A pre-generated matrix-based method for real-time robotic drilling chatter monitoring

Currently, due to the detrimental effects on surface finish and machining system, chatter has been one crucial factor restricting robotic drilling operations, which improve both quality and efficiency of aviation manufacturing. Based on the matrix notch filter and fast wavelet packet decomposition, this paper presents a novel pre-generated matrix-based real-time chatter monitoring method for robotic drilling. Taking vibration characteristics of robotic drilling into account, the matrix notch filter is designed to eliminate the interference of spindle-related components on the measured vibration signal. Then, the fast wavelet packet decomposition is presented to decompose the filtered signal into several equidistant frequency bands, and the energy of each sub-band is obtained. Finally, the energy entropy which characterizes inhomogeneity of energy distribution is utilized as the feature to recognize chatter on-line, and the effectiveness of the presented algorithm is validated by extensive experimental data. The results show that the proposed algorithm can effectively detect chatter before it is fully developed. Moreover, since both filtering and decomposition of signal are implemented by the pre-generated matrices, calculation for an energy entropy of vibration signal with 512 samples takes only about 0.690 ms. Consequently, the proposed method achieves real-time chatter monitoring for robotic drilling, which is essential for subsequent chatter suppression.     

On the estimation of regional covariance functions of TEC variations over Canada

Spatial and temporal variations of Total Electron Content (TEC) can affect GNSS high accuracy positioning. Enhanced estimation of ionospheric variations and their de-correlation can benefit differential and point positioning rapid solutions. Global and regional TEC maps can provide the overall state of ionopsheric variations in space and time domains within their accuracy limits. In this paper, these maps are exploited to retrieve ionospheric variations by means of variograms and their associated covariance functions of TEC residuals over Canadian region during geomagnetically quiet and disturbed conditions. A number of theoretical variogram functions are reviewed for modeling covariance of TEC residuals. The variogram modeling of residuals during a strong geomagnetic storm revealed variances of one order of magnitude larger compared to a rather quiet condition. Variogram models are also used in regional and local kriging interpolation experiments and their performances are evaluated. Global maps of TEC RMS by International GNSS Service and two of its analysis centres are also compared over the Canadian region during a two-year period. Realistic representation of regional variances using estimated variograms when compared to global ionospheric RMS maps are also presented.     

一种分布式异步航迹融合算法

在多被动传感器目标跟踪中,融合中心处理的信息一般是同步的,然而实际情况并非如此。另外,一些被动传感器只能得到目标的方位信息,无法单独形成有效航迹,这就需要将各传感器数据同步到相同时刻,然后应用同步融合算法。针对被动传感器探测系统,采用传感器到传感器融合和系统到传感器融合的分布式融合结构,并对各局部传感器引入全局反馈,对相关信息采用协方差交叉算法进行处理,完成被动传感器异步数据的融合,仿真结果表明,该算法具有较好的融合效果。     

分析/试验模型相关及修正技术若干问题

本文对模型修正技术的发展及其国内外研究状况做了系统介绍和综合评述，并讨论了该领域中存在的一些主要问题以及进一步研究的方向。文中还给出了有限元模型修正技术在航空航天领域、汽车船舶领域成功应用的实例。     

ATS矩阵开关自检研究

矩阵开关作为一种最灵活的开关拓扑结构,在ATS系统中得到了广泛的应用,也是ATS自检的关键部件之一.受限于自身结构特性,矩阵开关可靠性相对较低,且一般不自带自检功能.依据ATS中矩阵开关的特性、常见故障及其自检目的,研究和分析了矩阵开关自检的内容,并针对某型ATS中的双线矩阵,设计了不同的自检方法,通过分析和对比,可为其他ATS矩阵开关自检方法设计提供参考.     

磺化Resol-Novalak共聚酚醛树脂热解特征的TG-MS研究

合成了一种合磺酸基的热固性Resol—Novalak共聚酚醛树脂(C——PF／SPF)。TG—MS(热失重—质谱)的研究结果表明，C—PF／SPF在低于350℃时，主要发生与磺酸基相关的热分解井退出SO2等产物；在450℃—820℃范围，只观察到CO2(m／z＝44)、C0(m／z＝28)和H20(m／z＝18)等产物及其碎片；在110℃—820℃的测试温度范围未检测到与主链断裂有关的酚类热解产物，显示出优越的热稳定性；这是由于部分磺酸基中的硫在热处理过程中与酚醛树脂的芳环发生交联，从而大大增加了C——PF／SPF的热稳定性。基于TG—MS结果的理论计算表明，C——PF／SPF经350℃热处理后的理论残碳率可达80％，是一种具有应用前景的C／C复合材料用基体前驱体。     

具有挤压油膜阻尼器的多转子系统双稳态分析

采用弯扭耦合传递矩阵法计算具有挤压油膜阻尼器(SFD)的多转子系统在弧齿锥齿轮啮合作用下的振动特性。给出了对多转子系统进行双稳态特性分析的方法和具有SFD时峰值转速计算方法;改进了偏心率及峰值转速的计算方法和软件,提高了计算精度和效率。首次分析在较大的弧齿锥齿轮啮合力与不平衡力综合作用下,复杂转子的双稳态特性。得出了该转子可能发生双稳态现象的偏心率界限为ε>0 61。分析了后支承刚度、传动功率、油膜分布对双稳态特性影响,研究了排除和改善双稳态现象的方法。     

基于测距观测的静地卫星定轨精度分析

在卫星动力法定轨的协方差分析基础上,提出了一种针对地球静止轨道(GEO)卫星的简化定轨精度分析方法。根据GEO卫星的线性化状态转移方程,通过设定地面跟踪网坐标和卫星星下点经度计算叠加矩阵,由观测弧长和采样间隔直接计算定轨精度评定公式中的主要部分。公式扩展后,能比较各种系统误差源对定轨精度的影响,并将影响较大的作为附加参数纳入估计过程并重新评价定轨精度。用该法对10 m定轨精度的测距跟踪网优化设计和测距偏差对定轨精度的影响特性进行分析的结果表明,测量系统中的系统性误差可能以近20的放大倍率传播到卫星沿迹方向和法向,且不能通过自校准测距常值偏差提高定轨精度。     

状态转移矩阵及系统响应函数

本文分析了系统状态转移矩阵及函数矩阵L,M的性质。给出了新的彼此转换关系。推导了系统的输入信号响应函数,及积分响应函数的表达式,说明了它们的计算方法。