Anchor plate for the movement inhibition of a wristwatch, and adapted manufacturing process

Description

Technical field

[0001] The present invention relates to an escapement pallet, in particular an escapement pallet made of diamond. The present invention also relates to a method of manufacturing such a pallet. State of the art

[0002] Mechanical parts for mechanical watch movements are most often made of metal. Moving parts, such as axles, wheels, pinions, escapement lever, escape wheel, balance wheel, springs, and balance springs, are frequently made of steel, or elinvar steel for the balance spring. The base plate and bridges are generally made of brass or steel. Other materials are used less frequently, such as ruby ​​for bearings or pallets, or ceramic for some bearings.

[0003] Intensive research has been conducted to replace these conventional materials and avoid some of their drawbacks. For example, silicon is now used industrially for the manufacture of escapement and balance spring components in particular. EP732635A1 (CSEM) describes a micromechanical part, for example an anchor for a watch movement, cut from a silicon wafer by etching using a plasma gas around a shaped mask previously provided on the face of the wafer.

[0004] Silicon has the advantage of being easy to machine, reproducibly, with technologies that are perfectly mastered for the manufacture of integrated circuits or MEMS in particular. However, it has certain disadvantages, notably an insufficient tribological surface finish and a relatively high coefficient of friction.

[0005] CH669109A1 (The Swatch Group R&D Ltd) suggests improving this surface finish by depositing a layer of DLC ("Diamond Like Carbon") on the silicon. Similarly, US2002 / 114225 (Damasko) describes a steel escapement lever coated with a DLC ("Diamond Like Carbon") layer. US2012 / 0263909 (Diamaze Microtechnology SA et al.) describes another example of a mechanical part coated with diamond or a DLC layer.

[0006] DLC coatings have some of the properties of natural diamond, although their crystal structure is very different. Typically, these coatings are produced using carbon deposition processes such as plasma, filtered arcs, ion beams, sputtering, etc. These rapid, high-energy processes do not allow the carbon atoms to arrange themselves in the typical sp3 cubic arrangement of diamond; the arrangement of atoms is generally amorphous, with a tangle of differently oriented crystal microstructures.

[0007] Furthermore, known DLC coating deposition processes generate a material with significant proportions, greater than 10%, of hydrogen, graphitic carbon or other components.

[0008] A steel or silicon part coated with a DLC layer therefore has tribological surface conditions that are certainly improved, but still far from perfect. The adhesion of the DLC coating to the substrate is also a weak point. In any case, the additional step required for the deposition of this DLC layer complicates manufacturing. Furthermore, it is difficult to precisely control the shape of the part after the coating has been deposited.

[0009] The anchors in the escapement of mechanical movements are particularly subject to severe constraints. It is first of all desirable to reduce their mass and moment of inertia as much as possible in order to limit the energy required for the high-frequency oscillation of these moving parts, and therefore to increase the watch's power reserve. The anchor, in particular the anchor pallet, is however subjected to repeated shocks at each alternation, or during shocks of the watch, and must therefore be sufficiently solid. In addition, a rigid anchor is generally desired that does not deform at each alternation, which also limits the minimum thickness of the part.

[0010] On the other hand, the anchor and in particular the pallets mounted on the anchor must be able to receive an impulse from the escape wheel at each alternation, then to block this same escape wheel. A coefficient of friction as low as possible between the pallet impulse plane and the teeth of the escape wheel makes it possible to increase the energy efficiency of the escapement and therefore to increase the rate of the watch. The tribological condition of the pallet impulse plane must therefore be as good as possible. The pallets must also be hard enough to absorb the shocks transmitted by the escape wheel without deformation.

[0011] For this purpose, the use of ruby ​​pallets is widespread. Furthermore, DE102008029429A1 suggests, in relation to Figure 20, a silicon anchor that integrates the pallets and can be coated with a DLC layer. This anchor, however, suffers from the inherent defects of silicon, namely great brittleness.

