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Machines Like Us

Helping robots hold on

Friday, 11 November 2011
by Nancy Stauffer

Based on simulations, the researchers have developed a manufacturing technique that can combine multiple modules as shown above. Credit: MIT

MIT researchers design a ‘controllable adhesion system’ for underwater robots.

Since the 1970s, when early autonomous underwater vehicles (AUVs) were developed at MIT, Institute scientists have tackled various barriers to robots that can travel autonomously in the deep ocean. This four-part series examines current MIT efforts to refine AUVs’ artificial intelligence, navigation, stability and tenacity.

If an underwater robot is to open a valve or repair a damaged pipe, it needs to anchor itself to a solid surface so it can apply force to carry out its task without pushing itself away. It then needs to detach and move on to its next assignment.

A group of MIT researchers has designed a “controllable adhesion system” for underwater robots that offers the needed features: a high holding force on various geometries and textures, low energy consumption, chemical resistance to seawater, and low maintenance requirements.

Underwater vehicles have become good at using propellers and thrusters to stay in one place, even in strong currents. But holding on to a surface while exerting force to do a job is quite another challenge—one that Sangbae Kim, the Esther and Harold E. Edgerton Assistant Professor of Mechanical Engineering, and his collaborators have been tackling for the past year. They are working on several approaches, but their best success to date has come using a magnet, or more specifically, an electromagnet: Take a bar of iron, wrap a coil of wire around it, send an electrical current through it and you have a magnet. Switch off the current, and the magnetic field disappears.

But there’s a drawback to this approach: You need to send electrical current to the robot all the while it’s completing its task. Stop the current and the magnet goes neutral, and the robot can float away.

So Kim’s group turned to “controllable electromagnets”—magnetic devices that can easily be turned on and off using little energy. The concept has been around for 30 years and has been used for various applications. However, there is little published information on how these devices are designed, what they’re made of and how they work, so the researchers had to develop an understanding of the fundamentals involved.

Guided by that understanding, they designed a module consisting of two parallel bar magnets next to each other. One is a very strong magnet made of neodymium, iron and boron (NIB). The other is a weak magnet made of aluminum, nickel and cobalt (alnico). Around the alnico magnet is a coil through which an electrical current can flow.