Balance spring made of micromachinable material with isochronism correction
A timepiece balance spring made of micromachinable material including a plurality of stages, each forming a spiral wound spring, parallel to each other and all attached to a common axial collet or to the same balance staff, each stage including, at its respective outer end, its own attachment to a balance spring stud which are independent of those of the other stages, the attachment including a position adjustment with respect to a balance spring stud which are also independent of those of the other stages, the attachment and the position adjustment together forming built-in isochronism correction mechanism for the balance spring, and the position adjustment including a plurality of discrete position adjustment positions including housings each arranged to retain a stud.
1. A timepiece balance spring made of micromachinable material comprising a plurality of stages, each forming a spiral wound spring, all parallel to each other and arranged to be assembled to each other at the respective inner ends thereof in a common axial collet or on the same balance staff, wherein each said stage includes, at the respective outer end thereof, specific means of attachment to a balance spring stud which are independent of those of said other stages, said means of attachment comprising means for position adjustment with respect to a balance spring stud which are also independent of those of said other stages, said means of attachment and said means for position adjustment together forming built-in isochronism correction means for said balance spring, wherein said position adjustment means of a said stage include a plurality of discrete position adjustment positions comprising housings each arranged to retain a stud.
2. The timepiece balance spring according to claim 1 , wherein said means of attachment are of variable stiffness depending on the position of said position adjustment means.
3. The timepiece balance spring according to claim 1 , wherein said position adjustment means of a said stage include a plurality of elastic multi-arms defining said discrete position adjustment positions.
4. The timepiece balance spring according to claim 3 , wherein said position adjustment means of a said stage include a plurality of elastic multi-arm assemblies which are of a different stiffness from each other.
5. The timepiece balance spring according to claim 3 , wherein said position adjustment means of a said stage include a plurality of elastic multi-arm assemblies which are of the same stiffness as each other.
6. The timepiece balance spring according to claim 3 , wherein said elastic multi-arm assemblies each include at least one inner point of attachment on a first inner area, and at least one outer point of attachment on a second outer area, further from the pivot axis of said balance spring than said first area.
7. The timepiece balance spring according to claim 3 , wherein said elastic multi-arm assemblies each include a U-shaped housing facing the exterior of said balance spring.
8. The timepiece balance spring according to claim 1 , wherein said discrete positions are angularly offset by a constant pitch comprised between 4° and 12° with respect to the pivot axis of said balance spring.
9. The timepiece balance spring according to claim 1 , wherein at least two said stages include springs wound in opposite directions.
10. The timepiece balance spring according to claim 9 , wherein the total stiffness of all of said stages wound in a first direction is equal to the total stiffness of all of said stages wound in a second direction opposite to said first direction.
11. The timepiece balance spring according to claim 1 , wherein each said stage includes angular indexing means arranged to cooperate in a complementary manner with complementary indexing means, comprised in said other stages to form together said compound balance spring, in a fixed and reproducible geometry.
12. An escapement mechanism including at least one sprung balance assembly comprising a balance coupled to at least one said balance spring according to claim 1 , and comprising at least one stud for fastening in position said outer end of at least one said stage.
13. The escapement mechanism according to claim 12 , wherein at least one said same stud is intended for the attachment of several said outer ends of said different stages.
14. The escapement mechanism according to claim 13 , wherein the mechanism includes one said rectilinear stud parallel to the axis of said balance spring.
15. The escapement mechanism according to claim 12 , wherein at least one said stud is made in the manner of a bimetallic attachment with two materials of different coefficients of thermal elongation, and is arranged to deform in the direction of the coil of said balance spring, one end of which is carried by said stud.
16. A mechanical timepiece movement including at least one escapement mechanism according to claim 12 .
17. A watch including at least one mechanical timepiece movement according to claim 16 .