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.