EP2881804B1 - Hairspring-stud assembly for timepiece - Google Patents

Description

Field of the invention

The invention relates to an assembly comprising a spiral which comprises two opposite lateral surfaces distant from a reference thickness, and a stud having a housing dimensioned for receiving said spiral, said stud having, around said housing, at least one monolithic component in shape memory alloy having at least two tabs together defining an air gap and each arranged to bear on one of said opposite side surfaces of said hairspring, and wherein in the free state, the minimum width of said air gap is greater than the maximum value of said reference thickness when said component is in an open position corresponding to a martensite structure, and wherein the maximum width of said gap is less than the minimum value of said reference thickness when said component is in a closed position corresponding to an austenitic structure.

The invention also relates to a watch movement comprising at least one such set.

The invention also relates to a timepiece comprising at least one such movement and / or at least one such set.

The invention further relates to a method of attaching a hairspring to a peg.

The invention relates to the field of mechanical clockwork oscillator mechanisms, comprising a spiral spring.

Background of the invention

Mechanical clockwork oscillator mechanisms, comprising a spiral spring, generally comprise a pin for fixing the outer end of the spiral spring.

The attachment of the hairspring to the pin is usually done by gluing, which is not perfectly reproducible, and can lead to pollution of the watch movement.

The document CH317531 A in the name of EBAUCHES BETTLACH SA describes a slotted stud, in a plastically deformable material so as to permanently secure the stud and the spiral.

The document EP1580625A1 in the name of ASULAB SA describes the fixing of a lift in a housing of an anchor, the portion comprising this housing is in a shape memory alloy capable of undergoing a reversible transformation between an austenitic phase and a martensitic phase.

Summary of the invention

The invention proposes to provide an alternative to the gluing of the hairspring in the eye, and to replace it with a reproducible fixation of the hairspring, less dependent on the operator performing the assembly.

To this end, the invention relates to an assembly comprising a hairspring which comprises two opposite side surfaces remote from a reference thickness, and such piton sized to receive said hairspring according to claim 1.

The invention also relates to a watch movement comprising at least one such set.

The invention also relates to a timepiece comprising at least one such movement and / or at least one such set.

The invention further relates to a method of fixing a hairspring to a peg, according to claim 10.

The invention also relates to another method of fixing a hairspring to a peg, according to claim 11.

Brief description of the drawings

• la figure 1 représente, de façon schématisée et selon une coupe transversale du spiral, un spiral présenté dans un logement que comporte un piton à géométrie variable selon l'invention, lequel piton est dans une position ouverte ;
• la figure 2 représente, de façon similaire à la figure 1, le même ensemble constitué du piton et du spiral, dans une position fermée du piton où le spiral est pincé entre deux pattes du piton ;
• la figure 3 représente, de façon similaire à la figure 2, un tel ensemble oû le spiral est en position de butée sur une face d'appui du piton, et dans une position fermée du piton où le spiral est pincé entre deux pattes du piton ;
• la figure 4 représente, de façon schématisée et en perspective, à l'état libre, un piton selon l'invention, en position fermée, et comportant deux pattes avec un profil de forme ;
• la figure 5 représente, de façon schématisée et en vue de dessous, le piton de la figure 4 coopérant en position fermée de pincement d'un spiral lequel comporte une succession de zones de moindre et de plus forte épaisseur ;
• la figure 6 représente, sous forme d'un schéma-blocs, une montre comportant un mouvement comportant un ensemble lui-même formé d'un spiral et d'un piton selon l'invention.

