Optoelectronic method of contactless reconstruction of the surface profile of complexly shaped three-dimensional objects

An optoelectronic method of contactless reconstruction of the surface profile of complexly shaped threedimensional objects with the use of structured light, phase triangulation, and a steady-state method of identification of interference patterns by means of stepwise shift is considered. Analytic estimates as well as estimates obtained experimentally (using the newly developed measurement system) of the error in measurements of surface profile with the use of the proposed method are presented.     

Testing of rod objects by grazing-incidence interferometry: experiment

A grazing-incidence interferometer for the testing of technical surfaces for macroscopic surface deviations is described. Computer-generated holograms serve as beam splitters and references for the workpieces tested. The sensitivity of the interferometer depends on the period of the computer-generated holograms. The method is demonstrated at a rod object of convex profile. Using phase-stepping techniques, the grazing-incidence interferometer provides fast measurements of the entire mantle surface of the test sample with submicrometer precision.     

Design and manufacture of a gradient-index axicon

A gradient-index axicon with its initial focus offset from the back surface was designed with the thin-lens approximation. Two samples were fabricated by means of the time-varying boundary condition diffusion method, which is based on the modified quasi-chemical diffusion model. Intensity profile measurements were taken along the focal region of the axicons. The samples produced extended line foci. From the intensity measurements, the central spot widths and back focal lengths were determined. The peak widths matched theoretical predictions made with the diffraction theory for the samples and showed good agreement with the predicted widths for a pseudo-Bessel beam, showing that the axicon produced a pseudo-diffractionless beam.     

非球面表面形状的线测量技术

描述了一种在超精密磨削机床上基于误差分离法的非球面表面形状精密测量系统.首先,论述了一般用于平面形状测量的两点法不能直接用于非球面形状测量的原因在于测头的设置误差会引起很大的形状测量误差.提出了先通过两点法测量平面形状得出机床的运动误差,然后对测量非球面形状的另外一个测头的输出进行补偿以得出正确的非球面形状.用此系统测量了一个直径为30 mm的非球面镜头的表面形状.     

Modeling of Transient Thermal Contact Resistance out of Conjugate Gradient Method

Temperature profile at contacting pairs of any material combination is crucial in many engineering applications. A new experimental approach is suggested to estimate the contact heat transfer coefficient as well as the thermal contact resistance. This method is based on temperature infrared measurements of contact bodies and then solve the inverse problem with conjugate gradient method. Different affecting parameters are studied namely; surface roughness, presence of interlayer, applied pressure and bodies temperature difference. The time dependant heat transfer coefficients resulting from the proposed method need to be validated by a computer model. Close results are shown with slight deviation by the increase of the applied pressure and the temperature difference.     

Fast scanning method for one-dimensional surface profile measurement by detecting angular deflection of a laser beam

A fast scanning method for one-dimensional surface profile measurement is proposed. The profile is measured by integration of a slope distribution of the surface obtained from angular deflection of a scanning laser beam. A scanning optical system that consists principally of a spherical concave mirror and a rotating scanner mirror has reasonably low cost and is insensitive to mechanical vibration because of its high-speed scanning, of the order of milliseconds. A surface profile of a polygonal mirror along a 5-mm width was measured with the scanning method and with an interferometer. The root-mean-square difference between the two measured results is 0.98 nm.     

Surface gradient integrated profiler for X-ray and EUV optics

A new ultraprecise profiler has been developed to measure, for example, asymmetric and aspheric profiles. The principle of our measuring method is that the normal vector at each point on the surface is determined by making the incident light beam on the mirror surface and the reflected beam at that point of coincident. The gradient at each point is calculated from the normal vector, and the surface profile is then obtained by integrating the gradients. The measuring instrument was designed in accordance with the above principle. In the design, four ultraprecise goniometers were applied to adjust the light axis for normal vector measurement. The angle-positioning resolution and accuracy of each goniometer are, respectively, 0.018 and 0.2 μrad. Thus, in the measuring instrument, the most important factor is the accuracy of the normal vectors measured by the goniometers. Therefore, the rotating angle-positioning errors were measured and calibrated. An elliptical profile mirror for nanometer hard-X-ray focusing was measured, and compared with the measured profile using a stitching interferometer. The absolute measurement accuracy of approximately 5 nm (peak-to-valley) was achieved. Then the measurements of 1000-mm-long flat, spherical and parabolic mirrors were demonstrated. The surface profiles of the mirrors were obtained by integrating the interpolated gradient.     

