Method for producing series of timepiece movements

Abstract

A method for manufacturing a series of timepiece movements (1), the method comprising the steps of:-manufacturing a plurality of hairsprings (13); -measuring the stiffness of each of the hairsprings (13) and classifying them according to a plurality of stiffness levels; manufacturing a plurality of balance wheels (11) according to a moment of inertia distribution determined according to the stiffness level of the balance spring (13); -measuring the moment of inertia of each of the balance wheels (11) and classifying them into a plurality of grades by moment of inertia; defining a first set of levels of hairsprings (13) and a second set of levels of hairsprings (13) wherein the levels in each individual set are sequential, the average stiffness of the hairsprings (13) in the second set of levels of hairsprings (13) being greater than the average stiffness of the hairsprings (13) in the first set of levels of hairsprings (13); -pairing each balance spring (13) rank with a corresponding balance wheel (11) rank; assembling a plurality of oscillators (9) of the balance (11)-hairspring (13) type, each oscillator comprising a hairspring (13) and a balance (11) that have been ranked paired; assembling a series of timepiece movements (1), each timepiece movement comprising one of said oscillators (9) of the balance (11)-hairspring (13) type, said oscillator being arranged to be held by an escapement mechanism (7, 15) comprising an escapement wheel (7) driven by a travel gear train (5), and wherein, for an oscillator (9) comprising a hairspring (13) from a second group of levels, the first group of levels of the first group of levels of the first group of levels of the second group of levels of the first group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels of the second group of levels The corresponding movement (1) is arranged such that the torque available at the escapement wheel (7) is less than the torque available at the escapement wheel (7) for a movement incorporating an oscillator (9) comprising a first set of levels of hairsprings (13).

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of watchmaking. More particularly, the present invention relates to a method for manufacturing a series of watch movements. BACKGROUND

[0002] In order to obtain a good oscillation frequency for a balance-spring type oscillator, great care must be taken in terms of the moment of inertia of the balance and the return torque provided by the spring associated therewith. When manufacturing large series of watches, it is economically unfeasible to require an experienced watchmaker to manufacture or modify these two components very precisely for each individual movement, and the industry makes use of equipment applying the "Omega standard" metrology in order to automatically determine the torque of the spring and the moment of inertia of the balance.

[0003] The torque distribution of the springs manufactured in series and the moment of inertia distribution of the balances both follow a roughly Gaussian curve, and each component is classified according to grades according to the torque and the moment of inertia respectively. The number of grades is generally 20, the difference between adjacent grades corresponding to a rate variation of generally 150 seconds per day.

[0004] Springs of the harder grades are matched with balances of the grades having a greater moment of inertia, and vice versa, each balance grade corresponding to a spring grade, so that for the majority of production of components, the difference in oscillation frequency is minimised. This method is described in the book Théorie d'Horlogerie by Reymondin et al, page 146, and is known as "pairing". Furthermore, the document EP3845770 discloses the classification of springs.

[0005] However, it is possible that a certain number of springs do not belong to the grades used, and are either rejected or undergo reworking, for example by adding material to increase the stiffness or removing material to decrease the stiffness, the latter possibility being generally chosen for springs made of non-metallic material (silicon, silicon oxide, etc.), but also for traditional springs made of metal.

[0006] If the number of grades is increased in order to cover a greater portion of the series of spring production, it is indeed possible to pair in terms of oscillation frequency by providing appropriately classified balances, but the amplitude variation between the oscillators comprising the springs of the most rigid grade and the oscillators comprising the springs of the least rigid grade becomes difficult to manage. Generally, for a conventional classification with 20 grades, the amplitude variation will be of the order of 20° to 25°, however, if 20 additional grades are added (each additional grade having 150 S / d), the amplitude variation increases by up to 50° over the entire series, which is not acceptable for a high-quality watch and compromises its timekeeping properties. Furthermore, if the oscillation amplitude becomes too great, the risk of escape increases, and should therefore be avoided.

