KEY FOR ATTACHING A DIAL TO THE CIRCUIT BOARD OF A CLOCK MOVEMENT

Description

Technical field of the invention

[0001] The invention falls within the field of watchmaking, and in particular devices for fixing a casing element onto a watch structure.

[0002] More specifically, the invention relates to a key for securing a dial to the plate of a watch movement. Technological background

[0003] The fixing of dials within timepieces, such as watches, is generally achieved using retaining keys.

[0004] More specifically, these retaining keys have a head designed to rest against a surface of a watch movement plate opposite a dial. The head is connected to the end of a rod designed to be inserted by a tight fit into a recess in said plate, in which it can be pivoted when sufficient torque is applied to overcome frictional forces.

[0005] The dial has feet engaged in housings arranged near the housings into which the key shafts are inserted, and open onto the surface of the plate opposite the dial.

[0006] The keys have, around their head, a collar truncated in a direction parallel to the longitudinal axis of the shaft, said collar having a frustoconical cross-section and designed to penetrate, by means of a cutting edge, into the adjacent foot following the pivoting of the key. Such an arrangement is described, for example, in document EP0465988 A1.

[0007] This penetration generates a tearing of material forming a burr that can detach from the dial foot and form a chip that can block or damage moving components of the watch movement.

[0008] In addition, mechanical play may occur between the foot and the key if one wishes to reattach a foot that has already been deformed.

[0009] This dial fixing solution also generates significant mechanical stresses on the foot and / or the key, as the cutting edge through which the collar enters the foot is relatively large. Summary of the invention

[0010] The invention solves the aforementioned drawbacks by offering a solution allowing the maintenance of a dial without risk of causing material to be torn from its feet.

[0011] More specifically, the invention aims to minimize foot deformations, while ensuring its tightening by the key.

[0012] For this purpose, the present invention relates to a key for retaining a dial foot, said key comprising a cylindrical head arranged at the end of a rod, the head and the rod being coaxial, the head comprising a flat and a collar extending over a portion of its periphery in an angular sector defined around the longitudinal axis of the rod, on either side of the flat.

[0013] The collar comprises a right section of truncated cone shape and forms, in relation to the periphery of the head, a minimal radial projection, substantially zero, at the ends of this angular sector and forms a maximum radial projection between these ends.

[0014] In particular embodiments, the invention may further comprise one or more of the following features, taken individually or in all technically possible combinations.

[0015] In particular embodiments, the collar has a shape of revolution whose axis of revolution is eccentric with respect to the axis of the head.

[0016] In particular embodiments, the collar is arranged symmetrically on either side of a plane of symmetry passing through the longitudinal axis of the head and orthogonal to the plane defined by the flat.

[0017] In particular embodiments, the maximum radial projection formed by the collar is diametrically opposite to the flat.

[0018] According to another aspect, the present invention also relates to a dial fixing device comprising at least one foot engaged through a first housing of a watch structure and at least one key as described above, the stem of which is engaged in a second housing adjacent to the first housing. The device is configured such that, in a first angular position, referred to as the "rest position," the flat surface is not in contact with the foot and that, in a second angular position, referred to as the "fixing position," when the key is rotated about the longitudinal axis of the head from its rest position to its fixing position, said collar comes into contact with the foot by the minimal radial projection it forms relative to the periphery of the head. Brief description of the figures

[0019] Other features and advantages of the invention will become apparent from the following detailed description, given by way of non-limiting example, with reference to the accompanying drawings in which: there figure 1 represents a perspective view of a dial key according to a preferred embodiment of the invention; the figure 2 represents a top view of the key to the figure 1 ; there figure 3 represents a longitudinal cross-sectional view along the cutting axis AA of the figure 2 ; there figure 4 represents a detailed view of a dial fixing device, in which the key is in the rest position; the figure 5 represents a detailed view of a dial fixing device, in which the key is in the position of fixing a dial foot, said key exerting maximum stress on said foot. Detailed description of the invention

[0020] There figure 1shows a key 10 for holding a dial foot 20 according to the invention. The key 10 has a cylindrical head 11 connected to the end of a rod 12 intended to be engaged in a housing made in a watch structure, for example consisting of a watch movement plate 30.

