RESTLESSNESS OF A CLOCK

Description

Technical field and state of the art

[0001] The invention relates to a balance wheel of a timepiece and to a method for adjusting the rate of the timepiece. Background of the invention

[0002] In a timepiece, a resonator typically includes a sprung balance. This sprung balance is the true heart of mechanical movements in timepieces, as it regulates the passage of time through its oscillations and is responsible for the precision of such pieces. The oscillation period of a sprung balance depends in particular on the inertia of the balance and the rigidity of the balance spring. This period is affected by numerous secondary phenomena, including variations in the rigidity of the balance spring depending on temperature, variations in air friction on the balance, the existence of an unbalance on the balance, or even play in the pivots of the balance spring's axis.A deviation of around a few seconds per day is generally tolerated for a timepiece equipped with a mechanical movement; however, all the aforementioned secondary phenomena must be scrupulously controlled during the manufacture of the resonator or the casing of the watch movement.

[0003] Traditionally, the inertia and unbalance of the balance wheel are adjusted by removing material through machining during several successive measurement and machining steps in order to tighten the isochronism curves of the resonator as much as possible. However, it has been observed that the rate changes significantly when the movement is cased due to the stresses generated on the movement by casing or due to aerodynamic modifications induced by a closed environment of the case. It is therefore necessary to carry out a final adjustment to precisely adjust the rate of the movement after casing this movement.This latter adjustment can be made in different ways, in particular by adjusting the position of the weights arranged on the balance wheel, by adjusting the active length of the balance spring using a rack system, by removing material from the balance wheel using a laser source or by adding material by projection onto the balance wheel.

[0004] These different ways of making this last adjustment, however, have several drawbacks.

[0005] For example, adjusting the position of the balance weights or the active length of the balance spring is a delicate operation for an operator and difficult to automate. Furthermore, the index system is likely to become deregulated over time, particularly in the event of an impact. Laser ablation of material degrades the aesthetic appearance of the balance wheel and can cause deposits of calcined material in the movement. Finally, adding material by spraying the material in liquid form using an automated process carried out in particular by an Aerosol Jet type printer can cause splashes, resulting from the impact of the material on the balance wheel, which can spread and contaminate the watch movement.

[0006] Document WO2018015071 A1 describes a clock balance in which flared recesses are made to accommodate masses of material. Summary of the invention

[0007] An aim of the invention is therefore to propose a balance wheel of a resonator of the sprung balance type adapted for precise adjustment of the rate of the movement by projection of material and optimized to overcome in particular the problem of splashes which can spread in the movement.

[0008] Another aim of the invention is to propose a method for adjusting a timepiece comprising a resonator equipped with the balance wheel according to the invention.

[0009] For this purpose, the invention relates to a balance of a timepiece comprising an adjustment face provided with at least one recess intended to receive a projected material for carrying out an adjustment of the rate of said timepiece by modifying the inertia and the unbalance of the balance, said recess comprising an opening and a bottom, in this balance: said background being at most partially visible from a position defined above said opening, in particular on a central axis of the opening.

[0010] In other embodiments: the opening is configured in the adjustment face relative to the bottom of said recess making said bottom at most partially visible from said position; the opening comprises an edge defining a surface which is lower or substantially lower than a surface of the bottom of the recess; the recess extends in a direction forming an acute angle with the central axis of the opening; the recess has a vertical cross-section of essentially flared, rectangular or circular shape; the recess has a vertical cross-section of essentially rectangular, square, circular, or trapezoidal shape; the recess comprises an internal wall provided with a bulge extending substantially horizontally or horizontally in whole or in part over a portion of a surface of said wall;balance wheel comprises a rim, a hub intended to be pivotally mounted on a balance shaft, and at least one arm connecting the rim to the hub, the rim of the balance wheel comprising said at least one recess; balance wheel comprises several arms, at least one of which comprises said at least one recess; several recesses are distributed regularly or irregularly around the periphery of the rim, and at least three recesses are distributed regularly around the periphery of the rim, each recess extending along an arc of a circle with an angle varying between 20° and 90°, preferably between 40° and 60°. ;

[0011] The invention also relates to a method for adjusting the rate of a timepiece comprising this balance, the method comprising the following steps: measuring the rate of the timepiece; determining a correction value to be applied to the inertia and / or unbalance of the balance wheel to obtain a corrected rate of said timepiece, and applying a material in one or more recesses arranged on the balance wheel in order to modify the inertia of the balance wheel according to said correction value.

