Glossary of Terms
Ndrive HL User’s Manual
A-6 www.aerotech.com
error from 90° from which two surfaces of axes are aligned.
Overshoot
In a servo system, referred to the amount of velocity and/or
position overrun from the input command. Overshoot is a result
of many factors including mechanical structure, tuning gains,
servo controller capability, and inertial mismatch.
PID
A group of gain terms in classical control theory (Proportional
Integral Derivative) used in compensation of a closed-loop
system. The terms are optimally adjusted to have the output
response equal the input command. Aerotech controllers utilize
the more sophisticated PID FVFA loop which incorporates
additional terms for greater system performance.
Pitch (of travel)
Angular motion of a carriage around an axis perpendicular to the
motion direction and perpendicular to the yaw axis.
Pitch Error
Positioning error resulting from a pitching motion.
PLC
Programmable Logic Controller. A programmable device that
utilizes “ladder logic” to control a number of input and output
discrete devices.
PWM
Pulse Width Modulation. Switch-mode technique used in
amplifiers and drivers to control motor current. The output
voltage is constant and switched at the bus value (160 VDC with
a 115 VAC input line).
Quadrature
Refers to the property of position transducers that allows them to
detect direction of motion using the phase relationship of two
signal channels. A 1000-line encoder will yield 4000 counts via
quadrature.
Radial Run-Out
Positioning error of the rotary stage in the horizontal direction
when the tabletop is oriented in the horizontal plane. Radial run-
out is defined as the total indicator reading on a spherical ball
positioned 50 mm above the tabletop and centered on the axis
of rotation.
Ramp Time
Time it takes to accelerate from one velocity to another.
Range
The maximum allowable travel of a positioning stage.
RDC
Resolver to Digital Converter. Electronic component that
converts the analog signals from a resolver (transmitter type)
into a digital word representing angular position.
Repeatability
The maximum deviation from the mean (each side) when
repeatedly approaching a position. Unidirectional repeatability
refers to the value established by moving toward a position in
the same direction. Bidirectional repeatability refers to the value
established by moving toward a position in the same or opposite
direction.
Resolution
The smallest change in distance that a device can measure.
Retro-reflector
An optical element with the property that an input light beam is
reflected and returns along the same angle as the input beam.
Used with laser interferometers.
Roll (of travel)
Angular motion of a carriage around an axis parallel to the
motion direction and perpendicular to the yaw axis.
Roll Error
Positioning error resulting from a roll motion.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com