EP4428621A1 - Method for manufacturing a series of clock movements - Google Patents

Abstract

Method for manufacturing a series of watch movements (1), comprising steps of: - manufacturing a plurality of spiral springs (13); - measuring the stiffness of each of said spiral springs (13) and sorting them according to a plurality of stiffness classes; - manufacturing a plurality of balances (11) according to a distribution of moments of inertia determined according to said stiffness classes of said spiral springs (13); - measuring the moment of inertia of each of said balances (11) and sorting them according to a plurality of classes by moment of inertia; - defining a first group of classes of spiral springs (13) as well as a second group of classes of spiral springs (13), the classes of each individual group being sequential, the average stiffness of the spiral springs (13) of the second group of classes of spiral springs (13) being greater than the average stiffness of the spiral springs (13) of the first group of classes of springs hairsprings (13);- pairing each class of hairsprings (13) with a corresponding class of balances (11);- assembling a plurality of hairspring-balance oscillators (9) (11, 13) each comprising a hairspring (13) and a balance (11) paired by classes;- assembling a series of watch movements (1) each comprising one of said hairspring-balance oscillators (9) (11, 13) arranged to be maintained by an escapement (7, 15) comprising an escape wheel (7) driven by a finishing gear (5), in which, for the oscillators (9) comprising a hairspring (13) of the second group of classes, said corresponding movements (1) are arranged such that the torque available to said escapement wheel set (7) is less than the torque available to the escapement wheel set (7) for movements incorporating oscillators (9) comprising a hairspring (13) of the first group of classes.

Description

Technical field

The present invention relates to the field of watchmaking. It concerns, more particularly, a method of manufacturing a series of watch movements.

State of the art

In order to obtain a good oscillation frequency of a balance-spring oscillator, maximum care is required with regard to the moment of inertia of the balance and the return torque provided by the associated balance spring. When manufacturing large series of timepieces, it is not economical to call upon an experienced watchmaker to manufacture or modify these two components very precisely for each individual movement, and the industry uses devices applying the "Omega-Metric" process in order to automate the determination of the torque of the balance springs and the moment of inertia of the balances.

The distributions of the torques of the balance springs and the moment of inertia of mass-produced balances each follow a substantially Gaussian curve, and each component is sorted into classes, depending on the torque and the moment of inertia respectively. The number of classes is typically 20, the difference between adjacent classes corresponding to a rate variation of typically 150 seconds per day.

The balance springs of a stiffer class are paired with balances of a class with a higher moment of inertia, and vice versa, each class of balances corresponding to a class of balance springs in such a way as to minimize the differences in oscillation frequencies over the greater part of the production of the components. This process is described in the work Théorie d'Horlogerie, Reymondin et al, page 146 and is called "pairing".

However, it is possible that a certain number of hairsprings do not fit into the classes used, and are either rejected or subjected to reworking, such as, for example, by adding material to increase the stiffness, or removing material to reduce it, the latter possibility being typically retained for hairsprings made of non-metallic material (silicon, silicon oxide etc.) but which is also applicable for traditional hairsprings made of metal.

If the number of classes is increased to encompass a larger portion of the production run of hairsprings, it is indeed possible to achieve matching at the oscillation frequency level, by providing appropriately graded balances, but the amplitude variation between an oscillator comprising a hairspring of the stiffest class and an oscillator comprising a hairspring of the least stiff class becomes unmanageable. Typically, for a conventional 20-class classification, the amplitude variation will be of the order of 20° to 25°, whereas, if 20 additional classes of 150 s/d each are added, the amplitude variation rises to 50° over the entire run, which is unacceptable for a quality timepiece and is detrimental to its chronometric properties. Furthermore, if the oscillation amplitude becomes too large, the risk of galloping is increased and should be avoided.

The aim of the invention is therefore to propose a method of manufacturing a series of watch movements in which the above-mentioned defects are at least partially overcome, and which allows a wider range of hairsprings to be used without requiring reworking.

