dancing in sync
Broadcasting data allows
machines to coordinate
By Rachel Ehrenberg
You don’t have to watch Dancing with
the Stars to know that keeping in sync is
tough, and it’s tougher still for a robot.
But a new approach keeps robots in step,
and even enables a robot that loses its
footing to resynchronize with its peers.
One way to synchronize a group of
robots is for each to communicate with
one another about its position, but distance between the robots can lead to
time delays. And when many robots are
involved, the complexity of this communication network grows. To skirt such
problems, researchers from MIT have
taken inspiration from bacteria that synchronize their behavior not by checking
in with each other, but by checking in
with their environment.
Synchronizing robots this way might
work well in rescue operations where
robots are damaged and need to be
replaced, says Paola Flocchini, a distributed computing expert at the University
of Ottawa in Canada.
Many bacteria coordinate via a process called quorum sensing, which
involves both releasing a steady stream
of signaling molecules into the environment and then sensing the signaling
molecules. When enough bacteria are
around that the local concentration of
these molecules soars, it’s time for group
action: Genes get turned on, molecular
switches are flipped and the bacteria all
change their behavior in sync.
Similarly, MIT’s Jean-Jacques Slotine
and Patrick Bechon coordinated the
behavior of eight dancing humanoid
robots by having the bots send information to — and get information from — an
external computer server.
The work appeared online
May 14 at arXiv.org.
The robots go through
cycles of prescribed
actions, such as bobbing
their heads, and send the
server information about
where they are in these
cycles. The server then
sends the average of this
information back to all
the robots. So a robot joining its dancing peers will
check in with the server about what
the other robots are doing. It can then
calculate what the next movement
is in the synchronized cycle and rejoin
the group. Information about the music
—in the test case, Michael Jackson’s
“Thriller” —is also embedded in the
information sent back to the robots.
Incorporating math that describes
Sending information to and from an outside server
keeps these robots in sync and even allows a robot
that has fallen out of step to rejoin the group.
the oscillating movements of body parts,
such as arms and heads, is quite clever,
says Mehran Mesbahi of the University of Washington in Seattle, whose
research includes spacecraft navigation
and control. It’s much harder to incorporate information on position, angles
and music, he says, than to have a simple
command such as “March.” s
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