Compensation of rate variation in a watch

Abstract

One aspect of the invention relates to a method for rate compensation as a function of the temperature of a watch (1), the sealed case (2) of which contains a movement (3) comprising a regulating member which has an oscillator (4) and is pivoted on pivots (9) lubricated with a lubricant of viscosity η, wherein the nature of the lubricant and the rule for the variation of the viscosity η as a function of the temperature η = f (T) are determined in the factory by measurement and / or computation, such that the thermal coefficient Ct of the movement (3) varies as a function of the temperature according to a predetermined law Ct = g (T), and such that the rate of the movement varies as a function of the temperature T of the thermal coefficient Ct so as to generate variations in the rate of the movement (3) as a function of the temperature, in the opposite direction to the variations in rate generated by the pressure P of the gas.

Description

COMPENSATION FOR RATE VARIATION IN A WATCH Technical field of the invention

[0001] The invention relates to a method for compensating the rate as a function of the temperature of a waterproof watch, the waterproof case of which contains a movement itself comprising a regulating member comprising an oscillator and pivoted on lubricated pivots, said case containing, on leaving the factory after the initial rate adjustment, an internal volume V occupied by n moles of a gas of constant R substantially following the law of ideal gases.

[0002] The invention also relates to a watch suitable for implementing this method.

[0003] The invention relates to the field of adjusting the rate of mechanical or electromechanical watches. Technological background

[0004] The operation of a watch is subject to numerous parameters, such as, but not limited to, the position of the watch in space, lubrication, wear, the winding of the springs constituting the energy sources, friction, and of course the physical parameters of the environment in which the watch is placed.

[0005] The variation of rate as a function of temperature is a constant concern of watch manufacturers. The elastic return means of the oscillator are particularly sensitive to temperature variations. In the particular and non-limiting case where these elastic return means comprise a balance spring or several balance springs, the thermal coefficient Ct of the regulating organ varies the rate of the movement as a function of temperature. We can consider, as an example and to simplify the calculations, that the step varies substantially linearly as a function of the thermal coefficient Ct.

[0006] To achieve greater movement accuracy, the thermal coefficient is typically targeted at 0 seconds per day per Kelvin. With these parameters, temperature variations should have no impact on the movement's performance. The typical thermal coefficient distribution for producing identical movements is a symmetrical curve, closer to a triangular peak than a bell.

[0007] It is known in watchmaking that the rate of a movement varies according to the pressure of the environment in which it is located. Several explanations can be put forward, such as the variation in the inertia of the oscillator (inertia of the balance and the air inside) because the density of the air inside varies and therefore its inertia as well. The case of the balance and that of the air are special cases; more generally, we will speak of inertial mass, and of gas or mixture of gases. The various experiments carried out show that if the pressure decreases, the rate increases.

[0008] It is therefore a question of compensating the watch's performance according to the variation in physical parameters: temperature of the environment, body temperature of the user, expansion or contraction of the watch case according to the temperature, pressure of the place, altitude, hygrometry. However, there is no simple adjustment to deal in particular with the problems inherent in variations in temperature and pressure. Summary of the invention

[0009] The invention relates to the compensation of the variation in the rate of a watch, based on temperature and pressure.

[0010] To this end, the invention relates to a method for compensating the rate as a function of the temperature of a waterproof watch, according to claim 1.

[0011] The invention also relates to a watch suitable for implementing this method. Brief description of the figures

[0012] The aims, advantages and characteristics of the invention will appear better on reading the detailed description which follows, with reference to the appended drawings, where: - Figure 1 superimposes three graphs illustrating on the ordinate the rate, in seconds per day, as a function of the pressure on the abscissa, in hectopascals, for three different mechanical movements; - Figure 2 superimposes two graphs illustrating on the ordinate the pressure in hectopascals in a watch case in an environment with variable temperature, as a function of time on the abscissa, in days, one in solid line calculated with the ideal gas law, the other measured; - Figure 3 shows, schematically, a watch whose waterproof case contains a movement itself comprising an oscillator, equipped with compensation means which include a waterproof volumetric device for modifying the internal volume of the case, a waterproof conduit for injecting or extracting gas, and a thermal device allowing the controlled and momentary increase of its internal temperature. Detailed description of the invention

[0013] The invention relates to the compensation of the variation in the rate of a watch, based on temperature and pressure.

