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.

Chronicling Covered Construction : NDE Helps To Record Historic Bridges

Covered bridges are part of the fabric of American history, and several hundred historic covered bridges still exist to this day. Although much effort is expended to preserve these structures, the high cost of restoration, neglect, vandalism, and arson often take their toll. Many are lost forever.

One of the more famous bridges from The Bridges of Madison County movie was burned in 2003, and Hurricane Irene destroyed a number of New England bridges in 2011.

Because we cannot completely prevent these types of incidents from occurring, the National Park Service’s Historic American Engineering Record (HAER), in cooperation with the Forest Products Laboratory (FPL), has efforts under way to document these historic structures.

A single laser scan of the Roseman Bridge, Madison County, Iowa. (NRRI).

With the help of laser imaging technology, these two organizations are ensuring that the construction triumphs of yesterday are recorded and preserved for future generations.

Three-dimensional (3D) laser scanners are nondestructive evaluation (NDE) instruments that record precise and accurate surface data of objects in a nondestructive manner. These instruments use an infrared beam of light to calculate and record the distance to an object, typically as data points with spatial coordinates.

These data are then analyzed using various types of computer software to generate a detailed image of coordinates and dimensions.

Three-dimensional laser scanners have successfully been used to digitize objects of various sizes ranging from small diagnostic artifacts to large, complex sites of monumental architecture — and now, nestled between these two extremes, are some of our country’s historic bridges.

For more information, please see Chapter 13 of the FPL’s publication Nondestructive Evaluation of Wood: Second Edition.