Single crystal mineral gemstone provided with a cone for realigning a pivoting member and method of manufacturing the same

Abstract

The invention relates to a method for manufacturing a gemstone (10), in particular for timepieces, from a monocrystalline mineral body, the gemstone (10) comprising a hole (8). The method comprises an ablation step in which the body is subjected to material ablation by scanning at least one face of the body with ultrashort pulse laser radiation, the duration of which is less than one hundred picoseconds and whose beam is guided by a precession system of at least three axes configured to at least partially eliminate the conical focusing angle of the laser, the laser ablation step comprising the excavation of a cone (12) at the entrance to the hole (8). The invention also relates to a monocrystalline mineral gemstone, in particular for timepieces, the gemstone comprising a face (6) provided with a hole (8) formed in the body of the gemstone (10) and a functional element at the entrance to the hole (10). The functional element has the shape of a cone (12).

Description

Technical Field

[0001] The invention relates to a drilled jewel provided with a cone for centering a pivoting part, in particular for a timepiece movement.

[0002] The invention also relates to a method for producing such a drilled gemstone.

[0003] The invention also relates to a timepiece movement comprising such a drilled jewel. Background Art

[0004] In the prior art of watchmaking, gemstones of the ruby ​​or sapphire type are used in particular to form counter-pivots or guide elements known as bearings. These counter-pivots and guide elements are intended to contact the pivot so as to enable it to move in rotation with minimal friction. Thus, they form, for example, all or part of a bearing assembly for a rotatably mounted shaft.

[0005] In principle, synthetic gemstones are used in watch movements. In particular, the Verneuil-type method is known for the manufacture of monocrystalline gemstones. There are also polycrystalline gemstones, which are produced by pressing a precursor in order to obtain a green body of the new gemstone from the pressing tool. The gemstone is then (machined) to obtain the finished shape with the desired dimensions.

[0006] The jewel used as a rotation guide element for the pivoting member usually has a through hole into which the pivoting member is inserted to rest on the pivoting counterpart. It is known to form a substantially hemispherical recess around the hole on the insertion face of the pivoting member to facilitate the insertion of the pivoting member. In addition, it allows the pivoting member to be put back in place if it comes out due to an impact. The recess is obtained, for example, by turning with a diamond chisel.

[0007] However, the recess obtained using this method has a protruding rim at the edge of the hole, so that if the pivoting part escapes from the hole and reenters, the pivoting part may be damaged by the rim, for example under the effect of an impact, and vice versa.

[0008] In order to avoid this, it is known to replace the recess with a cone with a smaller angle, so that the edge is less prominent. This can in particular prevent wear on the pivoting part.

[0009] As regards the polycrystalline gemstone guide element, a pressing tool is provided, for example, with a conical shape and a wire which participates in the construction of a hole blank provided with a cone at the inlet.

[0010] The monocrystalline gemstone is first drilled with a laser to obtain a hole blank. The final size of the hole is then obtained by (machining) with a diamond chisel. However, it is not known how to form a cone in a monocrystalline gemstone, because conventional (machining) does not allow to obtain such a shape. Summary of the invention

[0011] The object of the present invention is to alleviate all or part of the above-mentioned drawbacks by proposing a method for manufacturing a gemstone, in particular for timepieces, from a monocrystalline mineral body, the gemstone comprising a hole.

[0012] To this end, the method is notable in that it includes an ablation step in which material is ablated from the body by scanning at least one face of the body with ultrashort pulse laser radiation having a duration of less than one hundred picoseconds and whose beam is guided by a precession system of at least three axes configured to at least partially eliminate the conical focusing angle of the laser, the laser ablation step comprising digging out a cone at the entrance of the through hole.

