Design of Humanoid Robot Foot to Absorb Ground Reaction Force by Mimicking Longitudinal Arch and Transverse Arch of Human Foot

In this paper, we describe a double arched robotic Foot-1 (DARFT-1) for a humanoid robot. The feet of many humanoid robots are equipped with force/torque (F/T) sensors for various purposes of walking control, including the calculation of zero-moment-point (ZMP), contact detection, and contact force control. However, there are cases where unexpectedly large ground reaction force (GRF) is applied to the F/T sensor when the humanoid robot walks on uneven ground, causing the F/T sensor to break easily. To protect the F/T sensor and achieve the mechanical filter effect, various robot feet are being studied. We propose a robot foot that mimics the longitudinal arch and transverse arch of a human foot to absorb GRF effectively. Each arch of the proposed foot consists of passive joints and springs and is designed with a 2-degrees-of-freedom (DoF) structure. Furthermore, DARFT-1 is designed to prevent external obstacles from entering the sole of the foot, while also being designed for shape adaptation to uneven ground. To verify the effectiveness of the designed foot, GRF measurement experiments were conducted by mounting the DARFT-1 on the humanoid robot DRC-HUBO+. Through the experiments, the DARFT-1 reduced GRF by an average of 9.8% and 10.02% in three trials when placing the obstacle on the front and side of the foot, respectively, compared to the previous foot. In addition, the proposed foot performed as a mechanical filter by reducing the rate of change in the GRF. Furthermore, the reduced GRF decreased the ZMP, improving the stability of the humanoid robot's walk.