Design and implementation of a robust and nonlinear flight control system for an unmanned helicopter

In this work, we focus on the design and implementation of a robust flight control system for an unmanned helicopter. A comprehensive nonlinear model for an unmanned helicopter system, which is built by our research team at the National University of Singapore, is first presented. A three-layer control architecture is then adopted to construct an automatic flight control system for the aircraft, which includes (1) an inner-loop controller designed using the H_∞ control technique to internally stabilize the aircraft and at the same time yield good robustness properties with respect to external disturbances, (2) a nonlinear outer-loop controller to effectively control the helicopter position and yaw angle in the overall flight envelope, and lastly, (3) a flight-scheduling layer for coordinating flight missions. Design specifications for military rotorcraft set for the US army aviation are utilized throughout the whole process to guarantee a top level performance. The result of actual flight tests shows our design is very successful. The unmanned helicopter system is capable of achieving the desired performance in accordance with the military standard under examination.     

Design and implementation of a fault tolerant controller for EMS systems

Conventional EMS (electromagnetic suspension) systems are susceptible to instability problems, and could even break down upon failures of the air-gap sensor or the accelerometer. Therefore, in order to improve EMS performance, a fault tolerant controller and a fault detection and isolation (FDI) algorithm are presented in this work. The fault tolerant controller is an extended version of the linear fault tolerant controller designed for known actuator or sensor failures, and it adopts the LMI-based H_∞ control for a class of nonlinear systems. The fault detection algorithm employs fuzzy inference. The merits of the proposed control scheme have been verified by the experiments with a single-axis two-magnet suspension system subjected to failures of the actuator or the sensors.     

无人机模糊小波神经网络轨迹线性化控制

针对系统存在不确定和有界干扰的情况,提出了一种基于模糊小波神经网络的轨迹线性化控制方法。利用模糊小波神经网络对非线性函数的逼近能力,减小不确定干扰对系统的影响,并与轨迹线性化方法结合设计了无人机飞控系统控制器。采用Lyapunov稳定性理论,证明了在所设计的控制器下,闭环系统所有信号一致最终有界。最后对系统存在不确定的情况下进行了仿真,并与没有加模糊小波神经网络的轨迹线性化控制器进行了对比,仿真结果证明了所提方法的有效性和鲁棒性。     

化学力滴定技术:一种新的测定自组装膜表面解离常数的方法

本文介绍了一种新的测定自组装膜表面官能团解离常数的方法－－化学力滴定技术。利用这种新方法，测定了自组装膜表面酸碱基团的解离常数。与接触角滴定相比，化学力滴定技术具有高度的空间局域性，反映了自组膜表面官能团的局域解离性质。     

基于亚波长光栅理论的二维光子晶体的禁带特性研究

本文根据光子晶体自身的结构特点,提出适合于二维光子晶体的光栅组模型,从而利用光栅的矢量衍射理论来分析光子晶体的禁带结构。采用该方法,本文讨论了几类典型的二维光子晶体的禁带特性。