[0013] Thanks to this method, it is possible to remove material from the gemstone with extreme precision, thereby obtaining shapes and surfaces that would not be possible with the laser methods known in the prior art. This device allows focusing the laser beam with great precision, while at least partially eliminating the cone angle formed by the laser beam and caused by the focusing of said laser. In fact, the focusing produces a laser in the shape of a cone, which does not allow the same beam diameter over the entire height at the point where the laser is positioned, and therefore does not ablate material. This system allows eliminating the cone angle on at least one side of the beam, which makes it possible in particular to obtain straight cuts. These straight cuts cannot be obtained with conventional cutting lasers.

[0014] It is thus possible to obtain a cone at the entrance of the hole in a monocrystalline body, which is not possible with other systems. In particular, such a cone can be used for the pivot of a softer non-magnetic shaft. In fact, such a shaft combined with a monocrystalline stone is deformable under the effect of an impact, which is therefore absorbed by the shaft.

[0015] Additionally, the laser’s ultrashort pulses prevent the gemstone from heating up, which could adversely affect its quality.

[0016] Furthermore, the surface condition Ra of the gemstones obtained with the method according to the invention is about 0.1, which thus allows the gemstones to be polished with conventional polishing means. The method thus offers significant advantages while keeping its implementation not very complicated.

[0017] According to a particular embodiment of the invention, the cone obtained during the ablation step has an angle lying within the interval ranging from 30° to 120°, preferably from 45° to 90°.

[0018] According to a particular embodiment of the invention, the ablation is performed layer by layer, the thickness of each layer being in the range of 1 to 10 μm, preferably 2 to 4 μm.

[0019] According to a particular embodiment of the invention, the duration of the pulses is in the range of 50 to 400 fs, preferably in the range of 250 to 300 fs or 80 to 100 fs.

[0020] According to a particular embodiment of the invention, the wavelength of the laser light is in the range 400 to 600 nm, preferably between 450 and 550 nm, or even 500 nm.

[0021] According to a particular embodiment of the invention, the mineral body comprises Al2O3.

[0022] According to one particular embodiment of the invention, the method comprises a preliminary step of manufacturing the body by a Verneuil-type method.

[0023] According to a particular embodiment of the invention, the method comprises further finishing steps, such as grinding and / or brushing and / or polishing of the mineral body after the laser step, in particular on the ablated areas.

[0024] According to a particular embodiment of the invention, the laser ablation step consists in excavating said hole, which is preferably a through hole between the lower surface and the upper surface of the gemstone.

[0025] The invention also relates to a monocrystalline mineral gemstone, in particular for timepieces, comprising a face provided with a hole formed in the body of the gemstone and a functional element at the entrance of the hole. This gemstone is notable in that the functional element has a conical shape.

[0026] According to a particular embodiment of the invention, the gemstone comprises an upper surface and a lower surface, the lower surface comprising said cone.

[0027] According to a particular embodiment of the invention, said hole is a through hole so as to connect said cone to the upper surface of said gemstone.

[0028] According to a particular embodiment of the invention, said gemstone comprises Al2O3.

[0029] Finally, the invention also relates to a timepiece comprising such a jewel, in particular for a shock absorber bearing assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other characteristics and advantages will emerge clearly from the following description given in an indicative and non-limiting manner with reference to the accompanying drawings, in which:

[0031] - Figure 1 is a block diagram of producing a gemstone according to the method of the present invention;

[0032] - Figure 2is a schematic representation of a gemstone obtained after a laser ablation step using the method according to the invention;

[0033] - Figure 3 Yes Figure 2 Schematic illustration of an assembly of a jewel and an axle provided with a pivot member. DETAILED DESCRIPTION

[0034] As mentioned above, the invention relates to a method for manufacturing a jewel capable of forming a guide element of a timepiece. For example, the jewel is intended to contact a pivot so as to enable the latter to move in rotation with minimal friction. It will therefore be understood that the invention allows in particular the production of a jewel that can form all or part of a bearing assembly for a shaft mounted in rotation.

[0035] The gemstone is formed from a monocrystalline mineral body. The body comprises, for example, Al2O3.

