Hairspring for timepiece resonator mechanism provided with symmetrical means for adjusting the stiffness

Abstract

The invention relates to a balance spring, particularly for a resonator mechanism in watchmaking, the balance spring (100) comprising a flexible ribbon (2) wound upon itself in several turns, the ribbon (2) having a predefined stiffness, the balance spring (100) comprising means for adjusting its stiffness, the adjustment means comprising a flexible element (5) arranged in series with the ribbon (2), the flexible element (5) connecting one end (4) of said ribbon (2) to a fixed support (38), so as to add additional stiffness to the ribbon (2), the flexible element (5) preferably having a stiffness greater than that of the ribbon (2), characterized in that the flexible element (5) comprises two flexible parts (15, 16) each connecting the ribbon (2) to the fixed support (38), the two flexible parts (15, 16) being arranged relative to each other by axial symmetry along an axis (A) passing through preferably substantially through the center (0) of the spiral spring.The invention also relates to a clockwork resonator mechanism comprising such a spiral spring.

Description

Technical field of the invention

[0001] The invention relates to a balance spring for a resonator mechanism in watchmaking, the balance spring being equipped with symmetrical means for adjusting its stiffness. The invention also relates to a resonator mechanism in watchmaking equipped with such a balance spring. Technological background

[0002] In most mechanical watches, the energy needed to rotate the hands (e.g., minute and hour indicator hands) is stored in a barrel and then released by a balance-spring system, which includes a flywheel called a balance wheel, associated with a spring in the form of a spirally wound ribbon, called a balance spring.

[0003] At one internal end, the spiral is fixed to a shaft that is rotating with the balance wheel; at one external end, the spiral is fixed to a stud mounted on a stud holder which is itself fixed to a bridge (or cock).

[0004] The balance wheel's rotation is maintained—and its oscillations counted—by an escapement mechanism comprising an anchor with a low-amplitude oscillating motion, equipped with two pallets that engage the teeth of an escape wheel. Thus engaged, the escape wheel is imparted a step-by-step rotational movement whose frequency is determined by the anchor's oscillation frequency, itself synchronized with the balance wheel's oscillation frequency.

[0005] In a traditional escapement mechanism, the oscillation frequency is approximately 4 Hz, or about 28,800 vibrations per hour (A / h). One objective of skilled watchmakers is to ensure the isochronism and regularity of the oscillations (or constant rate) of the balance wheel.

[0006] It is known to regulate the course of the balance wheel by adjusting the active length of the balance spring, defined as the curvilinear length between its inner end and a counting point, located in the vicinity of the outer end of the balance spring and generally defined by a pair of stops carried by a key mounted on a rack system.

[0007] In operation, this regulator system is fixed in rotation relative to the axis of the balance spring. However, it is possible, by manual intervention, to finely adjust its angular position, e.g. by pivoting, using a screwdriver, an eccentric that acts on the regulator system in the manner of a cam.

[0008] The assembly comprising the bridge, the regulator system, the key, the stud holder, the stud, the arbor, the spring, and the balance wheel is commonly referred to as the "regulating organ." Examples of regulating organs are provided by international application WO 2016 / 192957 and by European patent EP 2 876 504, both in the name of the watch manufacturer ETA.

[0009] There are racket systems with a stud holder to which one end of the balance spring is attached, and whose racket system key allows for some play to permit the balance spring to move between the two stops. However, the chronometric properties, particularly anisochronism as a function of amplitude, are very sensitive to play in the racket key, while this play is difficult to control precisely.

[0010] In some mechanisms, the stops are adjustable to tighten the balance spring and eliminate play, particularly during its operation. In this case, the rate is first set by moving the regulator key, then the balance spring is tightened with the key. However, tightening the balance spring with the regulator key risks putting stress on it and creating chronometric errors, notably by misaligning the coils. Furthermore, eliminating the play also alters the rate, and once the balance spring is tightened, the regulator key cannot be moved along the spring to fine-tune the rate.

