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[DPRG] Encoders and PLCs

Subject: [DPRG] Encoders and PLCs
From: D. Daniel McGlothin ddm at mcglothin.info
Date: Thu Aug 20 20:09:32 CDT 2009

I'd be happy to share advice with you on this topic, as this stuff is my 
'day job'.

What Allen Bradley PLC series/model do you have, as well as mfg/model of 
the other parts of the system already committed?  Many encoders have an 
index pulse in addition to the pulse stream, but an absolute encoder 
could serve just as well for positioning.  Also you would need to state 
a quantified definition of how "very accurate" you need as well how 
"high" is the inertia involved.  A sense of budget size would help 
position the solution, as typically the more 'very accurate' the 
solution, the more $.


John Dolecek wrote:
> Hey all.  I need to be able to interface some existing Allen Bradley 
> PLCs with encoders.  The PLC is way to slow to do it on it's own, so 
> it'll need an expansion board of some sort.  I've done some reading 
> through ABs site but it's hard to find what you need when you don't 
> know what it's called. ;) I hope to use an absolute encoder as this 
> machine stops and starts each revolution.  It would be nice to not 
> have to add an additional prox to indicate home position.  All in all, 
> I need a solution for closed-loop control of the drive system using 
> the PLC to control and verify the speed and the park position (as well 
> as a couple other key positions).  The main thing we're trying to get 
> out of this is very accurate control over the deceleration of a high 
> inertia rotating part.  The system must be able to monitor changes in 
> speed as the part contacts the material (or doesn't contact anything) 
> it's working on and adjust the application point of the constant 
> torque braking so as to keep a consistent stopping position.
> Hope that all makes sense.  This would be so easy if I could just use 
> an arduino!
> Thanks,
> John

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