The paper presents the impact of lighting type and direction on measurements of surface asperities using focus-variation microscopy. Particular attention was paid to the direction of lighting when ...using a light ring. It was pointed out that the lighting direction directly affects the values of the parameters Rt, Rz, and Rc. The article also presents the impact of a light polarizer on the surface topography parameters. It has been shown that the positioning of a sample with a regular and directed structure relative to the optical axis of the light polarizer affects the accuracy of mapping surface asperities. The largest differences were observed for Rz and Rt parameters. A method of using an external polarizer mounted on a focus variation microscope lens was also presented. Keywords: surface topography,
In dem folgenden Artikel konnte anhand verschiedener Messreihen gezeigt werden, dass die optische Erfassung von Bauteiloberflächen unter verschiedenen Betrachtungswinklen auch zu unterschiedlichen ...Oberflächentexturkennwerten führt. Die Ergebnisse rechtfertigen die Entwicklung einer daraufhin angepassten messtechnischen Erfassung von Zahnradflanken mit Hilfe einer optischen Strahlumlenkung.
Numerous studies have focused on determining whether objective statistical methods can be used to discriminate between known matches and nonmatches when comparing laboratory prepared toolmarks. This ...study involved an analysis of striated toolmarks made as a function of varying vertical and horizontal angles of attack. Comparisons based on experimental data show that replicate toolmarks from the same tool show high correlation values at identical vertical and horizontal angles, with the correlation decreasing as the angular difference increases, especially for horizontal angular changes. Comparisons between nonmatching samples produce low correlation values that remain unchanged as horizontal angular differences increase. While complete statistical separation was not achieved between matching and nonmatching samples, there is evidence demonstrating that toolmarks can be identified if the variation in horizontal angle is within 10°. The experiment shows that computer‐aided comparison techniques could be viable for identification with the proper statistical algorithm.
Abstract
Saw-cut rock surfaces, classically utilized to estimate basic friction angle of discontinuities by means of tilt test and other procedures, may seem planar to the naked eye. Nevertheless, ...they actually present roughness at a micrometric scale. Aiming at characterizing some of these saw-cut rock surfaces and assessing the possible implications between their microscale topography and the resulting tribological behavior, the authors of this study resorted to the 3D focus-variation technique to analyze different surface-texture parameters. Tilt tests were carried out on specimens cut on three rock types, and the involved sliding surfaces were evaluated at a microscale for different testing stages (prior to any test and after two series of repeated tests). An apparently logical inverse correlation between repeated testing and friction angle has been observed, more marked for the smoother surfaces. Higher roughness at the scale of the analysis tends to produce lower friction-angle values, as otherwise observed for mismatched natural rock surfaces. In addition, saw-cut rock surfaces present systematically negative skewness and high values of kurtosis for their height distributions, indicating the occurrence of narrow and deep pits or valleys. Directional hybrid parameters and, in particular, the root mean square (RMS) of the gradient of the surface in the direction of sliding correlates rather well with the measured sliding angle. The authors concluded that the 3D focus-variation technique represents a powerful tool to assess surface-texture parameters of saw-cut rock surfaces, in addition to being useful for understanding some features of the tribological, or wear and frictional, behavior of these type of surfaces.
Spatial bandwidth limitations frequently introduce large biases into the estimated values of rms roughness and autocorrelation length that are extracted from topography data on random rough surfaces. ...The biases can be particularly severe for focus-variation microscopy data because of the reduced lateral resolution (and therefore dynamic range) inherent in the technique. In this paper, we describe a measurement protocol-something similar to a deconvolution algorithm-that greatly reduces these biases. The measurement protocol is developed for the case of surfaces that are isotropic, and whose topography displays an autocovariance function that is exponential, with a single autocorrelation length. The protocol is first validated against Monte Carlo-generated mock surfaces of this form that have been filtered so as to simulate the lateral resolution and field-of-view limits of a particular commercial focus-variation microscope. It is found that accurate values of roughness and autocorrelation length can be extracted over a four octave range in autocorrelation length by applying the protocol, whereas errors without applying the protocol are a minimum of 30% even at the absolute optimum autocorrelation length. Then, microscopy data on eleven examples of rough, outdoor building materials are analyzed using the protocol. Even though the samples were not in any way selected to conform to the model's assumptions, we find that applying the protocol yields extracted values of roughness and autocorrelation length for each surface that are highly consistent among datasets obtained at different magnifications (i.e. datasets obtained with different spatial bandpass limits).
