Patent Application
20150234356
This application claims priority from European Patent application 14155433.7 filed Feb. 17, 2014, the entire disclosure of which is hereby incorporated herein by reference.
The invention concerns a method of maintaining and regulating the frequency of a timepiece resonator mechanism around its natural frequency, the mechanism including at least one elastic return means that includes at least one balance spring or torsion wire or flexible guide member, where there is implemented at least one regulator device acting on said resonator mechanism with a periodic motion.
The invention also concerns a timepiece movement including at least one timepiece resonator mechanism devised to oscillate at a natural frequency, said timepiece resonator mechanism including at least one elastic return means comprising at least one balance spring or torsion wire or flexible guide member.
The invention also concerns a timepiece, more specifically a watch, including at least one such timepiece movement.
The invention concerns the field of time bases in mechanical watchmaking, in particular those based on a sprung balance resonator mechanism.
The search for improvements in the performance of timepiece time bases is a constant preoccupation. A significant limitation on the chronometric performance of mechanical watches lies in the use of conventional impulse escapements, and no escapement solution has ever been able to avoid this type of interference.
EP Patent Application No 1843227A1 by the same Applicant discloses a coupled resonator including a first low frequency resonator, for example around a few hertz, and a second higher frequency resonator, for example around one kilohertz. The invention is characterized in that the first resonator and the second resonator include permanent mechanical coupling means, said coupling making it possible to stabilise the frequency in the event of external interference, for example in the event of shocks.
CH Patent Application No 615314A3 in the name of PATEK PHILIPPE SA discloses a movable assembly for regulating a timepiece movement, including an oscillating balance maintained mechanically by a balance spring, and a vibrating member magnetically coupled to a stationary member for synchronising the balance. The balance and the vibrating member are formed by the same single, movable, vibrating and simultaneously oscillating element. The vibration frequency of the vibrating member is an integer multiple of the oscillation frequency of the balance.
The invention proposes to manufacture a time base that is as accurate as possible.
To this end, the invention concerns a method for maintaining and regulating the frequency of a timepiece resonator mechanism around its natural frequency, the mechanism including at least one elastic return means that includes at least one balance spring or torsion wire or flexible guide member, where there is implemented at least one regulator device acting on said resonator mechanism with a periodic motion, characterized in that said periodic motion imposes a periodic modulation, with a frequency regulation which is comprised between 0.9 times and 1.1 times the value of an integer multiple of said natural frequency, said integer being greater than or equal to 2 and less than or equal to 10, by controlling a periodic variation in the real part and/or in the imaginary part of the rigidity of at least one said elastic return means.
According to a feature of the invention, said periodic motion imposes a periodic modulation of the resonant frequency of said resonator mechanism, by imposing a modulation of the cross-section of at least one said elastic return means, and/or a modulation of the modulus of elasticity of at least one said elastic return means, and/or a modulation of the shape of at least one said elastic return means, and/or a modulation of the stresses at the attachment points of at least one said elastic return means.
According to a feature of the invention, there is implemented at least one said regulator device imparting a periodic motion to at least one component of said resonator mechanism or to a tool affecting the position of such a component of said resonator mechanism and said periodic motion is imparted to a said resonator mechanism comprising at least one elastic return means comprising at least one balance spring or torsion wire or flexible guide member, and at least one said regulator device is made to act by controlling a periodic variation in the rigidity of said elastic return means by modulating the cross-section and/or modulus of elasticity and/or shape thereof and/or the stresses at its points of attachment.
The invention also concerns a timepiece movement including at least one timepiece resonator mechanism devised to oscillate at a natural frequency, said timepiece resonator mechanism including at least one elastic return means comprising at least one balance spring or torsion wire or flexible guide member, characterized in that said movement comprises at least one regulator device arranged to control a periodic variation in the rigidity of said elastic return means with a regulation frequency comprised between 0.9 times and 1.1 times the value of an integer multiple of said natural frequency of said resonator, said integer being greater than or equal to 2 and less than or equal to 10, and in that said regulator device is arranged to impart a periodic motion to at least one component of said resonator mechanism to exert on said component a twisting or traction or compression force, and/or to impart a periodic motion to at least one tool affecting the position of such a component of said resonator mechanism, and in that at least one said regulator device is arranged to impose a modulation of the cross-section of at least one said elastic return means, and/or a modulation of the modulus of elasticity of at least one said elastic return means, and/or a modulation of the shape of at least one said elastic return means, and/or a modulation of the stresses at the attachment points of at least one said elastic return means.
