kamenges
Member
Originally posted by DickDV:
Using two different speeds to make tension is a ticket to trouble.
I hope not. We do this very regularly on paper and plastics web lines. Theoretically you can use this method with anything that can stretch. Practically you can only do this with materials whose percentage of elongation before ultimate failure is greater than the drive percent speed regulation. With modern closed loop FOC AC drives that is in the 0.001% class. Granted, you probably can't do this with steel. But draw control on carpet should be pretty easy. Carpet stretches like crazy, which is why installers can make it look so good.
Many people believe that any speed differential between two driven rolls will ultimately result in breaking a web between them. The thing many people forget is that the web coming into the zone hasn't been stretched yet. So each little sliver of web that comes into the zone between the two rolls will stretch and provide a percentage of it's length as additional material.
Now, in Combo's test case, where he is coupling two motor shafts together, you are correct. Since no new, unstretched material is entering the equation, sooner or later he will twist his coupling apart or, much more likely, the drives will go into torque limit and just operate there. But that is a completely different thing than running a web between two rolls.
Keith