Patent Publication Number: US-10768577-B2

Title: Push-piece winding button control device for a portable object of small dimensions

Description:
This application claims priority from European Patent Application No. 17177642.0 filed on Jun. 23, 2017, the entire disclosure of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention concerns a push-piece winding button control device for a portable object of small dimensions comprising a frame, a control stem that is mounted to pivot about a longitudinal axis and axially movable relative to the frame between at least a first position (“T 0 ”), which is transitory (or in other words unstable), and a second position (“T 1 ”) which is stable. The control device further includes a cam path, which has a longitudinal cam profile, and a cam follower arranged to cooperate with the longitudinal cam path. The cam path is arranged to move concurrently with the control stem when the latter is moved axially. The cam follower is mounted inside the frame and is arranged to be elastically returned against the cam path. The cam path includes a recess, which defines the stable position of the control stem, and a ramp-shaped profile portion which rises from the recess towards the transitory position. 
     BACKGROUND OF THE INVENTION 
     There are already known push-piece winding button control devices. European Patent No EP1930794, for example, describes a magnetic push-piece winding button control device for timepieces. According to this document, the push-piece winding button control stem has a profiled section which is essentially formed of two grooves and one inclined part. The profiled section is arranged to cooperate with the two arms of a split elastic ring in order to index the position of the push-piece winding button control stem by holding or returning the latter in or to a selected axial position. The control stem, which is symmetrical with respect to a determined plane passing through a longitudinal axis, is free to rotate between the two arms of the split elastic ring. By pressing or pulling out the push-piece winding button, the wearer of the watch can choose to make the control stem occupy three different, predefined positions. A stable first position, called the rest position, in which the arms of the split elastic ring are engaged in a first groove; a stable second position, called the pulled-out position, in which the arms of the split elastic ring are engaged in a second groove; and finally a transitory position, called the pushed-in position, in which the arms of the split elastic ring cooperate with the inclined part of the profiled section, such that, under the combined action of the pressure from the arms of the split elastic ring on the inclined part of the inclined section and the return force exerted by a spring, the control stem returns to the rest position as soon as the wearer of the watch releases pressure on the push-piece winding button. 
     Implementing a push-piece winding button control device like the one just described above is not, however, without a certain number of problems. In particular, one drawback lies in the fact that, in order to machine the cam path in a section of the control stem, the diameter of the control stem must be relatively large, which makes the use of such a control stem quite difficult, or even impossible, particularly in the field of wristwatches, where it is undesirable to have to machine large diameter holes in the case middle for passage of a control stem, in particular due to the thickness of the case middle. 
     Another example of such a control stem is illustrated in  FIG. 22 , annexed to this Patent Application. Designated as a whole by the general reference numeral  200 , this control stem includes a cylindrical portion  202  terminating with a push-piece winding button  204  at its end located outside the portable object (not represented) which is fitted with it. Towards its end opposite to push-piece winding button  204 , cylindrical portion  202  of control stem  200  is provided with a cam path  206  formed of three successive annular grooves  208   a ,  208   b  and  208   c  separated from each other by two flanges  210   a  and  210   b  of substantially rounded profile. The dimensions of annular grooves  208   a - 208   c  are adapted to those of the elastic arms  212  of a spring  214 , for example, a U-shaped spring, which projects, for example, into annular groove  208   a  of cam path  206 . It is understood that, in order to make elastic arms  212  of spring  214  move from annular groove  208   a  into annular groove  208   b , the user must exert on control stem  200  a traction force greater than the force necessary for elastic arms  212  to move apart and slide over flange  210   a  before closing again on annular groove  208   b . Conversely, if it is desired to move elastic arms  212  of spring  214  from annular groove  208   b  into annular groove  208   a , a thrust force must be exerted on control stem  200  sufficient to enable elastic arms  212  to deform and cross flange  210   a  and drop into annular groove  208   a . The same applies to the transition of elastic arms  212  of spring  214  from annular groove  208   b  into annular groove  208   c  and vice versa. 
     Thus, through cooperation between the elastic arms of a spring and a cam path which is integral with the cylindrical portion of a control stem, it is advantageously possible to define, for example, three stable positions of the control stem which each correspond to the setting of a given function. The drawback of this solution lies, however, in the fact that, in order to machine the cam path in the cylindrical portion of the control stem, the diameter of the cylindrical portion of the control stem must be relatively large, which makes the use of such a control stem quite difficult, or even impossible, especially in the field of wristwatches, where it is undesirable to have to machine large diameter holes in the case middle, in particular due to the thickness of the case middle. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the aforementioned problem of the prior art by providing a push-piece winding button control device conforming to the definition given in the preamble and wherein the pressure of the cam follower on the profile portion forming a ramp is sufficient to reliably return the stem to the stable position from the transitory position, even with a stem whose diameter is sufficiently small to be suitable for use in the field of horology, for example. 
     To this end, the present invention provides a push-piece winding button control device according to claim  1  annexed hereto. 
     According to the invention, the at least one cam path with which the at least one cam follower cooperates, is formed in a position indexing plate, which is arranged to be integral in translation with the control stem, but which remains stationary when the stem is pivoted. It will be understood that this feature means that the cam path, which allows the position of the control stem to be indexed, is transferred from the actual control stem to a position indexing plate which is machined separately from the control stem. Such an indexing plate is relatively thin and constantly maintains the same orientation, whereas, when the cam path is arranged on the control stem, this requires increasing the diameter of the control stem and therefore the height of the middle part of the portable object, so that the portable object is thicker, which it is sought to avoid, particularly in the field of timepieces. 