[0012] Advantageously, the application step comprises a sub-step of projecting the material into one or more of these recesses.

[0013] In particular, the projection sub-step comprises a phase of selective projection of the material into one or more of these recesses.

[0014] Advantageously, during the projection sub-step one or more types of material are projected onto the balance.

[0015] Furthermore, the method comprises a step of arranging a watch movement comprising the balance wheel in a case middle of a case of the timepiece.

[0016] The invention also relates to a timepiece comprising such a balance wheel. Summary description of the drawings

[0017] Other features and advantages will become clear from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, in which: there figure 1 is a top view of a balance wheel comprising three recesses, according to one embodiment of the invention; the figure 2 is a top view of the balance wheel comprising four recesses, according to the embodiment of the invention; the figures 3 to 6represent first variants of the recess each comprising a bottom which is at most partially visible from a position defined above an opening of this recess, according to the embodiment of the invention; the figures 7 And 8 represent variants not included in the invention. figures 9 and 10 represent second variants of the recess each comprising a bottom having a gap with an opening of this recess which is greater or substantially greater than the largest geometric dimension of said bottom, according to variants which are not included in the invention as claimed; the figure 11 represents a timepiece comprising such a balance wheel, according to the embodiment of the invention; the figure 12 represents a flowchart relating to a method of adjusting the running of the timepiece, according to the embodiment of the invention, and the figure 13is a top view of the balance comprising two arms and four recesses, according to the embodiment of the invention. Detailed Description of Preferred Embodiments

[0018] In reference to the figures 1 has 10 and 13 , the invention relates to a balance wheel 10 of a resonator 120 of the sprung balance type of a watch movement 110 of a timepiece 100 visible on the figure 11 Such a balance 10 is provided with at least one recess 15 provided to receive a projected material for carrying out an adjustment of the rate of the timepiece 100 and therefore of its movement 110. Such a recess 15 of the balance 10, also called a groove or cavity, is adapted to receive a projection of material during a method of adjusting the rate of this timepiece 100 described below.

[0019] For this purpose on the figures 1, 2 And 13, the balance 10 comprises a felloe 11, a hub 12 intended to be pivotally mounted on a balance staff 16, and one or more arms 13, for example two, three or four arms 13, connecting the felloe 11 to the hub 12. The balance 10 comprises an adjustment face 14 which is flat or substantially flat, and extending in a plane orthogonal to the balance staff 16. This adjustment face 14 is oriented towards the bottom of the case of the timepiece 100 when the balance 10 is included in a timepiece movement 110 which is mounted in this case. This adjustment face 14 comprises a first part 14a included / defined in the felloe 11 of the balance 10 and a second part 14b in the arms 13 of this balance 10.

