Abstract:
A foot for a humanoid robot includes a sole having an upright secured thereto, toes, a motorized connection, independent of the ankle, in rotation between the sole and the toes, wherein the toes are able to move on an angular travel about an axis of the connection, an actuator formed of a linear jack coupled to the upright and the toes, allowing the connection to be motorized, and means for controlling the actuator in a standalone manner. The foot is of particular utility in the production of humanoid robots coming as close as possible to the human morphology.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International patent application PCT/EP2009/056965, filed on Jun. 5, 2009, which claims priority to foreign French patent application No. FR 08 53713, filed on Jun. 5, 2008, the disclosures of which are incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a foot and a humanoid robot using the foot. The invention is of particular utility in the production of humanoid robots coming as close as possible to the human morphology. 
     BACKGROUND OF THE INVENTION 
     A mathematical model describing this morphology 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 parametrically, with respect to given human height and weight, the dimensions of all the parts of the body. Usually, the foot is described as having a sole and toes connected together by means of a joint with a degree of freedom in rotation in a sagittal plane of the foot. 
     For example, for a 14-year-old adolescent, 1.6 m tall and weighing 50 kg, the foot consists of an assembly of rectangular parallelepipeds. The total length of the foot is 243 mm, the width is 80 mm, the height of the heel is 62 mm and the distance between the back of the foot and the connection of the toes is 207 mm. 
     Currently, many humanoid robots have been developed, but none of them complies with the Hanavan model. In addition, the known robots have broad and solid feet, either with no mobility or with a passive mobility at the toes. Such feet degrade the fluidity of the gait of the robot and distance it substantially from the way of walking of the human being. 
     A dynamic calculation shows that to achieve a walk at a speed of 1.2 m/s, still for a robot of 1.6 m and 50 kg, the connection of the foot between sole and toes requires a torque of the order of 20 N·m, with a power of 30 W, and a range of movement from 0° to +60°. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved match between the production of a robot and the human anatomy, for example modeled on the Hanavan model. The invention further provides improved fluidity of the movements of the robot when it walks but without reproducing a complex modeling of the human foot. 
     The invention includes a foot of which the toes are able to move relative to the sole. The invention also includes application of a torque to the connection between the toes and the sole, without this torque being dependent on the angular travel of the toes in their rotary movements. Specifically, applying such a torque to the connection between the toes and the sole improves the propulsive phase of the foot of the robot in order to come closer to that provided by the human foot, in order to improve the fluidity of the gait of the robot. 
     Accordingly, the invention includes a foot for a humanoid robot, that can be connected to a leg by means of an ankle, the foot including:
         a sole,   toes,   a motorized connection, independent of the ankle, in rotation between the sole and the toes, the toes being able to move on an angular travel about an axis of the connection,   an actuator allowing the connection to be motorized, and   and means for controlling the actuator in a standalone manner.       

     The invention further includes a humanoid robot having at least one foot described herein. 
     Attempts have been made to apply to the toes a torque dependent on their angular travel. This torque is applied by means of a spring such as for example a torsion spring placed in the connection between the toes and the sole. It has been found that such a torque did not give significant results with respect to improving the propulsive phase of the foot. 
    
    
     
       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, which description being illustrated by the appended drawing in which: 
         FIG. 1  represents in perspective a foot according to the invention; 
         FIG. 2  represents the foot in section in a sagittal plane; 
         FIG. 3  represents the foot  10  in a top view; 
         FIG. 4  represents the articulation of a jack relative to a sole; 
         FIG. 5  represents the articulation of the toes relative to the sole; 
         FIG. 6  represents the articulation of the toes relative to the jack. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of clarity, the same elements will bear the same reference numbers in the various figures. 
