Abstract:
The invention relates to a single piece coaxial escape wheel set ( 100, 100′ ) including a first toothing ( 108, 108′ ) formed at the periphery of a plate ( 103, 103′ ) and a second toothing ( 113, 113′ ). According to the invention, the second toothing ( 113, 113′ ) is formed in a single piece with the plate ( 103, 103′ ) of the first toothing ( 108, 108′ ) so as to reduce any problems of alignment of one in relation to the other and to decrease the overall mass of the wheel set ( 100, 100′ ). 
     The invention concerns the field of timepieces.

Description:
This application claims priority from European Patent Application No. 10166896.0 filed Jun. 22, 2010, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a single piece wheel set, for example a coaxial escape wheel set, and more specifically to a wheel set of this type made of micro-machinable or electroformable material. 
     BACKGROUND OF THE INVENTION 
     In a known manner, the escapement of a mechanical timepiece movement, whether it is coaxial or a Swiss lever escapement, includes an escape wheel wherein the regularly spaced teeth undergo the shock of pallet-stones which are generally made of ruby. 
     An example of a coaxial escape system is presented in EP Patent No. 1 045 297. A mechanism of this type, as illustrated in  FIG. 11 , includes a wheel set formed of first  1  and second  11  escape wheels. The second escape wheel  11 , also called an impulse pinion, is mounted on the same arbour  3 . The angular position of teeth  13  of the second escape wheel  11  is indexed on the angular position of the teeth  8  of the first escape wheel  1 . 
     The first escape wheel  1  takes the form of a conventional Swiss lever escape wheel. The second escape wheel  11  also acts as escape pinion  15  by meshing with an intermediate wheel  17 , which has the advantage of reducing the height of the mechanism. 
     The roller  19  of the balance (not shown) carries an impulse-pin  21  and an impulse pallet-stone  23 . The impulse-pin  21  is for driving lever  25 , in a to-and-fro motion, via the fork  27  thereof, whereas impulse pallet-stone  23  is for cooperating with the teeth  8  of the first escape wheel  1 . 
     Lever  25  includes an impulse pallet-stone  24  which cooperates with the teeth  13  of the second escape wheel  11 . Lever  25  also includes two other, respectively entry and exit locking pallets  26 ,  28  which cooperate with the teeth  8  of the first escape wheel  1 . 
     The design of this coaxial escapement requires very high precision, particularly as regards the relative alignment of the first  1  and second  11  escape wheels, which makes it difficult to manufacture. Moreover, generally speaking, the gear trains of a two level timepiece like the usual wheel-pinion type always need to have perfect indexing between them. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome all of part of aforecited drawbacks by proposing a wheel set, such as for example a coaxial escape wheel set, wherein the problems of alignment are reduced and the inertia is decreased. 
     The invention therefore relates to a single piece wheel set including a first toothing formed at the periphery of a plate and a second toothing, wherein the second toothing is formed in a single piece with the plate of the first toothing so as to reduce any problems of alignment of one relative to the other and to decrease the overall mass of the wheel set and, in particular, a coaxial escape wheel set wherein the first toothing is arranged to cooperate with a pin and at least a first series of pallet-stones and a second toothing arranged to cooperate with a second series of pallet-stones. 
     The advantage of this wheel set is immediately clear, arising from the simplicity of design (single piece and less material) compared to two parts which are difficult to adjust in relation to each other at present. 
     In accordance with other advantageous features of the invention:
         each tooth of the second toothing is independent of the other teeth and projects relative to the plate of the first toothing;   the plate is formed of a hub connected to the first toothing via at least one arm;   each tooth of the second toothing is integral with said at least one arm of the plate;   the second toothing includes as many teeth as the plate has arms;   the plate includes an opening for cooperating with an arbour for rotatably mounting said coaxial escape wheel set;   the opening includes securing means that deform elastically to grip the arbour without exerting any destructive stress on the plate;   the opening includes securing means that deform plastically to grip the arbour without exerting any destructive stress on the plate;   the wheel set may be made of metal or a metal alloy or be silicon-based.       

