Patent Application
20190346812
The present invention relates to a balance-spring stud for fixing a spiral spring of a timepiece movement. More precisely, the present invention relates to a balance-spring stud in which a last turn on the outside of a spiral spring of a timepiece movement is fixed by adhesive bonding. The invention also relates to a method for manufacturing such a balance-spring stud.
In the field of horology, a spiral spring associated with a balance forms a time base for the mechanical timepieces. In a first approach, the spiral spring is in the form of a very fine spring wound in concentric turns. A first end of the spiral spring, referred to as the first turn on the inside, is fixed to a collet, and a second end of the spiral spring, referred to as the last turn on the outside, is fixed to a balance-spring stud.
More precisely, the time base for mechanical timepieces, also referred to as an oscillating system, comprises a balance/spiral spring pair and an escapement. The balance is composed of a balance staff pivoted between a first and a second bearing and connected to a balance rim by means of radial arms. The spiral spring is fixed via its first turn on the inside to the staff of the balance, for example by means of a collet. The spiral spring is fixed via its last turn on the outside to an attachment point formed by a balance-spring stud carried by a balance-spring stud holder where applicable. As for the escapement, this comprises a double-plate system consisting of a large plate that carries a plate pin and a small plate in which a notch is formed. The escapement also comprises pallets, a pallet staff of which is pivoted between a first and a second bearing. The pallets are composed of a lever that connects a fork to an input arm and to an output arm. The fork consists of an input horn and an output horn between which a dart extends. The movement of the fork is limited by an input limitation pin and an output limitation pin, which can be made in a single piece with a pallet bridge. The input arm and the output arm carry respectively an input pallet stone and an output pallet stone. Finally, the pallets cooperate with an escapement wheel comprising an escapement wheel staff pivoted between a first and a second bearing.
The spiral spring is in the form of a spiral wound in a horizontal plane, parallel to the plane of the timepiece movement. It serves only one function: once associated with a balance, it must turn in one direction and then in the other, that is to say oscillate about its equilibrium position at a frequency that is as constant as possible. It is said that the spiral spring breathes. However, everything contributes to preventing a spiral spring from always oscillating at the same frequency. The spiral spring must in particular withstand the oxidation and magnetism that stick the turns together and stop the watch. The influence of atmospheric pressure, on the other hand, is small. For a long time it is the temperature that has been the heart of the problem, since heat expands the metal, while cold shrinks it. The spiral spring must also be elastic so as to deform and nevertheless always regain its shape.
The material used for producing spiral springs is normally a steel. Ductile, such an alloy must resist corrosion. Recent developments propose producing spiral springs from silicon. Silicon spirals, in particular because they are insensitive to magnetism, are more precise than their steel predecessors. On the other hand, their cost price is higher and they are more difficult to assemble.
A spiral spring must be isochronous. No matter to what point the spiral spring turns, it must always take the same time to oscillate. If the spiral spring contracts by only a few degrees, it accumulates little energy and slowly returns to its equilibrium position. If the spiral spring is moved away far from its equilibrium position, it very quickly moves in the opposite direction. The important thing is that these two movements take place in the same period of time. The underlying idea is that the energy that the spiral spring has is not constant and that it must despite everything function whether the watch is completely wound up or is in its last hours of running reserve.
Because of their small dimensions, spiral springs are difficult to assemble. However, the way in which the two ends of the spiral spring are fixed also has a great of influence on the precision of the running of the timepiece movement. In the majority of mechanical timepiece movements, the two ends of the spiral spring are inserted in a pierced part and are immobilised by means of a pin force-fitted manually by means of pliers. A slight rotation of the spiral spring may then occur, which is detrimental to the precision of the running of the movement. To overcome this problem, the French timepiece manufacturer Lip, during the 1960s, proposed to bond a spiral spring with a grain of hot-melt glue, that is to say a glue that is hard at ambient temperature, but melting under the action of heat.
Nevertheless, even the technique consisting of bonding the end of the spiral springs by means of a hot-melt glue showed its limits. It has in fact been observed that, because of its viscosity, hot-melt glue, in melting, exerts by capillarity a traction force on the spiral spring and may press the end of the spiral spring against the walls of the balance-spring stud in which this end is engaged. The resulting deformation of the spiral spring causes mechanical stresses in it that are highly detrimental to the regularity of its running.
To remedy these problems, the applicant has already proposed a method for fixing a spiral spring that does not cause any mechanical stress in such a spiral spring and does not move it away from its idle position. This method consists of bonding the last turn on the outside of a spiral spring in a balance-spring stud by means of a drop of fluid glue polymerisable for example by means of ultraviolet radiation. Thus, even if, at the time the drop of glue is deposited, for example by means of a glue dispenser of the syringe type, the free end of the last turn of the spiral spring moves a little under the effect of the weight of the drop of glue, which causes undesired mechanical stresses in the spiral spring, the glue is, before hardening, sufficiently fluid to enable the free end of the last turn of the spiral spring to spontaneously regain its idle position. The mechanical stresses caused in the spiral spring at the moment of the deposition of the drop of liquid glue therefore disappear themselves, so that the regularity of the running of the spiral spring is not affected by the operation of bonding the latter.
