EP3997525A1

EP3997525A1 - Method for adjusting a flexibly pivoted clock oscillator

Info

Publication number: EP3997525A1
Application number: EP20737596.5A
Authority: EP
Inventors: David Chabloz
Original assignee: Patek Philippe SA Geneve
Current assignee: Patek Philippe SA Geneve
Priority date: 2019-07-12
Filing date: 2020-07-07
Publication date: 2022-05-18
Also published as: JP2022539880A; CN114127641B; CN114127641A; US20220317628A1; WO2021009613A1

Abstract

The invention relates to a method for adjusting a clock oscillator (1) comprising a balance wheel (2), a support (3) and a flexible pivot (4) which connects the balance wheel (2) to the support (3) and which guides the balance wheel (2) in terms of rotation relative to the support (3) about a virtual rotation axis, the flexible pivot (4) having, as an orthogonal projection in a plane perpendicular to the virtual rotation axis, an axis of symmetry (Y) which is also an axis of symmetry for the points (5a, 6a) connecting the flexible pivot (4) to the balance wheel (2). According to this method, the imbalance of the balance wheel (2) is adjusted so that, as an orthogonal projection in the above-mentioned plane, the centre of mass (M) of the balance wheel (2) is substantially in the axis of symmetry (Y) and at a different position from the position (O) of the virtual rotation axis and is selected so as to reduce and preferably to minimise the dependence of the oscillation frequency with respect to the orientation of gravitational force for a predetermined oscillation amplitude.

Description

Method of adjusting a flexible pivot watch oscillator

The present invention relates to a horological oscillator which can serve as a time base in a mechanical horological movement.

More specifically, the present invention relates to a flexible pivot horological oscillator, that is to say a horological oscillator without a physical axis of rotation rotating in bearings. Such an oscillator pivots around a virtual axis of rotation thanks to an arrangement of elastic parts.

Different types of flexible pivots exist, such as pivots with separate cross blades, pivots with non-separated cross blades or pivots with offset center of rotation known as “RCC” (Remote Center Compliance). In a separate cross-leaf pivot, the blades extend in two parallel planes to intersect without contact. In an unseparated cross-leaf pivot, they extend in the same plane to physically intersect. As for the offset center of rotation pivot, it includes two blades that do not intersect but extend along axes that intersect. In all cases, the intersection of the blades or their axes defines the virtual axis of rotation.

As with any watch oscillator, it is important that a watch oscillator with a flexible pivot is insensitive to gravity or in other words that its frequency varies as little as possible depending on its orientation with respect to the force of gravity.

For this purpose, we can play on the position of the crossing point of the blades or their axes. For example, in the context of an oscillator with separate crossed blades, patent application EP 291 1012 proposes to arrange the elastic blades such that their point of intersection is located at 7/8 ^th of their length in accordance with the theory developed by WH Wittrick in the article “The properties of crossed flexure pivots and the influence of the point at which the strips cross”, The Aeronautical Quarterly, vol. II, February 1951, the theoretical value being in fact 1/2 + 5/6, or about 87.3% of the length. This The position of the crossing point is in fact that which minimizes the parasitic displacements of the virtual axis of rotation and therefore the dependence of the frequency of the oscillator with respect to gravity.

It appears in fact that the choice of a particular position of the crossing point only minimizes the dependence of the frequency on gravity for a certain amplitude of oscillation, which is about 12 ° for an oscillator. with separate crossed blades. For other amplitudes of oscillation, in particular larger amplitudes, the variation in frequency depending on the position of the watch relative to gravity can be significant.

The present invention aims to provide a new way of improving the operating precision of a flexible pivot horological oscillator, which may or may not be combined with that consisting in choosing a particular position for the point of intersection of the blades or of their axes. .

