EP1868045B1 - Horological collet - Google Patents

Description

The present invention relates to a timepiece ferrule, more specifically a spiral-ferrule assembly, the ferrule for fixing the inner end of the spiral to the axis of a pendulum.

A disadvantage of certain conventional ferrules, particularly elastic ferrules, is that the distance between the junction point of the spiral to the ferrule and the center of the balance shaft is modified during the driving of the ferrule on the balance shaft, which offsets the hairspring and thus damages the isochronism of the sprung balance.

Solutions have been proposed to overcome this disadvantage. In documents EP 1,513,029 and EP 1 637 940 is described a ferrule comprising resilient arms arranged in a triangle and an outer frame that stiffens the junction areas between the elastic arms, in particular the junction zone where the junction point between the spiral and the ferrule is located. In the document EP 1 584 994 is described a ferrule constituted by a metal strip and whose shape is specially chosen, with a width and an angular distribution of the points of contact with the variable balance axis, so that the distance between the junction point with the spiral and the center of the balance shaft is substantially the same after driving.

The present invention aims to propose another solution to maintain the distance between the junction point of the spiral to the ferrule and the center of the balance shaft substantially constant during driving, in particular a solution that does not require or provide a frame externally, or to give the whole shell a particular form.

For this purpose there is provided a spiral-ferrule assembly according to claim 1 attached and a method of making a ferrule according to claim 13. Particular embodiments of the invention are defined in the dependent claims.

• la figure 1 montre une virole selon un premier mode de réalisation de l'invention, à laquelle est rattachée l'extrémité intérieure d'un spiral (montré partiellement), la virole étant chassée sur un axe de balancier ;
• la figure 2 montre le dessin d'une virole servant de base à la conception de la virole selon l'invention, cette virole de base étant représentée de manière exagérée dans un état déformé sous l'effet de forces radiales exercées par un axe chassé dans cette virole ;
• la figure 3 montre de manière exagérée les déformations locales de la virole selon l'invention causées par le chassage de l'axe de balancier dans cette virole ;
• la figure 4 montre de manière exagérée la virole selon l'invention avec son spiral (montré partiellement) telle que déformée après son chassage sur l'axe de balancier, les parties en gris correspondant à des déformations supérieures à 0,1 µm et les parties en blanc correspondant à des déformations inférieures à 0,1 µm ; et
• la figure 5 montre une virole selon un second mode de réalisation de l'invention, avec son spiral (montré partiellement).

Other features and advantages of the present invention will appear on reading the following detailed description given with reference to the accompanying drawings in which:

• the figure 1 shows a ferrule according to a first embodiment of the invention, to which is attached the inner end of a spiral (shown partially), the ferrule being driven on a balance shaft;
• the figure 2 shows the drawing of a ferrule serving as a basis for the design of the ferrule according to the invention, this base ferrule being represented in an exaggerated manner in a deformed state under the effect of radial forces exerted by an axis driven in this ferrule;
• the figure 3 shows in an exaggerated manner the local deformations of the ferrule according to the invention caused by the driving of the balance shaft in this ferrule;
• the figure 4 shows excessively the ferrule according to the invention with its spiral (shown partially) as deformed after its driving on the balance shaft, the gray parts corresponding to deformations greater than 0.1 microns and the corresponding blank parts at deformations less than 0.1 μm; and
• the figure 5 shows a ferrule according to a second embodiment of the invention, with its spiral (shown partially).

With reference to the figure 1 , a ferrule 1 according to the invention, for fixing the inner end of a spiral 2 to the axis 6 of a pendulum in a clockwork movement, comprises three elastic arms 3 arranged in a triangle. The elastic arms 3 define an equilateral triangular central opening 4 whose diameter of the inscribed circle is slightly smaller than the diameter of a cylindrical or slightly frustoconical bearing surface 5 of the balance shaft 6, so that the axis 6 can be driven into the ferrule 1, which deformation elastically deforms the arms 3 towards the outside of the shell 1. The inner end of the spiral 2 is attached to the shell 1 at a point 8 of one, 7a, of the three zones 7a, 7b , 7c junction between 3. When the ferrule 1 is driven on the axis 6, this inner end of the spiral is secured to the axis 6 and therefore follows the oscillating movements of the balance. The outer end of the hairspring 2, not shown, is fixed by a peg to a fixed part of the watch movement, typically the rooster, in a known manner. The triangular shape of the opening 4 allows precise contact between the axis 6 and the shell 1, in three discrete contact points 9.

Still referring to the figure 1 the width of the elastic arms 3 is preferably variable to make the distribution of the stresses exerted by the axis 6 more homogeneous and thus make it possible to increase the clamping force of the axis 6 and / or the deformation of the elastic arms 3, in the manner of the elastic arms of the ferrule according to the document EP 1 637 940 . More specifically, the width of each arm has maxima L0, L1, L2 where forces are applied, that is to say at the point 9 of contact with the axis 6 and at both ends of the arm 3, and minima L3, L4 where the stresses are lowest, that is to say at points located between the point of contact 9 and the two ends of the arm 3.

