Prediction of Fiber Orientation in Norway Spruce Logs Using an X-Ray Log Scanner: A Preliminary Study

Abstract

Previous studies have shown that a CT scanner can be used to accurately measure spiral grain in logs. However, the application of such a CT scanning system is of limited use in an industrial application because of the cost and processing time associated with CT scanning. The aim of this study was a preliminary assessment of predicting fiber orientation, an indication of spiral grain, in centerboards from Norway spruce (Picea abies) saw logs using an X-ray log scanner. The scanner is a highspeed commercial log-scanning device used to grade and sort logs based on internal quality characteristics.

In this study, nineteen logs were first scanned with a CT scanner. Afterwards, the CT images were used to simulate X-ray log scanner images, with which measurements of different variables such as diameter, taper, percentage of heartwood, density, and density variations could be calculated. Depending on the log diameter, two to four centerboards were then sawn from each log, and the fiber orientations of the boards were measured for observed spiral grain for each log. A statistical model for predicting fiber orientation was then developed using partial least squares (PLS) regression. The PLS-model was developed to predict the fiber orientation of a log at a distance of 50 mm from the pith based on different variables that are measurable with the industrial X-ray log scanner. The resulting PLS-model was shown to produce an R² = 0.45 for the training set and R² = 0.55 for the test set. The statistically significant variables used to predict spiral grain were green heartwood density, knot volume, and a measure of the unsymmetrical distribution of knot volume. Significant correlation of these variables warrants further research and development with the X-ray log scanner to nondestructively sort out logs with excessive spiral grain.