To this end, a method is provided for adjusting a watch oscillator comprising a balance, a support and a flexible pivot connecting the balance to the support and guiding the balance in rotation relative to the support around a virtual axis of rotation, the flexible pivot having, in orthogonal projection in a plane perpendicular to the virtual axis of rotation, an axis of symmetry which is also an axis of symmetry for the points of junction of the flexible pivot to the balance, characterized in that one adjusts the unbalance of the balance so that, in orthogonal projection in said plane, the center of mass of the balance is substantially on the axis of symmetry and at a position distinct from that of the virtual axis of rotation, said position being chosen so as to decreasing, and preferably minimizing, the dependence of the oscillation frequency on the orientation of gravity for a predetermined oscillation amplitude.

The present invention further provides a clock oscillator adjustable by the method as defined above.

The Applicant has discovered that a correlation exists between the amplitude of oscillation, the position of the center of mass of the balance and the sensitivity of the oscillator to gravity. From a given amplitude of oscillation, we can find a position of the center of mass of the balance along the axis of symmetry of the flexible pivot which minimizes the difference in rate between the different vertical positions of the oscillator by relative to the force of gravity. It is thus possible, by the adjustment according to the invention, to obtain a watch oscillator with performance at least equivalent to that of a Wittrick type oscillator and operating at a different amplitude, more suited to the characteristics of the movement for which it is intended. to be part.

Other characteristics and advantages of the present invention will become apparent on reading the following detailed description given with reference to the accompanying drawings in which:

- Figures 1 and 2 are respectively a top plan view and a perspective view of a flexible pivot horological oscillator according to a particular embodiment of the invention;

- Figures 3 to 5 are diagrams showing the operation of flexible pivot oscillators as a function of the amplitude of oscillation and the orientation of the oscillator with respect to gravity;

- Figure 6 is a diagram showing a relationship between the unbalance of the oscillator balance and the oscillation amplitude minimizing the deviation between the different vertical positions of the oscillator;

- Figures 7 and 8 are respectively a top plan view and a perspective view of a flexible pivot horological oscillator according to another embodiment of the invention.

In what follows, the geometric and dimensional characteristics of the clock oscillator are defined with reference to its rest position.

FIGS. 1 and 2 show a watch oscillator with a flexible pivot according to a particular embodiment of the invention, intended to fulfill the function of a sprung balance in a mechanical watch movement, in particular a wristwatch or pocket watch movement. This oscillator, designated by 1, comprises an oscillating body or balance 2, a support 3 and a flexible pivot 4. The support 3 is intended to be fixed to a fixed or mobile frame of the movement. The flexible pivot 4 is here in the form of two elastic strips 5, 6 extending in respective parallel planes P1, P2 and crossing without contact. Each of these blades 5, 6 is joined by one end 5a, 6a to the balance 2 and by its other end 5b, 6b to the support 3. The balance 2 is thus held to the support 3 only by the flexible pivot 4, which guides it in rotation relative to the support 3 around a virtual axis of rotation and resiliently returns it to a rest position, namely the position illustrated in Figures 1 and 2. The virtual axis of rotation extends perpendicularly to the planes P1, P2 and corresponds, in orthogonal projection in any one of these planes P1, P2 (cf. FIG. 1), to the point of intersection O between the plates 5, 6, more precisely to the point of intersection between the neutral fibers of these plates. In figure 1, the crossing point O is the center of a coordinate system (O, X, Y) whose Y axis is an axis of symmetry for the plates 5, 6, this axis of symmetry passing between the points 5a , 6a junction of the blades 5, 6 to the balance 2 and between the points 5b, 6b of junction of the blades 5, 6 to the support 3. In the example shown, the balance 2 is in the form of a ring surrounding the pivot flexible 4. It could alternatively be of the cut type.

