Many commercial robotic arms
perform what roboticists call ‘pick and place’ tasks: The arm picks up an
object in one location and places it in another. Usually, the objects — say,
automobile components along an assembly line — are positioned so that the arm
can easily grasp them; the appendage that does the grasping may even be tailored
to the objects’ shape. General-purpose household robots, however, would have to
be able to manipulate objects of any shape, left in any location. And today,
commercially available robots don’t have anything like the dexterity of the
human hand.
Most experimental general-purpose
robots use a motion-planning algorithm called the rapidly exploring random
tree, which maps out a limited number of collision-free trajectories through
the robot’s environment — rather like a subway map overlaid on the map of a
city. A sophisticated-enough robot might have arms with seven different joints;
if the robot is also mounted on a mobile base — as was the Willow Garage PR2
that the MIT researchers (Computer Science and Artificial Intelligence
Laboratory) used — then checking for collisions could mean searching a
10-dimensional space.
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