Method for testing and manufacturing inertial elements for horology

Abstract

A method for testing an inertial element (100) or an inertial element blank (100), the inertial element being required to have at least one predetermined inertia, the testing method comprising the following steps: a. applying, to the inertial element (100) or the inertial element blank (100), a vibratory excitation that varies over time to cover a predetermined frequency range, b. identifying at least one characteristic of a resonance frequency, such as a resonance peak, of the inertial element (100) or the inertial element blank (100) upon vibratory excitation over the predetermined frequency range, c. subjecting the resonance frequency characteristic identified in step b. to a prediction machine to determine an inertia of the inertial element (100) or the inertial element blank (100) and / or to determine whether dimensional correction of the inertial element (100) or the inertial element blank (100) is required to obtain the predetermined resonance frequency.

Description

Description METHOD FOR CONTROLLING AND MANUFACTURING INERTIAL WATCHMAKING ELEMENTS Technical field

[0001] The present invention relates to the field of control and manufacturing of parts for watchmaking. The invention relates more particularly to a method for controlling and manufacturing balances for a timepiece, otherwise known as inertial elements. State of the art

[0002] Mechanical watch movements are regulated by means of a mechanical regulator comprising an inertial element coupled to an elastic return member (i.e. an elastically deformable component responsible for returning the inertial element to a neutral position) and whose oscillations determine the rate of the watch. Many watches, for example, have a regulator comprising a hairspring as an elastic return member, mounted on the axis of a balance wheel also supporting a balance wheel, the whole being set into sustained oscillations by means of an escapement and an anchor. The natural frequency of the balance wheel-hairspring couple makes it possible to regulate the watch and depends in particular on the stiffness of the hairspring and the inertia of the balance wheel. In fact, the frequency f of the regulating organ formed by the hairspring of stiffness R coupled to a balance wheel of inertia I is given by the formula: [equation 1]

[0003] The geometry and / or material determining the inertia of the balance wheel also define its intrinsic vibrational characteristics, such as the natural frequency and resonance frequencies of the part alone (also influenced by the conditions of attachment of the part).

[0004] In the present application, the natural frequency of an inertial element or of an inertial element / elastic return member pair is the frequency at which this system oscillates when it is in free movement, that is to say without exciting force.

[0005] Furthermore, a resonance frequency of an elastic system (typically a part such as the inertial element alone) subjected to an exciting force is a frequency at which a local maximum of displacement amplitude can be measured for a given point of the elastic system. In other words, if the elastic system is excited with an excitation source of variable frequency over time, the displacement amplitude follows an upward slope before this resonance frequency, and follows a downward slope after, at any point which does not correspond to a vibration node. Typically, during such a test, the recording over time of the displacement amplitude as a function of the excitation frequency presents at least one displacement amplitude peak or resonance peak which is associated with or which characterizes the resonance frequency.

[0006] The inertia of an inertial element typically depends on the characteristics of its material (its density), as well as its dimensions. The moment of inertia l gz of a solid with respect to a z axis passing through its center of gravity is given more specifically by: [equation 2] lgz = Z(Am.r 2 ) with: r, the distance of an elementary volume to the z axis Am, the mass of the elementary volume.

[0007] The natural frequency of the regulating organ formed by the hairspring of stiffness R coupled to a balance wheel of inertia I is notably proportional to the square root of the stiffness of the hairspring and to the inverse of the square root of the inertia l gz The main specification of a balance wheel is its inertia l gz , which must be within a well-defined interval in order to be matched with a spiral spring, having a given stiffness. This matching operation is essential to precisely adjust the frequency of a mechanical oscillator. To measure the inertia of a balance wheel, it can be coupled with a balance spring of known stiffness and reference, to measure the oscillation frequency. It is also possible, according to the Jaquerod and Defossez method, to couple a balance wheel to be measured with a complete reference oscillator of known inertia, which has a modified balance staff with an elongated upper pivot that can receive the balance wheel to be measured. An oscillation frequency measurement with and without the balance wheel to be measured makes it possible to deduce the inertia of the balance wheel to be measured.

[0008] Thus, it is not possible to easily and quickly measure the inertia of a balance wheel without having to couple it to a reference element, such as a balance spring or oscillator. In industrial production of balance wheels, these are manufactured by bar turning and their inertia is measured by sampling, in order to control for drifts, particularly those linked to the wear of cutting tools. The time required for measuring operations can lead to production losses if an inspection reveals a balance wheel outside the specifications, while production continues during the inspection. It is also not easy to determine the point at which the parts produced are no longer within the planned specifications.

[0009] Also, there is great interest in a new method of controlling an inertial element or an inertial element blank, which can be carried out on the inertial element alone or on an inertial element blank alone.

[0010] The present invention aims to propose an approach free from the above drawbacks, which allows a faster production flow and / or with less risk of pollution(s), and / or greater sampling, and / or more precise measurement of inertia. Disclosure of the invention

[0011] More specifically, the invention relates to a method for controlling an inertial element, or a rough version of an inertial element, of a clock oscillator, the inertial element or the rough version of an inertial element having to have at least one predetermined inertia and / or at least one predetermined resonance frequency, the control method comprising the following steps: a. applying to the inertial element, or to the inertial element blank, a time-varying vibrational excitation to cover a predetermined frequency range, b. identifying at least one resonant frequency characteristic, such as a resonance peak, of the inertial element or of the inertial element blank, upon, or in response to, the vibrational excitation over the predetermined frequency range, c. submitting to a prediction machine said at least one resonant frequency characteristic identified in step b. to determine an inertia of the inertial element or of the inertial element blank and / or determining whether a dimensional correction of the inertial element or of the inertial element blank is necessary to obtain the predetermined inertia.

[0012] The method according to the above implementation comprises a step of vibrational excitation of the inertial element or the inertial element blank and the measurement of a characteristic of a resonance frequency, to then deduce by prediction an inertia and / or whether a dimensional correction is necessary. There is no assembly with an elastic return member or another component, which saves time.

[0013] In addition, according to one embodiment, the measurement can be performed on the inertial elements alone or the blanks alone, which limits errors induced by other components or their assembly, as well as possible pollution. The measurement accuracy is improved because there are fewer sources of variability due to other components or pollution. In other words, the inertial element or the inertial element blank is tested alone. The vibration excitation is applied to the part or to the unit blank, not coupled to any spring, or elastic return element to form an oscillator.The method allows to control unitary and possibly free parts (i.e. parts with at least one free portion, and at the very least parts not attached to any mechanism or spring), which brings at least advantages of productivity gains (no assembly with a spring of an oscillating system), quality gains (no pollution of parts, nor breakage, and more parts can be tested in the same budget), a gain in precision (no error linked to other components of an oscillating system).

[0014] Advantageously, the method according to the invention is applicable to inertial elements or blanks of inertial elements produced in batches on a wafer, in particular by microfabrication techniques. An intermediate estimation or measurement of the inertia can make it possible to determine whether it is necessary to provide or quantify an individualized correction of the inertial elements and / or to carry out such an individualized correction of the inertial elements, which can be produced on a wafer.

[0015] The invention may then be defined with the following characteristics, taken individually or in combination.

[0016] According to one embodiment, the time-varying vibrational excitation is provided to vibrate the inertial element or the inertial element blank. In particular, the inertial element or the inertial element blank elastically deforms upon, or in response to, the vibrational excitation.

[0017] According to one embodiment, at least a portion or certain points of the inertial element or the inertial element blank exhibit(s) movements, during or in response to the time-varying vibrational excitation. In other words, the inertial element or the inertial element blank forms an elastically deformable system, and the time-varying vibrational excitation causes periodic deformations or vibrations in this elastically deformable system formed by the inertial element (or its blank).

[0018] According to one embodiment, the identification of at least one resonant frequency characteristic, such as a resonance peak, of the inertial element or the inertial element blank, is based on or comprises: - the detection and / or measurement of vibrations or elastic deformations of the inertial element or the inertial element blank, and / or - the detection and / or measurement of the vibration speeds or elastic deformation speeds of the inertial element or the inertial element blank.

[0019] According to one embodiment, the inertial element is a balance wheel of a watch oscillator, and the inertial element blank is a blank of a balance wheel of a watch oscillator.

[0020] In particular, the inertial element may comprise at least: - a serge or a rim, and / or - a hub, and / or - a board or spokes connecting the hub to the rim or serge.

[0021] In particular, the inertial element may comprise at least: - a part made of silicon, and / or - a part made of metal, and / or - a part formed by additive manufacturing.

