Patent Application
20230195040
This application is claiming priority based on European Patent Application No. 21216225.9 filed on Dec. 21, 2021.
The invention relates to a method for compensating the rate as a function of the temperature of a water-resistant watch, wherein the water-resistant case contains a movement itself including an oscillator, said case containing, on leaving the factory after the initial rate setting, an internal volume V occupied by n moles of a gas of constant R substantially observing the ideal gas law.
The invention further relates to a watch suitable for the implementation of this method, particularly during after-sales operations.
The invention relates to the field of the rate adjustment of mechanical or electromechanical watches.
The rate of a watch is subject to numerous parameters, such as, non-restrictively the spatial position of the watch, lubrication, wear, winding of the springs forming the sources of energy, friction, and obviously the physical parameters of the environment wherein the watch is placed.
Rate variation according to the temperature is a constant concern of watch manufacturers. The elastic return means of the oscillator are particularly sensitive to temperature variations. In the specific and non-restrictive case where these elastic return means include a balance-spring or several balance-springs, the thermal coefficient Ct of each balance-spring causes the rate of the movement to vary as a function of the temperature. It can be considered, by way of example and to simplify the calculations, that the rate varies substantially linearly as a function of the thermal coefficient Ct.
To obtain a better movement precision, the thermal coefficient is targeted at 0 seconds per day per Kelvin. With such parameters, the temperature variations should not influence the rate of the movement. The typical distribution of the thermal coefficient for a product of identical movements is a symmetrical curve, closer to a triangular peak than to a bell.
It is known in watchmaking that the rate of a movement varies as a function of the pressure of the medium wherein it is located. Several explanations can be put forward such as for example the variation of the inertia of the oscillator (inertia of the balance and the loaded air) as the loaded air density varies and therefore also the inertia thereof. The case of the balance and that of the air are specific cases, more generally reference will be made to inertial mass, and gas or gas mixture. The various experiments conducted show that if the pressure drops, the rate increases.
Therefore, it is necessary to compensate the rate of the watch as a function of the variation of the physical parameters: temperature of the medium, user's body temperature, expansion or contraction of the watch case as a function of the temperature, pressure of the location, altitude, hygrometry. However, there is no simple development for particularly handling the problems inherent to temperature and pressure variations.
The invention relates to the compensation of the rate variation of a watch, based on the temperature and the pressure.
For this purpose, the invention relates to a method for compensating the rate as a function of the temperature of a water-resistant watch, according to claim 1.
The invention further relates to a watch suitable for the implementation of this method, particularly during after-sales operations.
The aims, advantages and features of the invention will become more apparent upon reading the following detailed description, with reference to the appended drawings, wherein:
The invention relates to the compensation of the rate variation of a watch, based on the temperature and the pressure.
The experiment conducted in a vessel in under-pressure shows a relatively good linearity of the rate variations for a pressure varying from atmospheric pressure (970 hPa) up to a pressure of 200 hPa, the rate variation in seconds per day on the y-axis, as a function of the pressure in hectopascal on the x-axis, the measurement being made in a vessel in under-pressure.
An experiment on watches equipped with another gauge than those in
In respect to the pressure variation as a function of the temperature, we will make the assumption that the ideal gas law (P*V=n*R*T) is sufficient to define the situation.
In a closed watch, the volume of air available is considered to be given and finite (assuming that the leaks are zero). We will also make the assumption that the pressure differential between the pressure inside the watch and outside the watch is not sufficient to distort the watch; the volume available in the watch does not vary and therefore remains constant.
The experiment shows us that these approximations are relatively correct. In
The initial assumptions showed that the leaks from the watch are considered to be zero, the watch case cannot be distorted and the enclosed gas remains the same. It can therefore be concluded that the parameters n, R and V are constants; the pressure therefore varies linearly as a function of the pressure.
The invention proposes to essentially treat the compensation with regard to temperature and pressure variations. A combination of both effects is aimed at opposing them so that their effects cancel each other out (or are minimised). The main advantage for the user is better precision of the watch when worn.
