2023
Modeling and Application of an SMA-Actuated Lightweight Human-Inspired Gripper for Aerial Manipulation
Machines, 11(9), 859, 2023.
The increasing usage of multi-rotor aerial platforms and the reliability of flights enabled researchers to add equipment and devices to them for application. The addition of lightweight manipulators, grippers, and mechanisms to fulfill specific tasks has been reported frequently recently. This work pushes the idea one step ahead and uses an Artificial Human Hand (AHH) in an uncrewed aerial vehicle for aerial manipulation, device delivery, and co-operation with human workers. This application requires an effective end-effector capable of grasping and holding objects of different shapes. The AHH is a lightweight custom-made human-inspired design actuated using Shape Memory Alloy (SMA) materials. The SMA actuators offer significantly high forces with respect to their light weights though the control of these new actuators is a challenge that has been successfully demonstrated in this paper. The control of the SMA actuators could be achieved via heat exchange on the actuator, indirectly carried out by changing the current. The benefit of using this new actuator is removing the motors and mechanical mechanisms and simplifying the design. A soft cover is developed for the AHH to add friction and make it closer to a human hand. The modeling of the structured actuators on the system through tendons is presented, and a series of experiments for handling and manipulating different objects have been conducted. The objects were chosen with different weights and shapes to show the effectiveness of the design. An analysis of a generated torque of the manipulator for different cylindrical objects has been carried out. An analysis and comparison for grasping a series of items, pressure and temperature analysis, and the weight-to-volume ratio have been presented.
@article{Perez-Sanchez2023Modeling, title={Modeling and Application of an SMA-Actuated Lightweight Human-Inspired Gripper for Aerial Manipulation}, author={Perez-Sanchez, V.; Garcia-Rubiales, F.J.; Nekoo, S.R.; Arrue, B.; Ollero, A}, journal={Machines}, year={2023}, publisher={MDPI} }
Closed-loop nonlinear optimal control design for flapping-wing flying robot (1.6 m wingspan) in indoor confined space: Prototyping, modeling, simulation, and experiment
ISA Transactions, 2023.
The flapping-wing technology has emerged recently in the application of unmanned aerial robotics for autonomous flight, control, inspection, monitoring, and manipulation. Despite the advances in applications and outdoor manual flights (open-loop control), closed-loop control is yet to be investigated. This work presents a nonlinear optimal closed-loop control design via the state-dependent Riccati equation (SDRE) for a flapping-wing flying robot (FWFR). Considering that the dynamic modeling of the flapping-wing robot is complex, a proper model for the implementation of nonlinear control methods is demanded. This work proposes an alternative approach to deliver an equivalent dynamic for the translation of the system and a simplified model for orientation, to find equivalent dynamics for the whole system. The objective is to see the effect of flapping (periodic oscillation) on behavior through a simple model in simulation. Then the SDRE controller is applied to the derived model and implemented in simulations and experiments. The robot bird is a 1.6 m wingspan flapping-wing system (six-degree-of-freedom robot) with four actuators, three in the tail, and one as the flapping input. The underactuated system has been controlled successfully in position and orientation. The control loop is closed by the motion capture system in the indoor test bed where the experiments of flight have been successfully done.
@article{nekoo2023closed, title={Closed-loop nonlinear optimal control design for flapping-wing flying robot (1.6 m wingspan) in indoor confined space: Prototyping, modeling, simulation, and experiment}, author={Nekoo, Saeed Rafee and Ollero, Anibal}, journal={ISA Transactions}, year={2023}, publisher={Elsevier} }
A 94.1 g Scissors-Type Dual-Arm Cooperative Manipulator for Plant Sampling by an Ornithopter using a Vision Detection System
Robotica, pp. 1-18, 2023.
The sampling and monitoring of nature have become an important subject due to the rapid loss of green areas. This work proposes a possible solution for a sampling method of the leaves using an ornithopter robot equipped with an onboard 94.1 g dual-arm cooperative manipulator. One hand of the robot is a scissors-type arm and the other one is a gripper to perform the collection, approximately similar to an operation by human fingers. In the move toward autonomy, a stereo camera has been added to the ornithopter to provide visual feedback for the stem, which reports the position of the cutting and grasping. The position of the stem is detected by a stereo vision processing system and the inverse kinematics of the dual-arm commands both gripper and scissors to the right position. Those trajectories are smooth and avoid any damage to the actuators. The real-time execution of the vision algorithm takes place in the lightweight main processor of the ornithopter which sends the estimated stem localization to a microcontroller board that controls the arms. The experimental results both indoors and outdoors confirmed the feasibility of this sampling method. The operation of the dual-arm manipulator is done after the perching of the system on a stem. The topic of perching has been presented in previous works and here we focus on the sampling procedure and vision/manipulator design. The flight experimentation also approves the weight of the dual-arm system for installation on the flapping-wing flying robot.
@article{nekoo202394, title={A 94.1 g scissors-type dual-arm cooperative manipulator for plant sampling by an ornithopter using a vision detection system}, author={Nekoo, Saeed Rafee and Feliu-Talegon, Daniel and Tapia, Raul and Satue, Alvaro C and Mart{\'\i}nez-de Dios, Jose Ramiro and Ollero, Anibal}, journal={Robotica}, pages={1--18}, year={2023}, publisher={Cambridge University Press} }
Equivalent Vertical Dynamics of Flapping-Wing Flying Robot in Regulation Control: Displacement Transmissibility Ratio
2023 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 1301-1307, 2023.
This paper presents an equivalent dynamic model for vertical regulation control of a flapping-wing flying robot. The model is presented based on the data of a series of flight experiments for an available platform. The system shows oscillations in motion in all experiments with an approximate frequency between [3.5, 4.5](Hz), changing within a limited range. The behavior of the equivalent model represents a system with base excitation. The displacement transmissibility ratio (TR) is found for the model to investigate the oscillatory behavior in the system during the flight. Reduction of the oscillations through the transmissibility ratio will decrease the uncertainty in flight and consequently, that could increase the success rate of perching on a branch (now it has a 10 - 15(cm) uncertain periodic motion); perching needs precision on the last meter approaching phase. An analytical expression for TR is presented which is used for parameter selection, tuning, and selection of the flapping frequency, as the base excitation source. The study shows that the robot works in a proper zone of the frequency ratio, and also, the sensitivity of the TR is high concerning the changes in the stiffness constant.
@inproceedings{nekoo2023equivalent, title={Equivalent Vertical Dynamics of Flapping-Wing Flying Robot in Regulation Control: Displacement Transmissibility Ratio}, author={Nekoo, Saeed Rafee and Ollero, Anibal}, booktitle={2023 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={1301--1307}, year={2023}, organization={IEEE} }
Theoretical and Experimental Investigation on Body Control After Perching for Flapping-Wing Robots: Extending the Workspace for Manipulation
2023 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 948-955, 2023.
