FeatureMatching Combining Variable Velocity Model with Reverse Optical Flow

The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an inaccurate pose estimation or failed tracking.To address the challenge above,a new method of feature point matching is proposed in this paper,which combines the variable velocity model with the reverse optical flow method.First,the constant velocity model is extended to a new variable velocity model,and the expanded variable velocity model is used to provide the initial pixel shifting for the reverse optical flow method.Then the search range of feature points is accurately determined according to the results of the reverse optical flow method,thereby improving the accuracy and reliability of feature matching,with strengthened interframe tracking effects.Finally,we tested on TUM data set based on the RGB-D camera.Experimental results show that this method can reduce the probability of tracking failure and improve localization accuracy on SLAM(Simultaneous Localization and Mapping)systems.Compared with the traditional ORB-SLAM2,the test error of this method on each sequence in the TUM data set is significantly reduced,and the root mean square error is only 63.8%of the original system under the optimal condition.

Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros

Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros （SGCMGs） as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws.

Estimator-Based GPS Attitude and Angular Velocity Determination

In this paper,the estimator-based Global Positioning System(GPS)attitude and angular velocity determination is presented.Outputs of the attitude estimator include the attitude angles and attitude rates or body angular velocities,depending on the design of estimator.Traditionally as a position,velocity and time sensor,the GPS also offers a free attitude-determination interferometer.GPS research and applications to the field of attitude determination using carrier phase or Doppler measurement has been extensively conducted.The rawattitude solution using the interferometry technique based on the least-squares approach is inherently noisy.The estimator such as the Kalman filter(KF)or extended Kalman filter(EKF)can be incorporated into the GPS interferometer,potentially providing several advantages,such as accuracy improvement,reliability enhancement,and real-time characteristics.Three estimator-based approaches are investigated for performance comparison,including(1)KF with measurement involving attitude angles only;(2)EKF with measurements based on attitude angles only;(3)EKF with measurements involving both attitude angles and body angular rates.The assistance from body mounted gyroscopes,if available,can be utilized as the measurements for further performance improvement,especially useful for the case of signal-challenged environment,such as the GPS outages.Modeling of the dynamic process involving the body angular rates and derivation of the related algorithm will be presented.Simulation results for various estimator-based approaches are conducted;performance comparison is presented for the case of GPS outages.

Attitude Controller Design on Variable Rolling Velocity Aerocraft Based on ATmega16

Owing to the effect of crosswind, initial disturbance and the deviation of engine parameters.etc in the initial aviation, vari- able rolling velocity aerocraft will produce attitude angle deviation in the ideal orientations. This paper adopts AVR microcontroller atmega16 and relevant signal process circuit to design the attitude controller and take the method of frequency discrimination and am- plitude discrimination to process attitude angle deviation of aerocraft. Accordingly, it amends attitude angle deviation of aerocraft ef- fect and implements the self- adapting attitude control of aerocraft’s rolling velocity.

Reliability analysis of the velocity matching of coal cutting and caving in fully mechanized top-coal caving face

The matching relationship between coal cutting and caving in fully mechanized top-coal caving face is analyzed in detail from the angle of reliability. The coupling equation of reliability is established correspondingly, and the mathematical equation of the coefficient of velocity matching of coal cutting and caving is obtained, which meets a certain reliability demand for making the working procedure of coal caving not influence coal cutting of coal-cutter. The results show that the relationship between the coefficient of the velocity matching and the reliability of coal cutting and caving system is linear on the whole when R <0.9. It is pointed out that different numerical value should be selected for different coal face according to different demand for reliability.

