Feasibility of automatic detection of knots in maritime pine timber by acousto-ultrasonic scanning

In order to assess the lengthwise variation of mechanical properties of maritime pine (Pinus pinaster Ait.) a study on the possibility of automatically detecting knots by ultrasonic readings across the grain was carried out. A through-transmission acousto-ultrasonic (AU) setup was implemented allowing acquisition of AU profiles along the central mid-third of each specimen. An algorithm was proposed and successfully implemented for enhancing variations on the AU profiles due to knot presence. Discriminant analysis was applied to the AU profiles. The results show the possibility of automatically differentiating clear wood zones from zones with a knot area ratio value above 20% or 30%, with a success rate of 75% to 83% depending on the dimension of the specimens tested.This research project was supported by the Foundation for Science and Technology (FCT) under contract Nos. PBIC/C/AGR/2296/95 and POCTI/33967/AGR/2000