Patent GB-1463990-A (GB)
Title: Synchronization method for electromechanical oscillators of timepieces
IPC: G04C3/04
Filed: 1974-02-21
Abstract: 1463990 Electronic timepieces ITT INDUSTRIES Inc 21 Feb 1974 [24 Feb 1973] 7950/74 Heading G3T In an electronic timepiece, oscillations of an electro-mechanical resonator, e.g. a balance wheel, are stabilized by synchronizing the oscillations with and locking on to a synchronizing signal which is substantially at the natural frequency of the resonator and derived from a crystal controlled oscillator followed by a frequency divider, the duration and/or time position of driving and damping current pulses through the drive coil of the resonator being controlled, with respect to the natural rest position of the resonator, as a function of the phase difference between the synchronizing signal and a signal derived from the resonator oscillations. The provision of damping pulses to withdraw energy from the resonator is said to extend the synchronizing or capture range of the synchronizing signal with respect to the mechanical resonator. In Fig. 4 a switch K is operated by a balance wheel carrying magnets which co-operate with a drive coil L. A transistor Ti is controlled by the synchronizing signal being rendered conductive during period "A" Fig. 2a (not shown) of the signal. In Fig. 2, "N" indicates driving current pulses triggered after the balance has passed its rest position and "V" pulses triggered before the balance has reached its rest position. Drive current will flow in coil L when the closed period of switch K occurs during the period "A". If, as illustrated in Fig. 2c, (not shown), T1 is switched OFF before switch K opens the direction of the current pulse in L is reversed as energy in L discharges via a diode D, a resistor R and switch K, thus acting as a damping current pulse N'. Such would be the case if the resonator frequency had decreased with respect to the synchronizing signal frequency or if their mutual phase displacement had altered. The consequent reduction in drive current and the damping will increase the frequency of the resonator oscillations to the  frequency of the synchronizing signal. If the closing time of K lies outside the conducting period of T1, then damping current due to voltage induced in L by the magnet system, will flow during the entire closing time, Fig. 2d (not shown) illustrates the case where excessive phase difference occurs e.g. due to externally applied disturbance; in this case only damping current pulses N' are produced after the balance passes its rest position. In an embodiment described with reference to Figs. 3, 5 (not shown) the drive pulses are controlled by a synchronizing signal I and the damping current pulses by a synchronizing signal II at the same frequency as signal I and having a duty factor equal to or less than that of signal I. Fig. 6 (not shown) illustrates an embodiment wherein a balance is maintained in oscillation by a circuit employing current feedback from the balance and is stabilized by driving and damping pulse synchronizing signals. The discharge path of the drive coil may include in combination or individually - a resistor, a diode, a transistor; alternatively the coil may be periodically short-circuited.