Patent GB-629328-A (GB)
Title: Improvements in or relating to differential electric contact devices
IPC: G05D3/12
Filed: 1947-05-02
Abstract: 629,328. Electric follow-up systems. PRECISION DEVELOPMENTS CO., Ltd., and OLAH, G. May 2, 1947, No. 11904. [Class 40 (i)] The servomotor 1 of a follow-up mechanism is controlled by a differential switch, the moving contacts of which, in addition to their switching movement, rotate relatively to the fixed contacts, this rotation minimising contact deterioration by the polishing effect and by the circuit being interrupted on different parts of the contacts. A controlling shaft 16, Figs. 1-3, having an arm 23, is coaxial with a sleeve 15 driven through a gear 25 by the servomotor 1. A pin 18 insulatedly carried by the sleeve 15 pivotally supports a metal contact carrier 19 having an opening receiving the arm 23 normally centralised therein by spring plungers 24, 27 engaging insulated metal inserts 29, 30. A contact brush 22 in the carrier 19 always engages the centre one 14 of three insulated. contact rings 13, 14, 17 on a stationary body 11, the outer rings 13, 17 co-operating with contact pins 20, 21 axially spaced on the carrier 19. The ring 14 is connected to the servomotor armature 1 and the rings 13, 17 to the reverse field windings 31, 32. When the controlling shaft 16 and the controlled sleeve 15 are in positional correspondence, the pins 20, 21 do not contact the rings 13, 17, hence there is no circuit through the servomotor. A slight relative movement of members 15, 16 causes displacement between the members 19, 23 and compression of a plunger 24 or 27, and contact is made by one of the pins 20, 21 with its ring 13 or 17. This action establishes a circuit through the armature 1 and the appropriate field winding 31 or 32 of the servomotor which drives the sleeve 15 into correspondence again with the shaft 16. A lost-motion coupling comprising a pin 34 on the shaft 16 engaging a clearance hole 37 in the sleeve 15 provides a direct drive to limit the force transmitted by the switch contacts when the relative movement of the members 15, 16 is excessive. In Fig. 4, which shows a modification of Fig. 2 of Specification 570,521 a sleeve 36 driven through the gear 26 by the controlling shaft has an inclined slot 45 engaging a pin 46 on. a bush 42, which is rotatable with but slidable on a controlled shaft 35 by a key 44. A contact ring 41 insulatedly mounted on the bush 42 continually engages a brush 52 in an insulating holder 47, and also engages resilient contact pin 50 or 51 when the bush 42 is axially displaced by relative movement of the members 35, 36. The contacts 50, 52, 51 correspond to contacts 13, 14, 17 of Figs. 1, 2, and the circuit is similarly connected so that the servomotor drives the shaft 35 through a gear 25 into positional correspondence with the sleeve 36. A lostmotion direct driving connection is provided by a pin 56 on the sleeve 36 engaging a clearance hole 57 in the gear 25. In alternative constructions, a screw and nut drive connects the parts 42, 36 and the pin 46 may be replaced by a projection having rollers engaging the slot 45. Further, the holder 47 may be resiliently mounted.