Diffraction pattern amplitude analysis for use in fabric inspection

Abstract

A technique is provided for analyzing the shape of the amplitude envelope of a diffraction pattern's first order side lobe resulting from passing coherent light through a fabric material. The light intensity of the lobe is scanned from one side of the lobe to the other by a linear photo-diode array to provide successive voltage signals whose respective voltage values are a function of the light intensity at successively spaced increments from one side of the lobe to the other. Each of these successive voltage signals are compared with a series of reference voltages of substantially less number than the number of spaced increments, each reference voltage having a value greater than the value of the preceding reference voltage in the series to define a voltage range encompassing the highest voltage in the series of voltage signals. A numerical count is then provided of those voltage signals which have voltage values falling between the values of adjacent reference voltages in the series of reference voltages so that a plurality of counts is provided which indicates the amplitude distribution of light in the light lobe. The plurality of counts is substantially less in number than the number of spaced increments thereby reducing storage data requirements in the analysis of the amplitude envelope of the light lobe. Successive first order side lobes developed by successively passing the light beam through different areas of the fabric to cover a large area are analyzed to provide a succession of the pluralities of counts.