Paperboard Coating Detection Based on Full-Stokes Imaging Polarimetry

• Published in: Sensors (Basel, Switzerland) Vol. 21; no. 1; p. 208
• Main Authors: Brugés Martelo, Javier, Lundgren, Jan, Andersson, Mattias
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.01.2021; MDPI
• Subjects: Algorithms; Cameras; Classification; Coating; extruded plastic coatings; Extrusion; Food packaging industry; Imaging; imaging polarimetry; Inspection; Light; Low density polyethylenes; Manufacturing; Optical properties; Paper board; Pinholes; Polarimetry; Polyethylene; Process controls; Product quality; Quality assessment; Spatial resolution; Statistical methods; stokes parameters; Support vector machines; Vertical polarization; Vision systems; support vector machines; extruded plastic coatings; stokes parameters; imaging polarimetry
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s21010208

The manufacturing of high-quality extruded low-density polyethylene (PE) paperboard intended for the food packaging industry relies on manual, intrusive, and destructive off-line inspection by the process operators to assess the overall quality and functionality of the product. Defects such as cracks, pinholes, and local thickness variations in the coating can occur at any location in the reel, affecting the sealable property of the product. To detect these defects locally, imaging systems must discriminate between the substrate and the coating. We propose an active full-Stokes imaging polarimetry for the classification of the PE-coated paperboard and its substrate (before applying the PE coating) from industrially manufactured samples. The optical system is based on vertically polarized illumination and a novel full-Stokes imaging polarimetry camera system. From the various parameters obtained by polarimetry measurements, we propose implementing feature selection based on the distance correlation statistical method and, subsequently, the implementation of a support vector machine algorithm that uses a nonlinear Gaussian kernel function. Our implementation achieves 99.74% classification accuracy. An imaging polarimetry system with high spatial resolution and pixel-wise metrological characteristics to provide polarization information, capable of material classification, can be used for in-process control of manufacturing coated paperboard.