What fails when the web flutters in front of the lens
When the web flutters in front of the lens and leaves the focal plane, fine defects and fine type fail first. The picture goes soft. The system misses them or reports the soft edge as a defect. Press the web back into the depth of field first. Do not loosen the threshold first.
When the web flutters in front of the lens and leaves the focal plane, fine defects and fine type fail first. The picture goes soft. The system misses them, or it reports the soft edge as a defect. Press the web back into the depth of field first. Do not loosen the threshold first.
Why it is judged this way
The depth of field is only a thin layer. Once the web lifts, the same label is sometimes sharp and sometimes blurred. Those alarms do not stay in one place, and wiping the lens does not help. Steady the idlers, the pressure plate, and the tension first, then see whether a real defect is still there.
What to compare
| What you see | Call it | Do not |
|---|---|---|
| Sometimes sharp, sometimes blurred, and the place is not fixed | The web has left the focal plane | Call it soft printing |
| Blurred the whole way | Check focus and cleaning first | Add sensitivity |
| After it is held steady, the fine type comes back | Production may continue | Leave the tension unchecked |
Check at a job change or a new roll
- Look before and after the lens and see whether the web is flapping.
- Add an idler or a pressure plate so the web at the inspection point stays on the focal plane.
- Use the smallest text to confirm it is sharp again, then resume production.
