CORRECTION METHOD FOR THE ACCURACY AND / OR AMPLITUDE OF A SPIRAL UNREST TYPE OSCILLATOR WITH VERTICAL POSITIONS

Description

[0001] The present invention relates to a method for correcting the rate and / or amplitude of a spiral balance oscillator in vertical positions.

[0002] A traditional balance-spring type oscillator is shown in figures 1a et 1b consists of a balance wheel 1 and a spiral spring attached at its ends to the balance wheel 1 and to the stud 9 itself fixed to the cock. The balance wheel 1 is formed of a rim 1a attached to a balance staff 2. The balance staff 2 comprises two pivots 3, 4 without bearing surfaces, formed by a cylindrical portion 3a, 4a connected by a fillet 3b, 4b to the pivot pin of the staff 2. The pivots 3, 4 pass through the hole of a pivot jewel 5, 6 and bear with their rounded end or pivot tip 3c, 4c against the face of a second jewel called the counter-pivot or counter-stone 7, 8. Generally, a lubricant is used to improve the pivoting between the pivots 3, 4 and the pivot jewels 5, 6 and the counter-stones 7, 8. The dimensions of the pivots 3, 4 and of the holes in the pivot jewels 5, 6 are generally less than 100 µm.The balance shaft 2 also carries, on one side of the balance wheel 1, at least one plate 10 as well as the plate pin 11, through which the impulse of the escapement arrives.

[0003] In practice, the oscillations of a balance wheel and hairspring powered by an escapement are not isochronous, meaning they do not all occur in equal time. The duration of the oscillations of a balance wheel and hairspring, and therefore its isochronism (its ability to oscillate in equal times, regardless of external influences, see Illustrated Professional Dictionary of Watchmaking, G.-A. Berner), is affected by the following main factors: the escapement, the contact between the pivots of the balance staff and their bearings (jewels and counter-jewels), the balance of the balance wheel and hairspring assembly, defects in the assembly, and the shape of the hairspring.

[0004] Watchmakers generally study the oscillations of a balance wheel and hairspring maintained by an escapement in six specific positions of said balance wheel and hairspring and of the watch: two horizontal positions, horizontal top (HH, on background, natural position of the hand in pronation) and horizontal bottom (HB, on glass, position rarely observed when the hand is in supination) and four vertical positions, vertical top (VH, 3 o'clock at the top), vertical bottom (VB, 9 o'clock at the top), vertical right (VD, 12 o'clock at the top) and vertical left (VG, 6 o'clock at the top).

[0005] The isochronism of the balance wheel and hairspring can, for example, be evaluated by associating the amplitude of the oscillations with the instantaneous rate of the movement for each of the six standard positions. Rate is a setting term that traditionally refers to the difference between two states of the watch separated by 24 hours. It is possible to measure the instantaneous rate M [s / d] as a function of the period of the balance wheel's oscillations: M = − 86400 T − T o T where, T is the observed period of the oscillator, T o is the theoretical period of the oscillations (perfect isochronism) and 86400 is the number of seconds in 24 hours.

[0006] Thus, if the observed period T is shorter than the theoretical period To, the balance wheel and hairspring are faster, the instantaneous rate is positive, and the movement is ahead. Conversely, if the observed period T is longer than the theoretical period To, the balance wheel and hairspring are slower, the instantaneous rate is negative, and the movement is behind.

[0007] By thus associating the amplitude of the oscillations with the instantaneous rate of the movement, it is possible to obtain curves, called isochronism curves, characterizing the isochronism of a balance-spring type oscillator maintained by an escapement. figure 2a illustrates these isochronism curves in the six typical positions. The watchmaker more generally considers the amplitude range between 180° and 300° visible on the figure 2b .

[0008] The loss of amplitude is greater in vertical positions than in horizontal positions (on the figure 2a (maximum amplitude at approximately 260° for vertical positions, compared to a maximum amplitude of 285° for horizontal positions). This is due to the fact that friction is greater in vertical positions than in horizontal positions, because the contacts are different. Vertical positions correspond to the balance wheel supported by two jewels (the resisting couple: lever arm related to the radius of the pivot cylinder), while horizontal positions correspond to the balance wheel supported by a counter-stone (the resisting couple: lever arm related to the radius of the pivot end).

[0009] Furthermore, because the balance wheel 1 is not fixed symmetrically with respect to the pivots 3, 4 on the balance wheel axis 2 of the figure 1a , and that the double plate pin is not coplanar with the balance wheel, the curves obtained for the horizontal top HH and horizontal bottom HB positions are not equivalent in course and amplitude.

[0010] Watchmakers still use three concepts to study the oscillations of a balance wheel and hairspring: the case back-to-glass offset is the difference in rate between the HB position and the HH position for a given amplitude (see the figure 3 ); the flat-hanging offset in motion is the difference in path length between the average of the horizontal positions HH and HB and the average of the vertical positions VB, VH, VG and VD (see the figure 4 ); while the flat-hanging offset in amplitude is the difference between the average of the maximum amplitudes of the horizontal positions HH and HB and the average of the maximum amplitudes of the vertical positions VB, VH, VG, and VD. On the curves of figures 3 et 4 The following results are obtained: Flat-hanging offset in operation at maximum amplitudes (285° and 255°): 3s / day. Flat-hanging offset in amplitude: 30°.

