Abstract:
The invention relates to a joystick ( 200 ) for controlling an aircraft, including a frame ( 201 ), a lever ( 202 ) mounted so as to be rotatably movable relative to the frame, and a mechanical linking assembly ( 203 ) for connecting the lever to the frame, the mechanical linking assembly ( 203 ) including: a first linking piece ( 213, 223 ) movably mounted relative to the frame ( 201 ) about a first rotation axis (X), a second linking piece ( 233, 243 ) movably mounted relative to the frame ( 201 ) about a second rotation axis (Y), the second rotation axis forming a non-zero angle with the first rotation axis, a third intermediate piece ( 255, 265 ) mounted so as to the rotatably movable relative to the first linking piece ( 213, 223 ) about a third rotation axis (Y′), a fourth intermediate piece ( 275, 285 ) mounted so as to be rotatably movable relative to the second linking piece ( 233, 243 ) about a fourth rotation axis (X′), the fourth rotation axis forming a non-zero angle with the third rotation axis, in which the linking pieces ( 213, 223; 233, 243 ) or the intermediate pieces ( 255, 265; 275, 285 ) are rotatably movable in relation to one another about a fifth rotation axis (Z′) forming a non-zero angle with the first rotation axis (X) and the second rotation axis (Y) or with the third rotation axis (Y′) and the fourth rotation axis (X′), respectively, so as to enable a variation of the angle formed between the first rotation axis and the second rotation axis or of the angle formed between the third rotation axis and the fourth rotation axis, respectively.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a joystick for controlling an aircraft. 
       PRIOR ART 
       [0002]    Aircraft are traditionally equipped with a steering lever for the pilot to operate the ailerons and elevator to control the attitude of the aircraft on the pitch and roll axes. The steering handle is positioned between the legs of the pilot who uses the strength of his arm to actuate the handle. 
         [0003]    In some planes equipped with electric flight controls, the control lever has been replaced by a control device called a “joystick”. More compact than a conventional control lever, the joystick is generally integrated into a pilot&#39;s seat armrest and comprises a lever which the pilot operates solely by the movement of his wrist. Installing joysticks has freed up the space between the pilot and the dashboard so that other equipment can be installed. 
         [0004]    Also, the joystick generally includes a set of springs for exerting a return force on each of the axes of rotation of the lever (roll axis and pitch axis) and to return the lever to a neutral position when the pilot exerts no force on the lever. 
         [0005]    However, existing mechanical joystick structures do not generally allow decoupling of return forces between the two axes of rotation of the lever. In other words, the return force exerted on an axis of the lever depends on the angular position of the lever according to the other axis. 
         [0006]    Also, neither do these structures generate linear return forces (that is, the intensity of which is proportional to the angular position of the lever along the relevant axis of rotation). 
       SUMMARY OF THE INVENTION 
       [0007]    An aim of the invention is to propose a joystick structure allowing decoupling between the return forces exerted on each of the axes. 
         [0008]    This problem is resolved within the scope of the present invention thanks to a joystick for controlling an aircraft, comprising a frame, a lever mounted mobile in rotation relative to the frame, and a mechanical linking assembly of the lever to the frame, the mechanical linking assembly comprising:
       a first linking piece mounted mobile relative to the frame about a first axis of rotation,   a second linking piece mounted mobile relative to the frame about a second axis of rotation, the second axis of rotation forming a non-zero angle with the first axis of rotation,   a third intermediate piece mounted mobile in rotation relative to the first linking piece about a third axis of rotation,   a fourth intermediate piece mounted mobile in rotation relative to the second linking piece about a fourth axis of rotation, the fourth axis of rotation forming a non-zero angle with the third axis of rotation,       
 
         [0013]    in which the linking pieces or the intermediate pieces are mobile in rotation one relative to the other about a fifth axis of rotation forming a non-zero angle respectively with the first axis of rotation and the second axis of rotation or with the third axis of rotation and the fourth axis of rotation so as to authorise respectively a variation of the angle formed between the first axis of rotation and the second axis of rotation or of the angle formed between the third axis of rotation and the fourth axis of rotation. 
         [0014]    Because of the joystick structure proposed, it is possible to exert return forces on the first linking piece and on the second linking piece totally independently. 
         [0015]    In addition, the existence of a fifth axis of rotation enables misalignment between the first axis of rotation and the fourth axis of rotation and/or between the second axis of rotation and the third axis of rotation. This added degree of liberty enables displacement of the lever in rotation simultaneously according to the first axis of rotation and according to the second axis of rotation, despite misalignment occurring between the axes of the fixed framework materialised by the frame (first and second axes of rotation) and the axes of the pivoting framework materialised by the linking pieces (third and fourth axes). 
