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Micro Robots Made to Climb in Curved, Inverted Spaces

HAMR-E device

HAMR-E device and U.S. penny (Wyss Institute, Harvard University)

19 Dec. 2018. A robotics lab at Harvard University created a tiny, 4-legged robot that travels through tight spots, climbing on vertical surfaces and even upside down. The device, described in today’s issue of the journal Science Robotics (paid subscription required), was designed to meet the inspection needs of jet engine manufacturer Rolls-Royce, but its developers say the small robots can be deployed into a variety of systems, buildings, and vital infrastructure.

The Harvard Microrobotics Laboratory led by Robert Wood, also affiliated with Harvard’s Wyss Institute for Biologically Inspired Engineering, studies devices made from a wide range of materials and at various scales to solve difficult problems in unpredictable environments. In this case, Wood and colleagues tackled the difficulty of inspecting complex jet engines on aircraft carrying hundreds of passengers for many hours at a time. And these devices must work quickly and in coordination with many other similar devices deployed inside the engine.

A particular challenge in building these robots is the need to remain adhered to vertical, curved, and cylindrical surfaces, of which jet engines have many. Operating while on curved or cylindrical surfaces requires remaining attached and functioning while upside down, which usually needs a good deal of force to keep from coming detached. This requirement, say the researchers, goes well beyond most current climbing robots, and usually calls for magnetic or vacuum-powered suction with large, heavy components.

The team’s solution builds on the lab’s earlier work that created the Harvard Ambulatory Microrobot, or HAMR, inspired by cockroaches. HAMRs are 4-legged centimeter-scale devices designed to move at high speeds, as well as jump, climb, and in some cases swim. Their climbing abilities, however, do not go beyond vertical surfaces, which means adding the ability to move while inverted. Their solution uses electroadhesion that applies electrostatic forces between the robot’s feet and the target surface where the robot is traveling, and can be achieved with lightweight components.

The researchers’ device, called Harvard Ambulatory Microrobot with Electroadhesion, or HAMR-E, is 4.5 centimeters long and weighs about 1.5 grams. Each of HAMR-E’s 4 ankle joints is designed using origami-style folding, based on the Japanese art form producing elegant designs with folded paper, which the lab sometimes uses in its systems. In this case, the folding has a more practical goal, to enable the device to maintain its original orientation while climbing on vertical or inverted surfaces.

At the end of each HAMR-E legs is an electroadhesive footpad using about the same power as the HAMR-E device alone, and switches the electric field on and off to enable the device to engage or release from the target surface. To move, HAMR-E swings each of its legs forward in a designated order that keeps three legs of the device attached to the target surface at any one time.

The team tested HAMR-E devices on horizontal, tilted, vertical, and inverted surfaces, recording speeds comparable to or faster in most cases than other climbing robots, and executing 180-degree turns. The tests also included travels over curved and inverted surfaces in a jet engine, where the devices stayed attached even on rough substrates. In these proof-of-concept tests, the HAMR-Es were wired, allowing the operators to increase power to boost their adhesion, but their light weight should enable them to eventually carry their own power sources.

“This iteration of HAMR-E,” says Wood in a university statement, “is the first and most convincing step toward showing that this approach to a centimeter-scale climbing robot is possible, and that such robots could in the future be used to explore any sort of infrastructure, including buildings, pipes, engines, generators, and more.”

The following video demonstrates HAMR-E devices.

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