Phase-space-based fusion of angular and height data in tactile and optical surface texture measurement for tribological analysis

Abstract

Accurate characterization of surface topography is essential for understanding and optimizing tribological processes. A wide range of tactile and optical measurement techniques – such as stylus profilometry, scattered light sensors, white light interferometry, confocal microscopy, and focus variation – are available, each with distinct advantages and inherent nonlinearities that may introduce method-specific artefacts. This study introduces a novel approach for mapping and assessing surface topography using a phase-space representation that integrates both height and angular information and enables a joint analysis and fusion of both characteristics. This exhibits potential for efficient and compact monitoring of tribological processes. We investigate the informational content and limitations of various measurement techniques by surface texture and angular parameters, highlighting the differences and the impact of the statistics of a surface. Then, the overall height and angular distributions of the measured topographies are compared. Angular representations offer an additional dimension of analysis, enhancing the robustness of surface characterization. For the angular distribution, tactile and optical methods often yield differing results, particularly for complex surface features. A direct angular measurement offers another perspective on the surface topography and the combination of height and angular information enables a more holistic surface description. The proposed phase-space representation is exemplified through the analysis of cylinder liner surfaces, illustrating its potential to improve the accuracy and interpretability of tribological assessments and demonstrating the potential of this representation to expose even slightest changes in the surface topography. The fusion of the independent variables height and slope can allow a precise monitoring of tribological processes where only one of the two distributions may change and thus allows a novel perspective on the tribological assessment of surfaces.