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H.W. Kropholler and A.R. Guesalaga. Comments on the effects of chaos on “Controllability”. In Fundamentals of Papermaking, Trans. of the IXth Fund. Res. Symp. Cambridge, 1989, (C.F. Baker & V. Punton, eds), pp 358–363, FRC, Manchester, 2018.


Below are appended some general comments on SESSION 8 “CONTROLLABILITY”, and some implications for the development of control systems, with particular reference to the phenomenon of chaos.

There are many interesting aspects and the examples of process modelling and identification in the papers of this session. The complexity of the papermaking process and hence the requirements of an effective control system are very clearly illustrated. There is a vast useful literature on control theory and applications.

The total process performance and its profitability must determine the role of the control system. The subject can be presented as a series of facets developed in an orderly manner. First there are some basic theoretical definitions such as controllability (in its specialised technical meaning), observability, sampled data systems, instability and chaos. After that, there is the process performance which needs to be considered: as a design or static system; as a dynamic operating system; and quality assurance. It is also important to encompass mill wide performance.

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