Method for manufacturing clock spiral springs

Abstract

One aspect of the invention relates to a method for manufacturing a batch of watch hairsprings (2a) whose stiffnesses have an average included in a predetermined range, comprising the following steps: a) forming (20) in a plate (1) the watch hairsprings (2b, 2c) according to dimensions different from the dimensions necessary to obtain the batch of watch hairsprings (2a) whose stiffnesses have the average included in said predetermined range; b) forming (21) in the plate (1) systems (3) for indicating a reference stiffness for determining the stiffnesses of the watch hairsprings (2a) whose average is included in said predetermined range; c) determining (22) the stiffnesses of said systems (3) formed; d) calculating (26) a dimensional correction to be applied to the watch hairsprings (2b, 2c) formed, from the stiffnesses of said systems (3) determined;e) modifying the dimensions of the watch balance springs (2b, 2c) formed, from a dimensional correction calculated to obtain the batch of watch balance springs (2a) whose stiffnesses have the average included in said predetermined range.;

Description

Technical field of the invention

[0001] The present invention relates to the field of manufacturing parts for watchmaking. The invention relates more particularly to a method of manufacturing a batch of watch balance springs whose stiffnesses have an average within a predetermined range. Technological background

[0002] In the state of the art, it is known to use processes for manufacturing watch springs in wafers which implement engraving techniques such as laser engraving, plasma engraving, deep reactive ion engraving known as DRIE or even wet engraving.

[0003] However, it is noted that the implementation of such processes classically generates a geometric dispersion between the watch spirals all formed according to the same pattern in the same plate.

[0004] To overcome these drawbacks, solutions are proposed in the state of the art, in particular in patents EP3181938 and EP 3181939 which describe processes for manufacturing hairsprings.

[0005] In patent EP 3181938 the manufacturing method comprises the following steps: a) a hairspring is formed in dimensions greater than the dimensions necessary to obtain a hairspring of a predetermined stiffness, b) the stiffness of the hairspring formed during step a) is determined by measuring the frequency of the hairspring coupled with a balance wheel having a predetermined inertia, c) the thickness of material to be removed to obtain the hairspring of a predetermined stiffness is calculated and d) the calculated thickness of material is removed from the hairspring formed during step a), steps b), c) and d) can be repeated to further improve the dimensional quality.

[0006] In patent EP 3181939, the manufacturing method comprises the following steps: a) a hairspring is formed in dimensions smaller than the dimensions necessary to obtain a hairspring of a predetermined stiffness, b) the stiffness of the hairspring formed during step a) is determined by measuring the frequency of the hairspring coupled with a balance wheel having a predetermined inertia, c) the missing material thickness is calculated to obtain the hairspring of a predetermined stiffness and d) the hairspring formed during step a) is modified to compensate for the missing material thickness, it being possible for steps b), c) and d) to be repeated to further improve the dimensional quality.

[0007] Such methods can be improved in particular in order to limit the contamination of the wafer which can be generated during the measurement step which they implement.

[0008] Under these conditions, we understand that there is a need to find solutions that will lead to such an improvement. Summary of the invention

[0009] An aim of the present invention is to propose a method for manufacturing a batch of watch balance springs making it possible to meet the aforementioned needs.

[0010] Another goal is to improve the precision of the manufacturing of the batch of watch hairsprings whose stiffnesses have an average within a predetermined range.

[0011] The invention relates to a method for manufacturing a batch of watch balance springs whose stiffnesses have an average within a predetermined range, comprising the following steps: a) forming in a wafer the watch hairsprings according to dimensions different from the dimensions necessary to obtain the batch of watch hairsprings whose stiffnesses have the average included in said predetermined range; b) forming in the wafer systems for indicating a reference stiffness for determining the stiffnesses of the watch hairsprings whose average is included in said predetermined range; c) determining the stiffnesses of said formed systems; d) calculating a dimensional correction to be applied to the formed watch hairsprings, from the stiffnesses of said determined systems; e) modifying the dimensions of the formed watch hairsprings, from a dimensional correction calculated to obtain the batch of watch hairsprings whose stiffnesses have the average included in said predetermined range.

