The paper deals with the level controls in a laboratory two-tanknsystem. The plant is strongly nonlinear due to the basic dynamicnequations and the characteristics of the valves. We developed annonlinear control law which achieves robust almost time-optimal controlnover the full range of operation conditions. The development is based onnideas from fuzzy control, but in contrast to usual fuzzy controllerndesigns, most of the rules are not derived from heuristics but rathernare mathematical formulae which, together with the standard fuzzynquantization of the system's variables, approximate the time-optimalncontrol law. This approximation is improved by heuristic rules whichnwere gained from the observation of the behaviour of the controllednplant. The resulting nonlinear control law exhibits a performance whichnis not attainable with standard linear control nor with classicalntime-optimal control
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