Method for manufacturing balance spring

Abstract

To provide a method for manufacturing a batch of a plurality of horologic balance springs having an average rigidity within a predetermined range.SOLUTION: The method includes: a) a step 20 of forming, on a wafer, a plurality of horologic balance springs different from those required to obtain a batch of horologic balance springs; b) a step 21 of forming, on the wafer, a plurality of systems exhibiting a reference rigidity for determining the rigidity of a plurality of timepiece balance springs; c) a step 22 of determining the rigidity of the plurality of systems formed; d) a step 26 of calculating a dimensional correction to be applied to the plurality of timepiece balance springs formed, based on the determined rigidity of the plurality of systems; and e) a step of modifying the dimensions of the formed timepiece balance springs on the basis of the dimensional corrections calculated to obtain a batch of timepiece balance springs whose average rigidity is within a predetermined range.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to the field of manufacturing watch parts. More specifically, the present invention relates to a method for manufacturing a batch of a plurality of watch beard hairsprings having an average rigidity within a predetermined range.

Background Art

[0002] Prior art documents describe methods for manufacturing a plurality of watch beard hairsprings on a wafer using etching techniques such as laser etching, plasma etching, deep reactive-ion etching (DRIE), or wet etching.

[0003] However, when using such methods, it is typical for geometric variations to occur between the hairsprings formed in the same pattern on the same wafer.

[0004] In order to overcome these drawbacks, solutions have been proposed in prior art documents, particularly Patent Documents 1 and 2, which describe methods for manufacturing hairsprings.

[0005] In Patent Document 1, the manufacturing method includes the following steps: a) forming a hairspring having dimensions larger than those required to obtain a hairspring of a predetermined rigidity; b) determining the rigidity of the hairspring formed in step a) by measuring the vibration frequency of the hairspring combined with a template having a predetermined inertia; c) calculating the thickness of the material to be removed to obtain a hairspring of a predetermined rigidity; and d) removing the calculated thickness of the material from the hairspring formed in step a), and steps b), c), and d) can be repeated to further improve the dimensional quality.

[0006] In Patent Document 2, the manufacturing method includes the following steps, namely: a) forming a mustache oscillator having dimensions smaller than those required to obtain a mustache oscillator with a predetermined rigidity; b) determining the rigidity of the mustache oscillator formed in step a) by measuring the oscillation frequency of the mustache oscillator combined with a template having a predetermined inertia; c) calculating the insufficient thickness of the material that must be added to obtain a mustache oscillator with a predetermined rigidity; and d) modifying the mustache oscillator formed in step a) to compensate for the insufficient thickness of the material. Steps b), c), and d) are repeatable to further improve the dimensional quality.

[0007] Such a method can be improved, in particular, so as to limit the contamination of the wafer that may occur during the measurement steps to be implemented.

[0008] In such a situation, it is understood that there is a need to find a solution leading to such an improvement.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

[0010] One object of the present invention is to propose a method for manufacturing a batch of a plurality of watch mustache oscillators that meet the above-mentioned requirements.

[0011] Another object is to improve the accuracy during the manufacture of a batch of a plurality of mustache oscillators whose average rigidity is within a predetermined range.

[0012] The present invention relates to a method for manufacturing a batch of a plurality of watch mustache oscillators whose average rigidity is within a predetermined range, and this method a) forming a plurality of whiskers on the wafer having dimensions different from the dimensions required to obtain a batch of a plurality of clock whiskers with an average stiffness within the predetermined range; b) forming a plurality of systems on the wafer that indicate a reference stiffness for determining the stiffness of the plurality of clock whiskers having an average within the predetermined range; c) determining the stiffness of the plurality of formed systems; d) calculating a dimensional correction to be applied to the plurality of formed clock whiskers based on the determined stiffness of the plurality of systems; e) modifying the dimensions of the plurality of formed clock whiskers based on the dimensional correction calculated to obtain a batch of the plurality of clock whiskers having an average stiffness within the predetermined range including.

