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See detailA Review of Radio Frequency Based Localisation for Aerial and Ground Robots with 5G Future Perspectives
Kabiri, Meisam UL; Cimarelli, Claudio UL; Bavle, Hriday UL et al

in Sensors (2022), 23(1), 188

Efficient localisation plays a vital role in many modern applications of Unmanned Ground Vehicles (UGV) and Unmanned Aerial Vehicles (UAVs), which contributes to improved control, safety, power economy ... [more ▼]

Efficient localisation plays a vital role in many modern applications of Unmanned Ground Vehicles (UGV) and Unmanned Aerial Vehicles (UAVs), which contributes to improved control, safety, power economy, etc. The ubiquitous 5G NR (New Radio) cellular network will provide new opportunities to enhance the localisation of UAVs and UGVs. In this paper, we review radio frequency (RF)-based approaches to localisation. We review the RF features that can be utilized for localisation and investigate the current methods suitable for Unmanned Vehicles under two general categories: range-based and fingerprinting. The existing state-of-the-art literature on RF-based localisation for both UAVs and UGVs is examined, and the envisioned 5G NR for localisation enhancement, and the future research direction are explored. [less ▲]

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See detailVisual SLAM: What Are the Current Trends and What to Expect?
Tourani, Ali UL; Bavle, Hriday UL; Sanchez Lopez, Jose Luis UL et al

in Sensors (2022), 22(23), 9297

In recent years, Simultaneous Localization and Mapping (SLAM) systems have shown significant performance, accuracy, and efficiency gain. In this regard, Visual Simultaneous Localization and Mapping (VSLAM ... [more ▼]

In recent years, Simultaneous Localization and Mapping (SLAM) systems have shown significant performance, accuracy, and efficiency gain. In this regard, Visual Simultaneous Localization and Mapping (VSLAM) methods refer to the SLAM approaches that employ cameras for pose estimation and map reconstruction and are preferred over Light Detection And Ranging (LiDAR)-based methods due to their lighter weight, lower acquisition costs, and richer environment representation. Hence, several VSLAM approaches have evolved using different camera types (e.g., monocular or stereo), and have been tested on various datasets (e.g., Technische Universität München (TUM) RGB-D or European Robotics Challenge (EuRoC)) and in different conditions (i.e., indoors and outdoors), and employ multiple methodologies to have a better understanding of their surroundings. The mentioned variations have made this topic popular for researchers and have resulted in various methods. In this regard, the primary intent of this paper is to assimilate the wide range of works in VSLAM and present their recent advances, along with discussing the existing challenges and trends. This survey is worthwhile to give a big picture of the current focuses in robotics and VSLAM fields based on the concentrated resolutions and objectives of the state-of-the-art. This paper provides an in-depth literature survey of fifty impactful articles published in the VSLAMs domain. The mentioned manuscripts have been classified by different characteristics, including the novelty domain, objectives, employed algorithms, and semantic level. The paper also discusses the current trends and contemporary directions of VSLAM techniques that may help researchers investigate them. [less ▲]

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See detailUnclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors
Agha, Hakam UL; Geng, Yong UL; Ma, Xu UL et al

in Light: Science and Applications (2022), 11(309), 10103841377-022-01002-4

The seemingly simple step of molding a cholesteric liquid crystal into spherical shape, yielding a Cholesteric Spherical Reflector (CSR), has profound optical consequences that open a range of ... [more ▼]

The seemingly simple step of molding a cholesteric liquid crystal into spherical shape, yielding a Cholesteric Spherical Reflector (CSR), has profound optical consequences that open a range of opportunities for potentially transformative technologies. The chiral Bragg diffraction resulting from the helical self-assembly of cholesterics becomes omnidirectional in CSRs. This turns them into selective retroreflectors that are exceptionally easy to distinguish— regardless of background—by simple and low-cost machine vision, while at the same time they can be made largely imperceptible to human vision. This allows them to be distributed in human-populated environments, laid out in the form of QR-code-like markers that help robots and Augmented Reality (AR) devices to operate reliably, and to identify items in their surroundings. At the scale of individual CSRs, unpredictable features within each marker turn them into Physical Unclonable Functions (PUFs), of great value for secure authentication. Via the machines reading them, CSR markers can thus act as trustworthy yet unobtrusive links between the physical world (buildings, vehicles, packaging,...) and its digital twin computer representation. This opens opportunities to address pressing challenges in logistics and supply chain management, recycling and the circular economy, sustainable construction of the built environment, and many other fields of individual, societal and commercial importance. [less ▲]

