CLOCK WITH INTEGRATED ACTIVATOR THAT INCLUDES AN ELECTROMECHANICAL DEVICE

Description

Technical field of the invention

[0001] The present invention relates to a timepiece incorporating an actuator formed by an electromechanical device which comprises an electromagnetic system formed by a permanent magnet and a coil. The electromechanical device comprises a mechanical element capable of undergoing movement between a rest position and a position of contact with a predetermined part of the timepiece when the electromagnetic system is activated by an electrical control circuit.

[0002] The actuator according to the invention can in particular be used to carry out mechanical braking pulses which are applied to a mechanical resonator, in particular to the balance of a sprung balance forming such a mechanical resonator, to regulate its average frequency or correct a time drift detected in the operation of the timepiece. Technological background

[0003] An actuator of the type given above is for example described in patent application WO 2018 / 177779 in connection with the figure 4 . The actuator comprises a flexible blade which is actuated by a coil-magnet electromagnetic system. A problem with such an actuator arises from the fact that in the absence of power to the coil, the flexible blade can easily undergo untimely displacements from the intended rest position in the event of shocks or even relatively small accelerations generated by movements of the forearm of a wearer of the timepiece incorporating the actuator. These displacements can generate parasitic braking pulses which are applied to the sprung balance and which then disrupt its operation and in particular the intended regulation of its average frequency. The flexible blade can even oscillate following a shock or a sudden movement by the user of the timepiece and generate a series of parasitic braking pulses.

[0004] Indeed, although the flexible blade is mechanically returned to a rest position in the absence of activation of the electromagnetic system, as is provided between the generation on command of the braking pulses (the activation of the electromagnetic system being provided only during the generation of the braking pulses to limit the electrical consumption of the actuator), this mechanical return force is weak near the rest position. As is known, the elastic force increases linearly with the distance of the flexible blade from its rest position. Thus, this flexible blade vibrates easily and can easily exhibit untimely movements whose amplitude is sufficient for the flexible blade to come into contact with the balance. Summary of the invention

[0005] The aim of the present invention is to overcome the technical problem highlighted in the technological background by providing a timepiece incorporating an actuator whose rest position of a flexible member, actuated by an electromagnetic system, is more stable to prevent or at least reduce, in the event that the timepiece is subjected to accelerations when worn on a user's wrist, the risk of untimely movements of this flexible member with an amplitude such that the actuator can generate a parasitic impulse on a determined part of the timepiece, in particular on the balance of a mechanical resonator.

[0006] To achieve the aforementioned objective, the invention relates to a timepiece incorporating an actuator formed by an electromechanical device, comprising an electromagnetic system and a mechanical element which is movable in translation and associated with the electromagnetic system, and an electrical control circuit. The electromagnetic system is formed by a permanent magnet and a coil, one of the two of which is carried by a flexible member of the electromechanical device and the other by a support of this flexible member.The mechanical element is part of the flexible member and the actuator is arranged so as to allow, in response to an electrical activation signal generated by the electrical control circuit and supplied to the coil to generate an electromagnetic force between this coil and the permanent magnet, a movement of the mechanical element from a rest position, in which it is intended that the mechanical element remains in the absence of activation of the electromagnetic system, to a position of contact with a determined part of the timepiece.Then, the flexible member is formed at least partially by an elastic element which is arranged so as to generate a mechanical force for returning the mechanical element towards the rest position over at least a major part of the distance that the mechanical element can travel, when the electrical control circuit generates said electrical activation signal, between the rest position and the contact position, this contact position ending said at least a major part of said distance.In addition, the actuator further comprises a magnetic element which is arranged so as to be able to interact with the permanent magnet to generate between them a magnetic force which is exerted on the mechanical element when the latter is in the rest position, this magnetic force having a direction opposite to that of the electromagnetic force over at least an initial part of said distance from the rest position and an intensity which decreases, over said at least one initial part, when the mechanical element moves away from the rest position, this intensity being less than the intensity which the electromagnetic force presents for any position of the mechanical element in said at least one initial part.

[0007] By arranging an additional magnetic element in the actuator according to the invention, the rest position of the flexible member is made more stable, so that the mechanical element movable in translation generally remains in this rest position in the absence of an electrical activation signal supplied to the coil. Thus, the risk of contact between the mechanical element and the determined part of the timepiece, in the absence of an electrical activation signal, is greatly reduced. In particular, said determined part is a balance wheel forming a mechanical oscillator of a mechanical mechanism that the timepiece comprises. Brief description of the figures

