电极圆锥内螺纹的无损检测

将CT技术和图像处理技术相结合,提出了电极圆锥内螺纹的无损检测方法。目前普通螺纹常用的测量方法大多为接触测量,有关文献介绍了非接触检测方法,但它们仅限于圆柱内螺纹,圆锥内螺纹的图像处理及非接触测量未见报道。从CT技术入手,探讨了电极圆锥内螺纹的图像检测方法,即在一个系统中实现对工件内部缺陷的检测及几何参数的测量。通过使用图像预处理、阈值选取及二值化、边缘检测及提取等方法,提取了螺纹轴截面齿形轮廓,并对不同处理方法进行了比较。使用自编程序测量计算了内螺纹的螺距、牙型角和锥角,测量精度分别达到了0 03mm,0 24°和0 02°。分析了误差产生的原因。理论分析及实验结果表明该方法正确可行。     

Development of a novel scattered triangulation laser probe with six linear charge-coupled devices (CCDs)

The objective of this paper is to develop an inexpensive, robust, and precise scattered-type triangulation laser probe system with six linear charge-coupled devices (CCDs), that can be used to measure simultaneously the distance and inclination angle of a workpiece surface. The developed system has been configured and assembled based on Scheimpflug's principle. Through the specific arrangement of the six linear CCDs, four different measurement modules for the developed system were possible, namely the standard triangulation probe module, the double triangulation probe module, the pentagon-like triangulation probe module, and an approximately circular triangulation probe module. Angular measurements of an inclined surface were possible using the double triangulation probe module. The measuring range of the developed laser probe was ±2 mm and the resolution was 2 μm/pixel. The performance tests among the different measurement modules of the developed probe and the commercial circular triangulation laser probe OTM3-03 have been carried out. The measurement uncertainty of the developed laser probe system, with respect to different surface roughness and slope, was generally smaller than ±20 μm within the measuring range using the pentagon-like triangulation probe module with the statistical methodology of skewness (S_k) and kurtosis (K_u) analysis by setting the appropriate threshold values for S_k and K_u, respectively. The developed probe has been integrated with a PC-based 3-axis micro-positioning stage to construct an automatic non-contact 3D measurement system and to digitize the 3D profile of a small complex object.     

红外地球敏感器扫描镜摆角激光动态测试方法

为解决扫描镜摆角实时动态非接触测量问题,基于激光检测技术和CCD探测技术,提出一种红外地球敏感器扫描镜摆角激光动态测试方法,并研制了扫描镜摆角动态测试系统,其可实现扫描镜的摆动频率、零位角、幅值、峰峰值平均等参量的动静态激光非接触测量。介绍了系统的组成和总体结构,着重对扫描镜摆角动态测量理论和大视场、大相对孔径特殊线性扫描光学系统的设计方法进行了分析与探讨,通过建立系统的数学模型,解决了测量数据误差修正与图形处理问题。对测量系统的精度进行了验证,结果表明系统的摆角测量范围为0~±12°,分辨力为0.01°,动静态测量精度优于±0.04°。     

Multi-beam method to increase the stability of bridge deflection measurement

The main limitation to the accuracy of the detection of a bridge deflection using laser-based optical solutions is atmospheric turbulence because of the laser beam propagation in ground proximity. The multi-beam method is presented to increase the stability of bridge deflection measurement. It is based on the use of a four-beam optical system and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, different algorithms for measuring the position of the deflected beam in different optical systems are tested and compared. Based on this comparison, the four-beam method based on the macropixels iteration centroid and four-beam optical system is selected, and an accuracy of 0.16 pixels is obtained by the determination of the beam position in our setup. The proposed method is adopted to detect the bridge deflection and an accuracy of 0.01 mm is gained when the scintillation index C_n² is 3×10⁻⁴ m^−2/3.     

