The Effect of the Toe Joint on Bipedal Walking

Abstract

Bipedal robots are being developed to assist humans in various forms, including standalone robots and those integrated with human contacts, such as exo-suits and robotic prosthetic limbs. Understanding human-like movements is crucial in bipedal robot research, and the relatively understudied toe joint plays a significant role in walking. This study employs simulation methods and optimal control theory to investigate the impact of the toe joint on bipedal robot locomotion. Using the direct collocation method, a simulation was conducted on a 9-link bipedal model with a toe joint and a 7-link model without a toe joint. The results showed that the 9-link model exhibited a wider stride length, faster walking speed, and lower objective function value. The analysis of the toe joint angle-torque graph indicated the influence of the toe joint in walking, leading to the determination of an optimal toe joint stiffness of 1.04 Nm/deg, suitable for practical implementation. Experimental optimal toe joint stiffness was validated using subject preference surveys. The results aligned with the optimal stiffness identified in the simulation. The toe joint-ankle joint power analysis further supported the optimal toe joint stiffness efficiency. However, statistical significance was limited due to the small subject sample size and incomplete experimental data. Future research aims to address these limitations by increasing the number of subjects and conducting comprehensive experiments to validate the optimal toe joint stiffness. Additionally, confirming the interaction between the ankle and toe joints identified in the experimental study will be explored.