The application of piezoelectric actuators for active vibration control (AVC) of rotating machinery is examined. Theory is derived and the resulting predictions are shown to agree closely with results of tests performed on the air turbine driven-overhung rotor. The test results show significant reduction in unbalance, transient, and subsynchronous responses. Results from a 30 hour endurance test support the AVC system reliability. Various aspects of the electromechanical stability of the control system are also discussed and illustrated. Finally, application of the AVC system to an actual jet engine is discussed.

The active control of rotordynamic vibrations and stability by magnetic bearings and electromagnetic shakers has been discussed extensively in the literature. These devices, though effective, are usually large in volume and add significant weight to the stator. The use of piezoelectric pushers may provide similar degrees of effectiveness in light, compact packages. This paper contains analyses which extend quadratic regulator and derivative feedback control methods to the “prescribed displacement” character of piezoelectric pushers. The structrual stiffness of the pusher is also included in the theory. Tests are currently being conducted at NASA Lewis Research Center with piezoelectric pusher-based active vibration control. The paper presents results performed on the NASA test rig as preliminary verification of the related theory.

Although considerable effort has been put into the study of steady-state vibration control, there are few methods applicable to transient vibration control of rotor-bearing systems. In this paper optimal control theory has been adopted to minimize rotor vibration due to sudden imbalance, e.g., blade loss. The system gain matrix is obtained by choosing the weighting matrices and solving the Riccati equation. Control forces are applied to the system via a feedback loop. A seven mass rotor system is simulated for illustration. A relationshp between the number of sensors and the number of modes used in the optimal control model is investigated. Comparisons of responses are made for various configurations of modes, sensors, and actuators. Furthermore, spillover effect is examined by comparing results from collocated and noncollocated sensor configurations. Results show that shaft vibration is significantly attenuated in the closed-loop system.

Past research on this subject has treated piezoelectric actuators as ideal devices that have tip displacements proportional to their input voltages, at any instant in time. This assumption neglected phase lag and amplitude change at high frequencies. This characteristic of any actuator may lead to coupled control system-structural system instability that limits the amount of active stiffness or active damping that can be obtained. The paper presents a method for simulating the coupled “electromechanical” system to predict rotordynamic stability and unbalance response along with control system stability. The piezoelectric actuators and their amplifiers are represented as equivalent linear electrical circuits. The electromechanical system modeling approach is utilized to correlate test results from a double overhung rotor rig at NASA Lewis. The test results also show the effectiveness of the control system for suppressing the unbalance response of two modes using active stiffness and active damping.

Past research on this subject has treated piezoelectric actuators as ideal devices that have tip displacements proportional to their input voltages, at any instant in time. This assumption neglected phase lag and amplitude change at high frequencies. This characteristic of any actuator may lead to coupled control system-structural system instability that limits the amount of active stiffness or active damping that can be obtained. The paper presents a method for simulating the coupled “electromechanical” system to predict rotordynamic stability and unbalance response along with control system stability. The piezoelectric actuators and their amplifiers are represented as equivalent linear electrical circuits. The electromechanical system modeling approach is utilized to correlate test results from a double overhung rotor rig at NASA Lewis. The test results also show the effectiveness of the control system for suppressing the unbalance response of two modes using active stiffness and active damping.