Nikos Aspragathos

The determination of the optimal position of a robotic task within a manipulator’s workspace is crucial for the manipulator to achieve high performance regarding selected aspects of its operation. In this paper, a method for determining the optimal task placement for a serial manipulator is presented, so that the required joint torques are minimized. The task considered comprises the exercise of a given force in a given direction along a 3D path followed by the end effector. Given that many such tasks are usually conducted by human workers and as such the utilized trajectories are quite complex to model, a Human Robot Interaction (HRI) approach was chosen to define the task, where the robot is taught the task trajectory by a human operator. Furthermore, the presented method considers the singular free paths of the manipulator’s end-effector motion in the configuration space. Simulation results are utilized to set up a physical execution of the task in the optimal derived position wi...

In this paper, an approach is proposed for the simultaneous manipulation of multiple hexagonal and square plastic–glass type microparts that are positioned randomly on a smart platform (SP) using electrostatic forces applied by the suitable activation of circular conductive electrodes. First, the statics analysis of a micropart on the SP is presented in detail and the forces and torques that are applied to and around the center of mass (COM) respectively due to the activation of a SP electrode are determined. The “single electrode activation” (SEA) and the “multiple electrodes activations” (MEA) algorithms are introduced to determine the feasible SP electrodes activations for the microparts manipulation considering their initial configuration. An algorithm for the simultaneous handling of multiple microparts is studied considering the collision avoidance with neighboring microparts. An approach is presented for the simultaneous centralization and alignment of the microparts preparin...

In this paper, methodologies are presented for the development of intelligent robot systems for the manipulation of linear and sheet like objects with low and/or very low bending rigidity. In the introduction the non-rigid objects are defined and classified considering their shape, bending rigidity and extensibility. The industrial and service applications of these systems are presented and the state of the art approaches for the manipulation of various categories of the non-rigid objects are presented. A brief State-of the-Art on the manipulation of the deformable objects with relatively low bending rigidity and presenting elastic behavior like foam, sheet metal is presented as well.The main part of the paper is devoted to the robotic manipulation of the sheet-like objects with very low rigidity such as fabrics and leather. Laboratory demonstrators accompany the presentation of the developed intelligent robotic systems for manipulation of non-rigid objects and the paper concludes w...

This paper considers the mission design problem for a service robot which is operating in a partly known indoor environment. A service robot is requested to serve a set of work stations in the environment providing transport and delivery tasks while avoiding collisions with the obstacles during its travel. The objective is to determine the optimum sequence of the work-stations visited by the service robot exactly once assuring that the robot’s path through the work-station is collision free. The problem addressed in this paper combines two computationally hard problems: the task scheduling problem and the motion planning between the successive work stations.

ABSTRACT In the present paper a closed loop fuzzy control scheme for the correction of the drop-foot syndrome is presented. The control scheme is based on EMG signals from the contralateral, unimpaired lower limb and its efficiency is tested by the application of the controller to a simulated bipedal locomotion with one lower limb suffering from the Drop-Foot Syndrome. Two are the major characteristics of the controller: identification of the phase where the stimulation must be provided using EMG signals from the contralateral, unimpaired lower limb and correction of the excitation signal according to the phase using EMG signals from the collateral impaired lower limb.

... Elias Xidias1, Nikos A. Aspragathos2, and Philip Azariadis1 ... (ii) The SR is a mobile manipulator, where the mobile platform is represented by a rectangular-shaped body with two rear wheels and two directional front wheels with a limited steering angle [8] and a PUMA 560 is ...

In the present paper a new mathematical fuzzy-logic-based formulation of the design objects and the rules that govern a design problem during the conceptual design phase is presented.. A procedure for the automatic generation of degrees of satisfaction of the design specifications for each feasible solution - subjected to design constraints - is introduced. A table containing the satisfaction degrees

... The evaluation of chromosomes is the most critical portion of a GA, since the generated values are used to control the evolution of the ... maximize the fitness function by forcing the energy function E′(ω) to a minimum value, ideally, to a zero value (case of a developable surface). ...

