EP4492157A1 - Method for adjusting the isochronism of a balance-hairspring regulator - Google Patents

Abstract

The present invention relates to a method for adjusting the isochronism of a regulating member of the sprung balance type (1, 2) comprising a hairspring (1). The sprung balance (1, 2) is mounted on a watch movement or a subassembly of the watch movement, the frame (5) of which comprises a stud (3) whose position relative to the axis of the sprung balance (1, 2) is adjustable. The outer end (1b) of the hairspring (1) is introduced into the stud (3) without constraining the hairspring (1) by adjusting the radial position of the stud (3) relative to the axis of the sprung balance (1, 2). The position of the stud (3) is adjusted relative to the axis of the sprung balance (1, 2) to constrain the outer end (1b) of the hairspring (1) and adjust the isochronism and the rate of the sprung balance (1, 2) accordingly.

Description

The present invention relates to a method for adjusting the isochronism of a regulating organ of the sprung balance type comprising a hairspring. Preferably, the hairspring is made of a material that can be micro-machined without plastic deformation, in particular silicon.

In watch regulating organs, the hairspring is generally attached by its inner end to the balance shaft and by its outer end to the frame, generally to the balance bridge called a balance cock. To do this, said outer end is secured, typically by pinning or gluing, to an attachment point comprising a stud which is fixed in a stud holder. The stud holder is mounted on the balance bridge.

To improve the chronometry of a timepiece, we seek to obtain an isochronous balance spring whose oscillations are regular and with the same period regardless of the starting point. There are several types of adjustments for a regulating organ of the balance-spring type and the escapement associated with it.

The position of the stud holder is generally adjustable in rotation relative to the balance spring axis or the balance shaft in order to perform a reference point adjustment of the escapement. The purpose of this operation is to ensure that at the equilibrium position of the regulating organ, the plate pin is centered on the lever-balance axis. If this is not the case, the functions of the escapement will not be symmetrical relative to the equilibrium position.

The frequency of the regulating organ can be adjusted by modifying the inertia of the balance wheel with screws or weights or by modifying the elastic torque of the hairspring. For this last adjustment, some regulating organs then include an index assembly with in particular an index and two pins or stops allowing to change the counting point by lengthening or shortening the active length of the hairspring (which changes the elastic torque).

There are also regulating organs without a racket in which the piton point of the outer end of the hairspring defines the active length of the latter. For these regulating organs without a racket, the position of the piton can then have an impact on the adjustment of the hairspring. Thus, to allow the adjustment of the counting point, the piton is frequently mounted mobile in rotation on the piton holder.

In general, pitonnage is a delicate operation. The document FR1460220 explains in particular that the end of a hairspring, held for example by pinching between two parts, exerts a force on the last turn of the hairspring, thus modifying its original characteristics.

As for balance springs made of silicon or other similar materials without plastic deformation (glass, ceramic, etc.), these generally have a terminal curve on the last coil that is rather straight or slightly curved outwards. Since they are not plastically deformable, these balance springs are generally incompatible with the use of an index designed rather for metal balance springs. Thus, the possibilities of adjusting the regulating organ with this type of balance spring after assembly in a watch movement are limited, in particular to an adjustment of the inertia of the balance as described above.

Furthermore, in the case of balance springs made of silicon or other similar deformation-resistant materials, even if a batch of balance springs is manufactured using the same manufacturing process, there may be significant variability in the radius of the terminal curves of the balance springs in the batch, with some having a larger radius and others having a smaller radius than the theoretical radius targeted by the manufacturing process. Although the elastic torque of these balance springs is generally not affected by a difference in the radius of their terminal curve - the active length and the section (thickness, height) remaining the same - it has been observed that the regulating organs equipped with these balance springs nevertheless exhibit a difference in isochronism. This difference is potentially due to a non-linear torque linked to the displacement of the center of gravity relative to the balance spring axis and the assembly preload which forces the balance spring to oscillate around a position which is not optimal. It is also necessary to consider the impact of friction in the balance pivots, which can be more or less accentuated depending on the level of preload.

This difference in the radii of the terminal curves of the balance springs of the same production batch also makes the assembly of the balance-spring regulating organ and in particular the pitonnage of the outer end of the balance spring more difficult: there is a risk of damaging or even breaking the balance spring. In addition, the introduction of an unexpected pre-stress on the balance spring during pitonnage can make any subsequent adjustment step longer and more complex.