[0008] The invention will be described below in detail with the aid of the appended drawings, given as non-limiting examples, in which: there Figure 1is a perspective view, with the back open and the oscillating weight removed, of a first variant of a first embodiment of a watch according to the invention; Figure 2 is a partial enlargement of the Figure 1 ; THE Figures 3A and 3B are linear representations of the electromechanical device of the actuator incorporated in the watch of the Figure 1 , respectively in a rest position of the flexible member of this electromechanical device and in a position of contact with the balance of the watch; Figures 4A and 4B are linear representations, similar to those of Figures 3A and 3B , of a second variant of the electromechanical device according to the first embodiment; the Figures 5A and 5B show force curves as a function of a displacement of the mechanical element, along a Z axis, for various forces occurring in the electromechanical device of the second variant represented in Figures 4A and 4B ; There Figure 6gives a curve showing the dynamics of the mechanical element during a braking impulse applied to the balance wheel of the watch; The Figure 7 represents lines of the magnetic field of a permanent magnet in the form of a solid disc forming the electromagnetic system of the first embodiment; the Figures 8A and 8B are linear representations, similar to those of Figures 3A and 3B , of a second embodiment of the electromechanical device of a watch according to the invention; the Figure 8C is a partial enlargement of the Figure 8A ; THE Figures 9A, 9B and 9C relate to a third embodiment of a watch according to the invention and are representations similar to those of the Figures 8A to 8C ; THE Figures 10A and 10B are partial representations of the electromechanical device of the third embodiment respectively for two different positions of the mechanical element formed by this electromechanical device; Figures 11A and 11Bshow force curves as a function of a displacement, along a Z axis, of a magnetic element for stabilizing the rest position of the flexible member, forming the electromechanical device of the third embodiment, for various forces occurring in the electromechanical device of the third embodiment; Figures 12A, 12B and 12C relate to a fourth embodiment of a watch according to the invention and are representations similar to those of the Figures 9A to 9C ; THE Figures 13A and 13B show force curves as a function of a displacement, along a Z axis, of a magnetic element for stabilizing the rest position of the flexible member, forming the electromechanical device of the fourth embodiment, for various forces occurring in the electromechanical device of the third embodiment. Detailed description of the invention

[0009] In reference to the Figures 1 to 6, a first embodiment of a timepiece according to the invention will be described below.

[0010] A first variant is represented in Figures 1 to 3B . Watch 2, shown in Figures 1 and 2 without the bottom of the case and without the oscillating mass of the mechanical movement 4, incorporates an actuator formed by an electromechanical device 6 and an electrical control circuit 8. The electromechanical device comprises an electromagnetic system 10 and a mechanical element 22 which is movable in translation, along an axis Z, and associated with the electromagnetic system. The electromagnetic system 10 is formed by a permanent magnet 12 and a coil 14, the latter being carried by a flexible member 16, forming the electromechanical device, while the permanent magnet is carried by a support 18 of this flexible member. It will be noted that at the Figure 2, the part of the support to which the flexible member 16 is fixed by means of two screws has been removed to reveal the permanent magnet.

[0011] The flexible member 16 is formed at least partially by an elastic element 20. This flexible member comprises the mechanical element 22 which may be part of this elastic element or be fixed thereto. The elastic element 20 is arranged so as to generate a mechanical force for returning the mechanical element 22 towards a rest position of the flexible member over at least a major part of the distance that this mechanical element can travel along the Z axis, when the electrical control circuit generates an electrical activation signal, between its rest position, defined by the position Z = 0.0 at the Figure 3A, and the contact position with the rim 24 of a balance of the mechanical resonator of the mechanical movement 4, this contact position ending said at least a major part of said distance. The contact position corresponds substantially to a distance Z = 0.5 mm for the mechanical element 22. In the variant shown, the elastic element is advantageously formed by an elastic blade 20 which is folded back on itself so as to increase its length for a given size of the electromechanical device 6.

[0012] The flexible member is formed by a base fixed to the support 18, the elastic blade 20, a flat disc 21 at the free end of the elastic blade and the mechanical element 22 which is integral with the flat disc and which is connected to the latter via a bent part. It will be noted that the mechanical element 22 forms a sort of pad making it possible to apply mechanical braking pulses to the felloe 24 by contact between this pad and the underside of this felloe. To do this, it is necessary for the mechanical element 22 to be able to exert a certain force on a lower surface of the felloe 24, which is made possible by the actuator described here.The mechanical element 22 is therefore part of the flexible member 16 although it is not itself necessarily flexible, but it is connected to the free end of the elastic element 20, directly or by another part of the flexible member, so that it can undergo a displacement when the elastic element is subjected to a deformation force generated by the electromagnetic system 10, as shown in . Figure 3B .

