Abstract:
The invention relates to a humanoid robot comprising two elements connected by a spherical joint with three degrees of freedom in rotation, the joint being moved by three actuators each acting in one of the three degrees of freedom. The invention is of particular use in the production of humanoid robots coming as close as possible to the human anatomy. According to the invention, the first and the second of the actuators act in parallel and the third of the actuators acts in series with the first and the second of the actuators.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International patent application PCT/EP2009/003340, filed on May 11, 2009, which claims priority to foreign French patent application No. FR 08 53061, filed on May 9, 2008, the disclosures of which are incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a humanoid robot using a spherical joint. The invention is of particular use in the production of humanoid robots coming as close as possible to the human anatomy. 
     BACKGROUND OF THE INVENTION 
     A mathematical model modeling this anatomy was developed in the 1960s in the United States by Aerospace Medical Research Laboratories in Dayton, Ohio. This model, well known as the Hanavan model, describes in a parametric manner, in relation to a given human size and weight, the dimensions of all the parts of the body. In particular, the ankle is described as a joint having three degrees of freedom in rotation. The dimensions of the leg, the part of the body extending between the knee and the ankle, are also described. For example, for a 14-year-old adolescent, 1.6 m tall, and weighing 50 kg, the leg can be represented by a truncated cone with a height of 392 mm, with 29 mm for the small radius and with 47 mm for the large radius. The foot is modeled by a set of rectangular parallelepipeds of which the overall length is 243 mm, the width is 80 mm, the heel height is 62 mm, and the distance between the back of the foot and the connection to the ankle is 72 mm. The height of the leg is defined as the distance between the ankle joint and that of the knee. 
     At the present time, many humanoid robots have been developed, but none of them complies with the Hanavan model, notably in the space requirement of the leg. For example, robots are found in which the ankle is reduced to an universal joint type, that is to say comprising only two degrees of freedom, a rotation in the sagittal plane and a rotation in the frontal plane. Moreover, the actuation mechanisms used to motorize these two degrees of freedom extend beyond the dimensions specified in the Hanavan model. 
     The design of the ankle is one of the most difficult problems in the design of a humanoid robot. This is due on the one hand to the fact that the ankle is the joint that needs the most torque in the locomotive apparatus and, on the other hand, because of the constraints of size and weight. For example, a dynamic calculation shows that, to achieve a walk at a speed of 1.2 m/s, for a 1.6 m and 50 kg robot, it is necessary to produce a torque of almost 80 N·m for the rotation in the sagittal plane, with a speed of 4.5 rad/s and an joint range of movement of minus ten degrees to plus thirty degrees. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to improve the extent to which a robot accurately reproduces the human anatomy, for example modeled on the Hanavan model. The invention is not limited to the production of an ankle. The invention applies to any spherical joint used in a humanoid robot. 
     It is therefore an object of the present invention to provide a humanoid robot comprising two elements connected by a spherical joint with three degrees of freedom in rotation, the joint being moved by three actuators each acting on one of the three degrees of freedom, wherein the first and the second of the actuators act in parallel and wherein the third of the actuators acts in series with the first and the second of the actuators. This type of joint is called hybrid in the sense that it combines a parallel mechanism and a serial mechanism. Its usefulness lies in combining the advantages of the two conventional families of serial mechanisms on the one hand and of parallel mechanisms on the other hand. 
     The invention can be applied to an ankle of the humanoid robot, the ankle connecting a leg and a foot of the robot, the ankle comprising a joint between the leg and the foot, characterized in that the ankle comprises three actuators placed in the leg making it possible to move the joint each in a rotation of the ankle on one axis, and in that the axes of the three rotations are distinct and intersecting. 
     In the case of the ankle, by virtue of three degrees of freedom respectively, in the frontal plane, the sagittal plane and a horizontal plane, the walk of a humanoid robot using an ankle according to the invention will be much more anthropomorphic than that of a robot in which the ankle has only two degrees of freedom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given as an example, the description being illustrated by the appended drawing in which: 
         FIG. 1  represents in perspective an ankle according to the invention; 
         FIG. 2  represents the ankle in section in a sagittal plane; 
         FIG. 3  represents the ankle in section in a frontal plane; 
         FIGS. 4, 5 and 6  represent in detail an actuator allowing the rotation of the ankle about a vertical axis; 
         FIGS. 7 and 8  represent a wrist according to the invention; 
         FIGS. 9 and 10  represent a neck according to the invention. 
