Wonsuk Lee

A cooperative guidance law for target estimation by multiple unmanned aerial vehicles

A new cooperative guidance law is proposed for target estimation of multiple unmamed aerial vehicles (UAVs) without involving numerical computational work. The guidance law derivation is based upon the Fisher Information Matrix (FIM) to quantify the amount of target information. For two UAVs, an analytical one-step determinant of FIM is introduced, which sufficiently reflects the trend of previous well-known optimal manoeuvers. Therefore, by considering only one-step information, as opposed to accumulated total information, a new feedback guidance law with intuitive physical analysis is induced and then its validity is verified by comparing it with the results of previous approaches. To apply the proposed idea to more multiple UAVs, a generalized formulation is derived as a weighted combination of each guidance law. Also, for more realistic application, the proposed guidance law is modified to deal with an avoidance problem of risk zone.

Switchable Photonic Crystals Using One-Dimensional Confined Liquid Crystals for Photonic Device Application

Photonic crystals (PCs) have recently attracted considerable attention, with much effort devoted to photonic bandgap (PBG) control for varying the reflected color. Here, fabrication of a modulated one-dimensional (1D) anodic aluminum oxide (AAO) PC with a periodic porous structure is reported. The PBG of the fabricated PC can be reversibly changed by switching the ultraviolet (UV) light on/off. The AAO nanopores contain a mixture of photoresponsive liquid crystals (LCs) with irradiation-activated cis/trans photoisomerizable azobenzene. The resultant mixture of LCs in the porous AAO film exhibits a reversible PBG, depending on the cis/trans configuration of azobenzene molecules. The PBG switching is reliable over many cycles, suggesting that the fabricated device can be used in optical and photonic applications such as light modulators, smart windows, and sensors.

Trajectory optimization by cooperative maneuver with multiple sensors

Using Fisher Information Matrix(FIM), the optimal trajectory which is generated in order to localize the specific target is obtained as optimal problem. However, it is more effective to use more vehicles with various sensor in order to gather information about target. So, since we just check how multi vehicles with various sensors by cooperative maneuver affect the trajectory in this paper. Analytical solution is obtained from the above formulation and then the solution is verified through several simulations.

Digital DNA detection based on a compact optofluidic laser with ultra-low sample consumption

Optofluidic laser that has a single layer of DNA molecules on the ring resonator surface is proposed. A target DNA can be detected in truly digital manner only with a single pulse of laser excitation.

Efficient Thrust Distribution with Adaptive Pressure Control for Multinozzle Solid Propulsion System

An integrated approach for chamber pressure control and thrust distribution for multiple nozzles of a solid propulsion system is presented. In this study, a solid propulsion system with variable nozzle throat area controlled by a pintle actuator is considered. To keep the hardware configuration simple and lightweight, multiple nozzles share a combustion chamber. Consequently, changing the throat area of one nozzle results in an unintended change of chamber pressure and thrust from other nozzles. Therefore, pressure stabilization and thrust distribution for multiple nozzles should be conducted simultaneously to achieve the desired performance. For the inner control loop, an adaptive sliding mode controller with feedback linearization is used for pressure stabilization. With the pressure control loop working properly, a thrust distribution algorithm into 10 nozzles for translation and attitude maneuver is developed as an outer control loop.

Passive Jitter Isolation for Reaction Wheel of Satellites

Passive jitter isolation for reaction wheel of satellites is studied. The principal idea of vibration isolation is to filter out the response of the system over the corner frequency. The isolation objectives are to transmit the attitude control torque within the bandwidth of the attitude control system and to filter all the high frequency components coming from vibration equipment above the bandwidth. However, when a reaction wheels or control momentum gyros control spacecraft attitude, vibration inevitably occurs and degrades the performance of sensitive devices. Therefore, vibration should be controlled or isolated for missions such as earth observing, broadcasting and telecommunication between antenna and ground stations. For space applications, technicians designing controller have to consider a periodic vibration and disturbance to ensure system performance and robustness completing various missions. In this paper, a passive reaction wheel jitter isolation system is studied. This paper shows the simulation and experimental results of passive reaction wheel jitter isolation in satellite

Dynamic modeling and fuzzy control for a small tiltrotor unmanned aerial vehicle

Dynamic modeling and fuzzy control of a tiltrotor unmanned aerial vehicle are presented. In order to design a full-conversion flight controller for a tiltrotor unmanned aerial vehicle, the dynamic characteristics of a small tiltrotor unmanned aerial vehicle during helicopter-to-airplane conversion is investigated. A six-degree-of-freedom nonlinear equation of motion using powered wind tunnel test data is developed based on a Bell Model 301 tiltrotor research aircraft. The time-varying characteristics of the conversion maneuver, over which system dynamics change rapidly, are handled by a Takagi–Sugeno fuzzy control approach in both longitudinal and lateral axes. Simulation results indicate that a small tiltrotor unmanned aerial vehicle exhibits nacelle tilt during the backward conversion flight from airplane to helicopter mode.

Tracking of ground objects using image information for autonomous rotary unmanned aerial vehicles

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Electro-tunable liquid crystal laser based on high-Q Fabry-Pérot microcavity

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A cooperative guidance law with decentralized structure for target estimation

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