topic Re: Four way conveyor intersection in FlexSim Forum

Four way conveyor intersection

WordenskjoldDK — Fri, 14 Jul 2023 11:15:46 GMT

[ FlexSim 23.1.3 ]

Hey everybody.

I am working on a conveyor model, and have hit a snag.

The conveyor system has two directions side by side, and in some places, there will be 4-way intersections, where each item can go in one of four directions. (Counting a 'U-turn').

I had initially hoped that simply crossing the conveyors would create transfer points, but that doesn't seem to be the case, unless I am missing something.

I suspect thwere is some obvious answer for this problem, but I just haven't found it yet.

Is there anyone out there who has tried something similar, and who has any experiences to share?

Best regards

Christian

Re: Four way conveyor intersection

joerg_vogel_HsH — Fri, 14 Jul 2023 12:27:20 GMT

@Christian Wordenskjold , you can start with your roundabout crossing section.

conveyor_intersection_roundabout.fsm

conveyor_intersection_roundabout1to4.fsm

Re: Four way conveyor intersection

WordenskjoldDK — Fri, 14 Jul 2023 13:36:15 GMT

Hi Joerg.

Thanks for taking your time with the models.

I like that idea a lot, but the system I am simulating doesn't work that way. (See below) The intersections are one of the main worries of the architects, so determining whether they will cause bottlenecks is crucial to the project.

I have also looked into a method where I used pusher-objects with custome kinematics inside the intersections. That gets the visuals, control logic and the process times right, but it also has the drawback of the conveyors being disconnected, and thus I'm not able to rely on the conveyor system for send-item-based navigation. In that case I will have to write a navigation algorithm for the intersections.

Perhaps that is simply the best way of going about it unless I find a more generic option.

Again, Thanks for your time, Joerg.

Re: Four way conveyor intersection

jason_lightfoot_adsk — Fri, 14 Jul 2023 15:06:40 GMT

Can you not begin with default behavior?:

Model attached.

ConveyorInterchange.fsm

Re: Four way conveyor intersection

WordenskjoldDK — Fri, 14 Jul 2023 15:49:26 GMT

Hi Jason.

Using default behavior seems like a brilliant plan. This works exactly as I intended.

I don't know why it didn't work for me earlier.

Thanks a lot.

Re: Four way conveyor intersection

jason_lightfoot_adsk — Fri, 14 Jul 2023 15:52:38 GMT

This is more tricky than it appears - you need to precisely align all the conveyors which is almost impossible interactively using the mouse - even with snap threshold lowered. I did it by increasing the displayed decimal precision in model settings and then changing the properties fields. A better way might be to write a script to construct the layout precisely.

Re: Four way conveyor intersection

WordenskjoldDK — Fri, 14 Jul 2023 16:19:05 GMT

I agree, it is tricky, and I have realise that the alignment issue is why it didn't work in my initial model.

I will work on a script solution to place the intersection along with 1 meter of conveyor on each of the four sides.

Thanks again.

Re: Four way conveyor intersection

WordenskjoldDK — Tue, 18 Jul 2023 11:03:06 GMT

@Jason Lightfoot, I have played around with the model you attached, and everything works as intended. I copy/paste-expanded your intersection to a large system, and every box found its direct way to its destination. I also added some decision points to prevent deadlocks.

Then I decided to start a new model from scratch with 0.8 meter wide conveyors, and I simply can't get it to work. Some of the boxes go the right way, while others get caught going in circles.

I did all the following to try to get it to work:

I made a script, that rounds all x- and y positions off to 1 decimal. Then I placed them and used to script to get them to the precise location.
I increased decimal precision to 6 digits and everything looks right in the property fields.
I compared conveyor system and type properties to yours, but didn't find anything to explain this behavior.
I checked distance along properties for all inline and side transfers.
I looked at my Conveyor.sendItem, and that seems ok as well
I even tried rearranging the conveyors in your model and putting them back in place with the same methods, and it still worked as intended.

I think I am missing something obvious, and now it is time to call for help 🙂

Any thoughts to nudge me in the right direction?

Thanks in advance.

Intersection Model.fsm

Re: Four way conveyor intersection

jason_lightfoot_adsk — Tue, 18 Jul 2023 11:54:16 GMT

I've put in a request to the developers to not use double comparisons (which lack precision) for the distalong of the side transfers and to use a "reasonable modelling error tolerance" instead. Unfortunately this will not help until a possible future release and is far from guaranteed.

In the meantime the trick will be to get the side transfers offset such that the potential side exit is further along the conveyor being crossed than then side entry point.

Re: Four way conveyor intersection

WordenskjoldDK — Tue, 18 Jul 2023 12:20:42 GMT

Ok, I tested the workaround, and it seems to work as intended.

It seems, that only a very minute change is required, and if I understood you correctly, the soution should look like this, right? (Just for anyone else who reads through this answer)

Re: Four way conveyor intersection

jason_lightfoot_adsk — Tue, 18 Jul 2023 12:29:51 GMT

Correct, or change all the central side transfers to 0.39.