Other features and advantages of the invention will appear on reading the detailed description which follows, with reference to the appended drawings, in which:

• the figure 1 represents, schematically and in a cross sectional view of the hairspring, a hairspring presented in a housing that comprises a peg with variable geometry according to the invention, which bolt is in an open position;
• the figure 2 represents, similarly to the figure 1 , the same set consisting of the stud and the spiral, in a closed position of the peak where the spiral is pinched between two legs of the piton;
• the figure 3 represents, similarly to the figure 2 such a set where the hairspring is in abutment position on a bearing face of the pin, and in a closed position of the pin where the hairspring is pinched between two legs of the pin;
• the figure 4 represents, schematically and in perspective, in the free state, a pin according to the invention, in the closed position, and having two tabs with a shape profile;
• the figure 5 represents, schematically and in a view from below, the peak of the figure 4 cooperating in the closed pinch position of a spiral which comprises a succession of areas of smaller and thicker;
• the figure 6 represents, in the form of a block diagram, a watch comprising a movement comprising a set itself formed of a spiral and a stud according to the invention.

Detailed Description of the Preferred Embodiments

Mechanical clock oscillator mechanisms, comprising a spiral spring whose outer end is fixed to a pin, itself attached to a plate, a bridge, a cock or the like.

The invention proposes to provide a reproducible fixation of the hairspring, less dependent on the operator performing the assembly, and preferably achievable with automated production means such as a robot assembly or the like, performing the gripping and the relative positioning of the components between them, to which this robot component is capable of selectively applying heating or cooling in a localized and almost instantaneous manner.

The invention thus relates to a clock 1 having a housing for receiving a hairspring 3, this hairspring 3 conventionally comprising two opposite lateral surfaces 31, 32, distant from a reference thickness ER.

According to the invention, this stud 1 comprises, around the housing, at least one monolithic component 8 of shape memory alloy.

The shape memory alloy may be chosen from different families of materials, in particular and without limitation heat-activated shape memory alloys, magnetically activated shape memory alloys, or shape memory polymers.

The invention is described herein in a particular nonlimiting example with a thermally activated shape memory alloy.

For such shape memory alloys, a so-called martensitic state and a so-called austenitic state, which correspond to different structuring of the material, and to spatial distributions of the different atoms in space, are generally distinguished.

This component 8 comprises at least two lugs 11, 12, which together define an air gap E and each arranged to bear on one of the opposite lateral surfaces 31, 32, of such a hairspring 3.

In the free state, the minimum width of this gap E is greater than the maximum value of the reference thickness ER when the component 8 is in an open position corresponding to a martensitic structure, and the maximum width of the gap E is less than the minimum value of the reference thickness ER when the component 8 is in a closed position corresponding to an austenitic structure.

The Figures 1 and 2 illustrate these two open and closed positions of the component 8 around the hairspring 3. The lugs 11 and 12 pinch the hairspring 3, preferably with a bearing on the entire height of the lateral surfaces 31 and 32 of the hairspring, and over the entire thickness L piton 1.

In a particular embodiment, as visible on the figure 3 , the piton housing 1 comprises an axial abutment support surface 9 arranged to receive a support 33 of a hairspring 3.

In a particular embodiment, as visible on the Figures 1 to 4 , piton 1 is monolithic with component 8.

In a particular embodiment of the piton 1, the shape memory alloy is chosen so that the piton 1 supports, without significant modification of its clamping, a minimum service temperature TSMIN of -20 ° C.

In another particular embodiment of the piton 1, the shape memory alloy is chosen so that the piton 1 supports, without significant modification of its clamping, a maximum operating temperature TSMAX of + 70 ° C.

The invention also relates to an assembly 10 comprising such a hairspring 3 which comprises two opposite lateral surfaces 31, 32, remote by a reference thickness ER, and such a pin 1 sized to receive this hairspring 3. In a particular embodiment, such that visible on the figure 5 , the spiral 3 locally comprises at least one zone of lesser thickness, the minimum thickness of which is the reference thickness ER, for which the piton 1 is designed, and which is framed by areas of great thickness 35 whose minimum thickness is greater than the reference thickness ER.

More particularly, the spiral 3 comprises an alternation of such areas of lesser thickness and such thick zones 35, for the adjustment of the active length of the spiral 3 by the discrete cooperation of the stud 1 with one of these zones. The hairspring 3 can, again, be graduated at these different positions of adjustment in active length.

