2021

Autonomous Aerial Filming with Distributed Lighting by a Team of Unmanned Aerial Vehicles

Vit Krátký, Alfonso Alcántara, Jesús Capitán, Petr Štěpán, Martin Saska and Aníbal Ollero

RA-L/IROS 2021, Accepted

This paper describes a method for autonomous aerial cinematography with distributed lighting by a team of unmanned aerial vehicles (UAVs). Although camera-carrying multi-rotor helicopters have become commonplace in cinematography, their usage is limited to scenarios with sufficient natural light or of lighting provided by static artificial lights. We propose to use a formation of unmanned aerial vehicles as a tool for filming a target under illumination from various directions, which is one of the fundamental techniques of traditional cinematography. We decompose the multi-UAV trajectory optimization problem to tackle non-linear cinematographic aspects and obstacle avoidance at separate stages, which allows us to re-plan in real time and react to changes in dynamic environments. The performance of our method has been evaluated in realistic simulation scenarios and field experiments, where we show how it increases the quality of the shots and that it is capable of planning safe trajectories even in cluttered environments.

@ARTICLE{kratky_alcantara_ral, author = "V\'{i}t Kr\'{a}tk\'{y} and Alfonso Alc\'{a}ntara and Jes\'{u}s Capit\'{a}n and Petr \v{S}t\v{e}p\'{a}n and Martin Saska and An\'{i}bal Ollero", journal = {IEEE Robotics and Automation Letters}, title = {Autonomous Aerial Filming with Distributed Lighting by a Team of Unmanned Aerial Vehicles}, year = {2021}, volume = {}, number = {}, pages = {}, doi = {}, issn = {}, note = {The contents of this paper were also selected by the IROS'21 Program Committee for presentation at the conference.}, }

Safe Local Aerial Manipulation for the Installation of Devices on Power Lines: AERIAL-CORE First Year Results and Designs

J. Cacace, S. M. Orozco-Soto, Al. Suarez, A. Caballero, M. Orsag, S. Bogdan, G. Vasiljevic, E. Ebeid, J. A. Acosta Rodriguez and A. Ollero

Applied Sciences, Published

The power grid is an essential infrastructure in any country, comprising thousands of kilometers of power lines that require periodic inspection and maintenance, carried out nowadays by human operators in risky conditions. To increase safety and reduce time and cost with respect to conventional solutions involving manned helicopters and heavy vehicles, the AERIAL-CORE project proposes the development of aerial robots capable of performing aerial manipulation operations to assist human operators in the power lines inspection and maintenance allowing the installation of devices like bird flight diverters or electrical spacers and fast delivery and retrieval of tools. This manuscript describes the goals and functionalities to be developed for safe local aerial manipulation, presenting preliminary designs and experimental results obtained in the first year of the project.

@Article{CacaceAppliedSciences2021, AUTHOR = {Cacace, Jonathan and Orozco-Soto, Santos M. and Suarez, Alejandro and Caballero, Alvaro and Orsag, Matko and Bogdan, Stjepan and Vasiljevic, Goran and Ebeid, Emad and Rodriguez, Jose Alberto Acosta and Ollero, Anibal}, TITLE = {Safe Local Aerial Manipulation for the Installation of Devices on Power Lines: AERIAL-CORE First Year Results and Designs}, JOURNAL = {Applied Sciences}, VOLUME = {11}, YEAR = {2021}, NUMBER = {13}, ARTICLE-NUMBER = {6220}, ISSN = {2076-3417}, DOI = {10.3390/app11136220} }

Past, Present, and Future of Aerial Robotic Manipulators

A. Ollero, M. Tognon, A. Suarez, D. Lee, A. Franchi.

IEEE Transactions on Robotics, Page(s): 1 - 20

This article analyzes the evolution and current trends in aerial robotic manipulation, comprising helicopters, conventional underactuated multirotors, and multidirectional thrust platforms equipped with a wide variety of robotic manipulators capable of physically interacting with the environment. It also covers cooperative aerial manipulation and interconnected actuated multibody designs. The review is completed with developments in teleoperation, perception, and planning. Finally, a new generation of aerial robotic manipulators is presented with our vision of the future.

@ARTICLE{9462539, author={Ollero, Anibal and Tognon, Marco and Suarez, Alejandro and Lee, Dongjun and Franchi, Antonio}, journal={IEEE Transactions on Robotics}, title={Past, Present, and Future of Aerial Robotic Manipulators}, year={2021}, volume={}, number={}, pages={1-20}, doi={10.1109/TRO.2021.3084395}}

Introducing autonomous aerial robots in industrial manufacturing

F. J. Pérez-Grau, J. R. Martinez-de Dios, J. L. Paneque, J. J. Acevedo, A. Torres-González, A. Viguria, J. R. Astorga, A. Ollero

Journal of Manufacturing Systems, Volume 60, July 2021, Pages 312-324

Although ground robots have been successfully used for many years in manufacturing, the capability of aerial robots to agilely navigate in the often sparse and static upper part of factories makes them suitable for performing tasks of interest in many industrial sectors. This paper presents the design, development, and validation of a fully autonomous aerial robotic system for manufacturing industries. It includes modules for accurate pose estimation without using a Global Navigation Satellite System (GNSS), autonomous navigation, radio-based localization, and obstacle avoidance, among others, providing a fully onboard solution capable of autonomously performing complex tasks in dynamic indoor environments in which all necessary sensors, electronics, and processing are on the robot. It was developed to fulfill two use cases relevant in many industries: light object logistics and missing tool search. The presented robotic system, functionalities, and use cases have been extensively validated with Technology Readiness Level 7 (TRL-7) in the Centro Bahía de Cádiz (CBC) Airbus D&S factory in fully working conditions.

@article{PEREZGRAU2021312, title = {Introducing autonomous aerial robots in industrial manufacturing}, journal = {Journal of Manufacturing Systems}, volume = {60}, pages = {312-324}, year = {2021}, issn = {0278-6125}, doi = {https://doi.org/10.1016/j.jmsy.2021.06.008}, url = {https://www.sciencedirect.com/science/article/pii/S0278612521001321}, author = {Francisco J. Perez-Grau and J. Ramiro {Martinez-de Dios} and Julio L. Paneque and J. Joaquin Acevedo and Arturo Torres-González and Antidio Viguria and Juan R. Astorga and Anibal Ollero}, keywords = {Aerial robot co-worker, Factory automation, Industrial application} }

Control Aware of Limitations of Manipulators with Claw for Aerial Robots Imitating Bird’s Skeleton

D. Feliu-Talego, J. Á. Acosta, and A. Ollero,

IEEE Robotics and Automation Letters, Published

Winged animals such as birds, flying mammals or insects have lightweight limbs which allow them to perform different tasks. Although in robotics there are some examples ofwinged robots (called ornithopters), it has not been yet studied how to add them some manipulation-like capabilities, similarly to the anatomy of animals limbs. Adding those capabilities to ornithopters will outperform multirotor platforms giving the possibility to perch in unaccessible places, grasp objects and perform some kind of manipulation while being in proximity to humans. The special manipulator imitates the anatomy of the birds, having a kinematic chain with actuated joints except the first passive one that resembles the claw of a bird with a grasping force. This work analyzes in depth these ornithopterlike manipulators and proposes a nonlinear controller aware of the limitation in the grasping force of the claw, modeled as static friction. The solution is based on a methodology to control constrained-nonlinear systems via diffeomorphisms providing an explicit controller with low torques demand to meet aerial requirements. It is verified on a realistic simulator with 5DOF links—claw, low/upp-er leg, body, neck and beak–, and experimentally validated in a simpler 3DOF prototype.

Event-based human intrusion detection in UAS using Deep Learning

M. A. Pérez-Cutiño, A. Gómez-Eguíluz, J. R Martínez-de-Dios and A. Ollero

ICUAS 2021, Accepted pp. 91-100

Automatic intrusion detection in unstructured and complex environments using autonomous Unmanned Aerial Systems (UAS) poses perception challenges in which traditional techniques are severely constrained. Event cameras have high temporal resolution and dynamic range, which make them robust against motion blur and lighting conditions. This paper presents an event-by-event processing scheme for detecting human intrusion using UAS. It includes: 1) one method for detecting clusters of events caused by moving objects in static background; and 2) one method based on Convolutional Neural Networks to compute the probability that a cluster corresponds to a person. The proposed scheme has been implemented and validated in challenging scenarios.

@inproceedings{perezcutino2021event, title={Event-based human intrusion detection in UAS using Deep Learning}, author={Pérez-Cutiño, Miguel Angel and Gómez-Eguı́luz, Augusto and Martı́nez-de-Dios, José Ramiro and Ollero, Aníbal}, booktitle={2021 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={91--100}, year={2021}, organization={IEEE} }

Analysis of Forces Involved in the Perching Maneuver of Flapping-Wing Aerial Systems and Development of an Ultra-Lightweight Perching System

V. Perez-Sanchez, A. E. Gomez-Tamm, F.J. Garcia-Rubiales, B. C. Arrue, and A. Ollero

ICUAS 2021,

Trying to optimize the design of aerial robotics systems, this work presents an optimized low-weight landing system for flapping-wing aerial robots. The design, based on the use of low-sized neodymium magnets, intends to provide that these aerial robots have the capability of landing in restricted areas by using the presented solution. This capacity will increase the application range of these robots. A study of this situation has been done to analyze the perching maneuver forces and evaluate the system. The solution presented is low-weight, low-sized, and also relatively inexpensive. Therefore, this solution may apply to most ornithopter robots. Design, analysis of the implied forces, development and experimental validation of the idea are presented in this work, demonstrating that the developed solution can overcome the ornithopter's payload limitation providing an efficient and reliable solution.

@article{perezanalysis, title={Analysis of Forces Involved in the Perching Maneuver of Flapping-Wing Aerial Systems and Development of an Ultra-Lightweight Perching System}, author={P{\'e}rez-S{\'a}nchez, V and G{\'o}mez-Tamm, AE and Garc{\'\i}a-Rubiales, FJ and Arrue, B and Ollero, A} }

Soft-Tentacle Gripper for Pipe Crawling to Inspect Industrial Facilities Using UAVs

F. J. Garcia Rubiales, P. Ramon Soria, B. C. Arrue and A. Ollero

Sensors, 2021, Vol:21, Num: 12, 4142

This paper presents a crawling mechanism using a soft-tentacle gripper integrated into an unmanned aerial vehicle for pipe inspection in industrial environments. The objective was to allow the aerial robot to perch and crawl along the pipe, minimizing the energy consumption, and allowing to perform contact inspection. This paper introduces the design of the soft limbs of the gripper and also the internal mechanism that allows movement along pipes. Several tests have been carried out to ensure the grasping capability on the pipe and the performance and reliability of the developed system. This paper shows the complete development of the system using additive manufacturing techniques and includes the results of experiments performed in realistic environments

@Article{s21124142, AUTHOR = {Garcia Rubiales, F. Javier and Ramon Soria, Pablo and Arrue, Begoña C. and Ollero, Anibal}, TITLE = {Soft-Tentacle Gripper for Pipe Crawling to Inspect Industrial Facilities Using UAVs}, JOURNAL = {Sensors}, VOLUME = {21}, YEAR = {2021}, NUMBER = {12}, ARTICLE-NUMBER = {4142}, URL = {https://www.mdpi.com/1424-8220/21/12/4142}, ISSN = {1424-8220}, ABSTRACT = {This paper presents a crawling mechanism using a soft-tentacle gripper integrated into an unmanned aerial vehicle for pipe inspection in industrial environments. The objective was to allow the aerial robot to perch and crawl along the pipe, minimizing the energy consumption, and allowing to perform contact inspection. This paper introduces the design of the soft limbs of the gripper and also the internal mechanism that allows movement along pipes. Several tests have been carried out to ensure the grasping capability on the pipe and the performance and reliability of the developed system. This paper shows the complete development of the system using additive manufacturing techniques and includes the results of experiments performed in realistic environments.}, DOI = {10.3390/s21124142} }

Soft-Landing of Multi-Rotor Drones using a Robust Nonlinear Control and Wind Modeling

S. R. Nekoo, J. A. Acosta, G. Heredia and A. Ollero

ICUAS 2021, pp. 1070-1079

Grasping, manipulation, and inspection by multirotor systems require soft landing without any bumps; hence, the one-shot landing subject is critical due to aerodynamics effects under a multirotor unmanned aerial vehicle (UAV). One of the tasks in the HYFLIERS project is landing on a rack of pipes for inspection, mainly measurement of the pipe thickness and corrosion. The rack of pipes generates an unknown disturbance caused by the induced airflow by the propellers during the landing phase. The modeling of this problem is developed for two cases, landing on the ground and rack of pipes. The ground effect modeling is straightforward; however, the rack of pipes imposes more uncertainty on the system modeling. The source of aerodynamics disturbance also could be either external wind or the one caused by the UAV’s propellers near the pipes or ground. This work proposes a solution for the one-shot landing of a quadrotor considering the ground effect. First, the induced wind by the rotors near the ground is computed and then the reflection model of that near the ground is defined. Modeling of the quadrotor considering the wind in the environment is done. Next, the reflected wind by the ground is set in the wind model of the system. The uncertainty in the modeling exists due to interference of airflow under the UAV and behavior of that, so a robust nonlinear control is selected to control the system. The correction gain of the sliding mode controller was defined based on the steady-state thrust that plays the role of an upper bound of uncertainty. A simulation has been successfully done to present the advantages of the soft landing method considering the ground effect. The resultant input thrust decreased smoothly near the pipes that compensated the ground effect thrust.