[0011] Other balance springs incorporate an integrated adjustment mechanism. In these balance springs, the rate is not adjusted by changing the effective length of the balance spring, but by applying a force or torque to an elastic element arranged in series with the balance spring. Specifically, a flexible element is placed in series with the ribbon between one end of the ribbon and a fixed support to modify the stiffness of the attachment point and provide additional flexibility to the resonator. Thus, the effective stiffness of the resonator comprises the stiffness of the ribbon and the stiffness of the flexible element.

[0012] A variable force or torque is then applied to pre-stress the flexible element. By pre-stressing the flexible element, its stiffness, which partly determines the restoring force acting on the pendulum, changes, while the stiffness of the ribbon remains unchanged. By modifying this stiffness of the flexible element, the stiffness of the entire resonator (ribbon stiffness and flexible element stiffness) changes, which consequently alters the resonator's rate and allows for precise adjustment of the timebase frequency. This results in high precision in rate tuning, as only one element is being adjusted to change the stiffness.

[0013] Such a spiral spring equipped with an elastic element is described for example in patent application EP4009115 filed in the name of Omega SA.

[0014] However, the geometric configuration of the flexible element creates a risk of creep in the adhesive that secures the fixed support of the spiral spring during movement. Indeed, the position of the fixed support and the orientation of the force or torque applied to the flexible element create stresses on the adhesive, which can lead to creep and thus a reduction in the accuracy of the adjustment.

[0015] Furthermore, the direction in which the adjustment force is applied may differ from the intended direction due to manufacturing, assembly, alignment errors, etc. This difference will alter the operation and degrade the accuracy of the adjustment.

[0016] Furthermore, due to shocks and friction, hysteresis can occur in the adjustment mechanism, as the direction of force application changes and does not return to its initial direction after the shock. This results in altered operation and reduced adjustment accuracy. Summary of the invention

[0017] The aim of the present invention is to overcome all or part of the disadvantages mentioned above, in particular to minimize the sensitivity to changes in the direction of the adjusting force, by proposing a balance spring equipped with effective and precise adjustment means, configured in particular to regulate the rate of a timepiece by modifying the effective stiffness of said balance spring.

[0018] To this end, the invention relates to a spiral spring for a resonator mechanism of watchmaking, the spiral spring comprising a flexible ribbon wound on itself in several turns, the ribbon having a predefined stiffness, the spiral spring comprising means for adjusting its stiffness, the adjustment means comprising a flexible element arranged in series with the ribbon, the flexible element connecting one end of said ribbon to a fixed support, so as to add additional stiffness to the end of the ribbon, the flexible element preferably having a stiffness greater than that of the ribbon.

[0019] The invention is remarkable in that the flexible element comprises two flexible parts, each connecting the ribbon to the fixed support, the two parts being arranged relative to each other by axial symmetry along an axis, the axis (A) preferably passing substantially through the center of the spiral spring.

[0020] Thanks to the symmetrical arrangement of the two-part flexible element, a balanced variable force or torque can be applied, avoiding the risk of creep in the adhesive used to fix the stationary support during movement. This is because the force or torque is better distributed across the flexible element, and therefore across the joint with the stationary support during movement.

[0021] According to a particular embodiment of the invention, the flexible element is arranged at an external end of the ribbon.

[0022] According to a particular embodiment of the invention, the two flexible parts are substantially identical.

[0023] According to a particular embodiment of the invention, each flexible part comprises one or two flexible necks.

[0024] According to a particular embodiment of the invention, each flexible part comprises a translation table equipped with two substantially parallel flexible blades and a movable rigid part to which the ribbon is connected.

[0025] According to a particular embodiment of the invention, the flexible element comprises a flexible guide equipped with two uncrossed blades.

[0026] According to a particular embodiment of the invention, the flexible part comprises a flexible blade.

[0027] According to a particular embodiment of the invention, each flexible part comprises a flexible arm to which the ribbon is connected.

[0028] According to a particular embodiment of the invention, each flexible part comprises a flexible hook.

[0029] According to a particular embodiment of the invention, the adjustment means comprise pre-stressing means for applying a variable force or torque to the flexible element, so as to vary only the stiffness of the flexible element.

[0030] According to a particular embodiment of the invention, the prestressing means are configured to apply a variable force or torque to each part of the flexible element.

