Process flow merge controller with accumulating slug conveyor

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Craig DIckson asked Nov 25, '19 Craig DIckson commented Nov 27, '19

Process flow merge controller with accumulating slug conveyor

@anthony.johnson I just used the process flow merge controller from your article "Process Flows for Two Types of Merge Controller" - specifically the Fixed Gap version. It works fine for one of the two merges in my model, but the second merge actually uses accumulating slug conveyors, and these don't always work as well.Specifically, if items are continuing to arrive, it appears that the slug conveyor will continue to add them to the slug after it has been released. The result is that these extra items tend to collide with items from the next lane released. (Or you could look at it as the next lane is released to early, because it didn't know about the added cartons).

I spent some time experimenting with some of the time calcs in the process flow, but wasn't able to get it to work consistently enough. Can you suggest a way to either stop the slug conveyors from adding the extra items, or for the next release to account for them?

Software Version:

FlexSim 19.2.4

merge controller slug building process flow merge controller

Answer 1 · 2019-11-27T19:10:49Z

anthony.johnson answered Nov 27, '19 Craig DIckson commented Nov 27, '19

Theoretically this should not happen because there should be no accumulation of new items onto the slug during the slug release (the slug release speed should be at least as fast as the conveyor's slug build speed, and the slug should not be running into items ahead of it because you're implementing a gap, so items shouldn't be bumping onto the back of the slug). However, it appears that in some scenarios it does happen, e.g. if the conveyor is completely full when you release the slug, and another item comes on after releasing the slug that is up against the back of the slug. Below are some suggestions for ensuring that this doesn't happen.

1. Pull a small gap on the take-away conveyor. Give the conveyors after the slug build conveyor an ever-so-slightly faster speed. This will ensure that when items are taken away from the slug build conveyor, they will advance a little farther than their behind items, so the behind items won't have to "stop" for 0 time and create a possibility for a behind item to bump into the slug and consequently append itself onto the slug.

2. Force a tiny gap at the beginning of the slug build conveyor. Make the conveyor's item entry space a tiny bit bigger than the convey and stop spacing values. This will again give items just a tiny bit of room so they don't append themselves onto the slug after it has been released.

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Craig DIckson commented · Nov 27, 2019 at 09:44 PM

@anthony.johnson Thanks, that got me headed in the right direction.

I tried #2 first, and it seemed to cause the conveyors to get "stuck" - after some point the slugs stopped releasing. I then tried # 1, and I think it would work if I pulled a bigger gap, but that is not what my conveyor engineers designed ... ;-)

So what I ended up doing was adding a couple eyes and some code to each lane so that when the slug conveyor was nearly full, it stopped new cartons from entering it until it was released, and that seemed to work. Thanks.

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