Why a rack does not receive items even if it's empty ?

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Clair A asked Oct 17, '16 Matt Long edited Oct 17, '16

Why a rack does not receive items even if it's empty ?

Hi,

The attached model is inspired from the AGV tutorial lesson 3. I just added a rack with a maximum content of 2. If you run the model, you'll see that the agvs transport 2 items to the rack, these 2 items leave the rack however the rack's input port stays red and it blocks the upstream source. I tried also with a queue with a maximum content of 2 and noticed the same behavior. Am I missing something to make it work ?

Software Version:

FlexSim 16.2.1

agv rack

agv-tutorial-lesson-3-with-a-rack.fsm (106.6 KiB)

Answer 1 · 2016-10-17T17:55:16Z

Phil BoBo answered Oct 17, '16 Matt Long edited Oct 17, '16

This appears to be a bug with how the dropoff point process in the AGV ProcessFlow works.

When you are using dropoff points, the AGV unloads the item to the control point, a Dropoff Retrieval Time delay happens, then the item is moved into the destination.

Because you are using ports to send the item from the source to the rack, the rack's nroftransportsin variable is incremented for each item coming in.

The AGV ProcessFlow isn't decrementing that variable appropriately because it isn't unloading directly into the destination.

If you add a custom code to the Retrieval Process that calls

transportincomplete(getlabel(token, "destination"), getlabel(token,"item"));

then it fixes this bug in this situation.

Attached is a model that shows this change.

Be cautious with this change though. You may run into other bugs where a downstream object can receive more than its max content if you apply this change and then later have AGVs using dropoff points to unload items that weren't sent using a Request Transport From field.

I'll add a note to the dev list to look into a better solution to this issue.

3145-agv-tutorial-lesson-3-with-a-rack-1.fsm (107.2 KiB)

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