EP2466401B1 - Magnetic resonator for mechanical timepiece - Google Patents

Description

Technical area

The present invention relates to a magnetic resonator for a mechanical timepiece, in particular for a wristwatch.

More specifically, the invention relates to such a magnetic resonator comprising
a tuning fork type oscillator having first and second branches arranged substantially U-shaped, at least one of the branches carrying at least one first permanent magnet defining a first magnetic field,
an escape wheel, free from any mechanical contact with the oscillator and intended to be arranged in engagement with a first mobile of a finishing train to allow it to be driven from a power source of the timepiece and located within reach of the first permanent magnet to undergo the influence of the first magnetic field.

The high quality factor of an oscillator as a tuning fork, about ten to fifty times that of a conventional balance wheel, makes it attractive in the context of a watch application.

Furthermore, the present invention also relates to a watch movement provided with such a resonator and a timepiece, in particular but not exclusively of the wristwatch type, equipped with such a watch movement.

By permanent magnet, it is necessary to understand here, without departing from the scope of the invention, an element producing a permanent magnetic field, whatever the form, that is to say that it may be constituted by a portion of material taken into the mass and having undergone a treatment in order to present the required magnetic properties, by an insert, or even by a deposited layer, of a suitable magnetic material.

State of the art

Numerous clock devices comprising a tuning fork as oscillator have already been disclosed in the state of the art.

For example, Max Hetzel is at the origin of a large number of patented inventions, relating to the implementation of a tuning fork as an oscillator, which led to the production of the Accutron wristwatch (brand filed), marketed by Bulova Swiss SA.

The Accutron watch however includes an electronic resonator since each branch of the corresponding tuning fork carries a permanent magnet associated with an electromagnet mounted fixed on the frame of the watch. The operation of each electromagnet is controlled by the vibrations of the tuning fork, by means of the magnets which it carries, in such a way that the vibrations of the tuning fork are maintained by the transmission of periodic magnetic pulses from the electromagnets to the permanent magnets. . One of the branches of the tuning fork actuates a pawl for rotating the mobile wheels of the finishing gear of the watch.

The patent US 2,971,323 for example, from a deposit dating back to 1957, describes such a mechanism that can not however be suitable for the realization of a purely mechanical watch, that is to say without electronic circuits. Indeed, a real need exists, in terms of market, for purely mechanical timepieces with increased running accuracy compared to known parts.

It should be noted that the Accutron coin is still marketed by Bulova Swiss SA.

The patent CH 594201 , from a 1972 deposit, describes a dual oscillator resonator system. The frequency stability of the oscillations of a tuning fork is advantageously used, by magnetic interaction, to stabilize the oscillations of a balance of conventional shape, thus having a lower quality factor than that of the tuning fork. For this purpose, the branches of the tuning fork, on the one hand, and the balance, on the other hand, carry permanent magnets arranged to cooperate with each other. The corresponding interaction makes it possible both to maintain oscillations of the tuning fork and to stabilize oscillations of the pendulum in frequency.

However, if this does not appear explicitly in this patent, it is obvious that this mechanism is necessarily coupled to a mechanical escapement to convert the periodic oscillation of the balance into a unidirectional movement to ensure the drive of the mobile of a cog finishing. Thus, it is likely that the balance is coupled to a conventional mechanical escapement arranged to maintain the oscillations. Consequently, the mechanism described in this document makes it possible to improve the frequency stability of the oscillations of a balance wheel, but this is done at the cost of a complexity and a much larger space requirement compared to a conventional one-way mechanism. oscillator. In addition, the high quality factor of the tuning fork is only partially used in the solution presented since, in the end, it is the pendulum which controls the movements of the finishing gear train, in a similar way to what is being done. works in classical systems.

Alternative solutions, more adapted to the spatial constraints specific to the construction of a wristwatch, had also been disclosed. Indeed, the patent US 3,208,287 , from a deposit dating from 1962, describes a resonator comprising a tuning fork coupled to an escape wheel by means of magnetic interactions. More specifically, the tuning fork carries permanent magnets cooperating with the escape wheel, the latter being made of a magnetic conductive material. The escape wheel is kinematically connected to a source of energy which may be mechanical or take the form of a motor, while it comprises openings, in its thickness, as it forms a magnetic circuit of variable reluctance when it is rotated, in relation with the magnets carried by the tuning fork.

