Patent GB-1535366-A (GB)
Title: Method and apparatus for synchronising a mechanical oscillating system to the accuracy of a quartz standard
IPC: G04C11/08
Filed: 1976-03-25
Abstract: 1535366 Electrical control of mechanical oscillator frequency in timepieces H JAUCH 25 March 1976 [27 March 1975 6 Sept 1975 22 Jan 1976] 12034/76 Headings G3R and G3T The oscillation frequency of a mechanical oscillatory system in a timepiece is stabilized by detecting the oscillation frequency of the system, comparing in a phase comparator the detected frequency signal with timing signals derived from a quartz oscillator to produce a deviation signal which is used to correct the deviation in a two-step or proportional manner. Inductive, capacitive or field plate pick-ups or mechanical switches may be used to produce the actual detected frequency signal. In Fig. 1, a frequency divider 12 derives from a crystal oscillator 10, positive timing pulses at its output "a" occurring in the 1st, 3rd, 5th,---- seconds only and from its output "b" pulses in the 2nd, 4th 6th, - - - - seconds only and which are respectively applied to transistors 14, 14 functioning as AND gates to perform phase comparison. The mechanical oscillator (e.g. a pendulum) frequency is detected by a coil 16 the voltage induced in which by a magnet on the pendulum is amplified and applied via C22 to the base electrodes of 14, 14'. If the clock is running too fast such that the detected frequency signal is so misphased as to coincide with the timing signal from "a", then transistor 14 is rendered conductive and consequently transistors 24, 26, 28 conduct, thus exciting a coil 30 which causes a control member to reduce the oscillatory system frequency. When the oscillation frequency drops sufficiently so that the detected f signal coincides with the timing signal from "b" corresponding to the clock running too slow, the transistor 14' conducts and coil 30' is excited and control member is switched again to the too-fast condition and the cycle repeats. Twostep control of the pendulum frequency is thereby effected. To ensure sufficient excitation of coil 30 even if the pulse from transistor 30 is very short, the transistors 24, 26 are inter-connected by C32, R34 to form a monostable MV. In an embodiment Fig. 2 not shown) a deviation signal is derived and proportional control of a control motor (62) is effected, the motor (62) being rotated in the required direction by an amount sufficient to correct the deviation. A magnet (37) on the pendulum co-operates with a field plate (38) to produce the detected frequency signal. In an embodiment Figs. 3 and 4 (not shown) the control circuit excites either a deceleration coil (108) or an acceleration coil (118) to control a balance wheel frequency in dependence upon detected deviation. The deceleration coil also serves as a pick-up detector. The two-step control circuit Fig. 1 may be applied to stabilize a pendulum 140, Fig. 7 pivotal with its armature 160 on a shaft 164. The armature engages a balance 162. The pendulum carries a magnet 170 which co-operates with a detector coil 172. The lower end of a leaf-spring 174 is fixed to the pendulum and the spring swings therewith. The deviation signal controls an electromagnet 176 which co-operates with magnets 182 on a linkage coupled to a lever 184. To increase the pendulum frequency, the forked end 186 is caused to engage the free end of the leaf spring and exert a repelling torque on the pendulum. In a proportional control, the circuit (Fig. 2) may be used to drive a motor 62 Fig. 5 which moves horse shoe magnets 144 via gears with respect to a magnet 142 on the pendulum. In the control of a balance wheel oscillation Fig. 16 (not shown), a gripper controlled by a solenoid acts on the outer turn of the balance hair spring to limit its movement while in Fig. 17 (not shown) a control motor alters the effective length of the hair spring. In an electrically maintained balance system Fig. 18 (not shown) the balance wheel carries a magnet which is acted upon by the field from an acceleration or deceleration coil. The manner in which the mechanical system oscillations are maintained in the other embodiments, is not specified. Additionally, the quartz crystal oscillator may be synchronized with a standard frequency transmitter controlled by an atomic clock.