Current machine vision technology relies largely on defect detection by digital cameras, which have difficulty identifying a significant percentage of knots in lumber. Use of X-ray devices to detect defects is employed by two machine vision companies to insure accurate knot detection. There are, however, perceived hazards associated with X-ray use in industrial settings. The DHM detects knots in lumber by creating an electric field between a linear array of opposed electrodes. Lumber is passed through the electric field between the electrodes.
Electricity travels with higher strength through higher density knot wood than through clear wood.
The DHM identifies as knots those areas where higher voltage is detected. The DHM has been licensed to a machine vision company to augment information from their current digital camera system. The company is successfully marketing this technology to scan for lumber defects ahead of rip and crosscut saws in roughmills and for automated lumber grading systems.