Evaluation of the light line displacement location for object shape detection

Abstract

The ability for detecting the location of the displacement of a projected light line with subpixel resolution is examined. This evaluation is carried out for measuring a three-dimensional object shape. The technique for measuring the object shape is based on the light line projection. To determine the height data, displacement of the light line is measured on a reference point and on the object surface. This line displacement is measured by approximating the line intensity to a continuous function by the least-squares method, the Gaussian approximation and the Bezier curves method. The light line position is defined by calculating a maximum from this continuous function. To evaluate these three methods it is necessary to know the best accuracy of the experimental results. To achieve this, the results extracted by these methods are compared with a contact method. This contact method is made with a coordinate-measuring machine. The rms error is calculated using data from these three methods and the data from the contact method to carry out this evaluation. Height data are obtained with great accuracy from the method, which has a better rms value. The time necessary for processing a light line using each of these three methods is also presented. In addition to this information, a correlation coefficient is presented giving the deviation of each function generated by these methods. This line projection technique has a great potential because a very simple experimental set-up is used which is inexpensive. This evaluation is tested with complicated objects and its experimental results are presented.     

Impact damage detection in composite plates using deflectometry and the Virtual Fields Method

This paper presents a new method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a “signature” from the measured surface slopes. Firstly, this method is applied to plate specimens using numerical and experimental data. Secondly, damage indicator based on a new application of the virtual fields method to compute local apparent gaps in equilibrium is presented and used to process the measurements on plates. It is shown that the damage indicator is very sensitive, allowing detection of damage that is difficult to identify directly from the strain maps.     

Measurements of the surface tension for R290, R600a and R290/R600a mixture

The surface tensions of R290, R600a and R290/R600a mixture have been measured by the modified differential capillary-rise method. Twenty-two data points for R290 and 21 data points for R600a were obtained in the temperature range between 273 K and 354 K, and 43 data points for R290/R600a mixture on three isotherms of 278 K, 300 K and 320 K were obtained. The experimental uncertainties of temperature and surface tension are estimated to be within 20 mK and 0.2 mN m⁻¹, respectively. Surface tension correlations as a function of temperature for pure R290 and R600a were formulated in the temperature range between 253 K and critical temperature, and the correlation as a function of the composition for R290/R600a mixture was discussed at 278 K, 300 K and 320 K. It is found that the surface tension for R290/R600a mixture can be reproduced by the simple mixing rule by mole fraction with the correlations of both pure components.     

Determination of the refractive index and thickness of holographic silver halide materials by use of polarized reflectances

A method to determine the refractive index and thickness of silver halide emulsions used in holography is presented. The emulsions are in the form of a layer of film deposited on a thick glass plate. The experimental reflectances of p-polarized light are measured as a function of the incident angles, and the values of refractive index, thickness, and extinction coefficient of the emulsion are obtained by using the theoretical equation for reflectance. As examples, five commercial holographic silver halide emulsions are analyzed. The procedure to obtain the measurements and the numerical analysis of the experimental data are simple, and agreement of the calculated reflectances, by use of the thickness and refractive index obtained, with the measured reflectances is satisfactory.     

Light diffraction from rough gratings

Two holographic diffraction gratings with very similar parameters, designed for maximum performance inTM polarization, are investigated, their diffraction efficiency measured, an electron microscopic picture of their surface observed, and numerical simulation of light diffraction done with the surface roughness taken into account. It is demonstrated numerically that a small-scale roughness imposed on the grating surface could increase significantly both scattering and absorption from the surface, this influence being greater in the TM case. A very good coincidence between the numerical and experimental data is obtained in TE polarization, whereas in TM polarization only a qualitative agreement exists.     

Two-dimensional ultrasonic tomography in nondestructive evaluation by using area functions

It is shown that the (normalized) area function based on the Born approximation offers a simple connection between the ultrasonic scattering response and the monochromatic ray sum in X-ray CT (computerized tomography). Because of this simple association, it is possible to apply the ultrasonic signals in the computationally direct and efficient parallel-beam X-ray CT algorithm to reproduce the vertical thickness function of an ultrasonic scatterer. The development of this imaging methodology is demonstrated for flaws of simple geometry; theoretical as well as experimental results for two model scatterers using this imaging technique are reported. Specifically, the area functions for a two-to-one spheroid and a circular cylinder are calculated and applied to a filtered backprojection algorithm of X-ray CT to obtain the vertical thickness function images. These images are then compared with the true vertical thickness functions of the targets based on their geometry. With theoretical data, this method was found to work very well. Even when experimental data containing creeping waves were used, the method produced satisfactory results for objects with continuously smooth surface.     

