Our research publications are listed here. Most research papers can be accessed by the Digital Object Identifier (doi) links, or from publication resources, e.g. IEEE Xplore, AIAA NRC, and arXiv. Some papers have preprint or submission versions in PDF file format that can be downloaded/viewed for general readership, please consult official publications for citation. If you are citing our work, please use the BibTeX entries for citations.
2024
353.
Qin*, Chao; Michet*, Maxime S. J.; Chen*, Jingxiang; Liu, Hugh H. -T.
Time-Optimal Gate-Traversing Planner for Autonomous Drone Racing Inproceedings
In: 2024 IEEE International Conference on Robotics and Automation (ICRA), IEEE, 2024.
@inproceedings{ICRA2024CQ,
title = {Time-Optimal Gate-Traversing Planner for Autonomous Drone Racing},
author = {Chao Qin* and Maxime S.J. Michet* and Jingxiang Chen* and Hugh H. -T. Liu},
year = {2024},
date = {2024-01-31},
urldate = {2024-01-31},
booktitle = {2024 IEEE International Conference on Robotics and Automation (ICRA)},
publisher = {IEEE},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
352.
Go*, Hei Helson; Liu, Hugh H. -T.
Trajectory Optimization for Cooperatively Localizing Quadrotor UAVs Inproceedings
In: 2024 IEEE International Conference on Robotics and Automation (ICRA), IEEE, 2024.
@inproceedings{ICRA2024HG,
title = {Trajectory Optimization for Cooperatively Localizing Quadrotor UAVs},
author = {Hei Helson Go* and Hugh H. -T. Liu},
year = {2024},
date = {2024-01-31},
urldate = {2024-01-31},
booktitle = {2024 IEEE International Conference on Robotics and Automation (ICRA)},
publisher = {IEEE},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
351.
Zanjanpour, Darya; Kokate, Sana; Liu, Hugh H-T; Plaks, Jason E
Quantifying Trust in Human-Drone Interaction for Advanced Air Mobility Systems Inproceedings
In: 2024 IEEE International Conference on Human-Machine Systems (ICHMS), IEEE, 2024.
@inproceedings{ICHMS2024DZ,
title = {Quantifying Trust in Human-Drone Interaction for Advanced Air Mobility Systems},
author = {Darya Zanjanpour and Sana Kokate and Hugh H-T Liu and Jason E Plaks},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2024/02/ICHMS2024DZ_fi.pdf},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
booktitle = {2024 IEEE International Conference on Human-Machine Systems (ICHMS)},
journal = {International Conference on Human-Machine Systems},
publisher = {IEEE},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
2023
350.
Qian*, Longhao
Trajectory Control of A Fixed-wing Crop Monitoring Drone: A Case Study Conference
Canadian Aeronautics and Space Institute AERO 23, 2023.
@conference{CASI2023LHQ,
title = {Trajectory Control of A Fixed-wing Crop Monitoring Drone: A Case Study},
author = {Longhao Qian*},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/11/CASI-2023-longhao_final.pptx.pdf},
year = {2023},
date = {2023-11-14},
urldate = {2023-11-14},
booktitle = {Canadian Aeronautics and Space Institute AERO 23},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
349.
Elahi*, Zaheed
Intelligent Control for Electric-Vertical Take Off and Landing (e-VTOL) Aircraft Conference
Canadian Aeronautics and Space Institute AERO 23, 2023.
@conference{CASI2023ZE,
title = {Intelligent Control for Electric-Vertical Take Off and Landing (e-VTOL) Aircraft},
author = {Zaheed Elahi*},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/11/CASI_AERO_2023_Presentation_Zaheed.pdf},
year = {2023},
date = {2023-11-14},
urldate = {2023-11-14},
booktitle = {Canadian Aeronautics and Space Institute AERO 23},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
348.
Qian*, Longhao
Robust Stabilization Of A Quadrotor as A 5G Access Point Using Acceleration Feedback Conference
2023 IEEE 9th World Forum on Internet of Things, 2023.
@conference{WFIT2023LHQ,
title = {Robust Stabilization Of A Quadrotor as A 5G Access Point Using Acceleration Feedback},
author = {Longhao Qian*},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/10/Longhao-WF_IOT-2023.pdf},
year = {2023},
date = {2023-10-19},
urldate = {2023-10-19},
booktitle = {2023 IEEE 9th World Forum on Internet of Things},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
347.
Qin*, Chao; Yu*, Qiuyu; Go*, Shing Hei Helson; Liu, Hugh H. -T.
Perception-Aware Image-Based Visual Servoing of Aggressive Quadrotor UAVs Journal Article
In: IEEE/ASME Transactions on Mechatronics, 2023.
@article{TMech2023CQ,
title = {Perception-Aware Image-Based Visual Servoing of Aggressive Quadrotor UAVs},
author = {Chao Qin* and Qiuyu Yu* and Shing Hei Helson Go* and Hugh H. -T. Liu},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {IEEE/ASME Transactions on Mechatronics},
abstract = {The maintenance of visual features within the sensor field of view (FOV) poses a significant challenge for underactuated aerial vehicles like quadrotors, especially during aggressive maneuvers. However, existing image-based visual servo control (IBVS) methods rely on strict target visibility assumptions or impose excessive constraints on the quadrotor's agility to meet this requirement. Furthermore, the effectiveness of the visibility constraint defined in prior works remains unverified in aggressive flight tests. To address these issues, we present a robust IBVS scheme for quadrotors to perform aggressive maneuvers while ensuring target visibility. Based on the nonlinear model predictive control (NMPC) framework, we propose a novel underactuation compensation scheme to eliminate the need for a virtual camera frame, which enables us to formulate the true target visibility constraint. We then introduce a quaternion-based representation of spherical visual features to handle the nonsmooth vector field problem on the 2-sphere and derive its corresponding image kinematics. We validate our method through three challenging visual servo tasks where agile maneuvers are desired: fast landing, aggressive long-distance flight, and dynamic object tracking. Extensive simulation and experiment show that our method consistently achieves a target-visible rate of 100% in all image frames, even under a maximum pitch of 21.04$^circ$. The results validate the effectiveness of our visibility constraint under large robot rotations and underscore its importance in enabling robust and aggressive flights.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The maintenance of visual features within the sensor field of view (FOV) poses a significant challenge for underactuated aerial vehicles like quadrotors, especially during aggressive maneuvers. However, existing image-based visual servo control (IBVS) methods rely on strict target visibility assumptions or impose excessive constraints on the quadrotor's agility to meet this requirement. Furthermore, the effectiveness of the visibility constraint defined in prior works remains unverified in aggressive flight tests. To address these issues, we present a robust IBVS scheme for quadrotors to perform aggressive maneuvers while ensuring target visibility. Based on the nonlinear model predictive control (NMPC) framework, we propose a novel underactuation compensation scheme to eliminate the need for a virtual camera frame, which enables us to formulate the true target visibility constraint. We then introduce a quaternion-based representation of spherical visual features to handle the nonsmooth vector field problem on the 2-sphere and derive its corresponding image kinematics. We validate our method through three challenging visual servo tasks where agile maneuvers are desired: fast landing, aggressive long-distance flight, and dynamic object tracking. Extensive simulation and experiment show that our method consistently achieves a target-visible rate of 100% in all image frames, even under a maximum pitch of 21.04$^circ$. The results validate the effectiveness of our visibility constraint under large robot rotations and underscore its importance in enabling robust and aggressive flights.
346.
Qin*, Chao; Yu*, Qiuyu; Go*, Shing Hei Helson; Liu, Hugh H. -T.
Perception-Aware Image-Based Visual Servoing of Aggressive Quadrotor UAVs Inproceedings
In: Advanced Intelligent Mechatronics (AIM), IEEE, 2023.
