CH708760A2 - Balance with adjustable moment of inertia. - Google Patents

Abstract

A pendulum for a timepiece according to the invention, with inertia adjustment, comprises a serge (2) and at least two regularly spaced connecting elements (3) connected to said serge (2). The connecting elements (3) are fixed by their other end (7) to an element (8) in the center of the balance. The connecting elements (3) have in the vicinity of said serge (2), a threaded portion (5) on which is positioned a nut (6A, 6B). The threaded portion is in length up to half the length of said connecting member (3) while the portion of the connecting members (3) extending from the threaded portion to the member (8) at center of the balance is devoid of thread.

Description

Description

The present invention relates to a timepiece having a rocker with variable moment of inertia.

In general, a rocker with variable moment of inertia comprises a wheel-shaped part comprising the serge, connecting elements between the serge and the axis of the balance and a certain arrangement of screws nuts or flyweights fixed on the balancing serge that allow by adjusting their positions to change the imbalance and the moment of inertia of the pendulum.

[0003] Several mechanical oscillators have already been proposed for timepieces. Such oscillators are generally designed in the form of a balance spring which generates oscillations defining the frequency which divides the time into strictly identical units. Thus, the accuracy of a watch equipped with a spring balance depends essentially on the frequency stability of its sprung balance.

[0004] Different parameters affect the frequency stability of a balance spring whose variations in the amplitude of the pendulum oscillations. These amplitude variations are notably related to the positions of the watch, to the loss of the moment of force, to the friction, in particular with the pivots of the balance shaft and the unbalance of the latter. This has the effect of causing a lack of isochronism of the sprung balance, this isochronism defect having an impact on the precision of the timepiece.

To adjust the running of a timepiece, the adjustment means are the adjustment of the moment of inertia and balancing of the balance. To do this, the rockers can be provided with movable screws or nuts, acting as flyweights, arranged radially at the periphery of the beam mounted on the serge, and likely, depending on their screwing, to modify the inertia of the balance or its axis of inertia.

[0006] CH 196 706 discloses a rocker which comprises adjustment screws screwed radially into the beam of the beam from the outside thereof. This balance has drawbacks which are mainly the decrease of the diameter of the beam of the balance, resulting in a heavier balance for a moment of identical inertia and therefore more sensitive to shocks that the watch wears. In addition, the aerodynamic friction is great, requiring more energy to maintain the oscillations of the sprung-balance, this being done at the expense of accuracy. One or the other of the screws can unscrew partially or totally, to the detriment of the reliability.

[0007] EP 1 837 719 discloses a balance for movement comprising a serge, and four arms connecting said serge to the axis of the balance. Weights mounted on the serge between the adjacent arms can adjust an unbalance and adjust the moment of inertia. The serge has pads radially inward. The serge and the studs are crossed by a tapped hole in which the weights are screwed from inside the serge.

[0008] US 131 782 discloses a beam having a serge on which are fixed, by one end, four threaded arms over their entire length each with a nut. These four arms are connected at their other end to a central element of annular shape comprising a threaded rod and a nut passing through said central element which unbalances the balance. This balance has the disadvantage of being bulky and would be more suitable for a marine chronometer than a watch movement.

There is also an embodiment that has provided a balance of nuts on threaded rods, driven inside the serge between adjacent arms, this balance allows a high precision adjustment. One of the drawbacks of this embodiment is aerodynamics which is not optimum and which requires more energy to oscillate than the beam of the present invention.

There are other systems that are configured to adjust the inertia of the balance. Most systems are nevertheless still perfectible in regulating the amplitude of the oscillator (balance / spiral).

The object of the present invention is therefore to provide a rocker with improved moment of inertia variable to reduce the gait of a timepiece and adjust very precisely the frequency of oscillation, while maintaining the lowest aerodynamic friction.

According to the invention, a pendulum for a timepiece, with variable moment of inertia, comprises a serge in which at least two regularly spaced connecting elements are connected to said serge. The connecting elements are interconnected at their other end by an element in the center of said serge. The connecting elements have on their end arranged with said serge, a threaded portion on which is positioned a nut. The threaded portion represents in length up to half the length of said connecting member while the portion of the connecting members extending from the threaded portion to the member at the center of the serge is threadless and is preferably smooth.

