GB1453459A - Electronic quartz crystal clock - Google Patents

Abstract

1453459 Electronic timepieces ITT INDUSTRIES Inc 19 Dec 1973 [22 Dec 1972] 58734/73 Heading G3T The frequency of oscillation of a balance wheel in a timepiece is stabilized by "locking on" to synchronizing pulses derived by a frequency divider F t , Fig. 2, from the output of a crystal controlled oscillator circuit O s . The balance, Fig. 1, includes a pair of discs 1 carrying permanent magnets 6 and counterweights 7, which magnets co-operate with a stationary coil system 8, including drive coil L 1 and control coil L 2 , and with a ferromagnetic member 10 (e.g. soft iron or nickel plated copper). The member 10 is increasingly effective on the magnet system toward the end of the oscillatory movement thereof to modify the natural period of oscillation and render the balance system anisochronous i.e. render the oscillation frequency more dependent upon oscillation amplitude. The free end of member 10 is shaped to conform to the arc swept by the magnets. The member 10 is displaceably mounted for fine adjustment. In Fig. 2, a drive transistor T 2 is rendered conductive by square wave pulses having a duty cycle of 0À5, from the divider. Movement of the magnets across coil L2 induces current pulses therein which render a transistor T 1 conductive during periods of coincidence of these pulses with synch. pulses which have a longer duration. Thus only sufficient drive current to maintain the balance synchronized with the divider output, will be passed through the coil L 1 and battery consumption is minimized. Alternatively the control circuit may include a mechanical switch operated by the balance wheel. The oscillation of the balance may be initiated by a lever tangentially engaging the balance wheel. Inherent frequency deviation of the balance introduced by the ferromagnetic member assists in the quick "capture" of the mechanical oscillation by the synchronizing signal the frequency of which corresponds to the natural frequency of the balance system.