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See detailA Lightweight Universal Gripper with Low Activation Force for Aerial Grasping
Kremer, Paul UL; Rahimi Nohooji, Hamed UL; Sanchez Lopez, Jose Luis UL et al

E-print/Working paper (2022)

Soft robotic grippers have numerous advantages that address challenges in dynamic aerial grasping. Typical multi-fingered soft grippers recently showcased for aerial grasping are highly dependent on the ... [more ▼]

Soft robotic grippers have numerous advantages that address challenges in dynamic aerial grasping. Typical multi-fingered soft grippers recently showcased for aerial grasping are highly dependent on the direction of the target object for successful grasping. This study pushes the boundaries of dynamic aerial grasping by developing an omnidirectional system for autonomous aerial manipulation. In particular, the paper investigates the design, fabrication, and experimental verification of a novel, highly integrated, modular, sensor-rich, universal jamming gripper specifically designed for aerial applications. Leveraging recent developments in particle jamming and soft granular materials, the presented gripper produces a substantial holding force while being very lightweight, energy-efficient and only requiring a low activation force. We show that the holding force can be improved by up to 50% by adding an additive to the membrane’s silicone mixture. The experiments show that our lightweight gripper can develop up to 15N of holding force with an activation force as low as 2.5N, even without geometric interlocking. Finally, a pick and release task is performed under real-world conditions by mounting the gripper onto a multi-copter. The developed aerial grasping system features many useful properties, such as resilience and robustness to collisions and the inherent passive compliance which decouples the UAV from the environment. [less ▲]

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See detailGNC of a cargo spacecraft for on-orbit servicing of Herschel at L2
Siena, Andrea; Mahfouz, Ahmed UL; Menzio, Davide et al

in IAC 2022 congress proceedings, 73rd International Astronautical Congress (IAC) (2022, September)

t is anticipated that space exploration will need to rely on In Situ Resource Utilization (ISRU) in order toextend spacecraft lifetime and/or reduce the missions cost and/or the cruise time. For the Moon ... [more ▼]

t is anticipated that space exploration will need to rely on In Situ Resource Utilization (ISRU) in order toextend spacecraft lifetime and/or reduce the missions cost and/or the cruise time. For the Moon and, inthe future, Mars colonization, relying on in-situ resources is a necessary step to become independent fromthe Earth. The possibility to produce resources on the Moon is advantageous for those missions that aretoo far from the Earth to be resupplied. At the SnT Research Centre, the Luxembourg Space Agency issupporting a feasibility study to assess the benefit of on-orbit servicing (OOS), exploiting lunar resourcesfor the Herschel Space Observatory. Herschel ended its operations in 2013 as a consequence of the depletionof its coolant and, in turn, of the capability of cooling down its instruments. To extend its operations,a resupply mission has been envisaged relying on an adapted cargo spacecraft employed in lunar gatewayoperations. This paper deals with the trajectory design and optimization of the cargo on its journey from theMoon to rendezvous with Herschel and with orbit and attitude control. Considering Herschel’s orientationon its orbit, with the sunshield in the direction of the Sun and the need to access to Herschel’s rear panelto perform the resupply operation, a final approach along the negative x-axis, where the primaries lie, isconsidered. A multiple shooting technique is used to perform a flanking manoeuvre. Moreover, an attitudecontrol algorithm is adopted to track the attitude trajectory provided by the guidance algorithms which, inturn, ensure minimum thrusting errors of the cargo spacecraft and a continuous visibility of Herschel. Infuture works, different perturbations will be considered and angular rates induced by the movement of therobotic arms will be compensated [less ▲]

