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Title:	Ultrasonic Inspection of Wooden Pallet Parts Using Time of Flight
Author(s):	Schmoldt, Daniel L.; Nelson, Robert M.; Ross, Robert J.; McDonald, Kent A.
Date:	1997
Source:	Review of Progress in Quantitative Nondestructive Evaluation. 16B: 1791-1798.
Description:	Wooden pallets are the largest single use of sawn hardwood logs in the USA. Unfortunately, millions of wooden pallets are discarded annually due to damage or because their low cost makes them readily disposable. In general, pallets are constructed from stringers and deckboards of random quality. Higher quality wooden pallets, however, can be built from higher quality parts, and have a much longer life cycle and a lower cost per trip. Because manual grading and sorting of pallet parts is infeasible, the long-term goal of this project is to develop an automated pallet part inspection system. Ultrasonic time of flight (TOF) measurements in a pitch-catch arrangement are being used to distinguish different types of defects, including knots, decay, cross grain, and voids, from clear wood. Three different frequency rolling transducers (84 kHz, 0.5 MHz, and 1.25 MHz) have been used to collect measurements on four oak deckboards of 5/8î thickness. Ultrasonic C-scans taken at 1/2î intervals indicate that TOF can reliably distinguish between various defects and clear wood. The smaller footprint of the higher-frequency rolling transducers provides greater sensitivity at the 1/2î scanning resolution. Additional experiments on other wood species will verify whether the observed trends are consistent and will eventually lead to a classification algorithm.
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