步进电机脉冲当量及回程差的微位移测量系统

摘要:为了精确测量步进电机的脉冲当量和回程差,提出了一种基于薄膜干涉原理的激光微位移测量系统。该系统以He-Ne激光器为光源,配以牛顿环仪系统、面阵电荷耦合器（CCD）视频信号采集系统、计算机及数据处理软件等。采用条纹记数法实现微位移测量,具有四百分之一波长的位移分辨率。与传统测量方法相比,其精度、灵敏度及稳定性都有较大提高,特别适合范围在微米及微米以下的位移测量。在对TSA50-C型商用步进电机的测量中,结果验证了这种测量系统在普通实验室环境噪声中可以达到纳米级的位移测量精度。实验数据处理结果表明,对于5微米以下的脉冲当量及回程差的测量,该测量系统的相对误差分别为2.63%和0.44%。     

高重频激光回波信号检测新方法

针对高重频激光回波探测的应用背景,提出了一种基于信号积累和大步长参数下LMS自适应处理过程的微弱周期脉冲信号检测算法,指出脉冲信号在大步长参数下的自适应处理中会引起滤波器估计误差和自适应权向量的反复振荡,生成较大的值,通过观察该参数的变化,并做进一步处理,可以检测出微弱脉中信号.仿真表明,在适合的步长参数下,该方法有较...     

New finite difference formulations for general inhomogeneousanisotropic bioelectric problems

Due to its low computational complexity, finite difference modeling offers a viable tool for studying bioelectric problems, allowing the field behaviour to be observed easily as different system parameters are varied. Previous finite difference formulations, however, have been limited mainly to systems in which the conductivity is orthotropic, i.e., a strictly diagonal conductivity tensor. This in turn has limited the effectiveness of the finite difference technique in modeling complex anatomies with arbitrarily anisotropic conductivities, e.g., detailed fiber structures of muscles where the fiber can lie in any arbitrary direction. Here, the authors present both two-dimensional and three dimensional finite difference formulations that are valid for structures with an inhomogeneous and nondiagonal conductivity tensor. A data parallel computer, the connection machine CM-5, is used in the finite difference implementation to provide the computational power and memory for solving large problems. The finite difference grid is mapped effectively to the CM-5 by associating a group of nodes with one processor. Details on the new approach and its data parallel implementation are presented together with validation and computational performance results. In addition, an application of the new formulation in providing the potential distribution inside a canine torso during electrical defibrillation is demonstrated     

新型分裂步长时域有限差分法

提出一种新型的分裂步长时域有限差分(NSS-FDTD)法,并对其数值色散进行分析。该方法基于Split-Step方案和Crank-Nicolson方案,采用新的矩阵分解形式,与传统的FDTD算法、SS-FDTD算法相比,减少了计算复杂度。新型算法的推导程序简单,且具有良好的数值色散特性,还加入了一阶Mur吸收边界条件,给出一阶Mur吸收边界差分方程。将数值实验的结果和传统FDTD方法及理论值进行比较,数值结果一致性较好。     

基于加窗DFT的相位差高精度测量算法

本文提出一种基于加窗离散傅立叶变换(DFT)的相位差微机高精度测量算法，详细论述算法原理及实现步骤。采用该算法，相位差测量值理论上与信号频率无关，从而不需要跟踪测量信号频率，不需要对信号整周期采样。算法实现简单，计算量较小，精度高，对高次谐波和噪声具有较强的抑制能力，仿真计算和工程应用验证了其可行性和有效性。     

一次回风系统与二次回风系统的比较实例

混合式空调系统中一次回风系统与二次回风系统是两种常见的处理方式,两种方式各有优缺点.通过工程实例中,就两种方式组合式空调机组设计的不同,对一次回风系统与二次回风系统进行比较.     

基于图像匹配的无人机自主返航技术

文中基于无人机机载的视觉信息,在GPS信号不可靠的环境下实现自主返航的功能。利用无人机底部垂直向下的摄像头,对图像计算光流可以较精确地获得无人机的速度信息。在去程中,无人机每隔一定距离记录一次位移信息与向前摄像头图像的关键帧;在回程时,无人机先根据位移信息到达关键帧图像附近,然后比较当前图像与目标关键帧纠正误差,对下一帧重复这两歩直到回到起点。仿真实验证明文中所述方法能较好地实现定点悬停和自主返航的功能。     

基于温差扰动补偿的红外纹理生成新方法

针对传统红外视景仿真中红外纹理生成效果生硬,真实感欠缺的问题,提出了一种基于温差扰动补偿的红外纹理生成新方法。该方法以实测红外图像为数据源,模拟红外成像机理构建红外成像链路模型,解耦环境影响因素得到红外图像各像素点对应的温度值,通过建立的目标表面热平衡方程和一阶导热方程求解实测与仿真时刻表面温度均值,利用各点温度与实测时刻均值温度的差值求得表面温差扰动,最后对仿真时刻均值温度进行温差补偿,得到表面的预测温度分布,并将计算出的辐亮度数据存储为DDS(Direct Draw Surface)纹理格式,以提高纹理生成的实时性。实验结果表明,该方法充分考虑到真实红外数据源的可靠性,同时兼顾红外纹理生成效率,在红外视景仿真中具有较好的工程实用价值。     

王者再临

诺基亚9系列推出第三代机型了，一脉相承的外形设计和更高端的科技内涵使9500通讯器早已成为多少机友们梦寐以求的那把偃月刀!有它在手，何足惧?     

