Patent Publication Number: US-2021191335-A1

Title: Flexible horological component, particularly for an oscillator mechanism, and horological movement including such a component

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is claiming priority based on European Patent Application No. 19219083.3 filed on Dec. 20, 2019. 
     FIELD OF THE INVENTION 
     The present invention relates to flexible horological components, particularly for an oscillator mechanism of a horological movement with a positive thermoelastic coefficient. 
     The invention also relates to a horological movement including such a component. 
     BACKGROUND OF THE INVENTION 
     Horological movements generally comprise a barrel, an escapement mechanism and a mechanical oscillator mechanism. The escapement mechanism particularly includes a pallet assembly and an escapement wheel, whereas the oscillator mechanism comprises a spiral spring associated with an oscillating inertia-block referred to as a balance. 
     Technical progress in composite materials now enables certain components to be manufactured in innovative and high-performance materials, which enables, at least in part, metallic materials not to be used. At the present time, the use of nanotubes or nanowires, for example, for manufacturing components is being tried. Such materials with nanotubes or nanowires offer advantages in terms of light weight and strength. Thus, the document JP2008116205A describes a spiral spring comprising a graphite and amorphous carbon matrix, reinforced by carbon nanotubes which are dispersed in the matrix and aligned in the longitudinal direction of the spiral. 
     However, flexible components, for example resonators, are generally subject to deformations and modifications of the elastic properties thereof, which are due to temperature variation during the repetitive movements that they make. The variation of the frequency as a function of temperature in the case of a sprung-balance observes substantially the following formula: 
     
       
         
           
             
               
                 
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     where: 
     
       
         
           
             
               
                 Δ 
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                 Δ 
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     is me frequency variation as a function of temperature; 
     
       
         
           
             
               
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     is the variation of the Young&#39;s modulus as a function of temperature, i.e. the thermoelastic coefficient (TEC) of the balance-spring;
         α s  the expansion coefficient of the balance-spring, expressed in ppm.° C −1 ;   α b  the expansion coefficient of the balance, expressed in ppm.° C −1          

