METHOD OF MANUFACTURING A TIMEPIECE SHAFT

Abstract

The method of manufacturing a timepiece shaft (1) includes grinding a ceramic piece, especially to form a balance shaft (1), having a functional portion (2a; 2b) including at least one part (221a; 221b) of a pivot-shank (22a; 22b) and/or at least one part (211a; 211b) of a pivot (21a; 21b), the first functional portion being made of ceramic and a first outer diameter (D1) of the first functional portion being less than 0.5 mm, or less than 0.4 mm, or less than 0.2 mm, or less than 0.1 mm.

Claims

1-15. (canceled)

16. A method of manufacturing a timepiece shaft, comprising: forming a ceramic piece entirely made in a homogeneous ceramic by extruding a ceramic thread, by injection molding a ceramic, or by pressing a ceramic preform, the ceramic having a hardness in a range of 1100-1600 HV1, and grinding the ceramic piece to form a first functional portion having a surface of revolution including at least one part of a pivot-shank and at least one part of a pivot, the first functional portion formed by the grinding having at least one dimension of greater than 20 μm, and a maximum diameter forming an outer diameter of the shaft of less than 0.5 mm, wherein the ceramic piece has a second functional portion, wherein the ceramic piece having the first and second functional portions forms the timepiece shaft without subjecting the first functional portion to a heat treatment nor rolling.

17. The method as claimed in claim 16, wherein the ceramic piece having the first and second functional portions forms the timepiece shaft having conform geometry and sufficient hardness without subjecting the first functional portion to any treatment after the grinding.

18. The method as claimed in claim 16, wherein the ceramic is for the most part composed of: zirconium oxide, or alumina, or a combination of these two oxides.

19. The method as claimed in claim 16, wherein the ceramic is for the most part composed of silicon nitride.

20. The method as claimed in claim 18, wherein the ceramic comprises one or more elements selected from the group consisting of: carbon nanotubes, graphene, fullerenes, yttrium oxide, cerium oxide, zirconium carbide, silicon carbide, titanium carbide, zirconium boride, boron nitride, titanium nitride, and silicon nitride.

21. The method as claimed in claim 19, wherein the ceramic comprises one or more elements selected from the group consisting of: carbon nanotubes, graphene, fullerenes, zirconium oxide, aluminum oxide, yttrium oxide, cerium oxide, zirconium carbide, silicon carbide, titanium carbide, zirconium boride, boron nitride, and titanium nitride.

22. The method as claimed in claim 16, wherein the first functional portion has a convex or concave or conical or truncated conical end.

23. The method as claimed in claim 16, wherein the first functional portion has a surface adapted for contact with, and rotating and translating movement relative to, a surface of another component, without deformation of the first functional portion.

24. The method as claimed in claim 16, wherein the first functional portion has a border separating the at least one part of the pivot-shank and the at least one part of the pivot, each of the at least one part of the pivot-shank and the at least one part of the pivot having a respective surface selected from the group consisting of a cylindrical surface, a truncated conical surface, or a curve generating surface, and the border having a surface selected from the group consisting of a cylindrical surface, a truncated conical surface, a curve generating surface, and a flange surface.

25. The method as claimed in claim 24, wherein the border is a flange.

26. The method as claimed in claim 24, wherein the surface of the at least one part of the pivot-shank has a minimum first diameter, the surface of the at least one part of the pivot has a maximum second diameter smaller than the minimum first diameter, and the surface of the border has a reduction in diameter from a side of the at least one part of the pivot-shank to a side of the at least one part of the pivot, wherein the surface of the border does not merge with the surface of the at least one part of the pivot-shank and the surface of the at least one part of the pivot.

27. The method as claimed in claim 24, wherein the surface of the border is a surface of a seat.

28. The method as claimed in claim 16, wherein the second functional portion has an outer diameter less than 2 mm.

29. The method as claimed in claim 28, wherein a ratio of the maximum diameter of the first functional portion to the outer diameter of the second functional portion is less than 0.9.

30. The method as claimed in claim 16, wherein the second functional portion is selected from the group consisting of: a second functional portion adapted for receiving a timepiece component, a second pivoting portion adapted for a timepiece component on the shaft, and a second intermeshing portion.

31. The method as claimed in claim 29, wherein the second functional portion is adapted for receiving a timepiece component selected from the group consisting of a balance, a plate, a spiral spring collet, a toothed wheel, another shaft, and a movement blank.

