Surface roughness measurement for semi-spherical workpieces based on Bessel structured beam

Laser triangulation method is a method in common use to measure surface roughness. In the traditional laser triangulation method, a Gaussian beam is used to scan the measured surface point by point. Since the data is collecting by means of point scanning, a considerable number of measurements are essential for the whole measured surface. Hence the measurement of a semi-spherical surface is costly and time consuming. In this paper Bessel structured beam is used in the triangulation measurement system instead of Gaussian beam. Owing to the characteristics of its longer focal depth, the system using Bessel structured beam possesses the advantages of wider measurement range, higher theoretical measurement accuracy and resolution over the traditional laser triangulation measurement system. With scanning the measured surface using the concentric rings of Bessel structured beam, a piece of area on the workpieces' surface can be measured through only once measurement. Taking a latitudinal circle with a radius of 5mm as an example, it takes only 9.3s to obtain the surface profiles of the whole latitudinal circle with the proposed system in this paper, while it must be measured point by point with the stylus device and more than 60s are needed.