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  • 1.
    Berglund, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Johansson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Value optimized log rotation for strength graded boards using computed tomography2014In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 72, no 5, p. 635-642Article in journal (Refereed)
    Abstract [en]

    A possible application for an industrial computed tomography scanner in a sawmill is finding an optimal rotational position of logs with respect to knots and outer shape. Since a computed tomography scanner is a great investment, it is important to investigate potential profitability of such an investment for different production strategies. The objective of this study was to investigate the potential value increase of the sawn timber of Norway spruce (Picea abies (L.) Karst.) by rotating logs to their optimum position prior to sawing compared with sawing all logs in horns down position. The production strategy evaluated by log breakdown simulation in this case study was to produce strength graded timber of the center boards, while the side boards were appearance graded. This case study showed an average value increase with respect to the value of center boards, side boards and chips of 11 %.

  • 2.
    Fredriksson, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Reconstruction of knots from simulated discrete x-ray images of Pinus Sylvestris logs2012Conference paper (Refereed)
    Abstract [en]

    For many years it has been of interest to be able to predict the properties of sawn wood products from tree features. X-ray technology has made it possible to measure internal as well as external features of saw logs, and to use these features for predicting log quality. However, data available for simulation of the sawing process and prediction of sawn timber quality has, until now, been limited to logs scanned using computed tomography.The objective of this study is to develop a method for reconstruction of parametrically described whorls and knots from industrial scanning of Scots pine (Pinus sylvestris L.) logs, using discrete Xray images. The method is designed using the logs in the Swedish pine stem bank (SPSB) as data basis, and is based on a few predictor features extracted from these logs, namely whorl volume, distance between whorls, and distance between pith and surface. These features are measured in simulated discrete X-ray images of the logs in the SPSB, and virtual models of the whorls and knots are created, using a feature- and knowledge based model. Virtual logs are then composed using the reconstructed knots within the original shape of the logs. Simulated test sawing of the virtual logs shows that the reconstruction method results in a representative model of the knot structure in the log, when considering the grade distribution of the sawn timber produced by the simulation program. The results of this study can for instance be used for improved online quality predictions at sawmills. One step in this direction is to use industrial X-ray data to enlarge the amount of log data available for sawing simulation research. Future work should focus on developing practical applications of the results presented here.

  • 3.
    Grönlund, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Use of x-ray for detection of internal log features2012Conference paper (Refereed)
    Abstract [en]

    To have knowledge about internal features in saw logs have always been a very important wish among people working in the sawmill industry. The reason for that wish is that with this knowledge it is possible to disintegrate logs in an optimal way.X-ray linear attenuation depends mainly on density and size of the object that is hit by the X-ray beam. This makes X-ray technology suitable for detection of different features in saw logs as there is a density difference between clear wood and many important internal features such as different kind of knots.Medical computer tomography (CT) utilise X-ray to detect internal features in human bodies but is also a very good tool for detection of features in saw logs. However, medical CT-scanners are only used for research purposes in the wood sector as they are far to slow for use in the industry.In order to be able to detect internal log features in industrial speed Log-Scanners with one to four fixed X-ray sources have been developed. With these scanners, that now are used at many sawmills, it is possible to detect and measure features such as: diameter under bark, log type, species, knot parameters, annual ring width, density, heartwood, strength etc. These scanners with fixed sources have a much lower information density than medical CT-scanners but are much faster. The time for scanning a log has been reduced from about two hours to 1.5 seconds. The big draw-back with the scanners with fixed sources is that they give very little information about how defects are located in the rotational direction. However, in order to overcome this drawback, an industrial CT-scanner is now under development. This scanner will operate in industrial speed and will at the same time have an information density that is comparable with a medical CT-scanner.The aim of this presentation is to summarize the current knowledge on X-ray scanning of wood and to propose some suitable applications and strategies for using a fast CT scanner in the wood industry.

