Patent Publication Number: US-10761484-B2

Title: Balance-spring stud-holder for a mechanical timepiece movement

Description:
This application claims priority from European patent application No. 17188811.8 filed on Aug. 31, 2017, the entire disclosure of which is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention deals with the field of watchmaking, and more particularly to the field of mechanical watchmaking, where the regulation of the motive energy is supplied by a spring oscillator. The invention relates, more specifically, to a balance-spring stud-holder for a mechanical movement. 
     TECHNOLOGICAL BACKGROUND 
     In most mechanical watches, the energy necessary for the rotation of the hands (for example hands indicating minutes and hours) is accumulated then dispensed by a balance-hairspring system, which comprises an inertia flywheel called balance, associated with a spring in the form of a spirally-wound tape, called hairspring. 
     By an internal end, the hairspring is fixed onto an axis secured in rotation to the balance; by an outer end, the hairspring is fixed onto a balance-spring stud mounted on a balance-spring stud-holder which is itself secured to a fixed bridge (or cock). 
     Traditionally, the hairspring is made from a steel alloy based on cobalt, nickel and chrome. A quenching and an annealing are commonly applied to this alloy, which has the advantage of conferring upon it a high limit of elasticity and therefore a good breaking strength. Another advantage of the steel is its suitability for repair. However, a drawback of the steel is its magnetizable nature, which is detrimental to behaviour under load (and therefore to the accuracy of the timepiece movement); in addition, the fixing of the balance-spring stud by gluing is difficult on steel. 
     It is also known practice (although less commonplace) to use, for the production of the hairspring, silicon. According to Vermot et al ( Traité de Construction Horlogère , Presses Techniques et Universitaires Romandes, 2014, pp. 712-713), silicon has the advantage of exhibiting a low moment of inertia, a low expansion coefficient, a good corrosion resistance and of being amagnetic. In addition, it is possible to fix the balance-spring stud at the outer end of the silicon spring by means of a two-component glue activated by ultraviolet radiation, which offers a very high fixing power. However, the main drawback with silicon is its breakable nature, in the conditions described hereinbelow. 
     The rotation of the balance is maintained—and its oscillations counted—by an escapement mechanism comprising a pallet assembly driven by an oscillating movement of low amplitude, provided with two pallets which drive the teeth of an escapement wheel. Thus driven, the escapement wheel has imposed on it a stepwise rotational movement whose frequency is determined by the frequency of oscillation of the pallet assembly, which is itself locked onto the frequency of oscillation of the balance (that is to say of the hairspring). 
     In a traditional escapement mechanism, the frequency of oscillation is approximately 4 Hz, or approximately 28 800 alternations per hour (Ah). One objective of the good watchmakers is to ensure the isochronism and the regularity of the oscillations (or constancy of the rate) of the balance. 
     It is known practice to set the rate of the balance by adjusting the active length of the hairspring, defined as the curvilinear length between its inner end and a counting point, located in the vicinity of the outer end of the hairspring and generally defined by a pair of abutments borne by a key mounted on a regulator. 
     In operation, this regulator is fixed in rotation relative to the axis of the hairspring. However, it is possible, by a manual intervention, to finely set the angular position thereof, for example by pivoting, by means of a screwdriver, an eccentric acting on the regulator in the way of a cam. 
     The assembly comprising the bridge, the regulator, the key, the balance-spring stud-holder, the balance-spring stud, the axis, the spring and the balance, is commonly called “adjustment mechanism”. Examples of adjustment mechanisms are proposed by the international application WO 2016/192957 and by the European patent EP 2 876 504, both in the name of timepiece manufacturer ETA. 
     Some interventions on the adjustment mechanism can require the unwinding (even the complete dismantling) of the hairspring. The balance-spring stud, secured to the outer end of the hairspring, then has to be separated from the balance-spring stud-holder. 
     This operation, called de-pegging, is difficult. The watchmaker generally holds the balance-spring stud by means of a pair of tweezers, then delicately removes the balance-spring stud. 
