EP2796939B1 - Divided stem and related assembly method - Google Patents

Description

The present invention relates to a particular assembly method for a stem of a timepiece.

TECHNOLOGICAL BACKGROUND

In the field of watchmaking, and more particularly of wristwatches, it is known to use stems in two parts, in particular winding stems, also called broken stems, to facilitate the mounting of the movement in the caseband. These rods are used in particular for watches having a large diameter or a large thickness, for which automatic assembly of the movement in the middle on assembly lines is no longer possible. Broken stems are even necessary for fine watchmaking mechanical parts comprising an ornate case, for example with decorative motifs engraved in a one-piece caseback made in one piece with the caseband. For such boxes without a removable bottom, it is impossible to set up a classic winding stem. In this case, a stem is used, a first part of which is coupled to the movement, and housed in the middle part with the rest of the movement, to which is added, at its free end, a second part introduced by its proximal end through an orifice in the build. This second part also typically comprises, at its distal end, a grip ring to allow the user to perform adjustment operations in particular.

The coupling between the part of the stem integral with the movement and that comprising the crown is generally made using elements male and female, for example by screwing or driving. However, each of these two mounting methods has drawbacks respectively in terms of cost and reliability of assembly. Indeed, if an assembly by screwing is preferred, it is necessary to carry out the bar turning operation, carried out within the framework of the machining of the threads and tappings of the assembly parts of the rod, with extreme precision to guarantee a sufficient tightening torque, at the end of travel, to ensure maintenance in the assembled position even in the event of shocks, vibrations or even significant thermal variations, which proves to be very expensive. If, on the other hand, an assembly by driving in is chosen, it will be very difficult to machine the male and female parts with adequate precision, because the slightest deviation in terms of size will have very harmful consequences either in terms of ease of assembly, or in terms of holding force: a large difference in dimensions between the male and female parts may either require the exercise of a very significant force to introduce the male part into the female part of the assembly, thus risking damaging the parallel movement, or, if this insertion force is too weak, it will not allow the stem to pass from one axial position to another, such as that corresponding to the winding of the watch to that of the resetting hour, without risk of tearing off the part of the stem integral with the crown. Furthermore, more specifically for rods made of plastic material, it is difficult to guarantee lasting retention of the assembly of the two parts of the rod due to creep.

In order to overcome these drawbacks, other types of assembly means intended to make each of the rod parts integral in rotation and axially have been proposed, in particular by means of elastic jaws provided on one of the parts and in which axially engages the end of the other part. However, the machining of such coupling elements still remains relatively delicate due to the small dimensions of the rod, which greatly weakens the part and increases its risk of breakage, and does not allow the rod to be disengaged. outside the caseband in different axial positions, each corresponding to different modes of operation.

The document EP2579103 relates to another type of a broken rod, the main purpose of which is to be able to compensate for axial tolerance errors relating to parts to be assembled during assembly using a piston mechanism. The device for coupling the two parts of the control rod is effected for example by means of a conical polygonal end in a coupling housing. The proposed solution aimed at simplifying the assembly and disassembly operations, it however necessarily involves a reversible coupling and is therefore incompatible with any final connection between the two parts to be assembled, although it is more reliable in terms of robustness.

Otherwise, we know from the document JPS5769271 a broken rod, the coupling between the two parts of which is made by welding; a drawback of this solution is to form beads at the joint zones, which can prove to be unsightly and needs to be hidden, thus conditioning the respective lengths of each of the two parts to be assembled.

There is therefore a need for an assembly method and device for two-part rods free from these known limitations.

SUMMARY OF THE INVENTION

To this end, the present invention relates to a method for assembling a two-part stem of a timepiece, the stem comprising a first part provided with a first proximal end cooperating with a movement, and a first distal fixing end, and a second part provided with a second proximal fixing end and a second distal end, characterized in that it contains a step for welding or gluing the first distal end of attachment of the first part of the rod to the second proximal end of attachment of said second part of the rod.

The invention also relates to a two-part stem of a timepiece comprising a first part provided with a first proximal end cooperating with a movement, and a first distal end for fixing, and a second part provided with a second proximal fixing end and a second distal end, the first distal fixing end of the first part of the rod being welded or glued to the second proximal fixing end of the second part of the rod.

