Strange behavior and disappearing items on conveyors

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Claire Krupp asked Aug 24, '22 Claire Krupp commented Aug 26, '22

Strange behavior and disappearing items on conveyors

I have a large model of a High Speed Sortation system. In the real world, the packages will be spread across the width of the conveyors and will sometimes bump up against each-other. In the model I am allowing packages to be side-by-side by allowing an overlap, and I think this is the root cause of the problems I have been having. There have been many examples of packages getting stuck, where previous packages have travelled with no problem. It's usually located at a transfer between conveyors. Each time I have changed the behavior of the transfer, or reduced the amount of overlap, and it clears the problem for a while, and then another one pops up. I feel like I'm playing whack-a-mole!

The current example has packages travelling between two conveyors on a slide or chute (modeled by another shorter, sloped, conveyor.) At time 16.34 the package highlighted (red) approaches the slide, partially overlapped by a larger yellow box in front of it.

You can see this area using the view “XBelt Sorter & Re-induct” shown here:

The large yellow box transfers to the downstream conveyor ("IFP1_5") with no problem, but the red one gets to the slide and then disappears from view. The tree shows it as a sub-node of the upstream conveyor ("ISF3_2_Merge"), and then by 16.36 it becomes a sub-node of the slide (“ISF3_to_IPF1_5”), but it never transfers to “IFP1_5” and remains as a sub-node of the slide. If you select it and show it in the display, it has moved way over to an unused part of the display.

Subsequent packages seem to travel as expected, but every so often another one is added to the slide conveyor's tree. By time 24.5 there are four in the tree. A red package goes down the slide and continues in the plane of the slide conveyor past the end and on down towards the floor of the model.

Then at 24.6 a large yellow box travels across the downstream conveyor and continues moving in that plane. All the packages on “IPF1_5” behind that point become blocked and eventually the whole line is stopped.

There have previously been problems in this area with the upstream conveyor becoming blocked, but nothing I can see is blocking it.

My question is: is there anything I can do to stop this happening? Is it a bug, or just a consequence of stretching the capabilities of the conveyors a bit too far?

I'm uploading the model "CKrupp_conveyor_items_disappearing"

Thanks!

Software Version:

FlexSim 22.2.0

conveyor transfers

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Kavika F ♦ commented · Aug 25, 2022 at 08:32 PM

Hey @Claire Krupp, I found part of the problem you're facing. It seems that sometime before the problem starts, you've got some flowitems being spawned way outside of the conveyor system.

(I circled the yellow box coming in.) I'll continue investigating.

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Claire Krupp Kavika F ♦ commented · Aug 25, 2022 at 08:38 PM

I think those may be the items that are still sub-nodes of the slide "ISF3_2_to _IPF1_5". They seem to continue moving back towards the slide and then later cause the "Crash".

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Answer 1 · 2022-08-25T20:04:06Z

Claire Krupp answered Aug 25, '22 Claire Krupp commented Aug 26, '22

There seem to be some weird movements as the items cross the transfer to the slide, which is wider than the upstream conveyor. I discovered that if I reduced the width of the slide to match the upstream conveyor, and then moved it away, and repositioned it so that it creates new transfers, then all the problems go away.

I have no idea why, or if it will pop up again later!

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Kavika F ♦ commented · Aug 25, 2022 at 08:49 PM

That should fix your problems with this issue. Sometimes flowitems get drawn onto conveyors incorrectly if there are Non-accumulating conveyors or if there are a large amount of flowitems going through a transfer. A similar problem occurs if you try to take flowitems off of a conveyor or put them on without using an EntryTransfer or ExitTransfer.

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Claire Krupp Kavika F ♦ commented · Aug 26, 2022 at 03:12 PM

Ok thanks for the info.

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