Patent Publication Number: US-11385598-B2

Title: Portable object comprising a rotating control stem whose actuation is detected by means of two inductive sensors

Description:
FIELD OF THE INVENTION 
     The present invention concerns a portable object of small dimensions such as a timepiece, comprising a rotating control stem for controlling at least one electronic or mechanical function of the portable object. More specifically, the invention concerns such a portable object wherein actuation of the rotating control stem is detected by measuring magnetic induction by means of two inductive sensors. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns portable objects of small dimensions, such as wristwatches, that comprise a rotating control stem, the actuation of which controls a mechanical or electronic function of the portable object in which the rotating control stem is arranged. 
     To properly perform the mechanical or electronic function concerned, it must be possible to detect the actuation of the rotating control stem. Among various possible solutions, one consists in measuring the variation in magnetic induction produced by the rotation of a magnet integral with the control stem. To detect this variation in magnetic induction, it is possible to use a magnetic sensor such as a Hall effect sensor which is capable of measuring the value of magnetic induction of the environment in which it is located. 
     A recurrent problem that arises in the field of detecting the rotation of a control stem by measuring magnetic induction is that of knowing precisely how far and in which direction the control stem is rotated. To overcome this problem, systems have already been proposed that include a pair of magnetic sensors such as magnetoresistors or Hall-effect sensors. In these known systems, the magnetic sensors detect the variation in magnetic induction produced by the rotation of the magnet integral with the control stem in two orthogonal directions in space. 
     One drawback of such systems lies in the fact that, since the magnetic sensors measure variations in magnetic induction in two orthogonal directions, it is not possible to subtract from the measuring signal produced by the magnetic sensors the effects due to magnetic disturbances outside the portable object when these magnetic disturbances are directed along the axis of measurement of only one of the two magnetic sensors. Indeed, in that case, the other magnetic sensor does not sense the external magnetic disturbance, so the influence of this magnetic disturbance on the two measuring signals is not symmetrical and therefore cannot be eliminated. It is therefore necessary to provide the portable object with an electromagnetic shield, which is particularly cumbersome and costly. Other solutions are known but more particularly intended for measuring the Earth&#39;s magnetic field. In such applications, the magnetic sensor or sensors exhibit high sensitivity since the Earth&#39;s magnetic field to be measured is very low, typically on the order of 20 to 60 μT. However, these magnetic sensors cannot usually measure magnetic induction in excess of 5 mT, whereas the values associated with magnets of small dimensions frequently reach 100 mT. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the aforementioned problems, in addition to others, by providing a portable object comprising a rotating stem for controlling at least one mechanical or electronic function of the portable object, the actuation of the rotating stem being detected in a reliable and reproducible manner by means of inductive sensors. 
     To this end, the present invention concerns a portable object comprising a control stem, the actuation of which in rotation can control at least one electronic or mechanical function of the portable object, a magnetized ring being driven in rotation by the rotating control stem, the rotation of the control stem and the position of the latter being detected by two inductive sensors arranged to be sensitive to a variation in magnetic induction produced by rotation of the magnetized ring in only two directions in space, which are parallel to each other. 
     According to other embodiments of the invention which form the subject of the dependent claims:
         the two inductive sensors are arranged at an equal distance from a centre of rotation of the magnetized ring, symmetrically with respect to a plane passing through the centre of rotation of the magnetized ring;   the two inductive sensors are only sensitive to a variation in magnetic induction in a vertical direction. In other words, the two inductive sensors are sensitive to a variation in magnetic induction in a direction perpendicular to a back of the portable object, the longitudinal axis of symmetry of the control stem extending parallel to said back;   the two inductive sensors are arranged with respect to the control stem such that, when the magnetized ring rotates as a result of actuation of the control stem, the two inductive sensors produce signals that are phase-shifted with respect to each other by a value comprised between 60° and 120°;   the portable object includes a frame arranged to serve as a cradle for the control stem, the inductive sensors being disposed inside at least one housing provided in the frame inside which they are held by elastic means;   the two inductive sensors are disposed inside two distinct housings arranged in the frame;   the portable object includes a holding plate provided with at least one elastic finger which, by pressure on the inductive sensors, holds the inductive sensors inside the at least one housing in which they are disposed;   the holding plate is provided with two elastic fingers and the inductive sensors are fixed to a printed circuit sheet on which the elastic fingers press at the locations where the inductive sensors are fixed;   the printed circuit sheet is flexible and folded down onto the frame so that the inductive sensors are disposed inside the housings;   the elastic fingers immobilise the inductive sensors in a vertical direction;   the elastic fingers are arranged to force the inductive sensors against the bottom of the housings inside which they are disposed.       