This work investigates a post-perching control for flapping-wing flying robots (FWFRs) to control and move the system on a branch. The flapping-wing aerial systems are lightweight platforms that mimic the birds’ flight and they could serve for monitoring and inspection. The interaction of the FWFRs with the environment needs to fulfill perching on a branch, as a preliminary step, then moving the body to gain access to the desired pose and workspace. The leg of the robot moves the bird to the proper position. This work studies the mathematical modeling, simulation, and experimental implementation of this topic. A three-degree-of-freedom system is presented to model the robot’s body, tail, and leg. A nonlinear controller, so-called feedback linearization (FL) is used for the control of the robot. A linear quadratic regulator (LQR), plus an integrator, are embedded in the FL controller to deliver optimal control for the linearized system. The simulation results show that the actuated leg extends the workspace of the robot significantly and confirms the effectiveness of the proposed strategy for body control. Experimental results present similar behavior of the system using the proposed controller for different desired setpoints.
@inproceedings{luque2023theoretical, title={Theoretical and Experimental Investigation on Body Control After Perching for Flapping-Wing Robots: Extending the Workspace for Manipulation}, author={Luque, Pablo Serrano and Satue, Alvaro C and Nekoo, Saeed Rafee and Acosta, Jose Angel and Ollero, Anibal}, booktitle={2023 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={948--955}, year={2023}, organization={IEEE} }
A Proportional Closed-loop Control for Equivalent Vertical Dynamics of Flapping-Wing Flying Robot
2023 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 1294-1300, 2023.
The closed-loop position control of a flapping-wing flying robot (FWFR) is a challenging task. A complete six-degree-of-freedom (DoF) modeling and control design is preferable though that imposes complexity on the procedure and analysis of the oscillations in the trajectory. Another approach could be studying independent state variables of the system and designing a controller for them. This will provide the possibility of a better understanding of the dynamic, comparing to experimental data, then use this information for moving forward to complete 6-DoF modeling. In this work, a simple linear proportional closed-loop controller is proposed and analyzed for an equivalent dynamic model of the flapping-wing flying robot. The equivalent dynamic modeling considers the flapping motion as a base excitation that disturbs the system in oscillatory behavior. The frequency of the oscillation and data of the motion was obtained from previous experimental results and used in the modeling. The designed controller performed the regulation task easily and regulated the system to a series of set-point control successfully. The motivation for the selection of a proportional control is to keep the design as simple as possible to analyze the excitation and behavior of the flapping more precisely. A discussion on the transient and steady-state flight and the role of control design on them have been presented in this work.
@inproceedings{nekoo2023proportional, title={A Proportional Closed-loop Control for Equivalent Vertical Dynamics of Flapping-Wing Flying Robot}, author={Nekoo, Saeed Rafee and Ollero, Anibal}, booktitle={2023 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={1294--1300}, year={2023}, organization={IEEE} }
Unsteady Propulsion of a Two-Dimensional Flapping Thin Airfoil in a Periodic Stream
American Institute of Aeronautics and Astronautics (AIAA) Journal, 2023.
The cruising velocity of animals, or robotic vehicles, that use flapping wings or fins to propel themselves is not constant but oscillates around a mean value with an amplitude usually much smaller than the mean, and a frequency that typically doubles the flapping frequency. Quantifying the effect that these velocity fluctuations may have on the propulsion of a flapping and oscillating airfoil is of great relevance to properly modeling the self-propelled performance of these animals or robotic vehicles. This is the objective of the present work, where the force and moment that an oscillating stream exerts on a two-dimensional pitching and heaving airfoil are obtained analytically using the vortical impulse theory in the linear potential flow limit. The thrust force of the flapping airfoil in a pulsating stream in this limit is obtained here for the first time. The lift force and moment derived here contain new terms in relation to the pioneering work by Greenberg (1947), which are shown quantitatively unimportant. The theoretical results obtained here are compared with existing computational data for flapping foils immersed in a stream with velocity oscillating sinusoidally about a mean value.
@article{sanchez2022unsteady, title={Unsteady propulsion of a two-dimensional flapping thin airfoil in a periodic stream}, author={Sanchez-Laulhe, Ernesto and Fern{\'a}ndez-Feria, Ram{\'o}n and Ollero, Anibal and others}, journal={American Institute of Aeronautics and Astronautics}, year={2023}, publisher={AIAA} }
Benchmark Evaluation of Hybrid Fixed-Flapping Wing Aerial Robot with Autopilot Architecture for Autonomous Outdoor Flight Operations
IEEE Robotics and Automation Letters, 8(7), pp. 4243-4250, 2023.
This letter is focused on the benchmark evaluation and comparison of the flapping and fixed wing flight modes on an hybrid platform developed for the realization of autonomous inspection operations outdoors. The platform combines the high range and endurance of fixed-wing UAVs (unmanned aerial vehicles), with the higher maneuverability and intrinsic safety of flapping wing in the interaction with humans during the hand launch and capture. A unified model of the hybrid platform is derived for both configurations following the Lagrange formulation to express the multi-body dynamics and aerodynamic forces of the flapping wing and the propellers. The proposed control scheme exploits the similarities of both flight modes in the tail actuation and in the generation of thrust either with the flapping wings or the propellers, in such a way that it can be implemented on conventional autopilots, facilitating in this way the adoption of this type of aerial platforms. To evaluate and compare the performance of both modes, a set of benchmark tests and metrics are defined, including the energy efficiency in forward flight, trajectory tracking, hand launch and capture, and accuracy in visual inspection. Experimental results in outdoors validate the developed prototype, identifying the fixed/flapping transitions, and evidencing the higher energy efficiency of the flapping wing mode compared to the fixed wing.
@article{gayango2023benchmark, title={Benchmark Evaluation of Hybrid Fixed-Flapping Wing Aerial Robot with Autopilot Architecture for Autonomous Outdoor Flight Operations}, author={Gayango, Diego and Salmoral, Rafael and Romero, Honorio and Carmona, Jose Manuel and Suarez, Alejandro and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, year={2023}, publisher={IEEE} }
Experimental Energy Consumption Analysis of a Flapping-Wing Robot
International Conference on Robotics and Automation 2023 Workshop on Energy Efficient Aerial Robotic Systems, 2023
One of the motivations for exploring flapping-wing aerial robotic systems is to seek energy reduction, by maintaining manoeuvrability, compared to conventional unmanned aerial systems. A Flapping Wing Flying Robot (FWFR) can glide in favourable wind conditions, decreasing energy consumption significantly. In addition, it is also necessary to investigate the power consumption of the components in the flapping-wing robot. In this work, two sets of the FWFR components are analyzed in terms of power consumption: a) motor/electronics components and b) a vision system for monitoring the environment during the flight. A measurement device is used to record the power utilization of the motors in the launching and ascending phases of the flight and also in cruising flight around the desired height. Additionally, an analysis of event cameras and stereo vision systems in terms of energy consumption has been performed. The results provide a first step towards decreasing battery usage and, consequently, providing additional flight time.
