CA2024832A1 - Non-invasive force analysis system - Google Patents
Non-invasive force analysis systemInfo
- Publication number
- CA2024832A1 CA2024832A1 CA 2024832 CA2024832A CA2024832A1 CA 2024832 A1 CA2024832 A1 CA 2024832A1 CA 2024832 CA2024832 CA 2024832 CA 2024832 A CA2024832 A CA 2024832A CA 2024832 A1 CA2024832 A1 CA 2024832A1
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- Canada
- Prior art keywords
- patch
- photoelastic
- birefringent
- torque
- analyzer
- Prior art date
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
- Force Measurement Appropriate To Specific Purposes (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
1~31 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 measur applied torque 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. Further, the data obtained can also be used at least to identify other stress-induced strains, for example, a mis-alignment of the bearings for a shaft.
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 object. 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 also 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. OnP 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. Even though telemetric devices are currently used in some helicopters, it would greatly simplify design if a less obtrusive torque meter could be used.
202~2 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 is 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.
One main disadvantage of the Zandman system, is ehat it bases its valuefor torque on the readings taken at one point on the surface of an object.
This system only works under conditions of pure torque, but when a bending component is introduced, the accuracy of Zandman's system is greatly reduced. This limits the potential uses of the system to carefully monitored environments. It is therefore desirable to measure torque in such a fashion so as to allow the value for pure torque to be separated from the other forces affecting the object.
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 physica] 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 202fl~3~
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.
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 example9 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 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 plastic 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 plasic 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 plastic 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 facilitating 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.
~2~
In the case of bending components taking several readings about an object will allow these to be isolated. In the case of a uniform force such as compression or tension, a load cell placed on another object providing or supporting the specific forc~J such as the load bearingssupporting a rotating shaft, can be used for isolation purposes. In this way it is possible to measure torque, total force on the component, tension or compression, bending, or any combination of these elements.
In a first broad aspect this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the object at least one patch of a birefringent photelastic material of known photoelastic properties at at least one preselected locus on the object;
(ii) applying the forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
(iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic slgnal corresponding to at least the applied torque; and (vii)processing the obtained signal to provide a value for the applied substantially torsional force.
In a more detailed embodiment, this invention seeks to provide a methodfor measuring forces including a torsional force applied to an object, 2a~$3~
such as a shaft transmitting a power load, contained by a housing which comprises in comblnation, (i) fixedly applying to the object at least one first patch of a birefringent photoelastic material of known photoelastic properties;
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties;
(iii)applying forces including a torsional force to the object;
(iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately located suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means;
(vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an optical analyæer means together with a fringe counter means to provide an electronic signal corresponding to the applied forces induced strains; and (viii)processing the obtained signal to provide a value for the applied forces.
In a second more detailed embodiment this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the object at least one patch of a birefringent photelastic material of known photoelastic properties at at least one preselected locus on the object comprising a strip around a preselected locus of the object;
(ii) applying the forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
~2~32 (iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal, (vi) obtaining an electronic signal corresponding to at least the applied torque; and (vii~processing the obtained signal to provide a value for the applied substantially torsional force.
In a third more detailed embodiment, this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the ob~ect at least one first patch of a birefringent photoelastic material of known photoelastic properties comprising a strip around a preselected locus of the object;
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties, (iii)applying forces including a torsional force to the object, (iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately spaced suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means, (vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes related to torque induced strain in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an 2~2~3~
optical analyzer means together with a fringe counter means to provide an electronic signal corresponding to at least the torque induced strai~; and (viii)processing the obtained signal to provide a value for the applied forces.
Preferably, the suitable illumination means provides circularly polarized light.
Preferably the birefringent photoelastic material is a plastic to facilitate molding and affixing.
Preferably, the birefringent photoelastic plastic material is fixedly applied to the object by means of a reflective glue or cement such as an epoxy glue.
Preferably, the method is used in an environment of dynamic use under dynamic load.
Preferably~ the method is used in an environment of statlc use under static load.
Preferably the method is used in test environments providing both static and dynamic testing.
Preferably, the method is used to obtain values for both the applied torque and other applied non-torsional forces.