According to the invention, the zone 7a of junction of the arms 3 to which is connected the spiral 2 is specially shaped so that the distance R between the point 8 of junction between the spiral 2 and the shell 1 and the center O (in the plane of the ferrule 1) of the axis 6 is not substantially modified by the driving of the shell 1 on the axis 6. It can be seen on the figure 1 that the zone 7a does not have the same shape as the other junction zones 7b, 7c. Zone 7a has indeed, unlike zones 7b, 7c, lateral recesses 10.

To understand how the shape, position and dimensions of the recesses 10 are selected, reference can be made to figure 2 which represents by small arrows the direction of the local deformations undergone by a shell 1 'identical to the ferrule 1 but not including the recesses 10, under the effect of radial forces F exerted by the axis 6 at the contact points 9. It is found that the zone 7a of junction between the arms 3, like the other two junction zones 7b, 7c, comprises a part of lesser deformation or "node" 11, that is to say a part which does not deform or little and which in any case deforms less than the rest of the zone 7a. In the illustrated example, because of the substantially symmetrical nature of the ferrule 1, the node 11 is located in the central angular portion of the angular sector 12 of vertex center O of the axis 6 and in which is inscribed the zone 7a. The node 11 is closer to the inner contour of the ferrule 1 '. To the right and to the left of this node 11, with respect to a radial axis 13 passing through the center O of the axis 6 and the center of the node 11, the local deformations tend to bypass this node 11 and to distance the material , in particular the junction point 8 between the spiral 2 and the ferrule 1 ', of the center O. To reduce this effect, the present invention proposes to remove from the junction zone 7a, during the design of the shell, parts of which the deformation significantly contributes to the distance of the junction point 8. In the example shown, it removes left and right side portions 14 located in the immediate vicinity of the node 11 and farther from the center O than the node 11. The two resulting recesses ( figure 1 ) define an intermediate portion 15 between the junction point 8 and the node 11. This intermediate portion 15 is narrower (in the direction orthogonal to the radial axis 13) than the rest of the junction zone 7a and in particular that the inner portion 19 of the zone 7a including the node 11. This intermediate portion 15 is further located in the central angular portion of the angular sector 12 in which is inscribed the junction zone 7a, as the node 11.

As shown in figure 3 , where the arrows indicate the direction of the local deformations undergone by the shell 1 but also, by their length, the intensity of these deformations, the recesses 10 prevent the deformations of the two parts 16 of the junction zone 7a located on the right and to the left of the node 11 and substantially at the same distance from the center O as the node 11, deformations which tend to bypass the node 11, are transmitted to the intermediate portion 15 and the junction point 8. The intermediate portion 15 is deformed therefore very little during the driving of the axis 6 in the shell 1, so that the point of junction 8 moves very little. A change in the distance R between the point 8 and the center O much lower than the generally accepted maximum value, 5 microns, can thus be obtained. A modification of the distance R less than 0.1 μm can even be obtained, as shown in FIG. figure 4 where the gray parts correspond to deformation after driving greater than 0.1 microns and the white parts correspond to strains after driving less than 0.1 microns. We can see on this figure 4 the deformations less than 0.1 μm relate to the spiral 2, the intermediate portion 15, the node 11 of the junction zone 7a and the nodes 17 of the other two junction zones between the arms 3.

The very slight change in the distance R mentioned above can be obtained without weakening to a great extent the junction zone 7a. The intermediate portion 15 of the junction zone 7a defined by the recesses 10, although narrower than the rest of the junction zone 7a, can indeed maintain a sufficient width, greater than that of the turns of the spiral 2, to avoid to deform during the operation of the spiral 2 (pendulum oscillations). The width of the intermediate portion 15 is typically equal to about three times the width of the turns of the hairspring 2.

The recesses made in the junction zone 7a to keep the distance R substantially constant during the driving process do not necessarily have the shape of the recesses illustrated in FIGS. figures 1 , 3 and 4 . The figure 5 shows another embodiment of the ferrule 1 according to the invention, wherein the recesses are notches 18 made transversely to the radial axis 13 on each side of the junction zone 7a near the node 11. These notches 18 define an intermediate portion 15 between the junction point 8 and the node 11, intermediate portion 15 which is narrower than the inner portion 19 of the zone 7a including the node 11 and an outer portion 21 of the zone 7a including the point of junction 8.

