GB1295741A - - Google Patents

Abstract

1295741 Toothed gearing R HARTWIG 3 March 1970 [4 March 1969] 10193/70 Heading F2Q [Also in Divisions G3 and H1] A time measuring device such as a clock or time switch comprises first and second discs 29, 17 which are independently rotatable about a common axis 12 and provided with peripheral teeth 31, 18, respectively; the root diameter of the teeth 31 being greater than the outer diameter of the teeth 18 so that a tangential driving pawl (38, Figs. 7, 10, not shown) which engages successive teeth 31 to advance the disc 29 is prevented from engaging the teeth 18 except when the pawl enters a deeper tooth notch 32, whereupon the pawl engages both the discs 29, 17 and advances them together by one step. Fig. 1 shows a clock in which the seconds, minutes, and hours are indicated by strips 41, 28, (46, Fig. 6, not shown), on discs 29, 17, 44 respectively, which are moulded of transparent plastics. The seconds disc 29 is rotatably mounted on a hub 22 on the disc 17, the hours disc 44 being similarly mounted on a further hub 24 which lies on an axis 26 eccentric with respect to the axis 12. The assembly of the three discs is mounted in a casing 11, 51 by means of a pin 54 which projects from rear wall 52 of the casing part 51 concentrically with the axis 12 and which engages a blind hole 56 in a hollow knob 21 on the disc 17. The knob 21 projects through the transparent front part 11 to permit setting of the minutes and hours discs 17, 44. The front 11 carries dial markings (14, Fig. 3, not shown). The minutes disc 17 drives the hours disc 44 through reduction gearing which comprises an annular portion 47 on the disc 44 which has twelve internal teeth 48, Fig. 2, and is coaxial with the axis 26. The twelve internal teeth 48 co-operate with eleven external teeth 58 on a wheel 57 which is moulded within a recess 59 on the casing part 51. This gives a reduction ratio between the discs 17, 44 of 12 : 1 but another embodiment is envisaged which is a twenty-four hour, hundred minute, and hundred second clock. The driving pawl (38) is reciprocated by a synchronous motor, through reduction gearing contained in the base (88, Fig. 8, not shown) of the clock, at one cycle per second. For use as a time switch the time indicating strips 41, 28, (46) are omitted and electrical contacts are fixed to the discs 29, 17, 44 so as to co-operate with stationary contacts on the case. The switched circuit may use contacts on two or more of the discs.