EP3336613B1 - Timepiece resonator with two balances arranged to oscillate in a single plane - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to a resonator for a timepiece comprising a support structure intended to allow the mounting of the resonator in a timepiece, two pendulums arranged to oscillate in the same plane, and a plurality of elastic elements arranged to connect the two pendulums to the support structure, the configuration of the plurality of elastic elements determining two parallel axes of elastic pivoting for the two pendulums, and the plurality of elastic elements also forming elastic return means arranged to angularly recall each of the two pendulums to a rest position.

PRIOR ART

Known mechanical watches usually use a balance spring as a regulating member. The latter is made up of three main parts: a balance wheel in the form of a flywheel, an axis which carries the balance wheel and which is terminated by two pivots making it possible to mount the balance wheel in a timepiece frame, and finally, a spiral spring which produces a return torque proportional to the magnitude of the angle separating the balance from its equilibrium position. As is well known, the balance-spring has been the almost exclusive time base of mechanical watches for over 300 years.

The use of a balance-spring as a time base gives the possibility of having robust watches that demonstrate chronometric precision of the order of 15 seconds per day. We can therefore say that balance-spring is a reliable and precise resonator. The fact remains that the precision of quartz watches is still much higher than that of mechanical watches equipped with a balance-spring. This difference in accuracy is due in part to the fact that a quartz tuning fork has a considerably higher quality factor than that of a balance-spring.

The amplitude of the oscillations of a balance-spring is considerable. It usually varies between 180 ° and 315 ° depending on the degree of winding of the mainspring and according to the rather horizontal or rather vertical position of the watch. Under these conditions, the two bearings in which the pendulum axis rotates are very stressed, which causes the dissipation of a fraction of the energy of the pendulum by friction. It will be understood that this friction contributes to lowering the quality factor of the balance spring. Great efforts have been made to provide pendulum bearings with optimized tribological properties. The fact remains that the negative effect of friction on the quality factor has not yet been eliminated.

In order to remedy the problems which have just been described, it has been proposed to replace the traditional pivoting of the pendulums with a flexible pivoting. The patent document CH 709 291 A2 , in particular, describes a resonator for a timepiece comprising a support element, intended to allow the mounting of the resonator in a timepiece, a balance in the form of a flywheel, and finally two elastic blades which connect the support element to the pendulum crossing. The configuration of the two elastic blades is chosen so as to define a geometric pivot axis concentric with the balance. In addition, the two blades are arranged so as to exert a restoring torque on the pendulum. With this construction, when the resonator oscillates, the two blades are deformed, playing both the role of spiral spring and flexible pivoting. It will be understood from the above that the solution proposed in this prior document makes it possible to eliminate one of the main causes of friction, since it eliminates the bearings of the balance wheel to replace them by a flexible pivoting. According to the document CH 709 291 A2 , the proposed oscillator has a quality factor about 10 times higher than that of a balance spring.

However, the above-mentioned resonator has certain drawbacks. According to this document, the amplitude of the pendulum's oscillations is typically 20 °. Under these conditions, the effect of a possible collinearity between, on the one hand, the angular moment of the pendulum, and on the other hand, its geometric pivot axis, cannot simply be neutralized by rotation. Furthermore, it is feared that a flexible pivot balance like that which has just been described is more sensitive to shocks than a balance spring. In order to remedy these last two problems, the patent document EP 3,035,127 A1 proposes to couple two flexible pivot resonators, so as to form a tuning fork shape. According to this proposal, the coupling between the two resonators is ensured by a mobile connecting element to which the elastic blades of the two resonators are fixed by one end. The other end of each pair of blades is connected to one of the two pendulums as before. It will be understood that according to this second prior document, the connecting element carries the two pendulums, while itself being elastically fixed on a support element rigidly mounted in the timepiece. With such an arrangement, the geometric axes of pivoting of the two pendulums each occupy a fixed position relative to the connecting element, while being collectively movable relative to the frame of the timepiece.