[0007] It is therefore the object of the present application to propose a method for manufacturing a series of watch movements in which at least some of the above-mentioned drawbacks are overcome, and which makes it possible to use a wider range of hairsprings without requiring rework. SUMMARY

[0008] More particularly, the present application relates to a method for manufacturing a series of watch movements as defined in claim 1. The method comprises the following steps:

[0009] - manufacturing a plurality of hairsprings;

[0010] - measuring the stiffness of each of the hairsprings and classifying them according to a plurality of stiffness classes (also generally in classes of 150 seconds / day);

[0011] - manufacturing a plurality of balances having a determined moment of inertia distribution depending on the stiffness class of the hairsprings, that is to say that at least a portion of the balances can be correctly matched with the hairsprings manufactured and classified into a chosen class of hairsprings;

[0012] - measuring the moment of inertia of each of the balances (11) and classifying them according to a plurality of classes divided by moment of inertia;

[0013] - defining a first group of classes of hairsprings and a second group of classes of hairsprings, in which the classes of hairsprings in each individual group are sequential, the average stiffness (and therefore the return torque) of the hairsprings in the second group of classes of hairsprings being greater than the average stiffness of the hairsprings in the first group of classes of hairsprings;

[0014] - pairing each class of hairsprings with a corresponding class of balances;

[0015] - assembling a plurality of balance-hairspring type oscillators, each oscillator comprising a hairspring and a balance thus paired by class;

[0016] - assembling a series of watch movements, each watch movement comprising one of the balance-hairspring type oscillators, the oscillators being arranged to be kept in oscillation by any type of escapement comprising an escape wheel arranged to be driven by a timekeeping train, in which, for the oscillators comprising a hairspring of the second group of classes, the corresponding movement is arranged so that the torque available at the escapement is lower than the torque available at the escapement for a movement incorporating an oscillator comprising a hairspring of the first group of classes.

[0017] With these devices, the tendency of the oscillation amplitude of the oscillator to increase by compensating the most rigid grades of the hairspring and also, without the need for rework, a greater variation of the torque of the hairspring can be used. This is achieved by reducing the torque available at the escapement during the operation of the movement and this reduces the strength of the impulse provided by the escapement to the balance-hairspring type oscillator and thus brings the oscillation amplitude back within an acceptable range. The loss of production of hairsprings and / or rework of part of the production can be reduced or even eliminated.

[0018] Of course, the same principle can be applied to more than two groups of grades.

[0019] In one variant, said torque available at the escapement is determined by adjusting the output torque of the constant force mechanism included by each movement.

[0020] In another variant, said torque available at the escapement is determined at the barrel, for example by providing main barrels with at least two different powers, the main barrels with the greater power being selected for movements containing hairsprings of the first group of grades and the main barrels with the smaller power being selected for movements containing hairsprings of the second group of grades.

[0021] In yet another variant, said torque available at the escapement is determined according to the form of the teeth of a predetermined element of the going train. For example, two types of said predetermined element can be provided with two forms of teeth arranged to have two different gear efficiencies, one of said predetermined elements with the higher gear efficiency being selected for movements containing hairsprings of the first group of grades and one of said predetermined elements with the lower efficiency being selected for movements containing hairsprings of the second group of grades.

[0022] Advantageously, said two forms of teeth are cut by the same form of tool, the tool being adjusted to cut the teeth with a greater radius to obtain the element with said lower efficiency and to cut the teeth with a smaller radius to obtain the element with said higher efficiency.

[0023] In doing so, the two types of element can be manufactured with the same tool, the only difference being the position of the tool when cutting the relevant teeth.

[0024] Generally, said predetermined element of the going train is a third element, the third wheel being provided with said two different forms of teeth, said third wheel generally meshing with the second pinion. However, the builder is free to select the element and the relevant teeth.

[0025] As regards the distribution of the plurality of sets of grades, in one variant, all the grades of the set of grades of the first set of grades are different from all the grades of the set of grades of the second set of grades: in other words, there is no common grade between the two sets, each grade of the first set being different from each grade of the second set. However, a part of the grades of the first set can also overlap with a part of the grades of the second set, so that some of the grades of the first set of grades correspond to some of the grades of the second set of grades.

