Anders Grönlund

Simulated grading of logs with an X-ray Log Scanner : Grading accuracy compared with manual grading

Today sawmills have started to use automatic methods for log grading. The methods used are either optical or gamma‐ray scanners. However, the signals from these scanners are too coarse for accurate...

Measuring the outer shape of Pinus sylvestris saw logs with an x-ray LogScanner

The accuracy of measuring the outer shape of Scots pine (Pinus sylvestris L.) saw logs with an X‐ray LogScanner has been compared with the accuracy of using a 2‐axis optical scanner, a 3‐axis optical scanner and an ideal 3‐D optical scanner. The different scanners were simulated using computed tomography (CT) data from the Swedish Stem Bank. The outer shape of 60 saw logs was measured every third centimeter. The error attributable to bark when using optical scanners was simulated separately. The results from the simulations showed that when measuring the outer shape on bark, the X‐ray LogScanner facilitated measurement of the minimum shadow diameter with the same accuracy as with a 3‐D optical scanner. The results also showed that the potential of combining the X‐ray LogScanner with a 3‐D optical scanner should be investigated.

Increased Yield in Sawmills by Applying Alternate Rotation and Lateral Positioning

Modern sawmills are increasingly like process industries, running continuously with very large volumes flowing through the process every second. This fact makes it vital for every company to utilize its equipment and raw material as effectively as possible to maximize yield and value. The objective of this simulated breakdown study was to analyze the potential to increase volume yield in Swedish sawmills. While the commonly used horns-down position performs well on an average basis, the results show that the optimal rotation position for an individual log is most often found at another position. Results from extended simulations show that the average volume yield can be increased further by applying the optimal combination of rotation and parallel positioning in cant and deal saw. An increase in average volume yield by 4.5 percentage points (8.6%) would enable a typical Swedish sawmill to produce a further 17,300 m 3 of boards per year and thereby increase potential annual income by US

Automatic grading of Scots pine (Pinus sylvestris L.) sawlogs using an industrial X-ray log scanner

3.7 million per year. This optimization concept requires a preevaluation of every log in order to define the optimal combination of settings. Some of these procedures must be performed online within a split second to accommodate production speed demands. Modern technology such as industrial x-ray in combination with traceability methods, multivariate models, breakdown simulation software, and high-performance computers enables evaluation and optimization of every log online at full production speed. Sawing machines will need development in order to be able to perform optimization online without loss of production capacity.

Predicting board strength by X-ray scanning of logs: The impact of different measurement concepts

Abstract The successful running of a sawmill is dependent on its ability to achieve the highest possible value recovery from the sawlogs, i.e. to optimize the use of the raw material. Such optimization requires information about the properties of every log. One method of measuring these properties is to use an X-ray log scanner. The objective of the present study was to determine the accuracy when grading Scots pine ( Pinus sylvestris L.) sawlogs using an industrial scanner known as the X-ray LogScanner. The study was based on 150 Scots pine sawlogs from a sawmill in northern Sweden. All logs were scanned in the LogScanner at a speed of 125 m/min. The X-ray images were analyzed on-line with measures of different properties as a result (e.g. density and density variations). The logs were then sawn with a normal sawing pattern (50×125 mm) and the logs were graded depending on the result from the manual grading of the center boards. Finally, partial least squares (PLS) regression was used to calibrate statistical models that predict the log grade based on the properties measured by the X-ray LogScanner. The study showed that 77–83% of the logs were correctly sorted when using the scanner to sort logs into three groups according to the predicted grade of the center boards. After sawing the sorted logs, 67% of the boards had the correct grade. When scanning the same logs repeatedly, the relative standard deviation of the predicted grade was 12–20%. The study also showed that it is possible to sort out 10 and 16%, respectively, of the material into two groups with high quality logs, without changing the grade distribution of the rest of the material to any great extent.

Main cutting force models for two species of tropical wood

Abstract The objective of this study was to compare the individual board strength predictions from an X-ray log scanner by using either two or four X-ray directions. The benefit of applying traceability between log and board was also studied. In total, 119 Norway spruce [Picea abies (L.) Karst.] sawlogs were scanned by an X-ray log scanner at the log sorting station of a sawmill and sawn into two centre pieces per log. Individual board traceability was enabled by following the rotational position of the log in the scanner and at the succeeding sawing. All boards were graded by a commercial strength grading machine before destructive testing was done. The resulting data were used to derive variables for building multivariate partial least squares strength prediction models. In the modelling a hierarchical modelling approach was used, where annual ring width, dry density and elasticity were also modelled. For all concepts studied the models’ fit was similar. Only minor benefits could be found when using four directions and traceability compared with two directions and no traceability. One conclusion is that the result for traceability, from four directions in particular, is more sensitive for the interior knot reconstruction result. The strength prediction was on the same R 2 level as for the strength grading machine.

