Gas-sensing property and mechanism of CaxLa1−xFeO3 ceramics

LaFEO₃ and Ca_xLa_1−xFeO₃ ceramic powders have been prepared by the coprecipitation method from La(NO₃)₃, Fe(NO₃)₃ and Ca(NO₃)₂ aqueous solutions. The orthorhombic perovskite phases of LaFeO₃ and Ca_xLa_1−xFeO₃ are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La³⁺ in LaFeO₃ with Ca²⁺ can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO₃ sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive and lattice oxygen govern the sensing properties of LaFeO₃ and Ca_xLa_1−xFeO₃ ceramics.     

基于图像的多接收元合成孔径声纳运动补偿方法

多接收元合成孔径声纳成像是当前研究的热点问题,偏航和侧摆是影响多接收元合成孔径声纳成像质量的关键因素。建立了多接收元合成孔径声纳偏航和侧摆运动误差的几何模型,提出了一种基于图像估计偏航和侧摆的新方法。该方法允许声纳系统以满足空间采样理论的最大速度运行,利用强点目标的每个脉冲回波数据的成像结果估计偏航和侧摆。计算机仿真结果表明新算法有效地估计出了偏航和侧摆,提高了成像质量,明确地确定出了目标的位置。     

Performance evaluation of parallel iterative deepening A on clusters of workstations

In this paper we investigate the performance of distributed heuristic search methods based on a well-known heuristic search algorithm, the iterative deepening A^* (IDA^*). The contribution of this paper includes proposing and assessing a distributed algorithm for IDA^*. The assessment is based on space, time and solution quality that are quantified in terms of several performance parameters such as generated search space and real execution time among others. The experiments are conducted on a cluster computer system consisting of 16 hosts built around a general-purpose network. The objective of this research is to investigate the feasibility of cluster computing as an alternative for hosting applications requiring intensive graph search. The results reveal that cluster computing improves on the performance of IDA^* at a reasonable cost.     

基于三维成像声纳技术的AUV前视避障方法

针对自主式水下航行器（ AUV）在水下自主航行过程中的避障问题,提出了一种基于三维成像声纳技术的前视避障方法。该方法使用三维成像声纳探测目标,通过声纳目标图像处理提取目标,完成目标的运动状态分析和轨迹预测。通过设置碰撞区域,建立避障模型和设计避障规则,实现了AUV的智能化避障。借助于其他传感器,这些关联模块构成了一个集目标探测、目标提取、轨迹预测、避障与路线回归等功能于一体的闭环系统。     

无人直升机悬停至前飞切换控制

模态切换控制是无人直升机实现全天候自主飞行的关键,实现飞行模态闯快速平稳的切换是无人直升机控制器设计的主要目的。针对无人直升机悬停至前飞过切换程时高度不能保持现象和对象无人直升机高度一航向通道之间存在耦合,提出了前飞速度和航向角速率补偿设计高度通道控制律,升降速度和总距风扇联动关系补偿设计航向通道控制律。最后通过大量仿真试验验证了此方法的可行性和有效性。     

激光雷达窄脉冲回波信号采集系统设计

激光雷达发射出窄脉冲激光信号,在照射到目标物体后产生回波,由雪崩型光电传感器将其转换为电脉冲信号。针对该ns级电脉冲,提出8GSPS高速并行采样方案与通道校正方案。仿真与实验结果表明：雪崩型光电传感器具备良好的窄脉冲响应能力,高速并行采样可以实现窄脉冲信号采集重构,通道校正方案减少了通道失配对系统的影响。系统完成对4 ns窄脉冲回波信号的实时采样。     

Terrain‐based vehicle orientation estimation combining vision and inertial measurements

A novel method for estimating vehicle roll, pitch, and yaw using machine vision and inertial sensors is presented that is based on matching images captured from an on‐vehicle camera to a rendered representation of the surrounding terrain obtained from a three‐dimensional (3D) terrain map. U.S. Geographical Survey Digital Elevation Maps were used to create a 3D topology map of the geography surrounding the vehicle, and it is assumed in this work that large segments of the surrounding terrain are visible, particularly the horizon lines. The horizon lines seen in the captured video from the vehicle are compared to the horizon lines obtained from a rendered geography, allowing absolute comparisons between rendered and actual scene in roll, pitch, and yaw. A kinematic Kalman filter modeling an inertial navigation system then uses the scene matching to generate filtered estimates of orientation. Numerical simulations verify the performance of the Kalman filter. Experiments using an instrumented vehicle operating at the test track of the Pennsylvania Transportation Institute were performed to check the validity of the method. When compared to estimates from a global positioning system/inertial measurement unit (IMU) system, the roll, pitch, and yaw estimates from vision/IMU Kalman filter show an agreement with a (2σ) bound of 0.5, 0.26, and 0.8 deg, respectively. © 2008 Wiley Periodicals, Inc.     

