Control design for multi-rotor aerial vehicles (MAVs) is quite challenging problem due to their nonlinearitles, unknown dynamics, parametric uncertainties, an underactuated property, a nonlinear coupling dynamics and external disturbances. This paper introduces a first order sliding mode control (FOSMC) for robust stabilization of an under-actuated quad-rotor unmanned aerial vehicle (UAV) operating in the presence of external disturbances. The proposed FOSMC guarantees a finite time convergence of the system trajectories to the sliding surface. Obtained simulations show that the FOSM based approach improves robustness properties compared with the concurrent techniques, and enhance tracking performance of the quad-rotor UAV exposed to external disturbances.

This paper introduces a novel approach for state-space representation of linear time invariant (LTI) systems, so-called Future Inputs Elimination (FIE) method. It can be applied to single-input-single-output (SISO) or multiple-input-multiple-output (MIMO) systems, continuous-time or discrete-time systems, whose dynamic equations are coupled or separated (uncoupled) in terms of their inputs and outputs. The FIE method closely parallels to the controllable canonical method when restricted to a class of SISO LTI systems. Moreover, it retains an easy implementation and effortless computation even for a class of MIMO LTI systems. The proposed approach may be used for representation of LTI systems with multiple or complex-conjugate poles. Many representative numerical examples are provided in order to illustrate the effectiveness of the elimination state-space method for representation of both SISO and MIMO LTI systems.

Control design for trajectory tracking of multi-rotor aerial vehicles (MAVs) represents a challenging task due to the under-actuated property, highly nonlinear and cross-coupled dynamics, modeling errors, parametric uncertainties and external disturbances. This paper presents the design of the first order sliding mode control (FOSMC) algorithm for trajectory tracking of the octo-rotor unmanned aerial vehicle (UAV) in the presence of various disturbances. The highly nonlinear octo-rotor UAV dynamics is considered via the generalized framework for MAVs modeling. The stability analysis of the closed-loop system is presented using the Lyapunov based approach. The developed FOSMC exhibits finite-time convergence of the octo-rotor trajec-tories to the sliding manifold and the asymptotic stability of the equilibrium in the presence of vanishing disturbances. Simulation studies show a superior tracking performance and robustness properties of the FOSMC in comparison with the concurrent techniques for trajectory tracking of the octo-rotor UAV in the presence of internal and external disturbances.

Abstract The magnitude-based Fourier descriptors (FD) are frequently used in shape-based image retrieval, due to their efficiency and effectiveness. Unlike the phase-preserving Fourier descriptors, the magnitude-based Fourier descriptors are inherently invariant under rotation and starting point change, but they discard all valuable information contained in the phase of the Fourier coefficients (FCs). In order to preserve the coefficients’ phase, the orientation and starting point of the shape must be determined. In this paper, we conducted a comprehensive evaluation of different state-of-the-art methods for determining nominal shape orientation, which can be used to extract phase-preserving Fourier descriptors: the point of maximal radius, the axis of least inertia (moments), the phase of the first harmonic, the cross-correlation, the Procrustes distance and the pseudomirror points. The methods were compared in terms of sensitivity to non-rigid transformations, retrieval performance, computational complexity and computational time. The experimental results give insight into the pros and cons of all analyzed methods.

This paper introduces the robust internal-loop compensator based sliding mode control (SMRIC) scheme for multiple-input multiple-output (MIMO) nonlinear systems subjected to mismatched uncertainties, which are time-varying and non-vanishing with non-constant steady-state values. The proposed approach extends an application area of the robust internal-loop compensator (RIC), as well as a class of mismatched uncertainties that could be imposed on the system. The developed SMRIC technique allows substantial alleviation of the chattering phenomenon in the presence of disturbances while retaining the nominal performance of the system in the absence of disturbances. The stability analysis of the closed-loop system is performed using the Lyapunov-based approach. The proposed SMRIC method guarantees the finite-time convergence of the system trajectories to the sliding surface and provides asymptotic stability of the equilibrium. The simulation results of the numerical example and both simulation and experimental results of the application example show that the proposed SMRIC technique exhibits, in comparison with the concurrent algorithms, excellent tracking performance and robustness properties in the presence of modeling uncertainties, parameter variations, external disturbances, and mismatched uncertainties.

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.

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.

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.

Control design for a small-scale helicopter is quite challenging due to its nonlinearities, unknown and unmodelled dynamics, strong cross-coupling effects produced by the vehicles actuators, parametric uncertainties and external disturbances. This paper introduces the design of robust and stable disturbance observer (DOB) based sliding mode control (SMC) to meet these issues. It consists of the disturbance observer in the inner control loop which estimates and attenuates plant input generalized disturbance, and the sliding mode controller in the outer control loop which enforces convergence to the reference and stability of the equilibrium. Introduced disturbance observer is a linear low-pass filter capable to compensate unwanted chattering effects of the sliding mode control. The highly nonlinear helicopter model is introduced to illustrate effectiveness of the proposed control method. Designed controllers are implemented in the simulation mode and experimentally tested in a realistic environment. Obtained results showed that developed DOB based SMC controllers improve tracking performances o ver the entire range of the helicopter output variables even in the presence of additional parametric uncertainties, and external disturbances in the form of wind gusts.

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.

This paper describes the capabilities of fuzzy logic based controllers in the process of pneumatic active suspension of a heavy vehicle seat vibrations. The pneumatic active suspension system is introduced to solve conflicting requirements of comfort and handling. The air spring is used as an active element and the damper is used as passive element for reducing vibrations. The usage of the active air spring enhances passenger comfort by comparison with passive, semi-active and active hydraulic suspension, during long time drives at a very bumpy road. Description of the seat, including its mechanical characteristics, is given in the paper. The mathematical model was created according to the physical setup of the vehicle seat at the testing laboratory. MATLAB and Simulink are used as tools for developing the simulation model of the driver seat. Control system description and implementation at the experimental setup using dSPACE module, are also explained. The SEAT value is used for the validation of control quality. The obtained simulations show that the developed road adaptive suspension controllers provide superior driver's comfort for most difficult types of road.

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.