Active cancellation of unwanted excitation when measuring dynamic stiffness of resilient elements

Laboratory measurements of the vibro-acoustic transfer properties of resilient elements are dealt with in a series of ve International Standards (ISO-10846-1 through 10486-5, partly still forthcoming). The measured quantity that is standardised, is dynamic stiness. Because of the multidirectional nature of the vibration transmission, the standards cover separate measurements of stiness for three perpendicular excitation directions. For each of the three orthogonal translational excitations, the input for the unwanted directions have to be at least 15 dB lower. To meet this requirement over a large frequency band may be quite dicult, especially in case of `transverse' excitation. Then special measures have to be taken to suppress rotation inputs. In this paper active vibration control on the input side of a test element is shown to be useful to suppress unwanted input rotations. The applicable frequency range depends on the controller available. The results presented show the feasibility of the method and good suppression results up to 250 Hz. New tests with a state-of-the-art controller are planned to cover a wider frequency range and to enable the use of a chirp as a driving signal.