As the title of the document indicates EP 3,035,127 A1 , the oscillator he describes constitutes a form of tuning fork. In this regard, we know that an advantage linked to the symmetry of the tuning forks is that it favors a few well-defined oscillation modes having a high quality factor. Among these oscillation modes, the two most basic modes are the symmetrical mode and the asymmetric mode. With regard to horological applications, the asymmetric mode (the tuning fork branches move at the same time in opposite directions) is the most advantageous because of its lower sensitivity to external phenomena; to shocks in particular. With a tuning fork intended for a horological application, it is therefore important that the symmetrical oscillation mode (the branches of the tuning fork move at the same time in the same direction) is always effectively damped. In this context, the document EP 3,035,127 A1 teaches to couple the oscillations of the two pendulums using a connecting element suspended elastically on a fixed element. A special feature of the asymmetric resonance mode is that the center of mass of the system remains at rest, the forces acting on the link element of the tuning fork mutually neutralizing each other. Under these conditions, to favor the antisymmetrical resonance mode, it is necessary to adjust the suspension of the connecting element so that the vibrations of this element are strongly damped, while ensuring that the connecting element remains free from transmitting to the second balance the excitation pulses received on the first balance. In view of the above, it can be feared that it is very difficult to adjust the suspension of the connecting element satisfactorily.

BRIEF STATEMENT OF THE INVENTION

An object of the present invention is to provide a resonator with a high quality factor, and which comprises two pendulums mechanically coupled, the coupling between the pendulums being designed to favor the asymmetric oscillation mode. The invention achieves this object by providing a resonator according to claim 1 appended hereto.

In the present patent application, the expression “support structure” does not necessarily designate a single support part. Indeed, in accordance with the invention, the support structure may for example comprise two separate support elements, one of the support elements used for mounting the first balance and the other support element used for mounting the second balance.

BRIEF DESCRIPTION OF THE FIGURES

• la figure 1 est une vue en plan de dessus d'un résonateur pour pièce d'horlogerie conforme à un premier mode de réalisation particulier de l'invention ;
• les figures 2A et 2B sont des vues partielles de dessus montrant en détail la paire de lames élastiques qui relie un des balanciers à la structure de support du résonateur, conformément respectivement à une deuxième et à une troisième variante du premier mode de réalisation illustré dans la figure 1 ;
• les figures 3 et 4 sont des vues en perspectives d'un résonateur pour pièce d'horlogerie conforme à un deuxième mode de réalisation particulier de l'invention.

Other characteristics and advantages of the present invention will appear on reading the description which follows, given solely by way of nonlimiting example, and made with reference to the appended drawings in which:

• the figure 1 is a top plan view of a timepiece resonator according to a first particular embodiment of the invention;
• the Figures 2A and 2B are partial views from above showing in detail the pair of elastic blades which connects one of the pendulums to the support structure of the resonator, in accordance respectively with a second and a third variant of the first embodiment illustrated in the figure 1 ;
• the figures 3 and 4 are perspective views of a timepiece resonator according to a second particular embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The figure 1 is a top plan view of a timepiece resonator, which is in accordance with a particular embodiment of the invention. According to the invention, the illustrated resonator comprises a support structure intended to allow its mounting on a frame (not shown) of a mechanical watch. In the present example, the support structure consists of two flanges respectively referenced 2 and 4. The resonator further comprises two pendulums generally referenced 6 and 8 which, in the example illustrated, generally each have the shape of an ellipse with a large central notch. When the pendulums are in their rest position as shown, the two notches open facing each other. It can also be seen that the two flanges 2, 4 of the support structure are each arranged inside one of the notches. Each balance also comprises a twill 10 provided to give it greater inertia. The serge extends along the periphery of the pendulum. The first and second balance preferably have the same mass and the same dimensions so that it is easy to oscillate them at the same frequency.