Robust Tracking Control of a Quadrotor Helicopter

In this paper, a robust tracking control method for automatic take-off, trajectory tracking, and landing of a quadrotor helicopter is presented. The designed controller includes two parts: a position controller and an attitude controller. The position controller is designed by the static feedback control method to track the desired trajectory of the altitude and produce the desired angles for pitch and roll angles. By combining the proportional-derivative (PD) control method and the robust compensating technique, the attitude controller is designed to track the desired pitch and roll angles and stabilize the yaw angle. It is proven that the attitude tracking error of each channel can converge to the given neighborhood of the origin ultimately. Experimental results demonstrate the effectiveness of the designed control method.     

Titania NOx sensors for exhaust monitoring

Oxide semiconductors have been examined to develop NO_x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al³⁺, Sc³⁺, Ga³⁺ or In³⁺, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO_x has been fabricated. Many kinds of interference gases, such as C₃H₆, CO and SO₂, have been found to have only a slight influence on the sensor response to NO. The influence of O₂ and H₂O is also negligible, except for the cases of 0% H₂O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.     

Teach‐and‐repeat path following for an autonomous underwater vehicle

This paper presents a teach‐and‐repeat path‐following method for an autonomous underwater vehicle (AUV) navigating long distances in environments where external navigation aides are denied. This method utilizes sonar images to construct a series of reference views along a path, stored as a topological map. The AUV can then renavigate along this path, either to return to the start location or to repeat the route. Utilizing unique assumptions about the sonar image‐generation process, this system exhibits robust image‐matching capabilities, providing observations to a discrete Bayesian filter that maintains an estimate of progress along the path. Image‐matching also provides an estimate of offset from the path, allowing the AUV to correct its heading and effectively close the gap. Over a series of field trials, this system demonstrated online control of an AUV in the ocean environment of Holyrood Arm, Newfoundland and Labrador, Canada. The system was implemented on an International Submarine Engineering Ltd. Explorer AUV and performed multiple path completions over both a 1 and 5 km track. These trials illustrated an AUV operating in a fully autonomous mode, in which navigation was driven solely by sensor feedback and adaptive control. Path‐following performance was as desired, with the AUV maintaining close offset to the path.     

多波束声纳图像处理关键技术的研究

海底地形地貌探测是海洋资源开发和工程建设的基础,多波束声纳图像是反映水下地形地貌的重要手段,对其处理技术的研究具有重要意义。文中介绍了多波束声纳图像的形成原理及其特点,分析了影响多波束声纳图像的主要因素,从回波强度数据修正、声纳图像的生成和声纳图像改正三个方面,对多波束声纳图像处理的关键技术进行了详细介绍。总结和分析了目前国内外多波束声纳图像主要处理技术的研究现状和发展趋势,提出了研究多波束声纳图像处理技术的若干建议。     

提高车辆安全性的输出反馈自适应控制

研究含有时变参数的车辆动力学模型的输出跟踪控制问题.控制目标是使车辆的横摆角速度和质心侧偏角分别跟踪理想的设定值,通过反推方法设计输出反馈自适应控制器.控制器的输出为主动横摆力矩,通过控制主动横摆力矩来控制车辆的输出响应跟踪理想的输出信号,从而提高车辆的安全性.仿真结果表明,该控制器能更好地适应车速和路况的变化,鲁棒性强.     

基于级联方法的欠驱动AUV全局K指数3 维直线跟踪控制

采用非线性系统级联方法,提出一种欠驱动自主水下航行器的3维直线跟踪控制算法,首先将3维直线跟踪误差模型分解为水平面运动受垂直面运动扰动的级联结构;然后分别设计俯仰角指令和航向角指令,进一步将平面直线跟踪模型分解为位置跟踪误差受俯仰角/航向角跟踪误差扰动的级联结构,并设计了俯仰角和航向角的跟踪控制律,通过逐级应用级联系统稳定性理论证明了3维直线跟踪误差的全局κ指数稳定性;最后通过数学仿真验证了所提出跟踪控制算法的有效性。     

3-D Source Seeking for Underactuated Vehicles Without Position Measurement

Our past work introduced source seeking methods for GPS-denied autonomous vehicles using only local signal measurement and operating in two dimensions. In this paper, we extend these results to three dimensions. The 3-D extensions introduce many interesting challenges, including the choice of vehicle models in 3-D, sensor placement to allow probing-based gradient estimation of an unknown signal field in 3-D, the question of what type of pattern of vehicle motion can be produced in an underactuated 3-D vehicle to allow tuning by single-loop or multiloop extremum seeking, and the shape of attractors, which become very complex in 3-D. We present two control schemes that address these questions. The first scheme focuses on vehicles with a constant forward velocity and the ability to actuate pitch and yaw velocities. The second scheme employs vehicles with constant forward and pitch velocities and actuate only the roll velocity. Our results include convergence analysis and simulation results.      

