Classifications

• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B17/00—Mechanisms for stabilising frequency
  • G04B17/20—Compensation of mechanisms for stabilising frequency
  • G04B17/22—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature
  • G04B17/227—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature composition and manufacture of the material used

Definitions

• the invention relates to a thermocompensated resonator for equipping a regulating member of a timepiece and a method of manufacturing said resonator.
• the invention also relates to a resonator whose adjusted Young's modulus value and / or stiffness is adjusted.
• the time base of a timepiece uses a resonator whose oscillations must be maintained.
• a resonator with a given resonant frequency usually fulfills this function. It is known, in particular, resonators such as the pendulum (which involves gravity), quartz (piezoelectricity), the tuning fork (vibrating blades) or the return springs of more diverse shapes, depending on whether they are designed for oscillate on large or small amplitudes.
• the regulating member is constituted by the pendulum / spiral assembly.
• the spiral spring is in this case fixed by one end on the balance shaft and the other end on a bridge in which pivots the axis of the balance. In this way, the spring contracts and relaxes alternately around its center during pendulum oscillations. Since its creation, a few hundred years back, and until today, the spiral springs are mainly made from a metal blade of rectangular section wound on itself in the form of spiral Archimedes.
• thermoelastic coefficient of the modulus of elasticity of this material is however too important to ensure the frequency accuracy of such a resonator.
• Research on the subject led to the addition of a layer of a material whose thermoelastic coefficient is opposite to that of silicon.
• Berry and Pritchet IBM Technical Disclosure Bulletin # 1237, Vol 14, No. 4, 1971
• amorphous silica SiO 2
• the document EP1422436 discloses a spiral spring from the cutting of a plate ⁇ 001 ⁇ Silicon. This invention aims to overcome the disadvantages described above proposing a spiral whose sensitivity to temperature variations and magnetic fields is minimized. In addition the precision manufacturing technology (Ion Etching) proposed for the shaping of these spirals, combined with a
• thermocompensated resonator comprising a ceramic spring whose surface is coated with at least one second material whose CTE (thermoelastic coefficient) is of opposite sign to the CTE of the material used for the spring core.
• Concentric spring (arming and disarming) can result in the breakage of the coating or in its delamination, resulting in a significant change in the frequency of oscillation.
• patent EP1958031 which reports a thermal compensation by modifying the thermoelastic properties of a so-called photostructurable glass following exposure to a UV source.
• This technique has several limitations inherent in the choice of material and process. The material is on the one hand limited to a particular category of so-called "photostructurable" glasses, which are doped glasses in particular with a photoactive element such as cerium and with a photoactive agent.
• a resonator for equipping a regulator member, or resonator, of a timepiece, the resonator comprising a body used in deformation and being made of a vitreous material having a first thermoelastic coefficient (CTE), said vitreous material having a modified portion so that said modified portion has a second CTE different from the first CTE, so that the resonator is thermally compensated.
• CTE thermoelastic coefficient
• the present invention also relates to a method of manufacturing the resonator, comprising the steps of machining a piece of vitreous material having a first CTE to form the body used in deformation of the resonator; and locally modifying the vitreous material to form said modified portion having a second CTE different from the first CTE.
• the local modification is carried out using an irradiation method such as a laser treatment.
• the irradiation process may involve multiphoton absorption in the vitreous material.
• the modified portion is adjusted so that its physical properties compensate for the physical properties of the rest of the vitreous material (unmodified portion).
• the resonator is thermocompensated, and its stiffness can also be adjusted.
• the resonator thus obtained is non-magnetic and thermocompensated while avoiding the use of coatings.
• the invention also relates to a spiral spring made of a material which is not necessarily vitreous but which is transparent to the wavelengths of a laser (femtosecond type).
• the present invention relates to a spiral spring made of a partially or even entirely crystalline material, especially comprising glasses, silicon (monocrystalline, polycrystalline), glass-ceramics, ceramics, etc.
• a timepiece comprises a body used in deformation, the body being made of a material transparent to the wavelengths of a laser and having a first Young's modulus; said material having a portion locally modified so that said modified portion has a second Young's modulus which differs from the first Young's modulus of the unmodified portion of the material.
• the material may also comprise a portion locally modified so that said modified portion has a second stiffness which differs from the first stiffness of the unmodified material.
• the invention also relates to a method of manufacturing the resonator, comprising the steps of:
• the material may also be modified locally so as to form said modified portion having a second stiffness different from the first stiffness of the unmodified material.
• the method comprises adjusting the frequency of the spiral spring. This adjustment can be made before the assembly of the spiral spring with a balance.
• the frequency of the spiral spring is adjusted so as to match the spiral spring with the balance.
