Surface roughness estimation of wood boards using speckle interferometry

Abstract

A problem present in the wood boards industry is the lack of knowledge of its roughness. The roughness causes the formation of voids between the board and the protective cover commonly used to give a special finish to the board. This leads to poor adhesion between the adhesive and the cover which affects the quality of the final product. Thus, a precise and fast way to measure the roughness that allows characterization in line and across the board is required.Speckle interferometry is a widely used technique to perform non-invasive measurements, mainly by illuminating objects under study with coherent light. In this study, laser speckle interferometry is used to determinate surface roughness in different wood boards. The proposed method uses an optical system and an image processor that correlates a series of successive images of intensity speckle pattern. These images are obtained varying the illumination angle.In order to obtain the roughness parameters of the boards, the measured correlations were adjusted to a theoretical function by using a numerical regression algorithm. The obtained values of roughness for different boards varied between 1.55 µm and 12.69 µm. Our results show a good agreement with the measurements obtained using conventional methods.Finally, we present a discussion of how laser speckle interferometry can be adapted to characterize roughness during production in real time and in wide area boards.