A series of watch movement manufacturing methods

Abstract

A method for manufacturing a series of timepiece movements is provided, the method comprising the steps of: manufacturing a plurality of balance springs, measuring the stiffness of each of the balance springs and classifying the balance springs according to a plurality of stiffness classes, manufacturing a plurality of balance wheels according to a determined moment of inertia distribution depending on the stiffness classes of the balance springs, measuring the moment of inertia of each of the balance wheels and classifying the balance wheels according to a plurality of classes for each moment of inertia, defining a first group of classes of balance springs and a second group of classes of balance springs, the classes of each individual group being consecutive, and the average stiffness of the balance springs of the second group of classes of balance springs being higher than the average stiffness of the balance springs of the first group of classes of balance springs; The method includes the steps of pairing a class with a corresponding class of balance, assembling a plurality of balance-hairspring oscillators including balance springs and balance wheels paired by class, and assembling a series of timepiece movements each including one of the balance-hairspring oscillators, the balance-hairspring oscillators being configured to be maintained in oscillation by an escapement including an escapement wheel driven by a gear train, and for oscillators including balance springs of the second class group, the corresponding movement is configured so that the torque available at the escapement wheel is lower than the torque available at the escapement wheel for a movement incorporating an oscillator including balance springs of the first class group.

Description

[Technical Field]

[0001] The present invention relates to the field of watchmaking, and more particularly to a method for manufacturing a series of watch movements. [Background technology]

[0002] To obtain a good vibration frequency for the balance-hairspring oscillator, careful consideration must be given to the balance's moment of inertia and the restoring torque generated by the associated hairspring. Because it is economically impractical to require a skilled watchmaker to manufacture or adjust these two components very precisely for each individual movement when mass-producing watches, the industry uses devices that apply the "Omega-Metric" method to automatically determine the hairspring torque and the balance's moment of inertia.

[0003] The torque distribution of mass-produced hairsprings and the distribution of the moment of inertia of the balance wheel each roughly follow a Gaussian distribution, and each component is classified into classes according to its torque and moment of inertia. There are typically 20 classes, and the difference between adjacent classes typically corresponds to a rate difference of 150 seconds per day.

[0004] A hairspring of a more rigid class is paired with a balance wheel of a class having a larger moment of inertia, and conversely, a hairspring of a less rigid class is paired with a balance wheel of a class having a smaller moment of inertia. Each class of balance wheel is associated with a corresponding hairspring class, minimizing the difference in vibration frequency in the production of the majority of components. This method is described in Non-Patent Document 1 and is called "pairing." Patent Document 1 further discloses the classification of hairsprings.

[0005] However, there may be a certain number of balance springs that do not belong to the class used, and these are either discarded or subjected to reworking. Reworking involves, for example, adding material to increase stiffness or removing material to decrease stiffness. The latter method is typically chosen for balance springs made of non-metallic materials (silicon, silicon oxide, etc.), but is also applicable to conventional balance springs made of metal.

[0006] If the number of classes were increased to cover a larger range of balance spring production series, pairing based on oscillation frequency would be possible with appropriately classified balances. However, the amplitude difference between the oscillator containing the stiffest balance spring class and the oscillator containing the least stiff balance spring class would exceed the acceptable range. Typically, the amplitude difference is approximately 20° to 25° in the traditional 20-class classification. However, adding 20 classes with a daily deviation of 150 seconds would result in an amplitude difference of 50° for the entire series, which is unacceptable for a high-quality watch and would impair its chronometric characteristics. Furthermore, excessive oscillation amplitude increases the risk of skipping (tripping), which must also be avoided.

[0007] It is therefore an object of the present invention to provide a method for manufacturing a series of timepiece movements which overcomes at least some of the above-mentioned drawbacks and allows a wider range of balance springs to be used without the need for reworking. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 3845770 [Non-patent literature]

[0009] [Non-Patent Document 1] Theorie d'Horlogerie [The Theory of Horology], Reymondin et al, page 146 Summary of the Invention

[0010] More specifically, the invention relates to a method for manufacturing a series of timepiece movements as defined by claim 1. The method comprises the following steps:

[0011] - manufacturing a plurality of balance springs.

