<div>Multi-robot systems have demonstrated strong capability in handling environmental operations. In this study, We examine how a team of robots can be utilized in covering and removing spill patches in a dynamic environment by executing three consecutive stages: deployment, coverage, and rendezvous. </div><div> </div><div>For the deployment problem, we aim for robot allocation based on the discreteness of the patches that need to be covered. With the deep neural network (DNN) based spill detector and remote sensing facilities such as drones with vision sensors and satellites, we are able to obtain the spill distribution in the workspace. Then, we formulate the allocation problem in a general optimization form and provide solutions using an integer linear programming (ILP) solver under several realistic constraints. After the allocation process is completed and the robot team is divided according to the number of spills, we deploy robots to their computed optimal goal positions. In the robot deployment part, control laws based on artificial potential field (APF) method are proposed and practiced on robots with a common unicycle model. </div><div> </div><div>For the coverage control problem, we show two strategies that are tailored for a wirelessly networked robot team. We propose strategies for coverage with and without path planning, depending on the availability of global information. Specifically, in terms of coverage with path planning, we partition the workspace from the aerial image into pieces and let each robot take care of one of the pieces. However, path-planning-based coverage relies on GPS signals or other external positioning systems, which are not applicable for indoor or GPS-denied circumstances. Therefore, we propose an asymptotic boundary shrink control that enables a collective coverage operation with the robot team. Such a strategy does not require a planned path, and because of its distributedness, it shows many advantages, including system scalability, dynamic spill adaptability, and collision avoidance. In case of a large-scale patch that poses challenges to robot connectivity maintenance during the operation, we propose a pivot-robot coverage strategy by mean of an a priori geometric tessellation (GT). In the pivot-robot-based coverage strategy, a team of robots is sent to perform complete coverage to every packing area of GT in sequence. Ultimately, the entire spill in the workspace can be covered and removed.</div><div> </div><div>For the rendezvous problem, we investigate the use of graph theory and propose control strategies based on network topology to motivate robots to meet at a designated or the optimal location. The rendezvous control strategies show a strong robustness to some common failures, such as mobility failure and communication failure. To expedite the rendezvous process and enable herding control in a distributed way, we propose a multi-robot multi-point rendezvous control strategy. </div><div> </div><div>To verify the validity of the proposed strategies, we carry out simulations in the Robotarium MATLAB platform, which is an open source swarm robotics experiment testbed, and conduct real experiments involving multiple mobile robots.</div>

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Autonomous multi-robot systems have found many real-world applications in factory settings, rescue tasks and light shows. Albeit these successful applications, the multi-robot system is usually pre-programmed with limited flexibility for online adaptation. Having a human-in-the-loop feature would provide additional flexibility such as handling unexpected situations, detecting and correcting bad behaviours and supporting the automated decision making. In addition, it would also allow for an extra level of cooperation between the robots and the human that facilitates certain real-world tasks, for example in the agricultural sector. Control barrier functions (CBFs), as a convenient modular-design tool, will be mainly explored. CBFs have seen a lot of development in recent years and extending them to the field of multi-robot systems is still new. In particular, creating an original distributed approach, instead of a centralized one, will be one of the key topics of this Master’s thesis project. In this thesis work, several multi-robot coordination protocols and safety constraints will be identified and these constraints will be enforced using a control barrier function-enabled mixer module. This module will take in the commands from both the planner and the human operator, prioritizing the commands from the human operator as long as the safety constraints are not violated. Otherwise, the mixer module will filter the commands and send out a safe alternative. The underlying multi-robot tasks are expected to be achieved whenever feasible. Simulations in ROS, Python and MATLAB environments are developed to experimentally assess the safety and optimality of the system, and experiments with real robots in a lab are performed to show the applicability of this algorithm. Finally, a distributed approach to the mixer module has been developed, based on previous research and extended to allow for more versatility. This is of key importance since it would allow each robot to compute its own controller based on local information, making the multi-robot system both more robust and flexible to be deployed on real-world applications. / Autonoma multirobotsystem har fått många verkliga tillämpningar i fabriksmiljöer, räddningsuppdrag och ljusshower. Trots dessa framgångsrika tillämpningar är multirobotsystemet vanligtvis förprogrammerat med begränsad flexibilitet för anpassning online. En människa i loopen skulle ge ytterligare flexibilitet, t.ex. när det gäller att hantera oväntade situationer, upptäcka och korrigera dåliga beteenden och stödja det automatiska beslutsfattandet. Dessutom skulle det också möjliggöra en extra samarbetsnivå mellan robotarna och människan som underlättar vissa verkliga uppgifter, till exempel inom jordbrukssektorn. Kontrollbarriärfunktioner (CBF), som ett bekvämt verktyg för modulbaserad utformning, kommer huvudsakligen att undersökas. CBF:er har utvecklats mycket under de senaste åren och det är fortfarande nytt att utvidga dem till flerrobotsystem. Att skapa ett originellt distribuerat tillvägagångssätt i stället för ett centraliserat kommer att vara ett av de viktigaste ämnena i detta examensarbete. I detta examensarbete kommer flera samordningsprotokoll och säkerhetsbegränsningar för flera robotar att identifieras och dessa begränsningar kommer att upprätthållas med hjälp av en mixermodul med kontrollbarriärfunktion. Denna modul kommer att ta emot kommandon från både planeraren och den mänskliga operatören och prioritera kommandon från den mänskliga operatören så länge säkerhetsbegränsningarna inte överträds. I annat fall kommer mixermodulen att filtrera kommandona och skicka ut ett säkert alternativ. De underliggande multirobotuppgifterna förväntas uppnås närhelst det är möjligt. Simuleringar i ROS-, Python- och MATLAB-miljöerna utvecklas för att experimentellt bedöma systemets säkerhet och optimalitet, och experiment med riktiga robotar i ett labb utförs för att visa algoritmens tillämpbarhet. Slutligen har ett distribuerat tillvägagångssätt för mixermodulen utvecklats, baserat på tidigare forskning och utökat för att möjliggöra större mångsidighet. Detta är av central betydelse eftersom det skulle göra det möjligt för varje robot att beräkna sin egen styrning utifrån lokal information, vilket gör systemet med flera robotar både mer robust och flexibelt för att kunna användas i verkliga tillämpningar.