     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. 
     As a result of these features, the present invention provides a portable object in which detection of the rotation of a control stem controlling at least one mechanical or electronic function of the portable object is obtained by measuring the variation in magnetic induction caused by rotation of a magnet driven by the control stem by means of two inductive sensors. These two inductive sensors are arranged to be sensitive to a variation in magnetic induction in only one direction in space. It is clear that the magnetic induction produced by the environment in which the portable object is located is added to the magnetic induction produced by the magnetized ring. By teaching that the pair of inductive sensors are arranged so that the sensors exhibit sensitivity to magnetic induction in only a single direction, the present invention makes it possible, via a suitable signal processing treatment, to completely eliminate from the measurement result the influence of the magnetic induction of the environment in which the portable object is located. In fact, as a result of these measures, the case where magnetic disturbances produced by the environment in which the portable object is located are directed along the axis of measurement of only one of the two inductive sensors cannot occur. Consequently, the case where one of the two inductive sensors does not sense the external magnetic disturbance is precluded, so that the influence of the external magnetic disturbance on the measurement signals is the same for both inductive sensors and can therefore be eliminated. It is consequently unnecessary to magnetically shield the portable object to avoid the influence of magnetic induction outside the portable object, which saves space. This is very advantageous in the case of a portable object of small dimensions in which the available space is necessarily very limited. The lack of shielding also simplifies the manufacture of the portable object and thus ensures better reliability and a lower cost price. 
     The invention also concerns a method for detecting a position of a control stem, the actuation of which in rotation controls an electronic or mechanical function of a portable object provided with the control stem, a magnetized ring being driven in rotation by the control stem, the rotation of the control stem and the position of the latter being detected by two inductive sensors arranged to be sensitive to a variation in magnetic induction produced by rotation of the magnetized ring in only one direction in space, the method comprising the step which consists in calculating the arctangent function of the ratio between the signals produced by each of the inductive sensors to determine the direction of rotation and the position of the control stem. 
     As a result of these features, it is possible, regardless of the direction of rotation of the control stem, to determine the absolute position of the control stem, i.e. it is possible at any time to know the angular position of the stem. The resolution of the position detection measurement of the control stem is thus high and reproducible from one object to another, even in the case of large scale production. 
    
    
     
       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 portable object according to the invention, this example being given purely 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 in the Figure, extends from its rear end to its front end. 
         FIG. 4  is a perspective view, in an unassembled state, of the smooth bearing and of the magnetic assembly formed of a support ring and a magnetized ring. 
         FIG. 5  is a longitudinal cross-sectional view along a vertical plane of a control device inside which are arranged 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 area encircled in  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, the control stem being in stable position T 1 . 
         FIG. 12B  is a similar view to that of  FIG. 12A , with the control stem in an 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 first and second contact springs. 
         FIGS. 14A and 14B  are schematic views that illustrate the cooperation between the fingers of the control stem position indexing plate and third and fourth contact springs. 
         FIG. 15  is a partial, perspective view of the flexible printed circuit sheet on which are arranged the contact pads of first and second 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 fixed by screws to the control device. 
         FIG. 18  is an elevation view of the system for detecting the position of the magnetized ring by means of two inductive sensors. 
         FIG. 19  is an elevation view of the system for detecting rotation of the magnetized ring by means of a single inductive sensor. 
         FIG. 20  is a perspective view of the control device installed in a portable object. 