[0012] It would therefore be desirable to produce anchors and pallets of anchors in materials that are stronger, lighter and have a better coefficient of friction than ruby ​​or conventional DLC coatings. According to a first aspect of the invention, this anchor and / or in any case the pallets are made of diamond; micromechanical parts made of diamond are already known. Thus, WO2004 / 029733A2 (Fore Eagle Co Ltd) describes watch components made at least partially of this material. This document lists various advantages of diamond, including its hardness, a low coefficient of friction, good shock resistance, high mechanical strength, a high modulus of elasticity, a low coefficient of thermal expansion, transparency and the ability to not scratch.

[0013] EP2407831A1 (Rolex SA) describes a hairspring for a watch oscillator that can be made of a low-density material such as silicon, diamond, or quartz. The hairspring can be made by a chemical etching process using plasma (DRIE, Deep Reactive Ion Etching).

[0014] CH701155B1 (Complitime SA) describes a balance wheel for a timepiece comprising a plate which can be made of diamond, quartz, silicon or corundum.

[0015] WO2005 / 017631 (Fore Eagle Co Ltd) describes another balance wheel made of diamond and obtained by chemical etching using a plasma.

[0016] EP2107434A1 describes a mechanical part, in particular an anchor wheel for watchmaking, made of silicon or diamond.

[0017] EP2233989 (Ulysse Nardin Le Locle SA) describes a diamond spiral spring obtained by deep engraving.

[0018] CH701369 describes a diamond barrel spring.

[0019] DE102008029429 concerns watch parts, for example parts of the oscillating organ, made of diamond. For pallets, this document recommends a non-metallic material, preferably polycrystalline silicon.

[0020] Although the use of diamond for the manufacture of mechanical parts is known, its use is reserved for the manufacture of wheels, balance springs, balance wheels, or as DLC coating for anchors.

[0021] On the other hand, the type of diamond used for the above pieces is usually not specified in these documents. In practice, it is always polycrystalline synthetic diamond, which costs 10 to 50% less than natural diamond, and can be produced in shapes suitable for the intended use.

[0022] Various methods for manufacturing synthetic diamond are known. US8088221B2 (Z. Shapiro) describes a process for manufacturing synthetic diamond at low temperature and relatively low pressure. EP2189555A2 (Appollo Diamond Inc) describes another process for producing synthetic diamond. Processes using CVD growth or explosive detonation have also been suggested, notably in US2003 / 205190.

[0023] WO99 / 22049 describes various methods for polishing the pulse plane for a polycrystalline diamond pallet, such polishing methods being also described in EP2511229 and WO01 / 75197. DE 100 62 933 relates to the manufacture of an anchor and its associated anchor wheel, with materials having different hardnesses, in particular a rough diamond anchor and a carbon steel wheel.

[0024] Finally, document EP2581794 A1 discloses two mechanical components for watchmaking made of monocrystalline diamond, these two elements being able to be a pallet / escape wheel pair. Brief summary of the invention

[0025] There is, however, a need, particularly in mid-range and high-end watchmaking, for micromechanical components made from materials offering a better compromise between the desired properties of hardness, mechanical strength, lightness, low thermal expansion, stability of the modulus of elasticity, and ease of high-precision machining.

[0026] According to the invention, these aims are achieved in particular by means of the clockwork movement according to the appended claim 1.

[0027] In the present application, the term "pallet" means the part at the interface between the regulating organ and the escapement, on the regulating organ side, which receives from the escapement the energy intended to oscillate the regulating organ and / or which makes it possible to block the escapement at each alternation. The pallet may be embedded in an arm of the anchor, for example a Swiss anchor. Pallets often have a parallelepiped shape, with an inclined plane on the escape wheel side and intended to receive the impulse from the escape wheel; other pallet shapes can however be imagined, including pallets with a curved face on the escape wheel side. The pallet may also be an integral part of the anchor or another part of the escapement, which in this case may be made monolithically from single-crystal diamond. The pallet may be rigid or even flexible.

[0028] A palette is said to be "made entirely of diamond" if it is made of a single diamond crystal, without a substrate in another material, without a surface coating and generally without assembly. Impurities in small quantities, for example less than 3%, may at most be present, particularly in the case of natural diamonds, but also synthetic diamonds. Impurities can, for example, be formed by doping.