Consequently, a permanent interaction of substantial intensity takes place between the tuning fork and the escape wheel, which can be described as magnetic locking, such a construction therefore consisting of a non-free exhaust. The energy input of the escapement wheel to the tuning fork to maintain oscillations, even if it is weak, is continuous and constitutes a significant source of disturbance. from the point of view of the isochronism of these oscillations. Similarly, the guidance of the escape wheel by the tuning fork is continuous.

Thus, the type of interaction involved in this construction is close to a contact, which is unfavorable from the point of view of the accuracy of operation.

It should be noted that a large number of patents exist to cover technical solutions based on the principle of reluctance. We can notably mention the patents GB 660,581 , whose filing dates back to 1948, the patent GB 838,430 , whose deposit dates back to 1955, or even the patent US 2,571,085 the filing date of 1949. The patent US 3,132,522 , whose filing dates from 1960, presents similar solutions.

Disclosure of the invention

A main object of the present invention is to overcome the disadvantages of tuning fork resonators known from the prior art, by proposing a resonator for a mechanical timepiece, in particular for a wristwatch, having a quality factor and isochronism high.

For this purpose, the present invention relates more particularly to a resonator of the type mentioned above, characterized in that the escape wheel carries at least two permanent magnets, preferably at least four, arranged in such a way that the vibrations of the branch of the tuning fork, on the one hand, control the speed of rotation of the escape wheel and, on the other hand, are maintained periodically by the magnetic interaction between the first permanent magnet of the tuning fork and the permanent magnets of the wheel of escape, to define a free escape.

Thanks to these characteristics, the resonator according to the present invention offers the full benefits of the high quality factor of the tuning fork, that is to say without the nature of the exhaust collaborating with it attenuating these benefits, as it does. is the case of known mechanisms of the prior art.

Indeed, the nature of the interaction between the tuning fork and the escape wheel, as well as the ability to adjust the magnetic properties of the permanent magnets used according to the needs, make it possible to optimize the operation of the resonator according to the invention, especially for the legs of the tuning fork exercise a control of the speed of rotation of the escape wheel, by their vibrations, while recovering from the latter the amount of energy sufficient to ensure the maintenance of their vibrations with a excellent isochronism.

This magnetic interaction, between the permanent magnets positioned on the escape wheel and the permanent magnet placed on one of the branches of the tuning fork, is of very small amplitude and of a very short duration. It intervenes only when one of the permanent magnets of the escape wheel is arranged opposite the magnet of the tuning fork. The interaction is only of magnetic nature, a space remaining between the two permanent magnets arranged face to face. The arrangement of the magnets of the escape wheel associated with the magnet or magnets positioned on the branches makes it possible to maintain the free oscillations of the branches of the tuning fork. These free oscillations are natural natural oscillations. An advantage of this type of resonator with regard to the state of the art is the reduction of oscillations disturbances. The weak interaction of the magnets makes it possible to achieve a free escape.

Note that these resonators have not experienced major innovation for almost forty years, which could suggest that everything had been invented in this area. Thus, the merit of the Applicant lies in having designed the resonator according to the present invention, against all odds, in which the amplitude of the magnetic interaction occurring between the tuning fork and the escape wheel is substantially greater than that intervening in the mechanisms based on the principle of reluctance, which appears a priori to be unfavorable from the point of view of isochronism, this increase of the amplitude being compensated by the implementation of a shorter time of the concerned interaction, ie free escape as opposed to known mechanisms, leading overall to a more favorable result.

Furthermore, the magnetic exhaust mechanical resonator according to the present invention has a simplified construction and assembly compared to conventional free exhausts such as Swiss anchor escapements or expansion exhausts. The conventional mechanical free exhausts are particularly more complex in the adjustment of the relative positions of their constituents.

In addition, the resonator according to the present invention has neither ratchet system nor mechanical contact. The durability of such a resonator is therefore greater than that of conventional mechanical resonators.

Preferably, the escape wheel carries 2n permanent magnets, n being at least 1, preferably less than or equal to 40. These magnets are advantageously evenly distributed near the periphery or at the periphery of the escape wheel, to ensure a regular rotation of the latter.

According to a preferred embodiment, two adjacent magnets of the escape wheel are arranged relative to each other to present to the magnet of the tuning fork, or to each magnet of the tuning fork, respective inverted polarities, when the wheel exhaust turns on itself.

Thanks to these characteristics, the respective movements of the tuning fork leg and the escape wheel are synchronized in such a way that, when the tuning fork branch deviates from the escape wheel, the latter has a magnet giving rise to a repulsion in relation to the magnet of the branch, while, when the branch is close to the escape wheel, the latter has a magnet giving rise to an attraction in relation to the magnet of the branch.

