Abstract:
An escapement mechanism adapted for transmitting mechanical energy pulses from a driving source to an oscillating regulator of a timepiece via a blade spring ( 12 ) operating in a buckling manner about a curvature point, wherein the blade spring ( 12 ) can build up the energy from the driving source between two pulses and transmit the same to the oscillating regulator upon each pulse via first ( 18 ) and second ( 26 ) levers. In order to optimize the adjustment of the tension of the blade spring ( 12 ), the latter is mounted on a frame ( 50 ) capable of symmetric deformation relative to a first axis (AA) extending through the rotation axes of the regulator, the levers ( 18, 26 ) and through the curvature point, and relative to a second axis (BB) perpendicular to the first one and extending through the ends of the blade spring ( 12 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns the field of mechanical horology. It more particularly concerns an escapement mechanism arranged to transmit mechanical energy pulses from a driving source to an oscillating regulator of a timepiece via a blade spring operating in a buckling manner about a curvature point. The blade spring is capable of accumulating the energy from the driving source between two pulses and transmitting it to said oscillating regulator upon each pulse via first and second yokes. 
       BACKGROUND OF THE INVENTION 
       [0002]    A mechanism of this type is known from document WO 99/64936, which more generally discloses a method for transmitting mechanical energy pulses from a driving source to an oscillating regulator via a blade spring operating in a buckling manner. More particularly, this method is implemented in particular using an escapement mechanism illustrated in  FIG. 1 , designed to maintain the oscillations of a regulator, of the sprung balance  10  type, for example, by delivering energy to it received from a driving source, such as a barrel for example, not shown in the drawing, via a blade spring  12 , the ends of which are positioned such that it occupies a stable position corresponding to a second mode buckling. 
         [0003]    The mechanism includes a plate  14  provided with an impulse-pin  16 , mounted on the balance  10 . The mechanism also includes a first detent yoke  18 , ending with a fork  20  of a traditional type, provided with an inlet horn  20   a  and an outlet horn  20   b  and a dart  20   c , designed to cooperate with the pin  16  and the plate  14 , respectively. The lever ends with a tail  22  and also supports first  24  and second  25  protruding active elements, situated in the plane of the blade spring  12 . 
         [0004]    The mechanism also includes a second winding yoke  26 , comprising a central portion and two symmetrical wings, each supporting, at their end, a key-pin assembly  28  and  29 , designed to cooperate with the blade spring  12 . The central portion also receives third  30  and fourth  31  active elements, designed to cooperate with first  32  and second  34  escapement wheels. 
         [0005]    The two yokes  18  and  26  are mounted free in rotation in reference to each other. However, banking and guide means, which will not be described in detail, connect them, but with play, such that a movement of one yoke causes the movement of the other, but with a certain staggering. 
         [0006]    The first  32  and second  34  escapement wheels are arranged on either side and symmetrically in relation to a line passing through the axes of rotation of the balance  10 , the yokes  18  and  26  and via the curvature point of the blade spring  12 . The wheels  32  and  34  each include a pinion  36  and  38  and mesh with the last wheel  40  of the going train. The wheels  32  and  34  include a particular toothing, the shape of which is adapted to cooperate with the first and second active elements of the second yoke, on one hand to transmit energy to that yoke and, on the other hand, to block the rotation of the wheels, according to operating phases that will be summarized below. For more details, see the document cited in the introduction. 
         [0007]    During the main part of an operating cycle, the escapement wheels  32  and  34  can pivot and are not blocked through contact with the third  30  and fourth  31  active elements of the second yoke  26 . Thus, in a winding phase, when the balance  10  performs its additional arc, the first escapement wheel  32  turns freely and the second escapement wheel  34  cooperates with the fourth active element  31  of the second yoke  26  to cause it to pivot. The keys-pins  28  and  29  then exert two opposing forces on the blade spring  12 , identical and symmetrical in relation to its curvature point. The blade spring  12  then leaves its initial stable state corresponding to a second mode buckling and deforms while winding, without, however, acting on the first yoke  18  at its active elements  24 ,  25 . At this stage, the relative rotational play between the yokes  18  and  26  allows the first yoke  18  to remain immobile. 
