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  #1  
Old 08-28-2015
Nathan Moriarty
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Default Pull when empty

I'm having some trouble setting up the pull logic for my most recent simulation. I have a queue feeding into a combiner, and that queue needs to draw the flowitems from one queue, wait until the combiner uses all of said items, and THEN draw the next set of flowitems from the next queue in line. I've tried everything I can think of, but my experience is limited. Help?
I'm using Flexsim 5.0.
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  #2  
Old 08-31-2015
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Ben Wilson Ben Wilson is offline
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Default

Not sure about version 5.0, but in the current version 7.5.4, you can view the Event List (Main Menu>Debug>Event List). Open your model, then open the Event List, then hit reset. You'll see all the events that are scheduled for time 0.

Every event can spawn new events. Try hitting the Step button once. After one step, several things have happened:

- the first source created its first flowitem
- the first flowitem flowed from Source8 to the FeederQueue, where the CombinerQueue pulled it and sent it on to the Combiner
- the CombinerQueue's Exit trigger made it into the condition where it was empty, so it incremented its inputport label
- the CombinerQueue will now pull from input port 2
- the first source made the rest of its flowitems from the first row of its schedule

We need to account for all of these things happening at time 0 - we don't want CombinerQueue to pull from the 2nd FeederQueue after just one flowitem pulled from the first FeederQueue. If I understand the problem correctly, you want the following events to occur in order:

1) Sources create all their flowitems and populate their feeder queues
2) CombinerQueue pulls all the items from the top feeder queue
3) CombinerQueue feeds the combiner until CombinerQueue is empty
4) CombinerQueue pulls all the items from the next feeder queue
5) repeat steps 3 and 4 until there are no more feeder queues

What we need to do is keep #2 from happening at all until #1 is totally complete. And we need to keep flowitems from flowing through the CombinerQueue to the Combiner until CombinerQueue has pulled all flowitems from the FeederQueue.

In the attached model I've made the following changes:
- CombinerQueue onReset trigger: added closeinput, closeoutput, plus delayed messages after 0.000001 time elapsed to open output then input
- CombinerQueue onMessage trigger: added cases that will open and close input and output on demand
- CombinerQueue onExit trigger: added delayed messages if the queue is emptying. Messages will close outputs then inputs, then open input (reevaluates the pull requirement, allows queue to fill), before opening output
- CombinerQueue Pull Strategy - changed to pull from any port. The problem with specifying a port here is that its hard to change later. Once the queue has requested something from a particular port and it is waiting for a flowitem on that port, it is stuck there until a flowitem actually arrives over that port. Best to just pull from any port and put the logic into...
- CombinerQueue Pull Requirement - since this can be reevaluated on openinput(), we put the specific port requirement (based on label value) here

This model was built in FlexSim 7.5.4. You can install 7.5 in its own directory - it won't overwrite anything from 7.3 or older installations. If you don't have a license, no worries. Version 7.5.4 will install in the feature-limited Express mode, which will still allow you to view and run this sample model.

Reply back if I misunderstood the problem and the attached model isn't what you were looking for.

Thanks!

PS - Version 5.0 was released in May 2010. Any chance of upgrading to the latest version?
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The Following 5 Users Say Thank You to Ben Wilson For This Useful Post:
Jing Chen (08-31-2015), Jörg Vogel (08-31-2015), Nathan Moriarty (09-01-2015), Sebastian Hemmann (09-10-2015), syseo (09-01-2015)
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