Attitude stabilization of a pico-satellite by momentum wheel and magnetic coils

The three-axis active attitude control method with a momentum wheel and magnetic coils for a pico-satellite is considered. The designed satellite is a 2.5 kg class satellite stabilized to nadir pointing. The momentum wheel performs a pitch-axis momentum bias, nominally spinning at a particular rate. Three magnetic coils are mounted perpendicularly along the body axis for precise attitude control through the switch control mechanism. Momentum wheel start up control, damping control and attitude acquisition control are considered. Simulation results show that the proposed combined control laws for the pico-satellite is reliable and has an appropriate accuracy under different separation conditions. The proposed strategy to start up the wheel after separation from the launch vehicle shows that its pitch momentum wheel can start up successfully to its nominal speed from rest, and the attitude convergence can be completed within several orbits, depending on separation conditions.     

Real-time localization estimator of mobile node in wireless sensor networks based on extended Kalman filter

Localization of the sensor nodes is a key supporting technology in wireless sensor networks (WSNs). In this paper, a real-time localization estimator of mobile node in WSNs based on extended Kalman filter (KF) is proposed. Mobile node movement model is analyzed and online sequential iterative method is used to compute location result. The detailed steps of mobile sensor node self-localization adopting extended Kalman filter (EKF) is designed. The simulation results show that the accuracy of the localization estimator scheme designed is better than those of maximum likelihood estimation (MLE) and traditional KF algorithm.     

一种基于核岭回归与卡尔曼滤波的定位算法

传感器定位技术作为无线传感器网络的重要课题之一,为实现目标实时定位,提出一种基于核岭回归与卡尔曼滤波的定位算法。该算法在离线阶段使用核岭回归算法（KRR）对无线位置指纹数据库进行训练,从而得到一个可反映信号强度指标（RSSI）与位置坐标之间映射关系的函数|在线阶段先利用离线阶段得到的函数对目标进行粗定位,再结合卡尔曼滤波（KF）方法对目标进行精确定位。实验结果表明,在真实室内办公环境下,相比 KNN 算法与核函数（Kernel）算法,该算法能实现更好的定位精度,平均定位误差为 1.898 3m。     

基于Kalman滤波的多传感器分布式数据融合算法及其并行实现

1Introduction Inrecentyears,multisensordatafusiontechniques havefoundwidespreadapplicationsinmanytracking andsurveillancesystemsaswellasinapplications wherereliabilityisofamainconcern[1].Multisensor datafusionisdefinedasaprocessofintegratingdata frommulti…     

基于MPU9250的无人机姿态信息采集及处理

研究MPU9250多轴姿态传感器在无人机上的姿态信息采集,通过对九轴传感器内的陀螺仪,重力加速度计,磁力计的数据接收后,结合卡尔曼滤波算法对其数据进行精准的解算;搭建了一个无人机姿态模拟的物理实验平台,进行无人机运动状态下的信息采集;最后,在MATLAB的数据仿真下测试其性能。实验结果表明该方法可使无人机信息采集的精准度提升一倍。     

A New Recursive Parameter Estimation Algorithm of Multi－Variable Time－Varying AR Model

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Optimal linear attitude estimators via geometric analysis

Three optimal linear attitude estimators are proposed for single-point real-time estimation of spacecraft attitude using a geometric approach. The final optimal attitude is represented by modified Rodrigues parameters (MRPs). After introducing incidental right-hand orthogonal coordinates for each pair of measured values, three error vectors are obtained by the use of dot or/and cross products. Corresponding optimality criteria are rigorously quadratic and unconstrained, which do not coincide with Wahba’s constrained criterion. The singularity, which occurs when the principal angle is close to π, can be easily avoided by one proper rotation. Numerical simulations show that the proposed three optimal linear estimators can provide a precision comparable with those complying with the Wahba optimality definition, and have faster computational speed than the famous quaternion estimator (QUEST).     