         [0008]    The balance  10  freely continuing its rotation, the escapement wheels  32  and  34  also continue their movement, until the second wheel  34  locks on the fourth active element  31 . The second yoke  26  has continued its pivoting, and the keys-pins  28  and  29  have acted on the blade spring  12 , which has continued its winding to a metastable state close to an unstable state corresponding to a fourth mode buckling. The blade spring  12  is then maximally wound. By cooperating with the tail of the first yoke  18 , the fourth active element  31  positions the first  24  and second  25  active elements. 
         [0009]    During the following step, the balance  10  continuing its oscillation, the pin  16  strikes the inlet horn  20   a  of the fork  20 . The first yoke  18  then acts on the blade spring  12  via the first active element  24 . The blade spring  12  then suddenly tilts from its unstable position to a stable state corresponding to a second mode buckling opposite the previous one. This change of state allows the blade spring  12  to act on the keys-pins  28  and  29 , which causes the second yoke  26  to pivot, driving the unlocking of the second escapement wheel  34 . The second yoke  26  pivots until the third active element  30  encounters one of the teeth of the first escapement wheel  32 . During the change of state of the blade spring  12 , this also acts on the second active element  25  of the first yoke  18 , thereby communicating to the balance  10  the energy accumulated during the winding of the blade spring  12 , via the outlet horn  20   b.    
         [0010]    During the following alternation, the phases described above are reproduced symmetrically in relation to the plane passing through the axes of rotation of the balance  10 , first  18  and second  26  yokes and through the curvature point of the blade spring  12 . 
         [0011]    Such an escapement mechanism is particularly interesting, in particular for the advantages mentioned in the aforementioned document. More particularly, it makes it possible to obtain an interesting efficiency, by decreasing the stop times of the different elements and the inertias to overcome during operation. 
         [0012]    However, it has been observed that adjusting the tension of the blade spring  12  and its position was particularly important to obtain correct operation of the mechanism. In the mechanism disclosed in the aforementioned document, the blade spring  12  is mounted in compression between two settings or using pivot organs. However, adjusting the tension is very delicate with a configuration as proposed in the prior art. 
         [0013]    The present invention aims in particular to resolve this problem. It also proposes a particularly advantageous embodiment in its implementation. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0014]    This aim is achieved owing to an escapement mechanism whereof the features are detailed in the claims. 
         [0015]    The invention also concerns a part implemented in the assembly of the mechanism and a method for that assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Other features of the present invention will appear more clearly upon reading the description that follows, done in reference to the appended drawings, in which, aside from  FIG. 1  described above in reference to the state of the art: 
           [0017]      FIG. 2  is a top view of the essential parts of the escapement mechanism according to the invention, 
           [0018]      FIG. 3  is a particular view of a blade spring according to one advantageous embodiment of the invention, and 
           [0019]      FIGS. 4 and 5  show successive views of the assembly of the mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 2  shows an escapement mechanism according to the invention. The components of the mechanism according to the invention that are also found in the mechanism described above in reference to  FIG. 1  were designated by the same numbers. They will therefore not be described again in detail. 
         [0021]    We will simply note that one finds, arranged on a frame of a clockwork movement, the following components:
       the balance  10  supporting the plate  14  and the impulse pin  16 ,   the first detent yoke  18 ,   the second winding yoke  26  with the two symmetrical wings and the central portion provided with third  30  and fourth  31  active elements, and   the first  32  and second  34  escapement wheels.       
 
         [0026]    According to a first aspect of the invention, the blade spring  12  is mounted on a deformable chassis  50 . More particularly, the chassis is symmetrically deformable in relation to a first axis AA passing through the axes of rotation of the balance  10 , yokes  18  and  26  and via the curvature point of the blade spring  12  and in relation to a second axis BB, perpendicular to the first and passing through the ends of the blade spring  12 . In one preferred embodiment, the chassis  50  is elastically deformable. The deformation along the first AA and second BB axes is guaranteed via guide organs forcing the chasses  50  to deform along said axes. Said guide organs can be oblong housings  52  arranged in pairs and along the axes AA and BB in the chassis  50 . They cooperate with pins  54  fixed on the frame of the movement. According to one particular feature, the chassis forms a frame that surrounds the axes of the components of the escapement mechanism. 
