Hairspring of a balance-hairspring assembly of a mechanical clock movement

Abstract

The invention relates to a balance spring (1) of a balance wheel and balance spring assembly of a mechanical watch movement, the balance spring (1) being formed of a succession of turns (S1,...,Sn) extending between a first free end, called the first inner turn (2), and a second free end, called the last outer turn (6), the turns of the balance spring being arranged off-center in the free state of the spring, the last outer turn (6) of the balance spring (1) terminating in a retaining means for its attachment to a stud (14), the balance spring (1) being centered and its turns concentric when this balance spring (1) is mounted in the balance wheel and balance spring assembly, the turns rearranging concentrically when this balance spring is mounted, the attachment of the balance spring to the stud inducing in the turns of the balance spring (1) an elastic stress by means of which the retaining means is fixed in a way that cannot be lost on the piton (14).

Description

Technical field of the invention

[0001] The present invention relates to a balance spring for a balance wheel and hairspring assembly of a watch movement. The present invention also relates to a watch assembly comprising a balance spring and a stud. Technological background

[0002] In watchmaking, a balance spring, combined with a balance wheel, forms a regulating organ commonly called a 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 means of 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 carrying a plate pin and a smaller plate with a notch. The escapement also includes an anchor lever, the stem of which is pivoted 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 is made up of an entry horn and an exit horn, between which a dart extends. The fork's travel is limited by an entry limiting pin and an exit limiting pin, which may be made as a single unit with an anchor bridge. The entry arm and exit arm carry an entry pallet and an exit pallet, respectively. Finally, the anchor cooperates with an escape wheel comprising an escape wheel axle 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, it tensions the balance spring. 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 relaxes. However, since the balance wheel has acquired a certain speed, and therefore kinetic energy, it overshoots its equilibrium position in the opposite direction, which tensions the balance spring again until the restoring torque it exerts on the balance wheel stops it once more 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 stop the watch. 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 making balance springs is usually steel. Being ductile, such steels must be corrosion-resistant. Recent developments also propose making balance springs from silicon. Silicon balance springs, particularly because they are insensitive to magnetism, are more precise 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 spring rotates, it must always take the same amount of time to oscillate. If the spring contracts by only a few degrees, it accumulates little energy and slowly returns to its equilibrium position. If the 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 yet it must function regardless of whether the watch is fully wound or running on its last few 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] We also know from document CH708429 of a flat balance spring intended to be mounted on the balance staff of a mechanical watch regulator. The balance spring has several inner coils for which the distance between each point and the center of rotation of the spring varies linearly according to the angular position of that point when the spring is at rest. In CH708429, the balance spring is composed of regularly concentric coils in its free state. The lesson of CH708429 is limited to modifying the outermost coil by giving it a non-linear shape in order to reduce imbalance and improve isochronism. Document CH714 775 discloses a balance spring-pin assembly designed to ensure the reliable attachment of the outermost coil to the pin. Summary of the invention

[0012] The present invention aims to remedy the problems mentioned above and others by providing a spiral whose last outer coil can be reliably fixed to a stud without the use of glue or pins or operations such as pinching, crimping or others.

[0013] For this purpose, the present invention relates to a watch assembly consisting of a spiral and a stud for a balance wheel-spiral assembly of a mechanical watch movement as defined by claim 1 of the patent.

[0014] According to one embodiment, the present invention also relates to a watch assembly consisting of a balance spring and a stud for a balance wheel and balance spring assembly of a mechanical watch movement, the balance spring being formed of a succession of turns extending between a first free end, called the first inner turn, and a second free end, called the last outer turn, the turns of the balance spring being arranged in an off-center manner when it is in the free state, that is to say, a position in which the distance separating the second turn from the third turn is not the same as the distance separating the first turn from the second turn, the same thing being repeated as one moves away from the center of the balance spring between each pair of consecutive turns, the last outer turn of the balance spring ending with a stopping means,The stud comprises a base in which a recess is provided into which the locking means is received; the coils are rearranged concentrically when this spiral is mounted in the balance wheel-spiral assembly mounted in the mechanical watch movement; the fixing of the spiral onto the stud induces an elastic stress in the spiral coils by means of which the locking means is irrevocably engaged in the recess of the stud.

[0015] According to a special embodiment of the invention, the stopping means is shaped like a hook.

[0016] According to a special embodiment of the invention, the hook is shaped in a T, an L, a U or in the shape of a marine anchor.

[0017] According to another special embodiment of the invention, the spiral is made of silicon, for example by plasma cutting of a silicon plate.