[0012] In other embodiments: the steps of forming the batch of watch hairsprings and said systems are carried out by etching, in particular by deep reactive ion etching; in the forming step, each system is produced in the wafer for a hairspring of the batch of watch hairsprings; the step of forming said systems provides for the production in the wafer of a plurality of oscillating elements constituting each system surrounding the hairspring with which this system is associated in the wafer; the step of forming said systems provides for the production in the wafer of a single oscillating element constituting each system near the hairspring with which this system is associated in the wafer; the determining step comprises a sub-step of estimating at least one resonance frequency of each system associated with a hairspring of the batch of watch hairsprings;the determination step comprises a sub-step of defining the stiffness of each system from an electronic device executing an algorithm for calculating this stiffness on the basis of the estimated resonance frequency; the stiffness defined for each system is the stiffness of one of its oscillating elements, the average stiffness of all its oscillating elements or the average stiffness of a sample of its oscillating elements; the calculation step comprises a sub-step of determining from the determined stiffness a thickness of material to be added or removed from at least one dimension of the hairspring of the batch of watch hairsprings; the oscillating element has the shape of a tuning fork. Brief description of the figures

[0013] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment of the invention, given as a simple illustrative and non-limiting example, and the appended figures, among which: there Figure 1 is a schematic view of a plate comprising a batch of watch hairsprings having been formed at the same time in particular by engraving all in this plate, according to embodiments of the invention; Figure 2 is a larger scale view of an oscillating element of a reference stiffness indication system, this system being included in the plate shown in the Figure 1 , according to the embodiments of the invention; the Figure 3is a schematic view of a section of a blade of the hairspring manufactured from the method, the section having dimensions necessary to obtain the batch of watch hairsprings whose stiffnesses have the average included in the predetermined range, according to embodiments of the invention; Figure 4 is a schematic view of a section of a hairspring blade formed in the wafer from the process, the section having dimensions greater than the dimensions of the fabricated hairspring blade section illustrated in the Figure 3 , according to embodiments of the invention; the Figure 5 is a schematic view of a section of a hairspring blade formed in the wafer from the process, the section having dimensions smaller than the dimensions of the fabricated hairspring blade section illustrated in the Figure 3 , according to embodiments of the invention, and the Figure 6is a flowchart relating to a method for manufacturing a batch of watch balance springs whose stiffnesses have an average within a predetermined range, according to embodiments of the invention. Detailed description of the invention

[0014] There Figure 6 shows a schematic representation of the manufacturing process of a batch or set of 2a watch hairsprings whose stiffnesses have an average within a predetermined range. Such a process aims to ensure very high dimensional precision of the 2a hairsprings manufactured and, incidentally, to guarantee a more precise stiffness of these 2a hairsprings.

[0015] On the Figure 1, a batch of watch hairsprings 2b, 2c is formed in a plate 1. In this batch, each hairspring 2b, 2c comprises a collet intended to be secured to a pivoting shaft. This watch hairspring 2b, 2c also comprises an elastically flexible strand connected by one end to the collet and wound in a spiral so as to form several consecutive turns, the last of which is extended by an attachment segment intended to be attached to a fixed balance bridge, for example by means of a stud.

[0016] Such a method comprises a step 20 of forming in the plate 1 the watch balance springs 2b, 2c according to dimensions E, E3, H2, H3 different from the dimensions E1, H1 necessary to obtain the batch of watch balance springs 2a whose stiffnesses have the average included in the predetermined range.

[0017] During this step 20, the spirals 2b, 2c are formed in the wafer 1 of material. These spirals 2b, 2c are preferably formed simultaneously in this wafer 1. The formation of these spirals 2a, 2c in the wafer 1 can be carried out by etching, for example by deep reactive ion etching, by laser etching, by chemical etching or by etching using a focused ion beam. It will be noted that these spirals 2b, 2c preferably have similar geometries.

