Every Cut Counts II : Lumber Lasers Illuminate Imperfections

Earlier, we looked at nondestructive evaluation (NDE) laser scanning as applied to logs prior to sawing, but the utility of laser technology extends to dimensional lumber as well.

A typical lumber mill will use two laser scanners which capture two distinct data types — profile scanning data, and tracheid effect data.

pine

A photo demonstrating the tracheid effect across six different samples of white pine. Notice how the shape of the laser changes depending on the defect present in the sample.

A profile scanning laser is aimed at the board in shallow angle, and is primarily used to detect wane (insufficient wood at a corner or along an edge, due to surface curvature) on the board’s edges as well as splits, cracks, and holes. It also yields accurate measurements of the amount of wane, which are used to automate the edging and trimming of the lumber.

profile

Sample laser profile image of a board. The lighter shades of grey show the wane of the wood. The jagged white abnormality in the upper left hand corner could indicate a defect.

Profile scans will yield grey-level images with the normal, level surface of the board shaded in dark gray. Slightly higher areas of the board are represented as darker shades of gray, and lower areas will be shown as lighter shades of gray. This additional information about the board’s surface helps industry professionals optimize the cutting processes and eliminate waste.

Diagram of a typical laser scanner used in a lumber mill. Notice how the laser on the right is angled for tracheid effect scanning.

A tracheid effect scanning laser, on the other hand, is aimed at the board at a sharper angle. When the beam strikes the surface of the wood, the beam is propagated along the board’s elongated cells, the tracheids, creating the titular effect. The angle of glow of the laser beam shows the angle of the wood grain, and by analyzing how the laser beam’s glow changes shape, researchers and industry professionals can predict a board’s strength or even reveal defects such as knots and pitch pockets.

This type of scanning technology was first used commercially to locate defects in hardwoods and softwoods for the production of furniture and mouldings, but has since expanded. Today, there are several manufactures producing commercial laser scanning equipment capable of tracheid effect scanning.

This blogpost was adapted from FPL’s publication Nondestructive Evaluation of Wood: Second Edition.