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See detailA Hybrid Modelling Approach For Aerial Manipulators
Kremer, Paul UL; Sanchez Lopez, Jose Luis UL; Voos, Holger UL

in Journal of Intelligent and Robotic Systems (2022)

Aerial manipulators (AM) exhibit particularly challenging, non-linear dynamics; the UAV and its manipulator form a tightly coupled dynamic system, mutually impacting each other. The mathematical model ... [more ▼]

Aerial manipulators (AM) exhibit particularly challenging, non-linear dynamics; the UAV and its manipulator form a tightly coupled dynamic system, mutually impacting each other. The mathematical model describing these dynamics forms the core of many solutions in non-linear control and deep reinforcement learning. Traditionally, the formulation of the dynamics involves Euler angle parametrization in the Lagrangian framework or quaternion parametrization in the Newton-Euler framework. The former has the disadvantage of giving birth to singularities and the latter being algorithmically complex. This work presents a hybrid solution, combining the benefits of both, namely a quaternion approach leveraging the Lagrangian framework, connecting the singularity-free parameterization with the algorithmic simplicity of the Lagrangian approach. We do so by offering detailed insights into the kinematic modeling process and the formulation of the dynamics of a general aerial manipulator. The obtained dynamics model is validated experimentally against a real-time physics engine. A practical application of the obtained dynamics model is shown in the context of a computed torque feedback controller (feedback linearization), where we analyze its real-time capability with increasingly complex AM models. [less ▲]

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See detailRelative State Estimation for LEO Formations with Large Inter-satellite Distances Using Single-Frequency GNSS Receivers
Mahfouz, Ahmed UL; Menzio, Davide; Dalla Vedova, Florio et al

Scientific Conference (2022, June)

Relative baseline estimation is an integral part of satellite formation flying missions. GNSS-based relativepositioning has been a dominating technology for formation missions in LEO, where very precise ... [more ▼]

Relative baseline estimation is an integral part of satellite formation flying missions. GNSS-based relativepositioning has been a dominating technology for formation missions in LEO, where very precise estimatescould be obtained for formations with small inter-satellite distances (1 − 10 km). Larger baselines betweenthe satellites (> 10 km) pose the problem of considerable differences in the ionospheric delays experiencedby the signals received by each receiver. This problem could be mitigated by using precise ionospheric-freecombinations that could only be obtained by dual-frequency receivers, which is not a cost-efficient optionfor modern low-cost miniature missions. In this paper, the problem of relative baseline vector estimation isaddressed for formation missions with large inter-satellite distances equipped with single-frequency receivers.The problem is approached using the space-proven relatively simple Extended Kalman Filter with anadvantageous setting for the observation vector [less ▲]

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See detailFrom SLAM to Situational Awareness: Challenges and Survey
Bavle, Hriday UL; Sanchez Lopez, Jose Luis UL; Schmidt F, Eduardo et al

E-print/Working paper (2021)

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See detailAtmospheric Re-entry Energy Storage (ARES)- A Novel concept for utilizing atmospheric re-entry energy
Pandi Perumal, Raja UL; Abbud-Madrid, Angel; Voos, Holger UL

in Proceedings of the Conference GLEX 2021 (2021, June 18)

As the aspirational goal of Mars settlement starts to slowly materialize, it is apparent that its viability hinges on the utilization of its energy and material resources. Although Mars has a thinner ... [more ▼]