@article{nekoosoft, title={Soft-Landing of Multi-Rotor Drones using a Robust Nonlinear Control and Wind Modeling}, author={Nekoo, Saeed Rafee and Acosta, Jose {\'A}ngel and Heredia, Guillermo and Ollero, Anibal} }

Design of the High-Payload Flapping Wing Robot E-Flap

R. Zufferey, J. Tormo-Barbero, M. M. Guzmán, F. C. Maldonado, E. Sanchez-Laulhe, P. Grau, M. Pérez, J. A. Acosta, A. Ollero

IEEE Robotics and Automation Letters, Vol: 6 pp. 3097-3104

Autonomous lightweight flapping-wing robots show potential to become a safe and affordable solution for rapidly deploying robots around humans and in complex environments. The absence of propellers makes such vehicles more resistant to physical contact, permitting flight in cluttered environments, and collaborating with humans. Importantly, the provision of thousands of species of birds that have already mastered the challenging task of flapping flight is a rich source of solutions. However, small wing flapping technology is still in its beginnings, with limited levels of autonomy and physical interaction capability with the environment. One significant limitation to this is the low payload available. Here we show the Eagle-inspired Flapping-wing robot E-Flap, a 510 g novel design capable of a 100% of payload, exceeding the requirement of the computing and sensing package needed to fly with a high degree of autonomy. The concept is extensively characterized, both in a tracked indoor space and in outdoor conditions. We demonstrate flight path angle of up to 50 ∘ and velocities from as low as 2 m/s to over 6 m/s. Overall, the robotic platform has been proven to be reliable, having performed over 100 flights. Through mechanical and electronics advances, the E-Flap is a robust vehicle prototype and paves the way towards flapping-wing robots becoming a practical fully autonomous flying solution

@article{zufferey2021design, title={Design of the High-Payload Flapping Wing Robot E-Flap}, author={Zufferey, Raphael and Tormo-Barbero, Jes{\'u}s and Guzm{\'a}n, M Mar and Maldonado, Fco Javier and Sanchez-Laulhe, Ernesto and Grau, Pedro and P{\'e}rez, Mart{\'\i}n and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, volume={6}, number={2}, pages={3097--3104}, year={2021}, publisher={IEEE} }

Design and comparison of tails for bird-scale flapping-wing robots

M. M. Guzmán, C. Ruiz Páez, F. J. Maldonado, R. Zufferey, J. Tormo-Barbero, J. A. Acosta and A. Ollero

IROS 2021, Accepted

Flapping-wing robots (so-called ornithopters) are a promising type of platform to perform efficient winged flight and interaction with the environment. However, the control of such vehicles is challenging due to their under-actuated morphology to meet lightweight requirements. Consequently, the flight control of flapping-wing robots is predominantly handled by the tail. Most ornithopters feature a tail with two degrees of freedom but the configuration choice is often arbitrary and without indepth study. In this paper, we propose a thorough analysis of the design and in-flight performance for the three tails. Their design and manufacturing methods are presented, with an emphasis on low weight, which is critical in ornithopters. The aerodynamics of the tails is analyzed through CFD simulations and their performance compared experimentally. The advantages and performance metrics of each configuration are discussed based on flight data. Two types of 3D flight tests were carried out: aggressive heading maneuvers and level turns. The results show that an inverted V-tail outperforms the others regarding maneuverability and stability. From the three configurations, only the inverted V-Tail can perform an aggressive stable banked level turn with a radius of 3.7 m at a turning rate of 1.6 rad/s. This research work describes the impact of the tail configuration choice on the performance of bird-scale flapping-wing robots.

Autonomous Fire-fighting with Heterogeneous Team of Unmanned Aerial Vehicles

F. Real, Á. R. Castaño, A. Torres-González, J. Capitán, P. J. Sánchez-Cuevas, M. J. Fernández, H. Romero, A. Ollero

Field Robotics,

Unmanned Aerial Traffic Management System Architecture for U-Space In-Flight Services

C. Capitan,H. Pérez, J. Capitán, A. Castaño and A. Ollero

Applied Sciences,

This paper presents a software architecture for Unmanned aerial system Traffic Management (UTM). The work is framed within the U-space ecosystem, which is the European initiative for UTM in the civil airspace. We propose a system that focuses on providing the required services for automated decision-making during real-time threat management and conflict resolution, which is the main gap in current UTM solutions. Nonetheless, our software architecture follows an open-source design that is modular and flexible enough to accommodate additional U-space services in future developments. In its current implementation, our UTM solution is capable of tracking the aerial operations and monitoring the airspace in real time, in order to perform in-flight emergency management and tactical deconfliction. We show experimental results in order to demonstrate the UTM system working in a realistic simulation setup. For that, we performed our tests with the UTM system and the operators of the aerial aircraft located at remote locations with the consequent communication issues, and we showcased that the system was capable of managing in real time the conflicting events in two different use cases.

@article{capitan2021unmanned, title={Unmanned Aerial Traffic Management System Architecture for U-Space In-Flight Services}, author={Capit{\'a}n, Carlos and P{\'e}rez-Le{\'o}n, H{\'e}ctor and Capit{\'a}n, Jes{\'u}s and Casta{\~n}o, {\'A}ngel and Ollero, An{\'\i}bal}, journal={Applied Sciences}, volume={11}, number={9}, pages={3995}, year={2021}, publisher={Multidisciplinary Digital Publishing Institute} }

Bio-Inspired Morphing Tail for Flapping Wings Aerial Robots using Macro Fiber Composites

V.Perez-Sanchez, A.E. Gomez-Tamm, E.Savastano, B.C. Arrue, A. Ollero

Applied Sciences,

The aim of this work is to present the development of a bio-inspired approach for a robotic tail using Macro Fiber Composites (MFC) as actuators. The use of this technology will allow achieving closer to the nature approach of the tail, aiming to mimic a bird tail behavior. The tail will change its shape, performing morphing, providing a new type of actuation methodology in flapping control systems. The work is intended as a first step for demonstrating the potential of these technologies for being applied in other parts of the aerials robotics systems. When compared with traditional actuation approaches, one key advantage that is given by the use of MFC is their ability to adapt to different flight conditions via geometric tailoring, imitating what birds do in nature. Theoretical explanations, design, and experimental validation of the developed concept using different methodologies will be presented in this paper.

@article{perez2021bio, title={Bio-Inspired Morphing Tail for Flapping-Wings Aerial Robots Using Macro Fiber Composites}, author={Perez-Sanchez, Vicente and Gomez-Tamm, Alejandro E and Savastano, Emanuela and Arrue, Bego{\~n}a C and Ollero, Anibal}, journal={Applied Sciences}, volume={11}, number={7}, pages={2930}, year={2021}, publisher={Multidisciplinary Digital Publishing Institute} }

Optimal trajectory planning for cinematography with multiple unmanned aerial vehicles

A. Alcántara, J. Capitán, R. Cunha, A. Ollero

Robotics and Autonomous Systems, 140 (2021), pp. 103778

This paper presents a method for planning optimal trajectories with a team of Unmanned Aerial Vehicles (UAVs) performing autonomous cinematography. The method is able to plan trajectories online and in a distributed manner, providing coordination between the UAVs. We propose a novel non-linear formulation for this challenging problem of computing multi-UAV optimal trajectories for cinematography; integrating UAVs dynamics and collision avoidance constraints, together with cinematographic aspects like smoothness, gimbal mechanical limits and mutual camera visibility. We integrate our method within a hardware and software architecture for UAV cinematography that was previously developed within the framework of the MultiDrone project; and demonstrate its use with different types of shots filming a moving target outdoors. We provide extensive experimental results both in simulation and field experiments. We analyze the performance of the method and prove that it is able to compute online smooth trajectories, reducing jerky movements and complying with cinematography constraints.

@article{alcantara2021optimal, title={Optimal trajectory planning for cinematography with multiple unmanned aerial vehicles}, author={Alc{\'a}ntara, Alfonso and Capit{\'a}n, Jes{\'u}s and Cunha, Rita and Ollero, An{\'\i}bal}, journal={Robotics and Autonomous Systems}, volume={140}, pages={103778}, year={2021}, publisher={Elsevier} }

Optimal trajectory planning for cinematography with multiple unmanned aerial vehicles

A. Alcántara, J. Capitán, R. Cunha, and A. Ollero

Science Direct,

This paper presents a method for planning optimal trajectories with a team of Unmanned AerialVehicles(UAVs) performing autonomous cinematography. The method is able to plan trajectoriesonline and in a distributed manner, providing coordination between the UAVs. We propose a novelnon-linear formulation for this challenging problem of computing multi-UAV optimal trajectoriesfor cinematography; integrating UAVs dynamics and collision avoidance constraints, together withcinematographic aspects like smoothness, gimbal mechanical limits and mutual camera visibility. Weintegrate our method within a hardware and software architecture for UAV cinematography that waspreviously developed within the framework of theMultiDroneproject; and demonstrate its use withdifferent types of shots filming a moving target outdoors. We provide extensive experimental resultsboth in simulation and field experiments. We analyze the performance of the method and provethat it is able to compute online smooth trajectories, reducing jerky movements and complying withcinematography constraints.©2021ElsevierB.V.Allrightsreserved.1. IntroductionDrones orUnmanned Aerial Vehicles(UAVs) are spreading fastfor aerial photography and cinematography, mainly due to theirmaneuverability and their capacity to access complex filminglocations in outdoor settings. From the application point of view,UAVs present a remarkable potential to produce unique aerialshots at reduced costs, in contrast with other alternatives likedolliesorstaticcameras.Additionally,theuseofteamswithmul-tipleUAVsopensevenmorethepossibilitiesforcinematography.On the one hand, large-scale events can be addressed by filmingmultiple action points concurrently or sequentially. On the otherhand, the combination of shots with multiple views or differentcameramotionsbroadenstheartisticalternativesforthedirector.Currently,mostUAVsincinematographyareoperatedinman-ual mode by an expert pilot. Besides, an additional qualifiedoperator is required to control the camera during the flight, astaking aerial shots can be a complex and overloading task. Evenso, the manual operation of UAVs for aerial cinematography is✩This work was partially funded by the European Union’s Horizon 2020research and innovation programme under grant agreements No 731667 (Mul-tiDrone), and by the MULTICOP project (Junta de Andalucia, FEDER Programme,US-1265072).∗Corresponding author.E-mail addresses:aamarin@us.es (A. Alcántara), jcapitan@us.es (J. Capitán),rita@isr.utl.pt (R. Cunha), aollero@us.es (A. Ollero).still challenging, as multiple aspects need to be considered: per-forming smooth trajectories to achieve aesthetic videos, trackingactors to be filmed, avoiding collisions with potential obstacles,keeping other cameras out of the field of view, etc.There exist commercial products (e.g.,DJI Mavic[1] orSky-dio[2]) that cope with some of the aforementioned complex-ities implementing semi-autonomous functionalities, likeauto-followfeatures to track an actor or simplistic collision avoidance.However, they do not address cinematographic principles formulti-UAV teams, as e.g., planning trajectories considering gim-bal physical limitations or inter-UAV visibility. Therefore, solu-tions for autonomous filming with multiple UAVs are of interest.Some authors [3] have shown that planning trajectories aheadseveral seconds is required in order to fulfill with cinemato-graphicconstraintssmoothly.Others[4,5]haveevenexploredthemulti-UAVproblem,butonlinetrajectoryplanningformulti-UAVcinematography outdoors is still an open issue.In this paper, we propose a method for online planning andexecutionoftrajectorieswithateamofUAVstakingcinematogra-physhots.Wedevelopanoptimization-basedtechniquethatrunsontheUAVsinadistributedfashion,takingcareofthecontroloftheUAVandthegimbalmotionsimultaneously.Ourmethodaimsat providing smooth trajectories for visually pleasant video out-put;integratingcinematographicconstraintsimposedbytheshottypes, the gimbal physical limits, the mutual visibility betweencameras and the avoidance of collisions.https://doi.org/10.1016/j.robot.2021.1037780921-8890/©2021 Elsevier B.V. All rights reserved.

@article{alcantara2021optimal, title={Optimal trajectory planning for cinematography with multiple unmanned aerial vehicles}, author={Alc{\'a}ntara, Alfonso and Capit{\'a}n, Jes{\'u}s and Cunha, Rita and Ollero, An{\'\i}bal}, journal={Robotics and Autonomous Systems}, volume={140}, pages={103778}, year={2021}, publisher={Elsevier} }

Auto-Tuned Event-Based Perception Schemefor Intrusion Monitoring With UAS

J. P. Rodríguez-Gómez, A. Gómez Eguíluz, J. R. Martínez-de Dios, A. Ollero

IEEE Access, 9(2021), pp. 44840-44854

This paper presents an asynchronous event-based scheme for automatic intrusion monitoring using Unmanned Aerial Systems (UAS). Event cameras are neuromorphic sensors that capture the illumination changes in the camera pixels with high temporal resolution and dynamic range. In contrast to conventional frame-based cameras, they are naturally robust against motion blur and lighting conditions, which make them ideal for outdoor aerial robot applications. The presented scheme includes two main perception components. First, an asynchronous event-based processing system efficiently detects intrusions by combining several asynchronous event-based algorithms that exploit the advantages of the sequential nature of the event stream. The second is an off-line training mechanism that adjusts the parameters of the event-based algorithms to a particular surveillance scenario and mission. The proposed perception system was implemented in ROS for on-line execution on board UAS, integrated in an autonomous aerial robot architecture, and extensively validated in challenging scenarios with a wide variety of lighting conditions, including day and night experiments in pitch dark conditions.

