Continuous wavelet transform-based estimation of modal parameters with scale selection

This paper improves the method for the estimation of modal parameters from free decay response of a structural system using continuous wavelet transform (CWT). The CWT of free decay response is investigated especially for the case when closely spaced modes need to be analyzed. A robust iteratively reweighted least-squares (IRLS) linear regression method is introduced to fit wavelet amplitude and phase curves. The selection of the appropriate analyzing scale is proposed to improve the modal parameter estimation of the system with poorly separated modes, and scale selection is performed by searching the locations of the local minima of fitting error functions. Both numerical and experimental studies are performed to demonstrate the method and verify its accuracy. The experimental system is a minimally invasive surgery manipulator with force sensing ability. The results show that the estimation accuracy is significantly improved in the presence of close modes.