Magnus Fredriksson

Log sawing position optimization using computed tomography scanning

Abstract 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.

Validating a crosscutting simulation program based on computed tomography scanning of logs

Wood scanners and software for calculating crosscutting positions have been used in the wood industry for some years now. The scanners are used to detect biological and geometrical deviations on the sawn timber, which makes it possible to remove undesired defects using crosscut saws. Yield calculations for crosscutting have not been investigated to the same extent as sawing yield calculations for primary breakdown of logs, especially if the whole chain from log to end product is considered. The objective of this study was to validate the result of a computer program developed for simulating crosscutting of boards. The crosscut simulations were performed with respect to knot characteristics on Scots pine (Pinus sylvestris L.) board surfaces. Validating a crosscutting simulation program would mean that it can be used to investigate how raw material and customization of quality rules affect the yield in a wood production chain from log to crosscut end product. The validation showed that crosscutting yield for boards could be predicted with a root mean square error of 13 percentage points, and the technique can be used to identify unsuitable logs for a certain product at an early stage of production.

Wood material features and technical defects that affect yield in a finger joint production process

Abstract A cost efficient process is the goal of all production, and each manufacturing step affects the material utilization and cost efficiency. There is high diversity in the inherent features of wood, and manufacturing steps must be able to handle this. The overall objective was to study the potential and problems in manufacturing production processes in terms of material utilization efficiency. The production of finger jointed bed sides was chosen as a study case, where the chain of production units are the sawmill, finger joint plant and furniture plant. This article describes the impact of raw material and wood defects that could affect the total yield. A total of 177 logs of three types were tested: butt, intermediate and fresh knot logs. The test material quality was detected and measured through all steps in the manufacturing chain. The results show differences between log types in down-grade causes, reject volume and final yield. Also, the test material showed high levels of defective components with process-related defects, which suggested the need for technical improvement in the manufacturing process. The intermediate log group showed the overall best result.

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.

Rotational position of curved saw logs and warp of the sawn timber

Abstract With the development of scanning technology in sawmills, it is possible to optimise log rotational position when sawing. However, choosing a different rotational position than horns down might be detrimental for the board shape after drying, especially for curved logs. Thus, there is a need to investigate at what level of log curve it is possible to freely rotate logs without causing board warp. This study was carried out through a test sawing that was conducted at a sawmill situated in the middle of Sweden. The tests were made on 177 Norway spruce logs, with varying amount of curve. Half of the logs were sawn in the horns-down position, half were sawn rotated perpendicular to horns down. Log shape and warp of the dried boards were measured. The results indicated a relationship between board spring, log curve and choice of rotational position. Furthermore, board bow was related to log curve but not rotational position. It can be concluded that for straight logs, with a bow height of less than 15 mm, an unconventional rotational position does not cause excess spring in the boards. Bow and twist are not affected by the rotational position at all.

Potential for increasing volume yield by reducing planing allowance

ABSTRACT About half the volume of sawlogs ends up as sawn and planed timber. The rest is lost due to drying shrinkage or is turned into by products. As the raw material is a major expense for a sawmill, it is important to reduce waste. To investigate how much the volume yield in the production of sawn and planed timber could be increased by reducing the target dimensions in the sawing stage in a sawmill, two groups of sawn timber were planed under similar conditions. One group consisted of sawn Scots pine timber with a large variation in twist. The other group consisted of sawn Norway spruce timber planed under different pressure settings. Using X-ray images, the minimum dimension for avoiding planer misses was calculated for each board, to find the smallest green target dimension. This was compared to actual measured dimensions. It was found that most sawn timber had unnecessarily large dimensions, and it was also found that a reduction in the target dimensions could increase the volume yield for sawn and planed timber by more than 3 percentage points. Boards with large twist would however need a higher planing allowance. The effect of the planer pressure setting was negligible.

Handling positioning errors when optimizing sawing of Scots pine and Norway spruce logs using CT scanning

Since computed tomography (CT) X-ray scanning is becoming a reality in sawmills, different studies have been made to establish how well the sawing position of a log can be optimized using CT data. It is also known that positioning errors have an adverse effect on optimization, since the optimization methods used are rather sensitive to positioning errors. To mitigate the effect of positioning errors, a method is proposed in this article that filters results produced by sawing simulation, using a Gaussian filter of a size according to the positioning error. Using these filtered values for optimization, it is possible to retain two percent extra value of the sawn timber, when rotation and offset errors are present, compared to a regular optimization method. A method more robust to positioning errors is more useful in practice, since positioning errors of various magnitudes are always present in sawmills. The main contribution of this paper is, therefore, an optimization method that reduces the effect of positioning errors.