EP2788826B1 - Method for adapting a timepiece movement intended to operate in atmospheric to the functioning at a lower pressure,. - Google Patents

Description

The documents FR1546744 , FR2054540 , and GB1272183 explain that in a watch under reduced pressure, the quality of these watches over time is improved, in particular since the risks of oxidation of the movement and of the oils are eliminated and since the aging of the lubricants and the wear due to oxidation and corrosion are reduced.

In addition, as stated in the document FR2054540 , by reducing the pressure prevailing inside a watch case, the energy loss due to the friction of the air tends to zero and therefore the quality factor of the oscillator of the watch movement increases considerably. By "vacuum" or "protected atmosphere" or "low pressure atmosphere" here is meant a pressure generally low compared to atmospheric pressure, with or without an added gas which is maintained inside a box which has been optimized to keep this pressure low.

A movement according to FR2054540 is designed according to the high vacuum in which its oscillator operates, and it is unable to function correctly at normal atmospheric pressure due to the large difference between atmospheric pressure and its expected operating pressure which is of the order of 1 / 10 to 1/100000 mmHg. Consequently, the movement of this watch is entirely designed according to the high vacuum in which its oscillator operates. However, designing a movement in a protected and controlled low pressure atmosphere is a complex, inconvenient, and ineffective task, and the document FR2054540 gives no indication of how this can be accomplished.

The object of the present invention is a method for adapting (or even resizing and / or reconstructing to a certain extent) a mechanical watch movement intended to operate at ambient atmospheric pressure at operation in a protected atmosphere at low pressure between 0.1 mbar and 200 mbar in a practical, efficient, calculated and optimal way.

The invention is preferably applied to a purely mechanical watch movement comprising at least one barrel, a regulating member in the form of a balance spring, an escapement maintaining the oscillations of the balance spring, and a gear train transmitting the driving force of the barrel to the exhaust. It applies more particularly to a line of movements of the same caliber comprising equivalent components. It is particularly applicable to the adaptation of a movement originally designed to operate at atmospheric pressure.

1. 1. mesurer le facteur de qualité FQ du mouvement à la pression atmosphérique, de manière optique ou acoustique, par oscillation libre, et calculer la perte d'énergie ΔE à la pression atmosphérique selon la formule $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$
   
2. 2. mesurer le facteur de qualité FQ du mouvement à une pression basse prédéterminée correspondant à la pression de fonctionnement prévue pour le mouvement, typiquement à une pression comprise entre 0,1 et 200 mbar, de manière optique ou acoustique, par oscillation libre, et calculer la perte d'énergie ΔE à ladite pression basse prédéterminée selon la formule $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$
   
3. 3. calculer le gain énergétique entre la perte d'énergie ΔE à la pression atmosphérique calculée à l'étape 1 et la perte d'énergie ΔE à la pression basse prédéterminée calculée à l'étape 2 sous la forme d'un pourcentage,
4. 4. modifier le mouvement prévu pour fonctionner à la pression atmosphérique ambiante en augmentant le rapport de réduction du rouage de finissage, en diminuant le couple du barillet, ou en augmentant l'inertie du balancier, d'une valeur correspondant au pourcentage déterminé précédemment pour obtenir un mouvement fonctionnant à ladite pression basse prédéterminée.

The method according to the invention comprises the following steps.

1. 1. measure the quality factor FQ of the movement at atmospheric pressure, optically or acoustically, by free oscillation, and calculate the energy loss ΔE at atmospheric pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$
   
2. 2. measure the quality factor FQ of the movement at a predetermined low pressure corresponding to the operating pressure provided for the movement, typically at a pressure between 0.1 and 200 mbar, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at said predetermined low pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$
   
3. 3. calculate the energy gain between the energy loss ΔE at atmospheric pressure calculated in step 1 and the energy loss ΔE at the predetermined low pressure calculated in step 2 as a percentage,
4. 4. modify the movement intended to operate at ambient atmospheric pressure by increasing the reduction ratio of the gear train, by reducing the torque of the barrel, or by increasing the inertia of the balance wheel, by a value corresponding to the percentage determined previously for obtaining a movement operating at said predetermined low pressure.

Preferably, the quality factor is measured at a plurality of low pressures in order to obtain an evolution of the latter as a function of the pressure, and subsequently the low operating pressure is chosen, which gives a particular energy gain.