Verification and application of a finite-difference model for quasi-electrostatic scanning impedance imaging

We have previously introduced liquid-contact scanning impedance imaging (SII) as a high resolution, high contrast method for imaging electrical impedance. This technique has shown its potential to measure the impedance distribution of biological tissues. In this paper, a numerical model is developed to describe the SII system based on the finite difference method. Good correspondence can be observed when comparing data simulated using the model with experimental data. The relationships between measurable resolution and system parameters such as height are shown in both simulation results and measurements. It is shown that the numerical model provides a good explanation for experimental results and can also assist in the design of the dual-conductor impedance probe used in this imaging method. Model predictions on both the conductor spacing and the resistor R used in the system have been made indicating their relationships to an empirical notion of resolution. The simulation result of the conductor spacing also gives an insight to the function of the dual-conductor probe. Based on this model, an optimum probe design can be obtained by balancing ultimate resolution with the signal-to-noise ratio by adjusting spacing and resistor values.     

Theoretical analysis of 2D acceleration laser sensor and several design parameters

Having adopted several sets of new technology and techniques, we have developed a new type of laser angle sensor that can be used to measure two-dimensional (2D) angle of moving target. On this basis, a new design for 2D acceleration laser sensor has been advanced. The optics-type sensor can be used to measure 2D acceleration of motion object, and it has high sensitivity, high precision and longer measuring range. Under these design parameters that are given in this paper, the measuring range will achieve 177 g, while its sensitivity is 13.5 s². The experimental results show that the measuring error is not greater than 0.1 g. In this paper, several design parameters and measuring results for 2D acceleration laser sensor are given.     

Determination of the material properties of microstructures by laser based ultrasound

In most applications of MEMS the mechanical properties of the used materials are key parameters for the perfect working of the microsystems. Measuring bulk acoustic waves excited in MEMS structures with ultra-short laser pulses is a powerful method for the accurate and non-destructive evaluation as well as for the characterization of material properties. The pump-probe laser-based acoustic method generates bulk acoustic waves in a thermo-elastic way by absorbing the pump laser pulses. The acoustic waves are partly reflected at any discontinuity of the acoustic impedance. At the surface of the specimen the reflected acoustic pulses cause changes of the optical reflection coefficient, which are measured with the probe laser pulses. Thin membranes are part of numerous microelectromechanical systems (MEMS) like sensors, activators and bulk acoustic wave (BAW) filters for example. The described non-destructive and non-contact method is the right approach for testing such thin and brittle structures like membranes. Results of measurements on freestanding aluminium-silicon nitride multi-layer membranes with total thicknesses in the order of several hundred nanometers are presented and compared with thermo-elastic models and with measurements of the supported case. The measured results are used for the determination of the moduli of the membranes.     

Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique

The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.     

Determination of the octane number of a fuel by the IR spectroscopy method

The near-IR spectroscopy method of control of the octane number (o.n.) of a fuel is studied. An analysis is made of a device developed as an alternative of a measuring system based on a nonselective IR radiation source and of an analyzer based on a laser semiconductor diode. It is shown that the use of the methods of multicomponent regression analysis of spectral data allows measurement of the octane number with an accuracy of S ∼ 0.17 octane number units. The characteristics of the semiconductor laser-based analyzer are investigated and the parameters of radiators are discussed that provide the required sensitivity of the measuring system (up to 10⁻⁴ with respect to optical absorption) in controlling the octane number of a fucl. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 244–248, March–April, 2000.     

Laser spectroscopy methods for probing highly charged ions at GSI

We describe two opposite and partly complementary experimental approaches for performing high-precision laser spectroscopy of dipole-forbidden transitions in highly charged ions. We report on the wavelength determination of the ground state hyperfine transitions in hydrogen-like and lithium-like bismuth ions confined in the experimental storage ring at GSI. Direct comparison of the experimental results with theoretical predictions reveals an agreement of the specific hyperfine-structure splitting difference $\Delta ^{\prime }E$ within the 1- σ confidence interval of the experimental value. Additionally, we discuss an experimental strategy based on ion manipulation and cooling in a cylindrical open-endcap Penning trap to further increase the precision of the previous measurement. Trapping and laser cooling of external produced singly charged magnesium ions is demonstrated. This represents a first step towards sympathetic cooling of simultaneously confined ion species in order to perform laser spectroscopy measurements on highly charged ions nearly at rest. These measurements will offer new prospects in the field of laser-based tests of quantum electrodynamics in strong electric and magnetic fields.     

