An X-ray LogScanner : a tool for control of the sawmill process

Abstract

Wood is a biological material with great variability. Every piece of wood is a unique individual. The great challenge in the wood products manufacturing process has always been to select pieces of wood with properties that fulfil the product requirements. This will be even more important in the future as customers increasingly demand sawn products with special properties regarding dimension, moisture content, wrap and last, but not least, biological or aesthetic features. To be albe to fulfil these requirements, the right logs have to be selected for a certain product before the sawing process. This means that an accurate tool that can measure external and internal features is needed. The main objective of this work was to develop and evaluate algorithms for nondestructive measurement of external and internal properties in sawlogs with the aid of a bidirectional X-ray LogScanner. The LogScanner outlines and the LogScanner signals were simulated using CT (computer tomography) images from the Swedish Pine (Pinus sylvestris) Stem Bank and the European Spruce (Picea abies) Stem Bank. With the aid of data from the stem bank databases, the simulated scanner signals, the saw simulation program virtual SawMill (vSM), and statistical analysis programs, new control algorithms were developed and evaluated. The studies show that an X-ray LogScanner with two X-ray sources has a great potential to become a powerful tool for control of the sawmill process. The most important conclusions of work presented in this thesis were that: - X-ray based technology is a suitable technique for nondestructive measurement of internal features in green sawlogs. - CT scanning is a powerful research tool for measurement and visualisation of different log properties. - Parameterisation is an efficient method for reduction of the amount of data from a CT scanner. - It is very efficient to use data from a “Stem Bank data-base” based on CT scanning for simulation, analysis and development of the sawing process and different measurement technologies. - An X-ray LogScanner with two X-ray sources can measure log features such as diameter under bark, species, log type, knot structure, rotational position of knots, density, heartwood content, annual ring width and predict strength and grade of sawn boards.Godkänd; 1999; 20061117 (haneit