[0011] Watchmakers strive to optimize the balance wheel and hairspring's operation, thereby reducing the rate of change (the difference between the case back and the crystal, and between the flat and the pendulum during operation), optimizing isochronism, and maximizing the amplitude of the oscillations. In practice, the goal is to eliminate or cancel out all potential imperfections (friction, influence of the escapement, shape of the hairspring, balance, construction constraints, etc.).

[0012] CH 708 217 describes a balance shaft whose pivot ends have a geometric shape with rotational symmetry of order N about the geometric axis of the balance shaft, where N is an integer between 2 and 8. This rotational symmetry implies the presence of shapes on the pivot ends that can, during their rotation, push a quantity of oil in front of them. The purpose of this document is to improve the lubrication of the pivots in the horizontal position at relatively low rotational speeds.

[0013] Document EP 2 551 732 seeks to reduce the flat-hanging gap by defining a condition to be respected for the diameter D, the frequency f and the inertia I of the pendulum: D 5 ·f / l ≤ 20 10 -2 m 3 kg -1 s -1. The flat-hanging gap is therefore adjusted by modifying the size and weight of the pendulum.

[0014] EP 1 986 059 describes a particular shape for the bearings chosen so that the torque of the friction forces varies very little between the different possible orientations of the timepiece.

[0015] The aim of the present invention is to propose a method for correcting the rate and / or amplitude of a spiral balance oscillator at vertical positions.

[0016] The present invention relates to a method for correcting the rate and / or amplitude at vertical positions for a balance-spring type oscillator of a watch part according to claim 1.

[0017] The invention will now be described in detail with reference to the attached figures.

[0018] THE figures 1a et 1b illustrate a balance-spring type oscillator and its traditional pivoting means as described above.

[0019] THE figures 2 à 4 , also discussed in the introduction, are isochronism curves obtained for a certain clockwork movement whose oscillator is of the balance-spring type illustrated in figures 1a et 1b It has the following characteristics: frequency 4Hz, balance mass 47mg, moment of inertia 4.7 mg cm2, steel balance axle, 63 µm diameter pivots, pivot ends with smooth contact surface, ruby ​​pivot stones and counter-stones.

[0020] There figure 5 is a cross-sectional view of a pivot in its pivot stone of a prior art oscillator-pivot stone assembly in the vertical position of the oscillator, wherein the clearance between said pivot and its stone is 12 µm.

[0021] There figure 6 is a cross-sectional view of a pivot in its pivot stone of an oscillator-pivot stone assembly according to the invention in the vertical position of the oscillator, in which the clearance between the pivot and its stone is 22 µm.

[0022] There figure 7 illustrates the movement in vertical positions as a function of the play between the pivot and its pivot stone for an amplitude between 260° and 270°.

[0023] There figure 8 illustrates the average of the steps in horizontal positions (up and down) and the average of the steps in vertical positions as a function of the amplitude for a first example of an oscillator-stone assembly according to the invention as illustrated in the figure 6 .

[0024] There figure 9 illustrates the step as a function of the amplitude in the horizontal positions HB and HH for a coefficient of friction of 0.05 for the two pivot end / counterstone pairs.

[0025] There figure 10 illustrates the range in vertical positions as a function of the pivot diameter.

[0026] An oscillator of the spiral balance type illustrated in figures 1a et 1b has already been partially described above.

[0027] In the vertical positions of the balance wheel, the balance staff 2 bears, via its two pivots 3 and 4, into the holes of the pivot jewels 5 and 6. Specifically, the cylindrical surfaces 3a and 4a of the pivots 3 and 4 bear against the inner walls of each of the holes in the pivot jewels 5 and 6. Depending on the amplitude of the oscillations of the balance wheel and hairspring, friction in the vertical positions is divided between rolling friction and sliding friction for the remainder of the oscillation. This short rolling phase is responsible for a gain of several seconds per day and therefore influences the timekeeping.

[0028] Similarly, it is also demonstrated that friction in vertical positions causes a significant loss of amplitude for the oscillator's oscillations (regardless of the vertical position considered), and that this loss of amplitude is greater than in horizontal positions. Consequently, the flat-hanging amplitude shift is generally significant (30° according to the curves of the figure 2b ).

[0029] The play between a pivot 3, 4 of the oscillator and its respective pivot stone 5, 6 corresponds to the difference between the inner diameter of the hole in the pivot stone 5, 6 and the outer diameter of the pivot 3, 4.

[0030] The plaintiff was able to establish a link between the movement between the pivots and their respective stones and walking in vertical positions when said pivots are supported by said stones. This link is illustrated by the curve of the figure 7 for an amplitude between 260° and 270°. It is possible to obtain results similar to those of the figure 7 for all other amplitudes. It has indeed been observed that the curves obtained are similar and only undergo a vertical shift.

