Patent Application
20110103200
This application claims priority from European Patent Application No. 09174421.9 filed Oct. 29, 2009, the entire disclosure of which is incorporated herein by reference.
The invention relates to a system for securing a part made of a material that has no usable plastic domain, i.e. which cannot be driven in and, more specifically, a part of this type formed of silicon-based material.
It is known, in watchmaking, to mount parts on arbours by driving in said parts, i.e. via plastic deformation of the part and/or the arbour. The advent of parts made of silicon, makes it impossible to secure said parts by driving them onto arbours because of the risk of breakage thereof. In current fabrication systems, a polymer type adhesive material is used to secure the silicon parts to their arbours or another locking system involving a third mechanical part. However, these solutions are not satisfactory because, in the first solution, the adhesive materials age randomly and sometimes very prematurely and the second solution is too complex to implement.
It is an object of the present invention to overcome all or part of the aforementioned drawbacks by proposing a system for securing a part made of material with no usable plastic domain onto an arbour, which uses neither driving in nor bonding techniques.
The invention therefore relates to a system for securing a part made of material with no usable plastic domain, which includes a securing device on an arbour, said arbour passing through a hole in said part, characterized in that the securing device has a recess that communicates with the hole in said part and securing means attached to the arbour and at least partly matching the shape of the recess in order to make the movement of the part integral with that of the arbour, without driving in or bonding the part.
Advantageously, the part made of material with no usable plastic domain is not stressed in its plastic domain (no driving in) but simply moved mechanically by the assembly comprising the arbour and securing means.
According to other advantageous features of the invention:
The invention also relates to a timepiece, characterized in that it includes a securing system in accordance with any of the preceding variants.
Finally, the invention relates to a method of securing a part made of material with no usable plastic domain onto an arbour, characterized in that it includes the following steps:
According to other advantageous features of the invention:
Other features and advantages will appear more clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which:
In the example illustrated in
Sprung balance resonator 1 has a pivoting arbour 3, a balance 5, a balance spring 7 and a securing system 9. Pivoting arbour 3, which may also be called the balance staff in the example of
Preferably, balance spring 7 has a collet 2 which is integral therewith. This balance spring 7 may, for example, be obtained from a plate which is etched throughout, by photolithography of a photosensitive resin and then etching the parts of the plate that have no resin.
According to the invention, securing system 9 is for joining balance spring 7 to arbour 3. Thus, securing system 9 includes a securing device 11 that has a recess 4 and securing means 6. Recess 4, in the example of
Securing means 6 are intended for attachment to arbour 3 and to at least partially match the shape of recess 4. Preferably, securing means 6 includes an insert made of metallic material which, according to three embodiments, can be obtained by partially melting arbour 3 or by melting a solder or by shrink fitting said metallic material in amorphous form.
Thus, as visible in
It is thus clear that securing means 6 do not have to be attached to collet 2 but only to arbour 3. However, the rotation movement of arbour 3, which imparts the same movement to securing means 6, also drives collet 2 mechanically, i.e. balance spring 7, via said stud—mortise connection. Consequently, advantageously according to the invention, balance spring 7 made of material with no usable plastic domain, is not stressed in its plastic domain.
Preferably, securing device 11 further includes a collar 13 mounted on arbour 3 to act as a shoulder for balance spring 7 in proximity to collet 2. Indeed, this configuration allows collet 2 to be locked relative to the length of arbour 3 via contact between collar 13, which forms a shoulder, and securing means 6, which form a stud.
The three embodiments of the fabrication method will now be explained. According to a first step a), the method starts with fabrication of part 7 with a hole 8 for receiving arbour 3 and a recess 4 that communicates with hole 8 as illustrated in
According to a second step b) which may be carried out prior to, during or after step a), the method continues with fabrication of arbour 3 preferably with shoulder 13. In a third step c), the method continues with the assembly of arbour 3 in hole 8 of balance spring 7, preferably until it abuts against collar 13 of arbour 3.
The method then includes a fourth step d) for filling recess 4 with securing means 6 such as, for example, a metallic material so that it matches the shape of the recess and part of the external diameter of arbour 3. Finally, the method ends with a fifth and final step e) of hardening the metallic material so as to secure balance spring 7 to arbour 3.
According to a first embodiment, step d) is achieved by localised melting of arbour 3, i.e. arbour 3 is partially melted at zone 12 so that one liquid part of arbour 3 runs into recess 4 as illustrated in
According to a second embodiment, step d) is achieved by melting a solder, i.e. a metallic material between zone 12 and recess 4 is melted so that the solder is made liquid and runs into recess 4 in a similar manner to the first embodiment. The melting according to the second embodiment is also preferably achieved by high energy radiation, for example, by means of a laser source.
According to a third embodiment, step d) is achieved by shrink fitting said metallic material in amorphous form, i.e. the metallic material is heated to between its vitreous transition temperature and crystallisation temperature, then pressed into recess 4 so that it is moulded to the shape of said recess 4.
Thus, whichever embodiment is used, in the fifth and final step e), securing means 6 cool down and can be attached to arbour 3 to form said stud which will allow balance spring 7 to be driven in rotation via its collet 2. Thus, advantageously, even if the part, i.e. balance spring 7, is made of a material with no usable plastic domain, it is possible to secure it to an arbour 3 without having to drive in or bond said part.
Of course, the present invention is not limited to the illustrated example, but is capable of various variants and alterations which will be clear to those skilled in the art. In particular, slope 10 can be replaced by a vertical wall and a horizontal wall, i.e. recess 4 includes a bottom that is approximately parallel to the top surface of collet 2. In both examples, it is clear that recess 4 is blind, i.e. it does not pass right through the part which needs to be secured.
It is also clear that although the part in the above example is a balance spring 7, whose collet 2 includes hole 8 and recess 4, the invention can perfectly well be adapted to a wheel set type part whose hub includes the hole and recess or even to escapement pallets whose lever includes the hole and recess. As explained above, these examples concern the field of watchmaking. However, the invention can be applied to other fields.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09174421.9 | Oct 2009 | EP | regional |