In a second broad aspect this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one patch of birefringent photoelastic material with known photoelastic properties adaptPd to be afEixed to the surface of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object and provide a reflective surface between the patch and the sur~ace of the ob;ect;
202~32 (iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)a plurality of observation means adapted to receive a portion of the light reflected through the birefringent phctoelastic material derived from morP than one of the separately located illumination means 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;
(vi) a 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 torqueO
In a more detailed embodiment this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one first patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
(iii)an affixing means adapted to secure the patches to the object and provide a reflective surface between the first patch and the suface of the object and between the second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch w~th suitable light;
(v)at least one illumination means adapted to illum{nate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the il~umination means and pass it to the analyzer means;
2~2~32 (vii)at least one analyzer means adapted to receive the at least some llght passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at least the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the applied forces.
In a second more detailed embodiment this invention seeks to provide anapparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination~
(i~ at least one patch of birefringent photoelastic material with known photoelastic properties generally in the form of a continuous strip or ring 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 objece and provide a reflective surface between the patch and the suface of the object;
(iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)a plurality of observation means adapted to receive a portion of the light reflected through the birefringent photoelastic material derived from more than one of the separately located illumination means 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;
~vi) a 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 third more detailed embodiment this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an _ 9 _ 20~32 object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one first patch of birefringent photoelastic material with known photoelastic properties generally in ~he form of a continuous strip or ring adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
~iii)an affixing means adapted to secure the patches to the object and to the housing and provide a reflective surface between the first patch and the suface of the object and the second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch with suitable light;
(v)at least one illumination means adapted to illuminate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the separately located illumination means and pass it to the analyzer means;
(vii)at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at lea.st the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the applied forces.
Preferably, the illumination means consists of circularly polarized light source.
Preferably, the photoelastic material is a plastic.
2~2'~,~3~
Preferably, the observation means includes fiber optic cables and suitable optics.
Preferably, the processor means processes the input signal into a valuefor the applied torque.
Preferably, the analyzer means includes an optical analyzer/detector and a fringe counter means.
Alternately the analyzer means includes a spectral analyzer means.
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 separate (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 end on view of the shaft in the preferred embodiment.
The invention in its broadest embodiment comprises at least one illumination means 1, at least one patch of birefringen~ photoelastic material 5 affixedly attached to the object to which the applied torque is being measured, at least one observation means 3, at least one analyzer means 7, at least one processor means 9, and at least one output means 10.
The light emitted by the light source 17 is polarized by a polarizer 2 before it reaches the birefringent photoelastic plastic material 5. Once it has passed through the coating 5 it is reflected off the affixing means 6 back through the coating 5. An observation means 3 receives the reflected light waves which contain a phase shift. It is analyzed by an optical analyzer 4 and a fringe pattern is produced. The analyzer means 17 comprises a fringe counting analyzer means 7 and an analog to digital 2~2'~3 ~
converter 8. The fringe counting analyzer means 7 calculates the fringe order, and the offset from the last fringe boundary, and the analog to digital converter 8 converts the results into 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 properties of the test object and of the birefringent photoelastic plastic material which can be passed to the output means 10.
The output means 10 may comprise a display means 11, a storage means 12, and a feedback means 13.
A 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 audio/visual display means.
A storage means 12 can comprise a printer, a chart recorder, a magneticdisk, an optical disk, a random access memory, an electronic memory, a magnetic tape, a videotape, and any other suitable storage means.
A 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 the preferred embodiment, shown as FIGURES 2 and 3, the invention comprises a constant light source 17 and a perimeter of birefringent photoelastic material 5 applied to the ob;ect, such as a shaft, with reflective epoxy. Several fiber optic cables 14 are used to transmit the polarized light from the one light source to the object allowing for the other components to remain at a remote location. The observation means 3 comprises several other fiber optic cables 34 which transmit the reflected light back to the remote location where it is analyzed by the optical analyzer 4. The fringe patterns which result pass to the analyzer means 17. The values calculated at the fringe counting analyzer means 7 are digitized by an A/D converter 8 in the analyzer means 17. A load cell 15 2 ~ 2 ~ 2 located on the bearlngs 16 provides a value for the applied tension ~o the processing means 9. At least one processor means 9 receives all the data and calculates the applied torque as well as any information desired by the user or necessary for feedback. This can be accomplished through the use of the several fiber optic cables illuminating the patch at specific points such that each cable is of a pair a~ 90 degrees ~o each oth~r. The desired information is transmitted to at least one output means 10.
device to measur applied torque 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. Further, the data obtained can also be used at least to identify other stress-induced strains, for example, a mis-alignment of the bearings for a shaft.
