Tension Control

W

Thread Starter

Web Control Novice

I am new to web handling so perhaps someone can help. I am feeding labels on a web. I want to control tension on the web at the peel plate. The web has a servo driven nip roll before and after the peel plate. How do I adjust tension? I see two possibilities; have the front servo drive velocity faster than the back drive or have the front servo drive index distance be slightly greater than the back servo drive. Will either of these schemes work? Thanks!
 
I think both of the schemes you propose have problems. I would run the feed servo in position mode and the tention roller run in constant torque mode (just constant current through the motor).
 
The web tension control maybe obtained by special tension controller (Montalvo, Warner) or motion controller (Galil, Baldor). The dancer arm, load cell or ultrasonic sensor based structures are widely used. But motor torque (current) control only would be applied for low performance tension control.
 
W

web control novice

Thank you for your response. Just a point of clarification. Does it matter which servo is the feed? It is better that the front servo pulls the web in position control, back servo holds back the web and runs at constant torque. Or Back servo feeds label and the front servo winds up the slack at constant torque? Thank you again for your help.
 
W

William Sturm

If you are indexing (start/stop), then programming a
slightly longer distance will work well. Calculate
the percentage and make it a programmable parameter.
It is called "draw". If you are feeding continuously,
such as printing, then the speed percentage will work
well.
 
Use the pulling motor in position or velocity mode with full torque authority. Limit the torque on the holdback motor to achieve the desired tension. As long as you are running at steady state speed - you will have reasonably good tension control.
 
M
If the pick up roll diameter change as web is picked up, and linear web speed is constant, then constant web tension = constant picku up motor shaft power (think on the web itsel - it travels linearly until it is being picked up, so P=F*V - P=Power, F=Force, V=Speed).

If you can subtract (variable) motor losses from motor input power, then you get shft power.

Meir
 
Top