Patent Publication Number: US-8979359-B2

Title: Balance spring with two hairsprings

Description:
This application claims priority from European Patent Application No. 11181307.7 filed Sep. 14, 2011, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a balance spring for a sprung balance resonator and more particularly to a balance spring comprising two hairsprings. 
     BACKGROUND OF THE INVENTION 
     Forming a balance spring using two hairsprings connected by a raised terminal curve device is known from EP Patent No. 2 405 312. This balance spring gives good results as regards the isochronism of the timepiece but may be problematic to mount in a timepiece movement if the free end of the balance spring, opposite to the end pinned up to the collet, is too close to the balance staff. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome all or part of the aforementioned drawbacks, by providing a balance spring with two hairsprings comprising a device for shifting the point of pinning up to the stud. 
     The invention therefore relates to a balance spring comprising a first hairspring, the inner coil of which includes a collet arranged to be mounted on a staff, a second hairspring connected to the outer coil of the first hairspring by a raised terminal curve device, characterized in that the inner coil of the second hairspring includes a device for shifting the pinning point comprising a free end arranged to be secured to a balance spring stud in the plane of said second hairspring. 
     It is therefore clear that the balance spring will be pinned up to the stud between two of its coils without, however, touching said coils during development, i.e. during both the contraction and expansion phases. 
     In accordance with other advantageous features of the invention:
         The shifting device includes a piece extending from the inner coil of the second hairspring, said piece being more rigid than said second hairspring to avoid providing elastic torque.   The extension piece is connected to the inner coil via a substantially U-shaped bend.   The extension piece is integral with the second hairspring.   The extension piece is made more rigid by a thickness that is at least three times greater than that of said second hairspring.       

     The invention also relates to a movement comprising a sprung balance resonator including a balance rotatably fitted to a staff mounted between a plate and a bridge, characterized in that it includes a system of pinning up to the stud which cooperates with said free end of the balance spring according to any of the preceding variants, via a balance spring stud connecting said balance spring to said bridge. 
     In accordance with other advantageous features of the invention:
         The system of pinning up the balance spring to the stud includes a device for adjusting the stud, arranged between said stud and said bridge, to make the positioning of said stud adjustable.   According to a first embodiment, the stud adjusting device includes a means of clamping said stud and a means of attachment to the bridge.   The clamping means includes an elastic clamp controlled by a cam to selectively clamp said stud.   The attaching means includes an attachment which cooperates in a friction tight fit against said bridge to enable the position of the stud to be adjusted relative to the bridge.   The attachment forms two substantially annular arms intended to be attached to a cylindrical body of circular section of said bridge in order to alter the position of the stud concentrically to said staff.   According to a second embodiment, the stud adjusting device includes a means of locking said stud and a means of attachment to the bridge.   The locking means includes a part retaining one end of the stud against said means of attachment to the bridge in order to clamp said stud.   The attaching means includes an attachment which is screwed against said bridge so that the position of the stud can be selectively adjusted relative to the bridge.   The attachment includes a recess which slides against a cylindrical body of circular section of said bridge in order to alter the position of the stud concentrically to said staff.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will appear clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which: 
         FIGS. 1 and 2  are perspective views of a first embodiment of a movement according to the invention. 
         FIGS. 3 to 6  are perspective views of a second embodiment of a movement according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment of a movement  1  according to the invention is presented in  FIGS. 1 and 2 . Movement  1  according to the invention is preferably intended to be mounted in a timepiece (not shown). 
     As seen in  FIGS. 1 and 2 , movement  1 , which is preferably a timepiece movement, includes a resonator  3  of the sprung balance  7 ,  5  type. According to the invention, movement  1  includes a balance  5  rotatably fitted to a staff  2  mounted between a plate (not shown) and a bridge  4 . In the example of  FIG. 2 , balance  5  is of the variable inertia type. It is clear that other types of balance may be used. 
     Advantageously according to the invention, movement  1  further includes a pinning system  9  intended to cooperate with a free end  6  of balance spring  7  via a balance spring stud  8  connecting balance spring  7  to bridge  4 . 
     Preferably according to the invention, balance spring  7  includes a first hairspring  11 , the inner coil of which comprises a collet  10 , arranged to be mounted on staff  2 , and a second hairspring  13  connected to the outer coil of the first hairspring  11  by a raised terminal curve device  15 . The raised terminal curve device  15  between hairsprings  11  and  13  is preferably the device disclosed in CH Patent No. 0795/10 in the name of the Applicant. Moreover, balance spring  7  preferably follows the teaching of Patent No. CH 1144/10 also in the name of the Applicant and is therefore preferably made from a silicon base. CH Patent Nos. 0795/10 and 1144/10 are incorporated by reference in the present Application. 