[0012] - measuring the stiffness of each of said balance springs and classifying said balance springs according to a number of stiffness classes (typically based on a deviation of 150 seconds per day).

[0013] - manufacturing a plurality of balances with a determined distribution of the moment of inertia depending on the stiffness class of the balance spring, i.e. manufacturing balances at least some of which can be properly combined with the balance spring manufactured and classified into the selected class of balance spring.

[0014] - measuring the moment of inertia of each of said balances and classifying said balances according to a number of classes according to their moment of inertia.

[0015] - defining a first class group of hairsprings and a second class group of hairsprings, the classes of each individual group being consecutive, and the average stiffness (and therefore the restoring torque) of the hairsprings of the second class group of hairsprings being higher than the average stiffness of the hairsprings of the first class group of hairsprings.

[0016] - Pairing each hairspring class with the corresponding balance wheel class.

[0017] - assembling a plurality of balance-hairspring oscillators each including a hairspring and a balance paired by class.

[0018] - assembling a series of timepiece movements each including one of said plurality of balance-hairspring oscillators configured to be maintained in oscillation by any type of escapement including an escapement wheel configured to be driven by a wheel train, wherein for said movements including oscillators with hairsprings of the second class group, said corresponding movements are configured so that the torque available at the escapement wheel is lower than the torque available at the escapement wheel for movements incorporating oscillators with hairsprings of the first class group.

[0019] In this way, by compensating for the tendency of the stiffest balance springs to increase the oscillator's oscillation amplitude, a greater range of balance-hairspring torque variation can be utilized without the need for reworking. This is achieved by reducing the torque available to the escapement wheel while the movement is running, which reduces the intensity of the shock the escapement imparts to the balance-hairspring oscillator, thus bringing the oscillation amplitude back within an acceptable range. This can reduce or completely eliminate losses in the manufacture of the balance spring and / or the reworking of parts of the product.

[0020] Of course, the same principles can be applied to groups of more than two classes.

[0021] In one variant, the torque available to the escapement wheel is determined by adjusting the output torque of a constant force mechanism included in each movement.

[0022] In another variant, the torque available to the escapement wheel is determined by the barrel, for example by providing springs with at least two different outputs, the more powerful spring being selected for movements including balance springs of a first class and the less powerful spring being selected for movements including balance springs of a second class.

[0023] In yet another variation, the torque available to the escapement wheel is determined based on the tooth profile configuration of predetermined wheels of the going train. For example, two predetermined wheels with different tooth profile configurations configured to have two different gear efficiencies can be provided. The predetermined wheel with the higher gear efficiency is selected for movements including balance springs of a first class family, and the predetermined wheel with the lower efficiency is selected for movements including balance springs of a second class family.

[0024] Preferably, the two tooth forms are cut by the same cutting tool, and the cutting tool is adjusted to cut the tooth form with a larger radius to obtain the wheel with the lower efficiency and to cut the tooth form with a smaller radius to obtain the wheel with the higher efficiency.

[0025] This allows two different cars to be made with the same tooling, the only difference being the position of the cutting tool when cutting the relevant tooth profile.

[0026] Typically, the predetermined wheel of the train is a third wheel, and the two different tooth profiles are provided on the third wheel, which typically meshes with the seconds hand pinion, although the designer is free to choose the wheel and associated tooth profile.

[0027] Regarding the distribution of the class group, in one variation, all of the classes in the first class group are different from all of the classes in the second class group. In other words, there are no common classes between the two groups, and each class in the first class group is different from each class in the second class group. However, some classes in the first class group may overlap with some classes in the second class group, and some classes in the first class group may correspond to some classes in the second class group.