[0022] According to one embodiment, the vibrational excitation is variable over time. According to one embodiment, the application of the time-variable vibrational excitation comprises exposing, during an exposure time, the inertial element or the inertial element blank to a vibrational signal whose frequency varies during the exposure time.

[0023] According to one embodiment, a time derivative of the frequency of the vibration signal is different from zero for at least 50% of the exposure time, preferably for at least 70% of the exposure time, preferably for at least 80% of the exposure time. According to one embodiment, the frequency of the vibration excitation can vary by at least 2.5 kHz per second for example, by at least 5 kHz per second for example, by at least 10 kHz per second for example.

[0024] According to one embodiment, the exposure time is at least 0.1 s, preferably at least 0.2 s, preferably at least 0.5 s, preferably at least 0.8 s.

[0025] According to one embodiment, the vibrational excitation is According to one embodiment, the vibrational excitation is applied to the inertial element or to the inertial element blank having at least one end or at least one portion fixed to a wafer or to a clamp. From a mechanical point of view, it can be considered schematically that the vibrational excitation is applied to a mass (located at the center of gravity of the inertial element) connected to a reference frame (a gripping clamp for an inertial element alone, or the remainder of a substrate or of a wafer for a blank for example in silicon and not detached) by a spring (the body of the inertial element). The vibrational excitation sets in motion the suspended mass connected to the chassis by the spring (formed by the body of the inertial element). According to one embodiment, the vibrational excitation is applied to the inertial element or to the inertial element blank having at least two portions fixed to a plate or to a clamp. According to one embodiment, the vibrational excitation is applied to the inertial element or to the inertial element blank having at least three portions fixed to a plate or to a clamp.

[0026] It can also be noted that if it is determined that a dimensional correction must be made to the tested part (or to all the unit parts attached to the same wafer, or to the unit parts attached to an area of ​​a wafer, including or not the tested part), this can be done on the unit part(s) without re-disassembling anything (for example, it can be planned to apply a material addition or removal operation directly at the end of the test). It is therefore possible to add or remove material to the unit part(s) to vary its intrinsic inertia. In other words, the dimensional correction can be made on the unit part(s), by changing its dimensions (typically the width and / or the thickness of parts of the inertial element).It is also possible to deposit material on specific parts (by catalytic deposition or by physical vapor deposition for example), or to remove material from specific parts (by chemical etching, by oxidation for example).

[0027] The method according to the above implementation therefore makes it possible to test inertial element blanks during manufacture while limiting the risks of pollution or assembly errors. A dimensional correction (of section, height and / or thickness or by adding or removing material) is then possible. The method according to the above implementation also makes it possible to test finished inertial elements, for example to carry out a classification by inertia increments, in order to plan a pairing with an elastic return element (typically a spiral spring) of a particular class. As mentioned above, in the case of a watch oscillator, the inertial element is coupled to an elastic return member.

[0028] Of course, the frequency range of the spectrum obtained depends not only on the source of vibration excitation but also on the sensor of the measuring instrument used. Thus, the frequency range is related both to the excitation frequency range and to the frequency range over which the instrument measuring the oscillation amplitude (vibrometer or other) is sensitive. However, the Sequential excitation range will be chosen so as to include at least one resonance frequency of the inertial element or blank under test.

[0029] The predetermined resonant frequency (function of the predetermined inertia) that the inertial element must have once finished may be a target natural frequency or a target resonant frequency, or a target natural frequency range, or a target resonant frequency range defined by a tolerance around a target value. In any case, the predetermined resonant frequency that the inertial element must have once finished is a function of or represents an inertia or more precisely the moment of inertia of the inertial element around its axis of rotation once mounted in the timepiece.In particular, the applicant noticed that it was possible to very precisely correlate the moment of inertia of the inertial element around its axis of rotation once mounted in the timepiece with at least one resonance frequency observed during the vibration of the inertial element (or its blank) attached to a measuring chassis by a clamp or by bridges with a wafer or a substrate if the part is manufactured by an etching technique (etching of silicon by deep ion reaction for example).

[0030] The dimensional correction predicted by the prediction machine can typically be a correction of the section of parts forming the inertial element or the inertial element blank, i.e. a correction of either the height, or the thickness, or both. It is also possible to plan to intervene (add / remove material) only on certain parts of the inertial element, such as the serge.

[0031] In the above method, the characteristic of a resonant frequency is a characteristic of the oscillatory response measured over a predetermined frequency range, comprising at least one resonant frequency. Such a characteristic is typically identified after processing a raw measurement signal (for example, measuring the amplitudes or speeds or accelerations of displacement of certain points of the inertial element or of the inertial element blank), the processing possibly including, for example, a Fourier transform to identify resonance peaks and therefore resonance frequencies.

[0032] It can be noted that the process can determine an inertia in order to then classify the part, and / or to then calculate / deduce a correction level dimensional correction to be applied to obtain a target inertia. However, only the identified resonance frequency can be taken into account to directly calculate / deduce a level of dimensional correction to be applied to obtain a target inertia.

[0033] According to one embodiment, in step a, the frequency range is applied simultaneously to a plurality of inertial elements or inertial element blanks. Speed ​​is improved because the vibrational excitation can typically be imposed on a wafer supporting several hundred inertial element blanks, which would for example still be attached to the wafer.

[0034] According to one embodiment, the frequency range is predetermined to encompass at least one frequency range: - centered on the predetermined resonant frequency, and - a range of at least 30% of the predetermined resonant frequency, i.e. ±15% of the predetermined resonant frequency. For example, if the predetermined resonant frequency is 20 kHz, then the frequency range will be from 17000 Hz to 23000 Hz.

[0035] According to one embodiment, the inertial element or inertial element blank has at least two predetermined resonant frequencies, and the frequency range is predetermined to cover at least the two predetermined resonant frequencies. By covering or sweeping a wide frequency range, multiple resonant peaks (or resonant frequencies) can be measured, which can provide improved accuracy.

[0036] According to one embodiment, step a comprises the use of a vibratory excitation source, such as a piezoelectric source, making it possible to induce or impose an acoustic excitation on a wafer (for example its edge) supporting the inertial element blank, or preferably on, or even under the inertial element or the inertial element blank to be specifically excited.

[0037] According to one embodiment, the vibration excitation source may be an acoustic source coupled to an excitation cone chosen to excite at least one inertial element or an inertial element blank. Preferably, if a plate supports several inertial element blanks, then the acoustic source may be coupled to an excitation cone chosen to excite at least part and preferably all of the inertial element blanks.

[0038] According to one embodiment, the acoustic source can be chosen and / or adjusted to generate the variable vibrational excitation over time to cover the predetermined frequency range: - with an amplitude sufficient to generate vibrations of the inertial element or of the inertial element blank of amplitude sufficient to be detected by the means for measuring amplitude or speed or acceleration of displacement of at least one point of the inertial element or of the inertial element blank and / or - for a sufficient duration to deduce vibrational spectra of the inertial element or the inertial element blank.

[0039] According to one embodiment, step a comprises the use of a source of vibration excitation, such as a vibrating pot with a coil traversed by an electric current and placed in a magnetic field. It is possible to provide a high-power electronic amplifier necessary for powering the coil, an accelerometer and a controller which make it possible to control the vibrations.

[0040] According to one embodiment, step b comprises the use of an optical measuring means, such as a laser vibrometer using the Doppler effect.

[0041] According to one embodiment, step b is based on a measurement over time of an amplitude or a speed, or even an acceleration of displacement of at least one point of the inertial element or of the inertial element blank, preferably carried out at least partially during step a.

[0042] According to one embodiment, step b comprises: - a step of identifying a resonance frequency of the inertial element or the inertial element blank as a function of an operational or modal deformation of at least one point of the inertial element or the inertial element blank. An operational or modal deformation is typically defined by an amplitude or speed of displacement or even an acceleration and a direction of oscillation (outside or in a particular plane) as a function of the excitation frequency.

[0043] According to one embodiment, the inertial element or the inertial element blank is contained in a base plane, and step b comprises: - a step b' of measuring an amplitude or a speed or an acceleration of displacement of at least one point of the inertial element or of the inertial element blank in a direction normal to the base plane, and / or - a step b” of measuring an amplitude or a speed or an acceleration of displacement of at least one point of the inertial element or of the inertial element blank in a direction contained in the base plane.

[0044] Measurements of displacements or speeds in several directions make it possible to better identify resonance peaks and frequencies.