         [0016]    The joystick according to the invention can in addition have the following characteristics:
       the mechanical linking assembly comprises a linking member comprising an external ring and an internal ring rotatably mounted one relative to the other about the fifth axis of rotation, each of the linking pieces or respectively intermediate pieces being connected to a respective ring of the linking member, the lever being connected to the third intermediate piece and/or the fourth intermediate piece,   one of the rings of the linking member is fixed relative to the first linking piece and the other ring is fixed relative to the second linking piece,   one of the rings of the linking member is fixed relative to the frame so as to authorise rotation only of the first linking piece or only of the second linking piece relative to the frame about the fifth axis of rotation,   the linking member comprises at least one roller rotatably mounted about an axis of rotation fixed relative to the frame, the roller being interposed between the internal ring and the external ring such that rotation of one of the rings relative to the frame concurrently causes rotation in the opposite direction of the other ring relative to the frame,   one of the rings of the linking member is fixed relative to the third intermediate piece and the other ring is fixed relative to the fourth intermediate piece,   one of the rings of the linking member is fixed relative to the lever so as to authorise rotation of the lever only relative to the third intermediate piece or only relative to the fourth intermediate piece about the fifth axis of rotation,   the linking member comprises at least a roller rotatably mounted about an axis of rotation fixed relative to the lever, the roller being interposed between the internal ring and the external ring such that rotation of one of the rings relative to the lever concurrently causes rotation in the opposite direction of the other ring relative to the lever,   the mechanical linking assembly comprises a linking member comprising a fixed part and a part mounted mobile relative to the fixed part, the linking member comprising at least two flexible blades, each flexible blade connecting the parts together and being elastically deformable to authorise rotation of the mobile part relative to the fixed part, the flexible blades being capable of generating compensating torque tending to oppose rotation of the parts relative to each other,   the third intermediate piece or the fourth intermediate piece is fixed to a part of the linking member and the lever is fixed to the other part of the linking member,   the lever is connected to the frame by a ball-joint link enabling rotation of the lever according to the three axes of rotation relative to the frame,   the lever is connected to the frame by a cardan link enabling only rotation of the lever according to the first axis and rotation of the lever according to the second axis relative to the frame,   the lever is capable of simply bearing on the third intermediate piece and on the fourth intermediate piece to urge the intermediate pieces in rotation respectively according to the third and fourth axes so as to authorise relative rotation of the intermediate pieces relative to the lever according to the fifth axis of rotation,   one of the intermediate pieces comprises a stop arranged such that the lever is capable of bearing on the stop to stress the intermediate piece and cause rotation of the intermediate piece in a single direction of stress,   the lever is capable of bearing on the stop according to a rectilinear line of contact, parallel to the fifth axis of rotation,   the lever is capable of bearing on the stop according to a cylindrical contact surface, having an axis of revolution parallel to the fifth axis of rotation,   the joystick comprises a return member capable of urging one of the intermediate pieces of the linking member to oppose rotation of the intermediate piece,   the return member comprises a traction spring connecting the first linking piece or the second linking piece to the intermediate piece which is driven in rotation under the action of the lever,   the return member comprises a ribbon connecting the traction spring and the intermediate piece, the ribbon being capable of winding about a cylindrical element and connected to the intermediate piece.       
 
     
    
     
       PRESENTATION OF DRAWINGS 
         [0035]    Other characteristics and advantages will emerge from the following description which is purely illustrative and non-limiting, and must be considered with respect to the appended drawings, in which: 
           [0036]      FIGS. 1A and 1B  schematically illustrate a joystick according to a first embodiment of the invention with cradles, 
           [0037]      FIGS. 2A and 2B  schematically illustrate the action of a return member on an external ring of a cradle of the joystick, 
           [0038]      FIG. 3  schematically illustrates the arrangement of a return member on an internal ring of a cradle of the joystick, 
           [0039]      FIGS. 4A and 4B  schematically illustrate the arrangement of two return members on the internal rings of two cradles, 
           [0040]      FIGS. 5A to 5D  schematically illustrate a return member having double stiffness, 
           [0041]      FIGS. 6A to 6C  schematically illustrate an example of a cardan system which can be used to mount the lever on the casing of the joystick, 
           [0042]      FIGS. 7A to 7C  schematically illustrate a joystick according to a second embodiment of the invention with bearings, 
           [0043]      FIGS. 8A to 8C  schematically illustrate fixing of the return member to a ring of a bearing, 
           [0044]      FIGS. 9A and 9B  schematically illustrate two examples of contact between the lever and the cradles to realise the joystick of  FIGS. 1A and 1B , 
           [0045]      FIG. 10  schematically illustrates a first variant of the joystick of  FIGS. 7A to 7C , 
           [0046]      FIG. 11  schematically illustrates a second variant of the joystick of  FIGS. 7A to 7C , 
           [0047]      FIG. 12  schematically illustrates a third variant of the joystick of  FIGS. 7A to 7C , 
           [0048]      FIG. 13  schematically illustrates a fourth variant of the joystick of  FIGS. 7A to 7C , 
           [0049]      FIG. 14  schematically illustrates a fifth variant of the joystick of  FIGS. 7A to 7C , 
           [0050]      FIG. 15  schematically illustrates a linking member which can be used in the variants of  FIGS. 12 ,  13  and  14  in place of the fifth bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0051]      FIGS. 1A and 1B  schematically illustrate a joystick  100  according to a first embodiment of the invention. 
