In this work, we deal with a double control task for a group of interacting agents having a second-order dynamics. Adopting the leader-follower paradigm, the given multi-agent system is required to maintain a desired formation and to collectively track of a velocity reference provided by an external source to a single agent. We prove that it is possible to optimize the group performance by persistently selecting online the leader among the agents. To do this, we first define a suitable error metric able to capture the tracking performance of the multi- agent group while maintaining a desired formation through a (even time-varying) communication-graph topology. Then we show that this depends on the algebraic connectivity and on the maximum eigenvalue of the Laplacian matrix of a special directed graph induced by the identity of the chosen leader. By exploiting these theoretical results, we finally design a fully- distributed adaptive procedure able to periodically select online the optimum leader among the neighbors of the current one. The effectiveness of the proposed solution against other possible strategies is confirmed by numerical simulations.

In this paper, we shed light on two fundamental actuation capabilities of multirotors. The first is the degree of coupling between the total force and total moment generated by the propellers. The second is the ability to robustly fly completely still in place after the loss of one or more propellers, in the case of mono-directional propellers. These are formalized through the definition of some algebraic conditions on the control allocation matrices. The theory is valid for any multirotor, with arbitrary number, position, and orientation of the propellers. As a show case for the general theory, we demonstrate that standard star-shaped hexarotors with collinear propellers are not able to robustly fly completely still at a constant spot using only five of their six propellers. To deeply understand this counterintuitive result, it is enough to apply our theory, which clarifies the role of the tilt angles and locations of the propellers. The theory is also able to explain why, on the contrary, both the tilted star-shaped and the Y-shaped hexarotors can fly with only five out of six propellers. The analysis is validated with both simulations and extensive experimental results showing recovery control after rotor losses.

Over the past few years, a huge number of distributed camera calibration strategies have been proposed for video surveillance and monitoring systems involving mobile terminals. Many of the proposed solutions rely on consensus-based algorithms, which aim at estimating the configuration of the network via a message passing protocol. In this paper we propose an improved consensus-based distributed camera calibration strategy that exploits a robust initialization, together with a pruning protocol to remove faulty links which could propagate excessively-noisy information through the network reducing the convergence time. The proposed solution seems to improve the state-of-the-art strategies in terms of accuracy, convergence speed, and computational complexity.

Over the last decades, small satellites have become very appealing among the space community for their low complexity and high flexibility. Many proposed mission concepts foresee the employment of miniature spacecraft for a variety of applications, many of which are economically unfeasible with traditional vehicles. This is due to the fact that the development of miniaturized and standardized space vehicles may considerably reduce the design, manufacturing and lunch costs involved. Furthermore, the reduced unitary mass of small satellites allows launches of multiple vehicles equipped with independent functionalities, thus achieving increased flexibility and redundancy. In the future, one additional opportunity could be given by the capability to assemble spacecraft in orbit to form reconfigurable structures. This would further boost the number of possibilities in terms of applications and operations. Nevertheless, the novelty of such concept and the intrinsic complexity of its practical realization still require a considerable research effort. In fact, only few navigation and docking technologies for nano- and micro satellites have been designed and proved in relevant environment. In this framework, the authors focus on the development and validation of critical technologies for close navigation, rendezvous and docking suitable for nanosatellites.

This paper presents a laboratory experiment for the validation on a complete rendezvous, navigation and docking package compatible with the common CubeSat standard. The experiment is conducted on a low friction table, with one free moving vehicle (chaser) that approaches and docks to a fixed target interface. The test facility allows three degrees of freedom to the nanosat mock-up. The vehicle is equipped with an autonomous package that features (1) a camera-based vision system for relative navigation, (2) a set of independent electro-magnetic coils for final alignment and soft docking, (3) a single-actuator hard docking system for structural connection between the chaser and the target, (4) a dedicated electronics package for motion control and system status monitoring. The mobile platform is also equipped with a set of flat air bearing with a dedicated high-pressure pneumatic circuit for frictionless in-plane motion.

This paper describes the docking package, the CubeSat mock-up and the test facility in details, with reference to the main design considerations. Numerical simulations have been conducted to foresee the dynamical behaviour of the system and to select the appropriate control algorithm. An intensive experimental campaign aims at the validation of numerical results and at the functional verification and performance estimation for each subsystem and for the system as a whole. The numerical and experimental results are presented and compared, allowing to draw useful conclusions for the future development steps. 

Standard hexarotors are often mistakenly considered ‘by definition’ fail-safe multi-rotor platforms because of the two additional propellers when compared to quadrotors. However this is not true, in fact, a standard hexarotor cannot statically hover with ‘only’ five propellers. In this paper we provide a set of new general algebraic conditions to ensure static hover for any multi-rotor platform with any number of generically oriented rotors. These are elegantly formulated as the full-rankness of the control moment input matrix, and the non-orthogonality between its null-space and the row space of the control force input matrix. Input saturations and safety margins are also taken into account with an additional condition on the null-space of control moment input matrix. A deep analysis on the hoverability properties is then carried out focusing on the propeller loss in a hexarotor platform. Leveraging our general results we explain why a standard hexarotor is not robust and how it can be made robust thanks to a particular tilt of the rotors. We finally propose a novel cascaded controller based on a preferential direction in the null-space of the control moment input matrix for the large class of statically hoverable multi-rotors, which goes far beyond standard platforms, and we apply this controller to the case of failed tilted hexarotor.

Wireless sensor networks (WSNs) can provide numerous benefits in industrial automation. By removing the cable infrastructure, the wireless architecture enables the possibility for nodes in a network to dynamically and autonomously group into clusters according to the communication features and the data they collect. This capability allows to leverage the flexibility and robustness of industrial WSNs in supervisory intelligent systems for high-level tasks, such as, for example, environmental sensing, condition monitoring, and process automation. In this paper, a clustering strategy is studied that partitions a sensor network into a nonfixed number of nonoverlapping clusters according to the communication network topology and measurements distribution: To this aim, both a centralized and a distributed algorithm are designed that do not require a cluster-head structure or other network assumptions. As a validation, these strategies are tested on a real dataset coming from a structured environment and the effectiveness of the clustering procedure is also investigated to perform anomalies detection in an industrial production process.

In  this  paper  we  address  the  average  consensus problem in a Wireless Sensor-Actor Network with the particular focus  on  autonomous  fault  detection.  To  this  aim,  we  design  a distributed  clustering  procedure  that  partitions  the  network into  clusters  according  to  both  similarity  of  measurements and communication connectivity. The exploitation of clustering techniques   in   consensus   computation   allows   to   obtain   the detection   and   isolation   of   faulty   nodes,   thus   assuring   the convergence  of  the  other  nodes  to  the  exact  consensus  value. More  interestingly,  the  algorithm  can  be  integrated  into  a Kalman filtering framework to perform distributed estimation of  a  dynamic  quantity  in  presence  of  faults.  The  proposed approach is validated through numerical simulations and tests on a real world scenario dataset.