Time Domain and Frequency Domain Techniques For Multi Shaker Time Waveform Replication

摘要

This paper describes two techniques for controlled Multi Degree of Freedom (MDOF) time waveform replication with examples of their application to a variety of test conditions. The paper outlines the basic concepts of time domain and frequency domain control and illustrates the techniques using MDOF applications where one or the other method is more suitable. The time domain technique is an iterative technique, involving additive corrections to the shaker drive based on measured error between control and reference time histories. The frequency domain technique is both iterative and adaptive, involving convolution1 of the measured Inverse Multiple Input Multiple Output (MIMO) Frequency Response Function (FRF) matrix with the matrix of reference time histories. In contrast to the time domain technique, the frequency domain technique can adapt during a test by performing real time updates of the FRF matrix between drive and control signals. Topics covered include typical configurations of MDOF time waveform replication vibration tests, data acquisition considerations for reproducing MDOF motion, control of non-linear structures, over determined control (more controls than drives), and optimization of control techniques based on structural dynamic response and reference time history considerations.