Image-plane measurements of coexistence curve diameters

The diameter of the coexistence curve has been measured for several fluids to determine differences from linear form. The experimental method consists of optical interference measurements in a Mach-Zehnder interferometer supplemented by measurements of deviation in a hollow prism. The fluid sample is contained in a temperature-stabilized cell in one branch of the interferometer. A variation in cell temperature causes the density profile within the cell to change, resulting in a change of the interference pattern, which is monitored photographically. From the relation of this pattern at any temperature to the pattern at the critical temperature, information on the refractive indices of the liquid and vapor phases is obtained. This information is combined with measurements of the Lorentz-Lorenz coefficient to obtain liquid and vapor densities along the coexistence curve. The average of liquid and vapor densities is analyzed in terms of RG theory. The results of the experiment yield information on three body interactions. Studies have been completed on ethane, ethylene, hydrogen, and fluoroform.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

基于粗大误差估计的表面测量稳健滤波方法研究

将粗大误差估计理论与高斯滤波方法相结合,提出了一种新的表面测量稳健方法。首先由kσ准则对表面轮廓中的畸形信号进行判定、识别、修正,详细论述了相应算法;然后由移动平均逼近方法实现高斯滤波,建立表面轮廓中线;最后由原始轮廓和得到的稳健滤波中线分离出表面粗糙度轮廓,实现了稳健滤波目的。该方法算法简单、易于实现,对表面畸形信号能够较好地抑制。     

The non-stationary response of flexible pavements to moving loads

In this paper, the pavement surface deterioration is investigated based on field measurements of surface roughness profiles obtained in Sweden. A predictive function for surface deterioration, based on average gradient of yearly measurements of the road surface profile in Swedish road network, is proposed. In order to characterise the dynamic loads induced on the pavement by moving traffic a quarter car model is used. Afterwards a non-stationary stochastic approach is used to obtain the yearly response of the pavement to moving loads. The solution is in frequency–wavenumber domain and is given for a non-stationary random case as the pavement surface deteriorates in pavement service life thus influencing the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined for a specific case of quarter car model and pavement structure. The results showed approximately a 100% increase in the dynamic component of stresses induced in the pavement.     

Depth profile analysis of solar cells by Secondary Neutral Mass Spectrometry using conducting mesh

Depth profile analysis of solar cells was performed by Secondary Neutral Mass Spectrometry (SNMS), which is a suitable technique for quantitative analysis of the composition of layered structures. However, in the case of insulating samples or samples prepared on non-conductive substrates (e.g. microslide, oxidized silicon wafer) the charge accumulation on the sample surface due to ion beam bombardment can cause a serious problem by destroying the resolution of depth profile. The high frequency (HF) mode of electron-gas SNMS seems to be a good solution for this problem. Another method to prevent the charge accumulation on a sample surface can be a conducting mesh (e.g. copper, stainless steel) placed on the surface. Using one of the two methods mentioned above can help us to get rid of the charging effect, i.e. to neutralize the surface charge during measurements. But in the case of solar cell analysis these two methods should be applied simultaneously during depth profiling. The experimental results performed on p-i-n:Si (p-type/intrinsic/n-type) diodes have proved that SNMS measurement in HF operation mode combined with a mesh is very efficient in the determination of doping levels of phosphorus and boron with good depth resolution, even in the case of 500-600 nm thick samples.     