[0028] The invention also relates to a series of timepiece movements manufactured according to the method described above, and to a timepiece including a movement belonging to said series of movements. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a conventional clock movement. [Figure 2] 1 is a schematic diagram of a clock movement incorporating a constant force mechanism. [Figure 3] FIG. 10 is a diagram of the gearing between the third wheel and the seconds hand pinion configured to provide higher gear efficiency. [Figure 4] FIG. 4 is a diagram of a gearing between the third wheel and the seconds hand pinion configured to provide a lower gear efficiency than FIG. 3 . DETAILED DESCRIPTION OF THE INVENTION

[0030] Other details of the invention will become clearer from the following description, taken in conjunction with the accompanying drawings.

[0031] 1 shows a schematic side view of a conventional timepiece movement 1. The tooth profiles are shown by their reference circles and the pivot axes of the various parts are shown by dashed lines.

[0032] The movement includes a barrel 3 containing a conventional mainspring (not shown) and a gear train 5 kinematically connecting the barrel 3 to an escapement wheel 7. The escapement wheel 7 supports an oscillator 9 consisting of a balance 11 and a balance spring 13 by means of a pallet 15. The pallet 15 cooperates with an impulse pin 17 of a roller 19 that rotates integrally with said balance 11. Naturally, other forms of escapement (e.g., detent escapement, Omega-Daniel escapement, etc.) can also be used, and the invention is not limited to any particular type of escapement. Furthermore, the form of the balance can also be freely selected.

[0033] Conventionally, the inner end of the balance spring 13 is fixed to a collet that rotates integrally with the balance 11, and the outer end is fixed to a regulator assembly R. Elements of the regulator assembly R are not shown but are well known to those skilled in the art. By fixing the outer end of the balance spring 13 and varying its effective length, the regulator assembly controls the rate of the oscillator 9 and, therefore, the rate of the movement. The present invention is not limited to a specific shape of the balance spring 13, and encompasses spiral or spherical balance springs 13, Breguet balance springs, and the like, and is not limited to a specific material. For example, the balance spring 13 can be made of conventional metals, metallic glasses (amorphous metals), silicon, silicon oxide, synthetic diamond, aluminum oxide, ceramics, ceramic glass, or any other material known to those skilled in the art. It can be manufactured by any manufacturing method suitable for the material, such as rolling and winding, in-mold sintering, additive manufacturing, LIGA, cutting from a plate by laser machining or etching, etc.

[0034] The wheel train 5 may take any known form, but in this embodiment employs a conventional structure and includes a second wheel 23 (and possibly a central wheel). The second wheel 23 meshes with the barrel 3 via a second pinion and with the pinion of a third wheel 25 via a second wheel. A third wheel 25a of the third wheel 25 meshes with a second hand pinion 27a of a second hand wheel 27, and the second hand wheel of the second hand wheel 27 meshes with the escapement pinion of the escapement wheel 7. Naturally, the rotation speed and the number of wheels can be determined at the discretion of the designer.

[0035] To ensure that the natural frequency of the oscillator 9 is close enough to the desired frequency so that the movement can be controlled simply by adjusting the regulator assembly, a production series of hairsprings 13 and balance wheels 11 are produced and classified into stiffness classes and moment of inertia classes, respectively. For example, this is done according to the Omega-Metric method, where the balance wheels 11 are manufactured to target a moment of inertia distribution that matches the stiffness distribution of the hairspring 13. Typically, this method classifies hairsprings 13 and balance wheels 11 into 20 classes, with a daily deviation difference of 150 seconds between adjacent classes. The classes are paired by pairing hairsprings 13 that tend to be ahead of the rate (i.e., stiffer hairsprings 13) with balance wheels 11 that tend to be behind the rate (i.e., balance wheels 11 with a larger moment of inertia), and vice versa, to obtain an oscillator 9 that can be appropriately controlled by the regulator assembly. In movements that qualify for certification, the difference in vibration amplitude between an oscillator 9 including a hairspring 13 of class 1 and an oscillator 9 including a hairspring 13 of class 20 is generally in the range of 20° to 25°, i.e., approximately ±12.5° around the average amplitude of the set of oscillators 9. Naturally, the amplitude deviation can be set to a different value, and the values ​​shown here are merely examples.