This paper introduces a method for applying texture from a two-dimensional domain to a three-dimensional surface which is divided into two stages: the pre-processing stage, where a proper planar development of the three-dimensional surface is generated and the stage of mapping texture from the plane to the given surface. Several techniques for generating planar developments are studied and a new

In this paper, two methods for generating a planar development of a three-dimensional (3D) surface are proposed. The first method is based on the solution of a global optimization problem without constraints taking into consideration the geodesic curvature of the surface isoparametric curves. The second method is based on the solution of a global optimization problem subject to constraints which

Abstract—A method for the determination of the optimum docking or hovering position of an Underwater Unmanned Vehicle is proposed for performing a desired intervention task with high dexterity. The optimization problem is formulated taken into account primarily the ...

Abstract— An approach for the determination of the optimum docking or hovering position of an Underwater Unmanned Vehicle is proposed towards the optimum performance for a desired intervention task. An underwater scenario with a UUV equipped with a 6 DOF manipulator ...

Abate, Alessandro Delft University of Technology, Netherlands Aitouche, Abdel LAGIS/HEI, France Albertos, Pedro Univ. Politécnica de Valencia, Spain Alonso, Alejandro Universidad Politécnica de Madrid, Spain Álvarez Bel, Carlos Universidad Politécnica de Valencia, Spain Andújar, José Manuel Universidad de Huelva, Spain Armengol Llobet, Joaquim Universitat de Girona, Spain Aspragathos, Nikos University of Patras, Greece Aubrun, Christophe University Henri Poincaré, France Benzaouia, Abdellah University of Cadi Ayyad, Morocco Bittanti, Sergio ...

In the design of a compliant admittance controller for physical human-robot interaction, it is necessary to ensure stable and effective cooperation. The stability of the admittance controller is mainly threatened by a stiff environment. Many methods that guarantee stability in arbitrary environments, impose conservative control gains that limit the effectiveness of the cooperation. Inspired by previous work in frequency domain stability observers, a method is proposed in this paper to detect unstable behavior and stabilize the robot with online adaptation of the admittance control gains. The introduced instability index is based on frequency domain analysis, which very quickly detects unstable behavior by monitoring high frequency oscillation in the force signal. To treat the instability, an adaptation scheme of the admittance parameters is proposed, that relaxes conservative gains and improves the cooperation by considering the effect of variable admittance on the operators' effort. We investigate two human-robot co-manipulation tasks; cooperation within a zero stiffness environment and cooperation in contact with a stiff double-wall virtual environment. The proposed methods are validated experimentally with a number of subjects in cooperation with an LWR manipulator.

ABSTRACT This paper presents an approach for the optimal design of a reconfigurable robot. The presented method derives the near optimal position of the path to be followed by the end-effector as well as the near optimal anatomy of the reconfigurable manipulator, namely link lengths, twist angles and offsets, for the given task. The main goal is to maximize the velocity performance of the manipulator along the end effector path of given shape, which is approximated by a generalized Taylor's method, using a cubic interpolation for the position and a Spherical Quadrangle Interpolation (squad) based on quaternions for the determination of the end effector's orientation along the path. The approximate minimum of the Manipulator Velocity Ratio is then computed along the path and used as an objective function to be maximized. Genetic Algorithms are used for the determination of the optimal robot anatomy and the optimal location of the path. 1 INTRODUCTION The last two decades, the robotics research community is focusing their efforts on reconfigurable robots for industrial application. Reconfigurable robots present higher capabilities than nowadays used fixed anatomy industrial manipulators due to their ability to take various physical configurations and therefore to adapt easily to a variety of single or multiple tasks. This particular ability is quite promising for the enhancement of robot application in the industry of the future. Designing a reconfigurable robotic workcell is a very complicated task. The designer has to determine not only the optimal placement of the robot's base, or that of the robotic task's if the base is fixed, but the optimal configuration of the manipulator as well, in order to achieve the highest possible efficiency for a given task, or set of multiple tasks. Different approaches have been followed in order to determine the optimal configuration of a reconfigurable manipulator for a given task. Chen [7] presented a methodology for the optimization of the configuration of a reconfigurable robotic workcell, where the objective function was formulated considering task performance. A "software agent" approach was deployed to speed up the optimization process, using a cluster of networked computers. In another approach, Yang and Chen [6] presented a method for the optimal design of a reconfigurable robot satisfying particular task requirements based on the minimal degrees of freedom approach. A kinematic graph based representation, termed Assembly Incidence Matrix (AIM) was introduced to mathematically describe modular robot configurations. The objective function is defined as the weighted sum of the different types of modules, while task related kinematic measures are used as design constraints. An evolutionary algorithm approach was deployed for the solution of the formulated optimization problem.