[0045] According to one embodiment: - for a first predetermined resonance frequency, only step b' of measuring a displacement or a speed of at least one point of the inertial element or of the inertial element blank in a direction normal to the base plane is carried out, and / or - for a second predetermined resonance frequency, only step b” of measuring a displacement or a speed of at least one point of the inertial element or of the inertial element blank in a direction contained in the base plane is carried out.

[0046] Depending on the resonance frequency, one can choose to measure in one direction or another, to measure the largest possible displacements or velocities, so as to minimize the measurement error. Indeed, depending on the geometry of the inertial element or the inertial element blank, the vibration mode (typically the vibration direction) in response to the vibration excitation can vary.

[0047] According to one embodiment, step b comprises a step of processing the measurement signal with for example a Fourier transform, to identify resonance peaks of displacement amplitude or speed or acceleration, and / or phase, as a function of the excitation frequency.

[0048] According to one embodiment, step b comprises: - a step of identifying a resonance peak of the inertial element or of the inertial element blank as a function of an amplitude or a speed of displacement of at least one point of the inertial element or of the inertial element blank.

[0049] According to one embodiment, the resonance frequency is identified based on the width of the resonance or amplitude peak, at half height of the maximum value of the amplitude resonance peak. This processing method makes it possible to limit calculation errors which could be made based solely on the identification of the frequency position of the peak defined by its maximum value.

[0050] According to one embodiment, step c comprises a step of calculating an inertia of the inertial element or of the inertial element blank. The calculation of the inertia makes it possible to determine with improved precision a conformity, a class of the inertial element, and / or whether a dimensional correction is necessary, and what value this correction must be. In addition, this also makes it possible to pre-dimension or choose an elastic return member to couple the inertial element once it has been finished manufacturing.

[0051] According to one embodiment, if a dimensional correction is necessary, then the method comprises a step: d. calculating, with the prediction machine, the dimensional modification (change in section, height and / or thickness, quantity of material to be added, removed, location of the part where the material is added or removed) to be applied from the resonance frequency characteristic identified in step b.

[0052] According to one embodiment, step b comprises a plurality of measurements over time of an amplitude or a speed, or even an acceleration of displacement, each carried out on a particular and specific point of the inertial element or of the inertial element blank, preferably carried out at least partially during step a. According to this embodiment, it is possible to measure the displacements, speeds, acceleration on several points of the same part (simultaneously or sequentially), for example to identify an unbalance or to determine whether a distribution of the mass of the inertial element is homogeneous around the axis of rotation of the inertial element once mounted in the timepiece.

[0053] According to one embodiment, the prediction machine implements a polynomial formula to predict inertia or whether a dimensional correction is necessary. For example, linear regression modeling can be performed.

[0054] According to one embodiment, the prediction machine implements a classification carried out for example by a neural network to predict inertia or whether a dimensional correction is necessary.

[0055] According to one embodiment, the prediction machine implements a classification based on a partitioning into k-means or k-medians to predict inertia or whether a dimensional correction is necessary.

[0056] According to one embodiment, the inertial element blank being formed on a wafer comprising a plurality of inertial element blanks distributed over several sectors of the wafer, step b comprises a step of identifying at least one characteristic of a resonance frequency of at least one inertial element blank for each sector, and step c comprises a step of determining an inertia of the inertial element blank and / or determining for the inertial element blanks of each sector whether a dimensional correction is necessary. The accuracy of the dimensional correction (section, height and / or thickness) is improved by refining the analysis by sectors of the wafer.

[0057] According to one embodiment, the control method comprises a step of calculating, with the prediction machine, the inertia or the dimensional modification to be applied for the inertial element blanks of each sector.

[0058] According to one embodiment, step a comprises a step of modifying a direction of vibrational excitation over time, preferably in a direction pointing at the inertial element or the inertial element blank whose resonance frequency characteristic is identified in step b.

[0059] According to one embodiment, the control method comprises a preliminary step of taking into account a geometry and / or a material of the inertial element or of the inertial element blank, and of adjusting a maximum amplitude of the vibrational excitation and / or a frequency range of the range predetermined frequency depending on the geometry and / or material of the inertial element or the inertial element blank.

[0060] According to one embodiment, the frequency range extends over a frequency range from 0 Hz to 500 kHz, and / or from 0 Hz to 100 kHz, and / or from 100 kHz to 200 kHz, and / or from 200 kHz to 300 kHz, and / or from 300 kHz to 400 kHz, and / or from 400 kHz to 500 kHz, preferably from 5 kHz to 150 kHz, more preferably from 5 kHz to 100 kHz, and very preferably from 10 kHz to 80 kHz. The applicant has noticed that the accuracy of the prediction could be better for peaks or resonance frequencies located over a high frequency range. Indeed, if we focus on inertia, and considering the mass of the inertial element, excitation and measurement are more reliable and efficient in high frequency ranges (for example between 10 kHz and 100 kHz), so that sensitivity and precision are better over this particular range.

[0061] According to one embodiment, step a and step b are repeated at least several times for the same measurement point of the inertial element or the inertial element blank.

[0062] According to one embodiment, step a and step b are synchronized. Such synchronization provides the possibility of detecting a phase shift, or an attenuation, or a coupling, the taking into account of which can improve the accuracy of the prediction, or make it possible to adjust or recalibrate the source of vibrational excitation.

[0063] A second aspect of the invention relates to a method of manufacturing an inertial element having at least one predetermined inertia, comprising the steps of: • forming at least one inertial element or an inertial element blank to obtain an inertial element or an inertial element blank having an inertia and / or a material and / or dimensions within predetermined tolerances necessary to obtain the predetermined resonant frequency, • controlling the inertial element or the inertial element blank according to the control method of the first aspect.

[0064] According to one embodiment, the manufacturing method comprises a step consisting of: • correcting at least one dimension of the inertial element blank formed during step a., according to the calculation of step d., in order to obtain an inertial element having the predetermined inertia.

[0065] The dimensions (section, height and / or thickness) can be corrected by removing or adding material. In the case of a composite part, a specific material can be added or removed. Specific material can be added or removed at specific locations on the part in question (in particular, action can be taken on the balance rim and / or on peripheral areas of the inertial element).

[0066] According to one embodiment, the inertial element or the inertial element blank is formed from silicon, or glass, or ceramic, or metal, or carbon nanotubes. In particular, conventional inertial elements made of metal (steel, nickel-phosphorus alloy, etc.) can be tested. In this case, the metallic inertial element is clamped or taken as a reference by a tool which positions it opposite the source of vibration excitation and the displacement measuring device.

[0067] According to one embodiment, the inertial element blank is formed on a wafer, with a plurality of other inertial element blanks.

[0068] A third aspect of the invention relates to a method for learning a prediction machine to implement step c of the control method of the first aspect, comprising the steps of: i- forming inertial elements or inertial element blanks, ii- applying to each of the inertial elements or to each of the inertial element blanks a vibrational excitation that varies over time to cover a predetermined frequency range, iii- identifying at least one characteristic of a resonance frequency of each inertial element or each inertial element blank during the vibrational excitation over the predetermined frequency range,iv'- mounting a plurality of inertial elements or inertial element blanks in an oscillating mechanism with an elastic reference return member (having a known stiffness) so as to measure for each inertial element or each inertial element blank a free oscillation frequency or an inertia, and / or, iv”- modeling in a simulation tool a plurality of inertial elements or inertial element blanks in an oscillating mechanism with an elastic reference return member so as to calculate for each inertial element or each inertial element blank a free oscillation frequency or an inertia, v- providing the prediction machine, and for each inertial element or each inertial element blank: the characteristic of the resonance frequency identified in step iii-; the free oscillation frequency or the inertia measured in step iv'- and / or calculated in step iv”-.

[0069] Preferably, it will be chosen to use a measuring instrument that is sufficiently sensitive over the chosen frequency range, and ensuring that the vibrational behavior of the inertial element can be used over this chosen frequency range.

[0070] According to one embodiment, step iii- comprises a preliminary phase of identifying reference measurement points with: - the measurement of a displacement or a speed of displacement of a plurality of predetermined points of the inertial element or of the inertial element blank, - identifying nodes among the plurality of predetermined points, which have at least one resonance frequency or peak a displacement amplitude of zero or less than a first threshold peak value, - selecting reference points to be measured during the inspection from among the plurality of predetermined points, which are different from the identified nodes, and which preferably each have a peak displacement amplitude greater than a second threshold peak value.

[0071] Such a step of identifying reference points allows to eliminate points or areas that are nodes (i.e., immobile points) at one or more resonant frequencies.