32. A method of manufacturing an assembly comprising a shaft and at least one guide, the method comprising: providing the shaft by implementing the method as claimed in claim 16, and arranging the shaft forming the assembly with the at least one guide, the shaft being designed to perform at least one of the following: rotate or pivot in the at least one guide, wherein the at least one part of the pivot cooperates with the guide; and move in translation in the at least one guide, wherein the at least one part of the pivot cooperates with the guide.

33. The method as claimed in claim 32, wherein the at least one guide comprises a bearing stone and an endstone, the stones cooperating with the pivot to guide the shaft in the guide.

34. The method as claimed in claim 32, wherein the at least one guide comprises a ball race way and balls, the balls cooperating by contact with the pivot to guide the shaft in the guide.

35. The method as claimed in claim 32, wherein the assembly is an oscillator of a sprung balance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The appended figures represent, as an example, three embodiments of a timepiece shaft according to the invention, different embodiments of systems according to the invention and an embodiment of a timepiece according to the invention.

[0069] FIG. 1 is a view of a first embodiment of a timepiece according to the invention, comprising a first embodiment of a shaft according to the invention.

[0070] FIG. 2 is a view of a first variant of a first embodiment of a shaft and guide assembly according to the invention.

[0071] FIG. 3 is a view of a second variant of the first embodiment of the shaft and guide assembly according to the invention.

[0072] FIG. 4 is a view of a second embodiment of the shaft and guide assembly according to the invention.

[0073] FIG. 5 is a view of a second embodiment of the shaft according to the invention.

[0074] FIG. 6 is a diagram of variations in the quality factor of a sprung balance oscillator in different clock positions, the oscillator being outfitted with a classical shock-absorbing bearing.

[0075] FIG. 7 is a diagram of variations in the quality factor of a sprung balance oscillator in different clock positions, the oscillator being outfitted with a ball bearing.

[0076] FIG. 8 is a view of a third embodiment of the shaft according to the invention.

[0077] FIG. 9 is a cross sectional view in the plane A-A of FIG. 8 of the third embodiment of the shaft according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0078] An embodiment of a timepiece 120 is described below with reference to FIG. 1. The timepiece is a watch, for example, in particular a wristwatch. The timepiece comprises a watch movement 110, in particular a mechanical movement. The watch movement comprises an oscillator 100, in particular a sprung balance 8 oscillator. The balance is, for example, fitted to a balance shaft 1.

[0079] The balance shaft 1 comprises a first functional portion 2a; 2b including: [0080] at least one part 221a, 221b of a pivot-shank 22a; 22b, and/or [0081] at least one part 211a, 211b of a pivot 21a, 21b.

[0082] The first functional portion is made of ceramic and the first functional portion has a first outer diameter D1, for instance a maximal outer diameter, less than 0.5 mm, or less than 0.4 mm, or less than 0.2 mm, or less than 0.1 mm.

[0083] In the first embodiment represented in FIG. 1, the shaft 1 comprises a first pivot 21a, a first pivot-shank 22a, a portion 33 for receiving a plate 9, a seat 34 for receiving the balance 8, a portion 32 for receiving the balance 8, a portion 31 for receiving a collet of the spiral (not shown), a second pivot 21b and a second pivot-shank 22b. Advantageously, the pivot-shank part has a dimension greater than 0.1 mm, or greater than 0.2 mm, or greater than 0.25 mm in at least one direction, or in all directions. Advantageously, the pivot part has a dimension greater than 0.04 mm, or greater than 0.05 mm, or greater than 0.1 mm in at least one direction, or in all directions, Preferably, the first pivot-shank part comprises a longitudinal piece of the pivot-shank (or at least the outer surface of a piece of the pivot-shank) for a length of at least 0.2 mm. Preferably, the first pivot part comprises a longitudinal piece of the pivot (or at least the outer surface of a piece of the pivot) for a length of at least 0.1 mm.

[0084] In the first embodiment represented in FIG. 1, the shaft 1 comprises two first functional portions 2a and 2b each one including: [0085] at least one part 221a, 221b of a pivot-shank 22a; 22b, and/or [0086] at least one part 211a, 211b of a pivot 21a, 21b.

