Dynamic Parameterization for Path Following Control

Path following is a basic skill for robots in industrial use. Since the objective of path following is to make a robot follow the reference path, the velocity of the robot or the timing of the motion does not need to be strictly controlled. In this paper, the reference path is defined as a function of the parameter that has dynamics. Using this parameter, we can define the contour error, which is the error that enables us to measure the distance from the reference path to the configuration of the robot. Although the contour error is suitable for use in path following, the dynamics of the parameter contain singular points at which the dynamics cannot be defined. In order to overcome this difficulty, globally defined dynamics are introduced, and two dynamics are integrated with a switching scheme. In this paper, the asymptotic stability of the whole system is proved theoretically. Computer simulation results also show the effectiveness of the method.     

Solar Airplane Conceptual Design and Performance Estimation

Solar airplanes exhibit a fascination due to their energy sustainability aspect and the potential for sustained flight lasting several day-night cycles. Resulting monitoring and measurement applications at high altitudes but also close to the Earth surface would be extremely useful and are targeted by several research groups and institutions. The question of how to choose the main design parameters of the airplane for a specific mission, considering the current state-of-the-art technologies involved, however, is not easy to answer. A tool is presented performing such a multi-disciplinary optimization. Solar airplanes using both batteries as energy storage devices as well as their capability of flying performance-optimizing altitude profiles can be sized and evaluated in terms of various performance measures. Simulation results show that sustained flight in the Stratosphere is hard to achieve, if the altitude needs to be kept constant. A simulated Remote Control (RC) model size solar airplane allowed to vary altitude proves to be capable of flying multiple day-night cycles at medium and high latitudes during summer.     

水下无人航行器水平面路径跟踪控制方法研究

针对水下无人航行器(Unmanned Underwater Vehicle,UUV)运动控制具有非线性和强耦合特点,设计了基于SDRE (State -Dependent- Riccati Equation)方法的UUV水平面路径跟踪控制器,通过将非线性动力学方程伪线性化,解代数黎卡提方程得到控制律;针对以往SDRE权系数矩阵选择使用手工调试,过程复杂且很难得到最优解的问题,引入粒子群寻优算法,将改进后的粒子群算法用于SDRE权系数矩阵的寻优,从而得到优化后的控制器参数;对所设计的控制系统进行了仿真验证,结果显示UUV可以很好地跟踪上期望轨迹.     

未标定相机的高精度位姿估计方法

针对未标定相机的位姿估计问题,提出了一种焦距和位姿同时迭代的高精度位姿估计算法。现有的未标定相机的位姿估计算法是焦距和相机位姿单独求解,焦距估计精度较差。提出的算法首先通过现有算法得到相机焦距和位姿的初始参数;然后在正交迭代的基础上推导了焦距和位姿最小化函数,将焦距和位姿同时作为初始值进行迭代计算;最后得到高精度的焦距和位姿参数。仿真实验表明提出的算法在点数为10,噪声标准差为2的情况下,角度相对误差小于1%,平移相对误差小于4%,焦距相对误差小于3%;真实实验表明提出的算法与棋盘标定方法的精度相当。与现有算法相比,能够对未标定相机进行高精度的焦距和位姿估计。     

Vector Field Path Following for Miniature Air Vehicles

In this paper, a method for accurate path following for miniature air vehicles is developed. The method is based on the notion of vector fields, which are used to generate desired course inputs to inner-loop attitude control laws. Vector-field path-following control laws are developed for straight-line paths and circular arcs and orbits. Lyapunov stability arguments are used to demonstrate asymptotic decay of path-following errors in the presence of constant wind disturbances. Experimental flight tests have demonstrated mean path-following errors on less than one wingspan for straight-line and orbit paths and less than three wingspans for paths with frequent changes in direction.     

残冰检测中飞机图像特征点精确提取算法

传统角点检测算法无法精确提取感兴趣的特征点。为此,提出一种新的特征点提取算法。通过曲率角点检测算法提取飞机图像的特征点,并作为待匹配图像,采用像素相关性匹配算法进行特征点提取,利用飞机机身固定结构约束匹配算法去除误匹配对。实验结果表明,该算法具有较好的适应性,能够精确提取特征点。     

Path Coordinates in a 3D Path Following Problem

Two approaches to 3D path coordinates used when solving a path following problem for aerial vehicles are proposed. The first approach lies in reducing the problem to a two-dimensional case by projection. The second approach is based on introducing an adaptive frame at the target point. The choice of the adaptive frame determines the complexity of the algorithm of the control synthesis. It is shown that the parallel transport frame, or the Bishop frame, is most convenient.     

