Surface Profilers Research Articles

Predicting International Roughness Index Based on Surface Distresses in Various Climate and Traffic Conditions Using Laser Crack Measurement System

Roughness is one of the most significant parameters in the evaluation of pavement performance. Surface distresses are among the main factors leading to roughness. The collection and evaluation of roughness data require the application of modern equipment such as road surface profilers. In the absence of such equipment, roughness prediction models that are based on surface distresses might provide a desirable assessment of pavement conditions. This research employs the laser crack measurement system (LCMS) to detect and measure surface distresses and roughness along 268 km of primary roads in Iran. Compared with manual survey, LCMS provides maximum detection and measurement accuracy. Based on the LCMS output, distresses with a higher correlation with the International Roughness Index (IRI) were selected as predictors in linear regression models and artificial neural networks (ANN). The models were developed for 10 m and 100 m length sections of the roads under different climate and traffic conditions. The results indicate that the performance of ANN for the 100 m sections with coefficient of determination ( R2) of 0.82 is superior to other models. The best case was that of using ANN in 100 m sections for regions with moderate climate and medium traffic levels, with a 0.94 correlation. Satisfactory results in field validation of the models demonstrated that agencies can use other methods of data collection (e.g., manual, right of way [ROW]) to assess the surface distresses and roughness condition of their roads from the developed models with minimum spending and without expensive equipment. Such estimates can be employed to make informed decisions in pavement maintenance programs at the network level.

Correction of spherical surface measurements by confocal microscopy

Refractive microlenses are nowadays widely used in optical systems. Characterizing their surface is essential to ensure their quality and to optimize their fabrication process. This is realized by optical surface profilers thanks to their vertical resolution, short measurement time and areal information. However, when measuring non-flat surfaces, errors appear caused by aberrations of the microscope objective used in such systems, which significantly limit the achievable quality of the manufactured spherical surfaces. Approaches have been proposed to tackle these errors, but none of them demonstrated its validity for measurements of high quality microlenses. In this work, we demonstrate that the surface error depends on the surface position within the field of view of the microscope objective and on the surface slope. We then explain how to record the value of this error experimentally: this can be done by measuring a reference ball placed at different positions in the field of view. We finally use a machine learning algorithm to fit the experimental data in order to correct subsequent measurements. We apply this approach to measurements performed by a 20× numerical aperture 0.6 microscope objective of a confocal microscope. The effectiveness of the proposed method is demonstrated by showing that the surface error corresponds to a RMS wavefront error of λ/7 before correction and of λ/50 after correction for glass microlenses used in the visible range. This method thus allows the use of high numerical aperture microscope objectives for an accurate characterization of microlenses. Likewise, the fabrication capability of microlenses in terms of slope and quality is greatly extended, which is especially important for aspheres or freeforms.

A new method for detecting surface defects on curved reflective optics using normalized reflectivity.

Detection of surface defects is critical in quality control of reflective optics. In this note, we propose a new surface defect detection method for reflective optics using the normalized reflectivity, which is calculated from the signal intensity of a chromatic confocal surface profiler. This detection method first scans the surface to acquire signal intensity data and then models the intensity data to calculate the normalized local reflectivity map. The reflectivity map is further processed by threshold segmentation to extract defects from normal areas. Measurement experiments on an Al-coated concave reflector with artificial defects were carried out to demonstrate the feasibility of the method. This detection method can provide existing optical surface profilers with defect detecting capabilities without extra equipment.

Machining of Ti–6Al–4V using diffusion annealed zinc-coated brass wire in WEDHT

Titanium is predominantly used in the industrial sectors such as bio-medical, chemical, aircraft and marine because of its improved properties such as corrosion resistance and strength. Other properties such as increased toughness, hardness, poor thermal diffusivity make the material to fall under the category of difficult-to-cut, and this gave rise to the introduction of advanced machining processes. Wire electrical discharge hybrid turning (WEDHT) is one such process which could machine electrically conductive material and is discussed in this present research work. WEDHT of Ti–6Al–4V alloy is performed with diffusion annealed zinc-coated wires in the presence of deionised water as the dielectrics. The objective of the present work is to analyse the quality of the machined surface and the amount of material removed during hybrid turning process. The input parameters chosen for the present experimentation are wire feed rate (3, 4, 5 m/min), pulse ON time (108, 111, 114 µs), servo feed (5, 7, 9 mm/min), to conduct 27 experiments. The surface quality of the machined component is studied and analysed using 2D and 3D surface profilers along with scanning electron microscopic images. The effect of heat on the machined sample and its effect on the work material surface are studied with the help of micro-hardness analysis. The amount of material removed is calculated by measuring the weight of the sample prior to and after machining. From experimentation, the lower surface roughness of 2.0087 µm is obtained at 108 µs of pulse ON time, 5 m/min of wire feed rate and 5 mm/min of servo feed. The increased material removal 0.0169 g/min is obtained at 114 µs of pulse ON time, 5 m/min of wire feed rate and 5 mm/min of servo feed. On comparison, diffusion annealed zinc-coated brass wires outperformed uncoated brass wires with 18.95% and 44.37% for surface roughness and material removal rate criteria, respectively.

