HK1183111B - Metal pallets with polymer horns - Google Patents

Description

Metal pallet fork with polymer fork

Technical Field

The present invention relates to an escapement system for a timepiece, and more particularly to a system of the type comprising a pallet fork, wherein the function of the lever and the function of the fork can be separated.

Background

Free escapements of the swiss lever type are difficult to improve, since they are a compromise between the lowest possible inertia of the pallet stones and the best possible friction performance of the fork. Therefore, it is difficult to prevent sticking between the disc pin (impulse pin) and the jaw (horn) of the fork head while maintaining a minimum inertia and even insensitivity to magnetic fields.

Disclosure of Invention

The aim of the present invention is to overcome all or part of the above drawbacks by proposing a method for manufacturing a pallet fork comprising a low inertia lever and a fork with good friction properties.

The invention therefore relates to a method for manufacturing a pallet for an escapement system, characterized in that it comprises the following steps:

a) forming a lever of the pallet fork using a first material, the lever comprising a dart (dart) at a first end and two arms each for receiving a pallet stone;

b) overmolding (over-mold) a second material on the first end to form a pallet fork;

c) the pallet stones and a shaft are adjusted to allow the pallet to be rotatably mounted.

According to a first alternative embodiment, the manufacturing method according to the invention differs in that it comprises the following steps:

a') forming a lever of a pallet fork from a first material, the lever comprising a fork pin at a first end and two arms at a second end, each arm forming an integral pallet stone;

b) overmolding a second material on the first end to form a pallet fork;

c') mounting the shaft to allow the pallet to be rotatably mounted.

According to a second alternative embodiment, the manufacturing method according to the invention differs in that it comprises the following steps:

a) forming a lever of a pallet fork using a first material, the lever comprising a prong pin at a first end and two arms at a second end, each arm for receiving a pallet stone;

b') overmolding a second material on said first end so as to form a pallet fork and overmolding a second material on said second end so as to form said pallet stone;

c') mounting the shaft to allow the pallet to be rotatably mounted.

Advantageously, therefore, according to the invention, the mechanical features provided by the lever material are no longer dependent on the mechanical features of the fork. Thus, by way of example, the lever may advantageously provide low inertia and optimized prong friction performance.

According to other advantageous features of the invention:

step a) or a') is carried out by LIGA process, stamping or bar turning.

-the first material is a metal or a metal alloy.

The first material comprises titanium, aluminium or an austenitic cobalt alloy (austenitic cobalt alloy).

-step b) or b') is carried out by injection into a mould formed using the LIGA process.

-the second material is a polymer.

-the second material comprises polyoxymethylene.

The shaft is formed of steel, brass or a copper-nickel-zinc alloy.

Finally, the invention relates to a timepiece characterized in that it comprises an escapement system with pallets obtained by a method according to any one of the above embodiments.

Drawings

Further features and advantages will emerge clearly from the description that follows, given by way of non-limiting example with reference to the accompanying drawings, in which:

fig. 1 is a view of a pallet fork according to the invention.

Fig. 2 is a partial section of a timepiece including a pallet according to the invention.

Fig. 3 is a view of a pallet fork according to the invention, which has not yet been completed.

Figure 4 is a view of an overmoulding step according to the invention.

Fig. 5 is a block diagram of the method according to the invention.

Detailed Description

The example shown in fig. 1 and 2 illustrates an escapement system 1 for a timepiece. As shown in the sectional view of fig. 2, escapement system 1 comprises, in particular, a pallet 3 for cooperating with a pallet 5. The roller 5 preferably bears on the balance staff 2 and comprises a small roller 4 provided with a recess 6 and a large roller 8 provided with a roller pin 7.

The pallet 3 preferably comprises a lever 9 formed of a first metallic material, preferably chosen for its low density, low sensitivity to magnetic fields and possibly the ability to vary, for example, the red jewel pallet 10, 12.

Thus, preferably, the material of the lever 9 may be, for example, titanium, aluminum or an austenitic cobalt alloy.

Lever 9 comprises an arm 11 and an arm 13, said arms 11 and 13 being intended to carry pallet stones 10 and 12 in order to cooperate with at least one escape wheel (not shown) of escapement system 1. Mounted between these two arms 11 and 13 is a pallet fork shaft 14 for pivotably mounting pallet fork 3. The shaft 14 may be made of a material such as, for example, steel, brass, or a copper-nickel-zinc alloy. Finally, the lever 9 has, at the opposite ends of the arms 11 and 13, a fork pin 15 and a pallet fork 17.

