Second or fractional second hand for clocks

Description

[0001] The present invention relates to a second or fractional second indicator hand for a timepiece and a timepiece, in particular a mechanical timepiece, provided with such a hand.

[0002] Indicator hands are generally made of brass, steel, gold, aluminum, or alloy. Most of these materials have a high density, which translates into a high mass for the hand, and therefore a high inertia. A high inertia hand causes its drive mechanism to consume more energy. This is problematic in the case of seconds or fractional seconds hands because of their high rotation speed. In particular, when a chronograph is triggered, the rotation of the chronograph seconds hand and any fractional seconds hands contributes to a peak in energy consumption, which causes a loss of amplitude in the oscillator and consequently a reduction in the power reserve and chronometry. It is therefore important that these hands are lightweight.

[0003] Among the materials traditionally used for the manufacture of indicator needles, aluminum certainly has a low density but its rigidity is not sufficient for very long needles.

[0004] Another disadvantage of the above-mentioned materials is that the manufacturing techniques associated with them, namely machining and stamping, lack precision, which requires additional finishing operations such as deburring, polishing, etc.

[0005] To facilitate the manufacture of needles and reduce their mass, patent application WO 2006 / 122873 proposes to make them from a crystalline silicon-based material and to use etching techniques from the field of microelectronics. The shapes that can be obtained using such techniques are, however, limited, making it difficult to optimize the lightness of the needle without compromising aesthetics.

[0006] Needles made of transparent plastic or glass are described in documents FR 2867285, DE 29604580 U and DE 822293 but the objective sought in these documents is quite different from that of reducing the inertia of the needles.

[0007] Finally, we know of document EP 055753 A1 which discloses minute or hour hands having an elongated sapphire body whose front face is faceted.

[0008] The present invention aims to solve, at least in part, the above-mentioned problems and to this end proposes a second or fractional second indicator hand, as defined in claim 1.

[0009] Particular embodiments of the invention are defined in the appended dependent claims.

[0010] Other features and advantages of the present invention will become apparent from the following detailed description given with reference to the appended drawings in which: there Figure 1 is a top view of a seconds or fractions of a second hand for a timepiece according to a particular embodiment of the invention; Figure 2 is a partial longitudinal sectional view of the needle, taken along line AA of the Figure 1 ; there Figure 3 is a cross-sectional view of the needle stick, taken along line BB of the Figure 1 ; THE figures 4 to 7 are cross-sectional views of needle sticks according to other embodiments of the invention; figures 8 to 12 show the cross-sectional shape of needle rods according to still further embodiments of the invention.

[0011] THE Figures 1 and 2show an indicator hand 1 for a timepiece, in particular for a wristwatch, pocket watch or clock, according to a particular embodiment of the invention. The hand 1 is a second or fractional second indicator hand. In the case of a second hand, it may be that of an ordinary watch or a chronograph. It may also be a split-seconds hand. The timepiece is typically mechanical.

[0012] The hand 1 comprises a fixing part 10 pierced with a hole 11 allowing the mounting of the hand by driving, gluing, soldering or other on an axis. From the fixing part 10 extends radially a rod 12 intended to point towards numbers and / or indexes of a graduation of the dial of the timepiece. The hand 1 may further comprise a counterweight 15 extending from the fixing part 10 in the opposite direction to the rod 12.

[0013] The rod 12 and preferably the entire needle 1 is made of mineral or organic glass, preferably tempered mineral glass, or sapphire. These materials have a low density, allowing the needle to be light and therefore to have low inertia, and also have sufficient rigidity to prevent the needle from deforming under the effect of its weight.

[0014] To further reduce the inertia, the upper surface 17 of the rod 12, that is to say the surface seen by the user when looking at the dial from above (or from the front), is faceted by two opposite longitudinal chamfers 17a, 17b (cf. Figure 3 ) or has, in cross section, a curved shape, therefore without edges (cf. Figure 4 ) or a semi-oblong shape (straight segment with curved ends; cf. Figure 5). In addition, preferably, the interior of the rod 12 is hollowed out. More specifically, a groove 20 is formed in the lower surface 18 of the rod 12 over a depth which typically exceeds half the height h of the rod 12 and over a length which is at least 50%, preferably at least 75% of the length L of the rod 12. This provides minimal inertia for the needle 1 without departing from the usual aesthetics of a needle. The bottom 20a of the groove 20 is preferably rounded, as shown, to increase rigidity.

[0015] In other embodiments of the invention shown in Figures 6 and 7, the groove 20 is replaced by a recess 21 formed inside the rod 12 and which does not open onto the lower surface 18 or onto the other external surfaces of the rod 12, this over all or almost all of the length of the recess 21, or over at least 50% or even at least 75% of the length of the recess 21. This recess 21 can over another part of its length communicate with the outside of the rod 12 by one or more holes left during manufacture. These embodiments make it possible to eliminate or reduce the risk of dirt or other undesirable elements entering the needle.

