How to have 2 TEs traveling together with A*

Question

question

Patrick Cloutier asked Apr 13 2020 at 4:08 PM Matt Long commented Apr 22 2020 at 8:45 PM

How to have 2 TEs traveling together with A*

In the simple attached model, I'm trying to have 2 TEs travel together. One does the picking (Picker) and transfers the parts to the other (Transporter). I have 2 problems:

1 - How can I make the Transporter go right next to the Picker and not in a different aisle like it does? It does that even if I decrease the Node Spacing.

2 - How can I trigger the A* logic to recalc (optimizenetwork) when the model blocks like it does for token #5?

Thanks a lot for any ideas.

2 TEs working together.fsm

Software Version:

FlexSim 20.1.0

flexsim 20.1.0 astar

· 2

Answer 1 · 2020-04-21T14:37:13Z

tannerp answered Apr 21 2020 at 2:37 PM Matt Long commented Apr 22 2020 at 8:45 PM

Hi @Patrick Cloutier,

The nature of A* requires the task executors to avoid each other because they are potential collisions, just like other objects in an A* model. So, fundamentally, you're not going to be able to get the TE to travel close enough that they might collide.

Based on your explanation, however, you want to have the Transporter and the Picker travel together, so we can just put the Picker inside the Transporter and then move objects into it as we would a trailer or an operator pushing a cart. This is essentially the same functionality, although it will look a little different.

Please review my attached model and let me know what you think. Like I said, it's not going to be aesthetic, but it is functional.

two TE together.fsm

two-te-together.fsm (54.2 KiB)

· 5

Patrick Cloutier commented · Apr 22 2020 at 1:37 PM

Thanks for the idea. It solves part of the problem.

But, they don't go in the same aisle where the product is. They go to the next aisle. I had this problem in my version with the Transporter but, at least, my Picker went into the correct aisle. Now they both go into the wrong aisle.

Any way to make them go in to the correct aisle?

0 ·

tannerp Patrick Cloutier commented · Apr 22 2020 at 4:22 PM

Glad that it helped partially solve the problem, @Patrick Cloutier.

I looked at why this was happening and it appears that the A* logic will try and get as close as it can to the item using the shortest route possible. I attached a version of the model with wider aisles and you'll notice the same behavior; the AGV is in the "correct" aisle, but not exactly the same grid space (in the y dimension) as the box.

In the case of the first couple of boxes in your model, the shortest route means going to the grid space next to the box rather than directly in front of it. This is just part of how A* works. If you're looking for a specific pickup point, it might be to your benefit to use an AGV network so there's more control and less ambiguity over the pickup/dropoff locations.

@Matthew Gillespie may have more to add regarding A*, but I think you're going to have more control using AGVs.

two te correct aisle.fsm

0 ·

two-te-correct-aisle.fsm (53.7 KiB)

Patrick Cloutier tannerp commented · Apr 22 2020 at 4:28 PM

I am evaluating the different methods to help a client. And it's now clearer and clearer that AGV is the way to go. Thanks a lot,

1 ·

Show more comments

Matt Long Patrick Cloutier commented · Apr 22 2020 at 8:45 PM

@Patrick Cloutier if you use a Travel To Location task activity they will move down the correct aisle. This changes how the navigator calculates the travel path to the item. I've attached Tanner's model with that change.

AGV may be a better way to go, alternatively you can add more process flow logic to better control how the te's travel. For instance, figure out which direction the te is facing. Then do a travel task to the end of the aisle in the forward direction. Then travel to the item.

two-te-together.fsm

0 ·

two-te-together.fsm (54.0 KiB)

question