Efficient utilization of sawlogs using scanning techniques and computer modelling

Sammanfattning: The main question asked of the work described in this thesis was howthe sawing of logs into sawn timber can be performed more efficientlywith respect to the choice of raw material, volume and value yield in thesawing and in the grading of the sawn timber produced.The development of industrial computed tomography scanning providesinformation about the external and internal properties of a sawlogat production speed. This opens up new possibilities of controlling theflow of raw material early in the process and of optimizing the breakdownof each sawlog. Another use of industrial computed tomography scanningis for predicting the strength of sawn timber better than is possible withcurrent visual and machine strength grading equipment.A more traditional way of increasing sawmill profitability is by increasingthe volume of sawn timber. One way of doing this is by reducing thesaw blade thickness which results in less sawdust. With the use of thinnersaw blades however there is a risk that the saw blades become misalignedwhich in turn leads to saw mismatch, an unevenness seen on the surfaceof the sawn timber. In this work, attempts were made to automaticallymeasure and monitor saw mismatch in a sawmill during ongoing production.It is also possible for a sawmill to increase its profitability by measuresnot related to the sawing process. One such example is customer adaptationwhen delivering the sawn timber. Different customers use the sawntimber for different purposes and consequently have different requirements,which is why the sawn timber produced is graded and sorted before it isdelivered to the customer. In this work, an alternative method for gradingsawn timber more efficiently using a multivariate method was developedand evaluated.The following results have been obtained:Log breakdowns of 716 Scots pine logs and 750 Norway spruce logsthat had been scanned using computed tomography were simulated andthe rotational position of each log was optimized. The results showedan average relative value increase of 16% for appearance graded sawntimber compared to the conventional horns down position. When simulating log breakdowns of 677 Norway spruce logs with respect to visuallystrength graded sawn timber, an average relative value increase of 11%was obtained. The effect that errors in knot detection algorithms had ona breakdown optimization was also analysed when optimizing breakdownof 57 Norway spruce sawlogs. The results showed that errors in the knotdiameter had the most severe impact on the average relative value increaseof a log rotation optimization, followed by errors in the dead knot border.The smallest effect was observed in the case of errors in rotational positionof 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 simulationsoftware for cross-cutting optimization based on computed tomographydata was developed and it was shown that there was a reasonable correlationbetween these results and the results of an industrial system. Sincethe developed software can be combined with log breakdown simulationsbased on computed tomography data, it is evident that computed tomographycan be used to identify logs that would result in a poor volume yieldin 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 basedon laser triangulation was developed and the measurements were well correlatedwith manual measurements of saw mismatch. When laser triangulationwas used to measure saw mismatch in a sawmill, a distinguishabletrend of increasing magnitude and frequency of saw mismatch was observed.Finally, ways in which the sawn timber in a sawmill could be gradedand sorted more efficiently was investigated. It was found that by using agrading method based on multivariate techniques it is possible to increasethe proportion of higher sawn timber grades by up to 10 percentage points,which may increase sawmill profitability.