Patent ES-359675-A1 (ES)
Title: Photoelectric defect detector which determine coordinate of defect by magnitude of scanning voltage and current at position of defect
IPC: G01N21/89
Filed: 1968-10-28
Abstract: At least one of the co-ordinates of a defect in a sheet or strip is determined by successively scanning adjacent bands of the sheet or strip by a radiation beam displaced directly or indirectly by at least one electrical factor, the magnitude of which at the instant when the beam encounters a defect being used as a measure of the co-ordinate of such defect. Defects may be detected by the transmission or reflection of a light or electron beam and the results may inform a computer controlling the cutting of metal, glass, plastics or paper strips. A glass sheet 301, Fig.4, is scanned rasterwise by a television type camera tube 331 fed by X and Y sweep generators 401, 4011. A line of light is located near the start of the line scans so that the video signal from electrode 381 includes reference pulses in addition to pulses due to defects. The video pulses trigger a digital volmeter 431 to sample the X deflection signal, values corresponding to reference and defect pulses being transmitted to lines 451 and 581 respectively. A differentiator 481 delects the flyback of the camera spot causing gate 471 to blank the video signal and bi-stable circuit 511 to set, informing voltmeter 431 that the next video pulse will be a reference pulse. A further digital voltmeter 4311 samples the Y deflection signal in response to defect pulses, but ignores reference pulses. A discriminator circuit 571 determines whether or not each defect signal (a) is of more than a predetermined amplitude, (b) is of more than a predetermined duration, or (c) has more than a predetermined rate of change and if so opens respective pairs of gates 641, 6411 651, 6511 631 , 6311 to apply the co-ordinate values from voltmeters 431, 4311 to lines 611, 6111 621, 6211 601 , 6011 Discriminator 571 includes means for distinguishing a single defect giving rise to a video signal which changes sign once or more from a plurality of separate smaller defects. If the glass sheet moves rapidly, the camera tube may make a linear scan, Fig. 3 (not shown). Readout of the digital voltmeter is synchronized with presentation of information thereon by an arrangement of bi-stable circuits and gates, Fig. 5 (not shown). If a slow acting digital voltmeter is used the deflection signal samples are held on a capacitor which is discharged in response to the scan flyback, Fig. 6 (not shown). In a circuit giving directly the difference between the co-ordinates of a defect and the reference line, Fig. 7, the deflection signal applied at 704 charges capacitors 702 and 703 equally until a reference pulse at 709 sets a bi-stable 709 to cut off transistor 706. Capacitor 702 continues to charge, and voltmeter 701 which monitors the voltage difference between capacitors 702 and 703 is read out by a defect pulse at 717 opening a gate 719 via a synchronizing circuit 718. In another embodiment, Figs. 1 and 2 (not shown) scanning is performed by a mirror galvanometer which, energized by a signal of the form A arc tan Bt, deflects a light beam through a glass sheet on to a linearly extensive photo-sensitive device. For wide strips, a plurality of scanners may be used, Fig.8 (not shown) or a single scanner may be traversed across the strip, Fig.9 (not shown).