[0013] The actuator is arranged so as to allow, in response to an electrical activation signal generated by the electrical control circuit 8 generally in the form of electrical pulses and supplied to the coil 14 to generate an electromagnetic repulsion force between this coil and the permanent magnet 12, a movement of the mechanical element 22 from the rest position (Z = 0.0), in which it is intended that the mechanical element remains in the absence of activation of the electromagnetic system 10, to the contact position (Z = 0.5 mm) with the rim 24 of the balance, and more generally with a determined part of the timepiece according to the application intended for the actuator.It will be noted that, in an alternative embodiment where the axial positions of the mechanical element and the balance rim are reversed and in which the electromagnetic system has, when this electromagnetic system is inactive and therefore at rest, a free space between the permanent magnet and the coil, the electromagnetic force is then provided to be attractive in order to actuate the mechanical element from its rest position to its contact position.

[0014] According to the invention, the actuator further comprises a magnetic element arranged in a fixed position relative to the axis of rotation of the balance of the mechanical resonator and arranged so as to be able to interact with the permanent magnet 12 to generate between them a magnetic force which is exerted on the mechanical element 22 when the latter is in its rest position and which defines a restoring force of this mechanical element towards its rest position over at least an initial part of the distance from the rest position to the contact position. In the specific case where the actuator is provided in two separate parts, one of which incorporating the coil is removable, the magnetic element has a stable position relative to the coil when the actuator is in a functional configuration allowing it to be actuated. In the particular variants shown, the magnetic element 26 is integral with the coil 14.

[0015] The magnetic force has a direction opposite to that of the electromagnetic force, which is generated in the electromagnetic system 10 when the coil 14 is energized, over at least an initial portion of the distance from the rest position to the contact position. Then, the magnetic force has an intensity which decreases, over said at least an initial portion, when the mechanical element 22 moves away from the rest position and which is less than the intensity which the repulsive electromagnetic force has for any position of the mechanical element in said at least an initial portion. The magnetic element 26 is aligned with the central axis of the permanent magnet 12 when the mechanical element 22 is in the rest position, as shown in Figure 3A. In the first variant of the first embodiment described here, the magnetic element is formed by an element 26 made of a ferromagnetic material, hereinafter called ferromagnetic element.

[0016] In the first embodiment described here, the permanent magnet 12 has a disc shape, more generally a solid wafer shape. Similarly, the magnetic element 26 has a disc shape, more generally a solid wafer shape.

[0017] In the absence of activation of the electromagnetic system, the magnetic force provided is very effective in stabilizing the flexible member 16 and thus the mechanical element 22 in the rest position. The magnetic element 26 is arranged so that it exerts a force of increasing intensity as the mechanical element approaches the rest position, unlike the elastic force of the flexible member. Thus, without electrical power, the flexible member is subjected to a magnetic force which tends to maintain it in its rest position and to strongly recall it towards it in the event of an external disturbance which may momentarily move it away from the rest position, by limiting the distance of the mechanical element 22 and also the amplitude of any rebounds which the flexible member may exhibit following such a distance. Indeed, the magnetic force is relatively significant when the mechanical element 22 is in the rest position and close to it.This will be seen even more precisely in the following description of a second variant.

[0018] To Figures 4A and 4BA second variant of the first embodiment is shown. This variant is distinguished from the first variant by a spatial inversion of the electromagnetic system 10A of the electromechanical device 6A. Thus, the permanent magnet 12 is carried by the elastic blade 20 on the side of its free end while the coil 14 is fixed to the support 18 with the magnetic element 26 arranged in the interior space of the coil. An advantage of this second variant lies in the fact that the coil undergoes neither movement nor shock against the rim 24 of the balance when the electromagnetic system 10A is activated. This makes it possible not to stress the electrical connections of the coil to the electrical control circuit, and therefore to avoid a break in these connections. On the other hand, this second variant is more sensitive to external magnetic fields than the first variant since the permanent magnet is carried by a movable part of the flexible member.

[0019] The dimensions of the magnetic element are smaller than those of the permanent magnet 12. For example, the coil has an outer diameter of 2.4 mm, an inner diameter of 0.9 mm and a height of 0.4 mm. The permanent magnet 12 has a diameter of 2.0 mm and a height of 1.0 mm. The ferromagnetic element 26 has a diameter of 0.15 mm and a thickness of 0.05 mm. It will be noted that these values ​​can be optimized depending on the type of magnet selected, the distance between the permanent magnet and the ferromagnetic element, the electrical pulses that the electrical control circuit provides to the electromagnetic system, the desired dynamics for the mechanical element 22 and other parameters.It is important to find a size of the magnetic element 26 and a positioning thereof relative to the permanent magnet to obtain an attractive force which is strong enough to properly stabilize the flexible member, in particular its mechanical element, in the rest position in the absence of activation of the electromagnetic system, while ensuring that the electromagnetic force is sufficient to overcome the magnetic force and to allow a movement of the mechanical element such that the latter can exert a force of a certain intensity on the rim of the balance against which it must be able to momentarily exert sufficient pressure to carry out a braking impulse in an application for regulating the rate of the watch.