[0072] According to one embodiment, the inertial element or the inertial element blank has a radius Ra defined between a free central portion (typically the center of the balance, or supported during the vibration test) and a recessed peripheral portion, and at least two reference points, and preferably four reference points are chosen and located: - in a first zone less than 0.20 x Ra, or - in a second zone between 0.05 x Ra and 0.30 x Ra, or - in a third zone between 0.35 x Ra and 0.65 x Ra, or - in a fourth zone between 0.65 x Ra and 0.85 x Ra. The choice of these areas ensures that the points whose movements are tracked have sufficient displacement amplitude to be measured correctly and with good precision.

[0073] Alternatively, it is possible to plan to measure the displacements / movements / vibrations only at a particular point preferably located on an area of ​​the part which has large dimensions and / or which does not deform (or marginally compared to the deformations linked to the oscillations of the inertial element). In particular, it is possible to plan to point the measurement at a point on the hub or the rim of the inertial element or the inertial element blank. Indeed, on the one hand the hub or the rim has large dimensions compared to the spokes which makes aiming the measuring tool easier, and on the other hand, the hub or the rim can be considered non-deformable during vibration excitation and all the points of the hub (or possibly the rim) have similar displacements / movements / vibrations.As a result, aiming the measuring point (4 pm in size for a laser sensor, for example) on the hub or rim will be easier, and / or a small error in locating the measuring point on the hub or rim will have little impact on the final result. Furthermore, by choosing a particular measuring point on the part, a particular frequency range can be identified and chosen to conduct the inertia prediction.

[0074] According to an embodiment in which several parts still attached to a substrate or to a tool are to be tested in series, it is possible to provide: - a step of capturing images of the parts to be tested, - an image analysis step to, for example, recognize each type of part, and / or the position and / or orientation of each part, - a step of selecting one or more points to be measured for each part, and / or of selecting an excitation vibration spectrum to be imposed for each part and / or each selected point, - for each part to be tested, a step of positioning the substrate or the tooling supporting the parts to be tested in a vibration excitation and measurement device. According to this implementation, excitation and measurement can be automated in the case of a wafer which still carries the inertial element blanks: - one or more images of the plate are taken, - an automatic image analysis is carried out to know at least the XY position of each part (we can also do a recognition of the type or model of part), - depending on the position and / or orientation and / or type of part recognized, particular pre-established measuring points are identified or selected (for example on the hub or the rim), it is also possible to select a particular excitation cycle depending on the type of part or a particular point, - for example, with a tool that carries the wafer and includes a table that moves in XY, each blank of inertial element is successively automatically placed opposite the source of vibration excitation and the measuring device to be tested by aiming at the right measuring point and applying the right excitation specification. Optionally, an autofocus step can be carried out, i.e. an adjustment of the relative position according to z of the position of the vibrometer head, making it possible to obtain the sharpest possible image of the observed part. The laser beam is thus focused exactly on the surface of the part, provided that the focal planes of the laser beam and the observation camera are the same, or that their offset is known and systematically compensated.

[0075] According to one embodiment, depending on the measurement point selected on the part to be tested and / or depending on the excitation frequency, and / or depending on the model of the part to be tested, a step can be provided consisting of giving a particular orientation to the excitation direction and / or to the measurement direction. For this purpose, an excitation direction (or an axial direction of the vibratory excitation source) can be chosen perpendicular to the part to be tested to maximize the displacements perpendicular to the plane formed by the part at rest. An excitation direction (or an axial direction of the vibratory excitation source) can be chosen inclined relative to the part to be tested to maximize displacements contained in the plane formed by the part at rest. With regard to the measurement, a measurement direction (or an axial direction of a laser beam of the apparatus) can be chosen measurement) perpendicular to the part to be tested to maximize the measurement accuracy of displacements perpendicular to the plane formed by the part at rest. A measurement direction (or an axial direction of a laser beam from the measuring device) inclined relative to the part to be tested can be chosen to maximize the measurement accuracy of displacements contained in the plane formed by the part at rest. In the case of measurement along an inclined axis, a reception sensor adapted to receive the reflected signal can be provided, depending on the roughness of the parts: for slightly rough "mirror" parts, a reception sensor with a large collection cone (which preferably covers at least twice the inclination angle) or offset can be provided, while for "rough" parts, the reception sensor can be combined with the light emission source.

[0076] According to an embodiment in which several parts are attached to a substrate such as a wafer, it is possible to provide for sampling by detaching one or a few parts to test them individually, and to deduce therefrom a particular excitation frequency to be applied, and / or a particular measurement point to be used, and / or a particular domain of the vibration spectrum to be taken into account to derive the desired resonance frequency characteristic. In other words, this preliminary sampling makes it possible to test single parts under good conditions (measurement errors and interference are limited) to choose the best test conditions for the parts remaining attached to the substrate. In the case of the excitation of parts attached to a substrate, it is possible to provide for exciting and measuring the response of the substrate, in order to subsequently identify and exclude the spectral ranges over which it vibrates. Brief description of the drawings

[0077] Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which: Figure 1 represents a perspective view of an inertial element, Figures 2A-2F are a simplified representation of a manufacturing process of an inertial element, here a balance, on a wafer, Figure 3 schematically represents the implementation of the evaluation of the inertia of inertial element blanks by vibration analysis, Figure 4 represents an example of frequencies applied to a silicon wafer supporting inertial element blanks, to impose a vibration excitation, Figure 5 represents an example of measurement of the displacement amplitudes of a point of an inertial element blank, in response to the imposed frequency range of Figure 4, Figure 6 represents in detail a resonance peak identified at a particular frequency in Figure 5, Figure 7 represents resonance peaks measured on several parts and superimposed for the particular frequency of Figure 6, Figure 8 represents an example prediction model built from data extracted from Figure 7; Figure 9 represents an alternative implementation of the evaluation of the inertia of inertial element blanks by vibration analysis of Figure 3; Figure 10 represents a perspective view of an alternative of the inertial element of Figure 1;Figure 11 represents a first resonance mode of the inertial element of Figure 10, at a first resonance frequency; Figure 12 represents a second resonance mode of the inertial element of Figure 10, at a second resonance frequency.; Method of carrying out the invention

[0078] Figure 1 represents a perspective view of an inertial element 100 (here a balance) coupled to a balance shaft 120. The balance shaft 120 supports a double roller 130 in a conventional manner. To form a resonator or an oscillator, the inertial element 100 mounted on its balance shaft 120 must still be coupled to an elastic return member, typically a spiral spring, which is not shown in Figure 1.

[0079] In this example, the inertial element 100 comprises a rim 101, arms 102 and a central hub 103. The inertial element 100 may be made of a metallic material, but may also be made of a non-metallic material, such as silicon, carbon or glass. A composite inertial element 100 may be provided, i.e. formed from several materials: the rim 101 may be coated with a dense material to provide a particular inertia, for example. An inertial element 100 may be provided formed by an assembly of several parts. In particular, it may be provided, for example, to fix weights to the rim 101.

[0080] In the case where the inertial element 100 is made of silicon, FIGS. 2A-2F are a simplified representation of a method of manufacturing an inertial element 100 on a wafer 10.

[0081] The wafer 10 is illustrated in Figure 2A as a SOI (silicon on insulator) wafer and includes a substrate or handler 20 carrying a sacrificial silicon oxide (SiO2) layer 30 and a monocrystalline silicon layer 40. For example, the substrate 20 may have a thickness of 500 μm, the sacrificial layer 30 may have a thickness of 2 μm, and the silicon layer 40 may have a thickness of 120 μm to 500 μm. The monocrystalline silicon layer 40 may have any crystal orientation.

[0082] A lithography step is shown in Figures 2B and 2C. By "lithography" is meant the set of operations allowing an image or pattern to be transferred onto or above the wafer 10 to the latter. Referring to Figure 2B, in this exemplary embodiment, the layer 40 is covered with a protective layer 50, for example made of a polymerizable resin. This layer 50 is structured, typically by a photolithography step using an ultraviolet light source as well as, for example, a photomask (or another type of exposure mask) or a stepper and reticle system. This structuring by lithography forms the patterns for the plurality of inertial elements in the layer 50, as illustrated in Figure 2C.

[0083] Subsequently, in the step of Figure 2D, the patterns are machined, in particular etched, to form the plurality of inertial elements 100 in the layer 40. The etching can be carried out by a deep reactive ion etching technique (also known by the acronym DRIE for "Deep Reactive Ion Etching"). After etching, the remaining portion of the protective layer 50 is subsequently removed.