基于EKF和RBF的路面附着系数估计

针对车辆行驶下的路面附着系数估计问题,提出了扩展卡尔曼滤波算法(EKF,Extended Kalman Filter)与径向基神经网络(RBF,Radial Basis Functionneural network)相融合。通过扩展卡尔曼滤波算法得出路面附着系数估计所需要的车辆状态参数,结合轮速等直接数据采用径向基神经网络对路面附着系数进行估计。神经网络的训练样本通过Carsim/Simulink收集不同行驶工况,并采用差值寻优的方法对径向基神经网络算法中的决定系数进行优化。基于双移线工况验证了该算法在路面附着系数估计上具有较高的精准度。     

基于UKF算法的电池荷电状态SOC估算研究

新能源汽车锂电池荷电状态是反映电池及电源系统的重要参数,为达到实时估算SOC目的,基于无迹卡尔曼滤波算法提出SOC估算解决方案。在MATLAB/Simulink环境中建立一阶Thevenin等效电路模型和无迹卡尔曼滤波算法,通过建立混合功率脉冲特性实验,辨析出不同SOC和温度对电池模型的影响参数,将辨析出来的参数代入到UKF算法中进行仿真实验。实验结果表明,该荷电状态估算具有较高的精准度。     

气浮台控制系统设计及在航天工程类专业教学中的应用

航天器姿态控制系统作为航天器的重要分系统之一,在航天器三轴稳定控制、姿态敏捷机动等方面起着重要的作用.在航天专业实践教学中,由于无法模拟真实的空间环境,学生无法直观地了解航天器的姿态控制过程,给相关课程的学习带来一定的难度.微型三轴气浮台控制系统是航天器地面半物理仿真设备的核心,能够验证全新的航天器智能控制算法,与课堂...     

基于计算机视觉的无人机物体识别追踪

提出一种将ROS系统的AR.Drone飞行器作为载体,基于飞行器实现物体识别追踪的具体优化方案。在计算机视觉方面,结合物体识别OpenCV模块中的Haar级联分类器与卡尔曼滤波,实现无人机的目标识别以及对错误目标的过滤功能,使飞行器在搭载摄像头模块后,可结合现有视觉模型完成目标识别要求,算法融合后的系统性能具有良好的鲁棒性;在飞行器控制方面,结合飞行器自身的反馈控制模块与基于相对位置控制的PD位置控制器,优化飞行器自身姿态及目标追踪过程中的动态参数调节优化功能,使飞行器在目标追踪过程中具有良好的自适应性。基于以上两点优化方案建立实验模型,取得了较好的实验效果。具体相对位置估计均方根误差实验结果为：在x方向上为0.124 5m,在y方向上为0.243 7m,在z方向上为0.176 8m,证明了该优化方案的实用性。     

基于组合导航的四旋翼飞行器控制系统研究

根据刚体动力学原理,建立了四旋翼飞行器的动力学模型,利用捷联惯导和GPS组合作为四旋翼飞行器的导航系统,采用方向余弦矩阵的变换方法,实现了对飞行器的姿态解算;采用卡尔曼滤波算法实现姿态角信号的校正,实现了四旋翼飞行器的导航;采用基于PID算法的悬停状态的控制策略,实现了四旋翼飞行器的垂直起降和稳定的悬停．     

Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems

A particle filter is proposed to perform joint estimation of the carrier frequency offset (CFO) and the channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling (SIS), and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling (SIR). Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations.     

Hybrid analytical resolution approach based on ambiguity function for attitude determination

When satellite navigation receivers are equipped with multiple antennas, they can deliver attitude information. In previous researches, carrier phase differencing measurement equations were built in the earth-centered, earth-fixed （ECEF） coordinate, and attitude angles could be obtained through the rotation matrix between the body frame （BF） and the local level frame （LLF）. Different from the conventional methods, a hybrid algorithm is presented to resolve attitude parameters utilizing the single differencing （SD） carrier phase equations established in LLF. Assuming that the cycle integer ambiguity is known, the measurement equations have attitude analytical resolutions by using simultaneous single difference equations for two in-view satellites. In addition, the algorithm is capable of reducing the search integer space into countable 2D discrete points and the ambiguity function method （AFM） resolves the ambiguity function within the analytical solutions space. In the case of frequency division multiple access （FDMA） for the Russian Global Orbiting Navigation Satellite System （GLONASS）, a receiver clock bias estimation is employed to evaluate its carrier phase. An evaluating variable and a weighted factor are introduced to assess the integer ambiguity initialization. By static and dynamic ground experiments, the results show that the proposed approach is effective, with enough accuracy and low computation. It can satisfy attitude determination in cases of GPS alone and combined with GLONASS.     

