A new laser-based system was successfully developed in the pilot plant for veneer thickness and roughness measurements. This system was tested for both green and dry spruce veneer. The comparisons were made between the green veneer measurement and dry veneer measurement, and between the laser-based system measurement and actual digital measurement. A linear mixed effect model was used to estimate the within-sheet and between-sheet variations of veneer thickness and roughness and their causes.
A good correlation was found between the laser-measured thickness and caliper-measured thickness. The laser-measured average roughness could also capture the trend of veneer surface roughness determined by the visual classification. Thus, the new laser-based system can be a useful tool for measuring both veneer thickness and roughness.
For veneer thickness, the within-sheet variation seemed to be larger than the between-sheet variation, and the laser-based measure had a larger variation than the digital-based measure for both green and dry veneer sheets. With the green veneer, higher veneer moisture content and density would lead to a larger difference between the two measurements. The laser-based method tended to classify more "thick" sheets than the digital-based method, but this tendency was not obvious with the dry veneer. Such tendency also became negligible by factoring in either veneer moisture content or density. Thus, in the real applications, the accuracy of the new laser system can be improved for measuring green veneer thickness with a calibration of moisture content and/or density.
For veneer roughness, the within-sheet variation was again larger than the between-sheet variation, and the dry veneer had a larger variation than the green veneer. Further, the tight side variation was generally larger than the loose side variation. The above information is deemed useful for establishing an overall veneer quality criterion for industrial applications. Further work is scheduled to adopt the new laser-based system for real-time measurement of green veneer thickness and roughness.