Stop item ignored on non accumulating conveyor?

Question

question

Ralf Gruber asked Jun 28, '23 Julie Weller commented Jul 12, '23

Stop item ignored on non accumulating conveyor?

Hi,

we found a possible bug on a conveyor: The model attached is part of a bigger model using the process flow to control a side transfer. The zone makes sure, that only 1 pallet can be on the side transfer, so the first pallet can enter the zone, the second is stopped by the max wait timer and has to wait, until the first has completely left the transfer and reached the blue DP.

The problem seems to arise because the second pallet is already stopped due to reaching the non accumulating conveyor and is stopped again in the PF after a 1s technical delay:

Once the 5s Delay for the first pallet has passed and it starts to move again, the second pallet moves with it although it ought to be stopped. Resume is not called before the first pallet leaves the zone and allows the second pallet to enter. The second pallet´s tree still shows the numStopRequests and wasStoppedBeforeStop both set to "1":

The expected behavior was for the second pallet to wait before entering the second conveyor until it is resumed after the first pallet reached the blue DP. Is this a bug?

Thx

Ralf

TestTransfer_23.1.2.fsm

Software Version:

FlexSim 23.1.2

conveyor stop item side transfer

testtransfer-bug-1.png (319.5 KiB)

testtransfer-bug-2.png (416.3 KiB)

testtransfer-2312.fsm (48.4 KiB)

· 4

Jason Lightfoot ♦ commented · Jun 28, 2023 at 11:38 AM

Any idea why the first pallet tries to enter the transfer zone at this position ? (representing the one second delay displacement)

while the second pallet tries to enter at this position:

It seems they should be at the same position

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1687952181848.png (62.7 KiB)

Ralf Gruber ♦ Jason Lightfoot ♦ commented · Jun 28, 2023 at 12:03 PM

Thanks for looking into this, Jason: The first pallet continues for the full 1s delay, which brings it partially into the empty transfer conveyor before being stopped from the process flow. The second pallet is stopped by the non-accumulation second conveyor, caused by the first pallet being stooped on DP2, before the one second has fully passed. Stop item is called on that second pallet, while it was stopped before. Does that make sense?

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Jason Lightfoot ♦ Ralf Gruber ♦ commented · Jun 28, 2023 at 12:33 PM

Thanks - not sure why I hadn't registered that - need coffee perhaps.

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Julie Weller commented · Jul 12, 2023 at 03:31 PM

Hi @Ralf Gruber, was Jeanette F's answer helpful? If so, please click the "Accept" button at the bottom of their answer. Or if you still have questions, add a comment and we'll continue the conversation.

If we haven't heard back from you within 3 business days we'll auto-accept an answer, but you can always comment back to reopen your question.

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Answer 1 · 2023-07-06T21:57:14Z

Jeanette F answered Jul 6, '23 Ralf Gruber commented Jul 7, '23

Hello @Ralf Gruber,

I sent this into Dev for their review. It does seem to be bug like to me. I understand this is part of a larger model, however it is a little confusing as to why you have chosen to model this way though. Would using area restrictions and a station also accomplish what you are trying to do? Could you explain the 1s delay after the arrival at the first DP? If the item is stopped before the transfer to the non accumulating conveyor then there is no issue.

· 1

Ralf Gruber ♦ commented · Jul 07, 2023 at 08:28 AM

Hi @Jeanette F ,

Thanks for looking into this. It is not my model, but a clients. The client needs to build the model close to reality, because they want at some point connect it to their PLC. The 1s delay is a technical delay for controls communication.

I know there are workarounds, but they will not mimic the real behavior exactly.

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