Jul 2 2020
New jellyfish-inspired soft robots developed by engineering researchers at North Carolina State University and Temple University have been found to outswim their real-life counterparts.
Illustration of a soft robot jellyfish. Image Credit: NC State University.
In effect, the new jellyfish-bots feature a method that involves using pre-stressed polymers to render 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. 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.
Jie Yin, Assistant Professor of Mechanical and Aerospace Engineering, NC State University
Yin is the corresponding author of a paper based on the new research.
The team used two bonded layers of the same elastic polymer to develop the new soft robots. One of the layers was pre-stressed or stretched, while the other one contained an air channel and was not pre-stressed.The team used two bonded layers of the same elastic polymer to develop the new soft robots. One of the layers was pre-stressed or stretched, while the other one contained an air channel and was not pre-stressed.
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.
Jie Yin, Assistant Professor of Mechanical and Aerospace Engineering, NC State University
It works like this. Upon combining both the layers with an intermediate layer—a third stress-free layer—the pre-stressed layer shows the tendency to move in a specific direction. For instance, a piece of pre-stressed polymeric strip can be formed by pulling it in two directions.
Once the pre-stressed material is attached to the intermediate layer, the outcome would be a bilayer strip that tends to curve down, similar to a frowning face. In case the thickness of the bilayer strip, also known as the pre-stressed layer, is lower compared to the layer containing the air channel, the frowning curve will turn into a smiling curve when air is pumped into the channel layer.
But if the thickness of the pre-stressed layer is greater than that of the channel layer, the frown will become more and more obvious upon pumping air into the channel layer. In any case, once the air leaves the channel layer, the material returns to its original, “resting” state.
This simple example illustrates one of the soft robots developed by the researchers—a fast-moving soft crawler. It looks like a larval insect that curls its body and then jumps forward while quickly releasing its stored energy.
The jellyfish-bot is somewhat more complex as the pre-stressed disk-like layer is stretched in four directions (consider it as being pulled east and west at the same time, and then being pulled north and south at the same instance). Moreover, even the channel layer is different, including a ring-like air channel. The outcome is a dome that resembles a jellyfish.
The dome tends to curve up, similar to a shallow bowl, when the jellyfish-bot “relaxes.” Upon pumping air into the channel layer, the dome swiftly curves down and propels itself forward by pushing out water.
During experiments to test the jellyfish-bot, it featured an average speed of 53.3 mm/second. That is pretty good given that none of the three jellyfish species investigated by the researchers moved faster than an average of 30 mm/second.
Finally, the researchers developed a three-pronged gripping robot, but with a twist. A majority of the grippers hang open when “relaxed” and need energy to hold on to their cargo upon lifting and moving it from one point to another.
However, Yin and his colleagues employed the pre-stressed layers to develop grippers with a clenched-shut default position. Although the opening of the grippers requires energy, once they are in position, they return to their “resting” mode and hold 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.
Jie Yin, Assistant Professor of Mechanical and Aerospace Engineering, NC State University
The study was performed with financial support from the National Science Foundation under grants 2010717 and 2005374.
Jellyfish-Inspired Soft Robots Can Outswim Their Natural Counterparts
Soft robots inspired by jellyfish, insects. Video Credit: Jie Yin, NC State University.
Journal Reference:
Chi, Y., et al. (2020) Leveraging Monostable and Bistable Pre‐Curved Bilayer Actuators for High‐Performance Multitask Soft Robots. Advanced Materials Technologies. doi.org/10.1002/admt.202000370.