@article{tapia2023experimental, title={Experimental Energy Consumption Analysis of a Flapping-Wing Robot}, author={Tapia, R. and Satue, A. C. and Nekoo, S. R. and Martínez-de Dios, J. R. and Ollero, A.}, journal={arXiv:2306.00848}, year={2023} }
2022
How ornithopters can perch autonomously on a branch
Nature Communications, 13(7713), 2022.
Flapping wings produce lift and thrust in bio-inspired aerial robots, leading to quiet, safe and efficient flight. However, to extend their application scope, these robots must perch and land, a feat widely demonstrated by birds. Despite recent progress, flapping-wing vehicles, or ornithopters, are to this day unable to stop their flight. In this paper, we present a process to autonomously land an ornithopter on a branch. This method describes the joint operation of a pitch-yaw-altitude flapping flight controller, an optical close-range correction system and a bistable claw appendage design that can grasp a branch within 25 milliseconds and re-open. We validate this method with a 700 g robot and demonstrate the first autonomous perching flight of a flapping-wing robot on a branch, a result replicated with a second robot. This work paves the way towards the application of flapping-wing robots for long-range missions, bird observation, manipulation, and outdoor flight.
@Article{RePEc:nat:natcom:v:13:y:2022:i:1:d:10.1038_s41467-022-35356-5, author={Raphael Zufferey and Jesus Tormo-Barbero and Daniel Feliu-Talegón and Saeed Rafee Nekoo and José Ángel Acosta and Anibal Ollero}, title={{How ornithopters can perch autonomously on a branch}}, journal={Nature Communications}, year=2022, volume={13}, number={1}, pages={1-11}, month={December}, keywords={}, doi={10.1038/s41467-022-35356-}, abstract={ Flapping wings produce lift and thrust in bio-inspired aerial robots, leading to quiet, safe and efficient flight. However, to extend their application scope, these robots must perch and land, a feat widely demonstrated by birds. Despite recent progress, flapping-wing vehicles, or ornithopters, are to this day unable to stop their flight. In this paper, we present a process to autonomously land an ornithopter on a branch. This method describes the joint operation of a pitch-yaw-altitude flapping flight controller, an optical close-range correction system and a bistable claw appendage design that can grasp a branch within 25 milliseconds and re-open. We validate this method with a 700 g robot and demonstrate the first autonomous perching flight of a flapping-wing robot on a branch, a result replicated with a second robot. This work paves the way towards the application of flapping-wing robots for long-range missions, bird observation, manipulation, and outdoor flight.}, url={https://ideas.repec.org/a/nat/natcom/v13y2022i1d10.1038_s41467-022-35356-5.html} }
Optimal Elastic Wing for Flapping-wing Robots Through Passive Morphing
IEEE Robotics and Automation Letters , 2022.
Flapping wing robots show promise as platforms for safe and efficient flight in near-human operations, thanks to their ability to agile maneuver or perch at a low Reynolds number. The growing trend in the automatization of these robots has to go hand in hand with an increase in the payload capacity. This work provides a new passive morphing wing prototype to increase the payload of this type of UAV. The prototype is based on a biased elastic joint and the holistic research also includes the modelling, simulation and optimization scheme, thus allowing to adapt the prototype for any flapping wing robot. This model has been validated through flight experiments on the available platform, and it has also been demonstrated that the morphing prototype can increase the lift of the robot under study by up to 16% in real flight and 10% of estimated consumption reduction.
@article{ruiz2022optimal, title={Optimal elastic wing for flapping-wing robots through passive morphing}, author={Ruiz, Cristina and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, year={2022}, publisher={IEEE} }
Combination of Terminal Sliding Mode and Finite-time State-dependent Riccati Equation: Flapping-wing Flying Robot Control
Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, 09596518221138627, 2022
A novel terminal sliding mode control is introduced to control a class of nonlinear uncertain systems in finite time. Having command on the definition of the final time as an input control parameter is the goal of this work. Terminal sliding mode control is naturally a finite-time controller though the time cannot be set as input, and the convergence time is not exactly known to the user before execution of the control loop. The sliding surface of the introduced controller is equipped with a finite-time gain that finishes the control task in the desired predefined time. The gain is found by partitioning the state-dependent differential Riccati equation gain, then arranging the sub-blocks in a symmetric positive-definite structure. The state-dependent differential Riccati equation is a nonlinear optimal controller with a final boundary condition that penalizes the states at the final time. This guides the states to the desired condition by imposing extra force on the input control law. Here the gain is removed from standard state-dependent differential Riccati equation control law (partitioned and made symmetric positive-definite) and inserted into the nonlinear sliding surface to present a novel finite-time terminal sliding mode control. The stability of the proposed terminal sliding mode control is guaranteed by the definition of the adaptive gain of terminal sliding mode control, which is limited by the Lyapunov stability condition. The proposed approach was validated and compared with state-dependent differential Riccati equation and conventional terminal sliding mode control as independent controllers, applied on a van der Pol oscillator. The capability of the proposed approach of controlling complex systems was checked by simulating a flapping-wing flying robot. The flapping-wing flying robot possesses a highly nonlinear model with uncertainty and disturbance caused by flapping. The flight assumptions also limit the input law significantly. The proposed terminal sliding mode control successfully controlled the illustrative example and flapping-wing flying robot model and has been compared with state-dependent differential Riccati equation and conventional terminal sliding mode control.
@article{nekoo2022combination, title={Combination of terminal sliding mode and finite-time state-dependent Riccati equation: Flapping-wing flying robot control}, author={Nekoo, Saeed Rafee and Acosta, Jos{\'e}{\'A}ngel and Ollero, Anibal}, journal={Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering}, pages={09596518221138627}, year={2022}, publisher={SAGE Publications Sage UK: London, England} }
Gravity compensation and optimal control of actuated multibody system dynamics
IET Control Theory & Applications, 16 (1), pp. 79-93, 2022.
This work investigates the gravity compensation topic, from a control perspective. The gravity could be levelled by a compensating mechanical system or in the control law, such as proportional derivative (PD) plus gravity, sliding mode control, or computed torque method. The gravity compensation term is missing in linear and nonlinear optimal control, in both continuous- and discrete-time domains. The equilibrium point of the control system is usually zero and this makes it impossible to perform regulation when the desired condition is not set at origin or in other cases, where the gravity vector is not zero at the equilibrium point. The system needs a steady-state input signal to compensate for the gravity in those conditions. The stability proof of the gravity compensated control law based on nonlinear optimal control and the corresponding deviation from optimality, with proof, are introduced in this work. The same concept exists in discrete-time control since it uses analog to digital conversion of the system and that includes the gravity vector of the system. The simulation results highlight two important cases, a robotic manipulator and a tilted-rotor hexacopter, as an application to the claimed theoretical statements.