Use of the Method of Guidance by a Required Velocity in Control of Spacecraft Attitude

We apply the method of guidance by a required velocity for solving the optimal control problem over spacecraft’s reorientation from known initial attitude into a required final attitude.We suppose that attitude control is carried out by impulse jet engines.For optimization of fuel consumption,the controlling moments are calculated and formed according to the method of free trajectories together with principle of iterative control using the quaternions for generating commands to actuators.Optimal solution corresponds to the principle“acceleration-free rotation-separate corrections-free rotation-braking”.Rotation along a hitting trajectory is supported by insignificant correction of the uncontrolled motion at discrete instants between segments of acceleration and braking.Various strategies of forming the correction impulses during stage of free motion are suggested.Improving accuracy of achievement of spacecraft's final position is reached by terminal control using information about current attitude and angular velocity measurements for determining an instant of beginning of braking(condition for start of braking based on actual motion parameters is formulated in analytical form).The described method is universal and invariant relative to moments of inertia.Developed laws of attitude control concern the algorithms with prognostic model,the synthesized control modes are invariant with respect to both external perturbations and parametric errors.Results of mathematical modeling are presented that demonstrate practical feasibility and high efficiency of designed algorithms.

Adaptive Angular Velocity Tracking Control of Spacecraft with Dynamic Uncertainties

The tracking of orientation and angular velocity is a primary attitude control task for an on-orbit spacecraft.The problem for a rigid spacecraft tracking a desired angular velocity profile is addressed using an adaptive feedback control.An angular velocity feedback tracking algorithm is firstly developed based on the precisely known attitude dynamics of the spacecraft,and the global tracking of the control algorithm is proved based on the Lyapunov analysis.An adaptation mechanism is then designed to deal with the dynamic uncertainties of the spacecraft.Such an adaptation mechanism enables the controller to track any desired angular velocity trajectories even in the presence of uncertain inertia parameters,although it does not guarantee the inertia tensor being precisely identified.To verify the effectiveness of the proposed adaptive control policy,computer simulations on dynamic equations of a spacecraft are conducted and their results are discussed.

Adaptive Sliding Mode Control for Re-entry Attitude of Near Space Hypersonic Vehicle Based on Backstepping Design

Combining sliding mode control method with radial basis function neural network(RBFNN), this paper proposes a robust adaptive control scheme based on backstepping design for re-entry attitude tracking control of near space hypersonic vehicle(NSHV) in the presence of parameter variations and external disturbances. In the attitude angle loop, a robust adaptive virtual control law is designed by using the adaptive method to estimate the unknown upper bound of the compound uncertainties. In the angular velocity loop, an adaptive sliding mode control law is designed to suppress the effect of parameter variations and external disturbances. The main benefit of the sliding mode control is robustness to parameter variations and external disturbances. To further improve the control performance, RBFNNs are introduced to approximate the compound uncertainties in the attitude angle loop and angular velocity loop, respectively. Based on Lyapunov stability theory, the tracking errors are shown to be asymptotically stable. Simulation results show that the proposed control system attains a satisfied control performance and is robust against parameter variations and external disturbances.

Investigation of Domain Wall Velocity to External Fields for High-Quality Waveguide-Type Periodically Poled LiNbO3 Fabrication

The Ti-doped waveguide-type periodically poled LiNbO3 (PPLN) were fabricated and the dependence of domain wall velocity on an external field applied for domain inversion was investigated. The whole polarization reversal process was computer-controlled to regulate domain wall expansion at a feedback time shorter than 5 μs. The coercive voltage and several values of excess voltage were applied on 500 μm-thick wafers serially connected to a 1-MOhm external resistor which had an effect of the poling current reduction, i.e. the deceleration of domain wall expansion. The domain wall velocity is sensitive to the poling voltage, precisely speaking, to the excess voltage. The domain wall velocities were 28.70, 16.02 and 5.75 μm·s-1 under poling field of 23.5, 22.0 and 21.0 kV·mm-1, respectively. Moreover, average duty cycle of PPLN is about 49.93%.

