PART FOR ATTACHING AN OUTER LAST COIL OF A BALANCE SPRING OF A HOROLOGICAL MOVEMENT

Abstract

An attachment part for attaching a free end of an outer last coil of a balance spring of a horological movement, this balance spring taking the form of a ribbon wound in coils and being delimited by first and second faces which extend parallel to and at a distance from one another, the attachment part including elastically deformable clamping means which are arranged to be brought into contact with the free end of the outer last coil of the balance spring in order to exert a resilient clamping force on this free end so as to guarantee the immobilisation thereof, this resilient clamping force being exerted along at least a first line of contact (A; B) on the first face of the balance spring and along a contact surface (S) on the second face.

Claims

1. A part arranged to attach a balance spring of a horological movement, said balance spring, wound in coils, being delimited by first and second faces which extend at a distance from one another, said attachment part comprising elastically deformable clamping devices which are arranged to be brought into contact with the balance spring in order to exert a resilient clamping force on said balance spring so as to guarantee the immobilisation thereof, said resilient clamping force being exerted along at least a first line of contact (A; B) on the first face of the balance spring and along a contact surface (S) on the second face.

2. The attachment part according to claim 1, wherein the resilient clamping force is exerted on the first face of the balance spring along the first and second lines of contact (A, B).

3. The attachment part according to claim 2, wherein the clamping device takes the form of separate first and second clamping devices which face one another.

4. The attachment part according to claim 3, wherein the first and second clamping devices take the form of two elastically deformable arms, the free ends whereof facing one another being arranged to be brought into contact with the free end of the outer last coil of the balance spring in order to exert a resilient clamping force (F1) on said free end in a direction (Z) perpendicular to a plane (X, Y) wherein the balance spring extends.

5. The attachment part according to claim 4, wherein the attachment part takes the form of a tuning fork closing in on itself at the free ends facing the two arms.

6. The attachment part according to claim 1, wherein the attachment part is provided with gripping devices which are arranged to allow the devices for clamping the free end of the outer last coil of the balance spring to be moved apart in order to release said free end.

7. The attachment part according to claim 1, wherein the attachment part comprises a device for being mounted on a balance cock or around a pivot bearing of the balance.

8. The attachment part according to claim 1, wherein the assembly between the attachment part and the free end of the outer last coil of the balance spring is removable.

9. The attachment part according to claim 1, wherein the attachment part is obtained by stamping and bending.

10. The attachment part according to claim 1, wherein the attachment part is made of a harder material than the material from which the balance spring is made.

11. The attachment part according to claim 1, wherein the balance spring takes the form of a ribbon, the first and second faces whereof extend parallel to one another.

12. The attachment part according to claim 1, wherein the balance spring is provided with a plate on which the clamping device exert the resilient clamping force to ensure the immobilisation thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0028] Other features and advantages of the present invention will more clearly emerge upon reading the following detailed description of one embodiment of a part for attaching a balance spring according to the invention, this example being provided for the purposes of illustration only and not intended to limit the scope of the invention, given with reference to the accompanying drawing, in which:

[0029] FIG. 1A is a perspective top view of an attachment part according to the invention, this attachment part, arranged like a tuning fork, allowing a free end of an outer last coil of a balance spring to be immobilised by clamping;

[0030] FIG. 1B is a more large-scale view of the encircled area in FIG. 1A;

[0031] FIG. 2 is a perspective bottom view of the tuning fork in FIG. 1A;

[0032] FIG. 3 is a perspective top view of a sprung balance assembly fitted with the attachment part according to the invention;

[0033] FIG. 4 is a perspective bottom view of the sprung balance assembly according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention was drawn from the general inventive idea consisting of providing a part which allows a free end of an outer last coil of a balance spring to be attached without the use of adhesive. More specifically, in accordance with the invention, the attachment part is conventionally provided with a first and a second arm which, depending on the chosen embodiment, exert a resilient clamping force on the free end of the outer last coil of the balance spring in a direction perpendicular to the plane in which this last coil extends. For example, when produced by stamping and bending, the attachment part is such that the arms can be bent over the free end of the outer last coil of the balance spring, so as to exert a sufficient resilient clamping force on this free end to guarantee the immobilisation thereof. Moreover, given that the blocking of the outer last coil of the balance spring is obtained by bending the arms, it is easy to understand that, where necessary, the assembly formed by the attachment part and the balance spring can be disassembled simply by unbending the arms. Moreover, the attachment part is inexpensive to produce, as it can be obtained by stamping and bending. The cost price is further reduced in the case where the attachment part is provided with means for attaching it to a cock such as a balance cock of the horological movement; in the latter case, the invention provides a part which acts both as a stud and as a stud-holder.

[0035] Denoted as a whole by the general reference numeral 1, the part according to the invention is intended to allow for the attachment of a free end 8 of an outer last coil 10 of a balance spring 12 for a horological movement. In the example shown in the drawing, the balance spring 12 is provided with a plate 13 attached by any suitable means such as welding or made in one piece with the free end 8 of the outer last coil 10. To this end, according to the invention, the attachment part 1 comprises elastically deformable clamping means which are arranged to be brought into contact with and to clamp a plate 13 provided at the free end 8 of the outer last coil 10 of the balance spring 12 in order to exert a resilient clamping force F1 on this plate 13 in a direction Z perpendicular to a plane X, Y in which the balance spring 12 extends.