     
    
    
     In the interests of clarity, the same elements will bear the same reference numbers in the various figures. 
     DETAILED DESCRIPTION 
     A humanoid robot according to the invention may comprise one or more spherical joints according to the invention. The joint links two elements which, in the case of the ankle, are a leg and a foot. In the case of the neck, the two elements are a body and a head of the robot. In the case of the wrist, the two elements are a forearm and a hand of the robot. 
       FIG. 1  represents an ankle  10  according to the invention. By convention, an ankle is specified as being an assembly comprising a foot  11 , a leg  12  and a joint  13  between the leg  12  and the foot  11 . 
     The ankle  10  comprises three actuators placed in the leg  12 . The actuators can use hydraulic or electric power. A first actuator  14  allows the ankle to rotate about a vertical axis  15 . A second actuator  16  allows the ankle to rotate about a sagittal axis  17  and a third actuator  18  allows the ankle to rotate about a frontal axis  19 . The three axes  15 ,  17  and  19  are distinct and intersecting. In the example shown, the three axes  15 ,  17  and  19  are perpendicular. By convention, the sagittal axis is specified as an axis perpendicular to the sagittal plane, the plane in which the walking movement mainly takes place. Similarly, the frontal axis is specified as an axis perpendicular to the frontal plane of the robot. The frontal plane is perpendicular to the sagittal plane. 
     The first actuator  14  is situated above the other two actuators  16  and  18  which are situated substantially on the same level of the leg  12 . More precisely, the leg  12  comprises three zones. The actuator  14  is situated in an upper zone  20  and the actuators  16  and  18  are situated in a lower zone  22 . The actuators  16  and  18  advantageously act in parallel on the foot  11 . This action in parallel makes it possible to prevent one of the actuators from supporting the other, as is the case in most known robots. The actuator  14  acts in series on the assembly formed by the two actuators  16  and  18 . 
     More generally, the actuator  18  is placed upstream of the actuators  14  and  16  relative to the body of the robot and advantageously the three actuators  14 ,  16  and  18  are placed in the element furthest upstream relative to the body. 
     A middle zone  21  situated between the zones  20  and  22  contains no actuator and is, for example, available for receiving one or more hydraulic pumps making it possible to power the actuators  14 ,  16  and  18 . In  FIG. 2 , three rods  23  to  25  are used to maintain the rigidity of the middle zone  21 . 
     The middle zone  21  has a characteristic dimension, in a plane perpendicular to the axis  15 , greater than the same dimensions of the upper zone  20  and lower zone  22 . These three dimensions form part of the Hanavan model, the middle zone  21  forming a calf of the leg  12 . 
       FIG. 2  represents an ankle  10  in section in a vertical plane containing the axis  15 . This is a sagittal plane. The actuator  14  situated in the upper zone  20  advantageously comprises a rotary hydraulic motor comprising a stator  30  secured to a bottom portion  31  of a knee and to a rotor  32  that can move in rotation about the axis  15  relative to the stator  30 . The rods  23  to  25  are secured to the rotor  32 . 
     In  FIG. 2 , in the lower zone  22 , only the actuator  16  allowing the foot  11  to move about the sagittal axis  17  is shown. Advantageously, the actuator  16  is linear and acts by means of tie-rods  33  and  34  attached on the one hand to the actuator  16  and on the other hand to the foot  11 . Similarly the actuator  18  is linear and acts by means of tie-rods  35  and  36 . The actuator  18  is not in the plane of  FIG. 2  and only the tie-rod  36  appears. The use of tie-rods acting between the actuators and the foot  11  means that the actuators can act in parallel and not in series. 
     Advantageously, the actuators  16  and  18  each comprise two single-acting cylinders each acting as a tie-rod on the foot  11 . For the actuator  16 , the cylinders  37  and  38  each comprise a piston, respectively  39  and  40 , moving in a respective liner  41  and  42 . The cylinders  37  and  38  each comprise a chamber, respectively  43  and  44 , powered by a hydraulic fluid. This fluid is for example supplied by a hydraulic pump placed in the middle zone  21 . When a pump is associated with a single actuator, in this instance the actuator  16 , the pump draws the fluid into one of the chambers  43  or  44  in order to discharge the fluid into the other chamber depending on the direction of angular movement of the foot  11  about the axis  17 . 
