ES2321440T3 - BROOCH THAT DISPLAYS FOR BRACELET. - Google Patents

Abstract

The clasp has an articulation axle (17) between side-rails (5) of a rigid base, and a rigid crosspiece (11) to connect rigid arms (9) of rigid buckles (7). A locking/unlocking mechanism co-operates with male and female hooking elements (20, 21) e.g. projection element and recess. The side-rails are formed by two independent rigid pieces, and slide on the axle while being maintained closer or spaced from each other by elastic units (25) for maintaining the locked hooking units. The hooking units are unlocked by exerting a pressure on the side-rails to compress the elastic units.

Description

Brooch that unfolds for bracelet.

Technical scope

The present invention relates to a clasp that it is deployed for a bracelet, especially for a bracelet clock, which can comprise one or two loops that are deployed and that It includes a small number of parts to assemble, offering a great ease of handling, especially to unlock the brooch and allow the user to remove the watch from his wrist and conversely prevent any accidental opening.

Technical background

Numerous wristwatches are equipped with brooches that unfold, more aesthetic than the classic brooch bracelet strap by buckle and nail, but not necessarily more easy to use to increase the diameter of the bracelet to allow it to be removed from the wrist.

In its beginning, the brooch that unfolds It has a base in contact with the wrist, one or two buckles articulated in the base and interlocking and unlocking means to allow to keep the clasp in closed position or vice versa open it With respect to interlocking means and interlocking numerous constructions have already been proposed, among which the following documents can be retained.

EP 0 115 740 describes a clasp that It contains two buckles that are deployed articulated on a base that It has a closed contour, but in which the stringers have a certain elasticity to allow the buckles to snag by pressure on the base. The device does not contain buttons, and to open the clasp, you have to pull the two cords of the bracelet fixed to the ends of the buckles. It is evident that the repeated opening and closing maneuvers can lead to a certain fatigue of the stringers ceasing to provide guarantees necessary to close, or may cause an opening accidental.

In EP 0 383 039 the stringers must be equally flexible but the opening system of the buckles is operated by two pushbuttons that prevent an opening accidental. These push buttons are arranged below the stringers and buckles in closed position, which has for inconvenience that increases the thickness of the clasp and creates discomfort when carrier to form protrusion against the skin of your wrist.

To alleviate this problem, it has also it has been proposed to provide an interlocking device and unlocking and a push button system near the ends free of each buckle, the set being generally masked by a protective layer. A brooch of this type is described for example in document EP 0 913 106, see also WO 9 808 409, EP 1 238 599, FR 782 250. The solution proposal is technically very satisfactory, but it means increasing the thickness on the outside and the protective layers are completely visible.

Summary of the Invention

The present invention therefore has object a brooch that unfolds that does not cause inconvenience  of the prior art previously cited, especially thanks to a sturdy construction that only contains rigid parts, in small number and easy to assemble, without therefore involving a increased thickness

For this purpose, the invention aims at a clasp that unfolds for a bracelet that contains:

- a base comprising two rigid stringers that they have a mechanical union between them;

- at least one buckle that unfolds formed by two rigid arms joined by at least one crossbar rigid, which hold the fixing means of a cord bracelet, the ends of the two arms of the buckle being articulated around joining means between distant parts of the stringers, and

- an interlocking mechanism and interlocking by cooperation of male hitch organs and female provided on the sides in front of the stringers and buckle arms.

The brooch is characterized because both stringers are two independent rigid pieces, that is conceived  so that they do not have any flexibility in the transverse direction. These two stringers slide on the joining means when they are held close to or separated from each other by elastic means to keep the hooking organs locked, said means of hitch can be unlocked exerting pressure on the stringers that compress the elastic means.

The device according to the invention can therefore both act either in action, or in reaction according to the form of realization and according to the type of interlocking mechanism and unlocking adopted. The clasp according to the invention indeed it can be conceived with one or two buckles that have arms placed on the outside of the stringers, or on the contrary in the inside the stringers.

Likewise the interlocking mechanism and unlocking can be of the "double action" type, that is  that allows both interlocking and unlocking, or type of "simple action", that is to say that allows the interlocking but that you need a push button system to decouple the organ of male coupling of the female organ.