In Figure 3 is shown the rate of oscillator 1 as a function of its oscillation amplitude and its orientation with respect to the force of gravity for a point of intersection O of the blades 5, 6 located at 87.3% of their length, that is to say at the optimal position proposed by WH Wittrick. This position of the crossing point O is measured from the points 5a, 6a of junction of the blades 5, 6 to the balance 2 but can, as a variant, be measured from the points 5b, 6b of the junction of the blades 5, 6 to the support 3, the crossing point O can equally well be situated on the side of the support 3 or of the balance 2. The simulation result of FIG. 3 has also been obtained with a balanced balance 2, of which the center of mass coincides with the crossing point O in orthogonal projection in any one of the planes P1, P2. In addition, the angle a between the blades 5, 6 was chosen as an angle of 71 ° within the range of 68 ° to 76 ° which minimizes the anisochronism due to the non-linearity of the elastic torque produced by the flexible pivot 4 , according to the teaching of patent application WO 2016/096677. It is therefore under the optimal conditions described in the prior art that the simulation was carried out, the result of which is shown in FIG. 3.

On the diagram in Figure 3, the rate in seconds / day is plotted on the ordinate and the oscillation amplitude in degrees on the abscissa. The four curves C1 to C4 correspond respectively to four vertical positions of the oscillator spaced 90 ° apart. In these four vertical positions, respectively, the force of gravity is directed along the semi-axis (O, -Y), the semi-axis (O, X), the semi-axis (O, -X) and the semi-axis. axis (O, Y). Curves C2 and C3 are merged taking into account the symmetry of the oscillator with respect to the Y axis. It can be seen that the operating difference between these vertical positions is minimal for an oscillation amplitude of about 12 ° and that it is high for larger amplitudes, in particular for the amplitude of 30 °, which means that at large amplitudes the oscillation frequency depends quite strongly on the orientation of the oscillator with respect to gravity . However, while small amplitudes have the advantage of reducing the effect of the non-linearity of the elastic return torque on isochronism, they also have drawbacks. In particular, they make it more difficult, if not impossible, to maintain oscillations using a conventional escapement such as a Swiss lever escapement. We may therefore wish to increase the amplitude of oscillation to values of 25 ° or 30 ° for example.

To increase the amplitude of oscillation without degrading the performance in terms of sensitivity to gravity, the invention provides for unbalancing the balance 2 so that its center of mass M is distinct from the cross point O of the blades 5, 6 and therefore of the center of rotation of the balance 2, in orthogonal projection in any one of the planes P 1, P2. We observe in fact that moving the center of mass M on the Y axis from the point O, the oscillation amplitude is modified for which the rate difference between the various vertical positions of the oscillator is minimal. This is illustrated in Figures 4 and 5 which were obtained with the same parameters as for Figure 3 but with a center of mass M of the balance 2 located on the Y axis at a distance DU from point O equal to 30 pm (corresponding at an unbalance of 15 nN.m) for FIG. 4, and at a distance DU from point O equal to 50 μm (corresponding to an unbalance of 25 nN.m) for FIG. 5. In FIG. 4, the amplitude of oscillation at which the frequency is least dependent on the orientation of gravity is about 24 °. In Figure 5, it is around 30 °. Figures 4 and 5 illustrate the effect of a displacement of the center of mass M on the semi-axis (O, Y). One can of course move the center of mass M on the semi-axis (O, -Y) if a reduction in the oscillation amplitude is desired.

FIG. 6 shows the relationship between the oscillation amplitude giving the minimum operating difference between the four aforementioned vertical positions of oscillator 1 and the unbalance of balance 2. It can be seen that for each oscillation amplitude we can find an unbalance, more exactly a position of the center of mass M of the balance 2 on the Y axis, which corresponds to it.

In general, in the invention, the distance DU between the center of mass M of the balance 2 and the crossing point O is preferably at least 1.4 μm, more preferably at least 2 μm, more preferably at least 5 µm, more preferably at least 10 µm, more preferably at least 20 µm, more preferably at least 40 µm. The unbalance, for its part, is preferably at least 0.7 nN.m, more preferably at least 1 nN.m, more preferably at least 2.5 nN.m, more preferably at least 5 nN.m, more preferably at least 10 nN.m, more preferably at least 20 nN.m, in absolute value.

