Log sawing position optimization using computed tomography scanning

When disjoining a log, several factors affect the value of the sawn timber. There are log features, such as outer shape, knots, rot, and so on. There are also sawing parameters, such as sawing pattern, log position, and so on. If full information about log features is available, sawing parameters can be adapted in order to maximize product value in sawmills. This is soon possible, since computed tomography (CT) scanners for the sawmill industry are being realized. This study aimed at investigating how CT data can be used to choose rotational position, parallel displacement, and skew of sawlogs, to maximize the value of the sawn products. The study was made by sawing simulation of 269 CT scanned logs of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] H. Karst.). The results showed that value recovery could be improved by 13% in average, compared to a sawing position based on log outer shape, and 21% compared to sawing logs centered and horns down. It can be concluded that a CT scanner, used in a sawline to optimize sawing parameters, has a large potential for increasing value recovery and thus profit.     

Influence of growth stresses and material properties on distortion of sawn timber — numerical investigation

? The board distortion that occurs during the sawing and the drying process causes major problems in the utilisation of sawn timber. The distortion is highly influenced by parameters such as spiral grain angle, modulus of elasticity, shrinkage, growth stresses and sawing pattern.

? In this study a finite element simulation of log sawing and timber drying was performed to study how these parameters interact to affect board distortion. A total of 81 logs with different material combinations were simulated. From each simulated log four boards with different annual ring orientation were studied.

? The results showed that the elastic modulus, shrinkage coefficient and growth stresses had a large influence on the final bow and spring deformation. After sawing of the log into boards, the release of growth stresses was the main contributor to the bow and spring deformation. For boards with low modulus of elasticity, the bending distortion became larger than for the boards with high modulus of elasticity. The twist deformation was very small after sawing but increased significantly during drying of the boards. The results showed that spiral grain angle and the board location within the log were the main contributors to the twist deformation.

     

Application of the wood properties of large-diameter Sugi (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) logs to sorting logs and sawing patterns

The purposes of this study were to accumulate fundamental data on wood properties within large Sugi logs and to take applicable variations in wood properties into consideration for sorting logs and sawing patterns. The characteristics of basic density, moisture content, growth ring width, and microfibril angle (MFA) were measured and the relationship with log and lumber quality was examined. It was considered reasonable to estimate the lumber moisture content based on the moisture content of heartwood rather than that of whole logs, especially when producing large-sized lumber. The MFA reached a constant value before the 15th ring, and within a distance of 10 cm or less from the pith. Since the E _fr of lumber correlated with that of the log affected by MFA, it would be possible to produce lumber with a higher E _fr from the outer position of the log, based on selecting a log above the E _fr . Since the MFA would also affect the lumber warp, a sawing pattern avoiding the area around the pith or enlarging the rough sawn size when a large warp was expected could be effective in improving the lumber quality. To improve the lumber quality, not only one but also multiple wood properties must be applied to the sawing pattern.     

Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield

The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.     

The use of the first industrial X-ray CT scanner increases the lumber recovery value: case study on visually strength-graded Douglas-fir timber

Key message

Industrial computed tomography scanning of logs provides detailed information on timber quality prior to sawing. A sawing simulation—considering log rotation angle and knot size accuracy—revealed an average value increase of up to 20% for the best angle compared to the conventional horns-up position.

Context

Computed tomography (CT) scanning has the potential to improve the value of products sawn from logs and meets the increasing demands of the wood industry for detailed information on log quality prior to processing.

Aims

In a validation step, automated measurements of knot cluster variable DAB (DIN 4074-1:2012-06) using CT were compared with manual measurements. In a second optimization step, the hypothesis that the value of the sawn products is increased by sawing at the best rotation angle as opposed to the horns-up position was tested.

Methods

A sample of 36 Douglas-fir logs were scanned in an industrial CT scanner, and sawn into boards. Knots on the boards were manually measured, and compared with the corresponding knots on virtual boards created from the CT data. The error of the DAB was measured by comparing CT data to manual measurements. An optimized sawing simulation was performed, using the measured DAB error to account for CT measurement errors, as well as a rotational error to account for errors in the log turning equipment. Using the results of the sawing simulation, Monte Carlo simulations were performed to show the potential and benefit of an industrial CT scanner.

