EP3211486B1 - Method for attaching a hairspring for mechanical clock movement - Google Patents

Description

Technical field of the invention

The present invention relates to a method of fixing a spiral for a mechanical clockwork movement. The present invention relates in particular to a process for bonding silicon spirals.

Technological background of the invention

In the field of watchmaking, the balance spring constitutes with the balance the time base of the mechanical timepieces. The spiral is schematically in the form of a very thin spring wound in concentric turns and a first end called the first turn inside is connected to a ferrule, and a second end called last turn outside is connected at a peak.

More specifically, the oscillating system comprises a sprung-balance pair and an escapement. The balance consists of a balance shaft connected to a serge by means of radial arms and pivoted between a first and second bearings. The hairspring is fixed via a first turn inside to the balance shaft for example by means of a ferrule. The hairspring is fixed via a last outer turn at a point of attachment formed by a pin possibly carried by a peg holder. The exhaust comprises a double plate consisting of a large plate which carries a plateau pin and a small plate in which is formed a notch. The escapement also includes an anchor with an anchor axis pivoted between first and second bearings. The anchor consists of a rod that connects a fork to an input arm and an output arm. The fork is made up of an entrance horn and an exit horn between which a dart extends. The travel of the fork is limited by an entry limiting pin and an output limiting pin that can be made from one piece with an anchor bridge. The inlet arm and the output arm respectively carry an entry pallet and an exit pallet. Finally, the anchor cooperates with an escape wheel comprising an exhaust wheel axle pivoted between a first and a second bearing.

The material used for making the spirals is usually an alloy based on cobalt, nickel and chromium. Ductile, such an alloy must resist corrosion. Recent developments, however, propose making the silicon spirals. Silicone spirals are more accurate than their steel predecessors. Their cost price is nevertheless higher. Due to their small dimensions, such spirals are however difficult to assemble.

The hairspring is an Archimedes spring, wound in the horizontal plane, which serves only one function: once paired with a pendulum, it must turn in one direction, then in the other, that is to say swing around its equilibrium position. He is said to breathe. Now, everything helps to prevent a hairspring from always oscillating at the same frequency. The hairspring must in particular withstand the oxidation and magnetism that sticks the turns between them and stops the watch. The influence of atmospheric pressure is weak. For a long time, it was the temperature that was the crux of the problem because the heat expands the metal, the cold shrinks it. The hairspring must also be elastic to deform and yet still find its shape.

Above all, the hairspring must be isochronous. No matter how far the spiral turns, it must always be the same time to oscillate. If the hairspring contracts by a few degrees, it accumulates little energy and slowly returns to its equilibrium position. If the hairspring is moved away from much of its equilibrium position, it goes very quickly in the opposite direction. The important thing is that these two trips are made in the same duration. The underlying idea is that the energy available to the hairspring is not constant and that it must still work whether the watch is fully recovered or that it is in its last hours of power reserve.

The material used for making the spirals is usually an alloy based on cobalt, nickel and chromium. Ductile, such an alloy must resist corrosion. Recent developments, however, propose making the silicon spirals. Silicone spirals that are especially insensitive to magnetism are more accurate than their steel predecessors. Their cost price is nevertheless higher.

Due to their small dimensions, such spirals are however difficult to assemble. However, the way in which the two ends of a hairspring are fixed also has a great influence on the precision of the watch movement. In most mechanical watch movements, both ends of the hairspring are inserted into a pierced part and are immobilized by means of a pin mounted manually by force with a clamp. It can then occur a slight rotation of the spiral, which is detrimental to the accuracy of movement. To overcome this problem, the French watch manufacturer Lip, in the 1960s, proposed to glue a hairspring with a grain of hot melt glue, that is to say a glue solid at room temperature, but melting under the action of heat.

Nevertheless, even the technique of sticking the end of the spirals with a hot-melt glue has shown its limits. It has indeed been observed that because of its viscosity, the hot-melt adhesive, by melting, exerts a pulling force on the hairspring by capillary action and can press the end of the hairspring against the walls of the pin in which this end is engaged. The resulting distortion of the spiral induces in it mechanical stresses that are very detrimental to the regularity of its operation.

Requirement WO 2014/023584 discloses a method of fixing a last turn outside a watch hairspring in a piton, this method comprising the step of sticking the last turn to the outside of the watch hairspring by means of a fluid glue .

Summary of the invention

The present invention aims to overcome the aforementioned drawbacks as well as others by providing a method of fixing a hairspring which does not induce mechanical stresses in such a hairspring and does not separate it from its position rest.

For this purpose, the subject of the present invention is a process for fixing a last turn outside a watch spiral in a peak, this process comprising the step of sticking the last turn outside the clockwork spiral by means of a fluid adhesive whose viscosity is between 200 and 400 mPa.s.

