Patent GB-567129-A (GB)
Title: Improvements in or relating to electric resistance elements and apparatus for manufacturing the same
IPC: H01C17/04
Filed: 1943-04-23
Abstract: 567,129. Making electric resistances. MAPP, A. G., and BOYDELL, K. R. April 23, 1943, No. 6577. [Classes 83 (ii) and 83 (iv)] [Also in Groups IX and XXXVI] Coiling.-Wire resistances, for use as strain gauges, are wound on a cylindrical former as a single layer, the rate of axial traverse being varied at intervals to produce a plurality of closely-spaced turns separated by widely-spaced turns. After cementing the wire to the former, the latter is flattened and protected by a cemented paper cover and finally severed at the widely-spaced turns to provide separate resistance elements. Winding is effected on a machine comprising a carriage travelling uniformly lengthwise of a winding spindle and a thread-guide carried on a lever mounted on the carriage, the lever being rocked to reciprocate the thread-guide relatively to the carriage at a speed less than that of the carriage. As shown in Fig. 2, a cylindrical tube 10 of thin paper is formed by wrapping the paper on a cylindrical former provided with driving means. A very fine resistance wire 11 is wound on the former 10 in groups of closely-spaced turns 12 separated by widely-spaced turns 13. The paper tube is coated with cement prior to winding the wire, and another coating of cement is applied over the wire after winding. The tube 10 is then removed from the former and flattened and the two flat sides are cemented together. Each of the closely-spaced groups of turns 12 constitute a gauge, the various gauges being separated by cutting off in the region of the widely-spaced turns 13. Stout connections are secured to the ends of the wire by soldering or welding, and a sheet of paperis applied over the wire and cemented in place. Separate sheets may be applied on each side of the flat strip. Fig. 5 shows a machine for winding the resistances. Between a pair of side plates 16, 17 carried by a base-plate 15 is a fixed guide rod 18 and a feed-screw 19 journalled in bearings in the side plates. On the feed-screw is mounted a carriage 20 provided with guides 21 which slide on the rod 18. One end wall 22 of the carriage is screw-threaded to engage the feedscrew 19 so that rotation of the feed-screw gives a traversing movement to the carriage. Between the end walls 22, 23 of the carriage is a sleeve 24 keyed at 25 to the feed-screw so as to rotate therewith, bearings 26 being provided between the sleeve 24 and the carriage 20. The sleeve 24 is provided with a worm thread which engages a worm-wheel 27 mounted on a shaft 28. On this shaft is fixed a cam 29, Fig. 7, which engages one end of a lever 30 pivoted to the carriage at 31. The other end of the lever 30 carries a guide pulley 32. A spindle 33 on which the coils are wound is mounted between a head-stock 34 and a tail-stock 35, the head-stock driving the spindle by means of a pin 36. The head-stock 34 is driven directly from a driving-shaft 38, which also drives the feed-screw 19 through reduction gearing 39,40. The carriage 20 carries a spool 41 for the resistance wire, a brake 47 being provided. The wire 42 passes from the spool 41 over the guide pulley 32 on to the paper former which is mounted on the spindle 33. The carriage 20 is set at the left-hand end of its traverse and the machine is set into operation so that the carriage is traversed towards the right. When the cam 29, which rotates anti-clockwise, is in the position shown in Fig. 7, the guide pulley 32 starts traversing towards the left at a speed slightly less than that of the carriage towards the right so that the resultant feed of the wire 42 is the difference of these two speeds, resulting in a very closely spaced winding 12, Fig. 2. When the cam has rotated to bring the part 43 into engagement with the end of the lever 30 the motion of the lever is reversed and the feed of the wire is the sum of the speeds of the carriage 20 and guide pulley 32, thereby causing widely spaced turns 13, Fig. 2. A second nut 44 is mounted on the feed-screw 19 and engages the carriage 20 by a pin 45, a spring 46 taking up backlash.