topic Re: Task sequence problem in Process Flow in FlexSim Forum

Task sequence problem in Process Flow

lcdiazM6QFX — Wed, 29 Apr 2026 10:48:56 GMT

In my FlexSim model (attached), in the ProcesFlow called ProcesFlow_emparejamiento, the Robot (placed in he zone: EMPAREJAMIENTO) has to talke one AGUJA, TOBERA and MUELLE with the same label value "Tol", which can be 1, 2 or 3, and one TUERCA (without the label "Tol") and then join them in the combiner called Assembly, resulting in an INYECTOR. The model worked fine in very trials, but after some modifications not related to this Process Flow, it suddenly it stops working. It always happens around 12:02 on 19/10/2025. The message is the one that I copy below, and what we see is that the Robot takes an item with a "Type" label INYECTOR, which was not requested in the process flow.

We had a similar problem with a similar program which was solved by @FelixMoehlmann here: https://forums.autodesk.com/t5/flexsim-forum/task-sequence-problem-in-process-flow-robot-picking-up-an-item/td-p/13938018 . So, we tried to apply the same solution, activating the "Allow Multiple Pushes Before Back Order Fulfillment" option in the list "ComponentItems". However, after doing that we get the following errors:

Could it be another bug? How could we solved it?

Thank you very much.

Re: Task sequence problem in Process Flow

FelixMoehlmann — Thu, 30 Apr 2026 07:43:33 GMT

There is duplicated logic in the model. The "FIFO TOBERA/AGUJA Clasif" queues receive items through a port-connection and the "FIFO PIEZAS Clasif pre Emparejamiento" Process Flow also releases the same items. This eventually causes items to be represented twice in the logic which likely cascades into the task sequence error.

Either remove/deactivate the Process Flow or set the upstream queues to "Do Not Release Item" in their Send to Port option.

Re: Task sequence problem in Process Flow

borja_lorenzo — Thu, 30 Apr 2026 10:43:24 GMT

Hi,

First of all, Moehlmann’s observation seems to be correct.
In my test, after disabling the Sources in the Process Flow "FIFO PIEZAS Clasif pre Emparejamiento", the error:

FlexScript exception: invalid index at MODEL...

disappears. This suggests that the issue is indeed related to duplicated logic, where items are handled both by physical port connections and by the Process Flow.

Additionally, I noticed a potential race condition in "ProcessFlow_Emparejamiento". At the time indicated in the error (~80442.52), multiple tokens are trying to execute Pull item simultaneously, while the queues (QueueTOBERA, QueueAGUJA, QueueMUELLE) are pushing items to the ComponentsItems list from the 3D object logic.

To test this, I added a small loop before the Pull item using a Wait for Event, so tokens wait for a list change and recheck the condition before pulling. I also added a second condition to avoid blocking when no more items arrive.

With this approach, the error also disappears, even if the duplicated output logic in the FIFO queues is kept. So it seems both the duplicated logic and the race condition on the list access may contribute to the issue.

I was not able to reproduce the issue where the robot picks an "INYECTOR", and from what I see in the model, "Robot1" does not appear to be extracting that item.

I’m not an expert, just looked into this out of curiosity. Moehlmann’s solution is likely the correct one, I just wanted to share this additional observation.

Re: Task sequence problem in Process Flow

lcdiazM6QFX — Thu, 30 Apr 2026 14:44:47 GMT

Thank you very much to both of you. iI didn't want to deactivate the Process Flow "FIFO PIEZAS Clasif pre Emparejamiento", so I set the upstream queues "FIFO TOBERA/AGUJA Clasif" to "Do Not Release Item" in their Send to Port option. It seems that it has worked and I do not get the error anymore.