Help with SLC500 keeping track

[bdingus76]

Hey guys I am new to these forums and I am relearning PLC's after a 10 year break from it. What I am trying to do is keep track of cans that get connected to a hang line. I only have Three sensors to do this with. There is 400 holders and not every holder gets a can depending on producton run time. right now i have a BSL set up that shows me which holder has a can and which does not. My question is how can I compare the bits and know is a can has fell. Two sensors are for seeing the can and holder going in to process and the last sensor is to see can come out. but with out spending alot of resources Any ideas or help I thank you in advance.

 

[Lancie1]

There is 400 holders and not every holder gets a can depending on producton run time.

If your SLC 500 (RSLogix 500 software) Bit Shift Left is set up properly, it should have a bit memory location for all 400 positions on the overhead conveyor. To find if any specific location has a can, simply look at the value (1 or 0) of the bit for that location of the can. For example, if your 400 postions start at B9:1 and run to B10:144, and you want to look at Conveyor hang postition 200, then that should be bit B9:200. So you could use the XIO instruction to Do Something when that bit is "0" (assuming 1 means that there is a can in Position 200 or Bit B9:200 and 0 means that there is no can).

 

|  BSL Position    Do Something   |

|    B9:200             OTE       |

|-----|/|---------------(  )------|

|                                 |

 

[Lancie1]

I am trying to see the holder and the can (with out hundreds of lines of logic) at the start and make sure it is the same at the end. That way we know if a can has fell. Is there a way to do this logically?

I am answering this at your original post to help keep the responses together in case someone else wants to join the discussion.

Yes, I can see how it could be done. At the can-loading point, you insert a 1 or 0 into a bit-shift stream that essentially saves the string of bits (including ones that are unloaded or 0) into a 400-bit memory range (call it B3:0/0 to B3:24/15 which should be about 25 words x 16 bits). Then at the end, as each can holder passes a sensor, you compare its current sensed value at Sensor S3 with the previous value that was stored in the BSL register.

I can help you set up the BSL to do this. You will need several bits of information:

1. Most important is something to use to index the BSL, shifting it one bit each time the physical can holders move 1 position. If your have two sensors at the loading point, aim one at the holder frame so that when a new frame (empty or not) comes to the loading point, the sensors returns a TRUE or 1, then that bit can be used to advance the BSL (call is Sensor 1 input at I:1/6).

2. You need a Sensor #2 at the can loading point to insert a 1 or 0 into the BSL, as the BSL is indexed or advanced by Sensor #1. Say Sensor S2 is wired to Iput I:1/7).

3. You need a Sensor #3 at the end, or at bit-shift position 400, say S3 = I:1/8. Luckily, you need only 3 sensors and that is what you have. Funny how that worked out, isn't it?

Your logic rung for the end-of-line at Sensor #3 would look something like this: (See attached picture). Of course you will need to use something other than the NEQ for comparing bits (instead of words). What bit instructions could you use when say B3:24/15 = 1, then is I:1/8 = 0 at that same time?

You will need to add all the bells and whistles to make a complete system. For example, when you first start the chain running, the first 359 positions at the end will not have any data. Can you think of a way to work around that problem? What if you used a counter and counted the first 359 postions and ignored those until the counter = 400 or greater?

 

[bdingus76]

Thanks Lancie1 that's pretty much how I had it set up. I've been watching them ones and zeros go around for a few days now. I wish every holder got a can but the stop and go process eliminates that. So the empty holders what's giving me a issue. Was hoping if I starred at the screen long enough it would just flash back to me and be like oh yeah that's it. But for the life of me with out writing tons of logic to keep track of which holder was full at the beginning to the end is evading me.

 

[Lancie1]

But for the life of me with out writing tons of logic to keep track of which holder was full at the beginning to the end is evading me.

Evade no more! Rung 001 will tell you which can holder was full at the beginning but also lost its can along the way, if you write it like this:

| S1 INDEX SENSOR    BSL AT END   S3 SENSOR   CAN WAS LOST |

|    I:1/6            B3:24/15     I:1/8          O:2/0    |

|-----| |---------------| |---------|/|------------(  )----|

|                                                          |

Whether or not the logic works will depend on how you locate and aim the sensors.

S1 Index Sensor should look at the narrowest part of the can holder support, at the center of the can support.

S2 and S3 Can Sensors should detect the can across it entire width while in the holder. In other words, they should go ON before S1 goes on and go off after S1 goes off.

 

[bdingus76]

HaHa! Lancie1 I thank you very much. For what ever reason I was convinced I was going to get a false reading for the can not in place. I am well out of practice and I looked forward getting back in the routine of doing more projects. It's good to know this forum is here for the simple task(like mine is) and the more advance ones i have read on here. Lots of knowledge on these boards. Again I can not thank you enough.

 

[Lancie1]

This is indeed a useful site. I learn new things here all the time. (Some of them are what I once knew but have forgotten).

 

[jaywillnot]

Lancie,
I just have to say, I truly wish I'd had you as my PLC instructor when I was in college. I took three long semesters of PLC 1 thru PLC 3....starting from SLC500 to the 5000.
I still believe till this day that my biggest issue with not learning what was completely essential was the fact that my instructor was an extremely brilliant man, who had worked in the field for over 30 years as an engineer who wore many hats. This man had his Masters in Electrical Engineering from MIT, his Masters in Mechanical Engineering from GA Tech, and his Bachelors in Bio-medical Engineering from Michigan.
With all of these miraculous attributes he employed, he had no earthly idea how to convey his thought patterns to his vocal or kinetic extremities. So needless to say, we were always 2 3/4 steps behind.
I really appreciate the way you and Ron put things into perspective and I thank you for that...and I'm sure I am not the only one who feels that way. :site:

 

[Lancie1]

Thanks, Jay. I learn as much here as I teach, so it is a win-win for me.