An adaptive moving total least squares method for curve fitting

The moving least squares (MLS) method and the moving total least squares (MTLS) method have been developed to deal with the measured data contaminated with random error. The local approximants of MLS method only take into account the error of dependent variable, whereas MTLS method considers the errors of all the variables, which determines the local approximants in the sense of the total least squares. MTLS method is more reasonable than MLS method for dealing with errors-in-variables (EIV) model. But because of the weight function with compact support, it is complicated to choose fitting method for the best performance. This paper presents an Adaptive Moving Total Least Squares (AMTLS) method for EIV model. In AMTLS method, a parameter λ associated with the direction of local approximants is introduced. MLS method and MTLS method can be considered as special cases of AMTLS method. Curve fitting examples are given to prove the better performance of AMTLS method than MLS method and MTLS method.     

主轴回转精度测量方法

首先介绍了各种机床主轴回转精度测量方法及其原理,包括单点法、双点法、三点法、虚拟仪器法、CCD法和轴向窜动误差的测量;然后介绍了测量数据的处理和误差分析方法,指出各种测量方法的特点,并总结了各种测量方法的一般性选择原则。     

井下工具通过性计算方法及发展趋势

分析了井下工具通过性的计算方法,将计算方法按原理分为几何法、力学法与有限元法,并对各种计算方法的发展状况和应用情况进行了描述.结合各种方法的实际应用情况,分析了各种方法的优点和缺点,总结出了井下工具通过性计算方法的发展趋势,即由简单的刚性通过性分析转向柔性通过性分析,更加注重管柱串的下入安全,并综合应用几何法、力学法与有限元法分析通过性.     

基于间隙热源法的车轮踏面制动摩擦温升研究

针对传统模拟车轮踏面制动摩擦热流边界的加载方式存在的不足,如均布热源法计算精度较低和移动热源法计算效率较低,提出基于间隙热流加载法的车轮踏面制动摩擦温升有限元计算方法。以重载列车紧急制动为研究对象,通过与以往的移动热源法和均布热源法进行对比,研究新方法的计算精度和计算效率。计算结果显示:在计算精度方面,新方法不仅可以达到移动热源法的计算精度,还能体现均布热源法无法模拟的因闸瓦和踏面的接触-脱离现象导致的车轮踏面温度时间历程曲线波动现象。在计算时间方面,新方法的计算效率与均布热源法的相当,但新方法的计算速度比移动热源法的快4.3倍。     

反电动势过零点检测法的研究

主要介绍了无刷直流电动机采用的反电动势过零点检测法。提出了用端电压法、相电压法两种反电动势过零点检测法检测电机转子位置,并对端电压法和相电压法做了进一步的说明。     

陶瓷磨削表面残余应力测试方法的研究

用研磨抛光法与连续腐蚀法测试陶瓷磨削表面残余应力 ,与 X射线衍射法相比较 ,具有经济、简便、测试精度高的优点。在避免了应变信号的不稳定性与附加应力的条件下 ,对于非金属氧化物陶瓷来说 ,这两种方法完全可以取代 X射射线衍射法     

An improved three-point method based on a difference algorithm

The reason for the rounding error in a measurement system under the condition of a limited sampling period is analysed, and a three-point method based on the difference algorithm (D3P method) is proposed. The effect of the rounding error is reduced by differential approximation of the roundness error and reconstruction of the transfer function. The generalized three-point method (G3P method), the three-point method based on the first-order difference algorithm (I-D3P method) and the three-point method based on the second-order difference algorithm (II-D3P method) are compared and analysed by simulation. The results show that the accuracy of the D3P method is greatly improved compared with that of the G3P method under the restricted sampling period and that the D3P method retains high precision in the case of failed error separation of the G3P method. An experimental system was constructed to realize error separation, and the experimental results show that the D3P method has higher accuracy than the G3P method over a small sampling period.     

小波变换方法评价曲线的分形特征

应用小波变换对Kiesswetter曲线和3种方法生成的分数维布朗运动（FBm）进行了分析,验证了该方法计算分形维数具有较高的精度。在宽广的分形维数范围内,与其他7种计算方法比较表明,小波变换方法的精确性和一致性都最好。小波变换为进一步分辨确定性信号、分形特征的信号或完全随机性的信号提供了一种有效工具,为评价粗糙表面形貌的分形特征提供了前提条件。     

液压油污染检测技术的评述

对近年来油液污染检测技术的发展作了综合评述,主要有秤重法、颗粒计数法、电测法、库尔特法、机械缝隙法、超声波法、光测法及淤积法等,并对基于淤积法的检测仪进行阐述。油液污染检测技术集多技术理论于一体,具有典型的跨学科特征,尤其是与信息技术相结合,使得油液污染检测技术在系统设计、控制、性能等方面有了长足的进步。最后对油液污染检测技术的发展前景进行了预测,指出在线检测、多参数及智能化、远程检测、信息融合是未来发展方向。     

基于拉丁超立方抽样及响应面的结构模糊分析

在对边值模糊分析方法和优化边值模糊分析方法研究的基础上,将拉丁超立方抽样和响应面方法引入结构模糊分析,提出一种基于拉丁超立方抽样及响应面的模糊分析方法。讨论这种方法的数学运算,并与Monte Carlo方法进行比较。最后基于这种方法,对一个用隐式方程描述的有限元悬臂梁模型进行模糊分析,得到变形模糊结果。     

Free vibration analysis of straight-line beam regarded as distributed system by combining Wittrick-Williams algorithm and transfer dynamic stiffness coefficient method

We developed a method for analyzing the free vibration of a structure regarded as a distributed system, by combining the Wittrick-Williams algorithm and the transfer dynamic stiffness coefficient method. A computational algorithm was formulated for analyzing the free vibration of a straight-line beam regarded as a distributed system, to explain the concept of the developed method. To verify the effectiveness of the developed method, the natural frequencies of straight-line beams were computed using the finite element method, transfer matrix method, transfer dynamic stiffness coefficient method, the exact solution, and the developed method. By comparing the computational results of the developed method with those of the other methods, we confirmed that the developed method exhibited superior performance over the other methods in terms of computational accuracy, cost and user convenience.     