[0021] The head 11 and the shaft 12 extend along coaxial longitudinal axes. The head 11 comprises an upper surface 110 opposite a lower surface 111. Here, the terms "upper" and "lower" refer to the position of the key 10 as shown in the diagram. figures 1 to 5 .

[0022] The lower surface 111 defines a plane orthogonal to the longitudinal axes of the rod 12 and the head 11 and is intended to rest against the plate 30 of the watch movement.

[0023] The head 11 has a flat 13 extending between the upper surface 110 and the lower surface 111 and defining a plane parallel to the longitudinal axis of the head 11.

[0024] The head 11 further comprises a collar 14 arranged on a portion of its periphery, according to an angular sector defined around the longitudinal axis of the head 11, on either side of the flat 13. The collar 14 has a right section of frustoconical shape whose surface varies around the periphery of the head 11.

[0025] In particular, as illustrated in the figures, the collar 14 forms, in relation to the periphery of the head 11, a minimal radial projection, or even substantially zero, at the ends of the angular sector and forms a maximum radial projection between these ends.

[0026] The collar forms a minimal radial projection, or even practically zero, in the sense that it is negligible, for example that it is on the order of at most one tenth of a millimeter.

[0027] In other words, the distance between the periphery of the head 11 and the periphery of the collar 14 is minimal at the ends of the angular sector along which the collar 14 extends and is maximal between these ends.

[0028] More specifically, as shown in the top view of the figure 2 , the collar 14 has a shape of revolution whose axis of revolution is eccentric with respect to the axis of the head 11.

[0029] Advantageously, the collar 14 is arranged symmetrically on either side of a plane of symmetry passing through the longitudinal axis of the head 11 and orthogonal to the plane defined by the flat 13. The maximum projection formed by the collar 14 is therefore diametrically opposite to the flat 13.

[0030] This feature allows the dial foot 20 to be fixed by rotating the key 10 clockwise and counterclockwise.

[0031] The collar 14 is delimited by an upper surface 140 and by a lower surface 141.

[0032] The lower surface 141 defines a plane coplanar to that defined by the lower surface 111 of the head 11 and is intended to rest against the plate 30 of the watch movement. In other words, the lower surface 141 of the collar 14 is located in line with the lower surface 111 of the head 11, as shown in the cross-sectional view of the figure 3 .

[0033] The upper surface 140 of the flange 14 is arranged so as to define an angle with the lower surface 141, for example, greater than 0 degrees and less than or equal to 45 degrees. The smaller this angle, the easier it is for the flange 14 to penetrate the dial foot 20, at the expense of the flange 14's strength; conversely, the larger the angle, the greater the torque required for penetration into the foot 20 and the greater the stresses on the foot 20.

[0034] Advantageously, the head 11 is configured so as to be able to receive and transmit torque, and for this purpose includes a conformation adapted to cooperate with a tool manipulated by a user.

[0035] In the embodiment shown in the figures, such a conformation is formed by a diametrical slot 15 extending from the upper face of the head 11. The slot 15 is intended to receive a blade of a tool, for example a screwdriver.

[0036] Alternatively, such a conformation can be formed by a cavity with a non-circular cross-section, a prismatic head shape, i.e. having sides on its periphery, for example, so that its cross-section is polygonal in shape, etc.

[0037] With the head 11 and the rod 12 having coaxial longitudinal axes, the torque is transmitted without parasitic lever arm effect.

[0038] The present invention also relates more generally, according to another aspect, to a dial fixing device comprising at least one foot 20 engaged through a first housing of a watch structure, for example of the plate 30 of a watch movement.

[0039] The first housing is adjacent to a second housing receiving the shaft 12 of the key 10, the fastening device being configured so that, in a first angular position, called the "rest position", as illustrated in the detail view of the figure 4 , the flat surface 13 escapes any contact with the foot 20 and that, in a second angular position shown in the detail view of the figure 5 , known as the "fixing position", the collar 14 penetrates the foot 20.