Disclosure of the invention

• fabriquer une pluralité de ressorts spiraux ;
• mesurer la raideur de chacun desdits ressorts spiraux et les trier selon une pluralité classes de raideur (également typiquement par classes de 150 s/jour) ;
• fabriquer une pluralité de balanciers présentant une distribution de moments d'inertie déterminée en fonction desdites classes de raideur desdits ressorts spiraux, c'est-à-dire des balanciers dont au moins une partie sont susceptible d'être appairés correctement avec les ressorts spiraux fabriqués et triés dans les classes de ressorts spiraux retenues ;
• mesurer le moment d'inertie de chacun desdits balanciers (11) et les trier selon une pluralité de classes par moment d'inertie ;
• définir un premier groupe de classes de ressorts spiraux ainsi qu'un deuxième groupe de classes de ressorts spiraux, dont les classes de chaque groupe individuel sont séquentielles, la raideur (et donc le couple de rappel) moyenne des ressorts spiraux du deuxième groupe de classes de ressorts spiraux étant supérieure à la raideur moyenne des ressorts spiraux du premier groupe de classes de ressorts spiraux ;
• appairer chaque classe de ressorts spiraux avec une classe correspondante de balanciers ;
• assembler une pluralité d'oscillateurs balancier-spiral comprenant chacun un ressort spiral et un balancier ainsi appairés par classes ;
• assembler une série de mouvements horlogers comprenant chacun l'un desdits oscillateurs balancier-spiral agencé pour être entretenu en oscillation par un échappement de type quelconque comprenant une roue d'échappement agencée pour être entraînée par un rouage de finissage, dans lesquels, pour les oscillateurs comprenant un ressort spiral du deuxième groupe de classes, lesdits mouvements correspondants sont agencés de telle sorte que le couple disponible au mobile d'échappement est inférieur au couple disponible audit mobile d'échappement pour des mouvements incorporant des oscillateurs comprenant un ressort spiral du premier groupe de classes.

More specifically, the invention relates to a method of manufacturing a series of watch movements, as defined by claim 1. This method comprises steps of:

• manufacture a plurality of spiral springs;
• measuring the stiffness of each of said spiral springs and sorting them according to a plurality of stiffness classes (also typically by classes of 150 s/day);
• manufacturing a plurality of balance wheels having a distribution of moments of inertia determined as a function of said stiffness classes of said spiral springs, i.e. balance wheels of which at least some are capable of being correctly paired with the spiral springs manufactured and sorted into the selected spiral spring classes;
• measuring the moment of inertia of each of said balance wheels (11) and sorting them into a plurality of classes by moment of inertia;
• defining a first group of spiral spring classes and a second group of spiral spring classes, the classes of each individual group being sequential, the average stiffness (and therefore the restoring torque) of the spiral springs of the second group of spiral spring classes being greater than the average stiffness of the spiral springs of the first group of spiral spring classes;
• pair each class of spiral springs with a corresponding class of balance wheels;
• assembling a plurality of balance-spring oscillators each comprising a balance spring and a balance thus paired by classes;
• assembling a series of watch movements each comprising one of said balance-spring oscillators arranged to be kept in oscillation by an escapement of any type comprising an escape wheel arranged to be driven by a finishing gear train, in which, for oscillators comprising a balance spring of the second group of classes, said corresponding movements are arranged such that the torque available to the escape wheel is less than the torque available to said escape wheel for movements incorporating oscillators comprising a balance spring of the first group of classes.

By these means, a greater torque variation of the spiral springs can be used without requiring rework, compensating for the tendency of the hairsprings in the steeper classes and also to increase the oscillation amplitude of the oscillator. This is done by decreasing the torque available to the escapement wheel during operation of the movement, which reduces the intensity of the impulses supplied by the escapement to the balance-spring oscillator, and thus brings the oscillation amplitude back into an acceptable range. Manufacturing losses of the hairsprings and/or reworking of part of the production can be reduced or even eliminated.

Of course, the same principle can apply to more than two class groups.

In one variant, said torque available to the escapement wheel is determined by adjusting the output torque of a constant force mechanism that each movement comprises.

In another variant, said torque available to the escapement wheel is determined at the barrel, such as, for example, by providing mainsprings having at least two different powers, a more powerful mainspring being chosen for movements containing balance springs of the first group of classes and a less powerful mainspring being chosen for movements containing balance springs of the second group of classes.

In yet another variant, said torque available to the escapement wheel is determined at the level of the shape of the teeth of a predetermined wheel of the finishing gear train. For example, two types of said predetermined wheel may be provided having two shapes of teeth arranged so as to have two different gear efficiencies, one of said predetermined wheels with a higher gear efficiency being retained for movements containing hairsprings of the first group of classes and one of said predetermined wheels with a lower efficiency being retained for movements containing hairsprings of the second group of classes.

