Rewinder tension loop with PID/speed control on motor

[dojenman]

Any advice on where loop gains and integral control should be set using a 180:1 motorized rewinder controlled by a tension load cell? We are getting oscillations at rest, and then when we feed material into the tension zone, the load cell sees a drastic drop in tension, so it ramps up the AC motor drive very quickly, resulting in faulting out the servo pinch motor which is feeding material into the zone.

 

[Skogsgurra]

I wouldn't do it that way. Always problems like those you describe. Use current control instead.

Gunnar Englund

http://www.gke.org

 

[Compositepro]

Current control of tension through a 180:1 gearbox doesn't work well either. A lot of engineers think that dancer arms are old and obsolete technology. But they often provide the most consistent tension control. Theoretically all the different methods work but when it comes down to practice torque control though a gearbox and load cells controlling speed often have problems with mechanical imperfections causing tension pulsations. A well designed dancer arm can compensate for a lot more mechanical problems. Anyway, a load cell is really just a dancer arm with about 0.005" of movement.

 

[Skogsgurra]

Yes, right. Didn't notice that 180:1 ratio. A dancer is absolutely the best way to go in this case. The control structure is the same as you have now. So there is not much you need to change. The great benefit with a dancer is that a small speed change doesn't immediately produce a big change in web tension. The dancer acts as a buffer and the f0 of the tension loop goes from an impossible tens of Hz to a comfortable fractions of a Hz. You will notice that you need some D action in the feed-back to stabilize the system.

Gunnar Englund

http://www.gke.org

 

[dojenman]

Hey thanks a lot for your down to earth advice on using a dancer here instead of the load cell. Very valuable to get opinions outside this office.