Real-time control of both stiffness and damping in an active vibration neutralizer

Recent improvements to the vibration neutralizer have involved the incorporation of a variable-stiffness device so that the natural frequency can be adjusted. The device can then track an excitation frequency that is varying slowly with time. This paper describes a neutralizer where both damping and stiffness in the neutralizer are adjustable, so that the performance of the device can be improved in addition to its tracking capability. An experimental investigation is described in which the feasibility of real-time control of both stiffness and damping properties was assessed. A fuzzy controller was designed to adjust the resonance frequency of a beamlike neutralizer by changing its geometry, and to adjust the gain in a velocity feedback loop to reduce the damping in the device. The dot product of the complex velocity vectors of the neutralizer and host structure was used as an indicator of the tuning error. Damping was controlled by a fuzzy rule base, which used the rms level of neutralizer and host structure velocities as errors. Significant improvements in the vibration attenuation of a host structure were achieved compared with a passive neutralizer.