EP1584994B1 - Collet without deformation of the spiral fixing radius and fabrication method of such a collet - Google Patents

Abstract

A collet for mounting balance spring, is formed by a metal band whose inner contour includes a discrete number of points of contact with a balance staff distributed along angular apertures alpha and in that width "I" of the band varies such that the compression forces of the contact points on the staff do not alter the distance R after driving in, leading to a friction torque allowing annular orientation of the collet on the staff. A collet for mounting a balance spring (9), is formed by a metal band (10) whose inner contour (11) delimits recesses (11a-c) for driving the collet onto a balance staff (2) and whose outer contour (12) includes a function point between the collet and the balance spring located at the end (14) of an arm (14) at a distance R from the center 0 of the staff greater than that of any other point of the outer contour. The inner contour includes a discrete number of points of contact (1, 3, 5) with the staff, one of the points being aligned with the staff and the function point, the angular apertures a of the function points not being all identical. The portions of band opposite the points of contact not aligned with the staff and the join point (4) form function of greater width I 6, I 8than the other parts of the band.

Description

TECHNICAL AREA

The present invention relates to a ferrule without deformation of the spiral fixing radius for securing the curve inside a spiral, and can also be incorporated into a spiral assembly in a single piece. The invention also relates to a method for obtaining such a ferrule and its possible incorporation into a whole in a single piece.

BACKGROUND

In a clockwork mechanical movement, the ferrule is an assembly interface of the balance spring. Originally it is a washer driven on the balance shaft and having at least one attachment point of the curve inside the spiral, for example using a conical pin, by gluing, or still by welding. Since welding, and in particular laser welding, is now the preferred method of attachment, the ferrule may be made of steel, and more particularly of special steels incorporating variable proportions of Ni, Mo, Co or Cr. The ferrule must first be small to have a small influence on the moment of inertia, and not introduce unbalance, but we expect a small room many other properties to contribute to the regularity of the regulating organ. For example, it is necessary, after driving on the balance shaft, to be able to rotate it without difficulty in order to carry out the reference, ie the alignment of the plate anchor and the anchor-balance shaft at dead point. It is also desirable that the driving has the least possible influence on maintaining a given distance between the balance shaft and the attachment point and that the outer contour of the ferrule is such that it does not disturb the active length of the curve in the center of the spiral.

Many patents filed in the sixties and seventies provide a solution to certain quality criteria listed above, but no ferrule has at the same time all the qualities required, as explained briefly below.

When the ferrule is made of special steel, the friction torque on the balance shaft after driving may be too great and make it difficult to benchmark. To remedy this drawback the first solution is to make a slot of elasticity between the hole of axis and the edge of the shell as described for example in the patent CH 347 142 for a perfectly circular ferrule on which the spiral is fixed by means of a conical pin located in the plane of symmetry passing through the axis and the slot. The patent CH 508 233 describes a ferrule of the same type, spiral riveted or glued in a groove, but of asymmetrical shape in racket with a shift of the axis hole, eliminating the risk of support of the first turn on the periphery of the ferrule. These split rings with a circular axis hole, however, have two disadvantages. When driving on the balance shaft the movement of the attachment point is not controllable with great rigor, and when performing the benchmarking the risk is great to cause disruption of flat and centering. To reduce the friction torque facilitating the setting at the benchmark without having to make a slot, it is proposed in the patent US 3,429,120 to realize a two-piece shell having an inner barrel of brass, or other non-ferrous material, and an outer portion of steel to allow the welding of the curve inside the hairspring. The results obtained are technically satisfactory but the manufacturing and assembly costs are prohibitive.

In order to reduce the friction torque in a ferrule made of special steel without an elastic slot, it seems a priori logical enough to reduce the friction surface to discrete contacts between the balance shaft and the flange opening of the ferrule. The process described in the patent CH 311 287 consists of ovalizing a hole initially having a circular shape, the contour of the shell retaining its initial circular shape. Having thus only two symmetrical points of support, one finds the same problems as those evoked for the cracked ferrule.

In patents CH 466 807 , US 3,430,435 and FR 2,386,850 it is proposed to give the ferrule opening opening a regular polygonal contour illustrated by an equilateral triangle with broken angles, or even an opening of hypocycloidal shape. In this embodiment, it will be observed that the clamping points of the ferrule on the axis have an angular distribution and that the ferrule almost necessarily has a regular contour and inscribed in a circle, in particular so as not to have problems with unbalance, but having in return the disadvantage of presenting a risk of contact of the turn in the center.

SUMMARY OF THE INVENTION

The invention therefore relates to a ferrule whose particular shape makes it possible to have no change in attachment radius of the spiral after driving, ensuring perfect centering without unbalance. This makes it possible to have a driving force and an optimum holding torque, without excessive blocking on the balance shaft, so as to facilitate the subsequent operation of setting the benchmark, or even dismantling. The invention also relates to a spiral-wound assembly and a method of manufacturing the ferrule and the spiral-wound assembly.

For this purpose the invention relates to a ferrule according to claim 1 attached.

