Robustness of Objective and Subjective Speckle Patterns in the Speckle Strain Gauge

The robustness to rigid body object motions of three optical systems used in the speckle strain gauge were experimentally investigated and compared with analytical results of the correlation. It was found that an out-of-plane motion of the object damaged the reliability of the strain measure when recording the objective speckle patterns while subjective speckle patterns were more robust. Besides out-of-plane object motions, the robustness of a free-space geometry and an afocal imaging configuration are approximately the same, while a telecentric imaging system is more robust to rigid body motions but more sensitive to deformation gradients (basically in-plane rotation and tilt). Results from a measurement of the relaxation in a lead-tin alloy used in organ pipes is also presented.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Wako, Saitama, Japan.     

Design of a hybrid diffractive/refractive achromatized telecentric f·θ lens

The design of a hybrid diffractive/refractive achromatized telecentric f·θ lens with a field of view (FOV) 50° and an effective focal length of 750 mm is presented. The optical stop is placed at the front focal plane so that it is a telecentric system. The design is based on a traditional refractive counterpart, and the designed system consists of a hybrid diffractive/refractive lens and four refractive lenses. The designed f·θ lens shows a considerable reduction in weight with a simplified structure, and exhibits superior performance compared to the refractive system. It is emphasized that the designed f·θ lens can be applied to modern color scanning systems that operate in the visible wavelength range with high performance. It can also be applied to high-energy scanning systems. When applying the designed hybrid diffractive/refractive f·θ lens to the high-energy scanning system, a big laser operating in one longitudinal mode can be replaced by a small multi-mode laser, and the scanning system can be simplified greatly with the accuracy improved.     

Single-lens 3D digital image correlation system based on a bilateral telecentric lens and a bi-prism: Systematic error analysis and correction

Recently, we proposed a single-lens 3D digital image correlation (3D DIC) method and established a measurement system on the basis of a bilateral telecentric lens (BTL) and a bi-prism. This system can retrieve the 3D morphology of a target and measure its deformation using a single BTL with relatively high accuracy. Nevertheless, the system still suffers from systematic errors caused by manufacturing deficiency of the bi-prism and distortion of the BTL. In this study, in-depth evaluations of these errors and their effects on the measurement results are performed experimentally. The bi-prism deficiency and the BTL distortion are characterized by two in-plane rotation angles and several distortion coefficients, respectively. These values are obtained from a calibration process using a chessboard placed into the field of view of the system; this process is conducted after the measurement of tested specimen. A modified mathematical model is proposed, which takes these systematic errors into account and corrects them during 3D reconstruction. Experiments on retrieving the 3D positions of the chessboard grid corners and the morphology of a ceramic plate specimen are performed. The results of the experiments reveal that ignoring the bi-prism deficiency will induce attitude error to the retrieved morphology, and the BTL distortion can lead to its pseudo out-of-plane deformation. Correcting these problems can further improve the measurement accuracy of the bi-prism-based single-lens 3D DIC system.     

基于机器视觉检测的大视场双远心光学系统设计

基于机器视觉的大视场非接触精密检测的需求,参照卡尔蔡司公司的TVM150／11／0．1远心镜头指标,设计了一款大视场双远心光学系统。采用了近对称的结构和半部设计的设计思路,较好地控制了畸变和倍率色差,实现了长工作距离（大于160mm）、大视场（物方视场达到西150mm）、低畸变（最大畸变小于1个像素）、高分辨（在2／3″CCD全视场200lp／mm处光学传函优于0．3）、宽景深（设计景深达到了±38mm）和双远心系统的设计要求。着重分析了系统各器件偏心对畸变的影响,通过对关键器件的偏心控制,有效地抑制了由于生产制造过程中的偏差产生的随机畸变对测量误差的影响,从而为实际生产提供了理论指导。     

基于同心圆光栅的远心三维测量系统

针对条纹投影术对简化系统模型、降低运算量并有效抑制误差扩散等要求,提出并构造了一种基于同心圆光栅的广义远心三维测量系统。该系统利用菲涅尔透镜与投影仪产生平行光线建立线性投影模型,降低运算复杂度,利用傅里叶变换得到经物体高度调制的初始相位信息,同时结合同心圆光栅标定技术的并行运算,通过逐点计算获取真实相位。全过程只需对一个系统参数进行标定,并且摆脱解相过程,有效抑制了误差扩散。对最大高度20 mm的物体进行形貌测量,最大误差0.23 mm,相对误差仅为1.15%。     

