MEMS加速度计组合在分度头上的标定方法

提出了一种在分度头上标定MEMS加速度计组合的测试方法,该方法可以标定出加速度计组合的刻度系数误差、加速度计零偏、三轴不正交度误差、安装误差角,同时可以分离出分度头转位机构角位置误差.首先通过建立一系列坐标系,推导了重力加速度在加速度计敏感轴的分量表达式.然后采用谐波分析法给出了误差标定方程,利用最小二乘法和Kalman滤波器进行误差参数的估计,并对估计结果进行了对比分析.最后通过三次独立实验标定结果的重复性和残差验证了该方法的正确性.     

Methods to determine stress profile in ALT based on theoretical life models

With the recent products being more reliable,engineers cannot obtain enough failure or degradation information through the design period and even the product lifetime,therefore,accelerated life test(ALT)has become the most popular way to quantify the life characteristics of products.Test design is the most essential topic,such as testing duration,stress profile,data inference,etc.In this paper,a method and procedure based on theoretical life models is proposed to determine the accelerated stress profile.Firstly,the method for theoretical life calculation is put forward based on the main failure mechanism analysis and the theoretical life models.Secondly,the method is provided to determine the accelerated stress profile,including the method to determine the accelerated stress types and the stress range on the basis of the main failure mechanism analysis,the method to determine the acceleration factor and the accelerated stress level based on life quantitative calculation models,and the collaborative analysis method of the accelerated test time while taking the multiple failure mechanisms into consideration.Lastly,the actuator is taken as an example to describe the procedure of the method and the engineering applicability and the validity are verified.     

管道惯性测量系统散热仿真分析

基于FLUENT商用软件建立了在60℃高温油内使用的管道惯性测量系统的传热数值模型,模拟了系统在自然对流、不同风冷强制对流和不同热辐射系数下散热的温度分布,分析了风扇布置、空气流量及结构件表面热辐射系数对系统温度分布的影响.通过仿真分析取得了系统有效的散热配置,试验验证结果与仿真计算情况基本吻合,两者相差1.1％.     

大涵道比涡扇发动机喷流降噪实验

对大涵道比分开排气喷管的缩比模型进行了吹风实验,模拟了双涵道喷流在加热条件下的远场噪声特性,分析了4种不同几何参数的锯齿构型对喷流噪声的影响。结果表明:喷流噪声以大尺度涡产生的低频噪声为主导,主要贡献方向为下游150°附近;锯齿喷管可以有效抑制低频部分及下游方向的噪声,最高可降低峰值声压级(SPL)约6 dB;锯齿的切入程度可以显著的影响降噪量,4种锯齿构型中切入程度高的外涵锯齿构型降噪效果最优,总声压级(OASPL)最高可降低3 dB;内涵锯齿构型的降噪效果比外涵锯齿低,总声压级最高降噪量在1 dB以内;内外涵锯齿构型可以在外涵锯齿的基础上进一步抑制低频噪声,下游方向总声压级最高降噪量为17 dB。     

Effects of Alloying Elements Ti, Cr, Al, and Hf on β-Nb5Si3 from First-principles Calculations

The energy, lattice parameters, electronic structures, and elastic constants of the intermetallic compound β-Nb₅Si₃ alloyed by Ti, Cr, Al, and Hf elements are investigated using first-principles methods based on plane-wave pseudopotential theory. From the impurity formation energy calculated, it is found that Ti, Cr, and Hf prefer to occupy the Nb_I, Nb_I, and Nb_II site, respectively, and that Al decreases the stability of β-Nb₅Si₃. Ti and Cr atoms reduce the c/a ratio of crystal lattices and Hf atom transforms the crystal lattice of β-Nb₅Si₃ from the tetragonal system to the orthorhombic system. The total state density of pure β-Nb₅Si₃ system and Ti, Cr, and Hf doped systems shows that Ti, Cr, and Hf improve the conductibility of β-Nb₅Si₃ system. The bulk modulus, shear modulus, and elastic modulus are obtained using Voight approximation equation. Ti and Cr increase the hardness and reduce the ductility of β-Nb₅Si₃. In contrast, Hf decreases the hardness and improves the ductility.     