In a particular embodiment, each zone of lesser thickness 30 has a length substantially equal to, slightly greater than, the thickness of the lugs 11, 12, of the peak 1.

In a particular execution, illustrated by the Figures 4 and 5 these zones of lesser thickness 30 all have the same profile, and in that the lugs 11, 12, of the piton 1 each have a complementary profile of the spiral profile 3 which faces them in each zone of lesser thickness 30.

The invention also relates to a watch movement 100 comprising at least one such stud 1, or / and such an assembly 10.

The invention also relates to a timepiece 1000 comprising at least one such movement 100, or / and at least one such pin 1, and / or such a set 10.

• une première phase de déformation initiale du composant 8 en alliage à mémoire de forme dans un état martensitique et à une température inférieure à une première température de début de transformation As, caractéristique du début de la transformation de la structure martensitique en structure austénitique lors d'un chauffage ;
• suivie d'une deuxième phase de mise en coopération du composant 8 avec le spiral 3, toujours dans cet état martensitique et à une température inférieure à la première température de transformation As ;
• une troisième phase, dans laquelle le serrage du composant 8 sur le spiral 3 est réalisé par le chauffage à une température supérieure à une deuxième température de fin de transformation Af, qui est caractéristique de la fin de la transformation de la structure martensitique en structure austénitique lors d'un chauffage, et qui est donc supérieure à la première température de transformation As. L'assemblage conserve ensuite sa force de serrage tant qu'il ne repasse pas en-dessous d'une troisième température de transformation Ms, qui est caractéristique du début de la transformation de la structure austénitique en structure martensitique lors d'un refroidissement (la fin de cette transformation correspondant à une quatrième température de transformation Mf). L'emploi d'un matériau à large hystérèse (différence entre Ms et As) permet par exemple un montage à une température de l'ordre de l'ambiante (voisine de 20°C), un chauffage limité et le serrage conserve ensuite ses propriétés sur une large plage d'utilisation.

The assembly process comprises successive phases:

• a first phase of initial deformation of the shape memory alloy component 8 in a martensitic state and at a temperature below a first transformation start temperature As, characteristic of the beginning of the transformation of the martensitic structure into austenitic structure when a heater ;
• followed by a second phase of cooperation of the component 8 with the spring 3, still in this martensitic state and at a temperature below the first transformation temperature As;
• a third phase, in which the tightening of the component 8 on the spiral 3 is achieved by heating to a temperature higher than a second end-of-transformation temperature Af, which is characteristic of the end of the transformation of the martensitic structure into austenitic structure during heating, and which is therefore greater than the first transformation temperature As. The assembly then retains its clamping force as long as it does not pass again below a third transformation temperature Ms, which is characteristic of the beginning of the transformation of the austenitic structure into a martensitic structure during cooling (the end of this transformation corresponding to a fourth transformation temperature Mf). The use of a material with a large hysteresis (difference between Ms and As) makes it possible, for example, to mount at a temperature of the order of the ambient (close to 20 ° C.), a limited heating and the clamping then retains its properties over a wide range of use.

The objective is not to go below the transformation temperature Ms during the service, so as to avoid modifying the clamping by a possible phase transformation, even partial (that is to say without necessarily reaching the fourth transformation temperature Mf at which the transformation of austenitic structure into a martensitic structure is completely realized).

In one embodiment, the shape memory alloy constituting component 8 is selected to allow a minimum operating temperature TSMIN of -20 ° C.

In a second embodiment, the shape memory alloy constituting the component 8 is chosen so as to allow a maximum operating temperature TSMAX of + 70 ° C.

The processing and fixing temperatures must be low enough to prevent loosening of the hairspring if the watch in which it is incorporated remains cold.

