HK1222461B - Flexible collet - Google Patents

Description

Flexible inner pile

Technical Field

The present invention relates to an elastic collet for fixing to an arbour, an integrated balance spring/elastic collet assembly and a method for manufacturing the integrated assembly.

Background Art

Typically, the balance spring is mounted on the balance staff via a collet, a ring that presses against the staff and is pierced laterally to receive the inner end of the balance spring. The staff can also be welded or brazed to the collet. Microfabrication techniques, such as deep reactive ion etching (DRIE) for silicon, have made it possible to create collets with novel shapes and geometries. In particular, the collet and balance spring can be fabricated as a single piece.

Silicon is a material with numerous advantages for making balance springs, and microfabrication techniques make it possible to create a one-piece balance spring/colt assembly. However, its primary disadvantage is its inability to deform plastically. Consequently, the colt is susceptible to fracture if stress exceeds its elastic limit. Therefore, the colt must be sized to retain the balance spring on the balance staff during oscillator operation (minimum clamping torque) while allowing the collet to be assembled to the arbour without fracture (or plastic deformation), provided that the balance staff diameter and colt geometry vary within given tolerances.

European patents EP 1513029 and EP 2003523 propose a collet with a triangular opening. The balance spring is fixed at an attachment point located at one of the vertices of the triangle. The collet consists of an external reinforcement structure to which a flexible arm is attached, which deforms to receive the balance staff.

A balance spring-colt assembly is also known from patent WO 2011026725, the colt having a hole provided with four circular support portions for receiving the balance staff. The support portions are defined by longitudinal grooves formed in the collet hole.

The geometries described in these documents are not entirely satisfactory, and therefore many balance springs (made of silicon, diamond, quartz, etc.) mounted on movements are provided with a collet adhesively bonded to the balance staff.

Summary of the Invention

It is an object of the present invention to overcome all or part of the above-mentioned disadvantages.

To this end, the invention relates to a timepiece collet comprising a point of attachment to the balance spring and a channel or opening for receiving the balance staff.

According to the invention, the channel is substantially cylindrical and is configured to deform elastically in a plane perpendicular to the axis of the channel when the balance staff is inserted into the channel and to elastically clamp the balance staff by means of at least two contact lines extending at the level of the inner wall of the channel.

It can therefore be understood that this collet allows an optimum pressing force and holding torque and that the deformation force which clamps the collet against the balance staff is greater than the nominal holding torque.

One advantage of the present invention is that the entire collet deforms, unlike the collets of the prior art which have no protrusions or other rigid parts. In the case of the present invention, in fact the entire collet deforms except for the attachment points of the collet.

According to other advantageous variants of the invention:

- the channel is oval;

- the three contact lines have angular openings α, β, θ, one of which is diametrically opposite the point of attachment to the balance spring;

– the angular openings α, β, θ are greater than 90°;

– the angular openings α, β, θ are equal to 120°;

The distance between the balance staff and the collet at the concave portion is between 0 and one quarter of the balance staff diameter, and more preferably between 0 and 50 μm.

– The inner pile has a variable cross-section.

The invention also relates to an integrated collet/balance spring assembly comprising a collet according to the invention.

According to other advantageous variants of the invention:

– The collet and balance spring are made of silicon;

The collet and the balance spring are made of a material that does not deform plastically.

The invention also relates to a timepiece movement or a timepiece comprising a collet/balance spring assembly according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages will become apparent from the following description given by way of non-limiting example with reference to the accompanying drawings, in which:

FIG1 is a schematic diagram of an inner pile undergoing elastic deformation;

FIG. 2 is a schematic top view of a collet/balance spring assembly according to the present invention.

DETAILED DESCRIPTION

As mentioned above, the present invention relates to a collet made of a material having no usable plastic range, ie having a very limited plastic range.

The collet/balance spring assembly shown in Figure 2 is manufactured as a single, integral component, typically made of silicon. It comprises a collet 1 and a balance spring 2, which is attached via its inner coil 20 to an attachment point S1 on the outer circumference of collet 1. The collet/balance spring assembly is retained on balance staff 4, which has a circular cross-section, by press-fitting collet 1 onto the latter.

Collet 1 comprises a substantially cylindrical channel 10 configured to deform elastically in a plane P perpendicular to the axis of channel 10, so as to receive and elastically clamp balance staff 4. Flexible channel 10 is oval, more preferably triangular-elliptical, and comprises at least two contact lines with balance staff 4.

According to a preferred embodiment shown in the figures, the flexible channel 10 is triangular-elliptical and has three contact lines 11a, 11b and 11c with the balance staff 4, said three contact lines forming, for example, an equilateral triangle. The three contact lines 11a, 11b and 11c with the balance staff 4 form angles α, β and θ between them.

Contact lines 11 a , 11 b , 11 c define recessed portions 10 a , 10 b , and 10 c between collet 1 and balance staff 4 , these recessed portions 10 a , 10 b , and 10 c being non-contact areas.

As can be seen in FIG. 1 , one of the contact lines is diametrically opposite the point of attachment to balance spring 2 , so collet 1 is not subject to deformation at the point of attachment and the position of the point of attachment of balance spring 2 does not change when collet 1 is positioned.

