Patent GB-1343340-A (GB)
Title: Horological instrument
IPC: G04C3/06
Filed: 1971-07-06
Abstract: 1343340 Electronic watches TIMEX CORP 6 July 1971 [6 July 1970] 31751/71 Heading G3T Relates to a battery powered electronic watch wherein a self-starting transistor multivibrator circuit drives a mechanical oscillatory member (e.g. a balance wheel) and after the starting period the said member determines the frequency of the multi-vibrator circuit, or alternatively the circuit may synchronized by an external circuit (not shown). The oscillatory member may be a full balance wheel or, as shown Fig.1, a cross-shape balance 13 having a staff 11 and hair spring 12 also a counter balance portion 14 and carrying, or being formed integral with, a coil 15 comprising a short-circuited single turn. The coil 15 is movable in the air-gap 18 of a U-shaped magnetic circuit 17 which is embraced by a stationary coil 16. The coil 15 is also movable in the air-gaps of a second magnetic circuit including a lower yoke member 22 (detailed in Fig. 5), an upper and similar yoke member 21 and a permanent magnet 20. The second magnetic circuit is embraced by a drive coil 19. In operation, movement of coil 15 in airgap 18 induces a voltage in coil 16 in opposition to the supply voltage and the consequent current change in coil 16 renders a transistor 33 conductive which in turn causes a transistor 36 to conduct passing current through coil 19. Also an e.m.f. is induced in coil 15 due to increasing current in coil 16 and the resulting current in coil 15 reacts with the magnetic field produced by current in coil 19 to provide a drive impulse to the balance member. A transistor 42 is blocked at this time by voltage induced in coil 16. Also a capacitor 45 is at this stage fully charged via a diode 38 and a capacitor C 46 becomes fully charged so that current in coil 19 also coil 16 will decrease. As a result the control current of Tr 33 decreases further decreasing the current in coil 19 and coil 16 and Tr 36 until finally Tr 36 is blocked. At this stage current in coil 16 falls rapidly causing C 45 to charge to above the battery voltage. The decreasing current in coil 16 induces a reverse current in coil 15 and the transistor 42 is rendered conductive by the charging current of C 40 so that C 46 discharges via Tr 42 and coil 19 in opposite direction to battery current. The resulting reverse flux in the magnetic circuit of coil 19 reacts with the reverse current in coil 15 to produce a drive impulse to the balance in the same direction as the first impulse, and so on. The circuit Fig.3 will operate as a selfstarting self-oscillating multi-vibrator when the balance member is stopped, its frequency at this time being determined by the values of R 39 C 40, and will induce current pulses in the balance coil 15 at that frequency, to start the watch. Alternatively the circuit may be synchronized by pulses from an external circuit (not shown) including a quartz crystal controlled oscillator and frequency dividers. The balance wheel may drive an index wheel in a conventional manner, or alternatively coil 16 or coil 19 may be provided with a movable armature (not shown) which indexes an index wheel.