The invention also concerns a timepiece, more specifically a watch, including at least one such timepiece movement.
Other features and advantages of the invention will appear upon reading the following detailed description, with reference to the annexed drawings, in which:
It is an object of the invention to produce a time base for making a mechanical timepiece, particularly a mechanical watch, as accurate as possible.
One method of achieving this consists in associating different resonators, either directly or via the escapement.
To overcome the factor of instability linked to the escapement mechanism, a parametric resonator system makes it possible to reduce the influence of the escapement and thereby render the watch more accurate.
According to the invention, a parametric oscillator utilises, for maintaining oscillations, parametric actuation which consists in varying one of the parameters of the oscillator with a regulation frequency ωR comprised between 0.9 times and 1.1 times the value of an integer multiple of the natural frequency ω0 of the oscillator system to be regulated, said integer being greater than or equal to 2, and preferably an integer multiple (particularly double) of the natural frequency ω0. By convention and in order to differentiate clearly between them, “regulator” 2 refers here to the oscillator used for maintaining and regulating the frequency of the other maintained system, which is referred to here as “resonator” 1.
The Lagrangian L of a parametric resonator of dimension 1 is:
where T is the kinetic energy and V the potential energy, and the inertia I(t), rigidity k(t) and rest position x0(t) of said resonator are a periodic function of time, x is the generalized coordinate of the resonator.
The forced and damped parametric resonator equation is obtained via the Lagrange equation for Lagrangian L by adding a forcing function f(t) and a Langevin force taking account of the dissipative mechanisms:
where the coefficient of the first order derivative at x is:
γ(t)=[β(t)+{dot over (I)}(t)]/I(t),
β(t)>0 being the term describing losses, and where the coefficient of zero order term depends on the resonator frequency ω(t)=√{square root over (k(t)/I(t))}{square root over (k(t)/I(t))}.
The function f(t) takes the value 0 in the case of a non-forced oscillator.
This function f(t) may also be a periodic function, or be representative of a Dirac impulse.
The invention consists in varying, via the action of a maintenance or regulator oscillator, one or another or all of the terms β(t), ω(t), by modifying the real and/or imaginary part of the rigidity, with a regulation frequency ωR that is comprised between 0.9 times and 1.1 times the value of an integer multiple, this integer being greater than or equal to 2 (particularly double) of the natural frequency ω0 of the oscillator system to be regulated.
In a particular embodiment, the regulation frequency ωR is an integer multiple, particularly double, of the natural frequency ω0 of the resonator system to be regulated.
In a variant, the rest position x0(t) varies simultaneously with the parameters β(t), ω(t), with a regulation frequency ωR which is comprised between 0.9 times and 1.1 times the value of an integer multiple, said integer being greater than or equal to 2 (particularly double) of the natural frequency ω0 of the oscillator system to be regulated.
Preferably, all the terms β(t), ω(t), x0(t), vary with a regulation frequency ωR which is preferably an integer multiple (particularly double) of the natural frequency ω0 of the resonator system to be regulated.
Generally, in addition to modulating the parametric terms, the maintenance or regulator oscillator therefore introduces a non-parametric maintenance term f(t), whose amplitude is negligible once the parametric regime is attained [W. B. Case, The pumping of a swing from the standing position, Am. J. Phys. 64, 215 (1996)]. In a variant, the forcing term f(t) may be introduced by a second maintenance mechanism.
The parameters of this equation are the frequency term ω and the friction loss term β. The oscillator quality factor is defined by Q=ω/β.
To better understand the phenomenon, it can be likened to the example of a pendulum whose length is varied. In such case,
where L is the length of the pendulum and g the attraction of gravity.
In this particular example, if length L is modulated in time periodically with a frequency 2ω and sufficient modulation amplitude δL (δL/L>2β/ω), the system oscillates at frequency ω without damping.
[D. Rugar and P. Grutter, Mechanical parametric amplification and thermomechanical noise squeezing, PRL 67, 699 (1991), A. H. Nayfeh and D. T. Mook, Nonlinear Oscillations, Wiley-Interscience, (1977)].
