CH703581B1 - Spiral spring for regulating member of a mechanical chronograph. - Google Patents

Abstract

A helical spring (1) for a regulating member of a mechanical chronograph, characterized by a sufficiently high stiffness to allow the balance spring (1) to oscillate with an oscillation frequency of 500 Hz or more when This spring-spring (1) is mounted on a spiral axis (2). The invention also relates to a mechanical chronograph comprising such a spiral spring.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spiral spring for a regulating member of a mechanical chronograph.

STATE OF THE ART [0002] Mechanical watches generally comprise a regulating member composed of an inertial flywheel called a balance, on the axis of which is fixed a spiral spring called a spiral. The sprung balance oscillates about its equilibrium position at a frequency which depends in particular on the stiffness of the balance spring and the moment of inertia of the balance.

[0003] The known pendulums consist of an annular mass, the serge, held by two or three arms. Given the available energy, the pendulums have a high moment of inertia for a small mass; That is to say that their diameter is as large as the volume available, and that the mass is concentrated at the periphery in the serge. This moment of inertia can also be modified to adjust the watch either manually by means of screws or automatically in the case of bimetallic balances which deform with the temperature. Unintentional deformations of the pendulum, for example due to expansion, however, have the effect of disturbing the movement of the watch.

In other words, the balance acts as a flywheel and fills the lack of energy stored in the balance spring during deformation. However, the pendulum is a source of many disturbances, due to the inaccuracies of its inertia during its manufacture, dilatations, etc.

[0005] A given balance coupled to a given hairspring oscillates at a determined frequency. The number of intervals per unit of time determines the time resolution of the regulator. For example, a mechanical watch displaying the seconds of the current time must include a regulating member performing at least 3600 vibrations per hour. In practice, the usual regulating elements perform 28 800 or sometimes 36 000 vibrations per hour, which makes it possible to measure the time with a resolution of 0.125 and 0.1 second respectively.

[0006] By increasing the oscillation frequency, the temporal resolution is improved, which makes it possible to count shorter time intervals. An improved temporal resolution is especially useful for chronographs, for which a time resolution of one hundredth of a second is sometimes desired. However, a high oscillation frequency generates significant energy losses, particularly at the exhaust, which reduces the watch's power reserve. For this reason the oscillation frequency chosen is usually a compromise between the chronograph resolution requirements and the desire to maintain a power reserve as high as possible for the display of the current time.

The usual chronograph watches take the energy necessary for the operation of the chronograph on the kinematic chain linking the barrel to the regulating member and the indicators of the watch. As a result, the watch is disturbed when the chronograph is started.

The patent application WO 03/065 130 in the name of TAG Heuer SA and the contents of which is incorporated by reference suggests a construction in which a basic movement intended for displaying the current time is provided with a First barrel and a first regulating member performing 28,800 oscillations per hour, while an auxiliary chronograph module is equipped with a second barrel and a second regulating member performing 360,000 oscillations per hour. This construction makes it possible to produce a chronograph watch capable of measuring the time with a resolution of one hundredth of a second, without affecting the power reserve of the basic movement used for displaying the current time. Moreover, since the two kinematic chains are independent, The start of the chronograph does not affect the precision of the basic movement and the movement of the watch. This solution was implemented in the "Caliber 360" of TAG Heuer which demonstrated the technical feasibility of the solution.

[0009] The known spiral springs would not be adapted to a regulating member operating at 3,600,000 vibrations per hour.

BRIEF SUMMARY OF THE INVENTION An object of the present invention is to propose a spiral spring for a regulating member of an effective mechanical chronograph and adapted to work with a regulating member at 3,600,000 vibrations per hour or more.

According to the invention, these objects are achieved in particular by means of a spiral spring for a regulating member of a mechanical chronograph comprising the characteristics of the main claim and a mechanical chronograph comprising such a spiral spring.

The balance spring for a regulating member of a mechanical chronograph according to the invention is characterized by a sufficiently high stiffness to allow the balance spring to oscillate with an oscillation frequency is 500 Hz or more when this spring Spiral is mounted on a spiral axis. The frequency of oscillation also depends on the moment of inertia of the axis and other elements as will be seen later.

This solution has, in particular, the advantage over the prior art of being adapted to a regulating member operating at 3,600,000 vibrations per hour.

