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Lucie L2 avatar image
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Lucie L2 asked Matthew Gillespie edited

Conveyor skew not working?

Hello,

I am working on a model where cartons are skewed to the side along portions of conveyors. However, it does not seem to work as it should. The cartons pass through a "skewing" conveyor and are aligned to the side, but when they pass on to the next they are again centered. And on a small testI did with only 2 conveyors, the skew is not maintained for the first item.skew-problem.fsm

When I do it in another model, it works fine...

I haven't changed much settings in this one... Can someone help me see what I am doing wrong?

Thank you very much!

FlexSim 19.0.2
roller skew angle
skew-not-working.png (41.6 KiB)
skew-problem.fsm (11.4 MiB)
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Jeff Nordgren avatar image Jeff Nordgren commented ·

@Lucie L2,

I guess I don't understand exactly what the problem is with the model(s). When you use a "skewing" conveyor, the parameters for that "type" of conveyor ONLY exist for that type of conveyor. So when a flowitem is on the skewed conveyor, it stays there until it hits another conveyor that is NOT of the same, skewed type. In your models, you go from a skewed conveyor to a normal one. Works just as I would expect. Goes from skewed in one conveyor back to normal when it hits the normal type conveyor. If you were to put another conveyor of the same skewed type, then the flowitem would appear not to change from being skewed earlier.

So, what am I missing? Can you explain more about the problem?

Thanks.

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Lucie L2 avatar image Lucie L2 Jeff Nordgren commented ·

@Jeff Nordgren,

Yes, that is what is happening in my model, but in other models (like the one attached) the position was maintained through out the system.

And, when I do a test on a simple 2 conveyor system, first skewed and second normal, that is not what happens. The box gets skewed and maintains its relative position throughout the rest of the system.

skew-problemv2.fsm

I am a bit confused as well...

Thanks!

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skew-problemv2.fsm (28.9 KiB)
annotation-2019-05-22-111540-skew.png (79.6 KiB)

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Phil BoBo avatar image
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Phil BoBo answered Phil BoBo edited

This looks like a bug with the roller skew angle when using inches for the length model unit. I'm still debugging it; I'll let you know what I learn.

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Lucie L2 avatar image Lucie L2 commented ·

@phil.bobo, thanks! Let me know if there is a way to work around it for the time being

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Phil BoBo avatar image Phil BoBo ♦♦ Lucie L2 commented ·

In 18.2, we updated the conveyor roller skew kinematics to be based on item travel distance instead of time. This bug is being caused by a part of the code that wasn't updated properly to use distance instead of time for the kinematics.

I've fixed this bug for the next bugfix release.

For the time being, you can mostly work around the issue by using an entry transfer into the skew angle conveyor instead of an in-line transfer:

A-connect the upsteam conveyor to make Exit and Entry Transfers,

Then delete the in-line transfer. (Selecting that transfer is difficult, but it is easier if you put the view into a Perspective Projection.)

See the attached example. 19249-skew-workaround.fsm

This will make it so that when the code incorrectly uses the time (instead of correctly using the distance) to prune the roller skew kinematics, the kinematics calculation starts from 0 to the end of the roller skew conveyor instead of including the distance along the upstream conveyor.

This workaround isn't perfect; there are still moments near the beginning of the model run where an item may jump incorrectly because the current model time is a very low value, but it should help mitigate the issue.

When the model units are in meters instead of inches, it accidentally hides the issue for the same reason as why the workaround helps. The problem only manifests itself early in the model run, and with meter units, the time when it starts working correctly is earlier than with inches units.

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