         [0052]    The joystick  100  comprises a frame  101  intended for example to be integrated into an armrest of a seat, a lever  102  mounted mobile in rotation relative to the frame, and a mechanical linking assembly  103  of the lever on the frame for generating a force feedback on the lever according to two axes of rotation. 
         [0053]    The lever  102  has a general elongated form according to a longitudinal direction (axis Z′). More precisely, the lever  102  comprises an elongated upper part  112  intended to be gripped by the hand of the pilot, an elongated lower part  122  capable of cooperating with the mechanical linking assembly  103 , and an intermediate part  132  having a spherical external surface  142 . 
         [0054]    The frame  101  comprises a support part having a spherical internal surface  111  receiving the intermediate part  132  of the lever  102 . The lever  102  is connected to the frame  101  by a ball-joint link  150  constituted by the spherical external surface  142  of the intermediate part  132  of the lever  102  and the complementary spherical internal surface  111  of the support part of the frame  101 . 
         [0055]    The mechanical linking assembly  103  comprises two pairs of linking pieces, including a first pair of linking pieces  113 ,  123  and a second pair of linking pieces  133 ,  143 . 
         [0056]    Each linking piece  113 ,  123  of the first pair is mounted mobile in rotation relative to the frame  101  about a first axis of rotation (axis X) by means of first pivot links  110  and  120 . 
         [0057]    Similarly, each linking piece  133 ,  143  of the second pair is mounted mobile relative to the frame  101  about a second axis of rotation (axis Y) by means of second pivot links  130  and  140 . 
         [0058]    When the joystick  100  is in neutral position (that is, when the pilot is exerting no stress on the lever  102 ), the second axis of rotation (axis Y) is perpendicular to the first axis of rotation (axis X). Also, the first axis of rotation and the second axis of rotation intersect at a point of intersection O which is also the centre of rotation of the lever  102  relative to the frame  101 , centre of the ball-joint link  150  (shown offset in the figure according to the axis Z′ with the sole purpose of clarifying the view of the pieces on the drawing). 
         [0059]    The mechanical linking assembly  103  also comprises four sets of cradles  153 ,  163 ,  173  and  183 , including two first sets of cradles  153 ,  163  and two second sets of cradles  173 ,  183 . Each set of cradles comprises a cradle frame and a lever cradle. 
         [0060]    In each first set of cradles  153 ,  163 , the cradle frame  154 ,  164  is mounted connected to the first linking pieces  113 ,  123 , such that rotation of the first linking pieces  113 ,  123  about the first axis of rotation X also causes rotation of the first sets of cradles  153 ,  163 . Also, the lever cradle  155 ,  165  is mounted mobile in rotation relative to the cradle frame  154 ,  164  according to a third axis of rotation (axis Y′) perpendicular to the first axis of rotation (axis X). 
         [0061]    Similarly, in each second set of cradles  173 ,  183 , the cradle frame  174 ,  184  is mounted connected to the second linking pieces  133 ,  143 , such that rotation of the second linking pieces  133 ,  143  about the second axis of rotation Y also causes rotation of the second sets of cradles  173 ,  183 . Also, the lever cradle  175 ,  185  is mounted mobile in rotation relative to the external cradle  174 ,  184  according to a fourth axis of rotation (axis X′) perpendicular to the second axis of rotation (axis Y). 
         [0062]    In this first embodiment, the lever cradles  155 ,  165 ,  175  and  185  constitute intermediate pieces of the mechanical linking assembly  103  to link the linking pieces to the lever  102 . 
         [0063]    More precisely, in each first set of cradles  153 ,  163 , the lever cradle  155 ,  165  is capable of being driven in rotation relative to the cradle frame  154 ,  164  (and consequently relative to the first linking piece) under the action of the lever  102  about the third axis of rotation. As is clear from  FIG. 1B , rotation of the lever  102  about the third axis (axis Y′) concurrently causes rotation of the second sets of cradles  173 ,  183  and the second linking pieces  133 ,  143  about the second axis of rotation relative to the frame (axis Y). 
         [0064]    Similarly, in each second set of cradles  173 ,  183 , the lever cradle  175 ,  185  is capable of being driven in rotation relative to the cradle frame  174 ,  184  (and consequently relative to the second linking piece) under the action of the lever  102  about the fourth axis of rotation. As is clear from  FIG. 1A , rotation of the lever  102  about the fourth axis (axis X′) concurrently causes rotation of the first sets of cradles  153 ,  163  and the first linking pieces  113 ,  123  about the first axis of rotation relative to the frame  101  (axis X). 
         [0065]    This is why the sets of cradles  153 ,  163 ,  173 ,  183  constitute for the lever  102  pivoting frameworks relative to the fixed framework defined by the frame  101 . 
