Magnetic Induction Tomography Using Magnetic Dipole and Lumped Parameter Model

This paper presents a novel approach to analyze the magnetic field of magnetic induction tomography (MIT) using magnetic dipoles and a lumped parameter model. The MIT is a next-generation medical imaging technique that can identify the conductivity of target objects and construct images. It is noninvasive and can be compact in design and, thus, used as a portable instrument. However, it still exhibits inferior performance due to the nonlinearity, low signal-to-noise ratio of the magnetic field, and ill-posed inverse problem. To overcome such difficulties, the magnetic field of the MIT system is first modeled using magnetic dipoles and a lumped parameter. In particular, the extended distributed multipole (eDMP) model is proposed to analyze the system, using magnetic dipoles. The method can dramatically reduce the computational efforts and improve the ill-posed condition. Hence, the forward and inverse problems of MIT are solved using the eDMP method. The modeling method can be validated by comparing with experiments, varying the modeling parameters. Finally, the image can be reconstructed, and then, the position and shape of the object can be characterized to develop the MIT

Dynamics estimator based robust fault-tolerant control for VTOL UAVs trajectory tracking

This paper investigates the control issue of the trajectory tracking of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) in the presence of partial propeller fault and external disturbance. In particular, a robust passive fault-tolerant control strategy is proposed by introducing a first-order filter based dynamics estimator. First, a bounded force command is exploited by employing a new smooth saturation function in the output of the estimator. A sufficient condition in terms of a specified parameter selection criteria is provided to ensure the nonsingularity extraction of the command attitude. Then, a torque command is applied to the attitude loop tracking. Since there is merely one filter parameter involved in the dynamics estimator, the practical implementation and parameter tuning can be significantly simplified. Stability analysis indicates that the proposed control strategy guarantees the semi-globally ultimately bounded tracking of VTOL UAVs subject to partial propeller fault and external disturbance. Simulation and experiment results with comparison examples are performed to validate the effectiveness of the proposed strategy. Experimental results show that the proposed strategy achieves the trajectory tracking with a good performance (mean deviation 0.0074 m and standard deviation 0.1202 m) in the presence of 35% propeller fault and 4 m/s persistent wind disturbance

Computationally efficient control and local planning for the safe flight of UAVs

Department of Mechanical EngineeringThis research aims to provide safety belts to unmanned aerial vehicles (UAVs). Numerous dangers exist on operating UAVs. Failures of flight control computer, sensors, communication, actuators, collision, unstable control system. This article concentrates on coping with actuator fault, collision, and performance of control system. A number of FTC and collision avoidance algorithms are developed, but most of them require heavy computational resources for optimization, mapping and others. In real application, the objectives of UAVs will be the commercial or military mission, which would need several functions such as object recognition, Simultaneous localization and mapping (SLAM), and etc. Furthermore, the limit of computational power is tighter compared to the ground vehicles because the payload is low. The performance of heavy algorithms can decrease and even utilizing mapping and complex path planning algorithms could be prohibited. Therefore, the objective of this thesis is providing safety with low computational efforts as a role of safety belt. In FTC, it is designed to be general and simple. Light weight collision avoidance algorithms are designed, ensuring the safety independent to the planning and mapping algorithms. As a result, UAVs can concentrate computing power more for other important missions. Also, it is expected to be available for small UAVs.clos

Fault-tolerant Control of Multirotor UAVs by Control Variable Elimination

This article presents to develop a fault-tolerant control (FTC) to cope with defective thrust systems in multirotor unmanned aerial vehicles (UAV). Faults can occur for a number of reasons in flight, including defective motor performance and damaged propellers. The faults deform both the thrust and torque outputs that could result in the UAV crashing and causing secondary accidents. The FTC method in the article is developed to reconfigure thrust systems using the optimal control when significant degrees of failure occur in a number of defective motors. Orientation control could be abandoned to maintain the controllability of altitude when the control output loss cannot be compensated for because of motor saturation. Specifically, yaw motion control is sacrificed, resulting in a rapid rotation and divergence of position control. The divergence can be resolved by a feed forward control loop on the roll and pitch angles. Both simulations and experiments are implemented to demonstrate the performance of the FTC. The results indicate that the proposed FTC can be implemented to minimize accidents from failures of main thrust systems

