CH711961A2 - A method of manufacturing a hairspring of a predetermined stiffness by adding material. - Google Patents

Abstract

The invention relates to a method for manufacturing a hairspring of predetermined stiffness comprising the steps of manufacturing a hairspring (5a) according to dimensions which make it possible to obtain a deliberately lower stiffness, of determining the stiffness of the hairspring. formed and modifying the formed hairspring to compensate for said thickness of missing material to obtain the hairspring at the dimensions necessary for said predetermined stiffness. The invention relates to the field of watchmaking.

Description

Description

FIELD OF THE INVENTION [0001] The invention relates to a method for manufacturing a hairspring of predetermined stiffness and, more specifically, to such a hairspring used as a compensating hairspring cooperating with a predetermined inertia beam to form a hairspring. resonator having a predetermined frequency.

BACKGROUND OF THE INVENTION [0002] It is explained in EP 1 422 436, incorporated by reference into the present application, how to form a compensating balance spring comprising a silicon core coated with silicon dioxide and cooperating with a balance wheel. predetermined inertia for thermally compensating the assembly of said resonator.

[0003] Making such a compensating hairspring provides many advantages but also has drawbacks. In fact, the step of etching several spirals in a silicon wafer offers a non-negligible geometrical dispersion between the spirals of the same wafer and a greater dispersion between spirals of two wafers etched at different times. Incidentally, the stiffness of each spiral engraved with the same engraving pattern is variable by creating significant manufacturing dispersions. SUMMARY OF THE INVENTION [0004] The object of the present invention is to overcome all or part of the disadvantages mentioned above by proposing a method of manufacturing a spiral whose dimensions are sufficiently precise not to require retouching.

For this purpose, the invention relates to a method for manufacturing a hairspring of a predetermined stiffness comprising the following steps: a) forming a hairspring according to dimensions smaller than the dimensions necessary to obtain said hairspring of a predetermined stiffness; b) determining the stiffness of the hairspring formed during step a); c) calculating the thickness of missing material to obtain said hairspring of a predetermined stiffness; d) modifying the spiral formed during step a), to compensate for said thickness of missing material to obtain the spiral (5c) to the dimensions necessary for said predetermined stiffness.

It is therefore understood that the process ensures a very high dimensional accuracy of the spiral and, incidentally, to ensure a more precise stiffness of said spiral. Each manufacturing parameter, which can induce geometric variations during step a), can be completely rectified for each spiral manufactured or rectified on average for all the spirals formed at the same time to drastically reduce the scrap rate.

According to other advantageous variants of the invention: during step a), the dimensions of the spiral formed during step a) are between 1% and 20% lower than those necessary to obtain said spiral to said predetermined stiffness; step a) is carried out using deep reactive ion etching or chemical etching; during step a), several spirals are formed in one and the same plate with dimensions smaller than the dimensions necessary to obtain several spirals of a predetermined stiffness or several spirals of several predetermined stiffnesses; the spiral formed during step a) is based on silicon, glass, ceramic, metal or metal alloy; step b) comprises the phases b1): measuring the frequency of an assembly comprising the spiral formed during step a) coupled with a balance having a predetermined inertia and b2): deducing from the measured frequency, the stiffness of the hairspring formed during step a); according to a first variant, step d) comprises the step d1): depositing a layer on a part of the outer surface of the spiral formed during step a) in order to obtain the spiral with the dimensions necessary for said predetermined stiffness ; according to a second variant, step d) comprises the step d2): modifying the structure according to a predetermined depth of a portion of the outer surface of the hairspring formed during step a) in order to obtain the hairspring with dimensions necessary for said predetermined stiffness; according to a third variant, step d) comprises the step d3): modifying the composition according to a predetermined depth of a part of the external surface of the hairspring obtained during step a) in order to obtain the hairspring with dimensions necessary for said predetermined stiffness; after step d), the method performs at least one more step b), c) and d) to refine the dimensional quality; in a first variant, step e) comprises the step e1): depositing a layer on a portion of the outer surface of said hairspring of a predetermined stiffness; in a second variant, the step e) comprises the phase e2): modifying the structure according to a predetermined depth of a part of the external surface of said hairspring with a predetermined stiffness; in a third variant, step e) comprises the step e3): modifying the composition according to a predetermined depth of a portion of the external surface of said hairspring with a predetermined stiffness.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] Other particularities and advantages will become clear from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which: FIG. 1 is a perspective view of an assembled resonator according to the invention; fig. 2 is an example of spiral geometry according to the invention; figs. 3 to 5 are spiral sections at different stages of the process according to the invention; FIG. 6 is a perspective representation of a step of the method according to the invention; fig. 7 is a diagram of the process according to the invention.

