Ndrive HP 10/20/30 Manual
Glossary of Terms
www.aerotech.com A-3
Coordinated Motion
Multi-axis motion where the position of each axis is dependent
on the other axis, such that the path and velocity of a move can
be accurately controlled. Drawing a circle requires coordinated
motion.
Critical Speed
A term used in the specification of a lead screw or ball screw
indicating the maximum rotation speed before resonance
occurs. This speed limit is a function of the screw diameter,
distance between support bearings, and bearing rigidity.
Current Command
Motor driver or amplifier configuration where the input signal is
commanding motor current directly, which translates to motor
torque/force at the motor output. Brushless motors can be
commutated directly from a controller that can output current
phase A and B commands.
Current, Peak
An allowable current to run a motor above its rated load, usually
during starting conditions. Peak current listed on a data sheet is
usually the highest current safely allowed to the motor.
Current, RMS
Root Mean Square. Average of effective currents over an
amount of time. This current is calculated based on the load and
duty cycle of the application.
Cycle
When motion is repeated (move and dwell) such as repetitive
back-and-forth motion.
DC Brushless Servo
A servomotor with stationary windings in the stator assembly
and permanent magnet rotor. (See AC Brushless Servo)
Deceleration
The change in velocity as a function of time.
Duty Cycle
For a repetitive cycle, the ratio of on-time to total cycle time used
to determine a motor’s RMS current and torque/force.
Dwell Time
Time in a cycle at which no motion occurs. Used in the
calculation of RMS power.
Efficiency
Ratio of input power vs. output power.
Electronic Gearing
Technique used to electrically simulate mechanical gearing.
Causes one closed loop axis to be slaved to another open or
closed loop axis with a variable ratio.
Encoder Marker
Once-per-revolution signal provided by some incremental
encoders to accurately specify a reference point within that
revolution. Also known as Zero Reference Signal or Index Pulse.
Encoder Resolution
Measure of the smallest positional change, which can be
detected by the encoder. A 1000-line encoder with a quadrature
output will produce 4000 counts per revolution.
Encoder, Incremental
Position encoding device in which the output is a series of
pulses relative to the amount of movement.
Feedback
Signal that provides process or loop information such as speed,
torque, and position back to the controller to produce a closed-
loop system.
Flatness (of travel)
Measure of the vertical deviation of a stage as it travels in a
horizontal plane.
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