[0020] For the second variant described here, with dimensions for the electromagnetic system and the ferromagnetic element approximately equal to those given as an example previously, the Figure 5Agives a) curve 30 of the magnetic force generated between the permanent magnet 12 and the ferromagnetic element 26 as a function of a displacement of the mechanical element along the Z axis, this force defining a magnetic return force over the entire displacement range represented and in particular over the distance that the mechanical element 22 can travel between the rest position (Z = 0.0 mm) and the contact position (Z = 0.5 mm); b) curve 32 of the electromagnetic force, with the coil 14 supplied with a voltage of 2.5 V, as a function of the displacement of the mechanical element along the Z axis; c) curve 34 of the total magnetic force, resulting from the addition of the electromagnetic force and the magnetic return force, as a function of the displacement of the mechanical element along the Z axis.

[0021] There Figure 5Bintroduces the mechanical restoring force, defined by the force exerted by the elastic blade 20 when it moves away from its rest position, which is given by curve 36, which is determined by the coefficient of elasticity of the elastic blade. Then, curve 38 represents the total restoring force, resulting from the addition of the magnetic force (curve 30) and the mechanical restoring force (curve 36), as a function of the displacement of the mechanical element along the Z axis. It is observed that the total restoring force increases in intensity from the contact position to the rest position where it is maximum, and this thanks to the ferromagnetic element. Finally, curve 40 gives the overall force exerted on the flexible member 16, at the level of the mechanical element 22, as a function of the displacement of the mechanical element along the Z axis.Although this overall force changes mathematical sign and therefore direction over the range of displacement represented, it nevertheless remains positive over the entire distance between the rest position and the expected contact position.

[0022] The graphs given at the Figure 5Brelate to the particular case where the elastic element 20 is fully relaxed when the flexible member is in the rest position (Z = 0.0), so that the mechanical force in this position is zero. In other variants, a preload of the elastic element is provided in the rest position. Such a preload can be provided either positive, so that the mechanical restoring force (elastic force) is driving over an initial part of the distance from the rest position to the contact position, or negative so that the mechanical restoring force is greater than that occurring in the variant shown over the entire said distance. A preload of the flexible member at rest thus makes it possible to adjust the total restoring force, in particular for the rest position and close to it, and therefore the quantity of energy to be supplied to the flexible member via the electromagnetic system during a braking pulse.It is understood that this adjustment makes it possible to determine the dynamics of the mechanical element when it is actuated via an electrical pulse supplied by the electrical control circuit to the coil 14. The . Figure 6 gives the displacement along the Z axis of the mechanical element 22 during an electrical pulse of approximately 4 ms activating the electromagnetic system. Curve 42 shows the real case with the element 22 which comes into contact with the rim 24 of the balance to provide it with a braking pulse, while curve 44 shows the corresponding virtual case in the absence of the balance. The duration of each electrical pulse can be determined according to the intensity of the desired shock between the mechanical element 22 and the rim 24 of the balance. In addition, this duration can be provided to be greater than the time of movement of the mechanical element between the rest position and the contact position to extend the duration of contact between the mechanical element 22 and the rim 24.

[0023] In two other variants of the first embodiment, the ferromagnetic element in the two variants described above is replaced by a second permanent magnet having a magnetic axis parallel to that of the permanent magnet 12 and the same polarity as this magnet. Thus the first magnet 12 and the second magnet for stabilizing the flexible member in the rest position are in magnetic attraction for any position of the mechanical element between the rest position, including, and the contact position. Preferably, the second permanent magnet has a solid wafer shape, in particular a disc shape.

[0024] There Figure 7is an introduction to the second embodiment which will be described below. This figure shows the electromagnetic system 10 described previously. The magnetic field lines generated by the permanent magnet 12 are shown, these magnetic field lines defining two zones, Zone 1 and Zone 2, for a second magnet placed at the periphery of the magnet 12 and having a magnetic axis in the same direction. If the two magnets have the same polarity along said direction (Z axis), then they have a magnetic attraction in Zone 1 and a magnetic repulsion in Zone 2. This observation is the basis of the second embodiment shown in Figures 8A to 8C .

[0025] In reference to the Figures 8A to 8C, a variant of a second embodiment is proposed in which the magnetic element for stabilizing the rest position of the flexible member 16 is a second permanent magnet 50 which has an annular shape defining a central circle. For a rectangular cross-section as shown in the figures, the diameter of this central circle is conventionally given by the intersection of the two diagonals of this cross-section. References identical to those of the first embodiment relate to elements or parts which are similar or similar to the corresponding elements or parts of this first embodiment.