[0026] The application also relates to a series of watch movements manufactured according to the method described above and to a watch comprising a movement belonging to said series of movements. BRIEF DESCRIPTION OF DRAWINGS

[0027] Other details of the application will become more clearly apparent on reading the following description, which is given with reference to the attached drawings, in which:

[0028] Figure 1 is a schematic view of a conventional watch movement;

[0029] Figure 2 is a schematic view of a watch movement comprising a constant-force mechanism;

[0030] Figure 3 is a view of the transmission between the third wheel and the second pinion, arranged to provide a greater gear efficiency;

[0031] Figure 4 is a view of the transmission between the third wheel and the second pinion, arranged to provide a gear efficiency lower than that of Figure 4 in figure 1. DETAILED DESCRIPTION

[0032] Figure 1 A conventional watch movement 1 is shown schematically from the side, the toothing being shown by its division circle, and the pivoting axes of the various members being shown by dashed lines.

[0033] The movement comprises a barrel 3 containing a conventional mainspring (not shown), a time train 5 kinematically connecting the barrel 3 to an escapement 7, the escapement 7 supporting an oscillator 9 of the balance 11 hairspring 13 type by means of an anchor 15 cooperating with an impact pin 17 of a roller 19 rotating integrally with said balance 11. Of course, other forms of escapement (for example, a pallet escapement, an Omega-Daniels escapement, etc.) can also be used, and the application is not limited to a particular type of escapement. Furthermore, the form of the balance can also be freely chosen.

[0034] Typically, the inner end of the hairspring 13 is fixed to a collet that rotates integrally with the balance 11, while the outer end is fixed to a rating assembly R, the elements of which are not shown but are well known to those skilled in the art, and serve to fix the outer end of the hairspring 13 and vary its effective length, in order to adjust the rate of the oscillator 9, and thus the rate of the movement, by means of a conventional rating assembly. The present invention is not limited to a particular form of hairspring 13 (spiral or spherical hairspring 13, Breguet hairspring, etc.), nor to a particular material. For example, the hairspring 13 can be manufactured from a conventional metal, a metallic glass (amorphous metal), silicon, silicon oxide, synthetic diamond, alumina, ceramic, ceramic glass, or any other material known to those skilled in the art, by any method suitable for the relevant material (rolling and winding, sintering in a mould, additive manufacturing, LIGA, cutting from a sheet by laser or etching, etc.).

[0035] The going train 5 can take any known form, and in this case takes a conventional construction comprising a second mobile 23 (or, alternatively, a central mobile, where appropriate) which is engaged by a second pinion with the barrel 3 and by a second wheel with a pinion of a third mobile 25, the third wheel 25a of which is in turn engaged with a seconds pinion 27a of a seconds mobile 27, the seconds wheel of which is engaged with an escape pinion of the escapement mobile 7. Of course, the speed of rotation and the number of mobiles can be determined according to the choice of the constructor.

[0036] In order to make the natural frequency of the oscillator 9 sufficiently close to the desired frequency, such that only the rating assembly needs to be adjusted to tune the movement, production series of hairsprings 13 and balances 11 are produced, and classified by grade of stiffness and moment of inertia respectively (for example according to the Omega scale), the balances 11 being manufactured with a distribution of moments of inertia that is adapted to the distribution of stiffness of the hairsprings 13. Typically, this method classifies the hairsprings 13 and balances 11 in 20 grades, which means a rate difference of 150 seconds per day (s / d) from one grade to the adjacent grade, the pairs being made between these grades in order to put together a hairspring 13 that tends to cause a rate gain (i.e. a stiffer hairspring 13) with a balance 11 that tends to cause a rate loss (i.e. a balance 11 with a greater moment of inertia), and vice versa, in order to obtain an oscillator 9 that can be correctly adjusted by the rating assembly. For a certified movement, the difference in amplitude of oscillation of an oscillator 9 comprising a first class of hairspring 13 is of the order of 20° to 25° with respect to an oscillator 9 comprising a twentieth class of hairspring 13, that is to say ±12.5° around the average amplitude of the series of oscillators 9. Of course, different amplitude deviations are possible, and the figures are given by way of example only.

