Online dimensional analysis of surfaces using optical filtering and elaboration techniques in the Fourier plane

A simple and efficient method for online dimensional analysis and quality control of one-dimensional and two-dimensional objects is presented. It is based on optical image elaboration using filtering techniques in the Fourier plane. The Fourier spectrum of the light transmitted through the object is filtered by suitable means to eliminate unwanted spatial components. Inverse transformation of the spectrum provides the filtered light distribution to the detector. The method makes it possible to enhance greatly the signal-to-background ratio both in the case of a uniform light background and in the case of undesired spatial components in the image light distribution. It provides a quasi-digital presentation of the object profile directly to the detector without any need for time-consuming computer elaborations. A preliminary implementation of the system is described, both for one-dimensional and two-dimensional objects, and experimental results are presented