[0026] This second embodiment is distinguished from the previous one essentially by the fact that the magnetic element of the electromechanical device 6B is a second permanent magnet, which has an annular shape defining a central circle, or by the fact that this magnetic element is constituted by a plurality of permanent magnets arranged along a geometric circle. The central circle has a diameter which is greater than the external diameter of the first permanent magnet and it is, when the flexible member is in the rest position ( Figures 8A and 8C ), centered on the central axis of the first permanent magnet 12. The diameter of the central circle is selected so that the magnetic force between the first permanent magnet 12 and the second annular permanent magnet 50 has a reversal of direction during a movement of the mechanical element 22 from the rest position to the position of contact with the balance 24. As observed in Figures 8C and 8B, the annular permanent magnet 50 is located in Zone 2 when the flexible member is at rest, so that the magnetic force between the two magnets is in attraction, whereas in the contact position, the annular permanent magnet is in Zone 1 so that the two magnets are then in magnetic repulsion.

[0027] Thus, in the rest position, the annular permanent magnet 50 plays its role of returning it to the rest position. On the other hand, during activation of the electromagnetic system, this annular magnet crosses the boundary between Zone 2 and Zone 1 and thus the magnetic force becomes positive and consequently a driving force, which modifies the dynamics of the movement of the mechanical element 22 relative to the first embodiment. It will be noted that the position along the Z axis of the annular magnet 50 can easily be adjusted. It is in particular possible for the central circle to be at the level of the upper surface of the first magnet 12, or even below. A part 48 made of non-magnetic material forms a core of the coil 14 and a flange which is surrounded by the magnet 50. This part 48 undergoes the impact between the flexible member 16 and the magnet 12.It is thus possible to select its material to preserve the first magnet, this material preferably having a good energy absorption capacity during the impact between the part 48 and the first magnet during a return of the mechanical element to the rest position after it has struck against the rim 24 of the balance during a braking impulse.

[0028] In a variant not shown, the annular magnet 50 is replaced by a plurality of separate permanent magnets which are arranged along a geometric circle. In this case, it is the geometric circle which has a diameter greater than the outer diameter of the first permanent magnet 12 and which is, when the flexible member is in the rest position, centered on the central axis of the first permanent magnet. The diameter of the geometric circle is selected so that the magnetic force between the first permanent magnet and the plurality of permanent magnets has a reversal of direction during the movement of the mechanical element between the rest position and the contact position. This variant has the advantage of not having to produce an annular magnet of small cross-section.In a first case, the plurality of magnets may consist of two small magnets arranged diametrically opposite and preferably oriented orthogonally to the direction of the end portion of the elastic blade 20 connected to the disc 21 supporting the coil and the part 48. In a second case, four magnets are provided distributed regularly along the geometric circle. These magnets may be housed in cavities in the flange of the contact part with the first magnet.

[0029] In reference to the Figures 9A to 11B, a third embodiment of the invention will be described below. The references already described previously will not be described again in detail here. This third embodiment is characterized by an electromagnetic system 10C whose permanent magnet 52, called the first permanent magnet or first magnet, has an annular shape and by a magnetic element constituted by a permanent magnet 54, called the second permanent magnet or second magnet, having a solid wafer shape, in particular a disc shape. The second magnet is arranged so as to be aligned on a central axis of the first magnet when the mechanical element 22 is in the rest position ( Figures 9A and 9C). This second magnet is placed in a housing of a support 48A forming a core for the coil 14 and furthermore a flange which covers the lower surface of this coil, as in the second embodiment. The zero position along the Z axis is defined by the upper surface of the first magnet and the rest position of the flexible member 16 corresponds to a positioning of the second magnet, which is movable synchronously with the mechanical element 22, in which its lower surface is substantially at the zero position. Figure 9B shows the electromechanical device 6C of the actuator considered in a situation / state where the flexible member, in particular its mechanical element, is in the position of contact with the balance.

[0030] Then, the second magnet 54 is arranged so that the magnetic force between the first annular magnet 52 and this second magnet has a reversal of direction during a movement of the mechanical element 22 from its rest position to the position of contact with the rim 24 of the balance, in response to an electrical pulse supplied to the coil 14 by the electrical control circuit to generate a braking pulse. Figures 10A and 10B a second embodiment variant is partially shown which has an arrangement of the first and second magnets which is similar to that of the first variant given in Figures 9A to 9C. Thus the interaction between these two magnets is identical in both variants. The only difference lies in the fact that the support 48B of the second magnet in the second variant only forms a non-magnetic core for the coil 14 while the support 48A of the first variant also has a flange covering the lower surface of the coil. Figures 10A and 10B, the magnetic field lines of the first annular magnet and the second magnet have been partially represented. The interior space of the first magnet 52 defines a central void of cylindrical shape. The annular shape of the first magnet has the particularity that its magnetic field lines inside the cylindrical central void have a direction opposite to that of the magnetic field in the magnet itself. Thus, in a Zone 3 encompassing the interior space and two complementary zones extending respectively on either side of this interior space, the direction of the magnetic field generated by the first magnet is opposite, along the Z axis, to the direction of the magnetic field of this first magnet in a zone extending Zone 3 above said interior space.