In accordance with the invention, the pendulums are connected to the support structure by a plurality of elastic elements. More specifically, in the illustrated embodiment, each balance 6, 8 is connected to one of the two flanges 2, 4 by a pair of elastic blades (referenced respectively 12a, 12b and 14a, 14b). As shown in the figure, one end of each blade is attached to the balance by the bottom of the notch, while the other end is secured to the flange located in the same notch, so that each pair of elastic blades is arranged inside the pendulum notch to which it is attached. We can also see that the two elastic blades of the same pair intersect so as to form a X which extends in the plane of the pendulum inside the notch. A person skilled in the art will understand from the above that the configuration of the pair of blades connecting one of the pendulums to the support structure determines a geometric elastic pivot axis X ′, X ″ for this balance. The geometric pivot axis is perpendicular to the plane of the pendulum and it passes through the point of intersection of the two blades of the X. This point of intersection moves very slightly during the movement of the pendulums.For reasons which will appear more clearly later, the X formed by the elastic blades is preferably positioned in the notch so that the intersection of the geometric pivot axis with the plane of the balance coincides with the center of mass of the balance.

The figure 1 also shows that the two elastic blades 12a, 12b or 14a, 14b which form the X have their junction point midway between their two ends. Simulations show in fact that the configuration in which the two blades of the X structure intersect in the middle, allows to obtain a clean rotation without friction around the geometric axis of pivoting. In addition, such a flexible pivot in X has the advantageous characteristic of producing a return torque proportional to the magnitude of the angle separating the balance from its equilibrium position, and this in one direction as in the other. It will also be noted that the expression “proper rotation” used above designates a rotation which minimizes the displacement of the pivot axis.

It will be assumed for the remainder of this description that the height of the blades corresponds to their extension perpendicular to the plane of the balance, while their thickness corresponds to their extension in the plane of the balance, perpendicular to their length. The thickness of the blades is preferably reduced so as to give the elastic blades sufficient flexibility in the plane of the balance. The height blades is determined so as to give them sufficient rigidity to contain the oscillations of the balance in the same determined plane. The two pairs of blades are preferably made of the same material. In addition, as shown in the figures, the two flexible pivots in X preferably have identical dimensions so that the first and the second pendulum have the same fundamental frequency of resonance when they have the same mass and the same moment of inertia.

The Figures 2A and 2B are enlarged partial views showing a second and a third variant configuration of the pair of elastic blades connecting one of the pendulums to the support structure of the resonator of the invention. By comparing the Figures 1, 2A and 2B , it can be observed in particular that these figures are distinguished by the value of the angle made between them by the two elastic blades from one of the flanges 4, 4 ′ or 4 ". figure 1 , this angle is substantially equal to 90 °, in the figure 2A , it is significantly less than 90 °, and finally in the figure 2B , it is significantly larger than 90 °. The angle at which the blades cross has an impact on the excitability of certain modes of oscillation out of plane of the pendulums. These higher modes are undesirable for most horological applications of the resonator of the invention. In practice, the angle between the elastic blades will be chosen according to the shape of the pendulums and the desired rigidities according to the different planes.

According to the invention, the resonator further comprises a flexible blade 16 which constitutes a strap arranged so as to couple the first and the second pendulum 6 and 8. The flexible blade is attached to the first and to the second pendulum, the junctions, respectively 16a and 16b, of the flexible blade with the first and the second pendulum are located in the same plane parallel to the plane of oscillation of the two pendulums and are symmetrical to each other with respect to the point central of the figure (referenced O). Always referring to the figure 1 , it can be seen that between the two junction points 16a and 16b, the shape of the blade 16 has a central symmetry around the central point O. It will however be understood that this characteristic is only present when the pendulums 6, 8 are in their rest position. As can be seen in the figure, the center of symmetry O is located halfway between the geometric pivot axes of the two pendulums.

The figure 1 also shows a straight line d which passes through the center O and through the junctions 16a, 16b of the flexible blade 16 with the two pendulums 6, 8. According to the invention, the straight line d makes an angle α of at least 30 ° , preferably at least 45 °, with the plane containing the first and the second geometric pivot axis.

