HK1260951B - Spring balance oscillator for timepiece - Google Patents

Description

The present invention relates to a spiral-swing oscillator for a watchpiece, especially one with an improved isochronism. Isochronism means variations in the stroke according to the swing amplitude and the position of the watchpiece. The smaller these variations, the more isochronic the oscillator.

The gait of a swing-spiral oscillator is equal to the sum of the gait due to the balance of the swing and the gait due to the spiral. In the vertical position, the balance of the swing disrupts the regularity of the oscillations. To minimize this disruption, it is customary to rebalance the swing by milling or by means of a screw adjusting the swing. The gait variations due to the spiral are, however, caused mainly by the eccentric development and weight of the spiral.

In recent years, improvements have been made to the geometry of the spirals to reduce their contribution to the lack of isochrony of the oscillator. Patent applications EP 1445670, EP 1473604, EP 2299336 and WO 2014/072781 describe spirals with variations in stiffness and/or step along their blades. Modern manufacturing techniques and materials such as silicon allow such spirals to be obtained. However, this approach of treating the spiral walk separately from the balance ball is almost impossible due to the possible limit of gain in overall isochrony of the oscillator.

The application for a patent WO 2014/001341 describes a process for determining and modifying a buffer characteristic of an oscillator or spiral balancing assembly.

The present invention is intended to propose another approach to improve the isochronism of a spiral-swing oscillator and in particular to reduce the drift between its various vertical positions.

To this end, a watch movement oscillator is provided, comprising a balance and a spiral, the balance having an imbalance, characterized by the imbalance of the balance and the geometry of the spiral being such that (a) the curves representing the oscillator's movement due to the weight of the coil in relation to the amplitude of oscillation of the coil in at least four vertical positions of the coil spaced 90° apart, preferably in all vertical positions, each pass through the zero value at an oscillator's movement amplitude between 200° and 240°, preferably between 210° and 230°, preferably between 215° and 225°;

Thus, the present invention proposes to design the balance and the spiral in such a way that the gait due to the balance failure of the balance and the gait due to the weight of the spiral compensate at least partially and preferably substantially entirely in all or almost all of the normal operating range of the balance. Contrary to the state of the art, the present invention does not seek to cancel the balance's gait, it may even be high. Similarly, it does not seek to minimize the gait due to the weight of the spiral. This new approach allows very small gait gaps to be obtained between the different vertical positions of the oscillator and thus improves the precision of the watchpiece.

In practice, the amplitude of oscillation at which the curves representing the oscillator's movement due to the weight of the spiral pass through zero may be slightly different from one curve to another.

In preferential embodiments, the balance defect and the geometry of the coil are such that the mean slope of each curve among the said curves representing the oscillator's movement due to the balance defect is approximately the same absolute value as the mean slope of the corresponding curve among the said curves representing the oscillator's movement due to the weight of the coil, in the range of oscillation amplitudes from 150° to 280°.

The balance failure and the geometry of the coil may be such that the maximum deviation of the oscillator's movement due to balance failure and coil weight between these vertical positions in the range of oscillation amplitudes from 150° to 280° is less than 4 seconds/day, or even 2 seconds/day, or even 1 second/day, or even 0.7 seconds/day.

The distance between the inner end of the coil and the centre of rotation of the coil may be greater than 500 μm, or even 600 μm, or even 700 μm.

The balance bearing may be larger than 0,5 μg.cm or even 1 μg.cm.

In typical embodiments, the inner spiral has a rigid portion and/or is conformed to a Grossmann curve.

In other embodiments, the spiral has a rigidity and/or pitch that varies continuously over at least several spires.

