EP2887151B1 - Oscillating element for a clockwork - Google Patents

Description

Technical area

The present invention relates to an oscillating element for mechanical clockwork movement.

State of the art

Mechanical clock movements comprise numerous oscillating elements, in particular elements rotated alternately in one direction and then in the other. The balance wheel, the hairspring, the escapement anchor, the winding mass, and certain complications are examples of such oscillating elements.

The power reserve of a mechanical watch depends especially losses due to friction in the train and in the pivot of the regulating member. It is therefore advantageous to reduce these friction in order to increase the power reserve. Friction at the parts oscillating rapidly, especially in the exhaust, are particularly critical. The performance of a typical Swiss lever escapement is typically of the order of about 40%; 60% of the energy transmitted by the gear train to the exhaust is lost in friction.

A substantial part of this friction occurs at the bearings. Despite the use of rubies and progress in lubrication, the friction between the anchor axis and the bearing that maintains this axis is therefore a critical factor in the loss of energy stored in the barrel.

In addition, conventional bearings require a clearance between the pivots of the movable axis and the bearing to allow the axis to rotate. The accuracy of this game depends on manufacturing tolerances and progressive wear of the bearing. This results in poorly controlled positioning of the axis and the component mounted on this axis. In the case of an anchor, this game is reports on the relative position of the pallets and the anchor wheel, which also causes energy losses.

Compliant mechanisms are known in the state of the art which are often used to reduce friction or improve the accuracy of a displacement. A compliant mechanism is a mechanism that, unlike rigid body-based mechanisms, allows displacement by the flexibility of at least one limb. For example, a compliant element allows the rotation of an axis thanks to the flexibility of at least one member. The compliant elements therefore partially or completely avoid the friction of moving parts relative to each other, and the energy losses and the wear of the parts that result from this friction. They also make it possible to elegantly solve the problems caused by the play of conventional bearings.

An application of complying elements to the horological field is described in the patent application EP2037335A2 . This document describes in particular an exhaust anchor without axis and which can rotate thanks to the deformation of two arms whose axes intersect at the point of virtual rotation of the anchor. The attachment arms and the anchor form a relatively fragile single piece. In addition, the attachment arms occupy a relatively large area in the plane of the anchor which is often particularly congested; this place is not available for other organs.

EP2273323A2 describes a mechanical oscillator based on a compliant mechanism. The mechanism illustrated on the figure 4 comprises a prestressing system exerted from the axis of the balance.

WO2012 / 010408 describes an escapement anchor with an elastic pivot.

US3678683 describes a regulating organ and an exhaust. The anchor is mounted on a conventional axis.

DE2714020 describes a gear wheel for quartz watches, allowing rotation without noise and with minimal torque. The pivot is replaced by flexible blades between the periphery of the pinion and the ring gear, thus allowing this ring to rotate with an elastic game.

EP2455821 relates to an escape wheel whose pivot is replaced by a compliant mechanism.

WO2011 / 1201801 discloses a gear lock device based on another compliant link. Again, this device is made in one piece or in one piece with the exception of pallets, making its design difficult. A compliant link integrated in the blocker also has the disadvantage of not be easily adapted to an existing blocker; it is necessary to completely redraw the entire blocker.

Another disadvantage of the solutions described in these prior art is that it is very difficult to control or modify the torque required for the rotation of the locking devices.

Brief summary of the invention

An object of the present invention is to provide an oscillating element for a watch movement free from the limitations of known oscillating elements, in particular an oscillating element capable of oscillating with minimal torque and energy losses as small as possible.

Another object of the present invention is to provide an oscillating element for a watch movement capable of oscillating with a torque and energy losses as constant as possible.

Another object of the present invention is to provide an oscillating element based on a compliant connection but which does not have the drawbacks of existing compliant links.

Another object of the present invention is to provide an oscillating element for a watch movement based on a compliant connection and whose overall size in the plane of the oscillating anchor is as small as possible.

