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Contactless measurements for surface roughness - EMPIR project publishes paper

Digital 3D render of rough terrain

Methods detailed by the paper will help to improve non-destructive surface measurements for industry

The project

The surface topography of manufactured parts can have a huge effect on their functionality, efficiency and longevity. Around 10 % of manufactured parts fail due to surface effects and rough surfaces can negatively affect processes such as lithography and 3D printing. Although fast, high-resolution, contactless measurements of surface topography can be achieved using systems such as optical microscopes and optical distance sensors, complex interactions between the device and the measured surface can cause challenges to their use in industry. Instead, non-optical methods are often used, despite being destructive, slow and costly in comparison.

EMPIR project ‘Traceable industrial 3D roughness and dimensional measurement using optical 3D microscopy and optical distance sensors’ (20IND07, TracOptic) is enabling traceable roughness and dimensional measurements using optical methods. The project is developing models to predict the response of sensors to surface geometry, as well as industry guidance for choosing the most suitable instruments for required measurements.

Journal paper

‘Simulation of realistic speckle fields by using surface integral equation and multi-level fast multipole method’, published in the journal Optics and Lasers in Engineering, details the simulation of speckle fields. These are random optical patterns produced when rough surfaces are illuminated, which can reveal information about the surface being analysed. Silver and silicon surfaces were simulated to demonstrate different requirements for metallic and dielectric (insulating) materials.

The simulation of these fields will help develop understanding of their generation and evolution, which will improve the quality of optical surface roughness measurements.

The project has also published:

‘Harvey–Shack theory for a converging–diverging Gaussian beam’, published in the Journal of the Optical Society of America B
‘A virtual microscope for simulation of Nanostructures’, published in EPJ Web of Conferences
‘Three-Dimensional Transfer Functions of Interference Microscopes’, published in Metrology

Presentations

The project has also presented its findings at a number of events:

Invited oral presentation “State of the art in traceable industrial 3D roughness and dimensional measurement using optical 3D microscopy and optical distance sensors” at the Wiley Analytical Science Conference
Appearance at Control International Trade Fair for Quality Assurance
Invited oral presentation “Fourier optics modelling of coherence scanning interferometers” at SPIE Optical Engineering + Applications

Project coordinator Uwe Brand (PTB) has said about the project:

“The project will develop Good Practice Guides for end-users on how to measure roughness and texture of technical surfaces as well as dimensional parameters of spheres and other microstructures with 3D microscopes and optical distance sensors.”

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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