[0020] As already mentioned, the balance 10 comprises at least one recess 15. Such a recess 15 may be a groove, a cavity or even a concave structure, being provided with an opening 15a, a solid bottom 15b which may have a substantially flat surface as well as an internal wall 15c connecting said opening 15a to said bottom 15b. A solid bottom must be understood here as being a bottom without an opening / orifice. In a variant, this recess 15 may be a through hole, forming a through hole then comprising an opening and a bottom forming / comprising in whole or in part an orifice / opening. The recess 15 can be defined in the rim 11 or one of the arms 13 of the balance 10. When the balance 10 comprises several recesses 15, these can be distributed only in the arms 13 of this balance 10 or only in the rim 11 or in the arms 13 and the rim 11 of this balance 10.Alternatively, when the balance 10 comprises a recess 15, this can be defined in the adjustment face 14 over the entire contour of the felloe 11. This latter configuration makes it possible in particular to ensure adjustment of the rate of the movement by a more effective correction of the unbalance of the balance because in this context the movement is already in a vertical position for the rate measurements, therefore less handling. In addition, the effect of the correction made is accentuated in comparison with a balance whose recess(es) are defined in other parts of the adjustment face 14 of the felloe 11, because in this alternative the deposition of material is carried out as far as possible from the axis of rotation of the balance with, in addition, less material added for the same correction or obtaining a greater correction for the same quantity of material added.

[0021] Such a recess 15 may be produced in the balance 10 using milling and / or deep laser engraving operations. This recess 15 may also be produced during a three-dimensional manufacturing operation of the balance 10 (for example by printing or DRIE engraving, or laser exposure and wet engraving) or of the rim or arms that constitute it, or from an assembly operation of two layers of parts, one of which has a through hole. This assembly operation may use a technique of the “wafer bonding” type or processes of double-sided deep reactive ion etching, ultrasonic welding or pin driving or screwing, etc.

[0022] In examples illustrated on the Figures 1 and 2where recesses 15 are defined only in the part 14a of the adjustment face 14 of the balance 10, that is to say only in the felloe 11, the latter then comprises several openings 15a giving access to an interior volume of the corresponding recesses 15. In this configuration, each recess 15 and therefore each corresponding interior volume, is intended to receive a projection of material in order to modify the inertia of the balance 10. In a non-limiting manner, this projected material may be in the liquid, pasty or solid state and may comprise an adhesive, a paint or a metal suspension. Such a material is in the present embodiment preferably a material in liquid form / state. It will also be noted that this material may be hardenable when exposed for example to a cold source or even to a heat source capable of cooperating with a ventilation device.Alternatively, when this projected material is in the solid state, comprising for example an ink containing silver, tungsten or even tungsten carbide in the form of flakes or pieces, it does not require any particular subsequent treatment after its projection onto the balance 10.

[0023] On figure 1 , the felloe 11 comprises several recesses 15, for example three recesses 15, distributed around the periphery of the felloe 11 defined in the part 14a of the adjustment face 14. Each recess 15 extends along an arc of a circle with an angle of, for example, between 5° and 120° and preferably between 30° and 60°. On the figure 2 , the felloe 11 comprises a multitude of recesses 15, for example four or more recesses 15, which are distributed around the periphery of this felloe 11. These recesses 15 extend along an arc of a circle with an angle of less than 90° and preferably less than 5°.

[0024] In these two embodiments, the recesses 15 can for example be distributed over this periphery of the rim 11 of the balance 10 in a regular manner so as to obtain a symmetrical distribution of the material projected into all the recesses or some of them in order to modify the inertia of the balance 10 without modifying its center of mass during the last adjustment, thus contributing to precisely adjusting the rate of the movement 110. The recesses 15 according to the two aforementioned embodiments can, according to another example, be distributed over the periphery of the rim 11 in an asymmetrical manner in order to modify the inertia of the balance 10 and its center of mass by projection of material into all the asymmetrical recesses or some of them.In another example, the recesses 15 of the balance 10 are distributed symmetrically on the rim 11 of the balance 10 and the material can be projected only into some of these recesses 15 which have an asymmetrical configuration relative to each other.

[0025] Advantageously, the recess 15 has a specific shape so as to contain in its interior volume any splashes resulting from the impact of the material projected against its bottom 15b and thus prevent contamination of the watch movement 110 during a final adjustment necessary to precisely adjust the running of the movement once it has been arranged / driven into a caseband of the timepiece 100.

