Reduction of the torque requirements of an active ankle prosthesis using a parallel spring

The present manuscript describes the combined effect of using a parallel spring in conjunction with a variable-stiffness actuator to reduce the torque and power requirements of an ankle-foot prosthesis during normal walking. The behavior of both elements is analyzed in terms of the reduction of the required motor peak power, energy and torque with respect to a conventional actuator. The proposed actuator is based on the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator concept. The advantages and disadvantages of the referred actuation scheme are discussed and experimental results are used to illustrate the actual reduction of motor torque requirements.