     Advantageously, the pistons of the linear actuators  16  and  18  move on vertical axes parallel to the axis  15 . More generally, the axes of the pistons are parallel. This arrangement of the pistons allows the ankle to be better included in the dimensions of the Hanavan model. This arrangement also makes it possible to limit the inertia of the ankle  10  during its various rotations and during the rotation of the knee. 
       FIG. 3  represents a partial section of the ankle  10  in a frontal plane. The tie-rods  35  and  36  may each comprise a cable crimped at its ends into sleeves. The tie-rod  35  comprises a first sleeve  50  secured to one of the pistons of the actuator  18 , a cable  51  and a second sleeve  52  secured to a sole  53  belonging to the foot  11 . Similarly, the tie-rod  36  comprises a first sleeve  54  secured to one of the pistons of the actuator  18 , a cable  55  and a second sleeve  56  secured to the sole  53 . When the cylinders of the actuator  18  pull on one of the tie-rods  35  or  36 , relaxing the force on the other, the sole  53  rotates about the axis  19  perpendicular to  FIG. 3 . Similarly, the tie-rods  33  and  34  connected to the actuator  16  may each comprise a cable. The use of a cable allows the tie-rod concerned to follow the rotary movement of the foot by deforming. The use of cables also provides a certain longitudinal flexibility of the tie-rods allowing the ankle  10  to cushion possible vertical impacts due to the placing of the foot  11  on the ground with each step. It is possible to provide a turnbuckle making it possible to adjust its length. 
     The joint  13  allowing the foot  11  to rotate on the two axes of rotation  17  and  19  comprises a cross-piece  60  that can rotate about the axis  17  relative to the leg  12  and about the axis  19  relative to the foot  11 . More precisely, the cross-piece  60  rotates about the axis  17  relative to a housing  61  of the actuators  16  and  18  in which the chambers of the cylinders, notably the cylinders  37  and  38 , are made. The housing  61  is secured to the rods  23 ,  24  and  25 . Two bearings  62  and  63  placed between two ends of the cross-piece  60  and the housing  61  guide the rotation of the cross-piece  60  about the axis  17 . 
     Moreover, the cross-piece  60  rotates about the axis  19  relative to the two uprights  64  and  65  of the foot  11 . The uprights  64  and  65  are secured to the sole  53 . The upright  64  stands at an anterior and upper portion of the foot called a toe-kick and the upright  65  stands at the heel. A bearing  66  guides the rotation of the cross-piece  60  about the axis  19  relative to the upright  64  and a bearing  67  guides the rotation of the cross-piece  60  about the axis  19  relative to the upright  65 . 
     The ankle  10  advantageously comprises means for measuring the angular range of movement of the foot about its two axes of rotation  17  and  19  relative to the leg  12 . Accordingly use is made, for example, of two potentiometers  68  and  69  measuring the angular range of movement of the cross-piece  60  at the bearings, respectively  62  and  67 . 
     The cross-piece  60  comprises two branches  70  and  71 , the branch  70  extending along the axis  17  between the bearings  62  and  63  and the branch  71  extending along the axis  19  between the bearings  66  and  67 . The tie-rods  35  and  36  pass through the cross-piece  60  at the branch  70  and the tie-rods  33  and  34  pass through the cross-piece  60  at the branch  71 . To allow the traversing of the cross-piece  60 , each branch  70  and  71  comprises two bushes,  72  and  73 , for the branch  70 , and  74  and  75  for the branch  71 . Each tie-rod can slide in a bush when the cylinders are actuated. In order to allow the cross-piece  60  to rotate about its two axes  17  and  19 , the walls of the various bushes advantageously have the shape of a torus portion substantially tangential with the tie-rod which passes through the corresponding bush. The shape like a portion of a torus also allows the cables  51  and  55  of the tie-rods  35  and  36  to rest on the walls of the corresponding bushes when the foot  11  rotates. 