@article{, author={Rodríguez-Gómez, Juan Pablo and Eguíluz, Augusto Gómez and Martínez-De Dios, José Ramiro and Ollero, Anibal}, title={Auto-Tuned Event-Based Perception Scheme for Intrusion Monitoring With UAS}, year={2021}, volume={9}, number={}, pages={44840-44854}, doi={10.1109/ACCESS.2021.3066529}}

Why fly blind? Event-based visual guidance for ornithopter robot fligh

A. Gómez Eguíluz, J.P. Rodríguez-Gómez, R. Tapia, F. J. Maldonado, J. Á. Acosta, J. R. Martínez de Dios and A. Ollero

IROS 2021, Accepted

The development of perception and control meth-ods that allow bird-scale flapping-wing robots (a.k.a. ornithopters) to perform autonomously is an under-researched area. This paper presents a fully onboard event-based method for ornithopter robot visual guidance. The method uses event cameras to exploit their fast response and robustness against motion blur in order to feed the ornithopter control loop at high rates (100 Hz). The proposed scheme visually guides the robot using line features extracted in the event image plane and controls the flight by actuating over the horizontal and vertical tail deflections. It has been validated on board a real ornithopter robot with real-time computation in low-cost hardware. The experimental evaluation includes sets of experiments with different maneuvers indoors and outdoors.

Aerodynamic Reduced-order Volterra Model of an Ornithopter under High-amplitude Flapping.

C. Ruiz, J.Á. Acosta and A. Ollero

Journal of Aerospace Science and Technology , Submitted

The unsteady aerodynamics of apping low-aspect-ratio ellipsoidal-wings in ornithopters is analyzed and modeled by the use of three dimensional Computational Fluid Dynamics (CFD) simulations. The range of interest is large amplitude, moderate frequency apping, and low to moderate angles of attack at Reynolds around 10^5, where autonomous ornithopters like GRIFFIN, are able to perform complex maneuvers such as perching. The results obtained show that the Leading Edge Vortex is produced above a certain Strouhal and angle of attack at downstroke. These aerodynamic loads are compared with the classical analytical models by the frequency response, observing that analytical models based on abscence of viscosity and small perturbations are not appropriate for the range of interest as the hypotheses are not fulfilled. Through the 3D CFD aerodynamic loads database, a finite memory Volterra model is identified in order to predict the characteristics of forces and moments produced by the apping wing. This reduced order model depends on the efective angle of attack of the surrogate airfoil located at 70 % of the semi-span at three-quarters chord on the airfoil. This state has been found appropriate for being the one with the greatest regression, comparing the 3D CFD simulations with others that have been carried out in 2D, in agreement with the literature. Finally, a methodology to validate the identified model without the need of wind tunnel is proposed and validated for lift force. By the use of the aerodynamic forces extracted from ight data, measured by a high accuracy Motion Capture System at diferent apping wing kinematics, it is concluded that the model provides better estimates than classical analytical models. The structure of the model and its predictability make it possible to use it in control tuning, in addition to being able to append nonlinear or aeroelastic terms using a similar method, also because of the execution time, provide a potential solution for online forces prediction.

The GRIFFIN Perception Dataset: Bridging the Gap Between Flapping-Wing Flight and Robotic Perception

J.P. Rodrı́guez-Gómez, R. Tapia, J. L. Paneque, P. Grau, A. Gómez Eguı́luz, J.R. Martı́nez-de Dios and A. Ollero

IEEE Robotics and Automation Letters (RA-L), 6(2021), pp. 1066-1073

The development of automatic perception systems and techniques for bio-inspired flapping-wing robots is severely hampered by the high technical complexity of these platforms and the installation of onboard sensors and electronics. Besides, flapping-wing robot perception suffers from high vibration levels and abrupt movements during flight, which cause motion blur and strong changes in lighting conditions. This letter presents a perception dataset for bird-scale flapping-wing robots as a tool to help alleviate the aforementioned problems. The presented data include measurements from onboard sensors widely used in aerial robotics and suitable to deal with the perception challenges of flapping-wing robots, such as an event camera, a conventional camera, and two Inertial Measurement Units (IMUs), as well as ground truth measurements from a laser tracker or a motion capture system. A total of 21 datasets of different types of flights were collected in three different scenarios (one indoor and two outdoor). To the best of the authors' knowledge this is the first dataset for flapping-wing robot perception.

@article{, author={Rodríguez-Gómez, Juan Pablo and Tapia, Raul and Paneque, Julio L. and Grau, Pedro and Gómez Eguíluz, Augusto and Martínez-de Dios, Jose Ramiro and Ollero, Anibal}, journal={IEEvolume={6},E Robotics and Automation Letters}, title={The GRIFFIN Perception Dataset: Bridging the Gap Between Flapping-Wing Flight and Robotic Perception}, year={2021}, volume={6}, number={2}, pages={1066-1073}, doi={10.1109/LRA.2021.3056348}}

Cartesian Aerial Manipulator with Compliant Arm

A. Suarez, M. Perez, G. Heredia, A. Ollero

Applied Sciences, vol. 11, pp. 1001.

This paper presents an aerial manipulation robot consisting of a hexa-rotor equipped with a 2-DOF (degree of freedom) Cartesian base (XY–axes) that supports a 1-DOF compliant joint arm that integrates a gripper and an elastic linear force sensor. The proposed kinematic configuration improves the positioning accuracy of the end effector with respect to robotic arms with revolute joints, where each coordinate of the Cartesian position depends on all the joint angles. The Cartesian base reduces the inertia of the manipulator and the energy consumption since it does not need to lift its own weight. Consequently, the required torque is lower and, thus, the weight of the actuators. The linear and angular deflection sensors of the arm allow the estimation, monitoring and control of the interaction wrenches exerted in two axes (XZ) at the end effector. The kinematic and dynamic models are derived and compared with respect to a revolute-joint arm, proposing a force-position control scheme for the aerial robot. A battery counterweight mechanism is also incorporated in the X–axis linear guide to partially compensate for the motion of the manipulator. Experimental results indoors and outdoors show the performance of the robot, including object grasping and retrieval, contact force control, and force monitoring in grabbing situations.

@article{suarez2021cartesian, title={Cartesian Aerial Manipulator with Compliant Arm}, author={Suarez, Alejandro and Perez, Manuel and Heredia, Guillermo and Ollero, Anibal}, journal={Applied Sciences}, volume={11}, number={3}, pages={1001}, year={2021}, publisher={Multidisciplinary Digital Publishing Institute} }

Geometric control using the state-dependent Riccati equation: Application to aerial-acrobatic maneuvers

S. R. Nekoo, J. Á. Acosta and A. Ollero

International Journal of Control,

Acrobatic flip is one of the most challenging representatives of aggressive maneuvers to test the performance of an aerial system’s capability or a controller. A variable-pitch rotor quadcopter generates thrust in both vertical directions for the special design of the rotor’s actuation mechanism. This research proposes two possible solutions for the flip: a regulation solution based on the geometric control approach; and tracking a predefined optimal smooth trajectory covering a turnover. The first solution uses a geometric control approach that is immune to singular points since the rotation matrix is integrated on the manifold on SO(3). The second solution proposes an optimal trajectory generation for flip maneuver using open-loop optimal control, two-point boundary value problem (TPBVP) approach. Since generated open-loop state information is not applicable without a controller, the state-dependent differential Riccati equation (SDDRE) is chosen for trajectory tracking.

@article{rafee2021geometric, title={Geometric control using the state-dependent Riccati equation: application to aerial-acrobatic maneuvers}, author={Rafee Nekoo, Saeed and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={International Journal of Control}, pages={1--13}, year={2021}, publisher={Taylor \& Francis} }

Experimental Evaluation of a Team of Multiple Unmanned Aerial Vehicles for Cooperative Construction

F. Real, Á. R. Castaño, A. Torres-González, J. Capitán, P. J. Sánchez-Cuevas, M. J. Fernández, M. Villar, A. Ollero

IEEE Access, vol.9, pp.6817-6835

This article presents a team of multiple Unmanned Aerial Vehicles (UAVs) to perform cooperative missions for autonomous construction. In particular, the UAVs have to build a wall made of bricks that need to be picked and transported from different locations. First, we propose a novel architecture for multi-robot systems operating in outdoor and unstructured environments, where robustness and reliability play a key role. Then, we describe the design of our aerial platforms and grasping mechanisms to pick, transport and place bricks. The system was particularly developed for the Mohamed Bin Zayed International Robotics Challenge (MBZIRC), where Challenge 2 consisted of building a wall cooperatively with multiple UAVs. However, our approach is more general and extensible to other multi-UAV applications involving physical interaction, like package delivery. We present not only our results in the final stage of MBZIRC, but also our simulations and field experiments throughout the previous months to the competition, where we tuned our system and assessed its performance.

@article{real2021experimental, title={Experimental Evaluation of a Team of Multiple Unmanned Aerial Vehicles for Cooperative Construction}, author={Real, Fran and Casta{\~n}o, {\'A}ngel R and Torres-Gonz{\'a}lez, Arturo and Capit{\'a}n, Jes{\'u}s and S{\'a}nchez-Cuevas, Pedro J and Fern{\'a}ndez, Manuel J and Villar, Manuel and Ollero, An{\'\i}bal}, journal={IEEE Access}, volume={9}, pages={6817--6835}, year={2021}, publisher={IEEE} }

2020

Towards UAS Surveillance using Event Cameras

J.R. Martínez-de Dios, A. Gómez Eguíluz, J.P. Rodríguez-Gómez, R. Tapia; A. Ollero

SSRR, pp.71-76

Aerial robot perception for surveillance and search and rescue in unstructured and complex environments poses challenging problems in which traditional sensors are severely constrained. This paper analyzes the use of event cameras onboard aerial robots for surveillance applications. Event cameras have high temporal resolution and dynamic range, which make them very robust against motion blur and lighting conditions. The paper analyzes the pros and cons of event cameras and presents an event-based processing scheme for target detection and tracking. The scheme is experimentally validated in challenging environments and different lighting conditions.

@INPROCEEDINGS{9292606, author={Martínez-de Dios, J.R. and Gómez Eguíluz, A. and Rodríguez-Gómez, J.P. and Tapia, R. and Ollero, A.}, booktitle={2020 IEEE International Symposium on Safety, Security, and Rescue Robotics (SSRR)}, title={Towards UAS Surveillance using Event Cameras}, year={2020}, volume={}, number={}, pages={71-76}, doi={10.1109/SSRR50563.2020.9292606}}

Aerial physical interaction in grabbing conditions with lightweight and compliant dual arms

A. Suarez, P. J. Sanchez-Cuevas, G. Heredia, and A. Ollero

Applied Science, Vol. 10, iss. 24, p. 8927

This paper considers the problem of performing bimanual aerial manipulation tasks in grabbing conditions, with one of the arms grabbed to a fixed point (grabbing arm) while the other conducts the task (operation arm). The goal was to evaluate the positioning accuracy of the aerial platform and the end effector when the grabbing arm is used as position sensor, as well as to analyze the behavior of the robot during the aerial physical interaction on flight. The paper proposed a control scheme that exploits the information provided by the joint sensors of the grabbing arm for estimating the relative position of the aerial platform w.r.t. (with respect to) the grabbing point. A deflection-based Cartesian impedance control was designed for the compliant arm, allowing the generation of forces that help the aerial platform to maintain the reference position when it is disturbed due to external forces. The proposed methods were validated in an indoor testbed with a lightweight and compliant dual arm aerial manipulation robot

@article{suarez2020aerial, title={Aerial Physical Interaction in Grabbing Conditions with Lightweight and Compliant Dual Arms}, author={Suarez, Alejandro and Sanchez-Cuevas, Pedro J and Heredia, Guillermo and Ollero, Anibal}, journal={Applied Sciences}, volume={10}, number={24}, pages={8927}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

High-Level Modular Autopilot Solution for Fast Prototyping of Unmanned Aerial Systems

C. R. de Cos, M. J. Fernández, P. J. Sánchez Cuevas, J. Á. Acosta and A. Ollero

IEEE Access, Vol. 8, pp .223827 - 223836

A redundant fast prototyping autopilot solution for unmanned aerial systems has been developed and successfully tested outdoors. While its low-level backbone is executed in a Raspberry Pi R 3 + NAVIO2 R with a backup autopilot, the computational power of an Intel R NUC mini-computer is employed to implement complex functionalities directly in Simulink R , thus including in-flight debugging, tuning and monitoring. Altogether, the presented tool provides a flexible and user-friendly high-level environment with enhanced computational capabilities, which drastically reduces the prototyping timespans of complex algorithms -between 50% and 75%, according to our long and proven experience in aerial robotics-, while preventing incidents thanks to its redundant design with a human-in-the-loop pilot on the reliable PX4. Three typical outdoor cases are carried out for validation in real-life scenarios, all mounted in a DJI © F550 platform. Full integration results and telemetry for more than 50 hours of outdoor flight tests are provided.

@article{carlos2020high, title={High-Level Modular Autopilot Solution for Fast Prototyping of Unmanned Aerial Systems}, author={Carlos, R and Fernandez, Manuel J and Sanchez-Cuevas, Pedro J and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IEEE Access}, year={2020}, publisher={IEEE} }

Analysis of unstable behavior of planing craft speed using the qualitative theory of dynamical systems

A. González-Cantos, M. Lopez, and A. Ollero

Nonlinear dynamics, Pp. 1–21

This paper deals with the inherent instability observed in the speed of a planing type craft. In the case of displacement craft, the systems governing the speed are stable hence closed-loop control is trivial. In the case of planing craft, however, there may exist instability in their speed. By using the Qualitative Theory of Dynamical Systems (QTDS), this paper shows that there may exist a set of speeds in which planing craft are not able to achieve adequate stability. This instability problem cannot be acceptable in many applications (such as that examined in this paper, an Unmanned Surface Vehicle, USV, of planing craft type). The observed instability is explained by means of the appearance of bifurcations which bring new attractors to the state space, such as equilibrium points or limit cycles. This paper proposes a novel solution to manage the vessel instability behavior. This is done by way of increasing the droop characteristic in the propulsion thrust with respect to speed. By increasing the droop, the system becomes more robust. The key advantage of this approach is that it is achieved by way of modifying the propulsion controller rather than by changing the hydrodynamic profile of the vessel, the mass distribution or by adding extra control surface (i.e., flaps). Resulting in a more cost-effective control system. Furthermore, due to this method acting on propulsion and its control, it is compatible with the other methods aforementioned. Stability analysis is undertaken. This analysis is very general, because it considers a wide range of controller and propulsion systems. Open-loop control and analysis into different types of propulsion is also presented. The effect of each propulsion type on stability is explained. In addition, the effect in the control loop of the electro-mechanical actuators inaccuracy (dead-zone) has also been analyzed. The paper explains that this inaccuracy, though small, can make the speed oscillate in planing craft. A practical implementation of this analysis is validated by way of sea trials with a real planing craft

@article{gonzalez2020analysis, title={Analysis of unstable behavior of planing craft speed using the qualitative theory of dynamical systems}, author={Gonzalez-Cantos, A and Lopez, MJ and Ollero, A}, journal={Nonlinear Dynamics}, pages={1--21}, year={2020}, publisher={Springer} }

Autonomous Execution of Cinematographic Shots With Multiple Drones

A. Alcántara, J. Capitán, A. Torres-González, R. Cunha, and A. Ollero

IEEE Access, Vol. 8, p. 201300–201316, 2020.