[0014] The experiment carried out in a pressure vessel shows a relatively good linearity of the operating variations for a pressure varying from atmospheric pressure (970 hPa) up to a pressure of 200 hPa, the variation in rate in seconds per day on the ordinate, as a function of the pressure in hectopascals on the abscissa, the measurement being carried out in a pressure vessel. Figure 1 presents the results of measurements carried out on various well-proven classical mechanical movements. We note the very linear general appearance of the daily rate as a function of the pressure, all other things being equal, with slopes, in seconds per day per hectopascal, respectively of (-0.0206) for the upper curve, of (-0.0161) for the middle curve, of (- 0.0145) for the lower curve.

[0015] An experiment on watches equipped with a different caliber and closed at different altitudes than those in Figure 1 shows a variation in rate of around 0.95 seconds per day, for an altitude difference of approximately 570m. Based on the following altitude formula: - p(h)=1013.25*(1 -(0.0065*h / 288.15)) A5 255 , we can find that the variation of rate as a function of altitude for this caliber is of the order of -0.03 seconds per day per hPa. We will call this value the pressure coefficient: Cp.

[0016] Regarding the variation of pressure as a function of temperature, we will assume that the ideal gas law (P*V=n*R*T) is sufficient to define the situation.

[0017] In a closed watch, the available volume of air is considered to be given and finite (assuming that leaks are zero). We will also assume that the pressure difference between the pressure inside the watch and outside the watch is not sufficient to deform the watch; the available volume in the watch does not vary and therefore remains constant.

[0018] Experience shows us that these approximations are relatively correct. In Figure 2, the pressure measured in a watch is compared to a theoretical pressure based on the ideal gas law: P=(n*R / V)*T. We see that the measurements and the theoretical approximation are relatively comparable. In addition, experience has shown us that leaks are relatively low for a waterproof watch even with a large pressure difference between the inside of the watch and the environment in which it is located. We will therefore assume that the watch is perfectly waterproof.

[0019] The initial assumptions showed that the watch leaks are considered to be zero, the watch case is undeformable and the enclosed gas remains the same. It is therefore possible to conclude that the parameters n, R and V are constants; the pressure therefore varies linearly as a function of temperature.

[0020] The invention mainly aims to compensate for temperature and pressure variations. A combination of the two effects aims to oppose them so that their effects cancel each other out (or are minimized). The main advantage for the user is better accuracy of the watch when worn.

[0021] The influence of humidity is weaker than that of temperature and pressure. The working hypothesis is that the humidity level changes little with temperature or pressure in the usual ranges for wearing a watch. An approximate calculation consists of neglecting this variation.

[0022] The following assumptions are made to simplify the calculations: - the pressure in the watch varies substantially linearly as a function of temperature: P = [(n*R) / V] * T; - the rate of movement varies according to the temperature, and according to the thermal coefficient Ct of the movement, which also depends on the temperature: m(T )= Ct * T; - the rate of movement varies linearly according to the gas pressure: m(P) = Cp * P.

[0023] The invention thus relates to a method for compensating the rate as a function of the temperature of a waterproof watch 1, the waterproof case 2 of which contains a movement 3 comprising a regulating organ itself comprising an oscillator 4 and which is pivoted on pivots 9 lubricated with a lubricant of viscosity q. This case 2 contains, on leaving the factory after the initial rate adjustment, an internal volume V occupied by n moles of a gas of constant R substantially following the law of ideal gases. The constant R (or Avogadro number) is known. It depends on the gas which is in the watch (in our case generally air). The number of moles n will depend on the conditions of the closing of the watch (atmospheric pressure, temperature or closing and blocking of the back for example).