1. a) dessiner une virole, la forme de cette virole pouvant être choisie selon des critères indépendants de la question de la modification de la distance R lors du chassage de la virole sur l'axe, par exemple pour augmenter la force de serrage de l'axe et/ou la déformation des bras élastiques de la virole,
2. b) calculer les déformations locales subies par la virole, plus particulièrement les déformations locales subies dans la zone du point de jonction entre le spiral et la virole, lors du chassage de la virole sur l'axe,
3. c) modifier le dessin de la virole en enlevant de ladite zone une ou des parties dont les déformations contribuent à modifier la distance R, et
4. d) fabriquer la virole selon le dessin ainsi modifié.

Les étapes a) et c) sont typiquement effectuées par CAO (conception assistée par ordinateur) et l'étape b) par la méthode des éléments finis. La virole selon l'invention est de préférence fabriquée d'un seul tenant avec le spiral. Dans un exemple de réalisation, l'ensemble unitaire spiral-virole est fabriqué en une matière à base de silicium au moyen du procédé de gravure profonde DRIE (Deep Reaction Ion Etching).In practice, and in a general manner, the ferrule according to the invention is produced by implementing the following steps:

1. a) draw a ferrule, the shape of this ferrule may be chosen according to criteria independent of the question of the change in the distance R when driving the ferrule on the axis, for example to increase the clamping force of the axis and / or the deformation of the elastic arms of the ferrule,
2. b) calculate the local deformations undergone by the ferrule, more particularly the local deformations undergone in the zone of the junction point between the spiral and the ferrule, during the driving of the ferrule on the axis,
3. c) modifying the drawing of the ferrule by removing from said zone one or more parts whose deformations contribute to modifying the distance R, and
4. d) manufacture the ferrule according to the drawing thus modified.

Steps a) and c) are typically done by CAD (computer-aided design) and step b) by the finite element method. The ferrule according to the invention is preferably manufactured in one piece with the spiral. In an exemplary embodiment, the unitary spiral-ferrule assembly is made of a silicon-based material by means of deep etching process DRIE (Deep Reaction Ion Etching).

It will be noted that the ferrule according to the invention and its method of realization have the advantage in particular of not requiring that the entire shape of the ferrule be designed in order to maintain substantially constant the distance between the junction point of the spiral to the ferrule and the center of the axis. Thus, as already explained with reference to the figure 1 , the arms 3 of the shell may have a particular shape, variable width, to increase the clamping force of the axis 6 and / or the deformation of the arms 3 by distributing more homogeneously the stresses inside the arms 3. In the example of figure 5 and according to another characteristic of the invention, the ferrule further comprises abutments formed by discrete portions 20a, 20b and 20c of the outer contour of the shell, at the junction areas 7a, 7b, 7c respectively. These stops 20a, 20b, 20c are located at respective distances Ra, Rb, Rc of the center O which are small enough not to interfere with the normal operation of the hairspring 2 but large enough, in the event of shock suffered by the movement, to allow the inner turn of the hairspring 2 to abut against one or more stops 20a, 20b and 20c before the elastic limit of this inner turn, including at the junction point 8, is exceeded. The risks of rupture of the balance spring 3 during an impact are thus reduced. The abutments 20a, 20b and 20c typically have an arcuate shape of center O and radii Ra, Rb and Rc respectively. Advantageously, these distances or radii Ra, Rb and Rc grow in the direction D of winding of the spiral 2 going from the inside to the outside from the point 8 of junction of the spiral 2 to the shell 1, this to take into account in that the radius of the inner turn of the spiral 2, like that of all the other turns, increases in this direction D. Thus, the stop 20b closest to the junction point 8 in the direction D is at a distance Rb from center O which is smaller than the distance Rc separating the next stop 20c from the center O, which is smaller than the distance Ra separating the next stop 20a from the center O. The distance R8 separating the point 8 of junction between the hairspring 2 and the ferrule 1 of the center O is it typically greater than or equal to the distance Rb and less than the distances Rc and Ra.

Another advantage of the present invention is that it does not require a stiffening frame surrounding the deformable portion of the ferrule.

It will be further noted that the principle of the present invention, as defined by design steps a), b) and c) set forth above, can be applied to other ferrule shapes than the triangular shape shown in FIGS. figures 1 and 5 , for example to other polygonal shapes, regular or not, or even non-polygonal shapes. The ferrule according to the invention could thus, in a variant, have the conventional general shape of a split annular ring, with the junction point of the spiral to the ferrule located opposite the slot. In this variant, the ferrule could be considered as comprising two deformable arms whose junction zone comprises the junction point of the spiral to the ferrule.