[0031] According to a particular embodiment of the invention, the torque or force is continuously adjustable by means of prestressing.

[0032] According to a particular embodiment of the invention, the prestressing means are configured to apply an identical variable force or torque to each part of the flexible element.

[0033] According to a particular embodiment of the invention, the prestressing means comprise a screw configured to bear against the flexible element.

[0034] According to a particular embodiment of the invention, the prestressing means comprise two flexible levers, each connected to a flexible part.

[0035] According to a particular embodiment of the invention, the prestressing means comprise two springs, each spring being connected to a flexible part.

[0036] According to a particular embodiment of the invention, the prestressing means comprise a secondary flexible blade connected to each flexible part.

[0037] According to a particular embodiment of the invention, the two levers are connected to each other by a movable body.

[0038] The invention also relates to a rotary resonator mechanism, in particular for a watch movement, comprising an oscillating mass and such a balance spring. Brief description of the figures

[0039] The aims, advantages and features of the present invention will become apparent from the reading of several embodiments given solely by way of non-limiting examples, with reference to the accompanying drawings in which: there figure 1 schematically represents a top view of a spiral spring according to a first embodiment of the invention, the figure 2 schematically represents a top view of a spiral spring according to a second embodiment of the invention, the figure 3 schematically represents a top view of a spiral spring according to a third embodiment of the invention, the figure 4schematically represents a top view of a spiral spring according to a fourth embodiment of the invention, the Figure 5 schematically represents a top view of a spiral spring according to a fifth embodiment of the invention, the figure 6 schematically represents a top view of a spiral spring according to a sixth embodiment of the invention, the figure 7 schematically represents a top view of a spiral spring according to a seventh embodiment of the invention, the figure 8 schematically represents a top view of a spiral spring according to an eighth embodiment of the invention, the figure 9 schematically represents a top view of a spiral spring according to a ninth embodiment of the invention, the figure 10 schematically represents a top view of a spiral spring according to a tenth embodiment of the invention, the figure 11schematically represents a top view of a spiral spring according to an eleventh embodiment of the invention, the figure 12 schematically represents a top view of a spiral spring according to a twelfth embodiment of the invention, and the figure 13 schematically represents a top view of a spiral spring according to a thirteenth embodiment of the invention, and the figure 14 is an enlarged view of a portion of the spiral spring according to the thirteenth embodiment of the invention of the figure 13 . Detailed description of the invention

[0040] THE figures 1 to 13Each figure shows a schematic representation of a different embodiment of a balance spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, particularly for a resonator mechanism in a watch. Here, the balance spring extends substantially in a plane. The balance spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 comprises a flexible ribbon 2 wound around itself in several turns, the ribbon 2 having a predefined stiffness. The balance spring includes means for adjusting its stiffness. For example, the adjustment means are particularly actuable when the balance spring is mounted on a plate of a watch movement.

[0041] The adjustment means comprise a flexible element 5 arranged in series with the ribbon 2, the flexible element 5 connecting one end 4, 9 of said ribbon 2 to a fixed support 11, 14, 17, 24, 29, 38, 44 and integral with one end 4, 9 of the ribbon 2. The flexible element 5 adds additional stiffness to that of the ribbon 2. The flexible element 5 preferably has a stiffness greater than that of the ribbon 2. The flexible element 5 is arranged following the ribbon 2, in its extension. Preferably, the adjustment means 5 and the ribbon 2 are a single piece, or even formed from the same material.

[0042] The spiral spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 also includes preload means 6 to apply a variable force or torque to the flexible element 5. Thus, the stiffness of the spiral spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 can be adjusted, in particular to improve the accuracy of the movement's operation.

[0043] Preferably, the end of the ribbon 2 remains substantially stationary, regardless of the preload adjustment. The force or torque applied to the flexible element 5 does not change the position of the end 4 of the ribbon 2 to which the flexible element is attached. Only the flexible element 5 is acted upon to modify its stiffness, without directly affecting the ribbon 2. This results in even greater precision, as only one element is used for stiffness adjustment. During oscillations, the end 4 of the ribbon 2 can be mobile.

