Advances in Six Degree of Freedom Vibration Testing

Abstract

Vibration testing is used in many different industries to qualify components and evaluate performance. Components can range widely in size, shape, and function. Typical vibration tests in the aerospace industry implement single degree of freedom (DOF) input (either translation or rotation) due to complexity in control while meeting specific specification levels. Previous efforts were presented in 2007 on a 6-DOF test bed using multiple electro-dynamic modal shakers to apply simultaneous vibration in all six rigid body degrees of freedom. An algorithm was originally developed for single sine inputs at a total of 17 frequencies simultaneously. This paper describes two major developments in this test bed and control algorithm.

The first development was the addition of two additional shakers to control a more complex test structure. A flexible bracket had been added to the unit under test, which added additional dynamics and complicated the original control; adding additional control shakers solved this issue.

The second development involved the extension of the control algorithm to allow for broadband random excitation in 6-DOF. The updated algorithm attempts to match both the magnitude and relative phase of all 6 DOF across the entire frequency range of interest.