  • 4.
    Johansson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berglund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. SP Sveriges Tekniska Forskningsinstitut, SP Trä.
    Comparing predictability of board strength between computed tomography, discrete x-ray, and 3D scanning of Norway spruce logs2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 2, p. 116-125Article in journal (Refereed)
    Abstract [en]

    Strength graded boards of Norway spruce (Picea abies (L.) Karst.) are important products for many Scandinavian sawmills. If the bending strength of the produced boards can be predicted before sawing the logs, the raw material can be used more efficiently. In previous studies it is shown that the bending strength can be predicted to some extent using discrete X-ray scanning of logs. In this study, we have evaluated if it is possible to predict bending strength of Norway spruce boards with higher accuracy using computed tomography (CT) scanning of logs compared to a combination of discrete X-ray and 3D scanning. The method was to construct multivariate models of bending strength for three different board dimensions. Our results showed that CT scanning of logs produces better models of bending strength compared to a combination of discrete X-ray and 3D scanning. The main reason for this difference was the benefit of knowing the position of where the boards were cut from the logs and therefore detailed knot information could be used in the prediction models. Due to the small number of observations in this study, care should be taken when comparing the resulting prediction models to results from other studies

  • 5.
    Johansson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Johansson, Dennis
    SP Technical Research Institute of Sweden, Skellefteå.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Automated knot detection for high speed computed tomography on Pinus sylvestris L. and Picea abies (L.) Karst. using ellipse fitting in concentric surfaces2013In: Computers and Electronics in Agriculture, ISSN 0168-1699, E-ISSN 1872-7107, Vol. 96, p. 238-245Article in journal (Refereed)
    Abstract [en]

    High speed industrial computed tomography (CT) scanning of sawlogs is new to the sawmill industry and therefore there are no properly evaluated algorithms for detecting knots in such images. This article presents an algorithm that detects knots in CT images of logs by segmenting the knots with variable thresholds on cylindrical shells of the CT images. The knots are fitted to ellipses and matched between several cylindrical shells. Parameterized knots are constructed using regression models from the matched knot ellipses. The algorithm was tested on a variety of Scandinavian Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) with a knot detection rate of 88–94% and generating about 1% falsely detected knots.

  • 6.
    Olofsson, Linus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    RISE Bioeconomy, Research Institutes of Sweden, Skellefteå, Sweden.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Multivariate product adapted grading of Scots pine sawn timber for an industrial customer, part 1: Method development2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 6, p. 428-436Article in journal (Refereed)
    Abstract [en]

    Rule-based automatic grading (RBAG) of sawn timber is a common type of sorting system used in sawmills, which is intricate to customise for specific customers. This study further develops an automatic grading method to grade sawn timber according to a customer’s resulting product quality. A sawmill’s automatic sorting system used cameras to scan the 308 planks included in the study. Each plank was split at a planing mill into three boards, each planed, milled, and manually graded as desirable or not. The plank grade was correlated by multivariate partial least squares regression to aggregated variables, created from the sorting system’s measurements at the sawmill. Grading models were trained and tested independently using 5-fold cross-validation to evaluate the grading accuracy of the holistic-subjective automatic grading (HSAG), and compared with a resubstitution test. Results showed that using the HSAG method at the sawmill graded on average 74% of planks correctly, while 83% of desirable planks were correctly identified. Results implied that a sawmill sorting station could grade planks according to a customer’s product quality grade with similar accuracy to HSAG conforming with manual grading of standardised sorting classes, even when the customer is processing the planks further.