Advantageously, said two tooth shapes are cut using the same cutter shape, said cutter being adjusted to cut a toothing to a larger radius to obtain mobiles having said lower efficiency, and to cut a toothing to a smaller radius to obtain mobiles having said higher efficiency.

In doing so, both types of mobiles can be manufactured by the same tools, the only difference being the position of the cutter when cutting the relevant toothing.

Typically, said mobile of the predetermined finishing gear is the middle mobile, said two different toothings being provided for the middle wheel, which typically meshes with the seconds pinion. However, the choice of mobile and toothing concerned is free to the manufacturer.

As for the distribution of the class groups, in one variant, the set of classes in the first class group is different from the set of classes in the second class group. However, it is also possible that some of the classes in the first group overlap some of those in the second group, such that some of the classes in the first class group correspond to some of the classes in the second class group.

The invention also relates to a series of watch movements manufactured according to the method described above, as well as a timepiece comprising a movement belonging to said series of movements.

Brief description of the drawings

• Figure 1 est une vue schématique d'un mouvement horloger conventionnel ;
• Figure 2 est une vue schématique d'un mouvement horloger incorporant un mécanisme à force constante;
• Figure 3 est une vue de l'engrenage entre la roue moyenne et le pignon de secondes agencé pour fournir un rendement d'engrenage supérieur ;
• Figure 4 est une vue de l'engrenage entre la roue moyenne et le pignon de secondes agencé pour fournir un rendement d'engrenage inférieur à celui de la figure 4.

Other details of the invention will appear more clearly on reading the following description, given with reference to the appended drawings in which:

• Figure 1 is a schematic view of a conventional clock movement;
• Figure 2 is a schematic view of a clock movement incorporating a constant force mechanism;
• Figure 3 is a view of the gearing between the middle wheel and the second pinion arranged to provide superior gearing efficiency;
• Figure 4 is a view of the gearing between the middle wheel and the second pinion arranged to provide a lower gearing efficiency than the figure 4 .

Embodiments of the invention

There figure 1 schematically illustrates, seen from the side, a conventional clockwork movement 1, the teeth being illustrated by their primitive circles and the pivot axes of the various parts by dotted lines.

The movement comprises a barrel 3 housing a conventional mainspring (not shown), a finishing gear train 5 kinematically connecting the barrel 3 to an escapement wheel 7, which maintains an oscillator 9 of the balance 11 spiral 13 type via an anchor 15 which cooperates with a pin 17 of a plate 19 integral in rotation with said balance 11. Of course, other forms of escapement (for example detent, Omega-Daniels, etc.) can also be used, and the present invention is not limited to a particular type of escapement. Furthermore, the shape of the balance can also be freely chosen.

Conventionally, the inner end of the spiral spring 13 is fixed to a collet integral in rotation with said balance 11, and the outer end is fixed to an index assembly R, the elements of which have not been illustrated but which are well known to those skilled in the art, which serve to fix the outer end of the spiral spring 13 and to modify its active length in order to adjust the rate of the oscillator 9, and therefore of the movement, by means of a conventional index. The present invention is not limited to a particular shape of the spiral spring 13, helical, spherical, terminally curved Breguet and other spirals 13 also being concerned, and it is also not limited to specific materials. For example, the hairspring 13 may be made of conventional metal, metallic glass (amorphous metal), silicon, silicon oxide, synthetic diamond, aluminum oxide, ceramic, glass-ceramic or any other material known to those skilled in the art, manufactured by any process suitable for the material. concerned (rolling and plating, sintering in a mold, additive manufacturing, LIGA, cutting of a plate by laser or engraving, etc.)

The finishing gear train 5 can take any known form, and here uses a conventional construction, comprising a large-medium wheel set 23 (or alternatively the center wheel set, if applicable) meshing on the one hand with the barrel 3 via the large-medium pinion and with the pinion of a medium wheel set 25 via the large-medium wheel, the medium wheel 25a of the medium wheel set 25 meshing in turn with the seconds pinion 27a of a seconds wheel set 27, the seconds wheel of which meshes with the escapement pinion of the escapement wheel set 7. Of course, the rotation speeds and the number of wheels can be determined at the discretion of the manufacturer.