     Advantageously, one of the actuators allowing the rotation of the foot about the frontal axis and the sagittal axis is operated by means of a cable and of an angle transmission. This angle transmission is mainly useful for the rotation about the sagittal axis  17  in order to increase the maximum angular range of movement possible for the joint  13  about this axis, and the torque transmitted by the corresponding tie-rod. 
     Accordingly, the foot comprises a circular plate portion  80  with an axis  81  parallel to the axis  17  and situated beneath the latter. The circular plate  80  is secured to the foot  11 . The tie-rods  33  and  34  roll on the periphery of the circular plate  80  and the sleeve attached to the foot  11 , belonging to each tie-rod  33  and  34 , extends parallel to the axis  19  in order to be attached in each of the uprights, respectively  65  and  64 .  FIG. 3  shows two grooves  82  and  83  made in the circular plate  80 . Each of the grooves  82  and  83  makes it possible to guide one of the tie-rods respectively  33  and  34 . 
     The actuator  14  allowing the foot  11  to rotate about the vertical axis  15  is clearly visible in  FIGS. 4, 5 and 6 . The actuator  14  is formed of a rotary hydraulic cylinder comprising the stator  30  and the rotor  32 . The stator  32  comprises a liner  90  placed between two closure parts  91  and  92 . The liner  90 , the closure parts  91  and  92  and the bottom portion  31  of the knee are held together for example by means of screws  93 . 
     The rotor  32  comprises a butterfly element  94  and an output shaft  95  secured together. The output shaft  95  is for example attached to the butterfly element  94  by means of a thread  96  placed in a bore  97  of the butterfly element  94 . The bore  97  extends along the axis  15 . The rods  23 ,  24  and  25  are secured to the output shaft  95 . Seals  100 ,  101 ,  102  and  103 , for example O-rings, provide the seal between the rotor  32  and the stator  30 . 
       FIG. 5  is a view in section through a plane  105  perpendicular to the axis  15 . Four chambers  106 ,  107 ,  108  and  109  are arranged between the butterfly element  94  and the liner  90 . The chambers  106  and  107  communicate by means of a radial channel  110  extending in the plane of  FIG. 5  while passing through the butterfly element  94  in order to emerge into an annular groove  111  carved out of the output shaft  95 . Similarly the chambers  108  and  109  communicate by means of a radial channel, not shown, and emerge into a groove  112 . This second radial channel and the groove  112  are made in a plane parallel to the plane  105 . O-rings  113 ,  114  and  115  seal the grooves  111  and  112 . A pressure difference of a hydraulic fluid between the two pairs of chambers, respectively  106  and  107 ,  108  and  109 , makes it possible to rotate the rotary hydraulic cylinder. 
     In  FIG. 5 , the butterfly element  94  is shown in the middle position allowing a range of movement of approximately +/−20° about the axis  15  relative to this position. It is of course possible to increase the angular dimensions of the chambers  106 ,  107 ,  108  and  109  to obtain a greater range of movement. For example, in a configuration with four chambers, it is possible to obtain a range of movement of +/−40° about the axis  15 . If, on the other hand, a smaller range of movement is sufficient, it will be possible to increase the number of chambers in order to increase the torque of the rotary cylinder or to reduce its radial dimensions while retaining the same torque. 
     The butterfly element  94  can rest between two flat surfaces  116  and  117  of the closure parts  91  and  92 , surfaces perpendicular to the axis  15 . Advantageously, the rotary cylinder comprises a hydrostatic film placed between the rotor  32  and the stator  30  in a plane perpendicular to the vertical axis of rotation  15 . More precisely, the hydrostatic film is established between the flat surfaces  116  and  117  and the surfaces facing the butterfly element  94 . The hydrostatic film is supplied by annular grooves  118  and  119  made in the butterfly element  94  and emerging facing the flat surfaces  116  and  117 . The annular grooves  118  and  119  have for example a depth of the order of 0.5 mm. The hydrostatic film is limited by the seals  102  and  103  on the one hand, and  100  and  101  on the other hand. The hydrostatic film makes it possible to limit the friction between the rotor  32  and the stator  30 . It also makes it possible to cushion possible vertical impacts that the foot  11  could register when the robot walks. 
