How do you track Style on a Conveyor

I need to know the Style of a Car as it travels down a Conveyor.
Scenario: We build 4 styles of cars (for this example: Red, Yellow, Blue and Green.). Cars travel down Conv_1, at random intervals and random style mixes, and then they exit Conv_1 onto Power Roller Bed_3 which is the first station of Conv_2.
When Car is positioned on PRB_3, if Hold Table_4 is empty, PRB_3 lowers and car travels to HT_4. If PRB_5 is empty, HT_4 lowers and Car travels down to PRB_5. As of now the Cars travel down Conv_2 then alternates their routes going onto Conv_3 or traveling down to HT_6, then PRB_7 and onto Conv_4.
PLC knows the car Style on PRB_ 3 but does not track it as car travels down Conv_2. I would like to have the ability to track Car Styles on Conv_2. When car gets to PRB_5, I’d like to know the Style of Car (Red, Yellow, Blue or Green) so I can make a decision on where to route car.
Example: say I need to route all Yellow Cars down Conv_3 and all other color cars can go down either Con_3 or Conv_4. At the present time I have the ability, if I stay at Work Station and watch every car, to manually manipulate the logic and route cars down Conv_3 or Conv_4 as I choose. I would like to do this automatically with a selector switch or push button so, when needed, operation does not require a person to be at site all day to watch and manually control routing.
I have proximity switches on Hold Tables and Power Roller Beds sensing Table/Bed is “RAISED” or “LOWERED” and if a Car is present on Table or PRB. There are also positional stops that raise and lower to hold car in position on moving conveyor chain as Table/Bed rises.

I am asking for help on the best way to do this. I have looked at Fifo Instructions and Bit Shift Instructions. I do not know how to utilize these instruction. I do not know how I would trigger Fifo and keep track of the location of different Styles?
Sometimes Conv_2 is empty, sometimes it is full, and sometimes it partially filled, never an identical pattern. I have never used either one of these instructions but would like to learn. Maybe a MOV or COPY instruction is what I need to use? I am an electrician by trade but enjoy learning and working with A/B PLC Logix_5000.

Conv_2, Conv_3, Conv_4 are all controlled by the same PLC 5000.

I would appreciate any help you would provide. Thank you in advance.

Hello, Factoryrat. Welcome to this forum. I hope you will enjoy your browsing and learning while here.

I recommend that you use FIFO-type instructions. A FIFO only needs to track the order of the parts, not the exact position on the conveyor. FIFO logic is suitable where you only need to know the type of the next object, not its position on the transport device. A bit-shift register COULD be used, but it is better suited to use where you have a conveyor or other transport method that has an encoder that provices an index trigger, so that each time the conveyor moves a certain distance, the bits in the PLC memory (representing objects on the conveyor) also shift 1 position.

PLC knows the car Style on PRB_ 3 but does not track it as car travels down Conv_2. I would like to have the ability to track Car Styles on Conv_2. When car gets to PRB_5, I’d like to know the Style of Car (Red, Yellow, Blue or Green) so I can make a decision on where to route car.

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For your cars of different colors, to make it easy, assign a number to each color (Red = 1, Yellow = 2, Green = 3, Blue = 4). Then as each car leaves PRB_3, insert its color number into the FFL #1 (FIFO Load) instruction's Source word address. Do this for each new car that leaves PRB_3. Then on another rung, as the cars arrive at PRB_5, use a FFU #1 (FIFO Unload) to unload the FIFO to a Destination word address. As each car unloads, use a comparision instruction to route it to Conveyor 3 or to a second set of FIFO instructions that track the next leg of Conveyor 2 down to PRB_7. In other words, some of the cars being unloaded from PRB_5 (FFU Destination word = "4" for Blue cars) might go to Conveyor 3 and not continue on Conveyor 2. The remainder get inserted into a new FIFO #2 that tracks them down to PRB_7.

There are several other methods that would work (bit-shift, copy), but I think in this case the FIFOs would be best.

FIFO stacks or RFID tags on the car carriers.

Best to fit FIFOs and position based tracking "pieces" together in some situation, depending on what data might be changeable or where some sections may be slow moving with no alterations going on.

FIFOs are great for indexing sections that may have empty spots or have a variable size. You do have to carefully and timely perform the loading and unloading and ensure that it is fault proof with respect to sensor bounce and such.

I like position based tracking where there is sorting or merging going on. I use a pointer driven by conveyor speed signal (often open loop calculation based on VFD command reference, encoders are preferred) to represent the conveyor/carrier, then have a data table set up to map the contents using that pointer and offsets for each area of operation and to handle merge/unload sections. I use LIM blocks (range checks) of those calculated positions to drive the bits that make actions occur or interlocks or data manipulation.

Position based tracking never gets out of sync if set up right, but is a bit of work in PLC code to set up and use. Once set up, it is easy to modify and adjust.

I agree with Lancie, bits are cheap, use a Fifo stack over a bit-shift register, there is little to lose as long as your controller is not overburdened. I almost always end up with parallel stacks to correlate more than one parameter to keep attached to that vehicle.

What PLC(s) are you using?

Our PLC is an Allen Bradley 1756-L73S Control Lobix 5573S Safety Controller. I do not know how the Version deal works but our software covers V13 thru Version 19.

My only experience with PLC'S is using them to troubleshoot and fix problems as quickly as possible to keep lines running. $$ I am not a programmer but I do have that desire to do more than just look at program. I know that can be dangerous but I want to understand the programs and just learn more about them. I believe that is a good positive thing as long as my curiosity doesn't cause any unnecessary problems and interrupt production.

I did create my own Routine for the STYLE TRACKING and wrote some logic to track the style. I used MOV instructions. I will see if I can attach it for your perusing. It actually works but it is a little messy.