The document EP 3 081 996 describes a watch hairspring made of micro-machinable material comprising a plurality of stages each constituting a spring wound in a spiral, all parallel to each other and arranged to be assembled integrally at their respective inner end at a common axial collet. Each stage comprises, at its respective outer end, its own means of attachment to a stud which are independent of those of the other said stages, the attachment means comprising means of adjustment in position relative to a stud which are also independent of those of the other said stages. According to this document, the attachment means and the position adjustment means together constitute intrinsic means of correcting the isochronism of the multi-stage hairspring. This document recognizes that with a hairspring made of micro-machinable material, the fine adjustment capacity is generally limited, but indicates that by acting on the outer attachment position of the hairspring, it is also possible to control the isochronism of the regulating organ. However, the solution proposed in EP 3 081 996 is complex and is not applicable to a conventional single-stage hairspring, regardless of its material.

Other documents like EP 1 918 791 , CH 714 809 , CH 717 088 Or CH 707 742 describe the possibility of modifying the radial position of the stud and/or the stud holder relative to the center of the hairspring (the balance shaft).

However, the adjustment of the isochronism requires a very precise control of the radial position of the outer end of the hairspring, control and precision that the solutions of these documents do not allow. Moreover, all these documents do not allow to avoid an undesirable preload of the hairspring that could be introduced during the pitonnage of the hairspring.

The aim of the present invention is therefore to propose a method for adjusting the isochronism of a regulating organ of the balance-spring type comprising a balance spring and preferably a balance spring made of a material that can be micro-machined without plastic deformation, in particular silicon, which makes it possible to adjust the position of the stud relative to the central axis of the balance spring. An aim of the present invention is in particular to avoid undesirable pre-stressing of the balance spring during the studding while exploiting the possibility of adjusting the radial stress at the stud in order to compensate for the variability of the radius of the terminal curve of the balance spring relative to a theoretical radius which could affect the isochronism.

The present invention therefore relates to a method for adjusting isochronism according to claim 1.

• La figure 1 est une vue du dessus d'un organe régulateur de type balancier spiral comprenant notamment un spiral, un balancier et un coq.
• La figure 2 est une vue de dessous du balancier-spiral de la figure 1.
• La figure 3 est une vue éclatée du balancier-spiral de la figure 1.
• La figure 4 est une vue en coupe du balancier-spiral de la figure 1 selon un plan passant par l'axe central du spiral et la vis de fixation.

The attached drawings illustrate schematically and by way of example an embodiment of a clock device for implementing the isochronism adjustment method according to the invention.

• There figure 1 is a top view of a regulating organ of the spiral balance type comprising in particular a spiral, a balance and a cock.
• There figure 2 is a bottom view of the balance spring of the figure 1 .
• There figure 3 is an exploded view of the balance spring of the figure 1 .
• There figure 4 is a sectional view of the sprung balance of the figure 1 according to a plane passing through the central axis of the hairspring and the fixing screw.

In the present application, the term "adjust" is used in its commonly accepted definition in watchmaking, namely to put into a state of proper operation, to eliminate or reduce that which can alter the running of a timepiece. Adjustment is therefore a particular operation, reproducible and distinct from assembly and fixing operations, even if fixing means can participate in the adjustment. In addition, the adjective "fine" is used in this application to characterize what is applied with precision and accuracy.

A first step of the method according to the invention consists in obtaining a hairspring. Preferably, the hairspring is made of a material without plastic deformation, in particular silicon or other similar materials (ceramics, glasses, etc.). The hairspring can be made using a known micromachining process (for example DRIE) and be part of a batch of hairsprings manufactured together in the same wafer (or plate of the material machinable without plastic deformation). Alternatively, the hairspring could be metallic or made of any suitable material. The hairspring is characterized by an actual terminal curve radius that differs from the theoretical terminal curve radius determined during the design of the hairspring and targeted during manufacture. This difference is due to the manufacturing process of the hairspring and can go in one direction or the other: actual radius larger or smaller than the theoretical radius.

In a second step of the method according to the invention, the balance spring is assembled with a balance wheel to form a regulating member of the balance-spring type. The characteristics of the balance wheel are not decisive for the method according to the invention and said balance wheel will not be described in more detail here.

