Semi-active ankle and foot prosthesis powered by a lockable series-elastic actuator
A semi-powered foot and ankle prosthesis ( 100 ) has a foot member ( 128 ) coupled to the ankle frame ( 112 ) and movable with respect to the ankle frame ( 112 ). A linear actuator ( 144 ) is coupled to and between the ankle frame ( 112 ) and the foot member ( 128 ) to move the foot member ( 128 ) with respect to the ankle frame ( 112 ). The linear actuator ( 144 ) has a drive motor ( 150 ). A locking mechanism ( 104 ) selectively engages the drive motor ( 150 ) to selectively lock movement of the drive motor ( 150 ) to resist a force on the foot member ( 128 ) from backdriving the linear actuator ( 144 ).
1. A semi-powered foot and ankle prosthesis, comprising:
an ankle frame configured to be coupled to a connector and the ankle frame having a first joint;
a foot member coupled to the ankle frame and movable with respect to the ankle frame, the foot member comprising a toe frame spaced-apart from and movable with respect to the ankle frame, and the toe frame having a second joint;
a linear actuator coupled to and between the ankle frame and the foot member, and coupled to and between the first and second joints, and configured to move the foot member with respect to the ankle frame, and the linear actuator having a drive motor;
a locking mechanism selectively engaging the drive motor and configured to selectively lock movement of the drive motor to resist a force on the foot member from backdriving the linear actuator;
a foot shell pivotally coupled to and between an ankle joint of the ankle frame and a toe joint of the toe frame, the foot shell forming a rigid link between the ankle joint and the toe joint, the foot shell having a hollow therein; and
at least one of:
the linear actuator and the locking mechanism being at least partially located in the hollow of the foot shell; and
the drive motor being at least partially located in the hollow of the foot shell.
2. The foot and ankle prosthesis of claim 1 , further comprising:
at least two modes of operation, including:
an active mode in which the drive motor is powered, and the locking mechanism is unlocked, and associated with lower torque ambulation activities; and
a passive mode in which the drive motor is unpowered, and the locking mechanism is locked, and associated with higher torque ambulation activities.
3. The foot and ankle prosthesis of claim 1 , further comprising:
a drive shaft having first and second ends extending from the drive motor;
a gearbox coupled to the first end of the drive shaft; and
the locking mechanism engaging the second end of the drive shaft.
4. The foot and ankle prosthesis of claim 1 , wherein the linear actuator comprises an integrated series elastic actuator, comprising:
a screw coupled to the drive motor to rotate the screw;
a nut engaged by the screw and with rotation of the screw moving the nut along the screw; and
a spring coupled to the nut with the screw and spring coupled in series.
5. The foot and ankle prosthesis of claim 4 , further comprising:
the drive motor having a drive shaft with opposite first and second ends;
the first end of the drive shaft being coupled to the screw; and
the second end of the drive shaft being coupled to the locking mechanism.
6. The foot and ankle prosthesis of claim 5 , further comprising:
a non-back-drivable gear box coupled between the first end of the drive shaft and the screw, the gear box having a gear reduction ratio configured to resist a force applied to the foot member from backdriving the linear actuator.
7. The foot and ankle prosthesis of claim 1 , wherein the locking mechanism further comprises:
a rotor coupled to a drive shaft of the motor; and
at least one brake pad positioned proximate the rotor and selectively abutting the rotor.
8. The foot and ankle prosthesis of claim 7 , wherein the locking mechanism further comprises:
a brake motor; and
a non-back-drivable gear box coupled between the brake motor and the at least one brake pad, the gear box having a worm driven by the brake motor and a worm wheel engaging the worm.
9. The foot and ankle prosthesis of claim 7 , wherein the locking mechanism further comprises:
the at least one brake pad including a pair of brake pads, including:
a first movable brake pad on a first side of the rotor; and
a second stationary brake pad on a second side of the rotor and carried by a frame of the locking mechanism.
10. The foot and ankle prosthesis of claim 7 , wherein the locking mechanism further comprises:
the rotor being slidably positioned on the drive shaft; and
the rotor being keyed radially to the drive shaft with the rotor and the drive shaft rotating together.
11. The foot and ankle prosthesis of claim 7 , wherein the locking mechanism further comprises:
a cam engaging the at least one brake pad and having a lobe with a greater radial length configured to press the brake pad towards the rotor, and a heel with a lesser radial length configured to release the brake pad from the rotor; and
a brake motor coupled to and selectively turning the cam.
12. The foot and ankle prosthesis of claim 11 , wherein the cam has multiple positions with respect to the at least one brake pad and the rotor configured to apply a damping torque to the drive motor.
13. The foot and ankle prosthesis of claim 11 , wherein the locking mechanism further comprises:
a resilient pad positioned between the cam and the at least one brake pad.
14. The foot and ankle prosthesis of claim 11 , wherein the locking mechanism further comprises:
the brake motor and the drive motor positioned side-by-side and proximate one another.
15. The foot and ankle prosthesis of claim 11 , further comprising:
the ankle frame having an ankle joint;
the drive motor and the brake motor being at least partially located in the hollow of the foot shell; and
the cam and the at least one brake pad being located in the hollow of the foot shell.
16. The foot and ankle prosthesis of claim 1 , wherein the locking mechanism engages the drive motor under speed and torque; and wherein the locking mechanism engages the drive motor under load with the foot and ankle prosthesis transitioning between active and passive modes without waiting for the locking mechanism to lock.
