EP2154583B1 - Hairspring for sprung balance - Google Patents

Description

The present invention relates to a hairspring for a sprung balance resonator comprising n blades, n ≥ 2 (1a, 1b, 1c), integral at least by their respective homologous ends and wound in spirals with an angular offset capable of neutralizing the forces lateral generated when the homologous ends of said blades located at a first end of the hairspring are angularly displaced with respect to the homologous ends of said blades located at the second end of the hairspring.

A hairspring of the aforementioned type has already been described in EP 2,063,325 , published after the priority date of the present invention.

We know that the center of gravity of a flat hairspring moves during the oscillating movement of the balance. This is due to the fact that one end of the hairspring is fixed, while the other moves while always remaining at the same distance from the balance axis. This displacement of the center of gravity has an influence on isochronism, because it generates lateral forces on the pivots of the balance axis.

Abraham-Louis Breguet had the idea of fitting the flat hairspring with one or two end curves to remedy this defect. This curve was then theorized by Ed. Phillips.

Before the solution devised by Breguet and Phillips, T. Mudge had proposed using two springs attached to the same balance and offset by 180 °. The hairsprings working in synchronism, but in phase opposition, the variations of their respective centers of gravity compensate each other, but their axial offset nevertheless creates a slight torque in a plane containing the balance axis. This solution has been taken up in recent achievements.

The problem with this solution lies in the fact that you need two superimposed hairsprings, increasing the height, two eyebolts and two eyebolts offset by 180 ° around the balance axis, two rackets and that each hairspring must be adjusted in perfect synchronism with the other, leading to an extremely complex and difficult solution to develop. In addition, it doubles the number of pieces.

This solution has been used in several publications, in particular in US 3'553'956, in FR 2'447'571, as well as in CN 1'677'283.

The aim of the present invention is to benefit from the advantages of this solution by overcoming, at least in part, the aforementioned drawbacks.

To this end, the subject of this invention is a hairspring for a sprung balance resonator according to claim 1.

• La figure 1 est une vue en plan d'une première forme d'exécution;
• la figure 2 est une vue en plan d'une forme d'exécution ne relevant pas de l'invention;
• la figure 3 est un diagramme de variation du pas du spiral en fonction des tours depuis le centre vers l'extérieur pour la forme d'exécution de la figure 2;
• la figure 4 est un diagramme de variation de l'épaisseur le long de la lame en fonction des tours depuis le centre vers l'extérieur pour la forme d'exécution de la figure 2;
• la figure 5 est une vue en plan d'une deuxième forme d'exécution;
• la figure 6 est une vue en plan d'une troisième forme d'exécution;
• la figure 7 est une vue en plan d'une quatrième forme d'exécution;
• la figure 8 est une vue en plan d'une cinquième forme d'exécution;
• la figure 9 est une vue en élévation d'une forme d'exécution ne relevant pas de l'invention;
• les figures 10a, 10b sont des vues en élévation de deux variantes d'une forme d'exécution ne relevant pas de l'invention;
• la figure 11 est une vue en élévation d'une forme d'exécution ne relevant pas de l'invention.

The accompanying drawings illustrate, schematically and by way of example, several embodiments of the hairspring which is the subject of the present invention.

• The figure 1 is a plan view of a first embodiment;
• the figure 2 is a plan view of an embodiment not falling within the scope of the invention;
• the figure 3 is a diagram of the variation of the pitch of the hairspring as a function of the turns from the center to the outside for the embodiment of the figure 2 ;
• the figure 4 is a diagram of the variation of the thickness along the blade as a function of the turns from the center to the outside for the embodiment of the figure 2 ;
• the figure 5 is a plan view of a second embodiment;
• the figure 6 is a plan view of a third embodiment;
• the figure 7 is a plan view of a fourth embodiment;
• the figure 8 is a plan view of a fifth embodiment;
• the figure 9 is an elevational view of an embodiment not falling within the scope of the invention;
• the figures 10a , 10b are views in elevation of two variants of an embodiment not coming under the invention;
• the figure 11 is an elevational view of an embodiment not falling within the scope of the invention.

