A fast compass alignment method for SINS based on saved data and repeated navigation solution

Compared with Gimbaled Inertial Navigation System (GINS), there are two differences in the compass alignment process for Strapdown INS (SINS) as follows: (1) the input signal is the projected sensor data from body frame to calculated navigation frame, not the sensor data; (2) the output control signal participates in navigation solution rather than driving navigation frame directly. Considering these characteristics, a fast compass alignment method based on iterative calculation is designed for SINS in this paper. With the help of high performance computer, the iterative process can be finished fast and the alignment time can be shortened obviously. However, there exist two problems in the new method, one of which is how to use the saved data, and the other is how to ensure the real-time property of alignment result. For the first problem, our simulation result shows that the forward–forward navigation solution method is more effective for compass alignment than the backward–forward one. And to solve the second problem, Multi-tasking method combined with Real Time Multi-tasking Operating System (RTOS) is used to trace the change of body frame and update the body frame of attitude matrix when the alignment is finished. The car test on a type of fiber-optic gyro SINS indicates that the alignment accuracy of the proposed method processed for 142 s is as precise as that of the classical compass alignment method for 720 s.     

QUKF算法及其在SINS初始对准中的应用

针对捷联惯导系统初始对准过程中的大失准角情况,建立了乘性四元数姿态误差方程。结合UKF算法,提出了基于四元数的UKF算法(QUKF)。以姿态矩阵为对象,通过构造姿态矩阵代价函数的方法来求取四元数的一步预测均值,保证了均值四元数的规范化;利用乘性误差四元数表示四元数Sigma点与均值四元数的距离,以求取四元数的预测协方差矩阵。四元数状态更新中,采用乘性四元数更新保证了滤波过程中四元数的规范化。基于该算法的SINS在粗对准水平失准角为小角度、方位失准角为大角度条件下的仿真实验结果表明,与常规EKF相比,纵、横摇角对准精度均略有提高,而航向角误差估计精度提高显著。     

基于CKF的SINS大方位失准角初始对准

大方位失准角捷联惯导系统(strapdown inertial narigation system,SINS)误差方程是非线性的,为改善非线性模型下初始对准的精度,提出将一种新的非线性滤波方法(cubature Kalman filter,CKF)应用于捷联惯导系统初始对准中。为此建立了大方位失准角下初始对准非线性模型,分析了基于spherical-radial cubature准则的CKF滤波原理,对非线性模型进行了CKF滤波仿真。仿真结果表明CKF能够很好地处理初始对准中的非线性问题,提高初始对准精度,方位失准角误差能够收敛到-33.13’,接近理论估计精度-32.40’,优于EKF的-84.14’。     

A novel algorithm for marine strapdown gyrocompass based on digital filter

With the rapid development of strapdown gyrocompass, few corresponding strapdown algorithms occur in publications, so that we have to use the conventional one designed for platform gyrocompass. Enlightened by IXSEA ideals, we proposed a novel algorithm which is suitable for marine strapdown gyrocompass. In our proposed algorithm, gyro outputs are used to track the body frame rotation, and the observation of the pure gravity slow drift in the inertial gives the navigation frame rotation. We also separate the pure gravity from interferential accelerations with a FIR low-pass digital filter. The analysis and numerical results show the better performance of the proposed algorithm than the conventional one.     

Strapdown gyrocompass algorithm for AUV attitude determination using a digital filter

The strapdown gyrocompass can provide attitude by measuring the Earth’s gravity vector. In practical applications, there usually exists unwanted disturbance accelerometers that will distort the accelerometer measurements, hence a filtering out procedure is essential. Current attitude determination method based on pendulum cutting off technology has the limitation for vehicle moving mode. This paper proposes a new strapdown gyrocompass algorithm via processing the accelerometer measurement with Butterworth low-pass filter (LPF) to remove the high frequency dynamic disturbance components. When the gravity variation in inertial frame is regulated, LPF can be applied to properly get the gravity even in the presence of acceleration disturbances, and subsequently can be applied to calculate the strapdown gyrocompass attitude. The proposed algorithm does not require declination information and inertial element biases estimation. The field test has been conducted and the results verified the effectiveness and reliability of the proposed AUV attitude determination method and have also shown that the gravity is proportional to the latitude and altitude of AUV.     

