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Oja, Johan
Publications (10 of 57) Show all publications
Olofsson, L., Möller, C.-J., Wendel, C., Oja, J. & Broman, O. (2019). New possibilities with CT scanning in the forest value chain. In: 21st International Nondestructive Testing and Evaluation of Wood Symposium: . Paper presented at International Nondestructive Testing and Evaluation of Wood Symposium.
Open this publication in new window or tab >>New possibilities with CT scanning in the forest value chain
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2019 (English)In: 21st International Nondestructive Testing and Evaluation of Wood Symposium, 2019Conference paper, Published paper (Other academic)
Abstract [en]

Industrial high-resolution X-ray computed tomography (CT) scanners have recently been installed at several sawmills worldwide for the description of roundwood interior features and external log shape. These CT scanners represent a technological advancement for sawmill businesses that open a way to higher volume and value yields and new production planning strategies. This paper will present an indicative study of innovative use of non-destructive CT log data in a Swedish softwood sawmill, linking high-quality information of the wood material along the wood-value chain. Sawn timber was observed throughout the sawmill process line, i.e. from the log yard through the sawmill process until grading after the timber was dried. Before sawing, the CT scanner scanned the logs and calculated knot measurements from the 3D CT log data of simulated value-optimized center yield. A corresponding set of knot measurements were later calculated from the camera-based grading of the dried timber. Only considering knots from the two sets of measurements, the sawn timber was automatically given a quality assessment based on CT data, by camera-based scanning data, and by manual visual grading for reference. Partial least squares regression was used to create prediction models by correlating the two sets of knot measurements with the automatically determined grade from the dry-sorting. The prediction models tested increased the grading consistency between the grading based on CT data of virtual planks and based on camera data of the same planks. Furthermore, a traceability algorithm was tested as a tool to generate large data sets for future studies.

Keywords
sawn timber grading, computed tomography, partial least squares
National Category
Wood Science
Identifiers
urn:nbn:se:ltu:diva-75506 (URN)
Conference
International Nondestructive Testing and Evaluation of Wood Symposium
Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14
Berglund, A., Broman, O., Oja, J. & Grönlund, A. (2015). Customer adapted grading of Scots pine sawn timber using a multivariate method (ed.). Scandinavian Journal of Forest Research, 30(1), 87-97
Open this publication in new window or tab >>Customer adapted grading of Scots pine sawn timber using a multivariate method
2015 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 30, no 1, p. 87-97Article in journal (Refereed) Published
Abstract [en]

To define new grading rules, or to customize the ones in use in a rule-based automatic grading system of boards, is a time-consuming job for a sawmill engineer. This has the effect that changes are rarely made. The objective of this study was to continue the development of a method that replaces the calibration of grading rule settings by a holistic-subjective automatic grading, using multivariate models. The objective was also to investigate if this approach can improve sawmill profitability and at the same time have a satisfied customer. For the study, 323 Scots pine (Pinus sylvestris L.) boards were manually graded according to preferences of an important customer. That is, a customer that regularly purchases significant volumes of sawn timber. This manual grading was seen as reference grading in this work. The same boards were also scanned and graded by a rule-based automatic grading system, calibrated for the same customer. Multivariate models for prediction of board grade based on aggregated knot variables, obtained from the scanning, were calibrated using partial least squares regression. The results show that prediction of board grades by the multivariate models were more correct, with respect to the manual grading, than the grading by the rule-based automatic grading system. The prediction of board grades based on multivariate models resulted in 76-87% of the boards graded correctly, according to the manual grading, while the corresponding number was 63% for the rule-based automatic grading system.

National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-12739 (URN)10.1080/02827581.2014.968359 (DOI)000349118400008 ()2-s2.0-84926255283 (Scopus ID)be6cca49-b5fa-4769-b182-a4dfe5d69400 (Local ID)be6cca49-b5fa-4769-b182-a4dfe5d69400 (Archive number)be6cca49-b5fa-4769-b182-a4dfe5d69400 (OAI)
Note

Validerad; 2015; Nivå 2; 20140804 (bendar)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Vikberg, T., Hansson, L., Schajer, G. S. & Oja, J. (2012). Effects on microwave measurements and simulations when collecting data close to edges of wooden boards (ed.). Paper presented at . Measurement, 45(3), 525-528
Open this publication in new window or tab >>Effects on microwave measurements and simulations when collecting data close to edges of wooden boards
2012 (English)In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 45, no 3, p. 525-528Article in journal (Refereed) Published
Abstract [en]

Parameters like strength, moisture content, density and grain direction are important when sorting wood according to their individual properties. All those parameters can be correlated to microwave measurements of phase shift and attenuation. Measurements of phase shift and attenuation are, however, affected by the vicinity of a board edge. In this article a simulation of the measurement system is used to create a compensation function for the measurements taken close to edges as if those were taken where no effects of the board edge could be noticed. It is shown, by comparison with real measurements, that by doing this the deviation between the values measured close to the board edges and those measured in the middle of the board is decreased, meaning a higher accuracy can be achieved by using the compensating function.