[0018] These watch hairsprings 2b, 2c formed in this plate 1, have blades having sections 4b, 4c of dimensions E2, H2, E3, H3 - characterized by a height H1, H2, H3 and a thickness E1, E2, E3 of this section 4a, 4b, 4c when such a blade is of polygonal shape - which are different from the dimensions E1, H1 necessary to obtain the batch of watch hairsprings 2a whose stiffnesses have the average included in the predetermined range. In other words, the blade of each hairspring 2b, 2c can have a section 4b, 4c whose dimensions E2, H2, E3, H3 are greater or less than the dimensions E1, H1 necessary for the section 4a of the blade of the manufactured hairspring 2a which makes it possible to obtain a stiffness in the average included in the predetermined range.

[0019] In the context of this method, the wafer 1 is preferably made of doped or undoped silicon. This silicon can be monocrystalline, polycrystalline or amorphous silicon. In addition, this silicon can be of orientation {1,1,1}, {-1,1,1}, {1,-1,1}, {-1,-1,1} for which the Young model of silicon is the most important. Alternatively, this wafer 1 can be made of quartz, glass, ceramic, metal or alloy.

[0020] It should be noted that during this training step 20 the watch spirals 2b, 2c formed can have: dimensions E2, H2 greater than the dimensions E1, H1 necessary to obtain the batch of watch hairsprings 2a whose stiffnesses have the average included in the predetermined range, that is to say a height H2 of the blade and / or a thickness E2 of the blade greater than the height H1 and / or the thickness E1 (s) of the blade of the watch hairsprings 2a whose stiffnesses have the average included in the predetermined range; dimensions E3, H3 less than the dimensions E1, H1 necessary to obtain the batch of watch hairsprings 2a whose stiffnesses have the average included in the predetermined range, that is to say a height H3 of the blade and / or a thickness E3 of the blade less than the height H1 and / or the thickness E1 of the blade of the watch hairsprings 2a whose stiffnesses have the average included in the predetermined range.

[0021] The method also comprises a step 21 of forming in the wafer 1, systems for indicating a reference stiffness 3, for determining the stiffnesses of the watch balance springs 2a whose average is included in the predetermined range. This step 21 is carried out in the same wafer 1 comprising the watch balance springs 2b, 2c formed and this, preferably simultaneously with the step 20 of forming these balance springs 2b, 2c. During this step 21, a system 3 is formed in the wafer 1 for each balance spring 2b, 2c of the batch of watch balance springs formed. This system 3 consists of at least one oscillating element 10 which is arranged in the immediate vicinity of the corresponding balance spring 2b, 2c. As for the step 20 of forming the balance springs 2b, 2c, the oscillating element 10 of each system 3 is preferably formed by etching.It will be noted that there may be in this plate 1 as many systems 3 as there are balance springs 2b, 2c and the height of the oscillating element 10 is similar to that of the plate 1 and therefore to that of the balance springs 2b, 2c. Alternatively, this plate 1 may include a minimum sample of system 3 making it possible to obtain a good representation of the stiffnesses on this plate 1.

[0022] As we have seen, this system 3 preferably comprises a plurality of oscillating elements 10. Such an element 10 comprises at least one blade and can extend essentially in a rectilinear manner. This element 10 comprises an attachment end 5a and at least one free end 5b, 5c. This element 10 has a geometric shape and dimensions which are different from those of a hairspring of this plate 1, with the exception of course of the height as we have specified previously.

[0023] Each oscillating element 10 is included in an opening 9 made in the plate 1. This opening 9 defines a space in which the oscillating element 10 can freely execute a controlled / controlled mechanical oscillation movement.

[0024] In particular, this oscillating element 10 comprises an attachment end 5a and two free ends 5b, 5c. Indeed, this oscillating element 10 comprises a stem / trunk 6 provided with the attachment end 5a. This stem 6 extends rectilinearly in the opening 9 and comprises in its extension two arms 7, 8 forming two flexible blades, or two flexible branches, which are folded along the stem 6. More precisely, such arms 7, 8 are arranged in the opening 9 while being located close to the stem 6 and are in this configuration essentially parallel to the latter. These two arms 7, 8 are connected to each other forming the letter “U” and each comprise a free end of the oscillating element 10. It will be noted that these arms 7, 8 may each have a thickness similar or substantially similar to that of the hairspring.