Results

The three largest DABs measured by the CT showed good correlation to the measurements on the manual boards. The simulation revealed an average increase of value from 4 to 20% compared to the conventional horns-up position depending on the relative price differences between the strength grades.

Conclusion

By using a CT scanner to optimize sawing, sawmill owners can process logs in a better way to produce final products with increased added value.

     

Choosing green sawing dimensions for Norway spruce from stochastic simulations

The high accuracy of log positioning and the stability of saw blades in breakdown machinery in modern sawmills have reduced the need to add margins for sawing variations. Oversize green sawing dimensions are still needed, but mainly to allow for drying shrinkage. This has put a new focus on better adapting green sawing dimensions to the shrinkage behavior of wood. In this study, a method for optimization of green sawing dimensions using stochastic simulation is presented. Normal distributions were generated for planed dry dimensions, kerf width, and target moisture content. The minimum share of boards exceeding the specified dry dimensions was decided, and deformations in boards from all positions in the cross section in a number of logs were simulated. The simulated shrinkage allowance from stochastic simulations was compared to experimental results from an industry test and to finite element results based on material data for Norway spruce. The results showed that the green width of the sawn boards should increase when the number of boards in the center yield increases. The green thickness of boards should be thinner for center boards and outer boards than for inner boards.     

Finite element study of growth stress formation in wood and related distortion of sawn timber

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.     

Combined production of sawn timber and firewood billets at a birch sawmill in Finland: A simulation approach

Abstract

Growing markets for chopped firewood have created alternative uses for the by-products of sawmills. Based on empirical data and simulated results, the potential of birch (Betula pendula Roth, Betula pubescens Ehrh.) from commercial thinnings for combined industrial production of sawn timber and firewood billets was investigated. In the simulations, different sawing patterns were used for logs intended to combine production of sawn timber and billets for chopped firewood (‘sawlogs’), and for logs intended only to firewood production (‘firewood logs’). Finally, economical feasibility analysis was done concerning the differences between the sawmills’ traditional business concept and the novel concept combining sawn wood and firewood production. The bucking results for the volume yield of different timber assortments varied only slightly between the different bucking options, i.e. the combinations of timber assortments. The main differences in the volumes of timber assortments were due to the stand type where the birch trees were sampled (planted, naturally regenerated, mixed birch–spruce). In the sawing procedure, the output of sawn timber varied between 24% and 42% of the log volume in the sawlogs, depending on the log diameter class. As the volume yield of sawn timber and firewood billets was counted together in the case of sawlogs, the log consumption was c. 1.75 m³ of roundwood per 1 m³ of sawn timber and firewood billets. In the case of the firewood logs, the log consumption rate was considerably lower, only c. 1.35. The economic calculations showed that using the firewood approach in sawing may increase the net added value of products by €1.9–5.4 m^?3 of logs, depending on their diameter class. As a conclusion, parallel production of sawn timber and firewood from logs from the first and second commercial thinning of birch-dominated stands is a concept that could work as an alliance between a sawmiller and a firewood entrepreneur. The concept could be competitive compared with both traditional sawmilling and production of chopped firewood.     

Reconstruction of Pinus Sylvestris knots using measurable log features in the Swedish Pine Stem Bank

Abstract

The objective of this study was to develop a method for reconstruction of parametrically described whorls and knots from data possible to extract from industrial scanning of logs, using X-ray scanners. The method was conceived using the logs in the Swedish Pine Stem Bank as a foundation, and was based on a few predictor features extracted from these logs; namely whorl volume, distance between whorls and distance between pith and surface. These features were not measured in images but calculated from existing parameterised knots. Simulated test sawing 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 could, 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 can, therefore, focus on developing a practical application of the results presented here.     