[0018] Thanks to these features, the present invention provides a watch assembly consisting of a stud and a balance spring, the outermost coil of which can be reliably fixed to the stud. Indeed, the transition of the balance spring from a position where its coils are arranged off-center when it is free to a position where its coils are centered when the free end of its outermost coil is fixed to the stud causes an elastic tension in the spring's coils, thereby permanently engaging the locking mechanism in the stud. Thanks to the invention, the balance spring can therefore be fixed to its stud without the use of glue, pins, or operations such as pinching, crimping, or other methods. This eliminates the problem of glue degradation, which can cause the balance spring to detach from the stud, resulting in the watch stopping.Similarly, securing the balance spring according to the invention requires a simple operation of engaging the free end of its last coil outside the recess provided in the stud. This minimizes any assembly operations, thereby reducing assembly and production time and consequently lowering costs. Likewise, strictly limiting assembly operations also ensures excellent reproducibility of the operation of balance-spring assemblies incorporating a balance spring according to the invention. Thus, with the balance spring according to the invention, the coils S1, ..., Sn-1 of the balance spring 1 are arranged off-center when the balance spring 1 is in its concentric state, and rearrange themselves concentrically when the balance spring is mounted in the balance-spring assembly, this assembly being at rest.

[0019] Furthermore, it is also interesting to note that, unlike the prior art where it is always ensured that the free end of the last coil outside the balance spring can be fixed on the stud by generating as little stress as possible in order to preserve the isochronic qualities of the resulting regulating assembly, in the case of the invention, the fixing of the stopping means on the stud is done under stress, this stress inducing in the balance spring a mechanical tension which will simultaneously guarantee the locking of the last coil outside the balance spring on the stud and the chronometric performance of the regulating assembly by concentric rearrangement of the coils of the balance spring. Brief description of the figures

[0020] Other features and advantages of the present invention will become clearer from the following detailed description of an embodiment of the spiral 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 1 is a top view of a spiral according to the invention in its free state in which the worst are off-center; the Figures 2A and 2B are perspective views of a piton according to the invention; the figure 3A is a perspective view showing the spiral fixed by its last turn to the outside of the stud; the figure 3B is a larger-scale view of the peak of the figure 3A ; there figure 4 is a cross-sectional view of a silicon bar; the figures 5 to 7 illustrate different forms of embodiment of the stopping means provided at the free end of the last coil outside the spiral according to the invention. Detailed description of the invention

[0021] The present invention proceeds from the general inventive idea of ​​providing a spiral which, in its unmounted state, when no stress other than the force of gravity is acting upon it, has its turns off-center, such that the space between two consecutive turns and the two following turns is not the same as one moves away from the center of the spiral, represented by its first inner turn. In contrast, the spiral according to the invention is arranged so that, when it is fixed to the pin by the free end of its outermost outer turn, its turns become centered, so that its turns extend concentrically.According to an advantage of the invention, the transition of the balance spring from its free state, in which its coils are off-center, to its fixed state on the stud, in which its coils are centered, causes its coils to be placed under elastic tension. This tension causes the retaining means provided at the free end of its outermost coil to become permanently engaged in the recess provided in the stud. The balance spring is thus fixed according to the invention without the need for glue or any special tools. This fixing method is therefore simpler, faster, and more reliable than with prior art balance springs.Furthermore, since the fixing of the spiral according to the invention on its stud is done without practically any assembly operation other than that of sliding the stopping means into the stud clearance, the operation of the resulting spiral-balance assemblies depends less on the skill of the operators or the correct adjustment of the machines for fixing the spirals and is therefore much more reproducible.

[0022] An example of an embodiment of a spiral according to the invention is shown in the figure 1 Designated as a whole by the general numerical reference 1, this spiral comprises a plurality of turns S1, S2,..., Sn extending between a first inner turn 2 located at the center 4 of the spiral 1, and a final outer turn 6 located outside the spiral 1. As represented in the figure 1Spiral 1 is in a free state in which no constraints are exerted upon it, except for the force of Earth's gravity. In this free state, spiral 1 is in a rest position in which its turns S1,..., Sn are off-center, that is, a position in which the distance R2,3 separating the second turn S2 from the third turn S3 is not the same as the distance R1,2 separating the first turn S1 from the second turn S2. The same thing is repeated as one moves away from the center 4 of spiral 1 between each pair of consecutive turns. We also see on the figure 1The outermost coil 6 terminates in a retaining means that is integral with the spiral 1. This retaining means takes the form of a hook 8, for example, in the shape of a "T," comprising a foot 10 and a head 12 perpendicular to each other. In the example illustrated in the drawing, the foot 10 and the head 12 of the hook 8 are each formed from a bar with the same cross-section as the coils S1,..., Sn of the spiral 1. Of course, particularly when the spiral 1 is produced by cutting from a silicon or metal plate using a LIGA process, the hook 8 may have a different cross-section than the coils S1,..., Sn of the spiral 1. It may even be possible to vary the cross-section of the hook 8 locally in order to adapt the mechanical stiffness of the various elements composing the hook 8 for optimal attachment of the hook 8 to the pin 14.The hook 8 is arranged so that, in the case where it is shaped in a "T", the bar which constitutes the head 12 of this hook 8 extends substantially parallel to the last turn Sn of the spiral 1. It will be noted that the stopping means such as the hook 8 does not participate in the active length of the spiral 1.

