Task-Space Control of a Powered Ankle Prosthesis

Powered lower-limb prostheses have shown promise in helping individuals with amputation regain function- ality that passive prostheses cannot provide. However, the best method for controlling these devices in coordination with their users is still an open research topic. While powered devices can replicate normative joint kinematics and kinetics, active control also holds the potential to shape system-level characteristics such as the center of mass (CoM) that play an important role in balance. Controlling the prosthesis based on these system- level, or task-space, variables would further represent a new way of coordinating the user and their device. This paper explores the initial implementation of task-space control for a powered ankle prosthesis, characterizing the emergent outcomes of this new coordination strategy. One able- bodied subject walked using a bypass adapter while prosthesis torques were commanded based on reference ground reaction force (GRF) and CoM trajectories. The subject could walk comfortably and continuously at their preferred walking speed, achieving normative ankle torques and joint trajectories despite not tracking explicit joint-level references in stance.