An advanced excitation technique for measurement of unloaded multidirectional mobilities

This paper describes a technique to determine the mobility matrix (including rotational degrees of freedom) from measurements. The determination is performed without loading from the excitation equipment (lever, force transducers, etc.) and uses only one set-up. The advantages of using only one set-up are that an improved consistency of the mobility matrix is achieved in comparison to traditional techniques, and that it saves set-up time which usually is a large portion of the total time required for the actual measurements.The measurements are performed in two steps. During the first step, the mass- and inertia-loaded mobility matrix is determined by using sequential measurements and a physical model of the excitation equipment. In a second step, the loaded mobility matrix is used to actively compensate for the mass and inertia of the excitation equipment; thereafter the unloaded mobility matrix is obtained. The two steps are explained theoretically and are demonstrated experimentally for a freely suspended beam vibrating in bending motion.