Titel Deelnemers "Korte inhoud"
"Optimal autonomous multirotor motion planning in an obstructed environment" "Fabrizio Giulietti, Goele Pipeleers" "© 2019 Elsevier Masson SAS This paper addresses a methodology for autonomous motion planning of multirotor aircraft in obstructed environments. The control strategy allows the vehicle to online generate quasi-optimal trajectories with limited computational load while performing collision avoidance tasks. The problem is formulated in a model-predictive control architecture in which motion planning and trajectory tracking processes are solved separately. The first process is based on a spline path planning approach to generate smooth and safe trajectories. The second process elaborates trajectory inputs in terms of commanded thrust magnitude and desired attitude rates in order to steer the vehicle during the mission task. Results of both numerical simulations and, for the first time, an experimental validation are provided in order to assess the performance of the approach in the presence of external disturbances and unmodeled dynamics, provided adequate time horizon and update frequency are selected for the numerical optimization algorithm."
"Two-time-scale control of a multirotor aircraft for suspended load transportation" "Fabrizio Giulietti, Goele Pipeleers" "© 2018 Elsevier Masson SAS This paper presents a trajectory control strategy for a multirotor aircraft carrying a suspended load. The load is modeled as a pendulum connected by a rigid link to the center of gravity of the vehicle. Starting from the dynamic equations describing the motion of the coupled vehicle slung-load systems, a nonlinear controller is proposed that simultaneously performs trajectory tracking and payload swing damping. Controller gains are chosen so that the system exhibits a two-time-scale behavior, with fast dynamics for the pendulum and slow dynamics for the positioning task. Under these conditions, the basic results of singular perturbation theory are evoked for both the proof of stability and the preliminary design of control gains. Results of numerical simulations are provided in order to assess the stability and performance of the considered approach."
"Multirotor aircraft formation flight control with collision avoidance capability" "Emanuele L de Angelis, Fabrizio Giulietti, Gianluca Rossetti" "© 2018 Elsevier Masson SAS An analytical and experimental framework addressing formation control of multirotor aircraft with collision avoidance capability is developed and presented. The proposed strategy applies to a formation of cooperating vehicles under the assumption of a broadcast transmission of position data. Starting from the point-mass dynamic model of the single aircraft in the formation, a set of constraints on the vehicles position is introduced and a nonlinear controller based on potential field method is proposed to simultaneously perform trajectory tracking, formation geometry keeping, and collision avoidance. Stability of the closed-loop control system is then proven by means of the Lyapunov method. Results of both numerical simulations and an experimental validation are provided in order to assess the proposed approach in the presence of external disturbances and unmodeled dynamics."
"Optimal Autonomous Quadrotor Navigation in an Obstructed Space" "Ruben Van Parys, Goele Pipeleers, Fabrizio Giulietti" "This paper shows an ambitious methodology of autonomous navigation for multirotor UAVs in obstructed environments. The following strategy was formulated to ensure to ultirotor vehicles the capability to produce autonomously quasi-optimal and safe trajectories, although generally they have at their disposal limited computational resources on board. The problem is formuled in a model predictive control (MPC) architecture in which motion planning and trajectory tracking processes are solved separately like they were stored in two different devices. The first one uses a spline-based motion planning approach to generate smooth and safe trajectories. At this step also a multicopter’s simplified dynamic model and environment information are taken in account. The second one uses trajectory inputs (total thrust and attitude angle rates) to steer the multicopter during the flight. Both adequate time horizon and update frequency are chosen in order to take in account disturbances and dynamics model mismatch. The following methodology will be validated with simulations and future work include experimental tests in outdoor environement."
"Single-Axis pointing of an underactuated spacecraft equipped with two reaction wheels" "Fabrizio Giulietti" "A smooth time-invariant wheel rate command is defined, based on angular momentum balance considerations, which causes the spacecraft to rotate approximately about the admissible rotation axis, which is lying on the plane identified by the two RW axes, implementing the kinematic planning scheme at a dynamic level. Convergence toward the prescribed alignment under the action of the proposed control law is proven using a Lyapunov approach, exploiting the cascade nature of system dynamics. Asymptotic convergence in a finite region around the desired final condition is proven first."