     Further, the inner coil of the second hairspring  13  preferably comprises a device  17  for shifting the pinning point of the free end  6  arranged to be pinned up to a stud  8  in the plane of the second hairspring  13 . Shifting device  17  is particularly useful for preventing particular shapes of balance spring  7  from making it impossible to assemble said balance spring due to the proximity of the free end  6  thereof to staff  2 . 
     As seen in  FIG. 2 , shifting device  17  includes a piece  12  extending from the inner coil of the second hairspring  13 . Preferably, piece  12  is more rigid than second hairspring  13  so as to avoid providing elastic torque to resonator  3 . As seen more clearly in  FIG. 2 , piece  12  is preferably made more rigid by a greater thickness, such as for example at least three times greater, than the thickness of second hairspring  13 , i.e. the width of the blade thereof. It is therefore clear that the shape of piece  12  is partly adapted according to the curve of the coils of second hairspring  13  so that no contact occurs. 
     Further, according to a particular alternative, it is preferable for piece  12  to be integral with second hairspring  13  and, preferably, for the height of said hairspring to be substantially equal to that of piece  12 , i.e. contained within the same plane. 
     The extension piece  12  is further preferably connected to the inner coil of second hairspring  13  via a substantially U-shaped bend  14  in order to further limit the supply of any elastic torque. It is clear that extension piece  12  and bend  14  potentially bring closer the fixed point formed by bridge  4  at free end  6  of balance spring  7 . 
     Finally, in the first embodiment of  FIGS. 1 and 2 , piece  12  has a recess  16 , which may be a blind or through recess, of substantially rectangular section, intended to cooperate with pinning system  9  and, more precisely, stud  8 . 
     Pinning system  9  preferably includes a device  19  for adjusting the stud  8  mounted between said stud and bridge  4  to make the position thereof adjustable. Adjusting device  19  preferably includes a means  18  of locking stud  8  and a means  20  of attachment to bridge  4 . 
     Preferably according to the invention, locking means  18  includes a part  22  retaining one end of stud  8  against said means of attachment  20  (in the example of  FIG. 1 , attachment  21 ) in order to clamp stud  8 . In the example illustrated in  FIG. 1 , the end of stud  8  is L-shaped and locked in a groove of attachment  21  by the overlapping part  22 , which is screwed against attachment  21 . 
     Means of attachment  20  preferably includes attachment  21 , which is intended to be screwed and locked against bridge  4  so that the position of stud  8  can be selectively adjusted relative to bridge  4 . This is made possible by the oblong hole  23  made in attachment  21  which receives the shaft of screw  24 , which cooperates with bridge  4 . It is thus clear that attachment  21  can be locked in several positions by sliding the shaft of screw  24  into hole  23  before it is screwed in. 
     Finally, attachment  21  includes a recess  25  intended to slide against a cylindrical body  26  of circular section of bridge  4  so as to alter the position of stud  8  concentrically to staff  2 . In the example illustrated in  FIG. 1 , it can be seen that cylindrical body  26  is a portion of the shock absorber bearing of movement  1 . Preferably according to the invention, the shock absorber bearing is that disclosed in CH Patent No. 0720/05 in the name of the Applicant and incorporated by reference in this Patent Application. 
     As seen in  FIG. 1 , in order to fit attachment  21  to said shock absorber bearing, it is noted that a recess has been made so that the elastic arm operates properly. It is thus clear that any required modifications can be made to shifting device  17  or pinning system  9  in order to fit other components of movement  1 . 
     Consequently, movement  1  according to the first embodiment includes a double balance spring  7  which is secured to bridge  4  by pinning system  9 , allowing preferably concentric adjustment of the position of stud  8  relative to staff  2 . 
     A second embodiment of a movement  31  according to the invention is shown in  FIGS. 3 to 6 . Movement  31  according to the invention is preferably intended to be mounted in a timepiece (not shown). 
     As seen in  FIGS. 3 and 6 , movement  31 , which is preferably a timepiece movement, includes a resonator  33  of the sprung balance  37 ,  35  type. According to the invention, movement  31  includes a balance  35  rotatably fitted to a staff  32  mounted between a plate  34 ′ and a bridge  34 . In the example of  FIGS. 3 and 6 , balance  35  is of the variable inertia type. It is clear that other types of balance may be used. 
     Advantageously according to the invention, movement  31  further includes a pinning system  39  intended to cooperate with a free end  36  of balance spring  37  via a balance spring stud  38  connecting balance spring  37  to bridge  34 . 