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 object. 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 also 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. OnP 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. Even though telemetric devices are currently used in some helicopters, it would greatly simplify design if a less obtrusive torque meter could be used.
202~2 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 is 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.
One main disadvantage of the Zandman system, is ehat it bases its valuefor torque on the readings taken at one point on the surface of an object.
This system only works under conditions of pure torque, but when a bending component is introduced, the accuracy of Zandman's system is greatly reduced. This limits the potential uses of the system to carefully monitored environments. It is therefore desirable to measure torque in such a fashion so as to allow the value for pure torque to be separated from the other forces affecting the object.
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 physica] 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 202fl~3~
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.
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 example9 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 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 plastic 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 plasic 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 plastic 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 facilitating 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.
~2~
In the case of bending components taking several readings about an object will allow these to be isolated. In the case of a uniform force such as compression or tension, a load cell placed on another object providing or supporting the specific forc~J such as the load bearingssupporting a rotating shaft, can be used for isolation purposes. In this way it is possible to measure torque, total force on the component, tension or compression, bending, or any combination of these elements.
In a first broad aspect this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the object at least one patch of a birefringent photelastic material of known photoelastic properties at at least one preselected locus on the object;
(ii) applying the forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
(iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic slgnal corresponding to at least the applied torque; and (vii)processing the obtained signal to provide a value for the applied substantially torsional force.
In a more detailed embodiment, this invention seeks to provide a methodfor measuring forces including a torsional force applied to an object, 2a~$3~
such as a shaft transmitting a power load, contained by a housing which comprises in comblnation, (i) fixedly applying to the object at least one first patch of a birefringent photoelastic material of known photoelastic properties;
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties;
(iii)applying forces including a torsional force to the object;
(iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately located suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means;
(vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an optical analyæer means together with a fringe counter means to provide an electronic signal corresponding to the applied forces induced strains; and (viii)processing the obtained signal to provide a value for the applied forces.
In a second more detailed embodiment this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the object at least one patch of a birefringent photelastic material of known photoelastic properties at at least one preselected locus on the object comprising a strip around a preselected locus of the object;
(ii) applying the forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
~2~32 (iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal, (vi) obtaining an electronic signal corresponding to at least the applied torque; and (vii~processing the obtained signal to provide a value for the applied substantially torsional force.
In a third more detailed embodiment, this invention seeks to provide a method for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, contained by a housing which comprises in combination, (i) fixedly applying to the ob~ect at least one first patch of a birefringent photoelastic material of known photoelastic properties comprising a strip around a preselected locus of the object;
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties, (iii)applying forces including a torsional force to the object, (iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately spaced suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means, (vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes related to torque induced strain in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an 2~2~3~
optical analyzer means together with a fringe counter means to provide an electronic signal corresponding to at least the torque induced strai~; and (viii)processing the obtained signal to provide a value for the applied forces.
Preferably, the suitable illumination means provides circularly polarized light.
Preferably the birefringent photoelastic material is a plastic to facilitate molding and affixing.
Preferably, the birefringent photoelastic plastic material is fixedly applied to the object by means of a reflective glue or cement such as an epoxy glue.
Preferably, the method is used in an environment of dynamic use under dynamic load.
Preferably~ the method is used in an environment of statlc use under static load.
Preferably the method is used in test environments providing both static and dynamic testing.
Preferably, the method is used to obtain values for both the applied torque and other applied non-torsional forces.
