Hybrid Control Of Flexible Structure Vibration

Vibrating machinery must be isolated from a supporting flexible structure which is likelyto cause noise radiation by the vibration excitation. Active vibration isolation can be appliedin these situations to extend the low frequency performance of passive vibration isolators.This paper describes a theoretical and experimental investigation into an activefour-mount vibration isolation system in which an electromagnetic inertial actuator isinstalled under the base plate which is connected to an equipment plate through a passivemount. Each actuator of this study operates independently by a hybrid control strategy whichis consist of two control loop. The inner force, integrated force or compensator feed-backcontrol loop is to modify the actuator’s transfer function. The outer loop, to minimize the baseplate velocity, can be either the decentralized down-isolator velocity feed-back control orfeed-forward control based on filter x-LMS algorithm.As to the double feedback control strategy, the inner feed-back control is able to stabilizethe outer velocity feed-back control system that will be unstable at a high velocity gain due tothe inertial actuator’s additional phase effects. In this case, the stabilities and controlperformances of the outer feed-back loop with three kinds of modified actuator are compared.It is found that a compensator within the internal control loop and an external velocityfeed-back control loop offer a very promising solution both in terms of stability andperformance of the system. Another hybrid control strategy that a modified actuator withinthe feed-forward control is analyzed. A general theoretical solution of optimum control forcewhich the modified actuator demands using the impedance method is presented, and isverified in simulations using the Simulink software. More explicit investigations on theconverging speed and remnant of the mean square error are discussed.