Advantageously, according to the invention, the prongs 15 are integral with the lever 9 and preferably on an extension of the lever 9. The fork pin 15 is intended to cooperate with the small disc 4 to prevent accidental movement of the pallet fork 17.

Pallet fork 17 preferably comprises a coating 19 formed of a second material, preferably different from the first material of lever 9, intended to improve the friction properties of fork 17 on disc pin 7 and at the same time avoid adverse effects on the overall inertia of pallet 3. Preferably, the material of fork 17 is also paramagnetic, so as to reduce the sensitivity of pallet 3 to magnetic fields.

The material of pallet fork 17 is ideally a material that exhibits low wear and has a low coefficient of friction associated with the pallet pin 7 of large pallet 8. Such a material may be a polymer.

Preferably, the polymer used is Polyoxymethylene (POM) because of its characteristic impact damping properties, low sensitivity to magnetic fields and very good tribological properties. During development, it was therefore found that the hertzian pressure exerted by the ruby disk nail on the polyoxymethylene prongs was limited to 54MPa, i.e. a reduction of 85% in mechanical stress compared to the standard steel prongs.

Fork 17 is preferably overmoulded on lever 9 at prong pin 15 and comprises two prongs 16 and 18 intended to come into contact with disc pin 7 of large disc 8 in order to pivot pallet 3 in a reciprocating motion about axis 14 after rotation of disc pin 7.

Advantageously, according to the invention, making the material of pallet fork 17 different from that of lever 9 optimizes, on the one hand, the performance of pallet 3 between the desired magnetic field sensitivity and/or the desired inertia of lever 9, and, on the other hand, the low wear and low friction coefficient of pallet fork 17 associated with pallet pin 7.

Preferably, the coating of the pallet fork 17 encases (trap) the lever 9, so as to ensure that it does not come off. Thus, as shown in fig. 2 and 4, the lever 9 comprises notches 25, 26, which notches 25, 26 are such that the cladding forms bridges 20 and 21 of polymer material locking the fork 17 against the lever 9.

Of course, the lever 9, the pallet stones 10, 12 or the shaft 14 may be different. Thus, by way of example, according to a first alternative embodiment, the pallet stones 10, 12 may be integral with the lever 9 if it is not desired to be able to change the pallet stones 10, 12. For the same purpose, according to a second alternative embodiment, the pallet stones 10, 12 can be overmoulded in the same or similar way with respect to the pallet fork 17, i.e. using a polymer, for example polyoxymethylene.

Now, a method 31 for manufacturing pallet 3 will be described with reference to fig. 5. Method 31 comprises a first step 33 for forming the body of pallet 3 using a first material, the first end of the body of the pallet comprising a prong pin 15 and the second end comprising two arms 11, 13, each carrying one pallet stone 10, 12.

Step 33 may be accomplished by a variety of techniques such as LIGA process, stamping, or bar turning. This step 33 allows the lever 9, the arms 11, 13 and the prongs 15 to be manufactured in one piece. As shown in fig. 3, the lever 9 has a hole 22 for fitting the shaft 14. Furthermore, each arm 11, 13 has a hole 23, 24 for fitting a pallet stone 10, 12.

Of course, in the case of the first alternative embodiment described above, step 33 also serves to form an integral pallet stone 10, 12 on each arm 11, 13.

Finally, step 33 also preferably forms recesses 25, 26, as described above, which recesses 25, 26 will be filled with future cladding layers.

Method 31 continues with a second step 35 for overmoulding a second material on the first end, i.e. close to the prong pin 15, to form the pallet fork 17, and possibly on said second end to form the pallet stones 10, 12. Preferably, to guarantee an optimal structural quality, the mold 27 for overmolding is obtained by means of a LIGA process, i.e. electroforming after photolithography.

The mould 27 comprises stops 28 and 29 for locking the arms 13, 11 and the lever 9 respectively. Only the cavity 30 of the mould 27 will be filled. Of course, several coatings may be made within the same mould 27, i.e. the mould 27 may comprise several cavities 30, several pallet levers may be placed in the mould and/or other parts of the lever 9 may be overmolded, for example in order to make the second alternative embodiment.

