Optical measurement of wood grain direction

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The successful running of a sawmill depends critically on its ability to achieve the highest possible value recovery from the highly variable raw material. Accurate material evaluation is essential to make this happen, else good wood will end up underutilized and inferior wood will fail to meet specifications. Wood grain direction is a primary quality-controlling feature of wood. It strongly affects wood strength, most commonly in the distorted grain around knots and in spiral grain. A grain deviation of just 15 degrees can halve wood strength. This project uses an optical approach to measure wood grain direction. The cellular structure of the wood grain causes directional reflection of light from the wood surface in the direction perpendicular to the grain. It is this behaviour that gives polished wood its characteristic sheen. This directional reflection response of light can be exploited to determine grain direction in three dimensions, both the surface and diving grain angles. Previously, some grain angle detectors were developed that made optical measurements at discrete points along a circular line. These could give only a limited view of the surface reflection. The approach proposed here is to exploit the capability, speed and low cost of modern CCD camera technology to make full maps of the light reflection from a wood surface and to develop a practical wood grain angle sensor suitable for industrial use.