The first step in the process of adapting a conventional timepiece movement operating at ambient atmospheric pressure for its operation in a low pressure atmosphere consists in measuring the quality factor of the mechanical timepiece movement operating at atmospheric pressure by a classic method. Preferably, the quality factor is measured directly, but alternatively it can be measured indirectly, for example by measuring the amplitude of the pendulum and subsequently calculating the quality factor.

The second step of the method consists in placing the mechanical clockwork movement under an atmosphere at a predetermined low pressure typically between 0.1 and 200 mbar corresponding to the operating pressure of the movement and then measuring the quality factor. In this step, it is more difficult to measure the quality factor directly and then it may be preferable to do it indirectly, at least in part.

To measure the quality factor indirectly, the entire movement can be placed in a vacuum and the acoustic gain of the movement balance can be measured acoustically or optically as a function of pressure. This method has the advantage of being fast because you can lower the pressure in successive stages and take a measurement at each stage. It has the disadvantage of not directly giving the value of the quality factor (we deduce it by calculation) which will then be used to size and adapt the movement.

The following diagram gives an example of measuring the evolution of the balance's amplitude as a function of the internal pressure of the watch.

To carry out this measurement, we can also put the movement without the amplitude maintenance system (we remove the anchor from the escapement) in a vacuum and measure optically the loss of amplitude of the balance according to the time.

• Il faut donner une impulsion nécessaire pour "lancer" le balancier à grande amplitude (supérieur à 350°).

This direct measurement is more complicated to implement for several reasons:

• It is necessary to give a necessary impulse to "throw" the pendulum at large amplitude (greater than 350 °).

If this operation is relatively simple in the open air, it becomes more complicated when the movement is in a vacuum enclosure.

• Pour chaque mesure on est obligé de retourner à pression atmosphérique pour réarmer le balancier.

Depending on the technical solution that has been chosen, which is not the only one possible, the pendulum is pre-arm at an angle of, for example, 350 ° and it is locked in this position. The movement is then placed under vacuum at the desired pressure, the balance is released and the evolution of the balance's amplitude as a function of time is measured optically. If there is one on the movement tested, the pendulum stop system can be used (in the time setting position) to lock the pendulum at 350 °. To release the balance for the measurement, it suffices to push the rod back.

• For each measurement, it is necessary to return to atmospheric pressure to reset the balance.

This measurement is more precise but more tedious to perform. It is preferable to carry out the first measurement first, to "target" the seconds.

The following diagram illustrates an example of measuring the quality factor (at 280 ° of amplitude of the balance) as a function of the pressure according to this example.

It can be seen from these measurements that the pressure range of interest for the gain in energy performance of the movement is above all between 5 mbar and 0.1 mbar, in any case preferably below 200 mbar.

Preferably, we remain for the operating pressure of the movement in the range of 5 mbar and 0.1 mbar even if the quality factor increases for lower pressures. Indeed, falling below a pressure of 0.1 mbar will bring other problems, such as degassing of oils (if lubricated movement), maintenance of tightness over an extremely complex long term (see impossible if not maintained), critical increase in the hanged plate (losses by dry friction of the pendulum become predominant and therefore the difference in amplitude between the horizontal and vertical positions increases).

The third step of the movement adaptation process consists in calculating the gain of the quality factor between the operation at atmospheric pressure and the operation at predetermined reduced pressure of the movement.

soit si E = 2 x π² x f² x I_bal x θ² par exemple $$\mathrm{FQ}=\frac{4\times {\pi }^3\times f^2\times I_{\mathit{bal}}\times {\theta }^2}{\mathrm{\Delta }E}$$

Où:

FQ

: facteur de qualité

f

: fréquence du balancier

I_bal

: inertie du balancier

θ

: amplitude du balancier

ΔE

: énergie perdue par oscillation du balancier.

The quality factor is given by the formula: $$\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$$

either if E = 2 x π ² xf ² x I _bal x θ ² for example $$\mathrm{FQ}=\frac{4\times {\pi }^3\times f^2\times I_{\mathit{ball}}\times {\theta }^2}{\mathrm{\Delta }E}$$

Or:

FQ

: quality factor

f

: pendulum frequency

I _bal

: balance inertia

θ

: balance amplitude

.DELTA.E

: energy lost by oscillation of the pendulum.

où K = raideur du spiral.In a variant one could consider that $$\mathrm{E}=\frac{1}{2}\times \mathrm{K}\mathrm{hairspring}\times {\mathrm{\theta }}^2$$

where K = stiffness of the hairspring.