An advantage of the present invention is to provide a more efficient, safer and more durable fixing method and device for a broken stem of a timepiece. The risk of breakage, particularly during operations involving axial pulling of the crown by the user, is practically eliminated, and the stem is more resistant to all the other normal use constraints of a watch in terms of shocks, vibrations and thermal variations.

Another advantage of the proposed solution is that it makes it easier to mount the part of the stem outside the mainplate, while hiding the place of attachment in the caseband, without risk of damaging the movement, but while guaranteeing nevertheless a solid fixation and a better lifespan.

Yet another advantage of the proposed solution is that it does not slow down the production rate, the proposed assembly operation being able to be carried out on a production line within a period substantially equivalent to that corresponding to a screwing or driving-in operation.

BRIEF DESCRIPTION OF FIGURES

• les figures 1A, 1B et 1C montrent des vues respectivement de profil, en coupe et en perspective des deux parties d'une tige selon un mode de réalisation préférentiel de l'invention;
• les figures 2A et 2B, et 2C montrent des vues respectivement de profil, en coupe et en perspective des deux parties de la tige illustrée aux figures 1A, 1B et 1C en position assemblée;
• la figure 3 montre une vue en perspective d'une tige selon un mode de réalisation préférentiel, accouplée au mouvement et logée dans la platine du mouvement.

Other characteristics and advantages of the invention will emerge more clearly from the detailed description and the drawings, given by way of example and not intended to be limiting, in which:

• the figures 1A, 1B and 1C show views respectively in profile, in section and in perspective of the two parts of a rod according to a preferred embodiment of the invention;
• the figures 2A and 2B, and 2C show views respectively in profile, in section and in perspective of the two parts of the rod illustrated in figures 1A, 1B and 1C in assembled position;
• the picture 3 shows a perspective view of a stem according to a preferred embodiment, coupled to the movement and housed in the movement plate.

DETAILED DESCRIPTION

The figures 1A, 1B and 1C show the two parts of a rod 10 before their assembly, the figure 1B being a sectional view of the Figure 1A along axis AA. The Figure 1A is a profile view of each of these parts, the left part constituting a first part 1 of the stem intended to be coupled to the movement, here by means of the gear wheel 13 (better visible on the figure 1C in perspective), while the right part constitutes a second part 2 intended to be manipulated by the user, here by means of a crown 23 arranged at its end. On each of the first part 1 and second part 2 of the stem, the proximal end will be called that which is closest to the center of the watch in which the stem is intended to be housed, and the distal end respectively, that which is located farther from the center of the watch. One therefore moves with an increasing radius relative to the center of the watch to go from the proximal end to the distal end.

The rod according to the preferred mode of the invention illustrated by the figures 1A, 1B and 1C in the disassembled position and by the figures 2A, 2B, 2C East thus a stem for a watch, such as for example a winding stem for a totally mechanical watch or even a simple time-setting stem for a quartz watch, the gear wheel 13 of which with the movement is arranged at the level of a first proximal end 11 of the first part 1 of the rod, while the ring 23 for gripping and handling is arranged at a second distal end 22 of the second part 2 of the rod. A series of grooves 17 is arranged on the first part 1 of the rod to allow the positioning of a jumper - not shown - determining different axial positions of the rod. On the illustrated embodiment, three splines can be distinguished which can for example correspond to a current operating mode, a fast date correction mode and a time setting mode. A groove 26 can also be arranged on the second part 2 of the rod to typically house therein a seal 5, not shown on the Figures 1A-C and 2A-C but visible on the picture 3 .

The assembly of the first and second parts of the rod is carried out at the level of the first distal end 12 of the first part 1 and of the second proximal end 21 of the second part 2 of the rod, by introducing a tenon 25 arranged on the second part 2 of the rod in a blind hole 16 arranged in the first distal end 12 of the first part 1 of the rod. This fitting operation may or may not be accompanied by a slight driving of the tenon 26 into the hole 16, but does not require very precise machining tolerances for the correspondence between the diameter of the hole 16 and that of the tenon 25, because the final fixing operation is carried out during a subsequent welding operation, illustrated in particular by the Figures 2A, 2B described below.

