EP2090941B1 - Mechanical oscillator - Google Patents

Description

Technical area

The present invention relates to mechanical oscillators, especially those which equip the timepieces. It relates, more particularly, such an oscillator with a device for adjusting and correcting its frequency.

State of the art

Conventional oscillators that equip mechanical timepieces conventionally comprise a spring element, or spiral, allowing the return to the neutral position of a regulating element, or balance. The energy dissipated by the oscillation is compensated by the application of a motor torque provided by a load spring, or barrel spring. However, this driving torque exerted by the mainspring varies over time depending on the load (or reassembly state) of the latter and, in most mechanical timepieces, especially when the cylinder is coupled directly. to the workings of the dynamic chain, this variation has the effect of modifying the amplitude of oscillation as well as, to a certain extent, the period of the oscillator. Such a modification can be translated, for some embodiments, by a deviation of one to several tens of seconds per day.

To compensate for the effect of motor torque variation, it has been proposed to use a device called a rocket (see GA Berner's "Professional Illustrated Dictionary of Watchmaking"), which helps to regulate the driving force. transmitted to the wheel by the mainspring. However, such a device is difficult to miniaturize and, for this reason, can not be really applied in mechanical watches.

Another correction device has been described in connection with FIG. 7 of the European patent application EP 1 736 838 in the name of the plaintiff. In this last document, it is proposed to act on the driving torque of the mainspring on a flexible member, which controls the active length. of an element that participates in the oscillation constant of the mechanical oscillator. As in the case of the rocket, such a device is not simple to implement. We also know by the patent CH 279 954 , a mechanical oscillator comprising an oscillating system formed of a rocker and its return spring and a frequency correction device. The corrector is based on the control of the active length of the return spring by a mechanism controlled directly by the rotation of the winding pin of the mainspring, which is a function of the engine torque.

However, none of these correction devices makes it possible to take into account the variations in torque that would be due to friction existing, for example, at the level of the various parts including the oscillator as well as the gear trains for transmitting torque to the latter.

In a quasi-permanent oscillation regime, that is to say when the intensity of the engine torque varies sufficiently slowly with respect to the oscillation period, it can be assumed that the induced period variation is equivalent to that which would be induced by a nonlinear booster torque depending on the deflection. Such an isochronism defect can be corrected by a non-linearity of the return spring.

Disclosure of the invention

A first object of the invention is to provide an oscillator for a mechanical watch equipped with means for correcting the isochronism defect induced by the variations of the engine torque of the mainspring, according to a principle of correction as a function of the amplitude.

More generally, the object of the invention is to be able to maintain a constant frequency of the oscillator, in its useful range of operation, based on the amplitude variations to correct an effect comparable to a non-linearity of the spring of recall.

Concretely, the present invention relates to a mechanical oscillator of the type comprising an oscillating system mounted on a frame and formed of a rocker and its return spring. This oscillator further comprises a frequency correction device formed of at least a first and a second element respectively fixed to said frame and to the oscillating system, the first of these elements comprising a resilient flexible blade fixed by one of its ends and the second being a connecting member weighing, during part of the oscillation, against the free end of said blade.

The oscillator according to the invention may comprise only one flexible blade but, advantageously, it comprises two acting in opposition on the connecting member and offset, with respect to each other, a half-cycle of the oscillation, in order to symmetrize the characteristic of the return correction as a function of the deflection.

In both cases, the single blade - or both blades - is fixed - or are fixed - to the frame via an interface allowing a position adjustment in translation and rotation.

According to a first position adjustment, the single blade - or both blades - is - or are - in contact, at a non-zero pressure, with the connecting member when the balance is in the neutral position, that is to say say when its angle relative to its rest position is equal to zero, so as to obtain an increase in the frequency when the amplitude decreases (negative correction).

According to a second position adjustment, the single blade - or the two blades - is - or is not - in contact, at a non-zero pressure, with the connecting member when the balance is in a neutral position, so that to obtain an increase of the frequency when the amplitude increases (positive correction).

The connecting member may be fixed to the balance either directly or by an intermediate piece of the return spring oscillating at a reduced deflection angle relative to that of the balance.