[0084] In Figure 2E, the inertial elements 100 are released from the substrate 20 by locally removing the sacrificial layer 30 or even by etching all or part of the silicon of the substrate or handler 20. At this stage, blanks of the inertial element 100 are obtained. Smoothing (not shown) of the etched surfaces may also take place before the release step, for example by a thermal oxidation step followed by a deoxidation step, consisting for example of wet etching based on hydrofluoric acid (HF). It may also be provided to form a layer of silicon oxide on the parts.

[0085] Figure 2F shows an inertial element 100 with, in the section considered, the rim 101 and the hub 103. It can be noted that the arms 102 obviously connect the rim 101 and the hub 103 and are in a plane other than the section plane of Figure 2F. It can also be noted that the inertial element 100 remains attached to the plate 10 by bridges not visible in Figure 2F.

[0086] The present invention proposes to determine at least one inertia of a sample of inertial elements 100 on the wafer in step 2E and whether a geometric correction of the inertial elements 100 is necessary. If so, the present invention can propose to precisely calculate a thickness of material to be modified (to be removed or added) to obtain the dimensions leading to obtaining the inertia (adjusting the natural frequency and / or the resonance frequencies) corresponding to target values, according to a more efficient method than the methods of the prior art.

[0087] Thus, the invention proposes to determine at least one characteristic of a resonance frequency of a sample of inertial elements 100 by vibration measurement and to apply a predictive method (for example a numerical model or a classification or categorization method) to link the result of said vibration measurement to the inertia of the inertial elements 100 and / or to the necessary geometric correction.

[0088] The modal properties of the inertial element 100 still attached to the plate 10 are thus exploited. During a learning phase, and using an analytical and numerical approach, it is possible to set up an inertia prediction machine. by establishing a predictive model linking the dimensions (in particular the thickness) and / or the inertia to certain frequencies (natural frequency or resonance frequencies associated with a resonance peak or a width at half-maximum) specifically chosen.

[0089] Once the learning phase is complete (once the modes to be used and the excitation frequencies have been determined), it is possible to move on to a prediction phase and use the prediction machine by using the predictive model to control the inertial elements 100 of a produced wafer, in order to predict their inertia, and / or perform a classification and / or determine whether a correction of the dimensions is necessary, and if so, calculate or predict the exact correction to be made to the dimensions of the inertial elements 100 (by removal if the blank is produced with dimensions greater than the required final dimensions, or by adding material if the blank is produced with dimensions smaller than the required final dimensions, for example).

[0090] Thus, it is possible to integrate the control method into a manufacturing method to correct, if necessary, the vibration characteristics of the inertial elements 100 (natural frequency and / or resonance frequencies, and / or inertia) to obtain a particular and predetermined natural oscillation frequency, once the inertial elements 100 are each coupled to an elastic return member of a given watch mechanism. Vibrational excitation

[0091] The measurement of the vibration response of the inertial elements 100 makes it possible to deduce at least one characteristic of a resonance frequency, such as for example a value of a resonance frequency (a resonance peak). In detail, one must first impose a vibration excitation on the wafer. Several options are offered: a. Measurements in the frequency domain: 1 - Use a piezoelectric source (or any other source of vibrational excitation - for example an electromagnet - making it possible to induce or impose a vibrational excitation such as an acoustic excitation) on the edge of the wafer 10, on, or under the draft inertial element 100 to be specifically excited (preferential) which excites at a particular frequency fo (continuous single-frequency excitation). In this variant, the excitation is maintained. 2- Alternatively, the piezoelectric source (or any other source of vibrational excitation - for example an electromagnet - making it possible to induce or impose a vibrational excitation such as an acoustic excitation) can also be used on the edge of the wafer 10, on, or under the blank of the inertial element 100 to be specifically excited (preferred) which excites at a frequency that varies over time to cover a predetermined frequency range, for example from 0 to 500 kHz, preferably from 0 to 100 kHz, preferably from 5 kHz to 100 kHz, preferably from 5 kHz to 80 kHz, and preferably from 10 kHz to 80 kHz. The entire frequency range can be scanned or covered in a time interval that can range from a fraction of a second to a few seconds. For example, one may expect to sweep or cover the frequency range of the frequency range in less than 0.5 s, less than 1 s, or less than 1.5 s.In this variant, the excitation frequency changes continuously or according to a variable profile. b. Measurements in the time domain: use an excitation hammer (or any other source of vibrational excitation allowing the induction of an impulse vibrational excitation, or even an impulse acoustic excitation) on the edge of the wafer 10, on, or under the inertial element 100 to be excited specifically (preferred) which gives the shortest possible acoustic pulse (multi-frequency impulse excitation). In this variant, the excitation is punctual and not sustained.

[0092] Furthermore, measurements can be performed following a particular sampling, for example according to a sampling range of 4, 2 or 1 Hz. Indeed, the resolution for processing the acquisition data according to, for example, a Fourier transform depends directly on the duration and frequency of this acquisition.

[0093] Furthermore, a signal sampling frequency of at least 200 kHz can be chosen if the frequency range extends up to 100 kHz, for example.

[0094] Generally speaking, we can finally plan to change the direction of excitation, that is to say the direction of the movements imposed by the source of vibratory excitation (we can impose vibrations according to one or more axial direction(s), and changing this or these direction(s) over time). In the case where a wafer 10 comprising a plurality of inertial element blanks 100 is excited, it is possible to adjust the direction of the vibrations so as to point at one or other of the inertial elements 100, as a function of the displacement amplitude measurements described below.

[0095] Finally, it is possible to couple the acoustic source to a divergent cone directed towards the inertial element blanks 100 to be excited, and to adjust the acoustic source to emit an excitation signal with an amplitude sufficient to impose a vibrational excitation of the inertial element blank(s) 100 and having an amplitude sufficient to be detected and measured precisely by the chosen measuring instruments. Measurement of amplitude or speed, or acceleration of displacement

[0096] During excitation, the amplitude and phase (relative to the source of vibration excitation) of oscillation in the 3 directions X, Y (in the plane) and Z (out of plane) of the specifically excited inertial element are recorded using a suitable measuring means. The following possible measuring means may be mentioned, without limitation: Optical methods by interferometry: a. By 3D Doppler effect (laser vibrometer by Doppler effect), b. Holographic, Stroboscopic optical methods, High temporal resolution chromatic confocal profilometry, Optical reflectometry: a. Vibration analysis by beam deflection on multi-dial detector or camera, b. Analysis by temporal analysis type TCSPC, Acoustic methods using Doppler ultrasound.

[0097] Figure 3 schematically represents a silicon wafer 10 on which a plurality of inertial element blanks 100 are formed. A vibration excitation source 300 is coupled to the wafer 10, so as to be able to impose a vibration excitation. Consequently, each inertial element blank 100 will start to vibrate, and a laser vibrometer 200, here focused on a point of the right-hand inertial element blank 100, will be able to measure the vibration amplitudes of the measurement point over time. It is possible to measure the displacements in a direction normal to the plane of the plate 10, but it is just as possible to measure the displacements in one or more directions contained in the plane of the plate 10. It is of course possible to provide a vibration excitation source 300 detached or peeled off from the plate 10 to generate an acoustic excitation of all or part of the inertial element blanks 100.

[0098] Once a particular point has been studied, the laser vibrometer 200 can be moved to another measurement point on the inertial element blank 100, or moved to another inertial element blank 100 on the wafer 10. Of course, the inertial element blank 100 can alternatively be moved relative to the laser vibrometer.

[0099] Figure 4 represents an example of vibration excitation over time. In the example given, the excitation frequency varies over time, between 0 Hz and 50 kHz, and a succession of rising edges can be imposed, each spaced by a rest period without excitation. For each measurement point on the inertial element blank 100, a plurality of rising edges can be imposed (between 2 rising edges and 60 rising edges), each lasting between 0.5 s and 2 s for example.

[0100] Figure 9 represents an alternative implementation of the evaluation of the inertia of inertial element blanks by vibration analysis of Figure 3. In this alternative implementation, the inertial element (a balance) 100 is previously embedded on a test shaft 402 (for example with a mounting with an elastic support ring), the shaft 402 being clamped by a movable jaw 401 in a vice 400.

[0101] Once the test shaft 402 is clamped, a vibration source 300 can be attached to the movable jaw 402. The coupling of the vibration source 300 to the movable jaw 402 can be achieved by gluing, by mechanical clamping, by magnetic clamping, by suction, etc.