National Category
Bio Materials Other Mechanical Engineering
Research subject
Wood Physics; Wood Technology
Identifiers
urn:nbn:se:ltu:diva-13716 (URN)10.1016/j.measurement.2011.10.016 (DOI)000301221100037 ()2-s2.0-84856718891 (Scopus ID)d000846a-5371-436b-94c5-823e67abe824 (Local ID)d000846a-5371-436b-94c5-823e67abe824 (Archive number)d000846a-5371-436b-94c5-823e67abe824 (OAI)
Note
Validerad; 2012; 20111021 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Vikberg, T., Oja, J. & Antti, L. (2012). Moisture content measurement in Scots pine by microwave and X-rays (ed.). Paper presented at . Wood and Fiber Science, 44(3), 280-285
Open this publication in new window or tab >>Moisture content measurement in Scots pine by microwave and X-rays
2012 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 44, no 3, p. 280-285Article in journal (Refereed) Published
Abstract [en]

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%.

National Category
Bio Materials Other Mechanical Engineering
Research subject
Wood Physics; Wood Technology
Identifiers
urn:nbn:se:ltu:diva-12168 (URN)b41861f7-d32d-495d-9142-d55296fb2d9a (Local ID)b41861f7-d32d-495d-9142-d55296fb2d9a (Archive number)b41861f7-d32d-495d-9142-d55296fb2d9a (OAI)
Note
Validerad; 2012; 20120315 (tomvik)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Broman, O., Wixe, D., Grönlund, A. & Oja, J. (2011). Råvarustyrning för materialeffektiv produktion av limfog: En studie utförd vid Norrfog AB (ed.). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Råvarustyrning för materialeffektiv produktion av limfog: En studie utförd vid Norrfog AB
2011 (Swedish)Report (Other academic)
Abstract [sv]

Norrfog AB i Malå tillverkar limfogskivor i olika kvaliteter, bland annat till gör-det-själv- (GDS)-limfog, möbelfog och IKEAs hyllkoncept Ivar. Då Norrfog planerar att öka sin producerade volym av limfog ökar behovet av en effektiv styrning av rätt råvara till rätt slutprodukt. Samtidigt stiger råvarupriserna och det blir allt viktigare att maximera volyms- och värdeutbytet. Vid tidpunkten för studien: Norrfog AB köper klena furustockar och försorterar stockarna i diameterklasser med hjälp av en 2D-mätram. Ingen sortering sker på stocktyp och därmed blandas rotstockar, svartkviststockar och friskkviststockar. Stockarna sågas med en 2ex postning till plankor som efter torkning kapas upp till komponentlängder som därefter klyvs till färdiga lameller för limfogsproduktion. Huvudsyftet med detta projekt var att undersöka möjligheterna att styra rätt kvalitet av timmer till rätt slutprodukt; Ivarhyllan, GDS-limfog och möbelfog samt för- och nackdelar med att införa ett alternativt sågsätt – genomsågning. Inom ramen för studien fanns följande forsknings- och utvecklingsfrågor: •Stocklängdens betydelse för volymutbytet av limfog? •Stocktypens betydelse för kvaliteten på producerad limfog? •Går det att hitta rätt typ av stockar till en specifik produkt redan vid timmerplanen med hjälp av befintlig 2D-mätram och förbättrar 3D eller röntgen-skanning denna klassificering av stockar? •Finns det ett motstånd till fingerskarv bland konsumenter och vad anses vara ett önskvärt utseende på en träyta av limfog? Studien visar att den stocktyp som gav den bästa kvaliteten var friskkviststockarna, men även de stockar som sorterades som svartkvistiga visade sig innehålla mestadels friska kvistar i de aktuella timmerdimensionerna. Ett tydligt resultat var att rotstockar innehöll den lägsta kvaliteten med för många och/eller för stora svarta kvistar och det visade sig vara lämpligt att om möjligt sortera bort dessa stockar för att såga dessa separat till produkter med lägre krav på kvalitet. Sorteringsalgoritmer för olika mättekniker för timmer speciellt anpassade för att maximera utbytet kvalitet 1 i den färdiga limfogen testades. Med befintlig 2D-mätram sorterades 81 % av rotstockarna bort och med röntgenmätning ökade andelen bortsorterade rotstockar till 98 %. Ett viktigt resultat var att genomsågning gav i snitt 13 % högre volymutbyte än 2ex-sågning och att korta stockar gav ökat volymutbyte jämfört med fullängdsstockar. En separat undersökning angående skivornas utseende visar att fingerskarvade limfogskivor är något konsumenten kan tänka sig, så länge färgskiftningarna mellan lamellerna är små. Stora färgskiftningar och små svarta kvistar var det som respondenterna rankade som minst tilltalande för alla skivor oavsett fingerskarv eller inte.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2011. p. 125
Series
Technical report / Luleå University of Technology, ISSN 1402-1536
Keywords
Materials science - Functional materials, Materialstyrning, Teknisk materialvetenskap - Funktionella material
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-24610 (URN)bb422cc7-049c-4f12-9a03-faca7f9b16d9 (Local ID)978-91-7439-268-5 (ISBN)bb422cc7-049c-4f12-9a03-faca7f9b16d9 (Archive number)bb422cc7-049c-4f12-9a03-faca7f9b16d9 (OAI)
Note
Godkänd; 2011; 20110511 (olof)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Kvarnström, B. & Oja, J. (2010). Applications of RFID to improve traceability in continuous processes. In: Cristina Turcu (Ed.), Sustainable Radio Frequency Identification Solutions: (pp. 69-86). Paper presented at . Vienna, Austria: IN-TECH
Open this publication in new window or tab >>Applications of RFID to improve traceability in continuous processes
2010 (English)In: Sustainable Radio Frequency Identification Solutions, Vienna, Austria: IN-TECH, 2010, p. 69-86Chapter in book (Other academic)
Place, publisher, year, edition, pages
Vienna, Austria: IN-TECH, 2010
National Category
Reliability and Maintenance Other Mechanical Engineering
Research subject
Quality Technology and Management; Wood Technology
Identifiers
urn:nbn:se:ltu:diva-20997 (URN)a1ccf7b0-d2bd-11de-bae5-000ea68e967b (Local ID)978-953-7619-74-9 (ISBN)a1ccf7b0-d2bd-11de-bae5-000ea68e967b (Archive number)a1ccf7b0-d2bd-11de-bae5-000ea68e967b (OAI)
Note