[0029] A diamond is considered monocrystalline if it consists of a single crystal, or essentially a single crystal except for a limited number of distinct crystals, often smaller than the main crystal, which are unwanted but result for example from the manufacturing process or from imperfect crystallization around impurities or edges.

[0030] The invention is based in particular on the observation that monocrystalline diamond has many advantages over the more widespread polycrystalline diamond, and even more so over DLC coatings.

[0031] In particular, monocrystalline diamonds have the advantage over polycrystalline diamonds of being extremely strong; in fact, no crack initiation exists between the different grains. This strength makes it possible to produce thinner and therefore lighter parts with the same strength. For example, it is possible to produce parts such as, without limitation, anchor wheels or anchors with a thickness of less than 120 microns, preferably less than 100 microns, for example between 20 and 60 microns, from monocrystalline diamond. In the case of a pallet, the thickness is advantageously between 100 and 400 microns, for example 320 microns, or between 100 and 160 microns, preferably between 100 and 120 microns. Such thicknesses would be practically impossible to achieve with parts made of steel, silicon or polycrystalline diamond, because these parts would be too fragile and very difficult to assemble without breaking them.

[0032] Thanks to this extreme thinness, it is possible on the one hand to reduce the thickness of the movement, and above all to reduce the inertia of the moving parts. This makes it possible to increase the watch's power reserve, and to increase the oscillation frequency of the regulating organ.

[0033] On the other hand, monocrystalline diamonds generally have a smoother surface finish than polycrystalline diamonds or DLC coatings, whose grain structure does not allow for an optimal tribological surface.

[0034] Polycrystalline diamonds known in the prior art for the manufacture of mechanical parts are extremely hard, harder than usual monocrystalline natural diamonds. However, contrary to popular belief, such high hardness is not always necessary or even advantageous for a watch component. This hardness results in high polishing costs and faster wear of the softer parts in contact.

[0035] It has also been observed that the pulse plane parallel to the {001} or preferably {011} crystal plane allows to obtain a better tribological state after polishing than a crystal plane parallel to the {111} plane or oblique to these planes.

[0036] The pallet can be made by cutting from a flat plate.

[0037] Plates can be cut using a laser from a non-flat diamond. The laser can be tilted during cutting. The laser direction can be changed using a mirror during cutting. Cutting can be performed from both ends of the workpiece.

[0038] Cutting flat parts from a plate can be performed using a laser oriented perpendicular to the plate. The cutting path can be defined using laser path control software. The path can be optimized to minimize the risk of cracking in any direction other than the cutting direction. The path can be optimized taking into account the shape and dimension of the laser beam. Polishing thickness gauges can be cut to control the depth to which the part must be polished subsequently.

[0039] The palette can be made of natural or synthetic monocrystalline diamond.

[0040] Natural monocrystalline diamonds of a size suitable for the manufacture of mechanical parts have a reputation for being very expensive, so there was a strong prejudice against their use in the manufacture of such parts. However, it has been noted that many natural monocrystalline diamonds are discovered each year with shapes that do not allow them to be cut for use in jewelry, for example. Such diamonds are most often split to reduce them to smaller usable diamonds, or reduced to diamond powder for industrial applications. The value of such pieces is therefore significantly lower than that of diamonds commonly used in watchmaking and jewelry.

[0041] Synthetic diamonds are in the vast majority of cases polycrystalline; it is generally considered difficult to produce single-crystal synthetic diamonds, especially large diamonds. However, it has been observed more recently that technological developments allow the production of single-crystal synthetic diamonds of more than 1 carat at relatively low costs.

[0042] Single-crystal synthetic diamonds can, for example, be obtained by growing carbon using CVD around a single-crystal diamond seed. The single-crystal diamond seed can be reused to successively grow several single-crystal synthetic diamonds. It is important that the seed be made of single-crystal diamond so that the structure that is deposited is itself single-crystal. Carbon can be obtained from methane in a CVD reactor.

[0043] Synthetic monocrystalline diamond can also be obtained by compressing carbon at high pressure and high temperature. However, this solution results in higher costs, especially for the production of large monocrystalline diamonds.

