because schematic representations of it often
look like a capital letter V.
velocity error
the final steady difference
between a ramp setpoint and the process out-
put in a unity feedback control system. Thus,
it is the asymptotic error in position that arises
in a closed loop system that is commanded
to move with constant velocity.
See also
acceleration error
and
position error
.
velocity error constant
a gain
K
v
from
which the velocity error
e
v
is readily deter-
mined. It is a concept that is useful in the de-
sign of unity feedback control systems since
it transforms a constraint on the final error
to a constraint on the gain of the open loop
system. The relevant equations are
e
v
=
1
K
v
and
K
v
=
lim
s → ∞ sq(s)
where
q(s) is the transfer function model
of the open loop system, including the con-
troller and the process in cascade. See also
acceleration error constant
and
position error
constant
.
velocity filtering
means for discriminat-
ing signals from noise or other undesired sig-
nals because of their different apparent veloc-
ities.
velocity flow field
the velocity field cal-
culated in optical flow computation.
velocity manipulability ellipsoid
an el-
lipsoid that characterizes the end-effector ve-
locities that can be generated with the given
set of joint velocities, with the manipulator
in a given posture.
Consider a set of generalized joint veloc-
ities
˙q of constant, unit norm ˙q
T
˙q = 1. Tak-
ing into account the differential kinematics
J and properties of the pseudo-inverse of
the geometrical Jacobian, the unit norm can
be rewritten as follows:
v
T
(J J
T
)
−1
v = 1,
which is the equation of the points on the
surface of an ellipsoid in the end-effector ve-
locity space.
velocity of light
in vacuum, a constant
equal to 2
.997928 × 10
8
meters/second. In
other media, equal to the vacuum value di-
vided by the refractive index of the medium.
velocity saturation
a physical process in
a semiconductor where the carrier velocity
becomes constant independent of the electric
field due to high energy scattering and energy
loss, compared to low electric field transport
where the velocity is linearly related to the
field by the mobility.
verification
the process of proving that
the implementation of hardware or software
meets the published system requirements.
verification kit
known impedance stan-
dards traced to NIST, other than calibration
standards, used to verify the calibrated per-
formance of a vector network analyzer sys-
tem.
Versa Module Europe bus (VME bus)
a
standardized processor backplane bus system
originally developed by Motorola. The bus
allows multiple processors to share memory
and I/O devices.
vertical cavity laser
semiconductor laser
in which the electromagnetic fields propagate
in a direction perpendicular to the amplifying
plane (the vertical direction).
vertical deflection
the direction of an en-
tity is caused to move by some physical ac-
tion; commonly describes the vertical move-
ment of an electron beam caused by electro-
static or magnetic forces applied to produce
a required scan. Magnetic deflection is fre-
quently used with a CRT video display and
requires a large deflection angle.
vertical microinstruction
a field that
specifies one microcommand via its op code.
In practice, microinstructions that typically
contain three or four fields are called verti-
cal.
c
2000 by CRC Press LLC