Toward online non-contact roughness profile measurements with a sensor based on conoscopic holography: current developments

Abstract

On-line non-contact roughness metrology is still an open problem. Usual methods involve either contact (stylus-type devices) or perform indirect evaluations of some roughness parameters, such as R a , with light scattering techniques or speckle measurement (among the most common optical techniques), inductance (only for magnetic materials) or ultrasound methods. However, a generic method able to obtain every roughness parameter (what means recording the real distance profile), able to work with a variety of surface types, and able to be installed in production lines is still to be developed. In this article, the ongoing work towards the construction of a non-contact optical profile measuring sensor that could be used for roughness measurements is presented. Our approach is based on Conoscopic holography, a common-path interferometric technique which is a good candidate for industrial applications. Current research effort is focused in enhancing accuracy in these systems, by both reducing the coherence of the illuminating source (laser) and changing the hardware and software setup, with the aim of building a sensor able to capture a profile of an object's surface in a single shot with high precision from a relatively long standoff (several cm).