[0044] Polycrystalline diamonds are most often transparent or gray; due to the multiple interfaces between different crystal grains with different orientations, they produce little or no reflections, and virtually no iridescence effects.

[0045] In contrast, single crystal diamonds, including natural single crystal diamonds, come in a wide variety of colors, including transparent, black, blue, yellow, red, etc. On the other hand, the play of light reflecting off different faces oriented in various ways produces highly valued iridescence effects.

[0046] Synthetic monocrystalline diamond can be doped. Natural monocrystalline diamond can be doped.

[0047] Doped monocrystalline diamond is obtained by deliberately introducing a doping element into the diamond, either during the growth of a synthetic diamond or into an already formed synthetic or natural diamond.

[0048] The doping process thus produces a diamond that is different from diamonds found in nature, and different from undoped synthetic monocrystalline diamonds. The difference comes from the type of impurities, their distribution and / or their concentration. The doping is chosen to modify the mechanical and tribological properties of the diamond piece.

[0049] Doping of synthetic monocrystalline diamond can be achieved during its manufacture by adding impurities to the CVD reactor gas. This doping can be done with virtually no additional cost when growing a synthetic monocrystalline diamond.

[0050] Doping of synthetic or natural monocrystalline diamond can also be achieved by ion implantation using a high-energy beam.

[0051] Doping can be homogeneous throughout the volume of the part.

[0052] Doping can be limited to the surface, or different on the surface and in depth. Doping can be chosen to control hardness and / or color and / or elasticity and / or Young's modulus sensitivity to temperature. Different single-crystal diamond pieces of the same movement can be doped differently.

[0053] Different mechanical parts of the same movement can be made from different varieties of monocrystalline diamond. For example, different mechanical parts of the same movement can be made from different colors of monocrystalline diamond. It has been noted in the context of the invention that the color of the monocrystalline diamond, which is due to impurities, influences its hardness. For example, transparent monocrystalline diamond is less hard than black monocrystalline diamond doped with boron ions. The type or color of monocrystalline diamond chosen for different parts of the same movement is therefore determined according to the desired hardness, or according to other mechanical properties dependent on this color.

[0054] In order to reduce wear, it is advantageous for the pallets of the escapement anchor, or the complete anchor if the pallets are integrated, to be harder than the anchor wheel with which they collaborate; an anchor wheel less hard than the pallets makes it possible to absorb shocks. According to the invention as claimed in the appended set of claims, the watch movement comprises an anchor pallet in a hard monocrystalline diamond, and an anchor wheel in a less hard monocrystalline diamond. The anchor or pallets may for example be made of black monocrystalline diamond doped with boron while the anchor wheel may be made of transparent or yellow monocrystalline diamond.

[0055] The pulse plane of the vane is obtained by polishing the side surfaces of the vane after it has been cut from a single crystal diamond plate. Polishing can be done mechanically, for example with a grinding wheel in a direction parallel to the pulse direction.

[0056] At least a portion of these lateral mechanical surfaces of the pallet may be polished or corrected, for example with a laser beam or an ion beam. Advantageously, at least a portion of these surfaces is corrected in order to have a better tribological state than before the correction. At least a portion may be corrected so that this portion is substantially perpendicular to the lower and upper faces of the part.

[0057] The pallet can be held by vacuum during polishing. This allows it to be positioned very precisely in height, and avoids inaccuracies in the thickness of the part which result from an uncontrolled thickness of glue in the polishing processes for glued parts used in the prior art.

[0058] The paddle can be mounted in the anchor before polishing, the anchor then being used to hold the paddle during polishing.

[0059] At least one of the surfaces of the blade may be heat-treated, for example by exposing it to a temperature between 600° and 750°C, preferably between 650 and 680°C, in order to burn off the carbon in the form of graphite produced by the cutting of the diamond and which may remain on the surface. This heat treatment also makes it possible to polish the diamond, by burning the tips on the surface, without however degrading the surface condition by a high-temperature attack.

[0060] At least one of the surfaces can be ground using a laser.

[0061] The condition of at least one surface of the diamond is advantageously treated by both heat treatment, mechanical polishing and laser grinding.