     According to an advantageous variant of the invention, when the push-piece winding button is pressed from the stable position, the reaction force that must be overcome to push in the push-piece winding button is high until the cam follower passes over a transition point. Beyond that point, the reaction force that has to be overcome is considerably lower. The abrupt drop in force on crossing the transition point produces a click sensation. It will be understood that such a click cannot be obtained with a known type of push-piece winding button arranged to be returned to the rest position by the force exerted by a return spring. Indeed, the force exerted by a spring can only increase monotonically as the spring is compressed and cannot pass through a point after which the force drops abruptly. Conversely, with a push-piece winding button according to the invention, the reaction force that must be overcome to enable the cam follower to climb the ramp profile portion, is determined by the slope of the ramp. Thus, according to the present advantageous variant, the ramp profile portion includes a first part that extends between the recess and a point of transition, and whose slope is steep. The profile portion further includes a second part that extends in a more moderate slope than the first part from the transition point towards the transitory position. 
     According to other features of preferred embodiments of the invention which form the subject of dependent claims:
         the control device includes two cam followers respectively returned against two longitudinal cam paths arranged in the position indexing plate symmetrically with respect to a plane of symmetry containing the axis of the stem;   the two cam followers are formed by the ends of two arms of a positioning spring mounted inside the frame;   the two longitudinal cam paths are arranged symmetrically with respect to a vertical plane which extends perpendicularly to a plane in which the control stem extends;   the cam followers are elastically returned against the two cam paths with forces which are exerted in substantially the same horizontal plane, perpendicularly to the axis of the stem;   the position indexing plate is housed in a cylindrical section of reduced diameter of the control stem, the cylindrical section of reduced diameter forms a groove delimited by two shoulders of the stem.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will appear more clearly from the following detailed description of an example embodiment of a control device according to the invention, this example being given solely by way of non-limiting illustration with reference to the annexed drawing, in which: 
         FIG. 1  is a perspective view, in an unassembled state, of a device for controlling at least one electronic function of a portable object of small dimensions. 
         FIG. 2  is a top, perspective view of the lower frame. 
         FIG. 3  is a perspective view of the control stem which, from right to left, extends from its rear end to its front end. 
         FIG. 4  is a perspective view, in an unassembled state, of the magnetic assembly formed of a support ring and a magnetized ring and the smooth bearing. 
         FIG. 5  is a longitudinal cross-sectional view along a vertical plane of a control device inside which are arranged in particular the smooth bearing and the magnetic assembly formed of the support ring and the magnetized ring. 
         FIG. 6  is a bottom, perspective view of the upper frame. 
         FIG. 7A  is a top, perspective view of the plate for indexing the position of the control stem. 
         FIG. 7B  is a larger scale view of the encircled area of  FIG. 7A . 
         FIG. 8  is a perspective view of the positioning spring arranged to cooperate with the plate for indexing the position of the control stem. 
         FIG. 9  is a top, perspective view of the spring for limiting the displacement of the control stem position indexing plate. 
         FIG. 10  is a perspective view of the disassembly plate. 
         FIG. 11  is a longitudinal cross-sectional view of one part of the control device showing the hole into which a pointed tool is inserted to release the control stem from the position indexing plate. 
         FIG. 12A  is a perspective view showing the control stem cooperating with the position indexing plate and the positioning spring, with the control stem in stable position T 1 . 
         FIG. 12B  is a similar view to that of  FIG. 12A , with the control stem in unstable pushed-in position T 0 . 
         FIG. 12C  is a similar view to that of  FIG. 12A , with the control stem in stable pulled-out position T 2 . 
         FIG. 13  is a perspective view of the contact springs. 
         FIGS. 14A and 14B  are schematic views that illustrate the cooperation between the fingers of the control stem position indexing plate and contact springs. 
         FIG. 15  is a partial, perspective view of the flexible printed circuit sheet on which are arranged the contact pads of the contact springs. 
         FIG. 16  is a perspective view of the free portion of the flexible printed circuit sheet on which are fixed the inductive sensors. 
         FIG. 17A  is a perspective view of the control device, onto a rear face of which is folded the free portion of the flexible printed sheet. 
         FIG. 17B  is a perspective view of the control device, onto a rear face of which the free portion of the flexible printed circuit sheet is folded and held by means of a holding plate secured by screws to the control device. 
         FIG. 18  is a perspective view of the control device installed in a portable object. 
         FIG. 19  is a similar view to that of  FIG. 18 , with the control stem removed from the portable object. 
         FIG. 20A  is a top, perspective view of the position indexing plate for the control stem which defines only two stable positions. 
         FIG. 20B  is a larger scale view of the encircled area of  FIG. 20A . 
         FIG. 21A  is a top, perspective view of the position indexing plate for the control stem which defines only one stable position and one unstable pushed-in position. 
         FIG. 21B  is a larger scale view of the encircled area of  FIG. 21A , and 
         FIG. 22 , already cited, is a perspective view of a control stem according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION 
     The present invention proceeds from the general inventive idea which consists in transferring a position indexing mechanism for a stem controlling at least two electronic and/or mechanical functions of a portable object of small dimensions, such as a timepiece, from this control stem to a plate that is machined separately from said control stem. By doing so, it is possible to reduce the diameter of the control stem and thus at the same time reduce the thickness of the middle part of the portable object, such as a timepiece. This result is achieved as a result of the fact that, instead of being structured straight onto the control stem, the indexing mechanism, which typically takes the form of at least one, and preferably two cam paths cooperating with an elastic member, is made in a thin plate which forms a separate part from the control stem and which is mechanically coupled to the latter. Since the control stem is devoid of its indexing mechanism, its diameter can be reduced, and due to its small thickness, the position indexing plate of the invention does not entail any significant increase in the dimensions of the control stem of the invention. 
