PLCopen Motion

Overview

Use MC function blocks to command simulated single axes and straight Cartesian paths. MotionGroup and its child MotionAxis components configure the PLC’s motion task. The task writes position signals; drive behaviours such as Drive_FollowPosition consume those signals. It never directly moves a Drive.

The implemented subset follows PLCopen Motion Control Part 1 v2.0 and Part 4 v1.0, with the limits described below.

The PLC never moves a drive directly: the motion task writes position set-point signals, and the drive's own behaviour follows them. Live or forced set-points are never overwritten.

Properties

MotionGroup property	Type / unit	Default
Kind	enum	Cartesian
Program	ComponentReference to owning PLCProgram	unbound; required
Variable	string, program handle variable name	empty; required
Velocity	number, mm/s	500
Acceleration	number, mm/s²	5000
Deceleration	number, mm/s²	5000
Jerk	number, mm/s³	100000

Profile defaults must be finite and strictly positive. Add MotionAxis components to child nodes; nested groups own their own descendants.

MotionAxis property	Type / unit	Default
Name	string; unique X, Y or Z	empty; required
Setpoint	PLCOutputFloat signal slot, mm	unbound; required
Feedback	PLCInputFloat signal slot, mm	unbound; optional
Min / Max	number, logical mm	-1000000 / 1000000
Offset	number, mm	0
Sign	enum 1 / -1	1

Min and Max must be finite with Min < Max. The signal value is Offset + Sign × logical position; feedback uses the inverse. Without Feedback, readers use the simulated set-position. A configured invalid feedback produces an error.

The inspector uses the standard reference picker, signal slot rows, selects and number/string editors. Runtime position and command state are read-only. Redeploy after changing motion configuration.

Quick start

1. Add a PLCProgram and a MotionGroup.
2. Add one to three child MotionAxis nodes, configure coordinate names and bounds, and bind each Setpoint to a PLCOutputFloat position signal.
3. Configure each drive’s position-following behaviour to consume the matching signal.
4. Enter the program below. Set MotionGroup.Program to that PLCProgram and Variable to motion.
5. Deploy, then Run in continuous simulation. Raise Start after enablement.

PROGRAM Positioning
VAR
  motion : AXES_GROUP_REF;
  enable : MC_GroupEnable;
  move : MC_MoveLinearAbsolute;
END_VAR
VAR_EXTERNAL Start : BOOL; END_VAR
  enable(AxesGroup := motion, Execute := TRUE);
  move(AxesGroup := motion, Execute := enable.Done AND Start,
       PositionX := 100.0, PositionY := 50.0, PositionZ := 0.0);
END_PROGRAM

Zero profile inputs select group defaults. Hold Start through completion, then release and raise it for another move. Use AXIS_REF and Axis for a group containing exactly one MotionAxis. Handles belong only in PROGRAM VAR, are required on every MC call and cannot be assigned, calculated or passed through user POUs.

To check the profile on a running machine, open Axis forces for the mechanism and switch to Motor torque. Jerk-limited moves show smooth, repeating peaks without spikes:

Available function blocks

Single axis	Purpose
MC_Power	Level-sensitive logical enable; Status/Valid
MC_Reset	Clear a resolved fault at standstill
MC_ReadActualPosition	Enable → Valid/Busy/Position
MC_MoveAbsolute	Absolute Position
MC_MoveRelative	Signed Distance from position at activation
MC_MoveVelocity	Continuous Velocity; InVelocity when speed is reached
MC_Halt	Interruptible controlled stop
MC_Stop	Controlled stop with held-Execute interlock

Cartesian group	Purpose
MC_GroupEnable / MC_GroupDisable	Enable coordination / immediately cancel and hold
MC_GroupReset	Clear a resolved fault at standstill
MC_MoveLinearAbsolute	Straight move to PositionX/Y/Z
MC_GroupStop	Controlled stop with held-Execute interlock
MC_GroupReadActualPosition	Enable → Valid/Busy/PositionX/Y/Z

Execute commands trigger on a rising edge; falling Execute does not cancel the motion. Call instances cyclically to observe completion. Positional moves expose Done, Busy, Active, CommandAborted, Error and ErrorID. Stop has no Active port; MoveVelocity has InVelocity instead of Done. Readers use Enable, Valid and Busy, plus Error/ErrorID.