         FIG. 21  is a similar view to that of  FIG. 20 , with the control stem removed from the portable object. 
         FIG. 22  is a schematic, perspective view of the sensing element of an inductive sensor and of the direction in which this element is sensitive to fluctuations in magnetic induction. 
     
    
    
     DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION 
     The present invention proceeds from the general inventive idea which consists in detecting the rotation of a control stem mounted in a portable object of small dimensions, such as a timepiece, in a reliable and reproducible manner from one portable object to another, particularly in the case of mass production. To overcome this problem, it is proposed to drive a magnetized ring in rotation via the control stem and to detect the variation in magnetic induction caused by rotation of the ring by means of a pair of inductive sensors. These two inductive sensors are arranged to be sensitive each to fluctuations in magnetic induction in only one direction in space. Consequently, the influence of magnetic induction outside the portable object is the same on the measuring signals of both inductive sensors, so that, via a suitable signal processing process, it is possible to completely eliminate from the measurement result the influence of the magnetic induction of the environment in which the portable object is located. 
     The invention also concerns a method for detecting the position and the direction of rotation of a rotating control stem which consists in calculating the arctangent function of the ratio between the signals produced by two inductive sensors arranged to be sensitive to fluctuations in magnetic induction in two directions in space parallel to each other. Since the magnetic induction of the environment in which the portable object is located only exercises an influence on the sensing elements of the two inductive sensors in one direction in space, calculating the arctangent function of the ratio between the signals produced by these two inductive sensors can eliminate the signal component due to the influence of magnetic induction outside the portable object. 
     In all that follows, the back-to-front direction is a rectilinear direction which extends horizontally along longitudinal axis of symmetry X-X of the control stem from the external actuation crown towards the interior of the portable object equipped with the control device, parallel to a plane in which a back of the portable object extends. Thus, the control stem will be pushed from back to front, and will be pulled from front to back. Further, the vertical direction is a direction that extends perpendicularly to the 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 a lower frame  2 , for example made of an injected plastic material or of a non-magnetic metallic material such as brass, and 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. 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 crown  8  (see  FIG. 20 ). 
     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 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  abuts. 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  18  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 any 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 material, such as brass. These two lower and upper frames  2  and  36  will be described in detail below. 
     It is important to note that the magnetic assembly  14  and smooth bearing  16  described above are indicated purely 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 . To this end (see  FIG. 2 ), 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 tested prior to being integrated 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 integrated in the portable object, control stem  4  passes through a hole  42  provided in case middle  48  of the portable object in which it is guided and supported (see  FIG. 21 ) and which is delimited downwardly by a back  49 . 
     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 an annular collar  50  for axially locking magnetic assembly  14 . 
     As visible 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 POT text as filed primitive diameter of a rear section  54  of said control stem  4 , at the end of which is fixed actuation crown  8 . This cylindrical section  52  of reduced diameter forms a groove  56  inside which is placed a position indexing plate  58  for control stem  4  (see  FIG. 7A ). To this end, position indexing plate  58  has a curved portion  60  which follows the profile of reduced diameter cylindrical section  52 . 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  (see in particular  FIG. 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 bracing 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  (see in particular  FIG. 7B ). 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 the two ends  78  of a positioning spring  80  (see  FIG. 8 ). 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  78  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  FIGS. 9 and 11 ), 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 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 move 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 dismantability of control device  1 . Indeed, in the absence of displacement limiting spring  88 , position indexing plate  58  would have to be 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 transverse piece  102  and  104  are attached. The first transverse piece  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 . Position indexing plate  58  then leaves groove  56  provided in control stem  4  and exerting a slight backward traction on control stem  4  is sufficient to remove 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 , in which no commands can be entered into the portable object equipped with control device  1 , corresponds to the position in which ends  78  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 . From this 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  78  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 (see  FIG. 7B ). To force ends  78  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  78  of arms  86  engage on a second ramp profile  118  which extends first ramp profile  114  with a second slope β lower than first slope α of first ramp profile  114 . At the instant that ends  78  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 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 return down first ramp profile  114  and their ends  78  will again lodge 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 first stable position T 1 . 
