Online Acoustic Wave Sensing for Paperboard Score Quality Control
Inline acoustic wave sensing detects sub-surface paperboard delamination during scoring, stopping un-creased board defects before downstream cartoning line jams.
Optical Microphone
Acoustic Sensing
High-precision sensors detect sound waves by measuring the movement of light rather than the vibration of a physical diaphragm. An optical microphone uses a laser beam to capture the tiny fluctuations in a reflective surface or the air itself when a sound passes through. This allows for the recording of very high frequencies that a traditional coil or capacitor could not reach.
Laser Interferometry
Sensing begins by splitting a light beam into two paths and looking for the interference pattern created when one path is disturbed by a sound wave. In the context of material testing, an optical microphone picks up the ultrasonic signals generated by lasers hitting a sheet of paper. This method is incredibly sensitive and can operate in environments with high heat or electrical interference where normal electronics would fail.
Because the sensor does not need to be near the paper, it can monitor the web from a distance as it moves through the press. This lack of contact means the microphone does not change the sound it is trying to measure. It provides a pure signal that relates directly to the internal stiffness of the fibre network.
Quality Assessment
Data from these sensors are used to calculate the physical strength of the board in real time. The optical microphone is a central part of modern non-destructive testing systems in paper mills. It allows for the constant monitoring of quality without stopping the machine.