, a chart recorder, a meter, a buzzer, a television display, or any other suitable audio visual display means.
The storage means 12 can comprise a printer, a chart recorder, a magnetic disk, an optical disk, a random access memory, an electronic memory, a magnetic tape, a videotape, and any other suitable storage means.
The feedback means 13 may comprise any suitable control means having as at least one input thereto a signal from or generated by or as a result of a signal from or generated by the processor means 9.
The processor means 9 may comprise markings on a metering device, a comparison means, a microprocessor devise, or any other means of rendering the input signal readable.
In one preferred embodiment, shown as FIGURE 2, the invention comprises a stroboscopic light source 19 and a patch of birefringent photoelastic plastic material such as epoxy applied to the object 20, such as a shaft, with reflective adhesive 6 such as epoxy glue. A fiber optic cable containing at least two fibers 14 and 34 serves to transmlt the light.
_ g _ 2 1~ 2 ~
Fiber 14 is used to transmit the polarized light from the light source 19 to the object 20 allowing for the other components to remain at a remote location. The observation means 3 includes fiber 34, which transmits the reflected light back to the remote location where it is analyzed by the optical analyzer 4, The fringe pattern which results is passed to the fringe counting analyzer means 7. The value calculated is digitized by an A/D converter 8 in the analyzer means. A processor means 9 receives all the data and calculates the applied substantially torsional force as well as any information desired by the user or necessary for feedback. This information is transmitted to an output means 10. For testing purposes the processor means 9 and the output means 10 can be in the form of what is commonly referred to as a personal computer.
It would be prefererable to measure a substantially torsional force with the fewest other force components. One method to accomplish this is by locating the point at which the torsional force is the greatest contributor (by percentage~ to the measured value. This can be accomplished by using more than one illumination means at appropriate locations in order to facillitate the selection of the value relating most closely to pure torque.
This simple system can be expanded relatively easily 80 that a torque can be measured at more than one point. The optical properties of the patch 5 can be viewed at more than one point by using a plurality of pairs of optical fibers 14 and 34. The resulting light beams are analyzed by either a multiple channel analyzer means 17, or by several optical analyzers. Similarly, several output means 10, or a multiple channel means is also then necessary to deal with the plurality of signals being developed, In FIGURE 3, a further embodiment for measuring the applied strain in an object such as an aircraft wing 20als shown. The birefringent photoelastic coating 5 is applied fixedly in the form of a patch to the inside of the wing assembly 20a using reflective epoxy 6a. At least one illumination means 1 emits light which passes through the birefringent photoelastic plastic material 5 and is reflected off the reflective epoxy 6a back through the birefringent photoelastic plastic material 5. Even though the wing is static, the applied strain can be analyzed and used to ~02~
predict failure by avoiding the on~et of meta]. fatigue or to improve maintenance.
Claims (22)
1. A method for measuring a substantially torsional force applied to an object which comprises in combination:
(i) fixedly applying to a preselected locus on the surface of the object a suitable sized patch of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least some of the strained patch with a single beam illumination means;
(iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
(v) correlating the observed changes with the known properties of the birefringent photoelastic material; and (vi) deriving a value for the substantially torsional force from the correlation data.
(i) fixedly applying to a preselected locus on the surface of the object a suitable sized patch of a birefringent photoelastic material of known photoelastic properties;
(ii) applying torque to the object thereby causing strain in both the object and the patch;
(iii)illuminating at least some of the strained patch with a single beam illumination means;
(iv) observing changes in at least some of the light reflected from the strained birefringent photoelastic material which has passed through the affixed patch of birefringent photoelastic material;
(v) correlating the observed changes with the known properties of the birefringent photoelastic material; and (vi) deriving a value for the substantially torsional force from the correlation data.
2.The method of claim 1 wherein the correlation is performed by an optical analyzer means together with a fringe counting analyzer means.
3.The method of claim 2 wherein the correlated information is provided as an electronic signal to a processor means which provides the desired measurements to an output means.