According to a first embodiment, which It contains two buckles that can be deployed, the arms of the buckles are placed on the outside of the stringers by keeping said stringers separated by elastic means, the device of buttons arranged in the middle part of the base, which is constituted by two pushbuttons that act with the stringers and that allow to act in compression on a spring arranged between  stringers

According to a second embodiment, which It comprises two buckles that can be deployed, the arms of the buckles are placed inside the stringers to be held near said stringers by elastic means, the push button device arranged in the middle part of the base state constituted by two push buttons that cross each stringer, each button allowing to hold a rod that separates the opposite stringer when push buttons are pressed to release The hooking organs.

According to a third embodiment, the clasp only comprises a buckle, with an interlocking mechanism  and unlocking according to one of the embodiments above and with a way of joining the laces of the bracelet adapted to this embodiment.

According to still other embodiments the brooch, one or two buckles that can be deployed, may not have any push-button when the male hitch is formed by a projection that has two inclined planes.

Brief description of the drawings

Other features and advantages of this invention will become apparent in the following description of various embodiments, provided by way of illustration and not limiting, with reference to the drawings attached in the which:

- Figures 1 and 2 represent in perspective a first embodiment with the clasp respectively in closed and semi-deployed position;

- Figure 2A represents in section the organ of male hitch;

- figure 3 represents the clasp of figure 1 in view from above;

- Figure 4 represents one of the stringers of the base seen from above;

- Figure 5 represents one of the buckles on top view;

- Figures 6 and 7 represent components for the mounting of the clasp according to the first embodiment;

- Figures 8 and 9 represent in perspective a second embodiment with the clasp respectively in closed and semi-deployed position;

- figure 10 represents the clasp of figure 8 in view from above;

- Figure 11 represents one of the stringers from the base seen from above;

- Figure 12 represents one of the buckles on top view;

- Figures 13A, 13B represent in view from above a button according to two embodiments;

- Figures 14A, 14B represent one of the interlocking and unlocking mechanism rods according to two embodiments;

- figure 15 represents a view from above of the tie rod that constitutes the rod mounting element of the interlocking and unlocking mechanism;

- Figure 16 is a section of the tie according to the line XVI-XVI of figure 15;

- Figure 17 represents the screw that enters on the brace;

- Figure 18 represents in top view a variant of the second embodiment;

- Figures 19 and 20 represent in perspective a third embodiment respectively in position closed and in semi-deployed position;

- figure 21 represents the clasp of figure 19 seen from above;

- Figure 22 represents in view of this above the tie rod of the third embodiment;

- figure 23 represents the shoulder of the figure 22 seen from the side;

- Figures 24 and 25 represent in perspective a fourth embodiment, respectively in position closed; in semi-deployed position;

- Figure 25A represents in section the organ of male hitch;

- figure 26 represents the clasp of figure 24 in view from above; Y

- Figure 27 represents in perspective a fifth embodiment of the clasp in position semi-expanded

For a better understanding, all drawings do not they have been made on the same scale, but the identical elements or that fulfill the same function are designated by the same references in the figures.

Detailed description of the invention

A first form of embodiment with reference to figures 1 to 7. In the perspective representations of the brooch respectively in closed position and open position is seen in figures 1 and 2 that the clasp is formed by a rigid base 3 constituted by two spars separated 5 and by two identical rigid buckles 7, mounted on each end of the stringers 5 and having between them mechanical joining means 17. In this embodiment the means of mechanical union are constituted by an axis of articulation 17 hunted at the ends 15 of the arms 9 of the buckles 7 and that freely cross the ends of each stringer 5.

With reference also to the view from above from figure 5, it is seen that the arms 9 of the buckles 7 are joined by a rigid crossbar 11 that supports the means of fixing 13 of the bracelet cords (not shown) that they cover each buckle 7 in closed position (figure 1) and that they comprise at their ends transverse steps 10 for the axes articulation 17. In the example shown the fixing means 13 are constituted by a small tube 14 provided in the part crossbar mean 11. Equivalently these means of fixing may consist of two small tubes arranged on the edges of the crossbars 11, or by any means known by a person skilled in the art to fix the bracelet laces to a watch clasp.

It is also seen, in particular in Figure 2, that each stringer 5 is provided with a button 19 that reaches said stringer, perpendicular to it and extending slightly beyond the arms 9 of the buckles 7, so that it marks its location so that the two buttons 19 can be pressed between two fingers to allow simultaneous unlocking of the two buckles 7. This unlocking is done by approximation of the two stringers 5, as indicated by the small arrows of Figure 2, according to a relatively simple mechanism that you will understand better by referring now to figures 3 to 7.