[0037] In the case of a mass production series, there can be a large number of hairsprings 13 falling outside the classification according to twenty grades (each grade having 150 s / d) or, where appropriate, classified by different bands. In order to minimize production losses, as many of these hairsprings 13 as possible are generally reworked by various means in order to bring them to fall within the grades used and to minimize production losses. For hairsprings 13 that are not rigid enough and that return insufficient torque, it is possible to add material by inkjet printing or by vacuum deposition, ion implantation to increase the shear modulus. In the case of hairsprings 13 that are too rigid, the typical solution is to remove material by laser.

[0038] In order to avoid or minimize reworking, it is possible in principle to simply increase the number of grades of hairsprings 13 and to manufacture corresponding balance wheels 11 in order to be able to match them and thus obtain a suitable natural oscillation frequency. However, this approach increases the variation in amplitude and, for forty grades (each having 150 s / d), this variation can increase by up to 50° in total (that is to say, up to ± 25° around the average amplitude of the series of oscillators). This is not acceptable in terms of chronometric properties and can even increase the risk of tripping if the oscillation amplitude becomes too high.

[0039] The solution of the invention is as follows. The number of grades of hairsprings 13 is increased and this number of grades is divided into two groups, the first group having a lower average stiffness and the second group having a greater average stiffness.

[0040] The set of grades in the two groups can be continuous, that is to say representing only one distribution (generally Gaussian) of hairsprings 13, or can represent two distributions (again generally Gaussian) by means of manufacturing operations for the two such distributions. In the latter case, some of the lower grades of the second group will correspond to some of the higher grades of the first group, that is to say, there will be an overlap between the grades of the two groups.

[0041] The balance wheels 11 are manufactured and classified by moment of inertia in the same way, so that the number of different grades of balance wheels 11 corresponds to the number of different grades of hairsprings 13 in order to be able to implement the pairing of each so-classified hairspring 13. For example, if the hairsprings 13 are classified according to two different groups of 20 grades per group, 40 grades of balance wheels will be manufactured and used. However, if, for example, 5 of the higher grades of the first group correspond to 5 of the lower grades of the second group, the number of different grades of balance wheels will be 35 due to the 5 grades overlapping between the two groups.

[0042] Since the hairsprings of the second group are stiffer and thus provide a greater torque than the hairsprings of the first group, at least on average (if not absolutely in the case where there is no overlap between the grades of the two groups), the oscillation amplitude will be greater to the same extent (where appropriate, on average or absolutely).

[0043] By obtaining a first predetermined torque at the escapement, the overall design of the movement 1 is such as to obtain a good average amplitude of the first set of hairsprings 13 (for example 280° in the DU position with the main barrel fully wound). Of course, this predetermined torque will be affected by standard manufacturing variations and can vary depending on the winding state of the main barrel housed in the barrel 3, as will be understood by the person skilled in the art.

[0044] With respect to the movement 1 adapted to use the first set of hairsprings 13, the torque available at the escapement is reduced for the second set of hairsprings 13. This reduction in torque with respect to the design of the first set of hairsprings 13 can be obtained in various ways, as will be made clearer below, and serves to reduce the oscillation amplitude of the oscillator 9 and return it to a normal and acceptable range, even if the hairsprings are stiffer and provide a greater torque than usual. Indeed, the reduction in torque at the escapement means a reduction in the force of the impulses provided to the oscillator 9 by means of the escapement mechanism and therefore a reduction in the amplitude.

[0045] By means of these devices, and considering the conventional classification into 20 grades (each with 150 s / d), it is possible to use up to twice as many grades of hairsprings 13, that is to say 40 unique grades (each with 150 s / d), by simply adjusting the torque available on the escapement. Of course, even more groups of grades can be provided and the variation in stiffness of the hairsprings 13 that can be accommodated can be further increased, the present invention not being limited to two groups.

