US3797224A - Compensation of the thermal frequency drift of a mechanical oscillator for timekeeping - Google Patents

Compensation of the thermal frequency drift of a mechanical oscillator for timekeeping Download PDF

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Publication number
US3797224A
US3797224A US00166060A US3797224DA US3797224A US 3797224 A US3797224 A US 3797224A US 00166060 A US00166060 A US 00166060A US 3797224D A US3797224D A US 3797224DA US 3797224 A US3797224 A US 3797224A
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Prior art keywords
magnets
thermal
resonator
oscillator
magnetic
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Expired - Lifetime
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US00166060A
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English (en)
Inventor
R Favre
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Movado Watch Co SA
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Fabriques Movado
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    • G—PHYSICS
    • G04—HOROLOGY
    • G04C—ELECTROMECHANICAL CLOCKS OR WATCHES
    • G04C3/00—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means
    • G04C3/08—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically
    • G04C3/10—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically driven by electromagnetic means
    • G04C3/101—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically driven by electromagnetic means constructional details
    • G04C3/102—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically driven by electromagnetic means constructional details of the mechanical oscillator or of the coil
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B17/00—Mechanisms for stabilising frequency
    • G04B17/20—Compensation of mechanisms for stabilising frequency
    • G04B17/22—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature
    • G—PHYSICS
    • G04—HOROLOGY
    • G04C—ELECTROMECHANICAL CLOCKS OR WATCHES
    • G04C3/00—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means
    • G04C3/08—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically
    • G04C3/10—Electromechanical clocks or watches independent of other time-pieces and in which the movement is maintained by electric means wherein movement is regulated by a mechanical oscillator other than a pendulum or balance, e.g. by a tuning fork, e.g. electrostatically driven by electromagnetic means

