CLOCK ARRANGEMENT WITH COIL SPRING AND STEPPER

Description

Technical field of the invention

[0001] The present invention relates to a balance spring for a clockwork movement. The present invention also relates to a pin for attaching a final coil to the outside of such a balance spring. The invention further relates to a method for manufacturing such a balance spring. Technological background

[0002] In watchmaking, a balance spring, combined with a balance wheel, forms a regulating organ commonly called a balance and balance spring assembly for mechanical timepieces. Essentially, the balance spring is a very thin spring that winds itself in concentric coils when no force is applied. In its assembled state, one end of the balance spring, called the innermost coil, is attached to a ferrule fitted onto a balance wheel pivot, and the other end, called the outermost coil, is attached to a stud, which is typically secured by a stud holder in the balance bridge, also known as the balance cock.

[0003] More specifically, the timekeeping mechanism for mechanical timepieces, also called the oscillating system, comprises a balance wheel and hairspring assembly and an escapement. The balance wheel consists of a balance staff pivoted between a first and second bearing and connected to a balance rim by means of radial arms. The hairspring is attached via its first inner coil to the balance staff, for example by means of a ferrule, and via its outer outer coil to a fixed attachment point such as a stud mounted on a stud holder.

[0004] As for the escapement, in a very common embodiment, it comprises a double-plate system consisting of a large plate with a plate pin and a smaller plate with a notch. The escapement also includes an anchor lever, the stem of which pivots between a first and a second bearing. The anchor consists of a rod connecting a fork to an entry arm and an exit arm. The fork comprises an entry horn and an exit horn and carries a dart. The fork's travel is limited by an entry limiting pin and an exit limiting pin, which may be formed as a single unit with an anchor bridge. The entry arm and exit arm each carry an entry pallet and an exit pallet, respectively.Finally, the anchor cooperates with an escapement mechanism comprising an escape wheel and an escape pinion, this assembly formed by the escape wheel and the escape pinion being pivoted between a first and a second bearing.

[0005] A balance spring is a spring that, as its name suggests, takes the form of a spiral when at rest. Winded in a horizontal plane, parallel to the plane of the clockwork mechanism, the balance spring serves only one function: to make the balance wheel oscillate around its equilibrium position, also called the dead center, at the most constant frequency possible. When the balance wheel leaves its equilibrium position by pivoting in a given direction, the balance spring contracts. This creates a restoring torque in the balance spring, which causes the balance wheel to return to its equilibrium position. During this oscillation, the balance spring unwinds. However, since the balance wheel has acquired a certain speed, and therefore kinetic energy, it overshoots its equilibrium position in the opposite direction until the restoring torque exerted by the balance spring on the balance wheel stops it again and forces it to rotate in the other direction.

[0006] The balance spring therefore expands and contracts alternately: it is said to "breathe." However, many factors can prevent a balance spring from developing isochronously during these expansion and contraction phases. In particular, the balance spring must resist oxidation and magnetism, which cause the coils to stick together and tend to disrupt the watch's accuracy, or even stop it completely. The influence of atmospheric pressure, on the other hand, is minimal. For a long time, temperature was the primary concern, as heat expands the metal, while cold shrinks it. The balance spring must also be elastic enough to deform and yet always return to its original shape.

[0007] The material used for balance springs is usually steel. Being ductile, the steel used must be corrosion-resistant. For the past two decades, developments have also been underway to make balance springs from silicon. Silicon balance springs, particularly because they are insensitive to magnetism, allow for greater timekeeping accuracy than their steel predecessors. However, their production cost is higher and, being fragile, they are more difficult to assemble.

[0008] A balance spring must be isochronous. No matter how far the balance wheel rotates, it must always take the same amount of time to oscillate. If the balance spring contracts by only a few degrees, it accumulates little energy and returns slowly to its equilibrium position. If the balance spring is displaced significantly from its equilibrium position, it moves very quickly in the opposite direction. The important thing is that these two movements occur in the same amount of time. The underlying idea is that the energy available to the balance spring is not constant, and it must still function whether the watch is fully wound or is in its final hours of power reserve.

[0009] Due to their small size, balance springs are difficult to assemble. However, the way in which the two ends of a balance spring are secured also greatly influences the accuracy of the watch movement. In most mechanical watch movements, the two ends of the balance spring are inserted into a drilled section and held in place by a pin that is manually pressed in using pliers. This can result in a slight rotation of the balance spring, which is detrimental to the movement's accuracy.

