Patent GB-1363729-A (GB)
Title: Timer for an appliance
IPC: H01H43/12
Filed: 1971-08-31
Abstract: 1363729 Time switches; stencil switches MALLORY TIMERS Ltd 31 Aug 1971 [3 Sept 1970] 40634/71 Heading H1N A timer for controlling circuits in accordance with a predetermined programme comprises at least one rotatable cam and switch responsive thereto, at least one member carrying a plurality of conductive paths with an insulating masking member overlying said paths and apertured to expose selected portions thereof, at least one bridging member arranged to make contact with exposed portions of the paths, the bridging member or the masking member being rotatable by driving means which also rotates the cam or cams, the switch or switches and the said paths and bridging member or members forming switching means for controlling said circuits. Preferably the or each switch has a greater current-carrying capacity than the said paths and bridging member or members. In a first embodiment (Fig. 4) a synchronous motor 11 drives, through reduction gearing and stepping mechanism 32, a gear-wheel 46 and, by means of notches 44 mating with tongues 42, a face cam 36 having a plurality of tracks 381. Change-over switches 24 are actuated by respective followers 66 co-operating with cam tracks 38<SP>1</SP>. An insulating board 58, carrying conductors 60 connected to tags 62 and partially covered by an insulating stencil layer 54, is interposed between gear 46 and cam 36. Bridging wipers 70 carried by cam 36 selectively interconnect conductors 60 under control of arcuate slots 55 in layer 54. Wipers 70<SP>1</SP> may also be provided on gear 46 to co-operate with further conductors on the underside of board 58. The wipers 70, 70<SP>1</SP> may control light current circuits while switches 24 handle heavier currents. Gear 46 and cam 36 are journalled on a shaft 26 which may be moved axially between two positions located by a U-shaped spring 28 engaging grooves 23 or 21. When moved such that spring 28 enters groove 21, a pin 50 enters slots 48 in the hub 40 of cam 36 for manual setting of the programmer. This movement of shaft 26 displaces an actuator 52, pivoted at 53, to open a line switch 56 and cut off power to the timer during manual rotation. Cam 36 is provided with teeth 3811 for alternative drive when gear 46 (and wipers 70<SP>1</SP>) are not fitted. The cover 18, carrying switches 24 and removable windows 22, has tongues 18<SP>1</SP> which mate with notches 16<SP>1</SP> in base.16 and allow the cover to be fitted in alternative orientations. In a second embodiment (Fig. 8) similar drive means 11, 32 step a plurality of edge cams 94 with wipers 98 co-operating with stencil means 100. In each embodiment a second motor may be provided (as shown) for rapid advance of the cams. It is stated that the functional relationship of stationary stencil means 34, 100 with rotating wipers 70, 98 may be reversed, but details of this are not described. Three stepping mechanisms are described, a Geneva motion (Fig. 10, not shown) and two snap-stepping systems (Figs. 11 and 12, not shown) wherein a torsion spring (236, 314) is alternately tensioned and released to provide 180 degree rotary outputs. Each of the latter two mechanisms is provided with a form of damping escapement to avoid excessive wear due to too vicous stepping. Each drive arrangement includes a unidirectional ratchet clutch and also a continuously-driven sub-interval switching cam (196, 264 or 338). Interconnections between terminals, which may include the sub-interval contacts (Fig. 14, not shown), may be made by special bussing means (Figs. 6, 7, 15 and 16, not shown) which fit over the terminals of the cam switches and the wiper switches to ensure good contact and avoid external leads.