The balance spring is then mounted on a watch movement or a subassembly of a watch movement (for example, an escapement holder), the frame of which comprises a stud whose radial position relative to the axis of the balance spring assembly is adjustable. Preferably, the stud is radially movable in the general plane in which the balance spring extends. It is also possible to adjust the position of the central axis of the stud by pivoting it relative to the central axis of the hairspring so that the central axis of the stud is no longer parallel to the central axis of the hairspring and that this results in a radial displacement of the stud relative to the axis of the balance-spring assembly. The outer end of the hairspring is then introduced into the stud without constraining the hairspring. To do this, the radial position of the stud is adjusted to allow the introduction of the outer end of the hairspring without constraining the hairspring.

The next step of the method according to the invention consists in making the outer end of the hairspring integral with the stud, for example by gluing or pinning or any other suitable means.

The balance spring can now be started and its isochronism and rate can be measured.

The isochronism and the rate of the sprung balance are then adjusted by adjusting the position of the stud relative to the axis of the sprung balance to constrain the outer end of the spring to achieve the target chronometric performances for the regulating organ. The stud is then moved to bring the outer end of the spring into a position that allows the target chronometric performances to be achieved. Preferably, to correct the isochronism, the position of the stud is adjusted radially relative to the axis of the sprung balance assembly in the general plane in which the spring extends. Alternatively, instead of or in addition to such a radial adjustment, the position of the stud may be adjusted in height relative to the general plane of the spring and/or the central axis of the stud may be pivoted in rotation relative to the central axis of the spring so that the central axis of the stud is no longer parallel to the central axis of the spring.

Other adjustment steps can be carried out independently after or before this last step: setting the reference point, adjusting the balance inertia, adjusting the counting point, etc.

The method can be applied to a plurality of hairsprings, in particular hairsprings made of a plastically non-deformable material, manufactured in the same batch and each characterized by a distinct and different actual terminal curve radius from the radius of the theoretical terminal curve targeted at manufacture. In this case, the above steps are applied to each of the hairsprings. In a final step, the position of the stud, and preferably the radial position of the stud, relative to the balance-spring axis of each of the hairsprings is adjusted to constrain the outer end of each hairspring and adjust the isochronism and rate of each hairspring to tend towards an essentially similar isochronism and rate for all the hairsprings in the batch or towards a chosen target isochronism and rate or target chronometric performances.

With the method according to the invention, it is possible to compensate for the variabilities of the radius of the terminal curve of a hairspring which are due to the manufacturing process of the hairspring and which could affect the isochronism. The stress applied to the outer end of the hairspring can be precisely adjusted to tend towards the theoretical value of the radius of the terminal curve of the hairspring and therefore towards an optimal rate, an adjustment which does not prejudice other steps of adjustment of the hairspring balance such as setting the reference mark, adjusting the counting point or adjusting the inertia of the balance. In addition, the pitonnage is facilitated and is done with little risk of damage or breakage for the hairspring, in particular in the case where the hairspring is made of a material which cannot be plastically deformed, since an undesirable prestressing is avoided during this operation.

In the following, an embodiment of a watch device allowing the implementation of the method for adjusting the isochronism of a sprung balance according to the invention is described by way of example and with reference to the appended figures. In this example, the stud is in particular radially movable relative to the axis of the sprung balance assembly.

The watch device illustrated in the figures comprises a hairspring 1 whose inner end 1a is fixed by any suitable means to the shaft 20 of a balance wheel 2 and whose outer end 1b is fixed in a stud 3. The stud 3 is intended to be fixed in a stud holder 4 itself intended to be mounted on an element of the frame such as a balance cock or bridge 5. The cock 5 can be fixed to the movement in one or several positions, and it can also include height adjustment means, or even in a direction extending parallel to the balance shaft 20. The cock 5 carries a shock-absorbing bearing 8 in which a first end 20a of the balance shaft 20 is pivoted.

In this example, the radial position of the stud holder 4 on the balance-cock 5 relative to the central axis of the hairspring 1 or the balance shaft 20 is finely adjustable. In the illustrated embodiment, the stud holder 4 is constituted by a sliding plate 40 indirectly attached to the balance-cock 5. To do this, the watchmaking device further comprises a base plate 6. The sliding plate 40 and the base plate 6 are both semi-circular and arranged to be superimposed on the balance-cock 5, the sliding plate 40 above the base plate 6, itself directly attached to the balance-cock 5.

The stud 3 is fixed to the stud holder 4 and in particular to the sliding plate 40 by any suitable means: for example, it is retained in an opening 41 of said sliding plate 40 by means of a lateral screw 31.

