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Measurement of OSB strand size and orientation - image processing methods, implementation, and experiences with production monitoring

: Plinke, B.

BioComposites Centre, Bangor:
Eighth Panel Products Symposium 2004. Proceedings : Llandudno, Wales, UK, 13th, 14th and 15th October 2004
Bangor: The BioComposites Centre, 2004
ISBN: 1-8422-0071-2
European Panel Products Symposium <8, 2004, Llandudno>
Conference Paper
Fraunhofer WKI ()

Strands for OSB show certain geometric properties which are influenced by the flaking process. Strand shape, orientation and homogeneity during mat forming are crucial quantities which determine the board quality. These properties are usually evaluated by visual assessment of single strands, of the mat before pressing or of the board surface because on-line measurement methods for OSB strands and mats are not yet state of the art. At Fraunhofer WKI off-line and on-line evaluation methods based on image processing have been developed and tested to close this gap. If manual handling and separating of strands is acceptable, then size and shape measurement can be performed using a low-cost flat-bed scanner for image acquisition. For each individual strand its parameters such as length, width, area, length/width ratio and form factors to characterize the "rectangularity"can be achieved and used to classify the stands and to compute frequency distributions. This method is useful e.g. for control measurements in the lab and /or for measurements to optimize the flaking process. For on-line measurements, separating of strands is not possible, but parameters to characterize strand orientation and size distribution can be computed from images showing a cut-out of the mat. Strand orientation correlates with the orientation of edges of a grey tone image of the scene. By transformation of the image into the frequency domain a contour image can be obtained which also correlates well with the deviation of the strand orientation angles form the making direction. Size distribution of strands can be derived using a multi-step processing sequence which separates those parts of the strands which are visible in the top view. Software using these methods had been developed and tested. These approaches do not require that every single strand is recognized as an individual particle and then measured. They do not produce statistics for individual particle parameters but indices which characterize the production process and which are useful for monitoring. However, this is a novel and unusual view and needs calibration to the "true" distribution of particle size and orientation. Actual results of field tests with these methods to characterize OSB strands are reported.