EP3620867B1 - Timepiece comprising a mechanical oscillator whose average frequency is synchronised to that of a reference electronic oscillator - Google Patents

Description

Technical area

The present invention relates to a timepiece comprising a mechanical movement the rate of which is improved by a device for correcting a possible time drift in the operation of the mechanical oscillator which rates the rate of the mechanical movement. The timepiece comprises a mechanical oscillator, the average frequency of which is synchronized to a reference frequency determined by an auxiliary electronic oscillator.

• un mécanisme indicateur d'au moins une donnée temporelle,
• un résonateur mécanique susceptible d'osciller le long d'un axe général d'oscillation autour d'une position neutre correspondant à son état d'énergie potentielle minimale,
• un dispositif d'entretien du résonateur mécanique formant avec ce dernier un oscillateur mécanique qui est agencé pour cadencer la marche du mécanisme indicateur,

et, d'autre part, par un dispositif de synchronisation agencé pour asservir la fréquence moyenne de l'oscillateur mécanique sur une fréquence de consigne déterminée par une base de temps de référence.In particular, the timepiece is formed, on the one hand, by a mechanical movement comprising:

• a mechanism indicating at least one temporal datum,
• a mechanical resonator capable of oscillating along a general axis of oscillation around a neutral position corresponding to its state of minimum potential energy,
• a device for maintaining the mechanical resonator forming with the latter a mechanical oscillator which is arranged to rate the operation of the indicator mechanism,

and, on the other hand, by a synchronization device arranged to control the average frequency of the mechanical oscillator on a reference frequency determined by a reference time base.

Technological background

Timepieces as defined in the field of the invention have been proposed in some prior documents. The patent CH 597 636, published in 1977 , offers such a timepiece in reference to his figure 3 . The movement is equipped with a resonator formed by a sprung balance and a conventional maintenance device comprising an anchor and an escape wheel in kinematic connection with a barrel provided with a spring. This watch movement further comprises a device for regulating the frequency of its mechanical oscillator. This regulation device comprises an electronic circuit and an electromagnetic braking device formed of a flat coil, arranged on a support under the rim of the balance, and two magnets mounted on the balance and arranged close to each other of so that they both pass over the coil when the oscillator is activated.

The electronic circuit comprises a time base comprising a quartz resonator and serving to generate a reference frequency signal FR, this reference frequency being compared with the frequency FG of the mechanical oscillator. The detection of the FG frequency of the oscillator is carried out via the electrical signals generated in the coil by the pair of magnets. The comparison between the two frequencies FG and FR is carried out by a bidirectional counter receiving at its two inputs these two frequencies and providing at output a signal determining a difference of periods counted for the two frequencies. The electronic circuit further comprises a logic circuit which analyzes the output signal of the counter to control a brake pulse application circuit as a function of this output signal, so as to brake the balance when the logic circuit has detected a time drift corresponding to a value of the frequency FG of the oscillator greater than the reference frequency FR. The braking pulse application circuit is arranged to be able to generate a momentary braking torque on the balance wheel via an electromagnetic magnet-coil interaction and a switchable load connected to the coil.

The document US 2005/036405 describes a mechanical watch movement fitted with an electromagnetic frequency regulation system of oscillation of the mechanical resonator incorporated in this mechanical movement. This regulation system is of the closed loop type and it is suitable only for correcting the rate of the mechanical movement in the case where this rate is too fast, that is to say in the case where this mechanical movement becomes slow. advance. The control circuit determines whether the mechanical resonator oscillates with too high a frequency and, if so, then decreases this frequency by braking pulses applied to the balance wheel via the electromagnetic system.

The document FR 2 162 404 describes a mechanical movement and an electromechanical system designed to control the oscillation frequency of the mechanical resonator to a reference frequency supplied by an auxiliary quartz oscillator. The electromechanical system comprises a stop projecting from the rim of the balance and an actuator whose finger is briefly actuated periodically in the direction of the rim, at the set frequency, so as to allow the stop to abut against this finger in the as this stop passes through the fixed angular position of the finger when the latter is briefly in its position of possible interaction with the balance via the stop. The document EP 3 584 645 B1 explains in more detail, in its section 'Technological background', why the synchronization sought in the document FR 2 162 404 seems unlikely, and at least not sure.

Summary of the invention

An aim of the present invention is to simplify as much as possible the electronic circuit of a synchronization device arranged to control the average frequency of the mechanical oscillator of a mechanical movement on a reference frequency determined by an electronic oscillator. auxiliary, without losing precision in the operation of the timepiece equipped with such a synchronization device.

In the context of the present invention, it is generally sought to improve the accuracy of the rate of a mechanical watch movement, that is to say to reduce the maximum daily error of this mechanical movement and more generally to decrease very significantly a possible time drift over a longer period (for example a year). In particular, the present invention seeks to achieve such an aim for a mechanical watch movement the rate of which is initially adjusted to the best. Indeed, a general aim of the invention is to find a device for correcting the rate of a mechanical movement in the event that the natural functioning of this mechanical movement would lead to a certain daily error and consequently to an increasing time drift. (increasing cumulative error), without however renouncing that it can operate autonomously with the best precision that it is possible for it to have thanks to its own characteristics, that is to say in the absence of the correction device or when the latter is inactive.

To this end, the present invention relates to a timepiece as defined in independent claim 1 attached. Preferred embodiments are defined in the dependent claims.

Thanks to the characteristics of the invention, surprisingly, the mechanical oscillator of the horological movement is slaved to the auxiliary oscillator in an efficient and rapid manner, as will become clear from the detailed description of the invention which will follow. The oscillation frequency of the mechanical oscillator (slave mechanical oscillator) is synchronized to the setpoint frequency determined by the auxiliary oscillator (master oscillator), and this without closed-loop servo-control and without requiring a motion measurement sensor. oscillation of the mechanical oscillator. The synchronization device therefore operates in an open loop and it makes it possible to correct both an advance and a delay in the rate. of mechanical movement, as will be explained later. This result is quite remarkable.

By synchronization on a master oscillator we understand a slaving (open loop, therefore without feedback) of the mechanical oscillator slave to the master oscillator. The operation of the synchronization device is such that the frequency at which the time intervals intervene, where the impedance of the circuit connected to the two terminals of the coil is reduced, is imposed on the slave mechanical oscillator which rates the operation of the indicator mechanism of a temporal data. More generally, it is not even necessary that the succession of such distinct time intervals occur periodically at a given frequency, since it suffices that the beginnings (or, in an equivalent manner, the middle instants) of any two successive time intervals among these distinct time intervals have between them a time distance D _T as defined above, with a positive integer N which can vary over time. We are not here in the standard case of a forced oscillator, nor even in the situation of coupled oscillators.

In the present invention, the _{possible temporal distances D T} , for a predefined reference period T0c, determine the average frequency of the mechanical oscillator and therefore the timing of the operation of the mechanism. As the temporal distances are determined by a precise auxiliary oscillator, the average frequency is determined by this auxiliary oscillator so that the precision of the rate of the mechanism is in direct relation with that of the auxiliary oscillator. By 'timing the operation of a mechanism' is understood the fact of timing the movement of the movable elements of this mechanism when it is operating, in particular of determining the speeds of rotation of its wheels and thus of at least one indicator of a temporal datum.

In a main embodiment, the mechanical resonator is formed by a balance oscillating around an axis of oscillation, and the synchronization device is arranged so as to periodically trigger the distinct time intervals T _P , which have the same value. , and so that the trigger frequency F _D of these distinct time intervals is equal to twice a setpoint frequency F0c, equal by definition to the inverse of the setpoint period T0c, divided by a positive integer M, i.e. F _D = 2 · F0c / M, the value of the distinct time intervals T _P being less than the reference half-period, that is to say T _P <T0c / 2. In a preferred variant, the value of the distinct time intervals T _P is expected less than a quarter of the setpoint period T0c, i.e. T _P <T0c / 4.

Brief description of the figures

• La Figure 1 montre un premier mode de réalisation d'une pièce d'horlogerie selon l'invention,
• La Figure 2 est une vue partielle du premier mode de réalisation selon la Figure 1,
• La Figure 3 montre le schéma électronique d'une première variante du circuit de commande du dispositif de freinage électromagnétique selon l'invention,
• La Figure 4 montre le schéma électronique d'une deuxième variante du circuit de commande du dispositif de freinage électromagnétique selon l'invention,
• Les Figures 5A, 5B et 5C sont des graphes donnant l'évolution temporelle de divers paramètres physiques de l'oscillateur mécanique et du dispositif de synchronisation du premier mode de réalisation pour diverses relations entre la fréquence de consigne F0c et la fréquence naturelle F0 de l'oscillateur mécanique, respectivement F0 > F0c, F0 < F0c, F0 = F0c,
• La Figure 6 montre l'application d'une première impulsion de freinage à un résonateur mécanique dans une certaine alternance de son oscillation avant qu'il passe par sa position neutre, ainsi que la vitesse angulaire du balancier de ce résonateur mécanique et sa position angulaire dans un intervalle temporel au cours duquel intervient la première impulsion de freinage,
• La Figure 7 est une figure similaire à la Figure 6 mais pour l'application d'une deuxième impulsion de freinage dans une certaine alternance de l'oscillation d'un oscillateur mécanique après qu'il a passé par sa position neutre,
• Les Figures 8A, 8B et 8C montrent respectivement la position angulaire d'un balancier-spiral au cours d'une période d'oscillation, la variation de la marche du mouvement horloger obtenue pour une impulsion de freinage de durée fixe, pour trois valeurs d'un couple de freinage constant, en fonction de la position angulaire du balancier spiral, et la puissance de freinage correspondante,
• Les Figures 9, 10 et 11 montrent respectivement trois situations différentes pouvant intervenir dans une phase initiale suite à l'enclenchement du dispositif de correction dans une pièce d'horlogerie selon l'invention,
• La Figure 12 est un graphe explicatif du processus physique intervenant suite à l'enclenchement du dispositif de correction dans la pièce d'horlogerie selon l'invention et conduisant à la synchronisation voulue pour le cas où la fréquence naturelle de l'oscillateur mécanique esclave est supérieure à la fréquence de consigne,
• La Figure 13 représente, dans le cas de la Figure 12, une oscillation de l'oscillateur mécanique esclave et les impulsions de freinage dans une phase synchrone stable pour une variante où une impulsion de freinage intervient dans chaque alternance,
• La Figure 14 est un graphe explicatif du processus physique intervenant suite à l'enclenchement du dispositif de correction dans la pièce d'horlogerie selon l'invention et conduisant à la synchronisation voulue pour le cas où la fréquence naturelle de l'oscillateur mécanique esclave est inférieure à la fréquence de consigne,
• La Figure 15 représente, dans le cas de la Figure 14, une oscillation de l'oscillateur mécanique esclave et les impulsions de freinage dans une phase synchrone stable pour une variante où une impulsion de freinage intervient dans chaque alternance,
• Les Figures 16 et 17 donnent, respectivement pour les deux cas des Figures 12 et 14, le graphe de la position angulaire d'un oscillateur mécanique et les périodes d'oscillation correspondantes pour un mode de fonctionnement du dispositif de correction où une impulsion de freinage intervient toutes les quatre périodes d'oscillation,
• Les Figures 18 et 19 sont respectivement des agrandissements partiels des Figures 16 et 17,
• La Figure 20 représente, de manière similaire aux deux figures précédentes, une situation spécifique dans laquelle la fréquence d'un oscillateur mécanique est égale à la fréquence de freinage,
• La Figure 21 montre schématiquement l'oscillateur mécanique et le dispositif électromagnétique d'un deuxième mode de réalisation,
• La Figure 22 donne, dans le cadre du deuxième mode de réalisation, des graphes de l'évolution temporelle de la position angulaire de l'oscillateur mécanique, de la tension induite dans une bobine du dispositif électromagnétique en fonction d'un signal de commande de ce dispositif électromagnétique en régime stationnaire,
• La Figure 23 montre schématiquement l'oscillateur mécanique et le dispositif électromagnétique d'un troisième mode de réalisation,
• La Figure 24 donne, dans le cadre du troisième mode de réalisation, des graphes de l'évolution temporelle de la position angulaire de l'oscillateur mécanique, de la tension induite dans une bobine du dispositif électromagnétique en fonction d'un signal de commande de ce dispositif électromagnétique en régime stationnaire,
• La Figure 25 est similaire à la Figure 24 pour une variante de commande du dispositif électromagnétique dans le cadre du troisième mode de réalisation,
• La Figure 26 est une vue en coupe de l'oscillateur mécanique et du dispositif électromagnétique d'un quatrième mode de réalisation,
• La Figure 27 est coupe transversale, selon la ligne A-A de l'oscillateur mécanique et du dispositif électromagnétique de la Figure 26, et
• Les Figures 28A, 28B et 28C sont des graphes donnant l'évolution temporelle de divers paramètres physiques de l'oscillateur mécanique et du dispositif de synchronisation du quatrième mode de réalisation pour diverses relations entre la fréquence de consigne F0c et la fréquence naturelle F0 de l'oscillateur mécanique, respectivement F0 > F0c, F0 < F0c, F0 = F0c.