The cock 5 comprises a hole 50 intended to receive the shock-absorbing bearing 8 in which the balance shaft 20 is pivoted by its first end 20a. In the illustrated embodiment, the base plate 6 comprises an essentially circular or semi-circular portion 60 formed by two arms arranged to surround the shock-absorbing bearing 8. The shock-absorbing bearing 8 thus ensures that the base plate 6 is maintained in translation on the cock 5, both in a plane essentially parallel to the cock 5 and along an axis essentially parallel to the axis of the balance shaft 20.

The sliding plate 40 is therefore intended to be placed above the base plate 6 attached to the balance-cock 5. This sliding plate 40 comprises a first radial guide opening 90 of oblong shape and arranged radially relative to the central axis of the balance spring 1 and to the balance shaft 20 in the service position of the sliding plate 40. This first radial guide opening 90 is intended to receive a pin 91 secured to the base plate 6. base 6 for guiding the movement of the sliding plate 40. Preferably, the first radial guide opening 90 is oblong and closed to ensure greater stability in the positioning of the stud holder 4. The first radial guide opening 90 and the pin 91 constitute radial guide means for guiding the radial movement of the sliding plate 40 on the base plate 6 and on the balance-cock 5 relative to the central axis of the balance spring 1 in the service position of the device. Preferably, the timepiece device comprises second radial guide means which, in the illustrated embodiment, have the shape of a second radial guide opening 92 present on the base plate 6 and arranged to receive and cooperate with a radial guide surface 93 of the sliding plate 40. In the illustrated embodiment, this radial guide surface 93 is the outer surface of an oblong portion 44 of the sliding plate 40 comprising the opening 41 receiving the stud 3. As illustrated in the figures, the first radial guide opening 90 in the sliding plate 40 is closed while the second radial guide opening 92 in the base plate 6 is open.

The watch device comprises means for fine radial adjustment of the radial position of the stud holder 4 on the balance-cock 5 relative to the central axis of the hairspring 1 or the balance shaft 20. In the illustrated embodiment, these adjustment means comprise an oblong opening 42 arranged on the sliding plate 40 radially relative to the central axis of the hairspring 1 and to the balance shaft 20 in the service position of the watch device and an eccentric 9 arranged to pass through said oblong opening 42 and to be fixed in the base plate 6. Preferably, the eccentric 9 is driven into a hole 62 in the base plate 6 and passes through said hole 62, a recess 52 being provided in the balance-cock 5 to serve as a clearance for the eccentric 9. As will be seen in detail below, the eccentric 9 cooperating with the oblong opening 42 of the sliding plate 40 and the hole 62 of the base plate 60 here constitute fine adjustment means allowing the movement of the sliding plate 40 on the cock 5 for the fine adjustment of the radial position of said sliding plate 40 and of the stud 3 relative to the central axis of the hairspring 1 in the service position of the device.

The sliding plate 40 further comprises a first curved segment 43 with an opening 45 intended to cooperate axially with a fixing screw 7 for fixing the sliding plate 40 on the cock 5. The fixing screw 7 passes through this opening 45 of the first curved segment 43 as well as an opening 65 in a corresponding second segment 63 on the base plate 6 and is screwed into a thread 53 provided for this purpose on the cock 5.

In an intermediate position of the fixing screw 7, its bearing surface 70 makes it possible to ensure the maintenance of the sliding plate 40 along an axis parallel to the central axis of the balance spring 1 or to the balance shaft 20. Once the position of the stud holder 4 has been adjusted, this fixing screw 7 can be screwed into a locking position in which it makes the stud holder 4 and the base plate 6 integral with the balance cock 5. In its locking position, the fixing screw 7 also ensures the locking of the device, the stud holder 4 and the base plate 6 against any possible angular displacement in the event of an accidental impact.

To assemble the device and the sprung balance, the base plate 6 is placed on the balance-cock 5, its semi-circular portion 60 surrounding the shock-absorbing bearing 8 received in the hole 50. Driving the shock-absorbing bearing 8 into the hole 50 of the balance-cock 5 ensures that the base plate 6 is held in a direction perpendicular to the plane of said base plate 6 or in a direction essentially parallel to the central axis of the balance-spring 1 or to the balance shaft 20. In this position, the arrangement of the shock-absorbing bearing 8 and the base plate 6 means that the latter can pivot on the balance-cock 5 around said shock-absorbing bearing 8 but is integral in translation with the balance-cock 5.

