Optics: measuring and testing – By polarized light examination – Of surface reflection
Patent
1997-12-05
1999-11-02
Kim, Robert H.
Optics: measuring and testing
By polarized light examination
Of surface reflection
356 33, G01B 1106, G01B 1116
Patent
active
059780878
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an optical collector head, a stress analysis device, and to a reflection polariscope for strain analysis of a component. Typical uses are in the aeronautical or automobile industries, to facilitate strain analysis of real components, applicability for crack detection; operation for static, dynamic and cyclic events; and provision for full-field principal strain data.
DESCRIPTION OF PRIOR ART
In Strain 27(2):49-56, 1991, is an Article by E. A. Patterson and Z. F. Wang entitled "Towards full field automated photoelastic analysis of complex components" is described a technique for the sequential capture of images.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided an optical collector head comprising:
An optical collector head comprising: beams in different directions; collimated, beam to the beam splitting device and, for each output beam from each output beam, with each output beam having different orientations of the quarter wave plate, or plate producing a similar effect and of the polarizer.
According to a second aspect of the invention, there is provided a polarimetric device for stress or chemical analysis comprising an optical collector head as defined above and a source of polarised light.
According to a third aspect of the invention there is provided a reflection polariscope comprising an optical collection head as defined above and a source of polarized light.
PREFERRED FEATURES OF THE INVENTION
Preferably, the beam splitting device is capable of producing four output beams, preferably of equal intensity, whilst the recording device is preferably a CCD (charge coupled device) camera.
Whilst the beam splitting device could consist of a mirror system, preferably the beam splitting device consists of three cube beam splitters, preferably with a 50/50 splitting ratio. It is also preferred to provide each assembly with a band width filter.
From the practical viewpoint alignment and focusing of the recording devices is much simplified if, in accordance with another preferred feature, the optical components and recording devices are mounted on a machined optical bench.
With the device of the second aspect, the object to be examined, e.g. in chemical analysis, may itself have a polarized light source.
With the third aspect, the polariscope, the light source is conveniently a quartz tungsten hallogen lamp, e.g. of 100 W, and may be used in a reflective mode or a direct mode.
The optical collector head in accordance with the first aspect of the invention produces monochromatic images that are registered by a recording device. The images are phase-stepped and allow the relative retardation and isoclinic angle to be evaluated for the object being viewed. Subsequent data processing allows the relative retardation to be converted from a periodic map to a continuous map of isochromatic fringe order, but a calibration at two points is required to produce unambiguously a map of absolute isochromatic fringe order. This calibration is provided manually by the operator and is thus potentially subject to error. However, recent research has shown that the spectral contents of the polarized light can be used to determine the absolute isochromatic fringe order when a white light source is used, but measurement of the spectral contents over the entire field of an image is limited by the lack of availability of devices capable of measuring simultaneously multiple-wavelength spectral at many spatial points (e.g. 65,536 in a 256.times.256 array), whilst scanning devices are limited by the speed of processing. It has been shown that 8 wavelengths are sufficient to allow absolute fringe orders up to approximately 6 to be measured reliably.
According to another feature of the invention, the optical collector head in accordance with the first aspect is provided with a calibration device comprising, for each output of the beam splitting device, a pair of cube beam splitters, the first cube beam splitter, of each pair passing an
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Patterson Eann Alexander
Wang Zhi Fan
Kim Robert H.
Smith Zandra V.
The University of Sheffield
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