Timepiece movement comprising a rotating element provided with a magnetized structure having a periodic configuration
A timepiece movement includes a magnetic escapement formed of a magnetic escape wheel with an annular magnetized structure and a pallet fork whose shaft is formed by a ferromagnetic material. The pallet shaft exerts on the escape wheel a magnetic disturbance torque due to the fact that the annular magnetized structure exhibits an angular variation of at least one defining physical parameter thereof, such that the magnetic attraction varies as a function of the angular position of the escape wheel and has a tangential component. A magnetic compensation pin is incorporated in the timepiece movement, this magnetic compensation pin being arranged such that the second magnetic disturbance torque that it exerts on the escape wheel exhibits an angular phase shift relative to the first magnetic disturbance torque generated by the pallet shaft, so as to compensate largely for this first magnetic disturbance torque.
1. A timepiece movement comprising:
a mechanism including:
a rotating element, provided with an annular magnetized structure exhibiting an angular variation of at least one physical parameter defining said annular magnetized structure, and
a first set of magnetic elements which is formed of one functional magnetic element or of a plurality of functional magnetic elements, said first set of magnetic elements not being integral in rotation with said rotating element and having overall with the annular magnetized structure a first magnetic interaction which generates on said rotating element a first magnetic disturbance torque; and
a second set of magnetic elements which includes a magnetic compensation element or of a plurality of magnetic compensation elements, said second set of magnetic elements not being integral in rotation with said rotating element and having overall with the annular magnetized structure a second magnetic interaction which generates on said rotating element a second magnetic disturbance torque, and
wherein the second set of magnetic elements is arranged relative to the first set of magnetic elements such that the maximum absolute torque value resulting from the addition of the first and second magnetic disturbance torques is lower than the maximum absolute value of the first magnetic disturbance torque.
2. The timepiece movement according to claim 1 , wherein the first magnetic disturbance torque as a function of the angular position of said rotating element defines a first sinusoidal curve having an angular period equal to 360°/N, with N being an integer number greater than one (N>1); and wherein the second set of magnetic elements is arranged relative to the first set of magnetic elements such that the second magnetic disturbance torque as a function of the angular position of said rotating element defines a second sinusoidal curve also having said angular period, and such that the first and second magnetic disturbance torques exhibit therebetween an angular phase shift substantially equal to 180°.
3. The timepiece movement according to claim 2 , wherein the second set of magnetic elements consists only of said magnetic compensation element; and wherein the annular magnetized structure is configured and said magnetic compensation element is arranged such that the maximum absolute value of said resultant torque is less than 30% of the maximum absolute value of the first magnetic disturbance torque.
4. The timepiece movement according to claim 2 , wherein the second set of magnetic elements consists of K magnetic compensation elements or K groups of magnetic compensation elements substantially having the same configuration, K being an integer number greater than one (K>1); and wherein said K magnetic compensation elements or groups of magnetic compensation elements are arranged such that K individual magnetic disturbance torques generated on the rotating element respectively by said K magnetic compensation elements or groups of magnetic compensation elements, exhibit relative to said first magnetic disturbance torque respectively K angular phase shifts which are respectively equal to substantially J·360°/(K+1) with J being an integer number ranging from one to K, i.e. J=1, . . . , K.
5. The timepiece movement according to claim 4 , wherein the integer number K is equal to two (K=2), wherein the two magnetic compensation elements or groups of magnetic compensation elements are similar to each other, one of the two magnetic compensation elements or groups of magnetic compensation elements exhibiting relative to the other an angular offset whereby the remainder of the integer division by said angular period is equal to 360°/(3·N).
6. The timepiece movement according to claim 5 , wherein the annular magnetized structure is configured and the two magnetic compensation elements are arranged such that the maximum absolute value of said resultant torque is less than 15% of the maximum absolute value of the first magnetic disturbance torque.
7. The timepiece movement according to claim 4 , wherein the integer number K is greater than two (K>2), wherein said K magnetic compensation elements or groups of magnetic compensation elements are similar to each other, a certain magnetic compensation element or group of magnetic compensation elements among said K magnetic compensation elements or groups of magnetic compensation elements exhibiting relative to the other magnetic compensation elements or groups of magnetic compensation elements K−1 angular offsets whereby the K−1 remainders of the integer division of each by the angular period are respectively equal to J·360°/[(K+1)·N] where J is an integer number ranging from one K−1, i.e. J=1, . . . , K−1.
8. The timepiece movement according to claim 4 , wherein the first set of magnetic elements considered consists only of said functional magnetic element, the positive integer number N thus being equal to a number of angular periods exhibited by the annular magnetized structure; wherein said K magnetic compensation elements ( 50 , 52 ) are arranged to exhibit relative to said functional magnetic element K angular offsets whereby the K remainders of the integer division of each by said angular period are respectively equal to J·360°/[(K+1)·N] where J is an integer number ranging from one to K, namely J=1, . . . , K.
9. The timepiece movement according to claim 1 , wherein said rotating element is a magnetic escape wheel forming a magnetic escapement.
10. The timepiece movement according to claim 9 , wherein said functional magnetic element is a shaft of a magnetic pallet fork also forming said magnetic escapement, said shaft being formed by a ferromagnetic material; and wherein the annular magnetized structure defines magnetic barriers for the magnetic pallet fork which are angularly offset by said angular period.
11. The timepiece movement according to claim 9 , wherein said magnetic compensation element is a pin arranged at the periphery of the magnetic escape wheel and formed by a ferromagnetic material.
12. The timepiece movement according to claim 9 , wherein the annular magnetized structure has a constant thickness, said angularly variable physical parameter being the radial width of said annular magnetized structure.
13. The timepiece movement according to claim 9 , wherein the annular magnetized structure is configured such that the external profile thereof is circular and continuous.
14. The timepiece movement according to claim 1 , wherein said magnetic compensation element is arranged such that the position thereof relative to said rotating element can be adjusted to regulate said angular phase shift and to optimise said maximum intensity of said resultant torque.