The influence of humidity is less than those of temperature and pressure. In the working assumption, the humidity level changes little as a function of the temperature or the pressure, in the usual ranges of watch wearing. An approximated calculation consists of disregarding this variation.
The following assumptions are made to simplify the calculations:
The invention thus relates to a method for compensating the rate as a function of the temperature of a water-resistant watch 1, wherein the water-resistant case 2 contains a movement 3 itself including an oscillator 4. This case 2 contains, on leaving the factory after the initial rate setting, an internal volume V occupied by n moles of a gas of constant R substantially observing the ideal gas law. The constant R (or Avogadro's number) is known. It is dependent on the gas which is in the watch (in our case generally air). The number of moles n will depend on the watch closure conditions (atmospheric pressure, temperature or closure and locking of the back for example).
The volume available V is dependent on the case geometry. It is optionally possible to modify the design of the external parts to influence this point.
According to the invention, this pressure coefficient Cp of the movement 3 is determined in the factory by measurement and/or calculation, defining the relatively linear variation of the rate of the movement 3 as a function of the pressure P of the gas (or gas mixture where applicable). The pressure coefficient of the movement Cp can be measured experimentally or calculated theoretically. It is dependent on each movement.
Similarly, a value of the humidity coefficient Ch of the movement 3 is determined in the factory after measurement and/or calculation, defining the maximum relatively linear variation of the rate of the movement 3 as a function of the humidity H in the movement 3: m(H)=Ch*H. Failing a linear variation, the maximum slope value of the highest tangent to the rate/humidity graph is considered.
An optimal value Cto of the thermal coefficient Ct of the oscillator 4 is calculated, defining the relatively linear variation of the rate of the oscillator 4 as a function of the temperature T, this optimal value Cto being intended to compensate the pressure and humidity deviations according to the formula:
Cto=−[Cp*(n*R)/V]−[(Ch*H)/T].
Indeed, in order to enhance the precision of the watch (and not of the movement), we can establish the relation: m(T)+m(P)+m(H)=0, from which the value Cto above is obtained. Indeed, Cto is the optimal value, for which the sum of the rate deviations attributable to the pressure, temperature, and humidity, is zero; failing that, Cto is the value for which this total of the rate deviations has the lowest possible value.
Cto=−[Cp*(n*R)/V]−[Ch*H/T]
In the present example, it was considered that the thermal coefficient and the pressure coefficient are constant and vary the rate linearly as a function of the temperature. It is possible to construct a similar model if these parameters observe a non-linear law as a function of the temperature.
Given that the relative humidity will vary as a function of the temperature and that the rate of the watch will vary according to the humidity variations (via Ch), this theoretical model integrates the humidity parameter.
However, this parameter can, in temperate regions, be disregarded as the influence of the humidity on the rate is substantially less than that of the temperature. In a simplified calculation, the humidity coefficient Ch of the movement 3 is determined at the value zero. In order to enhance the precision of the watch (and not of the movement), it is then possible to establish the simplified relation: m(T)+m(P)=0, from which the optimal value Cto of the thermal coefficient Ct of the oscillator 4 is calculated according to the formula: Cto=−[Cp*(n*R)/V], in accordance with the ideal gas law.
The method can be implemented differently, according to whether it consists of performing initial factory settings, or after-sales operations. In the case of after-sales, it is difficult or even impossible to have controlled-atmosphere chambers, but it is necessary to enable the after-sales technician to perform settings, with special tools that the end user could not have. The scope is greater in respect of factory settings, since it is possible to combine therein means for placing in a controlled atmosphere and controlled temperature, and also these means specifically designed for after-sales.
Thus, according to the invention:
More specifically, the pressure P and/or the number of moles n are modified by modifying the pressure P and/or by varying the temperature T of the watch 1 before closing the case 2.