[0044] Furthermore, the torque or force is continuously adjustable by means of prestressing 6. In other words, the torque or force is not restricted to point values. Thus, the stiffness of the flexible element 5 can be adjusted with high precision.

[0045] The prestressing means 6 preferably allow the flexible element 5 to move in translation or rotation within the plane of the spiral spring. This allows the stiffness of the flexible element 5 to be varied.

[0046] The embodiments described below include a flexible element 5 attached to the outer end 4 of the ribbon 2. The inner end 9 of the ribbon 2 is assembled to a support 3 for an oscillating mass of the resonator. According to alternative embodiments, not shown in the figures, the flexible element is connected to the inner end of the ribbon, so as to be in series between the ribbon and the support for the oscillating mass.

[0047] In the embodiments of spiral springs 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 described in the figures 1 to 13 , the flexible element 5 comprises two flexible parts 15, 16 each connecting the ribbon 2 to the fixed support 11, 14, 17, 24, 29, 38, 44.

[0048] According to the invention, the two flexible parts 15, 16 are arranged relative to each other by axial symmetry about an axis A of the spiral spring. In other words, the two flexible parts 15, 16 are positioned so as to be symmetrical with respect to said axis A.

[0049] Preferably, the axis A passes substantially through the center 0 of the spiral spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, and on the other hand, the axis A passes, preferably, through the outer end 4 of the ribbon 2.

[0050] Thus, the two flexible parts 15, 16 are arranged at the periphery of the spiral spring, so that the two flexible parts 15, 16 are arranged at the same distance from the center 0 of the spiral spring 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120.

[0051] The two flexible parts 15, 16 are preferably arranged relative to each other in a "mirror" effect with respect to axis A. To this end, the two flexible parts 15, 16 are preferably substantially identical.

[0052] Preferably, the prestressing means 6 apply a substantially identical force or torque to each flexible part 15, 16. The directions of the forces are preferably substantially parallel.

[0053] In one variant, the prestressing means 6 apply forces or couples independent of each other on each flexible part 15, 16.

[0054] Alternatively, the prestressing means 6 apply a single force or torque, which is redistributed over the two flexible parts 15, 16, preferably in a substantially equal manner.

[0055] In the spiral spring 1 of the first embodiment, the adjustment means include a single flexible blade 7 as a flexible part 15, 16. The flexible element 5 further includes a fixed support 14 in the form of a two-pronged fork 17, 18. Each flexible blade 7 connects the end 4 of the ribbon 2 to a different prong 17, 18 of the fixed support 14. The flexible blades 7 are arranged on the same axis in the rest position of the spiral spring 1.

[0056] For example, the figure 2 Each flexible portion 15, 16 of the flexible element 5 of the spiral spring 1 comprises a neck 8 thinned within the material thickness, the neck 8 being flexible. The flexible element 5 further includes a fixed support 14 in the form of a two-pronged fork 17, 18 as in the first embodiment. Each neck 8 connects the end 4 of the ribbon 5 to a prong 17, 18, the necks 8 being arranged in the same direction.

[0057] The third embodiment of the spiral spring 10 of the figure 3 shows flexible parts comprising two flexible necks connected by a rigid section.

[0058] For the fourth embodiment of the spiral spring 20 of the figure 4 Each flexible portion 15, 16 of the flexible element 5 of the spiral spring 20 comprises a pivot with uncrossed flexible leaves. Here, the pivot comprises two uncrossed flexible leaves 51, 52 joined, on one side, to the end 4 of the ribbon 2, and on the other side to the teeth of the fixed support 24, spreading apart from each other. A first flexible leaf of each pivot is arranged in a direction tangential to the end 4, while a second flexible leaf is oblique, extending away from the end 4.

[0059] THE Figures 5, 6, 7The figures show a spiral spring 30 in which the flexible parts of the flexible element 5 include a translation table. The translation table comprises two flexible blades. The flexible blades 21, 22 are substantially parallel and are arranged on different lines. Preferably, the flexible blades 21, 22 of a translation table are joined to the same face 25 of the fixed support. The rigid part 23 has an elongated rectangular shape, to which the outer end 4 of the ribbon 2 is joined in its extension to one side of the rigid part 23. The secondary flexible blades 21, 22 are substantially perpendicular to the rigid part 23 and to the outer end 4. In the figure, the variable force or torque is applied to the rigid part 23, preferably parallel to the blades 21, 22.