4. The method of claim 1 wherein the illumination means provides circularly polarized light.
5. The method of claim 1 wherein the suitable illumination means provides a continuous beam of light.
6. The method of claim 1 wherein the suitable illumination means provides stroboscopic light.
7. The method of claim 1 wherein the birefringent photoelastic material is a plastic.
8. The method of claim 1 wherein the adhesive is a reflective glue or cement which provides a reflective surface between the patch and the object.
9. The method of claim 8 wherein the adhesive is a reflective epoxy glue.
10. An apparatus for measuring a substantially torsional force applied to an object comprising in combination, (i) a patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the surface of the object;
(iii)an illumination means adapted to illuminate the patch with suitable light;
(iv) an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and to pass it to the correlation means;
(v) a correlation means adapted to receive the at least some light passed from the observation means, and to convert it into an input signal adapted to act as the input into a signal processor means;
(vi) a signal processor means adapted to receive the input signal and provide an appropriate output signal to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
(ii) an affixing means adapted to secure the patch to the surface of the object;
(iii)an illumination means adapted to illuminate the patch with suitable light;
(iv) an observation means adapted to receive at least some of the light reflected through the birefringent photoelastic material and to pass it to the correlation means;
(v) a correlation means adapted to receive the at least some light passed from the observation means, and to convert it into an input signal adapted to act as the input into a signal processor means;
(vi) a signal processor means adapted to receive the input signal and provide an appropriate output signal to the output means; and (vii)an output means adapted to provide in a readable form an output related to the observed value for the torque.
11.The apparatus of claim 10 wherein the patch comprises a continuous strip or ring of birefringent photoelastic material.
12.The apparatus of claim 10 wherein the optical analyzer and the analyzer means provide a signal relating to at least the torque induced strain and adapted to act as the input to the processor means.
13.The apparatus of claim 10 wherein the illumination means consists of an circularly polarized light source.
14.The apparatus of claim 10 wherein the the illumination means consists of a continuous light source.
15.The apparatus of claim 10 wherein the illumination means consists of a stroboscopic light source.
16.The apparatus of claim 10 wherein the photoelastic material is a plastic.
17.The apparatus of claim 10 wherein the observation means includes fiber optic cables and suitable optics.
18. The apparatus of claim 10 wherein the analyzer means includes an optical analyzer/detector, a fringe counter means, and an analog to digital converter.
19. The apparatus of claim 10 wherein the fringe counting analyzer means includes a spectral analysis means.
20. The apparatus of claim 10 wherein the affixing means is a reflective glue or cement.
21. The apparatus of claim 10 wherein the reflective glue is an epoxy glue.
22. The apparatus of claim 10 wherein the output means includes a display means, a storage means, a display/storage means, or both a display and a storage means, in which the storage and display functions can be seperate or combined.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2024831 CA2024831A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive torquemeter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2024831 CA2024831A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive torquemeter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2024831A1 true CA2024831A1 (en) | 1992-03-08 |
Family
ID=4145917
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2024831 Abandoned CA2024831A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive torquemeter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2024831A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0578422A3 (en) * | 1992-06-30 | 1994-03-23 | Lucas Ind Plc | |
| US5699159A (en) * | 1996-04-26 | 1997-12-16 | Jatom Systems Incorporated | Loadmeter employing birefringence to measure mechanical loads and stresses |
| US5825492A (en) * | 1996-04-26 | 1998-10-20 | Jaton Systems Incorporated | Method and apparatus for measuring retardation and birefringence |
-
1990
- 1990-09-07 CA CA 2024831 patent/CA2024831A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0578422A3 (en) * | 1992-06-30 | 1994-03-23 | Lucas Ind Plc | |
| US5699159A (en) * | 1996-04-26 | 1997-12-16 | Jatom Systems Incorporated | Loadmeter employing birefringence to measure mechanical loads and stresses |
| US5825492A (en) * | 1996-04-26 | 1998-10-20 | Jaton Systems Incorporated | Method and apparatus for measuring retardation and birefringence |
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