In order to make the natural frequency of the oscillator 9 sufficiently close to the desired frequency, so that only an adjustment of the index is necessary to regulate the movement, a production series of hairsprings 13 and balances 11 are produced and sorted by classes of stiffness respectively of moment of inertia, for example according to the Omega-Metric method, the manufacture of the balances 11 being carried out aiming at a distribution of moments of inertia suitable for the distribution of stiffnesses of the hairsprings 13. Typically, this method sorts the hairsprings 13 and the balances 11 by twenty classes which imply a difference in rate of 150 seconds per day (s/d) from one class to the adjacent class, a pairing between the classes being carried out to put hairsprings 13 tending to generate an advance (i.e. stiffer hairsprings 13) together with balances 11 tending to generate a delay. (i.e. balance wheels 11 with a greater moment of inertia) and vice versa, to obtain oscillators 9 capable of being correctly adjusted by means of the index. For approved movements, the difference in oscillation amplitude of an oscillator 9 comprising a hairspring 13 of the first class compared to an oscillator 9 comprising a hairspring 13 of the twentieth class is of the order of 20° to 25° in total, i.e. ± 12.5° around the average amplitude of the series of oscillators 9. Of course, a deviation different amplitude is possible, and the figures are given as examples only.

In a large production run, it may occur that a significant quantity of 13 hairsprings fall out of the twenty-grade classification at 150 s/d each (or out of the different grades, if applicable). In order to minimize production losses, as many of these 13 hairsprings as possible are typically reworked by various means to bring them into the grades used and minimize production losses. For 13 hairsprings that are not sufficiently stiff and whose restoring torque is inadequate, material addition by inkjet or vacuum deposition, ion implantation to increase the shear modulus or the like may be performed. In the case of 13 hairsprings that are too stiff, material removal by laser is the typical solution.

In order to avoid, or minimise, rework, it would in principle be possible simply to increase the number of classes of hairsprings 13, and to manufacture corresponding balances 11 in order to be able to pair them and thus obtain a suitable natural oscillation frequency. However, this way of proceeding increases the variation in amplitude, and for forty classes at each 150 s/d, this variation can increase up to 50° in total (i.e. 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 galloping if the oscillation amplitude becomes too high.

The solution of the present invention is as follows. The number of classes of spirals 13 is increased, and the number of these classes is divided into two groups, the first of which has a lower average stiffness, and the second of which has a higher average stiffness.

The set of classes of the two groups can be consecutive, i.e. representing a single distribution (typically Gaussian) of spirals 13 or can represent two distributions (again typically Gaussian) by a manufacture aimed at two such distributions. In the latter case, certain lower classes of the second group will correspond to certain higher classes of the first group, that is to say, there will be an overlap between the classes of the two groups.

Balance wheels 11 are manufactured and classified by moment of inertia in the same way, such that the number of distinct classes of balance wheels 11 corresponds to the number of distinct classes of hairsprings 13, in order to be able to perform a matching for each hairspring 13 thus classified. For example, if hairsprings 13 are classified into two distinct groups of 20 classes each, 40 classes of balance wheels will be manufactured and used. However, if, for example, the 5 upper classes of the first group correspond to the 5 lower classes of the second group, the number of distinct classes of balance wheels will be 35, due to the overlap of 5 classes between the two groups.

Since the second group's hairsprings are stiffer and therefore provide more torque than the first group's hairsprings, at least on average (if not in absolute terms in the case where there is no overlap between the classes of the two groups), the oscillation amplitude will be greater to the same extent (on average or in absolute terms, as the case may be).

The general design of the movement 1 is calculated to obtain a good average amplitude for the balance springs 13 of the first group (for example 280° in the HH position with the mainspring fully wound), by means of obtaining a first predetermined torque at the escapement wheel. This predetermined torque will, of course, be subject to standard manufacturing variations, and may vary depending on the winding state of the mainspring housed in the barrel 3, as will be well understood by those skilled in the art.

For the 13 hairsprings of the second group, the torque available at the escapement wheel is reduced compared to a movement 1 adapted for the use of a 13 hairspring of the first group. This reduction in torque compared to the design for the 13 hairsprings of the first group can be obtained by various means, as will become more clearly apparent later, and serves to reduce the oscillation amplitude of oscillator 9 and to bring it back into the normal and acceptable range even if the balance springs are stiffer and provide more torque than usual. Indeed, a reduction in torque at the escapement wheel implies a reduction in the strength of the impulses given to oscillator 9 via the escapement, and thus a reduced amplitude.