This paper presents a system for the execution of autonomous cinematography missions with a team of drones. The system allows media directors to design missions involving different types of shots with one or multiple cameras, running sequentially or concurrently. We introduce the complete architecture, which includes components for mission design, planning and execution. Then, we focus on the components related to autonomous mission execution. First, we propose a novel parametric description for shots, considering different types of camera motion and tracked targets; and we use it to implement a set of canonical shots. Second, for multi-drone shot execution, we propose distributed schedulers that activate different shot controllers on board the drones. Moreover, an event-based mechanism is used to synchronize shot execution among the drones and to account for inaccuracies during shot planning. Finally, we showcase the system with field experiments filming sport activities, including a real regatta event. We report on system integration and lessons learnt during our experimental campaigns.

@article{alcantara2020autonomous, title={Autonomous execution of cinematographic shots with multiple drones}, author={Alc{\'a}ntara, Alfonso and Capit{\'a}n, Jes{\'u}s and Torres-Gonz{\'a}lez, Arturo and Cunha, Rita and Ollero, An{\'\i}bal}, journal={IEEE Access}, volume={8}, pages={201300--201316}, year={2020}, publisher={IEEE} }

Kinodynamic planning for an energy-efficient autonomous ornithopter

F. Rodrı́guez, J. Dáz-Báñez, E. Sanchez-Laulhe, J. Capitán, and A. Ollero

Arxiv, Preprint arxiv: 2010.12273

This paper presents a novel algorithm to plan energy-efficient trajectories for autonomous ornithopters. In general, trajectory optimization is quite a relevant problem for practical applications with \emph{Unmanned Aerial Vehicles} (UAVs). Even though the problem has been well studied for fixed and rotatory-wing vehicles, there are far fewer works exploring it for flapping-wing UAVs like ornithopters. These are of interest for many applications where long flight endurance, but also hovering capabilities are required. We propose an efficient approach to plan ornithopter trajectories that minimize energy consumption by combining gliding and flapping maneuvers. Our algorithm builds a tree of dynamically feasible trajectories and applies heuristic search for efficient online planning, using reference curves to guide the search and prune states. We present computational experiments to analyze and tune key parameters, as well as a comparison against a recent alternative probabilistic planning, showing best performance. Finally, we demonstrate how our algorithm can be used for planning perching maneuvers online.

@article{rodriguez2020kinodynamic, title={Kinodynamic Planning for an Energy-Efficient Autonomous Ornithopter}, author={Rodr{\'\i}guez, Fabio and D{\'\i}az-B{\'a}{\~n}ez, Jos{\'e}-Miguel and Sanchez-Laulhe, Ernesto and Capit{\'a}n, Jes{\'u}s and Ollero, An{\'\i}bal}, journal={arXiv preprint arXiv:2010.12273}, year={2020} }

SMA Actuated Low-Weight Bio-Inspired Claws for Grasping and Perching Using Flapping Wing Aerial Systems

A.E. Gomez-Tamm, V. Perez-Sanchez, B.C. Arrue and A. Ollero

IROS 2020, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

Taking inspiration from nature, the work presented in this paper aims to develop bio-inspired claws to be used for grasping and perching in flapping-wing aerial systems. These claws can be 3D printed out of two different materials and will be capable of adapt to any shape. Also, they will be soft for avoiding undesired damages on the objects when performing manipulation. These claws will be actuated by shape memory alloys (SMA) springs to get rid of the weight of traditional servos. The design of all the components will be explained in this work. Also, the challenges of being able to control SMA using only a LiPo battery on an aerial vehicle will be exposed. The solutions applied and electronics used will be also described. Lastly, experiments made both in test bench as on flight will be summarized.

@inproceedings{gomez2020sma, title={SMA Actuated Low-Weight Bio-Inspired Claws for Grasping and Perching Using Flapping Wing Aerial Systems}, author={Gomez-Tamm, AE and Perez-Sanchez, V and Arrue, BC and Ollero, A}, booktitle={Proceedings of the 2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Las Vegas, NV, USA}, pages={25--29}, year={2020} }

MHYRO: Modular HYbrid RObot for contact inspection and maintenance operations in chemical plants

Abraham Lopez, Pedro J. Sanchez-Cuevas, A. Garofano-Soldado, A. Suarez, A. Ollero, G. Heredia

IROS 2020, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

In this paper, we propose a new concept of robot which is hybrid, including aerial and crawling subsystems and an arm, and also modular with interchangeable crawling subsystems for different pipe configurations, since it has been designed to cover most industrial oil & gas end-users’ requirements. The robot has the same ability than aerial robots to reach otherwise inaccessible locations, but makes the inspection more efficient, increasing operation time since crawling requires less energy than flying, and achieving better accuracy in the inspection. It also integrates safety-related characteristics for operating in the potentially explosive atmosphere of a refinery, being able to immediately interrupt the inspection if a hazardous situation is detected and carry the sensible parts such as batteries and electronic devices away as soon as possible. The paper presents the design of this platform in detail and shows the feasibility of the whole system performing indoor experiments.

@inproceedings{lopez2020mhyro, title={MHYRO: Modular HYbrid RObot for contact inspection and maintenance in oil \& gas plants}, author={Lopez-Lora, A and Sanchez-Cuevas, PJ and Suarez, A and Garofano-Soldado, A and Ollero, A and Heredia, G}, booktitle={2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)}, pages={1268--1275}, year={2020}, organization={IEEE} }

ASAP: Adaptive Scheme for Asynchronous Processing of event-based vision algorithms

R. Tapia, A. Gómez Eguíluz, J.R. Martínez-de Dios and A. Ollero

ICRA 2020, IEEE International Conference on Robotics and Automation (ICRA)

Event cameras can capture pixel-level illumination changes with very high temporal resolution and dynamic range. They have received increasing research interest due to their robustness to lighting conditions and motion blur. Two main approaches exist in the literature to feed the event-based processing algorithms: packaging the triggered events in event packages and sending them one-by-one as single events. These approaches suffer limitations from either processing overflow or lack of responsivity. Processing overflow is caused by high event generation rates when the algorithm cannot process all the events in real-time. Conversely, lack of responsivity happens in cases of low event generation rates when the event packages are sent at too low frequencies. This paper presents ASAP, an adaptive scheme to manage the event stream through variable- size packages that accommodate to the event package processing times. The experimental results show that ASAP is capable of feeding an asynchronous event-by-event clustering algorithm in a responsive and efficient manner and at the same time prevent overflow.

@inproceedings{tapia2020asap, title={ASAP: Adaptive scheme for asynchronous processing of event-based vision algorithms}, author={Tapia, R and Egu{\i}luz, A G{\'o}mez and Mart{\i}nez-de Dios, J and Ollero, A}, booktitle={2020 IEEE ICRA Workshop on Unconventional Sensors in Robotics. IEEE}, year={2020} }

Asynchronous Event-based Line Tracking for Time-to-Contact Maneuvers in UAS

A. Gómez Eguíluz, J.P. Rodríguez-Gómez, J. R. Martínez-de Dios, A. Ollero

IROS 2020, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). Pp. 5978-5985

This paper presents an bio-inspired event-based perception scheme for agile aerial robot maneuvering. It tries to mimic birds, which perform purposeful maneuvers by closing the separation in the retinal image (w.r.t. the goal) to follow time-to-contact trajectories. The proposed approach is based on event cameras, also called artificial retinas, which provide fast response and robustness against motion blur and lighting conditions. Our scheme guides the robot by only adjusting the position of features extracted in the event image plane to their goal positions at a predefined time using smooth timeto-contact trajectories. The proposed scheme is robust, efficient and can be added on top of commonly-used aerial robot velocity controllers. It has been validated on-board a UAV with real-time computation in low-cost hardware during sets of experiments with different descent maneuvers and lighting conditions.

@article{eguiluzasynchronous, title={Asynchronous Event-based Line Tracking for Time-to-Contact Maneuvers in UAS}, author={Egu{\i}luz, A G{\'o}mez and Rodr{\i}guez-G{\'o}mez, JP and Mart{\i}nez-de Dios, JR and Ollero, A} }

Adaptive Nonlinear Control For Perching of a Bioinspired Ornithopter

F. J. Maldonado, J. Á . Acosta, J. Tormo-Barbero, P. Grau, M. M. Guzmán and A. Ollero

IROS 2020, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

This work presents a model-free nonlinear controller for an ornithopter prototype with bioinspired wings and tail. The size and power requirements have been thought to allocate a customized autopilot on board. To assess the functionality and performance of the full mechatronic design, a controller has been designed and implemented to execute a prescribed perching 2D trajectory. Although functional, its 'handmade' nature forces many imperfections that cause uncertainty that hinder its control. Therefore, the controller is based on adaptive backstepping and does not require any knowledge of the aerodynamics. The controller is able to follow a given reference in flight path angle by actuating only on the tail deflection. A novel space-dependent nonlinear guidance law is also provided to prescribe the perching trajectory. Mechatronics, guidance and control system performance is validated by conducting indoor flight tests.

@inproceedings{maldonado2020adaptive, title={Adaptive nonlinear control for perching of a bioinspired ornithopter}, author={Maldonado, FJ and Acosta, JA and Tormo-Barbero, J and Grau, P and Guzman, MM and Ollero, A}, booktitle={2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)}, pages={1385--1390}, year={2020}, organization={IEEE} }

Asynchronous Event-based Line Tracking for Time-to-Contact Maneuvers in UAS

A. Gomez Eguíluz, J.P. Rodríguez-Gomez, J.R. Martínez-de Dios and A. Ollero

IROS 2020, pp. 5978-5985

The development of automatic perception systems and techniques for bio-inspired flapping-wing robots is severely hampered by the high technical complexity of these platforms and the installation of onboard sensors and electronics. Besides, flapping-wing robot perception suffers from high vibration levels and abrupt movements during flight, which cause motion blur and strong changes in lighting conditions. This paper presents a perception dataset for bird-scale flapping-wing robots as a tool to help alleviate the aforementioned problems. The presented data include measurements from onboard sensors widely used in aerial robotics and suitable to deal with the perception challenges of flapping-wing robots, such as an event camera, a conventional camera, and two Inertial Measurement Units (IMUs), as well as ground truth measurements from a laser tracker or a motion capture system. A total of 21 datasets of different types of flights were collected in three different scenarios (one indoor and two outdoor). To the best of the authors' knowledge this is the first dataset for flapping-wing robot perception.

@article{eguiluzasynchronous, title={Asynchronous Event-based Line Tracking for Time-to-Contact Maneuvers in UAS}, author={Egu{\i}luz, A G{\'o}mez and Rodr{\i}guez-G{\'o}mez, JP and Mart{\i}nez-de Dios, JR and Ollero, A} }

Audio-Based Aircraft Detection System for Safe RPAS BVLOS Operations

J. Mariscal-Harana, V. Alarcón, F. González, J. J. Calvente, F. J. Pérez-Grau, A. Viguria, and A. Ollero

Electronics, Vol. 9, iss. 12, p. 2076

For the Remotely Piloted Aircraft Systems (RPAS) market to continue its current growth rate, cost-effective ‘Detect and Avoid’ systems that enable safe beyond visual line of sight (BVLOS) operations are critical. We propose an audio-based ‘Detect and Avoid’ system, composed of microphones and an embedded computer, which performs real-time inferences using a sound event detection (SED) deep learning model. Two state-of-the-art SED models, YAMNet and VGGish, are fine-tuned using our dataset of aircraft sounds and their performances are compared for a wide range of configurations. YAMNet, whose MobileNet architecture is designed for embedded applications, outperformed VGGish both in terms of aircraft detection and computational performance. YAMNet’s optimal configuration, with >70% true positive rate and precision, results from combining data augmentation and undersampling with the highest available inference frequency (i.e., 10 Hz). While our proposed ‘Detect and Avoid’ system already allows the detection of small aircraft from sound in real time, additional testing using multiple aircraft types is required. Finally, a larger training dataset, sensor fusion, or remote computations on cloud-based services could further improve system performance.

@article{mariscal2020audio, title={Audio-Based Aircraft Detection System for Safe RPAS BVLOS Operations}, author={Mariscal-Harana, Jorge and Alarc{\'o}n, V{\'\i}ctor and Gonz{\'a}lez, Fidel and Calvente, Juan Jos{\'e} and P{\'e}rez-Grau, Francisco Javier and Viguria, Antidio and Ollero, An{\'\i}bal}, journal={Electronics}, volume={9}, number={12}, pages={2076}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

A 4d trajectory follower based on the “carrot chasing” algorithm for uas within the u-space context

H. Perez-Leon, J. J. Acevedo, I. Maza, and A. Ollero

ICUAS 2020, Pp. 1860–1867.