         [0027]    In one advantageous embodiment, the blade spring  12  is made of monocrystalline silicon. Interesting elastic characteristics have, simply as an illustration, been obtained with a blade spring  12  measuring 0.02 mm in the direction of the first axis and about 0.1 mm thick. Silicon allows particularly precise machining, for extremely reduced dimensions. 
         [0028]    To obtain effective cooperation between the second yoke  26  and the blade spring  12 , despite its small dimensions, the latter includes two open slots  55 , arranged symmetrically in relation to its curvature point, inside which fingers  56  and  57  are positioned, arranged protruding in relation to the yoke and replacing the keys-pins  28  and  29 . The transmission of the energy, on one hand, and the precision of the positions of the yoke  26  and blade spring  12 , on the other hand, are thus completely controlled. 
         [0029]    So that the chassis  50  can be freely moved in reference to the oblong housings  52 , it should undergo the least amount of gripping stress possible. It should, however, be positioned precisely in reference to the thickness of the movement, since it conditions the position of the blade spring  12 , and should also be influenced as little as possible by outside shocks. Traditional fastening means are poorly suited to serve these purposes. It is proposed, according to one preferred embodiment, that the chassis be provided with maintenance surfaces  58 . With a silicon frame  50 , it is very easy to produce said surfaces directly, in a single piece with the chassis. These maintenance surfaces  58  are placed directly on the frame of the movement. For good efficiency, they are arranged symmetrically in relation to the two axes of symmetry of the chassis. In the example, there are four of these surfaces  58 . Adjusting screws, not shown in the drawing, are housed in the frame of the movement such that the maintenance surfaces bear on the end thereof. Thus, these screws define the height of the chasses  50 , which is positioned in reference to the thickness of the movement. 
         [0030]    Maintenance organs, mounted on the frame of the movement, cooperate with the maintenance surfaces  58 . To limit the stresses undergone by the chassis  50 , these maintenance organs are elastically deformable in the direction of the thickness of the movement. They assume the form of arms  60 , crossing the maintenance surfaces  58  remotely. The arms  60  have appendages  62 , designed to be placed on the maintenance surfaces  58 . The position of the arms  60  can be adjusted in reference to the thickness of the movement, so as to apply the maintenance surfaces on the screws, by adjusting the pressure applied on the maintenance surfaces  58 . Preferably, the screws and the appendages  62  are positioned opposite each other, on either side of the maintenance surfaces  58 . 
         [0031]    Means for adjusting the position of the ends of the spring are provided. They are positioned on the frame of the movement, so as to act on the chassis  50 , symmetrically to the axes AA and BB. According to the example, two levers  64  act on the outer edge of the chassis  50 , and first and second points situated on the second axis of symmetry, on either side of the first. The levers  64  can be provided with runners  66  to act on the chassis  50 . Once the position of the ends of the spring is adjusted, the levers  64  are kept in place, for example by an eccentric system  68  or by other means within the grasp of one skilled in the art. To this end, a type of self-centered gripper, of the catch-up gripper type, may be used. The position of the ends of the blade spring  12  could also be adjusted by separating the zones of the chassis  50  crossing the axis AA from each other. 
         [0032]    Preferably, the chassis  50  is also made of silicon. The blade spring  12  and the chassis  50  can then be made in a single piece, arranged in a monocrystalline silicon plate. The DRIE (Deep Reactive Ion Etching) technique can be used. For example, the blade spring can be realized along crystallographic plane [110], plane [100] being the plane orthogonal to the wafer from which the chassis  50  comes. Other orientations can of course be chosen, one need only take into account the variations of Young&#39;s Modulus of Silicon as a function of the anisotropy of the Silicon, to dimension the chassis  50  and the blade spring  12 . 
