Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.     

结合天空分割和雾气浓度估计的图像去雾

针对图像去雾算法在天空区域出现恢复不真实以及雾气浓度估计精度不足等问题,本文提出天空区域分割和雾气浓度估计的去雾算法.首先,为了提高透射率的估计精度以及提升去雾效果,利用梯度阈值和亮度阈值分割天空区域.其次,采用改进的暗通道先验和四叉树细分法估计大气光值.最后,针对天空区域和非天空区域采用不同的透射率估计方法,对于天空...     

基于模型性能评估的递推PLS建模及应用

为了降低递推部分最小二乘(RPLS)建模方法的模型校正频率,开发了一种基于模型性能评估的RPLS(MPA-RPLS)模型.首先,根据过程的初始特性,自动生成模型的置信限,以均方根误差(RMSEP)为性能指标,评估模型性能;依据模型性能的评估结果,选择性地启动模型校正和置信限校正.然后,引入滑动平均滤波器消除过程变量中的噪声,探讨噪声对模型性能的影响程度.最后,将MPA-RPLS模型应用于一个化学反应过程--C₈芳烃临氢异构化过程,基于大量工业数据,进行仿真验证.仿真结果表明:本文开发的模型仅以微小的精度损失换取了模型计算效率的大幅提高(即模型校正频率大幅下降);滑动平均滤波器可有效地处理变量的噪声,改善模型的预测精度.     

孟塞尔颜色系统与人眼主观亮度的关系

颜色亮度测量值与人眼主观亮度感受不一致的矛盾,在孟塞尔颜色体系中也明显地表现出来。这反映在孟塞尔等明度面上各种不同颜色的主观亮度并不相等。我们通过理论分析和主观亮度匹配实验,得出了孟塞尔等明度面颜色亮度与人眼主观亮度的对应关系。     

风向风速测量仪设计

随着人类对自然界风认识的深入,越来越多的场合需要使用到风的测量。本文主要介绍一套高精度、低功耗的风向风速测量系统。其主要特点是风速测量范围宽、测量精度高、传感器采用数字量输出,可靠性高,传输距离远,系统功耗低。因此可以采用太阳能供电,适合野外使用,可广泛地应用于气象、民航、公路、建筑、能源等行业。     

Evaluation of surrogate models for optimization of herringbone groove micromixer

Surrogate models have been applied to shape optimizations of a micromixer with the aim of assessing the performance of the models. The surrogate models considered include polynomial response surface approximation, Kriging, and radial basis neural network. In addition, a weighted average model based on global error measures is constructed. A mixing index at the exit of the micromixer is used as the objective function. The mixing index is calculated based on Navier-Stokes equations. Two cases of optimization, one with two design variables and the other with three design variables, have been tested. The design variables are selected among the ratio of the groove depth to channel height, the angle of groove, and the ratio of groove width to groove pitch. D-Optimal design generated sampling points are used for sampling. It is found that although the weighted average model does not predict the best optimal point, it does show consistent and reliable performance.     

红外传感器的信号提取和数据采集的设计

对于解决一类适合低频调制技术，且输出信号非常微弱的红外传感器的信号检测和提取，设计采用选频加窄带通滤波器的方法，再应用中位值平均滤波的数据采集方法很好地解决了对这一类红外传感器信号的数据采集。通过理论和实验证明该设计方法很好地提取了反映变化量性质的有用信号，同时也很好地提高了系统的信噪比，满足了实际情况的需要。     

硫化钡回转窑红外温度测量与分析

硫化钡回转窑的窑头温度是反映硫化钡焙烧情况的关键变量.但是回转窑红外测温结果存在较大波动,影响操作工人对焙烧质量的判断.本文从红外测温的原理出发,分析了影响红外温度测量的多种可能因素及其干扰程度,最后结合温度测量信号的频谱特性和回转窑的结构特点,发现窑炉转动过程中物料的翻动是导致测量结果波动的主要原因.针对物料翻动对温度测量扰动的特点,给出参数合适的移动平均滤波方法.理论分析和仿真结果表明,在选择适当的采样周期和移动平均的阶数的情况下,该方法可以有效地消除这种扰动.     

经验模式分解的改进及其对球轴承缺陷的诊断

在分析经验模式分解存在问题的基础上，改进了经验模式分解的算法，提出用窗口平均法取代原极值包络法来计算局部均值。给出了窗口平均法的具体算法，并通过模拟信号进行了验证。结果表明，改进的算法减少了三次样条插值使用的次数，从而减少了信号分解的时间，并且所有的数据都参与了局部均值的计算，提高了数据的利用率。同时，用改进的EMD方法取代传统包络分析中的带通滤波器，对实际的缺陷轴承进行了诊断。结果表明，经验模式分解方法比传统的包络分析更有效。     

磁流变减振器在参数激励与强迫激励联合作用下的主共振-基本参数共振分析

针对1/4汽车悬架模型,采用改进的B ingham模型描述磁流变阻尼力。在建立了该系统的动力学控制方程的基础上,用平均法研究了参数激励与强迫激励联合作用下的主共振-基本参数共振,得到了系统的理论解,并对理论解进行了数值验证。最后,研究了各个参数对主共振-基本参数共振的影响,为磁流变阻尼器的设计和控制提供理论依据。