Allowing the web to reverse in s slitting section creates little slivers which show at the edges of a roll.
Any drive which lifts product or machinery should not fall in the wrong direction when moved. This could be a hazard to personnel.
Generally incorrect direction occurs on stopping or starting. When starting, torque in the correct direction must be achieved before releasing the brake. It may take 1/3 of a second after energizing the drive before the motor develops torque. Torque and brake timing are critical.
When stopping, the drive usually generates to a very slow speed. Then the motor coasts to a stop. The brake is applied just as the motor comes to a complete stop, but before tension can pull it backward.
Most new drives have brake control incorporated. Parameters associated with brake timing must be entered in the drive to achieve smooth starts and stops in the correct direction.