[0013] In other embodiments, · The steps of forming a batch of a plurality of clock whiskers and the system are performed by etching, particularly deep reactive ion etching. · In the forming step, each system is fabricated in a wafer for one whisker of a batch of a plurality of clock whiskers. · The step of forming the plurality of systems provides for manufacturing, in the wafer, a plurality of vibrating elements constituting each system so that the system surrounds the whisker associated therewith in the wafer. · The step of forming the plurality of systems provides for manufacturing, in the wafer, a single vibrating element constituting each system in the vicinity of the whisker associated therewith in the wafer. · The determining step includes a sub-step of estimating at least one resonance frequency of each system associated with a whisker among a batch of a plurality of clock whiskers. · The determining step includes a sub-step of defining the stiffness of each system using an electronic device that executes an algorithm for calculating the stiffness based on the estimated resonance frequency. · The rigidity defined for each system is the rigidity of one of its plurality of vibrating elements, the average rigidity of all of its plurality of vibrating elements, or the average rigidity of a sample of its plurality of vibrating elements, · The calculating step includes a sub-step of determining, from the determined rigidity, the thickness of the material to be added to or removed from at least one dimension of the whiskers in a batch of a plurality of clock whiskers, · The vibrating element has a tuning fork shape.

Brief Description of the Drawings

[0014] Other features and advantages of the present invention will be well understood by reading the following description given for non-limiting specific embodiments of the present invention. The description is given for illustrative purposes with reference to the following accompanying drawings.

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying out the Invention

[0016] FIG. 6 schematically shows a method for manufacturing a batch or a set of multiple beard hairsprings 2a whose average rigidity is within a predetermined range. The purpose of such a method is to ensure a very high dimensional accuracy of the manufactured multiple beard hairsprings 2a, and incidentally, accurate rigidity is guaranteed for these beard hairsprings 2a.

[0017] In FIG. 1, a batch of multiple clock beard hairsprings 2b, 2c is formed on a wafer 1. In the batch, each beard hairspring 2b, 2c includes a collet intended to be rigidly connected to a pivoting mandrel. The clock beard hairsprings 2b, 2c further include an elastically flexible strand. One end of this strand is connected to the collet, and it is spirally wound to form a plurality of continuous turns, and the last turn is extended by an attachment segment. The attachment segment is intended to be attached to a stationary temp cock, for example, by a stud.

[0018] Such a method includes step 20 of forming multiple beard hairsprings 2b, 2c having dimensions E, E3, H2, H3 different from the dimensions E1, H1 required to obtain a batch of multiple beard hairsprings 2a whose average rigidity is within a predetermined range on the wafer 1.

[0019] During step 20, a plurality of hairspring 2b, 2c are formed on the material wafer 1. These hairsprings 2b, 2c are preferably formed on the wafer 1 simultaneously. These hairsprings 2a, 2c can be formed on the wafer 1 by, for example, deep reactive ion etching, laser etching, chemical etching, or etching using a focused ion beam. It should be noted that these hairsprings 2b, 2c preferably have similar geometries.

[0020] These hairsprings 2b, 2c formed on the wafer 1 have blades with cross-sections 4b, 4c having dimensions E2, H2, E3, H3. When the shape of such a blade is polygonal, the cross-sections 4a, 4b, 4c are characterized by heights H1, H2, H3 and thicknesses E1, E2, E3. These dimensions are different from the dimensions E1, H1 required to obtain a batch of a plurality of watch hairsprings 2a with an average rigidity within a predetermined range. In other words, the blade of each hairspring 2b, 2c may have cross-sections 4b, 4c, and the dimensions E2, H2, E3, H3 of the cross-sections are larger or smaller than the required dimensions E1, H1 of the cross-section 4a of the blade of the manufactured hairspring 2a that allows obtaining an average rigidity within a predetermined range.