@article{nekoo2021gravity, title={Gravity compensation and optimal control of actuated multibody system dynamics}, author={Nekoo, Saeed Rafee and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IET Control Theory \& Applications}, year={2021}, publisher={Wiley Online Library} }
Simplified Model for Forward-Flight Transitions of a Bio-inspired UAV
Aerospace, 9 (10) 617, 2022.
A new forward-flight model for bird-like ornithopters that uses results from potential, un-steady aerodynamics to characterize the forces generated by the flapping wings is presented. Numerical results show that variables such as the pitch angle and the angle of attack oscillate with the flapping frequency and that their mean values converge towards steady state values, with amplitudes during the transitional phases also evolving towards stationary values. However, in order to implement real-time on-board predictions, numerical computations are too expensive. Theoretical formulation shows separation of time scales that substantially simplifies the interpretation and the solution of the dynamic equations. The smallness of the wing’s angle of attack observed numerically follows theoretically from this. Thus, the asymptotic separation into three time scales allows to divide the problem into a much simpler set of linear equations. The theoretical solution, which shows a very good agreement with the numerical results, provides a direct look into the influence of the design and control parameters. Therefore, this model provides an useful tool for the design, guidance and control of flapping wing UAVs.
@Article{aerospace9100617, AUTHOR = {Sanchez-Laulhe, Ernesto and Fernandez-Feria, Ramon and Ollero, Anibal}, TITLE = {Simplified Model for Forward-Flight Transitions of a Bio-Inspired Unmanned Aerial Vehicle}, JOURNAL = {Aerospace}, VOLUME = {9}, YEAR = {2022}, NUMBER = {10}, ARTICLE-NUMBER = {617}, URL = {https://www.mdpi.com/2226-4310/9/10/617}, ISSN = {2226-4310}, ABSTRACT = {A new forward-flight model for bird-like ornithopters is presented. The flight dynamics model uses results from potential, unsteady aerodynamics to characterize the forces generated by the flapping wings, including the effects of the dynamic variables on the aerodynamic formulation. Numerical results of the model, which are validated with flapping flight experimental data of an ornithopter prototype, show that state variables such as the pitch angle and the angle of attack oscillate with the flapping frequency, while their mean values converge towards steady-state values. The theoretical analysis of the system shows a clear separation of timescales between flapping oscillations and transient convergence towards the final forward-flight state, which is used to substantially simplify both the interpretation and the solution of the dynamic equations. Particularly, the asymptotic separation into three timescales allows for dividing the problem into a much simpler set of linear equations. The theoretical approximation, which fits the numerical results, provides a direct look into the influence of the design and control parameters using fewer computational resources. Therefore, this model provides a useful tool for the design, navigation and trajectory planning and control of flapping wing UAVs.}, DOI = {10.3390/aerospace9100617} }
ASAP: Adaptive Transmission Scheme for Online Processing of Event-based Algorithms
Autonomous Robots, 2022.
Online event-based perception techniques on board robots navigating in complex, unstructured, and dynamic environments can suffer unpredictable changes in the incoming event rates and their processing times, which can cause computational overflow or loss of responsiveness. This paper presents ASAP: a novel event handling framework that dynamically adapts the transmission of events to the processing algorithm, keeping the system responsiveness and preventing overflows. ASAP is composed of two adaptive mechanisms. The first one prevents event processing overflows by discarding an adaptive percentage of the incoming events. The second mechanism dynamically adapts the size of the event packages to reduce the delay between event generation and processing. ASAP has guaranteed convergence and is flexible to the processing algorithm. It has been validated on board a quadrotor and an ornithopter robot in challenging conditions.
@article{tapia2022asap, title={ASAP: Adaptive Transmission Scheme for Online Processing of Event-based Algorithms}, author={Tapia, Raul and Dios, Jos{\'e} Ramiro Mart{\'\i}nez-de and Egu{\'\i}luz, Augusto G{\'o}mez and Ollero, Anibal}, journal={arXiv preprint arXiv:2209.08602}, year={2022} }
Experimental method for perching flapping-wing aerial robots
IROS 2022 Workshop: Agile Robotics: Perception, Learning, Planning, and Control, 2022.
In this work, we present an experimental setup and guide to enable the perching of large flapping-wing robots. The combination of forward flight, limited payload, and flight oscillations imposes challenging conditions for localized perching. The described method details the different operations that are concurrently performed within the 4 second perching flight. We validate this experiment with a 700 g ornithopter and demonstrate the first autonomous perching flight of a flapping wing robot on a branch. This work paves the way towards the application of flapping-wing robots for long-range missions, bird observation, manipulation, and outdoor flight.
Fuselage Aerodynamics and Weight Trade-Off at Low-Speed Ornithopter Flight
2022 International Conference on Unmanned Aircraft Systems (ICUAS), 2022.
This work presents a thorough study on the effect of the inclusion or not of a fuselage in flapping wing robots, for which no clear criterion has been found so far. The study consists in a dynamic analysis for level flight conditions at both configurations, of an actual prototype. An overall aerodynamic model based on CFD simulations are used for modeling the average in-flight forces performed by the ornithopter elements, wing, body and tail. Experimental thrust correction is developed to include the effects of wing flexibility, thus increasing the accuracy of the results. Results show a better performance at low speeds when the ornithopter does not carry the fuselage. At higher speeds, the lower drag provided by the fuselage becomes important. However, the increased weight always need a higher flapping frequency for the low velocity range of our prototype, creating a disadvantage for this regime. The results highlights a fuselage design criteria, which can be extrapolated to other bird-scaled flapping wing robots performing slow maneuvers, as perching, as well as to hybrid flapping-fixed wing UAVs.
@inproceedings{sanchez2022fuselage, title={Fuselage Aerodynamics and Weight Trade-Off at Low-Speed Ornithopter Flight}, author={Sanchez-Laulhe, E and Ruiz, C and Acosta, J{\'A} and Ollero, A}, booktitle={2022 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={310--318}, year={2022}, organization={IEEE} }
Modeling and Under-actuated Control of Stabilization Before Take-off Phase for Flapping-wing Robots
ROBOT 2022, ROBOT2022: Fifth Iberian Robotics Conference. ROBOT 2022. Lecture Notes in Networks and Systems, vol 590. Springer, Cham., pp. 376–388, 2023.
This work studies a stabilization problem of flapping-wing flying robots (FWFRs) before a take-off phase while a robot is on a branch. The claw of the FWFR grasps the branch with enough friction to hold the system steady in a stationary condition. Before the take-off, the claw opens itself and the friction between the claw and branch vanishes. At that moment, the mechanical model turns into an under-actuated multi-link (serial configuration) robotic system where the first joint can rotate freely without any friction as opposed to rotation. The stabilization and balancing are the crucial tasks before take-off. This work explores a new methodology to control an under-actuated lightweight manipulator for its future adaptation to FWFR to improve the stabilization performance before take-off. The setup tries to mimic the birds with two-link legs, a body link, and 2-DoF (degrees of freedom) arms, being all active links except the first passive one. In contrast to common arms, the lightweight-design restriction limits the frame size and requires micromotors. With all of these constraints, control design is a challenge, hence, the system is categorized: a) the leg subsystem (under-actuated), including the two first links, and b) the body and arm subsystem (fully actuated) with the rest of links. The fully-actuated links are controlled by feedback linearization and the under-actuated part with active disturbance rejection control (ADRC) for estimation and rejection of the coupling between both subsystems. The mechanical design, modeling, and control of the proposed system are reported in this work. Experimental results have been also proposed to present a proof of concept for this modeling and control approach.