The oscillator may advantageously comprise a fixed stop located opposite the connecting member for a deflection angle of the balance relative to its rest position equal to zero, and intended to exert a prestress on said blade when said connecting member n is not in contact.

Brief description of the drawings

• la figure 1 est un schéma de principe d'un oscillateur selon l'invention, avec le dispositif de correction agissant directement sur le balancier ;
• la figure 2 montre une courbe du moment de correction de l'oscillateur en fonction de l'angle de déflexion, pour une correction négative ;
• la figure 3 montre une courbe du moment de correction de l'oscillateur en fonction de l'angle de déflexion, pour une correction positive ;
• la figure 4 est un schéma de principe d'un oscillateur selon l'invention, avec le dispositif de correction agissant directement sur une pièce intermédiaire oscillant à amplitude réduite ;
• la figure 5 illustre une variante de l'oscillateur incorporant une butée supplémentaire ; et
• la figure 6 montre une courbe du moment de correction de l'oscillateur de la figure 5 en fonction de l'angle de déflexion.

Other objects, features and advantages of the present invention will be better understood on reading the following description of particular embodiments, said description being made purely for illustrative purposes and in connection with the accompanying drawings in which:

• the figure 1 is a block diagram of an oscillator according to the invention, with the correction device acting directly on the pendulum;
• the figure 2 shows a curve of the moment of correction of the oscillator as a function of the angle of deflection, for a negative correction;
• the figure 3 shows a curve of the moment of correction of the oscillator as a function of the angle of deflection, for a positive correction;
• the figure 4 is a block diagram of an oscillator according to the invention, with the correction device acting directly on an oscillating intermediate piece with reduced amplitude;
• the figure 5 illustrates a variant of the oscillator incorporating an additional stop; and
• the figure 6 shows a curve of the moment of correction of the oscillator of the figure 5 depending on the angle of deflection.

Embodiments of the invention

The oscillator for mechanical watch according to the invention is particularly applicable to the exhaust system described in the document EP 1 736 838 , already cited, in particular in Figure 2a. We recognize a rocker 1 (partially shown) oscillating about its axis 2 and its return spring, or spiral spring, 3 fixed between the arm 1a of the beam and the frame 4 of the watch.

According to the teaching of the document EP 1 736 838 , an escape wheel 5 is driven by two elastic blades 6 and 7, connected to the arm 1a of the balance 1 by one end and whose other end, or pallet, engages in the teeth (not shown) of the wheel exhaust 5.

By oscillating, under the impulse of a driving torque delivered by a mainspring, the oscillating system (balance 1 and spiral 3) rotates the escapement wheel 5 at a rate which must be as regular as possible, because he determines the accuracy of the watch he controls. However, as mentioned above, mechanical watches and, more particularly, those equipped with an exhaust system as just described, suffer from a defect of isochronism that can result in a difference of about ten seconds a day for a variation of the engine torque of ten percent, corresponding to an amplitude variation of five percent. Such a difference is due to the fact that, unlike free escapement systems, such as those known as Swiss anchor, the particular anchor of the above-mentioned EP document is, by means of its elastic blades, in permanent contact with the wheel. 5. During its discharge, the driving torque of the mainspring decreases, resulting in a corresponding decrease in oscillator oscillation amplitude (to maintain the balance with the dissipated power) and also in its frequency by the effect of permanent contact. For small variations, corresponding to the operating range, it can be assumed that the frequency varies linearly with the variations of the motor torque.

The principle of the invention is to provide the oscillator with a correction device 20 having a frequency characteristic inverse to its own in the operating range.

For this purpose, the correction device 20 comprises two resilient blades 9 and 10 which bear, in opposition, on a connecting member or stop 8, T-shaped, connected to the arm 1 a of the balance 1, to the nearest of its center of rotation. These elastic blades 9 and 10 are, via lugs 12 and 13, linked at their other end to a fixing and adjusting interface 11 by means of locking screws 15 and 16, respectively.

The interface 11, secured to the frame 4 by a screw 17, can be positioned relative to the axis 2 of the beam by moving it along a slide 14 of the frame against which it is applied under the action of a spring 18.