Analysis of weather radar return

A mathematical model of detected clutter from an airborne weather radar of conventional design is developed. The model is the joint probability density of samples of radar return from hydrometeors at the same nominal range and scan angle. It is developed from analysis of the effect on the received signal of the following parameters: inhomogeneous hydrometeor motion, radar frequency stability, pulsewidth, antenna beamwidth, scan angle, scan rate, and aircraft speed. In addition, the influence of finite pulse volume on radar sensitivity to hydrometeor motion is examined.     

Clutter return from vegetated areas

An analytical stochastic model to predict relevant statistical scattering features of electromagnetic waves propagating within vegetated environments is presented. The propagation phenomena are described by formulating the scattering associated with random permittivity fluctuations superimposed on a lossy deterministic background slab. The distorted wave Born approximation is employed to determine the backscattered power, and its temporal spectrum.     

新型电荷泵DC/DC变换器

新型非隔离、降压式、低电压、大电流、超低压差电荷泵DC／DC变换器在结构上没有泵电容,其主要特点有：输出电流大,可达800mA;输出电压精度高(见表1及表2);超低压差,特别适用于便携式产品;有输出电压连续可调及固定输出电压两种类型;有输出短路保护及输入电压过压保护;模块做成三端器件,仅需外接输入电容器及输出电容器,使用十分方便;无电感器;电路简     

安全增强的迂回路由机制

分析了移动IPv6中使用的迂回路由机制及其安全性,提出了针对迂回路由机制的一种中间人攻击方案.提出了安全增强的迂回路由机制,分析了其安全性,证明它抵御了中间人攻击.     

地形地表的不规则起伏对雷电电磁场传输的影响

为了探讨真实地形对雷电定位精度的影响,利用二维时域有限差分（two-dimensional finite-difference time-domain, 2D FDTD）算法,采取共形网格剖分技术,通过与平坦地面相比,首先研究了云南昆明地区复杂地形地貌对雷电电磁场传播的影响,然后利用时差定位算法,进一步探讨了该地区复杂地形地貌对雷电定位精度的可能影响。结果表明：1）由于复杂山体对雷电高频信号的优先衰减作用,传播路径上的山体越高大,相应的雷电电磁波波头时间越长,即信号到达时间(time of arrival, TOA)可能会延迟。从本文选取的昆明研究区域看,脉冲波形峰值到达滞后时间大概分布在4～5 μs。2）根据脉冲信号TOA的不同定义方式,无论是平坦地面还是考虑复杂地形地貌的真实地表,峰值到达法的误差最大。对假定的平坦地面而言,除了峰值到达法,绝大多数TOA时差定位偏差在200 m以内,甚至重合。但对真实传播路径而言,不同雷击点对应不同的传播路径,有的偏差在100～200 m左右,有的偏差在2 000 m左右。     

Concepts of lightning return stroke models

Return stroke models have been reviewed according to the assumptions they make and their underlying concepts. We have investigated the roots of the modern concepts used to describe return stroke related phenomena and illustrated their developments and deviations from the original idea. We discuss the return stroke models in two categories in accordance with the direction of the charge transfer along the channel. We show that all the models that we have considered can be described by two general sets of mathematical equations. The validation and comparison of models in reproducing measured lightning parameters are discussed. We also show the different methods employed by return stroke models to estimate the return stroke speed and discuss possible improvements that could be introduced into return stroke models in the future     

立体声信号相位差电平差测试仪

提出了一种立体声信号相位差电平差测试仪的设计方法。用单片机为控制核心,主要由相位差检测模块、电平差检测模块、频谱分析及处理模块、电源模块、键盘和显示模块组成。将LR立体声信号经频谱分析、整形及占空比检测电路进行处理,采用过零鉴相法,通过测矩形波占空比,实现相位差的测试。将LR信号用AD736专用芯片实现AC/DC转换,通过单片机编程,得到LR电平差。试验数据表明该仪器实现了LR信号相位差电平差的测试,且具有较高的测试精度,并能存储和显示相关信息。本设计具有创新性和实用性,为高质量立体声广播和研发制造高质量音响设备奠定了基础。     

Time difference amplifier

Accurate measurement of edge time differences down to 10 ps or less is required for tests of timing in digital systems. A circuit is described that is aimed at reliably amplifying these time differences by a factor between 3 and 10 before measurement to enable greater accuracy.