Page 63 - Concise Encyclopedia of Robotics

Coexistence
After motion begins, a position sensor detects possible errors in the tra-
jectory. If an error is detected, the sensor outputs a signal that operates
through a feedback circuit to bring the manipulator back on course. The
term derives from the fact that the feedback and control-signal circuits
together constitute a closed loop.
The main asset of closed-loop control is accuracy. In addition,
closed-loop control can compensate for rapid, localized, or unexpected
changes in the work environment. The principal disadvantages are
greater cost and complexity than simpler schemes such as ballistic control.
Compare BALLISTIC CONTROL.
CLOSED-LOOP SYSTEM
A closed-loop system is a set of devices that regulates its own behavior.Closed
loops can be found in many kinds of machines, from the engine in a
car (governor) to the gain control in a radio receiver (automatic level
control).
A closed-loop system, also known as a servomechanism, has some
means of incorporating mechanical feedback from the output to the input.
A sensor at the output end generates a signal that is sent back to the
input to regulate the machine behavior. A good example of this is a back
pressure sensor. Another example is closed-loop control of a robot manip-
ulator. Compare OPEN-LOOP SYSTEM.
See also BACK PRESSURE SENSOR, CLOSED-LOOP CONTROL, and SERVOMECHANISM.
CMOS
See COMPLEMENTARY METAL-OXIDE SEMICONDUCTOR.
COEXISTENCE
The term coexistence refers to programmed interactions among insect
robots that share a working environment. The robots in such a system do
not communicate directly with each other, but they all communicate
with a central controller. There are three general schemes: ignorant coex-
istence, informed coexistence, and intelligent coexistence.
In ignorant coexistence, none of the robots is aware that any of the
others exists. In this sense, when two robots encounter one another, each
machine regards its counterpart as an obstruction. Most mobile robots
are programmed to avoid obstacles and hazards, maintaining a minimum
distance of, say, 1 m. Thus, if there are numerous robots in a given envi-
ronment and they all have ignorant coexistence, they tend to stay away
from each other. If the robot “population density” is moderate to high,
the machines tend to be more or less evenly spaced in the work environ-
ment at all times.

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