• Figures 1 to 6 show a sectional view of a leaf of a spiral spring, according to one embodiment
• Figure 7 shows a top view of a spiral spring 1 according to one embodiment
• Figure 8 shows a detail of a section of the spiral spring of Figure 7;
• FIG. 9 shows a wafer made of glassy material in which a plurality of spiral springs is produced, according to one embodiment
• Fig. 10 is a sectional view of the wafer of Fig. 9 during an irradiation process, according to one embodiment.
• Figure 11 illustrates the sectional view of Figure 9 after a machining step, according to one embodiment.
• a spiral spring intended to equip a spiral balance-type resonator of a mechanical watch is made of a vitreous material.
• the term "vitreous material” includes in particular pseudo-amorphous (that is to say non-crystalline) materials having the glass transition phenomenon.
• the glass transition is a reversible transition between the hard form and the "melted” or rubbery form of an amorphous material.
• the temperature of Glass transition of an amorphous material is always lower than the melting point of its crystalline form.
• the term “vitreous material” is also understood to mean a material that is partially vitreous (therefore at least
• the vitreous material may comprise any glass as defined above.
• the vitreous material has a low coefficient of thermal expansion, that is to say less than 1 ppm / ° C.
• the vitreous material is silica-based (amorphous aSiO 2) having a coefficient of thermal expansion of about 0.5 ppm / ° C.
• the vitreous material may comprise a pure amorphous silica, a borosilicate, an aluminosilicate, or a silica-based glass with a controlled impurity level.
• the spiral spring 1 comprises a vitreous material having a first ⁇ .
• the vitreous material is locally modified so as to produce a modified portion 3 of the same vitreous material, the modified portion 3 of the vitreous material having a second CTE ⁇ 2 different from the first CTE ⁇ .
• the modified portion comprises said vitreous material having undergone, locally, modifications
• the spiral spring 1 is characterized by an effective CTE ⁇ ⁇ which is defined by the combination of the first CTE ⁇ and the second CTE ⁇ 2.
• the presence of the modified portion minimizes the thermal drift of the resonator formed by the spiral spring and the balance.
• the vitreous material also has a first coefficient
• the spiral spring 1 is therefore also characterized by an effective coefficient of thermal expansion a e ff which is defined by the combination of the first and second coefficients
• FIGS. 1 to 6 show a section of the blade of a spiral spring 1 comprising a matrix in an at least partially vitreous material 2 and a modified portion 3. Said modified portion may
• the exposed areas 3 may have varied geometries and distributions, an asymmetry of these areas may also be chosen to overcome different compressive and tensile stresses compared to the neutral fiber of the blade. These different geometries can be, if necessary, combined on portions distributed along the blade to respect the isotropy of the material or to meet other needs.
• the exposed areas 3 can be anywhere in the blade, preferably without contact with the surface thereof.
• the configuration of the modified portion 3 may also vary along the spiral spring 1.
• this variation may comprise the geometric configuration of the modified portion 3 which varies along the spiral spring 1, but also a variation the value of the second CTE ⁇ 2, and possibly also the second thermal expansion coefficient OC2 and the second Young's modulus E2, in the various modified portions 3, along the spiral spring 1.
• the modified portion 3 can be arranged from so as to extend in the longitudinal direction of the spiral spring 1 in a continuous manner (such as continuous fibers) or discontinuously. In the same way, elongate geometries of the modified portion 3 may be oriented in any direction, preferably in the longitudinal direction of the spiral spring 1.
• the geometry of the spiral spring 1 may advantageously incorporate fastening means at both ends, as they are known in the art. the person skilled in the art, with rigid mounting means or, preferably, elastic. For various identification purposes (pairing, etc.), identification references may be micro-engraved on the spiral spring
• the thermal drift of the resonator relates to the relative variations of the oscillation frequency of the regulating organ following temperature changes in the range of 8 to 38 ° C.
• the relative frequency variations with the temperature mainly depend on the effective coefficient of thermal expansion oc e ff and the effective CTE e ff spiral spring 1.
• the oscillation frequency can be written according to:
• Eeff is the effective Young's modulus of the spiral spring
• h is the spiral spring height
• e is the spring-spiral thickness
• L is the spring-spiral length
• thermo compensation is obtained through the growth of an amorphous S1O2 layer around the spring-spring core.
• Amorphous S1O2 is one of the few materials with a positive CTE, of the order of 200 ppm / C.
• the thickness of the S1O2 layer for the thermocompensation of the spiral spring is predicted according to the dimensions of the spiral spring blade as described in EP1422436.
• the CTE of the spiral spring is in this case an effective CTE p e ff comprising the contribution of the monocrystalline silicon core of the spiral spring and the contribution of the outer layer of amorphous S1O2.
• a method of manufacturing the resonator comprises the steps of:
• the machining step may be performed by a chemical etching process, a physical etching process or a combination of both methods.