Further features and advantages of the present invention will be apparent from the following detailed description made by reference to the attached drawings in which: Figure 1 shows a spiral-swing oscillator according to a first embodiment of the invention;Figure 2 shows the spiral of the oscillator according to the first embodiment of the invention;Figure 3 shows the oscillator's swing according to the invention, seen from the other side of Figure 1;Figure 4 shows curves representing the oscillator's movement due to the weight of the spiral according to the first embodiment of the invention;Figure 5 shows curves representing the movement of the oscillator due to the balance of the balance due to the first embodiment of the invention;Figure 6 shows curves representing the movement of the oscillator due to the balance of the balance due to the weight of the balance and the weight of the oscillator according to the other embodiment of the invention;Figure 7 shows the spiral of the oscillator's movement due to the weight of the balance;Figure 8 shows the movement of the spiral oscillator's swing according to the second embodiment of the invention;Figure 9 shows the movement of the spiral oscillator's curves due to the weight of the balance due to the balance of the balance;Figure 8 shows the movement of the spiral oscillator's movement due to the weight of the balance of the balance due to the second embodiment of the invention;Figure 9 shows the movement of the spiral oscillator's swing according to the second embodiment of the balance;Figure 8 shows the weight of the balance of the balance due to the second embodiment of the balance.

For the purposes of Figures 1 to 3, a spiral-swing oscillator according to a first embodiment of the invention, for a watch movement intended to equip a watchmaking part such as a wristwatch or a pocket watch, comprises a swing 1 mounted on a swing axis 2 and a spiral 3 whose inner end 3a is fixed to the swing axis 2 by means of a coil 4 and whose outer end 3b is fixed to the movement of the building by means of one or more organs.The outer end 3b could, however, be fixed to the barrel in another way, e.g. by means of a traditional piton. The assembly comprising the spiral 3, the virole 4 and the rigid attachment part 5 may be monolithic and made of e.g. silicon or diamond. The balance axis 2 also carries a tray or double tray 7 which carries itself a tray peg 8 and is part of a flap used to maintain and count the oscillations of the oscillator.

The spiral 3 does not have the traditional shape of a constant-blade Archimedean spiral. The geometry of the spiral is irregular in that it has a section and/or step that varies along its blade. In the example shown, a portion 3c of the outer spiral (hereinafter external rigid portion ) and a portion 3d of the inner spiral (hereinafter internal rigid portion ) have a larger section, hence greater rigidity, than the rest of the blade forming the spiral 3.The step of the spiral 3 is constant from a 3e' point on its inner spiral to a 3e point on its outer spiral. From the inner end 3a to 3e' point the step increases slightly. After the 3e point the step increases sharply, with the outer spiral deviating from the penultimate spiral relative to the Archimedean spiral path to prevent these two spires from touching during the expansions of the spiral.

In other variants, instead of changing the section of the spiral blade only locally at the level of the inner and outer spire, one could continuously change the section along the whole blade or on several spires, i.e. on a number (not necessarily whole) of spires greater than 1, e.g. equal to 2 or more. One could also continuously vary the pitch of the spiral blade or along several spires, by replacing or varying the blade. One could also change the section of the spiral blade in a more or less continuous way, for example by changing its length or thermal treatment.

The speed of a swing-spiral oscillator is equal to the sum of the speed due to the swing and the speed due to the spiral. The swing influences the speed in the vertical positions only. The speed of the swing due to the swing is caused by the balance of the swing, i.e. because, due to manufacturing tolerances, the centre of gravity of the swing is not on the axis of rotation of the swing.As we shall see later, the balance's ballast A and the angular position θb of its centre of gravity G (defined for example with respect to a swing arm, in projection in a plane perpendicular to the rotation axis 2, as shown in Figure 3) are parameters for adjusting the gait due to the balance of the balance.The eccentric development of the spiral causes varying reactions in the bearings of the balance axis at all positions of the oscillator; in addition, in the vertical positions, the shift of the centre of gravity of the spiral caused by the eccentric development of the latter creates a defect in isochronism due to the weight of the spiral applied to that centre of gravity. This disturbance is different from the elastic gravitational sagging effect of the spiral, which is neglected in the present invention.