The fingerprint method: Using over-bark and under-bark log measurement data generated by three-dimensional log scanners in combination with radiofrequency identification tags to achieve traceability in the log yard at the sawmill

Abstract The aim of the study was to evaluate the main cutting force for two species of tropical Mozambican wood and to develop predictive models. Cutting these hardwoods is difficult. Determination of cutting parameters is required to optimize cutting processes, machines and tools in the cutting operations. This determination would enable the forestry and wood sector to achieve higher financial results. Samples of a lesser-known wood species Pseudolachnostylis maprounaefolia (ntholo) and a well-known wood species Swartzia madagascariensis (ironwood) were machined in a test apparatus. A standard single saw tooth mounted on a piezoelectric load cell was used to evaluate the main cutting force. Data were captured using an A/D converter integrated with National Instruments LabVIEW software. The measured signals were recorded at a sampling frequency of 25 kHz. The experimental set-up used response surface methodology for developing predictive models. The experimental clearly determined the relationship between the main cutting force and edge radius, wood density, rake angle, chip thickness, moisture content (MC) and cutting direction (CD). Among the studied variables, chip thickness and CD had the highest effect on the main cutting force level while wood density, MC and rake angle had the lowest effect.

Predicting spiral grain by computed tomography of Norway spruce

In the forestry–wood chain the concept and the technologies of traceability are in a mature development phase. Important advances in marking and reading techniques have been made in different parts along the forestry–wood chain. For Swedish sawmills the most critical information gap is located between the log sorting station and the saw intake, where the forest log batch identity disappears and the logs are mixed according to different sorting criteria. This study utilizes radiofrequency identification tags for automatic log marking/reading to develop a traceability system for logs, which is free of marking/reading, between the log sorting station and the saw intake, i.e. the fingerprint method. The originality of the fingerprint approach rests on the hypothesis that logs are separate entities with individual features. The results show that the log parameters and the search algorithm developed, combined with the negative influence of the measurement uncertainty due to bark thickness and bark damage, made it possible to achieve an individual separation for 57% of the tested logs.

Tool wear for lesser known tropical wood species

Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. The aim of this study was to investigate the possibility of predicting spiral grain based on variables that should be measurable with an X-ray LogScanner. The study was based on 49 Norway spruce (Picea abies) logs from three stands in Sweden. The logs were scanned with a computed tomography (CT) scanner every 10mm along the log. Concentric surfaces at various distances from the pith were then reconstructed from the stack of CT images. The spiral grain angle was measured in these concentric surface images, and a statistical model for predicting spiral grain was calibrated using partial least squares (PLS) regression. The PLS model predicts the spiral grain of a log at a distance 50mm from the pith based on different variables that should be measurable with an industrial X-ray LogScanner. The result was a PLS model withR2=0.52 for the training set andR2=0.37 for the test set. We concluded that it should be possible to predict the spiral grain of a log based on variables measured by an industrial X-ray LogScanner. The most important variables for predicting spiral grain were measures of sapwood content, variation in the ratio between the heartwood and log areas, and the standard deviation for the mean log density in 10mm thick cross slices along the log. The accuracy when sorting the logs into two groups with spiral grain of ≥2.0° and of <2.0°, respectively, was 84% of the correctly sorted logs.

Modelling of adequate pretwist for obtaining straight timber

Abstract This study investigated the relationship between tool wear and some chemical and physical properties for four different Mozambican lesser known tropical species,: Pseudolachnostylis maprounaefolia (ntholo), Sterculia appendiculata (metil), Acacia nigrescens (namuno) and Pericopsis angolensis (muanga). Tool wear is an important aspect for sawmilling and for the woodworking industry. For Mozambique, the utilization of available lesser known wood species will help to increase domestic industry and the economic usage viability of sustainable forest management. A set of experiments was performed on a shaper with a mechanical feed mechanism. Tools of a cemented carbide grade for woodworking were used, and the cutting parameters were fixed. Edge recession and tool wear radius were measured for monitoring tool wear. The wear mechanism was investigated using a scanning electron microscope. The experimental results showed that the chemical properties of the wood species have a great effect on tool wear. Wood silica content was the most important factor affecting tool wear. Wood density and extractives had a low influence on tool wear. The highest tool wear was observed in ntholo, which also had the highest ash and silica contents. A single parameter for evaluation of tool wear was not sufficient to describe the amount of total tool wear.