[0046] A first way of obtaining this variation in torque at the escapement 7 is to provide an adjustable constant force mechanism 29 within the movement 1, as shown in Figure 2 In this arrangement, the adjustable constant force mechanism 29 is shown schematically as being kinematically located in the going train 5 between the barrel 3 and the cannon pinion 23, but in an alternative it can be arranged between any two of the going train 5, or integrated into any of the going train, or even integrated into the barrel or the escapement.

[0047] By adjusting the output torque of the constant force mechanism 29 according to the grade group to which the hairsprings 13 assembled in the movement 1 belong, it is possible to adjust the torque available at the escapement 7 in order to obtain an oscillation amplitude within an acceptable range (for example 280° ± 12.5° in the DU position with the main barrel fully wound).

[0048] The details of the adjustable constant force mechanism 29 are not essential to the invention, non-limiting examples of such mechanisms are disclosed in documents CH716126, EP3182217 and EP2166419. Of course, to the best of the Applicant's knowledge, until now no use of such mechanisms has been proposed to be able to adapt greater variations in the stiffness of the hairsprings 13 during series production.

[0049] Another way to obtain this reduced torque at the escapement 7 is at the barrel 3, for example by providing two types of mainsprings, one with a higher average power (and therefore a higher average torque) to be used in combination with the first group of hairsprings 13, the other with a lower average power (and therefore a lower average torque) to be used in combination with the second group of hairsprings 13, so as to obtain substantially the same amplitude distribution (in terms of average amplitude and total amplitude deviation for each group, for example 280° ± 12.5° at the DU position with the mainspring fully wound) for the oscillator 9 comprising the two groups of hairsprings 13.

[0050] When manufacturing large series of parts, perhaps the most advantageous way is to vary the gear efficiency of the going train 5. This can be achieved in an effective way by varying the profile of the teeth of one of the wheels or of one of the pinions. To this end, two types of specific elements 23, 25, 27 can be provided, the first type comprising a wheel or a pinion with "normal" teeth, the second type comprising a wheel or a pinion with "modified" teeth, in which the profile of the wheel or pinion has been predetermined to produce a reduction in the gear efficiency with respect to the "normal" teeth.

[0051] Although it is possible to modify the form of the teeth of any toothed member (wheel or pinion) of the going train, experiments have shown that the modification of the third wheel 25a (or more generally of the wheel of the second element upstream kinematically of the escapement) optimizes the effect of the modified teeth in a manageable way.

[0052] Figure 3 The interaction between the "normal" teeth of the third wheel 25a and the seconds pinion 27a is shown, which for this transmission obtains an average efficiency of 93.93% (calculated) and a total efficiency of 69% for the going train 5.

[0053] Figure 4The same interaction between the "modified" toothing of the third wheel 25a and the seconds pinion 27a is shown, which obtains an average efficiency of 92.18% (calculated) for the transmission and a total efficiency of 67% for the going train 5. Experiments have shown that this difference is sufficient to reduce the average amplitude of the oscillator 9 comprising the second group of hairsprings 13, providing substantially the same average amplitude and the same amplitude deviation range of the oscillator 9 comprising the first group of 20 steps of hairsprings 13, each step having 150 s / d, with no overlap between the groups. Thus, in the case of a fully wound barrel, an entire production series of 40 steps (each step having 150 s / d) of hairsprings 13 can fall within the same distribution of amplitudes of the oscillator 9, for example 280° ± 12.5°.

[0054] Although it is possible to completely redesign the form of the toothing of the modified toothed members, in the example given in Figure 3 and Figure 4 the only difference in the manufacturing process is the tool offset for the third wheel 25a, which is used to make the contact path towards the axis of the seconds pinion 27a (as shown by the scale in the figures) by adjusting the tool to perform a slightly shallower cut of the order of 30 pm on the shown wheel 25a, so as to increase its diameter. This minimal difference and the use of the same tool for both types of mobiles is extremely efficient and economical in terms of production.

[0055] Thus, in the present example, two types of third mobiles 25 are manufactured, more generally two types of mobiles 23, 25, 27 modified for the oscillator comprising the second group of hairsprings, and during the assembly of the movement 1, the first "normal" type of mobiles 23, 25, 27 is used in combination with the oscillator comprising the first group of hairsprings, and the second "modified" type is used in combination with the oscillator comprising the second group of hairsprings. In the case of more than two groups of steps, the number of types of mobiles 23, 25, 27 is adjusted accordingly.