DIE INVLOED VAN RADIALE HARSGEïNFILTREERDE KERNSKEURE OP DIE GESAAGDE OPBRENGS UIT PINUS ELLIOTTII ENGELM.-SAAGBLOKKE / THE EFFECT OF RADIAL RESIN-INFILTRATED SPLITS ON THE YIELD OF SAWN TIMBER FROM PINUS ELLIOTTII ENGELM. SAWLOGS

A number of complaints, regarding the presence of resin-infiltrated splits in seasoned boards produced from Pinus elliottii sawlogs supplied from certain stands in State Forests, led to an investigation to determine the incidence of the defect and to find possible causes.

This paper deals mainly with the study of the first aspect. In the investigation two samples of stems were selected by a semi-random method from one mature stand, being clearfelled, in Entabeni State Forest (Northern Transvaal) and from three stands receiving, or due to receive, their fifth thinning. The clearfelling and thinning had produced logs containing heart shakes and this had given rise to the complaints.

During log preparation it was attempted to prepare as much as possible of the stem length into the longest sawlogs, working as closely as possible to the maximum limits for sweep and knots allowed by the departmental log specifications. This attempt resulted in the preparation of some logs containing slightly more than the permissible defects. Observations were made on stump surfaces of the orientation of shakes, and on log ends of their occurrence higher up in the stem, in an attempt to find a link between shake orientation and the known direction of strong winds, and to determine the height in the stem to which shakes extended from the stump. The orientation study produced no definite proof that wind was responsible, although there were strong indications.

This was followed by sowings up the logs mainly into structural timber, kiln seasoning and grading in two ways, viz A ignoring the resin-infiltrated checks and splits but taking all other defects pertinent to the relevant grades into consideration, and B taking all defects, including the checks and splits into consideration (Table 4). During the grading further measurements were taken on boards containing splits, to determine to what heights in the stem the shakes extended.

From the grading results, total and graded yields of sawn timber were computed, the differences in yields between the two grading procedures being a measure of the incidence and seriousness of the shake defect. Within log classes, (see footnote to Table 2) the yields obtained separately for each 2 cm top U.B. diameter class into which the logs had been segregated prior to sawing, were weighted according to the percentage size distributions of the logs yielded by the clearfelling and thinning operations in the relevant compartments, to obtain a weighted average for the log class.

The heights to which shakes were present in the stems of the two samples are shown in Table 3(a) while their incidence in logs of the various size classes are shown in Table 3(b). It is seen that shakes were more frequent and serious in the larger logs.

The presence of shake in the log samples, taken as a whole, caused only minimal yield losses (Table 4) but had the effect of somewhat reducing average board length (Table 5). However, sawn and graded yields are still excellent and the species should not be discriminated against in afforestation, because of the sporadic occurrence of the defect.

The yield figures should be of some value to sawmillers processing both normal and shake-containing logs of this species.     

Optimal timing of early genetic selection for sawn timber traits in <Emphasis Type="Italic">Picea abies</Emphasis>

In breeding Norway spruce, selection for improved growth and survival is performed at age 10–15 years in order to optimize genetic gain per year. We investigated whether a selection based on wood traits such as density and grain angle, measured under bark in the field at the same age would be informative enough with respect to structural quality traits of sawn boards. To achieve this objective, a sawing study was conducted on the butt logs of 401 trees from a 34-year-old Norway spruce progeny trial situated in southern Sweden. Stem discs were excised from the top of the logs and radial profile data of grain angle, and wood density was recorded for specific annual rings. The sawn and dried boards were assessed for structural traits such as twist, board density, bending stiffness (static modulus of elasticity, sMoE) and bending strength (modulus of rupture, MoR). Additive genetic correlations (r_a) between single annual ring density measurements and board density, sMoE and MoR were consistently strong (r_a>?0.7) for annual rings 5–13. Genetic correlations of similar magnitude between grain angle and board twist were estimated for all investigated annual rings (from 2 to around 26 under bark). Consequently, it was found that indirect selection for wood density and grain angle at the tree age 10–16 years would result in more genetic gain per year than selection at later ages. This makes it feasible to perform simultaneous selection of progeny in the field for both growth and wood traits at similar ages.     

