Detecting knots and voids in lumber with dielectric sensors

Abstract

A system has been developed which uses the dielectrical properties of wood to detectknots and voids in lumber. The knot and void detection (KVD) system rapidly scans the surface of wide boards for defects using a series of transducers and provides a defect map of the lumber surface. The transducers are electrified flat plates that act as capacitors when used in conjunction with the wood as the dielectric. Knots and voids change the dielectrical properties of wood and the change can be detected by monitoring the output signal of the capacitors. A prototype system is being tested and refined. The initial results show that small knots and voids can be consistently and reliably detected in both wet and dry wood.