Many robotic systems rely on infrared sensors, lasers, cameras and/or ultrasonic transducers for perceiving their environment. Most of these sensors can easily determine the distances to the surrounding objects, and even their shape. However, they are often unable to discriminate among different nearby-placed objects, obstacles, materials or surfaces. This paper presents the design and development of a low-cost ultrasonic-based sensory system, which is able to exploit the information contained in the magnitudes of the reflected sound waves. Therefore, the common ultrasonic distance measurement is complemented with the value of the acoustic reflection coefficient of the observed object. The estimated reflection coefficient facilitates the classification of different materials. Experiments are conducted to demonstrate solid performance of the proposed sensory system.

This paper presents the design procedure of the integral sliding mode controller with enhanced robustness properties for a class of nonlinear uncertain systems. The integral sliding mode control (I-SMC) is synthesized with the generalized disturbance attenuation scheme called robust internal-loop compensator (RIC) through the Lyapunov redesign framework, thus introducing a generalisation of the well-known case for linear systems. The resulted two-layer control structure employs the classical controller with the feedforward term in the outer control loop to track the reference, while the inner control loop compensates the generalized disturbance and provides robust stability. The closed-loop system is proved to be asymptotically stable via Lyapunov stability theory. The developed control algorithm is used for attitude tracking of the small-scale helicopter system in the presence of additional parametric uncertainties and external disturbances. An excellent tracking performance and robustness stability of the proposed control method are revealed through computer simulations and experimental testing over the whole domain of the helicopter outputs.

Different sensors may be used for a robot environment analysis: infrared sensors, laser sensors, sonars, RGB and depth cameras. Most of them provide satisfying information about the distance and the shape of observed objects. However, the main drawback of these sensors is the inability to discriminate among different analyzed objects if the latter share the same color, texture or distance. A distributed ultrasound-based sensory system composed from multiple ultrasonic cells is proposed. The system uses a master-slave control architecture. This paper presents the most important part of such system - a low-cost ultrasonic cell with the ability to classify objects by exploiting the magnitude of reflected ultrasonic waves. Traditional ultrasonic sensors only provide information about the distance, but the presented ultrasonic cell also measures the acoustic reflection coefficient of analyzed object. This coefficient allows to differ among materials or objects. Experiments are conducted to demonstrate the performance of the proposed ultrasonic cell.

Contour-based Fourier descriptors are very simple and effective shape description method used for content-based image retrieval. Similarity between Fourier descriptors is usually computed using measures such as City-block or Euclidean distance. These similarity measures consider all harmonics to be equally important, therefore harmonics with larger magnitude tend to have larger significance during the computation of shape similarity. In order to increase the importance of harmonics with lower magnitude, we propose to use weighted City-block distance for computing shape similarity. The proposed weighting coefficients are inspired by the contrast sensitivity of the human visual system to different spatial frequencies, known as the Contrast Sensitivity Function (CSF). Although weighted distances generally do not improve the retrieval performance, experimental results clearly demonstrate that human observers favour the retrieval system based on the weighted distances, and find it more accurate and relevant.

Contour-based Fourier descriptors are established as a simple and effective shape description method for content-based image retrieval. In order to achieve invariance under rotation and starting point change, most Fourier descriptor implementations disregard the phase of the Fourier coefficients. We introduce a novel method for extracting Fourier descriptors, which preserve the phase of Fourier coefficients and have the desired invariance. We propose specific points, called pseudomirror points, to be used as shape orientation reference. Experimental results indicate that the proposed method significantly outperforms other Fourier descriptor based techniques.

Many robotic systems rely on infrared sensors, lasers, cameras and/or ultrasonic transducers for perceiving their environment. Most of these sensors can easily determine the distances to the surrounding objects, and even their shape. However, they are often unable to discriminate among dif- ferent nearby-placed objects, obstacles, materials or surfaces. This paper presents the design and development of a low-cost ultrasonic-based sensory system, which is able to exploit the information contained in the magnitudes of the reflected sound waves. Therefore, the common ultrasonic distance measurement is complemented with the value of the acoustic reflection coeffi- cient of the observed object. The estimated reflection coefficient facilitates the classification of different materials. Experiments are conducted to demonstrate solid performance of the proposed sensory system. Keywords—Ultrasound; Sensor; Distance; Material; Reflec- tion; Robotics

Shape, color and texture are the most important discriminative elements for content based image retrieval. Fourier descriptors are widely used in shape based image retrieval problems. This paper presents a novel method of extracting Fourier descriptors from the simplest shape signature - complex coordinates. Instead of the commonly used scale normalization with the magnitude of the first harmonic, normalization with the sum of magnitudes of all harmonics is used. This leads to an improved shape scale normalization. All the experimental results indicate that the proposed method outperforms many other state-of-the-art Fourier descriptors based methods, both in terms of retrieval performance and computational time.