  • 7.
    Olofsson, Linus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Multivariate Product Adapted Grading of Scots Pine Sawn Timber for an Industrial Customer, Part 2: Robustness to Disturbances2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed)
    Abstract [en]

    Holistic-subjective automatic grading (HSAG) of sawn timber by an industrial customer's product outcome is possible through the use of multivariate partial least squares discriminant analysis (PLS-DA), shown by part one of this two-part study. This second part of the study aimed at testing the robustness to disturbances of such an HSAG system when grading Scots Pine sawn timber partially covered in dust. The set of 308 clean planks from part one of this study, and a set of 310 dusty planks, that by being stored inside a sawmill accumulated a layer of dust, were used. Cameras scanned each plank in a sawmill's automatic sorting system that detected selected feature variables. The planks were then split and processed at a planing mill, and the product grade was correlated to the measured feature variables by partial least squares regression. Prediction models were tested using 5-fold cross-validation in four tests and compared to the reference result of part one of this study. The tests showed that the product adapted HSAG could grade dusty planks with similar or lower grading accuracy compared to grading clean planks. In tests grading dusty planks, the disturbing effect of the dust was difficult to capture through training.

  • 8.
    Sehlstedt-Persson, Margot
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wamming, Thomas
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Processanpassning för funktionsbeständiga träprodukter: vilken roll spelar torkningen för virkets beständighet i utomhusprodukter ovan mark?2008Report (Other academic)
    Abstract [sv]

    Torkningsprocessens inverkan på beständigheten hos centrumsågat furuvirke 50x125 mm har studerats. Som utvärderingsmetod har röttester med brunrötesvampen Coniophora puteana (källarsvamp) gjorts på prov från splintved samt inre och yttre kärnved. Stor massförlust efter röttest visar på dålig beständighet. De torkningar som utvärderats är lufttorkning, artificiell torkning vid 70°C och 90°C samt en högtemperaturtorkning vid 110°C. För 70°C och 90°C torkningarna har två principscheman använts: ett med snabb temperaturökning i virket tidigt i torkningen och ett där virkestemperaturen når maxtemp i ett betydligt senare skede. Även inverkan av ångkonditionering i slutet av torkningen har utvärderats. Skanning med UV-ljus har utförts på virkestvärsnitt från samtliga torkningar för att undersöka hur UV-fluorescens av pinosylvin i kärnved påverkas av torkning samt om denna skanningsmetod kan användas för att prediktera massförlust (beständighet). Kapillärupptag av vatten i splint från de olika torkningarna har studerats i tomograf. Totalhalten av fenoliska ämnen i torkad kärnved, som av andra forskare visats ha stor betydelse för rötbeständighet mot källarsvamp på färsk ved, har bestämts med Folin-Ciocalteu (FC) metoden. Inledningsvis gjordes två serier med homogent spån (från virke som ej ingår i torkförsöken) som värmdes vid olika temperaturer. När resultaten från röttesterna från det torkade försöksvirket var kända utvaldes provplankor med lägst och högst massförlust ut från samtliga torkningsserier och analyserades med avseende på extraktivämneshalt och totalfenolhalt enligt FC-metoden. Resultaten sammanfattas under följande rubriker Råvaran Vid röttest med källarsvamp på torkat furuvirke konstateras Splintved ha betydligt sämre rötbeständighet än kärnved. Ingen skillnad i rötbeständighet mellan inre och yttre kärnved. Stor spridning i rötbeständighet mellan olika plankindivider men även inom en och samma planka i längdled. Svag indikation att högre veddensitet har bättre beständighet. Trolig förklaring är extraktivämneshalt. Totalfenolhalten vara högre i kärnved med hög extraktivämneshalt jämfört med låg extraktivämneshalt. Totalfenolhalten i spån från fet kärnved minskar vid värmning över 40°C upp till 110°C. Högre totalfenolhalt indikera lägre massförlust även i torkad furukärna. Torkning Vid beständighetstest med källarsvamp på furuvirke torkat vid olika temperaturer konstateras Splintved ha betydligt större massförlust än kärnved i samtliga torkningar Kärnved från lufttorkat virke ha minst massförlust vid röttest. Splintved och kärnved från virke torkat vid 90°C med snabb temperaturökning i virket ha störst massförlust vid röttest. Ångkonditionering efter torkning öka massförlusten vid röttest i furusplint. UV-skanning Vid UV-skanning av virkestvärsnitt från samtliga torkningar konstateras att färgkomponenter kan separera: - Virke torkat vid 20°C och 70°C från virke torkat vid 90°C och 110°C. - Inre kärnved från yttre kärnved och splintved. att signalerna måste kalibreras då möjligen även inslag av "vanlig färg" iveden ingår i signalerna. Kapillärförsök Då ingen fullständig utvärdering av tidsskäl hunnit göras konstateras här endast att Skillnader mellan olika torkningar kan ses i fuktgradienternas utseende i axiell led efter 6 dygns uppsugning. En tänkbar förklaring kan vara övergångar mellan olika mekanismer för vattenupptagning som har att göra med torkningssätt och temperatur, exempelvis söndertrasade pormembran i det artificiellt torkade virket eller förändrade vätningsegenskaper i veden vid högre temperatur. Projektets målsättning att formulera rekommendationer för beständighetsanpassad torkning av furuvirke sammanfattas enligt följande: Den kritiska parametern under torkningsprocessen för beständigheten i kärnved är virkestemperaturen tidigt i torkningen. För artificiell torkning i virkestork bör därför torkstyrningen anpassas så att virkestemperaturen hålls nere tidigt i torkningen när fuktkvoten är hög. För rötbeständighet i splintved är ångkonditionering efter torkning mindre lämplig.