Figure 3 corresponds to Figure 1 in view from above, with representation of the hidden parts in strokes. The same components are found as those previously described, but the hidden parts, represented separately in Figures 6 and 7 allow explaining the locking mechanism and unlocking The middle part between the buttons is provided to allow the placement of elastic means 25 that allow keep stringers 5 apart when the clasp is in position closed. In the example shown, these elastic means are constituted by a tubular pin 35, of the type of those that they can find for fixing the wrist cords between The antlers of a watch case. As seen in the major court scale of figure 6, the tubular pin 35 allows to accommodate a spring 36, in compression on two pivots 37. Pivots 37 they are placed in two blind holes 38 arranged in an envelope thickness 6 of the stringers 5 in its middle part. Obviously without leaving the scope of the present invention, other ones can be contemplated  elastic means and other locations. By way of example no limiting, small helical springs of compression 26 on the articulation axes 17 between the two stringers 5. The tubular pin 35 can also be combined and compression springs 26. Figure 7 represents a guide tube 40 crossed by each axis of articulation 17 and presented in its middle part a narrowing 42. This guide tube 40 allows at the same time masking the articulation axis 17 with an aesthetic object and limit the movement (?) of the stringers 5 that reach butt in a bowl 18a of step 18 located at the ends of each stringer 5.

Figures 3 and 4 also show how to perform the hooking means in this first form of realization. Each stringer 5 comprises on the one hand and on the other side of the push button 19 a cantilever element 20 containing a plane inclined 20a on the side of the buckle 7 and a plane 20b on the side of the base 3, as best seen in the cut of figure 2A. Every arm 9 of each buckle 7 contains a recess 21 whose shape is complementary to that cantilever element 20. The interlocking of the buckles is made by pressing them against the base 3 and the unlocking acting on buttons 19 to bring the stringers 5 and release the male organs 20 from the female organs 21. Accidental unlocking is not possible. This form of realization is remarkable because it contains a very small number of parts that can be assembled without screwing.

A second one is described here below embodiment with reference to figures 8 to 17, in the which components that have the same functions are designated by the same references.

This second embodiment rests on the same principle as the previous one, but it differs in that buckles 7 are placed inside the stringers 5 of the base 3. This results in somehow reversing the interlocking and unlocking mechanism, as explained more later in this document.

With reference to figures 8, 9 and 12, it is seen that the buckle 7 has an entirely closed contour constituted by two arms 9 joined by a crossbar 11 that holds the means fixing 13 of the cords of the bracelet and for a second crossbar 12 that rigidly gathers the ends of the arms 9. As seen in Figure 12, the second cross member 12 contains a passage running through 10 for the articulation means 17 of each buckle 7 with the two stringers 5 located outside. The middle part of each stringer 5 is provided with a push button that crosses 29 and of a brace 39 arranged at the same level to contain and mask the interlocking and unlocking mechanism to be explained later in this document.

To move from the interlocking position (figure 8) to the unlocking position (figure 9) the user it rests on the two buttons 29, as indicated by the arrows, which causes the separation of the stringers 5 indicated by the small arrows that allows you to release the hooking organs male and female 20, 21.

Figure 10 corresponds to Figure 8 in view from above with representation in points of the hidden parts that concern especially the interlocking mechanism and unlocking The description of the visible parts already described.

With reference also to figure 11, it is seen that the middle part of the clasp contains on each outer side of the stringers 5 a push button 29, represented in isolation in the Figure 13A, which can be maneuvered inside a recess corresponding 22 of each stringer 5. A rod 31, represented isolated in Fig. 14A and a spring 28 are associated with each button 29 to form two assemblies whose movement and joint  mechanics are secured by a brace 39 represented in isolation in figures 15 and 16. The references of the two rods 31, arranged feet against heads, and the parts that make up will be completed below by the indexes "a" and "b", if necessary.

With more particularly reference to the figures 13A and 14A it is seen that rod 31 contains a head 32 that is fits in a neckline 30a correspondingly arranged in the end of button 29 oriented inwards. Rod 31 it also contains a part of its length a throttling 33 and at its end a narrowing 53 of diameter that forms a shoulder 54.