[0023] There figure 2A This is a perspective view of a screw eye according to the invention. Designated as a whole by the general reference numeral 14, this screw eye may, without limitation, be in the form of a cylinder. The screw eye 14 comprises a base 16 in which a recess is provided such that a groove 18 extends through the base 16. This groove 18 opens into a slot 20 formed in the screw eye 14 transversely to the groove 18.

[0024] There figure 3Ais a perspective view on which is shown the spiral 1 fixed to the stud 14 by its last outer coil 6. To achieve this result, the hook 8 is slid into the groove 18 of the stud 14, then immobilized by bringing its head 12 to rest against the bottom 22 of the slot 20. According to the invention, once the spiral 1 is fixed to the balance staff by its first inner coil 2 and to the stud 14 by its last outer coil 6, the spiral 1 adopts a centered position in which its coils S1,..., Sn are arranged concentrically, preferably but not necessarily at equal distances from each other. The fact that the spiral 1 moves from its eccentric position at rest, when it is free, to its centered position once it is fixed on the pin 14, induces in the free end of the last outer coil 6 an elastic stress thanks to which the stopping means becomes irrevocably engaged in the slot 20 of the pin 14.Indeed, when the spiral 1, once fixed to the pin 14, is in its centered position in which the turns S1,..., Sn are concentric, the resulting elastic force F1, directed radially outwards from the spiral, tends to push the head 12 of the hook 8 radially outwards, against the bottom 22 of the slot 20, which makes the assembly virtually impossible to lose. In fact, for the retaining means to separate from the pin 14, a force comprising (see . figure 3B) a first component F2 directed radially towards the center 4 of the spiral 1 to allow the head 12 of the hook 8 to disengage from the slot 20 of the stud 14, and a second component F3 directed outwards from the groove 18 made in the base 16 of the stud 14, in order to allow the foot 10 of the hook 8 to disengage from this groove 18, which is practically impossible in the event of mechanical shocks for example during normal use of the watch.

[0025] The spiral 1 according to the invention can, for example, be formed from a silicon bar with a width w and a thickness t (see figure 4 ) obtained using the process described in European patent application EP 1 422 436 A1. It can, for example, be produced by plasma cutting of a single-crystal silicon wafer and comprise a silicon core coated with an external layer of silicon oxide having thermal compensation properties.

[0026] The spiral 1 according to the invention can also be obtained using the manufacturing process described in international application WO 2019 / 180177 A1. Briefly described, this manufacturing process for a silicon spiral consists of: To use a SOI disk, which consists of two layers of silicon bonded together by a buried layer of silicon oxide. Each of these three layers has a specific role: the top silicon layer, called the "device," is formed from a single-crystal silicon wafer and its thickness determines the thickness of the spirals to be manufactured; the bottom silicon layer, called the "handle," which essentially serves as mechanical support, is also formed from a single-crystal silicon wafer, generally with the same crystallographic orientation as the top silicon layer; finally, the buried oxide layer intimately binds the two upper and lower silicon layers and acts as a barrier during subsequent operations; grow a layer of silicon oxide on the surface of the top silicon layer;Deposit a layer of photosensitive resin onto the silicon oxide layer and, using photolithography, create a mask within the resin layer corresponding to the desired spirals in the upper silicon layer; etch the silicon oxide layer in the open areas of the mask; perform deep reactive ion etching (DRIE) of the upper silicon layer to form the spirals, this etching stopping when it reaches the buried silicon oxide layer that connects the upper and lower silicon layers; the spirals to be fabricated are then structured throughout the entire thickness of the upper silicon layer, now revealed by this DRIE etching. The components remain attached to the lower silicon layer by the buried silicon oxide layer.to grow a new layer of silicon oxide on the surface of the silicon to protect the spirals during the operation used to separate them from the lower silicon layer.

[0027] The spiral 1 according to the invention can also be made of metal or a metal alloy, for example, using the LIGA (Lithographische Galvano Abformung in German) process: after depositing a layer of photosensitive polymer onto a substrate by centrifugation, this photosensitive polymer layer is used to form a hollow structure corresponding to the desired contour of the spiral 1 by photolithography. For this purpose, the photosensitive polymer layer, the thickness of which corresponds to the desired height of the spiral 1's turns, is exposed to light through a photolithography mask and then chemically etched to obtain the hollow structure corresponding to the desired contour of the spiral 1. The hollow structure is then filled with a metal or a metal alloy, for example, by electrodeposition or by compression and sintering (US 4 661 212), and finally, the hollow structure is chemically dissolved, releasing the spiral 1.

