采用宽带光源的双光束干涉中零光程差位置测量研究

提出了一种可以快速实现采用宽带光源的双光束干涉中零光程差位置测量的方法。在测量中，以双光束干涉条纹间距的四分之一大小为采样间隔，以相邻的四个采样值为一组进行相应的干涉条纹调制度计算，以干涉条纹调制度的最大值位置作为零光程差位置。还对光电测量系统中的机械与光电转换精度、采样点位置、采样点密度、双光束光强比、光源相干长度等多方面对测量精度的影响进行了定量分析。     

Transmission path phase compensation for gear monitoring under fluctuating load conditions

Vibration can be monitored under fluctuating load conditions if provision is made for taking into account the fluctuation in machine speed, the response amplitude modulation caused by the change in input force, and the amplitude and phase effects on the measured response from the transmission path. Methodologies have been developed to compensate for the effects of fluctuating speed and amplitude modulation. However, this article investigates the effect of the transmission path phase. This is discussed in terms of the effect this phase has on synchronous averaging. A new approach is presented to resolve the influence that the transmission path phase has on synchronous averaging. The approach is used for the experimental data measured on a helical gear test rig. A significant improvement in the rate of convergence was obtained by adopting the new approach which compensates for the phase shifting in the measured structural response. This contrasts with conventional synchronous averaging with order tracking which does not compensate for structural response phase shifting.     

非共振光声红外气体传感器结构参量分析

非共振光声红外气体传感器在气体检测领域有很好的应用前景。对基于MEMS红外光源的非共振光声红外气体传感器进行了一维模拟,分析了光声腔及红外吸收光路结构对传感器性能的影响;计算了吸收腔气体压强变化量与吸收腔长度及调制频率的关系,研究了光路内壁反射率、样品气室长度对样品气体红外吸收效率的影响。简化的理论分析和计算结果,可以为非共振光声红外气体传感器的结构设计提供参考。     

A control system for the optical-fiber piezoelectric modulator of the optical path

The operating principle of an optical-fiber piezoe lectric modulator of the optical path in all-opti-cal-fiber interferometers is described. The control system of the optical-fiber piezoelectric modulator is composed of a controller based on a field programmable gate array, a digital-to-analog converter, an analog low-pass filter, and a power amplifier. A 4.4-m/s speed of chan ge in the optical length of the fiber has been attained with an error of 0.1% at a modulation length of the optical path of >1 mm.     

An unmodulated bi-directional fringe-counting interferometer system for measuring displacement

A bi-directional fringe-counting Michelson interferometer is described that is used in conjunction with a frequency-stabilised laser for precise length measurement. The two counting signals, in phase quadrature and sinusoidally related to path difference, are produced by a novel system that does not employ any form of modulation. Under optimum conditions, the instrument is capable of measuring displacement to a precision of 0.1 μm and the correct fringe-count is maintained even with a signal attenuation corresponding to a 99% loss of intensity in one arm of the interferometer. This performance can be further improved by the application of an automatic gain control system. The interferometer is simple in concept, cheap to produce and easy to set up and align.     

波导式偏振调制测距系统

为消除体相位调制器工作过程中热效应对偏振调制测距精度的影响,提出了利用波导式相位调制器替代体相位调制器的全光纤波导式偏振调制测距方法.对波导式偏振调制测距系统进行原理分析,利用琼斯矩阵得出传输过程中测量光偏振态的变化规律,建立调制信号频率、偏振光强度与被测距离的函数关系.然后,进行了直波导相位调制器特性测试,验证其半波...     

二维光子晶体中反常Doppler效应的相位演变

光在具有负等效折射率的二维光子晶体中传输时会产生反常Doppler现象,为了分析光在该反常效应中传输时的相位变化,首先用时域有限差分(FDTD)法仿真了光经过静止光子晶体时的负折射现象,然后对光子晶体中沿光传输方向的Bloch波做快速傅里叶(FFT)处理。对滤波后的频谱,用iFFT反演出各平面波分量,并通过分析各平面波分量的相位演变,分离出与负折射产生有关的后退波分量。然后,将实验中的连续运动过程分解为各静止瞬间,分析了各相邻时刻探测面上信号光和参考光的相位变化,此处两束光的相位变化差随时间的变化量就是差频。静态FDTD方法仿真计算得到的差频与理论值的误差约为20%,能较好解释反常Doppler效应发生过程中光的相位变化。本文的研究揭示了反常Doppler效应发生时光子晶体中起作用的分量的相位变化,也为研究光在运动介质中的传输特性提供了新的思路。     

Potential Accuracy of Estimation of the Information Parameter of a Homodyne Laser Doppler Vibrometer Signal

This paper describes the analysis of the potential accuracy of estimation of the signal modulation index of a homodyne laser Doppler vibrometer with frequency modulation and known and unknown non-information parameters of the signal. The Rao — Cramer inequality is used to obtain expressions for calculating the lower bound of variance of the modulation index estimate and study its relationship with a signal/noise mixture. Recommendations on the choice of conditions for measuring the amplitude of vibro-displacement by the homodyne Doppler laser vibrometer are given.     

