CH711960A2 - A method of manufacturing a hairspring of predetermined stiffness by removing material. - Google Patents

Abstract

The invention relates to a method for manufacturing a hairspring of predetermined stiffness comprising the steps of manufacturing a hairspring according to oversize dimensions, determining the stiffness of the hairspring (5a) formed in order to remove the volume of the hairspring. material to obtain the spiral to the dimensions necessary for said predetermined stiffness. This 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 greater 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 material to be removed to obtain the dimensions necessary to obtain said hairspring of a predetermined stiffness; d) removing the hairspring formed during step a), said thickness of material to obtain the hairspring to the dimensions necessary for said predetermined stiffness.

It is therefore clear that the method 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% greater 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 the same plate in dimensions larger 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 phases d1): oxidizing the spiral formed during step a) in order to transform said thickness of silicon-based material to be removed into silicon dioxide and thus form a spiral oxidized, and 62): removing the oxidized spiral oxide to obtain the spiral to the dimensions necessary for said predetermined stiffness; in a second variant, step d) comprises the step d3): etching the spiral formed during step a) in order to obtain the spiral to the dimensions required for said predetermined stiffness. after step d), the method performs at least one more step b), c) and d) to refine the dimensional quality; - After step d), the method further comprises step e): forming, on at least a portion of said hairspring of a predetermined stiffness, a portion for correcting the stiffness of the hairspring and forming a hairspring less sensitive to thermal variations; 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 6 are spiral sections at different stages of the process according to the invention; fig. 7 is a perspective representation of a step of the method according to the invention; fig. 8 is a diagram of the process according to the invention.

Detailed Description of the Preferred Embodiments

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 corresponds 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; - AT 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. ° C'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 formulas (1) - (6), that it is possible to pair the hairspring 5 with the balance 3 so that the frequency / resonator 1 is almost insensitive to temperature changes.

The invention relates more particularly to a resonator 1 in which the hairspring 5 is used to compensate the entire resonator 1, that is to say all the parts and in particular the balance 3. Such a hairspring 5 is generally 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 hairspring 5, 15 offers the advantage of being precise by the existing methods of wrecking and to have 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 as compensating spiral 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 whatever its crystalline 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. 8, a first step 33 intended to form at least one hairspring 5a, for example based on silicon, in dimensions Da greater 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 Hi and a thickness E-i.

Preferably, the dimensions Da of the spiral 5a are substantially between 1% and 20% higher 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. 7. 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 can be formed in the same plate 23 according to dimensions Da, Hi, E-ι greater than the dimensions Db, H3, E3 necessary to obtain several spirals 5c d ' a predetermined stiffness C or several spirals 5c of several predetermined stiffnesses C.

Step 33 is also not limited to the formation of a hairspring 5a in dimensions Da, H-ι, E-ι greater than the dimensions Db, H3, E3 needed to obtain a hairspring 5c of a predetermined stiffness C, formed using a single material. Thus, step 33 could equally well form a hairspring 5a with dimensions Da, H-ι, E-ι greater than the dimensions Db, H3, E3 necessary to obtain a hairspring 5c of a 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 sample spirals 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 and then, using the relationship (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 implemented 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 relation (2), the thickness of material to withdrawing on the assembly of the hairspring to obtain the overall dimensions Db necessary to obtain said hairspring 5c of a predetermined stiffness C, that is to say the volume of material to be removed homogeneously or not on the surface of the hairspring 5a .

The method is continued with a step 39 for removing the excess material of the hairspring 5a to the dimensions Db necessary to obtain said hairspring 5c of a predetermined stiffness C. 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 uniform thickness over the entire outer surface can be removed, a non-uniform thickness over the entire outer surface can be removed, a uniform thickness only on a portion of the outer surface can be removed or a non-uniform thickness only on part of the outer surface can be removed. By way of example, step 37 could consist of removing material only according to the thickness E-ι or the height H-ι of the spiral 5a.

In a first variant relating to a silicon-based material, step 39 comprises a first phase d1 intended to oxidize the hairspring 5a in order to transform said thickness of silicon-based material to be removed into silicon dioxide and thus forming an oxidized spiral 5b. Such a phase d1 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 5a.

