Method for manufacturing timepiece hairspring

Abstract

One aspect of the invention relates to a method for manufacturing a batch of timepiece hairsprings (2a) having an average stiffness within a predetermined range, said method comprising the following steps: a) forming (20) timepiece hairsprings (2b, 2c) in a wafer (1), the dimensions of which differ from the dimensions required to obtain said batch of timepiece hairsprings (2a) having an average stiffness within said predetermined range; b) forming (21) in the wafer (1) a system (3) for indicating a reference stiffness for determining the stiffness of the timepiece hairspring (2a) with an average stiffness within the predetermined range; c) determining (22) the stiffness of the formed system (3); d) calculating (26) a dimensional correction to be applied to the formed timepiece hairspring (2b, 2c) based on the determined stiffness of the system (3); e) modifying the dimensions of the formed timepiece hairsprings (2b, 2c) on the basis of the calculated dimensional corrections to obtain a batch of timepiece hairsprings (2a) having an average stiffness within said predetermined range.

Description

Field of the Invention

[0001] The present invention relates to the field of manufacturing watch components. More specifically, the present invention relates to a method for manufacturing a batch of hairsprings for watches having an average stiffness within a predetermined range. Background Art

[0002] Prior art documents describe methods for manufacturing hairsprings for watches in wafers using etching techniques such as laser etching, plasma etching, deep reactive ion etching (DRIE) or wet etching.

[0003] However, using such methods typically results in geometric dispersion between the hairsprings because all the hairsprings are formed in the same pattern on the same wafer.

[0004] To overcome these drawbacks, solutions have been proposed in the prior art documents, in particular European patents EP3181938 and EP3181939, which describe methods for manufacturing hairsprings.

[0005] In European patent EP3181938, the manufacturing method comprises the following steps: a) forming a hairspring having a size larger than the size required to obtain a hairspring with a predetermined stiffness, b) determining the stiffness of the hairspring formed in step a) by measuring the frequency of the hairspring coupled to a balance wheel having a predetermined inertia, c) calculating the thickness of the material to be removed to obtain a hairspring with a predetermined stiffness, and d) removing the material of the calculated thickness from the hairspring formed in step a), and steps b), c) and d) can be repeated to further improve the dimensional quality.

[0006] In European patent EP3181939, the manufacturing method comprises the following steps: a) forming a hairspring having a size smaller than the size required to obtain a hairspring with a predetermined stiffness, b) determining the stiffness of the hairspring formed in step a) by measuring the frequency of the hairspring coupled to a balance wheel having a predetermined inertia, c) calculating the thickness of the missing material, which is the material that must be added to obtain a hairspring with a predetermined stiffness, and d) modifying the hairspring formed in step a) to compensate for the missing material thickness, and steps b), c) and d) can be repeated to further improve the dimensional quality.

[0007] Such methods can be improved, especially to limit the wafer contamination that may occur in the measurement steps implemented therein.

[0008] In these cases, it should be understood that it is necessary to find solutions that can bring about such improvements. Summary of the Invention

[0009] An object of the present invention is to propose a method for manufacturing a batch of hairsprings for watches that meet the above requirements.

[0010] Another object is to improve the manufacturing precision during the production of a batch of hairsprings having an average stiffness within a predetermined range.

[0011] The present invention relates to a method for manufacturing a batch of hairsprings having an average stiffness within a predetermined range, the method comprising the following steps:

[0012] a) forming in a wafer hairsprings having dimensions different from those required to obtain said batch of hairsprings having an average stiffness within said predetermined range;

[0013] b) forming in the wafer a system for indicating a reference stiffness, said reference stiffness being used to determine the stiffness of a hairspring having an average stiffness within said predetermined range;

[0014] c) determining the stiffness of the formed system;

[0015] d) calculating, based on the determined stiffness of the system, a dimensional correction to be applied to the formed hairsprings;

[0016] e) modifying the dimensions of the formed hairsprings based on the calculated dimensional correction to obtain a batch of hairsprings having an average stiffness within said predetermined range.