[0031] It has been observed that by increasing the clearance between the pivots and their respective stones in vertical positions, the step in vertical positions is increased. Thus, the average step in vertical positions is also raised and approaches the average step in horizontal positions, as illustrated in the figure 8 The flat-hanging offset during operation has therefore been reduced and improved.

[0032] To increase the clearance between the pivots and their respective stone in vertical positions, it is possible either to reduce the outer diameter of the pivot, or to increase the inner diameter of the hole in the pivot stone in which said pivot pivots in vertical positions.

[0033] There is also a relationship between the outer diameter of the pivot and the amplitude of the oscillations in vertical positions. This relationship is illustrated by the curve of the figure 10 The amplitude θ is thus proportional to the diameter d of the pivot according to the following equation: θ = − 0 , 53 d + 294 .

[0034] Indeed, by decreasing the diameter of the pivot, the rolling of said pivot in the hole in the stone is facilitated and the friction at the contact is reduced.

[0035] Thus, by decreasing the pivot diameter, it is also possible to increase the maximum oscillation amplitude in vertical positions. The flat-to-hanging amplitude difference is then also reduced and improved.

[0036] Preferably, the play is increased for both pivot / bearing pairs of the oscillator to maintain symmetry in the pivoting motion. Alternatively, the play could be increased for only one pivot / bearing pair, either the upper or lower pivot / bearing pair.

[0037] The present invention relates to a method for correcting the rate and amplitude at vertical positions for a balance wheel oscillator of a clock movement.

[0038] The first step of the process consists of providing an assembly comprising a balance wheel-type oscillator with a spiral, including a shaft ending in two pivots and two pivot bearings in which the oscillator pivots rotate in the vertical positions of the oscillator. Each bearing has a hole characterized by an inner diameter, while each pivot has an outer diameter strictly smaller than the inner diameter of the pivot bearings.

[0039] In a second step, the reference clearance between the pivots and their respective bearing is determined, defined as the difference between the inner diameter of the bearing and the outer diameter of the pivots.

[0040] The third step consists of correcting the gait and / or amplitude of the oscillator's oscillations in the vertical positions by increasing the reference throw either by increasing the inner diameter of the bearing or by decreasing the outer diameter of the pivot for one or both bearing / pivot pairs of the oscillator.

[0041] For example, for the oscillator of the figure 1 The reference clearance between the pivots and their respective bearings, defined as the difference between the inner diameter of the bearing and the outer diameter of the pivots, is approximately 12µm, and the method according to the invention consists of acting on the bearing and / or the pivot so as to increase the inner diameter of the hole in the bearing or decrease the outer diameter of the pivot to obtain a clearance greater than 12µm.

[0042] The rate and / or amplitude of the oscillator's oscillations in vertical positions can be determined for free or sustained oscillations. That is to say, the process may further include a step consisting of providing a clockwork movement comprising an escapement mechanism designed to maintain the oscillator's oscillations, and correcting the rate and / or amplitude of the sustained oscillator's oscillations by said escapement mechanism.

[0043] Any appropriate technical means may be used to act on the bearing and / or the pivot so as to increase the inner diameter of the bearing hole or decrease the outer diameter of the pivot.

[0044] The present invention has been described above in relation to a balance staff and its pivot bearings. It is conceivable that the principles of the invention could be applied to other pivoted systems between bearings, such as the anchor axis of a lever escapement.

Claims

1. Method for correcting the rate and amplitude in vertical positions for a balance-hairspring-type oscillator (1) of a timepiece movement, comprising the following steps: • providing a balance-hairspring-type oscillator comprising a spindle terminated by two pivots (3, 4) and two pivot bearings in which the pivots of the oscillator pivot in the vertical positions of the oscillator, each bearing comprising a hole intended to receive a pivot and having an inner diameter, whilst each pivot (3, 4) has an outer diameter strictly smaller than said inner diameter of the pivot bearings; • determining the reference clearance between the pivots (3, 4) and their respective bearing defined as the difference between the inner diameter of the bearing and the outer diameter of the pivots (3, 4); • correcting the rate of the oscillations of the oscillator in the vertical positions by increasing the difference between the inner diameter of the bearing and the outer diameter of the pivots with respect to the reference clearance either by increasing the inner diameter of the bearing or by decreasing the outer diameter of the pivot for one or both bearing / pivot pairings of the oscillator such that the average of the rates in vertical positions is increased and approximates the average of the rates in horizontal positions.

2. Method as claimed in claim 1, characterised in that the amplitude of the oscillations of the oscillator in the vertical positions is also corrected by increasing the clearance between the pivots and their respective stone with respect to the reference clearance by decreasing the outer diameter of the pivot for one or both bearing / pivot pairings of the oscillator such that the maximum oscillation amplitude in the vertical positions is increased to approximate the maximum oscillation amplitude in the horizontal positions.

3. Method as claimed in any one of the preceding claims, characterised in that there is also provided a timepiece movement comprising an escapement mechanism intended to support the oscillations of the oscillator, and in that the rate and / or amplitude of the oscillations of the oscillator supported by said escapement mechanism is corrected.