[0102] As shown in Figure 9, the vibration source 300 can generate vibrations which are transmitted directly to the movable jaw 401, to the test shaft 402 and therefore to the inertial element 100. The inertial element 100 therefore undergoes the vibratory excitation imposed by the vibratory source 300, the frequency of which varies over time, and the vibrations of the inertial element 100 can be measured in the same way as for figure 3.

[0103] Figure 10 shows a perspective view of an inertial element 100 according to an alternative of the inertial element of Figure 1, comprising an axle hole 103 formed in a central bearing, arms 102 and a rim 101.

[0104] Figure 11 shows a first resonance mode of the inertial element 100 of Figure 10, at a first resonance frequency, so as to show a first deformation mode of the inertial element 100. The arms 102 are bent in a uniform and regular manner (there is no slope inversion or turning point) to form arches, and the rim 101 is deformed with four changes of slopes, or four curve peaks.

[0105] Figure 12 shows a second resonance mode of the inertial element 100 of Figure 10, at a second resonance frequency so as to show a second deformation mode of the inertial element 100. The arms 102 are flexed with slope reversals or turning points, and the rim 101 is deformed with eight alternating changes of slopes, or eight curve peaks along the periphery of the rim 101.

[0106] It is noted that the resonance modes illustrated in figures 11 and 12 can be encountered according to the test assembly of figure 3 or according to the test assembly of figure 10. It is also noted that the resonance modes perfectly illustrate the deformable nature of the inertial elements 100, and in particular it is also noted that the resonance modes illustrate elastic deformation modes of the inertial element 100, the latter being embedded or held immobile at at least one point of its structure (a point of the rim in the case of the tests of figure 3, the axle hole in the case of the tests of figure 9). Selection of reference points to measure

[0107] With regard to the measurement of displacement amplitude, during the learning phase, a step can be provided consisting of identifying points of the inertial element 100 for which the vibration response is significant. Indeed, in the case of an inertial element to which a vibration is imposed, especially if the frequency varies over time, the vibration response will cause nodes to appear on the inertial element 100, i.e. particular points of the inertial element 100 whose displacement amplitude is low or zero. If a displacement measurement is carried out on a point of the inertial element which turns out to be a node at one or more particular frequency(ies), the identification of resonance frequency characteristics will be negatively affected.

[0108] Thus, it is advantageous to provide a preliminary step of measuring displacement on a plurality of predetermined points of the inertial element 100, for example at least ten predetermined points, preferably at least twenty predetermined points, and very preferably at least thirty predetermined points. It is possible to provide for selecting the predetermined points arranged on an orthonormal XY reference frame in the plane of the inertial element.

[0109] At the end of this preliminary step of amplitude measurement on the predetermined points, it is possible to identify for each measurement point resonance frequencies, and then a step of selecting reference points for which the measurement of displacement amplitude during the excitation shows that they are not nodes at these resonance frequencies. In other words, the identified nodes have, at at least one resonance frequency, a displacement amplitude of zero or less than a first threshold peak value, and these points forming nodes are removed from the reference points to be considered for the subsequent measurements. It may also be noted that the reference points may be different depending on the position of the inertial element blank 100 on the wafer 10. [001 10] Typically, it can be considered that at least two reference points will be selected, and preferably at least four reference points will be selected. In the case where the inertial element 100 has a radius Ra and is anchored or embedded on the plate 10 by a bridge, it is preferably possible to select four chosen and located reference points: - in a first zone less than 0.20 x Ra (for example on hub 103), or - in a second zone between 0.05 x Ra and 0.30 x Ra (for example on arms 102), or - in a third zone between 0.35 x Ra and 0.65 x Ra (for example on the 102 arms, especially if the latter do not have a constant cross-section), or - in a fourth zone between 0.65 x Ra and 0.85 x Ra (for example on serge 101). Also, the reference points can be chosen to be far from the part anchored on the plate 10 and can naturally have a significant oscillatory displacement capacity, which ensures better precision of the displacement measurement. [001 1 1 ] Furthermore, it is also possible to measure the displacements of a point on the body of the wafer, and / or of a point on the source of vibrational excitation, to identify or measure, for example, a phase shift or a vibrational attenuation, or even a resonance resulting from a vibrational coupling or from the wafer 10. These additional measurements make it possible to ensure that the identified peaks are indeed those of the inertial element alone. It is also possible to synchronize the measurement of the displacement amplitude and the vibrational excitation. Determination of vibration characteristics [001 12] We then have several scenarios depending on the domain previously chosen for the excitation: a. Measurements in the frequency domain 1 - variant with sustained excitation: i. Temporally integrate the oscillation amplitude and phase long enough to have good spectral resolution at the excitation frequency fo, ii. Shift the oscillation frequency by delta f to excite at frequency fo + A f and repeat integration step i, iii. Reconstruct the oscillation amplitude and phase spectra as a function of the excitation frequency (possibly with several peaks at several frequencies). 2- variant with excitation whose frequency varies over time: i. Record the amplitude and phase of oscillation over time during the frequency sweep of the frequency range, ii. Repeat step i- at ​​least once, preferably at least three times, iii. Reconstruct the amplitude and phase spectra of oscillation as a function of the excitation frequency (possibly with several peaks at several frequencies). b. Measurements in the time domain: i. Record the temporal displacement of the measurement point along X, Y and Z over a sufficiently long period of time to obtain a sufficiently representative signal, such as a few seconds. ii. One can choose to record the signal to make it a reference signal to compare with other signals measured on other parts. One can also choose to perform Fourier transform type signal processing to identify resonance frequencies in the recorded signal. [001 13] As a result, at least one resonance peak can be identified for each inertial element blank or each excited inertial element, and it is proposed to determine the resonance frequency not on the basis of the top of the resonance peak, i.e. on the maximum amplitude, but rather on an area of ​​the curve located between 25% and 75% of the maximum amplitude value of the resonance peak, for example from its width at half-height. Indeed, this processing method which focuses on a part of the curve between 25% and 75% of the maximum amplitude value of the resonance peak makes it possible to limit the errors due to the singularity of the maximum amplitude point and to the approximation calculations for reconstructing the top part of the resonance peak.The area of ​​the curve between 25% and 75% of the maximum amplitude value of the resonance peak has better accuracy than the part above 75% (typically the peak), which provides better accuracy on the exact resonance frequency determined. For example, the middle of the segment connecting the two points at mid-height of the resonance peak can be used to determine the resonance frequency associated with the peak in question. [001 14] Figure 5 represents an example of a vibration spectrum for a point of a blank of an inertial element 100 of Figure 1 or 3, reconstructed from the displacement amplitude measurements of the measurement point considered in response to the vibration excitation of Figure 4, between 15 kHz and 65 kHz. The presence of three amplitude peaks can be noted, at approximately 25 kHz, 37 kHz, and 53 kHz. Although this is not shown, it is typically possible to identify between 10 and 30 peaks. amplitude if the vibrational excitation sweeps a frequency range between 0 Hz and 50 kHz. Each amplitude peak has a resonance frequency, and the maximum amplitudes vary greatly. [001 15] Figure 6 shows in detail the processing that can be done on an amplitude peak, that at 37.5 kHz for example. The aim is to find the resonance frequency and to give it as precise a value as possible. Instead of basing this processing on the maximum value of the peak, the applicant has noticed that better precision can be achieved by determining the length of the segment connecting the rising part and the falling part of the curve, at mid-height of the peak. The resonance frequency is typically the value in the middle of this segment. However, it is possible to perform an interpolation on points in the vicinity of the resonance peak to improve the precision, and to shift the chosen point on the segment, which will not be the middle, in particular if the actual position of the resonance peak is shifted for example due to the chosen sampling frequency. [001 16] Figure 7 represents, for the example of an amplitude peak at approximately 37 kHz, the amplitude peaks constructed for about ten inertial element blanks 100 tested. It can be noted that from one inertial element blank to another, the frequency position of the amplitude peak varies (from approximately 37 kHz to 38 kHz), and that the maximum displacement amplitude varies in a ratio of approximately 1 to 5. Since the peaks of the amplitude peaks are not truly symmetrical, it appears judicious to determine the resonance frequency on the basis of the width of the peak at mid-height. Determination of the inertia and / or actual dimensions of the inertial elements tested

[0117] To establish a prediction model that can receive as input the vibration characteristics (typically a resonance frequency) and output an inertia and / or a dimensional correction, it is necessary, during the learning phase, to provide the data relating to the real inertia and / or the real dimensions of the inertial elements tested to link them to the resonance frequencies of figure 7 for example. Also, for this purpose, it is possible to plan to concretely measure a natural oscillation frequency of a balance spring system in an environment similar to that of a particular watch mechanism.