@inproceedings{AIM2023CQ,
title = {Perception-Aware Image-Based Visual Servoing of Aggressive Quadrotor UAVs},
author = {Chao Qin* and Qiuyu Yu* and Shing Hei Helson Go* and Hugh H. -T. Liu},
url = {https://www.youtube.com/watch?v=X2-SMGD99oA},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {Advanced Intelligent Mechatronics (AIM)},
journal = {IEEE/ASME International Conference on Advanced Intelligent Mechatronics},
publisher = {IEEE},
abstract = {The maintenance of visual features within the sensor field of view (FOV) poses a significant challenge for underactuated aerial vehicles like quadrotors, especially during aggressive maneuvers. However, existing image-based visual servo control (IBVS) methods rely on strict target visibility assumptions or impose excessive constraints on the quadrotor's agility to meet this requirement. Furthermore, the effectiveness of the visibility constraint defined in prior works remains unverified in aggressive flight tests. To address these issues, we present a robust IBVS scheme for quadrotors to perform aggressive maneuvers while ensuring target visibility. Based on the nonlinear model predictive control (NMPC) framework, we propose a novel underactuation compensation scheme to eliminate the need for a virtual camera frame, which enables us to formulate the true target visibility constraint. We then introduce a quaternion-based representation of spherical visual features to handle the nonsmooth vector field problem on the 2-sphere and derive its corresponding image kinematics. We validate our method through three challenging visual servo tasks where agile maneuvers are desired: fast landing, aggressive long-distance flight, and dynamic object tracking. Extensive simulation and experiment show that our method consistently achieves a target-visible rate of 100% in all image frames, even under a maximum pitch of 21.04$^circ$. The results validate the effectiveness of our visibility constraint under large robot rotations and underscore its importance in enabling robust and aggressive flights.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The maintenance of visual features within the sensor field of view (FOV) poses a significant challenge for underactuated aerial vehicles like quadrotors, especially during aggressive maneuvers. However, existing image-based visual servo control (IBVS) methods rely on strict target visibility assumptions or impose excessive constraints on the quadrotor's agility to meet this requirement. Furthermore, the effectiveness of the visibility constraint defined in prior works remains unverified in aggressive flight tests. To address these issues, we present a robust IBVS scheme for quadrotors to perform aggressive maneuvers while ensuring target visibility. Based on the nonlinear model predictive control (NMPC) framework, we propose a novel underactuation compensation scheme to eliminate the need for a virtual camera frame, which enables us to formulate the true target visibility constraint. We then introduce a quaternion-based representation of spherical visual features to handle the nonsmooth vector field problem on the 2-sphere and derive its corresponding image kinematics. We validate our method through three challenging visual servo tasks where agile maneuvers are desired: fast landing, aggressive long-distance flight, and dynamic object tracking. Extensive simulation and experiment show that our method consistently achieves a target-visible rate of 100% in all image frames, even under a maximum pitch of 21.04$^circ$. The results validate the effectiveness of our visibility constraint under large robot rotations and underscore its importance in enabling robust and aggressive flights.
345.
Xiong*, Shangyi; Liu, Hugh H. -T.
A Model-Based Drift Correction Control for UAV in GNSS-Degraded Environments Inproceedings
In: IEEE Conference on Control Technology and Applications, 2023.
@inproceedings{CCTA2023SX,
title = {A Model-Based Drift Correction Control for UAV in GNSS-Degraded Environments},
author = {Shangyi Xiong* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/08/CCTA_Presentation.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {IEEE Conference on Control Technology and Applications},
journal = {IEEE Conference on Control Technology and Applications},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
344.
Feng*, Cindi; Liu, Hugh H. -T.
Collision-free Path Planning and Control of Coordinated UAVs with Tethered Payloads Inproceedings
In: IEEE Conference on Control Technology and Applications, 2023.
@inproceedings{CCTA2023CF,
title = {Collision-free Path Planning and Control of Coordinated UAVs with Tethered Payloads},
author = {Cindi Feng* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/09/Cindi_CCTA_Presentation.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {IEEE Conference on Control Technology and Applications},
journal = {IEEE Conference on Control Technology and Applications},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
343.
Go*, Shing Hei Helson; Qian*, Longhao; Liu, Hugh HT
Data-Driven and Robust Path-following Control of a Quadrotor Slung Load Transport System Inproceedings
In: AIAA SciTech, 2023.
@inproceedings{SciTech2023HG,
title = {Data-Driven and Robust Path-following Control of a Quadrotor Slung Load Transport System},
author = {Shing Hei Helson Go* and Longhao Qian* and Hugh HT Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/scitech2023hg_final.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {AIAA SciTech},
journal = {AIAA SciTech},
abstract = {In this paper, a robust path following control law for a quadrotor Slung Load Transport System is developed. A Gaussian Process-augmented Extended Kalman Filter is proposed to estimate payload states. In this approach, Gaussian Processes are used to compensate for unmodelled dynamics in the process model, and they are trained on previously collected data of a Slung Load Transport System in flight. Both simulations and experiments verify the estimation and control system framework and demonstrate successful stabilization and trajectory tracking of the Slung Load Transport System, overcoming model inaccuracy and disturbances. I. Nomenclature F − → = NED inertial frame F − → = Quadrotor body-fixed frame, fixed at the mass center of the quadrotor vehicle = Quadrotor mass J = Quadrotor moment of inertia = Payload mass = Cable length g = Gravity vector in the world frame ∈ R 3 = Vector spanning the length of the cable x ∈ R 3 = Absolute position of the payload mass center v ∈ R 3 = Absolute velocity of the payload mass center, expressed in F − → r ∈ R 2 = Relative position of the quadrotor mass center w.r.t. the payload, projected onto the XY plane of F − → v ∈ R 2 = Relative velocity of the quadrotor mass center w.r.t. the payload, projected onto the XY plane of F − → ˜ v ∈ R 2 = Difference between v predicted by some dynamics model and the true value B ∈ R 3×2 = Projection from v to the time derivative of R ∈ SO(3) = Rotation of F − → relative to F − → ∈ R 3 = Angular velocity of the F − → relative to F − → , expressed in F − → f ∈ R 3 = Total thrust delivered by the actuators ∈ R 3 = Total torque delivered by the actuators d ∈ R 3 = Disturbance acting on the payload d ∈ R 3 = Disturbance acting on the quadrotor body d ∈ R 3 = Sum of disturbances acting on the SLTS e ∈ R 3 = Positional (radial) error of the payload from some given path e ∈ R 3 = Velocity (tangential) error of the payload from some given path × : R 3 → R 3×3 = Maps a 3-vector to a 3-by-3 skew-symmetric (cross product) matrix ∨ : R 3×3 → R 3 = The inverse operation of the × mapping * Ph.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
In this paper, a robust path following control law for a quadrotor Slung Load Transport System is developed. A Gaussian Process-augmented Extended Kalman Filter is proposed to estimate payload states. In this approach, Gaussian Processes are used to compensate for unmodelled dynamics in the process model, and they are trained on previously collected data of a Slung Load Transport System in flight. Both simulations and experiments verify the estimation and control system framework and demonstrate successful stabilization and trajectory tracking of the Slung Load Transport System, overcoming model inaccuracy and disturbances. I. Nomenclature F − → = NED inertial frame F − → = Quadrotor body-fixed frame, fixed at the mass center of the quadrotor vehicle = Quadrotor mass J = Quadrotor moment of inertia = Payload mass = Cable length g = Gravity vector in the world frame ∈ R 3 = Vector spanning the length of the cable x ∈ R 3 = Absolute position of the payload mass center v ∈ R 3 = Absolute velocity of the payload mass center, expressed in F − → r ∈ R 2 = Relative position of the quadrotor mass center w.r.t. the payload, projected onto the XY plane of F − → v ∈ R 2 = Relative velocity of the quadrotor mass center w.r.t. the payload, projected onto the XY plane of F − → ˜ v ∈ R 2 = Difference between v predicted by some dynamics model and the true value B ∈ R 3×2 = Projection from v to the time derivative of R ∈ SO(3) = Rotation of F − → relative to F − → ∈ R 3 = Angular velocity of the F − → relative to F − → , expressed in F − → f ∈ R 3 = Total thrust delivered by the actuators ∈ R 3 = Total torque delivered by the actuators d ∈ R 3 = Disturbance acting on the payload d ∈ R 3 = Disturbance acting on the quadrotor body d ∈ R 3 = Sum of disturbances acting on the SLTS e ∈ R 3 = Positional (radial) error of the payload from some given path e ∈ R 3 = Velocity (tangential) error of the payload from some given path × : R 3 → R 3×3 = Maps a 3-vector to a 3-by-3 skew-symmetric (cross product) matrix ∨ : R 3×3 → R 3 = The inverse operation of the × mapping * Ph.