Interferometer-based structured-illumination microscopy utilizing complementary phase relationship through constructive and destructive image detection by two cameras

In an interferometer-based fluorescence microscope, a beam splitter is often used to combine two emission wavefronts interferometrically. There are two perpendicular paths along which the interference fringes can propagate and normally only one is used for imaging. However, the other path also contains useful information. Here we introduced a second camera to our interferometer-based three-dimensional structured-illumination microscope (I(5)S) to capture the fringes along the normally unused path, which are out of phase by π relative to the fringes along the other path. Based on this complementary phase relationship and the well-defined phase interrelationships among the I(5)S data components, we can deduce and then computationally eliminate the path length errors within the interferometer loop using the simultaneously recorded fringes along the two imaging paths. This self-correction capability can greatly relax the requirement for eliminating the path length differences before and maintaining that status during each imaging session, which are practically challenging tasks. Experimental data is shown to support the theory.     

Fiber-optic liquid level sensor based on coupling optical path length variation

The concept for a new and simple fiber-optic liquid level sensor is presented and experimental results are shown to demonstrate the principle. The sensing principle is based on light intensity modulation when rising and falling mode of liquid level causes coupling optical path distance variation between two optical fibers. Near continuous mode of liquid level variation could be monitored with resolution as low as 1 mm can be measured in the length scale of 25 cm.     

正交调制降频相位式激光测距

为了提高激光测距的精度与稳定性,通过改良传统相位激光测距仪,设计了新型正交调制降频与最小二乘法解相位的相位式激光测距仪。使用反射镜实现内外测距光路,通过正交调制技术对发射激光进行幅度调制,接收模块接收到的回波信号经过混频器后再经过低通滤波器将回波信号降频,降低解相难度并提升解相精度。改用分时测量得到距离相位从而消除二次混频方法所产生的附加相移,分别对内外光路低频回波信号采样进行模数转换后使用最小二乘法求解相位。采用多频率调制测量兼顾激光测距范围与测量精度,最后通过超定方程解模糊算法求解多频测距的待测距离。在国家标准基线上进行样机测试,实验结果表明,在60m量程内正交调制激光测距仪的测量平均误差控制在1.5mm以内,测距量程内标准差保持在0.9mm以内。     

齿轮疲劳裂纹诊断中相位信息的精化处理

本文在分析带有疲劳裂纹的齿轮的振动诊断中相位调制诊断原理及方法的基础上,针对现有方法所提取的相位信息存在多种干扰信号的情况,着重研究了相位信息的精化,提出了一种新的处理方法,并获得了令人满意的实验效果.利用该方法所获得的相位信息图,可大大提高诊断的精确程度,而且可实现裂纹长度的定量诊断.     

A novel approach to the prediction of musculotendon paths

One of the most important aspects of the modelling of musculoskeletal systems is the determination of muscle moment arms which are dependent upon the paths of the muscles. These paths are often required to wrap around passive structures that can be modelled as simple geometric shapes. A novel technique for the prediction of the paths of muscles modelled as strings when wrapping around smooth analytical surfaces is presented. The theory of geodesics is used to calculate the shortest path of the string on the surface and a smoothness constraint is used to determine the correct solutions for the string path between insertions. The application of the technique to tapered cylinders and ellipsoids is presented as an extension of previous work on right-circular cylinders and spheres. The technique is assessed with reference to a particular biomechanical scenario; string lengths and moment arms are calculated and compared with alternative approximate methods. This illustrates the potential of the technique to provide more accurate muscle moment arm predictions.     

正弦变载荷工况下液压泵振动信号的形态学滤波方法

液压泵的振动信号在受到大幅度变载荷作用时将引起振动特征的变化,特别是在正弦载荷变化的作用下,将会产生幅值调制现象。采用传统的单一尺度结构元素的形态学方法对该类信号进行滤波的效果不一定理想。因此,针对正弦载荷液压泵振动信号的特点,在单尺度形态滤波分析方法的基础上,提出了兼顾形态学结构元素长度和高度尺度的多尺度形态学滤波方法。首先,以冲击特征比值和二阶原点矩作为评价指标,提出综合考虑结构元素长度和高度尺度的寻优方法,确定最优长度和高度尺度算子组合。然后,用最优尺度组合对正弦载荷模拟仿真信号和变载荷液压泵故障振动信号进行滤波处理,分析结果证实其滤波效果优于单尺度滤波方法滤波效果。     

High-temperature multipass cell for infrared spectroscopy of heated gases and vapors

