Towards Exoskeletons with Balance Capacities

Current exoskeletons replay pre-programmed trajectories at the actuated joints. Towards the employment of exoskeletons with more flexible and adaptive behavior, we investigate human balance control during gait. We study human balance control by applying brief force pulses at the pelvis in different directions, with different amplitude, and applied at different phases of the gait phase. The observed changes were dependent on the phase at which the perturbation was applied and the walking velocity. From the results we concluded that foot placement was the dominant strategy in the frontal plane, center of pressure (CoP) modulation in the double support phase was utilized in the sagittal plane, and the duration of the swing and double support phase changed. Without the ability to control the CoP through an ankle torque, humans also used a foot placement strategy in the sagittal plane. The center of pressure with respect to the center of mass at the end of the double support phase was linearly related to velocity of the center of mass at the end of the preceding swing phase, which is in agreement with extrapolated center of mass or capture point based stepping strategies previously applied in simple models.