[0024] We understand that the pivots 9 can be the pivots of a balance wheel, as well as those of an anchor, or even of an escape wheel.

[0025] The viscosity variation of the lubricated anchor-anchor wheel and anchor-oscillator contact is also considered.

[0026] The available volume V depends on the geometry of the box. It may be possible to modify the construction of the casing to influence this point.

[0027] According to the invention, the following are determined in the factory by measurement and / or calculation: - a value of the pressure coefficient Cp of movement 3, defining the relatively linear variation of the rate of movement 3 as a function of the pressure P of the gas (or of the gas mixture where appropriate) according to the equation m(P) = Cp * P. The pressure coefficient of movement Cp can be measured experimentally or calculated theoretically. It depends on each type of movement, - a value of the humidity coefficient Ch of said movement 3, defining the maximum relatively linear variation of the rate of said movement 3 as a function of the humidity H in said movement 3 according to the equation m(H) = Ch * H. In the absence of linear variation, the maximum value of the slope of the highest tangent to the rate / humidity graph is considered, - the nature of the lubricant and the rule of variation of the viscosity q as a function of the temperature q = f (T), such that the thermal coefficient Ct of the movement 3 varies as a function of the temperature according to a predetermined law Ct = g (T), and such that the operation of the movement varies as a function of the temperature T and as a function of the thermal coefficient Ct of said movement 3 according to the equation m(T)= Ct * T = g (T)* T, so as to generate variations in operation of the movement 3 as a function of the temperature, in the opposite direction to the variations in operation generated by the pressure P of the gas.

[0028] More particularly, we determine this rule of variation of the viscosity n as a function of the temperature q = f (T), so as to generate variations in the rate of movement 3 as a function of the temperature inverse to the variations in the rate generated by the pressure P of the gas.

[0029] In this example, it has been considered that the pressure coefficient Cp is constant.

[0030] The temperature coefficient Ct follows a non-linear law as a function of temperature according to a predetermined law Ct = g (T), where .

[0031] The function g(T) is, for example, defined by the equation: where c^ llat+autre is the thermal coefficient of motion generated by the expansion of components and other physical phenomena, C is the coefficient of variation of the movement rate according to the density of the gas mixture, and C^ ubis the thermal coefficient generated by the variation in viscosity of the lubricant with:

[0032] The viscosity of the lubricant is, for example, determined experimentally using a viscometer.

[0033] The function h( ]) can also be determined experimentally by measuring the same movement with several lubricants of different viscosities, and such that the rate of the movement varies as a function of the temperature T and as a function of the thermal coefficient Ct of said movement 3 according to the equation: m(T) = JC T dT = J g (T) dT.

[0034] Since relative humidity will vary with temperature and the rate of the watch will vary with humidity variations (via Ch), this theoretical model incorporates the humidity parameter. However, in temperate regions, this parameter can be neglected because the influence of humidity on the rate is much less than that of temperature. In a simplified calculation, the humidity coefficient Ch of movement 3 is determined to be zero.

[0035] More particularly, the pressure P and / or the number of moles n are adjusted by modifying the pressure P and / or by varying the temperature T of the watch 1 at the time of closing the case 2.

[0036] The thermal coefficient Ct of the regulating organ is linked to the pressure coefficient Cp by the environment in case 2 of watch 1 (the gas of constant R present, the volume V inside the watch and the quantity of moles n in the watch).

[0037] In particular, the thermal coefficient of oscillator 4 depends among other things on the elastic return means of the oscillator, and their rigidity. In the particular and non-limiting case where this oscillator 4 is a balance-spring, when producing a balance-spring made of silicon and / or silicon oxide, the thermal coefficient Ct of the balance-spring assembly can be adjusted in particular as a function of the thickness of the oxide layer which covers this balance-spring. Similarly, the production of the blades of a flexible-guided oscillator can modify the thermal coefficient Ct.