Modularized multibody multirotor for independent attitude and position control*

This paper presents the novel design and development of a multibody multirotor (MBMR) capable of controlling orientation independent of the position by tilting the passive thrust vector without any additional actuators. Conventional multirotors have a limitation in controlling the orientation independently of the position control. In particular, it is important to control the orientation independently since it affects flight efficiency and mission. Thus, various tiltrotors have been developed to control the orientation independently but require additional servo motors. The MBMR consists of a main fuselage and thrust modules without a servo motor. Each of the thrust modules can be utilized by a conventional quadrotor with four rotors connected to the fuselage by passive rotational joints. Two thrust modules, the minimum to form the MBMR, are implemented to demonstrate performance. Toward usability of the MBMR, a hierarchical control system is developed to compute relative thrust and moment vectors with respect to the fuselage. Thrust heading alignment control (THAC) is proposed to overcome a lack of roll angle control. The control system allows the heading angle of the MBMR to track the direction of thrust force so that it can maintain the near-zero tilt angle of the fuselage while generating acceleration. Experimental validation is implemented demonstrating the performance of the MBMR with independent orientation control. It is successfully achieved to regulate the fuselage's pitch angle at 80 degrees angle and track the circular trajectory within the fuselage's tilt angle under 2.6 degrees angle

Propulsion model and system identification of an electrical multiple tail rotor system

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Online parameter identification framework for a multirotor UAV: Application to an arm stretchable morphing multirotor

This paper presents a new framework to identify the dynamic characteristics of a multirotor unmanned aerial vehicle (MUAV). In particular, the identification framework is applied for an arm stretchable morphing MUAV. This MUAV is capable of adjusting the arm length during flight to maximize performance as well as stability. However, it is challenging to develop a flight controller without understanding several parameters of the MUAV, even though it has similar dynamic characteristics compared to conventional MUAVs. The framework consists of three sequentially operated steps: constrained roll dynamics on the ground, yaw dynamics, and roll/ pitch dynamics in flight. A system is excited safely by a designed command for each step. Then, the Extended Kalman Filter (EKF) is utilized to estimate the unknown parameters that can best match the motion data with the dynamic model. The identification framework offers an effective means to design the controller by providing its dynamic characteristics. It is validated by numerical simulations and experiments with the arm stretchable MUAV. Furthermore, the identified parameters are utilized to maximize control performance using particle swarm optimization (PSO) in experiments. The flight performance along with the identified parameters has been experimentally demonstrated

Finite-Time Control of Multirotor UAVs Under Disturbances

A new finite-time control method based on a sliding mode for a multirotor unmanned aerial vehicle (UAV) is developed to improve both the transient and steady-state responses, including overshoot and steady-state error in the presence of uncertainties and external disturbances. First, a virtual control with nonlinear sliding manifolds is designed to achieve position-tracking capability, as well as to guarantee the fast convergence of the UAV to a desired position. Furthermore, an ultimate control is developed for the desired attitude-tracking performance. Various uncertainties, including torque due to the discordance between the centre of mass and rotation and wind disturbances are considered. The Lyapunov stability theorem is then applied step-by-step to prove the asymptotically stable and finite-time convergence in position and attitude controllers. Second, the proposed controller is implemented in an open-source hardware platform for a quadrotor UAV. Both numerical and experimental results are compared to validate the tracking performance for attitude and position control, as well as robustness under disturbances

Moving Target Landing of a Quadrotor Using Robust Optimal Guaranteed Cost Control

Dear Editor, This letter proposes a robust control strategy for the autonomous landing of a quadrotor on a moving target. Specifically, a force command that consists of a cascade dynamics estimator and an optimal guaranteed cost control law is exploited for the position-loop tracking. Then, an orientation constraint torque command is employed for the attitude-loop tracking such that the quadrotor refrains from flipping during the landing operation. Stability analysis indicates that the overall closed-loop system is asymptotically stable. Finally, flight experiments validate and access the theoretical results