Este trabajo analiza la idoneidad de dos de los principales métodos de asignación de tareas en entornos con restricciones temporales. Se pondrá de manifiesto que ambos tipos de mecanismos presentan carencias para tratar tareas con deadlines, especialmente cuando los robots han de formar coaliciones. Uno de los aspectos a los que esta tesis dedica mayor atención es la predicción del tiempo de ejecución, que depende, entre otros factores, de la interferencia física entre robots. Este fenómeno no se ha tenido en cuenta en los mecanismos actuales de asignación basados en subastas. Así, esta tesis presenta el primer mecanismo de subastas para la creación de coaliciones que tiene en cuenta la interferencia entre robots. Para ello, se ha desarrollado un modelo de predicción del tiempo de ejecución y un nuevo paradigma llamado subasta doble. Además, se han propuesto nuevos mecanismos basados en swarm

L’objectif principal de cette thèse est d’étudier le problème du contrôle de suivi distribué pour les systèmes de formation de multi-robots à contrainte non holonomique. Ce contrôle vise à entrainer une équipe de robots mobile de type monocycle pour former une configuration de formation désirée avec son centroïde se déplaçant avec une autre trajectoire de référence dynamique et pouvant être spécifié par le leader virtuel ou humain. Le problème du contrôle de suivi a été résolu au cours de cette thèse en développant divers contrôleurs distribués pratiques avec la considération d’un taux de convergence plus rapide, une précision de contrôle plus élevée, une robustesse plus forte, une estimation du temps de convergence explicite et indépendante et moins de coût de communication et de consommation d’énergie. Dans la première partie de la thèse nous étudions d’abord au niveau du chapitre 2 la stabilité à temps fini pour les systèmes de formation de multi-robots. Une nouvelle classe de contrôleur à temps fini est proposée dans le chapitre 3, également appelé contrôleur à temps fixe. Nous étudions les systèmes dynamiques de suivi de formation de multi-robots non holonomiques dans le chapitre 4. Dans la deuxième partie, nous étudions d'abord le mécanisme de communication et de contrôle déclenché par l'événement sur les systèmes de suivi de la formation de multi-robots non-holonomes au chapitre 5. De plus, afin de développer un schéma d'implémentation numérique, nous proposons une autre classe de contrôleurs périodiques déclenchés par un événement basé sur un observateur à temps fixe dans le chapitre 6. / The main aim of this thesis is to study the distributed tracking control problem for the multi-robot formation systems with nonholonomic constraint, of which the control objective it to drive a team of unicycle-type mobile robots to form one desired formation configuration with its centroid moving along with another dynamic reference trajectory, which can be specified by the virtual leader or human. We consider several problems in this point, ranging from finite-time stability andfixed-time stability, event-triggered communication and control mechanism, kinematics and dynamics, continuous-time systems and hybrid systems. The tracking control problem has been solved in this thesis via developing diverse practical distributed controller with the consideration of faster convergence rate, higher control accuracy, stronger robustness, explicit and independent convergence time estimate, less communication cost and energy consumption.In the first part of the thesis, we first study the finite-time stability for the multi-robot formation systems in Chapter 2. To improve the pior results, a novel class of finite-time controller is further proposed in Chapter 3, which is also called fixed-time controller. The dynamics of nonholonomic multi-robot formation systems is considered in Chapter 4. In the second part, we first investigate the event-triggered communication and control mechanism on the nonholonomic multi-robot formation tracking systems in Chapter 5. Moreover, in order to develop a digital implement scheme, we propose another class of periodic event-triggered controller based on fixed-time observer in Chapter 6.

<p dir="ltr">Autonomous robots can perform dangerous and tedious tasks, eliminating the need for human involvement. To deploy an autonomous robot in the field, a typical planning and control hierarchy is used, consisting of a high-level planner, a mid-level motion planner, and a low-level tracking controller. In applications such as simultaneous localization and mapping, package delivery, logistics, and surveillance, a group of autonomous robots can be more efficient and resilient than a single robot. However, deploying a multi-robot team by directly aggregating each robot's planning hierarchy into a larger, centralized hierarchy faces challenges related to scalability, resilience, and real-time computation. Distributed algorithms offer a promising solution for introducing effective coordination within a network of robots, addressing these issues. This thesis explores the application of distributed algorithms in multi-robot systems, focusing on several essential components required to enable distributed multi-robot coordination, both in general terms and for specific applications.</p>