"Terminal height estimation using a Fading Gaussian Deterministic filter" "Fabrizio Giulietti" "© 2016 Elsevier Masson SAS In a recent work by the authors the concept of Fading Gaussian Deterministic filter was investigated. The algorithm is based on a set of equations derived from the minimization of a cost function where earlier data are progressively de-weighted by a fading factor. In such a way, the estimation was proved to be less prone to problem unknowns. A tuning procedure was proposed that allows the resulting globally best estimator to evaluate the covariance of an effective measurement noise and the true estimation error, without any a-priori assumption. In the present paper, a general formulation is derived where the observed system is influenced by a control input. Also, a proof is derived for the proposed tuning criterion, which is shown to provide, under certain assumptions, the fading factor that best dampens the modeling errors with respect to measurement noise. The validity of the proposed approach is investigated by means of both numerical simulations and an experimental campaign, where height estimation is performed by fusing information from MEMS accelerometers and a barometric altimeter."
"Visual aids for safe operation of remotely piloted vehicles in the controlled air space" "Fabrizio Giulietti" "© Institution of Mechanical Engineers. The paper presents a set of visual AIDS for enhancing remote pilot perception of potential violations of allowed fly areas or conflicts with conventional air traffic when operating remotely piloted aerial vehicles. Assuming a video stream from an on-board camera is available to the remote pilot, visual AIDS are provided in a head-up display modality by means of reality augmentation techniques. The main visual element consists of a dynamic set of fences allowing for a safe aircraft separation away from no-fly zones and from neighboring vehicles. The shape of the fences is varied according to aircraft current speed and altitude, in order to allow for a sufficient safety margin, also in case of a loss-of-control accident. As a further visual aid, the predicted future position of the aircraft is determined and fence color is changed in order to highlight potential violations of the allowed operational area. The proposed methodology is validated by means of simulations in a reference operational scenario. Results demonstrate the effectiveness of the proposed approach in improving pilot awareness."
"Spacecraft dynamics under the action of Y-dot magnetic control law" "Fabrizio Giulietti" "© 2016 IAA. Published by Elsevier Ltd. All rights reserved. The paper investigates the dynamic behavior of a spacecraft when a single magnetic torque-rod is used for achieving a pure spin condition by means of the so-called Y-dot control law. Global asymptotic convergence to a pure spin condition is proven on analytical grounds when the dipole moment is proportional to the rate of variation of the component of the magnetic field along the desired spin axis. Convergence of the spin axis towards the orbit normal is then explained by estimating the average magnetic control torque over one orbit. The validity of the analytical results, based on some simplifying assumptions and approximations, is finally investigated by means of numerical simulation for a fully non-linear attitude dynamic model, featuring a tilted dipole model for Earth's magnetic field. The analysis aims to support, in the framework of a sound mathematical basis, the development of effective control laws in realistic mission scenarios. Results are presented and discussed for relevant test cases."
"Spacecraft Attitude Control Using Magnetic and Mechanical Actuation" "Fabrizio Giulietti" "© Copyright 2015 by the American Institute of Aeronautics and Astronautics, Inc. The aim of this paper is the analysis of simultaneous attitude control and momentum-wheel management of a spacecraft by means of magnetic actuators only. A proof of almost global asymptotic stability is derived for control laws that drive a rigid satellite toward attitude stabilization in the orbit frame when the momentum wheel is aligned with one of the principal axes of inertia. Performance of the proposed control laws is demonstrated by numerical simulations under actuator saturation. Robustnesstoexternal disturbances and model uncertaintiesisalso evaluated."
"Unified kinematic framework for a non-nominal Euler axis/angle rotation" "Fabrizio Giulietti" "© 2015 IAA. Published by Elsevier Ltd. All rights reserved. In this paper, kinematics equations of attitude parameters are derived for cases where the Euler rotation theorem cannot be applied and the single rotation that takes an initial reference frame to a target reference frame cannot be performed. It is the case when the nominal rotation is not allowed along a prescribed direction in space, namely an ""underactuation"" direction. As a matter of fact, a non-nominal maneuver planning scheme, expressed in terms of Euler axis/angle parameters, is admitted for the minimization of the alignment error between the target and the attainable attitude. The derivation of kinematic equations, describing the time evolution of non-nominal rotation parameters, is performed by means of rigorous algebraic manipulations within a unified framework, where the underactuation direction is prescribed in either the moving frame or the target frame."