[0036] Figure 1 The method 1 shown in comprises a first step 2 of manufacturing a crystalline mineral body by a Verneuil type method well known in the watchmaking field. The material is formed from a powder melted at over 2000° C. by means of an oxyhydrogen torch. After cooling below the melting point, the body crystallizes. The dimensions of the body are designed so as to obtain dimensions close to those required, in particular to facilitate its future (machining) processing. This step provides a monolithic single-crystal body.

[0037] According to the invention, the method comprises a second laser ablation step 3 in order to form the entrance cone of the hole in the gemstone. During the laser ablation step 3, the material of the body is ablated by scanning at least one face of the body with ultrashort pulse laser radiation, the duration of which is less than one hundred picoseconds and whose beam is guided by a precession system of at least three axes configured to eliminate the cone angle of the laser due to the focusing of said laser. Such a device is described, for example, in document WO 2017029210. There are different types of devices capable of at least partially eliminating the cone angle of the laser. Some devices use a five-axis or six-axis precession system.

[0038] The laser beam thus has at least one substantially straight edge, making it possible for these devices to dig into the surface of the gemstone and to give it a specific conical shape at the entrance to the hole of the monocrystalline mineral body. Thanks to this cone, if the pivoting piece comes out of the hole due to an impact, it returns to the hole without being damaged by the edge of the hole edge. Such a cone facilitates the insertion of the pivoting piece into the hole and avoids the risk of wear of the pivoting piece in the event of an impact. Since the edge of the cone protrudes less, the risk of wear is greatly reduced. For example, an angle between 30° and 120°, preferably between 45° and 90°, is chosen.

[0039] Ablation is done layer by layer, the laser scans an area of ​​the body to excavate it. Each layer has a thickness in the interval of 1 to 10 μm, preferably 2 to 4 μm, for example. Material is removed layer by layer until the desired shape is obtained.

[0040] For example, the laser has a wavelength between 400 and 600 nm, preferably between 450 and 550 nm or even about 500 nm. The duration of the pulse is less than a picosecond, for example in the range of 50 to 400 fs, preferably in the range of 250 to 300 fs or 80 to 100 fs. Such characteristics allow the body to be excavated without adversely affecting the properties of the material forming the gemstone.

[0041] It is also possible to drill a hole in the gemstone. This step of the method allows the hole to be drilled directly to the correct size without having to go through a blank and then a (machining) step so that the hole has a precise and uniform size throughout the height of the hole.

[0042] Finally, a third finishing step 4 allows the stone to be given a surface state compatible with its use. For example, one seeks to obtain a surface state Ra=0.05 μm. Thus, this finishing step may include grinding and / or brushing and / or polishing, allowing the final dimensions to be adjusted and / or edges to be removed and / or the roughness to be modified locally.

[0043] like Figure 2 and 3 As shown, the invention also relates to a gemstone 10 obtainable by the above method, which, for example, forms a guide element intended to be mounted in a shock absorber bearing assembly of a timepiece. However, this gemstone is not limited to the watchmaking field, but can be applied to any element that is movably mounted relative to a bearing assembly. The gemstone 10 comprises the features described in the above method. In particular, it is formed of a single-crystal mineral material, for example including ALO3.

[0044] Advantageously, the gemstone 10 is traversed by a hole 8 intended to receive a pivot 17 (also called trunnion). The gemstone comprises an upper surface 5 and a lower surface 6, one of which comprises a cone 12 communicating with the through hole 8. In other words, the hole 8 communicates with the upper surface 5 and also with a substantially conical hollow defined in the lower surface 6. This hollow then forms the engagement cone of the drilled gemstone 2. The cone 12 is preferably cylindrical. The cone 12 has a first opening 19 at its base and a second opening 21 at its top. The first opening 19 is larger than the second opening 21 and is formed in the lower surface 6 of the gemstone 10. The cone 12 and the hole 8 establish a connection via the second opening 21 to form the rim 15.