A rocker with variable moment of inertia according to the invention consists of several component parts and a precise adjustment of the frequency of the oscillations. Changing the moments of inertia of a balance provides greater accuracy while giving increased reliability. Thanks to this device, the accuracy of the time indicators as well as the resistance capacity of the watch in case of shock are improved.

The balance with variable moment of inertia according to the invention is equipped with several elements that promote its balance and the modification of its inertia. It has adjusting or regulating nuts, which can be for example

2 in gold, allowing the decrease of volume, which are useful for the modification of the moment of inertia and thus of the frequency (the number of oscillations per second) which results from it. These nuts are fixed on the connecting elements of the balance.

The balance with variable moment of inertia according to the invention ensures a high accuracy of the watch because the precise modification of the inertia of this body during adjustments affects the frequency of oscillations. These changes make it possible to obtain a greater accuracy of the frequency of the oscillations. These settings thus ensure the accuracy of the stability of the oscillation frequency.

In general, the variable moment inertia balance beam is a device necessary for the stability and precise running of a watch.

The characteristics of the invention will appear more clearly on reading a given embodiment only by way of example, in no way limiting with reference to the schematic figures, in which:

Fig. 1 represents a view from above of a variable moment-inertia beam according to the invention;

Fig. 2 shows a sectional view of the balance with variable moment of inertia according to the invention;

Fig. 3 is a sectional view of FIG. 1 of the pendulum with variable moment of inertia assembled with a balance shaft;

Fig. 4 shows a top view of the connecting elements, on which nuts have been screwed and a central element of annular shape made of a single piece;

Fig. 5 shows a sectional view of a nut and an end of a connecting element which is of square section to facilitate the introduction of the nut on the thread;

Fig. 6 shows a bottom view of a rocker whose serge has four openings to install and rigidly fix four connecting elements; and

Fig. 7 is a sectional view of FIG. 6.

As illustrated in FIG. 1, the balance 1 with inertia adjustment comprises a serge 2 in which four connecting elements 3 are connected to the serge 2 and regularly arranged around the center by 90 ° angles. The connecting elements 3 have on their end arranged with said serge 2, a threaded portion 5 on which is positioned a nut 6A, 6B. The threaded portion represents, in this example, in length approximately one third of the length of said connecting element 3, that is to say from one end of the connecting element 3 to the other, while the part connecting members 3 extending from the threaded portion to the element 8 in the center of the serge is smooth and threadless. The non-threaded ends 4 of the connecting elements 3 are driven into the serge 2.

The connecting elements 3 are interconnected by their other end 7 by an annular element 8 in the center of said serge 2. A laser welding can for example be used to fix the connecting elements 3 to the annular element 8 .

The element 8 could be annular, square or be the axis of the pendulum.

In this example, the connecting elements 3 of the balance 1 are preferably rods of cylindrical shape, threaded and possibly milled on opposite sides, but can also be for example elliptical, ovoid or rectangular section. Whatever the shape in section, for better aerodynamics the unthreaded part of these rods is smooth. The four connecting elements 3, of circular section, are independent and connected by a central element 8.

In the embodiments comprising connecting elements 3 of rectangular section, said connecting elements 3 may be thinner which offers more lightness and less space. In addition, the thread is no longer continuous which provides better control of the friction torque with the nut 6A, 6B. Finally, the end 4 of each connecting element 3 which can be driven, welded or glued in the serge 2 can be rectangular or cylindrical décolleté.

In a variant, not shown, the balance 1 may comprise eight connecting elements 3 connected to the serge 2 and regularly arranged around the center by 45 ° angles to ensure easier dynamic adjustment.

In other variants, not illustrated, the balance 1 may comprise two or three connecting elements 3 connected to the serge 2 and regularly arranged around the center by angles of 180 ° or 120 ° or the pendulum 1 can have six connecting elements 3 connected to the serge 2 and regularly arranged around the center by 60 ° angles.

As illustrated for example in FIG. 1, the length of the threaded portion of said connecting elements 3 is less than half the length of the connecting elements 3.

The connecting elements 3 are rigidly connected firstly to the serge 2 and secondly to said central element 8, in particular by driving, gluing or welding.

