Motion controllers and PLCs

In short:If the machine is mostly logic and I/O with simple point-to-point moves, a PLC with motion function blocks is usually enough. If it is mostly synchronised motion, such as camming, interpolation or many coordinated axes, a dedicated motion controller or a PLC with an integrated EtherCAT motion engine is the better fit.

The controller is the brain of the machine. It runs the sequence, reads sensors, drives outputs, talks to the operator through an HMI, and tells each servo drive where to be and when. On a motion-heavy machine, the controller choice also fixes the programming tool, the fieldbus, the drives you can use and, often, who can support the machine in ten years’ time.

This hub covers PLCs, dedicated motion controllers, HMIs and remote I/O, and how to choose between them.

PLC vs dedicated motion controller

The most useful question, as A3’s guidance puts it, is whether the job is primarily machine control or primarily motion control.

	PLC	Dedicated motion controller	PLC with integrated motion (e.g. CODESYS + EtherCAT)
Strengths	I/O, sequencing, many fieldbuses, long-term support	Tightly synchronised multi-axis profiles, interpolation, cams	Logic and motion in one IEC 61131-3 project and one network
Motion capability	Point-to-point, jogging, simple gearing; more with a motion module	Coordinated paths, electronic cams, flying shears, gantry control	PLCopen single-axis, gearing, cams; coordinated groups on capable platforms
Weak points	Separate motion module can mean two programs to maintain	Limited onboard I/O, so remote I/O is often needed	Axis count and cycle time limited by CPU; check the vendor’s figures
Typical machines	Conveyors, process skids, simple indexing	Converting, printing, CNC-like and robotic cells	Packaging, assembly, pick-and-place, test rigs

A3 notes that a PLC with a separate motion module brings camming and interpolation but “requires the maintenance of two separate programs”, and that dedicated motion controllers typically need remote I/O beyond about 16 inputs and 16 outputs. PC-based control suits R&D and lab systems, or machines that already need a PC.

Rules of thumb (ours, not a standard):

• Up to a handful of independent positioning axes with lots of I/O: a PLC driving drives that run their own profiles over a fieldbus or pulse/direction.
• Axes that must stay in phase (master/slave gearing, cams, registration): a controller with PLCopen gearing and cam support, ideally over EtherCAT.
• Paths in two or three dimensions (dispensing, cutting, gantries, delta and SCARA robots): a controller with coordinated motion (PLCopen Part 4 or a robotics/CNC package).

IEC 61131-3 and CODESYS

IEC 61131-3 defines five PLC programming languages: Ladder Diagram, Function Block Diagram, Structured Text, Instruction List and Sequential Function Chart (Process Online). Ladder suits interlocks and simple logic; Structured Text suits maths, recipe handling and motion calculations; Sequential Function Chart suits stepwise machine sequences.

CODESYS is a hardware-independent IEC 61131-3 environment used by many controller manufacturers. Its SoftMotion add-on provides certified PLCopen blocks for single and multi-axis motion, a graphical cam editor, virtual axes, and integrated drivers for CANopen and EtherCAT drives, including generic CiA 402 devices. A CNC and robotics package adds path interpolation and kinematics.

Practical consequence: with a CODESYS controller, an OEM can often keep its application code while changing controller hardware, and can use third-party drives that follow CiA 402. Check, though, which CODESYS version, which SoftMotion licence and which drive device descriptions the controller vendor supports.

Example CODESYS EtherCAT controllers: Kinco AK and Leadshine MC500. For logic-led machines, compact PLCs such as the Kinco K6S or an all-in-one HMI with built-in PLC such as the Kinco MK can be enough.

PLCopen motion and coordinated motion

PLCopen standardises motion function blocks on top of IEC 61131-3:

• Parts 1 and 2: single and multi-axis blocks such as MC_Power, MC_Home, MC_MoveAbsolute, MC_GearIn and MC_CamIn.
• Part 3: user guidelines and examples.
• Part 4: coordinated motion: axis groups, coordinate transformations, and linear and circular group moves.
• Part 5: homing procedures.
• Part 6: fluid power.

Every PLCopen axis follows the same state machine (Disabled, Standstill, Homing, Discrete Motion, Continuous Motion, Synchronized Motion, Stopping, ErrorStop), so error handling and recovery code looks the same across platforms. PLCopen’s stated aim is that application code becomes less hardware-dependent and scalable across control solutions.

Coordinated motion (Part 4) is different from master/slave gearing. In gearing, a slave axis follows a master. In a coordinated group, the controller plans one path for all axes together, which gives better trajectory planning and means every axis in the group knows when another faults. If your machine draws lines or arcs with the tool, you need group motion, not gearing.

EtherCAT masters and drive networks

Most multi-axis servo systems now use EtherCAT. The controller is the master; drives, I/O and encoders are slaves on one network. Hilscher quotes cycle times of 100 µs or less, jitter below 1 µs, hardware-based distributed clocks, and up to 65,535 devices per segment.

For servo motion the controller usually commands drives in cyclic synchronous position (CSP) mode under the CiA 402 profile, sending a new setpoint every cycle while the drive closes the current, velocity and position loops. KEB points out that vendors may support only part of CiA 402, so confirm the modes and homing methods on both ends.

Choosing a cycle time (rule of thumb): 1 ms is ample for most conveyors, indexing and packaging axes; tightly coupled, high-dynamic axes or interpolated paths benefit from 250 to 500 µs. Shorter cycles cost CPU time, so check the controller’s published axis count at your target cycle time, not its headline maximum.

Alternatives: PROFINET IRT on Siemens platforms, EtherNet/IP with CIP Motion on Rockwell platforms, CANopen for low-cost mobile machines, and pulse/direction outputs for simple stepper or servo axes.