In another particular embodiment, the component is produced in one of the "Nitinol" nickel titanium alloys, in a first form at a temperature below -40 ° C., and in a second form at an ambient temperature of between -20 ° C. and + 70 ° C, this second form to ensure the clamping required for a correct and controlled friction of the spiral. Medical tools, and in particular orthodontics, allow very rapid cooling to -50 ° C or -60 ° C, or even lower temperatures, to bring the component in the first form that allows its threading on the piton body. It is sufficient to reduce the assembly to the temperature of the assembly room, conventionally close to + 20 ° C, to ensure the tightening of the component in its second form, and immediately perform the torque measurement test. friction to validate the component for its direct use in a movement.

The invention also relates to an assembly method that can be easily automated with a manipulator robot comprising heating means or cooling in a localized and almost instantaneous manner, by which different successive steps are carried out.

• on réalise, pour la réception d'un spiral 3 d'épaisseur de référence ER, un tel piton 1 comportant, autour d'un logement prévu pour la réception de ce spiral 3, au moins un composant 8 monolithique en alliage à mémoire de forme comportant au moins deux pattes 11, 12, définissant ensemble un entrefer E où, à l'état libre du piton 1, la largeur minimale de l'entrefer E est supérieure à la valeur maximale de l'épaisseur de référence ER quand le composant 8 est dans une position ouverte dans une structure martensitique, et la largeur maximale de l'entrefer E est inférieure à la valeur minimale de l'épaisseur de référence ER quand le composant 8 est dans une position fermée dans une structure austénitique ;
• on effectue une première phase de déformation d'ouverture du composant 8 dans un état martensitique et à une température inférieure à une première température de début de transformation As, caractéristique du début de la transformation de la structure martensitique en structure austénitique lors d'un chauffage ;
• on introduit un spiral 3 dans le logement , dans une position déterminée ou jusqu'à l'atteinte d'une position de butée ;
• on effectue une deuxième phase de déformation de fermeture du composant 8, dans laquelle on réalise le serrage des pattes 11, 12, sur le spiral 3 par le chauffage du composant 8 à une température supérieure à une deuxième température de fin de transformation Af.

According to the invention, this method of fixing a hairspring 3 to a pin 1. comprises the following successive steps:

• for the reception of a hairspring 3 of reference thickness ER, there is provided such a peg 1 comprising, around a housing provided for receiving this hairspring 3, at least one monolithic component 8 made of a shape memory alloy. having at least two tabs 11, 12, together defining an air gap E where, in the free state of the piton 1, the minimum width of the gap E is greater than the maximum value of the reference thickness ER when the component 8 is in an open position in a martensitic structure, and the maximum width of the gap E is less than the minimum value of the reference thickness ER when the component 8 is in a closed position in an austenitic structure;
• a first phase of opening deformation of the component 8 is carried out in a martensitic state and at a temperature below a first start transformation temperature As, characteristic of the beginning of the transformation of the martensitic structure into austenitic structure during heating ;
• a hairspring 3 is introduced into the housing in a determined position or until a stop position is reached;
• a second phase of closure deformation of the component 8, in which the tabs 11, 12 are tightened on the spring 3 by heating the component 8 to a temperature higher than a second end of transformation temperature Af.

• on réalise, pour la réception d'un spiral 3 d'épaisseur de référence ER, un tel piton 1 comportant, autour d'un logement prévu pour la réception du spiral 3, au moins un composant 8 monolithique en alliage à mémoire de forme comportant au moins deux pattes 11, 12, définissant ensemble un entrefer E où, à l'état libre du piton 1, la largeur minimale de l'entrefer E est supérieure à la valeur maximale de l'épaisseur de référence ER quand le composant 8 est dans une position ouverte dans une structure martensitique, et en ce que la largeur maximale de l'entrefer E est inférieure à la valeur minimale de l'épaisseur de référence ER quand le composant 8 est dans une position fermée dans une structure austénitique à une température de service ;
• on effectue une première phase de déformation d'ouverture du composant 8 dans une structure martensitique ;
• on insère le spiral 3 dans le logement, et on les positionne l'un par rapport à l'autre en position adéquate ;
• on les maintient l'un et l'autre en position jusqu'au retour à la température ambiante.