[0016] The cross-section of the rod 12 may have shapes different from the semi-octagonal, semi-circular or oblong shapes illustrated in figures 3 to 5 respectively. The figures 8 to 11 show additional examples of cross-sectional shapes for rod 12 where the top surface is faceted ( figures 8 and 9: semi-hexagonal shape; Figure 10 : triangular shape; Figure 11 : hexagonal shape). The Figure 12 shows a circular cross-section giving the upper surface a domed shape.

[0017] The needle according to the invention is typically manufactured by 3D printing or by the technique known as FEMTOPRINT (registered trademark) which consists of locally changing the properties of a transparent material such as glass or sapphire by means of a femtosecond laser and then subjecting the transparent material to a chemical etching operation aimed at removing the parts treated by the laser. The FEMTOPRINT process makes it possible to obtain single-piece parts with complex shapes, including internal recesses, chamfers, roundings, etc., with high manufacturing precision. The freedom in the choice of shapes is much greater than with an anisotropic etching process such as deep reactive ion etching known as DRIE.

[0018] The outer surface of the needle according to the invention may be treated and / or bear one or more coatings. For example, at least a first section of the rod 12, transparent, may bear an anti-reflective coating 16 over its entire surface or at least on its upper and / or lower surface and a second section of the rod 12, typically a distal end portion, constituting the indicator portion of the needle, may be made opaque or less transparent than the first section at least for a user looking at the needle from above. The first section may thus facilitate the reading of information on the dial above which the needle moves. The second section may be made opaque or less transparent by depositing a layer 19 such as a layer of paint or a metallic layer or by a treatment such as texturizing or frosting.Conversely, the entire rod 12 or the entire needle 1 can be treated, for example textured, frosted or painted, to be clearly visible.

[0019] To mount the needle 1 on its axis, an intermediate piece, for example made of brass, can be brazed or elastically fixed in the hole 11 then driven onto the axis.

[0020] The width e of the rod 12 can be variable, as shown in Figure 1 where the rod 12 is tapered, in order to better distribute the stresses and in particular increase its stiffness where the forces are highest, namely near the fixing part 10. Instead of a variable width e as in the example of the Figure 1 , or in addition to such a variation in width, the height h of the rod 12 can be variable and can for example decrease from its end joined to the fixing part 10 to its free end, for better distribution of the stresses.

[0021] The needle according to the invention may also have a non-rectilinear profile, of a curved shape or with offsets, for example to follow a curvature of the dial or to pass above the barrel of another needle or another three-dimensional organ while keeping the indicator part of the needle close to the dial.

[0022] All these geometric features of the needle are made possible by the material used, glass or sapphire, and the associated manufacturing techniques.

Claims

1. Hand for indicating seconds or fractions of a second for a timepiece comprising a fixing part (10) intended to be mounted on a spindle and a rod (12) made of glass or sapphire extending from the fixing part (10), a hand in which, over at least a section of the rod (12), the upper surface (17) of the rod (12) is facetted or has, in cross-section, a domed shape or a semi-oblong shape, i.e. a straight segment with curved ends.

2. Indicating hand as claimed in claim 1, characterised in that said section represents at least 50% of the length (L) of the rod (12).

3. Indicating hand as claimed in claim 1, characterised in that said section represents at least 75% of the length (L) of the rod (12).

4. Indicating hand as claimed in any one of claims 1 to 3, characterised in that it is formed as one piece.

5. Indicating hand as claimed in any one of claims 1 to 4, characterised in that the rod (12) is hollow at least over said section.

6. Indicating hand as claimed in claim 5, characterised in that the rod (12) is made hollow by a flute (20) formed in the lower surface (18) of the rod (12).

7. Indicating hand as claimed in claim 6, characterised in that the bottom (20a) of the flute is rounded.

8. Indicating hand as claimed in claim 5, characterised in that the rod (12) is made hollow by a gap (21) formed inside the rod (12) and which, over at least 50% of its length, does not open onto any outer surface of the rod (12).

9. Indicating hand as claimed in claim 8, characterised in that the gap (21) does not open onto any outer surface of the rod (12) over at least 75% of its length.

10. Indicating hand as claimed in any one of claims 1 to 9, characterised in that the width (e) of the rod (12) varies along the rod (12).

11. Indicating hand as claimed in any one of claims 1 to 10, characterised in that the width (e) of the rod (12) decreases from its end joined to the fixing part (10) to its free end.

12. Indicating hand as claimed in any one of claims 1 to 11, characterised in that the height (h) of the rod (12) varies along the rod (12).

13. Indicating hand as claimed in claim 12, characterised in that the height (h) of the rod (12) decreases from its end joined to the fixing part (10) to its free end.

14. Timepiece, in particular a mechanical timepiece, comprising an indicating hand as claimed in any one of claims 1 to 13.