     In all that follows, the back-to-front direction is a rectilinear direction which, with respect to a bottom of the portable object, extends horizontally along longitudinal axis of symmetry X-X of the control stem from the external actuation push-piece winding button towards the interior of the portable object equipped with the control device. Thus, the control stem will be pushed from back to front and will be pulled from front to back. Further, the vertical direction z is a direction that extends perpendicularly to the horizontal plane in which the control stem extends. 
       FIG. 1  is a perspective view, in an unassembled state, of a device for controlling at least one electronic function of a portable object of small dimensions, such as a wristwatch. Designated as a whole by the general reference number  1 , this control device includes (see  FIG. 2 ) a lower frame  2 , made for example of an injected plastic material or of a non-magnetic metallic material such as brass. This lower frame  2  serves as a cradle for a control stem  4  preferably of elongated and substantially cylindrical shape, provided with a longitudinal axis of symmetry X-X (see  FIG. 3 ). This control stem  4  is arranged to slide from front to back and from back to front along its longitudinal axis of symmetry X-X and/or to rotate about said same axis of longitudinal symmetry X-X in the clockwise and anticlockwise direction. 
     At a rear end  6 , which will be located outside the portable object once the latter is equipped with a control device  1 , control stem  4  will receive an actuation push-piece winding button  8  (see  FIG. 18 ). 
     At a front end  10 , which will be located inside control device  1  once the latter is assembled, control stem  4  has, for example, a square section  12  and receives in succession a magnetic assembly  14  and a smooth bearing  16 . 
     Magnetic assembly  14  includes a bipolar or multipolar magnetized ring  18  and a support ring  20 , on which magnetized ring  18  is fixed, typically by adhesive bonding (see  FIG. 4 ). Support ring  20  is a component of generally cylindrical shape. As seen in  FIG. 5 , support ring  20  has, from back to front, a first section  22   a  having a first external diameter D 1  on which is engaged magnetized ring  18 , and a second section  22   b  having a second external diameter D 2  greater than first external diameter D 1  and which delimits a shoulder  24  against which magnetized ring  18  moves into abutment. The first section  22   a  of support ring  20  is pierced with a square hole  26  which is adapted in shape and size to square section  12  of control stem  4  and forms with control stem  4  a sliding pinion type system. In other words, support ring  20  and magnetized ring  28  remain immobile when control stem  4  is made to slide axially. However, control stem  4  drives support ring  20  and magnetized ring  18  in rotation when control stem  4  is rotated. It is clear from the foregoing that magnetized ring  18 , carried by support ring  20 , is not in contact with control stem  4  which makes it possible to protect it in the event of shocks applied to the portable object equipped with a control device  1 . 
     Smooth bearing  16  defines (see  FIG. 5 ) a cylindrical housing  28  whose first internal diameter D 3  is very slightly greater than the diameter of the circle in which is inscribed square section  12  of control stem  4 , to allow control stem  4  to slide axially and/or to rotate inside this cylindrical housing  28 . Smooth bearing  16  thus ensures perfect axial guiding of control stem  4 . 
     It is noted that the square hole  26  provided in first section  22   a  of support ring  20  is extended towards the front of control device  1  by an annular hole  30  whose second internal diameter D 4  is fitted onto third external diameter D 5  of smooth bearing  16 . Support ring  20  is thus fitted for free rotation on smooth bearing  16  and moves into axial abutment against smooth bearing  16 , which ensures the perfect axial alignment of these two components and makes it possible to correct problems of concentricity that may be caused by a sliding pinion type coupling. 
     It is observed that, for axial immobilization thereof, smooth bearing  16  is provided on its outer surface with a circular collar  32  which projects into a first groove  34   a  and into a second groove  34   b , respectively arranged in lower frame  2  (see  FIG. 2 ) and in an upper frame  36  (see  FIG. 6 ), arranged to cover lower frame  2  and, for example, made of an injected plastic material or of a non-magnetic metallic material, such as brass. These two lower and upper frames  2  and  26  will be described in detail below. 
     It is important to note that the magnetic assembly  14  and smooth bearing  16  described above are mentioned only for illustrative purposes. Indeed, smooth bearing  16 , for example made of steel or brass, is arranged to prevent control stem  4 , for example made of steel, rubbing against lower and upper frames  2  and  36 , and causing wear of the plastic material of which these two lower and upper frames  2  and  36  are typically made. However, in a simplified embodiment, it is possible to envisage not using such a smooth bearing  16  and arranging for control stem  4  to be directly carried by lower frame  2 . 
     Likewise, magnetized ring  18 , and support ring  20  on which magnetized ring  18  is fixed, are intended for the case where rotation of control stem  4  is detected by a local variation in the magnetic field induced by the pivoting of magnetized ring  18 . It is, however, entirely possible to envisage replacing magnetic assembly  14 , for example with a sliding pinion which, according to its position, will for example control the winding of a mainspring or the time-setting of a watch equipped with control device  1 . 
     It is also important to note that the example of control stem  4  provided on one part of its length with a square section is given purely for illustrative purposes. Indeed, in order to drive magnetic assembly  14  in rotation, control stem  4  may have any type of section other than a circular section, for example triangular or oval. 