[0087] In the first embodiment represented in FIG. 1, the two first functional portions are made of ceramic and each of the two first functional portions has a first outer diameter D1, for example a maximal outer diameter, less than 0.5 mm, or less than 0.4 mm, or less than 0.2 mm, or less than 0.1 mm.

[0088] The first functional portion may provide various functions, such as in particular: [0089] a guiding function, especially in pivoting and/or translatory movement, that is, the portion has a surface of contact with another component, in particular a guide, to ensure the pivoting and/or the translatory movement and that there is a contact and a relative movement between the portion and this other component, and/or [0090] a receiving function, that is, the portion has a surface of contact with another component to ensure the positioning and/or the holding of the other component on the portion, and/or [0091] an intermeshing function, that is, the portion has a surface of contact in the form of teeth with another component to ensure the intermeshing between the portion and this other component, and/or [0092] a force transmission or force absorbing function, that is, the portion is mechanically stressed.

[0093] In the first embodiment represented in FIG. 1, the first and second pivots 21a, 21b provide a pivoting function and a force absorbing function in the event of impact or, more generally, in the event of acceleration undergone by the timepiece containing the shaft. The first and second pivot-shanks 22a and 22b provide a force absorbing function in event of impact or, more generally, in event of acceleration undergone by the timepiece containing the shaft.

[0094] The shaft may also have a second functional portion 3, especially: [0095] a second functional portion 31, 32, 33; 34 for receiving a timepiece component, especially the balance 8, the plate 9, the spiral spring collet, or a toothed wheel or another shaft 6 in another embodiment which will be described further below, or [0096] a second pivoting portion for a timepiece component, such as a wheel, on the shaft in another embodiment, so as to allow the pivoting of this timepiece component with respect to the shaft, or [0097] a second intermeshing portion, especially a toothing, in another embodiment.

[0098] In the first embodiment represented in FIG. 1, the portions 31, 32 and 33 each provide a receiving function.

[0099] Advantageously, the second functional portion has a second outer diameter D2, for example a maximal outer diameter, less than 2 mm, or less than 1 mm, or less than 0.5 mm. Preferably, the second functional portion is made of ceramic.

[0100] Again advantageously, the ratio of the dimension of the first diameter to the dimension of the second diameter is less than 0.9, or less than 0.8, or less than 0.6, or less than 0.5, or less than 0.4.

[0101] The fact that the first functional portion and/or the second functional portion is made of ceramic means that this functional portion is entirely made of ceramic. Preferably, the realization of the functional portion in a material composed of ceramic grains bonded together by a nonceramic matrix, such as a metal matrix, is excluded. “Ceramic” is understood to mean a homogeneous or substantially homogeneous material, including on the microscopic level. Preferably, the ceramic is homogeneous in at least one direction, or in all directions, for a distance greater than 6 μm, or greater than 10 μm, or greater than 20 μm. Again preferably, the ceramic does not have non-ceramic material in at least one direction, or in all directions, for a distance greater than 6 μm, or greater than 10 μm, or greater than 20 μm.

[0102] Advantageously, the first functional portion has dimensions greater than 20 μm or 40 μm or 50 μm in at least one direction or in three directions mutually perpendicular to each other and/or the first functional portion has a diameter equal to that of the shaft in the area of any point of this first functional portion and/or the first functional portion is situated between two planes perpendicular to the geometrical axis of the shaft.

[0103] Advantageously, the second functional portion has dimensions greater than 20 μm or 40 μm or 50 μm in at least one direction or in three directions mutually perpendicular to each other and/or the second functional portion has a diameter equal to that of the shaft in the area of any point of this second functional portion and/or the second functional portion is situated between two planes perpendicular to the geometrical axis of the shaft.

[0104] Advantageously, the ceramic is for the most part or principally composed (by weight or by moles) of: [0105] zirconium oxide, and/or [0106] alumina.

[0107] Thus, zirconium oxide and/or alumina may be the preponderant elements in the ceramic. Nevertheless, the proportion by weight or by moles of zirconium oxide and/or alumina may be less than 50%.

[0108] Optionally, the ceramic comprises, in addition to zirconium oxide and/or alumina, one or more of the following elements: [0109] carbon nanotubes, [0110] graphene, [0111] fullerenes, [0112] yttrium oxide, [0113] cerium oxide, [0114] zirconium carbide, [0115] silicon carbide, [0116] titanium carbide, [0117] zirconium boride, [0118] boron nitride, [0119] titanium nitride, and [0120] silicon nitride.