[0031] There Figure 10Apartially shows the electromechanical device 6C, in particular the disc 21 of the flexible member 16, the electromagnetic system 10C and the additional magnetic element 54, in a situation corresponding to that of the Figure 9B where the flexible member, in particular its mechanical element, is in the contact position. In this state, the second magnet, which has a polarity opposite to that of the first annular magnet (i.e. between the lower surface and the upper surface of this first magnet), undergoes magnetic repulsion. The Figure 10B partially shows the electromechanical device 6C in a situation corresponding to that of the Figures 9A and 9C where the flexible member is in its rest position. In this state, the second magnet 54 is located in Zone 3 and it then undergoes a magnetic attraction from the first annular magnet.

[0032] To the Figure 11Ais given the curve 60 of the magnetic force as a function of the displacement of the magnetic element 54 from its zero position, corresponding to the rest position of the flexible member / the mechanical element and in which its lower surface is coincident with the upper surface of the first magnet which defines this zero position, up to the contact position of the mechanical element 22 with the balance. Note that the magnetic interaction between the two magnets is indicated by 'B' in the legends to Figures 11A, 11B, 13A and 13B , while 'EM' indicates the electromagnetic interaction between the coil and the first magnet 52, which is either activated ('ON') or deactivated ('OFF'). The reversal of the direction of the magnetic force can be seen on the graph of the Figure 11A, the curve 60 intercepting the Z=0 axis. It is noted that the intensity of the magnetic force is relatively strong for the rest position (Z=0), so that the second magnet correctly plays its role of stabilizing the flexible member in the rest position, then it decreases rapidly to be equal to zero just above 0.2 mm. Then, after passing through the zero value, the magnetic force is positive but its intensity remains relatively low. However, over the intended displacement distance (0.5 mm), the amount of energy required to overcome the magnetic force is significantly less than that required in the first two embodiments.The inversion of the magnetic force during a movement of the mechanical element 22 between the rest position and the position of contact with the rim 24 of the balance wheel therefore changes the dynamics of the movement of this mechanical element during an electrical pulse supplied to the coil 14, which generates an electromagnetic force given by the curve 62. The total magnetic force (addition of the magnetic force and the electromagnetic force during an activation of the electromagnetic system 10C) is represented by the curve 64. It is observed in the example given that this total magnetic force varies relatively little over the distance of movement of the magnetic element.

[0033] To the Figure 11Bvarious forces are represented as a function of the displacement of the magnetic element 54, taking into consideration the mechanical force of the elastic element 20 forming the flexible member and whose mechanical restoring force is given by curve 36. Curve 66 gives a total restoring force equal to the sum of the magnetic force and the mechanical force. Curve 68 corresponds to the sum of the electromagnetic force and the mechanical restoring force. Finally, curve 70 gives the curve of the overall force for all the forces present, with the electromagnetic system powered, as a function of the displacement of the magnetic element, respectively of the mechanical element (with a small variation in scale along the Z axis).It is observed that the various elements involved first in the total restoring force (curve 66) and then in the overall force (curve 70) are selected and arranged so that the overall force is positive over the entire travel distance and the total restoring force is negative over the entire travel distance, i.e. for any position between the rest position and the contact position.Concerning this last condition, in other words, the first annular magnet, the second permanent magnet and the elastic element are configured and arranged in such a way that the sum of the mechanical restoring force and the magnetic force presents, over the entire distance that the mechanical element 22 can travel, a direction opposite to the direction of movement of this mechanical element from the rest position to the contact position, so as to form over this entire distance a total restoring force of the mechanical element towards the rest position.

[0034] In reference to the Figures 12A to 12C and to the Figures 13A and 13B, a fourth embodiment of the invention will finally be described. The references already described in detail previously will not be described again. This fourth embodiment is essentially distinguished from the previous embodiment by the fact that the magnetic element 74 of the electromechanical device is made of a ferromagnetic material and that this ferromagnetic element 74 is positioned along the Z axis at a different level. Furthermore, in order to avoid shocks between the annular magnet 52 and the coil 14 during electrical pulses supplied successively to the coil to generate a plurality of braking pulses, a circular tube 76 is provided around the electromagnetic system 10D in the rest position.The cylindrical tube is arranged so that the disc 21 of the flexible member bears against the upper surface of this cylindrical tube when the flexible member is at rest, the height of the cylindrical tube being selected so that the coil 14 is at a distance from the permanent magnet 52 in the rest position of the flexible member.

