How does the AGV wait next to the processor after unloading an item?

[christian_w3]

[ FlexSim 18.1.2 ]

After unloading an iteam at the processor, the AGV should wait until the process is finished and load this finished item. I use the "stock" AGV flowchart, but I have no idea how to stop the AGV. After unloading, the AGV travelles automaticlly to the next controll point.

How do I implement a wait before the AGV loads the finished item?

process-schwarmmontage.fsm

[tanner_p · Accepted solution]

Hi @Christian W3,

This isn't a feature that is built in to the "stock" AGV flowchart, but it's something we can add. Thanks for posting your model. I have updated it to include logic that will achieve the behavior you illustrated in your question. Let me explain what steps I took to get there:

1) I created labels on the fixed resources that designate what time of resource they are. The label is "FRType" and the values are either "queue" or "processor". This is used in a Decide Activity after the Unload Activity in Process Flow.

2) The Decide Activity will send the token to a Wait for Event Activity depending on whether the item went to a "processor" type or "queue" type fixed resource. (Note that the "up" command simply takes the unloadItem label and goes up one level in the model tree to its container, which will either be a processor or a queue in your model.)

3) If the "FRType" label is "processor", the token goes to a Wait for Event Activity that listens to the processor's "On Process Finish". When this occurs, the token is released to its original path.

Hopefully this helps and makes sense. Feel free to comment back and tag me @tanner.p with any feedback or further questions. I've attached your updated model below.

schwarmmontage-update.fsm

[christian_w3]

@tanner.p
Hi, thank you for your for quick help. I'm going to check this as soon as possible.

Kind regards
Christian

[christian_w3]

Hi @tanner.p,

our main problem was solved by your answer. Now we have an other question / problem. We want to run more AGV's in our network. In our simulation, a maximum of 3 AGVs are active and load/unload the boxes. How can we activate more than 3 AGVs? If you look at the AGV process flow, you can see that there are tokens next to the "Wait for activation".

Furthermore, some items don't get picked up after the process (especially item type 4 and 5). But this happens only in one of 15 to 20 cases...

Kind regards!

schwarmmontage-autosave.fsm

[Brandon_Peterson]

Christian,

The AGV process flow will automatically park an AGV if the following conditions are met:

1. The AGV is at a NextLookForWork control point that has ParkPoint connections

2. The AGV battery is below the low threshold OR the load balancing heuristic says that there is not enough work to do.

The load balancing heuristic basically tries to keep the number of active AGVs equal to the number of active Items.

The reason that your model never seems to have more than 3 AGVs working at one time is that the number of active Items never gets above 4 (almost always never more than 3 except for very infrequent and short times). You can change the load balancing heuristic to keep more AGVs active but that would mean that you had AGVs moving on the network with nothing to do (i.e. it would be inefficient). The only other way to have more active AGVs will be to modify the times in the model so that there are more items.

I did notice that in some cases an item leaving "Processor1" will have to wait for an AGV coming from "Queue2" instead of getting one from parking. You can change this by moving the control point "AGVStartingPoint" to just after the drop off point for "Queue2".

I hope this helps, Brandon

[tanner_p]

Hi @Christian W3,

I think I understand your question, but if I'm off, please feel free to correct me. The maximum number of AGVs that are active is actually not limited by the Process Flow. The limiting factor is the availability of work and control points for the AGVs. Only 3 work at a time because there's usually 3 or less items that need loading/unloading.

If we add another queue with a large supply of work, you'll notice that all of the AGVs are utilized now.

Example showing utilization of all AGVs: schwarmmontage-newqueueexample.fsm

I ran your model looking for times that items are not picked up and I noticed that some do wait for a long time before being picked up, but they are eventually picked up. I'm not exactly sure why this is happening. I noticed that in one case, the item at the processor was not being pushed to the Load List. I can't figure out why, though, so I might have to keep looking at this.