Lorenzo SABATTINI - personale UniMoRe

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Lorenzo SABATTINI

Professore Associato
Dipartimento di Scienze e Metodi dell'Ingegneria

Pubblicazioni

2024 - Coverage Control for Exploration of Unknown Non-convex Environments with Limited Range Multi-robot Systems [Relazione in Atti di Convegno]
Catellani, Mattia; Pratissoli, Federico; Bertoncelli, Filippo; Sabattini, Lorenzo
abstract

2024 - Distributed Control of a Limited Angular Field-of-View Multi-Robot System in Communication-Denied Scenarios: A Probabilistic Approach [Articolo su rivista]
Catellani, M.; Sabattini, L.
abstract

Multi-robot systems are gaining popularity over single-agent systems for their advantages. Although they have been studied in agriculture, search and rescue, surveillance, and environmental exploration, real-world implementation is limited due to agent coordination complexities caused by communication and sensor limitations. In this work, we propose a probabilistic approach to allow coordination among robots in communication-denied scenarios, where agents can only rely on visual information from a camera with a limited angular field-of-view. Our solution utilizes a particle filter to analyze uncertainty in the location of neighbors, together with Control Barrier Functions to address the exploration-exploitation dilemma that arises when robots must balance the mission goal with seeking information on undetected neighbors. This technique was tested with virtual robots required to complete a coverage mission, analyzing how the number of deployed robots affects performances and making a comparison with the ideal case of isotropic sensors and communication. Despite an increase in the amount of time required to fulfill the task, results have shown to be comparable to the ideal scenario in terms of final configuration achieved by the system.

2024 - Distributed Coverage Control for Spatial Processes Estimation With Noisy Observations [Articolo su rivista]
Mantovani, Mattia; Pratissoli, Federico; Sabattini, Lorenzo
abstract

2024 - How Can We Understand Multi-Robot Systems? a User Study to Compare Implicit and Explicit Communication Modalities [Relazione in Atti di Convegno]
Villani, Valeria; Vercellino, Cristina; Sabattini, Lorenzo
abstract

2024 - On Limited-Range Coverage Control for Large-Scale Teams of Aerial Drones: Deployment and Study [Relazione in Atti di Convegno]
Bertoncelli, Filippo; Belal, Mehdi; Albani, Dario; Pratissoli, Federico; Sabattini, Lorenzo
abstract

2023 - A Complete Set of Connectivity-aware Local Topology Manipulation Operations for Robot Swarms [Relazione in Atti di Convegno]
Soma, Karthik; Khateri, Koresh; Pourgholi, Mahdi; Montazeri, Mohsen; Sabattini, Lorenzo; Beltrame, Giovanni
abstract

2023 - A General Pipeline for Online Gesture Recognition in Human–Robot Interaction [Articolo su rivista]
Villani, Valeria; Secchi, Cristian; Lippi, Marco; Sabattini, Lorenzo
abstract

2023 - Coherent movement of error-prone individuals through mechanical coupling [Articolo su rivista]
Pratissoli, Federico; Reina, Andreagiovanni; Kaszubowski Lopes, Yuri; Pinciroli, Carlo; Miyauchi, Genki; Sabattini, Lorenzo; Groß, Roderich
abstract

: We investigate how reliable movement can emerge in aggregates of highly error-prone individuals. The individuals-robotic modules-move stochastically using vibration motors. By coupling them via elastic links, soft-bodied aggregates can be created. We present distributed algorithms that enable the aggregates to move and deform reliably. The concept and algorithms are validated through formal analysis of the elastic couplings and experiments with aggregates comprising up to 49 physical modules-among the biggest soft-bodied aggregates to date made of autonomous modules. The experiments show that aggregates with elastic couplings can shrink and stretch their bodies, move with a precision that increases with the number of modules, and outperform aggregates with no, or rigid, couplings. Our findings demonstrate that mechanical couplings can play a vital role in reaching coherent motion among individuals with exceedingly limited and error-prone abilities, and may pave the way for low-power, stretchable robots for high-resolution monitoring and manipulation.

2023 - Distributed Control for Human-Swarm Interaction In Non-Convex Environments using Gaussian Mixture Models [Articolo su rivista]
Catellani, Mattia; Mazzocco, Eloisa; Bertoncelli, Filippo; Sabattini, Lorenzo
abstract

2023 - Hierarchical Traffic Management of Multi-AGV Systems With Deadlock Prevention Applied to Industrial Environments [Articolo su rivista]
Pratissoli, F; Brugioni, R; Battilani, N; Sabattini, L
abstract

This paper concerns the coordination and the traffic management of a group of Automated Guided Vehicles (AGVs) moving in a real industrial scenario, such as an automated factory or warehouse. The proposed methodology is based on a three-layer control architecture, which is described as follows: 1) the Top Layer (or Topological Layer) allows to model the traffic of vehicles among the different areas of the environment; 2) the Middle Layer allows the path planner to compute a traffic sensitive path for each vehicle; 3) the Bottom Layer (or Roadmap Layer) defines the final routes to be followed by each vehicle and coordinates the AGVs over time. In the paper we describe the coordination strategy we propose, which is executed once the routes are computed and has the aim to prevent congestions, collisions and deadlocks. The coordination algorithm exploits a novel deadlock prevention approach based on time-expanded graphs. Moreover, the presented control architecture aims at grounding theoretical methods to an industrial application by facing the typical practical issues such as graphs difficulties (load/unload locations, weak connections,), a predefined roadmap (constrained by the plant layout), vehicles errors, dynamical obstacles, etc. In this paper we propose a flexible and robust methodology for multi-AGVs traffic-aware management. Moreover, we propose a coordination algorithm, which does not rely on ad hoc assumptions or rules, to prevent collisions and deadlocks and to deal with delays or vehicle motion errors. Note to Practitioners-This paper concerns the coordination and the traffic management of a group of Automated Guided Vehicles (AGVs) moving in a real industrial scenario, such as an automated factory or warehouse. The proposed methodology is based on a three-layer control architecture, which is described as follows: 1) the Top Layer (or Topological Layer) allows to model the traffic of vehicles among the different areas of the environment; 2) the Middle Layer allows the path planner to compute a traffic sensitive path for each vehicle; 3) the Bottom Layer (or Roadmap Layer) defines the final routes to be followed by each vehicle and coordinates the AGVs over time. In the paper we describe the coordination strategy we propose, which is executed once the routes are computed and has the aim to prevent congestions, collisions and deadlocks. The coordination algorithm exploits a novel deadlock prevention approach based on time-expanded graphs. Moreover, the presented control architecture aims at grounding theoretical methods to an industrial application by facing the typical practical issues such as graphs difficulties (load/unload locations, weak connections, ), a predefined roadmap (constrained by the plant layout), vehicles errors, dynamical obstacles, etc. In this paper we propose a flexible and robust methodology for multi-AGVs traffic-aware management. Moreover, we propose a coordination algorithm, which does not rely on ad hoc assumptions or rules, to prevent collisions and deadlocks and to deal with delays or vehicle motion errors.

2023 - Improved Path Planning Algorithms for Non-Holonomic Autonomous Vehicles in Industrial Environments with Narrow Corridors: Roadmap Hybrid A∗ and Waypoints Hybrid A∗ [Relazione in Atti di Convegno]
Bonetti, A.; Guidetti, S.; Sabattini, L.
abstract

This paper proposes two novel path planning algorithms, Roadmap Hybrid A∗ and Waypoints Hybrid A∗, for car-like autonomous vehicles in logistics and industrial contexts with obstacles (e.g., pallets or containers) and narrow corridors. Roadmap Hybrid A∗ combines Hybrid A∗ with a graph search algorithm applied to a static roadmap. The former enables obstacle avoidance and flexibility, whereas the latter provides greater robustness, repeatability, and computational speed. Waypoint Hybrid A∗, on the other hand, generates waypoints using a topological map of the environment to guide Hybrid A∗ to the target pose, reducing complexity and search time. Both algorithms enable predetermined control over the shape of desired parts of the path, for example, to obtain precise docking maneuvers to service machines and to eliminate unnecessary steering changes produced by Hybrid A∗ in corridors, thanks to the roadmap and/or the waypoints. To evaluate the performance of these algorithms, we conducted a simulation study in an industrial plant where a robot must navigate narrow corridors to serve machines in different areas. In terms of computational time, total length, reverse length path, and other metrics, both algorithms outperformed the standard Hybrid A∗.

2023 - Multi-Robot Adversarial Resilience using Control Barrier Functions [Articolo su rivista]
Cavorsi, M.; Sabattini, L.; Gil, S.
abstract

2023 - Nonsmooth Control Barrier Function design of continuous constraints for network connectivity maintenance [Articolo su rivista]
Ong, Pio; Capelli, Beatrice; Sabattini, Lorenzo; Cortés, Jorge
abstract

2023 - Use of EEG Signals for Mental Workload Assessment in Human-Robot Collaboration [Relazione in Atti di Convegno]
Ruo, Andrea; Villani, Valeria; Sabattini, Lorenzo
abstract

2022 - A Cognitive Architecture for Robot-Assisted Surgical Procedures [Articolo su rivista]
Zini, Elena; Minelli, Marco; Sabattini, Lorenzo; Ferraguti, Federica
abstract

2022 - Comparison of Routing Protocols and Communication Interfaces for the Implementation of Collision Avoidance Capabilities in Fleets of Industrial Mobile Robots [Articolo su rivista]
Bonetti, Alessandro; Sabattini, Lorenzo
abstract

2022 - Multi-Robot Adversarial Resilience using Control Barrier Functions [Relazione in Atti di Convegno]
Cavorsi, Mcavorsi@G. Harvard. Edu M.; Capelli, B.; Sabattini, L.; Gil, Sgil@Seas. Harvard. Edu S.
abstract

In this paper we present a control barrier functionbased (CBF) resilience controller that provides resilience in a multi-robot network to adversaries. Previous approaches provide resilience by virtue of specific linear combinations of multiple control constraints. These combinations can be difficult to find and are sensitive to the addition of new constraints. Unlike previous approaches, the proposed CBF provides network resilience and is easily amenable to multiple other control constraints, such as collision and obstacle avoidance. The inclusion of such constraints is essential in order to implement a resilience controller on realistic robot platforms. We demonstrate the viability of the CBF-based resilience controller on real robotic systems through case studies on a multi-robot flocking problem in cluttered environments with the presence of adversarial robots.

2022 - On Coverage Control for Limited Range Multi-Robot Systems [Relazione in Atti di Convegno]
Pratissoli, F.; Capelli, B.; Sabattini, L.
abstract

This paper presents a coverage based control algorithm to coordinate a group of autonomous robots. Most of the solutions presented in the literature rely on an exact Voronoi partitioning, whose computation requires complete knowledge of the environment to be covered. This can be achieved only by robots with unlimited sensing capabilities, or through communication among robots in a limited sensing scenario. To overcome these limitations, we present a distributed control strategy to cover an unknown environment with a group of robots with limited sensing capabilities and in the absence of reliable communication. The control law is based on a limited Voronoi partitioning of the sensing area, and we demonstrate that the group of robots can optimally cover the environment using only information that is locally detected (without communication). The proposed method is validated by means of simulations and experiments carried out on a group of mobile robots.

2022 - On the Communication Requirements of Decentralized Connectivity Control - A Field Experiment [Relazione in Atti di Convegno]
Panerati, Jacopo; Ramtoula, Benjamin; St-Onge, David; Cao, Yanjun; Kaufmann, Marcel; Cowley, Aidan; Sabattini, Lorenzo; Beltrame, Giovanni
abstract

Redundancy and parallelism make decentralized multi-robot systems appealing solutions for the exploration of extreme environments. However, effective cooperation can require team-wide connectivity and a carefully designed communication. Several recently proposed decentralized connectivity maintenance approaches exploit elegant algebraic results drawn from spectral graph theory. Yet, these proposals are rarely taken beyond simulations or laboratory implementations. The contribution of this work is two-fold: (i) we describe the full-stack implementation—from hardware to software—of a decentralized control law for robust connectivity maintenance; and (ii) we assess, in the field, our robots’ ability to correctly exchange the information required to execute it.

2022 - Optimized Direction Assignment in Roadmaps for Multi-AGV Systems Based on Transportation Flows [Relazione in Atti di Convegno]
Digani, V.; Sabattini, L.
abstract

In this paper we propose a method for optimizing the design of a roadmap, used for motion coordination of groups of automated guided vehicles for industrial environments. Considering the desired flows among different locations in the environment, we model the problem as a multi-commodity concurrent flow problem, which allows us to assign the directions of the paths in an optimized manner. The proposed solution is validated by means of simulations, exploiting realistic layouts, and comparing the performance of the system with those achieved with a baseline roadmap.

2022 - Passivity and Control Barrier Functions: Optimizing the Use of Energy [Articolo su rivista]
Capelli, B.; Secchi, C.; Sabattini, L.
abstract

Passivity-based control ensures the implementation of a desired behavior in a controlled system, while preserving robust stability. In this letter, we propose a new method to guarantee passivity, based on energy-tank control and Control Barrier Functions. The goal is to accomplish a desired behavior with minimal modification, while ensuring passivity. The proposed method is suitable for a wide range of applications: whenever some desired control action may disrupt the passivity of the system, the designed Control Barrier Function will modify the behavior to enforce the preservation of passivity. Simulations and real experiments were carried out to prove the effectiveness and the flexibility of the proposed method: in particular, a simple case of variable stiffness in a mass-spring-damper system and a multi-robot controller based on a time-varying artificial potential field.

2022 - Preservation of Giant Component Size After Robot Failure for Robustness of Multi-robot Network [Relazione in Atti di Convegno]
Murayama, T.; Sabattini, L.
abstract

This paper approaches a network topology control method for networked multi-robot systems. Although robustness of network connectivity against robot failures is a matter of concern for the multi-robot control, the robustification impedes the motion of robots because of limitations of the wireless communication. For mitigating the impediments, we focus our attention on the giant connected component size after a single robot fails, and aim to control such component size. A modified algebraic connectivity is introduced here as an indicator of the component size: a threshold for the algebraic connectivity is analyzed to preserve the component size. Theoretical properties and numerical examples are shown to demonstrate our control method.

