[Help] Micrologix 1100 Sequencer

Anyone want to give me some advice? I'm an electronic tech. by trade but have limited experience with PLC's. I know that doesn't make sense but we usually make our own controls because my VP would rather have us figure it out for the "fun" of learning. Also PC based things work better in our applications.

Anyway I need to develop controls for a machine that will automatically fold a square cardboard box around a said product. My mechanical co-hort has a lot of the frame, pneumatics, and limit switches mounted. I picked an AB MicroLogix 1100 for my PLC because of the expandable I/O, about 15 valves and 10 switches. The machine is completely repetitive so I'd like to us some sort of sequencer instead of the normal way PLC's scan. There would just be one start button and out pops a box. There isn't any variables at all either. In RSLogix I see there is a function for it but have no idea how to use it. My question is really how would someone normally write this? Just using normal contacts, latches and opening the rung before each step to make it act like a sequencer or should I read my AB instruction set manual more about this? Also is the sequencer function even act like a drum sequencer?

Thanks for your time

In my opinion:

A-B sequencers are hard to work with and when done are cumbersome to alter and the logic behind it all is obscure.

If I were doing the project I'd use sequential logic of this type:

SEQ_VAL = an integer which changes as the logic steps through the cycle.

STEP_VAL = a constant which identifies each distinct step of the operation.

So, at step one, SEQ_VAL = 1 and STEP_VAL = 1. A comparison done (EQU) on these two values enables whatever outputs you need for this step of the machine. Also enabled is logic which will sense when the conditions which satisfy this step have been met. When the conditions are met, a MOV instruction loads the next value, here a '2', into SEQ_VAL. Graphically;

    SEQ_VAL = 1         Step '1' outputs

-------|=|---+----------------( )----

             |

             |

             |   Conditions

             |      Met?              MOV

             +------| |--------| 2-> SEQ_VAL|--

In step two different outputs turn on and different inputs are sensed. When step two is complete a '3' is loaded to SEQ_VAL and so on, and so on.

Of course, there may be more than one output for each step and probably multiple conditions for each step.

If the 1100 does Sequential Function Charts, that could be a possiblity too. Actually, the logic shown is conceptually very much like an SFC.

Doug-P's example is very good. One thing to look out for:

If a given output would be on for more than one step then it may be best to define all the steps this way but leave the turning on of the outputs to another section. In that section list the steps in parallel which turn on each output, with any safety or overall permissive contacts of course. All this is to avoid the dreaded double coil feature of ladder logic.

Dougs way is good. I usually dedicate an integer to each output, then OTE a unique bit of the integer for whenever I want the output on.
Then in a separate section I have a NEQ to zero compare of the integer to energise the output. Saves having a lot of parrallel rungs for the output.
Regards Alan Case