[0017] In other embodiments:

[0018] - the steps of forming a batch of hairsprings and the system are carried out by etching, in particular deep reactive ion etching;

[0019] - in the forming step, each system is made in the wafer for one hairspring of a batch of hairsprings;

[0020] - the forming step of forming the system is available for making in the wafer a plurality of oscillating elements constituting each system, said oscillating elements surrounding the hairspring in the wafer associated with that system;

[0021] - the forming step of forming the system is available for making in the wafer a single oscillating element constituting each system, said oscillating element being located near the hairspring in the wafer associated with that system;

[0022] - the determining step includes a sub-step of estimating at least one resonance frequency of each system associated with one hairspring of the batch of hairsprings;

[0023] - the determining step includes a sub-step of defining the stiffness of each system using an electronic device, said electronic device executing an algorithm for calculating said stiffness based on the estimated resonance frequencies;

[0024] - 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;

[0025] - The calculation step includes a sub-step of determining the thickness of the material to be added or removed from at least one dimension of the hairspring among the batch of watch hairsprings according to the determined stiffness.

[0026] - The shape of the oscillating element is similar to that of a tuning fork. Description of the Drawings

[0027] Other features and advantages of the present invention will be better understood after reading the following description of non - limiting specific embodiments of the present invention provided with reference to the accompanying drawings, in which:

[0028] - Figure 1 is a schematic view of a wafer including a batch of watch hairsprings, all of which have been simultaneously formed in the wafer, particularly by etching;

[0029] - Figure 2 is a larger - scale view of the oscillating element of a system for indicating a reference stiffness according to an embodiment of the present invention, and this system is included in Figure 1 the wafer shown;

[0030] - Figure 3 is a schematic cross - sectional view of a hairspring strip / leaf manufactured using the method according to an embodiment of the present invention, and this cross - section has the dimensions required to obtain a batch of watch hairsprings with an average stiffness within a predetermined range;

[0031] - Figure 4 is a schematic cross - sectional view of a hairspring strip formed in a wafer using the method according to an embodiment of the present invention, and the dimensions of this cross - section are larger than Figure 3 the dimensions of the cross - section of the manufactured hairspring strip shown;

[0032] - Figure 5 is a schematic cross - sectional view of a hairspring strip formed in a wafer using the method according to an embodiment of the present invention, and the dimensions of this cross - section are smaller than Figure 3 the dimensions of the cross - section of the manufactured hairspring strip shown in

[0033] - Figure 6 is a logic diagram related to the method for manufacturing a batch of watch hairsprings with an average stiffness within a predetermined range according to an embodiment of the present invention. Detailed Description

[0034] Figure 6 Schematically shows a method for manufacturing a batch or a set of watch hairsprings 2a with an average stiffness within a predetermined range. The purpose of this method is to ensure that the manufactured hairsprings 2a have very high dimensional accuracy and, incidentally, to ensure that these hairsprings 2a have more precise stiffness.

[0035] InFigure 1 In a wafer 1, a batch of hairsprings 2b, 2c is formed. In this batch of hairsprings, each hairspring 2b, 2c includes an inner stud which is intended to be rigidly connected to a pivot spindle. The hairsprings 2b, 2c also include an elastic flexible strip, one end of which is connected to the inner stud and is wound in a spiral to form a plurality of continuous turns, and the last turn extends through an attachment section which is intended to be attached, for example by means of an outer stud, to a fixed balance cock.

[0036] This method includes a forming step 20 of forming hairsprings 2b, 2c in the wafer 1, wherein the dimensions E, E3, H2, H3 of the hairsprings are different from the dimensions E1, H1 required to obtain a batch of hairsprings 2a with an average stiffness within a predetermined range.

[0037] During this forming step 20, the hairsprings 2b, 2c are formed in the material wafer 1. These hairsprings 2b, 2c are preferably formed simultaneously in the wafer 1. These hairsprings 2a, 2c can be formed in the wafer 1 by etching, for example by deep reactive ion etching, laser etching, chemical etching or even by etching using a focused ion beam. It should be noted that these hairsprings 2b, 2c preferably have similar geometries.