BRIEF DESCRIPTION OF THE DRAWINGS [0014] Examples of the implementation of the invention are indicated in the description illustrated by the appended figures in which:

FIG. 1 illustrates a perspective view of a regulating member comprising the spiral spring according to the invention.

FIG. 2 illustrates a plan view of a regulating member comprising the spiral spring according to the invention.

FIG. 3 illustrates a perspective view of the axis, the hub and the plate of a regulating member comprising the spiral spring according to the invention.

FIG. 4 illustrates a launcher.

FIG. 5 illustrates a top view of an anchor.

FIG. 6 illustrates a bottom view of the anchor of FIG. 5.

FIG. 7 illustrates a three-dimensional view of the regulating member as well as the spiral spring according to the invention, the anchor and the anchor wheel.

An embodiment of a regulating member according to an embodiment of the invention is illustrated in FIGS. 1 and 2. This regulating member is in particular intended to serve as a regulator for the chronograph function of a mechanical chronograph: a same movement may comprise two regulating members on the same plate, or on two separate plates, one of the regulating organs serving to Adjust the running of the watch while the other regulating member, similar or similar to that described in this application, is used to set the chronograph function. A separate barrel provides the energy required for each regulator, thus avoiding disturbances in the running of the watch when the chronograph is switched on.

The power reserve of the second barrel, which indicates the time that can still be timed before having to reload the second barrel, is preferably indicated on the dial by means of a chronograph power reserve indicator. The power reserve of the first drum charging the first regulating member used for the display of the current time is advantageously indicated separately on the dial by means of a power reserve indicator of the watch. The two barrels may preferably be loaded simultaneously by means of a common winding rod which engages on the two barrels and / or by means of a common oscillating mass. In another variant, the first barrel is automatically raised and the second cylinder is manually re-mounted. In a variant, The two barrels can be raised separately by means of two separate winding rods and / or oscillating masses. In another variant, one of the barrels (for example the chronograph barrel) is loaded by the other barrel wound up manually or automatically; The energy available is then distributed between the two barrels.

The regulator illustrated comprises a balance spring 1 mounted by means of a ferrule 5 on a spiral axis 2. The regulating member is devoid of a balance. According to the example, the chronograph regulator is sized to oscillate at frequencies never reached before, preferably at a frequency of 3,600,000 vibrations per hour, ie 500 Hz.

In order to reach these high frequencies, the regulating member comprises in particular an axis 2, which is intended to rotate between two bearings (not shown) when the hairspring 1 stretches and relaxes. A plate 4 mounted on this axis carries the plate pin 40 which collaborates with the horns 60, 65 and with the pin 61 of an anchor 6 shown in FIGS. 5 and 6, similar to the more conventional Swiss anchor exhausts.

The plate 4 is advantageously made of silicon or ceramic or of another material with a lower density than that of axis 2 in order to reduce its moment of inertia. It is advantageously formed of two disks: the large plate 42 and the small plate 43, connected to each other by a barrel 45. The small plate may comprise a notch 430 for the dart. A single tray, with a single disc, can also be used.

The axis 2 also carries a hub 3 which is driven or glued to serve as a bearing surface for the whip 72 of the launcher, described below in connection with FIG. 4. The axis of the regulating member is thus accelerated almost instantaneously when the push-button 75 is engaged in order to impart a pulse to the hub 3 through the blade 73, the column wheel 74 and the launcher 7. When the chronograph is stopped, the pressure of the whisk 72 on the hub makes it possible to lock the hub by maintaining the chronograph regulating member and thus preserving the position of the hands of the chronograph.

[0021] In contrast to a balance, the hub 3 is devoid of spokes; Its mass is therefore concentrated near the center, so as to reduce its moment of inertia. The hub 3 is advantageously made of silicon or of another material with a lower density than that of the axis 2, in order to reduce its moment of inertia. In a variant, the hub is made of titanium and / or aluminum and / or an alloy containing at least one of these materials.

Blind openings 30 in a plane perpendicular to the axis 2 make it possible to further lighten the hub 3. Blind or through openings in other directions, including holes passing through the hub parallel to the axis or according to Can also be used to lighten the hub 3. It is also possible to lighten the hub 3 by making it with a lighter core coated with a more resistant coating on which the whip 72 of the launcher can give a Pulse without deforming the hub 3.

