Why AGV moves without any work on ground floor, but lot of work in first floor
Accepted solution
Your problem with the AGVs not using the elevator on the way down was caused by not placing the Redirect CP before the connection between floors. This is from your model:
It should come before the connection between floors in order to reroute the AGVs to the elevator, like this:
As for optimizing the movement of your AGV, I would suggest experimenting with your model and seeing what works best. I'm not sure how much you can change your model or the routes in it, but here are a few suggestions:
1. Eliminate Unnecessary "Next Look for Work" connections that cause the AGVs to travel extra distance or visit paths that have no items to pick up.
2. (This is part of #1) Use "Look for Work" connections in the place of "Next Look for Work" since those let the AGV check if items are at a control point without having to travel there. These are usually brown in color. You can find more information on them in the "LookForWork Forwarding" section of the AGV Process Flow.
3. Set the Deallocation Type on each of your control points to "Deallocate When Past Current":
This will allow your AGVs to follow each other more closely, making them slow each other down less.
I applied all of these suggestions in this updated model: medleagvanswer.fsm
Note that in this updated model, I removed an activity from the "AGV Elevator" Process Flow since it was causing the AGVs to loop an extra time before getting on the elevator.
Check all your suggestions, thanks! As optimising, just one AGV is enough to do all work from 6.00 to 15.00 hour.
Have few questions about AGV moving:
1. 6.00 to 6.51 - AGV travel to 1. floor, load at D7, unload at R7, than go back to base floor, make loop (no work), go to 1. floor, make short loop and go back to base floor. Why do this, when there is a lot to load at D8,D9,D10,D11 and D12?
2. Would extra short path nearby R4 help, to AGV not travel everytime back to base floor and turn before enter the elevator?
3. Why AGV use shortcut when load at D7 and travel to unload at R7(right on the picture),
but never use shortcut left from this one, to load at D8, always travel around?
Thanks again!
Each of the problems you mentioned has to do with the placement of your Queues and your network of "Next Look For Work" connections.
The thing with AGVs when using the AGV process flow is that they don't know how to get to the items that are available for pickup unless there are "Next Look For Work" connections or "Look For Work" connections leading to them.
AGVs follow these steps when collecting items:
1. They follow the "Next Look For Work" connections until they find an item to pick up. If there are no "Next Look For Work" or "Look For Work" connections to a control point, it won't go there to pick up items.
2. They load the item.
3. They travel directly to the destination of that item (regardless of where "Next Look For Work" connections lead).
4. They unload the item.
5. They follow the "Next Look For Work" connection from their current Control Point and continue looking for work.
Here are my answers to your questions:
1. Following the steps I described above, the AGV loads at D7 and travels to R7 using the shortest path possible, then unloads the item. Then it follows the "Next Look For Work" connection to continue searching for work. Referring to the image below, it follows the "Next Look For Work" connections until it travels back to the base floor.
It continues traveling like this until it finds work at D2. It then travels directly to the destination for D2, which is R2. From R2, the "Next Look For Work" connections lead back to the base floor, which is why it returns to the base floor even when there is no work available there.
You can try fixing this problem by reorganizing where your source and destination queues are, by changing the AGV paths, or by changing the network of "Next Look For Work" connections. For example, you could move R2 next to R4 (I don't know if that is possible for you), so that after delivering the item from D2 to R2, the "Next Look For Work" connections would lead it to the other queues with items (D8, D11, etc.).
The difficult part about fixing the inefficiency in your model is that everything is so spread out, it's hard to check every queue without wasting some time. You can play around with it and see what makes it more efficient.
2. Yes, that would reduce travel time. If you can, I would recommend removing most of the path above R4 and then moving the floor-to-floor connection, the elevator entrance and the elevator redirect down.
3. I'm not sure I understand this question. Are you asking why the AGV doesn't travel directly from R7 to D8? If so, refer to my answer to question 1.
Hope this helps!
As you suggest, i removed some NexLookForWork and add extra path and LookForWork
so AGV after first loop(unload at R2) dont go back to base but travel to D7...
Also to be more realistic, i change at AGV load and unload time and Elevator travel.
Just noticed few loop with no work at: 9.70, 12.24, 13,95 and last loop at 14.48 with no work, but cant find why.
I can not move any of Queues, because they are at position as in real, i put CAD drowing as template.
Thanks again to sharing your knowledge so i can finish my first model in FlexSim.
It Will be a part of my Masters degree.
Regards, Marko
The problem you were having with each of those times in your model comes from your "Next Look For Work" connections on this point:
The problem with having two "Next Look For Work" connections out of one point is that it will alternate which connection to take. In your model, it was taking the path I marked "1" first and then the next time it came by it was taking path "2".
AGVs are not actually smart, they just follow the paths you give them until they find items. Therefore, you have to set it up so that they will travel exactly where you tell them to go.
Can you move or add any of your control points? I found a solution that would make your model more efficient by moving one control point, adding another control point, adding a "Look For Work" connection, and removing the "Next Look For Work" connection I marked with a "1" in the picture above.
Here is the model with this solution: medleagvanswer2.fsm
