CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent Application No. 17208988.0 filed on Dec. 20, 2017, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention concerns a device for autonomous adjustment of the active length of a balance spring, for an oscillator of the balance/balance spring type.

The invention also concerns a timepiece movement comprising the device for autonomous adjustment of the active length of a balance spring, for an oscillator of the balance/balance spring type.

The invention also concerns a timepiece, particularly a watch, including the timepiece movement.

BACKGROUND OF THE INVENTION

In the field of watches provided with mechanical oscillators of the balance/balance spring type, there are known manual devices for adjusting the active length of the balance spring.

For example, in ordinary manual adjustment mechanisms, the outer end of the balance spring is immobilised by a stud fixed to a stud holder integral with a cock. A regulator that is movable in rotation with respect to the stud holder is provided for adjusting the active length of the balance spring, thereby allowing the frequency of the balance/balance spring to be adjusted. The regulator is a pivoting lever, generally with two arms, centred on the axis of the balance staff. A first arm of the regulator carries, for example, two pins, between which the balance spring is free. A second arm of the regulator can be actuated manually to rotate the regulator through a certain angle about the balance staff. This allows the real position of the counting point to be changed. When the regulator pivots, the active length of the spring is reduced or increased. However, one drawback of such a manual adjustment device is that terrestrial gravity affects the oscillation frequency of the balance/balance spring as a function of the orientation of the corresponding timepiece movement. Thus, the rate of the watch may have a significant deviation of rate, especially between its horizontal and vertical positions. Further, when the balance spring moves between the pins because of play between the spring and the pins, the oscillations of the balance disturb its active length and thus cause a slight variation in the oscillation frequency of the balance/balance spring assembly.

To limit the negative effects of gravity a solution is known, in particular from Swiss Patent No CH70560561, which implements a device for adjusting the active length of the balance spring, wherein the regulator carries clamping means intended to clamp an end portion of the spring to define its active length. The outer end of the spring is also integral with an attachment system movably mounted relative to the regulator and arranged to cooperate therewith. The clamping means, formed for example of a pin/cam clamping system wherein the end portion of the spring is clamped, can be loosened or tightened at will by a watchmaker. When the watchmaker has loosened the pin/cam clamping system, he can move the attachment system using a tool, thereby moving the spring relative to the regulator, which remains fixed, and thus relative to the pin, which allows the active length of the spring to be changed. The watchmaker can then clamp the spring against the pin by tightening up the clamping system, to place the adjustment device in the operating position again. However, this solution remains a manual adjustment solution, which has the drawback of considerably limiting adjustment precision in compensating for the effects of gravity. Further, such a solution is tedious to implement, due to the various manual adjustment steps to be performed by a watchmaker for the adjustment.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a device for adjusting the active length of a balance spring, for an oscillator of the balance/balance spring type, which makes it possible to offset, in a simple, precise and autonomous manner, the effects of gravity, particularly disturbances to the isochronism of the balance of the oscillator, and overcomes the aforementioned drawbacks of the state of the art.

To this end, the invention concerns a device for adjusting the active length of a balance spring, for an oscillator of the balance/balance spring type, which includes the features mentioned in the independent claim1.

Specific embodiments of the adjustment device are defined in the dependent claims2to13.

One advantage of the adjustment device according to the invention lies in the fact that it includes elastic stress means configured to exert on the regulator an elastic, return-to-position action, and an inertia block mounted for free rotation on the cock and connected to the pivot arm of the regulator. A rotation of the inertia block, subject to gravity, thus causes a displacement of the pivot arm of the regulator, between a position of rest and a correction position of the device, and simultaneously acts on the means for changing the active length of the balance spring, allowing the spring to be adjusted to offset disturbances to the isochronism of the balance caused by gravity. Consequently, the adjustment device according to the invention makes it possible to precisely adjust the operation of the oscillator as a function of its position in space, by offsetting disturbances to the isochronism of the balance caused by gravity, in an autonomous manner.

According to a preferred embodiment of the invention, the adjustment device further includes a cam driving the pivot arm of the regulator, said cam being integral with the inertia block and in contact with the pivot arm.

Advantageously, the cam is in contact with the pivot arm of the regulator regardless of the position of the inertia block. This makes it possible to permanently adjust the operation of the oscillator according to its position in space, and to further improve correction precision.

According to a particular embodiment of the invention, the elastic stress means include an elastically deformable arm, with a first end of the arm resting against a part integral with the cock and a second end of the arm being attached to the regulator.

Advantageously, the regulator, the pivot arm and the elastically deformable arm together form one piece. This both reduces the space required and improves the reliability of the adjustment device.

Advantageously, the adjustment device further includes means for adjusting the elastic stress defined by the elastic stress means. This allows a user to adjust the intensity of the elastic return action exerted on the regulator, according, for example, to the type of use desired for the watch provided with the adjustment device.

To this end, the invention also concerns a timepiece movement including the adjustment device described above, and which includes the features defined in the dependent claim14.

To this end, the invention also concerns a timepiece comprising the timepiece movement described above, and which includes the features mentioned in the dependent claim15.