     However, it often happens that the balance-spring stud escapes from the tweezers, which provokes an abrupt release of the hairspring whose outer end is thus freed. 
     This incident is inconsequential when the hairspring is made of steel (and more specifically of steel alloy, as indicated above), because the quenching and tempering treatments which are applied to it make it sufficiently ductile to allow for a rewinding of the hairspring. 
     On the other and, that same incident for a hairspring made of silicon which, statistically, breaks in more than one case in every two, is dramatic. 
     The objective of the invention is to allow for a de-pegging by limiting, even eliminating, the risk of breaking. 
     SUMMARY OF THE INVENTION 
     There is proposed, firstly, a balance-spring stud-holder as defined in Claim  1 . 
     That way, the balance-spring stud extracted from the notch is blocked in the abutment, which prevents the spring (hairspring) from being abruptly relaxed during the de-pegging. The risk of breaking of the spring is thus limited. 
     Advantageous features of the balance-spring stud-holder, that can be taken alone or according to all technically possible combinations, are defined in the dependent claims. 
     There is proposed, secondly, an assembly comprising such a balance-spring stud-holder. 
     Advantageous features of the assembly, that can be taken alone or according to all technically possible combinations, are defined in the dependent claims. 
     There is proposed, thirdly, a timepiece movement comprising such an assembly. 
     There is proposed, fourthly, a watch comprising such a mechanical timepiece movement. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other objects and advantages of the invention will become apparent in light of the description of an embodiment, given hereinbelow with reference to the attached drawings in which: 
         FIG. 1  is an exploded perspective view partially showing a watch comprising a mechanical timepiece movement including an adjustment mechanism; 
         FIG. 2  is a perspective view from above showing the adjustment mechanism on its own; 
         FIG. 3  is a perspective view from below showing the adjustment mechanism; 
         FIG. 4  is an exploded perspective view, from above, of the adjustment mechanism; 
         FIG. 5  is an exploded perspective view, from below, of the adjustment mechanism; 
         FIG. 6  is a perspective view of the balance-spring stud-holder with which the adjustment mechanism of the preceding figures is equipped; 
         FIG. 7  is a partial perspective view showing the balance-spring stud-holder, the balance-spring stud (in dotted lines) mounted on the balance-spring stud-holder, and a part of the outer strand of the spring (also in dotted lines); 
         FIG. 8  is a perspective view similar to  FIG. 7 , showing the balance-spring stud-holder with the balance-spring stud extracted from the notch and in abutment against the bend; 
         FIG. 9  is a view from below of the balance-spring stud-holder alone; 
         FIG. 10  is a view from below of the balance-spring stud-holder with, in dotted lines, the balance-spring stud snap-fitted into the notch and, in solid lines, the balance-spring stud extracted from the notch, in abutment against the bend. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a watch  1 . 
     This watch  1  comprises a middle  2 , which can in particular be made of metal (for example steel), or of a synthetic material (for example, a composite material comprising a polymer matrix filled with fibres, typically of carbon). 
     The watch  1  also comprises, for wearing on the wrist, a bracelet  3  which is fixed onto the middle  2  between horns  4  formed protruding therefrom. 
     The watch  1  also comprises a glass and a bottom (not represented), fixed onto the middle  2  on either side thereof. 
     The watch  1  comprises, finally, a timepiece movement  5 , hereinafter simply called “movement”, which comprises a mainplate  6  intended to be housed in the middle  2  by being fixed thereto, for example by means of screws. The mainplate  6  forms a support for various mechanisms such as gear-train, adjustment mechanism, escapement, transmission, motion work, winding mechanism (list not exhaustive). 
     This timepiece movement  5  is mechanical, its motive energy source being supplied by a barrel spring and regulated by a spring oscillator. To protect this oscillator, the movement  5  incorporates an adjustment mechanism  7 , which is mounted on the mainplate  6 . 