The sliding plate 40 is then superimposed on the base plate 6 so that the pin 91 of the base plate 6 passes through the first radial guide opening 90 of the sliding plate 40 and the guide surface 93 of the sliding plate 40 cooperates with the second radial guide opening 92 of the base plate 6. The first and second segments 43, 63 and their respective openings 45, 65 are essentially superimposed. The sliding plate 40 and the base plate 6 are arranged so that, in their superimposed position on the cock 5, the sliding plate 40 is integral in rotation with the base plate 6 which can pivot about the shock-absorbing bearing 8 in order to allow the escapement to be aligned. In the illustrated embodiment, this is possible by the cooperation of the pin 91 of the base plate 6 with the first radial guide opening 90 of the sliding plate 40.

The eccentric 9 is driven through the oblong opening 42 of the sliding plate 40 into the hole 62 of the base plate 6, the recess 52 of the cock 5 avoiding any contact between the eccentric 9 and the cock 5.

The fixing screw 7 is screwed through the openings 45, 65 of the first and second segments 43, 63 into its thread 53 on the cock 5 at least in its intermediate position.

The device is then ready to receive the balance wheel 2-hairspring 1 assembly: the balance wheel 2 is pivoted by the first end 20a of its shaft 20 in the shock-absorbing bearing 8.

For the pinning, the outer end 1b of the balance spring 1 must be inserted into the pin 3 fixed in the opening 41 of the pin holder 4 by means of the lateral screw 31 and then made integral with said pin 3 by gluing, pinning or any other suitable means. With the fixing screw 7 in its intermediate position, it is possible by actuating the eccentric 9 to move the sliding plate 40 and therefore the pin 3 radially relative to the central axis of the balance spring 1 in order to be able to insert the outer end 1b of the balance spring 1 into the pin 3 without constraining the balance spring 1.

Indeed, by rotating the eccentric 9 in one direction or the other, the sliding plate 40 moves relative to the base plate 6 and to the balance-cock 5 radially relative to the central axis of the balance spring 1, preferably in a plane essentially parallel to the plane of the balance wheel 2 or of the balance spring 1. The movement of the sliding plate 40 is limited by the size of the eccentric and is guided by the means radial guide which are the pin 91 of the base plate 6 passing through the first radial guide opening 90 of the sliding plate 40 and the second radial guide opening 92 of the base plate 6 cooperating with the radial guide surface 93 of the sliding plate 40. Depending on the direction of rotation of the eccentric 9, the stud 3 and therefore the outer end 1b of the balance spring 1 will thus move away from or move closer radially to the central axis of said balance spring 1 or to the balance shaft 20.

Preferably, the device is arranged so that the stud 3 can move radially by at most ± 0.50 mm and even more advantageously by at most ± 0.20 mm relative to a median radial position of the device. Such a range of radial movement can correspond for example to a rotation of the eccentric 9 by 90° in each direction. The use of the eccentric 9 guarantees all the precision necessary for a fine adjustment of the position of the stud holder 4 and the stud 3.

Once the outer end 1b of the hairspring 1 is inserted into the stud 3 and it is ensured that no stress is exerted on said hairspring, it is then possible to make the outer end 1b of the hairspring 1 integral with the stud 3 and to screw the fixing screw 7 back into the cock 5 in its locking position to ensure the locking of the two plates relative to each other and make them integral with the cock 5.

The sprung balance 2, 1 is started and its rate and isochronism are measured. If an isochronism defect or a difference in isochronism with another spring from the same production batch is found, it is possible, in this example, to adjust the radial position of the stud 3 relative to the central axis of the spring 1 to reduce or cancel this defect or difference. To do this, the fixing screw 7 must be returned to its intermediate position and the eccentric 9 actuated as described above to move the sliding plate 40 relative to the balance cock 5 in a radial direction relative to the axis of the sprung balance 1, 2 according to the measurements taken.

Such a radial adjustment is achieved by a radial displacement of the stud 3 in the general plane P of the balance spring 1. Alternatively, to correct the isochronism, instead of or in addition to such a radial adjustment in the plane P of the balance spring 1, the position of the stud 3 in height relative to the plane P of the balance spring 1 can be adjusted and/or the position of the central axis A of the stud 3 in rotation relative to the central axis of the balance spring 1 can be adjusted so that these two axes are no longer parallel to each other.

Once the radial position of the stud holder 4 is adjusted for the desired isochronism and rate adjustment, the fixing screw 7 is screwed back into the cock 5 in its locking position to ensure the locking of the two plates relative to each other and make them integral with the cock 5.

