Page 41 - Introduction to AI Robotics

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1 From Teleoperation To Autonomy
heavier. The end result is that it is not uncommon for a 2 ton robot to be
able to handle only a 200 pound payload. Another simplifying solution is to
avoid the computations in the dynamics and kinematics and instead have the
TEACH PENDANT programmer use a teach pendant. Using a teach pendant (which often looks
like a joystick or computer game console), the programmer guides the robot
through the desired set of motions. The robot remembers these motions and
creates a program from them. Teach pendants do not mitigate the danger
of working around a 2 ton piece of equipment. Many programmers have to
direct the robot to perform delicate tasks, and have to get physically close
to the robot in order to see what the robot should do next. This puts the
programmer at risk of being hit by the robot should it hit a singularity point
in its joint configuration or if the programmer makes a mistake in directing
a motion. You don’t want to have your head next to a 2 ton robot arm if it
suddenly spins around!
AUTOMATIC GUIDED Automatic guided vehicles, or AGVs, are intended to be the most flexible con-
VEHICLES veyor system possible: a conveyor which doesn’t need a continuous belt or
roller table. Ideally an AGV would be able to pick up a bin of parts or man-
ufactured items and deliver them as needed. For example, an AGV might
receive a bin containing an assembled engine. It could then deliver it au-
tomatically across the shop floor to the car assembly area which needed an
engine. As it returned, it might be diverted by the central computer and in-
structed to pick up a defective part and take it to another area of the shop for
reworking.
However, navigation (as will be seen in Part II) is complex. The AGV has
to know where it is, plan a path from its current location to its goal desti-
nation, and to avoid colliding with people, other AGVs, and maintenance
workers and tools cluttering the factory floor. This proved too difficult to do,
especially for factories with uneven lighting (which interferes with vision)
and lots of metal (which interferes with radio controllers and on-board radar
and sonar). Various solutions converged on creating a trail for the AGV to
follow. One method is to bury a magnetic wire in the floor for the AGV to
sense. Unfortunately, changing the path of an AGV required ripping up the
concrete floor. This didn’t help with the flexibility needs of modern manu-
facturing. Another method is to put down a strip of photochemical tape for
the vehicle to follow. The strip is unfortunately vulnerable, both to wear and
to vandalism by unhappy workers. Regardless of the guidance method, in
the end the simplest way to thwart an AGV was to something on its path.
If the AGV did not have range sensors, then it would be unable to detect
an expensive piece of equipment or a person put deliberately in its path. A