• un axe ;
• une ancre monté sur une première partie de cet axe de manière à pouvoir tourner avec cet axe ;
• un élément compliant monté sur une deuxième partie de l'axe de manière à permettre audit axe de tourner lorsque l'élément compliant se déforme élastiquement ;
• l'élément compliant comportant plusieurs poutres flexibles formant une intersection, ledit axe étant monté à l'intersection entre lesdites poutres;
• un élément élastique de précontrainte pour exercer une force de précontrainte sur l'élément compliant de manière à modifier le couple nécessaire à la mise en rotation dudit axe ;
• ledit élément élastique de précontrainte comportant au moins deux brins;
• une extrémité de chaque brin étant liée rigidement à une extrémité d'une desdites poutres.

According to a first aspect of the invention, these objects are achieved by means of an oscillating element for a watch movement comprising:

• an axe ;
• an anchor mounted on a first part of this axis so as to be rotatable with this axis;
• a compliant element mounted on a second part of the axis so as to allow said axis to rotate when the compliant element deforms elastically;
• the compliant element comprising a plurality of flexible beams forming an intersection, said axis being mounted at the intersection between said beams;
• an elastic prestressing element for exerting a prestressing force on the compliant element so as to modify the torque necessary for the rotation of said axis;
• said elastic prestressing element having at least two strands;
• an end of each strand being rigidly connected to one end of one of said beams.

According to this aspect, this construction makes it possible to separate the two functions of the oscillating element into two components on two different planes. The first functional component, that is to say the anchor, is on a first plane and the second component is constituted by a compliant element on another plane. The anchor is a functional component in the foreground that provides a function in the context of the watch movement; the second compliant component on the second plane provides no function other than that of "virtual" pivot for the axis of the first component. Preferably, the first and second parts of the axis are first and second ends of the axis respectively.

The compliant element therefore occupies no space in the foreground of the anchor. Both components can be made and dimensioned independently of each other, allowing uncompromising optimization of each component. The compliant element can for example be used with existing functional components, without modification of these components. The two components are linked to each other by an axis.

In addition, the compliant element acts on an axis (which is integral with the functional component) and not directly on the periphery of the functional component as is the case in the prior art. This is advantageous, for example for fragile components or that have complex shapes.

The expression "compliant element" designates in this text an element that allows a displacement of a part, for example a rotation of an axis, thanks to the elastic deformation, for example the bending, of at least a part of the 'element. With respect to a bearing or a bearing for example, a compliant element can therefore operate without friction between the moving part (for example an axis) and fixed part.

Advantageously, the compliant element is made to allow rotation of an axis with a torque as low as possible. It therefore exerts no return force on the axis, or only a negligible return torque or in any case voluntarily chosen to be as low as possible, at least in the expected range of oscillations.

In an advantageous embodiment, the compliant element comprises two flexible beams forming a cross intersection. This construction minimizes clutter and facilitates synthesis and simulation. The beams may be for example straight beams.

Other types of compliant elements may also be used.

The axis is mounted at the intersection between said beams. One or preferably two ends of two adjacent branches of the cross may be attached to the frame of the movement by means of mounting points provided for this purpose. The mounting points may for example be openings for the driving or gluing of fixing pins. The one or both ends of the one or both limbs can thus be fixed relative to the frame, while the end of the two other limbs, as well as the point of intersection, can be movable when the limbs of the compliant element are deformed. .

The elastic prestressing element makes it possible to exert a prestressing force on the compliant element so as to modify the torque necessary for the rotation of said axis. Preferably, the prestressing is chosen so as to minimize the torque necessary for the rotation of the axis. Prestressing is advantageously exercised simultaneously on two adjacent branches of the cross of the compliant element.

The elastic prestressing element may be integrally bonded to the compliant element, or even form a single element, which facilitates assembly and alignment.