[0021] In the context of the method, the wafer 1 is preferably made of doped or undoped silicon. The silicon can be single crystal, polycrystalline, or amorphous. Further, the silicon may have crystal orientations {1,1,1}, {-1,1,1}, {-1,-1,1}, {-1,-1,1} where the Young's modulus of silicon is maximum. Alternatively, the wafer 1 may be made of quartz, glass, ceramic, metal, alloy.

[0022] It should be noted that during the forming step 20, the plurality of formed watch hairsprings 2b, 2c are ·Dimensions E2 and H2 that are larger than dimensions E1 and H1 required to obtain a batch of a plurality of clock whiskers 2a having an average rigidity within a predetermined range, that is, a blade height H2 and / or a blade thickness E2 that are larger than the blade height H1 and / or the blade thickness E1 of the clock whiskers 2a having an average rigidity within a predetermined range, may be provided. ·Dimensions E3 and H3 that are smaller than dimensions E1 and H1 required to obtain a batch of a plurality of clock whiskers 2a having an average rigidity within a predetermined range, that is, a blade height H3 and / or a blade thickness E3 that are smaller than the blade height H1 and / or the blade thickness E1 of the plurality of clock whiskers 2a having an average rigidity within a predetermined range, may be provided.

[0023] The method further includes step 21 of forming on the wafer 1 a system 3 indicating a reference rigidity for determining the rigidity of a plurality of clock whiskers 2a having an average within a predetermined range. This step 21 is preferably performed simultaneously with step 20 of forming the whiskers 2b, 2c on the same wafer 1 including the plurality of formed whiskers 2b, 2c. During this step 21, a system 3 for each of the plurality of formed clock whiskers 2b, 2c of a batch is formed on the wafer 1. The system 3 is composed of at least one vibration element 10 disposed in the immediate vicinity of the corresponding whiskers 2b, 2c. Similar to step 20 of forming the whiskers 2b, 2c, the vibration element 10 of each system 3 is preferably formed by etching. It should be noted that there are as many systems 3 on the wafer 1 as there are whiskers 2b, 2c, and the height of the vibration element 10 is the same as the height of the wafer 1 and thus the same as the height of the whiskers 2b, 2c. Alternatively, the wafer 1 may include a minimum sample of the system 3 in order to obtain a good representation of the rigidity in this wafer 1.

[0024] As already mentioned, the system 3 preferably includes a plurality of vibrating elements 10. Such elements 10 include at least one blade and can extend essentially linearly. The element 10 includes an attachment end 5a and at least one free end 5b, 5c. The element 10 has a geometry and dimensions different from those of the whiskers of the wafer 1. Of course, the height mentioned above is an exception.

[0025] Each vibrating element 10 is enclosed within an opening 9 made in the wafer 1. The opening 9 defines a space in which the vibrating element 10 can freely perform a controlled mechanical vibration movement.

[0026] Specifically, the vibrating element 10 includes an attachment end 5a and two free ends 5b, 5c. The vibrating element 10 includes a rod / stem 6 provided with the attachment end 5a. The rod 6 extends linearly into the opening 9, and at its extension, has two arms 7, 8 that form two flexible blades or two flexible branches folded along the rod 6. More specifically, such arms 7, 8 are arranged near the rod 6 in the opening 9 and in this configuration are substantially parallel. These two arms 7, 8 are connected so as to form a "U", each including a free end of the vibrating element 10. It should be noted that these arms 7, 8 may each have a thickness similar or substantially similar to that of the whiskers.

[0027] In the vibrating element 10, the rod 6 is more rigid than the two arms 7, 8 that make up the vibrating element 10. Further, 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 and 60 μm, preferably 30 μm.

[0028] Furthermore, this vibrating element 10 has the general shape of a tuning fork or is a tuning fork.

[0029] As described above, each vibrating element 10 is selected to allow for an optimal decoupling of the influence of the embedded part with respect to the resonance frequency. More specifically, during harmonic excitation, there is a non-negligible influence of the embedded part with respect to the resonance frequency. In the case of the vibrating element 10, there is a significant decoupling between the embedded part and the resonance frequencies of the arms 7, 8. The correlation between the resonance frequency and the stiffness becomes independent of the quality of the etching of the embedded part.