2022 - Promoting operator's wellbeing in Industry 5.0: detecting mental and physical fatigue [Relazione in Atti di Convegno]
Villani, V.; Gabbi, M.; Sabattini, L.
abstract

2022 - Task-Oriented Contact Optimization for Pushing Manipulation with Mobile Robots [Relazione in Atti di Convegno]
Bertoncelli, F.; Selvaggio, M.; Ruggiero, F.; Sabattini, L.
abstract

This work addresses the problem of transporting an object along a desired planar trajectory by pushing with mobile robots. More specifically, we concentrate on establishing optimal contacts between the object and the robots to execute the given task with minimum effort. We present a task-oriented contact placement optimization strategy for object pushing that allows calculating optimal contact points minimizing the amplitude of forces required to execute the task. Exploiting the optimized contact configuration, a motion controller uses the computed contact forces in feed-forward and position error feedback terms to realize the desired trajectory tracking task. Simulations and real experiments results confirm the validity of our approach.

2022 - To collaborate or not to collaborate: understanding human-robot collaboration [Relazione in Atti di Convegno]
Villani, Valeria; Ciaramidaro, Angela; Iani, Cristina; Rubichi, Sandro; Sabattini, Lorenzo
abstract

2022 - Use of Interaction Design Methodologies for Human-Robot Collaboration in Industrial Scenarios [Articolo su rivista]
Prati, E; Villani, V; Grandi, F; Peruzzini, M; Sabattini, L
abstract

The key concept of collaborative robotics is represented by the presence of a strict interaction between a human user and the robotic system. As such, the study of the interaction is of paramount importance for a successful implementation of the system. In this article, we propose a novel approach to address the problem of designing a collaborative robotic system for industrial applications, focusing on the characteristics of the interaction. In particular, we will propose a set of methodologies focused on interaction design, inspired by those used for the design of user interfaces. These methodologies will allow the design of collaborative robotic systems following a user-centered approach, thus putting emphasis not only on safety and adaptability of the robotic systems (which have been widely addressed in the literature), but also on the interaction experience. While the proposed methodology was developed considering general collaborative robotics applications, two real industrial case studies were considered, to instantiate the considered framework and showcase its applicability to the real-world domain.

2021 - A User Study for the Evaluation of Adaptive Interaction Systems for Inclusive Industrial Workplaces [Articolo su rivista]
Villani, V.; Sabattini, L.; Zanelli, G.; Callegati, E.; Bezzi, B.; Baranska, P.; Mockallo, Z.; Zolnierczyk-Zreda, D.; Czerniak, J. N.; Nitsch, V.; Mertens, A.; Fantuzzi, C.
abstract

In recent years, production systems have become highly sophisticated and complex. As a result, while on the one hand, the least-skilled labor has been partially displaced by machines, high-skilled labor is more required to supervise and control advanced automation systems. In many cases, the complexity of machines implies an increased complexity of human-machine interfaces (HMIs), which are the main point of contact between the operator and the machine. To enable effective use of HMIs and to enable their usage by workers with different knowledge and capabilities, novel design approaches have been proposed. In particular, in this article, we consider the approach developed in the framework of the European research project INCLUSIVE, which aimed at designing industrial HMIs that adapt to the skills and capabilities of human operators. As a case study, we consider an adaptive interaction system for the woodworking industry and present an extensive evaluation carried out in real production environment with shopfloor workers. The effectiveness of the INCLUSIVE approach has been assessed with subjective and objective measurements and compared to that of interaction systems customarily used in industry. Results have shown that users appreciated the INCLUSIVE system and largely preferred it over the customary system. Moreover, with regard to objective performance-related measurements, they performed better when using the INCLUSIVE system since they received tailored guidance during the considered working tasks.

2021 - An approach based on VR to design industrial human-robot collaborative workstations [Articolo su rivista]
Prati, E.; Villani, V.; Peruzzini, M.; Sabattini, L.
abstract

This paper presents an integrated approach for the design of human-robot collaborative workstations in industrial shop floors. In particular, the paper presents how to use virtual reality (VR) technologies to support designers in the creation of interactive workstation prototypes and in early validation of design outcomes. VR allows designers to consider and evaluate in advance the overall user experience, adopting a user-centered perspective. The proposed approach relies on two levels: the first allows designers to have an automatic generation and organization of the workstation physical layout in VR, starting from a conceptual description of its functionalities and required tools; the second aims at supporting designers during the design of human-machine interfaces (HMIs) by interaction mapping, HMI prototyping and testing in VR. The proposed approach has been applied on two realistic industrial case studies related to the design of an intensive warehouse and a collaborative assembly workstation for automotive industry, respectively. The two case studies demonstrate how the approach is suited for early prototyping of complex environments and human-machine interactions by taking into account the user experience from the early phases of design.

2021 - Characterization of Grasp Configurations for Multi-Robot Object Pushing [Relazione in Atti di Convegno]
Bertoncelli, Filippo; Ruggiero, Fabio; Sabattini, Lorenzo
abstract

2021 - Decentralized Connectivity Maintenance with Time Delays using Control Barrier Functions [Relazione in Atti di Convegno]
Capelli, Beatrice; Fouad, Hassan; Beltrame, Giovanni; Sabattini, Lorenzo
abstract

2021 - Hierarchical and Flexible Traffic Management of Multi-AGV Systems Applied to Industrial Environments [Relazione in Atti di Convegno]
Pratissoli, Federico; Battilani, Nicola; Fantuzzi, Cesare; Sabattini, Lorenzo
abstract

2021 - Network Connectivity Maintenance via Nonsmooth Control Barrier Functions [Relazione in Atti di Convegno]
Ong, Pio; Capelli, Beatrice; Sabattini, Lorenzo; Cortes, Jorge
abstract

2021 - Optimized Direction Assignment in Roadmaps for Multi-AGV Systems Based on Transportation Flows [Relazione in Atti di Convegno]
Digani, Valerio; Sabattini, Lorenzo
abstract

2021 - Planar Pushing Manipulation with a Group of Mobile Robots [Relazione in Atti di Convegno]
Bertoncelli, F.; Sabattini, L.
abstract

This paper addresses the problem of collaborative manipulation of an object performed by a group of robots. In particular, the objective is achieved by means of pushing, implemented by a group of small wheeled mobile robots. The proposed method exploits the well known Voronoi-based coverage control method to deploy the robots in the environment according to a given probability density function. The shape of such a density function is defined, in a time varying manner, by a pushing policy function to enable planar manipulations, considering only the footprint of the manipulated object. The proposed method is validated by means of extensive simulations and real world scenario experiments with different sized robot groups and different manipulated objects.

2021 - Preservation of Giant Component Size after Robot Failure for Robustness of Multi-Robot Network [Relazione in Atti di Convegno]
Murayama, Toru; Sabattini, Lorenzo
abstract

2021 - The INCLUSIVE System: A General Framework for Adaptive Industrial Automation [Articolo su rivista]
Villani, Valeria; Sabattini, Lorenzo; Baranska, Paulina; Callegati, Enrico; Czerniak, Julia N.; Debbache, Adel; Fahimipirehgalin, Mina; Gallasch, Andreas; Loch, Frieder; Maida, Rosario; Mertens, Alexander; Mockallo, Zofia; Monica, Francesco; Nitsch, Verena; Talas, Engin; Toschi, Elisabetta; Vogel-Heuser, Birgit; Willems, Jeanmarc; Zolnierczyk-Zreda, Dorotadorota; Fantuzzi, Cesare
abstract

2021 - The index of cognitive activity - eligibility for task-evoked informational strain and robustness towards visual influences [Articolo su rivista]
Czerniak, Julia N.; Schierhorst, Nikolas; Villani, Valeria; Sabattini, Lorenzo; Brandl, Christopher; Mertens, Alexander; Schwalm, Maximilian; Nitsch, Verena
abstract

2021 - Toward Future Automatic Warehouses: An Autonomous Depalletizing System Based on Mobile Manipulation and 3D Perception [Articolo su rivista]
Aleotti, Jacopo; Baldassarri, Alberto; Bonfè, Marcello; Carricato, Marco; Chiaravalli, Davide; Di Leva, Roberto; Fantuzzi, Cesare; Farsoni, Saverio; Innero, Gino; Lodi Rizzini, Dario; Melchiorri, Claudio; Monica, Riccardo; Palli, Gianluca; Rizzi, Jacopo; Sabattini, Lorenzo; Sampietro, Gianluca; Zaccaria, Federico
abstract

This paper presents a mobile manipulation platform designed for autonomous depalletizing tasks. The proposed solution integrates machine vision, control and mechanical components to increase flexibility and ease of deployment in industrial environments such as warehouses. A collaborative robot mounted on a mobile base is proposed, equipped with a simple manipulation tool and a 3D in-hand vision system that detects parcel boxes on a pallet, and that pulls them one by one on the mobile base for transportation. The robot setup allows to avoid the cumbersome implementation of pick-and-place operations, since it does not require lifting the boxes. The 3D vision system is used to provide an initial estimation of the pose of the boxes on the top layer of the pallet, and to accurately detect the separation between the boxes for manipulation. Force measurement provided by the robot together with admittance control are exploited to verify the correct execution of the manipulation task. The proposed system was implemented and tested in a simplified laboratory scenario and the results of experimental trials are reported.

2021 - Towards Optimized Distributed Multi-Robot Printing: An Algorithmic Approach [Relazione in Atti di Convegno]
Karpe, Kedar; Sinha, Avinash; Raorane, Shreyas; Chatterjee, Ayon; Srinivas, Pranav; Sabattini, Lorenzo
abstract

2021 - Worker satisfaction with adaptive automation and working conditions: a theoretical model and questionnaire as an assessment tool [Articolo su rivista]
Villani, Valeria; Sabattini, Lorenzo; Żołnierczyk-Zreda, Dorota; Mockałło, Zofia; Barańska, Paulina; Fantuzzi, Cesare
abstract

2020 - A connectivity preserving node permutation local method in limited range robotic networks [Articolo su rivista]
Khateri, K.; Pourgholi, M.; Montazeri, M.; Sabattini, L.
abstract

Limited communication range, together with mobility of robots, makes it crucial to design the control plans such that connectivity of a multi-robot network is maintained. Recently, many local and global connectivity maintenance schemes have been proposed to preserve connectivity of a robotic network. The traditional local connectivity maintenance method (LCM) is known to preserve every existing link, even though some of the existing connections might not be necessary for maintaining a path between each pair of robots, which is the aim of global connectivity maintenance (GCM) methods. However, the flexibility of movement provided by the global method costs restriction on speed and bandwidth. In this paper, a modified local connectivity maintenance method is provided to gain more flexibility of movement, while preserving the properties and simplicity of a local method. The proposed method is based on traditional local connectivity maintenance equipped with a basic operation to exchange the neighbors between two adjacent robots. Permutation of robots could be beneficial in many robotic applications such as exchanging the leader role in a V-formed robotic group or providing a path for a robot to reach its desired position while preserving the networks connectivity.

2020 - Cognitive Human Modeling in Collaborative Robotics [Articolo su rivista]
Fruggiero, Fabio; Lambiase, Alfredo; Panagou, Sotirios; Sabattini, Lorenzo
abstract

2020 - Connectivity Maintenance: Global and Optimized approach through Control Barrier Functions [Relazione in Atti di Convegno]
Capelli, B.; Sabattini, L.
abstract

Connectivity maintenance is an essential aspect to consider while controlling a multi-robot system. In general, a multi-robot system should be connected to obtain a certain common objective. Connectivity must be kept regardless of the control strategy or the objective of the multi-robot system. Two main methods exist for connectivity maintenance: keep the initial connections (local connectivity) or allow modifications to the initial connections, but always keeping the overall system connected (global connectivity). In this paper we present a method that allows, at the same time, to maintain global connectivity and to implement the desired control strategy (e.g., consensus, formation control, coverage), all in an optimized fashion. For this purpose, we defined and implemented a Control Barrier Function that can incorporate constraints and objectives. We provide a mathematical proof of the method, and we demonstrate its versatility with simulations of different applications.

2020 - Decentralized local-global connectivity maintenance for networked robotic teams [Articolo su rivista]
Khateri, K.; Pourgholi, M.; Montazeri, M.; Sabattini, L.
abstract

A prerequisite for a team of robots to cooperate is to maintain connectivity among robots. Connectivity maintenance has been extensively studied recently and several local and global connectivity maintenance algorithms have been proposed for the distance dependent communication topology. Local methods are known to be very restrictive and it will be shown that global methods, based on power iteration estimation, could be sluggish in the presence of communication delay and non-converging in large and sparse robot teams. Therefore, a method based on k-hop routing is proposed, where k is a design parameter to determine the locality level of the proposed method. Before any link disconnection, a test for an alternative k-hop path is executed and, based on its result, the disconnection is allowed or blocked. Blocking displacement for maintaining connectivity will eventually immobilize (freeze) the network. Therefore, a procedure for unfreezing the network is also proposed. Simulation results are provided to further investigate the proposed method.

2020 - Guest editorial: special issue on multi-robot and multi-agent systems [Articolo su rivista]
Ayanian, Nora; Robuffo Giordano, Paolo; Fitch, Robert; Franchi, Antonio; Sabattini, Lorenzo
abstract

2020 - Human-Friendly Multi-Robot Systems: Legibility Analysis [Relazione in Atti di Convegno]
Capelli, Beatrice; Sabattini, Lorenzo
abstract

2020 - Human-Friendly Robotics 2019. HFR 2019. [Monografia/Trattato scientifico]
Ferraguti, F.; Villani, V.; Sabattini, L.; Bonfè, M.
abstract

2020 - Humans interacting with multi-robot systems: a natural affect-based approach [Articolo su rivista]
Villani, V.; Capelli, B.; Secchi, C.; Fantuzzi, C.; Sabattini, L.
abstract

This paper proposes a novel human–multi-robot-system interaction approach that enjoys two main features: natural interaction and affect-based adaptation of robots behavior. Specifically, the proposed system enables interaction by means of a wrist-worn device, such as a commercial smartwatch, which allows to track user’s movements and heart activity. Thus, on the one side, the proposed system allows the user to intuitively drive the robots by establishing a natural mapping between wrist movements and robots velocity. On the other side, the system estimates user’s mental fatigue during interaction by means of the analysis of heart rate variability. The proposed interaction system adapts then the behavior of the multi-robot system when the interacting user gets overwhelmed with the interaction and control task, which is then simplified. Experimental validation is provided, to show the effectiveness of the proposed system. First, the natural and affect-based interaction are considered separately. Then, the approach is tested considering a complex realistic scenario, which is simulated in virtual reality in order to get an immersive and realistic interaction experience. The results of the experimental validation clearly show that the proposed affect-based adaptive system leads to relieving the user’s fatigue and mental workload.