Normally, the serge 2 of the balance 1 and the connecting elements 3 are of the same material, such as brass, but in one embodiment, the serge 2 of the balance 1 and the connecting elements 3 are of different materials. The

3

Claims (9)

Thermal expansion stresses of the materials must then be taken into account in order not to lose the advantages of the balance 1 according to the present invention. In the example illustrated in FIG. 1, the nuts 6A, 6B, movable using a suitable tool, are of two different sizes. Indeed, two nuts 6A are larger than the other two nuts 6B. This size difference between the 6A and 6B nuts provides more precision for the setting since the large 6A nuts will be used for coarse adjustment while the smaller 6B nuts are used for a finer adjustment of the nuts. frequency. The nuts 6A, 6B may be of the same material as the serge but, in a variant, be of gold, or other precious metal (platinum, etc.) of high density, to obtain a smaller volume. In one embodiment, the large nuts 6A have a length of about half the length of the threaded portion 5 of the connecting elements 3. The nuts 6B of smaller size have a length of about one third of the length of the threaded portion 5 of the connecting elements 3. Of course, these length ratios may vary depending on the materials used. In general, the nut 6A, 6B occupies between 25% to 65% of the threaded portion. In the example illustrated in FIG. 4, the connecting elements 3 and a central element 8 of annular shape are made of a single piece. As previously described, these connecting elements 3 may for example be of rectangular sectional shape. In the embodiment illustrated in FIG. 5, the connecting elements 3 are of rectangular section and the nut 6A, 6B is octagonal. The nuts 6A, 6B are of equal or different lengths and have opposite octagonal faces. The distance between two opposite faces of a nut 6A, 6B can extend up to one and a half times the height of the serge 2. The distance between two opposite faces of a nut 6A, 6B should not extend beyond one and a half times the height of the serge 2 because it would be too cumbersome in the movement and would harm the aerodynamics of the balance 1. In the example illustrated in FIG. 6, a rocker 1 comprises a serge 2 having, on its inner part, four openings 9 in which the unthreaded end 4 of each threaded portion is arranged. These openings 9 make it possible to arrange the non-threaded ends 4 of each threaded portion. As illustrated in FIG. 7, the openings 9 make it possible to arrange the connecting elements 3 and to fix them rigidly on the serge 2. Various factors (temperature, pressure ...) lead to a daily lead or delay of a few seconds mechanical watches. The fine adjustment of the back and forth movements of the variable inertia balance according to the invention thus makes it possible to eliminate these daily irregularities. Thus, in the long term the variable inertia balance according to the invention significantly reduces inaccuracies and inaccuracy of the time indicators. It ensures the accurate measurement of the flow of time, while constituting a guarantee of reliability. Another aspect of the invention relates to a watch movement comprising the balance described above. claims 1. Pendulum for a timepiece, with variable moment of inertia, comprising a serge (2) in which at least two regularly spaced connecting elements (3) are connected to said serge (2), said connecting elements (3) ) being interconnected by their other end (7) by an element (8) in the center of said serge (2), characterized in that said connecting elements (3) have on their end (4) arranged with said serge (2), a threaded portion (5) on which is positioned a nut (6A, 6B), the threaded portion representing in length up to half the length of said connecting member (3) while the portion of the elements link (3) extending from the threaded portion to the element (8) in the center of the serge is threadless. 2. balance for timepiece according to claim 1, wherein the connecting elements (3) are rectangular or circular section. 3. balance for timepiece according to claim 1 or 2, comprising three, four, six or eight connecting elements (3). 4. balance for a timepiece according to one of the preceding claims, wherein the connecting elements (3) are rigidly connected on the one hand to the serge (2) and on the other hand to said central element (8), especially by gluing or welding. 5. balance for timepiece according to one of the preceding claims, wherein the central element (8) is constituted by the axis of the balance and is connected to the connecting elements (3) without intermediate piece. 6. balance for timepiece according to one of the preceding claims wherein the connecting elements (3) and said central element (8) are formed in one piece. 7. balance wheel for a timepiece according to one of the preceding claims, wherein the serge comprises, on its inner part, openings (9) in which the ends (4) unthreaded of the threaded portion are arranged. 4 8. balance for a timepiece according to one of the preceding claims wherein the nuts (6A.6B) are of equal or different lengths and have opposite faces including hexagonal or octagonal faces and the distance between two opposite faces of a nut (6A, 6B) does not exceed one and a half times the height of the serge. 9. Watchmaking movement comprising a balance according to one of the preceding claims. 5