[0038] The hairsprings 2b, 2c formed in the wafer 1 have strips which have cross-sections 4b, 4c of dimensions E2, H2, E3, H3, characterized in that when the shape of such a strip is polygonal, its cross-sections 4a, 4b, 4c have heights H1, H2, H3 and thicknesses E1, E2, E3 - these dimensions are different from the dimensions E1, H1 required to obtain a batch of hairsprings 2a with an average stiffness within a predetermined range. In other words, the strip of each hairspring 2b, 2c can have cross-sections 4b, 4c whose dimensions E2, H2, E3, H3 are greater than or less than the necessary dimensions E1, H1 of the cross-section 4a of the strip of the fabricated hairspring 2a, thus allowing an average stiffness within a predetermined range to be obtained.

[0039] In the context of this method, the wafer 1 is preferably made of doped or undoped silicon. The silicon can be single-crystalline, polycrystalline or amorphous. In addition, the silicon can have orientations {1, 1, 1}, {-1, 1, 1}, {1, -1, 1}, {-1, -1, 1} for which the Young's modulus of silicon is maximum. Alternatively, the wafer 1 can be made of quartz, glass, ceramic, metal or alloy.

[0040] It should be noted that during this forming step 20, the formed hairsprings 2b, 2c can have:

[0041] - Dimensions E2, H2, which are greater than the dimensions E1, H1 required to obtain a batch of hairsprings 2a of an average stiffness within a predetermined range, i.e., the strip height H2 and / or the strip thickness E2 are greater than the strip height H1 and / or the strip thickness E1 of a batch of hairsprings 2a of an average stiffness within a predetermined range;

[0042] - Dimensions E3, H3, which are less than the dimensions E1, H1 required to obtain a batch of hairsprings 2a of an average stiffness within a predetermined range, i.e., the strip height H3 and / or the strip thickness E3 are less than the strip height H1 and / or the strip thickness E1 of a hairspring of an average stiffness within a predetermined range.

[0043] The method further includes step 21 of forming in the wafer 1 a system 3 for indicating a reference stiffness for determining the stiffness of the hairsprings 2a, the average value of the stiffness being within a predetermined range. This step 21 is carried out in the same wafer 1 including the formed hairsprings 2b, 2c, preferably simultaneously with the forming step 20 of forming these hairsprings 2b, 2c. During this step 21, a system 3 is formed in the wafer 1 for each of the hairsprings 2b, 2c in the formed batch of hairsprings. The system 3 consists of at least one oscillating element 10 which is arranged in the immediate vicinity of the corresponding hairspring 2b, 2c. Like the forming step 20 of forming the hairsprings 2b, 2c, the oscillating element 10 of each system 3 is preferably formed by etching. It should be noted that the number of systems 3 in the wafer 1 can be the same as the number of hairsprings 2b, 2c, and the height of the oscillating element 10 is similar to the height of the wafer 1 and thus similar to the height of the hairsprings 2b, 2c. Alternatively, the wafer 1 can include a minimum sample of the system 3 to obtain a good representation of the stiffness on the wafer 1.

[0044] As described above, the system 3 preferably includes a plurality of oscillating elements 10. Such an oscillating element 10 includes at least one blade and can extend substantially linearly. The oscillating element 10 includes an attachment end 5a and at least one free end 5b, 5c. The geometry and dimensions of the oscillating element 10 are different from those of the hairsprings of the wafer 1, except for the above-mentioned height, of course.

[0045] Each oscillating element 10 is contained within an opening 9 made in the wafer 1. The opening 9 defines a space in which the oscillating element 10 can freely perform a controlled mechanical oscillating motion.

[0046] Specifically, the oscillating element 10 includes an attachment end 5a and two free ends 5b, 5c. The oscillating element 10 includes a rod / trunk 6 provided with the attachment end 5a. The rod 6 extends linearly into an opening 9 and has two arms 7, 8 in its extending portion, and the arms form two flexible blades / strips or two flexible branches, and the arms are folded along the rod 6. More specifically, such arms 7, 8 are arranged in the opening 9 close to the rod 6 and are substantially parallel to it in this configuration. The two arms 7, 8 are connected to form the letter "U", and each arm includes a free end of the oscillating element 10. It should be noted that these arms 7, 8 may each have a thickness similar or substantially similar to that of a hairspring.