[0062] The part can be polished until the surface is flush with previously cut polishing marks.

[0063] The part can be ultrasonically polished. It can be cleaned with gasoline. Brief description of the figures

[0064] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: THE Figures 1A to 1E illustrate different successive stages of a manufacturing process for an escapement anchor incorporating pallets according to the invention. The figure 2 illustrates an escapement anchor incorporating pallets according to the invention. The Figures 3A to 3B schematically illustrate an operation of polishing or grinding at least a portion of the lateral sides of a pallet according to the invention. The Figures 4A to 4C illustrate a process for laser cutting a flat surface in a diamond using a laser oriented in different directions. The Figure 5 illustrates a pallet manufactured according to the method of the invention. Example(s) of embodiment of the invention

[0065] THE figures 1 to 3schematically illustrate a method of manufacturing a pallet according to the invention, here integrated into an escapement anchor. A similar method can be implemented to manufacture a discrete pallet separate from the anchor.

[0066] There Figure 1A illustrates an uncut monocrystalline diamond 1 used to manufacture one or more parts according to the invention. The monocrystalline diamond may be a natural diamond or a synthetic diamond, advantageously weighing more than 1 carat, preferably more than 3 carats.

[0067] In the case of a natural diamond, it may be a diamond with a shape or other properties that make it unsuitable for use in jewelry.

[0068] Synthetic single-crystal diamond can be produced, for example, by using a filtered arc to deposit carbon onto a single-crystal diamond seed, without the addition of hydrogen or other materials. Alternatively, CVD deposition of carbon produced from a hydrocarbon such as methane onto a single-crystal diamond seed can be performed. The seed can be reused after cutting plates from the mass deposited above the seed.

[0069] A third, less advantageous, possibility is to produce a synthetic monocrystalline diamond by subjecting a carbon source to simultaneous high temperature and high pressure. Other processes could be used.

[0070] The monocrystalline diamond thus formed can be doped. In one embodiment, the doping product can be introduced during the formation of the synthetic diamond, for example by adding traces of doping product in the filtered arc or in the CVD reactor. In another embodiment, the doping product is added after the formation of the synthetic diamond, for example by means of a high-energy ion beam. The doping can be carried out homogeneously throughout the mass of the diamond, and / or only on the surface. A first doping can be carried out in the mass and a different doping, for example with another doping product and / or with another concentration, can be carried out on the surface.

[0071] Doping can be selected to modify the hardness of parts produced from this diamond; depending on the doping product, it is possible to increase or decrease this hardness. For example, the inclusion of nitrogen as a doping product can reduce the hardness of a part, while the inclusion of boron ions can increase it.

[0072] In one embodiment, the hardness of the pallet is increased by doping, for example by including boron ions, while a single-crystal diamond anchor wheel intended to collaborate with this pallet in the escapement is undoped, or doped so as to reduce its hardness, for example with nitrogen, in order to obtain a hardness lower than that of the pallet. It is indeed advantageous to have very hard pallets, to reduce their wear and the coefficient of friction on the impulse plane, and a less hard escape wheel to absorb the shock of the anchor at each oscillation. In another embodiment, the anchor wheel is doped with a relatively high concentration of nitrogen, while the pallet is doped with a lower concentration of nitrogen.The inclusion of nitrogen during the manufacture of synthetic monocrystalline diamond by CVD growth makes it possible to increase the manufacturing speed, and therefore reduce the cost, while obtaining pallets that remain harder than conventional ruby ​​pallets.

[0073] Doping can also be selected to control the color of the diamond. Doping can be selected to control the Young's modulus of the diamond. Doping can be selected to reduce the sensitivity of the Young's modulus to temperature, in order to produce parts whose stiffness is as independent as possible of temperature. Doping can be selected to reduce the coefficient of expansion of the diamond, in order to produce parts whose dimensions are as independent as possible of temperature.

[0074] The doping agent and the concentration of this agent are further chosen so as not to interfere with the monocrystalline structure of the diamond, or to minimize this interference. In one embodiment, the diamond is doped with boron ions. Different diamonds used for the production of different parts in the same watch may be doped differently depending on the desired properties.