According to the theory, the curve representing the oscillator's motion due to the balance of the balance due to the oscillation amplitude of the balance, in any vertical position of the balance, passes through the zero value (i.e. crosses the axis of the abscissa) at an oscillation amplitude of 220°.

The present invention is based on the finding that it is possible to choose parameters A, θb of the pendulum and spiral geometries so that the gait due to the imbalance of the pendulum and the gait due to the weight of the spiral compensate each other, thus reducing, or even making substantially zero, the gait differences between the different vertical positions.

In the example in Figure 2, the spiral 3 has 14 spirals. The eo-thickness of the blade forming the spiral, measured along a radius from the centre of rotation O of the spiral, is 28,1 μm, except along the outer rigid portion 3c and the inner rigid portion 3d where it is larger. The spiral pitch between the 3e' and 3e points is 86,8 μm. The R-radius of the spiral 4, or the distance between the inner end 3a of the spiral and the centre O, defined as the radius of the circle O passing through the centre (at half the eo-thickness) of the inner end 3a,The maximum thickness ed of the inner rigid portion 3d, measured along a radius from the centre of curvature Cd of the beginning of the inner spiral (between points 3a and 3e'), is 73 μm. The angular extent θd of the inner rigid portion 3d, measured from the centre of curvature Cd, is 78°. Its angular position αd (position of its centre relative to the inner end 3a), measured from the centre of curvature Cd, is 82°. The maximum thickness of the outer rigid portion 3c, measured along a radius from the centre of curvature Cc of the terminal part of the 3f spiral 3, is 82°.is 88 μm. The angular extent θc and the angular position αc (position of its centre in relation to the outer edge 3b of the spiral 3) of the outer rigid portion 3c, measured from the centre of curvature Cc, are 94° and 110° respectively.

The movement of the oscillator 1, 2, 3 due to the weight of the spiral 3 was shown in Figure 4 as a function of the oscillation amplitude of the pendulum 1 in each of four vertical positions of the oscillator 90° apart, namely a high vertical position VH (3 hours up) (curve S1), a straight vertical position VD (12 hours up) (curve S2), a left vertical position VG (6 hours up) (curve S3) and a low vertical position VB (9 hours up) (curve S4). The concept of the 'swing' is described in the book Traité de construction horlogère by M. Vermot, P. Bovay, D. Prongué et S. Dordor, published by the Presses polytechniques et universitaires romandes, 2011, where μ is the march, Ms is the mass of the spiral, L is the length of the spiral, E is the Young's modulus of the spiral, I is the quadratic moment of the spiral, g is the gravitational constant, θ is the elongation of the swing relative to its equilibrium position, θ0 is the amplitude of the swing relative to its equilibrium position, φ is the phase (θ = θ0 φ), yg is the order of the center of gravity of the spiral in the reference plane (O, x, y) where the 3a axis is the opposite of the finite number, and δ is the gravitational derivative of the spiral. The components were then derived numerically from the integral and the derivative of the center of gravity.

As can be seen, the curves S1 to S4 intersect at a point P1 on the axis of the abscissa at an oscillation amplitude of about 218°, an amplitude which is therefore close to the 220° oscillation amplitude at which the corresponding curves of a swing intersect. The part of the spiral 3 which has the most influence on the position of the intersection point P1 is the inner rigid portion 3d. The outer rigid portion 3c allows to fine-tune the gait of the intersection point P1, and/or to compensate for a forward offset which causes a delay caused by the escapement as described in the present invention's patent applications WO 2013/093462 and WO 2014/072781. In practice, the intersection point P1 or P1 occurs at all the verticale positions of the intersection point.

