任意等分圆光栅的刻划

本文介绍了用简单的BASIC语言程序对任意等分圆光栅的分度进行计算,以及具体的调整刻制方法,从而在未任何附加装置的圆刻机上刻制出任意等分圆光栅,且保证了一定的刻划精度。此法简单、易行,而且同样适用于任意等分度盘的刻划。文末附有BASIC程序。此外,还简单介绍了微机控制圆刻机进行任意等分刻划的原理。     

基于多路DAC伪插值的任意波形合成技术研究

针对任意波形发生器的设计中数模转换器(DAC)转换速度的瓶颈问题,提出了一种基于多路DAC进行伪插值的任意波形合成方法,从理论上证明其可行性,并对其实现过程中的误差来源进行了探讨,给出了相应的补偿思路.着重分析了DAC零阶保持特性和伪插值时钟误差对输出信号频谱的影响,推导了关于频域特征和信噪比的重要结论.并通过计算机仿真和500 MSPS任意波形发生器项目对结论进行了验证.这些结论可用于任意波形发生器设计中的杂散评估和方案选择,同时也可为指标分配提供理论依据.     

Analytical synthesis of invariant reduced-order state observers

An algorithm for the analytical synthesis of reduced-order observers for dynamic systems with an output matrix of arbitrary form is proposed, and invariance conditions for the constructed observer with respect to external disturbances are formulated. Solvability conditions for the synthesis problem are obtained in the form of a system of linear matrix equations. The proposed algorithm is based on a nondegenerate transformation of the state vector using the matrix canonization technique and methods for solving linear matrix equations of arbitrary dimension.     

Dynamic and quasi-static behaviors of magneto-thermo-elastic stresses in a conducting hollow circular cylinder subjected to an arbitrary variation of magnetic field

In the present paper, dynamic and quasi-static behaviors of magneto-thermo-elastic stresses in a conducting hollow circular cylinder subjected to an arbitrary variation of magnetic field are investigated. It is assumed that a magnetic field defined by an arbitrary function of time acts on the outer surface in the direction parallel to its surface. Fundamental equations of plane axisymmetrical electromagnetic, temperature and elastic fields are formulated. Then, solutions of magnetic field, eddy current, temperature change and both dynamic solutions and quasi-static ones of stresses and deformations are analytically derived in the forms including the arbitrary function. The solutions of stresses are determined to be sums of thermal stress caused by eddy current loss and magnetic stress caused by Lorentz force. For the case that the arbitrary function is given by the sine function, the dynamic and quasi-static behaviors of the stresses are examined by numerical calculations.     

Prediction of vibration of rotating damped beams with arbitrary pretwist

A solution procedure for the bending–bending vibration of a rotating damped beam with arbitrary pretwist and an elastically restrained root is derived. The viscous damping is assumed to be proportional to the distributed mass. The general complex system is divided into two subsystems. The physical meanings of the subsystems are studied. The exact complex frequency relations between two viscously damped beams with arbitrary pretwist and elastic root are revealed. The underdamping, critical damping and overdamping systems are analyzed. Moreover, the influence of the parameters on the decay rate, the natural frequencies, the critical damping, and the phenomenon of divergence instability are investigated.     

任意连续梁内力包络图的自动绘制法

根据内力包络图设计梁的断面,可以保证满足安全和经济两方面的要求。但是按传统方法绘制梁的内力包络图手续十分繁琐,对于连续梁之类的多跨梁尤其如此。介绍一种利用奇异函数对连续梁进行力学分析的新方法及其智能分析软件。该方法利用奇异函数与拉普拉斯变换相结合的方法导出连续梁变形和内力的普遍表达式,利用变形和内力的边界条件确定约束反力,然后再在内力普遍表达式的基础上建立一种内力包络图的自动绘制方法。该方法和程序对承受任意恒载和活载、具有任意跨数的连续梁具有普遍的适用性。     

基于FPGA的双DDS任意波发生器设计与杂散噪声抑制方法

研究基于DDS(直接数字频率合成)的任意波信号产生的机理,在FPGA内嵌SOPC,配置了32位的软微处理器NiosII,利用FPGA实现双DDS的相位累加器,通过数字方法直接实现任意波形的各种频率调制.分析了高速相位累加器截断误差,幅度量化误差和D/A非线性引起的杂散分量产生的原因.推导出DDS相位噪声模型,针对信号的频谱成份设计了高阶低通滤波器对输出信号滤波.结合NiosII,设计硬件电路对输出信号进行幅频校正,保证了信号幅值的稳定输出及实际显示数值的一致性.测试表明,信号波形发生器能输出稳定、高带宽、高速度、高精度、低衰减的任意波形,三角波的输出频率大于1 MHz,输出信号幅度峰峰值在50 mV～20 V范围内以10 mV的步进调节.     

Thermal effects in conical bearings

An oil lubricated conical bearing is analysed taking into account the dependence of viscosity on temperature. The bearing surfaces are maintained at constant but arbitrary temperatures. When the temperature of the rotating part is continuously decreased from an arbitrary value higher than the temperature of the stationary part to some arbitrary value lower than the temperature of that part, the load capacity monotonically increases.     

任意铺层复合材料开口圆柱层压壳结构热翘曲分析

研究任意铺层复合材料开口层压圆柱壳固化过程中温度变化引起的变形.基于瑞利里兹能量法,根据任意铺层复合材料开口层压壳的变形特征,将其翘曲变形分解为关于壳体几何对称轴对称弯曲变形和关于壳体几何中心点对称弯曲变形,并且考虑开口圆柱层压壳体大挠度变形引起的几何非线性影响,提出描述任意铺层复合材料开口圆柱层压壳热翘曲变形的翘曲函数,推导热翘曲函数的求解表达式.通过算例对模型预测结果与有限元数值模拟结果进行比较,认为模型中采用的翘曲函数能正确反映开口圆柱壳的热翘曲变形特征,该模型可以用于预测复合材料开口圆柱层压壳的热翘曲变形.     

任意结构数控机床机构运动学建模与求解

建立了一种适合于任意结构数控机床的机构模型与运动模型及机床运动求解的通用方法。对于具有任意轴数、轴运动方向为空间任意方向的数控机床,均可通过机床机构的型和结构参数来描述其机构模型,并据此建立其运动模型和进行机床运动求解。     

板成形面积测量的研究

介绍了研制的任意形状板件面积测量仪的原理、结构和测量方法,并以汽车用典型冲压件为例,对其面积进行实测,其测量结果可供板成形工艺制定者参考。任意面积测量仪具有结构简单、测量精度高的特点,不仅能测量密度大于水的密度的板件的任意面积,还可以测量密度小于水的密度的板件的任意面积。     

基于基础解的电磁轴承静动特性计算方法研究

研究了电磁轴承静动特性的计算方法,定义了基于局部坐标系的电磁轴承静动特性基础解,推导了任意磁极结构的电磁轴承动力学特性与基础解之间的坐标转换关系;在此基础上提出了利用基础解计算任意磁极结构的电磁轴承静动特性的方法,该方法简捷、快速,是电磁轴承静动特性计算的一套规范化、标准化的方法。     

Dynamic responses of a functionally graded pyroelectric hollow sphere for spherically symmetric problems

The spherically symmetric thermoelastic problem of a functionally graded pyroelectric hollow sphere is considered. The functionally graded material is restricted to the variations of density and other material constants as a certain power of the radial distance. By virtue of the introduction of a dependent variable as well as the separation of variables technique, a Volterra integral equation of the second kind related to a function with respect to time is derived, which is solved successfully by using an interpolation polynomial to approximate the unknown function. The corresponding recursive formulae are derived, based on which numerical solution can be obtained step by step. The present method can provide accurate numerical results efficiently and is suitable for a functionally graded pyroelectric hollow sphere with an arbitrary thickness and subjected to arbitrary spherically symmetric thermal loads. Numerical results are finally presented.     

LZ50车轴钢的概率循环本构模型

试验研究了LZ50车轴钢随机循环本构模型。验证了先前在焊缝金属试验中的发现与推断,即工程材料的循环本构存在随机性,与广泛所认识的循环应变—寿命关系的随机性一样,是固有的疲劳现象。同时考虑数据分散性规律和数据量对概率评价的影响,基于Ramberg-Osgood方程及其修正形式,提出了任意存活概率和置信度的随机循环本构模型及其参数的求解方法。LZ50车轴钢试验数据的分析验证了模型的有效性和实用性。     

任意分布参数平面连杆机构运动精度可靠性灵敏度设计

将可靠性设计理论与灵敏度分析方法相结合,讨论了任意分布参数平面连杆机构运动精度可靠性灵敏度设计问题。首先,结合机构精确度理论和可靠性理论,提出任意分布参数平面机构运动精度可靠性评估方法。然后,引入灵敏度设计理论,推导出任意分布参数平面机构运动精度可靠性灵敏度设计方法。最后,以平面四杆机构为例,详细阐述了设计参数的改变对平面连杆机构运动精度可靠性的影响,为平面连杆机构的运动精度可靠性设计和可靠性维护提供了理论依据。     

任意拓扑结构机床运动轴误差传递链建模方法

在对任意结构机床进行空间几何误差建模时,必须要获得该机床运动轴误差传递链,从而基于微分变换实现任意结构机床误差建模。通过运用多体系统理论,构建任意结构机床拓扑结构与低序体阵列,利用机床拓扑结构与低序体序列提出了机床运动轴连接支承件相对运动矩阵与机床支承件连接矩阵概念,建立了获取运动轴误差传递链的数学模型。该数学模型将描述机床拓扑结构的低序体序列与机床支承件相对运动关系结合起来,给出了获取任意机床运动轴误差传递链的建模方法。并且将利用此建模方法获得的运动轴误差传递链运用于基于微分变换的机床空间几何误差建模中,实现了对任意结构机床空间几何误差建模。最后以五轴立式加工中心为算例,验证了该运动轴误差传递链建模方法的有效性。     

任意三角形控制网格的二元四次箱样条曲面算法

二元三方向剖分是方向最少的三角剖分,建立在其上的二元三向箱样条在工程曲面造型等领域有着极为广 泛的应用。规范的二元三向四次箱样条曲面计算仅针对网格中点的价数均为6的情形,从规范的算法出发,提出 了一种任意价数控制点的情形下的曲面计算算法,并对算法进行了较为详细的分析。分析及试验结果表明,按该 算法生成的曲面有较好的整体光顺特性,各面片间是C1连续的,而对某一个三角面片内部则是C2连续的。由于 本算法适用于任意的三角形控制网格,因此在CAD／CAGD等曲面造型中有很高的实用价值。     

Relation between correction masses and bearing forces in a rigid rotor

Bearing forces on a rigid rotor are mainly characterized by unbalance distribution. The forces can be divided into two arbitrary planes along a rotor shaft since any unbalance in the rigid rotor is able to be expressed on two planes. The correction mass quantities on two arbitrary planes are analytically found in terms of the bearing force measurements from the basic concept of three-dimensional rigid body dynamics. The quantities are expressed in terms of the geometry of rotor — the distance between two bearings and the positions of two planes from the bearings — and the bearing forces: amplitudes of the alternating component of forces and angular positions of their peak values. The validity of the proposed method is proved using a simulation example.     

Strul--a method for 3D alignment of single-particle projections based on common line correlation in Fourier space

A central problem of 3D reconstruction in single-particle electron microscopy is the determination of relative orientations of the individual projections contributing to the reconstruction. This article describes an implementation of the method of common lines correlation in Fourier space that allows generation of common lines between an arbitrary number of projections which might posses an arbitrary point group symmetry. Based on this method, it is possible to optimize rotational and translational alignment parameters for individual single-particle projections. The underlying philosophy and details of implementation are discussed, and as an illustration a 3D reconstruction in ice of peroxisomal alcohol oxidase from Pichia pastoris, an octameric assembly with 422-symmetry and a molecular weight of 592 kDa is presented.     

基于VXI总线的新型AWG的设计

基于VXI总线的任意波形发生器是随着计算机技术和微电子技术在测试仪器中的应用而形成和发展起来的一类新型测试仪器。任意波形发生器的价值在于它能真正产生任意波形。文中提出了一种新型的任意波形发生器结构，介绍了基于VXI总线C尺寸任意波形发生器设计的全过程，开发了VXI总线寄存器基接口、用DDS技术设计了功能电路、开发了AWG的软面板、应用控制程序和仪器驱动器，所设计的任意波形发生器的特点是：高速、模块化、方便的波形输入以及和VXI资源相结合。该任意波形发生器模块已应用于模块化雷达自动测试设备中，能提供测试系统所需要的任何波形激励信号。