[0038] Let us consider that the variation of the rate of a movement as a function of pressure varies as follows: Cp = -0.015 seconds per day per hectopascal. Considering a watch case with a generic casing, we experimentally obtain that the constant (n*R) / V is approximately 3.3 hPa / K. It was calculated on the basis of pressure and temperature measurements in the watch head using the ideal gas law.

[0039] In order for the watch to be as less sensitive to temperature variations as possible, it would be advisable to target a thermal coefficient of the regulating organ 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).

[0040] By targeting the thermal coefficient of the balance spring at a value other than 0 seconds per day per Kelvin, the chronometric measurements in motion will be disturbed. For example, when passing a certification as a chronometer with phases at 8°C and 38°C, there would be a rate difference of around 1.5 seconds per day generated by the thermal coefficient of the movement between the hot and cold phases. However, if we fit this movement into the watch from the previous example (Cp=-0.015, (n*R) / V=3.3), the rate becomes practically insensitive to the temperature variation.

[0041] It is therefore necessary to ensure that the law of variation of the viscosity q = f (T) of the lubricant of the pivots (in the case of a sprung balance) is compatible with these limits.

[0042] More particularly, 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 thickness of the silicon oxide layer.

[0043] More particularly, the elastic return means of the oscillator 4 are produced in the form of elastic thin blades by a “LIGA” process, and, during factory preparation, the thermal coefficient of these elastic return means which the oscillator 4 comprises is modified by applying a coating and / or by local ablation and / or by adjusting the shape ratios.

[0044] More particularly, the elastic return means of the oscillator 4 are produced in the form of thin elastic blades by a wire drawing or rolling process, and, during factory preparation, the thermal coefficient of these elastic return means which the oscillator 4 comprises is modified by applying a coating and / or by local ablation and / or by adjusting the shape ratios.

[0045] An alternative embodiment consists of working on the geometry of the interior of the watch, by modifying the interior volume of the case by a stroke imparted to a moving member such as a piston or similar.

[0046] Thus, in a variant designed in particular for an after-sales application, the compensation means 10 comprise a sealed volumetric device 5 allowing a technician to modify the internal volume of the box 2, which comprises at least one movable piston in the box 2, under the action of an external micrometric control which can be screwed and locked in position by a special tool not supplied to the user.

[0047] As can be read in document EP21216225A1, it is also possible to combine several effects simultaneously (variation of the Ct, the Cp, the casing conditions or the volume in the watch) in order to achieve the desired objective.

[0048] From a general point of view, it appears that the dispersion of Ct must be minimized in order to minimize the effect of temperature on a watch.

[0049] The invention also relates to a watch 1 suitable for implementing this method. This waterproof watch 1 comprises a waterproof case 2, which contains a movement 3 itself comprising an oscillator 4, which is pivoted on pivots 9 lubricated with a lubricant of viscosity q varying with the temperature according to a law q = f (T) determined according to this method.

Claims

CLAIMS 1. Method for compensating the rate as a function of the temperature of a waterproof watch (1), the waterproof case (2) of which contains a movement (3) itself comprising a regulating member comprising an oscillator (4) and pivoted on pivots (9) lubricated with a lubricant of viscosity q, said case (2) containing, on leaving the factory after the initial rate adjustment, an internal volume V occupied by n moles of a gas of constant R substantially following the law of ideal gases, characterized in that the following are determined in the factory by measurement and / or calculation: - a value of the pressure coefficient Cp of said movement (3), defining the relatively linear variation of the rate of said movement (3) as a function of the pressure P, at constant temperature, of said gas according to the equation m(P) = Cp * P, - a value of the humidity coefficient Ch of said movement (3), defining the maximum relatively linear variation of the rate of said movement (3) as a function of the humidity H in said movement (3) according to the equation m(H) = Ch * H, - the nature of said lubricant and the rule of variation of said viscosity q as a function of the temperature q = f (T), such that said thermal coefficient Ct of said movement (3) varies as a function of the temperature according to a predetermined law Ct = g (T), and such that the operation of the movement varies as a function of the temperature T and as a function of said thermal coefficient Ct of said movement (3) according to the equation m(T)= Ct * T = g (T)* T, so as to generate variations in operation of said movement (3) as a function of the temperature, in the opposite direction to the variations in operation generated by said pressure P of said gas.

