Online Identification of a Mechanical System in the Frequency Domain with Short-Time DFT

A proper system identication method is of great importance in the process of acquiring an analytical model that adequately represents the characteristics of the monitored system. While the use of dierent time-domain online identication techniques has been widely recognized as a powerful approach for system diagnostics, the frequency domain identication techniques have primarily been considered for oine commissioning purposes. This paper addresses issues in the online frequency domain identication of a exible two-mass mechanical system with varying dynamics, and a particular attention is paid to detect the changes in the system dynamics. An online identication method is presented that is based on a recursive Kalman lter congured to perform like a discrete Fourier transform (DFT) at a selected set of frequencies. The experimental online identication results are compared with the corresponding values obtained from the oine-identied frequency responses. The results show an acceptable agreement and demonstrate the feasibility of the proposed identication method.