Biped robots usually adopt feet with a rigid structure that simplifies walking on flat grounds and yet hinders ground adaptation in unstructured environments, thus jeopardizing stability. We recently explored in the SoftFoot the idea of adapting a robotic foot to ground irregularities along the sagittal plane. Building on the previous results, we propose in this paper a novel robotic foot able to adapt both in the sagittal and frontal planes, similarly to the human foot. It features five parallel modules with intrinsic longitudinal adaptability that can be combined in many possible designs through optional rigid or elastic connections. By following a methodological design approach, we narrow down the design space to five candidate foot designs and implement them on a modular system. Prototypes are tested experimentally via controlled application of force, through a robotic arm, onto a sensorized plate endowed with different obstacles. Their performance is compared, using also a rigid foot and the previous SoftFoot as a baseline. Analysis of footprint stability shows that the introduction of the transverse arch, by elastically connecting the five parallel modules, is advantageous for obstacle negotiation, especially when obstacles are located under the forefoot. In addition to biped robots' locomotion, this finding might also benefit lower-limb prostheses design.

翻译：双足机器人通常采用刚性结构的足部，这简化了在平坦地面上的行走，但在非结构化环境中却阻碍了地面适应能力，从而影响稳定性。我们近期在SoftFoot中探索了使机器人足部沿矢状面适应地面不规则性的理念。基于先前成果，本文提出一种新型机器人足部，能够像人类足部一样在矢状面和额状面实现适应。该足部包含五个具有固有纵向适应性的平行模块，可通过可选的刚性或弹性连接组合成多种设计方案。采用系统化设计方法后，我们将设计空间缩小至五种候选足部方案，并在模块化系统上实现。通过机械臂控制施加力，在装有不同障碍物的传感器板上对原型进行实验测试。以刚性足部和先前SoftFoot为基准，比较其性能。足迹稳定性分析表明：通过弹性连接五个平行模块引入横向足弓，有利于越障能力提升，尤其当障碍物位于前足下方时。除双足机器人运动外，该发现或可为下肢假肢设计提供参考。