     First and second contact springs  120   a  and  120   b  are arranged compressed 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 first and second contact springs  120   a ,  120   b . Consequently, the precision with which position T 0  of control stem  4  is detected 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  78  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, first cavity  122   a  will be, for example, longer than second cavity  122   b , 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 first stable position T 1 . The first and second contact springs  120   a ,  120   b  thus act simultaneously as electrical contact parts and elastic return means for control stem  4  in its first stable position T 1 . 
     From first stable position T 1 , it is possible to pull control stem  4  backwards into a second stable position T 2  (see  FIG. 12C ). During this movement, ends  78  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 second stable 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 (see  FIGS. 14A and 14B ). 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 . 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 contact on a reduced surface 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 one and, in the example represented, two inductive sensors  150 . Fixing inductive sensors  150  to third contact pads  148  allows these inductive sensors  150  to be connected, via flexible printed circuit sheet  128 , to a power source and to a microprocessor (not represented) housed inside the portable object. The power source will supply inductive sensors  150  with the energy required to operate, and the microprocessor will receive and process the signals supplied by inductive sensors  150 . 
     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 lower face  112  of lower frame  2 , so that inductive sensors  150  penetrate two housings  156  arranged 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 at least one elastic finger  160  (two in the example represented), which exerts on inductive sensors  150  an elastic pressure force directed vertically upwards so as to press these inductive sensors  150  against the bottom of their housings  156  (see  FIG. 17B ). Elastic fingers  160  press on flexible printed circuit  128  preferably at the place where inductive sensors  150  are fixed. Holding plate  158  is fixed to plate  140 , for example by means of two screws  162 . 
     Control stem  4  is carried by lower frame  2  which acts as a cradle. Likewise, the two inductive sensors  150  are disposed inside two housings  156  provided in said lower frame  2 , and are pressed against the bottom of these housings  156  by one or two elastic fingers  160  (see  FIG. 18 ). Consequently, the relative positioning precision of inductive sensors  150  and magnetized ring  18 , which is rotationally fixedly mounted relative to control stem  4 , is determined only by the precision with which lower frame  2  is made. The manufacturing precision of lower frame  2 , which is for example made of injected plastic, is sufficient to guarantee the proper positioning of inductive sensors  150  and of magnetized ring  18 , even in the case of large scale production. Further, since inductive sensors  150  are elastically forced against the bottom of housings  156  by elastic finger(s)  160 , this makes it possible to compensate for any play resulting from manufacturing tolerances. These manufacturing tolerances may, in particular, result from the step of soldering Hall-effect components  150  on flexible printed circuit sheet  128 . This soldering operation is performed, for example, in a furnace using a soldering paste deposited on contact pads  148  of flexible printed circuit sheet  128 . 
     Inductive sensor or sensors  150  each include a sensing element  154  which, in a simplified manner, takes the form of a parallelepiped element sensitive to fluctuations in magnetic induction in a direction S perpendicular to the large side of the parallelepiped (see  FIG. 22 ). In the example illustrated in  FIG. 18 , inductive sensors  150  are preferably oriented such that their sensing element  154  detects a fluctuation in magnetic induction only in vertical direction z. In other words, the inductive sensors are completely insensitive to horizontal components along the orthogonal x and y axes of magnetic induction. 
