Safety question.
Safety question.
(OP)
I'm refurbing a paper roller that pulls paper off a three ton roll of paper and spools it onto 20 pound rolls.
During the small roll setup the operator uses a foot pedal that runs the machine at a very slow speed using the VFD's jog function. Subsequently the machine switches to run mode and spools up to high speed.
I'll be using the analog out of a PLC to control the speed allowing the user to set the ultimate peak speed via the HMI.
I can obviously and simply use the same speed control to jog the system for setup.
The question is this.
Do you think this injects a hazard that wouldn't be there if I stuck with running the jog via the VFD's digital jog function.
During the small roll setup the operator uses a foot pedal that runs the machine at a very slow speed using the VFD's jog function. Subsequently the machine switches to run mode and spools up to high speed.
I'll be using the analog out of a PLC to control the speed allowing the user to set the ultimate peak speed via the HMI.
I can obviously and simply use the same speed control to jog the system for setup.
The question is this.
Do you think this injects a hazard that wouldn't be there if I stuck with running the jog via the VFD's digital jog function.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Safety question.
Brad Waybright
It's all okay as long as it's okay.
RE: Safety question.
TTFN (ta ta for now)
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RE: Safety question.
RE: Safety question.
Coaxing the paper web onto the new cardboard spool is a moderately hand accomplished task, poking and squeezing and guiding and tucking the (approximately 4 foot wide) paper onto the empty cardboard spool. This occurs with the Jog function and the take-up shaft turning about 60rpm driven by the operator's foot pedal. e.g. the operator is in the paper-space which is a shaft in front of him/her. Once the paper is sufficiently started a two-handed set of buttons need to get pushed within 300ms of each other, demonstrating the operator's hands are out of the way. Directly above and slightly beyond this take-up roll is a cable E-Stop spanning the machine. Push or pull on the cable and the machine will brake to a stop. I've also added an E-Stop to the operator's panel to the operator's immediate left where the power switch and the HMI are located.
Hi IR; This is a relatively simple PLC program that will ramp the analog out to the VFD to do the major spool wrap and I'm contemplating the same system ramp only to the slow jog speed too.
Lionel; I'm really just contemplating the issues of, say, noise on the speed signal causing an unexpected speed-up during the jog phase. I suppose using a fixed pot on the front panel (the original speed setting) could have the same issue too, so no real increase in the hazard.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Safety question.
Brad Waybright
It's all okay as long as it's okay.
RE: Safety question.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Safety question.
It's an old drive that will likely have to be replaced soonish (Reliance GP2000) and I was thinking a single analog in would carry over the easiest but thinking about it they all have digital jogs with set jog speeds so any replacement will likely work with little change.
Thanks all!
Keith Cress
kcress - http://www.flaminsystems.com
RE: Safety question.
RE: Safety question.
RE: Safety question.
John, I am not using a pot this time around. I want all mechanical failure stuff minimized. Instead the PLC will be generating the 0-10V via a dedicated analog-out module set by a touch-screen setting. I've decided I'm comfortable with this, after all, because I'll be limiting the actual output by:
1) The HMI has the ability to limit the allowed speed setting during entry.
2) I can limit the output in the PLC with a standard "higher than X? : Set to X".
3) This is going out to a VFD where I will instruct the VFD to limit the output frequency to the maximum safe speed value. This is a fundamental limit that doesn't care what speed value is received.
Keith Cress
kcress - http://www.flaminsystems.com