Neural efferent and afferent control of spring equilibrium, damping, and power in backdrivable and non-backdrivable series-elastic actuators comprising variable series stiffness mechanisms
A prosthetic device includes a frame defining an output axis, a cantilever beam spring attached to the frame, a moment arm attached to the spring, and a rigid output arm coupled to the frame and rotatable about the output axis. A connector assembly is configured to apply a moment to the cantilever beam spring via the moment arm while applying a torque about the output axis via the output arm. An ankle-foot device includes foot and ankle members connected for two-degree of freedom movement relative to one another, allowing for rotation about an ankle axis and rotation about a subtalar axis. Two linear actuators, each coupled to corresponding series elastic element, link the foot and ankle members. Driving the actuators in the same direction causes rotation about the ankle axis and driving the actuators in opposing directions causes rotation about the subtalar axis. A processor receives sensory information from a sensor and drives the actuators to control an equilibrium position of the series elastic elements. A rotary actuator for a prosthetic device includes a housing frame, a motor mounted within the housing frame, and a cycloidal drive coupled to the motor within the housing frame. A torsion shaft can extend through the actuator to an output and provide a series elastic element.
1. A prosthetic device, comprising:
a frame defining an output axis;
a cantilever beam spring having a first end attached to the frame and a second end;
a moment arm attached to the second end of the cantilever beam spring;
a rigid output arm coupled to the frame and rotatable about the output axis;
a connector assembly connecting the moment arm to the output arm, the connector assembly coupled to the moment arm by a moment pivot and coupled to the output arm by an output pivot located at a distance from the output axis, the connector assembly configured to apply a moment to the cantilever beam spring via the moment arm while applying a torque about the output axis via the output arm; and
a carriage translatable along a length of the cantilever beam spring, the carriage forming a structural pivot for dynamic control of deformation of the cantilever beam spring to provide for a variable spring stiffness.
2. The device of claim 1 , wherein the connector assembly is configured to vary the distance between the moment pivot and the output pivot.
3. The device of claim 1 , wherein the connector assembly is configured to set the distance between moment pivot and the output pivot at a fixed length.
4. The device of claim 1 , wherein the connector assembly comprises a linear actuator.
5. The device of claim 1 , wherein the connector assembly comprises a mechanical transformer that converts rotary motion into linear motion.
6. The device of claim 5 , wherein the mechanical transformer is backdriveable.
7. The device of claim 6 , wherein the mechanical transformer comprises a motor, a screw passing through the motor, and a nut rotatable about the screw, the motor configured to rotate the nut, rotation of the nut causing linear motion of the screw relative to the motor.
8. The device of claim 7 , wherein the linear motion of the screw creates load on the output arm and rotary motion of the output arm about the frame.
9. The device of claim 7 , wherein the motor includes a rotor and the nut is integrated into the rotor, rotation of the rotor causing the linear motion of the screw.
10. The device of claim 9 , wherein the motor includes a stator coupled to the moment pivot at the moment arm, and wherein an end of the screw is coupled via a push rod to the output pivot at the output arm.
11. The device of claim 10 , further comprising a load cell between the screw and the push rod, to measure load on the screw.
12. The device of claim 1 , further comprising a rotary encoder at the frame to measure rotation of the output arm about the frame.
13. The device of claim 5 , wherein the mechanical transformer is non-backdriveable.
14. The device of claim 13 , wherein the mechanical transformer comprises a screw and a nut configured to rotate about the screw, rotation of the nut causing linear motion of the screw.
15. The device of claim 14 , wherein the mechanical transformer further comprises a motor configured to provide rotation of the nut.
16. The device of claim 15 , wherein the rotation of the nut is by means of meshing gears, friction drive, or belt drive transforming motion of the motor to rotation of the nut.
17. The device of claim 1 , further comprising a rotatable beam screw that extends parallel to the cantilever beam spring and engages a nut coupled to the carriage, rotation of the beam screw causing linear motion of the carriage along a length of the cantilever beam spring.
18. The device of claim 17 , further comprising a drive motor for providing rotation of the beam screw.
19. The device of claim 1 , further comprising a carriage and a shock absorber that extends parallel to the cantilever beam spring and engages the carriage, the shock absorber providing linear motion of the carriage along a length of the cantilever beam spring.
20. The device of claim 1 , wherein the device is a prosthetic ankle device and the output arm engages a prosthetic foot.
21. The device of claim 1 , wherein the device is a prosthetic knee device and the output arm engages a prosthetic limb or a prosthetic socket.
22. The device of claim 1 , further comprising one or more support arms attached to the frame and supporting a base plate, wherein the base plate supports an attachment for a prosthetic limb or a prosthetic socket.
23. The device of claim 22 , further comprising a prosthetic socket attached at the base plate, the prosthetic socket including a battery mount fixture to secure a battery at the socket and an electronics mount fixture to secure electronic circuitry powered by the battery at the socket.
24. A prosthetic knee device, comprising:
a frame defining an output axis;
a cantilever beam spring having a first end attached to the frame and a second end;
a moment arm attached to the second end of the cantilever beam spring;
a rigid output arm coupled to the frame and rotatable about the output axis; and
connector assembly connecting the moment arm to the output arm, the connector assembly coupled to the moment arm by a moment pivot and coupled to the output arm by an output pivot located at a distance from the output axis connector assembly configured to apply a moment to the cantilever beam spring via the moment arm while applying a torque about the output axis via the output arm, the output arm engaging a prosthetic limb or a prosthetic socket.