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Brad Noorman avatar image
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Brad Noorman asked Sam Stubbs answered

Problems with Conveyors and Decision Points

Hello,

I am having a few problems with my simulation. I have 3 different models, two of which have worked in the past, that are all experiencing similar issues.

I have modeled a pick-to-light pick and pass operation. There are 9 Pickers in 9 Pick Zones. When a box enters the zone, a display will tell the picker what (if any) items to pick and how much of each item. The picker will pick the items and put them into the box. If the box is complete, they will push the box to a takeaway conveyor, if the box still has more picks to complete it will continue into the next zone.

I have used a series of Decision Points to ensure the flow item Box does not get ahead of the corresponding token. The token waits until the box enters the zone before executing any of the picking logic and the box waits at the end of the zone until all of the zone picks are complete.

When I run the model 1 of 3 problems will occur:

  1. The box will not trigger the "Wait for Event" for DP1, thus preventing new orders.
  2. The box will not resume on the conveyor, thus preventing the boxes to flow.
  3. The box will not stop at the decision points, thus throwing off the synchronization of token and box. The token will then wait for the box to arrive at the next decision point, which has already happened.

Every time i run the model, it seems that a different box is causing the issues. I have set up a trace for the tokens in the picking logic and the logic seems to be working correctly.

Thank you for your help.

dperror.fsm

FlexSim 17.1.4
process flowconveyorsdecision points
dperror.fsm (952.2 KiB)
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Jeff Nordgren avatar image Jeff Nordgren commented ·

@Brad Noorman

Attached is your model file back. I didn't do anything to it, except save it to another file name. The model seems to run, near as I can tell. Flowitems flow and entries into the OutputTable are written. So I'm not sure exactly what to look for.

Please take a look at the attached model an explain to me what I'm missing.

Thanks.

dperror2.fsm

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dperror2.fsm (933.2 KiB)
Mischa Spelt avatar image Mischa Spelt Jeff Nordgren commented ·

"I didn't do anything to it, except save it to another file name." - Interesting, that happened to me a few times as well... customer complained that their model was broken, I opened it and Saved As, then sent it back - fixed. I was never able to figure out why this sometimes works either.

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Brad Noorman avatar image Brad Noorman Jeff Nordgren commented ·

@Jeff Nordgren

Thank you for taking a look at it. I'm still having issues on my end. Can you make sure that all 21000 rows in the output table are complete. If not and there are no packages in the system, the model is most likely experiencing error number 1 from above.

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Jeff Nordgren avatar image Jeff Nordgren Brad Noorman commented ·

@Brad Noorman

I ran the model to 83233.78 (see graphic), which was the point that it ran out of flowitems.

But as you can see, it does not fill in every row in the OutputTable global table. But what it does tell me is that no flowitems are being held up at DP1, which was your original question/problem. So I'm not sure what problem you are having with the model.

As far as problem 1 is concerned, it may not appear to fire but the code in DP1 which writes to OutputTable does fire or there wouldn't be any entries in OutputTable. And the reason that it doesn't appear to fire is that there is no "time" between the actions in that PF block after the Source. So, I put in a delay of 1 time unit at the beginning of that block (see model) which will show you that it is doing what it is supposed to do. So there really is no issue with question 1.

I've run the model a few times and it runs until there are no more flowitems. So I think this question should be closed.

If you are having other issues with your model, other than above, then I would suggest that you create a new question.

dperror2-jn1.fsm

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Sam Stubbs avatar image
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Sam Stubbs answered

So I've gotten the model to a point where I can replicate where it stops. (You didn't have the operators have a set restart position. IF you read the section in the User Manual about model repeatability it gives a few good points about how to set your model up, so that things like this are easier to debug.)

If you run the attached model with all 3d / Process views closed and on Max Speed, you'll see the model hangs up at 146460.22

7914-dperror.fsm

When I had the 3D model view open it ran into a Conveyor OnDraw error once, and also another time with the 3D model view open it didn't get hung up at all. I'm wondering if there is a bug in the Conveyor draw code that could be causing this model to hang up?

. @Matt Long @anthony.johnson Could either of you take a look at this one?


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