In this example, the presence of the base plate 6 makes it possible to perform a rotational adjustment of the position of the stud 3 for a reference point of the escapement associated with the 2-spiral balance regulator 1. This reference point setting operation can be done independently of the radial adjustment of the position of the stud 3 described above.

For the reference setting, the fixing screw 7 is slightly unscrewed to allow the rotation (possibly with friction) of the base plate 6 on the cock 5 around the shock-absorbing bearing 8. The base plate 6 is then pivoted in one direction or the other, for example by pushing it by any suitable means (tweezers). As the sliding plate 40 is integral in rotation with the base plate 6, it will follow the rotation imposed on the base plate 6 for the reference setting. As for the radial adjustment of the position of the stud holder 4, once the reference setting is complete, the fixing screw 7 must be screwed back into the cock 5 to ensure that the two plates are locked relative to each other and that they are integral with the cock 5.

Preferably, the first segment 43 of the sliding plate 40 and the corresponding second segment 63 of the base plate 6 and their respective openings 45, 65 are arranged to allow rotation of the plate assembly. base 6/sliding plate 40 of at most ± 30° relative to a middle position and preferably, of at most ±13° around the shock bearing 8.

The above watchmaking device for implementing the method for adjusting the isochronism according to the invention has been described by way of example only. Other devices or arrangements may make it possible to implement the method according to the invention for adjusting the isochronism of a regulating organ of the sprung balance type comprising a hairspring by adjusting the position of the outer end of the hairspring relative to the axis of the sprung balance and by avoiding an undesirable stress when pinning the hairspring.

Claims (7)

Method for adjusting the isochronism of a balancing-spring type regulating organ (1, 2) comprising a balance spring (1), the method being characterized by the following steps: (a) Provide a hairspring (1) characterized by an actual terminal curve radius different from the theoretical terminal curve radius targeted during the manufacture of the hairspring (1); b) Assembling said hairspring (1) with a balance wheel (2) to form a regulating organ of the hairspring-balance type; c) mounting the balance spring (1, 2) on a watch movement or a subassembly of the watch movement, the frame (5) of which comprises a stud (3) whose position relative to the axis of the balance spring (1, 2) is adjustable; d) inserting the outer end (1b) of the hairspring (1) into the stud (3) without constraining the hairspring (1) by adjusting the radial position of the stud (3) relative to the axis of the hairspring balance (1, 2); e) Make the outer end (1b) of the hairspring (1) integral with the stud (3); f) Start the balance spring (1, 2) and measure its isochronism and its rate; g) Adjust the position of the stud (3) relative to the axis of the balance spring (1, 2) to constrain the outer end (1b) of the balance spring (1) and adjust the isochronism and the rate of the balance spring (1, 2) accordingly. Method according to the preceding claim, characterized in that the position of the stud (3) relative to the axis of the balance spring (1, 2) is radially adjustable in the general plane (P) in which the balance spring (1) extends; and in that the outer end (1b) of the balance spring (1) is introduced into the stud (3) without constraining the hairspring (1) by adjusting the radial position of the stud (3) relative to the axis of the hairspring balance (1, 2) in said general plane (P). Method according to the preceding claim, characterized in that the radial position of the stud (3) relative to the axis of the sprung balance (1, 2) is adjusted to constrain the outer end (1b) of the spring (1) until reaching chronometric performances or a target rate and isochronism for the regulating organ. Method according to the preceding claim, characterized in that during step g), the radial position of the stud (3) is adjusted in the general plane (P) in which the balance spring (1) extends. Method according to one of the preceding claims, characterized in that a plurality of balance springs are provided, manufactured in the same batch and each characterized by a distinct real terminal curve radius different from the theoretical terminal curve radius targeted at manufacture; in that steps b) to f) of the method are applied to each of the balance springs; and in that for each of the balance springs obtained, the position of the stud (3) relative to the axis of the balance spring (1, 2) is adjusted to constrain the outer end (1b) of the balance spring (1) and adjust the isochronism and the rate of each balance spring (1, 2) to make them tend towards an isochronism and a rate that is essentially similar for all the balance springs in the batch or towards a target isochronism and a rate chosen beforehand. Method according to one of the preceding claims, characterized in that the spiral (1) is made of a material which is not plastically deformable. Method according to the preceding claim, characterized in that the spiral (1) is made of silicon.

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