[0026] The recesses 15 in this balance 10 have a generally concave shape and can be of two types depending on whether they belong to a first or a second variant of recess 15. In the first variant of recess 15 visible on the figures 3 to 6 the bottom 15b of the latter is at most partially visible from a position defined above its opening 15a. The position is here “a point of view” which is arranged above the adjustment face 14 of the balance 10 and preferably on a central axis 17a of the opening 15a visible on the figure 3 This position is similar to that of an outlet orifice of a device intended to project the material into this recess 15. It is therefore understood that the production of such a recess 15 can therefore provide for configuring the opening 15a relative to the corresponding bottom 15b of the recess 15.

[0027] In the variant of the figures 3 to 6, the opening 15a of this recess 15 may comprise an edge defining an access space comprising a surface which is less than or substantially less than a surface of the bottom 15b of the recess 15. In this configuration, the central axes 17a, 17b of the bottom 15b and of the opening 15a and therefore of their respective surfaces, are preferably merged. Thus a more or less large part of the bottom 15b of the recess 15 is then masked by the edge of the opening 15a. In another variant illustrated in the figure 7, the recess 15 extends in a direction 18 forming with the central axis 17a of the opening 15a an acute angle α. In other words, the opening 15a of this recess 15 is arranged in an offset manner relative to the bottom 15b so that this bottom 15b is at most partially visible from the position defined above this opening 15a. In this configuration, the central axes 17a, 17b of the bottom 15b and of the opening 15a and therefore of their respective surfaces, are not merged. In another variant not included in the invention as claimed and visible on the figure 8, the recess 15 comprises an internal wall 15c provided with a bulge 19 extending substantially horizontally or horizontally in whole or in part over a portion of a surface of said wall 15c. This bulge 19 may be integral with the internal wall 15c or be an added part (for example a screw) arranged in the interior volume of the recess 15. It is understood that this bulge 19 is defined to partially conceal / mask the bottom 15b of the recess 15 so that this bottom 15b is at most partially visible from the position defined above this opening 15a.

[0028] In this first variant, the recess 15 has a section of essentially rectangular, square, circular, or even trapezoidal shape. This section, otherwise called vertical cross-section, is included in a vertical transverse plane which is perpendicular to the adjustment face 14 of the balance 10.

[0029] In another variant not included in the invention as claimed and visible on the figures 9 and 10 , the bottom 15b has a gap with said opening 15a which is greater or substantially greater than the largest geometric dimension of its bottom 15b. This gap corresponds to the depth of the recess 15 and the largest geometric dimension can here be a length when this bottom 15b has an essentially rectangular shape or even a diameter if the shape of this bottom 15b is substantially circular. In this variant, the recess 15 has a vertical cross-section of essentially flared, rectangular or even circular shape.

[0030] It should be noted that the shape of the section of these two variants of the recess 15 contributes in particular to: confine any splashes subsequent to the projection of material; geometrically define the position of the deposit of material on the adjustment face 14; improve the aesthetics of the deposit of material on the adjustment face 14; facilitate the adhesion of the deposit of material on the adjustment face 14, independently of the preparation of the adjustment face 14; protect the deposit of material from any tweezers that may occur during handling of the watch movement 110.

[0031] In this context, the recess 15 opens onto the adjustment face 14 of the balance 10, this face 14 being intended to be arranged opposite the back of the case of the timepiece 100 when the watch movement 110 is mounted in this case. According to this arrangement, it is consequently possible to make a final adjustment of the rate of the watch movement 110 when it is mounted in the caseband of the timepiece 100, before the assembly of the back of the case with the caseband, by adjusting the material projection device above the balance 10 while ensuring that the oscillating mass of this timepiece 100 is clear of the resonator of the movement 110 for an automatic type movement. The material projection device may for example be an Aerosol Jet type printer which allows very precise projection with a very small volume of material.