     Moreover, the invention relates to a coaxial escape system for a timepiece including a lever that cooperates with a single piece coaxial escape wheel set according to one of the preceding variants, wherein the first toothing of the wheel set is arranged to cooperate with a pin integral with a balance and intended to cooperate with a first series of pallet-stones of the lever, the second toothing is intended to cooperate with a second series of pallet-stones of the lever and arranged to form the escape pinion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will appear clearly from the following description, given by way of non-limiting indication, with reference to the annexed drawings, in which: 
         FIGS. 1 to 4  are diagrams of successive steps of the method of manufacturing an escape wheel set according to a first embodiment of the invention; 
         FIGS. 5 to 8  are diagrams of successive steps of a method of manufacturing an escape wheel set according to a second embodiment of the invention; 
         FIG. 9  is a perspective diagram of a coaxial escape wheel set according to a first variant of the invention; 
         FIG. 10  is a perspective diagram of a coaxial escape wheel set according to a second variant of the invention; 
         FIG. 11  is a perspective diagram of a coaxial escape system. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Advantageously according to the invention, any problems of alignment between the first and second wheels are reduced by manufacturing a wheel set  100 ,  100 ′ that joins said wheels to each other to make a single piece. Consequently, only teeth  113 ,  113 ′ of one of the wheels are still necessary, which means that most of the plate of one of the two wheels is no longer needed, thereby also decreasing the mass of the escape wheel set  100 ,  100 ′ and, incidentally, the inertia thereof. For greater simplicity, the following explanation is given with reference to a coaxial escape wheel. It is nonetheless clear that the invention is applicable to any type of wheel set with at least two levels. 
       FIGS. 9 and 10  illustrate two example embodiments according to the invention of single piece coaxial escape wheel sets  100 ,  100 ′. These wheel sets  100 ,  100 ′ each include two distinct patterns over one level. 
     According to the first embodiment, shown in  FIG. 9 , the first pattern forms a toothed wheel  101  corresponding to the first escape wheel  1  of  FIG. 11 . It includes a plate  103  forming a hub  102 , the centre of which has an opening  104  and from which arms  106  start. The end of each arm forms a tooth  108  corresponding to a tooth  8  of  FIG. 11 . A plate  103  with a first toothing at the periphery thereof is thus obtained. 
     As illustrated in  FIG. 9 , opening  104  includes elastic securing means  105  intended to cooperate radially with an arbour of the type referenced  3  in  FIG. 11 , by elastic deformation, to rotatably mount escape wheel  101  and, consequently, escape wheel set  100 . This elastic securing means  105  is formed by elongated parts made by hollowing out a portion of hub  102 . The elongated parts enable the arbour to be gripped, i.e. wheel set  100  thereof to be secured, without subjecting the rest of plate  103  to any stress. 
     Of course, other elastic means may be envisaged. Such elastic means may, for example, take the form of that disclosed in FIGS. 10A to 10E of EP Patent No. 1 655 642, or that disclosed in FIGS. 2 to 5 of WO Patent No. 2007/099068, both documents being incorporated herein by reference. 
     Thus, advantageously according to the invention, rather than adding a second escape wheel  11  as in  FIG. 11 , since wheel set  100  is in a single piece, the second pattern  111 , which projects from the first  101 , is formed solely by a second toothing comprising teeth  113  corresponding to the teeth  13  of  FIG. 11 . 
     Preferably, according to the invention, the teeth  113  are independent of each other and integral with arms  106 . In the particular example of  FIG. 9 , it is noted that each tooth  113  is integral with a distinct arm  106 . It is therefore clear that the second toothing includes as many teeth  113  as plate  103  has arms  106 . However, this feature is not essential and there could very well be several teeth  113  on a single arm  106 . 
     According to the second embodiment, seen in  FIG. 10 , the first pattern forms a toothed wheel  101 ′ corresponding to the first escape wheel  1  of  FIG. 11 . It includes a plate  103 ′ forming a hub  102 ′ the centre of which has an opening  104 ′ and from which arms  106 ′ start, each end of said arms forming a tooth  108 ′ corresponding to a tooth  8  of  FIG. 11 . A plate  103 ′ including a first toothing at the periphery thereof is thus obtained. 
