Controlling torque in a prosthesis or orthosis based on a deflection of series elastic element

Abstract

In some embodiments of a prosthetic or orthotic ankle/foot, a prediction is made of what the walking speed will be during an upcoming step. When the predicted walking speed is slow, the characteristics of the apparatus are then modified so that less net-work that is performed during that step (as compared to when the predicted walking speed is fast). This may be implemented using one sensor from which the walking speed can be predicted, and a second sensor from which ankle torque can be determined. A controller receives inputs from those sensors, and controls a motor's torque so that the torque for slow walking speeds is lower than the torque for fast walking speeds. This reduces the work performed by the actuator over a gait cycle and the peak actuator power delivered during the gait cycle. In some embodiments, a series elastic element is connected in series with a motor that can drive the ankle, and at least one sensor is provided with an output from which a deflection of the series elastic element can be determined. A controller determines a desired torque based on the output, and controls the motor's torque based on the determined desired torque.