In the preferred case of a compliant element comprising two crossed beams forming a cross intersection with four branches in X, the elastic prestressing element can exert a prestressing force on both ends of two adjacent branches of the cross.

This prestressing force can be exerted directly by the elastic prestressing element on the compliant element.

This prestressing force can be exerted by the elastic prestressing element on the compliant element through a support piece through two branches. This solution has the advantage of distributing the prestressing force on the two branches.

This prestressing force can be exerted by the elastic prestressing element on the compliant element through a support piece through two branches and an articulated connection. This solution has the advantage of allowing a relative displacement of the elastic prestress element with respect to the compliant element.

The elastic prestressing element may be shaped so as to comprise two strands. One end of each strand is rigidly connected to one end of a fixed branch of the cross, another portion of each strand exerts a prestressing force on the free end of another branch of the cross. Preferably, the elastic prestress element and the compliant element is at least partly in the same plane.

The elastic prestressing element being dimensioned and structured so as to exert a substantially constant prestressing force on the compliant element even when the compliant element is deformed. Calculations and simulations have shown that a constant prestressing force makes it possible to minimize the torque necessary for the rotation of the axis, and to prevent this torque from being dependent on the angular position.

The strands may be bonded to each other so as to form a ring.

The axis can be driven out and / or glued in the anchor and / or in the compliant element.

• une ancre;
• un élément compliant qui permet à l'ancre de tourner lorsque l'élément compliant se déforme élastiquement ;
• ledit élément compliant comportant au moins deux poutres déformables qui se croisent entre elles à distance de leurs extrémités, de manière à former une croix,
• le centre de rotation de l'ancre étant au centre de ladite croix.

According to an independent aspect of the invention, the aforementioned aims are achieved by means of an oscillating element for a watch movement comprising:

• an anchor;
• a compliant element that allows the anchor to rotate when the compliant element deforms elastically;
• said compliant element comprising at least two beams deformable which cross each other at a distance from their ends, so as to form a cross,
• the center of rotation of the anchor being in the center of said cross.

This arrangement of the cross beams makes it possible to obtain a central symmetry of the forces exerted by the deformable beams on the point of rotation.

In this case, the anchor and the compliant element may be in the same plane (at least partially) without necessarily being interconnected by an axis. Alternatively, the anchor and the compliant element can be in different planes linked together by an axis.

In this case also, at least one elastic prestressing element may optionally be provided to exert a prestressing force on the compliant element so as to modify the torque necessary for rotating the functional component. This elastic prestressing element can act for example on the distal ends of the beams.

The anchor can be a Swiss anchor for Swiss anchor escapement.

According to an independent aspect, the invention also relates to a regulating member comprising a compliant oscillating anchor, for example an oscillating anchor by means of an oscillating element according to any of the embodiments described in this application, fixed on an exhaust door which also carries the escape wheel and, preferably, the balance shaft with the balance and the balance spring.

Brief description of the figures

• La figure 1 illustre une vue en perspective d'un élément oscillant selon un premier mode de réalisation de l'invention.
• La figure 2 illustre une vue de dessus d'un élément oscillant selon le premier mode de réalisation de l'invention.
• La figure 3 illustre une vue de côté d'un élément oscillant selon l'invention.
• La figure 4 illustre une vue en perspective d'un élément oscillant selon un deuxième mode de réalisation de l'invention.
• La figure 5 illustre une vue en perspective d'un élément oscillant selon un troisième mode de réalisation de l'invention.
• La figure 6 illustre une vue de dessus d'un élément oscillant selon un quatrième mode de réalisation de l'invention.
• La figure 7 est une vue en éclaté d'un élément oscillant selon un cinquième mode de réalisation de l'invention.