2020 - Linear Time-Varying MPC for Nonprehensile Object Manipulation with a Nonholonomic Mobile Robot [Relazione in Atti di Convegno]
Bertoncelli, F.; Ruggiero, F.; Sabattini, L.
abstract

This paper proposes a technique to manipulate an object with a nonholonomic mobile robot by pushing, which is a nonprehensile manipulation motion primitive. Such a primitive involves unilateral constraints associated with the friction between the robot and the manipulated object. Violating this constraint produces the slippage of the object during the manipulation, preventing the correct achievement of the task. A linear time-varying model predictive control is designed to include the unilateral constraint within the control action properly. The approach is verified in a dynamic simulation environment through a Pioneer 3-DX wheeled robot executing the pushing manipulation of a package.

2020 - Network Robotics [Capitolo/Saggio]
Sabattini, Lorenzo; Secchi, Cristian; Melchiorri, Claudio
abstract

2020 - Robustness of multi-robot systems controlling the size of the connected component after robot failure [Relazione in Atti di Convegno]
Murayama, T.; Sabattini, L.
abstract

This study approaches a robustification method for a multi-robot network connectivity. Instead of the vertex connectivity, which is commonly used as a robustness index, here we consider the size of the connected component remaining after one robot has been removed from the network, and we propose a distributed control law for improvement and preservation of the remaining connected component size. Some conditions of a modified graph Laplacian eigenvalue are analyzed for the improvement and the preservation, and then the control strategy is composed using the Laplacian eigenvalue as an indicator of the remaining connected component size. From simulations, we observed that a multi-robot system with our control method achieves a convincing state regarding the trade-off between a network robustness and a coverage task performance.

2020 - Self-optimization of resilient topologies for fallible multi-robots [Articolo su rivista]
Minelli, Marco; Panerati, Jacopo; Kaufmann, Marcel; Ghedini, Cinara; Beltrame, Giovanni; Sabattini, Lorenzo
abstract

2020 - Teleoperation of Multi-Robot Systems to Relax Topological Constraints [Relazione in Atti di Convegno]
Sabattini, L.; Capelli, B.; Fantuzzi, C.; Secchi, C.
abstract

Multi-robot systems are able to achieve common objectives exchanging information among each other. This is possible exploiting a communication structure, usually modeled as a graph, whose topological properties (such as connectivity) are very relevant in the overall performance of the multirobot system. When considering mobile robots, such properties can change over time: robots are then controlled to preserve them, thus guaranteeing the possibility, for the overall system, to achieve its goals. This, however, implies limitations on the possible motion patterns of the robots, thus reducing the flexibility of the overall multi-robot system. In this paper we introduce teleoperation as a means to reduce these limitations, allowing temporary violations of topological properties, with the aim of increasing the flexibility of the multi-robot system.

2020 - The impact of agent definitions and interactions on multiagent learning for coordination in traffic management domains [Articolo su rivista]
Chung, J. J.; Miklic, D.; Sabattini, L.; Tumer, K.; Siegwart, R.
abstract

The state-action space of an individual agent in a multiagent team fundamentally dictates how the individual interacts with the rest of the team. Thus, how an agent is defined in the context of its domain has a significant effect on team performance when learning to coordinate. In this work we explore the trade-offs associated with these design choices, for example, having fewer agents in the team that individually are able to process and act on a wider scope of information about the world versus a larger team of agents where each agent observes and acts in a more local region of the domain. We focus our study on a traffic management domain and highlight the trends in learning performance when applying different agent definitions. In addition, we analyze the impact of agent failure for different agent definitions and investigate the ability of the team to learn new coordination strategies when individual agents become unresponsive.

2020 - Wearable devices for the assessment of cognitive effort for human-robot interaction [Articolo su rivista]
Villani, Valeria; Righi, Massimiliano; Sabattini, Lorenzo; Secchi, Cristian
abstract

This paper is motivated by the need of assessing cognitive effort in affective robotics. In this context, the ultimate goal is that of assessing the mental state while the subject is interacting with a robotic system, by gathering implicit and objective information unobtrusively. To this end, we focus on wearable devices that do not affect the interaction of a human with a robot. In particular, we consider some commercial multi-purpose wearable devices, such as an armband, a smartwatch and a chest strap, and compare them in terms of accuracy in detecting cognitive effort. In an experiment setting, thirty participants were exposed to an increase in their cognitive effort by means of standard cognitive tests. Mental fatigue was estimated by measuring cardiac activity, in terms of heart rate and heart rate variability. The results have shown that the analysis of heart rate variability measured by the chest strap provides the most accurate detection of cognitive effort. Nevertheless, also measurements by the armband are sensitive to cognitive effort.

2019 - A Comparison between Decentralized Local and Global Methods for Connectivity Maintenance of Multi-Robot Networks [Articolo su rivista]
Khateri, Koresh; Pourgholi, Mahdi; Montazeri, Mohsen; Sabattini, Lorenzo
abstract

Range limitation of communication links among robots in a multi-robot network, mixed with the mobility of the robots, creates a potential threat of disconnection of the communication network due to the robots movements. Recently, local methods have been proposed for maintaining the initial graph of connections, as well as global methods for maintaining a path between each pair of robots. This letter compares these methods in different aspects: the freedom of movement and the workspace provided by global methods is challenged by the amount of data needed to be exchanged with the local methods. Also, in the delayed networks, it is shown that local methods are leading to less restriction on the speed of the robots involved in the network. Simulation and numerical results are provided to further illustrate this comparison.

2019 - A General Approach to Natural Human-Robot Interaction [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Villani, Valeria; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper proposes a scheme for letting a human interact with a generic robot in a natural manner. Based on the concept of natural user interfaces, the proposed methods exploit recognition of the users’ forearm motion to produce commands for the robotic system. High-level commands are provided based on gesture recognition, and velocity commands are computed for the robot by mapping, in a natural manner, the motion of the user’s forearm. The method is proposed in a general manner, and is then instantiated considering two different robotic systems, namely a quadrotor and a wheeled mobile robot. Usability of the system is evaluated with experiments involving users.

2019 - A General Methodology for Adapting Industrial HMIs to Human Operators [Articolo su rivista]
Villani, Valeria; Sabattini, Lorenzo; Loch, Frieder; Vogel-Heuser, Birgit; Fantuzzi, Cesare
abstract

Modern production systems are becoming more and more complex to comply with diversified market needs, flexible production, and competitiveness. Despite technological progress, the presence of human operators is still fundamental in production plants, since they have the important role of supervising and monitoring processes, by interacting with such complex machines. The complexity of machines implies an increased complexity of human-machine interfaces (HMIs), which are the main point of contact between the operator and the machine. Thus, HMIs cannot be considered anymore an accessory to the machine and their improvement has become an important part of the design of the whole machines, to enable a nonstressful interaction and make them easy to also use less skilled operators. In this article, we present a general framework for the design of HMIs that adapt to the skills and capabilities of the operator, with the ultimate aim of enabling a smooth and efficient interaction and improving user's situation awareness. Adaptation is achieved by considering three different levels: Perception (i.e., how information is presented), cognition (i.e., what information is presented), and interaction (i.e., how interaction is enabled). For each level, general guidelines for adaptation are provided, thus defining a meta-HMI independent of the application. Finally, some examples of how the proposed adaptation patterns can be applied to the case of procedural and extraordinary maintenance tasks are presented. Note to Practitioners-This article was motivated by the problem of facilitating the interaction of human operators with human-machine interfaces (HMIs) of complex industrial systems. Standard industrial HMIs are static and do not consider the user's characteristics. As a consequence, least-skilled operators are prevented from their use and/or have poor performance. In this article, we suggest a novel methodology to the design of adaptive industrial HMIs that adapt to the skills and capabilities of operators and compensate their limitations (e.g., due to age or inexperience). In particular, we propose a methodological framework that consists of general rules to accommodate the user's characteristics. Adaptation is achieved at three different levels: Perception (i.e., how information is presented), cognition (i.e., what information is presented), and interaction (i.e., how interaction is enabled). The presented rules are independent of the target application. Nevertheless, we establish a relationship between such design rules and user's impairments and capabilities and kind of working tasks. Hence, designers of HMIs are called to instantiate them considering the specific requirements and characteristics of the users and the working tasks of the application at hand.

2019 - A Soft-Bodied Modular Reconfigurable Robotic System Composed of Interconnected Kilobots [Relazione in Atti di Convegno]
Pratissoli, F.; Reina, A.; Lopes, Y. K.; Sabattini, L.; Groß, R.
abstract

We describe the Kilobot Soft Robot, a novel soft-bodied robot that is modular and reconfigurable. The Kilobot Soft Robot is realized by inter-connecting a group of miniature mobile modules, based on the commercially available Kilobot, through an elastic material. It moves and deforms fully autonomously. Each module executes a distributed algorithm that exploits only information that is locally obtained using omnidirectional, infrared based signaling. A series of experiments were conducted to validate the algorithm, investigating the ability of the robot to follow a predefined trajectory, to squeeze and extend its shape and to control its motion independently of the number of modules.

2019 - A variable admittance control strategy for stable physical human–robot interaction [Articolo su rivista]
Ferraguti, Federica; Talignani Landi, Chiara; Sabattini, Lorenzo; Bonfè, Marcello; Fantuzzi, Cesare; Secchi, Cristian
abstract

Admittance control allows a desired dynamic behavior to be reproduced on a non-backdrivable manipulator and it has been widely used for interaction control and, in particular, for human–robot collaboration. Nevertheless, stability problems arise when the environment (e.g. the human) the robot is interacting with becomes too stiff. In this paper, we investigate the stability issues related to a change of stiffness of the human arm during the interaction with an admittance-controlled robot. We propose a novel method for detecting the rise of instability and a passivity-preserving strategy for restoring a stable behavior. The results of the paper are validated on two robotic setups and with 50 users performing two tasks that emulate industrial operations.

2019 - An Adaptive Virtual Training System Based on Universal Design [Relazione in Atti di Convegno]
Loch, Frieder; Fahimipirehgalin, Mina; Czerniak, Julia N.; Mertens, Alexander; Villani, Valeria; Sabattini, Lorenzo; Fantuzzi, Cesare; Vogel-Heuser, Birgit
abstract

The increasing complexity of manufacturing environments requires effective training systems to prepare the operation personnel for their tasks. Several training systems have been proposed. A common approach is the application of virtual environments to train interactions with an industrial machine in a safe, attractive, and efficient way. However, these training systems cannot adapt to the requirements of an increasingly diversified workforce. This paper introduces an approach for the design of an adaptive virtual training system based on the idea of universal design. The system is based on a two-step approach that consists of an initial adaptation to the user capabilities and real-time adaptations during training based on measurements of the user. The adaptations concern the use of different representations of lessons with different complexity and interaction modalities. The proposed approach provides a flexible training system that can adapt to the needs of a broad group of users.

2019 - Communication Through Motion: Legibility of Multi-Robot Systems [Relazione in Atti di Convegno]
Capelli, B.; Secchi, C.; Sabattini, L.
abstract

The interaction between a user and a multi-robot system in a shared environment is a relatively uncharted topic. But, as these types of systems will increase in the future years, an efficient way of communication is necessary. To this aim, it is interesting to discover if a multi-robot system can communicate its intentions exploiting only some motion-variables, which are characteristics of the motion of the robots. This study is about the legibility of a multi-robot system: In particular, we focus on the influence of these motion-variables on the legibility of more than one group of robots that move in a shared environment with the user. These motion-variables are: Trajectory, dispersion and stiffness. They are generally used to define the motion of a group of mobile robots. Trajectory and dispersion were found relevant for the correctness of the communication between the user and the multi-robot system, while stiffness was found relevant for the rapidity of communication. The analysis of the influence of the motion-variables was carried out with an ANOVA (analysis of variance) based on a series of data coming from an experimental campaign conducted in a virtual reality set-up.

2019 - Coordination of multiple AGVs: a quadratic optimization method [Articolo su rivista]
Digani, Valerio; Hsieh, M. Ani; Sabattini, Lorenzo; Secchi, Cristian
abstract

This paper presents an optimization strategy to coordinate a fleet of Automated Guided Vehicles (AGVs) traveling on ad-hoc pre-defined roadmaps. Specifically, the objective is to maximize traffic throughput of AGVs navigating in an automated warehouse by minimizing the time AGVs spend negotiating complex traffic patterns to avoid collisions with other AGVs. In this work, the coordination problem is posed as a Quadratic Program where the optimization is performed in a centralized manner. The proposed method is validated by means of simulations and experiments for different industrial warehouse scenarios. The performance of the proposed strategy is then compared with a recently proposed decentralized coordination strategy that relies on local negotiations for shared resources. The results show that the proposed coordination strategy successfully maximizes vehicle throughput and significantly minimizes the time vehicles spend negotiating traffic under different scenarios.

2019 - Decentralized state estimation for the control of network systems [Articolo su rivista]
Boem, Francesca; Sabattini, Lorenzo; Secchi, Cristian
abstract

The paper proposes a decentralized state estimation method for the control of network systems, where a cooperative objective has to be achieved. The nodes of the network are partitioned into independent nodes, providing the control inputs, and dependent nodes, controlled by local interaction laws. The proposed state estimation algorithm allows the independent nodes to estimate the state of the dependent nodes in a completely decentralized way. To do that, it is necessary for each independent node of the network to estimate the control input components computed by the other independent nodes, without requiring communication among the independent nodes. The decentralized state estimator, including an input estimator, is developed and the convergence properties are studied. Simulation results show the effectiveness of the proposed approach.

2019 - Effect of Stubborn Agents on Bounded Confidence Opinion Dynamic Systems: Unanimity in Presence of Stubborn Agents [Relazione in Atti di Convegno]
Khateri, K.; Pourgholi, M.; Montazeri, M.; Sabattini, L.
abstract

In this paper, various bounded confidence opinion dynamic algorithms are examined to illustrate the effect of a stubborn minority groups on opinion dynamics. A notion of variable opinion stubborn agent is defined and it is shown that stubborn minorities are able to fully control the opinions of a Hegselmann-Krause opinion dynamic system through deliberate slow variation in the opinions of stubborn agents. Furthermore, an upper bound for the change rate of stubborn agents to preserve connectivity and control other flexible agents is given. Moreover, a method based on population and growing confidence bound is presented to achieve both unanimity and stubborn opinion rejection. To support the proposed method simulation results are provided.

