PLC Programming Standards in Motion Control

The IEC 61131-3 standard defines 5 programming languages for PLCs and distributed control systems. More recently, dedicated motion companies such as Launching Ideas are incorporating the standard into their motion control hardware.

What is a PLC, and why do standards matter?

A programmable logic controller (PLC) is the ruggedized industrial computer at the heart of most automated machinery — it reads sensors, executes control logic on a deterministic cycle, and drives outputs like motors, valves, and actuators. For decades, every PLC vendor shipped its own proprietary programming environment, which meant control logic written for one platform had to be rewritten from scratch for another. The IEC 61131-3 standard changed that by defining a common set of programming languages and a common software model that vendors across the industry now support.

The five IEC 61131-3 languages

• Ladder Diagram (LD) — a graphical language that mimics relay logic schematics; still the most widely used, and immediately readable by plant electricians.
• Function Block Diagram (FBD) — graphical blocks wired together by signal flow; well suited to continuous processes and signal processing.
• Structured Text (ST) — a high-level, Pascal-like text language; the natural choice for algorithms, math, and complex data handling.
• Sequential Function Chart (SFC) — organizes a program into steps and transitions; ideal for machines that move through defined states.
• Instruction List (IL) — a low-level, assembler-like language, now deprecated in the standard but still found in legacy code.

The languages can be mixed within one project, so each part of a machine's control program can be written in the notation that fits it best.

What this means for motion control

Motion control — coordinating servo and stepper axes for positioning, camming, gearing, and interpolation — was historically the most proprietary corner of automation, with each drive vendor exposing its own command set. The industry's answer is the PLCopen motion control specification, which defines standardized function blocks (such as MC_MoveAbsolute, MC_MoveVelocity, and MC_CamIn) on top of IEC 61131-3. A machine builder who programs against these blocks gets motion logic that behaves consistently across compliant hardware platforms.

The practical benefits show up over the whole life of a machine:

• Portability — control logic survives a change of PLC or drive vendor without a ground-up rewrite.
• Maintainability — standardized structure means any controls engineer familiar with the standard can read, debug, and extend the program.
• Easier validation — modular, well-defined function blocks are simpler to test and document, which matters for safety reviews and regulated industries.
• Reusable libraries — proven blocks for homing routines, fault handling, and axis coordination carry forward from project to project.

All of this matters when motion control hardware ends up inside a commercial product or on a production line: standardized, portable, maintainable control logic protects the investment your machine represents.

When your product needs motion control

Motion control isn't just for factory floors. Consumer and commercial products — from automated furniture and medical devices to camera rigs and dispensing equipment — increasingly embed coordinated motion. Getting it right requires both electrical engineering (drive selection, feedback, control architecture) and mechanical engineering (load calculations, transmission design, frame stiffness) working together from the first sketch.

Need motion control expertise for your product or production equipment? Contact us for a free quote.