This paper is focused on the trajectory following problem for unmanned aerial systems in the context of the U-space and the 4D trajectory based operations (4D-TBO). A trajectory follower implementation for UASs, based on the carrot chasing algorithm, is presented with the twofold objective of minimizing the mean normal distance to the user-defined path and the mean difference with respect to the defined arrival times through the whole flight. The paper presents simulated and real flights carried out under the ROS (Robotic Operating System) framework that allow us to compare and analyze the behavior of the proposed solution for different policies.

@inproceedings{perez20204d, title={A 4D trajectory follower based on the’Carrot chasing’algorithm for UAS within the U-space context}, author={Perez-Leon, Hector and Acevedo, Jose Joaquin and Maza, Ivan and Ollero, Anibal}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={1860--1867}, year={2020}, organization={IEEE} }

Energy-based cooperative control for landing fixed-wing uavs on mobile platforms under communication delays

T. Muskardin, A. Coelho, E. R. Della Noce, A. Ollero, and K. Kondak

IEEE Robotics & Automation Letters, vol. 5, iss. 4, p. 5081–5088, 2020

The landing of a fixed-wing UAV on top of a mobile landing platform requires a cooperative control strategy, which is based on relative motion estimates. These estimates typically suffer from communication or processing time delays, which can render an otherwise stable control system unstable. Such effects must therefore be considered during the design process of the cooperative landing controller. In this letter the application of a model-free passivity-based stabilizing controller is proposed, which is based on the monitoring of energy flows in the system, and actively dissipating any given active energy by means of adaptive damping elements. In doing so, overall system passivity and consequently stability is enforced in a straightforward and easy to implement way. The proposed control system is validated in numerical simulations for round trip delays of up to 4 seconds.

@article{muskardin2020energy, title={Energy-based cooperative control for landing fixed-wing uavs on mobile platforms under communication delays}, author={Muskardin, Tin and Coelho, Andre and Della Noce, Eduardo Rodrigues and Ollero, Anibal and Kondak, Konstantin}, journal={IEEE Robotics and Automation Letters}, volume={5}, number={4}, pages={5081--5088}, year={2020}, publisher={IEEE} }

Autonomous Planning for Multiple Aerial Cinematographers

E. L. Caraballo, A. Montes-Romero, J. M. Díaz-Báñez, J. Capitán, A. Torres-González and A. Ollero

IROS 2020,

This paper proposes a planning algorithm for autonomous media production with multiple Unmanned Aerial Vehicles (UAVs) in outdoor events. Given filming tasks specified by a media Director, we formulate an optimization problem to maximize the filming time considering battery constraints. As we conjecture that the problem is NP-hard, we consider a discretization version, and propose a graph-based algorithm that can find an optimal solution of the discrete problem for a single UAV in polynomial time. Then, a greedy strategy is applied to solve the problem sequentially for multiple UAVs. We demonstrate that our algorithm is efficient for small teams (3-5 UAVs) and that its performance is close to the optimum. We showcase our system in field experiments carrying out actual media production in an outdoor scenario with multiple UAVs.

@article{caraballo2020autonomous, title={Autonomous planning for multiple aerial cinematographers}, author={Caraballo, Luis-Evaristo and Montes-Romero, Angel and D{\'\i}az-B{\'a}{\~n}ez, Jos{\'e}-Miguel and Capit{\'a}n, Jes{\'u}s and Torres-Gonz{\'a}lez, Arturo and Ollero, An{\'\i}bal}, journal={arXiv preprint arXiv:2005.07237}, year={2020} }

A bio-inspired manipulator with claw prototype for winged aerial robots: Benchmark for design and control

D. Feliu-Talegon,J. Á. Acosta, A. Suarez and A. Ollero

Applied Sciences, vol. 10, no. 18, pp. 6516

Nature exhibits many examples of birds, insects and flying mammals with flapping wings and limbs offering some functionalities. Although in robotics, there are some examples of flying robots with wings, it has not been yet a goal to add to them some manipulation-like capabilities, similar to ones that are exhibited on birds. The flying robot (ornithopter) that we propose improves the existent aerial manipulators based on multirotor platforms in terms of longer flight duration of missions and safety in proximity to humans. Moreover, the manipulation capabilities allows them to perch in inaccessible places and perform some tasks with the body perched. This work presents a first prototype of lightweight manipulator to be mounted to an ornithopter and a new control methodology to balance them while they are perched and following a desired path with the end effector imitating their beaks. This allows for several possible applications, such as contact inspection following a path with an ultrasonic sensor mounted in the end effector. The manipulator prototype imitates birds with two-link legs and a body link with an actuated limb, where the links are all active except for the first passive one with a grabbing mechanism in its base, imitating a claw. Unlike standard manipulators, the lightweight requirement limits the frame size and makes it necessary to use micro motors. Successful experimental results with this prototype are reporte

@article{feliu2020bio, title={A Bio-Inspired Manipulator with Claw Prototype for Winged Aerial Robots: Benchmark for Design and Control}, author={Feliu-Talegon, Daniel and Acosta, Jos{\'e} {\'A}ngel and Suarez, Alejandro and Ollero, Anibal}, journal={Applied Sciences}, volume={10}, number={18}, pages={6516}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

Asynchronous event-based clustering and tracking for intrusion monitoring in UAS

J.P. Rodríguez-Gomez, A. Gómez Eguíluz, J.R. Martínez-de Dios, A. Ollero

ICRA2020, pp. 8518-8524

Automatic surveillance and monitoring using Unmanned Aerial Systems (UAS) require the development of perception systems that robustly work under different illumination conditions. Event cameras are neuromorphic sensors that capture the illumination changes in the scene with very low latency and high dynamic range. Although recent advances in eventbased vision have explored the use of event cameras onboard UAS, most techniques group events in frames and, therefore, do not fully exploit the sequential and asynchronous nature of the event stream. This paper proposes a fully asynchronous scheme for intruder monitoring using UAS. It employs efficient event clustering and feature tracking modules and includes a sampling mechanism to cope with the computational cost of event-by-event processing adapting to on-board hardware computational constraints. The proposed scheme was tested on a real multirotor in challenging scenarios showing significant accuracy and robustness to lighting conditions.

@INPROCEEDINGS{, author={Rodríguez-Gomez, J.P. and Eguíluz, A. Gómez and Martínez-de Dios, J.R. and Ollero, A.}, booktitle={2020 IEEE International Conference on Robotics and Automation (ICRA)}, title={Asynchronous event-based clustering and tracking for intrusion monitoring in UAS}, year={2020}, volume={}, number={}, pages={8518-8524}, doi={10.1109/ICRA40945.2020.9197341}}

Aerial Manipulator with Rolling Base for Inspection of Pipe Arrays

Alejandro Suarez, Alvaro Caballero, Ambar Garofano, Pedro J. Sanchez-Cuevas, Guillermo Heredia, and Anibal Ollero

IEEE Access, vol. 8, pp. 162516-162532, 2020

This paper considers the inspection by contact of long arrays of pipe structures in hard-to-reach places, typical of chemical plants or oil and gas industries, presenting the design of a hybrid rolling-aerial platform capable of landing and moving along the pipes without wasting energy in the propellers during the inspection. The presented robot overcomes the limitation in terms of operation time and positioning accuracy in the application of flying robots to industrial inspection and maintenance tasks. The robot consists of a hexarotor platform integrating a rolling base with velocity and direction control, and a 5-DOF (degree of freedom) robotic arm supported by a 1-DOF linear guide system that facilitates the deployment of the arm in the array of pipes to inspect their contour once the platform has landed. Given a set of points to be inspected in different arrays of pipes, the path of the multirotor and the rolling platform is planned with a hybrid RRT* (Rapidly exploring Random Tree) based algorithm that minimizes the energy consumption. The performance of the system is evaluated in an illustrative outdoor scenario with two arrays of pipes, using a laser tracking system to measure the position of the robot from the ground control station.

@article{suarez2020aerial, title={Aerial Manipulator With Rolling Base for Inspection of Pipe Arrays}, author={Suarez, Alejandro and Caballero, Alvaro and Garofano, Ambar and Sanchez-Cuevas, Pedro J and Heredia, Guillermo and Ollero, Anibal}, journal={IEEE Access}, volume={8}, pages={162516--162532}, year={2020}, publisher={IEEE} }

A 4D Trajectory Follower Based on the 'Carrot Chasing' Algorithm for UAS within the U-Space Context

H. Pérez-León, J.J. Acevedo, I. Maza and A. Ollero

ICUAS, Proceedings of the ICUAS 2020, pp 1860-1867, September 2020

This paper is focused on the trajectory following problem for unmanned aerial systems in the context of the U-space and the 4D trajectory based operations (4D-TBO). A trajectory follower implementation for UASs, based on the carrot chasing algorithm, is presented with the twofold objective of minimizing the mean normal distance to the user-defined path and the mean difference with respect to the defined arrival times through the whole flight. The paper presents simulated and real flights carried out under the ROS (Robotic Operating System) framework that allow us to compare and analyze the behavior of the proposed solution for different policies.

@inproceedings{perez20204d, title={A 4D trajectory follower based on the’Carrot chasing’algorithm for UAS within the U-space context}, author={Perez-Leon, Hector and Acevedo, Jose Joaquin and Maza, Ivan and Ollero, Anibal}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={1860--1867}, year={2020}, organization={IEEE} }

Collision Avoidance of SDRE Controller using Artificial Potential Field Method: Application to Aerial Robotics

S.R. Nekoo, J.A. Acosta, and A. Ollero

ICUAS, Proceedings of the ICUAS 2020, pp 551-556, September 2020

This work presents the problem of collision avoidance of the state-dependent Riccati equation (SDRE) controller using the artificial potential field (APF) method. Two themes were selected to illustrate the importance of the problem, collision avoidance between the end-effectors of serial links manipulators and unmanned aerial vehicles (UAVs), working in a shared workspace. The structure of the SDRE has a good potential to accommodate APF formulation in the weighting matrix of states. The distance between the end-effectors or the center-of-mass (CoM) of UAVs is penalized to autonomously guide the robots in a collision-free trajectory while they are working in a common environment. If the robots get close to each other, the weighting matrix of states increases, which actuates the systems to escape from a possible collision. Several simulation studies were done to investigate the proposed controller and the effect of collision avoidance function. It was found that the higher power of the collision avoidance function handles the threat of the impact better. The distance between robots was considered as an index to assess the performance of the controller which showed successful results in the simulations.

@inproceedings{nekoo2020collision, title={Collision Avoidance of SDRE Controller using Artificial Potential Field Method: Application to Aerial Robotics}, author={Nekoo, SR and Acosta, J{\'A} and Ollero, A}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={551--556}, year={2020}, organization={IEEE} }

Autonomous Drone with Ability to Track and Capture an Aerial Target

M. Garcia, R. Caballero, F. González, A. Viguria and A. Ollero

ICUAS, Proceedings of the ICUAS 2020, pp 32-40, September 2020

This article presents an autonomous aerial system developed for the first challenge of Mohamed Bin Zayed International Robotics Competition (MBZIRC) 2020, consisting of the autonomous interception of an aerial target flying on a variable trajectory and speed, and also bursting several balloons randomly placed over a certain area, also fully autonomous. This work presents a prototype of a capture aerial robot designed specifically for the scenario under consideration, with the aim of integrating the necessary equipment to autonomously detect, track and capture the target drone. Both the hardware architecture and the software that allows to perform this fully autonomous complex mission are described in the paper, as well as the tools used for the integration and execution of the different functional modules. Apart from that, the Guidance, Navigation and Control (GNC) algorithms implemented for the tracking of the target are also explained. Finally the system is tested in a simulation environment and also validated with real experiments, which most interesting results are presented.

@inproceedings{garcia2020autonomous, title={Autonomous drone with ability to track and capture an aerial target}, author={Garc{\'\i}a, Manuel and Caballero, Rafael and Gonz{\'a}lez, Fidel and Viguria, Antidio and Ollero, An{\'\i}bal}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={32--40}, year={2020}, organization={IEEE} }

Effects of Unsteady Aerodynamics on Gliding Stability of a Bio-Inspired UAV

E. Sanchez-Laulhe, R. Fernandez-Feria, J. Á. Acosta and A. Ollero

ICUAS, Proceedings of the ICUAS 2020, pp. 1596-1604, September 2020

This paper presents a longitudinal dynamic model to be used in the control of new animal flight bio-inspired UAVs designed to achieve better performance in terms of energy consumption, flight endurance, and safety when comparing with conventional multi-rotors. In order to control these UAVs, simple models are needed to predict its dynamics in real time by the on-board autopilots, which are very limited in term of computational resources. To that end, the model presented considers transitional aerodynamic unsteady effects, which change significantly the evolution of the system. The physical relevance of these aerodynamic unsteady terms in gliding flight is validated by comparing with results when these new terms are neglected. Finally, an analysis of dynamic stability is proposed in order to characterize the transitional phases of gliding flight.

@INPROCEEDINGS{9213965, author={Sanchez-Laulhe, Ernesto and Fernandez-Feria, Ramon and Acosta, José Ángel and Ollero, Anibal}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, title={Effects of Unsteady Aerodynamics on Gliding Stability of a Bio-Inspired UAV}, year={2020}, volume={}, number={}, pages={1596-1604}, doi={10.1109/ICUAS48674.2020.9213965}}

A Geometrical Approach Based on 4D Grids for Conflict Management of Multiple UAVs Operating in U-Space

J.J. Acevedo, C. Capitán, J. Capitan, A. Rodríguez Castaño and A.Ollero

ICUAS, Proceedings of the ICUAS 2020, pp 261-268 , September 2020

This paper addresses the problem of conflict management from the tactical point of view for multiple UAVs operating in a common U-space. The proposed solution is based on the representation of the trajectories into a 4D grid to optimize the conflict searching tool and an iterative geometric approach to resolve the conflicts, splitting the multi-conflict problem into several simpler sub-problems, and provide an alternative set of trajectories free of conflicts. The method is assessed through two different metrics: the processing time to find the solution and the deviation from initial trajectories; getting a significantly better performance in comparison with other traditional method.

