How to prevent conveyor from falsely loading conveyor space?

[cody_f]

[ FlexSim 19.1.1 ]

I have the blue buffer locations acquiring and releasing restricted areas to maintain the gaps and pallet counts in each area of conveyor. The orange are work stations. The photo eye sets variables to tell if the pallet should continue or move onto the loop conveyors when it comes to the decision point. The issue I have is when the buffer with the photo eye and the buffer on the first leg of the loop are both occupied. When this happens, the system will load a pallet into the small space on the conveyor between the entry transfer and the first buffer and then one into the queue that is connected to the entry point on the loop conveyor. How can I have my one decision point look to acquire two possible buffer locations, and if they are busy, it waits at the decision point location for the fist available buffer to travel to?

[zac_higleyQBKLZ]

Could you post your model?

[cody_f]

model-conveyor-loops.fsm

[zac_higleyQBKLZ]

@Cody F

I have not been able to recreate your problem. But if I am looking at the TopEastLoop Process Flow then Wait for Event is looking at the wrong Object. If I'm not mistaken, changing it from Queue3 to Queue5 might fix the problem. Let me know if that works and if not let me know at what Run Time the error normally occurs.

[cody_f]

Thanks, I fixed that but still get the issue. It happens right around the 23000 second mark in the top west loop. Once the conveyors ahead of the top west loop backs up to the point of the decision point, it then gives me errors and does some weird stuff at the photo eye location and loads to the queue. It happens at each of my loop locations once they get backed up in the same situations but at different times.

[joseph_g3 · Accepted solution]

@Cody F

Here's an updated version of your model with a solution to the loop problem: modelconveyorloopsanswer.fsm

Mostly I just modified your existing Process Flow for TopWestLoop, adding some more decides and some logic to stop and start items at the right times. I also added another photoeye on the loop conveyor with a global variable called TopWestLoop2 to keep track of whether that conveyor is blocked or not. This doesn't have to be done with a photoeye, you could also assign labels to stations when the onArrival or onContinue triggers fire, similar to the "busy" label on the stations you have after the elevators.

I also moved up the event-triggered source to the station before DP606 since the items were moving past that station while DP606 was still occupied. If you don't care if the items are doing that, you can always move the source back to DP606 and remove the first "stop item", "resume item", and "Wait for Item to ARrive at DP606" activities.

I also noticed you were getting some errors after running the model for longer. Most of them are coming from the OnClear custom code in the photoeyes. I'm not sure if you are doing anything there besides updating global variables (like TopWestLoop), but you could probably eliminate all of the code there besides updating the global variable. There are also errors coming from the OnContinue triggers of some stations. What you currently have in the condition for "On Continue" is causing errors. I don't think you need anything in the condition besides "true" for it to work anyways.

Let me know if you have any questions about any of this!

[cody_f]

Thanks for your support and the explanation, works great.