Detailed Description of the Preferred Embodiments [0009] As illustrated in FIG. 1, the invention relates to a resonator 1 of the balance 3-spiral type 5. The balance 3 and the spiral 5 are preferably mounted on the same axis 7. In such a resonator 1, the moment of inertia I of the balance 3 responds to the formula:

(1) in which m represents its mass and r its radius of gyration which also depends on the temperature via the coefficient of expansion ab of the balance.

In addition, the stiffness C of the spiral 5 constant section meets the formula:

(2) in which E is the Young's modulus of the material used, its height, its thickness and L its developed length.

In addition, the stiffness C of a spiral 5 variable section meets the formula:

(3) wherein E is the Young's modulus of the material used, its height, its thickness, its developed length and the curvilinear abscissa along the turn.

In addition, the stiffness c of a spiral 5 variable thickness but constant height meets the formula:

(4) wherein E is the Young's modulus of the material used, its height, its thickness, its developed length and the curvilinear abscissa along the turn.

Finally, the frequency / resonator 1 sprung balance responds to the formula:

(5) [0014] According to the invention, it is desired that the variation of the frequency as a function of the temperature of a resonator is substantially zero. The variation of the frequency / as a function of the temperature T in the case of a sprung balance resonator substantially follows the following formula:

(6) where:

is the relative frequency variation; - ΔΓ is the variation of the temperature;

is the relative variation of the Young's modulus as a function of the temperature, ie the thermoelastic coefficient (GTE) of the spiral; - as is the coefficient of expansion of the spiral, expressed in ppm. ° C'1; - Ab is the coefficient of expansion of the balance, expressed in ppm.O'1; Oscillations of any resonator for a time base or frequency to be maintained, the thermal dependence also includes a possible contribution of the maintenance system such as, for example, a Swiss lever escapement (not shown) cooperating with the pin 9 of the plate 11 also mounted on the axis 7.

It is therefore understood from the formulas (1) - (6) that it is possible by the choice of materials used to couple the spiral 5 with the balance 3 so that the frequency / resonator 1 is almost insensitive to temperature variations.

The invention relates more particularly to a resonator 1 in which the hairspring 5 is used to thermally compensate the entire resonator 1, that is to say all the parts and in particular the balance 3. Such a hairspring 5 is usually called a compensating hairspring. Therefore, the invention relates to a manufacturing method for ensuring a very high dimensional accuracy of the spiral and, incidentally, to ensure a more precise stiffness of said spiral.

According to the invention, the compensating spiral 15 is formed from a material, optionally coated with a thermal compensation layer, and intended to cooperate with a balance 3 predetermined inertia. However, nothing prevents to provide a pendulum with movable weights to offer a setting parameter before or after the sale of the timepiece.

The use of a material, for example based on silicon, glass or ceramic, for the manufacture of a spiral 5, 15 offers the advantage of being precise by the existing engraving methods and possess good mechanical and chemical properties, in particular being very insensitive to magnetic fields. It must however be coated or superficially modified to form a compensating hairspring.

Preferably, the silicon-based material used for producing the compensating hairspring may be monocrystalline silicon regardless of its crystalline orientation, doped monocrystalline silicon whatever its crystalline orientation, amorphous silicon, porous silicon, polycrystalline silicon, silicon nitride, silicon carbide, quartz irrespective of its crystal orientation or silicon oxide. Of course other materials can be envisioned as a glass, a ceramic, a cermet, a metal or a metal alloy. For simplicity, the explanation below will be focused on a silicon-based material.