342.
Fu*, Han; Liu, Hugh H. -T.
Defending a Target Area with a Slower Defender Journal Article
In: IEEE Control Systems Letters, 7 , pp. 661-666, 2023.
@article{LCSS2023FF,
title = {Defending a Target Area with a Slower Defender},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/LCSS2023FF.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {IEEE Control Systems Letters},
volume = {7},
pages = {661-666},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
341.
Fu*, Han; Liu, Hugh H. -T.
Justification of the geometric solution of a target defense game with faster defenders and a convex target area using the HJI equation Journal Article
In: Automatica, 149 , 2023.
@article{Automatica2023FF,
title = {Justification of the geometric solution of a target defense game with faster defenders and a convex target area using the HJI equation},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/automatica2023FF.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Automatica},
volume = {149},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
340.
Fu*, Han; Liu, Hugh H. -T.
Defending a Target Area with a Slower Defender Inproceedings
In: American Control Conference, 2023.
@inproceedings{ACC2023FF,
title = {Defending a Target Area with a Slower Defender},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/06/acc_2023_FF_slides.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {American Control Conference},
journal = {American Control Conference},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
339.
Wedage*, Pravin; Liu, Hugh H. -T.
A UDE-Based Controller with Targeted Filtering for the Stabilization of a Fixed-Wing UAV in the Harrier Maneuver Inproceedings
In: American Control Conference (ACC), 2023.
@inproceedings{ACC2023PW,
title = {A UDE-Based Controller with Targeted Filtering for the Stabilization of a Fixed-Wing UAV in the Harrier Maneuver},
author = {Pravin Wedage* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/ACC2023PW_final.pdf
https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/06/acc_2023_PW_slides.pdf},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
booktitle = {American Control Conference (ACC)},
journal = {American Control Conference (ACC)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
338.
Fan*, Shichen; Liu, Hugh H. -T.
Multi-UAV Cooperative Hunting in Cluttered Environments Considering Downwash Effects Journal Article
In: Guiance, Navigation and Control, 3 , 2023.
@article{JGNC2023SF,
title = {Multi-UAV Cooperative Hunting in Cluttered Environments Considering Downwash Effects},
author = {Shichen Fan* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/06/JGNC2023SF_published.pdf},
doi = {10.1142/S2737480723500048},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Guiance, Navigation and Control},
volume = {3},
abstract = {This paper presents a novel solution to the three-dimensional (3D) cooperative hunting of multiple drones that deals with surrounding a target simultaneously while navigating around obstacles in the cluttered dynamic 3D environment. Meanwhile, drones avoid the airflow downwash force created by the spinning propellers on unmanned aerial vehicles (UAVs) and their effect on the other UAVs. This solution consists of a 3D Simultaneous Encirclement strategy, the cooperative hunting objective with a novel revised particle swarm optimization (PSO*) path planning algorithm, a flocking theory-inspired obstacle avoidance algorithm, and a cascade PI controller. Simulation results with varying conditions were carried out to validate the effectiveness of the proposed solution by successfully taking care of the downwash effects, and having multiple hunter UAVS hunt and encircle a moving or stationary target in a dynamic or static obstacle-rich cluttered environment.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper presents a novel solution to the three-dimensional (3D) cooperative hunting of multiple drones that deals with surrounding a target simultaneously while navigating around obstacles in the cluttered dynamic 3D environment. Meanwhile, drones avoid the airflow downwash force created by the spinning propellers on unmanned aerial vehicles (UAVs) and their effect on the other UAVs. This solution consists of a 3D Simultaneous Encirclement strategy, the cooperative hunting objective with a novel revised particle swarm optimization (PSO*) path planning algorithm, a flocking theory-inspired obstacle avoidance algorithm, and a cascade PI controller. Simulation results with varying conditions were carried out to validate the effectiveness of the proposed solution by successfully taking care of the downwash effects, and having multiple hunter UAVS hunt and encircle a moving or stationary target in a dynamic or static obstacle-rich cluttered environment.
2022
337.
Yang*, Huiliao; Jiang, Bin; Yang, Hao; Liu, Hugh H. -T.
Fault Tolerant Cooperative Control for Multiple Vehicle Systems Based on Topology Journal Article
In: IEEE Transactions on Cyberneticsernetics, 52 (7), pp. 6649–6661, 2022.
@article{Tcyber2022HLY,
title = {Fault Tolerant Cooperative Control for Multiple Vehicle Systems Based on Topology},
author = {Huiliao Yang* and Bin Jiang and Hao Yang and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2022/09/tcyber2022hly_preprint.pdf},
doi = {10.1109/TCYB.2020.3035557},
year = {2022},
date = {2022-09-07},
urldate = {2022-09-07},
journal = {IEEE Transactions on Cyberneticsernetics},
volume = {52},
number = {7},
pages = {6649--6661},
abstract = {In this article, the fault-tolerant synchronization and time-varying tracking control problem is investigated for nonlinear multivehicle systems (MVSs) in the presence of partial loss-of-control-effectiveness (LoCE) faults. Based on the graph theory, a two-level fault-tolerant cooperative control framework is proposed, namely, the low-level distributed nominal control scheme and the high-level topology reconfiguration protocols. The low-level scheme is developed to guarantee system performances in the fault-free scenario. With the low-level scheme, the high-level topology reconfiguration protocols, each of which corresponds to one partial LoCE fault scenario, are then proposed to mitigate the fault impact by adjusting the underlying topology. Accordingly, without modifying the structure or the design parameter of the low-level control scheme, the proposed framework can guarantee the synchronization and tracking errors of the MVS asymptotically convergent to zero in both fault-free and fault scenarios. Finally, the effectiveness of the proposed control method is verified via a simulation study of three degree-of-freedom helicopters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this article, the fault-tolerant synchronization and time-varying tracking control problem is investigated for nonlinear multivehicle systems (MVSs) in the presence of partial loss-of-control-effectiveness (LoCE) faults. Based on the graph theory, a two-level fault-tolerant cooperative control framework is proposed, namely, the low-level distributed nominal control scheme and the high-level topology reconfiguration protocols. The low-level scheme is developed to guarantee system performances in the fault-free scenario. With the low-level scheme, the high-level topology reconfiguration protocols, each of which corresponds to one partial LoCE fault scenario, are then proposed to mitigate the fault impact by adjusting the underlying topology. Accordingly, without modifying the structure or the design parameter of the low-level control scheme, the proposed framework can guarantee the synchronization and tracking errors of the MVS asymptotically convergent to zero in both fault-free and fault scenarios. Finally, the effectiveness of the proposed control method is verified via a simulation study of three degree-of-freedom helicopters.
336.
Chen*, Chih-Chun; Liu, Hugh H. -T.
Model of UAV and Downwash for Multi-UAV Path Planning Inproceedings
In: AIAA SciTech Forum, 2022.
@inproceedings{SciTech2022CC,
title = {Model of UAV and Downwash for Multi-UAV Path Planning},
author = {Chih-Chun Chen* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2022/01/scitech2022cc_submission.pdf
https://arc.aiaa.org/eprint/ZKBTBXKR8KTTFGRQMZJT/full/10.2514/6.2022-0757
https://youtu.be/MC34Yy4fwEQ
},
doi = {10.2514/6.2022-0757},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
booktitle = {AIAA SciTech Forum},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
335.