This paper addresses the challenges of the disturbance observer (DOB) algorithms faced with highly nonlinear electromechanical systems which are dealing with high resolution and high speed operations. It describes the synthesis of robust and stable controllers and their applications in controlling azimuth and elevation angles of the helicopter model CE 150 supplied by Humosoft. Description of the helicopter, including its mechanical characteristics and mathematical model, is given in the paper. Tracking error, transient performances, power consumption and motor strains are used for the validation of control quality. Implementation of the control system on the experimental setup is also explained. MATLAB and Simulink are used as tools for developing the simulation model of the helicopter system. Obtained simulations are showing that developed controllers provide significantly improved results even in the presence of unknown and unpredictable inputs (disturbance and noise), unpredictable and unknown dynamics, external forces (torques) and change of the system parameters.

Adresa za dopisivanje Emir Sokic Mr.Sci. Sveuciliste u Sarajevu Elektrotehnicki fakultet Zavod za automatsku kontrolu i elektroniku Zmaja od Bosne bb., 71000 Sarajevo Bosna i Hercegovina Tel. 00387 61 798 874 esokic@etf.unsa.ba Sažetak Koristenjem radiograma istraživala se ucinkovitost razlicitih numerickih tehnika za poluautomatske procjene stupnja sazrijevanja vratnih kralježaka (CVM). Metode: Kefalogrami 211 pacijenata snimljeni su i spremljeni u digitalnom obliku. Nakon toga su, s pomocu posebno razvijenog softvera i tih pohranjenih radiograma, specijalisti ortodoncije oznacili i mjerili za svakog pacijenta nekoliko karakteristicnih kefalometrijskih obilježja. Rezultati su bili potrebni za automatsko određivanje stupnja sazrijevanja vratnih kralježaka s nekoliko numerickih tehnika, među kojima K znaci klasteriranje (grupiranje), a Fuzzy C – dusteriranje (rasipanje). Rezultati su uspoređeni s podacima koje su dobili specijalisti. Rezultati: Najbolji rezultati dobiveni su koristenjem Fuzzy C rasipanja. Tocna ocjena stupnja CVM-a iznosila je oko 70 posto, a procjena klase bila je visa od 99 posto. Zakljucak: Eksperimentalni rezultati pokazuju da se može razviti potpuno automatizirani sustav za procjenu i predviđanje stupnjeva CVM-a, premda jos treba rijesiti manje teskoce prije primjene u klinickoj praksi.

The paper deals with design, construction and implementation of bilateral control system using fuzzy regulation. The aim of paper is implementation of a system which can be used as a didactic tool for better understanding of bilateral control concepts, as well as a base for further work. The system is composed of mechanical model of haptic paddle with one degree of freedom and virtual model of haptic paddle and its environment, interconnected using acquisition card. Virtual environments control is created using fuzzy logic. After implementing control algorithm and connecting two models - the mechanical and virtual, the functionality of system was confirmed by experimental data.

This paper examines the capabilities of fuzzy logic based controllers in the process of active suspension of a heavy vehicle seat vibrations. The hydraulic cylinder is used as an active element, while the damper and the air spring are used as passive elements for reducing vibrations. MATLAB and Simulink are used as tools for developing the simulation model of the driver seat. The mathematical model was created according to the physical setup of the vehicle seat at the testing laboratory. Description of the seat, including its mechanical characteristics and mathematical model, is given in the paper. Control system description and implementation on the experimental setup using dSPACE module, is also explained. The SEAT value is used for the validation of control quality. The obtained simulations show that the developed suspension controllers provide superior passenger comfort for different types of road.

The human experience in the analysis of the handwriting of male and female writers indicates that gender affects the appearance of the handwritten text. These differences are usually very difficult to describe numerically. In order to analyze the handwriting differences between male and female writers, several shape description techniques, such as the tangent angle function, curvature function and Fourier descriptors, were used in this paper. As an additional contribution of the paper, a database of 3766 off-line handwritten cursive and capitalized written words has been created. The database consists of male and female handwriting samples, classified by gender and handedness. The experimental results show that typical attributes of male and female handwritings imply certain differences in shape decriptors, and those differences have the potential for usage in gender handwriting discrimination.

Many undergraduate students find it difficult to learn, understand and conceptualize some of the the basic topics of signal processing and analysis theory such as: analog and digital signals, frequency domain, Fourier Transform, Discrete Fourier Transform, Nyquist-Shannon sampling theorem, aliasing etc. This paper presents an effective method to introduce some of the most important topics in an introductory Signal Theory course. A set of laboratory exercises is developed, where students experiment with several basic and advanced signal analysis and processing techniques, almost through game and play. The results of a poll show that students find considerable improvement in course organisation and greater usefulness of laboratory exercises in understanding course material.

This paper discusses some of the interesting properties of stability analysis of a discretized wave equation. The solutions of the wave equation are wave functions, hence oscillating, so when testing stability the discretization scheme usually shows marginal stability. Marginal stability is a sufficient condition for a discrete scheme convergence and many authors don't bother with mathematical consistency. However, inadequatly chosen discretization method may lead to the additional unwanted oscillations. This paper illustrates this effect in a different approach. First, the wave equation is introduced together with a Perfectly matched layer (PML). Then the 1D wave equation is discretized by using Finite Differences Method (FDM) and Finite-differences Time-domain method (FDTD). It is shown that the latter method does not produce spurious oscillations in the solution. Eigenvalue analysis is done to explain this effect and discuss stability of the numerical scheme.