@inproceedings{Feliu-Talegon2022Modeling, title={Modeling and Under-actuated Control of Stabilization Before Take-off Phase for Flapping-wing Robots}, author={Feliu-Talegon, Daniel and Rafee Nekoo, Saeed and Suarez, Alejandro and Acosta, Jose Angel and Ollero, Anibal}, booktitle={Iberian Robotics conference}, pages={376--388}, year={2023}, organization={Springer} }
How ornithopters can perch autonomously on a branch
arXiv preprint, arXiv:2207.07489, 2022.
Flapping wings are a bio-inspired method to produce lift and thrust in aerial robots, leading to quiet and efficient motion. The advantages of this technology are safety and maneuverability, and physical interaction with the environment, humans, and animals. However, to enable substantial applications, these robots must perch and land. Despite recent progress in the perching field, flapping-wing vehicles, or ornithopters, are to this day unable to stop their flight on a branch. In this paper, we present a novel method that defines a process to reliably and autonomously land an ornithopter on a branch. This method describes the joint operation of a flapping-flight controller, a close-range correction system and a passive claw appendage. Flight is handled by a triple pitch-yaw-altitude controller and integrated body electronics, permitting perching at 3 m/s. The close-range correction system, with fast optical branch sensing compensates for position misalignment when landing. This is complemented by a passive bistable claw design can lock and hold 2 Nm of torque, grasp within 25 ms and can re-open thanks to an integrated tendon actuation. The perching method is supplemented by a four-step experimental development process which optimizes for a successful design. We validate this method with a 700 g ornithopter and demonstrate the first autonomous perching flight of a flapping-wing robot on a branch, a result replicated with a second robot. This work paves the way towards the application of flapping-wing robots for long-range missions, bird observation, manipulation, and outdoor flight.
@article{zufferey2022ornithopters, title={How ornithopters can perch autonomously on a branch}, author={Zufferey, Raphael and Barbero, Jesus Tormo and Talegon, Daniel Feliu and Nekoo, Saeed Rafee and Acosta, Jose Angel and Ollero, Anibal}, journal={arXiv preprint arXiv:2207.07489}, year={2022} }
High-Performance Morphing Wing for Large-Scale Bio-Inspired Unmanned Aerial Vehicles
IEEE Robotics and Automation Letters, 21861439, pp. 8076-8083, 2022.
This paper proposes a novel bio-inspired wing design to improve some characteristics of Flapping Wing Unmanned Vehicles (FWUV) related to their potential applications such as payload capability, maneuverability, low injury risk, and energy improvement. The suggested solution takes advantage of a broadly based avian research, focusing on the integration of advanced bird-like features ranging from bird-like high-compliant airfoil to active morphing strategies to mimic the ways birds naturally manage flights. The proposed conceptual design is supported by Unsteady Vortex Latex Method simulations provided by a novel flapping-oriented open-source solver. Prototype validation relies on both test-bench and real-flights results. A motion capture system is used to validate the wing aero-elastic characteristics. The resulted improvements are highlighted by a comprehensive comparison with different similar-size prototypes.
@article{savastano2022high, title={High-Performance Morphing Wing for Large-Scale Bio-Inspired Unmanned Aerial Vehicles}, author={Savastano, E and Perez-Sanchez, V and Arrue, BC and Ollero, A}, journal={IEEE Robotics and Automation Letters}, year={2022}, publisher={IEEE} }
A 79.7g Manipulator Prototype for E-Flap Robot: A Plucking-Leaf Application
IEEE Access, 21818500, pp. 65300-65308, 2022.
The manipulation capabilities of flapping-wing flying robots (FWFRs) is a problem barely studied. This is a direct consequence of the load-carrying capacity limitation of the flapping-wing robots. Ornithopters will improve the existent multirotor unmanned aerial vehicles (UAVs) since they could perform longer missions and offer a safe interaction in proximity to humans. This technology also opens the possibility to perch in some trees and perform tasks such as obtaining samples from nature, enabling biologists to collect samples in remote places, or assisting people in rescue missions by carrying medicines or first-aid kits. This paper presents a very lightweight manipulator (79.7g) prototype to be mounted on an ornithopter. The distribution of the mass on the flapping-wing robot is sensitive and an extra lumped mass far from the center-of-mass (CoM) of the robot deteriorates the flight stability. A configuration was proposed to avoid changing the CoM. Flight experiments show that adding the arm to the robot only moved the CoM 6mm and the performance of the flight with the manipulator has been satisfactory. Plucking leaf is chosen as an application to the designed system and several experimental tests confirmed successful sampling of leaves by the prototype.
@article{nekoo202279, title={A 79.7 g Manipulator Prototype for E-Flap Robot: A Plucking-Leaf Application}, author={Nekoo, Saeed Rafee and Feliu-Talegon, Daniel and Acosta, Jose Angel and Ollero, Anibal}, journal={IEEE Access}, year={2022}, publisher={IEEE} }
A Search Algorithm for Constrained Engineering Optimization and Tuning the Gains of Controllers
Expert Systems with Applications, 206, 117866, 2022.
In this work, the application of an optimization algorithm is investigated to optimize static and dynamic engineering problems. The methodology of the approach is to generate random solutions and find a zone for the initial answer and keep reducing the zones. The generated solution in each loop is independent of the previous answer that creates a powerful method. Simplicity as its main advantage and the interlaced use of intensification and diversification mechanisms--to refine the solution and avoid local minima/maxima--enable the users to apply that for a variety of problems. The proposed approach has been validated by several previously solved examples in structural optimization and scored good results. The method is also employed for dynamic problems in vibration and control. A modification has also been done on the method for high-dimensional test functions (functions with very large search domains) to converge fast to the global minimum or maximum; simulated for several well-known benchmarks successfully. For validation, a number of 9 static and 4 dynamic constrained optimization benchmark applications and 32 benchmark test functions are solved and provided, 45 in total. All the codes of this work are available as supplementary material in the online version of the paper on the journal website.
@article{nekoo2022search, title={A Search Algorithm for Constrained Engineering Optimization and Tuning the Gains of Controllers}, author={Nekoo, Saeed Rafee and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={Expert Systems with Applications}, pages={117866}, year={2022}, publisher={Elsevier} }
Stabilizing Event Data on Flapping-wing Robots for Simpler Perception
Workshop on Challenges of Flapping-wing aerial robots of the IEEE International Conference on Robotics and Automation (ICRA) 2022, 2022.
