16 Drive Multi-Shaker Control

Spectral Dynamics Inc. has been delivering multi shaker control (MIMO) systems since about 2001. Over this time the requirements for additional output Drives has grown steadily as 3 DOF and 6 DOF testing gains in popularity. We now offer up to 16 controlled Drives in a single standard system and these capabilities are described below. The vibration testing of large structures has evolved over the past few years as several factors have converged to create a possible “Perfect Test” scenario. The introduction of MIL-STD-810G in October, 2008 for the first time both gave emphasis to “Multi-Exciter Testing” and included a separate section on Time Waveform Replication. Also, for the past several years an increasing number of technical papers have been presented on various aspects of Multi-Exciter (MIMO) testing. These have included both fundamental presentations, exploring various new testing methodologies and many practical reports showing the results of performing many different kinds of MIMO tests. Some of these have also included the use of measured field data as the basis for the laboratory Multiple Input Multiple Output (MIMO) test. The realization that a single, very large, shaker is not always the most effective way to test a large or unusually shaped structure has contributed as much as anything, to the increasing use of multiple, smaller shakers to perform very realistic testing. It has also been shown that by describing a complex, multi-exciter test setup in terms of a Spectral Density Matrix, all of the critical system parameters can be seen in a compact, efficient formulation. By repeatedly solving this matrix during a test, realistic simulation of non-linear events and test systems is now possible with great precision. So whether it is a satellite, a long missile system or a multi-layered circuit card, many test articles can now be tested with greater precision than ever, using a MIMO approach. An example of an 8 by 8 Spectral Density Matrix (SDM) used to describe a system with 8 exciters and 8 control points is seen in figure 1.