Conveyor Position Tracking

I've looked through the posts on this topic and seen some pretty good ideas on how to do this. I've written a routine to track pallets along a conveyor that I think will work, but I'd like some input on it.

Our basic system is a barcode scanner at the beginning of the conveyor with 4 90 degree transfers along the length. Each transfer is about 10 feet apart, with the pallets being 1 foot square.

The pluses I can see from a system like this is that if a pallet is taken off or added to the conveyor it really shouldn't matter as the positions will never be right when it makes a sensor at a transfer.

The negatives I can see are my use of jump instructions. I don't think this routine would scale well to a larger stack as the watchdog timer and address space would be an issue.

If anyone has any tips or thoughts on the program, please share them. This is my first time attempting a tracking system and my first attempt at indexed addressing.

Can you sketch a visual aid for us that shows the conveyors and transfer stations? That would help me to understand the situation better.

OkiePC said:

Can you sketch a visual aid for us that shows the conveyors and transfer stations? That would help me to understand the situation better.

Click to expand...

The basic layout is that pallets travel down a belt conveyor with a barcode scanner mounted on the underside. Along this belt conveyor there are 4 pneumatic transfers that pop-up and drive the pallet into the auto packaging stations. These pop-ups are roller conveyor. The goal here is to automatically sort the pallets to the packaging stations. The main belt conveyor can have up to 10 different parts travelling on it at the same time but we only can only auto-pack 4 different parts at a time. (1 part on each line). The program I posted only focuses on 1 auto-line and a part number of either 1 or -1 (yes or no).

It looks like the main conveyor is all one piece, so you could take a different approach and create a data table "map" of the conveyor.

At regular intervals, update a "pointer" address that references the position of the entry point onto the conveyor. Have a rollover point that is at least the length of the conveyor. Use a floating point value for best accuracy, then use the absolute value of it when referencing points in the map.

When a new pallet is detected, simply drop it's ID Code into the map at the index referenced by the pointer.

Each PLC scan, calculate the position of each of the diverters as offsets from the pointer, again, deal with the rollover effect so that none of your position values are out of range.

If there is data at the calculated diverter offset, then take the appropriate action, including zeroing out that data point once the pallet is successfully transferred.

What you end up with is more efficient logic and you are still tracking by position. If you want to get real fancy, you can even animate the pallets on an HMI.

This is a little bit hard to describe in text, so I will try to come up with an illustration of the concept.

Paul