An interdisciplinary team of roboticists, engineers and biologists at the University of Harvard John A. Paulson School of Engineering and Applied Sciences has developed a new robot that can mimic the punch of a mantis shrimp. These creatures have the strongest punch of any thanks to their club-like appendages that accelerate faster than a bullet from a gun. Biologists have long tried to understand how mantis shrimp produce these ultra-fast movements, but new high-speed imaging advancements are shedding new light.
The research was published in the Proceedings of the National Academy of Sciences.
Robert Wood is the Harry Lewis and Maryln McGrath Professor of Engineering and Applied Sciences at the Harvard John A. Paulson School of Engineering and Applied Sciences at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). He is also senior author of the paper.
“We are fascinated by so many remarkable behaviors we see in nature, in particular when these behaviors meet or exceed what can be achieved by human-made devices,” said Wood. “The speed and force of mantis shrimp strikes, for example, are a consequence of a complex underlying mechanism. By constructing a robotic model of a mantis shrimp striking appendage, we are able to study these mechanisms in unprecedented detail.”
Latching Mechanisms Among Small Organisms
Small organisms like frogs and chameleons rely on the release of a latching mechanism to produce ultra-fast movements. They store elastic energy and rapidly release it though that latching mechanism. In the specific case of mantis shrimp, two small structures called sclerites are embedded in the tendons of the muscles and these act as the appendage’s latch.
One of the noticeable differences between mantis shrimp and other similar organisms is that the former has a delay when the sclerites unlatch in a mantis shrimp’s appendage.
Nak-seung Hyun is a postdoctoral fellow at SEAS and co-first author of the paper.
“When you look at the striking process on an ultra-high-speed camera, there is a time delay between when the sclerites release and the appendage fires,” said Hyun. “It is as if a mouse triggered a mouse trap but instead of it snapping right away, there was a noticeable delay before it snapped. There is obviously another mechanism holding the appendage in place, but no one has been able to analytically understand how the other mechanism works.”
Emma Steinhardt is a graduate student at SEAS and first author of the paper.
“We know that mantis shrimp don’t have special muscles compared to other crustaceans, so the question is, if it’s not their muscles creating the fast movements, then there must be a mechanical mechanism that produces the high accelerations,” said Steinhardt.
When sclerites initiate unlatching, biologists believe the geometry of the appendage acts as a secondary latch. This helps control the movement of the arm while it continues to store energy. However, this is just an untested theory.
Developing a Shrimp-Scale Robot
The team set out to test this hypothesis by studying the linkage mechanics of the system before constructing a physical, robotic model. After building the robot, the team developed a mathematical model of the movement and mapped four distinct phases of the mantis strike. They started with the latched sclerites and finished with the strike of the appendage.
The researchers found that after the sclerites unlatch, the geometry of the mechanism takes over and holds the appendage in place until it reaches an over-centering point before the latch releases.
“This process controls the release of stored elastic energy and actually enhances the mechanical output of the system,” said Steinhardt. “The geometric latching process reveals how organisms generate extremely high acceleration in these short duration movements, like punches.”
The process was mimicked in a 1.5-gram, shrimp-scale robot. Despite not reaching the speed of a mantis shrimp strike, the robot demonstrated an impressive speed of 26 meters per second in air. This acceleration rate means the device is faster than any similar ones at the same scale.
Shella Patek is co-author and Professor of Biology at Duke University
“This study exemplifies how interdisciplinary collaborations can yield discoveries for multiple fields,” said Patek. “The process of building a physical model and developing the mathematical model led us to revisit our understanding of mantis shrimp strike mechanics and, more broadly, to discover how organisms and synthetic systems can use geometry to control extreme energy flow during ultra-fast, repeated-use, movements.”
By combining physical and analytical models, biologists and roboticists will gain a deeper understanding of how certain organisms undertake extraordinary tasks.
Other co-authors of the research include Je-sung Koh, Gregory Freeburn, Michelle H. Rosen and Fatma Zeynep Temel.