Wrong output if all machines run at 85%

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Karina GM2 asked Aug 27, '19 Joseph Gillespie commented Aug 28, '19

Wrong output if all machines run at 85%

I have 3 machines (Starting in source 16). The first one's CT is 12 seconds, the second machine's CT is 16 seconds and the third one's 12 s. As you can tell, the bottleneck is my 16 second one. The simulation goes for 520 mins = 31200. Therefore, the first machine can produce 2210 pcs, 2nd one can produce 1658 and 3rd can produce 1409 due to the fact that the second one is not fully pushing all the 2212 pcs it needs. Considering they all run at 85%, could you please check why I am not getting an output of 1409 pcs in sink 16? I get that the first one ran at 63.8% because it was waiting on the 2nd one. But why am I getting an output of 1658 pcs. if I am running at 85%? I used "breakdowns" and "flow" tabs. buffer.fsm

Software Version:

FlexSim 19.1.0

output data

buffer.fsm (35.3 KiB)

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Answer 1 · 2019-08-27T20:51:50Z

Joseph Gillespie answered Aug 27, '19 Joseph Gillespie commented Aug 28, '19

@Karina GM2

I tried running your model and I got an input of 1636 in Sink16.

As you said in your question, the bottleneck in your system is the second machine since it has the longest CT. Since the third machine has a lower CT than the second machine, by the time the second machine finishes processing an item, the third machine will be available to receive it (unless it is down). Therefore, all of the items (except the last one) processed by the second machine will make it to the sink by the end of the simulation. The only reason why the input of Sink16 is 1636 and not 1658 is because sometimes the second machine has to wait while the third machine is down (you'll notice that the output of machine 2 is only one more than machine 3: it's output is 1637).

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Karina GM2 commented · Aug 27, 2019 at 11:59 PM

I get what you mean. I ran it and I am still getting the 1658, not sure how you got the 1636 from? How could I configure the 3rd machine to give me an output of 1402 though? Considering that that is the theoretical output I am supposed to be getting based on the 85% in a one piece flow system.

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Joseph Gillespie Karina GM2 commented · Aug 28, 2019 at 04:38 PM

@Karina GM2

Here is a screenshot of the results I get when running your model:

This is after 31200 seconds.

Your theoretical output is incorrect. Your assumptions about how many items you should get from your third machine are wrong. The third machine, like the first one, can produce 2210 pcs during the run of the simulation. The only reason why it doesn't produce 2210 pcs is because it only receives 1637 pcs from machine 2.

This is where your assumptions are wrong. The fact that machine 3 is running at 85% doesn't mean that it is only going to process 85% of the items it receives from machine 2. Machine 3 runs faster than Machine 2, so it will be able to process all of the items it receives from Machine 2.

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capture.png (2.0 KiB)

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