topic Re: Double pallet elevator with process flow in FlexSim Forum

Double pallet elevator with process flow

imanol_oa — Mon, 04 Apr 2022 08:56:17 GMT

[ FlexSim 22.0.1 ]

Hi,

I am trying to define this elevator as a double pallet elevator. I've been trying to do this with the object process flow but I couldn't make it work. The main idea is that the elevator will only go down once it has two pallets.

Thanks!

doubleelevator.fsm

Re: Double pallet elevator with process flow

joerg_vogel_HsH — Mon, 04 Apr 2022 13:22:30 GMT

doubleelevator.fsm

Re: Double pallet elevator with process flow

joerg_vogel_HsH — Tue, 05 Apr 2022 07:09:46 GMT

ATTENTION! This approach has nothing to do with process flow. It just delays a tasksequence task evaluation for a break tasktype to let find for a break for requirement function in a taskexecuter a suitable second item to load. To achieve such a delay I have added a delay task to any received tasksequence if the Taskexecuter is empty or in this case: there aren’t any subnodes attached to him.

A process flow logic must check, if there are two pallets available for loading. You would do it by looking for items on a conveyor or by a photo eye counting items. Then you wait for any identified item and load it onto the elevator. After this you let travel the elevator to your destination and you unload each item on him to an entry transfer by a sub flow structure.

Re: Double pallet elevator with process flow

imanol_oa — Wed, 13 Apr 2022 06:46:54 GMT

Hi @Joerg Vogel,

Yes, I realised because I changed some station times and it is not working. Is there any way that I could do it with a process flow? (In order to avoid failing if there is any other change).

Thanks!

Re: Double pallet elevator with process flow

joerg_vogel_HsH — Wed, 13 Apr 2022 07:10:39 GMT

Sure, it is. But I adjust an internal created tasksequence. If you use process flow, you can do it, too. you can insert into a tasksequence a delay.

You can replace any internal created tasksequence by a process flow created tasksequence.

Re: Double pallet elevator with process flow

imanol_oa — Wed, 13 Apr 2022 08:10:39 GMT

I've been trying for a while and I don't get it right. Would you mind helping me by giving an example or something? You may use the model I sent in the first message.

Thanks!

Re: Double pallet elevator with process flow

joerg_vogel_HsH — Mon, 18 Apr 2022 07:10:12 GMT

I an working on it for some time, too. It is not easy. You have two situations to get evaluated. First one pallet is entering and then there is a waiting time for another pallet. How long can you wait for a second pallet, which will be transported with the first together?

Second two pallets entering elevator right behind another. Maximum waiting time has not passed out.
You have a two branch process starting with one event: entering elevator.

Each entering item starts a timer in another sub process. If the timer is not run out, than another item has arrived in time. You can batch your tokens together in first process flow branch and initiate elevator moving down. You preempt all timer tokens and destroy them in a sink.
If a timer token is waiting to long in a delay activity, this token set a label to stop any item in a photo eye on your conveyor. This token initiates moving elevator down.

Once the elevator gets empty at lower location he moves up again.
Arriving in upper level he resets responsible label value to stop items in photo eye and resumes any stopped item on conveyor.
With an item entering your elevator the process starts again.

Re: Double pallet elevator with process flow

jason_lightfoot_adsk — Mon, 18 Apr 2022 12:39:55 GMT

This becomes really simple if you use lists and push the items when they arrive at the exit transfer and model the elevator's behaviour as a single cycle rather than a process for each item.

Getting the elevator to travel to any transfer seems tricky - I added a user command for getting a transfer's location.

Model attached.

doubleelevator_jl2.fsm

Re: Double pallet elevator with process flow

myriam_srdg — Wed, 20 Apr 2022 18:42:55 GMT

Thank you @Jason Lightfoot, that was helpful. I managed to edit your logic and do it with three pallets. Unfortunately, I was not able to edit my model properly.

In your model, this script provides a 3D array with the x, y and z position of the ExitTransfer position.

However, when I try to replicate this in my model, I get the following error.

I’m not sure what this is for. I’m aware that you use this in the source to determine the pickup and dropoff locations (getEntryExitTransferLocation(current.pickupTransfer)). Was it to check something?

To solve this problem, I’ve set my coordinates (both in source and travel). [Again, I’m not sure where this information is used]

However, it seems that apart from this there is something else that I’m not doing correctly because it doesn’t go over this state.

Can you help me with this? I provide my model.

doubleelevator_jl_ms.fsm

Many thanks!

Myriam

Re: Double pallet elevator with process flow

jason_lightfoot_adsk — Wed, 20 Apr 2022 19:00:24 GMT

I added the usercommand to your model and made the List in the process flow point to the Global List in the toolbox: "ElevatorItems".

doubleelevator-jl2-ms.fsm

Re: Double pallet elevator with process flow

myriam_srdg — Thu, 21 Apr 2022 09:43:32 GMT

Oh yes, I see that you created the command using modeling logic > user command. Thank you very much @Jason Lightfoot

Just one more curiosity, pallets come to the elevator in a fast move while they go out smoothly. Why is this so?

Re: Double pallet elevator with process flow

jason_lightfoot_adsk — Thu, 21 Apr 2022 14:35:22 GMT

It is moving it onto the elevator using a kinematic - the problem is that the item is still on the conveyor which is overriding the kinematic position. This is kind of a bug/design flaw.

If you move the item into the model before it is loaded then the animation can be observed (model attached with the elevator moved away to show the effect).

doubleelevator-jl3-ms.fsm