In a second broad aspect this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one patch of birefringent photoelastic material with known photoelastic properties adaptPd to be afEixed to the surface of the object at a preselected locus;
(ii) an affixing means adapted to secure the patch to the object and provide a reflective surface between the patch and the sur~ace of the ob;ect;
202~32 (iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)a plurality of observation means adapted to receive a portion of the light reflected through the birefringent phctoelastic material derived from morP than one of the separately located illumination means 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;
(vi) a 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 torqueO
In a more detailed embodiment this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one first patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
(iii)an affixing means adapted to secure the patches to the object and provide a reflective surface between the first patch and the suface of the object and between the second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch w~th suitable light;
(v)at least one illumination means adapted to illum{nate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the il~umination means and pass it to the analyzer means;
2~2~32 (vii)at least one analyzer means adapted to receive the at least some llght passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at least the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the applied forces.
In a second more detailed embodiment this invention seeks to provide anapparatus for measuring forces including a torsional force applied to an object, such as a shaft transmitting a power load, within a housing comprising in combination~
(i~ at least one patch of birefringent photoelastic material with known photoelastic properties generally in the form of a continuous strip or ring 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 objece and provide a reflective surface between the patch and the suface of the object;
(iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv)a plurality of observation means adapted to receive a portion of the light reflected through the birefringent photoelastic material derived from more than one of the separately located illumination means 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;
~vi) a 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 third more detailed embodiment this invention seeks to provide an apparatus for measuring forces including a torsional force applied to an _ 9 _ 20~32 object, such as a shaft transmitting a power load, within a housing comprising in combination, (i) at least one first patch of birefringent photoelastic material with known photoelastic properties generally in ~he form of a continuous strip or ring adapted to be affixed to the surface periphery of the object at a preselected locus;
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
~iii)an affixing means adapted to secure the patches to the object and to the housing and provide a reflective surface between the first patch and the suface of the object and the second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch with suitable light;
(v)at least one illumination means adapted to illuminate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the separately located illumination means and pass it to the analyzer means;
(vii)at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at lea.st the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the applied forces.
Preferably, the illumination means consists of circularly polarized light source.
Preferably, the photoelastic material is a plastic.
2~2'~,~3~
Preferably, the observation means includes fiber optic cables and suitable optics.
Preferably, the processor means processes the input signal into a valuefor the applied torque.
Preferably, the analyzer means includes an optical analyzer/detector and a fringe counter means.
Alternately the analyzer means includes a spectral analyzer means.
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 separate (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 end on view of the shaft in the preferred embodiment.
The invention in its broadest embodiment comprises at least one illumination means 1, at least one patch of birefringen~ photoelastic material 5 affixedly attached to the object to which the applied torque is being measured, at least one observation means 3, at least one analyzer means 7, at least one processor means 9, and at least one output means 10.
The light emitted by the light source 17 is polarized by a polarizer 2 before it reaches the birefringent photoelastic plastic material 5. Once it has passed through the coating 5 it is reflected off the affixing means 6 back through the coating 5. An observation means 3 receives the reflected light waves which contain a phase shift. It is analyzed by an optical analyzer 4 and a fringe pattern is produced. The analyzer means 17 comprises a fringe counting analyzer means 7 and an analog to digital 2~2'~3 ~
converter 8. The fringe counting analyzer means 7 calculates the fringe order, and the offset from the last fringe boundary, and the analog to digital converter 8 converts the results into 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 properties of the test object and of the birefringent photoelastic plastic material which can be passed to the output means 10.
The output means 10 may comprise a display means 11, a storage means 12, and a feedback means 13.
A 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 audio/visual display means.
A storage means 12 can comprise a printer, a chart recorder, a magneticdisk, an optical disk, a random access memory, an electronic memory, a magnetic tape, a videotape, and any other suitable storage means.