2019 - Improvement of network fragility for multi-robot robustness [Relazione in Atti di Convegno]
Murayama, Toru; Sabattini, Lorenzo
abstract

2019 - Measurement and classification of human characteristics and capabilities during interaction tasks [Articolo su rivista]
Villani, V.; Czerniak, J. N.; Sabattini, L.; Mertens, A.; Fantuzzi, C.
abstract

In this paperwe address the need to design adaptive interacting systems for advanced industrial production machines. Modern production systems have become highly complex and include many subsidiary functionalities, thus making it difficult for least skilled human operators interact with them. In this regard, adapting the behavior of the machine and of the operator interface to the characteristics of the user allows a more effective interaction process, with a positive impact on manufacturing efficiency and user's satisfaction. To this end, it is crucial to understandwhich are the user's capabilities that influence the interaction and, hence, should be measured to provide the correct amount of adaptation.Moving along these lines, in this paper we identify groups of users that, despite having different individual capabilities and features, have common needs and response to the interaction with complex production systems. As a consequence,we define clusters of users that have the same need for adaptation. Then, adaptation rules can be defined by considering such users' clusters, rather than addressing specific individual user's needs.

2019 - Robust area coverage with connectivity maintenance [Relazione in Atti di Convegno]
Siligardi, L.; Panerati, J.; Kaufmann, M.; Minelli, M.; Ghedini, C.; Beltrame, G.; Sabattini, L.
abstract

Robot swarms herald the ability to solve complex tasks using a large collection of simple devices. However, engineering a robotic swarm is far from trivial, with a major hurdle being the definition of the control laws leading to the desired globally coordinated behavior. Communication is a key element for coordination and it is considered one of the current most important challenges for swarm robotics. In this paper, we study the problem of maintaining robust swarm connectivity while performing a coverage task based on the Voronoi tessellation of an area of interest. We implement our methodology in a team of eight Khepera IV robots. With the assumptions that robots have a limited sensing and communication range - and cannot rely on centralized processing - we propose a tri-objective control law that outperforms other simpler strategies (e.g. a potential-based coverage) in terms of network connectivity, robustness to failure, and area coverage.

2019 - Robust connectivity maintenance for fallible robots [Articolo su rivista]
Panerati, Jacopo; Minelli, Marco; Ghedini, Cinara; Meyer, Lucas; Kaufmann, Marcel; Sabattini, Lorenzo; Beltrame, Giovanni
abstract

Multi-robot systems are promising tools for many hazardous real-world problems. In particular, the practical application of swarm robotics was identified as one of the grand challenges of the next decade. As swarms enter the real world, they have to deal with the inevitable problems of hardware, software, and communication failure, especially for long-term deployments. Communication is a key element for effective collaboration, and the ability of robots to communicate is expressed by the swarm’s connectivity. In this paper, we analyze a set of techniques to assess, control, and enforce connectivity in the context of fallible robots. Past research has addressed the issue of connectivity but, for the most part, without making system reliability a constitutional part of the model. We introduce a controller for connectivity maintenance in the presence of faults and discuss the optimization of its parameters and performance. We validate our approach in simulation and via physical robot experiments.

2019 - SPRINTER: A Discrete Locomotion Robot for Precision Swarm Printing [Relazione in Atti di Convegno]
Karpe, Kedar; Chatterjee, Ayon; Srinivas, Pranav; Samiappan, Dhanalakshmi; Ramamoorthy, Kumar; Sabattini, Lorenzo
abstract

2019 - Stop, Think, and Roll: Online Gain Optimization for Resilient Multi-robot Topologies [Relazione in Atti di Convegno]
Minelli, Marco; Kaufmann, Marcel; Panerati, Jacopo; Ghedini, Cinara; Beltrame, Giovanni; Sabattini, Lorenzo
abstract

Stop, Think, and Roll: Online Gain Optimization for Resilient Multi-robot Topologies

2019 - Systematic Approach to Develop a Flexible Adaptive Human-Machine Interface in Socio-Technological Systems [Relazione in Atti di Convegno]
Czerniak, J. N.; Villani, V.; Sabattini, L.; Loch, F.; Vogel-Heuser, B.; Fantuzzi, C.; Brandl, C.; Mertens, A.
abstract

Modern automatic machines in production have been becoming more and more complex within the recent years. Thus, human-machine interfaces (HMI) reflect multiple different functions. An approach to improve human-machine interaction can be realised by adjusting the HMI to the operators’ requirements and complementing their individual skills and capabilities, supporting them in self-reliant machine operation. Based on ergonomic concepts of information processing, we present a systematic approach for developing an adaptive HMI after the MATE concept (Measure, Adapt & Teach). In a first step, we develop a taxonomy of human capabilities that have an impact on individual performance during informational work tasks with machine HMI. We further evaluate three representative use cases by pairwise comparison regarding the classified attributes. Results show that cognitive information processes, such as different forms of attention and factual knowledge (crystalline intelligence) are most relevant on average. Moreover, perceptive capabilities that are restricted by task environment, e.g. several auditory attributes; as well as problem solving demand further support, according to the experts’ estimation.

2019 - Teleoperation of a Multi-robot System with Adjustable Dynamic Parameters [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Fantuzzi, Cesare; Secchi, Cristian
abstract

Teleoperation of a Multi-Robot System with Adjustable Dynamic Parameters

2019 - The impact of agent definitions and interactions on multiagent learning for coordination [Relazione in Atti di Convegno]
Chung, J. J.; Miklic, D.; Sabattini, L.; Tumer, K.; Siegwart, R.
abstract

2019 - Understanding Multi-Robot Systems: on the Concept of Legibility [Relazione in Atti di Convegno]
Capelli, Beatrice; Villani, Valeria; Secchi, Cristian; Sabattini, Lorenzo
abstract

2019 - Wheel Slip Avoidance through a Nonlinear Model Predictive Control for Object Pushing with a Mobile Robot [Relazione in Atti di Convegno]
Bertoncelli, Filippo; Ruggiero, Fabio; Sabattini, Lorenzo
abstract

Wheel slip may cause a significative worsening of control performance during the movement of a mobile robot. A method to avoid wheel slip is proposed in this paper through a nonlinear model predictive control. The constraints included within the optimization problem limit the force exchanged between each wheel and the ground. The approach is validated in a dynamic simulation environment through a Pioneer 3-DX wheeled mobile robot performing a pushing manipulation of a box. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

2018 - A Decentralized Control Strategy for Resilient Connectivity Maintenance in Multi-robot Systems Subject to Failures [Relazione in Atti di Convegno]
Ghedini, Cinara; Ribeiro, Carlos H. C.; Sabattini, Lorenzo
abstract

A Decentralized Control Strategy for Resilient Connectivity Maintenance in Multi-robot Systems Subject to Failures

2018 - A Framework for Affect-Based Natural Human-Robot Interaction [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we present a general framework for affective human-robot interaction that allows users to intuitively interact with a robot and takes into account their mental fatigue, thus simplifying the task or providing assistance when the user feels stressed. Interaction with the robot is achieved by naturally mapping user's forearm motion, detected with a smartwatch, into robot's motion. High-level commands can be provided by means of gestures. An approach based on affective robotics is used to adapt the level of robot's autonomy to the cognitive workload of the user. User's mental fatigue is detected from the analysis of heart rate, also measured by the smartwatch. The framework is general and can be applied to different robotic systems. In this paper, we consider its experimental validation on a wheeled mobile robot.

2018 - An Adaptive Speech Interface for Assistance in Maintenance and Changeover Procedure [Relazione in Atti di Convegno]
Loch, Frieder; Czerniak, Julia; Villani, Valeria; Sabattini, Lorenzo; Fantuzzi, Cesare; Mertens, Alexander; Vogel-Heuser, Birgit
abstract

Machine operators remain important in future production environments and need intuitive and powerful interaction techniques. Many assistance and support applications for machine operators use speech-based interfaces since they are suitable during manual tasks and when visual attention cannot be occupied. Due to developments like the demographic change or the need for skilled personnel, the skills and capabilities of the workers will become increasingly diverse. Speech-based interfaces therefore need to be adaptable to the capabilities, limitations and preferences of individual operators. This paper addresses this requirement and proposes an adaptive speech interface that supports machine operators during maintenance and changeover procedures. All aspects of the proposed application can be adapted to the requirements of the user. The system uses a process model, instruction templates, a user model, and a model of the input vocabulary to describe the components of the application. This allows a flexible adaptation of the speech interface and the provided instructions to the requirements of individual users and to further use cases.

2018 - An Industrial Social Network for Sharing Knowledge Among Operators [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Levratti, Alessio; Fantuzzi, Cesare
abstract

Due to the increasing complexity of modern automatic machines typically used in several industrial applications, the need for assistive technologies is becoming very relevant. Typical approaches consist in designing advanced and adaptive human-machine interfaces (HMIs) that can be effectively used by any operator and that provide guided procedures for the most common situations. However, when dealing with complex systems, infrequent and unforeseen situations may happen, whose solution require the experience owned by a limited number of skilled operators. To this end, in this paper we propose an industrial social network concept to allow an effective exchange of information among the operators and to facilitate the solution of unforeseen events, such as unscheduled maintenance activities or troubleshooting.

2018 - Controlling the interaction of a multi-robot system with external entities [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we consider a multi-robot system that shares the environment with external entities, and we propose a methodology for controlling the interaction with them. In particular, we consider the problem of achieving a desired dynamic interaction model, in such a way that the multi-robot system exchanges desired forces with external entities. This is obtained by introducing local deformations of the coupling actions among the robots. The proposed method ensures preservation of the passivity property, which provides safety guarantees in the interaction with the (possibly poorly known) external entities.

2018 - Distributed Laplacian Eigenvalue and Eigenvector Estimation in Multi-robot Systems [Relazione in Atti di Convegno]
Zareh, Mehran; Sabattini, Lorenzo; Secchi, Cristian
abstract

Distributed Laplacian Eigenvalue and Eigenvector Estimation in Multi-robot Systems

2018 - MATE Robots Simplifying My Work: The Benefits and Socioethical Implications [Articolo su rivista]
Villani, Valeria; Sabattini, Lorenzo; Czerniak, Julia N.; Mertens, Alexander; Fantuzzi, Cesare
abstract

With the increasing complexity of modern industrial automatic and robotic systems, an increasing burden is put on the operators, who are requested to supervise and interact with very complex systems, typically under challenging and stressful conditions. To overcome this issue, it is necessary to adopt a responsible approach based on the anthropocentric design methodology, such that machines adapt to the humans capabilities, and not vice versa. Moving along these lines, in this paper we consider an integrated methodological design approach, which we call MATE, consisting in devising complex automatic or robotic solutions that measure current operator's status, adapting the interaction accordingly, and providing her/him with proper training to improve the interaction and learn lacking skills and expertise. Accordingly, a MATE system is intended to be easily usable for all users, thus meeting the principles of inclusive design. Using such a MATE system gives rise to several ethical and social implications, which are discussed in this paper. Additionally, a discussion about which factors in the organization of companies are critical with respect to the introduction of a MATE system is presented.

2018 - Methodological Approach for the Evaluation of an Adaptive and Assistive Human-Machine System [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Villani, Valeria; Fantuzzi, Cesare; Czerniak, Julia N.; Mertens, Alexander; Loch, Frieder; Vogel-Heuser, Birgit
abstract

With the increasing complexity of modern industrial automatic and robotic systems, an increasing burden is put on the operators, who are requested to supervise and interact with such complex systems, typically under challenging and stressful conditions. To overcome this issue, it is necessary to adopt a responsible approach based on the anthropocentric design methodology, such that machines adapt to the humans capabilities. Moving along these lines, a methodological approach called MATE was introduced in [1], which consists in devising complex automatic or robotic solutions that measure current operator's status, adapting the interaction accordingly, and providing her/him with proper training to improve the interaction and learn lacking skills and expertise. In this paper we propose an evaluation and validation procedure to guarantee the achievement of the requirements of a MATE system.

2018 - Passivity preserving force scaling for enhanced teleoperation of multirobot systems [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Capelli, Beatrice; Fantuzzi, Cesare
abstract

In this letter, we address the problem of teleoperating a multirobot system, and we propose a methodology for letting the user teleoperate the group of robots according to some desired dynamic behavior. Specifically, we propose a novel methodology for the teleoperation of multirobot systems, where a local control action and interrobot relationships are tuned in order to reduce their effect on the force feedback perceived by the operator. The proposed methodology is developed guaranteeing preservation of the passivity property. The effectiveness of the proposed teleoperation scheme is validated experimentally, on real robots and in a virtual reality environment.

2018 - Perturbation Analysis of Decentralized Estimators [Relazione in Atti di Convegno]
Karpe, Kedar; Samiappan, Dhanalakshmi; Ramamoorthy, Kumar; Sabattini, Lorenzo
abstract

Perturbation Analysis of Decentralised Estimators

2018 - Relieving operators’ workload: Towards affective robotics in industrial scenarios [Articolo su rivista]
TALIGNANI LANDI, Chiara; Villani, Valeria; Ferraguti, Federica; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper proposes a novel approach based on affective robotics that can be applied to industrial applications. Considering a human-robot interaction task, we propose to analyze the mental workload of the operator, and subsequently adapt the behavior of the robotic system, introducing assistive technologies. These technologies would prevent the performances deterioration caused by the human stress, helping him/her only when needed and decreasing the user's mental workload. This represents a general methodology, which can be applied to several industrial applications, leading to increase the overall performances of human-robot interaction exploiting principles of human-centered design. As a case study, we consider a teleoperation task, where virtual fixtures are utilized as an assistive technology. The stress of the operator is monitored in terms of heart rate variability, measured by means of a wearable sensor tied at the operator's wrist. Experimental validation of the proposed architecture is performed on a group of 15 users that teleoperate an industrial robot for performing a pick and place task.

2018 - Shaping the force feedback by dynamic scaling in the teleoperation of multi-robot systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Fantuzzi, Cesare; Secchi, Cristian
abstract

In passivity based bilateral teleoperation of multi-robot systems the coupling among the robots produces unwanted dynamic effects that deteriorates the force fed back to the user. In this paper we propose a passivity based dynamic scaling strategy for compensating these disturbing terms. The effectiveness of the proposed methodology is experimentally validated.