The first embodiment of the hairspring which is the subject of the invention is illustrated by figure 1 . This flat hairspring comprises two blades 1a, 1b wound in the same direction, but with an offset of 2π / 2, ie 180 °. The respective internal ends of these blades 1a, 1b are integral with a ferrule 2 and their external ends are integral with a fixing ring 3. These external ends are also angularly offset by 180 °. The fixing ring 3 of the outer ends of the blades 1a, 1b of the hairspring has an opening 3a to allow its attachment to the balance bridge. This fixing ring 3 therefore replaces the traditional eyebolt.

The two blades 1a, 1b of the hairspring must not touch each other during their contraction and expansion. This risk increases with the amplitude. This risk can therefore be reduced by limiting the amplitude. Advantageously, however, the diameter of the balance spring can also be increased.

Yet another solution is that which consists in varying the pitch of the turns and the thickness of the blades. This is shown by the embodiment of the figure 2 , as well as the diagrams of figures 3 and 4 which respectively illustrate the variation of the pitch of the turns in micrometers and of the thickness of the blades in micrometers as a function of the number of turns of the turns Nt of the blades 1a, 1b wound on the figure 2 , starting from the center towards the outside of the hairspring, to prevent the turns of the blades 1a, 1b from touching each other during the alternation of expansion and contraction of the hairspring. The figure 3 allows you to plot one of the two blades 1a, 1b by the formula r (θ) = p (θ) * (θ / (2π)) + r0, where r represents the distance from the axis to the neutral fiber of the blade, r (θ = 0) = r0 = 600 micrometers in the case of figures 2 to 4 , and θ = Nt * 2π.

As a variant, the height of the blade of the hairspring could also be varied.

In the case of balance-springs made of mono-crystalline silicon, a material capable of being used for making the balance-spring which is the subject of the invention, the thermo-compensation of the balance-spring is obtained by the formation, on the surface of the blades of the balance-spring, of a layer of amorphous silicon oxide, whose thermal coefficient of Young's modulus is of the opposite sign to that of monocrystalline silicon, as described in EP 1 422 436 . This layer of amorphous silicon oxide allows compensation of the thermal coefficient of the Young's modulus whatever the crystallographic orientation of Si, (100), (111) or (110).

The number of blades forming the hairspring is not limited to two. One can imagine as a variant various other solutions, such as that illustrated by figure 5 which is a variant of that of the figure 1 , but which comprises three blades 1a, 1b and 1c attached on the one hand to the ferrule 2 and on the other hand to the fixing ring 3. The internal and external ends of these blades are angularly offset, with respect to each other. others, at an angle 2π / 3. This angular offset will advantageously be 2π / n, n corresponding to the number of blades.

Simulations carried out on the basis of the balance springs figures 1 and 2 have shown that it should be possible to very significantly improve the isochronism of a sprung balance resonator equipped with a spring which is the subject of the present invention.

In the embodiments described so far, the blades forming the hairspring are attached to each other by their two respective ends. The embodiment illustrated by figure 6 represents a hairspring with two blades 1a, 1b attached by their only internal ends to the ferrule 2. Their external ends are free, which allows to exert, on the two plates, a pre-tension in one direction or the other, in order to adjust the isochronism in particular.

Other variants using the same concept, namely a hairspring with several coplanar blades angularly offset and attached by at least one of their respective homologous ends are possible.

Thus it is possible to have a hairspring comprising four blades, two blades 1a, 1b arranged between the ferrule 2 and an intermediate ring 4 to which their outer ends are fixed and two blades 1c, 1d arranged between the intermediate ring and the fixing ring 3. To make the intermediate ring 4 as light as possible, its structure can be hollowed out to reduce its mass as much as possible.

