At the Robosphere 2002
conference held at the NASA Ames Research Center in Silicon
Valley November 14-15, Wei-Min Shen of the USC School of
Engineering's Information Sciences Institute (ISI) presented
an overview of an audacious project to have pieces of the
proposed half-mile-long Space Solar Power System satellite put
themselves together--self-assemble--without the help of
astronauts.
Shen and co-principal investigator Peter Will are doing
more than proposing. They are already testing the hardware and
software the system would use in the ISI Polymorphic Robotics
Laboratory, of which Shen is director.
Over the past two and a half years, Shen and Will have
developed modular individual robot units, each with a computer
chip programmed with what the researchers call "hormonal"
software. Shen said that such software allows "bifurcation,
unification, and behavior shifting" by the modules.
The units can unite themselves into larger wholes, or
divide themselves up into smaller ones. "If a six-unit snake
splits in half," explained Shen, "you get two smaller,
three-unit snakes that function as the larger one did."
Separated units communicate using infrared signals,
maneuvering their coupling units into a lock in cooperative,
coordinated fashion.
"Behavior shifting" means that the individual units--which
are identical--exhibit different behavior according to their
position in the assembly.
Will and Shen's CONRO project created working units that
use the software. Shen and Will's new SOLAR space station
proposal, funded by a consortium including NASA, the NSF, and
the Electric Power Research Institute (EPRI), proposes to use
this architecture on a gigantic scale.
They propose a self-assembling space station consisting of
two species of robotic devices, both controlled by the same
software.
One species will be the parts that will actually make up
the station: solar power units, including necessary utility
conduits. Each of these will have a microprocessor running
hormonal software. Sets of contiguious units will, once
released into space, arrange themselves into the desired
configuration.
When these subassemblies are ready, they will signal and
alert the second species of robot, the "free-flying
intelligent fiber rope matchmaker units," or whips.
Whips will consist of two modular robot units connected by
a long connector line that can shorten or lengthen at the
direction of the software. They will also have solar-powered
rockets, enabling them to move in space, GPS sensors to find
their position, communicators, and connectors.
When a completed subassembly signals, a whip will maneuver
toward it, lock on, wait for a call from a second assembly,
tow the first over, pull them together by winching in the
fiber rope, so that the two can attach to each other.
Once mating accomplished, the whip unit would then fly off
to find other parts to assemble.
The design, said Will, combines the advantages of
free-flying and tethered systems.
In the laboratory, Shen and Will have modeled the concept
in two-dimensional form, working with an air-hockey table on
which prototype individual units will learn to find each other
by sensing each other's infrared signals, maneuver next to
each other using built-in fans, lock on, and pull units
together using a motorized cable.
"This will give both the hardware and software a realistic
test," said Shen. Researcher Harshit Suri has built a first
prototype unit.
Shen and Will won the grant from the NSF/NSA/EPRI
consortium that funds their work in a rigorous competition in
which 76 proposals were received and only four were funded.
Shen, Will, and ISI collaborator Behnam Salemi published a
detailed paper, "Hormone-Inspired Adaptive Communication and
Distributed Control for CONRO Self-Reconfigurable Robots," in
IEEE Transactions on Robotics and Automation. in
October, 2002. They have recently applied for a U.S. patent on
the technology.
Working with Shen and Will in the field of space assembly
are two faculty members from the USC School of Engineering:
Berokh Khoshnevis of the department of industrial and systems
engineering; and George Bekey, of the department of computer
science. Along with Suri and Salemi, Yusuf Akteskan is working
on the space system project.
The ISI Polymorphic Robotics Laboratory is one of six
laboratories associated with the USC School of Engineering's
Center for Robotics and Embedded Systems.
Schematic diagram of architecture of
self-assembling solar power satellite. Seeker
"whip" units, (yellow) powered at both ends,
listen for signals from subassemblies, find them,
and pull them together.