Advantageously, the escape wheel can be arranged between the branches of the tuning fork, the second branch then being preferably provided with a second permanent magnet defining a second magnetic field. In this case, the magnets of the tuning fork are preferably diametrically opposed with reference to the escape wheel. In addition, the magnets of the escape wheel are advantageously arranged, in this case, so that they are diametrically opposed in pairs by having magnetic orientations such that they have similar interactions with the magnets of the tuning fork.

Such a relative arrangement of the magnets makes it possible to ensure that the tuning fork oscillates according to its first mode of vibration, namely that its two branches move away from each other and approach each other simultaneously. .

Furthermore, the present invention also relates to a watch movement, for a mechanical timepiece, comprising a resonator meeting the above characteristics as well as a timepiece equipped with such a watch movement.

According to an alternative embodiment, the escape wheel may be located outside the branches of the tuning fork.

In all cases, it is conceivable to provide several escape wheels with identical or different oscillation frequencies, as well as their respective diameters and / or their respective rotational speeds, in order to meet different needs.

According to an illustrative variant embodiment, it is possible to provide that the mechanism according to the invention comprises a first escape wheel, associated with a first leg of the tuning fork for rotating with a first rotation speed, as well as a second transmission wheel. exhaust, associated with the other branch of the tuning fork, to rotate with a second speed of rotation. In this case, one of the escape wheels may be associated with display members of the current time, while the other may be associated with short time display members, in particular by means of a chronograph type function.

Brief description of the drawings

Other features and advantages of the present invention will appear more clearly on reading the detailed description of a preferred embodiment which follows, made with reference to the accompanying drawings given by way of non-limiting examples and in which:

- the figure 1 represents a simplified front view of a magnetic exhaust mechanical resonator, in a first configuration, comprising an escape wheel placed between the branches of a U-shaped tuning fork;

- the figure 2 represents a simplified front view of the resonator of the figure 1 in a second configuration;

- the figure 3 represents a simplified front view of the resonator of the figure 1 in a third configuration;

- the figure 4 represents a simplified front view of a resonator according to an alternative embodiment in which it comprises two escape wheels positioned outside the branches of the tuning fork in a first configuration;

- the figure 5 represents a simplified front view of the resonator of the figure 4 in a second configuration;

- the figure 6 represents a simplified front view illustrating an alternative mode of attachment of the tuning fork to the frame of a watch movement;

- the Figures 7a and 7b represent a simplified perspective view of a resonator according to a second variant embodiment, and

- the Figures 8a and 8b represent a simplified perspective view of a resonator according to a third embodiment variant.

Mode (s) of realization of the invention

The Figures 1 to 3 illustrate, schematically and in a simplified manner, the operation of a tuning fork mechanical resonator according to a preferred embodiment of the present invention, in respective first, second and third configurations.

The resonator comprises a U-shaped tuning fork 1 having a pair of branches 2, 3 each of which carries a permanent magnet 4, 5 near its free end defining first and second magnetic fields.

Each magnet is disposed on its branch with its poles arranged in a direction substantially perpendicular to the longitudinal direction of the branch. In addition, the magnets 4 and 5 are substantially aligned and oriented here in the same way, that is to say by presenting each other opposite poles.

An escape wheel 6 is schematically illustrated on the Figures 1 to 3 , this being arranged between the two branches 2 and 3 of the tuning fork 1.

The escape wheel 6 here carries six permanent magnets 61 to 66 regularly arranged at its periphery with their poles substantially aligned in radial directions. Two adjacent magnets of the escape wheel have opposite orientations, from the point of view of the magnetic field produced, with reference to the center of the escape wheel. In other words, two adjacent permanent magnets of the escape wheel are arranged relative to one another to present to a given magnet of the tuning fork, when the escape wheel rotates, respective reversed polarities when they are located in look at it.

Advantageously, the escapement wheel 6 is kinematically connected to a power source (not shown) via a conventional finishing train, with a predefined gear ratio and, the implementation of which will not pose no particular difficulty to the skilled person. In particular, the escape wheel preferably carries an exhaust pinion arranged in engagement with a first mobile of the work train. Through this kinematic connection, the escapement wheel undergoes a permanent force tending to rotate it in a predefined direction of rotation (clockwise on the figures 2 and 3 ).