As shown in FIG. 4, the spiral section 5b has a height H2 and a thickness E2. It can be seen that the hairspring 5b is formed of a central part 22 based on silicon according to the overall dimensions Db required for the hairspring 5c at said predetermined stiffness C and a peripheral portion 24 made of silicon dioxide. In addition, it is visible that the crenellated form is always reproduced on a portion of the peripheral portion 24 but is no longer or less present the central portion 22.

Step 39 ends, as shown in FIG. 5, with a second phase d2 intended to remove the oxide of the spiral 5b making it possible to obtain a spiral 5c with the single silicon-based part 22 with the overall dimensions Db necessary to obtain said predetermined stiffness C, the section comprising in particular a height H3 and a thickness E3. Such a phase d2 may, for example, be obtained by chemical etching. Such a chemical bath may comprise, for example, a hydrofluoric acid for removing the silicon oxide spiral 5b.

In a second variant, step 39 comprises a single phase d3 for etching the spiral 5a to obtain the spiral 5c silicon-based dimensions Db, H3, E3 required for said predetermined stiffness C. Of course, depending on the material used, other variants such as laser etching or localized ion etching, for removing the excess material from the hairspring 5a to the dimensions Db necessary to obtain said hairspring 5c of a predetermined stiffness C, can to be considered.

Step 39 may finish process 31. However, after step 39, method 31 may 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. 8 comprising optional steps 41, 43 and 45. Advantageously according to the invention, the method 31 can thus be continued with the step 41 intended to form, on at least a part of the hairspring 5c, a portion 28 making it possible to form a hairspring 5, 15 less sensitive to thermal variations.

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

In the case where the portion 22 is a silicon-based material, the e1 phase may consist of oxidizing the spiral 5c to coat with silicon dioxide to form a spiral which is thermocompensated. 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.

Thus the balance spring 5,15 is obtained as shown in FIG. 6 which, advantageously according to the invention, comprises a core 26 based on silicon and a coating 28 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 H4 and the thickness E4, and, incidentally, a thermal compensation of the entire resonator 1 very thin.

In the case of a silicon-based hairspring, the overall dimensions Db can be found by using the teachings of 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, the 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, it can be expected to crystallize it to a predetermined depth.

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. For example, if a monocrystalline or polycrystalline silicon is used, it may be provided to dope or to diffuse interstitial or substitutional atoms to a predetermined depth.

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; 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 coil 12 thickened 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 to various variations and modifications that will occur to those skilled in the art. In particular, as explained above, the pendulum, even if it

Claims (18)

carries a predefined inertia of construction, 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 iteration (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 ) greater than the dimensions (Db, H3, E3) 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 material to be removed to obtain the dimensions (Db, H3, E3) necessary to obtain said hairspring (5c) of a predetermined stiffness (C); d) removing (39) from the hairspring (5a) formed during step a), said material thickness making it possible to obtain the hairspring (5c) with the dimensions (Db, H3, E3) necessary for said predetermined stiffness (C) . 2. Method (31) of manufacture according to the preceding claim, characterized in that, in step a), the dimensions (Da, H-ι, E ·) of the spiral (5a) formed during the step a) are between 1% and 20% higher than those (Db, H3, E3) 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 a same plate (23) in dimensions (Da, H · ,, E ·,) greater than the dimensions (Db, H3, E3) 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 claim 6, characterized in that step d) comprises the following phases: d1) oxidize the spiral (5a) formed during step a) to transform said thickness of material silicon-based material to be removed from silicon dioxide and thus forming an oxidized spiral (5b); d2) removing the oxidized spiral oxide (5b) for obtaining the spiral (5c) to the dimensions (Db, H3, E3) required 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: d3) etch the spiral (5a) formed in step a) so to obtain the hairspring (5c) of dimensions (Db, H3, E3) necessary for said predetermined stiffness (C). 14. Method (31) for manufacturing 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. 15. Method (31) for manufacturing according to one of the preceding claims, characterized in that, after step d), the method further comprises 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. 16. The method (31) of manufacture according to claim 15, 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. 17. The method (31) of manufacture according to claim 15, 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). 18. Method (31) of manufacture according to claim 15, characterized in that step e) comprises the following step: e3) modifying the composition to a predetermined depth of a portion of the outer surface of said hairspring (5c) d a predetermined stiffness (C).