We propose a stabilization method for event cameras mounted onboard flapping-wing robots. Differently from frame-based cameras, event cameras do not suffer for motion blur that typically occurs due to strong changes in the camera orientation. The method intends to offer an alternative to heavy gimbals mounted on ornithopters. It has been tested on event data acquired by a large-scale ornithopter (1.5m wingspan).
@article{Gomez2022Stabilizing, title={Stabilizing Event Data on Flapping-wing Robots for Simpler Perception}, author={Rodríguez-Gómez, J. P., Gallego, G., Martı́nez-de Dios, J. R., and Ollero, A.}, booktitle={Workshop on Challenges of Flapping-wing aerial robots of the IEEE International Conference on Robotics and Automation (ICRA) 2022}, year={2022}, }
Numerical-experimental evaluation and modelling of aerodynamic ground effect for small-scale tilted propellers at low Reynolds numbers
Aerospace Science and Technology, 126, 107625, 2022, Published
In recent years, aerial manipulators with fully-actuated capabilities are gaining popularity for being used in aerial manipulation operations such as critical infrastructure inspection or aerial manipulation tasks. Those scenarios usually demand the aerial platform to operate in constrained and narrow scenarios. It is well known that in these situations, the interaction of the wake generated by the propellers with the environment can significantly alter and change the performance of the rotors. Most studies have addressed this problem by considering the ground effect in hover conditions or during the landing maneuver for co-planar multirotor. However, few works analyze the behaviour of tilted rotors, which are used in fully actuated multirotor configurations thanks to their omnidirectional motion capabilities. This paper presents a numerical-experimental evaluation of the aerodynamic ground effect for small-scale tilted propellers at low Reynolds numbers. This aerodynamic effect has been experimentally evaluated through an extensive testing campaign in a testbench designed for this purpose which has been complemented by a CFD-based study. CFD results have been validated through a mesh independence study and a CFD-experimental propeller performance comparison. A numerical model has been also proposed to capture the dependence of thrust with distance to the ground and angle of inclination between the propeller and ground planes. We demonstrate that the proximity to the ground of tilted rotors decreases the thrust increment due to the ground effect as the tilt angle (θ) increases. This means that Cheeseman's classical theory is inapplicable, as it only considers the distance from the ground without reference to how the thrust increment changes with the tilt angle. This outcome enables future aerial robotic applications that strongly demand accurate aerodynamic effect models to operate close to obstacles and narrow environments.
@article{GAROFANOSOLDADO2022107625, title = {Numerical-experimental evaluation and modelling of aerodynamic ground effect for small-scale tilted propellers at low Reynolds numbers}, journal = {Aerospace Science and Technology}, pages = {107625}, year = {2022}, issn = {1270-9638}, doi = {https://doi.org/10.1016/j.ast.2022.107625}, url = {https://www.sciencedirect.com/science/article/pii/S1270963822002991}, author = {Ambar Garofano-Soldado and Pedro J. Sanchez-Cuevas and Guillermo Heredia and Anibal Ollero}, keywords = {Aerodynamic Effect, Aerial Robot, UAV, CFD, Propeller}, abstract = {In recent years, aerial manipulators with fully-actuated capabilities are gaining popularity for being used in aerial manipulation operations such as critical infrastructure inspection or aerial manipulation tasks. Those scenarios usually demand the aerial platform to operate in constrained and narrow scenarios. It is well known that in these situations, the interaction of the wake generated by the propellers with the environment can significantly alter and change the performance of the rotors. Most studies have addressed this problem by considering the ground effect in hover conditions or during the landing maneuver for co-planar multirotor. However, few works analyze the behaviour of tilted rotors, which are used in fully actuated multirotor configurations thanks to their omnidirectional motion capabilities. This paper presents a numerical-experimental evaluation of the aerodynamic ground effect for small-scale tilted propellers at low Reynolds numbers. This aerodynamic effect has been experimentally evaluated through an extensive testing campaign in a testbench designed for this purpose which has been complemented by a CFD-based study. CFD results have been validated through a mesh independence study and a CFD-experimental propeller performance comparison. A numerical model has been also proposed to capture the dependence of thrust with distance to the ground and angle of inclination between the propeller and ground planes. We demonstrate that the proximity to the ground of tilted rotors decreases the thrust increment due to the ground effect as the tilt angle (θ) increases. This means that Cheeseman's classical theory is inapplicable, as it only considers the distance from the ground without reference to how the thrust increment changes with the tilt angle. This outcome enables future aerial robotic applications that strongly demand accurate aerodynamic effect models to operate close to obstacles and narrow environments.} }
Free as a Bird: Event-based Dynamic Sense-and-Avoid for Ornithopter Robot Flight
IEEE Robotics and Automation Letters, 7 (2), pp. 5413 - 5420, 2022.
Autonomous flight of flapping-wing robots is a major challenge for robot perception. Most of the previous sense- and-avoid works have studied the problem of obstacle avoidance for flapping-wing robots considering only static obstacles. This paper presents a fully onboard dynamic sense-and-avoid scheme for large-scale ornithopters using event cameras. These sensors trigger pixel information due to changes of illumination in the scene such as those produced by dynamic objects. The method performs event-by-event processing in low-cost hardware such as those onboard small aerial vehicles. The proposed scheme detects obstacles and evaluates possible collisions with the robot body. The onboard controller actuates over the horizontal and vertical tail deflections to execute the avoidance maneuver. The scheme is validated in both indoor and outdoor scenarios using obstacles of different shapes and sizes. To the best of the authors’ knowledge, this is the first event-based method for dynamic obstacle avoidance in a flapping-wing robot.
@article{Rodríguez-Gómez2022Free, title={Free as a Bird: Event-based Dynamic Sense-and-Avoid for Ornithopter Robot Flight}, author={Rodriguez-Gomez, Juan Pablo and Tapia, Raul and Garcia, Maria del Mar Guzman and Martinez-de Dios, JR and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, year={2022},, volume={7}, number={2}, pages={5413-5420}, publisher={IEEE} }
Perception-Aware Perching on Powerlines with Multirotors
IEEE Robotics and Automation Letters, 7(2), pp. 3077-3084, 2022.
Multirotor aerial robots are becoming widely used for the inspection of powerlines. To enable continuous, robust inspection without human intervention, the robots must be able to perch on the powerlines to recharge their batteries. Highly versatile perching capabilities are necessary to adapt to the variety of configurations and constraints that are present in real powerline systems. This paper presents a novel perching trajectory generation framework that computes perception- aware, collision-free, and dynamically-feasible maneuvers to guide the robot to the desired final state. Trajectory generation is achieved via solving a Nonlinear Programming problem using the Primal-Dual Interior Point method. The problem considers the full dynamic model of the robot down to its single rotor thrusts and minimizes the final pose and velocity errors while avoiding collisions and maximizing the visibility of the power- line during the maneuver. The generated maneuvers consider both the perching and the posterior recovery trajectories. The framework adopts costs and constraints defined by efficient mathematical representations of powerlines, enabling online on-board execution in resource-constrained hardware. The method is validated on-board an agile quadrotor conducting powerline inspection and various perching maneuvers with final pitch values of up to 180. We will release our code fully open-sourced upon acceptance.