Measuring the distance and orientation of a planar surface usingnonstructured lighting-3-D measurement system for indoor mobile robots

This paper describes a novel method for measuring the distances to planar surfaces and their orientations. The measurement system consists of a TV camera and two ordinary lamps. The lamps are switched on alternately, and images under each lighting condition are taken. If the two light sources are arranged at appropriate positions with respect to the camera, the peak positions in the two images directly give the surface orientation and the perpendicular distance to the plane. By measuring the two peak positions, this method promises to speed up the acquisition of geometrical information on an entire scene considerably because the distance and orientation can be obtained without analyzing range maps. Since the equipment setup is very simple, the proposed technique will be useful, for example, for real-world robotic applications such as navigation of indoor mobile robots. The experimental results on the error of measurement show that the method is sufficient for such purposes     

Modeling of the temperature field of the casting ladle lining

We propose a method for calculating the temperature field of the casting ladle lining by a modified relaxation method. Given such initial data as the metal temperature in the ladle, the ambient temperature, and the lining structure, this method permits calculating the stationary temperature fields both inside the lining and on the surface of the ladle jacket. The model was tested by comparing experimentally measured temperature values on the surface of the ladle jacket with calculated temperatures. A satisfactory agreement between calculated and experimental temperature values of the ladle surface has been obtained.     

阻尼矩阵与刚度矩阵的一种直接修正方法

提出了一种利用复模态测量数据同时修正有限元阻尼与刚度矩阵的有效方法。借助于矩阵的奇异值分解得到了满足动力方程的最小修正矩阵。该方法有一个简洁的表达式,修正过程简单而且容易实现,数值试验表明修改后的结构参数能准确地同试验值吻合。     

Modelling the fracture of cementitious materials

The crack band and the fictitious crack line models of the fracture process zone in cementitious materials are discussed. The two methods are quite similar. However, the fictitious crack model is shown to lend itself to a simple K-superposition method which makes use of known analytical expressions. This method is shown to give very similar results to a finite-element analysis of the fictitious crack model and has the advantage that it can be programmed for a personal computer. The predictive capability of the fictitious crack model is demonstrated by comparison of the experimental load-deflection curve for a small notch bend mortar specimen with a theoretical curve calculated from data obtained from larger beams. It is suggested that the RILEM test method for the determination of the fracture energy should be used also to establish a bilinear stress-displacement relationship for the strain-softening of the fracture process zone.     

Thermal Resistance Formulation of Fourier Equation and Its Application in the Study of Inhomogeneous Materials and Inverse Problems

In this work, considering that all the thermal properties of a sample depend on the position, it is shown that the Fourier heat transport equation can be written in terms of just the square of the thermal effusivity, by introducing the thermal resistance as a new variable. The conditions, in which analytical solutions of this equation can be obtained, are discussed. Based on these results, an inversion method is proposed to retrieve the profile of the thermal property profiles, if the surface temperature is provided. The method requires the assumption of a local thermal-effusivity profile, such that the temperature profile can be analytically obtained, to generate a global thermal-effusivity profile, which is independent of the initial assumed profile. Applying this method to a pair of simple but representative cases of one-dimensional layered systems, the accuracy and stability of the method is verified. In particular, the noise sensitivity is investigated by carrying out the inversion procedure with white Gaussian noise added to the simulated experimental data. The proposed approach could be useful for the development of methodologies to interpret experimental data and to retrieve the in-depth variations of thermal properties of materials.     

道路交通噪声源强快速建模方法

道路交通噪声源强的预测是道路交通噪声预测的关键。由于车辆状况、道路状况等在我国具有不同的特点;因而在采用国外道路交通噪声源强模型时将导致准确性降低。建立源强模型通常采用的实验方法对场地要求严格,样本数量需求巨大,不易获得本地模型。基于标准实验情况建立的模型不一定适用于复杂的城市交通流。为此,提出一种简单快速建立符合本地城市交通特点模型的方法,该方法以实测交通流数据计算观测点噪声,通过优化算法求解最优参数,确定本地化源强模型。该方法利用多辆车共同作用得到的等效声级,反演得到单车模型,既包含了丰富的样本,又节省测量时间。以北京选取道路的实践为例,建立模型并验证,结果表明本方法快速易行,准确性高。     

Single-shot surface profiling by local model fitting

A new surface profiling algorithm called the local model fitting (LMF) method is proposed. LMF is a single-shot method that employs only a single image, so it is fast and robust against vibration. LMF does not require a conventional assumption of smoothness of the target surface in a band-limit sense, but we instead assume that the target surface is locally constant. This enables us to recover sharp edges on the surface. LMF employs only local image data, so objects covered with heterogeneous materials can also be measured. The LMF algorithm is simple to implement and is efficient in computation. Experimental results showed that the proposed LMF method works very well.     

A simple method for predicting the chloride diffusivity of cement paste

A simple method for predicting the chloride diffusivity of cement paste is presented. In this method, cement paste is modeled as a two-phase composite material, consisting of solid matrix and pore space. By incorporating the classical percolation theory into the effective medium approach, an explicit solution is formulated for the chloride diffusivity of cement paste. Two parameters involved in the solution are determined by fitting the solution to experimental data. After the validity of the simple method is verified with experimental results obtained from the literature, the effects of the water/cement ratio and the degree of hydration on the chloride diffusivity of cement paste are evaluated in a quantitative manner. The paper concludes that the proposed simple method can predict the chloride diffusivity of cement paste with reasonable accuracy.     

