This application claims priority from European Patent Application No. 10187740.5 filed Oct. 15, 2010, the entire disclosure of which is incorporated herein by reference.
The invention relates to the assembly of a part, made of a material that is brittle, i.e. having no plastic domain, to a member comprising a different type of material.
Current assemblies including a silicon-based part are generally secured by bonding. However, bonding is not satisfactory as regards long term hold. Moreover, the operation requires extremely delicate application which makes it expensive.
EP Patent No. 1 850 193 discloses a first, silicon-based part which is assembled on a metal arbour using an intermediate metallic part. However, the shape variants proposed in this document are not satisfactory and either result in the silicon part breaking during assembly, or do not bind the parts sufficiently well to each other.
It is an object of the present invention to overcome all or part of the aforecited drawbacks by providing an adhesive-free assembly which can secure a part made of a material that is brittle, i.e. with no plastic domain, to a member comprising a ductile material, such as, for example, a metal or metal alloy.
The invention therefore relates to the assembly of a member, made of a first material, in the circular aperture of a part, made of a second material that is brittle, using an intermediate part, made of a third material, mounted between said member and said part, characterized in that the intermediate part is a continuous cylinder comprising a hole for receiving said member, so that the intermediate part absorbs, radially and in a uniform manner, at least part of the axial driving force of said member by elastic and/or plastic deformation, and in that the part includes pierced holes distributed around the circular aperture thereof for absorbing any of said radial force not absorbed by the intermediate part, in order to secure the assembly in a manner that is non-destructive for said part.
This configuration advantageously enables the assembly comprising the part-intermediate part-member to be secured without bonding to an ordinary, precision controlled member, while ensuring that the part is not subject to destructive stresses, even if it is formed, for example, from silicon.
In accordance with other advantageous features of the invention:
Moreover, the invention relates to a timepiece characterized in that it includes an assembly according to any of the preceding variants.
Finally, the invention relates to a method of assembly wherein a member made of a first material is axially driven into a part made of a second material that is brittle, i.e. having no plastic domain. The method includes the following steps:
a) forming the part with a circular aperture and pierced holes distributed around the circular aperture intended to form elastic deformation means;
b) inserting an intermediate, continuous cylindrical part, made of a third material and including a hole, into the circular aperture without any stress:
c) rolling and elastically and/or plastically expanding the intermediate part via the hole therein using said member to exert uniform radial stress against the wall of the part around said circular aperture by relying on said elastic deformation means of the part.
This method advantageously allows the member to be driven in axially without any axial stress being applied to the part. Indeed, advantageously according to the invention, only uniform, radial, elastic deformation is applied to the part. Finally, this method unites the assembly comprising the part—intermediate part—member by adapting to the dispersions in manufacture of the various components.
In accordance with other advantageous features of the invention:
Other features and advantages will appear clearly from the following description, given by way of non-limiting indication, with reference to the annexed drawings, in which:
As explained above, the invention relates to an assembly and the method of assembling the same, for securing a fragile material, i.e. which is brittle or has no plastic domain such as a silicon-based material, to a ductile material such as a metal or metal alloy.
This assembly was devised for applications within the field of horology. However, other domains may very well be envisaged, such as, notably, aeronautics, jewellery, the automobile industry or tableware.
In the field of horology, this assembly is required due to the increasing importance of fragile materials, such as those based on silicon, quartz, corundum or more generally ceramics. By way of example, it is possible to envisage forming the balance spring, balance, pallets, bridges or even the wheel sets, such as the escape wheels, completely or partially from a silicon base. However, the fact of always having to use ordinary steel arbours, the fabrication of which has been mastered, is a constraint which is difficult to reconcile with the use of parts that are brittle, i.e. having no plastic domain. Indeed, it is impossible to drive in a steel arbour and this systematically breaks fragile parts, i.e. those which are brittle, with no plastic domain.
This is why the invention relates to an assembly wherein a member made of a first material, for example a ductile material such as steel, is axially driven into the circular aperture in a part made of a second material that is brittle, i.e. having no plastic domain, such as a silicon-based material, by using an intermediate part, made of a third material, more ductile than the first material, which is mounted between said member and said part.
