Patent GB-576929-A (GB)
Title: Improvements in or relating to electric snap action circuit controlling devices
IPC: H01H21/28
Filed: 1944-06-07
Abstract: 576,929. Retractive switches ; snap-action switches. IGRANIC ELECTRIC CO., Ltd. June 7, 1944, No. 10925. Convention date, June 7, 1943. [Class 38 (v)] A snap-action limit switch has its movable contacts 22, 23 resiliently urged apart by a spring 25 in a carrier 6 movably carried by a frame 5 consisting of two parallel plates 10 secured together by two pins 11 and a pin 12, the latter being fixed in lugs 13. The carrier 6 is pivoted to the frame 5 by levers 16, 17, Fig. 8, and projections 20 on insulating members 19. The pins 11 also support a U-shaped operating member 7 by means of slots 27. Further slots 28, 29 carry pins 28a, 29a which are inter-connected by a spring 8. The levers 16, 17 have notches receiving the pins 28a, 29a and projections 16a, 17a which are respectively engaged by a latch member 9 when the switch is in its extreme positions. When the operating member 7 is moved to the right, Fig. 2, the left hand end of slot 29 pushes pin 29a with it and, since lever 16 is latched, stresses the spring 8. Eventually cam surfaces 31 on member 7 engage cam surfaces 33 on latch 9 to release the lever 16, which is moved by spring 8, thereby moving the carrier 6 to the left so that contacts 22 engage contacts 37. When moved to the left, member 7 moves pin 28a to the left and releases lever 17, thereby returning the carrier to its original position. The fixed contacts 36, 37 are L-shaped to provide a terminal portion and a contact portion, and are fixed in a recess of an insulating base 35, the contacts 37 being adjustable. The base 35, flanges 14 of frame 5, and an insulating plate 41 are bolted to the casing 3 by screws 40. The enlarged end 54 of the operating spring-plunger 50 of the member 7 is actuated by the camportion 70 of a cam shaft 51 attached to a lever 59. When this lever is rotated clockwise, the edge 71a of the surface 71 moves the plunger inwards to operate the switch. The recessed surface 72 permits anti-clockwise movement of the lever 59 without affecting the plunger 50. The cam shaft is supported in a block 52 which is detachable from casing 3 and has a circular recess in its end, Fig. 5, which contains a spring 60, the ends of which are received in recesses in the shaft 51 and block 52 so as to bias the shaft 51 into its normal position. A washer, with a tongue acting in the recesses, limits the rotation of the shaft 51. The hub 73 of the lever 59 is held in position on the reduced left hand end of the shaft 51 by a pin 81 on a washer 79 insertable, for adjustment purposes, in any one of nine notches in a washer 75 and also in any one of ten notches in the hub 73. The operating head may be modified, Figs. 12, 13 (not shown), by the use of either of two slightly different camshafts, one of which permits free movement of the handle 59 clockwise and not anti-clockwise, and the second which operates the plunger 50 whichever way the lever is moved. A further modification, Figs. 14, 15 (not shown), comprises an operating head of the push type, the plunger being fitted with a large cylindrical head which serves in place of the lever 59.