[0060] On the Figure 5The fixed support 14 has a two-pronged fork shape, and the blades of a translation table connect the end 4 to one tine of the fork. The blades are arranged in a direction tangential to the end 4 of the ribbon 2.

[0061] In the spiral spring 50 of the figure 6 , the flexible blades of the translation tables of each flexible part 16, 17 are substantially parallel to the axis of symmetry A of the flexible element 5. Each fixed support 29 has an inverted T shape, the flexible blades connecting the top of the T to the end 4 of the ribbon 2. The end 4 has an elongated shape tangential to the ribbon 2, and on which the flexible blades of the translation tables are joined.

[0062] To modify the overall stiffness of the spiral springs 1, 10, 20, 30, 40, 50 of the preceding embodiments, the prestressing means 6 apply a variable force or torque to each flexible part 16, 17 of the flexible element 5. For example, forces F1, F2 are represented by arrows directed against the flexible parts 16, 17.

[0063] Thus, we modify the stiffness of the flexible parts 15, 16 of the flexible element 5 and therefore of the assembly comprising the ribbon 2 and the flexible element 5.

[0064] The prestressing means 6 include, for example, a screw (not shown in the figures) in contact with each flexible part 16, 17 to apply the said forces F 1 , F 2 .

[0065] Alternatively, the prestressing means 6 include one or more actuators in contact with the flexible parts 16, 17 of the flexible element 5.

[0066] Preferably, the variable force or torque applied to each flexible part 15, 16 is identical. However, in these embodiments, the variable force or torque applied to each flexible part 15, 16 may be different.

[0067] In the spiral spring 60 of the figure 7 , the flexible blades of the translation tables of each flexible part 16, 17 are substantially parallel to the axis of symmetry A of the flexible element 5. Each fixed support 29 has an inverted T shape, the flexible blades connecting the top of the T to the end 4 of the ribbon 2. The end 4 has an elongated shape tangential to the ribbon 2, and on which the flexible blades of the translation tables are joined.

[0068] The flexible parts 16, 17 of the spiral spring 60 of the figure 7include two movable bodies 35, 36 each connected to the end 4 of the ribbon 2 by a secondary flexible blade 7 substantially tangential to the ribbon 2. The flexible blades 42, 43 of a translation table connect a movable body 35, 36 to the fixed support 29 in the shape of an inverted T, and are substantially perpendicular to the secondary blades 7.

[0069] The prestressing means 6 further include a third movable body 19 in the shape of a circular arc, connected to the two movable bodies 35, 36 of the flexible element 5 by two flexible levers 26, 27. Each flexible lever 26, 27 partially surrounds the wound ribbon 2. The third body 19 is arranged on the opposite side of the spiral spring 60 from the fixed support 38.

[0070] To modify the overall stiffness of the spiral spring 60, the prestressing means 6 apply a variable force or torque to the third movable body 19 of the prestressing means 6. For example, a force F is represented by an arrow directed against the third body 19. Preferably, the force F is parallel to the axis A.

[0071] In this case, a substantially identical force is transmitted to the two flexible parts 16, 17 of the flexible element 5, from a single force F applied to the third body 19, via the two levers 26, 27.

[0072] On the figure 8 , the flexible parts 15, 16 of the flexible element 5 of the spiral spring 70 have a rounded flexible hook 28 in place of the teeth of the fixed support 44. The tip of the flexible hooks 28 is oriented towards the end 4 of the ribbon 2, and are connected to the end 4 of the ribbon 2 by a single flexible blade 7.

[0073] The flexible hooks 28 are further connected by two flexible levers 26, 27, to a body in the shape of an arc of a circle, arranged on the other side of the spiral spring 70 with respect to the fixed support 29, as in the previous embodiment.