Godkänd; 2010; 20091116 (bjokva)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-03-13Bibliographically approved
Skog, J. & Oja, J. (2010). Density measurements in Pinus sylvestris sawlogs combining X-rayand three-dimensional scanning (ed.). Paper presented at . Scandinavian Journal of Forest Research, 25(5), 470-481
Open this publication in new window or tab >>Density measurements in Pinus sylvestris sawlogs combining X-rayand three-dimensional scanning
2010 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 25, no 5, p. 470-481Article in journal (Refereed) Published
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.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-13057 (URN)10.1080/02827581.2010.509326 (DOI)000282594700009 ()2-s2.0-77955258875 (Scopus ID)c3738820-dcee-11df-8b36-000ea68e967b (Local ID)c3738820-dcee-11df-8b36-000ea68e967b (Archive number)c3738820-dcee-11df-8b36-000ea68e967b (OAI)
Note
Validerad; 2010; 20101021 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Skog, J., Vikberg, T. & Oja, J. (2010). Sapwood moisture content measurements in Scots Pine sawlogs combining X-ray and 3D scanning (ed.). In: (Ed.), Tom Morén; Lena Antti; Margot Sehlstedt-Persson (Ed.), 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"]. Paper presented at International IUFRO Wood Drying Conference : 18/01/2010 - 22/01/2010 (pp. 357-362). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Sapwood moisture content measurements in Scots Pine sawlogs combining X-ray and 3D scanning
2010 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2010
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-28117 (URN)1cd480d0-25f8-11df-be83-000ea68e967b (Local ID)1cd480d0-25f8-11df-be83-000ea68e967b (Archive number)1cd480d0-25f8-11df-be83-000ea68e967b (OAI)
Conference
International IUFRO Wood Drying Conference : 18/01/2010 - 22/01/2010
Note
Godkänd; 2010; 20100302 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Skog, J., Vikberg, T. & Oja, J. (2010). Sapwood moisture-content measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning (ed.). Paper presented at . Wood Material Science & Engineering, 5(2), 91-96
Open this publication in new window or tab >>Sapwood moisture-content measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning
2010 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 2, p. 91-96Article in journal (Refereed) Published
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.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-12910 (URN)10.1080/17480272.2010.484868 (DOI)2-s2.0-77955256090 (Scopus ID)c0ef62a0-a6a6-11df-a707-000ea68e967b (Local ID)c0ef62a0-a6a6-11df-a707-000ea68e967b (Archive number)c0ef62a0-a6a6-11df-a707-000ea68e967b (OAI)
Note
Validerad; 2010; 20100813 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Skog, J. & Oja, J. (2009). Combining x-ray and three-dimensional scanning of sawlogs: comparison between one and two x-ray directions (ed.). In: (Ed.), Peter Zinterhof (Ed.), Proceedings of the 6th International Symposium on Image and Signal Processing and Analysis, 2009: ISPA 2009 ; Salzburg, Austria, 16 - 18 Sept. 2009. Paper presented at International Symposium on Image and Signal Processing and Analysis : 16/09/2009 - 18/09/2009 (pp. 353-358). Piscataway, NJ: IEEE Communications Society
Open this publication in new window or tab >>Combining x-ray and three-dimensional scanning of sawlogs: comparison between one and two x-ray directions
2009 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2009
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-39501 (URN)e4978040-e65b-11de-bae5-000ea68e967b (Local ID)978-1-424-45649-9 (ISBN)e4978040-e65b-11de-bae5-000ea68e967b (Archive number)e4978040-e65b-11de-bae5-000ea68e967b (OAI)
Conference
International Symposium on Image and Signal Processing and Analysis : 16/09/2009 - 18/09/2009
Note
Godkänd; 2009; 20091211 (ysko)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
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