The escape wheel 6 and its magnets 61 to 66 are sized such that the latter are located within range of the magnets 4, 5 of the tuning fork, so that the magnetic fields of each other can interact.

It will be noted by way of example that for a tuning fork of 25 mm length vibrating at 360 Hz, the amplitude of the vibrations of its branches is of the order of 5 hundredths of a millimeter.

Because of the relative configurations of the magnets of the escape wheel, each of the magnets of the tuning fork alternately undergoes attractions and repulsions with reference to the escape wheel.

Indeed, the escape wheel 6 is free to turn on itself, in the direction of clockwise rotation, as a consequence of the permanent force that it undergoes from the energy source of the corresponding timepiece. .

In doing so, starting from the configuration of the figure 1 in which the interactions between his magnets and those of the tuning fork are almost null, it turns up to the configuration illustrated on the figure 2 .

The tuning fork can advantageously be secured to the frame of a watch movement in a conventional manner, that is to say by an arm secured to the frame by a first end and from the point situated in the middle of the base 8 of the tuning fork by its other end. In this situation, it is preferable that the tuning fork vibrates according to its first vibratory mode, that is to say with its branches presenting exactly opposite displacements. In other words, the two branches 2 and 3 deviate and move closer to each other.

Thus, the configuration illustrated on the figure 2 corresponds, at first, to a mutual approximation of the two branches 2 and 3. Given the orientations and relative positions of the magnets 4, 5 and 61 to 66, the branches 2 and 3 of the tuning fork are attracted towards the wheel exhaust 6 defining a transfer of energy from the escape wheel to the tuning fork, aiming to maintain the vibrations of the latter.

At the same time, the tuning fork acts as a magnetic brake on the escape wheel by slowing down its rotation induced by the force exerted by the energy source of the watch movement.

Since the amplitude of the force resulting from the magnetic interaction between the tuning fork and the escapement wheel is very small with reference to oscillations of the tuning fork, the latter naturally continue and the branches 2, 3, after having reached a maximum relative approximation , deform in opposite directions to deviate from each other.

The escape wheel 6 continues its rotational movement at the same time, which brings it to its position of the figure 3 , while the branches 2, 3 are still in their phase of relative spacing.

In the configuration of the figure 3 , the magnets facing each other have opposite polarities mutually, which results in the generation of a repulsive force between the branches 2, 3 of the tuning fork and the escape wheel. This repulsion defines a new transfer of energy from the escape wheel to the tuning fork, aiming to maintain the vibration of the latter.

It can be seen from the foregoing that an exhaust wheel carrying six permanent magnets performs a complete revolution on itself in six steps corresponding to three complete oscillations of the tuning fork, therefore the frequency of rotation of the escape wheel is equal here. one third of that of the tuning fork.

In general, the escape wheel advances two steps during each complete oscillation of the tuning fork. In other words, the frequency of the pitch of the escape wheel is double compared to the frequency of vibration of the tuning fork, whereas its frequency of rotation is of f / n Hz when it carries 2n permanent magnets, f being the frequency of vibration of the tuning fork.

It emerges that the rotational speed of the escape wheel and the gear ratios of the finishing and display workings can be adjusted according to the needs, independently of the frequency of oscillation of the tuning fork, in particular by modifying the number of permanent magnets carried by the escape wheel.

Of course, the vibration frequency of the tuning fork can be adjusted according to the needs, in a conventional manner, in particular by modifying the distribution of the masses in its branches or its material.

Advantageously for a watch application, it can be provided that the vibration frequency of the tuning fork present in the resonator according to the invention is substantially between 2 and 1000 Hz.

A vibration frequency higher than the oscillation frequencies of conventional balance wheels can, for example, be used in applications such as short time measurements. For example, for the realization of a chronograph function allowing measurement to hundredths of seconds, the escape wheel must advance at least one hundredths of a second. It must therefore have a step frequency of 100 Hz (or a multiple of 100 Hz), which corresponds to a vibration frequency of the tuning fork of 50 Hz (or a multiple of 50 Hz). Such operating frequencies can not be envisaged today in wristwatches using a spring-balance type oscillator for short and well-defined durations. Note that the realization of a mechanical exhaust operating at such frequencies is not without problems, especially in terms of wear. Since the escape wheel is the end part of a mechanical gear train, it is preferable that it operates with a low frequency of rotation, for the same reasons of wear and mechanical simplicity. This is possible by providing a suitable number of magnets. By way of example, if twelve magnets are provided on the escape wheel, with a vibrating tuning fork at 50 Hz, the escape wheel rotates with a rotation frequency of 8.33 Hz, similar to that which it presents in known watch movements, while allowing the measurement of hundredths of a second.