The equation Ct=−[Cp*(n*R)/V] shows that the thermal coefficient Ct of the oscillator 4 is linked with the pressure coefficient Cp by the environment in the case 2 of the watch 1 (the gas present of constant R, the volume inside the watch V and the quantity of moles in the watch n). In order to render the watch insensitive (or reduce the sensitivity of the watch) to temperature, it is possible to work on the following parameters independently or in combination:
A first embodiment consists of working on the thermal coefficient of the oscillator 4. In the specific and non-restrictive case where this oscillator 4 is a spring balance, when producing a silicon and/or silicon oxide balance-spring, the thermal coefficient Ct of the sprung balance assembly can be adjusted particularly as a function of the thickness of the oxide layer which covers this balance-spring.
Let us consider that the rate variation of a movement as a function of the pressure varies as follows: Cp=−0.015 seconds per day per hectopascal. Considering external watch parts with a generic casing, we obtain experimentally that the constant (n*R)/V equals approximately 3.3 hPa/K. It was calculated on the basis of the measurements of the pressure and the temperature in the watch head in the ideal gas law.
So that the watch is least sensitive to temperature variations, it would be necessary to target a thermal coefficient of the oscillator at 0.05 seconds per day per Kelvin. This value is calculated on the basis of the equation Ct=−[Cp*(n*R)/V]: (0.015*3.3=0.05).
By targeting the thermal coefficient of the spring balance at a value different from 0 seconds per day per Kelvin, the chronometric measurements in movement will be disturbed. For example, when running a certification as a chronometer with phases at 8° C. and 38° C., there would be a rate difference of the order of 1.5 seconds per day generated by the thermal coefficient of the movement between the hot and cold phases. However, if this movement is cased in the watch from the preceding example (Cp=−0.015, (n*R)/V=3.3), the rate becomes practically insensitive to the temperature variation.
More specifically, the elastic return means of the oscillator 4 are made of silicon and/or silicon oxide, and, during the preparation in the factory, the thermal coefficient of these elastic return means is modified by modifying the silicon oxide layer thickness.
More specifically, the elastic return means of the oscillator 4 are made in the form of thin elastic strips with a “LIGA” method, and, during the preparation in the factory, the thermal coefficient of these elastic return means included in the oscillator 4 is modified by applying a coating and/or by local ablation.
More specifically, the elastic return means of the oscillator 4 are made in the form of thin elastic strips with a drawing or rolling method, and, during the preparation in the factory, the thermal coefficient of these elastic return means included in the oscillator 4 is modified by applying a coating and/or by local ablation.
A second embodiment consists of modifying the quantity of gas in the watch. Indeed, if the number of moles of gas is changed in the watch, Ct and Cp can be compensated. The link between the two preceding constants is expressed in the equation Ct=−[Cp*(n*R)/V]. For example, if Ct=0.055 seconds per day per Kelvin, Cp=−0.015 seconds per day per hectopascal and (n*R)/V=3.3 hectopascal per Kelvin, the number of air molecules in the watch should be multiplied by 1.1 (0.055/(0.015*3.3)=1.1).
In order to change the number of molecules in the watch, there are two solutions:
The temperature and the pressure are linked together by the ideal gas law, therefore, it is necessary to ensure that the two parameters are monitored in order to prevent errors linked with atmospheric pressure variation, the altitude or temperature variation.
Modifying the pressure before casing up is relatively complex; particularly in after-sales when a store does not have the suitable equipment. Modifying the temperature of the watch before casing up seems to be relatively easy to implement; for example by placing the open watch on a heating or cooling plate. The main problem of this implementation is that Ct and Cp can only cancel each other out if they are of opposite signs. Moreover, if Ct has a 5% variation, this represents approximately 20° C. Therefore, it should be expected that the temperatures required to compensate Ct are potentially difficult to reach.
More specifically, during the preparation in the factory, the number of moles of gas in the watch 1 is modified, either by closing the case 2 with a pressure defined by calculation to render the rate of the watch insensitive to temperature, or by closing the case 2 with a temperature defined by calculation to render the rate of the watch insensitive to temperature, and by slow cooling of the case 2 after the closure thereof.
