Analysis of Dynamometer Signals of Interrupted Cutting by Time-Frequency Localization Methods

Abstract

In this work the force sensor signals of an interrupted metal cutting process were analyzed by continuous wavelets (CWT) and Hilbert-Huang Transformation (HHT). The main purpose was to characterize the signal through the typical behavior of its dominant frequencies and, at the same time, to compare the performances of the two frequency localizing methods applied. It was found that the low dominant frequencies are approximately constant while the values of the high dominant frequencies (above one kHz) show strong fluctuations. Here we show that the fluctuations revealed by the CWT method are caused partly by numeric effects of the method itself and partly by real variations in the frequency values. These variations are responsible for the non-stationary behavior of the signal. Regarding the methods applied, it was found that the wavelet analysis method is capable of tracing fast varying frequencies of the signal with values close to each other by the proper choice of the central frequency parameter of the mother wavelet. In comparison with the HHT, the wavelet method proved much more robust in this case.