Automatic measurement of wood fiber orientation and knot detection using an optical system based on heating conduction

Vincent Daval,Mohamed Belkacemi,Fabrice Meriaudeau,Robert Collet,Guillaume Pot

doi:10.1364/oe.23.033529

Abstract

In this paper, a new approach to computing the deviation of wood grain is proposed. To do this, the thermal conduction properties of timber are used (higher conduction in the fiber direction). Exciting the surface of the wood with a laser and capturing the thermal conduction using a thermal camera, an ellipse can be observed. Using a method similar to the tracheid effect, it is possible to extract information from this ellipse, such as the slope of grain and the presence of knots. With this method it is therefore possible to extend the mechanical model (assessing the mechanical properties of timber) to take certain singularities into account. Using this approach, the slope of grain can be estimated for any wood species, either hardwood or softwood, which was not possible with the existing tracheid effect.

Highlights

Since 2010 in the European Union, wood used for structural purposes must satisfy several mechanical requirements
the slope of grain can be estimated for any wood species
Wood must therefore be mechanically graded to ensure that the product complies with the requirements

Summary

Introduction

Since 2010 in the European Union, wood used for structural purposes must satisfy several mechanical requirements. Mechanical grading of timber must guarantee three properties [1]: density, modulus of elasticity (MOE) and bending strength called modulus of rupture (MOR). Machines can be used to perform the mechanical grading of wood, in accordance with the relevant European standards [2,3,4,5].Wood grading machines are based on various principles, such as density measurement, vibrational measurement of the MOE [6,7,8] or singularity detection using optical means, X-rays, or scattering measurement techniques [9,10,11]. A recent study [12] shows that for a species with large knots (such as douglas fir produced in southern Europe), a mechanical model based on local measurements of singularities, and grain slope measurements, significantly improves MOR prediction, since timber strength decreases non-linearly as the slope of grain increases [13]

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