The interface 11 makes it possible to adjust the position of the fulcrum of the elastic blades 9 and 10 on the connecting member 8 and, therefore, their effective length and their stiffness. The lugs 12 and 13 make it possible to adjust the orientation of these elastic blades with respect to the stop and, thereby, to adjust the angle of deflection of the rocker relative to its rest position for which they come in contact or leave. this same stop. The position adjustment thus makes it possible to adjust the amplitude of the frequency variation, while the adjustment of the contact angle makes it possible to adjust the useful deflection range as well as the sign of the non-linearity.

According to the embodiment of the figure 1 , for small amplitudes of the balance, the two elastic blades 9 and 10 are in contact with the stop 8 and they constitute an additional spring which acts on the balance in addition to the spiral spring 3. If the amplitude of the oscillations increases, it happens a moment when one of the blades ceases to be in contact with the stop, thus modifying the elastic constant of the overall return spring. This creates a negative non-linearity (i.e., a decrease in slope) in the response of this global return spring, as will be discussed later with respect to the figure 2 , and it is this non-linearity that makes it possible to compensate for the positive isochronism defect mentioned above (that is to say, a frequency which increases when the amplitude increases).

If we consider an elastic blade whose end is on the path of the trajectory of an oscillating stop, the blade being substantially perpendicular to this trajectory, when the deflection D passes through a value Φ ₀ (point A or B of the figure 2 ), the blade can either come into contact with the stop (the additional spring becomes active in parallel with the spiral spring) or leave it (the additional spring becomes inactive). This results in a break of the return characteristic (or non-linearity). Depending on the relative importance of the active and inactive phases during the oscillation, the effect of the (or) blade (s) will be more or less felt, which affects the average stiffness during the oscillation time and therefore, the oscillation frequency.

In the case of the aforementioned EP document, the frequency of the oscillator decreases as the maintenance torque and the oscillation amplitude decrease. It is therefore necessary to apply a negative compensation, that is to say produce a lower average return stiffness at high amplitudes.

The figure 2 shows the curve of the additional return moment generated by the blades as a function of the deflection angle of the balance relative to its rest position, that is to say the variation of the torque ΔM as a function of the deflection D. this figure, the dotted upper curve is relative to the blade 10, the dotted lower curve is relative to the blade 9 and the solid line curve is relative to the combined effect of the two blades.

For small deflections, either between the contact limit angles A and B, the global curve versus deflection has a slope of 2.ΔK (K is the elastic constant of the global return spring) due to the action of two elastic strips 9 and 10 added to that of the spiral spring 3. For a deflection beyond point B or below point A, the slope of the response curve is only ΔK, which corresponds to the fact that there is only one elastic blade (9 or 10) bearing on the abutment 8.

In the deflection range A-B, the slope 2.ΔK is constant. When the oscillation of the balance is within this range, the frequency variation Δf, with respect to the frequency f in the absence of the corrector device, is therefore constant and is equal to Δf = f.ΔK / K. When the amplitude of oscillation exceeds the AB interval, the torque correction ΔM as a function of deflection is no longer linear and the average slope lies between 2.ΔK at small amplitudes and ΔK at large amplitudes. The corresponding frequency variation changes from Δf = f.ΔK / K to small amplitudes at Δf = f.ΔK / 2.K at large amplitudes. The useful area of correction is in the vicinity, but outside, of the interval A-B.

When the mainspring discharges, the oscillation amplitude decreases and the correction frequency variation Δf increases, which makes it possible to compensate for the frequency decrease that the uncorrected oscillator would have under the influence of the driving torque. .

$${\mathrm{\Delta K}}_{\mathrm{equ}}\mathrm{=}\mathrm{\Delta K}\left(1+{\mathrm{\Phi }}_{\mathrm{0}}/\mathrm{\Phi }\right)\mathrm{,}\mathrm{pour\; \Phi }\ge {\mathrm{\Phi }}_{\mathrm{0}},$$

où ΔK représente la rigidité angulaire d'une lame en appui sur sa butée. Cette expression a le mérite de représenter assez bien la correction, tout en restant très simple. La sensibilité à la correction ΔK_equ/ΔK est d'autant plus élevée que l'amplitude Φ est proche de Φ₀.
En prenant les valeurs Φ = 35° et Φ₀ = 30°, cela donne : $${\mathrm{\Delta K}}_{\mathrm{equ}}\left(\mathrm{30}\mathrm{°}\right)\mathrm{-}{\mathrm{\Delta K}}_{\mathrm{equ}}\left(\mathrm{35}\mathrm{°}\right)\mathrm{=}\mathrm{0.14}\mathrm{K}\mathrm{.}$$