     As illustrated in  FIG. 10 , opening  104 ′ includes plastic securing means  107  intended to cooperate radially with an arbour of the type referenced  3  in  FIG. 11 , for rotatably mounting escape wheel  101 ′ and, consequently, escape wheel  100 ′. This plastic securing means  107  is formed by a washer made of metallic material allowing wheel set  100 ′ to be driven against said arbour via plastic deformation without subjecting plate  103 ′ to stress. Of course, other plastic securing means may be envisaged. 
     Thus, advantageously according to the invention, rather than adding a second escape wheel  11  as in  FIG. 11 , since wheel set  100 ′ is in a single piece, the second pattern  111 ′, which projects from the first  101 ′, is formed solely by a second toothing comprising teeth  113 ′ corresponding to the teeth  13  of  FIG. 11 . 
     Preferably according to the invention, teeth  113 ′ are independent of each other and integral with arms  106 ′. In the particular example of  FIG. 10 , it is noted that each tooth  113 ′ is integral with a distinct arm  106 ′. It is therefore clear that the second toothing includes as many teeth  113 ′ as plate  103 ′ has arms  106 ′. However, this feature is not essential and there could very well be several teeth  113 ′ on a single arm  106 ′. 
     These two embodiments of  FIGS. 9 and 10  may be formed using many different materials. However, an electroformable material, on the one hand, or a micro-machinable material, on the other hand, are preferred. Indeed, to date, reactive ion etching and LIGA type electroforming are the only processes capable of making parts with the precision necessary (on the order of a few microns) for coaxial wheel set  100 ,  100 ′ to operate properly. However, any other process capable of respecting the same fabrication tolerances is applicable. 
     An electroformable material may be formed with gold and/or copper and/or silver and/or indium and/or platinum and/or palladium and/or nickel, although this is not an exhaustive list of compounds. Indeed, other compounds such as phosphorus may be added in smaller quantities. A micro-machinable material may be formed of silicon carbide, crystallised silicon, crystallised alumina or crystallised silica, although this list of compounds in not exhaustive. 
     The two types of manufacture will be presented respectively in  FIGS. 1 to 4  and  5  to  8 .  FIGS. 1 to 4  show the main successive steps of micro-machining for improved comprehension. Preferably, the method includes a first step consisting in taking a substrate  31  including a top layer  33  and a bottom layer  35  made of micro-machinable materials and secured to each other by an intermediate layer  34 . This type of substrate  31  is also known by the abbreviation S.O.I. (Silicon on Insulator). 
     In a second step, at least one pattern  36  is etched in the top layer  33  until intermediate layer  34  is revealed so as to form at least a first toothing (teeth  108 ,  108 ′) of escape wheel set  100 ,  100 ′ at the periphery of a plate  103 ,  103 ′. This second step thus allows one or several first pattern(s)  101 ,  101 ′ of wheel set  100 ,  100 ′ to be made in top layer  33 . 
     As illustrated in  FIG. 2 , a mask  37  is formed, for example by photolithography, to protect the part of top layer  33  which is to be kept and then, as illustrated in dotted lines, the top part of substrate  31  is subjected to D.R.I.E. (Deep Reactive Ion Etching). As illustrated in  FIG. 3 , the first pattern  36 , which includes a first level  101 ,  101 ′ of at least one escape wheel set  100 ,  100 ′, is obtained. 
     In a third step, at least one second pattern  38  is etched in bottom layer  33  until the intermediate layer  34  is revealed, so as to form at least a second toothing (teeth  113 ,  113 ′) in a single piece with the plate  103 ,  103 ′ of the first toothing (teeth  108 ,  108 ′) of the escape wheel  100 ,  100 ′. This third step thus enables one or several second pattern(s)  111 ,  111 ′ of wheel set  100 ,  100 ′ to be formed in bottom layer  35 . 
