EP2874019B1 - End curve for a spiral driven by the outer end thereof - Google Patents

Description

Technical area

The present invention relates to a spiral spring intended to be included in a regulating member with a balance of a watch movement. The invention also relates to a regulating member comprising the spiral spring and a watch movement comprising the regulating member.

State of the art

The mechanical regulating organs include a balance driven on a rotating axis and a balance spring whose contractions determine the rate of the watch. The inner end of the hairspring is integrally linked to the axis of the balance through the ferrule. The outer end of the hairspring is for its part integrally linked to the plate or to the balance bridge through a stud.

This traditional arrangement is however detrimental to the precision and isochronism of the watch. Indeed, it is known that the center of gravity of the balance spring moves when the balance spring winds and unwinds around the axis. The hairspring winds and therefore unwinds by deforming eccentrically relative to the balance axis during its operation. This displacement produces the same effect as an unbalance of the balance and generates an undesirable fluctuation in the torque applied to the axis of the balance. To remedy this imprecision, the balance springs often include an outer tail, the shape of which is calculated in order to maintain the center of gravity of the balance spring on the axis of the balance spring. Since the spring is flexible, the correction does not however apply in the same way to all the turns of the spring whose spiral shape tends to deform. A significant correction is applied to the external turns, while the internal turns which act more directly on the balance axis are less affected. Consequently, the torque applied to the central axis varies and the isochronism is not perfect.

By using a Breguet-type curve on the outer end of a hairspring, or even where this terminal curve is produced above the main plane of the hairspring, we can obtain a hairspring which generally operates in a concentric manner, but the point of pitonnage of such a hairspring is not located at a radius large enough not to disturb the free operation of the hairspring.

On the other hand, any shocks imparted to the movement are transmitted to the large mass of the balance through its central axis. To absorb these shocks, damping elements must be provided. For this purpose, shock absorbers such as Incablocs® systems are generally used, which allow axial shocks to be absorbed on the axis of the balance, while allowing rotation with less friction. However, these shock absorbers make the regulating member more expensive and increase its complexity and the difficulty of assembly.

Finally, the balance axis is generally linked to a balance bridge which increases the thickness of the movement.

Requirement EP1605322 describes a regulating member in which the inner end of the spring is linked to the axis of the balance through a ferrule free to move axially along this axis. This solution does not solve the mentioned isochronism problem.

Requirement EP2063325 by the present applicant discloses a regulating member with a balance and a double hairspring, in which the outer end of each hairspring is secured to the balance, and the inner end of each hairspring is secured to a fixed point of the movement, for example of a fixed axis. The outer end of each hairspring includes a 90 ° bend.

The use of a fixed axle eliminates the shock absorbers and the balance bridge. On the other hand, isochronism disturbances are to a large extent avoided, since the correction of the position of the center of gravity caused by the tail of the hairspring is applied near the point of attachment to the balance. In the solution disclosed in EP2063325 , however, the center of gravity of each hairspring remains far from the axis of rotation and the torque induced by the right angle elbow causes the deployment of the hairspring in operation to be non-concentric. There may even be a displacement of the center of gravity of the hairspring during its operation. This is why the demand solution EP2063325 comprises two identical concentric hairsprings, the outer ends of which are fixed at 180 degrees to each other. The incorporation of such a double hairspring, however, increases the complexity and the cost of the regulating member significantly.

The document FR1540160 describes a hairspring for a clockwork movement, the end of at least one of its end turns of which is coiled, out of the plane of the hairspring, to constitute the ferrule, alternately the hairspring peak or both.

The document EP2196867 discloses a hairspring with rising curve in silicon-based material comprising a hairspring made in one piece and coaxially with a ferrule, an end curve and a lifting device between the outer turn of said hairspring and said end curve .

Requirement CH700260 reveals a spiral spring with an inner part 12 fixed on the shaft 6 and an outer part fixed on the balance 2. The terminal curve does not extend out of the plane from the outer coil and has only one radius of curvature.

Brief summary of the invention

An object of the present invention is to provide a spiral spring free from the limitations of the state of the art.