[0035] The ferromagnetic element 74 has a solid pancake shape, in particular a disc shape, and is arranged to be aligned with a central axis of the annular permanent magnet when the mechanical element is in the rest position. The ferromagnetic element is fixed to a projecting portion of a support 78 forming a core of the coil 14. As can be seen in the Figure 12C, the ferromagnetic element is arranged inside the interior space of the annular permanent magnet when the flexible member is in its rest position and it thus has a negative offset HR relative to the second permanent magnet of the previous embodiment, that is to say that its lower surface is located below the position Z=0 which is defined, as in the third embodiment, by the level of the upper surface of the permanent magnet 52. In general, the ferromagnetic element is arranged so as to be positioned at least partially in an interior space of the annular permanent magnet 52 when the mechanical element is in the rest position.

[0036] To Figures 13A and 13B are given two graphs with curves representing the same forces, as a function of the displacement of the ferromagnetic element, as in the graphs of Figures 11A and 11B. Curve 80 concerns the magnetic force between the annular permanent magnet and the ferromagnetic element. It is observed that the positioning of the ferromagnetic element in the interior space of the annular permanent magnet, when the flexible member is at rest, makes it possible to have a negative direction for the magnetic force, and therefore a magnetic restoring force, over a first part of the distance that the ferromagnetic element, respectively the mechanical element, can travel from the rest position of the flexible member and an intensity of this magnetic force which is relatively high when this flexible member is in its rest position (Z=0). Curve 82 of the electromagnetic force is identical to curve 62. Curve 84 represents the total magnetic force (addition of the magnetic force and the electromagnetic force during an activation of the 10D electromagnetic system).We observe in the example given that this total magnetic force varies considerably over the distance of displacement of the magnetic element, but it remains positive and relatively significant over the entire distance between the rest position and the contact position (Z=0.5 mm).

[0037] To the Figure 13Bvarious forces are represented as a function of the displacement of the ferromagnetic element 74, taking into consideration the mechanical force of the elastic element 20 forming the flexible member and whose mechanical restoring force is given by curve 36. Curve 86 gives a total restoring force equal to the sum of the magnetic force and the mechanical force. Curve 88 corresponds to the sum of the electromagnetic force and the mechanical restoring force. Finally, curve 90 gives the curve of the overall force for all the forces present, with the 10D electromagnetic system powered, as a function of the displacement of the ferromagnetic element, respectively of the mechanical element (with a small variation in scale along the Z axis).It is observed that the various elements involved first in the total restoring force (curve 86) and then in the overall force (curve 90) are selected and arranged so that the overall force is positive over the entire displacement distance and the total restoring force is negative for any position of the ferromagnetic element between the rest position and the contact position of the mechanical element.In other words, according to this last condition which concerns a preferred variant, the annular permanent magnet 52, the ferromagnetic element 74 and the elastic element 20 are configured and arranged in such a way that the sum of the mechanical restoring force and the magnetic force has, over the entire distance that the mechanical element 22 can travel, a direction opposite to the direction of movement of this mechanical element from the rest position to the contact position, so as to form over the entire said displacement distance a total restoring force of the mechanical element towards the rest position. It will be noted that it is not necessary, although preferred, for the overall force to be positive up to the contact position.Indeed, given the dynamics of the movement of the mechanical element, the latter arrives at the contact position with a certain kinetic energy so that a slightly negative overall force over a final part of said displacement distance does not pose a major problem. Finally, although preferred, it is not essential that the total restoring force remains negative over the entire said displacement distance, and that it therefore loses its restoring force character over a certain intermediate section. Indeed, after an impact between the mechanical element and the balance at the contact position, the mechanical element 22 sets off again in the opposite direction towards the rest position with a certain energy.Furthermore, if the total restoring force is significant over the said final part of the placement distance, then the mechanical element stores a certain kinetic energy which can enable it to cross a certain intermediate section where the total restoring force would have momentarily changed direction.