     Lower frame  2  and upper frame  36 , the combined assembly of which defines the external geometry of control device  1 , are for example, of generally parallelepiped shape. Lower frame  2  forms a cradle which receives control stem  4  (see  FIG. 2 ). To this end, lower frame  2  includes, towards the front, a first receiving surface  38  of semicircular profile, which serves as a seat for smooth bearing  16  and in which is provided the first groove  34   a  which receives circular collar  32 . Both axial and rotational immobilization of smooth bearing  1  are thus ensured. 
     Lower frame  2  further includes, towards the back, a second receiving surface  40 , whose semicircular profile is centred on longitudinal axis of symmetry X-X of control stem  4 , but whose diameter is greater than that of control stem  4 . It is important to understand that control stem  4  only rests on second receiving surface  40  at the stage when the assembled control device  1  is being tested prior to incorporation in the portable object. At this assembly stage, control stem  4  is inserted into control device  1  for test purposes and extends horizontally, supported and axially guided by smooth bearing  16  at its front end  10  and via second receiving surface  40  at its rear end  6 . However, once control device  1  is incorporated in the portable object, control stem  4  passes through a hole  42  arranged in the middle part  48  of the portable object in which it is guided and supported (see  FIG. 19 ). Control stem  4  extends in the plane of lower frame  2 , parallel to a back cover  49  of the portable object. 
     Third and fourth clearance surfaces  44   a  and  46   a  of semicircular profile are also provided in lower frame  2  and complementary clearance surfaces  44   b  and  46   b  (see  FIG. 6 ) are provided in upper frame  36  for receiving magnetic assembly  14 , formed of magnetized ring  18  and of its support ring  20 . It will be noted that magnetized ring  18  and its support ring  20  are not in contact with third and fourth clearance surfaces  44   a  and  46   a  and complementary clearance surfaces  44   b  and  46   b  when control device  1  is assembled and mounted in the portable object. It is also noted that third clearance surface  44   a  and its corresponding complementary clearance surface  44   b  are delimited by a circular collar  50  for axially locking magnetic assembly  14 . 
     As seen in  FIG. 3 , behind square section  12 , control stem  4  has a cylindrical section  52  whose diameter is comprised between the diameter of the circle in which is inscribed square section  12  of control stem  4  and the pitch diameter of a rear section  54  of said control stem  4 , at the end of which is fixed actuation push-piece winding button  8 . This cylindrical section  52  of reduced diameter extends between two shoulders  56   a ,  56   b  to form a groove  56 , inside which is placed a plate  58  for indexing the position of control stem  4  (see  FIGS. 7A and 7B ). To this end, position indexing plate  58  has a curved portion  60  which follows the profile of reduced diameter cylindrical section  52  and which allows position indexing plate  58  to extend substantially horizontally. Position indexing plate  58  may be, for example, obtained by stamping a thin, electrically conductive metal sheet. However, it is also possible to envisage making position indexing plate  58 , for example, by moulding a hard plastic material loaded with conductive particles. The engagement of position indexing plate  58  in groove  56  ensures the coupling in translation, from front to back and from back to front, between control stem  4  and position indexing plate  58 . However, as will become clearer below, position indexing plate  58  is free with respect to control stem  4  in a vertical direction z perpendicular to the longitudinal axis of symmetry X-X of control stem  4 . 
     As visible in  FIG. 7A , position indexing plate  58  is a substantially flat and generally U-shaped part. This position indexing plate  58  includes two substantially rectilinear guide arms  62  which extend parallel to each other and which are connected to each other by curved portion  60 . These two guide arms  62  are axially guided, for example, against two studs  64  arranged in lower frame  2 . Guided by its two guide arms  62 , position indexing plate  58  slides along a rim  68  arranged in upper frame  36  and whose perimeter corresponds to that of position indexing plate  58  (see  FIG. 6 ). Position indexing plate  58  also includes two fingers  66   a ,  66   b  which extend vertically downwards on either side of the two guide arms  62 . In sliding along rim  68 , position indexing plate  58  has the function of ensuring the translational guiding of control stem  4  from front to back and from back to front. Fingers  66   a ,  66   b , are intended, in particular, to prevent position indexing plate  58  from bending when the latter moves in translation. 
     Two apertures  70  exhibiting an approximately rectangular contour are provided in guide arms  62  of position indexing plate  58 . These two apertures  70  extend symmetrically on either side of longitudinal axis of symmetry X-X of control stem  4 . The sides of the two apertures  70  closest to longitudinal axis of symmetry X-X of control stem  4  have a cam path  72  of substantially sinusoidal shape, formed of a first and a second recess  74   a ,  74   b  separated by a peak  76 . 
     The two apertures  70  provided in guide arms  62  are intended to receive a cam follower  78 . According to a preferred but non-limiting embodiment of the invention, cam follower  78  takes the form of a positioning spring  80  whose two ends  81  are received in apertures  70  of guide arms  62  (see  FIG. 8 ). More specifically, this positioning spring  80  is generally U-shaped with two arbors  82  which extend in a horizontal plane and which are connected to each other by a base  84 . At their free end, the two arbors  82  are extended by two substantially rectilinear arms  86  which stand upright. Positioning spring  80  is intended to be mounted in control device  1  through the bottom of lower frame  2 , so that ends  81  of arms  86  project into apertures  70  of position indexing plate  58 . It will be seen below that the cooperation between position indexing plate  58  and positioning spring  80  makes it possible to index the position of control stem  4  between an unstable pushed-in position T 0  and two stable positions T 1  and T 2 . 
