Efficient utilization of sawlogs using scanning techniques and computer modelling

Sammanfattning: The main question asked of the work described in this thesis was how the sawing of logs into sawn timber can be performed more efficiently with respect to the choice of raw material, volume and value yield in the sawing and in the grading of the sawn timber produced. The development of industrial computed tomography scanning provides information about the external and internal properties of a sawlog at production speed. This opens up new possibilities of controlling the flow of raw material early in the process and of optimizing the breakdown of each sawlog. Another use of industrial computed tomography scanning is for predicting the strength of sawn timber better than is possible with current visual and machine strength grading equipment. A more traditional way of increasing sawmill profitability is by increasing the volume of sawn timber. One way of doing this is by reducing the saw blade thickness which results in less sawdust. With the use of thinner saw blades however there is a risk that the saw blades become misaligned which in turn leads to saw mismatch, an unevenness seen on the surface of the sawn timber. In this work, attempts were made to automatically measure and monitor saw mismatch in a sawmill during ongoing production. It is also possible for a sawmill to increase its profitability by measures not related to the sawing process. One such example is customer adaptation when delivering the sawn timber. Different customers use the sawn timber for different purposes and consequently have different requirements, which is why the sawn timber produced is graded and sorted before it is delivered to the customer. In this work, an alternative method for grading sawn timber more efficiently using a multivariate method was developed and evaluated.The following results have been obtained: Log breakdowns of 716 Scots pine logs and 750 Norway spruce logs that had been scanned using computed tomography were simulated and the rotational position of each log was optimized. The results showed an average relative value increase of 16% for appearance graded sawn timber compared to the conventional horns down position. When simulating log breakdowns of 677 Norway spruce logs with respect to visually strength graded sawn timber, an average relative value increase of 11% was obtained. The effect that errors in knot detection algorithms had on a breakdown optimization was also analysed when optimizing breakdown of 57 Norway spruce sawlogs. The results showed that errors in the knot diameter had the most severe impact on the average relative value increase of a log rotation optimization, followed by errors in the dead knot border. The smallest effect was observed in the case of errors in rotational position of the knots.Computed tomography scanning can also be used in a sawmill for log sorting in relation to different end-uses of the sawn timber. A simulation software for cross-cutting optimization based on computed tomography data was developed and it was shown that there was a reasonable correlation between these results and the results of an industrial system. Since the developed software can be combined with log breakdown simulations based on computed tomography data, it is evident that computed tomography can be used to identify logs that would result in a poor volume yield in the subsequent cross-cut optimization.Destructive bending strength tests were performed on 113 pieces of Norway spruce sawn timber. Multivariate models for predicting the bending strength of the sawn timber were created using computed tomography data of the sawlogs from which the sawn timber originated. The results showed that computed tomography scanning of logs produced prediction models of bending strength with a higher accuracy than discrete X-rayscanning. The main advantage was the detailed knot information that could be used in the prediction models. A method to measure saw mismatch automatically in a sawmill based on laser triangulation was developed and the measurements were well correlated with manual measurements of saw mismatch. When laser triangulation was used to measure saw mismatch in a sawmill, a distinguishable trend of increasing magnitude and frequency of saw mismatch was observed. Finally, ways in which the sawn timber in a sawmill could be graded and sorted more efficiently was investigated. It was found that by using a grading method based on multivariate techniques it is possible to increase the proportion of higher sawn timber grades by up to 10 percentage points, which may increase sawmill profitability.