Subsurface quality of polished SiO2 surface evaluated by quasi-Brewster angle technique

As a surface-sensitive optical method, the quasi-Brewster angle technique is extended to evaluate the subsurface qualities of quartz crystal and fused silica. By measuring the ellipsometry parameters at λ = 900 nm with variable incidence angle, a fitting process is executed using a proper subsurface nanostructure with an exponential porosity distribution. The fitting results predict the surface and subsurface information which are in good agreement with that of the Zygo interference microscope measurements and etching methods. In addition, the shift characteristics of phase change at the Brewster angle of such crystal and non-crystal material are compared and demonstrated.     

Low temperature radio-frequency transverse susceptibility measurements using a CMOS oscillator circuit

A transverse susceptibility (TS) measurement system based on a simple inverter CMOS cell oscillator cross-coupled to a LC tank is presented. The system has been implemented to operate at a Quantum Design Physical Properties Measurement System (PPMS). We introduce several improvements with respect to similar currently operating TS measurement equipments. The electronics have been redesigned to use CMOS transistors as active devices, which simplifies the circuit design and enlarge the tuning range, thus making the proposed electronic block more feasible, predictable, and precise. Additionally, we propose a newly designed sample holder, which facilitates the procedure to change a sample and improves reproducibility of the circuit. Our design minimizes the thermal leak of the measuring probe by one order of magnitude, allowing to measure from 1.8 K in standard PPMS systems, thanks to the use of a low temperature beryllium–copper coaxial cable instead of the conventional RG402 Cu coaxial cable employed in the insert for the PPMS in similar systems. The data acquisition method is also simplified, so that the measuring sequences are implemented directly in the PPMS controller computer by programming them in the Quantum Design MultiVu software that controls the PPMS. We present the test measurements performed on the system without sample to study the background signal and stability of the circuit. Measurements on a Gd₂O₃ calibrating sample yield to the estimation of the system sensitivity, which is found to be on the order of 10⁻⁶ emu. Finally, measurements on a TmCo₂ Laves phase sample with a ferrimagnetic transition temperature around 4 K are described, demonstrating that the developed system is well suited to explore interesting magnetic phenomena at this temperature scale.     

Theoretical analysis of 2D laser angle sensor and several design parameters

Having adopted several sets of new technology and techniques, such as cube-corner prism of higher refractive index, orthogonal holographic grating, non-linear compensation, and fringe fractionization, etc., we have developed a new type of laser angle sensor that can be used to measure two-dimensional angle of moving target. The sensor has high sensitivity, high precision and longer measuring range compared with the original sensor, and its measuring range will achieve ±35°, while its minimum resolution angle is 0.004°. The experimental results show that the measuring error is not greater than ±0.01°. In this paper, several design parameters and measuring results for 2D laser angle sensor are given.     

Trace gas monitoring with infrared laser-based detection schemes

The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO₂-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine samples. PACS 33.20.Ea; 42.62.Fi; 42.72.Ai; 87.64.km; 92.60.Sz     

Predicting the performance data for a fiber laser by measuring the emitted fluorescence power of the end-on pumped fiber

Abstract

A novel method is described that enables the prediction of the main laser parameters (threshold pump power, output power, slope- and extraction efficiency) without having realized the laser itself. The emitted fluorescence power of an end-on pumped fiber is absolutely measured along the fiber. Using specific material parameters of the doped glass and the waveguide attenuation, we calculate the laser properties without taking the resonator losses into account. This approach is extremely useful for fibers with special design parameters. We have used this method to characterize a fiber with a novel design, the M-profile fiber. Combining the results with the measurements on the realized laser, the impact of resonator losses (e.g., tilted fiber endfaces, effects of butt-coupled mirrors) can be inferred and improvements can be undertaken.     

