Dragan Antić

Modelling of dynamical systems based on almost orthogonal polynomials

A new class of the almost orthogonal filters is described in this article. These filters are a generalization of the classical orthogonal filters commonly used in the circuit theory, control system theory, signal processing, and process identification. Almost orthogonal filters generate the series of almost orthogonal Legendre functions over the interval (0, ∞). It is well known that all real systems suffer from some imperfections, so the models of these systems should reflect this fact. A new method for obtaining an imperfect system model is proposed. This method uses an almost orthogonal filter, which is based on almost orthogonal functions. Experiments with modular servo drive were performed to validate theoretical results and demonstrate that the method described in the article is suitable for modelling of imperfect systems.

Outage capacity of FSO link with pointing errors and link blockage.

In this paper, we analyze the outage capacity performance of free-space optical (FSO) systems. More precisely, taking the stochastic temporary blockage of the laser beam, atmospheric turbulence, misalignment between transmitter laser and receiver photodiode and path loss into account, we derive novel accurate analytical expressions for the outage capacity. The intensity fluctuations of the received signal are modeled by a Gamma-Gamma distribution with parameters directly related to the wide range of atmospheric conditions. The analytical results are validated by Monte Carlo simulations. Furthermore, when the intensity fluctuations are caused only by atmospheric turbulence, derived expressions are reduced to the simpler forms already presented in literature. The numerical and simulation results show that the link blockage causes appearance of the outage floor that is a significant energetic characteristic of an FSO system. The results also show that there exists an optimal value of the laser beam radius at the waist for minimizing outage probability in order to achieve the specified outage capacity. This optimal value depends on atmospheric turbulence strength and standard deviation of pointing errors, but it is also strongly dependent on the probability of link blockage.

Low Complex Forward Adaptive Loss Compression Algorithm and Its Application in Speech Coding

Low Complex Forward Adaptive Loss Compression Algorithm and Its Application in Speech Coding This paper proposes a low complex forward adaptive loss compression algorithm that works on the frame by frame basis. Particularly, the algorithm we propose performs frame by frame analysis of the input speech signal, estimates and quantizes the gain within the frames in order to enable the quantization by the forward adaptive piecewise linear optimal compandor. In comparison to the solution designed according to the G.711 standard, our algorithm provides not only higher level of the average signal to quantization noise ratio, but also performs a reduction of the PCM bit rate for about 1 bits/sample. Moreover, the algorithm we propose completely satisfies the G.712 standard, since it provides overreaching the curve defined by the G.712 standard in the whole of variance range. Accordingly, we can reasonably believe that our algorithm will find its practical implementation in the high quality coding of signals, represented with less than 8 bits/sample, which as well as speech signals follow Laplacian distribution and have the time varying variances.

Digital Sliding Mode Control of Anti-Lock Braking System

The control of anti-lock braking system is a great challenge, because of the nonlinear and complex characteristics of braking dynamics, unknown parameters of vehicle environment and sy ...

Approximation based on orthogonal and almost orthogonal functions

Abstract In this paper, we define a class of almost orthogonal rational functions of Legendre type in a new manner. Relations of these functions with classical exponentional functions orthogonal over interval (0, ∞), as well as classical polynomials orthogonal over (0, 1) are explained. Defining relations of these functions can be used for designing almost orthogonal filters. These filters are generators of orthogonal signals and can be successfully applied in finding the best signal approximation in the sense of the mean square error. The filters orthogonal property enables building of physical (in this case electrical) models of dynamical systems (the sources of signals to be approximated) either with less components for the same model accuracy or higher accuracy for the same number of components than the other known models. New filters represent further improvement of previously designed filters, by the same authors, in the sense of simplicity, higher accuracy, lesser approximation time and even a possibility to approximate signals generated by systems with built-in imperfections. Series of experiments were performed to analyze the dependence of approximation accuracy and the number of filters sections.

Variable structure systems for control of redundant robot

Abstract A combination of one class of kinematic control of redundant robot and Variable Structure Systems (VSS) in manipulating tasks that require large accelerations or decelerations is the main issue of this paper. The inverse kinematic problem will, on a tactical control level, be solved through Distributed Positioning (DP) concept, while the solution of the executive control level will be solved by using a combination of two common VS control algorithms with PI controller. A complete synthesis of VS local regulators for the redundancy, along with stability analysis, will be given. Comparison of VS with PD controller tracking characteristics will be studied on a suitable SCARA robot with redundancy performing one typical pick-and-place movement.

Quasi-Sliding Mode Control With Orthogonal Endocrine Neural Network-Based Estimator Applied in Anti-Lock Braking System

This paper presents a new control method for nonlinear discrete-time systems, described by an input-output model which is based on a combination of quasi-sliding mode and neural networks. First, an input-output discrete-time quasi-sliding mode control with inserted digital integrator, which additionally reduces chattering, is described. Due to the presence of various nonlinearities and uncertainties, the model of the controlled object cannot be described adequately enough. These imperfections in modeling cause a modeling error, resulting in rather poor system performances. In order to increase the steady-state accuracy, an estimated value of the modeling error in the next sampling period is implemented into the control law. For this purpose, we propose two improved structures of the neural networks by implementing the generalized quasi-orthogonal functions of Legendre type. These functions have already been proven as an effective tool for the signal approximation, as well as for modeling, identification, analysis, synthesis, and simulation of dynamical systems. Finally, the proposed method is verified through digital simulations and real-time experiments on an anti-lock braking system as a representative of the considered class of mechatronic systems, in a laboratory environment. A detailed analysis of the obtained results confirms the effectiveness of the proposed approach in terms of better steady-state performances.

An introduction to bond graph modelling of dynamic systems

The paper presents the basics of bond graph modelling of dynamic systems, the features of the bond graph elements and the way in which a model of a system can be represented by bond graphs. Also, the advantages of bond graph modelling are given.

On a new class of quasi-orthogonal filters

In this article, a new class of quasi-orthogonal filters, based on the Legendre and Malmquist-type quasi-orthogonal polynomials, is presented. These filters are generators of quasi-orthogonal functions for which we derive and present all important properties and relations. Our article is based on the classical theory of orthogonality and orthogonal functions, and also on new results in this field of mathematics. Based on theoretical results, we design schemes for the realisation of these filters. Finally, a trail quasi-orthogonal filter is practically realised and its quasi-orthogonality is proven by performing experiments. Quasi-orthogonal filters can be successfully used for signal approximation as well as for modelling, identification, analysis, synthesis and simulation of dynamical systems.

Optimal fuzzy sliding mode control with a time-varying sliding surface

It is well known that sliding mode control can achieve good transient performance and system robustness. However, the sensitivity of the sliding mode control before reaching the sliding surface and the presence of chattering may introduce problems to the tracking control of the system. In this paper, a new sliding surface design approach is proposed that varies the sliding surface in a nonlinear and time-varying fashion. Slope constant of the sliding surface is varied by fuzzy controller based on the ratio between the derivate of error and error itself. Optimal parameters of the fuzzy controller are determined using genetic algorithms. Proposed optimal fuzzy sliding mode control has been applied to an electrical servo drive system and the performed experiments have verified efficiency and improvements of a new control method.