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Paula P7 avatar image
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Paula P7 asked Paula P7 commented

Problem with task sequence (task executor)

Hello!

I have a problem with task sequence. The idea of this model should be: task executer delivering one palette when the process is finished and just after that taking back that pallete which is done.

All processes have different processing time. I tried to use the preempt option and prioritize tasks. Everything works perfectly until finished process interrupts delivering palette to the sink (because I prioritized delivering palette, if I don’t task executer is delivering and collecting pallets separately). Any ideas how to fix it?

The problem starts about 9800 s (what’s more the task executer takes more than one pallete though it’s capacity is 1).

The model is based on standard 3D model with connections. :)


model2.fsm

FlexSim 20.2.3
processflowtasksequencetaskexecutor
model2.fsm (225.0 KiB)
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1 Answer

Felix Möhlmann avatar image
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Felix Möhlmann answered Paula P7 commented

The transport capacity only really matters for the "Break To" option, which determines whether another item should be loaded before delivering the current one. Preempting a task will cause the task executer to work on the new task regardless of current load.

That said, I don't think preemption makes a lot of sense in your model, since the task executer travels on a strict one way circuit anyway and the source and sink are close to each other. So unloading an already loaded empty pallet before bringing a new one costs very little time.

My suggestion would be to only increase the priority of bringing new pallets but not preempt. That way, if there are multiple tasks to choose from, delivering new pallets is always done first.

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Paula P7 avatar image Paula P7 commented ·
Thank you for your answer. Unfortunately increasing priority doesn't work. The idea of this model is to load new palette when the process is finished, so the task executor has to exchange pallets. When increasing priority that doesn't work. Just in the beginning task executor takes green (processed) palette and delivering it to the sink, then he's loading a new palette. Also while task executor is idle he should be waiting around source to be ready to take palette.
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Felix Möhlmann avatar image Felix Möhlmann Paula P7 commented ·

So what needs to be done is to make sure that the task to get a new pallet is created before the task to retrieve the old one. In the first attached model I do this by placing a floor storage with a minimum dwell time of 0s between the processors and their respective queues. This 0s delay before the pallet enters the queue makes sure the logic to bring a new pallet to the now empty processor fires first.

I also have the source move the fresh pallets into a queue first, so more than one processor can request one at a time (a source is limited to one outgoing item at a time).

The only instance where this will likely not work is if two or processors finish at the exact same time (unlikely but theoretically possible). In that case the transport would first bring all new pallets before retrieving the old ones.

model2_fm1.fsm

In this second model I instead use the "On Receive Task Sequence" trigger to listen for a new task to bring a new pallet. I then check if there is an item in the respective and add tasks to bring it back to sink to the task sequence manually. This will work as long as these are the only tasks the transport receives. Otherwise more checks would be needed to determine if the received task sequences does involve bringing a new pallet.

model2_fm2.fsm

In both models I also use the "On Resource Available" trigger to have the transport drive to the source if there are no pending tasks.

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model2-fm1.fsm (106.6 KiB)
model2-fm2.fsm (97.1 KiB)
Paula P7 avatar image Paula P7 commented ·
Thank you! :)
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