60例不典型肝血管瘤患者声速匹配技术及剪切波弹性成像表现及其与肝细胞癌的鉴别

目的分析肝血管瘤患者声速匹配技术及剪切波弹性成像表现及其与肝细胞癌的鉴别。方法2019年7月—2020年7月唐山市第三医院收治的经CT确诊的60例肝血管瘤患者,另外选择经病理穿刺确诊的肝细胞癌患者40例,将其作为肝血管瘤组(n=60)和肝癌组(n=40)。比较两组声速匹配技术及剪切波弹性成像表现,采用受试者工作特征曲线(ROC)分析声速匹配技术及剪切波弹性成像鉴别肝血管瘤与肝细胞癌的价值。结果肝血管瘤组声速匹配值、弹性模量值、剪切波速度最大值、剪切波速度平均值分别为(22.4±3.5)m/s、(16.1±2.5)kPa、(2.7±0.3)m/s、(2.3±0.2)m/s,均低于肝癌组[(40.6±4.5)m/s、(33.5±2.5)kPa、(3.8±0.6)m/s、(3.4±0.4)m/s,P<0.05];ROC曲线分析结果显示,声速匹配值、弹性模量值、剪切波速度最大值、剪切波速度平均值在鉴别肝血管瘤与肝细胞癌中具有极高的价值。结论声速匹配值、弹性模量值、剪切波速度最大值、剪切波速度平均值在鉴别肝血管瘤与肝细胞癌中具有极高的价值,声速匹配技术及剪切波弹性成像可用于鉴别肝血管瘤与肝细胞癌。

频域反射法阻抗匹配技术及其在电缆衰减补偿与相速度计算中的应用

频域反射法(frequency domain reflectometry,FDR)是诊断电缆绝缘状态的有效方法。针对现场FDR测试中存在的首端阻抗不匹配问题,该文提出了一种有效的FDR首端阻抗匹配技术。该文通过引入可变串联阻抗模型,结合估计得到的电缆特性阻抗,有效解决了FDR现场测试中分叉引线对测试结果的影响。首先,通过搭建电缆模型,结合行波的多次折反射原理推导了电缆首端的反射系数,阐述了信号在电缆内部的传输过程。然后,给出了电缆首端存在分叉引线时的首端阻抗匹配技术。最后,在同轴电缆及10 kV电力电缆上开展了电缆首端阻抗匹配试验,验证了该方法的有效性和准确性。结果表明:该方法可有效解决现场测试中存在的电缆首端阻抗不匹配问题,并且利用首端阻抗匹配处理后得到的数据,亦可实现电缆衰减的有效补偿及电缆相速度的准确计算。

基于三相Biot速度应力波动方程的水合物储层波场数值模拟

天然气水合物储层可以看作由骨架、水合物和孔隙水构成的三相孔隙介质。以三相Biot一阶速度应力波动方程作为声波在水合物储层传播的控制方程,用有限差分法(FDTD)进行数值模拟。波场快照可以清楚展现3个纵波和两个横波,与Biot理论相符。根据实测速度优化控制方程参数,使数值速度与实测速度相符。结果表明:孔隙度对水合物剪应力分量影响最显著,对水合物、孔隙水和骨架速度分量的影响次之,所以储层中孔隙度最适合用水合物剪应力分量来分析。骨架速度分量和应力分量受饱和度的影响较小,水合物剪应力分量受饱和度的影响最大,所以分析储层中水合物饱和度的最佳选择是水合物剪应力分量。

惯性角速度匹配测量方程的耦合误差分析

针对惯性角速度匹配测量方程得不到理论精确解的问题,根据角速度匹配测量方程建立了形变角估计误差与船体角运动和动态形变角的相关函数模型,从理论上证明了船体角运动与动态形变角之间的交叉耦合将产生形变角估计误差。在动态形变角和船摇角幅度分别为20″和2°的仿真条件下,当船体运动角速度与动态形变角速度不相关时,形变角估计误差均值分别为-1.8"、3.7"、3.8";当船体运动角速度与动态形变角速度完全相关时,形变角估计产生约50"的偏置误差。仿真和实验结果表明,误差的大小与二者之间的相关系数呈正相关。研究结果可为舰船形变测量和传递对准相关的理论研究和工程应用提供参考。