An experimental method for eliminating effect of rigid out-of-plane motion on 2D-DIC

The out-of-plane motion is one of the most important factors that affect the precision of two-dimensional digital image correlation (2D-DIC). In this paper, a novel solution is presented to improve conventional 2D-DIC by eliminating the effect of out-of-plane motion, including translation and rotation. Firstly, an experimental technique using two projected laser strips is proposed to measure the out-of-plane motion of a planar specimen. A theoretical model is then established to predict the pseudostrains caused by out-of-plane motion based on the pin-hole imaging model. Using the measured out-of-plane displacement, the captured deformed images used in 2D-DIC are amended to eliminate the effect of out-of-plane motion by the theoretical model. Finally, two experiments were conducted to validate the effectiveness of the proposed method. Results indicate that application of the proposed method can effectively eliminate the errors caused by out-of-plane motion.     

大口径光学非球面元件拼接优化及精度验证

针对磨削阶段大口径光学非球面元件拼接测量精度不高的问题,提出一种基于两段拼接的优化算法。首先根据多体系统运动学理论、斜率差值及逆推法建立两段面形轮廓的拼接数学模型;其次针对拼接算法中工件运动量和运动误差对拼接精度的影响,仿真分析了350mm非球面工件的两段拼接。仿真结果表明,随着平移误差增大,拼接误差明显增大,而当控制旋转角度在8°以内、平移量在10mm以内、旋转误差在60′以下及平移误差在3μm以下时,拼接误差的标准偏差值在0.2μm波动;最后利用Taylor Hobson轮廓仪和高精度辅助测量夹具对120mm口径的非球面光学元件进行测量实验并研究工件运动量对拼接测量精度的影响。实验结果表明,当控制平移量在10mm以内和旋转角度在8°以下时,拼接误差的标准偏差值在0.2~0.6μm之间,能满足磨削阶段光学元件亚μm级精度的面形检测要求。     

Free-space optical links for board-to-board interconnects

We describe two free-space optical links for multichannel optical interconnects. The targeted aggregate data rate is 240 Gb/s. In one implementation we use a unique implementation of telecentric optics and achieved an optical link that is simple, robust, and modular. We describe a simple, inexpensive telecentric lens that can accommodate all optical channels within a 1-mm-diameter sweet zone. We also describe the performance of an optical link with a 4×4 array of VCSELs and matching detectors. The integrity of the optical link is not significantly degraded with a>±2 mm translational misalignment between the VCSEL and detector arrays. With the telecentric optical link, we need only two low-bandwidth, single-axis active servomechanisms to compensate for static tilt and possibly low-frequency thermally-driven shift between the transmitter and receiver arrays. In the other implementaion we use two matching arrays of 1×12 optical fibers. Data are coupled optically through an air gap of 2 mm by means of a pair of collimating microlens arrays that are aligned to one another via precision mechanical subassemblies. We describe a simple, inexpensive, and robust mechanical coupling for the optical link achieved by using miniature high-flux magnets.     

Brownian Motion with Dry Friction

A small object (Solid or droplet) is placed on a horizontally vibrating plate, imposing an acceleration γ(t) in the form of a white noise. The object experiences dry friction (due to soild/solid interaction, or to contact angle hysteresis in the case of a droplet). The object is driven by a force γ(t) – Δσ(t) where σ(t), =±1, depending on the sign of the velocity. We discuss the motion at two levels: (i) in terms of simple scaling laws, (ii) by a propagator technique. (a) When Δ is below a certain crossover value Δ*, we expect an unperturbed (Langevin) Brownian motion. (b) When Δ > Δ*, we expect a reduced diffusion coefficient proportional to Δ⁻⁴ for small Δ.     

