腿式机器人运动对颗粒介质的敏感依赖性
Sensitive dependence of the motion of a legged robot on granular media
AI总结：
研究六足机器人SandBot在颗粒介质上的运动，发现其速度敏感依赖堆积分数与肢体频率，调整步态参数可提升速度，提出旋转行走运动学模型并揭示需深入理解颗粒介质物理。
摘要：
在流动地面（如颗粒介质）上的腿式运动与硬地面上的运动不同，因为足部在穿透表面时会同时受到类固体和类流体的力。近期受生物启发的腿式机器人在硬地面上的相对身体尺寸速度可与蟑螂等高性能生物相当，但在沙子等流动材料上的性能会显著下降。在实验室实验中，我们研究了小型（2.3 kg）六足机器人SandBot在颗粒介质床（1 mm罂粟籽）上奔跑时的性能（速度）。对于颗粒床上的交替 tripod 步态，标准步态控制参数实现的速度最多比硬地面上的2体长/秒（≈60 cm/s）小两个数量级。然而，对这些控制参数进行经验调整，使其偏离硬地面设置，可恢复良好性能，产生30 cm/s的最高速度。机器人速度敏感依赖于堆积分数φ和肢体频率ω，且当φ足够小和/或ω足够大时，会发生从旋转行走到缓慢游泳的剧烈转变。我们基于颗粒介质中弯曲肢体的穿透和滑动的一般特征，提出了旋转行走模式的运动学模型。该模型捕捉了机器人速度对肢体频率的依赖性以及行走与游泳模式之间的转变，但强调需要更深入地理解颗粒介质的物理学。
英文摘要：
Legged locomotion on flowing ground ({\em e.g.} granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bio-inspired legged robots display speed relative to body size on hard ground comparable to high performing organisms like cockroaches but suffer significant performance loss on flowing materials like sand. In laboratory experiments we study the performance (speed) of a small (2.3 kg) six-legged robot, SandBot, as it runs on a bed of granular media (1 mm poppy seeds). For an alternating tripod gait on the granular bed, standard gait control parameters achieve speeds at best two orders of magnitude smaller than the 2 body lengths/s ($\approx 60$ cm/s) for motion on hard ground. However, empirical adjustment of these control parameters away from the hard ground settings, restores good performance, yielding top speeds of 30 cm/s. Robot speed depends sensitively on the packing fraction $ϕ$ and the limb frequency $ω$, and a dramatic transition from rotary walking to slow swimming occurs when $ϕ$ becomes small enough and/or $ω$ large enough. We propose a kinematic model of the rotary walking mode based on generic features of penetration and slip of a curved limb in granular media. The model captures the dependence of robot speed on limb frequency and the transition between walking and swimming modes but highlights the need for a deeper understanding of the physics of granular media.
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