Each of the parts of the rod also contains bearing surfaces, intended to be brought into contact with each other before the welding operation. Thus the first part of the rod 1 comprises a first annular bearing surface 14 surrounding the hole 16, and the second part of the rod 2 comprises a second bearing surface 24 surrounding the tenon 25, referenced on the figures 1A and 1B . It can also be seen in these figures that the diameter of the first part 1 of the rod is slightly smaller, at the level of the first distal end 12 of attachment, than that of the body of this first part 1 of the rod. The narrowing of the diameter at this level therefore reveals a shoulder 15, the function of which is in particular to prevent the formation of prominent beads after the welding or bonding operation 100, on the one hand, and on the other hand to be able easily affix, thanks to the presence of an axial abutment surface provided by the shoulder 15, a clamp to retain the first part 1 of the stem coupled to the movement in the middle part and thus release a working crown (not shown) before to mount the second part 2 of the rod. The function of this working crown will be explained in more detail using the picture 3 .

The figures 2A, 2B and 2C show views identical to those of the figures 1A, 1B and 1C , first part 1 and second part 2 of the rod 10, but this time with the parts assembled to one another. These first part 1 and second part 2 are no longer referenced except on the figure 2B , which is a sectional view of the Figure 1A along the BB axis. One can thus always distinguish the gear wheel 13 at the level of the first proximal end 11 of the first part 1, and the series of grooves 17, but no longer the respective bearing surfaces of each of the parts of the rod 10 when that -it was mounted following the fitting operation 200 of the tenon 25 of the second part 2 in the hole 16 of the first part 1. It will be understood that instead of the hole and the tenon, other types male and/or female elements can be envisaged to assemble each of the parts of the rod, without fixing them definitively. The definitive and irreversible fixing operation is carried out thanks to the welding or gluing step 100, preferably laser welding for reasons of efficiency and productivity. However, ultrasonic welding is also possible as well as gluing. The advantage of laser welding over ultrasonic welding is that it does not generate any potentially harmful mechanical vibrations on such small parts; the Bonding has the advantage of not generating any rise in temperature during the assembly operation but on the other hand affects productivity due to the time required for the polymerization of the glue. This welding or gluing step 100 mutually secures the first annular bearing surface 14 to the second annular bearing surface 24 and thus definitively and irreversibly eliminates any relative degree of freedom in translation and in rotation of the second part 2 of the rod with respect to the first part 1 of the rod 10. An advantage of the proposed fixing method between the two parts of the rod is that it does not require, in addition to less restrictive machining tolerances with respect to a mode fixing by screwing or by driving in, not an effective contact between the two bearing surfaces of each of the parts of the rod. For rods with a diameter between 1.5mm and 2.5mm, and a length between 15mm and 25mm as in the context of the present invention, a mutual gap between the bearing surfaces of up to 0.1mm can be tolerated and remedied by melting parts, preferably made of metal or plastic. The laser adjustment parameters in terms of power and frequency can in this case be adapted to the nature of the material.

The welding operation is preferably carried out using a laser operating with a 200 micrometer light pipe, with a power of 250 W, and operating at a frequency of 15 Hz. The welding or gluing step 100 preferably comprises applying a first spot of welding or glue to secure the first part 1 of the upper to the second part 2 of the upper. Then, the second part 2 of the rod is driven in rotation around its axis, for example using a gripping tool acting on the crown 23 at an angular speed preferably equal to one half-turn per second, so that 30 points of welding or glue are formed over the entire periphery of the diameter of the rod, thus forming a quasi-continuous connection over the entire periphery of the bearing surfaces of each of the parts of the rod.

The picture 3 illustrates a rod according to one embodiment of the present invention, the two parts of which are joined together by a welding or gluing operation 100, preferably laser welding carried out while the first part 1 of the rod is coupled to a movement 4. The preliminary casing operation 200 is in this case also carried out when the first part 1 of the stem has been mounted in the plate 3 of the movement 4, itself cased in a watch middle (not shown).