         [0066]    As is illustrated in  FIGS. 2A and 2B , the joystick  100  comprises a linking piece  113 , a set of cradles including a cradle frame  154  fixed relative to the linking piece  113  and a lever cradle  155  mobile relative to the cradle frame fixed  154  (and therefore relative to the linking piece), and a return member  156  extending between a linking piece  123  and the mobile lever cradle  155 . The return member  156  is capable of exerting compensating torque tending to oppose rotation of the lever cradle  155  relative to the cradle frame  154 , that is, oppose rotation of the lever  102  relative to the frame  101 . The return member  156  comprises a linear coil spring  157  and a ribbon  158  winding about a portion of cylindrical surface of the lever cradle  155 . 
         [0067]    The ribbon  158  has a first end fixed to the portion of cylindrical surface and a second end fixed to a second end of the spring. The spring  157  has a first end fixed to the linking piece and a second end fixed to the second end of the ribbon. As is illustrated in  FIG. 2B , rotation of the lever cradle  155  relative to the cradle frame  154  causes a winding of the ribbon  158  and extension of the spring  157 , the extension of the spring  157  being proportional to the angle of rotation θ of the lever cradle  155  relative to the cradle frame  154  about the axis Y′. This mounting produces a linear return of force on the lever  102 . 
         [0068]    In  FIGS. 2A and 2B , the lever cradle  155  is the external cradle and the cradle frame  154  is the internal cradle of the set of cradles  153 . This is why the return member  156  exerts a return force on the external lever cradle  155 . 
         [0069]      FIGS. 3 ,  4 A and  4 B show a example of mounting in which, in each set of cradles  173 ,  183 , the lever cradle  175 ,  185  is the internal cradle and the cradle frame  174 ,  184  is the external cradle. The return member  176 ,  186  exerts a return force on the internal lever cradle  175 ,  185 . 
         [0070]    In these figures, only the second linking pieces  133 ,  143  and the second sets of cradles  173 ,  183  have been shown. However, the same mounting is done for the first linking pieces  113 ,  123  and the first sets of cradles  153 ,  163 . 
         [0071]    As is apparent in  FIGS. 4A and 4B , the lower part  122  of the lever  102  comprises four protuberances  152 ,  162 ,  172  and  182 . Also, each lever cradle  155 ,  165 ,  175  and  185  has a stop. Each protuberance  152 ,  162 ,  172  and  182  is capable of supporting against a corresponding stop of a lever cradle  155 ,  165 ,  175  and  185  to drive the lever cradle in rotation. 
         [0072]    The protuberances and the stops are arranged such that rotation of the lever  102  according to the fourth axis of rotation (axis X′) in a first direction causes rotation of the lever cradle  175  relative to the cradle frame  174 , without driving the lever cradle  185  in rotation. Inversely, rotation of the lever  102  according to the fourth axis of rotation (axis X′) in a second direction, opposite the first direction, causes rotation of the lever cradle  185  relative to the cradle frame  184 , without driving the lever cradle  175  in rotation. 
         [0073]    As each lever cradle  155 ,  165 ,  175 ,  185  is fitted with its own return member, it is possible to provide return members  156 ,  166 ,  176 ,  186  having different characteristics to produce a different return of force according to the direction of stress of the lever about the axis X′ and of the axis Y′. 
         [0074]    Also, the proposed mounting allows working the return members  156 ,  166 ,  176 ,  186  only in traction, such that no guide device of the return members is necessary and any risk of buckling of the elements constituting these return members is eliminated, whether this is the ribbon  158  or the linear coil spring  157 . 
         [0075]    Also, this mounting creates a joystick  100  in which the return members  156 ,  166 ,  176 ,  186  are mounted by being prestressed in traction, that is, each return member  156 ,  166 ,  176 ,  186  exerts a non-zero return force on the lever  102  when the lever  102  is in neutral position. This creates a force threshold to be overcome during initialisation of displacement of the lever. 
         [0076]      FIGS. 5A to 5C  schematically illustrate an example of a return member  156  for generating double stiffness in a direction of rotation. 
         [0077]    To this end, the return member  156  comprises a spring  157  and a stop  159 . The spring  157  has a first spring portion  1571  and a second spring portion  1572  mounted in series with the first spring portion  1572 , the stop  159  being interposed between a coil of the first spring portion  1571  and a coil of the second spring portion  1572 . 
         [0078]    In  FIG. 5A , the spring  157  is initially in neutral position, that is, the lever  102  is not subjected to any stress by the pilot. 
         [0079]      FIGS. 5B and 5C  illustrate the spring  157  when the lever  102  is stressed by the pilot about the axis of rotation Y′. 
         [0080]    In  FIG. 5B , during a first phase, the spring  157  has been stretched by a first length L. The two spring portions  1571  and  1572  have elongated until a coil of the first spring portion  1571  is supported against the stop  159 . Once the coil of the first spring portion  1571  is supported against the stop  159 , the first spring portion  1571  can no longer be elongated. 
         [0081]    In  FIG. 5C , during a second phase, the spring a been stretched by a second length L 2 , greater than the first length L 1 , but only the second spring portion  1572  has elongated, the first spring portion  1571  being neutralised by the stop  159 . 