A comparison of 2D and 3D PIV measurements in an oblique jet

A stereo PIV (SPIV) acquisition and analysis system was developed to measure three velocity components in planar flow fields. The analysis software is based on a third order mapping function method. The system was calibrated by imaging a square grid in three measurement planes with two Kodak Megaplus cameras oriented at 30 to the bisector between them. The camera images were dewarped into real coordinates by employing a set of transform matrices computed for each calibration plane. Bias and rms errors were determined by comparing displacements measured directly with displacements estimated from the dewarping and recombination algorithm. The bias errors in the directions parallel with the measurement plane were negligible while the bias in thez direction was about 0.6 pixel. The rms errors, 0.2–0.3 pixels, were largest in thez direction. These errors were thought to result from limitations in the calibration method. The SPIV system was tested in a two-dimensional oblique jet with Reynolds number of 1800. The three dimensional results were taken in a vertical (x, y) plane parallel with the jet span. The SPIV results were compared with LDV data and two-dimensional PIV data obtained in a vertical (y, z) plane of the same jet. The SPIV measurements yielded accurate values for the in-plane mean and rms velocity components. The measured out-of-plane mean component was underestimated due to the bias error mentioned above. The rms component was accurate in part of the field but overestimated in another part due to local variations in rms error. It is expected that in the future, the out-of-plane errors can be minimized by improving the calibration and transformation procedures.     

Microscopic structured light 3D profilometry: Binary defocusing technique vs. sinusoidal fringe projection

This paper compares the binary defocusing technique with conventional sinusoidal fringe projection under two different 3D microscopic profilometry systems: (1) both camera and projector use telecentric lenses and (2) only camera uses a telecentric lens. Our simulation and experiments found that the binary defocusing technique is superior to the traditional sinusoidal fringe projection method by improving the measurement resolution approximately 19%. Finally, by taking the speed advantage of the binary defocusing technique, we presented a high-speed (500 Hz) and high-resolution (1600×1200) 3D microscopic profilometry system that could reach kHz.     

Deformation, displacement and vibration investigations in manufacturing applications using a new hologram interferometry technique

The use of sandwich hologram interferometry makes it possible to investigate objects of interest to an engineer that is was not possible to investigate before. The paper presents the sandwich technique as well as some different applications of the technique. Static deformation of a milling machine and a dynamic study on a vibrating hand-drill are included. Another application is a study of a test object one metre in length, where the object was removed from the holographic set-up between exposures and holes were drilled in one wall of the object. The deformation around the drilled holes could be studied, after that a second recording of the object repositioned in the holographic set-up was performed. Finally it is shown how an in-plane rigid body motion of 1 mm could be compensated for, and a tilt of 1.5 × 10^-3 degrees of a special test object evaluated in spite of the large translation motion.     

Simultaneous Measurement of Refractive Index and Thickness of Transparent Plates by Low Coherence Interferometry

We demonstrate a novel low coherence Michelson interferometer which can provide simultaneous measurement of the refractive index and thickness of transparent plates used as a measured object. Unlike the existing low coherence interferometers reported so far, either an object or a focusing lens aligned on the signal arm is scanned repeatedly by a precise translation stage in synchronization with movement of a reflection mirror on the reference arm. The so-called object or lens scanning method gives us two measured quantities a movement distance of the stage between two light focusing states on the front and rear planes of an object and the corresponding optical path difference. These two measured quantities, result in desirable values of the index and thickness of the object with a short calculation. The measurement accuracy of ≤0.1% is expected for a thickness of more than 1 mm. In the experiment using the object scanning method, the accuracy of 0.3% or less was successfully attained for nearly 1-mm thick plates of fused quartz, sapphire, LiTaO₃ and slide glass.     

Rotational motion in sensorless freehand three-dimensional ultrasound

Freehand three-dimensional ultrasound is usually acquired with a position sensor attached to the ultrasound probe. However, position sensors can be expensive, obtrusive and difficult to calibrate. For this reason, there has been much research on alternative, image-based techniques, with in-plane motion tracked using conventional image registration methods, and out-of-plane motion inferred from the decorrelation between nearby B-scans. However, since out-of-plane motion is not the only source of decorrelation, image-based positions determined in this way suffer from cumulative drift errors. In this paper, we consider the effect of probe rotation on correlation and how this affects the position estimates. We then present a novel technique to compensate for out-of-plane rotations, by making use of orientation measurements from an unobtrusive sensor. Using simulations and in vitro experiments, we demonstrate that the technique is able to reduce the drift error in elevational positioning by 57% on average.     