In the preferred embodiment, the other two contact points have, relative to the first contact point which is diametrically opposite the junction point between the ferrule and the spiral, angular openings greater than 90 °. As will be seen in the following detailed description, the metal band forming the ferrule may have the shape of a ribbon of unequal width, or a more massive snowshoe shape whose opening for driving on the axis has an outline. oval.

A ferrule according to the invention can be obtained according to known stamping methods, but according to a preferred method, especially for a ribbon-shaped strip, use is made of the Liga technique which has the advantage of allowing the simultaneous formation of a single piece of the ferrule and hairspring, and thereby provide even greater control over the value of R.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 représente un premier mode de réalisation d'une virole selon l'invention;
• la figure 2 est un graphique donnant le déplacement du point de soudure de la virole représentée à la figure 1 en fonction de l'angle α₃, pour un serrage nominal donné.
• la figure 3 représente un deuxième mode de réalisation; et
• la figure 4 est un graphique donnant le déplacement du point de soudure de la virole représentée à la figure 3 en fonction de l'angle α₃.

Other characteristics and advantages of the present invention will become apparent in the description of various exemplary embodiments, given by way of nonlimiting illustration, with reference to the appended drawings in which:

• the figure 1 represents a first embodiment of a ferrule according to the invention;
• the figure 2 is a graph giving the displacement of the weld point of the ferrule represented in the figure 1 depending on the angle α ₃ , for a given nominal tightening.
• the figure 3 represents a second embodiment; and
• the figure 4 is a graph giving the displacement of the weld point of the ferrule represented in the figure 3 depending on the angle α ₃ .

DETAILED DESCRIPTION OF THE INVENTION

To the figure 1 a first embodiment of a ferrule according to the invention made of special steel, for example steel or nickel, and having a uniform thickness of the order of 0.2 mm, is shown in plan view on a large scale. This ferrule is intended to be driven on a balance shaft 2 (shown in dotted lines) of center 0. As can be seen, the ferrule is continued by a continuous strip whose contours, inside 11 and outside 12, have a particular shape whose width "l" is not uniform at all points of the strip 10, and whose inner contour 11 does not comprises three points of contact 1, 3, 5 with the axis 2 away from it to form recesses 11a, 11b, 11c.

The strip has a first recess 11a constituting an arm 14, whose end comprises on the outer contour 12 a junction point 4 at a distance R from the center 0 of the axis 2, and on which will be welded the end of the Curve inside the spiral 9.

The distance R, which is the radius of attachment of the hairspring to the ferrule, corresponds to an essential characteristic of construction in that its value should ideally not be modified by the driving operation in order to maintain a perfectly centered hairspring. According to the most demanding standards in the horological field, the displacement of the junction point 4 must not be greater than 5 μm and, as will be demonstrated later, this threshold can be very strongly lowered with a ferrule according to the invention.

The center 0 of the balance shaft and the junction point 4 define an axis of symmetry xx 'for the ferrule, that is to say for its outer contour 12 and inner 11 bearing on the balance shaft 2 by the three contacts 1, 3 and 5. A first contact point 1 is diametrically opposite the junction point 4 and the other two contact points 3, 5 are symmetrical with respect to the axis xx 'with an angular offset by relative to the first contact point 1 of α ₁ for the contact point 3 in the clockwise direction and of α ₅ for the contact point in the counterclockwise direction the angles α ₁ and ars having the same value greater than 90 °. This therefore defines between the symmetrical contact points 3, 5 an angular offset α ₃ whose value is one of the determining factors for the purpose of the invention, as will be understood later.

If we now consider the outer contour 12, we see that the strip 10 has two symmetrical handles 16, 18 joining at the three contact points 1, 3, 5. The handles 16, 18 are substantially diametrically opposed to the contact points symmetrical 3, 5 and delimit symmetrical recesses 11b, 11c. The ends 6, 8 of the loops 16, 18 are located, with respect to the center 0 of the axis 2, at a distance less than the radius R of fixing the hairspring, so that the curve inside the hairspring 9 can not not come into contact with the outer contour 12 of the ferrule during pendulum oscillations.

Given the very small dimensions of the shell, the radius R is of the order of 0.5 mm, and very strict construction parameters, it does not appear clearly on the figure 1 that according to another essential feature of the invention, the width "1" of the strip 10 is not uniform all around. In the example shown, the widths l ₁ , l ₃ , l ₅ at the contact points 1, 3, 5 are identical. At the junction point 4, the band has a width l ₄ greater about 15% and at the loops 16, 18, the widths l _θ , l _δ are 30% to 35% greater than 1 ₁ . It is obvious that the preceding values are given only as examples and that they could vary according to the material used and the size of the handles 16, 18.

Another characteristic of a ferrule according to the invention relates to the value that should be given to the angle α ₃ between the second contact point 3 and the third contact point 5 to have a minimum dR variation of the radius R. The graph reproduced at figure 2 shows the variation of dR as a function of the value of the angle α ₃ . From this graph we see that the optimal value of α ₃ would be 105 °. In reality for the contour represented in figure 3 , α ₃ = 104 ° which corresponds to a displacement dR of the junction point 4 almost zero. In other words, such a result is obtained by combining a particular choice of the contour of the strip 10, widths "1" at its different points, and angles α between the various points of contact with the axis. 2, making the resultant compressive forces on the axis 2 is virtually zero, while having an asymmetrical ferrule eliminating the risk of contact of the curve inside the spiral on the ferrule.

