In a recent article published in the journal Defence Technology, researchers introduced an innovative bionic foot structure called the Harmonious Terrain Adaptability and Stability (HTEC) foot. This new design aims to enhance the mobility and adaptability of humanoid robots in complex environments by addressing the limitations of existing passive bionic foot structures.
Study: HTEC foot: A novel foot structure for humanoid robots combining static stability and dynamic adaptability. Image Credit: Shutter z/Shutterstock.com
Background
Humanoid robots have attracted significant attention for their versatility and potential in public safety, border security, and unmanned reconnaissance. A key factor in enabling these robots to navigate various terrains effectively is the foot structure. Traditional rigid flat feet with rubber soles offer stability and limited adaptability to uneven surfaces within a few millimeters. However, adapting to larger terrain variations typically requires complex control systems and high-precision sensors, which can be costly.
To address this challenge, researchers have explored passive bionic foot designs that mimic human foot features, such as smaller contact areas, flexible components, and passive compliance. While these designs enhance adaptability, they often compromise static stability due to their under-actuated nature.
About the Research
In this paper, the authors set out to design a foot structure that merges the stability of rigid feet with the adaptability of passive bionic feet. They developed the HTEC foot model, drawing inspiration from the biomechanical features of the human foot, such as its longitudinal and transverse arches, joints, ligaments, and muscles.
The HTEC foot model incorporates simplified bone groups, elastic hinges, and linear springs, all of which mimic the flexibility and compliance of a human foot. The researchers established the kinematics and developed a reduced-order elastic-hinge (REH) dynamics model for the HTEC foot. This model served as the foundation for a nonlinear stiffness-matching optimization method (NOSM). By considering various constraints like contact conditions and range of motion, this optimization approach aims to achieve an ideal balance between static stability and dynamic adaptability.
Research Findings
The researchers conducted several experiments to validate the performance of the HTEC foot. They assessed its static stability under various disturbances and stiffness parameters through simulations. The results showed that the HTEC model consistently exhibited self-stabilizing behavior, returning to a stable upright state across different stiffness configurations. To measure effectiveness, the authors introduced a convergence efficiency indicator, which identified the optimal stiffness configuration for balancing stability and adaptability.
In addition to static tests, dynamic adaptability simulations were performed on three types of terrains: noisy, field, and waving. The findings indicated that the HTEC foot provided superior adaptability compared to a rigid foot, enabling easier navigation over uneven surfaces. Further experimental validation was carried out using a robot center of mass (COM) simulated platform and a full-sized humanoid robot, BHR-B2.
The static stability experiments confirmed that the HTEC foot could effectively maintain stability even when subjected to various disturbances. Meanwhile, dynamic walking tests on various terrains, including square steel, lawn, and cobblestone, showcased the HTEC foot's superiority over a rigid foot, particularly in terms of impact reduction, ankle adaptation, and overall adaptability.
Applications
The newly presented foot design has significant potential for improving the mobility of humanoid robots in various applications. Its ability to navigate complex terrains with greater stability and adaptability opens up new possibilities for deploying these robots in challenging environments.
For example, in public safety scenarios, humanoid robots equipped with HTEC feet could navigate disaster zones or assist in search and rescue operations. In border security, these robots could patrol challenging terrains with greater efficiency. Similarly, in unmanned reconnaissance, HTEC feet could enable robots to easily explore difficult environments.
Conclusion
In summary, the novel HTEC foot structure for humanoid robots effectively addressed the trade-off between static stability and dynamic adaptability. By combining the strengths of rigid and passive bionic foot designs, the HTEC foot enabled humanoid robots to navigate a wider range of terrains with greater robustness and mobility. The successful integration of the HTEC foot on the BHR-B2 robot and the promising experimental results suggested that this technology could revolutionize how humanoid robots interact with and adapt to complex environments and real-world applications.
Looking ahead, the authors recognized the limitations and challenges of the current design. They suggested further optimizing the HTEC foot by incorporating damping mechanisms to enhance shock absorption. They also highlighted the need to explore different materials and structures to improve reliability and skid resistance. Furthermore, integrating the HTEC foot with advanced robot control systems was deemed essential for achieving coordinated whole-body motion, which is key to further enhancing the robot's mobility and overall performance.
Journal Reference
Zhang, J., et, al. HTEC foot: A novel foot structure for humanoid robots combining static stability and dynamic adaptability. Defence Technology, 2024. DOI: 10.1016/j.dt.2024.08.010, https://www.sciencedirect.com/science/article/pii/S2214914724001946
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