Null
First Claim
1. A method of measuring strain in a workpiece that is insensitive to ambient temperature fluctuations, comprising the steps of:
- illuminating a strain-sensitive material with a beam of selectively polarized light, the beam of selectively polarized light being substantially perpendicular to the surface of the workpiece, the strain-sensitive material being in physical contact with the surface of the workpiece;
measuring an intensity of at least one polarization component of the beam of selectively polarized light making at least one pass through the strain-sensitive material, the at least one polarization component being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material so that it has a projection along both strain-induced fast and slow orthogonal axes; and
calculating from said intensity a difference between strains along the strain-induced fast and slow orthogonal axes in the strain-sensitive material, the difference being substantially independent of ambient temperature fluctuations.
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Accused Products
Abstract
The present invention provides a simple design for a temperature-insensitive extrinsic polarimetric strain sensor. The sensing element is a thin sheet of photoelastic material that is bonded to the test object. It is illuminated with linearly polarized light with the polarization direction at 45 degrees relative to the strain-induced fast and slow axes in the photoelastic material. The sensor measures the difference between the strains along these two orthogonal directions. The reduced sensitivity of the sensor to temperature results from the fact that the illumination is perpendicular to the surface of the test object. All polarization components that are parallel to the surface will experience identical refractive index changes due to thermal effects. Consequently, a measurement of the difference in strains along two directions in the surface plane is insensitive to temperature.
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Citations
23 Claims
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1. A method of measuring strain in a workpiece that is insensitive to ambient temperature fluctuations, comprising the steps of:
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illuminating a strain-sensitive material with a beam of selectively polarized light, the beam of selectively polarized light being substantially perpendicular to the surface of the workpiece, the strain-sensitive material being in physical contact with the surface of the workpiece;
measuring an intensity of at least one polarization component of the beam of selectively polarized light making at least one pass through the strain-sensitive material, the at least one polarization component being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material so that it has a projection along both strain-induced fast and slow orthogonal axes; and
calculating from said intensity a difference between strains along the strain-induced fast and slow orthogonal axes in the strain-sensitive material, the difference being substantially independent of ambient temperature fluctuations. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of measuring strain in a workpiece that is insensitive to ambient temperature fluctuations, comprising the steps of:
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illuminating a strain-sensitive material with a beam of selectively polarized light, the beam of selectively polarized light being substantially perpendicular to the surface of the workpiece, the strain-sensitive material being in physical contact with the surface of the workpiece;
measuring a first intensity of a first polarization component and a second intensity of a second polarization component of the beam of selectively polarized light making at least one pass through the strain-sensitive material, the first and second polarization components being orthogonal to each other and tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that each of said first and second polarization components has a projection along both strain-induced fast and slow orthogonal axes; and
calculating from the first and second intensities a difference between strains along the strain-induced fast and slow orthogonal axes in the strain-sensitive material, the difference being substantially independent of ambient temperature fluctuations. - View Dependent Claims (9, 10, 11, 12)
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13. A temperature insensitive strain sensor that is insensitive to ambient temperature fluctuations, comprising:
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a strain-sensitive material adapted to be physically contacted to a surface of a workpiece;
light source means and light beam polarization means for illuminating said strain-sensitive material with a beam of selectively polarized light, said beam of selectively polarized light being substantially perpendicular to the surface of the workpiece; and
detection means for measuring an intensity of at least one of a first polarization component and a second polarization component in the beam of selectively polarized light making at least one pass through said strain-sensitive material, the at least one of a first and second polarization components being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that at least one of the at least first and second polarization components has a projection along both strain-induced fast and slow orthogonal axes; and
processing means connected to said detection means for calculating from the intensity of the at least one of a first polarization component and a second polarization component a difference between strains along the strain-induced fast and slow orthogonal axes in said strain-sensitive material, the difference between strains being substantially independent of ambient temperature fluctuations. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A temperature insensitive strain sensor that is insensitive to ambient temperature fluctuations, comprising:
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a strain-sensitive material adapted to be physically contacted to a surface of a workpiece;
light source means and light beam polarization means for illuminating said strain-sensitive material with a beam of selectively polarized light, said beam of selectively polarized light being substantially perpendicular to the surface of the workpiece; and
detection means for measuring an intensity of a first polarization component and a second polarization component in the beam of selectively polarized light making at least one pass through said strain-sensitive material, each of the first and second polarization components being tilted with respect to strain-induced fast and slow orthogonal axes in the strain-sensitive material parallel to the surface of the workpiece so that each of the first and second polarization components have a projection along both strain-induced fast and slow orthogonal axes; and
processing means connected to said detection means for calculating from the intensities of the first and second polarization components a difference between strains along the strain-induced fast and slow orthogonal axes in said strain-sensitive material, the difference between strains being substantially independent of ambient temperature fluctuations. - View Dependent Claims (20, 21, 22, 23)
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Specification