According to a complementary feature of the invention, the last turn outside of the watch winder is glued in a groove in the peak.

According to another characteristic of the invention, the fluid adhesive is polymerizable by means of ultraviolet radiation.

Thanks to these features, the present invention provides a method of fixing a watchmaker's hairspring in which the last turn outside the watch hairspring is glued to the peak by means of a drop of fluid glue. Thus, even if at the time of depositing the drop of glue, for example by means of an automated glue dispenser, the free end of the last turn of the spiral deforms a little under the effect of the weight of the glue, which induces unwanted mechanical stresses in the hairspring, the adhesive is, before curing, sufficiently fluid to allow the free end of the last turn of the hairspring to return spontaneously to its rest position. The stresses induced in the hairspring at the time of deposition of the glue drop therefore disappear by themselves, so that the smooth running of the hairspring is not affected by the fixing operation of the hairspring.

Fluid glue can also be a glue that hardens on contact with air.

According to another characteristic of the invention, the watch winder is formed of a coil of concentric turns comprising a last turn on the outside which ends with a wafer which is thicker than the other spiral turns, the wafer being provided with at least one notch to promote the adhesion of the glue once it hardened.

Brief description of the figures

• la figure 1 est une vue générale en perspective d'un système oscillant pour mouvement d'horlogerie auquel s'applique la présente invention ;
• les figures 2A et 2B illustrent schématiquement un spiral dont une extrémité extérieure est collée sur un piton au moyen d'une colle photo-polymérisable, et
• la figure 3 est une vue d'un spiral horloger dont la dernière spire à l'extérieur se termine par une plaquette plus épaisse que les autres spires du spiral et dans laquelle sont ménagées des encoches pour favoriser l'accrochage de la colle.

Other characteristics and advantages of the present invention will emerge more clearly from the following detailed description of an exemplary implementation of the method according to the invention, this example being given for purely illustrative and nonlimiting purposes only in connection with the drawing. annexed in which:

• the figure 1 is a general perspective view of an oscillating system for a watch movement to which the present invention applies;
• the Figures 2A and 2B schematically illustrate a spiral whose outer end is glued to a stud by means of a photo-polymerizable glue, and
• the figure 3 is a view of a clockwork spiral, the last turn outside ends with a wafer thicker than the other turns of the spiral and in which are formed notches to promote the attachment of the glue.

Detailed description of an exemplary embodiment of the invention

The present invention proceeds from the general inventive idea of sticking the last coil outside a hairspring on a peak by means of a fluid adhesive whose viscosity is between 200 and 400 mPa.s. It has indeed been observed that when the last turn is glued to the outside of a hairspring, for example by means of a heat-fusible glue, the The viscosity of such an adhesive is such that it exerts capillary forces on the hairspring which tend to move the hairspring away from its rest position and to induce in the latter mechanical stresses which considerably impair its running accuracy. On the contrary, in the case of a sufficiently fluid glue, even if the spiral deviates from its rest position at the moment when the glue is deposited, the spiral can spontaneously return to its resting position free of any stress before the glue does not harden. In this way, the precision of the spiral is not affected by the operation of sticking it on the stud.

According to a first variant embodiment of the invention, the glue used is a fluid adhesive which hardens on contact with air. According to a second variant embodiment of the invention, the fluid adhesive is an adhesive which cures by polymerization under the effect of exposure to ultraviolet radiation.

By photopolymerizable glue is meant a polymer adhesive capable of polymerizing under the effect of ultraviolet radiation. This is why photo-polymerizable adhesives are usually referred to as UV glue. Photopolymerizable adhesives have a large number of advantages: they are monocomponent, their polymerization is fast and can, in some cases, be done without solvent, their application is easy, they allow to carry out heat-sensitive collages and do not have pot life or pot life in Anglo-Saxon terminology. Pot life is the period of time available to use a resin before complete curing from the moment when the two components of the resin are mixed, and the chemical reaction takes place.

Very schematically, a photo-polymerizable glue consists of a base resin, a photoactivator and, where appropriate, one or more additives.

The base resin which may be a monomer or an oligomer has well-defined functional groups which, after UV polymerization, will condition the physical and resulting polymer. The polymerization reaction may be based either on radical mechanisms to which the acrylic components are subjected, for example, or on cationic mechanisms to which the epoxy components are subjected for example. In the case of a radical-type reaction, the photo-polymerization phenomenon is interrupted as soon as the exposure to ultraviolet radiation ceases. In addition, radical systems of acrylic type are subject to inhibition by oxygen. On the contrary, in the case of a cationic type reaction, the photo-polymerization phenomenon continues even after interruption of the UV illumination and is not inhibited by oxygen. In addition, it is possible to complete the UV polymerization by a last thermal polymerization step.