• the step of forming said modified portion 3 can be performed before, during or after the machining step.
• the method may further comprise another step of forming the modified portion, after the machining step.
• the step of locally modifying the vitreous material comprises a laser treatment.
• the laser is operated in non-ablative mode. That is, no material is removed in the area where the laser is focused.
• the laser uses durations
• ultrashort pulses that is to say pulse durations between a few femtoseconds to a few nanoseconds
• Ultra-short laser pulse durations induce structural modifications resulting from complex nonlinear phenomena which also give rise to a local modification of the CTE of the modulus of elasticity as well as the modulus of elasticity itself.
• the use of pulse durations between a few femtoseconds and a few picoseconds promote
• Pulse times between a few femtoseconds and a few nanoseconds can be obtained with several types of lasers of very different wavelengths, for example, and preferably a Ti: Sapphire laser (650 to 1100 nm) , a Yb laser (1030 nm) or a laser in the mid-infrared (mid infrared, 1050 nm).
• the precise nature of the laser-material interaction will be different.
• the first CTE ⁇ of the vitreous matrix will be modified, at least locally so as to obtain the modified portion 3 having the second CTE ⁇ 2.
• the same reasoning also applies to obtain the modified portion 3 having the second coefficient of thermal expansion 0C2 different from the first thermal expansion i and having a second Young's modulus E2 different from the first Young's modulus E L
• Such a laser treatment would change the effective CTE e ff hairspring 1, to modify the coefficient of thermal expansion oceff effective and / or adjust the value of the effective Young's modulus E eff of said spring 1
• the fine adjustment of the effective Young's modulus E f e of spring 1 makes it possible to adjust its stiffness (and thus the frequency of the resonator) without having to modify either the height nor the thickness of the vibrating body (1). This facilitates for example the spiral-balance balancing operations at the same time as allowing a significant increase in the efficiency of these operations.
• FIG. 7 shows a top view of a spiral spring 1 according to one embodiment.
• the spiral spring 1 comprises an inner end curve 4 and an outer end curve 5.
• a detail of a section 6 of the spiral spring 1 is shown in FIG. 8.
• the modified portion 3 comprises a portion 3 'extending in the direction
• the structure of a solid material having the glass transition phenomenon (in other words, its specific volume or density) can be set according to the thermal cycle (heating-cooling ramp) to which it is subjected. It is therefore possible, depending on the thermal cycle, to freeze the structure of a material having the
• vitreous transition phenomenon either in a particular vitreous state or even in a crystalline state.
• a glass it is possible to freeze its structure by subjecting it to a thermal cycle which does not include a passage in the liquid state of the material. That said, by remaining in the solid vitreous zone of the material, it is possible to change its structure by subjecting it to a particular thermal cycle.
• Silica-based glasses are densified following an increment of their fictitious temperature.
• the fictional temperature of a glass is the
• the local modification of the vitreous material by a focused laser treatment using ultrashort laser pulse durations makes it possible to obtain a modified portion by means of phenomena of a thermal nature such as those described above.
• the phenomena of thermal nature leading to a local change in the structure of the glassy material can be adjustable, in particular by playing with the repetition rate of the laser.
• the modified portion 3 has a density that differs from the density of the vitreous material.
• the different density of the modified portion 3 may comprise the creation of a crystalline polymorph of an amorphous silica (such as, for example, alpha or beta quartz, stishovite, tridymite, chalcedony or cristobalite), or the formation metal clusters according to the presence or absence of impurities or the formation of a densified region following a local increment of the fictitious temperature of the silica, or the formation of zones
• an amorphous silica such as, for example, alpha or beta quartz, stishovite, tridymite, chalcedony or cristobalite
• the laser is focused at the nanoscale or micrometer scale.
• Such a laser allows the generation of the modified portion whose modulus of elasticity CTE and stiffness can be modified, and this in proportions that are not necessarily constant or linear.
• the formation of the modified portion having a second CTE different from the first CTE ⁇ makes it possible to adjust, on a case by case basis, the value of the effective CTE e ff of the resonator.
• the method of the invention offers the advantage of being able to accurately and individually adjust the thermomechanical properties of each resonator for the purpose of a fine adjustment of the temperature behavior of the oscillator.
• FIG. 9 shows a wafer 7 made of vitreous material in which a plurality of spiral springs 1 are manufactured.
• FIG. 10 shows a sectional view of the wafer of FIG. 9 during the local modification step making it possible to form the modified portion 3, for example, by irradiation with a focused laser 8.
• the laser beam 8 can move, for example x, y, z, so as to carry out the local modification in a more specific form. or less complex, here an "annular" shape in the body body of the spiral spring 1.
• the parts indicated by the numeral "9" correspond to the vitreous material which is machined in the machining step.