The principle can be used in a timepiece or a watch which includes a mechanical sprung balance resonator, with one end of the balance spring fixed to a collet integral with the balance, and the other end fixed to a balance spring stud.
Parametric maintenance of this type of sprung balance system can be achieved notably by periodically making the balance spring stud movable.
Oscillation can be maintained and the accuracy of the system is clearly improved.
The choice of an excitation oscillator frequency which is double the frequency of the system whose oscillation regularity is required to be stabilised makes it possible to perform modulation over one complete vibration, and to obtain zero or negative damping.
Industrialization of these parametric oscillator systems is connected to the two essential functions: the supply of energy and counting.
These two functions may be separated, as illustrated in
It may be preferred to modify friction losses in the air rather than causing the frequency term to oscillate or to modify the inertia of the balance by means of an unbalance.
For maximum efficiency, maintenance is advantageously performed with an integer multiple frequency, notably double, of the maintained resonator frequency. The mechanical maintenance means may take various forms.
The present invention consists in varying the rigidity of the balance spring.
Excitation at double the frequency can be achieved with a square signal, or with a pulsed signal; sinusoidal excitation is not necessary.
The maintenance regulator does not need to be very accurate: any lack of accuracy results only in a loss of amplitude, but with no frequency variation (except of course if the frequency is very variable, which is to be avoided). In fact, these two oscillators, the regulator that maintains and the maintained resonator, are not coupled, but one maintains the other, in a single direction.
In a preferred embodiment, there is no coupling spring between these two oscillators.
It is quite clear that the invention differs from other known coupled oscillators: indeed, the implementation of the invention does not require reversibility of the transfer of energy between two oscillators, but rather, insofar as possible, a transfer of energy in a single direction from one oscillator to the other.
The invention more specifically concerns the frequency regulation of a timepiece resonator via action on the rigidity of an elastic return means.
Thus, the invention concerns a method of regulating the frequency of a timepiece resonator mechanism 1 around its natural frequency ω0. This method implements at least one regulator device 2 imparting a periodic motion to at least one component of resonator mechanism 1 or to a tool affecting the position or the rigidity of such a component of resonator mechanism 1.
This periodic motion imposes a periodic modulation of at least the resonant frequency of resonator mechanism 1, by acting on at least the rigidity of an elastic return means comprised in resonator mechanism 1 with a regulation frequency ωR which is comprised between 0.9 times and 1.1 times the value of an integer multiple of natural frequency ω0, this integer being greater than or equal to 2 and less than or equal to 10.
In a particular implementation of the invention, the periodic motion imposes a periodic modulation of the resonant frequency of resonator mechanism 1 by imposing both a modulation of the rigidity of resonator mechanism 1 and a modulation of the inertia resonator mechanism 1.
In a particular implementation of the invention, the periodic motion imposes a periodic modulation of the resonant frequency of resonator mechanism 1, by imposing a modulation of the cross-section of an elastic return means, particularly but not restrictively a spring, comprised in said resonator mechanism 1 and/or a modulation of the modulus of elasticity of a return means comprised in resonator mechanism 1, and/or a modulation of the shape of a return means comprised in said resonator mechanism 1.
In a particular application, this periodic motion may also require a periodic modulation of the resonant frequency of resonator mechanism 1, by also imposing a modulation of the active length of an elastic return means, particularly of a spring, comprised in resonator mechanism 1.
In a particular implementation of the invention, the periodic motion imposes a periodic modulation of the resonant frequency of resonator mechanism 1 by imposing both a modulation of the rigidity of resonator mechanism 1 and a modulation of the rest point of resonator mechanism 1.
In a particular application illustrated by the Figures, there is implemented at least one said regulator device 2 imparting a periodic motion to at least one component of resonator mechanism 1 or to a tool affecting the position of such a component of resonator mechanism 1, and this periodic motion is imparted to a resonator mechanism 1 comprising at least one elastic return means 40 comprising at least one balance spring 4 or torsion wire 46 or flexible, elastic, guide member, particularly with a virtual pivot (such as a butterfly guide member, or RCC guide member with 4 collars, a combination of flexible strips, or a set of crossed strips, or similar, made in one-piece using technologies for micromachinable materials, “MEMS”, “LIGA” or similar), and at least one said regulator device 2 is made to act by controlling a periodic variation of the rigidity of elastic return means 40 by modulating its cross-section and/or modulus of elasticity and/or shape and/or the stresses at its points of attachment.