[0032] In reference to the figure 12, the invention also relates to a method for adjusting the rate of the watch movement 110. This method comprises a step 20 of arranging the watch movement 110 comprising the balance 10 in the case middle of the case of the timepiece 100. Subsequently, the method provides a step 21 of measuring the rate of this watch movement 110 thus arranged in the case middle. This measurement can preferably be carried out without contact given that access to the resonator is particularly narrow. In a known manner, the measurement of the rate of the movement can thus be carried out, for example, in optical or acoustic form. This measuring step 21 makes it possible to compare the measured rate with a desired rate. Furthermore, it also makes it possible to know the beat of the balance 10 in order to be able to synchronize it with the projection of material to precisely deposit the material in the recess 15 or in each recess 15 of the balance 10.

[0033] The method then comprises a step 22 of determining the correction value to be applied to the inertia of the balance 10 to obtain a corrected rate. This correction value is determined by the following known formulas: For a balance-spring type resonator, the moment of inertia l of the pendulum responds to the formula: I = mr 2 in which m represents the mass of the pendulum 10 and r its radius of gyration which also depends on the temperature via the coefficient of expansion of the balance 10.

[0034] Furthermore, the elastic torque C of the constant section hairspring responds to the formula: C = Ehe 3 12 L in which E is the Young's modulus of the material used, h its height, e its thickness and L its developed length.

[0035] Finally, the frequency f of the resonator 120 including the sprung balance meets the formula: f = 1 2 π C I

[0036] Then, this method comprises a step 23 of applying the material into one or more recesses of the balance 10 in order to modify the inertia of the balance 10 according to the correction value. The recess(es) 15 may be located either only on the felloe 11 or at least one arm 13, or on the felloe 11 and on one or more arms 13 of the balance 10 or in the contour of the felloe 11 defined in the adjustment face. Such a step 23 comprises a sub-step 24 of projecting the material into one or more recesses of the balance 10. This sub-step 24 makes it possible to avoid any mechanical contact with the balance 10 as part of the rate adjustment.

[0037] It will be noted that this projection sub-step 24 may be preceded by a sub-step of removing the balance 10 from the watch movement 100, for example when this balance 10 comprises one or more recesses 15 corresponding to the through hole. In this context, the projection of material into this through hole is then carried out outside the movement 110 with the use of: of a support applied for example on a face of the balance 10 comprising the bottom of this recess 15 provided with the orifice and / or a projected material having a high viscosity index.

[0038] Since the adjustment of the rate according to this method only allows the increase of the inertia of the balance 10, the balance 10 is manufactured so as to have a mass deficit so that the watch movement 110 has a rate advance which will be corrected during this sub-step 24 of projection of material in all the recesses 15 of this balance 10 or in some of them.

[0039] According to one embodiment, the correction value may correspond to a projection of the material into several recesses 15 of the balance 10 so as to obtain a symmetrical distribution of the projected material in order to modify the inertia of the balance 10 without modifying its center of mass. In this case, the recesses of the balance 10 are distributed symmetrically in particular on the rim 11 of the balance 10 and the quantity of projected material is identical for each recess 15 so as not to create an imbalance.

[0040] According to one embodiment, the correction value is determined by comparing, on the one hand, the measured rate and, on the other hand, the desired unbalance and frequency for the resonator 120. In this case, the correction value corresponds to the asymmetrical distribution of the addition of material by projection in recesses 15 of the balance 10 distributed symmetrically on the rim 11 of the balance 10. Alternatively, the recesses 15 of the balance 10 are distributed symmetrically on the rim 11 of the balance 10 and the material is projected only into some of these recesses 15 which have an asymmetrical configuration relative to each other. In such a context, the projection sub-step 24 comprises a phase of selectively projecting the material into one or more of these recesses 15.

[0041] In addition, it will be noted that during the projection sub-step 24 one or more types of material are projected onto the balance 10. Thus the recesses 15 of the same balance 10 can: comprise the same projected material, or each comprise a projected material different from those of all the other recesses of this balance 10 or of at least one of the other recesses 15 of this balance 10.