Experimental study on ultra-precision grinding characteristics of WC-Ni hard metals

Tungsten carbide (WC) hard metals are universally used in industrial fields owing to their superior properties, and the machining accuracy of WC products is playing an important role in their service performance. However, how to achieve a balance between high accuracy and processing cost according to different applications is a key engineering issue. Thus, it is necessary to reveal the material removal characteristics of such difficult-to-cut hard metals. In this article, ultra-precision grinding characteristics of WC-Ni hard metals were investigated based on the wafer rotation grinding method using #120, #600, #2000, and #12000 diamond cup wheels as coarse, semi-finished, fine, and finish grinding wheels, respectively. A polished sample was taken for comparison. The optical surface profilers, scanning electron microscope, and atomic force microscope were employed for checking surface topographies, surface morphology, and cutting depth. An ultra-smooth and defect-free WC-Ni surface with less than 2 nm Ra and the average cutting depth of about 10 nm can be obtained using a #2000 diamond wheel, which can replace polishing and satisfy the requirements of most high-performance applications. This study provides useful observations for ultra-precision manufacturing of hard metal products.

A Simplified Method of Detecting Spot Surface Defects by using Quasi-3D Data from a Conventional Road Profiler

It is important to maintain safety and ride quality for toll expressway users in Japan. However, since porous asphalt became the standard road surface, spot defects have gradually spread nationwide. To deal with the problem, this research attempted to develop a less costly but effective way of identifying surface defects. Since transverse data for rutting measurement was the only basic data available for general road profilers, first, quasi-three-dimensional (3D) profile data was successfully obtained by deleting gradient effects on the profiles in both the transverse and longitudinal directions. Among other elements, the standard deviation (SD) of the quasi-3D profile height using spot defect size was best matched for identifying spot defects, including pumping of underlying layer materials of the pavement. To improve the efficiency of detecting spot surface defects, deep learning was examined by converting the SD values into visual images. As a result, it was verified that a simplified classification with basic color information of red, green, and blue gave practically the same engineering judgement. Finally, this method of identifying irregularly emerging target defects using deep learning was validated by relearning the target visuals. A good result with high accuracy was achieved with just 150 images for each defect level. This approach may be universally applied anywhere surface profilers are used.

Characterization of micro structure through hybrid interference and phase determination in broadband light interferometry.

Broadband light interferometry, which is a well-developed method for surface profiling, has been applied with great success in the past years. Conventional multi-wavelength interferometric surface profilers mostly utilize the light irradiance to locate the zero fringe order, but the accuracy and stability can be negatively influenced by intensity fluctuations and external light disturbance, which is a serious problem. In this paper we discuss a hybrid technique combining light intensity and spectral modulation to determine zero optical path difference in which the light instability can be effectively suppressed. Additionally, the phase evaluation at each pixel will provide a high vertical resolution to obtain the characterization of the micro structure. The hybrid-interference method will not only improve the sensitivity of the measurement system but also level up the robustness and stability. Both simulation and experiment on a micro-dome structure have been presented to verify the effectiveness. Furthermore, the proposed method may be promising to replace the previously intensity-based method, especially in a complex application environment.

Measuring nanoparticle size using optical surface profilers

Optical surface profilers are state-of-the-art instruments for measuring surface height profiles. They are not conventionally applied to nanoparticle measurements due to the presence of diffraction artifacts. Here we use a theoretical model based on wave-optics to account for diffraction-based artifacts in optical surface profilers. This then enables accurate measurement of nanoparticles size of a known geometry. The model is developed for both phase shifting interferometry and vertical scanning interferometry modes of operation. It is demonstrated that nanosphere radii as small as 12 nm, and nano-cylinder radii as small as 10-15 nm can be measured from a standard profile measurement using phase shifted interferometry interpreted using the wave-optics approach.

Femtosecond laser pulses for fast 3-D surface profilometry of microelectronic step-structures

Fast, precise 3-D measurement of discontinuous step-structures fabricated on microelectronic products is essential for quality assurance of semiconductor chips, flat panel displays, and photovoltaic cells. Optical surface profilers of low-coherence interferometry have long been used for the purpose, but the vertical scanning range and speed are limited by the micro-actuators available today. Besides, the lateral field-of-view extendable for a single measurement is restricted by the low spatial coherence of broadband light sources. Here, we cope with the limitations of the conventional low-coherence interferometer by exploiting unique characteristics of femtosecond laser pulses, i.e., low temporal but high spatial coherence. By scanning the pulse repetition rate with direct reference to the Rb atomic clock, step heights of ~69.6 μm are determined with a repeatability of 10.3 nm. The spatial coherence of femtosecond pulses provides a large field-of-view with superior visibility, allowing for a high volume measurement rate of ~24,000 mm3/s.