In the same way, it is also possible to lighten the tray 4 by making openings through or through, by giving it a non-circular shape, in order to reduce its moment of inertia.

[0024] The regulating member is devoid of a balance; Its adjustment is therefore made only with the tapping of the hairspring 1, advantageously by adjusting the length of the oscillating portion of the hairspring by means of a screw perpendicular to the plate and making it possible to adjust the point of attachment of the outer end of the hairspring The deck or on a bridge. This system allows a very precise adjustment of the length of the hairspring, but other known types of adjustment are applicable to the hairspring.

The diameter of the hub 3 is as small as possible, always with a view to reducing its moment of inertia. In a preferred embodiment, the diameter of the hub 3 is between 1.5 and 10 times the maximum diameter of the axis 2, for example between 5 and 6 times the diameter of the axis 2. In the example illustrated, the The outer diameter of the hub 3 is identical to the outer diameter of the plate 4. If a bearing surface for the larger launcher 7 is required, a hub 3 may be used slightly larger than the plate 4, Not double the maximum diameter of the large plate 42.

Unlike a regulating member comprising a balance, which provides a potential and kinematic energy substantially greater than that of axis 2, the potential and kinetic energy accumulated by the hub 3 is less than that which is accumulated By the axis 2 at each oscillation, preferably negligible with respect to that of the axis 2.

The hub 3 may also be an integral part of the axis 2. In a variant, the hub 3 and the plate 4 are integrated in a single element, for example produced by turning, which carries the plate pin 40 is on Which bears the launcher 7. In another variant, the ferrule also is integrated in this element. This element may advantageously be made of titanium and / or aluminum and / or an alloy containing at least one of these materials.

The ferrule 5 makes it possible to maintain the inner end of the hairspring 1 on the axis 2. It is advantageously made in the form of a circular disk, two or more segments of which are truncated in order to lighten it and reduce its moment of inertia. A notch 50 in the side of the ferrule 5 makes it possible to fix the balance spring. The maximum diameter of the ferrule is preferably of the same order of magnitude as the maximum diameter of the plate and of the hub. For example, the diameter of the hub 3 may be between 1 and 3 times the maximum diameter of the ferrule 5.

The balance spring 1 may be made of metal, preferably invar, silicon, diamond, corundum or any other suitable material. Advantageously, the hairspring is significantly steeper than a conventional hairspring, and thus exerts a return torque towards the rest position which is considerably greater than that of a conventional hairspring. The stiffness of the spiral is given by the following formula, which defines the stiffness of a spiral spring as a function of the material used to make it: C = Μ / φ C = stiffness constant of the balance spring, M = torque Of the balance spring, φ = torsion angle.

A high stiffness required for an oscillation at 500 Hz can be obtained by combining at least two of the following measures: The number of turns is less than in the traditional spirals, so as to reduce the length of the vibrating part. Advantageously, the hairspring has less than 5 turns, for example 4, 5, preferably 3 turns or less. The spiral is thicker than the conventional spirals: for example, its thickness is greater than 40 μm, preferably greater than 50 μm, for example 55 μm. It is higher than the conventional spirals: for example, its height is greater than 200 μm, preferably greater than 215 μm, for example 230 μm. It may be made of a more rigid material, preferably not sensitive to temperature variations. - Ribs or a rectangular section can be used to stiffen it. - A surface coating can be used to stiffen it. - The section of the balance spring may be non-constant along the spiral to stiffen it.

The ratio (e3 · h) / l, e being the thickness of the balance spring, its height and its length, which defines the stiffness of a spiral spring as a function of the geometrical parameters and independently of the material Used to make it, is at least 20 times greater than the same ratio of a conventional balance spring, preferably 30 times.

The spiral is advantageously constituted by a perfect spiral of Archimedes, which is favorable to isochronism. Due to its rigidity and its short length, it virtually does not deform under the effect of gravity so that Philips end curves may not be necessary or even advantageous. Its stiffness also makes it less sensitive to disturbances due to magnetostriction. Moreover, a rigid spring has the effect of increasing the frequency of the oscillations and of reducing their amplitude, which makes it possible to operate it in a reduced range of oscillations favorable to isochronism. Oscillations of reduced amplitude provide, in other words, great precision for the watch. Since the oscillations of the balance spring are practically isochronous, the use of a coating,

The stiffness of the spiral gives it an effective geometrical stability: the spiral therefore does not deform almost in different planes of the space. Advantageously, therefore, this stiff spring has a greater static and dynamic stability compared to conventional spirals at 3-5 Hz. The stiffness of the balance spring also makes it non-self-starting, unlike the conventional balance and spring regulating elements.