@inproceedings{acevedo2020geometrical, title={A Geometrical Approach based on 4D Grids for Conflict Management of Multiple UAVs operating in U-space}, author={Acevedo, Jos{\'e} Joaqu{\'\i}n and Capit{\'a}n, Carlos and Capitiin, Jesirs and Casta{\~n}o, Angel R and Ollero, An{\'\i}bal}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={263--270}, year={2020}, organization={IEEE} }

POSITRON: Lightweight Active Positioning Compilant Joints Robotic Arm in Power Lines Inspection

M. Perez-Jimenez, M. A. Montes-Grova, P. Ramon-Soria, B.C. Arrue and A. Ollero

ICUAS, Proceedings of ICUAS 2020, PP 729-736

This paper presents the design and implementation of a compliant lightweight manipulator with an special end-effector to attach to power-lines. The manipulator can be mounted in aerial robots allowing to compute its relative position from the contact point. The purpose of this device is to obtain an estimate of the UAV's position to close the control loop. Controlling the position of the UAV close to the power-line enables a new wide range of inspection and maintenance tasks in this infrastructure. The article describes the model of the positioning tool and the sensors it uses to provide the necessary information for the UAV controller. It can be built using additive manufacturing techniques and its components are low-cost and available in common robotic stores so anyone can reproduce and use it. Validation experiments have been carried out in an Optitrack system as ground-truth.

@inproceedings{perez2020positron, title={POSITRON: Lightweight active positioning compliant joints robotic arm in power lines inspection}, author={Perez-Jimenez, M and Montes-Grova, MA and Ramon-Soria, P and Arrue, BC and Ollero, A}, booktitle={2020 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={729--736}, year={2020}, organization={IEEE} }

Procedures for the Integration of Drones into the Airspace Based on U-Space Services

Víctor Alarcón, Manuel García, Francisco Alarcón, Antidio Viguria, Ángel Martínez, Dominik Janisch, José Joaquín Acevedo, Ivan Maza, and Anibal Ollero

Aerospace, 7(9), 1-18.1 September 2020

A safe integration of drones into the airspace is fundamental to unblock all the potential of drone applications. U-space is the European approach to the integration of a large number of drones into the airspace, especially at Very Low Level (VLL). Then, this research work is focused on the demonstration of technologies and procedures that will facilitate a safe integration of drones into the airspace using U-space, and was developed in the framework of SESAR SAFEDRONE project. The presented demonstrations cover three important aspects: designs of procedures related to No-Fly Zones, ensure separation with manned aircraft, and autonomous non-cooperative detect and avoid (DAA) technologies and its integration in U-space. This work summarizes the main results after analysing a large number of experimental flights in order to gain practical experience that will help in the design of future implementations of U-space services and procedures. An important number of conclusions have been obtained from the experimental results. Especially significant are the results related to No-Fly Zones where specific recommendations about procedures to exit and avoiding No-Fly Zones are presented. Also, it has been concluded that the use of surveillance information of manned aircrafts will allow a more efficient use of the airspace while maintaining a proper safety level, avoiding the creation of large geofence areas. Finally, the demonstration flights have shown the technical feasibility of integrating advanced functionalities in small drones to autonomously detect and avoid obstacles and its integration with U-space services.

@article{alarcon2020procedures, title={Procedures for the Integration of Drones into the Airspace Based on U-Space Services}, author={Alarc{\'o}n, V{\'\i}ctor and Garc{\'\i}a, Manuel and Alarc{\'o}n, Francisco and Viguria, Antidio and Mart{\'\i}nez, {\'A}ngel and Janisch, Dominik and Acevedo, Jos{\'e} Joaqu{\'\i}n and Maza, Ivan and Ollero, An{\'\i}bal}, journal={Aerospace}, volume={7}, number={9}, pages={128}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

An aerodynamic extension for motion planning with dynamics awareness in aerial long-reach manipulators

Alvaro Caballero, Pedro J. Sanchez-Cuevas, Manuel Bejar, Guillermo Heredia, Miguel A. Trujillo, Anibal Ollero

IJ Aerospace Engineering, vol. 2020, Article ID 6348035, 17 pages, 2020.

This paper presents a novel method for motion planning of aerial long-reach manipulators that considers the aerodynamic effects generated by close surfaces in the trajectory generation process. The aerial manipulation system consists of a multi-rotor equipped with a robotic long-reach arm that enables multi-directional inspection and also increases considerably the safety distance between the rotors and the inspected elements. Since these systems operate in the proximity of elements that can modify significantly the rotors' airflow, the inclusion of Aerodynamics Awareness within the motion planning process is required to ensure robust obstacle avoidance. To this end, a proper characterisation of the aerodynamic effects based on both theoretical and experimental considerations has been derived. This characterisation is taken into account in the trajectory generation process to discard states whose associated aerodynamic phenomena are not well compensated by the system controller and to explore alternatives that lead to the most efficient trajectories within the area of safe operation. Moreover, the motion planner also stands out for three other relevant features: the joint consideration of the multi-rotor and the robotic long-reach arm, the generation of efficient trajectories in terms of energy consumption, and the Dynamics Awareness of the strong coupling between the aerial platform and the robotic arm. The resulting motion planner has been successfully tested in a simulated environment that faithfully reflects an application scenario strongly affected by aerodynamic effects: the inspection of bridges to find potential cracks in the surface of pillars.

@article{caballero2020aerodynamic, title={An Aerodynamic Extension for Motion Planning with Dynamics Awareness in Aerial Long-Reach Manipulators}, author={Caballero, Alvaro and Sanchez-Cuevas, Pedro J and Bejar, Manuel and Heredia, Guillermo and Trujillo, Miguel A and Ollero, Anibal}, journal={International Journal of Aerospace Engineering}, volume={2020}, year={2020}, publisher={Hindawi} }

Unmanned aerial vehicle abstraction layer: An abstraction layer to operate unmanned aerial vehicles

Fran Real, Arturo Torres-González, Pablo Ramón-Soria, Jesús Capitán, Aníbal Ollero

International Journal of Advanced Robotic Systems (IJARS), Volume: 17 issue: 4, 2020.

This article presents a software layer to abstract users of unmanned aerial vehicles from the specific hardware of the platform and the autopilot interfaces. The main objective of our unmanned aerial vehicle abstraction layer (UAL) is to simplify the development and testing of higher-level algorithms in aerial robotics by trying to standardize and simplify the interfaces with the unmanned aerial vehicles. Unmanned aerial vehicle abstraction layer supports operation with PX4 and DJI autopilots (among others), which are current leading manufacturers. Besides, unmanned aerial vehicle abstraction layer can work seamlessly with simulated or real platforms and it provides calls to issue standard commands such as taking off, landing or pose, and velocity controls. Even though unmanned aerial vehicle abstraction layer is under continuous development, a stable version is available for public use. We showcase the use of unmanned aerial vehicle abstraction layer with a set of applications coming from several European research projects, where different academic and industrial entities have adopted unmanned aerial vehicle abstraction layer as a common development framework.

@article{realijars2020, author = {Fran Real and Arturo Torres-González and Pablo Ramón-Soria and Jesús Capitán and Aníbal Ollero}, title ={Unmanned aerial vehicle abstraction layer: An abstraction layer to operate unmanned aerial vehicles}, journal = {International Journal of Advanced Robotic Systems}, volume = {17}, number = {4}, pages = {1729881420925011}, year = {2020}, doi = {10.1177/1729881420925011}, eprint = {https://doi.org/10.1177/1729881420925011} }

Winged Aerial Manipulation Robot with Dual Arm and Tail

A. Suarez, P. Grau, G. Heredia and A. Ollero

APPLIED SCIENCES, PP: 20

This paper presents the design and development of a winged aerial robot with bimanual manipulation capabilities, motivated by the current limitations of aerial manipulators based on multirotor platforms in terms of safety and range/endurance. Since the combination of gliding and flapping wings is more energy efficient in forward flight, we propose a new morphology that exploits this feature and allows the realization of dexterous manipulation tasks once the aerial robot has landed or perched. The paper describes the design, development, and aerodynamic analysis of this winged aerial manipulation robot (WAMR), consisting of a small-scale dual arm used for manipulating and as a morphing wing. The arms, fuselage, and tail are covered by a nylon cloth that acts as a cap, similar to a kite. The three joints of the arms (shoulder yaw and pitch, elbow pitch) can be used to control the surface area and orientation and thus the aerodynamic wrenches induced over the cloth. The proposed concept design is extended to a flapping-wing aerial robot built with smart servo actuators and a similar frame structure, allowing the generation of different flapping patterns exploiting the embedded servo controller. Experimental and simulation results carried out with these two prototypes evaluate the manipulation capability and the possibility of gliding and flying

@article{suarez2020winged, title={Winged aerial manipulation robot with dual arm and tail}, author={Suarez, Alejandro and Grau, Pedro and Heredia, Guillermo and Ollero, Anibal}, journal={Applied Sciences}, volume={10}, number={14}, pages={4783}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

Fully-Actuated Aerial Manipulator for Infrastructure Contact Inspection: Design, Modeling, Localization, and Control

P. J. Sanchez-Cuevas, A. Gonzalez-Morgado, N. Cortes, Diego B. Gayango, A. E. Jimenez-Cano, A. Ollero, and G. Heredia

Sensors, 2020, 20(17), 4708

This paper presents the design, modeling and control of a fully actuated aerial robot for infrastructure contact inspection as well as its localization system. Health assessment of transport infrastructure involves measurements with sensors in contact with the bridge and tunnel surfaces and the installation of monitoring sensing devices at specific points. The design of the aerial robot presented in the paper includes a 3DoF lightweight arm with a sensorized passive joint which can measure the contact force to regulate the force applied with the sensor on the structure. The aerial platform has been designed with tilted propellers to be fully actuated, achieving independent attitude and position control. It also mounts a “docking gear” to establish full contact with the infrastructure during the inspection, minimizing the measurement errors derived from the motion of the aerial platform and allowing full contact with the surface regardless of its condition (smooth, rough, ...). The localization system of the aerial robot uses multi-sensor fusion of the measurements of a topographic laser sensor on the ground and a tracking camera and inertial sensors on-board the aerial robot, to be able to fly under the bridge deck or close to the bridge pillars where GNSS satellite signals are not available. The paper also presents the modeling and control of the aerial robot. Validation experiments of the localization system and the control system, and with the aerial robot inspecting a real bridge are also included.

@Article{sanchezsensors2020, AUTHOR = {Sanchez-Cuevas, Pedro J. and Gonzalez-Morgado, Antonio and Cortes, Nicolas and Gayango, Diego B. and Jimenez-Cano, Antonio E. and Ollero, Aníbal and Heredia, Guillermo}, TITLE = {Fully-Actuated Aerial Manipulator for Infrastructure Contact Inspection: Design, Modeling, Localization, and Control}, JOURNAL = {Sensors}, VOLUME = {20}, YEAR = {2020}, NUMBER = {17}, ARTICLE-NUMBER = {4708}, URL = {https://www.mdpi.com/1424-8220/20/17/4708}, ISSN = {1424-8220}, DOI = {10.3390/s20174708} }

An Efficient Distributed Area Division Method for Cooperative Monitoring Applications with Multiple UAVs

J. J. Acevedo, I. Maza, A. Ollero and B. C. Arrue

Sensors, Vol 20(12), pp. 1-17

This article addresses the area division problem in a distributed manner providing a solution for cooperative monitoring missions with multiple UAVs. Starting from a sub-optimal area division, a distributed online algorithm is presented to accelerate the convergence of the system to the optimal solution, following a frequency-based approach. Based on the “coordination variables” concept and on a strict neighborhood relation to share information (left, right, above and below neighbors), this technique defines a distributed division protocol to determine coherently the size and shape of the sub-area assigned to each UAV. Theoretically, the convergence time of the proposed solution depends linearly on the number of UAVs. Validation results, comparing the proposed approach with other distributed techniques, are provided to evaluate and analyze its performance following a convergence time criterion.

@article{acevedo2020efficient, title={An Efficient Distributed Area Division Method for Cooperative Monitoring Applications with Multiple UAVs}, author={Acevedo, Jos{\'e} Joaqu{\'\i}n and Maza, Ivan and Ollero, Anibal and Arrue, Bego{\~n}a C}, journal={Sensors}, volume={20}, number={12}, pages={3448}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

Explicit Aerodynamic Model Characterization of a Multirotor Unmanned Aerial Vehicle in Quasi-Steady Flight

C. Rodríguez de Cos and J. A. Acosta

Journal of Computational and Nonlinear Dynamics, Aug 2020, 15(8): 081005 (9 pages); 10.1115/1.4047388

In the last years, the research on unmanned aerial systems (UASs) has shown a marked growth and the models to simulate UASs have been deeply studied. Although onboard controller algorithms have increased their complexity, most of them still rely on simplistic models. In essence, aerodynamic forces/torques are generally considered either insignificant compared to propulsion and inertial forces or acceptably modeled with constant aerodynamic coefficients estimated in a particular flight regime. However, the increase of power in the onboard computers allows to make controller algorithms more complex, and therefore, to increase the total performance of the UAS. In this regard, this work provides an explicit aerodynamic model for multirotor UAS that, unlike most of the current models, does not need iterations to be adjusted to the flight conditions at a higher computational cost. This explicit nature makes it an excellent choice for being implemented in onboard computers, thus covering a broad range of applications, from controller design to numerical analysis (e.g., the capture nonlinear phenomena like bifurcations). To obtain this accurate explicit mathematical aerodynamic model, a thorough analysis of a batch of simulations is carried out. In these simulations, the aerodynamic forces and torques are estimated using computer fluid dynamics (CFD), and the propulsive effects are taken into account via blade element momentum theory (BEMT). A study of its implementation for different regimes and platforms is also provided, as well as some potential applications of the solution, like robust control strategies or machine learning.

