An Optically Based Assessment of Pedestrian Balance Behaviour While Walking on a Laterally Oscillating Treadmill

Abstract eng:
This paper reports findings from an experimental campaign in which subject balance behaviour while walking on a laterally oscillating treadmill was recorded. A 3-dimensional motion capture camera system was used to track the position of 31 active markers, placed on each subject during walking tests. A range of deck oscillation frequencies and amplitudes were tested. The campaign was executed with the aim of identifying the interaction mechanism by which pedestrians produce force harmonics, that resonate with the oscillating structure on which they walk. These so-called self-excited forces have been experimentally identified by others but the underlying reason for their existence has remained an open question. Analysis has revealed that subject balance response to sinusoidal base motion is dominated by periodic alteration of foot placement position. This results in amplitude modulation of the lateral component of the ground reaction force (GRF). The frequency of modulation was found to be equal to the modulus of the difference between the lateral forcing and deck oscillation frequencies. This is consistent with the identification of interaction force harmonics as frequency sidebands. The underlying reason for gait width modulation was revealed by examining the subject’s CoM oscillation and recognising the influence of a sinusoidally varying inertia force experienced by the subject. Furthermore, the degree to which the subject alters their gait is determined by the degree to which their frontal plane stability is impaired by deck motion. Thus the link between frontal plane balance behaviour and the generation of the self-excited component of the lateral GRF is established. Further analysis suggests that subject centre of mass (CoM) motion while walking on a laterally oscillating deck is predominantly passive. The simple inverted pendulum model is thus an excellent model of pedestrian CoM motion in the frontal plane during the single stance gait phase. This was established by comparison between simulated and observed CoM motion.

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