The invention will be described below in detail with the aid of the appended drawings, given by way of non-limiting examples, in which:

• The Figure 1 shows a first embodiment of a timepiece according to the invention,
• The Figure 2 is a partial view of the first embodiment according to Figure 1 ,
• The Figure 3 shows the electronic diagram of a first variant of the control circuit of the electromagnetic braking device according to the invention,
• The Figure 4 shows the electronic diagram of a second variant of the control circuit of the electromagnetic braking device according to the invention,
• The Figures 5A , 5B and 5C are graphs giving the temporal evolution of various physical parameters of the mechanical oscillator and of the synchronization device of the first embodiment for various relationships between the setpoint frequency F0c and the natural frequency F0 of the mechanical oscillator, respectively F0> F0c, F0 <F0c, F0 = F0c,
• The Figure 6 shows the application of a first braking pulse to a mechanical resonator in a certain alternation of its oscillation before it passes through its neutral position, as well as the angular speed of the balance of this mechanical resonator and its angular position in an interval time during which the first braking pulse occurs,
• The Figure 7 is a figure similar to the Figure 6 but for the application of a second braking pulse in a certain alternation of the oscillation of a mechanical oscillator after it has passed through its neutral position,
• The Figures 8A, 8B and 8C respectively show the angular position of a sprung balance during a period of oscillation, the variation in the rate of the watch movement obtained for a braking pulse of fixed duration, for three values of a constant braking torque, depending on the angular position of the spiral balance, and the corresponding braking power,
• The Figures 9 , 10 and 11 respectively show three different situations that may occur in an initial phase following the engagement of the correction device in a timepiece according to the invention,
• The Figure 12 is an explanatory graph of the physical process occurring following the engagement of the correction device in the timepiece according to the invention and leading to the desired synchronization for the case where the natural frequency of the slave mechanical oscillator is greater than the setpoint frequency,
• The Figure 13 represents, in the case of Figure 12 , an oscillation of the slave mechanical oscillator and the braking pulses in a stable synchronous phase for a variant where a braking pulse occurs in each alternation,
• The Figure 14 is an explanatory graph of the physical process occurring following the engagement of the correction device in the timepiece according to the invention and leading to the desired synchronization for the case where the natural frequency of the slave mechanical oscillator is lower than the setpoint frequency,
• The Figure 15 represents, in the case of Figure 14 , an oscillation of the slave mechanical oscillator and the braking pulses in a stable synchronous phase for a variant where a braking pulse occurs in each alternation,
• The Figures 16 and 17 give, respectively for the two cases Figures 12 and 14 , the graph of the angular position of a mechanical oscillator and the corresponding oscillation periods for an operating mode of the correction device where a braking pulse occurs every four oscillation periods,
• The Figures 18 and 19 are respectively partial enlargements of the Figures 16 and 17 ,
• The Figure 20 represents, similarly to the two previous figures, a specific situation in which the frequency of a mechanical oscillator is equal to the braking frequency,
• The Figure 21 schematically shows the mechanical oscillator and the electromagnetic device of a second embodiment,
• The Figure 22 gives, within the framework of the second embodiment, graphs of the temporal evolution of the angular position of the mechanical oscillator, of the voltage induced in a coil of the electromagnetic device as a function of a control signal of this electromagnetic device in steady state,
• The Figure 23 schematically shows the mechanical oscillator and the electromagnetic device of a third embodiment,
• The Figure 24 gives, in the context of the third embodiment, graphs of the temporal evolution of the angular position of the mechanical oscillator, of the voltage induced in a coil of the electromagnetic device as a function of a control signal of this electromagnetic device in steady state,
• The Figure 25 is similar to Figure 24 for a control variant of the electromagnetic device in the context of the third embodiment,
• The Figure 26 is a sectional view of the mechanical oscillator and the electromagnetic device of a fourth embodiment,
• The Figure 27 is cross section, along line AA of the mechanical oscillator and the electromagnetic device of the Figure 26 , and
• The Figures 28A , 28B and 28C are graphs giving the temporal evolution of various physical parameters of the mechanical oscillator and of the synchronization device of the fourth embodiment for various relations between the reference frequency F0c and the natural frequency F0 of the mechanical oscillator, respectively F0> F0c, F0 <F0c, F0 = F0c.

Detailed description of the invention

A first embodiment of a timepiece according to the invention will be described with reference to Figures 1 to 4 and 5A to 5C . To the Figure 1 is shown, in part schematically, a timepiece 2 comprising a mechanical movement 4 which comprises at least one mechanism 12 indicating time data. The mechanism 12 comprises a cog 16 driven by a barrel 14 (the mechanism is shown partially on the Figure 1 ). The mechanical movement further comprises a mechanical resonator 6, formed by a balance 8 and a hairspring 10, which is arranged on a plate 5 defining a support for the mechanical resonator, and a device for maintaining this mechanical resonator which is formed by an escapement. 18, this maintenance device forming with the mechanical resonator a mechanical oscillator which rates the operation of the indicator mechanism. The escapement 18 conventionally comprises an anchor and an escape wheel, the latter being kinematically connected to the barrel via the gear 16. The mechanical resonator is capable of oscillating around a neutral position (position rest / zero angular position) corresponding to its state of minimum potential energy, along a circular axis (the radius of this axis is irrelevant since the position of the balance along this axis is given by an angle). The circular axis defines a general axis of oscillation which indicates the nature of the movement of the mechanical resonator, which may for example be linear in another embodiment.

Each oscillation of the mechanical resonator defines an oscillation period which is formed by two alternations, each between two extreme angular positions of the oscillation and with a rotation in the opposite direction of the other. When the mechanical resonator reaches an extreme angular position, defining the oscillation amplitude, its speed of rotation is zero and the direction of rotation is reversed. Each half-cycle has two half-cycles (the duration of which may be different depending on disturbing events), i.e. a first half-cycle occurring before the mechanical resonator passes through its neutral position and a second half-cycle occurring after this passage through the neutral position.

The timepiece 2 comprises a device 20 for synchronizing the mechanical oscillator, formed by the mechanical resonator 6 and the escapement 18, on a reference time base 22 constituted by an auxiliary oscillator which comprises a quartz resonator 35 and a clock circuit 36 maintaining the quartz resonator and delivering a reference frequency signal S _R. The crystal oscillator defines a master oscillator. The reference time base is associated with the control device 24 of the synchronization device to which it supplies the signal S _R. It will be noted that other types of auxiliary oscillators can be provided, in particular an oscillator integrated entirely into an electronic circuit with the control circuit. Generally, the auxiliary oscillator is by nature or by construction more precise than the mechanical oscillator arranged in the watch movement, this mechanical oscillator defining an oscillator slave in the context of the invention. In general, as will be understood below, the synchronization device 20 is arranged to control the average frequency of the mechanical oscillator to a reference frequency determined by the auxiliary oscillator.

Then, the synchronization device 20 comprises an electromagnetic braking device 26 of the mechanical resonator 6. By 'electromagnetic braking' is understood a braking of the mechanical resonator generated via an electromagnetic interaction between at least one permanent magnet, carried by the mechanical resonator or a support of this mechanical resonator, and at least one coil carried respectively by the support or the mechanical resonator and associated with an electronic circuit in which a current induced in the coil by the magnet can be generated. In general, the electromagnetic braking device is thus formed of at least one coil 28 and at least one permanent magnet which are arranged so that an induced voltage is generated between the two terminals 28A, 28B of the coil 28 in each alternation of the oscillation of the mechanical resonator for a useful operating range of the mechanical oscillator. The coil 28 is of the wafer type (disc having a height less than its diameter), without a ferromagnetic core. In the first embodiment, there is provided a plurality of bipolar magnets 30, 32 which are arranged juxtaposed on the rim 9 of the balance with an alternation of the magnetic polarities in the direction of the axis of oscillation 34. In an equivalent variant, there is provided an annular magnet having an axial magnetization with successive sectors corresponding to the bipolar magnets 30, 32, these successive sectors having alternating polarities and each defining an angle at the center (an angular 'opening') having substantially a same value. In the variant shown, the bipolar magnets 30, 32 define eight magnetized annular sectors each having an angular distance of 45 ° with alternating magnetic polarities. In the case of the first embodiment, there is an even number 2N of magnetized annular sectors, N being a positive integer, these sectors being arranged in a circular manner, in particular on the rim 9 of the balance 8 forming the mechanical resonator 6.