Pyrometry inside an arc furnace using a ray-tracing correction for surface emissivity

A general method using a ray-tracing analysis has been developed to improve the accuracy of surface temperatures measured by pyrometry inside a furnace. This method allows temperature correction for enclosed non-ideal black-body surfaces, having temperature gradients, by taking into account the contributions from the reflected fraction of the pyrometer field-of-view. The development has been made possible by the recent availability of internal furnace scanning pyrometry technology for complete temperature profile measurements inside furnaces. The correction method can be expressed in terms of the solution of a square matrix having a dimension corresponding to the number of spatially resolved points in the temperature profile, with the number of non-zero elements depending on the number of field-of-view reflective surface bounce points used in the analysis. The utility of this method is demonstrated for the correction of 19-point temperature profiles measured inside a dc arc furnace. Reflective contributions from two, three, and four field-of-view surface bounce points are considered. Generally, the lower the surface emissivity and the higher the temperatures, the more bounces needed in the analysis. It is shown that there can be significant corrections to internal furnace temperatures measured by pyrometry when temperature gradients exist.     

Two-dimensional surface profile imaging technique based on a double-grating frequency shifter

A two-dimensional surface profile imaging technique that uses a low-coherence heterodyne interferometer is proposed. A double-grating frequency shifter was used in a tandem interferometer to provide the achromatic frequency shift for low-coherence light. A chopper, together with a processing circuit, was implemented to modulate the interference fringes. The surface profile was measured from the interference fringes taken by a CCD camera using a five-step method. The uncertainty in the displacement measurement is 0.34 microm for a displacement range of 43 microm. The surface profile of a glass sample with low effective reflectivity was acquired.     

Effect of Shot Peening Parameters to Residual Stress Profiles and Barkhausen Noise

The production of gear components includes numerous manufacturing operations which are carried out to ensure proper surface characteristics of components to deal with wear and fatigue. Surface shot peening is one way to increase the compressive residual stresses on the surface and thus ensure better wear and fatigue resistance. An experimental plan for shot peening was conducted to produce samples with varying surface characteristics. Residual stress profile and Barkhausen noise measurements were carried out for the samples. The objective of the study was to evaluate the interactions between the shot peening parameters studied, the residual stress profiles and the Barkhausen noise measurements. A multivariable regression analysis was applied for the task. Some remarkable correlations were found between the shot peening parameters, residual stress profile and Barkhausen noise features. The most important finding was that when the shot peening intensity was high enough, over 0.5 mmA, it dominated the shot peening coverage density parameter and thus no correlations could be gained. On the other hand, if the intensity parameter was lower than the limit of 0.5 mmA, the correlation between residual stress and Barkhausen noise measurements was remarkable. This means that the surface Barkhausen noise measurements could be used for the evaluation of the stress gradient in the shot peening process.     

Retrieval of geophysical parameters from moderate resolution imaging spectroradiometer thermal infrared data: evaluation of a two-step physical algorithm

A two-step physical algorithm that simultaneously retrieves geophysical parameters from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements was developed. The retrieved geophysical parameters include atmospheric temperature-humidity profile, surface skin temperature, and two surface emissivities within the shortwave (3-5-mum) and the longwave (8-14.5-mum) regions. The physical retrieval is accomplished in two steps: (i) The Tikhonov regularization method is employed to generate a regularization solution along with an optimum regularization parameter; (ii) the nonlinear Newtonian iteration algorithm is carried out with the regularization solution as a first-guess profile to obtain a final maximum probability solution for geophysical parameters. The algorithm was tested with both simulated and real MODIS Airborne Simulator (MAS) data. Sensitivity studies on simulated MAS data demonstrate that simultaneous retrievals of land and atmospheric parameters improve the accuracy of the retrieved geophysical parameters. Finally, analysis and accuracy of retrievals from real MAS data are discussed.     

