Dynamic Optical Displacement Calibration Protocols across Folding Boxboard Converting Lines
Dynamic blue-laser displacement calibration eliminates light-penetration drift, securing exact FBB crease metrics and stopping false sheet rejection.
Zero-Point Float
Sensor Drift
Uncontrolled shift in the reference baseline of an optical or mechanical thickness sensor on a paper machine scanner causes inaccurate measurement profiles over time. This instability, commonly called zero-point float, arises from thermal expansion or mechanical wear within the sensing head during continuous operation. The issue compromises the accuracy of the closed-loop control system, which can lead to off-specification paperboard production.
Correction Protocol
To counteract this drift, modern scanners utilize an off-sheet calibration routine where the sensor head moves beyond the deckle edge to scan a known standard or measure empty space. This routine allows the software to reset the measurement baseline to a true zero before the head begins its next traverse across the moving web. If this calibration is not performed regularly, the system may register a false trend in board caliper, resulting in unnecessary or incorrect adjustments to the calender rolls.
Ensuring a stable reference point is critical for maintaining the tight thickness tolerances required by high-speed converting lines.
Environmental Influence
Rapid fluctuations in the ambient temperature and humidity around the paper machine can exacerbate the drift of the sensors. Shielding the sensor housing and using active cooling systems helps minimize these environmental disturbances.