Geometry-based CT scanner for measuring logs in sawmills

• Presents an X-ray CT scanner for log measurement suitable for industrial use.
• Uses geometry-based voxels to guide and stabilize the feature identification.
• Coarse spatial and density resolutions allow the use of simple algebraic inversion.
• Good results can be achieved using relatively low quality data.
• A laboratory prototype has been constructed and successfully demonstrated.

Significant economic advantage can be achieved by assessing logs at the inlet of a sawmill so that they can be optimally processed to produce the highest possible value products from the available raw material. Computed Tomography (CT) scanning is of particular interest because it can identify the locations and sizes of internal quality-controlling features such as knots, heartwood/sapwood extent, rot, cracks and holes. Conventional CT scanning is based on medical-style equipment, which needs to have very high spatial and density resolution. This need sets very high requirements on the measurement resolution and accuracy, and substantially increases equipment complexity and cost. These features make such equipment unsuited for typical sawmill applications. However, for log scanning applications, high spatial and density resolution and measurement accuracy are not needed because most targeted internal features are fairly large and have specific geometrical shapes. Based on this thought, this paper proposes a novel geometry-based CT reconstruction approach and corresponding density reconstruction algorithms. A prototype CT scanner was built and the CT reconstructions were determined by processing the measured data using the proposed density reconstruction approach. The results obtained compare well with the results computed from conventional CT reconstruction. The good comparison gives confidence in the usefulness and applicability of the proposed CT approach for industrial use in sawmills for log scanning.

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