CH716153B1 - Oscillating weight for a timepiece. - Google Patents

Abstract

The invention relates to an oscillating weight (1) for a timepiece, comprising: a support (7) arranged to be mounted on a bearing defining an axis of rotation of said oscillating weight (1), a peripheral part (3) carried by said support (7) and defining an unbalance; characterized in that said oscillating mass (1) comprises: at least one porous zone (9) having a relative density less than or equal to 65% of the density of the material constituting it. The invention also relates to a method of manufacturing such an oscillating weight (1).

Description

Technical area

The present invention relates to the field of watchmaking. It relates, more particularly, to an oscillating mass for the automatic winding of a mechanical timepiece or for driving an electric generator for an electric or electronic timepiece.

State of the art

[0002] Oscillating weights, also called "rotors", are well known for winding a mechanical timepiece and for driving an electric generator of an electric or electronic timepiece of the type " Seiko Kinetic“. These oscillating masses comprise a relatively heavy zone carried by a support which links the latter to a bearing, which is typically a ball bearing, arranged to allow the mass to pivot thanks to the unbalance defined by the heavy zone. The overall shape of such a rotor can generally follow a sector of a circle or can be circular. In the latter case, the unbalance is typically created in a hidden manner, by incorporating heavy elements into the rotor, in order to provide an unbalance and/or by removing material from its invisible face in order to lighten part of the latter.

[0003] The design of such an oscillating mass always involves a compromise between several parameters and constraints.

[0004] First, the oscillating weight must have enough unbalance to obtain sufficient torque and efficiency to drive the barrel or the generator, if necessary. However, the total weight of the mass must not be excessive at the risk of damaging the bearing in the event of shocks in particular. A mass with too great an imbalance winds/raises the barrel too quickly and generates premature wear of the sliding flange of the barrel. The winding speed, and therefore the time after which the wearer will have completely wound the barrel of his watch, also depends on the physical activity of the wearer. The level of activity of the wearer is an important parameter in the dimensioning of the rotor.

[0005] During shocks having an axial component with respect to the axis of rotation of the rotor, the bearing is subjected to significant forces, and a certain flexibility of the support is therefore advantageous in order to absorb these shocks. During high-intensity shocks, the support is sized to allow the outer part of the mass to come into contact with adjacent elements of the frame or of the movement of the timepiece to preserve the integrity of the bearing. However, if the flexibility of the support is too high, the external part of the mass may repeatedly come into contact with adjacent elements of the frame or of the movement of the timepiece during low intensity shocks. This is undesirable because the aesthetic appearance of the contacted parts is deteriorated. A clearance is provided to take this clearance into account.

[0006] To this end, mention may be made, for example, of document EP 2 230 570, which proposes a rotor whose support has been perforated so as to optimize the unbalance while keeping the rotor relatively light. In addition, document CH371993 proposes a rotor in two parts, the heavy part being supported by a sheet metal plate which has been perforated provided with slots in order to confer more flexibility on the support in order to absorb shocks.

[0007] However, these solutions are not optimal and it is difficult to obtain the desired unbalance/total weight ratio while maintaining appropriate rigidity.

The object of the invention is therefore to provide an oscillating mass in which the aforementioned defects are at least partially overcome.

Disclosure of Invention

More specifically, the invention relates to an oscillating mass for a timepiece as defined by claim 1. This oscillating mass constitutes a rotor comprising: a support arranged to be mounted on a bearing defining an axis of rotation of said oscillating weight; a peripheral part carried by said support and defining an imbalance with respect to said axis of rotation.

According to the invention, said oscillating mass comprises at least one porous zone having a relative density less than or equal to 50% of the density of the material constituting it, that is to say that the overall density of said zone is 65% or less of the density of a solid block of the same material having the same dimensions. This relative density can advantageously be at most 50% or even at most 30%.

[0011] By arranging one or more porous zones in the support and/or in the peripheral part, the mechanical and dynamic properties can be optimized according to the needs of the manufacturer, in particular by conferring an optimization of the unbalance, the total weight and the rigidity mass.

[0012] Advantageously, the support may comprise one or more of said porous zone(s) and may even consist entirely of a said porous zone. In this case, the weight of the support can be minimized while maintaining a desired rigidity.

[0013] Alternatively, said support may comprise at least one said porous zone and at least one solid part, said at least one solid part being able for example to be superposed (that is to say stacked in the thickness of the support) or juxtaposed (that is to say arranged side by side in the plane of the support) to said porous zone. These options provide a large number of design possibilities. In the case where a solid part is superimposed on a so-called porous zone, the latter can be hidden from the wearer and therefore made invisible.

