GB1387320A - Detecting surface defects in moving metal sheet - Google Patents

Abstract

1387320 Detecting and classifying flaws in a moving sheet HOOGOVENS IJMUIDEN BV 26 Oct 1972 [27 Oct 1971] 49484/72 Heading G1A In a flaw detecting device for inspecting sheet metal for classifying and counting the flaws, one or more units, each unit comprising a source and a plurality of detectors (photo-diodes) are employed, the detectors being positioned to view separate areas (2 mm<SP>2</SP>) spaced across the metal sheet and the output signals being processed individually in parallel paths. Several different circuits are disclosed for detecting specks, lines perpendicular to the direction of travel of the sheet, lines parallel to the direction of travel, and stains:- Specks are detected by a circuit Fig. 5; for each detector 7 comprising an amplifier 8, high pass filter 9 a maximum value comparator 10 and a minimum value comparator 11 which will provide an output (a logical "L") if the resultant signal S 3 h is greater than a predetermined maximum value "Max. sp" or less than a predetermined minimum value "Min. sp". The comparator outputs from a number of adjacent detectors may be fed via an "OR" gate to a counter to give a measurement of the number of specks in a given area. Lines across the travel direction are detected by a circuit, Fig. 6, comprising a counter 12 which receives the amplified and high pass filtered outputs S 3 h of a number of adjacent detectors, simultaneously counts them and feeds the result to a comparator similar to above. Lines parallel to the travel direction are detected by a circuit Fig. 7 (not shown) similar to the "Specks circuit" Fig. 5 except that a low pass filter is employed and that the detector and source unit is vibrated in a direction perpendicular to the travel direction. Stains may be detected by a circuit Fig. 8 (not shown) comprising a counter being fed by a number of amplified low pass filtered outputs of a series of adjacent detectors. The counter's output is then fed to a comparator arrangement as before. All the different types of flaw detector circuit may be combined into a single circuit Fig. 9 (not shown).