2. Method according to claim 1, characterized in that said rule of variation of said viscosity q is determined as a function of the temperature q = f (T), so as to generate variations in the rate of said movement (3) as a function of the temperature inverse to the variations in the rate generated by said pressure P of said gas. Method according to claim 1 or 2, characterized in that the pressure P and / or the number of moles n are adjusted by modifying the pressure P and / or by varying the temperature T of said watch (1) before closing said case (2). Method according to one of claims 1 to 3, characterized in that the humidity coefficient Ch of said movement (3) is determined at the zero value.Method according to one of claims 1 to 4, characterized in that, for an after-sales application, said box (2) is equipped with a sealed volumetric device (5) allowing an after-sales technician to modify the internal volume of said box (2), and / or at least one sealed gas injection or extraction conduit (6), and / or a thermal device (7) allowing the controlled and momentary increase of its internal temperature. Method according to claim 5, characterized in that said volumetric device (5) comprises at least one piston movable in said box (2) and under the action of an external micrometric control screwable and lockable in position by a special tool not supplied to the user. Method according to claim 5, characterized in that said sealed gas injection or extraction conduit (6) is lockable in position by a special tool not supplied to the user.Method according to claim 5, characterized in that said thermal device (7) comprises means for converting light energy and / or means for storing energy. Method according to one of claims 1 to 8, characterized in that said elastic return means of said oscillator (4) are produced in. silicon and / or silicon oxide, and in that, during factory preparation, the thermal coefficient of said elastic return means is modified by modifying the thickness of the silicon oxide layer. Method according to one of claims 1 to 8, characterized in that said elastic return means of said oscillator (4) are produced in the form of elastic thin blades by a "LIGA" process, and in that during factory preparation, the thermal coefficient of said elastic return means that said oscillator (4) comprises is modified by applying a coating and / or by local ablation and / or by adjusting the aspect ratios.Method according to one of claims 1 to 8, characterized in that said elastic return means of said oscillator (4) are produced in the form of thin elastic blades by a wire drawing or rolling process, and in that during the factory preparation, the thermal coefficient of said elastic return means included in said oscillator (4) is modified by applying a coating and / or by local ablation and / or by adjusting the aspect ratios. Method according to one of claims 1 to 11, characterized in that during the factory preparation, the number of moles of gas in said watch is modified, either by closing said case (2) with a pressure defined by calculation to make the running of the watch insensitive to temperature, or by closing said case (2) with a temperature defined by calculation to make the running of the watch insensitive to temperature, and by slowly cooling said case (2) after its closure.Method according to one of claims 1 to 12, characterized in that during the factory preparation, the nature of the gas contained in the watch is modified, by total or partial exchange of said gas with a new gas or mixture of gases having another value of said constant. R, adapted for the adequate adjustment of said thermal coefficient Ct to make the running of the watch insensitive to temperature. Method according to claim 13, characterized in that said case (2) is sealed after said gas exchange, to prevent any action by the user in the absence of a special tool. Method according to one of claims 1 to 14, characterized in that during the factory preparation, the internal volume of said case (2) is modified by adjusting the stroke of at least one piston, under the action of a screwable micrometric control which can be locked in position by a special tool not supplied to the user. Method according to one of claims 1 to 15, characterized in that during the factory preparation, the gas or gas mixture contained in said case (2) is dried, to reduce the humidity H.Method according to one of claims 1 to 16, characterized in that during the factory preparation, a desiccant is inserted into said case, to fix the residual humidity H therein. Waterproof watch (1), the waterproof case (2) of which contains a movement (3) itself comprising an oscillator (4), characterized in that said oscillator (4) is pivoted on pivots (9) lubricated with a lubricant of viscosity q varying with the temperature according to a law q = f (T) determined according to one of claims 1 to 17.

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