According to the invention, the first and the second pendulum have the same fundamental resonance frequency. Due to the presence of the strap 16, when one of the pendulums deviates from its equilibrium position by pulling the strap after it, the other pendulum is forced to follow the movement by deviating from its position of balance the other way. In particular, with reference to the figure 1 , it can be understood that if the first balance 6 rotates clockwise, it exerts traction on the strap 16. The inertia of the strap being very low compared to that of the pendulums, the tension to which the strap is subjected affects the second balance 8 at the junction 16b. The second balance thus undergoes a torque which tends to rotate it counterclockwise. By thus deviating from their rest position, the two pendulums deform the elastic X-shaped blades 12a, 12b, 14a, 14b which connect them to the support structure (the flanges 2 and 4). The deformation of the two pairs of elastic blades generates two return couples which are exerted respectively on the first and the second balance. We can understand from the above that the presence of the strap 16 has the effect of synchronizing the oscillations of the two pendulums. It may also be noted in passing that the oscillations of the two pendulums coupled to the resonant frequency are said to be antisynchronous, and not simply synchronous, when the oscillations occur in an antisymmetric mode in accordance with what has just been described.

The figures 3 and 4 are perspective views of a timepiece resonator according to a second particular embodiment of the invention. As can be seen, the resonator illustrated in the figures 3 and 4 is very similar to the resonator of the figure 1 . However, in accordance with the second particular embodiment of the invention which is the subject of this example, the resonator comprises a pair of straps 116, 118 attached to each other at mid-length by a rigid coupling element. 120. The shoulder straps 116, 118 are also each attached to the first and to the second pendulum 6 and 8. On the figure 3 , one has designated one half of the strap 116, which extends between the first balance 6 and the coupling element 120, by the reference 116 ′, and the other half of the strap 116, which has been designated, has been designated extends between the coupling element and the second balance 8, by the reference 116 ". Similarly, a half of the strap 118, located between the first balance and the coupling element, has been designated by the reference 118 ', and the other half by the reference 118 ".

We can observe on the figure 3 in particular that, when the pendulums are in their rest position as illustrated, the straps 116, 118 are symmetrical to each other relatively, on the one hand, to the plane containing the first and second geometric pivot axes X ' and X ", and on the other hand, relative to a parallel mediating plane and equidistant from the two geometric pivot axes (the trace of the mediating plane in the plane of the pendulums is represented in the figure 3 by a broken line designated by the reference m).

Still referring to figures 3 and 4 , it can be observed that the pair of suspenders 116, 118 is mainly constituted by a first flexible blade attached to the first balance 6 by its two ends, and by a second flexible blade attached to the second balance 8 by its two ends. It can be seen that the two flexible blades are further connected to each other via the coupling element 120. The two flexible blades are connected to the coupling element in the middle, and it will be understood that in the construction shown, the two halves of the first flexible blade respectively constitute the half 116 'of the strap 116 and the half 118' of the strap 118. Similarly, the two halves of the second flexible blade respectively constitute the other half 116 "of strap 116 and the other half 118" of strap 118.

According to the illustrated embodiment, the coupling element 120 is rigid and it is arranged to rigidly connect a central portion of the first flexible blade and a central portion of the second flexible blade, so that these two central portions are kept spaced apart and parallel to each other. An advantage of the second embodiment which has just been described is its highly symmetrical character which gives even more stability to the antisymmetrical oscillation mode of the resonator. Another advantage is that the oscillations of the balance at resonance result in a back-and-forth movement of the rigid coupling element 120 according to a rectilinear trajectory in the plane of symmetry of the resonator (the mediator plane already mentioned) . The fact of having a part performing a back-and-forth along a rectilinear trajectory could in particular be used to associate an exhaust with the resonator.

In the example illustrated in figures 3 and 4 , the serge 10 of each pendulum 6, 8 is located on the lower side of the pendulum. She can however, alternatively, be located on the upper side or on both sides of the balance.

The resonator according to the invention can be produced in a single piece from silicon and / or silicon oxide, diamond, quartz or metal, for example. For this purpose, DRIE or LIGA type techniques can be used. The resonator according to the invention can also be obtained by an assembly of parts.