Claims (18)

1. Horological balance spring-collet assembly comprising a balance spring (2) and a collet (1), the balance spring (2) being attached by its inner end to the collet (1) at a joining point (8), the collet (1) having no external stiffening frame, the collet (1) comprising at least two deformable arms (3) between which a shaft (6) with a circular cross-section can be driven and, in the zone (7a) of the joining point (8), constituting a joining zone between the two arms (3), at least one recess (10; 18) shaped so that the change in the distance (R) between the joining point (8) and the centre (O) of the shaft (6) during driving of the collet (1) onto the shaft (6) is less than 0.1 µm, the recess or recesses (10; 18) being close to a lower-deformation part (11) of the joining zone (7a), i.e. to a part (11) which deforms less than the rest of the joining zone (7a) when the collet (1) is being driven onto the shaft (6), and defining, in the joining zone (7a), an intermediate part (15) between the joining point (8) and the lower-deformation part (11), this intermediate part (15) being narrower than an inner part (19), with respect to said centre (O), of the joining zone (7a), this inner part (19) including the lower-deformation part (11), each deformable arm (3) being arranged to be in point-contact with the shaft (6) and having a variable width (L0-L4) having maxima (L0, L1, L2) substantially at the point (9) of contact with the shaft (6) and at the two ends of the arm (3) which are attached to one or more other arms (3) of the collet and minima (L3, L4) between said contact point (9) and the two ends of the arm (3), in order to render the distribution of stresses exerted on this arm by the shaft (6) more homogenous.
2. Balance spring-collet assembly as claimed in claim 1, characterised in that the recess or recesses (10; 18) provide the joining zone (7a) with a shape different from that of one or more other joining zones (7b, 7c) between said arms (3).
3. Balance spring-collet assembly as claimed in claim 1 or 2, characterised in that the recess or recesses (10; 18) comprise first and second recesses located on both sides of the intermediate part (15).
4. Balance spring-collet assembly as claimed in any one of claims 1 to 3, characterised in that the collet (1) comprises at least three deformable arms (3) disposed to form a polygon.
5. Balance spring-collet assembly as claimed in claim 4, characterised in that the polygon is a regular polygon.
6. Balance spring-collet assembly as claimed in claim 4 or 5, characterised in that the collet (1) comprises three deformable arms (3) disposed to form a triangle.
7. Balance spring-collet assembly as claimed in any one of claims 1 to 6, characterised in that said deformable arms (3) are elastic.
8. Balance spring-collet assembly as claimed in any one of claims 1 to 7, characterised in that the recess or recesses comprise one or more notches (18).
9. Balance spring-collet assembly as claimed in any one of claims 1 to 8, characterised in that the outer contour of the collet (1) defines at least one stop (20a, 20b, 20c) against which the inner turn of the balance spring (2) can come into abutment in the event of an impact before the elastic limit of the inner turn is exceeded.
10. Balance spring-collet assembly as claimed in claim 9, characterised in that said at least one stop consists of a plurality of discrete stops (20a, 20b, 20c) located at respective distances (Ra, Rb, Rc) from the centre (O) of the shaft (6) which increase in the direction (D) of the balance spring (2) from the inside towards the outside from the point (8) where the balance spring (2) joins the collet (1).
11. Balance spring-collet assembly as claimed in any one of claims 1 to 10, characterised in that it is produced in one piece.
12. Balance spring-collet assembly as claimed in any one of claims 1 to 11, characterised in that it is produced from a silicon-based material.
13. Method of producing a horological collet (1) to be driven onto a shaft (6) in order to fix the inner end of a balance spring (2) to this shaft (6), characterised in that it comprises the following steps:

    a) drawing a collet (1') comprising a point (8) of joining with the balance spring (2), the shape of this collet being selected according to criteria independent of the question of the change in the distance (R) between the joining point (8) and the centre (O) of the shaft (6) when the collet is being driven onto the shaft (6),

    b) calculating the local deformations undergone by the collet (1') in the zone (7a) of the joining point (8) when the collet is being driven onto the shaft (6),

    c) modifying the drawing of the collet (1') by removing from said zone (7a) at least one part (14) the deformations of which contribute to changing of the distance (R) between the joining point (8) and the centre (O) of the shaft (6) when the collet is being driven onto the shaft (6), and

    d) producing the collet.
14. Method as claimed in claim 13, characterised in that step a) consists of drawing a collet (1') having at least two deformable arms (3) between which the shaft (6) can be driven and a joining zone (7a) between these two arms (3), the joining zone (7a) constituting said zone of the joining point (8).
15. Method as claimed in claim 14, characterised in that step c) consists of removing from the joining zone (7a) at least one part (14) located in the proximity of a lower-deformation part (11) of said zone (7a).
16. Method as claimed in claim 15, characterised in that said at least one part (14) comprises first and second parts located on each side of the joining zone (7a).
17. Method as claimed in any one of claims 14 to 16, characterised in that step a) consists of drawing a collet comprising at least three deformable arms (3) disposed to form a polygon.
18. Method as claimed in claim 17, characterised in that the polygon is a regular polygon.

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