Monitoring motor current

Welcome to page 4...

Tim said:
Ok,WARNING A LOT OF RAMBLING ABOUT TO TAKE PLACE
Rambling is good. You explained the process very well!... :nodi:

You seem to have covered all the bases you can cover, short of detecting the part(s) DURING transfer, which I agree would be difficult. Monitoring motor current sounds like the best (or at least simplest and cheapest) solution, but you already knew that. Thanks to your "rambling", now I know that as well... :cool:

BUT... We build a LOT of "indexed motion" rotary assembly equipment (yours IS a rotary machine, right?), and have always relied on a mechanical clutch to prevent damage. When properly set, I would not feel too uneasy about sticking my finger in the works. Granted, I probably wouldn't do it ON PURPOSE! I'm just saying that a correctly sized (and properly adjusted) overload clutch does just that... Disengage when an overload occurs.

Although, on our rotary machines, we use barrel-cam style indexers (Camco, Stelron, etc.), so the cam provides the accel/decel ramps, NOT the motor drive. IOW, the motor continues to run at a constant speed even when the indexer is stopped (in dwell). Actually, I DO stop the motor during dwell, but the motor's accel and decel occur during dwell, so the load doesn't vary much. I'm guessing that yours is direct drive, so you wind up with very aggressive (IOW, steep) ramps? This would probably disengage a mechanical clutch during accel/decel because of the high inertia loads you achieve.

That said, I'll now shut up about mechanical clutches... ;)

beerchug

-Eric
 
Why apologize?

Eric, a mechanical clutch is a valid answer for some applications as long as it satifies the kinetic energy/energy dissipation issue. Also,a clutch cannot provide breaking forces like a good motion controller or drive can.

I am surprised that no one has asked about the kinetic energy issue yet, but this is not a physics forum.
 
You're right Peter, but my apology was directed more towards the fact that I was dragging the topic WAAAY off the P-L-C subject. Isn't that what we're supposed to be discussing here?... :rolleyes:

I only keep pestering about mechanical clutches because I feel that one should be in place no matter what additional OTHER methods are used. Unless Tim has some really steep accel/decel ramps, I don't see why a clutch wouldn't be included in this application. And if they are that steep, do they really NEED to be? In my opinion, a clutch is mandatory. Anything else is just "icing on the cake".

Kinetic energy? You bet! Nothing will stop a big mass traveling at high speed better than a fixed object!... lolis

But, if this is the case, we are wasting our time. If you can't anticipate the impending damage, you're screwed. IOW, if there's a distinctive "BANG" noise when a jam occurs, then all this stuff we're sensing is happening A-F-T-E-R that BANG... utoh

Wait a minute!... My "spring-centered device" (post #36) COULD anticipate that impending BANG!. The springs could allow enough "non-damaging" movement to allow deceleration to a stop... :nodi:

beerchug

-Eric
 
Tim, thanks for your more detailed description of your transfer system. Do I understand correctly that the inverter-motor is driving the rotary motion of the transfer arm?

If not, what part does the inverter-motor play in this? Or is it part of the hydraulic power pack for the operation of the cylinders?
 
This is a very elementary drawing. Hope it helps.
Eric, I brought a rep. in today thats getting me hooked up with a torque limiter. I am going to use the inverter and the torque limiter. The torque limiter will cover my decel and accel points and the current monitor paramater on the VFD works good enough to not cause any damage. Thanks DickDV, for hammering the issue about using the VFD. You were correct that it will stop the motor very quickly. Now I decided to go ahead with the torque limiter for additional safety and so I didn't have to mess around with the accel and decel timing.

Eric, you were also correct that paramater 156 table, which is no where near the current setting page in the manual, will bypass my accel and decel points. IOW, it won't fault out the system at these points. Now this is why I want to also get the torque limiters to cover these points,"just in case something gets jammed at the start or the end of the transfer movement". This hasn't happened yet, but why wait. I could have went with many other things that many of you have mentioned. Hats off to you all.
Thanks

transfer.jpg
 
I forgot to mention on the drawing that the moving portion is of massive size. It looks small next to the motor, but its not. No scaling done on the drawing.
Again, Thanks
PS. Phil this may be a plc site, but "MAN" look at all the veiws on this post.
Tim
 

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