redOrbit Staff & Wire Reports – Your Universe Online
The research popularity of soft robots, which are robots with soft exteriors powered by fluid flowing through flexible channels, has grown to such an extent that a new journal has been created about the topic – Soft Robotics (SoRo), a peer-reviewed journal from Mary Ann Liebert, Inc., publishers.
In the journal’s flagship issue this month, researchers from MIT and Worcester Polytechnic Institute describe their work in building the first self-contained autonomous soft robot capable of rapid body motion – a “fish” with a flexible spine that allows it to execute an escape maneuver in just a fraction of a second, nearly as fast as a real fish could perform such a move.
The researchers describe the design, modeling, fabrication, and control mechanisms of the robotic fish, along with the novel fluidic actuation system, embedded muscle-like actuators, and an onboard control system that give the fish autonomy and the ability to perform continuous forward swimming motion and rapid accelerations.
“This innovative work highlights two important aspects of our emerging field; first it is inspired and informed by animal studies (biomimetics), and second it exploits novel soft actuators to achieve life-like robot movements and controls,” said Barry Trimmer, Editor-in-Chief of Soft Robotics and director of Neuromechanics and Biomimetic Devices Laboratory at Tufts University.
Daniela Rus, one of the researchers who designed and built the robotic fish, said the field of soft robots offers additional benefits in the area of safety.
“We’re excited about soft robots for a variety of reasons,” said Rus, professor of computer science and engineering, and director of MIT’s Computer Science and Artificial Intelligence Laboratory.
“As robots penetrate the physical world and start interacting with people more and more, it’s much easier to make robots safe if their bodies are so wonderfully soft that there’s no danger if they whack you,” she said in an interview with Larry Hardesty of MIT News.
Rus noted that another reason to study soft robots is because “with soft machines, the whole robotic planning problem changes.”
In most robotic motion-planning systems, avoiding collisions with the environment is top priority, which often leads to inefficient motion because the robot has to settle for collision-free trajectories that it can find quickly. However, with soft robots, collision poses little danger to either the robot or the environment.
“In some cases, it is actually advantageous for these robots to bump into the environment, because they can use these points of contact as means of getting to the destination faster,” Rus said.
But the robotic fish described in the current report was designed to explore yet a third advantage of soft robots.
“The fact that the body deforms continuously gives these machines an infinite range of configurations, and this is not achievable with machines that are hinged,” Rus said.
The continuous curvature of the fish’s body when it flexes is what allows it to change direction so quickly.
“A rigid-body robot could not do continuous bending,” Rus said.
The robotic fish was built by Andrew Marchese, a graduate student in MIT’s Department of Electrical Engineering and Computer Science and lead author of the SoRo paper.
Each side of the fish’s tail is bored through with a long, tightly undulating channel. Carbon dioxide released from a canister in the fish’s abdomen causes the channel to inflate, bending the tail in the opposite direction. Each half of the fish tail has two control parameters – the diameter of the nozzle that releases gas into the channel, and the length of time it is left open. In previous experiments, Marchese found that the angle at which the fish changes direction – which can be as high as 100 degrees – is almost entirely determined by the duration of inflation, while its speed is almost entirely determined by the nozzle diameter.
The “decoupling” of these two parameters is something that biologists had observed in real fish, Marchese said.
“To be honest, that’s not something I designed for. I designed for it to look like a fish, but we got the same inherent parameter decoupling that real fish have.”
Rus said this highlights another possible application of soft robotics – biomechanics.
“If you build an artificial creature with a particular bio-inspired behavior, perhaps the solution for the engineered behavior could serve as a hypothesis for understanding whether nature might do it in the same way,” she said.
Marchese constructed the robotic fish in Rus’ lab using a 3-D printer to build the mold in which he cast the fish’s tail and head from silicone rubber, and the polymer ring that protects the electronics in the fish’s guts. The fish can execute 20 or 30 escape maneuvers, depending on their velocity and angle, before it exhausts its carbon dioxide canister.
However, the relatively simple maneuver of swimming back and forth across a tank drains the canister quickly, Marchese said.
“The fish was designed to explore performance capabilities, not long-term operation. Next steps for future research are taking that system and building something that’s compromised on performance a little bit but increases longevity.”
Marchese, Rus and postdoc Cagdas Onal said they hope to build a new version of the fish with the same body design but use pumped water instead of carbon dioxide to inflate the channels. This will allow the robotic fish to swim continuously for around 30 minutes.
Such a robot could infiltrate schools of real fish to gather detailed information about their behavior in nature, Rus added.
“If we learn how to incorporate all these other sorts of materials whose response you can’t predict exactly, if we can learn to engineer that to deal with the uncertainty and still be able to control the machines, then we’re going to have much better machines,” said Trimmer, editor of SoRo.
The robotic fish described in the report “is a great demonstration of that principle.”
“It’s an early stage of saying, ‘We know the actuator isn’t giving us all the control we’d like, but can we actually still exploit it to get the performance we want?’ And they’re able to show that yes, they can.”