As mentioned above, the second material is preferably a polymer. Thus, step 35 preferably comprises overmoulding the lever of the pallet by injecting a polymer into cavity 30 of mould 27, so as to form the body of pallet fork 17, in particular with fork 16 and 18, and possibly forming pallet stones 10, 12 on arms 11, 13 according to the second alternative embodiment.

The third step 37 of the method 31 is for mounting the pallet stones 10, 12 in the holes 23, 24 and the staff 14 in the hole 22, so that the pallet 3 can be rotatably mounted. At the end of these last two steps, pallet 3 is completed and can be installed in the timepiece as an element of a swiss lever escapement system 1.

Of course, in the first and second alternative embodiments, step 37 must be considered as being limited to the mounting of shaft 14 in hole 22, so that pallet 3 can be rotatably mounted.

Thus, pallet 3 is of composite type, i.e. formed of two different materials. Thus, as shown in fig. 2, the height of pallet 3 is preferably formed entirely of the second material on axis a, since the notch 25 made in step 31 forms an opening, in particular in lever 9.

Of course, the invention is not limited to the examples shown, but encompasses variants and modifications which may be apparent to a person skilled in the art.

In particular, the shape of pallet 3 and/or of disc 5 may be different. Pallet 3 may also comprise, for example, at least a third pallet stone for carrying the application of the invention to a coaxial escapement system.

It is also possible to envisage modifying the shape of pallet fork 17 and more particularly of fork 16 and 18, to fit another type of disc or another type of material of the disc spike, so as to prevent wear and sticking in continuous contact.

Finally, the first and second materials may also differ in that the outer coating is different, but the core of the materials is the same. By way of example, the lever 9 can also be formed of a polymer coated with silicon, without departing from the fact that: the first material of the lever 9 is different from the second material of the prong 17.

Claims (11)

1. A method (31) for manufacturing a pallet (3) for an escapement system (1), characterized in that it comprises the following steps:

a) forming (33) a lever of a pallet fork (3) using a first material, the first end of the lever comprising a prong pin (15) and the second end comprising two arms (11, 13), each for receiving a pallet stone (10, 12);

b) overmoulding (35) a second material on the lever (9) at the prong pin (15) so as to form a pallet fork (17);

c) -mounting (37) the pallet stone and a shaft (14) so that the pallet (3) can be rotatably mounted.

2. A method (31) for manufacturing a pallet (3) for an escapement system (1), characterized in that it comprises the following steps:

a') forming (33) a lever of a pallet fork (3) using a first material, the first end of the lever comprising a fork pin (15) and the second end comprising two arms (11, 13), each forming an integral pallet stone (10, 12);

b) overmoulding (35) a second material on the lever (9) at the prong pin (15) so as to form a pallet fork (17);

c') mounting (37) a shaft (14) so that said pallet (3) can be rotatably mounted.

3. A method (31) for manufacturing a pallet (3) for an escapement system (1), characterized in that it comprises the following steps:

a) forming (33) a lever of a pallet fork (3) using a first material, the first end of the lever comprising a prong pin (15) and the second end comprising two arms (11, 13), each for receiving a pallet stone (10, 12);

b') overmoulding (35) a second material on the lever (9) at the prong pin (15) so as to form a pallet fork (17), and overmoulding (35) a second material on the lever (9) at the arms (11, 13) so as to form the pallet stones (10, 12);

c') mounting (37) a shaft (14) so that said pallet (3) can be rotatably mounted.

4. Method (31) according to any one of claims 1 to 3, characterized in that step a) or a') is carried out by LIGA process, stamping or bar turning.

5. The method (31) according to any one of claims 1 to 3, wherein the first material is a metal or a metal alloy.

6. The method (31) of claim 5, wherein the first material comprises titanium, aluminum, or an austenitic cobalt alloy.

7. The method (31) according to any one of claims 1 to 3, wherein step b) or b') is carried out by injection into a mould formed using the LIGA process.

8. The method (31) according to any one of claims 1 to 3, wherein the second material is a polymer.

9. The method (31) of claim 8, wherein the second material comprises polyoxymethylene.

10. The method (31) of any of claims 1-3, wherein the shaft (14) is formed of steel, brass, or a copper-nickel-zinc alloy.

11. Timepiece, characterized in that it comprises an escapement system (1) with pallets obtained by a method (31) according to any one of claims 1 to 3.