The coil 28 is arranged on the plate 5 so as to be traversed by the magnetic flux of the bipolar magnets / magnetized annular sectors when the balance oscillates. Advantageously, the diameter of the coil 28 is provided so that it is substantially included in an angular opening, relative to the axis of oscillation, which is substantially equal to that defined by each bipolar magnet / magnetized annular sector. However, in other variants, the diameter of the coil 28 can be made larger and have for example an angular opening corresponding to substantially twice that of a magnetized annular sector. In addition, in another variant, there is provided a plurality of wafer coils having between them, taken in pairs, an angular offset corresponding to an integer number of magnetic periods (a magnetic period being given by the angular distance of two annular sectors adjacent magnets). These coils thus not exhibiting any electromagnetic phase shift (that is to say that the phase shifts are integer multiples of 360 °), the voltages induced in these coils each have an identical time variation and simultaneous with the others, so that these induced voltages add up. The plurality of coils can be arranged in series or in parallel. The number of magnetized annular sectors, the number of coils and their characteristic dimensions are selected as a function of the strength of the electromagnetic interaction desired to allow the desired servo-control of the mechanical oscillator.

According to the invention, the synchronization device is designed to be able to temporarily reduce the impedance between the two terminals of the coil. According to a general synchronization mode implemented in the synchronization device of the invention, the latter is arranged so as to reduce the impedance between the two terminals of the coil during distinct time intervals T _P and so that the respective beginnings of any two successive time intervals, among these distinct time intervals, have between them a time distance D _T equal to a positive whole number N multiplied by half of a set period T0c (that is to say by a reference half-period) for the mechanical oscillator, _{i.e. D T} = N · T0c / 2. The synchronization device is arranged to determine by means of the reference time base 22 the start of each of the distinct time intervals so as to satisfy the aforementioned mathematical relationship between the time distance D _T and the reference period T0c.

In the embodiments described, the mechanical resonator is formed by a balance rotating around an axis of oscillation. In the synchronization modes implemented in the synchronization devices which are shown in Figures 5A to 5C and 28A to 28C , provision is made to periodically trigger the distinct time intervals T _P during which the impedance between the terminals of the coil is reduced, that is to say that these time intervals are provided with a time distance T _D between them that is constant. The tripping frequency F _D of these distinct time intervals is equal to twice the setpoint frequency F0c, equal by definition to the inverse of the setpoint period T0c, divided by a positive integer M, _{i.e. F D} = 2F0c / M. Next, preferably, the distinct time intervals T _P have the same value which is expected to be less than the reference half-period, ie T _P <T0c / 2. Finally, the synchronization device is arranged so as to generate a short-circuit between the two terminals 28A and 28B of the coil 28 during the distinct time intervals T _{P in order} to reduce the impedance between the two terminals of this coil.

In the variant of the first embodiment described using the Figures 5A to 5C , the integer M is equal to two (M = 2), so that the tripping frequency F _D is equal to the setpoint frequency F0c and the _{successive time distances T D} are equal to the period of setpoint T0c. Then, the value of the distinct time intervals T _P is advantageously less than a quarter of the reference period T0c, ie T _P <T0c / 4. In this first embodiment, as can be seen in Figures 5A to 5C , the electromagnetic braking device 26 is arranged so that an induced voltage is generated in the coil 28 substantially without interruption for any oscillation of the mechanical resonator 6 in the useful operating range of the mechanical oscillator formed by this mechanical resonator.

Before considering in more detail the Figures 5A to 5C , the behavior of a mechanical oscillator subjected to short duration braking pulses will first be summarized here, although a more detailed discussion on this subject will be given later. It has been observed that, when the braking pulse is generated between the start of an alternation and the passage of the resonator through its neutral position in this alternation, such a braking pulse induces a negative time phase shift in the oscillation of the resonator. Thus, the duration of the alternation concerned is increased relative to the duration T0 / 2 of an alternation during the natural oscillation of the mechanical oscillator. This therefore generates a punctual reduction in the frequency of the mechanical oscillator and makes it possible to generate a certain delay in the operation of the timepiece in order to correct, if necessary, an advance taken by this mechanical oscillator. On the other hand, when the braking pulse is generated between the passage of the resonator through its neutral position in one half-wave and the end of this half-wave, such a braking pulse induces a positive time phase shift in the oscillation of the resonator. Thus, the duration of the alternation concerned is reduced relative to the duration T0 / 2 of an alternation during the natural oscillation of the mechanical oscillator. This therefore generates a one-off increase in the frequency of the mechanical oscillator and makes it possible to generate a certain advance in the operation of the timepiece in order to correct, if necessary, a delay taken by this mechanical oscillator.

To Figures 5A to 5C are shown, in a stable phase of the synchronization obtained by the synchronization device according to the invention, the curves of the angular position and of the angular speed of the sprung balance 6 as well as a digital control signal Sc generated in the circuit control 24 and supplied to a switch 40 arranged to short-circuit the two terminals 28A, 28B of coil 28 (see Figures 3 and 4 ) during pulses 58 which define the distinct time intervals T _P. In addition, in these figures are shown a signal of the voltage induced in the coil 28, resulting from the oscillation of the mechanical resonator 6 and short-circuit pulses 58, and a signal of the braking torque applied to the mechanical resonator during short circuit pulses. It will be noted that the stable phase represented here occurs following a transient phase (initial phase) which will be described below. Remarkably, during the stable phase, also called synchronous phase, the oscillation frequency of the mechanical resonator is slaved to the reference frequency F0c and the first and second parts T _B and T _A of the short-circuit pulses 58 exhibit a substantially constant and defined ratio. In this stable phase, the synchronization device automatically stabilizes, without a sensor measuring a parameter of the oscillation of the mechanical resonator 6 and without a feedback loop, the oscillation frequency of this mechanical resonator at the setpoint frequency F0c.

The Figure 5A corresponds to a situation where the natural frequency F0 of the mechanical oscillator of the timepiece is greater than the setpoint frequency F0c, so that this timepiece without the synchronization device would exhibit a positive time drift corresponding to a advance in the march of the timepiece. It is observed that the short-circuit pulses 58 intervene around an extreme angular position, that is to say that the distinct time intervals T _P include a reversal of the direction of the oscillation movement which occurs between an alternation A2 and an alternation A1 of the oscillation while the speed of rotation (angular speed) is zero. The oscillation periods are equal to the reference period T0c, but it is noted that the two vibrations A1 and A2 which constitute each oscillation period are not equal. In fact, the alternation A1 lasts here longer than the alternation A2, because more braking occurs in the alternation A1, before the passage of the mechanical resonator through its neutral position (angle 0 °), than in the alternation A2 after the mechanical resonator has passed through its neutral position. It will be noted that no braking torque is applied to the mechanical resonator neither after the passage of the mechanical resonator through its neutral position in the half-wave A1, nor before the passage of the mechanical resonator through its neutral position in the half-wave A2.

The braking pulse is formed by two small lobes 50 located respectively on each side of the instant of passage of the mechanical resonator through the extreme angular position, exhibiting central symmetry relative to this instant (the opposite mathematical signs of the two lobes 50 originates from the change of direction in the oscillation movement), and from a lobe 52 of greater amplitude which intervenes in the alternation A1 of each period of oscillation, in the first half-wave before the passage of the mechanical resonator through its neutral position. The effects of the two lobes 50 are compensated for and therefore generally do not generate any phase shift in the oscillation of the mechanical resonator, while the braking torque caused by the lobe 52 in each alternation A1 causes an increase in the duration of the latter, so that the duration of the oscillation period concerned is equal to that of the reference period T0c. The instantaneous oscillation frequency is thus equal to the reference frequency F0c which is, as indicated, lower than the natural frequency F0 of the mechanical oscillator. The appearance of the lobe 52 only in the halfwaves A1 results from the fact that the mid-instants of the short-circuit pulses 58 occur with a certain delay relative to the passages of the mechanical resonator through a position extreme angular, this resulting from the fact that the natural frequency F0 of the mechanical oscillator is greater than the reference frequency F0c. In fact, the part T _B of the pulses 58 occurring before the passage of the mechanical resonator through an extreme position is less than the part T _A of the pulses 58 occurring after this passage.

The Figure 5B corresponds to a situation where the natural frequency F0 of the mechanical oscillator of the timepiece is lower than the setpoint frequency F0c, so that this timepiece without the synchronization device would exhibit a negative time drift corresponding to a delay in the progress of the timepiece. It is also observed that the short-circuit pulses 58 occur around an extreme angular position and that the alternation A1 lasts longer than the alternation A2, because a greater braking occurs in the alternation A2, here after the passage of the mechanical resonator by its neutral position (angle 0 °), than in the alternation A1 before the passage of the mechanical resonator through its neutral position. As in the previous situation, no braking torque is applied to the mechanical resonator neither after the passage of the mechanical resonator through its neutral position in the half-wave A1, nor before the passage of the mechanical resonator through its neutral position in the half-wave A2 . The braking pulse is here formed of two small lobes 50 located respectively on each side of the extreme angular position and of a lobe 54 of greater amplitude which occurs in the alternation A2 of each oscillation period, in the second half-wave after the mechanical resonator has passed through its neutral position.

The effects of the two lobes 50 are always compensated for, while the braking torque caused by the lobe 54 in each alternation A2 causes a reduction in the duration of the latter, so that the duration of the period of oscillation concerned is equal to that of the setpoint period T0c. The instantaneous oscillation frequency is thus equal to the reference frequency F0c which is, as indicated, greater than the natural frequency F0 of the mechanical oscillator. The appearance of the lobe 54 only in the alternations A2 results from the fact that the mid-instants of the short-circuit pulses 58 occur here with a certain advance relative to the passages of the mechanical resonator through an extreme angular position, this resulting from the fact that the frequency natural F0 of the mechanical oscillator is lower than the reference frequency F0c. In fact, the part T _A of the pulses 58 occurring after the passage of the mechanical resonator through an extreme position is less than the part T _B of the pulses 58 occurring before this passage.

For the sake of completeness, we have shown Figure 5C a situation where the natural frequency F0 of the mechanical oscillator of the timepiece is equal to the setpoint frequency F0c. It follows from this situation that the part T _A of the pulses 58 occurring after the passage of the mechanical resonator through an extreme angular position is equal to the part T _B of the pulses 58 occurring before this passage, so that the parts 50A of the braking pulses intervening in the halfwaves A2 just before the passage of the mechanical resonator through an extreme position have the same profile, with an opposite mathematical sign, that the parts 50B of the braking pulses intervening in the halfwaves A1 just after this passage and thus have a central symmetry relative to the instant of passage through the extreme angular position concerned. Consequently, the effects of the parts 50A and 50B of the braking pulses occurring during the short of each short-circuit pulse 58, and therefore of each separate time interval T _P , compensate each other so that, in this particular case, the synchronization device does not influence the operation of the timepiece, which is precise insofar as it is naturally synchronous with the reference time base 22.

