Exoskeleton including a mechanical ankle link having two pivot axes

1. An exoskeleton comprising:

a foot structure comprising a support plane configured to receive a foot of a user,

a lower leg structure configured to receive a lower portion of a user's leg,

a mechanical knee link configured to connect the lower leg structure to an upper leg structure configured to receive an upper portion of a user's leg, the mechanical knee link having a pivot axis, and

a mechanical ankle link, connecting the foot structure to the lower leg structure, the mechanical ankle link comprising a first pivot link having a first pivot axis, said first pivot axis being substantially parallel to the pivot axis of the mechanical knee link,

the exoskeleton being characterized in that the mechanical ankle link further comprises a second pivot link having a second pivot axis, said second pivot axis extending in a plane perpendicular to the first pivot axis and forming with the support plane an angle comprised between 30° and 60° when the exoskeleton is standing and at rest.

2. The exoskeleton according to claim 1 , wherein the second pivot axis forms an angle comprised between 40° and 50° with the support plane when the exoskeleton is standing and at rest, preferably of the order of 45°.

3. The exoskeleton according to claim 1 or 2 , further comprising two actuators in parallel, fixed between the foot structure and the lower leg structure and configured to control an angular position of the foot structure about the first and the second pivot axis of the mechanical ankle link.

4. The exoskeleton according to claim 3 , wherein the actuators are fixed in parallel on both sides of the lower leg structure.

5. The exoskeleton according to claim 3 , wherein the actuators each comprise:

a linear actuator, mounted on the lower leg structure, and

a connecting rod, mounted, on the one hand, on the linear actuator and on the other hand on the foot structure using a pivot joint, so that a translation of the linear actuator causes a rotation of the connecting rod relative to the foot structure.

6. The exoskeleton according to claim 5 , wherein the linear actuators comprise a cylinder associated with a motor, preferably of the ball screw or screw-nut type.

7. The exoskeleton according to claim 6 , wherein the cylinder comprises a threaded rod driven in rotation by the motor and a nut fixed in rotation relative to the foot structure, the connecting rod comprising one end mounted on the nut so that a translation of the nut causes a translation of the end of the connecting rod.

8. The exoskeleton according to claim 7 , wherein each actuator further comprises at least one slide having a guide rail fixed to the lower leg structure, and a carriage, movable in translation along the guide rail, the nut being fixed to the carriage of the slide.

9. The exoskeleton according to claim 8 , wherein the carriage comprises a first slider and a second slider, mounted movable in translation on the guide rail of the slide and connected integrally by a connecting part, the nut and the connecting rod being fixed to the connecting part of the carriage.

10. The exoskeleton according to claim 7 , wherein a mechanical link between the nut and the connecting rod comprises a pivot link and a mechanical link between the connecting rod and the foot structure comprises a pivot joint.

11. The exoskeleton according to claim 10 , wherein the mechanical link between the nut and the connecting rod comprises a universal joint, or two pivot links of substantially perpendicular axis.

12. The exoskeleton according to claim 7 , wherein the cylinder further comprises a simple mechanical bearing interposed between an output of the motor and the threaded rod, said mechanical bearing having a misalignment comprised between five minutes of arc and fifteen minutes of arc, typically about ten minutes of arc.

13. The exoskeleton according to one of claim 1 , wherein:

the first pivot link is positioned on the foot structure so as to face a medial malleolus and a lateral malleolus of a user wearing the exoskeleton and/or

the second pivot link is positioned on the foot structure so as to face a heel or a user's Achilles tendon.

14. The exoskeleton according to one of claim 1 , wherein the first pivot axis and the pivot axis of the mechanical knee link form an angle comprised between 0° and about fifteen degrees, preferably between 6° and 10°, for example 8°.

15. The exoskeleton according to claim 1 , wherein the first pivot axis extends in a plane parallel to the ground when the exoskeleton is standing and at rest.

16. The exoskeleton according to claim 1 , further comprising an intermediate part which is mounted, on the one hand, on the foot structure being free to rotate relative to the foot structure about the second pivot axis, and on the other hand, pivotally mounted about the first pivot axis on the lower leg structure.

17. The exoskeleton according to claim 16 , wherein the intermediate part is mounted on the lower leg structure and on the foot structure with passive pivot links.

18. The exoskeleton according to claim 16 , further comprising a compression spring assembly, fixed, on the one hand, to the intermediate part and on the other hand, on the lower leg structure.

19. The exoskeleton according to claim 18 , wherein the spring assembly comprises a first elastically deformable member, the first member being connected, on the one hand, to the intermediate part, between the first and the second pivot link, by means of a fastening element, and on the other hand, to the lower leg structure, said first member being configured to apply a tensile force on the intermediate part.

20. The exoskeleton according to claim 19 , wherein the fastening element is flexible.

21. The exoskeleton according to claim 19 , wherein the spring assembly further comprises a substantially elongated hollow body having a first end and a second end opposite the first end, said hollow body being mounted in a housing formed in the lower leg structure, the first end of the hollow body being facing a bottom of the housing and the first member being mounted in the housing and compressed between the bottom of said housing and the second end of the hollow body.

22. The exoskeleton according to claim 21 , further comprising a second elastically deformable member, housed in the hollow body, the second member being fixed near the first end of the hollow body, the fastening element cooperating with the second member so that the second member is configured to tension the fastening element and the fastening element being housed in the hollow body and projecting from the first end of said hollow body and the bottom of the housing.

23. The exoskeleton according to claim 22 , wherein the first member and/or the second member comprises a compression spring.

24. The exoskeleton according to claim 23 , wherein the first member and the second member comprise a compression spring, the second member having a lower stiffness than the stiffness of the first member.

25. The exoskeleton according to one of claim 21 , wherein the fastening element has a thickened portion, housed in the hollow body and the second member comprises a locking part configured to form a stop for the thickened portion.

26. The exoskeleton according to claim 21 , wherein the fastening element further comprises a stopper fixed to the fastening element, and the hollow body further comprises a protrusion fixed to an inner wall of the hollow body and configured to cooperate with the stopper and form an obstacle for the stopper of the fastening element.

27. The exoskeleton according to claim 21 , wherein the hollow body further comprises a bolt, fixed near its second end, the first member abutting against said bolt.