By these means, and taking into account a conventional classification into 20 classes of each 150 s/d, it is possible to use up to double the number of classes of hairsprings 13, i.e. 40 single classes of each 150 s/d, by a simple adjustment of the torque available to the escapement wheel. Of course, it is also possible to provide even more groups of classes, and to further increase the variation in stiffness of the hairsprings 13 which can be absorbed, and the invention is therefore not limited to two groups.

A first way to obtain this variation in torque at the escapement wheel 7 is to provide an adjustable constant force mechanism 29 within the movement 1, as illustrated in figure 2 . In this arrangement, this adjustable constant force mechanism 29 is schematically illustrated as being kinematically located in the finishing gear 5 between the barrel 3 and the hour wheel set 23, but alternatively, it is possible to arrange it between any two wheels of the finishing gear 5, or integrated into any wheel set of the finishing gear or even into the barrel or the escapement wheel set.

By adjusting the output torque of the constant force mechanism 29 according to the class group to which the hairspring 13 incorporated in the movement 1 concerned belongs, the torque available at the escapement wheel 7 can be adjusted to obtain an oscillation amplitude within an acceptable range (for example the 280° ± 12.5° in the HH position with the mainspring fully wound mentioned above).

The details of the adjustable constant force mechanism 29 are not important to the present invention, non-limiting examples of such mechanisms being revealed in the documents CH716126 , EP3182217 And EP2166419 . Of course, the use of such a mechanism for the purpose of being able to absorb more variation in the stiffness of hairsprings 13 during mass production has never, to the knowledge of the applicant, been proposed until now.

Another way to obtain this reduced torque at the escapement wheel 7 is at the barrel 3, for example by providing two types of mainspring, one with a higher average power (and therefore average torque) for use in combination with the balance springs 13 of the first group, the other with a lower average power (and therefore average torque) for use in combination with the balance springs 13 of the second group, so as to obtain substantially the same amplitude distribution (at the level of the average amplitude of each group and the total amplitude deviation, such as for example the 280° ± 12.5° in the HH position with the mainspring fully wound mentioned above) for oscillators 9 comprising balance springs 13 of both groups of classes.

Perhaps the most interesting way in the production of large series of parts is to vary the gear efficiency of the finishing gear 5. This can be done in an efficient manner by modifying the profile of the teeth of one of the wheels or one of the pinions. For this purpose, two types of a particular mobile 23, 25, 27 can be provided, a first type comprising a wheel or pinion with "normal" teeth, a second type comprising a wheel or pinion with "modified" teeth, in which the profile of the wheel or pinion has been predetermined to cause a reduction in the gear efficiency compared to the "normal" teeth.

Even if it is possible to modify the shape of the teeth of any toothed organ (wheel or pinion) of the finishing gear, experiments have shown that a modification of the middle wheel 25a (or more generically the wheel of the second mobile kinematically upstream of the mobile exhaust) optimizes the influence of the modified toothing in a manageable manner.

There figure 3 illustrates the interaction between the “normal” toothing of the middle wheel 25a with the second pinion 27a, which obtains an average efficiency of 93.93% (calculated) for this meshing, and a total efficiency of 69% for the finishing gear 5.

There figure 4 illustrates the same interaction between the "modified" toothing of the middle wheel 25a with the seconds pinion 27a, which achieves an average efficiency of 92.18 (calculated) for this meshing, and a total efficiency of 67% for the finishing gear 5. Experiments have shown that this difference is sufficient to reduce the average amplitude of the oscillators 9 comprising hairsprings 13 of the second group so as to provide substantially the same average amplitude and the same range of deviation of 20° to 25° (in total) of amplitude as for the oscillators 9 comprising hairsprings 13 of the first group of 20 classes at 150 s/d each, with no overlap between the groups. Therefore, the entire production series of 13 hairsprings of 40 classes at 150 s/d each can fit into the same oscillator amplitude distribution 9 of, for example, 280° ± 12.5° in HH position with mainspring fully wound.

Although it is possible to completely redesign the shape of the teeth of the modified toothed organ, in the example given in the figures 3 And 4 , the only difference, during manufacturing, is an offset of the cutter of the middle wheel 25a, which serves to bring the meshing line towards the axis of the second pinion 27a (as shown by the scale in these figures), by adjusting the tool to make a slightly less deep couple, of the order of 30 µm for the wheel 25a illustrated, to increase its diameter. At the production level, this minimal difference and the use of the same tools for both types of mobiles, is extremely efficient and economical to implement.

