I am trying to use an AC servomotor in a winding application that will wind with constant tension.
I read somewhere that the way was constant HP but this makes no sense as current will be very very high at slower speeds.
I have also been trying to use the tension * radius = torque equation but can not get this to work either as test results show varying tension as the role gets bigger and as speed is changed.
I need to know how to calculate my current so that tension remains constant with increase in diameter and speed/rpm.
any insight here would be greatly appreciated
Thanks

I did some tension stuff before, but as it turned out we didn't have to use it.

Your tension eqn makes sense at constant speed and constant r.

If you have varying r, you can estimate r mathematically. I lost the eqn. but it won't help you with the speed variable.

Tension is best measured, if you can.

If not, you can use two electromagnetic infinate control clutches. One thing that needs to be done is that tension controllers change the sign of the current into the supply side, so it's guaranteed to be disengaged. In other words a small negative current is used.

Tension control then becomes much easier.

Choice #1:
1. Directly measure

Choice #2:
Know how much material you have (Spool diameter) or measure the tension directly and vary the current through the clutch.

Choice #3
Try to control it with two servo motors. Probably a lost cause.

The supply has the tension control clutch. The take-up can pull at any rate it wants too.

Sorry.

I don't have a load cell to use and Im sure there are several "other" methods of attempting this, but I only have the system I have, so other methods are not an option right now.
I have the motor coupled to the winding spindle through a belt (no clucthes) so it as if the motor is directly attached to the spindle that is winding the paper.
I can determine diameter, speed, and rpm.
I can tell the drive what current to go.
So what I need is to find an equation to relate current to radius and speed.

I=f(r,s)

OK, find no-load speed vs current.

Now determine speed vs weight on driven spindle. You should be able to find something that will work.

Im not really sure what you mean:

>find no-load speed vs current.

Plot speed/rpm vs current?

>Now determine speed vs weight on driven spindle.

Not sure on this one

>You should be able to find something that will work.

Not sure on this one either.

Are you suggesting a complete derivation of the formula through experimental data?

Quote:

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Originally Posted by EEtryingControl

Im not really sure what you mean:

>find no-load speed vs current.

plot speed/rpm vs current?

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NO LOAD - nothing on the spindle

Quote:

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>Now determine speed vs weight on driven spindle.

not sure on this one

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As you add material to the spindle, the weight increases, thus the amount of current necessary to move that weight increases. Another variable that influences I.

Quote:

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>You should be able to find something that will work.

not sure on this one either.

Are you suggesting a complete derivation of the formula through experimental data?

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Pretty much. One of the simplest tension gages is a spring loaded arm. You measure the displacement of the arm with a simple potentiometer.

When I was trying to control tension, I did not have the luxury of having access to the web.