Effect of pH on Surface Texture Of Glass Ionomer Containing /based Restorative Materials: An In-vitro Study

This study determined the effect of pH on the surface texture of commonly used posterior glass ionomer basedcontaining restorative materials. The materials evaluated included a compomer Dyract a giomer Beautifil II and two highly viscous glass ionomer cements Fuji IX and Ketac Molar. A resin composite Spectrum TPH was used for comparison. Thirty six specimens 5-mm diameter X 2-mm depth were made for each material. The specimens were divided into six groups and conditioned in the following solutions at 37degC for one week Citric acid pH 2 3 4 5 and 6 and distilled water pH 7. After conditioning the surface roughness Ra microm of each specimen was measured using a surface profilometer WYKO Surface Profilers Veeco Metrolog Group Arizona USA. Data was analysed using one-way ANOVA and Scheffes test at a significance level of 0.05. The effects of pH on the surface texture of glass-ionomer basedcontaining restoratives were material dependent. Ra values ranged from 0.03 microm to 0.85 microm and 0.06 microm to 4.90 microm for pH 7 and 2 respectively. With the exception of the composite the surface roughness of all materials evaluated was significantly affected by acids of low pH. The surface texture of highly viscous glass ionomer cements deteriorated significantly when conditioned in solutions of low pH which makes them more susceptible to clinical failure.

Slow deformation measurement of biological samples with 3D interferometric microscope

The 3D interference microscope is used to measure the mechanical and structural properties of biological samples. In this paper the pulsation of the eye of the zebrafish embryo and the motion of the neuron is measured. The measurement is often performed on a microsphere placed on a biological sample. The microsphere reflects a strong signal, and by applying a magnetic field the sphere can induce a controlled and varying pressure on the object. The deformation of the object and the motion of the sphere provide information about different mechanical properties of the biological sample. This paper specifically concentrates on the measurement of nanometric deformation at frequencies below 10Hz. Full Text: PDF References http://www.bruker-axs.com/white_light_interferometric_profilometers.html [Direct link] J. Schmit, K. Creath, J.C. Wyant, "Surface Profilers, Multiple Wavelength, and White Light Interferometry" in Optical Shop Testing, 667-755 (ed. D. Malacara, John Wiley, Hoboken 2007). J. Reed, M. Frank, J.J. Troke, J. Schmit, S.Han, M.A. Teitell J.K. Gimzewski, Nanotechnol. 19, 235101 (2008). [CrossRef] References 1-9 within: J. Reed, S. Ramakrishnan, J.Schmit, J.K. Gimzewski, "Mechanical interferometry of nanoscale motion and mechanical properties of living zebrafish embryos", www.acsnano.org 3(8), 2090 (2009). J. Reed, S. Ramakrishnan, J. Schmit, J. K. Gimzewski, "Mechanical interferometry of nanoscale motion and mechanical properties of living zebrafish embryos", www.acsnano.org 3(8), 2090 (2009). J. Schmit, K. Creath, App. Opt. 34(19), 3610 (1995). [CrossRef] J. Schmit, P. Unruh, E. Novak, "Measurement of object deformation with optical profiler", US Patent 7283250 (2007)

Design and fabrication of a silicon probe for surface profilers

A micromachining probe for surface profilers is reported in this paper. This probe employs single crystal silicon double-ended tuning forks (DETFs) as the sensitive unit to achieve high resolution and frequency read-out. The frequency shift of the DETFs caused by the induced axial stress is directly proportional to the undulation of the measured surface. Moreover, one-stage and two-stage microleverage amplification mechanisms are respectively implemented to improve the probe performance. The silicon on glass (SOG) process which can provide high aspect ratio single crystal silicon structures has been adopted to enhance the performance of the probes. The testing results indicate that the probe with two-stage mechanical amplifiers has a frequency-displacement sensitivity of 257.1 Hz/μm with a nominal frequency 27.3 kHz at room temperature in atmosphere, which is in close agreement with the simulation results.

Focus on test and measurement

Focus on test and measurement

Random errors in interferometry with the least-squares method

This investigation analyzes random errors in interferometric surface profilers using the least-squares method when random noises are present. Two types of random noise are considered here: intensity noise and position noise. Two formulas have been derived for estimating the standard deviations of the surface height measurements: one is for estimating the standard deviation when only intensity noise is present, and the other is for estimating the standard deviation when only position noise is present. Measurements on simulated noisy interferometric data have been performed, and standard deviations of the simulated measurements have been compared with those theoretically derived. The relationships have also been discussed between random error and the wavelength of the light source and between random error and the amplitude of the interference fringe.

