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- Axelsson, Ann
(författare)
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How planing affects warp
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although planers and wood machining researchers have been around a long time, the interactions between planks and planers have been neglected in basic research. With a solid understanding of the movements of planks during planing, planers and planing strategies can be developed to reduce waste and improve the value yield.Cutting depths, changes in the amount of warp and cross-sectional shape were used to analyse the movements of the planks during planing, the alignment between the planks cross-sections and planers cutters and the improvement potential. The feeding roller in the planer intake had most control over the plank motion. Apart from cup reduction, the parts mostly affected by planing were the top and the butt end, where twist-induced misalignment between the cross-sections and the planers cutters resulted in skewed cross-sections and reduced rectangularity. By adjusting the cutting depths and in some cases the sawing oversize, planer misses could have been avoided but improvements in rectangularity would have required changes in the planer setting or planer design.This thesis increases the knowledge on how a 4-side planer works together with warp to affect 50 × 150 mm planks. For the 20 planks used in this study, the planer removed cup, it decreased the amount of twist and crook but had no effect on bow. The major factor reducing the rectangularity of the planed planks was twist. In the future, knowledge derived from this thesis can be used to create a simulation tool to model the behaviour of warped planks in a planer.
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2. |
- Axelsson, B., et al.
(författare)
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Lateral forces in wood cutting
- 1991
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Ingår i: Proceedings of the Tenth International Wood Machining Seminar : Oktober 21 - 23, 1991. - : University of California at Berkeley.
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Konferensbidrag (refereegranskat)
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4. |
- Chiorescu, Sorin, et al.
(författare)
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The influence of missing bark on measurements performed with a 3D log scanner
- 2001
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Ingår i: Forest products journal. - 0015-7473. ; 51:8, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- Nowadays the sawmill industry is in possession of sophisticated measurement equipment, which is the key to the successful running of the wood transformation process. New technologies such as three-dimensional (3D) scanners are becoming more and more common in Swedish sawmills. These scanners are used for sorting sawlogs according to different criteria such as diameter, length, or quality. They also perform the automatic scaling of the sawlogs that is the basis for estimating volume. Both scaling and sorting are done on bark, i.e., before debarking the logs. Specific functions for the double bark thickness are used to estimate the diameter under bark of the logs. However, these functions do not take into account the eventual missing/damaged bark from the surface of the logs. The errors caused by this lack of precision negatively affect the quality of both scaling and sorting procedures. In this study, with the aid of a simulation technique and field tests, questions regarding the size of these errors and how missing bark affects the measurement procedure when using a 3D log scanner are tackled. Finally, a new system for bark deduction is proposed, implemented, and evaluated in a Swedish sawmill. The results show that paying more attention to missing bark when scaling and sorting sawlogs can considerably increase the accuracy of these operations, thus leading to improvements in the forestry-wood chain.
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5. |
- Ekevad, Mats, et al.
(författare)
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Modelling of adequate pretwist for obtaining straight timber
- 2006
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 1:2, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic-ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists
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7. |
- Grundberg, Stig
(författare)
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An X-ray LogScanner : a tool for control of the sawmill process
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood is a biological material with great variability. Every piece of wood is a unique individual. The great challenge in the wood products manufacturing process has always been to select pieces of wood with properties that fulfil the product requirements. This will be even more important in the future as customers increasingly demand sawn products with special properties regarding dimension, moisture content, wrap and last, but not least, biological or aesthetic features. To be albe to fulfil these requirements, the right logs have to be selected for a certain product before the sawing process. This means that an accurate tool that can measure external and internal features is needed. The main objective of this work was to develop and evaluate algorithms for nondestructive measurement of external and internal properties in sawlogs with the aid of a bidirectional X-ray LogScanner. The LogScanner outlines and the LogScanner signals were simulated using CT (computer tomography) images from the Swedish Pine (Pinus sylvestris) Stem Bank and the European Spruce (Picea abies) Stem Bank. With the aid of data from the stem bank databases, the simulated scanner signals, the saw simulation program virtual SawMill (vSM), and statistical analysis programs, new control algorithms were developed and evaluated. The studies show that an X-ray LogScanner with two X-ray sources has a great potential to become a powerful tool for control of the sawmill process. The most important conclusions of work presented in this thesis were that: - X-ray based technology is a suitable technique for nondestructive measurement of internal features in green sawlogs. - CT scanning is a powerful research tool for measurement and visualisation of different log properties. - Parameterisation is an efficient method for reduction of the amount of data from a CT scanner. - It is very efficient to use data from a “Stem Bank data-base” based on CT scanning for simulation, analysis and development of the sawing process and different measurement technologies. - An X-ray LogScanner with two X-ray sources can measure log features such as diameter under bark, species, log type, knot structure, rotational position of knots, density, heartwood content, annual ring width and predict strength and grade of sawn boards.
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8. |
- Grundberg, Stig, et al.
(författare)
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Detecting knots in logs using a simulated X-ray cone-beam scanner
- 2004
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Ingår i: Fourth workshop "Connection between forest resources and wood quality: modelling approaches and simulation software" : Harrison Hot Springs, British Columbia, Canada, September 8 - 15, 2002 ; proceedings. - : International Union of Forestry Research Organisations.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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9. |
- Grundberg, Stig, et al.
(författare)
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Feature extraction with the aid of an X-ray log scanner
- 1998
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Ingår i: Proceedings from the 3rd International Seminar/Workshop on Scanning Technology and Image Processing on Wood. - Luleå : Luleå tekniska universitet.
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Konferensbidrag (refereegranskat)
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10. |
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