Each type of material may be superficially modified or coated with a layer to thermally compensate the base material as explained above.

If the step of etching spirals in a silicon-based wafer, by means of a deep reactive ion etching (also known by the abbreviation "DRIE"), is the most accurate, phenomena that occur during engraving or between two successive engravings can nevertheless induce geometric variations.

Of course, other types of manufacturing can be implemented, such as laser etching, localized ion etching (known by the abbreviation "FIB"), galvanic growth, growth by chemical deposition in phase gaseous or chemical etching, which are less accurate and for which the process would make even more sense.

Thus, the invention relates to a method 31 for manufacturing a spiral 5c. According to the invention, the method 31 comprises, as illustrated in FIG. 7, a first step 33 intended to form at least one hairspring 5a, for example based on silicon, according to dimensions Da less than the dimensions Db necessary to obtain said hairspring 5c of a predetermined stiffness C. As shown in fig. 3, the spiral section 5a has a height H-ι and a thickness E- |.

Preferably, the dimensions Da of the spiral 5a are substantially between 1% and 20% lower than those Db spiral 5c necessary to obtain said spiral 5c of a predetermined stiffness C.

Preferably, according to the invention, step 33 is carried out using a deep reactive ion etching in a wafer 23 of a silicon-based material as illustrated in FIG. 6. It can be seen that the opposite faces F 1, F 2 are corrugated because a Bosch deep reactive ion etching causes a structured slot etching by the successive stages of attack and passivation.

Of course, the method can not be limited to a particular step 33. By way of example, step 33 could equally well be obtained by chemical etching in a wafer 23 of a material for example based on silicon. In addition, step 33 means that one or more spirals are formed, i.e., step 33 makes it possible to form bulk spirals or alternately formed in a wafer of a material.

Therefore, during the step 33, several spirals 5a may be formed in the same plate 23 according to dimensions Da, Hi, E-ι less than the dimensions Db, H2, E2 necessary to obtain several spirals 5c d ' a predetermined stiffness C or several spirals 5c of several predetermined stiffnesses C.

Step 33 is not limited to the formation of a hairspring 5a in dimensions Da, Hi, E-ι less than the dimensions Db, H2, E2 necessary to obtain a hairspring 5c of a stiffness C predetermined, formed using a single material. Thus, step 33 could equally well form a hairspring 5a with dimensions Da, H-ι, E-ι less than the dimensions Db, H2, E2 necessary to obtain a hairspring 5c of predetermined stiffness C of a composite material that is to say comprising several different materials.

The method 31 comprises a second step 35 for determining the stiffness of the hairspring 5a. Such a step 35 may be carried out directly on the hairspring 5a still attached to the wafer 23 or on the hairspring 5a previously detached from the wafer 23, on the whole, or on a sample of the spirals still attached to a wafer 23 or on a spiral sample previously detached from a wafer 23.

Preferably according to the invention, the hairspring 5a being detached or not from the wafer 23, the step 35 comprises a first phase intended to measure the frequency / of an assembly comprising the hairspring 5a coupled with a balance provided with a predetermined inertia I then, using the relation (5), deduce, in a second phase, the stiffness C spiral 5a.

Such a measurement phase can in particular be dynamic and carried out according to the teachings of document EP 2 423 764, incorporated by reference into the present application. However, alternatively, a static method, carried out according to the teachings of document EP 2 423 764, can also be used to determine the stiffness C of the spiral 5a.

Of course, as explained above, the method is not limited to the etching of a single spiral per wafer, step 35 may also consist of a determination of the average stiffness of a representative sample or the set of spirals formed on the same plate.

Advantageously according to the invention, from the determination of the stiffness C of the spiral 5a, the method 31 comprises a step 37 intended to calculate, using the relationship (2), the thickness of the missing material. to obtain the hairspring 5c of a predetermined stiffness C, that is to say the volume of material to be added and / or to modify homogeneously or not on the surface of the hairspring 5a.