A third embodiment consists of modifying the composition of the gas in the watch. By modifying the composition of the gas in the watch 1, for example by closing the watch 1 in a saturated medium with another gas, the constant R of the equation Ct=−[Cp*(n*R)/V] would thus be modified. For example if Ct=0.02 seconds per day per Kelvin, Cp=−0.015 seconds per day per hectopascal and the constant (n*R)/V=3.3 hectopascal per Kelvin, the air (R=287 J/kg/K) in the watch could, for example, be replaced by sulphur dioxide (R=130 J/kg/K). In this case, the correction would be made to 90% (0.015*3.3*130/287=0.0224). As a general rule, by selecting the correct gas or gas mixture (modification of R and with no impact on the materials in contact), it is theoretically possible to minimise the effect of the temperature in the watch. It is assumed that the influence of modifying the gas on Cp is negligible. Furthermore, considering that Ct has a certain variability, this means a specific gas mixture would be needed for each watch. A further disadvantage lies in that each closure of the back should be performed in a controlled atmosphere. Finally, this solution is theoretically only realistic when Ct and Cp are of opposite signs.
More specifically, during the preparation in the factory, the nature of the gas contained in the watch is modified, by complete or partial exchange of the gas with a new gas or gas mixture having another value of said constant R, adapted for the suitable adjustment of the thermal coefficient Ct to render the rate of the watch insensitive to temperature.
More specifically, the case 2 is sealed after this gas exchange, to prevent any action of the user in the absence of a special tool.
A fourth embodiment consists of working on the geometry of the interior of the watch. Indeed, the equation Ct=−[Cp*(n*R)/V] can be expressed in the form V/(n*R)=−Cp/Ct. Let us consider that Cp=−0.015 seconds per day per hectopascal and Ct=0.04 seconds per day per Kelvin. For a given practical case, we have identified that (n*R)/V=3.3 hPa/K. In order to minimise the effects on the rate of the watch, the air volume in the watch should be corrected such that it is 1.24 (3.3*0.015/0.04) times greater than that currently available. As the value of Ct varies from one movement to another, this means that the external parts should be adapted to each movement. Furthermore, as the volumes are already well optimised, it appears to be difficult to apply this method without influencing the watch design. A solution consists of modifying the internal volume of the case with a travel imparted to a mobile organ such as a piston or similar.
Thus, in an alternative embodiment designed particularly for an after-sales application, the compensation means 10 include a water-resistant volumetric device 5 enabling an after-sales technician to modify the internal volume of the case 2, and/or at least one water-resistant gas injection or extraction conduit 6, and/or a thermal device 7 for the controlled and momentary increase of the internal temperature thereof.
More specifically, this volumetric device 5 includes one piston mobile in the case 2 and under the action of an external micrometric control screwable and lockable in position with a special tool not supplied to the user.
More specifically, during the preparation in the factory, the internal volume of the case 2 is modified by adjusting the travel of at least one piston, under the action of an external micrometric control screwable and lockable in position with a special tool not supplied to the user.
More specifically, this water-resistant gas injection or extraction conduit 6 is lockable in position with a special tool not supplied to the user.
More specifically, this thermal device 7 includes means for converting light energy and/or means for storing energy.
More specifically, during the preparation in the factory, the gas or gas mixture contained in the case 2 is dried, to reduce the humidity H.
More specifically, during the preparation in the factory, a desiccator is inserted into the case, to fix the residual humidity H therein.
Finally, it is also possible to combine several effects simultaneously (variation of Ct, Cp, casing conditions or volume in the watch) in order to achieve the desired aim.
Generally, it appears that the dispersion of Ct must be minimised in order to minimise the effect of temperature on a watch.
The invention further relates to a watch 1 suitable for the implementation of this method, particularly in after-sales service. This water-resistant watch 1 includes a water-resistant case 2, which contains a movement 3 itself including an oscillator 4. This watch 1 includes compensation means 10, each lockable in position with a special tool not supplied to the user, which include a water-resistant volumetric device 5 enabling an after-sales technician to modify the internal volume of the case 2, and/or at least one water-resistant gas injection or extraction conduit 6, and/or a thermal device 7 for the controlled and momentary increase of the internal temperature thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21216225.9 | Dec 2021 | EP | regional |
