GB1056652A - Flaw detection apparatus - Google Patents

Abstract

1,056,652. Detecting flaws photo-electrically INTERNATIONAL STANDARD ELECTRIC CORPORATION. April 9, 1965 [April 14, 1964], No. 15239/65. Heading G1A. In an arrangement for illuminating an article and detecting flaws by means of a parameter of a time based video signal produced by scanning, the video signals from predetermined areas are blanked by the signal developed by scanning, in a manner identical and in synchronism with the scanning of the article, an illuminated mask having contrasting areas thereon corresponding to the areas which are, or are not, required to be investigated. Light may be transmitted through the article if transparent, or may be reflected from its surface and the rate of scan may differ over different areas. Additionally the video signals may be compared with a threshold voltage which is different for different areas of the article in order that the arrangement may respond only to flows of a size predetermined according to their location. A glass article over which the investigation is made by a circular scan is described with reference to Fig. 7 ( not shown), and an apertured mask for blanking the signals from areas of surface ornamentation 26, 27, is described with reference to Fig. 8 (not shown). The illuminated object is investigated by an image dissector 24, Fig. 2, under the control of a scan generator 37, and the beam from a flying spot scanner 34, also controlled by generator 37, develops a signal in a photo-multiplier 35 to operate a blanking gate 43 when the beam is outside of the areas defined by the mask. The different rates of scanning i.e. the spacing of scanning lines are determined by a deflection amplitude generator 55, under the control of monostable multivibrators 57-59 and a bistable multivibrator 60, the output signal 62 being amplitude modulated on the sinusoidal output of a generator 66 to energize the scanning coils 74-77. A wanted flaw signal from the image dissector, after passing the blanking gate is amplified and applied to a unit 89 which permits the passage of signals above a predetermined level, these being amplified and inverted, and added to a step function voltage 100 in network 102. The steps are also positioned by the outputs from the multivibrators 57-60, and the superimposed signals exceeding a predetermined threshold are detected in 104 and applied with the differentiated trailing edge of pulse T4 from multivibrator 60 to produce a reject pulse of fixed length at a particular time relative to the scanning cycle. Conventional transistors circuitry is described and component values are exemplified.