[0030] This does not apply to a vibrating element composed of a blade whose cross-section in the main linear direction is variable and whose distal end terminates in a part of a locally enlarged cross-section forming a mass body. In such a configuration, variations in the thickness of the blade result in a change in the embedded part, which in turn results in a change in resonance. The correlation here brings about a complexity that does not exist in the method according to the present invention for implementing a vibrating element 10 such as a tuning fork, since the influence of the embedded part needs to be considered. Furthermore, since the blade is provided with closed corners, complex operations need to be implemented to form the blade on the wafer by deep reactive ion etching. In such a situation, it is understandable that large variations occur at each of these corners, changing the resonance frequency. As an example, when the radius of the neck casting of the embedded part varies on the order of 2 μm, a difference on the order of 20 nm occurs in the prediction of the etching thickness of the linear blade. Furthermore, for the blade and other types of blades different from the tuning fork, the manufacturing tolerances of the embedded part are an obstacle to obtaining a good frequency-stiffness correlation.

[0031] During step 21, the vibrating elements 10 of each system 3 associated with the whiskers 2b, 2c are arranged on the wafer 1 at the periphery of the whiskers 2b, 2c, particularly in the immediate vicinity of the whiskers 2b, 2c. That is, a plurality of vibrating elements 10 of the system 3 are formed on the wafer 1 so as to surround the whiskers 2b, 2c with which it is associated.

[0032] It should be noted that the arrangement of these vibrating elements 10 of each system 3 in the wafer 1 preferably positions the arms 7, 8 such that the Young's modulus is maximized or minimized, particularly when the wafer 1 is silicon-based. More specifically, since silicon is anisotropic, this arrangement prevents the Young's modulus from varying as a function of angle when determining rigidity. Further, in order to improve the accuracy of the correlation between rigidity and measurement frequency, the maximum Young's modulus is preferred.

[0033] It should be noted that during the step 21, the system 3 is configured such that the average rigidity of the clock whiskers 2b, 2c manufactured in the wafer 1 is within a predetermined range.

[0034] Furthermore, such vibrating elements 10 are configured so that their rigidity can be easily determined using an electronic device that determines the rigidity of these systems 3. This electronic device implemented by this method is, in a non-limiting and non-exhaustive manner, · A processing unit such as a computer, · A module that drives / induces the mechanical vibration motion of the vibrating element 10 around its stable equilibrium position, · Includes a module that measures the resonance frequency of the vibrating element 10 in the mechanical vibration motion.

[0035] The processing unit of the electronic device includes at least one processor and a memory element. The processing unit can execute instructions implementing a computer program intended to drive / control, for example, the drive module and the measurement module, and can also execute the calculation / processing operations during the implementation of at least one algorithm stored in the memory element. The algorithm may include a machine learning algorithm and / or a mathematical formula. The algorithm can implement a prediction model or a simulation model. This allows the rigidity of the system 3 to be determined from the measurement of its resonance frequency.

[0036] It should be noted that such a vibration element 10 can be likened to a tuning fork in the sense that it vibrates at a stable frequency despite changes in certain parameters particularly related to the embedding portion and the manufacturing process. The stable frequency varies according to one determined parameter, in this case, rigidity.

[0037] By significantly changing one of the parameters of the vibration element 10, the influence of other parameters becomes negligibly small.

[0038] The method then includes step 22 of determining the rigidity of the system 3 related to the whiskers 2b, 2c formed on the wafer 1. Such step 22 includes sub-step 23 of estimating at least one resonance frequency of each system 3 related to the whiskers 2b, 2c. During the sub-step 23, at least one vibration element 10 of at least one system 3 is driven in a mechanical vibration motion around its stable equilibrium position. During the motion, the resonance frequency of the vibration element 10 is determined in the measurement phase 24.