     The adjustment mechanism  7  comprises, firstly, a bridge  8 . This bridge  8 , also called “cock”, takes the form of a rigid part (which can be metal) fixed onto the mainplate  6 . The bridge  8  forms both a support and a guide for the other components of the adjustment mechanism  7 . 
     According to an embodiment illustrated in the drawings, and in particular in  FIG. 1  and in  FIG. 3 , the bridge  8  comprises a base  9 . It is by this base  9  that the bridge  8  is fixed onto the mainplate  6  by means of a screw  10  which, passing through a hole  11  formed in the base  9 , helically engages with a tapped hole  12  drilled in the mainplate  6 . 
     The accurate positioning of the bridge  8  relative to the mainplate  6  is ensured by means of feet  13  which protrude from an inner face of the base  9  and are fitted into complementary bores  14  formed in the mainplate  6 . 
     For the fixing and the guiding of the other components of the adjustment mechanism  7 , the bridge  8  comprises an apron  15 , formed of a single piece with the base  9 . The bridge  8  is provided with a bore  16  formed in the apron  15 , at an overhanging end thereof. 
     The adjustment mechanism  7  comprises, secondly, a main axis  17 , which takes the form of a staged single-piece part mounted to rotate relative to the bridge  8 . More specifically, the main axis  17  is mounted to rotate between the mainplate  6  and the bridge  8 . 
     According to a particular embodiment (illustrated in particular in  FIG. 4  and  FIG. 5 ), in order to ensure the rotation of the axis  17  relative to the bridge  8 , the adjustment mechanism  7  comprises a shock damper  18 , driven into the bore  16 , and which comprises, on an inner face, a hole  19  for guiding a first end of the main axis  17 . 
     As can also be seen in  FIG. 1 , the mainplate  6  is provided with a hole  20  for guiding a second end of the main axis  17 . 
     To limit the frictions in the rotation of the main axis  17 , the ends thereof advantageously cooperate with a hard mineral, such as ruby or diamond. 
     The adjustment mechanism  7  comprises, thirdly, a spring  21  spirally wound around the main axis  17 . More specifically, the spring  21 , hereinafter called “hairspring”, has an inner end  22 , secured to the axis  17 , and an outer turn  23  which is terminated by an outer end  24 . 
     According to an advantageous embodiment, the hairspring  21  is produced in silicon, possibly covered with a layer of oxide. 
     When it is armed, the hairspring  21  provides a return torque which is exerted on the axis  17 . 
     To increase this torque supplied by the hairspring  21  and the amplitude of its oscillations, the adjustment mechanism  7  comprises, fourthly, an inertia flywheel in the form of a balance  25  secured in rotation to the axis  17 . 
     This balance  25 , produced for example in brass, comprises a hub  26 , by which it is driven onto the axis  17 , a felloe  27 , and spokes  28  (here, three, but this number is only illustrative) which link the hub  26  to the felloe  27 . 
     The adjustment mechanism  7  comprises, fifthly, a balance-spring stud-holder  29  which comprises a ring  30 , by which it is secured to the bridge  8 , and a pair of tabs, namely a front tab  31  and a rear tab  32  (front and rear being defined in the direction of winding of the hairspring  21 , from the inner end  22  to the outer end  24 ) which protrude radially from the ring  30  and, together, define a notch  33 . 
     The balance-spring stud-holder  29  is advantageously produced in a metal material, for example steel. 
     According to an embodiment illustrated in  FIG. 4 , the ring  30  of the balance-spring stud-holder  29  is driven onto a barrel  34  which protrudes from the apron  15  coaxially to the bore  16 . 
     The adjustment mechanism  7  comprises, sixthly, a balance-spring stud  35  secured to the outer end  24  of the hairspring  21 . This balance-spring stud  35  is for example produced in steel. According to an embodiment, the balance-spring stud  35  is fixed to the outer end  24  of the hairspring  21  by gluing, by means of a photo-polymerizable glue whose adhesion properties are activated by exposure to a photon radiation in the ultraviolet. 