[0025] In this oscillating element 10, the rod 6 is more rigid than the two arms 7, 8 which constitute it. In addition, these arms 7, 8 have a length of between 1 mm and 2 mm, preferably 1.5 mm. These arms 7, 8 have a thickness of between 10 and 60 µm, preferably 30 µm.

[0026] Furthermore, this oscillating element 10 has a general shape of a tuning fork or is a tuning fork.

[0027] As previously specified, each oscillating element 10 is chosen to allow optimal decoupling of the embedding effect on resonance frequencies. Indeed, during harmonic excitations, there is a significant effect of the embedding on the resonance frequency. In the case of this oscillating element 10, there is significant decoupling between this embedding and the resonance frequency of the arms 7, 8. The correlation between the resonance frequency and the stiffness becomes independent of the quality of the embedding engraving.

[0028] This is not the case for an oscillating element consisting of a blade having a variable section along its main rectilinear direction and ending, at its distal end, with a locally enlarged section portion forming a mass. In such a configuration, the variation in the blade thickness leads to a modification of the embedding and therefore of the resonance. The correlation here requires taking into account the impact of this embedding, which induces a complexity that is nonexistent in the method according to the invention implementing an oscillating element 10 such as a tuning fork. In addition, this blade is provided with closed angles, the formation of which in a wafer by deep reactive ion etching requires the implementation of complex operations. Under these conditions, it is understood that there can therefore be a large variability on each of these angles, which modifies the resonance frequency.For example, a variation of the order of 2 µm on the radius of the embedding fillet, leads to a difference in the prediction of the etching thickness of the rectilinear blade of the order of 20 nm. In addition, for this blade and other types of blades other than the tuning fork, the dimensions on the manufacture of the embedding are an obstacle to obtaining a good frequency-stiffness correlation.

[0029] During this step 21, the oscillating elements 10 of each system 3 associated with a balance spring 2b, 2c, are arranged in the plate 1 in the periphery of this balance spring 2b, 2c and in particular in the immediate vicinity of this balance spring 2b, 2c. Thus the plurality of oscillating elements 10 of the system 3, is formed in the plate 1 by surrounding the balance spring 2b, 2c with which it is associated.

[0030] It will be noted that the arrangement of these oscillating elements 10 of each system 3 in this wafer 1 is preferably made in such a way that its arms 7, 8 are placed so that the Young's modulus is at its maximum or minimum, in particular when this wafer 1 is manufactured from silicon. Indeed, silicon being anisotropic, this arrangement makes it possible to avoid the variability of the Young's modulus as a function of the angle when determining the stiffness. In addition, the maximum of the Young's modulus will be favored to increase the accuracy of the correlation between the stiffness and the measured frequency.

[0031] It will be noted that during this step 21, said systems 3 are configured so that the average of the stiffnesses of the watch balance springs 2b, 2c produced in the plate 1 is within the predetermined range.

[0032] Furthermore, such an oscillating element 10 is configured so that its stiffness can be easily determined from an electronic device for determining the stiffness of these systems 3. This electronic device which is implemented by this method, comprises in a non-limiting and non-exhaustive manner: a processing unit such as a computer; a module for driving / triggering a mechanical oscillating movement in the body of an oscillating element 10 around its stable equilibrium position; a module for measuring a resonant frequency of the oscillating element 10 in mechanical oscillating movement.

[0033] The processing unit of this electronic device comprises at least one processor and memory elements. This processing unit is capable of executing instructions for implementing a computer program intended, for example, to ensure the control / monitoring of the training and measurement modules and also calculation / processing operations during which at least one algorithm, stored in the memory elements, is implemented. This algorithm may comprise a machine learning algorithm and / or mathematical formulas. This algorithm is capable of implementing a predictive model or a simulation model making it possible to determine the stiffness of a system 3 from a measurement of its resonance frequency.

