Tsai M., Sun Y.

In this paper, an active-passive vibration isolation platform has been developed using piezoelectric actuators. The active layer is similar to a pendulum where the outer case and the center mass are connected with three steel ropes. In the middle of the ropes, piezoelectric actuators are embedded using a flexible hinge such that the length of the ropes can be adjusted by the actuators. In between the center mass and upper mass, elastomer is inserted to serve as the passive layer and provide the damping capability for high frequency. It is designed that ground disturbance coming from the horizontal direction higher than the first natural frequency will be attenuated. The design methodology is to utilize the piezoelectric layer to reduce vibration within the low frequency range (2~60 Hz) and the passive layer is designed to suppress vibration above 60 Hz. Dynamic models are derived via Lagrange approach in both vertical and horizontal directions. Nonlinear properties of the spring and elastomer under different loading condition are observed and discussed. The resulting system uncertainties are modeled by using an approximate model where the concept is similar to that of the describing function techniques, which represent the input-output relationship of a single-input/single-output nonlinear element by the magnitude and phase relationship between a sinusoidal input and the fundamental harmonic of the corresponding output. The parameters in the uncertainty model can be obtained by experiments both in time and frequency domain. With the developed model, the robust H[inf] controller is designed. The experimental results shows that more than 35dB at some particular frequency ranges, and the average 12 dB can be achieved for 2 to 60 Hz. Payload conditions changing from 30 to 60 Kg are tested and the promising results validate the efficiency of the proposed controller.