Final Report: NASA ACRP NCC7-7,
Bush Robots, Hans Moravec, Jesse Easudes
Most present day remote controlled and robot arms fall short of
human dexterity, especially in their viselike hands, which are unable
to manipulate complicated objects, or apply the combinations of forces
needed to accomplish some simple tasks. These limitations, among
others, exclude them from many interesting applications in
construction, repair and exploration.
Some research manipulators achieve better dexterity by imitating
the structure of the human hand, often at the expense of precision,
strength, reliability and especially economy. Robot hands with three,
four and five dexterous fingers have demonstrated the ability to roll
eggs, twirl batons and tie knots.
There are imaginable tasks (for instance, those requiring
simultaneously maneuvering together more than three uncooperative
components in a precise way) for which even human dexterity is
inadequate. Today, most are never attempted, while a few are
approximated using specialized tools and fixtures.
It may be possible in future to leapfrog the dexterity not only of
conventional mechanical manipulators, but of human hands. Consider
the following observation.
Once upon a time, the most complex animal was a worm. The
stick-like shape was poorly adapted for manipulation and even
locomotion. Then these stick-like animals grew smaller sticks, called
legs, and locomotion was much improved, although they were still poor
at manipulating. Then the smaller sticks grew yet smaller sticks, and
hands, with manipulating fingers were invented and precise
manipulation of the environment became possible.
Generalize the concept. Visualize a robot that looks like a tree,
with a big stem, repeatedly branching into thinner, shorter and more
numerous twigs, finally ending up in vast numbers of microscopic
cilia. Each intermediate branch would have several degrees of freedom
of sensed and controlled motion. Though each branch would be a rigid
mechanical object, the overall structure would have an organic
flexibility because of the huge numbers of degrees of freedom. At the
outer extremes, the machine would have an enormous number of
individually positionable and naturally swift manipulators,
coordinated for simultaneous execution of otherwise unimaginable tasks
by signals and power from the central regions.
Taken far enough, the smallest fingers operate at nanoscale, able
to shape matter at the atomic level. Compared to the free-floating,
self-powered, self-directed nanobots envisioned by others, each nano
finger in a bush robot would be a simple device, controlled,
coordinated and powered by mechanically connected computers and energy
sources located in the direction of its stem. Bush robots may provide
a uniform, top down, incremental bridge to nanotechnology.
Macroscopic machines with a few levels of branching could be built
today, and could exhibit human-like dexterity. As microtechnology
advances, the number of branching levels could be increased with ever
finer sub-fingers. An ultimate nanoscale bush robot might begin with a
stem a meter in length and a few centimeters in diameter, able to move
with a one second timescale. At 30 levels of branching, one might
find a billion fingers each a micron long, able to move at a
megahertz. At 50 levels, there could be 1015 fingers, each a
nanometer long, and in principle able to move at gigahertz rates, if
not constrained by exotic physical effects.