     The deformations and modifications of the properties of the material induce a variation of the modulus of elasticity of the flexible component. However, these temperature-induced variations of the modulus of elasticity impede the precision of horological movements. 
     SUMMARY OF THE INVENTION 
     An aim of the invention is hence that of providing a flexible horological component, which avoids the problem cited above. 
     For this purpose, the invention relates to a flexible horological component for an oscillator mechanism of a horological movement, the component extending along a principal plane and including at least a part made of a composite material. 
     The component is remarkable in that the composite material comprises a matrix and a multitude of nanotubes or nanowires distributed in the matrix, the nanotubes or nanowires being juxtaposed and disposed substantially parallel with an axis substantially perpendicular to the plane of the component, the matrix including a flexible filling material to fill the interstices between the nanotubes or nanowires, the filling material comprising at least in part a thermal compensation material wherein the thermoelastic coefficient is of the opposite sign to that of the other materials of the composite material. 
     Thus, thanks to such a flexible component, it is possible to compensate for the modifications of the properties of the material, for example for a spiral spring, when the temperature varies. Indeed, the thermal compensation material having a thermoelastic coefficient of opposite sign to the other materials of the composite material, the variation of the modulus of elasticity of the compensation material occurs inversely to that of the deformation of the other materials of the component, which have a thermoelastic component of opposite sign. Thus, the performance of the component remains substantially the same, regardless of the temperature of use of the component, in particular in the case of significant temperature variation. 
     According to an advantageous embodiment, the thermal compensation material has a thermoelastic coefficient greater than 0. In this case, the thermal compensation material compensates for other materials having a thermoelastic coefficient less than zero. 
     According to an advantageous embodiment, the thermal compensation material includes silicon oxide SiO2, preferably predominantly, or even entirely. 
     According to an advantageous embodiment, the thermal compensation material includes Niobium, preferably predominantly, or even entirely. 
     According to an advantageous embodiment, the thermal compensation material forms an outer layer of the matrix, the outer layer preferably surrounding the matrix entirely. 
     According to an advantageous embodiment, the thermal compensation material is arranged directly on the nanotubes or nanowires. 
     According to an advantageous embodiment, the nanotubes are made of carbon. 
     According to an advantageous embodiment, the nanotubes are multi-walled. 
     According to an advantageous embodiment, the nanowires are made using an element to be selected from the following list: gold, silicon, silicon oxide, boron nitride, gallium nitride, silicon nitride, zinc oxide, gallium arsenide, tungsten sulphide, silver, copper, manganese arsenide, indium arsenide. 
     According to an advantageous embodiment, the nanotubes or nanowires have a diameter within a range ranging from 2 to 50 nm, preferably within a range ranging from 3 to 15 nm, or from 5 to 10 nm. 
     According to an advantageous embodiment, the nanotubes or nanowires have a length within a range ranging from 100 to 500 microns, preferably within a range ranging from 100 to 300 microns, or from 150 to 200 microns. 
     According to an advantageous embodiment, the filling material further comprises an element to be selected from the following list: silicon, tungsten, organic materials such as parylene, hexagonal boron nitride, Al2O3 type monocrystalline ruby, diamond, tungsten or molybdenum disulphides, graphite, lead, silicon carbide, nickel, indium phosphide, titanium oxide. 
     According to an advantageous embodiment, the component is a spiral spring of an oscillator mechanism, or a flexible blade guide of an oscillator mechanism. 
     The invention also relates to a horological movement comprising a flexible horological component according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will emerge on reading several embodiments given merely by way of non-limiting examples, with reference to the appended drawings wherein: 
         FIG. 1  schematically represents a through perspective view of a composite material according to a first embodiment of the invention, 
         FIG. 2  schematically represents a through perspective view of a composite material according to a second embodiment of the invention, 
         FIG. 3  schematically represents a perspective view of a balance equipped with a spiral spring of an oscillation mechanism, and 
         FIG. 4  schematically represents a cross-sectional view of the composite material during the method for manufacturing the first embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description, we describe flexible components for a horological movement. The component is a flexible component to be selected from a list comprising for example an oscillator mechanism spiral spring or a flexible oscillator mechanism blade guide. 
     The flexible component is preferably flat and extends along a principal plane (P). The component includes at least a part made of a composite material  1  represented in  FIG. 1 . Preferably, the component is made entirely of this composite material  1 . Thus, the components from the preceding list can be made of this composite material  1 . 
     The composite material  1  comprises a matrix  2  and a multitude of nanotubes or nanowires  3  distributed in said matrix  2 . The component has, for example, a substantially flat shape extending along a preferential plane P. 
     The nanotubes or nanowires  3  form a structure of the composite material  1 , wherein they are juxtaposed and disposed substantially parallel with one another. The term nanotube denotes tubes wherein the inside is generally hollow, whereas nanowires are generally solid, i.e. one-piece. 
     The nanotubes or nanowires  3  are disposed substantially parallel with an axis A, perpendicular to the plane P of the component  1 . They are evenly distributed so as to be spaced apart homogeneously in the matrix  2 . Advantageously, the composite material is embodied such that nanotubes or nanowires  3  are present in the entire mass of the matrix  2 . 
     The nanotubes or nanowires  3  have, for example, a diameter D within a range ranging from 2 to 50 nm. Preferably, the nanotubes or nanowires  3  have a diameter within a range ranging from 3 to 15 nm, or from 5 to 10 nm. 
     The nanotubes or nanowires  3  can have a length L within a range ranging from 100 to 500 microns. Preferably, the nanotubes or nanowires  3  have a length within a range ranging from 100 to 300 microns, or from 150 to 200 microns. 
     In a first embodiment, the composite material includes nanotubes  3  made of carbon. The carbon nanotubes  3  are generally multi-walled, but can also be optionally single-walled. 