In a variant of this method of fixing a hairspring 3 to a pin 1, the method comprises the following successive steps:

• for the reception of a hairspring 3 of reference thickness ER, there is provided such a peak 1 comprising, around a housing provided for receiving the hairspring 3, at least one monolithic component 8 made of a shape memory alloy comprising at least two tabs 11, 12, together defining an air gap E where, in the free state of the peak 1, the minimum width of the gap E is greater than the maximum value of the reference thickness ER when the component 8 is in an open position in a martensitic structure, and in that the maximum width of the gap E is less than the minimum value of the reference thickness ER when the component 8 is in a closed position in an austenitic structure at a temperature on duty ;
• a first phase of opening deformation of the component 8 is carried out in a martensitic structure;
• the hairspring 3 is inserted into the housing and positioned relative to each other in an adequate position;
• they are held in position until the return to room temperature.

In a variant, a first phase of opening deformation of the component 8 is carried out in a martensitic structure, then cooling or heating of the shape memory alloy component 8 is carried out, then the spiral 3 is inserted into the housing, and positioned relative to each other in an adequate position. We understand that we must not cool more, nor warm more, before inserting the hairspring.

The temperatures M _s and M _f must be low enough not to allow the hairspring to loosen if the watch remains cold. Ideally A _s and A _f are around 20 ° C to 30 ° C but can also take different values.

Those skilled in the art will be able to extrapolate the invention for other configurations, in particular a reverse application of the invention.

The piton in its storage state, before mounting the hairspring, may or may be parallel branches in which case a spacer operation is performed just before mounting, or be divergent branches, in which case it is only y present the hairspring in position. In either case, the spacing must be the result of prior deformation, so that the shape memory allows to find the pre-deformation state.

The technical terms contained in the above description (austenite, martensite, A _s , A _f , M _s , M _f ) are relevant primarily for thermally activated shape memory alloys. These concepts nevertheless apply magnetically activated shape memory alloys as well as shape memory polymers.

In the case of magnetically activated shape memory alloys, the notions of transition temperatures must be replaced by notions of magnetic field thresholds. This solution is advantageous, in the case where the positioning is done under a magnetic field, to eliminate any possibility of loosening at low temperature.

In the case of shape memory polymers, which are often block copolymers, the so-called "austenitic" and "martensitic" phases do not exist as such, and the transition occurs at the molecular level at a transition temperature. This temperature may correspond to the glass transition temperature of one of the blocks or to its melting temperature.

• ou bien des alliages à mémoire de forme activés thermiquement :
  • Ag-Cd
  • Au-Cd
  • Co-Ni-Al
  • Co-Ni-Ga
  • Cu-Al-Ni
  • Cu-Al-Be
  • Cu-Zn-Al
  • Cu-Zn-Si
  • Cu-Zn-Sn
  • Cu-Zn
  • Cu-Sn
  • In-Ti
  • Mn-Cu
  • Nb-Ru
  • Ta-Ru
  • Ni-Al
  • Ni-Ti
  • Ni-Ti-Fe
  • Ni-Ti-Cu
  • Ni-Ti-Nb
  • Ni-Ti-Pd
  • Ni-Ti-Hf
  • Fe-Pt
  • Fe-Mn-Si
  • Fe-Pd
  • Fe-Ni-Co-Ti
  • Ti-Pd
  • Ti-Pt
  • Ti-Au
• ou bien des alliages à mémoire de forme activés magnétiquement :
  • Ni-Mn-Ga
  • Fe-Ni-Ga
  • Co-Ni-Ga
  • Fe-Pd
  • Fe-Pt
• ou bien des polymères et copolymères à mémoire de forme :
  • PET-PEO
  • Polynorbornene
  • PE-Nylon
  • PE-PVA
  • PS-Poly(1,4-Butadiène)
  • Polyuréthanes.