Figure 13A shows that the button contains also a well or slot 30b intended to accommodate one end of the spring 28, the other end resting on a circular housing 23 provided at the bottom of the corresponding recess 22 and in diameter larger than the passage through 41 planned to place the end of a rod 31.

With reference also to figures 15, 16 and 17, it is explained later in this document how the different components of the push button device by means of the brace 39 and what is the operation.

The brace 39 is constituted by a plate rectangular whose side is the same length as buckles 7 and the other sides are perforated with steps that cross 41a, 41b to allow free passage of the rods 31a, 31b. A threaded blind hole 47 is drilled in the center of the tie rod in its lower face, with a diameter provided to form holes 45 in the steps that cross 41a, 41b.

To mount the push button device, it is enough to perform the following operations:

- on each rod 31a, 31b string a spring 28;

- place the head 32 of each rod 31a, 31b in the necklines 30a of each button 29;

- place the rods 31a, 31b inside the steps that cross 24a, 24b of each stringer 5, then in the passages that cross 41a, 41b of the strut 39;

- press the two buttons 29 until you have the throttles 33a, 33b of the rods 31a, 31b opposite of the threaded hole 47, and

- screw the screw 48 to be attached to through holes 45 between the bottlenecks 33a, 33b of each rod 31a, 31b so as to ensure a joint between the buttons 29 and limit your movement.

To finish the assembly of the clasp, it is enough to put the buckles 7 in place between the stringers 5 and mount them at the ends of said stringers 5 by joining means 17. In the embodiment shown, as can be seen in Figures 10 and 11, each joining means 17 is constituted by two slotted cylindrical head screws 17a, each screw 17a freely crossing from the outside a step that crosses 18 from one end of a stringer 5 to be threaded to one end of a intermediate sleeve 17b which passes freely through the passage which crosses 10 of the rigid crossbar 12 of a buckle 7. The bowl 18b intended to accommodate the screw head 17a has a depth greater than head height so that allows sufficient movement of the stringers 5 to move them away from each other when the buttons 29 are pressed for the unlocking the clasp by undocking each other's organs hitch 20 and 21. In effect, when buttons 29 are pressed, the springs 28 and the projections 54a, 54b of the rods are compressed  31a, 31b exert pressure on the edges of the steps that they cross 16a, 16b of the stringers 5 distancing each other.

With reference now to figure 18, represents a variant that differs from the second form of embodiment, as depicted in Figure 10, by the placement of elastic means 25 and by the way of securing the rods 31a, 31b.

The elastic means 25 are located at the level of the joining means 17, constituted by a spring 28 interposed between the screw head 17a and the bottom of the bowl 18b of the passage through 18. It will also be noted that the screws 17a are directly screwed into the crossbar rigid 12 of each buckle 7.

With reference now also to the figures 13B and 14B it is seen that the rods 31a, 31b are modified because head 32 is replaced by a thread 34, the other end 53 comprising a groove 53a that allows threading directly rods 31a, 31b in threaded holes 30c of the buttons 29.

With reference now to figures 19 to 23, describes here below a third embodiment that differs from the two previous embodiments in that the clasp it contains a single buckle that unfolds, said form of embodiment being illustrated by a push button system that they work on the same principle as that of the second form of realization.

To move from the interlocking position (figure 19) to the unlocking position (figure 20), the user rests, as indicated by the arrows, on two pushbuttons 29 placed near one end of the rigid base 3, which which causes the separation of the stringers 5 indicated by the small arrows that allow you to release the hooking organs 20, twenty-one.

Figure 21 corresponds to Figure 19 in view from above with representation in points of the hidden parts that concern especially the interlocking mechanism and unlocking A brace 49, represented separately in the Figures 22 and 23 allow housing a locking mechanism and unlocking, operated by buttons 29, all identical to that already described for the variant of the second form of realization, and that will not be described therefore later. He tie 49 also contains a part 49a that extends to the end of the stringers 5. Part 49a is perforated with a passage through 44 to allow the passage of a joining means 17 between the two stringers 5, identical to that already described for the First embodiment. Part 49a itself is prolonged by an extension 51 and constitutes the fixing means 13 of a bracelet cord. It will also be noted that the means of junction 17 between the stringers 5 and the buckle 7 also comprise elastic means 25 in all identical to those already described in the variant of the second embodiment.