     The rotary cylinder may also comprise a ring  120  in the form of a flat shim with an axis  15  placed between the closure part  92  and the output shaft  95  in order to limit the friction between these two parts. The ring  120  is made of a material having a low coefficient of friction with respect to the closure part  92  and the output shaft  95 . 
       FIG. 6  shows the rotary cylinder in section in a vertical plane perpendicular to that of  FIG. 4 . The rotary cylinder comprises couplings  122  and  123  making it possible to supply the chambers  107  and  109  and the hydrostatic films with hydraulic fluid. Outlets  124  and  125  of the couplings are advantageously oriented parallel to the axis  15  in order to limit the radial space requirement of the leg  12 . 
       FIGS. 7 and 8  represent a wrist  130  according to the invention.  FIG. 7  is a view in perspective of the wrist  130  and  FIG. 8  is a view in section. The wrist  130  connects a forearm  131  of the robot and a hand  132  of the robot. In this wrist, there are actuators  14 ,  16  and  18  each allowing the hand  132  to rotate about an axis, respectively  15 ,  17  and  19 , relative to the forearm  131 . The actuator  14  acts in series on the assembly formed by the two actuators  16  and  18  acting in parallel on the hand. The actuator  14  is placed upstream of the two actuators  16  and  18  relative to the forearm  131 . 
       FIG. 8  represents the wrist  130  in section in a plane containing the axes  15  and  19 . In this view, there are the zones  20  and  22  containing the actuator  14  for the zone  20  and the actuators  16  and  18  for the zone  22 . The zone  21  placed between the zones  20  and  22  is not shown, but the latter can be produced in order to place therein, for example, one or more hydraulic pumps making it possible to supply the actuators  14 ,  16  and  18 . 
     As for the ankle, the actuator  14  of the wrist  130  is for example a rotary hydraulic motor. The actuators  16  and  18  are advantageously linear and act on the hand  132  in parallel by means of tie-rods. Shown in  FIG. 8  are the tie-rods  33 ,  34  and  36 . The description of the actuators  14 ,  16  and  18  made for the ankle can be completely repeated for the wrist  130 . The connection between the actuators  16  and  18  and the hand  132  can be identical to that connecting the foot. It is possible notably to find therein an angle transmission made by means of the circular plate  80  for one of the two actuators  16  or  18  making it possible to increase the angular range of movement of the hand  132  on one of its axes of rotation. 
       FIGS. 9 and 10  represent a neck  140  according to the invention.  FIG. 9  is a view in perspective of the neck  140  and  FIG. 10  is a view in section. The neck  140  connects a body  141  of the robot and a head  142  of the robot. In this neck  140  there are the actuators  14 ,  16  and  18  each allowing the head  142  to rotate about an axis, relative to the body  141 . The axis  15  of the actuator  14  is a vertical axis of the body  141 . The actuator  14  acts in series on the assembly formed by the two actuators  16  and  18  acting in parallel on the head  142 . The actuator  14  is placed upstream of the two actuators  16  and  18  relative to the body  141 . 
       FIG. 10  represents the wrist  130  in section in a plane containing the axis  15 . In this view, there are the zones  20  and  22  containing the actuator  14  for the zone  20  and the actuators  16  and  18  for the zone  22 . The zone  21  placed between the zones  20  and  22  is not shown, but the latter can be produced in order to place therein, for example, one or more hydraulic pumps making it possible to supply the actuators  14 ,  16  and  18 . For the neck, it is advantageous to dispense with the zone  21  in order to reduce the inertia of the head when it rotates about the axis  15 . 
     As for the ankle, the actuator  14  of the neck is for example a rotary hydraulic motor. The actuators  16  and  18  are advantageously linear and act on the head  142  in parallel by means of tie-rods.  FIG. 10  shows the tie-rods  33 ,  34  and  36 . The description of the actuators  14 ,  16  and  18  made for the ankle can be completely repeated for the neck  140 . The connection between the actuators  16  and  18  and the head  142  can be identical to that connecting the foot. However, in the neck  140 , there is no angle transmission for one of the two actuators  16  or  18 . Specifically, the angular range of movement about the axes  17  and  19  is less than for other joints such as the ankle and the wrist.