3. Multi–input Multi–output Active Vibration Control for High Frequency Random Vibration

Electromagnetic shakers and closed loop control systems are commonly used in qualification tests for environmental vibration conditions. However, at high frequencies shakers have resonances and anti-resonances. Resonances can be beneficial in that the shaker needs to exert less force to achieve the desired environment, but they can make it more challenging for the control system to match the desired environment. Anti-resonances are more problematic because they represent frequencies where the voltage input to the shaker causes little motion (at some locations on the slip table or adapter plate). Hence, these can cause the system to require driver voltage levels above the controller capacity and cause the test to abort. Furthermore, an anti-resonance is in essence a motion that is unobserved at the point(s) of interest, and hence they may lead to damage if internal components experience much higher vibration levels than the control accelerometer. This paper proposes and characterizes a hybrid shaker system that would use a piezoelectric actuator in addition to the electromagnetic shaker to create a MIMO control system. It is hoped that the additional control effort introduced by the piezoelectric actuator could be used to expand the frequency range over which the desired environment can be achieved.