     As illustrated in the drawings, and more particularly in  FIG. 4 ,  FIG. 5 ,  FIG. 7  and  FIG. 8 , the balance-spring stud  35  comprises a cylindrical body  36  by which the balance-spring stud  35  is snap-fitted into the notch  33 , and, on either side of the body  36 :
         a widened head  37  by which the balance-spring stud  35  bears against the balance-spring stud-holder  29 ,   a fork  38  in which is housed (by being glued) the outer end  24  of the hairspring  21 .       

     Fixed thus onto the balance-spring stud-holder  29 , the balance-spring stud  35  ensures the securing (that is to say the immobilization relative to the bridge  8 ) of the outer end  24  of the hairspring  21 . 
     The oscillations of the hairspring  21  are maintained (and counted) by an escapement pallet assembly (not represented) which communicates to it a kinetic energy, which arms the hairspring  21  by driving it beyond its position of equilibrium. 
     In being disarmed, that is to say in tending to return to its position of equilibrium, the hairspring  21  rotationally drives the main axis  17 , to which it is secured by its inner end  22 , with the balance  25  which is itself secured to the axis  17 . Having arrived at a complete relaxation, the hairspring  21  is immobilized (with the axis  17  and the balance  25 ) then, under the effect of its elasticity, tends to be compressed once again and then drives the axis  17  and the balance  25  in a rotation in the reverse direction. 
     The oscillations of the hairspring  21 —balance  17  system serve to regulate the alternating switchover movements of the escapement pallet assembly, which is provided with a pair of pallets alternately driving an escapement wheel whose stepwise rotation, at a frequency determined by the oscillations of the pallet assembly (that is to say of the spring), is transmitted to a motion work provided with one (or more) hand(s) indicating hours (and/or minutes). 
     The frequency of the oscillations of the hairspring  21 —balance  17  system can be finely regulated, by hand, by an intervention on the adjustment mechanism  7 , which, to this end, comprises, seventhly, a regulator  39 . 
     The regulator  39  is fixed to the bridge  8  with the possibility of angular travel relative thereto about the main axis  17 . 
     More specifically, the regulator  39  comprises:
         a tail  40  bearing a key  41  which defines a pair of abutments  42  arranged on either side of the outer turn  23  of the hairspring  21 , and   at least one indexing finger  43  which cooperates with an eccentric  44 , mounted on the bridge  8  to adjust the angular position of the regulator  39  by rotation of the eccentric  44 .       

     According to a preferred embodiment illustrated in particular in  FIG. 4  and  FIG. 5 , the regulator  39  comprises two distinct secured elements, namely:
         an upper regulator element  45 , which bears the indexing finger  43 ;   a lower regulator element  46 , which bears the tail  40 .       

     In the example illustrated, the upper element  45  comprises a central ring  47  and a pair of indexing fingers  43  which extend radially in a V from this central ring  47 . 
     In this same example, the lower element  46  comprises a ring  48 ; the tail  40  comprises a pair of tongues  49  which protrude radially from the ring  48  and define between them a slit  50  into which the key  41  is inserted. 
     The central ring  47  of the upper element  45  comprises a protruding bush  51  driven into the ring  48  of the lower element, which secures the upper element  45  and the lower element  46 . 
     Moreover, the central ring  47  of the upper element  45  is provided with a chamfer  52  complementing a tapered reach  53  formed on the shock damper  18 , which ensures the rotational guiding of the regulator  39  about the axis  17 . 
     The abutments  42  together form, for the hairspring  21 , a counting point, which, with the inner end  22 , defines an active (curvilinear) length on which the frequency of the oscillations of the hairspring  21  depends. The (manual) rotation of the eccentric  44  varies the angular position of the regulator  39  and therefore of the counting point, which increases (or, on the other hand, reduces) the active length (and therefore the frequency of the oscillations) of the hairspring  21 . 