Control system for dynamic testing platform of asymmetrical pitch mechanism

A novel asymmetrical pitch system for rotary wing is presented. The pitch control characteristics are studied and analyzed. Because elastic linkage is a key part in whole asymmetrical pitch system, in order to obtain the variation of the elastic linkage deformation, an experimental platform mainly based on the device of micro aerial vehicles (MAVs) and a new control system mounted on TMS320LF2407 are designed. This control system has its compacted configuration and reliability. Finally, using this system to control the MAV for simulating the flying forward, experimental results show the MAV’s flight attitude can be controlled based on the variation of the elastic linkage. Project supported by the National Natural Science Foundation of China (Grant No.60605028), the National High-Technology Research and Development Program of China (Grant No.2007AA04Z225), the Shanghai Rising-Star Program (Grant Nos.07QA14024, 07QH14006), the Shanghai Shuguang Program (Grant No.07SG47), and the Shanghai Leading Key Laboratory of Mechanical Automation and Robotics Science Foundation (Grant No.ZZ0805)     

基于模糊PID控制的飞机俯仰姿态控制

针对传统PID控制的一些缺陷,结合模糊控制的优势,在常规PID控制的基础上加入变论域模糊控制算法,对飞机俯仰姿态角控制系统进行调整.通过仿真结果表明,加入模糊控制之后系统的超调量、稳态误差变小,到达稳定状态的时间显著缩短,控制效果明显变好.     

Predictive control of a class of bilinear systems based on global off-line models

INTRODUCTION Bilinear systems are a kind of important nonlinear systems with relatively simple structure, and many industrial processes can be described as a bilinear system. Thus research on the control of this kind of systems is very important. On the other hand, model predictive control (MPC) (Clarke et al., 1987) has been widely used in industrial applications and many predictive control methods focusing on bilinear systems are emerging (Bloemen et al., 2001; Fontes et al., 2004; He…     

The influence of theoretical tools on teachers’ orientation to notice and classroom practice: a case study

Assumptions about the construction and the transmission of knowledge and about the nature of mathematics always underlie any teaching practice, even if often unconsciously. I examine the conjecture that theoretical tools suitably chosen can help the teacher to make such assumptions explicit and to support the teacher’s reflection on his/her previous as well as future educational practice. In particular, I show how an epistemological vision of mathematics in resonance with a model of cognitive dynamics can work as a powerful tool to support a teacher’s stable and autonomous attitude of noticing. To support this argumentation, I present some experimental data concerning a case study of one teacher. Through a methodological frame suitably arranged I try to describe how the teacher’s ability to rely on this particular theoretical frame affects: the choice of the global goals in mathematics education; the design of educational interventions; the interpretation of learners’ cognitive behaviours; and the assessment.     

ADAPTIVE ESTIMATION OF THE MEANS AND COVARIANCES OF SYSTEM NOISES

This paper presents a simple and feasible method of estimating the means andcovariances of system noises.The information about the means and covariances is derivedfrom a suboptimal Kalman filter formed via the approximate statistics.An efficientalgorithm is obtained through WLS(weighted-least-square)estimation by using themeasurement residuals of the suboptimal Kalman filter.Simulations are given to show theefficiency of the method.     

Developing rigid constraint for the estimation of pose and structure from a single image

INTRODUCTION Pose and structural parameters analysis of 2Dimages sets find application in many areas such asobject recognition, motion estimation, navigationplanning, and structural analysis of 3D objects(Huang and Netravali, 1994), image communica-tion, and image coding (Mitiche and Aggarwal,1986). Normally, given one set of 3D object pointdata and their corresponding 2D projective imagepoint data, the 3D-2D calibration problem is re-ferred to as the estimation of the camera par…