Yu*, Qiuyu; Qin*, Chao; Luo, Lingkun; Liu, Hugh H-T; Hu, Shiqiang
CPA-Planner: Motion Planner with Complete Perception Awareness for Sensing-Limited Quadrotors Journal Article
In: IEEE Robotics and Automation Letters, 2022.
@article{yu2022cpa,
title = {CPA-Planner: Motion Planner with Complete Perception Awareness for Sensing-Limited Quadrotors},
author = {Qiuyu Yu* and Chao Qin* and Lingkun Luo and Hugh H-T Liu and Shiqiang Hu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/RAL2022JY_accept.pdf},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
journal = {IEEE Robotics and Automation Letters},
publisher = {IEEE},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
334.
Qian*, Longhao; Liu, Hugh H. -T.
Robust Control Study for Tethered Payload Transportation Using Multiple Quadrotor UAVs Journal Article
In: AIAA Journal of Guidance, Control and Dynamics, 45 , pp. 435-452, 2022.
@article{JGCD2022LHQ,
title = {Robust Control Study for Tethered Payload Transportation Using Multiple Quadrotor UAVs},
author = {Longhao Qian* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/jgcd2022lhq.pdf},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
journal = {AIAA Journal of Guidance, Control and Dynamics},
volume = {45},
pages = {435-452},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
333.
Fu*, Han; Liu, Hugh H. -T.
An Isochron-Based Solution to the Target Defense Game Against a Faster Invader Journal Article
In: IEEE Control Systems Letters, 6 , pp. 1352-1357, 2022.
@article{LCSS2022FF,
title = {An Isochron-Based Solution to the Target Defense Game Against a Faster Invader},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/LCSS2022FF.pdf},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
journal = {IEEE Control Systems Letters},
volume = {6},
pages = {1352-1357},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
332.
Zepp*, Noah D.; Fu*, Han; Liu, Hugh H. -T.
Autonomous Strategic Defense: An Adaptive Clustering Approach to Capture Order Optimization Inproceedings
In: AIAA SciTech Forum, 2022.
@inproceedings{SciTech2022NZ,
title = {Autonomous Strategic Defense: An Adaptive Clustering Approach to Capture Order Optimization},
author = {Noah D. Zepp* and Han Fu* and Hugh H. -T. Liu},
url = {https://arc.aiaa.org/eprint/DV82XSBYNEMIZQDEJU5A/full/10.2514/6.2022-2215},
doi = {10.2514/6.2022-2215},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
booktitle = {AIAA SciTech Forum},
journal = {AIAA SciTech Forum},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
331.
Chen*, Ti; Shan, Jinjun; Liu, Hugh H. T.
Transportation of Payload Using Multiple Quadrotors via Rigid Connection Journal Article
In: International Journal of Aerospace Engineering, 2022 , pp. 1-13, 2022, ISSN: 1687-5974.
@article{IJAE2022TC,
title = {Transportation of Payload Using Multiple Quadrotors via Rigid Connection},
author = {Ti Chen* and Jinjun Shan and Hugh H. T. Liu},
editor = {Adel Ghenaiet},
url = {https://www.hindawi.com/journals/ijae/2022/2486561/},
doi = {10.1155/2022/2486561},
issn = {1687-5974},
year = {2022},
date = {2022-01-01},
journal = {International Journal of Aerospace Engineering},
volume = {2022},
pages = {1-13},
abstract = {Due to the limited payload capability of an aerial robot, multiple quadrotors can be used to manipulate payloads in aerial transportation, construction, and assembly tasks. This paper focuses on the cooperative transportation of a payload rigidly attached to multiple quadrotor bodies. These quadrotors may have different orientations. The dynamics equation of a rigid body in 3-D space is derived to describe the motion of such a transportation system. Robust position and attitude controllers are designed to drive the system to the desired pose. To assign control signals for each quadrotor, the control command allocation method compatible with the case that partial or all quadrotors are in parallel planes is developed. Finally, experimental results are presented to validate the effectiveness of the proposed controllers and control command allocation methods. Different from classical works in this field, this paper can solve the dynamics modeling, controller design, and control command allocation problems for the transportation of a rigidly connected payload using a team of quadrotors with different orientations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Due to the limited payload capability of an aerial robot, multiple quadrotors can be used to manipulate payloads in aerial transportation, construction, and assembly tasks. This paper focuses on the cooperative transportation of a payload rigidly attached to multiple quadrotor bodies. These quadrotors may have different orientations. The dynamics equation of a rigid body in 3-D space is derived to describe the motion of such a transportation system. Robust position and attitude controllers are designed to drive the system to the desired pose. To assign control signals for each quadrotor, the control command allocation method compatible with the case that partial or all quadrotors are in parallel planes is developed. Finally, experimental results are presented to validate the effectiveness of the proposed controllers and control command allocation methods. Different from classical works in this field, this paper can solve the dynamics modeling, controller design, and control command allocation problems for the transportation of a rigidly connected payload using a team of quadrotors with different orientations.
330.
Xiong*, Shangyi; Liu, Hugh H. -T.
Low-Altitude Flight Control for Crop Dusting Inproceedings
In: American Control Conference, pp. submitted, 2022.
@inproceedings{ACC2022SX,
title = {Low-Altitude Flight Control for Crop Dusting},
author = {Shangyi Xiong* and Hugh H. -T. Liu},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
booktitle = {American Control Conference},
journal = {American Control Conference},
pages = {submitted},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
329.
Zhu*, Yang; Qi*, Yuhua; Zhu, Bo; Liu, Hugh H. -T.
Rejecting Measurement Error by Embedding MEE into UDE-based Position Control for Quadrotors in Indoor Environments Journal Article
In: IEEE Transactions on Instrumentaion & Measurement, pp. TIM-S-22-00046, 2022.
@article{TIM2022YZ,
title = {Rejecting Measurement Error by Embedding MEE into UDE-based Position Control for Quadrotors in Indoor Environments},
author = {Yang Zhu* and Yuhua Qi* and Bo Zhu and Hugh H. -T. Liu},
year = {2022},
date = {2022-01-01},
journal = {IEEE Transactions on Instrumentaion & Measurement},
pages = {TIM-S-22-00046},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
328.
Fan*, Shichen; Song*, Ge; Chen*, Chih-Chun; Shi, Peng; Liu, Hugh H. -T.
Multi-UAV Cooperative Hunting Using PSO in 3D Cluttered Environment Inproceedings
In: International Conference of Guidance, Navigation and Control, pp. 1-10 (accepted), 2022.
@inproceedings{ICGNC2022SF,
title = {Multi-UAV Cooperative Hunting Using PSO in 3D Cluttered Environment},
author = {Shichen Fan* and Ge Song* and Chih-Chun Chen* and Peng Shi and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/icgnc2022.pdf},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
booktitle = {International Conference of Guidance, Navigation and Control},
journal = {International Conference of Guidance, Navigation and Control},
pages = {1-10 (accepted)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
2021
327.
Chen*, Ti; Shan, Jinjun; Liu, Hugh H -T
Cooperative Transportation of a Flexible Payload Using Two Quadrotors Journal Article
In: AIAA Journal of Guidance, Control and Dynamics, 2021.
@article{JGCD2021TC,
title = {Cooperative Transportation of a Flexible Payload Using Two Quadrotors},
author = {Ti Chen* and Jinjun Shan and Hugh H -T Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2021/07/jgcd2021tc.pdf
},
doi = {10.2514/1.G005914},
year = {2021},
date = {2021-07-07},
journal = {AIAA Journal of Guidance, Control and Dynamics},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
326.
Hsu*, MoWei; Liu, Hugh H -T
Design of a Nonlinear Hierarchical Adaptive Controller for a Tilt-Rotor VTOL AquaUAV Inproceedings
In: AIAA SciTech Forum, pp. 1–10 (submitted), 2021.
