Optics: measuring and testing – By polarized light examination
Patent
1986-12-08
1990-03-20
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
264 402, B29C 5512
Patent
active
049096303
ABSTRACT:
An interference image of a biaxially stretched film strip 4 is generated optically. Streaks in the film strip are areas of different orientation and/or thickness d which are distinguished from the streakfree areas in the interference image by clearly different intensities. In order to generate the interference image, a light-source 1, a diffuser screen 2 and a polarizer 3 are arranged on one side of the film strip 4, and an analyzer 5 and a filter 6 are arranged on the other side of the film strip 4. The light beam of the light source 1 is polarized by the polarized 3 and, within the film (whose main refractive indices n.sub.1 and n.sub.2 have an angle of 45.degree. or 135.degree. respectively to the polarization plane) is split into two beams, oscillating perpendicularly to one another, which have a path difference .GAMMA.=(n.sub.1 -n.sub.2)d after emerging from the film. Of the light behind the film, in general elliptically polarized, only that portion of the light which oscillates parallel to the analyzer plane, which is perpendicular to the polarization plane, passes through the analyzer 5. In general, a colored interference image is obtained if the light source emits polychromatic light. A detector 7 as light-sensitive element, e.g. a video camera, comprising a light-sensitive diode matrix, which is connected to an image analysis and computing unit 8 for evaluation of the interference image, is arranged behind the filter, which serves to increase the contrast of the image.
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Trubnyakov et al, "Equipment for Continuously Monitoring the Quality of Film Materials", Meas. Tech, vol. 21, No. 9 (Sep. 1978).
Foppl, Monch "Praktische Spannungsoptik", Berlin 1972, Springer-Verlan, S. 6-17, pp. 192-196.
Gawrisch Wolfgang
Trzebiatowski Thomas
Hoechst Aktiengesellschaft
Rosenberger Richard A.
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