# Complex procedures with an Allen-Bradley SLC-5



## Mike in Canada (Jun 27, 2010)

I've never programmed Allen-Bradley PLCs before. I know most of the stuff is going to be similar, but what I need to know in a hurry is whether using the sequencer would be worth it in this application.
Best description: imagine you're controlling a crane that has a lawnmower hanging from it and you're mowing your lawn by controlling the crane (pretty cool thought, that, actually.... :thumbsup and so I need to have the crane swing back and forth and at the end of each row move forward a bit so that it cuts a new row each time. Now after the first pass I have to change from back and forth to front and back, so essentially like the quick chicken-scratch that I have added to this message. The patterns alternate dozens of times. I know I can do this with a few boolean variables, but I want to know if the sequencer is the more elegant - more proper - choice.


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## MDShunk (Jan 7, 2007)

If the pattern is to change from time to time... Sure, use a sequencer. If not, maybe just a shift register. Million ways to do anything.


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## Mike in Canada (Jun 27, 2010)

MDShunk said:


> If the pattern is to change from time to time... Sure, use a sequencer. If not, maybe just a shift register. Million ways to do anything.


 The patterns stay the same, but they alternate, and I can't be certain where I'm going to end up when a pattern finishes. I might be at the front right this time, and at the back right the next time that pattern finishes.


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## John Valdes (May 17, 2007)

Sounds to me a servo control and motor with resolver or encoder feedback would be required as you need three axis control. Forward, Over/Down/Up, Reverse.
The drives today are pretty smart especially if you add a feedback device. I am not certain either way.
I have fallen way behind on technology and probably should just listen and learn, instead of trying to give outdated advice.


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## industrial951 (Jan 29, 2011)

i like using the sequencer block, to me it just looks nice in a program. well it seems to me using a seq block would be fine for this application since your just stepping the lawn mower one increment at a time.


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## Jlarson (Jun 28, 2009)

I'd probably use a sequencer.


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## BBQ (Nov 16, 2010)

Jlarson said:


> I'd probably use a sequencer.


The title says it is complex so why did you even click on it? :laughing:


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## Jlarson (Jun 28, 2009)

BBQ said:


> The title says it is complex so why did you even click on it? :laughing:


Yeah I know complex is kinda beneath my level of genius but I was bored. :lol:


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## BBQ (Nov 16, 2010)

I believe that the correct term is 'Super Genius'


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## Mike in Canada (Jun 27, 2010)

John Valdes said:


> Sounds to me a servo control and motor with resolver or encoder feedback would be required as you need three axis control. Forward, Over/Down/Up, Reverse.
> The drives today are pretty smart especially if you add a feedback device. I am not certain either way.
> I have fallen way behind on technology and probably should just listen and learn, instead of trying to give outdated advice.


 This a big machine, and precision is neither necessary nor particularly feasible. Plus or minus 6" is pretty darned good. Up and down is not particularly important - it's dealt with, but it's not a big deal. The two axis have counters tied to proxes and I know how many counts I have from zero to maximum, so I can do the math to figure out how far to step each time I hit the end of a row.


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## Mike in Canada (Jun 27, 2010)

Alright, it sounds like the sequencer is the sexier way to do it, so I'll investigate that. Does anyone have a favourite book that covers it, by chance?


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## HARRY304E (Sep 15, 2010)

Mike in Canada said:


> Alright, it sounds like the sequencer is the sexier way to do it, so I'll investigate that. Does anyone have a favourite book that covers it, by chance?


Mike check out this link it may help you out.

http://www.google.com/#hl=en&xhr=t&...gc.r_pw.&fp=8a58e93555963d21&biw=1253&bih=510

I'm not up to speed on this stuff myself good thread..:thumbup:


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## JeffKiper (Jul 23, 2011)

I don't use the SQO in AB world very often. There is to much that can get out of sequence. Which PLC 5 are you using there are a few differences in some If the really old firmware compared to today's versions. 
I prefer to roll my own sequencer. If someone new is coming behind you troubleshooting this system they will have a hard time with the relationship between the source, destination, step Control word. I have been bitten by this a few times trying to make my logic small and compact.
10 minutes in Microsoft excel and you can have this program 95% done.


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## Mike in Canada (Jun 27, 2010)

JeffKiper said:


> 10 minutes in Microsoft excel and you can have this program 95% done.


 You lost me, here. What are you doing in excel?


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## JeffKiper (Jul 23, 2011)

Sorry I run to fast sometimes. 
I use excel to help me write a lot of my repetitive code thy only increments in a few places.
I found that if your coding is consistent in style the guy following you can pick it up and run fast. Sometimes that guy is you 5 years later and you ask yourself if that guy was off his medication when he wrote this.


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