According to the invention, the intermediate part is a continuous cylinder with a hole for receiving said member so that the intermediate part absorbs, radially and in a uniform manner, part of the axial driving force of said member, by elastic and/or plastic deformation. Indeed, when research was carried out, it was clear that the intermediate part had to distribute the radial stresses induced by the rolling and expansion operation over the wall thereof in a uniform manner around the circular aperture.
Consequently, a continuous cylinder, i.e. having no radial slot or axial pierced hole, is required to prevent any localised stresses on part of the wall of the aperture in the fragile part which could break said part.
This interpretation also justifies not using a collar on the top or bottom part of the continuous cylinder. Indeed, during the rolling and expansion operation, this type of collar transmits part of the axial force from the member onto the top (or bottom) of the fragile part. Hence, the shearing exerted, in particular, by the corners of the collar on the top (or bottom) of the fragile part similarly generates localised stresses that can break the fragile part.
Consequently, the continuous cylinder with a hole may be interpreted, if the cylinder section is circular, as a full ring with continuous internal and external walls, i.e. without any grooves or more generally any discontinuity of material. The continuous cylinder therefore only generates uniform radial stress by elastic and/or plastic deformation on the wall around the circular aperture, without any requirement to observe a particular axial direction for driving in the member.
Moreover, the part includes pierced holes forming elastic deformation means which are distributed around and at a distance from the circular aperture therein and which are for absorbing any said radial forces not absorbed by the intermediate part so as to secure the assembly in a manner that is non-destructive for said part. The elastic deformation of the fragile part due to the pierced holes thus secures said fragile part to the assembly comprising the intermediate part—member secured by the plastic deformation of the continuous cylinder.
The assembly according to the invention will be better understood with reference to
Pallets 1, by way of example, include two assemblies 2, 12 according to the invention, respectively for securing the dart 7 and pivot pin 17 to the lever 5. As seen in
The escape wheel 3, and more generally wheel set 3 includes, by way of example, an assembly 22 respectively for securing pivot pin 27 to body 25 of wheel 3. As seen in
It is thus immediately clear that the example assembly 22 can be applied to any type of wheel set. Further, pivot 27 may comprise a pinion in a single piece so as to form the finished wheel set.
Examples of pierced holes are shown in
As seen in
In a first variant of the first embodiment illustrated in
In a second variant of the first embodiment illustrated in
Advantageously according to the invention, holes 31, 33 and 35 and slots 36 are used to form elastic deformation means capable of absorbing radial stresses, i.e. forces exerted from the centre of circular aperture 28 towards the wall of body 25 surrounding said circular aperture.
Of course, the two or three series may be closer to or further from each other and/or of different shapes and/or different dimensions according to the maximum desired clearance and the desired stress for deforming beams 32, 34.
By way of example, an alternative to
Preferably, pierced holes 26, 26′, 26″, 26′″ extend over a width comprised between 100 μm et 500 μm from the edge of circular aperture 28. Further, slots 36 are comprised between 15 μm et 40 μm. Finally, the diameter of circular aperture 28 is preferably comprised between 0.5 and 2 mm.
According to a second embodiment illustrated in
Thus,
As seen in
Further, each triangular hole 53 communicates with circular aperture 28 via a notch 57.
In a variant of the second embodiment illustrated in
Of course, as in the first embodiment, the two or three series may be closer to or further from each other and/or of different shapes and/or of different dimensions according to the maximum desired clearance and the desired stress for deforming beams 52, 54.
Preferably, pierced holes 46, 46′ extend over a width comprised between 100 μm et 500 μm from the edge of circular aperture 28. Further, slots 56 or notches 57 are comprised between 15 μm et 40 μm. Finally, the diameter of circular aperture 28 is preferably comprised between 0.5 and 2 mm.
The method of assembly will now be explained with reference to the schematic
This step may be achieved by dry or wet etching, for example a DRI etching.
Further, in a second step, the method consists in forming pivot pin 27 in a second material with a maximum section e6. As explained hereinbefore, the second step can be carried out in accordance with ordinary arbour fabrication processes. Pivot pin 27 is preferably metal and may for example be formed of steel.
In a third step, the method consists in forming intermediate continuous cylindrical part 24 in a third material with a hole 23 of internal section e2 and external section e3. The third step can thus be achieved by conventional machining or electroforming. Intermediate part 24 may thus have a thickness of between 100 et 300 μm and a width l, i.e. the external section e3 minus the internal section e2 (l=e3−e2), also comprised between 100 et 300 μm.
