Laboratory apparatuses measuring 3D displacement fields involved in distortion of commercial size wood products due to moisture content change

摘要

Two apparatuses developed in our laboratory and based on the same principle are described and tested. They semi-automatically acquire the 3D location of dots making up a network at the surface of wood-products in order to measure the resulting displacement field. The location of each dot is achieved by means of an image analyser coupled with a 2-axis robot to determine the location of the barycentre in the corresponding plan. The third co-ordinate is obtained through a displacement sensor. The accuracy of each device is studied and discussed through the analysis of repeated measurements performed on three products such as: small oak plank (150x120x27 mm), commercial size oak plank (1930x150x30 mm), 3ply cross-laminated douglas fir panel (390x390x6 mm). Two kinds of testing are performed: A-Test without motion of the sample to assess the accuracy in dot detection, and B-Test corresponding to a real measurement where no variation of moisture content has occurred and which theoretically leads to displacements equal to zero.