Smart sensor for surface inspection: concepts and prototype description

The purpose of this paper is to present the conception of what could be a smart laser range finder. A smart distance sensor should be able to adapt its different parameters to the real measurement case and to the different steps of the measurement process. The system chosen here is based on phase shift measurement method. The implemented solution for phase shift measurement is the IF sampling method that means under-sampling technique, associated to digital synchronous detection. Its main advantage is a global simplification of the electronic system, leading to a quite simple development of a twofold modulation frequency system that is required for high resolution measurement within a wide range. Frequencies at 10 MHz and 240 MHz have been retained and the system is designed with only one PLL, which is a digital one, reducing the phase noise. The emission and detection parts are designed for wideband operation and to be digitally controlled, in order to adapt their characteristics to the measurement situation. The whole measurement sequence is described, including different steps at both modulation frequencies, and calibration of the system.