[0074] The embodiments of the spiral spring 90 of the figures 9 And 10 include flexible parts 15, 16, each equipped with a translation table 31, a single flexible blade 7, and a first movable body 32 as in the embodiment of the figure 7 .

[0075] The first moving bodies 32 are curved, and the blades 33 of the translation table 31 are arranged at one end of the first moving body 32.

[0076] The prestressing means 6 further include a spring 34 connecting the first moving body 32 to a second moving body 37. The spring 34 is here formed of several substantially parallel tertiary blades, for example three tertiary blades, connected to the other end of the first moving body 32.

[0077] The second moving bodies 37 are arranged on either side of the spiral spring 80. The second moving bodies 37 receive a variable force or torque, which they transmit to the first moving bodies 32 via the springs 34.

[0078] In the embodiment of the spiral spring 90 of the figure 10 , the prestressing means 6 further comprise two levers 39 each connecting the second movable body 37 to a third movable body 41 in the shape of an arc of a circle arranged on the other side of the spiral spring 90 with respect to the fixed support 38.

[0079] The variable force or torque is applied to the third moving body 41, for example by means of an actuator or a screw in contact with the third moving body 41. The variable force or torque is at least partly transmitted to the flexible parts 15, 16 of the flexible element 5, via the springs 34.

[0080] The eleventh embodiment of the 100 spiral spring of the figure 11 shows flexible parts 15, 16 comprising two first movable bodies 49 each connected by a collar 53 to the fixed support 38 in the shape of an inverted T. Each first movable body 49 is further connected to the outer end 4 of the ribbon 2 by a single flexible blade 7.

[0081] The prestressing means 6 further comprise two levers 26 each connecting the second movable body 37 to a third movable body 19 in the shape of an arc of a circle arranged on the other side of the spiral spring 100 with respect to the fixed support 38.

[0082] The variable force or torque is applied to the third moving body 19, for example by means of an actuator or a screw in contact with the third moving body 19. The variable force or torque is at least partly transmitted to the necks 53 of the flexible parts 15, 16 of the flexible element 5, via the levers 26.

[0083] In the twelfth embodiment of the figure 12 The flexible parts 15, 16 each comprise a curved flexible rod 54, preferably forming a semicircle, extending from the end of the fixed support 44 in the shape of an inverted T. Each curved flexible rod 54 is further connected to the outer end 4 of the ribbon 2 by a single flexible blade 7.

[0084] The prestressing means 6 further comprise two levers 26 each connecting the curved flexible rod 54 to a movable body 19 in the shape of an arc of a circle arranged on the other side of the spiral spring 110 with respect to the fixed support 44.

[0085] The variable force or torque is applied to the third moving body 19, for example by means of an actuator or a screw in contact with the third moving body 19. The variable force or torque is at least partly transmitted to each curved flexible rod 54 of the flexible parts 15, 16 of the flexible element 5, via the levers 26.

[0086] The thirteenth mode of realization of the figure 13 is a variant of the implementation of the figure 12 The curved rods are replaced by curved flexible blades 55. The fixed support 53 has a trapezoidal shape open on the long side towards the outer end 4 of the ribbon 2. The movable body 19 has a U-shape, allowing it to engage with an actuator 57 equipped with a notch or finger inserted in the U, as it is positioned tangentially to the levers 26.

[0087] There figure 14 is an enlarged view of the curved blade 55 of the spiral spring 120 of the figure 13The curved blade 55 forms a semi-circular curve, which is extended by the single flexible blade 7 at one end and by the fixed support 53 at the other. The end 56 of the support itself forms a curve with a counter-curve opposite to that of the curved blade 55. The end 56 of the support 53 is semi-rigid so as to be able to partially deform.

[0088] This arrangement of curvature and counter-curvature prevents altering the isochronism of the regulating organ when the operating mode is modified using the adjustment means. Indeed, the force exerted on the top of the curved blade 55 is compensated by the reaction force of the counter-curvature at the end 56, as shown by the arrows on the figure 14 Thus, only the single flexible blade 7 is subjected to the force or torque applied by the prestressing means 6.

[0089] The flexible blades described in the different embodiments of the spiral spring can be continuous flexible blades, as is generally the case in the figures, or blades with rigid sections and flexible necks connecting the sections.