晃动基座下激光陀螺捷联导航系统初始对准预滤波新方法

激光陀螺捷联惯性导航系统在晃动基座下进行初始对准,外界的干扰会令激光陀螺和加速度计的噪声增大,从而使初始对准的时间延长,甚至不能完成对准。对激光陀螺和加速度计输出简单的采用低通滤波的方法,并不能有效的抑制传感器噪声。采用小波方法,虽然能够抑制噪声的影响,但是由于小波的高计算复杂度和块处理结构,很难在线实现。针对这个问题,本文提出一种新的预滤波方法,将传感器输出通过低通滤波之后再通过一个基于隐式马尔可夫模型的稳态卡尔曼滤波,这样就能有效的降低基座晃动带来的噪声,同时不降低对准的精度。实验结果表明,本文提出的预滤波方法计算复杂度低,滤波效果明显,能够很好的辅助激光陀螺捷联导航系统在晃动基座下完成精对准。     

An innovative transfer alignment method based on federated filter for airborne distributed POS

The real-time and high-precision transfer alignment between the master and slave systems is the key issue for the airborne distributed Position and Orientation System (POS) to realize real-time and high-precision measurement of multipoint motion parameters. To solve the problem, this paper proposes a transfer alignment method based on federated filter, in which the high-dimensional state vector is divided into two parts and as the state vector of two local filters respectively instead of estimating in a centralized filter. This idea reduces the dimension of the system state vector; thus the computation speed is improved. The results of simulation and static ground experiment show that the proposed method runs faster than centralized filter by more than 10% and its alignment precision has the same level as centralized filter’s.     

数字滤波及陷波器在心电图信号检测中的应用

本文在心电图信号检测电路中应用了数字滤波器，它具有性能稳定，调整简单，易于修改的优点。另外，为了克服工频干扰，本文设计了数字陷波器，两者结合使用，效果最佳。     

适用于强阵风干扰下的捷联惯导自对准算法

对于处于起竖状态的车载武器来说,在强阵风的干扰下会产生较大摇晃,由于其捷联惯导系统(SINS)的重心较高,SINS的测量值很容易受到晃动所带来的角运动和线运动干扰,SINS难以快速地实现自对准,针对该问题,提出了强阵风干扰下SINS自对准算法。该算法利用惯性坐标系下的姿态更新来实时地反映载体在晃动干扰下的姿态变化,以消除角运动干扰的影响;利用武器存在零速摇晃中心的特点,通过获取加速度计在零速摇晃中心的等效输出来消除线运动干扰的影响,然后结合姿态的最优估计实现初始对准。仿真结果表明,该算法不需要进行粗对准,能够在强阵风干扰下快速地实现自对准。     

SINS/LBL组合导航序贯滤波方法

在长基线水声定位系统(LBL)实际应用过程中,由于信标作用距离限制、障碍物遮挡等多种原因,使得水下无人航行器(UUV)可能无法接收到所有信标的应答信号而产生量测更新延迟问题。对UUV在无法接收到所有信标信号时的导航滤波算法进行了研究;结合捷联惯性导航系统(SINS)误差模型和声速误差,建立了SINS/LBL组合导航模型,并将异步量测序贯处理方法引入该模型,实现了SINS/LBL组合导航滤波算法的实时量测更新;通过湖上试验数据分析,对比了SINS/LBL组合导航序贯滤波方法与常规方法的位置误差。结果表明,该方法即使在应答信号有缺失的情况下,仍然能够利用有限的应答信号量测值进行实时量测更新,保障了组合导航的精度。     

Initial alignment on moving base using GPS measurements to construct new vectors

Strapdown inertial navigation system cannot easily implement initial alignment on moving base if without the prior “one shot” transfer from another master inertial navigation system and strict constraints on moving trajectory, because the initial coarse attitude cannot be effectively achieved. In this paper, a novel method using the GPS measurements to assist to solve initial attitude matrix is investigated as coarse alignment. Specific vectors are constructed with GPS measurements and used for attitude matrix computation like in analytic alignment algorithm. Several moving conditions of carrier are assumed to test the new alignment method, and the results indicate that the initial attitude angles can be achieved with small errors, which is suitable for the conventional fine alignment afterward.     

Assessment approach for calculating transfer alignment accuracy of SINS on moving base

This study aims to evaluate the accuracy of transfer alignment of SINS on moving base. To this end, index of alignment degree (IAD) was put forward to try out in the engineering application of transfer alignment accuracy evaluation and identification. The direct statistical formulas were inference as the estimation foundation and the evaluation scheme of transfer alignment on moving base was designed while the attitude error cannot be directly measured. The mathematical estimation model was built and the algorithms of fixed point smoothing (FPS), fixed interval smoothing (FIS), inverted sequence recursive estimation (ISRE) and Kalman filtering (KF) were discussed which adaptable in alignment accuracy evaluation. Depending on theoretical calculation and simulated analysis, it shows: IAD reflects not only the alignment time and alignment accuracy, but also the differences of maneuver scheme, which is suitable as an integrated evaluation index; Four algorithms can all be used to transfer alignment accuracy evaluation and identification, FIS is recommended in engineering practice; Generalized IAD should be calculated according to the tactical requirement.     