One still distinguishes, on the first part 1 of the rod, the grooves 17 determining the discrete axial operating positions of the rod, but now also a protruding portion 18 out of the plate 3, this protruding portion remaining despite everything preferably at the inside of a watch middle, not shown for reasons of readability, in order to always hide the method of fixing as well as the parts welded or glued from the outside of the case for aesthetic reasons, such as for broken rods conventional. On the second part 2 of the rod, there is a seal 5 preferably housed in a groove, as well as the grip ring 23 for manipulations carried out by the user. According to a preferred embodiment chosen for the assembly and fixing of the rod 10, the welding operation for the mutual fixing of the first and the second part of the rod 10 is carried out while the first part 1 of the rod has not only been previously coupled to movement 4 after having been introduced into an orifice 31 of plate 3 and another through-hole in the caseband, after plate 3 and movement 4 have themselves already been fitted into the caseband, but also tested in its various axial operating positions using a working rod/crown - not shown - which is then detached from the first part 1 of the rod using pliers affixed to the shoulder (not referenced in this figure, but better visible on the Figures 1A-1B ) which makes it possible to axially retain the first part 1 of the rod during the removal of this working crown. Although a portion 18 of the first part 1 of the rod, of a length greater than that of the shoulder, is necessarily projecting out of the plate 3 in order to be able to affix holding clamps (also not shown) during the operation of removing this working crown, it is also necessary, for this intermediate operation, to provide a clearance 32 in the plate 3 for affixing the holding clamps so that the latter can reach as far as abutment on the shoulder 15 of the first part 1 of the rod, without first coming into abutment against an external part of the plate 3. Such a release 32 at the level of the orifice 31 of the plate 3 also makes it possible to reduce the length of the first part 1 of the rod and therefore to reduce the protruding portion 18 outside the plate, and therefore to minimize the free space between the plate 3 and the caseband in which the latter is fitted.

Although the rod corresponding to the preferred embodiment illustrated by the previously described figures comprises a simple shoulder 15 (see Figures 1A-1C in particular) at its fixing end, it is possible, according to an alternative embodiment not illustrated, to make a complete groove at the level of the first distal fixing end 12, such a groove comprising an additional retaining surface useful for manipulation axial tension of the rod during preliminary operating tests before the actual welding or gluing operation. However, this convenience of use in terms of handling would nevertheless at the same time make a welding operation more delicate to carry out due to the small thickness which results therefrom, for a given size of the first rod part, of the rim between the new axial abutment and the first bearing surface 14 intended to be welded.

It may be noted that, in the context of the invention, the fixing of the two parts of the rod is preferably always carried out outside the plate, due to the welding or gluing operation 100 carried out at the level of the first distal end 12 for fixing the first part 1 of the rod, and which must not alter other elements of the movement 4. Such an arrangement of a protruding portion 18 could also extend to the outside of the middle part, which would however have the disadvantage of no longer masking the mode of assembly or the welded or glued parts.

Although the stem described corresponds to a winding or time-setting stem according to the preferred embodiment illustrated, which applies both to a mechanical watch and to a quartz watch, it will be understood that the fixing method described applies to other types of stems for timepieces without departing from the scope of the present invention defined by the appended claims.

It will also be understood that not only laser or ultrasonic welding can be envisaged as a technique for joining together definitively and irreversibly the two parts of the rod, but also other types of thermal welding, as well as brazing.

Claims (3)

1. A method for assembling a two-part stem (10) in a timepiece, said stem (10) comprising a first part (1) provided with a first proximal end (11) cooperating with a movement, and a first distal fastening end (12), and a second part (2) provided with a second proximal fastening end (21) and a second distal end (22), said method comprising a step of welding or gluing (100) said first distal fastening end (12) of said first part (1) of said stem (10) to said second proximal fastening end (21) of said second part (2) of said stem (10) carried out after a preliminary step (200) of interlocking a male assembly element arranged at said second proximal fastening end (21) of said second part (2) into a female assembly element arranged at said first distal fastening end (12) of said first part (1), said welding or gluing step (100) being carried out at a clearance (32) in the plate (3) of the movement (4), said first distal fastening end (12) including a part (18) protruding from said plate (3).
2. The method for assembling a two-part stem of a timepiece according to claim 1, said first distal fastening end (12) of said first part (1) and second proximal fastening end (21) of said first part (2) having respectively a first annular bearing surface (14) and a second annular bearing surface (24) which are at most 0.1 mm apart after said preliminary interlocking step (200).
3. The method for assembling a two-part stem of a timepiece according to one of the preceding claims, characterised in that said welding or gluing step (100) comprises placing a first weld or glue point then rotating said second part (2) of said stem using a tool for placing other weld or glue points.

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