Without limitation, shape memory materials that can be used for the implementation of the invention are:

• or thermally activated shape memory alloys:
  • Ag-Cd
  • In-Cd
  • Co-Ni-Al
  • Co-Ni-Ga
  • Cu-Al-Ni
  • Cu-Al-Be
  • Cu-Zn-Al
  • Cu-Zn-Si
  • Cu-Zn-Sn
  • Cu-Zn
  • Cu-Sn
  • In-Ti
  • Mn-Cu
  • Nb-Ru
  • Ta-Ru
  • Ni-Al
  • Ni-Ti
  • Ni-Ti-Fe
  • Ni-Ti-Cu
  • Ni-Ti-Nb
  • Ni-Ti-Pd
  • Ni-Ti-Hf
  • Fe-Pt
  • Fe-Mn-Si
  • Fe-Pd
  • Fe-Ni-Co-Ti
  • Ti-Pd
  • Ti-Pt
  • Ti-Au
• or else magnetically activated shape memory alloys:
  • Ni-Mn-Ga
  • Fe-Ni-Ga
  • Co-Ni-Ga
  • Fe-Pd
  • Fe-Pt
• or polymers and copolymers with shape memory:
  • PET-PEO
  • polynorbornene
  • PE-nylon
  • PE-PVA
  • PS-Poly (1,4-butadiene)
  • Polyurethanes.

Of course, these shape memory materials that can be used for the implementation of the invention may, again, be heat-activated shape memory alloys and / or magnetically activated.

Thanks to the invention, the clamping force of the stud on the spiral is precisely controlled in a perfectly reproducible assembly.

Claims (11)

1. Assembly (10) including a balance spring (3) which comprises two opposite lateral surfaces (31, 32) separated by a reference thickness (ER), and a balance spring stud (1) including a housing dimensioned to receive said balance spring (3) with two opposite lateral surfaces (31, 32) separated by a reference thickness (ER), said stud (1) including, around said housing, at least one one-piece component (8) made of a shape memory alloy and including at least two lugs (11, 12) defining together an air gap (E) and each arranged to rest on one of said opposite lateral surfaces (31, 32) of said balance spring (3), and wherein, in the free state, the minimum width of said air-gap (E) is greater than the maximum value of said reference thickness (ER) when said component (8) is in an open position corresponding to a martensitic structure, and wherein the maximum width of said air-gap (E) is less than the minimum value of said reference thickness (ER) when said component (8) is in a closed position corresponding to an austenitic structure, characterized in that said balance spring (3) locally includes at least one area of lesser thickness (30) whose minimum thickness is said reference thickness (ER) for which said stud (1) is devised, and which is surrounded by areas of large thickness (35) whose minimum thickness is greater than said reference thickness (ER).
2. Assembly (10) according to claim 1, characterized in that said housing of said balance spring stud (1) includes an axial abutment surface (9) arranged to receive in abutment an edge (33) of a said balance spring (3).
3. Assembly (10) according to claim 1 or 2, characterized in that said stud (1) is made in one piece with said component (8).
4. Assembly (10) according to any of claims 1 to 3, characterized in that said balance spring (3) includes an alternation of said areas of lesser thickness (30) and areas of large thickness (35), for adjustment of the active length of said balance spring (3) through the discrete cooperation of said stud (1) with one of said areas of lesser thickness (30).
5. Assembly (10) according to any of claims 1 to 4, characterized in that each said area of lesser thickness (30) has a length substantially equal to the thickness (L) of said lugs (11, 12) of said stud (1).
6. Assembly (10) according to any of claims 1 to 5, characterized in that said areas of lesser thickness (30) all have the same profile, and in that said lugs (11, 12) of said stud (1) each have a complementary profile to the profile of said balance spring (3) which faces said lugs in each said area of lesser thickness (30).
7. Timepiece movement (100) including at least one assembly (10) according to any of claims 1 to 6.
8. Timepiece (200) including at least one movement (100) according to claim 7 or and an assembly (10) according to any of claims 1 to 6.
9. Method for attaching a balance spring (3) to a balance spring stud (1) characterized in that the method includes the following steps:

   - a said balance spring stud (1) is produced for receiving a balance spring (3) of reference thickness (ER), said stud including, around a housing provided for receiving said balance spring (3), at least one one-piece component (8) made of a shape memory alloy and including at least two lugs (11, 12), defining together an air-gap (E) wherein, in the free state of said stud (1), the minimum width of said air-gap (E) is greater than the maximum value of said reference thickness (ER) when said component (8) is in an open position in a martensitic structure, and in that the maximum width of said air-gap (E) is less than the minimum value of said reference thickness (ER) when said component (8) is in a closed position in an austenitic structure;

   - said balance spring (3) is produced, locally including at least one area of lesser thickness (30) whose minimum thickness is said reference thickness (ER), for which said stud (1) is devised, and which is surrounded by areas of large thickness (35) whose minimum thickness is greater than said reference thickness (ER),

   - there is effected a first phase of deformation to open said component (8) in a martensitic state and at a lower temperature than a first transformation start temperature (As), characteristic of the start of transformation of the martensitic structure into an austenitic structure on heating;

   - - a balance spring (3) is inserted into said housing in a determined position or until a stop position is reached;

   - - there is effected a second phase of deformation to close said component (8), in which said lugs (11, 12) are clamped onto said balance spring (3) by heating said component (8) to a higher temperature than a second temperature (Af) at which the transformation from the martensitic structure to the austenitic structure ends.
10. Method for attaching a balance spring (3) to a balance spring stud (1) characterized in that the method includes the following steps:

    - a said balance spring stud (1) is produced for receiving a balance spring (3) of reference thickness (ER), said stud including, around a housing provided for receiving said balance spring (3), at least one one-piece component (8) made of a shape memory alloy, whose temperature at which the transformation from the martensitic structure to the austenitic structure ends is lower than the ambient temperature, and including at least two lugs (11, 12), defining together an air-gap (E) wherein, in the free state of said stud (1), the minimum width of said air-gap (E) is greater than the maximum value of said reference thickness (ER) when said component (8) is in an open position in a martensitic structure, and in that the maximum width of said air-gap (E) is less than the minimum value of said reference thickness (ER) when said component (8) is in a closed position in an austenitic structure at an operating temperature;

    - said balance spring (3) is produced, locally including at least one area of lesser thickness (30) whose minimum thickness is said reference thickness (ER), for which said stud (1) is devised, and which is surrounded by areas of large thickness (35) whose minimum thickness is greater than said reference thickness (ER);

    - there is effected a first phase of deformation to open said component (8) in a martensitic structure;

    - said balance spring (3) is inserted in said housing , and the spring and housing are properly positioned with respect to each other;

    - they are maintained in position until the ambient temperature is reached again.
11. Method according to claim 10, characterized in that the method includes the following series of steps:

    - a said balance spring stud (1) is produced for receiving a balance spring (3) of reference thickness (ER), said stud including, around a housing provided for receiving said balance spring (3), at least one one-piece component (8) made of a shape memory alloy and including at least two lugs (11, 12), defining together an air-gap (E) wherein, in the free state of said stud (1), the minimum width of said air-gap (E) is greater than the maximum value of said reference thickness (ER) when said component (8) is in an open position in a martensitic structure, and in that the maximum width of said air-gap (E) is less than the minimum value of said reference thickness (ER) when said component (8) is in a closed position in an austenitic structure at an operating temperature;

    - there is effected a first phase of deformation to open said component (8) in a martensitic structure;

    - cooling or heating is performed on said shape memory alloy component (8);

    - said balance spring (3) is inserted in said housing , and the spring and housing are properly positioned with respect to each other;

    - they are maintained in position until the ambient temperature is reached again.

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