Carrier Items are a special type of Item that interacts with some objects (DropOff; PickUp; Dispatcher) in a different way to standard items. Carrier Items play a role as transporter of other items. A Carrier Item can pick-up one or more items at a location, and then move them to another location and drop them in the new location.
PickUp and DropOff Objects provide the means for Carrier Items to transport standard items. They enable a Carrier Item to pick up one or more items and move them, as a group, to a different part of the model. The carried items can then be released, either as a batch or individually. Carrier Items can be delayed using objects that can have a time delay specified. This is useful for modeling transport times with the Carrier Item representing the means of transport.
Carrier Item Behaviour
During a run, Carrier Items are created at Entry objects, just like items.
Normal items can enter any object at any time (if the object is not busy or at its capacity).
Carrier Items cannot enter PickUp Objects until they are required. If the Carrier Item's path leads to a PickUp Object that is not ready for it, the Carrier Item must wait for the call.
Creating a Default Carrier Item Class
After you have made an Item Class, you may decide you want all new items of that Class to behave as Carrier Items by default. To do this you edit the Item Class to change its default behaviour.
RIght Click on the Item's Icon in the Item Palette:
To alter the default behaviour, click on the Default Behaviour Option in this Menu.
Changing Item Behaviour during a Model Run
During a Model Run, you can make individual regular Items behave as Carrier Items (and turn them from Carrier Items back to regular items) by passing them through a Change Object during a model run.
You change the individual item's behaviour by using a Routine Operation to set the System Item Attribute ItemActAsCarrier.
The default setting of this attribute is whatever has been set for the Item Class as a whole (see above).
- Set ItemActAsCarrier to 1 to make the Item behave as a Carrier Item.
- Set ItemActAsCarrier to 0 to make the Item behave as a regular Item.
Note: For proper operation, you must ensure that the change made to this system attribute is made (and therefore detected by the system) during lookahead.
Carrier Item States
Carrier Items differ from regular items in that they have two states.
Setting the Default Behaviour option to "Carrier" gives the Item Class an additional, default icon representing a human operator, to distinguish it from a normal item.
A Carrier Item's state is determined by whether it is carrying any items.
Different icons can be set for Carrier Items when they are carrying items, via the Choose Icons option in the Item Edit Menu.
Advanced Usage Note
The ability to change an individual item's behaviour back and forth enables you to carry items within items within items, which can be exciting. However the ability to read the attributes of carried items is restricted to the collection of items held by the 'top level' Carrier Items.