Claims

1. Timepiece (2) incorporating an actuator formed by an electromechanical device (6; 6A; 6B; 6C; 6D), which comprises an electromagnetic system (10; 10A; 10B; 10C; 10D) as well as a mechanical element (22) that is mobile in translation and associated with the electromagnetic system, and by an electric control circuit (8), the electromagnetic system being formed by a permanent magnet (12, 52) and a coil (14), one out of the two of which is carried by a flexible member (16) of the electromechanical device and the other by a support (18) of this flexible member, said mechanical element being formed by said flexible member and the actuator being arranged in such a way as to allow, in response to an electric activation signal generated by the electric control circuit and provided to the coil to engender an electromagnetic force between this coil and said permanent magnet, a movement of the mechanical element from a rest position, in which it is provided that the mechanical element remains in the absence of an activation of the electromagnetic system, to a position of contact with a determined part (24) of the timepiece, in which said flexible member is formed at least partially by an elastic element (20) that is arranged in such a way as to engender a mechanical force of return of the mechanical element in the direction of said rest position over at least a majority of the distance that the mechanical element can travel, when the electric control circuit generates said electric activation signal, between the rest position and the contact position, this contact position ending said at least a majority of said distance, the actuator further comprising a magnetic element (26; 50; 54; 74) arranged in such a way as to be able to interact with said permanent magnet (12; 52) to engender between them a magnetic force that is exerted on the mechanical element when the latter is in the rest position, this magnetic force having a direction opposite to that of said electromagnetic force over at least an initial part of said distance from the rest position and an intensity which decreases, over said at least an initial part, when the mechanical element moves away from the rest position and which is less than the intensity that said electromagnetic force has for any position of said mechanical element in said at least an initial part.

2. Timepiece according to claim 1, characterised in that said magnetic element (26; 74) consists of a ferromagnetic material.

3. Timepiece according to claim 1, wherein said permanent magnet is a first magnet, characterised in that said magnetic element (50; 54) is formed by a second permanent magnet arranged in magnetic attraction with the first magnet when said mechanical element (22) is in the rest position.

4. Timepiece according to claim 2, characterised in that said permanent magnet (12) has a solid, flat, round shape, in particular the shape of a disc, and in that said magnetic element is arranged in such a way as to be aligned on a central axis of the permanent magnet when the mechanical element is in the rest position.

5. Timepiece according to claim 3, characterised in that the first permanent magnet (12) has a solid, flat, round shape, in particular the shape of a disc, and in that said magnetic element is arranged in such a way as to be aligned on a central axis of the first permanent magnet when the mechanical element is in the rest position.

6. Timepiece according to claim 4, characterised in that said ferromagnetic element (26; 74) has a solid, flat, round shape, in particular the shape of a disc.

7. Timepiece according to claim 5, characterised in that the second permanent magnet (54) has a solid, flat, round shape, in particular the shape of a disc.

8. Timepiece according to claim 5, characterised in that< / b> said magnetic element (50) consists of the second permanent magnet, which has an annular shape defining a central circle, or of a plurality of permanent magnets arranged along a geometric circle; in that said central circle or said geometric circle has a diameter that is greater than the outer diameter of the first permanent magnet (12) and is, when the flexible member is in the rest position, centred on the central axis of the first permanent magnet; and in that the diameter of the central circle or of the geometric circle is selected so that said magnetic force between the first permanent magnet and the second permanent magnet, respectively the plurality of permanent magnets, has an inversion of direction during said movement of said mechanical element (22) from the rest position to the contact position.

9. Timepiece according to claim 2, characterised in that said permanent magnet (52) has an annular shape.

10. Timepiece according to claim 3, characterised in that the first permanent magnet (52) has an annular shape.

11. Timepiece according to claim 9, characterised in that said ferromagnetic element (74) has a solid, flat, round shape, in particular the shape of a disc, and in that this ferromagnetic element is arranged in such a way as to be aligned on a central axis of said permanent magnet when the mechanical element is in its rest position.

12. Timepiece according to claim 11, characterised in that the ferromagnetic element is arranged in such a way as to be positioned at least partially in an inner space of the annular permanent magnet when said mechanical element is in the rest position.

13. Timepiece according to claim 11 or 12, characterised in that the permanent magnet (52), the ferromagnetic element (74) and the elastic element (20) are configured and arranged in such a way that the sum of said mechanical return force and said magnetic force has, over all of said distance that said mechanical element can travel, a direction opposite to the direction of said movement of this mechanical element from the rest position to the contact position, so as to form over all of said distance a total force of return of the mechanical element towards the rest position.

14. Timepiece according to claim 10, characterised in that the second permanent magnet (54) has a solid, flat, round shape, in particular the shape of a disc, and in that the second permanent magnet is arranged in such a way as to be aligned on a central axis of the first permanent magnet when the mechanical element is in the rest position.

15. Timepiece according to claim 14, characterised in that the second permanent magnet is arranged so that said magnetic force between the first permanent magnet (52) and the second permanent magnet (54) has an inversion of direction during said movement of said mechanical element (22) from the rest position to the contact position.

16. Timepiece according to claim 15, characterised in that the first permanent magnet, the second permanent magnet and the elastic element (20) are configured and arranged in such a way that the sum of said mechanical return force and said magnetic force has, over all of said distance that said mechanical element (22) can travel, a direction opposite to the direction of said movement of this mechanical element from the rest position to the contact position, so as to form over all of said distance a total force of return of the mechanical element towards the rest position.