Multivariable control problems in dynamic structural testing

Abstract

The problem of designing controllers for multi-channel dynamic structural test systems is discussed. The structure under test, a uniform cantilever, is subjected to sinusoidal force inputs from two electromagnetic vibrators which are attached to the mid-point and the end of the beam. The deflection of the beam is measured at these locations and considered as the system output. Consequently, the system consists of two control loops which are cross-coupled through the dynamics of the beam. The aim is to minimise interaction in the two channels, so providing the opportunity for a systematic approach to the design of the controllers in the individual loops. The Inverse Nyquist Array method is applied to an analytical model. It is shown that the design problem can be divided into three categories according to the relative stiffness of the beam to the vibrator. The results demonstrate that controllers, which give significant reductions in interaction, can be designed for each case.