[0010] Another technique involves fixing the ends of the balance springs with glue. However, this technique has also shown its limitations. It has been observed that, due to its viscosity, the glue exerts a tensile force on the balance spring through capillary action and can press its ends against the walls of the stud in which they are inserted. The resulting deformation of the balance spring induces mechanical stresses that are detrimental to the regularity of its movement.

[0011] To remedy these problems, the Applicant has already proposed a method for fixing a spiral spring consisting of gluing the last coil to the outside of the spiral spring in a pin using a drop of fluid adhesive that polymerizes, for example, with ultraviolet radiation. Thus, even if, at the moment the drop of adhesive is applied, for example using a syringe-type adhesive dispenser, the free end of the last coil of the spiral moves slightly under the weight of the adhesive drop, which induces unwanted mechanical stresses in the spiral spring, the adhesive is, before hardening, sufficiently fluid to allow the free end of the last coil of the spiral to spontaneously return to its resting position.The mechanical stresses induced in the spiral spring at the time of the deposit of the drop of liquid glue therefore disappear on their own, so that the regularity of the movement of the spiral spring is not affected by the operation of gluing the latter.

[0012] The above solution allows a balance spring to be fixed by the free end of its last coil to a stud, completely or at least largely eliminating the mechanical stresses that are usually induced in such a balance spring during its assembly. The regularity of the balance spring's operation is thus greatly improved. However, in practice, the Plaintiff has found that the hardened adhesive blob formed when the drop of liquid glue used to fix the free end of the last coil to the outside of the balance spring is polymerized sometimes tends to detach from the stud, which, of course, leads to the immediate failure of the watch movement in which the balance spring is installed. This situation is due in particular to surface finish problems on the stud, which prevent the adhesive blob from adhering perfectly, as well as to the aging of the adhesive blob over time.In addition, when the ambient temperature increases, most glues soften, which has the effect of changing the active length, and therefore the stiffness of the spiral, and thus negatively affecting the operation of the watch movement.

[0013] Finally, it should be noted that, particularly in the case of high-end watch movements, the use of glues or synthetic products is avoided as much as possible.

[0014] Document CH 42 750 A describes an assembly for fixing the outer end of a spiral to a pin. Summary of the invention

[0015] The present invention aims to remedy the problems mentioned above and others by providing a fixing assembly for a spiral spring whose last coil on the outside can be reliably immobilized without the use of glue or pins or manual operations such as pinching, crimping or others whose success depends largely on the skill of the operators.

[0016] To this end, the present invention relates to an assembly for fixing a free end of a last coil outside of a balance spring for a watch movement, this fixing assembly comprising a stud and a locking element, the stud being provided with a groove in which the balance spring is engaged at a point along its length, the locking element also being engaged in the groove, in contact with the balance spring, the fixing assembly also comprising a clamping member which presses the locking element against the free end of the last coil outside of the balance spring, so that the free end of the last coil outside of the balance spring is immobilized in the groove of the stud in a direction perpendicular to the plane in which the winding of the coils extends.

[0017] According to a particular embodiment of the invention, the spiral spring is engaged in the groove of the pin by the free end of its last coil on the outside.

[0018] According to the invention, the immobilization of the free end of the last coil outside the spiral spring is ensured by mechanical clamping and locking in a direction perpendicular to the plane in which this free end of the spiral spring extends.

[0019] According to yet another particular embodiment of the invention, the groove extends from an outer wall of the eyelet and towards the inside of the latter.

[0020] According to yet another particular embodiment of the invention, the groove has a height and the locking element a thickness such that, once the locking element is engaged in this groove, there remains sufficient space to be able to engage the free end of the last coil outside the spiral spring in the groove.

[0021] According to yet another particular embodiment of the invention, the space in which the free end of the last coil outside the spiral spring is engaged extends between the locking element and a bottom of the groove.

[0022] According to yet another particular embodiment of the invention, the free end of the last coil outside the spiral spring terminates in a plate which is fixed to this free end or which is made of one piece with this free end.

[0023] According to yet another particular embodiment of the invention, a hole in which the clamping member is engaged is provided in the pin so that the clamping member opens into the groove and presses against the locking element and presses the latter against the free end of the last coil outside the spiral spring.

[0024] According to yet another particular embodiment of the invention, the clamping member is a threaded rod and in that the hole is tapped.

[0025] According to yet another particular embodiment of the invention, the locking element is a clamp equipped with two jaws connected to each other at a distal end, these two jaws delimiting between them an open space on the side of their proximal end.

