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 SCIENCE NEWS
November 16, 2006
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Resilient Robot Hobbles Along, Even if Injured
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New four-legged machine can assess damage to its body and adapt its gait accordingly
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Image: © SCIENCE
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MYSELF AND I: The resilient robot and, in its reflection, a rendering of the model it uses to plot its next move.
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When a person stubs his toe, he compensates by
favoring his other leg. More dramatically, if he loses use of both his
legs, he can still crawl to get from point A to point B. Now a robot
shaped like a four-legged starfish can do the same. Designed at Cornell
University, the nine-piece device can advance toward a goal even after
incurring damage. In a paper published in this week's Science, the researchers describe the algorithm by which this mechanical beast can assess its own condition.
"The main advance here was not just the diagnosis and recovery, but
how the robot does that, which is to build a model of itself," explains
Josh Bongard, a computer scientist now at the University of Vermont. In
the past, robots attempting to recover from damage would have attempted
upward of hundreds of thousands of movements in an inefficient
trial-and-error process designed to overcome injury. But if these
robots are to become "the next generation of planetary rovers," Bongard
points out, "you can't assume that this robot can perform hundreds of
thousands of trials. It may damage itself further or fall off a cliff."
So, Bongard, along with his colleagues Victor Zykov and Hod Lipson,
programmed their robot to carefully select its actions so that it makes
as few movements as possible. |
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"actuation-sensation" system, the robot runs through a number of
possibilities before deciding what to do. In its electronic brain, the
robot will perform a random five-second movement--such as lifting its
left leg and then lifting its right leg. It will then plug that
movement into 15 randomly chosen models, which are essentially 15
guesses as to how the robot is put together. It will then process all
the results of performing the particular action in each model--one may
predict that it will cause the robot to tilt left, for instance;
another may indicate the machine will tilt right. Finally, the robot
performs the action.
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If the robot ends up tilted left--which the four
sensors on its body can determine--it will throw out all the models
that did not make that prediction. "It's basically a rough analogue of
natural selection," notes Bongard. "This is a population of 15
self-models and the ones that are more fit propagate, and the ones that
are less fit die off."
The researchers had the robot go through the algorithm when it was
in tip-top shape, and found that its chosen mode of movement was to
generate enough momentum to throw its body forward, somewhat like an
inchworm would. When Bongard severed one of its limbs, it hobbled
forward instead. Ronald Arkin, a roboticist at the Georgia Institute of
Technology, says this new resilient robot reminds him of the cyborg
played by Arnold Schwarzenegger in the first Terminator movie:
the machine "muddles on" to its goal despite suffering several
mechanical setbacks. In the real world, however, "it could have some
significant value in cases where people can't reach it," he remarks.
"It has some applications for search and rescue or extraterrestrial
exploration."
Right now, the robot isn't exactly ready for any operation that
is time sensitive. The time between movements was set to 20 minutes by
the researchers, because at this stage they were just trying to see if
the robot could overcome adversity. Bongard is confident that in the
future, the robot could run through its algorithm much faster. "There's
no reason why this robot couldn't communicate wirelessly with a bank of
computers," Bongard says. "You could actually parallelize this process
rather quickly." --Nikhil Swaminathan
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RELATED LINKS:
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Long-Distance Robots
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The Spirit of Exploration
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You, Robot
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Android Science
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Rise of the Robots
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