[0040] More specifically, the fastening device is configured so that, when the key 10 is driven in rotation around the longitudinal axis of the head 11, from its rest position, it comes into contact with the foot 20 by the collar 14, first at the level of the minimum radial projection formed by said collar 14.

[0041] The collar 14 then gradually enters the foot 20 during the rotation of the key 10, without risking causing material to be torn from the foot 20.

[0042] In particular, thanks to the specific shape of the collar 14, radial and axial forces are exerted progressively within the foot 20, as the portion of the collar 14 penetrating the foot as the key 10 rotates increases in thickness and width.

[0043] The terms "thickness" and "width" here refer respectively to the dimension of the collar in a radial direction and in an axial direction.

[0044] The flat 13 allows the first and second housings to be arranged at a reduced distance from each other, and therefore allows the fixing device to gain in compactness.

[0045] The dial can be easily detached from the plate 30 by rotating the key 10 to its rest position.

[0046] Advantageously, thanks to the characteristics of the key 10, and in particular thanks to the shape of the collar 14, the same dial foot 20 can be fixed to the plate 30 and detached, and this several times.

[0047] Furthermore, the present invention allows very precise control of the degree of rotation of the key 10, and therefore of the penetration of the collar 14 into the foot 20 of the dial.

[0048] Managing the degree of rotation of the key 10 is crucial to allow optimal fixing of the dial foot 20, in that too much rotation generates unnecessary mechanical stresses and material deformation on the dial foot 20, and too little rotation induces insufficient penetration of the collar 14 into the foot 20, and consequently insufficient fixing which can lead to accidental detachment of the dial.

[0049] Managing the degree of rotation of the key 10 is all the more important as the degree of rotation required for optimal fixing varies depending in particular on the material in which the dial foot 20 is made, its hardness, its diameter, and the weight of the dial.

[0050] Furthermore, depending on the material from which the dial is made, it is necessary to precisely control the degree of rotation of key 10 to avoid visible cracks or deformations. This situation can arise, in particular, when the dial is made of a fragile material, for example mother-of-pearl, sapphire, ceramic, etc., or when it is very thin.

[0051] Finally, it is also necessary to adjust the degree of rotation of the wrench 10 according to the number of fastening / unfastening cycles undergone by the dial. Indeed, after a fastening / unfastening cycle, the fastening of the dial's foot 20 is achieved by a greater angular displacement of the wrench 10 than that used for the previous fastening in order to reach the same level of clamping force as that present during the previous fastening.

Claims

1. Key (10) for holding a dial foot (20), said key including a cylindrical head (11) arranged at the end of a rod (12), the head (11) and the rod (12) being coaxial, the head (11) including a flat (13) and a collar (14) extending over a portion of its periphery in an angular sector defined around the longitudinal axis of the rod (12), on either side of the flat (13), wherein said collar (14) comprises a cross section with a frustoconical shape and, with respect to the periphery of the head (11), forms a minimum radial projection, substantially zero, at the ends of this angular sector and forms a maximum radial projection between these ends.

2. Key (10) according to claim 1, wherein the collar (14) has a shape formed by revolution the revolution axis of which is off-centre with respect to the axis of the head (11).

3. Key (10) according to one of claims 1 or 2, wherein the collar (14) is arranged symmetrically on either side of a symmetry plane passing through the longitudinal axis of the head (11) and orthogonal to the plane defined by the flat (13).

4. Key (10) according to one of claims 1 or 2, wherein the maximum radial projection formed by the collar (14) is diametrically opposed to the flat (13).

5. Device for attaching a dial comprising at least one foot (20) engaged through a first housing of a horological structure and at least one key (10) according to one of claims 1 to 4, the rod (12) of which is engaged in a second housing adjacent to the first housing, the device being configured so that, in a first angular position, referred to as the "position of rest", the flat (13) avoids any contact with the foot (20) and, in a second angular position, referred to as the "attaching position", when the key (10) is rotated about the longitudinal axis of the head (11), from its position of rest as far as its attaching position, said collar (14) comes into contact with the foot (20) through the minimum radial projection that it forms with respect to the periphery of the head (11).