水下目标多亮点回波仿真及应用研究

水下目标回波的亮点结构是重要的目标特征,因此,水下目标亮点特征的提取也是主动探测系统进行目标识别与跟踪的主要内容.该文研究了水下目标亮点的结构模型及亮点回波信号模型,重点分析了窄带系统中目标亮点回波信号的幅度、时延、频移以及相位的仿真计算方法.配合波束形成、参数估计及弹道逻辑,实现了对水下目标进行动态跟踪的仿真弹道,并给出了仿真实例.该仿真方法已经在水下武器仿真系统中得到了很好的应用,具有重要的使用价值.     

Decentralized discrete-time neural control for a Quanser 2-DOF helicopter

Control design for helicopters is a complicated and challenging problem due to the strong inter-couplings and nonlinear uncertainties in the system model. This paper deals with the decentralized control problem for the output trajectory tracking in a Quanser 2 degree of freedom (DOF) helicopter. High order neural network (HONN) is an important technique to approximate non-linearities in the model. Two different discrete-time schemes with a decentralized structure are used. Neural backstepping and neural sliding mode block control techniques are considered in order to control pitch and yaw positions. On one hand, backstepping control divides the whole system into two subsystems which are used to track the pitch and yaw references respectively. Real and virtual controls are approximated by HONNs. On the other hand, block control technique is applied to HONNs which can identify the system helicopter model. Each discrete-time high order neural network is trained on-line with an extended Kalman filter based algorithm. Without the previous knowledge of the plant parameters neither its model, we show via simulations the good performance of both strategies. The block control technique presents slightly better results than backstepping algorithm.     

基于核相关滤波的无人机偏航角跟踪控制系统设计

针对非线性自抗扰控制技术设计的系统、线性自抗扰技术设计的系统受到噪声影响,导致信号传输受到阻碍,出现偏航角跟踪控制结果精准度低的问题,提出了基于核相关滤波的无人机偏航角跟踪控制系统设计;在系统总体架构支持下,采用STM32F407型号主控芯片,保证无人机控制系统稳定性;在方向盘下安装有转向角传感器,为ESP电子控制单元提供方向盘;使用频率为2.4 GHz遥控器接收机生成具有不同脉冲宽度PWM信号,通过控制旋翼偏航控制器,推动旋翼在不同角度指令下旋转;利用核相关滤波器过滤目标图像,通过滤波器的输运来估计目标运动位置,并确定地面参考坐标系与无人机机体坐标系,构成无人机在空间中六个自由度,由此设计偏航角跟踪控制软件流程,跟踪控制无人机偏航角;由实验结果可知,该系统滚转角与实际值轨迹一致,误差为0;俯仰角与实际值轨迹有偏差,误差为0.05°,为无人机向不同方向精准飞行提供系统支持.     

A study of two-dimensional sensor placement using time-difference-of-arrival measurements

Finding the position of a radiative source based on time-difference-of-arrival (TDOA) measurements from spatially separated receivers has important applications in sonar, radar, mobile communications and sensor networks. Each TDOA defines a hyperbolic locus on which the source must lie and the position estimate can then be determined with the knowledge of the sensor array geometry. While extensive research works have been performed on algorithm development for TDOA estimation and TDOA-based localization, limited attention has been paid in sensor array geometry design. In this paper, an optimum two-dimensional sensor placement strategy is derived with the use of optimum TDOA measurements, assuming that each sensor receives a white signal source in the presence of additive white noise. The minimum achievable Cramér–Rao lower bound is also produced.     

A Rotating Sonar and a Differential Encoder Data Fusion for Map-Based Dynamic Positioning

In this paper, a dynamic positioning system using a rotating sonar and a differential encoder is proposed. The method is implemented by employing an indirect feedback Kalman filter. The state equation is written for encoder propagation and its error characteristic. A measurement equation describes a map-based measurement equation based on rotating sonar sensor data. In other words, sonar data compensates for the system and navigation errors of the differential encoder. The positioning system calculates the position and headings of a mobile robot. The real-time calculation is performed by a map-based measurement update utilizing wide-angle beam characteristics of the sonar sensor and the Kalman filter. In addition, an observability analysis for the positioning system is performed. Experimental results show that the proposed hybrid positioning system successfully provides accurate position and headings in real-time. The position and heading errors arc bounded within few centimeters and within few degrees, respectively.     

NOx sensing properties of In2O3 nanoparticles prepared by metal organic chemical vapor deposition

In₂O₃ nanoparticles were deposited by low-temperature metal organic chemical vapor deposition. The response of 10-nm thick In₂O₃ particle containing layers to NO_x and O₂ gases is investigated. The lowest detectable NO_x concentration is 200 ppb and the sensor performance is strongly dependent on the gas partial pressure as well as on the operating temperature. The sensor response towards 200 ppm of NO_x is found to be above 10⁴. Furthermore, the cross-sensitivity against O₂ is very low, demonstrating that the In₂O₃ nanoparticles are very suitable for the selective NO_x detection.