[0042] Although the projection sub-step 24 can advantageously be carried out using an Aerosol Jet printer, any other maskless projection or printing technology is also possible. As already discussed, the material deposited in all or some of the recesses 15 may comprise an adhesive, a paint or a metal suspension.

[0043] Preferably, the sub-step 24 of projection of material may be followed by a sub-step 25 of solidification of the projected material, in particular if the material is in the liquid or pasty state. This sub-step 25 may, depending on the material used, consist of evaporating a solvent, thermosetting the material or crosslinking the material in the recess. A polymer may also be deposited in the recess 15 or each recess 15 of the balance 10 and then crosslinked by means of ultraviolet radiation.

Claims

1. Balance (10) of a timepiece (100) comprising an adjustment face (14) provided with at least one recess (15) intended to receive a projected material for adjusting the rate of said timepiece (100) by modifying the inertia and the unbalance of the balance (10), said recess (15) comprising an opening (15a) and a bottom (15b), characterised in that said bottom (15b) is at most partially visible from a defined position above said opening (15a).

2. Balance (10) according to claim 1, characterised in that the opening (15a) is configured in the adjustment face (14) relative to the bottom (15b) of said recess (15) making said bottom (15b) at most partially visible from said position.

3. Balance (10) according to any one of claims 1 and 2, characterised in that the opening (15a) comprises an edge defining a surface area which is smaller than or substantially smaller than a surface area of the bottom (15b) of the recess.

4. Balance (10) according to any one of claims 1 and 2, characterised in that the recess (15) extends in a direction (18) forming an acute angle (α) with the central axis (17a) of the opening (15a).

5. Balance (10) according to any one of claims 1, 2 and 3, characterised in that the recess (15) has a vertical cross-section of essentially rectangular, square, circular or trapezoidal shape.

6. Balance (10) according to any one of claims 1 to 2 and 4, characterised in that the recess (15) comprises an internal wall (15c) provided with a bulge (19) extending substantially horizontally or horizontally in whole or in part over a portion of a surface of said wall (15c).

7. Balance according to any one of the preceding claims, characterised in that it comprises a felloe (11), a hub (12) intended to be mounted so as to pivot about a balance staff (16), and at least one arm (13) connecting the felloe (11) to the hub (12), the felloe (11) of the balance (16) comprising said at least one recess (15).

8. Balance (10) according to any one of the preceding claims, characterised in that it comprises a plurality of arms (13), at least one whereof comprises said at least one recess.

9. Balance (10) according to claim 8, characterised in that a plurality of recesses (15) are distributed in an even or uneven manner around the periphery of the felloe (11).

10. Balance (10) according to any one of claims 7 and 9, characterised in that at least three recesses (15) are evenly distributed around the periphery of the felloe (11), each recess (15) extending along an arc of a circle at an angle varying between 20° and 90°, preferably between 40° and 60°.

11. Method for adjusting the rate of a timepiece (100) comprising a balance (10) according to any one of the preceding claims, the method comprising the following steps of: - measuring (21) the rate of the timepiece; - determining (22) a correction value to be applied to the inertia and / or unbalance of the balance (10) to obtain a corrected rate for said timepiece (100), and - applying (23) a material in one or more recesses arranged in the balance (10) in order to modify the inertia of the balance (10) according to said correction value.

12. Method according to the preceding claim, characterised in that the application step comprises a sub-step (24) of projecting material into one or more of these recesses.

13. Method according to the preceding claim, characterised in that the projection sub-step (24) comprises a phase (26) of selectively projecting material into one or more of these recesses (15).

14. Method according to any one of claims 12 and 13, characterised in that during the projection sub-step (24), one or more types of material are projected onto the balance (10).

15. Method according to any one of claims 11 to 13, characterised in that it comprises a step of arranging (20) a horological movement (110) comprising the balance (10) in a middle of a case of the timepiece (100).

16. Timepiece (100) comprising a balance (10) according to any one of claims 1 to 10.