[0047] In the oscillating element 10, the rod 6 is stiffer than the two arms 7, 8 that constitute it. In addition, the length of these arms 7, 8 is between 1 mm and 2 mm, preferably 1.5 mm. The thickness of these arms 7, 8 is between 10 μm and 60 μm, preferably 30 μm.

[0048] In addition, the oscillating element 10 has a substantially shape of a tuning fork or is itself a tuning fork.

[0049] As described above, the selection of each oscillating element 10 should allow for the best decoupling of the embedding effect on the resonance frequency. More specifically, during harmonic excitation, the influence of the embedding on the resonance frequency cannot be ignored. In the case of this oscillating element 10, there is a significant decoupling between the embedding and the resonance frequencies of the arms 7, 8. The correlation between the resonance frequency and the stiffness is independent of the quality of the embedding etching.

[0050] This is not the case for an oscillating element composed of a strip, which has a variable cross-section in its main linear direction and terminates at its distal end in a part of a locally enlarged cross-section forming a mass. In this configuration, the change in the strip thickness will cause a change in the embedding, thus resulting in a change in resonance. The correlation here needs to consider the influence of such an embedding, which leads to complexity, while there is no such complexity in implementing the oscillating element 10 (such as a tuning fork) according to the method of the present invention. In addition, the strip has closed corners, and implementing complex operations is required to form closed corners in the wafer by deep reactive ion etching. In this case, it can be understood that there may be significant variations at each corner, thus changing the resonance frequency. For example, a change in the order of magnitude of the die radius of the embedding neck by 2 μm will result in a difference in the predicted etching thickness of the linear strip on the order of 20 nm. In addition, for such a strip and other types of strips different from tuning forks, the manufacturing tolerances of the embedding are an obstacle to obtaining a good frequency-stiffness correlation.

[0051] During this step 21, the oscillating elements 10 of each system 3 associated with the hairsprings 2b, 2c are arranged in the wafer 1, at the periphery of the hairsprings 2b, 2c and, in particular, in close proximity to the hairsprings 2b, 2c. Thus, a plurality of oscillating elements 10 of the system 3 are formed in the wafer 1, around the hairsprings 2b, 2c with which they are associated.

[0052] It should be noted that the arrangement of these oscillating elements 10 of each system 3 in the wafer 1 is preferably such that their arms 7, 8 are placed so that the Young's modulus is at its maximum or minimum value, especially when the wafer 1 is based on silicon. More specifically, since silicon is anisotropic, this arrangement prevents the Young's modulus from varying with the angle when determining the stiffness. In addition, the maximum Young's modulus is preferred to increase the accuracy of the correlation between the stiffness and the measured frequency.

[0053] It should be noted that, in this step 21, the system 3 is configured such that the average stiffness of the horological hairsprings 2b, 2c made in the wafer 1 is within a predetermined range.

[0054] Furthermore, such an oscillating element 10 is configured in such a way that its stiffness can be easily determined using an electronic device for determining the stiffness of these systems 3. The electronic device implemented by this method includes, in a non-limiting and non-exhaustive manner:

[0055] - a processing unit, such as a computer;

[0056] - a module for driving / triggering the mechanical oscillatory movement of the body of the oscillating element 10 around its stable equilibrium position;

[0057] - a module for measuring the resonant frequency of the oscillating element 10 during the mechanical oscillatory movement.

[0058] The processing unit of the electronic device includes at least one processor and a storage element. The processing unit is capable of executing instructions for implementing computer programs and performing computing / processing operations, such as computer programs designed to drive / control the driving and measuring modules, and implementing at least one algorithm stored in the storage element during the computing / processing operations. The algorithm may include machine learning algorithms and / or mathematical formulas. The algorithm is capable of implementing a prediction model or a simulation model, thereby allowing the determination of its stiffness based on the measured values of the resonant frequency of the system 3.

[0059] It should be noted that such an oscillating element 10 can be compared to a tuning fork, since it vibrates at a stable frequency despite changes in certain parameters (especially those related to the embedding and manufacturing processes). This stable frequency varies according to a single determined parameter (in this case, the stiffness).