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

• The figure 1 illustrates a perspective view of an oscillating element according to a first embodiment of the invention.
• The figure 2 illustrates a top view of an oscillating element according to the first embodiment of the invention.
• The figure 3 illustrates a side view of an oscillating element according to the invention.
• The figure 4 illustrates a perspective view of an oscillating element according to a second embodiment of the invention.
• The figure 5 illustrates a perspective view of an oscillating element according to a third embodiment of the invention.
• The figure 6 illustrates a top view of an oscillating element according to a fourth embodiment of the invention.
• The figure 7 is an exploded view of an oscillating element according to a fifth embodiment of the invention.

Example (s) of embodiment of the invention

A particular embodiment of the invention will now be described. In this preferred example, the functional component 2 that is to be oscillated at one end of the axis 3 is an anchor, more particularly a Swiss anchor for Swiss anchor escapement.

In this example, the anchor 2 comprises two pallets 20A and 20B, a fork 21 and a stinger 22. It may be made of steel or advantageously of silicon or of another material allowing a production by one of the methods of photolithography, DRIE (abbreviation for "Deep Reactive Ion Etching") or LIGA (abbreviation for "Lithography, Galvanoformung, Abformung"). It is mounted on a first end of the axis 3 by driving, for example in the case a metal anchor, or by gluing, for example in the case of a silicon anchor. Alternatively, the axis 3 and the anchor 2 can be formed in one piece. An anchor integrating the pallets and / or the stinger into a monolithic assembly can also be envisaged.

Axis 3 is not a conventional moving axle that pivots in bearings. Instead, the oscillating element preferably comprises at the other end of the axis 3 a compliant element 4. In the embodiment of Figures 1 to 3 the compliant element is of the cross type and therefore comprises two rectilinear beams 5A, 5B which intersect at X. The axis 3 is mounted at the intersection between the two beams 5A, 5B, this intersection being coincident with the center rotation of the compliant element. Non-rectilinear beams may be used, including curved or bent beams. The four branches of the cross are referenced by the numbers 7A to 7D.

The distal ends of two adjacent branches 7A, 7B of the cross are provided with attachment points 6A, 6B to fix them on a part of the movement frame, such as the plate, a bridge, an exhaust door, or a cage of whirlwind. In a preferred embodiment, the oscillating element is fixed by means of pins or pins or screws inserted into these two attachment points. The oscillating element can be fixed on an exhaust-door which also carries the escape wheel and, preferably, the balance shaft with the balance and the hairspring. This configuration facilitates the alignment and mounting of various components of the regulating member.

In the illustrated embodiment, a connecting member 60 is integrally bonded to the distal end of the two legs 7A, 7B and provided with two attachment points 6A, 6B in the form of through holes. This configuration makes it possible in particular to move the fixing bridges with respect to the elastic beams 5A, 5B whose deformable length can thus be maximized.

Numerical simulations have demonstrated that the torque necessary to rotate the axis 3 can be controlled, and for example reduced or even minimized, by constantly exerting a force of stress on the beams 5A, 5B. In the embodiment of Figures 1 to 3 , the two branches 7C, 7D are free and opposite to the two fixed branches 7A, 7B. In this case, a force of stress is exerted by means of an elastic element, here of an annular spring defining two strands 80A, 80B. This elastic element is advantageously integral with the two beams 5A, 5B of the cross. This monolithic solution allows in particular to facilitate the assembly and alignment of the various components. Note that with this solution, the center of rotation is not completely fixed, but the displacement of it is controlled, repeatable and generally lower than the traditional game of a pivot of a conventional anchor rod in a stone, which is typically between 4μm to 14μm.

The two strands 80A, 80B leave the connecting element 60 near the fixed ends of the cross and surround the two beams 5A, 5B so as to exert a prestressing force on the distal ends of the free branches 7C, 7D. More particularly, one end 81A, 81B of each strand is rigidly connected to one end of each fixed branch 7A, 7B of the cross. They are thus united in a single ring.

In this example, the elastic member 80A, 80B bears directly at the points 81C, 81D against the distal ends of the branches 7C, 7D.

