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| 2. |
- Ah Shenga, Pedro, et al.
(författare)
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3D Phase-shift Laser Scanning of Log Shape
- 2014
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 9:4, s. 7593-7605
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a portable scanner to determine the 3D shape of logs was evaluated and compared with the measurement result of a computer tomography scanner. Focus was on the accuracy of the shape geometry representation. The objective is to find a feasible method to use for future data collection in Mozambique in order to build up a database of logs of tropical species for sawing simulations. The method chosen here was a 3D phase-shift laser scanner. Two logs, a birch log with bark and a Scots pine log without bark, were scanned, resulting in 450 cross sectional “images” of the pine log and 300 of the birch log. The areas of each point cloud cross section were calculated and compared to that of the corresponding computer tomography cross section. The average area difference between the two methods was 2.23% and 3.73%, with standard deviations of 1.54 and 0.91, for the Scots pine and birch logs, respectively. The differences in results between the two logs are discussed and had mainly to do with presence of bark and mantle surface evenness. Results show that the shape measurements derived from these methods were well correlated, which indicates the applicability of a 3D phase-shift laser scanning technology for gathering log data.
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| 3. |
- Ah Shenga, Pedro António, et al.
(författare)
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External Log Scanning for Optimizing Primary Breakdown of Tropical Hardwood Species
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The sawing of tropical hardwood species is a big challenge for sawmills in developing countries. In order to investigate sawing strategies and volume recovery of tropical hardwood species, a log shape database was created using a portable 3D laser scanner. The data were collected in Mozambique, where twelve Jambirre (Millettia stuhlmannii Taub.) and five Umbila (Pterocarpus angolensis DC) logs were scanned. The logs were selected among the most commercialized species and the crook was the main selection parameter. In addition, straight logs were incorporated as reference. A saw simulation Matlab algorithm that combines skew and rotation was developed. The results show that point cloud data from the 3D scanner provide detailed models of the external log geometry and accurately describe the log shapes and volumes. Preliminary results from breakdown simulation revealed that the through-and-through sawing pattern yields more than the cant saw pattern and that the increase in yield was almost the same for both species.
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| 4. |
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| 5. |
- Ah Shenga, Pedro António, et al.
(författare)
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Simulated Breakdown of Two Tropical Hardwood Species
- 2015
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Ingår i: Pro Ligno. - 1841-4737 .- 2069-7430. ; 11:4, s. 450-456
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Tidskriftsartikel (refereegranskat)abstract
- A simulation study has been performed on a small log database of tropical hardwoods consisting of 10 Jambirre (Millettia stuhlmannii Taub.) and 5 Umbila (Pterocarpus angolensis D.C.) logs. The outer log shape was acquired by a 3D laser scanner before sawing and the heartwood content was estimated by measurement on images of the centre slabs after through-and-through sawing. Yield and value recovery using different sawing techniques and different sawing patterns, together with rotational and skew positioning errors, are presented. The results show that through-and-through sawing in the best rotation and skew positions tested improves the yield of Umbila logs by an average of 4.5 percentage points and Jambirre logs by 3.6 percentage points compared to cant sawing. It can be concluded that positioning and sawing patterns have a great influence on the yield and value recovery of these species and that log grade and species have an impact on the sawing pattern that should be used.
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| 6. |
- Ah Shenga, Pedro, et al.