     It was mentioned above that position indexing plate  58  is coupled in translation to control stem  4 , but that it is free with respect to control stem  4  in the vertical direction z. It is thus necessary to take steps to prevent position indexing plate  58  disengaging from control stem  4  in normal conditions of use, for example under the effect of gravity. To this end (see  FIG. 9 ), a spring  88  for limiting the displacement of position indexing plate  58  in vertical direction z is placed above and at a short distance from position indexing plate  58 . Displacement limiting spring  88  is captive between lower frame  2  and upper frame  36  of control device  1 , but is not, in normal conditions of use, in contact with position indexing plate  58 , which prevents parasitic friction forces being exerted on control stem  4 , which would make the latter difficult to operate and cause problems of wear. Displacement limiting spring  88  is, however, sufficiently close to position indexing plate  58  to prevent the latter being inadvertently uncoupled from control stem  4 . 
     Displacement limiting spring  88  includes a substantially rectilinear central portion  90  from the ends  81  of which extend two pairs of elastic arms  92  and  94 . These elastic arms  92  and  94  extend on either side of central portion  90  of displacement limiting spring  88 , upwardly away from the horizontal plane in which central portion  90  extends. As these elastic arms  92  and  94  are compressed when upper frame  36  is joined to lower frame  2 , they impart elasticity to displacement limiting spring  88  along vertical direction z. Between the pairs of elastic arms  92  and  94  there is also provided one pair, and preferably two pairs, of stiff lugs  96  which extend perpendicularly downwards on either side of central portion  90  of displacement limiting spring  88 . These stiff lugs  96  which come into abutment on lower frame  2  when upper frame  36  is placed on lower frame  2 , ensure that a minimum space is provided between position indexing plate  58  and displacement limiting spring  88  in normal operating conditions of control device  1 . 
     Displacement limiting spring  88  guarantees the disassemblability of control device  1 . Indeed, in the absence of displacement limiting spring  88 , position indexing plate  58  would have to be made integral with control stem  4  and, consequently, control stem  4  could no longer be dismantled. If control stem  4  cannot be dismantled, the movement of the timepiece equipped with control device  1  cannot be dismantled either, which is inconceivable, particularly in the case of an expensive timepiece. Thus, when control device  1 , formed by joining lower and upper frames  2  and  36 , is mounted inside the portable object and control stem  4  is inserted into control device  1  from outside the portable object, control stem  4  slightly lifts position indexing plate  58  against the elastic force of displacement limiting spring  88 . If control stem  4  continues to be pushed forwards, there comes a moment when position indexing plate  58  drops into groove  56  under the effect of gravity. Control stem  4  and position indexing plate  58  are then coupled in translation. 
     A disassembly plate  98  is provided to allow disassembly of control stem  4  (see  FIG. 10 ). This disassembly plate  98  is generally H-shaped and includes a straight segment  100  which extends parallel to longitudinal axis of symmetry X-X of control stem  4  and to which a first and a second crosspiece  102  and  104  are attached. The first crosspiece  102  is also provided at its two free ends with two lugs  106  folded up substantially at right angles. Disassembly plate  98  is received inside a housing  108  provided in lower frame  2  and located underneath control stem  4 . This housing  108  communicates with the outside of control device  1  via a hole  110  which opens into a lower face  112  of control device  1  (see  FIG. 11 ). By inserting a pointed tool into hole  110 , a thrust force can be exerted on disassembly plate  98  which, via its two lugs  106 , in turn pushes position indexing plate  58  against the elastic force of displacement limiting spring  88 . It is then sufficient to exert a slight traction on control stem  4  in order to extract the latter from control device  1 . 
     From its stable rest position T 1 , control stem  4  can be pushed forwards into an unstable position T 0  or pulled out into a stable position T 2 . These three positions T 0 , T 1  and T 2  of control stem  4  are indexed by cooperation between position indexing plate  58  and positioning spring  80 . More precisely (see  FIG. 12A ), the stable rest position T 1  corresponds to the position in which ends  81  of arms  86  of positioning spring  80  project into first recesses  74   a  of the two apertures  70  provided in guide arms  62  of position indexing plate  58 . Stable position T 1  may correspond to a position in which no commands can be entered into the portable object equipped with control device  1  according to the invention. Nonetheless, it is also possible to envisage that, in stable position T 1  of control stem  4 , a rotation of the latter can be detected in one direction or the other in order to operate a function. In that case, either the rotation of control stem  4  can be detected at any time, but the electronic components would then have to be constantly powered by electrical current, which may cause problems in the case of a portable object of small dimensions whose electrical energy reserves are necessarily limited; or the rotation of the control stem in its stable position T 1  is detected after the latter has been brought into its unstable position T 0  for a determined duration. 
     From its stable rest position T 1 , control stem  4  can be pushed forwards into an unstable position T 0  (see  FIG. 12B ). During this displacement, ends  81  of arms  86  of positioning spring  80  leave first recesses  74   a  and follow a first ramp profile  114  which gradually moves away from longitudinal axis of symmetry X-X of control stem  4  on a first steep slope α. To force ends  81  of arms  86  of positioning spring  80  to leave first recesses  74   a  and to engage on first ramp profile  114  by moving away from each other, the user must therefore overcome a significant resistance force. 