Figure 5 shows the oscillator 1, 2, 3 movement due to balance failure of the pendulum 1 as a function of the amplitude of oscillation of the pendulum 1 in each of the above four vertical positions of the oscillator, namely the upper vertical position VH (curve B1), the right vertical position VD (curve B2), the left vertical position VG (curve B3) and the lower vertical position VB (curve B4). The following equations are used in the above-mentioned book Clockwork theory , where μ is the stroke, θ0 is the amplitude of the pendulum relative to its equilibrium position, Mb is the mass of the pendulum, g is the gravity constant, d is the radial position of the center of gravity of the pendulum, Jb is the moment of inertia of the pendulum, ω0 is the proper pulsation of the oscillator, J1 is the Bessel function of order 1 (which cancels for a value of θ0 of about 220°), β is the angular position of the center of gravity of the pendulum relative to the peg of the 8th plane (cf. Fig. 3 ; θb = 45°) and φ is the angular position of the peg of the 8th plane relative to the direction of gravity.

In particular, the diagram in Figure 5 is of a pendulum with a bulwark A of 0.6 μg.cm and whose angular position θb of the center of gravity is 60°. It is found that the slope, especially the mean slope, of each curve B1 to B4 is of opposite sign to that of the slope, especially the mean slope, of each curve S1 to S4 respectively. In other words, the curves S1 and S2 decrease while the curves B1 and B2 increase, and the curves S3 and S4 increase while the curves B3 and B4 decrease.This is particularly true in the normal operating range of a swing in the vertical position, i.e. the range of oscillation amplitudes from 150° to 280°. This feature of the slopes of the curves S1 to S4 and B1 to B4 combined with the fact that the intersection point P1 of the curves S1 to S4 is close to the intersection point P2, at 220°, of the curves B1 to B4, allows the gait due to the imbalance of the swing 1 and the gait due to the weight of the spiral 3 to compensate each other, at least partially.The slope of the curves B1 to B4 is adjusted by varying the ballurd A of the oscillator and the angular position θb of its center of gravity. At constant ballurd A, varying the angular position θb of the center of gravity of the oscillator changes the relative position of the curves B1 to B4. Therefore, a value θb must be chosen so that the order of the curves B1 to B4 (depending on their slope) is the inverse of that of the curves S1 to S4. At constant value θb, varying the ballurd A increases or decreases the slope of each curve B1 to B4,This allows for the optimum degree of compensation between the balance and the spiral.

Figure 6 shows the oscillator speed due to balance failure and spiral weight (sum of balance failure and spiral weight speed) in each of the above four vertical positions, namely the high vertical position VH (curve J1), the right vertical position VD (curve J2), the left vertical position VG (curve J3) and the low vertical position VB (curve J4).

In practice, on a manufactured balance, the ballast A and the angular position θb of the centre of gravity can be adjusted by milling and/or by means of adjusting screws which equip the balance and/or by means of bolts which equip the balance. However, to facilitate the manufacture and adjustment of the balance, a second embodiment of the invention provides for a larger ballast A. However, increasing ballast A results in an increase in the slope of the curves B1 to B4.

Thus, Figure 7 shows a 3' spiral of the same type as the 3 spiral shown in Figure 2 but with an increased virole radius R from 545 μm to 760 μm. The values eo, ec, ed, θc, θd, αc, αd, measured in the same way as for the 3 spiral, are as follows: The following equation is used for the calculation of the concentration of the product: The step of the 3' spiral is 96.5 μm. The number of spirals is 10.

Figure 8 shows the movement of the oscillator 1, 2, 3' due to the weight of the 3' spiral according to the amplitude of oscillation of the pendulum 1 in each of the four vertical positions above, namely the high vertical position VH (curve S1'), the straight vertical position VD (curve S2'), the left vertical position VG (curve S3') and the low vertical position VB (curve S4').

Figure 9 shows the oscillator 1, 2, 3' gait due to balance failure of the balance 1 according to the amplitude of oscillation of the balance 1 in each of the four vertical positions above, namely the high vertical position VH (curve B1'), the straight vertical position VD (curve B2'), the left vertical position VG (curve B3'), and the low vertical position VB (curve B4'). The diagram in Figure 9 was obtained with a balance having a bulge A of 1,25 μg.cm and whose angular position θb of the centre of gravity is 55°. It can be seen that the slopes of the curves S1' to S4' and the slopes of the curves B1 to B4 allow for a compensation of gait between the balance and the spiral 1 3'.

