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Abstract

Wood grain direction is a very important quality control feature in wood industry because it is a good indicator of wood strength and uniformity. It is a three-dimensional quantity that is defined by its angles within and into the plane of the measured surface. These are respectively called the surface and dive angles. An interesting method to measure these angles involves measuring the spatial reflection from the wood surface when illuminated by concentrated light. The cellular shape of the wood microstructure causes the light reflection to be greatest perpendicular to the wood grain. This effect allows the surface and dive angles to be determined by analyzing the spatial variation of the reflected light. The conventional method for doing this involves sampling the reflection intensities around a circle above the wood surface. However, this method is effective only for small dive angles. A new method is described here where light reflection intensity variation is measured along two parallel lines on either side of the illuminated area. It is able to measure the full ranges of surface and dive angles that occur in practice. A laboratory device for making the required spatial reflection measurements is described and experimental results are presented. Based on the linear method, an equipment can be developed for industrial purpose, which consists of two parallel lines of sensors sparsely distributed along the longitudinal axis of lumber. To investigate this proposed arrangement of sensors, an interpolation study was undertaken on the associated low-resolution data, with the results compared with those from high-resolution full-field data. With the proposed sensor arrangement, grain angle measurements can be made at very high speed, which makes the equipment suitable for industrial use in sawmills and wood products factories.