The Figure 3 is a diagram which shows a first variant embodiment 24A of the control circuit 24 of the synchronization device 20. The control circuit 24A is connected on the one hand to the clock circuit 36 and, on the other hand, to the coil 28. The clock circuit maintains the quartz resonator 35 and in return generates a clock signal S _R at a reference frequency, in particular equal to 2 ¹⁵ Hz. The signal d The clock S _R is supplied successively to two dividers DIV1 and DIV2 (these two dividers being able to form two stages of the same divider). Divider DIV2 supplies a periodic signal S _D directly to a timer 38 ('Timer'). On each detection of a characteristic transition in the periodic signal S _D , the timer turns on the switch 40 during a time interval T _P , to short-circuit the coil 28, by supplying it with a control signal Sc, having a trigger frequency F _D identical to that of the periodic signal S _D , which periodically triggers the timer 38. Since the duration of the braking pulses (corresponding to that of the short-circuit pulses) is provided here preferably less than T0c / 4 ( for example T0 _c = 250 ms) and even much lower than this value in the case considered, in particular between 10 ms and 30 ms, the timer 38 receives a timing signal from the divider DIV1.

For example, in the case of a reference frequency F0c = 4 Hz and a tripping frequency F _D equal to this reference frequency, as in the example given in Figures 5A to 5C , the divider DIV2 directly supplies trigger pulses to the timer at the frequency F _D = 4 Hz. If it is intended to provide a short-circuit pulse every second, that is to say every four periods of oscillation , and thus to have a temporal distance D _T = 1 s between the distinct time intervals T _P where the impedance between the terminals 28A and 28B of the coil is reduced, then we can use the terminal output of a divider circuit classic watchmaker who supplies, at the output of the terminal stage of his division by two chain, a periodic signal at a frequency of 1 Hz. For a triggering frequency F _D = 4 Hz mentioned above, it is also possible to use a conventional clockwork divider circuit, but taking as output the signal supplied two stages before the terminal output in the division chain. It will be noted that the control circuit 24A of the synchronization device is very simple. It can be miniaturized easily and its power consumption is very low. No microcontroller is needed.

It will be noted that in a particular mode of synchronization, provision can be made to generate the short-circuit pulses in groups, for example a succession of sequences with four pulses in four successive oscillation periods then no pulse for ten seconds, i.e. for forty periods for a frequency F0c = 4 Hz. In another synchronization mode, provision can be made to vary the time intervals T _P (therefore the duration of the short-circuit pulses), for example by providing a longer duration in a phase initial, to generate a greater braking torque, than in a nominal speed which follows it. It will be noted that the synchronization method is robust. For example, it is not necessary for the time intervals T _{P to} be measured precisely, that is to say with as much precision as the time distances D _T between the beginnings of these time intervals. Thus, one could provide a timer with its own timing circuit, less precise than the reference time base 22.

In a second variant embodiment 24B, shown in Figure 4 , of the control circuit 24 of the synchronization device 20, the dividers DIV1 and DIV2 together form a conventional clockwork divider circuit which therefore provides at output a periodic signal S _D having a frequency equal to 1 Hz. This signal S _D is supplied to a counter at N which defines an additional divider, which generates the periodic signal S _{P which} it supplies to the timer 38. The control signal Sc supplied by the timer to the switch 40 has a frequency of trigger F _D equal to that of the periodic signal S _P. Thus, in an example where the reference frequency F0c of the mechanical oscillator is equal to 4 Hz (F0c = 4 Hz) and the number N is equal to eight, the trigger frequency F _D of the periodic signals S _P and Sc is then 1/8 Hz, which means that there is a braking pulse (short-circuit pulse) per 32 setpoint periods T0c, i.e. about one pulse after 32 periods of the mechanical oscillator insofar as its natural frequency F0 is expected to be close to the reference frequency F0c.

To the Figure 4 , the synchronization device further comprises a power supply device 44 formed by a rectifier circuit 46 (of the single or full-wave type) and by a storage capacitor C _AL connected to ground (reference potential of the synchronization device). The rectifier circuit is constantly connected at the input to a terminal of the coil so that apart from the short-circuit pulses it can rectify a voltage induced in the coil 28 by the permanent magnets 30, 32. This induced voltage, rectified and accumulated in the storage capacity, is used for the power supply of the synchronization device in the useful operating range of the mechanical oscillator. The control circuit 24B of the synchronization device is very simple and autonomous. It consumes little and takes a minimum of energy from the mechanical oscillator to efficiently perform the synchronization according to the invention.

Hereinafter, with reference to Figures 6 and 7 , a remarkable physical phenomenon brought to light in the context of developments which led to the present invention and which intervenes in the synchronization method implemented in the timepiece according to the invention. Understanding this phenomenon will make it possible to better understand the synchronization obtained by the synchronization device regulating the rate of the mechanical movement.

To Figures 6 and 7 , the first graph indicates the instant t _{P1 at} which a braking pulse P1, respectively P2 is applied to the mechanical resonator considered in order to correct the rate of the mechanism which is clocked by the mechanical oscillator formed by this resonator. The last two graphs show respectively the angular velocity (values in radians per second: [rad / s]) and the angular position (values in radians: [rad]) of the oscillating member (subsequently also 'the balance ') of the mechanical resonator over time. The curves 90 and 92 correspond respectively to the angular speed and to the angular position of the freely oscillating balance (oscillation at its natural frequency) before the intervention of a braking pulse. After the braking pulse, the speed curves 90a and 90b are shown corresponding to the behavior of the resonator respectively in the case disturbed by the braking pulse and in the undisturbed case. Likewise, the position curves 92a and 92b correspond to the behavior of the resonator respectively in the case disturbed by the braking pulse and the undisturbed case. In the figures, the instants t _P1 and t _{P2 at} which the braking pulses P1 and P2 intervene correspond to the temporal positions of the middle of these pulses. However, the start of the braking pulse and its duration are considered as the two parameters which temporally define a braking pulse.

By braking pulse, one understands the momentary application of a torque of force to the mechanical resonator which brakes its oscillating member (balance), that is to say which opposes the oscillating movement of this oscillating member. In the case of a non-zero torque which is variable, the duration of the pulse is generally defined as the part of this pulse which presents a significant force torque to brake the mechanical resonator. It will be noted that a braking pulse can exhibit a strong variation. It can even be chopped and form a succession of shorter pulses.

Each period of free oscillation T0 of the mechanical oscillator defines a first half-wave A0 ¹ followed by a second ^{half-wave A0 2} each occurring between two extreme positions defining the amplitude of oscillation of this mechanical oscillator, each half-wave having an identical duration T0 / 2 and having a passage of the mechanical resonator through its zero position at a median instant. The two successive alternations of an oscillation define two half-periods during which the balance respectively undergoes an oscillating movement in one direction and then an oscillating movement in the other direction. In other words, an alternation corresponds here to a swing of the balance in one direction or the other direction between its two extreme positions defining the amplitude of oscillation. In general, there is a variation in the oscillation period during which a braking pulse occurs and therefore a punctual variation in the frequency of the mechanical oscillator. In fact, the temporal variation concerns the only half-wave during which the braking pulse occurs. By median instant ', we understand an instant occurring substantially in the middle of the alternations. This is precisely the case when the mechanical oscillator oscillates freely. On the other hand, for the half-waves in which regulation pulses intervene, this median instant no longer corresponds exactly to the middle of the duration of each of these half-waves due to the disturbance of the mechanical oscillator generated by the regulation device.

We will first describe the behavior of the mechanical oscillator in a first case of correction of its oscillation frequency, which corresponds to that shown in Figure 6 . After a first period T0 then begins a new period T1, respectively a new alternation A1 during which a braking pulse P1 occurs. At the initial instant t _D1 the alternation A1 begins, the resonator 14 occupying a maximum positive angular position corresponding to an extreme position. Then the braking pulse P1 intervenes at the instant t _P1 which is situated before the median instant t _{N1 at} which the resonator passes through its neutral position and therefore also before the corresponding median instant t _N0 of the undisturbed oscillation. Finally, the alternation A1 ends at the final instant t _F1 . The braking pulse is triggered after a time interval T _A1 following the instant t _D1 marking the start of the alternation A1. The duration T _A1 is less than one half-wave T0 / 4 minus the duration of the pulse of braking P1. In the example given, the duration of this braking pulse is much less than one half-wave T0 / 4.

In this first case, the braking pulse is therefore generated between the start of a half-wave and the passage of the resonator through its neutral position in this half-wave. The angular speed in absolute value decreases at the moment of the braking pulse P1. Such a braking pulse induces a negative time phase shift T _C1 in the oscillation of the resonator, as shown in Figure 6 the two curves 90a and 90b of the angular speed and also the two curves 92a and 92b of the angular position, that is to say a delay relative to the theoretical undisturbed signal (shown in broken lines). Thus, the duration of the alternation A1 is increased by a time interval T _C1 . The oscillation period T1, comprising the alternation A1, is therefore prolonged relative to the value T0. This generates a punctual reduction in the frequency of the mechanical oscillator and a momentary slowing down of the associated mechanism, the operation of which is clocked by this mechanical oscillator.

With reference to the Figure 7 , the behavior of the mechanical oscillator will be described below in a second case of correction of its oscillation frequency. After a first period T0 then begins a new period of oscillation T2, respectively an alternation A2 during which a braking pulse P2 occurs. At the initial instant t _D2 the alternation A2 begins, the mechanical resonator then being in an extreme position (maximum negative angular position). After a quarter of a period T0 / 4 corresponding to a half-wave, the resonator reaches its neutral position at the median instant t _N2 . Then comes the braking pulse P2 at the instant t _P2 which is located in the halfwave A2 after the median instant t _{N2 at} which the resonator passes through its neutral position. Finally, after the braking pulse P2, this alternation A2 ends at the final instant t _{F2 at} which the resonator again occupies an extreme position (maximum positive angular position in the period T2) and therefore also before the final instant corresponding t _F0 of the undisturbed oscillation. The braking pulse is triggered after a time interval T _A2 following the initial instant t _D2 of the alternation A2. The duration T _A2 is greater than one half-wave T0 / 4 and less than one half-wave T0 / 2 reduced by the duration of the braking pulse P2. In the example given, the duration of this braking pulse is much less than half a wave.

