Measurement of Unloaded and Loaded Multidirectional Mobilities 2005-01-2268
The paper describes a technique to determine the full 6 by 6 mobility matrix of a point (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.
The loaded mobility matrix determined for two structures first a 3-dimensional beam-structure where results are compared to FE-calculations and secondly on a wheel suspension on a car.
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 second step is explained theoretically and is demonstrated experimentally for 2-DOFs (translation and rotation) for a freely suspended beam vibrating in bending motion.