@inproceedings{SciTech2021WH,
title = {Design of a Nonlinear Hierarchical Adaptive Controller for a Tilt-Rotor VTOL AquaUAV},
author = {MoWei Hsu* and Hugh H -T Liu},
year = {2021},
date = {2021-01-01},
booktitle = {AIAA SciTech Forum},
pages = {1--10 (submitted)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
325.
Fu*, Han; Liu, Hugh H. -T.
Autonomous Strategic Defense: An Adaptive Clustering Approach to the n-Invader Capture Order Problem Inproceedings
In: IEEE Conference on Decision and ControlConference, pp. 1-6 (submitted), 2021.
@inproceedings{CDC2021FF,
title = {Autonomous Strategic Defense: An Adaptive Clustering Approach to the n-Invader Capture Order Problem},
author = {Han Fu* and Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {IEEE Conference on Decision and ControlConference},
journal = {IEEE Conference on Decision and ControlConference},
pages = {1-6 (submitted)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
324.
Fu*, Han; Liu, Hugh H. -T.
Optimal Solution of a Target Defense Game with Two defenders and a Faster Intrude Journal Article
In: Unmanned Systems, 09 , pp. 247-262, 2021, ISSN: 2301-3850.
@article{US2021FF,
title = {Optimal Solution of a Target Defense Game with Two defenders and a Faster Intrude},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.worldscientific.com/doi/abs/10.1142/S2301385021410016},
doi = {10.1142/S2301385021410016},
issn = {2301-3850},
year = {2021},
date = {2021-01-01},
journal = {Unmanned Systems},
volume = {09},
pages = {247-262},
abstract = {A target defense game with two defenders and a faster intruder is solved based on the classic differential game theory. In the game, the intruder seeks to enter a circular target area, while the defenders endeavor to capture it outside of the target. Under the faster intruder assumption, the game has two phases, where the optimal trajectories are straight and curved, respectively. In the second phase, a peculiar phenomenon exists where the intruder moves at the edge of one defender’s capture region, yet this defender cannot force capture. Because of this, the terminal states of the game are singular, therefore the standard method of integrating optimal trajectories from terminal states is not applicable. The way to circumvent this singularity is to solve the optimal trajectories of a two-player game between the intruder and the closer defender, and assemble them with the trajectory of the other defender. The key contribution of this paper is the solution of the intruder-closer-defender subgame against a circular target area. In the vector field of the optimal trajectories, two singular surfaces and a singular point are observed. Each singular surface indicates a discontinuity in the closer defender’s control, while the singular point represents a situation where the target is successfully protected by a single defender. The complete solution of the two-defender game is solved based on the result of the intruder-closer-defender subgame. The proposed solution is verified through a special case where the capture range is zero. This verification also presents a simpler approach of solving the zero capture range problem.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A target defense game with two defenders and a faster intruder is solved based on the classic differential game theory. In the game, the intruder seeks to enter a circular target area, while the defenders endeavor to capture it outside of the target. Under the faster intruder assumption, the game has two phases, where the optimal trajectories are straight and curved, respectively. In the second phase, a peculiar phenomenon exists where the intruder moves at the edge of one defender’s capture region, yet this defender cannot force capture. Because of this, the terminal states of the game are singular, therefore the standard method of integrating optimal trajectories from terminal states is not applicable. The way to circumvent this singularity is to solve the optimal trajectories of a two-player game between the intruder and the closer defender, and assemble them with the trajectory of the other defender. The key contribution of this paper is the solution of the intruder-closer-defender subgame against a circular target area. In the vector field of the optimal trajectories, two singular surfaces and a singular point are observed. Each singular surface indicates a discontinuity in the closer defender’s control, while the singular point represents a situation where the target is successfully protected by a single defender. The complete solution of the two-defender game is solved based on the result of the intruder-closer-defender subgame. The proposed solution is verified through a special case where the capture range is zero. This verification also presents a simpler approach of solving the zero capture range problem.
323.
Fu*, Han; Liu, Hugh H. -T.
On the Strategies of Defending a Target against Multiple Intruders Inproceedings
In: AIAA SciTech Forum, pp. 1-10 (submitted), 2021.
@inproceedings{SciTech2021FF,
title = {On the Strategies of Defending a Target against Multiple Intruders},
author = {Han Fu* and Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {AIAA SciTech Forum},
journal = {AIAA SciTech Forum},
pages = {1-10 (submitted)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
322.
Liao*, Jacky; Liu*, Che; Liu, Hugh H. -T.
Model Predictive Control for Cooperative Hunting in Obstacle Rich and Dynamic Environments Inproceedings
In: IEEE International Conference on Robotics and Automation, pp. 1-8, 2021.
@inproceedings{ICRA2021JL,
title = {Model Predictive Control for Cooperative Hunting in Obstacle Rich and Dynamic Environments},
author = {Jacky Liao* and Che Liu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/05/ICRA2021JL.pdf},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {IEEE International Conference on Robotics and Automation},
journal = {IEEE International Conference on Robotics and Automation},
pages = {1-8},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
321.
Zhang*, Qingrui; Liu, Hugh H. T.
Robust Nonlinear Close Formation Control of Multiple Fixed-Wing Aircraft Journal Article
In: Journal of Guidance, Control, and Dynamics, 44 , pp. 572-586, 2021, ISSN: 1533-3884.
@article{JGCD2021QZ,
title = {Robust Nonlinear Close Formation Control of Multiple Fixed-Wing Aircraft},
author = {Qingrui Zhang* and Hugh H. T. Liu},
url = {https://arc.aiaa.org/doi/10.2514/1.G004592},
doi = {10.2514/1.G004592},
issn = {1533-3884},
year = {2021},
date = {2021-01-01},
journal = {Journal of Guidance, Control, and Dynamics},
volume = {44},
pages = {572-586},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
320.
Fan*, Shichen; Liu, Hugh H. -T.
Aerodynamic Effect in 3D Multi-UAV Cooperative Huntingitle Inproceedings
In: CASI AERO, 2021.
@inproceedings{CASI2021SF,
title = {Aerodynamic Effect in 3D Multi-UAV Cooperative Huntingitle},
author = {Shichen Fan* and Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {CASI AERO},
journal = {CASI AERO},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
319.
Lin*, Zhongjie; Liu, Hugh H. -T.
Autonomous Wildfire Hotspot Detection Using a Fixed Wing UAV Journal Article
In: International Journal of Aerospace Sciences and Systems Engineering, 1 , pp. 68-84, 2021.
@article{IJASSE2021ZL,
title = {Autonomous Wildfire Hotspot Detection Using a Fixed Wing UAV},
author = {Zhongjie Lin* and Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
journal = {International Journal of Aerospace Sciences and Systems Engineering},
volume = {1},
pages = {68-84},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
318.
Liu, Hugh H. -T.
Editorial: Special Issue on Interactive Unmanned Systems and Intelligent Applications Journal Article
In: Unmanned Systems, 09 , pp. 199-200, 2021, ISSN: 2301-3850.
@article{US2021e,
title = {Editorial: Special Issue on Interactive Unmanned Systems and Intelligent Applications},
author = {Hugh H. -T. Liu},
url = {https://www.worldscientific.com/doi/abs/10.1142/S2301385021020015},
doi = {10.1142/S2301385021020015},
issn = {2301-3850},
year = {2021},
date = {2021-01-01},
journal = {Unmanned Systems},
volume = {09},
pages = {199-200},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
317.
Liu, Hugh H. -T.
Interactive Unmanned Systems and Intelligent Applications Book
2021.
@book{US2020E,
title = {Interactive Unmanned Systems and Intelligent Applications},
author = {Hugh H. -T. Liu},
editor = {Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
journal = {Unmanned Systems},
volume = {Special Ed},
keywords = {},
pubstate = {published},
tppubtype = {book}
}
316.
M.*, S. Reza Fattahi; Liu, Hugh H. -T.