         [0082]      FIG. 5D  illustrates the intensity of the return force F generated by the return member  156  as a function of the extension L of the spring  157 . It is evident that the force F generated follows a double slope law of force. During the first phase, the two spring portions are stressed, such that the force generated exhibits a linear variation having a first slope. During the second phase, only the second spring portion is stressed such that the force exhibits a linear variation having a second slope, greater than the first slope. 
         [0083]    In a variant of the first embodiment, the ball-joint link  150  connecting the lever  102  to the frame  101  can be replaced by a cardan link  20 .  FIGS. 6A  to  6 C schematically illustrate an example of a cardan system  21  which can be used to mount the lever  102  on the casing  101  of the joystick  100 . The system illustrated reduces friction forces and eliminates any risk of scuffing. Also, the generally flat form of the cardan system  21  illustrated frees up space above the centre of rotation  132  of the lever  102 , which is particularly advantageous in a cramped environment. 
         [0084]    The cardan system  21  illustrated in  FIGS. 6A to 6C  comprises a base plane  22 , a flat intermediate piece  23 , and two support pieces  24  and  25 . The base plane  22  is fixed to the frame  101  of the joystick  100  and the lever  102  is fixed to the two support pieces  24  and  25 . 
         [0085]    The cardan system  21  comprises in addition two flexible blades  26 ,  27  linking the base  22  to the intermediate piece  23  and enabling rotation of the intermediate piece  23  relative to the flat base  22  according to a first axis of rotation (axis x). 
         [0086]    The cardan system  21  also comprises two flexible blades  28 ,  29  linking the intermediate piece  23  to the support pieces  24 ,  25  and enabling rotation of the support pieces  24 ,  25  relative to the intermediate piece  23  according to a second axis of rotation (axis y) perpendicular to the first axis of rotation. 
         [0087]    In this way, the lever  102  can be driven in rotation relative to the casing according to the two axes of rotation x and y, these two axes of rotation being fixed relative to the frame  101 . 
         [0088]      FIGS. 7A to 7C  schematically illustrate a joystick  200  according to a second embodiment of the invention. 
         [0089]    In this second embodiment, the sets of cradles  153 ,  163 ,  173  and  183  have been replaced by ball bearings  253 ,  263 ,  273 ,  283 , each bearing comprising a ring lever  255 ,  265 ,  275 ,  285  and a ring frame  254 ,  264 ,  274 ,  284 . 
         [0090]    In  FIGS. 7A to 7C , the joystick  200  comprises a frame  201 , a lever  202  mounted mobile in rotation relative to the frame, and a mechanical linking assembly  203  of the lever on the frame. 
         [0091]    The mechanical linking assembly  203  comprises two pairs of linking pieces, including a first pair of linking pieces  213 ,  223  and a second pair of linking pieces  233 ,  243 . 
         [0092]    Each linking piece  213 ,  223  of the first pair is mounted mobile in rotation relative to the frame  201  about a first axis of rotation (axis X) by means of first pivot links  210  and  220 . 
         [0093]    Similarly, each linking piece  233 ,  243  of the second pair is mounted mobile relative to the frame  201  about a second axis of rotation (axis Y) by means of second pivot links  230  and  240 . 
         [0094]    The mechanical linking assembly  203  also comprises four bearings  253 ,  263 ,  273  and  283 , including a first couple of bearings  253 ,  263  and a second couple of bearings  273 ,  283 . Each bearing comprises a ring lever and a ring frame. 
         [0095]    In each bearing  253 ,  263  of the first couple, the ring frame  254 ,  264  is mounted connected to the first linking pieces  213 ,  223 , such that rotation of the first linking pieces  213 ,  223  about the first axis of rotation X also causes rotation of the bearings  253 ,  263 . Also, the ring lever  255 ,  265  is mounted mobile in rotation relative to the ring frame  254 ,  264  according to a third axis of rotation (axis Y′) perpendicular to the first axis of rotation (axis X). 
         [0096]    Similarly, in each bearing  273 ,  283  of the second couple, the ring frame  274 ,  284  is mounted connected to the second linking pieces  233 ,  243 , such that rotation of the second linking pieces  233 ,  243  about the second axis of rotation Y also causes rotation of the bearings  273 ,  283 . Also, the ring lever  275 ,  285  is mounted mobile in rotation relative to the ring frame  274 ,  284  according to a fourth axis of rotation (axis X′) perpendicular to the second axis of rotation (axis Y). 
         [0097]    In this second embodiment, the lever rings  255 ,  265 ,  275  and  285  constitute intermediate pieces of the mechanical linking assembly  203  to link the linking pieces to the lever  202 . 
         [0098]    As is illustrated in  FIGS. 8A to 8C , the joystick  200  comprises a return member  256  extending between a linking piece  223  and the ring lever  255 , as in the first embodiment. The return member  256  is capable of exerting compensating torque tending to oppose rotation of the ring lever  255  relative to the ring frame  254 , that is, opposing rotation of the lever  202  relative to the frame  201 . The return member  256  comprises a linear coil spring  257  and a ribbon  258  winding about a portion of cylindrical surface  259  of the ring lever  255 . 
         [0099]      FIG. 8A  illustrates the return member  256  when the lever  202  is in neutral position. 