光电探测系统辅助SINS的动态对准方法

针对陆地战车对定位和定向系统的要求越来越高,提出了一种高精度的对准方法。采用光电探测系统计算出精确的车辆位置和航向,在两次光学定位过程中利用运动约束与零速修正组合的方法估计出惯导系统系统误差,进而估算出光电探测系统与捷联惯导系统之间的敏感轴安装偏角。仿真结果表明:光电探测系统的定向精度优于10″,定位精度优于0.1 m,敏感轴安装偏角的估计精度优于20″,因此本系统满足陆用战车的高精度动态对准需求。     

An innovational transfer alignment method based on parameter identification UKF for airborne distributed POS

Airborne distributed Position and Orientation System (POS) depends on transfer alignment to obtain high accuracy motion parameters of sub-systems by using accurate motion information of main system, including position, velocity and attitude. Complicated aircraft flexure will decrease the accuracy of transfer alignment. Usually, the flexure angle is idealized as Markov process with fixed parameters, while these parameters are unknown and time-varying in real application. Accordingly, the accuracy of state model and statistic characters of noise will be incorrect, which consequently increases the error of transfer alignment. To solve the mentioned problem, this paper proposes a parameter identification method and then combines it with UKF. As a result, transfer alignment based on parameter identification UKF (PIUKF) is designed, and verified by simulations and static experiment. The results show that transfer alignment method based on PIUKF improves the accuracy of sub-systems compared with those based on UKF and strong tracking UKF.     

Near-infrared spectroscopy using digital phase-sensitive detection

Scanning near-infrared (NIR) spectrometers commonly employ analog lock-in amplifiers for demodulation that require complex circuitry and are sensitive to electromagnetic interference. Here, a new sampling system based on digital phase-sensitive detection is reported that used a quadrature sampling algorithm to establish the sampling frequency as an integral multiple of four times the optical signal frequency. A complex programmable logic device was used to control the analog-to-digital converter. A digital signal processor was used to receive data, complete the quadrature calculations, and transfer the results to a computer. Consequently, the circuitry was simplified with reduced electromagnetic interference. Spectra were obtained using instrumentation based on analog and digital sensitive detection that showed the latter provided more accurate results. The optimum signal-to-noise ratio of 66.34 dB was higher than the value obtained by the analog system.     

An initial alignment method for strapdown gyrocompass based on gravitational apparent motion in inertial frame

Inspired by the alignment mechanism of Octans, an initial alignment method for strapdown gyrocompass is designed based on gravitational apparent motion in inertial frame. In this method, the gyro outputs are used to trace the body frame and the measurement from accelerometers are projected to the inertial frame to form the track of gravitational apparent motion. According to the calculations on the vectors involved in this track, the attitude matrix between the inertial frame and navigation frame can be obtained and further alignment can be finished. In order to identify the true gravitational apparent motion from the accelerometer measurement containing random noise as well as to avoid the collinear of vectors in vector operation, a reconstruction algorithm concerning parameter identification and reconstruction of apparent motion is devised and simulated. Simulation and turntable test show that the proposed alignment method can realize self-alignment in a swinging condition. The alignment accuracy is able to reach the theoretical one determined by sensor errors and no external information is needed.     

一种区域公差约束的叶片模型配准方法

针对航空发动机涡轮叶片几何形状检测中的模型配准定位问题,依据叶片型面区域公差设计的特点,提出一种区域公差约束的叶片模型配准方法,尽可能把模型配准控制点集约束在公差带以内。在迭代最近点配准方法的目标函数的基础上,附加区域公差约束条件,建立区域公差约束的叶片模型配准目标函数,并给出了基于遗传算法叶片模型约束配准求解方法。使用叶片的仿真与实测数据进行了模型配准实验,结果表明,所提出的方法能显著减少配准控制点集的超差点数目。     

Two-dimensional top hat filter for extracting spots and spheres from digital images

The top hat filter is a computer algorithm that extracts small, compact or rounded objects from digital images. Examples show application of the filter to micrographs and electron diffraction patterns.     

Novel digital iteration algorithm for fluorescence lifetime measurement of multi-probe fiber thermometer

We report a novel digital iteration algorithm for fluorescence lifetime (FL) measurement, which is proved suitable for the fluorescence lifetime-based multi-probe fiber thermometer application. The algorithm utilizes only one set of fluorescence decay sampling data to decide the FL by using the basic addition and subtraction computation. Iteration number of about 10–12 times is sufficient to reach the final stable value. As a result, the algorithm features robust, high efficiency, strong anti-noise and immune to background level. The algorithm has been successfully used in a sapphire fiber-based multi-probe thermometer covering the temperature range from room temperature to 1000 °C and confirmed suitable for practical application.