AGVs don't pick up items from a queue

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michela E asked Nov 23, '19 tannerp commented Nov 26, '19

AGVs don't pick up items from a queue

In my model there are 4 AGVs that have to pick up from 2 initial queues 2 types of products and through 2 elevators they bring them to 3 floors where there are some processors that have to process the items and put them in queues. Then the AGVs pick the finished items and have to bring them to 2 final queues (waste drugs and waste meals). The problem is that the last meals are not picked up from the queue after the processor and therefore they are not brought to the final queue. Where is the problem?

I attach the model and you should go till the end of the delivery of the yellow items (meals)

Software Version:

FlexSim 19.0.0

agv queue content

model.fsm (173.8 KiB)

5 |100000

Attachments: Up to 12 attachments (including images) can be used with a maximum of 23.8 MiB each and 47.7 MiB total.

Answer 1 · 2019-11-26T20:08:48Z

tannerp answered Nov 26, '19 tannerp commented Nov 26, '19

Hi @michela E,

I'm not sure that I have solved the problem, but I have at least located the source of the problem. Let me try to explain.

First of all, the AGVs will only change floors and look for work at the queue by the processors (like Queue1, Queue45, etc.) when they are instructed to carry an item from the main floor to be processed.

At one point in your model, the AGVs transition from moving blue items to moving yellow items. This can be seen if you stop the model at 29150 seconds and watch it play slowly.

If you look at AGV2, it is carrying a yellow item, so you would expect it to grab a yellow item to bring back...

But if we step ahead and watch which task it pulls, it pulls the blue item instead.

This leaves the yellow item in Queue45 without any AGV to come pick it up. The next time an AGV comes, it brings an additional yellow item and pretty soon, there are two yellow items in Queue45.

I think you might need to find a way to adjust the logic so that AGVs will look for work even at the control points on different levels. Otherwise, the AGVs end up in that infinite loop that you've been seeing. Does that make sense?

incoming-agv.png (137.0 KiB)

pulls-wrong-item.png (116.4 KiB)

no-agv.png (59.3 KiB)

· 1

5 |100000

Attachments: Up to 12 attachments (including images) can be used with a maximum of 23.8 MiB each and 47.7 MiB total.

tannerp commented · Nov 26, 2019 at 08:15 PM

You might consider connecting a CP in the main loop to a CP in each of the other floors so that the AGVs make sure they are exhausting the task list.

I tried this and it seems to work a little better.

added-next-look-for-work.fsm

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added-next-look-for-work.fsm (174.5 KiB)

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