Protection of a timepiece component made of micromachinable material

Timepiece sub-assembly including a component made of micromachinable material including an attachment area with a peripheral contact surface, and a shell element deformable between two shapes, one contracted and one expanded, arranged to hold the attachment area inside a housing with at least one degree of freedom, and which includes a complementary contact surface arranged, in its contracted shape, to exert a clamping force on the contact surface and to securely immobilise the attachment area in all directions, the shell element including a first element and a second element that are movable with respect to each other in its expanded shape, each including a complementary contact surface, and including clamping means for holding the first and second elements clamped together in its contracted shape.

This application claims priority from European Patent Application No 15197589.3 of Dec. 2, 2015, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention concerns a timepiece sub-assembly comprising, on the one hand, a timepiece component made of micromachinable material comprising at least one attachment area, and on the other hand, a shell element arranged to surround said attachment area, said attachment area comprising at least one peripheral contact surface, and said shell element being deformable with a geometry varying between a contracted shape and at least one expanded shape, and arranged to hold said attachment area inside a housing contained in said shell element, and said shell element comprising at least one complementary contact surface arranged, in said contracted shape of said shell element, to exert a clamping force on said at least one peripheral contact surface and to firmly immobilise said attachment area inside said shell element in all directions.

The invention also concerns a timepiece assembly, including at least one receiving component and at least one such sub-assembly.

The invention concerns a timepiece movement including at least one such assembly.

The invention concerns a watch including at least one such assembly.

The invention concerns the field of timepiece mechanisms comprising components made of micromachinable materials.

BACKGROUND OF THE INVENTION

It is always difficult to assemble micromachinable components to conventional mechanical components in timepiece mechanisms due to sensitivity to shear stress.

EP Patent 2755093 in the name of MASTER DYNAMIC discloses a balance spring collet for a press fit with the shoulder of a timepiece balance wheel, the collet comprising elastically deformable arms, forming an annular space and together delimiting an aperture, each arm comprising a curved concave engagement portion for engagement with such a shoulder, all of the same radius of curvature and equidistant from the central axis, in the free state at a first distance, less than the radius of the shoulder. These engagement portions have a radius of curvature such that, upon deformation of the arm portions, and engagement with the outer surface of the shoulder, the engagement portions substantially conform with the outer surface of the shoulder, and the press fit induced stresses are transferred to and distributed in the arms, so as to prevent any relative movement between the collet and the shoulder upon application of a return force from the balance spring.

EP Patent Application 2743782 A1 in the name of NIVAROX-FAR SA discloses, for timepiece components, a system of assembling a member made of a first material in the aperture of a part made of a second material having no plastic range, using an intermediate portion made of a third material, mounted between said member and said part. This part is received against a first level of the intermediate portion and is resiliently locked on a second level of the intermediate portion by the member in order to make integral the assembly of the member-intermediate portion-part.

SUMMARY OF THE INVENTION

The invention proposes to ensure the proper assembly of micromachinable components to conventional mechanical components.

To this end, the invention concerns a timepiece sub-assembly according to claim1.

The invention also concerns a timepiece assembly, including at least one receiving component and at least one such sub-assembly.

The invention concerns a timepiece movement including at least one such assembly.

The invention concerns a watch including at least one such assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention concerns a timepiece sub-assembly10which comprises, on the one hand, at least one timepiece component1made of micromachinable material, and on the other hand, a protective shell element arranged to surround one portion of this component1.

“Micromachinable material” broadly means any material for obtaining timepiece components made of silicon, silicon oxide, DLC, amorphous material, ceramic, or suchlike, and particularly through the implementation of methods such as MEMS or LIGA, now well known to those skilled in the art. It has been possible to achieve considerable progress in watchmaking, owing to the particularly advantageous features of components made of these materials with these methods: perfect reproducibility, high geometric precision, good, durable elastic characteristics, and it is now possible to produce components of very small dimensions in a repetitive manner. In particular, the fabrication of balance springs, pallet-levers, escape wheels, jumper springs, and balances is well mastered. These technologies also make it possible to reduce in the number of components in an assembly, since they are well suited to the production of one-piece components comprising flexible connections, articulated connections, suspended elements, or suchlike. The production of entirely new types of components has thus also been made possible: this is the case of the very particular, non-limiting application, illustrated by the Figures, to a torsion wire of rectangular cross-section, used as a return element in a balance wheel oscillator. There are, however, limitations on implementation, in particular the difficulty or impossibility of creating shapes in relief and low shear resistance, which limits the application of such components to functions where they are subjected to compression, elongation or torsion stresses. Consequently, holding these components may be difficult in some configurations.

The invention proposes, in particular, to prevent any damage to micromachinable components during mounting in a sub-assembly.

This is why the invention associates a component1with an at least partially enveloping shell element20, whose purpose is to protect component1and to absorb in its place any stresses that present a risk of destroying component1. Shell element20is similar to a clamp, which subjects component1only to compression forces, which cause no problem.