         [0100]      FIG. 8B  illustrates the return member  256  when the lever  202  is driven in rotation about the axis Y′ in a first direction of rotation. The ring lever  255 , driven in rotation by the lever  202 , does not drive the ribbon  258 , which does not wind about the cylinder portion of the ring lever  255 , leaving elongation of the spring  257  unchanged. 
         [0101]      FIG. 8C  illustrates the return member  256  when the lever  202  is driven in rotation about the axis Y′ in a second direction of rotation, opposite the first direction of rotation. The lever  202  drives in rotation the ring lever  255 , the effect of which is to wind the ribbon  258  about the ring lever  255 . The ribbon  258  exerts traction on the spring  257  which elongates and generates a return force tending to oppose rotation of the ring lever  255  relative to the ring frame  254 . 
         [0102]      FIGS. 9A and 9B  schematically illustrate an alternative mounting for producing dissociation of both directions of rotation on the same axis. In this alternative, each lever cradle  175  and  185  has a stop. The lower part  122  of the lever  102  is capable of supporting against a stop of the lever cradle  175  and  185  to drive the lever in rotation cradle. 
         [0103]    The stops are arranged such that rotation of the lever  102  according to the fourth axis of rotation (axis X′) in a first direction causes rotation of the lever cradle  175  relative to the cradle frame  174 , without driving the lever cradle  185  in rotation. Inversely, rotation of the lever  102  according to the fourth axis of rotation (axis X′) in a second direction, opposite the first direction, causes rotation of the lever cradle  185  relative to the cradle frame  184 , without driving the lever cradle  175  in rotation. 
         [0104]    In  FIG. 9A , the lever  102  is in contact with the stops according to a rectilinear line of contact. In  FIG. 9B , the lever  202  is in contact with the stops according to a cylindrical contact surface. In these two cases, contact between the lever  102  and the stops enables rotation of the lever  102  relative to the lever cradles  175  and  185  about the axis Z′ without engendering any parasite rotation of the lever cradles  175  and  185  relative to the frame cradles  174  and  184 , indispensable to not generate coupling between the axes X′ and Y. 
         [0105]    It is evident that the alternative mounting of  FIGS. 9A and 9B  needs the device to include linking of the lever  102  with the frame  101 , such as a ball-joint link  150  for example. 
         [0106]      FIG. 10  schematically illustrates a first variant of the joystick  200  of  FIGS. 7A to 7C . 
         [0107]    In this first variant, the pivots  220  and  210  are mounted fixed on the frame  201 , while the pivots  230  and  240  are rotatably mounted relative to the frame  201 . In other words, the second linking pieces  233  and  243  are mounted mobile in rotation relative to the frame  201  about a fifth axis (axis Z), the fifth axis being perpendicular to the first axis (axis X) and to the second axis (axis Y) and passing through the centre of rotation O of the lever  202 . 
         [0108]    For this purpose, the mechanical linking assembly  203  comprises a fifth bearing  293  comprising an external ring  294  mounted fixed relative to the frame  201  and an internal ring  295  mounted mobile in rotation relative to the external ring  294  (and therefore relative to the frame  201 ) about the axis Z. The linking pieces  233  and  243  are rotatably mounted on the internal ring  295  about the axis Y by means of the pivots  230  and  240 . 
         [0109]    This mounting enables rotation of the fixed frameworks (Y defined by the linking pieces  233  and  243 ) relative to the other framework fixed (X defined by the linking pieces  213  and  223 ) about the axis Z, whereas the two axes X′ and Y′ of the pivoting framework remain fixed and orthogonal relative to each other. 
         [0110]    This mounting enables a variation in the angle formed between the first axis of rotation X and the second axis of rotation Y, the first axis of rotation X being fixed relative to the frame  201 . 
         [0111]    Because of this mounting, misalignment between the second axis of rotation Y and the third axis of rotation Y′ is possible. This added degree of liberty, made indispensable by projection of rotation vectors, allows displacement of the lever  202  in rotation simultaneously according to the first axis of rotation X and according to the second axis of rotation Y. 
         [0112]      FIG. 11  schematically illustrates a second variant of the joystick of  FIGS. 7A to 7C  in which the first axis of rotation X and the second axis of rotation Y are mobile relative to the frame  201 . 
         [0113]    In this second variant, the mechanical linking assembly  203  comprises a fifth bearing  293  comprising an external ring  294  and an internal ring  295 , each of the rings  294  and  295  being mounted mobile in rotation relative to the frame  201  about the axis Z. The mechanical linking assembly  203  also comprises a plurality of rollers  296  interposed between the rings  294  and  295  and mounted mobile in rotation relative to the frame  201  about their axis, which are parallel to the axis Z and fixed relative to the frame  201 . 
         [0114]    The rollers  296  link the rings  294  and  295  in rotation such that rotation of one of the rings relative to the frame  201  in a direction concurrently causes rotation of the other ring in the opposite direction by an identical angle. 