According to the invention, these objects are achieved in particular by means of a spiral spring, according to independent claim 1, intended to be included in a member regulating with a balance of a watch movement and comprising an inner end, an end curve and an outer end; the inner end of the hairspring being integral with a fixed point of the movement; the outer end of the hairspring being integral with the balance so that the hairspring can be driven by its outer end; and the terminal curve extending above the plane of the hairspring from the outer turn thereof and having a shape allowing the position of the center of gravity of the hairspring to coincide with its center of rotation.

The end curve includes a first portion having a first radius of curvature and a second portion having a second radius of curvature reversed from the first radius of curvature.

In one embodiment, the terminal curve further comprises a rectilinear connection zone between the two portions.

The invention also relates to a regulating member comprising the spiral spring and a watch movement comprising the regulating member.

This solution has the particular advantage over the prior art of allowing a concentric deployment of the hairspring during training by the outer end, the center of gravity of the hairspring remaining close to the center of rotation of the hairspring. The shape of the terminal curve makes it possible to produce a regulating member offering very good isochronism. On the other hand, the use of a fixed axis eliminates the shock absorbers and the balance bridge. The manufacture of the hairspring of the invention poses no more constraints than the manufacture of a hairspring with a conventional end curve.

Brief description of the figures

• la figure 1 illustre une vue du dessus d'un ressort spiral pour un organe réglant d'un mouvement de montre, selon l'invention;
• la figure 2 représente une vue du dessus d'un balancier comprenant le ressort spiral selon un mode de réalisation; et
• la figure3 représente un spiral plat conventionnel.

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

• the figure 1 illustrates a top view of a spiral spring for a member regulating a watch movement, according to the invention;
• the figure 2 shows a top view of a balance comprising the spiral spring according to one embodiment; and
• the figure3 represents a conventional flat hairspring.

Example (s) of embodiment of the invention

With reference to the figure 1 , a clockwork spiral spring 1 (or spiral) according to the invention comprises a flat spiral part 10 and a raised end curve 3 extending outside (above or below) the flat spiral part 2 from a point 11 of the outer turn 8 of this flat spiral part 2. The hairspring 1 with its end curve 3 can be obtained by deformation of the outer turn 8 of an initial plane hairspring.

According to one embodiment, an inner end 2 of the hairspring 1 is intended to be fixed integral with a fixed point of the movement and an outer end 4 of the hairspring 1 is intended to be fixed integral with a balance of a regulating member d 'a mechanical watch movement.

In the present text, the expression "end of the hairspring" can encompass the end curve 3 or in general the entire portion at each end of the hairspring 1, the deformation of which is negligible compared to that of the entire hairspring, for example the last turn at each end of the hairspring.

The figure 2 shows a top view of a balance 5 comprising the spiral spring 1 according to the invention. In the illustrated embodiment, the inner end 2 of the hairspring 1 is fixed to a fixed axis 7 of the balance 1, for example, by means of a ferrule 70. In this configuration, the balance 5 is configured to be able to rotate around the fixed axis 7 relative to the movement of the watch, for example, relative to a plate (not shown). In such a configuration, the lateral and axial guidance of the balance 5 on the axis 7 can be provided by guide elements (not shown) integral with the balance. The axis 7 being fixed, shock absorbers are not necessary. In the figure 2 , the other elements of the regulating organ are conventional and are not shown. It is however accepted that the balance is set in motion, for example, thanks to the energy supplied by an escape wheel and an escape anchor (not shown).

The outer end 4 of the hairspring is integral with the balance 5 so that the hairspring can be driven by its outer end. In the embodiment illustrated on figure 2 , the outer end 4 is fixed to the balance 5 at an attachment point 12 located on one of the arms 50 of the balance. The attachment point 12 could also be located on a flywheel 51 of the balance. Note that it is however also possible to use a rotary axis, for example the axis of the balance, and to fix the inner end 2 of the hairspring 1 to another point by means of a piton and a bridge ( not shown).

The shape of the end curve 3 is determined so that the center of gravity of the hairspring 1 is permanently substantially coincident with the center of rotation 9, so that the turns of the flat spiral part 2 of the hairspring 1 are deformed concentrically during the oscillations. of the last. By “center of gravity” of the hairspring 1 is in fact meant the center of gravity of the elastic part of the hairspring 1. The center of gravity within the meaning of the invention is a center of deformation.