[0075] Boron doping carried out during the organic growth of synthetic diamond has the advantage of producing a non-radioactive black diamond, unlike doping processes involving the introduction of high-energy ions.

[0076] The single crystal diamond 1 is then cut as shown in the Figure 1B, for example by means of a diamond saw, or split using a hammer and blade, an electric arc, an ion beam, or preferably cut by means of a laser so as to obtain a flat surface 10. The laser is advantageously a pulsed laser, for example a pulsed laser at a frequency of 5 to 40 GHz.

[0077] In the embodiment illustrated in the Figures 4A to 4C , the diamond is sliced ​​from a first side by means of a first laser beam 20. The laser beam is pivoted by means of a movable mirror, so as to emit in a cone with an opening angle of less than 5°. The diamond is then attacked from the other side by means of another laser beam 21 pivoted in a cone ( Figure 4B). It is also possible to use the same laser beam to attack both sides of the part, turning it over between the two cuts. This cone machining makes it possible to widen the ablation zone and avoid poor surface finishes and the destruction of the crystalline structure that could occur if the ablation were carried out in a narrow channel, causing an excessive rise in temperature. The process is comparable, all things considered, to that of a lumberjack sawing a trunk by means of two oblique cuts from each side of the trunk.

[0078] The convex surface thus produced by this cutting is then ground or flattened, as illustrated in the Figure 4C, by means of a laser beam oriented parallel to the surface of the plate to be produced. The pulse frequency of this laser can be, for example, between 10 and 100 KHz, in order to obtain precise cutting without the problems of modifications to the crystalline structure caused by the high energy of faster pulsed lasers.

[0079] It is possible to scan the rough diamond beforehand using a 3D scanner in order to determine the optimal cutting plane to obtain the maximum number of 3 pieces and / or to facilitate cleavage; for example, a cut along a tetrahedral plane of the crystal will be preferred because it is faster and allows for a cleaner surface.

[0080] In a first embodiment, the cutting plane is determined in order to obtain an active surface of the part oriented according to the {111} crystal plane which is generally the hardest. In the case of a plate intended for the manufacture of pallets for watchmaking anchors, the cutting plane is preferably distinct from the {111} plane and chosen so as to allow the cutting of pallets whose impulse surface, obtained in the edge of the cut plates, is parallel to the {111} crystal orientation plane.

[0081] However, it has been found in the context of the invention that even if the {111} crystal plane is the hardest, this hardness decreases very abruptly in the event of a slight deviation from this ideal plane. For example, a part cut or polished according to a plane which deviates even by a few degrees from the {111} plane has a significantly reduced hardness and surface finish. However, it is difficult, particularly in the context of industrial manufacturing, to manufacture parts with surfaces oriented precisely according to the {111} plane, without any deviation. It is also sometimes desired to produce pallets whose impulse surface is non-planar.

[0082] Therefore, in a preferred embodiment, the cutting plane is determined in order to obtain an active surface of the part oriented substantially along the crystalline plane {001} or preferably along the plane {011} which is particularly hard; these planes are in fact less sensitive to deviations from the ideal surface. In the case of a plate intended for the manufacture of pallets for watchmaking anchors, the cutting plane is preferably chosen so as to allow the cutting of pallets whose impulse surface, obtained in the edge of the cut plates, is substantially parallel to the crystalline orientation plane {001} or preferably {011}. Substantially parallel means here that the deviation after polishing is at most +-5°.

[0083] It is possible to hold the diamond 1 during cutting, for example by cementing it or gluing it to a temporary support.

[0084] The rough face 10 obtained at the end of this cutting is then ground and / or polished so as to obtain a polished flat face 11 as illustrated in the Figure 1C .

[0085] The rectification of the face 11 can be carried out, as indicated, by means of a laser, for example a pulsed laser between 10 and 100KHz.

[0086] Polishing of face 11 may be carried out on a rotating wheel covered with synthetic diamond powder, for example polycrystalline diamond powder.

[0087] The roughness of face 11 can also be reduced by means of a high-energy ion beam parallel to the surface.

