Patent GB-1186985-A (GB)
Title: Inspection Apparatus in Circular Knitting Machine.
Inventor: VENCZEL JOSEPH
IPC: D04B35/18
Filed: 1968-07-22
Abstract: 1,186,985. Semi-conductor circuits. ELECTRONIT Ltd. 22 July, 1968, No. 34979/68. Heading H3T. [Also in Divisions D1 and G1] Broken needles in a circular knitting machine are detected photo-electrically. Needles are carried in spaced groups of four round the periphery of the rotating drum of the circular knitting machine, and the apparatus is designed so as not to respond to the spaces between groups of needles. The photo-electric apparatus, Fig. 2 (not shown), comprises a light source (6), light guides (7 and 9), provided with reflectors at their ends, and a phototransistor detector (8). Needles (2) pass sequentially through the gap between the mirrors at the ends of the light guides and produce rounded pulses from the phototransistor due to obstruction of part of the light reaching the latter. A broken needle produces a rounded pulse of lower amplitude than the general constant amplitude of the pulses produced by unbroken needles, Fig. 4a (not shown). The output of the phototransistor is amplified by a limiting amplifier (transistors 17, 18, Fig. 3) producing a square wave output and applied to a transistor trigger circuit 19, 20. The level of the trigger is set such that only the presence of a needle (broken or unbroken) will cause triggering, a space between groups of needles therefore not causing triggering. The trigger circuit output is a series of rectangular negative-going pulses, Fig. 4b (not shown), of the same amplitude but if due to a broken needle, having a reduced width, this width depending on the magnitude of the break. The rest of the circuit is designed to detect which of these pulses are due to broken needles. Then the trigger output is differentiated by an R.C. network (including capacitor 23) and applied to a monostable circuit 25, 26. This acts as a reference pulse generator, producing positive going, constant width pulses, Fig. 4d (not shown), on receipt of each negative going spike. Its output is differentiated by a capacitor 33 and applied to the collector of a gate transistor 31. Applied to the base of this transistor 31 are the output pulses of trigger 19, 20, which when they occur cause the transistor to be non-conductive. Thus only when there is a short pulse from trigger 19, 20 due to a broken needle, is the negative going spike of a differentiated reference pulse allowed to pass through the gate to the output line 34. When this occurs an alarm lamp (10) is lit, an audible alarm sounded and the brake applied to the knitting machine. Also a counting circuit is started so that the number of pulses (needles) occurring after detection of a broken needle and until stopping of the machine, is counted and displayed on counting tubes 11. The tolerance of the apparatus is decided by the values of the circuit components used and particularly by the adjustment of a resistor 30 in the monostable circuit. This is normally adjusted so that the reference pulses produced are of equal length to the pulses from the detector for unbroken needles, and so the very narrow tolerance required for detection of broken needles is provided. If the output of the limiting amplifier is suitable to operate the pulse generator and gate directly, the trigger circuit may be omitted.