Seungho Yoon

Fully Autonomous Vision-Based Net-Recovery Landing System for a Fixed-Wing UAV

This paper presents an autonomous vision-based netrecovery system for small fixed-wing unmanned aerial vehicles (UAVs). A fixed-wing UAV platform is constructed using various avionic sensors, and integrated with a flight control system and a vision system. The ground operation system consists of a vision station and ground control station that provide operation commands and monitor the UAV status. The vision algorithm to detect the recovery net and provide the bearing angle to the guidance algorithm is explained, along with the discussions on the techniques employed to improve the reliability of visual detection. The system identification process and controller are described, which enables to track given waypoints and to approach the detected net under the pursuit guidance law. Experimental results show the autonomous capabilities including take-off, waypoint following, and vision-based net recovery. The proposed technique can be an effective solution to recover fixed-wing UAVs without resorting to a complicated structure such as an instrumented landing system or expensive sensors such as a differential GPS.

Pursuit Guidance Law and Adaptive Backstepping Controller Design for Vision-Based Net-Recovery UAV

This paper presents a guidance law and a nonlinear controller for a vision-based netrecovery UAV. A vision sensor enhances the performance of precise interception with an accurate impact angle, which can be applied for the net-recovery UAV system. A pursuit guidance law and an adaptive backstepping controller are adopted for the vision-based netrecovery instead of tracking the pre-designed glide slope. The landing performance of a pure pursuit guidance, a lead pursuit guidance, and a pseudo pursuit guidance is compared. Dynamic characteristics of aircraft states and control surface actuators are considered in the design of the constrained adaptive backstepping controller. Six degree-of-freedom nonlinear aircraft landing simulation was performed to verify the performance of the proposed guidance law and controller.

Cooperative Control of Multiple Unmanned Aircraft for Standoff Tracking of a Moving Target

This paper presents a cooperative standoff tracking of a moving target using multiple unmanned aircraft. To provide guidance commands, vector fields are designed utilizing the Lyapunov stability theory. A roll angle command is generated to keep a constant distance from the target in a circular motion. A speed command and a heading angle command are designed to keep a constant phase angle with respect to the front aircraft and to prevent a collision between aircraft. Numerical simulation is performed to verify the tracking and collision performance of the proposed control laws.

Wireless stereo vision system development for rotary-wing UAV guidance and control

This paper presents the development of a wireless stereo vision system for a small rotary-wing unmanned aerial vehicle. A vision sensor enhances the navigation and guidance performance of the flight vehicle. A wireless stereo vision system was developed to minimize the size and weight of the payload. A ground image processing system was built to provide the position and distance to the targets such as a landing pad. The performance of the overall system was verified using a ground mobile testbed that simulates the yaw, pitch, forward, and descending motions of a helicopter.

Spiral Landing Trajectory and Pursuit Guidance Law Design for Vision-Based Net-Recovery UAV

This paper deals with spiral landing trajectory and terminal landing guidance law for a net-recovery landing of a fixed-wing UAV(Unmanned Aerial Vehicle). The net-recovery landing flight is divided into two phases. In the first phase, a spiral descending path is designed from any initial position to a final approaching waypoint toward a recovery net. The flight path angle of the UAV is controlled to be aligned to the approaching direction at the end of the spiral descent. In the second phase, the aircraft is directly guided from the approaching waypoint to the recovery net with a pseudo pursuit landing guidance law. Sequential imaginary landing and approaching points are generated using a cubic polynomial in the pseudo pursuit landing guidance law. Therefore, the UAV at high altitude with any heading angle can spiral down toward the recovery net without loitering and can fly into the recovery net smoothly. Six degree-of-freedom numerical simulation is performed to verify the performance of the spiral descent path and pseudo pursuit guidance law. Nomenclature α = angle of attack β = angle of sideslip γ = flight path angle a δ = aileron deflection angle e δ = elevator deflection angle r δ = rudder deflection angle A η = heading angle of aircraft ,0 c

Cooperative Standoff Tracking of a Moving Target using Decentralized Extended Information Filter

This paper deals with the tracking problem of a moving target using multiple unmanned aerial vehicles. A decentralized extended information filter is designed to cooperatively estimate the position and the velocity of the moving target. The extended information filter is adopted to consider the range and the line-of-sight angle as measurement data. The decentralized scheme is applied to enhance the estimation performance using the information provided by other vehicles. Numerical simulation is performed to verify the tracking performance of the proposed decentralized filters.

