John Sigalas’s research while affiliated with National and Kapodistrian University of Athens and other places

Design and implementation of a robotic vision system capable of efficiently manuscript scanning and recognition. To scan manuscripts and recognize manuscript components, the robotic system aims at using cutting-edge machine vision techniques. The robotic system is connected to an ontology-based manuscript editor, where the scanned text is automatically stored in. This ground-breaking method aims at effectively scanning and preserving handwritten textual resources so that scholars and researchers can access and study manuscripts in fully annotated format. As the proposed robotic system will be constructed using a 3D printer, its low weight and cost provide portability and reconfigurability with respect to the shape and the dimensions of the manuscript.

A circular manufacturing system will be studied in the presence of sensor/actuator faults. The models of the subsystems of the plant in the presence of faults will be developed in the form of finite deterministic automata. The events of the faults are considered to be observable through AI-based fault detection algorithms. A set of rules, guaranteeing that when a device is in faulty mode then some actions that may cause safety issues will be restricted, is proposed. The design of the supervisors will be based on a family of two-state supervisor automata, providing low complexity to the supervisory control scheme. The controllability of the desired languages will be proved, through the physical realizability of the synchronous product of the supervisors and the total system. Finally, the nonblocking property of the controlled automaton will be proved.

Differential drive mobile robots, being widely used in several industrial and domestic applications, are increasingly demanding when concerning precision and satisfactory maneuverability. In the present paper, the problem of independently controlling the velocity and orientation angle of a differential drive mobile robot is investigated by developing an appropriate two stage nonlinear controller embedded on board and also by using the measurements of the speed and accelerator of the two wheels, as well as taking remote measurements of the orientation angle and its rate. The model of the system is presented in a nonlinear state space form that includes unknown additive terms arising from external disturbances and actuator faults. Based on the nonlinear model of the system, the respective I/O relation is derived, and a two-stage nonlinear measurable output feedback controller, analyzed into an internal and an external controller, is designed. The internal controller aims to produce a decoupled inner closed-loop system of linear form, regulating the linear velocity and angular velocity of the mobile robot independently. The internal controller is of the nonlinear PD type and uses real time measurements of the angular velocities of the active wheels of the vehicle, as well as the respective accelerations. The external controller aims toward the regulation of the orientation angle of the vehicle. It is of a linear, delayed PD feedback form, offering feedback from the remote measurements of the orientation angle and angular velocity of the vehicle, which are transmitted to the controller through a wireless network. Analytic formulae are derived for the parameters of the external controller to ensure the stability of the closed-loop system, even in the presence of the wireless transmission delays, as well as asymptotic command following for the orientation angle. To compensate for measurement noise, external disturbances, and actuator faults, a metaheuristic algorithm is proposed to evaluate the remaining free controller parameters. The performance of the proposed control scheme is evaluated through a series of computational experiments, demonstrating satisfactory behavior.

Design and implementation of a robotic vision system capable of efficiently manuscript scanning and recognition. To scan manuscripts and recognize manuscript components, the robotic system aims at using cutting-edge machine vision techniques. The robotic system is connected to an ontology-based manuscript editor, where the scanned text is automatically stored in. This ground-breaking method aims at effectively scanning and preserving handwritten textual resources so that scholars and researchers can access and study manuscripts in fully annotated format. As the proposed robotic system will be constructed using a 3D printer, its low weight and cost provide portability and reconfigurability with respect to the shape and the dimensions of the manuscript.