基于代理模型的变复杂度方法在板料成形优化中的应用

板料成形优化中存在一些缺陷问题,如一步法与优化算法相结合时精度低、增量法与优化算法直接结合时效率低以及通过传统构造代理模型的方法构造高精度的代理模型时需要大量增量法模拟结果。为了充分发挥一步法和增量法各自的优点,提出采用变复杂度方法通过较少次数的试验样本点数据先在一步法和增量法间建立一个差值补偿响应面模型。通过一步法和差值补偿响应面模型构造新的试验样本点,在新构样本点和原有用增量法计算的样本点数据基础上建立移动最小二乘法代理模型,建立的移动最小二乘法代理模型精度和效率都较高。利用粒子群优化算法对移动最小二乘法代理模型进行优化求解。将该方法应用到了汽车某内板的成形性优化中,优化的结果显著地提高了板料的成形性。算例表明,该方法具有较高的精度和较强的工程实用性。     

冗余度机械手逆运动学问题的次优准则混合法

在梯度投影法的基础上，本文提出了处理冗余度机械手逆运动学问题的一种新方法次优准则混合法。该方法吸收了梯度投影法和最小范数法的优点。利用平面３Ｒ机械手进行了仿真研究，并将该方法与其它方法进行了分析比较     

多级电网短路电流的简便计算方法

在‘绝对值法’和‘相对值法’的基础上,对短路电流的计算找出了一种简便易学的方法,姑且称为‘准折算值法’。     

Advanced median method for timing jitter compensation

Timing jitter is one of the main factors that influence on the accuracy of time domain precision measurement. Timing jitter compensation is one of the problems people concern. Because of the flaws of median method, PDF deconvolution method and synthetic method, we put forward a new method for timing jitter compensation, which is called advanced median method. The theory of the advanced median method based on probability and statistics is analyzed, and the process of the advanced median method is summarized in this paper. Simulation and experiment show that compared with other methods, the new method could compensate timing jitter effectively.     

Development of high speed computation algorithm for transient analysis of rectangular plates

A new transient analysis method for a rectangular plate structure comprised of a large number of plate elements was developed in order to significantly reduce computational time and memory. This algorithm was derived from the combination of the transfer technique of the transfer mass coefficient method, the modeling technique of the finite element method, and the numerical integration technique of Newmark’s method. In this paper, the algorithm for the transient analysis of a rectangular plate structure is formulated by the proposed method. In order to verify the computational accuracy and efficiency of the proposed method, the results obtained by the proposed method were compared with those obtained by the finite element method and the finite element-transfer matrix method. The proposed method, the finite element-transfer mass coefficient method, could considerably reduce the computation time without the loss of accuracy, in spite of using small computation memory, by using the transfer rules successively.     

Energy based signal parameter estimation method and a comparative study of different frequency estimators

The influences of window functions and noise on the performance of the energy-based signal parameter estimation method are investigated, and the appropriate parameters and algorithm are recommended accordingly. The frequency, amplitude and phase estimation variances of the energy based method are deduced and verified by computer simulation. The performances of four frequency estimation methods are compared: the energy based method, the interpolation based method, the phase difference based method and the Fourier transform (FT) continuous zoom based method. For the second and third methods, the Quinn algorithm and the phase difference based method with factor η=0.5 are recommended, respectively. It was found that each method has its own advantages. The energy based method has the best stability compared with others. The interpolated method has the lowest frequency estimation variance when the frequency biasδ is large, while the phase-difference based method does better when δ is low. The change of δ does not influence the maximum frequency estimation error of the FT continuous zoom based method. Comparatively speaking, the phase-difference based method has the least frequency estimation error.     

浅谈保证装配精度的装配方法

产品是由许多零件组合而成的。尺寸精度反映装配中各相关零件的尺寸精度与装配精度的关系;相对位置精度反映装配中各有关零件的位置精度与装配精度的关系。根据不同的机械、不同的生产类型条件,选用不同的装配工艺方法。装配工艺方法归纳起来有4种:互换装配法、选配装配法、修配装配法和调整装配法。     

光刀中心自适应阈值提取法

在分析常用的几种光刀中心提取法的特点与不足的基础上 ,提出了光刀中心自适应阈值提取法 ,该方法将阈值法与极值法、重心法相结合 ,可消除噪声干扰 ,实现光刀中心的快速、精确定位。     

基于Excel的连续梁内力有限元数值迭代计算

建立了连续梁的内力计算有限元数值模型,以Excel 软件为计算工具,分别用雅克比迭代法、高斯-赛德尔迭代法、超松弛迭代法和共轭梯度法等4种常用方法对模型进行了迭代计算,并对4种迭代计算方法的收敛速度和效率进行了分析和研究,提出了一种基于Excel的快捷有效的有限元数值计算方法.