[0036] In mass production, a significant number of hairsprings 13 may deviate from the 20-class classification of 150 seconds per day (or classification into different bands as appropriate). To minimize production loss, as many of these hairsprings 13 as possible are reworked, typically by various means, to fit within the class in use. Hairsprings 13 that are not rigid enough and have insufficient restoring torque may be treated to improve the shear modulus by adding material using inkjet printing, vacuum deposition, ion implantation, or the like. Conversely, hairsprings 13 that are too rigid are typically resolved by laser material removal.

[0037] In theory, to avoid or minimize reworking, it would be possible to simply increase the number of classes of hairspring 13 and manufacture and combine them with the corresponding balance 11 to obtain the appropriate natural oscillation frequency. However, this approach would result in larger amplitude fluctuations. For example, in the case of 40 classes with a daily deviation of 150 seconds, the amplitude fluctuations would reach a total of 50° (i.e., ±25° around the mean amplitude of the series of oscillators). This is unacceptable from the perspective of chronometric performance, and excessive oscillation amplitudes would also increase the risk of the pallet skipping (tripping).

[0038] The solution of the present invention is as follows: increase the number of classes of hairsprings 13 and divide these classes into two groups, the first group having a low average stiffness and the second group having a high average stiffness.

[0039] The collection of classes in the two groups may be contiguous, i.e., represent a single (typically Gaussian) distribution of the balance spring 13, or may represent two such distributions (also typically Gaussian) by targeting them through a manufacturing process, in which case some of the lower classes in the second group correspond to some of the higher classes in the first group, i.e., there will be an overlap between the classes in the two groups.

[0040] The balance wheels 11 are manufactured and classified by moment of inertia in a similar manner, with the number of distinct classes of balance wheels 11 set to correspond to the number of distinct classes of hairsprings 13. This allows them to be appropriately paired with each of the thus-classified hairsprings 13. For example, if the hairsprings 13 are classified into two distinct groups of 20 classes each, 40 classes of balance wheels are manufactured and used. However, if, for example, the top five classes of the first group correspond to the bottom five classes of the second group, there will be an overlap of five classes between the two groups, resulting in a total of 35 distinct classes of balance wheels.

[0041] The second group of hairsprings, being stiffer, will generate more torque than the first group of hairsprings, and therefore will have at least on average (average, not absolute, if there is no overlap between the classes of the two groups) and equally large oscillation amplitudes (average, or, where applicable, absolute).

[0042] The general design of the movement 1 is calculated to obtain a first predetermined torque at the escapement wheel in order to obtain a good average amplitude for the first group of hairsprings 13 (e.g., 280° in the DU position when the spring is fully wound). This predetermined torque is of course subject to standard manufacturing tolerances, as will be understood by those skilled in the art, and may vary depending on the state of winding of the spring housed in the barrel 3.

[0043] For the second group of hairsprings 13, the torque available at the escapement wheel is reduced compared to a movement 1 adapted to use the first group of hairsprings 13. This torque reduction for the design of the first group of hairsprings 13 can be achieved by various means, which will be described below. This allows the oscillation amplitude of the oscillator 9 to be reduced and kept within normal and acceptable limits, even if the hairspring is stiffer than usual and generates a greater torque. In other words, reducing the torque at the escapement wheel means reducing the impulse force imparted by the escapement to the oscillator 9, which results in a reduced amplitude.

[0044] These measures allow the number of classes of the hairspring 13 to be doubled at most, i.e., to 40 specific classes of 150 seconds per day, simply by adjusting the torque available in the escapement wheel, even assuming the conventional classification of 20 classes of 150 seconds per day. Naturally, the invention is not limited to two classes, as it is possible to set up even more classes and further expand the range of variation in the stiffness of the hairspring 13 that can be accommodated.

[0045] A first way to obtain this variation of torque in the escapement wheel 7 is to provide an adjustable constant force mechanism 29 in the movement 1, as shown in Figure 2. In this configuration, this adjustable constant force mechanism 29 is shown schematically as being kinematically located in the gear train 5 between the barrel 3 and the hour wheel 23, but it could alternatively be arranged between any two wheels of the gear train 5, or it could be integrated into any wheel of the gear train and even incorporated into the barrel or escapement wheel.