[0026] According to yet another particular embodiment of the invention, the eyelet includes a wall which delimits the groove.

[0027] According to yet another particular embodiment of the invention, the inner face of one of the jaws of the clamp has a surface which moves away from the wall of the eyelet in the direction of engagement of the clamp on the eyelet.

[0028] According to yet another particular embodiment of the invention, the inner face of the jaws of the clamp is provided with a recess whose shapes are complementary and follow those of the wall, allowing the clamp to grip the wall and ensure sufficient hold while the operator engages the last coil outside the spiral spring in the groove made in the pin.

[0029] According to yet another particular embodiment of the invention, the spiral spring fixing assembly is removable.

[0030] Thanks to these characteristics, the present invention provides a fixing assembly for the free end of the curve on the outside of a balance spring for watch movements, with numerous advantages, including the fact that balance springs can be fixed without glue regardless of the type of material used to make them. Consequently, the watchmaker enjoys complete freedom in choosing the material from which the balance spring is made, and furthermore, since the free end of the balance spring is not glued, the fixing assembly according to the invention is detachable.Furthermore, since the locking element, which is pressed against the free end of the last coil outside the balance spring by the clamping mechanism, ensures that the balance spring is held in its rest position in the XY plane parallel to the plane in which the watch movement extends, no mechanical torque is transmitted to the balance spring. Therefore, the balance spring can be fixed in its rest position in the XY plane parallel to the plane in which the watch movement extends, with little to no influence on its accuracy. Indeed, it is known that the stress exerted on the free end of the last coil outside the balance spring, perpendicular to the plane in which this free end extends, is virtually nonexistent.Another great advantage of the fixing assembly according to the invention lies in the fact that the mounting of the free end of the last coil outside the spiral spring does not depend at all on the dexterity of the operator in charge of this mounting, so that the reproducibility of the operation of balance-spiral assemblies equipped with a fixing assembly according to the invention is quite remarkable. Brief description of the figures

[0031] Other features and advantages of the present invention will become clearer from the following detailed description of an embodiment of a fastening assembly according to the invention, this example being given purely for illustrative purposes and not as a limitation, only in connection with the accompanying drawing in which: there figure 1is a perspective top view of the assembly according to the invention in which a free end of a last coil is fixed to the outside of a spiral spring for a clockwork movement; the figure 2 is a perspective view from below of the fastening assembly according to the invention illustrated in the figure 1 ; there figure 3 is a perspective top view of the dissociated state of the fastening assembly according to the invention; the figure 4 is a perspective view from below, in a dissociated state, of the fastening assembly according to the invention; the figure 5 is a top view of the fastening assembly according to the invention in which the free end of the last coil is engaged outside of a spiral spring for a watch movement; the figure 6 is a cross-sectional view of the fastening assembly according to the invention along line VI-VI of the figure 5 ; there figure 7is a cross-sectional view of the fastening assembly according to the invention along line VII-VII of the figure 5 ; there figure 8 is a top view of the fixing assembly according to the invention mounted in a balance wheel and hairspring assembly for a watch movement; the figure 9 is a schematic view of a simplified embodiment of the fastening assembly according to the invention; the Figures 10 and 11 are perspective views, respectively from above and below, of the balance wheel and hairspring assembly equipped with the fastening assembly according to the invention, shown in top view at the figure 8 . Detailed description of the invention

[0032] The present invention proceeds from the general inventive idea of ​​securing the free end of the last coil outside a watch balance spring in a stud by means of a fastening assembly that immobilizes this free end through a combined mechanical pressing and locking action. In this way, securing the free end of the balance spring requires no gluing, thus allowing complete freedom in the choice of materials used to manufacture the balance spring. Furthermore, given the absence of any gluing, the fastening assembly according to the invention remains permanently detachable. Another major advantage of the fastening assembly according to the invention is that the free end of the last coil outside the balance spring is immobilized by mechanical clamping and locking in a direction perpendicular to the plane in which this free end of the balance spring extends.Therefore, securing this free end of the spiral spring does not induce any tensile or torsional torque in the free end of the last coil outside the spiral spring, so the smooth running of the spiral spring is in no way affected by securing the free end of its last coil outside the spring to the stud. This is all the more true when the mechanical stresses acting on the last coil outside the spiral spring in the direction perpendicular to the plane in which this last coil extends are zero or entirely negligible.