Morphological relaxation of glass surfaces

A model for calculating the morphological relaxation of two-dimensional glass profiles for arbitrary temperature-time schedules is described. The model is based on a Fourier expansion of the surface profile for which the decay with time can easily be calculated for each of the separate terms. The effect of the variable temperature with time was accounted for by discretization of the temperature-time profile. Necessary input data are the viscosity and surface tension of the glass. The sensitivity to various geometrical details is limited, but heating/cooling effects appeared to be important. The predictions of the model are verified by measurements on glass samples with various profiles and relaxed according to a certain temperature-time schedule. Using a surface tension value of 0.19 N m^–1, as determined with recent fibre-on-plate experiments, excellent agreement between theory and experiment was obtained. Possible options for extension to threedimensional profiles are indicated.     

Surface contouring by optical edge projection based on a continuous wavelet transform

A novel optical edge projection method for surface contouring of an object with low reflectivity is presented. A structured light edge is projected onto a dark surface, and the image is captured by a CCD camera. The surface profile of the object is then evaluated by an active triangular projection technique, and a whole-field three-dimensional contour of the object is obtained by scanning the optical edge over the entire object surface. An edge detection method based on a continuous wavelet transform (CWT) is employed to determine the location of the optical edge. The method of optical edge detection is described, and characteristic details of gray-level distribution along the edge are analyzed. It is shown that the proposed wavelet edge detection method is not dependent on any threshold values; hence the true edge position can be determined without subjective selection. A black low-reflectivity object surface made from woven carbon fiber is measured, and the experimental results show that the profile of a woven carbon fiber can be obtained by the proposed method.     

Retrieval of profile information from airborne multiaxis UV-visible skylight absorption measurements

A recent development in ground-based remote sensing of atmospheric constituents by UV-visible absorption measurements of scattered light is the simultaneous use of several horizon viewing directions in addition to the traditional zenith-sky pointing. The different light paths through the atmosphere enable the vertical distribution of some atmospheric absorbers, such as NO2, BrO, or O3, to be retrieved. This approach has recently been implemented on an airborne platform. This novel instrument, the airborne multiaxis differential optical absorption spectrometer (AMAXDOAS), has been flown for the first time. In this study, the amount of profile information that can be retrieved from such measurements is investigated for the trace gas NO2. Sensitivity studies on synthetic data are performed for a variety of representative measurement conditions including two wavelengths, one in the UV and one in the visible, two different surface spectral reflectances, various lines of sight (LOSs), and for two different flight altitudes. The results demonstrate that the AMAXDOAS measurements contain useful profile information, mainly at flight altitude and below the aircraft. Depending on wavelength and LOS used, the vertical resolution of the retrieved profiles is as good as 2 km near flight altitude. Above 14 km the profile information content of AMAXDOAS measurements is sparse. Airborne multiaxis measurements are thus a promising tool for atmospheric studies in the troposphere and the upper troposphere and lower stratosphere region.     

The surface tension of steels

Over many years NPL has carried out measurements of surface tension of steels using the levitated drop method. Much of this work has been to study variations in weld profile brought about by changes in Marangoni flow patterns in the liquid pool, and many of these data have remained unpublished. 49 ferritic and austenitic steels are compared, and relationships for surface tension, and the coefficient of surface tension against temperature, based on sulphur content of the steel, are presented. Data has been reassessed using the Cummings correction to allow for the effects of the levitation forces.     

Simple method for improving the sampling in profile measurements by use of the Ronchi test

We present a simple method for increasing the number of data points obtained during performance of profilometric measurements with the Ronchi test. The method is based on multiple ronchigram acquisitions that are superimposed after a few very simple data-processing operations. The measurement method, experimental setup, and data processing are described in detail from the ronchigram to the measured profile, and experimental results for a concave surface of an spherical ophthalmic lens are provided. The radius of curvature values measured for that surface are compared with the ones obtained with a high-precision radioscope, showing very good agreement and demonstrating the capability of the technique to measure topographic profiles of reflective samples.