Compliant Pneumatic Feet with Real‐Time Stiffness Adaptation for Humanoid Locomotion

This article presents the design, characterization, and experimental validation of compliant pneumatic feet with online stiffness control for humanoid walking. The proposed feet are constructed using soft materials and integrated air chambers that enable real‐time stiffness modulation through pressure adjustment. A vision‐based control system performs terrain classification and enables predictive adaptation of foot compliance based on ground conditions. Compression and step‐response tests characterize the mechanical behavior and dynamic response of the pneumatic sole. The system can vary stiffness from 0 to over 1200 Nm/rad within 100 ms, which is fast enough for per‐step adaptation during locomotion. Walking experiments on flat and irregular carpeted floors demonstrate that variable‐stiffness feet improve balance, reduce impact forces, and produce smoother center of mass and zero moment point trajectories compared to rigid or passively compliant feet. Complementary simulations on outdoor‐like uneven terrains further confirm that adaptive stiffness control enhances stability and terrain robustness. Although validation is limited to controlled conditions, the results indicate that the proposed pneumatic architecture offers a lightweight and low‐power platform for real‐time compliance adaptation. The combination of modular design, sub‐200 ms response, and sensor‐driven stiffness control represents a step toward safe and versatile humanoid locomotion on unpredictable ground.