2018 - The PAN-Robots Project: Advanced Automated Guided Vehicle Systems for Industrial Logistics [Articolo su rivista]
Sabattini, Lorenzo; Aikio, Mika; Beinschob, Patric; Boehning, Markus; Cardarelli, Elena; Digani, Valerio; Krengel, Annette; Magnani, Massimiliano; Mandici, Szilard; Oleari, Fabio; Reinke, Christoph; Ronzoni, Davide; Stimming, Christian; Varga, Robert; Vatavu, Andrei; Castells Lopez, Sergi; Fantuzzi, Cesare; Mayra, Aki; Nedevschi, Sergiu; Secchi, Cristian; Fuerstenberg, Kay
abstract

In modern manufacturing plants, automation is widely adopted in the production phases, which leads to achieving a high level of productivity and efficiency. However, the same level of automation is generally not achieved in logistics, that is typically performed by human operators, and manually driven vehicles. In fact, even though Automated Guided Vehicles (AGVs) have been used for a few decades for goods transportation in industrial environments [1], they do not represent a widespread solution yet, and are typically applied only in specific scenarios.

2018 - Toward efficient adaptive ad-hoc multi-robot network topologies [Articolo su rivista]
Ghedini, Cinara; Ribeiro, Carlos H. C.; Sabattini, Lorenzo
abstract

The availability of robust and power-efficient robotic devices boosts their use in a wide range of applications, most of them unfeasible in the recent past due to environmental restrictions or because they are hazardous to humans. Nowadays, robots can support or perform missions of search and rescue, exploration, surveillance, and reconnaissance, or provide a communication infrastructure to clients when there is no network infrastructure available. In general, these applications require efficient and multi-objective teamwork. Hence, successful control and coordination of a group of wireless-networked robots relies on effective inter-robot communication. In this sense, this work proposes a model that aims at providing more efficient network topologies addressing the issues of connectivity maintenance, collision avoidance, robustness to failure and area coverage improvement. The model performance was experimentally validated considering fault-free and fault-prone scenarios. Results demonstrated the feasibility of having simultaneous controls acting to achieve more resilient networks able to enhancing their sensing area while avoiding collision and maintaining the network connectivity with regard to fault-free scenarios.

2018 - Use of Virtual Reality for the Evaluation of Human-Robot Interaction Systems in Complex Scenarios [Relazione in Atti di Convegno]
Villani, Valeria; Capelli, Beatrice; Sabattini, Lorenzo
abstract

Human-robot interaction has gained a lot of attention in recent years, since the use of robots can complement and improve human capabilities. To make such interaction smooth, proper interaction approaches are needed. Customarily these are tested in simplified scenarios and tame laboratory environment, since reproducing complex real use cases is often difficult. Achieved results are then not representative of actual interaction in reality and do not scale to complex scenarios. To overcome this issue, in this paper we consider the use of virtual reality as an alternative tool to assess HRI in those scenarios that are difficult to reproduce in reality. To this end, we compare the interaction experience for the same task, which is carried out in both virtual reality and real environment. To assess user's interaction in the two scenarios, we consider quantitative task related metrics, mental workload sustained, and subjective reporting. Results show that virtual reality allows to reproduce a faithful interaction experience and, thus, can be used to reliably validate human-robot interaction approaches in complex scenarios.

2017 - A Natural Infrastructure-Less Human–Robot Interaction System [Articolo su rivista]
Villani, Valeria; Sabattini, Lorenzo; Riggio, Giuseppe; Secchi, Cristian; Minelli, Marco; Fantuzzi, Cesare
abstract

This letter introduces a novel methodology for letting a user interact with a robotic system in a natural manner. The main idea is that of defining an interaction system that does not require any specific infrastructure or device but relies on commonly utilized objects while leaving the user’s hands free. Specifically, we propose to utilize a smartwatch (or any commercial sensorized wristband) for recognizing the motion of the user’s forearm. This is achieved by measuring accelerations and angular velocities, which are then elaborated for recognizing gestures and for defining velocity commands for the robot. The proposed interaction system is evaluated experimentally with different users controlling a semiautonomous quadrotor. Results show that the usability and effective- ness of the proposed natural interaction system provide significant improvement in the human–robot interaction experience.

2017 - Achieving the desired dynamic behavior in multi-robot systems interacting with the environment [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we consider the problem of controlling the dynamic behavior of a multi-robot system while interacting with the environment. In particular, we propose a general methodology that, by means of locally scaling interrobot coupling relationships, leads to achieving a desired interactive behavior. The proposed method is shown to guarantee passivity preservation, which ensures a safe interaction. The performance of the proposed methodology is evaluated in simulation, over large-scale multi-robot systems.

2017 - Admittance control parameter adaptation for physical human-robot interaction [Relazione in Atti di Convegno]
Landi, Chiara Talignani; Ferraguti, Federica; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In physical human-robot interaction, the coexistence of robots and humans in the same workspace requires the guarantee of a stable interaction, trying to minimize the effort for the operator. To this aim, the admittance control is widely used and the appropriate selection of the its parameters is crucial, since they affect both the stability and the ability of the robot to interact with the user. In this paper, we present a strategy for detecting deviations from the nominal behavior of an admittance-controlled robot and for adapting the parameters of the controller while guaranteeing the passivity. The proposed methodology is validated on a KUKA LWR 4+.

2017 - Bounded control law for global connectivity maintenance in cooperative multirobot systems [Articolo su rivista]
Gasparri, Andrea; Sabattini, Lorenzo; Ulivi, Giovanni
abstract

In this paper, we address the connectivity maintenance problem for a multirobot system that moves according to a given bounded collective control objective. We assume that the interaction among the robotic units is limited by a given visibility radius both in terms of sensing and communication capabilities. For this scenario, we propose a decentralized bounded control law that can provably preserve the connectivity of the multirobot system over time. We characterize the effect of the connectivity control term on the achievement of the collective control objective by resorting to an input-to-state stability-like analysis.We provide numerical and experimental results to corroborate the theoretical findings and assess the effectiveness of the proposed bounded connectivity maintenance control law.

2017 - Collision avoidance for multiple Lagrangian dynamical systems with gyroscopic forces [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This article introduces a novel methodology for dealing with collision avoidance for groups of mobile robots. In particular, full dynamics are considered, since each robot is modeled as a Lagrangian dynamical system moving in a three-dimensional environment. Gyroscopic forces are utilized for defining the collision avoidance control strategy: This kind of forces leads to avoiding collisions, without interfering with the convergence properties of the multi-robot system's desired control law. Collision avoidance introduces, in fact, a perturbation on the nominal behavior of the system: We define a method for choosing the direction of the gyroscopic force in an optimal manner, in such a way that perturbation is minimized. Collision avoidance and convergence properties are analytically demonstrated, and simulation results are provided for validation purpose.

2017 - Cooperative cloud robotics architecture for the coordination of multi-AGV systems in industrial warehouses [Articolo su rivista]
Cardarelli, Elena; Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we introduce a novel cloud robotics architecture that provides different functionalities to support enhanced coordination of groups of Automated Guided Vehicles (AGVs) used for industrial logistics. In particular, we define a cooperative data fusion system that, gathering data from different sensing sources, provides a constantly updated global live view of the industrial environment, for coordinating the motion of the AGVs in an optimized manner. In fact, local sensing capabilities are complemented with global information, thus extending the field of view of each AGV. This knowledge extension allows to support a cooperative and flexible global route assignment and local path planning in order to avoid congestion zones, obstacles reported in the global live view map and deal with unexpected obstacles in the current path. The proposed methodology is validated in a real industrial environment, allowing an AGV to safely perform an obstacle avoidance procedure.

2017 - Coordinated dynamic behaviors for multirobot systems with collision avoidance [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper, we propose a novel methodology for achieving complex dynamic behaviors in multirobot systems. In particular, we consider a multirobot system partitioned into two subgroups: 1) dependent and 2) independent robots. Independent robots are utilized as a control input, and their motion is controlled in such a way that the dependent robots solve a tracking problem, that is following arbitrarily defined setpoint trajectories, in a coordinated manner. The control strategy proposed in this paper explicitly addresses the collision avoidance problem, utilizing a null space-based behavioral approach: this leads to combining, in a non conflicting manner, the tracking control law with a collision avoidance strategy. The combination of these control actions allows the robots to execute their task in a safe way. Avoidance of collisions is formally proven in this paper, and the proposed methodology is validated by means of simulations and experiments on real robots.

2017 - Interacting With a Mobile Robot with a Natural Infrastructure-Less Interface [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Riggio, Giuseppe; Levratti, Alessio; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we introduce a novel approach that enables users to interact with a mobile robot in a natural manner. The proposed interaction system does not require any specific infrastructure or device, but relies on commonly utilized objects while leaving the user’s hands free. Specifically, we propose to utilize a smartwatch (or a sensorized wristband) for recognizing the motion of the user’s forearm. Measurements of accelerations and angular velocities are exploited to recognize user’s gestures and define velocity commands for the robot. The proposed interaction system is evaluated experimentally with different users controlling a mobile robot and compared to the use of a remote control device for the teleoperation of robots. Results show that the usability and effectiveness of the proposed natural interaction system based on the use of a smartwatch provide significant improvement in the human-robot interaction experience.

2017 - Methodological approach for the design of a complex inclusive human-machine system [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Villani, Valeria; Czerniak, Julia N.; Mertens, Alexander; Fantuzzi, Cesare
abstract

Modern industrial automatic machines and robotic cells are equipped with highly complex human-machine interfaces (HMIs) that often prevent human operators from an effective use of the automatic systems. In particular, this applies to vulnerable users, such as those with low experience or education level, the elderly and the disabled. To tackle this issue, it becomes necessary to design user-oriented HMIs, which adapt to the capabilities and skills of users, thus compensating their limitations and taking full advantage of their knowledge. In this paper, we propose a methodological approach to the design of complex adaptive human-machine systems that might be inclusive of all users, in particular the vulnerable ones. The proposed approach takes into account both the technical requirements and the requirements for ethical, legal and social implications (ELSI) for the design of automatic systems. The technical requirements derive from a thorough analysis of three use cases taken from the European project INCLUSIVE. To achieve the ELSI requirements, the MEESTAR approach is combined with the specific legal issues for occupational systems and requirements of the target users.

2017 - Multi-robot systems implementing complex behaviors under time-varying topologies [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we address the problem of obtaining complex dynamic behaviors in multi-robot systems. In particular, those complex behaviors are modeled in terms of cooperative tracking of periodic setpoint trajectories. The proposed solution considers a heterogeneous group of robots: a few independent robots are used as a control input for the system, with the aim of controlling the position of the remaining robots, namely the dependent ones. The proposed control strategy explicitly considers changes in the communication topology among the robots, that lead to the definition of a switched system. In particular, these changes happen as the system evolves, since robots are equipped with finite range communication devices. A methodology is introduced for defining the system parameters in order to guarantee asymptotic stability of the switched system, thus guaranteeing the desired tracking performance, assuming that independent robots are able to measure or estimate the global state of the multi-robot system.

2017 - Multirobot systems [Articolo su rivista]
Ayanian, Nora; Fitch, Robert; Franchi, Antonio; Sabattini, Lorenzo
abstract

The Technical Committee (TC) on Multirobot Systems (MRS) was founded in 2014 to create a focal point for the wide and diverse community of researchers interested in MRS. Researchers interested in MRS represent an inherently diverse community because several competences are needed in this field, including control systems, mechanical design, coordination, cooperation, estimation, perception, and interaction. MRS research comprises three broad research areas. These areas of interest are modeling and control of MRS, planning and decision making for MRS, and applications of MRS and technological and methodological issues. The MRS TC sponsors many activities that bring our members together, both in person and online. Our flagship achievement to date is the founding of a new conference dedicated to multirobot and multiagent systems, the International Symposium on Multirobot and Multiagent Systems.

2017 - Natural interaction based on affective robotics for multi-robot systems [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we introduce a novel approach that enables users to interact with a multi-robot system in a natural manner. Additionally, interaction adapts to the user’s affect and stamina. To this end, we consider the use of a smartwatch for recognizing the motion of the user’s forearm, which is then translated in velocity commands for the robots. A natural mapping between user’s movements and robots commands is implemented, so that the user can intuitively drive the robots by mimicking real-world behavior. Additionally, the operator’s heart rate is measured, since it is a measure of mental stress. Thus, when an increase in mental stress is detected, the behavior of the multi-robot system is changed in order to simplify the interaction task and relieve the user. The proposed interaction system is tested with different users. Specifically, the effectiveness of the natural interaction is evaluated and compared to the use of a joypad and a haptic device. Moreover, we preliminarily test the affective interaction approach.

2017 - Optimized simultaneous conflict-free task assignment and path planning for multi-AGV systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we address the problem of assigning a set of tasks to a set of Automated Guided Vehicles (AGVs), in a conflict-free manner. Specifically, we consider a system of multiple AGVs, moving along a predefined roadmap, and utilized for transportation of goods in automated warehouses. Sequential application of task assignment and path planning often gives rise to pathological situations, such as deadlocks, in which AGVs block each other, thus preventing tasks completion. In this paper we propose a method for assigning tasks while taking into account the subsequent path planning, encoding possible conflicts into a conflict graph, that is subsequently utilized for defining constraints of an optimization problem. Simulations are performed on maps of real industrial environments, to compare the proposed method with traditional task assignment.

