Comments on "Analysis and design of fuzzy controller and fuzzy observer" [with reply]

The main advantage of Takagi-Sugeno (TS) fuzzy model is the ability to approximate the nonlinear systems from the input-output data without the complex mathematical equations. In order to obtain TS fuzzy model from the input-output data, all the system variables should be measurable. Therefore, in case of TS fuzzy model-based control, the observer design is of no good except the very special case. In this correspondence, we show this fact by analyzing the problems of the above paper by Ma et al. (ibid. vol.6 (1998)). In reply, Ma et al. point out that: 1) for TS fuzzy model, it is not necessary to make all the system variables measurable; 2) no accuracy is needed for the fuzzy model; and 3) the nonlinearities of the plant (31) given in the paper are the functions of variables x/sub 1/, x/sub 2/ and x/sub 4/.