# Robot unties knotted cables but can’t pick them up off the floor

A robot that can untangle long cables with just two simple grippers may be useful in aircraft and car manufacturing or as a household assistant

2 August 2022

A robot with a pair of grippers on its arms can untangle long, knotted cables. The technology could be used to fit electrical cables in aircraft or offer household assistance to older people, but at the moment, the robot struggles if it drops something, because it can’t bend down to pick it up again.

Ken Goldberg at the University of California, Berkeley, says his team’s work on the robot was inspired by untidy cables getting in the way in the laboratory, which made him think about how a robot would have to work to keep them tucked away. The problem requires dextrous mechanical arms, but also an understanding of knot theory, he says.

“There’s a beautiful mathematical body of theory out there on knots, and it’s very abstract. It generally abstracts the problem into graphs and graphical structures,” says Goldberg. “We applied certain aspects of that. Cables are difficult to perceive, even with the best of cameras and techniques, and they’re also difficult to manipulate because of their flexibility and their small size and their tendency to spring out and do things that are very unpredictable.”

The robot is mounted to a table on which a knotted cable also rests. It is fitted with a camera that can observe visible light and measure depth. The images it records are fed into an artificial intelligence, which interprets them and creates an accurate map of the orientation and configuration of the cable along its length.

There are several strategies that the robot’s control algorithm uses to untie knots, and it applies them iteratively as needed until the whole cable is straightened out. Initially, the robot uses its camera to scan the cable and form a map of the structure of any knots. If this is ambiguous, it can gently pull at the cable on either side of the knot to remove loose loops of cable and leave only knots remaining, or shake the cable to remove superfluous loops, and then scan again.

The robot can then grasp the cable at two different points and pull it apart, with both of its 3D-printed grippers able to either firmly seize the cable or hold it loosely to allow movement, in order to slowly unweave the knot. The final task is to slowly pass along the cable from one end to the other and check that all knots have been removed.

In experiments with a braided 2.7-metre micro-USB to USB cable, the robot had a success rate of 67 per cent on single, simple knots and 50 per cent on more complex tangles. Some of the failures included the cable falling off the table, from where the robot was unable to retrieve it.

Reference: arxiv.org/abs/2207.07813

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