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wonjo P avatar image
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wonjo P asked Jordan Johnson answered

I'm having a trouble on A* algorithm

Hello,

I'm trying to design the kiva system.

I got a error message, 'Unrecoverable deadlock encountered for". Model stopped when using Astar.

So, I click 'Ignore Inactive Members' to resolve the problem. But, I take a same message before.

All AGV in my picture are blocked.

What should I do to recover a error?

In addition, I got a error 'LINK PARITY ERROR(*)'frequently after using A*.

I want to know what error say. When I got a error, I click the RESET to recover.

Thank you.

astar-capture1.pngastar-capture2.png

FlexSim 19.0.2
agvastar
astar-capture1.png (451.1 KiB)
astar-capture2.png (393.6 KiB)
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Jordan Johnson avatar image
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Jordan Johnson answered

When using collision detection in A*, the travelers allocate and release nodes as they travel along their path. You can see these allocations if you check the "Show Allocations" box on the Visual tab of A* navigator's properties.

If a traveler has allocated a node, and a second traveler tries to allocate that node, a collision occurs. There is some default logic that attempts to resolve the collision. One of the options that can happen is that the second traveler will wait for the first to leave. If two or more travelers are waiting, and none can move unless another moves, then that is a deadlock, and that's what's happening.

To avoid deadlock, you usually need to find a way to avoid the deadlock situation. Sometimes, you can reduce the number of travelers. Sometimes, you can give travel tasks that generally won't cause a deadlock situation. When you attach a Task Executer to the A* navigator, that traveler gets a trigger called On A Star Block. You can also use this trigger to give a new task sequence when a collision occurs, one that gets out of the deadlock situation.

As far as the Link Parity error, you would need to post a model in order for us to debug that.

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