The frequency of oscillation of the conventional spiral-balance assemblies used in timepieces can be determined using the known formula 1). This frequency is thus inversely proportional to the square root of the moment of inertia / balance.

In the state of the art, the moment of inertia / of the rotating parts of the regulating member is determined almost exclusively by the serge which constitutes in approximation a portion of a hollow cylinder. 2)

From which is deduced: 3)

F Frequency of oscillation [Hz] M Elastic torque of the balance spring [Nm] I Balance mass moment of inertia [kg / m2] R External diameter of balance [m] ] P Specific mass of the balance [kg / m3] Equations 2) and 3) can not, however, be applied to the regulating member of the invention since this member is devoid of a balance. According to the invention, the regulating member is therefore dimensioned by integrating in the equation 1) above a moment of inertia / calculated taking into account elements that are traditionally neglected in the prior art, in particular by integrating into The calculation of the moment of inertia / the moments of inertia of the axis 2, the plate 4, the hub 3 and the balance spring 1 itself, which gives us an approximation for the oscillation frequency.

The moment of inertia of the hairspring 1, however, varies during each cycle when the hairspring is deformed, so that the application of the above formula gives only an approximation. In practice, a regulating member oscillating at the desired frequency is obtained using the formula 1) above, being approximated by summing the inertial mass of all the parts in rotation. An adjustment is then obtained by successive approximations by modifying by means of the cock, a racket with a screw on the top, or another adjustment element (not shown) the length of the portion of the hairspring 1 which can vibrate.

Prototypes have been produced with regulating organs capable of performing 500 oscillations per second, which makes it possible to measure timed durations with a resolution of one thousandth of a second. It is thus possible to realize a mechanical chrono at 500 Hz or a thousandth of a second.

[0041] FIGS. 5 and 6 illustrate an embodiment of an exhaust anchor 6 that can be used with such a regulating member. Compared to a conventional regulating member, the regulating member of the invention is characterized by substantially higher rotation speeds of the axis, for example 125 times greater. The pulse provided by the tooth of the anchor wheel (not shown) to the anchor 6 is therefore much shorter, the energy transmitted being on the other hand larger. This results in a much faster acceleration of the anchor 6: whenever the anchor wheel transmits a pulse to it, the anchor switches almost instantaneously (in less than one thousandth of a second) between a position and the position opposite. The speed of rotation of the teeth of the anchor wheel is such that the pallets can be suppressed and these teeth rest directly on the inlet and outlet arms of the anchor by projecting the inlet and outlet arms Of the anchor at a distance as soon as they strike them; The arms do not have time to slip on the teeth of the anchor wheel. In other words, the impulse response of the anchor is faster than those known and is of the annular type.