2017 - Semi-automated map creation for fast deployment of AGV fleets in modern logistics [Articolo su rivista]
Beinschob, Patric; Meyer, Mark; Reinke, Christoph; Digani, Valerio; Secchi, Cristian; Sabattini, Lorenzo
abstract

Today, Automated Guided Vehicles (AGVs) still have a low market share in logistics, compared to manual forklifts. We identified one of the main bottlenecks in the rather long deployment time which involves precise 2D mapping of the plant, 3D geo-referencing of pick-up/ drop positions and the manual design of the roadmap. The long deployment time has various reasons: in state-of-the-art plant installations, designated infrastructure is still necessary for the localization; the mapping process requires highly skilled personnel; in many cases unavailable or inappropriate position information of drop points for goods must be corrected on site. Finally, the design of the roadmap, performed by expert technicians is manually optimised in a tedious process to achieve maximum flow of goods for the plant operator. In total the setup of a plant to be ready for AGV operation is taking several months, binding highly skilled technicians and involves very time-consuming and costly on-site procedures. Therefore, we present an approach to AGV deployment which aims to drastically reduce the time, cost and involved personnel. First, we propose the employment of a novel, industrial-ready SICK 3D laser scanning technology in order to build an accurate and consistent virtual representation of the whole warehouse environment. By utilizing suitable segmentation and processing a semantic map is generated that contains 3D geo-referenced positions as well as a 2D localization map eliminating the need for dedicated solution to 2D mapping. Second, the semantic map provides a free space map which is used as a basis for the automatic roadmap creation in order to achieve optimal flow. So, this paper proposes an innovative methodology for obtaining, in a semi-automated manner, the map of an industrial environment where a system of multiple AGVs will be installed with less time and cost.

2017 - Toward fault-tolerant multi-robot networks [Articolo su rivista]
Ghedini, Cinara; Ribeiro, Carlos; Sabattini, Lorenzo
abstract

Applications based on groups of self-organized mobile robots are becoming pervasive in communication networks, monitoring, traffic, and transportation systems. Their advantage is the possibility of providing services without the existence of a previously defined infrastructure. However, physical agents are prone to failures that add uncertainty and unpredictability in the environments in which they operate. Therefore, a robust topology regarding failures is an imperative requirement. In this article, we show that mechanisms based solely on connectivity maintenance are not enough to obtain a sufficiently resilient network, and a robustness-oriented approach is necessary. Thus, we propose a local combined control law that aims at maintaining the overall network connectivity while improving the network robustness via actions that reduce vulnerability to failures that might lead to network disconnection. We demonstrate, from a theoretical point of view, that the combined control law maintains connectivity, and experimentally validate it under diverse failure distributions, from two perspectives: as a reactive and as a proactive mechanism. As a reactive mechanism, it was able to accommodate ongoing failures and postpone or avoid network fragmentation, including cases where failures are concentrated over short time spans. As a proactive mechanism, the network topology was able to evolve from potentially vulnerable with respect to failures to a more robust one. Â© 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 70(4), 388â400 2017.

2017 - Towards modern inclusive factories: A methodology for the development of smart adaptive human-machine interfaces [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Czerniaki, Julia N.; Mertens, Alexander; Vogel-Heuser, Birgit; Fantuzzi, Cesare
abstract

Modern manufacturing systems typically require high degrees of flexibility, in terms of ability to customize the production lines to the constantly changing market requests. For this purpose, manufacturing systems are required to be able to cope with changes in the types of products, and in the size of the production batches. As a consequence, the human-machine interfaces (HMIs) are typically very complex, and include a wide range of possible operational modes and commands. This generally implies an unsustainable cognitive workload for the human operators, in addition to a non-negligible training effort. To overcome this issue, in this paper we present a methodology for the design of adaptive human-centred HMIs for industrial machines and robots. The proposed approach relies on three pillars: measurement of user's capabilities, adaptation of the information presented in the HMI, and training of the user. The results expected from the application of the proposed methodology are investigated in terms of increased customization and productivity of manufacturing processes, and wider acceptance of automation technologies. The proposed approach has been devised in the framework of the European project INCLUSIVE.

2017 - Variable admittance control preventing undesired oscillating behaviors in physical human-robot interaction [Relazione in Atti di Convegno]
Landi, Chiara Talignani; Ferraguti, Federica; Sabattini, Lorenzo; Secchi, Cristian; Bonfe', Marcello; Fantuzzi, Cesare
abstract

Admittance control is a widely used approach for guaranteeing a compliant behavior of the robot in physical human-robot interaction. When an admittance-controlled robot is coupled with a human, the dynamics of the human can cause deviations from the desired behavior of the robot, mainly due to a stiffening of the human arm, and thus generate high-frequency unsafe oscillations of the robot. In this paper we present a novel methodology for detecting the rising oscillations in the human-robot interaction. Furthermore, we propose a passivity-preserving strategy to adapt the parameter of the admittance control in order to get rid of the high-frequency oscillations and, when possible, to restore the desired interaction model. A thorough experimental validation of the proposed strategy is performed on a group of 26 users performing a cooperative task.

2016 - A Probabilistic Eulerian Traffic Model for the Coordination of Multiple AGVs in Automatic Warehouses [Articolo su rivista]
Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian
abstract

The co-ordination of multiple automated guided vehicles (AGVs) is one of the main issues to address for the implementation of an efficient autonomous warehouse. Traffic jams are highly undesirable and, therefore, the motion of the AGVs should be planned by considering the current and future state of the fleet. This letter proposes a probabilistic model of the traffic in an autonomous warehouse to predict the evolution of possibly congested areas. Such a model is then exploited for building a predictive planner that is embedded in the traffic manager recently proposed in [1] to explicitely consider the evolution of the traffic up to a given horizon and to increase the efficiency of the fleet of AGVs in terms of delivery time. The proposed traffic manager is validated by means of comparative simulations on real plants.

2016 - Coordinated motion for multi-robot systems under time varying communication topologies [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Lotti, Marco; Fantuzzi, Cesare
abstract

This paper introduces a control strategy for obtaining cooperative tracking of periodic setpoint trajectories in multi-robot systems. A heterogeneous group of robots is considered: a few independent robots are used as a control input for the system, with the aim of controlling the position of the remaining robots, namely the dependent ones. The control strategy presented in this paper explicitly considers changes in the communication topology among the robots. These changes happen as the system evolves, since robots are equipped with finite range communication devices.

2016 - Decentralized biconnectivity conditions in multi-robot systems [Relazione in Atti di Convegno]
Zareh, Mehran; Sabattini, Lorenzo; Secchi, Cristian
abstract

The network connectivity in a group of cooperative robots can be easily broken if one of them loses its connectivity with the rest of the group. In case of having robustness with respect to one-robot failure, the communication network is termed biconnected. In simple words, to have a biconnected network graph, we need to prove that no articulation point exists. We propose a decentralized approach that provides sufficient conditions for biconnectivity of the network, and we prove that these conditions are related to the third smallest eigenvalue of the Laplacian matrix. Data exchange among the robots is supposed to be neighbor-to-neighbor.

2016 - Decentralized fault diagnosis for heterogeneous multi-agent systems [Relazione in Atti di Convegno]
Boem, Francesca; Sabattini, Lorenzo; Secchi, Cristian
abstract

The paper proposes a decentralized method for fault detection and isolation in heterogeneous multi-agents systems. The agents are partitioned into independent nodes, providing the control inputs and monitoring the system, and dependent nodes, controlled by local interaction laws and subject to faults. The approach uses a decentralized state estimation algorithm allowing the independent nodes to estimate both the state of the dependent nodes and the control input components computed by the other independent nodes, in a completely decentralized way, without requiring communication among the independent nodes. Suitable detection and isolation residuals and thresholds are derived. Detectability and isolability sufficient conditions are provided. Simulation results show the effectiveness of the proposed approach.

2016 - Enforcing biconnectivity in multi-robot systems [Relazione in Atti di Convegno]
Zareh Eshghdoust, Mehran; Sabattini, Lorenzo; Secchi, Cristian
abstract

Connectivity maintenance is an essential task in multi-robot systems and it has received a considerable attention during the last years. However, a connected system can be broken into two or more subsets simply if a single robot fails. Then, a more robust communication can be achieved if the network connectivity is guaranteed in the case of one-robot failures. The resulting network is called biconnected. In [1] we presented a criterion for biconnectivity check, which basically determines a lower bound on the third-smallest eigenvalue of the Laplacian matrix. In this paper we introduce a decentralized gradient-based protocol to increase the value of the third-smallest eigenvalue of the Laplacian matrix, when the biconnectivity check fails. We also introduce a decentralized algorithm to estimate the eigenvectors of the Laplacian matrix, which are used for defining the gradient. Simulations show the effectiveness of the theoretical findings.

2016 - Hierarchical coordination strategy for multi-AGV systems based on dynamic geodesic environment partitioning [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we consider the problem of coordinating the motion of a group of Automated Guided Vehicles (AGVs) utilized in industrial environments for logistics operations. In particular, we consider a hierarchical coordination strategy, where the environment is partitioned into sectors: coordination on the top layer defines the sequence of sectors to be traveled, while coordination on the bottom layer deals with traffic management inside each sector. In this paper we introduce a novel partitioning algorithm, that defines the sectors in a dynamic manner, taking into account both the shape of the (generally non-convex) environment, and the current distribution of the AGVs. This is achieved exploiting a clustering algorithm, and subsequently defining the sectors based on the geodesic distance.

2016 - Improving the fault tolerance of multi-robot networks through a combined control law strategy [Relazione in Atti di Convegno]
Ghedini, Cinara; Ribeiro, Carlos H. C.; Sabattini, Lorenzo
abstract

Applications based on groups of self-organized mobile robots and - more generically - agents are becoming pervasive in communication, monitoring, traffic and transportation systems. Their advantage is the possibility of providing services without the existence of a previously defined infrastructure and with a high degree of autonomy. On the other hand, physical agents, in general, are prone to failures, adding uncertainty and unpredictability in the environments in which they operate. Therefore, a robust topology regarding failures is an imperative requirement. In this paper, we show that mechanisms based solely on connectivity maintenance are not enough to obtain a sufficiently resilient network, and a robustness-oriented approach is necessary. Thus, we propose a local combined control law that aims at maintaining the overall network connectivity while improving the network robustness via actions that reduce vulnerability to failures that might lead to network disconnection. The combined control law performance was validated from two perspectives: as a reactive and as a proactive mechanism. As a reactive mechanism, it was able to accommodate ongoing failures and postpone or avoid network fragmentation. As a proactive mechanism, the network topology was able to evolve from a potentially vulnerable topology w.r.t. failures to a more robust one.

2016 - Multi-AGV systems in shared industrial environments: Advanced sensing and control techniques for enhanced safety and improved efficiency [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Cardarelli, Elena; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare
abstract

This chapter describes innovative sensing technologies and control techniques that aim at improving the performance of groups of automated guided vehicles (AGVs) used for logistics operations in industrial environments. We explicitly consider the situation where the environment is shared among AGVs, manually driven vehicles, and human operators. In this situation, safety is a major issue that needs always to be guaranteed, while still maximizing the efficiency of the system. This paper describes some of the main achievements of the PAN-Robots European project.

2016 - Smartwatch-Enhanced Interaction with an Advanced Troubleshooting System for Industrial Machines [Relazione in Atti di Convegno]
Villani, Valeria; Sabattini, Lorenzo; Battilani, Nicola; Fantuzzi, Cesare
abstract

Smartwatches are unobtrusive everyday devices which can be also exploited for effective gesture-based human-machine interaction. In this paper, we propose the use of a smartwatch to interact with an advanced troubleshooting application to be used in industrial environment. The application is a hypermedia information system aiming at assisting workers in performing preventive and corrective machine maintenance. The smartwatch allows a handsfree interaction, thus facilitating the use of the whole system when wearing personal protective equipment such as gloves or having fingers greased with oil or dust, which prevent operating touch screens. The algorithm for gesture recognition we have devised, which is based on template matching, is described in the paper, together with its experimental validation. Finally, we present a preliminary usability assessment of the overall system, meant as integration of the smartwatch with the hypermedia system.

2015 - A Quadratic Programming approach for coordinating multi-AGV systems [Relazione in Atti di Convegno]
Digani, Valerio; Hsieh, M. Ani; Sabattini, Lorenzo; Secchi, Cristian
abstract

This paper presents an optimization strategy to coordinate multiple Autonomous Guided Vehicles (AGVs) on ad-hoc pre-defined roadmaps used in logistic operations in industrial applications. Specifically, the objective is to maximize traffic throughput of AGVs navigating in an automated warehouse by minimizing the time AGVs spend negotiating complex traffic patterns to avoid collisions with other AGVs. In this work, the coordination problem is posed as a Quadratic Programming (QP) problem where the optimization is performed in a centralized manner. The optimality of the coordination strategy is established and the feasibility of the strategy is validated in simulation for different scenarios and for real industrial environments. The performance of the proposed strategy is then compared with a decentralized coordination strategy which relies on local negotiations for shared resources. The results show that the proposed coordination strategy successfully maximizes vehicle throughout and significantly minimizes the time vehicles spend negotiating traffic under different scenarios.

2015 - Advanced sensing and control techniques for multi AGV systems in shared industrial environments [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Cardarelli, Elena; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare; Fuerstenberg, Kay
abstract

This paper describes innovative sensing technologies and control techniques, that aim at improving the performance of groups of Automated Guided Vehicles (AGVs) used for logistics operations in industrial environments. We explicitly consider the situation where the environment is shared among AGVs, manually driven vehicles, and human operators. In this situation, safety is a major issue, that needs always to be guaranteed, while still maximizing the efficiency of the system. This paper describes some of the main achievements of the PAN-Robots European project.

2015 - Cloud robotics paradigm for enhanced navigation of autonomous vehicles in real world industrial applications [Relazione in Atti di Convegno]
Cardarelli, Elena; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

Autonomous vehicles require advances sensing technologies, in order to be able to safely share the environment with human operators. Those sensing technologies are in fact necessary for identifying the presence of unforeseen objects, and measuring their position and velocity. Furthermore, classification is necessary for effectively predicting their behavior. In this paper we consider the presence of sensing systems both on-board each vehicle, and installed on infrastructural elements. While the simultaneous presence of multiple sources of information heavily improves the amount (and quality) of available data, it generates the need for effective data fusion and storage systems. Hence, we introduce a centralized cloud service, that is in charge of receiving and merging data acquired by different sensing systems. Those data are then distributed to the autonomous vehicles, that exploit them for implementing advanced navigation strategies. The proposed methodology is validated in a real industrial environment to safely perform obstacle avoidance with an autonomously driven forklift.

2015 - Conducting multi-robot systems: Gestures for the passive teleoperation of multiple slaves [Relazione in Atti di Convegno]
Secchi, Cristian; Sabattini, Lorenzo; Fantuzzi, Cesare
abstract

When teleoperating a multi-robot system it is useful to control the kind of behavior of the fleet depending on the environment it is moving in. In this paper, a novel bilateral control architecture for teleoperating a group of mobile robots is proposed. The user can command the robots both as a flexible and amorphous group and as a set of agents executing different trajectories for achieving a desired task, mimicking a conductor-orchestra paradigm. Exploiting passivity based control, we ensure a stable and safe behavior for the user. The proposed teleoperation strategy is validated by means of experiments.

