GB910151A - Improvements in or relating to fault finders - Google Patents

Abstract

910,151. Photo-electric control apparatus. MEINERS OPTICAL DEVICES Ltd. Nov. 10, 1958 [Nov. 15, 1957], No. 35743/57. Class 40 (3). Apparatus for the detection of faults in a travelling band or web of material, e.g. textile fabric, comprises a plurality of photoelectric scanning devices mounted for simultaneous transverse movement over different parts of the material under inspection, the scanning devices receiving light reflected from or transmitted through the material, and each device feeding into a common signal channel so that a " fault detected " signal produced by any device, irrespective of the presence of condition of any other device, actuates warning or motionstopping means. Scanning arrangements.-As shown, Fig. 1, a web 12 of knitted fabric issuing from the needle bed of a flat bar knitting- machine 11 is scanned by a plurality of scanning heads 22, mounted on tubular stems 21 which extend downwards from a horizontal rail 20, which is reciprocated on rollers 19, by means not shown, so that the scanning heads 22 scan adjoining, and preferably overlapping, widths of the web 12. Each scanning head 22, Fig. 3, comprises a photoconductive diode 26 in a tubular housing 23 and a light source 37 in an offset housing 36. Light from the source 37 is reflected from the fabric 12 and from a chromium-plated strip mirror 39 below the fabric, through a focusing lens 35 and a slit aperture in a stop 34, on to the cell. A fault resulting from the absence of a warp thread causes an increased quantity of light to be reflected on to the cell ; alternatively, the mirror 39 may be dispensed with, so that the background to the fabric is less reflective than the fabric and the presence of a fault reduces the quantity of reflected light. Circuitry.-Fig. 4B shows the circuits of four scanning heads adapted for use when no mirror is located below the fabric. Each cell 1 . . . 4 is supplied with D.C. via line 50 and a resistor 52, and is connected through a capacitor 53 to the base electrode of a preamplifying transistor 54, the individual outputs of the transistors being fed through capacitors 59 and junction diodes 60 to a common output channel 61. Two-stage amplification of the signal in channel 61 is provided by a double triode, Fig. 4C (not shown), the output of which is applied to one stage of a bi-stable double-triode switching valve having the grid of each stage connected with the anode of the other stage, so that variation of the applied signal biases the second, normally non- conductive, stage to a conductive stage, thus energizing a relay winding in the anode circuit of the second stage. The relay has contacts in an A.C. circuit which operate to stop the knitting machine and light a warning lamp. The circuitry shown in Fig. 4B is borne by the traversing assembly, resistors 52 and capacitors 53 being disposed within stems 21, as shown in Fig. 3; the amplifying and switching circuits, in addition to a mains transformer and rectifying and smoothing circuits, are mounted on the machine frame. Modifications.-The reflector strip may be modified for use on machines producing openwork or net fabric. Rollers or fingers may keep the fabric straight at the margins. Germanium photo-transistors may replace the photo-cells, and a single light source, e.g. a strip-light, or a number of stationary lamps placed at intervals along the machine bed, may replace the traversing lamps, or the normal mill-lighting may be adequate for fault detection. The scanning- apparatus may be mounted beneath the fabric. All the circuitry may be stationary, or mounted on the traversing assembly; individual relays may replace or supplement the common channel relay; thyratrons may replace relays. The photocells may be connected into one or more bridge circuits. The apparatus is also suitable for fault-finding on weft knitting machines and weaving looms, and for detecting flaws in non- textile material, e.g. paper and plastic sheeting.