Accordingly, according to a characteristic independent of the invention, and as illustrated in FIGS. 5 and 6, the pallets are eliminated and an annular contact, that is to say a point contact on a stop or distributed according to a set of coplanar points and whose contact normals are concurrent, takes place directly between the teeth of the Wheel and the arms 62, 63 of the anchor. The length of the contact between the anchor and the anchor wheel is advantageously less than one tenth of a millimeter, instead of one millimeter of the prior art. Advantageously, the ends of these arms have a rounded shape, for example envelope or spiral or involute, which shape can be finely adjusted as a function of the frequency of the balance spring. In a variant, the teeth of the anchor wheel advantageously have a complementary engaging shape, which makes it possible to adapt better to high frequencies and to ensure a perfectly punctual contact. These forms of anchor arms are advantageous for ensuring rapid and punctual contact between the anchor and the anchor wheel, without bouncing and practically without slipping, even if, for example following an impact, the anchor or the wheel Of the anchor are not exactly at the position provided during the pulse. The arms may be provided with a coating, for example a Diamond-Like Carbon (DLC) coating to improve their impact resistance and further reduce the residual friction (if any) between the arms and the anchor wheel. Which makes it possible to adapt better to high frequencies and to ensure a perfectly punctual contact. These forms of anchor arms are advantageous for ensuring rapid and punctual contact between the anchor and the anchor wheel, without bouncing and practically without slipping, even if, for example following an impact, the anchor or the wheel Of the anchor are not exactly at the position provided during the pulse. The arms may be provided with a coating, for example a Diamond-Like Carbon (DLC) coating to improve their impact resistance and further reduce the residual friction (if any) between the arms and the anchor wheel. Which makes it possible to adapt better to high frequencies and to ensure a perfectly punctual contact. These forms of anchor arms are advantageous for ensuring rapid and punctual contact between the anchor and the anchor wheel, without bouncing and practically without slipping, even if, for example following an impact, the anchor or the wheel Of the anchor are not exactly at the position provided during the pulse. The arms may be provided with a coating, for example a Diamond-Like Carbon (DLC) coating to improve their impact resistance and further reduce the residual friction (if any) between the arms and the anchor wheel. The anchor or the anchor wheel are not exactly at the position provided during the pulse. The arms may be provided with a coating, for example a Diamond-Like Carbon (DLC) coating to improve their impact resistance and further reduce the residual friction (if any) between the arms and the anchor wheel. The anchor or the anchor wheel are not exactly at the position provided during the pulse. The arms may be provided with a coating, for example a Diamond-Like Carbon (DLC) coating to improve their impact resistance and further reduce the residual friction (if any) between the arms and the anchor wheel.

In order to be able to move rapidly, the anchor 6 is preferably made of a material that is lighter than steel, for example made of silicon. Through holes 64 make it possible to lighten it even more. The dart 61 is constituted by a bridge joining the two horns 60 and 65 but less thick than these horns and the rest of the anchor. The end of the dart 61 opposite the center of the anchor is pointed to cooperate with the plate peg 40.

The regulating member illustrated in the figures is advantageously employed as an independent regulator for a chronograph in order to adjust the movement of a chronograph hand at the center of the movement. For example, this regulating member can drive a needle in the center of the dial displaying the thousandths of a second of a timed duration and which traverses 100 graduations on the periphery of the dial in one tenth of a second. In order to avoid any play and energy loss, the regulating member is preferably arranged in an unusual manner very close to the center of the watch movement, thereby enabling the needle to be driven directly to the center, or in any case Through a chain of gear as short as possible, For example a gear chain comprising a single wheel for reversing the direction of rotation given by the anchor wheel. Preferably, the axis 2 of the balance spring is located in an imaginary circle coaxial to the movement and of diameter less than 50% of the maximum outside diameter of the movement, preferably less than 30% of the maximum outside diameter of the movement, and therefore very close to Center of movement.

The needle of the chronograph thus accelerated can be deformed in the manner of a fishing rod during accelerations, which affects the accuracy of reading during the displacement. In order to limit the extent of these deformations, the needle is advantageously ribbed and / or contoured to make it more rigid. The needle can also be replaced by a disc.

[0046] FIG. 4 illustrates the launcher mechanism which makes it possible to start the chronograph regulating member when the user presses the push-button 75 and then to block this regulating member when stopped. In the case of a regulating member according to the invention, the launcher comprises a flexible whisk 72 which bears directly on the hub 3. In a variant comprising a balance, this launcher mechanism may comprise a whisk 72 coming to rest On the pendulum. The whip may comprise one or more parts and is more flexible than the rest of the launcher, specifically to whip the hub and start it instantly. The pressure of the push-button 75 is transmitted by the blade 73 to the column wheel 74, which suddenly releases the launcher 7 which is actuated by the launcher spring 71. The energy of this spring 71 is transmitted to the whisk 72 which imparts a force to the hub 3 comprising a large tangential component so as to accelerate abruptly the hub or the balance and the axis of the balance spring which makes it possible to launch almost instantaneously 'oscillator. At rest, when the user has pressed the push-button 75, or on an additional push-button STOP (not shown), the whip 72 presses on the hub 3 exerting a considerable radial force in the position illustrated in FIG. 4, which instantly and energetically blocks the axis of the hub or of the balance. When the user has pressed on the push-button 75 or on an additional push-button STOP (not shown), the whip 72 presses on the hub 3 by exerting a considerable radial force in the position illustrated in FIG. 4, which instantly and energetically blocks the axis of the hub or of the balance. When the user has pressed on the push-button 75 or on an additional pushbutton STOP (not shown), the whip 72 presses on the hub 3 by exerting a considerable radial force in the position illustrated in FIG. 4, which instantly and energetically blocks the axis of the hub or of the balance.

