Technical data

Multi-Axis Controllers and ServoWire
®
Digital Drives – Subject to change – 12/2006
40
Glossary
Engineering Support
4
A
Absolute encoder
A position feedback device
employed in motion control
systems to maintain a given
mechanical location. The
output of an absolute encoder
is representative of the absolute
position of the motor shaft
within one (or more - in the
case of a multi-turn encoder)
revolutions. Output is usually
a parallel digital word.
Axis
In motion control, this term
normally refers to one of the
servomotors in the system,
either by name or Axis ID from
1 to 16. It is also used to refer
to any Master (Pacer) Encoders
in the system
C
CoDeSys
Controller Development System.
The IEC-61131-3 runtime system
developed by 3S Software used
on the SMLC.
CoDeSys IDE
The CoDeSys Integrated
Development Environment is
the Win32 based application
that allows you to develop,
download and debug SMLC
programs.
Command update rate
The rate at which the commands
will be sent from the motion
controller to the drive.
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.
E
Electronic cam
A technique used to perform
non linear motion electronically
similar to that achieved with
mechanical cams.
Electronic gearing
A method that simulates
mechanical gears by electrically
synchronizing one closed loop
axis to a second axis (open or
closed loop) through a variable
ratio.
Electronic line shaft
A virtual axis that is used as
the master axis on a machine
to which other axes are
synchronized by electronic
gearing or camming profiles.
Electromagnetic compatibility
EMC is the ability of a device
or a system to operate
satisfactorily in its electro-
magnetic environment without
emitting unacceptable electro-
magnetic interference to other
devices.
Encoder resolution
Measure of the smallest
positional change which can
be detected by the encoder.
F
Follower
A servo axis, which is controlling
its motion as a function of motion
data, generated by a pacer axis.
Following error
The difference between the
commanded position of an
axis and its actual position.
The amount of following error
present varies with the speed
of the axis.
FireWire
Bus standard for industrial
applications and digital
data exchange at high speed
between various devices
(IEEE 1394).
Feed Forward
A technique used to
pre-compensate a control
loop for known errors due
to motor, drive, or load
characteristics. Provides
improved response. This
technique depends only
on the command and not
the error.
H
Home Position
A reference position in a
motion control system
derived from a mechanical
datum or switch.
I
IEC-61131-3
A global standard defining
programming languages for
industrial control.
Incremental encoder
A type of feedback device
which converts mechanical
motion into electrical signals
(pulses) to indicate motor
shaft position. By counting
these pulses the motor shaft
position can be determined.
The frequency of the pulses
reflects the speed at which
the motor is rotating. Encoders
with quadrature output provide
information on the direction
of motion using the phase
relationship of the two channels.
Interpolation
Internal calculation by the
controller of intermediate
points on a path in a time grid.
The path is pre-defined with
interpolation points.
The intermediate points can
be on a straight line (linear
interpolation), on a circle
(circular interpolation), or
on a parabola (parabolic
interpolation). The path data
is used for simultaneous control
of motion axes.
L
Loop update rate (loop closure)
The rate at which the torque,
velocity and position loops are
closed in the drive. Loop update
involves the regulation of the
commanded and the actual
variable (torque, position, or
velocity) in order to minimize
the error between the actual
and commanded variable.
M
Master axis
Motion axis in a drive system
which controls the synchronized
motion of at least one drive axis.
MODBUS
The MODBUS
®
Protocol is a
messaging structure developed
by Modicon in 1979, to establish
master-slave/client-server
communication between
intelligent devices. It is a de facto
standard, truly open and a widely
used network protocol in the
industrial manufacturing
environment.
MODBUS/TCP
Modbus/TCP is an
implementation of the
MODBUS Protocol, allowing
MODBUS messages to be
transferred via Ethernet.
N
Noise
An unwanted electrical signal.
Typically from RFI or EMI induced
onto the drive’s components,
speed reference or feedback
wiring, and can cause the axis
to react unexpectedly. Sources
of noise are AC power lines,
motors, generators, transformers,
fluorescent lights, CRT displays,
and radio transmitters.