[0088] The diamond is then cut with a new cut parallel to the first cut, so as to obtain a thin plate 2 as illustrated in the Figure 1D. This delicate cutting is advantageously carried out by laser to avoid shocks which could break the plate. Like the cutting of the upper face, this cutting can be carried out according to the process illustrated on the Figures 4a to 4c , that is, by means of one or two laser beams deflected by a mirror to produce a conical ablation zone.

[0089] Depending on the type of part desired, this process allows extremely thin plates to be cut from a single-crystal diamond, for example plates with a thickness of less than 400 microns, for example plates with a thickness of between 100 and 400 microns, for example 320 microns, or between 100 and 160 microns, ideally between 100 and 120 microns, in the case of plates intended for machining pallets, and plates with a thickness of between 20 and 120 microns, for example between 40 and 80 microns, for example 60 microns, in the case of manufacturing anchor wheels or anchors.

[0090] This feature allows for the manufacture of extremely light parts and therefore reduces the energy required to move them.

[0091] The lower face 12 of the plate 2 is relatively rough. For many applications, particularly in watchmaking, this imperfectly polished appearance is entirely satisfactory since this face is not visible. However, it is possible to also polish this face 12 by producing a slightly thicker part, for example by mechanical polishing on a grinding wheel and / or laser. In one embodiment, the part is held without glue during its polishing, preferably by vacuum. It is thus possible to very precisely control the thickness of the part after polishing, without this thickness depending on the thickness of the glue.

[0092] The produced plate 2 can be visually inspected to eliminate plates that have too many impurities or a non-monocrystalline structure. In one embodiment, this inspection is carried out by illuminating the plate with polarized light, highlighting the imperfections. The inspection can be manual or carried out using a camera and image analysis software.

[0093] During the step illustrated on the Figure 1E , the pallet 3 (or an anchor incorporating one or more pallets) is cut into the surface of the plate 2. This cutting is for example obtained by means of a laser beam perpendicular to one of the surfaces 11, 12 or to the median plane of the plate 2. Like the cutting of the lower and upper faces, this cutting can be carried out according to the method illustrated in the Figures 4a to 4c , that is, by means of one or two laser beams deflected by a mirror to produce a conical ablation zone.

[0094] Multiple anchors or multiple pallets can be cut from a single plate.

[0095] There Figure 5 illustrates an example of a possible trajectory of the laser beam 6 when machining a pallet in a plate 11. The laser beam may have a relatively large dimension, for example a maximum diameter of the order of 20 microns. The shape of this beam 6 is generally non-circular, for example elliptical. The cutting trajectory is therefore advantageously determined by software arranged to determine a trajectory of the light beam which takes into account the dimension, shape and orientation of this beam relative to the part to be cut, so as to obtain a part after release whose dimensions correspond to the desired dimensions.

[0096] The trajectory is preferably started at a distance from the part to be produced, on a portion 32 which does not belong to the part produced. This avoids deformations due to the initial drilling. The trajectory is also preferably optimized, taking into account the crystalline orientation of the diamond, so that any cracks which propagate from the ablation point have a maximum chance of following the edge of the part, or of moving away from this part. For example, on the Figure 5 , the maximum risk of cracks occurs from the initial drilling point 32; the position of this point is therefore preferably chosen so that the most probable crack direction follows exactly the line followed by the beam.

[0097] As indicated above, the part to be cut is oriented on the diamond plate 11 so that the active surface of the part is in the {111} crystal plane. In the illustrated case of a pallet, the active surface 31 is constituted by the impulse surface (plane or non-plane) intended to be brought into contact with the anchor wheel. The pallet is therefore cut from the plate 11 so that this surface 31 is precisely in the {111} plane.

[0098] The 33 elements on the Figure 5 are cutting marks used during the subsequent polishing stage to define the ideal polishing depth. Polishing will therefore be carried out precisely until these marks disappear completely.

[0099] Other plates similar to plate 2 can then be cut from the same diamond 1, in order to make other pieces identical to, or different from, piece 3.