       FIG. 1  represents a foot  10  comprising a sole  11  and toes  12  articulated relative to the sole  11  by means of a connection  13  having a degree of freedom in rotation in a sagittal plane of the foot  10  about an axis  14 . In the example shown, the toes  12  are secured together and are made of a one-piece mechanical part. The toes have two ends  15  and  16 . The end  15  is situated on the axis  14  and the end  16  forms the tip of the foot  10 . The connection  13  allows the toes to move with an angular range of movement of approximately 60° about the axis  14 .  FIG. 1  shows the toes  12  in a first extreme position in their rotary movement about the axis  14 . In this position, the toes  12  are in line with the sole  11 . In other words, the sole extends mainly on a plane  17  and an axis  18  passing through the two ends  15  and  16  is situated in the plane  17  of the sole  11 .  FIG. 2  shows the foot  10  in section in a sagittal plane perpendicular to the plane  17  and  FIG. 3  shows the foot  10  in a top view. 
     A second extreme position of the toes  12  is reached when the toes  12  are raised to the maximum, in other words when the axis  18  containing the two ends  15  and  16  makes an angle of 60° with the plane  17  of the sole  11 . 
     When a robot walks fitted with feet  10  comprising articulated toes  12 , it is possible to use a damper as an actuator. Such an actuator applies to the toes  12  a torque which does not depend on the angular travel of the toes  12  but on their angular speed. Usually, the greater the angular speed, the greater the torque applied by the damper. The use of a damper makes it possible to vary the torque applied to the connection  13  as a function of the speed at which the robot moves when walking. When the robot runs, a damper makes it possible to apply to the connection a greater torque than when it walks. It is of course possible to supplement the torque exerted by the damper with a torque purely proportional to the travel. 
     The actuator can also be a motor in order to apply a driving torque to the connection  13 . This torque makes it possible to move the toes  12  from the second extreme position to the first extreme position. This torque, applied to the toes  12 , improves the propulsion of the robot generated by the foot  10  and reduces the energy necessary for walking by approximately 30%. 
     More generally, the foot comprises means for controlling the actuator  19  in a standalone manner, that is to say independently of any other joint of the robot. For example, the movements of the connection  13  are independent of the movements of the ankle of the robot or of the walking phase of the robot. The means for controlling the actuator  19  make it possible to choose a state from: 
     a complete rigidity of the connection  13 , 
     a restoring torque that is a function of the angular travel of the connection  13 , 
     a damping of the rotation of the connection  13 , 
     an addition of power during the rotation of the connection  13 . 
     It is possible to achieve this motorization by means of a rotary motor acting between the sole  11  and the toes  12  at the connection  13 . This type of motor might depart from the space requirement defined by the Hanavan model. Another alternative consists in producing this motorization by means of a linear jack  19  resting at one of its ends  20  on the toes  12  at their end  16  and at another of its ends  21  on an upright  22  secured to the sole  11 . The upright  22  stands perpendicular to the plane  17  of the sole  11 . 
     The bearing surface of the jack  19  on the upright  22  is situated above a plane  17  in which the sole  11  extends mainly so as to keep convergent the axis  23  of the jack  19  and the axis  18  linking the connection  13  and the bearing surface of the jack  19  on the toes  12 . In other words, the end  21  of the jack  19  is coupled to the upright  22  in its top portion above the plane  17  in order to prevent the axis  18  being in line with an axis  23  of the jack, the axis joining the ends  20 ,  21  irrespective of the position of the toes  12  when they move. Such an alignment would prevent the application of a torque to the connection  13 . The height of the upright  22  must nevertheless be limited in order to reduce the volume of the foot  10 . 
     The inclination of the jack  19  relative to the plane of the sole  11  also allows an angular range of movement of the toes  12  that can extend on either side of the plane of the sole  11 . More precisely, the angular range of movement mainly makes it possible to raise the toes  12  relative to the plane of the sole  11 . The inclination of the jack  19  also makes it possible to slightly lower the toes  12  below the plane of the sole  11 . Even without lowering the toes  12 , this inclination of the jack  19  makes it possible to increase the torque applied by the jack  19  to the toes  12 . This range of movement makes it possible to improve the propulsive phase of the gait of the robot. 
     The sole  11  extends from a heel  24  to the connection  13  situated at the front of the sole  11 . The upright  22  is attached toward the front of the sole  11 , thus freeing up the rear of the sole  11  making it possible to attach thereto an ankle of the robot, not shown. 