Translational and rotational motions of a diatomic molecule enclosed in a solid matrix

The hamiltonian for a molecule enclosed in a cavity may be written H = H ^R(θ) + H ^T(r) + U ^RT(θ, r), where θ and r denote the molecular orientation and the displacement of the centre of mass. The crystalline potential seen by the guest molecule can be explicitly calculated on the basis of atom-atom and electrostatic multipolar interactions, by using an nth-order gradient formula in the spherical representation. We take a N ₂ molecule encaged in β-quinol clathrate as our model system, and solve variationally the Schrödinger equation for H to clarify the translation-rotation coupling. Energy levels of H are obtained as a function of the height of the hindering potential for rotation, by modifying the strength of the electrostatic multipolar interaction. Three limiting cases of H ^R are important: (a) libration around the Z-axis, (b) free rotation, and (c) an oscillational rotation whose equilibrium orientation is perpendicular to the Z-axis. The constrained translation under consideration is an anharmonic and almost spherically symmetric oscillation. The Pauli principle must be applied to the eigenstate of H. Excepting the case (a), translational states of H are different for different nuclear spin species, and higher-order effects of U ^RT on these states are significant. For p-N₂, some modes of motion interchange if the rotational motion changes from case (a) to case (c). If the constraining potential for translation is steeper, the effect of U ^RT will become smaller. The anharmonicity involved in H ^T is not negligible in discussing this effect.     

The effect of external electric fields on molecular liquids and induced translational motion

A computer simulation is reported of the enantiomer S CHBrClF subjected in the liquid state to intense external fields of force : i) uniaxial electric field E_Z; ii) circularly polarised field at optical frequencies. The molecular dynamics are quantified in detail at field - on equilibrium in case i) using a range of auto correlation functions. The foremost result of the investigation is that the simple uniaxial field E_Z makes the sample $\text{translate}$ in a well defined direction. The direct effect of E_Z on an isolated molecule of S-CHBrClF is purely rotational, but intramolecular rotation/translation coupling converts this rotation into coherent centre of mass translation. This gives rise to direct, $\text{laboratory frame}$, cross correlations of the type <v(t)$\text{J}$^T(o)> where $\text{v}$ is the molecular centre of mass translational velocity and $\text{J}$^T the transposed molecular angular momentum vector. (The existence of these invalidates the classical theory of the Kerr effect.) The molecular dynamics of the hypothetical chiral ion S-CHBrClF^? are looked at with a view to corroborating the predictions by Baranova et al. concerning their response to electric field treatment. Despite the inherent instability of such an ensemble of like-charged ions the simulation can be used to produce a range of auto and cross-correlation functions with which to characterise the ionic dynamics. The effect of treating the ionic ensemble with a field E_Z is reported briefly in terms of the non-vanishing ensemble averaged centre of mass velocity <v_Z&>;.The induced translation in an electric field may be demonstrated on most liquids using a simple experimental set up. Its importance in optically active systems is such that it may be used to separate a racemic mixture into its enantiomers, the translational motion induced in the one enantiomer is necessarily, by symmetry, opposite to that induced in the other enantiomer. The observation therefore has technological importance. Other applications are discussed.     

Automatic 3D scanning surface generation for microphone array acoustic imaging

This work presents a new technique for automatically generating the 3D scanning surface for acoustic imaging using microphone arrays. Acoustic images, or maps, of sound coming from spatially distributed sources, may be generated from microphone array data using algorithms such as beamforming. Traditional 2D acoustic maps can contain errors in the near-field if the object being imaged has a 3D shape. It has been shown that using the 3D surface geometry of an object as a scanning surface for beamforming can provide more accurate results. The methods used previously to generate this 3D scanning surface have either required existing CAD (Computer-Aided Design) models of the object being acoustically imaged or have required separate equipment which is generally bulky and expensive. The new method uses one or more cameras in the array, a data projector, and structured light code to automatically generate the 3D scanning surface. This has the advantage that it is inexpensive, can be incorporated as an add-onto existing microphone arrays, has short scan time, and is capable of being extended to imaging dynamic scenes. This technique is tested using beamforming and CLEAN-SC (CLEAN based on spatial Source Coherence) algorithms for a spherical array and an Underbrink multi-arm spiral array. For sound sources located about 1.2 m from the array, the mean position errors obtained are 6 mm. This is a quarter of the diameter of the mini-speakers being used as a sound sources.     