@article{paneque2022perception, title={Perception-Aware Perching on Powerlines with Multirotors}, author={Paneque, Julio L and Martinez-de-Dios, Jose Ramiro and Ollero, Anibal and Hanover, Drew and Sun, Sihao and Romero, Angel and Scaramuzza, Davide}, journal={IEEE Robotics and Automation Letters}, year={2022}, publisher={IEEE} }
Aerodynamic Reduced-order Volterra Model of an Ornithopter under High-amplitude Flapping
Journal of Aerospace Science and Technology, 107331, 2022
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.
@article{RuizJAST2021, title={Aerodynamic reduced-order Volterra model of an ornithopter under high-amplitude flapping}, author={Ruiz, C and Acosta, J{\'A} and Ollero, A}, journal={Aerospace Science and Technology}, pages={107331}, year={2022}, publisher={Elsevier} }
A Lightweight Beak-Like Sensing System for Grasping Tasks of Flapping Aerial Robots
IEEE Robotics and Automation Letters, 7(2), pp. 2313-2320, 2022.
Many sensor systems in robotics are bio-inspired by similar mechanisms in living creatures. Birds frequently use their beaks to grasp and manipulate objects. This work proposes a very lightweight sensor system that emulates a bird’s beak, thus allowing flapping aerial robots to interact with the environment, as e.g. to perform grasping or manipulation tasks. The sensor system is composed of a flexible link (beam) actuated by a micro servomotor, two strain gauges placed on different points and a rigid link opposed. Additionally, a new algorithm is also developed that estimates the instant at which the beak impacts with an object, the contact position and the exerted force. Our sensor system outperforms the existing designs in robotics applications, because it is lightweight, small, cheap, with very low computational load and without any complementary perception. It is demonstrated that the adequate placement of two strain gauges allow the estimation of the force exerted between the beam and an object, and the accuracy achieved is enough to reckon properties of the object and develop force control systems. The validation has been made and reported through finite-element simulations and experiments, and the results illustrate the efficiency of the prototype and the proposed algorithm.
@article{Feliu2022ALightweight, title={A lightweight beak-like sensing system for grasping tasks of flapping aerial robots}, author={Feliu, Daniel and Acosta, Jose Angel and Feliu, Vicente and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, year={2022}, publisher={IEEE} }
2021
Kinodynamic planning for an energy-efficient autonomous ornithopter
Computers & Industrial Engineering, 107814, 2021.
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 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 it 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 the key parameters, as well as a comparison against a recent alternative probabilistic planner, showing best performance. Finally, we demonstrate how our algorithm can be used for planning perching maneuvers online.
@article{rodriguez2021kinodynamic, 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={Computers \& Industrial Engineering}, pages={107814}, year={2021}, publisher={Elsevier} }
Experimental evaluation of aerial manipulation robot in contact with 15 kV power line: Shielded and long reach configurations
IEEE Access, 9, pp. 94573-94585, 2021.
The use of aerial manipulators for the inspection and maintenance of the power grid requires the safe interaction of the robot with high voltage power lines. In order to identify possible faults or malfunctions during the approaching or interaction phases, this paper presents experimental results in a real 15 kV power line, considering four different configurations for the manipulator: 1) aluminum tube attached to the landing gear, 2) robotic arm attached to the multi-rotor base, 3) shielded aerial manipulator, and 4) long reach configuration (insulated). The paper investigates the electromagnetic susceptibility of the autopilot and the electronic speed controllers to the electrostatic discharge (ESD) raised when the manipulator touches the line, causing the momentary failure of the rotors. A model of the electromagnetic effects associated to the interaction with the line is provided, comparing later the effectiveness of the two solutions for the aerial manipulator: shielding, and insulation.
@article{suarez2021experimental, title={Experimental evaluation of aerial manipulation robot in contact with 15 kV power line: Shielded and long reach configurations}, author={Suarez, Alejandro and Salmoral, Rafael and Zarco-Peri{\~n}an, Pedro J and Ollero, Anibal}, journal={IEEE Access}, volume={9}, pages={94573--94585}, year={2021}, publisher={IEEE} }
Winged Aerial Robot: Modular Design Approach
2021 IEEE International Symposium on Safety, Security, and Rescue Robotics (SSRR), pp. 190-195, 2021.
This paper presents the design, modelling, control, and experimental validation of a novel flapping wing aerial robot built with servo actuators that could be applied in search, rescue, and assistance to injured people. The proposed concept design is intended to facilitate the construction of this kind of aerial robots following a modular and reconfigurable approach, consisting of a series of Servo-Flapping Engine (SFE) modules attached to the carbon fibre tube used as fuselage, and a tail servo, covering the structure with a light nylon cloth. The SFE modules are built with a pair of servos that rotate the wing rods with desired amplitude, frequency, and relative phase. Combining two SFE modules, it is possible to generate different flapping patterns and control the orientation of the aerodynamic surfaces. The paper covers the parametrization of the design, the hardware/software implementation, as well as the modelling and control. The proposed design is validated through gliding and flapping tests in an outdoor environment.
@inproceedings{diez2021winged, title={Winged Aerial Robot: Modular Design Approach}, author={Diez-de-los-Rios, Ivan and Suarez, Alejandro and Sanchez-Laulhe, Ernesto and Armengol, Inmaculada and Ollero, Anibal}, booktitle={2021 IEEE International Symposium on Safety, Security, and Rescue Robotics (SSRR)}, pages={190--195}, year={2021}, organization={IEEE} }
UAV human teleoperation using event-based and frame-based cameras
2021 Aerial Robotic Systems Physically Interacting with the Environment (AIRPHARO), pp. 1-5, 2021.
Teleoperation is a crucial aspect for human-robot interaction with unmanned aerial vehicles (UAVs) applications. Fast perception processing is required to ensure robustness, precision, and safety. Event cameras are neuromorphic sensors that provide low latency response, high dynamic range and low power consumption. Although classical image-based methods have been extensively used for human-robot interaction tasks, responsiveness is limited by their processing rates. This paper presents a human-robot teleoperation scheme for UAVs that exploits the advantages of both traditional and event cameras. The proposed scheme was tested in teleoperation missions where the pose of a multirotor robot is controlled in real time using human gestures detected from events.
@inproceedings{rodriguez2021uav, title={UAV human teleoperation using event-based and frame-based cameras}, author={Rodr{\'\i}guez-G{\'o}mez, JP and Tapia, R and Egu{\'\i}luz, A G{\'o}mez and Mart{\'\i}nez-de Dios, JR and Ollero, A}, booktitle={2021 Aerial Robotic Systems Physically Interacting with the Environment (AIRPHARO)}, pages={1--5}, year={2021}, organization={IEEE} }
Past, Present, and Future of Aerial Robotic Manipulators
IEEE Transactions on Robotics, 38(1), pp. 626-645, 2021.