[0090] The invention also relates to a rotary resonator mechanism, particularly for a watch movement. The resonator mechanism comprises an oscillating weight, not shown in the figures, and a balance spring as described above. The oscillating weight is, for example, an annular balance wheel. The oscillating weight is joined to the balance spring to be fixed to the support.

Claims

1. Spiral spring, in particular for a clock resonator mechanism, the spiral spring (1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120) comprising a flexible ribbon (2) wound on itself in several turns, the ribbon (2) having a predefined stiffness, the spiral spring (1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120) comprising means for adjusting its stiffness, the adjustment means comprising a flexible element (5) arranged in series with the ribbon (2), the flexible element (5) connecting one end (4, 9) of said ribbon (2) to a fixed support (11, 14, 17, 24, 29, 38, 44, 53), so as to add additional stiffness following the tape (2), the flexible element (5) preferably having a stiffness greater than that of the tape (2), characterized in thatthe flexible element (5) comprises two flexible parts (15, 16) each connecting the ribbon (2) to the fixed support (11, 14, 17, 24, 29, 38, 44, 53), the two flexible parts (15, 16) being arranged relative to each other by axial symmetry along an axis (A), the axis (A) preferably passing substantially through the center (0) of the spiral spring.

2. Spiral spring according to claim 1, characterized in that the two flexible parts (15, 16) are substantially identical.

3. Spiral spring according to claim 1 or 2, characterized in that the flexible element (5) is arranged at an outer end (4) of the ribbon (2).

4. Spiral spring according to any one of the preceding claims, characterized in that each flexible part (15, 16) comprises one or two flexible necks (8, 53).

5. Spiral spring according to any one of claims 1 to 3, characterized in thateach flexible part (15, 16) comprises a translation table provided with two flexible blades (21, 22, 42, 43, 74, 78) substantially parallel and a mobile rigid part (23, 45) on which the ribbon (2) is connected.

6. Spiral spring according to any one of claims 1 to 3, characterized in that each flexible part (15, 16) comprises a flexible guide provided with two uncrossed blades (51, 52).

7. Spiral spring according to any one of claims 1 to 3, characterized in that each flexible part (15, 16) comprises a flexible arm (18) to which the ribbon (2) is connected.

8. Spiral spring according to any one of claims 1 to 3, characterized in that each flexible part (15, 16) comprises a flexible blade (7).

9. Spiral spring according to any one of claims 1 to 3, characterized in that each flexible part (15, 16) comprises a flexible hook (28).

10. Spiral spring according to any one of the preceding claims, characterized in that the adjustment means comprise prestressing means (6) for applying a variable force or torque to the flexible element (5), so as to vary only the stiffness of the flexible element (5).

11. Spiral spring according to claim 10, characterized in that the prestressing means (6) are configured to apply a variable force or torque to each part of the flexible element (5).

12. Spiral spring according to any one of the preceding claims, characterized in that the torque or force is continuously adjustable by the prestressing means (6).

13. Spiral spring according to any one of the preceding claims, characterized in that the prestressing means (6) are configured to apply an identical variable force or torque to each part of the flexible element (5).

14. Spiral spring according to any one of the preceding claims, characterized in that the prestressing means (6) comprise a screw configured to bear against the flexible element (5).

15. Spiral spring according to any one of claims 1 to 13, characterized in that the prestressing means (6) comprise two flexible levers (26) each connected to a flexible part (15, 16).

16. Spiral spring according to claim 15, characterized in that the prestressing means (6) comprise two springs (34), each spring (34) being connected to a flexible part (15, 16).

17. Spiral spring according to any one of claims 1 to 13, characterized in that the prestressing means (6) comprise a secondary flexible blade (7) connected to each flexible part (15, 16).

18. Spiral spring according to any one of claims 15 to 17, characterized in thatthe two levers (26) are connected to each other by a movable body (19, 41).

19. Rotary resonator mechanism, in particular for a watch movement, comprising an oscillating mass, characterized in that it comprises a spiral spring (1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120) according to any one of the preceding claims.

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