The performance of mobile soft robots is usually characterized by their locomotion/velocity efficiency, whereas the energy efficiency is a more intrinsic and fundamental criterion for the performance evaluation of independent or integrated soft robots. In this work, a general framework is established to evaluate the energy efficiency of mobile soft robots by considering the efficiency of the energy source, actuator and locomotion, and some insights for improving the efficiency of soft robotic systems are presented. Proposed as the ratio of the desired locomotion kinetic energy to the input mechanical energy, the energy efficiency of locomotion is found to play a critical role in determining the overall energy efficiency of soft robots. Four key factors related to the locomotion energy efficiency are identified, that is, the locomotion modes, material properties, geometric sizes, and actuation states. It is found that the energy efficiency of most mobile soft robots reported in the literature is surprisingly low (mostly below 0.1%), due to the inefficient mechanical energy that essentially does not contribute to the desired locomotion. A comparison of the locomotion energy efficiency for several representative locomotion modes in the literature is presented, showing a descending ranking as: jumping ≫ fish-like swimming > snake-like slithering > rolling > rising/turning over > inchworm-like inching > quadruped gait > earthworm-like squirming. Besides, considering the same locomotion mode, soft robots with lower stiffness, higher density and larger size tend to have higher locomotion energy efficiency. Moreover, a periodic pulse actuation instead of a continuous actuation mode may significantly reduce the input mechanical energy, thus improving the locomotion energy efficiency, especially when the pulse actuation matches the resonant states of the soft robots. The results presented herein indicate a large and necessary space for improving the locomotion energy efficiency, which is of practical significance for the future development and application of soft robots.

中文翻译：

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移动软机器人的能源效率

移动软机器人的性能通常以其运动/速度效率为特征，而能量效率是独立或集成软机器人性能评估的更内在的和基本的标准。在这项工作中，建立了一个通用框架，通过考虑能源，执行器和运动的效率来评估移动软机器人的能源效率，并提出了一些改善软机器人系统效率的见解。建议以所需的运动动能与输入机械能之比来表示，运动的能量效率在确定软机器人的总体能量效率方面起着至关重要的作用。确定了与运动能效相关的四个关键因素，即运动模式，材料特性，几何尺寸和致动状态。已经发现，文献中报道的大多数移动软机器人的能量效率出乎意料地低（大部分低于0.1％），这是由于机械能效率低下，而机械能实际上并没有对所需的运动做出贡献。对文献中几种代表性运动模式的运动能效进行了比较，显示出降序排列为：跳跃≫鱼状游泳>蛇状滑行>滚动>上升/翻转>尺inch状点动>四足步态>像蠕虫一样蠕动。此外，考虑到相同的运动模式，具有较低刚度，较高密度和较大尺寸的软机器人往往具有较高的运动能效。而且，周期性的脉冲致动而不是连续的致动模式可以显着降低输入机械能，从而提高运动能效，尤其是当脉冲致动与软机器人的共振状态匹配时。本文介绍的结果表明，有很大的必要空间可用于提高运动能效，这对软机器人的未来开发和应用具有实际意义。