• FIG. 11 illustrates the sectional view of FIG. 9 after the machining step during which the parts 9 have been eliminated by machining, releasing the spiral springs 1 comprising the modified portion 3.
• FIG. 9 also shows parts 7a, 7b, 7c of the wafer 7 for which the spiral springs 1 have undergone a different irradiation treatment according to the part 7a, 7b, 7c of the wafer in which the springs are located.
• Spirals 1 Therefore, the spiral springs 1 in one of the different parts 7a, 7b, 7c may have a modified portion 3 whose physical properties differ from those of the modified portion 3 of the spiral springs 1 in the other parts 7a, 7b, 7c of the wafer 7.
• the step of locally modifying the vitreous material may therefore be performed locally not only at the scale of the body used in deformation (spiral spring) 1 but also at the scale of the wafer 7.
• the method also has the advantage of being applicable to a broad category of glasses including those called “non-photostructurables”. Therefore, the vitreous material processing process takes place directly without the need for additional steps such as
• thermoelastic properties of the vitreous material without any restriction as to the location of the modified portion in the volume of the vitreous material.
• the invention is not limited to a resonator-balance spring type but also applies to any type of resonator adapted to a watch application, such as a tuning fork-type resonator, whose body used in deformation, that is to say the spiral spring in the case of a balance spring resonator or the vibrating blades in the case of a tuning fork resonator, is made of a vitreous material having a first thermoelastic coefficient, and so as to include a modified portion 3 having a second CTE different from the first CTE ⁇ .
• a tuning fork-type resonator whose body used in deformation, that is to say the spiral spring in the case of a balance spring resonator or the vibrating blades in the case of a tuning fork resonator, is made of a vitreous material having a first thermoelastic coefficient, and so as to include a modified portion 3 having a second CTE different from the first CTE ⁇ .
• the discussion has concerned a spiral spring made of a vitreous material, as defined above.
• the present invention also relates to a spiral spring made of any material transparent to the wavelengths of a laser (for example of the femtosecond type).
• the present invention relates to a spiral spring made of a partially or even entirely crystalline material, especially comprising glasses, silicon (monocrystalline, polycrystalline), glass-ceramics, ceramics, etc.
• the material is locally modified (for example using a laser, preferably femtosecond type) so as to produce a modified portion 3 having a second Young's modulus E2 which differs from a first module of Young E1 of the unmodified portion of the material.
• the stiffness of the spiral spring 1 depends on its Young's modulus (its rigidity) but also the ratio of its section to its length. It can be assumed, however, that the ratio of the section to the length of the spiral spring will not be changed by the local modification.
• the material has a first stiffness K1 and the modified portion has a second stiffness K2 which may be different from the first stiffness K1.
• the adjustment of the effective Young's modulus E e ff of the hairspring 1 thus makes it possible to adjust a value of the effective stiffness K e ff of the hairspring 1, without having to modify either the height or the thickness of the spring -spiral 1.
• the effective stiffness K e ff spiral spring 1 is defined by the combination of the first and the second stiffness K1, K2.
• the local modification of the stiffness of the spiral spring 1 can be used for adjusting the frequency of the spiral spring 1, for example before assembly with a pendulum. This facilitates for example the spiral-balance balance pairing operations, or even pairing of the regulating organ as a whole with respect to the movement, while at the same time as allowing a significant increase in the efficiency of this operation.
• modified portion 3 may comprise a portion 3 'extending in the longitudinal direction of the spiral spring 1 continuously and / or discontinuously.
• the modification of the effective Young's modulus E e ff and / or of the effective stiffness K e ff in a specific portion of the spiral spring 1, as for example in the end curve of the spiral, makes it possible to optimize the concentricity of the its deployment relative to the axis of the balance. It is also possible to compensate for sagging effects due to gravity or other isochronous defects. According to another embodiment, the material is locally modified so as to adjust the internal stresses in the modified portion 3.
• the local modification is carried out using a laser treatment, preferably using a laser using ultra-short pulse durations, that is to say durations of pulses between a few femtoseconds to a few nanoseconds, and
• the modifications thus induced in the modified portion of the material may be of a continuous nature, the formation of (nano) self-organized structures, and / or the formation of empty nano.
• These modifications can induce different types of anisotropy in the modified portion of the material, which can have significant effects on the chemical, optical, thermal and / or mechanical properties.
• the change in the volume of the material resulting from the exposure induces stresses around the laser exposed areas, and thus changes in the internal stresses, which may be compressive or tensile stresses, in the modified portion.
• the stress induced depends mainly on two parameters: polarization and pulsation energy.
• the local modification can be performed so as not to influence the thermocompensation of the modified portion of the material, or at least not linearly.
• the effective Young's modulus and the effective CTE can be controlled by the total amount of modified areas while the residual stresses can be controlled by the location of the affected areas relative to the realized component.

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