A new chattering-free Sliding Mode Fuzzy Controller (SMFC) with smooth control law is proposed for a class of nonlinear system. The proposed controller employs the concept of variable structure system with sliding mode or Sliding Mode Control (SMC), for design, and preserves the most fundamental property of conventional SMC that is robustness and invariance to model uncertainties. However, unlike the conventional sliding mode control, SMFC eliminates chattering problem through the concept input-output mapping factor and behave like a linear controller in the neighborhood of its sliding manifold. To demonstrate the superiority of SMFC over SMC, we conducted simulation studies on balancing an inverted pendulum at its upright position in the presence model uncertainties and external disturbances.

A sliding-mode fuzzy controller (SMFC) was designed based on the principles of sliding mode control. Then, the concept of an input-output mapping factor was used to tune the parameters and the density of the controller's input and output membership functions. The tuned controller behaved like a linear controller in the neighborhood of the sliding manifold, and the chattering problem was eliminated. Furthermore, the controller was insensitive to system parameter variations and disturbances. To illustrate the SMFC's performance, we used this controller to stabilize an inverted pendulum in its upright position, starting from various initial conditions.

Statistical complexity measures are proposed as general indicators of structure or correlation. Lopez-Ruiz (1995) introduced another measure of statistical complexity C/sub LMC/ that, like others, satisfies the boundary conditions of vanishing in the extreme ordered and disordered limits. Feldman examined some properties of C/sub LMC/ and found that it is neither an intensive nor extensive thermodynamic variable, and proposed a simple alteration of C/sub LMC/ that renders it extensive. However the remedy results in a quantity that is a trivial function of the entropy density and hence of no use as a measure of structure or memory. We alter the disequilibrium term by the information of time irreversibility (information of nonlinear dynamics) and present a novel statistical complexity measure which is used to quantify the complexity caused by nonlinear dynamics. This statistical complexity measure allows reliable detection of periodic, quasi-periodic, linear stochastic and chaotic dynamics. When applied to the analysis of heart rate data, correlational structure in heart rate series is found, and the estimated statistical complexity appears to be correlated with different cardiac dynamics.

The paper presents a 1D maximum likelihood (ML) estimation procedure for both the direction of arrival /spl part/ and the frequency sweeping rate /spl alpha/ of a linear chirp signal impinging upon an M-element linear array. The estimates can be obtained by globally maximizing the likelihood function of the observed data on the /spl alpha//spl sim//spl part/ plane. To reduce the heavy 2-D ML computational load, a 1D ML procedure to search for the global maximum along the reduced 1D search space is proposed.>

The exponential-input describing function technique is used to investigate the transient response of a fuzzy controller. The rule-base of this fuzzy controller is generated by fuzzy addition and the partitioning of the universes of discourse of its input and output variables is based on an exponential mapping scheme. By using the symmetric features introduced by fuzzy addition in the decision table of the fuzzy control algorithm and the new mapping scheme, the effects of the output error time sequences can be represented by independent multilevel relays and a multiplication junction. Computer simulations on a second-order system confirm the behaviour of this analysis technique.>

The steady-state response of a fuzzy logic controller that uses fuzzy addition as the basis for its decision making process is analyzed mathematically. The nature of the look-up table constructed from fuzzy addition enables the decomposition of the fuzzy controller into three one-dimensional-multilevel relays. Unlike the sinusoidal-input describing function technique, the steady-state response of the closed-loop system is analyzed. The sufficient conditions derived depend on the parameters of the controller and can be used as guidelines to achieve a good step response at steady-state, one that does not lend itself to sustained oscillations or limit cycles.>

A complete design procedure for a fuzzy three-term PID controller is presented. A plant model is not required to achieve this design. A reduced look-up table containing the rules along with the quantization and tuning procedures by means of input and output mapping factors are introduced. The scaling factors of the output error time sequences are preselected arbitrarily and the search for an optimal input-to-output mapping factors ratio is performed through a phase diagram analysis. the applicability of the design procedure is demonstrated through computer simulations.>

In this paper, a One Step Adaptive Recursive Prediction Filter (OSARPF) is described. OSARPF is an adaptive filter for recursive systems and is suitable for parameter estimation problems. By representing the recursion in matrix notation, blocks of input data are used for adaptation. Using the past reference input for recursion, the adaptive filter can be shown to converge to an optimal solution. Adaptation equations are then developed for updating the coefficients of the adaptive filter and the adaptation process can be shown to converge to the optimal solution.

In this paper, an output error smoothing filter has been applied to the traditional gradient based adaptive filter. The rationale for this modification is to increase the convergence rate and decrease the minimum expected mean square error by ensuring a more stable region of operation. It was shown that smoothing the output error is equivalent to smoothing the desired response and the input. As a result, convergence to Wiener-Hopf solution is slightly modified to reflect the smoothing operation. However, convergence rate can be significantly improved and the minimum expected mean square error can be reduced with the proper choice of smoothing filter coefficients.

Signal processing to achieve gain is an important area for detection, localization, and classification purposes. Classical techniques include DFT as one of the best means to achieve coherent gain. Various long term time integration methods usually follow to provide extra non-coherent gain to avoid over-resolving the signal. An alternative method investigated here is to use an adaptive algorithm to track the signal in successive DFT's so that further coherent integration can be performed. The tracking part of this new algorithm is simular to Widrow's LMS algorithm (B. Widrow et al., Proc. of IEEE, Vol. 63, p. 1692-1716, Dec. 1975.) Characteristics of the new algorithm will be compared with other conventional techniques based on simulation results.

The concept of linguistic stress is vital in research in speech perception, speech production and computer speech recognition. The research described here has produced a new and reliable way, using computer analysis, to estimate the linguistic stress levels on individual syllables in complex utterances. An interactive "Computer Automated Stress Extraction System" (CASES) was developed to facilitate the research. This system can rapidly compute and display estimated syllable linguistic stress patterns, and all of the usual acoustic parameters from digitized speech. The following results were obtained: a) The computer estimated stress agreed well with perceived data. The stress measure adopted used a combination of five acoustic cues, and this yielded stable estimates of stress magnitudes, in simple utterances, even under variations of syllable locations and with speaker differences. With complex utterances, it was shown that in addition to the acoustic cues, listeners relied on previous linguistic knowledge in the perception of a general stress pattern. b) A new model of stress production was devised which suggested that the stress pattern of an utterance centered around a few special emphasis syllables with the stress pattern on the other syllables determined by anticipatory and recency effects.