[0056] During the assembly of the movement, since the only difference consists in selecting from the two mobiles according to the group of steps to which the hairsprings 13 of the oscillator 9 belong, this solution is very economical, does not require additional components (such as a constant force mechanism) and is easier to manage than providing two different barrels.

[0057] Although the application has been described in relation to particular embodiments, modifications are possible without departing from the scope defined by the appended claims.

Claims

1. A method for manufacturing a series of watch movements (1), the method comprising the steps of: - manufacturing a plurality of hairsprings (13); - measuring the stiffness of each of the hairsprings (13) and classifying them according to a plurality of stiffness classes; - manufacturing a plurality of balances (11) according to a determined moment of inertia distribution depending on the stiffness classes of the hairsprings (13); - measuring the moment of inertia of each of the balances (11) and classifying them according to a plurality of classes divided by moment of inertia; - defining a first group of hairspring (13) classes and a second group of hairspring (13) classes, wherein the classes in each individual group are sequential, the average stiffness of the hairsprings (13) in the second group of hairspring (13) classes being greater than the average stiffness of the hairsprings (13) in the first group of hairspring (13) classes; - pairing each hairspring (13) class with a corresponding balance (11) class; - assembling a plurality of balance (11) - hairspring (13) type oscillators (9), each oscillator comprising a hairspring (13) and a balance (11) paired by class; - assembling a series of watch movements (1), each watch movement comprising one of the balance (11) - hairspring (13) type oscillators (9), the oscillator being arranged to be supported by an escapement (7, 15) comprising an escapement wheel (7) driven by a time wheel train (5), wherein for the oscillators (9) comprising hairsprings (13) of the second group of classes, the corresponding movement (1) is arranged so that the torque available at the escapement (7) is lower than the torque available at the escapement (7) for a movement incorporating an oscillator (9) comprising hairsprings (13) of the first group of classes.

2. The method of claim 1, wherein, The torque available at the escapement (7) is determined by adjusting the output torque of a constant force mechanism (29) comprised by the movement (1).

3. The method of claim 1, wherein, The torque available at the escapement is determined at the barrel (3).

4. The method according to the preceding claim, wherein, The torque available at the escapement (7) is determined by providing a main barrel with at least two different powers, the more powerful main barrel being selected for movements incorporating hairsprings (13) of the first group of classes and the less powerful main barrel being selected for movements incorporating hairsprings (13) of the second group of classes.

5. The method of claim 1, wherein, The torque available at the escapement (7) is determined according to the form of the toothing of a predetermined element (23; 25; 27) of the time wheel train (5).

6. The method according to the preceding claim, wherein, The torque available at the escapement is determined by providing two types of the predetermined element (23; 25; 27) with two forms of toothing arranged to have two different gear efficiencies, one of the predetermined elements having the higher gear efficiency being selected for movements incorporating hairsprings (13) of the first group of classes and one of the predetermined elements having the lower efficiency being selected for movements incorporating hairsprings (13) of the second group of classes.

7. The method according to the preceding claim, wherein, Said two toothing forms are obtained by cutting of the same form, said tool being adjusted to cut the toothing with a greater radius to obtain the mobile with said lower efficiency and to cut the toothing with a smaller radius to obtain the mobile with said higher efficiency.

8. The method according to one of claims 5 to 7, wherein, Said predetermined mobile of said chronograph train is a third mobile (25).

9. The method according to the preceding claim, wherein, Said two different toothing are provided for a third wheel (25a) comprised by said third mobile (25).

10. The method according to one of the preceding claims, wherein, All the steps of the first set of steps are different from said steps of the second set of steps.

11. The method according to one of claims 1 to 9, wherein, Some steps of said first set of steps correspond to some steps of said second set of steps.

12. A series of timepiece movements (1) manufactured according to one of the preceding claims.

13. A timepiece comprising a timepiece movement (1) belonging to the series of movements according to claim 12.

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