A droid for all seasons
No job is too unusual for a breed of robots that reinvent themselves
IMAGINE an automaton that can design itself, assemble itself and even
kill itself. No, it's not the liquid metal robot from Terminator 2--but
this droid can certainly build itself to perform a particular task,
melt itself down and recycle itself, say researchers in Massachusetts.
The scientists have developed what they call a polymorphic robot--a
machine that can change its shape to suit the job in hand.
Shape-shifting robots could be used as planetary explorers, or for
search-and-rescue missions, changing their shape to meet each new
challenge and adapting to strange and unpredictable environments.
The researchers have produced a simple thermoplastic-framed robot, says
Hod Lipson, who developed it with Jordan Pollack at Brandeis
University, near Boston. "All the robot has to do is find a way to
move," he says. The prototype is very basic and has no sensors, so it
is unaware of the world, though sensors could be added at a later
The idea is that a task will be set for the robot, such as: "Figure out
how to move using only one leg and one motor." A computer will then
attempt to design a body that will help it to meet this challenge most
efficiently. At present, the robot's body is built using the "rapid
prototyping" technology common in the car industry, which can produce
complex three-dimensional structures very quickly. A device called a 3D
printer uses a nozzle to build up progressive layers of thermoplastic,
slowly creating the required structure (click on thumbnail graphic
Although 3D printers are large and cumbersome, says Lipson, much
smaller ones could one day be built into a robot, allowing it to change
parts of its body, for example, to reshape an arm to produce a new tool
for a novel situation. Mark Yim of the Xerox Palo Alto Research Center
(PARC) in California says this is one area in which polymorphic robots
could be most useful. There's no point in taking an entire toolkit into
space, he says, when you don't know which tools you'll need: a single
robot arm can be shaped to do the job of all of them.
It is also conceivable, says Lipson, that the 3D printing technology
will allow several materials to be printed, including conductive,
nonconductive and even semiconductive materials. "Wires, motors and
logic circuits, as well as structure, could be printed in one pass
without the need for assembly," Lipson predicts.
With each new task, the look of a polymorphic robot is impossible to
predict, because each design is "evolved" using a genetic algorithm.
The physical structure, and the neural network that will be the brains
of the proposed robot, are treated like genetic information that can be
combined and mutated in simulation to produce entirely new designs. The
"fitness" of these offspring is then evaluated and the best are "bred"
to produce more offspring. This process is repeated many times until
the design has evolved to do the best job.
To keep things simple, Lipson allowed the algorithm only basic
components with which to design the prototype robot: straight plastic
bars of varying lengths and electric motors that can extend or shrink
the length of a bar. Joints are all ball-and-socket designs, as these
are easily created by a 3D printer. From these basic parameters a host
of complex--sometimes lifelike--structures have been evolved.
Some versions push themselves along on one leg, while others produce a
hinge-like motion and crawl about like a fish out of water. Yet another
moves sideways like a crab. "The robot is ready to move when it comes
out of the printer," says Lipson. Its motor, however, must be inserted
by a person. But the aim is to make the robots totally independent,
much like the vengeful shape-shifter in Terminator 2.
When the robot has performed its task, it offers itself up to be melted
down, so its thermoplastic components can be recycled into another
useful droid by the 3D printer. The idea of building and melting down
robots is novel, says Yim, who makes modular robots that reshape
themselves by fitting smaller robots together. "I've never seen
anything like it." But he warns that to make truly useful robots,
stronger plastics and more materials are needed.
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