In a preferred embodiment, the prestressing force is exerted by the elastic element 80A, 80B through a support piece 9 which distributes and equalizes the pressure against the two branches 7C, 7D. This solution ensures equal pressure on the two branches 7C, 7D even in case of slight differences in length due for example to manufacturing imperfections. The support element 9 may be integral, monolithic with the two branches 7C, 7D.

An articulated connecting element 90 is advantageously pivotally connected on the one hand to the strands 80A, 80B, on the other hand to the support piece 9. This connecting element guarantees a constant distance between these two elements while allowing a rotation in relation to the blades 80A, 80B and relative to the part 9. In the illustrated example, it has a bone shape with a head, or epiphysis, approximately hemispherical at each end of a central portion. Each head collaborates with a corresponding dome in the strands 80A, 80B respectively in the support piece 9.

The prestressing force exerted by the strands 80A, 80B depends on the length of the connecting element 90 and the displacement it causes on the support piece 9 and on the ends of the branches 7C, 7D. For series production, an oscillating element can be delivered with several connecting elements of different lengths to adjust the prestressing force. The mounting of the oscillating element may comprise the choice of a connecting element 90 of suitable length among several connecting elements of different lengths. In a preferred embodiment, the ideal length of the connecting member 90 is determined by digital simulation once and for all during the design, and applied.

The compliant element is therefore constituted in this example of two parts: the cross structure 5A, 5B with the elastic element 80A, 80B and the elements 9 and 60; and the connecting element 90. As in the other variants described below, these two parts can be made of steel, silicon, etc.

The figure 4 illustrates a second variant of oscillating element 1 for watch movement. The oscillating component 2 is an anchor, represented without its pallets but which could naturally be equipped with pallets.

In this variant, the compliant element 4 comprises three flexible beams 5C, 5D 5E star about the axis 3. The elastic element of prestress 8 is constituted by three strands 80C, 80D, 80E forming a triangle, for example an equilateral triangle. The ends of the three beams are connected to the three respective points of the triangle.

Prestressing is therefore exerted in the same way on all three beams 5C to 5E. The end of the three beams is not blocked. One advantage is that the center of the axis 3 remains almost immobile even during rotation of the part 2.

The oscillating element 1 is fixed to the frame of the movement by the three mounting points 6C, 6D, 6E directly on the prestressing element 80C to 80E. In this example, the mounting points are linked to the media of the strands 80C to 80E. In this variant, it is a displacement applied on the strands 80C to 80E which creates the constraint. There is no support piece ("bone").

Compliant elements with a number of star arms different from three can be envisaged, for example compliant elements with 2, 4, 5, .. N star arms around the axis 3. The angular space between the different ras is preferably constant and equal to 360 ° / N.

The figure 5 illustrates a third compliant element variant 4 intended to be integrated in an oscillating element for a watch movement. As in the first variant, the compliant element 4 comprises two beams 5A, 5B forming a cross about the axis 3. The oscillating component, an exhaust anchor not shown, is intended to be mounted on the axis 3 in a other plan than the compliant element 4.

The two beams 5A, 5B X form four branches 7A to 7D whose ends are connected in pairs thanks to the connecting elements 60 and 61, respectively.

A resilient ring preload member 8 has two strands 80A, 80B which join the center of the connection member 60 with the center of the connecting element 61, forming a ring. This elastic element 8 exerts a prestressing force directly on the distal ends of the four branches 7A to 7D. More particularly, one end 81A, 81B of each strand is rigidly connected to one end of each fixed branch 7A, 7B of the cross. No connecting part 9 is used between the prestressing element and the connecting elements 60, 61.

The compliant element 4 is mounted on the movement frame by two mounting points 6F, 6G directly on the constraining element 8, for example in the middle of the strands 80A respectively 80B. Like the second variant, the amplitude of the prestressing force is identical on all the beams. The center of the axis 3 remains motionless even when rotating the workpiece 2.