The method continues with a step 39 for modifying the spiral 5a formed during step a), to compensate for said thickness of missing material to obtain the spiral 5c Db dimensions, H2, E2 necessary for said stiffness C predetermined. It is therefore understood that it does not matter that the geometric variations have occurred on the thickness and / or the height and / or the length of the hairspring 5a insofar as, according to equation (2), it is the product h e3 which determines the rigidity of the turn.

Thus, a homogeneous thickness over the entire external surface may be added and / or modified, a non-homogeneous thickness over the entire external surface may be added and / or modified, a uniform thickness only on a part of the external surface may to be added and / or modified, or a non-homogeneous thickness only on part of the outer surface may be added and / or modified. By way of example, step 39 could consist of adding material only according to the thickness E, or the height H ·, of the spiral 5a.

In a first variant, step 39 comprises a phase d1 intended to deposit a layer on a portion of the outer surface of the hairspring 5a formed during step 33 to obtain the hairspring 5c with dimensions Db, H2 , E2 necessary for said predetermined stiffness C. Such a phase d1 can, for example, be obtained by thermal oxidation, by galvanic growth, by physical vapor deposition (known by the abbreviation "PVD"), by chemical vapor deposition (known by the abbreviation "CVD"), by atomic layer deposition (known by the abbreviation "ALD") or by any other additive method.

Such a phase d1 may, for example, be carried out by a chemical vapor deposition for forming polysilicon on the monocrystalline silicon spiral 5a in order to obtain the spiral 5c with dimensions Db, H2, E2 necessary for the stiffness C predetermined.

As shown in FIG. 4, the spiral section 5c has a height H2 and a thickness E2. It can be seen that the hairspring 5c is formed of a central portion 22 based on monocrystalline silicon and a peripheral portion 24 made of polycrystalline silicon according to the overall dimensions Db required for the predetermined stiffness C.

In a second variant, step 39 may consist of a phase d2 intended to modify the structure to a predetermined depth of a portion of the outer surface of the hairspring 5a to obtain the hairspring 5c with dimensions Db, H2 , E2 necessary for the predetermined stiffness C. By way of example illustrated in FIG. 4, if amorphous silicon is used to form the hairspring 5a, it can be provided to crystallize it to a predetermined depth forming a central portion 22 of amorphous silicon and a peripheral portion 24 of polycrystalline silicon to obtain the hairspring 5c with the dimensions Db, H2, E2 necessary for the predetermined stiffness C.

In a third variant, step 39 may consist of a phase d3 for modifying the composition to a predetermined depth of a portion of the outer surface of the hairspring 5a of predetermined stiffness C. By way of example illustrated in FIG. 4, if a monocrystalline or polycrystalline silicon is used to form the hairspring 5a, it may be provided to dope or to diffuse interstitial or substitutional atoms therein at a predetermined depth forming a central portion 22 of monocrystalline or polycrystalline silicon and a peripheral portion 24 doped or diffused with the aid of atoms different from the silicon in order to obtain the spiral 5c with the dimensions Db, H2, E2 necessary for the predetermined stiffness C. It will be understood that this third variant does not necessarily imply an increase in volume but at least superficially increases the Young's modulus making it possible to obtain the predetermined stiffness C.

For these three variants, it is visible that the crenellated form is always reproduced on a portion of the peripheral portion 24 and the central portion 22. Thus, a smoothing step before step 39 may be provided to attenuate, even remove, the possible crenellated form of the spiral 5a.

Step 39 may finish the process 31. However, after step 39, the method 31 can also perform, at least one more time, steps 35, 37 and 39 in order to further refine the quality. dimensional spiral. These iterations of steps 35, 37 and 39 may, for example, be of particular interest when the execution of the first iteration of steps 35, 37 and 39 is performed on the set, or on a sample, of the spirals still attached to a wafer 23, then in a second iteration, on the assembly, or a sample, spirals previously detached from the wafer 23 having undergone the first iteration.

The method 31 may also continue with all or part of the process 40 illustrated in FIG. 7 having optional steps 41, 43 and 45. Advantageously according to the invention, the method 31 can thus continue with the step 41 intended to form, on at least a part of the hairspring 5c, a portion 26 for correcting the stiffness spiral 5c and form a spiral 5.15 less sensitive to thermal variations.

