Recently I have had items get stuck on accumulating conveyors. It happens at in-line transfers between beds, and doesn't happen all the time. In the attached picture, you can see the totes stopped at the circled location. Several hundred totes went through that same location earlier in the run (and in fact it never got stuck when running some other scenarios). It seems to happen more in high-volume situations where a lot of items accumulate.
I seem to remember a similar issue a few years ago?
Is your model repeatable up to this point or are other events also changing? If it's repeatable and they always get stuck at that time (even if it's after thousands of totes have been processed) it would be useful to examine the model to see what is going on.
@Jason Lightfoot No, I have no custom logic for merges. This is plain vanilla conveyors.
Again, it seems to occur when I have several accumulating beds in a row, each of which is an exact multiple of the accumulation zone length e.g., several 10' beds in a row where the zone length in each is e.g. 0 * L + 30"
The problem generally goes away if I make one of the beds an inch longer and the other an inch shorter. This is not a viable solution though, because this effects most of the beds in the models as I am following the exact bill-of-materials for the actual physical system, which not surprisingly has lots of beds of integer zone length.
Here is a very simple model where it happens, and a state file after it has happened.
ConveyorLock-up.fsm
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Hello @Craig DIckson,
I was able to verify that the bug you describe indeed occurs as you said. In fact, after running the experimenter over 100 replications, it turns out that it happens pretty often at some point in the run.
I would assume that this is a bug of some sort, and I'm sorry for any inconvenience it has caused you. Hopefully, there will be a fix for this bug soon.
Please let us know if there's anything else we can do to be of assistance. Thanks!
Looking forward to the bug fix when it's ready.
@Craig DIckson Thanks for the simple model that reproduces the error.
This issue seems to be happening because the conveyors are an exact length multiple of the items on the conveyor. This causes a lot of events to happen at the same time when items stop and start at the beginning and end of conveyors. It appears that at some point when the model time gets large that there is some floating point precision error happening that one or more of these events happening all at the same time get out of order. We're looking in to it to see if there's a way to fix this.
In the mean time this issue can be avoided by changing one of several different dimensions such that the items don't line up exactly with the start and end of the conveyors. For example, this model has an OnCreation trigger on the source that changes the items from size 1 to size 0.99999. This is enough to avoid the issue.
ConveyorLock-up_workaround.fsm
You could similarly change the length of the conveyor or the entry space of items by some small amount.
Sorry for the inconvenience.
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