Preferably, component1comprises one area of broader dimensions than the others, which is provided for assembling component1, and which is referred to as attachment area2. If no area satisfies this condition, attachment area2is simply the section of component1which is located in the intended attachment area. The same component1may of course comprise several such attachment areas2, which may take the form of cores.

For example, the median portion of component1ofFIG. 2comprises a first attachment area2, illustrated in more detail inFIG. 1, and which is provided for the relative attachment between a balance110and component1, as seen inFIG. 6, and the end portions thereof comprise two cores2for the attachment and tensioning of the torsion wire formed by this particular component1.

This attachment area2in turn comprises at least one peripheral contact surface3. In a particular embodiment, attachment area2also comprises at least one positioning surface4. Among the various surfaces delimiting attachment area2, a peripheral contact surface3is a junction surface with shell element20which, according to the invention, protects component1in particular during the assembly thereof. For example, if attachment area2is cylindrical, although this shape is difficult to obtain with the aforecited methods in the current state of the art, the peripheral contact surface is a single cylindrical surface. If attachment area2is flat, as seen in the other Figures, it comprises two peripheral contact surfaces3which are preferably the largest parallel and opposite surfaces, on either side of the thinner area of attachment area2. Other shapes of attachment area2are achievable, and require pressure on more than two surfaces:FIG. 9illustrates the theory of an attachment area2comprising three peripheral contact surfaces3.

Shell element20is arranged to hold this attachment area2inside a housing5comprised in shell element20, with at least one degree of freedom.

To this end, shell element20is deformable, with a geometry varying between a contracted shape and at least one expanded shape. “Deformable” means that the shell element is dimensioned to undergo without damage the relatively small deformations caused by a press fit or similar operation. Shell element20is devised to allow for easy insertion of component1into an inner housing5contained in shell element20, in an open position corresponding to an expanded shape, which is generally not an unique shape. Shell element20is devised to be closed around attachment area2of component1, during the change from the expanded shape to the contracted shape where attachment area2is held under pressure. This change from one shape to the other includes a decking step, which corresponds to simply resting shell element20on attachment area2with no application of force.

The contraction that follows this decking may be derived from an effort (force or moment) inherent to shell element20, as inFIGS. 5 and 9where snap-fit means ensure a force transmitted across attachment area2, or as inFIG. 4where the elasticity of some areas of shell element20both ensure that it is held in a closed position, and exert a pressure force on attachment area2.

The contraction may also be imposed by interaction with an external component, which compresses shell element20around attachment area2. This is the case ofFIG. 7where shell element20is an expanding clamp, of a type well known in machine tooling, forcibly held in a bore112. The same is true ofFIG. 6, where it is the insertion of shell element20, containing component1, into a bore112comprised in a receiving component110, here a balance, which ensures the application of a centripetal force on shell element20, which transmits a pressure force to attachment area2, which is thus securely held.

Shell element20advantageously comprises at least one complementary positioning surface40, which is arranged to cooperate with at least one positioning surface4, for the precise positioning of attachment area2inside such a housing5, with at least one degree of freedom.

Shell element20comprises at least one complementary contact surface30, which is arranged, in the contracted shape of shell element20, to exert a clamping force on this at least one peripheral contact surface3, and to securely immobilise attachment area2inside shell element20in all directions, by applying a pressure force on attachment area2.

Preferably, to ensure the proper positioning of attachment area2inside housing5, and then to hold it in the simplest manner, shell element20advantageously comprises at least a first element21and a second element22which move with respect to each other in an expanded shape.

First element21and second element or elements22(for example, in the example ofFIG. 9which comprises two second elements22) each comprise a complementary contact surface:30,31,32.

Shell element20comprises clamping means for holding first element21and second element22or second elements22clamped together in the contracted shape of shell element20.

In a particular variant, as illustrated inFIGS. 5 and 9, shell element20is in one-piece. First element21and second element(s)22comprised in shell element20are articulated to each other via articulations23, to allow the opening of shell element20for the insertion or removal of a component1, and, in the contracted shape of shell element20, to ensure that all the components1comprised in sub-assembly10remain clamped in position in an operating position of sub-assembly10.

In a particular variant, shell element20forms a sheath comprising a housing5for each attachment area2of each component1comprised in sub-assembly10, each attachment area2being, in the expanded shape, movable in an axial direction inside its respective housing5, and, in the contracted shape, enclosed in a substantially concentric manner inside housing5.

In a preferred variant, as seen inFIGS. 1 to 4, where they are made in the form of cylinder portions, first element21and second element(s)22comprised in shell element20are independent of each other to allow the opening of shell element20for the insertion or removal of a component1, and have complementary profiles to ensure that they remain clamped together in the contracted shape of shell element20, and to ensure that all the components1comprised in sub-assembly10remain clamped in position in an operating position of sub-assembly10.

