Many events happen during a turret winder index that make it very difficult to control tension. An old, but practical, technique for surviving an index is to put the outgoing spindle into Torque Hold mode.
Torque Hold is a drive function that memorizes the torque at a particular instant, and then runs the motor at that constant torque value. For the outgoing spindle drive on a turret winder, the torque is measured and memorized just after tension boost is applied, but before the lay-on roller or the turret are permitted to move.
Theoretically, the outgoing spindle will maintain or hold tension during the index if its torque is held at the last known good value. As the web path changes because the lay-on roller is moving or the turret is rotating, the speed of the spindle will vary appropriately, but still maintain tension.
Torque Hold mode is ended with the knife cut. After the knife cut, the outgoing spindle is no longer in control of the web and should be stopped. Torque Hold mode should also be ended if a web break occurs. If the spindle drive remains in torque hold mode after a web break, the spindle will accelerate without limit creating a hazardous Overspeed condition with a large roll.
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