In practice, after having chosen an oscillation amplitude, the unbalance of balance 2 is adjusted to minimize the rate difference between the positions vertical at this oscillation amplitude. The adjustment can be carried out by removing material from the balance 2, for example by milling or laser machining, or by adding material to the balance 2, for example by a deposition technique. Alternatively or cumulatively, the unbalance can be adjusted by means of an adjustment device carried by the balance 2.

An example of such an adjustment device is shown in Figures 1 and 2. It comprises a support 7 integral with the balance 2 and preferably monolithic with the latter. This support 7 extends radially from the internal face of the balance 2 facing the virtual axis of rotation. Two pins 8, 9 integral with the support 7 and preferably monolithic therewith are surrounded by, and serve as guides for, a frame 10 movable in translation relative to the support 7 along the Y axis. less of the pins 8, 9 has a larger diameter than the internal width of the frame 10 to elastically deform its two long sides and thus maintain it in position by elastic clamping. Applying sufficient force to the frame 10 in the direction of the Y axis moves the frame 10 to modify the unbalance of the balance 2. One or more recesses may be made on the balance 2 to compensate for the imbalance caused by the balance. support 7, the pins 8, 9 and the frame 10 so that, in a determined position of the frame 10, for example a position in which it abuts against one of the two pins 8, 9, the unbalance of the balance 2 is substantially zero. A displacement of the frame 10 then unbalances the balance 2 by moving its center of mass M along the Y axis from point O, allowing precise adjustment of the unbalance.

Adjusting the unbalance of balance 2 modifies the moment of inertia of the latter. The balance 2 can therefore also carry weights which will be used to adjust the moment of inertia, in a manner that is conventional in itself.

Alternatively to the adjustment device 7-10 as illustrated, the balance 2 could carry on its periphery one or more adjustment screws, for example one or two screws oriented along the Y axis, the adjustment being carried out by screwing more or minus these screws in the balance 2. FIGS. 7 and 8 show an oscillator 1 'according to another embodiment of the invention, in which the unbalance adjustment device is located in the center of the oscillator in order to modify the moment of inertia of the balance 2 as little as possible. and facilitate the adjustment of this moment of inertia by means of weights carried by the balance 2. The balance 2 here comprises a rim 2a and a diametral arm 2b. The diametral arm 2b is interrupted in its central part to allow the blades 5, 6 to pass through. In a variant shown schematically in dotted lines in FIG. 7, the two segments of the diametral arm 2b could be connected by a concave connection 2c on which s 'would stop the blades 5, 6, the crossing point of which would then be closer to the balance 2 than to the support 3.

In this embodiment of Figures 7 and 8, the unbalance adjustment device is mounted on the diametral arm 2b. It includes a support 11 fixed on top of the diametral arm 2b and carrying a central stud 12 centered on the virtual axis of rotation of the balance 2. The unbalance adjustment device further comprises an adjustment part 13 placed on the support 11. and having a slot 14 extending along the Y axis mentioned above, slot 14 which is crossed by the central stud 12 and by two tenons 15 driven into the support 11. The central stud 12 has a diameter large enough to elastically deform the slot 14 in order to hold the adjustment part 13 in position by elastic clamping. The two tenons 15 guide the adjustment part 13 in translation along the Y axis when sufficient force is applied to this part 13 to adjust the unbalance of the balance 2.

To achieve the desired amplitude of oscillation in the watch movement that oscillator 1, 1 ’is intended to equip, we can play on the dimensions of the movement's mainspring. These dimensions can be chosen so that the oscillator 1, 1 ’oscillates at the desired amplitude when the mainspring is fully charged.

The pendulum assembly 2 - support 3 - flexible pivot 4 of oscillator 1, 1 'can be made of different materials, for example silicon, silicon covered with oxide, glass, sapphire, quartz, metallic glass, a metal or alloy such as nickel, nickel alloy, steel, beryllium copper or nickel silver. Depending on the material chosen, it can be obtained by etching (in particular deep reactive ionic etching called DRIE), LIGA, milling, electroerosion, molding or the like. The set 2, 3, 4 can be monolithic.