[0046] By adjusting the output torque of the constant force mechanism 29 according to the class group to which the balance spring 13 incorporated in the movement 1 belongs, the torque available to the escapement wheel 7 can be controlled to obtain an oscillation amplitude within an acceptable range (for example, the aforementioned 280°±12.5° at the DU position when the spring is fully wound).

[0047] The details of the adjustable constant force mechanism 29 are not critical to the present invention, and non-limiting examples of such mechanisms are disclosed in CH 716126, EP 3182217 and EP 2166419. Naturally, to the applicant's knowledge, the use of such a mechanism to accommodate larger variations in the stiffness of the balance spring 13 during series production has not previously been proposed.

[0048] Another way to obtain this reduced torque in the escapement wheel 7 is to provide two types of springs in the barrel 3, for example a spring with a higher average power (and therefore average torque) for use in combination with the first group of hairsprings 13, and a spring with a lower average power (and therefore average torque) for use in combination with the second group of hairsprings 13. For an oscillator 9 including the two classes of hairsprings 13, it is possible to obtain a substantially identical amplitude distribution (for example the aforementioned 280°±12.5° in the DU position when the spring is fully wound, in terms of the average amplitude and total amplitude deviation of each group).

[0049] When mass-producing watches, the most advantageous method is to vary the gearing efficiency of the going train 5. This can be effectively achieved by changing the tooth profile of one of the wheels or one of the pinions. For this purpose, it is possible to provide two types of specific wheels 23, 25, 27: a first type containing wheels or pinions with a "normal" tooth profile, and a second type containing wheels or pinions with an "altered" tooth profile. The profile of the "altered" tooth profile wheel or pinion is predetermined to reduce the gearing efficiency compared to the "normal" tooth profile.

[0050] While it is possible to modify the tooth profile configuration of any toothed member of the gear train (wheel or pinion), experimentation has shown that modifying the third wheel 25a (or more generally the wheel of the second wheel kinematically upstream of the escapement wheel) optimizes the effect of the modified tooth profile in a manageable manner.

[0051] FIG. 3 shows the interaction between the "normal" tooth profile of the third wheel 25a and the seconds hand pinion 27a, with a calculated average efficiency of 93.93% and a total efficiency of the gear train 5 of 69%.

[0052] Figure 4 shows the same interaction between the "modified" tooth profile of the third wheel 25a and the seconds hand pinion 27a. This gearing has a calculated average efficiency of 92.18% and a total efficiency of 67% for the gear train 5. Experiments have shown that this difference sufficiently reduces the average amplitude of the oscillator 9, including the second group of hairsprings 13, resulting in a mean amplitude and amplitude deviation range (total) of 20° to 25°, essentially identical to that of the oscillator 9, including the first group of 20 hairsprings 13, each with a daily deviation of 150 seconds. Note that there is no overlap between groups. Therefore, the entire production series of 40 hairsprings 13, each with a daily deviation of 150 seconds, can fall within the same amplitude distribution of the oscillator 9, for example, a range of 280° ± 12.5° at the fully wound DU position.

[0053] While it would be possible to completely redesign the tooth profile configuration of the modified toothed member, in the example shown in Figures 3 and 4, the only difference in manufacturing is the offset of the cutting tool for the third wheel 25a, which brings the contact path closer to the axis of the seconds hand pinion 27a (as indicated by the scale of these figures). This offset adjusts the tool to make a slightly shallower cut of about 30 μm for the wheel 25a shown, thereby increasing its diameter. From a production standpoint, the minimal difference and the ability to use the same tool for both types of car makes this extremely efficient and economical to implement.

[0054] Thus, in this embodiment, two types of third wheels 25, more generally wheels 23, 25, 27, are manufactured that are modified for oscillators with balance springs of the second group. When assembling the movement 1, a first "normal" type of these wheels 23, 25, 27 is used in combination with oscillators with balance springs of the first group, and a second "modified" type is used in combination with oscillators with balance springs of the second group. If there are more than two class groups, the number of types of wheels 23, 25, 27 is set accordingly.