• les balanciers 6, 8 pourraient avoir une autre forme allongée que la forme d'une ellipse et pourraient aussi avoir une forme ronde, carrée, en aile de papillon ou autre. Les formes allongées sont toutefois préférées car elles permettent d'éloigner les points d'attache des bretelles 16, 116, 118 sur les balanciers 6, 8, ce qui facilite l'ajustement du couplage élastique entre lesdits balanciers ;
• au lieu de s'ouvrir en regard l'une de l'autre, les encoches des balanciers 6, 8 dans lesquelles se trouvent les brides 2, 4 et les lames élastiques 12a, 12b, 14a, 14b pourraient s'ouvrir vers l'extérieur des balanciers 6, 8 ou pourraient même être fermées ;
• l'orientation des brides 2, 4 et des lames élastiques 12a, 12b, 14a, 14b dans les encoches pourrait être différente de celle représentée. Par exemple l'une des brides 2, 4 ou les deux pourraient être tournées de plus ou moins 90° par rapport à leur position illustrée à la figure 1. Les orientations respectives des brides 2, 4 peuvent être identiques ou opposées ;
• au lieu d'être coplanaires et de se croiser physiquement comme dans les modes de réalisation illustrés, les lames élastiques 12a, 12b, 14a, 14b de chaque paire pourraient s'étendre dans deux plans parallèles différents pour former un pivot flexible de type « Wittrick ». Par rapport à un pivot flexible de type « Wittrick » le pivot flexible en X utilisé dans les modes de réalisation illustrés présente le désavantage d'un mouvement parasite plus important de l'axe géométrique de pivotement X', X" lors de la flexion, et de lames plus courtes dans lesquelles les concentrations de contraintes sont plus élevées. Par contre, la rigidité transversale des lames est bien plus élevée ce qui améliore la stabilité des balanciers 6, 8 dans leur plan de rotation et leur résistance aux chocs hors de leur plan de rotation ;
• d'autres types de pivot flexible qu'un pivot en X ou qu'un pivot « Wittrick » pourraient être utilisés pour relier chaque balancier 6, 8 à la structure de support 2, 4. De plus, le nombre de lames ou d'éléments élastiques formant chaque pivot flexible peut être supérieur à deux ou même égal à un.

It will further be understood that various modifications and / or improvements obvious to a person skilled in the art can be made to the embodiments which are the subject of the present description without departing from the scope of the present invention defined by the appended claims. In particular :

• the pendulums 6, 8 could have another elongated shape than the shape of an ellipse and could also have a round, square, butterfly wing or other shape. The elongated forms are however preferred since they allow the attachment points of the straps 16, 116, 118 to be moved away from the pendulums 6, 8, which facilitates the adjustment of the elastic coupling between said pendulums;
• instead of opening opposite one another, the notches of the pendulums 6, 8 in which the flanges 2, 4 are located and the elastic blades 12a, 12b, 14a, 14b could open towards the outside of the pendulums 6, 8 or could even be closed;
• the orientation of the flanges 2, 4 and the elastic blades 12a, 12b, 14a, 14b in the notches could be different from that shown. For example, one of the flanges 2, 4 or both could be turned more or less 90 ° relative to their position illustrated in the figure 1 . The respective orientations of the flanges 2, 4 may be identical or opposite;
• instead of being coplanar and physically crossing as in the illustrated embodiments, the elastic blades 12a, 12b, 14a, 14b of each pair could extend in two different parallel planes to form a flexible pivot of the “Wittrick” type " Compared to a flexible “Wittrick” type pivot, the flexible X pivot used in the illustrated embodiments has the disadvantage of a larger parasitic movement of the geometric pivot axis X ′, X ″ during bending, and shorter blades in which the stress concentrations are higher. On the other hand, the transverse rigidity of the blades is much higher which improves the stability of the pendulums 6, 8 in their plane of rotation and their resistance to shocks out of their rotation plane;
• other types of flexible pivot than an X-pivot or a “Wittrick” pivot could be used to connect each balance 6, 8 to the support structure 2, 4. In addition, the number of blades or elastic elements forming each flexible pivot can be greater than two or even equal to one.