  • 9.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Characterization of sawlogs using industrial X-ray and 3D scanning2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the Nordic countries, sawlogs are typically sorted upon arrival at the sawmill based on species and dimension. By processing batches of logs with similar size, the sawing process becomes more efficient; the need to change sawing pattern between individual logs is reduced, and the handling of sawn goods is simplified, since the number of different dimensions produced simultaneously decreases. However, since wood is a biological material with great heterogeneity, there will be a large variation in the properties also of boards sawn from logs of similar size. This means that a significant amount of the boards may be carrying unwanted combinations of dimension and grade, so called off-grade products. The problem with off-grade products may be addressed before sawing by the selection of suitable sawing patterns for each log, i.e., using the right logs for the right products. This requires knowledge of the internal quality of the log before sawing. Some information can be obtained from the outer shape measured by an optical three-dimensional (3D) scanner and more detailed information can be obtained using an X-ray log scanner. Today, the use of X-ray log scanners is becoming increasingly common, and most sawmills installing an X-ray scanner already have a 3D scanner present. This raises the question of possible benefits from combining the X-ray and 3D scanning techniques. In this thesis, a method is presented whereby the outer shape of the log measured by a 3D scanner is utilized to estimate the X-ray path lengths through the wood. This converts the X-ray images into green density images of the log, which may in turn be used to calculate quality variables such as heartwood diameter, dry density, moisture content and presence of top rupture. The methods have been tested on Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sawlogs using X-ray scanners with one or two measurement directions. The developed methods show a great improvement in precision compared to calculations based on uncompensated X-ray images, and most of the algorithms presented in the thesis have now been implemented in industrial scanner software and are ready for use at the sawmills. This will give the sawmill industry new possibilities to control the production of special products where heartwood diameter and density are important and will lead to less waste and improved profitability for the sawmills.The thesis also describes a method where X-ray scanning is utilized to automatically perform parts of the log grading for payment. This method can improve productivity in the sawmills by remedying a severe bottleneck in the production chain. An authorization of this method for semiautomatic log grading for payment is expected to further increase the industry’s interest in X-ray scanning.

