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In this paper, a surface measurement method based on dual-scan positioning strategy is presented to address the challenges of irregular surface patterns and complex geometries. A confocal sensor with an internal scanning mechanism was used in this study. By synchronizing the local scan, enabled by the internal actuator in the confocal sensor, and the global scans, enabled by external positioners, the developed system was able to perform noncontact line scan and area scan. Thus, this system was able to measure both surface roughness and surface uniformity. Unlike laboratory surface measurement equipment, the proposed system is reconfigurable for in situ measurement and able to scan free-form surfaces with a proper stand-off distance and approaching angle. For long-travel line scan, which is needed for rough surfaces, a surface form tracing algorithm was developed to ensure that the data were always captured within the sensing range of the confocal sensor. It was experimentally verified that in a scanning length of 100 mm, where the surface fluctuation in vertical direction is around 10 mm, the system was able to perform accurate surface measurement. For area scan, XY coordinates provided by the lateral positioning system and the Z coordinate captured by the confocal sensor were plotted into one coordinate system for 3D reconstruction. A coherence scanning interferometer and a confocal microscope were employed as the reference measurement systems to verify the performance of the proposed system in a scanning area of 1 mm by 1 mm. Experimental data showed that the proposed system was able to achieve comparable accuracy with laboratory systems. The measurement deviation was within 0.1 &micro, m. Because line scan mechanisms are widely used in sensor design, the presented work can be generalized to expand the applications of line scan sensors.

Mirror finish surface products are widely used in many industries such as aerospace, optics, semiconductor and biomedical device manufacturing. The surface texture of mirror finish products is usually measured by off-line instruments such as coherence scanning or phase shifting interferometers. However, most commercial interferometers are expensive and must be operated in a clean and vibration-free laboratory environment. In order to achieve both in-situ surface quality control and automated tool changing for the polishing process, fast and non-contact surface texture measurement are required. To address these in-situ measurement challenges, a surface texture measuring system based on fringe pattern illumination method is proposed in this paper. By analyzing the luminance contrast ratio of the fringe pattern reflection image and comparing to the measurement results from the referenced coherence scanning interferometer, the experimental results showed that the proposed system was able to measure different mirror finish surfaces with Sa and Sq values in the range of 15 nm to 120 nm and 30 nm to 160 nm respectively. In addition, the luminance contrast ratio was also correlated with directions of the machining marks and the projected fringes at different measurement angles. The surface texture aspect ratio parameter Str which provides information about the strength of the machining marks was experimentally evaluated and compared with luminance contrast change. In conclusion, the proposed measuring system was able to measure surface texture with a relative error less than 10% at measurement angle between 20° to 160°, and indicate machining pattern effects on the mirror finish surface.

Mirror-finished surface products have a wide range of applications in different engineering industries, such as power generation, aerospace, semiconductors and optics. The surface topography of mirror-finished products is typically measured in a metrology laboratory, which is typically time consuming and cannot be integrated into the manufacturing process. To allow for in-situ product quality assurance and automatic tool change for manufacturing processes, a more accurate and responsive surface-measurement method is needed. For highly polished surfaces, a sub-micron surface fluctuation makes it possible to use light-scattering effects and image processing for surface texture analysis. A non-contact surface inspection system using a fringe-patterned illumination method is proposed in this paper. A predesigned pattern was projected onto the target surface, and its reflected image was captured by a camera. It was found that the surface parameters Sa and Sq, which are widely used to evaluate surface quality, are significantly correlated with luminous-intensity distribution. Another parameter, Str, which quantifies the uniformity of surface-texture directions due to polishing or grinding marks, was traditionally quantified after a complete-surface topographic measurement. In this research, a new approach is proposed to determine surface isotropy through a luminance-intensity distribution analysis. By rotating the test coupon, the variation of specular reflection showed correlation with the significance of surface-texture direction. The experimental results demonstrate that mirror-finished surfaces with a large deviation in luminance intensity across the pattern possess low Str values, which indicates low uniformity in surface texture.

The characterization of surface topographic features on a component is typically quantified using two-dimensional roughness descriptors which are captured by off-line desktop instruments. Ideally any measurement system should be integrated into the manufacturing process to provide in-situ measurement and real-time feedback. A non-contact in-situ surface topography measuring system is proposed in this paper. The proposed system utilizes a laser confocal sensor in both lateral and vertical scanning modes to measure the height of the target features. The roughness parameters are calculated in the developed data processing software according to ISO 4287. To reduce the inherent disadvantage of confocal microscopy, e.g., scattering noise at steep angles and background noise from specular reflection from the optical elements, the developed system has been calibrated and a linear correction factor has been applied in this study. A particular challenge identified for this work is the in-situ measurement of features generated by a robotized surface finishing system. The proposed system was integrated onto a robotic arm with the measuring distance and angle adjusted during measurement based on a CAD model of the component in question. Experimental data confirms the capability of this system to measure the surface roughness within the Ra range of 0.2&ndash, 7 &mu, m (bandwidth &lambda, c/&lambda, s of 300), with a relative accuracy of 5%.

Surfaces made by Additive Manufacturing (AM) processes normally show higher roughness and more complicated microstructures than conventional machined surfaces. In this study, AM surface roughness measurements using both tactile and optical techniques are analyzed, theoretically and experimentally. Analytical results showed both techniques have comparable performance when measuring AM samples with good surface integrity. For surfaces with steep features, coherence scanning interferometry showed more reliable performance especially when peak-to-valley value was required. In addition of the benchmarking study, development of a low-cost measurement system, using laser confocal technology, is also presented in this paper. By comparing the measurement results with those from a coherent scanning interferometer, accuracy levels of the proposed system can be evaluated. It was concluded that with comparable accuracy, the proposed low-cost optical system was able to achieve much faster measurements, which would make it possible for in-situ surface quality checking. Published version

The results of experimental observation in the field show that the luminance contrast threshold ((epsilon) ) and the color difference threshold ((Delta) (Epsilon) *) are respectively tending towards the constants of 0.05 and 0.8 U*V*W* unit of color difference when the angular subtense ((theta) ) of the sample is larger than 30 feet. Otherwise, under the condition of small angular subtense, both (epsilon) and (Delta) (Epsilon) * are the functions of (theta) . For the black-white sample, the visual threshold is equal to the contrast threshold (epsilon) which increases exponentially with the decrease of (theta) . For the color sample, the visual threshold of color difference is determined not only by contrast, but also by chromatic difference. The effect of (theta) on color difference is reflected in the weighted components of U*, V*, and W* in CIE 1964 U*V*W* uniform colorspace. Nine color samples are used to carry out the experiment and calculation. The results are quantitatively described in this paper. These principles can be applied to image generation, especially to the perspective drawing on computers.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.