         [0115]    This mounting also enables rotation of the fixed frameworks X and Y relative to each other (defined on the one hand by the linking pieces  213  and  223  and on the other hand by the linking pieces  233  and  243 ) about the axis Z, while the two axes X′ and Y′ of the pivoting framework remain fixed and orthogonal relative to each other. 
         [0116]    Because of this mounting, misalignment between the first axis of rotation X and the fourth axis of rotation X′ on the one hand, and between the second axis of rotation Y and the third axis of rotation Y′ on the other hand, is possible, said misalignments being symmetrical. 
         [0117]    This added degree of liberty, made indispensable by projection of rotation vectors, allows displacement of the lever  202  in rotation simultaneously according to the first axis of rotation X and according to the second axis of rotation Y, and without causing rotation of the lever according to the axis Z′. 
         [0118]      FIG. 12  schematically illustrates a third variant of the joystick  200  of  FIGS. 7A to 7C  in which the bearings are mobile in rotation. 
         [0119]    In this third variant, the bearings  253  and  263  are mounted fixed relative to the lever  202 , while the bearings  273  and  283  are mounted to rotate relative to the lever  202 . Otherwise expressed, the intermediate pieces  275  and  285  (formed by the mobile rings of the bearings  273  and  283 ) are mounted mobile in rotation relative to the lever  202  about a fifth axis (axis Z′), the fifth axis being perpendicular to the third axis (axis Y′) and the fourth axis (axis X′) and passing through the centre of rotation O of the lever  202 . 
         [0120]    For this purpose, the mechanical linking assembly  203  comprises a fifth bearing  293  comprising an internal ring  295  mounted fixed relative to the lever  202  and an external ring  294  mounted mobile relative to the internal ring  295  (and therefore relative to the lever  202 ) about the axis Z′. The intermediate pieces  275  and  285  are mounted fixed on the external ring  294  of the fifth bearing  293 . 
         [0121]    This mounting enables rotation of the lever  202  relative to the pivoting frameworks (defined by the linking pieces  233  and  243 ) about the axis Z′ (longitudinal axis of the lever  202 ). 
         [0122]    This mounting enables variation in the angle formed between the third axis of rotation Y′ and the fourth axis of rotation X′, the third axis of rotation Y′ being fixed relative to the lever  202 . 
         [0123]    Because of this mounting, misalignment between the third axis of rotation Y′ and the second axis of rotation Y is possible. This added degree of liberty, made indispensable by projection of rotation vectors, allows displacement of the lever  202  in rotation simultaneously according to the first axis of rotation X and according to the second axis of rotation Y. 
         [0124]      FIG. 13  schematically illustrates a fourth variant of the joystick of  FIGS. 7A to 7C . This fourth variant has a function identical to that of the third variant. While the third variant allows the use of identical bearings  253 ,  263 ,  273  and  283 , the fourth variant is more compact and includes embedded bearings. 
         [0125]    In this fourth variant, the external ring  294  of the fifth bearing  293  is fixed to the internal lever rings  275  and  285  of bearings  273  and  283  of the second pair. 
         [0126]    The internal ring  295  of the fifth bearing  293  is fixed to the external lever rings  255  and  265  of the bearings  253  and  263  of the first pair. 
         [0127]      FIG. 14  schematically illustrates a fifth variant of the joystick of  FIGS. 7A to 7C , in which the fourth axis of rotation X′ and the third axis of rotation Y′ are mobile relative to the lever  202 . 
         [0128]    In this fifth variant, the mechanical linking assembly  203  comprises a fifth bearing  293  comprising an external ring  294  and an internal ring  295 , each of the rings  294  and  295  being mounted mobile in rotation relative to the lever  202  about the axis Z′. The mechanical linking assembly  203  also comprises a plurality of rollers  296  interposed between the rings  294  and  295  and mounted mobile in rotation relative to the lever about their axes which are parallel to the axis Z and fixes relative to the lever  202 . 
         [0129]    The rollers  296  link the rings  294  and  295  in rotation such that rotation of one of the rings relative to the lever  202  in a direction concurrently causes rotation of the other ring in the opposite direction by an identical angle. 
         [0130]    This mounting enables rotation of the lever  202  relative to each of the pivoting frameworks (the pivoting frameworks being defined respectively by the linking pieces  213  and  223  and by the linking pieces  233  and  243 ) about the axis Z′. 
         [0131]    Because of this mounting, misalignment between the first axis of rotation X and the fourth axis of rotation X′ on the one hand, and between the second axis of rotation Y and the third axis of rotation Y′ on the other hand, is possible, said misalignments being symmetrical. 
         [0132]    This mounting, because of this added degree of liberty made indispensable by projection of rotation vectors, also allows displacement of the lever  202  in rotation simultaneously according to the first axis of rotation X and according to the second axis of rotation Y, and without causing rotation of the lever according to the axis Z′. 
         [0133]      FIG. 15  schematically illustrates a linking member  393  which can be used in the variant of  FIG. 14  in place of the fifth bearing  293  and of the plurality of associated rollers  296 . 