配置姿控推力器的卫星大角速率协同阻尼策略

针对卫星大角速率阻尼问题,研究使用姿控推力器的速率阻尼策略,兼顾姿控推力器开机次数少且开机时长短的设计原则。提出了综合三轴同时阻尼方法和单轴依次阻尼方法的协同阻尼策略,当卫星任意两轴角速率大于设定角速率阈值时,采用施密特触发器进行三轴同时阻尼以实现卫星大角速率有效阻尼;反之,采用按照角速率大小的顺序进行单轴依次阻尼以减少推力器开关机次数。数值仿真结果表明,协同阻尼策略能够有效实现卫星大角速率阻尼,并且有效降低推力器的开机次数和开机时长。

GNSS gyroscopes:determination of angular velocity and acceleration with very high-rate GNSS

Although global navigation satellite systems(GNSS)have been routinely applied to determine attitudes,there exists no literature on determining angular velocity and/or angular acceleration from GNSS.Motivated by the invention of computerized accelerometers of the correspondence author and following the success of accurately recovering translational velocity and acceleration waveforms from very high-rate GNSS precise positioning by Xu and his collaborators in 2021,we propose the concept of GNSS gyroscopes and reconstruct angular velocity and acceleration from very high-rate GNSS attitudes by applying regularization under the criterion of minimum mean squared errors.The major results from the experiments can be summarized in the following:(i)angular velocity and acceleration waveforms computed by applying the difference methods to high-rate GNSS attitudes are too noisy and can be physically not meaningful and numerically incorrect.The same can be said about inertial measurement unit(IMU)attitudes,if IMU gyros are not of very high accuracy;(ii)regularization is successfully applied to reconstruct the high-rate angular velocity and acceleration waveforms from 50 Hz GNSS attitudes and significantly outperforms the difference methods,validating the proposed concept of GNSS gyroscopes.By comparing the angular velocity and acceleration results by using the difference methods and regularization,we find that the peak values of angular velocity and acceleration by regularization are much smaller by a maximum factor of 1.57 in the angular velocity to a maximum factor of 8662.53 times in the angular acceleration in the case of high-rate GNSS,and by a maximum factor of 1.26 in the angular velocity to a maximum factor of 2819.85 times in the angular acceleration in the case of IMU,respectively;and(iii)the IMU attitudes apparently lead to better regularized angular velocity and acceleration waveforms than the high-rate GNSS attitudes,which can well be explained by the fact that the former is of better accuracy than the latter.As a result,to suppress the significant amplification of noise in GNSS attitudes,larger regularization parameters have to be chosen for the high-rate GNSS attitudes,resulting in smaller peak angular accelerations by a maximum factor of 37.55 percent in the angular velocity to a maximum factor of 6.20 times in the angular acceleration in comparison of the corresponding IMU results.Nevertheless,the regularized angular acceleration waveforms for both GNSS and IMU look more or less similar in pattern or waveform shape.

延长小河东部油区长7段烃源岩特征研究

小河东部油区长7段发育良好烃源岩,为推进该地区石油勘探,需要深化该地区烃源岩认识。通过岩石热解、总有机碳、镜质体反射率等方法,研究了该地区烃源岩特征。结果表明,小河东部油区长7段有机质丰度总体上为好的生油岩类型,泥岩样品TOC变化范围是3%~5%,样品生烃潜量S_1+S_2含量主体分布在5~15mg/g,平均含量为13.8mg/g。有机质类型为Ⅰ-Ⅱ_1型,研究区长7段有机质总体上为成熟。该烃源岩生排烃为该地区内石油聚集成藏提供了物质基础。