Therefore, two types of medium mobile 25 are manufactured in the present example, more generically mobile 23, 25, 27 which is modified for oscillators comprising balance springs of the second group, and when assembling the movement 1, a first "normal" type of this mobile 23, 25, 27 is used in combination with oscillators comprising balance springs of the first group, and a second "modified" type in combination with oscillators comprising balance springs of the second group. In the case of more than two groups of classes, the number of types of mobiles 23, 25, 27 is adapted accordingly.

When assembling the movements, since the only difference is in the choice between two mobiles depending on the class group to which the hairspring 13 of oscillator 9 belongs, this solution is very economical, does not involve additional components (such as a constant force mechanism) and is more easily controlled than the provision of two different mainsprings.

Although the invention has been described in connection with particular embodiments, variations are possible without departing from the scope defined by the appended claims.

Claims (13)

Method of manufacturing a series of watch movements (1), comprising steps of: - manufacturing a plurality of spiral springs (13); - measuring the stiffness of each of said spiral springs (13) and sorting them according to a plurality of stiffness classes; - manufacturing a plurality of balance wheels (11) according to a distribution of moments of inertia determined as a function of said stiffness classes of said spiral springs (13); - measuring the moment of inertia of each of said balance wheels (11) and sorting them according to a plurality of classes by moment of inertia; - defining a first group of spiral spring classes (13) and a second group of spiral spring classes (13), the classes of each individual group being sequential, the average stiffness of the spiral springs (13) of the second group of spiral spring classes (13) being greater than the average stiffness of the spiral springs (13) of the first group of spiral spring classes (13); - pair each class of spiral springs (13) with a corresponding class of balance wheels (11); - assembling a plurality of oscillators (9) balance-spring (11, 13) each comprising a balance spring (13) and a balance (11) paired by classes; - assembling a series of watch movements (1) each comprising one of said sprung balance (11, 13) oscillators (9) arranged to be maintained by an escapement (7, 15) comprising an escape wheel (7) driven by a finishing gear (5), in which, for the oscillators (9) comprising a spiral spring (13) of the second group of classes, said corresponding movements (1) are arranged such that the torque available to said escapement wheel (7) is less than the torque available to the escapement wheel (7) for movements incorporating oscillators (9) comprising a spiral spring (13) of the first group of classes. A method according to claim 1, wherein said torque available to said escapement wheel (7) is determined by adjusting the output torque of a constant force mechanism (29) included in said movements (1). Method according to claim 1, in which said torque available to the escapement wheel is determined at the barrel (3). Method according to the preceding claim, in which said torque available to the escapement wheel (7) is determined by providing motor springs having at least two different powers, a more powerful motor spring being retained for the movements (1) containing spiral springs (13) of the first group of classes and a less powerful motor spring being retained for the movements (1) containing spiral springs (13) of the second group of classes. Method according to claim 1, in which said torque available to the escapement wheel (7) is determined at the level of the shape of the teeth of a predetermined wheel (23; 25; 27) of the finishing gear (5). Method according to the preceding claim, in which said torque available to the escapement wheel is determined by providing two types of said predetermined wheel (23; 25; 27) having two tooth shapes arranged so as to have two different gear efficiencies, one of said predetermined wheel sets with higher gear efficiencies being retained for movements (1) containing spiral springs (13) of the first group of classes and one of said predetermined wheel sets with lower efficiencies being retained for movements (1) containing spiral springs (13) of the second group of classes. Method according to the preceding claim, in which said two tooth shapes cut by means of a same shape of, said milling cutter being adjusted to cut a tooth at a greater radius to obtain mobiles having said lower efficiency, and for cutting teeth at a lower radius to obtain mobiles having said higher efficiency. Method according to one of claims 5 to 7, in which said mobile of the predetermined finishing gear is the middle mobile (25). Method according to the preceding claim, in which said two different toothings are provided for the middle wheel (25a) which said middle mobile (25) comprises. Method according to one of the preceding claims, in which the set of classes of the first group of classes is different from the set of classes of the second group of classes. Method according to one of claims 1 to 9, in which some of the classes of the first group of classes correspond to some of the classes of the second group of classes. Series of clock movements (1) manufactured according to one of the preceding claims. Timepiece comprising a timepiece movement (1) belonging to the series of movements of claim 12.

Images