Scanning Optical Head with Nontilted Reference Beam: Assuring Nanoradian Accuracy for a New Generation Surface Profiler in the Large-Slope Testing Range

Nanoradian Surface Profilers (NSPs) are required for state-of-the-art synchrotron radiation optics and high-precision optical measurements. Nano-radian accuracy must be maintained in the large-angle test range. However, the beams' notable lateral motions during tests of most operating profilers, combined with the insufficiencies of their optical components, generate significant errors of∼1 μrad rms in the measurements. The solution to nano-radian accuracy for the new generation of surface profilers in this range is to apply a scanning optical head, combined with nontilted reference beam. I describe here my comparison of different scan modes and discuss some test results.

Silicon probe for micromachined surface profilers

A single-crystal silicon probe for micromechanical surface profilers is presented, which uses a double-ended tuning fork (DETF) resonator as the displacement-sensing element. In addition, a two-stage micro-leverage mechanism for force amplification is introduced to increase the overall sensitivity. The frequency shift of the DETF caused by the induced axial stress is directly proportional to the displacement input. The probe was fabricated through a standard silicon-on-glass process, which can realise high aspect ratio single-crystal silicon structures. The experimental results indicated that the probe had a nominal resonant frequency of 54.5 kHz under atmosphere at room temperature. The scale factor and linearity of the probe with the input range of 0–10 µm were evaluated to be 359.7 Hz/µm and 6.3%, respectively. The measured scale factor shows good agreement with the simulated value of 330 Hz/µm using ANSYSTM.

Measurement of discontinuous surfaces using multiple-wavelength interferometry

Interferometric surface profilers using a single wavelength offer excellent vertical resolution, but have an ambiguity-free range of less than half a wavelength. Multiple-wavelength or white light interference techniques are used to overcome the problem. We discuss a three-wavelength interferometric technique used with a phase-shifting phase evaluation procedure. The phase evaluation at the three wavelengths gives wrapped phase at any pixel corresponding to these wavelengths. We use the fact that the variation of phase with wavenumber for a given profile height is linear to determine the absolute value of the profile height. The height is then used to ascertain the fringe order. The fringe order, along with the wrapped phase, gives the profile height with a resolution given by the phase-shifting technique. Experimental results for large step height measurement on etched silicon samples are presented.

Two-wavelength micro-interferometry for 3-D surface profiling

Three-dimensional non-contact optical techniques for rapid and accurate mapping of micro-machined surfaces are important for the optoelectronic industry. Interferometry is a well-established technique for 3-D surface profiling. The conventional interferometric surface profilers using a single wavelength offer excellent vertical resolution, but a serious limitation to their use is that they can only handle smooth profiles and step heights less than half a wavelength. In this paper we describe a two-wavelength micro-interferometric setup for 3-D surface profile characterization of smooth as well as rough micro-specimens. The method removes ambiguity associated with the single-wavelength data and also extends the phase measurement range compared to the conventional single-wavelength interferometry. Seven-phase step algorithm is used for quantitative fringe analysis. The design of the system along with experimental results on smooth and rough micro-specimens is presented.

A comparison of different methods of paper surface smoothness evaluation

Smoothness of paper surface is an important property from its printability. A number of techniques are available for characterizing the topographical features of the paper surface. These techniques have led to the development of smoothness testers of various types such as air-leak testers, optical contact testers, surface profilers, and a number of ink and liquid application apparatus to assess the smoothness. While all these methods are intended to serve the same purpose, they differ so greatly in their basic approach that the agreement between them cannot be taken for granted. In the present work, these methods have been applied to characterize the surface of handsheets of mechanical pulps. A comparison of these methods reveals that different methods grade these pulps differently, confirming the multidimensional nature of the surface structure and the fact that no single method is sufficient to describe it completely.

Analysis of Laser‐Scanned Topographic Data using Wavelet Methods

Soil surface profilers are commonly structured to collect and develop a Digital Elevation Model (DEM) on a point by point basis. This process is very time consuming. Structuring the profiler to scan the soil surface line by line instead of point by point may be considered a new contribution in this field. In this paper, at first it is shown how to design and implement a profiler to collect digital elevation data along a transect in a single measurement. For this purpose, a sheet of light is used to prepare a digital picture of transect and then a triangulation‐based method is utilized to convert the digital picture to a DEM. Then, a wavelet‐based approach is used to filter the collected data. A wavelet is a compact analyzing kernel that can be moved over a sequence of data to measure variations locally. Here, a wavelet transform is applied in order to decompose spatial data into a series of independent components at varying scales in a single coherent analysis. The proposed approach is applied to a real laboratory size case study and the efficiency of the method is demonstrated.