     According to an embodiment illustrated in  FIG. 2  and  FIG. 4 , the finger (fingers) is (are) housed in a hollowed-out reserve  54  formed in the apron  15  of the bridge  8 . A regulation  55 , and “−” and “+” signs, etched into the apron  15 , provide the watchmaker with indications as to the scale and the direction of rotation, useful to allow him or her to finely adjust (with eyepiece or microscope, or even by means of a specific apparatus, such as the REGO model marketed by the company CENTAGORA) the position of the eccentric  44  (notched to this end)—and therefore of the regulator  39 . 
     During manual interventions on the adjustment mechanism  7 , the de-pegging, that is to say the removal of the balance-spring stud  35  from the balance-spring stud-holder  29 , may be necessary. To avoid having the balance-spring stud  35  released from the balance-spring stud-holder  29  being thrown far away under the effect of an abrupt relaxation of the hairspring  21 , the balance-spring stud-holder  29  is provided with a retaining abutment for the balance-spring stud  35  extracted from the notch  33 . 
     More specifically, the rear tab  32  of the balance-spring stud-holder  29  comprises an extension  56  which defines, beyond the notch  33 , a bend  57  forming this abutment. 
     Thus, the rear tab  32  comprises, in a single piece:
         a lower section  58 , which, with the front tab  31 , defines the notch  33 ,   the extension  56 , which extends radially in the continuity of the lower section  58 .       

     According to an embodiment illustrated in the drawings, and more particularly in  FIG. 6  and  FIG. 9 , the extension  56  comprises a radial portion  59  (substantially collinear with the inner section  58 ), and a transverse portion  60  which extends the radial portion  59  in the way of a bracket. 
     The bend  57  is defined at the junction between the radial portion  59  and the transverse portion  60 . 
     As can be clearly seen in  FIG. 9 , the transverse portion  60  of the extension  56  is advantageously spaced apart from the front tab  31  to form with it a fairly wide passage  61  to allow the introduction (or the forced removal) of the balance-spring stud  35 , transversely. 
     The rear tab  32  preferentially has an inner connection hollow  62  at the level of the bend  57 . 
     The balance-spring stud  35  snap-fitted into the notch  33  is illustrated by dotted lines in  FIG. 7  and in  FIG. 10 . In this position, the body  36  of the balance-spring stud  35  cooperates with the facets of the notch  33  which thus ensures the retaining thereof for the purposes of standard operation of the hairspring  21  (and therefore of the movement  5 ). 
     The balance-spring stud  35  is extracted (that is to say unsnap-fitted) from the notch  33  manually, by an outward radial movement (that is to say tending to separate the balance-spring stud  35  from the ring  30 ), in the direction indicated by the arrows in  FIG. 7  and  FIG. 10 . Now, the position of equilibrium of the hairspring  21  is reached when the balance-spring stud  35  is in the notch  33  of the balance-spring stud-holder. During the manual intervention, the balance-spring stud therefore has a tendency to return thereto, and thus to be blocked in the bend  57  (and more specifically in the hollow  62 ) where it is thus retained, as illustrated in solid lines in  FIG. 8  and  FIG. 10 . 
     The bend  57  (and therefore the abutment that it forms) makes it possible to unsnap-fit the balance-spring stud  35  without risking having it escape when it is removed from the notch  31 . 
     It is then possible to modify the seizure of the balance-spring stud  7  to ensure a firmer holding thereof and then completely disengage it from the balance-spring stud-holder  29 , for example in order to dismantle the hairspring  21 . 
     Since the balance-spring stud  35  is then retained by the abutment formed by the bend  57 , it is possible to then change tool to ensure a more comfortable (and firmer) grasp of the balance-spring stud  35  (for example by means of a pair of tweezers) in order, for example, to completely dismantle the hairspring  21 , by a vertical movement, as illustrated by the arrow in  FIG. 10 . In other words, the de-pegging is performed in two stages. 
     The result thereof is a reduced, even eliminated, risk of breakage of the hairspring  21  in the de-pegging, to the benefit of the reliability of the adjustment mechanism  7 .