[0039] In this embodiment of the present invention, the resonance frequencies of all the plurality of vibration elements 10 of the system 3 are measured, and the average of these frequencies is then calculated to correspond to the resonance frequency of the system 3. In this context, the determined average frequency is regarded as representative of the frequency of each vibration element 10 of the system 3.

[0040] Alternatively, the measured resonance frequency of the system 3 may be the resonance frequency of a single vibration element among the plurality of vibration elements 10, or may be the resonance frequency of a sample of the plurality of vibration elements 10.

[0041] Once the resonance frequency is estimated, step 22 includes sub-step 25 of defining the rigidity of each system 3, during which the electronic device executes an algorithm for calculating the rigidity from the estimated resonance frequency of the system 3.

[0042] The method then includes step 26 of calculating dimensional corrections to be applied to each of the plurality of hairsprings 2b, 2c of a batch of hairsprings from the determined stiffness for the associated system 3. During said step 26, the quantification of the dimensional corrections to be applied to the hairsprings 2b, 2c is determined.

[0043] For this purpose, said step 26 is sub-step 27 of determining the thickness e of the material to be added to or removed from at least one dimension of the hairsprings 2b, 2c of a batch of the plurality of hairsprings formed during said forming step 20, based on the determined stiffness, said sub-step 27 including obtaining a batch of a plurality of hairsprings 2a having an average stiffness within a predetermined range.

[0044] Said dimensional corrections substantially correspond to the thickness e of the material removed from or added to the hairsprings 2b, 2c to vary at least one of the dimensions E2, H2, E3, H3 of the hairsprings 2b, 2c. By at least one of the dimensions E2, H2, E3, H3 is meant · only the height H2, H3 of the blade, or · only the thickness E2, E3 of the blade, or · both the height H2, H3 and the thickness E2, E3.

[0045] Said dimensional corrections may be made over one or more different lengths of the blades of said hairsprings 2b, 2c or over the entire length of the blades.

[0046] By determining the dimensional corrections, said sub-step 27 is used to help create the geometry of said hairsprings 2b, 2c that gives a stiffness within a predetermined range.

[0047] The method then includes step 28 of modifying the dimensions E2, E3, H2, H3 of a plurality of beard razors 2b, 2c based on the dimensional correction calculated to obtain a batch of a plurality of timekeeper beard razors 2a having an average stiffness within a predetermined range.

[0048] In this context, when the dimensions E2, H2 of the plurality of beard razors 2b are greater than the dimensions E1, H1 required to obtain a batch of a plurality of timekeeper beard razors 2a having an average stiffness within a predetermined range, step 28 includes a material removal sub-step 29 according to the calculated thickness e of the material to be removed. Such removal may be performed during a process well known in the prior art of oxidizing and then deoxidizing these plurality of beard razors 2b. The purpose of such sub-step 29 is to reduce the dimensions of the cross-section 4b of the blade of the beard razor 2b over a given length or the entire length of the blade.

[0049] When the dimensions E3, H3 of the plurality of beard razors 2c are smaller than the dimensions E1, H1 required to obtain a batch of a plurality of beard razors 2a having an average stiffness within a predetermined range, step 28 includes a material addition sub-step 30 according to the calculated thickness e of the material to be added. Such material addition may be performed during a process well known in the prior art, such as thermal oxidation, galvanic growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or other addition processes. The purpose of such sub-step 30 is to increase the dimensions E3, H3 of the cross-section 4c of the blade of the beard razor 2c over a given length or the entire length of the blade.

[0050] Therefore, by such a method, it becomes possible with high precision provided by the said system showing the reference stiffness 3 to correct the dimensional error of the beard razor manufactured by such a method implementing photolithography technology and / or DRIE technology.

