Measurement of tension in moving copper feed

[Ananym]

I'd like to implement some closed loop control for a machine winding a feed of copper pipe around some changing geometry. The tension in the copper pipe feed needs to be controlled to allow for suitably tight bends without damaging either the feed or the apparatus, but at the moment there is no hardware to measure it.

The problem is similar to something you might find in paper milling machinery - but in this case, dancers or strain transducer rollers are unhelpful since the substantial bend in the feed would cause unacceptable work hardening.

Are there any other obvious solutions for directly or indirectly measuring the tension in a moving feed without inducing significant hardening?

One speculative idea - change the winding motor mounting to allow for freedom of rotation around the motor shaft, then constrain the motor itself (a hefty ac induction thing) in place with a strain transducer. Since the load on the motor is related to the tension in the feed, with some substantial work we could potentially use this to indirectly find feed tension? Extreme accuracy isn't necessary, the aim is only to keep the tension reasonably constant within safe boundaries.

 

[IRstuff]

Maybe there's something ultrasonic that could be tried; I'd imagine that the tension would change the natural frequency of the pipe.

TTFN
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[Ananym]

Interesting idea!
I couldn't find any off the shelf ultrasonic solutions for this sort of thing, but I was reminded of an old school experiment involving wave propagation speed's relation to tension in strings. Obviously a length of copper pipe is fairly far removed from a guitar string, but might this still apply?

We could use a surface transducer to play a tone or pulse into the copper feed at one end, and and some fixed distance later use a piezoelectric transducer to read the vibration some distance later. By monitoring the change in phase difference or timing we could relate this to the change in feed tension? We probably wouldn't get an accurate absolute reading from it but relative tension changes would still be a step up.

Of course I'm not sure how feasible this really is. There would be other ambient vibrations of currently unknown magnitude that we would have to handle. I'm not really sufficiently well versed electronically to know how to implement something so time sensitive myself. This thread has morphed into something more appropriate for the acoustic/vibration section.

 

[Strong]

Did you Google: wire tension measurement device or wire dynamic tension measurement device?
Walt

 

[MintJulep]

Since the load on the motor is related to the tension in the feed,

Better stated, motor torque is related to tension by the radius of the drive roller.

Torque of an AC motor is knowable in a variety of ways.

Since you'll apparently need a VVVF motor drive, shop for one that allows you to control torque.

http://www.eng-tips.com/viewthread.cfm?qid=94601