As the aspirational goal of Mars settlement starts to slowly materialize, it is apparent that its viability hinges on the utilization of its energy and material resources. Although Mars has a thinner atmosphere than Earth, it still exerts large amounts of heat on entry vehicles, generating temperatures around ~1500 deg C. Therefore, the entry vehicle is covered with a thick layer of ablative heat shield to protect the inside from reaching undesired temperatures. However, the temperature on the Martian surface is significantly cold. It varies between -140 deg C and 30 deg C. One of the critical challenges in developing a settlement and operating equipment on Mars is to find adequate heat sources on its surface. The envisioned heat sources are solar energy, geothermal energy, greenhouse gases and Radioisotope Thermoelectric Generators (RTG). Although solar and possibly geothermal energy are the preferred sources for their unlimited supply, they are localized and require an elaborate infrastructure. Trapping greenhouse gases also requires extensive infrastructure. RTGs require a large amount of radioactive fuel and both the equipment and fuel have to be transported from Earth. Due to its hazardous nature, disposal/reprocessing of the fuel will be challenging. Interestingly, little to no effort has been spent to study the possibility of utilizing the large heat generated during vehicle entry. This paper proposes a novel concept to collect, store and utilize the atmospheric entry heat energy using Phase Change Materials (PCMs) obtained from the Martian moons. Mars settlement architectures suggest that Phobos and Deimos can be used to set up preliminary base camps. These moons are potentially trapped C-type asteroids and have the possibility to contain rich Lithium reserves. Lithium and its alloys have a relatively high latent heat of fusion and low density, making them an ideal PCM for this application. This concept takes advantage of the undesired heat generated during atmospheric entry to melt the PCMs. A storage system would store and insulate the melted PCM as it solidifies and heat energy is released. The utilized PCM could then be reused and consumed for a variety of purposes. With current technology limitations, the heat storage system could only store the heat energy obtained using PCMs for a few hours. While the results from ongoing research could considerably increase its efficiency, PCMs could be used as a temporary energy source in landing sites where no other energy generation infrastructure is available. Alternatively, the heat generated from PCMs could be converted to electricity using thermoelectric generators. [less ▲]

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See detailMetaheuristics for the Online Printing Shop Scheduling Problem
Tessaro Lunardi, Willian UL; Birgin, Ernesto G.; Ronconi, Débora P. et al

in European Journal of Operational Research (2020)

In this work, the online printing shop scheduling problem introduced in (Lunardi et al., Mixed Integer Linear Programming and Constraint Programming Models for the Online Printing Shop Scheduling Problem ... [more ▼]

In this work, the online printing shop scheduling problem introduced in (Lunardi et al., Mixed Integer Linear Programming and Constraint Programming Models for the Online Printing Shop Scheduling Problem, Computers & Operations Research, to appear) is considered. This challenging real scheduling problem, that emerged in the nowadays printing industry, corresponds to a flexible job shop scheduling problem with sequencing flexibility; and it presents several complicating specificities such as resumable operations, periods of unavailability of the machines, sequence-dependent setup times, partial overlapping between operations with precedence constraints, and fixed operations, among others. A local search strategy and metaheuristic approaches for the problem are proposed and evaluated. Based on a common representation scheme, trajectory and populational metaheuristics are considered. Extensive numerical experiments with large-sized instances show that the proposed methods are suitable for solving practical instances of the problem; and that they outperform a half-heuristic-half-exact off-the-shelf solver by a large extent. Numerical experiments with classical instances of the flexible job shop scheduling problem show that the introduced methods are also competitive when applied to this particular case. [less ▲]

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See detailMetaheuristics for the Online Printing Shop Scheduling Problem - Supplementary Material
Tessaro Lunardi, Willian UL; Birgin, Ernesto G.; Ronconi, Débora P. et al

Report (2020)

This document presents further numerical results of the experiments concerning the classical instances of the flexible job shop scheduling problem, performed in (Lunardi et al., Metaheuristics for the ... [more ▼]

This document presents further numerical results of the experiments concerning the classical instances of the flexible job shop scheduling problem, performed in (Lunardi et al., Metaheuristics for the Online Printing Shop Scheduling Problem, submitted). Additionally, this document gathers the best makespan values (upper bounds and lower bounds) found by state-of-the-art algorithms. [less ▲]

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See detailLarge scale realistic virtual environments for lunar robotics testing using real-time computer games engines
Ludivig, Philippe UL; Voos, Holger UL; Lamamy, Julien