2015 - Coordinated dynamic behaviors in multi-robot systems with time-varying topologies [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Levratti, Alessio; Cocetti, Matteo; Fantuzzi, Cesare
abstract

A control strategy for the execution of coordinated complex dynamic behaviors in multi-robot systems is introduced in this paper. In particular, considering a dependent-independent robot partitioning of a multi-robot system, we introduce a methodology for controlling the independent robots in such a way that, exploiting local interaction, the dependent robots are driven to track desired periodic setpoint trajectories. The control strategy is designed taking explicitly into account variations in the interconnection topology, due to relative movements among the robots.

2015 - Decentralized Connectivity Maintenance for Networked Lagrangian Dynamical Systems with Collision Avoidance [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Chopra, Nikhil
abstract

In order to accomplish cooperative tasks, multi–robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally considering only kinematic agents. In this paper we will introduce a control strategy that, exploiting a decentralized procedure for the estimation of the algebraic connectivity of the graph, ensures the connectivity maintenance for groups of Lagrangian systems. Collision avoidance control actions are also integrated with the connectivity maintenance. The control strategy is validated by means of analytical proofs and simulation results.

2015 - Decentralized Control of Cooperative Robotic Systems for Arbitrary Setpoint Tracking while Avoiding Collisions [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Levratti, Alessio; Fantuzzi, Cesare
abstract

Decentralized control strategies for multi-robot systems have been extensively studied in the literature, with the aim of regulating the overall state of the system to some desired configuration. Recently a few works have appeared that propose methodologies for solving more complex problems: in particular, partitioning of the multi-robot system into two subgroups can be exploited for cooperatively tracking arbitrarily defined setpoint functions. Specifically, a small number of independent robots can be exploited for controlling the overall state of the dependent robots. Based on this formulation, in this paper we exploit the null space based behavioral approach to obtain setpoint tracking for a multi-robot system, while avoiding inter-robot collisions.

2015 - Decentralized Estimation and Control for Preserving the Strong Connectivity of Directed Graphs [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Chopra, Nikhil
abstract

In order to accomplish cooperative tasks, decentralized systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally considering undirected communication graphs. In this paper, we introduce a decentralized control and estimation strategy to maintain the strong connectivity property of directed communication graphs. In particular, we introduce a hierarchical estimation procedure that implements power iteration in a decentralized manner, exploiting an algorithm for balancing strongly connected directed graphs. The output of the estimation system is then utilized for guaranteeing preservation of the strong connectivity property. The control strategy is validated by means of analytical proofs and simulation results.

2015 - Decentralized state estimation for heterogeneous multi-agent systems [Relazione in Atti di Convegno]
Boem, Francesca; Sabattini, Lorenzo; Secchi, Cristian
abstract

The paper proposes a decentralized state estimation method for the control of multi-agent networked systems, where the goal is the tracking of arbitrary setpoint functions. The cooperative agents are partitioned into independent robots, providing the control inputs, and dependent robots, controlled by local interaction laws. The proposed state estimation algorithm allows the independent robots to estimate the state of the dependent robots in a completely decentralized way. To do that, it is necessary for each independent robot to estimate the control input components computed by the other independent robots, without requiring communication among the independent robots. The decentralized state estimator, including an input estimator, is developed and the convergence properties are studied. Simulation results show the effectiveness of the proposed approach.

2015 - Edge-Weighted Consensus Based Formation Control Strategy With Collision Avoidance [Articolo su rivista]
Falconi, R.; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare; Melchiorri, C.
abstract

In this paper, a consensus-based control strategy is presented to gather formation for a group of differential-wheeled robots. The for- mation shape and the avoidance of collisions between robots are ob- tained by exploiting the properties of weighted graphs. Since mobile robots are supposed to move in unknown environments, the presented approach to multi-robot coordination has been extended in order to include obstacle avoidance. The effectiveness of the proposed control strategy has been demonstrated by means of analytical proofs. More- over, results of simulations and experiments on real robots are provided for validation purposes.

2015 - Eigenvalue placement for asymptotic stability in piecewise linear switched systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we provide an eigenvalue placement methodology that guarantees asymptotic stability in a piecewise linear switched system where a lowerbound on the dwell time is known in advance. In particular, considering the case where each subsystem is a linear controllable system, we introduce an algorithm for placing the eigenvalues of each subsystem in such a way that the overall switched system is asymptotically stable. This is obtained defining a relationship between the dwell time and the stability properties of each subsystem. Simulations of a heterogeneous multi-robot system are provided for validation purposes.

2015 - Ensemble Coordination Approach in Multi-AGV Systems Applied to Industrial Warehouses [Articolo su rivista]
Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper deals with a holistic approach to coordinate a fleet of automated guided vehicles (AGVs) in an industrial environment. We propose an ensemble approach based on a two layer control architecture and on an automatic algorithm for the definition of the roadmap. The roadmap is built by considering the path planning algorithm implemented on the hierarchical architecture and vice versa. In this way, we want to manage the coordination of the whole system in order to increase the flexibility and the global efficiency. Furthermore, the roadmap is computed in order to maximize the redundancy, the coverage and the connectivity. The architecture is composed of two layers. The low-level represents the roadmap itself. The high-level describes the topological relationship among different areas of the environment. The path planning algorithm works on both these levels and the subsequent coordination among AGVs is obtained exploiting shared resource (i.e., centralized information) and local negotiation (i.e., decentralized coordination). The proposed approach is validated by means of simulations and comparison using real plants.

2015 - Guest Editorial: Special Issue on Networked Cooperative Autonomous Systems [Articolo su rivista]
Sabattini, Lorenzo; Ehlers, Frank; Sofge, Don
abstract

The papers in this special section focus on the technology and applications supported by networked cooperative autonomous systems.

2015 - Implementation of Coordinated Complex Dynamic Behaviors in Multirobot Systems [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Cocetti, Matteo; Levratti, Alessio; Fantuzzi, Cesare
abstract

Decentralized control strategies for multirobot systems have been extensively studied over the past few years. Typically, these strategies aim at exploiting local interaction rules to regulate the overall state of the multirobot system toward a desired configuration, thus generating some desired coordinated behaviors, such as synchronization, swarming, deployment, or formation control. However, when considering the real-world application of multirobot systems, more complex cooperative dynamic behaviors are desirable. Along these lines, in this paper, we propose a methodology to control a multirobot system for cooperatively tracking arbitrarily defined periodic setpoint trajectories. This objective is fulfilled partitioning the multirobot system into independent robots (that can provide control inputs) and dependent robots (that are controlled through local interaction). The motion of the independent robots is then defined in such a way that, exploiting local interactions, the dependent robots are controlled to track the desired trajectories. The proposed control strategy is validated by means of simulations and experiments on real robots.

2015 - Improving AGV systems: Integration of advanced sensing and control technologies [Relazione in Atti di Convegno]
Oleari, Fabio; Magnani, Massimiliano; Ronzoni, Davide; Sabattini, Lorenzo; Cardarelli, Elena; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper focuses on the integration of advanced sensing and control technologies into advanced systems of multiple Automated Guided Vehicles (AGVs). In particular, we focus on the key technologies developed within the Plug-and-Navigate Robots (PAN-Robots) project, highlighting how those results contribute to improving the performance of AGV systems.

2015 - Improving robustness in multi-robot networks [Relazione in Atti di Convegno]
Ghedini, Cinara; Secchi, Cristian; Ribeiro, Carlos H. C.; Sabattini, Lorenzo
abstract

This paper addresses the topological robustness of robot networks under failures; a subject often neglected in the literature. Robots are likely to fail due to several causes, which may lead to a poorly connected or a fragmented network. Our purpose is to discuss how to design resilient robot networks. For that, we first demonstrate the problem analyzing the results from a protocol to simulate failures of both central and random (w.r.t. topology) robots. Then, we propose mechanisms for detecting the probability of a robot being in a fragile local configuration and for improving its local robustness. The procedures rely solely on local information: each robot estimates its probability of being in a harmful configuration based on the positions of its neighbors. Such probability is estimated as the number of paths connecting a robot to its 2-hop neighbors by the number of paths existing in the subgraph encompassing its 1-hop and 2-hop neighborhoods. For reversing an adverse configuration, robots change their position to an average position towards their 2-hop neighbors with fewer alternative paths. The results showed that the proposed mechanism is efficient for detecting fragile topological configurations and for improving the overall network robustness.

2015 - Interacting with a multi AGV system [Relazione in Atti di Convegno]
Cardarelli, Elena; Sabattini, Lorenzo; Digani, Valerio; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper introduces a novel Human Machine Interface (HMI) that allows users to interact with a fleet of Automated Guided Vehicles (AGVs) used for logistics operations in industrial environments. The interface is developed for providing operators with information regarding the fleet of AGVs, and the status of the industrial environment. Information is provided in an intuitive manner, utilizing a three-dimensional representation of the elements in the environment. The HMI also allows operators to influence the behavior of the fleet of AGVs, manually inserting missions to be accomplished.

2015 - Mission Assignment for Multi-Vehicle Systems in Industrial Environments [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Digani, Valerio; Lucchi, Matteo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we introduce a methodology for mission assignment in multiple vehicle system exploited in industrial environments for logistics operations. We explicitly consider the model of the traffic, for performing an optimized dynamic mission assignment. Simulation results are provided for comparing the proposed methodology with state-of-the-art techniques, that do not consider the state of the traffic while allocating missions.

2015 - Port-Hamiltonian based teleoperation of a multi-robot system on periodic trajectories [Relazione in Atti di Convegno]
Secchi, Cristian; Sabattini, Lorenzo; Fantuzzi, Cesare
abstract

In this paper, we exploit port-Hamiltonian systems for building a novel teleoperation architecture for a group of mobile agents that need to track a set of prede_ned trajectories. Using port-Hamiltonian system we can guarantee an intrinsically safe and passive bilateral teleoperation system while using linear regulation system we can ensure an asymptotic tracking. The performance of the teleoperation system are evaluated by means of experiments.

2014 - An automatic approach for the generation of the roadmap for multi-AGV systems in an industrial environment [Relazione in Atti di Convegno]
Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper deals with the automatic generation of a roadmap. We propose an approach to build a roadmap for Automated Guided Vehicles (AGVs) used for logistics operations in industrial environments. The algorithm computes a roadmap in such a way that the coverage, the connectivity and the redundancy of the paths are maximized. In this way the flexibility and the efficiency of the AGV system can be increased. The proposed approach is validated by means of comparison with different roadmaps manually built in real plants

2014 - Collective control objective and connectivity preservation for multi-robot systems with bounded input [Relazione in Atti di Convegno]
Gasparri, Andrea; Leccese, Antonio; Sabattini, Lorenzo; Ulivi, Giovanni
abstract

In this work, we address the connectivity main- tenance problem for a team of mobile robots which move according to a given collective control objective. In our frame- work, the interaction among the robots is limited by a given visibility radius both in terms of sensing and communication. For this scenario, we propose a bounded control law which can provably preserve the connectivity of the multi-robot system over time even in the presence of any desired bounded control objective. Furthermore, we characterize the effects of the connectivity control term on the collective control objective, in terms of robustness of the desired control objective to the disturbance of the connectivity, by resorting to the set Input- to-State Stability framework (set-ISS). For the validation of the proposed bounded connectivity control law we consider the encirclement problem as an example of collective control ob- jective. Simulations are provided to corroborate the theoretical results.

2014 - Controllability and Observability Preservation for Networked Systems with Time Varying Topologies [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Fantuzzi, Cesare; Secchi, Cristian
abstract

When dealing with networked systems, the concept of controllability refers to the possibility of controlling the overall state of a group of agents by providing an external input only to a subset of them, that are referred to as leaders. On the same lines, the concept of observability is related to the possibility of observing the whole state of the networked system from only a subset of the agents. In this paper we introduce a decentralized interaction rule that ensures preservation of the controllability and observability properties of a networked system. The proposed strategy is based on the fact that these properties are strongly related to the topology of the underlying communication graph. We will show that connectivity maintenance and a random choice of the edge-weights are key concepts to ensure controllability and observability preservation for a networked system

2014 - Cooperative dynamic behaviors in networked systems with decentralized state estimation [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

Networked systems and decentralized control strategies have been widely investigated in the literature, with the objective of obtaining coordinated emerging behaviors by means of local interaction. While typical approaches aim at solving regulation problems (e.g. synchronization, swarming, coverage, formation control) a few works have recently appeared that move towards the solution of more complex problems, such as tracking of arbitrary setpoint functions. Based on the formulation introduced in [1], this objective is obtained in this paper partitioning the networked systems into leaders (that can provide control inputs) and followers (that are controlled through local interaction). In this paper we provide a methodology for letting the leaders estimate the state of the followers in a decentralized manner: this estimate is then used for control purposes. Simulations are provided for validating the proposed control strategy

2014 - Hierarchical traffic control for partially decentralized coordination of multi AGV systems in industrial environments [Relazione in Atti di Convegno]
Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper deals with decentralized coordination of Automated Guided Vehicles (AGVs). We propose a hierarchical traffic control algorithm, that implements path planning on a two layer architecture. The high-level layer describes the topological relationships among different areas of the environment. In the low-level layer, each area includes a set of fixed routes, along which the AGVs have to move. An algorithm is also introduced for the automatic definition of the route map itself. The coordination among the AGVs is obtained exploiting shared resources (i.e. centralized information) and local negotiation (i.e. decentralized coordination). The proposed strategy is validated by means of simulations using real plant

2014 - Implementation of arbitrary periodic dynamic behaviors in networked systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Cocetti, Matteo; Fantuzzi, Cesare
abstract

Decentralized control of networked systems has been widely investigated in the literature, with the aim of regulating the overall state of the system to some desired configuration, thus obtaining coordinated emerging behaviors (e.g. synchronization, swarming, coverage, formation control) by means of local interaction. In this paper we introduce a methodology to solve a tracking problem, that is defining a decentralized control strategy for making a networked system follow an arbitrarily defined periodic setpoint function. The most suitable interconnection topology is defined together with the control law as the solution of a constrained optimization problem, in order to ensure asymptotic tracking. Simulations are provided for validating the proposed control strategy

2014 - Industrial AGVs: Toward a pervasive diffusion in modern factory warehouses [Relazione in Atti di Convegno]
Oleari, Fabio; Magnani, Massimiliano; Ronzoni, Davide; Sabattini, Lorenzo
abstract

This paper describes the technology behind the automation of modern factory warehouses with multiple Au- tomated Guided Vehicles (AGVs). In particular, we focus on intermediate results of Plug-and-Navigate Robots (PAN-Robots) project describing how the latest developed technologies have dealt with main issues about traffic, safety and performance of an automated warehouse. A survey about the market impact produced by first outcomes is then drafted and a roadmap to a pervasive diffusion of AGVs is finally presented.