Automatic detection of washboarding in bandsaws

This paper presents an on-line method for detecting washboarding generated in bandsaws. It uses a parameter based on the shape of sawing force amplitude distributions. The curve of the probability density function of the parallel sawing force amplitude obeyed a normal distribution for the normal sawn surface, but it changed to an M-shaped distribution when washboarding appeared on the sawn surface of the workpiece. The curve of probability density function of the normal sawing force amplitude obeyed the normal distribution for any sawn surface investigated. The workpiece including a knot did not influence use of the parameter for detecting the appearance of washboarding.     

Comparing predictability of board strength between computed tomography,discrete X-ray,and 3D scanning of Norway spruce logs

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.     

Variation in log quality and prediction of sawing yield in oak wood (Quercus robur)

Context

The commercial feasibility of sawmilling depends on the expected volume and value of sawn planks. Models that predict the volume of sawn timber of a particular quality and produced from logs of known characteristics are therefore very useful.

Aims

The objectives were to study variation in sawing yield and to obtain models that predict lumber volume and grade recovery on the basis of easy-to-measure predictor variables of saw logs.

Methods

Forty-six oak trees growing in Galicia (NW Spain) were felled and cut into logs. The logs were visually graded and sawn mainly into quartersawn planks, which were dried, planed and visually graded for structural purposes.

Results

The total volumetric sawing yield was 47.6 %. The sawing yield for planks of structural dimensions (cross-section, 70?×?120 or 70?×?170 mm) was 43.4 %, but decreased to 8.4 % for structural sized and quality grade beams because of wane and biotic damage in many pieces. Log grade did not significantly affect sawing yield in the sample analysed, despite the wide range of diameter over bark at the smallest end in the sampled logs (22–77 cm). The sawing pattern affected total sawing yield (F?=?4.913; p value?=?0.001) and the sawing yield for structural planks (F?=?6.142; p value?=?0.0002); radial sawing with one cut and live sawing of half logs provided the highest yields. Three models were proposed for estimating sawn volume in timber products, with the small-end log diameter over bark as the predictor variable and R _adj ² between 0.31 and 0.78 (p value?<?0.01).

Conclusion

For the purpose of producing oak timber destined for structural use, the presence of bark and sapwood in planks must be reduced in the sawing process; this would decrease the total lumber recovery but increase the timber value yield. Air drying must be accelerated to reduce biotic damage in sawn planks. Geometric mean diameter over bark at the smallest end (d) outperforms other measures as a predictor variable for total or structural sawn timber volume.     

径切板生产新工艺和新设备的研究

建立了１１种径切材下锯模型，并利用图像处理及曲面拟合方法将得到的任意形状原木进行模拟锯割，结果表明，用三开法生产径切板及旋切薄木具有较高的出材率。研制了专门用于生产三开材的剖料锯机及生产工艺。在现有的带锯机前安装该剖料锯机即能利用现有锯机和跑车生产径向材。     

Evaluation of non-destructive methods of measuring growth stress in Eucalyptus globulus: relationships between strain, wood properties and stress

High levels of growth stress are implicated in causing end splitting of logs, deflection during sawing and deformation of boards as stresses are released during sawing operations. Level of stress is a function of strain and the elastic modulus of the wood (MOE). Levels of peripheral strain can be measured on standing trees and, if the MOE is known, stresses can be estimated. The validity of using peripheral strain measurements relies on underlying theoretical models that relate strain to expected patterns of stress distribution and levels of board deflection. This study evaluates these theoretical relationships by determining relationships of stress and strain with board deflection, end splitting and a range of wood properties.

Peripheral strain levels were extremely variable within the bottom log and little evidence was found for consistent patterns of variation, although measurements generally increased with increasing height above ground. Sampling on two sides of the standing tree at breast height appeared to be a suitable strategy, with the mean for these strain readings having a correlation (r) of 0.86 with the average strain in the bottom log.

Growth strain was not a reliable predictor of board deflection and cannot be recommended as a non-destructive sampling method. Overall there was a poor relationship between growth strain and board deflection. No consistent relationships were found between a range of wood properties and growth strain or board deflection across both sites. Stress levels were calculated for each tree as the product of growth strain and modulus of elasticity and the relationship between calculated stress and mean board deflection determined. No relationship was found at either site with correlations being very close to zero.

