GB1486612A - Method of and an apparatus for inspecting a travelling sheet material to detect defects - Google Patents

Abstract

1486612 Photo-electric detection of flaws KAWASAKI STEEL CORP and TOEI DENSHI KOGYO KK 5 Nov 1974 [13 Nov 1973] 47844/74 Heading G1A To analyze defects in a travelling strip 1, Fig. 1, it is scanned with light from a source 2, and light reflected (or transmitted) by the strip is received by detector 5; the detector signal is then pro- cessed to find the width, quantity, length and depth of the defects in the scan, and each of these factors is quantified to show whether it is small, medium or large. The factors are then combined to give an indication of the usability of the strip. The detector signal is amplified at 6 and differentiated at 7; the parts of the signal due to the edges of the strip are blanked out. The width is measured at A, the quantity at B, the length at C and the depth at D. These factors are stored in memories M1-M9 and gated together at AND 1- AND 27 for printing to indicate usability. Width: the detector output for dark and bright defects is shown in Fig. 3, and the differentiated signal from 7 is shown at (a). This latter produces a pulse from bi-stable 11a or 11b depending on the initial polarity of the signal from the detector; the bi-stable's output lasts whilst the defect is being scanned, and is used to gate pulses from an oscillator 13 in timing section E to a counter 15. The counter output is thus a measure of the defect width, and is quantified into small, medium or large at pre-set outputs 16, 17 and 18. Quantity: the signal from 7 activates a differential amplifier 19 in section B whenever the signal exceeds a reference voltage 20. The number of times this happens in a scan is counted at 21 and quantified into small, medium or large on lines N1, N2 or N3. Length: whenever the signal from 7 exceeds reference voltages 23 or 25 in section D, their associated differential amplifiers activate OR gate 26 in section C. This in turn activates bi-stable 27 and counter 28; these also receive a pulse every 5mm. of travel of the sheet, so that the number of 5mm. lengths of travel which contain a defect are counted at 28. This count is quantified at 29, 30, 31. Depth: by comparing the signal from 7 with reference voltages 23, 25 in section D it is possible to determine whether the signal lies below both references, between them, or above both, thus quantifying the depth. Combination: The first three factors above are stored at M1-M9 and combined at AND 1-AND 27 with a timing signal derived from OR gate 26 via inverter 32 and capacitor 33; these AND gates operate a printer (not shown) which indicates which of 27 categories the sheet is in. The timing signal also resets the stores via delay 34. The 27 categories are formed into two groups indicating how usable the sheet is, and are connected to OR gates 41, 42; these gates are connected to AND gates 43-46 which also receive depth signals from section D and produce a further three outputs for operating a sorter to sort tested sheets into piles of good, less good and unusable.