Abstract
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 (150×120×27 mm), commercial size oak plank (1930×150×30 mm), 3ply cross-laminated douglas fir panel (390×390×6 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.
Zusammenfassung
Zwei Geräte wurden zu diesem Zweck entwickelt, die auf demselben Prinzip beruhen und die hier beschrieben und getestet werden. Sie registrieren die 3D-Position von Messpunkten auf der Oberfläche von Holzprodukten und messen anhand dieses Netzwerks das Verformungsfeld. Die Position der Messpunkte wird mittels Bildanalyse bestimmt. Ein zweiachsiger Roboter bestimmt dabei den Schwerpunkt der entsprechenden Ebene. Die dritte Koordinate wird über einen Dehnungssensor ermittelt. Die Genauigkeit der beiden Geräte wird untersucht und diskutiert anhand wiederholter Messungen an drei Proben: kleines Eichenbrett (150×120×127 mm), handelsübliches Eichenbrett (1930×150×30 mm) und dreilagiges Sperrholz aus Douglasienfurnier (390×390×6 mm). Zwei Prüfverfahren wurden durchgeführt: A-Test ohne Bewegung der Probe, um die Genauigkeit der Bestimmung der Messpunkte abzuschätzen sowie B-Test entsprechend einer realen Messung ohne Feuchteänderung, wobei theoretisch eine Verformung von Null zu erwarten ist.
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Acknowledgements
The authors are grateful for the financial support provided by the French Forestry Service (ONF) during the research contract "Silviculture and wood quality in sessile oaks "(Co-ordinator: Gérard Nepveu) during the period 1992–1998, and the European Commision during the EU FAIR project Oak-key 1996–1999 (CT 95-0823) "New silvicultural alternatives in young oak high forests. Consequences on high quality timber production "(Co-ordinator: Francis Colin). The experimental part of this work was achieved with the help of Claude Houssement.
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Constant, T., Farré, É. Laboratory apparatuses measuring 3D displacement fields involved in distortion of commercial size wood products due to moisture content change.. Holz Roh Werkst 61, 173–181 (2003). https://doi.org/10.1007/s00107-003-0370-0
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DOI: https://doi.org/10.1007/s00107-003-0370-0