Cette valeur permet de calculer la correction de fréquence relative : $$\mathrm{d}\left(\mathrm{\Delta f}\right)\mathrm{/}\mathrm{f}\mathrm{=}\mathrm{d}\left({\mathrm{\Delta K}}_{\mathrm{equ}}\right)\mathrm{/}\mathrm{2}\mathrm{K}\mathrm{=}\mathrm{0.07.}\mathrm{\Delta K}\mathrm{/}\mathrm{K}\mathrm{.}$$

In concrete terms, if one has an angular inertia balance I = 2.5 10 ^-9 kg.m ² , corresponding to a diameter of 10 mm for a mass of 0.1 gr, oscillating at the frequency f of 10 Hz, this determines a return constant K = 4.π ² .f ² . I = 10 ^-5 Nm ² / radian. The amplitude of oscillation Φ depends on the state of charge of the mainspring. Assuming an amplitude of the oscillator of 35 ° when the mainspring is fully loaded and an amplitude of 30 ° when unloaded, this corresponds to an amplitude variation of about 15% and a variation in the maintenance time of around 30%. It will be posited that Φ ₀ corresponds to the amplitude of the points A and B and will approximate the correction by an equivalent linear spring whose constant of return ΔK _equ depends on the amplitude Φ according to the following formulas (curve in mixed line): $${\mathrm{\Delta K}}_{\mathrm{equ}}\mathrm{=}\mathrm{2}\mathrm{\cdot }\mathrm{\Delta K}\mathrm{,}\mathrm{for\; \Phi }\mathrm{<}{\mathrm{\Phi }}_{\mathrm{0}},$$

$${\mathrm{\Delta K}}_{\mathrm{equ}}\mathrm{=}\mathrm{\Delta K}\left(1+{\mathrm{\Phi }}_{\mathrm{0}}/\mathrm{\Phi }\right)\mathrm{,}\mathrm{for\; \Phi }\ge {\mathrm{\Phi }}_{\mathrm{0}},$$

where ΔK represents the angular rigidity of a blade resting on its abutment. This expression has the merit of representing the correction fairly well, while remaining very simple. The sensitivity to the correction ΔK _equ / ΔK is even higher than the amplitude Φ is close to Φ ₀ .
Taking the values Φ = 35 ° and Φ ₀ = 30 °, this gives: $${\mathrm{\Delta K}}_{\mathrm{equ}}\left(\mathrm{30}\mathrm{°}\right)\mathrm{-}{\mathrm{\Delta K}}_{\mathrm{equ}}\left(\mathrm{35}\mathrm{°}\right)\mathrm{=}\mathrm{0.14}\mathrm{K}\mathrm{.}$$

This value is used to calculate the relative frequency correction: $$\mathrm{d}\left(\mathrm{.DELTA.f}\right)\mathrm{/}\mathrm{f}\mathrm{=}\mathrm{d}\left({\mathrm{\Delta K}}_{\mathrm{equ}}\right)\mathrm{/}\mathrm{2}\mathrm{K}\mathrm{=}\mathrm{0.07.}\mathrm{\Delta K}\mathrm{/}\mathrm{K}\mathrm{.}$$

Il faut exprimer que la somme des deux valeurs précédentes est nulle, c'est-à-dire que la correction compense l'erreur. On obtient alors : $$\mathrm{0.07.}\mathrm{\Delta K}\mathrm{/}\mathrm{K}\mathrm{-}\mathrm{3}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}\mathrm{=}\mathrm{0}\mathrm{,}\mathrm{dʹoù\; \Delta K}\mathrm{=}\mathrm{4.3}{\mathrm{10}}^{\mathrm{-}\mathrm{3}}\mathrm{.}\mathrm{K}\mathrm{=}\mathrm{4.3}{\mathrm{10}}^{\mathrm{-}\mathrm{8}}\mathrm{Nm}\mathrm{/}\mathrm{radian}\mathrm{.}$$

