机器人在弯曲空间中的运动违反标准物理定律 精选
2022-8-11 15:59




Experimental realization of a swimmer on a sphere with actuated motors on a freely rotating boom arm. Credit: Georgia Tech

据美国佐治亚理工学院(Georgia Institute of Technology202288日提供的消息,机器人在弯曲空间中的运动违反了的标准物理定律(Robotic motion in curved space defies standard laws of physics)。上述由佐治亚理工大学提供的图片,是在自由旋转的悬臂臂上,用驱动电机在球体上实现游泳运动员的实验。

当人类、动物和机器在世界各地移动时,它们总是会推动物体,无论是地面、空气还是水。直到最近,物理学家还认为这是一个常数,遵循动量守恒定律。现在,佐治亚理工学院的研究人员已经证明,当物体存在于弯曲的空间中时,情况恰恰相反,事实证明,它们实际上可以移动,而不会碰到物体。相关研究结果于2022728日已经在《美国国家科学院院刊》(Proceedings of the National Academy of Sciences简称PNAS)网站发表—— Shengkai LiTianyu WangVelin H. KojouharovJames McInerneyEnes AydinYasemin Ozkan-AydinDaniel I. Goldman, D. Zeb Rocklin. Robotic swimming in curved space via geometric phase. Proceedings of the National Academy of Sciences, Published July 28, 2022, 119 (31): e2200924119. DOI: 10.1073/pnas.2200924119. https://www.pnas.org/doi/10.1073/pnas.2200924119

在这篇论文中,由佐治亚理工大学物理学院助理教授泽布·罗克林(D. Zeb Rocklin)领导的一个研究小组创造了一种机器人,该机器人被限制在一个球面上,与周围环境的隔离程度达到了前所未有的程度,因此这些曲率诱导的效应将占主导地位。


《美国国家科学院院刊》(PNAS)还提供了一段视频。在这段视频中,研究人员展示了机器人实现零步态和游泳步态的演示,以及“球形游泳者”的正负游泳示例,以及与“圆柱形游泳者”的比较。详见:In this video, the researchers show demonstrations of the robot implementing the null gait and the swimming gait, as well as examples of the positive and negative swimming in the ‘spherical swimmer’ and a comparison to the "cylindrical swimmer." Credit: Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2200924119

创建弯曲路径(Creating a curved path

研究人员开始研究物体如何在弯曲空间(curved space)内移动。为了将物体限制在球体上,使其与弯曲空间中的环境之间的相互作用或动量交换最小,他们让一组电机作为运动质量在弯曲轨道上驱动。然后,他们将该系统整体连接到旋转轴上,以便电机始终在球体上移动。轴由空气轴承和衬套支撑,以最大限度地减少摩擦,轴的对齐方式根据地球重力进行调整,以最大限度地减少重力残余力。


在太空和太空以外的应用(Applications in space and beyond


泽布·罗克林说:“这项研究还与‘不可能的发动机(Impossible Engine)’研究有关。它的创造者声称,它可以在没有任何推进剂的情况下向前移动。这台发动机确实是不可能的,但由于时空是非常轻微的弯曲,一台设备实际上可以在没有任何外力或发射推进剂的情况下向前移动,这本身就是一个新发现。”


使用曲面微镜的自由空间光耦合(Free-space light coupling using curved micromirrors


In Newtonian dynamics, acceleration requires force, which is taken to imply that a stationary object cannot move without exchanging momentum with its environment. Here, we realize a system that defies this requirement: a robot confined to a sphere. As the device actively changes its shape, the noncommutativity of “translations” in curved spaces allows it to advance without frictional or gravitational forces, akin to how a falling cat can use shape changes to control its orientation but not its position. Under controlled frictional forces, the robot can achieve a state with finite momentum that nevertheless does not move forward. Our work demonstrates how the interaction between environmental curvature, active driving, and geometric phases yields rich, exotic phenomena.


Locomotion by shape changes or gas expulsion is assumed to require environmental interaction, due to conservation of momentum. However, as first noted in [J. Wisdom, Science 299, 1865-1869 (2003)] and later in [E. Guéron, Sci. Am. 301, 38-45 (2009)] and [J. Avron, O. Kenneth, New J. Phys, 8, 68 (2006)], the noncommutativity of translations permits translation without momentum exchange in either gravitationally curved spacetime or the curved surfaces encountered by locomotors in real-world environments. To realize this idea which remained unvalidated in experiments for almost 20 y, we show that a precision robophysical apparatus consisting of motors driven on curved tracks (and thereby confined to a spherical surface without a solid substrate) can self-propel without environmental momentum exchange. It produces shape changes comparable to the environment’s inverse curvatures and generates movement of 10−1 cm per gait. While this simple geometric effect predominates over short time, eventually the dissipative (frictional) and conservative forces, ubiquitous in real systems, couple to it to generate an emergent dynamics in which the swimming motion produces a force that is counter-balanced against residual gravitational forces. In this way, the robot both swims forward without momentum and becomes fixed in place with a finite momentum that can be released by ceasing the swimming motion. We envision that our work will be of use in a broad variety of contexts, such as active matter in curved space and robots navigating real-world environments with curved surfaces.





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