Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1991-06-21
1993-04-13
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
With light attenuation
250237G, G01B 1124
Patent
active
052027490
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for patterns observing moire patterns of surfaces to be tested by application of the moire method using phase shifting wherein object gratings to be observed are pictured on auxiliary gratings and the moire patterns generated thereby are detected, stored and/or processed by computer, wherein for one observation at least three phase-shifted moire patterns are respectively evaluated. Furthermore, the invention is related to a device for observing moire patterns of surfaces to be tested by application of the moire method using phase shifting, optionally comprising a grating projection arrangement, an object grating of the surface to be tested, an observation objective, an auxiliary grating, a camera arrangement, a memory and/or computer.
The process and the method of the first mentioned type are not restricted to the projection moire method, which is provided for out of plane measurements. Moreover, they can generally be applied to the observation, measuring and documentation of gratings and of their changings to be evaluated by applying the moire method, and therefore they are also provided for the observation and measurement of in-plane deformations, in the case of which gratings are fixedly applied on or in the surface of the object to be tested and thus deformation measurements can be made in the plane. Therefore, object grating here is to be understood being the grating on or in the object as well the projected grating.
By using a process and a device of the first mentioned type surfaces and their deformation are observed, wherein the surface shape and its deformation respectively are taken up and documented. The field of application extends from microscopic observation (e.g. in the field of material testing, biology or medicine) to the observation of surfaces having m.sup.2 size (e.g. in the automobile industry). The observation of surfaces and of their deformation can be made in different ways. Current processes of surfacelike observation are apart from the different moire methods the photogrammetry, the holography, and with restrictions the motography. These methods are applied partially in competition, partially complementary to one another.
In U.S. Pat. No. 4,641,972 a process for determining the surface profile of an object is described, wherein a light beam having a sinusoidally changing intensity pattern is directed to the object, wherein the phase of the sinusoidal pattern is modulated. A deformed grating image of the object is received by means of a detector arrangement for a number of different modulated phases of the impinging light beam. Thus, an object and a reference phase are obtained for the object and a reference plane point-by-point. The height of each point of the object surface is then determined in relation to the reference plane on basis of the phase differences.
The projection moire method is particularly simple and economical for observing surfaces and their deformation. The measuring principle involved is the following: A line grating is projected in an inclined manner at a defined angle onto the surface to be measured, wherein the brightness distribution of the grating generally corresponds to a trigonometric function. The surface is observed by a camera or the like at another angle, the observer or the camera respectively usually being present in the same vertical distance from the surface. Two observations or images respectively are superposed, which have a reference to different surface shapes and in this manner a moire pattern is generated. Thus, a relative measurement is performed using two observations made successively concerning time. Provided determined marginary conditions are kept, the single orders of the moire pattern correspond to equidistant contour lines. Studies of geometric factors affecting the use concerning the projection moire method are described by G. Wutzke in "On geometric factors affectinq the use in moire topography", Materialpru. 20 (1978), No. 9, pages 338 to 342.
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Idesawa et al., "Scanning moire method and automatic measurement of 3-D shapes", Applied Optics, vol. 16, No. 8, (Aug. 1977), pp. 2152-2162.
Wutzke, G., Uber geometrische, Materialprut 20 (1978).
Breuckmann, B. and Thieme, W., Ein rechner gestutztes Holographiesystem etc., VDI Bericht 552 (1985).
Breuckmann et al., Einsatz hochstauflosender etc. VDI-Bericht 679 (1988).
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