According to the invention, the three contact lines 11a, 11b and 11c form an angle between them, preferably greater than 90°, more preferably less than 150°, here substantially equal to 120°.

Under the action of elastic deformation, the channel 10 exerts an elastic restoring force at the contact lines 11 a , 11 b , 11 c , which causes the inner wall of the channel to return to contact with the balance shaft.

According to the invention, the distance between balance staff 4 and collet 1 at recesses 10a, 10b, 10c is greater than 0. Therefore, there is a clamping force at the three contact lines 11a, 11b, 11c, but no clamping force at recesses 10a, 10b and 10c.

Preferably, the distance between balance staff 4 and collet 1 at recesses 10a, 10b, 10c is between 0 and one quarter of the diameter of balance staff 4. More preferably, the distance between balance staff 4 and collet 1 at recesses 10a, 10b, 10c is between 0 and 50 μm.

Advantageously, the distance between balance staff 4 and collet 1 ensures a small amount of play when a clamping force is exerted on contact lines 11 a , 11 b and 11 c .

This arrangement has the particular advantage of maximizing the support radius of channel 10 of collet 1 on balance staff 4 while ensuring sufficient holding torque on balance staff 4 at a low level of stress compared to the maximum permissible stress of the material. Advantageously, a larger support radius provides a greater holding torque.

The thickness is determined such that the maximum stress exerted by balance staff 4 on channel 10 is below the elastic limit of the material forming collet 1 , so that collet 1 adapts to the manufacturing tolerances of balance staff 4 and the retention of collet 1 on balance staff 4 (torque, pressing force) is sufficient.

As shown in FIG. 2 , balance spring 2 comprises a strip 3 wound around itself in a plurality of turns, inner coil 20 being integral with collet 1 .

As can be seen in Figure 2, the attachment point S1 between inner ring 20 and collet 1 is provided on collet 1. It should also be noted that collet 1 is symmetrical with respect to an axis A passing through the centre C of collet 1 and the attachment point S1.

According to a preferred embodiment of the present invention, the collet 1 and the balance spring 2 are made of silicon.

According to another embodiment of the present invention, collet 1 and balance spring 2 are formed of a material that does not exhibit plastic deformation, such as single-crystal silicon, polycrystalline silicon, porous silicon, amorphous silicon, doped single-crystal silicon, doped polycrystalline silicon, doped or undoped silicon carbide, doped or undoped silicon nitride, doped or undoped silicon oxide, such as quartz or silica, or ceramic.

Collet 1 and balance spring 2 may also be made of a material such as amorphous metal.

Of course, the present invention is not limited to the examples shown, but is susceptible to various variations and modifications that may occur to those skilled in the art.

Parts List :

1 Inner pile

10 channels

10a Concave portion

10b Concave portion

10c Concave part

11a Contact line

11b contact line

11c contact line

2 hairsprings

3 Hairspring band

4. Oscillating shaft

α angle

β angle

θ angle

S1 attachment point

C inner pile center

D _a Diameter of the oscillating shaft

Claims (11)

1. A clock stud (1), comprising an attachment point (S1) to a balance spring (2) and a channel (10) for receiving a balance shaft (4), The feature is that the channel (10) is substantially cylindrical and is configured such that when the pendulum shaft (4) is inserted into the channel (10), the channel (10) elastically deforms in a plane (9) perpendicular to the axis of the channel (10), and elastically clamps the pendulum shaft (4) by at least two contact lines (11a, 11b, 11c) extending at the height of the inner wall of the channel (10). When the pendulum shaft (4) is inserted into the channel (10), the channel (10) forms three crescent-shaped recesses (10a, 10b, 10c), each crescent-shaped recess providing a gap between the pendulum shaft (4) and the inner wall of the channel (10), and The thickness of the inner stud (1) obtained from each of the crescent-shaped recesses (10a, 10b, 10c) to the outer surface of the inner stud (1) is substantially consistent around the entire circumference of the balance shaft (4). 2. The watch stud (1) according to claim 1, wherein the three contact lines (11a, 11b, 11c) have angular openings α, β, θ, wherein one contact line is diametrically opposite to the attachment point (S1) to the hairspring. 3. The clockwork stud (1) according to claim 2, wherein the angle openings α, β, θ are greater than 90°. 4. The clockwork stud (1) according to claim 2, wherein the angular openings α, β, θ are equal to 120°. 5. The watch stud (1) according to claim 1, wherein the distance between the balance shaft (4) and the stud (1) at the recessed portion (10a, 10b, 10c) is between 0 and one-quarter of the diameter of the balance shaft (4). 6. The watch stud (1) according to claim 1, wherein the distance between the balance shaft (4) and the stud (1) at the recessed portion (10a, 10b, 10c) is between 0 and 50 μm. 7. The clock stud (1) according to claim 1, wherein the stud (1) comprises a varying cross-section. 8. An integrated internal pile/hairspring assembly, comprising the internal pile (1) according to claim 1. 9. The integrated internal stud/hairspring assembly according to claim 8, wherein the hairspring (2) is made of silicon. 10. The integrated internal stud/hairspring assembly according to claim 8, wherein the hairspring (2) is made of a material that does not undergo plastic deformation. 11. A watch movement or watch, comprising the integrated stud/hairspring assembly as claimed in claim 8.