[0034] It will be noted that such an oscillating element 10 is comparable to a tuning fork in the sense that it vibrates at a stable frequency despite the evolution of certain parameters linked in particular to the embedding and the manufacturing process. This stable frequency varies according to a single parameter determined here: stiffness.

[0035] One of the parameters of the oscillating element 10 significantly varies the resonant frequency so that the influence of the other parameters is negligible.

[0036] The method subsequently comprises a step 22 of determining the stiffnesses of said systems 3 associated with the balance springs 2b, 2c formed in the wafer 1. Such a step 22 comprises a sub-step 23 of estimating at least one resonant frequency of each system 3 associated with its balance spring 2b, 2c. During this sub-step 23, at least one oscillating element 10 of at least one system 3 is driven in a mechanical oscillation movement around its stable equilibrium position. During this movement, the resonant frequency of this oscillating element 10 is then determined during a measurement phase 24.

[0037] In this embodiment of the invention, the resonance frequencies of all the oscillating elements 10 of the system 3 are measured and an average of its frequencies is then calculated to correspond to the resonance frequency of this system 3. In this context, this determined average frequency is considered to be representative of the frequency of each of the oscillating elements 10 of this system 3.

[0038] Alternatively, the measured resonant frequency of the system 3 may be a resonant frequency of a single one of its oscillating elements 10 or a resonant frequency of a sample of its oscillating elements 10.

[0039] Once the resonance frequency has been estimated, this step 22 includes a sub-step 25 defining the stiffness of each system 3 during which sub-step 25, the electronic device executes the algorithm for calculating this stiffness from the estimated resonance frequency of the system 3.

[0040] The method subsequently comprises a step 26 of calculating a dimensional correction to be applied to each spiral 2b, 2c of the batch of watch spirals from the stiffness determined for the system 3 associated with it. During this step 26, a quantification of the dimensional correction to be applied to the spiral 2b, 2c is then determined.

[0041] To do this, this step 26 comprises a sub-step 27 of determining, from this determined stiffness, a thickness e of material to be added or removed from at least one dimension of the hairspring 2b, 2c of the batch of watch hairsprings formed during the forming step 20 to obtain the batch of watch hairsprings 2a whose stiffnesses have the average included in the predetermined range.

[0042] This dimensional correction actually corresponds to a thickness e of material to be removed or added to the spiral 2b, 2c in order to vary at least one of its dimensions E2, H2, E3, H3, namely: only the height H2, H3 of its blade, or only the thickness E2, E3 of this blade, or both this height H2, H3 and this thickness E2, E3.

[0043] This dimensional correction can be made on one or more separate lengths of the blade or on the entire length of the blade of this 2b, 2c spiral.

[0044] Such a sub-step 27 thus makes it possible, by determining the dimensional correction, to participate in the shaping of a geometry of this spiral 2b, 2c which will give it a stiffness which will be included in the predetermined range.

[0045] The method then comprises a step 28 of modifying the dimensions E2, E3, H2, H3 of the watch balance springs 2b, 2c from a dimensional correction calculated to obtain the batch of watch balance springs 2a whose stiffnesses have the average in the predetermined range.

[0046] In this context, if the dimensions E2, H2 of the balance springs 2b are greater than the dimensions E1, H1 necessary to obtain the batch of watch balance springs 2a whose stiffnesses have the average included in the predetermined range, this step 28 then comprises a sub-step of material removal 29 according to the thickness e of material calculated to be removed. Such removal can then be carried out during a process of oxidation then deoxidation of these balance springs 2b well known in the state of the art. Such a sub-step 29 aims to reduce the dimensions of the section 4b of the blade of this balance spring 2b over a given length or over the entire length of this blade.

[0047] When the dimensions E3, H3 of the balance springs 2c are less than the dimensions E1, H1 necessary to obtain the batch of watch balance springs 2a whose stiffnesses have the average included in the predetermined range, this step 28 then comprises a sub-step of adding material 30 according to the thickness e of material calculated to be added. Such an addition of material can then be carried out during processes well known in the state of the art such as thermal oxidation, galvanic growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition or any other additive process. Such a sub-step 30 aims to increase the dimensions E3, H3 of the section 4c of the blade of this balance spring 2c over a given length or over the entire length of this blade.

