Nonlinear Passive Elements Using Cam-Based Springs for Powered Robotic Ankles

There is increasing interest in powered prosthesis. To reduce energy, power, and torque requirements on the active input, current systems, such as powered ankle prosthetics, utilize a combination of passive and active components. By storing and releasing energy during gait, the passive component reduces the energy/power/torque requirements of the active component. Therefore, it is advantageous to maximize the use of the passive component for achieving the desired motion. Typically, the passive component utilizes elastic elements such as springs, which cannot be easily adjusted to achieve a desired optimal nonlinear response. In this work, we report the use of a cam profile to achieve a general desired nonlinear response. The results show that the added design flexibility (to achieve nonlinear response of the passive element) can substantially reduce the energy/power/torque requirement of the active component.