Accurate frequency measurement on small structures with shaker excitation

Abstract

Measurement of the frequency response functions of a structure is an important part of modal analysis. Excitation of the structures is often by a shaker coupled to the structure through a stinger and force transducer. The force transducer adds a small, uncompensated, mass to the system while the stinger may add additional stiffness. These can lead to errors in determining natural frequency. Previous work, involving the model updating of small structures, had resulted in corrections to the Young’s Modulus of Aluminum that put it outside the normally accepted range. This was assumed to be the result of errors in natural frequency measurement resulting from the use of a stinger and force transducer. In this paper, this assumption is evaluated both experimentally and analytically. It demonstrates how the use of a shaker for excitation can change the measured FRF’s of a structure and proposes an FE model of a stinger and force sensor that can be used to assess the changes before testing.