Si on exprime ΔK en fonction des paramètres de lame, on peut écrire : $$\mathrm{\Delta K}\mathrm{=}\left(\left(\mathrm{E}\mathrm{.}\mathrm{b}\mathrm{.}{\mathrm{h}}^{\mathrm{3}}\right)\mathrm{/}\left(\mathrm{4.}{\mathrm{L}}^{\mathrm{3}}\right)\right)\mathrm{.}{{\mathrm{R}}^{\mathrm{2}}}_{\mathrm{but}}\mathrm{,}$$

où E est le module d'Young, b est la largeur de la lame, h son épaisseur, L la longueur utile et R_but le rayon de pivotement de la butée. Typiquement, E vaut 200'000 N / mm² (pour de l'acier), b est de l'ordre de 0.5 mm, L vaut 8 mm et R_but vaut 1 mm. On peut donc en déduire, en utilisant les formules précédentes, que l'épaisseur h de la lame est de l'ordre de 10^-5 m. Une telle lame peut être découpée dans une feuille de 10 microns d'épaisseur et pliée pour permettre la fixation.It will be assumed that the variation of the course to be corrected was measured at 5 sec / day per degree of amplitude, that is to say 25 sec / day for 5 degrees. In relative frequency, this gives: $$\mathrm{d}\left(\mathrm{.DELTA.f}\right)\mathrm{/}\mathrm{f}\mathrm{=}-25/86\mathrm{\text{'}}\mathrm{400}=-3{10}^{-4}\mathrm{.}$$

It must be stated that the sum of the two previous values is zero, that is, the correction compensates for the error. We then obtain: $$\mathrm{0.07.}\mathrm{\Delta K}\mathrm{/}\mathrm{K}\mathrm{-}\mathrm{3}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}\mathrm{=}\mathrm{0}\mathrm{,}\mathrm{where\; \Delta K}\mathrm{=}\mathrm{4.3}{\mathrm{10}}^{\mathrm{-}\mathrm{3}}\mathrm{.}\mathrm{K}\mathrm{=}\mathrm{4.3}{\mathrm{10}}^{\mathrm{-}\mathrm{8}}\mathrm{nm}\mathrm{/}\mathrm{radian}\mathrm{.}$$

If ΔK is expressed according to the blade parameters, we can write: $$\mathrm{\Delta K}\mathrm{=}\left(\left(\mathrm{E}\mathrm{.}\mathrm{b}\mathrm{.}{\mathrm{<figure-callout\; id="3"\; label="h"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">h</figure-callout>}}^{\mathrm{3}}\right)\mathrm{/}\left(\mathrm{4.}{\mathrm{The}}^{\mathrm{3}}\right)\right)\mathrm{.}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}^{\mathrm{2}}}_{\mathrm{goal}}\mathrm{,}$$

where E is the Young's modulus, b is the width of the strip, its thickness h, the effective length L and R _purpose the pivoting radius of the stop. Typically, E is 200,000 N / mm ² (for steel), b is of the order of 0.5 mm, L = 8 mm and R _goal is 1 mm. It can therefore be deduced, using the preceding formulas, that the thickness h of the blade is of the order of 10 ^-5 m. Such a blade can be cut into a sheet 10 microns thick and folded to allow attachment.

The figure 3 illustrates a variant of adjustment of the orientation of the elastic blades, in which they are positioned in such a way that they are not in contact with the stop when the balance is in the neutral position (deflection angle equal to zero) but contact for a deflection angle A or B. That is to say that ΔM is zero in the range between A and B and slope ΔM outside this range. Consequently, the frequency variation Δf is the opposite of that described above and allows therefore to correct a negative dependence as a function of the driving torque.

The correction device according to the invention can operate with a single elastic blade. In this case, the overall curve (solid line) of the torque ΔM merges with one of the two dotted curves of the Figures 2 and 3 . The answer is asymmetrical, the correction operating only on a single alternation of the oscillation of the balance.

