Design and Validation of a 3D Structurally-Elastic Bioinspired Humanoid Robot Foot for Elastic and Rigid Contact Behaviors

Abstract

Most current humanoid robot foot designs are limited to the incorporation of 2D properties and do not replicate the full 3D biomechanics of the human foot, especially the crucial differences in medial and lateral arch stiffness. As a result, existing designs are not capable of storing different amounts of energy according to different center of pressure trajectories over the foot the way a human foot does. Furthermore, they do not utilize the energy naturally stored in the human foot-ankle complex during the mid-stance phase. This results in suboptimal energy storage in favor of stability. This thesis addresses this gap by designing and validating a 3D structurally-elastic bioinspired humanoid robot foot with differentiated stiffness in the medial, center, and lateral regions. Carbon fiber beams of varying bending stiffness are used to enable both elastic and rigid contact depending on the center of pressure trajectory during mid-stance. Validation through finite element simulations, material testing, and dynamic experiments demonstrates significant variation (p=0.01) of stiffness and strain energy, consistent with human biomechanics. Dynamic mid-stance testing shows a strong correlation (ρ=0.84, p=0) between the center of pressure trajectory and longitudinal ground reaction force slope, confirming the achievement of elastic and rigid contact behaviors. The design better reproduces mid-stance energy storage mechanisms compared to a state-of-the-art energy-storage-and-return prosthetic foot, contributing a novel approach to energy-efficient humanoid robot locomotion.