Longitudinal Swing Angle Control for a Fixed-wing UAV with a Slung Load Inproceedings
In: CASI AERO, 2021.
@inproceedings{CASI2021RF,
title = {Longitudinal Swing Angle Control for a Fixed-wing UAV with a Slung Load},
author = {S. Reza Fattahi M.* and Hugh H. -T. Liu},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {CASI AERO},
journal = {CASI AERO},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
315.
Chen*, Chih-chun; Liu, Hugh H. -T.
Adaptive Modelling for Downwash Effects in Multi-UAV Path Planning Journal Article
In: Guidance, Navigation and Control, 1 , pp. (2140005) 1-16, 2021.
@article{JGNC2021CC,
title = {Adaptive Modelling for Downwash Effects in Multi-UAV Path Planning},
author = {Chih-chun Chen* and Hugh H. -T. Liu},
doi = {10.1142/S27374807214000572140005-1},
year = {2021},
date = {2021-01-01},
journal = {Guidance, Navigation and Control},
volume = {1},
pages = {(2140005) 1-16},
abstract = {This paper develops a novel method to model the air °ow downwash force generated by thequadrotor unmanned aerial vehicle (UAV) and its e®ect on the neighboring UAVs. Each UAV isshaped by a virtual structure for collision-free path planning. The shape is modi ̄ed from astandard spherical body to a proposed adaptive cylinder to optimize the path planning whileminimizing the downwash impact. The cylinder height varies based on the UAV circumstanceand the predicted downwash impact. Furthermore, the downwash model can aid in the cylinderheight extreme value appointment. A °ock-based path planning algorithm is investigated in thisstudy to compare the spherical UAV shape model with the proposed cylindrical UAV shapemodel. The UAV with the adaptive cylindrical model is simulated and veri ̄ed via Gazebo andRobot Operating System (ROS) simulation platform.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper develops a novel method to model the air °ow downwash force generated by thequadrotor unmanned aerial vehicle (UAV) and its e®ect on the neighboring UAVs. Each UAV isshaped by a virtual structure for collision-free path planning. The shape is modi ̄ed from astandard spherical body to a proposed adaptive cylinder to optimize the path planning whileminimizing the downwash impact. The cylinder height varies based on the UAV circumstanceand the predicted downwash impact. Furthermore, the downwash model can aid in the cylinderheight extreme value appointment. A °ock-based path planning algorithm is investigated in thisstudy to compare the spherical UAV shape model with the proposed cylindrical UAV shapemodel. The UAV with the adaptive cylindrical model is simulated and veri ̄ed via Gazebo andRobot Operating System (ROS) simulation platform.
314.
Chen*, Ti; Shan, Jinjun; Liu, Hugh H. -T.
Distributed control of flexible payload transportation using multiple quadrotors Inproceedings
In: IEEE/ASME International Conference on Advanced Intelligent Mechatronics, pp. 247-252, IEEE, 2021, ISBN: 9781665441391.
@inproceedings{AIM2021TC,
title = {Distributed control of flexible payload transportation using multiple quadrotors},
author = {Ti Chen* and Jinjun Shan and Hugh H. -T. Liu},
doi = {10.1109/AIM46487.2021.9517345},
isbn = {9781665441391},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
booktitle = {IEEE/ASME International Conference on Advanced Intelligent Mechatronics},
journal = {IEEE/ASME International Conference on Advanced Intelligent Mechatronics},
pages = {247-252},
publisher = {IEEE},
abstract = {This paper focuses on the distributed control of flexible payload transportation using multiple quadrotors. To design a distributed controller, the transportation system is described as a group of quadrotors subject to disturbance forces and torques from the flexible payload. A distributed finite-time observer is introduced for the quadrotors to estimate the virtual leader's information. The disturbances acting on quadrotors due to the transverse and torsional deformation of the flexible payload are estimated based on the deformation analysis. The unmodeled disturbances are approximated using a radial basis function neural network. A distributed hierarchical controller is developed with the compensation for these disturbances.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
This paper focuses on the distributed control of flexible payload transportation using multiple quadrotors. To design a distributed controller, the transportation system is described as a group of quadrotors subject to disturbance forces and torques from the flexible payload. A distributed finite-time observer is introduced for the quadrotors to estimate the virtual leader's information. The disturbances acting on quadrotors due to the transverse and torsional deformation of the flexible payload are estimated based on the deformation analysis. The unmodeled disturbances are approximated using a radial basis function neural network. A distributed hierarchical controller is developed with the compensation for these disturbances.
2020
313.
Heirendt*, Laurent; Liu, Hugh H-T; Wang, Phillip
LUBRICATION MECHANISM DESIGN FOR AIRCRAFT LANDING GEAR BEARINGS Patent
US 10,591,013 B2, 2020.
@patent{Heirendt*2020,
title = {LUBRICATION MECHANISM DESIGN FOR AIRCRAFT LANDING GEAR BEARINGS},
author = {Laurent Heirendt* and Hugh H-T Liu and Phillip Wang},
year = {2020},
date = {2020-03-17},
booktitle = {United States Patent},
number = {US 10,591,013 B2},
keywords = {},
pubstate = {published},
tppubtype = {patent}
}
312.
Semnani*, Samaneh Hosseini; Liu, Hugh H-T; Everett, Michael; de Ruiter, Anton; How, Jonathan P
Multi-agent Motion Planning for Dense and Dynamic Environments via Deep Reinforcement Learning Journal Article
In: IEEE Robotics and Automation Letters, 5 (2), pp. 3221-3226, 2020, ISSN: 2377-3766.
@article{RAL2020SS,
title = {Multi-agent Motion Planning for Dense and Dynamic Environments via Deep Reinforcement Learning},
author = {Samaneh Hosseini Semnani* and Hugh H-T Liu and Michael Everett and Anton de Ruiter and Jonathan P How},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2020/03/ral2020ss.pdf},
doi = {10.1109/LRA.2020.2974695},
issn = {2377-3766},
year = {2020},
date = {2020-01-01},
journal = {IEEE Robotics and Automation Letters},
volume = {5},
number = {2},
pages = {3221-3226},
abstract = {This letter introduces a hybrid algorithm of deep reinforcement learning (RL) and Force-based motion planning (FMP) to solve distributed motion planning problem in dense and dynamic environments. Individually, RL and FMP algorithms each have their own limitations. FMP is not able to produce time-optimal paths and existing RL solutions are not able to produce collision- free paths in dense environments. Therefore, we first tried improv- ing the performance of recent RL approaches by introducing a new reward function that not only eliminates the requirement of a pre supervised learning (SL) step but also decreases the chance of collision in crowded environments. That improved things, but there were still a lot of failure cases. So, we developed a hybrid approach to leverage the simpler FMP approach in stuck, simple and high-risk cases, and continue using RL for normal cases in which FMP can’t produce optimal path. Also, we extend GA3C- CADRL algorithm to 3D environment. Simulation results show that the proposed algorithm outperforms both deep RL and FMP algorithms and produces up to 50% more successful scenarios than deep RL and up to 75% less extra time to reach goal than FMP.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This letter introduces a hybrid algorithm of deep reinforcement learning (RL) and Force-based motion planning (FMP) to solve distributed motion planning problem in dense and dynamic environments. Individually, RL and FMP algorithms each have their own limitations. FMP is not able to produce time-optimal paths and existing RL solutions are not able to produce collision- free paths in dense environments. Therefore, we first tried improv- ing the performance of recent RL approaches by introducing a new reward function that not only eliminates the requirement of a pre supervised learning (SL) step but also decreases the chance of collision in crowded environments. That improved things, but there were still a lot of failure cases. So, we developed a hybrid approach to leverage the simpler FMP approach in stuck, simple and high-risk cases, and continue using RL for normal cases in which FMP can’t produce optimal path. Also, we extend GA3C- CADRL algorithm to 3D environment. Simulation results show that the proposed algorithm outperforms both deep RL and FMP algorithms and produces up to 50% more successful scenarios than deep RL and up to 75% less extra time to reach goal than FMP.
