Station Object

The Station object provides a fixed location for a Mover to stop at until it is ready to be released. A Station is a type of Objective, and provides a handle to the Mover object that is currently docked with the Station, allowing further motion commands to be issued to the Mover.

Setup & Execution

// Declaration
Station     : ARRAY [0..GVL.NUM_STATIONS-1] OF Station;

// Initialization
Station[1].Position     := 250;
Station[2].Position     := 500;
Station[3].Position     := 750;

Stations must also be added to the Mediator object. By default, this is handled automatically.

// Example implementation
Mediator.AddStation( Station[1] );

Mover Registration

Unlike other types of Objectives, Stations manage mover registration automatically. Any mover that is commanded with a MoveToStation is also automatically registered with that station. As an example, this implementation would be redundant:

Mover[2].MoveToStation( Station[3] );
Station[3].RegisterMover( Mover[2] );       // unnecessary

Stations also automatically unregister movers that have been redirected with another move command, even if that command's destination is the same location as the Station.

Mover[2].MoveToStation( Station[3] );
Mover[2].MoveToPosition( Station[3].Position );

Here, the Station will not report MoverInPosition when it arrives because the original command is interrupted by one where the CurrentMoveType is not MOVETYPE_STATION.

Methods

Cyclic

Cyclic()

Stations require a cyclic call in the Main program. This allows the station to automatically unregister movers from its Tracked list who have been redirected and are no longer destined for this Station.

The call to Cyclic() is handled automatically after the station has been registered with the Mediator.

Reset Statistics

ResetStatistics()

Resets the Statistics for this station. See the Statistics property.

Set track

SetTrack()

Station[1].Position := 1000.0;
Station[1].SetTrack(Track[2]);

Properties

.Blocked

BOOL

A station is considered blocked if a mover has left the station but that mover has not yet moved further than the mover's .Gap.

This value is used internally to calculate some values in the .Statistics property by detecting when a station does not have a mover, but also can not receive a mover because of the gap maintained by collision avoidance.

.CurrentMover

REFERENCE TO Mover

Reference variable that refers to the Mover that is docked with the Station

When no mover is present in the Station, .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.

It is recommended that all evaluations are nested inside IF checks for .MoverInPosition.

.Description

STRING

A text description of the station that is passed to the visualization tools. It's also visible within within the TwinCAT debugging tools for easier identification of stations.

This value can be changed at runtime and will update on the visualization. This offers the opportunity to put dynamic data on the XTS visualization such as a station part count.

.GroupSize

DINT

When multiple stations perform the same operation they are considered "grouped". This value represents the number of stations in the group.

This value is only used to help calculate throughput .Statistics on the mover and is used in combination with the .Blocked property.

.MoverInPosition

BOOL

Status boolean indicating that a mover is currently docked with the Station

.TrackedMoverCount

USINT

Simply reports the number of Movers that are currently registered with the Station. Because Stations automatically deregister movers that are not currently destined for this Station, this value also represents the current number of incoming movers.

Note

This property is part of Objective but is frequently used with stations and can be accessed as part of the Station object.

.Position

LREAL

Current placement of the Station along the track

This value is also used to place a marker on the visualization tools representing the station. See Visualization.

.Statistics

A set of timers and counts that track the throughput and utilization of the station.

Member	Type	Description
TimeOccupied	TIME	Current amount of time that the station has had a MoverInPosition
TimeEmpty	TIME	Current amount of time where MoverInPosition is FALSE
TimeBlocked	TIME	Current amount of time where station cannot receive a new mover because the previous mover has not moved far enough away from the station
OccupiedTimeHistory	ARRAY[0..63] OF TIME	Ring buffer of recent TimeOccupied values
EmptyTimeHistory	ARRAY[0..63] OF TIME	Ring buffer of recent TimeEmpty values
BlockedTimeHistory	ARRAY[0..63] OF TIME	Ring buffer of recent TimeBlocked values
AverageTimeOccupied	TIME	Average of all nonzero TimeOccupied values in the ring buffer
AverageTimeEmpty	TIME	Average of all nonzero TimeEmpty values in the ring buffer
AverageTimeBlocked	TIME	Average of all nonzero TimeBlocked values in the ring buffer
AverageTimeBetweenMovers	TIME	Sum of average TimeOccupied + AverageTimeEmpty
AverageUtilizationFactor	LREAL	Percentage value equal to AverageTimeOccupied / AverageTimeBetweenMovers
AverageMoversPerMinute	LREAL	MPM Throughput value, equal to 60 / AverageTimeBetweenMovers [s]
ThrottledThreshold	LREAL	A high throttled threshold (Blocked to Empty ratio) indicates a potential bottleneck station
ProcessedMoverCount	UDINT	Total number of movers processed by this station

.Track

REFERENCE TO Track

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

.TrackId

DINT

The numeric id of the track that this station is assigned to.

This value is read-only. Use the method .SetTrack() to set the station's assigned track.

Extra Examples

// Basic Station implementation with a 1s dwell time
IF Station[0].MoverInPosition THEN
    StationTimer( IN := TRUE, PT := T#1000MS ); // TON

    IF StationTimer.Q THEN
        Station[0].CurrentMover.MoveToStation( Station[1] );
    END_IF
ELSE
    StationTimer( IN := FALSE );
END_IF

// Immediately redirect all incoming shuttles to Station 1 instead of Station 0
FOR i := 0 TO Station[0].TrackedMoverCount-1 DO
    targetMover := Station[0].TrackedMovers[i];
    targetMover^.MoveToStation( Station[1] );
END_FOR

Station Labeling In Viewing Tools

See Visualization