Determination of topography fidelity with optical surface texture measuring instruments
Start: October 2020
Student: Athanasios Pappas
Supervisors: Lewis Newton, Richard Leach
Industrial Supervisor: Adam Haynes
Funding: University of Nottingham, Manufacturing Technology Centre
The continuous advances in the sectors of advanced manufacturing and precision engineering have resulted in a demand for structures with highly complex surface specifications. However, the nature of those surfaces (high slope angles, complex geometries, diffusely reflecting surfaces) makes the use of measuring instruments for the purpose of uncertainty evaluation a difficult task. This fact is evident by looking at the common issues encountered by researchers, including outliers, missing points and other unexpected topographic features. Introduced in the standard ISO 25178 part 600, topographic fidelity is a metrological characteristic that encapsulates the aforementioned aspects that relate to the interaction of an instrument and the surface (or profile) being measured.
Calibration methods can be found where a material artefact of similar geometry to that of the measurand is employed to quantify topographic fidelity. However, a number of issues become apparent as a single artefact cannot contain all possible surface structures or the fact that the data from a sample topography cannot be extrapolated to a different one. The aim of this project is the development of a framework for determining topographic fidelity and how it can be applied in the evaluation of uncertainty allowing for the prediction of the performance of an instrument for a number of different applications.
Figure 1 Imaging confocal microscopy a) noise map and b) flatness map for 20× magnification