According to this example, if for a given movement the quality factor at atmospheric pressure is 300, it can increase to 450 when it operates under reduced pressure. The energy loss per oscillation of the balance goes from 100 microJ to 70 microJ, which represents a gain of 30% for an operating amplitude of the balance of 280 °, a frequency of 4Hz and a inertia of the balance of 0.63 g.mm ² .

• rapport de réduction du rouage de finissage,
• couple du barillet,
• encombrement du barillet,
• inertie du balancier.

The fourth step of the process consists in adapting the dimensioning of the movement as a function of the energy gain obtained in particular by modifying one or more of the following elements of the movement:

• reduction ratio of the gear train,
• barrel couple,
• size of the barrel,
• balance inertia.

• augmentation de la réserve de marche,
• diminution de l'encombrement,
• augmentation de la précision de la montre.

This adaptation of the dimensioning of the movement is done according to the performance or qualities of the movement that we want to favor such as for example:

• increase in power reserve,
• reduction in size,
• increased accuracy of the watch.

One can for example, once the energy gain quantified, resize the train of finishing cogs in order to increase the power reserve.

According to this example, the energy required to maintain the pendulum at 280 ° amplitude goes from 100microJ to 70microJ. We will therefore be able to reduce the torque arriving at the exhaust in proportion to this gain.

Proportionality assumes that the exhaust efficiency remains constant. It is possible, by simulation for example, to calculate the torque necessary for the exhaust if we do not want to make the constant approximation.

The torque arriving at the exhaust can therefore be reduced by 30%

Keeping the same barrels will increase the reduction ratio of the gear train by 30%. The barrel will therefore rotate 30% slower, so we will see the power reserve increase by 30%.

Of course, the increase in the reduction ratio is done upstream of the deflection of the needle part to maintain the same speed of rotation of the needles.

It is also possible, by keeping the same cogs, to decrease the torque of the barrels by 30% while retaining their dimensions in this example. To reduce the torque we will reduce the thickness of the spring, so in the same size of barrel we will increase their number of development turns.

By passing the torque from 2.65 Nmm to 1.876Nmm, we obtain a blade of thickness 0.0685mm instead of 0.082mm (for a height of 0.74mm and a length of 370mm). By keeping the same ratio (bung radius by thickness), we go from a number of development turns from 9.6 turns to 12.5 turns per barrel, i.e. a gain in number of turns of 30% and a gain in power reserve of 30%.

Another possibility of exploiting this energy gain is the reduction in the size of the movement and in particular that of the barrel or barrels, while retaining the same power reserve.

In the same way as above, the exhaust torque can be reduced by 30% according to this example. However in this case the torque of the barrel (s) is reduced.

The torque of the barrels is therefore reduced by 30% (keeping the same number of reel turns). The simplest solution to reduce the torque of the barrel spring by 30% is to reduce the height of the spring by 30% (indeed the torque supplied is proportional to the height of the spring). We can of course completely resize a new spring.

The 30% reduction in the height of the leaf spring does not directly lead to a 30% reduction in the height of the barrel.

There is therefore a gain in size which is not proportional to the energy gain.

To reduce the torque, we played on the reduction in height of the spring. We could very well have played on other dimensions in order to better optimize the gain in size.

Another possibility is to increase the inertia of the balance wheel to keep the same energy loss by oscillation. The precision of the watch is in fact linked to the inertia of the balance wheel, in particular its resistance to external disturbances.

The above list of possible adaptations is of course not intended to be exhaustive, in particular one can very well carry out a mixed solution of all or part of the solutions described.

For the various calculations carried out, the inventors set out on a constant return on the workings and the exhaust. It is a first approximation fairly close to reality. We can of course complete these calculations taking into account the evolution of the yields of the different parts of the watch as a function of the different changes made (increase in the reduction ratio, the torque or the dimensions of the barrels).

Knowing the energy gain of the movement between its operation at atmospheric pressure and its operation at a predetermined reduced operating pressure makes it possible to greatly simplify the adaptation of the movement for its operation under reduced pressure.