Explanation of reference numerals

[0051] 1. Wafer including at least one beard razor 2a. Manufactured whisker 2b. Whisker formed on a wafer to have a cross-section with a dimension larger than the dimension of the cross-section of the manufactured whisker 2c. Whisker formed on a wafer to have a cross-section with a dimension smaller than the dimension of the cross-section of the manufactured whisker 3. System indicating reference rigidity 4a. Cross-section of the manufactured whisker 4b. Cross-section of the formed whisker with a dimension larger than the dimension of the cross-section of the manufactured whisker 4c. Cross-section of the formed whisker with a dimension smaller than the dimension of the cross-section of the manufactured whisker 5a. Attachment end of the vibration element 5b. First free end of the vibration element 5c. Second free end of the vibration element 6. Rod / stem of the vibration element 7. First flexible arm of the vibration element 8. Second flexible arm of the vibration element 9. Opening in which the vibration element is disposed 10. Vibration element

Claims

1. 1. A method for manufacturing a batch of watch balance springs (2a) whose average stiffness is within a predetermined range, comprising the steps of: a) forming (20) on a wafer (1) a number of hairsprings (2b, 2c) of dimensions different from those required to obtain said batch of said number of watch hairsprings (2a); b) forming (21) on said wafer (1) a plurality of systems (3) exhibiting reference stiffnesses for determining the stiffness of said plurality of watch balance springs (2a), the average of said stiffnesses being within said predetermined range; c) determining (22) the stiffness of the formed systems (3); d) calculating (26) dimensional corrections to be applied to the formed watch balance springs (2b, 2c) on the basis of the determined stiffnesses of the systems (3); e) modifying the dimensions of the plurality of formed watch hairsprings on the basis of the calculated dimensional corrections so as to obtain said batch of said plurality of watch hairsprings whose average stiffness is within said predetermined range; A method comprising:

2. 2. The method according to claim 1, wherein the step (20) of forming the batch of watch balance springs (2b, 2c) and the step (21) of forming the systems (3) are carried out by etching, in particular by deep reactive ion etching.

3. 2. The method according to claim 1, wherein in said forming step (21), each system (3) is manufactured on said wafer (1) for one hairspring of said batch of said plurality of watch hairsprings (2b, 2c).

4. 2. The method according to claim 1, wherein the step (21) of forming the plurality of systems (3) comprises manufacturing, on the wafer (1), a plurality of vibration elements (10) constituting each system (3) such that the system (3) surrounds the associated balance spring (2b, 2c) on the wafer (1).

5. 2. The method according to claim 1, wherein the step (21) of forming the plurality of systems (3) comprises manufacturing, on the wafer (1), a single vibrating element (10) constituting each system (3) in the vicinity of the balance spring (2b, 2c) with which it is associated on the wafer (1).

6. 2. The method according to claim 1, wherein said determining step (22) comprises the sub-step (23) of estimating at least one resonant frequency of each system (3) associated with a hairspring of said batch of said watch hairsprings (2b, 2c).

7. 2. The method according to claim 1, wherein said determining step (22) comprises the sub-step (23) of estimating at least one resonant frequency of each system (3) associated with a hairspring of said batch of said watch hairsprings (2b, 2c), said determining step (22) comprising the sub-step (25) of defining a stiffness of each system (3) using an electronic device executing an algorithm for calculating said stiffness on the basis of said estimated resonant frequencies.

8. 2. The method according to claim 1, wherein said determining step (22) comprises a sub-step (23) of estimating at least one resonant frequency of each system (3) associated with a hairspring of said batch of said plurality of watch hairsprings (2b, 2c), said determining step (22) comprising a sub-step (25) of defining a stiffness of each system (3) using an electronic device executing an algorithm for calculating said stiffness on the basis of said estimated resonant frequencies, said stiffness defined for each system (3) being the stiffness of one of its plurality of oscillating elements (10), the average stiffness of all of its plurality of oscillating elements (10), or the average stiffness of a sample of its plurality of oscillating elements (10).

9. 2. The method according to claim 1, wherein said calculating step (26) comprises the sub-step (27) of determining, from said determined stiffness, a thickness (e) of material to be added to or removed from at least one dimension of said one hairspring (2b, 2c) of a batch of said plurality of watch hairsprings (2b, 2c).

10. The method of claim 1 , wherein the vibrating element (10) is shaped like a tuning fork.

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