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These earthworm-inspired robots may one day crawl through aircraft engines

They can move at one body length per second.

These earthworm-inspired robots may one day crawl through aircraft engines
The robot navigates a transparent pipe. Tang et al. 

The engine of an aircraft is a labyrinth of twisting, turning pipelines that transport fluids and gases throughout the machine. Those geometries can make inspecting the pipelines extremely difficult.

A team of roboticists looked to nature for inspiration in developing a new, more efficient method. Their invention — mechanical earthworms with "muscles" made of dielectric elastomer actuators and "feet" fabricated from a carbon fiber composite — is described in a paper published Wednesday in the peer-reviewed journal Science Robotics. 

"Current aircraft engine inspection methods are time-consuming and require highly skilled engineers," mechanical engineer Huichan Zhao, one of the co-authors, tells IE. "In the future, we hope to see robots do such work to save time and effort," she says.

These earthworm-inspired robots may one day crawl through aircraft engines
Images of the robot with a camera installed at the front and the robot inspecting the environment in a stainless steel pipe at a driving frequency of 1 Hz. Scale bars, 10 mm. Source

Tiny pipelines impose a lot of design constraints 

This isn't the first robot designed to inspect centimeter- and millimeter-scale pipes. Other designs rely on wheels or other means to crawl or walk through the enclosed spaces. But those solutions aren't always practical, according to the researchers behind the new paper. One reason is that conditions can vary tremendously from one pipeline to another, even within the same engine. Those designs can also struggle to complete the two equally important tasks for this kind of robot: locomotion and inspection.

To mitigate those limitations, engineers have turned to pneumatically powered robots that use pressurized air to move their entire length, crawling along like an inchworm. These are easier to seal and shrink to small scales because they don't have complex protrusions like wheels or legs. However, these robots tend to be slow. That's a liability — and a potential expense — if the bot needs to inspect a long pipeline. 

From inchworms to earthworms

The new design powers its locomotion in a completely different way. Instead of pressurized air, the earthworm-like device uses electric charges to undulate its way through a pipe using a combination of longer "elongation units" and shorter "anchoring units."

These earthworm-inspired robots may one day crawl through aircraft engines
A schematic drawing of the robot.

"The key technology is the artificial muscles [also called "soft actuators" or “dielectric elastomer actuators”) that are powerful enough and small enough to drive the robot to move rapidly in a pipe," Zhao says. The charges cause the actuators to rapidly contract, allowing the 1.85-inch-long (47 mm) machine to move at a rate of one body length per second. The robot is made of segments that can be snapped together with magnets, allowing the operator to customize the exact design based on the specification of the line that needs inspecting.

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"We may put such a robot in the pipeline of an aircraft engine and have the robot navigate the pipeline all the way to the end, while sending back all the images along the way," Zhao says.

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