Claims (10)

1. Resonator for a timepiece comprising a support structure (2, 4) intended to permit mounting of the resonator in a timepiece, a first and a second balance (6, 8) which are arranged to oscillate in the same plane, at least one first elastic element (12a, 12b) arranged to connect the first balance (6) to the support structure, at least one second elastic element (14a, 14b; 14a', 14b'; 14a", 14b") arranged to connect the second balance (8) to the support structure, the configuration of the elastic elements determining two parallel geometrical elastic pivoting axes (X', X") for the two balances, and the elastic elements forming elastic return means arranged to angularly return each of the balances towards a rest position, characterised

   - in that it further comprises a strap (16; 116, 118) arranged to couple the first and the second balance (6, 8), the strap being attached to the first and to the second balance, in that the points (16a, 16b) joining the strap respectively to the first and the second balance are located in the same plane parallel to the plane of oscillation of the balances, and in that, when the balances are in their rest position, on the one hand, said joining points are symmetrical with respect to a centre of symmetry (O) located half way between the two geometrical pivoting axes, and on the other hand, a radius connecting the centre of symmetry (O) to the point (16a, 16b) of joining to the first or the second balance, parallel to the plane of oscillation, forms an angle (a) of at least 30° with the plane containing the first and the second geometrical pivoting axis (X', X").
2. Resonator as claimed in claim 1, characterised in that when the balances are in their rest position, the shape of the strap is symmetrical with respect to said centre of symmetry (O).
3. Resonator as claimed in claim 1 or 2, characterised in that when the balances are in their rest position, a radius connecting the centre of symmetry (O) to the point (16a, 16b) of joining to the first or second balance, parallel to the plane of oscillation, forms an angle (a) of at least 45° with the plane containing the first and the second geometrical pivoting axis (X', X").
4. Resonator as claimed in any one of the preceding claims, characterised in that it comprises a pair of straps (116, 118) attached to each other mid-length and each attached to the first and to the second balance (6, 8), the pair of straps comprising said strap, and

   - in that, when the balances (6, 8) are in their rest position, the two straps (116, 118) of the pair of straps are symmetrical with respect to each other relative, on the one hand, to the plane containing the first and the second geometrical pivoting axis (X', X") and, on the other hand, relative to a parallel intermediate plane (m) equidistant from the two geometrical pivoting axes.
5. Resonator as claimed in claim 4, characterised in that the pair of straps (116, 118) comprises a first flexible strip attached to the first balance (6) by its two ends, a second flexible strip attached to the second balance (8) by its two ends, and a coupling element (120) arranged to rigidly connect a central portion of the first flexible strip and a central portion of the second flexible strip so that the central portions of the two flexible strips are held spaced apart from and parallel with each other.
6. Resonator as claimed in any one of claims 1 to 5, characterised in that the first and the second balance (6, 8) have an elongate shape.
7. Resonator as claimed in claim 6, characterised in that the distance between the geometrical pivoting axis (X', X") of a balance and the edge of the same balance is at least 1.5 times, preferably at least two times, greater in a direction perpendicular to the plane containing the two geometrical pivoting axes (X', X") than in a direction parallel to this plane.
8. Resonator as claimed in any one of the preceding claims, characterised in that the at least one first elastic element (12a, 12b) comprises a first pair of elastic strips which are parallel to the plane of pivoting of the balances (6, 8), the strips of the first pair (12a, 12b) being fixed to the support structure (2, 4) by one end and to the first balance (6) by the other end, and in that the at least one second elastic element (14a, 14b; 14a', 14b'; 14a", 14b") comprises a second pair of elastic strips which are parallel to the plane of pivoting of the balances (6, 8), the strips of the second pair (14a, 14b; 14a', 14b'; 14a", 14b") being fixed to the support structure (2, 4) by one end and to the second balance (8) by the other end, the two geometrical pivoting axes (X', X") of the two balances each crossing perpendicularly the two elastic strips of one of the pairs.
9. Resonator as claimed in claim 8, characterised in that the pair of elastic strips (12a, 12b, 14a, 14b) perpendicularly crossing the same geometrical pivoting axis (X', X") are contained in the same plane parallel to the plane of pivoting of the balances so that the two elastic strips of the same pair have an intersection at the place where they cross with the geometrical pivoting axis.
10. Resonator as claimed in claim 9, characterised in that the two elastic strips (12a, 12b, 14a, 14b) of the same pair intersect in their middle

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