Power and Free conveyor stops model run after a certain time

[manu_n]

[ FlexSim 18.1.1 ]

Hello,

While working on a model with power & free conveyors, I found that power & free conveyors make the model stop running after a certain point of time, and this time reduces as I increase the conveyor speed or reduce the dog spacing. For example, a simple source-conveyor-sink system with a conveyor speed of 100,000 m/min and dog spacing of 0.5 m stops running after 10739 minutes.

I want my actual model to be able to run with very high conveyor speeds in certain situations (when I want to eliminate the delays due to the travelling time of flow items on conveyors).

Is this behaviour normal for a P&F conveyor? Am I missing something?

[SCHamoen]

@Manu N Could you post this simple source-conveyor-sink model? Than we can take a look if you missed something or if you found a bug.

[manu_n]

pfconveyor-test.fsm

Here you go @steven.hamoen

Thanks.

[SCHamoen · Accepted solution]

@Manu N

I don't see anything strange other that you create very small numbers by using these strange combinations. You model in minutes and give very high speeds this means that the clock has to make very small increments to make the correct calculation. Maybe you bumped against some kind of rounding problem @phil.bobo?

But I do wonder if you don't want to use any functionality of the conveyor (you want to eliminate travelling time) why do you use a conveyor? Why not a simple processor with a delay or even a queue if no delay is needed.?

[manu_n]

@steven.hamoen

The model that I'm working on is that of an assembly line and the client wants to use it for two applications:

1) to analyze the line for any bottlenecks in the conveyor and handling systems themselves, for which I'll use realistic speeds for the conveyors,

2) to analyze the operators' utilizations and whatnot, for which the operator should not stay idle while he is waiting for a part to reach the station. Practically, he will be assigned enough work to do (stock-up activities, acquiring tools/sub-assemblies etc.) while the part is being conveyed from the previous station to his station. But this work depends on the incoming part, so I'll be reading this process time from the incoming part when it reaches the station. So, for this case, I was trying to reuse the same model with very high conveyor speeds.

I used the conveyor object so that the same model can be used for both cases. The conveyors also have a few restrictions, loops and stops which I'm managing by decision points and are important for the study.

I'm not sure if you understood what I'm getting at.

[SCHamoen]

@Manu N Ok I understand.

I have tried to rebuild your simple model but now only using seconds and not minutes and set the speed to 166 m/s (which is around 10.000 m/min) and this also gives a problem. So I guess you have run into a bug of some kind. Sorry can't help you any further.

[manu_n]

Okay @steven.hamoen, thanks for your support anyway.

[philboboADSK]

Yes, this is a bug. We've fixed it for the next bug-fix releases (18.0.8 and 18.2.1). The power and free interval calculation had an overflowing variable when using such a large speed and small interval.

You can work around it for now by using a smaller value or modifying your code to avoid the conveyor using Send To logic instead of changing the conveyor's speed. I'd suggest having a global variable for whether you want to skip the conveyors and then connecting objects around them rather than cranking up their speed.