In the second case considered, the braking pulse is therefore generated, in an alternation, between the median instant at which the resonator passes through its neutral position (zero position) and the final instant at which this alternation ends. The angular speed in absolute value decreases at the moment of the braking pulse P2. Remarkably, the braking pulse here induces a positive time phase shift T _C2 in the oscillation of the resonator, as shown in Figure 4 the two curves 90b and 90c of the angular speed and also the curves 92b and 92c of the angular position, ie an advance relative to the theoretical undisturbed signal (shown in broken lines). Thus, the duration of the alternation A2 is reduced by the time interval T _C2 . The oscillation period T2 including the alternation A2 is therefore shorter than the value T0. This consequently generates a punctual increase in the frequency of the mechanical oscillator and a momentary acceleration of the associated mechanism, the operation of which is clocked by this mechanical oscillator. This phenomenon is surprising and not intuitive, which is why those skilled in the art have ignored it in the past. Indeed, obtaining an acceleration of the mechanism by a braking pulse is a priori astonishing, but such is the case when this rate is clocked by a mechanical oscillator and the braking pulse is applied to its resonator.

The aforementioned physical phenomenon for mechanical oscillators occurs in the synchronization method implemented in a timepiece according to the invention. Unlike general education in the watchmaking field, it is not only possible to reduce the frequency of a mechanical oscillator by braking pulses, but it is also possible to increase the frequency of such a mechanical oscillator also by braking pulses. Those skilled in the art expects to be able to reduce the frequency of a mechanical oscillator practically only by braking pulses and, as a corollary, to be able only to be able to increase the frequency of such a mechanical oscillator by the application of driving pulses. when energy is supplied to this oscillator. Such an intuition, which has prevailed in the watchmaking field and therefore comes first on board in the mind of a person skilled in the art, turns out to be false for a mechanical oscillator. Thus, as will be explained in detail below, it is possible to synchronize, via an auxiliary oscillator defining a master oscillator, a mechanical oscillator which is moreover very precise, whether it momentarily presents a frequency that is slightly too high or too low. It is therefore possible to correct too high a frequency or too low a frequency only by means of braking pulses. In summary, the application of a braking torque during an alternation of the oscillation of a sprung balance causes a negative or positive phase shift in the oscillation of this sprung balance depending on whether this braking torque is applied respectively before or after the sprung balance has passed through its neutral position.

The synchronization method resulting from the correction device incorporated in a timepiece according to the invention is described below. To the Figure 8A is shown the angular position (in degrees) of a mechanical clock resonator oscillating with an amplitude of 300 ° during an oscillation period of 250 ms. To the Figure 8B is shown the daily error generated by braking pulses of one millisecond (1 ms) applied in successive oscillation periods of the mechanical resonator as a function of the instant of their application within these periods and therefore in function of the angular position of the mechanical resonator. Here, we start from the fact that the mechanical oscillator works freely at a natural frequency of 4 Hz (undisturbed case). Three curves are given respectively for three pairs of force (100 nNm, 300 nNm and 500 nNm) applied by each braking pulse. The result confirms the physical phenomenon explained previously, namely that a braking pulse occurring in the first quarter of a period or the third quarter of a period generates a delay resulting from a decrease in the frequency of the mechanical oscillator, whereas a braking pulse occurring in the second quarter of a period or the fourth quarter of a period generates an advance originating from an increase in the frequency of the mechanical oscillator. Then, it is observed that, for a given torque of force, the daily error is equal to zero for a braking pulse occurring at the neutral position of the resonator, this daily error increasing (in absolute value) as we increase approaching an extreme position of the oscillation. At this extreme position where the speed of the resonator passes through zero and where the direction of movement changes, there is a sudden reversal of the sign of the daily error. Finally, at the Figure 8C The braking power consumed for the three above-mentioned force torque values is given as a function of the instant of application of the braking pulse during a period of oscillation. As the speed decreases as it approaches the extreme positions of the resonator, the braking power decreases. Thus, while the daily error generated increases as it approaches extreme positions, the braking power required (and therefore the energy lost by the oscillator) decreases significantly.

The error generated at the Figure 8B can correspond in fact to a correction for the case where the mechanical oscillator has a natural frequency which does not correspond to a reference frequency. Thus, if the oscillator has a natural frequency that is too low, braking pulses occurring in the second or fourth quarter of the oscillation period can allow a correction of the delay taken by the free oscillation (not disturbed), this correction being more or less strong depending on the instant of the braking pulses within the oscillation period. On the other hand, if the oscillator has a too high natural frequency, braking pulses occurring in the first or third quarter of the oscillation period can allow a correction of the advance taken by the free oscillation, this correction being more or weaker depending on the instant of the braking pulses in the oscillation period.

The teaching given previously makes it possible to understand the remarkable phenomenon of the synchronization of a main mechanical oscillator (slave oscillator) on an auxiliary oscillator, forming a master oscillator, by the only periodic application of braking pulses on the slave mechanical resonator to a braking frequency F _FR advantageously corresponding to double the setpoint frequency F0c divided by a positive integer N, i.e. F _FR = 2 · F0 _c / N. The braking frequency is thus proportional to the setpoint frequency for the master oscillator and depends only on this reference frequency as soon as the positive integer number N is given. As the reference frequency is provided equal to a fractional number multiplied by the reference frequency, the braking frequency is therefore proportional to the reference frequency and determined by this reference frequency, which is supplied by the auxiliary oscillator which is by nature or construction more precise than the main mechanical oscillator.

The aforementioned synchronization obtained by the correction device incorporated in the timepiece of the invention will now be described in more detail with the aid of the Figures 9 to 22 .

To the Figure 9 the angular position of the slave mechanical resonator, in particular of the sprung balance of a watch resonator, freely oscillating (curve 100) and oscillating with braking (curve 102) is shown in the top graph. The frequency of the free oscillation is greater than the reference frequency F0 _c = 4 Hz. The first braking pulses 104 (hereinafter also called 'pulses') occur here once per period of oscillation in a half-cycle between the passage through an extreme position and the passage through zero. This choice is arbitrary because the system provided does not detect the angular position of the mechanical resonator; it is therefore just one possible hypothesis among others that will be analyzed subsequently. We are therefore here in the case of a slowdown of the mechanical oscillator. The braking torque for the first braking pulse is provided here greater than a minimum braking torque to compensate for the advance that the free oscillator takes over a period of oscillation. This has the consequence that the second braking pulse takes place a little before the first within the quarter period in which these pulses occur. Curve 106, which gives the instantaneous frequency of the mechanical oscillator, in fact indicates that the instantaneous frequency decreases below the setpoint frequency from the first pulse. Thus, the second braking pulse is closer to the preceding extreme position, so that the effect of braking increases and so on with subsequent pulses. In a transient phase, the instantaneous frequency of the oscillator therefore gradually decreases and the pulses gradually approach an extreme position of the oscillation. After a certain time, the braking pulses include the passage through the extreme position where the speed of the mechanical resonator changes direction and the instantaneous frequency then begins to increase.

Braking is unique in that it opposes the movement of the resonator whatever the direction of its movement. Thus, when the resonator goes through a reversal of the direction of its oscillation during a braking pulse, the braking torque automatically changes sign at the instant of this reversal. There are then braking pulses 104a which have, for the braking torque, a first part with a first sign and a second part with a second sign opposite to the first sign. In this situation, we therefore have the first part of the signal which occurs before the extreme position and which opposes the effect of the second part which occurs after this extreme position. If the second part decreases the instantaneous frequency of the mechanical oscillator, the first part increases it. The correction then decreases to stabilize finally and relatively quickly at a value for which the instantaneous frequency of the oscillator is equal to the reference frequency (corresponding here to the braking frequency). Thus, the transient phase is followed by a stable phase, also called synchronous phase, where the oscillation frequency is substantially equal to the setpoint frequency and where the first and second parts of the braking pulses have a substantially constant and defined ratio.

The graphs of the Figure 10 are analogous to those of Figure 9 . The major difference is the value of the natural frequency of the free mechanical oscillator which is lower than the reference frequency F0c = 4 Hz. The first pulses 104 occur in the same half-wave as at the Figure 9 . As expected, a decrease in the instantaneous frequency given by the curve 110 is observed. The oscillation with braking 108 therefore momentarily takes even more delay in the transient phase, this until the pulses 104b begin to encompass the passage of the resonator. by an extreme position. From this moment, the instantaneous frequency begins to increase until it reaches the setpoint frequency, because the first part of the pulses occurring before the extreme position increases the instantaneous frequency. This phenomenon is automatic. Indeed, as long as the duration of the oscillation periods is greater than the duration of the setpoint period T0c, the first part of the pulse increases while the second part decreases and consequently the instantaneous frequency continues to increase until a stable situation where the setpoint period is substantially equal to the oscillation period. We therefore have the desired synchronization.

The graphs of the Figure 11 are analogous to those of Figure 10 . The major difference comes from the fact that the first braking pulses 114 occur in a different half-wave than at the Figure 10 , namely in a half-cycle between the passage through zero and the passage through an extreme position. According to what has been explained previously, an increase in the instantaneous frequency given by the curve 112 is observed here in a transient phase. The braking torque for the first braking pulse is here provided greater than a minimum braking torque to compensate for the braking torque. delay that the free mechanical oscillator takes over a period of oscillation. This has the consequence that the second braking pulse takes place a little after the first within the quarter period in which these pulses occur. Curve 112 in fact indicates that the instantaneous frequency of the oscillator increases above the reference frequency from the first pulse. Thus, the second braking pulse is closer to the following extreme position, so that the effect of braking increases and so on with subsequent pulses. In the transient phase, the instantaneous frequency of the oscillation with braking 114 therefore increases and the braking pulses gradually approach an extreme position of the oscillation. After a certain time, the braking pulses include passing through the extreme position where the speed of the mechanical resonator changes direction. From that moment, we have a phenomenon similar to the one explained above. The braking pulses 114a then have two parts and the second part decreases the instantaneous frequency. This decrease in the instantaneous frequency continues until it has a value equal to the setpoint for the same reasons as given with reference to the Figures 9 and 10 . The decrease in frequency stops automatically when the instantaneous frequency is approximately equal to the reference frequency. This results in stabilization of the frequency of the mechanical oscillator at the reference frequency in a synchronous phase.