Poster (2020, October 23)

Virtual simulation environments are a great tool for testing different rover systems before they are sent to the moon. They allow for perfect repeatability and give abetter idea how specific parameters ... [more ▼]

Virtual simulation environments are a great tool for testing different rover systems before they are sent to the moon. They allow for perfect repeatability and give abetter idea how specific parameters can impact the overall system. Most current simulators however suffer from low visual fidelity which is problematic for testing the vision sensors needed for autonomous navigation.Additionally, due to technical and practical limitations, most simulations are limited in environment scale. This is problematic for long range navigation testing needed for missions such as the mars sample fetch rover[1]. In order to solve both issues, we turn towards a popular computer game engine,Unreal Engine 4. It allows for larger environments than what is currently possible in robotics simulators such as Gazebo[2]or V-rep[3]. It also addresses the visual fidelity with a range of tools including real-time ray-tracing.The tradeoff is a low physics fidelity, which can be an issue when testing wheel-soil interaction. For our use-case we focus primarily on perception systems needed for rover navigation, such as mono and stereo camera systems, where visual fidelity is more important. [less ▲]

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See detailTESTING ENVIRONMENTS FOR LUNAR SURFACE PERCEPTION SYSTEMS; COMBINING INDOOR FACILITIES, VIRTUAL ENVIRONMENTS AND ANALOGUE FIELD TESTS.
Ludivig, Philippe UL; Olivares Mendez, Miguel Angel UL; Calzada Diaz, Abigail et al

Scientific Conference (2020, October 21)

This paper describes the different approaches which can be used to test vision systems for operations on robotic lunar surface missions. We investigate validating systems in virtual environments, lab ... [more ▼]

This paper describes the different approaches which can be used to test vision systems for operations on robotic lunar surface missions. We investigate validating systems in virtual environments, lab environments and analogue outdoor environments and demonstrate that a combination of all three approach-es is needed to sufficiently test systems for the lunar surface. [less ▲]

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See detailBUILDING A PIECE OF THE MOON: CONSTRUCTION OF TWO INDOOR LUNAR ANALOGUE ENVIRONMENTS
Ludivig, Philippe UL; Calzada-Diaz, Abigail; Olivares Mendez, Miguel Angel UL et al

in Proceedings of the 71st International Astronautical Congress 2020 (2020, October 12)

Developing and testing autonomous systems to ensure that they work reliably on the moon is a difficult task, as testing on location is not an option. Instead, engineers rely on simulations, testing ... [more ▼]

Developing and testing autonomous systems to ensure that they work reliably on the moon is a difficult task, as testing on location is not an option. Instead, engineers rely on simulations, testing facilities and outdoor lunar analogues. Due to the lack of lunar analogue testing facilities in Europe, ispace Europe and the University of Luxembourg have teamed up to build two of these facilities with the goal of designing new vision-based navigation systems. These systems will enable autonomous long-range traverses for lunar rovers. These two facilities have a surface area of 64 and 77 square meters, respectively. Regarding the type of testing needed for vision-based systems, the optical fidelity of the environment has been considered as the most important factor. Thus, different types of Basalt have been used for the two facilities to create a larger number of possible landscapes, such as craters, hills, rocky areas and smooth planar surfaces. Regolith simulant was also considered but, due to the health restrictions and the cost factor, basalt was selected instead. As a result, this has allowed for larger testing areas. The illumination setup has been designed to simulate the highland regions of the Moon, with a single light source positioned low above the horizon, casting long shadows over the entire area. To mitigate problems with feature detection algorithms picking up features at the edge of the facility, the walls have been painted black. This also produces high contrast shadows, which is exactly what makes vision-based navigation challenging in the polar regions. The outcome of this research is a set of lessons learned which will enable other researchers to replicate similar facilities and to reproduce the same fidelity in indoor testing for future vision-based navigation systems. [less ▲]