This process for adapting a rating intended for operation at atmospheric pressure to its operation at reduced pressure can also be used, as basic information, for the reconstruction of a new caliber or movement intended to operate under reduced pressure.

devant rester constant, on peut montrer que si

• pour ce mouvement traditionnel : I_bal vaut 6.3mgcm2 ; f=4Hz ; soit
• pour une amplitude de 290° et un facteur de qualité de 300 on a DeltaE = 106 nanojoules, et
• pour une amplitude de 290° et un facteur de qualité de 450 on a DeltaE = 71 nanojoules

For example, taking the results measured on a traditional manufacture movement, we go from an average quality factor of 300 at atmospheric pressure to a quality factor of 450 at reduced pressure. The quality factor calculated by the formula: $$\mathrm{FQ}=\frac{4\times {\pi }^3\times f^2\times I_{\mathit{ball}}\times {\theta }^2}{\mathrm{\Delta }E}$$

having to remain constant, we can show that if

• for this traditional movement: I _bal is 6.3mgcm2; f = 4Hz; is
• for an amplitude of 290 ° and a quality factor of 300 we have DeltaE = 106 nanojoules, and
• for an amplitude of 290 ° and a quality factor of 450 we have DeltaE = 71 nanojoules

The balance therefore needs 30% less energy to operate at the same amplitude.

This energy gain can be used to increase the power reserve by increasing the reduction ratio between the barrel (s) and the exhaust.

Modification process:

Torque required for exhaust before / after: $$\mathrm{DeltaE}=\left(\mathrm{yield}\mathrm{exhaust}\right)\times \left(\mathrm{couple}\mathrm{exhaust}\right)/\left(\mathrm{number}\mathrm{of}\mathrm{teeth}\mathrm{exhaust}\right)$$

The number of teeth of the escape wheel being 20 in this example, hence the torque at the exhaust will go from around 900 microN to 600microN (considering that the exhaust efficiency remains constant at 38%). We can also find the torques necessary for the exhaust by numerical simulation in order to take into account the variation in efficiency.

It is therefore necessary to reduce the exhaust torque by 30%.

We will reduce this torque by increasing the reduction ratio between the barrels and the escape wheel by 30%.

The reduction ratio of this traditional movement is 2135. It must therefore be increased to 2775. We can increase the reduction ratio on one of the gear trains, for example between the barrel and the large average (passing from a ratio of 100/19 in traditional to 130/19 in adaptation).

It must be verified that the modification of the gear train does not disturb the speeds of the hands, or otherwise in this case, it will also be necessary to modify the gear train between the gear train and the needles).

Advantage:

• Elle permet tout d'abord d'augmenter la réserve de marche de 30% (puisque les barillets tournent 30% moins vite) en ne changeant que le nombre de dents d'un train de rouage.
• Les modifications sont mineurs (deux nouvelles pièces seulement, un pignon et une roue)

This adaptation has several advantages:

• First of all, it increases the power reserve by 30% (since the barrels turn 30% slower) by only changing the number of teeth on a gear train.
• The modifications are minor (only two new parts, a pinion and a wheel)

This method makes it possible to quickly have a movement suitable for vacuum operation without the need to completely reconstruct a movement.

Another method to reduce the exhaust torque by 30% is to reduce the torque supplied by the barrels by 30%.

The torque of the barrels being directly proportional to the height of the barrel spring, a simple way to reduce the torque is to reduce the height of the spring by 30% and therefore reduce the height of the barrel by 30%.

Thus, if the movement considered has a barrel spring height of 1.5mm, we will be able to go to a spring height of 1.15mm or gain 0.35mm over the height of the barrel.

For this adaptation to be preferred, the height of the movement must be reduced and therefore the height of the movement must be limited by the height of the barrels. From this point of view, it brings more change than the previous adaptation (manufacture of a new barrel, spring, plate and bridge ...) so the gain of the adaptation must be more interesting than a reconstruction important movement. This application is therefore, for example, more indicated in the case of a watch with a "large" barrel, in a large complication for example.

The advantages of an adaptation according to the invention to a major reconstruction are that the gain of the vacuum can vary appreciably if the movement oscillator or the surroundings of this oscillator (rooster and platinum) are modified. If we make a significant reconstruction of the movement, it is therefore difficult to predict the final energy gain (quality factor under vacuum) and therefore to size the watch (we may have to resize the movement after the first prototype).

With an adaptation of the movement modifying only very little, if at all, the movement including the oscillator and its surroundings (for example by means of an increase in the reduction ratio), the energy gain between the original movement and the adapted movement remains stable and allows the adaptations to be sized correctly the first time.

A second advantage is of course the saving of time. It is much easier to modify the number of teeth on a wheel and a pinion to increase the reduction ratio than to reconstruct a complete movement.

