Predicting the Strength of Sawn Products by X-ray Scanning of Logs: A Preliminary Study

The aim of the study was to investigate the possibility of predicting the strength of centerboards from Norway spruce (Picea abies (L.) Karst.) saw logs, based on simulated X-ray LogScanner measurements. The study was based on eight logs. The logs were scanned using computed tomography (CT), four centerboards were sawn from each log, and the bending stiffness (MOE) and strength (MOR) of the boards were measured. The CT-images were used for simulations of the industrial X-ray LogScanner, resulting in simulated measurements of knot volume and the green density of heart-wood. Finally, multivariate models were calibrated using Partial Least Squares (PLS) regression. These models predict bending strength and stiffness based on the variables measured by the simulated X-ray LogScanner. Both bending strength and modulus of elasticity were defined as the mean value of the four boards from each log.The results were very promising, with strong models for prediction of both MOR (R2 = 0.73) and MOE (R2 = 0.94) mean values for all four boards from each log. The results indicate that the X-ray LogScanner can be used for the sorting of saw logs according to strength and stiffness. The next step should be to repeat the study on a larger sample of material

Moisture Content Measurement in Scots Pine by Microwave and X-Rays

There is demand in the Swedish sawmill industry to improve the accuracy of moisture content measurements, both to obtain a better tool to run production and to ensure that the products meet customer expectations. In this study, 240 well-conditioned pieces of Scots pine (Pinus sylvestris), sorted into five different groups by visual inspection, were measured using microwaves and X-rays. Models to predict moisture content of wood were made by measurements of an additional 45 pieces of wood. Using only measured quantities from the microwave system, ie attenuation and phase shift, the root mean square error (RMSE) of the estimated moisture content was 1.00%. By adding total density from the X-ray measurements, RMSE of the estimated moisture content was lowered to 0.89%. Mean errors of the different wood groups varied from -0.65 to 0.18%

X-ray measurement of properties of saw logs

A nondestructive method of measuring knot parameters for research purposes has been compared to alternative, destructive methods. The method is based on automatic analysis of CT-images. The image analysis algorithms were adjusted to and evaluated on Norway spruce. The possibilities of measuring resin pockets in CT-images have been studied and stereological methods have been applied on volume estimation of resin pockets in saw logs. For research purposes the study showed that compared to destructive methods, both accuracy and speed of the CT-method were competitive. It was also shown that resin pockets can be detected and measured in CT-images of Norway spruce. Data from the CT-scanned logs was used to simulate an industrial X-ray LogScanner. The X-ray LogScanner was based on two X-ray sources and designed for scanning at 3 m/s. The possibility of using this X-ray LogScanner to make nondestructive measurements of properties of saw logs has been investigated. The study showed that the X-ray LogScanner measures minimum shadow diameter under bark before debarking with an accuracy comparable to a 3D-scanner and that the sawing position could be controlled based on X-ray LogScanner measurements of the best half of the logs. The X-ray LogScanner could also be used to measure percentage of heartwood and green heartwood density. Based on the X-ray LogScanner measurements it was possible to calibrate PLS-models for prediction of the bending stiffness of the centerboards.Godkänd; 1999; 20061117 (haneit

Measuring knots and resin pockets in CT-images of Norway spruce

Godkänd; 1997; 20070418 (ysko

Improved log sorting combining X-ray and 3D scanning : a preliminary study

Quality sorting of sawlogs is becoming more and more common. This is the result of increasing production of customer specific products in combination with high raw material prices. Today, log quality sorting is being based on either 3D or X-ray scanning techniques. Previous research has shown that sorting accuracy is improved when using multivariate models to combine variables from both 3D and X-ray scanners. There is however a potential of further improving the sorting if 3D and X-ray data are combined at an earlier stage; from the measured 3D shape a better estimate of the X-ray path lengths through the log may be found, thus enabling the calculation of a log density profile from the measured X-ray attenuation. The development and evaluation of such a technique is the topic of current research at SP Trätek and Luleå University of Technology in Skellefteå. Preliminary results show that the method is good at calculating large scale properties such as heartwood content and heartwood and sapwood densities. When looking for smaller geometric objects, e. g., knot whorls, extra care must be taken so that observational errors from the 3D scanner do not compromise the X-ray data. Software simulating industrial X-ray scanner data from CT-scanned logs has also been developed. A very good agreement was found between simulated data and actual data from an industrial installation. This underlines that such a simulation tool is very valuable when developing algorithms for industrial X-ray scanners.Godkänd; 2007; 20081203 (ysko

Measuring knots and resin pockets in CT-images of Norway spruce

Godkänd; 1997; 20070418 (ysko

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

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

Predicting the Strength of Norway Spruce by Microwave Scanning: A Comparison with Other Scanning Techniques

In this study, 90 boards of Norway spruce (Picea abies (L.) Karst.) sized 48 x 148 mm in cross-section, have been examined using different scanning and measurement techniques. All of the boards originated from a sawmill located in southern Finland. Planar X-ray scanning, microwave scanning, and grain-angle measurement have been performed. In addition, strength and elastic properties were assessed for each piece by four point bending. The purpose of the study was to relate the potential of microwave scanning compared to other, industrially available techniques and to explain the physiological background of the microwave responses. The results show that the microwave signal, after transmission through wood, contains information about the bending strength and the modulus of elasticity. The correlation to density is a key factor. Annual ring width was also found to be correlated both to microwave measurements and strength properties