Why AGV moves without any work on ground floor, but lot of work in first floor

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Marko G asked May 28, '19 Mario E2 answered Jan 19, '21

Why AGV moves without any work on ground floor, but lot of work in first floor

I'm sending a model that is already running, but not quite as I would like. On the lower floor, both AGVs move (empty), even when they do not have any work, and they can already be in use on the upper floor. After a certain time when item goes (from ground floor)to the upper floor, then one or both AGVs are moving to upper floor and transfer items, but not all of them, and return to the ground floor where they circulate without work. I must also solve the problem that the movement of AGV from one floor to another will take place over the elevator (animation) and not through the connection of the two floors. If you see a possible solution, or if I have an error, I will be happy to receive any information.

AGV never transfer items from:

D12 to R12

D7 to R7

D11 to R_9_10_11

Software Version:

FlexSim 16.2.2

agv agv network properties

test-poto-nopo.fsm (171.7 KiB)

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Joseph Gillespie commented · Jun 06, 2019 at 10:06 PM

@Marko G

Was my answer helpful for you? Do you have any further questions?

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Answer 1 · 2019-05-30T22:48:32Z

Joseph Gillespie answered May 30, '19 Joseph Gillespie commented Jun 25, '19

@Marko G

The problem you were having was that there were no "Next Look for Work" connections leading to the upper floor. By adding a few of those connections I was able to solve both issues. Let us know if you have any further questions! test-poto-nopoanswer.fsm

test-poto-nopoanswer.fsm (171.0 KiB)

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Marko G commented · Jun 19, 2019 at 09:39 PM

@Joseph Gillespie

AGV moves to the upper floor with elevator, but went back from first floor via conection between two floors. Why it wont go back also vith Elevator? Is there missing any loop NextLookForWork on the first floor?

How can I optimize the movement of AGV?

medleagv-131-19-6-19.fsm

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medleagv-131-19-6-19.fsm (170.8 KiB)

Joseph Gillespie Marko G commented · Jun 20, 2019 at 05:18 PM

@Marko G

You said in your original question that you wanted the AGVs to use the connection between the floors instead of the elevator. Now, in this post you want them to not use the connection between floors but to use the elevator. Do you want them to only use the connection between floors, only use the elevator, or something different? I'm just a little confused by you changing your mind.

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Joseph Gillespie Marko G commented · Jun 20, 2019 at 10:25 PM

@Marko G

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.

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medleagvanswer.fsm (172.1 KiB)

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Marko G Marko G commented · Jun 23, 2019 at 09:47 PM

@Joseph Gillespie

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!

medleagv-131-23-6-19-1agv.fsm

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medleagv-131-23-6-19-1agv.fsm (160.6 KiB)

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Joseph Gillespie Marko G commented · Jun 24, 2019 at 04:51 PM

@Marko G

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!

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