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Position Trigger Object

Position Trigger objects monitor movers until they have crossed over a specified location on track, even if they do not stop there. Position Triggers will always point to the most recent registered mover which crossed over the Position Trigger's track position. When using track management the position trigger will only trigger if the mover crosses the specificed location and has a matching TrackId.



Setup & Execution

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// Declaration
PositionTriggerA        : PositionTrigger;

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// Initialization
PositionTriggerA.Position       := 2000;
PositionTriggerA.TriggerDirection   := mcDirectionPositive;



Methods

Cyclic

Cyclic()

Position Triggers require a cyclic call in the Main Program because they need to constantly monitor the positions of registered movers.



MuteCurrent

MuteCurrent()

Clears a Mover reference from the CurrentMover property, and resets MoverPassedPosition to be false. This can be done without the need to unregister a mover from a position trigger

Since Position Triggers uniquely latch their CurrentMover output, it is necessary to clear this value manually in order to prepare to process the next mover event.

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IF PositionTrigger[0].MoverPassedPosition THEN
    PositionTrigger[0].CurrentMover.MoveVelocity( 200 );
    PositionTrigger[0].MuteCurrent();
END_IF

In this way, it is possible to reset the position trigger without having to completely unregister and re-register a mover from the trigger.



Properties

.MoverPassedPosition

Status boolean indicating that at least one mover has passed over the threshold position since being registered

Position Triggers are unique in that the Current Mover output latches even though the mover may not still qualify under the trigger condition



.CurrentMover

Reference variable that refers to the most recent registered mover to cross over the track position since being registered

  • If no movers are tracked, or no tracked movers have yet satisfied the objective, then .CurrentMover is an invalid reference. In this case, an ErrorMover will replace the invalid reference. The user will receive notifications when this happens in the TwinCAT event logs. See Diagnostics > ErrorMovers for more information.

  • For this reason, it is recommended that all evaluations are nested inside IF checks for .MoverPassedPosition.

  • It is possible that multiple registered movers have crossed over a threshold position. Only the most recently valid mover handle is provided by .CurrentMover.



.Position

Current placement of the Position Trigger threshold along the track



.TrackId

Track that the station is assigned to when using track management. See the Track object.



Extra Examples

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// Basic Position Trigger implementation

// Begin monitoring Mover 1
IF bInit THEN
    Mover[1].MoveToPosition( 1000 );
    PositionTrigger.Position    := 800;
    PositionTrigger.RegisterMover( Mover[1] );
    bInit   := FALSE;
END_IF

// When Mover 1 crosses position 800, slow it down to 100mm/s
IF PositionTrigger.MoverPassedPosition THEN
    PositionTrigger.CurrentMover.SetVelocity( 100 );
    // MuteCurrent clears MoverPassedPosition and CurrentMover so that
    // Line 12 does not continually evaluate as true
    PositionTrigger.MuteCurrent();
END_IF