Rapid Detection of Knot Defects on Wood Surface by Near Infrared Spectroscopy Coupled with Partial Least Squares Discriminant Analysis

Abstract

Natural defects, especially knots, on the surface of veneers have a great influence on the sorting and degradation of veneers. To realize rapid and accurate knot detection, a study on the possibility of detecting knots was carried out. Samples of poplar, eucalypt, and masson pine were used. The experiments mainly focused on the ability of using the models built with samples from one type of knot and normal wood to predict samples from a different type of knot and normal wood within the same wood species; and when only the samples from middle-sized knots and normal wood were used, whether or not the model based on one species could predict the samples from another species. The results showed that using the model built with small knots and normal wood to predict the larger knots and normal wood was not satisfactory, but the model based on large knots and normal wood can predict the samples from smaller knots and normal wood under a certain condition. When only the middle-sized knots and normal wood from the three species were used, the model built with eucalypt samples could predict the samples from poplar, and vice versa; however, the model built with masson pine samples could not predict the other two sample species, and vice versa.

Detection of Knot Defects on Coniferous Wood Surface Using Near Infrared Spectroscopy and Chemometrics

“…The knot samples were found to have higher absorption amplitude than normal samples for each wood species. These changes in spectra were consistent with previous experiments by and Yang et al (2015Yang et al ( , 2016. This may be due to the difference in the orientation of the microfibrils within fibers between knots and normal wood, as the microfibrils of a knot's cells was substantially parallel to the NIR light incidence angle Yang et al 2015).…”

“…These methods mentioned above have produced good results. However, there are still some limitations (Szymani and McDonald, 1981;Nagai et al 2009;Yang et al 2016).…”

“…The results showed that NIRS coupled with SIMCA could identify knots. Yang et al (2012Yang et al ( , 2015 assessed the potential of visible-NIR spectroscopy for identifying knots in Pinus massoniana veneer and eucalypt veneer, with good classification results. Yang et al (2016) also investigated the feasibility of NIRS coupled with partial least squares discriminant analysis (PLS-DA) to discriminate knots on the surface of poplar, eucalypt (hardwood), and masson pine (softwood) veneers.…”

“…Yang et al (2012Yang et al ( , 2015 assessed the potential of visible-NIR spectroscopy for identifying knots in Pinus massoniana veneer and eucalypt veneer, with good classification results. Yang et al (2016) also investigated the feasibility of NIRS coupled with partial least squares discriminant analysis (PLS-DA) to discriminate knots on the surface of poplar, eucalypt (hardwood), and masson pine (softwood) veneers. The model built with eucalypt samples could predict the samples from poplar, and vice versa; nevertheless, the model built with masson pine samples could not predict the other two samples' species, and vice versa.…”

Potential of Near-infrared Spectroscopy to Detect Defects on the Surface of Solid Wood Boards

“…In addition, NIR spectroscopy has also been used to detect defects on the surface of veneers according to size (Yang et al 2016). All of these implementations show that NIR spectroscopy is a feasible tool to measure the properties of wood.…”