Published online: 16 November 2006; | doi:10.1038/news061113-16
Injured robots learn to limpMust...keep...going...
complete...mission.Heidi Ledford 
| The robot constantly models its own body to work out how best to limp along. Watch a video here. Science |
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Josh
Bongard's robots walk, but they do not stride. They flop, wiggle, and
scrape their way along on four, starfish-like legs. But what these
robots lack in grace, they make up for in ingenuity.
The
robots, created by Bongard and a team of engineers at Cornell
University in Ithaca, New York, can sense and respond to damage without
human instruction. Pluck off part of a leg, and they adjust their gait
to compensate. Eventually, says Bongard, robots like these could crawl
into high-risk areas on search-and-rescue missions, or explore distant
planets where no humans are around to repair robotic injuries.
Each
robot begins lying flat on the table, with no knowledge of how to walk.
It makes small, random motions with each leg while Bongard's team feeds
it information about its body's tilt and angle at each joint.
The
robot uses the information to construct computer models that predict
the outcomes of different movements, taking into account factors such
as gravity, friction and momentum. It gingerly tests each model with
small movements, much as a human leans on an injured foot to find out
how much weight it can bear.
"When
it's most uncertain about itself," says Bongard, who is now at the
University of Vermont in Burlington, "that's when it moves the least."
Once the robot has decided which movements best suit its situation, it
sets off.
On the catwalk
When
the robot's movements stop matching its model — if it has been injured,
for example — then the robot builds a new model incorporating current
conditions.
The
selected models are not always successful. Sometimes a misstep sends a
robot sprawling, or an errant thrust flips it onto its back, legs
flailing like a stranded beetle. But most of the time, Bongard's team
reports in this week's issue of Science, the robot can limp along1.
Other
robots can respond to damage only if they have been programmed with a
specific contingency plan, or if they randomly try all possible
movements, which can mean cycling through hundred of thousands of
permutations. Bongard's robots are more adaptable and efficient.
"I haven't seen anything quite like it," says Ronald
Arkin, director of the Mobile Robot Laboratory at the Georgia Institute
of Technology in Atlanta. Bongard's robots are a new development in
evolutionary robotics, says Arkin, a field that aims to build robots
that learn from their environment without human help, and then teach
other robots their skills.
At
this point, Bongard's robots act as individuals. The next step, he
says, is to create a network of robots that work together, with each
member of the group learning from the injuries and adjustments of
fellow robots.
The present generation reminds Arkin of the first Terminator
movie, in which an evil robot with amputated legs drags itself in
pursuit of the heroine. "One could argue that this is the precursor to
being able to do that," he says.
Visit our newsblog to read and post comments about this story.
References
- Bongard J., et al. Science, 314. 1118 - 1121 (2006).
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