Retention of ionizable compounds in reversed-phase liquid chromatography. Effect of the ionic strength of the mobile phase and the nature of the salts used on the overloading behavior

The retention mechanism of the protonated cation in propranolol chloride on C18-Xterra was investigated using mobile phases of various compositions. Accurate adsorption data were measured by frontal analysis, with a mixture of methanol and water (25% methanol), with no salt, as the mobile phase. The experimental isotherm has at least two inflection points, at concentrations of about 0.2 and 6.0 g/L, respectively. This precludes the modeling of these data with a simple convex-upward isotherm (e.g., Langmuir). The adsorption energy distribution or relationship between the number of sites on the adsorbent surface and the energy of adsorption on these sites was calculated by assuming Moreau isotherm behavior (S-shaped isotherm). This model has never been applied to describe the surface heterogeneity of any RPLC adsorbent. The calculation converged toward a bimodal energy distribution. Accordingly, the bi-Moreau model is the simplest theoretical model accounting for the adsorption data of propranolol from a mobile phase without salt. The complex-overloaded band profiles of propranolol measured in the presence of increasing concentrations of a supporting salt (KCl) in the mobile phase demonstrate that the same isotherm model applies also under these conditions, as was merely assumed in a previous work. The elution band profiles of propranolol calculated with the bi-Moreau isotherm model for solutions of salts of different natures (CaCl2, CsCl, Na2SO4) in the same mobile phase agree very well with the experimental band profiles.     

Data assimilation-based state estimation of composites during molding

Monitoring methods used to observe the molding process of carbon fiber-reinforced plastic (CFRP) facilitate the development of high-quality products. However, current monitoring methods provide only localized state information, and estimating the state of the entire material is difficult. This study proposes a method for estimating the overall state of CFRP during molding based on data assimilation, which integrates theoretical and experimental values. In this method, three types of specimens with different thermal conductivities were considered, and the temperatures throughout each specimen during molding were estimated by data assimilation of surface temperatures measured using thermocouples. To validate the accuracy of this method, the temperatures estimated by data assimilation were compared with those obtained using numerical simulations without data assimilation. The experimental results of all the specimens showed that data assimilation can be used to accurately estimate the surface temperature. The proposed method is therefore effective for monitoring composite molding processes.     

Orthogonal frequency coded filters for use in ultra-wideband communication systems

The use of ultra-short pulses, producing very wide bandwidths and low spectral power density, are the widely accepted approach for ultra-wideband (UWB) communication systems. This approach is simple and can be implemented with current digital signal processing technologies. However, surface acoustic wave (SAW) devices have the capability of producing complex signals with wide bandwidths and relatively high frequency operation. This approach, using SAW based correlators, eliminates many of the costly components that are needed in the IF block in the transmitter and receiver, and reduces many of the signal processing requirements. This work presents the development of SAW correlators using orthogonal frequency coding (OFC) for use in UWB spread spectrum communication systems. OFC and pseudonoise (PN) coding provide a means for UWB spreading of data. The use of OFC spectrally spreads a PN sequence beyond that of code division multiple access (CDMA) because of the increased bandwidth providing an improvement in processing gain. The transceiver approach is still very similar to that of a CDMA but provides greater code diversity. Experimental results of a SAW filter designed with OFC transducers are presented. The SAW correlation filter was designed using seven contiguous chip frequencies within the transducer. SAW correlators with a 29% fractional bandwidth were fabricated on lithium niobate (LiNbO3) having a center frequency of 250 MHz. A coupling-of-modes (COM) model is used to predict the SAW filter response experimentally and is compared to the measured data. Good correlation between the predicted COM responses and the measured device data is obtained. Discussion of the design, analysis, and measurements are presented. The experimental matched filter results are shown for the OFC device and are compared to the ideal correlation. The results demonstrate the OFC SAW device concept for UWB communication transceivers.     

Simultaneous determination of the optical constants and thickness of very thin films by using soft-x-ray reflectance measurements

A nonlinear, least-squares curve-fitting method is described that simultaneously determines the optical constants and the thickness of a very thin (? 100-?) film from reflectance versus angle of incidence (R - θ) data measured in the soft-x-ray region. The method is applied to R - θ data obtained for very thin, sputtered films of carbon (65 ? thick) and gold (94 ? thick) at photon energies of 60-900 eV. The results show that the present method is capable of accurately determining the thickness of very thin films even for transparent materials, and that the obtained optical constants are in good agreement with values reported for films with a thickness of 1000 ?.     

A simple experimental arrangement for measuring the vapour pressures and sublimation enthalpies by the Knudsen effusion method: Application to DNA and RNA bases

We measured the vapour pressure of several DNA and RNA bases—uracil, adenine, guanine, thymine and cytosine—in the 300–450 K range. In each case the sample mass loss rate was measured as function of temperature with a simple setup consisting of a commercial film deposition system and a homemade oven. Afterwards vapour pressure values were extracted from these data using the Knudsen effusion method. Sublimation enthalpy values, obtained from vapour pressure data by applying the Clausius–Clapeyron equation, are in very good agreement with literature values. The results suggest that crystal-based film thickness monitors may be useful in on-line cross-section measurements, monitoring the gas target thickness. They also show the viability of using this oven for producing a biomolecular gas target.