Gas-phase velocity field measurements in dense sprays by laser-based flow tagging

It is demonstrated in this work that gas-phase velocity measurements can be performed in dense sprays by using a new 2D laser-based flow tagging technique. Velocity measurements in dense sprays, such as automotive direct injection (DI) Otto and Diesel sprays, are difficult with conventional techniques because of the high number densities of droplets, the optical thickness of the medium, and multiple light scattering effects. The present flow tagging technique is performed by two consecutive laser pulses, i.e., 'write' and 'read' lasers. The write laser creates a grid of tracer molecules (NO) by inducing a photodissociation process. The tracer molecules are convected with the flow and probed by the read laser after a certain delay. The instantaneous velocity field is determined by time-of-flight analysis.     

结构现场可调的点激光精密测量系统

为了实现激光传感器测头可以根据现场条件来实时改变入射角度,建立了结构可调的点激光测量系统。建立了相机的针孔模型,利用张正友标定算法得到该相机模型的内部参数,定义点激光测量系统中的光心角,推导出利用像点坐标和相机内部参数实时求取光心角公式。建立了点激光测量系统的数学模型,引入点激光测量系统的结构参数:基线距和基准角,利用零平面和两个基准面标定系统结构参数。利用标定得到的系统结构参数进行实时的逆向工程在线测量。实验结果表明:测量系统量程为75mm时,该标定算法最大标定误差≤0.02mm,点激光测量系统的测量误差≤0.06mm,达到精密测量的要求。     

激光位移传感器的光学系统设计

针对目前国内自主研制的激光位移传感器精度低,测量范围小等问题,提出了一种采用光学设计软件预先仿真整个激光位移传感器光学系统的方法。在分析系统各部分的光学特性的基础上,结合具体要求设计了一个激光位移传感器的光学系统,其工作范围为（50±10）mm。采用系统分割的方法,将整个光学系统分为两部分进行设计,第一部分是激光束的整形透镜,要求在有效的工作范围内得到小而均匀的出射光斑,设计结果表明,在测量范围内,光斑大小能够控制在10-1mm量级;另一部分是被测面散射光接收的成像物镜,该系统的特点是物面和像面相对于光轴都有一定的角度,实验结果表明其成像满足Scbeimpflug条件。     

Development of a laser-based measurement system for evaluation of the scraping workpiece quality

A laser-based measurement system for evaluation of the scraping workpiece quality that can eliminate contact-induced measurement errors and increase measurement accuracy is proposed. The laser-based measurement system comprises a light-scattering-type triangulation laser, a computer numerical control (CNC) machine tool, and an analog-to-digital (A/D) card. The triangulation laser measures the depth of the scraping spots and the CNC machine tool locates their position. The 3D data of the scraping workpiece is then drawn using the least squares method. Cast iron and Turcite workpieces can be measured. Five parameters of the scraping workpiece, namely peak points per square inch, percentage of points, distribution of heights of points or depth of surroundings, edge shape of the grooves, and flatness, can be evaluated. The scanning rate and sampling rate of the laser-based measurement system are 100 mm/s and 10 KHz, respectively. In the future, an appliance machine based on the proposed system will be designed for the on-line detection of scraping workpieces.     

基于线结构光的视频内窥镜测量技术

针对视频内窥镜的测量需求，提出了一种基于线结构激光照射的测量技术。采用线激光作为定标光照射物体表面，建立了线结构光成像模型，标定了不同物距时的放大率和图像中线位置间的比例系数。通过构建测量平台计算了物体的几何参数，实验结果表明测量误差在10%以内，能够满足视频内窥镜观测和测量要求。