Referring now to the figure 3 there is shown a second embodiment corresponding to a somewhat more "massive" design, but which has all the features of the first embodiment. The inner contour 11 of the ferrule comprises three contact points 1, 3, 5 with the axis 2 of the balance, respectively having for angular offset α ₁ , α ₃ , α ₃ , but the recesses 11 _a , 11 _b and 11 _c the inner contour 11 between said contact points are reduced to "non-contact" areas. The outer contour 12 has a more regular shape resembling the shape of a racket, the junction point 4 at the end of the arm 14 being in the same way located at a distance R from the center 0 of the axis 2 greater than that any other points 6, 8, 13, 15 and 17 of said outer contour 12. In this construction, to obtain the smallest possible variation dR of the radius R, it will be observed that the relative values of the distances l ₁ to l ₈ are different from those of the first embodiment. It appears that l ₄ > l ₁ > l ₈ = l ₆ = l ₅ = l ₄ . As in the first embodiment the value that should be given to the angle α ₃ between the two points of contact 3, 5 symmetrical is critical for the resultant compression forces on the axis 2 is zero. The graph reproduced at figure 4 shows the variation of dR as a function of the value of the angle α ₃ . According to this graph we see that for the construction shown in the figure 3 a value of dR is almost zero for an angle α ₃ = 112 °. These values are given as an example, as it is obvious that changes in the relative values of l ₁ to l ₈ could lead to another choice of α ₃ , and even to have α ₁ = α ₃ = α ₅ by acting solely on the shape of the shell to have a resultant compression forces on the zero axis 2, while having an arm 14 to move the curve inside the spiral 9 of the other points of the outer contour of the ferrule.

The ferrules according to the invention which have just been described can be manufactured according to known methods by stamping. However, the preferred method, especially for the ferrule corresponding to the first embodiment and when the spiral comes from material with the shell is to use the LIGA technique known since the mid-1970s.

In a first step the method basically consists in spreading on a substrate previously coated with a sacrificial layer a positive or negative photoresist on a thickness corresponding to the desired height for the ferrule and forming by means of a mask by photolithography and etching a hollow structure corresponding to the desired contour for the ferrule or the ferrule-spiral assembly.

In a second step, said hollow structure is filled with a metal or a metal alloy either by electrodeposition as indicated for example in the patent US 4,661,212 or by compression and sintering nanoparticles, as indicated for example in the patent application US 2001/0038803 .

In a final step, the ferrule or the ferrule-spiral assembly of the substrate is released by elimination of the sacrificial layer.

This method also offers the advantage of being able to make a batch production and thus to lower the unit cost of the products obtained.

Claims (7)

1. Collet for the driving onto a balance staff (2) and the mounting a balance spring (9), said collet having symmetry along an axis xx' passing through the centre 0 of the staff (2) and through the function point (4) between the collet and the balance spring (9) and being formed by a metal band (10) whose inner contour (11) delimits recesses (11a, 11b, 11c) and includes three points of contact (1, 3, 5) with the staff (2) of angular apertures α₁, α₃ and α₅, the aperture α₃ being symmetric with reference to axis xx', oriented toward the function point (4) and having a value α₃ > 100°, characterised in that the outer contour (12) includes the function point (4) located at the end of an arm (14) at a distance R from the centre 0 of the staff (2) greater than that of any other point (6, 8, 13, 15) of the outer contour (12) and in that the band (10) forming the collet has a variable width, avoiding after driving to slightly alter the distance R.
2. Collet according to claim 1, characterised in that the angular apertures α₁ and α₅ have values such that α₁ = α₆> 90°.
3. Collet according to claim 1, characterised in that the band (10) has a strip shape that some parts substantially in the opposite direction of the points of contact (3, 5) not aligned with the axis xx' form loops (16, 18) of larger width l₆, l₈ than the other parts of the band (10).
4. Collet according to claim 1, characterised in that the recess (11a) has an ovalised shape and in that the outer contour (12) of the band (10) has a rectangular shape with rounded angles extended by the arm (14) including the function point (4) between the collet and the balance spring (9).
5. Collet according to claim 1, characterised in that the balance spring (9) is integral with the arm (14) of the metal band (10).
6. Collet according to claim 1, capable of being manufactured in batches by a method comprising the steps of:

   a - spreading over a substrate that has previously been coated with a sacrificial layer, a layer of positive or negative photoresist having the desired thickness of the collet;

   b - forming by means of a mask, by photolithography and chemical etching, a hollow structure corresponding to the inner and outer contours of a batch of collets:

   c - filling the hollow structure with a metal or a suitable metal alloy by electroplating , and

   d - releasing the batch of collets by removing the sacrificial layer.
7. Collet according to claim 6, characterised in that in step "b" the contour of the balance spring (9) is also formed.

Images