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See detailComparison of Multidisciplinary Design Optimization Architectures for the design of Distributed Space Systems
Pandi Perumal, Raja UL; Voos, Holger UL; Dalla Vedova, Florio et al

in Pandi Perumal, Raja; Voos, Holger; Dalla Vedova, Florio (Eds.) et al Proceedings of the 71st International Astronautical Congress 2020 (2020, October)

Advancement in satellite technology, and the ability to mass-produce cost-effective small satellites has created a compelling interest in Distributed Space System (DSS), such as Low Earth Orbit (LEO ... [more ▼]

Advancement in satellite technology, and the ability to mass-produce cost-effective small satellites has created a compelling interest in Distributed Space System (DSS), such as Low Earth Orbit (LEO) satellite constellations. Optimization of DSS is a complex Multidisciplinary Design Optimization (MDO) problem involving a large number of variables and coupling relations. This paper focuses on comparing three different MDO architectures for a DSS design problem. Initially, an overview of the constellation model, the subsystems model, and the coupling relationships between the subsystems and the constellation are provided. The modelling of the subsystems and the constellation configuration are carried out in OpenMDAO. Later, three monolithic MDO architectures, namely, Individual Discipline Feasible (IDF), Simultaneous Analysis and Design (SAND) and Multidisciplinary Feasible (MDF) are compared by implementing them to the developed DSS model. The results indicate IDF outperforms the rest of the architectures for the conceptual design of DSS. The optimum objective function obtained by IDF is 1% lower than SAND and 7% lower than MDF. While the functional evaluation required for IDF is 50% lower than SAND and 90% lower than MDF. [less ▲]

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See detailSemantic situation awareness of ellipse shapes via deep learning for multirotor aerial robots with a 2D LIDAR
Sanchez Lopez, Jose Luis UL; Castillo Lopez, Manuel UL; Voos, Holger UL

in 2020 International Conference on Unmanned Aircraft Systems (ICUAS) (2020, September)

In this work, we present a semantic situation awareness system for multirotor aerial robots equipped with a 2D LIDAR sensor, focusing on the understanding of the environment, provided to have a drift-free ... [more ▼]

In this work, we present a semantic situation awareness system for multirotor aerial robots equipped with a 2D LIDAR sensor, focusing on the understanding of the environment, provided to have a drift-free precise localization of the robot (e.g. given by GNSS/INS or motion capture system). Our algorithm generates in real-time a semantic map of the objects of the environment as a list of ellipses represented by their radii, and their pose and velocity, both in world coordinates. Two different Convolutional Neural Network (CNN) architectures are proposed and trained using an artificially generated dataset and a custom loss function, to detect ellipses in a segmented (i.e. with one single object) LIDAR measurement. In cascade, a specifically designed indirect-EKF estimates the ellipses based semantic map in world coordinates, as well as their velocity. We have quantitative and qualitatively evaluated the performance of our proposed situation awareness system. Two sets of Software-In-The-Loop simulations using CoppeliaSim with one and multiple static and moving cylindrical objects are used to evaluate the accuracy and performance of our algorithm. In addition, we have demonstrated the robustness of our proposed algorithm when handling real environments thanks to real laboratory experiments with non-cylindrical static (i.e. a barrel) objects and moving persons. [less ▲]

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See detailMixed Integer Linear Programming and Constraint Programming Models for the Online Printing Shop Scheduling Problem
Tessaro Lunardi, Willian UL; Birgin, Ernesto G.; Laborie, Philippe et al

in Computers and Operations Research (2020)

In this work, the online printing shop scheduling problem is considered. This challenging real problem, that appears in the nowadays printing industry, can be seen as a flexible job shop scheduling ... [more ▼]