17. The foot and ankle prosthesis of claim 1 , wherein the locking mechanism engages the drive motor in both directions of the linear actuator, and in dorsiflexion and plantarflexion of the foot and ankle prosthesis.
18. The foot and ankle prosthesis of claim 1 , wherein the locking mechanism remains in either a locked or unlocked position without power.
19. The foot and ankle prosthesis of claim 1 , wherein the locking mechanism applies a variable range of torque to a drive shaft of the drive motor.
20. The foot and ankle prosthesis of claim 1 , wherein:
the locking mechanism engages the drive motor in both directions of the linear actuator, and in dorsiflexion and plantarflexion of the foot and ankle prosthesis;
the locking mechanism remains in either a locked or unlocked position without power; and
the locking mechanism applies a variable range of torque to a drive shaft of the drive motor.
21. A semi-powered foot and ankle prosthesis, comprising:
an ankle frame configured to be coupled to a connector;
a foot member coupled to the ankle frame and movable with respect to the frame;
a linear actuator coupled to and between the ankle frame and the foot member, and configured to move the foot member with respect to the ankle frame, and the linear actuator having a drive motor; and
a locking mechanism selectively engaging the drive motor and configured to selectively lock movement of the drive motor to resist a force on the foot member from backdriving the linear actuator, the locking mechanism comprising:
a rotor coupled to a drive shaft of the motor;
at least one brake pad positioned proximate the rotor and selectively abutting the rotor;
a cam engaging the at least one brake pad and having a lobe with a greater radial length configured to press the brake pad towards the rotor, and a heel with a lesser radial length configured to release the brake pad from the rotor; and
a brake motor coupled to and selectively turning the cam.
22. A semi-powered foot and ankle prosthesis, comprising:
an ankle frame configured to be coupled to a connector;
a foot shell pivotally coupled to the ankle frame;
a toe frame pivotally coupled to the foot shell opposite the ankle frame;
a spring coupled between the ankle frame and the toe frame;
a prismatic joint coupled between the ankle frame and the toe frame;
the prismatic joint and the spring being coupled in series;
the prismatic joint comprising a nut coupled to the spring and a screw extending between the ankle frame and the nut;
a drive motor coupled to the screw and configured to rotate the screw relative to the nut;
a locking mechanism coupled to the drive motor and configured to selectively lock movement of the drive motor to resist a force on the foot and ankle prosthesis from backdriving the linear actuator, the locking mechanism comprising:
a rotor rotationally coupled to the screw and an output of the drive motor;
a brake pad proximate the rotor and selectively engagable with the rotor to resist rotation of the rotor and thus the screw;
a cam engaging a piston and having a lobe with a greater radial length configured to press the brake pad towards the rotor, and a heel with a lesser radial length configured to release the brake pad from the rotor; and
a brake motor coupled to and selectively turning the cam.
23. A semi-powered foot and ankle prosthesis, comprising:
an ankle frame configured to be coupled to a connector;
a foot member coupled to the ankle frame and movable with respect to the ankle frame;
a linear actuator coupled to and between the ankle frame and the foot member, and configured to move the foot member with respect to the ankle frame, and the linear actuator having a drive motor; and
a locking mechanism selectively engaging the drive motor and configured to selectively lock movement of the drive motor to resist a force on the foot member from backdriving the linear actuator, wherein the locking mechanism further comprises:
a rotor coupled to a drive shaft of the motor; and
at least one brake pad positioned proximate the rotor and selectively abutting the rotor.
24. The foot and ankle prosthesis of claim 23 , further comprising:
the ankle frame having a first joint;
the foot member comprising a toe frame spaced-apart from and movable with respect to the ankle frame, and the toe frame having a second joint;
the linear actuator coupled to and between the first and second joints;
a foot shell pivotally coupled to and between an ankle joint of the ankle frame and a toe joint of the toe frame;
the foot shell forming a rigid link between the ankle joint and the toe joint;
the foot shell having a hollow therein; and
at least one of:
the linear actuator and the locking mechanism being at least partially located in the hollow of the foot shell; and
the drive motor being at least partially located in the hollow of the foot shell.
25. The foot and ankle prosthesis of claim 23 , further comprising:
at least two modes of operation, including:
an active mode in which the drive motor is powered, and the locking mechanism is unlocked, and associated with lower torque ambulation activities; and
a passive mode in which the drive motor is unpowered, and the locking mechanism is locked, and associated with higher torque ambulation activities.
26. The foot and ankle prosthesis of claim 23 , wherein the locking mechanism further comprises one of:
a brake motor; and a non-back-drivable gear box coupled between the brake motor and the at least one brake pad, the gear box having a worm driven by the brake motor and a worm wheel engaging the worm;
the at least one brake pad including a pair of brake pads, including: a first movable brake pad on a first side of the rotor, and a second stationary brake pad on a second side of the rotor and carried by a frame of the locking mechanism;
the rotor being slidably positioned on the drive shaft and the rotor being keyed radially to the drive shaft with the rotor and the drive shaft rotating together; or
a cam engaging the at least one brake pad and having a lobe with a greater radial length configured to press the brake pad towards the rotor, and a heel with a lesser radial length configured to release the brake pad from the rotor, and a brake motor coupled to and selectively turning the cam.
27. The foot and ankle prosthesis of claim 23 , wherein the locking mechanism engages the drive motor under speed and torque; and wherein the locking mechanism engages the drive motor under load with the foot and ankle prosthesis transitioning between active and passive modes without waiting for the locking mechanism to lock.