On search and identification of tracks due to short-lived SHE nuclei in extraterrestrial crystals

The unique approach for search and unambiguous identification of short-lived (T_1/2=10³–10⁷ years) superheavy nuclei in cosmic-ray products of the recent nucleosynthesis in our Galaxy are discussed.It is based on: (a) the ability of non-conducting crystals to register and to store for many million years the tracks due to fast nuclei with atomic number Z20 (“fossil” tracks);(b) calibrations of the said crystals with accelerated heavy ions (20Z92) and on revealing the volume etchable track length (VETL) of the fast nuclei coming to rest inside crystals—both of fossil and “fresh” tracks—to determine the charge distribution of cosmic-ray nuclei tracks and(c) the so-called “four-zone” model of tracks in crystals (and also glasses) which provides not only the VETL track length dependence for 20Z92 nuclei but also demonstrates the regular annealing behavior of VETL of 20Z92 nuclei in a broad temperature interval.This approach was first applied in the early 1980s to investigate the “fossil” tracks due to 22Z92 cosmic-ray nuclei in olivine crystals from meteorites-pallasite Marjalahti and Eagle Station.The discovery of Th–U cosmic-ray nuclei tracks in 1980 was unambiguously confirmed by calibrations of the same crystals with ²³⁸U, ¹⁹⁷Au and ²⁰⁸Pb accelerated ions in the late 1980s. More than 1600 tracks due to cosmic-ray actinide nuclei were measured during the last two decades of the 20th century.Also, 11 anomalously long tracks (track length exceeds by a factor (1.6±0.1) the track length due to Th–U nuclei were measured. The detailed analysis shows that at least 5 of these tracks could not be attributed to the Th–U nuclei. It means that now we have a preliminary proof on the existence Z110 nuclei in cosmic-rays. The abundance is Z110/Th–U=(1–3)×10⁻³ in Z110 freshly formed cosmic-rays (time interval 10³–10⁷ years).The method proposed can provide the necessary and sufficient conditions for the discovery of Z110 nuclei in nature.     

αs from τ: a discussion of theoretical errors

Nominal errors on the determination of α_s(m_Z) from τ decay are so small that it may appear that this is the best method of measuring the strong coupling. While I agree that this way of determining α_s(m_Z) is a very good one, I think that the theoretical errors involved are larger than often asssumed, even if the QCD sum rule framework is accepted.     

D2O‐catalyzed proton transfer selectivity of 4 different NH protons in the same molecule

When N‐benzyl‐N′‐methylacetamidinium hydrochloride (pKa=11.8) is dissolved in D₂O/DCl(1 M), an equilibrium of 2 54:46 stereoisomers in an ~2:1 =(R)N^δ+H(D) D/H ratio is formed. Therefore, 2 R =N‐benzyl (E and Z) and 2 R =N‐methyl (E and Z) groups attached to the corresponding H(D) (Z and E) for a total of 8 ¹H‐NMR signals are observed. Consequently, their rates of H and D transfer to D₂O can be measured by means of the ¹H‐NMR broadness (line shape) of the =(R )N^δ+H doublets and =(R )N^δ+D broad singlets. Acidity selectivity is observed for both processes. In fact, the relative proton and deuterium transfer rates follow the acidity order: =(PhCH₂)N^δ+‐H(E) > =(PhCH₂)N^δ+‐H(Z) > =(Me)N^δ+‐H(E) > =(Me)N^δ+‐H(Z). Proton transfer rates are in the range of 8 to 0.5 s^‐1 with α = .92. This tendency is independently supported by the observed experimental chemical shift deuterium isotopic perturbation. The rate‐limiting step for proton exchange is the breaking of the hydrogen bond due to the fast amidine reprotonation (~10¹¹ s). =(R)N^δ+D/=(R)N^δ+H equilibration is reached at ~80 s, and it can be measured by the relative =(R) N^δ+H versus =(R) N^δ+D signal integrations. The equilibrium of the 4 =(R)N^δ+H(D) centers is shifted toward deuterium, but they are further shifted in the more basic centers. Equilibrium is completely shifted toward D in the 4 centers when OD^? contributes with the exchange process at pD > 3.