[0118] Alternatively, the tested inertial elements can be finished manufacturing in order to mount or couple them with a reference elastic return member (of known stiffness) individually to again measure a natural oscillation frequency of the reference elastic return member - inertial element pair.

[0119] An intermediate step can be taken to determine the inertia of each inertial element, and then the inertia and / or actual dimensions of the inertial elements tested can be determined. In other words, it is possible to determine the natural frequency or a resonance frequency and then the inertia or dimensions of the inertial element by analyzing the free oscillations of an inertial element coupled to a reference elastic return member. In this approach, a laser pointed at the balance arms records the passage times of the balance arms or a polarizer. An estimate of the period, then the frequency and finally the inertia and / or actual dimensions can then be deduced. The data collected are essentially point clouds of the passage times.

[0120] On the other hand, it is possible to estimate by simulation a natural frequency and / or a resonance frequency and / or the inertia for each inertial element or inertial element blank tested on the wafer. For this purpose, dimensional measurements can be made of each inertial element or inertial element blank tested to reconstruct by numerical modeling the part in question in order to simulate by numerical calculation its vibration response to the imposed spectrum, and to also find the inertia of the inertial element or inertial element blank.

[0121] A high-resolution 3D X-ray tomography approach would allow the extraction of point clouds giving the 3D material density of the inertial elements, and, through appropriate image reconstruction, a mapping of the section of the inertial elements. These different types of data make it possible to deduce the dimensions of the inertial elements and to estimate the inertia of the inertial elements by a geometric approach combined with weighing and / or by knowing the material density of the inertial elements.

[0122] Another approach consists of analyzing the forced oscillations of an inertial element coupled to an elastic reference return member and an escapement. A laser measurement of the passage times of the balance arms (point clouds), as presented above, makes it possible to measure the frequency and deduce the inertia. An alternative can be considered from an acoustic acquisition (Witschi type microphone) which records the shocks of the different operating phases of the escapement / lever system. The measured data are either point clouds of the passage times of the balance arms, or the temporal evolution of the acoustic pressure level. These types of experimental data make it possible to deduce the period, then the frequency, then the inertia and finally the dimensions of the bar of the inertial element. Establishment of the prediction model

[0123] During the learning phase, oscillation amplitude measurements are performed on physical inertial elements, and resonance frequencies are identified (see Figure 7 for example). In order to subsequently be able to link the resonance frequencies measured on inertial elements to inertias and / or dimensional corrections to be made, a correlation phase must be planned during which a predictive model is built.

[0124] The operations described above (vibration measurements, identification of resonance peaks, mid-height bandwidth and its mid or corrected value, determination of the inertia and / or dimensions of the inertial elements) make it possible to feed a database that can relate the position of the inertial element on the wafer, spectra or oscillation periods or mid-height bandwidth and its mid or corrected value with the effective inertias and / or dimensions of the inertial element. As seen above, this database can be built from numerical simulations on a finite element model of the inertial element. These simulations make it possible to generate reference spectra or oscillation periods associated with the inertias. This database can also be supplemented by experimental measurements by measuring vibration spectra, oscillation periods and the positions of inertial elements on the wafer as well as their associated inertias. One of the advantages of this approach is that the training database is enriched as the tests progress. This can allow for an adaptive model depending on the wafers and the inertial elements and contributes to the reduction of the standard deviation in inertia on the wafers.

[0125] This database can be used to build a prediction model, and several solutions are offered.

[0126] A numerical model, for example polynomial, can be constructed to calculate, as a function of a resonance frequency value, a real dimension, a dimensional correction or a real inertia.

[0127] Categorization can also be performed by performing a k-means partitioning of the input data (the results of vibration measurements, typically the frequency of resonance peaks) and the output data (the inertia, and / or the dimensions of the inertial elements) and linking them together to establish a correspondence.

[0128] It is also possible to process the images of the resonance peaks by a neural network, for example a perceptron, to perform a classification according to inertias or dimensions of the inertial elements, the classes being able to be defined by value increments.

[0129] In summary, the learning phase includes a test phase (excitation of the inertial elements or inertial element blanks with measurement of the vibration characteristics to reconstruct a vibration spectrum and identify resonance frequencies). A measurement phase of the inertias and / or dimensions of the inertial elements is also carried out. Once the input data (the resonance frequencies) and the output data (the inertias and / or the dimensions of inertial elements) for a significant sample available, the phase of construction of the prediction model can be carried out.

[0130] It may be noted that it may be advantageous to verify that the established prediction model has good sensitivity, i.e. that for two different input values, the model gives two distinct output values. The applicant noticed that the sensitivity of the prediction model was not the same for all resonance peaks. In particular, reference may be made to Figure 8 which represents a graphical construction of the prediction formula established with the data in Figure 7, where a leading coefficient of 0.0034 mg.cm may be noted. 2 / Hz and an ordinate at the origin of -114.46 mg.cm 2 for resonance peaks located around 37kHz.

[0131] On the one hand, the applicant has noticed that the direction coefficient could be larger for high resonance frequencies, which provides better prediction sensitivity, to predict distinct inertia or dimensional correction values, even from close resonance frequency values. It is advantageous to provide, during the learning phase, a step of comparing the sensitivity of the prediction to verify / confirm that it is preferable to consider and choose certain resonance peaks at high frequencies (for example above 10 kHz, preferably above 20 kHz) to then predict as accurately as possible an inertia and / or a dimensional correction as a function of the measured vibration response.

[0132] On the other hand, the applicant also noticed that even for close resonance frequencies, the resonance modes (in particular the deformation and / or displacement modes of the inertial elements) could differ significantly, which can also affect the sensitivity of the inertia prediction and / or dimensional correction. It is advantageous to provide, during the learning phase, a step for comparing the sensitivity of the prediction in order to choose to subsequently consider this or that resonance frequency and not another in order to predict as accurately as possible an inertia and / or a dimensional correction as a function of the vibration response.

[0133] From the above remarks relating to the study of the sensitivity of the prediction, we can foresee, during the learning phase, to classify the different resonance peaks identified according to the prediction sensitivity of the inertia and / or the dimensional correction. It is then possible to define the excitation frequency range (which will be applied during a pure prediction phase) to include at least one or more resonance peaks or frequencies which give(s) the best sensitivity. Thus, imposing a variable vibrational excitation on the frequency range thus predetermined will guarantee being able to make an accurate prediction for the identified resonance peak or predictions for each of the identified resonance peaks, which overlap or reinforce each other.

[0134] Generally speaking, the learning phase makes it possible to choose either resonance peaks at high frequencies and / or resonance peaks which correspond to particular resonance modes making it possible to predict precise and reliable values, and the frequency range will be predetermined to include at least one resonance peak and preferably several, in order to be able to make either a single prediction as precise as possible, or several predictions (one per resonance peak deemed interesting) in order to then carry out cross-checks, averages or even adjustments of the predicted values.

[0135] For example, it is possible to predict several inertia values ​​or dimensional corrections from several peaks or resonance frequencies, and then calculate a definitive value, by carrying out, from the predicted values, a weighted average by assigning weights to each predicted value, each weight being determined according to the sensitivity identified for each corresponding peak or resonance frequency.

[0136] Alternatively and preferably, it is possible to provide for having only one model which takes all the peaks or resonance frequencies as input and which returns the inertia or the dimensional correction, the learning phase of the model being used precisely to calculate the weightings on the input peaks or resonance frequencies. Prediction phase

[0137] Once the learning phase is complete, we can move on to a prediction phase, for example during an element control process The inspection process can typically be carried out on inertial element blanks made on a wafer and still attached to this wafer, so as to estimate the inertia and / or the dimensions of the inertial elements of the sample, in order to determine whether a dimensional correction is necessary.

[0138] Once the model is trained, the control procedure to be deployed is as follows: 1) Locating the position of the inertial element on the plate, vibration measurement of the spectra or oscillation period (as described above), 2) Prediction of the inertia and / or dimensions of the inertial element by application of the predictive model, 3) Determine whether dimensional correction is necessary to achieve the target natural frequency or inertia.

[0139] During the control process, it is also possible to quantify the exact correction to be made, so that the manufacturing process can include, in addition to the above control: 1) Knowing the effective inertia of the inertial element estimated according to the model and the target inertia and / or the target dimensions: apply the necessary correction dose. Repeat step 1) and step 2) of the control process to check the inertia / dimensions of the inertial element and confirm that the target values ​​are met, within a tolerance threshold, or repeat these steps and the dimensional correction until the inertia / dimension predicted by the model reaches the target values.