[0060] One of the parameters of the oscillating element 10 causes a significant change in the resonant frequency, such that the influence of the other parameters can be neglected.

[0061] Then, the method includes a step 22 for determining the stiffness of the system 3 associated with the hairsprings 2b, 2c formed in the wafer 1. This step 22 includes a sub-step 23 of estimating at least one resonant frequency of each system 3 associated with its hairsprings 2b, 2c. During this sub-step 23, at least one oscillating element 10 of at least one system 3 is driven in its mechanical oscillatory motion about the stable equilibrium position. During this motion, the resonant frequency of the oscillating element 10 is then determined in a measurement phase 24.

[0062] In this embodiment of the invention, the resonant frequencies of all the oscillating elements 10 of the measurement system 3 are measured, and then the average value of these frequencies is calculated to correspond to the resonant frequency of the system 3. In this context, the determined average frequency is considered to represent the frequency of each oscillating element 10 of the system 3.

[0063] Alternatively, the determined resonant frequency of the system 3 can be the resonant frequency of its individual oscillating element 10 or the resonant frequency of a sample of its oscillating elements 10.

[0064] Once the resonant frequency is estimated, this step 22 includes a sub-step 25 of defining the stiffness of each system 3, during which the electronic device executes an algorithm for calculating the stiffness based on the estimated resonant frequency of the system 3.

[0065] Then, the method includes a step 26 of calculating the dimensional correction to be applied to each of the hairsprings 2b, 2c in the batch of watch hairsprings according to the stiffness determined for the associated system 3. During this step 26, the quantification of the dimensional correction to be applied to the hairsprings 2b, 2c is then determined.

[0066] To this end, this step 26 includes a sub-step 27 of determining the material thickness e to be added or removed from at least one dimension of the hairsprings 2b, 2c of the batch of watch hairsprings formed during the forming step 20 in order to obtain a batch of watch hairsprings 2a with an average stiffness within a predetermined range.

[0067] This dimensional correction effectively corresponds to the material thickness e to be removed from or added to the hairsprings 2b, 2c in order to change at least one of their dimensions E2, H2, E3, H3, namely:

[0068] - only the height H2, H3 of its strips, or

[0069] - only the thickness E2, E3 of the strip, or

[0070] - both the height H2, H3 and the thickness E2, E3.

[0071] This dimensional correction can be carried out over one or more different lengths of the strip, or over the entire length of the strip of the hairsprings 2b, 2c.

[0072] By determining the dimensional correction, this sub-step 27 is used to help create the geometry of the hairsprings 2b, 2c so that they have a stiffness within a predetermined range.

[0073] The method then includes step 28 of modifying the dimensions E2, E3, H2, H3 of the horological hairsprings 2b, 2c based on the calculated dimensional correction to obtain a batch of horological hairsprings 2a with an average stiffness within a predetermined range.

[0074] In this context, if the dimensions E2, H2 of the hairspring 2b are greater than the dimensions E1, H1 required to obtain a batch of horological hairsprings 2a with an average stiffness within a predetermined range, then this step 28 includes a material removal sub-step 29 that depends on the calculated thickness e of the material to be removed. This removal can then be carried out during the oxidation and deoxidation processes of these hairsprings 2b that are well known in the prior art. The purpose of this sub-step 29 is to reduce the dimensions of the cross-section 4b of the strip over a given length or the entire length of the strip of the hairspring 2b.

[0075] When the dimensions E3, H3 of the hairspring 2c are less than the dimensions E1, H1 required to obtain a batch of horological hairsprings 2a with an average stiffness within a predetermined range, then this step 28 includes a material addition sub-step 30 that depends on the calculated thickness e of the material to be added. This material addition can then be carried out during processes well known in the prior art, such as thermal oxidation, electrochemical growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or any other addition process. The purpose of this sub-step 30 is to increase the dimensions of the cross-section 4c of the strip over a given length or the entire length of the strip of the hairspring 2c.