     In the case where a single inductive sensor  150  is provided (see  FIG. 19 ), the amplitude of rotation and the position of control stem  4  may be determined with only average precision. Indeed, when magnetized ring  18  rotates as a result of actuation of control stem  4 , inductive sensor  150  produces a sinusoidal signal whose amplitude of variation fluctuates according to the value of the angle concerned. In an area close to the value π/2, for example, the sinusoidal signal varies very little, so that control stem  4  can be rotated to quite a large extent without any significant modification in the signal provided by inductive sensor  150 . The position and displacement of control stem  4  can therefore only be detected with average precision. However, within an area close to value π, the sinusoidal signal fluctuates sharply, such that the amount of rotation and the position of control stem  4  can be determined with high precision. In the case where one can be satisfied with average precision in the detection of the position and amount of rotation of control stem  4 , the system described above is entirely suitable. However, in the case where very high measurement precision is required, it is preferable to equip the portable object according to the invention with two inductive sensors  150  (see  FIG. 18 ). Indeed, by providing for the use of two inductive sensors  150 , it is possible to determine both the amplitude and the direction of rotation of control stem  4  with increased precision. Thus, the two inductive sensors  150  are arranged at an equal distance from the centre of rotation O of magnetized ring  18 , symmetrically with respect to a plane P passing through the centre of rotation O of magnetized ring  18 . Preferably, the two inductive sensors  150  are arranged with respect to control stem  4  such that, when magnetized ring  18  rotates as a result of actuation of control stem  4 , the two inductive sensors  150  produce sinusoidal signals sin(x) and sin(x+δ) that are out of phase relative to each other by an angle δ comprised between 60° and 120°, and preferably equal to 90°. To calculate the relative arrangement of the two inductive sensors and magnetized ring  18 , it is possible, for example, to perform successive iterations by means of finite element calculation software. 
     Owing to the phase shift δ between the sinusoidal measurement signals sin(x) and sin(x+δ) produced by the two inductive sensors  150 , when the arctangent function of the ratio between these two measurement signals is calculated, a straight line is obtained. Consequently, it is possible, from a rotary motion of control stem  4 , to obtain a linear response from the system formed by control stem  4 , magnetized ring  18  and the two inductive sensors  150 . This linearization of the rotation of control stem  4  advantageously permits absolute detection of the position of control stem  4 . In other words, it is possible at any time to know the direction of rotation and the position of control stem  4 . Further, owing to phase shift δ, there is constantly a situation where, when sinusoidal measurement signal sin (x) produced by one of the two inductive sensors  150  varies slightly, the other sinusoidal signal sin(x+δ) varies more sharply and vice versa, such that the ratio between these two signals always gives precise information about the rotation of control stem  4 . 
     It was mentioned above that inductive sensors  150  were preferably oriented such that their sensing element only detects fluctuations in magnetic induction along the vertical axis z. This component of magnetic induction is the sum of inductions along axis z generated by magnetized ring  18  and by the magnetic field outside the portable object. However, given that inductive sensors  150  are very close to each other, the influence exercised thereon by the external magnetic field is substantially the same for both inductive sensors  150 . Consequently, calculating the ratio between the two sinusoidal signals sin(x) and sin(x+δ) eliminates the component of magnetic induction due to the magnetic field outside the portable object. The response of the system formed by control stem  4 , magnetized ring  18  and inductive sensors  150  is thus totally independent of the external magnetic field, and it is not necessary to take steps to magnetically shield the portable object. Likewise, the response of the system is independent of temperature insofar as the temperature has the same effect on both inductive sensors. 
     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 magnetized ring concerned here is preferably a bipolar ring but it may also be a multipolar magnetized ring. The dimensions of the magnetized ring could also be extended so that it corresponds to a hollow cylinder. 
     NOMENCLATURE 
     
         
           1 . Control device 
           2 . Lower frame 
           4 . Control stem 
         X-X. Longitudinal axis of symmetry 
           6 . Rear end 
           8 . Actuation crown 
           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 . Case middle 
           49 . Back 
           50 . Annular collar 
           52 . Cylindrical section 
           54 . Back section 
           56 . Groove 
           58 . Position indexing plate 
           60 . Curved portion 
           62 . Guide arm 
           64 . Studs 
           66   a ,  66   b  Fingers 
           68 . Rim 
           70 . Apertures 
           72 . Profile 
           74   a  First recess 
           74   b . Second recess 
           76 . Peak 
           78 . Ends 
           80 . Positioning spring 
           82 . Arms 
           84 . Base 
           86 . Arbors 
           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 
         α First slope 
           116 . Transition point 
           118 . Second ramp profile 
         β 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 
           154 . Sensing element 
           156 . Housings 
           158 . Holding plate 
           160 . Elastic fingers 
           162 . Screws