Phase controller outperforms impedance controller for a hip exoskeleton

Abstract

Developing controllers for exoskeletons has many challenging requirements: one of which is creating a torque command based on measured human data that that is in phase with the user (in-synchrony with the human gait). We show that the hip torque for walking gait can be modeled using a phase angle based on hip angular position and velocity. This model is superior to a standard impedance model based on inertia, damping, and stiffness parameters because the phase model uses less parameters and they change linearly with varying speed and weight. The controller has been tested on ten subjects (weighing from 68 to 118kg) wearing the hip exoskeleton walking at speeds from 0.7 to 1.8m/s in outdoor environments.