| dc.description.abstract | In this study, the skyhook active isolation control theory is developed and applied to a single-degree-of-freedom active isolation system. The equation of motion and proposed control algorithms are derived in detail. The numerical simulation analysis and experimental verification of the developed skyhook active isolation system are carried out. The proposed control algorithm improved the traditional skyhook control by adjusting the measurements from only the absolute velocity of the system to the velocity relative to the ground as feedback signal; meanwhile, it uses the ground velocity as the feedthrough signal. The velocity relative to the ground and ground velocity can have individual control gains. In addition, the ground velocity is obtained by integration of the measuring ground acceleration. This modification not only improves the convenience of measurements, but also enhances the stability of the feedback signal. To access the ground velocity from the ground acceleration, the real-time integral-filter is introduced and designed to process the integration and eliminate the caused steady-state error. Moreover, this integral-filter can be directly combined into the model of the skyhook active isolation system, so that the influence of the integral-filter, i.e. the time delay issue or stability problem, can be guaranteed. Since the proposed skyhook active isolation system is not using full-state feedback, the direct output feedback optimization can be adapted to determine the optimal control gains with the goal of minimizing the absolute acceleration of the system. Different with the traditional skyhook control, the proposed skyhook active isolation system uses the relative velocity and the ground velocity as measurements, so that the influence of inherent damping can be fully considered. Therefore, even though the system has different inherent damping ratios, by adapting different control gains, the skyhook active isolation system can achieve the same optimum isolated responses. In the frequency response function analysis, the skyhook active isolation system is more outperforming than the passive isolation system and traditional skyhook control, especially when the frequency of base excitation is between 0.1Hz to 10Hz which is the range of dominant frequency of normal earthquakes. Furthermore, in the time-history analysis, the performance of the skyhook active isolation system is much better than the passive isolation system whether subjected to far-field earthquake or near-fault earthquake. In the sensitivity analysis, the relative displacement, the absolute acceleration, and the control force of the skyhook active isolation system are all sensitive to the control gains. The stability analysis also showed that the skyhook active isolation system is always stable, even the control gains various within a certain range. Besides, the control gain, which is the ground velocity signal feedthrough, does not affect the stability of the system. Finally, the skyhook active isolation system is practiced by a linear servo slider to verify its feasibility by the shaking table experiment. The experimental results show that the skyhook active isolation system performs well to isolate seismic force. However, there is still a certain difference between experimental results and numerical simulation. The difference is majorly existing at high-frequency range which is observed by power spectral density of the absolute acceleration. Therefore, this high-frequency vibration is considered caused by the friction of the ball screw mechanism rather than the control algorithm. | en_US |