     When they reach a transition point  116 , ends  81  of arms  86  engage on a second ramp profile  118  which extends first ramp profile  114  with a second slope β smaller than first slope α of first ramp profile  114 . At the instant that ends  81  of arms  86  of positioning spring  80  cross transition point  116  and engage on second ramp profile  118 , the force required from the user to continue moving control stem  4  drops sharply and the user feels a click indicating the transition of control stem  4  between position T 1  and position T 0 . As they follow second ramp profile  118 , arms  86  of positioning spring  80  continue to move slightly away from their rest position and tend to try to move towards each other again under the effect of their elastic return force which opposes the thrust force exerted by the user on control stem  4 . As soon as the user releases pressure on control stem  4 , arms  86  of positioning spring  80  will spontaneously move back down first ramp profile  114  and lodge again inside first recesses  74   a  of the two apertures  70  provided in guide arms  62  of position indexing plate  58 . Control stem  4  is thus automatically returned from its unstable position T 0  to its stable first position T 1 . 
     First and second contact springs  120   a  and  120   b  which, on the one hand, participate in returning control stem  4  from its unstable position T 0  to its stable first position T 1 , are compressed and housed inside a first and a second cavity  122   a  and  122   b  provided in lower frame  2 . These first and second contact springs  120   a  and  120   b  could be helical contact springs, strip-springs or other springs. The two cavities  122   a ,  122   b  preferably, but not necessarily, extend horizontally. Because the two contact springs  120   a ,  120   b  are installed in the compressed state, their positioning precision is dependent on the manufacturing tolerance of lower frame  2 . The manufacturing precision of lower frame  2  is higher than the manufacturing precision of these two first and second contact springs  120   a ,  120   b . Consequently, the precision of detection of position T 0  of control stem  4  is high. 
     As visible in  FIGS. 13 and 15 , one of the ends of first and second contact springs  120   a ,  120   b  is bent to form two contact lugs  124  which will move into abutment on two corresponding first contact pads  126  provided at the surface of a flexible printed circuit sheet  128 . The moment that ends  81  of arms  86  of positioning spring  80  engage on second ramp profile  118  of the two apertures  70  provided in position indexing plate  58  coincides with the moment that fingers  66   a ,  66   b  of position indexing plate  58  come into contact with first and second contact springs  120   a ,  120   b . Since this position indexing plate  58  is electrically conductive, when fingers  66   a ,  66   b  come into contact with first and second contact springs  120   a ,  120   b , the electric current passes through position indexing plate  58  and closure of the electrical contact between first and second contact springs  120   a ,  120   b  is detected. 
     First and second contact springs  120   a ,  120   b  are of the same length. However, preferably, one of the first and second cavities  122   a ,  122   b  will be longer than the other, in particular to take account of tolerance problems (the difference in length between the two cavities  122   a ,  122   b  is several tenths of a millimetre). Thus, when control stem  4  is pushed forwards into position T 0 , finger  66   a  of position indexing plate  58 , which is lined up with first contact spring  120   a  housed inside the first, longest cavity  122   a , will come into contact with and start to compress first contact spring  120   a . Control stem  4  will continue to move forward and second finger  66   b  of position indexing plate  58  will come into contact with second contact spring  120   b  housed inside the second, shortest cavity  122   b . At that moment, position indexing plate  58  will be in contact with first and second contact springs  120   a ,  120   b  and the electric current will flow through position indexing plate  58 , which allows the closure of the electrical contact between the first two contact springs  120   a ,  120   b  to be detected. It is noted that fingers  66   a ,  66   b  of position indexing plate  58  move into abutment contact with first and second contact springs  120   a ,  120   b . There is thus no friction or wear when control stem  4  is pushed forwards into position T 0  and closes the circuit between first and second contact springs  120   a ,  120   b . It is also noted that, the difference in length of first and second cavities  122   a  and  122   b  ensures that closure of the electrical contact and entry of the corresponding command into the portable object equipped with control device  1  occur only after a click is felt. 
     When the two fingers  66   a ,  66   b  of position indexing plate  58  are in contact with first and second contact springs  120   a ,  120   b , first contact spring  120   a  housed inside first, longest cavity  122   a  is in a compressed state. Consequently, when the user releases pressure on control stem  4 , this first contact spring  120   a  relaxes and forces control stem  4  to return from its unstable pushed-in position T 0  to its stable first position T 1 . The first and second contact springs  120   a ,  120   b  thus act simultaneously as electrical contact parts and means for elastic return of control stem  4  into its stable first position T 1 . 
     From stable first position T 1 , it is possible to pull control stem  4  backwards into a stable second position T 2  (see  FIG. 12C ). During this movement, ends  81  of arms  86  of positioning spring  80  will elastically deform to pass from first recesses  74   a  to second recesses  74   b , crossing peaks  76  of the two apertures  70  provided in guide arms  62  of position indexing plate  58 . When control stem  4  reaches its stable second position T 2 , the two fingers  66   a ,  66   b  of position indexing plate  58  move into abutment against third and fourth contact springs  130   a    130   b  (see  FIG. 13 ), which are housed inside third and fourth cavities  132   a ,  132   b  provided in lower frame  2 . These third and fourth contact springs  130   a ,  130   b  could be helical contact springs, strip-springs or other springs. Third and fourth cavities  132   a ,  132   b  preferably extend vertically for reasons of space in control device  1 . Since position indexing plate  58  is electrically conductive, when fingers  66   a ,  66   b  come into contact with third and fourth contact springs  130   a ,  130   b , the electric current flows through position indexing plate  58  and closure of electrical contact T 2  between these contact springs  130   a ,  130   b  is detected. 
     It will be noted that, in the case of stable position T 2 , fingers  66   a ,  66   b  of position indexing plate  58  also come into abutment contact with third and fourth contact springs  130   a ,  130   b , thereby avoiding any risk of wear from friction. Further, third and fourth contact springs  130   a ,  130   b  are capable of bending when fingers  66   a ,  66   b  of position indexing plate  58  collide therewith, and therefore of absorbing any lack of precision in the positioning of position indexing plate  58 . 