It goes without saying that the present invention is applicable to other flexible pivots than separate cross blades, in particular to non-separate cross blades and to offset center of rotation (RCC) pivots.

Furthermore, the flexible pivot 4 could comprise, in addition to the elastic blades 5, 6, additional elastic blades, for example blades superimposed on the blades 5, 6 to increase its stiffness in the direction of the height. In general, in the invention, the Y axis is an axis of symmetry of the flexible pivot and is also an axis of symmetry for the points of junction of the flexible pivot to the balance and for the points of junction of the flexible pivot to the support, in orthogonal projection in a plane perpendicular to the virtual axis of rotation.

Claims

1. Method of adjusting a watch oscillator (1; 1 ') comprising a balance (2), a support (3) and a flexible pivot (4) connecting the balance (2) to the support (3) and guiding the balance (2) rotating with respect to the support (3) around a virtual axis of rotation, the flexible pivot (4) having, in orthogonal projection in a plane (P1; P2) perpendicular to the virtual axis of rotation, a axis of symmetry (Y) which is also an axis of symmetry for the points (5a, 6a) of junction of the flexible pivot (4) to the balance (2), characterized in that the unbalance of the balance (2) is adjusted so that, in orthogonal projection in said plane (P1; P2), the center of mass (M) of the balance (2) is substantially on the axis of symmetry (Y) and at a position distinct from that (O) of the 'virtual axis of rotation, the position (O) of the virtual axis of rotation not being modified by said unbalance adjustment, said position of the center of mass (M) being chosen so as to decrease, and preferably r At minimum, the dependence of the oscillation frequency on the orientation of gravity for a predetermined oscillation amplitude.

2. Method according to claim 1, characterized in that the adjustment of the unbalance of the balance (2) is carried out, in part at least, by means of an adjustment device (7-10; 11 -15) carried by the balance (2).

3. Method according to claim 2, characterized in that the adjustment of the unbalance of the balance (2) is carried out, in part at least, by moving at least one part (10; 13) of the adjustment device (7-10; 11) -15) along the axis of symmetry (Y).

4. Method according to any one of claims 1 to 3, characterized in that the adjustment of the unbalance of the balance (2) is carried out, in part at least, by removing or adding material on the balance (2).

5. Method according to any one of claims 1 to 4, characterized in that the flexible pivot (4) comprises first and second elastic blades (5, 6) extending in directions which intersect and are symmetrical with one another. on the other with respect to the axis of symmetry (Y) in orthogonal projection in said plane (P1; P2) perpendicular to the virtual axis of rotation.

6. Method according to claim 5, characterized in that the first and second elastic blades (5, 6) extend in two parallel planes to cross without contact.

7. Method according to claim 6, characterized in that, in orthogonal projection in said plane (P1; P2) perpendicular to the virtual axis of rotation, the point of intersection (O) of the first and second elastic blades (5, 6) ) is located about 87.3% of their length.

8. Method according to claim 6 or 7, characterized in that, in orthogonal projection in said plane (P1; P2) perpendicular to the virtual axis of rotation, the angle (a) between the first and second elastic blades (5 , 6) is between 68 ° and 76 ° and is preferably equal to about 71 °.

9. Method according to claim 5, characterized in that the first and second resilient blades (5, 6) extend in the same plane to physically intersect.

10. The method of claim 5, characterized in that the flexible pivot has an offset center of rotation.

11.Clock oscillator (1; 1 ') adjustable by the method according to any one of claims 1 to 10 and comprising a balance (2), a support (3) and a flexible pivot (4) connecting the balance (2) to the support (3) and guiding the balance (2) in rotation with respect to the support (3) about a virtual axis of rotation, the flexible pivot (4) presenting, in orthogonal projection in a plane (P1; P2) perpendicular to the virtual axis of rotation, an axis of symmetry (Y) which is also an axis of symmetry for the points (5a, 6a) of junction of the flexible pivot (4) to the balance (2), characterized in that the balance (2) carries at least one unbalance adjustment part (10; 13) movable along the axis of symmetry (Y).