Preferably, the escape wheel carries 2n permanent magnets, n being at least 1, preferably less than or equal to 40. These magnets are advantageously evenly distributed near the periphery or at the periphery of the escape wheel, to ensure a regular rotation of the latter. Of course, the diameter of the escape wheel can influence the number of magnets that it comprises. Too many magnets is undesirable because it tends to give rise to a quasi-continuous interaction between the escape wheel and the tuning fork, detrimental to the isochronism of the resonator according to the invention.

Of course, the escape wheel 6 may be arranged outside the tuning fork to cooperate with a single branch of the tuning fork, without departing from the scope of the present invention.

An example of an additional application, particularly interesting, is presented on the figures 4 and 5 .

According to this variant embodiment, two escape wheels 40 and 50 are respectively associated with the first and second branches 20, 30 of a tuning fork 10, making it possible to control two separate display wheels (not shown).

For reasons of simplification of the illustration, the two escape wheels illustrated on the figures 4 and 5 are the same. They can be used to control the respective displays of two running gear, for example, one displaying the solar time and the other the sidereal time.

The operating principle of the resonator illustrated on the figures 4 and 5 will not be discussed in detail inasmuch as it is similar to that of the embodiment of the preceding figures. The main difference with respect to the previous embodiment lies in the fact that pulses are transmitted independently to each of the branches of the tuning fork by the escape wheel associated therewith, their respective magnets 41, 51 being advantageously arranged outwardly. , next to the exhaust wheels.

In this case, it is also possible, alternatively, that the escape wheels 40 and 50 are different from each other, in particular that they carry different numbers of permanent magnets, without departing from the scope of the present invention. Likewise, the gear ratios of the display gearings respectively associated with one and the other of the escape wheels may be different, in such a way, for example, that one is associated with the display. of the current time, while the other is associated with a chronograph function.

Moreover, the figure 6 illustrates a variant of fixing the tuning fork on the frame of a watch movement. Instead of fixing the tuning fork by a single arm, solidary of the midpoint of its base as mentioned above, it it is possible to fix it by means of two arms connected to the tuning fork by its two primary nodes, in a known manner, without departing from the scope of the invention. Similarly, it is also possible to arrange the magnets at the secondary nodes.

The Figures 7a and 7b represent a resonator according to a second embodiment of the present invention.

In this variant, the tuning fork 1 and the escape wheel 60 are contained in respective planes that are substantially orthogonal to one another.

Those skilled in the art may choose to have any of these two members in a plane parallel to the general plane of the corresponding watch movement, the other member being then orthogonal to it, according to its needs. Insofar as the escape wheel is part of the mechanical gear train, it is preferable that it be arranged in the same plane as the watch movement, which implies that the tuning fork is substantially orthogonal to the general plane of the watch movement and of the watch. Such a configuration of the tuning fork has, in principle, never been the subject of a product marketed on the market so far.

The principle of operation of the resonator according to this embodiment variant is similar to what has been described above and will therefore not be repeated in detail.

The figure 7a illustrates a position of the escape wheel 60 in which one of its magnets interacts with the magnets of the tuning fork to give rise to a mutual attraction.

The figure 7b illustrates a position of the escape wheel 60 in which another of its magnets interacts with the magnets of the tuning fork to give rise to mutual repulsion.

The Figures 8a and 8b represent a resonator according to a third embodiment of the present invention.

In this variant, the tuning fork 100 and the escape wheel 60 are also contained in respective planes substantially orthogonal to each other, but this time, the tuning fork carries only one magnet arranged on one branches, to choose.

The principle of operation of the resonator according to this embodiment variant is similar to what has been described above and will therefore not be repeated in detail.

The figure 8a illustrates a position of the escape wheel 60 in which one of its magnets interacts with the magnet of the tuning fork to give rise to a mutual attraction.

The figure 8b illustrates a position of the escape wheel 60 in which another of its magnets interacts with the tuning fork magnet to give rise to mutual repulsion.

As already pointed out, the structure of the tuning fork is such that the magnetic interaction of only one of its branches with the escape wheel is sufficient to sustain its vibrations satisfactorily.

In general, the tuning fork may for example be made of silicon with addition of SiO ₂ (especially to allow batch machining), quartz or any other material having properties suitable for the implementation of the present invention, such as a combination of silicon and quartz to ensure stable behavior as a function of temperature.

