Laser Ultrasonic Measurement of Elastic Properties of Moving Paper: Mill Demonstration

An automated sensor has been developed for use during paper manufacture that can measure flexural rigidity (bending stiffness). Based on laser ultrasonic technology, this sensor provides continuous noncontact on‐machine measurements on paper having area densities from 35 to 205 g/m2, moving at commercial manufacturing speeds, at any angle in the plane of the sheet. It was demonstrated on a high speed printing paper grade machine during commercial production. For that demonstration, the sensor was integrated into an existing scanning sensor system. Cross‐direction profiles of flexural rigidity had the expected shape, and compared well with traditional bending stiffness measurements on samples collected for that comparison.