A 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 the preferred embodiment, shown as FIGURES 2 and 3, the invention comprises a constant light source 17 and a perimeter of birefringent photoelastic material 5 applied to the ob;ect, such as a shaft, with reflective epoxy. Several fiber optic cables 14 are used to transmit the polarized light from the one light source to the object allowing for the other components to remain at a remote location. The observation means 3 comprises several other fiber optic cables 34 which transmit the reflected light back to the remote location where it is analyzed by the optical analyzer 4. The fringe patterns which result pass to the analyzer means 17. The values calculated at the fringe counting analyzer means 7 are digitized by an A/D converter 8 in the analyzer means 17. A load cell 15 2 ~ 2 ~ 2 located on the bearlngs 16 provides a value for the applied tension ~o the processing means 9. At least one processor means 9 receives all the data and calculates the applied torque as well as any information desired by the user or necessary for feedback. This can be accomplished through the use of the several fiber optic cables illuminating the patch at specific points such that each cable is of a pair a~ 90 degrees ~o each oth~r. The desired information is transmitted to at least one output means 10.
Claims (32)
1. A method for measuring forces including a torsional force applied to an object contained by a housing which comprises in combination, (i) fixedly applying to the object at least one patch of a birefringent photelastic material of known photoelastic properties at at least one preselected locus on the object;
(ii) applying forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
(iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic signal corresponding to at least the applied torque; and (vii)processing the obtained signal to provide a value for the applied substantially torsional force.
(ii) applying forces to the object thereby causing strain in both the object and the at least one patch;
(iii)illuminating at least a portion of the strained at least one patch with a plurality of separately located single beam illumination means;
(iv) observing changes related to torque induced strain in at least some of the light reflected from the at least one strained patch derived from more than one of the separately located illumination means which has passed through the affixed birefringent photoelastic material;
(v) correlating the observed changes in at least some of the light reflected from the at least one patch with the known properties of the birefringent photoelastic material by means of an optical analyzer means together with a fringe counter means thereby providing an electronic signal;
(vi) obtaining an electronic signal corresponding to at least the applied torque; and (vii)processing the obtained signal to provide a value for the applied substantially torsional force.
2. A method for measuring forces including a torsional force applied to an object contained by a housing which comprises in combination, (i) fixedly applying to the object at least one first patch of a birefringent photoelastic material of known photoelastic properties;
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties;
(iii)applying forces including a torsional force to the object;
(iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately located suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means;
(vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an analyzer means to provide an electronic signal corresponding to the applied forces induced strain; and (viii)processing the obtained signal to provide a value for the applied forces.
(ii) fixedly applying to the housing at least one second patch of a birefringent photoelastic material of known photoelastic properties;
(iii)applying forces including a torsional force to the object;
(iv) illuminating at least a portion of the strained at least one first patch with a plurality of separately located suitable single beam illumination means;
(v) illuminating at least a portion of the strained at least one second patch with at least one suitable single beam illumination means;
(vi) observing changes related to strains induced by the applied forces in at least some of the light reflected from at least one first patch and at least one second patch which has passed through the affixed birefringent photoelastic material;
(vii)correlating the observed changes in at least some of the light reflected with the known properties of the birefringent photoelastic material by means of an analyzer means to provide an electronic signal corresponding to the applied forces induced strain; and (viii)processing the obtained signal to provide a value for the applied forces.
3. The method of claim 1 wherein the at least one first patch comprises a strip around a preselected locus of the object;
4. The method of claim 2 wherein the at least one first patch comprises a strip around a preselected locus of the object;
5. The method of claim 1 wherein the suitable illumination means provides circularly polarized light.
6. The method of claim 2 wherein the suitable illumination means provides circularly polarized light.
7. The method of claim 1 wherein the birefringent photoelastic material is a plastic.
8. The method of claim 2 wherein the birefringent photoelastic material is a plastic.
9. The method of claim 1 wherein the birefringent photoelastic plastic material is fixedly applied to the object by means of a reflective glue or cement.
10. The method of claim 2 wherein the birefringent photoelastic plastic material is fixedly applied to the object by means of a reflective glue or cement.
11. The method of claim 1 wherein the method is used to obtain values for both the applied torque and other applied non-torsional forces.
12. The method of claim 2 wherein the method is used to obtain values for both the applied torque and other applied non-torsional forces.
