Patent GB-536581-A (GB)
Title: Improvements in or relating to the grading of electrical resistances, and articles comprising them
IPC: G01R31/18
Filed: 1939-10-17
Abstract: 536,581. Resistance measurements. ASHCROFT, D. G., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Oct. 17, 1939, No. 28045. Addition to 494,103. [Class 37] In the apparatus for grading resistances such as fuse-heads claimed in the parent Specification, the annular cam and rotating spiders are replaced by a single pair of reciprocating spring fingers, to which the testing voltage is led without utilizing any sliding contacts, and one or more cams which co-act with the fingers so that these close on and hold each fuse-head to be transported, transport it, and then open and release it. Fig. 1 is an elevation from the feed side and Fig. 2 is a side elevation seen from the left-hand side of Fig. 1 with the frame casting on that side removed. A shaft 1 journalled in frame castings 2, 3 carries at one end a contact-breaker cam 4 and at the other end a ratchet-wheel 5. counter clockwise rotation of the shaft is prevented by a pawl 6. Freely mounted on the shaft 1 is a rocker 9 carrying a pawl 11 and reciprocated by a connecting-rod 10. The rocker also carries the device for transporting the fuse-heads and applying the test voltage. This comprises two metal plates 12, 13 carried by moulded insulating members 14, 15, 16. 'These plates extend to form a pair of spring fingers carrying contact-pins 17, 18 and ball-bearing rollers 19, 20 which protrude through slots in the fingers and reduce friction when moving over the cams that open the fingers in the appropriate positions. There are two of these cams, one formed by a fixed insulating quadrant 21 with inset metal tracks 22, 23 for the rollers, and the other consisting of a cam block 24 pivoted on a bracket 25 on the end frame 2. The cam block rests normally as shown in Fig. 2 against a stop on its bracket, but is free to rotate through a quarter-turn clockwise round its pivot. The block is provided with metal side plates 26, 27 over which the rollers run during the return motion of the spring fingers. The fuse-heads are fed in a series of combs 28 along a slot in the baseplate 29 to a combined stop and cutter. As the connecting rod 10 reaches the upward limit of its travel the fuse-head 35 is severed and gripped between the contact pins 17, 18, As the connecting rod commences its return motion the pawl 11 engages the ratchet-wheel 5 and rotates the shaft and with it the rocker and spring fingers. The rotation of the shaft causes the contact-breaker to close the testing circuit and apply voltage through the plates 12, 13 and contact-pins 17, 18 to the fuse-head. Continued rotation causes the rollers 19, 20 to ride on the tracks 22, 23 on the quadrant cam 21 which forces the spring fingers 12, 13 apart and allows the fuse-head to drop down the shoot 32. On the upward movement of the connecting rod 10 the pawl 6 locks the shaft 1 against rotation but the spring fingers 12, 13 move downwards and the rollers 19, 20 on leaving the quadrant tracks, strike the front end of the cam block 24. This causes the rollers to be forced apart, ride over the side plates 26, 27 and close behind them, so that the contact pins open and close on the fuse-head. In a modification the fixed quadrant cam is dispensed with and the movable cam, when it moves out of the working position at the pick-up point, moves into the position of the quadrant 21.