Patent GB-562450-A (GB)
Title: Improvements in and relating to apparatus for measuring lengths and correcting skew and bow in woven materials
IPC: D06H3/12
Filed: 1943-03-17
Abstract: 562,450. Automatic control systems. BRITISH THOMSON-HOUSTON CO., Ltd. March 17, 1943, No. 4314. Convention date, March 24, 1942. [Class 38 (iv)] [Also in Groups VIII, XXXVIII and XL] Relates to apparatus used in the manufacture of a woven material, for example a lace curtain material, in a continuous strip comprising a series of similar sections separated by transverse portions having light characteristics different from those of the sections. According to the invention, variations in length of the sections are detected by photo-electric devices spaced along the length of the strip passing through the apparatus and affected by the light characteristics of the transverse separating portions of the strip. Photo-electric devices are also provided for detecting skew and bow irregularities, and the several photo-electric devices are made to control automatic devices for correcting the detected irregularities. In the apparatus shown, the material is a strip comprising lace curtain sections separated by transverse portions comprising an open mesh "cutting mark" 40, Fig. 3, between closely woven dense portions 41, 41. A photo-electric device for detecting the passage of these transverse portions in the apparatus comprises three photo-electric cells 38, Fig. 4, affected by three light beams 37 spaced as. shown in Fig. 3, to be influenced by the transverse portions 41, 40, 41 respectively. The three light beams may emanate from three separate lamps or may be formed by screening a wider beam from a single lamp. For detecting variations in length of the lace curtain sections, two such photo-electric devices are placed at 23, 23<SP>1</SP>, Fig. 1, the correct distance apart along the centre line of the apparatus through which the strip of material 1 passes from right to left. If a section is of incorrect length, one of these photo-electric devices is affected before the other, and a circuit, such as indicated in Fig. 6, gives a signal at 80 and controls a motor to apply a correction to the apparatus. This correction for length is produced by speeding up or slowing down a feed roll 14 and a tenter 10 on the right of the photoelectric devices 23, 23<SP>1</SP> relatively to a feed roll 18 on the left. This speed regulation is effected by means of a differential 30 situated between a motor 11 and the roll 14, which is geared to the tenter 10, and operated by a motor 31 controlled by the photo-electric devices. Skew is detected by two laterally disposed photoelectric devices 22, 22<SP>1</SP> on the right of feed roll 14; and these devices control a motor 26 operating a differential 25 between the two side chains of the tenter 10 to correct anv skew thus detected. Bow is detected by two photoelectric devices 8, 81 on the left of feed roll 18, one device 8 near the edge and the other 8<SP>1</SP> on the centre line ; and these devices control a motor 33 operating a differential 32 between the tenter 10 and the roll 14 to correct any bow thus detected. The tenter 10 may be as described in Specification 499,753. In the photo-electric skew detecting and correcting circuit shown in Fig. 6, the two outer cells 38 of scanning head 22 are connected together in parallel, and in co-operation with the middle cell control an electric discharge device 46 energized by direct current, whereby a condenser 51 is charged and discharged. This controls another electric discharge device 55 energized by direct current from a rectifier 64 supplied with alternating current through a transformer 63. The other scanning head 22<SP>1</SP> controls a similar arrangement of electric discharge devices. If both scanning heads operate at the same time, two relays A, B are simultaneously operated by their respective discharge devices 55, 56 no charge is given to a condenser 70, the rectifier 64 is switched off, and the discharge devices cease to operate until the next operation of the scanning heads. If there is a skew in the material, one scanning head and therefore one of the relays A, B operates before the other, and the condenser 70 receives a charge depending on the time interval, after which the rectifier 64 is switched off, the discharge devices cease to operate and the voltage of the condenser 70 is applied to another condenser 72 an the grid circuit of an electric discharge device 74 which actuates an indicator 80 and controls a motor 26 to correct the skew. Similar circuits are used for the other pairs of photo-electric scanning heads.