@article{rodriguez2020explicit, title={Explicit Aerodynamic Model Characterization of a Multirotor Unmanned Aerial Vehicle in Quasi-Steady Flight}, author={Rodr{\'\i}guez de Cos, Carlos and Acosta, Jos{\'e} {\'A}ngel}, journal={Journal of Computational and Nonlinear Dynamics}, volume={15}, number={8}, year={2020}, publisher={American Society of Mechanical Engineers Digital Collection} }

Design, modeling, and control of an aerial manipulator for placement and retrieval of sensors in the environment

S. Hamaza, I. Georgilas, G. Heredia, A. Ollero, and T. Richardson,

Journal of field robotics, Vol. 37, iss. 7, p. 1224–1245

On-site inspection of large-scale infrastructure often involves high risks for the operators and high insurance costs. Despite several safety measures already in place to avoid accidents, an increasing concern has brought the need to remotely monitor hard-to-reach locations, for which the use of aerial robots able to interact with the environment has arisen. In this paper a novel approach to aerial manipulation is presented, where a compact manipulator with a single degree-of-freedom is tailored for the placement and retrieval of sensors in the environment. The proposed design integrates on-board sensing, a high-performance force controller on the manipulator, and a thrust-to-force mapping on the flight controller. Experimental results demonstrate the high reliability achieved during both placement and retrieval tasks on flat surfaces (e.g., a bridge wall) and cylindrical surfaces (e.g., tree trunks). A total number of 89 flight experiments were carried out to demonstrate the robustness and potential of the compact, bespoke aerial design.

@article{hamaza2020design, title={Design, modeling, and control of an aerial manipulator for placement and retrieval of sensors in the environment}, author={Hamaza, Salua and Georgilas, Ioannis and Heredia, Guillermo and Ollero, An{\'\i}bal and Richardson, Thomas}, journal={Journal of Field Robotics}, volume={37}, number={7}, pages={1224--1245}, year={2020}, publisher={Wiley Online Library} }

A Linearized Model for an Ornithopter in Gliding Flight: Experiments and Simulations

Lopez-Lopez, R., Perez-Sanchez, V., Ramon-Soria, P., Martin-Alcantara, A., Fernandez-Feria, R., Arrue, B. C., & Ollero, A

ICRA 2020,

This work studies the accuracy of a simple but effective analytical model for a flapping-wings UAV in longitudinal gliding flight configuration comparing it with experimental results of a real ornithopter. The aerodynamic forces are modeled following the linearized potential theory for a flat plate in gliding configuration, extended to flapping-wing episodes modeled also by the (now unsteady) linear potential theory, which are studied numerically. In the gliding configuration, the model reaches a steady-state descent at given terminal velocity and pitching and gliding angles, governed by the wings and tail position. In the flapping-wing configuration, it is noticed that the vehicle can increase its flight velocity and perform climbing episodes. A realistic simulation tool based on Unreal Engine 4 was developed to visualize the effect of the tail position and flapping frequencies and amplitudes on the ornithopter flight in real time. The paper also includes the experimental validation of the gliding flight and the data has been released for the community.

@inproceedings{lopez2020linearized, title={A Linearized Model for an Ornithopter in Gliding Flight: Experiments and Simulations}, author={Lopez-Lopez, R and Perez-Sanchez, V and Ramon-Soria, P and Martin-Alcantara, A and Fernandez-Feria, R and Arrue, Bego{\~n}a C and Ollero, An{\'\i}bal}, booktitle={2020 IEEE International Conference on Robotics and Automation (ICRA)}, pages={7008--7014}, year={2020}, organization={IEEE} }

Compliant Bimanual Aerial Manipulation: Standard and Long Reach Configurations

A. Suarez, F. Real, V. M. Vega, G. Heredia, A. Rodriguez-Castaño, A. Ollero

IEEE Access, vol. 8, pp. 88844-88865, 2020.

The ability of aerial manipulation robots to reach and operate in high altitude workspaces may result of interest in a wide variety of applications and scenarios that nowadays cannot be accessed easily by human operators. Consider for example the installation of sensors in polluted areas, the insulation of leaks in pipe structures, or the corrosion repair in power lines and wind turbines. This paper describes the application of a human-like dual arm aerial manipulator for the inspection of pipe structures, typical of chemical plants, involving the installation and retrieval of sensor devices. The goal is to reduce the time, cost, and risk with respect to conventional solutions conducted by human workers. Two configurations of the aerial robot are considered and compared: the standard, in which the arms are installed at the base of the multirotor, and the long reach configuration in passive pendulum, which extends the effective workspace of the manipulator and increases safety during the operation on flight. The kinematic and dynamic models of both configurations are derived, proposing a unified notation for the equations of motion, and a force/position control scheme that relies on the servo controller and the mechanical joint compliance. The paper also describes a simulation framework used for validating the execution of the aerial manipulation task before the realization of the real experiments, which contributes to reducing the probability of failure. The potential application of the standard and long reach configurations is evaluated in two sensor installation tasks carried out in an indoor testbed.

@ARTICLE{suarezaccess2020, author={A. {Suarez} and F. {Real} and V. M. {Vega} and G. {Heredia} and A. {Rodriguez-Castaño} and A. {Ollero}}, journal={IEEE Access}, title={Compliant Bimanual Aerial Manipulation: Standard and Long Reach Configurations}, year={2020}, volume={8}, number={}, pages={88844-88865},}

Hecatonquiros: open-source hardware for aerial manipulation applications

M. Perez-Jimenez, P. Ramon-Soria, B. Arrue, and A. Ollero

International journal of advanced robotic systems (IJARS), Vol. 17, iss. 2, p. 1729881420921622

This article presents Hecatonquiros, a complete open-source ecosystem for low cost and lightweight robotic manipulators. It has been released to focus on aerial manipulation applications but can be used in any other robotic application that requires the use of manipulators. The proposed framework provides the control system, a simulation environment, and a set of back ends to allow reusing the algorithms with different hardware setups. Additionally, it is released with a set of tools to ease its usage and various examples to teach the users. Several manipulators models and end-effectors are available for the users to adapt to their different requirements. All the hardware is designed to be three-dimensional printed and its components are low cost and available in common robotic stores, so anyone can reproduce and use them. The software is available in the GitHub repository https://github.com/Bardo91/hecatonquiros.

@article{perez2020hecatonquiros, title={Hecatonquiros: Open-source hardware for aerial manipulation applications}, author={Perez-Jimenez, M and Ramon-Soria, P and Arrue, BC and Ollero, A}, journal={International Journal of Advanced Robotic Systems}, volume={17}, number={2}, pages={1729881420921622}, year={2020}, publisher={SAGE Publications Sage UK: London, England} }

Accurate control of Aerial Manipulators outdoors. A reliable and self-coordinated nonlinear approach

J. A. Acosta, C. R. de Cos and A. Ollero

Aerospace Science and Technology, Núm. 105731. 10.1016/j.ast.2020.105731,2020

In recent years, standard Unmanned Aerial Vehicles have been enhanced in order to execute manipulation tasks, named Aerial Manipulators and composed of an Unmanned Aerial Vehicle and a Robot Manipulator. These aerial vehicles are extremely demanding on the flight control system, which needs to keep flight stability while autonomously executing complex tasks. This work continues a recent line of research where a nonlinear control strategy is proposed to comply with outdoor high-level demands to achieve enhanced accuracy and safety. This solution combines nonlinear control subsystems with decentralized priorities but coordinating their relative movements to allow the aerial vehicle to accommodate itself while reaching the manipulator target. The complete strategy is composed of: a passive nonlinear dynamic controller for the UAV, an integral kinematic multi-task controller for the manipulator, and an optimizer to coordinate their relative movements. Theoretical stability results are reported, along with implementation-oriented add-ons and an extensive analysis in realistic simulations. These include aerodynamic effects (e.g. unsteady wind disturbances and rotor propulsion models), collision avoidance, grasping and a comparison with a standard strategy on a benchmark mission complex enough for validation.

@article{acosta2020accurate, title={Accurate control of Aerial Manipulators outdoors. A reliable and self-coordinated nonlinear approach}, author={Acosta, JA and de Cos, CR and Ollero, A}, journal={Aerospace Science and Technology}, volume={99}, pages={105731}, year={2020}, publisher={Elsevier} }

Benchmarks for Aerial Manipulation

A. Suarez, V. M. Vega, M. Fernandez, G. Heredia and A. Ollero

Letters, vol. 5, no. 2, pp. 2650-2657

This letter is devoted to benchmarks for aerial manipulation robots (drones equipped with robotic arms), which are demonstrating their potential to conduct tasks involving physical interactions with objects or the environment in high altitude workspaces, being a cost effective solution for example in inspection and maintenance operations. Thus, the letter deals with different methods and criteria to evaluate and compare the performance of aerial manipulators. This is not an easy task, taking into account the wide variety of designs, morphologies and implementations that can be found in recent works. In order to cope with this problem, this letter analyzes the capabilities and functionalities of several aerial manipulation prototypes (aerial platform + manipulator), identifying a set of relevant metrics and criteria. A number of benchmarks are defined to evaluate the performance of the aerial manipulator in terms of accuracy, execution time, manipulation capability, or impact response. Experimental results carried out with a compliant joint aerial manipulator in test-bench and in indoor-outdoor testbeds illustrate some of the benchmarks.

@article{suarez2020benchmarks, title={Benchmarks for aerial manipulation}, author={Suarez, Alejandro and Vega, Victor M and Fernandez, Manuel and Heredia, Guillermo and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, volume={5}, number={2}, pages={2650--2657}, year={2020}, publisher={IEEE} }

Adaptive Integral Inverse Kinematics Control for Lightweight Compliant Manipulators

R. de Cos, Carlos, Acosta, José Ángel, Ollero Baturone, Anibal

Letters, Vol. 5. Núm. 2. pp. 3468-3474. 10.1109/Lra.2020.2977261, 2020

In this letter, an adaptive to unknown stiffness algorithm for controlling low-cost lightweight compliant manipulators is presented. The proposed strategy is based on the well-known transpose inverse kinematics approach, that has been enhanced with an integral action and an update law for the unknown stiffness of the compliant links, making it valid for soft materials. Moreover, the algorithm is proven to guarantee global task-space regulation of the end effector. This approach has been implemented on a very low-cost robotic manipulator setup (comprised of 4 actuated and 3 flexible links) equipped with a simple Arduino board running at 27 Hz. Notwithstanding, the strategy is capable of achieving a first-order-like response when undisturbed, and recover from overshoots provided by unforeseen impacts, smoothly returning to its nominal behaviour. Moreover, the adaptive capabilities are also used to perform contact tasks, achieving zero steady-state error. The tracking performance and disturbance rejection capabilities are demonstrated with both theoretical and experimental results

@article{de2020adaptive, title={Adaptive integral inverse kinematics control for lightweight compliant manipulators}, author={de Cos, Carlos Rodr{\'\i}guez and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, volume={5}, number={2}, pages={3468--3474}, year={2020}, publisher={IEEE} }

Towards flapping wing robot visual perception: Opportunities and challenges

A. Gómez Eguíluz, J.P. Rodríguez-Gómez, J.L. Paneque; P. Grau, J.R. Martínez de Dios, A. Ollero

RED-UAS, pp: 335-343.

The development of perception systems for bio-inspired flapping wing robots, or ornithopters, is very challenging due to their fast flying maneuvers and the high amount of vibrations and motion blur originated by the wing flapping. Visual sensors have been widely used in aerial robot perception due to their size, weight, and energy consumption capabilities. This paper analyzes the issues and challenges for vision sensors onboard ornithopter robots. Two visual sensors are evaluated: a monocular camera and an event-based camera. First, the pros and cons of integrating different sensors on flapping wing robots are studied. Second, the paper experimentally evaluates the impact of wing flapping frequency on both sensors using experiments with the ornithopter developed in the EU-funded GRIFFIN ERC project.

@INPROCEEDINGS{, author={Eguíluz, A. Gómez and Rodríguez-Gómez, J.P. and Paneque, J.L. and Grau, P. and de Dios, J.R. Martínez and Ollero, A.}, booktitle={2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS)}, title={Towards flapping wing robot visual perception: Opportunities and challenges}, year={2019}, volume={}, number={}, pages={335-343}, doi={10.1109/REDUAS47371.2019.8999674}}

Director Tools for Autonomous Media Production with a Team of Drones

A. Montes-Romero, A. Torres-Gonzalez, J. Capitan, M. Montagnuolo, S. Metta, F. Negro and A. Ollero

APPLIED SCIENCES, Appl. Sci. 2020, 10(4), 1494

This paper proposes a set of director tools for autonomous media production with a team of drones. There is a clear trend toward using drones for media production, and the director is the person in charge of the whole system from a production perspective. Many applications, mainly outdoors, can benefit from the use of multiple drones to achieve multi-view or concurrent shots. However, there is a burden associated with managing all aspects in the system, such as ensuring safety, accounting for drone battery levels, navigating drones, etc. Even though there exist methods for autonomous mission planning with teams of drones, a media director is not necessarily familiar with them and their language. We contribute to close this gap between media crew and autonomous multi-drone systems, allowing the director to focus on the artistic part. In particular, we propose a novel language for cinematography mission description and a procedure to translate those missions into plans that can be executed by autonomous drones. We also present our director’s Dashboard, a graphical tool allowing the director to describe missions for media production easily. Our tools have been integrated into a real team of drones for media production and we show results of example missions.

