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Paul
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Using queue size to permit entity creation

Asked by Paul
on 3 Feb 2013
Latest activity Edited by Tianhao Guo on 23 Apr 2016
I have a manufacturing model that has several queues after servers. I would like to use the number of entities in one particular queue to trigger a hold on entity creation i.e. if more than 20 entities in the queue then stop feeding in more raw materials from inventory.
I assume I'll use an event based entity generator (or time based with release gate) and know how to get queue size out of the queue but am unsure how to use this to generate the function to release or create an entity.
I can see Simulink has many logic (e.g. relational operator) functions that I can drag in but would have thought this so common that Simevents would have its own blocks.
Do I need to use logic blocks from Simulink to trigger entity creation / release or is there a more elegant or integrated way from Simevents?
Thanks
P

  1 Comment

I have almost the same question. Now I think we can make an output port from queue block "number of entities in block, n". Then use it.
The question is that I don't know how to trigger a function when the "number of entities in block, n" becomes zero
https://uk.mathworks.com/matlabcentral/answers/280589-how-to-determine-whether-a-queue-is-empty-in-simevents-and-do-some-actions-based-on-this-observation

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1 Answer

Answer by Devdatt Lad on 3 Feb 2013
Edited by Devdatt Lad on 3 Feb 2013
 Accepted Answer

If you can set the Capacity of the Queue to be 20, then the Time-Based Entity Generator that is feeding this Queue can be configured to Pause when it is blocked. Hence when the number of entities in the Queue is 20, the Generator will stop generating, until the number goes down to 19, in which case it will generate one more and so on. So you don't need any Logic blocks in this case. Just connect the Generator to the Queue and SimEvents will do the rest for you.
However, if you need the Queue Capacity to be more than your threshold or if your threshold (of 20) varies throughout the simulation based on some criteria, then your best bet is to use the Logic blocks from Simulink for this.

  3 Comments

Thanks Devdatt, I have a lot going on before this buffer (not straight to buffer) so can't use the blocked port approach and will revert to simulink logic blocks.P
It doesn't have to feed straight to the buffer. It can have blocks in between as long as these blocks are not other buffers (queues or servers).
thanks for clarifying. In this case there are both queues and servers between points.

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