Motion and automation controllers explained
By Warren Osak
A motion control system is a system that controls the position, velocity, force or pressure of some machine. As an example, an electro-mechanical based motion control system consists of a motion controller (the brains of the system), a drive (which takes the low power command signal from the motion controller and converts it into high power current/voltage to the motor), a motor (which converts electrical energy to mechanical energy), a feedback device (which sends signals back to the motion controller to make adjustments until the system produces the desired result), and a mechanical system (including actuators, which physically produce the desired end result).
A or is the primary intelligence, or brain, within a motion control system. It is responsible for calculating and generating the output commands for a desired motion path or trajectory. Motion controllers vary in complexity; sophisticated motion controllers typically consist of a trajectory generator (path planner), interpolator, and control loop for servo motor control.
A system that does not use feedback to verify the desired result, or output, has been reached. Most stepper motor systems are operated open loop.
A system that uses feedback to verify the desired result, or output, has been reached. As an example, a feedback device such as an encoder or resolver is commonly used to provide position or velocity information to a motion controller. A servo motor system requires the use of a feedback device.
based motion controllers typically utilise a digital output device,
such as a counter module, that resides within the PLC system to
generate command signals to a motor drive. They are usually
chosen when simple, low cost motion control is required but are
typically limited to a few axes and have limited coordination
based motion controllers typically consist of dedicated hardware
run by a real-time operating system. They use standard
computer busses such as PCI, Ethernet, Serial, USB, and others for
communication between the motion controller and host system.
PC based controllers generate a ±10V analog output voltage
command for servo control and digital command signals, commonly
referred to as step and direction, for stepper control. PC
based motion controllers typically are used when high axes count
and/or tight coordination is required. The drawbacks of this
topology include complex cabling and potentially long wiring
distances between the drive and motor.
is an industrial computer network system used for real-time
distributed control of industrial machines. Programmable
Fieldbus Controllers are typically used to connect multiple devices
within a manufacturing plant. The four basic fieldbus
networks are: sensor bus networks, device bus networks, control bus
networks and enterprise bus networks. Fieldbus networks allow
for daisy-chain, star, ring, branch, and tree network
A fieldbus based motion controller topology consists of a communication interface device and intelligent drive(s). The communication interface device typically resides within a PLC or PC system and connects to a single or multiple intelligent drives. The drives contain all the functionality of the motion controller and function as a complete single axis system. Often the drives can be daisy chained to other intelligent drives on the same fieldbus. The benefits include all digital communication, detailed diagnostics, reduced cabling, high axes count and short wiring distance between the drive and motor. This topology has a higher cost especially at lower axes count and has limitations providing tight coordination for multiple axes. Examples of this topology include Profibus, DeviceNet, RS-232/485, and others.
communication is the transmission of data, generally without the
use of an external clock signal, where data can be transmitted
intermittently rather than in a steady stream. Asynchronous
literally means not synchronous, meaning, data is not transmitted
at regular intervals, thus making possible variable bit rate, and
that the transmitter and receiver clock generators do not have to
be exactly synchronised all the time.
communication is the transmission of data reaching its destination
in a specific, predicable time. Time critical data transfer
must be guaranteed within short and precise configurable cycles,
while less critical data can be transmitted in asynchronous time
slots. Data reaching its destination at guaranteed times are
critical for motion control.
deterministic bus based motion controller topology splits the
motion controller functionality across a communication interface
device and intelligent drive via a deterministic digital network.
The communication interface device typically resides within a
PLC or PC system and contains the trajectory generator. The
intelligent drives typically contain the control loop and
interpolator and can be daisy chained to other intelligent drives
on the same network. The digital network is deterministic
with low jitter to allow for tight coordination in multi axes
applications. The benefits include all digital communication,
detailed diagnostics, reduced cabling, high axes count, tight
coordination, and short wiring distance between the drive and
motor. This topology has a higher cost especially at lower
axes count. Examples of this fieldbus topology include
EtherCAT, SERCOS, Ethernet Powerlink, PROFINET IRT, SynqNet,
CANopen, and others. These types of fieldbuses are also
referred to as Distributed Control Systems.
(DCS) is a control system for a
process where the individual control elements are not localised.
The system is made up of several control elements organised
into a hierarchy which are all connected to a central communication
system for monitoring and control. When building a DCS
system, it is important to consider all aspects of the system, from
the I/O to the PLC, the motion element and the supervisory HMI.
DCS systems often use a central PLC connected by network
cables to nodes which contain I/O devices such as: fieldbus
couplers, I/O slices (usually input/output, or digital/analog), and
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