Improving the analysis of laser welding process by the reassigned time-frequency representations Available to Purchase

On line quality monitoring, in industrial plants, is an open field for signal processing application. In this paper we explore the method of reassignment for extracting information from signals detected during the laser welding process. The reassignment method was first applied to the spectrogram by Kodera, Gendrin and de Villedary [22, 23] and later generalized to any bilinear time-frequency representation by Auger and Flandrin [24]. Key to the method is a nonlinear convolution where the value of the convolution is not placed at the center of the convolution kernel but rather reassigned to the center of mass of the function within the kernel. The resulting reassigned representation yields significantly improved components localization. We briefly recall the fundamental concepts of the theory of time-frequency representations, discussing some time-frequency distributions, after that we review the reassignment method. Finally we compare the proposed time-frequency distributions by analyzing signals detected during the laser welding of tailored blanks, demonstrating the advantages of the reassigned representation, giving practical applicability to the proposed method.