It is also recalled that, by permanent magnet, it is necessary to understand here, without departing from the scope of the invention, an element producing a permanent magnetic field, whatever its shape, that is to say that it can be constituted by a portion of material taken into the mass and having undergone a treatment in order to present the required magnetic properties, by an insert, or even by a deposited layer, of a suitable magnetic material. It will be possible to use any known iron oxide, or to make layers of samarium alloy and cobalt alloy, for example.

Note that the construction of the resonator according to the present invention allows its simple integration into an existing watch caliber, replacing the conventional resonator spiral balance, without requiring major modification of the caliber watch.

The foregoing description attempts to describe a particular embodiment by way of non-limiting illustration and the invention is not limited. to the implementation of certain particular characteristics which have just been described, such as for example the form specifically illustrated and described for the tuning fork, the escapement wheel or the permanent magnets.

Those skilled in the art will not encounter any particular difficulty in adapting the content of the present disclosure to their own needs and implement a mechanical resonator different from that according to the embodiment described here, but comprising a free magnetic escapement as described above, without departing from the scope of the present invention.

Note that if the tuning fork comprises two magnets aligned and having the same magnetic orientation, the escape wheel has 2 (2n + 1) permanent magnets to allow the tuning fork to vibrate in its main vibration mode, while it includes 4n permanent magnets if the respective orientations of the two magnets of the tuning fork are opposite.

In general, it should be noted that the invention is not limited to the number of magnets carried by the tuning fork, nor to their respective implantations on the branches of the tuning fork. It is indeed possible to provide one, one per branch or more than one per branch, at any level of the branch in its longitudinal direction as the corresponding amplitude of vibration is sufficient, without leaving of the scope of the invention.

Claims (10)

1. A magnetic resonator, for a timepiece, comprising
   an oscillator (1) of the tuning-fork type having first and second branches (2, 3) arranged substantially in the form of a U, at least one of said branches supporting at least one first permanent magnet (4, 5) defining a first magnetic field,
   an escape wheel (6), free of any mechanical contact with said oscillator, and designed to be arranged in engagement with a first mobile of a watchwork gear train in order to allow it to be driven by a power source of the timepiece and, situated within range of said first permanent magnet in order to undergo the influence of said first magnetic field,
   characterized in that said escape wheel (6) supports at least two permanent magnets (61 to 66), preferably at least four, arranged so that the vibrations of said branch of said tuning fork (1), on the one hand, control the rotation speed of said escape wheel and, on the other hand, are sustained periodically by the magnetic interaction between said first permanent magnet (4, 5) of said tuning fork and said permanent magnets (61 to 66) of said escape wheel in order to define a free escapement.
2. The resonator as claimed in claim 1, characterized in that said escape wheel (6) supports 2n permanent magnets (61 to 66), n being at least equal to 1, preferably less than or equal to forty.
3. The resonator as claimed in claim 2, characterized in that said permanent magnets (61 to 66) are evenly distributed close to the periphery of said escape wheel (6).
4. The resonator as claimed in any one of claims 1 to 3, characterized in that two adjacent permanent magnets (61 to 66) of said escape wheel (6) are arranged relative to one another in order to present to said first magnet (4, 5) of said tuning fork (1), when said escape wheel turns, respective inverted polarities when they are situated facing said first magnet.
5. The resonator as claimed in any one of claims 2 to 4, characterized in that said escape wheel (6) is arranged between said branches (2, 3) of said tuning fork (1).
6. The resonator as claimed in claim 5, characterized in that the other of said branches (2, 3) supports a second permanent magnet (4, 5) defining a second magnetic field and, in that said magnets (61 to 66) of said escape wheel (6) are arranged on the latter such that they are diametrically opposed in twos by presenting magnetic orientations such that they have interactions of the same nature with said magnets (4, 5) of said tuning fork (1).
7. The resonator as claimed in claim 6, characterized in that said magnets (4, 5) of said tuning fork (1) are substantially diametrically opposed to one another, with reference to said escape wheel (6).
8. The resonator as claimed in any one of the preceding claims, characterized in that said permanent magnets (4, 5) of said tuning fork (1) are placed close to the end of said corresponding branch (2, 3).
9. A clockwork movement for a mechanical timepiece comprising a resonator as claimed in any one of the preceding claims.
10. A mechanical timepiece comprising a clockwork movement as claimed in claim 9.

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