According to yet another variant, represented in figure 4 , in which the elements common to the figure 1 have been designated by the same reference numbers, the connecting member 8 is fixed, not on the rocker 1, but on an intermediate piece 19, T-shaped and serving as an anchor, whose horizontal bar 19a (on the figure) is the base of the elastic blades 6 and 7 and whose vertical bar 19b (in the figure) is mounted, free to oscillate, on the axis 2 of the balance 1. The spiral spring 3 is then fixed between the arm 1 a pendulum and the vertical bar 19b, which is subject, moreover, to the action of two return springs 21, acting in opposition.

The provision of the figure 4 has the effect of reducing the angle of oscillation of the anchor 19 relative to that of the balance 1, which allows, on the one hand, to use more rigid blades and, on the other hand, to avoid excessive deformation and friction.

The figure 5 shows yet another variant with a fixed stop 22 linked to the frame 4 facing the abutment 8 for a deflection angle of the balance 1 relative to its rest position equal to zero. This stop serves to connect and disconnect under prestressing the elastic blades 9 and 10 of the movable connecting member 8.

As shown in figure 6 , comparable to Figures 2 and 3 such an arrangement makes it possible to modify the position of the points A and B in A 'and B', while adding a jump to the change of slope, which allows a better optimization of the deflection domain and the frequency variation. This arrangement also makes it possible to avoid the appearance of parasitic oscillations of the blades when they are disconnected.

Thus is proposed an oscillator, advantageously usable in a mechanical timepiece, which is provided with means for correcting the defect of isochronism induced by the variations of the engine torque. The correction performed is all the more effective as the amplitude-defect isochronism equilibrium is stable, which is the case of an elastic suspension balance such as, for example, that of the figure 5 of the document EP 1 736 838 , already quoted.

Claims (10)

1. A mechanical oscillator comprising an oscillating system, mounted on a frame (4) and comprising a balance (1) and its return spring (3), and further comprising a frequency correction device (20), characterized in that said frequency correction device (20) comprises at least first and second elements fixed to said frame (4) and said oscillating system, respectively, the first of these elements comprising at least one flexible elastic strip (9, 10) fixed by one of its ends and the second being a connecting organ (8) designed to weigh, during part of the oscillation, against the free end of said strip.
2. The oscillator according to claim 1, characterized in that said strip (9, 10) is designed to be in contact, according to a non-zero pressure, with said connecting organ (8) for a deflection angle of the balance (1) in relation to its idle position equal to zero.
3. The oscillator according to claim 1, characterized in that said strip (9, 10) is designed to be not in contact with said connecting organ (8) for a deflection angle of the balance (1) in relation to its idle position equal to zero.
4. The oscillator according to claim 1, characterized in that the first of said elements comprises two elastic strips (9, 10) designed to act in opposition bearing on the connecting organ (8) and offset, in relation to each other, by a half-vibration of the oscillation.
5. The oscillator according to claim 4, characterized in that said strips (9, 10) are designed to be in contact, according to a non-zero pressure, with said connecting organ (8) for a deflection angle of the balance (1) in relation to its idle position equal to zero.
6. The oscillator according to claim 4, characterized in that said strips (9, 10) are designed to be not in contact with said connecting organ (8) for a deflection angle of the balance (1) in relation to its idle position equal to zero.
7. The oscillator according to anyone of claims 1 to 6, characterized in that said connecting organ (8) is fixed directly to said balance (1).
8. The oscillator according to anyone of claims 1 to 6, characterized in that said connecting organ (8) is fixed to said oscillating system by an intermediate part (19) of the return spring (3) oscillating according to a deflection angle reduced relative to that of the balance (1).
9. The oscillator according to anyone of claims 1 to 8, characterized in that it comprises a fixed stop (22) located across from the connecting organ (8) for a deflection angle of the balance (1) in relation to its idle position equal to zero, and designed to exert a pre-stressing on said strip when said connecting member is not in contact.
10. The oscillator according to anyone of preceding claims, characterized in that said elastic strip (9, 10) is fixed to the frame (4) via an interface (11) allowing adjustment of its position in translation and in rotation.

Images