Geometric Focus
Optical alignment geometry requires the lens plane, image sensor plane and object plane to intersect along a single line to maintain sharp focus across oblique surfaces. Non-contact laser sensors monitoring paper web thickness employ the scheimpflug condition to maintain accurate height measurements across tilted or fluttering webs. Tilting the image sensor relative to the camera lens extends the depth of field along the inclined laser line projected onto the paper surface.
Universal focus along the target line prevents measurement distortion during high-speed profile scanning.
Triangulation Geometry
Triangulation sensors measure paperboard profile variations by projecting a laser line onto the moving web at an angled trajectory. When the web surface moves vertically due to roll vibration or sheet flutter, traditional camera setups lose sharp focus, causing beam distortion on the sensor array. Aligning optical components according to the scheimpflug condition ensures that every point along the laser line remains sharply focused on the detector matrix regardless of web elevation changes.
Accurate focus allows sensor algorithms to calculate exact surface topography and thickness metrics during high-speed converting.
Flutter Boundary
Extreme web flutter exceeding sensor tilt range causes optical clipping. Out-of-range displacement distorts thickness measurements beyond sensor calibration limits.
