Optical Metrology
A non-contact optical instrument measures the surface topography and thickness of paperboard substrates with sub-micron resolution. By utilizing a confocal chromatic sensor, the system splits white light into a continuum of focused wavelengths, each representing a specific distance from the sensor head. The wavelength that is in perfect focus on the surface reflects back into a spectrometer to determine the position of the boundary.
This allows for precise measurements of wet coatings or soft paperboard without deforming the surface.
Measurement Physics
The sensor uses a specialized lens system with high chromatic aberration to disperse the incoming light along the optical axis. Each colour or wavelength focuses at a different distance from the sensor, creating a continuous line of focal points. The reflected light passes through a pinhole that blocks all out-of-focus wavelengths, leaving only the focused wavelength to reach the detector.
This spectral analysis yields highly accurate distance data, allowing the system to monitor surface roughness during rapid production.
Practical Advantage
Unlike traditional mechanical calipers, this optical approach avoids crushing the delicate fibres of the paper web. It can measure wet or sticky surface layers without fouling the optical head. This technique is therefore ideal for monitoring barrier coatings or thin polymer films on packaging boards.