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}}
Control Aware of Limitations of Manipulators with Claw for Aerial Robots Imitating Bird’s Skeleton
IEEE Robotics and Automation Letters, 6(4), pp. 6426-6433, 2021.
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.
@article{feliu2021control, title={Control Aware of Limitations of Manipulators With Claw for Aerial Robots Imitating Bird's Skeleton}, author={Feliu-Talegon, Daniel and Acosta, Jos{\'e} {\'A}ngel and Ollero, Anibal}, journal={IEEE Robotics and Automation Letters}, volume={6}, number={4}, pages={6426--6433}, year={2021}, publisher={IEEE} }
Event-based human intrusion detection in UAS using Deep Learning
2021 Aerial Robotic Systems Physically Interacting with the Environment (AIRPHARO), pp. 91-100, 2021.
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
2021 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 1284-1290, 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.
@inproceedings{perez2021analysis, 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}, booktitle={2021 International Conference on Unmanned Aircraft Systems (ICUAS)}, pages={1284--1290}, year={2021}, organization={IEEE} }
Design and manufacture of the folding mechanism for a Bioinspired Ornithopter
2021 Aerial Robotic Systems Physically Interacting with the Environment (AIRPHARO), pp. 1-6, 2021.
This paper presents a folding mechanism for ornithopter’s wings. The mechanism has been implemented using rods and joints to replicate wing performance of animal flight. In this sense, bio-inspiration has been the baseline of the design but hard requirements as lightweight and integration with the current platform have also been considered. The final specifications of volume ratio folded/unfolded of 1/3 and additional mass < 100 g/wing with respect to the current structure, make this concept quite promising. Moreover, unlike most of the existent creations, it is intended to allow control of the folding while perching. Bench experiments demonstrate its performance and compatibility with the prototype platform.
@inproceedings{calvente2021design, title={Design and Manufacture of the Wing Folding Mechanism for a Bioinspired Ornithopter}, author={Calvente, Lorena and Acosta, Jos{\'e} {\'A}ngel and Ollero, An{\'\i}bal}, booktitle={2021 Aerial Robotic Systems Physically Interacting with the Environment (AIRPHARO)}, pages={1--6}, year={2021}, organization={IEEE} }
Design of the High-Payload Flapping Wing Robot E-Flap
IEEE Robotics and Automation Letters, 6, pp. 3097-3104, 2021.
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
2021 International Conference on Intelligent Robots and Systems (IROS), pp. 6358-6365, 2021.
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.
Design and comparison of tails for bird-scale flapping-wing robots
2021 International Conference on Intelligent Robots and Systems (IROS), pp. 6358-6365, 2021.
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.
@inproceedings{guzman2021design, title={Design and comparison of tails for bird-scale flapping-wing robots}, author={Guzm{\'a}n, MM and P{\'a}ez, C Ruiz and Maldonado, FJ and Zufferey, R and Tormo-Barbero, J and Acosta, J {\'A} and Ollero, A}, booktitle={2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)}, pages={6358--6365}, organization={IEEE} }
Bio-Inspired Morphing Tail for Flapping Wings Aerial Robots using Macro Fiber Composites
Applied Sciences, 11(7), pp. 2930, 2021.
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} }
Auto-Tuned Event-Based Perception Schemefor Intrusion Monitoring With UAS
IEEE Access, 2021, 9, pp. 44840-44854, 2021.
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 flight
2021 International Conference on Intelligent Robots and Systems (IROS), pp. 1958-1965, 2021.
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.
@inproceedings{EguíluzIROS2021, title={Why fly blind? Event-based visual guidance for ornithopter robot flight}, author={Egu{\'\i}luz, A G{\'o}mez and Rodr{\'\i}guez-G{\'o}mez, JP and Tapia, R and Maldonado, FJ and Acosta, J{\'A} and Mart{\'\i}nez-de Dios, JR and Ollero, A}, booktitle={2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)}, pages={1958--1965}, organization={IEEE} }
The GRIFFIN Perception Dataset: Bridging the Gap Between Flapping-Wing Flight and Robotic Perception
IEEE Robotics and Automation Letters, 6(2), pp. 1066-1073, 2021.
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}}
2020
Towards UAS Surveillance using Event Cameras
2020 IEEE International Symposium on Safety, Security, and Rescue Robotics (SSRR), pp.71-76, 2020.
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
Applied Science, 10(24), pp. 8927, 2020.
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} }
Kinodynamic planning for an energy-efficient autonomous ornithopter
Arxiv, 201012273, 2020.
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
2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 8807-8814, 2020.
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} }
ASAP: Adaptive Scheme for Asynchronous Processing of event-based vision algorithms
IEEE International Conference on Robotics and Automation (ICRA) Workshop on Unconventional Sensors in Robotics, 2020.
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
2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 5978-5985, 2020.
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
2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 1385-1390, 2020.
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} }
A bio-inspired manipulator with claw prototype for winged aerial robots: Benchmark for design and control
Applied Sciences, 10(18), 6516, 2020.
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
2020 IEEE International Conference on Robotics and Automation (ICRA), pp. 8518-8524, 2020.
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}}
Effects of Unsteady Aerodynamics on Gliding Stability of a Bio-Inspired UAV
2020 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 1596-1604, 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}}
POSITRON: Lightweight Active Positioning Compilant Joints Robotic Arm in Power Lines Inspection
2020 International Conference on Unmanned Aircraft Systems (ICUAS), pp. 729-736, 2020.
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} }
Winged Aerial Manipulation Robot with Dual Arm and Tail
Applied Sciences, 10(14), pp. 4783, 2020.
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} }
A Linearized Model for an Ornithopter in Gliding Flight: Experiments and Simulations
2020 IEEE International Conference on Robotics and Automation (ICRA), pp. 7008-7014, 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} }
Benchmarks for Aerial Manipulation
IEEE Robotics and Automation Letters, 5(2), pp. 2650-2657, 2020.
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} }
Towards flapping wing robot visual perception: Opportunities and challenges
2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS), pp: 335-343, 2019.
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}}
2019
ROSS-LAN: RObotic Sensing Simulation Scheme for Bioinspired Robotic Bird LANding
ROBOT 2019: Robot 2019: Fourth Iberian Robotics Conference, pp: 49-59, 2019.
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}, }
Online Detection and Tracking of Pipes During UAV Flight in Industrial Environments
ROBOT 2019: Robot 2019: Fourth Iberian Robotics Conference, pp: 28-39, 2019.
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
2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS), pp. 352-361, 2019.
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
ROBOT 2019: Robot 2019: Fourth Iberian Robotics Conference, pp. 40-51, 2019.
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
2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Macau, China, pp 208-214, 2019.
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
2019 International Conference on Unmanned Aircraft Systems (ICUAS), Atlanta, Georgia (USA), pp 729-737, 2019.
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} }