@article{montes2020director, title={Director tools for autonomous media production with a team of drones}, author={Montes-Romero, Angel and Torres-Gonzalez, Arturo and Capitan, Jesus and Montagnuolo, Maurizio and Metta, Sabino and Negro, Fulvio and Messina, Alberto and Ollero, Anibal}, journal={Applied Sciences}, volume={10}, number={4}, pages={1494}, year={2020}, publisher={Multidisciplinary Digital Publishing Institute} }

2019

Optimized thrust allocation of variable-pitch propellers quadrotor control: A comparative study on flip maneuver

S. R. Nekoo, J. Á. Acosta, A. E. Gomez-Tamm, A. Ollero

2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS), pp. 86-95

Variable-pitch propellers quadrotors possess nonlinear algebraic relations between force/moment of the system and thrust factors of the rotor dynamics. The nonlinear relations make the thrust allocation a challenging topic in overall control design. The state-dependent Riccati equation (SDRE) is selected as a controller for regulation task in fully coupled six degree-of-freedom (DoF) mode. Common designs of the SDRE fail to deliver a fully coupled six-DoF control due to under-actuation. Virtual constraints are used to deliver a position and orientation control in a cascade design. Within the structure of the SDRE, four thrust allocation methods are proposed to compute the thrust factors based on the output results of control system. Practical implementation has been the main reason to generate such allocations. The use of Mean Value Theorem makes it possible to find an implementable formalism for thrust factors since they can be categorized as non-affine systems. Agile and aggressive maneuver is one of the application of the variable-pitch propellers quadrotors; so, flip maneuver is studied to highlight the advantages of the thrust allocation methods. Analysis of the four methods and comparisons are carried out to present the advantages and disadvantages of the proposed structures.

@inproceedings{nekoo2019optimized, title={Optimized thrust allocation of variable-pitch propellers quadrotor control: A comparative study on flip maneuver}, author={Nekoo, SR and Acosta, J{\'A} and Gomez-Tamm, AE and Ollero, A}, booktitle={2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS)}, pages={86--95}, year={2019}, organization={IEEE} }

ROSS-LAN: RObotic Sensing Simulation Scheme for Bioinspired Robotic Bird LANding

J.P. Rodríguez-Gómez, A. Gómez EguíluzJ, J.R. Martínez de Dios, A. Ollero

ROBOT-2019, pp: 49-59

Aerial robotics is evolving towards the design of bioinspired platforms capable of resembling the behavior of birds and insects during flight. The development of perception algorithms for navigation of ornithopters requires sensor data information to evaluate and solve the limitations presented during the flight of these platforms. However, the payload constraints and hardware complexity of ornithopters hamper the sensor data acquisition. This paper focuses on the development of a multi-sensor simulator to retrieve the sensor information captured during the landing maneuvers of ornithopters. The landing trajectory is computed by using a bioinspired trajectory generator relying on tau theory. Further, a dataset of the sensor information records obtained during the simulation of several landing trajectories is publicly available online.

@InProceedings{,author={Rodr{\'i}guez-G{\'o}mez, Juan Pablo and G{\'o}mez Egu{\'i}luz, Augusto and Mart{\'i}nez-de Dios, Jos{\'e} Ramiro and Ollero, An{\'i}bal}, editor={Silva, Manuel F. and Lu{\'i}s Lima, Jos{\'e} and Reis, Lu{\'i}s Paulo and Sanfeliu, Alberto and Tardioli, Danilo}, title={ROSS-LAN: RObotic Sensing Simulation Scheme for Bioinspired Robotic Bird LANding}, booktitle={Robot 2019: Fourth Iberian Robotics Conference}, year={2020}, publisher={Springer International Publishing}, address={Cham}, pages={48--59}, }

Fully coupled six-DoF nonlinear suboptimal control of a quadrotor: Application to variable-pitch rotor design

S. R. Nekoo, J. Á. Acosta, A. Ollero

2019 Iberian robotics conference, pp. 72-83

In this work, a fully coupled six degree-of-freedom (DoF) nonlinear suboptimal control of a variable-pitch quadrotor is studied using a state-dependent Riccati equation (SDRE) controller. The quadrotor control has been widely considered for attitude control; however, the position control is an uncontrollable problem with the common design of the SDRE. Due to the under-actuated nature of a quadrotor, the state-dependent coefficient (SDC) parameterization of state-space representation of a nonlinear system leads to an uncontrollable SDC pair. The control law is divided into two sections of position and attitude control. The position control provides the main thrust. A virtual constraint is regarded to provide stabilization for the quadrotor in attitude control. Two methods were designed for selection of a state vector or in other words, selection of feedback. The first one uses the position and orientation and their derivatives in global coordinate. The second one uses position and orientation in global and their velocities in local coordinate. The dynamics of a variable-pitch propeller quadrotor was imported to the problem and compared with a fixed-pitch propeller system. The simulation of the systems shows that the SDRE is capable of controlling the system with both fixed- and variable-pitch rotor dynamics.

@inproceedings{nekoo2019fully, title={Fully coupled six-DoF nonlinear suboptimal control of a quadrotor: Application to variable-pitch rotor design}, author={Nekoo, Saeed Rafee and Acosta, Jos{\'e} {\'A}ngel and Ollero, An{\'\i}bal}, booktitle={Iberian robotics conference}, pages={72--83}, year={2019}, organization={Springer} }

Online Detection and Tracking of Pipes During UAV Flight in Industrial Environments

A. Gómez Eguíluz, J.L. Paneque, J.R. Martínez de Dios, A. Ollero

ROBOT-2019, pp: 28-39

3D LiDaR-based perception has been used in robotics for obtaining accurate representations of the robot surroundings. As pipes are one of the most common objects in industrial environments, cylinder detection systems provide valuable information for robot navigation in industrial scenarios. However, most cylinder detection approaches using 3D LiDaRs suffer from high computational requirements and, therefore, their on-line implementation on real robots is limited for certain applications. This work proposes a computationally-light probabilistic approach to pipe detection and tracking suitable for aerial robot mapping and navigation. The proposed method was tested in both simulation and real scenarios. Through a combination of previous estimates and the localisation of the robot, the proposed approach is capable of reducing the computational cost of the RANSAC algorithm while keeping high detection accuracy.

@InProceedings{, author={G{\'o}mez Egu{\'i}luz, Augusto and Paneque, Julio Lopez and Mart{\'i}nez-de Dios, Jos{\'e} Ramiro and Ollero, An{\'i}bal}, editor={Silva, Manuel F. and Lu{\'i}s Lima, Jos{\'e} and Reis, Lu{\'i}s Paulo and Sanfeliu, Alberto and Tardioli, Danilo}, title={Online Detection and Tracking of Pipes During UAV Flight in Industrial Environments}, booktitle={Robot 2019: Fourth Iberian Robotics Conference}, year={2020}, publisher={Springer International Publishing}, address=Cham}, pages={28--39},}

Current State and Trends on Bioinspired Actuators for Aerial Manipulation

A.E. Gomez-Tamm, P. Ramon-Soria, B.C. Arrue and A. Ollero

International Workshop on Research, Education and Development on Unmanned Aerial Systems (RED-UAS), Cranfield, UK. pp. 352-361.

Recently, several research has been developed to embed manipulators and actuators in Unmanned Aerial Vehicles (UAVs) to allow them to interact with the environment. However, there are strong limitations with these actuators which are mainly related with the weight and efficiency. This article reviews the state of art of bio-inspired solutions for aerial manipulators and presents cutting edge bio-inspired technologies that are potentially profitable in the field of aerial robotics.

@inproceedings{gomez2019current, title={Current state and trends on bioinspired actuators for aerial manipulation}, author={Gomez-Tamm, AE and Ramon-Soria, P and Arrue, BC and Ollero, A}, booktitle={2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS)}, pages={352--361}, year={2019}, organization={IEEE} }

TCP muscle tensors: Theoretical analysis and potential applications in aerial robotic systems

A. E. Gómez Tamm, P. Ramón Soria, B. C. Arrúe and A. Ollero

Fourth Iberian Robotics Conference (ROBOT 2019), Porto, Portugal. Pp 40-51

The use of aerial systems in a variety of real applications is increasing nowadays. These offer solutions to existing problems in ways that have never seen before thanks to their capability to perform perching, grasping or manipulating in inaccessible or dangerous places. Many of these applications require small-sized robots that can maneuver in narrow environments. However, these are required to have also strength enough to perform the desired tasks. This balance is sometimes unreachable due to the fact that traditional servomotors are too heavyweight for being carried by such small unmanned aerial systems (UAS). This paper, offers a innovative solution based on twisted and coiled polymers (TCP) muscles. These tensors have a high weight/strength ratio (up to 200 times) compared with traditional servos. In this work, the practical and modeling work done by the authors is presented. Then, a preliminary design of a bio-inspired claw for an unmanned aerial system (UAS) is shown. This claw has been developed using additive manufacturing techniques with different materials. Actuated with TCP, it is intrinsically compliant and offers a great force/weight ratio.

@inproceedings{gomez2019tcp, title={Tcp muscle tensors: Theoretical analysis and potential applications in aerial robotic systems}, author={Gomez-Tamm, Alejandro Ernesto and Ramon-Soria, Pablo and Arrue, Bego{\~n}a C and Ollero, An{\'\i}bal}, booktitle={Iberian Robotics conference}, pages={40--51}, year={2019}, organization={Springer} }

Small-Scale Compliant Dual Arm With Tail for Winged Aerial Robots

A. Suarez, M. Pérez García, G. Heredia and A. Ollero

IEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2019), Macau, China. Pp 208-214.

Winged aerial robots represent an evolution of aerial manipulation robots, replacing the multirotor vehicles by fixed or flapping wing platforms. The development of this morphology is motivated in terms of efficiency, endurance and safety in some inspection operations where multirotor platforms may not be suitable. This paper presents a first prototype of compliant dual arm as preliminary step towards the realization of a winged aerial robot capable of perching and manipulating with the wings folded. The dual arm provides 6 DOF (degrees of freedom) for end effector positioning in a human-like kinematic configuration, with a reach of 25 cm (half-scale w.r.t. the human arm), and 0.2 kg weight. The prototype is built with micro metal gear motors, measuring the joint angles and the deflection with small potentiometers. The paper covers the design, electronics, modeling and control of the arms. Experimental results in test-bench validate the developed prototype and its functionalities, including joint position and torque control, bimanual grasping, the dynamic equilibrium with the tail, and the generation of 3D maps with laser sensors attached at the arms.

@inproceedings{suarez2019small, title={Small-Scale Compliant Dual Arm with Tail for Winged Aerial Robots}, author={Suarez, Alejandro and Perez, Manuel and Heredia, Guillermo and Ollero, Anibal}, booktitle={2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)}, pages={208--214}, year={2019}, organization={IEEE} }

A Simple Model for Gliding and Low-Amplitude Flapping Flight of a Bio-Inspired UAV

A. Martín-Alcántara, P. Grau, R. Fernandez-Feria, A. Ollero

International Conference on Unmanned Aircraft Systems (ICUAS), Atlanta, Georgia (USA). Pp 729-737.

Inspired by the efficiency of soaring birds in crossing very large distances with barely flap their wings, this work presents a simple model of UAV that, adopting the capabilities of these animals, could improve the existent multi-rotor devices, not only in efficiency but also in safety and accessibility. Thus, simple analytical approximations to reproduce the behavior of flapping wings UAVs are explored, expecting their integration in on-board CPUs to be solved in real-time flight episodes. A comparison between gliding and wing flapping with these models indicates that the thrust generated by wingstrokes should be controlled in further studies in order to mitigate the oscillations along the path of the vehicle. The geometric parameters of the ornithopter are found to be decisive in this sense, so special attention should be paid during the design stage.

@inproceedings{martin2019simple, title={A simple model for gliding and low-amplitude flapping flight of a bio-inspired UAV}, author={Mart{\'\i}n-Alc{\'a}ntara, A and Grau, P and Fernandez-Feria, R and Ollero, A}, booktitle={2019 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={729--737}, year={2019}, organization={IEEE} }

2017

Integration of a 4D-trajectory follower to improve multi-UAV conflict management within the U-Space context

H. Perez-Leon, J.J. Acevedo, Ivan Maza and A. Ollero

Journal of Intelligent & Robotic Systems (JINT), vol. 102, no. 3, pp. 62

A safe integration of UAVs into the airspace is fundamental to unblock all the potential of drone applications. U-space is the drone traffic management solution for Europe, intended to handle a large number of drones into the airspace, especially at Very Low Level (VLL). This paper is focused on conflict management for multiple unmanned aerial vehicles in the context of the U-space under 4D trajectory based operations (4D-TBO). A novel method for multi-UAV conflict management at tactical level for large-scale scenarios is presented. The integration of 4D-TBO in this context has been implemented with a four dimensional trajectory follower based on the carrot chasing algorithm. This method minimizes, through the whole flight, the mean normal distance to the defined trajectory and the mean difference with respect to the defined arrival times. Finally, the integrated system has been implemented in a software in the loop environment with a commercial autopilot. The simulation results show better performance with respect to other classical approaches.

@article{Perez-Leon_Acevedo_Maza_Ollero_2021, title={Integration of a 4D-trajectory Follower to Improve Multi-UAV Conflict Management Within the U-Space Context}, volume={102}, ISSN={0921-0296, 1573-0409}, DOI={10.1007/s10846-021-01415-0}, number={3}, journal={Journal of Intelligent & Robotic Systems}, author={Perez-Leon, Hector and Acevedo, Jose Joaquin and Maza, Ivan and Ollero, Anibal}, year={2021}, month={Jul}, pages={62} }