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

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.