The figure 6 illustrates a fourth compliant element variant 4 intended to be integrated in an oscillating element for watch movement. This variant corresponds to the third variant, except that the free ends of the four branches 7A to 7D are connected to the prestressing element 8 by means of two support pieces 9A, 9B connecting the branches two by two, and bone-shaped connecting members 90A, 90B bonding these support members 9A, 9B to the strands 80A, 80B of the prestressing member. These connecting elements allow a displacement according to several degrees of freedom of the prestressing element 8 relative to the support parts 9A, 9B and with respect to the end of beams. In this variant, it is a displacement applied on the support pieces 9A, 9B which creates the constraint.

The shape and structure of the elastic element is optimized, for example by successive approximations, so that the prestressing force remains substantially constant even when the various beams of the compliant element are deformed, throughout the deformation range. usual. This ensures that the restoring torque exerted on the axis 3 is independent of its angular position. In one embodiment, the thickness of the strands 80A, 80B is irregular to achieve this objective.

The figure 7 illustrates a fifth variant compliant element 4 intended to be integrated in an oscillating element for watch movement. This variant is different from that of the figure 5 mainly by the shape of the elastic prestressing element; the other elements may be identical to those described in relation to the figure 5 and will not be described.

The elastic prestressing element 8 is formed of two arms 80A, 80B which do not meet directly, but connect pairs of points on the connecting elements 60, 61. More specifically, the arm 80B connects the point 600 near one end of the connecting member 60 with the point 610 near the corresponding end of the other connecting member 61; the arm 80A connects the point 601 near one end of the connection element 60 with the point 611 near the corresponding end of the other connection element 61

The mounting points 6H, 61 of the constraint element 8 on the frame are on the prestressing element 8, as in FIG. figure 5 . However, these mounting points are not directly in the middle of the strands 80A, 80B, but are connected to these strands by elastic elements 80C respectively 80D. In this example, each of the resilient members 80C, 80D is constituted by a ring one point of which is connected to a strand 80A, respectively 80D, and another point to 180 ° is bound to one side of a mounting point 6H, 61 opposite to the strand. In this way, the mounting points 6H, 61 do not limit or almost no freedom of the strands 80A, 80B to move, which allows the constraint element 8 as a whole to exert a greater stress on the compliant element 4.

As illustrated on the figure 7 , the compliant element 4 can be assembled on a plate 11 made for example of LIGA and having pads 110 for receiving the mounting points 6H, 61. The plate 11 can be mounted on the frame of the movement or be part of it frame. This plate 11 makes it possible to obtain a better control of the prestressing applied to the compliant element 4 by a better accuracy of the distances between the studs 110. More particularly, the studs 110 and the wafer 11 preferably form a single piece, so misalignment during assembly can be practically. In addition, we obtain a greater ease of assembly of the assembly on the frame of the movement, and therefore the replacement of this set if necessary. Finally, this plate can be integrated into an exhaust door, and it can be used to adjust the position of the anchor by moving the plate on the movement frame. This plate 11 may be used in combination with oscillating elements different from that of the figure 7 , for example with an oscillating element according to any embodiment according to one of the Figures 1 to 6 .

All embodiments described above have a compliant element in a first plane connected by an axis to an anchor as a functional component in another plane. It is possible to modify these embodiments so that the compliant element and the anchor are wholly or partly in the same plane.

For example, it is possible to provide an oscillating element for a watch movement comprising an anchor, a compliant element in the same plane and which allows this anchor to rotate when the compliant element is deformed elastically, and at least one elastic prestressing element. which exerts a prestressing force on the compliant element so as to modify the torque necessary for the rotation of the anchor.

The elastic prestress element may be in the same plane as the compliant element, and / or in the same plane as the anchor, or in another plane.

In this case, the anchor and the compliant element may be in the same plane (at least partially) without necessarily being interconnected by an axis. Alternatively, the anchor and the compliant element can be in different planes linked together by an axis.