     The jack  19  may be electric, it may also be actuated by a hydraulic fluid. Accordingly, the jack  19  comprises a piston  30  that can move in a cylinder  31  on the axis  23 . The piston  30  is secured to a rod  32  attached to a yoke  33  forming the end  20  of the jack  19 . Inside the cylinder  31 , the piston  30  delimits two chambers  34  and  35  which the hydraulic fluid can enter under pressure via connectors, respectively  36  and  37 . A difference in pressure between the chambers  34  and  35  makes it possible to move the rod  32  so as to move the toes  12 . Seals are used to seal the chambers  34  and  35 . The toes  12  are raised or lowered as a function of the sign of the difference in pressure between the chambers  34  and  35 . The hydraulic fluid supplying the two chambers  34  and  35  may be supplied by a pump on board the robot. When the robot comprises several actuators, notably for its two feet, it is possible to provide a dedicated pump for each actuator. 
     In the variant in which the actuator is reduced to a damper, it is possible to use a damper similar to the jack  19  without external hydraulic supply. The two chambers  34  and  35  are then connected via a calibrated channel allowing the fluid to pass from one chamber to the other. It is possible to place a spring in one of the chambers  34  or  35  in order to bring the toes  12  into line with the sole  11 . The damping function may also be achieved by calibrating a flow rate of fluid passing from one chamber to the other through the pump. In this case, the control of the pump makes it possible to use the jack  19  either as a motor or as a damper as required. It will therefore advantageously be possible to vary the damping parameters for example while the robot is walking. In a more general manner, the same actuator may have a damping function or a motor function, these two functions being able to be combined. 
     In order to ensure an anthropomorphic gait, the thrust of the jack  19  in extension is crucial. It is possible to achieve the motorization with the aid of a single-acting jack in which only the chamber  34  is capable of being supplied with pressurized fluid. In order to ensure the return movement of the jack, a spring is then placed in the chamber  35  which is kept at atmospheric pressure. 
     The ends  20  and  21  of the jack  19  are articulated respectively relative to the toes  12  and relative to the upright  22 . Each joint has a degree of freedom in rotation about axes parallel to the axis  14 . 
       FIG. 4  represents the joint of the jack  19  relative to the upright  22 . This joint comprises a shaft  40  secured to a fork  41  of the jack  19 . The fork  41  forms the end  21  of the jack  19 . The shaft  40  extends on an axis  42  parallel to the axis  14 . The shaft  40  is attached to the fork  41  for example by means of screws  43 . The shaft  40  can pivot inside a bore  44  of axis  42  made inside the upright  22 . It is possible to place bearings  45  and  46  between the bore  44  and the shaft  40  in order to reduce the friction when the shaft  40  rotates in the bore  44 . The fork  41  prevents any translation of the jack  19  relative to the upright  11  on the axis  42 . 
       FIG. 5  represents the joint of the toes  12  relative to the sole  11 . This articulation, forming the connection  13 , can be produced like the joint of the jack  19  on the upright  22 . The sole  11  comprises a fork  50 . A shaft  51  of axis  14  is attached to a yoke  52  belonging to the toes  12  by means of screws  53 . The shaft  51  can slide in bores  54  and  55  of the fork  50 . Bearings  56  and  57  can be inserted between the shaft  51  and the bores, respectively  54  and  55 . 
     To measure the angular position of the toes  12  about the axis  14 , it is possible to place at the bearing  57  a potentiometer  58  delivering an item of electrical information as a function of the angular position of the shaft  51  secured to the toes  12  relative to the sole  11 . This information can be used to lock in the control of the jack  19 . 
       FIG. 6  shows the joint of the toes  12  relative to the jack  19 . This joint can also be produced like the two previous articulations. The end  16  of the toes  12  has the shape of a fork in which a shaft  60  of axis  61  is attached by means of screws  62  and  63 . The shaft  60  can pivot in a bore  64  of the yoke  33 . It is possible to place bearings  65  and  66  between the bore  64  and the shaft  60  to reduce the friction when the shaft  60  rotates in the bore  64 .