Mechanical pulp is produced using Mechanical Wood Pulp Refiners. These machines physically break the lignin (i.e. the natural glue) joints between individual wood fibres by applying cyclic loads to wood. Refiners also develop the properties of the individual fibres in the pulp.

The refining action can be controlled by varying refiner variables, such as speed, plate gap, pulp water content, etc. so that the desired pulp properties are obtained. These variables affect the forces applied to wood chips or floes of fibres inside the refiner. In order to improve the method of refiner control, and to advance the level of understanding of fibre development, it is desirable to measure the magnitude of the cyclic forces.

A piezo ceramic force sensor was designed and developed to measure the dynamic normal and shear forces applied to floes of fibres inside a mechanical refiner. The design addresses the determination of the applied forces from the piezo ceramic signals, frequency response and signal conditioning. Piezo ceramic behaviour was investigated and a large scale prototype was built to test the design concept. A prototype sensor was built and tested in a laboratory scale refiner at the University of British Columbia.

The sensor frequency response was flat, and encouraging cyclic sensor signals were obtained during refiner testing. It appears that complex refiner vibrations affect the sensor in an undesirable manner. Further investigation is required to refine the desigm.