[0100] The method of cutting the part 3 from a plate 2 using a laser has the disadvantage of producing lateral flanks 13 which are not perpendicular to the faces 11, 12, as shown in an exaggerated manner in the Figure 3A . Since diamond is more or less transparent, the cutting is actually obtained by attacking the plasma produced by the interaction between laser light and air. This results in non-perpendicular and not very smooth flanks. This surface quality is problematic, particularly for a pallet 3 whose impulse surface, intended to come into contact with the anchor wheel, is formed by a portion of this slice.

[0101] In order to remedy this problem, an optional operation of grinding the flanks 13, or at least a portion of these flanks, can be carried out using a grinding wheel in order to obtain flanks 14 which are smoother and perpendicular to the surfaces 11, 12, as illustrated in the Figure 3B. In the case of a pallet, at least the impulse surface 31 can be ground to the depth of the mark 33 by means of a grinding wheel coated with polycrystalline diamond powder. The grinding is preferably carried out by orienting the grinding wheel relative to the impulse surface so as to grind in a direction substantially parallel to the impulse direction, i.e. to the direction of movement of the escape wheel relative to the pallet. Although this grinding is slower than grinding in the transverse direction of the pallet, it makes it possible to obtain a micro-structuring of the impulse surface with extremely fine ribs oriented parallel to the direction of relative movement of the escape wheel and the pallet. Thus, micro-grooves oriented in the impulse direction are observed on the impulse surface of the pallet.

[0102] It is possible to hold the pallet 3 during polishing for example by cementing it or gluing it to a temporary support, or by holding it by vacuum, or preferably by mounting it before polishing in the anchor also used to hold the pallets during their polishing.

[0103] Polishing of the active surface 31 by sandblasting, ion beam, ultrasound, pulsed laser (for example femtolaser), etc., can also be considered, in addition to or as a replacement for polishing by grinding.

[0104] The surfaces of the part 3 thus obtained are preferably not coated; the monocrystalline diamond has a practically ideal surface condition both from an aesthetic point of view and in terms of the coefficient of friction or impact resistance for example. However, it happens that the surfaces 11, 12, 13 or 14 are covered with traces of graphitized carbon resulting from the destruction of the diamond structure during the cutting or polishing operations. In order to eliminate these traces, it is possible within the scope of the invention to subject the part 3 to a heat treatment, for example by leaving it for a few seconds or a few minutes in a furnace between 600° and 750°C, preferably between 650 and 680°C, preferably in ambient air; this operation makes it possible to burn the residual graphite on the surface without affecting the carbon in the form of diamond, and thus to improve the surface condition of the part.It is also possible to use a lower temperature with a higher oxygen level, or to oxidize the non-crystalline carbon without attacking the diamond by using, for example, an oxygen or fluorine plasma.

[0105] This operation also allows the palette to be polished by burning the tips on the surface.

[0106] The produced part can also be polished by means of an ion beam ("ion etching"), for example an ion beam parallel to the surface to be polished, for example parallel to the pulse plane 31. In one embodiment, this ion polishing is carried out after the polishing by heat treatment.

[0107] The resulting piece can also be polished using ultrasound. It can be cleaned with gasoline to improve the appearance of the diamond.

[0108] A mechanical watch movement within the scope of the invention is defined by the appended claims.

Claims

1. Watch movement comprising: at least one pallet for a watch movement escapement, comprising an impulse plane as active surface (31), made entirely of a first type of monocrystalline diamond, characterized in that it comprises an anchor wheel in a second type of monocrystalline diamond softer than said first type of monocrystalline diamond.

2. The movement according to claim 1, the anchor wheel and pallet being of different colors3. The movement according to claim 1, the hardness of the pallet is increased by doping, while the anchor wheel made of monocrystalline diamond is undoped, or doped so as to reduce its hardness, in order to obtain a hardness lower than that of the pallet.

4. The movement according to claim 3, the anchor wheel being made of a second type of monocrystalline diamond doped with nitrogen.

5. The movement according to claim 4, the diamond of the pallet containing a maximum of 3% doping impurities, without affecting its monocrystalline structure.

6. The movement according to claim 5, the doping being homogeneous in the mass of the piece.

7. Pallet according to claim 5, the doping being different on the surface than in the depth of the piece.