The underlying theoretical relationships between stress and strain were examined and several questions raised about the validity of such models.     

Prediction of Board Values in Pinus sylvestris Sawlogs Using X-ray Scanning and Optical Three-dimensional Scanning of Stems

As the sawmill industry strives towards customer orientation, the need for sorting of logs according to quality has been recognized, and automatic sorting based on measurements by three-dimensional (3D) optical log scanners has been implemented at sawmills. There is even a small number of sawmills using the X-ray log scanner for automatic log-sorting. At the log-sorting stage, the potential of the raw material to fulfil the needs has already been reduced by the decisions taken when the trees were bucked (cross-cut) into logs. Thus, the application of predictions of the boards’ properties at the bucking stage is desirable. This study investigates the possibility of predicting board values from logs based on 3D scanning alone and 3D scanning in combination with X-ray scanning of stems. This study is based on 628 logs scanned by computed tomography that make up the Swedish Pine Stem Bank. Simulated sawing of the logs gave product values for each log. Prediction models on product value were adapted using partial least squares regression and x-variables derived from the properties of the logs and their original stems, measurable with a 3D log scanner and the X-ray LogScanner. The results were promising. Using a 3D scanner alone, R ² was 0.68, and using a 3D scanner in combination with an X-ray LogScanner, R ² was 0.72.     

Optimization potential for perception-oriented appearance classification by simulated sawing of computed tomography-scanned logs of Norway spruce

Abstract

Wood, as a natural material, has favourable properties in both technical and aesthetic aspects. Due to its inherent variability, production of high-quality sawn timber demands adequate control of log conversion, which is feasible with computed tomography (CT) log scanning. Existing appearance grading rules for sawn timber might not fully reflect people's visual perception of wood surfaces, and therefore, an alternative, more perception-oriented appearance classification could be beneficial. An appearance classification of sawn timber based on partial least squares discriminant analysis (PLS-DA) of knot-pattern variables was developed and tested. Knot-pattern variables derived from images of board faces were used in training PLS-DA models against an initial classification of the board faces previously established by aid of cluster analysis. Virtual board faces obtained from simulated breakdown of 57 CT-scanned Norway spruce logs were graded according to the developed classification. Visual assessment of the grading results indicated that the classification was largely consistent with human perception of board appearance. An initial estimation of the potential to optimize log rotation, based on CT data, for the established appearance grades was derived from the simulations. Considerable potential to increase the yield of a desired appearance grade, compared to conventional log positioning, was observed.     

弯曲原木材积测定的实用近似公式探讨

本文采用柱坐标,以椭圆—阿基米德螺线包络组成解析曲线椭圆柱体的弯曲原木的数学模型。定义它为C型弯曲。并以材长和弯曲弓背长度定义,提出了一个实测参数的弯曲原木材积计算公式。定量地解决了弯曲造成原木材积统计时的损失。这种方法和理论,可以解决弯曲原木最佳出材率和弯曲原条最佳截断问题。为制材的数控软件编制提供了理论基础。     

Stiffness gradients in radiata pine trees

A mill study of 62 trees, in which boards were reassembled into their original logs, permitted the construction of wood quality maps. In this instance stiffness profiles were obtained from butt to upper-top logs, based on machine stress grading of all boards and then averaging values from the 62 trees. Traditionally the butt log has been perceived to be the most valuable log in a tree, because it is bigger and gives a higher recovery of lumber. However, it is shown to contain a wide cone of very low stiffness wood that is confined to the first 2.4–2.7 m above ground level. Above this point stiffness gradients become cylindrical with no noticeable decrease in stiffness up the tree stem. Stiffness in all logs increased radially from pith to cambium with the greatest change being associated with the wood nearest the pith. The low stiffness at the base of the tree suggests that an alternative log bucking strategy should be considered, namely cutting a short 2.4–2.7 m butt log for plywood/LVL or for bolter sawing and only cutting standard length logs above this point.The least stiff logs (lowest 20%) yielded lumber that had an average stiffness that was over 1 GPa less than the average for the population. A case can be made for separating these logs and processing them differently.