Limits of Dynamic Postural Stability with a Segmented Foot Model

Abstract

The human foot structure withstands complex interactions with the ground during balancing and locomotion tasks, leading to agile and stable movements. Despite this, several postural stability analysis methods are limited by the use of overly simplified foot structure and contact model. The proposed foot model has a toe link that enables multiple contact modes with the ground. A contact mode detection algorithm is created to map foot angles into discrete contact modes and associated constraints. Two surface functions provide continuous values for lower and upper center of pressure limits, as the foot traverses the non-specified sequence of discrete contact modes. The proposed foot and contact model are integrated in a planar mechanism for the analysis of whole-body postural stability in sagittal plane. Constrained optimization generates balancing trajectories and contact mode sequence for the legged system recovering from extreme velocity perturbations in the anterior-posterior direction. The entire set of initial perturbations that can be sustained in the anterior-posterior direction is numerically evaluated in the cases of flat and segmented feet, to investigate the effects of multimodal foot-ground interaction on the dynamic stability limits for human posture. By exploiting the segmented foot model and the multimodal contact sequence arising from the optimization solutions, the legged system can recover from greater velocity perturbations in the sagittal plane, as compared to the case of flat feet.