Stop and buffering

Stop/GroupStop reject new moves until standstill and Execute = FALSE, including after Done. Halt permits interruption. mcAborting (0) aborts old/queued requests and brakes before starting the replacement; mcBuffered (1) waits for standstill. Only these two buffer modes exist; GroupStop accepts only mcAborting. There is no blending.

Only the first call of one MC instance per scan evaluates inputs; later calls return cached values. Use separate instances for scan-order arbitration. Direction constants are mcPositiveDirection (1), mcShortestWay (2), mcNegativeDirection (3) and mcCurrentDirection (4). Absolute linear moves accept but ignore a valid Direction; MoveVelocity rejects shortest-way. Zero Velocity selects the default, not a stop.

Axis states are Disabled, Standby, DiscreteMotion, ContinuousMotion, Stopping and ErrorStop. Group states are GroupDisabled, GroupStandby, GroupMoving, GroupStopping and GroupErrorStop. Enable reaches standby; completed moves return to standby; faults require reset after the cause clears.

Execute starts a command on its rising edge. MC_Stop holds the axis in Stopping until it is at standstill and Execute is released; MC_Halt stops under control but can be interrupted by the next move.

Ownership and lifecycle

A group has exactly one owning PLCProgram occurrence. Many FB instances can share its handle, but one handle cannot bind two groups. Missing/duplicate bindings and competing program/group or group/group set-point writers refuse deployment with Problems entries.

Live controller values override local motion; the task writes nothing to live-bound or forced set-points. Authority loss suspends the group until authority returns and it is reset. Reconnect resynchronises without replaying commands. External operation/jog must enter the PLC as signals.

Runner Stop, scan error, COLD redeploy and group removal brake and hold under local authority. Simulation/PLC Reset is immediate, even while paused, and clears motion before the viewer resets drives. Power off/GroupDisable cancel immediately; use Stop first for a controlled stop.

Errors, limits and use cases

ErrorID	Meaning
16#8001	Invalid binding
16#8002	Disabled
16#8003	Axis bounds exceeded
16#8004	Invalid parameters
16#8005	Owner/writer conflict
16#8006	Forced/external authority
16#8007	Invalid BufferMode/Direction
16#8008	State/interlock refusal
16#8009	Invalid feedback
16#800A	Profile provider failure

These are realvirtual-specific positive DINT values. Parameter errors reject that request without disturbing healthy motion. Kernel faults latch ErrorStop/GroupErrorStop.

Use this subset for Cartesian handling, positioning and single-axis speed control. PositionX/Y/Z replace PLCopen position arrays; orientation, robot kinematics, homing, synchronisation and coordinate-system selection are absent. Acceleration/deceleration share the conservative limit min(A,D). Every replacement brakes first, including a collinear move. Done reports profile completion, with no hardware settling monitor. An unavailable protected profile core uses a warned trapezoid fallback without a jerk guarantee.

Continuous simulation and DES

PLCopen motion runs only in continuous simulation. A motion profile is integrated at a fixed step, and DES has no fixed step.

	Continuous simulation	DES (event-driven)
MC_ blocks	Run; the motion task advances the profile every simulation tick	Not supported
Program with MC_ blocks	Runs normally	The editor shows finding D5 and the badge not DES-ready. At its first DES scan the program goes into error
Suppress with (* @des: allow *)	—	Not possible for D5
Experiment batches	—	Refuse the model
Snapshots	Not possible for a program that declares MC_ blocks, even when it is stopped or the instance is never called	Not possible

Run models with motion programs in continuous simulation. For DES and experiments, use LogicSteps or ST programs without MC_ blocks.

See also

• Function blocks and libraries
• ST functions
• Virtual PLC