GB672152A - Apparatus for detecting faults in a moving textile fabric - Google Patents

Abstract

672,152. Photo-electric control apparatus. CELANESE CORPORATION OF AMERICA. June 23, 1950 [June 25, 1949], No. 15771/50. Class 40 (iii). Apparatus for detecting faults in a moving textile fabric comprises a carriage reciprocated across the fabric and carrying a pair of cells viewing different portions of the fabric, the cells feeding an amplifier to give a warning or stop the fabric when the illumination of one cell changes with respect to the illumination of the other. Preferably the warning or stopping occurs only when the rate of change of the relative illumination is low. A knitted fabric 21, Fig. 3, is drawn beneath a carriage 31 reciprocated at right angles to the direction of movement of the fabric. Light from the fabric is focused on two cells 39, Fig. 6, on the carriage, each cell feeding an amplifier 41 whose outputs are opposed in transformer 66 and condenser 65<SP>1</SP>. The cells are shielded by magnetic and electrostatic shields 63, 64 and each is enclosed in an inner shield 65 connected to the cathode of the corresponding valve 41. For a perfect fabric, the outputs of the two cells are equal and condenser 65<SP>1</SP> has no charge. When one cell scans a defect, the outputs become unequal and condenser 651 acquires a charge which disappears when the cell has passed the defect; this evanescent charge produces equal and opposite pulses in transformer 66, the magnitude of the pulse depending on the rate at which the condenser charges and discharges, i.e. on the nature of the defect. The negative pulses only are passed by a suitably biased valve 69 and further amplified by valve 70, condensers 71 by-passing variations above a predetermined frequency. The emergent pulses, if above a predetermined amplitude make valve 72 conducting to charge condenser 74 which retains its charge for a period sufficient to make valve 76 non-conductive and thus release the relay 77 to stop the knitting-machine. The level at which valve 72 conducts is adjusted by varying resistance 73. A contact 49 is closed at the end of each traverse of the carriage to prevent the operation of the stopping mechanism when the edge of the fabric is being scanned.