2cm 몸으로 14cm 점프 ‘소금쟁이 로봇’ Robots Reveal How Water Striders Jump on Water(VIDEO)
서울大 “소금쟁이 모사한 생체 모방 로봇 개발
Image: Seoul National University
Jumping robotic insect next to a water strider. source spectrum.ieee.org
맑은 물 위에 떠 있는 작은 로봇. 길이 2cm인 직사각형 몸통에 가늘고 긴 네 다리를 드리운 모습이 영락없는
소금쟁이다. 무게는 고작 68mg.
VIDEOS
CMU Water Strider Robot
Can a robot jump on water?
edited by kcontents
케이콘텐츠 편집
물 위에 평화롭게 앉아 있던 로봇이 길게 뻗은 네 다리를 몸쪽으로 모으는가 싶더니 이내 수직으로 솟구친다. 로봇이 뛰어오른 높이는 몸길이의 7배에 이르는 14.2cm. 뛰어난 점프력도 실제 소금쟁이와 비슷하다.
소금쟁이를 모사한 ‘소금쟁이 로봇’은 조규진 김호영 서울대 기계항공공학부 교수팀과 로버트 우드 미국 하버드대 교수팀이 공동으로 개발해 ‘사이언스’ 31일 자에 발표했다.
육지 동물은 다리로 지면을 박차면서 뛰어오르는 반면 소금쟁이는 넓게 벌린 네 다리를 가운데로 모았다가 점프한다. 이때 발이 수면을 누르면서 물 속으로 빠지지 않기 위해 물의 표면장력을 넘지 않을 정도로만 힘을 준다.
연구진은 소금쟁이의 도약 과정을 로봇으로 모사하기 위해 형상기억합금을 소재로 썼다. 형상기억합금은 잘 휘면서도 원래 상태로 되돌아오는 특성이 있어 로봇이 물에 떠 있을 때와 도약할 때 다리 모양을 바꿀 수 있다. 연구진은 다리에 초경량 액추에이터(구동 장치)를 달아 다리의 힘이 물의 표면장력보다 작아지도록 조절했다.
조 교수는 “그동안 소금쟁이가 수면 위를 미끄러지듯 달리는 과정에만 초점이 맞춰져 있었는데 이번에 처음으로 도약 과정을 밝혀냈다”면서 “생물학자, 유체역학자, 로봇공학자의 노력이 합쳐져 이뤄진 융합 연구의 대표적인 성공 사례”라고 말했다.
소금쟁이 로봇처럼 곤충만 한 크기로 간단한 기능을 수행하는 생체 모방 로봇은 재해나 오염 지역, 전장에서 대량으로 흩어져 감시, 정찰, 인명 발견 등의 목적에 사용될 수 있다. 조 교수는 벼룩의 다리 구조를 그대로 본뜬 ‘벼룩 로봇’도 개발한 바 있다. 동아사이언스 신선미 기자 vamie@donga.com |
Robots Reveal How Water Striders Jump on Water
By Evan Ackerman
Posted 30 Jul 2015
Image: Seoul National University
Jumping robotic insect next to a water strider. Water striders are little insects that spend their existence skating around on the surface of lakes, ponds, and streams, relying on surface tension to keep them dry and happy. Watching them zip around is very cool, and its equally cool to think about the physics going on between the water and their toes to allow them to do what they do. Water striders are also able to jump, which substantially ups the difficulty on the whole not-sinking thing, since they have to somehow exert a substantial amount of force on the surface of the water without breaking through. How do they do it? South Korean researchers built a robotic water strider to find out.
Our first encounter with a water strider robot was (as far as I know) back in 2007, from CMU’s Nanorobotics Lab, which may not exist anymore. Here’s an old press release and a video:
In 2012, roboticists from Harbin Institute of Technology in China published a paper on jumping microrobots inspired by water striders, although “inspired by” might be charitable for this portly fellow:
Those feet are made of nickel foam, and although the robot weighs 11 grams, it can jump 14 centimeters high, which is quite impressive.
Now, another group of researchers has built an even more impressive robotic water strider. In a paper published today in Science, Je-Sung Koh, Eunjin Yang, Gwang-Pil Jung, Sun-Pill Jung, Jae Hak Son, Sang-Im Lee, Piotr G. Jablonski, Robert J. Wood, Ho-Young Kim, and Kyu-Jin Cho from Seoul National Univeristy and Harvard’s Wyss Institute, describe how they combined the ability to jump with a true bio-inspired water strider design and scale
Image: Science
Jumping sequence of a water strider in side view (left column) and front view (right column).
Real water striders are spectacular jumpers, and from watching slow motion videos of the insects, the researchers were able to understand how they manage it. Interestingly, water striders are able to jump just as high on water as they are on land, suggesting that the technique that they use is unique to their environment, since most other insects that can jump on water are way more efficient jumping on land. The movement of water striders is all based on using surface tension to keep themselves on top of the water’s surface, and their jumping behavior is no different.
To jump, a water strider rises upward while smoothly pushing the water surface downward and closing four of its legs inward [right]. It’s very careful not to rupture the water’s surface (doing so dissipates an enormous amount of energy and renders jumping highly inefficient), and in fact manages to exert a peak force that’s consistently just below the amount of force that would break the surface tension of the water (about 144 mN/m). By closing its legs inward, the insect is also able to pull them across the surface of the water as it begins to jump, allowing it to exert up to 42 percent more force over the surface of the water.
Image: Seoul National University
The robot that the researchers designed has wire legs coated with a superhydrophobic material, and curve up at the toes, just like the real insect. The 68 milligram robot (with a 2-cm body) that the researchers designed to mimic this behavior is based closely on real water strider: the wire legs are coated with a superhydrophobic material, and curve up at the toes, just like the real insect. The “muscle” that does the jumping is a bio-inspired torque reversal catapult that’s based on the leg of a flea; when it’s triggered, it applies a gradually increasing amount of torque to the legs of the robot, driving them smoothly downwards and achieving a maximum vertical acceleration of just under 14 g.
Experiments showed that the robot could leave the surface of the water with a peak velocity of 1.6 m/s, resulting in a jumping height of 142 mm. Dynamic modeling suggests that it’s exerting a force of 140 mN/m on the surface of the water, just under the 144 mN/m limit, which is ideal. The robot is also better at jumping on water than on land, possibly because the water damps leg vibrations, making the jumping more efficient.
Sadly, the researchers don’t end their paper by promising us human-scale rideable water striders robots or anything. Rather, the point of this paper was to use robots to help us better understand the biology of water strider insects, and how they can take optimal advantage of the surface tension of water to move and jump.
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