311.
Zhu*, Yang; Zhu, Bo; Liu, Hugh H-T; Qin, Kaiyu
A Model-Based Approach for Measurement Noise Estimation and Compensation in Feedback Control Systems Journal Article
In: IEEE Transactions on Instrumentaion & Measurement, pp. 1–29, 2020.
@article{TIM2020YZ,
title = {A Model-Based Approach for Measurement Noise Estimation and Compensation in Feedback Control Systems},
author = {Yang Zhu* and Bo Zhu and Hugh H-T Liu and Kaiyu Qin},
url = {https://ieeexplore.ieee.org/document/9082005/},
doi = {10.1109/TIM.2020.2991290},
year = {2020},
date = {2020-01-01},
journal = {IEEE Transactions on Instrumentaion & Measurement},
pages = {1--29},
abstract = {This paper considers the problem of measurement noise rejection in a linear output-feedback control system. Specifically, we take into account not only the rejection of high-frequency stochastic noises, but also the compensation for low-frequency measurement errors like bias and drift which cannot be well-handled by classic frequency domain filters or Kalman filters. A novel noise estimator (NE)- based robust control solution is proposed. The NE is designed in the frequency domain by exploiting the system model and control structure information, and is embedded into the controller instead of being an independent functional module in the closed-loop system. The adverse effects of model uncertainties on the performance of NE-based solution are investigated, and an improved solution is proposed by incorporating a simple low-pass filter as the pre-filter of NE. This solution is applied to the angle tracking problem of a 2-DOF experimental helicopter platform equipped with a low-cost and low-accuracy MEMS IMU for angular position/rate measurements. Both numerical simulation and experimental comparisons with other existing approaches demonstrate: (i) constant bias and time-varying drift in the IMU measurements are systematically addressed by the solution; (ii) it is accessible to improve the steady-state tracking accuracy by tuning the parameter of NE to extend its bandwidth; and (iii) when model uncertainties limit the feasible bandwidth of NE, the improved solution is able to largely maintain its noise rejection performance.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper considers the problem of measurement noise rejection in a linear output-feedback control system. Specifically, we take into account not only the rejection of high-frequency stochastic noises, but also the compensation for low-frequency measurement errors like bias and drift which cannot be well-handled by classic frequency domain filters or Kalman filters. A novel noise estimator (NE)- based robust control solution is proposed. The NE is designed in the frequency domain by exploiting the system model and control structure information, and is embedded into the controller instead of being an independent functional module in the closed-loop system. The adverse effects of model uncertainties on the performance of NE-based solution are investigated, and an improved solution is proposed by incorporating a simple low-pass filter as the pre-filter of NE. This solution is applied to the angle tracking problem of a 2-DOF experimental helicopter platform equipped with a low-cost and low-accuracy MEMS IMU for angular position/rate measurements. Both numerical simulation and experimental comparisons with other existing approaches demonstrate: (i) constant bias and time-varying drift in the IMU measurements are systematically addressed by the solution; (ii) it is accessible to improve the steady-state tracking accuracy by tuning the parameter of NE to extend its bandwidth; and (iii) when model uncertainties limit the feasible bandwidth of NE, the improved solution is able to largely maintain its noise rejection performance.
310.
Semnani*, Samaneh Hosseini; de Ruiter, Anton; Liu, Hugh H-T
Force-based Algorithm for Motion Planning of Large Agent Teams Journal Article
In: IEEE Transactions on Cybernetics, pp. 1–10 (accepted), 2020.
@article{TCyber2020SS,
title = {Force-based Algorithm for Motion Planning of Large Agent Teams},
author = {Samaneh Hosseini Semnani* and Anton de Ruiter and Hugh H-T Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2020/06/tcyber2020ss_preview.pdf
https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2020/05/tcyber2020ss.mp4
https://youtu.be/pruxeMCniDM},
doi = {10.1109/TCYB.2020.2994122},
year = {2020},
date = {2020-01-01},
journal = {IEEE Transactions on Cybernetics},
pages = {1--10 (accepted)},
abstract = {This paper presents a distributed, efficient, scalable, and real- time motion planning algorithm for a large group of agents moving in 2 or 3- dimensional spaces. This algorithm enables autonomous agents to generate individual trajectories independently with only the relative position information of neighboring agents. Each agent applies a force-based control that contains two main terms: collision avoidance and navigational feedback. The first term keeps two agents separate with a certain distance, while the second term attracts each agent toward its goal location. Compared with existing collision-avoidance algorithms, the proposed force-based motion planning (FMP) algorithm can find collision-free motions with lower transition time, free from velocity state information of neighboring agents. It leads to less computational overhead. The performance of proposed FMP is examined over several dense and complex 2D and 3D benchmark simulation scenarios, with results outperforming existing methods.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper presents a distributed, efficient, scalable, and real- time motion planning algorithm for a large group of agents moving in 2 or 3- dimensional spaces. This algorithm enables autonomous agents to generate individual trajectories independently with only the relative position information of neighboring agents. Each agent applies a force-based control that contains two main terms: collision avoidance and navigational feedback. The first term keeps two agents separate with a certain distance, while the second term attracts each agent toward its goal location. Compared with existing collision-avoidance algorithms, the proposed force-based motion planning (FMP) algorithm can find collision-free motions with lower transition time, free from velocity state information of neighboring agents. It leads to less computational overhead. The performance of proposed FMP is examined over several dense and complex 2D and 3D benchmark simulation scenarios, with results outperforming existing methods.
309.
Zhu*, Yang; Zhu, Bo; Liu, Hugh H -T; Qin, Kaiyu
Rejecting the Effects of Both Input Disturbance and Measurement Noise : A Second-order Control System Example Journal Article
In: International Journal of Robust and Nonlinear Control, 30 (16), pp. 6813-6837, 2020.
@article{IJRNC2020YZ,
title = {Rejecting the Effects of Both Input Disturbance and Measurement Noise : A Second-order Control System Example},
author = {Yang Zhu* and Bo Zhu and Hugh H -T Liu and Kaiyu Qin},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2020/10/ijrnc2020_cover-1.jpg},
doi = {10.1002/rnc.5134},
year = {2020},
date = {2020-01-01},
journal = {International Journal of Robust and Nonlinear Control},
volume = {30},
number = {16},
pages = {6813-6837},
abstract = {This article originates from the well-accepted observations in practice: rejec- tion of both input disturbance and measurement noise is practically important for high-precision tracking control, and the classic estimators, such as the uncertainty and disturbance estimator (UDE) and disturbance observer, are proven to be inherently sensitive to measurement noises. Motivated by these observations, we develop a robust control solution and demonstrate the pos- sibility of unifying the design of noise estimator (NE) and UDE for a class of second-order systems. Interestingly, the NE and UDE have three important fea- tures in common: (i) the designs are based on system model and reliable state measurement; (ii) a first-order filter is used to ensure that the design is physical realizable, rather than to filter out undesired signals; (iii) the filter parameters are readily determined by an introduced singular perturbation parameter. The performance of UDE is improved when augmented with NE to reject measure- ment noises. Then, a simple mapping for parameter tuning is presented, by which the estimation performance can be explicitly analyzed using the singu- lar perturbation theory. Comparative simulation and experimental studies show that the proposed NE+UDE-based solution is not only less sensitive to mea- surement noise than the classic UDE-based control, but also able to deliver superior trajectory-tracking performance over other robust output feedback control approaches.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This article originates from the well-accepted observations in practice: rejec- tion of both input disturbance and measurement noise is practically important for high-precision tracking control, and the classic estimators, such as the uncertainty and disturbance estimator (UDE) and disturbance observer, are proven to be inherently sensitive to measurement noises. Motivated by these observations, we develop a robust control solution and demonstrate the pos- sibility of unifying the design of noise estimator (NE) and UDE for a class of second-order systems. Interestingly, the NE and UDE have three important fea- tures in common: (i) the designs are based on system model and reliable state measurement; (ii) a first-order filter is used to ensure that the design is physical realizable, rather than to filter out undesired signals; (iii) the filter parameters are readily determined by an introduced singular perturbation parameter. The performance of UDE is improved when augmented with NE to reject measure- ment noises. Then, a simple mapping for parameter tuning is presented, by which the estimation performance can be explicitly analyzed using the singu- lar perturbation theory. Comparative simulation and experimental studies show that the proposed NE+UDE-based solution is not only less sensitive to mea- surement noise than the classic UDE-based control, but also able to deliver superior trajectory-tracking performance over other robust output feedback control approaches.