风干扰下基于变船长比的无人水面艇路径跟踪方法

针对无人水面艇在路径跟踪过程中易受风环境干扰的问题,建立了风环境下无人水面艇的运动数学模型,提出一种用于抵抗风干扰的直线路径跟踪方法;首先,基于视距导航原理,设计了跟踪期望航向角的PD控制器,通过融合路径方向,距离偏差及船长比等信息,实时调整左右两侧推进电机的控制电压,实现无人水面艇直线路径跟踪;然后,针对不同船长比对直线路径跟踪的影响,采用模糊控制方法,设计了以跟踪过程中的距离偏差和距离偏差变化率为输入,以船长比为输出的模糊控制模块,对船长比进行自适应调整,以提高控制器的抗风干扰性能;仿真结果表明,所提方法可减小风干扰作用下的跟踪静差,较之传统单纯PD控制方法,抵抗风干扰的能力得到提高。     

A Path Following Algorithm for the Graph Matching Problem

We propose a convex-concave programming approach for the labeled weighted graph matching problem. The convex-concave programming formulation is obtained by rewriting the weighted graph matching problem as a least-square problem on the set of permutation matrices and relaxing it to two different optimization problems: a quadratic convex and a quadratic concave optimization problem on the set of doubly stochastic matrices. The concave relaxation has the same global minimum as the initial graph matching problem, but the search for its global minimum is also a hard combinatorial problem. We, therefore, construct an approximation of the concave problem solution by following a solution path of a convex-concave problem obtained by linear interpolation of the convex and concave formulations, starting from the convex relaxation. This method allows to easily integrate the information on graph label similarities into the optimization problem, and therefore, perform labeled weighted graph matching. The algorithm is compared with some of the best performing graph matching methods on four data sets: simulated graphs, QAPLib, retina vessel images, and handwritten Chinese characters. In all cases, the results are competitive with the state of the art.     

Path Loss Modelling for Location Service Applications

The aim of this paper is the path loss modelling for the radiolocation services in radio communication networks, particularly in cellular networks. The main results of the measurements obtained in the physical layer of the UMTS are introduced. A new method for the utilization of the multipath propagation phenomenon to improve the estimation of the distance between the MS （mobile station） and the BS （base station） is outlined. This method significantly increases the quality of location services in systems which use a radio interface with DS （direct sequence） CDMA （code division multiple access）.     

基于路径预测人工势场法的自动跟随小车路径规划

针对自动跟随小车实际工作环境下目标点和障碍物具有可移动特征,在传统人工势场法的基础上提出一种具有动态路径预测功能的路径规划方法。通过实时采集和计算小车、目标点和障碍物的距离、运动速度和方向,预测未来三者之间可能的位置关系。根据目标点预测结果采用人工势场法确定接近目标点路径,根据预测的障碍点运行轨迹确定绕过障碍点的路径。将基于路径预测人工势场法与传统人工势场法进行仿真对比,结果表明该方法在跟随效率和避障能力上具有显著的提高。     

The 2-NN Rule for More Accurate NN Risk Estimation

By proper design of a nearest-neighbor (NN) rule, it is possible to reduce effects of sample size in NN risk estimation. The 2-NN rule for the two-class problem eliminates the first-order effects of sample size. Since its asymptotic value is exactly half that of the 1-NN rule, it is possible to substitute the 2-NN rule for the 1-NN rule with a resultant increase in accuracy. For further stabilization of the risk estimate with respect to sample size, 2-NN polarization is suggested. Examples are included. The 2-NN approach is extended to M-class and 2k-NN.     

二维数字化目标周长的精确估计

本文设计了一种新的精确而又实用快速的基于8连通的m采样和分类(m-Sampling and Classified Method,MSC)方法,估计和预测其误差,为证实预期结果,对一系列不同直径的圆和矩形进行测量并与前人的工作进行了比较"取得满意的结果.     

一种实时精确的正弦波频率估计算法

针对Rife算法在被估计频率接近量化频率时的估计精度较差的特点,结合频谱细化技术构造了补充Rife算法.考虑到Rife算法和补充Rife算法性能互补的优点,提出了一种综合算法.仿真结果表明,在低信噪比(SNR)下,该综合算法不仅具有较高的估计精度,而且在整个频段上性能稳定.同时该综合算法只需一次FFT及两点DFT计算,计算量小,易于硬件实现.     