In this work, the online printing shop scheduling problem is considered. This challenging real problem, that appears in the nowadays printing industry, can be seen as a flexible job shop scheduling problem with sequence flexibility in which precedence constraints among operations of a job are given by an arbitrary directed acyclic graph. In addition, several complicating particularities such as periods of unavailability of the machines, resumable operations, sequence-dependent setup times, partial overlapping among operations with precedence constraints, release times, and fixed operations are also present in the addressed problem. In the present work, mixed integer linear programming and constraint programming models for the minimization of the makespan are presented. Modeling the problem is twofold. On the one hand, the problem is precisely defined. On the other hand, the capabilities and limitations of a commercial software for solving the models are analyzed. Extensive numerical experiments with small- , medium-, and large-sized instances are presented. Numerical experiments show that the commercial solver is able to optimally solve only a fraction of the small-sized instances when considering the mixed integer linear programming model; while all small-sized and a fraction of the medium-sized instances are optimally solved when considering the constraint programming formulation of the problem. Moreover, the commercial solver is able to deliver feasible solutions for the large-sized instances that are of the size of the instances that appear in practice. [less ▲]

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See detailA Survey of Computer Vision Methods for 2D Object Detection from Unmanned Aerial Vehicles
Cazzato, Dario UL; Cimarelli, Claudio UL; Sanchez Lopez, Jose Luis UL et al

in Journal of Imaging (2020), 6(8), 78

The spread of Unmanned Aerial Vehicles (UAVs) in the last decade revolutionized many applications fields. Most investigated research topics focus on increasing autonomy during operational campaigns ... [more ▼]

The spread of Unmanned Aerial Vehicles (UAVs) in the last decade revolutionized many applications fields. Most investigated research topics focus on increasing autonomy during operational campaigns, environmental monitoring, surveillance, maps, and labeling. To achieve such complex goals, a high-level module is exploited to build semantic knowledge leveraging the outputs of the low-level module that takes data acquired from multiple sensors and extracts information concerning what is sensed. All in all, the detection of the objects is undoubtedly the most important low-level task, and the most employed sensors to accomplish it are by far RGB cameras due to costs, dimensions, and the wide literature on RGB-based object detection. This survey presents recent advancements in 2D object detection for the case of UAVs, focusing on the differences, strategies, and trade-offs between the generic problem of object detection, and the adaptation of such solutions for operations of the UAV. Moreover, a new taxonomy that considers different heights intervals and driven by the methodological approaches introduced by the works in the state of the art instead of hardware, physical and/or technological constraints is proposed. [less ▲]

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See detailTrajectory Tracking for Aerial Robots: an Optimization-Based Planning and Control Approach
Sanchez Lopez, Jose Luis UL; Castillo Lopez, Manuel UL; Olivares Mendez, Miguel Angel UL et al

in Journal of Intelligent and Robotic Systems (2020), 100

In this work, we present an optimization-based trajectory tracking solution for multirotor aerial robots given a geometrically feasible path. A trajectory planner generates a minimum-time kinematically ... [more ▼]

In this work, we present an optimization-based trajectory tracking solution for multirotor aerial robots given a geometrically feasible path. A trajectory planner generates a minimum-time kinematically and dynamically feasible trajectory that includes not only standard restrictions such as continuity and limits on the trajectory, constraints in the waypoints, and maximum distance between the planned trajectory and the given path, but also restrictions in the actuators of the aerial robot based on its dynamic model, guaranteeing that the planned trajectory is achievable. Our novel compact multi-phase trajectory definition, as a set of two different kinds of polynomials, provides a higher semantic encoding of the trajectory, which allows calculating an optimal solution but following a predefined simple profile. A Model Predictive Controller ensures that the planned trajectory is tracked by the aerial robot with the smallest deviation. Its novel formulation takes as inputs all the magnitudes of the planned trajectory (i.e. position and heading, velocity, and acceleration) to generate the control commands, demonstrating through in-lab real flights an improvement of the tracking performance when compared with a controller that only uses the planned position and heading. To support our optimization-based solution, we discuss the most commonly used representations of orientations, as well as both the difference as well as the scalar error between two rotations, in both tridimensional and bidimensional spaces $SO(3)$ and $SO(2)$. We demonstrate that quaternions and error-quaternions have some advantages when compared to other formulations. [less ▲]

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