June 27, 2001 Australian scientists have added a new dimension to the grading of timber with the development of high speed scanning using microwave technology.
The CSIRO SpeedGrader was developed by world acclaimed timber innovator and Wallenberg Prize winner, Dr Bob Leicester of CSIRO Sustainable Materials Engineering.
"SpeedGrader utilizes microwaves to actually look inside the structure of air-dry timber that is up to 50 mm thick and measures the presence and size of natural features such as knots, slope of grain and juvenile wood," Dr Leicester says.
"Timber with these features is prone to warp and twist with changes in humidity, an undesirable feature in manufactured timber products.
"Detection of this undesirable wood with microwave scanners helps remove headaches for end users, saving replacement materials and dealing with unhappy customers," he says.
Using microwave technology also means fast scanning. SpeedGrader can "look" along a length of sawn timber at the comparatively high speeds of 15-20 kilometers an hour or even faster while it is being processed in a modern high speed mill.
Within mills that specialise in the production of structural timber, the SpeedGrader has the potential to increase by around 3%, the quantity of wood that is sorted into acceptable grades of structural timber.
For a large Australian mill with an output approaching a half a million cubic meters a year of structural timber, this could mean an increased profit of $ 4-6 million annually. The upgrading of timber to higher grades also has the potential to add a further $ 2-3 million a year.
On-line scanning has so far been mainly the role of traditional mechanical stress grading machines. Stress grading is relatively unsophisticated, bending timber to assess its stiffness and then using this property to assess strength and its structural grade. However it provides little other useful information.
Dr Leicester says that mechanical stress grading has a significant built in comfort zone. In other words, today's graded timber is highly over-graded to ensure its weakest parts are still strong enough to do the job required.
The prototype commercial stress-grader illustrated includes two sets of microwave scanners comprising a knot detector (KD) and a slope-of-grain measurement unit (SOG). These units are placed in line with a conventional mechanical stress-grading (MSG) unit.
Dr Leicester says the potential financial benefits from the application of microwave scanners in the grading timber are extremely promising.
SpeedGrader scanners are low-powered, around 0.15 milliwatts, (much less than the power of the average torch battery) and are extremely safe in service, considerably safer in fact than more expensive alternatives such as scanners based on x-ray technology.
One limitation in using this low power level is that the scanners are suitable only for timber with moisture content below 20 percent. A modified scanning system can be developed if it were required to grade timber at higher moisture contents.
Dr Leicester says the most important (and most difficult) aspect of developing SpeedGrader was to produce an algorithm (a mathematical picture) used by the computer to recognise the features being transmitted in the form of microwave signals.
These signals have different signatures (noises) depending on the type of material being encountered in the timber and a different algorithm is required for each timber species being graded.
This is high-end mathematics, which at the end of the day makes possible an efficient and cheap new system for wood grading.
Dr Leicester says the SpeedGrader can be made robust, consistent and effective and that it is now ready for final development into specific commercial applications.
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