Highly Accurate Attitude Estimation via Horizon Detection

Attitude (pitch and roll angle) estimation from visual information is necessary for GPS‐free navigation of airborne vehicles. We propose a highly accurate method to estimate the attitude by horizon detection in fisheye images. A Canny edge detector and a probabilistic Hough voting scheme are used to compute an approximate attitude and the corresponding horizon line in the image. Horizon edge pixels are extracted in a band close to the approximate horizon line. The attitude estimates are refined through registration of the extracted edge pixels with the geometrical horizon from a digital elevation map (DEM), in our case the SRTM3 database, extracted at a given approximate position. The proposed method has been evaluated using 1629 images from a flight trial with flight altitudes up to 600 m in an area with ground elevations ranging from sea level up to 500 m. Compared with the ground truth from a filtered inertial measurement unit (IMU)/GPS solution, the standard deviation for the pitch and roll angle errors obtained with 30 Mpixel images are 0.04° and 0.05°, respectively, with mean errors smaller than 0.02°. To achieve the high‐accuracy attitude estimates, the ray refraction in the earth's atmosphere has been taken into account. The attitude errors obtained on real images are less or equal to those achieved on synthetic images for previous methods with DEM refinement, and the errors are about one order of magnitude smaller than for any previous vision‐based method without DEM refinement.     

一种InSAR相关系数精估计方法

InSAR的相关系数是对SAR干涉图像对相似度的度量,是InSAR技术应用分析的一项基本参数。相关系数的估计是通过比较两幅SAR图像中对应位置的相邻像素值得到的,由于采样点数目的限制及存在由于地形起伏引起的干涉相位,估计结果往往与真实值相差较大。本文提出了一种能够大幅减小相关系数估计误差的方法,首先利用粗精度DEM仿真地形相位以消除地形起伏对相关系数估计的影响,随后采用第二类统计方法进一步提高了相关系数的估计精度。我们用SIR-C/XSAR的Etna火山干涉数据对本文方法进行了验证。     

UAV Path Following in Windy Urban Environments

This paper considers UAV path following in cluttered environments under windy conditions. Unstructured wind patterns in cluttered environments can make path following difficult resulting in high errors and possibly collisions with buildings. Combining a pursuit guidance law philosophy with a line-of-sight guidance law, we develop a novel guidance law that has low computational complexity and can track straight line paths, circular paths, a combination of both and waypaths accurately in the presence of wind blowing as high as fifty percent of the UAV’s air speed. Performance of the guidance law is demonstrated through numerical simulations.     

基于自适应神经网络的AUVs路径跟踪控制

为解决由于随时间变化水动力阻尼引起的参数变化和不确定性的问题,提出了基于径向基函数神经网络的未知评估算法,引入自适应算法以保证神经网络权值的最优评估.基于Lyapunov稳定性理论,设计一种自适应神经网络控制器以保证路径跟踪系统中所有误差状态都趋于稳定.为了验证该控制器的可行性,对系统施加如位置误差、方向误差等虚拟干扰,证明该控制器可将误差消减为零.另一方面,机器人在以恒定的速度行驶时,每个航点被指定一个适合半径的圆弧可以保证其有较高的精度.为了评估路径跟踪控制器的性能,提出直线型和直线加圆弧型路径方案.仿真结果表明,该控制器可以有效地消除机器人非线性和模型不确定性造成的干扰.     

一种球形滚动机器人的路径跟踪控制器设计

对一种球形滚动机器人的路径跟踪问题进行研究,设计一种基于自适应滑模控制策略的路径跟踪控制器。所设计的路径跟踪控制器采用鲁棒滑模自适应增益控制律,能够有效实现带有扰动和不确定性的实际球形滚动机器人的路径跟踪。推导球壳纯滚动和无自转非完整约束下球形滚动机器人的运动方程,并在此基础上设计自适应滑模路径跟踪控制器。对于给定的参考几何路径,所设计的路径跟踪控制器能够确保路径跟踪误差在有限时间内收敛至很小的零邻域内。基于Lyapunov稳定性理论证明了闭环控制系统的稳定性,数值仿真与样机实验结果进一步验证了所设计的路径跟踪控制器的有效性。     

IPv6网络路径容量测量方法研究

分组离散技术是常用的路径容量测量方法之一,它通常采用连续发送策略来发送测量分组。然而该策略对发送带宽的利用率较低,影响了测量的准确性。针对IPv6网络环境,提出了一种新的基于分片机制的路径容量测量方法。该方法通过构造长度大于路径最大传输单元的原始测量分组,迫使协议栈对该分组进行分片操作,生成长度相等的测量分片序列。实验结果表明,与经典的pathrate工具相比,该方法能够获得更小的源端分组离散以及更好的背景流量抑制能力。