Jellyfish-inspired soft robots can outswim their natural counterparts


Date:
July 1, 2020
Source:
North Carolina State University
Summary:
Engineering researchers have developed soft robots inspired by
jellyfish that can outswim their real-life counterparts. More
practically, the new jellyfish-bots highlight a technique that
uses pre-stressed polymers to make soft robots more powerful.



FULL STORY ========================================================================== Engineering researchers at North Carolina State University and Temple University have developed soft robots inspired by jellyfish that
can outswim their real-life counterparts. More practically, the new jellyfish-bots highlight a technique that uses pre-stressed polymers to
make soft robots more powerful.


==========================================================================
"Our previous work focused on making soft robots that were inspired by
cheetahs -- and while the robots were very fast, they still had a stiff
inner spine," says Jie Yin, an assistant professor of mechanical and
aerospace engineering at NC State and corresponding author of a paper on
the new work. "We wanted to make a completely soft robot, without an inner spine, that still utilized that concept of switching between two stable
states in order to make the soft robot move more powerfully -- and more quickly. And one of the animals we were inspired by was the jellyfish."
The researchers created their new soft robots from two bonded layers
of the same elastic polymer. One layer of polymer was pre-stressed,
or stretched. A second layer was not pre-stressed and contained an
air channel.

"We can make the robot 'flex' by pumping air into the channel layer,
and we control the direction of that flex by controlling the relative
thickness of the pre-stressed layer," Yin says.

Here's how it works. When combined with a third stress-free layer,
called an intermediate layer, the pre-stressed layer wants to move in a particular direction. For example, you might have a piece of polymeric
strip that has been pre-stressed by pulling it in two directions. After attaching the pre-stressed material to the intermediate layer, the
end result would be a bilayer strip that wants to curve down, like
a frowning face. If this bilayer strip, also called the pre-stressed
layer, is thinner than the layer with the air channel, that frowning
curve will bend into a smiling curve as air is pumped into the channel
layer. However, if the pre-stressed layer is thicker than the channel
layer, the frown will become more and more pronounced as air is pumped
into the channel layer. Either way, once the air is allowed to leave the channel layer, the material snaps back to its original, "resting" state.

In fact, this simple example describes one of the soft robots created
by the research team, a fast-moving soft crawler. It resembles a larval
insect curling its body, then jumping forward as it quickly releases
its stored energy.

The jellyfish-bot is slightly more complicated, with the pre-stressed
disk-like layer being stretched in four directions (think of it as
being pulled east and west simultaneously, then being pulled north and
south simultaneously). The channel layer is also different, consisting
of a ring-like air channel. The end result is a dome that looks like
a jellyfish.

As the jellyfish-bot "relaxes," the dome curves up, like a shallow
bowl. When air is pumped into the channel layer, the dome quickly curves
down, pushing out water and propelling itself forward. In experimental
testing, the jellyfish-bot had an average speed of 53.3 millimeters per
second. That's not bad, considering that none of the three jellyfish
species the researchers examined went faster than an average of 30
millimeters per second.

Lastly, the researchers created a three-pronged gripping robot -- with
a twist.

Most grippers hang open when "relaxed," and require energy to hold on to
their cargo as it is lifted and moved from point A to point B. But Yin
and his collaborators used the pre-stressed layers to create grippers
whose default position is clenched shut. Energy is required to open the grippers, but once they're in position, the grippers return to their
"resting" mode -- holding their cargo tight.

"The advantage here is that you don't need energy to hold on to the
object during transport -- it's more efficient," Yin says.


========================================================================== Story Source: Materials provided by North_Carolina_State_University. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yinding Chi, Yichao Tang, Haijun Liu, Jie Yin. Leveraging
Monostable and
Bistable Pre‐Curved Bilayer Actuators for
High‐Performance Multitask Soft Robots. Advanced Materials
Technologies, 2020; 2000370 DOI: 10.1002/admt.202000370 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200701151712.htm

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