     Preferably, but not necessarily, third and fourth contact springs  130   a ,  130   b  are arranged to work in flexion. Indeed, with contact springs  130   a ,  130   b  whose diameter is constant, fingers  66   a ,  66   b  of position indexing plate  58  come into contact with contact springs  130   a ,  130   b  over a large surface close to their points of attachment in lower frame  2  and upper frame  36 . The proximity of the contact surface to the attachment points of contact springs  130   a ,  130   b  induces shearing stresses in contact springs  130   a ,  130   b  which may lead to premature wear and breakage of the latter. To overcome this problem, contact springs  130   a ,  130   b  have, preferably substantially at mid-height, an increase in diameter  134  which comes into contact with fingers  66   a ,  66   b  of position indexing plate  58  when control stem  4  is pulled into its stable position T 2  (see  FIGS. 14A and 14B ). At their upper end, third and fourth contact springs  130   a ,  130   b  are guided in two holes  136  provided in upper frame  36  and come into contact with second contact pads  138  provided at the surface of flexible printed circuit sheet  128 . It is clear that, when control stem  4  is pulled backwards into its stable position T 2 , fingers  66   a ,  66   b  of positioning indexing plate  58  come into a reduced surface contact with third and fourth contact springs  130   a  and  130   b  at their largest diameter  134 , which allows contact springs  130   a ,  130   b  to bend between their two points of attachment in lower frame  2  and upper frame  36 . 
     In  FIG. 15 , lower and upper frames  2  and  36  have been deliberately omitted to facilitate understanding of the drawing. As represented in  FIG. 15 , flexible printed circuit sheet  128  is fixed on a plate  140  located on the dial side of the portable object. It takes the form, in particular, of a cutout  142  adapted in shape and size to receive upper frame  36 . One portion  144  of flexible printed circuit sheet  128  remains free (see  FIG. 16 ). This free portion  144  of flexible printed circuit sheet  128  carries a plurality of electronic components  146 , in addition to third contact pads  148 , on which are fixed at least two inductive sensors  150 . An ‘inductive sensor’ means a sensor that transforms a magnetic field passing therethrough into electric voltage due to the phenomenon of induction defined by Lenz&#39;s law and Faraday&#39;s law. By way of example, this may be a Hall effect sensor or a magnetoresistance component of the AMR (anisotropic magnetoresistance), GMR (giant magnetoresistance) or TMR (tunneling magnetoresistance) type. 
     The free portion  144  of flexible printed circuit sheet  128  is connected to the rest of flexible printed circuit sheet  128  by two strips  152 , which allow free portion  144  to be folded around the assembly of upper frame  36  and lower frame  2 , and then folded down against a lower surface  112  of lower frame  2 , so that inductive sensors  150  penetrate two housings  156  provided in lower surface  112  of lower frame  2 . Thus positioned inside their housings  156 , inductive sensors  150  are precisely located under magnetized ring  18 , which ensures reliable detection of the direction of rotation of control stem  4 . Once free portion  144  of flexible printed circuit sheet  128  has been folded down against lower frame  2  (see  FIG. 17A ), the assembly is covered by a holding plate  158 , provided with one or two elastic fingers  160 , which press inductive sensors  150  against the bottom of their housings  156  (see  FIG. 17B ). Holding plate  158  is fixed to plate  140 , for example by means of two screws  162 . 
     It goes without saying that the present invention is not limited to the embodiment that has just been described and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the annexed claims. In particular, the dimensions of the magnetized ring may be extended so that it corresponds to a hollow cylinder. It will be understood, in particular, that position indexing plate  58  may define only two distinct positions, namely two stable positions or one stable position and one unstable position, or it may define three or more distinct positions, namely at least three stable positions or at least two stable positions and one unstable position. 
       FIG. 20A  illustrates the case where position indexing plate  58  defines only two stable positions. In such case, two apertures  70 - 1  exhibiting an approximately rectangular contour are provided in guide arms  62  of position indexing plate  58 . These two apertures  70 - 1  extend symmetrically on either side of longitudinal axis of symmetry X-X of control stem  4 . The sides of the two apertures  70 - 1  closest to longitudinal axis of symmetry X-X of control stem  4  have a cam path  72 - 1  of substantially sinusoidal shape, formed of a first and a second recess  74   a - 1 ,  74   b - 1  separated by a peak  76 - 1 . The two apertures  70 - 1  provided in guide arms  62  are intended to receive the two ends  81  of arms  86  of positioning spring  80  in order to index the position of control stem  4  between a first and a second stable position T 1 - 1  and T 2 - 1 . 
     More precisely, the first stable position T 1 - 1  corresponds to the position in which ends  81  of arms  86  of positioning spring  80  project into first recesses  74   a - 1  of the two apertures  70 - 1  provided in guide arms  62  of position indexing plate  58 . From this first stable position T 1 - 1 , control stem  4  can be pulled back into a second stable position T 2 - 1 . During this movement, ends  81  of arms  86  of positioning spring  80  will elastically deform to pass from first recesses  74   a - 1  to second recesses  74   b - 1 , crossing peaks  76 - 1  of the two apertures  70 - 1  provided in guide arms  62  of position indexing plate  58 . 