(författare)
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Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield
- 2017
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 12:4, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Ah Shenga, Pedro
(författare)
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SAWING STRATEGIES FOR TROPICAL HARDWOOD SPECIES : Simulation studies based on industrial conditions of Mozambique
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The harvesting of Mozambique tropical hardwood species is considerable higher than the natural regrowth in the forest and the stock is decreasing drastically. Therefore, it is important to improve the material recovery when the wood is refined (i.e., in sawing and further refinement to products such as joineries, furniture etc.) to reduce the waste and to re-utilize efficiently the by-products to increase the added value. The wood processing industry is an important means to boost the industries in the rural areas and also to generate incomes for the local communities by creating jobs and business opportunities.The majority of the logging that can be used for sawmilling in Mozambique is exported as roundwood due to the inability of companies to meet the product standards set for export and to generate profit. The lack of capabilities of the local sawmills to generate profit, also foments the illegal logging because of the higher price of roundwood for export which contributes to increase the number of unlicensed individuals in harvesting. This threatens the law enforcement and thus the degradation of the local wood industry. An alternative to increase the profit and empower the local community could be to export more refined wood products such as sawn timber, parquet, and veneer instead of the roundwood.The objective of the work was to investigate alternative sawing strategies of tropical hardwood species that could increase the profitability of the Mozambique wood industry in general and at sawmill in particular. The subject was approached using a database of virtual logs and together with a sawing simulator. The thesis has two main focus areas: (1) creating the log database with the corresponding algorithms for sawing simulation, and (2) investigations of alternative sawing strategies.The first focus was to build the database of surface-scanned logs and develop the algorithm for the saw simulation. The results are a database of 15 logs models describing the logs outer shape in which 10 jambirre (Millettia stuhlmannii Taub.) and 5 umbila (Pterocarpus angolensis DC.), and the algorithm for the sawing simulation. The algorithm use “brute force” i.e., determines all volume yields of sawn timber from the combination of all settings of log-positioning parameters (offset, skew and rotation) and selects the maximum value of volume yield. From simulation, using three sawing patterns (cant-sawing, through-and-through sawing and square-sawing) combined with two positioning parameters (offset and rotation) it was found that the sawing pattern has great impact on volume yield and that the square-sawing gave higher yield followed by through-and-through sawing pattern.The second focus was on alternative sawing strategies; having in mind that the optimal volume yield is achieved by aid of computerized production systems and that these resources are not yet in use in Mozambique. Hence, the objective was to find the positioning parameters that can be set manually and improve the volume yield. The result have shown that the rotation is the most affecting parameter followed by offset and skew, and that the volume yield can decrease by between 7.7% and 12.5% from the optimal positioning when the logs are manually positioned with the knowledge about the optimal log position. In another study, using crook-up or horns-down positioning as alternative to the optimal positioning, the volume yield decreases by between 10% and 13% from the optimal positioning. By using bucked logs , the optimal volume yield increased by between 8% and 13% in relation to full lengths logs, and the volume yield of bucked logs when using crook up positioning decreases 2% in relation to optimal positioning of full length logs.It is concluded that there is an unexploited value potential in the wood chain which can be reached using alternative positioning and modern measurement techniques and that the grading of wood will facilitate and improve the sawing process.
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| 8. |
- Ah Shenga, Pedro, et al.
(författare)
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Simulation of Tropical Hardwood Processing – Sawing Methods, Log Positioning, and Outer Shape
- 2015
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 10:4, s. 7640-7652
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Tidskriftsartikel (refereegranskat)abstract
- To increase understanding of breakdown strategies for Mozambican timber, simulations were carried out using different sawing patterns that can be alternatives to the low degree of refinement performed for export today. For the simulations, 3D models of 10 Jambirre and 5 Umbila logs were used. The log shape was described as a point cloud and was acquired by 3D-laser scanning of real logs. Three sawing patterns (cant-sawing, through-and-through sawing, and square-sawing) were studied in combination with the log positioning variables skew and rotation. The results showed that both positioning and choice of sawing pattern had a great influence on the volume yield. The results also showed that the log grade had an impact on the sawing pattern that should be used for a high volume yield. The volume yield could be increased by 3 percentage points by choosing alternative sawing patterns for fairly straight logs and by 6 percentage points for crooked logs, compared to the worst choice of sawing pattern.
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| 9. |
- Ah Shenga, Pedro, et al.
(författare)
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The Effect of Log Position Accuracy on the Volume Yield in Sawmilling of Tropical Hardwood
- 2016
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 11:4, s. 9560-9571
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the effect of the positioning of the log before sawing on the volume yield of sawn timber from tropical hardwood species. Three positioning parameters were studied, the offset, skew, and rotation, combined with two sawing patterns of cant-sawing and through-and-through sawing. A database consisting of two tropical hardwood species with very different outer shapes, jambirre (Millettia stuhllmannii Taub.) and umbila (Pterocarpus angolensis DC.), was used to simulate the sawing process. The result of the simulation revealed that, according to the combined effect of offset, skew, and rotation positioning, the positioning of the log before sawing is extremely important to achieve a high volume yield of sawn timber. The positioning parameter that has the highest effect on the volume yield is the rotation, and the variation in the volume yield associated with a deviation in the positioning can reduce the volume yield of sawn timber by between 7.7% and 12.5%.
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| 10. |
- Berglund, Anders, et al.
(författare)
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Customer adapted grading of Scots pine sawn timber using a multivariate method
- 2015
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 30:1, s. 87-97
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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