[0045] Thus, the flaring of the cone 12 allows easy insertion of the pivot 17 of the shaft 16 of the rotatably movable part, in particular in the event of an impact. The angle of the cone is selected to prevent the rim 15 formed by the cone top and the hole 8 from protruding too much. For example, an angle between 30° and 120°, preferably between 45° and 90°, is selected.

[0046] It should also be noted that the inner wall of the body of the jewel 10 defined at the hole 8 comprises a rounded area intended to minimize contact with the pivot and to facilitate possible lubrication. It should be noted that minimizing contact with the pivot makes it possible in particular to reduce friction with the pivot.

[0047] The upper surface 5 of the gemstone comprises a flange 7, which is used in particular to laterally surround a pivoting counterpart in the case of a bearing assembly. The flange 7 is preferably circumferential, that is, it delimits the edge of the upper surface 5 of the gemstone 10. In addition, it defines an inner region 9 of the upper surface 5, which comprises the bearing surface 11 and the outlet of the through hole 8, as well as a concentric raised region 14 from the bearing surface 11 to the hole 8.

[0048] An upper surface 5 with such a flange 7 allows, for example, a lateral stop for an element arranged on the upper surface of the gemstone 10. In the case of a bearing assembly for a balance staff, in which the gemstone 10 serves as a guide element, the pivoting counterpart gemstone can be arranged in such a way that it is laterally stopped by the inner side 18 of the flange 7 while resting on the bearing surface 11. This pivoting counterpart gemstone is dimensioned to correspond to the laser-ablated region 9 of said gemstone. Thus, said gemstone forms an axial and radial support for the pivoting counterpart. A pivoting counterpart, not shown in the figures, can be fitted into the gemstone 10 in order to axially support it and to laterally retain it.

[0049] Furthermore, the gemstone 10 has a peripheral surface 13 which is partially flared to connect the lower surface 6 of the smaller surface to the upper surface 5 of the larger surface.

[0050] Of course, the invention is not limited to the examples shown and has various variants and modifications obvious to a person skilled in the art. In particular, other types of functional elements formed by a laser ablation step may advantageously be considered according to the invention.

Claims

1. A method (1) for manufacturing a gemstone (10) for a timepiece from a monocrystalline mineral body, the gemstone (10) being a synthetic gemstone, the gemstone (10) comprising a hole (8) formed in the body of the gemstone (10) and a functional element at the entrance of the hole (8), and the functional element having the shape of a cone (12), wherein: The method comprises a preliminary step (2) of manufacturing the body by a Verneuil type method, and further comprises a laser ablation step (3), wherein the material of the body is ablated by scanning at least one face of the body with ultrashort pulse laser radiation, the duration of the ultrashort pulse laser radiation being less than one hundred picoseconds, and the beam of the ultrashort pulse laser radiation being guided by a precession system of at least three axes, the precession system being configured to at least partially eliminate the conical focusing angle of the laser, the laser ablation step comprising digging out a cone (12) at the entrance of the hole (8), the laser ablation step (3) being performed layer by layer, the thickness of each layer being in the range of 1 to 10 μm.

2. The method according to claim 1, characterized in that The cone (12) obtained during the laser ablation step (3) has an angle in the interval ranging from 30° to 120°.

3. The method according to claim 1 or 2, characterized in that: The duration of the pulses is in the range of 50 to 400 fs.

4. The method according to claim 1 or 2, characterized in that: The wavelength of the laser light is in the range of 400 to 600 nm.

5. The method according to claim 1 or 2, characterized in that: The mineral body comprises Al2O3.

6. The method according to claim 1 or 2, characterized in that: The method comprises an additional finishing step.

7. The method according to claim 6, characterized in that The further finishing step comprises grinding and / or brushing and / or polishing the mineral body on the ablated areas after the laser ablation step.

8. The method according to claim 1 or 2, characterized in that: The laser ablation step (3) comprises digging the hole (8), which is a through hole between the lower surface (6) and the upper surface (5) of the gemstone (10).

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