Device for autonomous adjustment of the active length of a balance spring

1 . A device for independent adjustment of the active length of a spiral, for a balance-spiral type oscillator, comprising a cock mounted on a plate of a horological movement and in which a balance shaft pivots, the spiral including an inner end secured to the balance shaft and an outer end secured to a balance spring stud fastened to a balance spring stud holder, the balance spring stud holder being pivotably mounted on the cock concentrically with the balance shaft, and means for modifying the active length of the spiral,

wherein the means for modifying the active length of the spiral comprise:

a first arm capable of moving between a rest position and a correction position of the device, the at least one arm having a first free end and a second end cooperating with a first pair of pins mounted on the balance spring stud holder, the first pair of pins being angularly offset relative to the stud;

a second arm capable of moving between the rest position and the correction position of the device, the second arm having a first free end and a second end cooperating with a second pair of pins mounted on the balance spring stud holder, the second pair of pins being angularly offset relative to the first pair of pins and to the stud;

elastic biasing means configured to exert an elastic action on the arms for returning them in position;

two inertia blocks, each movable in translation in orthogonal planes, the inertia blocks being arranged to move in translation according to gravity, the movement of at least one of the inertia blocks causing a rotation of a shaft on which a first cam is mounted, the rotation of the first cam causing a movement of the arm and a second cam arranged so as to cooperate with the second arm and move it in translation, to act on the spiral and simultaneously modify the active length of the spiral; and

elastic return means configured to exert an elastic action on the inertia blocks for returning them in position.

2 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein each inertia block comprises a toothed sector arranged to cooperate with a pinion secured to the axis.

3 . The device for autonomous adjustment of the active length of a coil according to claim 2 , wherein the elastic return means are in the form of a pair of spring leaves arranged at each end of each inertia block.

4 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the cams are radial cams with an external profile.

5 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the cams are angularly offset with respect to one another.

6 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein, in the rest position of the device, a planar portion of each cam is in contact with one of the arms, and, in the correction position of the device, a wedge or an angle of the cam is in contact with one of the arms.

7 . The device for independent adjustment of the active length of a spiral according to claim 1 , wherein the cams are in permanent contact with the free end of each arm regardless of the position of the inertia block.

8 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the free end of the first arm comprises elastically-deformable adjustment means in the form of a spring leaf whose first end is secured to the arm and another end is free, the free end being arranged so as to be biased and adjust the length of the first arm.

9 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the free end of the second arm comprises elastically deformable adjustment means in the form of a spring leaf whose first end is secured to the arm and another end is free, the free end being arranged so as to be biased and adjust the length of the second arm.

10 . The device for autonomous adjustment of the active length of a spiral according to claim 8 , further comprising means for adjusting the elastic stress in the form of a screw, the screw passing through the free end and bearing against the arm.

11 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the first pair of pins is fastened to the balance spring stud holder via a first support, the arm being arranged so that it slides between the first pair of pins and the second pair of pins and comes into contact with the outer coil of the spiral in the correction position.

12 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the second pair of pins is fastened to the balance spring stud holder via a second support, the arm being arranged so that it passes between the first pair of pins and the second pair of pins and comes into contact with the outer coil of the spiral in the correction position.

13 . The device for autonomous adjustment of the active length of a spiral according to claim 1 , wherein the inertia blocks have a parallelepipedic shape.

14 . A horological movement including a balance-spiral type oscillator and the device for autonomous adjustment of the active length of the spiral according to claim 1 .

15 . A timepiece including the horological movement in accordance with claim 14 .