Claims (6)

1. Method of redimensioning a timepiece movement intended to operate at ambient atmospheric pressure to operating under a low-pressure atmosphere, characterised in that it comprises the following steps:

   1. measuring the quality factor FQ of the movement at atmospheric pressure, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at atmospheric pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$

   

   with $$\mathrm{E}=2\times {\mathrm{\pi }}^2\times {\mathrm{f}}^2\times {\mathrm{I}}_{\mathrm{bal}}\times {\mathrm{\theta }}^2$$

   

   wherein

   f : frequency of the balance

   I_bal : inertia of the balance

   θ : amplitude of the balance

   or $$\mathrm{E}=\frac{1}{2}\times \mathrm{K}\times {\mathrm{\theta }}^2$$

   

   wherein K = stiffness of the balance spring

   2. measuring the quality factor FQ of the movement at a predetermined low pressure corresponding to the operating pressure intended for the modified movement, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at said predetermined low pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$

   

   3. calculating the energy gain between the energy loss ΔE at atmospheric pressure calculated in step 1 and the energy loss ΔE at the predetermined low pressure calculated in step 2 as a percentage

   4. modifying the movement intended to operate at ambient atmospheric pressure by increasing the reduction ratio of the going gear train by a value corresponding to the previously determined percentage in order to obtain a movement operating at said predetermined low pressure.
2. Method of redimensioning a timepiece movement intended to operate at ambient atmospheric pressure to operating under a low-pressure atmosphere, characterised in that it comprises the following steps:

   1. measuring the quality factor FQ of the movement at atmospheric pressure, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at atmospheric pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$

   

   with $$\mathrm{E}=2\times {\mathrm{\pi }}^2\times {\mathrm{f}}^2\times {\mathrm{I}}_{\mathrm{bal}}\times {\mathrm{\theta }}^2$$

   

   wherein

   f : frequency of the balance

   I_bal : inertia of the balance

   θ : amplitude of the balance

   or $$\mathrm{E}=\frac{1}{2}\times \mathrm{K}\times {\mathrm{\theta }}^2$$

   

   wherein K = stiffness of the balance spring

   2. measuring the quality factor FQ of the movement at a predetermined low pressure corresponding to the operating pressure intended for the modified movement, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at said predetermined low pressure according to the formula $$\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$$

   

   3. calculating the energy gain between the energy loss ΔE at atmospheric pressure and the energy loss ΔE at the predetermined low pressure as a percentage

   4. modifying the movement intended to operate at ambient atmospheric pressure by reducing the barrel torque by a value corresponding to the previously determined percentage in order to obtain a movement operating at said predetermined low pressure.
3. Method as claimed in claim 1 or claim 2, characterised in that the energy gain is used in order to increase the power reserve of the movement.
4. Method as claimed in claim 2, characterised in that the energy gain is used to modify the barrel in order to reduce the size of the movement.
5. Method of redimensioning a timepiece movement intended to operate at ambient atmospheric pressure to operating under a low-pressure atmosphere, characterised in that it comprises the following steps:

   1. measuring the quality factor FQ of the movement at atmospheric pressure, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at atmospheric pressure according to the formula $\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$

   

   with $$\mathrm{E}=2\times {\mathrm{\pi }}^2\times {\mathrm{f}}^2\times {\mathrm{I}}_{\mathrm{bal}}\times {\mathrm{\theta }}^2$$

   

   wherein

   f : frequency of the balance

   I_bal : inertia of the balance

   θ : amplitude of the balance

   or $$\mathrm{E}=\frac{1}{2}\times \mathrm{K}\times {\mathrm{\theta }}^2$$

   

   wherein K = stiffness of the balance spring

   2. measuring the quality factor FQ of the movement at a predetermined low pressure corresponding to the operating pressure intended for the modified movement, optically or acoustically, by free oscillation, and calculating the energy loss ΔE at said predetermined low pressure according to the formula $$\mathrm{\Delta }E=\frac{2\times \pi \times E}{\mathit{FQ}}$$

   

   3. calculating the energy gain between the energy loss ΔE at atmospheric pressure calculated in step 1 and the energy loss ΔE at the predetermined low pressure calculated in step 2 as a percentage

   4. modifying the movement intended to operate at ambient atmospheric pressure by increasing the inertia of the balance by a value corresponding to the previously determined percentage in order to obtain a movement operating at said predetermined low pressure, the energy gain being used in order to increase the running precision of the movement.
6. Method as claimed in any one of the preceding claims, characterised in that the operating pressure is between 5 mbar and 0.1 mbar.