Almir Salihbegovic

High performance disturbance observer based control of the nonlinear 2DOF helicopter system

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.

Analysis of off-line handwritten text samples of different gender using shape descriptors

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.

Synthesis of the integral sliding mode control and the robust internal-loop compensator for a class of nonlinear systems with matched uncertainties

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.

Heuristic based evaluation of Mobile Services web portal usability

The paper presents heuristic based evaluation of mobile services web portal. Development context for the BH Telecom Mobile Services web portal is described, including the evaluation team organization and training. Usability evaluation is integrated with redesign proposals, and Heuristic Evaluation Report is established to support the process. The evaluation results are presented and discussed, highlighting several procedural and product improvements.

Multivariable sliding mode approach with enhanced robustness properties based on the robust internal-loop compensator for a class of nonlinear mechanical systems

This paper proposes the synthesis of the integral sliding mode control (I-SMC) and the robust internal-loop compensator (RIC) for nonlinear multiple-input multiple-output (MIMO) systems, introducing a generalization of the well-known single-input single-output (SISO) case for linear systems. The new control term is introduced in order to incorporate a RIC structure with a multivariable I-SMC scheme for a class of nonlinear mechanical systems affected by perturbations. The finite-time stability of the closed-loop system is discussed using a Lyapunov based approach. The designed algorithm is used to control attitudes of the small-scale laboratory helicopter system, representing a nonlinear MIMO system with significant cross-couplings and inherently unstable characteristics. An excellent tracking performance and robustness properties of the proposed control method is demonstrated through both, computer simulation and experimental testing, even in the presence of additional internal and external disturbances.