DUAL ADAPTIVE-CONTROL OF CHIP REFINER MOTOR LOAD - INDUSTRIAL RESULTS

A characteristic of wood chip refiners is that the incremental gain be tween the motor load and the plate gap is subject to a slow drift due to plate wear and sudden changes in sign due to pulp pad collapse. A p ad collapse can be caused by a change in operating point, or may occur suddenly due to a feed rate or consistency disturbance. This poses a problem for fixed-parameter linear controllers which may actually acce lerate pad collapse and induce plate clashing as a result of getting c aught in a positive feedback loop. The objective of this work is to de velop a chip refiner motor load controller capable of detecting the on set of pad collapse and, thereby, avoid plate clashing. The problem is approached from a fault detection and control viewpoint where the ref iner is treated as a linear dynamic system with fast time-varying para meters. The proposed adaptive control algorithm consists of an improve d parameter estimator and a controller containing ''dual'' features. T o track both drifts and jumps in the parameters, a multi-model approac h called adaptive forgetting through multiple models or AFMM is used. A method of modifying the AFMM to include information about what to ex pect in the event of a pad collapse is proposed. The main contribution of the work is the development of an active adaptive controller or AA C, which actively probes the system to improve the parameter estimates . The use of active learning or probing in the controller is justified by the fact that the parameter estimates are the key to identifying a pad collapse, and that probing targets a portion of the input manipul ations at continuously identifying these parameters. Finally, the AAC is combined with the AFMM, and the resulting combination is tested on an industrial refiner.