Method and system for detecting defects in optically transmissiv

Details Method and system for detecting defects in optically transmissiv Method and system for detecting defects in optically transmissiv

1996-10-21

1998-02-03

Font, Frank G.

Optics: measuring and testing

Inspection of flaws or impurities

Transparent or translucent material

356237, 356 71, G01N 2100

Patent

active

057150516

ABSTRACT:
Spectral transmittance of a dye coating for optical data is determined off-line. Light source wavelength is then matched to the wavelengths at which the dye has the least transmission (i.e. maximum absorbance). The method and system of the present invention are provided for detecting local and global defects in the coating wherein the inspection is done at the maximum absorbance wavelengths to produce a maximum change in a transmitted light signal for a given change in physical thickness of the dye coating. Relative change in thickness is determined based on the change in the transmitted light signal through the dye coating. In order to complete detection and measurement of the transmittance changes, a pair of electronic signals are split from a camera signal wherein one of the electronic signals is filtered by a FIR filter to identify local changes in dye thickness against a globally varying background. In order to detect global variations in the dye thickness, the other electronic signal is processed by a simple thresholding circuit.

REFERENCES:
patent: 4568984 (1986-02-01), Juergensen et al.
patent: 5067812 (1991-11-01), Sugimura et al.
patent: 5268735 (1993-12-01), Hayashi

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