• les composés époxydes qui regroupent les époxydes cycloaliphatiques et les époxydes glycidyliques, les éthers vinyliques et les composés vinyliques riches en électrons;
• les alcools en combinaison avec des composés époxydes, et
• les composés acryliques.

In the case of the present invention, one is interested as well in radical type polymerization reactions as cationic type. For this purpose, the base resin may be chosen from:

• epoxide compounds which include cycloaliphatic epoxides and glycidyl epoxides, vinyl ethers and electron-rich vinyl compounds;
• alcohols in combination with epoxy compounds, and
• acrylic compounds.

It will be appreciated that alcohols and polyols react together with epoxides and acrylics as chain transfer agents, generally improving the rate of polymerization of the formulations. It should also be noted that cycloaliphatic epoxy resins give rise to a faster cationic polymerization reaction than glycidyl epoxy resins because they have greater chain flexibility than the latter.

• les sels de diaryliodonium;
• les sels de triarylsulfonium;
• les sels de dialkylphenacylsulfonium.

In addition to a base resin, the composition of a UV glue is completed by a photoactivator. A photoactivator is a molecule that absorbs light and forms a reactive chemical species. These Photo-initiator compounds typically generate a hyper-acid that allows the crosslinking of cationic systems. These systems are therefore inhibited in basic or wet medium. On the other hand, they are not inhibited by the presence of oxygen. Conventional cationic photoactivators include:

• diaryliodonium salts;
• triarylsulfonium salts;
• dialkylphenacylsulfonium salts.

These short-wave reactive salts (200-300 nm) can be used alone or in combination with photo-sensitizers, ie molecules capable of absorbing light and transferring excitation to another molecule, for greater efficiency.

The photoactivators must have excellent reactivity, a suitable absorption spectrum, a lack of yellowing, good stability, compatibility with the monomers and substrates, minimum odor and non-toxicity.

The composition of a photo-polymerizable adhesive may be supplemented by one or more additives among which mention may be made of co-initiators, that is to say molecules which do not participate in the absorption of light but which contribute the production of reactive particles, antioxidants, UV stabilizers, reactive diluents or adhesion promoters or surfactants.

An exemplary embodiment of the invention is illustrated on the figure 1 attached. In this figure is represented an oscillating system for a watch movement generally designated by the general numerical reference 1. This oscillating system 1, mounted on a bridge 2 of the turntable of a watch movement, comprises a watch winder 4 formed of a very thin spring wound in concentric turns and which is fixed via a first turn inside 6 to a balance shaft 8 by means of a ferrule 10. The spiral 4 is fixed via a last outer turn 12 at an attachment point formed by a stud 14 carried by a stud holder or a bridge 16.

The oscillating system 1 also comprises a rocker 18 whose axis 8 is connected to a serge 20 by means of radial arms 22. The balance shaft 8 is pivoted between a first and a second bearing 24, only one of which is visible in the drawing. and which are hunted in bridge 2 and platinum of the watch movement.

Furthermore, the oscillating system 1 comprises a double-plate 26 consisting of a large plate 28 which carries a plate pin 30 and a small plate 32 in which is formed a notch 34.

The oscillating system finally comprises an anchor 36 whose axis 38 is pivoted between a first and a second pivot 40, only one of which is visible in the drawing. The anchor 36 consists of a rod 42 which connects a fork 44 to an input arm 46 and an output arm 48. The fork 44 consists of an input horn 50 and a horn of output 52 between which extends a stinger 54. The travel of the fork 44 is limited by an input limiting pin and an output limiting pin (not visible in the drawing) that can be made of a piece with a anchor bridge. The inlet arm 46 and the output arm 48 respectively carry an inlet pallet 56 and an outlet pallet 58.

Finally, the anchor 36 cooperates with an escape wheel 60 comprising an exhaust wheel axle 60 pivoted between a first and a second pivot 64.

In accordance with the embodiment of the invention illustrated in Figures 2A and 2B the last outer turn 12 of the spring 4 is glued to the stud 14 by means of a drop of photo-polymerizable adhesive 66. This drop of glue is for example deposited by means of an automated dispensing device such as a syringe still known by its Anglo-Saxon name "dispenser". The drop of photo-polymerizable glue 66 is polymerized by exposure to light radiation produced by an ultraviolet light source 68. Exposure to ultraviolet light is sufficient to cause complete polymerization of the glue. It should be noted that the first turn inside the spiral 4 can also be glued to the ferrule 10 by means of the same UV conductive glue as that used for gluing the spiral 4 to the stud 14.

