Laser Line Triangulation Profilometry Principles on Continuous Paperboard Substrates
Inline blue laser triangulation measures paperboard surface topography at high speeds by overcoming fiber light penetration and isolating mechanical flutter.
Spatial Wavelength Cutoff
Boundary Selection
The specific wavelength threshold used to separate high-frequency surface roughness from low-frequency sheet waviness determines the accuracy of profile measurements. Establishing a spatial wavelength cutoff is necessary to isolate the microscopic surface details that affect ink transfer from the larger-scale variations that influence sheet feeding. Variations below this threshold are categorized as roughness, while those above are analyzed as waviness.
This clear division ensures that different mills can compare paperboard surface quality on equal terms without conflicting results.
Filtering Calibration
Selecting the appropriate limit depends on the printing method and the properties of the inks being used. The spatial wavelength cutoff must be adjusted when analyzing board for high-viscosity offset inks compared to low-viscosity flexographic inks. A cutoff that is too long will include sheet waviness in the roughness value, which distorts the printability rating.
This adjustment is performed using standardized filters in the surface profiler software.
Metrology Standard
International metrology standards dictate the specific values for these limits based on the scan length. Using a standardized cutoff, such as zero point eight millimeters, ensures consistency across different testing laboratories. This conformity is essential for resolving disputes between board suppliers and commercial printers regarding surface defects.