Using the Figures 12 to 15 , we will present the behavior of the mechanical oscillator in the transition phase for any instant when a first braking pulse occurs during an oscillation period, as well as the final situation corresponding to the synchronous phase where the oscillation frequency is stabilized on the reference frequency. The Figure 12 represents a period of oscillation with the curve S1 of the positions of a mechanical resonator. In the case considered here, the natural oscillation frequency F0 of the free mechanical oscillator (without braking pulses) is greater than the reference frequency F0c (F0> F0 _c ). The oscillation period conventionally comprises a first alternation A1 followed by a second alternation A2, each between two extreme positions (t _m-1 , A _m-1 ; t _m , A _m ; t _{m + 1} , A _{m + 1} corresponding to the oscillation amplitude. Next, there is shown, in the first half-wave, a braking pulse 'Imp1' whose middle time position occurs at an instant t ₁ and, in the second half-wave, another braking pulse 'Imp2' whose middle temporal position occurs at an instant t _2. The pulses Imp1 and Imp2 have a phase shift of T0 / 2, and they are particular because they correspond, for a given profile of the braking torque, to corrections generating two unstable equilibria of the system As these pulses intervene respectively in the first and the third quarter of the period of oscillation, they therefore brake the mechanical oscillator to an extent which makes it possible to correct exactly the too high natural frequency of the o Free mechanical scillator (with the braking frequency selected for the application of the braking pulses). Note that the pulses Imp1 and Imp2 are both first pulses, each being considered for itself in the absence of the other. It will be noted that the effects of the pulses Imp1 and Imp2 are identical.

If a first pulse occurs at time t ₁ or t ₂ , there will therefore theoretically be a repetition of this situation during the next periods of oscillation and an oscillation frequency equal to the setpoint frequency. Two things should be noted for such a case. First, the probability that a first pulse occurs exactly at time t ₁ or t ₂ is relatively small although possible. Second, in case such a special situation arises, it cannot last for long. Indeed, the instantaneous frequency of a sprung balance in a timepiece varies a little over time for various reasons (oscillation amplitude, temperature, change in spatial orientation, etc.). Although these reasons constitute disturbances that one generally seeks to minimize in fine watchmaking, the fact remains that in practice such an unstable balance will not last very long. It will be noted that the higher the braking torque, the closer the times t ₁ and t ₂ are to the two times of passage of the mechanical resonator through its neutral position which respectively follow them. It will also be noted that the smaller the difference between the natural oscillation frequency F0 and the reference frequency F0 _c , the more the times t ₁ and t ₂ also approach the two transit times of the mechanical resonator through its neutral position which makes them. follow respectively.

Let us now consider what happens as soon as we deviate a little from the time positions t ₁ or t ₂ during the application of the pulses. According to the teaching given with reference to the Figure 8B , if a pulse occurs to the left (previous temporal position) of the pulse Imp1 in the zone Z1a, the correction increases so that during the following periods, the previous extreme position A _m-1 will gradually approach the braking pulse. On the other hand, if a pulse occurs to the right (posterior time position) of the pulse Imp1, to the left of the zero position, the correction decreases so that during the following periods the pulses drift towards this zero position where the correction becomes nothing. Then the effect of the pulse changes and an increase in instantaneous frequency occurs. As the natural frequency is already too high, the pulse will quickly drift towards the extreme position A _m . Thus, if a pulse takes place to the right of the pulse Imp1 in the zone Z1b, the pulses following will gradually approach the next extreme position A _m . The same behavior is observed in the second half-wave A2. If a pulse takes place to the left of the pulse Imp2 in the zone Z2a, the following pulses will gradually approach the previous extreme position A _m. On the other hand, if a pulse takes place to the right of the pulse Imp2 in the zone Z2b, the following pulses will gradually approach the next extreme position A _{m + 1} . It will be noted that this formulation is relative because in reality the frequency of application of the braking pulses is imposed by the master oscillator (given braking frequency), so that it is the periods of oscillation which vary and therefore is the extreme position in question which approaches the instant of application of a braking pulse. In conclusion, if a pulse occurs in the first half wave A1 at an instant other than t ₁ , the instantaneous oscillation frequency evolves in a transient phase during the following oscillation periods so that one of the two extreme positions of this first alternation (positions of reversal of the direction of movement of the mechanical resonator) gradually approaches the braking pulses. The same goes for the second alternation A2.

The Figure 13 shows the synchronous phase corresponding to a final stable situation occurring after the transient phase described above. As already explained, as soon as the passage through an extreme position occurs during a braking pulse, this extreme position will lock onto the braking pulses as long as these braking pulses are configured (the force torque and the duration) to be able to sufficiently correcting the time drift of the free mechanical oscillator at least by a braking pulse occurring entirely, as the case may be, just before or just after an extreme position. Thus, in the synchronous phase, if a first pulse occurs in the first halfwave A1, either the extreme position A _m-1 of the oscillation is set on the pulses Imp1a, or the extreme position A _m of the oscillation is set on the pulses Imp1b. In the case of a substantially constant torque, the pulses Imp1a and Imp1b each have a first part the duration of which is shorter than that of their second part, so as to correct exactly the difference between the too high natural frequency of the oscillator main slave and the setpoint frequency imposed by the master auxiliary oscillator. Likewise, in the synchronous phase, if a first pulse occurs in the second _{half-wave A2, either the extreme position A m} of the oscillation is set on the pulses Imp2a, or the extreme position A _{m + 1} of the oscillation is set on Imp2b pulses.

It will be noted that the pulses Imp1a, respectively Imp1b, Imp2a and Imp2b occupy stable relative temporal positions. Indeed, a slight deviation to the left or to the right of one of these pulses, due to an external disturbance, will have the effect of bringing a following pulse back to the initial relative temporal position. Then, if the time drift of the mechanical oscillator varies during the synchronous phase, the oscillation will automatically undergo a slight phase shift so that the ratio between the first part and the second part of the pulses Imp1a, respectively Imp1b, Imp2a and Imp2b varies to an extent which adapts the correction generated by the braking pulses to the new frequency difference. Such behavior of the timepiece according to the present invention is truly remarkable.

The Figures 14 and 15 are similar to Figures 12 and 13 , but for a situation where the natural frequency of the oscillator is lower than the reference frequency. Consequently, the impulses Imp3 and Imp4, corresponding to an unstable equilibrium situation in the correction made by the braking impulses, are respectively located in the second and the fourth quarter of a period (instants t ₃ and t ₄ ) where the impulses cause an increase in the oscillation frequency. The explanations in detail will not be given here again because the behavior of the system follows of the preceding considerations. In the transitional phase ( Figure 14 ), if an impulse takes place in the alternation A3 to the left of impulse Imp3 in zone Z3a, the previous extreme position (t _m-1 , A _m-1 ) will gradually approach the following impulses On the other hand, if a pulse takes place to the right of the pulse Imp3 in the zone Z3b, the next extreme position (t _m , A _m ) will gradually approach the following pulses. Likewise, if a pulse takes place in the alternation A4 to the left of pulse Imp4 in zone Z4a, the previous extreme position (t _m , A _m ) will gradually approach the following pulses. Finally, if a pulse takes place to the right of the pulse Imp4 in the zone Z4b, the next extreme position (t _{m + 1} , A _{m + 1} ) will gradually approach the following pulses during the transition phase.

In the synchronous phase ( Figure 15 ), if a first pulse occurs in the first _{half wave A3, either the extreme position A m-1} of the oscillation is set on the impulses Imp3a, or the extreme position A _m of the oscillation is set on the pulses Imp3b. In the case of a substantially constant torque, the impulses Imp3a and Imp3b each have a first part the duration of which is longer than that of their second part, so as to correct exactly the difference between the too low natural frequency of the oscillator main slave and the setpoint frequency imposed by the master auxiliary oscillator. Likewise, in the synchronous phase, if a first pulse occurs in the second _{half-wave A4, either the extreme position A m} of the oscillation is set on the pulses Imp4a, or the extreme position A _{m + 1} of the oscillation is set on Imp4b pulses. The other considerations made in the context of the case described above with reference to Figures 12 and 13 apply by analogy to the case of Figures 14 and 15 . In conclusion, whether the natural frequency of the free mechanical oscillator is too high or too low and whatever the instant of the application of a first braking pulse within an oscillation period, the correction device of the invention is efficient and quickly synchronizes the frequency of the mechanical oscillator, timing the operation of the mechanical movement, on the reference frequency which is determined by the reference frequency of the master auxiliary oscillator, which controls the braking frequency at which the pulses braking are applied to the resonator of the mechanical oscillator. This remains true if the natural frequency of the mechanical oscillator varies and even if it is, in certain periods of time, higher than the reference frequency, while in other periods of time it is lower than this reference frequency.

The teaching given above and the synchronization obtained by virtue of the characteristics of the timepiece according to the invention also apply to the case where the braking frequency for the application of the braking pulses is not equal to the setpoint frequency. In the case of the application of a pulse per period of oscillation, the pulses taking place at unstable positions (t ₁ , Imp ₁ ; t ₂ , Imp ₂ ; t ₃ , Imp3; t ₄ , Imp4) correspond to corrections to compensate for time drift during a single oscillation period. On the other hand, if the planned braking pulses have a sufficient effect to correct a time drift during several oscillation periods, it is then possible to apply a single pulse per time interval equal to these several oscillation periods. The same behavior will then be observed as for the case where a pulse is generated per period of oscillation. By considering the oscillation periods in which the pulses intervene, we have the same transient phases and the same synchronous phases as in the case described above. In addition, these considerations are also correct if there is an integer number of alternations between each braking pulse. In the case of an odd number of alternations, one passes alternately, according to the case, from the alternation A1 or A3 to the alternation A2 or A4 on the Figures 12 to 15 . As the effect of two pulses shifted by one half-wave is identical, it is understood that the synchronization is carried out as for an even number of alternations between two successive braking pulses. In conclusion, as already indicated, the behavior of the system described with reference to Figures 12 to 15 is observed as soon as the braking frequency F _FR is equal to 2F0 _c / N, FO _c being the reference frequency for the oscillation frequency and N a positive integer.

Although not very interesting, it will be noted that the synchronization is also obtained for a braking frequency F _FR greater than double the reference frequency (2F0), namely for a value equal to N times F0 with N> 2. In a variant with F _FR = 4F0, we adjust a loss of energy in the system without effect in the synchronous phase, because every other pulse occurs at the neutral point of the mechanical resonator. For a higher braking frequency F _FR , the pulses in the synchronous phase which do not occur at the extreme positions cancel their effects two by two. We therefore understand that these are theoretical cases without much practical meaning.

The Figures 16 and 17 show the synchronous phase for a variant with a braking frequency F _FR equal to a quarter of the reference frequency, a braking pulse therefore occurring every four oscillation periods. The Figures 18 and 19 are partial enlargements respectively of Figures 16 and 17 . The Figure 16 concerns a case where the natural frequency of the main oscillator is greater than the reference frequency F0 _c = 4 Hz, while the Figure 17 relates to a case where the natural frequency of the main oscillator is greater than this reference frequency. It is observed that only the periods of oscillation T1 * and T2 *, in which braking pulses Imp1b or Imp2a, respectively Imp3b or Imp4a, exhibit a variation relative to the natural period T0 *. The braking pulses generate a phase shift only in the corresponding periods. Thus, the instantaneous periods here oscillate around an average value which is equal to that of the setpoint period. It will be noted that, at Figures 16 to 19 , the instantaneous periods are measured from a zero crossing on a rising edge of the oscillation signal at such next pass. Thus, the synchronous pulses which occur at the extreme positions are entirely included in periods of oscillation. To be complete, the Figure 20 shows the specific case where the natural frequency is equal to the reference frequency. In this case, the oscillation periods T0 * all remain equal, the braking pulses Imp5 occurring exactly at the extreme positions of the free oscillation with the first and second parts of these pulses which have identical durations (case of a constant braking torque), so that the effect of the first part is canceled by the opposite effect of the second part.