The spiral spring 1 comprises an end curve 3 which extends outside the plane of the balance-spring from the outer turn 8 of the latter and whose shape is chosen to modify the position of the center of gravity of the balance-spring 1 and to make it coincide with its center of rotation 9. In particular, the shape of the terminal curve 3 makes it possible to satisfy the Phillips condition, that is to say, the shape of the terminal curve 3 makes it possible to bring the center of gravity of the hairspring 1 back to axis 7 (coinciding with its center of rotation 9) while having an attachment point 12 located at a radius (from this center of rotation) large enough to let the hairspring 1 operate freely. In particular, we see on the figure 2 that the point of attachment 12 is preferably at a radius which is considerably greater than the radius of the last turn of the flat spiral part 10

The end curve 3 participates in the elastic deformations of the hairspring 1 and allows the latter to deform concentrically during its operation. It consists of circular segments and / or rectilinear and is obtained by permanent deformation of the outer turn 8 of the initial plane balance spring 2.

In the preferred embodiment illustrated in figures 1 and 2 , the terminal curve 3 takes the form of an "S" curve.

The terminal "S" curve 3 may include a first portion 31 having a first radius of curvature and a second portion 32 having a second radius of curvature reversed with respect to the first radius of curvature. The terminal curve 3 can also include a rectilinear connection zone between the two portions 31, 32.

In operation, the torque created by the first and second curvatures 31, 32 compensates for the natural deployment of the hairspring 1 away from the attachment point 12 so that the center of gravity of the hairspring 1 remains very close to its center of rotation 9. For example, during operation of the hairspring 1 having the end curve 3 in "S", as illustrated in figures 1 and 2 , the position of the center of gravity has been measured, and the inventors have found that it has a variation of the order of 1 μm with respect to the center of rotation 9 of the hairspring 1. By way of comparison, in the case of a conventional flat hairspring, the end curve 3 of which is bent and in the same plane as the flat part 10 of the spiral 1 (see figure 3 ), the position of the center of gravity has a variation which is rather of the order of 10-100 µm with respect to the center of rotation 9 of the hairspring.

Reference numbers used in figures

1

spiral spring

2

inner end of hairspring

3

end curve of the hairspring

4

outer end of the hairspring

5

pendulum

6

fixed point

7

axis

8

outer coil

9

center of rotation

10

flat spiral part

11

point of the outer coil

12

attachment point

31

first portion

32

second portion

50

arms

51

steering wheel

70

ferrule

Claims (8)

1. Balance-spring (1) intended to be comprised in a regulating organ with a balance (5) of a watch movement and comprising an inner end (2), a terminal curve (3) and an external end (4);
   the inner end (2) of the balance-spring (1) is intended to be attached to a fixed point (6) of the movement;
   the external end (4) of the balance-spring (1) is intended to be attached to the balance (5) so that the balance-spring can be driven by its external end;
   characterised in that
   the terminal curve (3) extends outside the plane of the balance-spring from its external coil (8); the terminal curve (3) comprises a first portion (31) with a first radius of curvature and a
   second portion (32) with a second radius of curvature inverted in relation to the first radius of curvature in such a way as to make the position of the balance-spring's (1) centre of gravity coincide with its centre of rotation (9).
2. Balance-spring (1) according to claim 1,
   wherein the terminal curve (3) is in the shape of an S curve.
3. Balance-spring (1) according to claim 2,
   wherein the terminal curve (3) comprises furthermore a straight-lined connection zone between the two portions (31, 32).
4. Regulating organ comprising a balance (5) and the balance-spring (1) according to one of the claims 1 to 3 wherein the inner end (2) of the balance-spring (1) is attached to a fixed point (6) of the movement; and the outer end (4) of the balance-spring (1) is fixed to the balance (5) so that the balance-spring can be driven by its external end.
5. Regulating organ according to claim 4 wherein the balance staff (5) is fixed and the internal end (2) of the balance-spring (1) is fixed to this axis.
6. Regulating organ according to claim 4 or claim 5 wherein the attachment point (12) of the external end (4) of the balance-spring (1) is situated at a radius that is greater than the radius of the last coil of the balance-spring.
7. Regulating organ according to claim 6 wherein the attachment point (12) of the external end (4) of the balance-spring (1) is on an arm of the balance (5).
8. Watch movement comprising a regulating organ according to one of the claims 4 to 7.

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