  • 10.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Combining X-ray and 3D scanning of logs2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In Scandinavia, sawlogs are typically sorted upon arrival at the sawmill. Presorting of sawlogs according to dimension, e.g., using an optical three-dimensional (3D) scanner, is used to make the sawing process more efficient. However, since wood is a biological material with large variability, there will be large differences in the quality of wood sawn from different logs of similar size. For some dimensions of sawn goods, wood quality is very important and low grade products will be difficult to sell, while for other dimensions, grade is less important. This means that if the quality of the sawn goods may be predicted before actual sawing takes place, the production of off-grade products, i.e., products not meeting customer demands, may be reduced.Some quality information may be obtained using the outer shape information from a 3D scanner and more detailed information on the internal quality of the log can be obtained using an X-ray log scanner. Today, the use of X-ray log scanners is becoming increasingly common and most sawmills installing an X-ray scanner already have a 3D scanner present. This raises the question of possible benefits from combining the X-ray and 3D scanning techniques. In this thesis, a method has been developed where the log shape measured by the 3D scanner is utilized to estimate the X-ray path lengths through the wood. This allows the calculation of green density profiles of the log, which may in turn be used to calculate quality variables such as heartwood content and heartwood density. The hypothesis of this project has been that the precision in these variables will be improved by the 3D path length compensation of the X-ray data. The method has been tested on Scots pine (Pinus sylvestris L.) sawlogs, using both simulated and industrial log scanner data. Scanners with one and two X-ray directions have been used. The most important conclusions from the project are that: - Heartwood diameter predictions are significantly improved by the combination of 3D and X-ray data. - Dry and green heartwood densities can be calculated with improved precision relative to scanning using X-ray only. - The method was found suitable for application with both one- and two-directional X-ray scanners. - For a sawmill already using both 3D and X-ray scanners, there is a large improvement potential available using existing equipment. For sawmills thinking about investing in an X-ray scanner, the possibility of connecting it to the 3D scanner should make the rate of return of the equipment higher and encourage more sawmills to make this investment.

  • 11. Skog, Johan
    et al.
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Combining x-ray and three-dimensional scanning of sawlogs: comparison between one and two x-ray directions2009In: Proceedings of the 6th International Symposium on Image and Signal Processing and Analysis, 2009: ISPA 2009 ; Salzburg, Austria, 16 - 18 Sept. 2009 / [ed] Peter Zinterhof, Piscataway, NJ: IEEE Communications Society, 2009, p. 353-358Conference paper (Refereed)
    Abstract [en]

    In many sawmills, presorting of sawlogs is based on data from optical three-dimensional (3D) scanners. The use of x-ray log scanners is also becoming increasingly common and most sawmills installing an x-ray scanner already have a 3D scanner present. It is in this paper demonstrated how data from oneand two-directional x-ray scanners can be combined with 3D scanner data using path length compensation. Examples show how the resulting images may be processed in order to predict quality parameters such as heartwood diameter and green heartwood density. Using the proposed method, it is possible to improve the accuracy of these important quality sorting parameters using existing equipment. This will improve the presorting at sawmills, thus reducing the production of off-grade products carrying unwanted combinations of dimension and grade.

  • 12. Skog, Johan
    et al.
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Density measurements in Pinus sylvestris sawlogs combining X-rayand three-dimensional scanning2010In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 25, no 5, p. 470-481Article in journal (Refereed)
    Abstract [en]

    Wood density is an important quality variable, closely related to the mechanical properties of the wood. Precise wood density measurements in the log sorting would enable density sorting of logs for products such as strength-graded wood and fingerjointed wood. Density sorting of logs would also give more homogeneous drying properties and thus improve the quality of the final products. By compensating the radiographs from an X-ray log scanner for the varying path lengths using outer shape data from a three-dimensional (3D) scanner, it is possible to make precise estimates of both green and dry density. Measurements on simulated industrial data were compared with densities measured in computed tomographic (CT) images for 560 Scots pine (Pinus sylvestris L.) logs. It was found that green sapwood density could be measured with predictability R2 = 0.65 and root mean square error (RMSE) of 25 kg m-3. Green and dry heartwood densities were measured with similar precision: R2 = 0.79 and RMSE = 32 kg m-3 for green density and R2 = 0.83 and RMSE = 32 kg m-3 for dry density.

