Patent GB-1501612-A (GB)
Title: Delay timing arrangements
IPC: H01H43/10
Filed: 1972-12-15
Abstract: 1501612 Time switches FERRANTI Ltd 21 Jan 1974 [15 Dec 1972] 57954/72 Heading H1N A delay timing arrangement incorporates a fixed-frequency oscillator 14, Figs. 1 and 2(b), driving an electrical stepping motor 11 which drives a cyclometer type of mechanical register 13 having means 60 for setting it to indicate any required magnitude and electrical switch means 53 to 57 arranged to be actuated by the register in response to the indication of a predetermined magnitude (particularly zero). The invention is applied to an armament fuze. Electric motor, Fig. 2(a).-The stepping motor includes a cylindrical ferrite rotor 21 magnetized with a plurality of alternate N and S poles and a pair of stator windings 23, 24; winding 23 has an annular polepiece 25 with a number of projections 25(a) corresponding to the number of poles of one type on the rotor and a similar annular polepiece 26 has projections 26(a) interdigitated with projections 25(a), and winding 24 has a corresponding pair of polepieces 27, 28 with interdigitated projections displaced by half a pole pitch with respect to those of polepieces 25, 26. The windings 23, 24 are connected in series and a capacitor 29 is connected across winding 24. Oscillator and driving circuit, Fig. 2(b).- The oscillator comprises an operational amplifier 30 coupled in known manner to form an astable multivibrator. The motor-driving circuit consists of transistors 31 and diodes 32. The circuit operation is described. Gearing is arranged such that wheel 44, Fig. 1, displays a succeeding numeral each second or such that the wheel makes one revolution per second. Setting means 60, Fig. 1, incorporates a gear 62 slidable along a shaft 63 fixed to the body of the timing arrangement but biased away from  the toothed portion 61 of a connecting shaft 43 by a spring 64; an annular setting ring 65 has a toothed portion 66 in constant mesh with gear 62 and an abutment 67 which engages the non-toothed face of gear 62. To set the timing arrangement ring 65 is moved leftward against spring 64 bias to engage gear 62 with portion 61 of shaft 43 and ring 65 is then rotated as required. Alternative setting means applies stepping signals to the motor at an enhanced rate until the register indicates the set value. Supply 33, Fig. 2(b), may be from an airdriven generator.  An alternative switch utilizes a light-emitting-' diode and a photodiode or photo-transistor, Fig. 3 (not shown): when apertures in all cyclometer discs are aligned the photo-sensor delivers an output. Modifications.-Further sets of contacts may be added to arm a fuze after one preset period and detonate it after a further preset period. The invention is made particularly suitable for a mine by adding indicator wheels to enable a long counting period. The device may be reduced in size by shading the projections of the polepieces. A ring counter may be employed to energize the stator windings sequentially if they are each composed of two windings and the (bulky) capacitor 29 need not then be included. An e.m.f. produced by the motor when stepping may be utilized to automatically turn off the stepping pulse to reduce power drain.