13.An apparatus for measuring forces including a torsional force applied to an object within a housing comprising in combination, (i) at least one 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 object and provide a reflective surface between the patch and the suface of the object;
(iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv) a plurality of observation means adapted to receive a portion of the light reflected through the birefringent photoelastic material derived from more than one of the separately located illumination means 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;
(vi) a 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 object and provide a reflective surface between the patch and the suface of the object;
(iii)a plurality of separately located illumination means adapted to illuminate at least some of the patch with suitable light;
(iv) a plurality of observation means adapted to receive a portion of the light reflected through the birefringent photoelastic material derived from more than one of the separately located illumination means 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;
(vi) a 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.
14. An apparatus for measuring forces including a torsional force applied to an object within a housing comprising in combination, (i) at least one first patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the object at a preselected locus;
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
(iii)an affixing means adapted to secure the patches to the object and provide a reflective surface between any first patch and the suface of the object and any second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch with suitable light;
(v)at least one illumination means adapted to illuminate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the separately located illumination means and pass it to an analyzer means;
(vii)at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at least the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the torque.
(ii) at least one second patch of birefringent photoelastic material with known photoelastic properties adapted to be affixed to the surface of the housing at a preselected locus;
(iii)an affixing means adapted to secure the patches to the object and provide a reflective surface between any first patch and the suface of the object and any second patch and the surface of the housing;
(iv)a plurality of separately located illumination means adapted to illuminate at least some of the at least one first patch with suitable light;
(v)at least one illumination means adapted to illuminate at least some of the at least one second patch with suitable light;
(vi) a plurality of observation means adapted to receive a portion of the light reflected through at least one first patch and at least one second patch of birefringent photoelastic material derived from more than one of the separately located illumination means and pass it to an analyzer means;
(vii)at least one analyzer means adapted to receive the at least some light passed from the observation means and convert it into at least one input signal adapted to act as the at least one input into a processor means and relating to observed induced strain;
(viii)a processor means adapted to receive the at least one input signal process said at least one signal in order to provide at least one appropriate output signal relating to at least the torque induced strain to the output means; and (ix) an output means adapted to provide in a readable form an output related to the observed value for the torque.
15. The apparatus of claim 13 wherein the patch is generally in the form of a continuous strip or ring adapted to be affixed to the surface periphery of the object at a preselected locus.
16. The apparatus of claim 14 wherein the patch is generally in the form of a continuous strip or ring adapted to be affixed to the surface periphery of the object at a preselected locus.
17. The apparatus of claim 13 wherein the illumination means comprises circularly polarized light.
18. The apparatus of claim 14 wherein the illumination means comprises circularly polarized light.
19. The apparatus of claim 13 wherein the photoelastic material is a plastic.
20. The apparatus of claim 14 wherein the photoelastic material is a plastic.
21. The apparatus of claim 13 wherein the observation means includes fiber optic cables and suitable optics.
22. The apparatus of claim 14 wherein the observation means includes fiber optic cables and suitable optics.
23. The apparatus of claim 13 wherein the processor means processes the input signal into a value for the applied torque.
24. The apparatus of claim 14 wherein the processor means processes the input signal into a value for the applied torque.
25. The apparatus of claim 13 wherein the analyzer means includes an optical detector, a fringe counter means, and an analog to digital converter.
26. The apparatus of claim 14 wherein the analyzer means includes an optical detector, a fringe counter means, and an analog to digital converter.
27. The apparatus of claim 13 wherein the analyzer means includes a spectral analyzer means.
28. The apparatus of claim 14 wherein the analyzer means includes a spectral analyzer means.
29. The apparatus of claim 13 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.
30. The apparatus of claim 14 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.
31. The apparatus of claim 13 wherein the adhesive is an epoxy glue.
32. The apparatus of claim 14 wherein the adhesive is an epoxy glue.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2024832 CA2024832A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive force analysis system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2024832 CA2024832A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive force analysis system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2024832A1 true CA2024832A1 (en) | 1992-03-08 |
Family
ID=4145918
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2024832 Abandoned CA2024832A1 (en) | 1990-09-07 | 1990-09-07 | Non-invasive force analysis system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2024832A1 (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 2024832 patent/CA2024832A1/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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|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |