Indirect Measurement of Rotation/Moment Impedance Functions 951271

A testing procedure has been developed for measuring rotation/moment impedance functions. At connection points between components, both rotations and moments have important contributions in describing the dynamic characteristics of a coupled system. Analytically, both rotations and moments are included at connection points and are necessary for achieving a high fidelity model of a system. Experimentally, these effects have been historically neglected since no acceptable rotational transducers exist. If high fidelity impedance models are to be developed from experimental data, it is important to measure rotational impedance functions. In this paper a testing method is developed which uses the motion of a rigid body attached at a point of interest to determine displacements, forces, rotations and moments at the point of interest. A set of over-determined translational measurements made on the rigid body is used in a pseudo-inverse procedure to estimate the complete six-by-six impedance matrix at the point of interest. These impedance functions include all of the rotational information. A case study is presented involving measurements on a laboratory test structure designed to be very sensitive to rotations. The impedance functions include the six-by-six matrix at the connection point as well as cross measurements between the connection point and points located elsewhere on the structure.