[0014] Advantageously, said porous zone can be arranged to give said oscillating mass an imbalance around said axis of rotation. For this purpose, said zone can be located in the peripheral part and/or in the support in order to lighten the mass on one of its sides and thus to create the unbalance. For example, the peripheral part can be annular and can comprise at least one so-called porous zone.

[0015] In a variant, said at least one said porous zone (or at least one said porous zone among several) may comprise sintered material. In such a case, said porous zone can be manufactured by sintering a powder under pressure.

[0016] Alternatively, said porous zone comprises a structure comprising a plurality of repeated unit cells, in which case at least said porous zone can be manufactured by additive manufacturing, that is to say at least one said porous zone is thus manufactured or the entire mass is thus manufactured in one piece.

[0017] Advantageously, the process for manufacturing the mass may comprise steps of: determination of the level of physical activity of the wearer, for example by means of a questionnaire, tests or measurements; sizing of the oscillating weight, depending on the results of the determination step, production of the oscillating weight at least partially by additive manufacturing according to the dimensions determined during the dimensioning step.

[0018] In doing so, oscillating weights adapted to the level of physical activity of the wearer can be produced, which ensures that optimum winding can be ensured without winding the mainspring too much. Such excessive winding risks damaging the flange of the latter, and is therefore to be avoided.

Brief description of the drawings

Other details of the invention will appear more clearly on reading the description which follows, given with reference to the appended drawings in which: Fig. 1a is a schematic plan view of a first oscillating weight according to the invention; Fig. 1b is a schematic sectional view along line A-A of Figure 1a; Fig. 2 is a schematic view of a stochastic porous material; Fig. 3a and 3b represent two examples of non-stochastic porous materials which can be manufactured by additive manufacturing; Fig. 4 is a schematic view of a unit cell of the structure of Figure 3b; Fig. 5 is a schematic sectional view of a variant of an oscillating mass according to the invention; Fig. 6 to 11 are schematic plan views of several additional variants of oscillating weights according to the invention.

Embodiments of the Invention

Figures 1a and 1b schematically illustrate an oscillating mass 1 according to a first embodiment of the invention. This oscillating mass 1 constitutes a rotor intended to be integrated into a wristwatch in a known manner. In doing so, the mass 1 is in kinematic connection with a mainspring or an electric generator in order to supply it with energy for its drive following movements of the wearer's wrist.

The mass 1 of Figure 1 comprises a peripheral part 3 of annular shape, connected to a hub 5 via a support 7 comprising arms, which can have any desired shape. Alternatively, the support can be solid. The hub 5 is arranged to be fixed on a moving part of a ball bearing in a known manner, for example by means of driving in, shore, gluing, welding or the like.

In this embodiment, the peripheral part 3 has a height h perpendicular to the plane of Figure 1 which is greater than that of the support 7 and is made of a material having a relatively high density, such as gold , brass, steel or the like. The peripheral part also comprises a porous zone 9 which can be made of the same material as the rest of the mass 1 or of a different material, for example having a lower density. This porous zone 9 is located in an opening 3a which extends around a part, in particular half, of the peripheral part 3. Since it has a lower mass than that of the corresponding zone of the peripheral part 3 located on the opposite side of the axis of rotation, it defines an unbalance which allows the mass to pivot during the movements of the watch in which it is incorporated.

[0023] The porous zone 9 comprises an open-pore structure, which can be stochastic or non-stochastic. Since these pores are open, they are linked together in a stochastic (i.e. random) or non-stochastic (i.e. regular) network. The relative density of said zone 9 is less than or equal to 50%, ie the overall density of said zone 9 is less than or equal to 50% of the density of said material constituting it. Preferably, the porous zone has a relative density which is at most 30%.

[0024] In the case of a stochastic structure, this can be formed by conventional sintering of particles of a base material, such as particulate metal, particulate ceramic or glass or a mixture of such materials, or alternatively by a method of manufacturing a metal foam such as those described in documents FR 2 921 281, EP 2 118 328 and the like.

[0025] In order to obtain such a relative density by sintering, the size and shape of the sintered particles are adapted for this purpose. For example, the publication „The Effect of Particle Shape on Sintering Behavior and Compressive Strength of Porous Alumina“, Miyake et al, Materials 11(7):1137 July 2018, reveals the achievement of a relative density of 33.5% for a sintered sample comprising alumina particles in the form of rods. Such a structure is represented schematically in FIG. 2. Those skilled in the art will have no problem finding sintering parameters and basic particles in the literature to obtain a density relative to their needs.

[0026] Advantageously, the pores defined by the particles have an average size of at least 3 μm and communicate with each other.