     In a second embodiment, the composite material includes nanowires  3  made at least in part using a material to be selected from the following list: gold, silicon, boron nitride, gallium nitride, silicon nitride, zinc oxide, gallium arsenide, tungsten sulphide, silver, copper, manganese arsenide, indium arsenide. 
     The matrix  2  includes a filling material  4  to fill the interstices and join the nanotubes or nanowires  3  to one another. The material  4  can advantageously include the nanotubes or nanowires  3 , by being injected into the interstices  5  between the nanotubes or nanowires  3 . This material  4  helps provide cohesion between the nanotubes or nanowires  3  and thus modify the mechanical properties of all of the nanotubes or nanowires  3 , in particular to render the matrix flexible. In the first embodiment of the nanotubes, the material  4  can also be arranged inside  14  the nanotubes  3 . 
     The filling material  4  enables the flexibility of the component, the filling material 4 having elastic mechanical properties. Furthermore, a flexible component is obtained thanks to the geometric shape selected for the component. Thus, thanks to this flexible filling material  4 , specific components of the horological mechanism can be embodied. 
     According to the invention, the filling material  4  comprises at least in part a thermal compensation material  18  wherein the thermoelastic coefficient (TEC) is of opposite sign to that of the other materials of the composite material ( 1 ). 
     The thermoelastic coefficient (TEC) is for example within a range ranging from 1ppm/° C. to 100ppm/° C. 
     The volume fraction and the thermoelastic coefficient of the thermal compensation material  18  are selected to compensate for the thermoelastic coefficient of the filling material  4 . This choice can be made by calculation or empirically. 
     In a first alternative embodiment, the thermal compensation material  18  includes silicon oxide SiO2, preferably predominantly, or even entirely. The silicon oxide can be obtained by oxidising silicon. The silicon is deposited in thin layers, using known LPCVD type low-pressure vapour deposition techniques or by ALD type atomic layer deposition, by PECVD type plasma deposition, or indeed by epitaxial oriented growth. In this case, the thermoelastic coefficient of the thermal compensation material  18  is greater than zero, and enables materials wherein the thermoelastic coefficient is less than zero to be compensated for. 
     In a second alternative embodiment, the thermal compensation material  18  includes Niobium, preferably predominantly, or even entirely. Niobium is a transition metal which can be deposited using conventional known thin layer deposition techniques, such as PVD, CVD or ALD. 
     For both embodiments, the filling material  4  forming the matrix  2  can further comprise an additional element from the following list: tungsten, organic materials such as parylene, hexagonal boron nitride, Al2O3 type monocrystalline ruby, diamond, tungsten or molybdenum disulphides, graphite, lead, silicon carbide, nickel, indium phosphide, titanium oxide, or carbon. For example, the element of the filling material is Silicon, and the thermal compensation layer is silicon oxide. 
     In a first embodiment, represented in  FIG. 1 , the thermal compensation material  18  is arranged directly on the nanotubes or nanowires  3 . The thermal compensation material  18  is infiltrated between nanotubes or nanowires  3  to cover same at least partially. If there is one, the element of the filling material  4  is also infiltrated between the nanotubes or nanowires  3  to cover the thermal compensation material  18 . In this case, the composite material  1  is formed of the nanotubes or nanowires  3 , the thermal compensation material  18  and the additional element of the filling material  4 . 
     In the case of Niobium, the latter can be mixed with the element of the filling material  4 , for example titanium, to form an alloy offering the thermal compensation properties according to the invention. 
     In a first alternative embodiment, the element of the filling material  4  is infiltrated between the nanotubes or nanowires  3 , then is covered by the thermal compensation material. The thermal compensation material is also infiltrated between the nanotubes or nanowires, but is not directly in contact with the nanotubes or nanowires. 
     In a second alternative embodiment, only the thermal compensation material  18  is infiltrated between the nanotubes or nanowires to join them to one another and form the component. In this case, the filling material  4  is formed solely of the thermal compensation material, with no additional element. The composite material  1  is then formed by the nanotubes or nanowires  3  and by the thermal compensation material  18 . 
     In a second embodiment, the compensation material  18  forms an outer layer  19  of the matrix, the outer layer  19  preferably surrounding the matrix entirely, although it is possible to deposit a layer only on some faces. For this embodiment, the element of the filling material  4  is infiltrated between the nanotubes or nanowires  3  to form the core of the component, then a layer  19  of the thermal compensation material is deposited around the core to form the component. 
     The filling material  4  enables the flexibility of the component, the material  4  having flexible mechanical properties to enable an elastic deformation of the component. Furthermore, a flexible component is obtained thanks to the geometric shape selected for the component. The component is, for example, a spiral spring  6  of an oscillator mechanism  8  of a horological movement. 
     Thus, the horological components can benefit from the advantages of the composite materials based on nanotubes or nanowires, while retaining the essential properties for this type of component, for example for a spiral spring. 
       FIG. 3  represents a spiral spring  6  of a balance  8  made from such a flexible composite material. The spiral spring  6  is a narrow strip wound in an Archimedean spiral, such that there is a gap between the facing strip portions. Thus, by contracting and deforming the spiral, the desired spring effect is obtained. The balance  8  comprises a circular ring  9  and two rectilinear arms  11 ,  21  intersecting at the centre of the ring  9  and connecting two opposite sides of the ring  9 . The arms  11 ,  21  hold a shaft  12  substantially perpendicular to the plane of the ring  9 . The shaft  12  bears the spiral spring  6  in a plane parallel with that of the ring  9  by a first end. The second end is intended to be attached to another part  17  of the horological movement. 
     To manufacture the components, a method comprising the following steps is used, for example:
         a first step of preparing a substrate, for example a silicon substrate, preferably by photolithography, so that the nanotube or nanowire forest growth occurs at a specific location corresponding to the shape of the desired component. Thus, a flexible spiral or pivot shape is designed by photolithography.   a second step of growing the nanotubes or nanowires on a substrate, not shown in the figures,   a third step of inserting the constituent filling material of the matrix in the nanotube or nanowire distribution, and   a fourth step of detaching the component from the substrate.       