[0048] Thus, such a method makes it possible to correct, with great precision provided by said systems for indicating a reference stiffness 3, the dimensional errors of hairsprings manufactured by such methods using photolithography and / or DRIE etching technologies. Nomenclature

[0049] 1.Wafer comprising at least one hairspring 2a.Manufactured hairspring 2b.Hairspring formed in the wafer with a section of dimensions larger than those of the section of the manufactured hairspring 2c.Hairspring formed in the wafer with a section of dimensions smaller than those of the section of the manufactured hairspring 3.System for indicating a reference stiffness 4a.Section of manufactured hairspring 4b.Section of formed hairspring with dimensions larger than those of the section of the manufactured hairspring 4c.Section of formed hairspring with dimensions smaller than those of the section of the manufactured hairspring 5a.Attachment end of the oscillating element 5b.First free end of the oscillating element 5c.Second free end of the oscillating element 6.Stem / Trunk of the oscillating element 7.First flexible arm of the oscillating element 8.Second flexible arm of the oscillating element 9.Opening in which the oscillating element 10 is arranged. Oscillating element

Claims

1. Method for manufacturing a batch of watch hairsprings (2a) whose stiffnesses have an average included in a predetermined range, comprising the following steps: a) forming (20) in a plate (1) the watch hairsprings (2b, 2c) according to dimensions different from the dimensions necessary to obtain the batch of watch hairsprings (2a) whose stiffnesses have the average included in said predetermined range; b) forming (21) in the plate (1) systems (3) for indicating a reference stiffness for determining the stiffnesses of the watch hairsprings (2a) whose average is included in said predetermined range; c) determining (22) the stiffnesses of said systems (3) formed; d) calculating (26) a dimensional correction to be applied to the watch hairsprings (2b, 2c) formed, from the stiffnesses of said systems (3) determined;e) modifying the dimensions of the watch balance springs (2b, 2c) formed, from a dimensional correction calculated to obtain the batch of watch balance springs (2a) whose stiffnesses have the average included in said predetermined range.; 2. Method according to the preceding claim in which the steps of forming (20, 21) the batch of watch balance springs (2b, 2c) and said systems (3) are carried out by etching, in particular by deep reactive ion etching.

3. Method according to any one of the preceding claims, in which in the forming step (21) each system (3) is produced in the plate (1) for a hairspring of the batch of watch hairsprings (2b, 2c).

4. Method according to any one of the preceding claims, in which the step of forming (21) said systems (3) provides for the production in the plate (1) of a plurality of oscillating elements (10) constituting each system (3) surrounding the balance spring (2b, 2c) with which this system (3) is associated in the plate (1).

5. Method according to any one of claims 1 to 3, in which the step of forming (21) said systems (3) provides for the production in the plate (1) of a single oscillating element (10) constituting each system (3) near the balance spring (2b, 2c) with which this system (3) is associated in the plate (1).

6. Method according to any one of the preceding claims, in which the determining step (22) comprises a sub-step (23) of estimating at least one resonance frequency of each system (3) associated with a hairspring of the batch of watch hairsprings (2b, 2c).

7. Method according to the preceding claim, in which the determining step (22) comprises a sub-step (25) of defining the stiffness of each system (3) from an electronic device executing an algorithm for calculating this stiffness on the basis of the estimated resonance frequency.

8. Method according to the preceding claim, in which the stiffness defined for each system (3) is the stiffness of one of its oscillating elements (10), the average stiffness of all its oscillating elements (10) or the average stiffness of a sample of its oscillating elements (10).

9. Method according to any one of the preceding claims, in which the calculation step (26) comprises a sub-step of determining (27) from the determined stiffness a thickness (e) of material to be added or removed from at least one dimension of the balance spring (2b, 2c) of the batch of watch balance springs (2b, 2c).

10. A method according to any preceding claim, wherein the oscillating element (10) has the shape of a tuning fork.

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