As seen in the discussion of Figures 2A and 2B the last turn outside 12 of the hairspring 4 is arranged in a groove 70 formed at the upper end of the pin 14. Figure 2A , the drop of photo-polymerizable adhesive 66 has been deposited using a syringe and, under the effect of the gluing force of the glue, the end of the last turn outside 12 of the spiral 4 has moved slightly away from its rest position and touches the walls of the groove 70, which is very unfavorable to the precision of the spiral. However, as visible on the Figure 2B before the polymerization of the glue, the end of the last turn outside 12 of the spiral 4 is spontaneously returned to its rest position. This is made possible by the fact that the photo-polymerizable adhesive 66 is very fluid, its viscosity being between 200 and 400 mPa.s, so that the adhesive does not oppose the spontaneous return movement of the end of the spiral 4 in its equilibrium position. Therefore, the fixing operation of the hairspring 4 induces no mechanical stress in the hairspring 4, which is very favorable to the accuracy of the latter.

According to another characteristic of the invention, the last turn outside 12 of the spiral 4 ends with a plate 72 made in one piece with the end of the last turn outside 12 and which is thicker than the other spiral windings 4. For example only, the cross section of the wafer is 0.1x0.1 mm ² and its length L is 0.6 millimeters. It will also be observed that the wafer 72 is provided with at least one and, preferably, two notches 74 to promote the adhesion of the glue once it has hardened. Finally, it will be observed that the last turn outside 12 is not concentric with the other turns of the spiral 4. The latter turns outside 12 slightly away from the center of the turn 4 so that the penultimate turn 68 which precedes it does not touch the peak 14.

It goes without saying that the present invention is not limited to the embodiments which have just been described and that various modifications and simple variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the appended claims. It will be understood in particular that according to another embodiment of the invention, the last turn outside 12 of the spiral 4 can be glued to the stud 14 by means of a drop of glue which hardens on contact with the air . The material used for making the spirals is usually an alloy based on cobalt, nickel and chromium. Ductile, such an alloy must resist corrosion. Recent developments, however, propose making the silicon spirals. The silicon spirals are much more accurate than their steel predecessors. Their cost price is nevertheless significantly higher than that of steel spirals. Silicone spiral means a spiral made of a material comprising monocrystalline silicon, doped monocrystalline silicon, polycrystalline silicon, doped polycrystalline silicon, porous silicon, silicon oxide, quartz, silica, silicon nitride or silicon carbide. Of course, when the silicon-based material is in crystalline phase, any crystalline orientation can be used.

Nomenclature

• 1. Oscillating system
• 2. Bridge
• 4. Watchmaker's spiral
• 6. First turn inside
• 8. Balance shaft
• 10. Ferrule
• 12. Last outer turn
• 14. Piton
• 16. Post or bridge
• 18. Pendulum
• 20. Serge
• 22. Radial arms
• 24. First and Second Landings
• 26. Double-tray
• 28. Large plateau
• 30. Tray anchor
• 32. Small platter
• 34. Notch
• 36. Anchor
• 38. Axis
• 40. First and second pivot
• 42. Wand
• 44. Fork
• 46. Entry arm
• 48. Release arm
• 50. Horn of entry
• 52. Output horn
• 54. Dart
• 56. Entry pallet
• 58. Exit pallet
• 60. Exhaust wheel
• 62. Axis
• 64. First and second pivot
• 66. Photo-polymerizable adhesive
• 68. Ultraviolet light source
• 70. Groove
• 72. Plaque
• 74. Notches

Claims (5)

1. Method for attachment of a last outer coil (12) of a timepiece balance spring (4) in a balance spring stud (14), the method including the step of adhesive bonding the last outer coil (12) of the timepiece balance spring (4) by means of a fluid adhesive (66) whose viscosity is comprised between 200 and 400 mPa.s.
2. Method according to claim 1, characterized in that the last outer coil (12) of the timepiece balance spring (4) is adhesive bonded inside a groove (70) provided in the balance spring stud (14).
3. Attachment method according to any of claims 1 or 2, characterized in that the fluid adhesive (66) is cured by means of ultraviolet irradiation.
4. Attachment method according to any of claims 1 or 2, characterized in that the fluid adhesive is an adhesive that hardens on contact with the air.
5. Attachment method according to any of claims 1 to 4, characterized in that the timepiece balance spring (4) is formed of a winding of concentric coils and comprising a last outer coil (12) ending in a plate (72) which is thicker than the other coils of the balance spring (4), the plate (72) being provided with at least one notch (74) to promote the adhesion of the fluid adhesive (66) once the latter has hardened.

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