Ultra-precision manufacturing is essential to the production of workpieces of the highest quality in terms of form accuracy, surface accuracy, and integrity. Compared with physical and chemical ...material removal methods, it has the advantages of high efficiency, high flexibility, and low cost. Because of the direct interaction between the workpiece and the tool during the process of ultra-precision manufacturing, the geometrical parameters of the tool directly affect the surface quality of the workpiece and need to be measured accurately and comprehensively. However, due to the large surface slopes of some tools, some three-dimensional measurement methods cannot measure their geometrical parameters because of limited maximum measurement angle. In this work, we build a focus variation system to make three-dimensional measurements of tools and extract their geometrical parameters. The data processing procedures and the selection of experimental parameters are analyzed in detail using simulations and experiments. Furthermore, we use a step height standard to verify the high accuracy of the measurement system and a roughened flat surface to evaluate the measurement noise and vertical resolution. Measurements of the parameters of a round nose cutting tool and the surface texture parameters of a grinding tool are conducted and indicate that the focus variation system is suitable for measuring the geometrical parameters of tools for ultra-precision manufacturing.
The use of soft (bone, antler, tooth and wood) hammers and retouchers is a key innovation in early stone tool technology, first appearing in the archaeological record with Lower Palaeolithic handaxe ...industries (e.g. Boxgrove, UK ∼500 ka). Although organic knapping tools were undoubtedly a component of early human toolkits and are essential, for example, for the manufacture of finely-flaked handaxes, Mousterian scrapers and Upper Palaeolithic blades tools, such archaeological finds are exceptionally rare. In this study, we present qualitative and quantitative analyses (focus variation optical microscope, scanning electron microscope, micro-CT scanning and energy dispersive X-ray spectroscopy), of a newly discovered antler flint knapping from Laugerie-Haute West (France). This specimen was originally identified as a waste-product from splinter manufacture, and the use-damage appears to have been overlooked by earlier workers. The new analysis shows that prior to being used as a flint-knapping percussor, the red deer antler had been modified to reduce the length of its beam and to remove the tines. Although minimally used, characteristic use-damage includes attrition (pits and scores), compression of the antler matrix and flint chips embedded within some of the percussion features on the base of the burr. An AMS radiocarbon date of 12,385 ± 55 BP (12,647 ± 335 BC calibrated) confirms a Magdelenian context for the hammer. The fact that the Laugerie-Haute knapping hammer went unrecognised in a well-studied and accessible collection where it was stored for almost 200 years, suggests that antler hammers may be more common than generally assumed. Only further re-examination of prehistoric antlers in museum collections will confirm whether the apparent rarity of antler hammers during the Lower and Middle Palaeolithic is real phenomenon or the result of analytical biases.
Optical free-form surfaces have been widely studied and applied because of their good performance, and ultra-precision manufacturing with round nose cutting tool is an effective method for machining ...such surfaces. Because of the direct interaction between the workpiece surface and the cutting edge, the geometrical parameters of the round nose cutting tool directly affect the shape accuracy and the surface topography of the workpiece and need to be measured accurately and comprehensively. At present, the main method to measure the geometrical parameters of round nose cutting tool involves the method using machine vision, but this imposes some limitations, such as the strong dependence on the measurement angle and the inability of measuring multiple parameters at the same time. In this work, we built a focus variation system to make three-dimensional measurement of round nose cutting tool and used this system to obtain multiple geometrical parameters in a single measurement. The types of geometrical parameters and the extraction process are discussed in detail. And a standard step height is measured to verify the high accuracy of the measurement system. The repeated measurement results show that the standard deviation of the nose radius measurement can reach hundred-nanometer scale and the relative standard deviation can reach 0.028%.
PDF