In absorption spectroscopy, infrared spectra of heated gases or condensed samples in the vapor phase are usually recorded with a single pass heated gas cell. This device exhibits two orders of magnitude lower sensitivity than the high-temperature multipass cell presented in this article. Our device is a novel type of compact long path absorption cell that can withstand aggressive chemicals in addition to temperatures up to 723 K. The construction of the cell and its technical features are described in detail, paying special attention to the mechanisms that compensate for thermal expansion and that allow the user to vary the optical path length under any thermal or vacuum condition. The cell may be used with a laser source or implemented within a Fourier transform infrared spectrometer. Its design is compatible with optical arrangements using astigmatic mirrors or spherical mirrors in a Herriott configuration. Here we implement a homebuilt Herriott-type cell with a total optical path length of up to 35 m. In order to demonstrate the feasibility of the cell, methane and water vapor absorption lines showing dissimilar temperature effects on line intensity were recorded with the help of a mid-infrared laser source tunable between 3 and 4 microm. Emphasis is put on lines that are too weak to be recorded with a single pass cell.     

k阶循环矩解调用于滚动轴承故障特征提取

针对滚动轴承早期故障诊断中故障特征信号提取问题,提出了一种基于k阶循环矩的故障特征信号解调方法.在循环矩理论基础上,首先分析了时变调幅信号的k阶循环矩解调原理和方法;讨论了k阶循环矩的频率特性;得出了k阶循环矩不仅能解调出调制频率,还能解调出载波频率的规律;给出了k阶循环矩的计算方法,并利用仿真信号验证了该方法的有效性;最后通过滚动轴承振动信号进行了分析.结果表明,该方法能有效提取滚动轴承早期故障特征,识别故障类型,具有较高的可信度.     

旋转机械故障窄带信号的循环平稳特征分析

阐述了窄带叠加正弦调幅信号的循环平稳特征,指出了窄带叠加正弦调幅信号与其对应的确定性正弦调幅信号循环矩相比,循环频率不变,仅将确定性幅值变成了随机幅值,幅值的大小和相位发生了变化;并以旋转机械中使用最为广泛的轴承故障的诊断为例,对机械故障的窄带信号循环平稳特征进行了分析;使用傅氏级数及相关分析理论,给出了周期冲击信号循环自相关函数数学表达式,得到了故障存在于内外环和滚动体上的二阶循环频率大小;最后通过实例分析证明了理论的正确性。     

Spray jet penetration and distribution of modulated liquid jets in subsonic cross-flows

Modulated liquid jets injected into subsonic cross-flows are empirically studied by using a mechanical liquid jet modulation apparatus. Experimental investigations were conducted using water over a range of cross-flow velocities from 5 m/s to 143 m/s and with modulated liquid jet frequencies from 35.7 Hz to 166.2 Hz and so on. PDPA(phase Doppler particle anemometry) was employed to measure droplet diameter and velocity with various spray cross-sections from Z/d=20 to Z/d=60. The spray structure, penetration depth, SMD(Sauter mean diameter), volume flux and velocity characteristics of modulated liquid jets injected into cross-flows were examined. As oscillation of the periodic pressure that could make liquid jet moved up and down in cross-flow field, the mixing process was facilitated. This phenomenon has the advantage of mixing the spray concentration from the center area to the outer area. Also, a bulk liquid jet puff was detected in the upper field of the liquid jet surface. The modulation effect appears significant in the extent of the spray oscillation. The correlation equations for the liquid jet boundary of the upper and lower regions which related to the Strouhal number have been presented to predict the spray structure under modulation conditions. Because of the modulation frequency, an inclination of averaged SMD for the structured layer was evanescent which contributed to the promotion of the macroscopic spray mixing process. Cross-sectional characteristics of SMD had the same tendency over a range of various modulation frequencies. As the modulation frequency increased, the region of volume flux distribution also increased.     

Plastic design of beams: Optimal locations of supports and steps in yield moment

The minimum-weight plastic design of beams with segmentwise constant yield moment when the weight per unit length is proportional to the yield moment is discussed. Criteria for the optimal locations of supports and steps in yield moment are established and their use is illustrated by examples.     

傅里叶变换红外光谱仪动镜倾斜误差分析

通过建立傅里叶变换光谱仪中动镜、定镜和干涉面的坐标对应关系,对动镜存在多个方向倾斜时的干涉光路进行了详细的分析。建立了非准直状态下干涉面光强分布的二维数学模型,确立了干涉图函数的数学表达式,从调制度、相位误差和频率噪声的角度,对动镜倾斜造成的影响进行了系统分析。在动镜的运动中,左右方向的倾斜和俯仰方向的倾斜对系统的影响彼此具有独立性,又具有叠加性;干涉图中初相位因子随光程差改变缓慢变化或快速变化,对相位误差的影响也不全相同。在倾斜误差分析的基础上,对动镜的最大倾斜角度和减少误差的方法进行讨论,并提出了两种动态准直校正的思路。