     As illustrated in  FIG. 3 , a mask  39  is formed, for example by photolithography, to protect the part of bottom layer  35  that is to be kept and then, as illustrated in dotted lines, the bottom part of substrate  31  is subjected to D.R.I.E. As  FIG. 4  illustrates, the second pattern  38  is obtained, including at least one second level  111 ,  111 ′ in a single piece with one of the first levels  101 ,  101 ′ formed in the preceding steps. 
     It remains only to release each two-level wheel set  100 ,  100 ′ thereby formed from substrate  31  and, possibly, the exposed parts of intermediate layer  34 , so as to mount escape wheel  100 ,  100 ′ in the final escape system. Preferably, when escape wheel set  100 ,  100 ′ is formed from a silicon base, an additional oxidation step is performed so as to form at least one silicon dioxide part on the external surface thereof in order to increase the mechanical resistance of the wheel set. 
       FIGS. 5 to 8  show successive main electroforming steps for improved comprehension. Preferably the method includes a first step consisting in taking a substrate  41  that includes an electrically conductive top layer. This layer may be obtained by depositing an electrically conductive material on an insulating material or by the fact that the substrate is formed of an electrically conductive material. 
     The main electroforming steps consist in forming a mould and then filling the mould with the material, for example, by galvanoplasty. This type of electroforming is known by the abbreviation L.I.G.A. from the German term “röntgenLIthographie, Galvanoformung &amp; Abformung”. There are several types of L.I.G.A. processes depending upon whether the mould with several levels is formed between each galvanoplasty process or formed entirely and then only subsequently filled. For the explanation below, the technique presented consists in forming each level, i.e. forming one level of the mould and filling it before passing to the next level. Of course, any type of electroforming process capable of forming a single piece wheel set with at least two distinct levels may be envisaged, whether or not it is of the L.I.G.A. type. 
     As illustrated in  FIGS. 5 and 6 , in a first phase, the first level  47  of the mould is formed using, for example, photolithography of a resin as illustrated in  FIG. 5 . At least one cavity is formed in a shape matching the first pattern  101 ,  101 ′, i.e. at least a first toothing (teeth  108 ,  108 ′) of the escape wheel set  100 ,  100 ′ at the periphery of plate  103 ,  103 ′. The first level is then filled via electrodeposition of a metallic material  46 . 
     As illustrated in  FIG. 7 , in a similar way to the first phase, the second level  49  is formed in a second phase by using, for example, photolithography of a resin. At least one recess is formed in a shape matching the first pattern  111 ,  111 ′, i.e. at least a second toothing (teeth  113 ,  113 ′) of the escape wheel set  100 ,  100 ′ and communicating with said at least one cavity of the first level  47 . The second level  49  is then filled by electrodeposition of a metallic material  48 . 
     It remains only to release the two-level wheel set  100 ,  100 ′ thereby formed from substrate  41  and resins  47 ,  49 , as illustrated in  FIG. 8 , so as to mount escape wheel  100 ,  100 ′ in the final escape system. In the example of an escape wheel set  100 ,  100 ′ obtained by electroforming, it is clear that it is no longer necessary to form elastic  105  or plastic  107  securing means because the metallic material can be directly driven onto the arbour through opening  104 ,  104 ′ thereof. 
     Of course, this invention is not limited to the illustrated example but is capable of various variants and alterations that will appear to those skilled in the art. In particular, by way of alternative, the toothed wheels  101 ,  101 ′ could also include a felloe like the one referenced  9  in  FIG. 11 , without departing from the scope of the present invention. 
     Moreover, although the example of a coaxial escape wheel is given above, it is very clear that a wheel-pinion type wheel set of a gear train or even a normal escape wheel will have the same advantages. The first toothing  108 ,  108 ′ would be that of the wheel and the second toothing  113 ,  113 ′ that of the pinion or vice versa. 
     Finally, it must be understood that at least two levels are achieved in a single piece. Thus, it is perfectly possible to envisage least one additional level being formed underneath the plate, i.e. the opposite face to that carrying the second toothing  113 ,  113 ′, and/or above the latter.