Monitoring lumber size,shape and mismatch in double-arbour saws-Development and validation of scanning equipment

摘要

The costs for raw material amount to about 70% of the total costs for most sawmills.Consequently, it is very important to improve the saw yield for the economy and competitiveness of sawmills.The aim of an ongoing project in Sweden is to build knowledge and develop methods and techniques that enable an increase of the sawing yield. The idea is that the yield increase will be achieved through thinner kerfs, adapted shrinkage allowance and lower sawing allowance. One key parameter in the sawing process is sawing accuracy.We have as a part of the ongoing project developed scanning equipment with which we can measure the size and geometry of the produced lumber. The equipment is an off line research apparatus based on two laser triangulation devices. The industrial partners on the project have especially pointed out that a method is needed for measurement and evaluation of the mismatch on sawn surfaces produced by double arbour saw machines. The equipment has a measurement resolution that is better than 0.1 mm in the thickness direction and can measure thickness and width with a repeatability of 0.1 mm and bow, crook, twist and cup with a repeatability of<1 mm.As there is no standard for measurement and evaluation of mismatch, a special algorithm for this parameter has been developed and correlated against subjective judgements of skilled personnel from the sawmill industry. The correlation between manually judged mismatch and mismatch measured by the scanner was 0.76.