Tracking of Mechanical System Parameters by Phase-Locked Loops

The eigenfrequencies of a mechanical system depend on several parameters such as mass-, damping-, stiffness-distribution and boundary conditions. Variation of these parameters results in variation of the Frequency Response Function (FRF). An eigenfrequency can be tracked by resonant excitation with a Phase-Locked Loop (PLL) in order to monitor a certain parameter. As an example, a cantilever beam with a time-variant mass at its end is analyzed. In this contribution, the FRF of this beam will be derived, which is the prerequisite for the following resonant excitation. The modified PLL-design for the resonant excitation of higher modes will be explained and finally tested at the state-space model of the beam. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)