Robotic ankle
An ankle prosthesis is disclosed having an actuation system so as to act as a brake, modulated by motor means, proportional to the load stressing the prosthesis. The prosthesis is advantageously capable of reducing the work necessary to lift the prosthesis while maintaining an anthropometric encumbrance.
1 . An ankle prosthesis comprising:
a main body, having a foot portion configured to rest on a walking surface;
stump supporting means, configured to couple with a leg prosthetic element;
linear actuation means, comprising a coupling between a screw element and a nut screw element having a friction coefficient lower than 0.16,
wherein said stump supporting means, said screw element and said nut screw element are constrained to said main body according to a substantially four-bar linkage configuration, so that a relative rotation between said supporting means and said main body is allowed and so that said actuation means is configured to act as damping element along a damping direction (S) and is movable between an advanced position (P sup ) and a rearward position (P inf ) with respect to said damping direction (S), wherein said foot portion comprises a first and a second contact position during a resting phase on the walking surface, wherein to said first and second contact position corresponds a respective opposite movement of said actuation means between said advanced position (P sup ) and said rearward position (P inf ) during a damping condition of the loads transferred on said main body by the leg element.
2 . The ankle prosthesis according to claim 1 , wherein said actuation means is movable in approach to said rearward position (P inf ) in said first contact position and is movable in approach to said advanced position (P sup ) in said second contact position.
3 . The ankle prosthesis according to claim 1 , wherein said damping direction (S) is parallel to the axis of said screw element.
4 . The ankle prosthesis according to claim 1 , wherein the efficiency of the coupling between said screw element and said nut screw element is between 45% and 55%.
5 . The ankle prosthesis according to claim 1 , wherein said screw element has a helix angle of between 3° and 11°.
6 . The ankle prosthesis according to claim 1 , wherein said screw element is treated with a treatment selected from the group consisting of a diamond like carbon (DLC) treatment, a polytetrafluoroethylene treatment, a tungsten disulfide treatment and a molybdenum disulfide treatment.
7 . The ankle prosthesis according to claim 1 , wherein said screw element is made of steel and said nut screw element is made of a material selected from the group consisting of steel, bronze, brass and a reinforced polymer.
8 . The ankle prosthesis according to claim 1 , wherein a first arm of said four-bar linkage has a variable extension according to the rotation of said supporting element, said extension being variable between said advanced position (P sup ) and said rearward position (P inf ).
9 . The ankle prosthesis according to claim 1 , wherein a second arm of said four-bar linkage connects said supporting element and said nut screw element to each other.
10 . The ankle prosthesis according to claim 9 , wherein said second arm has a length between 40 mm and 60 mm.
11 . The ankle prosthesis according to claim 1 , wherein said supporting element and said main body are coupled at a joint lying on an axis, wherein said axis orthogonally intercepts a direction of development of said foot portion, when resting on the walking surface, at one third of its extension with respect to a heel terminal end.
12 . The ankle prosthesis according to claim 1 , wherein said actuation means comprises a planetary reduction gear.
13 . The ankle prosthesis according to claim 1 , further comprising sensor means configured to actuate said actuation means in function of a detection of a bending of said main body.
14 . The ankle prosthesis according to claim 1 , wherein said main body comprises an energy-returning carbon fibre foot structure.