Abdelkader Abdessameud

Attitude Synchronization of a Group of Spacecraft Without Velocity Measurements

We consider the coordinated attitude control problem for a group of spacecraft, without velocity measurements. Our approach is based on the introduction of auxiliary dynamical systems (playing the role of velocity observers in a certain sense) to generate the individual and relative damping terms in the absence of the actual angular velocities and relative angular velocities. Our main focus, in this technical note, is to address the following two problems: 1) Design a velocity-free attitude tracking and synchronization control scheme, that allows the team members to align their attitudes and track a time-varying reference trajectory (simultaneously). 2) Design a velocity-free synchronization control scheme, in the case where no reference attitude is specified, and all spacecraft are required to reach a consensus by aligning their attitudes with the same final time-varying attitude. In this work, one important and novel feature (besides the non-requirement of the angular velocity measurements), consists in the fact that the control torques are naturally bounded and the designer can arbitrarily assign the desired bounds on the control torques, a priori, through the control gains, regardless of the angular velocities. Throughout this technical note, the communication flow between spacecraft is assumed to be undirected. Simulation results of a scenario of four spacecraft are provided to show the effectiveness of the proposed control schemes.

On consensus algorithms for double-integrator dynamics without velocity measurements and with input constraints ✩

This note deals with consensus strategy design for double-integrator dynamics. Specifically, we consider the case where the control inputs are required to be a priori bounded and the velocity (second state) is not available for feedback. Two different design methods are proposed. First, based on the auxiliary system approach, we propose a consensus algorithm that extends some of the existing results in the literature to account for actuator saturations and the lack of velocity measurement. The proposed velocity-free control scheme, using local information exchange, achieves consensus among the team members with an a priori bounded control law, whose upper bound depends on the number of neighbors of the vehicle. Second, we propose another approach based on the use of a high order dynamic auxiliary system such that the upper bound of the control law is independent of the number of neighbors of the vehicle, and the performance of the closed loop system is improved in terms of the response damping. Finally, simulation results are provided to illustrate the effectiveness of the proposed algorithms.

Formation control of VTOL Unmanned Aerial Vehicles with communication delays

The formation control problem of a team of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) with communication delays is addressed. Based on the extraction algorithm presented in Abdessameud and Tayebi (2010a), we propose a new design methodology that simplifies the design of formation control laws with delayed communication for this class of under-actuated systems. Three control schemes are presented that provide delay-dependent and delay-independent results with constant and time-varying communication delays. The stability of the overall closed loop system in each scheme is established using Lyapunov-Krasovskii functionals. The proposed design methodology achieves global results in terms of the position and removes the requirement of the linear-velocity measurements. Simulation results are provided to show the effectiveness of the proposed control schemes.

Brief paper: Global trajectory tracking control of VTOL-UAVs without linear velocity measurements

This paper deals with the position control of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) without linear velocity measurements. We propose a multistage constructive procedure, exploiting the cascade property of the translational and rotational dynamics. More precisely, we consider the force as a virtual control input for the translational dynamics, from which we extract the required (desired) system attitude and thrust achieving the tracking objective. Thereafter, the control torque is designed to drive the actual attitude to the desired one. A nonlinear observer, as well as some instrumental auxiliary variables are used to obviate the need for the linear velocity. Global asymptotic stability of the overall closed loop system is achieved. Simulation results are provided to show the effectiveness of the proposed control scheme.

On consensus algorithms design for double integrator dynamics

This paper considers the consensus problem of double integrator multi-agent systems where: (i) each agent is subject to input saturations, and (ii) the velocity (second state) of each agent is not available for feedback. We present new consensus algorithms that handle simultaneously the above mentioned situations. Sufficient conditions are derived such that consensus algorithms developed for first- and second-order multi-agent systems in ideal situations can be used to account for input saturations and remove the requirement of velocity measurements. To illustrate the effectiveness of the proposed approach, we propose solutions to two different second-order consensus problems in the case where the input is saturated and the velocity states are not available for feedback and simulation results are provided in each case.

Attitude Synchronization of Multiple Rigid Bodies With Communication Delays

We consider the attitude synchronization problem of multiple rigid bodies (or spacecraft) in the presence of communication delays. Specifically, we propose a virtual systems-based approach that removes the requirement of the angular velocity measurements. First, we present a solution to the leaderless and leader-follower problems in the case of time-varying communication delays and undirected communication topology. Second, we present an attitude synchronization scheme that solves the leaderless problem under directed interconnection between rigid bodies in the presence of constant communication delays. Finally, we show that the proposed schemes can be extended in a straightforward manner to solve the cooperative attitude tracking control problem.

Synchronization of Lagrangian Systems With Irregular Communication Delays

The synchronization problem of networked Euler-Lagrange systems with unknown parameters is addressed. The information flow in the network is represented by a directed communication graph and is subject to unknown and possibly discontinuous time-varying communication delays with unknown upper bounds. We propose a control scheme that achieves position synchronization, i.e., all the positions of the systems converge to a common final position, provided that the directed communication graph contains a spanning tree. The convergence analysis of the proposed scheme is based on the multidimensional small-gain framework. Simulation results on a network of ten robot manipulators are given to illustrate the effectiveness of the proposed control scheme.

Image-based tracking control of VTOL unmanned aerial vehicles

This paper addresses the image-based control problem of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs). Specifically, we propose a control scheme allowing the aircraft to track a moving target captured by an onboard camera where the orientation and angular velocity of the vehicle are assumed available for feedback. The proposed approach relies on appropriate image features, defined based on perspective image moments along with a useful projection, and the design of a bounded adaptive translational controller without linear velocity measurements in the presence of external disturbances. Estimates of the targets acceleration and the disturbances as well as some auxiliary variables are used to simplify the control design and guarantee the stability of the overall closed loop system. Simulation examples are provided to show the effectiveness of the proposed theoretical results.

Synchronization of networked Lagrangian systems with input constraints

Abstract This paper addresses the synchronization problem of systems modeled by Euler-Lagrange equations and subject to input saturations. First, a new control design strategy, based on virtual systems, is proposed. This approach allows to generate control inputs that are a priori bounded in the presence of communication time-delays, regardless of the information flow topology between systems in the network. Second, we remove the requirement of the generalized velocities, leading to a velocity-free synchronization scheme with a priori bounded inputs. The effectiveness of the proposed control schemes is demonstrated through simulation examples on a network of four robot manipulator arms.

Attitude synchronization of a spacecraft formation without velocity measurement

We consider the quaternion-based attitude synchronization problem of multiple spacecraft without velocity measurements. First, we propose a leader-follower-type control scheme for the attitude synchronization of a spacecraft formation to a desired constant attitude (available only to a single spacecraft called the leader), while maintaining the same attitude during formation maneuvers. Second, we consider the consensus seeking problem, where, no reference attitude is specified, and all spacecraft are required to align their attitudes with the same (possibly time varying) final angular velocity. The communication flow between spacecraft is assumed to be bidirectional. Simulation results of a scenario of four spacecraft are provided to show the effectiveness of the proposed control scheme.