Measurement of fiber orientation by laser light scattering on dry and rough sawn green hardwoods

Abstract

Scanner measurements allow knot detection and machine strength grading on sawn timber, which answers the construction and sawmilling industry needs at high production rates. In particular, laser scanners measure fiber orientation by means of the so-called tracheid effect on wood surface where elliptically scattered laser light can be observed. Many studies showed that a red laser scanner is very effective on softwood species like spruce but ineffective on many hardwood species like oak. However, the LaBoMaP has recently developed a fiber orientation scanner, utilizing another kind of laser, effective on hardwood species, especially oak. Other studies showed that measurement quality is better on sanded and planed wood than on rough sawn timber. Besides, the influence of moisture content on tracheid effect is also known. In practice, light ellipses are biggest on fresh wood than on dry wood. In the present work, a method is proposed to measure the intensity of tracheid effect on fresh sawn hardwoods, according to the species, and the error of the fiber orientation measurement is also assessed. To achieve this, clean fresh wood test pieces were first scanned at 0° orientation and ellipse geometrical parameters were compared to that obtained on an isotropic surface. In a second time, test pieces were scanned at different orientations from 0° to 90°. Measurement error was defined as the difference of scanned fiber angle mean on each iteration and test piece orientation between these same iterations. Comparisons of results between species and moisture content will be presented at the conference.