The operation of this third form of embodiment is the same as that of the second embodiment  and therefore will not be described later in this document.

With reference now to figures 24 to 26, describes here a fourth embodiment, which contains as the anterior a single buckle that deploys 7, but without push buttons and whose construction is made simpler thanks to a different profile of the male hitch member 50, kept engaged in the organ female 21 in interlocking position.

As seen in the cut of Figure 25A, the male organ 50 is constituted by a shoulder comprising two inclined planes 50 that allow, against the action of means elastic, separate the stringers 5, either to lock the clasp, on the contrary to unlock it.

The absence of buttons also leads to a simplification of elastic means. As you can see in the figure 26 these elastic means are composed of two rods 31a, 31b, each rod crossing from the outside a bucket of a stringer 5 in which a helical spring of compression 28, then a passage through 41a, 41b of a strap 49 to finally be threaded into the opposite crossbar.

Figure 27 represents a fifth form of realization that constitutes, in some way, a duplication of the previous embodiment by containing two buckles that display The elastic means are then arranged in the middle part of the stringers 5. The operation is the same as previously and therefore will not be described later in this document.

In the different embodiments that have just been described, it should be noted that, in a closed position,  the brooch as such is entirely masked by the laces of the bracelet, with the exception of fixing means 13 and eventually the push buttons. This gives a wrist watch equipped with such a brooch a particular aesthetic that does not They can procure prior art brooches.

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The above description provides by way of example two push button systems arranged at the base level that act, either in action, either in reaction, to bring or distance the stringers 5 allowing the interlocking or unlocking of the hooking means between base 3 and buckles 7. It turns out Obviously a person skilled in the art can, without leaving within the scope of the present invention, conceive other systems of push buttons that fulfill the same functions.

Claims (22)

