Thermographic, ultrasonic and optical methods: A new dimension in veneered wood diagnostics

Modern production techniques in the wood-based industry reached a high quality standard at high output rates. While the speed of the production machines increases, it is necessary to introduce modern and faster working online inspection methods to supervise constantly the material for defects. For example, thermographic cameras are able to detect not only invisible defects within wood-based materials like laminated particle and fiberboards, but can be used also to detect defects in lumber and veneered wood [1-4]. In the latter case, there is the need to inspect more accurately the final pieces, given the exponential growth in worldwide sales. Therefore, in order to minimize adhesion problems [5], detecting surface and sub-surface cracks, define the geometry of the sub-surface detachment, in the veneered wood products, an integrated non-destructive test method is needed both during the production process that after to it [6]. Our system can provide a continuous control of the process and the product. In fact, this study compares the performance of transient thermography, three optical methods and ultrasonic testing applied together on a veneered wood sample with real and fabricated defects. The use of phase-shifting holography correlated to Double-Exposure HI and the wavelet transform applied as fusion of images between Thermographic Signal Reconstruction and Double-Exposure HI, are explored in this work.