       FIG. 21A  illustrates the case where indexing plate  58  defines only one stable position T 1 - 2  and one unstable position T 0 - 2 . In such case, two apertures  70 - 2  exhibiting an approximately rectangular contour are provided in guide arms  62  of position indexing plate  58 . These two apertures  70 - 2  extend symmetrically on either side of longitudinal axis of symmetry X-X of control stem  4 . The sides of the two apertures  70 - 2  closest to longitudinal axis of symmetry X-X of control stem  4  have a cam path  72 - 2  formed of a recess  74   a - 2  followed by a ramp profile  114 - 2  which gradually moves away from longitudinal axis of symmetry X-X of control stem  4  on a first steep slope α- 2 . To force ends  81  of arms  86  of positioning spring  80  to leave recesses  74   a - 2  and to engage on first ramp profile  114 - 2  by moving away from each other, the user must therefore overcome a significant resistance force. When they reach a transition point  1162 , ends  81  of arms  86  engage on a second ramp profile  118 - 2  which extends first ramp profile  114 - 2  with a second slope β- 2  smaller than first slope α- 2  of first ramp profile  114 - 2 . At the instant that ends  81  of arms  86  of positioning spring  80  cross transition point  116 - 2  and engage on second ramp profile  118 - 2 , the force required from the user to continue moving control stem  4  drops sharply and the user feels a click indicating the transition of control stem  4  between its stable position T 1 - 2  and its unstable position T 0 - 2 . As they follow second ramp profile  118 - 2 , arms  86  of positioning spring  80  continue to move slightly away from their rest position and tend to try to move towards each other again under the effect of their elastic return force opposing the thrust force exerted by the user on control stem  4 . As soon as the user releases pressure on control stem  4 , arms  86  of positioning spring  80  will spontaneously move back down first ramp profile  114 - 2  and lodge again inside recesses  74   a - 2  of the two apertures  70 - 2  provided in guide arms  62  of position indexing plate  58 . Control stem  4  is thus automatically returned from its unstable position T 0 - 2  to its stable position T 1 - 2 . 
     NOMENCLATURE 
     
         
           1 . Control device 
           2 . Lower frame 
           4 . Control stem 
         X-X. Longitudinal axis of symmetry 
           6 . Rear end 
           8 . Push-piece winding button 
           10 . Front end 
           12 . Square section 
           14 . Magnetic assembly 
           16 . Smooth bearing 
           18 . Magnetized ring 
           20 . Support ring 
           22   a  First section 
         D 1 . First external diameter 
           22   b . Second section 
         D 2 . Second external diameter 
           24 . Shoulder 
           26 . Square hole 
           28 . Cylindrical housing 
         D 3 . First internal diameter 
           30 . Annular hole 
         D 4 . Second internal diameter 
         D 5 . Third external diameter 
           32 . Circular collar 
           34   a  First groove 
           34   b . Second groove 
           36 . Upper frame 
           38 . First receiving surface 
           40 . Second receiving surface 
           42 . Hole 
           44   a ,  46   a  Third and fourth undercut surfaces 
           44   b ,  46   b  Complementary undercut surfaces 
           48 . Middle part 
           49 . Back cover 
           50 . Annular collar 
           52 . Cylindrical section 
           54 . Back section 
           56 . Groove 
           56   a ,  56   b  Shoulders 
           58 . Position indexing plate 
           60 . Curved portion 
           62 . Guide arm 
           64 . Studs 
           66   a ,  66   b  Fingers 
           68 . Rim 
           70 . Apertures 
           70 - 1 . Apertures 
           70 - 2 . Apertures 
           72 . Cam path 
           72 - 1 . Cam path 
           72 - 2 . Cam path 
           73 . Longitudinal cam profile 
           74   a  First recess 
           74   a - 1 . First recess 
           74   a - 2 . Recess 
           74   b . Second recess 
           74   b - 1 . Second recess 
           76 . Peak 
           78 . Cam follower 
           80 . Positioning spring 
           81 . Ends 
           82 . Arbors 
           84 . Base 
           86 . Arms 
           88 . Displacement limiting spring 
           90 . Central portion 
           92 . Pair of elastic arms 
           94 . Pair of elastic arms 
           96 . Stiff lugs 
           98 . Disassembly plate 
           100 . Straight segment 
           102 . First crosspiece 
           104 . Second crosspiece 
           106 . Lugs 
           108 . Housing 
           110 . Hole 
           112 . Lower face 
           114 . First ramp profile 
           114 - 2 . First ramp profile 
         α First slope 
         α- 2 . First slope 
           116 . Transition point 
           116 - 2 . Transition point 
           118 . Second ramp profile 
           118 - 2 . Second ramp profile 
         β Second slope 
         β- 2 . Second slope 
           120   a ,  120   b  First and second contact spring 
           122   a ,  122   b  First and second cavity 
           124 . Contact lugs 
           126 . First contact pads 
           128 . Flexible printed circuit sheet 
           130   a ,  130   b  Third and fourth contact springs 
           132   a ,  132   b  Third and fourth cavities 
           134 . Increase in diameter 
           136 . Holes 
           138 . Second contact pads 
           140 . Plate 
           142 . Cutout 
           144 . Free portion 
           146 . Electronic components 
           148 . Third contact pads 
           150 . Inductive sensors 
           152 . Strips 
           156 . Cavities 
           158 . Holding plate 
           160 . Elastic fingers 
           162 . Screw(s) 
           200 . Control stem 
           202 . Cylindrical portion 
           204 . Push-piece winding button 
           206 . Cam paths 
           208   a ,  208   b  Recess 
           210 . Peak 
           212 . Elastic arms 
           214 . Spring