[0027] Alternatively, the porous zone 9 may have the shape of a regular three-dimensional network, the structure of which is formed by a repetition of structural unit cells along three orthogonal axes. A large number of such structural unit cells are known, as discussed in the publications „Design and Analysis of Lattice Structures for Additive Manufacturing“, Beyer & Figueroa, J. Manuf. Science. Eng 138(12), 121014 (September 29, 2016), “Lattice Structures and Functionally Graded Materials Applications in Additive Manufacturing of Orthopedic Implants: A Review“, Mahmoud & Elbestawi, Journal of Manufacturing and Materials Processing, October 12, 2017, et al. .

Figures 3a and 3b illustrate two non-limiting examples of such regular structures, based on cubic unit cells. The structure of Figure 3a has a relative density of 55% and therefore a porosity of 45%, while that of Figure 3b has a relative density of 35% and a porosity of 65%.

Figure 4 illustrates the unit cell of cubic structure, its three-dimensional repetition forming the corresponding structure illustrated in Figure 3b. However, many other forms of unit cells described in the literature are of course possible, such as for example those disclosed in the aforementioned documents. More complex unit cell arrangements including for example voids in the structure or combinations of different but compatible unit cells are also possible; in the context of the present invention, "unit cell" is to be considered as representing at least one structural unit which is repeated in a regular manner in said zone 9.

[0030] Advantageously, the unit cell is repeated at least three times in the thickness h of the mass 1 in order to provide sufficient structural integrity, in particular in bending. The maximum number of repetitions of the unit cell in the thickness h is not limited and can be chosen according to the needs of the constructor as well as according to the size of the unit cell. Furthermore, the maximum size of the pores, that is to say the maximum sphere which can be defined inside a pore, is advantageously 1 mm or less, preferably 500 μm or less, in particular 200 μm or less, or even 100 µm or less.

[0031] If said zone 9 comprises a non-stochastic (that is to say regular) lattice structure, it can advantageously be manufactured by additive manufacturing, such as for example 3D printing, in particular by 3D photolithography, selective sintering by laser („SLS“) etc., but other known methods can also be used.

[0032] The production by 3D printing also offers the possibility of customizing the oscillating weight 1. This customization can be aesthetic. It can also be dimensional and functional. It is then possible to adapt the unbalance to the customer carrier. With regard to this last point, the wearer's level of physical activity can be determined on the basis of a questionnaire (duration of wear, activities carried out, etc.), determined by iteration (testing several different unbalanced rotors) or by measured using an accelerometer worn on the wrist for a certain time, for example. Following this determination, the oscillating mass 1 can be sized to optimize it, and then manufactured. For example, for a very active wearer, a mass with too much unbalance will raise the mainspring too much, which will wear the spring flange as mentioned above. Such a user will therefore benefit from a lighter mass having a relatively reduced unbalance. Otherwise, a wearer who is very static will benefit from an oscillating mass 1 having a more substantial unbalance. In doing so, the watchmaker can provide oscillating weights 1 that are perfectly adapted to the needs of the user.

In the embodiment illustrated in Figure 1, the porous zone 9 crosses the entire thickness of the peripheral part 3. However, as illustrated in Figure 5, it is possible to arrange the zone 9 invisibly, by arranging the opening 3a as a blind hole in the face of the peripheral part 3 of the mass which is intended to face the movement in the service position.

Figure 6 illustrates yet another variant of an oscillating mass 1 of annular shape. In this variant, the peripheral part 3 comprises a plurality of openings 3b arranged at regular angular intervals around said part 3. These openings 3b, which pass through the thickness of said part 3 but which can alternatively be blind, are provided with studs 3c, of which at least a part is made of porous material in order to constitute "porous zones 9" in the sense of the invention. By arranging studs 3c in heavy material (such as gold, steel or solid brass) on one side and in any porous material on the other side, it is possible to define an adequate unbalance, while minimizing the visibility of the difference between the plots.

[0035] Figure 7 illustrates a second embodiment of an oscillating mass 1 according to the invention, which generally takes the form of a segment. In this variant, the support 7 is solid and is made entirely of porous material. Therefore, the entire support constitutes the "porous zone 9" in the sense of the invention. The peripheral part 3 is again made of a relatively dense material, such as gold, steel or brass and typically has a higher height than that of the support 7.

In this configuration, the support 9 can be designed in such a way that it can have a lower mass than a conventionally perforated support (such as for example as mentioned in the context of the aforementioned document EP 2 230 570), while maintaining a bending stiffness that is similar or even higher. Alternatively, one can keep a similar stiffness by reducing the mass of the support 7.

FIG. 8 represents a variant of an oscillating weight 1 according to FIG. 7, in which the porous zone 9 is hidden by a solid part 7a, located on the bottom side of the support 7 (that is to say oriented visible when the watch in which mass 1 is integrated has a transparent back) and having a relative density of substantially 100% with respect to the material constituting it. This configuration makes it possible to optimize the stiffness and the inertia of the support while hiding the porous zone 9 from the user.

