lite receiving antennas and down-converter
receivers.
F (dB) = 10 log
10
(SNR
in
/SNR
out
)
direct burial
(1) the practice of burying a
specially-armored power or communications
cable in a ditch without the use of a surround-
ing conduit.
(2) a term applied to any cable which is
meant for direct burial.
direct control
bottom, first, control layer
of a multilayer controller, directly responsi-
ble for adjusting the manipulated inputs to the
controlled process; typical example of direct
control is the regulation layer of an industrial
control system, where the manipulated inputs
are used to make the controlled variables fol-
low the desired set point values.
direct control layer
See
direct control
.
direct converter
a frequency converter
that converts an RF signal to a baseband sig-
nal directly in receivers. It converts a base-
band signal to an RF signal directly in trans-
mitters.
direct current machine
a DC machine
is an electromechanical dynamo that either
converts direct current electrical power into
mechanical power (DC motor), or converts
mechanical power into direct current electri-
cal power (DC generator). Some DC ma-
chines are designed to perform either of these
functions, depending on the energy source to
the dynamo.
direct current motor
a rotation machine
energized by DC electrical energy and used
to convert electrical energy to mechanical en-
ergy.
direct digital synthesizer
an oscillator
that generates sinusoidal wave by digital cal-
culation and digital to analog conversion. It
can generate an arbitrary frequency signal in
a fine channel step.
direct drive
a drive in which no gear re-
ducer is used.
direct drive robot
a mechanical arm
where all or part of the active arm joints are
actuated with the direct drive. Due to the fact
that many actuators are best suited to rela-
tively high speeds and low torques, a speed
reduction system is required. Gears are the
most common elements used for reduction.
A robot with a gear mechanism is called a
geared robot. Gears are located at different
joints; therefore, usually geared robots have
a transmission system, which is needed to
transfer the motion from the actuator to the
joint.
direct dynamics
the direct dynamics
problem consists of determining the joint
generalized accelerations
¨q(t) assuming that
joint generalized forces
τ(k), joint positions
q(t), and joint velocities ˙q(t) are known. So-
lution of the direct dynamics leads to the dy-
namic simulation which is defined as follows:
for a given set of joint generalized forces and
initial values of the joint positions and veloci-
ties integrate the equations of motion in order
to find a set of joint accelerations, velocities,
and positions. The dynamics simulation is
very useful for manipulator simulation.
direct fuzzy control
the use of fuzzy con-
trol directly in the inner control loop of a
feedback control system.
direct kinematics
direct kinematics (or
forward kinematics) for an arbitrary manip-
ulator and given the joint variables vector
q(t) = [q
1
(t), q
2
(t), . . . , q
n
(t)]
T
and the ge-
ometric link parameters finds the position and
orientation of the end-effector of the manip-
ulator with respect to a reference coordinate
frame. The direct kinematics problem can
be solved by successive multiplication of the
D-H transformation matrices from the base
of the manipulator towards its end-effector.
More precisely the kinematics can be repre-
sented mathematically as a continuous map
assigning to every joint position (configu-
c
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