Preferably, the third material is more ductile than the second material of pin 27 so that the latter is not deformed during the rolling and expansion operation. Intermediate part 24 is preferably metal and may thus include nickel and/or gold. However, any other ductile material may advantageously be added to the third material or replace the latter.
Of course, the first three steps do not have to observe any particular consecutiveness and may even be performed at the same time.
In a fourth step, intermediate part 24 is inserted into circular aperture 28 without any contact. This means, as seen in
Preferably, the difference between diameter e4 of circular aperture 28 and external diameter e3 of intermediate part 24 is approximately 10 μm, i.e. a thickness of around 5 μm, which separates body 25 of part 3 relative to intermediate part 24.
Further, preferably, according to the invention, intermediate part 24 is held in circular aperture 28 using a shoulder 21 provided with a bore of section e1.
Finally, the method includes a fifth step consisting in rolling and elastically and/or plastically expanding intermediate part 24 via the hole 23 thereof by fitting pin 27 in axial direction A so as to exert a uniform radial stress B against the wall of circular aperture 28 by relying on the elastic deformation means of part 3, i.e. pierced holes 26.
Thus, first of all, as seen in
Preferably according to the invention, the rolling and expansion operation is set so that the clamping force is greater at the gap between the non-deformed intermediate part 24 and the wall of part 3 around circular aperture 28. Preferably, the clamping force is arranged to provide a displacement comprised between 8 and 20 μm.
Consequently, after the elastic and/or plastic deformation of intermediate part 24 in the first phase, it is desirable for the rolling and expansion operation to exert, in a second phase, elastic deformation of body 25 around circular aperture 28 so as to unite the assembly comprising pin 27, intermediate part 24 and wheel 3, as shown in
Advantageously according to the invention, it is possible to drive in pin 27 from any side of body 25 of wheel 3. Further, no axial force is applied to body 25 of wheel 3 during the process. Only radial elastic deformation is applied. It is also to be noted that the use of continuous cylinder intermediate part 24 allows uniform stress to be exerted on the wall of body 25 around circular aperture 28 during radial deformation B of intermediate part 24, in order to prevent breaking the fragile material of wheel 3 and to adapt to any dispersions in fabrication of the various components.
Of course, this invention is not limited to the illustrated example but is capable of various variants and alterations that will appear to those skilled in the art. In particular, the pierced holes of the part made of fragile material may include more or fewer series of holes than the embodiments presented hereinbefore.
Thus, as illustrated in
It is also possible to use assembly 2, 12, 22, 62 in place of elastic means 48 or the cylinders 63, 66 of WO Patent No. 2009/115463 (which is incorporated herein by reference) so as to fix a single-piece sprung balance resonator to a pivot pin.
Finally, assembly 2, 12, 22, 62 according to the invention can also unite any type of timepiece or other member, whose body is formed of a material that is brittle, i.e. having no plastic domain (silicon, quartz, etc.) with an arbour, such as, for example, a tuning fork resonator or more generally a MEMS (Microelectromechanical system).
Of course, two members like those described hereinbefore may also be secured to the same arbour using two distinct assemblies 2, 12, 22, 62 so as to unite their respective movements.
Number | Date | Country | Kind |
---|---|---|---|
10187740 | Oct 2010 | EP | regional |
Number | Name | Date | Kind |
---|---|---|---|
7926355 | Bannier et al. | Apr 2011 | B2 |
20060055097 | Conus et al. | Mar 2006 | A1 |
20080112274 | Bitterli et al. | May 2008 | A1 |
20100238772 | Verardo et al. | Sep 2010 | A1 |
20120159766 | Verardo et al. | Jun 2012 | A1 |
20120159767 | Verardo et al. | Jun 2012 | A1 |
20130286795 | Conus et al. | Oct 2013 | A1 |
20130309446 | Conus et al. | Nov 2013 | A1 |
Number | Date | Country |
---|---|---|
1 445 670 | Aug 2004 | EP |
1 850 193 | Oct 2007 | EP |
2 230 572 | Sep 2010 | EP |
1 427 115 | Feb 1966 | FR |
54-141964 | Oct 1979 | JP |
Entry |
---|
European Search Report issued Mar. 24, 2011, in European Application No. 10187740, filed Oct. 15, 2010. |
Number | Date | Country | |
---|---|---|---|
20120090933 A1 | Apr 2012 | US |