Tri-axial hybrid (passive-active) vibration isolator using single crystal piezoelectric actuators

Abstract

Results are presented for a laboratory study of a tri-axis hybrid (active-passive) vibration isolator. A previous report [J. Acoust. Soc. Am. 112 (2002)] described control studies performed using single-axis control. It identified the optimum physical control law by examining the placement order within the device consisting of a passive compliant spring, sensing layer, and piezoelectric actuator. Additionally, actuator materials were evaluated by examining the performance levels of three piezoelectric materials having different nonlinearity values: PZT-4, PZT-5A, and PMN-PT single crystal. The study described here extends this previous work to the required, more complicated case of three-axis control. Described are the development, design, and fabrication of a hybrid device that demonstrates stable, robust, and reproducible ‘‘local’’ vibration reductions of ∼30−−45 dB simultaneously in all three excitation axes. These results are found for both single and multiple tone tri-axis disturbances and with negligible out-of-band enhancement, where the total harmonic distortion of the system is less than 0.25%. The control approach, using base acceleration minimization, demonstrates ∼35 dB of ‘‘downstream’’ performance, which is ∼25 dB higher than that of the passive element alone. The device is sufficiently small and simple to fabrication that it offers potential for being used in practical applications.