[0121] Alternatively, the ceramic may be composed for the most part or principally (by weight or by moles) of silicon nitride.

[0122] Thus, silicon nitride may be the preponderant element in the ceramic. Nevertheless, the proportion by weight or by moles of silicon nitride may be less than 50%.

[0123] Optionally, the ceramic comprises, in addition to silicon nitride, one or more of the following elements: [0124] carbon nanotubes, [0125] graphene, [0126] fullerenes, [0127] zirconium oxide, [0128] aluminum oxide, [0129] yttrium oxide, [0130] cerium oxide, [0131] zirconium carbide, [0132] silicon carbide, [0133] titanium carbide, [0134] zirconium boride, [0135] boron nitride, and [0136] titanium nitride.

[0137] For example, the ceramic may be one of the ceramics of the following table:

TABLE-US-00001 Secondary Principal component(s) Brand name/resulting Hardness Fracture Toughness component and proportions composition [HV1] stress [MPa] [MPa .Math. m ½] ZrO.sub.2 Y.sub.2O.sub.3 3% mol TOSOH TZ3Y 1200-1400  900 -1500 5 to 10 ZrO.sub.2 MgO 3.5 wt % Metoxit PSZ 1500 1500 10 ZrO.sub.2 Al.sub.2O.sub.3 20 wt % TOSOH TZ3Y20A 1400-1600 1600-2000 5 to 8 Y.sub.2O.sub.3 3% mol ZrO.sub.2 Al.sub.2O.sub.3 21.5 wt % Panasonic NanoZr 1100-1300  900-1300 8 to 18 CeO.sub.2 10.6 wt % Si.sub.2N.sub.4 KYOCERA SN-235P 1200-1600 600-850 5 to 8.8 B.sub.4C TiB.sub.2 5 to 6.9 TiB.sub.2 CNT TiB.sub.2—TiC—CNT 3 to 5.2

[0138] One may consider making a shaft from an extruded ceramic thread, with the aid of various diamond grindstones. At the end of these steps, the pieces may be geometrically conformable and of a sufficient hardness to do without any after-treatment.

[0139] Alternatively, the injection molding or pressing of a preform only the ends of which will undergo grinding makes it possible to optimize the process, especially thanks to time savings in the manufacturing cycle.

[0140] Again alternatively, other manufacturing techniques make it possible to further improve of the properties of the obtained pieces, such as cold isostatic pressing (CIP), by reducing the number of defects present in the material before it is machined. In particular, this increases its toughness.

[0141] Thanks to the intrinsic properties of the extremely hard ceramics, as mentioned above, the pivots do not become marred by impact and the performance is maintained over time. Advantageously, in the event of a major impact, these pivots will not become deformed, whereas steel pivots may bend and thereby affect the chronometry of the timepiece. Thus, ceramics such as those presented above make it possible to maintain the geometrical integrity of the pivots over time.

[0142] Furthermore, ceramics offer the supplemental advantage of being non-magnetic, and not influencing the running of the timepiece when it is subjected to a magnetic field, especially a magnetic field greater than 32 kA/m (400 G).

[0143] Advantageously, the entire shaft is made of ceramic. However, it is conceivable to limit the ceramic part to the first functional portion which includes at least one pivot and/or at least one pivot-shank.

[0144] Advantageously, the first portion has a surface of revolution, especially a cylindrical surface or a conical surface or a truncated conical surface or a curve generating surface. The pivot-shank and the pivot may be merged or at least not be bounded off by a free border such as a flange. For example, the pivot-shank and the pivot can be separated by a truncated conical surface or a curve generating surface.

[0145] Two variants of a first embodiment of an assembly 41 comprising an shaft 1 as described above and at least one guide 51, especially a bearing 51, the shaft being designed to rotate or pivot in the at least one bearing, are shown respectively in FIGS. 2 and 3.

[0146] The guide may be in the form of a conventional shock-absorbing bearing. Thus, in the first embodiment, the at least one bearing 51 comprises a bearing stone 511 designed to cooperate with a cylindrical or truncated conical section of a pivot 21′ and an endstone 512 designed to cooperate with one end 212′ of the pivot. The stones thus cooperate with the pivot 21′ for the pivoting and the receiving, or axially bounding, of the shaft in the guide.