     Preferably according to the invention, balance spring  37  includes a first hairspring  41 , the inner coil of which comprises a collet  40 , arranged to be mounted on staff  32 , and a second hairspring  43  connected to the outer coil of the first hairspring  41  by a raised terminal curve device  45 . The raised terminal curve device  45  between hairsprings  41  and  43  is preferably the device disclosed in CH Patent No. 0795/10 in the name of the Applicant. Moreover, balance spring  37  preferably follows the teaching of Patent No. CH 1144/10 also in the name of the Applicant and is therefore preferably made from a silicon base. CH Patent Nos. 0795/10 and 1144/10 are incorporated by reference in the present Application. 
     Further, the inner coil of the second hairspring  43  preferably comprises a device  47  for shifting the pinning point of the free end  36  arranged to be pinned up to a stud  38  in the plane of the second hairspring  43 , which is comparable to that of the first embodiment. Shifting device  47  is particularly useful for preventing particular shapes of balance spring  37  from making it impossible to assemble said balance spring due to the proximity of the free end  36  thereof to staff  32 . 
     As seen in  FIG. 4 , shifting device  37  includes a piece  42  extending from the inner coil of the second hairspring  43 . Preferably, piece  42  is more rigid than second hairspring  43  so as to avoid providing elastic torque to resonator  33 . As seen more clearly in  FIG. 4 , piece  42  is preferably made more rigid by a greater thickness, such as for example at least three times greater, than the thickness of second hairspring  43 , i.e. the width of the blade thereof. It is therefore clear that the shape of piece  42  is partly adapted according to the curve of the coils of second hairspring  43  so that no contact occurs. 
     Further, according to a particular alternative illustrated in  FIG. 6 , it is preferable for piece  42  to be integral with second hairspring  43  and, preferably, for the height of said hairspring to be substantially equal to that of piece  42 , i.e. contained within the same plane. It is also noted that extension piece  42  is advantageously pierced with holes to reduce the mass thereof but without reducing its rigidity. 
     Extension piece  42  is also preferably connected to the inner coil of the second hairspring  43  via a substantially U-shaped bend  44  in order to further limit the supply of any elastic torque with the same advantages as in the first embodiment. 
     Finally, in the second embodiment of  FIGS. 3 to 6 , piece  42  has a recess  16 , which may be a blind or through recess, of substantially rectangular section, intended to cooperate with pinning system  39  and, more precisely, stud  38 . 
     Pinning system  39  preferably includes a device  49  for adjusting the stud  38  mounted between said stud and bridge  34  to make the position of stud  38  adjustable. Adjusting device  49  preferably includes a means  48  of clamping stud  38  and a means  50  of attachment to bridge  34 . 
     Preferably according to the invention, clamping means  48  includes an elastic clamp  52  controlled by a cam  53  in order to clamp stud  38  selectively. In the example illustrated in  FIGS. 4 and 5 , clamp  52  is formed by a fixed portion  54  relative to means of attachment  50  and, more particularly to attachment  51 , and includes a hole  59  for contactlessly receiving staff  32 . 
     Clamp  52  also includes a mobile portion  56  elastically connected to fixed portion  54  and controlled by cam  53 . It is thus clear that, in the  FIG. 5  view, clamping means  48  is in the position where cam  53  induces maximum force and consequently means  48  clamps stud  38  in a friction tight fit preventing the stud from imparting any relative movement with respect to clamping means  48 . Of course, the contact surfaces between clamping means  48  and stud  38  may be changed, for example grooved and/or fluted, in order to further limit said relative movement. 
     Means of attachment  50  preferably includes an attachment  51  intended to cooperate in a friction tight fit against bridge  34  so that the position of stud  38  can be adjusted with respect to bridge  34 . For this purpose, attachment  51  forms two substantially annular arms  55 ,  57  intended to be attached against a cylindrical body  58  of circular section of bridge  34  in order to alter the position of stud  38  concentrically to staff  32 . It is thus clear that attachment  51  may be locked in several positions by moving each arm  55 ,  57  against body  58 . 
     In the example illustrated in  FIG. 3 , it can be seen that cylindrical body  58  is a portion of the shock absorber bearing of movement  31 . Preferably according to the invention, the shock absorber bearing is that disclosed in CH Patent No. 0720/05 in the name of the Applicant and incorporated by reference in this Patent Application. 
     As in the first embodiment, is of course clear that any required modifications can be made to shifting device  47  or pinning system  39  in order to fit other components of movement  31 . 
     Consequently, movement  31  according to the second embodiment includes a double balance spring  37 , which is secured to bridge  34  by pinning system  39 , allowing preferably concentric adjustment of the position of stud  38  relative to staff  32 . Compared to the first embodiment, it is clear that the second embodiment allows resonator  33  to be more accessible and more visible. 
     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, it is possible to envisage piece  12  being partially pierced with holes to decrease its mass as for piece  42 . Moreover, as for pieces  12 ,  42 , it is possible to envisage that a more rigid part exists between collet  10 ,  40  and the first hairspring  11 ,  41  in order to optimise the development of balance spring  7 ,  37 .