US 4,909,630 A · Method and device for determining the change in thickness and/or orientation within a strip of optically active material

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.

Claims15

Dependent claims

A method for determining changes in thickness and molecule chain orientation within a strip of optically active material, comprising the steps of:

(a) passing a strip of optically active material between at least one pair of crossed polarizers;
(b) transilluminating at least a portion of the strip between the crossed polarizers with polychromatic light whereby the light, after passing through the strip and the crossed polarizers, is polarized;
(c) imaging said portion of the transilluminated strip onto a light-sensitive detector including a two dimensional array of imaging elements;
(d) subjecting said imaged portion of the transilluminated strip to an intensity analysis several times within a pre-specified time period;
and
(e) setting a pre-selectable threshold value for the intensity analysis of said imaged portion of the transilluminated strip.

3 more elements

A device for determining changes in thickness and molecule chain orientation within a strip of optically active material, comprising:

a first polarizing means;
a second polarizing means crossed with respect to said first polarizing means, wherein said first and second polarizing means are arranged on either side of the planar area of the strip of optically active material moved between the first and second polarizing means, and in the ray path of a polychromatic light source transilluminating at least a portion of the strip whereby the light, after passing through said first and second polarizing means and the strip, is polarized;
measuring means for measuring and analyzing the intensity of the transilluminated strip to determine changes in thickness and molecule chain orientation within the portion of the transilluminated strip, wherein said measuring means includes a light sensitive detector comprising a two dimensional array of imaging elements;
and
means for recording the changes in thickness and molecule chain orientation as a function of the width of the strip.

2 more elements

Dependencies are inferred from the claim text.

Method and device for determining the change in thickness and/or orientation within a strip of optically active material

Life of this patent

Method and device for determining the change in thickness and/or orientation within a strip of optically active material

Life of this patent

Abstract

Claims15