[0147] In the first variant of the first embodiment of the assembly, the shaft 1 comprises a pivot 21′ having an end 212′ which is bulging or convex.

[0148] In the second variant of the first embodiment of the assembly, the shaft 1 comprises a pivot 21″ having an end 212″ which is hollow or concave.

[0149] The fact of having shafts made of ceramic, a material which is both hard and tough, makes it possible to achieve geometries which can optimize and ensure permanent contact in the area of the pivot and the bearing in which it pivots, especially in the area of the ends of the pivot. This would be hard to accomplish with conventional rolled alloys such as 20AP steel where the risk of loss of performance when wearing would be more significant, especially on account of the very great contact pressure.

[0150] A second embodiment of an assembly 42 comprising a shaft 1 as described above and at least one guide, especially a bearing 52, the shaft being designed to rotate or pivot in the at least one guide, is represented in FIG. 4. In this second embodiment, the at least one guide 52 comprises a ball race way 521 and balls 522, the balls cooperating by contact with a pivot 21* having a conical end 212* for guiding the shaft in the guide. Of course, the end of the pivot 21* could alternatively have a truncated conical surface. The balls thus roll along the ball race way and the pivot at the same time.

[0151] FIGS. 6 and 7 illustrate the advantages of a ball bearing designed to cooperate with an oscillator of sprung balance type. In fact, one sees in FIGS. 6 and 7, obtained respectively by measuring in different clock positions an oscillator cooperating with a classical shock-absorbing bearing and by measuring in different clock positions an oscillator cooperating with a ball bearing, that the operation of the oscillator cooperating with a ball bearing shows fewer deviations of the quality factor between the different clock positions than those caused by the operation of the oscillator cooperating with a classical shock-absorbing bearing.

[0152] However, it is crucial for the proper working of the pivoting and reducing the deviations in timing that the geometry of the pivots is constant over time, regardless of the forces and impacts undergone by the watch, and this for all geometries of pivots. This is even more critical in certain cases: in fact, if a pivot associated with a ball bearing is bruised or presents plastic deformations due to impact, a good bit of the advantage of the solution will be lost.

[0153] Thus, the use of ceramics for the fabrication of the balls and the pivot makes it possible to optimize the use of a ball bearing and reduce in significant fashion the deviations in the quality factor between the different clock positions occupied by the timepiece.

[0154] A second embodiment of a timepiece shaft 1′ according to the invention is described below in regard to FIG. 5.

[0155] This shaft 1′ is designed to be mounted on a pivot shaft 6, particularly a pivot shaft made of a different material, especially a free-cutting steel.

[0156] Thus, the first functional portion may comprise a pivot 2a, but the second functional portion may be present for example in the form of a portion 35 designed to be fixed, in particular by driving or welding, inside a bore 36 formed in the body of the pivoting shaft 6.

[0157] The invention has been described above in regard to a balance shaft. However, this invention may obviously be applied to any other timepiece shaft, such as a pivoting shaft of a watch wheel such as a wheel involved in the finishing chain of a watch movement, especially a center wheel, or a large intermediate wheel, or a small intermediate wheel, or a seconds wheel.

[0158] A timepiece shaft according to the invention may also be implemented in the context of an optimization of a watch escapement and thus enable the pivoting of a pallet wheel or a blocker or a pallet involved in the escapement. Of course, this invention can be applied to any watch wheel involved in an additional timepiece function, such as a calendar or a chronograph.

[0159] In an alternative embodiment, shown in FIGS. 8 and 9, the first functional portion may provide a translatory movement function. The timepiece shaft here is present in the form of a pin 1″ comprising a first functional portion 2a which is present in the form of a pivot-shank 22a. This latter cooperates with a groove 53 formed inside a watch component, such as a chronograph hammer 91, so as to guide said component in translatory movement, in particular to guide said component in translatory movement in the longitudinal direction of said groove. The pin 1″ has a second functional portion which is present in the form of a pivot-shank 45 designed to be driven inside a bore 46 of a watchmaking movement-blank 81. In this embodiment, the first and second functional portions are bounded off by a flange 450, especially a seat 450.

[0160] Once shaped, the ceramic pieces require neither heat treatment nor rolling to obtain good performance in wear resistance.