Brief Introduction to Surface Metrology

December 04, 2013

Surface metrology is the science that deals with the measurement of topography, i.e. the characterization of a surface by the amplitude, spacing and shape of its features. The term "topography" is derived from the Greek "topo" meaning place and "graph" meaning a type of symbolic diagram.

Many engineering surfaces are manufactured to have functional properties such as bearing and sealing, or to have high fluid retention capabilities. According to the requirements of the engineering application, a functional surface has to have some specific topographic features that are beneficial to the application. Structural properties in particular are strongly related to functional requirements, and the measurement of such surfaces is very important, not only for the functionality of the products, but also as a feedback for the manufacturing units.

The development of surface metrology is traditionally based on tactile methods, which gather data by physical contact with the surface. Although this type of analysis is adequate for most applications, tactile methods are generally time-consuming and can damage the workpiece. Furthermore, the shape and the size of the stylus can limit its capacity to penetrate into surface structures and show their properties.

Thanks to the latest developments in measurement techniques, there are now many optical methods for characterizing technical surfaces. In comparison to surface profile measurements (like tactile ones), optical methods mostly provide areal information, making them statically more reliable and more representative.

The main task of such a topography measurement system is to capture the spatial coordinates of points on a surface. The information from these triple spatial coordinates is then used for the three-dimensional characterization of the shape and texture of unknown objects.

Although great efforts are being made to cover the three-dimensional measurement of surface texture by international standards, the process is still ongoing. The main development activities are being done by the research projects in Europe and other countries, and the relevant standards, like ISO 25178, are being considered by ISO TC 213.

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