In a first variant, the step 41 may consist of a phase e1 for depositing a layer on a portion of the outer surface of said hairspring 5c of predetermined stiffness C.

In the case where the parts 22/24 are a silicon-based material, the e1 phase may consist of oxidizing the spiral 5c to coat it with silicon dioxide in order to correct the stiffness of the spiral 5c and form a spiral 5, which is thermally compensated. Such a phase e1 can, for example, be obtained by thermal oxidation. Such thermal oxidation can, for example, be carried out between 800 and 1200 ° C under an oxidizing atmosphere using water vapor or oxygen gas to form silicon oxide on the spiral 5c.

This produces the spiral 5, 15 compensator as shown in FIG. 5 which, advantageously according to the invention, comprises a composite core 22/24 based on silicon and a coating 26 based on silicon oxide. Advantageously according to the invention, the balance spring 5, 15 compensator therefore has a very high dimensional accuracy especially as to the height H3 and the thickness E3, and, incidentally, a thermal compensation of the entire resonator 1 very thin.

In the case of a silicon spiral, the overall dimensions Db can be found by using the teachings of the document EP 1 422 436 to apply it to the resonator 1 which is intended to be manufactured, that is, that is, to compensate for all the constituent parts of the resonator 1 as explained above.

In a second variant, step 41 may consist of a phase e2 intended to modify the structure to a predetermined depth of a portion of the outer surface of said hairspring 5c of predetermined stiffness C. For example, if an amorphous silicon is used for the peripheral portion 24 and, optionally, the central portion 22, it can be provided to crystallize it to a predetermined depth in the peripheral portion 24 and, optionally, in the central portion 22.

In a third variant, the step 41 may consist of a phase e3 intended to modify the composition to a predetermined depth of a portion of the outer surface of said hairspring 5c of predetermined stiffness C. By way of example, if a monocrystalline or polycrystalline silicon is used for the peripheral part 24 and, possibly, the central part 22, it can be provided to dope it or to diffuse interstitial or substitutional atoms to a predetermined depth. in the peripheral portion 24 and, optionally, in the central portion 22.

Advantageously according to the invention, it is thus possible to manufacture, as illustrated in FIG. 2, without more complexity a hairspring 5c, 5, 15 comprising in particular: - one or more turns of section (s) more accurate (s) than that obtained by a single engraving;

Claims (19)

