Motion Coordination of Aerial Vehicles

The coordinated motion control of multiple vehicles has emerged as a field of major interest in the control community. This thesis addresses two topics related to the control of a group of aerial vehicles: the output feedback attitude synchronization of rigid bodies and the formation control of Unmanned Aerial Vehicles (UAVs) capable of Vertical Take-Off and Landing (VTOL). The information flow between members of the team is assumed fixed and undirected. The first part of this thesis is devoted to the attitude synchronization of a group of spacecraft. In this context, we propose control schemes for the synchronization of a group of spacecraft to a predefined attitude trajectory without angular velocity measurements. We also propose some velocity-free consensus-seeking schemes allowing a group of spacecraft to align their attitudes, without reference trajectory specification. The second part of this thesis is devoted to the control of a group of VTOL-UAVs in the Special Euclidian group SE(3), i.e., position and orientation. In this context, we propose a few position coordination schemes without linear-velocity measurements. We also propose some solutions to the same problem in the presence of communication time-delays between aircraft. To solve the above mentioned problems, several new technical tools have been introduced in this thesis to overcome the deficiencies of the existing techniques in this field

Thermodynamic Modeling of the Mg-Al-Li-Na-H System for Solid State Hydrogen Storage Applications

In this work a thermodynamic database describing the Mg-Al-Li-Na-H system was constructed using thermodynamic modeling through the CALPHAD method. The constructed database was used to assess the hydrogen storage properties of the system at different pressures and temperatures and to understand the phase relationships and reactions mechanisms. The liquid phase in the binary systems was reassessed using the modified quasichemical model (MQM) or taken from the literature. Since hydrogen atoms occupy the interstitial positions in the solid phases, terminal solid solution phases were described using the compound energy formalism (CEF). Two sublattices were used where Mg, Al, Li, and Na atoms mix randomly in the first sublattice to allow for their mutual solubility and H atom and vacancy mix in the second sublattice. All the gases included in this study were considered ideal. The calculated phase diagrams and thermodynamic properties were compared to experimental data from the literature and showed good agreement. The ternary systems were extrapolated from the corresponding binaries using the asymmetric Kohler-Toop technique where H is singled out as the asymmetric component. In this study, all the calculations were performed using the FactSage software where all the cited models are already coded and implemented. The constructed database allowed the calculation of pressure-composition isotherms of MgH2-10 wt. % NaH, Mg-10 at. % Al and Mg-4 at. % Al. Phase diagrams, pressure temperature diagrams, and reaction pathways of the composites MgH2-AlH3, MgH2-NaAlH4, MgH2-Na3AlH6, and MgH2-AlLiH4/AlLi3H6 were calculated and showed good agreement with the experimental data from the literature. The results provided more details about the de/hydrogenation processes, the amount and composition of phases, and the effect of the pressure and temperature. It is found that Al and Li when added to Mg improve the hydrogen potential of the system and the most promising compositions were predicted. The strategy used in this study will allow the experimental investigations to focus on the kinetics aspect of the de/hydrogenation reactions for these alloys

Advanced trajectory tracking for UAVs using combined feedforward/feedback control design

Trajectory tracking is a major challenge for UAVs. The more complex the trajectory is, the more accurate tracking is required with minimum divergence from the trajectory. Apart from active trajectory tracking mechanisms, current solutions to accurate trajectory tracking in narrow areas require low speed motions. This paper presents a systematic design methodology using centralised feedforward/feedback control architecture for advanced trajectory tracking without compromising the speed of the vehicle. Using the norm as a measure for the design criteria, the proposed method proves fast tracking with no overshooting and less actuators energy compared with single degree-of-freedom feedback control method. The results are verified using simulations for two systems: a tri-rotor VTOL UAV (fully actuated system), and a quadrotor trainer (over-actuated system)

Fault-tolerant formation driving mechanism designed for heterogeneous MAVs-UGVs groups

A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper

Distributed Adaptive Attitude Synchronization of Multiple Spacecraft

This paper addresses the distributed attitude synchronization problem of multiple spacecraft with unknown inertia matrices. Two distributed adaptive controllers are proposed for the cases with and without a virtual leader to which a time-varying reference attitude is assigned. The first controller achieves attitude synchronization for a group of spacecraft with a leaderless communication topology having a directed spanning tree. The second controller guarantees that all spacecraft track the reference attitude if the virtual leader has a directed path to all other spacecraft. Simulation examples are presented to illustrate the effectiveness of the results.Comment: 13 pages, 11 figures. To appear in SCIENCE CHINA Technological Science

Task space consensus in networks of heterogeneous and uncertain robotic systems with variable time-delays

This work deals with the leader-follower and the leaderless consensus problems in networks of multiple robot manipulators. The robots are non-identical, kinematically different (heterogeneous), and their physical parameters are uncertain. The main contribution of this work is a novel controller that solves the two consensus problems, in the task space, with the following features: it estimates the kinematic and the dynamic physical parameters; it is robust to interconnecting variable-time delays; it employs the singularity-free unit-quaternions to represent the orientation; and, using energy-like functions, the controller synthesis follows a constructive procedure. Simulations using a network with four heterogeneous manipulators illustrate the performance of the proposed controller.Peer ReviewedPostprint (author's final draft