THEORETICAL FOUNDATIONS OF MECHATRONIC CONTROL OF THE HYDROTHERMAL TREATMENT OF GRAIN: A CSTR-CASCADE MODEL AND SYNTHESIS OF AN ADAPTIVE FUZZY-PID CONTROLLER
Keywords:
grain conditioning, mechatronic system, residence time distribution, CSTR cascade, Arrhenius kinetics, structural invariance, adaptive fuzzy-PID control.Abstract
The paper discusses the theoretical description of the hydrothermal treatment (conditioning) of grain as an object of automatic control and the principles of synthesising a mechatronic control system for it. The moistening of a grain flow in a screw-type apparatus is treated as a distributed-parameter process which, on the basis of residence time distribution theory, is reduced to a lumped-parameter description in the form of a cascade of continuous stirred-tank reactors with an Arrhenius-type kinetics of water absorption. It is shown analytically that the mean residence time and the static gain of such an object depend on the rotational speed of the screw in a mutually compensating way, so that their ratio remains constant; this structural invariance is proposed as the basis of a tuning rule that does not require recalculation when the operating regime is changed. A two-level adaptive fuzzy-PID structure with a feedforward channel for transport delay compensation is synthesised, and the properties of the resulting loop are compared qualitatively with those of fixed-dose and classical PID control. The results are of a methodological character and are applicable to a wide class of continuous moistening and mixing apparatuses.
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