Page 214 - Concise Encyclopedia of Robotics

MTBF
All motors operate by means of electromagnetic effects.Electric current
flows through a set of coils, producing magnetic fields. The magnetic
forces result in rotation. The greater the current in the coils, the greater is
the rotating force. When the motor is connected to a load, the force
needed to turn the shaft increases. The more the force, the greater the
current flow, and the more power is drawn from the power source.
The illustration is a functional diagram of a typical electric motor. One
set of coils rotates with the motor shaft. This is called the armature coil.
The other set of coils is fixed, and is called the field coil. The commutator
reverses the current with each half-rotation of the motor, so that the shaft
keeps turning in the same direction.
The electric motor operates on the same principle as an electric gener-
ator. In fact, some motors can be used as generators.
See also GENERATOR, SELSYN, and SERVOMECHANISM.
MTBF
See MEAN TIME BEFORE FAILURE/MEAN TIME BETWEEN FAILURES (MTBF).
MULTIAGENT TEAM
See INSECT ROBOT.
MULTIPLEX
Multiplex is the transmission of two or more messages over the same line
or channel at the same time. Multiplex transmission is done in various
ways. The most common methods are frequency-division multiplex
(FDM) and time-division multiplex (TDM).
In FDM, a communications channel is broken down into subchannels.
Suppose a channel is 24 kHz (kilohertz) wide. Then it can theoretically
hold eight signals 3 kHz wide. The frequencies of the signals must be just
right, so they do not overlap. Usually there is a little extra space on either
side of each subchannel to ensure that overlapping does not occur.In FDM,
data is transmitted in parallel form. That is, the information in all the
channels is sent simultaneously.
Sometimes, data are cumbersome to transmit in parallel form. Such
data can be converted to serial form using TDM. In this mode, signals are
broken into pieces “timewise,” and then the pieces are sent in a rotating
sequence. This slows the rate of data transfer by a factor equal to the
number of signals. For example, if each of six messages is 1 s long if sent
by itself at full speed, the time-division-multiplexed signal will take 6 s.

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