1. Brooch that unfolds for a bracelet comprising: - a base (3) comprising two stringers (5) which have between them mechanical joining means (17); - at least one buckle that unfolds (7) formed by two rigid arms (9) joined by at least one rigid crossbar (11) that holds the fixing means (13) of a bracelet cord (4), the ends (15) of the two arms (9) of the buckle (7) being articulated around joining means (17) between the distant parts of the stringers (5); Y - an interlocking and unlocking mechanism by the cooperation of male and female coupling bodies (20, 21, 50) provided on the sides opposite the stringers (5) and the arms (9) of the buckle (7), the Brooch being characterized in that the two stringers (5) are formed by two independent rigid pieces that slide on the joining means (17) by keeping them close or separated from one another by elastic means (25) to keep the hooking members (20, 21, 50) interlocked, said engagement means being able to be unlocked by exerting pressure on the stringers (5) compressing the elastic means (25). 2. Clasp according to claim 1, characterized in that the arms (9) of the buckle (7) are placed outside the stringers (5). 3. Clasp according to claim 1 characterized in that the arms (9) of the buckle (7) are placed inside the stringers (5). 4. Clasp according to claim 1 characterized in that the male member of the locking and unlocking mechanism is constituted by a cantilever element (20) comprising an inclined plane (20a) on the side of the buckle (7) and a plane (20b ) on the side of the base (3) said element (20) engaging in a notch (21) opposite by pressure on the buckle (7) and which can be separated in the unlocking position, exerting a pressure on a push button device ( 19, 20) against the action of elastic means (25). 5. Brooch according to claim 1 characterized in that the male member of the interlocking and unlocking mechanism is constituted by a shoulder (50) containing two inclined planes (50a, 50b) that are coupled in a notch (21) opposite by pressure on the buckle (7) and that can be separated in the decoupling position by exerting traction on the cord of the bracelet (4) attached to the end of said buckle (7). 6. Brooch according to claims 2 to 4 characterized in that it contains two buckles (7) whose arms (9) are articulated at the ends of the stringers (5), said stringers (5) being kept separated from each other by elastic means (25 ) arranged between them and allowing the male and female organs (20, 21) of the interlocking mechanism to be coupled to each other and because the push-button device, arranged in the middle part of the base (3) is constituted by two push-buttons ( 19) formed each of them by an extension perpendicular to a crossbar (5) and which reaches it. 7. Snap according to claim 6 characterized in that the elastic means (25) are constituted by a tubular pin (35) that houses a spring (36) acting on two pivots (37) coupled in blind holes (38) of the two stringers (5) to the right of the push button system. 8. Brooch according to claim 6 characterized in that the elastic means (25) are constituted by pairs of springs (26) arranged between the stringers (5) on the articulation shafts (17). 9. Clasp according to claims 3 and 4 characterized in that it comprises two buckles (7) whose arms (9) are articulated at the ends of the stringers (5), said stringers (5) being held close (5) to each other by means elastic (25), which fit the male and female organs (20, 21) of the interlocking mechanism into each other and because the push button device is arranged in the middle part of the base (3) which is constituted by two push buttons ( 29) that cross each stringer (5), each pushbutton (29) allowing to hold a rod (31a, 31b) that separates the opposite stringer (5) when the pushbuttons (29) are pressed to release the coupling members (20, 21 ). 10. Clasp according to claim 9 characterized in that each buckle (7) is completely closed by a second rigid crossbar (12) containing a passage through (12a) for the articulation shaft (17). 11. Brooch according to claim 9 characterized in that the elastic means (25) are constituted by springs (28) arranged at the level of each rod (31a, 31b) that are housed in the necklines (30a) of the pushbuttons (29). 12. Clasp according to claim 9 characterized in that the elastic means (25) are formed by springs (28) arranged at the level of each axis of articulation (17) that are housed from the outside in a well (30) of the distant parts of the stringers (5). 13. Clasp according to claim 12 characterized in that the screws (32) for maintaining the springs (28) are screwed into a complementary rigid cross member (34) that closes the buckles (7). 14. Clasp according to claim 12 characterized in that screws (32) for maintaining the springs (28) pass through the ends of the arms (9) of the buckles (7) and are threaded to each other. 15. Brooch according to claim 9 characterized in that it further comprises to the right of the pushbuttons (29) a tie rod (39) containing two passages (41) for the free passage of rods (31a, 31b) and perpendicular to its plane a threaded bore (43), which forms holes (41) in the passages they pass through (41a, 41b), in which a screw (47) is screwed in front of a local throttle (33) of each rod (31a, 31b) to control the movement and establish a mechanical connection between a push button (29) and the opposite crossbar (5). 16. Clasp according to claims 3 and 4 characterized in that it comprises a single buckle (7) whose arms are articulated at one end of the stringers (5), said stringers (5) being held close (5) to each other by elastic means ( 25), which fit the male and female organs (20, 21) of the interlocking mechanism into one another and because the push button device is arranged at one end of the base (3) which is constituted by two push buttons (29) that they cross each stringer (5), each pushbutton (29) allowing to hold a rod (31a, 31b) that separates the opposite stringer (5) when the pushbuttons (29) are pressed to release the coupling members (20, 21). 17. Clasp according to claim 16 characterized in that the elastic means (25) are constituted by springs arranged at the same time at the level of the articulation axis (17) between the buckle (7) and the stringers (5) and at the level of the rods (31a, 31b) of push buttons. 18. Clasp according to claim 16 characterized in that it also contains to the right of the pushbuttons (29) a brace (49) comprising two passages that cross (41) for the free passage of the two rods (31a, 31b) and perpendicularly to its plane is a threaded hole (43) that forms holes in the crossings (41), in which a screw (47) is threaded in front of a strangulation of each rod (31a, 31b) to control the movement and establish the joint mechanical between a push button (29) and the opposite crossbar (5). 19. Clasp according to claim 18, characterized in that the strap (49) further comprises, on the one hand, a passage through (44) for a connecting means (27) between the ends of the two stringers (5), on the other hand a extension (23) which constitutes a means of fixing a cord of the bracelet at the base (3). 20. Clasp according to claims 3 and 5 characterized in that it comprises a single buckle (7) whose arms are articulated at one end of the stringers (5), said stringers (5) being held close to each other by elastic means arranged in the other end of the stringers that engage in each other the male and female organs (50, 21) of the interlocking mechanism. 21. Brooch according to claim 20, characterized in that the elastic means consisting of two rods (31a, 31b) that each cross a crossbar (5) and a tie rod (49) and are threaded on the opposite crossbar, the head of said rods compressing a spring housed from the outside in a well of each stringer (5). 22. Clasp according to claims 3 and 4 characterized in that it comprises two buckles (7) whose arms (9) are articulated at each end of the stringers (5), said stringers (5) being held close to each other by elastic means located in its middle part, by means of rods and springs that cross a brace.