Discrete Fourier Transform based Virtual Constraint Control of Powered Ankle-Foot Prosthesis

Active prosthetic devices have been controlled using several methods such as Echo Control, EMG signal based Position Control and Finite State Machine (FSM) based Impedance/Compliance Control. This manuscript proposes Virtual Constraint Control of active prosthesis which obviates any need for the classification of EMG signals, identification of the gait phase for state switching and potentially avoids an exhaustive procedure for the tuning of impedance parameters. In this paper, a Discrete Fourier Transform (DFT) based Virtual Constraint control is presented to characterize the ankle-foot joint trajectory as a function of the human-inspired phase variable in a unified manner. An optimization-based algorithm is employed for the robust generation of continuously monotonic and linear phase variable for DFT based Virtual Constraint Control. The results are generalized across various walking speeds for a specific user during the level ground walking.