HMIs, remote I/O and gateways

HMIs. Choose on screen size and viewing distance, environmental rating (front-panel IP rating for washdown), communication with your controller, and whether one project can scale across screen sizes. Examples: Kinco HMI MASS (cost-focused), Kinco HMI Green and Kinco HMI Future (higher performance).

Remote I/O. Put I/O near the sensors and valves to cut cabling, and keep it on the motion network so inputs are sampled in the same cycle as the axes, which matters for registration and fast sensing. Example: Kinco RP20 slice I/O with an EtherCAT coupler.

Gateways. Where the machine must report to MES or cloud systems, or bridge legacy serial devices, an IoT gateway such as the Kinco GW01 keeps that traffic off the real-time control network.

Common controller selection mistakes

• Choosing a PLC for its I/O, then discovering the motion needs cams or interpolation it cannot do without an add-on module and second program.
• Assuming any “EtherCAT servo drive” will work: check the controller has the drive’s device description and supports the needed CiA 402 modes.
• Sizing on maximum axis count without checking the cycle time at that count.
• Running HMI, data logging and IT traffic on the same network as real-time motion.
• Ignoring software licensing: motion, CNC/robotics and safety functions are often licensed separately per controller.
• Not planning safety: decide early whether safety is hardwired, via a safety PLC, or over FSoE/PROFIsafe.

What to send us for a controller quote

• Number of axes, and which must be synchronised or coordinated
• Motion types: point-to-point, gearing, cams, interpolated paths, robot kinematics
• I/O count and types (digital, analogue, high-speed counters, temperature)
• Preferred programming environment (CODESYS, a specific vendor, IEC 61131-3 language)
• Drives and fieldbus already chosen, if any
• HMI size and environment; remote access requirements
• Safety architecture and target SIL/PL
• Production volumes and support expectations

Use the spec builder to capture the details and our engineers will propose a controller, drive and I/O combination from our supply network. For feedback choices see encoders.

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Where controllers and plcs are used

What we need to know to specify controllers and plcs

These are the questions an applications engineer works through first. Approximate answers are fine: ranges narrow the options quickly, and we confirm the details with you.

• Axes to control: 1–4, 5–16, More than 16
• Network: EtherCAT, CANopen, PROFINET, Modbus TCP
• HMI needed: Yes, No

We also ask about the environment (washdown, outdoor, subsea, ATEX, vacuum, shock and EMC), annual quantities and timescale, because these decide whether a standard, modified or custom design is the best fit.

65 series compared

Series from 27 manufacturers, grouped by type. Figures are the highest published for each series. Open a series for the full specification and, for brands outside our supply network, the alternatives that meet or exceed it.

Motion controller (33)

HMI (14)

PLC (7)

Remote I/O (4)

IoT and remote I/O (4)

HMI / PLC (2)

Controllers, PLCs and HMIs (1)

Summarised from manufacturers' published data. Always confirm against the current datasheet; an engineer will check the fit before recommending anything.

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Frequently asked questions

Should I use a PLC or a dedicated motion controller?

Start by asking whether the machine is mainly machine control or mainly motion control. PLCs are strong on I/O, sequencing and multiple fieldbuses, and handle simple positioning and gearing well. Dedicated motion controllers excel at tightly synchronised, multi-axis profiles such as interpolation and electronic cams. Modern CODESYS-based controllers with EtherCAT blur the line by running both in one IEC 61131-3 project.

What is IEC 61131-3?

IEC 61131-3 is the international standard for PLC programming languages. It defines Ladder Diagram, Function Block Diagram, Structured Text, Instruction List and Sequential Function Chart, along with common data types and program organisation. Using it means engineers can move between controller brands with less retraining, although each vendor's environment and libraries still differ in detail.

What are PLCopen motion function blocks?

PLCopen publishes standard IEC 61131-3 function blocks for motion, such as MC_Power, MC_Home and MC_MoveAbsolute, plus a common axis state machine. Part 1 and 2 cover single and multi-axis moves including gearing and cams; Part 4 covers coordinated motion of axis groups; Part 5 covers homing. Using them makes motion code less dependent on a particular controller or drive.

What is CODESYS and why do so many controllers use it?

CODESYS is a hardware-independent IEC 61131-3 development environment licensed to many controller manufacturers. Its SoftMotion add-on provides certified PLCopen motion blocks, a graphical cam editor and integrated drivers for CANopen and EtherCAT drives, including generic CiA 402 devices. That lets an OEM use one programming tool across several hardware brands.

Do I need an EtherCAT master for servo motion?

Not always, but it is the most common route for multi-axis servo systems. An EtherCAT master in the controller sends synchronised setpoints to every drive each cycle, typically in cyclic synchronous position mode, with cycle times of 100 µs or less possible. Simpler machines can use pulse/direction outputs, CANopen or Modbus to drives that run their own position profiles.

When do I need remote I/O?

Use remote I/O when sensors and actuators are spread around a large machine, when the controller runs out of local I/O, or to cut cabling back to the cabinet. Dedicated motion controllers often have limited onboard I/O, so remote I/O on the same EtherCAT network keeps inputs and outputs synchronised with the motion cycle.

Sources

1. PLCopen: motion control specification overview
2. CODESYS SoftMotion product page
3. A3 (Association for Advancing Automation): choosing the right control scheme
4. Process Online: understanding the IEC 61131-3 programming languages
5. Hilscher: EtherCAT glossary
6. KEB America: using the CiA 402 drive profile for motion control

Figures are summarised from the sources above and from manufacturers' published data on the date shown. Always confirm against the current datasheet for your exact part.