Figure 10 shows the oscillator 1, 2, 3' gait due to balance failure of balance 1 and the weight of spiral 3' (sum of balance failure of balance 1 and gait due to weight of spiral 3') in each of the four vertical positions above, namely high vertical position VH (curve J1'), straight vertical position VD (curve J2'), left vertical position VG (curve J3') and low vertical position VB (curve J4').

The examples of embodiments described above are by no means exhaustive and it is clear that many configurations are possible to realize the invention as claimed.

Claims (10)

1. Oscillator for a timepiece, comprising a balance (1) and a hairspring (3; 3'), the balance having a lack of equilibrium, wherein the lack of equilibrium in the balance and the geometry of the hairspring are such that

   a) the curves (S1-S4; S1'-S4') representing the running of the oscillator owing to the weight of the hairspring as a function of the oscillation amplitude of the balance in at least four vertical positions of the oscillator spaced apart by 90° each pass through the value zero at an oscillation amplitude of the balance between 200° and 240°;

   b) between the oscillation amplitude of 150° and the oscillation amplitude of 280°, the curves (B1-B4; B1'-B4') representing the running of the oscillator owing to the lack of equilibrium in the balance as a function of the oscillation amplitude of the balance in said vertical positions of the oscillator each have an average slope of opposite sign to the average slope of the corresponding curve among said curves (S1-S4; S1'-S4') representing the running of the oscillator owing to the weight of the hairspring.
2. Oscillator as claimed in claim 1, characterised in that the geometry of the hairspring is such that said curves (S1-S4; S1'-S4') representing the running of the oscillator owing to the weight of the hairspring each pass through the value zero at an oscillation amplitude of the balance between 210° and 230°.
3. Oscillator as claimed in claim 2, characterised in that the geometry of the hairspring is such that said curves (S1-S4; S1'-S4') representing the running of the oscillator owing to the weight of the hairspring each pass through the value zero at an oscillation amplitude of the balance between 215° and 225°.
4. Oscillator as claimed in any one of claims 1 to 3, characterised in that the lack of equilibrium in the balance and the geometry of the hairspring are such that the average slope of each curve among said curves (B1-B4; B1'-B4') representing the running of the oscillator owing to the lack of equilibrium in the balance has substantially the same absolute value as the average slope of the corresponding curve among said curves (S1-S4; S1'-S4') representing the running of the oscillator owing to the weight of the hairspring, in the range of oscillation amplitudes of 150° to 280°.
5. Oscillator as claimed in any one of claims 1 to 4, characterised in that the lack of equilibrium in the balance and the geometry of the hairspring are such that the maximum discrepancy in the running of the oscillator owing to the lack of equilibrium in the balance and to the weight of the hairspring between said vertical positions in the range of oscillation amplitudes of 150° to 280° is less than 4 seconds/day, preferably less than 2 seconds/day, more preferably less than 1 second/day, more preferably less than 0.7 seconds/day.
6. Oscillator as claimed in any one of claims 1 to 5, characterised in that the distance (R) between the inner end (3a) of the hairspring (3') and the centre of rotation (O) of the hairspring (3') is greater than 500 µm, preferably greater than 600 µm, more preferably greater than 700 µm.
7. Oscillator as claimed in any one of claims 1 to 6, characterised in that the imbalance of the balance is greater than 0.5 µg.cm, preferably greater than 1 µg.cm.
8. Oscillator as claimed in any one of claims 1 to 7, characterised in that the inner turn of the hairspring (3; 3') has a stiffened portion (3d) and/or is shaped as a Grossmann curve.
9. Oscillator as claimed in claim 8, characterised in that the outer turn of the hairspring (3; 3') has a stiffened portion (3c).
10. Oscillator as claimed in any one of claims 1 to 7, characterised in that the hairspring has a stiffness and/or a pitch which vary continuously over at least several turns.