  • 13. Skog, Johan
    et al.
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Heartwood diameter measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning2009In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 24, no 1, p. 182-188Article in journal (Refereed)
    Abstract [en]

    Quality sorting of sawlogs based on three-dimensional (3D) or X-ray scanning or a multivariate combination of variables from both methods may be used to decrease the production of off-grade products carrying unwanted combinations of dimension and grade. There is, however, potential for further improving the sorting accuracy if 3D and X-ray raw data are combined at an early stage using path length compensation. From the measured 3D shape, a good estimate of the length of each X-ray path through the log can be made, enabling the calculation of a log density profile from the measured X-ray attenuation. The effect of this technique on heartwood diameter measurements of 423 Scots pine (Pinus sylvestris L.) logs was evaluated. By the addition of 3D data to the X-ray data it was possible to raise the predictability of the heartwood diameter from R 2=0.84 to 0.95 and to improve the root mean square error from 17 mm to 9.3 mm, primarily because of the enhanced contrast between heartwood and sapwood.

  • 14. Skog, Johan
    et al.
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Improved log sorting combining X-ray and 3D scanning: a preliminary study2007In: Quality control for wood and wood products: COST Action E 53 the first conference, October 15th/17th, 2007, Warsaw, Poland / [ed] Marek Grześkiewicz, Warsaw: Warsaw University of Life Sciences , 2007, p. 133-140Conference paper (Refereed)
    Abstract [en]

    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.

  • 15. Skog, Johan
    et al.
    Vikberg, Tommy
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sapwood moisture content measurements in Scots Pine sawlogs combining X-ray and 3D scanning2010In: Proceedings, 11th International IUFRO Wood Drying Conference: [... in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying"] / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010, p. 357-362Conference paper (Refereed)
    Abstract [en]

    Wood industry of today deals with large volumes in an almost automatic process, which is not fully adapted tothe variability of the raw material. Consequently, it is crucial to sort the wood according to material properties inorder to process the wood efficiently and to obtain high quality end products. One material property which could beused for sorting is the moisture content of the sapwood, an important parameter for both the processing and the endproducts.Most large Swedish sawmills are using 3D scanners for quality sorting of Scots pine (Pinus sylvestris L.)sawlogs based on outer shape. Recently, some sawmills have also invested in X-ray log scanners in order to sort thesawlogs based on inner properties. It has previously been shown that, by combining raw data from industrial 3D andX-ray log scanners using path length compensation, green sapwood density and dry heartwood density can beestimated.In this study, the dry heartwood density was used to find an estimate of the dry sapwood density, thus allowingthe calculation of the sapwood moisture content. The log scanner data used in this study was simulated from 560Scots pine sawlogs which had previously been scanned in a computed tomography (CT) scanner. The estimatedsapwood moisture contents were then compared to reference values calculated by drying samples to 9% moisturecontent.It was found that the moisture content estimate could be used to separate the logs into two groups with high andlow moisture content, correctly identifying all logs with very low moisture content as dry logs. Out of all logs, 70%were correctly classified. The moisture content estimate could also be compared to the dry density dependentmaximum moisture content and used to identify logs that have actually started to dry.

  • 16. Skog, Johan
    et al.
    Vikberg, Tommy
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sapwood moisture-content measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 2, p. 91-96Article in journal (Refereed)
    Abstract [en]

    Because today's sawmill processes are not fully adapted to the variability of the raw material, it is crucial to sort sawlogs according to material properties in order to process the wood efficiently and to obtain high-quality end-products. One material property that could be used for sorting is the moisture content (MC) of the sapwood, an important parameter for both the processing and the end-products. Most sawmills use three-dimensional (3D) scanners to sort logs and some have also invested in X-ray scanners. Previous studies have shown that, by combining raw data from 3D and X-ray log scanners, green sapwood density and dry heartwood density in Scots pine sawlogs can be estimated. In this study, the method was used to estimate sapwood MC in green logs. It was found that the MC estimate could be used to separate the logs into groups with high and low MC, correctly classifying all logs with MC below 100% as low MC logs. Out of all logs, 70% were correctly classified. The MC estimate could also be compared to the dry density-dependent maximum MC and used to identify logs that have actually started to dry.

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