         [0134]    The linking member  393  illustrated comprises a first part  394 , a second part  395  and a third part  396 . The first part  394  is mounted mobile relative to the third part  396 . Similarly, the second part  395  is mounted mobile relative to the third part  396 . 
         [0135]    The linking member  393  also comprises two couples of flexible blades  301  and  302 ,  303  and  304 . Each flexible blade  301 ,  302  of the first couple connects the first part  394  and the third part  396  together and is elastically deformable to enable rotation of the third part  396  relative to the first part  394 . The flexible blades  301  and  302  are capable of generating compensating torque tending to oppose the rotation of the parts  394  and  396  together. 
         [0136]    Similarly, each flexible blade  303 ,  304  of the second couple connects the second part  395  and the third part  396  together and is elastically deformable to enable rotation of the third part  396  relative to the second part  395 . The flexible blades  303 ,  304  are capable of generating compensating torque tending to oppose rotation of the parts  395  and  396  together. 
         [0137]    The first part  394  is fixed to the intermediate pieces  275  and  285 . 
         [0138]    The second part  395  is fixed to the intermediate pieces  255  and  265 . 
         [0139]    The third part  396  is fixed to the lever  202 . 
         [0140]    As in the case of the joystick of  FIG. 14 , this mounting enables rotation of the lever  202  relative to each of the pivoting frameworks (the pivoting frameworks being respectively defined by the linking pieces  213  and  223  and by the linking pieces  233  and  243 ) about the axis Z′. 
         [0141]    Because of this mounting, misalignment between the first axis of rotation X and the fourth axis of rotation X on the one hand, and between the second axis of rotation Y and the third axis of rotation Y′ on the other hand, is possible, said misalignments being symmetrical. 
         [0142]    This mounting, because of this added degree of liberty made indispensable by projection of rotation vectors, also enables displacement of the lever  202  in rotation simultaneously according to the first axis of rotation X and according to the second axis of rotation Y, and without causing rotation of the lever according to the axis Z′. 
       REFERENCE NUMBERS 
       [0000]    
       
           100  Joystick (first embodiment) 
           101  Frame 
           102  Lever 
           103  Mechanical link assembly 
           110  Pivot link (axis X) 
           111  Spherical internal surface 
           112  Lower part of the lever 
           113  Link piece (first pair) 
           120  Pivot link (axis X) 
           122  Lower part of the lever 
           123  Link piece (first pair) 
           130  Pivot link (axis Y) 
           132  Intermediate part of the lever 
           133  Link piece (second pair) 
           140  Pivot link (axis Y) 
           142  Spherical external surface 
           143  Link piece (second pair) 
           150  Ball-joint link 
           152  Protuberance 
           153  Set of cradles (first sets) 
           154  Frame cradle 
           155  Lever cradle 
           156  Return member 
           157  Linear coil spring 
           158  Ribbon 
           159  Stop 
           162  Protuberance 
           163  Set of cradles (first sets) 
           164  Frame cradle 
           165  Lever cradle 
           166  Return member 
           172  Protuberance 
           173  Set of cradles (second sets) 
           174  Frame cradle 
           175  Lever cradle 
           176  Return member 
           182  Protuberance 
           183  Set of cradles (second sets) 
           184  Frame cradle 
           185  Lever cradle 
           186  Return member 
           200  Joystick (second embodiment) 
           201  Frame 
           202  Lever 
           203  Mechanical link assembly 
           210  Pivot link (axis X) 
           213  Link piece (first pair) 
           220  Pivot link (axis X) 
           222  Lower part of the lever 
           223  Link piece (first pair) 
           230  Pivot link (axis Y) 
           233  Link piece (second pair) 
           240  Pivot link (axis Y) 
           243  Link piece (second pair) 
           253  Ball bearing (first couple) 
           254  Frame ring 
           255  Lever ring 
           256  Return member 
           257  Linear coil spring 
           258  Ribbon 
           259  Portion of cylindrical surface 
           263  Ball bearing (first couple) 
           264  Frame ring 
           265  Lever ring 
           266  Return member 
           267  Linear coil spring 
           269  Portion of cylindrical surface 
           273  Ball bearing (second couple) 
           274  Frame ring 
           275  Lever ring 
           276  Return member 
           277  Linear coil spring 
           279  Portion of cylindrical surface 
           283  Ball bearing (second couple) 
           284  Frame ring 
           285  Lever ring 
           286  Return member 
           287  Linear coil spring 
           289  Portion of cylindrical surface 
           293  Fifth bearing 
           294  External ring 
           295  Internal ring 
           296  Rollers 
           301  Flexible blade (first couple) 
           302  Flexible blade (first couple) 
           303  Flexible blade (second couple) 
           304  Flexible blade (second couple) 
           20  Cardan link 
           21  Cardan system 
           22  Flat base 
           23  Intermediate piece 
           24  Support piece 
           25  Support piece 
           26  Flexible blade 
           27  Flexible blade 
           28  Flexible blade 
           29  Flexible blade 
           393  Link member 
           394  First part of the linking member 
           395  Second part of the linking member 
           396  Third part of the linking member 
           1571  First spring portion 
           1572  Second spring portion