[0038] Figure 9 shows yet another variant of an oscillating weight according to Figure 7, in which the hub 5 is solid instead of porous, in order to give it improved mechanical strength.

[0039] Figure 10 further illustrates a variant of an oscillating weight according to Figure 7, in which the hub 5 is solid and is linked to the peripheral part by solid arms 7b. The interstices between the latter are filled with a porous material in order to constitute a plurality of porous zones 9 in the sense of the invention. This configuration gives even more mechanical and aesthetic possibilities.

In each of the above-described cases, it is of course possible to incorporate additional inserts in the peripheral part 3 in order to increase its inertia, for example by providing blocks or studs of material even denser than that of the peripheral part 3 , as generally known. It is also possible to leave empty areas inside or adjacent to the edges of the porous areas 9 in order to provide an openwork effect.

[0041] To the naked eye, the porous areas 9 may appear little different from the solid parts of the mass 1, which makes it possible to print a logo, a pattern or the like at least partially on the porous area 9. This principle is illustrated in Figure 11, which shows a mass 1 according to Figure 7 provided with a logo printed on the porous area 9 as well as on the peripheral part. Of course, the logo can be located exclusively on one or other of these sub-elements of mass 1.

As regards the methods of manufacturing such oscillating weights, several possibilities exist.

In the case where at least one porous zone 9 has a non-stochastic structure manufactured by additive manufacturing, it is possible to manufacture the entire mass 1 by such a process, in order to obtain a one-piece construction. A particularly advantageous method in such a case is selective laser sintering, since it is compatible with metals having a relatively high density.

Alternatively, it is possible to manufacture the solid parts of the mass 1 by machining or conventional molding, to place them on a support and then to manufacture the porous zones 9 by additive manufacturing in any suitable material. When the porous zones 9 are formed by conventional sintering (and not by selective laser sintering or the like), the conventionally manufactured solid parts can be placed in a suitable mold, and then a conventional sintering can be carried out in order to form the porous zones 9 .

Although the invention has been described above in connection with specific embodiments, additional variants are also possible without departing from the scope of the invention as defined by the claims.

In this regard, mention may be made, for example, of a variant not shown in which said oscillating mass 1 is pivoted on its outside in a known manner on a ball bearing or on rollers. In such a case, the ball bearing or the rollers constitute(s) the bearing, and the “support” 7 is integrated into the peripheral part 3 in order to support it and to cooperate with the bearing.

Claims (14)

1. Oscillating mass (1) for a timepiece, comprising: – a support (7) arranged to be mounted on a bearing defining an axis of rotation of said oscillating weight (1), – a peripheral part (3) carried by said support (7) and defining an imbalance with respect to said axis of rotation; characterized in that said oscillating mass (1) comprises: – at least one porous zone (9) having a relative density less than or equal to 65% of the density of the material constituting it. 2. Oscillating mass (1) according to one of the preceding claims, wherein said support (7) comprises at least one said porous zone (9). 3. Oscillating weight (1) according to the preceding claim, wherein said support (7) is constituted by a said porous zone (9). 4. Oscillating weight (1) according to claim 2, wherein said support (7) comprises at least one said porous zone (9) and at least one solid part (7a; 7b). 5. Oscillating weight (1) according to claim 4, wherein said solid part (7a) is superimposed on at least one said porous zone in the thickness of said support (7). 6. Oscillating weight (1) according to claim 4, wherein said solid part (7b) is juxtaposed with at least one said porous zone (9) in the plane of said support (7). 7. Oscillating mass (1) according to one of the preceding claims, wherein said peripheral part (3) is in the form of an arc of a circle. 8. Oscillating mass (1) according to one of claims 1 to 6, wherein said porous zone (9) is arranged to give said oscillating mass (1) an imbalance around said axis of rotation. 9. Oscillating weight (1) according to the preceding claim, wherein said peripheral part (3) is annular and comprises at least one said porous zone (9). 10. Oscillating weight (1) according to one of the preceding claims, wherein the support (7) and the peripheral part (3) are integral. 11. Oscillating mass (1) according to one of claims 1 to 10, wherein said porous zone (9) comprises a structure comprising a plurality of repeated unit cells. 12. A method of manufacturing an oscillating weight (1) according to one of claims 1 to 11, wherein at least said porous zone (9) is manufactured by additive manufacturing. 13. Method according to claim 12, characterized in that it comprises the following steps: – determination of the level of physical activity of the wearer, – sizing of the oscillating mass (1), according to the results of said determination step, – production of the oscillating mass (1) at least partially by additive manufacturing according to the dimensions determined during the dimensioning step. 14. A method of manufacturing an oscillating weight (1) according to one of claims 1 to 10, wherein at least said porous zone (9) is manufactured by sintering a powder.