Surface Texture Filtering
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Surface Texture Filtering
Theory and Application
Xiangqian Jiang and Paul J. Scott Centre for Precision Technologies, University of Huddersfield, Huddersfield, UK
Introduction Filtration has always been important in surface metrology: It is the means by which the surface features of interest are extracted from the measured data for further analysis. The first filters started with the fully analogue 2CR filter implemented as a two-stage CapacitorResistance network as shown in Fig. 1. Originally it was designed to remove the DC and slope of the measured surface profile but was quickly realized to have other useful properties, i.e., surface filtration. The 2CR filter formed the basis of the M-system (mean line system) of filtration. Unfortunately, it was found that the 2CR filter could badly distort profile features due to phase shifting of the different harmonic components in the profile. A symmetrical version, the phase corrected 2CR filter, resolved most of this distortion, but it still had problems, one being that it badly distorted the profile at the ends. This led to its eventual replacement by the modern digital Gaussian filter as the general default surface texture filter. The Envelope system (E-system) was first developed by Von Weingraber (1956). The E-system bases the reference lines upon the loci of centers of circles of different radii rolled along
Synonyms Roughness filtering; Surface topography filtering
Definition A filter separates the small-scale texture from the larger-scale texture in a surface. The value of the scale at the defined separation is called the nesting index although other names are used for specific filters (e.g., cut-off for linear filters). Scale can be defined in terms of: wavelength for linear filters, size of the structuring element (e.g., radius of a disk) for morphological filters. In Segmentation filters, the scale can be: the height difference between the highest (or lowest) points in the interior and on the boundary of a segment, the area of a segment, length of the boundary of a segment, etc.
# CIRP 2019 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, https://doi.org/10.1007/978-3-642-35950-7_16863-1
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Surface Texture Filtering
Surface Texture Filtering, Fig. 1 Twostage 2RC high pass filter (Whitehouse 2002). (Reproduced with permission from DJ Whitehouse)
Surface Texture Filtering, Fig. 2 Probe for E-system: T1 Skid, T2 stylus. (Reprinted from (Peters et al. 2001) with permission from Elsevier)
the profile. As Fig. 2 demonstrates, the locus of the center of the larger tip gives the curve of form, while that of the smaller tip gives the contacting profile. The difficulty appeared in building practical instruments as two elements are needed: a spherical skid (T1) to approximate the “enveloping circle” and a needle-shaped stylus (T2) moving in a diametric hole of the skid to measure the roughness as deviation with respect to the “generated envelope.” The advantages of the E-system were claimed to be that it is more physically signi
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