[0140] As an example, the applicant carried out tests with balance wheels similar to those in Figure 10. Parts with an inertia of 6.26165 mg.cm 2 and inertia parts 6.30110 mg.cm 2were tested with the setup in Figure 9. These parts each belong to distinct inertia classes. The resonance mode in Figure 12 was investigated and identified for each inertia class. It was identified that the parts with an inertia of 6.26165 mg.cm 2 exhibit a resonance peak for the resonance mode of Figure 12 at 45304 Hz, and that the inertia parts 6.301 10 mg.cm 2 exhibit a resonance peak for the resonance mode of Figure 12 at 45392 Hz. Consequently, there is a gap of 88 Hz, which is perfectly measurable for these parts belonging to distinct inertia classes. Sampling

[0141] It is known that several hundred inertial elements are produced on a wafer and that the dimensions of the produced inertial elements can vary depending on the regions of the wafer. While the inertia evaluation can be carried out on a single inertial element, in practice, it will be carried out on a sample of inertial elements, distributed over the wafer.

[0142] From the evaluations carried out, corrections can be made for the entire wafer in a homogeneous manner, or differentiated by region, if the results obtained vary from one inertial element to another. This allows the standard deviation of the dispersion of inertias on the same wafer to be reduced. Furthermore, if the inertias of all the inertial elements are known by applying the model, the optimal correction can be determined to reduce the overall dispersion.

[0143] We can even consider going as far as an evaluation of all the inertial elements of the wafer, in particular with a vibration evaluation, because this is very quick to carry out.

[0144] It is possible to provide for the manufacture of inertial elements having initial dimensions larger than the target dimensions and the correction step can then consist of removing material (by time-controlled dissolution, by time-controlled oxidation, etc.). Alternatively, it is also possible to provide for the production of inertial elements having dimensions or a mass smaller than the target dimensions or mass and the correction step can then consist of adding material (by time-controlled coating, etc.).

[0145] The method, consisting of identifying resonance frequencies by imposing a vibration excitation on the inertial element blanks alone, makes it possible to quickly obtain measurement data, without having to, for example, carry out assembly operations with an elastic return member, while limiting measurement errors because only the inertial element blank is tested (there is no error that can be linked to the elastic return member, such as its stiffness, its assembly position, its free length, pollution, etc.).

Claims

Claims 1. Method for controlling an inertial element (100), or a blank of an inertial element (100), of a clockwork oscillator, the inertial element (100) or the blank of an inertial element (100) having to have at least one predetermined inertia and / or at least one predetermined resonance frequency, the control method comprising the following steps: a. applying to the inertial element (100), or to the blank of an inertial element (100), a vibrational excitation varying over time to cover a predetermined frequency range, b. identifying at least one resonance frequency characteristic, such as a resonance peak, of the inertial element (100) or of the blank of an inertial element (100), during, or in response to, the vibrational excitation over the predetermined frequency range, c. submitting to a prediction machine the resonant frequency characteristic identified in step b.to determine an inertia of the inertial element (100) or the inertial element blank (100) and / or to determine whether a dimensional correction of the inertial element (100) or the inertial element blank (100) is necessary to obtain the predetermined inertia.

2. Control method according to claim 1, in which the frequency range is predetermined to encompass at least one frequency range: - centered on the predetermined resonant frequency, and - of an extent of at least 30% of the predetermined resonant frequency.

3. Control method according to one of claims 1 to 2, the inertial element (100) or the inertial element blank (100) having at least two predetermined resonant frequencies, in which the frequency range is predetermined to cover at least the two predetermined resonant frequencies.

4. Control method according to one of claims 1 to 3, in which step b is based on a measurement over time of an amplitude or a speed or an acceleration of displacement of at least one point of the inertial element (100) or of the inertial element blank (100), preferably carried out at least partially during step a.

5. Control method according to one of claims 1 to 4, the inertial element (100) or the inertial element blank (100) being contained in a base plane, in which step b comprises: - a step b' of measuring an amplitude or a speed or an acceleration of displacement of at least one point of the inertial element (100) or of the inertial element blank (100) in a direction normal to the base plane, and / or - a step b” of measuring an amplitude or a speed or an acceleration of displacement of at least one point of the inertial element (100) or of the inertial element blank (100) in a direction contained in the base plane.

6. Control method according to one of claims 4 to 5, in which step b comprises: - a step of identifying a resonance peak of the inertial element (100) or of the inertial element blank (100) as a function of an amplitude or a speed of movement of at least one point of the inertial element (100) or of the inertial element blank (100).

7. A control method according to claim 6, wherein the resonant frequency is identified on the basis of the width of the resonant peak, at half height of the maximum value of the resonant peak.

8. Control method according to one of claims 1 to 7, wherein, if a dimensional correction is necessary, then the method comprises a step consisting of: d. calculating, with the prediction machine, the dimensional modification to be applied from the resonance characteristic identified in step b.

9. Control method according to one of claims 1 to 8, in which the prediction machine implements a polynomial formula to predict whether a dimensional correction is necessary.

10. Control method according to one of claims 1 to 9, in which the prediction machine implements a classification carried out for example by a neural network to predict whether a dimensional correction is necessary.

11. Control method according to one of claims 1 to 10, the inertial element blank (100) being formed on a wafer comprising a plurality of blanks of inertial element (100) distributed over several sectors of the wafer, in which step b comprises a step of identifying at least one characteristic of a resonance frequency of at least one blank of inertial element (100) for each sector, and in which step c comprises a step of determining for the blanks of inertial element (100) of each sector an inertia and / or whether a dimensional correction is necessary.

12. Control method according to one of claims 1 to 11, comprising a preliminary step of taking into account the material of the inertial element (100) or of the inertial element blank (100), and of adjusting a maximum amplitude of the vibration excitation and / or a frequency range of the predetermined frequency range as a function of the material of the inertial element (100) or of the inertial element blank (100).

13. Control method according to one of claims 1 to 12, in which the frequency range extends over a frequency range from 0 Hz to 100 kHz, preferably from 0 Hz to 50 kHz, more preferably from 0 Hz to 40 kHz, and very preferably from 10 kHz to 35 kHz.

14. Method for manufacturing an inertial element (100) having at least one predetermined resonance frequency comprising the steps of: • forming at least one inertial element (100) or an inertial element blank (100) having dimensions within predetermined tolerances necessary to obtain the predetermined resonant frequency, • controlling the inertial element (100) or the inertial element blank (100) according to the control method of one of the preceding claims.

15. Manufacturing method according to the preceding claim, comprising a step consisting of: • correcting at least one dimension of the inertial element blank (100) formed during step a., according to the calculation of step d. of claim 8, in order to obtain an inertial element (100) having the predetermined resonance frequency.

16. Manufacturing method according to one of claims 14 to 15, in which the inertial element blank (100) is formed on a wafer, with a plurality of other inertial element blanks (100).

17. A method of training a prediction machine for implementing step c of the control method of one of claims 1 to 13, comprising the steps of: i- forming inertial elements or inertial element blanks (100), ii- applying to each of the inertial elements or each of the inertial element blanks (100) a time-varying vibrational excitation to cover a predetermined frequency range, iii- identifying at least one characteristic of a resonance frequency of each inertial element (100) or each inertial element blank (100) when applying the predetermined frequency range, iv'- mounting a plurality of inertial elements or inertial element blanks (100) in an oscillating mechanism having a predetermined inertia so as to measure for each inertial element (100) or inertial element blank (100) a free oscillation frequency or inertia,and / or iv”- modeling in a simulation tool a plurality of inertial elements or inertial element blanks (100) in an oscillating mechanism having a predetermined inertia so as to calculate for each inertial element (100) or inertial element blank (100) a free oscillation frequency or an inertia v- providing to the prediction machine, and for each inertial element (100) or inertial element blank (100): the characteristic of the resonance frequency identified in step iii-; the free oscillation frequency or the inertia measured in step iv'- and / or calculated in step iv”-., 18. Learning method according to the preceding claim, in which step iii- comprises a preliminary phase of identifying reference measurement points with: - measuring a displacement of a plurality of predetermined points of the inertial element (100) or of the inertial element blank (100), - identifying nodes among the plurality of predetermined points, which have at least one resonance frequency or peak a displacement amplitude of zero or less than a first threshold peak value, - selecting reference points to be measured during the inspection from among the plurality of predetermined points, which are different from the identified nodes, and which preferably each have a peak displacement amplitude greater than a second threshold peak value.

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