Optics: measuring and testing – Material strain analysis – By light interference detector
Patent
1996-09-13
1998-06-02
Font, Frank G.
Optics: measuring and testing
Material strain analysis
By light interference detector
G01L 124
Patent
active
057608881
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a method for determining the structural strength of a test object having a diffuse-scattering surface in accordance with the precharacterising clause of claim 1.
BACKGROUND OF THE INVENTION
A method according to the precharacterising clause is known from DE-OS 42 31 578 A1. In that method, a test object is irradiated with coherent light and the radiation scattered back from the test object is divided into two partial beams. The two partial beams are joined together again by shifting the two partial beams slightly (shearing effect). The partial beans carrying the image information are conveyed to an electronic image sensor system. The test object is imaged by the imaging component on the image sensor. The radiation impinging on the image sensor is converted into digital signals in accordance with an A/D conversion. The surface of the test object first of all has the state 1, and, after the application of deformation, the state 2. The surface state 1 is recorded by phase-shifting one partial beam in steps relative to the second partial beam in a first image sequence. The image sequence is typically stored in the temporary memory of a computer. A second image sequence is generated from the surface state 2 in the same manner. The individual steps of the first and second image sequences are further processed in a computer to form a modulo-2.pi. image. The aim of the deformation to be applied is always to recognise weak points as a result of the fact that such points have a significantly different deformation from that of the surrounding area. The image produced by this method is, on the one hand, the result of the constructional and geometrical form of the test object and, on the other hand, a consequence of structural irregularities. The disadvantage of this method is that the effect of structural irregularities can be recognised only when it is significantly greater than the effects caused by construction or geometry.
SUMMARY OF THE INVENTION
The object of the invention is further to develop the method known from DE-OS 42 31 578 A1 in such a manner that structural irregularities are distinguished in a simple manner from constructional and geometrical effects.
On the basis of the prior art according to the precharacterising clause, this problem is solved by the characterising features of claim 1. Advantageous embodiments of the method according to the invention form the subject-matter of claims 2 to 5.
The partial differentiation, carried out digitally and converted into a resulting grey scale value image, of a modulo-2.pi. image stabilised to form an initial grey scale value image enables structural irregularities to be differentiated from effects caused by construction or geometry because structural irregularities generally have larger gradients than do effects caused by construction or geometry. Owing to the fact that a further grey scale value shift of the second grey scale value image is carried out in the digital image processing method before the actual differentiation, it is even possible to recognise the gradient direction and consequently to classify the structural irregularity investigated as being of the concave or convex type.
An advantageous form of the method consists in illuminating the test object with coherent light from several laser diodes, each of which generates a light spot on the test object.
If in the case of a specific type of test object a typical structural irregularity occurs with an ellipse-like pattern and with a typical position arrangement, the method is advantageously carried out in such a manner that the shearing and differentiation direction coincides with the direction of the short semi-axis of the elliptically defined structural irregularity.
If in the case of a specific type of test object two typical structural irregularities occur with an ellipse-like pattern and with typical position arrangements at right-angles to one another, the direction that forms an angle of 45.degree. with both short ellipse semi-axes is advanta
REFERENCES:
patent: 4591996 (1986-05-01), Vachon
patent: 5011280 (1991-04-01), Hung
patent: 5020904 (1991-06-01), McMahan, Jr.
patent: 5065331 (1991-11-01), Vachon et al.
patent: 5091776 (1992-02-01), Tyson, II
patent: 5146289 (1992-09-01), Newman
patent: 5481356 (1996-01-01), Pouet et al.
Spooren et al., "Electronic shear interferometry: application of a (double-) pulsed laser", Applied Optics, 32(25):4719-4727, Sep. 1, 1993.
Stetson, "Phase-step interferometry of irregular shapes by using an edge-following algorithm", Applied Optics, 31(25):5320-5325, Sep. 1, 1992.
Schnars, "Direct phase determination in hologram interferometry with use of digitally recorded holograms", J. Opt. Soc. Amer., 11(7):2011-2015, Jul. 1994.
Font Frank G.
NOVA C.O.R.D. AG
Vierra-Eisenberg Jason D.
LandOfFree
Object to having a image processing for determining the structur does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Object to having a image processing for determining the structur, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Object to having a image processing for determining the structur will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1466707