308.
Qian*, Longhao; Liu, Hugh H. -T.
Path-Following Control of A Quadrotor UAV with A Cable-Suspended Payload under Wind Disturbances Journal Article
In: IEEE Transactions on Industrial Electronics, 67 , pp. 2021-2029, 2020, ISSN: 15579948.
@article{TIE2020LHQ,
title = {Path-Following Control of A Quadrotor UAV with A Cable-Suspended Payload under Wind Disturbances},
author = {Longhao Qian* and Hugh H. -T. Liu},
doi = {10.1109/TIE.2019.2905811},
issn = {15579948},
year = {2020},
date = {2020-01-01},
journal = {IEEE Transactions on Industrial Electronics},
volume = {67},
pages = {2021-2029},
publisher = {IEEE},
abstract = {A path-following controller based on an uncertainty and disturbance estimator (UDE) for a quadrotor with a cable-suspended payload is proposed in this paper. The quadrotor and the payload are subject to unknown wind disturbances. The controller resembles a cascade architecture. For the outer loop, a UDE-based translational control law is proposed. The controller asymptotically stabilizes the quadrotor along a given path and estimates the lumped disturbances with a low-pass filter. For the inner loop, an attitude tracking controller is used to control the direction of the lift vector so that the actual lift force can asymptotically follow the reference force generated by the translational controller. The stability of the system with the translational controller and the attitude tracking controller has been shown to be asymptotically stable using the reduction theorem. With the help of the reduction theorem, the design of the translational and the attitude control can be decoupled, providing the flexibility of implementing different attitude controllers without redoing the stability analysis. As shown in the simulation, the control law can stabilize the quadrotor on the desired path under different wind disturbances.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A path-following controller based on an uncertainty and disturbance estimator (UDE) for a quadrotor with a cable-suspended payload is proposed in this paper. The quadrotor and the payload are subject to unknown wind disturbances. The controller resembles a cascade architecture. For the outer loop, a UDE-based translational control law is proposed. The controller asymptotically stabilizes the quadrotor along a given path and estimates the lumped disturbances with a low-pass filter. For the inner loop, an attitude tracking controller is used to control the direction of the lift vector so that the actual lift force can asymptotically follow the reference force generated by the translational controller. The stability of the system with the translational controller and the attitude tracking controller has been shown to be asymptotically stable using the reduction theorem. With the help of the reduction theorem, the design of the translational and the attitude control can be decoupled, providing the flexibility of implementing different attitude controllers without redoing the stability analysis. As shown in the simulation, the control law can stabilize the quadrotor on the desired path under different wind disturbances.
307.
Graham*, Silas; Qian*, Longhao; Liu, Hugh H. T.
Guidance and Control Law Design for a Slung Payload in Autonomous Landing: A Drone Delivery Case Study Inproceedings
In: IEEE/ASME Conference on Advanced Intelligent Mechatronics, pp. 1-10 (accepted as concurrent paper), 2020.
@inproceedings{AIM2020sg,
title = {Guidance and Control Law Design for a Slung Payload in Autonomous Landing: A Drone Delivery Case Study},
author = {Silas Graham* and Longhao Qian* and Hugh H. T. Liu},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
booktitle = {IEEE/ASME Conference on Advanced Intelligent Mechatronics},
journal = {IEEE/ASME Conference on Advanced Intelligent Mechatronics},
pages = {1-10 (accepted as concurrent paper)},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
306.
Qian*, Longhao; Graham*, Silas; Liu, Hugh H. -T.
Guidance and Control Law Design for a Slung Payload in Autonomous Landing A Drone Delivery Case Study Journal Article
In: IEEE/ASME Transactions on Mechatronics, 25 , pp. 1773-1782, 2020.
@article{TMech2020sg,
title = {Guidance and Control Law Design for a Slung Payload in Autonomous Landing A Drone Delivery Case Study},
author = {Longhao Qian* and Silas Graham* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/06/TMech2020sg.pdf},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {IEEE/ASME Transactions on Mechatronics},
volume = {25},
pages = {1773-1782},
abstract = {This paper presents a novel guidance and control design for a parcel tethered to a drone in its delivery mission. The proposed proportional navigation based guidance, integrated with custom built control, enable to achieve autonomous payload landing. The novelty of the proposed method lies on two aspects: 1) the guidance law allows for soft landing; while 2) the path following control ensures the swing-free payload transportation that sets the solid foundation for landing. The development is verified by extensive simulations and further demonstrated by flight experiments.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper presents a novel guidance and control design for a parcel tethered to a drone in its delivery mission. The proposed proportional navigation based guidance, integrated with custom built control, enable to achieve autonomous payload landing. The novelty of the proposed method lies on two aspects: 1) the guidance law allows for soft landing; while 2) the path following control ensures the swing-free payload transportation that sets the solid foundation for landing. The development is verified by extensive simulations and further demonstrated by flight experiments.
305.
Fu*, Han; Liu, Hugh H. T.
Guarding a Territory Against an Intelligent Intruder : Strategy Design and Experimental Verification Inproceedings
In: Advanced Intelligent Mechatronics (AIM), pp. 1-8, 2020.
@inproceedings{AIM2020FF,
title = {Guarding a Territory Against an Intelligent Intruder : Strategy Design and Experimental Verification},
author = {Han Fu* and Hugh H. T. Liu},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
booktitle = {Advanced Intelligent Mechatronics (AIM)},
journal = {IEEE/ASME Conference on Advanced Intelligent Mechatronics},
pages = {1-8},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
304.
Fu*, Han; Liu, Hugh H. -T.
Guarding a Territory Against an Intelligent Intruder : Strategy Design and Experimental Verification Journal Article
In: IEEE/ASME Transactions on Mechatronics, 25 , pp. 1765-1772, 2020.
@article{TMech2020FF,
title = {Guarding a Territory Against an Intelligent Intruder : Strategy Design and Experimental Verification},
author = {Han Fu* and Hugh H. -T. Liu},
url = {https://www.flight.utias.utoronto.ca/fsc/wp-content/uploads/2023/06/TMech2020FF.pdf},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {IEEE/ASME Transactions on Mechatronics},
volume = {25},
pages = {1765-1772},
abstract = {This paper designs and tests a dominant region based strategy for a group of defenders to intercept an intruder before it enters a target area. The intruder is intelligent in the sense that it makes decisions based on the defenders’ strategies instead of following a pre-defined path, making the problem a differential game. The proposed strategy is optimal when the intruder moves slower than the defenders. When the intruder moves faster, the dominant region based strategy is still applicable, but with proper modifications. Crazyflie 2.1 is used as the experimental platform to test the proposed strategy. For fixed defender locations, a barrier line can be drawn such that the intruder is guaranteed to be captured outside the target area if it starts beyond.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper designs and tests a dominant region based strategy for a group of defenders to intercept an intruder before it enters a target area. The intruder is intelligent in the sense that it makes decisions based on the defenders’ strategies instead of following a pre-defined path, making the problem a differential game. The proposed strategy is optimal when the intruder moves slower than the defenders. When the intruder moves faster, the dominant region based strategy is still applicable, but with proper modifications. Crazyflie 2.1 is used as the experimental platform to test the proposed strategy. For fixed defender locations, a barrier line can be drawn such that the intruder is guaranteed to be captured outside the target area if it starts beyond.