The inner blades 1a, 1b and the outer blades 1c, 1d can all be wound in the same direction as illustrated by figure 7 , or the internal blades 1a, 1b can be wound in the opposite direction of the external blades 1c, 1d, as illustrated by figure 8 .

It is obvious that countless other combinations can be considered.

It is also obvious that the new design of the balance spring which is the subject of the invention does not lend itself to the manufacture according to the traditional methods of the Nivarox / Parachrom type balance springs.

In the present case, a method entirely suitable for the manufacture of the hairspring which is the subject of the invention is in particular that described in EP 1 422 436 already mentioned, which consists in cutting the hairspring, for example by plasma etching, in a {001} monocrystalline silicon wafer. The thermo-compensation of the hairspring is then obtained by the formation of a layer of amorphous silicon oxide on the surface of the blades of the hairspring, by heat treatment for example.

One could also use a quartz single crystal machined in the same way or by chemical machining. Other suitable materials, adapted to the manufacturing methods allowing the production of a hairspring in a plane are likely to be used.

The use of photo-lithographic processes such as UV-LIGA (Lithographie, Galvanisierung und Abformung) could also make it possible to produce the type of hairspring which is the subject of the present invention in a metal alloy.

The manufacturing process does not form part of the present invention. The examples of non-limiting methods, listed above by way of example, are only intended to show that the technical means for producing the new type of hairspring which is the subject of the invention already exist and that those skilled in the art has a range of possibilities for making this hairspring.

When we speak of a flat hairspring, it is the hairspring as it is obtained. However, nothing prevents, especially in the embodiment of the figure 9 , to locate the mounting points 5 and 6 of the outer ends of the blades 1a, 1b out of the plane of the hairspring. This is how we can locate these two fixing points respectively on either side of the plane of the hairspring, so that the two blades 1a, 1b will form two symmetrical cones on either side of the plane of the hairspring. spiral. This solution has the advantage of preventing the turns of the two blades from touching each other. This solution makes it possible to produce spirals of small diameter with a large number of turns. It therefore constitutes another means of avoiding contact between the blades of the hairspring during the alternation of expansions and contractions.

According to another variant of the invention, the two blades 1a, 1b are produced on an SOI (Silicon-On-Insulator, figures 10a, 10b ), which consists of a stack of layers of Si-SiO ₂ -Si. A blade 1a is etched from the outer face of one of the layers of Si and the other blade 1b is etched from the outer face of the second layer of Si. In this case, the inner ends of the two blades are made integral by the intermediate layer 8 of SiO ₂ . The advantage of this embodiment is to reduce the diameter of the hairspring, because the distance between two neighboring turns is increased. This advantage is even more pronounced if we extend the hairspring vertically as in the figure 10 .

The figure 11 illustrates another variant of figures 10a , 10b , in which the internal ends of the blades 1a, 1b are integral with the same ferrule, while their external ends are integral with the intermediate layer 5 of SiO ₂ .

Claims (8)

1. A hairspring for a balance wheel/hairspring resonator, which hairspring comprises n blades, where n ≥ 2, fastened via at least one of their respective homologous ends and wound in spirals with an angular offset capable of neutralizing the lateral forces likely to be exerted on its central arbor when one of the ends of each blade is moved angularly about said central arbor relative to its other end, the hairspring comprising a collet (2), the blades being coplanar and the intern ends being fastened to the collet.
2. The hairspring as claimed in the preceding claim, wherein the blades are fastened to each other via their two respective ends.
3. The hairspring as claimed in one of the preceding claims, wherein the pitch of the blades is variable.
4. The hairspring as claimed in one of the preceding claims, wherein the thickness of the blades is variable.
5. The hairspring as claimed in one of the preceding claims, wherein the height of the blades is variable.
6. The hairspring as claimed in one of the preceding claims, which is formed from single-crystal silicon.
7. The hairspring as claimed in claim 6, wherein the single-crystal silicon is covered with a layer of amorphous silicon oxide.
8. The hairspring as claimed in one of claims 1 to 4, which is formed from quartz.

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