[0036] By ensuring the immobilisation, by clamping, of the plate 13 provided at the free end 8 of the outer last coil 10 of the balance spring 12 in the direction Z only, any detrimental effect that the attachment of the balance spring 12 by means of the attachment part 1 according to the invention could have on the precision of the rate of a sprung balance assembly 14 fitted with such an attachment part 1 is limited as much as possible. More specifically, it is known that exerting a mechanical stress on the free end 8 of the outer last coil 10 of a balance spring 12 in a direction Z perpendicular to the plane X, Y in which the balance spring 12 extends is considerably (by a factor of the order of 10) less detrimental to the precision of the rate of a sprung balance assembly 14 than when the balance spring 12 is stressed in the plane X, Y in which it extends.

[0037] According to the invention, the attachment part 1 comprises separate first and second clamping means which immobilise the plate 13 with which the free end 8 of the outer last coil 10 of the balance spring 12 is provided, which in particular prevents any risk of this plate 13 slipping and pivoting about itself, which would of course be detrimental to the correct operation of the sprung balance assembly 14 and would require the timepiece fitted with such a sprung balance assembly 14 to be returned to the factory.

[0038] According to a preferred but non-limiting embodiment, the first and second clamping means take the form of two elastically deformable arms 16a, 16b, the respective free ends 18a, 18b whereof facing one another are arranged so as to be brought into contact with and clamp the plate 13 provided at the free end 8 of the outer last coil 10 of the balance spring 12 along two separate lines of contact A, B. Preferably but not exclusively, the attachment part 1 takes the form of a tuning fork-shaped clamp which closes in on itself at the free ends 18a, 18b facing the two arms 16a, 16b, the plate 13 present at the free end 8 of the outer last coil 10 of the balance spring 12 being clamped between the free ends 18a, 18b of these two arms 16a, 16b and a crosspiece 20 which connects these two arms 16a, 16b together. According to the invention, this crosspiece 20 resiliently clamps the plate 13 along a contact surface S.

[0039] It can thus be seen that bringing the two arms 16a, 16b into contact with the plate 13 by elastic deformation allows this plate 13 to be pressed against the crosspiece 20 of the attachment part 1 and allows the plate 13 to be immobilised via a resilient clamping force which, on one side of the ribbon forming the balance spring 12, is exerted along two lines of contact A, B and which, on the other side of this ribbon forming the balance spring 12, is exerted along the contact surface S.

[0040] The attachment part 1 can be produced by any appropriate means, for example by stamping and bending, so that the cost price thereof is very low. It can be attached to a cock 22 of the horological movement. For this purpose, according to a preferred embodiment of the invention, the attachment part 1 comprises means for being mounted around a pivot axis 24 of a balance 26 of the horological movement. To this end, the attachment part 1 is extended by a mounting element 28 provided with an opening 30 whose inside diameter is adjusted to an outside diameter of a shoulder of the balance cock 22 or of a pivot bearing 31 which can be of a type known to a person skilled in the art. The attachment part 1 according to the invention thus advantageously acts as both a stud and a stud-holder.

[0041] According to a special embodiment of the invention, the attachment part 1 is provided with gripping means, for example of the horn type 32, which are arranged so as to allow, when they are clamped using tweezers, the free ends 18a, 18b facing the two arms 16a, 16b of the free end 8 of the outer last coil 10 of the balance spring 12 to be moved apart in order to release this free end 8. Thus, where necessary, given the absence of adhesive and the elastically deformable nature of the attachment clamp 1, the assembly formed by the attachment part 1 and the balance spring 12 can be disassembled.

[0042] It goes without saying that the present invention is not limited to the embodiment described hereinabove and that various simple alternatives and modifications can be considered by a person skilled in the art without leaving the scope of the invention as defined by the accompanying claims. In particular, it should be understood that the presence of the plate 13 is not essential for the immobilisation of the balance spring 12 by resilient clamping. More specifically, the balance spring 12 can be immobilised by means of the attachment part 1 according to the invention by directly engaging the free end 8 of the outer last coil 10 of the balance spring 12 in the space delimited by the arms 16a, 16b and the crosspiece 20 of this attachment part 1. Similarly, it should be noted that, preferably but in a non-limiting manner, the attachment part 1 is made of a harder material than the material from which the balance spring 12 is made. Thanks to this feature, when the plate 13 or directly the free end 8 of the outer last coil 10 of the balance spring 12 is clamped, neither the arms 16a, 16b nor the crosspiece 20 of the attachment part 1 are marked by the balance spring 1. Thus, where necessary, during the life of the timepiece fitted with the attachment part 1 according to the invention, in order to remove the balance spring 12 by unbending the arms 16a, 16b of the attachment part 1, the arms 16a, 16b, after the operation, will be able to be bent again over the free end 8 of the outer last coil 10 of the balance spring 12 without the repositioning of this free end 8 being hindered by the presence of any grooves which may have been marked into the arms 16a, 16b or the crosspiece 20.

NOMENCLATURE

[0043] 1. Attachment part [0044] F1. Resilient clamping force [0045] Z. Direction [0046] X, Y. Plane [0047] 8. Free end [0048] 10. Outer last coil [0049] 12. Balance spring [0050] 13. Plate [0051] 14. Sprung balance assembly [0052] 16a, 16b. Arms [0053] 18a, 18b. Free ends [0054] A, B. Points of contact [0055] 20. Crosspiece [0056] 22. Cock [0057] 24. Pivot axis [0058] 26. Balance [0059] 28. Mounting element [0060] 30. Opening [0061] 31. Pivot bearing [0062] 32. Horns [0063] S. Contact surface