In the variant ofFIG. 7, the clamping means comprise at least one substantially annular peripheral component29, forming a circular clamp, and arranged to clamp together at least a first element21and a second element22, made here in the form of cylinder portions.

In the variants ofFIGS. 5 and 9, the clamping means comprise snap-fit means24,25, which are arranged to clamp together the at least one first element21and one second element22, on which are disposed the snap-fit means24,25, for example formed by beaks at the end of elastic tongues, cooperating with grooves or notches.

As seen in the variant ofFIG. 7, at least the first element21or the second element22comprises at least one element45,46which is more flexible than a stiffer portion47carrying complementary contact surface30. This element45,46forms the clamping means, in cooperation with another similar element46,45, or with an opposing stiff portion, and is arranged to elastically clamp the other of first element21or second element22, on complementary shoulders43,44.

In an advantageously very simple embodiment, each attachment area2is plane and comprises two parallel and opposite peripheral contact surfaces3, and each housing5is delimited by two complementary contact surfaces30which are parallel and opposite31,32.

In the variant illustrated inFIGS. 1 to 3, at least one attachment area2comprises at least one elastic arm6carrying a positioning surface4for each core. This positioning surface4is arranged to cooperate in a complementary manner with a complementary positioning surface40comprised in a stiff portion of shell element20. These elastic arms offer better positioning and centring of the silicon part. The elastic arms may be used on bearing points61to64(in plane and out of plane positioning by flexible strip).

In the variant ofFIG. 4, shall element20comprises, in each housing5, stiff portions47,48, represented here on first element21carrying two complementary positioning surfaces40which are parallel and opposite41,42, forming a U-shape with the respective complementary contact surface30. Each corresponding attachment area2comprises two elastic arms6, which are symmetrical and opposite61,62, and which are arranged to bear under stress on complementary positioning surfaces40, which are parallel and opposite41,42, at least in the contracted shape of shell element20.

Other embodiments may naturally be employed according to the particular geometrical configuration of the components to be held together.

The invention also concerns a timepiece assembly100, including at least one receiving component110and at least one such sub-assembly10.

Receiving component110comprises a receiving chamber111for each sub-assembly10. Inner surface112of each receiving chamber111is arranged to receive an outer surface26comprised in each corresponding shell element20of each sub-assembly10.

Advantageously, at least one inner surface112of a receiving chamber111is dimensioned to compress the outer surface26of the corresponding shell element20upon the insertion of the corresponding sub-assembly10into receiving chamber111, to cause shell element20to change from its expanded shape to its contracted shape upon said insertion.

Returning to the particular case ofFIGS. 1 to 4, receiving component110is a balance, and component1is a torsion wire. The invention provides a good solution for assembling a silicon component inside a metal component. In this case, the portion to be assembled, forming attachment area2, is a substantially parallelepiped plate. Shell element20is formed here of two half-moon portions, forming first element21and second element22, and which encase the silicon plate of attachment area2. Attachment area2comprises, on either side and in a symmetrical manner, two flexible elements6:61,62, which allow core1to be precisely positioned inside half-moon portions21and22. These half-moon portions21and22are dimensioned such that one press fits inside the other, and they apply only compression stresses on silicon attachment area2. In this manner, once the half-moon portions21and22are assembled on wire1, the assembly holds itself together and is easy to handle. Once wire1has been covered by shell element20with the two half-moon portions21and22, the entire assembly can be pressed into a receiving chamber111, notably a bore in balance110.

The positioning means4represented inFIGS. 1 to 4allow for lateral positioning in the flat plane of attachment area2via elastic arms61and62, and also axial positioning in the direction of wire1, by bearing points63and64comprised in attachment area2, and which are arranged to cooperate with corresponding surfaces65and66of first element21, as seen inFIG. 3. These bearing points63and64may comprise flexible elements to ensure precise positioning.

FIG. 8summarises another simple positioning method, wherein attachment area2comprises a bore7, arranged to cooperate with a trunnion or a pin33comprised in main complementary surface31. Naturally, the reverse configuration is also achievable.

The method of assembly may be summarised as follows:

Component1made of micromachinable material, notably silicon, is enveloped in an intermediate component formed by a shell element20, and the entire assembly is then pressed into a receiving component110. Component1experiences only compression stress during the press fit, but no friction or displacement;

component1may comprise guide elements, for obtaining precise positioning;

the intermediate component or components, here the two half-moon portions21and22, may form a self-supporting sub-assembly10, prior to being pressed into receiving component10.

The invention also concerns a timepiece movement200comprising at least one such assembly100.

The invention also concerns a watch300including at least one such assembly100.

The principle of the invention is applicable to other configurations of components, such as for example, the assembly of a silicon balance spring stud to a structure, or a silicon fixed pin or suchlike.

In short, owing to the invention, a component made of micromachinable material, notably silicon, can be press-fitted in another element. The invention may also be used for the assembly of certain fragile materials, such as glass, sapphire or suchlike, or for holding very thin microcomponents.