Fault-Tolerant Attitude Estimation for Satellite Using Federated Unscented Kalman Filter

Satellites provide various services essential to the modern life of human being. For example, satellite images are used for many applications such as reconnaissance, geographic information system, etc. Therefore, design and operation requirements of the satellite system have become more severe, and also the system reliability during the operation is required. Satellite attitude control systems including sensors and actuators are critical subsystems, and any fault in the satellite control system can result in serious problems. To deal with this problem, various attitude estimation algorithms using multiple sensors have been actively studied for fault tolerant satellite system (Edelmayer & Miranda, 2007; Jiancheng & Ali, 2005; Karlgaard & Schaub, 2008; Kerr, 1987; Xu, 2009). Satellites use various attitude sensors such as gyroscopes, sun sensors, star sensors, magnetometers, and so on. With these sensors, satellite attitude information can be obtained using the estimation algorithms including Kalman filter, extended Kalman filter (EKF), unscented Kalman filter (UKF), and particle filter. Agrawal et al. and Nagendra et al. presented the attitude estimation algorithm based on Kalman filter for satellite system (Agrawal & Palermo, 2002; Nagendra et al., 2002). Mehra and Bayard dealt with the problems of satellite attitude estimation based on the EKF algorithm using the gyroscope and star tracker as attitude sensors (Mehra & Bayard, 1995). In the EKF algorithm, the nonlinearities of the satellite system are approximated by the first-order Taylor series expansion, and therefore it sometimes provides undesired estimates when the system has severe nonlinearities. Recently, researches on UKF have been performed because the UKF can capture the posterior mean and covariance to the third order of nonlinear system. It is known that the UKF can provide better results for the estimation of highly nonlinear systems than EKF (Crassidis & Markley, 2003; Jin et al., 2008; Julier & Uhlmann, 2004). Crassidis and Markley proposed the attitude estimation algorithm based on unscented filter, and showed that the fast convergence can be obtained even with inaccurate initial conditions. The UKF was used to solve the relative attitude estimation problem using the modified Rodrigure parameter (MRP), where the gyroscope, star tracker, and laser rendezvous radar were employed as the attitude sensors (Jin et al., 2008). For multi-sensor systems, there are two different filter schemes for the measured sensor data process: centralized Kalman fileter (CKF) and decentralized Kalman filter (DKF) (Kim & Hong, 2003). In the CKF, all measured sensor data are processed in the center site, and

Cooperative Tracking of a Moving Target using Integrated Vector Field and Decentralized Extended Information Filter

Abstract This paper presents the decentralized target localization and control design for multiple unmanned aircraft to track a moving target. The extended information filter is applied to estimate the position and velocity of the target with additional target information provided by neighbor aircraft. The heading vector field considering both the distance error to the target and the phase spacing error between aircraft is proposed to track the fast target which changes its direction rapidly. Numerical simulation is performed to verify the proposed estimation and tracking scheme using four unmanned aircraft.

Decentralized phase angle control for standoff tracking using multiple unmanned aircraft

This paper presents a standoff distance control and a phase angle control for multiple aircraft to track a moving target. The roll angle command is generated to keep a constant distance from the target. The speed and the heading angle commands are generated to keep a constant phase angle between neighbor vehicles. Numerical simulation is performed to verify the tracking and collision performance of the proposed control laws.

Fault Tolerant Controller Design for Supersonic Advanced Trainer Using Model Following Adaptive Technique

In this study, a new fault tolerant controller based on a model following adaptive technique is applied to the reconfiguration mode of supersonic advanced trainer. The designed controller is applied to the flight control system of high performance aircraft. To verify the performance of the proposed controller, numerical simulations are executed using a non-realtime nonlinear verification tool.