The push button 75 in a preferred variant allows the user to perform the two functions START and STOP. Another push-button, not shown, allows the resetting.

When the user actuates the STOP function, it allows the launcher to mount on one of the columns of the column wheel 74. When the STOP function is activated, the spring of the launcher 71 allows the launcher 7 to fall into the column, Space between two columns of the column wheel 74 and at the same time to give a speed to the whip 72 which makes it possible to accelerate the hub or the barrel.

Advantageously, the blade 73 comprises a hook 730 which is intended to cooperate with the column wheel 74. In a variant, the blade and the hook constitute a single piece which is rather difficult to machine but which allows a reduction in the number of parts . In another variant, the hook 730 is a part distinct from the blade 73 and connected to it, for example through a screw, which makes it easier to machine.

[0050] FIG. 7 illustrates a three-dimensional view of the regulating member according to the invention, the spring 1, the anchor 6 and the anchor wheel 8. The rack 9 cooperates with the screw 90 for fine adjustment of the length of the spring 1 , With a tuning fork 10 as well as a bridge 12 which is connected to the stage of the movement through the screw 14.

The regulating member of the invention is also distinguished from the regulating organs of the prior art by the noise produced, which is different from the noise of the watch; Due to high oscillation frequencies, the usual tic-tac is replaced by a high frequency hum, with a main harmonic at 500 Hz and secondary harmonics at multiples of 500 Hz. This very characteristic and very noticeable buzzing allows the l The user is able to detect at the ear that the chronograph is running and thus avoid unwanted discharge of the chronograph barrel if the chronograph is started inadvertently or if one forgets to stop it. The distinct and characteristic noise of the chronograph regulator is therefore used as a signal indicating that the chronograph is operating.

According to an independent aspect of the invention, the balance spring of the regulating member according to the invention can be replaced by a magnetic return member.

Reference Numbers Used in the Figures 1 Spiral spring 10 Scale length 12 Bridge 14 Screw fixing the bridge to the plate 2 Axle of the balance spring 3 Hub 30 Recess in the hub 4 Plate 40 Plate anchor 42 Large tray 43 Small tray 430 Notch of small plate 45 Canon 5 Ferrule 50 Notch of ferrule 6 Anchor 60 Inlet horn 61 Dart 62 First arm of anchor 63 2nd arm of anchor 64 Holes through anchor 65 Horn 7 Launcher 71 Launcher spring 72 Whip 73 Blade 730 Blade hook 74 Column wheel 75 Push button

Claims (7)

8 Anchor wheel 9 Racket 90 Fine adjustment screw of the spiral length Claims

1. A balance spring for a mechanical chronograph, having at least two of the following characteristics so as to have a sufficiently high rigidity to enable said balance spring (1) to oscillate with an oscillation frequency Of 500 Hz or more when said balance spring (1) is mounted on a hairspring (2); Characterized in that said spiral spring (1) has a number of turns less than five, preferably three turns or less; Said spiral spring (1) has a thickness e greater than 40 μm; Said spiral spring (1) has a height h greater than 200 μm; Said spiral spring (1) is made of silicon and / or metal and / or diamond and / or corundum; Said spiral spring (1) comprises ribs; Said spiral spring (1) comprises a surface coating;

2. A spiral spring according to claim 1, characterized in that the spiral spring is in the form of a perfect Archimedes spiral.

3. The spiral spring according to claim 1, wherein all of the turns extend in a plane.

4. A mechanical chronograph comprising a balance spring (1) according to one of claims 1 to 3.

5. A mechanical chronograph according to claim 4, comprising an adjustment element arranged to adjust the length of the oscillating portion of said spiral spring.

6. A mechanical chronograph according to claim 5, comprising a plate, said adjustment element being a screw (90) perpendicular to the plate and arranged to adjust a fixing point on said plate or on a bridge of the outer end of said spring- Spiral (1).

7. Mechanical chronograph according to claim 5, comprising a ferrule (5), said ferrule (5) comprising a flank, said flank comprising a notch (50) configured to fix said spiral spring (1) to said ferrule Ferrule (5).