Definitions

  • ABSTRACT A system for compensation of the thermal frequency drift of a mechanical oscillator for timekeeping, wherein the compensating effect is obtained by interaction of magnets fixed to the oscillator, such magnets having a thermal coefficient of negative character.
  • a secondary compensating effect is obtained by means of magnetic shunts associated with said magnets, such shunts having a Curie-point at a suitable temperature.
  • T T T /2 F o, F 1 and F2 the frequency of the oscillator at the respective temperatures T0, T1 and T2.
  • the average thermal co-efficient of the frequency of the proposed oscillator is defined by the ratio: F l-F 2/ Tl-TZ
  • the secondary error includes the non-linearity of the thermal effect by the expression:
  • Time-keeping oscillators are generally associated with a system for displaying the time, and therefore the variations of frequency are often expressed by seconds per day and the thermal frequency effect by seconds per day degree C (s/d/C).
  • the thermal co-efficient of a mechanical oscillator having an elastic (resilient) structure of carbon steel is of the order of 10 s/d/C, which value is incompatible with the precision required today in many timepieces.
  • So-called compensating alloys known by various trade names such as DURINVAL, ISOVAL or NIVA- ROX, make it possible to cancel the thermal effect by simple cold-hammering (hammer-hardening) followed by a suitable heat treatment. In the annealed or hypertempered condition, these compensating alloys have a positive thermal co-efficient (the reverse of that of steel) of the order of 3s/d/C.
  • an auxiliary compensating device for the thermal frequency drift is advantageous, and is more particularly applicable when the elastic structure of the oscillator type includes a sharp bend.
  • a device for compensating the thermal frequency drift of a mechanical oscillator for timekeeping and in particular of an oscillator operating at an audible frequency and comprising at least one oscillating body and an elastic structure arranged as a resonator, wherein the said elastic structure includes a thermal drift co-efficient component of magnetic origin, capable of reducing the resultant overall thermal frequency drift.
  • the oscillator may have a folded (bent) tuning fork structure, with thermal effects compensated by the present invention.
  • FIG. 1 is a plan view of an oscillator according to the invention.
  • FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1;
  • FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 1, and
  • FIG. 4 is a cross-sectional view similar to FIG. 3 and showing a modification.
  • the oscillator comprises a bent tuning fork with two tines 1 and 2, two transducers 3 and 4 co-acting with a common fixed driving coil 15, a link 5 obtained by an oblique fold 5, and an elastically secured small tongue 6.
  • FIGS. 2 and 3 show the structure of the transducers in greater detail. Each of them comprises a thin U- shaped magnetic armature carrying pairs of magnets 7,8 and 11, 12 and pairs of magnetic shunts 9, 10 and 13, 14.
  • the material of the tuning fork shown is sharply bent it is necessary to start from an annealed or hypertempered compensating alloy, for example, of the DURINVAL type which may be hardened by simple heat treatment after bending in the hypertempered condition.
  • the nominal frequency thermal co-efficient is then of I the order of 3s/d/C.
  • the compensating effect consists in providing a magnetic repulsion interaction between the two transducers 3 and 4, obtained and adjusted by suitably locating the two pairs of magnets, and in selecting these magnets so that they produce a high negative thermal co-efficient, such as is obtained by ferrite magnets.
  • the amount of magnetic inter-action may be adjusted on assembly so as to cancel the average thermal co-efficient of frequency, but the curve of magnetisation against temperature shows a slight secondary error which it is desirable to eliminate in precision time keeping.
  • small magnetic shunts 9, 10, 13 and 14 are disposed on the opposed faces of the magnets, so as to constitute a screen against the increasing efficiency of interaction when the temperature falls, which condition is required for eliminating the secondary error.
  • the Curie point of the magnetic shunts must be approximately 20C and the radius of the induction graph curvature, near the Curie point, must be as large as possible for maximum cold hammering.
  • the thickness of the shunts may be very small, for example 0.1 mm. The width thereof is usually equal to the thickness of the magnets. The length is then determined so as to exactly compensate the secondary error over a range of useful temperatures which may extend from 0C to 40C.
  • the magnetic shunts are preferably directly cemented on the respective faces of the magnets.
  • the device of the present invention enables the thermal frequency drift of a mechanical oscillator to be cancelled by an operation applied during assembly, or subsequently thereto.
  • the transducers are not directly suitable for the desired magnetic interaction, it is obviously possible to equip the oscillator with auxiliary ferrite magnets l6, 17, 18 and 19, as shown in FIG. 4.
  • the thermal co-efficient and secondary error are easily reduced to less than 0.1 s/d/C, by a very rapid adjusting operation.
  • a device for compensating the thermal drift a mechanical oscillator for timekeeping and in particular of an oscillator operating at an audible frequency and comprising at least one oscillating body and a resilient structure arranged as a resonator, said resilient structure including a thermal drift co-efficient component of magnetic origin capable of reducing the resultant overall thermal frequency drift, said component of magnetic origin being obtained by interaction of magnets mounted on said resonator having a negative thermal coefficient, magnetic shunts mounted on the faces of said inter-acting magnets for reducing a secondary error, the shunts having a Curie point near the useful average temperature, the shunts forming a barrier the efficiency of whose inter-action increases with decreasing temperature.
  • a device according to claim 1, wherein the said component of magnetic origin is produced by the interaction of the magnets of the transducers for maintaining oscillation.
  • a device wherein the component of magnetic origin is produced by the inter-action of auxilliary magnets fixed to the resonator of the oscillator.
  • the resilient structure is a resonator shaped by deformation and includes at least one sharp bend.
  • a device in which the resilient structure is in the form of a tuning fork with permanent magnets fixed to the inside of the tines so that the inner surfaces of the magnets are located near to each other.
  • the resilient structure is a resonator including at least one sharp bend.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Metallurgy (AREA)
  • Electric Clocks (AREA)
  • Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)
US00166060A 1970-08-04 1971-07-26 Compensation of the thermal frequency drift of a mechanical oscillator for timekeeping Expired - Lifetime US3797224A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1170070A CH549829A (en, 2012) 1970-08-04 1970-08-04

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US3797224A true US3797224A (en) 1974-03-19

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US (1) US3797224A (en, 2012)
CH (1) CH549829A (en, 2012)
DE (1) DE2137087B2 (en, 2012)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4193008A (en) * 1977-04-18 1980-03-11 Murata Manufacturing Co., Ltd. Tuning fork formed of rolled invariable elasticity material

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3207900A (en) * 1961-11-29 1965-09-21 Fitzgerald John Vincent Radiation responsive dynamic mechanical system
US3283495A (en) * 1964-02-18 1966-11-08 Centre Electron Horloger Electronic watch
US3310757A (en) * 1966-09-15 1967-03-21 Bulova Watch Co Inc Decoupling mounting plates for tuning fork oscillators
US3496391A (en) * 1967-12-07 1970-02-17 Clarence Hunter Mcshan Resonant device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3207900A (en) * 1961-11-29 1965-09-21 Fitzgerald John Vincent Radiation responsive dynamic mechanical system
US3283495A (en) * 1964-02-18 1966-11-08 Centre Electron Horloger Electronic watch
US3310757A (en) * 1966-09-15 1967-03-21 Bulova Watch Co Inc Decoupling mounting plates for tuning fork oscillators
US3496391A (en) * 1967-12-07 1970-02-17 Clarence Hunter Mcshan Resonant device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4193008A (en) * 1977-04-18 1980-03-11 Murata Manufacturing Co., Ltd. Tuning fork formed of rolled invariable elasticity material

Also Published As

Publication number Publication date
DE2137087B2 (de) 1972-06-22
DE2137087A1 (de) 1972-02-10
CH549829A (en, 2012) 1974-05-31
CH1170070A4 (en, 2012) 1973-12-28

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