In an improved variant, the synchronization device is arranged so that the braking frequency can take several values, preferably a first value in an initial phase of the operation of the synchronization device and a second value, less than the first value, in a normal operating phase following the initial phase. In particular, the duration of the initial phase will be selected so that the normal operating phase occurs when the synchronous phase has probably already started. More generally, the initial phase includes at least the first braking pulses, following the engagement of the synchronization device, and preferably the major part of the transient phase. By increasing the frequency of the braking pulses, the duration of the transient phase is reduced. In addition, this variant makes it possible, on the one hand, to optimize the braking efficiency during the initial phase to ensure the physical process leading to synchronization and, on the other hand, to minimize the braking energy and therefore the energy losses for the main oscillator during the synchronous phase which continues as long as the synchronization device is not deactivated and the mechanical movement is functioning. The first braking pulses can occur near the neutral position of the resonator where the effect of braking is less on the time phase shift generated for the oscillation of the main oscillator. On the other hand, once the synchronization established, the braking pulses take place near the extreme positions of this oscillation where the braking effect is the greatest.

With reference to Figures 21 and 22 , we will describe a first variant of a second embodiment of the invention which is surprising by the simplicity of its electromagnetic braking device. This second embodiment differs from the first embodiment essentially by the magnetic system of the electromagnetic braking device which consists, in the first variant, of a single bipolar magnet 60 carried by the balance 8A of the mechanical resonator 6A and, in a second variant, by a single pair of bipolar magnets. In the first variant, when the resonator 6A is in its neutral position (situation shown in Figure 21 ), a reference semi-axis 62 starting from the axis of oscillation 34 and passing through the center of the magnet 60 defines an angular position zero ('0') in a polar coordinate system centered on the axis d oscillation and fixed relative to the plate of the watch movement. The coil 28, which completes the electromagnetic braking device in addition to the magnetic system, is integral with the plate and has an angular offset relative to the zero angular position. Preferably, the angular offset of the coil is substantially 180 °, as shown in Figure 21 .

To the Figure 22 are shown the curve 70 of the angular position of the balance 8A as a function of time, in the useful operating range of the mechanical oscillator considered which has in this range an amplitude greater than 180 ° and preferably greater than 200 ° (case shown ), and the curve 72 of the voltage induced in a synchronous phase of the operation of the synchronization device. Thus, in each alternation of the oscillation of the mechanical resonator 6A, two induced voltage pulses 74 _A and 74 _B are observed having substantially the shape of a period of a sine. Note that the pulses 74 _A and 74 _B are separated two by two by time zones without voltage induced in the coil. 28. In a variant ensuring great running stability of the timepiece, the distinct time intervals T _P , defined by the short-circuit pulses 58A generated at the setpoint frequency F0c and thus occurring in each period d oscillation, are substantially equal to or greater (case shown) to the time zones without voltage induced in the coil around the two extreme positions of the mechanical resonator in the useful operating range. However, as will be seen below, this condition is not necessary, the time intervals T _P possibly being less than the duration of these time zones without induced voltage.

It is observed that, provided that the natural time drift of the timepiece remains within a nominal range for which the synchronization device has been dimensioned and generally after a transient phase which follows the activation of the synchronization device, this part d 'watchmaking enters a stable and synchronous phase and where the mechanical oscillator presents the setpoint frequency F0c at which the short-circuit pulses 58A are generated here, and this regardless of the angular position of the balance 8A during a first short-circuit pulse. The Figure 22 corresponds to a situation where the natural oscillation frequency F0 of the mechanical oscillator is a little lower than the reference frequency F0c. It follows from this situation that, in each oscillation period T0c, a first distinct braking pulse, which is generated in the initial zone of each short-circuit pulse by an induced voltage pulse 74 _A and which occurs in the second half-wave A2 ₂ of the second half-wave A2 (at the start of the separate time intervals T _P ), is stronger than a second separate braking pulse which is generated in the end zone of each short-circuit pulse by a pulse of induced voltage 74 _B and which occurs in the first half-wave A1 ₁ of the first half-wave A1 (at the end of the distinct time intervals T _P ). Two braking pulses are distinct when they are separated by a time interval having a non-zero duration.

Thus, in the synchronous phase, during each time interval T _P where a short-circuit of the coil occurs, the positive phase shift generated by the voltage pulse 74 _B in each half-wave A2 ₂ is greater than the negative phase shift generated by the voltage pulse 74 _A in each half-wave A1 ₁ , so that a correction of the rate of the timepiece takes place here in each period of oscillation to ensure the synchronization of the mechanical oscillator on the baseline time base. As indicated previously, the generation of short-circuit pulses at the reference frequency is a special case. In another variant, short-circuit pulses are generated with a lower frequency corresponding to a fraction of the reference frequency. More generally, provision is made for the temporal distance D _T , separating a same characteristic instant of any two successive short-circuit pulses, satisfies the mathematical relationship D _T = M · T0c / 2, M being any positive integer. Thus, in the case of periodic generation of the braking pulses, the trigger frequency F _D of these braking pulses is selected to satisfy the mathematical relationship F _D = 2 · F0c / M (note that the two braking pulses distinct, generated in each time interval T _P respectively upon the appearance of the two induced voltage pulses 74 _A and 74 _B , are considered together as the same braking pulse for the question of temporal distances and the triggering frequency) . Those skilled in the art will know how to select a sufficiently high frequency, and therefore a value of M not too high, to ensure the desired synchronization.

In a second variant of the second embodiment, the electromagnetic braking device comprises a magnetic system formed by a pair of permanent magnets with axial magnetization and of opposite polarities, these two magnets being arranged symmetrically with respect to a reference semi-axis of the balance and sufficiently close to each other to add two lobes of induced voltage that they generate respectively when this pair of magnets pass in reel look. The reference half-axis defines a zero angular position when the mechanical resonator is in its neutral position. The coil has an angular offset relative to the zero angular position so that a voltage induced in this coil occurs, when the mechanical oscillator oscillates in the useful operating range, at least in one half-wave of each period of oscillation substantially before or after the passage of the mechanical resonator through its neutral position in this alternation. The angular offset of the coil is also preferably equal to 180 °. The extreme angular positions of the mechanical resonator in the useful operating range are, in absolute values, greater than the angular offset which is defined as the minimum angular distance between the zero angular position and the angular position of the center of the coil. This second variant corresponds to the electromagnetic device shown in Figure 23 , but without the second pair of magnets 66, 67 which relates to the third embodiment which will be described below.

In a third embodiment, shown in Figures 23 to 25 , the magnetic system of the electromagnetic braking device consists of a first pair of bipolar magnets 64, 65 and a second pair of bipolar magnets 66, 67 both carried by the balance 8B of the mechanical resonator 6B, as well as of a coil 28. Each pair of magnets has an axial magnetization of opposite polarities. The two magnets of the first pair are arranged symmetrically with respect to a reference half-axis 62A of the balance 8B, this reference half-axis defining a zero angular position when the mechanical resonator is in its neutral position. To the Figure 23 , it will be noted that the balance is in an angular position θ equal to 90 ° (θ = 90 °). Coil 28, as in second embodiment, has an angular offset relative to the zero angular position, this offset being preferably substantially equal to 180; but other angular offsets can be provided in other variants. The induced voltage curve 76 generated in the coil when the mechanical resonator oscillates is shown in figure Figure 24 , superimposed on the curve 70 giving the angular position of the balance 8B.

Positioning the coil 28 at an angle of 180 ° (variant shown in Figure 23 ) is a preferred variant, because the electromagnetic system that the coil forms with the first pair of magnets 64, 65 generates in each half-wave two induced voltage pulses 78 _A and 78 _B having a symmetry relative to the instant of passage of the resonator 6B by its neutral position. There is therefore a 78 _A pulse in each first half-wave A1 ₁ , A2 ₁ and a 78 _B pulse in each second half-wave A1 ₂ , A2 ₂ . Thus, the induced voltage pulses 78 _A and 78 _B have substantially the same amplitude and are each located at the same temporal distance from a passage of the mechanical resonator 6B through an extreme angular position, so that they are all liable to generate, during a coil short-circuit, a braking torque of the same intensity and a phase shift, positive or negative as the case may be, of the same value in the oscillation of the mechanical resonator. Then, as has been explained previously, it will be noted that an angular offset of 180 ° also has the advantage of high efficiency for the braking pulses generated. In addition, it will be noted that the amplitude of the balance in the useful operating range of the mechanical oscillator is conventionally expected to be greater than 180 °, which therefore makes it possible to generate the induced voltage pulses and thus to be able to generate braking pulses. , by reducing the impedance between the two terminals of coil 28 to correct the operation of the timepiece.

In a first variant shown in Figure 24 , the value of the distinct time intervals T _P is substantially equal to or greater than the duration of a temporal zone without voltage induced in the coil 28 around each extreme angular position of the mechanical resonator in the useful operating range of the mechanical oscillator. However, this value of the distinct time intervals T _P is expected to be less than the reference half-period, ie T _P <T0c / 2. In the synchronous phase of the synchronization method according to this first variant, the short-circuit pulses 58B are wedged between two induced voltage pulses 78 _A , 78 _B surrounding an extreme angular position and two distinct braking pulses occur respectively at the start and at the end of each time interval T _P , these two distinct braking pulses corresponding to two quantities of energy taken from the mechanical resonator which are variable (the variation of one being opposed to the variation of the other, so that if one of the two quantities of energy increases or decreases the other respectively decreases or increases), as a function of a positive or negative time drift of the mechanical oscillator in question. Note that the Figure 24 corresponds to the particular case where the natural frequency of the mechanical oscillator is equal to the setpoint frequency, so that the two aforementioned quantities of energy are here identical.