The above solution thus makes it possible to fix a spiral spring by the free end of its last turn on the outside in a balance-spring stud while totally or at least for the major part eliminating the mechanical stresses that are normally caused in such a spiral spring during assembly thereof. The regularity of running of the spiral spring is thus greatly improved thereby. With use, the applicant nevertheless realised that the spot of hardened glue formed when the drop of liquid glue used to fix the free end of the last turn on the outside of the spiral spring is polymerised sometimes had a tendency to become disconnected from the balance-spring stud, which of course causes the immediate failure of the timepiece movement in which this spiral spring is installed. Such a situation in which the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped becomes detached from the balance-spring stud is in particular due to problems of surface finish of the balance-spring stud that prevent the spot of glue from adhering perfectly to the balance-spring stud.
The aim of the present invention is to solve the aforementioned problems as well as yet others by procuring a novel type of balance-spring stud the shape of which makes it possible to guarantee that the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped will not become disconnected from the balance-spring stud even if this spot of glue no longer adheres to the balance-spring stud.
To this end, the present invention relates to a balance-spring stud used for fixing a free end of a last turn on the outside of a spiral spring for a timepiece movement, this balance-spring stud comprising a base that lies in a plane and on which a first arm and a second arm that are free at their end opposite to the base are erected, the first and second arms being separated from one another by a gap in which the free end of the last turn on the outside of the spiral spring that is trapped in a hardened spot of glue is housed, at least one of the first and second arms being provided with a stop means arranged to prevent the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped from being released from the gap in which it is housed when this spot of glue no longer adheres to the balance-spring stud.
According to a particular embodiment of the invention, at least one of the first and second arms is pierced right through with a hole.
According to another particular embodiment of the invention, at least the first arm is free at its end opposite to the base, and comprises a groove at a distance from its free end, this groove lying in a plane that forms an angle with the plane of the base.
According to yet another particular embodiment of the invention, the stop means projects into the gap designed to receive the spot of hardened glue in which the free end of the last turn on the outside of the spiral spring is trapped.
According to yet another particular embodiment of the invention, the stop means is at least one bead that is made in one piece with the corresponding arm of the balance-spring stud.
As a result of these features, the present invention procures a balance-spring stud used to fix the free end of the last turn on the outside of a spiral spring for a timepiece movement, this balance-spring stud being provided with a stop means designed to prevent the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped from disengaging from the gap in which this spot is housed when the latter is no longer adhering to the balance-spring stud.
The present invention applies to all types of known spiral spring. It may in particular be metal spirals typically produced from steel. It may also be spiral springs produced from silicon.
The present invention is also not limited to any type of glue in particular. This is because the free end of the last turn on the outside of the spiral spring may for example be bonded in the gap of the balance-spring stud by means of the adhesive well known by its name “Lacquer gum” (adhesive known by the same name or under the name “Shellac” in English terminology), or be bonded by means of a liquid glue which can for example be polymerised by means of UV radiation. The advantage of lacquer gum lies mainly in the fact that it adheres well and lastingly to the balance-spring stud. On the other hand, to the knowledge of the applicant, the bonding of spirals to balance-spring studs by means of a lacquer glue has never been automated and the success thereof remains entirely dependent on the dexterity of the operator responsible for this operation. Lacquer gum is a resin and the operator takes a small flake of it, which he places in the gap intended to receive the free end of the last external turn of the spiral spring. After having placed this end of the spiral spring in the gap in the balance-spring stud, the operator briefly heats the flake of lacquer gum, which melts and traps the free end of the last external turn of the spiral spring. The operator next leaves the lacquer gum to cool and, after a visual check, decides whether it is necessary to add an additional quantity of lacquer gum or whether he can pass to the following spiral spring/balance-spring stud assembly. It will be understood that such a succession of operations is difficult to automate. This is why it has been proposed to glue the spiral springs, in particular those produced from silicon, by means of a liquid glue polymerisable by means of UV radiation or able to harden in contact with air. As already mentioned above, the fluidity of such a type of glue is such that, after deposition of a drop of this glue, the free end of the last external turn of the spiral spring can spontaneously return to its idle position from which it has been moved apart during the deposition of the glue. In particular, the quantity of liquid glue deposited can be controlled very precisely and fully automated by means of a glue dispenser such as a syringe, also known by the English term dispenser. After deposition of the drop of liquid glue, the latter is hardened by insolation by means of a UV lamp. It will be understood well that such a method is easily automatable. On the other hand, the drawback of photopolymerisable glue is that adhesion thereof to the balance-spring stud is not very satisfactory and that the risks that the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped may become detached from the balance-spring stud are high.
