Rainer Brodmann

Extraction of shape and roughness using scattering light

The extraction of 3D shape and roughness by optical measurement techniques become more and more import in industrial applications. Optical systems are measuring fast with high accuracy and give reliable information about the workpiece form or surface roughness. The classical systems based on triangulation, white light, confocal, shadow or fringe projection techniques and are applied with a great success in recent years. In future there will be a growing interest in robust inline measurement techniques to monitor the manufacturing process. E. g. some automotive manufactures are using confocal systems to characterize the surface of cylinder liners inline. But there is another robust and powerful technique suitable for inline measurement purposes: scattered light sensors. In this paper, a special type of a scattered light sensor based on the former Rodenstock RM 400 sensor is considered. The sensor enables the user to measure form and roughness in a robust manner. The properties of the sensor are analyzed system-theoretically.

Light Scattering Methods

Light scattering belongs to a class of techniques known as area-integrating methods for measuring surface texture. Rather than relying on coordinate measurements of surface points, light scattering methods probe an area of the surface and yield parameters that are characteristic of the texture of the area as a whole. The specular beam intensity, the angle-resolved scatter and the angle-integrated scatter are examples of measurands from light scattering that can yield useful parameters of the surface texture. Uses of light scatter for inspecting the surfaces of mechanical and optical components as well as surfaces produced in semiconductor manufacturing are primarily reviewed here. Several documentary standards describing best practice are also briefly reviewed.