[0028] It goes without saying 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 should be noted that during the operation of a balance wheel and balance spring assembly equipped with a balance spring 1 according to the invention, when the balance spring 1 contracts and expands alternately, a tensile / pushing force F4 is exerted on the stopping means, directed along the outermost coil 6, without any risk of the stopping means separating from the stud 14, this being prevented by the engagement of the foot 10 of the hook 8 in the groove 18. Furthermore, other shapes of the hook 8 can of course be envisaged, for example, an "L" shape, oriented inwards (see figure 5A ) or exterior side (see figure 5B), or in the shape of a marine anchor (see figure 6 ), or even in a "U" shape (see Figures 7A and 7B Other forms of clearance in the base of the eyelet 14 can also be considered: rather than a slot 20 extending transversely to the groove 18, at least one, and preferably two, notches 24 can be formed parallel to the groove 18, on either side of it. This embodiment is particularly well suited to cases where the hook 8 is L-shaped or anchor-shaped. The free end of the last turn outside the spiral 1 on the peg 14 is always fixed by inserting the hook 8 into the groove 18 of the peg 14, then locking the free ends of the hook 8 into the notch(s) 24. It should be understood that the opening of the hook 8 must be equal to or close to the thickness of the wall 26 separating the groove 18 from the notch 24. As can be seen on the Figures 2B And7A , in the case where the hook 8 is shaped in a “U”, it is even possible to do without the groove 18 and to provide, on the piton 14, only one or two notches 24 made in the peripheral wall of the piton 14. Nomenclature

[0029] 1. Spiral 2. First inner coil S1, S2,..., Sn. Coils 4. Center 6. Last outer coil R1,2, R2,3 Distance 8. Hook 10. Foot 12. Head 14. Eyelet 16. Base 18. Groove 20. Slot 22. Bottom 24. Notches 26. Walls

Claims

1. A horology assembly formed by a balance spring (1) and by a balance spring stud (14) for a sprung balance assembly in a mechanical horology movement, the balance spring (1) being formed by a succession of coils (S1, ..., Sn) that extend between a first free end, referred to as the first inner coil (2), and a second free end, referred to as the last outer coil (6), the last outer coil (6) of the balance spring (1) ending in a stopwork for attaching it to a balance spring stud (14), the balance spring (1) being attached by its first inner coil (2) to a staff on the balance and by its last outer coil (6) to the balance spring stud when the balance spring (1) is in the mounted state inside the sprung balance assembly mounted in the mechanical horology movement, characterised in that: the coils (S1, ..., Sn) are arranged off-centre when the balance spring (1) is in the free state, that is, in a position in which the distance (R2, 3) that separates the second coil (S2) from the third coil (S3) is not the same as the distance (R1, 2) that separates the first coil (S1) from the second coil (S2), the same thing being repeated as the distance from the centre (4) of the balance spring (1) increases between each pair of consecutive coils, the coils (S1,. .., Sn) being concentrically rearranged when this balance spring (1) is in the mounted state, the attachment of the balance spring (1) to the balance spring stud inducing, in the coils of the balance spring (1), a resilient stress by means of which the stopwork is captively attached to the balance spring stud (14).

2. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 1, characterised in that the stopwork is in the shape of a hook (8).

3. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 2, characterised in that the hook (8) is T-, L-, U- or anchor-shaped.

4. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to any of claims 1 to 3, characterised in that the balance spring (1) is made of silicon.

5. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 1, characterised in that the balance spring stud (14) comprises a base (16) in which a recess is made in which the stopwork is held, the coils being concentrically rearranged when this balance spring (1) is in the mounted state inside the sprung balance assembly mounted in the horology movement, the attachment of the balance spring to the balance spring stud inducing, in the coils of the balance spring (1), a resilient stress by means of which the stopwork is captively engaged with the balance spring stud (14).

6. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 5, characterised in that the recess is formed by a groove (18) that extends on either side of the base (16), this groove (18) opening into a slot (20) in the balance spring stud (14) transverse to the groove (18).

7. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 5, characterised in that at least one notch (24) is made parallel to the groove (18).

8. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 7, characterised in that two notches (24) are made parallel to the groove (18), on either side thereof.

9. The horology assembly formed by a balance spring (1) and by a balance spring stud (14) according to claim 5, characterised in that the recess is formed by one or by two notches (24) made in the peripheral wall of the balance spring stud (14).

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