         [0033]    The assembly formed by the chassis  50  and the blade spring  12  defines a sort of double-bow, symmetrical along axes AA and BB. At each intersection with one of these axes, the chassis has an oblong housing  52 . The shape of the chassis  50  is defined so as to grant it the desired elasticity, allowing it to deform under the action of the levers  64 . A person skilled in the art can, through appropriate tests, arrive without difficulty at a shape making it possible to obtain an elastically deformable silicon chassis. 
         [0034]    According to another feature of the invention, the first yoke  18  is broken down, on one hand, into a first portion  18   a  including the horns  20   a  and  20   b  and, on the other hand, into a second portion  18   b , superimposed on the first, including the dart  20   c . The two portions are made integral, for example using lugs included in the first portion  18   a , cooperating in the openings formed in the second  18   b.    
         [0035]    The second portion  18   b  is situated in the plane of the blade spring  12  and is integral therewith, which makes it possible to do away with the first and second active elements present in the mechanism of the prior art. Preferably, the second portion  18   b  is made of silicon and forms a single piece with the blade spring  12  and the chassis  50 . It is provided with pivot means situated at the curvature point of the spring, allowing it to tilt to perform its functions. To improve the transmission of the torque between the blade spring  12  and the yoke  18 , it is proposed in the example illustrated in the drawing, to arrange pins  69  on the first portion  18   a  and cooperating with the blade spring  12 . Their role is different from that of the first and second active elements of the prior art, because they are not essential to the transmission of the torque between the blade spring  12  and the yoke  18 , but only improve it. The same result could also be obtained by increasing the section of the blade spring  12  in the immediate vicinity of the yoke  18 . 
         [0036]    To assemble the mechanism according to the invention, one acquires a single piece  70  shown in  FIG. 3 , made of silicon, comprising the chassis  50 , the blade spring  12  and the second portion  18   b . The features of the blade spring  12  do not make it possible to ensure good mechanical resistance of the second portion  18   b , for its assembly. Originally, the single piece  70  is produced by arranging a stiffening portion  72  between the second portion  18   b  and the chassis  50 , ensuring the mechanical resistance of the assembly. More precisely, the stiffening portion  72  is connected to the second portion  18   b  and to the chassis  50 , via particularly thin first and second break zones  74 , respectively, about 0.2 mm thick, that can be easily broken, as will be understood below. 
         [0037]      FIGS. 4 and 5  show different steps of the assembly of the mechanism according to the invention. In  FIG. 4 , a platform-escapement bottom plate is already in place, as well as the last wheel  40  of the going train. The levers  64  are also in position. The second yoke  26  and the first portion  18   a  of the first yoke  18  are assembled and the single piece  70  is arranged, housing the pins  54  in the corresponding oblong housings  52 , and assembling the first  18   a  and second  18   b  portions of the first yoke  18 . One will note the presence of the stiffening portion in  FIG. 4 . Then, the maintenance arms  60  are mounted before placing the escapement bridge ( FIG. 5 ), which includes the complementary pivot means in particular for the first  18  and second  26  yokes. These two yokes  18  and  26  being, at this stage, pivoted above and below, the stiffening portion  72  can be broken at the break zones  74 , and removed from the movement. The yokes can then oscillate. The tension of the blade spring  12  is then adjusted and it is buckled, such that its slots  55  cooperate with the fingers  56  and  57  of the second yoke. One will note that references and other indexes can be provided so as to apply a substantially equal force on both sides of the chassis. Owing to the guide organs, the chassis necessarily deforms symmetrically in relation to the two defined axes, guaranteeing that the blade spring is still correctly positioned. 
         [0038]    Thus proposed is an escapement mechanism implementing a spring working in buckling, the tension of which can be adjusted particularly simply, while guaranteeing correct operation of the escapement. The description above was provided as a non-limiting illustration of the invention and a person skilled in the art may consider possible changes without, however, going beyond the scope of the invention.