line profilers triangulate in the direction of board travel whereas multi-dots triangulate along the board length .
“ This is an important distinction as multi-dot scanner heads will see the rising and falling edge of the board whereas line profilers may not ( unless they use two cameras specifically to cover this case or position the scanner at an angle – say 45 ° – relative to board travel ),” Arden said .
“ Multi-dot scanners also use less space on the scanner frame ( say 4-6 in ) whereas line profilers require more of the conveyor deck ( typically 2-3 ft ).”
Multi-dots for tracheid In addition to multi-dot scanners minimizing scanner frame space and seeing both edges of a board , these scanners achieve another critical capability – the measurement of tracheid effect .
When a laser spot is projected onto healthy tracheid wood cells , laser light is scattered into the cells in the direction of cell growth . If the wood fibre is dead ( as in a knot ), then the laser light does not scatter .
This effect can be measured to identify good wood from defective wood and even determine grain angle .
Adding colour vision Over the past 10 years , the introduction of colour scanning to identify surface defects such as knots , splits , rot , speck , beetle damage , etc . has led to gradebased recovery optimization , where boards are cut into lumber to obtain the highest grade as opposed to extracting the highest volume . Higher-grade output leads to higher dollar returns from the input wood fibre .
Colour scanning requires the addition of white light to illuminate the board surface and megapixel colour cameras to build high resolution colour images . Resolutions down to 0.25 mm are typical in today ’ s high performance colour scanners .
Modular scanning with the Gocator 200 With the Gocator 200 series multidot scanners , a scanning system can now be designed based on a modular concept that mixes 3D profiles , tracheid , and colour , according to Arden . Colour , for example , may be used only on the wane up surface while profile and tracheid is used on both top and bottom board surfaces .
The Gocator smart sensor feature set offers onboard processing to configure triggering , exposure , resolution , board detection , filtering , stitching , measurement , built-in communication protocols to other factory equipment using Ether / IP , and advanced visualization .
“ With an open source SDK ,
( left to right ) colour , tracheid scatter , tracheid angle , knot detection , profile : ( left to right ) colour , tracheid scatter , tracheid angle , knot detection , profile
Stiched colour images of top and bottom board surfaces : Stitched colour images of top and bottom board surfaces
customers can build sophisticated scanning solutions and deliver unique capabilities that are specific to mill requirements ,” Arden said .
LMI Technologies Inc . 9200 Glenlyon Parkway Burnaby , BC V5J 5J8 Canada T : + 1 604 636 1011 http :// lmi3d . com / contact
Terry Arden CEO of LMI Technologies
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International Forest Industries | APRIL / MAY 2017 35