[0033] Designated as a whole by the general numerical reference 1, the fastening assembly according to the invention is shown in its entirety on the figures 1 and 2and includes, in particular, a stud 2. For illustrative purposes only, the stud 2 shown in the drawing is externally delimited by a generally cylindrical casing. It is understood that the shape of the stud 2 is not critical for the purposes of the invention; such a stud 2 may deviate from a cylindrical shape and be, for example, parallelepiped-shaped.

[0034] Preferably, but not exclusively, a groove 6 is cut from an outer face 4 of the piton 2 towards its interior, preferably with a square or rectangular cross-section, as can be seen in particular on the figures 3 and 4 . This groove 6 is intended to receive a free end 8 of a last coil outside 10 of a spiral spring 12 for watch movement for the locking of the latter as described in detail below.

[0035] The fastening assembly 1 according to the invention also includes a locking element 14 also intended to be engaged in the groove 6, in contact with the free end 8 of the last outer coil 10 of the spiral spring 12, and then to be pressed against this free end 8 to ensure the immobilization of the spiral spring 12 in this groove 6.

[0036] For this purpose, the fixing assembly 1 is further completed by a clamping member 16 which is arranged to press the locking element 14 in an adjustable manner against the free end 8 of the last coil on the outside 10 of the spiral spring 12.

[0037] According to the embodiment of the invention illustrated in the drawing (see for example the figure 3), the clamping member 16 may be of the type of a threaded rod 18 with a slotted head 20. This threaded rod 18 is intended to be screwed into a tapped hole 22 provided in the pin 2 so that this threaded rod 18 opens into the groove 6 and presses against the locking element 14 and presses the latter against the free end 8 of the last coil on the outside 10 of the spiral spring 12.

[0038] It is easy to understand that, depending on the degree of screwing of the threaded rod 18, one can precisely adjust the clamping force which, via the locking element 14, is exerted on the free end 8 of the last coil outside 10 of the spiral spring 12 and ensures the immobilization of this free end 8 in the groove 6 of the pin 2.

[0039] A friction surface 24, for example a knurling 26, may be provided on the eyelet 2. This friction surface 24 may in particular be used by the operator for a better grip on this eyelet 2 when he screws the threaded rod 18 into the tapped hole 22 of the eyelet 2.

[0040] As described above, the clamping member 16 is a threaded rod 18. Of course, this is only an example, the clamping member 16 can take other forms such as, for example, a simple pin engaged with sufficient friction in the hole provided in the pin 2 so as to be able to press against the locking element 14 and firmly press the latter against the free end 8 of the last outer coil 10 of the spiral spring 12, while being able to be released from this hole if necessary, for example if the spiral spring 12 breaks.

[0041] In its preferred but not limiting embodiment, the locking element 14 is of the type of a clamp 28 possessing a certain elasticity and having two jaws 30a and 30b, generally straight, extending substantially parallel to and at a distance from each other. Connected to each other at their distal ends 32a, 32b, these two jaws 30a, 30b delimit between them a space 34 open on the side of their proximal ends 36a, 36b.

[0042] Through its open space 34 on the proximal end 36a, 36b of its jaws 30a, 30b, the clamp 28 is engaged on either side of a wall 38 of the stud 2 resulting from the machining of the groove 6. The simple overlap of the clamp 28 on the wall 38 of the stud 2 is sufficient to ensure adequate retention of this clamp 28 for the time necessary for the operator to tighten the threaded rod 18. This retention can, however, be slightly increased by providing the inner face of one of the jaws 30a, 30b of the clamp 28 with a surface 40 that extends away from the wall 38 of the stud 2 in the direction of engagement of the clamp 28. The retention of the clamp 28 on the wall 38 of the stud 2 can be further improved by providing on the inner face of its jaws 30a, 30b recesses 42a, 42b whose shapes are complementary and follow those of this wall 38, thus allowing the clamp 28 to grip the wall 38 of the piton 2 and ensure its retention by friction.

[0043] It is important to understand that the height of the groove 6 is greater than the thickness of the jaws 30a, 30b of the clamp 28, so that, once the clamp 28 is engaged in this groove 6, there remains sufficient space to easily engage the free end 8 of the last coil outside 10 of the spiral spring 12 in the groove 6.

