FIFO Load and Unload

[Robb B]

Yes, this is a project for school, and I'm not looking for anyone to do my work for me. What I would like is some clarification on using FIFO load and unload. I've read the help files, as well as Borden & Cox's book's section on it, but I can't seem to make it integrate into my logic. Pretty sure it's about the last hang up I'm having with it. Maybe someone can point out what I'm doing wrong, or just a different approach to explaining the FIFO setup. This isn't for marks or anything, it's just "here's a setup, try to make it work" project.

Just an interesting note, it runs on a simulator on a desktop PC which is connected to a (physical) PLC. We get all the benefits of the actual PLC, but none of the space problems of the physical conveyor system. Great for schools!

The system is laid out like so:

Entry conveyor randomly loads 2 different height cases on pallets. The pallets are sent down to a turntable which spits them out (short cases on the left, tall cases on the right) to freight elevators. I think everything is fairly well described in the file, but if there's any questions I will try to clarify them.

Right now I've got the FIFO storing into #N7:0 and unloading into N7:5, then using the value in there to determine case height (6 is high, 2 is low, I believe).

Robb

 

[Gil47]

At home I don't have the ability to open your zip file, so I am going to make an assessment without that data .

When I use a file shift that does as a FIFO does, I would load the data into the N7:5 and unload at N7:0.
This may seem backwards but it stops the risk of shifting the load data to the unload in one step rather than the five steps you intended.
This is because the shift in a PLC happens, N7:0 - 1 - 2 - 3 - 4 - 5 so the data entered into 0 can end in just one scan at 5 instead of the intended timing rate.