In the same way, it is also possible to produce an oscillating element for a watch movement comprising a compliant element 4 formed of several intersecting beams 5A, 5B, the intersection point of the beams defining a center of rotation for the anchor in the same plane or in a different plane than the compliant element. The number of beams can be two, three, etc. The beams are advantageously arranged symmetrically around the center of rotation. An elastic prestressing element 8 is provided to exert a prestressing force on the distal ends of the beams, so as to modify the torque necessary for the rotation of the anchor.

Claims (15)

1. Oscillating element (1) for watch movement comprising:

   a staff (3);

   pallets (2) mounted on a first portion of said staff (3) so as to be rotatable with said staff;

   an elastically deformable element (4) mounted on a second portion of the staff (3) so as to allow this staff to rotate when said elastically deformable element deforms elastically;

   wherein the elastically deformable element (4) has a plurality of flexible beams (5A, 5B, 5C, 5D, 5E) forming an intersection, said staff (3) being mounted at the intersection between said beams;

   characterized in that the oscillating element comprises:

   an elastic biasing element (8) for exerting a biasing force on the elastically deformable element (4) so as to alter the torque required to rotate said staff (3);

   wherein said elastic biasing element (8) has at least two strands (80A, 80B);

   one end (81A, 81B) of each strand being connected to one end of one of said beams.
2. Element according to claim 1, wherein said strands (80A, 80B) are pressed against two adjacent free ends of two beams via a support member (9).
3. Element according to claim 2, comprising at least one mounting point (6A-6B) for mounting said oscillating element onto a frame of the watch movement, wherein said mounting point is connected to said support member (9).
4. Element according to one of the claims 1 or 2, comprising at least one mounting point (6C-6D; 6F-6G, 6H-6I) for mounting said oscillating element onto a frame of the watch movement, wherein said mounting point is linked to the elastic biasing element (8).
5. Element according to claim 4, wherein said at least one mounting point (6H-6I) is connected via an elastic connection (80C, 80D) to said elastic biasing element (8).
6. Element according to claim 4, wherein said at least one mounting point (6F-6G) is provided in said elastic biasing element (8).
7. Element according to one of the claims 1 to 6, wherein said elastic biasing element (8) and the elastically deformable element (4) form a single component.
8. Element according to one of the claims 1 to 7, wherein the elastically deformable element (4) comprises two beams (5A, 5B) forming a cross intersection with four branches (7A, 7B, 7C, 7D), wherein said elastic biasing element (8) exerts a prestressing force on the two ends of exactly two adjacent branches (7C, 7D) of said cross.
9. Element according to one of the claims 1 to 7, wherein the elastically deformable element (4) comprises two said beams (5A, 5B) forming a cross intersection with four branches (7A, 7B, 7C, 7D), wherein said elastic biasing element (8) exerts a prestressing force on the ends of each of these four branches.
10. Element according to one of the claims 1 to 7, wherein the elastically deformable element (4) comprises three branches (5A to 5C) in a star, wherein said elastic biasing element (8) exerts a prestressing force on the free ends of each of these three branches.
11. Element according to one of the claims 2 to 10, wherein said support member (9) is connected to said strands (80A, 80B) via an articulated connection (90).
12. Element according to one of the claims 1 to 11, wherein said strands (80A, 80B) are connected to each other so as to form a ring.
13. Element according to one of the claims 2 to 12, comprising a first support member (60) bearing simultaneously against two adjacent ends (7A, 7B) of said beams, a second support member (61) bearing simultaneously against two other adjacent ends (7C, 7D) of said beams, wherein each of said strands (80A, 80B) connects the first support member (60) with the second support member (61).
14. Element according to one of the claims 1 to 13, wherein said elastic biasing element (80A, 80B) is sized and structured so as to exert a substantially constant prestressing force on the elastically deformable element (5A, 5B) even when the elastically deformable element deforms.
15. Element according to one of the preceding claims, wherein the staff (3) is driven or glued in the pallets and/or in the elastically deformable element.

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