[0044] The operation of securing the free end 8 of the last coil to the outside 10 of the spiral spring 12 is carried out as follows: first, the clamp 28 is engaged by means of its opening 34 on the side of the proximal end 36a, 36b of its jaws 30a, 30b in the groove 6 of the pin 2, on either side of the wall 38 of this pin 2. The overlap of the clamp 28 on the wall 38 of the pin 2 is sufficient to ensure that the clamp 28 remains on this wall 38 for the time necessary to secure the free end 8 of the last coil to the outside 10 of the spiral spring 12 on the pin 2. During the assembly of the clamp 28, care is taken to ensure that this clamp 28 is positioned so that a sufficient space 44 remains between the jaws 30a, 30b. of this clamp 28 and a bottom 46 of the groove 6 so that the free end 8 of the last coil can be easily engaged outside 10 of the spiral spring 12.Once the clamp 28 is properly positioned and secured in the groove 6 of the stud 2, the free end 8 of the outermost coil 10 of the balance spring 12 is easily inserted into the groove 6, between the base 46 of the groove and the jaws 30a, 30b of the clamp 28. Frequently, the free end 8 of the outermost coil 10 of the balance spring 12 terminates in a plate 50. Depending on the case, this plate 50 is fixed to the free end 8 of the outermost coil 10 of the balance spring 12, for example by welding, or is made of a single piece with this free end 8. The reference mark is adjusted by pivoting the mounting assembly 1, in other words by pivoting the attachment point of the outermost coil 10 of the balance spring 12 around an axis 52 of a balance wheel 48, to align a pin 54 of a plate 56 with an escapement line 58 (see . figure 8 ). For this purpose (see Figures 10 and 11), the stud 2 is engaged in an opening 60 made in a stud-holder piece 62 which is supported by a bridge 64 commonly called a cock and which is pivotally mounted around the axis 52 of the balance wheel 48. Similarly, rather than being made in the stud 2 from the outside of the latter, the groove 6 can very well be made in the manner of a through hole 66 in the thickness of the stud 2 (see figure 9 ). In this through hole 66, a locking element 14, for example of the type of a rod 68, is engaged. Finally, the operator tightens the threaded rod 18 so that it presses against the jaws 30a, 30b of the clamp 28 and presses the latter against the free end 8 of the last outer coil 10 of the spiral spring 12. The assembly operations of the free end 8 of the last outer coil 10 of the spiral spring 12 are thus completed and the spiral spring 12 is fixed on the pin 2 in a removable manner.

[0045] It is understood that the present invention is not limited to the embodiment just described, and that various simple modifications and variations can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the appended claims. In particular, it will be understood that the groove 6 may have a cross-section other than square or rectangular. It will also be noted that the friction surface 24, such as the knurling 26 provided on the stud 2, is particularly useful after the stud 2 has been driven into the stud holder 62. Indeed, the threaded rod 18 can be screwed in quite easily until it reaches the locking position. Only the friction induced by the threads of the threaded rod 18 in the tapped hole of the stud 2 is likely to cause the stud 2 to rotate during this operation. At this stage of the operation, however, this friction is negligible compared to the torque required to rotate the stud 2.However, when the threaded rod 18 reaches its locking position in the tapped hole 22, a large portion of the tightening torque transmitted to the threaded rod 18 by the operator is transferred to the stud 2, which can cause the stud 2 to pivot relative to the stud holder 62. Naturally, such pivoting must be avoided, which is why the stud 2 is equipped, for example, with knurling 26. This knurling, through contact with the stud holder 62, increases the stud 2's resistance to this torque. It will also be understood that, depending on the geometric shape of the spiral spring 12, which may be specific, this spiral spring 12 may be engaged in the groove 6 of the stud 2 at a point along its length other than the free end 8 of its outermost coil 10.It will also be understood that the immobilization of the free end 8 of the last coil outside 10 of the spiral spring 12 is ensured by mechanical clamping and locking in a direction perpendicular to the plane in which this free end 8 of the spiral spring 12 extends. In the case where the spiral spring 12 terminates in a plate 50, if this plate 50 extends parallel to the plane in which the spiral spring 12 lies, the clamping and locking of this plate 50 will be perpendicular to the plane of the spiral spring 12. Conversely, if the plate 50 extends perpendicular to the plane in which the spiral spring 12 lies, the clamping and locking of this plate 50 will be in a direction parallel to the plane of the spiral spring 12. In other words, the threaded rod 18 will be screwed into the stud 2 in a direction perpendicular to the longitudinal axis of symmetry of the stud 2.It should also be noted that, since the spiral spring 12 is in the form of an extremely thin ribbon wound upon itself in a succession of turns, the plane in which the free end 8 of the last turn extends outside 10 of the spiral spring 12 is understood to be the plane in which this winding is contained. It should also be noted that the plate 50 is a surface element, for example, rectangular in shape, and that, depending on the case, this surface element is either contained within the plane of the spiral spring 12 or perpendicular to this plane. Nomenclature