A study of the plasmasphere density distribution using computed tomography methods from the EUV radiation data

In this paper, we introduce a new topic for imaging plasmasphere density with CT techniques. Both parallel-beam and fan-beam reconstruction formulas are derived with a special weighting function. Different from the traditional X-ray CT, the extreme ultraviolet (EUV) radiation may be totally absorbed by the Earth. Only the portion between the Earth and the detector enters the EUV sensor and be measured. The key step in our derivation is to remove the complete absorption effect with a specific weighting function. Computer-simulation studies are present to verify our formulas for the plasmasphere density.     

压气机叶片辊轧模具型腔前滑补偿方法

辊轧模腔是叶片无余量辊轧成形的关键,然而压气机叶片辊轧成形过程中存在前滑现象,造成叶片沿辊轧方向精度偏差,需要在模具型腔设计过程中补偿前滑量,以实现叶片沿积叠高度的精确成形。针对叶片辊轧前滑现象,本文提出并研究了基于辊轧前滑补偿的压气机叶片辊轧模具型腔优化设计方法。首先,在分析前滑成因及叶片截面前滑表征模型的基础上,研究了前滑补偿机理并建立了前滑补偿模型,即型腔中心角与叶片积叠高度的对应关系。在此基础上,通过提取表征叶片的工艺模型截面线族,顺次计算截面前滑值并基于前滑补偿模型对辊轧模具型腔中心角进行修正。然后,基于修正后的型腔中心角,建立叶片工艺模型截面线族到型腔截面线族的空间扇态映射法则并进行截面线映射变换,进而基于型腔截面线重构了基于前滑补偿的叶片辊轧模具型腔。最后,通过高置信度数值计算方法比较了前滑补偿模腔和直接空间几何映射模腔辊轧成形叶片的积叠高度。结果表明,优化后的模具型腔能够有效提高叶片积叠轴方向上的成形精度。     

采样机械臂关节月表环境适应性设计

文章针对月球表面采样任务对机械臂关节防尘、耐高低温和轻量化的特殊要求,提出一种由永磁同步电机驱动、2K-H行星减速器+谐波减速器传动的关节设计方案。该方案采用电机的齿槽转矩提供关节制动力矩,并采用前馈力矩补偿控制的方法消除齿槽转矩引起的速度波动,节省了制动器的配置;通过控制减速器传动侧隙、电机定子与壳体的过盈量及密封垫片厚度,实现关节在-100~160℃高低温环境的热匹配和防尘。仿真分析和样机试验结果验证了关节设计方案可满足月表采样的月面特殊环境要求。     

基于DP83640的秒脉冲移相器设计与实现

使用DP83640 IEEE 1588精密时间协议（PTP）收发芯片设计实现了一款秒脉冲精密移相器,它能与外部的标准秒脉冲（1 PPS）进行同步并进行精密相位微调,可应用于高精度相位微跃器。秒脉冲移相器采用DP83640芯片进行级联实现秒脉冲精密移相：利用ARM微处理器控制第二级DP83640实现与外部标准秒脉冲的相位粗调,控制第一级DP83640实现相位微调。相位调整时将外部输入的相位偏移量换算为8 ns整周期倍数的相位粗调值,以及不同时间长度档位的相位微调值,分别写入第二级和第一级DP83640共同实现高精度相位微跃。由于硬件电路特性和器件综合噪声的影响,经测试平均相位微跃准确度可以达到0.1 fs。     

飞机起落架用钢贝氏体组织的屈强比问题

本文根据强度设计规范要求和试验结果,指出飞机起落架用钢在满足屈强比σ_(0.2)/0_h>0.67的条件下,以适当降低该值更为行利。对40CrMnSiMoVA钢的研究证实,σ_(0.2)和σ_(0.2)/σ_h值在循环载荷作用下并非恒值。贝氏体组织较低的σ_(0.2)/σ_h值使其发生循环硬化,从而减轻钢的缺口敏感性并延长其疲劳裂纹形成寿命,同时具有更为明显的超载延寿效果。