2014 - Multisensor data fusion for obstacle detection in automated factory logistics [Relazione in Atti di Convegno]
Cardarelli, Elena; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper describes data fusion methodologies for obstacle detection in an automation system based on advanced Automatic Guided Vehicles (AGV), used for automated logistics in modern factories. We present the background of the problem, introducing generic aspects of the system architecture designed to cope with the obstacle detection in automated factory logistics; then, we focus on the system specification for the module responsible of integrating data from different sources and providing a global representation of the environment. Finally, we present a comparative analysis among different strategies of multisensor data fusion compliant with the requirements of the described system, highlighting their advantages and drawbacks

2014 - Obstacle avoidance for industrial AGVs [Relazione in Atti di Convegno]
Digani, Valerio; Caramaschi, Fabrizio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

IEEE International Conference

2013 - Closed-Curve Trajectory Tracking for Decentralized Systems of Multiple Mobile Robots [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we address the problem of making a group of mobile robots cooperatively track an assigned path. We consider paths described by com- pletely arbitrarily shaped closed curves. The proposed control strategy is a fully decentralized algorithm and it does not require any global synchronization. The desired behavior is obtained by means of some properly designed artificial poten- tial functions. Analytical proofs are provided to show the asymptotic convergence of the system to the desired behavior. Matlab simulations and experiments on real robots are described as well for validation purposes.

2013 - Collision Avoidance Using Gyroscopic Forces for Cooperative Lagrangian Dynamical Systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we introduce a collision avoidance control strategy for groups of mobile robots moving in a three-dimensional environment, whose dynamics are described according to the Lagrangian model. The proposed strategy is based on the use of gyroscopic forces, that ensure obstacle avoidance without interfering with the convergence properties of the multi-robot system's desired control law. Moreover, we introduce a method to define the direction of the force in an optimal way, in order to introduce the smallest possible perturbation with respect to the desired behavior of the system. Collision avoidance and convergence properties are analytically demonstrated, and simulation results are provided for validation purpose.

2013 - Decentralized Control Strategy for the Implementation of Cooperative Dynamic Behaviors in Networked Systems [Relazione in Atti di Convegno]
M., Cocetti; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

Decentralized control of networked systems has been widely investigated in the literature, with the aim of obtaining coordinated emerging behaviors (e.g. synchronization, swarming, coverage, formation control) by means of local interaction. In this paper we consider the possibility of injecting external inputs into the networked system, in order to obtain more complex cooperative behaviors. Specifically, we introduce a strategy that makes it possible to control the overall state of the networked system by directly controlling only a subset of the networked agents, namely the leaders. Exploiting local interaction rules, it is possible to define the inputs for the leaders in such a way that each follower is forced to track a desired periodic setpoint.

2013 - Decentralized Control for Maintenance of Strong Connectivity for Directed Graphs [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; N., Chopra
abstract

In order to accomplish cooperative tasks, decentralized systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally considering undirected communication graphs. In this paper we introduce a decentralized control and estimation strategy to maintain the strong connectivity property of directed communication graphs. The control strategy is initially developed for balanced digraphs, and is then extended to generic strongly connected digraphs, introducing a decentralized balancing algorithm. The control strategy is validated by means of analytical proofs and simulation results.

2013 - Decentralized Global Connectivity Maintenance for Interconnected Lagrangian Systems in the Presence of Data Corruption [Articolo su rivista]
Secchi, Cristian; Sabattini, Lorenzo; Fantuzzi, Cesare
abstract

In order to accomplish cooperative tasks, multi-robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. In this paper we develop a strategy based on Sabattini et al., Decentralized Connectivity Maintenance for Networked Lagrangian Dynamical Systems, 2012 for guaranteeing connectivity in the presence of data corruption. In fact, when dealing with real systems, several sources of data corruption can appear. For instance, sensor noise is one of the primary sources of data corruption. Moreover, when dealing with interconnected robotic systems, assuming instantaneous exchange of data is often unrealistic: com- munication delays are then another important source of data corruption. For this reason, we provide a solution to the connectivity maintenance problem for interconnected Lagrangian dynamical agents, in the presence of data corruption.

2013 - Decentralized connectivity maintenance for cooperative control of mobile robotic systems [Articolo su rivista]
Sabattini, Lorenzo; Chopra, N.; Secchi, Cristian
abstract

To accomplish cooperative tasks, robotic systems are often required to communicate with each other. Thus, maintaining connectivity of the communication graph is a fundamental issue in the field of multi– robot systems. In this paper we present a completely decentralized control strategy for global connectivity maintenance of the commu- nication graph. We describe a gradient–based control strategy that exploits decentralized estimation of the algebraic connectivity. Unlike previous approaches available in the literature, the proposed control algorithm solves the global connectivity problem in a decentralized manner providing theoretical guarantees, without requiring mainte- nance of the local connectivity between robotic systems. Moreover, results obtained with simulations and experiments on real robots are described for demonstrating the efficacy of the proposed algorithm.

2013 - Distributed Control of Multirobot Systems With Global Connectivity Maintenance [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Chopra, N.; Gasparri, A.
abstract

This work introduces a control algorithm that, exploiting a completely decentralized estimation strategy for the algebraic connectiv- ity of the graph, ensures the connectivity maintenance property for multi– robot systems, in the presence of a generic (bounded) additional control term. This result is obtained driving the robots along the negative gradient of an appropriately defined function of the algebraic connectivity. The proposed strategy is then enhanced, with the introduction of the concept of critical robots, that is robots for which the loss of a single communi- cation link might cause the disconnection of the communication graph. Limiting the control action to critical robots will be shown to reduce the control effort introduced by the proposed connectivity maintenance control law and to mitigate its effect on the additional (desired) control term.

2013 - Technological Roadmap to Boost the Introduction of AGVs in Industrial Applications  [Relazione in Atti di Convegno]
Sabattini, Lorenzo; V., Digani; Secchi, Cristian; Cotena, Giuseppina; D., Ronzoni; M., Foppoli; F., Oleari
abstract

This paper describes systems of multiple Automated Guided Vehicles (AGVs) used in factory logistics for the transportation of goods. We describe currently applied solutions, highlighting the main issues that, so far, have prevented a pervasive diffusion of these systems. A roadmap of technological solutions is then drafted, to improve the performance of AGV systems and boost their wide application in factory logistics.

2013 - Towards decentralized coordination of multi robot systems in industrial environments: A hierarchical traffic control strategy [Relazione in Atti di Convegno]
Digani, Valerio; Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

This paper describes an innovative approach to manage multiple Automated Guided Vehicles (AGVs) in an industrial environment. The proposed approach is based on a two layer architecture for path planning. This architecture consists of a topological layer, composed by macro-cells, and of a route map layer in which the AGVs have to move along fixed paths. The traffic is managed in a decentralized manner. Each AGV computes autonomously its own path both at topological layer and at route map layer. The coordination among the AGVs is based on the negotiation of shared resources. An early phase of validation is provided by the simulation in a structured environment.

2012 - Decentralized Connectivity Maintenance for Networked Lagrangian Dynamical Systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; N., Chopra
abstract

In order to accomplish cooperative tasks, multi– robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally con- sidering only kinematic agents. In this paper we will introduce a control strategy that, exploiting a decentralized procedure for the estimation of the algebraic connectivity of the graph, ensures the connectivity maintenance for groups of Lagrangian systems. The control strategy is validated by means of analytical proofs and simulation results.

2012 - Decentralized Global Connectivity Maintenance for Interconnected Lagrangian Systems with Communication Delays [Relazione in Atti di Convegno]
Secchi, Cristian; Sabattini, Lorenzo; Fantuzzi, Cesare
abstract

n order to accomplish cooperative tasks, multi robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. In this paper we extend the connectivity maintenance control strategy introduced in (Sabattini et al., 2012), in order to explicitly take into account the presence of communication delays. When dealing with interconnected robotic systems, in fact, assuming instantaneous exchange of data is often unrealistic. For this reason, we provide a solution to the connectivity maintenance problem for interconnected Lagrangian dynamical agents, in the presence of communication delays.

2012 - Enhanced Connectivity Maintenance for Multi-Robot Systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; A., Gasparri; Secchi, Cristian; N., Chopra
abstract

In this work, the decentralized control law proposed in [Sabattini et al., 2011b] for multi-robot connectivity maintenance is enhanced by means of a selective action. The idea is to identify critical agents, i.e. agents for which a disconnection might cause the split of the communication graph, and limit the control action to those agents. The objective is twofold: to reduce the control effort introduced by the connectivity maintenance control action as well as to avoid unnecessary action of the connectivity maintenance controller, thus reducing its effect on the overall performances of the system. A theoretical analysis of the proposed control law is discussed. Simulations along with experimental results are given to corroborate the theoretical results.

2012 - Experimental comparison of 3D vision sensors for mobile robot localization for industrial application: stereo–camera and RGB–D sensor [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Levratti, Alessio; F., Venturi; E., Amplo; Fantuzzi, Cesare; Secchi, Cristian
abstract

While RGB–D sensors are becoming more and more popular in mobile robotics laboratories, they are usually not yet adopted for industrial applications. In fact, in this field, depth measurements are generally acquired by means of laser scanners and, when visual information is needed, by means of stereo– cameras. The aim of this paper is to perform an experimental validation, to compare the performance of a stereo–camera and an RGB–D sensor, in a specific application: mobile robot localization for industrial applications. Experiments are performed exploiting artificial landmarks (defined by a self–similar pattern), placed in known positions in the environment.

2011 - A Graph-Based Collision- Free Distributed Formation Control Strategy [Relazione in Atti di Convegno]
R., Falconi; Sabattini, Lorenzo; Secchi, Cristian; C., Melchiorri; Fantuzzi, Cesare
abstract

n this paper we describe a consensus based control strategy to obtain a formation of groups of mobile robots. Weighted graphs are used to obtain the desired formation-shape while avoiding collisions among the robots. Since mobile robots usually move in unknown and unstructured environments, we show how to extend our control strategy to make the robots avoid collision with obstacles as well. To validate our control strategy, we provide both analytical proofs and simulative and experimental results.

2011 - Arbitrary shaped formations of mobile robots: Artificial Potential fields and coordinate transformation [Articolo su rivista]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we describe a novel decentralized control strategy to realize formations of mobile robots. We first describe how to design artificial potential fields to ob- tain a formation with the shape of a regular polygon. We provide a formal proof of the asymptotic stability of the sys- tem, based on the definition of a proper Lyapunov function. We also prove that our control strategy is not affected by the problem of local minima. Then, we exploit a bijective coordinate transformation to deform the polygonal forma- tion, thus obtaining a completely arbitrarily shaped forma- tion. Simulations and experimental tests are provided to val- idate the control strategy.

2011 - Distributed Control of Multi-Robot Systems with Global Connectivity Maintenance [Relazione in Atti di Convegno]
Sabattini, Lorenzo; N., Chopra; Secchi, Cristian
abstract

In this paper we present a decentralized control strategy for the connectivity maintenance for groups of mobile robots performing some desired task. Exploiting a completely decentralized estimation strategy for the algebraic connectivity of the graph, we prove the connectivity maintenance property in the general case, i.e. in presence of a generic (bounded) additional control term. Then, we address two specific decentralized control applications: rendezvous and formation control. We analytically prove that our control strategy ensures the global connectivity maintenance, while preserving the convergence properties of the rendezvous and formation controllers respectively. Simulations and experimental results are presented as well, in order to show the effectiveness of the proposed control law.

2011 - On Decentralized Connectivity Maintenance for Mobile Robotic System [Relazione in Atti di Convegno]
Sabattini, Lorenzo; N., Chopra; Secchi, Cristian
abstract

To accomplish cooperative tasks, robotic systems are often required to communicate with each other. Thus, maintaining connectivity of the interagent communication graph is a fundamental issue in the field of multi-robot systems. In this paper we present a completely decentralized control strategy for global connectivity maintenance of the interagent communication graph. We describe a gradient-based control strategy that exploits decentralized estimation of the algebraic connectivity. The proposed control algorithm guarantees the global connectivity of the communication graph without requiring maintenance of the local connectivity between the robotic systems. The control strategy is validated by means of an analytical proof and simulative results.

2010 - Bird's - Eye View Image for the Localization of a Mobile Robot by Means of Trilateration [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare; A., Stefani
abstract

In this paper we introduce a method for the localization of a low–cost mobile robot,based on the use of a monocular camera. We consider a robot moving in a bi–dimensionalenvironment, where some landmarks are placed in known positions. The acquired image of theenvironment is converted into a bird’s–eye view image, used to measure the distance of the robotfrom the landmarks, to compute the robot’s position by means of trilateration. The proposedstrategy is able to compute both the position and the orientation of the robot.

2010 - Tracking of Closed-Curve Trajectories for Multi-Robot Systems [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare; D., de Macedo Possamai
abstract

In this paper we address the trajectory tracking problem for groups of mobile robots. We consider trajecto- ries described by completely arbitrary shaped closed curves. The proposed control strategy is a completely decentralized algorithm, and does not require any global synchronization. The desired behavior is obtained by means of some properly designed artificial potential functions.

2009 - Potential Based Control Strategy for Arbitrary Shape Formations of Mobile Robots [Relazione in Atti di Convegno]
Sabattini, Lorenzo; Secchi, Cristian; Fantuzzi, Cesare
abstract

In this paper we describe a novel decentralized control strategy to realize formations of mobile robots. We first describe a methodology to obtain a formation with the shape of a regular polygon. Then, applying a bijective coordinates transformation, we show how to obtain a formation with an arbitrary shape. Our control strategy is based on the interaction of some artificial potential fields, but it is not affected by the problem of local minima.

Università degli studi di Modena e Reggio Emilia

Pubblicazioni