[0046] 1. Fixing assembly 2. Eye bolt 4. Outer wall 6. Groove 8. Free end 10. Last outer coil 12. Spiral spring 14. Locking element 16. Clamping member 18. Threaded rod 20. Slotted head 22. Tapped hole 24. Friction surface 26. Knurling 28. Clamp 30a, 30b. Jaws 32a, 32b. Distal ends 34. Gap 36a, 36b. Proximal ends 38. Wall 40. Surface 42a, 42b. Hollows 44. Space 46. Base 48. Balance wheel 50. Plate 52. Axle 54. Pin 56. Plate 58. Escapement line 60. Oblong aperture 62. Stud holder piece 64. Bridge 66. Through hole 68. Stem

Claims

1. An assembly (1) for fastening a free end (8) of a last outer turn (10) of a balance spring (12) for a horological movement, this fastening assembly (1) comprising a balance spring stud (2) and a locking element (14), the balance spring stud (2) being provided with a groove (6) in which the balance spring (12) is designed to be engaged at a point along its length, the locking element (14) also being engaged in the groove (6) and designed to come into contact with the balance spring (12), the fastening assembly (1) also comprising a clamping organ (16) arranged to press the locking element (14) against the balance spring (12), characterised in that the balance spring (12) is immobilised in the groove (6) of the balance spring stud (2) in a direction perpendicular to the plane in which the turns wind.

2. The fastening assembly according to claim 1, characterised in that the free end (8) of the last outer turn (10) of the balance spring (12) is immobilised by mechanical clamping and locking in a direction perpendicular to the plane in which this free end (8) of the balance spring (12) extends.

3. The fastening assembly (1) according to any of claims 1 or 2, characterised in that the groove (6) extends from an outer wall (4) of the balance spring stud (2) towards the inside of this stud.

4. The fastening assembly (1) according to claim 3, characterised in that the groove (6) has a height and the locking element (14) a thickness such that, once the locking element (14) is engaged in this groove (6), there is enough remaining space to be able to engage the free end (8) of the last outer turn (10) of the balance spring (12) in the groove (6).

5. The fastening assembly (1) according to claim 4, characterised in that the space in which the free end (8) of the last outer turn (10) of the balance spring (12) is to be engaged extends between the locking element (14) and a bottom (46) of the groove (6).

6. The fastening assembly (1) according to any of claims 1 to 5, characterised in that a hole (22) in which the clamping organ (16) is engaged is formed in the balance spring stud (2) such that the clamping organ (16) extends into the groove (6) and presses against the locking element (14), being arranged to press the latter against the free end (8) of the last outer turn (10) of the balance spring (12).

7. The fastening assembly (1) according to claim 6, characterised in that the clamping organ (16) is a threaded rod (18) and in that the hole (22) is tapped.

8. The fastening assembly (1) according to any of claims 6 and 7, characterised in that the locking element (14) is a clamp (28) with two jaws (30a, 30b) connected to each other at a distal end (32a, 32b), these two jaws (30a, 30b) delimiting between them a space (34) that is open on the side of their proximal end (36a, 36b).

9. The fastening assembly (1) according to claim 8, characterised in that the balance spring stud (2) comprises a wall (38) that delimits the groove (6).

10. The fastening assembly (1) according to claim 9, characterised in that the inner face of one of the jaws (30a, 30b) of the clamp (28) has a surface (40) that extends away from the wall (38) of the balance spring stud (2) in the direction of engagement of the clamp (28) on the balance spring stud (2).

11. The fastening assembly (1) according to any of claims 9 and 10, characterised in that the inner faces of the jaws (30a, 30b) of the clamp (28) are provided with cross-outs (42a, 42b) with complementary shapes that fit into those of the wall (38), enabling the clamp (28) to grip the wall (38) and remain in place.

12. An assembly comprising a fastening assembly (1) according to claim 1 and the said spring, characterised in that the balance spring (12) is engaged in the groove (6) of the balance spring stud (2) by the free end (8) of its last outer turn (10).

13. The assembly comprising a fastening assembly (1) according to claim 5 and the said spring, characterised in that the free end (8) of the last outer turn (10) of the balance spring (12) ends in a plate (50) that is fastened to this free end (8) or is made in one piece with this free end (8).