To the figure 25 , similar to Figure 24 , a second variant is shown in which the value of the distinct time intervals T _P is less than the duration of a time zone without voltage induced in the coil 28 around each extreme angular position of the mechanical resonator. The desired synchronization is also obtained. In fact, in the synchronous phase, the short-circuit pulses 58C also remain in a time window which is framed by two induced voltage pulses 78 _A , 78 _B surrounding an extreme angular position. The temporal position of the distinct time intervals T _P can vary within this time window during at least a terminal part of the transient phase (pulse 58C ₁ ) or in the synchronous phase if the frequency natural value of the mechanical oscillator is very close to the setpoint frequency, in particular if it varies very slightly around this value. Generally, in the synchronous phase, depending on whether the time drift of the mechanical oscillator is negative or positive, short-circuit pulses 58C ₂ or 58C ₃ are observed which respectively occur in the half-waves A1 ₂ and A2 ₁ of periods of oscillation partially simultaneously with the induced voltage pulses 78 _B and 78 _A , respectively, so that they generate braking pulses in the respective half-waves. Only the aforementioned electromagnetic system, formed of the coil and the first pair of magnets, intervenes to ensure the desired synchronization in the synchronous phase of the synchronization process, the second pair of magnets then having no influence for this synchronization process.

The second pair of bipolar magnets 66, 67, which is momentarily coupled to coil 28 in each half-wave of the mechanical resonator oscillation, serves primarily to supply power to the synchronization device, although it may be involved in an alternation. transient phase (initial phase after activation of the synchronization device) of the synchronization process. The timepiece comprises a supply circuit, formed by a rectifier circuit of a voltage induced in the coil and a storage capacitor, and the second pair of bipolar magnets has a middle half-axis 68 between its two magnets. which is offset by the angular offset exhibited by the coil 28 relative to the reference semi-axis 62A, so that this middle axis is aligned with the center of the coil when the mechanical resonator is in its rest position. The supply circuit is connected, on the one hand, to a terminal of the coil and, on the other hand, to a reference potential of the synchronization device at least periodically when the mechanical resonator passes through its neutral position, but preferably constantly. The second pair of magnets generates induced voltage pulses 80 _A and 80 _B when passing through the balance 8B by the zero angular position, these pulses having a greater amplitude than the pulses generated by the first pair of magnets and serving to supply the storage capacitor, the voltage of which is represented by curve 82 at the bottom. Figure 24 .

With reference to Figures 26, 27 and 28A-28C , a fourth embodiment of the invention will be described below. This fourth embodiment differs from the other embodiments essentially by the arrangement of the magnetic system. The shaft 82 of the balance 8C is pivoted between the plate 5 and a balance bridge 7 about the axis of oscillation 34. A bipolar magnet 84 with radial magnetization is arranged on the shaft 82 and placed in an opening 87 d a plate 86 made of a material with high magnetic permeability, in particular a ferromagnetic material. The plate 86 defines a magnetic circuit with a core 89 around which a coil 28C is arranged, in the manner of a conventional watch motor. The plate 86 has two isthmuses 88 at the opening 87 which partially prevent the magnetic flux of the magnet from closing on itself without passing through the coil core. However, preferably, these isthmuses are made less thin than in the case of a clock motor in order to limit the variation of the magnetic potential energy of the permanent magnet 84 as a function of its angle of rotation.

The Figures 28A to 28C are similar to Figures 5A to 5C , but for the fourth embodiment. The voltage curve induced at Figures 28A and 28B corresponds to a particular case where the oscillation amplitude is substantially equal to 180 °. For a higher amplitude, the voltage curve induced in coil 28C corresponds to the curve shown in Figure 28C . This last figure relates to a particular case where the natural oscillation frequency F0 of the mechanical oscillator is equal to the reference frequency. Since the braking generated by the braking pulses 50C is small, the oscillation amplitude of the resonator 6C is a little greater than that occurring at the Figures 28A and 28B where the braking pulses 56, respectively 57 generate more substantial braking. The pulses 50C do not generate a time phase shift in the oscillation of the mechanical resonator, given that they have a central symmetry relative to the instant of passage of the resonator 6C through an extreme angular position on the graph of the braking torque. It will be noted that the two parts T _B and T _A of distinct time intervals T _P , occurring respectively on both sides of the instant at which the resonator 6C passes through an extreme angular position, are here equal since the natural frequency is equal to the setpoint frequency. Thus the adjacent half-waves A2 ₂ and A1 ₁ have the same duration.

As a reminder, the time intervals T _P are defined by the short-circuit pulses 58 which have between their respective beginnings a time distance D _T determined by the reference time base. In the present example, the short-circuit pulses 58 are generated with a triggering frequency F _D equal to the setpoint frequency, so that the time distances D _T are here equal to a setpoint period T0c.

In the case of a natural frequency F0 that is too high, the first part T _B of the distant time intervals T _P is less than the second part T _A and the braking pulses 56 generated during these distant time intervals, by the pulses corresponding short-circuits, occur substantially in the first half-waves A1 ₁ (almost entirely in the specific example shown), so that they reduce the frequency of the mechanical oscillator to synchronize it on the auxiliary oscillator of the reference time base and thus impose the reference frequency F0c on this mechanical oscillator. In the case of a too low natural frequency F0, the first part T _B of the distant time intervals T _P is greater than the second part T _A and the braking pulses 57 generated during these distant time intervals, by the pulses corresponding short-circuits, substantially intervene in second half-waves A2 ₂ (also almost entirely in the specific example shown), so that they increase the frequency of the mechanical oscillator to synchronize it with the auxiliary oscillator.

Claims (13)

1. Timepiece (2) comprising a mechanical movement (4) which comprises:

   - an indicator mechanism (12) of at least one time data item,

   - a mechanical resonator (6,6A,6B,6C) suitable for oscillating along a general oscillation axis about a neutral position corresponding to the minimum potential energy state thereof,

   - a maintenance device (18) of the mechanical resonator forming therewith a mechanical oscillator which is arranged to time the running of the indicator mechanism,

   - an auxiliary oscillator (35) forming a reference time base (22) and determining a set-point frequency F0c, as well as a set-point period T0c equal by definition to the inverse of the set-point frequency, for the mechanical resonator;

   the timepiece further comprising a synchronisation device (20) arranged to slave the mean frequency of the mechanical oscillator on the set-point frequency F0c, the synchronisation device comprising an electromagnetic braking device of the mechanical resonator, this electromagnetic braking device being formed of at least one coil (28,28C) and at least one permanent magnet (30,32; 60; 64,65; 84) which are arranged such that, within a usable operating range of the mechanical oscillator, an induced voltage is generated between the two terminals of the coil in each alternation of this oscillation; the synchronisation device being arranged to be able to momentarily reduce the impedance between the two terminals of the coil;
   characterised in that the synchronisation device is arranged so as to reduce the impedance between the two terminals of the coil during distinct time intervals Tp and such that the starts of any two successive time intervals, among said distinct time intervals, exhibit therebetween a time distance D_T equal to a positive whole number N multiplied by half of the set-point period T0c for the mechanical oscillator, i.e. a mathematical relation D_T = N·T0c/2, the synchronisation device being arranged to determine by means of the reference time base the start of each of the distinct time intervals so as to fulfil the mathematical relation between the time distance D_T and the set-point period T0c.
2. Timepiece according to claim 1, characterised in that the synchronisation device is arranged to trigger periodically said distinct time intervals T_P, which have the same value, and such that the triggering frequency F_D is equal to twice the set-point frequency F0c divided by a positive whole number M, i.e. F_D = 2·F0c/ M, the value of the distinct time intervals Tp being less than half of the set-point period, i.e. T_P < T0c/2.
3. Timepiece according to claim 1 or 2, characterised in that the mechanical resonator is formed by a balance (8,8A,8B,8C) oscillating about an oscillation axis (34).
4. Timepiece according to claim 3, characterised in that the balance bears said at least one permanent magnet and a support (5) of the mechanical resonator bears said at least one coil.
5. Timepiece according to any one of the preceding claims, characterised in that the electromagnetic braking device is arranged such that an induced voltage is generated in said at least one coil substantially continuously for any oscillation of the mechanical resonator within the usable operating range of the mechanical oscillator.
6. Timepiece according to claim 5, characterised in that the value of the distinct time intervals T_P is advantageously less than one quarter of the set-point period T0c, i.e. T_P < T0c / 4.
7. Timepiece according to claim 4, characterised in that the electromagnetic braking device comprises a magnetic system borne by the balance and formed by a pair of bipolar magnets (64,65) with axial magnetisation and opposite polarities, these two bipolar magnets being arranged symmetrically relative to a reference half-axis (62A) of the balance, this reference half-axis defining a zero angular position when the mechanical resonator is in the neutral position thereof; and in that said coil exhibits an angular lag relative to the zero angular position such that an induced voltage in this coil occurs substantially, when the mechanical oscillator oscillates in the usable operating range, in each alternation alternately before and after the passage of the mechanical resonator via the neutral position thereof in this alternation, the end angular positions of the mechanical resonator in said usable operating range being, in absolute values, greater than said angular lag which is defined as the minimum angular distance between the zero angular position and the angular position of the centre of the coil.
8. Timepiece according to claim 7, characterised in that, within the usable operating range of the mechanical oscillator, the distinct time intervals T_P are substantially equal to or greater than time zones with no induced voltage in said coil about the two end positions of the mechanical resonator.
9. Timepiece according to claim 7 or 8, characterised in that said angular lag is substantially equal to 180°.
10. Timepiece according to any one of the preceding claims, characterised in that it comprises a power supply circuit (44) formed by a storage capacitor and by a rectifier circuit of a voltage induced in the coil by at least one permanent magnet when the mechanical resonator oscillates.
11. Timepiece according to claim 10, characterised in that the power supply circuit is constantly connected, on one hand, to a terminal of said coil and, on the other, to a reference potential of the synchronisation device; and in that said at least one permanent magnet generating the induced voltage rectified by the rectifier circuit, the coil and the power supply circuit are arranged such that, in the usable operating range of the mechanical oscillator, the electrical energy stored in the storage capacitor is sufficient to power the synchronisation device.
12. Timepiece according to any one of claims 7 to 9, characterised in that it comprises a power supply circuit (44) formed by a storage capacitor and by a rectifier circuit of a voltage induced in the coil by a further pair of permanent magnets (66,67) when the mechanical resonator oscillates, the further pair of permanent magnets having a midpoint axis (68) between the two permanent magnets thereof and being momentarily coupled with the coil in each alternation of the oscillation of the mechanical resonator, said midpoint axis being substantially offset by said angular lag relative to said reference half-axis (62A) such that this midpoint axis is substantially aligned on the centre of the coil when the mechanical resonator is in the neutral position thereof; and in that the power supply circuit is connected, on one hand, to a terminal of said coil and, on the other, to a reference potential of the synchronisation device at least periodically when the mechanical resonator passes via the neutral position thereof.
13. Timepiece according to any one of the preceding claims, characterised in that the synchronisation device is arranged so as to generate a short-circuit between the two terminals of said coil during said distinct time intervals.

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