Shape modulation refers here to a deformation, under the effect of an external stress, relative to the free shape of the elastic return means, and not the normal deformation in operation that, for example, a balance spring undergoes during its contraction and elongation. It is, for example, a deformation induced by contact, by aerodynamic friction, by a contactless force such as a force of magnetic or electrostatic origin, or other means.
Naturally, the elastic return means 40 considered here is the means used to ensure the oscillation frequency of resonator mechanism 1.
The preferred application of the invention concerns watches, more specifically for an application where elastic return means 40 is formed by a torsion wire.
According to the invention, this method is applied to a resonator mechanism 1 comprising at least one elastic return means 40 including at least one balance spring 4 or torsion wire 46 or flexible guide member 46, and at least one regulator device 2 is made to act by controlling a periodic variation in the real part and/or the imaginary part of the rigidity of elastic return means 40, the real pat of the rigidity defining the frequency of resonator mechanism 1, and the imaginary part of the rigidity defining the quality factor of resonator mechanism 1.
In the variants illustrated in
In the variant of
In the variant of
It is possible to give a specific rigidity to additional coil 18 and in particular:
either additional coil 18 is chosen to have equivalent flexibility to that of outer terminal curve 17,
or additional coil 18 is chosen to be more rigid than outer terminal curve 17.
In the variant of
In the variant of
In the variant of
In particular, the two strips 41, 42 are subjected to a different electromagnetic and/or electrostatic and/or magnetostatic field by a motion imparted to a ferromagnetic or magnetised or electrostatically conductive or electrified pole piece (particularly magnets or electrets) in immediate proximity to each strip so that an electric or magnetic or electrostatic or magnetostatic force is created between them and the strips move towards or away from each other. The rigidity of balance spring 4 is modified because its cross-section varies. The motion is preferably mechanically imparted to these pole pieces.
In a variant, the two strips 41, 42 are subjected to an electrical or electrostatic field so as to locally polarize balance spring 4 and locally modify its rigidity 4.
The variant of
Another variant uses an inhomogeneously magnetised rotating wheel set 28 to periodically modify the rigidity of balance spring 4 by the phenomenon of magnetostriction.
An electrostatic variant uses this type of regulator device 2, comprising a similar rotating wheel set 28, this time provided with electrets at its periphery, and whose electric field periodically cooperates with at least one electret placed on the outer terminal curve 17 of the balance spring 4 to periodically modify the rigidity of balance spring 4 by the phenomenon of piezoelectricity.
In yet another variant, rigidity is modulated via a temperature variation.
In an advantageous implementation of this method, valid for all the variants set out above, the regulation frequency ωR is double the natural frequency ω0.
In an advantageous implementation of the method, the relative amplitude of modulation of the real part of the rigidity of resonator mechanism 1 is more than two times the inverse quality factor of resonator mechanism 1.
The invention also concerns a timepiece movement 10 including at least one timepiece resonator mechanism 1 devised to oscillate at a natural frequency ω0, this timepiece resonator mechanism 1 comprising at least one elastic return means 40 including at least one balance spring 4 or torsion wire 46 or flexible guide member. According to the invention, this movement 10 comprises at least one regulator device 2 controlling a periodic variation of the rigidity of elastic return means 40 with a regulation frequency ωR, which is comprised between 0.9 times and 1.1 times the value of an integer multiple of the natural frequency ω0 of resonator 1, said integer being greater than or equal to 2 and less than or equal to 10.
In the variants illustrated in
In the variant of
In the variant of
Additional coil 18 is either of equivalent flexibility to that of outer terminal curve 17 or much more rigid than outer terminal curve 17.
In the variant of
In a particular embodiment, arm 20 is more rigid than outer terminal curve 17.
In the variant of
In the variant of
In the variant of
In the variant of
In yet another variant, electrostatic layers or elements may be implemented to vary the rigidity of a spring or balance spring by partially or completely covering it with a piezoelectric layer activated by a small electronic module.
Preferably, the regulation frequency ωR of regulator device 2 is double the natural frequency ω0 of resonator mechanism 1.
The invention also concerns a timepiece, more specifically a watch 30, including at least one such timepiece movement 10.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14155433.7 | Feb 2014 | EP | regional |
