Patent GB-742190-A (GB)
Title: Process and apparatus for timing and adjusting the frequency of vibration of a regulating device of a timepiece
IPC: G04D7/12
Filed: 1953-03-17
Abstract: 742,190. Testing timepiece balances. BULOVA WATCH CO., Inc., NEW YORK, SUC-- CURSALE DE BIENNE. March 17, 1953 [April 9, 1952], No. 7387/53. Class 139 A device for timing and adjusting the frequency of vibration of a balance and hair spring regulating device intended for assembly in clockwork comprises means for suspending the regulating device at the free end of the hair spring for oscillation about its longitudinal axis with the lower end of the balance staff abutting against a support of non-magnetic material, means for subjecting the balance to a high frequency rotary magnetic field, and means for deriving electric impulses from the instantaneous amplitude of the balance vibrations and controlling thereby the frequency and the direction of rotation of said high frequency rotary magnetic field, comparing these impulses with those of a standard regulating device and adjusting the length of the hair spring until identity is obtained. The balance and hair spring assembly to be timed and adjusted is supported on a glass plate 14, Fig. 1; the balance staff being kept vertical by a bar magnet 15 excited by a coil 17 and the hair spring 1 being gripped between two separable rollers 3, 4. The roller 4 is connected through gearing to a servomotor 8. The assembly is kept in oscillation by a high frequency magnet system 19-22 controlled, as described later, and its period is compared with a standard, the motor 8 driving the roller 4 one way or the other to shorten or lengthen the hair spring as required. When the assembly is in agreement with the standard an electromagnet 13 is energized to operate a knife 10 and cut the hair spring. The end 24 of a screened electrical conductor 23 is located within the hair spring 1 and the conductor 23 is connected to the grid of a valve 31. An alternating voltage of 1000 cycles/sec. is applied through a conductor 26 to a ring 25 below the glass 14 so that an electrical field between the ring 25 and the probe 24 is generated. As a result of the radial expansion and contraction of the hair spring 1 an amplitudemodulated alternating voltage is applied to the grid of the valve 31. This voltage is then passed through the amplifier 34, Fig. 2, the demodulator 35, the filter 36, the low frequency amplifier 37, the limiter 38, the direct current amplifier 39 and then to differentiators 40, 40' from each of which is obtained peak voltage impulses. The arrangement is such that the impulses from the differentiators 40, 40<SP>1</SP> coincide with the passing of the balance through its midposition in opposite directions. The impulses from the differentiator 40<SP>1</SP> are sent to a time measuring device 42 wherein the time between successive impulses is compared with the period of a standard oscillation. The servomotor 8 is controlled by the device 42 to rotate in the appropriate direction for correcting the effective length of the hairspring and when the device 42 indicates identity between the balance unit being tested and the standard oscillation the electromagnet 13 is energized to operate the knife 10, Fig. 1, and cut the hair spring. The impulses from the differentiators are sent to unilateral trigger arrangements 43, 43<SP>1</SP>, Fig. 2, respectively from which rectangular impulses are sent to a modulating transmitting arrangement comprising pairs of interconnected modulators 44, 44<SP>1</SP> and 45, 45'. The modulators 44, 45' are fed directly by a high frequency oscillator 50, the modulators 44<SP>1</SP>, 45 being fed through a capacitive phase shifter 47 and an inductive phase shifter 46 respectively. The coils 19, 21 are connected to the secondary winding of transformer 48, the primary of which is connected to the output of modulators 45, 45'. The coils 20, 22 are connected to the secondary winding of a transformer 49 the primary of which is connected to the output of modulators 44<SP>1</SP>, 45. The arrangement is such that when the modulator 44 receives an impulse from the trigger arrangement 43 the coil pair 19, 21 is fed through the transformer 48 with a current in phase and the coil pair 20, 22 through the transformer with a capacitively phase shifted current and the resulting high frequency rotary field impulses the balance in its direction of swing. When the modulator 45 receives an impulse from the trigger arrangement 44 the coil pair 19, 21 is again fed with a current in phase through the transformer 48 and the coil pair 20, 22 through the transformer 49 with an inductively phase shifted current and the resulting high frequency rotary field impulses the balance as it moves in its other direction of swing. Specifications 742,191 and 742,192 are referred to.