[0055] Since the only difference when assembling the movement is to select one of the two wheels depending on the class group to which the balance spring 13 of the oscillator 9 belongs, this solution is extremely economical, does not require any additional components (such as a constant force mechanism) and is easier to manage than having two different springs.

[0056] Although the present invention has been described with reference to specific embodiments, various modifications are possible without departing from the scope defined by the appended claims.

Claims

1. A method for manufacturing a series of timepiece movements (1), comprising: - manufacturing a number of balance springs (13), - measuring the stiffness of each of said balance springs (13) and classifying said balance springs (13) according to a number of stiffness classes; - manufacturing a plurality of balances (11) according to the determined distribution of the moment of inertia depending on the stiffness class of the balance spring (13); - measuring the moment of inertia of each of said balances (11) and classifying said balances (11) according to a number of classes according to their moment of inertia; - defining a first class group of hairsprings (13) and a second class group of hairsprings (13), the classes of each individual group being consecutive and the average stiffness of the hairsprings of said second class group of hairsprings (13) being higher than the average stiffness of the hairsprings of said first class group of hairsprings (13); - pairing each class of hairspring (13) with the corresponding class of balance (11); - assembling a plurality of balance-hairspring (11, 13) oscillators (9) comprising balance springs (13) and balances (11) paired by class; - assembling a series of timepiece movements each including one of said plurality of balance-hairspring (11, 13) oscillators (9), said plurality of balance-hairspring (11, 13) oscillators (9) being arranged to be kept in oscillation by an escapement (7, 15) including an escapement wheel (7) driven by a gear train (5); Including, For an oscillator (9) comprising a balance spring (13) of said second class group, the corresponding movement (1) is configured such that the torque available at the escapement wheel (7) is lower than the torque available at the escapement wheel (7) for a movement incorporating an oscillator (9) comprising a balance spring (13) of said first class group.

2. 2. The manufacturing method according to claim 1, wherein the torque available to the escapement wheel (7) is determined by adjusting the output torque of a constant force mechanism (29) included in the movement (1).

3. 2. A method according to claim 1, wherein the torque available in the escapement wheel is determined by a barrel (3).

4. The torque available to the escapement wheel (7) is determined by providing a spring with at least two different forces, a more powerful spring is selected for the movement (1) including a balance spring (13) of said first class group, 4. A manufacturing method according to any one of claims 1 to 3, wherein a weaker spring is selected for a movement (1) including a balance spring (13) of the second class group.

5. 2. A method according to claim 1, wherein the torque available at the escapement wheel (7) is determined with respect to the configuration of the tooth profiles of predetermined wheels (23, 25, 27) of the gear train (5).

6. the torque available in the escapement wheel is determined by providing two types of the predetermined wheels (23, 25, 27) each having a different tooth profile configuration, configured to have two different gear efficiencies; One of the predetermined wheels having a higher gear efficiency is selected for the movement (1) including the balance spring (13) of the first class group; 6. A manufacturing method according to any one of claims 1 to 5, wherein one of the predetermined wheels having a lower efficiency is selected for a movement (1) including a balance spring (13) of the second class group.

7. The two tooth forms are cut by cutting tools of the same form; 7. The method of claim 1, wherein the cutting tool is adjusted to cut a tooth profile with a larger radius to obtain a wheel having the lower efficiency and to cut a tooth profile with a smaller radius to obtain a wheel having the higher efficiency.

8. 8. A manufacturing method according to any one of claims 5 to 7, wherein the predetermined wheel of the train wheel is a third wheel (25).

9. 9. A manufacturing method according to any one of claims 1 to 8, wherein the two different tooth profiles are provided on a third wheel (25a) included in the third wheel (25).

10. The manufacturing method according to claim 1 , wherein all classes in the first group of classes are different from all classes in the second group of classes.

11. The manufacturing method according to claim 1 , wherein some classes of the first group of classes correspond to some classes of the second group of classes.

12. A complete watch movement (1) manufactured by the manufacturing method according to any one of claims 1 to 11.

13. A timepiece including a timepiece movement (1) according to claim 12.

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