[0076] Thus, this method makes it possible to correct the dimensional errors of hairsprings manufactured by methods such as those implementing lithography and / or DRIE techniques, taking advantage of the high precision provided by the system 3 for indicating the reference stiffness.

[0077] List of reference numerals

[0078] 1. A wafer including at least one hairspring

[0079] 2a. Manufactured hairspring

[0080] 2b. A hairspring formed in the wafer, having a cross-sectional dimension larger than that of the manufactured hairspring

[0081] 2c. A hairspring formed in the wafer, having a cross-sectional dimension smaller than that of the manufactured hairspring

[0082] 3. System for indicating reference stiffness

[0083] 4a. Cross-section of the manufactured hairspring

[0084] 4b. Cross-section of the formed hairspring, whose size is larger than the size of the cross-section of the manufactured hairspring

[0085] 4c. Cross-section of the formed hairspring, whose size is smaller than the size of the cross-section of the manufactured hairspring

[0086] 5a. Attachment end of the oscillating element

[0087] 5b. First free end of the oscillating element

[0088] 5c. Second free end of the oscillating element

[0089] 6. Rod / trunk of the oscillating element

[0090] 7. First flexible arm of the oscillating element

[0091] 8. Second flexible arm of the oscillating element

[0092] 9. Opening in which the oscillating element is arranged

[0093] 10. Oscillating element

Claims

1. A method for manufacturing a batch of timepiece hairsprings (2a) having an average stiffness within a predetermined range, the method comprising the following steps: a) forming (20) a timepiece balance spring (2b, 2c) in a wafer (1), the dimensions of the formed timepiece balance spring being different from the dimensions required to obtain a batch of timepiece balance springs (2a) having an average stiffness within a predetermined range; b) forming (21) in the wafer (1) a system (3) for indicating a reference stiffness for determining the stiffness of the timepiece balance spring (2a) having an average stiffness within the predetermined range; c) determining (22) the stiffness of the system (3) formed; d) calculating (26) the dimensional correction to be applied to the resulting timepiece balance spring (2b, 2c) based on the stiffness of the system (3) determined; e) modifying the dimensions of the formed timepiece balance springs (2b, 2c) based on the calculated dimensional correction in order to obtain a batch of timepiece balance springs (2a) having an average stiffness within said predetermined range.

2. The method according to claim 1, wherein: The steps (20, 21) of forming a batch of timepiece balance springs (2b, 2c) and of forming said system (3) are carried out by etching, in particular by deep reactive ion etching.

3. The method according to claim 1 or 2, wherein: In said forming step (21), each system (3) is made in said wafer (1) for one timepiece balance spring from said batch of timepiece balance springs (2b, 2c).

4. The method according to any one of claims 1 to 3, wherein: The forming step (21) of forming the systems (3) is used to make in the wafer (1) a plurality of oscillating elements (10) constituting each system (3), said plurality of oscillating elements surrounding a balance spring (2b, 2c) associated with the system (3) in the wafer (1).

5. The method according to any one of claims 1 to 3, wherein: The forming step (21) of forming the systems (3) is used to make in the wafer (1) a single oscillating element (10) constituting each system (3), the single oscillating element being located in the wafer (1) near the balance spring (2b, 2c) associated with the system (3).

6. The method according to any one of claims 1 to 5, wherein: The determination 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 timepiece hairsprings (2b, 2c).

7. The method according to claim 6, wherein: The determination step (22) comprises a sub-step (25) of determining the stiffness of each system (3) using electronic equipment executing an algorithm for calculating this stiffness based on the estimated resonant frequency.

8. The method according to claim 7, wherein: The stiffness determined for each system (3) is the stiffness of one of the oscillating elements (10) of the system, the average stiffness of all oscillating elements (10) of the system or the average stiffness of a sample of the oscillating elements (10) of the system.

9. The method according to any one of claims 1 to 8, wherein: The calculation step (26) comprises a sub-step (27) of determining, according to the determined stiffness, a thickness of material (e) to be added to or removed from at least one dimension of a balance spring in a batch of timepiece balance springs (2b, 2c).

10. The method according to any one of claims 1 to 9, wherein: The oscillating element (10) is in the shape of a tuning fork.

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