variations in thickness and / or pitch along the turn; a shell 17 in one piece; an internal turn 19 of the Grossmann curve type; a fastener 14 for one-piece punctuation; - an integral external mounting element; - A portion 13 of the outer turn 12 thickened and / or the inner turn 19 relative to the rest of the turns. Finally, the method 31 may also comprise step 45 intended to assemble a compensating hairspring 5, 15 obtained during step 41, or a hairspring 5c obtained during step 39, with a balance of inertia. predetermined step obtained in step 43 to form a resonator 1 spiral balance type which is thermally compensated or not, that is to say whose frequency / is sensitive or not to temperature changes. Of course, the present invention is not limited to the illustrated example but is susceptible of various variations and modifications that will occur to those skilled in the art. In particular, as explained above, the balance, even if it comprises a predefined construction inertia, may comprise movable weights to provide a setting parameter before or after the sale of the timepiece. In addition, an additional step, between step 39 and step 41, or between step 39 and step 45, could be provided in order to deposit a functional or aesthetic layer, such as, for example, a curing layer or a luminescent layer. It is also conceivable in the case where the method 31 performs, after step 39, one or more iterations (s) of steps 35, 37 and 39 that step 35 is not systematically implemented. claims 1. Method (31) for manufacturing a spiral (5c) of a predetermined stiffness (C) comprising the following steps: a) forming (33) a spiral (5a) according to dimensions (Da, Hi, E-i ) less than the dimensions (Db, H2, E2) necessary to obtain said hairspring (5c) of a predetermined stiffness (C); b) determining (35) the stiffness (C) of the hairspring (5a) formed in step a); c) calculating (37) the thickness of missing material to obtain said hairspring (5c) of a predetermined stiffness (C); d) modifying (39) the hairspring (5a) formed during step a), to compensate for said thickness of missing material making it possible to obtain the hairspring (5c) of dimensions (Db, H2, E2) necessary for said stiffness ( C) predetermined. 2. Method (31) of manufacture according to the preceding claim, characterized in that, during step a), the dimensions (Da, Hi, E-ι) of the spiral (5a) formed during step a) are between 1% and 20% lower than those (Db, H2, E2) necessary to obtain said hairspring (5c) at said predetermined stiffness (C). 3. Method (31) of manufacture according to claim 1 or 2, characterized in that step a) is carried out using a deep reactive ion etching. 4. Method (31) of manufacture according to claim 1 or 2, characterized in that step a) is carried out using a chemical etching. 5. Method (31) of manufacture according to one of the preceding claims, characterized in that, in step a), several spirals (5a) are formed in the same plate (23) in dimensions (Da, Hi , E-ι) smaller than the dimensions (Db, H2, E2) necessary to obtain several spirals (5c) of a predetermined stiffness (C) or several spirals (5c) of several predetermined stiffnesses (C). 6. Method (31) of manufacture according to one of the preceding claims, characterized in that the spiral (5a) formed in step a) is based on silicon. 7. Method (31) of manufacture according to one of claims 1 to 5, characterized in that the spiral (5a) formed in step a) is based on glass. 8. Method (31) of manufacture according to one of claims 1 to 5, characterized in that the spiral (5a) formed in step a) is based on ceramics. 9. The method (31) of manufacture according to one of claims 1 to 5, characterized in that the spiral (5a) formed in step a) is based on metal. 10. Method (31) of manufacture according to one of claims 1 to 5, characterized in that the spiral (5a) formed in step a) is based on metal alloy. 11. Method (31) of manufacture according to one of the preceding claims, characterized in that step b) comprises the following phases: b1) measure the frequency (/) of an assembly comprising the spiral (5a) formed during of step a) coupled with a beam having a predetermined inertia; b2) deduce from the frequency (/) measured, the stiffness (C) of the spiral (5a) formed during step a). 12. Method (31) of manufacture according to one of the preceding claims, characterized in that step d) comprises the following phase: d1) depositing a layer on a portion of the outer surface of the spiral (5a) formed during step a) in order to obtain the hairspring (5c) of dimensions (Db, H2, E2) necessary for said predetermined stiffness (C). 13. The method (31) of manufacture according to one of claims 1 to 11, characterized in that step d) comprises the following phase: d2) modify the structure to a predetermined depth of a portion of the outer surface of the spiral (5a) formed during step a) to obtain the spiral (5c) to the dimensions (Db, H2, E2) required for said predetermined stiffness (C). 14. The method (31) of manufacture according to one of claims 1 to 11, characterized in that step d) comprises the following phase: d3) modify the composition to a predetermined depth of a portion of the outer surface of the spiral (5a) obtained during step a) to obtain the spiral (5c) to the dimensions (Db, H2, E2) required for said predetermined stiffness (C). 15. Method (31) of manufacture according to one of the preceding claims, characterized in that, after step d), the method performs at least one more time steps b), c) and d) to refine the quality dimensional. 16. The method (31) of manufacture according to one of the preceding claims, characterized in that, after step d), the method comprises, in addition, the following step: e) forming, on at least a part of said spiral (5c) of a stiffness (C) predetermined, a portion for correcting the stiffness of the spiral (5c) and forming a spiral (5, 15) less sensitive to thermal variations. 17. The method (31) of manufacture according to claim 16, characterized in that step e) comprises the following phase: e1) depositing a layer on a portion of the outer surface of said spring (5c) of a stiffness (C ) predetermined. 18. Method (31) for manufacturing according to claim 16, characterized in that step e) comprises the following phase: e2) modifying the structure to a predetermined depth of a portion of the outer surface of said hairspring (5c) d a predetermined stiffness (C). 19. The method (31) of manufacture according to claim 16, characterized in that step e) comprises the following phase: e3) modifying the composition to a predetermined depth of a portion of the outer surface of said hairspring (5c) d a predetermined stiffness (C).