FA-SORT:轻量化的多车辆跟踪算法

近年来,无人机因体积小、灵活性好等优势被广泛应用在车辆跟踪领域。当无人机在高空飞行时,其捕捉的图像中车辆目标存在像素点少、拥挤以及被遮挡的情况。现有的多目标跟踪研究方法在车辆被遮挡过程中发生非线性运动时,使用卡尔曼滤波预测,会出现车辆位置预测不准确的问题。为了解决这些问题,采用先检测后跟踪(tracking by detection,TBD)范式,对YOLOv8检测算法进行改进,在网络结构中引入了BiFormer稀疏动态注意力模块,用于提取小目标特征信息。同时使用轻量级上采样算子CARAFE替换原最近邻插值上采样,减少上采样过程中小目标特征丢失的问题。提出一种轻量化跟踪模型FA-SORT,针对SORT算法提出三点改进:改进KF、添加速度方向一致性匹配和检测值匹配。在自制地组合了多个车辆数据集上验证改进的YOLOv8算法。实验结果表明,与YOLOv8相比,精确率(precision)提高了0.97%,召回率(recall)提高了0.898%。对所提出的FA-SORT算法使用UAVDT数据集进行验证,结果表明,与现有的多目标跟踪算法相比,HOTA指标首个达到70.05%,IDF1达到87.45%,跟踪速度达到29.93 FPS。验证了FA-SORT跟踪算法在多车辆跟踪任务中的优越性。

管道机器人过T型管垂直爬坡动态性能分析

为进一步了解复杂管道的内部环境,设计一种全驱动轮式管道机器人。通过坐标旋转法,分析管道机器人通过T型管垂直爬坡时的姿态调整过程与运动状态变化,运用ADAMS动力学分析软件,分析管道机器人通过T型管时各驱动轮的受力情况和驱动轮质心运动速度变化。研究发现管道机器人通过T型管时,其各驱动轮先后经历悬空状态并失去管壁支撑,4个驱动轮与管壁的接触力总的变化趋势均是先减小到0 N,然后随着驱动轮与管壁发生接触碰撞,接触力迅速增大,幅值超过其稳态值;前后2个驱动模块的驱动轮质心运动速度不同,前驱动模块驱动轮质心运动速度变化规律为类似正弦变化,后驱动模块由于接触碰撞,上部驱动轮与管壁发生打滑,驱动轮运动速度先轻微增大后迅速减小。研究结果为管道机器人的结构设计提供参考。

基于椭圆成像参数匹配的弹体姿态测量方法

一体化弹丸的弹托分离过程对弹体的飞行稳定性和打击效能具有显著的影响。为此,针对一体化弹丸出膛后弹托相对弹体的六自由度运动过程,提出了基于椭圆成像参数匹配的弹体姿态测量方法,即利用弹体底部为圆形在任意角度下成像为椭圆的特点,通过提取弹体底部椭圆成像轮廓上的几个点,解算得到椭圆参数,再结合双目椭圆成像参数相同的约束条件,通过优化弹体的成像角度实现参数的最优匹配,从而实现对弹体姿态角度的估算。测试结果表明:相比传统基于纹理信息以及基于轮廓匹配的姿态测量方法,该方法不需要识别弹体表面标记点或者完整的轮廓信息,大大提高了测量方法的通用性和可靠性,且测量精度可达0.4°,满足使用要求。

惯导系统传递对准模型的研究进展综述

初始对准是惯导系统开启工作后必须经历的阶段,而传递对准则是一种特殊的动基座初始对准技术,可有效提高武器装备的快速反应和精准打击能力。对惯导系统传递对准模型的研究进展进行了综合评述。首先,从姿态误差的定义出发,系统归纳了ϕ_(n)角误差模型、ϕ_(m) 角误差模型和相对姿态对准模型,对比分析了三类误差模型的特点。其次,给出了导航速度、相对速度和惯性速度的定义,理论推导了三种导航速度误差方程。然后,介绍了传递对准的量测模型,并重点归纳了基于相对姿态理论的文献所采用的量测模型。最后,讨论了传递对准有待解决的技术问题和未来研究方向。综述表明,误差的数学定义和参考坐标系以及匹配参数决定了传递对准模型的丰富性,在实际使用时,可以根据应用背景以及使用条件选择相应的传递对准模型,而在误差建模、误差激励、性能评估等方面,传递对准技术都有待进一步研究。