It is to respond to these problems that the present invention proposes providing a timepiece balance-spring stud with a stop means for preventing the spot of glue in which the free end of the last turn on the outside of the spiral spring is trapped from becoming detached from this balance-spring stud. The balance-spring stud is typically in the form of a base that lies in a plane from which two arms separated from one another by a gap designed to receive the free end of the last turn on the outside extend. The stop means may take various forms, among which mention can be made non-limitatively of a hole that passes right through at least one of the two arms.
Once the free end of the last turn on the outside of the spiral spring is positioned in the gap in the balance-spring stud, the drop of liquid glue is deposited. By capillarity, the latter will in particular diffuse in the hole, in which it will remain captive, and harden after insolation by means of UV radiation. Consequently if, over time, the spot of glue becomes disconnected from the balance-spring stud, it will however not manage to become released from the gap in which it is housed, so that this will have no effect on the functioning of the timepiece movement.
The stop means may also be provided in the form of an element, for example a bead, projecting in the gap in the balance-spring stud in which the free end of the last turn on the outside of the spiral spring is housed. In this case also, if the spot of glue in which the free end of the spiral spring is trapped becomes disconnected from the balance-spring stud, this spot of hardened glue will not be able to escape from the gap.
According to yet another particular embodiment of the invention, at least one of the first and second arms of the balance-spring stud comprises a groove that lies in a plane that forms an angle with the plane of the base. This groove delimits a hook that serves as a stop means for the spot of glue.
The invention also relates to a method for manufacturing a balance-spring stud used for fixing a free end of a last turn on the outside of a spiral spring for a timepiece movement, this balance-spring stud comprising a base that lies in a plane and a first and second arm that extend from this plane, the first and second arms being separated from one another by a gap in which the free end of the last turn on the outside of the spiral spring that is trapped in a spot of hardened glue is housed, the gap being initially produced with a first width, the method comprising the step that consists of widening the gap by stamping and creating, by upsetting, a stop means that projects in the gap designed to receive the spot of hardened glue in which the free end of the last turn on the outside of the spiral spring is trapped.
Other features and advantages of the present invention will emerge more clearly from the following detailed description of an example embodiment of a balance-spring stud according to the invention, this example being given purely for illustration and solely non-limitatively in relation to the accompanying drawing, on which:
The present invention proceeds from the general inventive idea that consists of providing a balance-spring stud intended for fixing a spiral spring of a timepiece movement with a stop means designed to prevent a free end of the last turn on the outside of the spiral spring from becoming uncoupled from the balance-spring stud and causing immediate stoppage of the timepiece movement. More precisely, the balance-spring stud comprises a base that lies in a plane from which first and second arms extend, separated from one another by a gap. This gap is designed to receive the free end of the last turn on the outside of the spiral spring, which will be immobilised by means of a spot of glue hardened by ultraviolet radiation. In accordance with the invention, at least one of the two arms of the balance-spring stud is provided with a stop means designed to prevent the spot of glue, and therefore the free end of the turn on the outside of the spiral spring, from escaping from the gap should the spot of glue become disconnected from the balance-spring stud. This stop means may be in various forms such as, non-limitatively, a hole, a bead or a hook.
In the following detailed description of several particular embodiments of the invention, the gluing of a silicon spiral by means of a liquid glue intended to be polymerised by means of ultraviolet radiation will be dealt with. It will however be understood that the invention is not limited to this particular embodiment and that it applies identically to any type of spiral spring such as metal spiral springs produced for example by means of a steel alloy.
Designated overall by the numerical reference 1, a first particular embodiment of a balance-spring stud 2 according to the invention is shown in
In accordance with the invention, the balance-spring stud 2 is provided with a stop means designed to prevent a spot of glue 16 in which a free end 18 of a last turn on the outside of a spiral spring 20 is trapped from escaping from the gap 10 in the case where the spot of glue 16 becomes disconnected from the balance-spring stud 2. According to the first particular embodiment 1 of the invention, this stop means is in the form of a hole 22 pierced right through in at least one of the first and second arms 6, 8. In the example illustrated in
The example of a silicon spiral spring 20 more particularly visible in
In the example illustrated in
Hereinafter, the elements identical to those described in relation to
Designated overall by the general numerical reference 36, a second particular embodiment of a balance-spring stud 2 according to the invention is shown in
Designated overall by the general numerical reference 44, a third particular embodiment of a balance-spring stud 2 according to the invention is shown in
One possible technique for producing the beads 46 is illustrated in
Another possible technique for creating an annular collar 52 is illustrated in
It goes without saying that the present invention is not limited to the embodiment that has just been described and that various simple modifications and variants can be envisaged by a person skilled in the art without departing from the scope of the invention as defined by the accompanying claims. In particular, in relation to
| Number | Date | Country | Kind |
|---|---|---|---|
| 18172195.2 | May 2018 | EP | regional |
