六自由度测试系统

本文所描述的测试系统基于激光全息分光技术和激光干涉测长技术,同时测定目标物体六个自由度的偏差。采用激光漂移补偿技术建立了稳定的激光束基准,采用磁光调制技术减小光强不稳定等因素对滚转角测量精度的影响,实现了多自由度较高精度的准直。实验表明,在激光光源距靶标１ｍ时,该系统σ重复性误差：线位移小于４μｍ,角位移小于４″,整个系统结构简单,测量效率高。     

一种双面凸轮的反求设计方法

提出一种双面凸轮的反求设计和误差控制方法。从动件类加速度对轮廓曲线误差敏感,通过修正从动件类加速度曲线,以间接提高凸轮廓线精度。通过数字化测量,获得凸轮双面轮廓的点云数据,对点云数据进行精简并进行重构、装配对齐,获得凸轮轮廓实体模型。对获得的凸轮轮廓数据二次求导并拟合,获得从动件类加速度曲线和类加速度误差值。基于类加速度误差与从动件位移误差的关系函数,对轮廓线进行修正,从而消除反求误差。     

螺旋锥齿轮数控磨齿机机床空间误差与机床调整参数的关系

为求得对各项机床调整参数影响较大的机床空间误差,分析螺旋锥齿轮加工过程中数控机床空间误差物理涵义,并建立七轴五联动数控磨齿机床空间误差模型.基于齐次变换矩阵方法建立机床空间误差与机床调整参数之间的几何等量关系,推导出两者间的关联函数并进行分析.通过实例分析,发现对机床刀位调整值影响较大的机床空间误差主要是三直线轴垂直度误差和x轴沿Z向垂直度误差;对机床轮位调整值影响较明显的机床空间误差为z轴、B轴沿x向直线度误差以及A轴的安装距误差.为机床调整参数优化及螺旋锥齿轮几何误差补偿提供了理论依据.     

基于主成分估计的自变量选择

研究了大型参数模型的模型选择问题,针对模型病态的情况,提出了基于主成分估计的自变量选择的Cp准则。应用于航天飞行器控制系统误差分离,以及外弹道跟踪测量系统误差估计,大量仿真计算与实测数据计算表明,运用该方法可以同时得到高精度的飞行器轨道参数控制系统误差和外弹道测量系统误差的估计。最后,提出了并行算法并分析了它的可扩展性。     

基于MAS的航空机务维修差错预警专家系统

机务维修是关系到民用航空安全和效益的重要因素之一,是飞行安全的基础,因此迫切需要建立航空机务维修差错预警专家系统。采用Agent技术作为低层支撑技术,将基于规则的不确定性推理和基于案例推理的预警方法引入航空机务维修差错预警领域,给出了总体结构的设计以及关键技术的实现,从而为航空机务维修差错预警提供了一种新的思路和方法。     

Performance of the Zero Forcing precoding MIMO broadcast systems with channel estimation errors

In this paper, the effect of channel estimation errors upon the Zero Forcing (ZF) precoding Multiple Input Multiple Output Broadcast (MIMO BC) systems was studied. Based on the two kinds of Gaussian estimation error models, the performance analysis is conducted under different power allocation strategies. Analysis and simulation show that if the covariance of channel estimation errors is independent of the received Signal to Noise Ratio (SNR), imperfect channel knowledge deteriorates the sum capacity and the Bit Error Rate (BER) performance severely. However, under the situation of orthogonal training and the Minimum Mean Square Error (MMSE) channel estimation, the sum ca- pacity and BER performance are consistent with those of the perfect Channel State Information (CSI) with only a performance degradation.     

一种新的阵列天线幅相误差校正算法

根据子空间的基本原理,提出一种新的阵列天线幅相误差校正算法,该方法利用粗略已知的校正源方位角信息进行优化,使用迭代的方法逼近幅相误差的真实值.由于不需要其他的迭代初始值,从而保证该方法能收敛到最优解.计算机仿真实验证明了该方法的有效性.     

Analysis of operator human errors in hydrogen refuelling stations: Comparison between human rate assessment techniques

The use of hydrogen as an energy carrier for road transport appears to be an optimal solution for the reduction of greenhouse gas emissions. Nevertheless, the development of this technology depends on the growth and diffusion of production, storage and refuelling infrastructures together with accurate risk analyses to appropriately design the safety and management systems used in these plants. Moreover, to improve safety standards, it is also important to focus attention on the estimation of hazards related to human factors, as this is one of the major causes leading to accidental events, especially in complex industrial technology. The paper reports a case study relevant to operator errors that occur during maintenance procedures on safety venting devices in refuelling station hydrogen storage systems performed using first- and second-generation Human Rate Assessment (HRA) techniques. HEART (Human Error Assessment and Reduction Technique) methodology, a first-generation HRA method, which was modified on the basis of the fuzzy set concept, was employed to evaluate the probability of erroneous actions. The obtained results have been compared with results obtained using CREAM (second-generation) methodology. The critical analyses of the obtained results have also allowed to provide procedural recommendations and suggestions regarding safety equipment and procedures which can be adopted to reduce the risk of accidents.     

Decentralized damage detection of seismically-excited buildings using multiple banks of Kalman estimators

Natural hazards result in ill-conditioned structures with unfavorable damage. To early recognize damage existence, structures can be screened by damage detection methods after a critical hazard event. These damage detection methods are often developed based on a centralized acquiring and computing system that challenges the feasibility of deployment in a large-scale structure. Decentralized damage detection methods alter a single system to multiple subsystems that allow spatially distributing in a structure and yield comparable performance with the centralized approach. In this study, a decentralized damage detection method based on modal prediction errors via multiple banks of Kalman estimators is proposed. First, a sensor network is comprised of multiple subsystems over a structure of which the subsystems have overlapped sensing nodes. These subsystems are individually identified by an input–output frequency-domain system identification method under ambient vibrations. The identified models are then converted into several banks of Kalman estimators, and the estimators generate the estimation of structural modal responses. The prediction errors are calculated from the differentiation between measured and estimated modal responses, and the accumulated standard deviations of modal prediction errors serve as the damage indices for recognizing the damage occurrence, locations, and levels. A numerical example is introduced to demonstrate the proposed method as well as to evaluate the detection effectiveness. Moreover, the proposed method is also experimentally verified by a scaled twin-tower building using shake table testing. The experimental results indicate that the proposed method is quite effective to inform damage of structures in terms of damage occurrence, locations, and levels.     

Digital Void Velocimeter

The paper describes the principle of measuring digitally the flow velocity of local voids, and discusses the accuracy of this method. It is shown that the spectrum of local void velocities can be determined reliably with digital values.

The measurement errors of void velocity u_g (m/sec) are within about ±9% in cases when the probes have detector head lengths of 0.8~1.0mm, and head diameters of 0.1 mmφ, when the voids have a flow velocity in the range of 0.2 m/sec≤u_g ≤1.2 m/sec and a radius of curvature of void of 2mm≤R≤16mm.