     During the second step, the nanotubes or nanowires 12 are grown parallel with an axis substantially perpendicular to the substrate. 
     For carbon nanotubes, examples of the first and second steps are found in the document “Mechanical and electrical properties of carbon-nanotube-templated metallic microstructures” by Richard Scott Hansen (June 2012), or in the Senior Thesis by Collin Brown (22 Apr. 2014) of Brigham Young University entitled “Infiltration of CNT forests by Atomic Layer Deposition for MEMS applications”. 
     In  FIG. 5 , the substrate  9  is coated with a layer of silica  10 , and a layer of catalyst  11 , for example iron. The carbon nanotubes  12  are formed on the layer of catalyst  11  by growth. 
     Upstream from the second step, additional nanotubes can be mixed in a solvent and dispersed on the layer of catalyst, for example by ultrasound, to define a top layer of nanotubes. This top layer  13  of nanotubes is porous so that the carbon (or other material) forming the nanotubes  12  can be deposited therethrough, such that the nanotubes  12  grow under the top layer  13 . Thus, regular and homogeneous growth of the nanotubes  12  is ensured so that they all have substantially the same length. The third step is also performed through the top layer  13  of nanotubes  12 , thanks to the porosity thereof. 
     As regards the manufacture of the nanowires, conventional techniques associated with the material selected in the list are used. Thin layer deposition is preferably used, for example by CVD (Chemical Vapour Deposition) type chemical deposition or by PVD (Physical Vapour Deposition) type physical deposition. As in the first embodiment, photolithography methods are used to select the locations of a substrate, for example made of silicon, where the nanowires are grown. The flexible material is inserted between the nanowires. Finally, the component is detached from the substrate once it is complete. 
     International patent application WO 2014/172660 gives an embodiment example of silica nanowires. Silica nanowires have a thermoelastic coefficient greater than zero. Thus, the thermoelastic compensation material of the filling material must have a thermoelastic coefficient less than zero to compensate for the material of the nanowires. 
     Naturally, the invention is not limited to the embodiments described with reference to the figures and alternative embodiments could be envisaged without leaving the scope of the invention.